Raman scattering of LiNi1−yAlyO2

We measured Raman spectra from LiNiO2 and LiNi1−yAlyO2 positive electrode materials for lithium-ion batteries. LiNiO2 oxide is unambiguously shown to have a layered rock-salt structure (R3̄m space group), which exhibits two Raman bands at 465 and 545 cm−1 assigned to the Eg and A1g species, respectively. Whereas LiNi1−yAlyO2 prepared at low temperature (450 °C) using the succinate sol–gel method develops a spinel structure, LiNi1−yAlyO2 prepared by the citrate route is a microcrystalline oxide indicating the α-NaFeO2 structure (R3̄m). The shift of the Raman peak positions suggest that replacement of Ni by Al increases the elementary cell volume and changes the intralayer bond covalency of LiNi1−yAlyO2, in good accordance with the X-ray diffraction (XRD) measurements.