A Perovskite Electrolyte That Is Stable in Moist Air for Lithium-Ion Batteries

Solid-oxide Li⁺ electrolytes of a rechargeable cell are generally sensitive to moisture in the air as H⁺ exchanges for the mobile Li⁺ of the electrolyte and forms insulating surface phases at the electrolyte interfaces and in the grain boundaries of a polycrystalline membrane. These surface phases dominate the total interfacial resistance of a conventional rechargeable cell with a solid-electrolyte separator. We report a new perovskite Li⁺ solid electrolyte, Li_0.38 Sr_0.44 Ta_0.7 Hf_0.3 O_2.95 F_0.05 , with a lithium-ion conductivity of σ_Li =4.8×10^-4  S cm^-1 at 25 °C that does not react with water having 3≤pH≤14. The solid electrolyte with a thin Li⁺ -conducting polymer on its surface to prevent reduction of Ta⁵⁺ is wet by metallic lithium and provides low-impedance dendrite-free plating/stripping of a lithium anode. It is also stable upon contact with a composite polymer cathode. With this solid electrolyte, we demonstrate excellent cycling performance of an all-solid-state Li/LiFePO₄ cell, a Li-S cell with a polymer-gel cathode, and a supercapacitor.