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An “Almost Perfect” Battery

Design with solid electrolyte significantly improves capacity and safety.

Everyone wants better batteries, whether to make smartphones last longer or to drive an electric car farther. So researchers around the world are focused on boosting the amount of energy that batteries can hold while improving their safety.

The molecular structure of the new electrode material includes lithium atoms (green), sulfur atoms (yellow), and tetrahedra of PS4 (purple) and GeS4 (blue).

Now researchers at MIT, working with Samsung and other collaborators, have developed a new approach that could make it practical for today’s most common rechargeable batteries to use a solid material for the electrolyte, the component that transports charged particles between two electrodes as a battery charges and discharges. The idea is that a solid electrolyte, rather than the liquid used today, could greatly improve battery life and safety—while significantly increasing the amount of energy stored in a given space.

The team, led by MIT postdoc Yan Wang and Gerbrand Ceder, a visiting professor of materials science and engineering, aimed to develop solid-state electrolytes for lithium-ion batteries. The electrolyte now used in such batteries—typically a liquid organic solvent—has been responsible for overheating and fires that, for example, temporarily grounded all of Boeing’s 787 Dreamliner jets, Ceder explains. Others have sought a solid replacement for the liquid electrolyte, but this group is the first to show that a solid material can conduct ions fast enough to work well in the types of batteries used today.

“All of the fires you’ve seen, with Boeing, Tesla, and others—they are all electrolyte fires,” Ceder says. “The lithium itself is not flammable in the state it’s in in these batteries.” With a solid electrolyte, “there’s no safety problem—there’s nothing there to burn,” he says.

The proposed solid electrolyte also holds other advantages. “With a solid-state electrolyte, there’s virtually no degradation reactions left,” Ceder says. And that means such batteries could last through “hundreds of thousands of cycles.”

The team’s initial findings focused on superionic lithium-ion conductors, which are compounds of lithium, germanium, phosphorus, and sulfur. But the principles derived from this research could lead to even more effective materials, the team says.

Solid-state electrolytes could be “a real game-changer,” Ceder says, solving “most of the remaining issues” in battery lifetime, safety, and cost. The result, he says, could be “almost a perfect battery.”

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