Study Of Transition Metal Sulfide/Graphene Composite Cathode Materials For Lithium-Sulfur Batteries

Lithium–sulfur batteries have garnered considerable attention in the last several years owing to their good potential in portable electronic devices and electric vehicles.But if it is commercialized,there are still many problems to solve.For the cathode,there are mainly"shuttle effect",poor conductivity and volume expansion.The first step in the commercialization of lithium–sulfur batteries is the logical design of a sulfur cathode.The graphene with excellent conductivity and the transition metal sulfide(CoS,NiS₂,CuS),which has strong interaction with the lithium sulfide,are introduced into the sulfur cathode material.The structure of graphene-transition metal sulfide is rationally constructed and the nanocomposite cathode material of graphene sulphur transition metal sulfide is obtained.Hence,in this paper,we mainly synthesized CoS/G/S?NiS₂/G/S?CuS/G/S composites based on micro-nano structured structure and researched the electrochemical performance.1.In this paper,we fabricated that polar CoS nanosheets directly grown on graphene as conductive nanostructured sulfur cathode to enhance the performance of Li-S batteries.As a result,CoS/G/S composites electrode can buffer volume expansion and suppress polysulfide diffusion effectively due to the rational structure of composite and stronger ability to adsorb to lithium polysulfides.We have demonstrated the strong chemical binds between CoS nanosheets and lithium polysulfide species.Due to CoS nanosheets reduced the charge transfer resistance and trapped lithium polysulfide,and excellent electrical conductivity of graphene,the battery maintains a higher specific capacity of 300 m A h g^-1 after 150 cycles at a rate of 1.5C with a Coulombic efficiency of about 97%.This work proved the CoS/graphene nanosheets can enhance the cycling stability,rate capacity and improve the utilization of sulfur of high-energy lithium sulfur batteries.2.Polar NiS₂ nanoparticles were directly grown on graphene as conductive nanostructured sulfur cathode to enhance the performance of Li-S batteries in this paper.As a result,NiS₂/G/S composite electrode can buffer volume expansion and suppress polysulfide diffusion effectively due to the rational structure of composite and stronger ability to adsorb to lithium polysulfides.We have demonstrated the strong chemical binds between NiS₂nanosheets and lithium polysulfide species.Due to NiS₂ nanoparticles catalyzed electrode reaction and trapped lithium polysulfide,and excellent electrical conductivity of graphene,the NGS95 maintains a higher specific capacity of 400 m Ah g^-1 after 800 cycles at a rate of 1.0 C with a Coulombic efficiency of about 98%.This work proved the NiS₂/G/S can enhance the cycling stability,rate capacity and improve the utilization of sulfur of high-energy lithium sulfur batteries.3.In order to improve the performance of the lithium sulfur battery,the Cu-MOF is used as a template to combine the CuS nanoscale with the graphene in situ,and it is used as the compound sulfur cathode of the lithium sulfur battery.At the same time,the sulfur content of the positive pole is further raised to about 80%.Using CuS nanoscale as an adsorbent for lithium sulfides,graphene enhances the conductivity of the sulfur positive pole,and the CuS nanoscale and graphene form a lamellar structure,and a reasonable cathode of lithium sulfur battery is constructed.Because the CuS nanoscale and the lithium sulfur species have strong chemical binding and excellent conductive graphene,the discharge specific capacity of the battery is 950 m Ah g^-1 under 0.2 C,and the capacity attenuates to 850 m A h g^-1 after 200cycles,and the coulomb efficiency is about 98%.