Flexible thin film electric double layer capacitors (EDLCs) are printed with silver paste and ink for a current collector and their electrochemical characteristics are characterized to apply for low cost solution-based printed electronic process. In addition, the durability and flexibility of the printed EDLC is discussed. The EDLCs are fabricated using screen printing, spray and slot die coating process. The electrochemical properties of the half cell of the printed EDLC are evaluated by using cyclic voltammetry in 1M sodium sulfate (Na2SO4)under the voltage application of ranging from ?0.5 V to 0.4 V.
In the screen printed EDLC, the highest specific capacitances of 63.27 F/g and 31.16 F/g are obtained at scan rate of 10 mV/s and 500 mV/s, respectively. In the spray coating process, the specific capacitances of 103.8 F/g and 76.8 F/g are obtained. In the slot die coating process, the specific capacitances on the electrode area are compared because the mass of the electrode can not be measured exactly. The specific capacitance of 38 mF/cm2 and 17 mF/cm2 are obtained.
To analyze the current response to AC voltage bias, the impedance is also examined. The current collector fabricated by the silver paste and ink shows better impedance characteristics than that fabricated by the stainless steel current collector. Also, equivalent series resistance (ESR), charge transfer resistance, and Warburg impedance of the half cell are lower than those measured from the SUS and Ni current collectors.
In addition, bending test has been performed to determine the flexibility of the printed EDLC. Crack was observed after the bending test but the electrical resistance was kept constant. The specific capacitance after the bending test of 5000 times was reduced by 30 %. However, this can be improved by optimizing the electrode material, thickness, and electrolyte.
For future study, the optimization of binder and additive materials in the electrode paste and ink, the synthesis of the electrolyte paste, the evaluation of the full cell with paste electrolyte and the integration of other energy storage devices will be examined.