State of health (SOH) assessment for LIBs based on characteristic electrochemical impedance

With the continuous development of high energy density cell technology, the electric transport industry proposed higher requirements for the accuracy and real-time performance of automotive lithium batteries (LIBs) health status assessment. A state of health (SOH) assessment is suggested based on electrochemical impedance at characteristic frequency in the study. The distribution of relaxation time is used to deconstruct the internal electrochemical reaction of the battery and the impedance value of electrochemical process is quantified as a feature to avoid the effect of state of charge (SOC) in the evaluation. The imaginary part of impedance feature is applied to characterize the internal temperature of the lithium battery based on the analysis of impedance differences. Thus, the correlation between the state of health and impedance characteristics is examined to obtain the SOH assessment model of lithium battery in the full SOC and wide temperature spectrum. In conclusion, the assessment demonstrates an exceptional goodness-of-fit, with an accuracy of 0.99 in evaluating the SOH of LIBs and internal temperature, thereby indicating the robustness and reliability of the approach.