Electrochemical Impedance Spectroscopy Simulations from Microstructure-Based Battery Models

Electrochemical impedance spectroscopy (EIS) is the standard tool for probing time-scale-separated processes in Li-ion cells. While EIS is a powerful method, data interpretation can be challenging, as insights into the state and performance of the battery must be extracted from the measured spectrum. In practice, researchers often fit the measured spectrum with an equivalent-circuit model (ECM) to simplify complex electrochemical phenomena. Although convenient, ECMs are a significant simplification: the fitted values depend strongly on the chosen equivalent circuit arrangement and often lead to different interpretations of the same data. This difficulty blocks the transfer of insights from impedance measurements to full-cell or microstructure simulations.

GeoDict 2026 bridges this gap by allowing direct EIS simulation with the very same model that is used for charge-discharge predictions. Two options are available: a fully resolved model directly on the three-dimensional microstructure, or a homogenized pseudo-two-dimensional Newman-type (enhanced DFN) model whose parameters are derived automatically from the battery's microstructure. By varying only the physical properties of the materials, such as diffusivity, conductivity, and interfacial kinetics, the simulated impedance spectrum shows clear, distinct signatures across frequency ranges: high frequencies reflect the ohmic resistance of the electrolyte and current collectors, medium frequencies are dominated by charge-transfer processes at the electrode–electrolyte interface, and low frequencies reveal mass-transport limitations in the bulk solid or liquid phases.

Consequently, the same microstructure-based physical model that reproduces a discharge curve also predicts the EIS spectrum without resorting to arbitrary equivalent circuit elements. The approach offers the advantage of analyzing EIS data and charge tests with one unified model. This also enables the reverse-engineering of material parameters at different temperatures, states of charge, or aging conditions using EIS measurements under the respective conditions.

Ultimately, GeoDict’s new EIS simulation capability connects impedance spectroscopy and microstructure-based modeling. It enables researchers to derive an integrated, physics-based description of their cells by simultaneously matching discharge curves and impedance data, thereby accelerating progress towards truly predictive model for Li-ion battery cell design.