The Preparation And Electrochemical Performance Of Cathode Composite Materials With Graphene For Lithium-Sulfur Battery

Lithium-sulfur batteries (Li-S batteries) will be one of the most promising the next generation secondary batteries because of their low production costs but high capacities, and graphene is regarded as the ideal substrate at the cathode composites for lithium-sulfur battery due to its excellent electrical conductivity and large specific surface area. This dissertation explores various sulfur-carbon composites with novel configurations on cathode composite materials for lithium sulfur battery, including Sulfur-graphene oxide composites (S/GO), Sulfur-reducted graphene oxide composites (S/rGO), Sulfur-carbon nanotube composites (S/CNTs), Expanded graphite-Sulfur-carbon nanotube composites (EG/S/CNTs) composites, and TG/DSC, XRD, SEM measurements were used to testify the feasibility of the synthetic composites as cathode materials for rechargeable Li-S batteries.S/GO composites were prepared by in-situ redox method in aqueous solution. The influence of preparation parameters on the characteristic and the electrochemical performance of composites were investigated, and the optimized preparation paremeteers through the results were obtained. The composite through this method, exhibits a specific capacity up to 660mAh·g-1 at the initial discharge at 100mA·g-1, and the specific capacity remained above 250mAh·g-1 after 100 cycles. Then we prepared S/rGO composite by hydrothermal which shows the low degree of reduction and seriously S-reunion structure, and the electrochemical properties of the electrode material are not significantly improved correspondingly.Then we prepared the S/CNTs composites by in-situ redox method at the same to make the sulfur particles nucleate and growth uniformly on the surface of CNTs, after that the composites were heated in vacuum atmosphere to make the sulfur particles into the interior of CNTs by absorption. The composites show improved electrochemical performance, and serious shuttle-effect during cycling due to the limited space-confinement effect to sulfur. So we let S/CNTs and an amount of EG dissolved in CS2, and stirred the solution follow with evaporation, then CNTs precipitated on the surface of EG uniformly and intercalated into EG to form a good three-dimensional conductive network structure, which reduced the accumulation of EQ and form an integrity porous structure, which can improve the utilization of sulfur and play a good role in limiting polysulfide to dissolve in the electrolyte. We studied the characteristic and the electrochemical performance of composites prepared with different sulfur content and proportions of carbon composites, the result shows when we prepared the composites on the sulfur content of 70% and EG:CNTs=4:1, the composites have the best electrochemical performance, which exhibits a specific capacity up to 760 mAh·g-1 at the initial discharge at 100mA·g-1, and the specific capacity remained above 500mAh·g-1 after 100 cycles, and still continue to rise.