Mitigation of Nonlinear Distortions in Online Li-ion Battery Impedance Measurement

Lithium-ion (Li-ion) batteries have become the primary energy storage solution for various applications, including electric vehicles, portable electronics, and renewable energy systems. Ensuring safe and long-lasting Li-ion battery operation requires real-time onboard state monitoring and performance maintenance. Despite ongoing development efforts, accurate and cost-effective battery diagnostic methods remain limited. Online internal impedance measurement has gained traction in recent years as an effective diagnostic tool. Recent studies have introduced methods based on broadband perturbations, enabling real-time battery impedance measurement. In these methods, the battery under test is subjected to controlled charge and discharge perturbations, while Fourier techniques are applied to extract impedance information from the measured voltage and current waveforms. However, applying broadband excitations often introduces nonlinear distortions, leading to inaccurate impedance readings. This work presents a simple method to mitigate the effects of nonlinear distortions in real-time battery impedance measurements under a constant-current stress condition. Experimental results from a commercial Li-ion battery cell are presented and analyzed.