Structural and Magnetic Nature for Fully Delithiated Li_<i>x</i>NiO₂: Comparative Study between Chemically and Electrochemically Prepared Samples

Abstract

Structural and magnetic properties of two LixNiO2 samples with x ≤ 0.1 have been studied by a powder X-ray diffraction, magnetic susceptibility (χ), and muon-spin rotation/relaxation (μSR) measurements. One of the two samples was prepared by an electrochemical (EC) reaction in a nonaqueous lithium cell, whereas the other sample by a chemical (C) reaction in a HNO3 aqueous solution. Although the crystal structure of both C-Li0.01NiO2 and EC-Li0.10NiO2 samples were assigned as a mixture of a cubic close-packed phase and a hexagonal close-packed phase, the effective magnetic moment (μeff) of Ni ions for C-Li0.01NiO2 was estimated as μeff = 1.43 μB and was very close to that for EC-Li0.5NiO2 (μeff = 1.39 μB). This implies that the vacant tetrahedral or octahedral sites in C-Li0.01NiO2 are partially occupied by H+ ions. Actually, the zero-field μSR time spectrum in the paramagnetic state for C-Li0.01NiO2 exhibited a large relaxation compared to those for EC-Li0.5NiO2 and EC-Li0.10NiO2. Furthermore, a pryrolysis gas chromatography/mass spectroscopy analysis confirmed the existence of H+ ions in the C-Li0.01NiO2 crystalline lattice. The actual composition of C-Li0.01NiO2 is, thus, determined to be H∼0.5Li0.01NiO2.