CALCE EPSC Graduate Student Theses and Dissertation Abstracts (2020)

Saxena, Saurabh (Ph.D.)
Effects of Rest Time and Temperature on Graphite - LiCoO2 Battery Degradation

Lithium-ion batteries are used as energy storage devices in a variety of applications ranging from small portable electronics to high-energy/high-power electric vehicles. These batteries degrade and lose their capacity, defined as the amount of charge the battery holds, as a result of charge–discharge operations and various degradation mechanisms. Degradation of lithium-ion batteries is affected by many operational and environmental conditions, including temperature, discharge and charge current, and depth of discharge. Another factor, which has not been given due attention, is the rest period after full charge during the cycling operation of the batteries. This study investigates the effects of rest period after charge operation on the degradation behavior of graphite–LiCoO2 pouch batteries under three different ambient temperatures. Battery degradation has been quantified in terms of the capacity fade and shifts in the peaks of the differential voltage curves which also provide inferences about the individual electrode degradation. Relation between rest time and battery state of charge has been established to explain the capacity fade trends of batteries. A capacity fade trend modeling analysis has been conducted and validated using experimental data of graphite-LiCoO2 pouch batteries from multiple sources with inactive material variations. The degradation mechanisms have been investigated using differential voltage analysis (DVA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) techniques. Applicability of rest time as an accelerating stress factor for Li-ion battery testing has also been discussed.