1,721,306 research outputs found
Mesoporous materials and nanostructured LiFePO4 as cathodes for secondary Li-ion batteries: synthesis and characterisation
No full textEnergy, environmental concerns and information technology (IT) have become thrust areas for the 21st century, as they are closely linked to the technological development. The search for energy sources to provide comfort and a smooth lifestyle has taken place since the beginning of civilization; however, the present energy needs are very much dependent on nuclear and fossil fuel (oil). Currently, as the internal combustion engine is a major user of fossil fuel, consuming about 1/3 of the annual total demand for energy, concern over global warming and air pollution has become evident. Consequently, there is a high worldwide incentive to find more efficient, convenient, pollution-free and safe power sources; examples of advanced techniques include fuel cells and solar cells.
Reliable methods for storing energy are just as important and secondary lithium-ion batteries provide an attractive solution. The lithium-based battery technology of today out-performs many other conventional systems, such as the lead-acid, nickel-cadmium and nickel-metal hydride batteries, because of its high energy and power density, and design flexibility, in combination with the use of environmentally acceptable constituents. Li-ion battery is a compact, lightweight, rechargeable power source stable to over 500 cycles. It can be fabricated in size ranging from a few microns to a large-scale battery capable of providing power for computer memory chips, communication equipments, colour motion pictures and, potentially, for the huge market of electric vehicles (EV) and hybrid-electric vehicles (HEV), where low cost, low environmental impact, as well as high specific performance batteries are needed.
Li-based battery chemistry is, however, relatively young. Thus, the constant demand for higher energy density, thinner, lighter and even more mechanically flexible batteries has motivated research into new cell configurations and new battery chemistries and electrode materials.
The scope of this thesis is the development of new cathode materials for secondary Li-ion batteries and the assessment of their structural-morphological characteristics and electrochemical performance.
Chapter I deals with the basic concepts for cells and batteries and with a brief description of the history of the battery and of the general characteristics of the mature portable power-source technologies (i.e., lead-acid, Ni-Cd and Ni-MH).
Chapter II discusses the historical developments, present status and future trends in Li-based batteries research. Their characteristics, working principles and components are also discussed.
The energy density of lithium batteries has not increased in the last 20 years, and the specific capacity (Ah/kg) has actually decreased. Thus, much effort is being directed at finding new materials, both electrode materials and electrolytes, that can provide higher capacities, lower costs, and are environmentally benign. This is shown in Chapter III, that presents the materials and components relevant to the Li-ion battery technology during recent years and for the next future. The cathode is particularly critical in determining the capacity of a Li-based battery, as it is the heaviest component, and it has the greatest potential for improvement. For this component, further basic requirements for the potentially wide market of EVs and HEVs are the availability, low cost (high Wh/€) and low environmental impact, as well as high power capability.
The experimental part of this thesis deals with the research work carried out on ordered modified mesoporous materials and nano-structured phospho-olivine LiFePO4 as cathode materials for Li-ion cells. In Chapter IV the characterization techniques and methods used to analyse the synthesized samples, either from the structural-morphological or electrochemical point of view, are briefly described.
In Chapter V, the experimental results are shown regarding the three different strategies adopted in order to produce transition-metal containing mesoporous materials, suitable as cathodes for Li-ion cells. In this connection, the first attempt was to produce siliceous (MCM-41 type) and alumino-phosphate (AlPO-type) mesoporous materials, trying to substitute the largest amount of Si and/or Al with Mn ions, by direct hydrothermal synthesis. As their electrochemical results in Li cells were not satisfying, we synthesized mesoporous MCM-48 silica supported with transition-metal oxides (both MnO2 and Fe2O3) nanoparticles, by the wet impregnation technique. Finally, the experimental results are reported regarding the strategy adopted in order to support nanoparticles of FePO4, which is a well-known and extensively studied material for Li-ion batteries, into the channels of an ordered mesoporous SBA-15 silica.
