Structural, Electronic, and Li Migration Properties of RE-Doped (RE = Ce, La) LiCoO2 for Li-ion Batteries: A First-Principles Investigation

Rare earth elements, known for their large radius, high charge, and strong self-polarization ability, are expected to bring improvements in Li-ion batteries. However, some basic issues such as structural variation, the nature of the improved Li mobility, and electronic conductivity in rare earth-doped electrode compounds are still unrevealed. In the present work, the structural, electronic, and Li migration properties of Ce- and La-doped LiCoO2 cathode materials are systematically studied by using the first-principles calculations. The results show that after rare earth elements are doped, the cell volume expands with local structure distortion around the substitution site. Meanwhile, the doped systems remain insulating characteristics with decreased band gap. The migration barriers vary considerably depending on different paths due to the competition between the increase of Li slab distance and the variation of potential energy surface caused by the doping of rare earth elements. The minimum activation barriers for Li motion decease significantly from 0.669 to 0.382 eV and to 0.239 eV upon Ce and La doping, respectively. Furthermore, Li ion migrations along the entire supercell are also studied.