Accurate impedance characterization under operating conditions is essential for understanding the electrochemical behavior of energy storage materials. However, conventional galvanostatic electrochemical impedance spectroscopy (GEIS), which applies a fixed AC perturbation, is prone to deviations from quasi-linearity across wide frequency and state of charge ranges, particularly in battery systems. In this work, we introduced amplitude modulated galvanostatic electrochemical impedance spectroscopy (AMGEIS), a method that adaptively adjusts the excitation amplitude at each frequency while maintaining the applied DC bias. The approach incorporates a rapid prescan routine that evaluates quasi-linearity based on harmonic content and dynamically selects an appropriate perturbation amplitude. This strategy provides high-fidelity spectra even under conditions where conventional GEIS exhibited measurable distortions. Validation using a nonlinear equivalent circuit and commercial lithium-ion battery demonstrated that AMGEIS improved spectral quality at low frequencies and extreme states of charge by reducing nonlinear contributions. The method enabled uninterrupted impedance monitoring during cell polarization and offered a scalable framework for reliable, automation-ready electrochemical characterization. Overall, AMGEIS addressed key limitations of fixed-amplitude and expanded the experimental space for impedance-based diagnostics in batteries and related electrochemical systems.
Parasinska et al. (2026) studied this question.