Boosting the Na‐Ion Conductivity in the Cluster‐Ion Based Anti‐Perovskite Na2BH4NH2

Abstract Solid‐state sodium‐ion/metal batteries (SSSBs) are highly desirable for next‐generation energy storage systems, while very limited Na‐ion solid‐state electrolytes are explored. The borohydride‐based solid electrolytes are expected to achieve the high energy density target, due to their low redox potential, low Young's modulus as well as high stability toward alkali metals. However, the biggest challenge of borohydride‐based electrolyte is the low ionic conductivity. In this study, an anti‐perovskite solid‐state electrolyte (SSE) material rich in vacancy defects is explored, Na 2 BH 4 NH 2 , to solve above problems. Benefitting from rich vacancy defects, a high ionic conductivity of 7.56 × 10 −4 S cm −1 with a low activation energy for Na + migration of 0.67 eV at 90 °C are achieved. The NaSn|Na 2 BH 4 NH 2 |NaSn symmetric cell cycles at a current density of 0.1 mA cm −2 for 500 h. Moreover, the universality of Na 2 BH 4 NH 2 electrolyte is verified by TiS 2 cathode, indicating that Na 2 BH 4 NH 2 has good compatibility with electrode material. These outstanding performances suggest that it is a viable strategy to increase the ionic conductivity by forming vacancy defects, leading to the further development of solid electrolytes with superior properties.