High voltage cathode materials for Na-ion batteries of general formula Na 3V 2O 2x(PO 4) 2F 3-2x

Paula Serras, Verónica Palomares, Aintzane Goñi, Izaskun Gil De Muro, Pierre Kubiak, Luis Lezama, Teófilo Rojo

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Abstract

Different samples of the sodium-vanadium fluorophosphate cathodic materials have been synthesized via the hydrothermal method, varying the type and content of carbon used in the synthesis. Structural characterization of the composites was performed by powder X-ray diffraction. Magnetic susceptibility measurements and EPR (Electron Paramagnetic Resonance) polycrystalline spectra indicate that some of the samples exhibit V 3+/V 4+ mixed valence, with the general formula Na 3V 2O 2x(PO 4) 2F 3-2x where 0 ≤ x < 1. The morphology of the materials was analyzed by Transmission Electron Microscopy (TEM). A correlation between the type and content of carbon with the electrochemical behavior of the different samples was established. Electrochemical measurements conducted using Swagelok-type cells showed two voltage plateaux at 3.6 and 4.1 V vs. Na/Na +. The best performing sample, which comprised a moderate percentage of electrochemical grade carbon as additive, exhibited specific capacity values of about 100 mA h g -1 at 1C (≈80% of theoretical specific capacity). Cyclability tests at 1C proved good reversibility of the material that maintained 98% of initial specific capacity for 30 cycles.

Original languageEnglish
Pages (from-to)22301-22308
Number of pages8
JournalJournal of Materials Chemistry
Volume22
Issue number41
DOIs
Publication statusPublished - 7 Nov 2012
Externally publishedYes

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ASJC Scopus subject areas

  • Materials Chemistry
  • Chemistry(all)

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