Study On The Cathode Material Of Lithium-sulfur Battery And Its Electrochemical Performance

With the rapid development of intelligent communications and electric vehicle industry,it is imminent to develop a new high energy density secondary battery system.Lithium-sulfur battery is a very promising energy storage system due to high energy density and low material costs.However,the lithium-sulfur battery due to shuttle effect and volume changes and other issues constraints,faces challenges to be used widely.In this paper,different methods were used to fabricate conductive materials with different structures and functions.Through the combination of sulfur and conductive materials,the conductivity of sulfur electrode was improved,the dissolution of intermediate product was restrained,and the performance of the battery was improved.N-doped porous carbon(LSC)was prepared as a sulfur-loaded support using green-friendly biomass material—loofah(LS).Sulfur is immersed in the LSC by a melt diffusion way to obtain LSC/S composites.The effects of KOH concentration and temperature on the preparation of LSC were studied,and the optimal preparation conditions for LSC were obtained.It was found that when LS was soaked in 8 M KOH solution at 120 ?,the as-prepared LSC after carbonizing possessed uniform pore structure and large specific surface area.LSC/S composites assembled Li-S battery after electrochemical performance test,the results show,the initial discharge capacity of LSC/S composites reached 1531.6 mAh/g at 0.1 C,the specific capacity can be maintained at 802 mAh/g after 100 cycles with the coulomb efficiency above 97%.The polypyrrole/sulfur composites were prepared by one-step deposition in situ.Chemical oxidation polymerization was used to prepare conductive polypyrrole with ammonium persulfate as oxidant,ethanol as dispersant,then in situ deposition of coated sulfur.The effects of the reaction ratio of ammonium persulfate and pyrrole monomer and the reaction time on the preparation of PPY/S composites were studied,and the optimum conditions for the preparation of PPY/S composites were obtained.The results showed that when the ammonium persulfate and pyrrole were reacted in a ratio of 1:1 for 12 h,the PPY/S composites showed a uniform distribution of core-shell structure.PPY/S composite assembled Li-S battery after electrochemical performance test,the results show that,the first discharge capacity of 985.8 mAh/g at 0.1 C,and the remaining specific capacity of 473.2 mAh/g after 50 cycles with a coulombic efficiency of over 97%per cycle.