  This work proposes a semi-empirical model for the SEI growth process during
the early stages of lithium-ion battery formation cycling and aging. By
combining a full-cell model which tracks half-cell equilibrium potentials, a
zero-dimensional model of SEI growth kinetics, and a semi-empirical description
of cell thickness expansion, the resulting model replicated experimental trends
measured on a 2.5 Ah pouch cell, including the calculated first-cycle
efficiency, measured cell thickness changes, and electrolyte reduction peaks
during the first charge dQ/dV signal. This work also introduces an SEI growth
boosting formalism that enables a unified description of SEI growth during both
cycling and aging. This feature can enable future applications for modeling
path-dependent aging over a cell's life. The model further provides a
homogenized representation of multiple SEI reactions enabling the study of both
solvent and additive consumption during formation. This work bridges the gap
between electrochemical descriptions of SEI growth and applications towards
improving industrial battery manufacturing process control where battery
formation is an essential but time-consuming final step. We envision that the
formation model can be used to predict the impact of formation protocols and
electrolyte systems on SEI passivation and resulting battery lifetime.
