Lithium iron phosphate (LiFePO4) has been synthesized by hydrothermal synthesis using pyrrole as an efficient reducing agent. The oxidized Fe3+ in the system reacts with pyrrole that can form polypyrrole (PPy) to generate Fe2+. The PPy can also be a carbon source for further calcination. The observations of scanning electron microscope (SEM) and transmission electron microscope (TEM) show that the particle size of LiFePO4 is around 500 nm and a layer of carbon coats on LiFePO4. The chemical composition of the LiFePO4 was characterized by elemental analysis (EA) and inductively coupled plasma mass spectroscopy (ICP/MS). The results of TEM and X-ray diffraction (XRD) show the structure of LiFePO4 is orthorhombic olivine. Raman and X-ray photoelectron spectroscopy (XPS) results indicate that pyrrole as a reducing agent prevents the impurity of Fe3+ formation and the resulting polypyrrole plays a role as carbon source. The calcination of LiFePO4 greatly affects the energy density. In addition, the carbon contain in the LiFePO4 powder is controllable using the addition of Fe3+ to enhance the electrical conductivity. Moreover, the electrochemical results show the energy capacity of the hydrothermal LiFePO4 is 152 mAh g−1. The LiFePO4 has a better rate discharge capability compared with LiFePO4 synthesized with ascorbic acid as a reducing agent.

Lithium iron phosphate (LiFePO4) is prepared by hydrothermal process using Fe(III) as precursor and pyrrole as an efficient reducing agent. The Fe(III) precursor in the system reacts with pyrrole to generate polypyrrole (PPy) and reduce Fe(III) to Fe(II). The different molar ratio Fe(III) polymerize different content of PPy and PPy can also be a carbon source for further calcination. The structural and morphological properties of LiFePO4 powder were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and a transmission electron microscope (TEM). The XRD and TEM results demonstrate that LiFePO4 powder has an orthorhombic olivine-type structure with a space group of Pnma. The SEM and TEM results show that the particle size of LiFePO4 is around 200 nm and a layer of carbon coats on LiFePO4. The chemical composition of the LiFePO4 powder was characterized by elemental analysis (EA) and inductively coupled plasma/mass spectroscopy (ICP/MS). Raman and X-ray photoelectron spectroscopy (XPS) results indicate that pyrrole as a reducing agent reduces and prevents the formation of Fe(III) impurity and the resulting PPy plays a role as carbon source. Among the synthesized cathode materials, LiFePO4 synthesized using 5% molar ratio of Fe(III) and subsequent calcinations of 600 ¢XC shows the best electrochemical property with an discharge capacity of 160 mAhg−1 close to its theoretical capacity 170 mAh g−1 at 0.2 C rate. Using 10% molar ratio of Fe(III), and the discharge capacity of LiFePO4 at 10 C rate reaches 106 mAhg−1.

This thesis investigates the high frequency discharging characteristics of the lithium iron phosphate battery. The investigation focuses on effects of the high-frequency current on the dischargeable capacity of the battery. Included are the current profiles of triangle, saw-tooth, and trapezoidal waves, which are produced from commonly used DC-DC converters. Experimental results show that the current with the higher frequency has less dischargeable capacity. On the other hand, the converter current resonating into and out from the battery results the additional losses. The possible reasons that affect the discharged capacities are explained by the equivalent circuit of the battery.

abstract: There was a growing trend in the automotive market on the adoption of Hybrid Electric Vehicles (HEVs) for consumers to purchase. This was partially due to external pressures such as the effects of global warming, cost of petroleum, governmental regulations, and popularity of the vehicle type. HEV technology relied on a variety of factors which included the powertrain (PT) of the system, external driving conditions, and the type of driving pattern being driven. The core foundation for HEVs depended heavily on the battery pack and chemistry being adopted for the vehicle performance and operations. This paper focused on the effects of hot and arid temperatures on the performance of LiFePO4 (LFP) battery packs and presented a possible modeling method for overall performance. Lithium-ion battery (LIB) packs were subjected to room and high temperature settings while being cycled under a current profile created from a drive cycle. The Federal Urban Driving Schedule (FUDS) was selected and modified to simulate normal city driving situation using an electric only drive mode. Capacity and impedance fade of the LIB packs were monitored over the lifetime of the pack to determine the overall performance through the variables of energy and power fade. Regression analysis was done on the energy and power fade of the LIB pack to determine the duration life of LIB packs for HEV applications. This was done by comparing energy and power fade with the average lifetime mileage of a vehicle. The collected capacity and impedance data was used to create an electrical equivalent model (EEM). The model was produced through the process of a modified Randles circuit and the creation of the inverse constant phase element (ICPE). Results indicated the model had a potential for high fidelity as long as a sufficient amount of data was gathered. X-ray powder diffraction (XRD) and a scanning electron microscope (SEM) was performed on a fresh and cycled LFP battery. SEM results suggested a dramatic growth on LFP crystals with a reduction in carbon coating after cycling. XRD effects showed a slight uniformed strain and decrease in size of LFP olivine crystals after cycling. / Dissertation/Thesis / Masters Thesis Engineering 2016

