Safety Cells

Burning hoverboards lit up the last holiday season. Before that, it was lap-blistering laptops and flammable phones.

The problem is lithium-ion batteries. Nothing else on the market packs as much energy, making them perfect for electricity-hogging devices. But they’re inherently unstable, ready to vent toxic gas, catch fire or even blow up if punctured or overcharged.

“It’s why airlines don’t let you check them in luggage,” says Chunsheng Wang, associate professor of chemical and biomolecular engineering. “It’s like carrying a small bomb.”

But now Wang and his collaborator, Army Research Laboratory senior research chemist Kang Xu, are closing in on technology to produce lithium-ion batteries that are both powerful and inherently fire-safe because these so-called “aqueous” batteries contain water.

While aqueous lithium-ion batteries themselves aren’t new, Wang and Xu changed the chemistry—mainly by adding lots of salt—to produce one that’s more powerful than any before. In a paper published last fall in the journal Science, they showed off a battery that delivers 2.3 volts, rather than the normal 1.5. If they can increase output to close to 3 volts—and Wang believes they will—aqueous lithium-ion batteries may be viable replacements for conventional battery technology in many applications.

The killer app would be electric car batteries, Wang says. Automakers are working to tap into the power of lithium-ion chemistry, which has far more punch than standard nickel-metal hydride battery packs. But current batteries have been blamed for a spate of recent car fires, and even caused the temporary grounding of Boeing’s newest airliner. The batteries Wang and Xu are developing might be a perfect fit—if they can pump up the power a bit more.

“If we succeed in increasing the energy density, people will no longer say this is only for small devices with low energy requirements,” he says. “It will have a huge future in safety-critical applications.”