Rapid microwave-assisted refluxing synthesis of hierarchical mulberry-shaped Na3V2(PO4)2O2F@C as high performance cathode for sodium & lithium-ion batteries

Unique hierarchical mulberry-shaped Na3V2(PO4)2O2F@C nanocomposite was fabricated by a rapid microwave-assisted low-temperature refluxing strategy. The V(acac)3 reverse micelle systems in the water-in-oil microemulsions played key roles in forming the self-assembly architectures. The prepared Na3V2(PO4)2O2F@C nanoparticles with the anisotropic growth along the [002] direction were in-situ encapsulated in carbon shells, which greatly contribute to fast Na+/e− transfer in electrodes. And the self-assemblies with high structure stability help to improve the cycle performance and mitigate voltage fading. The initial discharge capacity of Na3V2(PO4)2O2F@C as cathode for sodium ion batteries is about 127.9 mA h g−1 at 0.1 C. Besides, a high rate performance with a capacity of 88.1 mA h g−1 at 20 C has been achieved, and the capacity retains 82.1% after 2,000 cycles. In addition, the reaction kinetics and Na+ transportation mechanism of Na3V2(PO4)2O2F@C were preliminarily investigated by the ex situ X-ray diffraction, X-ray photoelectron spectroscopy and galvanostatic intermittent titration technique. More interestingly, when coupled with Li, the fabricated hybrid Li/Na-ion batteries also exhibit excellent rate and cycling performances. The proposed rapid refluxing strategy to synthesize mulberry-shaped Na3V2(PO4)2O2F@C opens up a new opportunity to develop high-performance electrode materials for the energy storage systems.