<p>Li-ion batteries are not only a technology for the future, they are indeed already the technology of choice for today’s mobile phones, laptops and cordless power tools. Their ability to provide high energy densities inexpensively and in a way which conforms to modern environmental standards is constantly opening up new markets for these batteries. To be able to maintain this trend, it is imperative that all issues which relate safety to performance be studied in the greatest detail. The surface chemistry of the electrode-electrolyte interfaces is intrinsically crucial to Li-ion battery performance and safety. Unfortunately, the reactions occurring at these interfaces are still poorly understood. The aim of this thesis is therefore to increase our understanding of the surface chemistries and stability phenomena at the electrode-electrolyte interfaces for three novel Li-ion battery electrode materials.</p><p>Photoelectron spectroscopy has been used to study the surface chemistry of the anode material AlSb and the cathode materials LiFePO₄ and Li₂FeSiO₄. The cathode materials were both carbon-coated to improve inter-particle contact. The surface chemistry of these electrodes has been investigated in relation to their electrochemical performance and X-ray diffraction obtained structural results. Surface film formation and degradation reactions are also discussed.</p><p>For AlSb, it has been shown that most of the surface layer deposition occurs between 0.50 and 0.01 V <i>vs.</i> Li°/Li⁺ and that cycling performance improves when the lower cut-off potential of 0.50 V is used instead of 0.01 V. For both LiFePO₄ and Li₂FeSiO₄, the surface layer has been found to be very thin and does not provide complete surface coverage. Li₂CO₃ was also found on the surface of Li₂FeSiO₄ on exposure to air; this was found to disappear from the surface in a PC-based electrolyte. These results combine to give the promise of good long-term cycling with increased performance and safety for all three electrode materials studied.</p>

Hydrothermal synthesis is a widely used technique for the preparation of fine particles. It can be carried out in batch or flow systems, although most studies have used batch reactors below 200 C. More recently, however, continuous hydrothermal synthesis has been employed in near- and supercritical water to obtain metal oxide particles. This technique offers tremendous promise for control of particle characteristics due to the rapidly changing properties of water with temperature and pressure in the critical region. However, the role of temperature in this process is not completely understood. Moreover, agglomeration of particles remains a problem in both batch and continuous hydrothermal techniques. This work is concerned with the use of continuous hydrothermal synthesis at near-critical and supercritical conditions to obtain iron oxide and lithium iron phosphate nanoparticles. Factors that affect size, size-distribution, and morphology of nanoparticles were investigated and the results have been used to resolve differences in the literature concerning the effect of temperature on particle size. It was shown that agglomeration can be minimized by using a protective polymer coating and this appears to be an effective method to control particle size. The continuous hydrothermal technique was also extended to materials other than metal oxides by synthesizing lithium iron phosphate. Differences in the particle sizes obtained using the batch and continuous methods were shown to be due to the different mechanisms of particle formation in the two techniques. Better particle characteristics (size, size distribution and morphology) were obtained using the continuous hydrothermal technique than using the batch hydrothermal method. Iron oxide nanoparticles were also deposited on the surface and in the pores of activated carbon pellets in a batch reactor in order to minimize agglomeration of particles. The resulting iron oxide activated carbon nanocomposites exhibited significant catalytic performance in the oxidation of propanal. Therefore, the use of supercritical water to deposit metal oxide particles on hydrophobic surfaces offers promise for carbon-supported catalyst preparation without the use of toxic or noxious solvents.

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.

