Research On Cathode Material Of Lithium Sulfur Battery

Lithium sulfur batteries（LSBs）are considered to be one of the most hopeful as the next-generation energy storage system to replace lithium ion batteries,due to their high energy density,environment friendliness and low cost.Despite these advantages,practical applications of LSBs are still impeded mainly due to their multiple intrinsic nature,including:（1）The insulation of elemental sulfur and its discharge product Li₂S/Li₂S₂ leads to low utilization of active materials;（2）Volumetric expansion of S to Li₂S upon lithiation leads to poor cycling stability;（3）The shuttling effect caused by a series of polysulfide dissolved in electrolyte during the discharge/charge process.These issues often accompany each other,restricting the practical application of LSBs.In order to solve these problems,we consider three parameters which are polarity,porosity,and conductivity to design two sulfur host materials for LSBs,HSS@FePS3and Ni₃（HITP）₂/S composite.We use a series of test methods to analyze and explore the reasons for this performance.The results are as follows:（1）Hermetically encapsulating sulfur by FePS₃ flakes for high-performance lithium sulfur batteries:we adopt exfoliated FePS₃ flakes,and fabricate a core-shell composite with hollow sulfur spheres encapsulated inside which hold a high sulfur content of⁸0wt%for LSBs.The electrochemical performance suggests that HSS@FePS₃ cathodes are as high as 1391 mAh/g at 0.1 C,comparing the electrochemical performance of HSS cathodes.It shows a capacity retention ratio of54%after 1000 cycles even at 1 C.The results show that the HSS@FePS₃ cathodes have a batter electrochemical performance,improving the cycling stability and rate performance.（2）Conductive Ni-MOF（Ni₃（HITP）₂）/S composite materials for high-performance lithium sulfur batteries:The Ni₃（HITP）₂/S composite is prepared by melt-diffusion method.Compared with the ordinary sulfur elemental material,the results show that the Ni₃（HITP）₂/S composite cathodes has a specific capacity of 1050 mAh/g for the first time discharge at a current density of 0.5 C,and it is much higher than that control group of 750 mAh/g.The capacity decreases slowly after that and it has 551mAh/g after 200 cycles.Even at a large rate of 1 C,the capacity retention rate is still68%after 500 cycles.The Ni₃（HITP）₂/S composite materials could reduce battery resistance and improve cycling performance and rate performance.This article has 37 figures,2 tables and 108 references in this paper.