水系锌离子电池用钒基正极材料的研究进展

水系锌离子电池(aqueous zinc-ion batteries,AZIBs)具有高安全性、低生产成本、锌资源丰富和环境友好等优点,被认为是未来大规模储能系统中极具发展前景的储能装置。目前,AZIBs的研究关键之一在于开发具有稳定结构和高容量的锌离子可脱嵌正极材料。钒基化合物用作AZIBs正极时,表现出可逆容量高和结构丰富可变等特点,受到了广泛的关注和研究。然而,钒基化合物的储锌机理较复杂,不同材料通常表现出各异的电化学性能和储能机理。在本综述中,我们全面地阐述了钒基化合物的储能机制,并探讨了钒基材料在水系锌离子电池中的应用和发展近况,以及它们的性能优化策略。在此基础上,也进一步地展望了水系锌离子电池及其钒基正极材料的发展方向。

Research Progresses on Vanadium-Based Cathode Materials for Aqueous Zinc-Ion Batteries

In the past few decades,lithium-ion batteries(LIBs)have dominated the market of rechargeable batteries and are extensively applied in the field of electronic devices(e.g.,mobile phones and computers).However,lack of lithium resources,high cost of lithium as well as toxic and flammable organic electrolytes significantly hinder further development and large-scale application of LIBs.Therefore,it is necessary to develop next-generation green rechargeable batteries to replace LIBs.Recently,aqueous zinc-ion batteries(AZIBs)have been considered as energy storage devices with substantial development prospects for future large-scale storage systems owing to their high safety performance,low production cost,abundant zinc resources,and environmental friendliness.Typically,we use zinc metal as the anode with neutral or weakly acidic aqueous electrolyte(pH:3.6–6.0).However,cathode materials have high requirements for AZIBs while considering the charge effect of multivalent metal ions.Currently,one of the research emphases is to develop suitable zinc ion intercalation cathode materials with stable structures and high capacities.Among all types of cathode materials,vanadium-based compounds have the advantages of low cost and high reversible capacity.Additionally,their structure is variable,mainly including layered,tunneled and natrium super ionic conductor(NASICON)structure.Therefore,vanadium-based compounds have clear application possibility in AZIBs.However,there are still several significant problems.In particular,vanadium-based compounds generally have poor conductivity and low voltage platform.Electrochemical performance can be significantly improved mainly by pre-inserting metal ions or water molecules,optimizing the electrolyte,and controlling morphology of nanomaterials(nanosheets,nanospheres,etc.).In addition,the zinc storage mechanism in vanadium-based compounds is more complicated and controversial,including Zn²⁺intercalation/deintercalation mechanism,co-insertion mechanism,and conversion reaction mechanism.Moreover,different materials usually exhibit different electrochemical properties and energy storage mechanisms.In this review,we comprehensively describe the energy storage mechanisms of vanadiumbased compounds and discuss the application as well as development status of vanadium-based materials in AZIBs.Further,several strategies for improving their performance are proposed,including structural design(e.g.,pre-insertion of metal ions or water molecules),morphology control(e.g.,carbon coating),and electrolyte optimization(e.g.,adjustment of composition and concentration).In particular,pre-insertion of metal ions or water molecules in the original structure can effectively solve these problems of low ion diffusion rate,poor conductivity,and structural instability,thereby achieving excellent electrochemical performance.Moreover,the application of a high-concentration electrolyte is a simple and effective strategy that can not only significantly widen the electrochemical stability window of the aqueous electrolyte but also suppress the dissolution of vanadium,thereby effectively improving energy density and cycling stability for AZIBs.Accordingly,the future development direction of AZIBs and their vanadium-based cathode materials is further prospected,aiming at designing high-performance electrode materials for AZIBs.