Superionic Conductivity in Sodium Zirconium Chloride-Based Compounds

All-solid-state sodium batteries are attracting intensive attention, and chloride-based solid electrolytes are promising candidates for use in such batteries because of their high chemical stability and low Young's modulus. Here, we report new superionic conductors based on polyanion-added chloride-based materials. Na_0.67 Zr(SO₄ )_0.33 Cl₄ showed a high ionic conductivity of 1.6 mS cm^-1 at room temperature. X-ray diffraction analysis indicated that the highly conducting materials are mainly a mixture of an amorphous phase and Na₂ ZrCl₆ . The conductivity might be dominated by the electronegativity of the central atom of the polyanion. Electrochemical measurements reveal that Na_0.67 Zr(SO₄ )_0.33 Cl₄ is a sodium ionic conductor and is suitable for use as a solid electrolyte in all-solid-state sodium batteries.