La recherche de batteries lithium-ion de hautes performances est nécessaire pour assurer nos besoins croissants en mobilité électrique. L’optimisation des matériaux d’électrodes et des électrolytes sont des voies très explorées. Par ailleurs, les collecteurs de courant jouent un rôle clé vis-à-vis des performances et de leur maintien au cours du cyclage en raison des problématiques d’adhésion, de résistance de contact électrique, et de corrosion, à l’interface électrode/collecteur. Dans ce but, des revêtements conducteurs et protecteurs pour collecteurs de courant en aluminium d’électrode positive ont été développés. Les phénomènes à l’interface entre l’électrode, de type LiFePO4 – PVdF, et le collecteur de courant ont été étudiés. Le mouillage de cette interface par l’électrolyte est apparu comme une origine majeure de la résistance de contact, probablement par la formation d’une double couche électrochimique. La sélection des matériaux utilisés dans la formulation des revêtements a permis de protéger la surface d’aluminium de ce contact avec l’électrolyte. Les conséquences sont très bénéfiques : diminution de la résistance de contact, augmentation des densités de puissance et d’énergie à hauts régimes, et protection de l’aluminium contre la corrosion dans un électrolyte de type LiTFSI. Il a notamment été montré qu’une des principales limitations d’une électrode de type LiFePO4 est sa résistance de contact avec le collecteur de courant, et qu’un revêtement performant permet d’éliminer totalement la part de carbone conducteur dans cette électrode tout en conservant de très bonnes performances. / Performance improvement is necessary in order to fulfill our increasing needs in electric mobility. Electrode and electrolyte materials optimization are privileged research directions. Furthermore, current collectors have a key role in the performance and their preservation, associated with electrode delamination, electrical contact resistance and corrosion issues at the current collector/electrode interface. To this end, conductive and protective coatings for aluminum current collectors have been developed. Interactions between a LiFePO4 – PVdF type electrode and current collectors were studied. The electrolyte wettability of this interface appeared to be a major contact resistance contribution, probably due to the formation of the electrochemical double layer. Protection of this interface was achieved through coatings’ material selection. Performance improvements have been observed: contact resistance decrease, higher power and energy densities at high rates and corrosion protection of aluminum substrates in LiTFSI-based electrolyte. It has been demonstrated that the contact resistance with current collectors is one of the major drawback of LiFePO4 electrodes, and an effective coating can allow the suppression of the electrode’s conductive carbon additives whereas performance are preserved.

In this research, we studied the effect of different structures of organic precursors on the performance of LiFePO4/C composite by co-precipitation route. The composite material¡¦s electrochemical and physical properties were characterized by CV, XRD, SEM, PSA, BET-surface area, TGA, and Raman spectroscopy.

Battery is the sole electrical energy source when electric vehicle(EV) is moving. To reduce traveling anxiety, an effective energy management system to indicate the state-of-charge (SOC) of the battery and make a balance between vehicle performance and endurance is very important. This research is aimed to develop a SOC estimation system with high accuracy. The proposed method in this thesis is based on under load voltage and multilevel Peukert's equation to estimate the SOC. The proposed method is compared with the open circuit voltage method for initial SOC estimation and with coulometric method for cumulative SOC estimation under various EV driving conditions simulated by an adjustable electronics load. Experimental results indicate that the proposed method can provide reasonable accuracy as compared with other tested methods for LiFePO4 battery SOC estimations.

abstract: Increasing demand for reducing the stress on fossil fuels has motivated automotive industries to shift towards sustainable modes of transport through electric and hybrid electric vehicles. Most fuel efficient cars of year 2016 are hybrid vehicles as reported by environmental protection agency. Hybrid vehicles operate with internal combustion engine and electric motors powered by batteries, and can significantly improve fuel economy due to downsizing of the engine. Whereas, Plug-in hybrids (PHEVs) have an additional feature compared to hybrid vehicles i.e. recharging batteries through external power outlets. Among hybrid powertrains, lithium-ion batteries have emerged as a major electrochemical storage source for propulsion of vehicles. In PHEVs, batteries operate under charge sustaining and charge depleting mode based on torque requirement and state of charge. In the current article, 26650 lithium-ion cells were cycled extensively at 25 and 50 oC under charge sustaining mode to monitor capacity and cell impedance values followed by analyzing the Lithium iron phosphate (LiFePO4) cathode material by X-ray diffraction analysis (XRD). High frequency resistance measured by electrochemical impedance spectroscopy was found to increase significantly under high temperature cycling, leading to power fading. No phase change in LiFePO4 cathode material is observed after 330 cycles at elevated temperature under charge sustaining mode from the XRD analysis. However, there was significant change in crystallite size of the cathode active material after charge/discharge cycling with charge sustaining mode. Additionally, 18650 lithium-ion cells were tested under charge depleting mode to monitor capacity values. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2016

