Comparison of Li3InxY(1−x)Cl6 Solid Electrolytes Synthesized by Mechanochemical and Water-Based Methods for All-Solid-State Batteries

Halide solid electrolytes (HSE) have shown remarkable stability against high-voltage cathodes. Some HSE, such as Li3InCl6 (LIC), can be readily synthesized via aqueous routes. Here, we expand the aqueous synthesis of LIC to include Y substitution, which has different hydration coordination strengths, to form Li3InxY1−xCl6 (LIYC, 0 ≤ x ≤1). This composition is intended to combine the high ionic conductivity of LIC with the superior stability of Li3YCl6 (LYC). We compared solution-synthesized products with those derived mechanochemically. We found that adding ammonium chloride in a 3:1 ratio to YCl3 + InCl3 produces a phase-pure product, with X-ray diffraction (XRD) revealing structure similarity for both routes. Through nuclear magnetic resonance (NMR) and impedance measurements, we evaluate how the synthesis method affects ionic transport, particularly regarding correlated motion. Despite lower initial grain boundary impedance in mechanochemical samples, full cells made from solution-synthesized samples show superior cycling performance. This work establishes a scalable aqueous synthesis route for LIYC that achieves properties comparable to traditional mechanochemical methods.