Study On Synthesis And Electrochemical Properties Of Vanadate-based Cathode In Aqueous Zinc Ion Batteries

The rapid development of electric vehicles and various intelligent devices,leading to the huge demand for energy storage devices with high energy density,long-cycle-life,safety,and cheap price is highly desirable.Rechargeable aqueous zinc-ion batteries（ZIBs）have been recognized as a promising alternative owing to its merits and advantages:（1）high operational safety;（2）low redox potential of Zn²⁺/Zn of anode（-0.76 V vs SHE）compared to other anodes in aqueous batteries;（3）high capacity of Zn(820 m Ah g^-1,5855 m Ah cm^-3);（4）stability in water due to high over-potential for hydrogen evolution.Thus the ZIBs have great potential in the future energy storage field.To date,various cathode materials in aqueous ZIBs have been developed and gained impressive progress.Vanadium-based compounds usually present a layered structure consisting of square pyramidal VO₅ units that link each other by sharing edges.Because of the large interlayer spacing,the vanadium-based cathode in aqueous ZIBs has a high Zn ions diffusion rate and valuable specific capacities.However,the problems of sluggish kinetics and capacity degradation of vanadium-based cathode materials must urgently be promoted.At present,various strategies for improving electrochemical performance for vanadium-based cathode materials in AZIBs are inserting ions or organic molecule,introducing functional groups,coating carbon compounds and so on,which could improve the capacity.But there is less discussion on the cycling stability,sluggish kinetics,and energy storage mechanism of the materials.Therefore,this paper carried out in the following thought:the electrochemical properties and the energy storage mechanism are investigated in detailed by inserting metal cations into vanadium oxide to increase the layer spacing and stabilize the structure of vanadium oxide.We demonstrate the robust synthesis of Cu pre-intercalated commercial-V₂O₅（c-V₂O₅）to obtain cathodes materials with composite phase of Cu_0.4V₂O₅and VO₂·n H₂O for AZIBs through simple one step hydrothermal approach（Figure 1）,which was marked as(Cu_0.4V₂O₅)_x·（VO₂·n H₂O）_y.The influence of the different ratio of Cu to the structure and electrochemical performance of the final product was discussed in detail.The activity of the(Cu_0.4V₂O₅)_x·（VO₂·n H₂O）_y was found to be highly dependent on their composition.When the molar ratio between Cu precursor and c-V₂O₅ in reaction solution was 1:2,the obtained material exhibits a superior reversible capacity of 332 m Ah g^-1at 0.2 A g^-1within the voltage window of 0.3 V-1.6 V.And the materials display the good long-term performance during 1000 cycles with the capacity attenuation of 0.035%per cycle at 2 A g^-1.We also elucidate the charge storage chemistry is the multi-step Zn²⁺insertion/extraction reaction with the replacement reaction.We report a novel material vanadium oxide Bi V_1.025O_4+x synthesized by microwave hydrothermal method and serve them as the cathode materials for AZIBs.Specifically,the three dimensional tunnelled structure with enlarged interlayer spacing can provide more transmission paths of Zn-ion and durable stability of the host,resulting in superb electrochemical properties.And a high capacity of 262 m Ah g^-1 at 0.1 A g^-1 and superior cycle performance(229 m Ah g^-1 with a high capacity retention of 96%after 1000 cycles at 2 A g^-1)can be obtained.Moreover,the Bi V_1.025O_4+x materials exhibit an outstanding rate property and a high energy density of 238 Wh kg^-1 at a specific power of 529 W kg^-1.In addition,Bi V_1.025O_4+x materials with quasi-solid-state electrolyte are fabricated for flexible soft-packaged ZIBs,demonstrating the potential for grid energy storage applications.We synthesize（Bi,Mn）-doped vanadium materials by microwave hydrothermal method and inserting Bi ions and Mn ions into vanadium oxide with different molar ratios（Bi:Mn:V）.（Bi,Mn）-doped vanadium materials are composited of Bi VO₄,Mn（VO₃）₂,and V₂O₂（OH）₂,showing excellent electrochemical properties.The first discharge capacity of 275 m Ah g^-1 can be obtained at 0.1 A g^-1 and the capacity retention of 90%after 1000 cycles can be observed.The GITT-determined diffusion coefficient for Zn(D_Zn)is in the range of 10^-8-10^-7 cm²s^-1.The high capacity,superb long term cycling performance and fast kenics of（Bi,Mn）-doped vanadium materials may be caused by the phase boundaries.The phase boundaries could absorb plenty of Zn²⁺and H⁺,resulting in higher capacity,better cycling and rate performance than that of single-phase materials.