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 sol–gel process with a post thermal treatment at 1000 °C. In contrast to the Ni-analogue Co- and Fe-doped samples show a fast degradation at 55 °C with an average capacity retention at RT of ∼55% for the Co- and of ∼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.

► We report the mechanisms of Li-intercalation/-de-intercalation in LiM0.5Mn1.5O4 (M = Fe, Co) spinels. ► The investigation of the mechanism was done by in situ synchrotron diffraction. ► The LiM0.5Mn1.5O4 (M = Fe, Co) spinels show a solid-solution mechanism of charge–discharge.