Flexible Carbon-fiber Supported Carbon-sulfur Electrode:Preparation,Physical Property And Electrochemical Performance

Lithium sulfur battery has attracted extensive attention as highly promising next generation of rechargeable battery.However,lithium sulfur battery,especial the sulfur cathode,is still under experimental exploration.Many problems still limit its commercial development and practical applications,such as the low conductivity of elemental sulfur?Sulfur,S₈?and discharge products?Li₂S₂ and Li₂S?,the shuttle effect of intermediate polysulfide?LiPS?,and the safety issues caused by the lithium dendrites,as well as the volume expansion of cathode during charging and discharging.In view of the technical problems of the above lithium-sulfur battery,the main content of this thesis is the study of carbon/sulfur composite electrode,including the preparation of the flexible carbon fiber-supported carbon-sulfur composite cathode and CeO₂ modified porous carbon and its application in lithium-sulfur battery.1.The carbon fiber felt with a porous three-dimensional network structure and porous carbon with micro-porous structure were used to form a cathode support,which benefited the energy density of the battery and the conductivity of the sulfur cathode,as a result,the interface resistance was reduced from 97.9?to 22.6?.Furthermore,the initial discharge capacity at 0.05 C rate was996.7 mAh/g and the discharge capacity at 2 C rate after 140 cycles was 666.7 mAh/g when the carbon fiber felt serves as the current collector,while their counterparts with aluminum foil as the current collector were 772.9 mAh/g and 471.6 mAh/grespectively.What's more,the environmental and low-cost binder LA132,super-P and the ball-milling technique,beneficial to mass synthesis were used in this study,providing reference for the industrial production and the application of lithium sulfur battery.2.In order to further improve the electrochemical performance of lithium-sulfur batteries,the polar metal oxide CeO₂ was used to modify the micro-porous carbon.As results,the sulfide was chemisorbed and the redox reaction was promoted by the electrocatalysis of CeO₂.The CS-CeO₂composite?with 1.84 wt%CeO₂?exhibits significantly improved electrochemical performance as a cathode material for Li-S batteries.The initial discharge capacity of assembled battery is as high as1434.1 mAh/g at 0.05 C and the discharge capacity retains 873.6 mAh/g with a low decay rate of0.077%per cycle after 200 cycles at 0.2 C.