First-Principles Study of the Doping Effect in Half Delithiated LiNiO₂ Cathodes

A systematic theoretical study of dopants in a half-delithiated lithium nickel oxide (Li 0.5 NiO 2 ) cathode is performed to determine the preferred occupation sites, dopant ion migration, and suppression of oxygen evolution. Dopants considered include Li, B, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, and W. For the nontransition metal dopants, the energy barrier governing dopant migration is correlated with the number of valence shell electrons so that it increases from left to right across a row of the periodic table. For these dopants, the energy barrier also decreases moving down a column of the periodic table. For transition metal dopants, the energy barrier depends on the number of unpaired valence electrons of the dopant, so that the energy barrier is maximum near the middle of a transition metal row. Oxygen stability is studied by calculating the gap between O-2p and Ni-3d band centers. Most dopants that prefer occupying octahedral sites in the transition metal layer bring higher oxygen stability. In particular, oxygen stability is enhanced mostly by Mo, Sb, and W doping.