Analysis of the phase stability of LiMO2 layered oxides (M=Co, Mn, Ni)

Transition-metal (TM) layered oxides have been attracting enormous interests in recentdecades because of their excellent functional properties as positive electrode materials in lithium-ionbatteries. In particular LiCoO2 (LCO), LiNiO2 (LNO) and LiMnO2 (LMO) are the structural prototypesof a large family of complex compounds with similar layered structures incorporating mixtures oftransition metals. Here, we present a comparative study on the phase stability of LCO, LMO andLNO by means of first-principles calculations, considering three dierent lattices for all oxides, i.e.,rhombohedral (hR12), monoclinic (mC8) and orthorhombic (oP8). We provide a detailed analysis--atthe same level of theory--on geometry, electronic and magnetic structures for all the three systems intheir competitive structural arrangements. In particular, we report the thermodynamics of formationfor all ground state and metastable phases of the three compounds for the first time. The finalGibbs Energy of Formation values at 298 K from elements are: LCO(hR12) ?672 8 kJ mol?1;LCO(mC8) ?655 8 kJ mol?1; LCO(oP8) ?607 8 kJ mol?1; LNO(hR12) ?548 8 kJ mol?1; LNO(mC8)?557 8 kJ mol?1; LNO(oP8) ?548 8 kJ mol?1; LMO(hR12) ?765 10 kJ mol?1; LMO(mC8)?779 10 kJ mol?1; LMO(oP8) ?780 10 kJ mol?1. These values are of fundamental importance forthe implementation of reliable multi-phase thermodynamic modelling of complex multi-TM layeredoxide systems and for the understanding of thermodynamically driven structural phase degradationsin real applications such as lithium-ion batteries.