Preparation Of Transition Metal Sulfide Electrode Materials And Study On Lithium/Sodium Storage Performance

In recent years,the market demand for portable electronic devices and electric vehicles that use lithium-ion batteries as the energy supply system has continued to expand,and higher requirements have been put forward for their energy density.Due to the limited reserves of lithium resources in the earth’s crust,the research of sodium ion batteries as a new generation of secondary battery systems has also attracted much attention.Overcoming the problems of existing materials and finding electrode materials with better performance are effective methods to increase energy density.Transition metal sulfide has the advantages of high theoretical capacity,abundant reserves,and high lithium/sodium intercalation potential,and is regarded as a promising negative electrode material.However,the widespread volume expansion during the charge and discharge process and the poor electrochemical reversibility during the conversion reaction have severely restricted the development of transition metal sulfides as negative electrode materials.In this paper,by preparing an electrolyte with a higher matching compatibility with a nano-scale hollow structure,optimizing the voltage window,and improving the lithium and sodium storage performance of metal sulfides.The specific main contents are:（1）Hollow I-Cu₂MoS₄ nanocubes composed of ultra-thin nanosheets were synthesized using Cu₂O nanocubes as a sacrificial template by solvothermal method.It can be seen that there is an obvious internal cavity structure inside,and the outer layer is assembled into nanosheets,and the synthesized cube is about 600nm.The presence of the surfactant PVP is a key factor to prevent the hollow cubic structure of Cu₂MoS₄ from collapsing and the formation of nanoplates.High reversible capacity(723mAhg^-1 at a current density of 0.1 Ag^-1),excellent rate performance(61%of the reversible capacity of 0.1 Ag^-1 at a current density of 5 Ag^-1)and significantly improved cycle performance(After 300 cycles,0.05 Ag^-1 maintains 706 mAh g^-1 and 2Ag^-1 maintains 314 mAh g^-1)indicating that the ether-based electrolyte shows better compatibility than the Cu₂MoS₄ electrode.XRD analysis shows that there is a highly reversible electrochemical reaction in the ether-based electrolyte.（2）The hollow nanocube Cu₂S@SWCNT is designed as a negative electrode material through the Cu₂O nanocube of the sacrificial template.The composition and morphology are analyzed by XRD,SEM,and TEM characterization methods,and the specific surface and pore size are analyzed by N2 adsorption experiment.The electrochemical performance of traditional carbon ester electrolyte and ether electrolyte is compared.Compared with pure Cu₂S,it can perform reversible charge and discharge reactions in a wider discharge interval（0.5V）.Excellent high cycle performance(in the LIBs system,after 350 cycles,it is 440 mAh g^-1 at a current density of 0.5 Ag^-1,and in the SIBs system,after 350 cycles,it is 440 mAh g^-1 at a current density of 2 Ag^-1 293 mAh g^-1).On the one hand,SWCNT and hollow structures facilitate the transport of Na/Li ions by providing diffusion bridge channels.On the other hand,the ultra-high conductivity of the SWCNT matrix promotes the oxidation of Cu₂S discharge products.In addition,the ether type electrolyte suppresses the soluble sodium polysulfide from the electrode to the electrolyte,reduces the loss of active materials and improves the cycle stability.XRD analysis shows that Cu₂S@SWCNT electrode has a highly reversible electrochemical reaction.