Anion-polarisation-directed short-range-order in antiperovskite Li$_2$FeSO
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 LiFeSO, 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 OLiFe oxygen coordination with a preference for polar cis-OLiFe over non-polar trans-OLiFe 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-OLiFe oxygen coordination and corresponding long-range crystallographic order. The absence of long-range order in LiFeSO can therefore be attributed to the relative stability of cis-OLiFe and other non-OLiFe 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.
Keywords
Cite
@article{arxiv.2212.13485,
title = {Anion-polarisation-directed short-range-order in antiperovskite Li$_2$FeSO},
author = {Samuel W. Coles and Viktoria Falkowski and Harry S. Geddes and Gabriel E. Pérez and Samuel G. Booth and Alexander G. Squires and Conn O'Rourke and Kit McColl and Andrew L. Goodwin and Serena A. Cussen and Simon J. Clarke and M. Saiful Islam and Benjamin J. Morgan},
journal= {arXiv preprint arXiv:2212.13485},
year = {2023}
}