Influence of Polysulfides on the Lithium Metal Anode and on Electrolyte Properties

Abstract

Because the electrification of our society has progressed rapidly in recent years, new high-performance batteries are needed to store electrical energy. Lithium-sulfur (Li-S) batteries have attracted a lot of interest in the last years due to the high theoretical specific capacity of sulfur (1672 mA h gS -1), its extraordinary theoretical specific energy of 2500 W h kg-1, the high abundance and therefore low cost of sulfur.[1] The charging and discharging mechanism of the Li-S battery is significantly different from the state of the art lithium-ion batteries. During the lithiation and delithiation of sulfur to lithium sulfide various long- and short-chain polysulfides (PS) emerge as intermediate reaction products.[2] In this work, we characterize the influence of varying amounts of polysulfides on the electrochemical performance of lithium metal anodes in sparingly solvating solvents. The addition of PS decreases and stabilizes the overpotential in Li/Li cells and therefore delays the cell degradation. The origin of this improvement is characterized by several ex-situ and operando analytical techniques such as optical microscopy, XPS and impedance spectroscopy.[3] One side effect of a higher polysulfide solubility is an increase in the electrolyte viscosity and therefore decrease in the ionic conductivity as well as an increased polysulfide shuttle. To analyse this hypothesis, the amount of dissolved polysulfides, viscosity and ionic conductivity of three different electrolytes are compared and discussed.Conclusions for electrolyte design towards overall improved Li-S cell performance will be presented based on these results. Reference s : [1] A. Manthiram, S.-H. Chung, C. Zu, Adv. Mater. 2015, 27, 1980. [2] M. Wild, L. O'Neill, T. Zhang, R. Purkayastha, G. Minton, M. Marinescu, G. J. Offer, Energy Environ. Sci. 2015, 8, 3477.[3] F. S. Reuter, C.‐J. Huang, Y.‐C. Hsieh, S. Dörfler, G. Brunklaus, H. Althues, M. Winter, S. D. Lin, B.‐J. Hwang, S. Kaskel, Batteries Supercaps 2021, 4, 347.