The Interplay of Electrode Heterogeneity, SEI Growth, and Li Plating in Li-Ion Batteries

Abstract

Newman-type or macrohomogeneous cell models have had a significant contribution toward designing and optimizing Li-ion batteries. In order to lower the computational cost and accommodate limited experimental information, this model assumes that battery electrodes are functionally homogenous. However, this assumption can be far from reality even for commercial-quality electrodes, due to variability in microstructure that arises during the manufacturing process. Previous work in our group showed that electrode heterogeneity can lead to non-uniform distribution of current density, positive and negative electrode states of charge, and charge/discharge capacities [1]. Consequently, heterogeneity can cause faster degradation of materials, prevent maximum utilization of active materials, and even lead to catastrophic failure of the cell. Among the different modes of cell aging, solid electrolyte interphase (SEI) growth and Li plating are considered mainly responsible for capacity fade due to loss of active Li. In this study, we will discuss how electrode heterogeneity can lead to non-uniform SEI growth and Li plating, and how the growth of this resistant layer affects the level of heterogeneity, performance, and lifetime of the cell. To better understand the interplay of the electrode’s heterogeneity and cell aging, we use a combination of a Newman-type model and an equivalent-circuit model for an NMC cathode and graphite anode. The equivalent-circuit model consists of three parallel resistances, each represent high, medium, and low conductivity regions in an electrode film. This research was funded by the BMR program of the US Department of Energy. [1] Forouzan et al., J. Electrochem. Soc. 165, A2127-A2144 (2018).