Recently, the iChEM researcher, Prof. Yongyao Xia’s group in FDU demonstrated pronounced suppression of polysulfide shuttle using an ionic liquid of electrolyte. The related work was published on Energy & Environmental Science as a title “Recent advances of pore system construction in zeolite-catalyzed chemical industry processes”.

Lithium–sulfur (Li–S) batteries are receiving tremendous attention due to their potential for high energy-density batteries in emerging electronics and vehicle applications. However, severe self-discharge associated with a rapid polysulfide redox shuttle process has remained a grand challenge, preventing the practical application of this attractive technology. Soluble polysulfide species (Li₂S_x, 4 ≤ x ≤ 8) would continue to dissolve and migrate to the negative side because of concentration gradient, and then react with metallic Li, resulting in a decrease of open-circuit voltage, loss of upper discharge plateaus and discharge capacity. To address this issue, we take a different approach to the Li–S battery by developing a room temperature ionic liquid (RTIL) of N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13TFSI)-based electrolytes. When working together with LiNO₃, zero self-discharge can be achieved to rest a full-charged cell for two days. From a systematic study of battery performance in terms of various kinds of electrolytes and comprehensive characterization on Li-electrodes, we conclude that both improvements on polysulfide diffusion control and stabilization of Li-metal should be fulfilled for a successful battery with low self-discharge. This approach shows the way forward to the practical use of Li–S batteries by selection and more rational design of electrolytes.

Li–S batteries generally suffer from severe self-discharge when resting due to an internal polysulfide shuttle effect. Soluble long-chain polysulfide species (Li₂S_x, 4 ≤ x ≤ 8) would continue to dissolve and migrate to the negative side to react with metallic Li. They demonstrate pronounced suppression of polysulfide shuttle using an ionic liquid of the N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13TFSI)-based electrolyte. When working in combination with LiNO₃, zero self-discharge can be achieved to rest a full-charged Li–S cell for two days. The fascinating study clearly demonstrates that a promising practical Li–S battery with low self-discharge depends on both improvements on polysulfide diffusion control and Li-metal stabilization. On the basis of the insight gained, they suggest the ultimate success of Li–S batteries depends on both improvements on polysulfide diffusion control and stabilization of Li-metal. Therefore, selection and design of electrolytes for Li–S batteries should fulfill both demands.

This work was financially supported by iChEM and NSFC.

http://pubs.rsc.org/en/content/articlepdf/2015/ee/c5ee02837j