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 Na3OBH4 with cubic antiperovskite structure by solid-state reaction from Na2O and NaBH4. Na3OBH4 exhibits ionic conductivity of 4.4 × 10–3 S cm–1 at room temperature (1.1 × 10–2 S cm–1 at 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 Na3OBH4 but also because of the rotation of BH4 cluster anion. This work deepens the understanding of the antiperovskite structure and the role of cluster anions for superionic conduction.

We first demonstrate the rational design and fabrication of novel atomically thick Co3O4 nanosheets (ATCNs) with a specific facet exposed by topochemical transformation from layered intermediate precursors to optimize energy storage. The eminently enhanced lithium storage performance can be attributed not only to the synergistic advantages of inorganic graphene analogues but also the increase of Co(2+) atoms and charge redistribution for ATCNs, which were first revealed by means of synchrotron radiation X-ray absorption near-edge spectroscopy. This work opens the window for the preparation of non-layered atomically thick nanosheets, which will significantly enrich the species of inorganic graphene analogues and optimize energy storage by reasonable materials design and fabrication.

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