Developing flexible capacitive synthetic fabric for wearable electronics

Abstract

In this study, polyester fabrics were metalized by electroless copper plating to become flexible metalized fabrics. PEO-based electrolytic material doped with different amount of LiClO₄ and different types of nanocarbons were solution casted on the fabric surface to form electrochemical double layer supercapacitors. The surface morphology, electrochemical properties, electrical performance and structural effects of these electrochemical systems were studied. In the experiment of PEO-based supercapacitors doped with different amount of LiClO₄, the copper-plated polyester fabrics were solution casted with pure PEO solution, and PEO solution doped with 1 g/L of LiClO₄ in different PEO:Li ratio (1000:1, 667:1, 500:1, 400:1, 333:1 and 100:1). The specific capacitance of sample casted with PEO:Li ratio of 100:1 was 33.56 nF/cm² at 40 Hz, which is nearly 18 times higher than that of the sample casted with pure PEO. Besides, the maximum current density of the sample casted with PEO:Li ratio of 100:1 obtained under the scan rate of 100 mV/s was 1.84 μA/cm², which was 10 times more than that of the sample casted with pure PEO. It was suggested that the presence of Li⁺ ions in PEO matrix could provide an enhancement of charge mobility in the electrolyte by providing sufficient ions to move between different active sites on the branches and backbones of the PEO matrix. Hence, the improvement of charge storage capability was then manifested. In the experiment of PEO-based supercapacitors doped with different types of nanocarbons, the copper-plated polyester fabrics were solution casted with four types of nanocarbons included single-walled carbon nanotubes (SW-CNT), double-walled carbon nanotubes (DW-CNT), multi-walled carbon nanotubes (MW-CNT) and mesoporous carbon nanopowders to form four different types of supercapacitors. Among four types of nanocarbons, DW-CNT gave the highest value of specific capacitance at 32.798 nF/cm², which was 17 times more than that of the sample casted with only pure PEO. On the side of maximum current density, 10.51 μA/cm² was recorded from the sample doped with DW-CNT, which was nearly 60 times higher than that of sample with only pure PEO at 40 Hz. For the experiment of various layer combinations, PEO-based supercapacitors doped with DW-CNT and Li⁺ ions under different layering combinations were fabricated and examined. The specific capacitance of sample with PEO:CNT active layers and PEO:Li spacer was 10.19 μF/cm², which was 5390 times more than that of the pure PEO sample. On the other hand, the maximum current density of sample with PEO:CNT:Li active layers and PEO:Li spacer was 49.75 μA/cm², which was 281 times than that of the pure PEO sample. Comparing to the samples doped with single dopant, it is no doubt that CNT and Li⁺ ions can enhance the charge storage capability of the electrochemical system, and improve the efficiency of current passing through the PEO matrix. Besides, it can be found that the charge storage capability of PEO-based supercapacitors doped with both CNT and Li⁺ ions were better than those samples have only doped either CNT or Li⁺ ions. By comparing all layering combinations, the sample with PEO and DW-CNT as active layers and PEO:Li as spacer gave the highest specific capacitance and highest number for charge-discharge cycles. It is suggested that the electrochemical system with PEO-based material can be enhanced by doping Li⁺ ions and DW-CNT separately to achieve a better performance instead of mixing both dopants together.