Harmonized Interphase Refinement for Robust Garnet Solid‐State Batteries

Abstract Garnet electrolyte Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) has been identified as a promising candidate for solid‐state batteries (SSBs). However, the implementation of garnet‐based SSBs is severely restricted owing to the Li dendrite originating from the uneven Li⁺ deposition and the electron leakage. Herein, one high‐performance garnet‐based SSB is proposed through the enhancement of interfacial dynamics and the inhibition of electron penetration, induced by an artificial harmonized interphase (LSF). The formation of a tightly bonded LLZTO|Li interface is facilitated by the Li₃Sb with lower interfacial energies against LLZTO and Li, elucidated by the density functional theory (DFT) calculations. Furthermore, electron leakage and dendrite infiltration are effectively suppressed by the LiF with the electron‐insulating nature and an exceptional γE value. Therefore, a low interfacial resistance of 4.8 Ω cm² is successfully achieved by the utilization of the functional LSF interphase layer, and the Li|LLZTO‐LSF|Li symmetric cell displayed prolonged Li plating/stripping stability over 1200 h at 0.3 mA cm⁻². Moreover, the LFP|LLZTO‐LSF|Li full cell also exhibited notable cycling performance (93.1% capacity retention after 200 cycles at 1 C). The utilization of a synergistic interlayer has been identified as an effective strategy for the advancement of garnet‐based solid‐state lithium batteries.