Advanced Electrochemical Impedance Spectroscopy (EIS) for Battery Testing

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Introduction to EIS

Lithium-ion batteries (LIB) are widely used in various applications due to their high energy and power density. The demand for rapid battery charging and high efficiency leads to continuous improvement in the cell chemistry and construction. Especially for automotive applications, the battery impedance (Z) has dropped to very low values. Today, battery impedance can be as low as few µΩs while the frequency range of interest is typically 1 mHz up to 10+ kHz. While LIB performance is continuously rising, the demand for high performance measurement equipment rises at the same time. Electrochemical impedance spectroscopy (EIS) is an established method providing insights into the electrochemistry and allowing to characterize the battery’s parasitic circuit elements. EIS is typically done for battery R&D, for in-line cell manufacturing and for off-line quality control. Based on EIS data, among others, the state-ofcharge (SOC) and state-of-health (SOH) can be quantitatively predicted using modeling procedures. This document presents EIS with a novel calibration workflow that allows for precise measurement of low battery impedances down to µΩ in a broad frequency range. Additionally, the calibrated data is used for equivalent circuit modeling and electrochemical interpretation, which is provided in the context of materials science and analytical electrochemistry.