Sulfur-Doped Li ₂ OHCl Antiperovskite Electrolyte for Stabilizing the Solid Electrolyte Interphase in Solid-State Lithium-Metal Batteries

The development of solid-state lithium-metal batteries is hindered by interfacial instability at the Li metal–electrolyte interface and limited Li+ transport in inorganic electrolytes. Lithium-rich antiperovskites such as Li2OHCl are promising but suffer from unclear SEI chemistry and insufficient ionic conductivity. Herein, sulfur doping is introduced for the first time as a targeted strategy to engineer both the bulk structure and interfacial behavior of Li2OHCl. Partial substitution of O2– with S2– induces a transformation from orthorhombic to cubic structure, accompanied by lattice distortion and weakened Li–S bonding, which collectively reduce the Li+ migration barrier and enhance ionic conductivity. Furthermore, sulfur doping drives the formation of a Li2S-rich solid electrolyte interphase at the Li2OHCl/Li interface, enabling homogenized Li+ flux and effective suppression of lithium dendrite nucleation. This work provides a general heteroatom-doping strategy to optimize both bulk and interfacial characteristics in LiRAP electrolytes for advanced solid-state batteries.