Preparation And Electrochemical Performance Of MNO2/RGO Composites

Lithium ion battery is a kind of energy storage equipment which is widely used in various fields with high energy density and high power density.Graphene is a two-dimensional material with high conductivity,large specific surface area(2600m2g-1),good mechanical properties and good thermal conductivity.Therefore,it has been widely studied by experts and scholars as the anode material of lithium ion battery.Metal oxide manganese dioxide(MnO2)has also been studied as a lithium ion anode material because of its environmental friendliness,low cost and high natural abundance.However,the above two materials have great defects when they are used separately as anode materials for lithium ion batteries.In order to get better performance of the lithium ion battery material,we combine the graphene with manganese dioxide by chemical reaction.In the composites,graphene can improve the conductivity of the composite,ease the volume expansion phenomenon of metal oxides in the process of lithium intercalation and lithium removal.And at the same time,functional groups on graphene surface can provide active sites for the combination of the two.Metal oxide can provide high specific capacity,reduce the aggregation phenomenon in graphene.Therefore,the effective surface area of graphene can be improved,and higher electrochemical activity can be obtained.1?In this paper,MnO2/RGO composites were synthesized by hydrothermal synthesis,and the synthesized materials were calcined at different temperatures in nitrogen atmosphere to explore the effect of calcination temperature on the properties of the samples.The results show that the composites prepared under hydrothermal time of 12h,the hydrothermal temperature of 120?,the calcining temperature of 500 ? have the best electrochemical properties.The charge and discharge cycle tests of materials were carried out under current density 0.1C(C=1000mA/g)conditions.After 50 cycles,the discharge specific capacity remained at 449.3mAh/g,and the cyclic retention rate was 68%.2.The Nb-MnO2/RGO composites were synthesized by a simple microwave method.The electrochemical properties of Nb doped and undoped composites were compared in term of electrochemical performance.The results show that the electrochemical properties of the proper Nb doped composites are better than those of the undoped and the over-doped composite.A proper amount of Nb doped composite material was charged and discharged at current density of 0.1 C(C=1000mA/g).After 50 cycles,the discharge specific capacity could still be kept at 556.6mAh/g,and the capacity retention rate was about 77%.