EIS non stationarity – Electrochemistry, Battery & Corrosion – Application Note 17Latest updated: May 6, 2020
An electrochemical impedance measurement is valid if the system is linear, time-invariant and causal. The time needed by a system to reach its stead-state and consequently the electrochemical impedance measurement can take can be very long. To avoid waiting for the steady-state of the system, the “Drift correction” feature can be used. This option compensates the effect of the transient state of the system on its response to the sinusoidal modulation used in impedance measurements. Generally the error caused is seen at lower frequency. Some examples of used are impedance measurements on batteries under charge or discharge, impedance measurements at various DC bias of a corroding system. “Drift correction” is a patented feature.
Several conditions are required to measure the electrochemical impedance of a system. Its behaviour must be linear, invariant vs. time, and the system should be in a steady-state. Indeed, if the steady-state is not reached by the system, the electrochemical impedance signal used to calculate the Fourier Transform is not periodic. Moreover, the presence of a transient period due to the excitation step implies in the result spectrum, a contribution to the response of the imposed sinusoid (Figure 1).
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