Materials strategy for advanced lithium-ion (shuttlecock) batteries: lithium nickel manganese oxides with or without cobalt

Recent progresses on insertion materials for lithium-ion batteries are described. Understanding of solid state chemistry and electrochemistry of LiCoO2, LiNiO2, LiMn2O4, LiC6, and so forth was a first step and their modification in terms of solid solution among the same crystal family was a second step. However, materials innovation is restricted because of the limitation of chemical species unless new concept is introduced. Old, but quite new concept is so-called "superlattice" model with which one can design hypothetical lithium insertion materials, calculate electronic and crystal structures by using computational methods, and develop effectively in an empirical, basis. To demonstrate the new concept, systematic researches on materials based on superlattice models in a phase triangle of LiCoO2-LiNiO2-LiMnO2 leading to novel binary or ternary oxides of lithium with transition metal elements, i.e., LiNi1/2Mn1/2O2, LiCo1/3Ni1/3Mn1/3O2, and Li[Ni-1/2/Mn-3/2]O-4, are highlighted.