Superionic Conductivity in Sodium Zirconium Chloride‐Based Compounds

Abstract

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. Na0.67Zr(SO4)0.33Cl4 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 Na2ZrCl6. The conductivity might be dominated by the electronegativity of the central atom of the polyanion. Electrochemical measurements reveal that Na0.67Zr(SO4)0.33Cl4 is a sodium ionic conductor and is suitable for use as a solid electrolyte in all‐solid‐state sodium batteries.

NaMCl6 (M = Nb and Ta): A New Class of Sodium-Conducting Halide-Based Solid Electrolytes

“…In the case of Na M Cl 6 , the electronegativity of Ta, Zr, and Nb are 1.30, 1.25, and 1.17, respectively, on the Pauling scale, and this trend in the electronegativity can explain the lowest activation energy in NaTaCl 6 (see also the schematic in Figure S9). Similar effects have been proposed in polyanion-added chloride-based materials, highlighting the trends in the ion transport may be governed by the electronegativity of the central atom of the polyanion . Therefore, here we propose the inductive effect plays a vital role in the anionic framework’s design of electrolytes possessing halogens in the structure; however, there are multiple criteria to quantify the electronegativity of different elements, requiring further experimental corroboration as was the case in sulfide electrolytes.…”

“…Similar effects have been proposed in polyanion-added chloride-based materials, highlighting the trends in the ion transport may be governed by the electronegativity of the central atom of the polyanion. 44 Therefore, here we propose the inductive effect plays a vital role in the anionic framework's design of electrolytes possessing halogens in the structure; however, there are multiple criteria to quantify the electronegativity of different elements, requiring further experimental corroboration as was the case in sulfide electrolytes.…”