Phospho-olivine lithium iron phosphate (LiFePO4) is a potential cathode material for the next generation of secondary Li-ion batteries, as it fulfils the requirements of high theoretical specific capacity, low toxicity, low cost and availability. In Chapter VI, the development of a new, easy and low cost hydrothermal synthetic route to produce high surface area and high performance nano-structured LiFePO4 powders is reported. The aim was to investigate the influence of the synthetic route and preparation conditions (presence of a surfactant during synthesis) on the chemical-physical properties of the LiFePO4/C composites and, as a consequence, on their electrochemical performances. CTAB has been chosen as the surfactant for its high dispersing activity. Moreover, during the firing step in inert atmosphere, CTAB favours the preparation and the homogeneity of the LiFePO4/C composites and the obtaining of a positive influence on their electrochemical performances
Fotopolimeri per l'energia: una nuova strategia nel campo di conversione e stoccaggio delle fonti rinnovabili
No full textL'irraggiamento di monomeri reattivi in condizioni blande genera fotopolimeri impiegabili come componenti di celle solari di terza generazione e batterie a ioni litio/sodio. Questa tecnologia sostenibile e a basso impatto migliora la durabilità e la sicurezza di questi dispositivi energetici di largo impieg
NOVEL NANOSTRUCTURED MATERIALS FOR ENERGY PRODUCTION AND STORAGE SYSTEMS
No full textThe increasing role of technology in our lives necessitates the development of advanced energy storage technologies, ranging from portable electronic devices to hybrid electric vehicles. Considered the most advanced of the available rechargeable technologies, lithium ion batteries rely on solid state intercalation compounds that are able to reversibly intercalate lithium within both electrode structures. Both cell voltage and capacity are governed by the materials chemistry. The capability to improve that chemistry resides in a better understanding of the processes that occur in the bulk in addition to the development of some new materials based on nanostructured concepts. Traditional electrode materials for lithium-ion storage cells are based on materials which have both mixed electron and ion transport (for Li+). They are typically crystalline layered structures such as metal oxides that have high redox potentials, and act as positive electrodes; and graphitic carbons capable of reversible uptake of Li at low potentials which act as negative electrodes. Recently, however, nanostructured solid state materials, which are comprised of two or more compositional or structural phases, have been considered. This new area has been particularly exploited in the area of negative electrode design, where the intimate mix of components at the nanoscale permits and enhances Li reversibility. It also include cathode materials where materials that function on the basis of intergrowth structures (internal composites) have been found to be beneficial; and insulating materials where the limitations to electron transport must be overcome by judicious design of nanostructured composites. The present communication is a brief overview of some developments based on our work that highlights key points in anode and cathode design based on this theme. The research trends and future prospects are also discusse
Materials for electrochemical energy conversion and storage: novel approaches and chemistry thereof
No full textEnergy has become one of the predominant scientific research areas in the 21st century. Fossil fuels can no longer represent the predominant energy supply for human being. Their use must be reduced and alternative sustainable energy resources have to be identified and rapidly exploited. Besides conversion technologies, also the energy storage must be considered. Electrochemical systems, such as batteries and supercapacitors that can efficiently store and deliver energy on demand in stand-alone power plants, as well as provide power quality and load leveling of the electrical grid in integrated systems, are playing a crucial role in this respect. Annual worldwide research efforts in the field of energy conversion and storage are immense, and more than 10,000 publications per year are indexed by ISI. At the same time, some of these technologies are implemented on a large scale, thus turning out that the materials traditionally used are often critical in terms of safety, cost and environmental impact. In this contribution, two of the most important energy technologies are thoroughly discussed: third-generation solar cells and secondary Li-/Na-ion batteries. Newly elaborated approaches on the selection, functionalization and investigation of materials are presented, also highlighting their key points with respect to those reported in the literature so far. The present communication is intended to show a brief overview of the promising prospects of abundant and readily available raw materials specifically selected and developed for energy storage and conversion devices. In particular, the use of water, (bio-)polymers and light-induced functionalization techniques are demonstrated to allow performance, stability and up-scalable feature previously unpredictable on the basis of traditional chemical and physical approaches. The research trends and future prospects are also discusse
Development of multipurpose ethylene oxide based polymer electrolytes for smart and energy efficient devices
