Accommodating High Transformation Strains in Battery Electrodes via the Formation of Nanoscale Intermediate Phases

Virtually all intercalation compounds exhibit significant changes in unit cell volume as the working ion concentration varies. Using synchrotron radiation powder X-ray diffraction (PXD) and pair distribution function (PDF) analysis, we discover a new strain-accommodation mechanism.

This article is co-authored by Dorthe Bomholdt Ravnsbæk and describes a very important aspect of strain in the performance of olivine cathode materials.

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.

Article details

Accommodating High Transformation Strains in Battery Electrodes via the Formation of Nanoscale Intermediate Phases: Operando Investigation of Olivine NaFePO4

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
Department of Material Science and Nanoengineering, Rice University, 6100 Main Street, Houston, Texas 77005, United States
X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States
Nano Lett., Article ASAP
DOI: 10.1021/acs.nanolett.6b04971
Publication Date (Web): February 21, 2017
Copyright © 2017 American Chemical Society

Permanent link to this article: http://batteriselskab.dk/artikel/videnskabelig/accommodating-high-transformation-strains-in-battery-electrodes-via-the-formation-of-nanoscale-intermediate-phases.htm