Selenium-sulfur solid solution -Lithium - Ion Battery Equipment

Discovery of Selenium and Sulfur Solid Solution by China University of Science and Technology -Lithium - Ion Battery Equipment

Lithium-sulfur battery is a secondary battery with sulfur as the positive material and lithium metal as the negative electrode. Its theoretical specific capacity and theoretical specific energy of the battery are 1672 mAh - 1 and 2600 Wh-kg - 1, respectively. It is considered as one of the high-energy lithium secondary battery systems with the most research value and application prospects. However, there are still many problems to be solved for lithium-sulfur batteries at present, such as low cycle life, low utilization of active substances, and poor conductivity of sulfur cathode materials and their discharge products.

Recently, the research group of Qian Yitai and Zhu Yongchun of the University of Science and Technology of China has developed a new type of lithium sulfur battery cathode material, selenium sulfur solid solution. Based on the binary phase diagram of commercial sulfur powder and selenium powder, the researchers compounded them with the porous carbon prepared in the early stage of the experimental group to obtain sulfur-rich S1-xSex/C (x≈ 0.1, 0.08, 0.06, 0.05) composites with different proportions. The results showed that the prepared S1-xSex/C composite still showed excellent cycle stability and rate performance in the carbonate electrolyte: at the current density of 0.5Ag-1 for 500 cycles, the specific capacity remained at 1105 mAh g-1; Even at the high current density of 20Ag-1, the specific capacity reaches 617 mAh g-1. Through liquid phase Raman and X-ray photoelectron spectroscopy, it is found that there are stable selenium-sulfur bonds in S1-xSex/C composites before and after cycling. This research work not only reveals the stability mechanism of selenium-sulfur solid solution, but also lays a foundation for further research and development of other new cathode materials for lithium-sulfur batteries. Relevant research papers were published in Energy Environment. Sci., 2015, DOI: 10.1039/C5EE01470K, and were selected as the internal illustrations of the 11th issue of the magazine in 2015. The important authors of this paper are Li Xiaona and Liang Jianwen, postdoctoral fellows of the research group.

On the other hand, selenium cathode materials of the same group as sulfur have also attracted much attention in recent years. The research group developed a new salt baking method to pour selenium into porous carbon, which prevents the protection of inert gas or vacuum atmosphere, and to some extent prevents the temperature fluctuation during the heating process, which is conducive to pouring molten selenium into porous carbon, so that the proportion of active Se in Se/C composites is reduced from 36&ndash previously reported; 54% to 72%. The prepared Se/C composite showed excellent lithium storage performance: the capacity retention rate reached 95.7% after 1000 cycles at 1C. In the test of Na-Se battery, Se/C composite still showed good cycle stability. The salt baking method proposed by the research group can not only be used as a universal method to pour other low melting point materials into porous carbon substrate materials, but also is simple and easy to operate, which is conducive to expanding production and is expected to promote the further development of Li-Se, Na-Se and other related batteries. The relevant results were recently published in Advanced Functional Materials, and were selected as the highlight research report by MaterialsViewChina under Wiley. The first author of the paper is Li Xiaona, a postdoctoral fellow of the research group.(Lithium - Ion Battery Equipment)

In addition, the research group also developed the ice-bath method to prepare graphene-coated selenium/polyaniline core-shell structure nanowires with excellent performance, which broke the previous idea of fusing Se into porous carbon for the first time, and combined the common use of graphene's high conductivity, unique conductive polyaniline shell and one-dimensional structure of selenium nanowires, making the composite show good electrochemical performance.



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