Keeping Batteries Charging...
Chris - We've probably all had the problem of the rechargeable battery that lasts less and less long after each recharge. Usually it's terminal (sorry about the pun) and the battery has to be replaced, which is not ideal given how much they can cost. But now help is at hand, with the equivalent of an internal plaster for a battery. Here's Scott White:
Scott - In a nutshell what we do is we put things into batteries that make them perform much better and a lot safer. These little things that we put in are microcapsules - very tiny capsules that you can think of as being like 'drugs'. And inside these capsules are special materials that when they get released, make the battery healthy and last longer and be a lot safer.
Chris - When you say "last longer", you're not just talking about how batteries go flat because they've run out of juice, you mean how their ability to recharge and discharge decays with time?
Scott - Exactly, well put. We would like batteries to last ten years. But they don't because of the charge and discharge cycling that we do to them.
Chris - What's actually happening - if I were to zoom in inside the battery with some kind of very powerful microscope and I could physically see inside the battery at a molecular level - what's going on to make my batteries last less long as they age?
Scott - There's a lot of things happening. Probably the simplest way to explain it is that there are small cracks that open up inside the battery. So physically, particles are breaking and two layers of different materials are separating. There's all kinds of interesting electrochemical reactions that are undergoing at the same time, but physically particles break, things separate, interfaces build up, and the end result is that the battery can no longer give you the power that you need.
Chris - But all of the ingredients are still in there, and so if you could stop that happening you'd have a battery that did continue to perform well. So what you're saying is that your work is dedicated to stopping that decay happening in that way?
Scott - Exactly. We're giving it a dose of loving medicine when it needs it. So when little cracks open up, we put things in there that heal those cracks so you're battery is like new.
Chris - OK, well could you explain that then in slightly more detail. So you are literally doping the electrodes with stuff so that if an area breaks it repairs itself. This is, I suppose, like those self-repairing car paints, where there are little capsules of various things, and when they get exposed by the paint being damaged they 'heal' the paint. You're doing the same with batteries?
Scott - Exactly, in fact we started with the very work that you're talking about - self-healing coating, self-healing paint, self-healing polymers. And in those systems we would put microcapsules in that would release a monomer, which is a polymer precursor, that would eventually heal that crack. So now we've translated that technology into batteries. The materials that we deliver to the batteries are of course completely different, they have different intended functions, but it's still predicated on the same thing: we have a capsule with a very thin wall, you can think of it as being like an egg shell, and inside our eggs are materials that will lead to the restoration of battery function. In terms of combating the longevity issue for this battery, we actually deliver conductive particles. So there are conductive particles on the inside of these egg shells that are in suspension, and when the egg shell breaks these particles come flooding out into the area of damage, where cracks have formed, and they bridge the cracks so they conduct electrons, so it restores conductivity.
Chris - I suppose you have to choose the composition of those repair particles very carefully so that they don't participate in other reactions inside the battery, which would be unsafe or, if given enough time, further erode the capacity of the battery.
Scott - Oh absolutely. We have one matre in our work and that is to do no harm, so whatever we put into the battery cannot disrupt its natural performance from the outset. What we do is we give it additional functionality, in this case self-healing behaviour.
Chris - And with this approach applied to a battery, how much better does it become? How much longer can you extend the working life of a Lithium cell?
Scott - Well I can't answer that conclusively yet because it is very new, but I can give you a flavour of how well this works. For example, some of the initial work that we have done on restoration of conductivity shows that within as little as 40 microseconds we get full restoration of conductivity. That's an incredibly short period of time - much faster than a humming bird can beat its wings - and it's 100% restoration of conductivity. Now, what that means in terms of how many more years you could use a battery, I don't know the answer yet. It's still way too new and a little bit far away to be able to predict. My goal is to be able to extend the lifetime by two, three or four times. If you did that, imagine how the economics of electric vehicles would change. We're not talking about replacing a battery pack every three or four years now, we're talking about one battery pack that could last the lifetime of the car or even longer.
Chris - Does this potentially also extend and expand the functionality of the battery? Certain batteries can only do certain things because the current required for some applications would be way beyond the capacity of the battery because they would degrade. So if you could enable them to put themselves right, does that mean that the batteries could be used in more different applications?
Scott - Absolutely. If you push a Lithium ion battery at a very high rate you see degradation mechanisms that kick in immediately and basically they toast your battery. So there's circuitry that's put in to prevent you from pushing the battery that hard. But certainly the battery is capable of doing it, and if this wouldn't hurt it, then you could use it very quickly and also for a long period of time. Hopefully these kinds of functionalities will be built in to the next generation of batteries and I'll give you everything you ever wanted.
Chris - Scott White, from the University of Illinois