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.
Lithium metal tends to react with a battery cell’s electrolyte, forming compounds that trap lithium ions and keep them from generating electrical current, steadily decreasing the amount of energy the battery can store. The reaction also creates dendrites, metal spikes that can cause short circuits that generate enough heat to ignite the flammable electrolyte.
The standard solution has been to replace the liquid electrolyte with a solid one that is less reactive and also acts as a physical barrier to prevent short circuits. But solid electrolytes don’t conduct ions as well as liquid ones, which hurts battery performance.
SolidEnergy’s solution is to use both a solid electrolyte and a liquid one. The solid electrolyte is applied to the lithium-metal foil—the ions don’t have far to travel through this thin material, so it doesn’t matter that they’re moving relatively slowly.
Once ions move through the solid electrolyte, they reach the liquid electrolyte, which provides a path into the opposite electrode. Unlike conventional liquid electrolytes, this one isn’t flammable. And it has additives that prevent the lithium metal from reacting with it and that prevent dendrites from forming.
As with most announcements of battery breakthroughs, this one should be viewed with some caution. The transition from making a few high-performing prototypes to making large volumes consistently can be very difficult, and over the past several years, several announcements of breakthroughs have come to nothing (see “The Sad Story of the Battery Breakthrough That Proved Too Good to be True”). Also, while SolidEnergy’s battery may prove a good fit for portable electronics, it can’t be recharged enough times to work well in electric cars.
In recent months, at least two other startups have made similar claims about using lithium-metal electrodes to double energy storage capacity, though they have used different means of solving these problems (see “A Prototype Battery Could Double the Range of Electric Cars”).
However, SolidEnergy’s technology stands out because, unlike some competing approaches, it doesn’t require new lithium-ion battery manufacturing equipment. Furthermore, while other prototype batteries can be recharged only a few times, the company says its prototype can be recharged 300 times while retaining 80 percent of its original storage capacity—closer to what you’d need in portable electronics. It also works at room temperature, whereas some other lithium-metal batteries operate at temperatures too hot to be practical.
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