This week in batteries (TWiB)

To be, or not to be (green), that is the question

2011-03-28T17:28:00.000-07:00

The title above was going to be my next blog post for GigaOm.

But, they thought a better title was “How Plug-In Hybrid Cars Could Be Game Changers”.

I still think my title is clever (and I’m sure Shakespeare would approve), but on a site like GigaOm, it does not say anything about the content of the blog post. I’ve never worried about things like that, but it’s the price you pay for playing in the Major Leagues :-)

Anyway, I’m beginning to think about the Chevy Volt. Not sure I agree with the title, but I’m seriously thinking about it.

Read all about it here

Venkat

One year and a change in TWiB

2011-03-19T11:31:00.000-07:00

Over the past couple of weeks, I have been in conversation with the folks at GigaOm network to be a guest writer for their cleantech blog called Earth2Tech.

After consulting with my employer (Lawrence Berkeley Lab), I have signed an agreement with GigaOm to be a guest writer.

What this means is that when I write a blog I will send it to them. If they think the post meets their needs, then it will appear on their site. This page will be updated with a small abstract of that post and a link to their site.

If GigaOm decides to not use that post, then the post will appear, in its entirety, on this page.

This Week in Batteries started just over a year ago on Feb 9, 2010. Over the last year, I have made ~30 posts on subjects ranging from the costs of PHEVs, the way to make a battery last longer, the batteries in your Roomba, all the way to how to calculate the energy density of a battery.

Making a blog post has become a hobby for me (probably the first true hobby I have ever had. Collecting stamps just did not cut it!). But like all hobbies it tends to be a fairly low item on the priority list. Regular readers will have noticed the long hiatus’ I have taken when work has demanded more of my hours.

When I wake up on a Sunday and feel like writing, I spend the morning making a post. If I have something else to do, then I don’t make a post. On average, I probably spend 2 hours on a blog post.

The return on the 2 h investment has been very gratifying. I average 5000 hits a month (please don’t ask how many of those are self hits!) with a peak at 10,000.

I have also become convinced that if I really worked at it, I could make this blog popular. But this requires a lot more of my time. And even if I did spend the time, I’m not sure how much more popular I can make it.

On the other hand, GigaOm gets 4 million hits a month. And some of their blog posts gets picked up by the New York Times, CNN, Business Week, and The Street.

Being able to get my posts onto GigaOm increases the visibility of this blog significantly, so the relationship is a no brainer.

The first post is now up on their site. Its called the “The Three Laws of Batteries (and a Bonus Zeroth Law)”. Check it out. They even added some nice pictures to accompany the words.

For the regular readers of this blog, this only means that you will need to, occasionally, click on one more link before you can read my post.

So wish me luck.

Venkat

I'll be back... in 8 hours

2011-02-07T07:50:00.000-08:00

Some of my readers have wondered why I have been off the blogosphere in the last few months. The reason is that we brought a house and the move from the apartment to our new place has been a bit of a time sink.

First we went through the four stages of home buying:

Stage 1: What the &%#@ do you mean they accepted our bid? I thought you said we were lowballing?

Stage 2: When you use words like "downpayment", does this involve us giving you a check?

Stage 3: I assume roof's are like batteries? Meaning, when you say it is at the end of its life, there is still 80% left, right?

Stage 4: Keep repeating after me: "Owning is better than renting" and, please, stop asking "why?"!

Then we realized that owning a house also meant owning things like leaf blowers and lawn mowers! So, when I saw that there was a battery-powered lawn mower, I jumped at the chance to push my favorite technology forward.

I was looking forward to using my expertise in batteries to maintain and extend the life of my lawn mower for many years to come.

I was not particularly looking forward to mowing the lawn, but owning a battery-powered mower seemed to make up for that.

Until I realized that the top-rated battery-powered mower uses lead-acid batteries.

Lead-acid!!! really! How old school can one really get.

My first thought: Start a battery company to make Li-ion batteries for lawn mowers.

Then I started thinking about this some more. There must be a catch here. So I started digging into what it was.

Let us do some math: The battery for this lawn mower cost ~$270/kWh. That is one expensive lead-acid battery. Presumably, it is a deep-discharge battery, and so it is better made than a car battery.

And there is probably a significant markup.

Did I mention that the mower was on sale for $300! More like a mark-way-way-up.

Considering a typical Northern California growing cycle, this mower will probably be used ~50 times a year (once a week). These deep-discharge batteries can probably go a few hundred cycles. So I'm thinking 4-5 years easy.

But the bigger problem is going to be the calendar life. Sulfation can kill these cells.

Having said that, the battery is probably going to be at the top-of-charge pretty much through its life (think about it: Mown for 1 hour. Keep it plugged in all week). And remember our rule for lead-acid batteries: Keep them charged. So I think we can expect to get ~3 years from these cells.

Lets do some math for a Li-ion battery. I bought one a few weeks ago. This battery will probably last me 3 years and get me ~300 cycles or so. So it has similar specs to the lead-acid battery.

The Li-ion battery, on the other hand, cost me a whooping $2300/kWh!! No... really. This is what it cost me.

Now... knowing Apple, a new word has to be coined for their level of markup. But still this is one expensive battery.

At this price, a Li-ion lawn-mower-battery would have cost me $800!

All you MBA-types are probably cringing because you all know that cost and price are very different from each other and that the price is dictated by what the market is willing to pay (my wife is an MBA and she gave me this spiel).

Granted. So let us do a cost-differential comparison. This comes out to be ~$50/kWh more expensive for a Li-ion cell. Using this, the cost of a Li-ion battery for this mower would be higher than the lead-acid battery by... the price of lunch!

Not at Chez Panisse. But at the LBNL cafeteria (same quality, but at a much lower price?)

So why not use a Li-ion instead. After all it is almost 5x the energy density.

The mower that I have been talking about in this blog is a push mower. So the battery does not need to drag itself. All it has to do is turn the cutting blade. And space is not a big constraint. The mower's size is dictated by the size of the blade anyway.

So why bother using a new type of battery when you don't really see much of a benefit?

Frankly, although I have not looked at the life-cycle, I'll take a bet that it is probably better for the environment to use a lead-acid battery considering how much of this lead is recycled. In comparison, all you recycle in a Li-ion is the high-value metals in the cathode. The rest, literally, goes down the drain.

Maybe the math will change for a self-propelled mower. Or if the weight of the mower is an issue. But I don't see any reason to jump to using a Li-ion battery for the mower I was looking at. This business plan does not appear to have much legs.

So what did I do? I got the corded version of this mower. It cost me $100 less.

I guess the price that I'm willing to pay to push my favorite technology forward is less than $100!

In my guilt I decided to do my part for the technology by buying a Roomba.

I'm not sure if you guys know about this amazing robotic vacuum. It is pretty interesting to watch. It has sensors that make it slow down when it approaches objects, detect dirt, and prevent it from falling off of stairs.

It is not particularly good at vacuuming. But it feels like it is cleaning the floors and isn't that what's important!

But here is the kicker. The one I have has a Ni-MH battery.

I suppose I should be thankful it is not a lead-acid, but Ni-MH? COME ON!

The last time I checked, the cost of Li-ion and Ni-MH batteries were pretty comparable. And the energy density of Li-ion is 2-3x greater. And remember that in this machine (unlike the mower) the vacuum has to drag its battery along. And space is a big deal. The smaller the footprint, the smaller the space it can vacuum.

So why use a 20th century battery for a 21st century machine? Strange.

A web search revealed that Li-ion Roomba's have apparently died prematurely. If this is the case, then iRobot (the company that makes the Roomba) needs to change battery suppliers.

The vacuum I got goes through 2 rooms and then runs out of juice. It could have finished my house in one charge if it had a Li-ion of the same size. Or you could have a better vacuum on it so that it actually picks up dirt instead of moving it around and still only vacuum 2 rooms. You get the point.

When I first saw this machine, I thought that all the things on Terminator (the movie) were coming true. Jokes apart, it really is a pretty decent robotic cleaner which does indeed find its way around. You can, pretty much, set it and forget it.

But then I realized that we had nothing to worry from the machines as long as battery technology evolves the way it has been in the past.

When Arnold Schwarzenegger's character said "I'll be back" on T2, he (it) actually meant "I'm running out of battery and I need to go find an outlet and charge for 8 h. I will then come back to look for you for the 1/2 hour my battery lasts. Wish me luck".

So much for the machines taking over.

If you constantly complain about how batteries are not evolving fast, did you ever consider for the second that maybe we are out to save the world in our own way?

Venkat

Did I say “Pull the Plug”? Meant to say “DO NOT pull the plug”

2011-01-31T07:47:00.000-08:00

This could be a mea culpa post. It is rare that I’m wrong; it is even rarer that I admit it! So listen up folks.

In the early days of this blog, one of my dedicated (?) readers had asked me about the urban myth about not keeping the laptop plugged in to extend the life of the battery. In response, I had written a post titled “Pull the plug, your battery will thank you”. This post is the single most popular post on this blog. Almost a year after the post was made, it still gets the most hits.

The logic behind doing this is very sound. As you can read from that post, it has to do with side reactions that occur in the battery at the top of charge. Letting the battery discharge a bit is good for life because the rate of these side reactions decreases with decrease in the voltage. Suffice to say that I recommended you wait for the battery to charge and then you pull the plug and let it self discharge. This way you can extend its life.

I follow this rule pretty diligently. And I thought it had worked well for me. I have one laptop that is 2 years old, has had 297 cycles and has lost 4% of its initial capacity. Not bad. This is my workhorse. I use it every day and although I pull the plug diligently, my usage is such that I keep it pretty close to fully charged. So over the last 2 years, it has spent its time at close to, say, 4 V.

I have another laptop which is 3 years old. It is my personal laptop which we (my wife and I) use typically only over the weekend. We pull the plug diligently, but then the computer sleeps all week; self discharges; and by the end of the week is pretty much discharged. This battery, as of last week, had not lost any appreciable capacity even after 350 cycles.

These two data points tell you something about batteries. The cell with more cycles and with more time is cycling better! No magic. Just a simple fact that the battery was sitting at a lower state of charge and so the side reactions were not as worse. Ergo, better life.

Did I mention that both these are Macs? I have a third laptop given to me by a startup where I spend some of my time. This is a PC assembled by a company whose name starts with a D and ends with an L and has 4 letters to it. That computer is on its 4th battery in 2.5 years. After I lost my first battery I spent significant time trying to understand why my rules were not working and trying to tweak the rules. Soon, I came to the conclusion that with some batteries there really is no point trying to find ways to extend life. They are beyond help.

Actually, these rules have been helping this battery also. But different battery companies make batteries with different quality (achieving tightly-bound quality metrics has been a challenge in the manufacturing of batteries). So when you start with a battery with bad quality, there is only so much you can do.

But let us get back to my Mac.

Well... last weekend, my 3 year old Mac with no capacity fade suddenly appeared to have a dead battery. Not a battery with some loss in capacity; or one with 20% loss in capacity (which is considered dead). It was just plain dead. No charge; pull the plug and it would shutdown. It was on life support, literally!

The only way this battery would have a second life was if it were a Hindu and had not attained enlightenment and so was eligible (I suppose doomed is a better word) to be reborn. Somehow it seemed like even with the 1000 (or is it 10,000) Hindu gods there was no way to get this battery back up.

My first reaction was one of disbelief. There was no way a battery can go from no fade to completely dead in a matter of 1 week of self discharge. It had to be a software glitch that was not allowing the battery to be used.

Two hours, a bit of heartburn, and a detailed scouring of the world wide web later, I found various tricks to reset the battery management software and a software to measure the voltage of the battery and came to the conclusion that it was indeed dead. The (average) individual cell potential appeared to be close to 1.5 V! The typical cutoff potential of these cells is around 2.5 V.

So I pulled the plug and my battery died!!

A call to Apple confirmed that I was out of warranty and was told to go to the Apple store for a “detailed diagnostics”.

So I dragged myself to see the “genius” at the store (I’m not being condescending here; they really call the tech support guys genius’. Apparently if Einstein were alive today he would be working at the Palo Alto Apple store!).

Albert plugged a USB stick into my laptop; my screen turned into a series of numbers. Albert then turned and says that my battery is dead. Clearly he was on his way to writing a paper on the unified field theory.

I apologetically told him something like “I understand a bit about batteries and I don’t expect them to fail like this” and he said “I would not expect them to do that early on, but after 3 years I fully expect this”. Not “its possible”, but “fully expect”!!!

I debated giving up versus trying to argue on the finer points of battery chemistry but it seemed like a lost cause. I’ve been very reluctant using my celebrity status as the author of TWiB, and I have to say that it is intimidating arguing with a “genius”!

So I shelled out $130 for a new battery; thanked the guy for his help; and left.

I drove back re-examining my whole life and everything I know. I always thought there was some merit to the George Costanza (of Seinfeld fame) principle of doing the opposite of what our instincts tell us. Maybe I had it all wrong. Maybe you should not be pulling the plug. Maybe my jingle on battery rules needed to be rewritten.

A couple of days later my confidence started to return. I decided to do what anyone looking for credible information does: perform a google search to see if plugging in your laptop battery is bad. I came across my original blog post on this topic. I sounded so convincing in the post that I started to get re-convinced that I was right about my rules.

So what is going on? How can a battery die when it is self discharging on sleep?

Here is my take.

All you PC folks are familiar with the hibernation mode that you can either force your computer to enter, or set it such that the power management utility moves the computer to hibernation after a while of being at sleep.

In sleep the computer stops many of the processes from running and thereby decreases the processing needs and hence drains the battery slowly. In hibernation, the computer (presumably) stops pretty much everything; stores the state in memory; and basically shuts down. This means there is very little drain on the battery.

