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Updated: Sep 20, 2025
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From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
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Structure and Ionic Conductivity of Halide Solid Electrolytes Based on NaAlCl4 and Na2ZnCl4
Hao Guo1,2, Michael Häfner1,2, Helen Grüninger1,2
1Department of Biology, Chemistry and Earth Sciences, University of Bayreuth, Universitätstraße 30, 95447, Bayreuth, Germany.
Summary
Researchers developed new sodium-based solid-state electrolytes (SSE) for safer, cost-effective batteries. These novel sodium metal halide SSEs show improved ionic conductivity, crucial for grid storage applications.
Area of Science:
- Materials Science
- Electrochemistry
- Solid-State Chemistry
Background:
- Sodium-based solid-state batteries (SSBs) offer a safe and cost-effective alternative to lithium-ion batteries, particularly for grid storage.
- Development of sustainable solid-state electrolytes (SSEs) with high ionic conductivity is essential for advancing SSB technology.
- Sodium metal halide SSEs are promising due to their ionic conductivity, electrochemical stability, and processability.
Purpose of the Study:
- To investigate novel SSEs based on NaAlCl4 (NAC) and Na2ZnCl4 (NZC) with the nominal composition Na1+xZnxAl1-xCl4.
- To explore the relationship between composition, crystalline structure, and ionic conductivity in these materials.
- To demonstrate the potential of these SSEs in working solid-state sodium batteries.
Main Methods:
- Synthesis of Na1+xZnxAl1-xCl4 compounds using ball-milling.
- Characterization of crystal structure using X-ray diffraction (XRD).
- Measurement of ionic conductivity via Electrochemical Impedance Spectroscopy (EIS).
- Investigation of ion transport mechanisms using molecular dynamics (MD) simulations and nuclear magnetic resonance (NMR).
Main Results:
- A two-phase system was identified, with a solid solution extending to approximately 34(3)% Al substitution in the Na2ZnCl4-type structure.
- The highest ionic conductivity (1.5×10⁻⁵ S cm⁻¹ at 25 °C) was observed near the miscibility gap edge (x=0.625), significantly exceeding that of pure NZC and NAC.
- MD simulations and NMR revealed the critical role of Na+ vacancies in both Na sublattices for enhanced ionic conduction.
Conclusions:
- A novel class of SSEs based on the Na2ZnCl4 olivine structure was successfully developed.
- These SSEs exhibit enhanced ionic conductivity, making them suitable for solid-state sodium batteries.
- The study provides fundamental insights into structure-property relationships governing ionic conduction in sodium metal halide SSEs.
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