Na₃(VO)₂(PO₄)₂F coated carbon nanotubes: A cathode material with high-specific capacity for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are one of the candidate technologies for large-scale energy storage systems due to their environmental friendliness, safety and resourcefulness. However, designing and synthesizing high -performance cathode materials with practical application value is currently a great challenge. Herein, we syn-thesize a carbon-nanotube-coated Na-3(VO)(2)(PO4)(2)F (Na-3(VO)(2)(PO4)(2)F@CNT) cathode material for AZIBs, which has a continuous and interconnected ion transport channel structure. A Zn2+/H+ co-intercalation mechanism is revealed by ex-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS) characterizations. The Na-3(VO)(2)(PO4)(2)F@CNT cathode material exhibits a high specific capacity of 143 mAh center dot g Wan et al. (2019). at 0.2 C in the electrolyte of 3 M Zn(OTf)(2) aqueous solution. In addition, Na-3(VO)(2)(PO4)(2)F@CNT shows a good low-temperature electrochemical performance in the electrolyte of 2 M Zn(OTf)(2) deionized water/ethylene glycol (DIW/EG) mixed solution with a different ion storage mechanism. This study provides a new polyanionic cathode material for AZIBs and an idea to modulate the electrolyte polarity to enhance the zinc storage capacity of the cathode material.