New batteries are often described with comparatives: they’re safer, lighter, or longer-lived than today’s versions. Solid-state batteries—those which contain no liquid—can make two such claims. With inorganic electrolytes, they’re much less likely to catch fire than traditional lithium-ion batteries, which have organic electrolytes. And by swapping out graphite for lithium as the anode, you can get a massive increase (up to 10-fold) in energy density, making solid-state batteries look especially promising for electric vehicles.
“That’s the Holy Grail. Lithium metal has the highest gravimetric density of all materials,” says Adam Best, who’s in charge of battery research at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia’s national science agency.
But a major snag remains in bringing solid-state batteries to market—how to manufacture electrolytes that are strong and durable, yet thin enough to be good ion conductors. Ideally, these electrolytes should be tens of microns thick, similar to the separators in today’s lithium-ion batteries, says materials scientist Ping Liu from the University of California, San Diego. “But because most solid electrolytes are ceramic, when you make a thin layer, they’re inherently brittle,” he says.