In a Mac there is a sleep option, but there is no hibernation option. However, if you are in sleep and if your battery drains down to some small state of charge (say 5%), then it automatically moves into a “hibernation” mode; freezes the state and stops all the processes.

One thing we had noticed in the dead Mac (before it died) was that when we opened it over the weekend it was pretty much in hibernation with little juice left in the battery.

Ideally hibernation in a low state of charge is a good thing. Remember the rule “don't charge them too high”? Higher the voltage of the battery, worse will be its capacity fade. So storing it at a low state of charge (or low voltage) is actually good for the battery.

Did I mention that keeping the voltage way too low (i.e., over-discharging) is a bad thing?

This is because many cathode materials can get irreversibly damaged on over-discharge. More importantly, if an anode is over-discharged you can start dissolving the current collector (copper).

When you discharge the battery and it reaches its end of discharge voltage, depending on the battery chemistry (i.e., the anode and cathode that it uses) and on the design of the cell, the battery is limited by either the anode not having any lithium left, or the cathode not being able to accept any more lithium.

As you cycle this battery there are side reactions in both the electrodes. The extent of these side reactions depends on the design of the cell, the chemistry of the electrodes, the composition of the electrolyte, the level of impurities in the manufacturing, the way the battery is formed etc.

In other words, the side reactions are pretty complicated.

However, what we need to understand is that these side reactions can actually change the way the electrode reaches the end of discharge. They can even change which electrode limits the end of discharge.

So here is my take on what happened to the Mac battery.

The battery management system had a methodology of estimating the state of the battery and deciding if its needs to jump from sleep (the usual mode) to hibernation. This estimation was probably pretty accurate at the beginning of the life of the battery.

But years pass (3 in my case); the side reactions chug along; and they start changing the shape of the voltage curves, especially at the end of the discharge. Slowly, but surely, the management system was making errors in its estimation on the remaining charge.

The battery was not fading appreciably. Instead it was becoming harder to predict the time it would take to go from, say, 5% SOC to being fully-discharged.

I think that as my battery kept fading, the transition from sleep to hibernation was not getting triggered correctly, the battery over-discharged.

This is why when I checked the battery voltage it was sitting at 1.5 V.

I have a sneaking suspicion that my battery may actually come back to life if charged but that the power management software is not allowing any charge to reach the battery because the battery voltage is so low. I should have asked for my old,dead battery to try to resuscitate it myself!

If this sounds like an easy explanation considering how complicated all this is, its because it is the only plausible explanation I can come up with. If Steve Jobs would like to disagree, I’m listening.

So I still believe that if you “pull the plug, your battery will thank you”. I am glad I don’t have to go back and change 7 of my posts and apologize to my regular readers (all 7 of them!)

So what can one do about all this? Download the desktop hibernation widget at http://deepsleep.free.fr/ This gives you a way to move your Mac directly into hibernation instead of to sleep. This is probably a good thing anyway to conserve battery on long trips etc.

Or you could buy one of the new Macbook air computers which comes standard with hibernation.

In the meantime, my rule stands: Pull the plug, and your battery WILL thank you.

When Albert at the Apple store told me he “fully expected” my battery to behave this way, maybe, just maybe, he actually knew all this. After all, he is a “genius”.

Venkat

If your cat has nine lives, shouldn't your battery have at least two?

2010-11-22T19:29:00.000-08:00

Let’s see if you can answer this pop quiz: How much capacity fade can you tolerate in your battery before you consider it “dead”?

The answer (as usual) depends on the application.

If you have a laptop and it is anything like mine, then “dead” is when you get 10 mins of run time and you decide to bite the bullet and get a new battery. With some laptops (the one that comes to mind is made by a company whose name starts with a D and ends with a L and has four letters) getting one year from your battery is considered very good.

But laptop batteries are $50. And most customers are probably going to go back and get their next laptop based on price anyway, so there is no long-term effect of giving someone a bad battery. And if your laptop battery dies you can use it plugged in (i.e., as a desktop).

But if you had an EV which run’s 200 miles and if in, say, 3 years you start to get 160 miles, you can be confident that you will sitting in the dealership demanding that they change the battery for you. At $10-$30k a pop you are not about to pay for another battery.

And running your car with a long cord connected to an outlet can be a bit problematic.

But, as definitions go, most manufacturers will consider a battery to be at the end-of-life if it has lost 20-25% of its capacity. In some applications (e.g., HEVs) 20% loss of power is considered end-of-life. The less expensive the battery, the higher the loss that is tolerated and vice versa.

What this means is that when your EV battery is considered dead, it still has 80% of its capacity left.

Despite the fact that you are reading this blog, I’m going to go out on a limb here and assume that you are a smart person. Right about now, you must be thinking to yourself that it is stupid to call something dead when there is 80% of it left.

Do you get new brakes or tires when they have depleted by 20%?

No! You wait till your tires are bald and you skid into your auto repair shop and stop the car by crashing into something soft.

By now you are, hopefully, having this epiphany that there may be a hidden business idea here. One that involves taking these “dead” EV/PHEV batteries and using it someplace else.

Maybe ship it to some other country where they may not be as picky about the number of miles you can get?

Or maybe if you can find an application where energy density were not important, you can repurpose these batteries to sell it for these applications.

While you chew on that, let me change subjects.

Did you know that as states like California decide to enact renewable standards, utilities companies are going to have a problem? California promises that by 2020, 33% of the state’s electricity will come from renewable sources. So let’s say that to satisfy the mandate, the utilities decide to build a giant solar farm in the middle-of-nowhere (Tracy?). But even in the middle-of-nowhere the sun does not shine at night.

So enter storage as the savior. You charge the battery during the day and discharge it to power the cities at night. Transmission allowed us to space-shift the electricity (generate in point A, use it at Point B); storage allows us to time-shift. Its the DVR (or TiVo) of the grid.

And how much electricity are we talking about storing? California uses electricity in the range of giga watt hours (GWh). So a lot!

Some of you may have heard of AB2514. Its a legislation in the state of California that requires utilities to incorporate storage in the grid. The utilities will need to store 2.25% of the daytime peak power by 2014 and 5% by 2020. This is probably the first explicit mandate calling for storage to be a part of the grid.

For all you veteran battery folks who thought the community did not know how to lobby, take heart. We may be nowhere close to what the hydrogen guys have done, but it is a start!

But let’s back to the storage issue.

So storage is the DVR of the grid. And because your DVR is not moving, it can be big (and ugly if it is like my DVR).

But DVRs cost extra money and they die every few years. Batteries are a lot more like your DVR than you can imagine!

Meaning, the energy density of the battery is not that important for this application. The great thing about middle-of-nowhere is that there is a lot of it out there. What is important, however, is the cost.

Hence the interest in taking “used” vehicle batteries and using it in grid applications. A second life, if you will.

Think of the possibilities: If your battery lasts say 15 years instead of 7 years, then you just doubled the time to amortize the upfront cost. You can ask the utilities to buy the car batteries and lease it to the consumer. Once the battery is “dead”, the utility moves it to grid applications and starts its second life. The consumer does not have to worry about paying $15,000 extra for the battery or worry about it dying on them. Someone else owns it; all I need to worry about is making sure I don’t get into a crash and ruin my warranty.

There are other themes on this business plan, but you get the idea.

All this is sounding so great that I’m contemplating sending an email to my bosses telling them what I really think about my job.

But wait a second. This whole blog survives only because we hate our energy storage devices. How many examples can we think of for our batteries lasted more than a few years? My car battery, which died after 7 years, has been the only battery that has done me proud. And I was lucky to get anything close to that!

We all spend an inordinate amount of time babying our batteries and asking how we can extend the life, and here I’m claiming that we can get a second life from our batteries. There must be a reason why my post “pull the plug, your battery will thank you” has the highest hit among all the posts.

What exactly are we missing?

Turns out that we are not missing anything. The second life concept is being pushed by business-types. For a biz. dev. guy this makes perfect sense. But the real question is: Does this make sense for the tech guy in the back actually doing the testing?

Let’s look at this in detail.

If you plot the capacity of a battery versus cycle number you will see that different batteries fade differently. Some batteries fade rapidly in the 1st few cycles and then the capacity stabilizes. Others increase in capacity in the 1st few cycles then level off and then starts a linear fade.

And in some batteries, as you keep cycling them there is a point where the curve starts to “roll over”. In other words, what began as a linear fade starts to accelerate. When this occurs, you are a few cycles away from a complete dead battery (i.e., you can’t even power your watch with it!).

Lets talk a bit more technical for a minute. Those not interested, move a few paragraphs over.

Let's take a Li-ion batteries with a NCM cathode with 14% 1st cycle irreversible loss and a graphite anode with 8% 1st cycle loss. After formation, the battery discharge is dictated by the voltage of the cathode when the battery reaching the cutoff voltage. There is still lithium in the anode. Think of this as an anode-discharge buffer.

But then let us assume that the cathode works very well. The anode, as anodes tend to do, still has a small side reaction because the SEI (which is a passive layer on the anode expected to protect it) is not quite as protecting as we hoped for.

As each cycle proceeds, the lithium comes out of the cathode and a small part goes into making a new SEI and does not intercalate into the anode. As you discharge, you start to slowly deplete this anode buffer. Each cycle slowly pushes the anode potential higher and higher. At some point, all the buffer is fully depleted.

Before this buffer was depleted, if you looked at the graph of capacity vs cycle number you would not have seen any capacity fade. When you hit this point, you will start to see the fade and what you observe is like a roll over. The slope of the capacity fade curve changed.

In some cases, this change starts to accelerate the fade because of the placement of the cutoff potential in the battery.

Ergo... battery fade is nonlinear and just because you have a particular kind of fade in the first five hundred cycles does not mean the fade can be predicted over the next five hundred cycles.

All right, so you think the battery you are making is different. It has a cathode that has less irreversible loss compared to the cathode. So you don’t have the same chemical problem.

But maybe you have a mechanical degradation problem.

All batteries “breath” as they charge and discharge. As each cycle proceeds, you are slowly swinging the volume of the battery. The whole electrode is under stress (compressive in one direction and tensile on the other). Fatigue starts to set in. After repeated cycling, at some point cracking and breaking start to become a problem. Now we have a definite capacity fade.

As some of the particles break and stop participating in the reaction, the rest of the particles have to take the load and these particles are stressed further and this accelerates their fade.

And these effects depend on the kind of cycling that has been conducted. A 3 hour discharge (like that in a EV) will have a different fade characteristic compared to a 1/2 hour discharge (like in a 10 mile PHEV).

Let us try a third case. Let’s say you have a battery pack consisting of 100’s of cells (or 8000 cells if you are at Tesla). Now, its kind of hard to make all the batteries exactly the same. When you manufacture batteries the yield is not that great and companies typically wait three to four weeks before binning (sorting) the batteries. But batteries are not binned for consistent life, because there is no way to do that. Instead they are binned for self-discharge, which does not tell us much about the life.

So let’s say that as the pack is cycled, you start having a few cells fading at a faster rate. Then the cells that are good are going to work that much harder and so they will start to fade more. This will also result in an acceleration of the fade. And because its not possible to predict a priori at what rate each cells will be fading, its impossible to predict how long the whole pack will last.

If that sounded complicated it was a desperate attempt to hide my insecurities by trying to convince you that I know something about batteries.

The short summary: Battery fade is complicated and difficult to predict.

Now, not all batteries are going to do this. Some battery chemistries are better than others. And some companies (that can make consistent cells) will be better than others. But the question remains: How do we predict what is going to happen in 15 years, when the weather report seems so far off for the next day?

But why predict. Why not just cycle these batteries; wait for them to die; and use this data to find out how to cost the battery and amortize it; and then sit back and watch the moolah pile up.

Because it takes.... 15 years to get this information and we don’t have another 15 years for this business plan to come into effect. To be fair, we have been testing these batteries for a few years now and have some data. But this is nowhere close to the number of years of data needed and so we still can’t say for sure how many more cycles/years the batteries will last.

So why not do accelerated testing, you ask? Because one is not sure if the method used to accelerate the fade (e.g. increasing the temperature) results in the different fade mechanism becoming dominant. Chemistry has this nasty habit of being hard!

So all the biz dev types have a problem: If you can’t predict how many cycles/years the battery will last how do you price the batteries today?

And the tech guy in the back of the room doing all the testing is sweating because he/she knows the complexity and knows that it is hard to predict how the battery is going to behave so far in the future.

Personally I think the concept is great and in time we will know how to make this a profitable business plan.

But for now, I’m not going to send that email to my bosses. I’m thinking about buying a house and I need the paycheck!

Venkat

This week in sulfation

2010-11-07T09:14:00.000-08:00

First off, I have to apologize to all 7 of my regular readers for not making a post in a while. I have been busy and hence the hiatus. Between watching reruns of Curb your Enthusiasm, election ads, and the Giants world series games, I need more time in a day. But all good things have to come to an end. I hope to resume regular postings starting now.

This week, I was rudely reminded that just because you know how batteries work does not mean that you can deal with a battery problem. But first some background.

Subaru's are excellent cars and I would highly recommend buying one. They are well made, they run great, and they hardly give you any problems (touch wood). But Subaru's also have small quirks that can be bewildering and a bit infuriating. Like not having a remote trunk opener or having only 3 wiper speeds. Or having this one light that does not turn off when the ignition is off and is so hidden that you can't tell that its on in the first place.

The light serves no real purpose, except to make sure to keep the battery industry thriving. Long story short, "someone" left that light on on Sunday (and I'm not saying who).

A bit more background: My car is 7 years old. My battery is (or was as of yesterday, but I'm getting ahead of myself) the original battery.

Monday morning at 7 AM I get to my car to start driving to San Francisco Intl. to catch a flight to Washington DC to be at the center of the action during election day (Tuesday). I was using a meeting on energy storage for grid applications (think storing solar and wind electricity) as an excuse to get someone else to pay for the trip. I was going to be gone all week.

