An in situ-formed LiI interface layer for garnet-based lithium metal batteries

With regard to solid-state electrolytes (SSEs), garnet-type Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZT) is a promising option due to its high ionic conductivity and steadiness against lithium metal. However, trace impurities, like Li₂CO₃ or LiOH, can be easily formed on its surface under ambient atmosphere and significantly influence the conductivity. Herein, the hydrogen iodide (HI) acid vapor is employed to remove surface impurities and a thin LiI layer was in situ generated concurrently. The layer exhibits surprising wetting behavior and high stability towards Li metal and SSE. Benefiting from its unique characteristics, the interface resistance between the LLZT electrolyte and lithium electrode decreased from 6160 to 30 Ω cm², and the critical current density (CCD) value achieved 1.5 mA cm⁻² at room temperature. Specifically, the lithium symmetric battery can cycle steadily for more than 1000 h at a current density of 0.6 mA cm⁻². Moreover, a cumulative Li plating capacity of 0.63 Ah cm⁻² can be attained. The assembled solid-state batteries (SSBs) show outstanding cycling stability over prolonged cycles at 0.1 C (LiFePO₄/LiCoO₂@room temperature) and a high rate capacity (LiFePO₄: 104.2 mAh g⁻¹ at 0.8 C). This work provides a plausible approach to interfacial issues, thereby paving the path for tangible advancements in SSBs.