Investigation of sodium insertion–extraction in olivine Na _x FePO ₄ (0 ≤ x ≤ 1) using first-principles calculations

Journal Article · Fri Sep 23 00:00:00 EDT 2016 · Physical Chemistry Chemical Physics. PCCP (Print)

DOI:https://doi.org/10.1039/C6CP00762G· OSTI ID:1322340

Saracibar, A.; Carrasco, J.; Saurel, D.; Galceran, M.; Acebedo, B.; Anne, H.; Lepoitevin, M.; Rojo, T.; Casas Cabanas, M.

Olivine NaFePO4 has recently attracted the attention of the scientific community as a promising cathode material for Na-ion batteries. In this work we combine density functional theory (DFT) calculations and high resolution synchrotron X-ray diffraction (HRXRD) experiments to study the phase stability of NaxFePO4 along the whole range of sodium compositions (0 ≤ x ≤ 1). DFT calculations reveal the existence of two intermediate structures governing the phase stability at x = 2/3 and x = 5/6. This is in contrast to isostructural LiFePO4, which is a broadly used cathode in Li-ion batteries. Na2/3FePO4 and Na5/6FePO4 ground states both align vacancies diagonally within the ab plane, coupled to a Fe2+/Fe3+ alignment. HRXRD data for NaxFePO4 (2/3 < x < 1) materials show common superstructure reflections up to x = 5/6 within the studied compositions. The computed intercalation voltage profile shows a voltage difference of 0.16 V between NaFePO4 and Na2/3FePO4 in agreement with the voltage discontinuity observed experimentally during electrochemical insertion.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
• Sponsoring Organization: FOREIGN
• OSTI ID: 1322340
• Journal Information: Physical Chemistry Chemical Physics. PCCP (Print), Vol. 18, Issue 18; ISSN 1463-9076
• Country of Publication: United States
• Language: ENGLISH