Except my grand plan was crumbling because my car appeared to have a dead battery. I quickly realized what had happened.

When professionals are thrown into a crisis, they do not think, they react. Think Jason Bourne coming across an assassin or Neo coming across Agent Smith (in the Matrix).

Just so there is no confusion: I consider myself to be a professional.

In a matter of seconds the pieces started to fall into place in my brain without any real thinking. I knew my battery was probably pretty sulfated (and corroded with lots of shedding, for that matter). I opened the hood, took one look at the battery and I could literally see the sulfation on the plates (through the grime that covered the hard polypropylene battery shell). I knew that if I jumped the car right away I had a chance of saving the battery. I also knew that if I left it in the discharged state all week, I would probably sulfate it more and maybe end up killing the battery altogether.

To remind you, when you discharge a lead-acid battery you form lead sulfate. Lead sulfate is pretty insulating. But it has a bit of solubility in the electrolyte (sulfuric acid). This leads to some Pb2+ ions in solution. When you charge, these Pb2+ ions allow you to get back to the charged compound. As you react the Pb2+, more lead sulfate dissolves.

Sulfation is a process by which the lead sulfate starts to agglomerate together to form large crystals. This leads to a loss of surface area. What this means is that you don't have enough area for the electrolyte to dissolve the lead sulfate to form Pb2+. So charging the battery gets harder. Sulfation takes a while; maybe in the order or days. Not hours.

Sulfation is reversible. But you have to charge the battery very very (very) slowly so that you slowly dissolve the large crystals of lead sulfate to Pb2+ and convert them back to the charged state. But, who has the patience to wait all week to charge a battery!

What this means is that discharged lead-acid batteries are bad news. You need to avoid them like the plague.

So the path was clear: Get a jump start, drive the car for the next hour and half to SFO and hope that the battery gets its life back. Like I said, a professional does not think. He/she reacts.

But a professional also recognizes his/her limitations. In my case, my limitation was that I was really cheap and had not invested in jumper cables or AAA insurance. A professional also typically has no real friends. I knew that none of my "friends" would be willing to stop by to give me a jump at 7 AM.

So I reacted to this problem by taking BART (i.e., public transport) to the airport.

I dont know if you guys encounter this, but sometimes when you have something on your mind it seems like the whole world is starting to think about the same thing. So here I was thinking about sulfation of lead-acid batteries and at this conference on grid storage, there was all this talk about the UltraBattery (this is a trade name) as a means of preventing sulfation. There were actually two talks completely dedicated to it.

I spoke about this advance a little while ago. The concept is to add some carbon into the negative plate when you make the electrodes. Everything else stays exactly the same. But for some magical reason the sulfation decreases significantly.

The talks were showing data where the battery was being cycled a little bit (like a Prius battery does) where the battery without the carbon tanks after a few hundred cycles but the one with the carbon works much better (thousands of cycles). Apparently, the carbon solves the sulfation issue.

There is a variant of this idea which involves connecting the negative plate in parallel to an electrode made of activated carbon. Activated carbon by itself is used to store energy in the double layer (i.e., a double layer capacitor). So essentially you are connecting a battery electrode in parallel to a capacitor electrode in both these configurations.

What was amazing was that they really had no idea why this was happening (although its been a few years since this first came out). DOE is actually funding a project to try to get to the bottom of this advance. Its sad but true- there is a fundamental change in a 150 year old technology but we have no idea why this change occurred.

Some things in life are really hard to reconcile (e.g., is there a God? why does EVERYBODY make more money than Scientists?) but this problem is not in the same class. I believe that this lack of understanding comes down to limited funding for research combined with the "herding" of research topics.

Lead-acid batteries are cheap. The one that I ultimately replaced my car with cost me $165/Kwh. Assuming I got ripped off (is that even an assumption for things car related?) it stresses the point that these batteries are cheap. Adding a few percent of activated carbon to the paste is not going to break the bank. All through the conference I kept wondering why lead-acid's are not being made with a bit of activate carbon to ensure that sulfation is not a problem.

As an aside, the cheapest battery we know of is the lead-acid battery. For grid applications, the thought is that we need batteries that cost less than $100/kWh. Something pretty radical has to happen for us to make these cost numbers. Making batteries the way we have made them in the past will not allow us to get there. But this is for another post.

So would adding a bit of carbon result in the battery lasting the life of the car (say 15 years)? The company that is commercializing this says it could last 7 or maybe 15. Meaning: they have no idea! Problem with not knowing why something works- there is no way to predict how long it will work. Moreover, the data they show is based on Prius-like cycling. My car does not have the same cycling profile. Unless we understand what is going on, we have no way to knowing how changing conditions will change performance.

In time, this data will show up and we will know if we will can make a better lead-acid car battery. But wouldn't it be better if we understood what was going on?

Truth be told, I'm not at all convinced that my battery was sulfated and could have been saved with a timely jump start. It lasted 7 years! That's a long time. Plates corrode and they shed. Maybe I ought not to expect more from my energy storage devices.

But being able control failure modes in batteries is crucial in ensuring that we can move to electric drive. And they will be crucial if we ever want to store the electricity from the sun. Solar panels last 25 years; do you really want to change your batteries every 5 or 7 years?

But to control the failure, you first need to understand them. And in many cases, we don't quite have life of batteries pinned down. They change with chemistry, multiple failure modes occur at the same time, and in some newer chemistries we just haven't had the time to collect the data to see what the failure mode is.

So we have clues and hypothesis for failure, but we can't quite predict failure rates with cycling conditions. There is no cycle/calendar life simulator for batteries.

Actually that is not true. There are many many life simulation tools for batteries. But none of them actually work!

To me this incident highlights the importance of fundamental research to understand real-world problems. There is quite a bit of fundamental research; and there is no dearth of real world-problems. What we don't do enough of is linking the two (The Program at Berkeley is unique in that its the only one that does this in the whole field of batteries).

It also highlights the fact that I really ought to stop being so cheap, spend some money, and get jumper cables.

Venkat

A Brief History of Batteries- Part 2

2010-09-06T13:54:00.000-07:00

Last week I posted on the need to understand the history of battery development and how this will influence the future of batteries. We conclude today with Part 2 of this series.

Chapter 3: If it is sparingly soluble, then lets talk.

The lead acid battery is the first rechargeable battery ever made. Its endurance over 150 years is a testimony to its robustness (or to the fact that battery researchers can’t seem to find anything better even after 150 years. It is all a point of view!).

The lead acid battery undergoes what is called dissolution-precipitation. This is the mechanism by which charge/discharge occurs in the battery. Basically, you dissolve the compound in solution and then it precipitates out.

The behavior of the lead-acid battery is remarkably similar to that of the zinc electrode in a Zn-manganese oxide alkaline battery or for that matter to the lithium thionyl chloride battery.

But if the lithium thionyl chloride is not a rechargeable battery and the zinc-manganese oxide is not a rechargeable battery, then why is the lead acid a rechargeable battery?

This is because the lead sulfate is soluble in sulfuric acid (which is the electrolyte) unlike the lithium chloride. But it’s not as soluble as the zinc oxide in potassium hydroxide.

Its solubility is not too much, nor too little. It’s just right! It’s referred to as a sparingly soluble salt.

This feature of having sparing solubility is critical in making a battery that undergoes dissolution-precipitation recharge.

This occurs because the reactants and the products are right next to each other. This means that when you go in reverse, there is a high probability that things go back to the same place where they came from. Not having something move around is a great way to prevent shape change.

Once you understand that solubility is key you begin to understand the decades that were spent on trying to change the solubility of zinc oxide in electrolyte using various techniques. And you begin to start thinking about ways to encapsulate the zinc. And you begin to wonder if you should never let the zinc precipitate as zinc oxide and if you should just keep it as zincate by, say, flowing it.

All these perfectly valid ideas start to make a lot of sense. What you can’t answer is if these ideas will succeed in solving the fundamental problem with the zinc electrode.

But we should remember that in general, the lead-acid is not the greatest battery in the world when it comes to recharging. Think sulfation. Remember the blog post on battery rules where I Haiku-ed my way to better battery life? Remember that sulfation occurs in the discharged state.

The reason for this is also fundamentally connected to this dissolution-precipitation mechanism. On the one hand, this mechanism allows you to make a good rechargeable battery, on the other hand, it also causes it to die in time.

Moral of this story: If you want good rechargebility, dissolution-precipitation is not a good idea, although we may be able to live with it.

Chapter 4: And you thought electroplating was easy.

Electroplating has been a gift that has been giving for decades. Probably the last big development was the via-hole plating of copper for making semiconductor chip interconnects.

In general, plating something uniformly is not easy, but it’s not an unsolvable problem either. We do have a lot of smoothly plated stuff all over the place.

This is until you try plating lithium (and a few other metals, including zinc). Plating lithium is sort of important because this would be the charging reaction if you want to make your watch battery a rechargeable battery or if you want to make a Li-sulfur or Li-air battery rechargeable.

People spent much of the 2-3 decades of the last century trying to make a rechargeable lithium (watch) battery. The last time I check, I was asked to buy a new watch battery and not try to recharge it.

This is because, in the case of lithium, the plating results in dendrites and lead to shorting of the battery.

The reason for this starts with surface inhomogeneities that lead to nucleation of the deposition process in one spot, after which ohmic and transport effects lead to further amplification of this inhomogeneity.

That complicated paragraph is tying to tell you that it plates out like a needle sticking out of the electrode. The needle can puncture through the separator and short to the cathode. As I keep mentioning in these blog posts, shorting a battery is not a good idea. Really, it is not.

Same problem happens in the zinc electrode. Zinc wants to plate out as a dendrite instead of a smooth surface. Same reasons as above.

Every electrochemist that learns of this issue immediately thinks of 10 things to try that could solve the problem. Turns out all 10 ideas probably don’t work.

There have been, literarily, thousands of studies on trying to solve this issue. The most promising appears to be using a separator that is hard and prevents the dendrite from growing.

But as of today, we do not have a method to prevent lithium dendrites at room temperature and give us good power capability. It’s a problem that is still around.

The moral of this story: If your battery requires you to plate out a metal, it is probably going to be an issue achieving good rechargebility.

And if you want to make a rechargeable Li-air or Li-S electrode, getting the lithium to recharge is, I’m pretty confident, a pre-requisite.

Epilogue: Rules to live by.

So how do we make a rechargeable Li-S and Li-air (or zinc-air) battery?

If I knew that I would not be writing blog posts!

But we need to beat three things that history has taught us:

1. Avoid electrodes that require a plating reaction.

2. If you have a product that is highly soluble, you are in trouble

3. If you don’t have any solubility, its worse

One can avoid all this by finding systems where no structural changes happen. Thus were born systems like Ni-MH, Li-ion, and Ni-hydrogen. These systems have their own problems, but atleast we are starting with something that has certain inherent advantage. I will elaborate on these problems in the very near future when I delve into the present-day developments in batteries.

But suffice to say, if you want to make the battery of the future, then you have to beat the three issues listed above.

Along the way, you may make the batteries of the past also work.

Venkat

A Brief History of Batteries- Part 1

2010-08-30T08:56:00.000-07:00

When I was around 13 years old I remember learning about primary batteries in school. This was about the time when I had also encounter lead-acid batteries and had realized that the car starter battery is being charged periodically. I began to wonder why some batteries could not be recharged while other could. Thus began my fascination with batteries.

The above story is probably not true. But it’s etched in my memory probably because it provides me with a romanticized notion of why I work on batteries today. In reality, I was probably contemplating something more useful like “what is the point of learning math?”.

Nonetheless, the question posed is an interesting one in that if we want to understand how to make a rechargeable battery that lasts a long time over many cycles, we first need to understand why some batteries do not recharge.

The development of batteries is deeply rooted in this understanding (atleast one hopes it is and that it isn’t a series of accidents!). Many of the ideas that people are proposing today for better batteries are in some ways trying to beat the fundamental limitations that prevent recharging of these primary batteries.

If you don’t want to make the mistakes of the past, you better understand the past. This post is an attempt to do just that.

The topic I’m discussing is technical. I’ve tried my best to make it accessible. In doing so, I lose some technical accuracy; but this is the price of making it understandable.

This blog post is written in the style of a novel. The story of rechargeability can be written in a very linear fashion which steps through time to illustrate the rules one after another. But this would make it easy to understand. Where is the fun in that!

So, I’ve borrowed a page from Quentin Tarantino’s movie Pulp Fiction and scrambled the narrative. Each storyline is distinct, and they are all interrelated. If the stories were arranged chronologically as the systems developed we would go Chapter 3, 2, 4, 1, Prologue, Epilogue. I personally think the scrambled version reads better.

This week I will start with the Prologue and Chapters 1 and 2. Next week I will finish with Chapters 3 and 4 and the Epilogue.

Fortunately, these stories are easier to follow when compared to Pulp Fiction.

And there is no swearing or violence.

Prologue: Do I smell sulfur in the air?

There has been a lot of interest over the last few years on two systems that have been around for years. These batteries are sold as going “beyond lithium-ion”. These systems use lithium metal as the negative electrode and air (rather, the oxygen in the air) or sulfur as the positive electrode. Some consider these systems to the Holy Grail of battery research.

The promise that these battery chemistries hold is enormous. In the case of lithium-air, the gravimetric energy is an order of magnitude higher than today’s batteries. Think cars that can drive 500+ miles, cell phones that actually last all day, laptops that can last the complete transatlantic flight... The volumetric energy is not that great, but hey, let us focus on the positives, shall we.

But there is a hitch (there always is).

In the case of lithium-air, it turns out that recharging lithium metal is a problem. And the oxygen in the air reacts to form a compound that is basically pretty insoluble.

