Multisine electrochemical impedance spectroscopy for Li-ion battery characterisation

Electrochemical impedance spectroscopy (EIS) is a valuable tool for non-invasive battery characterisation as it provides a compact data representation of physical processes over a wide range of time scales. Commonly, sinusoids at different frequencies are injected sequentially (single-sines). Alternatively, a multisine excitation (a sum of sines) is advantageous for reducing experiment time and allowing impedance to be measured during operational conditions (e.g.\ charging, discharging, relaxation, and during temperature changes). In this work, we demonstrate high-fidelity multisine EIS measurements on Li-ion cells over a wide frequency range (20 mHz to 1 kHz) taken with a commercial potentiostat, and compare these to single-sine EIS, discussing the advantages of both techniques and how to verify the conditions of linearity and stationarity. We also measure broadband multisine impedance at different operating conditions (during charging/discharging, relaxation, and temperature changes), showing how this tool gives new insights into battery dynamics, material properties, charge transfer processes, and thermal performance.