Boosting rate and cycling performance of K-doped Na3V2(PO4)2F3 cathode for high-energy-density sodium-ion batteries

As a promising cathode material, Na3V2(PO4)2F3 (NVPF) has attracted wide attention for sodium-ion batteries (SIBs) because of its high operating voltage and high structural stability. However, the low intrinsic electronic conductivity and insufficient Na ion mobility of NVPF limit its development. Herein, K-doping NVPF is prepared through a facile ball-milling combined calcination method. The effects of K-doping on the crystal structure, kinetic properties and electrochemical performance are investigated. The results demonstrate that the Na2.90K0.10V2(PO4)3F3 (K0.10-NVPF) exhibits a high capacity (120.8 mAh g−1 at 0.1 C), high rate capability (66 mAh g−1 at 30 C) and excellent cycling performance (a capacity retention of 97.5% at 1 C over 500 cycles). Also, the occupation site of K ions in the lattice, electronic band structure and Na-ion transport kinetic property in K-doped NVPF are investigated by density functional theory (DFT) calculations, which reveals that the K-doped NVPF exhibits improved electronic and ionic conductivities, and located K+ ions in the lattice to contribute to high reversible capacity, rate capability and cycling stability. Therefore, the K-doped NVPF serves as a promising cathode material for high-energy and high-power SIBs.