Fluorine Substitution at the O-Site Imparts Enhanced Chemical Stability for Garnet-Structured Electrolytes

Garnet-based superionic conductors hold great promise in next-generation lithium-ion batteries (LIBs) because of their favorable ionic conductivity and unique stability against Li-metal anodes; however, they still face the challenge of air stability for mass production/practical application. Herein, we identify their structural features and tailor the functional elements to enhance the chemical stability via synergistic control of doping and non-stoichiometry. The optimal composition of Li6.25Ga0.2La3Zr2O11.85F0.15 (LGLZO-0.15F) garnet exhibits great air durability without noticeable impurity accumulation, even during continuous air exposure for 60 days, owing to the high affinity of the fluorine dopant for lithium occupying the octahedral site. Meanwhile, LGLZO-0.15F possesses an appreciable Li-ion conductivity of 8.4 × 10–4 S cm–1 with an activation energy of 0.29 eV. Benefiting from these properties, hybrid and all-solid-state lithium batteries constructed with LGLZO-0.15F electrolytes demonstrate low overpotential, high Coulombic efficiency, and stable cycling performance.