XANES Investigation of Dynamic Phase Transition in Olivine Cathode for Li‐Ion Batteries |
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| Authors: | Sarawut Pongha Boonyarit Seekoaon Wanwisa Limphirat Pinit Kidkhunthod Sutham Srilomsak Yet‐Ming Chiang Nonglak Meethong |
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| Institution: | 1. Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen, Thailand;2. Synchrotron Light Research Institute, Nakhon Ratchasima, Thailand;3. Nanotec‐SUT Center of Excellence on Advanced Functional Nanomaterials, Suranaree University of Technology, Nakhon Ratchasima, Thailand;4. School of Ceramic Engineering, Suranaree University of Technology, Nakhon Ratchasima, Thailand;5. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA;6. Integrated Nanotechnology Research Center, Khon Kaen University, Khon Kaen, Thailand;7. Nanotec‐KKU Center of Excellence on Advanced Nanomaterials for Energy Production and Storage, Khon Kaen University, Khon Kaen, Thailand |
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| Abstract: | Dynamic phase transformation in olivine LiFePO4 involving formation of one or more intermediate or metastable phases is revealed by an in situ time‐resolved X‐ray absorption near edge structure (XANES) technique. The XANES spectra measured during relaxation immediately after the application of relatively high overpotentials, where metastable phases are expected, show a continuous shift of the Fe K‐edge toward higher energy. Surprisingly, the Fe K‐edge relaxes to higher energies after current interrupt regardless of whether the cell is being charged or discharged. This relaxation phenomenon is superimposed upon larger shifts in K‐edge due to changes in Fe2+/Fe3+ ratio due to charging and discharging, and implies an intermediate phase of larger Fe? O bond length than any of the known crystalline phases. No intermediate crystalline phases are observed by X‐ray diffraction (XRD). A metastable amorphous phase formed during dynamic cycling and which structurally relaxes to the equilibrium crystalline phases over a time scale of about 10 min after cessation of charging/discharging current is consistent with the experimental observations. |
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| Keywords: | dynamic phase transformation electronic structure in situ X‐ray absorption spectroscopy lithium iron phosphate overpotential effects |
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