{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/342064"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/342064","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Magnetic Resonance Studies of a Sodium-Ion Battery Cathode: Experiment and Theory","abstract":"Sodium-ion batteries (NIBs) are increasingly of interest in modern society as more affordable energy storage alternatives to lithium-ion batteries. At present, the electrochemical performance—the charge/discharge rate, lifetime and capacity—of NIBs is not optimised for practical applications and generally limited by the cathode material. To address these performance problems, a deeper understanding of the evolution of the chemical and electronic structure of NIB cathodes is required. In this thesis, Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂, a layered cathode material exhibiting fast charge/discharge rates, a large voltage hysteresis and a high reversible capacity, is studied. Experimental techniques which probe both the local and bulk structure are employed, in conjunction with first-principles calculations. The superstructure of Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂ is elucidated for the first time using synchrotron X-ray diffraction (XRD), total neutron scattering and high-frequency electron paramagnetic resonance spectroscopy (EPR). The effect of this superstructure on Na⁺-ion mobility (charge/discharge rates) is explored using variable-temperature solid-state ²³Na nuclear magnetic resonance (NMR) spectroscopy. Simulation of these spectra enables rationalisation of the relative mobilities of Na⁺ in different local environments. Using operando and ex situ XRD, as well as ex situ ²³Na NMR spectroscopy and first principles transition-state searching calculations, electrochemically-induced phase transformations are then identified, revealing that Mg²⁺ migration takes place during charge and contributes significantly to the observed hysteresis. Finally, the charge compensation mechanism is presented. Previous reports have attributed the large reversible capacity of Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂ to redox reactions involving oxide anions, O²⁻, but the mechanism remains unclear. Through a combination of spectroscopic techniques (¹⁷O and ²⁵Mg NMR, EPR and X-ray absorption spectroscopy), bulk magnetic susceptibility measurements and first-principles calculations, the origin of the high capacity is identified with the formation of delocalised electronic states between Mn and O. These states are generated by Mg²⁺ migration and stabilised by strong antiferromagnetic interactions. The properties of Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂—the superstructure, phase transformations, Na⁺ ion mobility and charge compensation mechanism—are summarised and a set of design rules for long lifetime, fast charging and high capacity NIB cathode materials is presented.","abstract_html":"Sodium-ion batteries (NIBs) are increasingly of interest in modern society as more affordable energy storage alternatives to lithium-ion batteries. At present, the electrochemical performance—the charge/discharge rate, lifetime and capacity—of NIBs is not optimised for practical applications and generally limited by the cathode material. To address these performance problems, a deeper understanding of the evolution of the chemical and electronic structure of NIB cathodes is required. In this thesis, Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂, a layered cathode material exhibiting fast charge/discharge rates, a large voltage hysteresis and a high reversible capacity, is studied. Experimental techniques which probe both the local and bulk structure are employed, in conjunction with first-principles calculations. The superstructure of Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂ is elucidated for the first time using synchrotron X-ray diffraction (XRD), total neutron scattering and high-frequency electron paramagnetic resonance spectroscopy (EPR). The effect of this superstructure on Na⁺-ion mobility (charge/discharge rates) is explored using variable-temperature solid-state ²³Na nuclear magnetic resonance (NMR) spectroscopy. Simulation of these spectra enables rationalisation of the relative mobilities of Na⁺ in different local environments. Using operando and ex situ XRD, as well as ex situ ²³Na NMR spectroscopy and first principles transition-state searching calculations, electrochemically-induced phase transformations are then identified, revealing that Mg²⁺ migration takes place during charge and contributes significantly to the observed