Stanford researchers design new battery sensitive to temperatures

Researchers with Stanford University on the U.S. west coast have designed a lithium-ion battery that shuts down at high temperatures to effectively prevent battery fires in various devices

A research published Monday by the journal Nature Energy says the battery restarts immediately when the temperature cools.

"People have tried different strategies to solve the problem of accidental fires in lithium-ion batteries," said Zhenan Bao, a professor of chemical engineering.

"We've designed the first battery that can be shut down and revived over repeated heating and cooling cycles without compromising performance," Bao added.

A typical lithium-ion battery consists of two electrodes and a liquid or gel electrolyte that carries charged particles between them. Puncturing, shorting or overcharging the battery generates heat. If the temperature reaches about 150 degrees Celsius, the electrolyte could catch fire and trigger an explosion.

Bao recently invented a wearable sensor to monitor human body temperature. The sensor is made of a plastic material embedded with tiny particles of nickel with nanoscale spikes protruding from their surface.

For the battery experiment, she and colleagues 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," said Zheng Chen, a postdoctoral scholar and 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," Zheng said.

When the researchers heated the battery above 70 degrees Celsius, the polyethylene film quickly expanded like a balloon, causing the spiky particles to separate and the battery to shut down. And when the temperature dropped back down to 70 degrees Celsius, the polyethylene shrunk, the particles came back into contact, and the battery started generating electricity again.

To test the stability of new material, the researchers repeatedly applied heat to the battery with a hot-air gun. Each time, the battery shut down when it got too hot and quickly resumed operating when the temperature cooled.

"We can even tune the temperature higher or lower depending on how many particles we put in or what type of polymer materials we choose," said Bao.

"For example, we might want the battery to shut down at 50 C or 100 C," she added. Endi