Size-dependent staging and phase transition in LiFePO4/FePO 4

Changbao Zhu, Lin Gu, Liumin Suo, Jelena Popovic, Hong Li, Yuichi Ikuhara, Joachim Maier

Research output: Contribution to journalArticlepeer-review

45 Citations (Scopus)

Abstract

The LiFePO4/FePO4 phase transition process is remarkable in terms of its excellent reversibility, making this redox system extremely promising for high rate lithium storage. The recent observation of ordering effects (Li0.5FePO4) during the phase transition challenges the traditional two phase models. In this work, the phenomenon of staging for LiFePO4 for different sizes (70 nm and 50 nm) by high resolution aberration corrected annular bright electron microscopy is detected, investigated, and discussed along with previous results on larger crystals. In the small crystals, staging is found throughout with a decrease of order from center to the surface. For the larger crystal, a staging phase occurs constituting the interfacial zone (width around 15 nm) between LiFePO 4 and FePO4. A comparison is made to recent experiments on even larger crystals showing such an interphase of smaller extent (around 2 nm). Thus it appears that these zones narrow with increasing size. These findings are discussed in the light of phase transition thermodynamics and kinetics. In particular, the possibility is discussed that the staging interphase may constitute a low energy solution to the LiFePO 4/FePO4 contact. The phenomenon of Li-ordering in the system LiFePO4/FePO4 is investigated by STEM-ABF for different sizes. While in small crystals, the ordering affect the whole particle; for larger crystals, it was found to characterize the LiFePO 4/FePO4 contact and the interfacial zones narrow with increasing size. These findings are discussed in the light of phase transition thermodynamics and kinetics.

Original languageEnglish
Pages (from-to)312-318
Number of pages7
JournalAdvanced Functional Materials
Volume24
Issue number3
DOIs
Publication statusPublished - 2014 Jan 22
Externally publishedYes

Keywords

  • phase transition
  • size-dependent
  • staging effect

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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