Replacing the flammable, liquid electrolyte with ion-conducting solids can lead to advances in the safety of high-energy-density batteries . Many solid electrolyte materials with room-temperature ionic conductivity of mS/cm have been developed in recent years. These include the families of the oxides (e.g. garnets ), phosphates (e.g. NaSICON ), sulfides (e.g. argyrodites Li6PS5X (X=Cl, Br, I 4 ), Li10GeP2S12-type ) or hydrides (e.g. borohydrides/closoboranes ). For solid-electrolytes to become a safer and feasible alternative, all-solid-state batteries need to be able to compete with liquid-electrolyte-based batteries both in terms of energy density and charging rates. Therefore, the amount of solid electrolyte has to be minimized both in the separator as well as in the cathode composite, without compromising on the internal resistance and electrode loading. This necessitates a solid electrolyte with a high ionic conductivity. The Li-ion conducting solid electrolytes with the highest conductivity so far are sulfide based, that can reach 10 -2 S/cm .