Deconvolution of an SoC- and SoH-Dependent Contact Resistance in a Multilayer Pouch Cell Using Impedance Spectroscopy

The electrical contact resistance between the electrode coating and the current collector of lithium-ion battery electrodes, a critical factor in battery performance, is influenced by the intrinsic properties of the active materials and the amount of conductive electrode additives. However, its role in impedance analysis of large-format cells is often overlooked due to the superposition of high-frequency inductive contributions and the lack of electrode-specific impedance data. In this study, the effect of electrode geometric area on the high-frequency impedance contributions, including contact resistance and stray inductance, is systematically investigated through impedance simulations and validated experimentally with lab-scale and large-format cells. The simulated impedance spectra demonstrate that increasing electrode area amplifies inductive contributions, complicating the detection and quantification of contact resistances. These findings are confirmed via full- and half-cell impedance analysis of cells having the identical microscale silicon-dominated anode and NCA cathode electrodes, comparing the impedance spectra of a 3.5 mAh Si||NCA T-cell, equipped with a micro-reference electrode, with those of a 5.5 Ah multilayer pouch cell. The results establish a direct correlation between the impedance spectra obtained for the lab-scale and the large-format cells, providing a framework for accurately interpreting high-frequency impedance features in large-format commercial lithium-ion battery cells.