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. 2023 Nov 22;14(1):7615.
doi: 10.1038/s41467-023-43436-3.

Design principles for sodium superionic conductors

Shuo Wang #  1 , Jiamin Fu #  2   3 , Yunsheng Liu  1 , Ramanuja Srinivasan Saravanan  1 , Jing Luo  2 , Sixu Deng  2 , Tsun-Kong Sham  3 , Xueliang Sun  4 , Yifei Mo  5   6
Affiliations

Design principles for sodium superionic conductors

Shuo Wang et al. Nat Commun. .

Abstract

Motivated by the high-performance solid-state lithium batteries enabled by lithium superionic conductors, sodium superionic conductor materials have great potential to empower sodium batteries with high energy, low cost, and sustainability. A critical challenge lies in designing and discovering sodium superionic conductors with high ionic conductivities to enable the development of solid-state sodium batteries. Here, by studying the structures and diffusion mechanisms of Li-ion versus Na-ion conducting solids, we reveal the structural feature of face-sharing high-coordination sites for fast sodium-ion conductors. By applying this feature as a design principle, we discover a number of Na-ion conductors in oxides, sulfides, and halides. Notably, we discover a chloride-based family of Na-ion conductors NaxMyCl6 (M = La-Sm) with UCl3-type structure and experimentally validate with the highest reported ionic conductivity. Our findings not only pave the way for the future development of sodium-ion conductors for sodium batteries, but also consolidate design principles of fast ion-conducting materials for a variety of energy applications.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. The ion diffusion channel in Li/Na-ion conductors.
The Li+/Na+ sites (green) coordinated with O2-/S2-/Cl- anions (yellow) connected to form the diffusion channel in representative a–c sodium and d–f lithium SICs.
Fig. 2
Fig. 2. Lithium-ion and sodium-ion diffusion in model anion sublattices.
a–c The diffusion pathways (left) and corresponding energy profile (right) for single Li+ (green) and Na+ (red) migration in fixed a body-centered cubic (bcc) S2−, b face-centered cubic (fcc) O2−, c hexagonal close-packed (hcp) Cl− anion sublattice. The fixed anion lattice is set to have the octahedral (Oct) and tetrahedral (Tet) site volume as the real materials, O3-type LiCoO2 (Oct: 12.0 Å3) and NaCoO2 (Oct: 15.7 Å3) for fcc O2−, Li2ZrCl6 (Oct: 23.8 Å3) and Na2ZrCl6 (Oct: 30.9 Å3) for hcp Cl-, Li10GeP2S12 (Tet: 7.4 Å3) and Na10SnP2S12 (Tet: 9.6 Å3) for bcc S2−. d–f The energy barrier of Na+ (red) and Li+ (green) migration as a function of site volume in the fixed d bcc S2−, e fcc O2−, f hcp Cl- anion sublattice.
Fig. 3
Fig. 3. Design principles for sodium-ion conductors.
a The schematics illustrate (lower) the Prism-Prism pathway between face-sharing high-CN sites in P2-type NaMO2, in comparison to (upper) the Oct-Tet-Oct pathway with intermediate Tet site in O3-type NaMO2, with (middle) the calculated energy profile for Na+ migration in the fixed O-anion sublattice at the lattice volume of 19.3 Å3 per O2−. b The comparison of the percolation radii pr and the average CNs of Li/Na sites along the diffusion channels in Li-ion and Na-ion conductors showing a clear distinction.
Fig. 4
Fig. 4. Discovery of sodium superionic conductors.
a High-throughput screening of Na-containing oxides, sulfides, and chlorides. b–d The crystal structures of representative discovered sodium SICs and (inset) their diffusion channels consist of face-sharing high-CN sites. e The high experimental Na+ conductivities σRT of Na0.86SmTa0.43Cl6, NaLa0.95Ta0.43Cl6, NaCe0.83Ta0.5Cl6, and NaNd0.83Ta0.5Cl6. f The Rietveld refinements of synchrotron-based diffraction pattern and g the fitting result of the pair distribution function of NaLa0.95Ta0.43Cl6.
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