In the case of sulfur, the lithium metal continues to be a problem. And the sulfur electrode undergoes a series of reactions giving products that are either highly soluble, or insoluble. All the products are a real pain to deal with and history shows us that dealing with them may not be for the faint of heart.

If we are to succeed in getting these batteries to work, we first need to understand why similar concepts have failed in the past.

Chapter 1: A business plan that can’t fail- Take cheese; make milk.

You may remember my previous blog post where I alluded to the lithium thionyl chloride battery.

This chemistry is used for missile applications. In this battery lithium dissolves from Li metal on the negative electrode and the resulting lithium ions combine with thionly chloride (SOCl2) to form lithium chloride (LiCl) in the positive electrode.

This is the process that occurs on discharge and it works pretty well. If you want to recharge this battery, you will need to take the lithium chloride and convert is into thionyl chloride. This is where the problem occurs.

Lithium chloride is an insoluble solid. Once you form it, it pretty much sits around and starts clogging up the whole cell. Converting lithium chloride back to thionyl chloride is like trying to find a Quentin Tarantino movie with no violence- its not hard to find; its impossible to find!

Think of this as taking a pot full of hot milk and adding lemon juice to it. The milk curdles and you get cheese. There is pretty much no way to get back to milk and lemon juice from cheese (as far as I know). Same story with lithium chloride.

If, on the other hand, the lithium chloride were soluble in the electrolyte and dissociated in the solution, one can think of trying to recharge the system. However, because lithium chloride is not soluble, there is no way to recharge the battery.

Moral of the story: If the product of your reaction leads to an insoluble product, in some batteries, recharging can be a problem.

The caveat “in some batteries”, is kind of important, but that is not for this post.

Something similar happens in the lithium carbon monofluoride system (Li-CFx). In this system, much like the thionly chloride system above, the lithium dissolves and reacts with the carbon monofluoride to form lithium fluoride and carbon; both solids. Trying to go back to the starting chemicals by reacting the lithium fluoride with the carbon is pretty much impossible. It’s the cheese to milk problem.

So solubility is something we ought to be paying attention to when it comes to recharging.

But what if the product of the reaction is highly soluble (think salt in water)? This must be the best thing possible for recharging, would it not?

Turns out that this is not true either. This would be the story of the zinc electrode. As in the zinc-manganese oxide alkaline battery (the Energizer-bunny battery).

Chapter 2: If only the Dead Sea weren’t as salty.

The alkaline battery is actually a rechargeable battery. It’s just that it is not a very good one. Some of you may remember that there were rechargeable alkaline batteries in the market that promised a few cycles. These all appear to be gone from the market. I guess no one wants to carry around a charger.

The positive electrode (MnO₂) in these batteries can recharge thousands of times if you are careful to avoid certain phases. I personally believe that this chemistry is worth revisiting.

It’s the zinc electrode that is the problem. The reaction involves zinc electrochemically reacting and forming a complex called zincate. As the concentration of zincate increases, it precipitates out as zinc oxide. Think of this as adding salt into water. You can only add so much salt before the solution gets saturated and any more salt you add stays as crystals.

This is the simple version.

The whole reaction scheme is actually pretty complicated. Turns out that five other reactions can happen in this battery depending on various conditions. Some years ago, I was involved in modeling of the zinc-MnO₂ battery and it is by far the most complicated battery chemistry there is. Lithium batteries are so much easier to understand with compared to this system.

The zinc oxide has pretty high solubility in the electrolyte (potassium hydroxide). What this means is that zinc oxide easily goes into solution to form zincate in the electrolyte. One would think this is great for recharging and it is. But it turns out that when you try to deposit the zinc from the zincate, it does not deposit in the same place where it dissolved.

This leads to the structure of the zinc electrode changing continuously as you charge and discharge the battery repeatedly. This is referred to as shape change. Shape change leads to the zinc depositing as a solid mass in the one part of the electrode. And this solid mass is hard to react. Slowly, as the solid mass gets more pronounced, the zinc electrode fades.

Reduce the solubility of zinc oxide and you can decrease the shape change and increase the cycle life. There is some wonderful data that shows that. This is like somehow making salt less soluble in water. Turns out that in reality this approach also kills the power of the battery and so this is not a real solution.

The reason why the shape change happens is a bit complicated, and probably not relevant at this stage. What does matter is that, in some batteries, very high solubility can be a bad thing and can decrease the ability to recharge.

Moral of the story: High solubility may not necessarily be a good thing for recharging.

So we have a problem. Neither no solubility nor high solubility appears to be a good idea. So how do we make a rechargeable battery?

We shall look at that in the next chapter. Next week.

Now… isn’t that a nice tease! Stay tuned.

Venkat

One battery chemistry to rule them all?

2010-08-16T11:59:00.000-07:00

Darwinism is alive and kicking in the battery world (despite the threat the theory faces in other spheres).

Let me elaborate.

The Bible (or Koran, or Gita or… take your pick) for most battery-related topics is the book “Handbook of Batteries” by David Linden. It’s page after page of different chemistries that allow us to store charge. Some of these are primary batteries (not rechargeable) and others are secondary (rechargeable). Some operate at high voltages, others at low. Some are water-based, others are non-aqueous. Some operate at room temperature, others at higher (much higher) temperatures.

What is not listed in the book are a bunch of chemistries that can still be made into a battery but are not worth listing because no one is interested in using them.

One can (literally) go to the periodic table, pick up two elements from it, and make a battery from these elements. In all probability the resulting battery will not be very good, but you can certainly make something (think lemon battery).

Of these numerous combinations of anodes, cathodes, and electrolytes that make a battery, natural selection kicks in and we identify the ones that give us favorable performance. From this Darwinian process we end up with the batteries that we all know and love (although love may be too strong a word to describe our relationship with our energy storage device!).

Volta and Daniell could be playing with the Zn electrode, but it took putting it with a MnO₂ electrode to make it a commercial success that endures to this day. Similarly, we could play all we want with a Li metal anode but it took pairing an oxide cathode with a graphite anode to make, what is come to be called, a lithium-ion battery for this concept to be a successful rechargeable battery.

Along the way, we have relegated a bunch of batteries to niche applications. No one has heard about a lithium-thionyl chloride battery because it’s used in obscure military applications involving missiles, nuclear bombs, remote launching, and a button in the White House (or so I’m told. Who knows). Similarly no one knows about the nickel-hydrogen battery, despite it being the chemistry that has the highest cycle/calendar life of all batteries we know of (the catch: it costs 100 times that of lithium-ion batteries. And you thought lithium-ion was expensive!). But it sits quietly in space powering our satellites day in and day out.

But natural selection does not happen overnight. There is a period of instability where it is not clear if a particular species (or battery chemistry) will make it or if it will left to the ash heap of history (being dodo-ed, so to speak). And similar to evolution, in battery chemistries, there is also such a thing as relegation to a niche (I will not give any examples from the animal kingdom because of the risk of offending someone). To survive you don’t have to be the fittest, you only need to be fit enough to have a market share, however small the share may be!

But let us stop this history lesson and get back to the modern day where I believe we are in the cusp of one (or two) such evolutionary change(s).

One is in the area of lithium batteries for vehicles.

The class of batteries that we have come to call lithium batteries is unlike the previous battery chemistries that we have encountered in that it does not represent a single anode/cathode/electrolyte combination.

When someone refers to a lead acid battery, they are talking about a battery that has a lead dioxide positive electrode and a lead negative electrode with sulfuric acid electrolyte. You may be using some carbon in the plate, or using a different current collector grid, but fundamentally you have not changed the voltage or capacity of this battery. In the same way a Ni-Cd or Ni-MH battery has a clear meaning in defining the anode/cathode/electrolyte.

When someone says they are using a lithium-ion battery that only tells you that the class of battery where the charge is carried by a lithium ion. The anode, cathode and (to a lesser extent) electrolyte are not specified. It could be a graphite/cobalt oxide battery that your cell phone uses or a graphite/lithium manganese oxide battery that your powertool uses. Both are called lithium-ion batteries.

In what I consider to be a public-relation disaster, the lithium battery community decided to club all these chemistries into one term, lithium-ion. If, instead of calling the graphite/cobalt oxide battery a lithium-ion battery, they had called it a, say, carbon-cobalt battery, today we would be talking about a carbon-manganese battery, a carbon-iron battery, a carbon-nickel battery, a titanate-nickel battery and so on and so forth.

If we had the foresight to do that (I use “we” to refer to the royal pronoun. I should not blame myself for this because I was but only a teenager when this happened) then it would seem like batteries are changing all the time. Instead, we get asked uncomfortable questions like “Lithium batteries have been around for 20 years. So… are you guys doing anything new?”. Not that I’m bitter or anything.

But let’s get back to the topic at hand.

Its becoming increasing clear that lithium-ion will be the choice for PHEVs in the near-term. What is not clear is which of these numerous chemistries will ultimately be the winner.

Would the low-cost, safe manganese system (the chemistry picked by LG Chem/CPI and Dow Kokam) win over the longer-life (presumably, although I have not seen such data) safe iron phosphate system (A123)? Would the higher energy nickelate system (Johnson Control and Saft) be the choice because of its higher energy despite its safety issues? Would the fast-charge capability of the titanate anode (Enerdel and Altair nano) be of any use in a world where even slow charging could be an infrastructure nightmare?

Each chemistry has its pros and cons. There are four criteria one looks for in a battery: Cost, life, performance, and safety. No one chemistry is the magic bullet that satisfies all these criteria. Each choice leads to a compromise. As of today, it appears hard to predict the winner.

We the consumer may be the ultimate deciding authority.

Will we choose a car with more trunk space and decide that we need to use the highest energy density battery we can get our hands on even if its only lasts 4-5 years or would we prefer something that may be a bit cheaper but that may be a small car that is only useful for a short commute?

Or maybe we will end up saying that gasoline is fine and that all this battery technology stuff is hype with no substance (now, that’s a blog post that is well worth making!).

We are at a time when we are unable to clearly see which one (or two or three…or maybe even none!) of these will be our future. GM and Nissan have chosen the manganese oxide system for the Volt and the Leaf, respectively, but this does not mean the race is finished. We live in interesting times, indeed.

Something similar is happening in the emerging market for grid-level electricity storage. With applications ranging from frequency regulation to storage of renewable applications, the time of discharge can range from less than a second all the ways to hours to days. It is clear that one battery will not serve as the solution for all these applications.

There are already many systems that are in various stages of deployment for grid applications. Lead-acid, sodium-sulfur, Ni-Cd, and Ni-MH are being deployed along with lithium-ion. And flow batteries are trying to make inroads. And similar to lithium batteries, flow batteries are a class and can represent anything from vanadium-based, halogen-based, or iron-based (I wonder if we are repeating our mistake with the lithium-ion by calling something a flow battery as opposed to, say, a hydrogen-halogen battery). Some of these systems have been around for a decades, while others are being developed as we speak.

And it’s not just batteries that compete in this application. Flywheels, capacitors, compressed air, and superconductors are jostling for space. Over the next decade, systems will be narrowed down and down-selected to ones that make sense. Something similar happened in the 90’s and in the early 2000’s in the vehicle space and technologies like electrochemical capacitors (or supercaps or pseudocaps) were slowly deemphasized. This is bound to happen in the grid storage space.

50 years from now, when we open the Handbook of Batteries (in whatever form we may be reading at that time), all these chemistries will be in the book. Question is, which chemistries will have the biggest chapters.

Venkat

A shout-out to the separator

2010-08-10T19:05:00.000-07:00

Anybody who has paid attention to batteries (especially, lithium batteries) and/or read this blog knows that in most batteries the anode and cathode materials are the main players for holding charge. There is a lot of research in trying to find new materials that hold more charge at high voltages. But as I have pointed out in my previous posts, we need a few other materials to ensure that we tap into this charge.

Things like current collectors, separators, and the electrolyte.

All these play as important a role as the electrode materials. In some cases, they are actually more important. I have decided to spend sometime giving them the credit they deserve.

I will start with a shout-out to the separator.

Most electrochemical systems (and, yes, batteries fall in the class of electrochemical systems) require some way to separate the anode and the cathode. One tries to keep these electrodes in very close proximity to decreases resistances for ions to travel between them while preventing shorts. An ideal way to achieve this is via the use of a separator. It’s a (arguably) simple physical barrier between the two electrodes that lets ions go through, but not electrons.

However, in some cases, the separator serves a larger purpose. For example, it also ensures that the anode and cathode reactants/products don’t mix. If you are trying to electrolyze water to make hydrogen and oxygen, it helps to not have them mix together (trust me). Separators help ensure that.

Be it a fuel cell, a flow battery or a containerized battery (like a lithium battery), a lot of effort is spent on the separator to make sure that it does its job. For the flow battery that we are planning to work on with a recent ARPA-E award, the separator will be an integral part of our developmental effort.

In the battery space, the separator has always had its part to play. In a lead-acid battery the absoptive glass mat (AGM) separator helps increase the life of the battery. In batteries that use zinc or lithium metal, the separator may help prevent dendritic shorts by retarding the growth of the dendrite. And in the Ni-MH battery it can help decrease the rate of self discharge.

Which bring me to the first news item that caught my eye.

After coming up with the magical iPhone and the magical iPad, Apple has recently unveiled the Magic Trackpad. Interestingly, Apple also announced that they were selling rechargeable batteries with a (magical?) charger for the trackpad (which operates on Bluetooth). Trust Apple to make a Ni-MH battery with a charger sound cool. Will the magic never stop?

In general, the Ni-MH battery is a terrible battery for Bluetooth applications. This battery has notoriously high self-discharge. A typical Ni-MH battery can discharge by as much as 20% of its capacity in 2 weeks in the SF Bay Area and 50% in balmy India, in summer. Bluetooth devices are used sparingly (hopefully your job does not require you to type 24 h a day), so the self-discharge can be a killer.

