Understanding what happens inside a battery during operation is essential for improving performance, safety and lifetime. A new study, conducted within the NEMO framework, introduces two innovative measurement protocols that make it possible to distinguish between two key factors affecting battery impedance during high-current excitation: electrochemical processes and self-heating.

Using advanced Electrochemical Impedance Spectroscopy (EIS) and Nonlinear EIS (NLEIS) techniques, the researchers developed methods that exploit the different time scales of these phenomena. While electrochemical nonlinearities occur almost instantaneously, temperature-related effects develop more slowly. By separating these contributions, the new approach provides a more accurate picture of battery behaviour under demanding operating conditions.

The methods were tested on a lithium nickel manganese cobalt oxide (NMC) battery cell and successfully quantified the relative impact of thermal and electrochemical effects on impedance changes. The results revealed that, under certain conditions, impedance reductions are driven entirely by electrochemical processes, while at higher excitation levels both electrochemical and thermal contributions play a role.

The study also challenges a widely used assumption in battery diagnostics. Researchers found that the battery remained within a linear operating regime at voltage amplitudes up to 280 mV, significantly higher than the commonly accepted 20 mV threshold. This finding could help simplify future impedance measurements and expand the practical use of impedance-based diagnostic techniques.

Read the full study on Zenodo: Quantitative separation of thermal and electrochemical contributions in nonlinear EIS measurements

Picture by Steve A Johnson on Unsplash

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