>Magister Scientiae - MSc / Spinel lithium manganese oxide (LiMn2O4), for its low cost, easy preparation and nontoxicity, is regarded as a promising cathode material for lithium-ion batteries. However, a key problem prohibiting it from large scale commercialization is its severe capacity fading during cycling. The improvement of electrochemical cycling stability is greatly attributed to the suppression of Jahn-Teller distortion (Robertson et al., 1997) at the surface of the spinel LiMn2O4 particles. These side reactions result in Mn2+ dissolution mainly at the surface of the cathode during cycling, therefore surface modification of the cathode is deemed an effective way to reduce side reactions. The utilization of a nanocomposite which comprises of metallic Cu and Au were of interest because their oxidation gives rise to a variety of catalytically active configurations which advances the electrochemical property of Li-ion battery. In this research study, an experimental strategy based on doping the LiMn2O4 with small amounts of Cu-Au nanocomposite cations for substituting the Mn3+ ions, responsible for disproportionation, was employed in order to increase conductivity, improve structural stability and cycle life during successive charge and discharge cycles. The spinel cathode material was synthesized by coprecipitation method from a reaction of lithium hydroxide and manganese acetate using 1:2 ratio. The Cu-Au nanocomposite was synthesized via a chemical reduction method using copper acetate and gold acetate in a 1:3 ratio. Powder samples of LiMxMn2O4 (M = Cu-Au nanocomposite) was prepared from a mixture of stoichiometric amounts of Cu-Au nanocomposite and LiMn2O4 precursor. The novel LiMxMn2O4 material has a larger surface area which increases the Li+ diffusion coefficient and reduces the volumetric changes and lattice stresses caused by repeated Li+ insertion and expulsion. Structural and morphological sample analysis revealed that the modified cathode material have good crystallinity and well dispersed particles. These results corroborated the electrochemical behaviour of LiMxMn2O4 examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The diffusion coefficients for LiMn2O4 and LiMxMn2-xO4 obtained are 1.90 x10-3 cm2 / s and 6.09 x10-3 cm2 / s respectively which proved that the Cu-Au nanocomposite with energy band gap of 2.28 eV, effectively improved the electrochemical property. The charge / discharge value obtained from integrating the area under the curve of the oxidation peak and reduction peak for LiMxMn2-xO4 was 263.16 and 153.61 mAh / g compared to 239.16 mAh / g and 120 mAh / g for LiMn2O4. It is demonstrated that the presence of Cu-Au nanocomposite reduced side reactions and effectively improved the electrochemical performance of LiMn2O4.

<p>LiMn₂O₄ is ideal as a high-capacity Li-ion battery cathode material by virtue of its low toxicity, low cost, and the high natural abundance of Mn. Surface related reactions and bulk kinetics have been the major focus of this work. The main techniques exploited have been: electrochemical cycling, X-ray diffraction, X-ray photoelectron spectroscopy, infrared spectroscopy and thermal analysis.</p><p>Interface formation between the LiMn₂O₄cathode and carbonate-based electrolytes has been followed under different pre-treatment conditions. The variables have been: number of charge/discharge cycles, storage time, potential, electrolyte salt and temperature. The formation of the surface layer was found not to be governed by electrochemical cycling. The species precipitating on the surface of the cathodes at ambient temperature have been determined to comprise a mixture of organic and inorganic compounds: LiF, Li_xPF_y (or Li_xBF_y, depending on the electrolyte salt used), Li_xPO_yF_z (or Li_xBO_yF_z) and poly(oxyethylene). Additional compounds were found at elevated temperatures: phosphorous oxides (or boron oxides) and polycarbonates. A model has been presented for the formation of these surface species at elevated temperatures. </p><p>The cathode surface structure was found to change towards a lithium-rich and Mn³⁺-rich compound under self-discharge. The reduction of LiMn₂O₄, in addition to the high operating potential, induces oxidation of the electrolyte at the cathode surface.</p><p>A novel <i>in situ</i> electrochemical/structural set-up has facilitated a study of the kinetics in the LiMn₂O₄ electrode. The results eliminate solid-phase diffusion as the rate-limiting factor in electrochemical cycling. The electrode preparation method used results in good utilisation of the electrode, even at high discharge rates.</p>

