Solid-state lithium metal batteries are facing huge challenges under practical working conditions1,2. Even when the ionic conductivity of composite solid-state electrolytes is increased to 1 mS cm−1, it is still difficult to realize long-life cycling of solid-state batteries above a current density of 1 mA cm−2 and an areal capacity of 1 mAh cm−2 (ref. 3). The fundamental cause is the brittle nature of the solid–electrolyte interphase (SEI) with sluggish lithium-ion transport and the resulting lithium dendrites and severe side reactions. Here we report a ductile inorganic-rich SEI that retains its structural integrity while allowing easy ion diffusion at high current densities and areal capacities. The ductility of the SEI is ascribed to the Ag2S and AgF components, which are formed by a substitution reaction between Li2S/LiF in the SEI and AgNO3 in the dielectric composite electrolytes. Even at a high current density of 15 mA cm−2 and an areal capacity of 15 mAh cm−2, a symmetrical lithium cell with such an SEI has a long cycle life of over 4,500 hours. Furthermore, the ductile SEI also works over 7,000 hours at −30 °C, even under practical conditions of 5 mA cm−2 and 5 mAh cm−2.