Apple, on the other hand, is promising 20% capacity loss in 1 year. Magical you think?

Not really. The answer, my friend, is (partly) a separator blowing in the wind.

There are three reasons why Ni-MH batteries self discharge. The first is oxygen evolution on the nickel electrode, the second is hydrogen evolution on the metal hydride electrode, and the third is a nitrate redox shuttle across the two electrodes. All three are forms of internal leaks that discharge the battery.

Mother Nature dictates the first two. It can be hard to beat Mother Nature, especially for mere mortals like me (and, yes… even Steve Jobs), but there are some things we can do to decrease the rate of these gas evolution reactions.

The third mechanism is what interests me in this post and it involves using a separator that traps the nitrates and prevents the ion from shuttling across. This prevents the battery from slowly leaking and keeps the battery charged. Very simple, yet very effective.

These developments in this mature chemistry are only 5 years old and have resulted in a significant decrease in the rate of self-discharge. Which takes me back to my post on how we tend to ignore older chemistries (read non-lithium) in most, if not all, R&D projects in this country.

So here is a shout-out to the humble separator.

Separators for lithium-ion batteries are more crucial in that they can be the difference between an iPhone that is plagued by dropped calls because of antenna issues and one that is burning your pant pocket.

Separators have a checkered history when it comes to lithium batteries. Remember that the volume occupied by this layer is excess space that is wasted. There have been many moves to try to decrease the thickness of the separator, but attempts at making this layer less than 20 microns result in the electrode shorting during a winding process that is part of battery assembly. Shorting a battery is typically not a good idea! Most separators today are 20-25 microns in thickness.

Moreover, these separators have what is called a “shut down” layer. This layer, made of a polymer that melts and shuts the pores if the temperature increases too much, is a mechanism by which reactions are stopped if a battery goes into thermal runaway (or “spontaneous disassembly”, as the industry calls it). However, there are some that say that when this melting occurs, the structural integrity of the separator decreases and the electrodes end up shorting with each other. Statements regarding shorting being a bad idea apply. This issue is still being played out.

As an aside, a couple of researchers at LBNL are doing something interesting with the separator. Tom Richardson and Guoying Chen incorporated a conducting polymer that prevents the battery from going to overcharge. Overcharge causes the thermal runaway in lithium batteries. The idea is to prevent the overcharge and hence make the battery safer.

But lets get back to the separator we use today.

You may remember that YouTube video’s of burning laptops. You may also remember that the cause was attributed to metal particles falling into the battery during assembly and leading to shorting. A way of dealing with this issue is to make a stronger separator; one that will prevent shorting even if particles fall into the battery. Some manufacturers are testing ceramic coatings on the (presently-used) polymer separators to see if this will increase the puncture resistance. This issue is also still being played out.

Obviously all these problems will go away if the electrodes were not kept so close to each other by using a thicker separator. But this decreases the energy density of the battery and decreases the power. Obviously, no one wants that!

Other than being crucial from a safety perspective, separators are also one of the culprits in making lithium batteries expensive.

Battery costs are impossible to find with any clarity (The US military can learn from battery companies on how to keep secrets and prevent incidents like the one with Wikileaks). But, estimates suggest that material costs can range from 50-80% of battery costs. And 25% of the material cost is the cost of the separator!

Think about this. This simple polymer layer, very similar to the polymer used to make grocery bags, can be as much as 20% of the cost of the battery! At the sake of repeating myself, batteries are expensive and we have to decrease the cost significantly to get any widespread penetration of EVs and PHEVs.

Part of the reason why separators are expensive is because of a process that creates the pores. And it appears that the market for separators does not have enough competition to drive down costs.

Which brings me to second news item.

Dupont just announced that they would be getting into the battery separator game by manufacturing their line of lithium battery separators. Information is scarce, but they appear to be using a different process than what their competitors use and promise higher power, and a higher operating temperature. No word on cost, but now there is one more player in this game bringing some competition. That can only be good.

Now if someone can come up with a way to make a really strong separator that is say, 5 microns thick, has a open path for ions, can withstand the winding process, does not puncture even when there are metal particles in the battery, and costs less than $1/square meter, then we should be all set.

For the uninitiated, the paragraph above is like hoping that Microsoft comes up with an operating system that does not crash all the time. It seems doable, but for some reason it never seems to happen!

Until then, let’s thank the separator that we do have.

Venkat

TWiB met TWiT and TWiB got 500 hits

2010-08-07T07:50:00.000-07:00

This blog post has nothing to do with anything that happened in the battery world. But it happened this week, and it happened to me, and it’s my blog so I will make this post.

Regular readers (all 3 of you) of this blog know that the name of this blog is inspired by the popular podcast This Week in Tech (TWiT) run by Leo Laporte. You can see more in my first post.

Without getting into details I got to go to the TWiT cottage (the place where they record the show) to watch a recording of episode 259 this Sunday afternoon. The name of the show is “Next Stop: Gilbert, Arizona”. You can listen to it here.

The whole process of making the episode was sort of fascinating. The TWiT cottage is in Petaluma (i.e., middle-of-nowhere North San Francisco Bay). It is basically a 4 room cottage that has been converted to a recording studio. There were 3 “watchers”, one guest on the show and Leo (there were 3 off-site guests on Skype). All 5 of us were jammed into a small room full of cameras, and recording mics. Leo was twiddling on knobs, turning things up and down, typing on his computer, AND talking all at the same time. Amazing!

Needless of say, everything said in the room is recorded and is streamed live.

The inhouse guest was Brian Brushwood (pictured below), who is a magician and fire eater (no, really!). The other guests were John C. Dvorak (who is a regular on the show and is a tech guru), Baratunde Thurston (the web editor of The Onion. You know The Onion, don’t you?), and Felicia Day (who is a star on the web series, The Guild).

When I entered the room, they were setting up for the show. I was introduced and immediately Leo and Brian started asking me questions on batteries: is there enough lithium?, is there a moore’s law of batteries?, what is happening to battery development? When the off-site guests heard who I was, they started with “should I discharge my lithium batteries all the way?”. Apparently, they don’t read my blog (sigh). Anyway, it was the perfect opportunity to plug TWiB.

Remember that all this is live. There are people out there who are listening to all this. They (apparently) heard me plug TWiB. Anyway, I was checking the stats on my blog afterwards and at 3 PM (around the time I was plugging TWiB), 500+ people logged into the site! Ah… the power of the plug.

At the end of the show, Leo volunteered to take pictures with the watchers. Here is mine with Leo. Brian is in the back doing something funny. The idea is apparently called Photo-bombing where someone in the crowd decides to ruin the great picture of your kids by doing something strange in the background. He was imitating that scenario.

Anyway, you can sum this experience up in one sentence: TWiB met TWiT and TWiB got 500 hits.

Venkat

How do we make the Volt cheaper?

2010-07-31T20:42:00.000-07:00

Two quick notes on things that happened this week. The first represents the present; the second (hopefully) the future.

Chevy Volt pricing:

Its $41,000. No surprise there. There is a tax rebate that gets this down to $33,500. The leasing option seems cheaper, but seems limited to 12,000 miles a year. I drive 18,000 a year and I rent (which means no charging at home for me). I will not be in line for one anytime soon.

The Nissan Leaf is $33,000 before rebates and $25,500 after. This seems so much more manageable, but its only a 100 miles range. You win some, you lose some. What we need is a cheaper battery.

Which leads me to…

A discussion of the future of the battery:

Those who follow this blog know that most of us at LBNL work as part of a large program called the Batteries For Advanced Transportation Technologies. The Program is funded by the US DOE and has researchers from all over North America. It’s the top battery people from Universities, National Labs, and companies. The team reads like the who’s who of the battery world. The goal of the Program is to perform the research needed to discover and make the next-generation batteries.

This week on Tuesday, all of us met for a day at LBNL to discuss the future of batteries. We discussed ways to make higher energy, lower-cost materials, methods to make the battery last longer, and the challenges with moving to new batteries that promise significantly higher energy density compared to today’s batteries. Below is a photograph that we took at lunch.

I will try to tag the picture at some point.

Venkat

If you build it, will they come?

2010-07-25T06:22:00.000-07:00

Many of you have probably come across the piece by Andy Grove titled “How to Make an American Job Before It's Too Late” that was published in Bloomberg. In the article, the former president of Intel argues that losing low-end commodity jobs from the US is a long-term problem. He uses batteries as an example.

In the battery space, all manufacturing of lithium-ion batteries happens in China, Korea, and Japan. Since the mid 90’s when it was becoming clear that lithium-ion was going to be a dominant force in the rechargeable battery market, several US companies have tried to enter the market by setting up plants in the US. None made it big. Some went under; others went back to their core business; still others survived (and continue to do so) on small government projects.

An article written by Ralph Brodd examines this issue in detail. The article is a bit dated, but is interesting reading. Ralph concludes that there are many complicated factors that come into play. Some of these involve the difficulty in penetrating OEM markets (that were all in Japan) for US companies and the fact that lower profit margins were sustainable in East Asia. Interesting he also notes that labor costs are not as significant in this “outsourcing” trend as some claim. I suppose if you automate you can depend on robots not to ask for a minimal wage irrespective of the geography!

Long story short, by the turn of the century, the battery community had accepted the fact that there was no real Li-ion manufacturing in the US. However, most of the community also believed that innovation in batteries happens in the US, and manufacturing (read “low end jobs”) was dominated by Asia.

There are very good reasons to believe that. The materials that power your laptop and cell phone batteries were discovered in the US. Some of the materials that may end up powering your plug-in hybrids and your electric cars were discovered in the US. Ergo... the US leads in the “high value” innovation; Asia does all the “low end” manufacturing.

Andy Grove had come to LBNL last Fall and during a discussion on battery research, he asked what the rest of the world was doing. I answered (echoing the popular belief) to the effect that Asia (read China, but also Korea and Japan) leads manufacturing and the US leads innovation. He cautioned that this was exactly what the semiconductor folks thought, but in time, they started to realize that Asia was starting to do more than just low-end stuff. And he cautioned that the realization might come too late.

What he was talking about was already happening in batteries; it’s just that I was not paying attention. Japan was always a powerhouse in battery R&D (with the Korean’s not far behind), but the last few years are showing that the Chinese are doing just fine, thank you. The number of papers coming from China is increasing and there is a lot more research activity than even a decade ago.

In effect, it is possible to outsource not just “low-end” jobs, but even “high value” R&D. Certainly the last decade has shown that industries ranging from software to pharma are outsourcing their research to China and India.

One could argue that quantity does not imply quality, and impact of papers from the US tends to high compared to most of the world, especially the developing world. But I would argue that as each year goes by, you can expect to see the quality and the impact improve. With money comes equipment, personnel to hire, ability to travel to conferences, and the ability to collaborate with the best and the brightest the world over. And despite the recession, China has continued to grow. If you are looking for money, China is the place to be.

If the manufacturing is in Asia, the talent is in Asia, and the funding is in Asia one can logically assume that future breakthroughs will happen in Asia.

The question then becomes: How does the US get back on the driver seat?

The US DOE decided that one way to do that was to bootstrap the development of a battery industry in the US by providing stimulus money to build factories. A few different companies got funded as part of this effort. These companies will be ramping up manufacturing of vehicle batteries in the coming years and slowly but steadily, the US will ramp up battery manufacturing for next-gen cars. Over the last week, the government issued a report on the impact of all this funding and their expectation of battery performance and cost over the next 5 years. The report, predictably, paints a rather optimistic future.

However, there a couple of problems to worry about. For one, the batteries that are being made have to be sold (Sounds obvious, but I think its worth reminding ourselves of this). For this to happen, there has to be a market for plug-in and electric cars. And as we pointed out these cars will be expensive because of the battery cost. Mass manufacturing will decrease the cost, but for mass manufacturing you need someone to buy these batteries and so you have a chicken and egg problem. And even the decreased cost will still make these cars expensive.

Moreover, most (if not all) of these companies are essentially using the money to build a building, and buying equipment from China, Japan, and Korea to make batteries pretty much exactly as they have been made in Asia except that they are doing it on US soil. Even the chemistry for the anode, cathode, and electrolyte that are being used for are not really unique.

Its not clear is there will be any unique intellectual property that will come out of this. Maybe in time, IP will come, but in the short term there will be little that is different from the batteries made in Asia. These will be expensive batteries with no clear technology advantage over the Asian rivals, but made in the US of A.

But the funding will create jobs, reduce battery costs, allow us to start the process of innovation and IP generation, and provide a pathway for the wonderful research in the Universities and National Labs to reach the marketplace. In the long run, all this can only help.

But in the short run, it is not clear which markets these companies will sell their batteries to and how they will stay in business long enough for all these benefits to occur. I believe that a vibrant PHEV or EV marketplace is key, but it’s not clear how one should enable this. None of the solutions are easy (e.g., a gas tax). But does appear that without incentives, it will hard to jumpstart an electric economy. We may be forced to make these hard choices.

This would be the “If you build it, they will come” route.

Instead of going this route, one could try to do something radically different; generate IP; use this IP to manufacture in the US, and leapfrog Asia. Leapfrogging in batteries is not easy (I suppose by its very definition leapfrogging is not easy!) and as I have noted, Moore’s law is like Murphy’s law for battery folks (we cringe at the mention of both). But one can imagine a new material or a new way of assembling a battery coming along that makes the existing methods obsolete and makes the US the leader in manufacturing as well as research.

