Towards Rational Design of Battery Formation Protocols: From Electrochemical Modeling to Factory Deployment

In battery manufacturing, the formation process is both paramount and problematic. It is paramount since all batteries undergo formation charging and aging steps to build a resilient solid electrolyte interphase (SEI) and to screen for defects. It is problematic because the formation process is expensive to operate, remains a major source of factory energy demand, requires larger factory footprints, and takes an order of magnitude longer than nearly every other manufacturing step. Despite the centrality of the formation process in battery manufacturing, steps taken to optimizing formation protocols remain ad-hoc in the absence of design principles and physical models. We highlight recent progress in developing a principled understanding of the SEI formation process applied towards industrial battery formation process (i.e. in the context of a full cell). We review a reduced-order electrochemical model of the formation process that captures first cycle charge dynamics and subsequent cycling and aging degradation behavior 1. The model predicts measurable quantities such as first cycle efficiency (FCE) and irreversible thickness growth under multiple formation protocols. We discuss opportunities to integrate the electrochemical formation model with differential voltage analysis (DVA) to visualize the connection between first cycle charge dynamics from the perspective of shifting electrode stoichiometries 2 and comment on applications towards physics-informed battery lifetime prediction 3. We finally share recent data elucidating the effect of formation temperature, pressure, and protocol on cycle life. References: Weng, Andrew, Everardo Olide, Iaroslav Kovalchuk, Jason B. Siegel, and Anna Stefanopoulou. 2023. “Modeling Battery Formation: Boosted SEI Growth, Multi-Species Reactions, and Irreversible Expansion.” Journal of the Electrochemical Society 170 (9): 090523. Weng, Andrew, Jason B. Siegel, and Anna Stefanopoulou. 2023. “Differential Voltage Analysis for Battery Manufacturing Process Control.” Frontiers in Energy Research 11. https://doi.org/10.3389/fenrg.2023.1087269. Weng, Andrew, Peyman Mohtat, Peter M. Attia, Valentin Sulzer, Suhak Lee, Greg Less, and Anna Stefanopoulou. 2021. “Predicting the Impact of Formation Protocols on Battery Lifetime Immediately after Manufacturing.” Joule 5 (11): 2971–92. Figure 1: SEI reaction and full cell thickness expansion dynamics during the first formation charge cycle as predicted by the formation model. (A) Full cell voltage, electrode potentials, and SEI reaction potentials. (B) Applied current and SEI reaction currents. (C) Full cell thickness expansion, including both reversible expansion from electrode intercalation and irreversible expansion from SEI components. EC: ethylene carbonate. VC: vinylene carbonate. (1) Negligible SEI growth occurs before the first charge cycle due to reaction limitations. (2) VC reduces first, followed by (3) EC reduction. (4) Expansion rate of lithiated graphite slows down at mid-SOCs, causing a (5) decrease in the EC reduction current as a result of the SEI growth boosting/de-boosting mechanism. Figure 1