American researchers have developed a new lithium-ion battery that shuts itself down before it starts to overheat, then restarts immediately when the temperature cools.
Zhenan Bao, a professor of chemical engineering at Stanford Univresity, said such a battery could prevent the kind of high-profile fires that have occurred on a range of battery-powered devices from computers to so-called hoverboards.
"People have tried different strategies to solve the problem of accidental fires in lithium-ion batteries," she said.
"We've designed the first battery that can be shut down and revived over repeated heating and cooling cycles without compromising performance."
Bao and her team had previously invented a wearable sensor to monitor human body temperature. This was made of a plastic material embedded with tiny particles of nickel with nanoscale spikes protruding from their surface. For the battery experiment, they modified the same design by coating the spiky nickel particles with graphene and embedding 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," said PhD student Zheng Chen, who was lead author of the study.
"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 nonconductive so that electricity can no longer flow through the battery."
When the researchers heated the battery above 70 C, the polyethylene film quickly expanded like a balloon, causing the spiky particles to separate and the battery to shut down. But when the temperature dropped back below 70 C, the polyethylene shrank, the particles came back into contact, and the battery started generating electricity again.
Bao said they were also able to tune the temperature higher or lower depending on how many particles they put in or what type of polymer materials they chose.