Metal-Free Hybrid Capacitor Using Intercalation of 1-Butyl-3-Methylimidazolium Cations

The hybrid capacitor with an activated carbon positive electrode, a carbon negative electrode, and 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) electrolyte was constructed and investigated as a high-performance hybrid capacitor. Three different carbon materials, Ketjen Black (KB), acetylene black, and graphite, were employed as negative electrode material. The insertion/extraction reaction of BMI+ cations into the carbon negative electrodes was suggested from the strength change of X-ray diffraction peaks. The KB negative electrode showed the highest charge-discharge cycle performance due to the multiple effect of the large surface area and small graphitic crystals, which is flexible to stand for the large volumetric expansion with BMI+ cation insertion reaction.