Long-lasting, quick-charging batteries are essential to the expansion of the electric vehicle market, but today’s lithium-ion batteries fall short of what’s needed — they’re too heavy, too expensive and take too long to charge. For decades, researchers have tried to harness the potential of solid-state, lithium-metal batteries, which hold substantially more energy in the same volume and charge in a fraction of the time compared to traditional lithium-ion batteries. “A lithium-metal battery is considered the holy grail for battery chemistry because of its high capacity and energy density,” said Xin Li, Associate Professor of Materials Science at the Harvard John A. Paulson School of Engineering and Applied Science (SEAS). “But the stability of these batteries has always been poor.” Now, Li and his team have designed a stable, lithium-metal solid state battery that can be charged and discharged at least 10,000 times — far more cycles than have been previously demonstrated — at a high current density. The researchers paired the new design with a commercial high energy density cathode material.