Study of fabric knitted using Ag-coated filaments to form stretchable electrodes for use in energy storage applications

Stretchable and flexible electrodes are desirable for use in mobile and wearable devices. When one surface of a fabric is non-conductive and the other surface is electrochemically active, such a fabric could potentially be used as an electrode in an electrochemical application without a separator because the non-conductive surface would prevent short circuits between the electrodes. In this study, a stretchable fabric with a conductive surface that has been knitted using Ag-coated filaments was cycled in aqueous (alkaline, acidic, and neutral) and non-aqueous (ionic liquid) electrolytes to study their electrochemical behaviors for their usability as energy storage devices. After study via cyclic voltammetry, KOH solution was selected as the most appropriate electrolyte among the four considered because the fabric showed stable oxidation and reduction peaks in this electrolyte after repetitive cycling. The Ag-based fabric electrode was also found to evolve (became stable) in this electrolyte. Electrochemical (cyclic voltammogram) and non-electrochemical (X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscopy) characterization of the electrode were carried out. The cycling of stretchable fabric was stopped at the oxidized and reduced potential in KOH electrolyte in order to characterize the crystalline, morphological, and compositional structure of the electrode as dependent on the applied potential. The capacitances of the electrode remained similar when the timescale was increased 40-fold, indicating that the electrode has a high power density. The reaction between the fabric and OH− electrolyte was found to proceed as a 'mixture' of a surface- and a diffusion-controlled mechanism. The areal and specific capacitances of the electrode were found to be 46 mF cm−2 and 36 F g−1, respectively. The stretchable fabric with Ag-coated filaments could potentially be used as an electrode in a hydroxide-based electrolyte for stretchable and flexible energy storage devices.