Jump to main content
Jump to site search

Issue 8, 2013
Previous Article Next Article

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

Author affiliations

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 = 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 Na-olivine. 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.

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

Back to tab navigation

Supplementary files

Publication details

The article was received on 16 Mar 2013, accepted on 16 May 2013 and first published on 17 May 2013


Article type: Paper
DOI: 10.1039/C3EE40914G
Citation: Energy Environ. Sci., 2013,6, 2257-2264
  •   Request permissions

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

    R. Tripathi, S. M. Wood, M. S. Islam and L. F. Nazar, Energy Environ. Sci., 2013, 6, 2257
    DOI: 10.1039/C3EE40914G

Search articles by author

Spotlight

Advertisements