title: Identifying the redox activity of cation-disordered Li-Fe-V-Ti oxide cathodes for Li-ion batteries.
abstract: Cation-disordered oxides have recently shown promising properties on the way to explore high-performance intercalation cathode materials for rechargeable Li-ion batteries. Here, stoichiometric cation-disordered Li2FeVyTi1-yO4 (y = 0, 0.2, 0.5) nanoparticles are studied. The substitution of V for Ti in Li2FeVyTi1-yO4 increases the content of active transition metals (Fe and V) and accordingly the amount of Li(+) (about (1 + y)Li(+) capacity per formula unit) that can be reversibly intercalated. It is found that Fe(3+)/Fe(2+) and V(4+)/V(3+) redox couples contribute to the overall capacity performance, whereas Ti(4+) remains mainly inert. There is no evidence for the presence of Fe(4+) species after charging to 4.8 V, as confirmed from the ex situ(57)Fe Mössbauer spectroscopy and the Fe K-edge absorption spectra. The redox couple reactions for iron and vanadium are examined by performing in situ synchrotron X-ray absorption spectroscopy. During charging/discharging, the spectral evolution of the K-edges for Fe and V confirms the reversible Fe(3+)/Fe(2+) and V(4+)/V(3+) redox reactions during cycling between 1.5 and 4.8 V.
authors.affiliation: Institute for Applied Materials - Energy Storage Systems, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany. sylvio.indris@kit.edu and Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany and Joint Electrochemistry Lab, KIST Europe/Saarland University, 66123 Saarbrücken, Germany. r.chen@kist-europe.de ruiyong.chen@uni-saarland.de.
authors.forename: Ruiyong
authors.initials: R
authors.lastname: Chen
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Witte
authors.affiliation: Bruker Biospin GmbH, 76287 Rheinstetten, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Heinzmann
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
authors.forename: Shuhua
authors.initials: S
authors.lastname: Ren
authors.affiliation: ANKA Synchrotron Radiation Facility, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mangold
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
authors.forename: Horst
authors.initials: H
authors.lastname: Hahn
authors.affiliation: Joint Electrochemistry Lab, KIST Europe/Saarland University, 66123 Saarbrücken, Germany. r.chen@kist-europe.de ruiyong.chen@uni-saarland.de.
authors.forename: Rolf
authors.initials: R
authors.lastname: Hempelmann
authors.affiliation: Institute for Applied Materials - Energy Storage Systems, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany. sylvio.indris@kit.edu.
authors.forename: Helmut
authors.initials: H
authors.lastname: Ehrenberg
authors.affiliation: Institute for Applied Materials - Energy Storage Systems, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany. sylvio.indris@kit.edu and Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
authors.forename: Sylvio
authors.initials: S
authors.lastname: Indris