Bimodal porous carbon as a negative electrode material for lithium-ion capacitors

Bimodal porous carbons consisting of interconnected macropores and spherical mesopores, were prepared by colloidal crystal templating method. The template was prepared by evaporation process of suspensions containing monodisperse poly[styrene-(co-2-hydroxyethyl methacrylate)] (PSHEMA) latex and colloidal silica in water. The carbonization of PSHEMA at 1000 degrees C under inert atmosphere provided very thin carbon layer on the colloidal silica in the template, and the macropore corresponding to the PSHEMA particle size were formed simultaneously. After this procedure, bimodal porous carbons were obtained by removing the silica particles with hydrofluoric acid. Three kinds of bimodal porous carbons were prepared using PSHEMA latex of 450 nm and colloidal silica with three different average diameters of 10 similar to 20 nm, 40 similar to 50 nm, and 70 similar to 100 nm, respectively. Bimodal porous structure was observed with a field emission-scanning electron microscope. Nitrogen adsorption/desorption measurements revealed that the prepared samples involved macropore and mesopore with small amount of micropore. The bimodal porous carbons were electrochemically evaluated as a negative electrode of lithium-ion capacitor in ethylene carbonate and diethyl carbonate containing 1 mol dm(-3) LiClO4. The bimodal porous carbon prepared using silica of 10 similar to 20 nm showed a large capacitance of 360 F g(-1) at a high current density of 7.4 A g(-1).