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 H^{δ -}-H^{δ +} comproportionation reaction between LiH and NH₄F 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 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.