Mapping of state of charge and cathode material in NCM Li-ion batteries: an in-situ study based on the quasi-static component of nonlinear guided wave

Lithium-ion batteries (LIBs) have emerged as a dominant energy storage technology for renewable energy systems, necessitating precise monitoring of both state of charge (SOC) and electrode health parameters to maintain system safety and ensure operational reliability. Currently, ultrasonic guided wave technology enables rapid, non-destructive, and sensitive monitoring of LIBs, yet its implementation faces challenges due to suboptimal acoustic directionality and signal interpretability. To overcome these limitations, this research proposes an innovative methodology incorporating quasi-static components of nonlinear guided waves (QSCNGW). Through systematic extraction of QSCNGW signals during cycling of nickel cobalt manganese oxide Li-ion batteries (NCM-LIBs), we conducted comprehensive time-frequency domain analyze and established correlations between waveform features and cathode microstructural evolution, which were verified through in-situ characterization method such as scanning electron microscopy (SEM), Raman spectroscopy (RS), and atomic force microscopy (AFM). Key findings reveal a linear correlation between QSCNGW signal timing and SOC, while magnitude variations quantitatively mirror cathode phase lattice transitions. Notably, the QSCNGW approach demonstrates enhanced reliability and measurement accuracy compared to conventional linear guided wave methods, eliminating the need for prior structural parameter inputs. This dual-functional technique not only facilitates real-time SOC monitoring but also deciphers electrode degradation mechanisms, thereby establishing a physics-informed framework for next-generation battery diagnostics and health management.