Electrochemical Double Layer Capacitors (EDLC), also known as supercapacitors, have been fabricated

using Single Walled Carbon Nanotubes (SWCNTs) as active material for electrode assembling.

In particular a new way of fabrication of ultra-thin electrodes (≤25  m) directly formed on the

separator has been proposed, and a prototype of EDLC has been realized and tested. For such

devices the specific capacitance is in the range 40–45 F/g and the internal resistances in the range

6–8  ·cm2, at current density of 2 mA·cm−2.

Keywords: Carbon Nanotube, Supercapacito

Guglielmotti,V

Kovalyuk, Z D

Motsnyi,F V

Orlanducci,S

Rossi,M

Tamburri,E

Terranova,M L

Toschi,F

Yurcenyuk,S P

Zinets,O S

Archivio della Ricerca - Università di Roma Tor vergata

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Copyright © 2008 American Scientiﬁc Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 8, 1–4, 2008
An Innovative and Viable Route for the Realization of
Ultra-Thin Supercapacitors Electrodes Assembled with
Carbon Nanotubes
Z. D. Kovalyuk1, F. V. Motsnyi2, O. S. Zinets3, S. P. Yurcenyuk1, E. Tamburri4∗, S. Orlanducci4,
V. Guglielmotti4, F. Toschi4, M. L. Terranova4, and M. Rossi5
1Chernivtsi Department of Institute for Problem of Materials Science, National Academy of Sciences of Ukraine,
5, I. Vilde Street, 58001 Chernivtsi, Ukraine
2V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine,
41 Prospect Nauky, 03028 Kyiv, Ukraine
3Institute for Nuclear Research, National Academy of Sciences of Ukraine,
47 Prospect Nauky, 03028 Kyiv, Ukraine
4Dipartimento di Scienze e Tecnologie Chimiche, MINASlab, Università di Roma Tor Vergata,
Via della Ricerca Scientiﬁca, 00133 Roma, Italy
5Dipartimento di Energetica, Università di Roma Sapienza, Via A. Scarpa 16, 00161 Roma, Italy
Electrochemical Double Layer Capacitors (EDLC), also known as supercapacitors, have been fab-
ricated using Single Walled Carbon Nanotubes (SWCNTs) as active material for electrode assem-
bling. In particular a new way of fabrication of ultra-thin electrodes (≤25 m) directly formed on the
separator has been proposed, and a prototype of EDLC has been realized and tested. For such
devices the speciﬁc capacitance is in the range 40–45 F/g and the internal resistances in the range
6–8  ·cm2, at current density of 2 mA ·cm−2.
Keywords: Carbon Nanotube, Supercapacitor, Thin Electrode, Capacitance.
1. INTRODUCTION
One of important applications of nanocomposite carbon-
based structures and of carbon nanotubes (CNT) is their
use as anodes in lithium-ion batteries and electrodes for
electrochemical capacitors with a high-speciﬁc capacity.12
In Electrochemical Double Layer Capacitors (EDLC) the
stored energy is based on the separation of charged species
across the electrode/electrolyte interface. Positive and neg-
ative electrodes are typically made from high surface area
carbon materials immersed in an electrolyte solution. By
either increasing the size of the electrode/electrolyte inter-
face, thus increasing the surface area of the electrodes, or
decreasing the separation between ions and electrode, the
stored capacitance increases. Therefore, for the realization
of the electrodes, the use of CNT, material characterized
by a very high speciﬁc surface area (∼600 m2 g−1 or
more) and exceptional conducting and mechanical prop-
erties, is expected to improve the performances of the
devices.3–5 Recently, many researches have been focused to
∗Author to whom correspondence should be addressed.
the production of carbon nanotubes based electrodes with
high performances. These include, for example, the real-
ization of composite electrodes made of carbon nanotubes
and conducting polymers.6–8 In these systems the energy
stored in the capacitor is either capacitive or pseudocapac-
itive, owing to the increased speciﬁc surface area of the
composite material and to the Faradic redox reactions that
occur within the conducting polymer matrix. Moreover the
introduction of CNT into polymers improves their elec-
tric conductivity and mechanical properties.9 Other studies
have been addressed to the realization of hybrid electrodes
by coupling carbon nanotubes with inorganic species such
as metals, metal oxides and metal hydroxides.10–12 The aim
of such investigations was again to improve the speciﬁc
capacitance of the ﬁnal supercapacitor by matching two
electrode materials with different charge-storage mecha-
nism in one composite electrode.
Anyway, EDLC performances are affected by a number
