Research On Preparation Of Cathode Material And Modification Of Functional Separator For Lithium Sulfur Batteries

With the widespread use of electric vehicles and various electronic devices and the continuous improvement of their performance,this has put forward new requirements for energy storage devices with high energy density.Lithium-sulfur batteries are expected to become the most promising battery system for the next generation by virtue of the advantages of high theoretical specific capacity,low cost,and environmental friendliness.However,lithium-sulfur batteries have various problems in practical applications.On the one hand,the poor conductivity of sulfur and lithium sulfide makes the utilization rate of the active material low.On the other hand,the dissolution and shuttle of polysulfides in the liquid electrolyte can lead to rapid capacity decay and poor cyclic stability.In this regard,this paper will use graphene aerogel as a cathode material and additives to modify the cathode and separator to improve the performance of lithium-sulfur batteries.Due to its excellent electrical conductivity and mechanical properties,graphene can be used as a conductive material for sulfur cathodes,improving the electrical conductivity of the cathode and encouraging active materials to participate in conversion.In this paper,a one-step hydrothermal method and soft template method were used to synthesize nitrogen-doped graphene aerogel.The graphene aerogel with great conductivity has a rich pore structure and nitrogen active sites,and can absorb polysulfides to participate in the reaction.After injecting elemental sulfur through the solvent penetration method,the prepared sulfur electrode was cycled at 0.5 C for 400times,and the discharge specific capacity was still maintained at 454 m Ah g^-1,and the average capacity decay rate per cycle was only 0.057%.The introduction of additives with adsorption effect on polysulfides into lithium-sulfur batteries can improve the performance of the battery.However,few people pay attention to the modification positions of the additives and the efficiency of the reaction.In this paper,Super P,Al₂O₃/SP and Pt/C materials are used as additives to modify the cathode and the separator.The results show that the battery modified with separator has better cycle stability and rate performance.At 0.5 C,the specific discharge capacity of the modified PP@Pt/C battery after 200 cycles was 586 m Ah g^-1,and the capacity retention rate was 57%,which was higher than the 518 m Ah g^-1 of the C-S-Pt/C battery and 436 m Ah g^-1 of PP battery.Compared with cathode doping,the material layer with great conductivity on the separator can be in close contact with the sulfur electrode to enhance conductivity,facilitate the conversion of polysulfides during cycling process,and improve the reaction efficiency.Moreover,the material layer can be stable on the separator during cycling,and it is not easy to peel off into the electrolyte.Separator modification can maximize the use of additives,improve the utilization of active substances and inhibit the shuttle effect of polysulfides.