LiMn2O4 is ideal as a high-capacity Li-ion battery cathode material by virtue of its low toxicity, low cost, and the high natural abundance of Mn. Surface related reactions and bulk kinetics have been the major focus of this work. The main techniques exploited have been: electrochemical cycling, X-ray diffraction, X-ray photoelectron spectroscopy, infrared spectroscopy and thermal analysis. Interface formation between the LiMn2O4 cathode and carbonate-based electrolytes has been followed under different pre-treatment conditions. The variables have been: number of charge/discharge cycles, storage time, potential, electrolyte salt and temperature. The formation of the surface layer was found not to be governed by electrochemical cycling. The species precipitating on the surface of the cathodes at ambient temperature have been determined to comprise a mixture of organic and inorganic compounds: LiF, LixPFy (or LixBFy, depending on the electrolyte salt used), LixPOyFz (or LixBOyFz) and poly(oxyethylene). Additional compounds were found at elevated temperatures: phosphorous oxides (or boron oxides) and polycarbonates. A model has been presented for the formation of these surface species at elevated temperatures. The cathode surface structure was found to change towards a lithium-rich and Mn3+-rich compound under self-discharge. The reduction of LiMn2O4, in addition to the high operating potential, induces oxidation of the electrolyte at the cathode surface. A novel in situ electrochemical/structural set-up has facilitated a study of the kinetics in the LiMn2O4 electrode. The results eliminate solid-phase diffusion as the rate-limiting factor in electrochemical cycling. The electrode preparation method used results in good utilisation of the electrode, even at high discharge rates.

<p>Proton exchange membrane fuel cells and lithium polymer batteries are important as future power sources in electronic devices, vehicles and stationary applications. The development of these power sources involves finding and characterising materials that are well suited r the application.</p><p>The materials investigated in this thesis are the perfluorosulphonic ionomer Nafion^TM(DuPont) and metal oxides incorporated into the membrane form of this material. The ionomer is used as polymer electrolyte in proton exchange membrane fuel cells (PEMFC) and the metal oxides are used as cathode materials in lithium polymer batters (LPB).</p><p>Crystallinity in cast Nafion films can be introduced by ion beam exposure or aging. Spectroscopic investigations of the crystallinity of the ionomer indicate that the crystalline regions contain less water than amorphous regions and this could in part explain the drying out of the polymer electrolyte membrane in a PEMFC.</p><p>Spectroscopic results on the equilibrated water uptake and the state of water in thin cast ionomer films indicate that there is a full proton transfer from the sulphonic acid group in the ionomer when there is one water molecule per sulphonate group.</p><p>The LPB cathode materials, lithium manganese oxide and lithium cobalt oxide, were incorporated <i>in situ</i> in Nafion membranes. Other manganese oxides and cobalt oxides were incorporated <i>in situ</i> inside the membrane. Ion-exchange experiments from HcoO₂to LiCoO₂within the membrane were also successful.</p><p>Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray diffraction were used for the characterisation of the incorporated species and the Nafion film/membrane.</p>

Proton exchange membrane fuel cells and lithium polymer batteries are important as future power sources in electronic devices, vehicles and stationary applications. The development of these power sources involves finding and characterising materials that are well suited r the application. The materials investigated in this thesis are the perfluorosulphonic ionomer NafionTM (DuPont) and metal oxides incorporated into the membrane form of this material. The ionomer is used as polymer electrolyte in proton exchange membrane fuel cells (PEMFC) and the metal oxides are used as cathode materials in lithium polymer batters (LPB). Crystallinity in cast Nafion films can be introduced by ion beam exposure or aging. Spectroscopic investigations of the crystallinity of the ionomer indicate that the crystalline regions contain less water than amorphous regions and this could in part explain the drying out of the polymer electrolyte membrane in a PEMFC. Spectroscopic results on the equilibrated water uptake and the state of water in thin cast ionomer films indicate that there is a full proton transfer from the sulphonic acid group in the ionomer when there is one water molecule per sulphonate group. The LPB cathode materials, lithium manganese oxide and lithium cobalt oxide, were incorporated in situ in Nafion membranes. Other manganese oxides and cobalt oxides were incorporated in situ inside the membrane. Ion-exchange experiments from HcoO2 to LiCoO2 within the membrane were also successful. Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray diffraction were used for the characterisation of the incorporated species and the Nafion film/membrane.

