Investigating Local Structure in Lithium-ion Battery Materials

Cook, Chris and Griffin, John (2025) Investigating Local Structure in Lithium-ion Battery Materials. PhD thesis, Lancaster University.

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Abstract

The planned widespread adoption of electric vehicles means increased demand for the batteries to power them. However, the current commercial standard materials are made from a limited range of elements, placing excessive demands on resources. There is therefore a motivation to develop new cathode chemistries, form a more diverse range of materials. A major obstacle to the commercialisation of these new materials is that they suffer from unwanted side reactions. These can occur at the material’s surface or within the bulk structure and can negatively impact performance. This thesis focusses on understanding these unwanted processes, and the performance of different countermeasures, by exploring the material’s local structure and how it changes when used in a battery. First, plasma polymerisation was explored as an alternative way of preparing protective coatings, to prevent surface reactions, using X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy and 1H solid-state nuclear magnetic resonance (SSNMR) spectroscopy. Precursor adhesion and substrate damage are shown to be important considerations when preparing coatings using this approach. Then oxyfluoride disordered rocksalt (DRX) materials were explored using a multinuclear SSNMR approach, supported by X-ray diffraction (XRD) and density functional theory (DFT) calculations. This showed that these materials are not truly disordered, with the formation of LiF-like regions potentially being important for stabling the material structure during cycling. Finally, the high-voltage behaviour of vanadium-based DRX materials was investigated, using SSNMR, XRD and EPR as well as pair distribution function (PDF) analysis and resonant inelastic X-ray scattering (RIXS) measurements. These results indicate that structural rearrangements that occur at high voltages may give the appearance of other side reactions. The work presented in this thesis uses multiple characterisation techniques to provide insight into the structures of potential next-generation cathode materials, that could serve to guide material synthesis.