Doctor of Philosophy (Ph.D.), University of Dayton, 2023, Electrical Engineering

Lithium-ion batteries (LIBs) have transformed modern electronics and rapidly advancing electric vehicles (EVs) due to high energy, power, cycle-life, and acceptable safety. However, the comprehensive commercialization of EVs necessitates the invention of LIBs with much enhanced and stable electrochemical performances, including higher energy/power density, cycle-life, and operation safety but at a lower cost. An unprotected lithium-ion battery (LIB) cell cathode using lithium metal anode and organic carbonate liquid electrolyte undergoes significant structural damage during the cycling (Li+ intercalation/ deintercalation) process. Also, a bare cathode in contact with a liquid electrolyte forms a resistive cathode electrolyte interface (CEI) layer. Both the cathode structure damage and CEI lead to rapid capacity fade. Different strategies have been used to mitigate the degradation of LIB electrodes, including designing electrolytes to enhance SEI/CEI formation, cycle stability, interface engineering with protective coatings to prevent the breakdown of active material particles during cycling, composition control of the electrode particles, synthetic optimization to control particle morphology, the use of composites made from conductive scaffolds and active materials and designing new electrode architectures to overcome volume changes and enhance transport properties. Cathode surface modification has been used to reduce CEI formation and structural damage, improving capacity retention, cycle life, energy density, power density, and safety of a LIB. Recently, the coating of the cathode with an intermediate layer (IL), which is transparent to Li+ conduction but impermeable to electrolyte solvent, has been developed to minimize CEI formation and structural damage. IL based on Li+ insulating ceramics, such as aluminum oxide (Al2O3), tin oxide (SnO2), and magnesium oxide (MgO), has been developed but to limited success in mitigating the above cathode degradation. The (open full item for complete abstract)

Doctor of Philosophy, Case Western Reserve University, 2020, Chemical Engineering

High-energy density batteries are essential for powering future electric vehicles (EVs) and electric aircraft. These technologies are limited by the capacity of their batteries. Enabling high-specific energy batteries could make longer-range electric vehicles and electric aircraft a reality. The Li-metal anode offers the highest theoretical specific energy among practically available anode materials. However, secondary Li-metal anodes experience capacity loss and safety hazards caused by the growth of dendrites on the anode surface during charging. After four decades of research on Li-metal batteries, rechargeable Li-metal anodes that do not evolve dendrites are still not commercially available. Understanding the physical causes and mechanisms of dendritic Li electrodeposition, in order to develop commercial Li-metal batteries, motivates the present work. It is shown herein that solid-state transport limitations within a dynamic solid electrolyte interphase (SEI) are dominant in controlling the time when Li dendrites first form. Chronopotentiometry and optical imaging provide experimental observations for when dendrites first appear on a Li electrode. Dendrite onset time is shown to increase with increasing temperature and decrease with increasing current density and initial SEI thickness. These phenomena are shown to be due to the onset of diffusion limitations brought on by a thickening SEI. Electrochemical impedance spectroscopy (EIS) provides evidence for SEI growth and enables estimation of the SEI growth rates during Li electrodeposition. These experiments guide the development of an analytical model that explains mechanistically how transport limitations within the SEI control the onset time of dendrite growth during Li electrodeposition. The model also provides predictions of Li dendrite onset times. These predictions agree qualitatively with the observed effects of current density, initial SEI thickness, temperature, and pulsing. Finally, it is shown th (open full item for complete abstract)