Research On Preparation And Performance Of Self-Supporting Cathode Materials In Lithium Sulfur Battery

As one of the new energy storage systems,lithium sulfur battery has the advantages of high theoretical specific capacity(1675 mA h/g)and energy density(2600 Wh/kg),low cost,environmental friendly,rich resources,which shows a broad application prospect in the field of energy storage.The traditional electrode slurry coating process greatly reduces the sulfur surface load due to the addition of conductive agents,binders and current collectors,which seriously limits the energy storage density of lithium-sulfur batteries.The key to improve the energy density and cycle performance of lithium sulfur battery is to design and develop high sulfur density and surface load cathode materials.Based on the biomass carbon matrix,this paper explored the preparation and electrochemical performance of pomelo peel with three-dimensional structure and paper with interwoven network as self-supporting integrated electrode of lithium sulfur battery,providing ideas and basis for the construction of other biomass self-supporting electrodes.The main research contents and results are as follows:(1)Porous carbon was prepared from paper and pomelo peel by pyrolysis and carbonization,respectively.The effects of the preparation process on the micro morphology and electrochemical properties of pomelo peel based and paper-based powder porous carbon materials were explored.The experimental results show that the powder porous carbon material prepared by carbonization activation process has higher specific surface area and richer pore structure,which provides space for the storage of active material sulfur and more active sites for electrochemical reaction.After being loaded with sulfur by the thermal melting method,it is used for the electrochemical test of the lithium-sulfur battery cathode.The electrochemical performance of the carbon/sulfur composite material prepared by the carbonization activation process is superior to pyrolysis carbonization.The results of morphology and performance analysis show that the porous carbon materials prepared by carbonization activation process is more suitable to be used as the matrix materials for loading active material sulfur,improving the electrochemical performance of the battery,and laying a good foundation for the preparation of self-supporting electrode.(2)Based on the lamellar structure of pomelo peel and paper,the carbon/sulfur composite self-supporting electrode material was prepared by pretreatment and carbonization activation process,which well preserved the network and three-dimensional pore structure of biomass.The results show that the biomass based self-supporting electrode material has the following advantages:①The preparation method is simple and low cost,and its preparation process and cost are better than those of traditional graphene,carbon nanotubes and other self-supporting electrodes;②The biomass based self-supporting electrode can be directly used as binder-free integrated lithium-sulfur battery cathode materials,which have rich pores and layered interweaving structure,which can realize high load of sulfur and provide sufficient space and active sites for electrochemical reaction;③Cycle performance of the paper-based selfsupporting electrodes has been greatly improved compared with the powder carbon electrode(capacity retention rate of 49.17%for 100 cycles).However,due to the lack of effective binding to polysulfide due to its open pore structure,the capacity of pomelo peel based self-supporting electrode decays rapidly,and its specific discharge capacity and cycle performance still need to be improved.(3)In order to further improve the conductivity and cycle stability of the self-supporting electrode,based on the structure of biomass self-supporting carbon matrix,graphene coated biomass based self-supporting electrode was prepared.Graphene coating improves the conductivity of the matrix material,and uses the oxygen-containing functional groups in graphene to improve the adsorption performance of poly sulfide.The results of electrochemical performance test showed that at the current density of 0.1 C,the first discharge specific capacity of pomelo peel based carbon/graphene/sulfur self-supporting electrodes was 1516.23 mA h/g,and the capacity was maintained at 934.13 mA h/g after 100 cycles,with a significant capacity retention rate(61.61%).The paper-based carbon/graphene/sulfur self-supporting electrodes has a specific discharge capacity of 1364.68 mA h/g for.The capacity remains at 860.04 mA h/g after 100 cycles,and the capacity retention rate is as high as 63.02%.Graphene coating greatly improves the discharge specific capacity and cycle performance of the battery.