Improved State of Health Assessment for Lithium-Ion Batteries Based on Electrochemical Impedance Spectroscopy Measurements
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Abstract
Conventionally, battery State of Health (SOH) is defined through the measurement of discharge capacity. However, such approaches are poorly suited for online and in-vehicle applications, as they require full charge/discharge cycles and accurate current integration over long periods. For this reason, indirect health indicators are widely adopted, especially in automotive PHM frameworks. In this context, Electrochemical Impedance Spectroscopy (EIS) has proven to be an effective tool for investigating battery degradation, as it provides detailed insight into internal electrochemical processes. Nevertheless, EIS measurements are strongly influenced by the operating conditions of the tested device, which reduces their practical value under high or variable stress levels. To address these limitations, this work proposes a robust procedure to extract a one-dimensional Health Indicator (HI) from EIS measurements performed after the electric vehicle (EV) charge phase. Instead of relying on full-spectrum fitting or equivalent circuit modeling which are often computationally intensive and difficult to implement online, the proposed method extracts multiple physically meaningful geometrical features directly from Nyquist plots. The features are normalized and evaluated through an adaptive selection process that identifies the most informative ones for degradation tracking and prognostics, ensuring robustness under varying stress conditions. The selected features are then combined through an innovative algorithm to generate a single HI that accurately reflects the battery degradation trend, enabling integration into automotive Battery Management Systems (BMS). To ensure generalizability and repeatability, the approach is validated at different processing stages using a custom dataset of lithium-ion cells tested under highly stressful charge and discharge conditions for a total of 400 cycles.
How to Cite
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Battery, EIS, State of Health
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