Progress in new sustainable technologies depends on the development of battery materials, specifically on safer, low-cost, and higher energy density batteries. One new type of materials are the halide solid electrolytes (HSEs), which have been shown to exhibit high ionic conductivity, deformability, and oxidative stability. Here, the synthesis of Li₃InCl₆ (LIC) HSEs by ball-milling followed by dry room annealing is investigated. Crystal structure, particle size, and ionic conductivity are analyzed using a combination of X-ray diffraction, transmission electron microscopy, and electrochemical impedance spectroscopy. Dry room annealing increases the presence of impurities in the sample but also increases the Li⁺ ionic conductivity up to 1.03 mS cm⁻¹. Additional pulsed-field gradient and relaxation time NMR measurements were performed to understand the lithium diffusion in the LIC samples. Two-dimensional diffusion – T₂ relaxation correlation and T₂ relaxation exchange measurements showed that there are multiple unique Li atomic motion sites, which are correlated to different rates of diffusive, micrometer-scale motion. This work outlines a simple solid-state synthesis approach and a novel strategy for designing advanced materials, understanding the ionic conduction, as well as the challenges in scalable wet processing of halide-based cathode sheets for solid-state battery applications.