There are a few governmental programs that are aiming to do just that. And certainly the whole of Sand Hill Road (which would be the street in Menlo Park that houses many of the Venture Capital firms in the SF Bay Area) is looking to see if they can find the next big startup with the winning idea. Only time will tell if the numerous startups and projects that are attempting to do something radical will end up being truly disruptive. And as I mentioned in my post on David vs. Goliath (or Tesla vs. Toyota), succeeding in the battery space can be hard.

In the meantime, all of you can do your part to keep the battery economy moving. Pay the $40K or $100K (depending on your affordability) and buy a Chevy Volt or a Tesla Roadster. This may mean selling your home, but, as the last few years has taught us, home ownership is overrated anyway.

Venkat

Have Solar Panel. Need Batteries.

2010-07-14T06:40:00.000-07:00

I'm on vacation in the east coast of the US for the week and the sun has been relentless. I can only hope to have clouds and maybe a shower or two to cool things down.

But mention clouds and the solar photovoltaic folks start to go berserk. Apparently solar panels have a hard time being of any use when there is no sun! An hour of clouds and your power generation tanks. Two days of rain can make dependance on renewable electricity seem like a return to the dark ages.

Enter batteries. Why not store the electricity during the times we generate it and use it in the night/when there are clouds etc? Sounds like a great idea, but the problem is... you guessed it... those batteries!

Anyway, long story short there are some batteries (different from vehicle batteries) that have the hope of being very useful for these sort of renewable storage applications. We are talking about MWh of storage (the M is for mega, so... big). There are a lot of batteries that are needed for this application, but the cost of these batteries is a problem and so is the lifetime. A third problem is that the energy efficiency of these batteries is not that great (maybe 50-70%). When someone tells you that the energy efficiency is 50% it means that you use twice the energy to charge the battery than you get on discharge. So 50% of your solar panels are a waste (great for the solar panel maker. Bad for the customer).

ARPA-E, the new kid on the DOE block, came up with a solicitation looking for ideas to fix these problems. This week, they announced a bunch of awards for some interesting new technologies that promise to solve these problems. One of the awards went to your faithfully (that would be me) along with two of my colleagues from LBNL- Vince Battaglia and Adam Weber. For the project we assembled a team consisting of Robert Bosch, DuPont, and 3M. We also had Proton Energy has a partner to help with some designs. Its an amazing team that beings together knowledge of electrochemistry, catalysts, membranes, and balance of plants to work on a battery called a "flow battery".

I will try to expand on what we proposed in the near future. If we (and any of the others funded) are successful, then we can get a step closer to having a more efficient grid. Click here for the list of awardees.

Till now, my blog has concentrated on vehicle batteries. I think its time I expanded into grid electricity. This is another big problem and something that needs attention.

In the meantime, for all your solar enthusiasts that complain about your batteries. Hold on... hold on. Give us a few years and we hope to have something for you.

Venkat

A 200 mile EV or a 13 mile PHEV? You choose.

2010-07-05T06:18:00.001-07:00

The big news of the week (after Brazil loss in the World Cup and the iPhone 4 antenna issues, I suppose) is the IPO of Tesla . With a IPO price set at $17 per share, Tesla saw its shares increase to $30 at some point. On Friday, it was back down to $19.2 a share, but I think we can all conclude that this was a successful IPO. The company got some much-needed cash and the early investors cashed out. The 1st week run reminds me of another greentech "success" story- A123 Systems.

A lot has been said by various analysts on the problems with Tesla (e.g., They have not yet made money and have no chance of making money for the next 3 years), but I think the IPO shows that its possible for a small company to compete with existing players. The same can be said for A123.

Just because a company has a successful IPO does not mean that it is really successful. Tesla has a lot of problems to deal with, chief among them the fact that their cars are a tad bit expensive. Similarly, A123 continues to bleed cash and competition is increasing. Its not clear when one should consider a startup to be successful. Is it when they start becoming profitable, or is it enough if the investors, founders, and early employees make money?

Anyone who has worked at a startup knows that its a roller-coaster ride. Its not the proverbial "two steps forward, one step back". Its more like "ten steps forward, nine steps back". Everything seems magnified. A million things have to come together to be successful. Often times one has to change direction (remember that A123 was not a LiFePO4 company when they began) and this can be hard to do. Suffice to say, start-ups are not for the faint of heart. For all the guys who went through this ride, getting to an IPO will probably be considered an amazing success (well... I suppose 6 months from IPO would be a more accurate date because that is when you can sell).

For the rest, being profitable may be the criteria for success. Obviously this is no easy task. A lot has been said about the ability of a Tesla to take on, say, a Toyota (or a Tata, depending on the market) or a A123 to take on, say, a Sanyo (or a BYD). All these are valid questions and make for interesting speculation. But I think the approach taken by Tesla and that by Toyota exemplify the differences between a start-up versus a traditional giant.

We all know Tesla's approach well. They want to commercialize a pure EV with a 200 mile range. They buy laptop batteries with energy approaching 180 Wh/kg and make battery packs with energy approaching 150 Wh/kg with a total energy of 56 kWh for the pack. Assuming that their car design gets them ~250 Wh for every mile*, they are pretty much using all the energy of the battery with very little guard-banding (meaning, they use close to 90-100% of the battery capacity).

Contrast this with the news that Toyota is coming out with a Prius PHEV using a Li-ion battery. Total driving range on the battery-13 miles! Toyota argues that most commutes are less than 10 miles, but a look at the battery specs is revealing.

It appears that the Toyota battery pack is ~330 pounds and has a energy of 5.2 kWh which means that the gravimetric energy of the pack is ~35 Wh/kg! I can only assume that this is useable energy (meaning the battery will have more energy but only 35 Wh/kg is used)

Granted that Toyota would want a battery that lasts 7-10 years and so unlike Tesla, they probably are using a battery that has a lower energy than 150 Wh/kg for the pack. But one would have to think that they are atleast using something that should be greater than 100 Wh/kg. Which means that Toyota is really only using 35% of the total battery capacity (at best). Talk about guard banding!

Just so we are all on the same page, you can get 35 Wh/kg from a Ni-MH battery. One is left wondering why Toyota would want to use a Li-ion battery with such a low State Of Charge (SOC) range of operation. One can only speculate, but it would logical to think that this is one way to get the life to be better. They will operate at a lower voltage and not allow the SOC to swing too much (remember the battery rules: don't charge them too high, don't swing them too wide...).

Moreover, if the battery is only charged to a partial SOC, then if there is a safety incident (leading to, what is referred to in the industry, as a spontaneous disassembly. For the normal person, this could be called an explosion) then the lower state of charge helps decrease the impact of the incident.

All this makes sense, but what is telling is that Toyota is being very very safe in their move to a Li-ion from a Ni-MH cell (by starting with a battery that is comparable). One wonders if this is more a PR move to tell the world that Toyota is moving to the latest and greatest battery, rather than using these batteries to actually get more performance.

Compare this to Tesla which is buying laptop Li-ion batteries (which are typically the highest energy density battery you can get your hands on) and trying to squeeze as much from them as possible. One is going for incremental, the other revolutionary, one prefers an appliance-like vehicle, the other a "sexy" ride, one could be considered boring, while the other could be considered a bit brash. No prizes for guessing which one is which.

Its easy to see Toyota's point of view. All you have to do is open the newspaper (I use "open" to mean clicking on a web link) to see their recent trouble with, this time, the Lexus brand. Toyota is got to be thinking that the last thing they need is a battery-related issue. Better to be safe and boring than sexy and sorry, I suppose. They cannot afford another recall.

This difference between a startup and an established player probably resonates across all areas, not just batteries. Remember Amazon in the late 90's taking on the big box retailers, or any of the open source softwares (Firefox or Linux) taking on Microsoft.

The only difference: If you screw up your internet software all that happens if your browser crashes or worse, you are infected with a virus. If you screw up your car, things can be a little bit dicey!

Time (next 3-5 years) will tell if these newer kids on the block will succeed in being profitable. Personally, I'm keeping my fingers crossed.

Venkat

Disclaimer: I don't own shares in Tesla, A123, or Toyota (as far as I know. My retirement plan is a complete mystery to me). As a matter of fact I make it a policy of not investing in greentech. My instincts tells me that they are a good buy, but I have a policy of doing the opposite of my instincts so...

* The previous version read "250 miles for each Wh". Its actually 250 Wh for each mile.

In batteries, 2+2=1. Actually more like 1/2. Well... maybe a bit less.

2010-06-28T12:31:00.000-07:00

This is a blog post I've wanted to write for a decade. The reason I haven't (other than the obvious problem that a decade ago, I did not know what a blog was!), is because its a tough post to write. But, folks tell me that I have a gift for explaining things (I use the world "folks" is a generic sense to indicate a number greater than 0), so I shall try.

Everyone wants to make a better battery. What they mean when they say "better" is a battery that has more energy. This is what many (not all) battery researchers are trying to do, and this is what every user wants. If you read my post titled "A Moore's law for batteries? Maybe not", you will know that the game is to find new materials that make up the anode and cathode of a battery.

The idea here is to find a new material that has more capacity than the existing material and/or find one that operates at a higher voltage. Capacity is a measure of the amount of charge (electrons) you can get per gram. More is obviously better. Capacity times the voltage is energy; for real-world applications what matters is the energy. Typical numbers for capacity for lithium-ion batteries would be 140 mAh/g for the cathode and 330 mAh/g for the anode. The typical voltage of a lithium-ion battery is 3.7 V.

A lot of research in lithium-ion batteries is focussed on increasing the capacity. There is also an active area of interest in increasing the voltage to above 3.7 V. Increasing the voltage is going to be hard (very hard), so increasing the capacity appears to be the way batteries will improve, atleast in the short-term.

Simple enough.

Those of you who are paying attention have probably noticed that for every gram of material, you only have ~1/2 the capacity in the cathode compared to the anode. If you want to make a battery with a capacity of, say 330 mAh, then you have to take 1 gram of the anode, but you need 2.35 g of the cathode (330/140). What this means is that you have a total weight of 3.35 g to get a capacity of 330 mAh. So the capacity of your battery is actually 98 mAh/g (330/3.35). So you started with a anode at 330 mAh/g, a cathode at 140 mAh/g and you get 98 mAh/g for the battery. A 2 mAh/g cathode with a 2 mAh/g anode give you a 1 mAh/g battery. 2+2 is actually only 1. Certainly not 4. Not even 2! Welcome to batteries.

If you have a new anode with say 10 times the capacity (so 3300 mAh/g) you can do the same math and you will get a cell capacity of 134 mAh/g (for a battery of capacity 3300 mAh the weight is 24.5 g). You go to all this effort to make something 10 times better and you get to use your iPhone for an extra 30% talk time. A bit disappointing! On the other hand, if you had an cathode that was, say, twice as good, at 280 mAh/g (with an anode at 330 mAh/g), then your cell capacity goes up to 151 mAh/g. Much better. 50% better. This is why most researchers want to find a better cathode. Its more bang for the buck.

All this is pretty simple. All battery folks know this. 2+2=1. End of story.

Or is it? There is another small factor that even battery researchers sometimes miss. This factor is the dead weight in a battery.

If you really want to use the anode and cathode, you need some extra real estate. Things like separators to keep the electrodes apart, current collectors to collect the current, and packaging to make sure you contain it in a neat little package. All these add weight and volume. It doesn't matter if you have 10 times the capacity in a new anode, you still have to carry this dead weight.

This is a lot like a gasoline-powered car. Only the gasoline has any useful energy in the car. But to use the gasoline, you need a tank, an engine, the wheels, the drivetrain.... you get the point.

Obviously, if you can make the weight of the rest of car as light as you can (no seats?), it helps you get more from your tank of gas. Similarly, if you can minimize the amount of unwanted weight, it helps a lot in the battery. What this means is that you try to increase the ratio of the active materials (the anode and cathode) to that of the inactive material (the separators, current collectors etc).

But there is a catch. Turns out that you can't increase the amount of the active material willy-nilly. It has to do with losses in a battery. If you put extra active material in, you have to add a bit of the inactive with it. And increasing the amount of active materials involves making the anode and cathode thicker and there is a limit to how thick these can be made before losses become prohibitive. One needs to account for these factors.

*Geek meter on*

Remember the example above where we calculated 98 mAh/g using a battery of capacity 330 mAh with a weight of 3.35 g? If you do the math on the extra weight for the inactive material, you have to add an extra ~3.35 g. You can do the math to convince yourself of this number or you can trust me. I would suggest doing the latter. So you actually only get a capacity of 49 mAh/g (1/2 of 98)! 2+2=1/2!

For you battery geeks, you can verify these numbers by calculating the theoretical energy of the battery using the 98 mAh/g and multiplying by 3.7 V to get 360 Wh/kg (the theoretical capacity of a graphite/LiCoO2 cell). You can calculate the practical capacity by multiple 49 mAh/g by 3.7 V to get ~180 Wh/kg (A typical value for a 18650 cell using cobalt oxide). Well well well... the math works, does it not?

Here is the rub. Remember the example where we had an anode that has 10x the capacity. We had a cell capacity of 134 mAh/g. If you do the calculation for the extra weight and recalculate the capacity you get only 55 mAh/g.

You have to think about this a little bit, but it turns out that if you have more capacity you will need less of the anode, so now the inactive weight becomes a larger fraction of the total weight of the battery. You could have compensated for this by taking the same weight of the anode and just talking a lot more cathode, but like I was saying, this is impossible because it increases the losses in the battery to a point where it would be useless.

So we have an anode with 10x the capacity and we gain 12% in cell capacity (and don't get me started on the voltage! That is for another post).

If you don't believe me, do the math. If you don't know how to do the math; I guess you have to believe me! It would be embarrassing if someone spots an error; but then again I'm assuming that no one has actually made it this far.

