Electrochemical double layer capacitor using an activated carbon electrode with gel electrolyte binder

An electric double layer capacitor (EDLC) was prepared with an activated carbon powder electrode witch poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) based gel electrolyte. Ethylene carbonate (EC) and propylene carbonate (PC) were used as plasticizer and tetraethylammonium tetrafluoroborate (TEABF₄) was used as the supporting electrolyte. An optimized gel electrolyte of PVdF-HFP/PC/EC/TEABF₄ = 23/31/35/11 mass ratio exhibited high ionic conductivity of 5×10^-3 S cm^-1 high electrode capacitance, and good mechanical strength. An electrode consisting of activated carbon (AC) with the gel electrolyte as the binder (AC/PVdF-HFP based gel, 7/3 mass ratio) showed a higher specific capacitance and a lower ion diffusion resistance within the electrode than a carbon electrode, prepared with PVdF-HFP binder without plasticizer. This suggests that an electrode mixed with the gel electrolyte has a lower ion diffusion resistance inside the electrode. The highest specific capacitance of 123 F g^-1 was achieved with an electrode containing AC with a specific surface area of 2500 m² g^-1. A coin-type EDLC cell with optimized components showed excellent cycleability exceeding 10⁴ cycles with ca. 100% coulombic efficiency achieved when charging and discharging was repeated between 1.0 and 2.5 V at 1.66 mA cm^-2.