Preparation Of CoS₂/rGO Composites And Their Application In Lithium-sulfur Batteries

High performance lithium sulfur(Li-S)batteries are gaining increasing attention as one of the most promising candidates for next generation energy storage systems.However,the insulating property of sulfur and lithium sulfide(Li₂S),the large volume change of sulfur cathode during charge/discharge process,and the shuttle effect and slow conversion kinetics of lithium polysulfide(Li PSs)lead to low sulfur utilization and poor electrochemical performance of Li-S batteries,which seriously hinder the commercial development of Li-S batteries.Cobalt disulfide(Co S₂)has been proved to have a strong chemical bond with Li PSs to effectively capture Li PSs on the surface and then catalyze the transformation from soluble Li PSs(Li₂S_n,4?n?8)to insoluble Li PSs(Li₂S₂/Li₂S),thus enhancing the redox kinetics of Li PSs.However,the electrical conductivity of Co S₂ is relatively low,and it is easy to agglomerate in the form of particles,resulting in the decrease of adsorption active sites.In order to solve the above problems,cobalt disulfide/graphene(CoS₂/rGO)composites were prepared by combining reduced graphene oxide(r GO)and Co S₂ nanoparticles with high conductivity and high specific surface area.The effects of CoS₂/rGO composites as modified separator functional interlayer and self-supporting sulfur cathode on the cycle performance of Li-S battery were investigated.The specific research contents are as follows:(1)The CoS₂/rGO composites were prepared by efficient microwave hydrothermal method and coated on commercial polypropylene(PP)separator as a functional interlayer to limit the shuttle effect to improve the electrochemical performance of Li-S batteries.The uniform CoS₂/rGO functional interlayer can immobilize the soluble polysulfides on the positive side and inhibit the shuttle effect of polysulfides by physical adsorption and chemical adsorption.And the coating layer can also act as the second current collector to reduce the internal resistance of the battery and help to speed up the kinetics of redox reaction.Therefore,the Li-S battery with CoS₂/rGO modified diaphragm has 60%capacity after 100 cycles at 0.2C,and shows good rate performance(0.1 C-2 C).At the current density of 0.5 C,the first discharge capacity of Li-S battery with CoS₂/rGO modified separator is 963.2 m Ah g^-1,and the capacity decay rate per cycle is only 0.08%after 400 cycles.(2)A self-supporting CoS₂/rGO aerogel was constructed as sulfur carrier for adsorption/electrocatalysis by a simple hydrothermal method to improve the electrochemical performance of Li-S batteries.Co S₂ nanoparticles grown uniformly on r GO sheets have strong trapping ability for Li PSs and catalyze its transformation,which accelerates the reaction kinetics and significantly suppresses the shuttle effect.Highly conductive three-dimensional porous r GO aerogels ensure rapid ion and electron transfer for electrocatalytic processes and electrochemical reactions.The results show that the electrode has a high initial capacity of1457 m Ah g^-1 at 0.2 C,a high rate capacity of 1156 m Ah g^-1 at 2 C,and a low capacity attenuation rate of only 0.04%for 400 cycles at 1 C.it also shows a high area capacity of 5.7m Ah cm^-2(high sulfur load is 6.37 mg cm^-2).