Recent Advances in Understanding the Capacitive Storage in Microporous Carbons

This paper presents a review of our recent work on capacitance of carbide-derived carbons (CDCs). Specific capacitance as high as 14 mu F cm(-2) or 160 F g(-1) was achieved using CDCs with tailored subnanometer pore size, which is significantly higher than 6 mu F cm(-2) or 100 F g(-1) for conventional activated carbons. Such high capacitance was obtained in several types of organic electrolytes with or without solvent. A maximum is obtained for the carbons with the mean pore size close to the bare ion size, ruling out the traditional point of view that mesoporosity is highly required for maximum capacitance. Surprisingly, carbons with subnanometer porosity exhibit high capacitance retention, since only a 10% loss is measured when 6 A g(-1) discharge is drawn. These findings show the importance of fitting the ion size with the mean pore size. The double layer theory falls short to explain such charge storage mechanisms at the nanometer scale; thus atomistic modelling is required to find out an alternative charge storage model.