title: Accommodating High Transformation Strains in Battery Electrodes via the Formation of Nanoscale Intermediate Phases: Operando Investigation of Olivine NaFePO4.
abstract: Virtually all intercalation compounds exhibit significant changes in unit cell volume as the working ion concentration varies. NaxFePO4(0 < x < 1, NFP) olivine, of interest as a cathode for sodium-ion batteries, is a model for topotactic, high-strain systems as it exhibits one of the largest discontinuous volume changes (∼17% by volume) during its first-order transition between two otherwise isostructural phases. Using synchrotron radiation powder X-ray diffraction (PXD) and pair distribution function (PDF) analysis, we discover a new strain-accommodation mechanism wherein a third, amorphous phase forms to buffer the large lattice mismatch between primary phases. The amorphous phase has short-range order over ∼1nm domains that is characterized by a and b parameters matching one crystalline end-member phase and a c parameter matching the other, but is not detectable by powder diffraction alone. We suggest that this strain-accommodation mechanism may generally apply to systems with large transformation strains.
authors.affiliation: Department of Material Science and Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Kai
authors.identifier: 0000-0001-5933-4644
authors.initials: K
authors.lastname: Xiang
authors.affiliation: Department of Material Science and Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Wenting
authors.initials: W
authors.lastname: Xing
authors.affiliation: Department of Material Science and Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.|Department of Physics, Chemistry and Pharmaci, University of Southern Denmark , Campusvej 55, 5320 Odense M, Denmark.
authors.forename: Dorthe B
authors.initials: DB
authors.lastname: Ravnsbæk
authors.affiliation: Department of Material Science and Nanoengineering, Rice University , 6100 Main Street, Houston, Texas 77005, United States.
authors.forename: Liang
authors.initials: L
authors.lastname: Hong
authors.affiliation: Department of Material Science and Nanoengineering, Rice University , 6100 Main Street, Houston, Texas 77005, United States.
authors.forename: Ming
authors.initials: M
authors.lastname: Tang
authors.affiliation: Department of Material Science and Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Li
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , 9700 South Cass Avenue, 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 , 9700 South Cass Avenue, 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 , 9700 South Cass Avenue, 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 , 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Chupas
authors.affiliation: Department of Material Science and Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Yet-Ming
authors.identifier: 0000-0002-0833-7674
authors.initials: YM
authors.lastname: Chiang
keywords: Phase transformations; batteries; olivines; operando; pair-distribution function; sodium iron phosphate