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

Samuel Coles, Viktoria Falkowski, Harry Geddes, Gabriel Pérez, Samuel Booth, Alex Squires, Conn O'Rourke, Kit McColl, Andrew Goodwin, Serena Cussen, Simon Clarke, M. Saiful Islam, Benjamin Morgan

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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 similar anion-polarisation--directed short-range-ordering may be present in other heterocationic materials that contain cations with different formal charges. Our analysis also 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.
Original languageEnglish
Pages (from-to)13016-13026
Number of pages11
JournalJournal of Materials Chemistry A
Volume11
Issue number24
Early online date12 Apr 2023
DOIs
Publication statusPublished - 28 Jun 2023

Bibliographical note

Funding Information:
The authors thank the Faraday Institution CATMAT and FutureCat projects (EP/S003053/1, FIRG016, FIRG017) for financial support. This work used the Michael computing cluster (FIRG030), the ARCHER2 UK National Supercomputer Service, with access provided by our membership of the UK's HPC Materials Modelling Consortium (EP/R029431), and the Isambard 2 UK National Tier-2 HPC Service operated by GW4 and the UK Met Office, and funded by EPSRC (EP/T022078/1). The authors acknowledge the Diamond Light Source for allocation of beamtime under proposal number CY27702. BJM thanks the Royal Society for financial support (URF/R/191006). AGS thanks the STFC Batteries Network for an Early Career Researcher Award (ST/R006873/1). HSG and ALG acknowledge funding from the ERC (grant 788144).

Publisher Copyright:
© 2023 The Royal Society of Chemistry.

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