Wet-chemistry continuous synthesis of cathodic materials for energy storage

Lithium-ion Batteries (LiBs) are the most prominent technology for the energy storage, and are one of the key elements in the upcoming and necessary global energy transition from a fossil fuel-powered society to sustainable and renewable sources. This immense challenge does not come without issues, and to accommodate such radical changes, the energy storage sector must develop and adapt quickly. In this sense, the exponential growth of the battery demand for electrified transportation and for energy storage from renewable sources has prompted the necessity to accelerate the transition of the developments at the laboratory scale to the mass production. In particular, the synthesis of active materials is a critical point, since rarely new methods developed at the research level are extended to the industry. In this context, continuous hydrothermal flow synthesis is a water-based, easily scalable and a more environmentally-friendly alternative to the classical solid-state methods for the synthesis of electrode materials, both for the cathode and the anode of LiBs. This method easily allows a production scale in the tens of kg/day range, and, at the same time, the systematic study of different systems and compositions to tailor and optimize new formulae, taking advantage of the extremely fast reaction (from seconds to minutes). Moreover, in the last years, a remarkable increase in the application of nanomaterials and particle engineering at the cathodic level has catalyzed the research, but the large scale implementation of these innovative technologies is hampered by the low adaptability of classical synthesis such as co-precipitation and calcination. In this Thesis, the Continuous Hydrothermal Flow Synthesis (CHFS) approach was employed to synthesize different cathodic materials (or their precursors), both already present at the commercial level, like the olivine LiFePO4 and the layered oxide LiNi0.33Mn0.33Co0.33O2 and others that are still at the development phase, like LiMn0.8Fe0.2PO4 and the high voltage spinel LiMn1.5Ni0.5O4, the latter never synthesized with this approach. The main objective was to determine whether the system is suitable for the large scale production of these materials and how the specific characteristics of this synthesis process affect the physico-chemical properties and the electrochemical performances of the final cell. A comprehensive characterization was carried out, including the investigation of the crystal structure through Rietveld refinement of XRD patterns and X-ray Absorption Spectroscopy (XAS) spectroscopy, morphological and compositional analysis. Moreover, the synthesis of the layered oxide with different degrees of nickel was optimized through a Design of Experiment (DoE) approach which, from an industrial perspective, allows to reduce the number of trials and speeds up the optimization process in the implementation of modifications or new formulae. The electrochemical results, conducted in semi coin cells, were related to the specific characteristics of the samples, enabling to set a relationship between the different synthetic conditions and the final specific capacity and capacity retention displayed.