Application Of Modified Porous Carbon In Lithium-Sulfur Batteries

In recent years, the application of lithium-ion batteries（LIBs） has been evolving from mobile electronics to large-scale energy storage and electric vehicles. However, the traditional LIBs have almost approached their theoretical energy densities and cannot meet the increasing demand. Advanced rechargeable batteries with higher energy-density and lower cost are in urgent need. Lithium-sulfur battery has been widely believed as one of the most promising successor of LIBs due to its high theoretical energy density of 2600 Wh kg-1, the low price and nontoxicity of raw materials. However, the ultralow electrical conductivity of sulfur, high volume expansion rate（80%） when sulfur transforms to Li2S during discharging, and diffusion of the soluble long-chain polysulfides（Sn2-, 3≤n≤8） intermediates in electrolyte, lead to low sulfur utilization and short lifespan of lithium-sulfur battery, which makes it beyond commercial application.In this paper, two research work was carried out aiming at addressing the main problems of lithium-sulfur:（1）polysulfides(S_n^2-, 4≤n≤8) intermediates tend to diffuse into electrolyte from the pores of carbon matrix, which lead to a poor cycle performance. To address the problem,we design a novel KB@C structure with rich hollows inside. The synthesis is easy and low-cost. The KB@C structure achieves a largely improved capacity retention ratio of 81.55% over 200 cycles, while only 37.37% for the original KB.（2） SnO₂ powder shows remarkable adorability for polysulfides（Sn2-, 4≤n≤8） intermediates in our experiment. To make the best use of SnO₂, a composite structure of porous carbon and SnO₂（HPC@SnO₂） was synthesized, which was applied as cathode additive or modifier for separator（or called “interlayer”）, respectively. It shows that SnO₂ can works as a higher-efficiency polysulfide adsorbent in interlayer than in cathode,with a capacity decay rate of 0.19% and 1.09%, respectively.