Research On Vanadium-based Cathode Material(Ag_0.33V₂O₅ And FeVO₄·nH₂O@rGO)for Aqueous Zinc Ion Batteries

Recently,aqueous zinc-ion batteries(AZIBs)have been attracted an increasing attention as a highly potential novel large-scale energy storage system that is environmental friendliness,low cost,highly safe.Especially in the research of flexible and wearable electronic products,because traditional lithium-ion batteries cannot meet the high safety requirements caused by mechanical stress and deformation during using progress.Vanadium-based materials serve as a potential zinc storage cathode materials for AZIBs,but low conductivity and easy collapse of the crystal structure during charge and discharge remain an obstacle.Therefore,in this paper,V2O5 was doped with silver ion by hydrothermal method,and on the other hand,FeVO4·nH2O was modified by graphene coating by solvothermal method.The specific research content includes the following two parts:(1)Vanadium pentoxide doped with silver ions was prepared by hydrothermal method,and characterized by XRD,XPS,infrared spectrum/Raman spectrum,scanning/transmission electron microscopy,etc.The results showed that the V2O5 nanorods changed from a layered crystal structure to a Ago.33V2O5 three-dimensional tunnel structure after silver ion doping.Using pure V2O5 and Ag0.33V2O5 two vanadium-based materials as the cathode materials for electrochemical performance testing,the reversible capacity of Ag0.33V2O5(125 mAh g-1)is higher than that of pure V2O5(99 mAh g-1)after 100 cycles at 0.5 A g-1 current density;In terms of rate performance,Ag0.33V2O5(2 A g-1:91 mAh g-1)is also superior to V2O5(2 A g-1:28 mAh g-1).The main reason is that silver ion doping improves the V2O5 conductivity and promotes the transmission of electrons and zinc ions;on the other hand,it enhances the stability of the crystal structure.Finally,the electrochemical reaction mechanism of the Ag0.33V2O5//Zn battery is studied.During the charge and discharge process,the ion exchange mechanism of Ag+and Zn2+causes the metal silver to continuously precipitate and recover,which leads to better electrochemical performance of the Ag0.33V2O5 cathode.(2)FeVO4·nH2O@rGO composite cathode material was prepared by solvothermal method,and characterized by XRD,XPS,Raman spectroscopy,scanning/transmission electron microscopy.The results show that the reduced graphene oxide nano sheets can be better wrapped with FeVO4·nH2O nanorods.Compared with pure FeVO4·nH2O and FeVO4 without crystal water,the capacity retention rate of FeVO4·nH2O@rGO(50.3%)is higher than that of FeVO4·nH2O(47.7%)and FeVO4(22.2%)after 50 cycles at a current density of 0.2 A g-1.In terms of rate performance,FeVO4·nH2O@rGO(2Ag-1:93.1 mAh g-1)is also superior to FeVO4-nH20(2 A g-1:53.9 mAh g-1)and FeV04(2 A g-1:18.4 mAh g-1).This shows that the reduced graphene oxide modified FeVO4·nH2O not only increases its conductivity,but also slows down the destruction of its crystal structure during the charge and discharge process.Finally,the electrochemical reaction mechanism of FeVO4-nH2O@rGO//Zn battery was studied.It was found that this excellent electrochemical performance was mainly attributed to the reversible changes in the redox process of Fe and V transition metal elements during charge and discharge.