Analysis of Lithium Kinetics in Lithium Nickel Cobalt Aluminum (NCA) Cells using GITT and EIS /

Abstract

Cathode degradation is an inevitable consequence of the charge and discharge process of lithium-ion batteries due to the phase transformations that occur during de-/lithiation. Several factors such as temperature, cut-off voltage, and current rates can cause irreversibility in the phase transformations during cycling, leading to rapid aging of lithium-ion batteries, especially those used in electric vehicle applications. To better understand the degradation of these batteries, this study used the galvanostatic intermittent titration technique (GITT) to measure the trends of the lithium-ion diffusion coefficient as a function of the lithium-ion concentration and potential in the lithium nickel cobalt aluminum oxide (NCA) cathode of the VTC5 lithium-ion cell. The study found that the diffusion coefficient values for lithium de- /intercalation in the NCA cathode ranged from 1.08E-17 m2 s -1 at 0.2 C rate at 25 ℃ temperature to 7.2829E-16 m2 s -1 at the lowest current rate of 0.05 C rate and at 45 ℃ temperature during discharging. The trend of diffusion coefficient values with changing temperature and current rates was investigated and correlated with the phase transformations in the structure of the cathode, indicative of a mixed-phase reaction mechanism. Additionally, electrochemical impedance spectroscopy data was used to reinforce the dependence of lithium-ion diffusion on temperature and voltage values. The study shows that changes in temperature and voltage can have a significant impact on the phase transformations during the charge and discharge process, ultimately leading to cathode degradation and reduced battery performance. The findings of this study highlight the importance of understanding the factors that contribute to the degradation of lithium-ion batteries and the role that phase transformations and diffusion coefficients play in this process. By gaining a better understanding of these mechanisms, researchers can develop strategies to improve the performance and lifespan of lithium-ion batteries for electric vehicle applications.