Effect of metal composition on the structure of layer-structured cathode materials for Li-ion batteries

Abstract

Layer-structured LiMO2 (M = Ni, Co, Mn, and dopants) is widely used as a cathode material for Li-ion secondary batteries. Ni-based LiMO2 is advantageous with respect to energy capacity and material cost compared to conventional LiCoO2, but its structural and thermal stabilities decrease with increases in Ni content. As a countermeasure for these decreases, the three-component design of M comprising Ni, Co, and Mn is used universally, and small amounts of foreign elements are often added to obtain doping or surface coating effects. The relation between the composition of M and structural characteristics of LiMO2 is investigated in this study. The features of defect generation, dopability of foreign elements, and formation of segregated secondary phases are analyzed by simulating phase diagrams based on density functional theory calculations. On this basis, a design strategy for the LiMO2 composition is provided, with a discussion on the proper selection of doping or coating materials to improve the cathodic properties.