Planting Repulsion Centers for Faster Ionic Diffusion in Superionic Conductors

Abstract

The successful launch of solid-state batteries relies on the discovery of solid electrolytes with remarkably high ionic conductivity. Extensive efforts have identified several important superionic conductors (SICs) and broadened our understanding of their superionic conductivity. Herein, we propose a new design strategy to facilitate ionic conduction in SICs by planting immobile repulsion centers. Our ab initio molecular dynamics simulations on the model system Na 11 Sn 2 PS 12 demonstrate that the sodium ionic conductivity can be increased by approximately one order of magnitude by simply doping large Cs ions as repulsion centers in the characteristic vacant site of Na 11 Sn 2 PS 12. Planting immobile repulsion centers locally induces the formation of high-energy sites, leading to a fast track for ionic conduction owing to the unique interactions among mobile ions in SICs. Seemingly non-intuitive approaches tailor the ionic diffusion by exploiting these immobile repulsion centers.

Computational Auxiliary for the Progress of Sodium-Ion Solid-State Electrolytes

“…(d,e) Energy diagram of sodium ions without Cs ion and with Cs ion, respectively. Reproduced with permission from ref . Copyright 2020 Wiley-VCH.…”

“…The analyses of calculated jump rate for sodium sites reveal that the anchored Cs ions facilitate repulsive ionic jumps through vacancies. The planted immobile repulsion centers near the diffusion pathways that are illustrated by the probability density distribution (yellow isosurfaces) of sodium shown in Figure b,c lead to a fast track for ionic transportation owing to the mutual Coulombic interactions among mobile ions in Na 11 Sn 2 PS 12 . These fast sodium ionic transport mechanisms of Na 10 MP 2 S 12 have broadened the understanding of superionic conductivity and would provide valuable enlightenment for designing future superionic conductors.…”

Influence of Reduced Na Vacancy Concentrations in the Sodium Superionic Conductors Na11+xSn2P1–xMxS12 (M = Sn, Ge)

“…25,27 Furthermore, the quasi-cubic 8b site hosts the Na (6), which bridges the Na (1) and Na (2) positions and was shown to take part in the diffusion mechanism by molecular dynamics simulations. 24,[30][31][32][33] Lastly, another unoccupied 32g site in an octahedral void has been discussed as the intermediate site in alternative diffusion pathways on the basis of bond valence sum analyses. 27,28 The sodium distribution over those sites seems to be heavily influenced by substitutions as, for example, the Na (6) site occupancy (at 298 K) in Na11.1Sn2.1P0.9Se12 was reported to be 74% while the site remains lowly occupied (< 22%) in Na11Sn2PS12.…”

“…Both sites usually show lower Na occupation than the other three octahedrally coordinated sites: Na(3) on a 16e site, Na(4) on a 16c site, and Na(5) on a 16f site. Especially on the Na(4) and Na(5) sites, large thermal displacement ellipsoids were reported and a splitting of the Na(4) site has been used to describe the Na + distribution in that octahedron. , Furthermore, the quasicubic 8b site hosts Na(6), which bridges the Na(1) and Na(2) positions, and was shown to take part in the diffusion mechanism by molecular dynamics simulations. ,− Finally, another unoccupied 32g site in an octahedral void has been discussed as the intermediate site in alternative diffusion pathways on the basis of bond valence sum analyses. , The sodium distribution over those sites seems to be heavily influenced by substitutions as, for example, the Na(6) site occupancy (at 298 K) in Na 11.1 Sn 2.1 P 0.9 Se 12 was reported to be 74% while the site remains lowly occupied (<22%) in Na 11 Sn 2 PS 12 . ,,, …”

Influence of Reduced Na Vacancy Concentrations in the Sodium Superionic Conductors Na11+xSn2P1−xMxS12 (M = Sn, Ge)

“…25,27 Furthermore, the quasi-cubic 8b site hosts the Na (6), which bridges the Na (1) and Na(2) positions and was shown to take part in the diffusion mechanism by molecular dynamics simulations. 24,[30][31][32][33] Lastly, another unoccupied 32g site in an octahedral void has been discussed as the intermediate site in alternative diffusion pathways on the basis of bond valence sum analyses. 27,28 The sodium distribution over those sites seems to be heavily influenced by substitutions as, for example, the Na(6) site occupancy (at 298 K) in Na11.1Sn2.1P0.9Se12 was reported to be 74% while the site remains lowly occupied (< 22%) in Na11Sn2PS12.…”