  A new superstructure of layered pristine LiNiO2 (LNO) was obtained optimizing
a large supercell of the 166 space group, the one observed experimentally by
XRD, and relaxing both cell parameters and internal positions. The crystal
structure shows size and charge disproportionation of the NiO6 octahedra
instead of the Jahn-Teller distortion. The decrease of the internal energy
obtained with the structural optimization of the supercell relative to the same
structure in its primitive unit cell is much larger than the one obtained by
relaxing similarly dimensioned supercells of monoclinic symmetry relative to
their primitive unit cells, although the monoclinic phase remains more stable.
The Ni-O bond length distribution of the new structure agree well with the
experiments. Our results show that the choice of the simulation cell is
important for determining the energetics of this class of oxide materials,
proposed for cathodes in lithium ion batteries (LIBs). We used this new
structure as a template for the study of the structural and electronic changes
induced by the delithiation and Mn for Ni cation substitution, originating the
solid solutions LiNiyMn(1-y)O2 (LNMO). Our results, surprisingly, agree well
with the existing experiments and explain observed trends better than previous
studies.
