Stanford researchers have been able to develop the first ever lithium-ion battery that will not explode – why? Because it has been designed to shut down upon reaching ‘risky’ levels of temperatures – temperatures high enough which might cause explosion. After shutting down automatically, the battery will cool down and then restart immediately once the temperature is below the danger threshold.
The new technology offers the solution to the age old problem of battery related accidents and fires which have prompted recalls and bans on a wide range of battery-powered devices, from computers to recliners and navigation systems to hover-boards.
“People have tried different strategies to solve the problem of accidental fires in lithium-ion batteries. “We’ve designed the first battery that can be shut down and revived over repeated heating and cooling cycles without compromising performance,” stated Zhenan Bao, a professor of chemical engineering at Stanford.
A standard lithium-ion battery comprises of two electrodes and a liquid or gel electrolyte that basically carries the charged particles between them. Puncturing, shorting or even overcharging the battery generates a lot of heat, If the temperature reaches somewhere around 150 degrees Celsius (300 degrees Fahrenheit), the electrolyte could easily catch fire and trigger an explosion.
In the past, several technologies have been used to prevent battery fire, such as adding flame retardants to the electrolytes itself to creating a ‘smart’ battery that will provide warning signs before getting too hot for comfort.
“Unfortunately, these techniques are irreversible, so the battery is no longer functional after it overheats,” stated study co-author Cui, an associate professor of materials science and engineering and of photon science. “Clearly, in spite of the many efforts made thus far, battery safety remains an important concern and requires a new approach.”
To cure this ‘un-curable problem’ Cui, Bao and Zheng Chen turned to nanotechnology. The researchers used a plastic material embedded with tiny particles of nickel with nanoscales spikes protruding from their surface and coated them 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 Chen, 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.”
Upon reaching high temperatures, i.e above 160 F, the polyethylene film quickly expanded like a balloon causing the spiky particles to separate and the battery to shut down. And when the battery cooled down, the film shrunk back to normal size and the battery started generating electricity again.
“Compared with previous approaches, our design provides a reliable, fast, reversible strategy that can achieve both high battery performance and improved safety,” Cui said. “This strategy holds great promise for practical battery applications.”
Steven Myers
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