Lithium-ion batteries are today finding use in automobiles aiming at reducing fuel consumption and emissions within transportation. The requirements on batteries used in vehicles are high regarding performance and lifetime, and a better understanding of the interior processes that dictate energy and power capabilities is a key to strategic development. This thesis concerns aging in lithium-ion cells using electrochemical tools to characterize electrode and electrolyte properties that affect performance and performance loss in the cells.   A central difficulty regarding battery aging is to manage the coupled effects of temperature and cycling conditions on the various degradation processes that determine the lifetime of a cell. In this thesis, post-mortem analyses on harvested electrode samples from small pouch cells and larger cylindrical cells aged under different conditions form the basis of aging evaluation. The characterization is focused on electrochemical impedance spectroscopy (EIS) measurements and physics-based EIS modeling supported by several material characterization techniques to investigate degradation in terms of properties that directly affect performance. The results suggest that increased temperature alter electrode degradation and limitations relate in several cases to electrolyte transport. Variations in electrode properties sampled from different locations in the cylindrical cells show that temperature and current distributions from cycling cause uneven material utilization and aging, in several dimensions. The correlation between cell performance and localized utilization/degradation is an important aspect in meeting the challenges of battery aging in vehicle applications.   The use of in-situ nuclear magnetic resonance (NMR) imaging to directly capture the development of concentration gradients in a battery electrolyte during operation is successfully demonstrated. The salt diffusion coefficient and transport number for a sample electrolyte are obtained from Li+ concentration profiles using a physics-based mass-transport model. The method allows visualization of performance limitations and can be a useful tool in the study of electrochemical systems. / <p>QC 20140512</p>

NMR experiments performed under the effect of electric fields, either continuous or pulsed, can provide quantitative parameters related to ion association and ion transport in solution.  Electrophoretic NMR (eNMR) is based on a diffusion pulse-sequence with electric fields applied in the form of pulses. Magnetic field gradients enable the measurement of the electrophoretic mobility of charged species, a parameter that can be related to ionic association. The effective charge of the tetramethylammonium cation ion in water, dimethylsulphoxide (DMSO), acetonitrile, methanol and ethanol was estimated by eNMR and diffusion measurements and compared to the value predicted by the Debye-Hückel-Onsager limiting law. The difference between the predicted and measured effective charge was attributed to ion pairing which was found to be especially significant in ethanol. The association of a large set of cations to polyethylene oxide (PEO) in methanol, through the ion-dipole interaction, was quantified by eNMR. The trends found were in good agreement with the scarce data from other methods. Significant association was found for cations that have a surface charge density below a critical value. For short PEO chains, the charge per monomer was found to be significantly higher than for longer PEO chains when binding to the same cations. This was attributed to the high entropy cost required to rearrange a long chain in order to optimize the ion-dipole interactions with the cations. Moreover, it was suggested that short PEO chains may exhibit distinct binding modes in the presence of different cations, as supported by diffusion measurements, relaxation measurements and chemical shift data. The protonation state of a uranium (VI)-adenosine monophosphate (AMP) complex in aqueous solution was measured by eNMR in the alkaline pH range. The question whether or not specific oxygens in the ligand were protonated was resolved by considering the possible association of other species present in the solution to the complex. The methodology of eNMR was developed through the introduction of a new pulse-sequence which suppresses artifactual flow effects in highly conductive samples. In another experimental setup, using NMR imaging, a constant current was applied to a lithium ion (Li ion) battery model. Here, 7Li spin-echo imaging was used to probe the spin density in the electrolyte and thus visualize the development of Li+ concentration gradients. The Li+ transport number and salt diffusivity were obtained within an electrochemical transport model. The parameters obtained were in good agreement with data for similar electrolytes. The use of an alternative imaging method based on CTI (Constant Time Imaging) was explored and implemented. / <p>QC 20140825</p>

Redox Flow Batteries are chemical based energy storage systems that accumulate energy in liquid electrolytes. Dissolved redox active substances undergo redox reactions in an electrochemical cell and so charge and discharge a battery. Recently, the introduction of organic materials as electrolytes raised research interest. Electrolytes that operate with the bromine/bromide redox couple are interesting due to their high energy density and fast reversible kinetics. They are used in combination with several anodic chemistries (e.g. Zinc, Hydrogen, Quinone), including organic materials.Due to the corrosive and volatile nature of bromine, practical electrolytes use Bromine Complexing Agents (BCAs) in order to bind bromine in a less volatile form and deal with safety issues. These additives have a strong influence on the battery’s operation by influencing the concentration of redox active species, the cell voltage and the electrolyte conductivity. Nevertheless, very little is known about the real properties of aqueous acidic bromine electrolytes, both in pure dilution and in presence of BCAs, which influence on the electrolyte is not predictable so far. The aim of this PhD project is to provide a comprehensive understanding of the behavior of an electrolyte based on bromine and bromide, with particular reference to the one used in semi-organic flow batteries. Along this work an analysis on the performance of a AQDS-Bromine flow battery cell was executed and an extensive study on the physico-chemical behavior of the positive electrolyte was developed. A review of the flow battery technology and of the metrics and methods available for diagnostics was firstly performed as a basis to define macro characteristics,such as State of Charge (SoC) and State of Health (SoH). The cycling behavior of an AQDS-Bromine flow battery was investigated by cell tests and possible degradation mechanisms have been highlighted and explained by interpretation of electrochemical measurements. Following, a broad characterization of the bromine-based electrolyte was performed, producing extended experimental data on physico-chemical properties and a modeling framework for the prediction of the electrolyte behavior.