Single-frequency impedance monitoring of Li-ion 18650 cells for battery management applications

This paper presents an impedance-based analysis of three types of cylindrical Li-ion 18650 cells subjected to controlled charge–discharge cycling under various temperatures and load conditions. The main objective was to evaluate whether single-frequency impedance monitoring can provide a reliable indicator of operational degradation that could be implemented in practical electronic systems. Measurements were performed using an RLC bridge in the frequency range of 42 Hz to 10 kHz, with particular emphasis on impedance at 100 Hz as a diagnostic reference point. Results demonstrate a clear correlation between impedance growth and the number of cycles, temperature, and discharge current, confirming the applicability of this method for real-time condition monitoring. The findings highlight the potential of simplified impedance diagnostics for integration into battery management systems (BMS), embedded electronics, and telecommunication power supply units, where compact, low-cost, and efficient diagnostic solutions are required.