Preparation And Electrochemical Properties Of Anode Materials For CoS₂-based Sodium Battery

Sodium-ion battery（SIBs）is a new generation of energy storage system that can replace lithium-ion battery（LIBs）because of its abundant sodium resources and low cost.Nowadays,graphite anode used in lithium-ion battery is not suitable for sodium-ion battery,so it is urgent to find a high-performance anode which is suitable for SIBs.In recent years,transition metal sulfides（TMSs）,especially cobalt-based sulfides(CoS₂,Co_1-xS,Co₈S₉,etc.),have attracted wide attention because of their high theoretical capacity.However,these cobalt sulfide compounds usually have low ionic conductivity and cycling stability,which lead to some obstacles for them to be used as SIBs anode materials.To solve the above problems,this work is devoted to exploring CoS₂-based SIBs anode materials,and the specific results are as follows:（1）Co_1-xS@C nanoparticles was prepared by pyrolytic carbonization and sulfurationof metal-organic skeleton compound ZIF-9.The strong conductivity and porous structure of carbon skeleton can not only improve the ion transport capacity of the composite material,but also prevent the agglomeration of Co_1-xS particles in the electrochemical reaction process and inhibit the volume expansion of Co_1-xS.The Co vacancy defects formed by controlling the curing temperature could provide more reactive sites for Na⁺.The DFT calculation shows that this structure reduces the energy barrier of sodium ions migration and improves the ionic conductivity of the composites.The electrochemical performance test shows that the initial discharge specific capacity is 1001mAhg^-1,the first cycle Coulomb efficiency is 62.3%,and the reversible capacity of 390mAhg-1 can still be maintained after 100 cycles at the current density of 1Ag^-1.At the high current density of 5Ag^-1,The reversible capacity of 300mAg^-1can still be maintained after 250 cycles.（2）CoS₂ with hollow spherical structure was prepared by hydrothermal method,andthe nucleation mechanism of the hollow spherical structure was investigated.The hollow structure can increase the specific surface area and shorten the migration path of Na⁺,and effectively inhibit the volume deformation of CoS₂ electrode material during the electrochemical process.The electrode exhibits a reversible capacity 799mAhg^-1 at the current density of 1Ag^-1,showing excellent rate performance.（3）The CoS₂@MXene composite was prepared by electrostatic adsorption.The two-dimensional MXene material as skeleton support function,can improve the electrical conductivity of the composite material,CoS₂@MXene electrode material shows good cycle stability and rate performance.At the current density of 1Ag^-1,the reversible capacity can still be maintained 380mAhg^-1 after 100 cycles.