Lithium-sulfur batteries use elemental sulfur as the positive electrode and metallic lithium as the negative electrode. The theoretical specific energy can reach 2600Wh kg-1, which is 3 to 5 times that of traditional lithium-ion batteries. And because elemental sulfur has abundant reserves and low prices in the earth It is considered to be one of the next generation high specific energy secondary battery systems with the most development potential. However, because the polysulfide generated during the charging and discharging of the lithium-sulfur battery is easily soluble in the electrolyte and reaches the metal lithium negative electrode through the separator, a serious "shuttle effect" is generated, causing loss of active materials and uneven deposition of sulfide. Resulting in poor battery cycling performance.
Based on the above problems, researchers from the Advanced Energy Storage Materials and Technology Research Group of the Qingdao Institute of Bioenergy and Processes, Chinese Academy of Sciences started with the modification of lithium-sulfur battery separators and introduced the transition metal compound CoNi1 / 3Fe2O4 (CNFO) on the surface of carbon nanotubes (CNT) , Successfully prepared CNFO @ CNT nanocomposite material, and evenly applied it to the surface of commercial membrane by vacuum suction filtration. Benefiting from the strong polar adsorption of CNFO and the conductive effect of CNT, the modified membrane can effectively adsorb the polysulfide compound dissolved in the positive electrode and recycle it. The schematic diagram of the preparation of CNFO @ CNT nanocomposites is shown in Figure (a) below.
The CNFO @ CNT modified separator was used in a lithium-sulfur battery. The experimental results showed that the capacity retention rate was as high as 84% ​​after cycling at normal temperature of 250 cycles at 2.0 C. Not only that, the researchers placed the modified lithium-sulfur battery at a high temperature of 60 ° C to test its cycle stability, and found that under the strong chemical adsorption of CNFO, after 0.5 C after 100 cycles, the capacity retention rate can still reach 78%, and maintain the Coulomb efficiency above 98%. Compared with the CNT-modified separator, the modified material has a greater improvement in the rate and cycle stability of lithium-sulfur batteries regardless of whether it is normal temperature or high temperature of 60 ° C.
Related results have been published in ACS Applied Materials & Interfaces (Tao Liu, et al, Jianfei Wu *. Doi: 10.1021 / acsami.9b02136). In addition, the all-solid-state lithium-sulfur battery that replaces the traditional electrolyte with a solid electrolyte can fundamentally solve the problem of dissolving polysulfide. Based on the currently developed lithium-sulfur battery and high-conductivity sulfide solid electrolyte, the research team next step Will continue to develop high-performance lithium-sulfur all-solid-state batteries, related results have been published in J. Mater. Chem.A (2018, 6, 23486–23494), Electrochim. Acta (2019, 295, 684-692) and other journals, research results Supported by the Chinese Academy of Sciences' First Action 100-Person Program, the National Natural Science Foundation of China, and the Qingdao Energy Institute-Dalian Chemical Institute Fusion Fund Project.
(A) Schematic diagram of CNFO @ CNT nanocomposite preparation; (b) UV absorption spectrum of CNFO @ CNT nanocomposite; (c) High temperature cycling performance of lithium-sulfur battery
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