Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (Ph.D.) - University of St Andrews, June 2009. / Restricted until 1st June 2011.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains vii, 92 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 89-92).

<p>The predicted growth in demand for electric vehicles (EVs) has given rise to increasing use of lithium-ion batteries (LIBs), which are the source of energy used in all EVs. Recycling of spent LIBs not only can supply more materials to manufacturing new LIBs, but also can mitigate haz-ardous waste disposal in the environment. Direct recycling focuses on separating cathode materials to be re-purposed or remanufactured. Delamination of cathode materials is the necessary first step; however, it is fraught with difficulties due to the strong adhesive forces provided by the polyvi-nylidene fluoride (PVDF) binder that is widely used in LIBs. The widely accepted delamination methods are N-Methyl-2-pyrrolidone (NMP) solvent dissolution and direct calcination, which are not desirable due to either environmental and health concerns or high energy consumption.</p> <p>The lithium chemical systems (LiCl, LiNO₃, and LiOH) and their binary eutectic systems, were systematically studied to recover heterogeneous cathode active materials (NMC 111 and LMO) from spent LIBs of EVs. The LiOH-LiNO₃ eutectic system showed 98.3% peel-off effi-ciency under preferable conditions. The recycled products were characterized using ICP-OES, XPS, SEM, and XRD. There were minimal changes in chemical composition, morphology, or crystal structure of the recycled cathode materials after LiOH-LiNO3 eutectic treatment, compared with those recycled with an AlCl₃-NaCl eutectic molten salt treatment that introduces more Al contamination and morphological defects.  </p> <p>In order to avoid corrosive chemicals and minimize particle agglomeration, additional lith-ium salts were investigated, including LiOAc (lithium acetate), Li₂CO₃, and Li₂SO₄. A peel-off efficiency of up to 98.5% was achieved at a LiOAc to LiNO₃ molar ratio of 3:2, salt to cathode mass ratio of 10:1, temperature of 300° C, and a holding time of 30 minutes. To validate the effect of the cations, the recycled products from the molten sodium salt system (NaOAc-NaNO3) were tested. The lithium salt system achieved separation at a lower temperature. Use of LiOAc-LiNO₃ minimized morphological changes compared with direct calcination.</p> <p>The effective separation in LiOH-LiNO3 or LiOAc-LiNO3 molten salt systems was based on promotion of PVDF decomposition, and these two systems may be feasible for recycling other typical cathodes (LCO and LFP) where PVDF is used as the binder. Use of molten lithium salts as alternatives to direct calcination or use of other solvents, may help facilitate recycling of spent LIBs, and even achieve a way for closed loop direct recycling of materials.</p> <p> Additionally, a chemical-free pressure washing system was studied to overcome the adhe-sion provided by PVDF. Although the pressure washing system was not able to remove PVDF from the cathode materials, nearly instant separation from the aluminum backing was achieved when the shear stress and normal stress provided by the impacting of high-pressure waterjet was stronger than the binding forces. Factors investigated included water pressure, distance between the nozzle and cathode, the incident angle of the water jet, and the nozzle type (sprayer angle). A 34-1 fractional factorial design was used to evaluate the parameters and find the optimal operating conditions. A small amount of Al and consistent morphology (of nearly pristine cathode active materials) were detected. Three kinds of recycled cathode materials (NMC&LMO, LCO, and LFP) were used as inputs to investigate a sulfuric acid leaching process, indicating high leaching effi-ciencies (lithium > 90% and cobalt > 85%).</p> <p>The degradation of cathode active materials or PVDF affects the adhesion force between cathode materials layer and Al current collector. Because delamination replies on inactivation of bonding forces provided by PVDF, it is believed that the storage environment (air, O₂ or H_{<strong>2</strong>}O) will affect the performances of delamination to some extent. Three representative methods (direct cal-cination, solvent extraction, and pressure washing system) of delamination were selected to eluci-date the effect from air exposure time. Direct calcination was barely influenced and stably sepa-rated CAMs in terms of peel-off efficiency. The pressure washing system or solvent extraction exhibited high peel-off efficiency using control samples, but the performance regarding either Al contamination or separation efficiency  significantly worsened after long air exposure time. This hypothesis could explain lack of reproducibility of some results in different studies and highlight the importance of strict storage condition of spent LIBs to direct recycling technology. </p> <p>Overall, this thesis examines innovative delamination methods for the development of cost-efficient and environmentally friendly direct recycling of spent LIBs. Application of the eutectic molten lithium salt system (LiOH-LiNO₃ and LiOAc-LiNO₃) or pressure washing system indicates promising benefits to reduce toxic gas emission and energy consumption, and accelerate the cir-cular economy.</p>

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L'étude de la déformation de la barre collectrice dans les conditions subies au sein de la cellule de réduction d'aluminium est d'une grande importance pour l'optimisation de l'efficacité et l'augmentation de la durée de vie de la cellule. Ce mémoire nous informe des résultats d'un programme expérimental réalisé sur une barre de collectrice en acier. Le but, est d' étudier son comportement en tenant compte de ses propriétés thermiques, mécaniques et de fluage. Des essais ont été effectués en compression à de basses tensions, de 0,5 à 2MPa et à une température élevée, de 900°C. Différents comportements ont été observés à de faibles contraintes, jusqu'à 2MPa, cela peut être justifié par le temps et le niveau de pression appliqué. L'inspection métallographique a montré l'apparition d'oxydation et de la corrosion sur des échantillons testés, ceci est dû à l'environnement agressif des conditions du test. D'importants efforts et modifications ont été fournis pour éradiquer cet effet et pour améliorer l'exactitude des données de test de fluage obtenus. / The study of the deformation behaviour of the collector bar at conditions experienced within the aluminium reduction cell is of great importance to optimizing the efficiency and increasing the life span of the cell. This mémoire communicates the results of an experimental program carried out on the steel collector bar material (AISI 1006) to investigate its behaviour in relation to its thermal, mechanical and the creep properties. Tests were carried out in compression at low stresses, 0.5 to 2 MPa and high temperature, 900 °C. Different behaviour was observed at low stresses up to 2 MPa, which can be characterised by time and applied stress level. Metallographic inspection showed effect of oxidation and corrosion on tested samples due to the aggressive environment of the test condition, major efforts and modification were made to eradicate this effect and to improve the accuracy of obtained creep test data.

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