If you do the same math on the battery where instead of the anode being better, the cathode is twice the capacity, where we calculated a cell capacity of 151 mAh/g without the inactive weight you will calculate a cell capacity of 68 mAh/g with the inactive material. So you made a cathode of twice the capacity and your cell capacity actually went up by 38% (remember we calculated this to be 50% better before).

Turns out that even if you make a battery with 3300 mAh/g for the anode (in a sense, this is close to the best Li-ion anode we know of) and a cathode of 280 mAh/g (the best Li-ion cathode we know of) we get a cell capacity of 110 mAh/g. 2.2x the present-day battery. But this assumes the voltage of the two are the same. In reality the materials that have this capacity have a lower voltage, which means that the energy is not really that high. Turns out that this best base scenario battery is better by maybe a factor of 1.8 to 1.9. Meaning, this battery will approach 340 Wh/kg.

*Geek meter off*

As a matter of fact, everything else being equal (i.e., amount of inactive material), the best Li-ion battery we can dream of making in the future, based on what we know as of late June 2010, will have a energy density of ~340 Wh/kg. If you want something better, you pretty much have to work on the inactive material. All these are for cell-level numbers. If you go to a battery pack, things get even worse, but that is for another post. If someone tells you that they can make a battery where the energy is greater than this, you better dig.

Most people, including battery researchers, don't think about this extra weight. Its actually a very important factor in a battery. There is such a great focus on new materials that folks forget that reality may be as good as your simple math leads you to believe. In addition to new materials, we have to think about ways to decrease the inactive materials in a battery. There is far too little research on this and a lot to be gained from doing something about it.

So next time you hear about a new material with more capacity, ask not how much more theoretical capacity you can get, instead ask how much practical energy you actually get. Remember that you can't just divide theory by 2 to get practical; it could be less (a lot less). And don't forget the voltage. Its also critical.

To help you, here is a link to a excel spreadsheet that has a battery simulator specifically for a lithium-ion battery. I hope the mac version of excel is compatible with a PC. The sheet that has the calculations is protected. Contact me to unprotect. Let me know if you catch errors. The simulator makes a LOT of assumptions. If you want them all relaxed, contact me.

Venkat

You say potato, I say...battery?

2010-06-20T19:19:00.000-07:00

Saw something interesting in the news on a potato battery. Its a Zn-Cu battery with the two rods inserted into a potato. Why is this new? The authors say that they boiled the potato and were able to get less resistance and more power! I swear I'm not making this up.

Check out http://jrse.aip.org/jrsebh/v2/i3/p033103_s1 for the abstract. They say its cheaper than a AA battery and can be used to power a low-power LED light. I have not dug into the numbers to see if the cost claims are right. It would seem that with the low power that one gets from each cell you will need a lot of potatoes; the authors say they need 5.

My dad is visiting us from India and is sitting across from me. He tells me that 5 potatoes in India costs Rupees 15 (~30 cents). He tells me that a AA battery is either a bit cheaper or comparable! And I still need to buy some zinc and copper (and a pot to boil the potatoes, and spend some money heating it)

I get the impression that this is sort of a cute press release of something we already know and I wonder if it solves anything. I have to boil the potato and so need energy; I gain a means of making electricity, but I lose food to do that. And we really need someone from countries in the developing world to tell us if the cost numbers are what my dad tells me they are in India.

Anyway... could not resist.

Venkat

Made in Afghanistan

2010-06-14T05:30:00.001-07:00

Many of you have probably heard the criticism against lithium batteries in that we are now dependent on a single resource for our energy storage needs. The trouble being that we substitute from one imported reserve for our transportation needs to another. And lithium is abundant in Bolivia and China (on the Tibetan plateau)- Two countries where US influence is weak. Now comes a report in the New York Times that the US has found vast reserves on lithium in Afghanistan. See http://www.nytimes.com/2010/06/14/world/asia/14minerals.html?hp

They also found copper, cobalt, etc., but its the lithium part that is intriguing to me. Apparently the reports coming out are that there is "potential for lithium deposits as large of those of Bolivia".

Now, in the short-term (i.e., a few lithium-based batteries in cars) there is no reason for any concern or interest in this story. There is more lithium than we need. If (and this is a big if), there is a significant conversion of the automotive fleet to batteries, lithium-based ones make the most sense. In this scenario, we can get lithium limited. But we are not talking about just running out of the metal (which could happen if we convert all our cars), its more the question of: can we mine the metal at the rate we will consume it. Obviously, just because we find deposits, this does not mean we can exploit it.

We shall have to wait and see what this means to the USGS estimates of lithium reserves. And I wonder if proximity of resources will play into which countries will take a lead in battery manufacturing. In the mean time, I'm sure all you conspiracy theorists will have a field day speculating on the cause for the war in Afghanistan.

Venkat

Tesota or maybe Toyola?

2010-05-20T21:22:00.000-07:00

Logged onto New York Times and was amazed to see that there is a tie up between Toyota and Tesla.

See link

They plan to produce the sedan EV in the NUMMI plant in Fremont, CA. NUMMI is close to where I live and I'm happy to see something happening to this shuttered plant.

Its good news for Tesla and for Toyota. Hopefully, this will be a fruitful relationship.

I've visited Tesla and sat on the passenger seat of their roadster (I suppose they did not trust me with a $100,000 car). It's an amazing ride. Its easy to fall in love with the car and the concept (the price tag notwithstanding). Despite Toyota's recent troubles, I've always thought they are very good at what they do.

Lets hope that this move will get us closer to an EV I can afford (and trust me, if I can afford it, so can you).

Venkat

John Newman wins the Acheson Award

2010-05-19T07:46:00.000-07:00

Professor John Newman has been selected to receive the Acheson Award of The Electrochemical Society. This prestigious award will be given to Professor Newman at the next meeting of the Society, to be held in Las Vegas during the week of October 10-15, 2010. Professor Newman’s greatest contribution to the “objects, purposes or activities of The Electrochemical Society” (i.e., the definition of the Acheson Award, as spelled out below)” has been his seminal approach to the analysis and design of electrochemical systems. Starting in the 1960s and continuing to this day, John has not only clarified the physicochemical laws that govern the behavior of electrochemical systems, he has also demonstrated how to use these laws to correctly formulate and solve problems associated with batteries, fuel cells, electrolyzers, and related technologies. His sophisticated approach to mathematically analyze complex electrochemical problems has been universally accepted by the academic and industrial communities, to the extent that it is now commonly referred to as “The Newman Method.”

John is a Professor of Chemical Engineering at the University of California Berkeley campus, a Faculty Senior Scientist and Principal Investigator in the Environmental Energy Technologies Division of the Lawrence Berkeley National Laboratory, and Director of the Department of Energy’s Batteries for Advanced Transportation Technologies Program. He is the author or co-author of more than 390 technical publications, numerous plenary and invited lectures, and the book Electrochemical Systems, which is now in its 3rd edition and is used throughout the world as a monograph and graduate text in electrochemical engineering. Professor Newman has mentored many graduate students, as well as post-doctoral fellows and visiting scientists. Additional details about Professor Newman and his research group can be found at http://www.cchem.berkeley.edu/jsngrp/

The Edward Goodrich Acheson Award of The Electrochemical Society (http://www.electrochem.org/awards/ecs/ecs_awards.htm) was established in 1928 for distinguished contributions to the advancement of any of the objects, purposes or activities of The Electrochemical Society, and it is awarded not more frequently than biennially. It includes a gold medal, a wall plaque, and a prize of $10,000. It is named for Edward Acheson, a U.S. inventor best known for the invention of the highly effective abrasive material Carborundum. Acheson also helped develop the incandescent lamp.

Beside the Acheson Award, John has received 9 other awards from the Electrochemical Society. He also was recognized as a Highly Cited Author, as identified by Thomson ISI; during 2002 he was an Onsager Professor at the Norwegian University of Science and Technology in Trondheim; and in 1999 he was elected to the National Academy of Engineering.

The Acheson is arguably the most prestigious award that an electrochemical scientist could hope to attain, short of a Nobel Prize or a National Medal of Science. The late Professor Charles W. Tobias (in 1972) is among those who have received the Acheson Award, and he the only other member of the Berkeley electrochemical community to be so recognized.

LBNL everywhere...?

2010-04-30T12:00:00.000-07:00

ARPA-E announced the results for their latest round of solicitations that they issued a few months ago on transformational energy projects. One of the areas was batteries for vehicles. 10 projects were identified to receive the award (Here is the list). 3 of these (that I can talk about) have an LBNL connection. Its a proud day for what I consider the top battery program in the country. Turns out that the number 3 is not the full story, but I can't talk about any other connections that may (or may not) exist. Welcome to the world of startup's and confidentiality and stealth.

That's the quick summary. Here are the details. ARPA-E stands for Advanced Research Projects Agency-Energy, is the DARPA (Defense Advanced....) of DOE. I guess no one liked EARPA! Their mission is to (I copy and paste here):

- Enhance U.S. economic security by identifying technologies with the potential to substantially reduce energy imports from foreign sources; cut energy-related greenhouse gas emissions; and improve efficiency across the energy spectrum.

- Ensure the U.S. remains a technological and economic leader in developing and deploying advanced energy technologies.

This is the official spiel. In reality, ARPA-E is the agency that is supposed to help identify the next transformative idea related to energy technology. Think, the next transistor, or the next light bulb, but related to energy. You get the picture. These bullets above also do not convey the level of buzz this new agency has generated in the battery community. We have been energized. Getting ARPA-E funding is now considered to be a big deal. A very big deal. There are huge bragging rights for the winners, and those who are finalists.

No officially numbers have been released, but my sources (is that an euphemism for "I pulled it out of you-know-where"?) tell me that 350 concept papers came in the battery area. Of these 70 were down selected for submitting a full proposal. Of these 70, 10 were funded (ARPA-E folks: Please feel free to correct this). Less than 3% of ideas are funded! Now you know why being one of the 75 is a big deal and being one of the 10 is an even bigger deal. So you can see why its a proud day for LBNL when we have 3 funded proposals that we are involved with.

LBNL was involved in 6 submissions in the concept paper stage. All 6 were selected for submitting a full proposal. 2 of these 6 were selected to receive an award. The first of these is a project on a lithium sulfur (Li-S) battery that was led by Sion Power. Li-S is a chemistry that promised very high energy density, but has a lot of problems that hinder it from being commercialized. Sion is in the forefront of developing this technology. They will be working with John Newman, who is, for those of you who don't know, the father of electrochemical engineering (For those who track these things- I consider Charles Tobias to be the grandfather of electrochemical engineering). He wrote the book on the subject, literally. If you don't believe me, check this link. John Newman will be helping Sion with modeling their system. Systems like Li-S, if commercialized, can solve the problem of range for EVs and can help us adopt this technology.

The second is one from Applied Materials. They want to develop a manufacturing process that will lead to low-cost batteries that have high energy. Cost, as I have pointed out again and again, is one of the show-stoppers that prevent large scale adoption of EVs and PHEVs. Addressing this issue is critical. Applied will be working with Gao Liu and Vince Battaglia- both experts in making battery electrodes and cells.

These are the two where LBNL appears in the list. But there is one more that is hidden (that I can talk about). This is Polyplus, which got funded to develop Li-air batteries. Polyplus is a LBNL spinoff started by Steve Visco and Lutgard De Jonghe . Some of the underlying work that led to the formation of Polyplus was conducted under, what is now, the BATT Program. Li-air is the Holy Grail of batteries- a system that has 10x the energy density of today's batteries on a mass basis. Polyplus is pretty much the top company in this area. If they succeed, we can make a big dent on the range issue with EVs.

Three very different projects; but they all promise to change the world if they succeed. The fact that the reviewers have picked so many of the projects that LBNL was involved with is a testimony to the cutting edge research that happens here. Congrats to all the winners. And did I mention that this is not all. There may (or may not) be other connections. Stay tuned.

In a future post, I will delve a bit more into these technologies and provide my thoughts on what the critical challenges are and what (I think) their approach will be.

Venkat

Lithium-lithium everywhere...

2010-04-11T10:38:00.000-07:00

Over the last 15 years the whole battery community has slowly starting looking at one single system: the lithium battery. I remember going to an Electrochemical Society meeting in 1996 to present a paper on Ni-MH batteries. My talk was scheduled for Monday AM (read prime time). By 1997, I was down to Wednesday, and by 1999, I was talking Friday PM with 3 people in the room (yours faithfully, the presenter before me, and the one after me. Even the session chair was missing!). If one was looking to read the signs, this was it.

This week I was talking to someone who was interested in electrochemical capacitors (more on this later) and he asked if all the research was only on lithium batteries or do we do anything else? I had to admit that there was very little that goes on other than lithium. Since that conversation, I've been thinking about the effectiveness of having all our eggs in the lithium basket and wondering if this is a good thing.

First off, I should note that when it comes to batteries, lithium has a lot more energy per weight or volume compared to the other batteries we have been looking at in the past. Its got 4-5 times the energy per mass as a lead-acid battery and 2-3 times that for a Ni-MH battery. There is still a lot more that can be done with this chemistry and so there is a reason for us to obsess about this. When it comes to batteries for a plug-in or an electric car, we need all the energy we can get and working on lithium does make a lot of sense.

But does this mean that there are no advances that can be made in other energy-storage technologies? And even if we do make advances in these other areas, does it really have any impact in the world? Let's look at the second question first.

Remember that we have argued that batteries for plug-in and EVs are going to very expensive and that they may not last very long either. Its far from given that we will indeed be driving in these battery-powered cars. We may not be cost competitive with gasoline for a while, and we may end up seeing that these cars as a niche market. Maybe hydrogen will take off as a carrier and batteries as a primary energy source will not be the future. The future is far from clear, but it is possible that we may end up finding out that hybrid vehicles (like your out-of-control Prius) may be the most common vehicle on the road for a decade. But even your Prius is not as popular as it could be because its expensive.

