Synthesis And Lithium Storage Performance Of Transition Metal Sulfide/Graphene Nanostructures Composites

Since the 21st century,environmental pollution and energy shortage problems have become increasingly serious,urgent need for the development and utilization of various clean and economical power sources.Lithium-ion batteries as a green energy has been widely used in a variety of devices power supply,but in the development of lithium-ion battery process,to improve the specific capacity of lithium-ion battery and cycle life is still the main problem of electrode materials research.Transition metal sulfides and graphene have a number of excellent physical and chemical properties due to their unique structure.Based on the compatibility of the two on the crystal structure and microstructure of the complementary and electrical properties of the complementary,the composite material to the maximum extent possible between the two synergies,as the lithium ion battery anode material not only has high electrochemical Lithium storage reversible capacity,but also has excellent cycle performance and good high rate charge and discharge characteristics.In this work,we designed various novel graphene/transition metal sulfide composites with suitable nanostruetures for rapid insertion/desertion of lithium ions by utilizing the confinement effect and interfacial interaction between metal sulfide and graphene sheets.Then,the formation mechanisms of these nano-structured composites were studied.And the effects of morphologies on the electrochemical performances for these graphene/transition metal sulfide composites were investigated in detail.1.MoS₂/reduced graphene oxide?MoS₂/rGO?intercalation composites are synthesized via a SiO₂-assisted hydrothermal method.This strategy discards addition of any amorphous carbon precursor for the synthesis of intercalation composites,and may reduce the defect degree and irreversible lithium storage sites in the final products.The structure and morphology characterization of the layered MoS₂/rGO intercalation composites shows that the MoS₂ composed of single layer or 2-4 layers display a highly exfoliated structure and disperse on the surface of graphene homogeneously and tightly,some of the interlayer spacing of MoS₂ are enlarged,ranging from 0.7 to 1.17 nm with the intercalation of graphene.Electrochemical tests demonstrate that the MoS₂/rGO-0.5 delivers a high reversible capacity of 1260.5 mAh/g in the initial cycle and retains 94.9%capacity after 50 cycles at 100 mA/g.Furthermore,the capacity can reach 988.3 mAh/g even at a high current density of 1000 mA/g.The excellent electrochemical performance of the MoS₂/rGO intercalation composite could be attributed to the excellent match between the structure and morphology of layered MoS₂ and graphene and the partial electron transfer from graphene to MoS₂,which would maximize the synergistic interaction of the MoS₂/rGO composite for reversible lithium storage.2.A novel strategy to fabricate heterostructured Ni3S₂/reduced graphene oxide?Ni3S₂/rGO?composite is developed by a SiO₂-assisted hydrothermal method.The Si02 particles hydrolyzed from tetraethyl orthosilicate are used as structure directing agent to realize the surface controllable co-growth of 3D nanoflowers and OD nanoparticles of heterostructured Ni3S₂ nanocomposite decorated on reduced graphene oxide.Serving as anode material in lithium ion battery,the microstructured composite with different morphologies and crystal structures can promote the synergetic interactions of each components and lead to excellent lithium storage performances.It turns out that the Ni3S₂/rGO composite delivers a high reversible capacity of 1187.0 mAh/g in the initial cycle and retains 94.3%capacity after 60 cycles at 100 mA/g.Furthermore,the capacity can reach 561.2 mAh/g even at a high current density of 5 A/g.3.The PS/Na2MoO₄/GO spherical precursor was obtained by freeze-drying process of graphene oxide?GO?and sodium molybdate were used as raw materials and polystyrene balls as templates.Then,the three-dimensional interconnected spherical graphene-loaded MoS₂ composites were synthesized by in situ calcination sulfurration of PS/Na2MoO₄/GO and thiourea mixed.The morphologies,structures and electrochemical properties of the final products were investigated by wash the PS sphere then calcination sulfuration?MoS₂@SG?and direct calcination sulfuration?PS-MoS₂@SG?two different processes.The results show that,the overall spherical structure composite of MoS₂@SG is keep it more complete,the shell wall thickness is thinner and more uniform?10-25 nm?,the oxygen-containing functional groups on the surface of graphene with molybdenum ions are combined,act as in situ sulfidation reaction during calcination site to be retained,so that the composite material has a low degree of disorder and provides an electron transport channel for the charge transfer between MoS₂ and graphene.Electrochemical tests show that MoS₂@SG composites have a high reversible capacity of 1134.2 mAh/g at a current density of 100 mA/g and exhibit good cycling stability and rate performance.