Hδ --Hδ + Comproportionation Enables Stable Li-N-H-F Solid Electrolyte.

Nitride family compounds are among the earliest explored materials for solid electrolytes (SEs). The main challenge lies in effectively enhancing their electrochemical stability without compromising their excellent Li-ion conductivity and Li metal compatibility. Herein, a Hδ --Hδ + comproportionation reaction between LiH and NH4F is employed to synthesize a Li-N-H-F complex, consisting of Li2+ xNHFx matrix and dispersed LiF nanoparticles. Density functional calculation results show that the incorporated F atoms in Li2NH lattice lead to structural variation and electron density redistribution, providing a more connected Li-ion network with low migration energy barriers. More importantly, the interfacial side reactions between the Li-N-H-F complex and electrodes are strongly self-limited due to the blocking effect of the in situ formed Li4NH/LiF-enriched interphases. The newly identified interphase Li4NH exhibits fast Li-ion migration ability and intrinsic stability toward Li, facilitating stable Li plating/stripping. Based on the superiority in Li-ion conduction and electrode compatibility, the Li-N-H-F solid electrolyte films prepared via cold pressing with 0.5 wt% binder enable stable cycling of Li||Li, Li||TiS2, and Li||LiCoO2 all-solid-state batteries.