Local and Long-Range Li+ Diffusion in Li3InCl6: Impact of Preparation Method on Ion Dynamics

Abstract

Ternary halide compounds, particularly Li₃InCl₆ (LIC), have gained significant attention as solid-state electrolytes for Li-ion batteries due to their high conductivity. The local defect structure and overall morphology of a sample often dictate its electrical properties. To investigate the influence of preparation methods on both local and long-range Li⁺ ion dynamics, we synthesized LIC via dissolution–precipitation and mechanochemical approaches, both yielding high conductivities (approximately 0.5 mS cm^–1 at 20 °C). At around 330 K, the diffusion coefficient D is approximately 9 × 10^–12 m²/s. We hypothesize that the fast Li⁺ transport in defect-poor crystalline LIC is linked to its layered structure, facilitating rapid low-dimensional (2D) diffusion. This hypothesis is strongly supported by frequency-dependent nuclear magnetic resonance (NMR) spin–lattice relaxation (SLR) measurements of the ⁷Li nuclei. Despite both samples showing high conductivity, the mechanochemically synthesized sample exhibits distinct NMR relaxation behavior, particularly at low temperatures. We attribute this to motional correlation effects, which lead to anomalously low activation energies in the defect-rich mechanosynthesized sample. As a result, local hopping is enhanced, potentially explaining the deviation of NMR SLR rates reported in the literature.