of factors such as pore size, surface area, surface chemistry
and graphitization of the electrode material. A key role is
moreover played by the electrode thickness.2–413–14 This
last point is connected with the process of the separation
J. Nanosci. Nanotechnol. 2008, Vol. 8, No. 12 1533-4880/2008/8/001/004 doi:10.1166/jnn.2008.435 1
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An Innovative and Viable Route for the Realization of Ultra-Thin Supercapacitors Electrodes Kovalyuk et al.
of active material particles from the geometrical surface of
an electrode that directly contacts the electrolyte, into the
depth of the electrode. This effect increases the internal
resistance of capacitors. Moreover remoteness of the active
material particles from the current collector also results in
an increase of the internal resistance of the supercapacitor.
Taking into account these factors, it appears that a viable
solution is the use of ultra-thin electrodes with a thick-
ness comparable to the size of the active material grains.
In practice, however, the formation of such ultra-thin elec-
trodes meets signiﬁcant technological difﬁculties.
We have developed a new methodology for the forma-
tion of ultra-thin electrodes directly on the supercapacitor
separators, using the same type of single-walled carbon
nanotubes (SWCNT) investigated in a previous paper.15
In the present paper the fabrication of electrodes using
SWCNTs is described and the charge–discharge character-
istics of the supercapacitors are reported and discussed.
2. EXPERIMENTAL DETAILS
2.1. Fabrication of Electrodes
Samples of commercial SWCNTs produced by arc-
discharge are treated following the protocols described in
Ref. [16]. The ﬁnal amount of nickel in the puriﬁed mate-
rial is about 3.2%. The electrolyte is a 30% w/w KOH
water solution. The SWCNTs suspension is prepared by
adding carbon nanotubes to the electrolyte solution. This
suspension is then transferred on the separator material by
spraying or drop casting. Materials “BAKHIT” and non-
woven polypropylene or CELGARD are used as separa-
tors. The separator is placed over two or three layers of
a ﬁltering paper which is properly humidiﬁed in order to
produce a good mechanical contact. The dispersion’s sol-
vent soaks up by the bottom layers of the ﬁltering paper
and the SWCNTs create a rather uniform thin layer on the
surface of the separator, which is ﬁnally used as electrode
of the supercapacitor.
2.2. Characterization of Electrodes
Surface morphologies of electrode were examined using
a ﬁeld emission scanning electron microscope (FE-SEM,
HITACHI S-4000) operating at an acceleration voltage of
20 kV.
Electrochemical measurements were performed by
means of an electrochemical workstation using two-
electrode electrochemical capacitor cells and a three-
electrode system in 30% w/w KOH aqueous solution. In
the three electrode system the SWCNTs ultra-thin layer
was used as working electrode, whereas a platinum wire
and a saturated calomel electrode (SCE) were used as the
counter and reference electrodes, respectively.
The SWCNTs electrodes performances were tested
using the following techniques: cyclic voltammetry in
the range of potential between −1.14 and +0.80 V
at scan rates from 5 to 50 mVs−1, galvanostatic
charging–discharging (current ranges 1–5 mA) and AC
impedance spectroscopy using the AC amplitude of 10 mV
in the frequency range from 1 mHz to 100 kHz.
3. RESULTS AND DISCUSSION
3.1. Morphological Characteristics of Electrodes
Figure 1 shows a FE-SEM image of a typical SWCNTs-
coated electrode surface. The entangled carbon nanotube
bundles form net-like systems characterized by high poros-
ity. The produced electrodes have a geometrical surface S
of about 0.5 cm2.
The layer thickness d is evaluated using the following
equation:
d = Nm
sph ·S
(1)
where m is the amount of the SWCNTs suspension, N is
the SWCNTs weight concentration of the suspension, S is
the geometrical surface of electrode and sph is the parti-
cles density calculated using the Smoothed Particle Hydro-
dynamics method.17 Such an approach allows us to take
into account the spatial distribution assumed by a highly
porous system produced from evaporation of a ﬂuid in
which particles have been properly dispersed. In this way,
it is possible to estimate a d value that is reasonably more
realistic than the one obtained using the theoretical den-
sity of carbon nanotubes. For our electrodes we estimated
a thickness d ranging between 15 and 18 m.
In order to verify these data, the layer thickness d
