H<i>^δ</i>⁻–H<i>^δ</i>⁺ Comproportionation Enables Stable Li–N–H–F Solid Electrolyte

Abstract 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 H δ − –H δ + comproportionation reaction between LiH and NH 4 F is employed to synthesize a Li–N–H–F complex, consisting of Li 2+ x NHF x matrix and dispersed LiF nanoparticles. Density functional calculation results show that the incorporated F atoms in Li 2 NH 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 Li 4 NH/LiF‐enriched interphases. The newly identified interphase Li 4 NH 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||TiS 2 , and Li||LiCoO 2 all‐solid‐state batteries.