Mechanochemical Synthesis and Structure of Lithium Tetrahaloaluminates, LiAlX4 (X = Cl, Br, I): A Family of Li-Ion Conducting Ternary Halides

Nicolás Flores-González; Nicolò Minafra; Georg Dewald; Hazel Reardon; Ronald I Smith; Stefan Adams; Wolfgang G Zeier; Duncan H Gregory

doi:10.1021/acsmaterialslett.1c00055

Mechanochemical Synthesis and Structure of Lithium Tetrahaloaluminates, LiAlX₄ (X = Cl, Br, I): A Family of Li-Ion Conducting Ternary Halides

ACS Mater Lett. 2021 May 3;3(5):652-657. doi: 10.1021/acsmaterialslett.1c00055. Epub 2021 Apr 20.

Authors

Nicolás Flores-González¹, Nicolò Minafra², Georg Dewald³, Hazel Reardon¹, Ronald I Smith⁴, Stefan Adams⁵, Wolfgang G Zeier², Duncan H Gregory¹

Affiliations

¹ School of Chemistry, University of Glasgow, Joseph Black Building, Glasgow G12 8QQ, U.K.
² Institute for Inorganic and Analytical Chemistry, University of Münster, Correnstrasse 39, 48149 Münster, Germany.
³ Institute of Physical Chemistry, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 17, D-35392 Giessen, Germany.
⁴ ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX, U.K.
⁵ Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, 117575, Singapore.

Abstract

State-of-the-art oxides and sulfides with high Li-ion conductivity and good electrochemical stability are among the most promising candidates for solid-state electrolytes in secondary batteries. Yet emerging halides offer promising alternatives because of their intrinsic low Li⁺ migration energy barriers, high electrochemical oxidative stability, and beneficial mechanical properties. Mechanochemical synthesis has enabled the characterization of LiAlX₄ compounds to be extended and the iodide, LiAlI₄, to be synthesized for the first time (monoclinic P2₁/c, Z = 4; a = 8.0846(1) Å; b = 7.4369(1) Å; c = 14.8890(2) Å; β = 93.0457(8)°). Of the tetrahaloaluminates, LiAlBr₄ exhibited the highest ionic conductivity at room temperature (0.033 mS cm^-1), while LiAlCl₄ showed a conductivity of 0.17 mS cm^-1 at 333 K, coupled with the highest thermal and oxidative stability. Modeling of the diffusion pathways suggests that the Li-ion transport mechanism in each tetrahaloaluminate is closely related and mediated by both halide polarizability and concerted complex anion motions.