Die vorliegende Dissertation beschäftigt sich mit der Synthese, den Li+-Transporteigenschaften und der Thermodynamik von Olivin-Typ LiFePO4. Es werden verschiedene Solvothermalsynthesen untersucht. Neben der Einstellung von Partikelgröße und Partikelmorphologie steht die Analyse der Hydrothermalsynthese aus Li3PO4 und Vivianit durch in situ Messung der elektrolytischen Leitfähigkeit im Vordergrund. Die Untersuchung des Li+-Transportes geschieht auf Basis von Redoxreaktionen. Die formalkinetische Auswertung von Lithiierungs- und Delithiierungsreaktionen und eine Nukleationsanalyse wird durch ein Modell zur Auswirkung von antisite-Defekten auf die Kapazität des Elektrodenmaterials ergänzt. Die Ramanspektroskopie wird in Verbindung mit Lösungsenthalpien zur Identifizierung reaktiver Spezies herangezogen. Schwerpunkt der thermodynamischen Charakterisierung ist die experimentelle Ermittlung der Wärmekapazität. Diese wurde unter Berücksichtigung einer magnetischen Phasenumwandlung im Bereich von 2 K bis 773 K ermittelt. Die Daten erlauben die Berechnung wichtiger thermodynamischer Funktionen.

Li-ion batteries are not only a technology for the future, they are indeed already the technology of choice for today’s mobile phones, laptops and cordless power tools. Their ability to provide high energy densities inexpensively and in a way which conforms to modern environmental standards is constantly opening up new markets for these batteries. To be able to maintain this trend, it is imperative that all issues which relate safety to performance be studied in the greatest detail. The surface chemistry of the electrode-electrolyte interfaces is intrinsically crucial to Li-ion battery performance and safety. Unfortunately, the reactions occurring at these interfaces are still poorly understood. The aim of this thesis is therefore to increase our understanding of the surface chemistries and stability phenomena at the electrode-electrolyte interfaces for three novel Li-ion battery electrode materials. Photoelectron spectroscopy has been used to study the surface chemistry of the anode material AlSb and the cathode materials LiFePO4 and Li2FeSiO4. The cathode materials were both carbon-coated to improve inter-particle contact. The surface chemistry of these electrodes has been investigated in relation to their electrochemical performance and X-ray diffraction obtained structural results. Surface film formation and degradation reactions are also discussed. For AlSb, it has been shown that most of the surface layer deposition occurs between 0.50 and 0.01 V vs. Li°/Li+ and that cycling performance improves when the lower cut-off potential of 0.50 V is used instead of 0.01 V. For both LiFePO4 and Li2FeSiO4, the surface layer has been found to be very thin and does not provide complete surface coverage. Li2CO3 was also found on the surface of Li2FeSiO4 on exposure to air; this was found to disappear from the surface in a PC-based electrolyte. These results combine to give the promise of good long-term cycling with increased performance and safety for all three electrode materials studied.

<p>Surface film formation at the electrode/electrolyte interface in lithium-ion batteries has a crucial impact on battery performance and safety. This thesis describes the characterisation and treatment of electrode interfaces in lithium-ion batteries. The focus is on interface modification to improve battery safety, in particular to enhance the onset temperature for thermally activated reactions, which also can have a negative influence on battery performance. </p><p>Photoelectron Spectroscopy (PES) and Differential Scanning Calorimetry (DSC) are used to investigate the surface chemistry of electrodes in relation to their electrochemical performance. Surface film formation and decomposition reactions are discussed.</p><p>The upper temperature limit for lithium-ion battery operation is restricted by exothermic reactions at the graphite anode; the onset temperature is shown to be governed by the composition of the surface film on the anode. Several electrolyte salts, additives and an anion receptor have been exploited to modify the surface film composition. The most promising thermal behaviour is found for graphite anodes cycled with the anion receptor, tris(pentafluorophenyl)borane, which reduces salt reactions and increases the onset temperature from ~80 °C to ~150 °C.</p><p>The electrochemical performance and surface chemistry of Swedish natural graphite, carbon-treated LiFePO₄ and anodes from high-power lithium-ion batteries are also investigated. Jet-milled Swedish natural graphite exhibits a high capacity and rate capability, together with a decreased susceptibility to solvent co-intercalation. Carbon-treated LiFePO₄ shows promising results: no solvent reaction products are detected. The amount of salt compounds increases, with power fade occurring for anodes from high-power lithium-ion batteries; the solvent reduction products comprise mainly Li-carboxylate type compounds.</p>