Research On The Carbon-Sulfur Composite Materials For Lithium-Sulfur Battery

The demand for high energy density, long cycle life, low cost and environment friendly batteries inspires many scholars to search for new systems with prominent performance. The lithium-sulfur (Li-S) battery seems to be a good fit considering its abundant and low-cost active materials, environmental benignity, high theoretical gravimetric capacity and energy density. In spite of these outstanding advantages, realizing its full capacity is difficult due to the low conductivity (5×10-30 S cm-1 at 25℃) of sulfur, the intermediate polysulfides that form during the discharge/charge processes are easily soluble in the electrolyte. In addition, because of the different densities between sulfur and its discharge product Li2S, obvious volume expansion will appear during the cycling performance. To solve these issues, two kinds of carbon-sulfur composite materials have been synthesized in this work. Here comes the specific work:1. Four kinds of micron elemental sulfur have been prepared by proper liquid phase precipitation process according to the principle of the oxidation of thiosulfate by Fe3+.Through the analysis of surface morphology and electrochemical performance test, we determine the best preparation program.2. Different dispersants (PEG 2000, SDS, CTAB) are used to prepare carbon-sulfur composites via liquid phase precipitation method. The results shows that:materials synthesized with PEG 2000 exhibit the best electrochemical performance.3. A high sulfur content (82.5%) carbon-sulfur composite (P-SO3-AB@S) cathode material has been successfully synthesized by the hetero-generous nucleation of sulfur onto conductive sulfonated acetylene black (AB) with grafting PEG. The P-SO3-AB@S composite thus produced exhibits discharge capacities of 1166 mA h g-1 in the first cycle and 820 mA h g-1 after 100 cycles at 100 mA g-1, respectively.4. Using sucrose as the carbon source, after carbonization by concentrated H2SO4, the process of depositing sulfur and reduction by hydrazine hydrate, carbon-sulfur composite with a lamellar structure has been prepared.