Analysis of lithium diffusion and overpotential in lithium nickle cobalt aluminum oxide based lithium ion cells

Abstract

Cathode degradation during the charge and discharge process is inevitable due to phase transformations during the de-/lithiation process. Various factors such as temperature, cut-off voltage, and current rates tend to cause irreversibility in the phase transformations during cycling, resulting in the quick aging of lithium-ion batteries for electric vehicle applications. This study aims to evaluate 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 through measurements by the galvanostatic intermittent titration technique (GITT). The lithium-ion cell has shown the lowest diffusion coefficient value of 1.08E−17 m2 s−1 at 0.2C rate at 25 °C temperature and the highest diffusion coefficient of 7.2829E−16 m2 s−1 at the lowest current rate of 0.05C rate and 45 °C temperature during discharging. The trend of diffusion coefficient values for lithium de-/intercalation with changing temperature and current rates is investigated and correlated with the phase transformations in the structure of the cathode and is indicative of a mixed-phase reaction mechanism. The electrochemical impedance spectroscopy data reinforces the dependence on lithium-ion diffusion on temperature, and voltage values and is supported by comparative analysis.