New Insight into the Shuttle Mechanism of Rechargeable Lithium-Sulfur Batteries

Lithium-sulfur batteries have become an appealing candidate for low-cost and high-energy-density power sources. It is generally believed that the shuttle effect in Li/S batteries causes serious performance degradation, such as low coulombic efficiency, sulfur loss, and so on. Here, we report a new mechanism based on the disproportionation reactions of polysulfides (PSs) to explain the rapid fading of capacity in Li/S batteries. Two different electrolytes (i.e., a carbonate-based electrolyte and an ether-based electrolyte) were adopted to study the disproportionation mechanism. We found that elemental sulfur was reprecipitated on the surface of the cathodes, forming a passive layer. The passive layer formed in the carbonate-based electrolyte is much denser than that formed in the ether-based electrolyte, resulting in the faster capacity fading in the carbonate-based electrolyte. The simulation of cathodic peaks and anodic peaks in CV profiles confirms the disproportionation reaction of PSs in the ether-based electrolyte. The electrochemical behavior of these Li/S batteries are well explained by an EC mechanism that involves an electron transfer reaction followed by a reversible disproportionation reaction. It is found that the disproportionation of PSs plays a more important role than the shuttle effect during the initial stage of the charge/discharge process.