What is the significance of impedance rise in the context of battery degradation?

Impedance rise is a significant indicator of battery degradation because it reflects an increase in the internal resistance of the battery, which directly impacts its performance and lifespan. Impedance refers to the opposition to the flow of alternating current (AC) within the battery and includes both resistance and reactance. As a battery degrades, various factors contribute to an increase in its internal impedance. The formation and growth of the Solid Electrolyte Interphase (SEI) layer on the electrodes, electrolyte decomposition, loss of active material, and corrosion of current collectors all increase the resistance to ion transport within the battery. An increase in impedance leads to several adverse effects. It reduces the battery's ability to deliver power, as a larger portion of the energy is lost due to internal resistance. It also increases heat generation during charging and discharging, accelerating further degradation. The voltage drops more significantly under load, reducing the usable capacity of the battery. Monitoring impedance rise can help to assess the State of Health (SOH) of the battery and predict its Remaining Useful Life (RUL). Electrochemical Impedance Spectroscopy (EIS) is a technique used to measure the impedance of a battery over a range of frequencies, providing detailed information about the degradation mechanisms occurring within the battery. By tracking impedance rise over time, operators can identify potential problems early on and take corrective actions to extend the battery's lifespan.