The wide availability of sodium makes sodium-ion batteries attractive replacements for lithium-ion batteries. All-solid-state sodium-ion batteries, which avoid the safety issues typical of batteries using flammable liquid electrolytes, are particularly promising. Existing solid-state electrolytes are based on single-anion frameworks, but now Xueliang Sun and collaborators, writing in Nature Materials, demonstrate that the use of dual-anion sublattices results in superior ionic conductivity and good cycling stability.

The ionic conductivity peaks for the composition at which the materials are amorphous owing to local structural rearrangements caused by the presence of oxygen. In the amorphous state, the intrinsic ionic conduction is unaffected by grain boundaries and is hence substantially higher than in single-anion, crystalline conductors. The electrolytes also act as electronic insulators, inhibiting electrical leakage and resulting in a long operational life.