title: Local coordination of Fe3+ in Li[Co(0.98)Fe(0.02)]O2 as cathode material for lithium ion batteries-multi-frequency EPR and Monte-Carlo Newman-superposition model analysis.
abstract: The local coordination of the Fe(3+)-centers in Li[Co(0.98)Fe(0.02)]O(2) cathode materials for lithium-ion batteries has been investigated by means of XRD and multi-frequency EPR spectroscopy. EPR clearly showed the Fe(3+) being in a high-spin state with S = 5/2. The set of spin-Hamiltonian parameters obtained from multi-frequency EPR experiments with Larmor frequencies ranging between 9.8 and 406 GHz was transformed into structural information by means of an expansion to standard Newton-superposition modeling, termed as Monte-Carlo Newman superposition modeling. Based on this analysis, an isovalent incorporation of the Fe(3+)-ions on the Co(3+)-sites, i.e. Fe(x)(Co), has been shown. With that respect, the positive sign of the axial second-order fine-structure interaction parameter B(0)(2) is indicative of an elongated oxygen octahedron, whereas B(0)(2) < 0 points to a compressed octahedron coordinated about the Fe(3+)-center. Furthermore, the results obtained here suggest that the oxygen octahedron about the Fe(3+)-ion is slightly distorted as compared to the CoO(6) octahedron, which in turn may impose mechanical strain to the cathode material.
authors.affiliation: Institut für Physikalische Chemie I, Universität Freiburg, Albertstr. 21, D-79104 Freiburg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Jakes
authors.forename: Emre
authors.initials: E
authors.lastname: Erdem
authors.forename: Andrew
authors.initials: A
authors.lastname: Ozarowski
authors.forename: Johan
authors.initials: J
authors.lastname: van Tol
authors.forename: Ronny
authors.initials: R
authors.lastname: Buckan
authors.forename: Daria
authors.initials: D
authors.lastname: Mikhailova
authors.forename: Helmut
authors.initials: H
authors.lastname: Ehrenberg
authors.forename: Rüdiger-A
authors.initials: RA
authors.lastname: Eichel