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

Abstract Composite solid electrolytes (CSEs) based on poly(vinylidene fluoride)‐co‐hexafluoropropylene (PVDF‐HFP) and Li _6.4 La ₃ Zr _1.4 Ta _0.6 O ₁₂ (LLZTO) show great potential in building high energy density all‐solid‐state lithium metal batteries (ASSBs). Nevertheless, the Li ₂ CO ₃ 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 Li ₂ CO ₃ into a stable Li ⁺ conductor of LiInO ₂ (LIO) on LLZTO. With this modification, high air stability of CSEs is achieved which prevents Li ₂ CO ₃ 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 Li ₂ CO ₃ ‐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/LiFePO ₄ 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.