Preparation Of Bi-Component Oxide Material Based On {V₁₀O₂₈} And Zinc Storage Properties

In recent years,rechargeable aqueous zinc-ion batteries（AZIBs）have been considered as a viable alternative to LIBs due to its low cost,easy material availability,environmental friendly and high theoretical capacity,so an increasing number of researches were reported focus on the AZIBs.However,its development was limited by the structural characteristics and performance of cathode materials.The polyoxometalates（POMs）perform formidable redox stability and able to participate in multi-electron transfer,which was suitable for application in energy storage devices.In the past,a large number of researches concentrate upon the application of different types of POMs in LIBs and SIBs have been reported.However,few researchers have noticed that the modified POMs can be well applied on the cathode of ZIBs.In this paper,vanadium POMs precursors with different cations were synthesized by{V₁₀O₂₈]^6-polyanion as template for the first time,and a class of bi-component polyoxometalate-derivative was obtained after simple annealing modification,which was insoluble and stable in the water electrolyte.KNiVO(the anneal product of K₂Ni₂[V₁₀O₂₈]·16H₂O)presented excellent electrochemical performance as cathode material of ZIBs.This material is composed of layered KV₃O₈ and three-dimensional NiV₃O₈,the layered structure acts as the migration and storage channel of Zn²⁺ions,and the three-dimensional structure supports the ion channel as a stable skeleton structure.This special bi-component structure exhibits unique electrochemical properties(A specific capacity of 229.4 mAh g^-1 at current density of 4.0 A g^-1,and with a capacity retention rate of 99.1%after 4500 cycles).In addition,the KNiVO material showed a special activation phenomenon.The K⁺ions were largely replaced by Zn²⁺,and the original KV₃O₈ structure disappeared and transformed into a new structure.Moreover,the stable existence of NiV₃O₈ skeleton helped Zn/KNiVO battery exhibit excellent high current tolerance and long cycle stability.To further explore the possibility of{V₁₀O₂₈]^6-POMs as precursors of cathode materials,the Ni²⁺ions in the crystal was replaced with Co²⁺,Mn²⁺,Zn²⁺,etc.,and the anneal crystals were applied on the cathode of AZIBs.It was found that these derivatives were bi-component structures,among which some layered structures acted as zinc ion storage and transfer(KV₃O₈,K_0.25V₂O₅,MnO₂),while others acted as stable structures（Co（VO₃）₂,Zn₂V₂O₇）.Similar to KNiVO material,KCoVO material has obvious activation phenomenon,and the specific capacity reached 169.2mAh g^-1 at 1.0 A g^-1 current density.However,KZnVO material showed no signs of activation during the cycle phase due to the difference of its composition,and the specific capacity of KZnVO was stable at about 150mAh g^-1 at the current density of 1.0 A g^-1.In addition,KMnVO material did not show outstanding electrochemical performance because of the unstable and easily dissolved support structure,and its capacity decays rapidly in the cycle process.From the characterization results,it can be found that the cathode material has a new composition structure after replaced the cation,which avoids the electrical activation phenomenon,and the capacity decreases rapidly for the cathode material lacked stable support.To optimize the activation of these cathode materials and further improve the electrochemical performance,Mn²⁺,Ni²⁺,Co²⁺can be introduced into[V₁₀O₂₈]^6-polyanion cluster.In this process,the proportion and combination of cations can be changed,and the precursors of POMs crystal with diverse structures can be obtained.The KNi CoVO material annealed at 300℃reached a specific capacity of 210.2 mAh g^-1 after 7cycles of activation at 0.1 A g^-1 current density,and remained stable in subsequent cycles.