Super-fast charging batteries

Each year Forbes Magazine publishes the Forbes 30 Under 30, what they dub their “annual encyclopedia of creative disruption”. These are people sitting on ideas and aspirations with the potential to change the world. And on the list this year is a group of Cambridge university engineers who want to change the way batteries work and the way we use them. Katie Haylor went to find out how...

Katie - Italian physicist Alessandro Volta is credited with creating the first electric battery in the 1800s. Although this voltaic pile, as it’s known, doesn’t look much like your average AA, both this and the batteries around today us chemical reactions which produce chemical energy. This is converted to electrical energy and that’s how things are powered in a circuit. These days, lithium ions are where battery power is at but despite their prevalence in computers, phones, power tools, and more, they’re not perfect. Here’s Jean de la Verpilliere from Cambridge University’s Engineering Department and spin out company Echion.

Jean - I’m sure you’re familiar with how the battery of your phone dies out quickly, how it takes time to recharge or, perhaps, you would be happy to switch from a petrol car to an electric car if you could use it more easily or drive longer on a single charge and that’s all down to the performance of the lithium ion battery. Essentially, we’re saying there’s a lot of room for improvement.

Katie - One area, Jean says, is safety. Lithium batteries can be dangerous if used at extreme temperatures or if they get significantly damaged. Another issue is energy density: how much energy you can store in the battery itself before you need to charge it again. But one specific issue that Jean and his colleagues are working on is charging time…

Jean - So right now, it takes anywhere between 40 minutes and 6 hours to recharge a battery. What we’re doing at Echion is we’re developing new materials that enable batteries to charge seven times faster, so you’re talking a full battery charge for your car or your phone, for whatever in five minutes.

Katie - Sounds promising! No more hanging around at a plug socket waiting for my ailing smartphone to come back to life. But how do these super-speedy charging batteries work and what makes them different from other lithium batteries? To find out, we took a trip down to the lab...

Jean - That’s a material production lab where we make large quantities of nanomaterials, so hundreds of times smaller than the diameter of your hair. We use this material to make electrodes and batteries. That’s a piece of kit that enables us to make kilogrammes of quantities of nanomaterials that are then used into the battery to store the lithium ions. The kit that you see here starts from a precursor to our material, which is basically rust.

Katie - As in the stuff that I have to scrape off my bike?

Jean - Yes. So that’s the idea. Essentially a very very finely divided rust and because it’s nano we can use it into a battery, it works with lithium ions.

Katie - How is the rust involved in the battery?

Jean - This rust is going to go onto the negative electrode of your battery, so that’s the component of the battery that stores the lithium ions, the electricity, when you charge the battery.

Katie - Coating the negative electrode of the battery with very very small particles of rust gives a much bigger surface area for the reaction with the lithium ions, which means more opportunity for interaction and faster charging. Also, Jean points out, bigger sized particles of rust don’t actually interact very well with lithium ions. But why use rust in the first place?

Jean - If you take the current standard for the negative electrode of lithium ion batteries, it’s a material called graphite, essentially what you have on your pencils. This graphite material cannot accept fast charge. Fast charging your battery means bombarding your negative electrode with a high rate of lithium ions. If you try and do this with a graphite battery, the lithium ions will not nicely intercollate and be stored into the graphite. Instead they will be plated on top of the electrode and you will grow what’s called metal dendrites, which are little towers of lithium metal that will short circuit your whole battery and that will lead to a fire and an explosion.

Using this nanoscale rust, fundamentally, we can’t have this dendrite growth and, therefore, we can bombard the material with as many lithium ions as you want, very fast and it will still be safe, and will charge the battery very fast.

Katie - So nanoscale rust on the negative electrode can safely capture lots of lithium ions at a fast rate. The team are also adding carbon nanotubes to the rust, which act as a sort of ‘electron highway’ conducting the heat and electricity out of the electrode. So what kind of impact could this technology have? Back in his office, Jean told me that whilst there’s still work to do to bring the size of these batteries up to what’s needed, charging a car battery in minutes rather than hours could help make electric cars a more practical option for many people.

Jean - Being able to charge in five minutes basically means that charging becomes painless. Five minutes is about the time it takes for you to refill your car at the petrol station. What we’re saying is that if you can charge easily your can recharge more frequently and, therefore, you don’t need to carry a huge battery with you. And that’s important because the cost of the battery in an electric car right now is more than 50% of the cost of the vehicle and that’s because we need huge batteries because they charge so slowly. Let’s reduce the size of the battery by a factor of four, that will save a lot on cost, also on weight of the electric car, or if you’re powering a bus, the weight of the battery will be reduced and so you’ll be able to carry more passengers for instance.