|Title||Accommodating High Transformation Strains in Battery Electrodes via the Formation of Nanoscale Intermediate Phases: Operando Investigation of Olivine NaFePO4|
|Publication Type||Journal Article|
|Year of Publication||2017|
|Authors||Xiang, K, Xing, W, Ravnsbaek, DB, Hong, L, Tang, M, Li, Z, Wiaderek, KM, Borkiewicz, OJ, Chapman, KW, Chupas, PJ, Chiang, YM|
|Pagination||1696 - 1702|
|Keywords||batteries, 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|
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 Title||Nano Lett.|