《Rotational Cluster Anion Enabling Superionic Conductivity inSodium-Rich Antiperovskite Na3OBH4》

Sodium superionic conductors are keys to develop high safety and low cost all-solid-state sodium batteries. Among developed sodium ionic conductors, antiperovskite-type ionic conductors have attracted vast interest due to their high structural tolerance and good formability. Herein, we successfully synthesize Na₃OBH₄with cubic antiperovskite structure by solid-state reaction from Na₂O and NaBH₄. Na₃OBH₄exhibits ionic conductivity of 4.4 × 10^–3S cm^–1at room temperature (1.1 × 10^–2S cm^–1at 328 K) and activation energy of 0.25 eV. The ionic conductivity is 4 orders of magnitude higher than the existing antiperovskite Na₃OX (X = Cl, Br, I). It is shown that such enhancement is not only due to the specific cubic antiperovskite structure of Na₃OBH₄but also because of the rotation of BH₄cluster anion. This work deepens the understanding of the antiperovskite structure and the role of cluster anions for superionic conduction.

https://pubs.acs.org/doi/10.1021/jacs.9b01746