Research On Structural Construction And Electrochemical Properties Of Cathodes For Aqueous Zinc-ion Batteries

In recent years,various energy storage systems such as lithium-ion batteries,sodium-ion batteries,and lithium-sulfur batteries have developed rapidly.As a new type of electrochemical energy storage device,aqueous rechargeable zinc-ion batteries（ARZIBs）have some unique advantages.Firstly,the global zinc reserves are enough,and the electrolyte is cheap and stable,which greatly reduces the cost of battery manufacturing.Besides,the aqueous electrolyte is safer and more environmentally friendly than the organic electrolyte,which has gradually attracted the attention of researchers.However,compared with lithium ions,zinc ions have more positive charges and larger radius when they combined with water molecules,so there has a strong electrostatic repulsion between zinc ions and the cathode material,which posed a certain demand to the stability of the cathode material.Transition metal oxides,which mostly have a layered or porous crystal structure,are considered to be one of the most potential cathode materials for ARZIBs due to their low cost and abundant valence states.This thesis focuses on the transition metal oxide-based cathode materials of ARZIBs.To improve the electrochemical performance of ARZIBs,vanadium oxide and manganese oxide cathode materials were synthesized and modified.（1）The MnO/C fiber composites were synthesized also by the electrospinning method,and Ni was introduced to improve the specific capacity during the charge and discharge process.The electrochemical properties of the composites were tested under different electrolyte conditions.It was found that the deposition of MnO₂ occurred during the charging process.The deposition efficiency of MnO₂ was improved by introducing Ni into the composites,and a specific capacity of 398 m Ah g^-1 was achieved during the first discharge process.（2）The porous vanadium pentoxide（V₂O₅）cathode material was synthesized by the hydrothermal method,this porous spherical morphology shortening the ion diffusion path allows rapid inserting/extracting of zinc ions.The sample prepared when the hydrothermal temperature is 180°C has the best electrochemical performance,and can reach a specific discharge capacity of 309 m Ah g^-1 at a current density of 100 m A g^-1,even at a current density of 500 m A g^-1,the specific discharge capacity is still 258 m Ah g^-1.The discharge specific capacity after 500 cycles is 128 m Ah g^-1,about 81.5%of the initial capacity.（3）The V₂O₅ porous nanofiber cathode material was synthesized by the electrospinning method,the influence of the molar ratio of NH₄VO₃ to H₂C₂O₄ on the electrochemical properties of the material was investigated respectively.The samples prepared when NH₄VO_3:H₂C₂O₄=1:2.5 have the best electrochemical performance.What’s more,Co²⁺and Ca²⁺were pre-inserted into the V₂O₅ crystal structure to expand the interlayer spacing.Co²⁺doping can improve the discharge specific capacity of the material,at a current density of100 m A g^-1,the discharge capacity can reach 281 m Ah g^-1.Ca²⁺doping can improve the cycle stability of the material,after 300 cycles at a current density of 300 m A g^-1,the capacity retention rate relative to the initial capacity is about 60%.