Application Of Porous Carbon Materials In Lithium-sulfur And Lithium-selenium Batteries

The theoretical specific capacity of sulfur is 1672 mAh g-1. When sulfur cathode is coupled with lithium anode, the lithium-sulfur battery can demonstrate a theoretical energy density as high as 2600 Wh kg-1, and its practical application is about to be 2-5 times of the stateof-art lithium ion batteries. In addition, sulfur is abundant, low-cost and environmentally benign. Therefore, lithium-sulfur battery is regarded as one of the most promising candidate for next generation secondary lithium batteries with high energy density. Selenium, a congener of sulfur, can also be used as a cathode material, which can deliver a comparable volumettic capacity with sulfur, but a much improved conductivity, which promises higher material utilization and rate capability. From this aspect, lithium-selenium battery may have great potential in some special area requiring miniaturization and high power density. In this paper, some research work was carried out aiming at addressing the main problems of lithium-sulfur and lithium-selenium batteries, and it can be summariesd in two aspects.(1) A novel double-cathode configuration was orignally designed in order to combine the advantages of mesoporous carbon and microporous carbon when used as carbon matrixes for sulfur. In this new configuration, sulfur and microporous carbon composite(S/MiPCS) cathode was placed between the sulfur and mesoporous carbon composite(S/CMK-3) cathode and the separator. Impressive improvement of cycling stability was obtained by this simple configuration adjustment. Compared with S/CMK-3 single cathode cell, capacity retention of 50 cycles was improved from 28% to 70%.(2) Selenium and microporous carbon composite(Se/MiPCS) was syntheisized, and its electrochemical behavior was compared in ether- and carbonate-based electrolyte. It was found no polyselenides was formed in carbonated-based electrolyte due to “solid-solid” transition mechanism. Therefore, carbonate-based electrolyte is more appropriate for this new imerging cathode material. Electrochemical tests showed reversible capacity of Se/MiPCS was 707 mAh g-1, and capacity retention after 100 cycles is 72.8% with coulumbic efficiency always approaching 100% at 0.5C. In addition, Se/MiPCS delivers excellent rate capabity up to 12 C with a discharge capacity of 335 m Ah g-1.