An iterative analytical model for aging analysis of Li-ion cells

Physics-based aging models are critical for understanding capacity degradation mechanisms in Li-ion batteries. This paper presents a technique for aging analysis of a Li-ion cell due to growth of the solid electrolyte interphase (SEI) layer driven by a solvent decomposition reaction at the electrode surface. The model employs an iterative technique based on the analytical solutions of the underlying conservation equations. The single-particle model describing Li-ion intercalation and de-intercalation processes is solved analytically using Green's function technique. The SEI formation problem is solved using the integral balance method. An iterative technique that combines these analytical solutions is shown to result in a converged result within a few iterations. The model is shown to agree well with results from past studies, as well as a numerical simulation. The capacity fade of Li-ion batteries is investigated under different operating conditions and different regimes, including both cycling and storage. The present model offers much faster computation time than numerical models for modeling the degradation of Li-ion cells. Further, the iterative technique described here may serve as a framework for semi-analytical solutions for other, more complicated problems. This work contributes towards improving the performance and reliability of electrochemical energy conversion and storage systems.