Study On The Materials Used In Lithium/Sulfur Secondary Batteries

Sulfur-based cathode material is one of the most promising electrode materials for the next generation of high-performance secondary lithium battery which, in itself, is a kind of portable energy sources with wide application potential.In this study, sulfur composite materials were synthesized through heating the mixture of element sulfur and conductive polymer or carbon with a high specific surface area. It is concluded that such kind of composite materials have a good conductivity and can improve sulfur's electrochemistry performance well. However, the cycle performance of these materials was not as good as expected. To solve this problem, two kinds of research methods were designed and investigated.One hand, the former material was coated by cane sugar to make a new type of carbon-coated material. It is proved that the coated material has a better cycle stability while maintaining a comparatively high discharge capacity, and its capacity has exceeded the uncoated one after 50 cycles. Meanwhile, the influences of amount of cane sugar and heat treatment temperature were investigated as well. It is concluded that appropriate amount of cane sugar and relatively low heat temperature are helpful to improve the performance of coated material.On the other hand, since the components of electrolyte used in lithium batteries often have great influence on the electrochemical properties of sulfur cathodes, such influence was investigated by composing a series of electrolytes with LiTFSI and various solvent such as DOL, DME and DGM. It is proveed that the lithium/sulfur batteries using electrolyte of LiTFSI/DOL+DME+DGM ( 0.5:1:1 volume ratio ) show the best electrochemical performance among the selected ones. Not only did it have a high charge-discharge capacity, the battery also exhibited a good cycle stability. It is concluded that this new electrolyte can enhance the usage rate of sulfur material, restrain the dissolution of active materials and improve the electrochemistry performance of sulfur cathode materials.