Preparation And Electrochemical Properties Of MnO₂ Cathode Material For Aqueous Zinc-ion Battery

Aqueous zinc-ion battery is a new type of green secondary battery which has been widely concerned and developed rapidly in recent years.Compared with the traditional lithium-ion battery,aqueous zinc-ion battery has the advantages of high safety performance,simple assembly process,non-toxic and environmental protection,which makes it have a bright application prospect in the fields of energy storage and transport tools.In the research and development of aqueous zinc-ion battery,the selection and application of positive materials has always been a difficult problem.As the most potential energy storage material,manganese dioxide has many advantages,such as low cost,environment-friendly,low toxicity and multivalent state.However,manganese dioxide has many problems in the process of charging and discharging,such as dissolution and structure collapse,which lead to poor cycle performance and limit the application of the material in aqueous zinc-ion battery.In this paper,different synthesis methods and preparation processes are used to control the structure and morphology of MnO2.And the electrochemical performance of MnO2 modified by oxide coating is improved.The main research contents are as follows:(1)Preparation and properties of the nanorod-shaped manganese dioxide materials.Manganese dioxide with different crystal forms and morphologies was prepared by hydrothermal method with MnSO4·H2O and KMnO4 as raw materials.Increasing the concentration of KMnO4 can drive the crystal structure of MnO2 from(3-MnO2 to ?-MnO2.The nanorod-shaped ?-MnO2 material has the best electrochemical performance which been prepared under the experimental conditions of hydrothermal reaction temperature 180 ? and KMnO4 concentration 0.06 mol/L.The maximum discharge specific capacity of the material is 211.4 mAh/g at the current density of 100 mA/g.The discharge specific capacity of the material is 157.2 mAh/g and the capacity retention rate is 74.4%after 100 cycles.(2)Preparation and properties of the microsphere-shaped manganese dioxide materials.Manganese dioxide with different morphologies was prepared by coprecipitation method with MnSO4·H2O and NH4HCO3 as raw materials.The microsphere-shapedl ?-MnO2 material has a particle size of about 2 ?m,regular morphology and good dispersion,which is prepared at the reactant concentration of MnSO4·H2O 0.007 mol/L and NH4HCO3 0.07 mol/L.The electrochemical properties show that the material has high specific discharge capacity and good cycle performance.The maximum discharge specific capacity is 243.2 mAh/g at the current density of 100 mA/g.The discharge specific capacity is 163.1 mAh/g and the capacity retention rate is 67.1%after 100 cycles.(3)Preparation and properties of the oxide coated microsphere-shaped manganese dioxide.The microsphere-shaped MnO2@Al2O3,MnO2@MgO and MnO2@La2O3 materials were synthesized by coprecipitation and thermal decomposition.The oxide coating not only increases the specific discharge capacity of the manganese dioxide material,but also significantly improves the cycle stability of the material.The MnO2@MgO material has a uniform particle size,regular morphology and good dispersion.It is found that the material has excellent electrochemical performance through the electrochemical performance test.The results show that MgO coating does not change the structure of MnO2,and the coating is composed of nano particles with a thickness of about 50 nm.The discharge specific capacity of MgO coating material is obviously improved.The maximum discharge specific capacity of MnO2@MgO material is mAh/g at the current density of 100 mA/g.Meanwhile,the coated material exhibited excellent cycle stability with 84.1%.Obviously,the MgO coating layer prevents directly contact between MnO2 and electrolyte,and suppresses the dissolution of manganese during the charge and discharge process,thus significantly improves the cycle performance of MnO2.