Annoyingly explosive hoverboards may become a thing of the past if a Stanford-designed solution takes off.
Their idea? Stop the device from overheating in the first place.
Shutting down the explosion-causing lithium battery before it overheats, gets volatile, and becomes a fire hazard could be the best solution, researchers at the university think.
Lithium batteries, of the kind found in smartphones, tablets, Boeing 787 Dreamliners, and the controversial two-wheeled scooters often called "hoverboards," can be volatile.
It's an unfortunate bi-product of energy—it explodes from time to time. After all, it's energy. That's what you got.
Mostly, as is the case in the smartphone and the now-corrected 787s, the technology can be tamed through the use of regulated charging, hard individual-cell containers, and special internal circuits to prevent uneven power distribution within the battery. Careful manufacturing helps, too.
However, if the battery's "thin separators" get damaged in use, or are faulty to begin with, all bets are off, the Economist says in an explainer.
One gets a manifestation scarily described as "thermal runaway." The thing just keeps getting hotter until it catches fire or explodes.
"Lithium batteries can also be damaged by using them in hot environments, and by excessive discharging and charging—which is why most lithium batteries contain special circuits to prevent this," the Economist says. "Catching fire if something goes wrong, then, is in their nature."
A lot of hoverboard owners can attest to this.
Solutions employed for years by lithium polymer battery users in the radio-controlled arena, such as in hobbyist drone building, have included storing and charging the batteries within fireproof bags.
The material is DuPont's Nomex, the stuff fire-fighter suits are made from. It doesn't catch fire. The Velcro-sealed bag contains the volatility in the event of a problem.
Another solution, often used in conjunction, is sophisticated digital charging, where each lithium polymer cell in the battery pack is balanced to equal voltage to the others.
Hobbyists can monitor the charging in real time too, and watch for anomalies displayed on a digital readout that can indicate a failed, and potentially problematic, lithium battery. They then discharge and discard it.
Stanford's solution is to simply shut the lithium ion battery down before it overheats.
The scientists have developed a thin film made from polyethylene and have embedded it "with nanoparticles of graphene-coated nickel."
That mixture detects overheating and shuts the battery down. Importantly, it does it without killing it. The battery can then be re-used, unlike with other shut-down techniques, such as adding flame-retardant material to the electrodes within the battery.
"We attached the polyethylene film to one of the battery electrodes so that an electric current could flow through it," says Zheng Chen, lead author of the study, on Stanford's website.
"To conduct electricity, 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," Chen says.
"If the temperature reaches about 150 degrees Celsius, the electrolyte could catch fire and trigger an explosion," Stanford says on its website.
When the lithium-ion battery gets above 70 degrees Celsius, the film expands; when it drops below that, the polyethylene and graphene shrinks back and allows power to flow again.
The question one might ask, of course, is whether you actually want the lithium battery to automatically restart if it has a problem.
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