First-principles investigation of the structural characteristics of LiMO2 cathode materials for lithium secondary batteries

• Point defects in layer-structured LiMO2 materials are investigated.
• Defect-free perfect crystal is thermodynamically stable for LiCoO2.
• Formation of Li- and O- vacancies is inevitable features in the synthesis of LiNiO2.
• Introduction of Co in LiNiO2 reduces vacancies and antisite defects.

The structural features related to the defects of LiMO2 (M = Ni, Co, Mn) cathode materials for lithium secondary batteries were investigated by a simulation of phase diagrams based on first-principle calculations. Crystal models with various types of point defects were designed and dealt with as independent phases, which enabled an examination of the thermodynamic stability of the defects. A perfect phase without defects appeared to be the most stable for LiCoO2, whereas the formation of Li vacancies, O vacancies, and antisites between Li and Ni was thermodynamically unavoidable for LiNiO2. The introduction of both Co and Mn in LiNiO2 was effective in reducing the formation of point defects, but increasing the relative amount of Mn was undesirable because the antisite defect remained stable with Mn doping. The simulation showed good agreement with the experimental data and previous reports. Therefore, the method and the results of this study are expected to be useful for examining the synthesis, structure and related properties of layer-structured cathode materials.

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