Exploiting metal-organic framework intercalation in vanadium oxide for enhanced cathodic performance in aqueous zinc-ion batteries

Vanadium oxides hold great promise in aqueous zinc-ion batteries due to their high theoretical capacity, however, the strong electrostatic interactions between Zn²⁺ and vanadium oxides hinder their development. Organic species-intercalated vanadium oxides can enhance the diffusion of Zn²⁺ between layers, showing positive results in improving for vanadium oxides. Nevertheless, most organic materials have poor conductivity and risk detaching from the layers during cycling. In this study, vanadium oxides intercalated with squaric acid (SQ) were synthesized. Then, the further introduction of Zn²⁺ and SQ²^- coordination to formed a metal-organic framework (Zn-SQ), which reduced the risk of squaric acid release and further stabilized the structure of V+Zn-SQ (Zn-SQ intercalated NH₄V₄O₁₀). DFT calculation, GITT, and impedance tests demonstrate that V+Zn-SQ exhibits higher conductivity and faster Zn²⁺ diffusion rates compared to V+SQ (SQ intercalated NH₄V₄O₁₀). Consequently, V+Zn-SQ demonstrates excellent electrochemical performance (413.0 mAh g⁻¹ at 0.2 A g⁻¹), particularly under high current densities (91.4 mAh g⁻¹ after 10,000 cycles at 10 A g⁻¹), where its capacity and stability surpass V+SQ. Furthermore, ex-situ experiments investigated the reaction mechanism of V+Zn-SQ, revealing that the square ligands participate in zinc storage alongside vanadium oxides. This work provides a new avenue for constructing high-performance vanadium oxides.