A Smart Non‐Sacrificial Interphase for Improved Lithium Reversibility in Anode‐Free Solid‐State Lithium Metal Batteries

Anode-free solid-state lithium metal batteries offer high energy density and enhanced safety, but their development is hindered by unstable solid electrolyte interphase formation and uncontrolled lithium deposition, which cause rapid capacity decay. To address these challenges, we introduced a smart non-sacrificial interphase (SNI) using 5-nitro-2-mercaptobenzimidazole (N-MBI) additive. N-MBI spontaneously forms an ultrathin self-assembled layer on copper current collectors before lithium deposition, creating a protective interface that isolates lithium metal from the electrolyte and suppresses parasitic reactions. During initial lithiation, the adsorbed N-MBI undergoes in-situ lithiation to form 5-amino-2-mercaptobenzimidazole lithium (Li-NH₂-MBI), which maintains strong interfacial adhesion and preferential affinity with lithium metal. This Li-NH₂-MBI SNI guides uniform lithium nucleation and growth beneath the protective interface, preventing dendrite formation. As a result, electrolyte decomposition is minimized, and lithium deposition and dissolution are highly reversible. This approach significantly improves performance: Li|Cu half-cells achieve an average Coulombic efficiency of 99.3%, and Cu||LiFePO₄ pouch cells retain 52.4% capacity at 0.2 C after 100 cycles, a 19.6% improvement over the widely adopted LiNO₃ sacrificial additive. At 0.5C, the N-MBI additive increases capacity retention after 100 cycles to 55.4%. The work validates an effective molecular-level strategy for stabilizing lithium metal anodes in anode-free configurations through SNI design.