Research Of Transition Metal Compound/Carbon Composite To Assist High-P Erformance Lithium-Sulfur Battery

In recent years,with the rapid development of small mobile electronic devices,power batteries and large-scale energy storage conversion systems,and the state’s emphasis on the development of new energy sources and higher standards have been proposed for the energy density of energy storage systems.Lithium-sulfur batteries are the focus of attention due to their absolute advantages in energy density.However,the problems of poor utilization of active materials,rapid capacity decay and low area capacity of lithium-sulfur batteries have cast a shadow over its application development.In this paper,lithium-sulfur battery with large discharge capacity,stable cycle performance and high area capacity is developed via combining physical confinement and chemical adsorption to suppress shuttle effect,constructing a highly-efficient and stable“conductivity-adsorption-catalyze”reaction interface to promote polysulfide conversion and designing high area capacity sulfur cathode.In order to slow down shuttle effect,the reduced graphene oxide coated hollow FePO4 nanospheres（FePO4@rGO）composites were designed and synthesized by low temperature hydrothermal method and electrostatic interaction,and used as sulfur host in lithium-sulfur batteries.Among them,evenly coated rGO provides an excellent conductive network.At the same time,the physical limitation to polysulfide by rGO coating and FePO₄ hollow spherical shell synergizes with the strong chemical adsorption toward polysulfide by FePO₄ itself,which effectively inhibits the shuttle effect and brings stable cycle performance.The capacity decay rate per cycle is only0.037%at 0.5 C after 1000 cycles.To enhance the polysulfide conversion kinetics to further limit shuttle effcet,a composite material in which NiCo2S4 nanoparticles were in situ grown on reduced graphene oxide sheets（NiCo₂S₄@rGO）was prepared by solvothermal method.And it was applied as a modified material on the PP separator of lithium-sulfur batteries to construct a highly-efficient and stable“conductivity-adsorption-catalysis”reaction interface to promote polysulfide conversion.Among them,the superior conductivity of rGO can ensure the rapid transmission of electrons on the interface.As the active center,NiCo2S4 nanoparticles can utilize strong chemical interactions to effectively capture polysulfides and then increase the kinetics of their conversion reactions.In addition,the multilayer structure of the coating layer can increase the efficiency of adsorption and catalytic polysulfide conversion and also provide an additional physical barrier to prevent migration of polysulfide to the anode.The reaction interface constructed by NiCo₂S₄@rGO strongly limits the dissolution and diffusion of polysulfide and slows down the shuttle effect,thereby obtaining good electrochemical performance.The capacity retention rate is 76%after 500 cycles at 1C,and it had a capacity of 680 mAh g^-1 even at a high current of 2 C.To achieve the lithium-sulfur battery with high area capacity,a NiCo₂S₄ array was grown on a nitrogen-sulfur-doped carbon cloth（NiCo₂S₄@NSCC）by a two-step hydrothermal reaction to act as a self-supporting sulfur host for lithium-sulfur battery.The doped carbon cloth has an excellent three-dimensional conductive skeleton,which can accelerate electron conduction.Its large specific surface and pore volume can bring a large amount of sulfur storage space,and the rich pore structure has physical limitation on the diffusion of polysulfide.NiCo2S4 arrays can efficiently adsorb polysulfides through strong chemical interactions and promote their conversion reaction,slowing their dissolution and diffusion.The excellent electrochemical performance was achieved with high sulfur loading of 3.5 and 4.9 mg cm^-2,and the reversible areal capacity of 3.5 and 4.4 mAh cm^-2 was obtained after 50cycles at 0.2 C.