hysteresis. Finally, the charge compensation mechanism is presented. Previous reports have attributed the large reversible capacity of Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂ to redox reactions involving oxide anions, O²⁻, but the mechanism remains unclear. Through a combination of spectroscopic techniques (¹⁷O and ²⁵Mg NMR, EPR and X-ray absorption spectroscopy), bulk magnetic susceptibility measurements and first-principles calculations, the origin of the high capacity is identified with the formation of delocalised electronic states between Mn and O. These states are generated by Mg²⁺ migration and stabilised by strong antiferromagnetic interactions. The properties of Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂—the superstructure, phase transformations, Na⁺ ion mobility and charge compensation mechanism—are summarised and a set of design rules for long lifetime, fast charging and high capacity NIB cathode materials is presented.","abstract_has_math":false,"creators":["Bassey, Euan"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Grey, Clare"],"committee_chairs":[],"committee_members":[],"year":2022,"date_issued":"2022-05-01","date_published":"2022-05-01","updated_at":"2026-07-22T22:24:11Z","subjects":["Batteries","EPR","Magnetism","NMR"],"languages":["eng"],"rights":[],"rights_urls":["https://www.rioxx.net/licenses/all-rights-reserved/"],"identifier_entries":[{"key":"dc:creator.authoridentifier","label":"Author Identifier","values":["0000000188277175"],"render_values":[{"text":"0000-0001-8827-7175","href":"https://orcid.org/0000-0001-8827-7175","code":true}]}]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.89480","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Grey, Clare"]},{"key":"dc:contributor.sponsor","label":"Sponsor","values":["EPSRC NPIF 2018 Grant"]},{"key":"dc:creator","label":"Author","values":["Bassey, Euan"]},{"key":"dc:creator.authoridentifier","label":"Author Identifier","values":["0000000188277175"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2022-05-01"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cambridge"]},{"key":"dc:relation.isreferencedby.uri","label":"Dc Relation Isreferencedby URI","values":["https://www.repository.cam.ac.uk/handle/1810/342064"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Batteries","EPR","Magnetism","NMR"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["https://www.rioxx.net/licenses/all-rights-reserved/"]},{"key":"dc:rights.embargotype","label":"Dc Rights Embargotype","values":["controlled.access"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["10.17863/CAM.89480"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/db3f7d23-fffe-485b-8221-5f8aad4ae51b/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Sodium-ion batteries (NIBs) are increasingly of interest in modern society as more affordable energy storage alternatives to lithium-ion batteries. At present, the electrochemical performance—the charge/discharge rate, lifetime and capacity—of NIBs is not optimised for practical applications and generally limited by the cathode material. To address these performance problems, a deeper understanding of the evolution of the chemical and electronic structure of NIB cathodes is required. In this thesis, Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂, a layered cathode material exhibiting fast charge/discharge rates, a large voltage hysteresis and a high reversible capacity, is studied. Experimental techniques which probe both the local and bulk structure are employed, in conjunction with first-principles calculations. The superstructure of Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂ is elucidated for the first time using synchrotron X-ray diffraction (XRD), total neutron scattering and high-frequency electron paramagnetic resonance spectroscopy (EPR). The effect of this superstructure on Na⁺-ion mobility (charge/discharge rates) is explored using variable-temperature solid-state ²³Na nuclear magnetic resonance (NMR) spectroscopy. Simulation of these spectra enables rationalisation of the relative mobilities of Na⁺ in different local environments. Using operando and ex situ XRD, as well as ex situ ²³Na NMR spectroscopy and first principles transition-state searching calculations, electrochemically-induced phase transformations are then identified, revealing that Mg²⁺ migration takes place during charge and contributes significantly to the observed hysteresis. Finally, the charge compensation mechanism is presented. Previous reports have attributed the large reversible capacity of Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂ to