Explosion-proof lithium-ion battery shuts down at high temperatures
19 January 2016
US scientists have designed a lithium-ion battery that self-regulates to prevent itself from overheating. Reaching high temperatures, the battery is able to shut itself down, only restarting once it has cooled. A team from Stanford University says the innovation will remove the danger of exploding batteries, seen recently in accidents involving laptops, phones and other devices.
Traditional lithium-ion batteries contain a pair of electrodes and a liquid or gel electrolyte to carry the charged particles. If the battery’s temperature reaches 150 degrees Celsius, the electrolyte can catch fire and cause an explosion.
"People have tried different strategies to solve the problem of accidental fires in lithium-ion batteries," said Zhenan Bao, a professor of chemical engineering at Stanford. "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 colleagues describe the new battery in a study published in the January 11 issue of the journal Nature Energy.
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, the 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.
The polyethylene film was attached to one of the battery electrodes so that an electric current could flow through it. 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 spiky particles separated and the battery shut down. But when it fell below 70 C, the polyethylene shrunk, the particles came back into contact, and the battery started generating electricity again.
"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."
Tests have shown that the technology holds great promise for practical battery applications.
Click the link below to see the Stanford video.