Tailor-made organic polymers towards high voltage aqueous ammonium/potassium-ion asymmetric supercapacitors

Engineering the polymers with electrochemical functionality is a topic of contemporary research towards developing lightweight and low-cost energy storage devices. In this study, a pair of organic polymers is successfully synthesized by coupling the redox-active moieties such as perylenetetracarboxylic diimide together through monosulfide and disulfide groups. The introduction of two different sulfide linkages in the polymeric chain yields two distinct morphologies due to the different structures of sulfide linkage groups. These polymers are tested as the electrode materials for supercapacitors in two different water-in-salt electrolytes. The interactions of K+/NH4+ ions with polymer electrodes are separately studied in 27 m potassium acetate (KAc) and 27 m ammonium acetate electrolytes. The polymer with monosulfide moieties shows better specific capacitance, rate capability, and cyclic stability in 27 m KAc compared to the one with disulfide moieties. In order to demonstrate the practical application, the asymmetric supercapacitors are fabricated by using the polymer and activated carbon as the negative and positive electrodes, respectively. The device with 27 m KAc delivers an energy density of 29.9 Wh kg−1 at the power density of 850 W kg−1 and exhibits 79% of the initial capacitance after 10,000 charge-discharge cycles at the current density of 2 A g−1.