Preparation And Electrochemical Performance Research Of Vanadium Oxides As Cathode Material For Hybrid Magnesium-lithium-ion Batteries

Recently,due to the problems of high price,low energy density and poor safety in lithium ion batteries(LIBs),magnesium ion batteries(MIBs)as substitutes have attracted extensive attention.However,it is difficult to achieve reversible de-intercalation of Mg2+ due to the strong polarization of divalent magnesium ions in the diffusion process,which results in poor cyclic stability of cathode materials and hinders the commercial application of MIBs.In order to solve this problem,the hybrid magnesium-lithium-ion batteries(MLIBs)was designed to combine the cathode which can rapidly and reversibly de-intercalate Li+and Mg anode with safety,stability,dendrite-free and low-cost by using magnesium-lithium dual-salt electrolyte.Vanadium oxides were proposed as its cathode materials and their preparation methods and electrochemical performance were studied.The main research results are as follows:(1)NH4V4O10 cathode material was obtained by hydrothermal synthesis method preparation.The effects of reactant concentration and reaction time on the structure and morphology of the product were systematically studied.The growth process of NH4V4O10 micro-flowers from growing,complexing and ripening was described by Oswald ripening mechanism.The effect of reaction temperature on product performance was investigated.The results showed that NH4V4O10 cathode material had excellent electrochemical performance when the hydrothermal temperature was 180℃.At the current density of 100 mA g-1 and the voltage window of 0.5-2 V,the initial discharge specific capacity was 228.9 mAh g-1.After 100 cycles,the specific capacity kept at 165.6 mAh g-1,and the capacity retention rate was 72.3%.The energy density reached 412 Wh kg-1.(2)By analyzing the electrochemical performances of NH4V4O10 cathode material in MLIBs and LIBs,it was found that the MLIBs combines the advantages of Mg and Li.It can achieve the same capacity performance as LIBs while using dendrite-free Mg as anode.Based on the characteristic of cyclic voltammetry and charge-discharge curves in the two systems,it was found that there was no electrochemical reaction of magnesium on cathode,but only the de-intercalation of lithium.And it was concluded that the difference of working voltage between the two systems was mainly affected by the anode potential.(3)VO2(B)cathode material was prepared by hydrothermal method.The effect of pH on the electrochemical performance of the product was investigated.VO2(B)material with high specific capacity was obtained when the pH is at 2.25.The capacity of VO2(B)cathode material was improved by composite modification with graphene.After modification,the first discharge specific capacities of the materials was 229.2 mAh g-1 and 268.1 mAh g-1,and the energy densities reached 391 Wh kg-1 and 450 Wh kg-1 at the current density of 100 mA g-1 and the voltage window of 0.5-2 V.