May 4, 2017

A ​battery that won't catch fire

Courtesy of Alexej Jerschow, NYU

Navy research chemists designed a battery that claims to solve one of the biggest problems plaguing the industry. Batteries run the risk, under some conditions, of growing small spikes of metal that can pierce other parts of the system, causing it to short circuit and catch fire. The new design seems to solve that issue for devices that use zinc (like the one developed by the Navy). The big question though is whether it could do the same for lithium-ion cells, which dominate the market. The short answer: yes, the design could potentially work for lithium, says the Navy's Debra Rolison.

Why it matters: These dendrite spikes are holding back potentially massive advances in drawing more energy from a lithium-ion battery. Batteries are a multi-billion dollar business with even more money to be made in a not-so-far-off-future where electric cars and maybe even airplanes are commonplace. Those markets will demand more energy output and less risks.

Rolison and her team at the U.S. Naval Research Laboratory developed a battery that relies on microscopic sponge-like structures made of zinc. Zinc batteries aren't anything new — standard alkaline batteries use the element — and are known to be safe because they use water rather than flammable organic liquids. The researchers devised a 3D porous structure that uniformly moves the charge in the battery to solve the risk of dendrites forming. "They've shown dramatic progress," says Venkat Viswanathan, a Carnegie Mellon University researcher who wasn't involved in the study.

How it performed: The zinc battery was on par with lithium-ion ones in terms of how much energy it could store and provide. To work in a hybrid electric car, a cell needs to be able to quickly charge and recharge as the vehicle starts and stops. The zinc battery completed more than 50,000 brief cycles, making it a feasible alternative for powering hybrid vehicles, the authors say.

What's next: The Navy's commercial partner, EnZinc, is working to scale up the battery. They would have to prove it can go for at least 500 high-rate cycles in order to be commercially viable and they have to string multiple cells together. (For reference, a Tesla Model S contains more than 7100 cells.)

They are focused on the zinc configuration because they say it would be significantly cheaper than today's lithium ion batteries that rely on relatively expensive cobalt. The industry is racing to reach a target of $100/kwh — a measure of how much energy output costs. Right now, lithium ion cells are about $150/kwh but add in manufacturing, assembly and monitoring the battery and that figure doubles. Michael Burz at EnZinc projects their zinc system will be $150/kwh, with negligible costs added from installing and operating the battery. But that figure hinges on any issues they might encounter in scaling it up and depends in part on the price of nickel, which is currently about a third of cobalt but is predicted to climb.

Bottom line: Our electronic worlds currently revolve around lithium ion batteries. If the researcher's approach could be applied to those batteries to eke more energy out of them, it would be a breakthrough. On the other hand, a zinc battery would have to beat lithium on cost without having to change the infrastructure of our devices in order to upset the industry.

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