Building an Air Stable and Lithium Deposition Regulable Garnet Interface from Moderate‐Temperature Conversion Chemistry

Abstract Garnet‐type electrolytes suffer from unstable chemistry against air exposure, which generates contaminants on electrolyte surface and accounts for poor interfacial contact with the Li metal. Thermal treatment of the garnet at >700 °C could remove the surface contaminants, yet it regenerates the contaminants in the air, and aggravates the Li dendrite issue as more electron‐conducting defective sites are exposed. In a departure from the removal approach, here we report a new surface chemistry that converts the contaminants into a fluorinated interface at moderate temperature <180 °C. The modified interface shows a high electron tunneling barrier and a low energy barrier for Li + surface diffusion, so that it enables dendrite‐proof Li plating/stripping at a high critical current density of 1.4 mA cm −2 . Moreover, the modified interface exhibits high chemical and electrochemical stability against air exposure, which prevents regeneration of contaminants and keeps high critical current density of 1.1 mA cm −2 . The new chemistry presents a practical solution for realization of high‐energy solid‐state Li metal batteries.