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XANES Investigation of Dynamic Phase Transition in Olivine Cathode for Li‐Ion Batteries
Author(s) -
Pongha Sarawut,
Seekoaon Boonyarit,
Limphirat Wanwisa,
Kidkhunthod Pinit,
Srilomsak Sutham,
Chiang YetMing,
Meethong glak
Publication year - 2015
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201500663
Subject(s) - xanes , materials science , metastability , phase (matter) , amorphous solid , relaxation (psychology) , ion , cathode , analytical chemistry (journal) , olivine , diffraction , crystallography , chemical physics , spectral line , mineralogy , chemistry , optics , physics , organic chemistry , psychology , social psychology , chromatography , astronomy
Dynamic phase transformation in olivine LiFePO 4 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 Fe 2+/ Fe 3+ ratio due to charging and discharging, and implies an intermediate phase of larger FeO 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.