Preparation And Electrochemical Properties Of Cobalt And Its Compound Sulfur Hosts

Lithium-sulfur batteries（LSBs）have attracted much attention as a new type of secondary battery,mainly due to the abundant S sources,low price,and environmental friendliness,as well as high theoretical capacity(1675 m A h g^-1)and energy density(2600Wh kg^-1).In recent years,the cathode materials of LSBs have been changed from carbon materials to various polar materials to various composite materials.Constantly exploring ways to overcome the problems faced by LSBs.Cobalt-based materials have attracted much attention due to their good adsorption capacity for lithium polysulfides（LPSs）and their ability to accelerate the conversion of LPSs.In this work,various cobalt-based compounds decorating carbon materials composite S hosts are prepared and applied in the S cathode of LSBs.The main work is as follows:（1）CoSe₂/h NCTs composite was prepared by in-situ growth and polymerization,and CoSe₂ was uniformly loaded on the carbon nanotubes,which was used as sulfur host for LSBs.First,the initial specific capacity of the CoSe₂/h NCTs/S electrode can reach 1156m A h g^-1 at 0.5 C.In the long cycle test,the specific capacity of the electrode remains at424 m A h g^-1 after 1000 cycles at 1 C,with an average capacity decay rate of 0.069%per cycle.Mainly due to the one-dimensional tubular structure can accelerate the ions and electrons transfer,the structure of the hollow tube can suppress the LPSs by physical,the CoSe₂ coated on carbon nanotubes surface can suppress the shuttle of LPSs through chemical adsorption and accelerate its conversion,so the electrode show excellent electrochemical performance.（2）Hollow carbon spheres were prepared by polymerization and heat treatment using silicon spheres as templates.CoSe₂/Se were loaded on the hollow carbon spheres.CoSe₂/Se/HCS/S electrode materials were prepared by loading sulfur and used as the S host for LSBs.CoSe₂/Se/HCS/S electrode exhibits excellent electrochemical performance because of the 3D sea urchin-like structure,which is conducive to the transmission of electron and ion,CoSe₂ loaded on the surface inhibits the shuttle of LPSs,and the hollow carbon spheres can inhibit the volume expansion in charging and discharging process.The electrode presents a high initial specific capacity of 1012 m A h g^-1 at 0.5 C,and the specific capacity remains at 511 m A h g^-1 after 400 cycles.（3）Co/CC composite S host was prepared by loading Co atoms on carbon cloth by solvothermal method.At first,the specific capacity of the Co/CC-S electrode can be kept at 396 m A h g^-1 after 300 cycles at 0.5 C.The excellent electrochemical performance of the material is attributed to the overall network structure of Co/CC,which is conducive to electron and ion transport.Co on the surface can enhance the polarity of the host,improve the adsorption of LPSs,and accelerate the transformation of polysulfide.（4）NiCoSe/CC S host was prepared by a simple solvothermal methode.Due to the honeycombed structure of NiCoSe/CC can facilitate electron and ion transport,NiCoSe on carbon fiber surface can inhibit the shuttle effect of LPSs through chemisorption and accelerate its transformation,so the NiCoSe/CC/S electrode exhibits excellent electrochemical properties.At 0.5 C,the electrode delivers a high initial specific capacity of 805 m A h g^-1,and after 200 cycles,the specific capacity remains at 590 m A h g^-1.