Investigations on average and local structures of Li(Li1/6Mn1/2Ni1/6Co1/6)O2 by the pair distribution function and the density functional theory

Abstract

We synthesize Li(Li1/6Mn1/2Ni1/6Co1/6)O2 with a coprecipitation method, and study the electrochemical properties and the atomic configuration by means of galvanostatic charge–discharge test, neutron total scatterings, and the density functional theory calculation. From the average-structure analysis using the Bragg profile, that is, the Rietveld analysis, it is found that the sample has the Li2MnO3-type layered structure (space group; C2/m) and Ni and Co exist at both the two sites (4g and 2b sites) in the transition-metal layer. The DFT calculation indicates that there is a local atomic ordering denoted as LiMn6 in the transition-metal layer in the same way as Li2MnO3. Moreover, such a local structure can explain a reduced pair distribution function, G(r), derived from neutron total scatterings. Detailed investigation on the G(r) also suggests a local distortion along the c axis perpendicular to the layer.