This process was repeated until the supernatant after centrifuging was not clear, indicating dispersed particles. This supernatant was then kept as the sample while the sediment was discarded. This allows to separate contaminants formed by abrasion of the ball milling jar and balls (see Figure S 1). For characterization and determination of the mass loading of the dispersion, 10 ml were dried in a petri dish at 100 °C and the dry powder was weighed, used for XRD and EIS to determine purity, crystallinity and conductivity.