EXPLORING LiFeV2O7 AS A POTENTIAL CATHODE FOR LITHIUM-ION BATTERIES: AN INTEGRATED STUDY USING 7Li NMR, DFT, AND OPERANDO SYNCHROTRON X-RAY DIFFRACTION

Abstract

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.