The Hero with four faces: Part 1

A few years ago, when I visited a battery company with a few colleagues, I saw data from the company that was pretty impressive.  Slide 1 showed the rate capability of the battery, which was better than the state-of-the-art; Slide 2 was a calculation of the energy density, which was better than the baseline; slide 3 was cycle life and this too looked impressive; slide 4 was…

You get the drill. 

Suitably impressed, I came out wondering what I needed to polish in my resume to land a job at the company before they went public… when my travelling companion wondered aloud if each slide was from a different battery!

 My colleague had a point.  Most (not all) battery chemistries can be made to perform well for a particular metric.  The trick is getting all the metrics to work out for the same battery. 

Make the electrodes thin to get power; make them thick to increase energy (but at the loss of power).  Increase the voltage to increase the energy, but at the loss of cycle life.  The endless games one can play.  This dependence of battery design, cycling conditions, voltage of operation, etc. on performance is the reason battery companies have been getting away with obfuscation. 

But is it really obfuscation?  A proof-of-concept can be a useful learning tool.  If going to high voltages yields more energy but kills the cycle life, while we know that the voltages being accessed should be possible, then it gives us hope that the problem is not fundamental and that a solution exists.  Given time, maybe we will find it. 

Then again, we have been looking for a cure for baldness for ages.  There is proof that baldness is not fundamental (after all, some are oh so lucky), but that does not mean we will find the answer to that problem either.    

But there is merit in learning about what the best possible system is and understanding why it is the best.  To this end, I thought I would list out the best-known (at least to me) battery chemistry for each of four metrics of importance:  energy, charge time, life, and cost.  Each would be a “Hero” battery; a term borrowed from other technology areas to denote a proof-on-concept that something amazing is possible for that metric.  While each metric has a different “Hero” battery there are probably lessons we can learn from them.  These lessons, I summarize in the end.

The energy-density Hero:  All seven readers of my blog know that Li-ion batteries are the highest energy density secondary batteries one can buy, with energy density in the range of 250 Wh/kg.  But the Hero is actually the Li-thionyl chloride battery, which has an energy density of 550 Wh/kg and is, more importantly, commercially available.  The catch is that it is a primary battery (i.e., not rechargeable). 

What gives?

Typical Li-ion cells have a graphite anode.  Moving from graphite to Li metal (which holds ten times the charge and results in a slightly higher voltage) bumps the energy by 50% without changing anything.  On top of that, the thionly chloride cathode has a capacity of 450 mAh/g compared to 180 mAh/g for typical Li-ion cathodes.  Combine the two and you get something much better than Li-ion.

Imagine a battery with 2x the energy density.  Maybe we double the range of a Nissan Leaf, making it a car that is actually useful (joking, joking, all you Leaf lovers) for the same cost.  Or cut the cost of the Tesla battery by half without sacrificing range, bringing it tantalizing closer to the point where everyone can continue to not be able to afford it. 

Unfortunately, all these will not come to pass because the Li anode does not recharge gracefully while the thionly chloride cathode is not at all rechargeable.  If you want to know why, you have to read my blog post titled “A Brief History of Batteries- Part 1” and “A Brief History of Batteries- Part 2”.  Frankly, everything you need to know about batteries is probably hidden somewhere in these pages. 

To make it rechargeable, you just need to change the anode, the cathode, and the electrolyte (i.e., all the three components that make a battery).  When you do that, the battery now cycles a lot better, but at the loss of capacity. 

So is 550 Wh/kg the ceiling?  No.  There is a lab demonstration of a 750 Wh/kg Li-air primary battery.  This would be a record for energy density.  But as I have alluded to in the past, a one-off lab demonstration does not a product make.  So, for now, we shall call 550 Wh/kg the Hero for energy density.  As an aside, the Li-air battery also does not cycle. 

Reversibility restricts us to certain materials; a constraint when removed, allows high energy density batteries to be made. 

An interesting question to ponder: Is it possible to get batteries that are rechargeable and at least as high in energy as these Hero’s?  

The fast-charge Hero:  One of my funnier blog post was titled  “I’ll be back…in 8 hours”.  That post had nothing to do with charging times (then again, this blog is like Seinfeld; its about nothing, as far as I can tell) but the title articulates the problem:  We tend to want to charge our batteries very slowly.

Charge them too fast and we have unwanted side reactions (lithium plating and electrolyte breakdown) that can degrade the battery.  1h charge is doable, 30 mins makes it degrade a bit; 10 mins a lot more; 1 min would basically kill the battery (and kill you from the fire that is creates). 

