Transition Metal Heterostructure Design ＆ Application Research Of Functional Separator For Lithium-sulfur Batteries

With the rapid development of new electronic devices and electric vehicles,the social demand for high energy density batteries is increasing.Lithium-sulfur batteries（Li SBs）have been the most potential next-generation high specific energy density batteries due to its high theoretical energy density of 2600 Wh/kg,low cost of sulfur and environmental friendliness.However,due to the"shuttle effect"caused by the dissolving of Li PSs in electrolyte and the slow electrochemical reaction kinetics between solid-liquid/liquid-solid phase,the conundrum of inferior cycle stability and low rate performance of Li SBs have seriously impeded the commercialization process of Li SBs.To solve the above problems,this paper studied from the aspect of separator and functional separator were modified by heterostructure composite materials.The synergistic strategy of"Adsorption-Diffusion-Catalysis"of functional diaphragm was used to effectively inhibit shuttle effect,accelerate the catalytic transformation of polysulfide,and ultimately improve the overall performance of Li SBs.The main content of the paper is as follows:（1）Fe₃O₄/Co₃O₄ heterostructure materials was fabricated by one-step method based on the controllable morphology and composition of Prussian Blue Analog（Fe-Co PBA）as precursor.The unique core-shell structure can accelerate the diffusion rate of Li⁺and play a physical limiting role on Li PSs.The presence of metal oxides in Fe₃O₄/Co₃O₄ can chemically anchor polysulfide,effectively accelerate the reaction rate in the cell,improve the utilization of active materials,and hinder the shuttle effect.The material modified in the separator can effectively inhibit the shuttle of polysulfide between positive and negative electrodes.After 500 cycles at 1 C rate,the attenuation rate is only 0.056%/per.After 1000cycles at a high rate of 2 C,the damping decrement is only 0.053%/per,which significantly improves the cycle stability of the battery.（2）Large-scale preparation of Fe₉S₁₀/Fe₃O₄@C heterostructure materials by spray drying technology combined with one-step carbon thermal reduction.The material is core-shell coated microsphere with clear heterostructure interface.DFT calculation strongly confirmed that Fe₉S₁₀/Fe₃O₄@C heterostructure polysulfide had excellent chemisorption capacity,and Fe₉S₁₀/Fe₃O₄@C heterostructure composite was used to modify the positive electrode side separator,which could significantly alleviate the shuttle effect of polysulfide The ration designed Fe₉S₁₀/Fe₃O₄@C heterostructure exhibits excellent cyclic stability based on the“adsorption-catalytic”synergy.After 500 cycles at 1 C rate,the capacity decay rate is only 0.08%/per.（3）Two-dimensional 1T-MoS₂/CoS₂ heterostructure was constructed by one-step hydrothermal method by introducing CoS₂.The introduction of CoS₂ induced the transformation of MoS₂ from 2H to 1T phase and the formation of heterostructure material,which significantly increased the content of 1T metal phase of MoS₂ in the material.The ion/electron transport in the 1T-MoS₂/CoS₂ heterostructure are enhanced,and the formation of heterostructure interface accelerates electron transfer at the interface.Combined with DFT calculation,the separator modified by this material has the synergistic effect of"adsorption-diffusion-catalytic"multi-functional coupling,and the battery performance,especially the large discharge performance,is significantly improved.At the high rate of 2C,the discharge capacity of the first lap can reach 817 m Ah/g,and the capacity decay rate of the single lap is only 0.034%after 1000 cycles.The high specific capacity of 726 m Ah/g is still maintained even at 5 C high rate.