Investigation of Aliovalent Substitution in the Solid Sodium Ion Electrolyte Na2ZrCl6

Abstract

The research community is working hard on the development of solid-state batteries (SSB) as an alternative to commercialized lithium-ion batteries, due to their higher energy density and enhanced safety. One of the core research areas of SSBs is the solid-state electrolyte (SE), which should fit the demand for high ionic conductivity and electrochemical stability at the same time. Recently, halide SEs have emerged because they are mechanochemical processable, similar to sulfidic SEs, but halide SEs exhibit excellent electrochemical oxidation stability compared to sulfidic SEs [1,2].However, the relatively low ionic conductivity at room temperature still hinders the application of halide SE in SSBs. Aliovalent substitution is a very widely used method to improve the ionic conductivity of SEs [3,4]. We are also motivated by the application of earth-abundance elements to reduce raw material costs.Recently, significant focus has been gained by Zr-based compounds such as Na2ZrCl6. We investigate here such compounds, focusing on elemental substitutions to gain increased ionic conductivity and on gaining insight into the influence of synthesis on SE crystal structure and electrochemical properties.In our work, different amounts of elemental substitutions are investigated, and the related materials are synthesized at different temperatures. In particular, the influence of a series of subsequent heating temperatures on the structure of the binary system is studied through XRD diffraction analysis and further refinement. The Ionic diffusion paths are also estimated through the band valence sum approach, in order to validate the electrochemical impedance spectroscopy (EIS) results.In summary, we report our early results on the development of novel solid electrolytes for Na-based solid-state batteries.REFERENCES[1] Kwak, H.; Lyoo, J.; Park, J.; Han, Y.; Asakura, R.; Remhof, A.; Battaglia, C.; Kim, H.; Hong, S.-T.; Jung, Y. S. Na2ZrCl6 enabling highly stable 3 V all-solid-state Na-ion batteries. Energy Storage Mater. 2021, 37, 47−54.[2] Tong Zhao, Alexander N. Sobolev, Roman Schlem, Bianca Helm, Marvin A. Kraft and Wolfgang G. Zeier. Synthesis-Controlled Cation Solubility in Solid Sodium Ion Conductors Na2+xZr1 - xInxCl6. ACS Appl. Energy Mater. 2023, XXXX, XXX, XXX-XXX.[3] Schlem, R.; Banik, A.; Eckardt, M.; Zobel, M.; Zeier, W. G. Na3-xEr1-xZrxCl6-A Halide-Based Fast Sodium-Ion Conductor with Vacancy-Driven Ionic Transport. ACS Appl. Energy Mater. 2020, 3, 10164−10173.[4] Wu, E. A.; Banerjee, S.; Tang, H.; Richardson, P. M.; Doux, J.M.; Qi, J.; Zhu, Z.; Grenier, A.;Li, Y.; Zhao, E.; Deysher, G.; Sebti, E.;Nguyen, H.; Stephens, R.; Verbist, G.; Chapman, K. W.; Clement, R.J.; Banerjee, A.; Meng, Y. S.; Ong, S. P. A stable cathode-solid electrolyte composite for high-voltage, long-cycle-life solid-state sodium-ion batteries. Nat. Commun. 2021, 12, 1256.