Defying the Kinetics Limitations of Na₃V₂(PO₄)₂F₃ Cathode by a Tailored Sol-Gel Thermal Protocol: Toward Ultra-Stable Sodium Storage at High Rates and Subzero Temperatures

Na₃V₂(PO₄)₂F₃ (NVPF) is a promising cathode material for sodium-ion batteries owing to its stable performance, yet its application is hindered by low electronic conductivity and sluggish ion diffusion kinetics. Herein, a temperature-regulated sol-gel strategy is developed to tailor the particle size, enhance carbon coating uniformity, and modulate sodium-site occupancy in NVPF. By optimizing the sol-gel temperature, it can effectively improve the chelation state of the precursor, reducing particle size and promoting the ordered assembly of primary particles into well-defined secondary particles, which shortens the Na⁺ transport distance. Simultaneously, the uniform carbon coating improves the electronic conductivity, while the tailored sodium-site occupancy enhances Na⁺ diffusion kinetics. The optimized NVPF cathode demonstrates a high specific capacity and excellent rate capability (124.5 mAh g⁻¹ at 1C; 103.6 mAh g⁻¹ even at 30C). Additionally, it demonstrates exceptional low-temperature performance, achieving an initial specific capacity of 100.1 mAh g⁻¹ at 0.1C under −30°C, with a capacity retention of 93.0% after 780 cycles. Furthermore, the full cell shows superior rate capability and cycling stability, reaching 103.0 mAh g⁻¹ at 10C. This work provides a robust strategy for enhancing the electrochemical performance of NVPF and highlights its potential for advanced sodium-ion battery applications.