Design And Preparation Of MoS₂/nitrogen-doped Graphene Nanocomposites And Their Performances In Lithium-ion Batteries

In recent years,due to the impact of energy and environmental issues,lithium-ion batteries have been greatly developed.For lithium-ion batteries,the most important part is the electrode materials.For the traditional graphite anode,its smaller theoretical capacity(372 m Ah/g)can not meet the requirements of battery development.For this reason,many researchers have been making efforts to develop a new type of high capacity alternative anode materials.Molybdenum disulfide(Mo S2)has attracted much attention due to its large theoretical specific capacity of 670 m Ah/g and the layered structure.However,Mo S2 also has its own shortcomings,such as large volume expansion and low conductivity,thus limiting its applications.Therefore,by combining with graphene with good conductivity and large specific surface area,it can enhance its electrical conductivity,alleviate the volume expansion effect during cycles,thereby improving its electrochemical performances.On the basis of the present research,Mo S2/nitrogen-doped graphene nanocomposites with well-defined morphologies and excellent lithium storage properties were prepared by a facile one-pot hydrothermal method.The main research contents are as follows:In the first part,we propose a facile one-pot hydrothermal route for synthesis of Mo S2/nitrogen-doped graphene composites by using sodium molybdate as the molybdenum source,thiourea as sulfur source with the help of polyvinyleneimide(PEI).In the composite,two-dimensional Mo S2 nanosheets are tightly loaded onto the surface of nitrogen-doped graphene.The experimental and theoretical results show that the effective combination of ultrathin Mo S2 nanosheets and highly electrically conductive graphene enhances the charge transfer kinetics of ion and Mo S2/N-graphene composites.In particular,the N atoms from PEI can provide additional storage locations for lithium-ion storage.As a result,the synthesized Mo S2/N-graphene composite electrode has a high reversible lithium storage capacity and good cycling stability,deliverling the reversible capacity of 1025 m Ah/g at a current density of 100 m A/g.In the second part,we develop a simple and effective method for preparation of flower-like Mo S2 onto the N-doped graphene(F-Mo S2/NG)by the induction assembly of surfactants(poly(vinylpyrrolidone),PVP).The 3D Mo S2 nanoflowers have highly oriented open microstructure and expanded interlayer spacing.The combination of graphene nanosheets and Mo S2 to increase charge transfer,The interlayer spacing of Mo S2 to promote lithium diffusion and the modification of graphene nanosheets by N-doping to enhance their interaction with active species during the cycles.Furthermore,the as-made F-Mo S2/ NG composite electrode has high reversible lithium storage capacity of 1060 m Ah/g at 100 m A/g even after 150 cycles,much higher than that of control Mo S2/G electrode(416 m Ah/g).The superior performances mat be mainly attributed to its unique architecture including well-defined Mo S2 nanoflowers,the doping of nitrogen onto graphene,and the enhanced synergistic effect between them.