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PANTS on FIRE? Too late for you. But others will benefit from singed trouser phone alert
That battery is SMOOOOKIN'
Boffins at Stanford University have invented a system which could banish the dreaded trouser fire to the annals of tech history.
Regular readers of The Reg will know that the batteries used in mobile phones have a horrible tendency to blow up at inopportune moments. Whether it's an iPad Nano going kaboom in Japan, a Swiss woman turned into a "burned pig" or the iPod Touch-related immolation of some poor chap's nylon pants, one thing is clear: your nether regions are not safe from the march of technological progress.
Until now, that is.
Stanford researchers have invented a "smart" lithium-ion battery that gives a warning before it goes bang.
"Our goal is to create an early-warning system that saves lives and property," said Yi Cui, associate professor of materials science and engineering at Stanford. "The likelihood of a bad thing like that happening is maybe one in a million. That's still a big problem, considering that hundreds of millions of computers and cellphones are sold each year. We want to lower the odds of a battery fire to one in a billion or even to zero."
The problem lies in the design of the lithium-ion battery, which is made up of a carbon anode and a lithium metal-oxide cathode with a thin strip of polymer keeping them separate. When this separator is damaged, the battery can short-circuit and ignite the electrolyte solution, which is no fun when its goes off in your pocket.
Shorting can also happen if the battery is charged too fast or the temperature is too low, which is known as overcharging.
"Overcharging causes lithium ions to get stuck on the anode and pile up, forming chains of lithium metal called dendrites," Cui added. "The dendrites can penetrate the porous separator and eventually make contact with the cathode, causing the battery to short.
"In the last couple of years we've been thinking about building a smart separator that can detect shorting before the dendrites reach the cathode."
To cut the risk of an explosion, Cui and his cronies fitted a nanolayer of copper onto one side of the polymer separator.
"The copper layer acts like a sensor that allows you to measure the voltage difference between the anode and the separator," said graduate student Denys Zhuo, who worked on the study. "When the dendrites grow long enough to reach the copper coating, the voltage drops to zero. That lets you know that the dendrites have grown halfway across the battery. It's a warning that the battery should be removed before the dendrites reach the cathode and cause a short circuit."
The new battery also makes it possible to detect any holes in the separator by measuring the electrical resistance between the separator and the cathode.
For more information on the battle to kill the trouser fire, click here. ®