has been evaluated by proﬁlometer surface measurements.
These analyses provide d values in the range 15–25 m.
Nevertheless, it must consider that such measurements
suffer of severe uncertainties, due to the highly porous
nature of the surfaces. Moreover, the deposition technique
also inﬂuences the uniformity of the layer, that strongly
Fig. 1. FE-SEM image of a SWCNTs ultra-thin layer surface.
2 J. Nanosci. Nanotechnol. 8, 1–4, 2008
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Kovalyuk et al. An Innovative and Viable Route for the Realization of Ultra-Thin Supercapacitors Electrodes
depends on the kind of separator and, in particular, on
its structure and pore size. In particular we found that
for the layers deposited by spraying the non-uniformity
of the thickness does not exceed 20–25% for the separa-
tor material of type “BAKHIT” and nonwoven polypropy-
lene; and 12–17% for the material CELGARD. For layers
deposited by the drop method these values are increased
by 4–8% in the case of CELGARD material and approx-
imately by 10% in the case of “BAKHIT” and nonwoven
polypropylene.
On the basis of such considerations, it is realistic
to assume a thickness ≤25 m for all our SWCNTs
electrodes.
3.2. Electrodes Characterization
Figure 2 shows a typical cyclic voltammogram obtained
for the SWCNTs electrodes in 30% w/w KOH water
solution in the potential range (−114÷+080) V. The
rectangular-like form (close to that of an ideal capacitor)
and the absence of peaks in the voltammogram evidence
the absence of faradic reactions, representing one of the
necessary conditions for effective energy storage in the
double electric layer.
The dependence of the imaginary part of impedance
versus its real part for the same electrode is reported in
Figure 3. Using this plot it is possible to calculate the
internal resistance and the equivalent scheme needed for
evaluation of the speciﬁc power and for comparison with
the performances of other supercapacitors.
3.3. Charge–Discharge Characteristics of
Supercapacitors
Charge–discharge characteristics of the supercapacitors
were measured in galvanostatic mode at the limit charge
voltage of 1 V. The voltage was limited by the use of the
KOH aqueous electrolyte solution.
Fig. 2. Cyclic voltammogram of SWCNTs electrodes in 30% w/w KOH
aqueous solution in range of potential (−114÷080) V at 50 mVs−1.
Fig. 3. Measured electrochemical impedance plot for a typical
SWCNTs electrode in 30% w/w KOH aqueous solution. The inset evi-
dences the details of the impedance curve at low values.
Figure 4 presents the typical discharge curves at differ-
ent resistance loads of the SWCNTs based supercapacitors.
Capacitors were charged under the following conditions:
the charge current was I 1c = 5 mA up to the capacitor volt-
age 0.9 V and I 2c = 1 mA up to the end capacitor voltage
0.95 V. The end voltage under discharge was 0.05 V.
Figure 5 presents curves of the charge–discharge cycles
when the Cd/Cc ≈ 1 Cd and Cc are the discharge and
the charge capacity, respectively) in galvanostatic mode
(Ic−d = const = 1 mA). At the beginning, the ratio Cd/Cc
was in the range 0.7–0.9 for all the produced EDLC, but
depending on the supercapacitors this ratio was found to
reach the unity after a different number of cycles, 10–20
or 70–90 cycles. These different performances of the fab-
ricated devices may be explained on the basis of electro-
chemical reactions at the electrodes and of the inertia of
the electric double-layer formation, ascribed to the pres-
ence of impurities in electrolytes.
The speciﬁc capacitance of electrodes was in the range
40–45 F/g. The internal resistance of the supercapacitors
equals ∼6–8 Ohm ·cm2 at the current density of 2 mA/cm2.
Fig. 4. Chronopotentiometry curves at resistance loads ranging from
10 to 100  in 30% w/w KOH aqueous solution for supercapacitors
fabricated using SWCNTs-based electrodes and charged with a charge
current of 1 mA.
J. Nanosci. Nanotechnol. 8, 1–4, 2008 3
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An Innovative and Viable Route for the Realization of Ultra-Thin Supercapacitors Electrodes Kovalyuk et al.
Fig. 5. Charge–discharge cycles measured for SWCNTs-based superca-
pacitors at charge–discharge current of Ic−d = 1 mA in 30% w/w KOH
aqueous solution when Cd/Cc ≈1.
The charge–discharge behavior reported in Figure 5 is
similar to those observed in Refs. [4, 5]. According to
Ragone’s diagram,18–19 values of 40–45 F/g and internal
resistance of ∼0.2  cm2 would correspond to a speciﬁc
