Combined electron imaging and diffraction methods for understanding disordered rocksalt cathodes
<p>The development of lithium-ion batteries is pivotal in the wide range of technologies required to make more efficient use of clean energy sources, notably the transition to the wide-scale use of electric vehicles. In recent years, research into layered cathode material has pivoted to more d...
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| Format: | Thesis |
| Language: | English |
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2023
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| _version_ | 1824459206541967360 |
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| author | Hedley, E |
| author2 | Nellist, PD |
| author_facet | Nellist, PD Hedley, E |
| author_sort | Hedley, E |
| collection | OXFORD |
| description | <p>The development of lithium-ion batteries is pivotal in the wide range of technologies required to make more efficient use of clean energy sources, notably the transition to the wide-scale use of electric vehicles. In recent years, research into layered cathode material has pivoted to more disordered systems, which do not require the incorporation of cobalt in the composition and aim to minimise structural changes through entropy-stabilised disorder. Disordered rocksalt (DRS) cathodes have emerged as promising candidates in the field. The nature of short range order (SRO) has been identified as a determining factor in the lithium migration properties, yet very few in-depth studies exist in the literature. This thesis uses a range of electron microscopy techniques to study structural aspects of DRS cathodes, including SRO. Prior to the structural investigation of these materials a digression is taken into optimising the workflow for 4-dimensional scanning transmission electron microscopy (4D-STEM) data, specifically, in the case of low-dose imaging of beam-sensitive materials, including potential cathode candidates.</p>
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<p>The aforementioned digression into optimising the handling of 4D-STEM data involves an in-depth investigating the feasibility of ptychographyic reconstructions from event-based binary data. The investigation finds the method effectively reduces the data storage and processing memory requirements. An adaptation of a neural network for identifying the entry point of electrons is tested simultaneously. It is proposed that by changing the training dataset, the POE-NN method is highly adaptable to a range of experimental conditions.</p>
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<p>The remainder of this thesis demonstrates using electron microscopy to investigate the nature of the SRO in DRS cathodes and explores its dependence on the transition metal combination. It is demonstrated that the SRO can be explained by cluster model-based correlations of 3-dimensional polyhedral. Annular dark field (ADF) imaging is used to visualise the SRO in real space and, therefore, understand the correlation length and distribution of clusters. Following this, an examination of the DRS phase of LiMnO<sub>2</sub> (LMO) is carried out, using ADF imaging to visualise the SRO for the first time. An investigation using 4D-STEM, which evidences the formation of a spinel phase upon cycling, is presented. Finally, the application of ptychography for elucidating structural aspects of DRS cathodes is established by showing that the tetrahedral sites are unoccupied in regions of the SRO and providing insights into the nature of the termination surface.</p> |
| first_indexed | 2025-02-19T04:38:06Z |
| format | Thesis |
| id | oxford-uuid:906b8bce-9145-4742-b582-21a25e663825 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2025-02-19T04:38:06Z |
| publishDate | 2023 |
| record_format | dspace |
| spelling | oxford-uuid:906b8bce-9145-4742-b582-21a25e6638252025-02-11T12:02:08ZCombined electron imaging and diffraction methods for understanding disordered rocksalt cathodes Thesishttp://purl.org/coar/resource_type/c_db06uuid:906b8bce-9145-4742-b582-21a25e663825Materials scienceEnglishHyrax Deposit2023Hedley, ENellist, PDBruce, PG<p>The development of lithium-ion batteries is pivotal in the wide range of technologies required to make more efficient use of clean energy sources, notably the transition to the wide-scale use of electric vehicles. In recent years, research into layered cathode material has pivoted to more disordered systems, which do not require the incorporation of cobalt in the composition and aim to minimise structural changes through entropy-stabilised disorder. Disordered rocksalt (DRS) cathodes have emerged as promising candidates in the field. The nature of short range order (SRO) has been identified as a determining factor in the lithium migration properties, yet very few in-depth studies exist in the literature. This thesis uses a range of electron microscopy techniques to study structural aspects of DRS cathodes, including SRO. Prior to the structural investigation of these materials a digression is taken into optimising the workflow for 4-dimensional scanning transmission electron microscopy (4D-STEM) data, specifically, in the case of low-dose imaging of beam-sensitive materials, including potential cathode candidates.</p> <br> <p>The aforementioned digression into optimising the handling of 4D-STEM data involves an in-depth investigating the feasibility of ptychographyic reconstructions from event-based binary data. The investigation finds the method effectively reduces the data storage and processing memory requirements. An adaptation of a neural network for identifying the entry point of electrons is tested simultaneously. It is proposed that by changing the training dataset, the POE-NN method is highly adaptable to a range of experimental conditions.</p> <br> <p>The remainder of this thesis demonstrates using electron microscopy to investigate the nature of the SRO in DRS cathodes and explores its dependence on the transition metal combination. It is demonstrated that the SRO can be explained by cluster model-based correlations of 3-dimensional polyhedral. Annular dark field (ADF) imaging is used to visualise the SRO in real space and, therefore, understand the correlation length and distribution of clusters. Following this, an examination of the DRS phase of LiMnO<sub>2</sub> (LMO) is carried out, using ADF imaging to visualise the SRO for the first time. An investigation using 4D-STEM, which evidences the formation of a spinel phase upon cycling, is presented. Finally, the application of ptychography for elucidating structural aspects of DRS cathodes is established by showing that the tetrahedral sites are unoccupied in regions of the SRO and providing insights into the nature of the termination surface.</p> |
| spellingShingle | Materials science Hedley, E Combined electron imaging and diffraction methods for understanding disordered rocksalt cathodes |
| title | Combined electron imaging and diffraction methods for understanding disordered rocksalt cathodes
|
| title_full | Combined electron imaging and diffraction methods for understanding disordered rocksalt cathodes
|
| title_fullStr | Combined electron imaging and diffraction methods for understanding disordered rocksalt cathodes
|
| title_full_unstemmed | Combined electron imaging and diffraction methods for understanding disordered rocksalt cathodes
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| title_short | Combined electron imaging and diffraction methods for understanding disordered rocksalt cathodes
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| title_sort | combined electron imaging and diffraction methods for understanding disordered rocksalt cathodes |
| topic | Materials science |
| work_keys_str_mv | AT hedleye combinedelectronimaginganddiffractionmethodsforunderstandingdisorderedrocksaltcathodes |