Defect Chemistry in Layered LiMO2 (M = Co, Ni, Mn, and Li1/3Mn2/3) by First-Principles Calculations

The defect chemistry in a series of layered lithium transition-metal oxides, LiMO2 (M = Co, Ni, Mn, and Li1/3Mn2/3), is investigated by systematic first-principles calculations. The calculations clearly show that Ni3+ ions in LiNiO2 are easily reduced, whereas Mn3+ ions in LiMnO2 are easily oxidized under ordinary high-temperature synthesis conditions. It is expected that LiCoO2 and Li(Li1/3Mn2/3)O-2 With low defect concentrations are easily synthesized. These results are highly consistent with the characteristics and conductive properties of the oxides observed in experiments. The calculations also suggest that the surfaces of the oxides are reduced at a nanometer scale by immersion of the samples in organic electrolytes of lithium-ion batteries, and the tendency of the surface reduction is consistent with the defect chemistry at high temperatures. The formation of the lithium vacancy and interstitial are elementary reactions of electrode active materials in the charging and discharging processes of lithium-ion batteries, respectively. The defect formation energies in conjunction with the electrode potentials can quantitatively describe the electrode behavior.