Construction And Electrochemical Performance Of Vanadate-based Cathode Materials For Aqueous Zinc-ion Batteries

Recently,aqueous zinc-ion batteries（AZIBs）have been considered as good candidates for grid energy storage systems due to their low cost,easy assembly,high safety and environmental friendliness.Currently,researchers have discovered a variety of materials that can be used as cathodes for AZIBs,while vanadate based cathode materials have received widespread attention due to their stable structure,high specific capacity,and good cycle stability.Therefore,in the first part of this paper,based on vanadate-based cathode materials,it can show stronger electrochemical reaction dynamics through morphology control,and accelerate the transfer rate of charge between the electrode/electrolyte interface,thus showing excellent zinc storage performance.In addition,the anode is also an important part of the AZIBs.The modification of the anode is another reliable means to improve the electrochemical performance.Therefore,in the second part of this paper,the combination of the interlayer engineering of the anode can not only promote the in-situ electrochemical conversion of the original cathode to the high-crystallinity vanadate-based cathode,but also build a Zn²⁺redistributor to reduce the growth of the zinc dendrite in anode,thus further improving the electrochemical performance of the electrodes.Therefore,we improve the electrochemical performance of AZIBs by synthesizing better cathode materials and combining the interlayer strategy of modifying the anode to improve the specific capacity and cycle life of the electrodes.Specifically,it includes the following two parts:（1）（NH₄）₂V₄O₉nanomaterials were synthesized by hydrothermal method and used as the cathode for AZIBs.This is the first report to obtain（NH₄）₂V₄O₉ nanomaterials with different morphologies by adjusting the amount of acetic acid added as the cathode for AZIBs.When the amount of acetic acid was 0.1ml,the nanosheet morphology of（NH₄）₂V₄O₉ showed excellent electrochemical performance.During the electrochemical cycle,（NH₄）₂V₄O₉ nanosheets are electrochemically transformed in situ into a mixed cathode material of NH₄V₄O₁₀/Zn₃（OH）₂V₂O₇·2H₂O,and maintain excellent electrochemical performance of the battery during subsequent cycles.When the current density is 0.3 A g^-1,the maximum discharge specific capacity of 358.0 m Ah g^-1 can be achieved.Even at a high current density of 5 A g^-1,a maximum discharge specific capacity of up to 207.3 m Ah g^-1 can be obtained.And the capacity retention rate can be maintained at 82.2%after 5000 long cycles at 10 A g^-1 high current density.This excellent electrochemical performance is attributed to the nanosheet morphology of（NH₄）₂V₄O₉,which can provide more abundant active sites,ensuring that Zn²⁺has a fast diffusion path.（2）VO₂ nanorods were prepared by a simple hydrothermal synthesis method and used as cathode materials for AZIBs.The portion of VO₂ nanorods were transformed into Zn₃（OH）₂（V₂O₇）（H₂O）₂ by in-situ electrochemical transformation during electrochemical cycling,and the electrochemical performance of electrodes was further improved by adding cellulose triacetate（CTA）interlayer between the zinc anode and the separator.Therefore,the Zn+CTA||VO₂ full battery with VO₂ as the cathode and CTA thin film as the interlayer achieves excellent electrochemical performance.It has a high discharge specific capacity(490.2 m Ah g^-1)at 0.2 A g^-1,excellent cycle stability performance（capacity retention rates of 60.2%and 71.5%）at 5 A g^-1 and 10 A g^-1and good rate performance.Such outstanding electrochemical performance is attributed on the one hand to the good structural stability of VO₂/Zn₃（OH）₂（V₂O₇）（H₂O）₂ cathode material,and on the other hand to the fact that the CTA interlayer can promote the desolvation process of zinc ion hydrate([Zn（H₂O）₆]²⁺),and act as an ion redistributor to promote the uniform distribution of Zn²⁺and inhibit the formation of zinc dendrites.