A series of cathode materials has been synthesized with the general formula LiMg δ Ni 0.5-δ Mn 1.5 O 4 (δ = 0.00, 0.05 and 0.10). These are promising cathode materials for lithium and Li-ion batteries due to the high voltage (> 4.7 V vs. Li/Li + ) and the high energy density (> 570 W h/kg). The cycling stability of these materials is strongly influenced by the method of synthesis and is particularly improved by a very low cooling rate. To study the effect of such slow cooling on the crystal structure, a detailed diffraction analysis was performed. Initial X-ray-diffraction (XRD) measurements revealed that the materials crystallized in the spinel structure, which is normally refined in the Fd(3̄)m space group. Neutron-diffraction (ND) experiments, however, indicate space group P4 3 32 and refinements of the ND and XRD patterns result in the site occupations: Li + on 8c, Mg 2+ and Ni 2+ on 4b, Mn 4+ on 12d and O 2- on 24e and 8c. It was also found that, as a function of the Mg content, the cubic lattice constant increases from 8.1685 Å (δ = 0.00) to 8.1733 Å (δ = 0.10).
|Journal||Applied Physics A: Materials Science and Processing|
|Publication status||Published - 1 Dec 2002|