Enhanced Cycling Stability and Rate Capability in a La-Doped Na3V2(PO4)3/C Cathode for High-Performance Sodium Ion Batteries

In recent years, phosphate Na3V2(PO4)3 (NVP) has attracted considerable attention as a promising cathode for high-performance sodium ion batteries owing to its open 3D framework structure. However, low rate capacity of the material greatly hampers the practical application due to its poor conductivity. Herein, La-doped Na3V2–xLax(PO4)3/C materials were prepared by a combination process of sol–gel and carbon-thermal reduction methods. All materials possess NASICON-type structure with the R3̅C space group. No impurity can be detected, and a thin carbon layer is coated on the surface of the materials. The doping of La3+ significantly reduces internal resistance and enhances fast Na+ mobility. As a result, the material with the addition of 2% La3+ exhibits excellent cyclic performance and rate capability: a high initial reversible capacity of 105.4 mA h g–1 at 0.2 C, capacity retentions of 96.5% at 1 C after 200 cycles, and excellent rate performance of 92.6 mA h g–1 at 30 C. Under a high current density of 20 C for 3000 cycles, it can still deliver a superior reversible capacity of 73.5 mA h g–1 with a high capacity retention of 93.5%. Even at 50 C, the Na3V1.98La0.02(PO4)3/C electrode can release a satisfactory initial capacity of 79.9 mA h g–1 with an average Coulombic efficiency of 99.3% after 8000 cycles. Our work demonstrates that La3+-doped Na3V2(PO4)3/C may be a promising candidate of cathode for high-performance sodium ion batteries.