Li-ion Battery Has Its Own Fire Alarm

It’s a rare lithium-ion battery that overheats and bursts into flames. But when one does, it can cause really bad things to happen. Phones burn through pants pockets, laptops explode while sending email, and even aircraft batteries catch on fire.

For years researchers have worked to develop battery technology that makes such flame-outs less likely. But battery fires are still happening with surprising regularity—just Google “phone battery fire” or “laptop fire” for the scary latest.

Until we have fireproof batteries, there’s another approach: the fire alarm battery. Researchers are developing technology to detect battery problems while they are developing—and before they cause a fire.

The latest approach, published in Nature Communications this month, comes from Stanford’s materials science and engineering department. Researchers there tweaked the traditional battery design to add a nanolayer of copper onto one side of the thin piece of polymer that separates the carbon anode and the lithium metal-oxide cathode. The copper layer doesn’t block the flow of lithium ions between the electrodes, but can detect problems that could create a short circuit and result in a fire.

The system depends on watching for the growth of dendrites in the battery. Dendrites are chains of lithium metal that can accumulate on the anode when the battery is charged too fast, for example, or when holes develop in the separator. 

Graduate student Denys Zhuo explained in a news release:

The copper layer acts like a sensor that allows you to measure the voltage difference between the anode and the separator. When the dendrites grow long enough to reach the copper coating, the voltage drops to zero. That lets you know that the dendrites have grown halfway across the battery. It's a warning that the battery should be removed before the dendrites reach the cathode and cause a short circuit. 

Exactly what kind of alarm that voltage drop will trigger has yet to be decided. I’m thinking Siri calmly suggesting that you take your phone out of your pocket and turn it off just isn’t going to be effective. Instead, perhaps we can dip back into television history, and lift a line from Mission Impossible: “This tape phone will self-destruct in five seconds. Good luck.”