Adsorption of Polysulfides from Electrolyte Using Porous Carbons

Due to their high theoretical specific energy density and the low costs of sulfur, Lithium-sulfur (Li‑S) batteries are of high interest as the storage of electric energy becomes more and more important. After several year of investigation, they still lack of a high cycling stability, which can be mainly ascribed to the formation of dendrites and particularly, to the so-called polysulfide (PS) shuttle mechanism. Therefore, the understanding of the latter and its possible inhibition is the aim of current research. Adding traces of LiNO₃ to the electrolyte or using composite cathodes with additional polysulfide reservoirs seems to prolong the battery life.^1,2 Other publications report on carbon host materials with specially designed porosity in order to avoid the polysulfide diffusion. Up to now, the detailed mechanism of the shuttle and the effect of PS reservoirs is not fully understood as previous studies concentrated more on electrochemical characterization of half-cells including other components, such as separator and anode.³

This study is focused on the liquid phase adsorption of stoichiometric and ex-situ synthesized polysulfides from a Li‑S battery electrolyte on porous carbons to simulate a simplified Li‑S cell environment. Several micro and meso and hierarchically structured porous carbons were investigated - both industrial reference materials and specially designed carbons. The latter are already electrochemically tested as carbon-sulfur cathode composite in Li-S cells. Li₂S_x(x=4,6,8) were synthesized by stirring stoichiometric amounts of Lithium and sulfur in DOL/DME (1:1) at 70°C under Argon until the solution reached equilibrium condition. Subsequently, the porous carbons were added and the PS adsorption was monitored by UV/Vis spectroscopy. The influence of different carbon porosities on the adsorption properties of the polysulfides species was investigated.

(1)          Ji, X.; Evers, S.; Black, R.; Nazar, L. F. Nat. Commun. 2011, 2, 325.

(2)          Aurbach, D.; Pollak, E.; Elazari, R.; Salitra, G.; Kelley, C. S.; Affinito, J. J. Electrochem. Soc. 2009, 156, A694.

(3)          Evers, S.; Yim, T.; Nazar, L. F. J. Phys. Chem. C 2012, 116, 19653–19658.