UC Santa Barbara

Rechargeable lithium-ion batteries (LIBs) are a critical component of global renewable energy infrastructure. However, increased reliance on LIBs requires improvements to their component materials’ performance and longevity. Typical graphitic anode materials suffer from inherent capacity limitations and low-voltage degradation, which reduces usable power and charging speeds. Meanwhile, energy density in state-of-the-art LIBs remains limited by the capacity of its cathode materials. This dissertation first investigates a high-rate LIB anode material, the Wadsley-Roth-derived NaNb13O33 phase, and examines its lithium insertion behavior and mechanisms for the first time. Following this, the structural and kinetic ramifications of lightly doping the energy-dense, layered transition-metal oxide cathode, LiNiO2, are explored in depth. Owing to their exceptionally high rate-capabilities, high volumetric capacities, and long cycle lives, Wadsley-Roth compounds are promising anode materials for high-performance lithium-ion batteries. Structural insights from neutron and synchrotron diffraction, as well as solid-state nuclear magnetic resonance (NMR), reveal sodium disorder and the presence of open, pseudo-2D channels that evolve minimally with cycling. Using electrochemical, magnetic resonance and spectroscopic techniques, supported by computational modeling, the high rate-performance and capacity of NaNb13O33 is demonstrated and rationalized as the result of multi-electron redox, fast multi-channel Li diffusion, and an insulator-to-metal transition upon lithiation. These results place NaNb13O33 within the ranks of promising new high-rate lithium anode materials that warrant further research. Next, we compare the effects of doping LiNiO2 with, separately, 3% Al and Mg ions. LiNiO2 experiences rapid capacity decay due to cycling-induced structural transformations that degrade Li extraction and insertion kinetics. Using long-range and local structural techniques, we examine the impacts of each dopant on the pristine structure and demonstrate that both planar and point defects can be modulated by dopant selection. We then show the impact of such structural changes to first cycle irreversibility and long-term structural and kinetic degradation. Insights from ex situ X-Ray diffraction, NMR, and transmission electron microscopy (TEM) reveal the importance of minimizing high-voltage cathode volume changes, as well as twin boundary defects, in reducing strain and kinetic hindrance accumulation with cycling. We show that twin boundaries functionally reduce the densified surface area, which is a key factor affecting kinetic capacity degradation.