TY - THES

T1 - Sodium ion storage in metal oxide electrodes for rechargeable sodium ion batteries

AU - Szabados, Lukas Martin Alexander

N1 - embargoed until null

PY - 2020

Y1 - 2020

N2 - Energy storage will become more important in the future, regarding the growing sector of electromobility and the increasing share of renewable energy from photovoltaics and wind in the electric grid. State of the art lithium-ion batteries (LIB) will not be able to meet the future demand for energy storage in the long term due to limited resources. Other technologies, such as sodium-ion batteries (SIB) can help to increase the diversification and replace LIB in certain areas, for example in the stationary energy storage. In this thesis, three different electrode materials, titanium(IV)-oxide in the anatase and amorphous phase and molybdenum(IV)-oxide, are investigated for their suitability in SIB. The synthesis and the corresponding material characterisation form the first part of this thesis. The titanium(IV)-oxide electrodes are synthesised by electrochemical oxidation and, for the anatase phase, by a phase transition upon thermal annealing in a tube furnace. The molybdenum(IV) oxide electrode is prepared by physical vapour deposition (PVD) of molybdenum in an oxygen/argon gas mixture with a ratio of 1/100 on a copper substrate. The phase purity of the electrodes is subsequently characterized by Raman and X-ray photoelectron spectroscopy (XPS). The electrodes are further characterized electrochemically in a SIB half-cell setup by potential dependent impedance spectroscopy, cyclovoltammetry (CV) and galvanostatic cycling with potential limitation (GCPL). Finally, post mortem analysis using XPS and scanning electron microscopy (SEM) are employed to investigate the composition and morphology of the surface films formed during battery half-cell cycling. The characterisation of the formed surface films adds important insights in the observed "self-improving" effect of oxide-based electrode materials in SIB. This “self-improving” characteristics are found to significantly influence the performance of the electrodes during long-term GCPL measurements in a Na containing electrolyte and are hence relevant to transition metal oxides, in general.

AB - Energy storage will become more important in the future, regarding the growing sector of electromobility and the increasing share of renewable energy from photovoltaics and wind in the electric grid. State of the art lithium-ion batteries (LIB) will not be able to meet the future demand for energy storage in the long term due to limited resources. Other technologies, such as sodium-ion batteries (SIB) can help to increase the diversification and replace LIB in certain areas, for example in the stationary energy storage. In this thesis, three different electrode materials, titanium(IV)-oxide in the anatase and amorphous phase and molybdenum(IV)-oxide, are investigated for their suitability in SIB. The synthesis and the corresponding material characterisation form the first part of this thesis. The titanium(IV)-oxide electrodes are synthesised by electrochemical oxidation and, for the anatase phase, by a phase transition upon thermal annealing in a tube furnace. The molybdenum(IV) oxide electrode is prepared by physical vapour deposition (PVD) of molybdenum in an oxygen/argon gas mixture with a ratio of 1/100 on a copper substrate. The phase purity of the electrodes is subsequently characterized by Raman and X-ray photoelectron spectroscopy (XPS). The electrodes are further characterized electrochemically in a SIB half-cell setup by potential dependent impedance spectroscopy, cyclovoltammetry (CV) and galvanostatic cycling with potential limitation (GCPL). Finally, post mortem analysis using XPS and scanning electron microscopy (SEM) are employed to investigate the composition and morphology of the surface films formed during battery half-cell cycling. The characterisation of the formed surface films adds important insights in the observed "self-improving" effect of oxide-based electrode materials in SIB. This “self-improving” characteristics are found to significantly influence the performance of the electrodes during long-term GCPL measurements in a Na containing electrolyte and are hence relevant to transition metal oxides, in general.

KW - Natrium-Ionen-Batterien

KW - Titan(IV)-oxid

KW - Molybdän(IV)-oxid

KW - Oberflächenfilm

KW - "Self-Improving"-Effekt

KW - Sodium-ion battery

KW - titanium(IV)-oxide

KW - molybdenum(IV)-oxide

KW - surface film

KW - self-improving effect

KW - electrochemical characterisation

M3 - Master's Thesis

ER -