Fabrication of textiles based capacitive device

Abstract

Metallized polyethylene terephthalate (PET) fabrics were prepared by wet chemical methods. Electroless nickel plating was firstly deposited on the fabric and then electroplating of copper or gold were coated on top of the nickel layer. A simple electrostatic capacitor was fabricated by using the metallized PET fabric as the base electrode. Polyvinyl alcohol (PVA) and cuprous oxide (Cu₂O) were used as the dielectric layer and cover with a layer of Poly(3,4-ethylenedioxythiophene) (PEDOT) as the top electrode. Their structural and electrical properties were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), Raman spectrometer and impedance analyzer. On the basis of the measurement, the capacitive behaviors of PVA electrostatic capacitor in different thickness have been revealed. Furthermore, a high quality Cu₂O films have been successfully grown on the metallized fabric using potentiostatic cathodic deposition technique. However, the cuprous oxide layer was still conductive due to defects and cracks which were formed on the surface, resulting in short circuit of the capacitor. Apart from simple electrostatic capacitors, solid state flexible supercapacitors (SC) were also fabricated on the metallized fabrics. Two different types of metal layer were used as current collector for the SC. Multi-walled carbon nanotubes (MWCNT) were employed as a large surface area electrode. The MWCNT were coated on the metallized fabrics using a simple dip-and-dry method. PVA with phosphoric acid were used as both the separator and electrolyte to bind the electrodes together. In this project, three different types of SC, namely, CNT/PET, CNT/Cu/PET and CNT/Au/PET SCs were fabricated. The capacitive performances of these SCs were characterized by an electrochemical station. Cyclic voltammetry, galvanostatic charge and discharge curve, cyclic stability and bending performance were investigated. The results showed that the additional current collector layer greatly improved the capacitive performance of the SCs. In order to further improve the energy storage capacity, two pseudocapacitance materials, Polyaniline (PANI) and Manganese dioxide (MnO₂) fabricated by cyclic voltammetric deposition and hydrothermal method respectively, were coated on top of the CNT/Au/PET SCs. The results demonstrated that the capacitance performance of the SC by adding PANI as the pseudocapacitance material was enhanced significantly; while the flexibility and durability of the SC were maintained. On the basis of our results, a portable, wearable and flexible solid state supercapacitor with high energy storage capacity value was fabricated successfully.