Variable EIS Measurement System Based on External Impedance Control

다국어 초록 (Multilingual Abstract)

As modern society advances, the demand for batteries continues to grow, yet we still cannot fully observe the complex chemical changes occurring inside batteries in real time. Electrochemical impedance spectroscopy (EIS) has long been recognized as one of the most powerful diagnostic tools for evaluating battery state of health (SOH) and degradation mechanisms. However, existing EIS systems suffer from limitations such as high dependence on battery BMS data, high equipment costs, limited portability, narrow frequency ranges, and difficulties in real-time field deployment. This study proposes a Variable External Impedance-based EIS measurement system (VEI-EIS) that redefines the fundamental principles of impedance spectroscopy.. To validate the proposed approach, experiments were conducted using automotive lithium-ion battery modules configured in a 2P6S structure (21.78 V, 111.2 Ah, 2421.9 Wh). Impedance measurements were performed across a state-of-charge (SOC) range of 40–100% for both a new battery module and a used battery module that had accumulated approximately 140,000 km of driving cycles. The reconstructed impedance spectra were analyzed using Nyquist plots derived from the measured time-domain data. The results revealed clear differences in the low-frequency impedance characteristics between the new and aged batteries.
In particular, the used battery exhibited a noticeable elongation of the impedance trajectory in the lowfrequency region around 1 Hz, indicating increased diffusion and charge-transfer resistance associated with long-term cycling degradation. These observations confirm that the proposed system can effectively distinguish battery health conditions based on impedance variation.