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.

Rechargeable magnesium batteries attract interest as advantageous energy-storage devices, but the application is being hampered by the deficiency of suitable cathodes. The traditional method to weaken the interaction between bivalent Mg 2+ cations and the cathode material is to increase the anion radius, but excessive expansion of the anion would lead to a decrease of the theoretical capacity and offset the performance improvement. Herein, a new strategy using a redox-active polyatomic anion is developed in terms of copper tetraselenophosphate (Cu 3 PSe 4 ) fabricated by the PSe 4 3− anion. The covalent P−Se bond facilitates the negative charge delocalization of the PSe 4 3− anion and weakens the interaction with Mg 2+ cations, which result in rapid solid-phase Mg 2+ diffusion kinetics. The PSe 43− anion also provides extra capacities by reversible valence state change of the P element. Cu 3 PSe 4 delivers a high Mg-storage capacity of 225 mAh g −1 at 50 mA g −1 and a superior rate performance of 62 mAh g −1 at 5000 mA g −1 , as well as a stable cyclability of 500 cycles. The redox-active polyatomic anion strategy herein opens a new avenue for the exploration of magnesium battery cathodes with a comprehensive consideration of kinetic performance and theoretical capacity.

The major difficulties for the development of flexible energy storage batteries lie in the scalable manufacture of high-performance flexible electrodes with bending tolerance. In the present study, large-scale CNT films...