context: Intermetallic Mg2Sn alloyed with extra Mg was presented as a new high-performance anode for MIBs. The 3Mg/Mg2Sn was composed of c-Mg, a-Mg, and Mg2Sn, and showed excellent electrochemical performance when cycled in Mg(HMDS)2:MgCl2/THF. During the 1st de-magnesiation, 3Mg/Mg2Sn first dissolved Mg2+ from c-Mg, which was then followed by the complete conversion of Mg2Sn to Sn with a partial release of a-Mg. The irreversible dissolution of c-Mg facilitated the reversible de-magnesiation/magnesiation in Mg2Sn and a-Mg, and allowed 3Mg/Mg2Sn to demonstrate unprecedented electrochemical properties. Thanks to the high surface area and pore volume ascribed to the irreversible dissolution of c-Mg, the 3Mg/Mg2Sn anode delivered reversible capacities of 805 and 430 mA h g−1 at 100 and 1500 mA g−1, respectively, with reasonable cycling stability. De-magnesiated 3Mg/Mg2Sn also showed similar electrochemical performance in other conventional electrolyte systems (Mg(TFSI)2:MgCl2/diglyme and Mg(TFSI)2/acetonitrile). In addition to the beneficial role of c-Mg with respect to the electrochemical properties of 3Mg/Mg2Sn in a half-cell configuration, irreversibly dissolved Mg2+ ions could ideally balance the Mg2+ ions trapped in a Mo6S8 cathode in a full-cell.
answer: Mo6S8 