Fluorinated Halide Solid Electrolytes for High-Voltage All-Solid-State Sodium-Ion Batteries Enabling Reversible Oxygen Redox

Abstract

Fluorinated halide solid electrolytes (FHSEs) enable integration with high-voltage layered oxides in all-solid-state sodium-ion batteries (ASSSIBs). Here, we demonstrate high-voltage ASSSIBs by pairing a fluorine-substituted UCl3-type chloride solid electrolyte, Na0.6Ta0.2La0.8Cl3.7F0.3, with a P2-type Na0.8Li0.1Ni0.2Mn0.7O2 cathode. The ASSSIB achieves reversible oxygen redox up to 4.6 V and delivers 132 mAh g–1 with long-term cycling stability, surpassing the performance of liquid electrolytes and nonfluorinated halide counterparts. Electrochemical and structural analyses reveal that, in liquid-electrolyte cells, oxygen redox above 4.2 V becomes irreversible due to solvent oxidation and surface-layer formation, while phase transitions further degrade structural reversibility. In contrast, the FHSE preserves the P2 framework and stabilizes oxygen-redox activity, enabling higher capacity and long-term cycling stability. Supported by integrated theoretical calculations, electrochemical analyses, and advanced characterizations, this work presents a viable strategy for advancing high-voltage ASSSIBs. Overall, FHSEs enable stabilized oxygen redox above 4.2 V and realize durable, high-energy ASSSIBs.