No full textWide interest is mounting on polymer electrolytes for application in energy efficient devices such as rechargeable batteries, electrochromics and photovoltaics. Solid polymer electrolytes exhibit unique advantages: mechanical integrity, variety of fabrication methods and intimate electrode/electrolyte interfacial properties. They also improve safety along with more compact and lightweight packaging. Since the discovery of ionic conductivity in alkali metal salt complexes of poly(ethylene oxide), PEO, lot of research was devoted on systems containing lithium salts to be used as electrolytes, particularly in Li-based batteries. In this work, highly ionic conducting PEO-based polymer electrolytes, encompassing lithium salts dissolved in Room Temperature Ionic liquids (RTIL), were successfully prepared via rapid hot-press and subsequently cross-linked via UV irradiation. All the prepared materials were thoroughly characterised in terms of their physical, chemical and morphological properties and tested for ionic conductivity, electrochemical stability and cycling performances. The UV-curing process on such materials led to the production of elastic and resistant polymer electrolyte membranes. The degree of PEO crystallinity was greatly reduced down to the amorphous state by addition of lithium salt and RTIL and UV-induced cross-linking process. As a consequence, a noticeably increased ionic conductivity was registered (> 10-4 Scm-1 at RT). The polymer electrolyte demonstrated a very stable interfacial stability versus lithium metal and a very wide electrochemical stability window (0-5.5 V vs. Li). In the presence of such an electrolyte, the laboratory-scale devices showed remarkable performances, only slightly lower than those using liquid electrolyte, respect to which demonstrated a much greater durability. The obtained findings demonstrate that our proposed preparation can provide a new, easy and low cost approach to fabricate polymer electrolytes with remarkable performance for the next generation of advanced flexible energy production and storage device
Towards green, efficient and durable quasi-solid dye-sensitized solar cells integrated with a cellulose-based gel-polymer electrolyte optimized by a chemometric DoE approach
No full textAn innovative biopolymer composite electrolyte for dye-sensitized solar cells (DSSCs), obtained by quasi-solidifying an indigenous liquid electrolyte containing supporting salts and I3−/I− redox couple with a mixture of polyethylene oxide (PEO) and carboxymethyl cellulose sodium salt (CMC) is proposed. This is the first ever report indicating the useful aspects of CMC as a component in the electrolyte of a photovoltaic device and the requisite parameters are thoroughly investigated. Moreover, the performances of the lab scale quasi-solid devices are presented by means of a combined photovoltaic-chemometric approach, definitely innovative for the study of polymer based electrolytes for DSSCs. We also present the durability of the devices inherited by different PEO : CMC ratios as well as the response of the cells to various wavelengths and irradiation intensities. The intriguing photovoltaic-chemometric approach allows developing a device with efficiencies up to 5.18% under 1 sun irradiation ([similar]7% under 0.4 sun). The cumulative effect by the strategic components employed in the gel-polymer electrolyte demonstrates an outstanding durability with an excellent efficiency as high as 98% even after 250 h of extreme aging condition
Natural Polymers for Dye-Sensitized Solar Cells: Electrolytes and Electrodes
No full textIt has been argued that the application of biosourced materials holds a promise for improved environmental performance. This promise has also been argued to apply to photovoltaic and solar cells. Frontrunners in this respect are the dye-sensitized solar cells (DSSCs), also known as Grätzel cells. DSSCs are the most investigated third-generation photovoltaic devices, due to a number of attractive features, including quasi-flexibility and quasi-transparency, which offer a variety of uses not applicable to glass-based systems, such as low-cost and ease of manufacturing via conventional roll-printing techniques. However, important drawbacks of DSSCs are represented by the poor long-term stability due to the volatility of the electrolyte contained organic solvent and the use of toxic and expensive components. DSSCs exploiting biosourced polymer electrolytes and electrode materials are presently under intense investigation as a next-generation sustainable solar energy converter because of their simple structure, low manufacturing cost, and green aspect. This article details the preparation and characteristics of some recently developed electrolytes and electrodes by using biosourced material
Ultrafast, low temperature microwave-assisted solvothermal synthesis of nanostructured lithium iron phosphate optimized by a chemometric approach
No full textNanostructured LiFePO4/C composites having ordered olivine structure are prepared by a newly elaborated low temperature microwave-assisted solvothermal synthesis in the presence of a cationic surfactant. The microwave-assisted approach is simple and cost effective: it significantly decreases reaction times compared to the conventional hydrothermal/solvothermal processes. A study on the influence of the synthesis parameters on both the morphology and the electrochemical behavior of the samples is performed by means of X-ray powder diffraction, N2 physisorption at 77 K, scanning electron microscopy, cyclic voltammetry and constant current charge/discharge cycling. Moreover, a chemometric approach through design of experiments (DoE) is here successfully demonstrated for the first time for the optimization and fine tuning of the experimental conditions, including synthetic procedure and electrochemical characteristics of the materials. As a result, we show a nanostructured LiFePO4/C with high rate capability and delivering a very stable cycling behavior for more than thousand cycles with excellent Coulombic efficiency and exceptional capacity retentio
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