Time–frequency coupled modeling of lithium-ion battery impedance: Insights into solid electrolyte interphase growth and lithium plating

We develop a time–frequency coupled degradation model for lithium-ion batteries to resolve dynamic aging phenomena such as the growth of the solid electrolyte interphase (SEI) and lithium plating. By decoupling slow cycling dynamics from fast impedance responses, the model captures frequency-specific signatures—SEI growth elevates high-frequency resistance (R_s), while lithium plating induces sharp changes in anode charge transfer resistance and electrical double-layer capacitance at lower frequencies. SEI rupture induces a non-monotonic dependence of R_s on the state of charge (SOC) during long-term cycling, while lithium plating and the reduction of anode porosity exacerbate current density heterogeneity, thereby promoting a further decrease in the R_s. These features, elusive to traditional electrochemical impedance spectroscopy (EIS), are clearly identified via dynamic electrochemical impedance spectroscopy (DEIS). Overall, the framework clarifies the physical origins of key DEIS features and establishes a mechanistic basis for interpreting frequency-dependent signatures associated with battery degradation.