Origin of Structural Phase Transitions in Ni-Rich Li x Ni 0.8 Co 0.1 Mn 0.1 O 2 with Lithiation/Delithiation: A First-Principles Study

In this work, nonmonotonic lattice parameter changes and phase transitions in LixNi0.8Co0.1Mn0.1O2 (LixNCM811) during delithiation are studied by combining an extensive set of electrostatic and density functional theory (DFT) calculations. To our knowledge,for the first time we simulated and explained the reason behind the experimentally observed hexagonal to monoclinic (H–M) phase transition at x = 0.50 as well as O3 → O1 phase transition at x = 0.00 in this system. An analysis of atomic and electronic structures of ions at each layer indicated that the H–M phase transition is driven by the Jahn–Teller (J–T) distortion effect. Moreover, it was found that the O3 → O1 phase transition is driven by electrostatic forces. This study also shows that the oxidation of Ni cations as well as their nature of bonds with O are not similar at different Ni/Ni, Ni/Co, and Ni/Mn layers. We also found that the significant decrease in the c lattice parameter for low values of x is due to the disappearance of J–T distortions as well as large covalent O–Ni bonds and oxidation of O and, more importantly, the sliding of O–TM–O layers with respect to each other