Superior Capacity in Electric Double-Layer Capacitors Employing Three-Dimensional Titanium Foam Electrodes

In this study, Ti foams with 80 to 85 pct porosity and 300 to 500 & mu;m pore size were fabricated using a unique space holder method. Because of their large surface area originated from sufficiently small pore size (a few hundreds of micrometers), good mechanical properties, interconnected three-dimensional (3D) structure with high electrical conductivity, and sufficiently short diffusion distances for electrons, they were successfully demonstrated as a novel 3D structured current collector for a next-gen electric double layer capacitor (EDLC). An additional heat treatment was performed on the fabricated Ti foams to further improve their mechanical properties, thus sustaining their structure over a long operational lifetime and enabling higher porosity 3D metal foam structure (a higher amount of slurry filling and enhanced capacity). Compressive test revealed a noticeable increase in the yield strength of the Ti foam due to the heat-treatment. The gravimetric capacity of the Ti foam-based electric double-layer capacitors was estimated to be between 33 and 37 F/g at 0.025 A/g. Furthermore, the novel 3D Ti foam electrodes, when compared with the typical foil-type electrodes, exhibited considerably more efficient charging/discharging reactions, thus resulting in enhanced volumetric capacitance as compared to commercially available EDLCs.