Na-ion mobility in layered Na2FePO4F and olivine Na[Fe,Mn]PO4

Rajesh Tripathi, Stephen M Wood, M Saiful Islam, Linda F Nazar

Research output: Contribution to journalArticle

145 Citations (Scopus)

Abstract

The Na-ion battery is currently the focus of much research interest due to its cost advantages and the relative abundance of sodium as compared to lithium. Olivine NaMPO4 (M ¼ Fe, Fe0.5Mn0.5, Mn) and layered Na2FePO4F are interesting materials that have been reported recently as attractive positive electrodes. Here, we report their Na-ion conduction behavior and intrinsic defect properties using atomistic simulation methods. In the olivines, Na ion migration is essentially restricted to the [010] direction along a curved trajectory, similar to that of LiMPO4, but with a lower migration energy (0.3 eV). However, Na/M antisite defects are also predicted to have a lower formation energy: the
higher probability of tunnel occupation with a relatively immobile M2+ cation – along with a greater volume change on redox cycling – contributes to the poor electrochemical performance of the Naolivine. Na+ ion conduction in Na2FePO4F is predicted to be two-dimensional (2D) in the interlayer plane with a similar low activation energy. The antisite formation energy is slightly higher; furthermore,
antisite occupation would not be predicted to impede transport significantly owing to the 2D pathway. This factor, along with the much lower volume change on redox cycling, is undoubtedly responsible for the better electrochemical performance of the layered structure. Where volume change and structural
effects do not incur impediments, Na-ion materials may present significant advantages over their Li counterparts.
Original languageEnglish
Pages (from-to)2257-2264
Number of pages8
JournalEnergy & Environmental Science
Volume6
Issue number8
Early online date16 May 2013
DOIs
Publication statusPublished - 1 Aug 2013

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Olivine
olivine
Ions
volume change
ion
occupation
defect
energy
Defects
lithium
Lithium
activation energy
Cations
relative abundance
Tunnels
electrode
tunnel
Activation energy
cation
Positive ions

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Na-ion mobility in layered Na2FePO4F and olivine Na[Fe,Mn]PO4. / Tripathi, Rajesh; Wood, Stephen M; Islam, M Saiful; Nazar, Linda F.

In: Energy & Environmental Science, Vol. 6, No. 8, 01.08.2013, p. 2257-2264.

Research output: Contribution to journalArticle

Tripathi, Rajesh ; Wood, Stephen M ; Islam, M Saiful ; Nazar, Linda F. / Na-ion mobility in layered Na2FePO4F and olivine Na[Fe,Mn]PO4. In: Energy & Environmental Science. 2013 ; Vol. 6, No. 8. pp. 2257-2264.
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