Friday, April 30, 2010

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.


Sunday, April 11, 2010

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.


Saturday, April 3, 2010

Nano for batteries: the challenge of volumetric density

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)