In situ synchrotron diffraction study of charge-discharge mechanism of sol gel synthesized LiM0.5Mn1.5O4 (M = Fe, Co)

Samples with nominal composition LiM0.5Mn1.5O4 (M = Fe, Co) were synthesized via a sal gel process with a post thermal treatment at 1000 degrees C. In contrast to the Ni-analogue Co- and Fe-doped samples show a fast degradation at 55 degrees C with an average capacity retention at RT of similar to 55% for the Co- and of similar to 59% for the Fe-substituted samples, respectively after 70 cycles for a C/2 rate. The PITT plots of the Fe doped spinel exhibited a sharp peak in the discharge capacity when cycled with a cut-off current rate C/5, which was assumed due to a kinetic limitation, which disappears when cycled at slower charge discharge rates. This assumption was checked, and the mechanisms of Li-intercalation/-de-intercalation were investigated in detail for the Fe and Co doped spinels by in situ synchrotron diffraction. The charge -discharge processes take place through a solid-solution mechanism in both cases, though the Fe-doped spinel exhibits a two-phase region during the discharge. (C) 2012 Elsevier B.V. All rights reserved.