V2CTX MXene-derived ammonium vanadate with robust carbon skeleton for superior rate aqueous zinc-ion batteries

Layered ammonium vanadate has become a promising cathode material for aqueous zinc ion batteries (ZIBs) due to its small mass and large ionic radius of ammonium ions as well as the consequent large layer spacing and high specific capacity. However, the irreversible de-ammoniation caused by N·H···O bonds damaged would impair cycle life of ZIBs and the strong electrostatic interaction between Zn²⁺ and V-O frame could slower the mobility of Zn²⁺. Furthermore, the thermal instability of ammonium vanadate also limits the use of common carbon coating modification method to solve the problem. Herein, V₂CT_X MXene was innovatively selected as a bifunctional source to in-situ derivatized (NH₄)₂V₈O₂₀·xH₂O with amorphous carbon-coated (NHVO@C) via one-step hydrothermal method in relatively moderate temperature. The amorphous carbon shell derived from the V₂CT_X MXene as a conductive framework to effectively improve the diffusion kinetics of Zn²⁺ and the robust carbon skeleton could alleviate the ammonium dissolution during long-term cycling. As a result, zinc ion batteries using NHVO@C as cathode exhibit superior electrochemical performance. Moreover, the assembled foldable or high loading (10.2 mg/cm²) soft-packed ZIBs further demonstrates its practical application. This study provided new insights into the development of the carbon cladding process for thermally unstable materials in moderate temperatures.