power of 5–5.1 Wh/kg. The higher internal resistance mea-
sured in our experiments could be caused by imperfec-
tion of the electric contacts between the electrode material
and the current collector surface due to the electrode sur-
face relieves. Due to feature of the nanotubes deposit on
the separator, electric contact of electrode-current collector
occurs through local dots formed by SWCNTs aggregates.
Hence, the contact surface area is very small. On the other
hand, imperfect electric contact between the nanotubes in
the electrode material also leads to increase the superca-
pacitor internal resistance. An upgrading of the fabrication
strategies, leading to a better distribution of the nanotubes
on the electrode and to the realization of more efﬁcient
conducting networks is needed in order to overcome these
problems.
Anyway the values of speciﬁc capacitance found for our
SWCNTs electrodes are very encouraging being higher of
the typical values (in the range 20–25 F/g) measured for
electrodes made solely by carbon nanotubes and used as
components of more complex devices.11–12
Finally, in order to better deﬁne the functional applica-
tions of our SWCNTs-based supercapacitors, we checked
the speciﬁc capacitance dependence on the frequency.
Figure 6 evidences that the speciﬁc capacitance decrease
with the frequency. The high capacitance values obtained
at frequencies below 0.01 Hz indicates the advantage
to use such supercapacitors, for instance, as devices for
energy storage working in a constant current mode.
4. CONCLUSIONS
A new route for the fabrication of ultra-thin (≤25 m)
supercapacitor electrodes that use only single-walled
carbon nanotubes as active material has been settled.
The electrodes are formed directly on the separator of the
supercapacitor cell. The internal resistance of the fabri-
cated supercapacitors is in the range 6–8 × cm2 at the
current density 2 mA/cm2 and speciﬁc capacitances in the
range 40–45 F/g have been measured with electrode thick-
ness in the range 15–25 m.
The material results stable under prolonged cycling and
the type of device assure intrinsically long operational life,
requiring basically no maintenance. Another advantage of
this innovative supercapacitor technology is the easy fab-
rication and the proﬁtable scaling-up.
The supercapacitors based on SWCNTs and realized fol-
lowing this operational route result particularly advanta-
geous for the use as energy accumulator at low frequencies
and could constitute the base material for the realization
of high performance electrode materials.
References and Notes
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Nanotechnology, edited by H. S. Nalwa, ASP, USA (2004), Vol. X,
p. 1.
2. H. J. In, S. Kumar, Y. Shao-Horn, and G. Barbastathis, Appl. Phys.
Lett. 88, 083104 (2006).
3. K. H. An, K. K. Jeon, J. K. Heo, S. C. Lim, D. J. Bae, and Y. H.
Lee, J. Electrochem. Soc. 149, A1058 (2002).
4. E. Frackowiak, J. Braz. Chem. Soc. 17, 1074 (2006).
5. A. B. Fuertes, G. Lota, T. Centeno, and E. Frackowiak, Electrochim.
Acta 50, 2799 (2005).
6. J. Wang, Y. Xu, X. Chen, and X. Sun, Compos. Sci. Tech. 67, 2981
(2007).
7. J. Y. Kim, K. H. Kim, and K. B. Kim, J. Power Sources 176, 396
(2008).
8. X. Lin and Y. Xu, Electrochim. Acta 53, 4990 (2008).
9. M. Moniruzzaman and K. I. Winey, Macromol. 39, 5194 (2006).
10. C. T. Hsieh, Y. W. Chou, and W. Y. Chen, J. Solid State Electrochem.
12, 663 (2008).
11. L. Su, X. Zhang, C. Yuan, and B. Gao, J. Electrochem. Soc. 155,
A110 (2008).
12. M. Skunik, M. Chojak, I. A. Rutkowska, and P. J. Kulesza,
Electrochim. Acta 53, 3862 (2008).
13. E. Rajmundo-Pinero, D. Cazorla-Amoros, A. Linares-Solano,
S. Delpeux, E. Frackowiak, K. Szostak, and F. Béguin, Carbon 40,
1597 (2002).
14. C. Largeot, C. Portet, J. Chmiola, P. L. Taberna, Y. Gogotsi, and
P. Simon, J. Am. Chem. Soc. 130, 2730 (2008).
15. A. A. Konchits, F. V. Motsnyi, Yu. N. Petrov, S. P. Kolesnik, V. S.
Yefanov, M. L. Terranova, E. Tamburri, S. Orlanducci, V. Sessa, and
M. Rossi, J. Appl. Phys. 100, 124315 (2006).
16. M. L. Terranova, S. Orlanducci, E. Fazi, V. Sessa, S. Piccirillo,
M. Rossi, D. Manno, and A. Serra, Chem. Phys. Lett. 381, 86 (2003).
17. J. J. Monaghan, Rep. Prog. Phys. 68, 1703 (2005).
18. R. Kötz and M. Carlen, Electrochim. Acta 45, 2483 (2000).
19. S. Arepalli, H. Fireman, C. Huffman, P. Moloney, P. Nikolaev,
L. Yowell, C. D. Higgins, K. Kim, P. A. Kohl, S. P. Turano, and
W. J. Ready, JOM 57, 26 (2005).
Received: 5 March 2008. Accepted: 24 April 2008.
4 J. Nanosci. Nanotechnol. 8, 1–4, 2008


