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

Abstract Garnet‐type Li 7 La 3 Zr 2 O 12 (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 Li 7 La 3 Zr 2 ‐x Sc x O 12 ‐x F 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 Li 7 La 3 Zr 1.85 Sc 0.15 O 11.85 F 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 LiFePO 4 and 84.1% over 140 cycles for LiNi 0.8 Co 0.1 Mn 0.1 O 2 (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.