Degradation-Safety Analytics in Lithium-Ion Cells: Part I. Aging under Charge/Discharge Cycling

Disparate degradation modes in lithium-ion cell components due to aging under continuous cycling cause capacity fade and safety concerns under abuse conditions. In this work, the interplay between aging and abuse conditions, namely overcharge and external short, is investigated in fresh and aged cylindrical lithium-ion cells for different degradation conditions and operating windows. The objective, to elicit insights into the potential hazards in an aged cell, is accomplished via a comprehensive and controlled experimental analytics of the electrochemical, thermal and morphological behavior of the cell components. The Part I of the study sets the baseline for the aging induced degradation. According to the results of the aging study, cycle life can be doubled by reducing 200 mV at either ends of the voltage window at the expense of having a 20% reduction in capacity utilization. Differential voltage and temperature analyses revealed a state-of-charge dependence of the internal resistance and heat generation rate. Post-mortem analyses showed that the loss of cyclable lithium inventory due to the solid electrolyte interphase (SEI) formation; and electrochemical deactivation of the cathode owing to delamination and particle cracking, are the primary degradation mechanisms responsible for the cell capacity fade due to aging under continuous cycling.