But when it comes to hybrids, its not energy that is critical, but the power. Many batteries, including the lead-acid and the Ni-MH batteries have the power capability to satisfy the requirements for a hybrid. The cheapest battery we know of is the lead-acid battery. So if we can get the power with a lead-acid battery and if its the cheapest battery we know of, why don't we use this for hybrids?

Remember the post on battery rules where we asked you to "keep you lead-acid charged"? You may also remember that this was important because if the lead-acid is ever discharged, it sulfates and causes capacity loss. In a hybrid, the battery is always sitting partially discharged. This is important because if you hit the brakes, you need to be able to accept the juice in your battery. Hybrid batteries operate around 50% state of charge because of this. Try using a lead-acid at a partially discharged state and you will have a dead battery long before the new car smell fades.

But something strange happened to the lead-acid battery when the rest of us were obsessing over the lithium battery. The companies working on this started using activated carbon in their negative plates. Lo and behold!, these companies started seeing much better cycling with this new concept. Some companies are doing variations of this by replacing the negative electrode with activated carbon so that its a hybrid between a battery and a capacitor. Companies doing this are promising all the cycle life you need at 1/4 the cost of the Li-ion for hybrids! The catch: they don't yet know if the batteries will last 10 years. So they can get the cycle life, but its not clear they can get the calendar life.

But that is not the point I want to make. What amazes me is that someone can take a 150 year old technology and show that they can make it better by solving a particular problem that stops it from being used for an application. I'll take a bet that 90% of the researchers in the field of batteries don't know of this advancement (all right, that may be a bit of an overstatement, but you get the point). I had worked on a mathematical model for a lead-acid battery a few years ago where I had included some features in the model that make it easy to address this advance. A person in the lead-acid industry had sent me a mail when these findings started coming out asking if I was doing anything to address these new findings. I had to (sadly) tell him that although this was interesting, I had no way of doing anything because all my funding is in the area of lithium batteries.

But what if we find out that the new lead-acid batteries do have a calendar life issue. Should we leave it to companies to figure this out by themselves, or should battery researchers be helping with this effort to see if we can find a solution? It seems to me that the answer has to be the latter, but I fear that this will not be the case. The chemistry is considered too "un-sexy" (for want of a better word). Try presenting a paper on this at the Electrochemical Society meeting and you will asked to present on a Saturday morning (after the conference has ended!). To be fair there has recently been government support for these technologies for trying to commercialize them; but I don't see anything happening at the research stage.

The story of the lead-acid is far from unique. The few (very few) folks who continue to work on the Ni-MH system talk about the use of carbon fiber instead of nickel plaques to decrease the weight and cost of the battery and increase its specific energy. The person working on capacitors was telling me that he had ideas for increasing the energy by the factor of 2 (which, as it turns out, could be huge for a hybrid). There are companies working on Ni-Zn batteries that think they can do something better than Li-ion in some applications. But look at research in the US on batteries and there is pretty much zero effort in these areas. None of these ideas may pan out, but the question remains: should battery researchers be looking at these issues along with companies or should we all focus on one system (the lithium system)?

Part of the problem is the amount of funding that is available for battery research. If there was unlimited funding available, all these problems will be looked at. But with funding being tight, one needs to focus on a few problems and not spread one-selves too thin. Another problem is the community. As in any other area, there is a bit of jumping on the bandwagon that happens. Its tough being the only guy doing something, especially when no one cares for what you do.

At LBNL I wear two hats: one as a researcher looking at mathematically modeling batteries and another as the technical manager of the Batteries or Advanced Transportation Technologies (BATT) program. In my latter role, I have a hand at picking the kind of systems we work on. And I know exactly why we have picked to focus on the lithium battery exclusively. But the advances in these less "sexy" fields makes we wonder if this strategy is right. Weigh in with your views.

Venkat

Nano for batteries: the challenge of volumetric density

2010-04-03T11:11:00.000-07:00

In my previous post I discussed some of the pros and cons of using our skills making materials in various nanoarchitectures in Li-ion battery technology, mainly related to the increase in surface area and shortening of diffusion paths. Today I will concentrate in other aspects: volume and density.

Most probably, you have heard how silicon-based electrodes can boost the storage of Li-ion batteries. And you may have even noticed that a lot of the releases announcing breakthroughs in this area have the word nano in them (here's a very recent example). Indeed, one of the most serious problems of silicon electrodes is that they expand and contract enormously upon cycling because they can uptake so much lithium (hence the boost in storage capacity). In brief, what happens with big particles is that they crack into much smaller ones due to these expansion/contraction cycles (think of freeze/thaw cycles in the winter) and lose contact with the electrode additives and the electrolyte, cripling the electrode life. So starting small (i.e., nano) bypasses this issue. With less volume in a particle, it is less likely to break in several domains.

Usually, electrodes composed of nanoparticles of silicon cycle better than those composed of bigger particles... provided that we are good at building the electrode structure so that all these new particles are well connected to the current collectors (and, subsequently, the battery leads) through the electrode additives. However, issues arise when using this strategy. Guess what one of the problems is? Yes, our friends the side reactions; silicon reacts outside the voltage of stability of the electrolyte. A second problem, related to the increase in surface, is that silicon nanoparticles are much more reactive with air than micron-size particles, bringing up the need for additional safety controls during handling. In fact, some people have even proposed primary silicon/air batteries.

It is quite likely that silicon will have to be used in nanometric form to make it a viable electrode with very high capacity. But be careful with overstating the numbers. A typical strategy to keep a good electrical contact is to use more conductive additives (carbon, basically) because there are more particles to connect to each other and the current collector. Increasing the amount of polymeric binder is another strategy that is commonly used to keep the particles together. And more carbon and/or binder means less silicon, which means that we are reducing the total capacity of the electrode. Yes, in terms of the silicon only, the capacity is unchanged, but we have to count everything when building the battery! Pay attention to what companies that announce silicon-based batteries show as capacity gains and you'll see they are more modest than would be expected theoretically.

In addition, nanoparticles have a very annoying tendency to form aggregates that is very difficult to control. These aggregates form rather disorderly and, therefore, leave a lot of dead space within, which can be helpful for electrolyte wetting but also be unnecessarily high. Finally, a lot of the strategies to alleviate volume expansions in silicon electrodes rely on placing the particles far from each other, so that they don't crush against each other upon expansion. Obviously, this also helps with the aggregation, but now we have even more inactive space between particles!

The result of all these approaches is always the same: the density (mass per unit of volume) of the electrode is lowered considerably with respect to an electrode made using more traditional methods with bigger particles. In general, it is very difficult to achieve bulk packing densities of materials using nanostructured electrodes, which may, after all, be something we have to live with, in some instances, if we want them to work.

Unfortunately, lower packing density also means lower total volumetric energy density of the electrode/battery. And volumetric energy density is no laughing matter when thinking of batteries for electric vehicles. There is very limited volume available for the battery (especially in a hybrid). Using certain nanostructures as electrodes can lead to very long life, but very modest volumetric densities, so that you still need a bigger battery to power your car. When volume is factored in, the gains of using nanoparticles are systematically much more modest or even totally offset. This is a problem that is still unsolved. Scientists are getting better at synthesizing nanoparticles and we are starting to be able to control aggregation and assembly, so there are possibilities that are being explored. Now, the methods associated may imply an increase in cost of manufacturing. But I'll leave this for another day.

More reading materials for those interested in the science of silicon electrodes:

Larcher et al., Recent findings and prospects in the field of pure metals as negative electrodes for Li-ion batteries, Journal of Materials Chemistry 17, 3759 - 3772 (2007)

What can nano do for batteries?

2010-03-23T16:22:00.000-07:00

First and foremost, I must express my gratitude to Venkat for his introduction and for encouraging me to participate in this new blog-adventure. Now that he cannot hear us, I will tell you that I learned quite a few things myself with his posts. It is a pleasure for me to offer a different perspective to his and I hope you will find it informative. Since he has already introduced me, I’ll move on to the fun stuff.

Nanotechnology is certainly one of the fields of research that has witnessed greatest progress in the last decade (although the concept itself is not all that new; Michael Faraday can be considered one of the first nanoscientists!). When it comes to functional materials, among other things, nanoscience offers the promise of enhanced catalytic properties, controllable band gaps that can have an impact on the efficiency of a solar cell and novel medical diagnostics and treatment tools (not to mention that most of suntan lotions contain nanoparticles nowadays!).

It is easy to wonder whether nanotechnology would also be a helpful tool toward better batteries. There are a few arguments in favor of using nanoparticles in a battery, particularly as part of the electrodes. We will just concentrate on a couple of them for now (and leave the rest for another day if I am still considered a guest after today!). Although the discussion relies on the Li-ion technology for examples, the ideas are pretty much applicable to many battery technologies.

One of the first incentives one can think of is the shorter distances for ions and electrons to travel through. Broadly speaking, think of it as you having to cross your living room as opposed to a football field. The second one has to with the surface area. Let’s imagine that the square in the picture below is made of 1 um edges:

divide each edge ten times and you now have 100 squares with edges of 100 nm:

All those new lines you see are new surfaces (if you want to entertain yourself, expand the exercise to a 3D cube and reduce it to particles of 10 nm). In a battery, all of this surface could ideally be exposed to the electrolyte, which is the media through which ions transfer from electrode to electrode (the key to battery operation).

Now we have (lithium) ions that can access the active material much more extensively (more surface) and have shorter distances to travel through the solid (remember the living room). Diffusion in the solid is typically, but not always, slower than in the liquid, so, in theory, the result is a lower resistance to ion transport and, therefore, better utilization of the material (i.e., higher stored charge/energy) and, potentially, higher rates of charge and discharge (i.e., shorter charging times and higher power).

There are many reports available that show that samples composed of nanoparticles, all things equal, can lead to better performance than (what we call) bulk counterparts. In materials with poor ion conduction, this effect has had an important impact. The now world famous lithium iron phosphate owes some of its glamour to the chemists that were able to nanostructure it. The same happens with an anode material that is getting a lot of exposure as of late: lithium titanate.

So in a sense, nanotechnology has an important role in the field of (Li-ion) batteries, and, in fact, there are many R&D projects that concentrate on exploiting the advantages of nanotechnology to developing advanced materials, including some in our very own Batteries for Advanced Transportation Technologies program (go through our recent scientific reports to see what's up) at the Department of Energy. So, it is settled! Nanotechnology is the way to go to make batteries with five times more energy density!

Hmmm... not so quick... Apart from the fact that geometrically increasing the energy density is much trickier than it seems (we’ll also leave this for another day), there is a key subtlety in the case of lithium iron phosphate and lithium titanate that makes the whole trick work: they are both active within the voltage window of stability of the components of the liquid electrolyte. Venkat has already told you that bad things happen when we fall outside this window. Unfortunately, one of the ways of increasing the energy density is precisely by increasing the voltage (remember, energy = voltage x charge). Graphite electrodes, for instance, ubiquitous as they may be, react outside that window.

If we start using materials that are only slightly outside the thermodynamic window of the electrolyte, the undesired reactions may happen at a rate that is slow enough for us to live with. But, hey, remember that increased surface area of nanoparticles? Yeah, it is increased for every component of the electrolyte, not just the ions. The immediate consequence of reducing the particle size of our electrode materials is that side reactions tend to be exacerbated. And those side reactions produce insoluble products that deposit, just our luck, precisely on the surface of the particles, covering them and producing layers that are resistive to the diffusion of ions. Automatically, the advantage of using nanoparticles is lost. And things can be so bad that we may be better off using slightly less active electrodes!

In conclusion, you can choose to have a lithium iron phosphate/lithium titanate battery that operates extremely well and has a long life thanks to the use of nanoparticles... but what if I told that such battery only has a voltage output of around 2 V (yeah, those lead-acid batteries don't look so bad anymore)? And if I mentioned that, in addition, the lithium titanate has about half the storage capacity of graphite, so the energy density of this great battery is lower than that in your cellphone Li-ion cells? If we are to increase the energy density of current batteries to make them more application friendly, we have to come up with inventive ways of using materials operating at high and low voltages; preferably, not in the form of nanoparticles… unless we find a way of stopping those annoying side reactions without killing the ion transport at the same time.

There are other issues that make nano only a partial answer (sorry, no Moore's law for batteries) to the performance barriers of batteries, among which are higher associated manufacturing or processing costs and lower packing densities. But this is for another post (or two!). If you are left wanting more, you can get even more knitty-gritty details by reading some scientific literature (if you have access to it, of course), which will also offer additional shades of grey to the arguments developed here:

Aricò et al., Nanostructured materials for advanced energy conversion and storage devices, Nature Materials 4, 366 - 377 (2005)

Bruce et al., Nanomaterials for Rechargeable Lithium Batteries, Angewandte Chemie International Edition 47, 2930 – 2946 (2008)

Welcome to Jordi Cabana

2010-03-23T11:50:00.000-07:00

Dear Blog readers- Over the past month or so, I have introduced various topics related to batteries and their use in, primarily, vehicle applications. As we move forward, I wanted to get different perspectives on this subject matter from other experts and broaden the discussion. This may be hard to believe, but I actually don’t know everything. (my family is going to save this post, because this would be the first time I’ve admitted this!)

The thought is that we will periodically bring in guest bloggers to write about something that interests them. We begin this week with a post by Jordi Cabana. Jordi is a scientist colleague at Lawrence Berkeley Lab and is an expert on synthesizing new electrode materials and characterizing them. He has a great understanding on many different issues related to this topic. Check out his website at http://berc.lbl.gov/jcabana/

Jordi will start by telling us a bit about nano as it applies to batteries. This is a hot topic and one that has a lot of complexity to it. Jordi’s post will be up shortly.

Stay tuned for more.

Venkat