Vanadium nitride/carbon fiber engineered with oxygen defects and vertically aligned nanosheets for high-rate flexible aqueous zinc-ion batteries

Flexible aqueous zinc-ion batteries (AZIBs) are promising candidates for wearable devices owing to their high safety and low cost. However, their progress is plagued by their sluggish ion-transport kinetics, which leads to inferior rate capability. Herein, a vanadium nitride/carbon fiber (VN/CF) cathode was structurally engineered to incorporate oxygen defects and a vertically aligned, porous, nanosheet architecture to overcome these issues. This structure was realized via the initial growth of vertically aligned V₂O₅ nanosheet templates on gas-spun carbon fibers, followed by high-temperature NH₃ treatment. The oxygen defects accelerate the kinetics of bulk diffusion within VN, while the vertically aligned VN nanosheet array possesses lower charge-transfer resistance, enhancing the kinetics of surface diffusion. These features synergistically improve the overall Zn²⁺ transport, affording high-rate performance. Consequently, the free-standing VN/CF cathode exhibits exceptional rate performance, delivering a capacity of 263.4 mAh g⁻¹ even at a high current density of 10 A g⁻¹. When assembled into flexible AZIBs, the device exhibits a high-rate capability of 249.7 mAh g⁻¹ at 10 A g⁻¹ and stable performance even under various bending deformations, demonstrating significant potential for next-generation wearable devices.