Solid‐Electrolyte Interphase During Battery Cycling: Theory of Growth Regimes

: The capacity fade of modern lithium ion batteries is mainly caused by the formation and growth of the solid-electrolyte interphase (SEI). Numerous continuum models support its understanding and mitigation by studying SEI growth during battery storage. However, only a few electrochemical models discuss SEI growth during battery operation. In this article, we develop a continuum model, which consistently captures the influence of open circuit potential, current direction, current magnitude, and cycle number on the growth of the SEI. Our model is based on the formation and diffusion of neutral lithium atoms, which carry electrons through the SEI. Recent short- and long-term experiments provide validation for our model. We show that SEI growth is either reaction, diffusion, or migration limited. For the first time, we model the transition between these mechanisms and explain empirically derived capacity fade models of the form $\Delta Q\propto t^\beta$ with $0 \leq \beta \leq 1$. Based on our model, we identify critical operation conditions accelerating SEI growth.