STUDIES OF THE EFFECTS OF HIGH VOLTAGE ON THE PERFORMANCE AND IMPEDANCE OF LITHIUM-ION BATTERIES
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Lithium-ion batteries play an important role in the transition away from non-renewable sources of energy. Technologies such as electric vehicles and grid energy storage require longer-lasting batteries with higher energy density and lower cost. Although increasing the upper cutoff potential of lithium-ion batteries would lead to higher capacity and higher energy density, achieving long-lasting high potential operation in lithium-ion cells is difficult. Impedance growth is one obstacle to high potential Li[Ni1-x-yMnxCoy]O2 lithium ion cells and is a large contributor to capacity fade and cell failure at high potential. Electrochemical impedance spectroscopy measurements are quick and non-destructive to the cell and can illuminate the processes occurring in lithium ion cells as a function of time, cycle number, and potential. The importance of performing these measurements during cycling, particularly during experiments that are representative of real-life lithium ion cell use, is demonstrated. The fitting of impedance spectra using equivalent circuit models is required to quantitatively study the processes occurring in lithium ion cells at various potentials. The effects of extended periods of time at high potential will be investigated. Furthermore, the effects that various cell components, electrode coatings, electrolyte solvents, and electrolyte additives have on lithium ion cells will be probed.