Growth of the solid electrolyte interphase (SEI) is a major driver of capacity fade in lithium-ion batteries. Despite its importance to this device and intense research interest, the fundamental mechanisms underpinning SEI growth remain unclear, primarily because of the complicated reaction pathways involved. SEI growth can be both electrochemical and chemical in nature, and thus, it is a strong function of the potential and degree of lithiation of the electrode. In this work, we model the early-stage growth of SEI by accurately capturing the potential dependence of its formation kinetics, and validating it against extensive experimental data. We use carbon black as our intercalant, which has graphitic structure but a higher rate of SEI growth than graphite and does not exhibit phase transformations during intercalation, and thus is easier to study, using precision coulometric measurements. The model considers SEI growing on top of a carbon black matrix, to be purely resistive to lithium ions and electrons passing through it. Using potential dependent charge-transfer mechanics of intercalation in carbon black, and of SEI formation, fitted to accurately capture the open-circuit voltage during intercalation, we decouple the total driving current into intercalation and SEI-forming components. Then we calculate the differential capacities of SEI formation/dissolution as a function of cell potential, and study it for various driving currents under galvanostatic conditions. Results indicate that the largest differential SEI capacities arise when the cell potential is low (&lt;0.4V), and the peak SEI-forming currents are higher for higher driving currents. Counterintuitively, despite higher peak SEI-forming currents, the highest differential capacities or ‘extent of SEI growth’ are seen for lower driving currents, which implies that SEI formation is a stronger function of potential and cycling time, than the current. Higher rates of growth (i.e. faster capacity fade) are observed during lithiation of carbon black than during de-lithiation, in both simulation and experiment, which can be attributed to the electrochemically irreversible nature of the products formed. This work holds promise for the predictive design of procedures for manufacture and formation of lithium-ion batteries for many energy storage applications.

Modeling irreversible capacity loss in carbon-black anodes

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.