Modeling cyclic voltammetry during solid electrolyte interphase formation: Baseline scenario of a dynamically...

The solid electrolyte interphase (SEI) is an insulating film on anode surfaces in Li-ion batteries, which forms via the reaction of Li ions with reduced electrolyte species. The SEI leads to a reduction in the electrochemical current in heterogeneous electrochemical redox reactions at the electrode/electrolyte interface. Hence, the growth of the SEI is, in principle, self-limited. Toward our ultimate goal of an improved understanding of SEI formation, we develop a baseline quantitative model within Butler-Volmer electrode kinetics, which describes the cyclic voltammetry (CV) of a flat macroelectrode during SEI growth. Here, the SEI building up electrochemically during CV forms a homogeneous single-phase electronically insulating thin film due to the corresponding current. The model is based on a dynamically evolving electron tunneling barrier with increasing film thickness. Our objective is to provide a framework, which allows for both the qualitative, intuitive interpretation of characteristic features of CV measurements and the quantitative extraction of physicochemical parameters via model fitting. We also discuss the limitations of the baseline model and give a brief outlook for improvements. Finally, comparisons to exemplary CVs from the literature relevant to Li-ion battery science are presented.