Electrical Double Layer Capacitors Based on Different Carbide Derived
Carbon Electrode Materials
A. Jänes, T. Thomberg, H. Kurig, I. Tallo, A. Laheäär, K. Tõnurist, E. Lust
Institute of Chemistry, University of Tartu, 14a Ravila Str., 50411 Tartu, Estonia
EXPERIMENTAL RESULTS
The study of the electrochemical characteristics of porous carbide derived carbon (CDC) materials is a very important problem taking into account the development of electrical double layer capacitors (EDLCs) with high specific performances.
To optimize the energy and power density of EDLC, microporous carbon properties like the hierarchical structure, pore volume, pore size distribution, medium diameter of micropores, specific surface area, ratio of micropore and mesopore
volumes have to be optimized. Comparison of the data in [1,2] shows some possibilities to increase the specific capacitance values further by designing materials with desirable pore size characteristics more compatible with partially desolvated
ion diameter and molar volume.
Therefore the so-called chlorine treatment method has been applied to synthesize various micro- and mesoporous CDC materials from different carbides (SiC, Al4C3, TiC, B4C, WC, Cr3C2, Cr7C3, Cr23C6, VC, Mo2C) in the temperature range
from 400 to 1200 °C [1,3-13]. The electrochemical characteristics of the EDLC cell based on the different micro- and mesoporous CDC electrodes in 1 M (C2H5)3CH3NBF4 acetonitrile solution have been studied using the cyclic voltammetry,
constant current charge/discharge and electrochemical impedance spectroscopy methods. All experiments have been carried out inside a glove box at clean and dry conditions. The two-electrode EDLC were assembled into hermetic aluminum
test-cell (Hohsen Corp., Japan). 25 mm thick TF4425 Nippon Kodoshi sheet was used between working electrodes as a separator. The ideal polarizability, low-frequency limiting capacitance and series resistance, phase angle, relaxation time
constant, complex power components, maximum gravimetric energy and gravimetric power and other parameters dependent on the CDC properties will be discussed and correlation with FIB-SEM, XPS and TOF-SIMS data will be given.
Mo2C-CDC
800oC
TiC-CDC
Incremental pore area / m2g-1
400
300
-SiC-CDC
VC-CDC
1100oC
Mo2C-CDC
Al4C3-CDC
VC-CDC
SBET = 1270 m2g-1
Mo2C-CDC
SBET = 1580 m2g-1
200
B4C-CDC
100
0
0.1
101
Pore Width / nm
1
10
100
Fig. 1. Pore size distribution for
different CDCs.
Fig. 2. HRTEM micrograph (a), SAED pattern (b) and corresponding
carbon-K ELNES (c) for amorphous (prepared at 800 °C) and partially
graphitisized (prepared at 1100 °C) WC-CDC.
VC-CDC 800oC
Fig. 3. X-ray diffraction patterns for different CDCs
prepared at various chlorination temperatures.
Fig. 4. Raman spectra for WC-CDC powders
prepared at various chlorination temperatures,
FWHM value of the D-band and G-band peaks and
ratio of peak intensities of ID and IG.
-400
-5.5
a
Z " / W cm
2
Mo2C-CDC
-300
Z " / W cm
2
0.2
0.5
1.0
1.5
2.1
2.7
3.0
-200
-100
-3.5
18.9 kHz
0.6 Hz
-1.5
95 Hz
RE
0
R E+R CE
2
4
6
Z ' / W cm2
R E+R CE+R pore
8
10
0
0
100
200
300
400
500
600
b
700
Z ' / W cm2
Fig. 5. Specific capacitance vs. cell voltage
curves, calculated from CV–curves at different
voltage sweep rates for the EDLCs completed
using VC–CDC electrodes prepared at 800 °C.
Fig. 6. Nyquist plots at different cell voltages for the
EDLCs completed using VC–CDC electrodes prepared
at 900 °C.
Fig. 7. Constant current charge/discharge cycles
at current density j = 1 mA cm-2 for the EDLCs
completed using Mo2C–CDC electrodes
prepared at different temperatures (°C).
E / W h kg-1
100
10
Fig. 8. Maximal specific energy (a) and power
(b) densities atU=3.0V for the EDLCs at
different temperatures.
800
1000
1100
6 min
a
36 s
1
0.36 s
3.6 s
0.1
1
10
100
P / kW kg-1
Fig. 9. Ragone plots for the EDLCs completed using
WC–CDC electrodes prepared at different temperatures
(°C).
Fig. 10. XPS spectra for positively (a) and
negatively (b) charged TiC-CDC electrodes after
40000 charge/discharge cycles.
Negatively charged electrode
Mean value
C 89.30 wt%
N 3.25 wt%
b
a
O 4.33 wt%
F 3.12 wt%
Total 100.0 wt%
Positively charged electrode
b
m/z
c
m/z
d
Fig. 12. Positive and negative ion-specific images of CN(A) for negatively and positively charged TiC-CDC
electrode; total ions and Al3+ ions for positively (B) and
negatively (C) charged TiC-CDC electrode. Image sizes are
400 x 400 mm2.
Mean value
C 70.40 wt%
N 5.78 wt%
O 5.39 wt%
F 14.57 wt%
Al 3.53 wt%
Total 100.0 wt%
m/z
m/z
Fig. 11. TOF-SIMS spectra for TiC-CDC supercapacitor for positive (a, c) and negatively (b, d) charged
electrode for negatively (c, d) and positively (a, b) charged secondary ions after 40000 charge/discharge cycles.
Fig. 13. Results of FIB-SEM and EDX analysis for TiC-CDC
electrodes for positively (a) and negatively (b) charged electrode
after 40000 constant current charging/discharging cycles.
Acknowledgements
This work was supported by the Estonian Science Foundation under Projects Nos. 8172 and 9184, Estonian Ministry of Education and Research project SF0180002s08, European Regional Development Fund Project SLOKT10209T,
Estonian Centre of Excellence in Research Project TK117T "High-technology Materials for Sustainable Development“ and graduate school „Functional materials and processes“ receiving funding from the European Social Fund under project
1.2.0401.09-0079 in Estonia. Dr. L. Matisen and Dr. A. Kikas (Institute of Physics, University of Tartu) are thanked for the help with the XPS measurements. Dr. G.L. Fisher from Physical Electronics, Inc. (Chanhassen, MN, USA) is thanked
for the assistance of TOF-SIMS measurements.
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