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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.

This thesis focuses on the state-of-the-art spectroscopic approaches in studying polymer electrolytes for proton exchange membrane fuel cells. With the aim to optimize architectural and chemical design of hydrogen fuel cells, a variety of perfluorosulfonic acid (PFSA) membranes were explored to establish characteristics that ultimately improve PFSA electrolyte performance. The results of the detailed spectroscopic analyses helped to unveil a structure performance relationship. Solid-state nuclear magnetic resonance (ssNMR) spectroscopy was used to distinguish F and C environments, while scanning transmission X-ray microscopy coupled with X-ray absorption spectroscopy provided complementary chemical structural information with direct access to S and O environments. The combination of these two techniques provided advantages in identifying subtle chemical alterations in PFSAs. Furthermore, a novel ssNMR technique was developed with the purpose of probing local dynamics from the polymer perspective. This ¬¬19F dipolar recoupling ssNMR approach was validated and applied to PFSA membranes by monitoring the normalized double quantum build-up curves as a function of relative humidity (%RH) and temperature, and the polymer side chain showed higher local motion as response to temperature and %RH elevation compared to the backbone. The effective dipolar coupling constant was extracted to represent local dynamics and compared amongst tested PFSAs. A standardized metric, the dynamic order parameter, was also introduced and applied to the materials to quantitatively compare them within the same class. This new method provided an alternative way to extract site-specific local dynamics profile for materials with multiple resonances. Additionally, the combination of in situ fuel cell performance evaluation and ex situ ssNMR characterization created a connection between fundamental chemistry and bulk electrochemical measurements. As the first study to correlate these physicochemical properties to material performances, this work parameterized the structural impact at a molecular level and provided insight into improving polymer electrolyte materials. / Thesis / Doctor of Philosophy (PhD) / Proton exchange membrane fuel cells, which help to reduce the reliance on fossil fuels by locally producing only water and heat, have received a significant amount of research attention as an alternative power generator for vehicular and stand-alone energy applications. Perfluorosulfonic acid (PFSA) membranes, the most common commercial polymer electrolyte materials, have been investigated using modern analytical spectroscopies. Solid-state nuclear magnetic resonance (ssNMR) spectroscopy and synchrotron-based scanning transmission X-ray microscopy were used in elucidating material compositions with complementary information. Moreover, an advanced ssNMR method was developed and applied to a variety of PFSAs. Polymer backbones and side chains were separated spectroscopically, and were distinguished based on different local dynamics profiles extracted from the ssNMR experiments. Additionally, bulk material performance evaluations from electrochemical analyses were correlated to PFSA side chain local dynamics profiles. The integrated spectroscopic study illustrated in this thesis provided insight into understanding the structure-performance relationship of PFSA electrolytes.