Poly(2,6-anthraquinonyl disulfide) as a high-capacity and high-power cathode for rechargeable magnesium batteries: extra capacity provided by the disulfide group

Abstract

Rechargeable Mg batteries (RMBs) are promising devices for large-scale energy-storage applications, but the lack of cathode materials is hindering their development. Conjugated organic polymers provide more selection by breaking the limit of the inorganic crystal lattice. Herein, a series of poly(2,6-anthraquinonyl polysulfide)s with different sulfur chains (AQ units are connected with polysulfides, 26PAQS_x, x = 1, 1.4, 1.9 and 2.2) are synthesized and investigated as RMB cathodes. 26PAQS_1.9 provides a high capacity of 270 mA h g⁻¹ at 50 mA g⁻¹ exceeding that of the two-electron carbonyl enolization, with the extra capacity being delivered by formation of the SO/S–O bond between the enolized carbonyl (C–O⁻) and the S–S unit. The sulfur chain of 26PAQS_x is stable when 1.0 < x < 2.0, and 26PAQS_1.9 exhibits a stable cycling for 500 cycles at 2C. The formation of the SO/S–O bond is highly reversible and fast, and 26PAQS_1.9 shows a good rate capability of 86 mA h g⁻¹ at 5.0 A g⁻¹ (about 20C). The new mechanism revealed herein would inspire new insight for the design of conjugated carbonyl polymers as RMB cathodes.