Revisiting High-Frequency Impedance in Li-Ion Batteries: Decoupling Solid Electrolyte Interphase Resistance from Pore Impedance.

Electrochemical impedance spectroscopy (EIS) is a cornerstone technique for probing the kinetic behavior of lithium-ion batteries (LIBs). However, in the high-frequency impedance analysis of porous electrodes, the strong coupling between pore-induced ionic diffusion resistance () and solid electrolyte interphase (SEI) resistance () significantly complicates the accurate extraction of , often introducing substantial estimation errors. In this study, we utilized a LiFePO//graphite three-electrode system by integrating experimental measurements with numerical simulations to quantitatively evaluate the influence of -to- coupling on the high-frequency impedance. When a quasi-blocking electrode state was induced in LIBs, was effectively decoupled and determined via a transmission line model (TLM). A mathematical inverse transformation was then applied to reconstruct an impedance spectrum devoid of effects. The transformed spectrum exhibited markedly enhanced fitting accuracy and improved adherence to the Arrhenius relationship. Furthermore, TLM-based simulations were performed to elucidate the coupling dynamics between and in the high-frequency regime. When was systematically varied, its dominant impact on impedance spectra was quantified, underscoring the necessity of a precise correction for reliable determination. This work advances high-frequency impedance interpretation and introduces a robust methodology for accurate quantification in LIBs.