The Chevrel phase (CP) is a well known material with high ion mobility. The general formula for a Chevrel phase is Mo 6 T 8 (T=S, Se or Te) with sulfur being the most used cage material. In its structure a nearly cubic sulfur cage holds an octahedral molybdenum cluster forming its unique crystal structure, as depicted in Figure . The CP cluster structure creates cavities and channels between the blocks within the crystal lattice and are classified as 3a, 3b, and 9d according to crystallographic symmetry. Sites 3a and 9d can be occupied by cations functioning as charge carriers, making them interesting candidates for potential applications in solid-state ionic conductors while sites 3b are unfavorable for cation storage due to the strong electrostatic repulsion with the face-sharing Mo atoms. An important factor for all solid-state ionic conductors is the quick delocalization inside the material, which is directly related to cations spacing and crucial for the cation mobility. In the CP this is achieved by the two intercalation sites at 3a and 9d. The first is the so-called inner ring site, which consists of six energetically equal sites that form a highly symmetric ring around the 3a position. The 3a position lies in a cavity which is coordinated with eight sulfur atoms, each being the corner of one CP cluster. The nearly degenerate nature of these positions, with a barrier of approximately 0.1 eV, 154 makes them favorable for accommodating a single Mg cation within the CP bulk. From there it can diffuse in all three lattice directions by passing through the channel 9d. About 0.5 Å away from the 9b site in the channel are the two outer ring sites. Upon occupying all inner ring sites with one cation each, the outer ring sites can accommodate an additional Mg cation per CP cluster. The CP can take up to 4 electrons until its valence band is filled and the structure transforms from a metal-like material to a semiconductor, making it possible to insert up to four monovalent cations. Upon intercalation of divalent Mg, the CP undergoes a two-step charge redistribution process, which is particularly fast, as X-ray photoemission spectroscopy experiments have revealed. The first electron is taken up by the sulfur cage, while the second one then gets transferred on the octahedral Mo-cluster. The CP was shown by Today it is mainly used as a cathode in magnesium batteries as well as for other multivalent charge carriers such as Zn 2+ . It is named after the French scientist J. R. Chevrel, who first discovered it in 1973. Using the CP as a cathode material overcomes the challenges of sluggish Mg ion insertion on the cathode side and the low reversibility of the process, which are commonly encountered issues with multivalent ions. This is attributed to the strong bonds they typically form with most cathode materials. 167