 electrons, and each such elementary charge needs a minimum space, a significant fraction of the electrode surface is not available for storage because the hollow spaces are not compatible with the charge's requirements.With a nanotube electrode the spaces may be tailored to size—few too large or too small—and consequently the capacity should be increased considerably.A 40-F supercapacitor with a maximum voltage of 3.5 V that employed forest-grown SWNTs that are binder- and additive-free achieved an energy density of 15.6 Wh kg−1 and a power density of 37 kW kg−1.