The phase transition behaviors of Li 1−xMn 0.5Fe 0.5PO 4 during lithium extraction studied by in situ X-ray absorption and diffraction techniques

Abstract

How the structural changes take place in LiMn yFe 1− y PO 4-type cathode materials during lithium extraction/insertion is an important issue, especially on if they go through the single-phase reaction (i.e., solid solution reaction) or the two-phase reaction regions. Here we report the studies on the phase transition behaviors of a carbon coated Li 1− x Mn 0.5Fe 0.5PO 4 (C Li 1−xMn 0.5Fe0 .5PO 4, 0.0 ⩽ x ⩽ 1.0) sample during the first charge using in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques. The combination of in situ XAS and XRD results clearly identify two two-phase coexistence regions at two voltage plateaus of 3.6 (Fe 2+/Fe 3+) and 4.2 V (Mn 2+/Mn 3+) and a narrow intermediate region which proceeds via single-phase reaction in between two two-phase regions. In addition, simultaneous redox reactions of Fe 2+/Fe 3+ and Mn 2+/Mn 3+ in the narrow single-phase region are reported and discussed for the first time.