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Lithium-sulfur batteries are secondary batteries containing sulfur as the positive electrode material and lithium metal sheet as the negative electrode. Their theoretical specific capacities and theoretical specific energy of the battery are relatively high, which are 1672 mAh·g-1 and 2600 Wh·kg-1, respectively. One of the most valuable and promising applications for high-energy lithium secondary battery systems. However, there are still many problems to be solved in lithium-sulfur batteries, such as low cycle life, low utilization of active materials, poor conductivity of sulfur cathode materials and their discharge products.
Recently, Qian Yitai and Zhu Yongchun of the University of Science and Technology of China have developed a new type of lithium-sulfur battery cathode material, selenium-sulfur solid solution. Researchers started from cheap commercial sulfur powder and selenium powder and based on the binary phase diagram of the two, they combined it with the porous carbon prepared in the early stage of the experimental group to obtain different proportions of sulfur-rich S1-xSex/C (x≈0.1). , 0.08, 0.06, 0.05) complexes. Studies have shown that the prepared S1-xSex/C composites still exhibit excellent cycle stability and rate performance in carbonate electrolytes: 500 cycles at a current density of 0.5Ag-1, the specific capacity remains at 1105mAhg−1 Even at a high current density of 20Ag-1, the specific capacity reaches 617mAhg−1. The liquid-phase Raman and X-ray photoelectron spectroscopy revealed that the S1-xSex/C composites had stable selenium-sulfur bonds before and after the cycle. This study not only revealed the stability mechanism of selenium-sulfur solid solution, but also laid the foundation for the subsequent research and development of other new lithium-sulfur battery cathode materials. The relevant research paper was published in Energy Environ.Sci. (2015, DOI: 10.1039/C5EE01470K) and was selected as the internal illustration of the magazine's 2015 issue 11. The dissertation mainly completed the postdoctoral fellow Li Xiaona and Liang Jianwen.
On the other hand, selenium cathode materials of the same family as sulfur are also attracting attention in recent years. The research group developed a new method of salt helium to inject selenium into porous carbon to avoid inert gas or vacuum atmosphere protection, to avoid temperature fluctuations in the heating process to some extent, and to facilitate the infusion of molten selenium into the In porous carbon, the proportion of active Se in the Se/C composite was increased from 36–54% previously reported to 72%. The prepared Se/C composite exhibits excellent lithium storage performance: 1000 cycles at 1C condition, the capacity retention rate is 95.7%. In the Na-Se battery test, Se/C composites still exhibited good cycle stability. The salt dome method proposed by the research group can not only be used as a universal method to infuse other low-melting-point materials into the porous carbon substrate material, but also the method is simple and easy to implement, which is conducive to the expansion of production, and is expected to promote Li-Se, Na-. Se and other related batteries are further developed. The related results were recently published in Advanced Functional Materials and were selected by Materials Research China of Wiley as a highlight research report. The first author of the dissertation was Li Xiaona, a postdoctoral fellow of the research group.
In addition, the research group also developed graphene-coated selenium/polyaniline core-shell structure nanowires with excellent performance for preparation of ice baths, which for the first time broke the idea of ​​melting and infiltrating many porous Se into porous carbon, and combined graphene The combination of high conductivity, a unique conductive polyaniline shell, and one-dimensional structure of selenium nanowires makes the composite exhibit good electrochemical performance. The relevant results were published in "Nano Energy" (Nano energy 2015, 13, 592-600). The first author of the paper was Dr. Zhang Jingjing of the research group.
The above work was funded by the National Natural Science Foundation of China.
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