Preparation Of Multi-porous Carbon Materials And Their Application In Lithium-sulfur Battery Research

Lithium-sulfur battery with high energy density, light weight, environmentally friendly, extensive source of sulfur cathode material advantages concern. However, Lithium-sulfur batteries suffer some bottleneck problems:(1) The elemental sulfur and its discharge products are insulating at room temperature; (2) The dissolution of the poly-sulfides have shuttling effect. These factors have confined the application of lithium-sulfur batteries. Therefore, improving the conductivity of the sulfur electrode and inhibit the dissolution and loss of polysulfide, is particularly critical. In this thesis EDTA was selected as the carbon source, and multi-porous carbon(MPC) were prepared through a one-tep pyrolytic method and were heated treatment with sulfur obtain carbon/sulfur composites(C/S). The specific research contents and conclusions are as follows:(1) With EDTA as carbon source, KOH as the pore-forming agent, high surface multi-porous carbon obtained by high temperature carbonization. By analyzing the influences of the carbonization temperature and reactants proportion, synthesis an optimum condition of MPC materials were proposed and the specific surface area of up to 1457.1 cm3·g-1. Then the MPC materials were used as conductive substrate for encapsulating sulfur to form C/S composite. The resulting materials were characterized by XRD, charge/discharge test and electrochemical workstation. The results indicated that the C/S composite has the best electrochemical properties when the mass ratio EDTA to KOH is 2:1 and the carbonization temperature is 600?:In the 0.2 C rate initial discharge capacity of 863.4 mAh·g-1,50 cycles remained at 758.7 mAh·g-1(2) Based on the Content (1), the influences of doping metal ions on the structure and electrochemical properties of MPC/S cathode were investigated. It was found that the MPC-Fe5 wt%/S composite have the best electrochemical properties. The initial discharge capacity at of 1471.5 mAh·g-1 at 0.1 C, when the current density increases to 2 C when its capacity is 429.6 mAh·g-1; And the initial discharge capacity of 666.9 mAh·g-1, after 100 cycles, the discharge capacity has remained 559.1 mAh·g-1 at 0.5 C. Meanwhile, MPC-Co25 wt% as surporter, we research the influences of MPC-Co25 wt% and sulfur in different proportions for the electrochemicalproperties of MPC-Co25 wt%/S composites. The results indicated that the MPC-Co25 wt%/3S composite has the best electrochemical properties when the mass ratio MPC-Co25 wt% to sulfur is 2:3. After 50 times cycles at 0.2C, MPC-Co25 wt%/3S remained discharge capacity of 533 mAh·g-1(3) The influences of doping N element on the structure and electrochemical properties of MPC/S and MPC-Co25 wt%/S composites were investigated. Electrochemical performance results show that the N-MPC-Co25 wt%/S composite show higher capacity and initial capacity of 916.5 mAh·g-1 is obtained at 0.2 C, when cycled at 0.2 C with 83.7% capacity retention after 50 cycles.