| Zinc ion secondary batteries are expected to replace lithium ion batteries to achieve lower cost,environmental protection and safety due to their good electrochemical performance and high energy density.However,the focus of hindering the development of zinc ion batteries is the lack of high reversible capacity,high cycle capacity,and a positive electrode material with good stability and sufficient working voltage.Among all ZIBs cathode materials,manganese oxide（MnOx）has low cost,abundant reserves,low toxicity,and rich valence(Mn0,Mn2+,Mn3+,Mn4+and Mn7+),which is one of the materials with the most potential applications.At present,the preparation of MnOxgenerally adopts hydrothermal method,co-precipitation method,etc.However,these methods have problems such as long synthesis cycle,difficulty in continuous production,complicated synthesis steps,etc.In response to the existing problems,this paper studies two common cathode materials for zinc-ion batteries,anα-MnO2 material with nanowire structures And a new type of zinc ion battery cathode material MOFs-derived Mn2O3.Firstly,the thesis preparedα-MnO2 nanowire material by hydrothermal method,and explored the influence of different preparation process conditions on the crystal form,morphology and crystallinity ofα-MnO2.When the hydrothermal time is 16 h,the hydrothermal temperature is 160℃,and the calcination temperature is 500℃,uniform and regularα-MnO2 nanowires are obtained.α-MnO2 is the most widely studied cathode material for zinc-ion batteries.Althoughα-MnO2 has high capacity,its conductivity and cycle performance is poor.This article also explores the preparation of manganese dioxide/graphene-polypyrrole（α-MnO2/rGO-PPy）composite material that can effectively change the above problems.The results show that the discharge capacity of theα-MnO2/rGO-PPy composite material is significantly improved compared to that ofα-MnO2.At a current density of 0.5 A g-1,the first discharge specific capacity ofα-MnO2/rGO-PPy can reach 248.8 m Ah g-1.after 100cycles,the discharge specific capacity is still 213.8 m Ah g-1,and the capacity retention rate is 85.9%.This has made a certain breakthrough in the modification ofα-MnO2 cathode materials for zinc-ion batteries by using carbon materials and conductive polymer materials.The thesis also prepared a new positive electrode material MOFs-derived Mn2O3,and synthesized Mn2O3 materials by the commonly used microwave method and solvothermal method of MOFs materials.In zinc-ion batteries,the discharge specific capacity of Mn2O3 prepared by the microwave method at a current density of 0.3 A g-1 can reach 226.6 m Ah g-1,and it still has a discharge capacity of 215.9 m Ah g-1 after 100 cycles（95.3%of capacity retention rate）.Its electrochemical performance is better than Mn2O3 prepared by solvothermal method（89.1%of the capacity retention rate）.The paper also studied the zinc storage mechanism of Mn2O3 cathode and the chemical reaction inside the battery.The results show that the structure of Mn2O3 changes during the process of intercalation and extraction of zinc ions.During intercalation,Mn2O3gradually transforms into layered Zn-birnessite compounds;during extraction,layered Zn-birnessite compounds can be restored to Mn2O3.This shows that MOFs-derived Mn2O3 has a good ability to store zinc ions. |
