Degradation Detection of Series-Connected Li-ion based ESS via Time Domain Reflectometry

This paper proposes a technique for degradation detection of series-connected lithium-ion batteries (LiBs) using time domain reflectometry (TDR). Since the internal impedance of the LiB changes during the degradation process, TDR can detect the degraded LiB with its location by analyzing the reference and reflected signals from the LiB under test. The proposed method is verified by experiments with a test to detect degraded LiB with a simultaneous monitoring test to observe changes in the reflected signal during thermal aging. To analyze the correlation between the magnitude of the reflected signal and the degree of degradation, the internal impedance of the LiBs under test is measured using electrochemical impedance spectroscopy. As the internal impedance increases due to degradation, the magnitude of the reflected signal increases, enabling the location of the degraded LiB to be detected using TDR.