VNxOy@C nanowires: a high-performance cathode material for aqueous zinc-ion batteries with dual-redox reaction mechanisms

Abstract

Vanadium nitride (VN), with appealing advantages of large specific capacity and metalloid-like high conductivity, is attracting intensive interest in the field of aqueous zinc-ion batteries (ZIBs), but faces challenges such as inferior structural stability and sluggish kinetics. In this work, VN_xO_y@C hybrid nanowires (VNO@C) with abundant oxygen-defects and carbon coating were designed and prepared via integrating the modification strategies of microstructure design, energy storage mechanism optimization, and carbon coating. The combined structural characteristics including the carbon-coated conductive network, abundant oxygen defects and the nanofiber structure can effectively facilitate internal electron and ion transport, greatly augmenting the electrochemical reaction kinetics of the electrode. Meanwhile, ex situ XPS characterization reveals an optimized energy storage mechanism of VNO@C, that is, a dual redox reaction involving both anions and cations (V³⁺ ↔ V²⁺/N³⁻ ↔ N²⁻), which further accelerate the electrochemical reaction process and enhance the specific capacity. Benefiting from these advantages, the obtained VNO@C cathode can deliver 433.2 mAh g⁻¹ (at 0.1 A g⁻¹) and maintain a capacity retention rate of 83.1% after 1000 cycles (at 5 A g⁻¹). This research provides a new perspective on the design of novel structured VN-based materials for superior ZIBs.