By designing a solid electrolyte that is rigid on one side and soft on the other, researchers have fabricated a lithium-metal battery that completely suppresses dendrite formation—a major safety hazard that can cause fires and shorten battery lifetime. This design also overcomes a tradeoff that is typically present in these batteries, by simultaneously eliminating dendrite growth and reducing the resistance at the electrode/electrolyte interface. Typical methods cannot achieve both of these goals at the same time.