A new kind of lithium-ion battery could let portable electronics such as smartphones and smart watches last twice as long between charges.

The battery was developed by SolidEnergy, a company spun out of MIT in 2012. The secret to boosting energy storage lies in swapping the conventional electrode material—graphite—for a thin sheet of lithium-metal foil, which can store more lithium ions.

Battery makers have been trying to use lithium-metal electrodes in batteries for decades, with only limited success. SolidEnergy seems to have solved a couple of key problems, which have caused such batteries to either stop working after a few charges or burst into flames.

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