The phase transition behaviors of Li1−xMn0.5Fe0.5PO4 during lithium extraction studied by in situ X-ray absorption and diffraction techniques |
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| Authors: | Kyung-Wan Nam Won-Sub Yoon Karim Zaghib Kyung Yoon Chung Xiao-Qing Yang |
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| Institution: | aChemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA;bSchool of Advanced Materials Engineering, Kookmin University, 861-1 Jeongneung-dong, Seongbuk-gu, Seoul 136-702, Republic of Korea;cInstitut de Recherche d’Hydro-Québec (IREQ), Varennes, Quebec, Canada J3X 1S1;dBattery Research Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea |
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| Abstract: | 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. |
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| Keywords: | Lithium-ion batteries Olivine structure LiFePO4 Solid solution mechanism X-ray absorption near edge structure |
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