New Data on Chemical Delithiation of Li xNi 2- xO 2 (0.6 < x < 1)

Abstract

New data on acid delithiation of lithium-nickel oxides, Li x Ni 2- x O 2 (0.6 < x < 1), are obtained using EPR of low-spin Ni 3+ ions, magnetic susceptibility measurements, and thermal analysis. It is shown that short-range and long-range cation order in the solid solutions Li x Ni 2- x O 2 specify their behavior toward acids. For Li x Ni 2- x O 2 oxides (0.6 < x < 0.9), where partial cation order occurs, acids remove lithium and impurity nickel ions from the LiO 2-layers, but do not attack Ni 2+ and Ni 3+ ions, which are segregated in the neighboring (111) cubic planes. For Li x Ni 2- x O 2 oxides ( x > 0.9), where long-range cation order is developed, the extraction of lithium and impurity nickel ions proceeds concomitantly with partial exchange between lithium from the LiO 2-layers and protons from the acid solution. The different chemical compositions of acid-treated oxides Li x Ni 2- x O 2 (0.6 < x < 0.9) and Li x Ni 2- x O 2 (0.9 < x < 1) are manifested by their thermochemical properties up to 200°C: for the partially ordered oxides (0.6 < x < 0.9), reduction of highly oxidized nickel ions and cation redistribution occur within the initial structural framework, whereas for the layered oxides ( x > 0.9), dehydration processes also take place.