Preparation Of Transition Metal Doped ZnS/rGO Composites And Their Application In Lithium Sulfur Batteries

Since the 2020s,the world has entered a new stage of development.The intensifying global competition for energy has led to a rapid increase in oil prices,making the development of sustainable electric vehicles a critical need.On the other hand,with the rapid development of electronic devices and the future intelligent social needs,to the portable battery energy storage device such as higher performance requirements are put forward.Therefore,it is necessary to develop large capacity,long battery life,fast charging and discharging,safe and cheap batteries to meet the future demand for energy storage equipment.Li-sulfur battery（LSB）is one of the most promising commercial batteries for next generation energy storage devices after Li-ion battery（LIB）due to its excellent high theoretical specific capacity(1675 m Ah g^-1)and high theoretical energy density(2600 Wh kg^-1)and cheap and environmentally friendly sulfur positive electrode.However,there are several issues in the research process of LSBs,such as poor conductivity of S and Li₂S,low utilization rate of active sulfur,and short cycle life that limit their practical applications.This paper employs graphene oxide（GO）as the carbon material and prepares transition metal sulfide composite materials by one-step hydrothermal method.The abundant oxygen-containing functional groups on the surface of GO and its physical adsorption and chemical bonding ability are utilized to capture intermediate polysulfides（Li PSs）and load them onto the surface of GO.Meanwhile,the highly polar metal-sulfur ion bond of transition metal sulfides is used to achieve efficient adsorption and catalysis of Li PSs,thus enhancing the capacity and cycling stability of LSBs.The research contents are as follows:（1）ZnS/rGO composites were prepared by one-step hydrothermal reaction using GO as carbon source,Zn（CH₃COO）₂·2H₂O as zinc source and CH₄N₂S as sulfur source,and then ZnS/rGO/S composites were prepared by melting diffusion method.The prepared ZnS/rGO/S composite material was applied to LSB cathode material,and the optimum performance conditions were obtained:When the hydrothermal time is 12 h,the hydrothermal temperature is 180℃,the theoretical addition amount of Zn S is 40 wt.%and the sulfur carrying amount is 70 wt.%,the prepared ZnS/rGO/S composite has the best electrochemical performance.At 200 m A g^-1,the specific capacity of the initial discharge is 848.0 m Ah g^-1,and after 100 cycles,the reversible capacity is maintained at494.4 m Ah g^-1,and the capacity retention rate is 58.3%.The physical and dynamic studies suggest that combining graphene oxide with transition metal zinc sulfide enhances the effective adsorption of Li PSs and catalytic transformation kinetics,increases ion diffusion,improves the utilization of active sulfur,and enhances the cyclic stability of LSBs.（2）The composite materials Zn_0.975Co_0.025S/r GO,Zn S-Fe S₂/r GO,and Zn S-Ni S₂/r GO were synthesized through a one-step hydrothermal reaction using GO as the carbon source,Zn（CH₃COO）₂·2H₂O as the zinc source,Fe Cl₃·6H₂O as the iron source,Co Cl₂·6H₂O as the cobalt source,Ni Cl₂·6H₂O as the nickel source,and CH₄N₂S as the sulfur source.Using the melt infusion of sulfur technique,we synthesized Zn_0.975Co_0.025S/r GO/S,Zn S-Fe S₂/r GO/S,and Zn S-Ni S₂/r GO/S composites,and subsequently studied their lithium storage electrochemical performance.The results show that the initial discharge specific capacity of Zn_0.975Co_0.025S/r GO composite material is896.3 m Ah g^-1 at a capacity of 200 m A g^-1.After 100 cycles,the reversible discharge specific capacity is maintained at 595.5 m Ah g^-1,with a capacity retention of 66.4%.Similarly,the initial discharge specific capacities of Zn S-Fe S₂/r GO and Zn S-Ni S₂/r GO composite materials are 876.5 and 875.7 m Ah g^-1,respectively.After 100 cycles,the reversible discharge specific capacities are maintained at 597.0 and 506.5 m Ah g^-1,respectively,with capacity retentions of 68.1%and 57.8%.This is mainly due to the successful formation of bimetallic and two-component sulfide complex composite material,whose catalytic activity is better than that of single-component ZnS/rGO composite material,and increase the surface area of the composite catalytic active site,so as to improve the utilization rate of active sulfur substances,and catalytic activity.Finally improve the cycle stability of lithium sulfur battery.