Investigation on Next Generation Materials for Rechargeable Lithium-ion Batteries: Alloying- and Conversion-based Materials as Viable Anode Candidates

The current lithium-ion batteries (LIBs) technology has allowed the spread of portable electronic devices such as cameras, laptops, and smartphones, and at the same time has triggered the development of the electric vehicles (EVs). In order to increase LIBs mass diffusion and meet the market demands, a reduction in costs and environmental impact are required. Graphite is the conventional anodic material, but because of its relatively low specific capacity (372 mAh g-1), and its implementation in the list of critical raw materials of European Union, it has to be replaced by more performant and environmentally-friendly materials. Since graphite has a capacity limitation due to its lithium storage mechanism (insertion process), the use of materials based on different lithium storage mechanisms, such as alloying and conversion materials, has been taken into consideration. Silicon is one of the most studied alloying materials because of its low cost, relatively low working potential, and high theoretical specific capacity of 3579 mAh g-1 (corresponding to the formation of Li15Si4 phase). Since the formation of the most lithiated phase is associated with a huge volume expansion (≈ 300%), silicon is plagued by structural instability resulting in poor performances and safety. Thus, it is mandatory to stabilize its structure in order to have it commercialized in the future. Several strategies have been proposed such as the use of nanosize active materials, the implementation of carbonaceous and inorganic matrices, the use of tailored electrolyte and additives, and the use of more elastic and eco-friendly binders. In this thesis, different approaches have been used in combination, in order to buffer the silicon volume expansion, thus enhancing its capacity, safety and long-term perfomances. The perfomances of two silicon-based composites (Si@V2O5 and Si@TiO2) have been evaluated by the means of structural, morphological and electrochemical characterizations. A whole chapter of this thesis will be focused on the scale-up of typical laboratory scale processes, where an in-depth study of silicon-based electrodes processing has been carried out. This study has been performed in a pre-industrial plant, starting from the electrode slurry preparation up to the electrochemical characterization of the assembled full cell. Different aspects have been taken into consideration, demonstrating that the scale-up of established laboratory-scale processes reserves important problems at an industrial level. At last, the use of a conversion material has been evaluated. These materials suffer from issues similar to those of alloying materials. Indeed, a big volume expansion associated with a low electronic conductivity and a large hysteresis in the first cycle hinder their commercialization. Fe2O3 nanoparticles have been synthesized using vanillin as soft template, in a cheap and very reproducible way. The electrochemical characterization showed remarkable cycling perfomances even at high currents.