Lithium/sulfur batteries: global and elementary modeling approaches

Kurzfassung

The lithium/sulfur (Li/S) battery is a promising system for energy storage. Its energy density (up to 2.6 kWh/kg) is the highest of all “closed-system” batteries known [1]. The global reaction of this type of cell is S8 + 16 Li ⇄ 8 Li2S, yielding 3400 kJ/mol and a open-circuit voltage of ~2.2 V. However, due to the complex redox chemistry of sulfur, numerous soluble intermediate species are formed during discharge, including S8, S82−, S62−, S42−, S22− and S2−. The large number and different properties of those intermediates represent a major challenge in understanding Li/S electrochemistry. A computational model of the Li/S cell is presented, including elementary kinetics, evolution of solid phases as well as mass and charge transport. Implemented reaction mechanisms include a global model, a semi-elementary model according to Kumaresan et al. [2] as well as a more detailed model with surface states and a total of almost 20 elementary reaction steps. The charge and discharge processes involve the dissolution and precipitation as well as the chemical transformation of phases in the cell’s electrodes [3]. The model is implemented in the in-house software DENIS [4]. We present simulated charge and discharge curves, concentration profiles and electrochemical impedance spectra. A typical discharge curve with phase behavior is shown in Fig. 1. The model is used to increase our understanding of the Li/S cell. References: 1. B. Scrosati, J. Garche, J. Power Sources, 195 (2010), 9, 2419–2430 2. K. Kumaresan, Y. Mikhaylik and R. E. White, J. Electrochem. Soc., 155 (2008), 8, A576–A582 3. J. P. Neidhardt, D. N. Fronczek, T. Jahnke, T. Danner, B. Horstmann, W. G. Bessler, J. Electrochem. Soc., in press (2012) 4. W. G. Bessler, S. Gewies and M. Vogler, Electrochim. Acta, 53 (2007), 4, 1782–1800