Changes in the structure and physical properties of the solid solution LiNi1–xMnxO2 with variation in its composition

The layered oxides LiNi1−xMnxO2 (x = 0.1–0.5) were synthesized and characterized using synchrotron X-ray diffraction, TOF neutron diffraction, SQUID magnetometry, ICP spectroscopy, XAFS, and electrochemical measurements. All the samples were single-phase and adopted the α-NaFeO2 structure; LiNi1−xMnxO2 can be represented as Li(Ni2+xNi3+1−2xMn4+x)O2. Structural analysis using synchrotron and neutron diffraction data demonstrated that the lattice parameters of LiNi0.5Mn0.5O2 are a = 2.892 A and c = 14.302 A and that the chemical composition can be expressed by referring to the Wyckoff positions 3a and 3b as [Li0.91Ni0.09]3a[Li0.09Mn0.5Ni0.41]3bO2. The lattice parameters a and c and the fraction of Ni at the 3a site of LiNi1−xMnxO2 increased with Mn content up to the x = 0.4 composition and then showed little change between x = 0.4 and 0.5. An increase in the Ni–O distance was observed with increasing x. The appearance of ferromagnetism was clearly observed at x = 0.4–0.5 as the Ni2+ and Mn4+ content increased. The discharge capacity of the Li/LiNi1−xMnxO2 cell decreased from 190 mAh g−1 (x = 0.1) to 140 mAh g−1 (x = 0.5).