Monday, August 16, 2010

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

10 comments:

  1. I have heard more recently about Vanadium which I assume would be the cathode that would allow for greater voltages in the 4.3 range per cell. As Vanadium is rather expensive would the greater voltage if they can be mass produce them be worth the possible additional cost or would it be a niche product.
    I enjoy reading your blog, very informative.

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  2. vanadium I beleieve actually usually produces lower voltages - more in the 3.5 or so range.

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  3. The Vandium cathode you are thinking of is <3 V (its an oxide). This used to be popular when Li-metal anodes were being considered (instead of graphite). It has a lot of capacity and hence the interest in the material. It turns out taht from an energy perspective, a cell made with vanadium cathode and a Li-metal anode has as much energy as one that used a Nickel-cobalt-manganese oxide cathode vs a Li anode. But, we can't make a Li metal anode work at room temperature (yet) so...
    The vanadium does not contain lithium as made, so you need a lithium source. Works well with Li metal; but not with graphite. Not sure why a lithiated vanadium cannot be made (do one of the materials folks know the answer to this?).

    There is a vanadium phosphate that works above 4.3 V but its low capacity. And it has cycling issues. Not sure if this is the vanadium the 1st post is thinking of.

    Venkat

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  4. I guess I could consider myself a "materials folk". V2O5, which is the compound you are probably thinking of, can accept Li to form Li4V2O5, hence its large capacity. Therefore, you would need to start from a composition equivalent to this one to get the same capacity with a lithiated electrode. Unfortunately, the only way of making a compound with reduced vanadium and so much Li is... electrochemically, in a Li battery.

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  5. The funny thing is that nearly all of these chemistries were already competing 30 years ago...and most of them are much older. The only newcomers I see in the list are the Li-ion batteries (and maybe the NiMH?).
    An external observer like me sometimes get the feeling than no real advance is being done. You see all those chemistries with high energy densities, but they never get produced at decent prices...too complex maybe? Or too much exotic material in their composition?

    On the other hand, an old chemistry like NaS, which looks incredibly simple, robust, has good energy density and only uses common materials ( Na, S, Fe, Al) is still produced at very expensive prices (>$1000/kwh) after 50 years.

    What is the problem that keeps all these chemistries so expensive? What's the advantage of lead-acid over them, that makes it so cheaper?
    It's a problem of required material purity, like the silicon needed in the solar industry?

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  6. Luis- Progress in batteries has been happening and lithium-ion is an example of this.
    To address your question as to why is lead-acid so cheap; its two things. The chemicals used are very cheap. And manufacturing the battery is cheap. I interned at a lead-acid plant during my undergrad in India and it really is a much easier system compared to Li-ion. Doing everything in the open (as opposed to a dry room) does make it easier and cheaper! And it really is a pretty forgiving system compared to Li-ion. You can see this even when you doing stuff in beakers in the Lab. Getting good data in aqueous systems is a lot easier.
    Li-ion is pretty finicky and this makes it expensive to manufacture.

    Venkat

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  7. I posted a while ago saying that I enjoy reading your blog, but a lot of this stuff is over my head. You replied saying that if I had questions, to speak up. In a separate post, you indicated you were going to occasionally stray from batteries used for cars and into other battery applications. Based on those things, here is a question that you can do what you wish with, but first, a little history.

    I've been buying NiMH batteries for my digital camera. I used to have a camera that used 4 batteries at a time. I had four green kodaks and 8 white batteries (maha?). When I'd use the kodaks, I'd always use those together as a set of 4. The other 8 white batteries would just get thrown in haphazardly (always fully charged though). Over time, the performance of the white batteries began to suffer while the kodaks kept doing well.

    Then I got a new camera that only uses 2 batteries. With the new camera I'd be randomly pairing the charged kodaks and the performance of those batteries began to fade too. The white batteries kept getting worse and worse as well. Sometimes, I get as few as 25 pictures on a charge compared to about 100+ when new)

    I did some research and it seems that I should pair up new batteries for life, otherwise they somehow get out of sync and can drag each other down. I bought a new 8 pack of eneloops and labeled them as four pairs (A-D) so they are consistently paired.

    My questions are:
    1) Should I pair the batteries up permanently like I'm doing now
    2) If yes to question 1, why did my mismatching affect performance. Is that permanent damage I did?
    3) Is there anything I can do with my old batteries to determine the best pairing and get some more useful life out of them?

    I don't know if this is the type of thing you want to cover. I do like your blog though and thought that if I could contribute a topic (even if you go in a completely different direction with it) that it might be a small way to say thanks for sharing your knowledge. Do what you wish with it. I'm not searching out free advice, just telling you about my own battery experience.

    Thanks and I hope you continue with this blog!

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  8. JC said, "... I'm not searching for free advice ..." Well, I like free advice. It keeps me from paying so much time and money on more advice. Someday I hope all the great advice I have been given freely will help me build a viable vehicle that I will likely spend a ton of money on. I'm to the point with free advice that I likely will have to go to work for a company so that I can get more "free" advice in order to get the proper results I need. Thank you Venkat and so many others!

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  9. JC: The question you pose regarding how to bin batteries is actually pretty important and worth a blog post. I shall make one soon.
    I appreciate the feedback.

    In general paring a weak battery with a strong one will kill the strong one. Its best to pair them the same. As for what you can do with your old battery; if you can measure the voltage, this may get you somewhere. It may help to charge all of them up, let them rest for say couple of hours and then match the ones whose voltage is the closest to each other.

    Venkat

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  10. Venkat, I'm a knuckle dragging mechanical guy with just enough materials science to make me dangerous, but the issue I see for ALL of the lithium ion chemistries is safety. Not just charging safety because the lithium iron chemistry is pretty safe in that regard (but at a severe hit on capacity). my concern is crash-worthiness, which granted is not really your bailiwick but it is something that needs to be factored into the decision tree. And as far as i am aware it applies to all of the chemistries. if the vehicle is in a crash and the batteries are ruptured, even if the battery does not instantly catch fire due to the resulting internal shorts, the first thing the fire department is going to do when they get there is hose things down to wash away the leaking fuel to prevent a fire (in the case of hybrids particularly, but you also must take into account of the fuel from any other vehicles involved.) which will of course CAUSE a fire when the water hits the exposed lithium. A fire that additional water will not put out but will in fact fuel. THIS is the thing that nobody seems to talk about. Can you comment on the safety aspects in the case of water exposure?

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