Anionic Sublattices in Halide Solid Electrolytes: A Case Study with the High‐Pressure Phase of Li3ScCl6

• Published in: Angewandte Chemie International Edition 2024-04, Vol.63 (15), p.e202401779-n/a
• Main Authors: Ding, Fenghua, Doi, Atsunori, Ogawa, Takafumi, Ubukata, Hiroki, Zhu, Tong, Kato, Daichi, Tassel, Cédric, Oikawa, Itaru, Inui, Naoki, Kuze, Satoru, Yamabayashi, Tsutomu, Fujii, Kotaro, Yashima, Masatomo, Ou, Xing, Wang, Zhijian, Min, Xiaobo, Fujita, Koji, Takamura, Hitoshi, Kuwabara, Akihide, Zhang, Tianren, Griffith, Kent J., Lin, Zhang, Chai, Liyuan, Kageyama, Hiroshi
• Format: Article
• Language: English
• Subjects: anion sublattice; Anions; Chemical reduction; Compressibility; Electrochemistry; Electrode materials; Electrolytes; High pressure; Lithium; Metal oxides; Molten salt electrolytes; non-centrosymmetric structure; Pressure; solid electrolyte; Solid electrolytes; Stability; Structural analysis; structure stability
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202401779

The Li3MX6 compounds (M=Sc, Y, In; X=Cl, Br) are known as promising ionic conductors due to their compatibility with typical metal oxide cathode materials. In this study, we have successfully synthesized γ‐Li3ScCl6 using high pressure for the first time in this family. Structural analysis revealed that the high‐pressure polymorph crystallizes in the polar and chiral space group P63mc with hexagonal close‐packing (hcp) of anions, unlike the ambient‐pressure α‐Li3ScCl6 and its spinel analog with cubic closed packing (ccp) of anions. Investigation of the known Li3MX6 family further revealed that the cation/anion radius ratio, rM/rX, is the factor that determines which anion sublattice is formed and that in γ‐Li3ScCl6, the difference in compressibility between Sc and Cl exceeds the ccp rM/rX threshold under pressure, enabling the ccp‐to‐hcp conversion. Electrochemical tests of γ‐Li3ScCl6 demonstrate improved electrochemical reduction stability. These findings open up new avenues and design principles for lithium solid electrolytes, enabling routes for materials exploration and tuning electrochemical stability without compositional changes or the use of coatings. A novel halide solid electrolyte, γ‐Li3ScCl6, is reported. The cation‐anion radius ratio is found to be a pivotal factor in determining whether the anion sublattice will form cubic close‐packed (ccp) and hexagonal close‐packed (hcp) lattices in the halide Li3MX6 family. Furthermore, γ‐Li3ScCl6 exhibits improved electrochemical reduction stability.