Citric Acid-Assisted Sol-Gel Synthesis of K₃V₃(PO₄)₄: Regulating Its Pore Structure and Pseudocapacitive Sodium-Ion...

Sodium-ion batteries (SIBs) are promising for large-scale energy storage, but the large ionic radius of Na⁺ restricts their transport kinetics. Polyanionic K₃V₃(PO₄)₄ (KVP) is an attractive cathode material owing to its stable crystal structure and excellent cycling performance, yet it suffers from metal ion segregation, particle agglomeration, and poor pore structure regulation during synthesis. Herein, a sol-gel method was employed to optimize KVP preparation. Adjusting the stoichiometric ratio of citric acid suppressed ion segregation, while optimizing the sintering temperature balanced crystallinity and porosity. Prepared with 2 mmol citric acid and sintered at 800°C, the optimized KVP2 exhibits excellent crystallinity, a uniform porous structure, and homogeneously distributed K, V, and P elements. Electrochemical tests reveal a pseudocapacitance-dominated charge storage mechanism (81% pseudocapacitive contribution at 1 mV s^-1). KVP2 delivers an initial discharge capacity of 64.7 mAh g^-1 at 10 mA g^-1 and retains 82.3% capacity after 500 cycles at 100 mA g^-1. This work effectively enhances the kinetics and structural stability of KVP via citric acid regulation and sintering optimization, providing a novel strategy for designing high-performance polyanionic cathodes and promoting SIB industrialization.