Studying In-Situ Passivating Interphase Between Halide Solid-Electrolyte and Li-Based Anode in All-Solid-State Batteries

All-solid-state batteries (ASSBs) have been highlighted as a promising alternative for future energy storage systems due to their high thermal stability and high energy density compared to lithium-ion batteries using liquid electrolytes. Among many types of solid electrolytes, halide solid electrolytes (SE) with high oxidative stability have been intensively proven as a feasible SE that enables cycling 4 V class cathode materials. However, undesirable thermodynamic instability of halide SEs to Li metal anode hinders achieving high energy density ASSBs for practical use. To this end, lithium-indium (Li-In) alloy has been extensively employed due to their (electro)chemical stability to halide SEs that enables stable cycling of ASSB using halide SEs. Although the decomposition of halide SEs and its reactants in direct contact with Li metal has been experimentally and theoretically studied, no in-depth investigations on interphase evolution and charge transfer mechanism at the LYC SE and Li-In anode interphase have been conducted. In this work, we report the evolution of the interphase layer between In metal anode and halide solid electrolyte, Li₃YCl₆ (LYC), that enables stable long-term cycling of ASSB coupled with crack-free single-crystal (SC) LiNi_0.8Co_0.1Mn_0.1O₂ (NMC811) cathode active material. Through the combination of high-resolution microscale x-ray based analysis on a cross-section of the ASSBs, we demonstrate the crosstalk between LYC and In anode that results in the evolution of interphase layer consists of InCl_x, YCl₃,, LiCl, and In diffused LYC which suppressed dendritic growth of Li-In alloy over the ASSB cycling.