The phase transition behaviors of Li1-xMn0.5Fe0.5PO4 during lithium extraction studied by in situ X-ray absorption and diffraction techniques

How the structural changes take place in LiMnyFe1-yPO4-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 Li1-xMn0.5Fe0.5PO4 (C-Li1-xMn0.5Fe0.5PO4, 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 (Fe2+/Fe3+) and 4.2 V (Mn2+/Mn3+) and a narrow intermediate region which proceeds via single-phase reaction in between two two-phase regions. In addition, simultaneous redox reactions of Fe2+/Fe3+ and Mn2+/Mn3+ in the narrow single-phase region are reported and discussed for the first time. (C) 2009 Elsevier B.V. All rights reserved.