Further improvements on energy storage systems have become essential for replacing fossil fuels with materials safer for humanity and less harmful environmentally. Lithium-based batteries are the most promising device among energy storage materials thanks to the high volumetric and gravimetric energy density of lithium and its outstanding electrochemical properties. Lithium polymer batteries commercially available are composed of a graphite anode and lithium cobalt oxide layered structure LiCoO2 as cathode active material; the electrolyte filling the area between the two electrodes is a gelled solution made of organic solvents, lithium salts and a polymer enveloping the mixture. This compartment of the cell is highly involved in safety issues concerning lithium batteries because it can contain materials sensitive to temperature changes, flammable, corrosive or volatile; for this reason lithium cells are sealed under inert atmosphere. Different strategies have been employed to control electrolyte¿s safety in lithium batteries, from replacing the most critical materials to reduce their harmful effects to adding small portion of inert species or stabilizing agents to reduce the damage due to degradation of components.
The aim of this proposal is the achievement of an increased safety in lithium based batteries with the development of an inert polymer separator. The prepared separator should have a controlled thickness, strong mechanical properties and a porosity that allows ion exchange through the membrane but avoids contact between positive and negative electrode of the cell. Moreover, the separator has to be inert and versatile because it can be used in complete electrochemical cells with electrolyte solutions of different nature, developing Gel Polymer Electrolytes (GPEs).
Once the synthesis and composition of the inert polymeric separator are optimized, the second part of the work will concern the physicochemical and electrochemical characterization of the GPE.
It is of high importance to investigate on the role of the separator for the worldwide diffusion of improved energy storage devices. The original contribution of this proposal is of high impact for the development of versatile separators suitable with every kind of electrolyte solutions. To accomplish this a considerable number of electrolyte solutions will be prepared, from the commercial one to the last improved composition of solvents and lithium salts. Another crucial aspect of the proposed separator is the synthesis procedure regarding a rapid and easy preparation of few materials. Considering the lack of lithium salts in the basic composition of the separator, because of its harmful hygroscopic behaviour, it is not necessary to develop a procedure under controlled atmosphere. Thanks to the high hydrophobicity of the polymer and the scarce water uptake of the solvents, the proposed membrane is going to have a negligible water content. Water contamination can be highly harmful in lithium based batteries because it can attack highly sensitive materials, affecting the electrochemical performances of the cell. To avoid this, usually membranes are prepared under the inert atmosphere of a glove box; this kind of preparation extends considerably time needed for the development of the separator principally because of drying steps.
Our proposed separator is expected to be ready after no longer then 5 hours including both drying time in a ventilated oven, to conclude the synthesis and remove volatile solvents, and in an oven under vacuum to clean from water content and store the developed membrane under inert atmosphere.