Copolymers of aniline and 2-aminoterephthalic acid as a novel cathode material for hybrid supercapacitors

Abstract

Hybrid supercapacitors (HSCs) have attracted increasing attention as they can deliver energy densities sufficient for batteries and power densities of supercapacitors. The exploration of novel types of capacitor cathode materials with higher energy densities than conventional active carbons is in demand. Here, a series of copolymers of aniline (ANI) and 2-aminoterephthalic acid (ATA) were synthesized by the chemical oxidation polymerization at different molar ratios of monomers (ANI/ATA). The morphologies of the products varied from nanoparticles to nanorods and then returned to granular nanoparticles with the increase of the ATA amount. The copolymer nanorods synthesized at an ANI/ATA ratio of 8 : 2 exhibited a high specific capacitance (198 F g⁻¹ at the current density of 20 mA g⁻¹), excellent rate capability (the maximum current density of 50 A g⁻¹), and excellent cycling stability (capacitance retention of 78.5% after 1000 cycles at 2 A g⁻¹). The appropriate amount of carboxyl groups enabled the delocalization of charge along the polymer backbone and the one-dimensional nanostructures facilitated the anion diffusion to the electrode, which enhanced the electrochemical activity of the copolymer significantly. The excellent rate capability as well as the anion doping/dedoping energy storage mechanism impelled the copolymer to be employed as the supercapacitor cathode of HSCs. The energy density of 153.9 W h kg⁻¹ and the power density of 3011.5 W kg⁻¹ of HSCs are obtained with commercial meso-carbon microbeads (MCMBs) and Li₄Ti₅O₁₂ (LTO) as anode materials, respectively.