Preparation And Electrochemical Performance Of Doping Mesoporous Carbon/Sulfur Material For Lithium Sulfur Batteries

Lithium-sulfur (Li-S) batteries have attracted researchers’attention due to its high specific capacity and large energy density. It is considered as one of the most promising next-generation secondary batteries. In spite of the above advantages, it still faces with several challenges to develop the Li-S batteries, including the low conductivity of sulfur and Li2S/Li2S2, poor cycle performance and rate performance, which derives from the shuttle effect. It needs to solve these problems for the application of Li-S batteries.In order to solve the above mentioned issues, a template method was adopted to prepare carbon materials as hosts with different pore sizes and element doping. The morphologies, structures and the electrochemical performance of materials were characterized using X-ray diffraction, X-ray photoelectron spectroscopy measurement, transmission electron microscopy and electrochemical work station. In our work, the carbon materials were prepared using SBA-15 as the template. They presented cross-linked rods and the morphologies were beneficial to the transport of ions and electrons. Carbon materials with different pore sizes were prepared by controlling the calcinated temperatures. The carbon materials with proper pore size and surface N-doping were prepared by mixing urea and the product via a step high temperature and metal doping flaky carbon material was obtained by using coordination complex as the template and directly calcinating the material..The results show that N-doping material can adsorb more active material and polysulfides because of its large specific surface area of 664.5 m2/g. It is confirmed that pyridinic nitrogen, pyrrolic nitrogen, graphitic nitrogen and C-S bonds are formed in carbon materials by XPS measurement. The modified carbon framework possessed partial positive charge which can adsorb the polysulfides. The results further indicate that N-doping materials can relieve the dissolution of polysulfides. Electrochemical tests show that N-doped carbon/sulfur materials exhibits a high initial discharge capacity of 1315.8 mAh g-1, and retains about 939 mAh g-1 after 100 cycles at 0.2 C. Furthermore, metal sulfide doping carbon/sulfur material also presents better electrochemical performance, it exhibits a discharge capacity of 1392.7 mAh g-1 and retains about 1037.5 mAh g-1 after 50 cycles at 0.2 C. The result is mainly attributed to the formation of Ni3S2 which can adsorb polysulfides.