Design and analysis of triangle phase diagram for preparation of new lithium manganese oxide solid solutions with stable layered crystal structure

A new phase diagram of AB(CD)1/2 system, where A, B, C, and D represent Li2MnO3, LiMO2 (M = Co, Al, Cr, etc.), LiMnO2, and LiM′O2 (M′ = Ni, Cu, Fe, etc.), respectively, was developed to express all compositions of solid solutions with layered manganese oxides. The phase diagram satisfied the theoretical manganese oxidation state of +4 over the whole triangle plane of the diagram and was expressed with a new design equation of Li[Mx(Li1/3Mn2/3)y(M′1/2Mn1/2)1−x−y]O2. Solid solutions whose compositions were randomly chosen from the phase diagram were experimentally prepared using a direct synthetic method and were subjected to the examination of the structural and electrochemical properties. All the synthesized solid solutions had layered structure with maintaining +4 and showed one-step monotonous discharge curve shape without structural transformation during charge/discharge processes.