Tsinghua team uses ultrathin MoS2/CNT interlayers to trap polysulfides in and improve performance of Li-S batteries

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Researchers at University in China have used and lightweight molybdenum sulfide (MoS2)/carbon nanotube (CNT) to in high- lithium–sulfur (Li–S) . A paper on their work is published in the Journal of Power Sources.

An electrode with the MoS2/CNT interlayer delivers an attractive specific capacity of 784 mAh g−1 at a high capacity rate of 10 C. In addition, the electrode demonstrates a high initial capacity of 1237 mAh g−1 and a capacity fade as low as −0.061% per cycle over 500 charge/discharge cycles at 0.2 C.

Yan
(a) Schematic diagram of a Li-S cell with the MoS2/CNT interlayer. (b) Schematic configuration of a Li−S cell with the MoS2/CNT-interlayer-coated separator (top) and the pristine separator (bottom). (c, d) Photographs of a MoS2/CNT-interlayer-coated separator showing its high flexibility. Yan et al.
Click to enlarge.

… the application of Li–S batteries is hindered by the following challenges. First, both the active material (sulfur) and the discharge products (Li2S2/Li2S) are electrically insulating. Second, the volume expansion during cycling reaches up to 80%. Last, and most important, the intermediate polysulfides (Li2Sn, 4 ≤ n ≤ 8) are highly dissolvable in the electrolyte and the shuttling of them between the electrodes results in a fast loss of capacity, i.e., the shuttle effect. All these issues lead to a low utilization of sulfur, fast capacity fading, poor rate capability, and significant self-discharge behavior. To overcome these difficulties, various approaches have been proposed for the design of sulfur composite cathodes.

… All these modifications can promote the electrochemical properties, accommodate the volume expansion, and restrain the diffusion of polysulfides to some extent. Nonetheless, the rapid capacity fading and severe self-discharge induced by the shuttle effect have not been fully addressed.

… It has been reported in the literature that MoS2 could effectively trap the polysulfides owing to the strong chemical interaction between MoS2 and polysulfides. However, it is still challenging to introduce MoS2 into the Li–S system to effectively suppress the shuttle effect and the cell performance. Herein, we report a simple and feasible strategy to develop MoS2/CNT interlayers by uniformly loading MoS2 nanosheets on a cross-stacked CNT film and taking advantage of the properties of both MoS2 and CNTs.

—Yan et al.

The CNT film—with its excellent conductivity and superior mechanical properties—provides a uniform conductive network, a supporting skeleton for the MoS2 nanosheets, and a physical barrier for the polysulfides.

The MoS2 nanosheets further suppress the shuttling effect through their chemical interactions with the polysulfides, resulting in the performance noted above.

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(a) Cycling performances of the electrodes with a MoS2/CNT-interlayer-coated separator, CNT film coated separator, and pristine separator at 0.2 C. (b) Rate
performances of the electrodes with a MoS2/CNT-interlayer-coated separator and a pristine separator. Yan et al. Click to enlarge.

The fabrication process of the MoS2/CNT interlayer can be easily scaled up; the method presents significant potential for the development of high-performance Li–S batteries, the researchers suggest.

Resources

  • Lingjia Yan, Nannan Luo, Weibang Kong, Shu Luo, Hengcai Wu, Kaili Jiang, Qunqing Li, Shoushan Fan, Wenhui Duan, Jiaping Wang (2018) “Enhanced performance of lithium-sulfur batteries with an ultrathin and lightweight MoS2/carbon nanotube interlayer,” Journal of Power Sources, Volume 389, Pages 169-177 doi: 10.1016/j.jpowsour.2018.04.015



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