This is true for most batteries, but it is not fundamental.  Meaning, there is no law that says that we cannot charge a battery fast.  One can design the battery for fast charge.  But the compromise is loss of energy. 

How fast do we really need to charge?  For an electric car, a really smart person (who shall not be named) told me that we needed to charge within the time frame of a restroom break.  Another smart person told me that we needed the battery to charge and discharge fully within the time frame of clouds covering a solar panel.  After a few experiments timing myself on restroom breaks and watching clouds move (I plan to watch grass grow next) we can approximate the charging time needs as 5 minutes.  What can I say: I was having an Austin-Powers-just-got-out-of-hibernation moment. 

The question of the grid actually handling this kind of electricity load is a whole other area of debate, but let us focus on the battery for a second.

Electrochemical capacitors can easily charge this fast.  But they have no energy.  Question is: Is there a battery chemistry that can mimic a capacitor’s charge rate?

There was one system that was kind-of-sort of commercialized that I would consider the Hero in this regard.  This was the Toshiba Super Charge battery, which is rated to charge to 80% capacity in 6 minutes and more than 95% in 10 mins!

Here the anode (lithium titanate) operates at a higher voltage than the typically used graphite anode. This helps because the potential of the anode is far away from the lithium plating potential.  This makes it much easier to charge fast and not worry about plating lithium, shorting, and the ensuing degradation and possible fires.   

But the downside is that the higher anode voltage decreases the overall cell voltage, which in-turn deceases the energy.  The battery has a third of the energy density of a typical Li-ion cell (so a third the driving range).  At 90 Wh/kg and 177 Wh/l at the cell level, it is far, far lower than most Li-ion batteries.  Cost of these devices scales with the energy:  this battery will probably cost three times a typical Li-ion cell!

So… an ideal EV battery for the super-rich-with-overactive-bladder demographic?  

Question is: can we get both high energy and fast charge?

If we want to get there I believe we cannot use thick porous electrodes.   While they are great to spread the current, it seems impossible to get away from the electrolyte losses of these highly-resistive organic electrolytes.  Which means that we cannot have thick bulky current collectors and separators.  But then how do we collect the current (especially if the currents are high, which seems likely with fast charge batteries)?

Should we move to electrodes that are not porous?  This limits the useable energy, unless we use electrodes that undergo deposition. One can continue to deposit the metal on top of itself and so “build” capacity, without the added losses from the porous structure.  This may be an avenue. 

My suspicion is that even if we find ways for the electrodes to accept the charge at that rate, the electrolytes in lithium-based batteries will not have the ability to move ions from one side to the other.  Unless we move toward much thinner separators.   This topic requires some careful thinking.

But let us revisit the question: how fast do we really need to charge? 

If we can ensure we have a 400-mile range battery, this should translate to an approximately 5-6 hour driving time (at 70-80 mph).  Then we may be willing to wait a half hour to charge the battery as we make a beeline to our favorite artery-clogging fast food joint. 

For the grid, if we can use the battery to not just take care of the intermittency, but also to time-shift from peak to off-peak, we can size the battery for the time shift and use the (big) battery for handling the small 5-min intermittency.  Each 5-min charge and discharge would only require the battery to swing by a few percent: easily possible with most systems. 

The catch: both of these would require us to pay for the bigger battery!  But hey, batteries are getting so cheap, and companies are going to give us money when they hand us the battery anyway. 

The cycle/calendar-life Hero:  I know what you are thinking: there is no such thing as a cycle-life Hero!  After all, every battery we own seems to last all of 1-2 years before they crap out.   You must be thinking that our Hero must be a 3-year life battery.

What if I told you there are batteries that last 20, even 30+ years and they cycle 20,000 times (no error there, really meant to have four zero’s)?  And what if I told you that these batteries are not the hybrid car batteries that cycle 3-5% per cycle but are cycled deep, greater than 50% of the capacity per cycle?  And that they are (at least they were) being used day in and day out? 

Imagine batteries that last as long as a solar panel.  Imagine being able to cycle them once a day and make them last those full 20 years with no maintenance.

Intrigued?  Come back next week and you shall learn more.

 Venkat

p.s. the title of this post is inspired by the Joseph Campbell book “The hero with a thousand faces.”  Campbell was trying to point out that all the world’s myths, across religions, shared a Hero figure with similar characteristics.  We will see next week that in batteries there is no one Hero.  We basically have four Hero’s with four faces.  

