A stepwise oxidation strategy for the synthesis of amorphous V2O5@V2CTx nanohybrid cathodes toward high-performance aqueous Zn-ion batteries

Abstract

Vanadium-based materials are a potential class of cathode materials for aqueous Zn-ion batteries (ZIBs). However, the low intrinsic conductivity, sluggish kinetics, and poor cycling stability are the key factors hindering their further application. Herein, we report a high-capacity and stable ZIB system based on an amorphous V₂O₅@V₂CT_x cathode and Zn@ZnMoO₄ anode. The amorphous V₂O₅@V₂CT_x cathode was achieved by chemical oxidation of V₂CT_x in a CO₂ atmosphere and subsequent in situ electrochemical oxidation at high potential (∼1.5–1.8 V vs. Zn/Zn²⁺) in a living cell. First-principles calculations indicate that the low Zn²⁺ diffusion energy barrier in amorphous V₂O₅ is the key factor for acquiring high Zn-storage performance. And the continuous formation of Zn₃(OH)₂V₂O₇·2H₂O (ZVO) with a high Zn²⁺ diffusion energy barrier on the cathode surface during the charging and discharging process is the culprit for the capacity decay. To ensure stable Zn-storage performance, the formation mechanism of the ZVO was investigated through various ex situ analyses. It was verified that the corrosion reaction of the bare Zn anode promoted the formation of ZVO. By optimizing the bare Zn anode to a reported hydrogen-suppressed Zn@ZnMoO₄ anode, the assembled amorphous V₂O₅@V₂CT_x//Zn@ZnMoO₄ battery can simultaneously achieve high capacity (643.6 mA h g⁻¹ at 0.1 A g⁻¹), excellent rate performance (302.4 mA h g⁻¹ at 20 A g⁻¹) and outstanding cycle stability. In addition, there is also solid evidence confirming the conventional co-intercalation/de-intercalation charge storage mechanism of H⁺ and Zn²⁺ in the amorphous V₂O₅@V₂CT_x cathode. This work not only reports a high-performance ZIB cathode material but also provides an explanation for the capacity decay of vanadium-based materials during cycling.