This work deals with issues of application of the graphene material in the field of electrochemical energy storage. It includes basic graphene properties, the overview of methods for the production of lithium-iron-phosphate/graphene composites and results of different research approaches. The general aim is to present growing opportunity of application of graphene based composites in the electrochemical energy storage field. In the experimental part of this work, a electrochemical exfoliation of graphite and a production of LFP/G composites with different amount of graphene material and with different types of graphene material are carried out. This work includes also x-ray diffraction spectroscopy measurements and the evaluation of impacts of graphene additives on final properties of the electrochemical energy storage.

The topic of this master thesis is the design of electric scooter. In the first part of this thesis consists if research of used structural designs and driver types. In following chapters are calculations and selection procedures of the electric motor, batteries and other accessories. Results from previous chapters were used to created complete 3D model of scooter in SolidWorks software. Based on the model, complete technical drawings were created.

No description available.

State-of-Health (SoH), a specified measure of stability, is a critical parameter for determining the safe operating area of a battery cell and battery packs to avoid abuse and prevent failure and accidents. A series of experiments were performed to evaluate the performance of a 4P1S battery array using electrochemical impedance spectroscopy to identify key frequencies that may describe battery state of health at any state of charge. Using a large sample number of cells, the state of health frequency, fSoH, for these LiFePO4 26650 cells is found to be 158 Hz. Four experiments were performed to evaluate the lifetime in different configurations: single-cell at 1C (2.6A), single-cell at 10C (26A), four cells in parallel at 10C (ideal match), and four cells in parallel (manufacturer match). The lifetime for each experiment set degraded substantially, with the final parallel series reaching end of life at 400 cycles, a 75.32% reduction in life compared to operating solo. Analysis of the fSoH data for these cells revealed a change in imaginary impedance at the critical frequency that corresponded to changes in the capacity and current data, supporting the development of a single-frequency diagnostic tool. An electrochemical model of the battery was generated, and it indicated the anode material was aging faster than the SEI layer, the opposite of normal cell degradation. A post-mortem analysis of cells from three configurations (baseline, single-cell, and parallel-cell) supported the modeling, as physical damage to the copper current collector in the anode was visible in the parallel-connected cell. / Ph. D. / Lithium-ion batteries are used in a large number of applications, from cellular phones to laptops and electric vehicles. In low power devices, such as a laptop, these batteries can be relatively stable if the associated circuitry is designed properly. However, as the amount of power required from the battery increases, the possibility of an internal battery fault will also increase. The ability to determine the stability of the battery for military applications such as laser weapon systems, electromagnetic railguns or commercial systems such as electric vehicles or industrial-scale micro-grids becomes critical to prevent catastrophic events such as fires. Additionally, the ability to determine the battery State-of-Health (SoH), a specified measure of stability, will enable advance warning of a failing battery to optimize the logistics chain in an operational system. A battery marked as “bad” can be scheduled for replacement before a failure actually occurs. This dissertation has designed a series of experiments that establishes the technology to detect these internals faults, and applies them to a scaled battery system that represents a much larger system. When batteries are placed in parallel and discharged at very high currents, typical of the military applications, the lifetime for the cells was reduced by 75% when compared to batteries discharged under the same conditions by themselves. A post-mortem analysis of cells from three different conditions (uncycled, single-cell, parallel-cell) reveals physical damage to the internal electrodes that indicates a high level of internal destruction occurs at high currents when in parallel arrays.

