Hideki Shiozaki

Aligned MWCNT Sheet Electrodes Prepared by Transfer Methodology Providing High-Power Capacitor Performance

We prepare a vertically aligned multiwalled carbon nanotube (MWCNT) sheet by a transfer procedure from a silicon substrate, covered with catalyst grains as a CNT seedbed, to an aluminum sheet as a current collector for the application of the sheet to an electrode for an electric double-layer capacitor. It is noteworthy that the MWCNT sheet electrode provides a discharge capacity of 10-15 F g -1 (of the aligned MWCNTs) even at an extremely high current density, 200 A g -1 , whereas no discharge capacitance is obtained at all with a typical high-performance activated carbon electrode at such a high current density.

Effect of MWCNT Bundle Structure on Electric Double-Layer Capacitor Performance

We demonstrate the effect of bundle structure, composed of multiwalled carbon nanotube (MWCNT) material in disordered MWCNT electrodes, on electric double-layer capacitor (EDLC) performance (i.e., their rate capability and specific capacitances). This is done by applying two types of MWCNTs with low (50-100) and high (2500-10,000) aspect ratios of their length to diameter. The use of these physically opposite values elucidates how the electronic pathways, pore distribution, and sidewall/edge balance of MWCNTs contribute to these electrodes kinetic and capacitive performance for EDLC.

Performance of Electric Double-Layer Capacitor with Vertically Aligned MWCNT Sheet Electrodes Prepared by Transfer Methodology

A variety of vertically aligned multiwalled carbon nanotube (MWCNT) electrodes, which maintain their original morphology prepared by a chemical vapor deposition technique, has been successfully fabricated by a transfer methodology from a seedbed substrate to a current collector. No ohmic potential drop on a galvanostatic discharge was observed for an electric double-layer capacitor (EDLC) containing electrodes with not only a MWCNT length of 10 μm but also a length of 200 μm. Cyclic voltammograms for electrodes with MWCNT lengths of both 10 and 200 μm showed no distorted current response, even at an extremely high scan rate of 50 V s -1 . These results demonstrate that the present EDLC with the MWCNT electrodes can provide an outstanding rate capability irrespective of the MWCNT length when prepared by our transfer methodology. To find suitable MWCNT electrodes for high-performance EDLCs, we investigated several relationships among the specific capacitances of aligned MWCNT electrodes and their major properties, i.e., their gravimetric and volumetric capacitances, length, diameter, and number density.