SAN FRANCISCO—Researchers at Stanford University have developed a lithium-ion battery that cycles on and off based on temperature to prevent battery fires.
Traditional lithium-ion batteries can overheat if punctured or shorted, and can catch fire or explode at about 300 degrees Fahrenheit. Techniques such as adding flame retardants to an electrolyte make the battery nonfunctional and, thus, don't truly solve a problem, said Stanford engineer Yi Cui.
To solve this issue, Cui, chemical engineering professor Zhenan Bao, and postdoctoral scholar Zheng Chen turned to nanotechnology and a wearable body temperature monitor recently invented by Bao. The sensor is made of a plastic material and is embedded with tiny particles of nickel that have nanoscale spikes protruding from their surface. For use in batteries, researchers coated the spiky nickel particles with graphene, an atom-thick layer of carbon, and embedded the particles in a thin film of elastic polyethylene.
"We attached the polyethylene film to one of the battery electrodes so that an electric current could flow through it," Chen, the lead author of the study, said in a release. "To conduct electricity, the spiky particles have to physically touch one another. But during thermal expansion, polyethylene stretches. That causes the particles to spread apart, making the film non-conductive so that electricity can no longer flow through the battery."
Nanoparticles of graphene-coated nickel. (Source: Stanford/Image: postdoctoral scholar Zheng Chen)
Above 160 F, the polyethylene film expands, causing the spiky particles to separate and the battery to shut down. When the temperature drops to 160 F, the polyethylene shrunk, the particles came back into contact, and the battery started generating electricity again. Bao said they can tune the temperature based on the number of nickle particles and the type of polymer.
Researchers repeatedly applied heat to the battery with a hot-air gun to test stability. Each time, the battery shut down when it got too hot and quickly resumed operating when the temperature cooled.
The research was supported by the SLAC National Accelerator Laboratory and the Precourt Institute for Energy at Stanford. The battery study is published in the Jan. 11 issue of the journal Nature Energy.