Nyquist Plot

Impedance Separation

Separating the different impedance contributions is achieved by analyzing the distinct shapes on the plot, which typically include high-frequency semicircles and low-frequency linear regions. Sourcing teams use these plots to evaluate the efficiency of the solid electrolyte interface and the kinetics of the charge transfer reaction. This analysis helps in comparing the performance of different cell suppliers and selecting those with the lowest internal resistance.

Sourcing contracts specify the acceptable range of impedance values at specific frequencies to ensure consistency across production lots.

Diagnostic Tool

Identifying degradation mechanisms such as electrode cracking, electrolyte dry-out, or lithium plating is a primary use of these plots during aging tests. Sourcing specialists analyze how the impedance curve shifts as the cell is cycled to predict its remaining useful life and to ensure it meets the warranty requirements. This non-destructive testing method is highly valuable for the qualification of cell designs and the detection of early failure modes.

This data allows for more accurate predictions of lifetime performance.

Production Monitoring

Monitoring the impedance curves during mass production ensures that the manufacturing processes are tightly controlled and that the cells are uniform in quality. Sourcing specialists use this data to identify any shifts in the chemistry or construction of the cells that could affect their performance in the field. This continuous quality control protects the buyer from the risk of receiving cells with higher internal resistance or poorer performance than the qualified samples.

This testing is essential for maintaining high yield and consistency.