Please cite this article in press as: H.-C. Wu, et al., High-performance carbon-based supercapacitors using Al current-collector with conformal carbon coating, Mater. Chem. Phys. (2009), doi:10.1016/j.matchemphys.2009.06.001 ARTICLE IN PRESS G Model MAC-13350; No. of Pages 7 Materials Chemistry and Physics xxx (2009) xxx–xxx Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys High-performance carbon-based supercapacitors using Al current-collector with conformal carbon coating Hsien-Chang Wu a , Yen-Po Lin a , Eric Lee a , Wen-Ting Lin b , Jui-Kai Hu b , Hung-Chang Chen b , Nae-Lih Wu a,∗ a Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan b Taiwan Textile Research Institute, Tucheng City, Taipei 236, Taiwan article info Article history: Received 14 December 2008 Received in revised form 27 May 2009 Accepted 7 June 2009 Keywords: Electrochemical properties X-ray photo-emission spectroscopy Chemical vapor deposition Microporous materials abstract Al current-collector with porous surface is coated with a conformal carbon (C) layer via a chemical vapor deposition process in CH 4 at 600 ◦ C. X-ray photoelectron spectroscopy analysis indicates that the coating process leads to the replacement of native aluminum oxide with a composite coating consisting of an Al 4 C 3 interfacial layer and a C top layer. Activated C-based supercapacitors employing the resulting C-coated Al current-collectors have exhibited remarkably enhanced high-rate performance, and the enhancement can be attributed to two accounts. Firstly, the current-collector/active-layer interface resistance is reduced due to removal of the insulating oxide layer and improved adhesion of the active-layer on the current- collector. Secondly, the presence of the conducting C layer shortens the effective current conduction distance from the solid-electrolyte interface to the current-collector, leading to reduced charge-transfer resistance within the active-layer. Combining the C-coated Al current-collector with a C fiber active-layer that contains a large mesoporous pore volume (0.4 cm 3 g -1 ) has resulted in high-performance superca- pacitors that exhibit, for instance, a cell specific energy of 18 Wh Kg -1 at 25 ◦ C or 7 Wh Kg -1 at -10 ◦ C under a cell specific power of 25 KW Kg -1 . © 2009 Elsevier B.V. All rights reserved. 1. 1.Introduction Supercapacitor, also known as electrochemical capactor, is an electrochemical energy storage device designed to give high-power charge/discharge capability. Although there are various types of supercapactiors employing different electrode materials [1–6], the activated carbon (C)-based supercapactior remains the most widely studied technology. This class of supercapacitor typically contains two identical electrodes of which each consists of an active-layer of activated C particles on an Al current-collector. Charge storage pro- ceeds mainly via reversible adsorption of ions at the C-electrolyte interface. The activated C particles are highly porous and pro- vide high (mostly > 1000 m 2 g -1 ) specific surface areas for sufficient energy storage. The high-power capability of a supercapacitor (and other elec- trochemical devices as well) is basically represented by the amount of energy delivered (or stored) under high current rates. The basic principle for achieving high-power capability is minimizing the overall resistance of the electrochemical system, which would oth- erwise cause energy loss during charge/discharge. In the case of ∗ Corresponding author. Tel.: +886 2 23627158; fax: +886 2 23623040. E-mail address: nlw001@ntu.edu.tw (N.-L. Wu). activated C electrodes described above, there are three major resis- tance sources, including (1) the ionic resistance associated with diffusion of electrolyte ions within the pores of C particles, (2) the electronic resistance within the framework of active-layer, and (3) the electronic resistance at the interface between current-collector and active-layer. The bulk electronic resistance of Al current collect is typically negligible. Earlier studies [e.g., 2, 7-9] on supercapacitor power perfor- mance have focused mainly on the pore structures of constituent C materials, which govern the ionic resistance. They in general suggested the beneficial effects by mesoporosity, in contrast to microporosity, of the C materials on facilitating diffusion of elec- trolyte ions without sacrifice of specific surface area. However, recent studies [10,11] showed anomalous increase in specific capac- itance within micropores with pore size less than 1 nm. In addition, introducing sufficient amount of conductive additive to exceed per- colation threshold has been shown to be critical to the reduction of electronic resistance of active-layer in some occasions [12]. Recent publications by Simon et al. [13–15] have drawn atten- tion to the importance of the electric resistance at the interface between Al current-collector and C active-layer. In their work, etched Al current-collector was coated with a polymeric film con- taining carbonaceous particles, which was subsequently pyrolyzed. The resulting supercapacitors showed significantly reduced interfa- 0254-0584/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2009.06.001