Polymerization increasing the capacitive charge storage for better rate performance: A case study of electrodes in aqueous sodium-ion capacitors

Organic molecules and polymers have been widely used in aqueous sodium-ion capacitors. However, the difference in the reaction kinetics of the electroactive polymer and its monomer has been overlooked. In this study, a comparative study of the sodium-ion storage performance and the reaction kinetics is performed. The poly(perylene diimides) which is named EDP exhibits decreased crystallinity, smaller particle size with a rough surface, higher specific capacitance, lower reduction potential, better cycling stability, and rate performance, compared with its monomer 3,4,9,10-perylenetetracarboxylic dianhydride. The reaction kinetics study proves that the EDP shows faster sodium-ion diffusion and more capacitive charge storage, which are responsible for the high-rate capability.