In-Situ Electrochemically Activated Surface Vanadium Valence in V2C MXene to Achieve High Capacity and Superior Rate Performance for Zn-Ion Batteries

Vanadium-based materials are fascinating potential cathodes for high energy density Zn-ion batteries (ZIBs), due to their high capacity arising from multi-electron redox chemistry. Most vanadium-based materials suffer from poor rate capability, however, owing to their low conductivity and large dimension. Here, we propose the application of V 2 C MXene (V 2 CT x ), a conductive 2D nanomaterial, for achieving high energy density ZIBs with superior rate capability. Through an initial charging activation, the valence of surface vanadium in V 2 CT x cathode is raised significantly from V 2+ /V 3+ to V 4+ /V 5+ , forming a nanoscale vanadium oxide (VO x ) coating that effectively undergoes multi-electron reactions, whereas the inner V-C-V 2D multi-layers of V 2 CT x are intentionally preserved, providing abundant nanochannels with intrinsic high conductivity. Owing to the synergistic effects between the outer high-valence VO x and inner conductive V-C-V, the activated V 2 CT x presents an ultrahigh rate performance, reaching 358 mAh g −1 at 30 A g −1 , together with remarkable energy and power density (318 Wh kg −1 /22.5 kW kg −1 ). The structural advantages of activated V 2 CT x are maintained after 2000 cycles, offering excellent stability with nearly 100% Coulombic efficiency. This work provides key insights into the design of high-performance cathode materials for advanced ZIBs.