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Sulfur Batteries Could Power Your Smartphone Four Times Longer

Sulfur is "practically free," researchers say.
Chengdu Liang shows off his newly-created lithium sulfur battery, which could let you play smartphone games way longer, via Oak Ridge National Laboratory

If you're anything like me, you know that when you get down to the last few percentage points on your smartphone battery, you've got to make some tough decisions: Should I keep streaming YouTube videos on the train or, you know, not do that so people can reach me? Department of Energy scientists at Tennessee's Oak Ridge National Laboratory might soon put an end to our great national nightmare with a newly developed battery that can hold a charge for four times longer than conventional lithium-ion batteries.

The new battery, which uses lithium and solid sulfur, has a couple of advantages over Li-ion batteries. According to Oak Ridge's Chengdu Liang, the solid-state battery isn't as prone to overheating as lithium batteries and isn't flammable, a problem with current batteries that sometimes comes up. Sulfur is also really, really cheap, mostly because it's a waste product.

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"Not only does sulfur store much more energy than the transition metal compounds used in lithium-ion battery cathodes, but a lithium-sulfur device could help recycle a waste product into a useful technology," Liang said. "Sulfur is practically free."

He's essentially right: Elemental sulfur trades for somewhere in the neighborhood of $200 for a ton, so we're talking 10 cents a pound.

Researchers have long thought a sulfur battery made sense theoretically, but fell into the trap of trying to design lithium sulfur batteries in much the same way Li-ion batteries are, with liquid electrolytes that flow from anode to cathode. Those liquid ions lead to overheating issues and cause the battery to eventually break down.

Instead, Liang's team created a new material, made almost entirely of sulfur, that is solid and conducts ions just as well as the liquid ions. Liang says the approach represents a "complete change from the current battery concept of two electrodes joined by a liquid electrolyte, which has been used over the last 150 to 200 years."

"This game-changing shift from liquid to solid electrolytes eliminates the problem of sulfur dissolution and enables us to deliver on the promise of lithium-sulfur batteries," Liang said. "Our battery design has real potential to reduce cost, increase energy density and improve safety compared with existing lithium-ion technologies."

After more than 300 charge cycles, the lithium sulfur battery maintained a capacity of 1,200 mAh per gram, compared to just 170 mAh/gram for Li-ion batteries. Because the sulfur battery puts out about half the voltage as a Li-ion battery, that translates to about four times as long to play Words With Friends, Snapchat, or, if you're so inclined, make phone calls.

No word on when you'll be able to pop this in your iPhone, but the team has just applied for a patent and is working on getting these out to market. A better battery is the current Holy Grail of technology, with everything from gadgets to electric vehicles waiting for a breakthrough. There's been a fair amount of promising research in the past few years, but bringing those developments to market is much harder. Still, considering how cheap sulfur is, this new work is worth paying attention to.