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

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