Polyanthraquinonyl sulfide cathodes for rechargeable magnesium batteries: Effect of structure on the performance

Rechargeable magnesium batteries (RMBs) attract special interests as a low-cost and reliable energy-storage technology, but the development is hindered by the low capacities and sluggish Mg2+ diffusion kinetics of the traditional inorganic cathode materials. Organic polymers break the hindrance of inorganic lattice and deliver plenty of candidates for RMB cathodes with the flexible and designable frameworks. Herein, three organic polyanthraquinonyl sulfides (PAQSs) are fabricated and investigated comparatively as RMB cathodes to reveal the effect of structure on the electrochemical magnesium-storage performance. It is demonstrated that the ca-pacity decay is primarily owing to the dissolution of the discharge products (magnesiation state) in the elec-trolyte. The degree of polymerization is an important factor for the cycling stability. Prominently, poly(2,6-anthraquinonyl sulfide) shows an outstanding comprehensive performance, providing a high capacity (145 mAh g-1 at 50 mA g-1), an outstanding rate capability (74 mAh/g at 10C) and an excellent cyclability (99 % capacity retained after 1000 cycles at 5C). Significantly, poly(2,6-anthraquinonyl sulfide) store Mg2+ rather than MgCl+, and exhibits a considerable specific energy density of 185 Wh kg-1. The present work would assist the rational design of advanced organic RMB electrode materials, and highlights the advantages of organic polymers based on enolization chemistry for high-performance magnesium-storage.