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

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  • Kai Xiang
  • Wenting Xing
  • Dorthe B. Ravnsbæk
  • Liang Hong
  • Ming Tang
  • Zheng Li
  • Kamila M. Wiaderek
  • Olaf J. Borkiewicz
  • Karena W. Chapman
  • Peter J. Chupas
  • Yet-Ming Chiang

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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.

TidsskriftNano Letters
Sidetal (fra-til)1696-1702
StatusUdgivet - 2017