Tailored Synthesis of High-Performance Na3V2(PO4)3 for Na-Ion Batteries through the Sol–Gel Process

Na3V2(PO4)3 is a typical cathode material for sodium-ion batteries and is usually prepared by the sol–gel method. However, Na3V2(PO4)3 is far from the level of tailored preparation due to the lack of understanding of the structure evolution during the sol–gel process. Here, we revealed that the initially formed vanadyl citrate is cross-linked by intermolecular hydrogen bonds, forming large polymers. Therefore, the crystal size of the precursor as well as the final Na3V2(PO4)3 can be controlled by adjusting the pH value of the solution. As a result, the optimized NVP-7 material exhibited a specific discharge capacity of 59.8 mAh g–1 at 50 C and can still retain 82.9% of the initial capacity after 500 cycles at 1 C. This study provides a theoretical basis for controllable preparation of NVP materials by the sol–gel method.