Microstructure Design And Electrochemical Properties Of Transition Metal Sulfides

In recent years,the development and utilization of coal,petroleum and other fossil fuels make the problems of environmental pollution and resource shortage increasingly prominent.It is urgent to develop new energy sources to replace fossil fuels.Therefore,wind energy,tidal energy,geothermal energy and other new energy sources have developed rapidly.However,the application of these energy resources limited by time,region and so on,and the storage of energy need to be further solved.In the current energy storage devices,due to their high energy density and long cycle life,lithium-ion batteries(LIBs)have been widely applied in many areas,such as large-scale power grid.So the demand of lithium-ion batteries is increasing.At the same time,it also puts forward higher requirements for the energy density of lithium-ion batteries.As an important part of lithium-ion batteries,the properties of anode affect the performance of lithium-ion batteries.The commercial anode material for lithium-ion batteries is graphite,which possesses the disadvantage of low theoretical specific capacity.Therefore,it is necessary to design the anode material with high specific capacity.Metal sulfides have attracted much attention due to their high specific capacity and high reversibility.However,when used as anode materials for lithium-ion batteries,it also has some disadvantages,such as low conductivity and large volume change.Therefore,in order to solve the problems of metal sulfide materials,structural design and compositing with other materials was carried out to improve its electrochemical performance.The main contents of this paper are as follows:(1)In this paper,the Co₃S₄ nanosheet array grown on carbon cloth,abbreviated as Co₃S₄@CC was fabricated,it can be used as electrode directly,without any additives and binders.At the same time,carbon cloth in the material can not only improve the conductivity,but also increase the mobility speed of Li⁺and contact area of the reaction.In addition,porous Co₃S₄ nanosheet makes the electrode possess high specific surface area,and the C-S bond between Co₃S₄ and carbon cloth can be formed,which can alleviate the volume expansion during the cycle of LIBs,and shorten the diffusion distance of Li⁺and make it contact with electrolyte effectively during cycling.The self-supporting Co₃S₄@CC electrode shows the Li⁺storage behavior is controlled by the pseudocapacitance and diffusion processes.At the current density of 250 mA g^-1,it can still maintain a specific capacity of 847 mAh g^-1 after 100 cycles.In addition,the self-supporting Co₃S₄@CC electrode also exhibits good rate performance.This work provides a method for design high capacity and high rate performance metal sulfide anode.(2)Using Polyvinylpyrrolidone(PVP)and Fe(NO₃)₃·9H₂O as carbon source and iron source,respectively,three-dimensional porous FeS₂/C was synthesized by vulcanization,in which FeS₂ nanoparticles were uniformly dispersed in three-dimensional porous carbon.At the same time,the effects of different PVP content of the 3D porous FeS₂/C composites were studied,and the PVP content was optimized.The results show that when the amount of PVP is 0.75 g,the composite exhibits the best electrochemical performance.When the current density is 500 mA g^-1,the 3D porous FeS₂/C composite can still present a specific capacity of 385 mAh g^-1 after 400cycles.