Rational Design of Electrode Architectures for Improved Performance of Li-metal and Li-ion Batteries

Vehicle electrification can have a significant impact on reducing greenhouse gas emissions and enabling increased use of renewable energy sources. To realize widespread adoption of electrified powertrains, a breakthrough in battery technology is needed. Particularly, improving energy density and reducing charging time are both critical for electric-vehicle-scale batteries. The primary goal of this thesis is to contribute to these metrics through the development of new fundamental understanding in lithium (Li) battery systems and designing novel electrode architectures for improved performance. This dissertation has two primary thrusts: (1) addressing the poor reversibility of Li-metal anodes in liquid electrolytes to realize next-generation batteries with high energy densities, and (2) enabling fast-charging of state-of-the-art Li-ion batteries with thick electrodes. In Thrust 1, an improved mechanistic understanding of the morphological evolution of Li metal anodes during cycling is developed, which provides insight into the voltage, capacity, and failure of Li-metal batteries. It is shown that mass transport limitations arise as a result of dead Li accumulation at the Li metal electrode, which introduces a tortuous pathway for Li-ion transport. In Li-Li symmetric cells, mass transport effects cause a change in the voltage shape and an increase in cell polarization. The accumulation of dead Li is also conclusively shown to directly cause capacity fade of full cells containing Li metal anodes. In order to reduce dead Li formation, a three-dimensional (3-D) current collector composed of highly uniform vertically aligned Cu pillars is further developed. By rationally tuning geometric parameters of the 3-D architecture, the Li morphology can be controlled. In addition, deposition of an ultrathin layer of zinc oxide by atomic layer deposition on the current collector surface can facilitate initial Li nucleation, which dictates the morphology and reversibility of subsequent Li growth. This core-shell pillar architecture allows the effects of geometry and surface chemistry to be individually controlled to optimize the electrode performance in a synergistic manner. Using this platform, Li metal anodes are demonstrated with Coulombic efficiency up to 99.5%. In Thrust 2, two approaches are demonstrated to improve the charge rate of Li-ion batteries with thick electrodes. In the first approach, a laser-patterning process is developed to produce 3-D graphite architectures with arrays of vertical pore channels through the electrode thickness, which enhance both through-plane and in-plane ionic transport. By applying the 3-D electrode design on industrially relevant pouch cells, it is shown that long-term fast-charge cycling (< 15 minute charging time) can be achieved with minimal capacity fade. The second approach addresses energy/power tradeoffs by fabricating hybrid anodes with uniform mixtures of graphite and hard carbon. By controlling the graphite/hard carbon ratio, it is shown that battery performance can be systematically tuned to achieve both high energy density and efficient fast charging. A detailed electrochemical analysis demonstrates that the enhanced performance is attributed to an improved homogeneity in reaction current distribution throughout the hybrid anode volume. In summary, this thesis furthered the understanding and performance of Li-metal and Li-ion batteries through the development of new fundamental insight and novel electrode architectures. The implications of this work could aid in the development of not only the state-of-the-art Li-ion batteries, but also next-generation battery systems using Li metal anodes.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/168000/1/knhgchen_1.pd