Science Interviews


Mon, 2nd Nov 2015

Lithium-air: big battery breakthrough

Professor Clare Grey, University of Cambridge

Listen Now    Download as mp3 from the show Electric Cars: Pollution Solution?

One problem with current electric cars is the range. This all boils down to storing Batteryenergy, and the present hold up is the battery technology weíre relying on. Now that could be about to change thanks a new discovery from Cambridge University's Clare Grey who's a world leading expert in the art of making better batteries, as she revealed to Chris Smith...

Clare - The heart of the battery is very much the two different materials that make up the electrodes and actually, store the energy. So, one of them is called the positive and one of them is called the negative. The positive electrode contains a material called lithium cobalt oxide and that contains layers of lithium, cobalt and oxygen, and the negative is made up of graphite. So thatís the same material thatís in pencils.

So, when you put it together, you have your lithium cobalt oxide, and your graphite, and thatís the battery thatís been around for 25 years. Itís in our mobile phones and itís in our laptops. Itís really sort of kicked off the whole portable electronics revolution.

Chris - So, itís sort of based chemically on the fact that you have two chemicals and one wants to give away electrons Ė negative charges - the other chemical wants to soak them up in some way by a chemical reaction happening and we can tap off those surplus electrons and send them around a circuit before allowing it to complete that journey.

Clare - Thatís right and work and do some load.

Chris - So, what's the problem with the present generation then of car batteries like the electric car that Waseem had that went flat on him? Why are the batteries not better?

Clare - Well, there were multiple problems but the biggest one is that the amount of electrons and the energy density. So the energy density is the voltage times the number of electrons you can get out of them is limited by the weight of the material and the type of material. And so, thatís problem number one. Problem number two is itís difficult to charge and discharge the batteries multiple times. So, you're used to your mobile phone batteries lasting for a couple of years if you're lucky.

But you want your car batteries last for 7 or 10 years because itís so expensive. And so, what's happening in these batteries is the lithiums are moving backwards and forwards from our lithium cobalt oxide to our graphite. And weíre expecting these materials not to change but they will eventually do that.

Chris - I suppose itís a bit like, if I keep shoving a key and a lock and pulling it out again, eventually, the lock wears and the key gets loosen the lock and itís sort of similar with your battery architecture.

Clare - Yes and the other problem also is that Ė so, if I put my battery together, it wouldnít work because I got lithium cobalt oxide, and graphite. They're not oxidised and reduced. So, what I need to do is I needed to charge them so I have to put them on my charger. And then I make very reactive materials and then those reactive materials can react with other components in the battery like the electrolytes. So, the electrolyte is the liquid that allows the lithium ions to move backwards and forwards.

And so overtime, all of these reactions create side products and they eat out lithium and gradually, the capacity dies. And so, thatís one of the major reasons your battery and your cell phone is dying is because of these side reactions.

Chris - And the research that you're announcing this week that may help to solve this problem, what is that and how does it work?

Clare - So itís a very different chemistry and I should stress there's a lot of work globally on this type of chemistry and itís called a lithium air battery. So, itís a battery where lithium reacts with oxygen in the air and that has the same theoretical energy densities as gasoline or it approaches it. So in gasoline is an amazing material because you're storing energy between the CC, the carbon bonds in these carbon hydrogen bonds. So, itís been very difficult to get to the same energy density.

But because you're reacting lithium and oxygen, and both of those are very light, if we could get that to work, itís the so-called ultimate battery chemistry. So, people have been able to make a lot of progress on this chemistry, but itís been very difficult to get the reaction of lithium peroxide and back to oxygen reversibly.

Chris - And have you managed to solve that?

Clare - We have done something quite different. What weíve shown is that if we add an extra chemical, in this case, itís lithium iodide Ė instead of forming lithium peroxide, we actually form lithium hydroxide. And so now, itís a reaction of lithium plus water and oxygen to form the lithium hydroxide and we can reversibly do this for multiple cycles. And so, our batteries have been out there for months, cycling backwards and forwards.

What's really interesting about the new chemistry is that itís got water in it. And so, what weíre doing is weíre getting one step closer to what we really want and thatís the lithium air battery.

So, we want a battery than can breathe the same air that we have although we all breathe that contains oxygen, nitrogen, carbon dioxide and water. Our battery for the first time actually tolerated the water.



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