Crystalline-Amorphous Phase and Oxygen Vacancies Synergistically Regulate Vanadium Electronic States for Unleashing Zinc-Ion Storage Performance

Abstract

Zinc-ion capacitors (ZICs) are emerging as a compelling choice for energy storage in future, promising high power and energy densities coupled with eco-friendly characteristics. This work presents a novel approach to enhance the performance of ZICs by employing a one-step solvothermal synthesis to growth V-MOF on the surface of V₂CT_X-MXene, followed by annealing to fabricate a 3D cross-linked VO_X/V₂CT_X-MXene-x(VO_X/MXene-x) composite. The unique structure demonstrates excellent conductivity and high redox reaction activity, which significantly shortens the Zn²⁺ diffusion path. Moreover, the intertwined crystalline-amorphous structure efficiently suppresses lattice volume expansion during Zn²⁺ (de)intercalation. Density functional theory (DFT) reveals that the amorphous V₂O₅ enhances conductivity, lowers the Zn²⁺ capture energy barrier, and improves charge transfer efficiency. The introduction of oxygen vacancies further enhances the electronic transport. The VO_X/MXene-4 composite exhibits a specific capacity of 336.39 mAh g⁻¹ at 1 A g⁻¹, maintaining 213.06 mAh g⁻¹ at 10 A g⁻¹, indicating outstanding rate performance, along with an energy density of 356.27 Wh kg⁻¹ and a power density of 1280 W kg⁻¹. This work offers novel insights for the design of electrode materials that feature intertwined crystalline-amorphous phases, providing valuable insights into ion transport mechanisms and strategies to enhance Zn²⁺ diffusion kinetics.