Electrochemical kinetics of SEI growth on carbon black, I: Experiments

TL;DR

This study introduces an electroanalytical method to investigate how SEI growth on carbon black in lithium-ion batteries depends on potential, current, and direction, revealing key factors influencing capacity fade.

Contribution

It provides new experimental insights into the dependence of SEI growth on cycling parameters and highlights the coupling between SEI formation and charge storage processes.

Findings

SEI growth increases with higher C rates.

SEI growth is more pronounced during lithiation.

Directional dependence of SEI growth observed in experiments.

Abstract

Growth of the solid electrolyte interphase (SEI) is a primary 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. In Part I of this work, we present an electroanalytical method to measure the dependence of SEI growth on potential, current magnitude, and current direction during galvanostatic cycling of carbon black/Li half cells. We find that SEI growth strongly depends on all three parameters; most notably, we find SEI growth rates increase with nominal C rate and are significantly higher on lithiation than on delithiation. We observe this directional effect in both galvanostatic and potentiostatic experiments and discuss hypotheses that could explain this observation. This work identifies a strong coupling between SEI growth and charge storage (e.g., intercalation and capacitance) in carbon negative electrodes.