A mixed-valence polyoxometalate-based 3D inorganic framework cathode material for high-efficiency rechargeable AZIBs

The global trend towards new energy storage systems has stimulated the development of electrochemical energy storage technologies. Among these technologies, rechargeable aqueous zinc-ion batteries (AZIBs) have attracted considerable interest as a potential alternative to lithium-ion batteries (LIBs) due to their affordable cost, environmental compatibility and high safety standards. In this study, a high-quality electrode for AZIBs has been successfully developed using a dehydrated mixed-valence polyoxometalate-based three-dimensional (3D) inorganic framework material known as [H₆Mn₃V^IV₁₅V^V₄O₄₆(H₂O)₁₂] (3D-MnVO). This innovative 3D-MnVO material is built from the alternate connections of {V₁₉O₄₆} "sphere-shaped" clusters and μ₂-{Mn(H₂O)₄} bridges, where each {V₁₉O₄₆} cluster is surrounded by three pairs of vertically distributed {Mn(H₂O)₄} units, thus resulting in the 3D interpenetrating grid-like network from the infinite [-{V₁₉O₄₆}-µ₂-Mn(H₂O)₄-{V₁₉O₄₆}]_∞ chains in three mutually perpendicular directions. The 3D framework structure of 3D-MnVO possesses abundant oxygen vacancies, spacious and multi-level interconnected channels for ion transport, which facilitates the efficient intercalation/deintercalation of hydrated Zn²⁺ into the pores of the primary structure via the intercalation capacitance mechanism. As a result, the 3D-MnVO electrode exhibits excellent diffusion rates and minimal interfacial resistance. At a current density of 0.1 A·g⁻¹, the 3D-MnVO cathode delivers a commendable discharge capacity of 170.5 mAh·g⁻¹ with 81.6% capacity retention after 100 charge/discharge cycles. Furthermore, even at a high current density of 1.0 A·g⁻¹, the 3D-MnVO electrode delivers a remarkable reversible capacity of 198.9 mAh·g⁻¹. Our research results provide valuable insights into the development of advanced polyoxometalate-based 3D inorganic framework electrode materials for high-performance rechargeable AZIBs.