Preparation And Electrochemical Properties Of Manganese-based Anode Composites

Rechargeable water zinc-ion battery is becoming a potential large-scale energy storage device due to its advantages of high energy density,low cost,high safety and environmental friendliness.Manganese matrix composites are often used as the positive electrode materials for water zinc ion batteries due to their low cost,low toxicity,abundant resources,multiple valence states,and a matching voltage range to stabilize the water battery system.Therefore,Mn-based materials are considered to be the most promising anode materials for water zinc ion batteries.However,Mn-based materials usually have a common obstacle,that is,the inherent poor electrical conductivity,and the large volume change caused by the phase transition during the cycle,which seriously affects the overall performance of the battery.To solve this problem,it can be combined with high conductivity additives to form manganese matrix composites.In order to improve the electrochemical performance of the cathode materials of zinc ion batteries in water system,the carbon and polymer materials with good conductivity were used to compound or doped with Mn-based materials to modify Mn-based materials.The main contents of this thesis are as follows:?1?Firstly,manganese sulfide?MnS?nanosphere materials were synthesized by simple hydrothermal method,and then MnS were attached to the surface of graphene.Finally,composite materials of MnS/RGO were prepared by calcining at high temperature.The preparation process is simple,convenient and easy to operate.The results of scanning electron microscopy?SEM?showed that the MnS nanospheres were coated or attached to the surface of GO.The addition of RGO greatly improved the electrical conductivity of the material,thus improving the electrochemical properties.Compared with pure MnS,MnS/RGO composite material as cathode material of zinc ion battery shows excellent cycling performance and rate performance.When the current density is 1000 mA g^-1,the reversible capacity can reach 80 mAh g^-1 after 700cycles.The MnS/RGO composite provides significant guidance for the further development of the cathode materials of zinc ion batteries in water system.?2?A novel Mn₃O₄@N doped carbon based composite nanorods?Mn₃O₄@NC Nrs?were synthesized by using self-sacrificing template MnOOH needle-like nanorods and polypyrrole?carbon and nitrogen source?.The results of EDX show that the nitrogen-doped carbon matrix is uniformly dispersed in the whole structure of Mn₃O₄,which increases its electrical conductivity.Benefiting from the N-doping carbon shell and the synergetic effect of Zn²⁺and Mn²⁺in electrolyte,the Mn₃O₄@NC Nrs show superior cycling stability and long cycling performance for ZIBs.Specifically,the zinc cell conducts a high reversible capacity of 280 mAh g^–1 at 100 mA g^–1 and it still retains a higher reversible capacity of 97 mAh g^–1 at 1000 mA g^–1 after 700 cycles.In addition,the work provides a new approach to fabricate the long-term and high-rate capability cathodes for ZIBs.?3?Firstly,the carbon sphere of glucose was prepared by hydrothermal method,dissolved in aqueous solution of pH=3.0 to form a homogeneous solution,slowly added potassium permanganate,and then the precursor was prepared by hydrothermal method.Finally,the product calcined at high temperature in muffle furnace is MnO₂/C composite.Due to the existence of a large number of mesopores and the buffering effect of carbon spheres,the MnO₂/C composites have high capacity and good long cycle performance as cathode materials for zinc ion batteries.At the current density of 1000mA g^–1,after 500 cycles,the reversible capacity is still 223.6 mAh g^–1.