Interfacial Engineering of Na₃V₂(PO₄)₂O₂F Cathode for Low-Temperature (-40 °C) Sodium-Ion Batteries

Na₃V₂(PO₄)₂O₂F (NVPOF) is considered a promising cathode material for sodium-ion batteries (SIBs) on account of its attractive electrochemical properties such as high theoretical capacity, stable structure, and high working platform. Nevertheless, the inevitable interface problems like sluggish interfacial electrochemical reaction kinetics and poor interfacial ion storage capacity seriously hinder its application. Construction of chemical bonding is a highly effective way to solve interface problems. Herein, NVPOF with interfacial V-F-C bonding (CB-NVPOF) is developed. The CB-NVPOF cathode exhibits high rate capability (65 mA h g^-1 at 40C) and long-term cycling stability (a capacity retention of 77% after 2000 cycles at 20C). Furthermore, it shows impressive electrochemical performance at temperatures as low as -40 °C, delivering a capacity of 56 mA h g^-1 at 10C and a capacity retention of ∼80% after 500 cycles at 2C. The interfacial V-F-C bond engineering significantly advances the electronic conductivity, Na⁺ diffusion, as well as interface compatibility at -40 °C. This study provides a novel idea for improving the electrochemical performance of NVPOF-based cathodes for SIBs aiming for low-temperature applications.