Effect of Polysulfide Species on Lithium Anode Cycle Life and Reversibility in Li-S Batteries

In a lithium-sulfur battery (LSB) discharge process, elemental sulfur is reduced to Li2S via a multi-step process. The soluble lithium-polysulfide (PS) (Li2Sn) intermediate species then diffuses through the electrolyte solution from the porous cathode to the lithium anode. These species react with the anode and form an interphase of insoluble lithium PS. This "shuttle" phenomenon is the main obstacle in the development of practical LSBs. The most previous reports dealt with LSBs focusing their attention on the cathode side, and the aspect of lithium reversibility influenced by the PS is not well quantified. In this paper, we designed an experimental protocol that allows us to control the exact amount of lithium in the cell and determine the influence of the different intermediate PS species on the reversibility of Li anode via spectroscopic, microscopic, and electrochemical techniques. We study the correlation between the electrochemical response and the morphology, topography, and composition of the anode in the presence of PS and present the destructive effect of PS on the lithium anode side. This work emphasizes the importance of the strategies that can help prevent the PS shuttling to the Li anode opening of the possibility for the development of practical metal anodes for Li-S batteries.