Ligno cellulosic materials for energy storage

The constantly increasing production of a large variety of portable consumer electronic devices and the urgent request of replacement of polluting, internal combustion cars with more efficient, controlled emissions vehicles, such as hybrid or electric vehicles require the development of new reliable and safe power sources. Furthermore the continuous decrease of the oil resources and the growing concern on the climate changes call for a larger use of green, alternative energy sources, such as solar and wind. But wind does not blow on command and the sun does not always shine thus, this discontinuity in operation leads to the need of suitable storage systems to efficiently run renewable energy plants. It is evident that a new energy economy has to emerge, and it must be based on a cheap and sustainable energy supply. Lithium ion batteries, due to their high-energy efficiency, appear as ideal candidates. Although these batteries are well established commercial products, further research and development is required to improve their performance to meet the market requirements. In particular, enhancement in safety, cost, and energy density are needed. A big portion of the R&D studies are nowadays devoted to the search for optimal materials both for the electrodes and the electrolyte of the battery: as far as the electrolyte is concerned, the main goal is to replace the liquid electrolyte with a solid one. The passage to a solid configuration gives concrete promise of increasing cell safety and reliability and, at the same time, of offering modularity in design and ease of handling. Behind the optimization of existing batteries a big effort in this field is the transformation of current batteries into a light, flexible, portable device. If integrated structures containing the three essential components (electrodes, spacer, and electrolyte) of the electrochemical cells can be made mechanically flexible, it would enable these to be embedded into various functional devices in a wide range of innovative products such as smart cards, displays, and implantable medical devices. In the fabrication of such a device the exploitation of cellulose as a flexible material and at the same time the exploitation of the papermaking and printing techniques for the development of paper electrodes and electrolytes and, in a future, of the full paper battery, is under consideration. This will also open the way to a reinvestment of the paper technologies in a high tech field such as the Lithium based batteries. Paper industry, as a matter of fact, is in Europe an important manufacturing industry but the economic change together with the development of electronics highly threaten the role and the surviving of such an activity. In this context grows the urgent need for higher value-added paper products and the conversion of the traditional paper industry. Introducing paper into new products with more profitable markets is crucial. The research work of the present thesis has been developed in collaboration with the “Centre Technique du Papier “(CTP) in Grenoble (Fr). The work has been focused on the use of cellulose in the form of handsheet or microfibrils for the production of innovative electrolyte membranes to be used in Li-based batteries. Two research lines have been followed: 1- Development of composite membranes based on cellulose microfibrils and a polymeric matrix obtained by photopolymerisation of reactive oligomers. 2- Development of multilayered membranes made of cellulose handsheet and polymeric layers obtained by photopolymerisation of reactive oligomers. Both the research lines adopt the photopolymerisation process for developing the membranes. In particular using multifunctional monomers, highly cross-linked polymer membranes are obtained which can be successfully used as gel or solid polymer electrolytes. The process is fast, low cost and versatile. In fact a fully cured polymer is obtained in seconds at room temperature irradiating a proper mixture of reactive molecules and photoinitiator.