Hidden Two-Step Phase Transition and Competing Reaction Pathways in LiFePO4

Yukinori Koyama, Takeshi Uyama, Yuki Orikasa, Takahiro Naka, Hideyuki Komatsu, Keiji Shimoda, Haruno Murayama, Katsutoshi Fukuda, Hajime Arai, Eiichiro Matsubara, Yoshiharu Uchimoto, Zempachi Ogumi

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)

Abstract

LiFePO4 is a well-known electrode material that is capable of high-rate charging and discharging despite a strong phase-separation tendency of the lithium-rich and poor end-member phases. X-ray diffraction measurements (XRD) with high time-resolution are conducted under battery operation conditions to reveal the phase-transition mechanism of LiFePO4 that leads to the high rate capability. We here propose a hidden two-step phase transition of LiFePO4 via a metastable phase. The existence of the metastable phase, not just a member of a transient solid solution, is evidenced by the operando XRD measurements. Our two-step phase-transition model explains the behavior of LiFePO4 under the battery operation conditions. It also explains asymmetric behavior during the charging and discharging at high rates and low temperatures, as well as apparent single-step two-phase reaction between the end members at low rates at room temperature. This model also suggests underlying, rate-dependent electrochemical processes that result from a competing disproportion reaction of the metastable phase.

Original languageEnglish
Pages (from-to)2855-2863
Number of pages9
JournalChemistry of Materials
Volume29
Issue number7
DOIs
Publication statusPublished - Apr 11 2017
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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