|dc.description.abstract||Li-ion batteries, owing to their unique characteristics with high power and energy density, are broadly considered a leading candidate for vehicle electrification. A pivotal performance drawback of the Li-ion batteries manifests in the lengthy charging time and the limited cycle life. Fast charging is one of the most desired characteristics for the emerging vehicle technologies, which is at a nascent stage and not well understood. Moreover, cycle life is a vital component of battery integration and market penetration. The objectives of this work include: (1) investigating the fast charging induced performance limitations with emphasis on temperature extremes; and (2) studying the implications of combined chemical and mechanical degradation modes on the battery cycle life.
In this work, a coupled electrochemical-thermal model is utilized to study the internal behavior and thermal interactions during fast charging process. Additionally, the cycle life predictions are realized by developing a capacity fade model consisting of a coupled chemical (irreversible solid electrolyte interface formation) and mechanical (intercalation induced damage) degradation formalism with thermal effect.
Primary results with conventional protocol at high rate (3C) show that at moderateand high operating temperatures the main performance limitations of fast charging originate from lithium ion transport in the electrolyte and ohmic resistance. However, charge transfer resistance is found to be the limiting mechanism for the conventional 1C charging rate at low temperatures. Furthermore, it was found that the concentration build-up at anode surface can be effectively manipulated by using an appropriate charging protocol such as pulse charging and boostcharging. However, it was concluded that at low temperatures, a successful charging protocol is achieved by utilizing the principle of thermal excitement. For battery cycle life, results show that mechanical degradation is the predominant mechanism for capacity fade at low temperatures and high rates. However, the temperature as a stress factor is the principle capacity fade source at high operating temperatures where mechanical degradation is not prominent. The importance of cooling condition, particle size and the exchange current density on life cycle have been emphasized. Finally, a degradation phase map that shows the significance of active particle size and stress factors (temperature and current rate) on the capacity fade is presented. It is concluded that the particle size showed a trade-off in the capacity faderesults at different temperatures.||en