Magnetic Resonance Investigations of Ion Transport Phenomena in Lithium-Ion Battery Electrolyte Materials

Abstract

The subject of this thesis is the application of magnetic resonance methods to the characterization and quantification of lithium-ion transport in a wide range of lithium-ion battery electrolyte materials relevant to the electromobility and energy storage sectors. In particular, field-gradient magnetic resonance techniques, in the form of PFG-NMR diffusivity measurements of both liquid- and solid-state electrolytes and in situ MRI of electrochemical cells, comprise the core means by which these characterizations were performed. PFG-NMR and ionic conductivity studies of a range of liquid-state electrolyte mixtures were performed, as a function of temperature, to assess how key mass and charge transport properties reflect differences in composition. In situ MRI was used to study the effect of temperature on steady-state concentration gradient formation in polarized liquid electrolytes, with the results quantitatively compared to model predictions. This approach was then extended, using a combination of MRI and spatially-resolved PFG-NMR, to study the interlinked effects of temperature and current density on concentration gradient formation, and to attempt a comprehensive characterization of the ion transport parameters with spatial resolution. Finally, PFG-NMR and MAS-NMR were applied in a solid-state electrolyte context to investigate compositional effects on ion transport in the argyrodite family of lithium-sulphide ion conductors, and the influence of macroscopic sample format (glass, crystalline powder, compressed crystalline pellet) on micro-scale ion transport in a thio-LISICON ion conductor. Taken together, the studies demonstrate the effectiveness of magnetic resonance methods for the robust elucidation of the means by which material properties impact ion transport in technologically-relevant lithium-ion electrolyte systems.