Insight Into Li/S Batteries: Elementary Kinetic Modeling and Impedance Simulation

Abstract

The lithium-sulfur (Li/S) battery is one of the most promising systems for portable electrochemical energy storage [1]. The complex redox chemistry of sulfur, the large number of soluble intermediates and the dissolution and precipitation of solids, however, present a major challenge to understanding Li/S electrochemistry. We present the first model of the Li/S cell based on a fully elementary reaction mechanism, building on the work of Kumaresan et al. [2]. A detailed model of the evolution of solid phases as well as multi-component (Li+, PF6–, S8, S82−, S62−, S42−, S22−, S2−) mass and charge transport are included, allowing for the simulation of discharge and charge curves, electro- chemical impedance spectra [3], and concentration profiles. The results confirm that the discharge behavior of the Li/S cell is governed by the presence of solid reactant and product phases in exchange with the dis- solved sulfur poly-anions. The first and second discharge stages are characterized by the presence of solid S8 and Li2S, respectively, while the inter- mediate dip corresponds to a situation where all chemical compounds are dissolved in the electrolyte. Simulated electrochemical impedance spectra are used to validate the model against experimental data.

References [1] B. Scrosati, J. Garche, J. Power Sources, 195 (2010), 2419–2430. [2] K. Kumaresan, Y. Mikhaylik and R.E. White, J. Electrochem. Soc., 155 (2008), A576–A582 [3] W.G. Bessler, J. Electrochem. Soc. 154, B1186–B1191 (2007).