Composition dependence of average and local structure of xLi(Li1/3Mn2/3)O2–(1 − x)Li(Mn1/3Ni1/3Co1/3)O2 active cathode material for Li ion batteries

•Large differences in the battery performance between composition of x = 0.2 and x ≥ 0.3.•Solid solution xLi(Li1/3Mn2/3)O2–(1 − x)Li(Mn1/3Ni1/3Co1/3)O2.•Local crystal structure was determined by pair distribution function method and EXAFS.•The ordering of LiMn6 and LiMn5Ni, which is likely to affect cathode performance.

This study focused on the composition dependence of the crystal structure and cathode performance of xLi(Li1/3Mn2/3)O2–(1 − x)Li(Mn1/3Ni1/3Co1/3)O2 (0 ≤ x ≤ 1) prepared by co-precipitation. From charge-discharge tests, it was found that there was large differences in the battery performance between the composition of x = 0.2 and x ≥ 0.3. For the samples, the average crystal structures were determined by the Rietveld refinement of neutron diffraction patterns. The results indicated that for x = 0.2, Li existed at both 2b and 4g sites, whereas for x ≥ 0.3, Li was localized at 2b sites and Mn occupied the 4g sites. In order to examine the local crystal structure, pair distribution function (PDF) and extended X-ray absorption fine structure (EXAFS) analyses were carried out. From the PDF analysis, a significant difference was seen in the short-range peaks associated with the transition metal layer for x = 0.2, 0.4 and 0.6. The EXAFS results indicated a large difference in the local structure around Mn for x = 0.2 and x ≥ 0.3. This is thought to be due to ordering of LiMn6 and LiMn5Ni, which is likely to affect cathode performance.