In Operando Impedance Based Diagnostics of Electrode Kinetics in Li-Ion Pouch Cells

Abstract

A key to understanding the coupled electrochemical and transport processes in Li-ion batteries is to distinguish the complex interactions between the electrode pair. In this study, an in operando impedance based diagnostics for a three-electrode Li-ion pouch cell configuration is presented in order to study the individual electrode kinetics under varying operating temperatures and depths of discharge. The electrochemical processes including intercalation, diffusion, and interfacial reactions occur at different timescales. Impedance analytics allows estimating the resistances and activation energies of different processes to identify the limiting mechanisms in each electrode. It was found that at −5°C, the effect of staging in the graphite electrode manifests as a piece-wise dependence of the pore resistance and the double layer capacitance in the anode. The dense and highly ordered stages 1, 2 of graphite exhibit higher ionic resistance than the disordered (2L,3L, and 4L) stages at −5°C, due to the added contribution of pore transport resistance at higher depths of discharge.