| With the increasing demand for sustainable energy supply,finding an electrochemical energy storage device with high energy density,high theoretical specific capacity,and green environmental protection has become an urgent task.Lithium sulfur batteries have the characteristics of ultra-high theoretical energy density(2600 Wh kg-1),abundant reserves,and environmental friendliness,and are considered as the next generation of promising electrochemical energy storage devices.Although using lightweight carbon materials as sulfur limiting carriers can effectively solve the problem of poor conductivity of sulfur cathode electrodes and increase the area loading capacity of sulfur,the low vibration density of carbon materials leads to a low volume energy density of sulfur cathode electrodes.More importantly,the lack of effective regulation of carbon materials in suppressing the shuttle effect of polysulfides and improving the catalytic conversion effect seriously hinders the practical application of lithium sulfur batteries.Although some materials with high solid density,such as metal oxides and metal sulfides,can effectively solve the problem of low stacking density of sulfur electrodes,their low conductivity can hinder electron transfer and ion diffusion rate.The enhanced polarity of metal nitrides and metal phosphides can effectively suppress the shuttle effect of polysulfides,and their high conductivity and strong catalytic activity can reduce the reaction barrier,accelerate the reaction rate,and improve the utilization rate of the active substance sulfur.Therefore,designing and preparing carbon based efficient catalytic sulfur limiting carriers loaded with metal nitrides and metal phosphides is of great significance for the practical application of lithium sulfur batteries.Based on the above ideas,this article designs two composite materials,carbon/vanadium nitride（C/VN）and carbon/molybdenum phosphide（C/Mo P）,as cathode limit sulfur carriers for lithium-sulfur batteries.The specific research results are as follows:（1）A high aspect ratio stepped C/VN composite material was successfully prepared through the impregnation roasting nitridation strategy.The metal organic framework（MOF）provides a high specific surface area and a large number of pores after carbonization,providing sufficient space for the uniform distribution of active substance sulfur.At the same time,the vanadium nitride uniformly loaded in the derived carbon pores,with its excellent catalytic activity and enhanced polarity,provides a large number of active site for the catalytic conversion of polysulfides,significantly speeds up the redox kinetics,and effectively inhibits the excessive dissolution of polysulfides in the electrolyte.After 100 cycles at a current density of 0.5 C,the initial discharge specific capacity of S@C/VN cathode electrode material reached 622.9 m Ah g-1;After 500 cycles at a high current density of 3 C,S@C/VN can still provide a discharge specific capacity of 370.3 m Ah g-1.（2）The embedded ultrafine Mo P nanoclusters C/Mo P composite material was successfully prepared using the impregnation freeze-drying phosphating strategy.After carbonization,Al-MOF has a high specific surface area and rich pore structure,allowing the active substance sulfur to be uniformly confined in these pores.The ultra-fine Mo P nanoclusters embedded in the pores not only effectively increase the catalytic area,but also provide rich active site for the catalytic conversion of polysulfides,and their reinforcement polarity effectively inhibits the shuttle effect of polysulfides.The C/Mo P composite material achieves dual physical and chemical adsorption of polysulfides.At a current density of 0.5 C,the S@C/Mo P sulfur containing cathode electrode exhibited an initial specific capacity of 950.8 m Ah g-1,and after 100 cycles,the discharge specific capacity was 734.2m Ah g-1;Even under lean electrolyte conditions with an E/S ratio of 5,after 100 cycles,the S@C/Mo P cathode electrode can still provide a discharge specific capacity of 365.4 m Ah g-1. |
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