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Detta projekt syftar till att undersöka den termiska rusningsprocessen hos ett litiumjonbatteri med en fluorfri elektrolyt och jämföra den med en kommersiellt använd fluor-innehållande elektrolyt. Battericellerna innehöll silikon-grafit som anod och LiNi0.6Mn0.2Co0.2O2 (NMC622) som katod. Den fluorfria elektrolyten var baserad på litium bis(oxalato)borat (LiBOB) i organisk lösning med additivet vinylen karbonat(VC). Det jämfördes med en fluor-innehållande elektrolyt med LiPF6 i samma organiska lösning tillsammans med VC och fluoroetylene karbonat (FEC). De termiska stabilitetstesterna utfördes med Accelerating Rate Calorimetry (ARC) och Differentiell svepkalorimetri (DSC). Både knappceller och pouchceller har undersökts med hjälp av ARC. Trots flera försök med olika uppställning kunde den termiska rusningen inte bli detekterad för någon av celltyperna, med slutsatsen att en störremängd aktivt material behövs. Istället användes DSC för att undersöka de termiska reaktionerna hos batteri-komponenterna. Resultaten visade att anoden var mer termisk stabil med den fluorfria elektolyten, medan samma elektrolyt visade mindre termisk stabilitet på katoden. Vidare undersökningar behövs dock för bekräftelse av katoden. / This project aims to investigate the thermal runaway process of fluorine-free lithium ion battery cells and to compare this with a commercially used fluorinated electrolyte. The cells consisted of a silicon-graphite composite anode and a LiNi0.6Mn0.2Co0.2O2(NMC622) cathode. The non-fluorinated electrolyte used was based on lithiumbis(oxalato)borate (LiBOB) in organic solvents with the additive vinylene carbonate(VC). Moreover, the fluorinated electrolyte consisted of LiPF6 in the same organic solvents together with VC and fluoroethylene carbonate (FEC). The thermal stability measurements have included Accelerating Rate Calorimetry (ARC) and Differential Scanning Calorimetry (DSC). Moreover, both coin cells and pouch cells have been examined by ARC. However, thermal runaway could not be detected for either type of cells, concluding that a greater amount of active material was needed. In order to measure the thermal reactions of the battery components, DSC was used. These results concluded that the anode was more thermally stable with a non-fluorinated electrolyte. However, the thermal stability appeared to be lower for the cathode, therefore, further investigation is needed for confirmation of the cathode.

<p>This thesis investigates the structure and ion mobility properties within the phosphate and fluorophosphate family of cathode materials for Li ion batteries using solid-state NMR. Developments in lithium ion battery technology are now directed towards automotive applications meaning that many of the cost and safety issues associated with current lithium ion battery technology need to be addressed. Within the current systems the high cost is largely attributed to the use of LiCoO₂ as the positive electrode. Many new and inexpensive Li intercalation materials have been put forward as alternatives to LiCoO₂, however the details concerning the structural and ion-transport properties of these new phases are not well defined. ^6,7Li, ³¹P, and ¹⁹F NMR measurements are an ideal tool to study these properties, as ^6,7Li is able to probe the local environment and dynamics of the mobile ion while ³¹P and ¹⁹F monitor changes in the host framework. Materials selected for study in this thesis include olivine LiFePO₄, monoclinic Li₃M₂(PO₄)₃ (M = V, Fe), the tavorite-based Li₂VPO₄F and Li₂VOPO₄, and the novel layered Li₅V(PO₄)₂F₂. The fluorophosphates have been introduced as higher voltage cathode materials for lithium batteries, however our ^6,7Li 1D selective inversion and 2D EXSY measurements reveal timescales of ion hopping that are relatively slow when compared to those measured in the phosphates. This indicates that the improved power output from the voltage gains may be lost to slow charge/discharge rates.</p> / Doctor of Philosophy (PhD)

<p>Lithium-ion batteries provide a more cost-effective and non-toxic source of reusable energy compare to other energy sources. Several research studies have lead to production of some more promising cathode components for lithium ion batteries. Recently, a new series of pyrophosphate-based composition Li₂FeP₂O₇ and Li₂MnP₂O₇ has been reported as cathode materials. They have shown a 3D framework structure and the two Lithium-ions in the three-dimensional tunnel structure make it possible that more than one lithium ion be extracted during cycling. Lithium solid state nuclear magnetic resonance (NMR) is an effective technique to study this cathode material, not only for analyzing local structure, but also for investigation of the microscopic processes that take place in the battery.</p> <p>In this work, Li₂FeP₂O₇ and Li₂MnP₂O₇ have been synthesized. The lithium environment of these materials is studied using 1D ^6,7Li NMR. Assignment of Li₂MnP₂O₇ spectrum has been made based on Fermi-contact interaction and crystal structure. Both variable temperature experiment and 1D selective inversion NMR are used to establish Li-ion pathways as well as Li hopping rates for Li₂MnP₂O₇. Also, ⁷Li MAS NMR measurements are used to characterize Li environments in LixFeP₂O₇after being electrochemically cycled to different points, and preliminary results regard to changes to ion mobility in LixFeP₂O₇at different electrochemical cycled points are presents here, solid-solution (de)lithetiation process is confirmed for this material.</p> / Master of Science (MSc)

