High-Frequency Impedance Spectroscopy: Measurement Reproducibility, Electromagnetic, and Ionic Effects in Cylindrical Lithium-Ion Cells

Accurate high-frequency electrochemical impedance spectroscopy (HF EIS) is critical for understanding lithium-ion battery (LIB) behavior under AC perturbations, relevant to electric vehicle systems and charging infrastructure. However, measurements at high frequencies are often distorted by external electromagnetic interference, poor contact quality, and wiring artifacts. This study investigates four experimental testbench configurations for HF EIS of cylindrical LIBs, highlighting the impact of contact resistance, Faraday shielding, wire twisting, and calibration. A coupled electrochemical-electromagnetic model is developed to isolate and analyze the skin effect and frequency-dependent electrolyte conductivity. Results show that spot-welded connections, twisted and shielded wiring, and calibration within a Faraday cage significantly improve measurement reproducibility, reducing both real and imaginary impedance variability. The model captures current redistribution from the skin effect and demonstrates that frequency-dependent electrolyte conductivity, modeled with a decaying profile, is necessary to match experimental impedance data across frequencies. It was shown that both testbench optimization and physical modeling are essential for reliable HF EIS. The findings emphasize that ionic and electromagnetic phenomena must be considered in future modeling, and that rigorous experimental protocols—such as shielding, calibration, and resting—are prerequisites for reproducible HF EIS of LIBs.