Optimized Electrochemical Behavior of Carbon-Coated Ti-Doped Na3V2(PO4)2F3 Cathodes for Sodium-Ion Batteries

Abstract

Na₃V₂(PO₄)₂F₃ (NVPF) has emerged as a very promising cathode material for sodium-ion batteries (SIBs), on account of its durable structural reliability and impressive electrochemical performance. However, their practical use is limited by low capacity, poor conductivity, slow Na-ion transport, and capacity fading, requiring structural and surface modifications. To overcome its inherent low conductivity, carbon-coated Ti-doped NVPF (designated as NVPF-Ti-x) is prepared via a sol–gel process, with x values of 0, 0.01, 0.02, 0.03, 0.04, and 0.05. Among these variants, NVPF-Ti-0.02 demonstrates the most remarkable electrochemical behavior of high reversible capacity and rate capability. NVPF-Ti-0.02 achieves an exceptional stabilized specific capacity of 133 mAh g⁻¹ at a current density of 50 mA g⁻¹ after the first cycle onward. It shows a high reversible capacity retention of 94.76% after 100 cycles and 81% after 300 cycles. These results highlight the effectiveness of Ti doping and carbon coating in significantly boosting the conductivity and mechanical stability of NVPF. The improved performance of NVPF-Ti-0.02 underscores its potential as a leading candidate for advanced SIB technologies, offering both high capacity and robust cycling stability.