title: Identifying the Structure of the Intermediate, Li2/3CoPO4, Formed during Electrochemical Cycling of LiCoPO4.
abstract: In situ synchrotron diffraction measurements and subsequent Rietveld refinements are used to show that the high energy density cathode material LiCoPO4(space groupPnma) undergoes two distinct two-phase reactions upon charge and discharge, both occurring via an intermediate Li2/3(Co2+)2/3(Co3+)1/3PO4phase. Two resonances are observed for Li2/3CoPO4with intensity ratios of 2:1 and 1:1 in the31P and7Li NMR spectra, respectively. An ordering of Co2+/Co3+oxidation states is proposed within a (a× 3b×c) supercell, and Li+/vacancy ordering is investigated using experimental NMR data in combination with first-principles solid-state DFT calculations. In the lowest energy configuration, both the Co3+ions and Li vacancies are found to order along theb-axis. Two other low energy Li+/vacancy ordering schemes are found only 5 meV per formula unit higher in energy. All three configurations lie below the LiCoPO4-CoPO4convex hull and they may be readily interconverted by Li+hops along theb-direction.
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge, Cambridgeshire CB2 1EW, United Kingdom.
authors.forename: Fiona C
authors.initials: FC
authors.lastname: Strobridge
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge, Cambridgeshire CB2 1EW, United Kingdom.
authors.forename: Raphaële J
authors.initials: RJ
authors.lastname: Clément
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge, Cambridgeshire CB2 1EW, United Kingdom.
authors.forename: Michal
authors.initials: M
authors.lastname: Leskes
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge, Cambridgeshire CB2 1EW, United Kingdom.
authors.forename: Derek S
authors.initials: DS
authors.lastname: Middlemiss
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Olaf J
authors.initials: OJ
authors.lastname: Borkiewicz
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Kamila M
authors.initials: KM
authors.lastname: Wiaderek
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Karena W
authors.initials: KW
authors.lastname: Chapman
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Chupas
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge, Cambridgeshire CB2 1EW, United Kingdom ; Department of Chemistry, State University of New York at Stony Brook , Stony Brook, New York 11794-3400, United States.
authors.forename: Clare P
authors.initials: CP
authors.lastname: Grey