The intense use of fossil fuels in the last two centuries is primarily responsible for global warming and severe environmental pollution. Moreover, the progressive depletion of the oil/gas resources and the strong dependence on foreign suppliers create national vulnerabilities. In this context, the development of renewable energy sources and the implementation of electric vehicles for transportation is becoming a worldwide imperative. Solar radiation, wind and waves are discontinuous energy sources, thus their use requires efficient energy storage devices to balance the supply with the demand. The most convenient way to store the energy is to convert it into chemical energy and, on demand, convert it back to electrical energy. This is exactly what batteries do. Batteries can also provide the portability of the stored energy and possess the ability to deliver the electricity with high efficiency and without gaseous emission. The development of batteries that can store sustainable energy with long term stability and have a very prolonged cycle life without environmental constraints is one of the main challenges of the 21st century. This is true also in the field of transportation where the use of electric vehicles will reduce the use of oil and pollution. Batteries with high energy and power densities, extended life and high safety are hence required. This type of ''green revolution'', implying an extended use of renewable energy sources to replace oil or carbon, may occur using Lithium ion batteries that dominate the consumer market (they are sold in billion pieces for laptop computers, cameras, etc) because of their ability to store a high density of energy, their high efficiency and prolonged cycle life. The performance of these devices depends on the physical-chemical properties of the anodic and cathodic reactants. The current lithium-ion technology is satisfactory for consumer electronics, but a quantum jump is necessary to meet the requirements for applications such as electric cars. Thus the research of new and advanced materials is currently challenging materials scientists. The research work presented in this thesis deals with the investigation of the electrochemical properties of electrode materials for rechargeable lithium ion batteries. Two different aspects have been studied that are both driven toward the development of greener, safer and cheaper lithium ion batteries. In the first part of my PhD thesis, the relationships between structural features and electrochemical performances of LiFePO4, a promising cathode material, have been investigated. The structure of LiFePO4 has been modified by introduction of vanadium (doping) in an attempt to overcome the intrinsic limitation (i.e. low electrical conductivity) of this material. The synthesized materials, with different concentrations of dopant, have better electrochemical performances than the pure LiFePO4. The structural modifications induced by vanadium were analyzed by means of X-ray diffraction and Synchrotron X-rays Absorption Spectroscopy and correlated with the improved electrochemical performances. The second part of the present dissertation describes the results obtained during my six months spent as a visiting PhD student at MEET (Ma'¼nster Electrochemical Energy Technology) at the WWU University of Ma'¼nster, Germany, under the supervision of Prof. Dr. Stefano Passerini. The work deals with the study of the effect water processible binders on anatase TiO2 anode electrochemical performances. The electrodes manufactured using aqueous binders showed improved electrochemical performance with respect to those made using traditional fluorinated binders. A full lithium ion cell comprising TiO2 anode and a high voltage cathode, both prepared using water as solvent (instead of toxic liquids) was assembled and successfully cycled The results reported within this thesis have been the subject of the following publications: A. Moretti, G.T. Kim, D. Bresser, K. Ranger, E. Paillard, R. Marassi, M. Winter, S. Passerini, ''Investigation of different binding agents for nanocrystalline anatase TiO2 anodes and its application in a novel, green lithium-ion battery'', Journal of Power Sources, 2013, 221, 419-426. L. Tabassam, G. Giuli, A. Moretti, F. Nobili, R. Marassi, M. Minicucci, R. Gunnella, L. Olivi, A. Di Cicco, ''Structural study of LiFePO4-LiNiPO4 solid solutions'', Journal of Power Sources, 2012, 213, 287-295. A. Moretti, G. Giuli, F. Nobili, A. Trapananti, G. Aquilanti, R. Tossici, R. Marassi, ''Structural and electrochemical characterization of Vanadium-doped LiFePO4 cathodes for Lithium-ion batteries'', Journal of the Electrochemical Society, submitted.
|Titolo:||Structural and electrochemical investigations of Li-ion battery electrodes. 1. Vanadium doping of LiFePO4 cathodes 2. Aqueous binders for anatase TiO2 anodes|
|Data di pubblicazione:||19-mar-2013|
|Appare nelle tipologie:||Tesi di dottorato (Pregresso)|