Conventional energy sources are diminishing and non-renewable, take million years to form and cause environmental degradation. In the 21st century, we have to aim at achieving sustainable, environmentally friendly and cheap energy supply by employing renewable energy technologies associated with portable energy storage devices. Lithium-ion batteries can repeatedly generate clean energy from stored materials and convert reversely electric into chemical energy. The performance of lithium-ion batteries depends intimately on the properties of their materials. Presently used battery electrodes are expensive to be produced; they offer limited energy storage possibility and are unsafe to be used in larger dimensions restraining the diversity of application, especially in hybrid electric vehicles (HEVs) and electric vehicles (EVs). This thesis presents a major progress in the development of LiFePO4 as a cathode material for lithium-ion batteries. Using simple procedure, a completely novel morphology has been synthesized (mesocrystals of LiFePO4) and excellent electrochemical behavior was recorded (nanostructured LiFePO4). The newly developed reactions for synthesis of LiFePO4 are single-step processes and are taking place in an autoclave at significantly lower temperature (200 deg. C) compared to the conventional solid-state method (multi-step and up to 800 deg. C). The use of inexpensive environmentally benign precursors offers a green manufacturing approach for a large scale production. These newly developed experimental procedures can also be extended to other phospho-olivine materials, such as LiCoPO4 and LiMnPO4. The material with the best electrochemical behavior (nanostructured LiFePO4 with carbon coating) was able to delive a stable 94% of the theoretically known capacity. / Konventionelle Energiequellen sind weder nachwachsend und daher nachhaltig nutzbar, noch weiterhin langfristig verfügbar. Sie benötigen Millionen von Jahren um gebildet zu werden und verursachen in ihrer Nutzung negative Umwelteinflüsse wie starke Treibhausgasemissionen. Im 21sten Jahrhundert ist es unser Ziel nachhaltige und umweltfreundliche, sowie möglichst preisgünstige Energiequellen zu erschließen und nutzen. Neuartige Technologien assoziiert mit transportablen Energiespeichersystemen spielen dabei in unserer mobilen Welt eine große Rolle. Li-Ionen Batterien sind in der Lage wiederholt Energie aus entsprechenden Prozessen nutzbar zu machen, indem sie reversibel chemische in elektrische Energie umwandeln. Die Leistung von Li-Ionen Batterien hängen sehr stark von den verwendeten Funktionsmaterialien ab. Aktuell verwendete Elektrodenmaterialien haben hohe Produktionskosten, verfügen über limitierte Energiespeichekapazitäten und sind teilweise gefährlich in der Nutzung für größere Bauteile. Dies beschränkt die Anwendungsmöglichkeiten der Technologie insbesondere im Gebiet der hybriden Fahrzeugantriebe. Die vorliegende Dissertation beschreibt bedeutende Fortschritte in der Entwicklung von LiFePO4 als Kathodenmaterial für Li-Ionen Batterien. Mithilfe einfacher Syntheseprozeduren konnten eine vollkommen neue Morphologie (mesokristallines LiFePo4) sowie ein nanostrukturiertes Material mit exzellenten elektrochemischen Eigenschaften hergestellt werden. Die neu entwickelten Verfahren zur Synthese von LiFePo4 sind einschrittig und bei signifikant niedrigeren Temperaturen im Vergleich zu konventionellen Methoden. Die Verwendung von preisgünstigen und umweltfreundlichen Ausgangsstoffen stellt einen grünen Herstellungsweg für die large scale Synthese dar. Mittels des neuen Synthesekonzepts konnte meso- und nanostrukturiertes LiFe PO4 generiert werden. Die Methode ist allerdings auch auf andere phospho-olivin Materialien (LiCoPO4, LiMnPO4) anwendbar. Batterietests der besten Materialien (nanostrukturiertes LiFePO4 mit Kohlenstoffnanobeschichtung) ergeben eine mögliche Energiespeicherung von 94%.

Darbe yra pateikti ličio geležies fosfato baterijų iškrovimo prie įvairių temperatūrų proceso tyrimai. Išanalizuotos įvairių rūšių baterijos ir nustatytos tinkamiausios baterijos panaudojimui elektra varomame transporte. Mokslinių straipsnių analizė, leido nustatyti ličio geležies fosfato baterijų trūkumus ir pranašumus bei išanalizuoti jų savybes ir ypatumus. Suprojektuotas eksperimentinių tyrimo stendas, pateikta tyrimo metodika ir atlikti ličio geležies fosfato baterijų iškrovimo prie skirtingų temperatūrų tyrimai. Išanalizuoti eksperimentinių tyrimų rezultatai, pateiktos išvados ir rekomendacijos. / In this work a research of lithium iron phosphate batteries discharge process at different temperatures has been carried out. Different types of batteries have been analyzed and the most suitable battery type for electric transport is chosen. Scientific publication analysis allowed to identify the limitations of lithium iron phosphate batteries and to analyze the characteristics and peculiarities of this battery type. A battery testing stand has been designed, a research methodology has been presented and discharge tests of lithium iron phosphate batteries at normal and low temperatures have been performed. The results have been analyzed and findings together with recommendations have been presented.