Preparation And Properties Of Porous Cathode Composite Material For Li-S Battery

Li-S Secondary battery consisted of the element sulfur or sulfide as the positive electrode, and the metal lithium as the negative electrode. The theoretical specific capacity of Li-S battery is up to 1675 mAh/g, and the theoretical energy density is 2600 Wh/Kg, which is considered to the most promising energy storage device in the future. In addition, the elemental sulfur has the advantages of abundant reserves, low price, and environmental friendliness. However, the Li-S battery is still faced with many problems:(1) the elemental sulfur is not conductive, resulting in the poor conductivity of cathode material; (2) the polysulfide lithium coming from the reaction of sulfur with lithium is easily dissolved in the electrolyte, and will result a "shuttle effect", finally decrease the utilization rate of active sulfur material and cycle stability of battery. Otherwise, Li2Sx precipitates on the surface of lithium anode, perhaps will prick the separate of battery; (3) During sulfur reduceing the lithium polysulfide, a volume expansion of 70% will produce. In this paper, the performance of Li-S battery is improved by changing the carbon structure of cathode material and metal oxide doping. Main research work as following:(1) We prepared the porous carbon by hard template method, and changed the ratio of sulfur to carbon so as to study the effect of sulfur to carbon ratio on the sulfur/carbon composite cathode materials of Li-S battery. The results show that when S:C is equal to 4:1, sulfur/carbon composite cathode materials is assembled into a battery, and its initial discharge capacity and after 100 cycles are 1390 mAh/g and 520 mAh/g at 0.2 C. The cyclic stability in three ratios are the best (S:C=3:1,4:1, 5:1).(2) D-glucose is as carbon source, and nano calcium carbonate is as template for the preparation of porous carbon with different template ratio.The effects of template ratio on Li-S battery properties are studied. The results show when the ratio of glucose to calcium carbonate is 4:4, the specific surface area of porous carbon is maximum (1437.51 m2/g). The battery initial discharge capacity assembled with this sulfur/carbon composite cathode materials is the highest (1480 mAh/g), after 100 cycles it still can maintain 600 mAh/g at 0.1 C.(3) D-glucose and polyvinyl alcohol were as carbon source, and two kindes of porous carbon were prepared with the same template ration. The results show that the battery performance of sulfur/carbon composite cathode materials with D-glucose as porous carbon source is the best, its initial discharge capacity is 1390 mAh/g, after 100 cycles it can still keep 520 mAh/g at 0.2 C.(4) Cu2O is doped in S/C cathode materials with different content.The results show that the cycle stability of battery inserted 10%Cu2O is the best. The electrochemical performance of the battery (MC-Cu2O(10%)-S) is best at 0.2 C, its initial discharge capacity is 1500 mAh/g, and it still keeps the 700 mAh/g after 100 cycles.