Optimized Sol–Gel Synthesis of Li3V2(PO4)3/C Composite Cathode Material: The Role of Pyrolysis Temperature and Carbon Content on Structural and Electrochemical Performance

Lithium-ion batteries require cathode materials with high capacity and cycling stability. Li3V2(PO4)3 (LVP) offers a theoretical capacity of 197 mAh/g but suffers from poor electronic conductivity. In this study, a Li3V2(PO4)3/carbon (LVP/C) composite was synthesized via a citric acid-assisted sol–gel method. The effects of pyrolysis temperature (700–1000 °C) and citric acid-to-salt ratio (1:1, 0.5:1, 0.25:1) were systematically investigated. The optimal composite was obtained at 900 °C with a 1:1 ratio. This material exhibited a well-crystallized monoclinic structure (space group P21/c) with unit cell volume of 890.61 Å3. The amorphous carbon coating provided a specific surface area of 33.03 m2/g. Electrochemically, the optimal LVP/C_1:1 composite delivered an initial specific capacity of 114 mAh/g at C/10 rate—twice that of samples with lower carbon content. It also demonstrated 100% capacity retention after 25 cycles with favorable coulombic efficiency (67%) and reduced charge-transfer resistance. These results show that pyrolysis at 900 °C with a 1:1 citric acid-to-salt ratio provides an optimal balance between crystallinity, carbon coating uniformity, and electrochemical performance for high-performance LVP/C composite cathodes.