Large-scale production of 18650 cylindrical supercapacitors: Effects of separators, electrode thickness, electrolyte additives, and testing protocols

Although supercapcitors have been widely studied, large-scale 18650 cylindrical supercapacitor cells have been rarely investigated and reported. Here, we investigated the effects of polymer separators, electrode thickness, electrolyte additives, testing protocols, reproducibility, and stability of the supercapacitors at the large-scale pilot plant. The supercapacitor cells with polyethylene (PE) and Al2O3-coated PE separators are good at low and high specific currents, respectively. The Al2O3-coated PE exhibits better stability than the one with the PE separator. The supercapacitor with a thickness of 250 μm has a cell capacitance of over 120 F from 100 to 1000 mA, which is higher than that of the other cells studied in this work. Also, the cell capacitances of supercapacitors can be enhanced by having redox mediator additives. 25 mM hydroquinone and ferrocene methanol are the optimized concentrations. We also found that the cell capacitance and equivalent series resistance of the supercapacitors are sensitive to the testing protocol, for which the highest capacitance was observed using the IEC62391-1 standard method, followed by the Maxwell method and conventional galvanostatic charge discharge method without dwell time. High reproducibility and stability of the as-fabricated supercapacitors in this work may lead to the further development of practical large-scale supercapcitors in the future.