Iron titanium phosphates as high-specific-capacity electrode materials for lithium ion batteries

R. Essehli, B. El Bali, A. Faik, M. Naji, S. Benmokhtar, Y. R. Zhong, L. W. Su, Z. Zhou, J. Kim, K. Kang, M. Dusek

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Abstract

Two iron titanium phosphates, Fe0.5TiOPO4 and Fe 0.5Ti2(PO4)3, were prepared, and their crystal structures and electrochemical performances were compared. The electrochemical measurements of Fe0.5TiOPO4 as an anode of a lithium ion cell showed that upon the first discharge down to 0.5 V, the cell delivered a capacity of 560 mA h/g, corresponding to the insertion of 5 Li's per formula unit Fe0.5TiOPO4. Ex-situ XRD reveals a gradual evolution of the structure during cycling of the material, with lower crystallinity after the first discharge cycle. By correlating the electrochemical performances with the structural studies, new insights are achieved into the electrochemical behaviour of the Fe0.5TiOPO 4 anode material, suggesting a combination of intercalation and conversion reactions. The Nasicon-type Fe0.5Ti2(PO 4)3 consists of a three-dimensional network made of corners and edges sharing [TiO6] and [FeO6] octahedra and [PO4] tetrahedra leading to the formation of trimmers [FeTi 2O12]. The first discharge of lithium ion cells based on Fe0.5Ti2(PO4)3 materials showed electrochemical activity of Ti4+/Ti3+ and Fe 2+/Fe0 couples in the 2.5-1 V region. Below this voltage, the discharge profiles are typical of phosphate systems where Li 3PO4 is a product of the electrochemical reaction with lithium; moreover, the electrolyte solvent is reduced. An initial capacities as high as 1100 mA h g-1 can be obtained at deep discharge. However, there is an irreversible capacity loss in Fe0.5Ti2(PO 4)3 due to the occurrence of insulating products as Li3PO4 and a solid electrolyte interface.

Original languageEnglish
Pages (from-to)434-441
Number of pages8
JournalJournal of Alloys and Compounds
Volume585
DOIs
Publication statusPublished - 1 Jan 2014

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Keywords

  • Crystal structure
  • Electrolyte
  • Lithium-ion batteries
  • Nasicon
  • Oxyphosphate

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

Cite this

Essehli, R., El Bali, B., Faik, A., Naji, M., Benmokhtar, S., Zhong, Y. R., Su, L. W., Zhou, Z., Kim, J., Kang, K., & Dusek, M. (2014). Iron titanium phosphates as high-specific-capacity electrode materials for lithium ion batteries. Journal of Alloys and Compounds, 585, 434-441. https://doi.org/10.1016/j.jallcom.2013.09.093