Module-Level Electrochemical Impedance Spectroscopy analysis for SOH monitoring of Lithium-ion Batteries

Lithium-ion batteries play a central role in energy storage for electric vehicles and renewable energy systems. Due to their high cost and sensitivity, an efficient monitoring of their state of health is required in most applications. A typical state of health monitoring is based on capacity measurement, which takes several hours and offers only limited diagnostic insight. This contribution proposes the use of electrochemical impedance spectroscopy as a faster, non-invasive alternative capable of capturing internal degradation phenomena with better detail. Although existing research focuses mainly on individual cells, practical applications require module-level diagnostics without disassembly. This study evaluates the correlation between the state of health and equivalent electrical circuit parameters derived from electrochemical impedance spectroscopy measurements on 2P3S battery modules aged from 100% to 60% state of health. Results show that Rs, R1, and N1 exhibit a strong correlation with the state of health, making them suitable for module-level diagnostics. The findings provide a foundation for developing reliable module-sorting strategies, for example at the transition between first-life and second-life applications.