Dipentamethylene thiuram tetrasulfide-based cathodes for rechargeable magnesium batteries

Abstract

Rechargeable Mg batteries (RMBs) represent a possible route for low-cost energy storage applications, but they are lacking a satisfactory cathode material. Conventional sulfur (S8) cathodes have shown promise, yet they suffer from poor cycling stability and low reversibility. Here, we investigate the organosulfur compound dipentamethylene thiuram tetrasulfide (PMTT) as the source of redox active sulfur. In its pristine form with carbon black as a conductive additive, an initial discharge capacity of 295 mA h g–1 is reported, which is one of the highest capacities reported for an organosulfur compound for RMBs. A reaction mechanism is proposed, supported by density functional theory calculations. Through a mild heat treatment, a PMTT-derived sulfur/mesoporous carbon composite is investigated. PMTT’s unique chemistry and the resulting molecular mixture of active and inactive components enable a high cycling stability (76% capacity retention in the 100th cycle after one formation cycle) and excellent rate performance (185 mA h g–1 at 500 mA g–1) for an RMB. The PMTT-derived sulfur/mesoporous carbon composite outperforms reference cells with a conventional S8 composite and, combining with further electrolyte development, may open up for cost-competitive RMBs.