Carbon quantum dot modified Na3V2(PO4)2F3 as a high performance cathode material for sodium ion batteries

Sodium-ion batteries (SIBs) are broadly regarded as a promising alternative to lithium-ion batteries (LIBs) for application in grid-scale energy storage because of abundant resources and the low cost of sodium. Nevertheless, there still exist some challenges, including low energy density, unsatisfactory cycling stability, and sluggish ion transfer. Herein, carbon quantum dot modified Na3V2(PO4)2F3 (NVPF@CQD) hierarchical microspheres were fabricated via a one-step solvothermal strategy followed by heat treatment. Furthermore, we systematically investigated how the solvothermal reaction time and content of carbon quantum dots influence the crystal structure, morphology and electrochemical performance, thereby obtaining the optimized final product. Impressively, the NVPF@CQD electrode presents awesome rate capability with a discharge capacity of 105.1 mA h g−1 at 20C, i.e., 83% retention of its capacity at 0.2C. When cycled at a rate of 30C, the capacity retention is 90.2% after 6000 cycles, corresponding to a capacity fading of 0.0017% per cycle. Moreover, for practical applications, a sodium-ion full-cell configuration is constructed using the NVPF@CQD cathode and a commercial hard carbon anode exhibiting a high operating voltage and impressive cycling stability at 500 mA g−1.