Li _{1+ <i>x</i>} TaO _<i>x</i> F _{6– <i>x</i>} Oxyfluoride Solid Electrolytes with Amorphization-Driven Enhancement of Ion Conduction Channels for 5 V All-Solid-State Batteries

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, Li 1+ x TaO x F 6– x ( x = 0.0–1.0), which exhibits over 3 orders of magnitude higher Li + conductivity than crystalline LiTaF 6, 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, Li 2 TaOF 5 was implemented as a shielding layer for 5 V-class LiNi 0.5 Mn 1.5 O 4 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 Li 2 TaOF 5 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.