Layered lithium transition metal oxide cathodes towards high energy lithium-ion batteries

Development and discovery of cathode materials with superior performance seem to be tremendous challenges for Li-ion battery scientists. Since the topotactic reaction was first demonstrated in the 1970s, layered Li transition metal oxides (LiMO2, M = Co, Ni, Mn) have been a shining star throughout the research and innovation in intercalation materials due to their appealing merits. Generally the basic LiMO2 with a single kind of transition metal ion suffers from safety concerns and structural instability and can not support high energy Li-ion batteries. Nowadays, Li-stoichiometric mixed metal oxides and Li-excess Mn-based oxides have been considered as the most promising families of cathode materials for large-scale Li-ion batteries with high energy density used for transportation. In the present paper, with the help of a phase diagram tetrahedron, we provide an overview of the major developments in the field of LiMO2 cathode materials. The changes in structure during Li extraction and the phase compatibility of Li mixed metal oxides are highlighted. The latest progress in the research of Li-excess Mn-based oxides is also included.