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Les estimations précises des états de charge (« State of Charge » - SoC) et de santé (« State of Health » - SoH) des batteries au lithium sont un point crucial lors d’une utilisation industrielle de celles-ci. Ces estimations permettent d’améliorer la fiabilité et la robustesse des équipements embarquant ces batteries. Cette thèse CIFRE est consacrée à la recherche d’algorithmes de détermination de l’état de santé de batteries lithium-ion, en particulier de chimie Lithium Fer Phosphate (LFP) et Lithium Manganèse Oxyde (LMO).Les recherches ont été orientées vers des solutions de détermination du SoH directement embarquables dans les calculateurs des véhicules électriques. Des contraintes fortes de coût et de robustesse constituent ainsi le fil directeur des travaux.Or, si la littérature actuelle propose différentes solutions de détermination du SoH, celles embarquées ou embarquables sont encore peu étudiées. Cette thèse présente donc une importante revue bibliographique des différentes méthodes d’estimation du SoH existantes, qu’elles soient embarquables ou non. Le fonctionnement détaillé ainsi que les mécanismes de vieillissement d’une batterie lithium-ion sont également explicités.Une partie majoritaire des travaux est consacrée à l’utilisation de l’analyse incrémentale de la capacité (« Incremental Capacity Analysis » - ICA) en conditions réelles, c’est-à-dire avec les niveaux de courant présents lors d’un profil de mission classique d’un véhicule électrique, avec les mesures disponibles sur un BMS (« Battery Management System ») industriel et avec les contraintes de robustesses associées, notamment une gamme étendue de température de fonctionnement. L’utilisation de l’ICA pour déterminer la capacité résiduelle de la batterie est mise en œuvre de façon totalement innovante et permet d’obtenir une grande robustesse aux variations des conditions d’utilisation de la batterie.Une seconde méthode est, elle, dédiée à la chimie LMO et exploite le fait que le potentiel aux bornes de la batterie soit représentatif de son état de charge. Un compteur coulométrique partiel est ainsi proposé, intégrant une gestion dynamique des bornes d’intégration en fonction de l’état de la batterie.A l’issue des travaux, une méthode complète et précise de détermination du SoH est disponible pour chacune des chimies LFP et LMO. La détermination de la capacité résiduelle de ces deux familles de batteries est ainsi possible à 4 % près. / Accurate lithium-ion battery State of Charge (SoC) and State of Health (SoH) estimations are nowadays a crucial point, especially when considering an industrial use. These estimations enable to improve robustness and reliability of hardware using such batteries. This thesis focuses on researching lithium-ion batteries state of health estimators, in particular considering Lithium Iron Phosphate (LFP) and Lithium Manganese Oxide (LMO) chemistries.Researches have been targeted towards SoH estimators straight embeddable into electric vehicles (EV) computers. Cost and reliability constraints are thus the main guideline for this work.Although existing literature offers various SoH estimators, those who are embedded or embeddable are still little studied. A complete literature review about SoH estimators, embedded or not, is therefore proposed. Lithium-ion batteries detailed operation and ageing mechanisms are also presented.The main part of this work is dedicated to Incremental Capacity Analysis (ICA) use with electric vehicle constraints, such as current levels available with a typical EV mission profile or existing measurements on the Battery Management System (BMS). Incremental Capacity Analysis is implemented in an innovative way and leads to a remaining capacity estimator with a high robustness to conditions of use variations, including an extended temperature range.A second method, dedicated to LMO chemistry, take advantage of the fact that the battery potential is representative of its state of charge. Partial Coulomb counting is thus performed, with a dynamic management of integration limits, depending on the battery state.Outcomes of this work are two complete and accurate SoH estimators, one for each chemistry, leading to a remaining capacity estimation accurate within 4 %.