Revisiting High-Frequency Impedance in Li-Ion Batteries: Decoupling Solid Electrolyte Interphase Resistance from Pore Impedance
Jianrong Lin, Wenxuan Hu, Jian Yang, Lixuan Pan, Xiwen Xia, Yimin Wei, Zhengliang Gong, Yong Yang
Abstract
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 ( R ion ) and solid electrolyte interphase (SEI) resistance ( R SEI ) significantly complicates the accurate extraction of R SEI, often introducing substantial estimation errors. In this study, we utilized a LiFePO 4 //graphite three-electrode system by integrating experimental measurements with numerical simulations to quantitatively evaluate the influence of R ion -to- R SEI coupling on the high-frequency impedance. When a quasi-blocking electrode state was induced in LIBs, R ion 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 R ion 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 R ion and R SEI in the high-frequency regime. When R ion was systematically varied, its dominant impact on impedance spectra was quantified, underscoring the necessity of a precise R ion correction for reliable R SEI determination. This work advances high-frequency impedance interpretation and introduces a robust methodology for accurate R SEI quantification in LIBs.