redox reactions involving oxide anions, O²⁻, but the mechanism remains unclear. Through a combination of spectroscopic techniques (¹⁷O and ²⁵Mg NMR, EPR and X-ray absorption spectroscopy), bulk magnetic susceptibility measurements and first-principles calculations, the origin of the high capacity is identified with the formation of delocalised electronic states between Mn and O. These states are generated by Mg²⁺ migration and stabilised by strong antiferromagnetic interactions. The properties of Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂—the superstructure, phase transformations, Na⁺ ion mobility and charge compensation mechanism—are summarised and a set of design rules for long lifetime, fast charging and high capacity NIB cathode materials is presented."]},{"key":"dc:format.checksum.md5","label":"Dc Format Checksum Md5","values":["77e3b9e6faa807b22840ef2515ce3d6c"]},{"key":"dc:title","label":"Title","values":["Magnetic Resonance Studies of a Sodium-Ion Battery Cathode: Experiment and Theory"]}]}],"canonical_facts":{"dc:contributor.advisor":["Grey, Clare"],"dc:contributor.sponsor":["EPSRC NPIF 2018 Grant"],"dc:creator":["Bassey, Euan"],"dc:creator.authoridentifier":["0000000188277175"],"dc:date.issued":["2022-05-01"],"dc:description.abstract":["Sodium-ion batteries (NIBs) are increasingly of interest in modern society as more affordable energy storage alternatives to lithium-ion batteries. At present, the electrochemical performance—the charge/discharge rate, lifetime and capacity—of NIBs is not optimised for practical applications and generally limited by the cathode material. To address these performance problems, a deeper understanding of the evolution of the chemical and electronic structure of NIB cathodes is required. In this thesis, Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂, a layered cathode material exhibiting fast charge/discharge rates, a large voltage hysteresis and a high reversible capacity, is studied. Experimental techniques which probe both the local and bulk structure are employed, in conjunction with first-principles calculations. The superstructure of Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂ is elucidated for the first time using synchrotron X-ray diffraction (XRD), total neutron scattering and high-frequency electron paramagnetic resonance spectroscopy (EPR). The effect of this superstructure on Na⁺-ion mobility (charge/discharge rates) is explored using variable-temperature solid-state ²³Na nuclear magnetic resonance (NMR) spectroscopy. Simulation of these spectra enables rationalisation of the relative mobilities of Na⁺ in different local environments. Using operando and ex situ XRD, as well as ex situ ²³Na NMR spectroscopy and first principles transition-state searching calculations, electrochemically-induced phase transformations are then identified, revealing that Mg²⁺ migration takes place during charge and contributes significantly to the observed hysteresis. Finally, the charge compensation mechanism is presented. Previous reports have attributed the large reversible capacity of Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂ to redox reactions involving oxide anions, O²⁻, but the mechanism remains unclear. Through a combination of spectroscopic techniques (¹⁷O and ²⁵Mg NMR, EPR and X-ray absorption spectroscopy), bulk magnetic susceptibility measurements and first-principles calculations, the origin of the high capacity is identified with the formation of delocalised electronic states between Mn and O. These states are generated by Mg²⁺ migration and stabilised by strong antiferromagnetic interactions. The properties of Na₀.₆₇[Mg₀.₂₈Mn₀.₇₂]O₂—the superstructure, phase transformations, Na⁺ ion mobility and charge compensation mechanism—are summarised and a set of design rules for long lifetime, fast charging and high capacity NIB cathode materials is presented."],"dc:format.checksum.md5":["77e3b9e6faa807b22840ef2515ce3d6c"],"dc:identifier.doi":["10.17863/CAM.89480"],"dc:identifier.uri":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/db3f7d23-fffe-485b-8221-5f8aad4ae51b/download"],"dc:language":["eng"],"dc:publisher.institution":["University of Cambridge"],"dc:relation.isreferencedby.uri":["https://www.repository.cam.ac.uk/handle/1810/342064"],"dc:rights":["https://www.rioxx.net/licenses/all-rights-reserved/"],"dc:rights.embargotype":["controlled.access"],"dc:subject":["Batteries","EPR","Magnetism","NMR"],"dc:title":["Magnetic Resonance Studies of a Sodium-Ion Battery Cathode: Experiment and Theory"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-22T22:24:11Z"}