Lithium-ion batteries have seen stunning improvements in their size, weight, cost, and performance. (See Physics Today, December 2019, page 20.) But they haven’t yet reached their full potential. One of the biggest remaining hurdles has to do with the electrolyte, the material that ferries lithium ions from anode to cathode inside the battery to drive the equal and opposite flow of charge in the external circuit.

Most commercial lithium-ion batteries use organic liquid electrolytes. The liquids are excellent conductors of lithium ions, but they’re volatile, flammable, and defenseless against the whisker-like lithium-metal dendrites that can grow between the electrodes and eventually short-circuit the battery. Because safety comes first, battery designers must sacrifice some performance in favor of not having their batteries explode or catch fire.

A solid-state electrolyte could solve those problems. For the past two decades, Jenny Pringle, Maria Forsyth, and colleagues at Deakin University in Melbourne,...

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