Morphologic Characterization of Metal-Sulfur Battery Electrodes Using the Lattice Boltzmann Method

Abstract

Metal-sulfur batteries, such as lithium-sulfur (Li-S) or magnesium-sulfur (Mg-S) are promising post lithium-ion battery chemistries [1]. From a sustainability perspective, Mg-S batteries are interesting because they avoid lithium as potentially scarce material altogether. However, from the technological stand point both battery chemistries are not yet fully matured, needing further development that ideally involves experiments, modelling, and simulation. So far, many one-dimensional models of metal-sulfur batteries have been developed [2] which concentrate on the charge and discharge behaviour and provide only limited support to the analysis of experimental results. Especially morphological changes due to surface reactions, dissolution and precipitation, are difficult to incorporate due to their physical and morphological complexity. Therefore, the realistic physical behaviour is often strongly abstracted [1,3,4] or a single volume element is used as a representative electrode structure [5]. However, morphological changes on the pore scale have a huge impact on the battery cyclability and performance. Characterization of these phenomena is therefore necessary for a profound understanding and focused development. In the present work, to better understand these complex phenomena, computational simulations at the mesoscopic level with the lattice Boltzmann method (LBM) are performed. The model includes relevant physico-chemical processes such as crystal growth and dissolution, and polysulfide diffusion. Simulations are performed on three-dimensional porous electrodes, fully resolved in sub-micron resolution. The effects of surface passivation, pore clogging, temporal varying tortuosity, diffusion pathways, available reactive surfaces, and capacity loss were analysed in detail. Special focus is set on the effect of pore clogging and how it reduces the effective battery performance.[1] Richter, R. et al. (2021) ACS Appl. Energy Mater., 4(3), pp. 2365-2376. [2] Kumaresan, K. et al. (2008) J. Electrochem. Soc., 155(8), p. A576. [3] Danner, T. and Latz, A. (2019) Electrochim. Acta, 322, p. 134719. [4] Ren, Y.X. et al. (2016) J. of Power Sources, 336, pp. 115-125. [5] Mistry, A. and Mukherjee, P.P. (2017) J. Phys. Chem. C, 121(47), pp. 26256-26264.