Lithium-Ion Transport in Nanocrystalline Spinel-Type Li[In_xLi_y]Br₄ as Seen by Conductivity Spectroscopy and NMR

Currently, a variety of solid Li⁺ conductors are being discussed that could potentially serve as electrolytes in all-solid-state Li-ion batteries and batteries using metallic Li as the anode. Besides oxides, sulfides and thioposphates, and also halogenides, such as Li₃YBr₆, belong to the group of such promising materials. Here, we report on the mechanosynthesis of ternary, nanocrystalline (defect-rich) Li[In_xLi_y]Br₄, which crystallizes with a spinel structure. We took advantage of a soft mechanochemical synthesis route that overcomes the limitations of classical solid-state routes, which usually require high temperatures to prepare the product. X-ray powder diffraction, combined with Rietveld analysis, was used to collect initial information about the crystal structure; it turned out that the lithium indium bromide prepared adopts cubic symmetry ((Formula presented.)). The overall and electronic conductivity were examined via broadband conductivity spectroscopy and electrical polarization measurements. While electric modulus spectroscopy yielded information on long-range ion transport, ⁷Li nuclear magnetic resonance (NMR) spin-lattice relaxation measurements revealed rapid, localized ionic hopping processes in the ternary bromide. Finally, we studied the influence of thermal treatment on overall conductivity, as the indium bromide might find applications in cells that are operated at high temperatures (330 K and above).