An innovative and viable routre for the realization of ultra-thin supercapacitor electrodes  assembled with carbon nanotubes

Electrochemical Double Layer Capacitors (EDLC), also known as supercapacitors, have been fabricated using Single Walled Carbon Nanotubes (SWCNTs) as active material for electrode assembling. In particular a new way of fabrication of ultra-thin electrodes (<= 25 mu m) directly formed on the separator has been proposed, and a prototype of EDLC has been realized and tested. For such devices the specific capacitance is in the range 40-45 F/g and the internal resistances in the range 6-8 Omega center dot cm(2), at current density of 2 mA center dot cm(-2)

Z. D. Kovalyuk

F. V. Motsnyi

O. S. Zinets

S. P. Yurcenyuk

E. Tamburri

S. Orlanducci

V. Guglielmotti

F. Toschi

M. L. Terranova

ROSSI, Marco

Archivio della ricerca- Università di Roma La Sapienza

An Innovative and Viable Route for the Realization of Ultra-Thin Supercapacitors Electrodes Assembled with Carbon Nanotubes

Electrochemical Double Layer Capacitors (EDLC), also known as supercapacitors, have been fabricated
using Single Walled Carbon Nanotubes (SWCNTs) as active material for electrode assembling.
In particular a new way of fabrication of ultra-thin electrodes (≤25  m) directly formed on the
separator has been proposed, and a prototype of EDLC has been realized and tested. For such
devices the specific capacitance is in the range 40–45 F/g and the internal resistances in the range
6–8  ·cm2, at current density of 2 mA·cm−2.
Keywords: Carbon Nanotube, Supercapacito

Motsnyi, F V

Zinets, O S

Yurcenyuk, S P

Tamburri, E

Orlanducci, S

Guglielmotti, V

Toschi, F

Terranova Persichelli, M L

Rossi, M

An innovative and viable route for the realization of ultra-thin supercapacitors electrodes assembled with carbon nanotubes

https://art.torvergata.it/retrieve/handle/2108/11475/11386/Capacitori_JNN.pdf

An innovative and viable routre for the realization of ultra-thin supercapacitor electrodes assembled with carbon nanotubes

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