Real-time SOC monitoring in NCM Li-ion batteries via quasi-static component of nonlinear guided wave

Abstract

We report real-time state-of-charge (SOC) monitoring in NCM Li-ion batteries using quasi-static nonlinear guided waves (QSC-NGW). An experimental system is developed to capture QSC-NGW during battery cycling. Empirical optimization of excitation parameters (cycle number, frequency) extracts high signal-to-noise ratio QSC-NGW signals, eliminating the need for battery-specific priors. During 1C cycling, real-time QSC-NGW magnitude-time data under varying SOC are fitted to quadratic polynomials. The obtained results clearly reveal a strong correlation of QSC-NGW with SOC of the batteries. Compared to the conventional linear ultrasonic method, QSC-NGW exhibits cleaner wave modes and reduced signal processing complexity. It maintains good consistency in different cycle multiplicities with different batteries of the same batch. This method enables effective SOC monitoring in NCM Li-ion batteries, showing significant potential for practical battery health assessment.