Preparation And Electrochemical Properties Of Graphene Loading With Binary Metal Sulfides

Recently, the binary metal sulfides have attracted widespread attention, because of unusual physical and chemical properties. However, as anodes for lithium-ion battery, the cycling properties of these materials were poor, this drawback could be ascribed to huge volume variation and pulverization during charge-discharge. To solve these problems,we synthesized nanosheets SnSx(SnS and SnS2), flower-like SnS microspheres and multihole MnS microspheres, which could well buffer the volume charge. The graphene material, for its honeycomb network construction has been widespread concern and wide application in many fields, such as mechanism, electrion device, transistor, optical energy and lithium-ion battery. In this paper, we prepared binary metal sulfide/graphene composites. Due to the synergistic effect of these two composites and the excellent electro-conductivity of graphene, the electrochemical performance of these composite materials were excellent. XRD,SEM,Raman,and TGA technologies were used to measure the microstructure and composition of these materials. Their electrochemical performance and impedance were also tested. The main contents of this thesis are as follows:Nanosheet-like SnSx/RGO composites were synthesized through a solvothermal method with TAA as the sulfur source and PEG-200 as the solvent. After introducing the RGO, the electrochemical properties of SnSx have been obviously improved. The superior performance was mainly originated from the outstanding conductivity and mechanical properties of RGO and the synergistic effect of SnSx and RGO. EIS measurement demonstrated that the RGO in the composite materials reduced the contact resistance of the electrode and promoted the electron transfer of Li-ion during insertion-deinsertion reaction.Flower-like SnS microspheres were synthesized through a hydrothermal method with PEG as the surfactant and thiourea as the sulfur source. Electrochemical properties of SnS/RGO composites and pure Sn S have been compared. The results revealed that the SnS/RGO composites exhibited a better reversible capacity and cycling stability than pure SnS. As a buffer layer, graphene can decrease the volume expansion of SnS during charge-discharge.Multihole MnS microspheres were also prepared through hydrothermal method with L-cysteine as the sulfur source. After 200 cycles, the MnS/RGO composites revealed a discharge capacity about 800 mAh/g, which is larger than pure multihole MnS microspheres. The cycling performance of the composite at the current density of 1 C also excellent. The outstanding performance of the composites could be attributed to the decresing size of MnS crystals and alleviation volume expansion of MnS in the presence of graphene.