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ZFit and equivalent electrical circuits (EIS Equivalent Circuit) – Battery- Application Note 14

Latest updated: August 31, 2021


This application note explains the general approach to fitting an Electrochemical Impedance spectrum, to an equivalent circuit. After a spectrum is recorded, an equivalent circuit can be picked from the list of pre-programmed circuits, or built by the user with the ‘Edit’ tool. Extra attention has to be paid to pick a circuit that appropriately represents the physical model of the sample under study. Often times different circuits can match the electrical response of the sample, but only one will correspond to its material characteristics (for example two different ladder models, Voigt or Maxwell). Values obtained with different models can be transformed using appropriate formulae.



It has long been known that different electrical circuits can explain EIS data in an equivalent manner, that is, they exhibit identical impedance for all frequencies [1-4].

EC-Lab® software is provided with a powerful tool for EIS data analysis called ZFit. This tool can perform electrical circuit identification with EIS experimental data files obtained with either Bio-Logic potentiostat/galvanostat or with other systems on the market. In fact, EC‑Lab® software can import ASCII text files generated by other electrochemical stations and perform efficient EIS fits. The user can choose between two different minimization algorithms, Simplex and Levenberg-Marquardt, to achieve the best electrical element values.

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