Evaluation of Ageing and Degradation for Lithium-Ion Batteries By Using Electrochemical Harmonic Analysis (EHA)

Abstract

Lithium-ion cells show a significant degradation in performance with time (1). This occurs as a result of physical and mechanical changes over time that impacts the electrochemical properties and operating parameters throughout the battery lifetime. These can affect the battery performance in terms of a rise in battery impedance and change in the potential difference that are known as a result of nonlinear electrochemical processes of batteries (2, 3). Therefore, the method of observing nonlinear behaviours have been outstanding to understanding and optimising battery performance (1, 3).In this research, the influences of battery ageing and degradation on harmonic distortion in lithium-ion batteries are investigated to understand nonlinear behaviours of batteries by using Electrochemical Harmonic Analysis (EHA). The study analysed the effects of wide range of temperatures, C-rates and state of charge on battery ageing and degradation. For this purpose, aged and pristine cells are tested in order to analysis harmonic distortion at a specific frequency range between 100mHz and 10kHz.The comparison of harmonic distortion at the same frequencies for aged and pristine cells illustrates that there is a relationship between ageing phenomena and harmonic distortion. The level of distortion increases proportionally according to the effects of ageing on the battery over time. The distortion was mostly seen in lower frequencies, which were in the range of 100mHz to 10Hz. This distortion proceeded directly from the diffusion process of lithium-ion cells. The findings indicate that lower levels of state of charge and higher temperatures have a decrease in total harmonic distortion (THD).The principal conclusion of this study is that the difference in the behaviour of aged and pristine cells clearly indicates that EHA technique can be used to identify the degree of ageing and degradation on lithium-ion cells. Keywords: Electrochemical Impedance Spectroscopy (EIS), Harmonic Analysis, Total Harmonic Distortion (THD), Distortion Integral (DI), Ageing, Degradation, Lithium-ion Battery, Temperature Effect, C-rates, State of Charge (SoC), State of Health (SoH). N. Harting, R. Schenkendorf, N. Wolff and U. Krewer, Applied Sciences, 8, 821 (2018).J. Vetter, P. Novák, M. R. Wagner, C. Veit, K.-C. Möller, J. Besenhard, M. Winter, M. Wohlfahrt-Mehrens, C. Vogler and A. Hammouche, Journal of power sources, 147, 269 (2005).M. Danzer, V. Liebau and F. Maglia, in Advances in Battery Technologies for Electric Vehicles, p. 359, Elsevier (2015).