Hollow sphere structured Co3V2O8 as a half-conversion anode material with ultra-high pseudocapacitance effect for potassium ion batteries

Abstract

New electrode materials with high capacity and cycling stability are desirable for potassium ion batteries. Herein, we synthesize a hollow sphere structured Co₃V₂O₈ (HS-Co₃V₂O₈) and use it as a new anode material with a reversible capacity of 409 mA h g⁻¹ and great rate performance. After 100 cycles, the electrode still retains a high reversible capacity of 252 mA h g⁻¹ at 100 mA g⁻¹ with a capacity retention of 82%. It can also deliver a capacity of 267.2 mA h g⁻¹ at 400 mA g⁻¹. The hollow porous structure alleviates the volume change in the potassiation and depotassiation processes and hence enhances the cycling stability. The mechanism of potassium ion storage in this HS-Co₃V₂O₈ electrode is determined as a half-conversion reaction combined with pseudocapacitive adsorption by means of ex situ XRD, HRTEM and ex situ XPS analyses. The half-conversion reaction mechanism also brings merits for this material to have superior electrochemical properties.