Application Of Graphene/Copper Selenide Composites For Lithium-Sulfur Batteries

Conventional Li-ion battery electrodes rely on intercalation materials,severely limiting their energy density.Lithium-sulfur batteries have the advantages of extremely high theoretical energy density and low cost,and have been widely concerned by researchers.However,the scientific problems existing in the cathode of lithium-sulfur batteries,including the insulating properties of sulfur and sulfides（Li₂S,Li₂S₂）,the shuttle effect of polysulfides,and the low sulfur utilization rate,have resulted in the low capacity and poor rate performance of Li-S batteries for practical applications.Especially in the case of high sulfur loading,the slow redox kinetics of the cathode severely limits the further development of lithium-sulfur batteries.In order to solve the above problems,a continuous electron and Li⁺ion transport channel should be constructed in the sulfur cathode,while the anti-shuttle barrier of the cathode should be designed through strong chemical bonding and effective physical adsorption.Therefore,the structural design and functional modification of cathode-side materials for lithium-sulfur batteries have been widely reported,such as the design of host materials and electrocatalysts for sulfur cathodes with multiple constraints,the modification of separators,and the addition of interlayers.Based on this,we composited graphene nanosheets with excellent electrical conductivity and large specific surface area with different copper selenides as sulfur host materials for lithium-sulfur batteries and functional modification layers of separators,to discuss the effect of copper selenide on the electrochemical performance of sulfur cathode.CuSe@rGO aerogel composites with honeycomb-like pores were designed by hydrothermal method and freeze-drying method,and CuSe@rGO/S cathode composites were further prepared by solution diffusion method.CuSe@rGO has a large specific surface area of260 m²/g,which provides a stable and sufficient space for sulfur anchoring and catalysis,thereby improving the overall redox kinetics of the sulfur cathode.Benefiting from the above advantages,the CuSe@rGO/S cathode achieves better electrochemical performance.After 400cycles at a current density of 1 C,the average decay per cycle is about 0.07%,while the capacity retention rate is 82%under 300 cycles at 2 C,and the average capacity decay is only 0.055%per cycle.Even at a high rate of 5 C,the battery still has a reversible capacity of 605 m Ah/g.A graphene 3D cross-linked network Cu_2-xSe@rGO with uniform loading of Cu_2-xSe nanoparticles was further constructed as a functional modification coating for lithium-sulfur battery separators.The large specific surface area and a large number of pores facilitate the rapid ion transport of electrolyte infiltration,and have a good physical confinement effect on lithium polysulfides.Moreover,the loose graphene network is well adapted to the volume expansion of the sulfur cathode during the lithiation process,effectively preventing the waste of the active material of the cathode.The uniform Cu_2-xSe catalyzes the rapid and uniform deposition of Li₂S on the sulfur cathode,preventing the migration of polysulfides.Therefore,the lithium-sulfur battery with Cu_2-xSe@rGO separator modified layer shows an average capacity decay of about 0.059%per cycle after 500 cycles at 2 C.The reversible specific capacity was maintained at about 805 m Ah/g after 100 cycles at a high sulfur loading of 3.0mg/cm².This fully demonstrates the strong catalytic ability of copper selenide towards sulfur.