Electrochemical, 6Li MAS NMR, and X-ray and neutron diffraction study of LiCoxFeyMn2-(x+y)O4 spinel oxides for high-voltage cathode materials

LiCo x Fe y Mn 2-(x+y) O 4 compounds (with x = 0.2, 0.4, 0.8, and 1, and y = 0.0, 0.2, and 0.4) have been prepared. Substitution of manganese by iron and/or cobalt decreases the cubic lattice parameter. The structure of LiCo 0.2 Fe 0.2 Mn 1.6 O 4 has been studied in detail by Rietveld refinement of the structure by using data obtained from neutron diffraction measurements. The electrochemical behavior has been tested in Li|LiPF 6 (EC:DEC)|LiCo x Fe y Mn 2-(x+y) O 4 cells, where an increase of the extension of the capacity delivered in the 5-V region and a decrease for the 4-V region was observed when manganese was substituted by iron and/or cobalt. The changes observed in the X-ray diffraction patterns upon lithium extraction have been studied for LiCoMnO 4 , LiCo 0.8 Fe 0.2 MnO 4 , and LiCo 0.2 Fe 0.2 Mn 1.6 O 4 . For all these samples a single cubic phase in which the lattice parameter decreases with lithium extraction was observed. The lattice contraction is more marked for Li 1-z Co 0.2 Fe 0.2 Mn 1.6 O 4 (from 8.187(1) A to ca. 8.06 A) and occurs mostly in the region near 4 V. The novel compound LiCo 0.8 Fe 0.2 -MnO 4 is shown to be a good 5-V cathode material with an initial discharge capacity of 100 mAhg -1 .