Li3YCl6 and Li3InCl6 solid electrolytes (SEs) were synthesized via intermittent high energy ball milling as previously reported . In summary, LiCl (Sigma-Aldrich) and YCl3 (Alfa Aesar), or LiCl and InCl3 (Alfa Aesar) were hand mixed using a mortar with a 3:1 stoichiometry. The mixture was then milled intermittently for 3 hours. In the case of Li3YCl6, a 10% molar excess of YCl3 was added to account for loss of material due to strong adhesion to the milling reactor. Material manipulation and synthesis was carried out in an Ar glovebox (O2 and H2O, <0.1 ppm). Li6PS5Cl (NEI Corporation) and Li1.48Al0.48Ge1.52(PO4)3 (MSE Supplies)