Particles of active electrode material are made by blending and fibrillizing (i.e., fibrillating) a mixture of activated carbon, conductive carbon, and fibrillizable binder. In selected embodiments, chloride level in the activated carbon is relatively low, a small amount of conductive carbon with low impurity levels and high conductivity is used, and the binder is inert. For example, chloride content of the activated carbon is below 50 ppm, and total impurities in the conductive carbon are below 120 ppm. The mixture may include about 10% of PTFE and 0.5% or less of conductive carbon. Blending and fibrillization may be performed without solvents. The fibrillized particles are dried, blended again to reduce clumping, and used to make active electrode material film. The film is attached to a current collector to obtain an electrode for use in various electrical devices, including double layer capacitors. The electrode increases breakdown voltage of the capacitor electrolyte.