Synergistic Catalysis And Adsorption Of Polysulfide By Composite Electrode With Heterogeneous Structure

lithium-sulfur batteries are considered to be the most promising secondary batteries because of its outstanding advantages such as high energy density（2600Wh/kg）and high theoretical specific capacity（1675 m Ah/g）.In addition,the active material sulfur has the advantages of non-toxicity,environmental friendliness and abundant reserves,which can help solve the current problems of high cost and unsafe lithium-ion batteries.However,the"shuttle effect"of lithium-sulfur batteries,sulfur insulation and volume expansion during charging and discharging,have severely restricted the commercialization of lithium-sulfur batteries.This paper mainly adjusts the adsorption and catalysis performance of positive electrode material for lithium polysulfide to inhibite the“shuttle effect”on the lithium sulfur batteries.Finally,we quantifies the ratio of adsorption and catalysis to the electrochemistry of the battery through experimental and theoretical calculations.The performance provides experimental and theoretical basis for proving the synergistic effect of catalysis and adsorption of lithium-sulfur battery cathode materials.The main content of this paper:（1）The MoS₂@C composite material was synthesized by hydrothermal method.In order to better utilize the adsorption performance of MoS₂for lithium polysulfide,effectively enhance the conductivity of MoS₂,thereby improving the catalytic conversion performance of the material.The annealing at 800°C makes MoS₂ form a C-S bond with the C matrix,which greatly improves the catalytic conversion performance of MoS₂.The MoS₂@C composite material greatly improves the catalytic conversion performance of MoS₂ on the basis of good adsorption through bond formation,so that the material can batter realize the synergistic effect of catalysis and adsorption,and effectively inhibit the shuttle effect.The electrochemical test results show that the initial capacity reaches 1211 m Ah/g at a rate of 0.5 C,700 cycles in a stable cycle,the capacity can still reach 1050 m Ah/g,the capacity attenuation per cycle is only 0.02%,and the coulombic efficiency always remains at 98%the above.（2）The sandwich-like TiN/VN heterostructure was prepared by the melamine thermal carbon reduction method.The TiN in the center has excellent electron transfer ability and regulates the electron conduction of the entire material.The VN in the outer layer provides more for the redox reaction.Active sites enable the entire material to smoothly complete the process of adsorption-transformation-deposition.The electrochemical performance was tested.It has an initial capacity of 1221 m Ah/g at a rate of 0.5 C.After 500 cycles,the capacity can still be maintained at 1098 m Ah/g,the capacity attenuation per cycle is only 0.042%,and the coulombic efficiency has been maintained.Above 99%,it proves that the material has very good reversibility properties.（3）A series of heterostructures of TiO_2-x/TiN heterostructures,Ti₄O_7-x/TiN heterostructures and Ti₃O_5-x/TiN heterostructures were prepared by the method of melamine thermal carbon reduction.The electrochemical performance of the battery was optimized by adjusting the proportion of their adsorption and catalytic materials,and the influence of adsorption and catalysis on the electrochemical performance is quantified through the DFT calculation method,and finally it is determined that the Ti₄O_7-x/TiN with the best adsorption-catalysis coordination has the best electrochemical performance.At a rate of 1 C,the initial capacity reaches 1219 m Ah/g.The capacity attenuation per cycle is only 0.032%in 500cycle,and the coulombic efficiency of the battery is always stable above 99.4%,which effectively proves Ti₄O_7-x/TiN heterostructure has good cycle stability.