Journal of Power Sources 156 (2006) 725–740
Requirements for performance characterization of C double-layer
supercapacitors: Applications to a high speciﬁc-area C-cloth material
Jianjun Niu, Wendy G. Pell, Brian E. Conway
Department of Chemistry, University of Ottawa, 10 Marie Curie Street, Ottawa, Ont., Canada K1N 6N5
Received 20 April 2005; received in revised form 31 May 2005; accepted 1 June 2005
Available online 22 July 2005
Electrochemical capacitors, based on the double-layer capacitance of high speciﬁc-area C materials, are attracting major fundamental and
technological interest as highly reversible, electrical charge-storage and delivery devices, capable of being operated at high power-densities.
A variety of applications have been described in the literature, e.g. for cold-start vehicle assist, in hybrid load-leveling conﬁgurations with
batteries, fuel-cells, as well as directly with internal combustion engines. Additionally, high capacitance C electrodes have been usefully
employed as anodes coupled with battery-type cathodes, e.g. Pb/PbO
, in so-called “asymmetric” capacitor cells.
On account of these perceived various applications, requirements for performance evaluation must be developed in systematic and comple-
mentary ways. In the present paper, we examine experimentally the following test procedures as exempliﬁed by application to an high
speciﬁc-area (ca. 2500 m
) woven C-cloth capacitor electrode material: (i) evaluation of the speciﬁc capacitances as a function of
charge/discharge rates employing cyclic-voltammetry and dc charging curves; (ii) as in (i), examination of reversibility and energy-efﬁciency
as a function of electrolyte (H
) concentration, i.e. conductivity; (iii) interpretation of effects in (i) and (ii) in terms of distributed resistance
and capacitance in the porous C matrix according to the de Levie model; (iv) interpretation of data obtained in (i) in terms of Ragone plots
which, for capacitor devices, require special treatment owing to the fundamental dependence of electrode- (or device) potential on state of
discharge; (v) interpretation of self-discharge (SD) kinetics in terms of porous-electrode structure. Performance data for the C-electrode are
given for capacitative charging up to high “C-rates”, extension of operational voltage windows and for SD behaviour.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Electrochemical capacitors; Supercapacitors; Carbon cloth electrode; Self-discharge; Float-current
In recent years, research and development of electrochem-
ical capacitors (ECs) has become a challenging and techno-
logically important ﬁeld [1–5] due to their perceived high
operating power-density and to demands for new applica-
tions involving high speciﬁc-power sources for power trains
of electric vehicles that can be operated with less or zero
toxic gas emission. However, compared with batteries, an
EC usually provideslower energy-density and exhibits higher
self-discharge rates which make it impossible to be simply
a substitute for batteries in commercial or industrial applica-
tions. Additionally, the approximately linear decline of volt-
Corresponding author. Tel.: +1 613 562 5481; fax: +1 613 562 5170.
E-mail address: email@example.com (B.E. Conway).
age with declining state-of-charge (SOC) is a fundamental
aspect of a capacitor’s electrical behaviour. However, oppor-
tunities arise for complementary operation of ECs that are
electrically coupled in discharge and recharge with batteries
to obtain more efﬁcient charge storage and power delivery.
Special attention has been recently given to the develop-
ment of hybrid battery–capacitor systems for electric-vehicle
drive trains [6–9]. Also, testing results have been reported
for hybrid power sources based on a combination of capac-
itor and battery-type electrodes [6,10] and a projected EC
with an energy-density of 20 kJ kg
and a power-density of
20 kW kg
has been developed .
Large capacitance ECs can be developed either by utiliz-
ing the so-called double-layer (d.l.) capacitance at electrode
interfaces or employing the large redox pseudocapacitance
that is developed at some transition metal oxide ﬁlms (e.g.
0378-7753/$ – see front matter © 2005 Elsevier B.V. All rights reserved.