If you build it, will they come?

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

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.

Tesota or maybe Toyola?

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

LBNL everywhere...?

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...

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

Pull the plug. Your battery will thank you.

One question that I have been asked frequently is “do laptop batteries fade faster if they are continuously plugged in?” A reader asked this question in the blog and I thought it would be good to get into battery failure using this specific question.

Batteries failure depends on the chemistry and can be broadly classified as mechanical failure and chemical failure. When I say mechanical, think cracking, breaking, and shedding of the electrode. Chemical means reactions, like corrosion, that alter the state of the battery for the worse. In lithium batteries both kinds of failure can happen. For example, people have shown that the electrode particles can break, especially when you fast charge the battery.

But the question that was posed regarding failure when you plug-in the battery is specifically chemical in nature.

First some basics. For chemical stability, the battery should be operated within the stability window of the electrolyte. For water-based batteries, the stability window is 1.2V. Go above this window and you split water and make hydrogen gas and oxygen gas. This is about the time you should be wondering how lead acid batteries even work considering that their voltage is ~2 V, but that is outside of the scope of this post.

But getting back to our laptop, the stability window is ~3.2V. Meaning that when you operate the battery above this the electrolyte is oxidized on the positive electrode and reduced on the negative electrode. Remember that we only want to oxidize and reduce the “active” materials and don’t want to do anything else. All these reactions other than the ones we want are called “side reactions” and these are really bad for the battery. The nominal voltage of a laptop battery is 3.7 V which means that something bad wants to happen as we use the battery. Just because things want to happen does not mean that they actually do (for example, I want to buy a Tesla or a Volt, but...).

So long story short, stuff (e.g., passive layers and poor kinetics of reactions) happens and things are not as bad as they seem and you can increase the voltage up to 4.2V without bad things really happening. All chargers for Li-ion cells today cut the battery off when it reaches 4.2V. What you have to realize is that at 4.2V, these side reactions are present in finite amounts and start to chemically kill the battery, but its not that dramatic.

Operating to 4.1V makes things better and extends the life, 4.0 V is even better and so on. So why don’t battery manufacturers cut the voltage off at, say, 4 V to get better battery life? Because every time you cut this voltage down you decrease the capacity of the battery and its run time. The 4.2V cutoff is a compromise between good run time and decent (read “not pathetic”) life.

Were you supposed to understand all that? Not really, I just wanted you to know that I’ve really thought about these things. What you do need to know is that if you keep your laptop plugged in, you force your battery to remain at 4.2V continuously and these side reactions continue to happen and slowly kill the battery.

On the other hand, if you charge the battery and then pull the plug (so to speak), the battery discharges some, the voltage drops, and these reactions become less of a problem and your battery life goes up. So the best things you can do is to charge the laptop (or cell phone, camera etc.) and once its charged, pull the plug. Your battery will thank you for it.

As a matter of fact, if you own a Lenovo Thinkpad, you can actually change the state of charge to which you charge the battery using the “Battery Maintenance” utility. You can change this from charging to 100% state (where the voltage is 4.2V) to 90% so that your voltage is less. You lose some energy is doing that, but atleast you can change it to 100% when you need battery power and put it back down to 90% when you can plug in. I wish my Mac has the same feature.

This problem has implications for PHEVs and EVs. Lets say you have a 15 kWh PHEV pack. You come home after a 40 mile commute and you plug it in at 6:00 PM. Let’s say you have a 120V, 15A outlet, so that you can put out 1.8 kW of power. So the battery is going to charge in 8 hours.

By 2 AM you have a fully charged battery. If you leave your house at 8:00 AM, your battery is going to be sitting at 4.2V for 6 hours in any 24 hour period. This is not going to be good for the battery. It gets worse if you decide to bump the amp/volts on your house to charge it faster. So we need to get these batteries charged faster, but we also want to make sure to have smart chargers that don’t do what I’ve described above. Something to think about.

What does this mean for researchers? If someone can find an electrolyte that has a wide voltage window of stability, then this problem goes away. Or you can try to use materials that work within this window (For example A123 Systems battery does this on the positive side). But this means the battery has a lower voltage, which means it has lower energy and less run time. We don't want that, do we? Finally, we can try to isolate the electrode and the electrolyte and see if we can kinetically hinder these reactions. In the Battery Program at Berkeley we are actively working on this problem so that we can get more energy and better life.

In the mean time, remember to pull the plug.

Venkat