On the origin of non-monotonic variation of the lattice parameters of LiNi1/3Co1/3Mn1/3O2 with lithiation/delithiation: a first-principles study†
Here, we show that the non-monotonic variation of lattice parameters of LixNi1/3Co1/3Mn1/3O2 during delithiation/lithiation can be predicted in good agreement with experimental results by applying an approach combining an extensive set of Coulomb energy and density functional theory calculations. Moreover, the influence of choosing an exchange-correlation functional on our results is discussed. By analyzing the local spin polarization, spin density plot, density of states, and Bader charges, the reason behind this behavior is explained. It is found that the presence/absence of electrostatic Li–O interactions and Jahn–Teller distortion and oxidation of O anions are key parameters to control the lattice parameter changes. In particular, the contraction of c for 0.5 > x, which has not been fully explained so far, is found to be due to the vanishing of the Jahn–Teller distortion in NiO6 octahedra. The O3 → O1 phase transition for low concentrations of Li, which has also not been justified until now, is shown to be driven by strengthening of ionic bonds and electrostatic interaction in the latter phase.