The XRD patterns obtained on the Mixed samples exhibit significantly broader reflections than those obtained on the pure powders (see Figure ). This broadening is at least in part due to a loss of crystallinity during the grinding step, as indicated by the broadening of the peaks observed in the XRD patterns obtained on each of the pure compounds (Li 3 InCl 6 and Li 3 PO 4 ) after a similar grinding procedure (see Figure ). Upon heat treatment of the Mixed 300 °C sample, the reflections corresponding to the Li 3 InCl 6 13 and Li 3 PO 4 phases sharpen, suggesting that some of the crystallinity is regained, but no new phases emerge (see Figure ). The good stability of this electrolyte pairing is further confirmed by Li and 31 P ssNMR. The spectra collected on the pure Li 3 InCl 6 and Li 3 PO 4 powder samples remain relatively unchanged after mixing at 25 °C, and even after a 300 °C heat treatment, as shown in Figure