Structural studies of Li1.2Mn0.55Ni0.15Co0.1O2 electrode material

• Complimentary techniques study the microstructure of a Li-rich electrode material.
• The structure is a solid solution rather than a coherent mixture of two phases.
• A spinel phase is observed at surface terminations.
• Ion irradiation transforms the crystallographic phase of the material.

A pristine Li-rich layered electrode material with composition Li1.2Mn0.55Ni0.15Co0.1O2 was characterized by X-ray diffraction, transmission electron microscopy, and scanning transmission electron microscopy to determine whether it is a coherent mixture of monoclinic C2/m Li2MO3 and trigonal R  3-m LiMO2 phases or a solid solution of the monoclinic phase. Contradictory results have been previously reported which can be attributed to the complexity and structural similarity of the monoclinic and trigonal phases. We resolved this uncertainty by combining diffraction and imaging techniques that probe complimentary length scales. Our results demonstrate that the structure is primarily monoclinic, supporting the solid solution model, although near surface structural alterations were also observed.