Non-porous Carbon for a High Energy Density Electric Double Layer Capacitor

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Abstract
Apparently non-porous activated carbon with a specific surface area less than 100 m2/g(BET) prepared from calcined carbon of petroleum coke is studied as the polarized electrode for an Electric Double Layer Capacitor(EDLC). The non-porous carbon makes negligibly small electric double layer when it is dipped into an electrolyte solution in the beginning. During the initial charging process, however, "solvent co-intercalation of ions" builds double layers in the positive and the negative electrodes, and during the discharging process, the excess ions go out, while the opposite ions come in, to maintain the double layers electrically neutral. After that, the electrodes behave like conventional activated porous carbon electrodes with an extra high dense capacitance. The observed phenomenon is discussed from the viewpoints of the inter-layer distance in graphite-like structure, the molecular volume of solvent for electrolyte, the residual functional groups such as active oxidized hydrogen observed by NMR, and of the elimination method for the residual active oxidized hydrogen by heat treatment in H2 atmosphere, as well as the preparation method for source carbon.