Figure 3-2 is a Nyquist plot showing the measured impedance spectra of multiple cells within a series-connected pack. Each curve represents the impedance of one individual cell, plotted as imaginary impedance versus real impedance across a range of frequencies.

All curves follow the same general trend, starting near the real axis at high frequencies, forming a distinct arc in the mid-frequency range, and extending downward into the negative imaginary plane at low frequencies. The high-frequency region, close to the origin, corresponds to the ohmic resistance of each cell, which is consistent across all units. The mid-frequency arc reflects the combined effects of charge transfer and capacitive behavior at the electrode interfaces. The low-frequency tail shows the typical response associated with mass transport processes inside the cell.

While all curves share the same fundamental shape, there is a small but noticeable spread between them. This indicates minor differences in impedance magnitude and phase across the cells, which is expected due to normal manufacturing variations and minor differences in operating history. No curve deviates significantly from the common trend, confirming that all cells are operating within a similar range of electrical behavior.

This measurement demonstrates the ability to consistently capture the impedance response of every cell in the pack. The plot provides a clear visual representation of the overall impedance distribution and confirms that all cells exhibit the expected behavior for this type of energy storage device.