<p>Lithium-ion (Li-ion) cells are increasingly used in many applications affecting our</p> <p>daily life, such as laptops computers, cell phones, digital cameras, and other portable</p> <p>electronic devices. Lithium-ion batteries are increasingly being considered for their use in Electric Vehicles (EV), Hybrid Electric Vehicles (HEV) and Plug-in Hybrid Electric Vehicles (PHEV) due to their high energy density, slow loss of charge when not in use, and for lack of hysteresis effect. New application domains for these batteries has placed greater emphasis on their energy management, monitoring and control strategies.</p> <p>In this thesis, a comparative study between different models and state of charge (SOC) estimation strategies is performed. Battery models range from black-box representation to detailed electrochemical reaction models that consider the underlying physics. The state of charge is estimated using the Extended Kalman filter (EKF) and the Smooth Variable Structure Filter (SVSF). The models and SOC estimation strategies are applied to experimental results from BMW Electrical and Hybrid Research and Development center and validated using a simulation model from AVL CRUISE software.</p> <p>Overall, different models and SOC estimation scenarios were studied. An average improvement of 30% in the estimation accuracy was shown by the SVSF SOC method when compared with the EKF SOC strategy. In general, the SVSF SOC estimation technique demonstrates excellent capability and a fast speed of convergence.</p> / Master of Applied Science (MASc)

Layered lithium transition metal oxides represent a major type of cathode materials that are widely used in commercial lithium-ion batteries. Nevertheless, these layered cathode materials suffer structural changes during electrochemical cycling that could adversely affect the battery performance. Clear explanations of the cathode degradation process and its initiation, however, are still under debate and are not yet fully understood. In this thesis, the cycling-induced chemical and structural evolution of LiNi1/3Mn1/3Co1/3O2 (NMC) and high-energy Li1.2Ni0.13Mn0.54Co0.13O2 (HENMC) cathodes are investigated in details using state-of-the-art electron microscopy techniques combined with other bulk measurements to uncover the mechanisms at the source of cell deterioration. / Thesis / Doctor of Philosophy (PhD)

This thesis concerns the use of advanced solid-state NMR methods to investigate local structural features and ion dynamics in a series of paramagnetic cathode materials for lithium and sodium ion batteries. A variety of polyanionic phosphate and fluorophosphate derivatives were explored to identify characteristics that ultimately improve battery performance. Solid-state NMR is an excellent method to probe such materials, as it offers the unique ability to track the charge-carrying alkali ion (Li or Na) over the course of the electrochemical process, adding insight not obtainable by bulk characterization techniques. Selective inversion exchange experiments were used to elucidate ion diffusion pathways in low-mobility Li ion conductors Li2MnP2O7 and Li2SnO3. Contrasting experimental results highlight significant differences observed when the method is applied to paramagnetic versus diamagnetic systems, with the former being much more complicated to study with traditional exchange spectroscopy methods. Selective inversion was similarly applied to a new lithium iron vanadate framework, LiFeV2O7, where the changing ion dynamics as a function of electrochemical state of charge were quantified, allowing for the development of a model to explain the corresponding phase changes in the material. This represents the first example of an ex situ Li-Li exchange study for a cathode material, particularly where the conductivity changes are linked directly to a change of ion exchange rates. Additionally, 23Na NMR spectroscopy was additionally used to investigate Na2FePO4F as a potential Na ion battery cathode, where ex situ NMR measurements successfully determined the local Na ion distribution in the electrode as a function of electrochemical cycling. In combination with density functional theory (DFT) calculations, the NMR results lead to the construction of a biphasic desodiation model for Na2FePO4F cathodes. Finally, possible defect formation in sodium iron fluorophosphate was investigated with a variety of methods including 23Na NMR, DFT calculations, powder X-ray diffraction and Mössbauer spectroscopy. / Thesis / Doctor of Philosophy (PhD) / Lithium ion batteries are considered to be at the forefront of current energy storage development, offering high energy density in a small and lightweight package. This thesis delineates the investigation of materials for both lithium and sodium ion batteries via nuclear magnetic resonance methods. Slow Li ion dynamics were investigated and quantified in three lithium-conducting materials: Li2MnP2O7, Li2SnO3, and LiFeV2O7 via the use of selective inversion NMR experiments. In the case of the latter, the ion dynamics were probed ex situ during the course of battery cycling, where a maximum in Li mobility is observed approximately half way through the charge-discharge cycle. Additionally, a potential Na ion cathode material, Na2FePO4F, was found by ex situ methods to reveal a biphasic mechanism for the desodiation of the electrode during charging. This mechanism and the NMR data used to discover it were further supported by ab initio calculations.