Abstract
In the previous lecture, we discussed the emergence of LiCo(Ni)O2 lamellar oxides as insertion compounds for Li ion batteries, and their major evolution over the years. These advances, achieved through chemical substitutions, have improved their electrochemical performance while lowering their Co content for geopolitical and ethical reasons. The oxides used today are either Li(NixCoyAl1-x-y)O2 phases known as "NCA", resulting from the partial substitution of Co and Ni by Al, or Li(NixMnyCo1-x-y)O2 phases known as "NMC", of which phase 622 (60% Ni, 20% Mn and 20% Co) is an industrial reference in the world of batteries. We have shown the science behind these various substitutions, highlighting the structural and chemical considerations that led to the choice of very specific elements. In view of the Co issue, current research is turning towards Ni-rich phases whose safety aspect remains to be improved. To address this aspect, current studies are focusing not only on doping these compounds, but also on modifying their morphology through the design of core-crown or concentration-gradient particles. We have noted that NMC electrodes are used in most vehicles because they offer the best possible compromise between cost, energy density and safety. NCA electrodes offer better energy density. However, they require finer temperature management, as they degrade at lower temperatures than NMC cathodes.
In addition to autonomy, the eco-compatibility of a battery is of paramount importance for societal and planetary reasons, justifying the development of Na-ion batteries. An inventory of Na-based lamellar oxides will therefore be carried out, highlighting the essential differences with their Li counterparts. They feature rich crystallochemistry and can exist in different structures, depending on whether the Na occupies octahedral sites (O-type structures) or trigonal-prismatic sites (P-type structures). In order to establish guidelines for the design of O- or P-type structures, iconicity diagrams and cationic potential diagrams will be presented. The lecture will close with a description of the incremental chemistry leading to the optimization of O3 phases, today's most coveted for the next generation of Na-ion batteries.
