Characterization of the Solid-Electrolyte Interphase Growth During Cell Formation Based on Differential Voltage Analysis

The solid-electrolyte interphase (SEI) in lithium-ion batteries is mainly built during cell formation. The SEI significantly influences safety, aging, and performance. Due to the manifold influential factors, it is time-consuming to systematically optimize the cell formation. Herein, a novel procedure to characterize the SEI growth during the first cycle of formation with low experimental effort is introduced. Coin cells in a three-electrode setup are tested under pseudo-open-circuit conditions. By evaluating the differential voltage, the capacity loss due to SEI formation during the first cycle is estimated. The identification of the SEI growth curve is carried out using various methods, which are compared in detail. The approach is exemplary applied to compare different electrolytes. It is shown that the approach can be used to parameterize SEI growth models. An analysis of these models indicates that the SEI growth can be explained by a combination of two growth mechanisms, that is, interstitial diffusion and electron tunneling, while the latter is dominant in the beginning of the formation. Further, based on the results it is suggested that the transition between these mechanisms is influenced by the electrolyte.