Controllable Design of Metal-Organic Framework-Derived Vanadium Oxynitride for High-Capacity and Long-Cycle Aqueous Zn-Ion Batteries.

ABSTRACT

Introducing N atoms in vanadium oxides (VOx) of aqueous Zn-ion batteries (ZIBs) can reduce their bandgap energy and enhance their electronic conductivity, thereby promoting the diffusion of Zn2+. The close-packed vanadium oxynitride (VON) generated often necessitates the intercalation of water molecules for restructuring, rendering it more conducive for zinc ion intercalation. However, its dense structure often causes structural strain and the formation of by-products during this process, resulting in decreased electrochemical performance. Herein, carbon-coated porous V2O3/VN nanosheets (p-VON@C) are constructed by annealing vanadium metal-organic framework in an ammonia-contained environment. The designed p-VON@C nanosheets are efficiently converted to low-crystalline hydrated N-doped VOx during subsequent activation while maintaining structural stability. This is because the V2O3/VN heterojunction and abundant oxygen vacancies in p-VON@C alleviate the structural strain during water molecule intercalation, and accelerate the intercalation rate. Carbon coating is beneficial to prevent p-VON@C from sliding or falling off during the activation and cycling process. Profiting from these advantages, the activated p-VON@C cathode delivers a high specific capacity of 518 mAh g-1 at 0.2 A g-1 and maintains a capacity retention rate of 80.9% after 2000 cycles at 10 A g-1. This work provides a pathway to designing high-quality aqueous ZIB cathodes.