Cathodes Development and Cell Manufacturing for Innovative Li-ion and Na-ion Batteries

The present thesis work is focused on the study of cathode materials and the related cell manufacturing to obtain Li-ion and Na-ion batteries for possible practical applications. In particular, the use of a Fe/Mn-based mixed olivine cathode in both systems, the scalability of electrode processing and manufacturing in Li-ion cells, and the proof-of-concept evaluation of full-cell balancing, coupling layered oxide cathodes and Sn- or Si-based alloying anodes, are herein studied in this thesis. Energy production has been worldwide moving toward renewable sources to overcome the several drawbacks presently attributed to the massive use of fossil fuels. In these regards, electrochemical energy storage (EES) systems, in particular rechargeable batteries, play the most relevant role in storing green energy. Relevantly, to achieve the goals of sustainability, good management, and safety, non-toxic, cheap, and stable polyanionic phospho-olivines have been promoted and largely used in commercial batteries, despite low ionic and electronic conductivity and relatively low working potential (i.e. 3.45 V vs. Li+ /Li for LiFePO4), which could be increased using other transition metals, such as Mn. Additionally, the possible implementation of Na-ion batteries for stationary storage could also increase the sustainability of EES systems, due to the abundancy of sodium with respect to lithium, while the alkali metal substitution requires notable and dedicated studies. Furthermore, the optimization of other practical aspects regarding electrodes and cell manufacturing (i.e. slurry properties, coating procedure, electrode balancing etc.) is another key parameter to obtain improvement on battery performances, especially on industrial scale. On the other hand, the high energy density of layered oxide cathodes is required in different applications, making relevant the study of these materials, particularly when combined with anodes with high theoretical capacity (i.e. alloying-based anodes). In the first chapter a mixed LiFe0.6Mn0.4PO4 (LFMP) olivine cathode was synthesized and characterized in terms of structure, morphology and electrochemical features in lithium metal cell. Therefore, due to the positive results in conventional electrolyte, LFMP was studied in a lithium metal polymer battery with a solid configuration, using a polyethylene glycol dimethyl ether-based electrolyte, showing promising outcomes in terms of capacity, efficiency, and retention. Subsequently, LFMP was electrochemically converted to NaFe0.6Mn0.4PO4 (NFMP) with triphylite structure for application in Na-ion battery. The NFMP cathode was deeply characterized in terms of structure, morphology and electrochemical features in sodium metal cell with encouraging findings, and afterwards compared with the lithium analogue LFMP in terms of ion transport and interfacial characteristics using various electrochemical techniques, combined with the calculation of the distribution of relaxation times (DRT) functions. Furthermore, the electrochemical reaction mechanism and structure of NFMP cathode were additionally investigated by means of ex-situ and in-situ (operando) XAS experiments. In the second chapter the role of conductive carbon additives and the refining of electrode manufacturing using commercial LiMn0.7Fe0.3PO4 (LMFP73) as active material have been studied. The optimization of additive content, mixing protocol, solid content, coating speed, and electrode loading was carried out to produce electrodes suitable for industrial use, subsequently coupled with graphite anode to achieve lab-scale coin-type full-cells and upscaled single-layer pouch cell, presenting promising stable capacity retained for over 100 cycles and good energy density at the electrodes level. The last chapter is focused on full-cell balancing using layered oxide cathodes and alloying-based anodes. LiNi0.2Co0.2Al0.1Mn0.45O2 (LNCAM) was synthetized and deeply characterized in Li-cell. Particularly, its relevant irreversibility during first charge is advantageously exploited for compensating the pristine inefficiency of a Li-alloying silicon oxide composite without any preliminary treatment in proof-of-concept full-cells with different N/P ratios. Moreover, a sodiated version of a tin-carbon (Sn-C) alloying material was obtained exploiting a versatile chemical strategy, and the NaxSn-C anode was combined with sodium-deficient layered oxide cathode (NaNi0.2Co0.2Al0.1Mn0.45O2, NCAM) for application in proof-of-concept Na-ion full-cell investigated by electrochemical impedance spectroscopy and ex-situ measurements. For both studied systems the applicability of the proposed balancing methods is evidenced, despite further optimization is required to enhance the efficiency of the batteries.