Zhenan Bao, a professor of chemical engineering at Stanford University reports a new lithium ion battery that shuts itself down if it overheats, then resets and resumes normal functioning after the temperature drops. Lithium ion batteries become dangerously hot when they reach an internal temperature of about 300 degrees Fahrenheit. That’s why every electric vehicle has either an air or liquid cooling system. One of the primary goals of battery research is to develop batteries that do not need such external cooling systems. Eliminating them would reduce cost, weight and complexity in electric cars.
Exploding lithium ion batteries are nothing new. They have been in the news recently because many of the batteries used to power a new generation of so-called hoverboards have burst into flames. Boeing had problems with the lithium ion batteries used in its new Dreamliner a few years ago. Others have invented batteries that shut themselves down when they overheat. The problem is, a fire may be prevented but the battery is useless afterwards. The new technology from Stanford allows the battery to resume normal function after it cools. It appears there is no limit on the number of times the “circuit breaker” action can be utilized.
“People have tried different strategies to solve the problem of accidental fires in lithium-ion batteries,” explains Bao, “We’ve designed the first battery that can be shut down and revived over repeated heating and cooling cycles without compromising performance.” “The potential for mass production is quite high,” notes Bao. She says the materials used are mostly inexpensive plastic and nickel. The new nanoparticle battery restarts without a notable loss of efficiency, which is a critical factor.
The secret is a polymer strip embedded with spikes of nano-scale nickel. When two of the strips are next to each other, the nickel conducts electricity. When the polymer heats up, the polymer distorts, causing the two strips to pull apart, which interrupts the flow of electrons. For non-technical people, think of it as two strips of Velcro that can be meshed together and separated many times without losing their bonding ability. Stanford’s new technology can be customized to interrupt the flow of electrons over a wide temperature range. “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,” explained Bao,