Structure determination of high-voltage LiMgδNi0.5-δMn1.5O4 spinels for Li-ion batteries

Abstract

A series of cathode materials has been synthesized with the general formula LiMgδNi0.5-δMn1.5O4 (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 crystallize in the spinel structure, which is normally refined in the Fd3m space group. Neutron-diffraction (ND) experiments, however, indicate space group P4332 and refinements of the ND and XRD patterns result in the site occupations: Li+ on 8c, Mg2+ and Ni2+ on 4b, Mn4+ on 12d and O2- 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).