Understanding calendar aging degradation in cylindrical lithium-ion cell: A novel pseudo-4-dimensional electrochemical-thermal model

This study presents a comprehensive investigation of calendar aging degradation in commercial 21,700 cylin- drical lithium-ion cells with a LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode and a silicon- graphite composite anode. The cells underwent accelerated aging at 60 ◦ C for 63 days at various states of charge to assess the impact of high-temperature calendar aging. Experimental analysis was performed using non-destructive electrochemical techniques, and a novel pseudo-4D electrochemical-thermal model was developed using COMSOL Multiphysics to provide insights into the degradation processes. This model extends the traditional 1D geometry of a pseudo- 2D model into a 3D framework to simulate the local heterogeneity of the real electrochemical and thermal processes in commercial cells with jellyroll configurations, providing detailed insights into the behavior of the cell. The model incorporates various degradation mechanisms while considering the interaction between the cathode aging products and the solid electrolyte interphase growth at the anode. Experimental validation was performed using charge/discharge tests and calendar aging results, emphasizing the complex interplay between degradation mechanisms.