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Fluoride solid electrolytes (SEs), despite their extremely low ionic conductivities, offer a promising pathway for enabling 5 V-class chemistries in all-solid-state batteries (ASSBs) owing to their exceptional oxidative stability. Herein, we report a new amorphous oxyfluoride SE, Li1+xTaOxF6–x (x = 0.0–1.0), which exhibits over 3 orders of magnitude higher Li+ conductivity than crystalline LiTaF6, reaching 1.08 × 10–6 S cm–1 at 30 °C (x = 1.0). Pair distribution function analysis, Raman spectroscopy, and X-ray absorption spectroscopy reveal an extended, corner-sharing chain of Ta(O/F)6/7 polyhedra framework. Melt-quenching ab initio molecular dynamics simulations further demonstrate that this interconnected structure broadens Li+ diffusion pathways. Leveraging high oxidative stability (>5 V) and improved Li+ conductivity, Li2TaOF5 was implemented as a shielding layer for 5 V-class LiNi0.5Mn1.5O4 cathodes, enabling exceptional cycling performance with 85.8% capacity retention after 1000 cycles at 1.0C and 30 °C. Even under high-mass-loading (49.3 mg cm–2) or low-temperature (−20 °C) conditions, the modified LNMO electrodes with Li2TaOF5 exhibited promising performance, achieving >5.9 mAh cm–2 with 94% retention. These findings underscore the efficacy of amorphization in advancing fluoride SEs and provide key design insights for advanced halide SEs in high-voltage ASSBs.
Park et al. (Thu,) studied this question.