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

TitleAccommodating High Transformation Strains in Battery Electrodes via the Formation of Nanoscale Intermediate Phases: Operando Investigation of Olivine NaFePO4
Publication TypeJournal Article
Year of Publication2017
AuthorsXiang, K, Xing, W, Ravnsbaek, DB, Hong, L, Tang, M, Li, Z, Wiaderek, KM, Borkiewicz, OJ, Chapman, KW, Chupas, PJ, Chiang, YM
JournalNano Letters
Volume17
Issue3
Pagination1696 - 1702
Date Published2017/03//
ISBN Number1530-6984
Keywordsbatteries, cathodes, diagram, electrochemical shock, high-resolution, lifepo4, lithium-ion batteries, miscibility gap, olivines, operando, pair-distribution function, Phase transformations, silicon, sodium iron phosphate, solid-solution, x-ray-diffraction
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 (similar to 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 similar to 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.

Short TitleNano Lett.