<p>This thesis investigates the structure and ion mobility properties within the phosphate and fluorophosphate family of cathode materials for Li ion batteries using solid-state NMR. Developments in lithium ion battery technology are now directed towards automotive applications meaning that many of the cost and safety issues associated with current lithium ion battery technology need to be addressed. Within the current systems the high cost is largely attributed to the use of LiCoO₂ as the positive electrode. Many new and inexpensive Li intercalation materials have been put forward as alternatives to LiCoO₂, however the details concerning the structural and ion-transport properties of these new phases are not well defined. ^6,7Li, ³¹P, and ¹⁹F NMR measurements are an ideal tool to study these properties, as ^6,7Li is able to probe the local environment and dynamics of the mobile ion while ³¹P and ¹⁹F monitor changes in the host framework. Materials selected for study in this thesis include olivine LiFePO₄, monoclinic Li₃M₂(PO₄)₃ (M = V, Fe), the tavorite-based Li₂VPO₄F and Li₂VOPO₄, and the novel layered Li₅V(PO₄)₂F₂. The fluorophosphates have been introduced as higher voltage cathode materials for lithium batteries, however our ^6,7Li 1D selective inversion and 2D EXSY measurements reveal timescales of ion hopping that are relatively slow when compared to those measured in the phosphates. This indicates that the improved power output from the voltage gains may be lost to slow charge/discharge rates.</p> / Doctor of Philosophy (PhD)

This thesis investigates the lithium-ion dynamics and structural changes in the novel cathode material LiFeV2O7 by solid-state NMR spectroscopy and density functional theory (DFT). With the escalating demand for high-performance lithium-ion batteries (LIBs), exploring cathode materials that can offer superior energy density, cycle stability, and safety is crucial. LiFeV2O7 presents a fascinating structure because it incorporates two transition metals capable of undergoing redox processes, a feature highly beneficial for lithium-ion batteries. The research employs advanced DFT calculations to predict the electronic structure and 7Li NMR shifts. These theoretical insights are essential for understanding how structural disorder influences NMR results and how the oxidation state of transition metal impacts the Fermi contact shift. Experimental techniques, including solid-state NMR spectroscopy and diffraction methods, are applied to study the lithium-ion exchange process and structural evolution during electrochemical cycling. Selective inversion NMR experiments were used to quantify the exchange rates relative to lithiation levels, and in combination with diffraction methods and DFT calculations, enabled the development of a structure model that elucidates the corresponding phase changes in the material. Moreover, the thesis discusses the impact of structural modifications on the lithium-ion dynamics within Li1.71FeV2O7, revealing a direct link between specific crystallographic changes and enhanced lithium mobility. The integration of DFT calculations with experimental observations provides a comprehensive understanding of the material's behavior, paving the way for improvements in cathode design. Overall, this research contributes significantly to the field of LIBs, offering novel insights into the complex interplay between structure, dynamics, and electrochemical performance in cathode materials. / Thesis / Doctor of Science (PhD) / This thesis explores the lithium-ion dynamics and structural changes in the new cathode material LiFeV2O7 using solid-state NMR spectroscopy and density functional theory (DFT). As the demand for high-performance lithium-ion batteries (LIBs) grows, discovering cathode materials with better energy density, stability, and safety becomes crucial. LiFeV2O7 is particularly interesting due to its structure, which includes two transition metals that undergo redox processes. This study combines advanced DFT calculations with experimental techniques to understand how structural disorder and the oxidation state of transition metals affect NMR results. Solid-state NMR spectroscopy and diffraction methods are used to examine lithium-ion exchange and structural changes during battery cycling. The research identifies how specific crystallographic changes enhance lithium mobility, providing insights that can improve cathode design. This comprehensive study contributes to the development of more efficient and stable LIBs by revealing the complex interplay between structure, dynamics, and electrochemical performance.