In Situ Neutron and Impedance Analysis of the Phase Evolution during Lithium-Indium Chloride Dehydration

Abstract

Rare-earth alkali halides (REAHs) have been shown to have superionic conductivity and are promising candidates for solid lithium electrolytes. The library of superionic materials of the form Li3MX6 (along with various substitutions) where M = Sc, Y, La, Er, and X = Cl, Br, I is ever increasing.[1] The most notable examples have room temperature lithium ionic conductivity surpassing 1 mS cm-1. Lithium Indium Chloride has been shown to adopt a similar structure to the Li3MX6 REAHs and has high conductivity, 1.5 mS cm-1.[2] A significant advantage that Li3MX6-based materials have over other solid electrolytes, such as garnets, is their low synthesis and processing cost.[3] As an example, we will describe how Li3InCl6 can be synthesized from concentrated aqueous solution through controlled dehydration.[3-4] Here, we probe this dehydration/reaction using a multimodal approach that combines in situ neutron diffraction, thermogravimetry, differential scanning calorimetry, and in situ impedance spectroscopy. Figure 1 shows the phase transitions as determined by in situ neutron scattering. Clearly, we observe three phase transitions, with the high conductivity phase forming at ~120 oC. We show that hydrate is readily cold-pressed into dense pellets that offer remarkable adhesion to a roughened blocking electrode surface. Controlled dehydration further maintains the pellet's density; however, removing trace H2O leads to mechanical strain and fracturing. This report provides a pathway for the direct synthesis and processing of REAHs from concentrated aqueous solutions.[4] This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Division of Materials Science and Engineering. This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory.[1] Park, K.-H.; Kaup, K.; Assoud, A.; Zhang, Q.; Wu, X.; Nazar, L. F. High-Voltage Superionic Halide Solid Electrolytes for All-Solid-State Li-Ion Batteries. ACS Energy Lett. 2020, 5, 2, 533–539.[2] Li, X.; Liang, J.; Luo, J.; Norouzi Banis, M.; Wang, C.; Li, W.; Deng, S.; Yu, C.; Zhao, F.; Hu, Y.; Sham, T.-K.; Zhang, L.; Zhao, S.; Lu, S.; Huang, H.; Li, R.; Adair, K. R.; Sun, X. Air-Stable Li3InCl6 Electrolyte with High Voltage Compatibility for All-Solid-State Batteries. Energy Environ. Sci. 2019, 12, 2665-2671.[3] Li, W.; Liang, J.; Li, M.; Adair, K. R.; Li, X.; Hu, Y.; Xiao, Q.; Feng, R.; Li, R.; Zhang, L.; Lu, S.; Huang, H.; Zhao, S.; Sham, T.-K.; Sun, X. Unraveling the Origin of Moisture Stability of Halide Solid- State Electrolytes by In Situ and Operando Synchrotron X-Ray Analytical Techniques. Chem. Mater. 2020,32, 16, 7019–7027.[4] Sacci, R.L.; Bennett, T.H.; Drews, A.R.; Anandan, V.; Kirkham, M.J.; Daemen, L.L.; Nanda, K. Phase evolution during lithium indium halide superionic conductor dehydration. J. Mater. Chem. A, 2021,9, 990-996. Figure 1