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 53C). Reversible four-electron redox with cationic-anionic contributions results in a specific discharge capacity of 155 mAh g -1 at the high current density of 1000 mA g -1 . Even at 4000 mA g -1 , it still delivers >70 mAh g -1 after 500 cycles, corresponding to an energy density of >92 Wh kg -1 at a high power of >5100 W kg -1 . The ability to provide such high-rate performance and long-life opens the way to the development of practical cathodes for multivalent metal batteries.