Stabilizing the Structure of LiCoPO4 Nanocrystals via Addition of Fe3+: Formation of Fe3+ Surface Layer, Creation of Diffusion-Enhancing Vacancies, and Enabling High-Voltage Battery Operation

Naohisa Okita, Kazuaki Kisu, Etsuro Iwama, Yuki Sakai, Yiyo Lim, Yusuke Takami, Moulay Tahar Sougrati, Thierry Brousse, Patrick Rozier, Patrice Simon, Wako Naoi, Katsuhiko Naoi

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Factors affecting the cyclability of the Fe-substituted LiCoPO4 (LiCo0.8Fe0.2PO4, LCFP) material were elucidated, including both the structural and electrode/electrolyte stability. Electrochemical characterization of the synthesized LCFP nanoparticles lends clear evidence for improved electrochemical stability of LCP, as well as enhanced rate capability, with Fe3+ substitution. Surface analysis using X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) suggest that Fe enrichment on the surface of LCFP occurs through the oxidation of Fe2+ into Fe3+ in the synthesis process. The Fe3+-rich phase on the LCP surface enhances the stability of the delithiated phase, preventing oxidative reactions with electrolytes during high-voltage operation. This surface protection persists as long as the electrochemical reduction of Fe3+ is avoided by ensuring that the full range of operating voltages lie above the Fe3+/Fe2+ redox potential. Our findings may offer new approaches to stabilize the structure of LCP and other high-voltage positive electrodes for use in 5 V-class Li-ion batteries.

Original languageEnglish
Pages (from-to)6675-6683
Number of pages9
JournalChemistry of Materials
Volume30
Issue number19
DOIs
Publication statusPublished - 2018 Oct 9
Externally publishedYes

ASJC Scopus subject areas

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

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