Abstract:
Aqueous zinc-ion batteries (AZIBs) exhibit broad development in the energy storage field due to their advantages of high energy density and intrinsic safety. However, because the large radius of hydrated Zn
2+ ions, the cathode materials are prone to structural collapse or irreversible phase transition during the charge-discharge process.Therefore, developing stable and efficient cathode for zinc-storage materials is one of the keys for the rapid development of AZIBs. Polyoxometalates (POMs for short), with their characteristics of high redox activity and multi-electron transfer, are regarded as promising electrochemical energy storage materials. Nevertheless, POMs suffer from problems such as easy agglomeration, high solubility and poor electrical conductivity, which results in unsatisfactory rate performance and cycle life. Based on this, a series of Keggin-type Phosphomolybdovanadic acids were prepared in this paper and then compounded with reduced graphene oxide (rGO)-polyaniline (PANI) substrates. This strategy not only inhibits the dissolution and agglomeration of POMs, but also enhances their electrical conductivity. The research results show that V-modified POMs have remarkably improved their redox capability attributed to the higher electronegativity of V. Therefore, the electrochemical performance, especially the rate capability, for the V-modified POMs have markedly improved. Among them, the POM-based electrode with 2 V substitutions delivers an outstanding discharge capacity of 286 mAh/g at 0.2 A/g. Moreover, after
1000 cycles at a high current density of 2 A/g, the capacity retention rate still remains at 77%. Further reaction kinetics studies confirm that the electrochemical reaction process of polyoxometalate-based electrode materials in AZIBs is controlled by diffusion and capacitance. These materials also exhibit a large Zn
2+ diffusion coefficient and favorable charge transfer kinetics, which can provide a solid guarantee for efficient zinc storage. This study is expected to offer new insights and strategies for the design and development of high-performance AZIBs electrode materials.