I'll be back... in 8 hours

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

One battery chemistry to rule them all?

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

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

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

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.

Lithium-lithium everywhere...

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