Simple but Highly-Efficient Polysulfide Trapping Strategy for Lithium-Sulfur Batteries

Abstract

Lithium-sulfur (Li-S) battery, as an attractive alternative to the state-of-the-art Li-ion battery by the merits of high energy density and abundant material sources, is expected to meet the urgent demand of next-generation electric vehicles. However, several challenges severely hinder its application process, including low conductivity of elemental sulfur and lithium sulfide, large volume expansion upon discharge, and unfavorable redox shuttle due to the soluble polysulfides (PSs). In order to increase sulfur utilization and cycle stability of the Li-S batteries, a variety of strategies on modifying sulfur cathode have been attempted, e.g. development of sulfur-carbon composite, introduction of extra surface coating and novel electrode component, etc. It is worthy to note that many studies involving PS’ trapping material/structure always brought about significant improvement of cell performance. This is because that the active species loss and shuttle side effect were reduced. Recently our research group has reported the good chemical affinity of polyacrylamide (PAM) to PSs, coming from the strong binding of the amide group in the PAM with Li-S• species. Therefore, the polymer was successfully used in the surface coating on either sulfur cathode or porous separator [1, 2]. Poly(acrylic acid) (PAA), another water-soluble polymer, also can act as a favorable PS blocking layer because the COOH groups in the long chain can form strong hydrogen bonds with the PS anions [3]. This research demonstrates a simple but highly-efficient PS trapping strategy that employs PAA and PAM as a functional binder and additive for sulfur cathode, respectively. The synergistic action of these two distinctive agents contributes to higher reversible capacity and longer cycle life of Li-S batteries compared to conventional electrode. The mechanism of trapping PSs in the artificially-designed cathode framework was discussed, and the enhancement of hydrophilic nature of the cathode to the liquid electrolyte was also considered. It needs to be emphasized that the novel cathode can be easily fabricated on a large-scale without any additional procedures. Fig. 1 Comparison of cycle performance of PAM/PAA-contained cathode and conventional sulfur cathode Reference: [1] T. Li, Y. Yuan, B. Hong, et al, Electrochim. Acta, 2017, 244, 192-198 [2] H. Lu, J. Wang, T. Li, et al, J Solid State Electrochem., 2018, 22, 953-958 [3] S. Zhang, D. Tran, Z Zhang, J. Mater. Chem. A, 2014, 2, 18288-18292 Acknowledgment: This work was financially supported by National Natural Science Foundation of China (No.51704222, 51604221 and 51574191), Natural Science Basic Research Plan in Shaanxi Province of China (No.2016JQ5040), and Special Scientific Research Program of Education Department of Shaanxi in China (No.17JK0427). Figure 1