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

초록

A new triangle phase disgram is developed to express all compositions of solid solutions with layered manganese oxides. Four triangle phase diagrams were first made by summarizing previously reported design equations for the solid solutions and then the composition of the solid solutions, which can form a stable layered crystal structure, was evaluated across the plane of the phase diagrams. The newly designed triangle phase diagram satisfied the theoretical manganese oxidation state of 4+ over the whole triangle plane of the phase disgram and was expressed with a design equation of Li[Mx(Li1/3Mn2/3)y(Mn`1/2Mn1/2)1-x-y]O2. 15compositions of solid solutions with lithium manganese oxide were randomly chosen from the phase diagram and were experimentally synthesized using both direct synthesis and solid reaction methods. The synthesized solid solutions were subjected to the examination of the structural and electrochemical propertyes. All the synthesized solid solution have layered structure with maintaining the manganese oxidation state of 4+ and show a monotonous discharge curve shape without structural transformation to spinel during charge/discharge processes. Thus synthesized solid solutions exhibit extremely high discharge capacity with negligible capacity fading after 50th cycle.