A ductile solid electrolyte interphase for solid-state batteries

Solid-state lithium metal batteries are facing huge challenges under practical working conditions^1,2. 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.