Improving thin film flexible supercapacitor electrode properties using ion-track technology

A novel self-supporting carbon thin film flexible supercapacitor electrode with high volumetric and areal capacitance was developed. The increase in capacitance performance is achieved by introducing channels across the carbon thin film using ion-track technology. In the first step of the electrode synthesis, latent tracks are inscribed in the starting polyimide (Kapton) foil by irradiation with 253 MeV Kr ions. Next, macropores in the form of cylindrical channels are formed by selective chemical etching with NaOCl along the ion tracks, creating ion-track polymer. With subsequent carbonization and activation of the ion-track polymer, activated ion-track carbon is produced. A range of samples are obtained by varying the chemical etching time of the irradiated polymer. In addition to channel formation the chemical etching time influences the composition of surface functional groups. The best results are obtained by chemical etching for 40 min, the thickness of the sample is 21 µm with channel density 2.4 × 10⁶ cm⁻² and average channel diameter 430 nm. Beside cylindrical macro channels this material is mainly microporous with 0.62 nm pore diameter and shows the highest areal (494 mF/cm²), volumetric (224 F/cm³) and gravimetric (178 F/g) capacitance. As a consequence of channel formation, the rate capability of the supercapacitor was also increased.