A Self-Conditioned Metalloporphyrin as a Highly Stable Cathode for Fast Rechargeable Magnesium Batteries.

Development of practical rechargeable Mg batteries (RMBs) is impeded by their limited cycle life and rate performance of cathodes. As demonstrated herein, a copper-porphyrin with meso-functionalized ethynyl groups is capable of reversible two- and four-electron storage at an extremely fast rate (tested up to 53 C). The reversible four-electron redox process with cationic-anionic contributions resulted in a specific discharge capacity of 155 mAh g at the high current density of 1000 mA g . Even at 4000 mA g , it still delivered >70 mAh g after 500 cycles, corresponding to an energy density of >92 Wh kg at a high power of >5100 W kg . The ability to provide such high-rate performance and long-life opens the way to the development of practical cathodes for multivalent metal batteries.