Modification Of Cathode Materials And Flame Retardant Additive For Lithium Sulfur Battery

In addition to the high specific capacity,as active material,sulfur has the advantages of natural abundance,low cost,and environmental friendly.However,the poor electronic conductivity,dissociation of discharge products and safety problems restricts its practical applications in lithium-sulfur batteries seriously.In this work,we focused on the study of pyrolyzed Polyacrylonitrile-Sulfur(pPAN/S)composite material for lithium-sulfur batteries.On one hand,the pPAN/S composite material which has a high sulfur content were coated in order to inhibit the dissolution of polysulfides and to improve the cycling performance of lithium-sulfur batteries.On the other hand,flame retardant additives was added to the normal electrolyte which not only reduced the electrolyte’s flammability but also improved the cycling and rate performance of the lithium-sulfur battery.pPAN/S composite material particles was coated with a layer of silicon dioxide、titanium dioxide and polypyrrole.SEM showed that the edges of composite material particles formed a uniform coating layer after silicon dioxide coated.The coating silicon dioxide layer could not only inhibited the dissolution of polysulfides,but also restrained the agglomeration of active materials particles during cycling.After being coated a layer of titanium dioxide,the surface of active materials particles also had a uniform coating layer.However,the coating layer had no influence on the performance of batteries.Due to the good electrical conductivity of polypyrrole,the active materials coated with polypyrrole had a better cycling performance.(Ethoxy)pentafluorocyclotriphosphazene(PFPN)with different mass fractions were added into the normal electrolyte,and we found that the additive amount of 3wt%PFPN could effectively retard and even eliminate flammability of the normal electrolyte when added 5wt%PFPN.In addition,the cycling and rate performances of batteries were significantly improved.When added 3wt%PFPN into the normal electrolyte,the batteries could cycled stably at 2C.EIS tests indicated that the addition of PFPN could reduce the interfacial resistance and the charge transfer resistance.TEM and XPS datas showed that PFPN optimized and stabilized the SEI film in the surface of the composite material and benefited for the migration of Li~+ion in the SEI film.Therefore,PFPN is a versatile electrolyte additives for rechargeable lithium sulfur batteries.