Neutron diffraction studies on structural effect for Ni-doping in LiCo1 − xNixO2
Abstract We report structural effect for Ni-doping in lithium cobalt oxide (LiCoO2) studied by the time-of-flight (TOF) neutron powder diffractions measured at RT. Crystal and local structures of LiCo1 − xNixO2 (x = 0, 0.2, 0.4, 0.6, 0.8, 1) powders, that were prepared by the solid-state reaction methods, have been respectively examined by using the IBARAKI Neutron Design Diffractometer (iMATERIA) of JPARC and Nanoscale-Ordered Material Diffractometer (NOMAD) of ORNL. The Rietveld refinement for neutron diffraction data of LiCo1 − xNixO2 that all have been indexed to the rhombohedral system with trigonal symmetry in the space group R-3m, revealed the lattice parameter c/a ratio that tends to the ideal value as decreasing Ni-contents, while the atomic pair distribution function (PDF) analysis for neutron data of LiCo1-xNixO2 revealed that the Co–O and the Ni–O pair correlation lengths under the first peak of G(r) that respectively vary from 1.88 to 1.9 A and from 1.98 to 2.0 A, with average Ni–O correlation length (1.99 A) seems to be slightly larger than average Co–O correlation length (1.89 A). Rather than that resulted by the Rietveld analysis, the PDF analysis suggested that the diffusion pathways between Co–O in the LiCo1 − xNixO2 system remain stable at ~ 1.89 A for all Ni-contents.