Investigation of possible superstructure and cation disorder in the lithium battery cathode material LiMn1/3Ni1/3Co1/3O2 using neutron and anomalous dispersion powder diffraction

A study has been conducted to discover whether the recently reported high-capacity lithium battery material LiMn1/3Ni1/3Co1/3O2 possesses a superstructure due to ordering of the transition metal cations. A recent paper in the literature concluded from ab initio calculations that, if a superstructure exists, it would likely take the form of a [√3×√3]R30° type superlattice rather than an ordered stacking of Co–O2, Ni–O2, and Mn–O2 slabs. A suitable technique to detect the presence or otherwise of a superstructure in this material is neutron diffraction due to the contrast between Mn, Ni, and Co neutron scattering lengths. An alternative method to enhance the contrast between elements close in the periodic table is to use resonant diffraction techniques. The beneficial contrasts afforded by each method may be retained by conducting a simultaneous refinement using both neutron and X-ray data. It was found that LiMn1/3Ni1/3Co1/3O2 did not appear to possess either of the proposed types of supercell and that the data were consistent with a random distribution of Mn, Ni, and Co over the R-3m 3a sites. Simultaneous Rietveld analysis showed that some nickel displaced lithium from the 3b site, whilst the manganese and cobalt remained solely on the transition metal 3a site.