Meaning
Frequency dependent resistance characterizes the internal physics of a galvanic cell when subjected to alternating current. Measuring electrochemical impedance provides a detailed view of ion diffusion and charge transfer resistance without dismantling the assembly. It maps the electrical response across a spectrum to identify specific hardware bottlenecks.
Signal Analysis
Small amplitude sinusoidal signals allow for the measurement of the system in a pseudo linear state. During the evaluation of electrochemical impedance, the phase shift between the applied voltage and the resulting current reveals the capacitive and inductive properties of the cell. These values represent the physical state of the separators and electrodes.
Diagnostic Utility
Health models use the data to predict the remaining useful life of a pack in the field. When electrochemical impedance increases at low frequencies, it indicates that the electrolyte is drying or the solid electrolyte interphase has thickened.
Frequency Range
Test equipment sweeps from millihertz to kilohertz to capture different chemical phenomena. High frequency results describe the ohmic resistance of the metal foils and tabs, while low frequency data points track the slow movement of ions through the bulk material. The data is often plotted on a Nyquist diagram to visualize the complex relationships between the real and imaginary components of the electrical response.
