Electrochemical impedance spectroscopy EIS is a modern method to investigate the electrical and electrochemical properties of batteries.

Electrochemical impedance spectroscopy allows the investigation and evaluation of battery cells including their components such as catalysts or electrolytes.

However, a module with several cells or the entire pack can also be examined during operation under different operating conditions, load conditions or current loads.

The test specimens usually have very low impedances. As the active area of the battery cells steadily increases, the electrochemical impedances become lower and lower (electrochemical impedance is inversely proportional to active area).

The battery is excited (modulated) with a sinusoidal current. The modulation current is up to ±50A. The resulting voltage is measured with amplitude and phase over a wider frequency range.

The impedance spectrum of a battery depends on the SOC of the battery in addition to its physical properties.