Solid-State Electrolyte Design for Lithium Dendrite Suppression.

All-solid-state Li metal batteries have attracted extensive attention due to their high safety and high energy density. However, Li dendrite growth in solid-state electrolytes (SSEs) still hinders their application. Current efforts mainly aim to reduce the interfacial resistance, neglecting the intrinsic dendrite-suppression capability of SSEs. Herein, the mechanism for the formation of Li dendrites is investigated, and Li-dendrite-free SSE criteria are reported. To achieve a high dendrite-suppression capability, SSEs should be thermodynamically stable with a high interface energy against Li, and they should have a low electronic conductivity and a high ionic conductivity. A cold-pressed Li3 N-LiF composite is used to validate the Li-dendrite-free design criteria, where the highly ionic conductive Li3 N reduces the Li plating/stripping overpotential, and LiF with high interface energy suppresses dendrites by enhancing the nucleation energy and suppressing the Li penetration into the SSEs. The Li3 N-LiF layer coating on Li3 PS4 SSE achieves a record-high critical current of >6 mA cm-2 even at a high capacity of 6.0 mAh cm-2 . The Coulombic efficiency also reaches a record 99% in 150 cycles. The Li3 N-LiF/Li3 PS4 SSE enables LiCoO2 cathodes to achieve 101.6 mAh g-1 for 50 cycles. The design principle opens a new opportunity to develop high-energy all-solid-state Li metal batteries.