Carbon-coated Na3V2(PO4)3 nanocomposite as a novel high rate cathode material for aqueous sodium ion batteries

Aqueous rechargeable sodium ion batteries has attracted a lot of interests because of its low cost, huge abundance of sodium resources and promising application for large-scale electric energy storage. Herein, we proposed the carbon-coated Na3V2(PO4)3 nanocomposite (Na3V2(PO4)3/C) as a cathode material, which was prepared using a simple sol–gel method. The structure and morphology analyses showed that the highly crystalline Na3V2(PO4)3 nanoparticle with an average size of 350 nm is well coated by a carbon layer with a thickness of 3 nm. Electrochemical tests showed that at high current rates, the Na3V2(PO4)3/C cathode exhibited excellent electrochemical performance. Impressively, it delivered a discharge specific capacity of 94.5 mAh/g at 10C (1176 mA/g), 90.5 mAh/g at 15C (1764 mA/g) and 71.7 mAh/g at 20C (2352 mA/g). To the best of our knowledge, the notable rate capability has never been reported before for aqueous sodium ion batteries. The enhanced electrochemical behavior could be attributed to the combined advantages of Na3V2(PO4)3 nanoparticles and carbon layer in the unique core–shell structure, which improved the intrinsic poor electronic conductivity of Na3V2(PO4)3 greatly. Our results confirmed the prepared Na3V2(PO4)3/C nanocomposite should be a promising cathode candidate for aqueous sodium ion batteries.