Compatible Interfaces Constructed by Surficial Indiumization on Garnet Solid Electrolyte for Long‐Cycling All‐Solid‐State Lithium Metal Battery

Composite solid electrolytes (CSEs) based on poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) show great potential in building high energy density all-solid-state lithium metal batteries (ASSBs). Nevertheless, the Li₂CO₃ passivation layer formed on the LLZTO surface not only induces dehydrofluorination of PVDF-HFP but also blocks Li⁺ transport at the interfaces of PVDF-HFP/LLZTO and CSE/electrodes. Herein, lithium acetate-assisted surficial indiumization with a thickness of 4 nm is carried out to convert the detrimental Li₂CO₃ into a stable Li⁺ conductor of LiInO₂ (LIO) on LLZTO. With this modification, high air stability of CSEs is achieved which prevents Li₂CO₃ regeneration and PVDF-HFP dehydrofluorination effectively. Attributed to the unblocked Li⁺ transport paths at the LLZTO@LIO/PVDF-HFP (LIO-CSE) interface, high ionic conductivity of 3.1 × 10^-4 S cm^-1 and the Li⁺ transference number of 0.673 are attained. The Li₂CO₃-free LLZTO also contributes to constructing robust solid electrolyte interphase with predominantly inorganic components, which successfully decreases the side reactions and ultimately realizes good compatibility at the LLZTO/polymer and electrolyte/electrode interfaces. The assembled Li|LIO-CSE|Li cells exhibit excellent electrochemical stability for 3100 h at 0.5 mA cm^-2. The Li/LIO-CSE/LiFePO₄ ASSB delivers high-capacity retention of 81.8% after 1000 cycles at 25 °C. This work provides a promising method toward remarkable interfacial compatibility for ASSBs.