Preparation Of Cathode Materials For Li-S Batteries And Study On Their Electrochemical Properties

Lithium-sulfur（Li-S）batteries have been widely studied in recent years,but the utilization of the sulfur cathode is still limited due to the low conductivity of the cathode material and the dissolution of polysulfide.Therefore,a variety of double-coated composite cathode materials were designed in this paper,and the differences and electrochemical properties of single material cladding and composite material cladding were compared.（1）Firstly,RGO/S@PPy nanocomposites were synthesized by in situ liquid deposition and chemical polymerization.Firstly,GO was converted to reduced GO（RGO）by reaction with sodium sulfide and H⁺.At the same time,sodium sulfide reacts with GO and sodium sulfite to obtain sulfur elements and disperse evenly between RGO sheets.Finally,the pyrrole monomer was polymerized and coated on the surface of RGO/S composite to form RGO/S@PPy.The initial discharge specific capacities of RGO/S and RGO/S@PPy at 0.2c are1031.4 m Ah·g^-1 and 1046.3 m Ah·g^-1,respectively.RGO/S rapidly attenuated to 435 m Ah·g^-1after 200 cycles,while RGO/S@PPy remained 631 m Ah·g^-1 after 300 cycles,and the average capacity of each cycle decreased only 0.132%.After coating PPy,due to the good conductivity and unique functional groups of the conductive polymer coating can interact with polysulfide,the dissolution loss of polysulfide in the electrolyte is inhibited,so the cyclic performance and rate performance of the composite material are significantly improved.（2）Firstly,Porous Ti O₂ nanospheres were synthesized and coated with a layer of polypyrrole conductive polymer on the surface by in situ chemical polymerization of pyrrole.Ti O₂/S and Ti O₂/S@PPy composite cathode materials were obtained by melting with sulfur at155°C.The initial discharge specific capacities of Ti O₂/S and Ti O₂/S@PPy were 856.6 m Ah·g^-1 and 821.4 m Ah·g^-1,respectively,at 0.5 C.After 300 cycles of Ti O₂/S,the average capacity attenuation of each cycle is only 0.17%,showing a good cycling performance.However,Ti O₂/S@PPy still maintained 567.0 m Ah·g^-1 after 300 cycles,with an average capacity attenuation of only 0.103%per cycle.Under the synergistic action of Ti O₂ and PPy,cycling performance and rate performance were improved obviously.（3）Firstly,Si O₂ nanospheres were prepared,hollow carbon nanospheres were prepared by template method,and coated with a layer of Ti O₂ nanolayers on their surfaces.Then,they were combined with sulfur by 155°C melting method to obtain C/S@Ti O₂ composite cathode materials.At the discharge rate of 0.5C,the specific discharge capacity of C/S@Ti O₂ remains at 517.0 m Ah·g^-1 after 300 cycles,and the average capacity attenuation of each cycle is 0.105%.Due to the chemisorption of polysulfide by polar Ti O₂ coated on the surface,the cyclic stability of the sulfur electrode is more favorable.