Synthesis And Study On The Lithium Sulfur Battery Cathode Materials

With the increasing demand of the world energy consumption, Li- ion batteries(LIBs) have been widely used as the primary electrical energy storage devices in various portable electronics for their lightweight, high energy density and environment- friendly relative to others. Recently, the demand for secondary batteries has led to a corresponding increase as the rapid development of portable electronic, communication devices as well as the electric vehicle, especially for higher energy density. Lithium sulfur battery(Li-S) is regarded as one of the most promising systems for next generation batteries due to a high theoretical capacity of 1675 mAh g-1 and a higher specific energy of 2600 Whkg-1. However, insulating polysulfides formed as intermediates during discharge progress can dissolve easily into the electrolyte, which will result in shuttle phenomenon. These problems has affected the lithium-sulfur battery’s actual capacity and cycling performance. In this article a series of new carbon-sulfur composite have been synthesized and we did some exploratory study on its morphology, structure and electrochemical properties.(1) In this paper, we use 12 nm particle size silica as a template, ammonium persulfate as the oxidant, through direct oxidation method with proton acid doped to make aniline polymerization on silica. After carbonizing and etching, a mesoporous carbon material is obtained. This material has a rich mesoporous structure with average pore size of 11.874 nm. Each silica aggregated by polyaniline to form a larger group unit which size is 200 ~ 300 nm. Then an in-situ polymerization have been made on those mesoporous carbon material to prepared mesoporous / microporous composites. The resulting material has specific surface area of 640 m2·g-1, the pore volume of 1.4 cm3·g-1, pore rate of 19.8%. the microporous structure of a multi- stage pore structure is more abundant. A lot of mesoporous can play the role of sulfur storage and the outer microporous structure can inhibit the shuttle effect.(2) In this paper, we compound multi-stage pore carbon material with sulfur. Then coat it with polyaniline and CNT. The cladding layer being interspersed with abundant carbon nanotubes. Amorphous sulfur is present in the composite material of carbon and sulfur, sulfur is defined nanoscale pores to achieve a sulfur nano. Material has good conductivity, cycling stability and rate properties which contain 62.3%S. The initial discharge specific capacity of the composite can be 1221.8 mAh·g-1 at a current density of 500 mA/g. the composite cathode delivered a high initial capacity of 1151.7 mAh/g and maintained a reversible capacity of 816 mAh/g after 100 cycles at a current density of 500 mA/g. Even under 2000 mA/g current density, the discharge capacity can still retain at 600 mAh·g-1 after 100 cycles. Hence, the active material utilization and cycle life were remarkably improved compared with the tradition sulfur electrode.