During the reference period, various cathode materials for use in high performance sodium-ion batteries were developed, the associated synthesis techniques investigated and their chemical-physical and functional characterization carried out.
In the course of the activity, cathode materials were prepared characterized by different levels of synthesis difficulty and by different methods of preservation, stability and relative electrochemical performance. Polyanionic materials, oxides and nasicon structures were studied, representing almost all categories of inorganic cathodes. For all the materials prepared, different ink mixtures were studied for the formation of the electrode, analyzing in particular the effect on the cathodes of conductive carbons, binders and different percentages of ink components.
Electrochemical characterization showed that the choice of electrolyte, based on the material and the potential range being investigated, is of fundamental importance. A search for the best standard electrolyte mixtures such as EC:DEC-NaPF6, PC-NaClO4, PC:FEC-NaClO4 was therefore initiated, followed by the evaluation of more complex solutions. In particular, the study focused on electrolytes with additional requirements such as non-flammability, hydrophobicity and synthesis using environmentally friendly processes. Ionic liquids were chosen and four different compositions and their mixtures with two different salts were studied. After electrochemical stability measurements of all eight mixtures, Pyr14FSI-NaFSI was identified as the most promising electrolyte, as it is stable at both the high and low potentials typical of the lower cycling limit of MXene.

Among the different materials studied, the in-depth experimental work carried out allowed us to identify two cathode materials of particular importance, even if not fully optimized, and one that can already be considered suitable for use in high potential sodium-ion batteries with MXene anodes.
Each of the materials identified belongs to one of the three categories of inorganic cathodes: Na3MnTi(PO4)3 (NASICON), Na0.67MnO2 (oxide) and Na3V2(PO4)2F3 (polyanion).
In particular, the polyanionic material, which was studied last year, has proved to be suitable for coupling with the ionic liquid-based electrolyte and therefore potentially suitable for use in a complete battery.