The primary reason hoverboards have become public enemy #1 in recent times is due to their unfortunate tendency to catch fire and explode due to their lithium-ion batteries overheating.
But a new lithium-ion battery developed by scientists in the US could put an end to such dramas. Researchers at Stanford University have made the world's first lithium-ion battery that shuts off before it overheats, then restarts immediately when its temperature has cooled.
Conventional lithium-ion batteries comprise a pair of electrodes and a liquid or gel electrolyte that carries charged particles between them. However, if the battery's temperature reaches around 150 degrees Celsius (300 degrees Fahrenheit) as a result of a defect or overcharging, the electrolyte can catch fire and trigger an explosion, as we've seen in many sad cases.
"We've designed the first battery that can be shut down and revived over repeated heating and cooling cycles without compromising performance," said chemical engineer, Zhenan Bao.
It's not the first time researchers have tried installing a cut-off mechanism in lithum-ion batteries to address the dangers of overheating. Previous efforts have implemented things like flame retardants and copper separators to forestall potential fire hazards.
"Unfortunately, these techniques are irreversible, so the battery is no longer functional after it overheats," said one of the researchers, Yi Cui.
By contrast, the advantage of the new method is it operates automatically and repeatedly to prevent overheating, due to a material composed of tiny particles of nickel with nanoscale spikes protruding from their surface. These particles are coated with graphene and embedded 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, who led the research. "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 non-conductive so that electricity can no longer flow through the battery."
In testing, the researchers applied heat to the battery with a hot-air gun. When the battery was heated above 70 degrees Celsius (160 degrees Fahrenheit), the polyethylene film expanded and caused the battery to shut down, but once the temperature dipped, the film would automatically shrink, allowing the battery to resume generating electricity.
According to the researchers, the temperature threshold could be tweaked depending on the particular composition of the polymer materials, enabling batteries to run cooler or hotter before the conduction/non-conduction kicks in.
The findings, reported in Nature Energy, won't just benefit hoverboards, but could potentially make all manner of lithium-ion battery-based devices less prone to overheating risks, including smartphones, tablets, and notebook computers.
"Compared with previous approaches, our design provides a reliable, fast, reversible strategy that can achieve both high battery performance and improved safety," said Cui. "This strategy holds great promise for practical battery applications."