Capacitance and equivalent series resistance (ESR) optimization using the Taguchi technique for EDLC´s

Optimizing the capacitance and equivalent series resistance (ESR) has been a key issue in the fabrication of Electric double layer capacitor (EDLC). The typical method used for identifying optimal parameters in the manufacturing process reported in the literature relies on “trial-and-error” method (optimizing one factor at a time), which is ineffective, inaccurate, time consuming and not systematic. Therefore, in this work, the Taguchi technique was applied to identify the most the significant process variables in order to optimize (maximize) capacitance and (minimize) ESR of the supercapacitor device. Design of experiments (DOE) with this method allows multiple parameters to be evaluated with a very small number of experiments. With the use of the Taguchi methodology in this paper the number of experiments can be reduced for three factors at three levels from (3³) = 27 experiments to only 9 set of experiments. In terms of the materials, the core supercapacitor materials that have been used in the present study is based on activated carbon (AC) as the active material, carbon black (CB) as the conducting agent and PVDF polymer as the binder material. A total of nine experiments were conducted, where the percentage composition of PVDF and CB were varied for different mixing times in order to find the most significant process parameter affecting the capacitance and the ESR. 1M lithium perchlorate (LiClO₄) in acetonitrile was used as the electrolyte. Button shape supercapacitors with a diameter of 13mm have been produced for the present study. The cell capacitance was found to range from 24.91 - 51.23mF, depending on the exact parameters used in the fabrication process. The capacitive properties of the fabricated cells were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and charge-discharge measurements using an Autolab (PGSTAT302N) potentiostat. The results indicated that binder percentage and mi- - xing time has greater effect on the capacitance, whereas for the ESR, PVDF and carbon black percentages were found to be more significant.