Anion-polarisation-directed short-range-order in antiperovskite Li2FeSO

Samuel W. Coles; Viktoria Falkowski; Harry S. Geddes; Gabriel E. Pérez; Samuel G. Booth; Alexander G. Squires; Conn O'Rourke; Kit McColl; Andrew L. Goodwin; Serena A. Cussen; Simon J. Clarke; M. Saiful Islam; Benjamin J. Morgan

doi:10.1039/D2TA10037A

Anion-polarisation-directed short-range-order in antiperovskite Li₂FeSO†

Samuel W. Coles,

*^ab Viktoria Falkowski,^bc Harry S. Geddes,

^bc Gabriel E. Pérez,

^bd Samuel G. Booth,

^be Alexander G. Squires,

^abf Conn O'Rourke,^ab Kit McColl,

^ab Andrew L. Goodwin,^bc Serena A. Cussen,^be Simon J. Clarke,

^bc M. Saiful Islam

^abg and Benjamin J. Morgan

*^ab

Author affiliations

* Corresponding authors

^a Department of Chemistry, University of Bath, Claverton Down, UK
E-mail: swc57@bath.ac.uk, b.j.morgan@bath.ac.uk

^b The Faraday Institution, Quad One, Harwell Science and Innovation Campus, Didcot, UK

^c Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, Oxford OX1 3QR, UK

^d ISIS Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Didcot OX11 0QX, UK

^e Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK

^f Department of Chemistry, University College London, London WC1H 0AJ, UK

^g Department of Materials, University of Oxford, Oxford, UK

Abstract

Short-range ordering in cation-disordered cathodes can have a significant effect on their electrochemical properties. Here, we characterise the cation short-range order in the antiperovskite cathode material Li₂FeSO, using density functional theory, Monte Carlo simulations, and synchrotron X-ray pair-distribution-function data. We predict partial short-range cation-ordering, characterised by favourable OLi₄Fe₂ oxygen coordination with a preference for polar cis-OLi₄Fe₂ over non-polar trans-OLi₄Fe₂ configurations. This preference for polar cation configurations produces long-range disorder, in agreement with experimental data. The predicted short-range-order preference contrasts with that for a simple point-charge model, which instead predicts preferential trans-OLi₄Fe₂ oxygen coordination and corresponding long-range crystallographic order. The absence of long-range order in Li₂FeSO can therefore be attributed to the relative stability of cis-OLi₄Fe₂ and other non-OLi₄Fe₂ oxygen-coordination motifs. We show that this effect is associated with the polarisation of oxide and sulfide anions in polar coordination environments, which stabilises these polar short-range cation orderings. We propose that similar anion-polarisation-directed short-range-ordering may be present in other heterocationic materials that contain cations with different formal charges. Our analysis illustrates the limitations of using simple point-charge models to predict the structure of cation-disordered materials, where other factors, such as anion polarisation, may play a critical role in directing both short- and long-range structural correlations.

This article is part of the themed collections: Celebrating the scientific accomplishments of RSC Fellows and Celebrating ten years of Journal of Materials Chemistry A

Journal of Materials Chemistry A

Anion-polarisation-directed short-range-order in antiperovskite Li₂FeSO†

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Anion-polarisation-directed short-range-order in antiperovskite Li₂FeSO

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