“We’ve designed the first battery that can be shut down and revived over repeated heating and cooling cycles without compromising performance,” said Zhenan Bao, professor of chemical engineering and one of the study researchers, in a statement.
We all know that a sharp poke, a short, or even overcharging can cause a lithium-ion battery to overheat. At about 300 degrees Farenheit, the electrolyte gel carrying particles between the two electrodes of the standard lithium-ion battery can ignite, and then boom goes the dynamite.
Designers have tried flame-retardant additions to the electrolyte, and things as simple as a battery warning system (also created by a Stanford engineer, back in 2014). The problem was those fixes were a one off. “These techniques are irreversible, so the batter is no longer functional after it overheats.” Co-author Yi Cui explained.
OK, maybe laptops haven’t been blowing legs off in recent years, but “hoverboards” have been making the news as fire hazards so often that they’re not even allowed on major airlines. The new nickel-filled plastic overlay was designed to prevent batteries from bursting into flame. A new battery with this overlay will shut down when it overheats, preventing combustion.
The experiment involved coating the nickel particles with graphene and an atom of carbon, then embedding them in elastic polyethylene. “To conduct electricity, the spiky particles [of nickel] 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.”
The researchers used a hot-air gun to turn up the temp, and each time the battery responded as it should – once the battery hit about 160 degrees, the film expanded and shut down the battery. When the battery cooled, the particles came back into contact at the battery began to work 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,” Bao said. “We might want the battery to shut down at 50 degrees Celsius [about 120 degrees Fahrenheit] or 100 C [about 210 F].”
SLAC National Accelerator Laboratory and the Precourt Institute for Energy at Stanford supported this research. The team published the results in Nature Energy. “Hoverboard” manufacturers should say thanks, even though it will be a while before this technology makes its way to consumers.
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