Study On Preparation Of Metal Sulfide/Selenide-Carbon Composites And Their Energy Storage In Lithium-Sulfur Batteries

With the rapid growth of energy demand,people are urgently seeking cheap and clean alternatives to replace limited fossil fuels.Among them,rechargeable secondary batteries stand out as large-scale renewable energy storage systems.At present,lithium-ion batteries（LIBs）have been widely used in electronic equipment and electric vehicles due to their high reversibility and long cycle stability.However,after improvements to existing battery components and package engineering,LIBs are gradually approaching their theoretical energy density limits.Therefore,more and more scholars have begun to look for another energy storage system with higher energy density and good cycle stability.Lithium-sulfur batteries（LSBs）have aroused a wide range of research upsurge due to their ultra-high theoretical energy density and green environmental characteristics.However,there are still many problems with LSBs in practical applications,such as the shuttle effect of polysulfides（LiPSs）,and the low electrical conductivity of active substances.In order to overcome these difficulties,this article uses different metal sulfides and metal selenides to composite with carbon materials,and uses these materials to modify the sulfur matrix and separator of LSBs,thereby improving the electrochemical performance of LSBs.（1）In order to improve the electrochemical performance of LSBs,the separator was modified with Fe₃S₄/rGO composite.Firstly,graphene oxide（GO）was synthesized by an improved Hummers method,and then Fe₃S₄/rGO composite was prepared by a one-step hydrothermal method.In order to ensure the successful preparation of the material,the material composition,molecular structure and morphology characteristics of the Fe₃S₄/rGO composite was investigated by various common material characterization methods.According to the electrochemical test results,LSBs with an S/MWCNT cathode and a Fe₃S₄/rGO-PP separator have a discharge specific capacity of 1293 mAh g^-1at 0.2 C.After 100 cycles,they can still maintain a discharge specific capacity of 750 mAh g^-1.At 1 C,the discharge specific capacity of LSBs after 300 cycles is 578 mAh g^-1,and the capacity decay rate per cycle is 0.052%.Due to the existence of GO,the Fe₃S₄/rGO composite has a high specific surface area,which provides rich sites for the adsorption of LiPSs and effectively inhibits the shuttle effect.At the same time,the electrical conductivity and mechanical properties of the Fe₃S₄/rGO modified separator have been improved,thereby improving the cycle stability of LSBs.（2）The electrochemical performance of LSBs was improved by using FeSe₂-NC@ZnSe-NC to modify the sulfur matrix.First,Prussian Blue（PB）was synthesized and coated with a layer of polydopamine（PDA）on its surface.And then chelating Zn²⁺on the material using the chelation effect of PDA on metal particles.The LSBs with S/FeSe₂-NC@ZnSe-NC cathode have an initial discharge specific capacity of1216 mAh g^-1 at 0.2 C,and it can still maintain a discharge specific capacity of 692mAh g^-1 after 100 cycles.After 500 cycles at 1 C,the LSBs also has a discharge specific capacity of 662 mAh g^-1 with a capacity decay rate of only 0.031%per cycle.The FeSe₂-NC@ZnSe-NC composite has strong physical and chemical adsorption properties,which can effectively inhibit the shuttle effect of LiPSs.Nitrogen-doped carbon endow the composite with high electrical conductivity.Besides,nitrogen-doped carbon and metal selenide jointly promote the catalytic conversion of LiPSs,improving the utilization rate of active materials and the reaction kinetics of the charge and discharge process.Thus,LSBs with S/FeSe₂-NC@ZnSe-NC cathode show good electrochemical performance.