Poly(1,5-diaminoanthraquinone) as a High-Capacity Bipolar Cathode for Rechargeable Magnesium Batteries

Rechargeable Mg batteries have the advantages of abundant reserves and high safety, but suitable inorganic cathodes are quite limited. Organic polymers break the hindrance of the inorganic Mg-storage crystal lattice and provide more selections, but the reports on organic rechargeable Mg battery cathodes are relatively few. Herein, high-capacity bipolar organic cathodes are developed for rechargeable Mg batteries. Poly(1,5-diaminoanthraquinone) with double polyaniline chains is used as a bipolar cathode. The carbonyl and amino groups are employed as the N-doping and P-doping centers, respectively, and the conjugated anthraquinone unit delocalizes the charge density change during the redox reactions. Considering the mass of Mg salt, the poly(1,5-diaminoanthraquinone) cathode provides a high corrected capacity of 267 mA h g–1 (non-corrected capacities of 297 mA h g–1) for bipolar reactions. Moreover, compared with the single-chained poly(1-aminoanthraquinone) (44% capacity maintained after 140 cycles), the double-chained poly(1,5-diaminoanthraquinone) shows a much better N-doping cycleability (97% capacity maintained after 300 cycles), as the double polyaniline chains enhance the structure stability during the Mg-storage reaction. The present study demonstrates the importance of a large conjugated double-chain structure to enhance the Mg-storage performance of organic polymers. It is also imagined that the bipolar organic materials with both of N- and P-dopings are a highly promising strategy for development of high-capacity organic Mg battery cathodes.