UCLA

Rechargeable battery systems are of increasing importance as the global demand for energy continues to skyrocket. Steps must be taken in regards to improving energy density and power density of battery materials in order to support a societal pivot from fossil fuel dependence to increasing reliance on renewable energy sources. This dissertation focuses on the improvement of anode materials for lithium and sodium-ion batteries with the goal of accessing higher energy densities. Alloy anode materials provide a much higher energy density than the commonly employed graphite anode, but suffer from volume expansion issues that give rise to particle pulverization and rapid capacity loss. Nanoporous architectures can be utilized to reduce this effect, as nanoporous alloy anodes have shorter lithium diffusion pathways, and reduced global particle expansion which contributes greatly to improved cycle stability. The first part of this work details a mechanistic study for the lithiation of a multicomponent alloy anode material SbSn, and how the nanoporous architecture improves the lithiation kinetics of the active material. The nanoporous material was synthesized by a facile dealloying synthesis, and then characterized in-situ using X-ray diffraction (XRD) and pair distribution function (PDF) to track structural rearrangement during lithiation. XRD results demonstrate that the nanoporous system separates into Sb and Sn domains significantly faster than the bulk analog, and PDF tracks the evolution of lithiated Sn phases to determine final Sn lithation stoichiometry as amorphous Li7Sn3. The second chapter of this thesis focuses on the influence of amorphous intermediates on cycle stability. Sb evolves entirely through crystalline intermediates during lithiation, contrary to the fully amorphous intermediates it evolves through during sodiation. Nanoporous Sb is synthesized by a simple dealloying reaction, and then is characterized with in-situ transmission X-ray microscopy (TXM) and XRD. TXM images demonstrate the impressive reversibility of Sb particles during sodiation when compared to the destructive particle pulverization observed during lithiation. XRD confirms the absence of crystalline intermediates when Sb is cycled with sodium, and the amorphous nature of Sb during (de)sodiation is credited for this remarkably reversible volume expansion. The final chapter of this thesis describes a novel 3D battery cell geometry designed to enable easy access to in-situ tomographic datasets. 3D tomographic reconstructions provide an unprecedented glimpse into the evolution of interior structures of active particles, and provide great insight into the mechanistic behaviors of active materials. Traditional 2D cell geometries present differing beam path lengths and increasing amounts of attenuating materials when rotated, issues that are circumvented by a 3D cell geometry that remains largely unchanging even when being rotated in the X-ray beam.