Construction Of MoS₂/Graphene Composite Materials And Lithium Storage Mechanism

The overuse of fossil fuels has wreaked havoc on the global environment and severe energy shortage have made the world’s new energy needs more pressing.Lithium-ion batteries are often used in electric vehicles and large energy storage systems due to their high stability,excellent energy density,high reversible capacity and without memory effect.Since electrode materials for battery components play a crucial role in electrochemical energy storage,the development of electrode materials with high specific capacity and high safety is key.This paper is based on MoS2/graphene,by adding a variety of nitrogen sources,using one-pot hydrothermal method combined with carbonization treatment and freeze-drying technology to successfully prepare MoS2/nitrogen-doped graphene composite material,and discuss the electrochemistry performance and lithium storage performance of the composite material.The main research contents and conclusions are as follows:(1)Using graphene oxide(GO)as the substrate material and carbon nitride as the nitrogen source,using the interaction between the charges,assisted hydrothermal method to induce the growth of MoS2 to prepare MoS2/nitrogen-doped graphene composite(MoS2/N-G),and study its electrochemical performance as a negative electrode material for lithium-ion batteries.In the MoS2/N-G composite,MoS2/has a flower-like structure,and graphene exhibits maintain the structure of ultra-thin nanosheets.The electrochemical test results show that MoS2/N-G exhibits good specific capacity and rate performance.At the current density of 0.1 A/g,MoS2/N-G composite can maintain an average specific capacity of 806.4 mAh/g after 100 cycles.When the current density increases to 5 A/g,the average specific capacity can reach 336.7 mAh/g.The study of the lithium storage mechanism of MoS2/N-G composite shows that more than 79.1%of the lithium storage in MoS2/N-G is controlled by the capacitance effect,which can effectively improve that the rate performance.N doping improves the storage of Li~+more active sites,the addition of graphene improves the overall conductivity and structure stability of the material,and the rich mesoporous structure promotes rapid charge transfer and improves the storage efficiency of Li~+.(2)With GO as the base material and polyvinylpyrrolidone(PVP)as the structure inducer,nitrogen-doped graphene-coated spherical MoS2 composite(MoS2@NG)can be prepared by hydrothermal treatment combined with pyrolysis technology.The MoS2@NG is a layered package structure,in which MoS2 is a "spherical" structure assembled by nanosheets,evenly dispersed between graphene sheets.Electrochemical test results show that:MoS2@NG electrode has excellent lithium storage performance.The lithium storage capacity can still maintain 975.9 mAh/g at a current density of 0.1 A/g after 100 cycles,even after 300 long cycles at a high current density of 5 A/g,it can still provide a reversible specific capacity of 325.2 mAh/g.The lithium storage mechanism research shows that the proportion of capacitance effect contribution in MoS2@NG is 57.7%.The high capacitance contribution can reduce the structural damage caused by the volume change during the charging and discharging process.At the same time,the rate performance can be improved.In the MoS2@NG composite,nitrogen-doped graphene as a conductive framework can improve the conductivity and structural stability of the electrode skeleton;the embedding of carbon can not only reduce the number of MoS2 stacks,but also increase the interlayer spacing of MoS2,and promote the rapid transmission of Li~+and electrons.In addition,ultra-high nitrogen doping provides more Li~+storage sites and promotes the rapid reaction of active materials with Li~+.