Garnet‐Type Solid‐State Electrolyte with Tailored Lithium Compatibility for High Performance All‐Solid‐State Lithium Batteries

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) solid-state electrolyte (SSE) demonstrates appealing ionic conductivity for all-solid-state battery applications. However, the interfacial compatibility between LLZO and the lithium electrode is yet to be addressed for the deployment of practical batteries at scale. Herein, tailored cubic-phase garnet-type Li₇La₃Zr₂ _-xSc_xO₁₂ _-xF_x (LLZSOF-x, x = 0-0.20) SSEs are designed, which features high lithium content and superior compatibility with the lithium metal electrode. The strong binding of fluorine dopant with octahedral lithium ions significantly inhibits Li⁺/H⁺ exchange, thus achieving intimate interfacial contact between composition-optimized Li₇La₃Zr_1.85Sc_0.15O_11.85F_0.15 (LLZSOF-0.15) and lithium electrode. Meanwhile, scandium substitution increases lithium content to 7.0, leading to improved reduction stability toward lithium metal. The LLZSOF-0.15 based symmetric cell yields high critical current density of 1.9 mA cm^-2, which meets the practical requirements for solid-state batteries. And LLZSOF-0.15 based all-solid-state lithium metal batteries show excellent cyclability, with high-capacity retention of 83.2% over 240 cycles for LiFePO₄ and 84.1% over 140 cycles for LiNi_0.8Co_0.1Mn_0.1O₂ (NCM) (0.5 C). Li/LLZSOF-0.15/NCM pouch cells maintain over 99.5% Coulombic efficiency and 94.9% capacity retention after 120 cycles at 0.5 C. This study establishes a material design approach for developing garnet SSEs with superior interfacial compatibility, promoting the deployment of advanced all-solid-state batteries at scale.