Garnet Si–Li₇La₃Zr₂O₁₂ electrolyte with a durable, low resistance interface layer for all-solid-state lithium metal batteries

Solid garnet electrolyte Li₇La₃Zr₂O₁₂ (LLZO) based Li metal batteries is a promising candidate for the next generation high energy device due to the advantages of electrochemical stability and relative high ionic conductivity at room temperature (10⁻⁴ S cm⁻¹). Here, a series of xSi-LLZO electrolytes are prepared by the traditional solid state sintering. The 0.15 Si-LLZO result shows the maximum Li ionic conductivity (6.68 × 10⁻⁴ S cm⁻¹, 25 °C) and minimum electronic conductivity (4.41 × 10⁻⁸ S cm⁻¹, 25 °C), meanwhile tactfully formes LLZO@LiAlSi₂O₆ (LLZO@LAS) electrolyte in this process. The hard-to-hard poor contact, resulting in a very large interfacial resistance and low Coulombic efficiency in Li metal bettries. Herein, we demonstrate a simple and effective to overcome the interfacial obstacles by introducing polymer poly(ethylene oxide) (PEO) electrolyte thin buffer layer to modify the bare garnet electrolyte, forming a P-0.15 Si-LLZO-P composite electrolyte. The integrated NCM811/P-0.15 Si-LLZO-P/Li and LFP/P-0.15 Si-LLZO-P/Li batteries show a high Coulombic efficiency of around 99.0% and 98.5% at 50 °C, respectively. Meanwhile, P-0.15 Si-LLZO-P composite electrolyte stays intact after cycling. In all, construcing a polymer interfacial modifacation is an convenient and effective way to realize all solid-state Li metal batteries.