Conclusions and Future Works

Abstract

Figure 10.1 shows the Li–Co–Mn–Ni–O pseudo-quaternary system with the Li–Co–Mn–O and Li–Mn–Ni–O faces shown, as determined with combinatorial samples quenched from 800 °C. Some approximations were made to join the two faces since the Li-Co-Mn-O face was synthesized in air while the nickel containing samples were made in oxygen. Nonetheless, the two faces join quite well. The pyramid strongly suggests that both single-phase regions of importance for battery materials, spinel and layered, extend into the pyramid and form relatively large three dimensional shapes. On the Li–Co–Mn–O system, the layered region is restricted to a single line showing that cobalt is always synthesized in the 3+ state as it is in LiCoO₂. By contrast, nickel can be in the 2+ state as in NiO rocksalt or the 3+ state as in layered LiNiO₂ such that a much larger and more complex layered region exists on the Li–Mn–Ni–O face. The spinel-layered co-existence region is also simpler in the Li–Co–Mn–O triangle with all tie-lines connecting to either the cobalt spinel, Co₃O₄, or the manganese layered material, Li₂MnO₃, while in the Li–Mn–Ni–O system there are 2 three-phase regions. The differences between the roles of cobalt and nickel should prove significant in upcoming combinatorial work in the Li–Co–Mn–Ni–O pseudo-quaternary system that is of extreme interest for battery materials as it includes commercial materials such as Li[Ni$_{1/3}$Mn$_{1/3}$Co$_{1/3}$]O₂ [93] as well as promising spinel-layered core-shell materials [88] and lithium-rich layered materials [3].