62
Electrochemical Supercapacitors for Energy Storage and Delivery
differential capacitance values for carbon porous materials. The reason is
the wide variety of carbon types, such as active carbon powders and fabrics, nanotubes, and aerogels.
Even a single carbon particle has a complex structure with several forms.
For example, an active carbon particle (SPECTRACAB) contains randomly
oriented single-layers, bilayers, and trilayers of small graphite sheets. These
graphite sheets contain two orientations, the basal plane, and the edge plane
[14]. Due to the different differential capacitances of the many forms of carbon, it is difficult to choose a differential capacitance value for the calculation. For carbon materials, the differential capacitance is between 0.05 and
1.0 F.cm -2 and depends on the carbon form and electrolyte used.
Using Equation (2.31), it is expected that the calculated specific capacitance
value based on BET surface area should be larger than that of the measured
value. This occurs because a small portion of the entire carbon particle area
is ineffective in the matrix layer. Thus the utilization of the particle area does
not reach 100%. For example, when using active carbon (Carbon Black BP2000,
Carbot Inc.) as the material to construct the electrode layer, the measured
specific capacitance of this material is ~90 F.g –1 [15]. This BP2000 carbon has a
BET surface of ~1500 m 2 .g –1 . If the differential capacitance for carbon material
is assumed to be in the range of 0.1 F.m –2 , the calculated specific capacitance
should be 150 F.g –1 , which is larger than the measured 90 F.g –1 . This suggests
that the calculated value does not practically reflect the real situation.
Rather than calculating the specific capacitance of the electrode material,
experimental measurements should be more practical in obtaining both the
specific and differential capacitances using the electrode layer constructed
from this material. In the experiments, the capacitance of the entire electrode
layer can be measured (expressed as ε 0 ), then the differential capacitance can
be obtained using the following equation:
C m
C dl =
(2.32)
S BET
This differential capacitance is called the apparent differential capacitance.
Table 2.3 lists both the differential and specific capacitances for several carbon materials [16].
2.5 Electrochemical Double-Layer Supercapacitors
2.5.1 Structure and Capacitance
The structure of an electrochemical double-layer supercapacitor is similar
to that of a battery: two electrodes comprised of a carbon material as shown
Electrochemical Supercapacitors for Energy Storage and Delivery
differential capacitance values for carbon porous materials. The reason is
the wide variety of carbon types, such as active carbon powders and fabrics, nanotubes, and aerogels.
Even a single carbon particle has a complex structure with several forms.
For example, an active carbon particle (SPECTRACAB) contains randomly
oriented single-layers, bilayers, and trilayers of small graphite sheets. These
graphite sheets contain two orientations, the basal plane, and the edge plane
[14]. Due to the different differential capacitances of the many forms of carbon, it is difficult to choose a differential capacitance value for the calculation. For carbon materials, the differential capacitance is between 0.05 and
1.0 F.cm -2 and depends on the carbon form and electrolyte used.
Using Equation (2.31), it is expected that the calculated specific capacitance
value based on BET surface area should be larger than that of the measured
value. This occurs because a small portion of the entire carbon particle area
is ineffective in the matrix layer. Thus the utilization of the particle area does
not reach 100%. For example, when using active carbon (Carbon Black BP2000,
Carbot Inc.) as the material to construct the electrode layer, the measured
specific capacitance of this material is ~90 F.g –1 [15]. This BP2000 carbon has a
BET surface of ~1500 m 2 .g –1 . If the differential capacitance for carbon material
is assumed to be in the range of 0.1 F.m –2 , the calculated specific capacitance
should be 150 F.g –1 , which is larger than the measured 90 F.g –1 . This suggests
that the calculated value does not practically reflect the real situation.
Rather than calculating the specific capacitance of the electrode material,
experimental measurements should be more practical in obtaining both the
specific and differential capacitances using the electrode layer constructed
from this material. In the experiments, the capacitance of the entire electrode
layer can be measured (expressed as ε 0 ), then the differential capacitance can
be obtained using the following equation:
C m
C dl =
(2.32)
S BET
This differential capacitance is called the apparent differential capacitance.
Table 2.3 lists both the differential and specific capacitances for several carbon materials [16].
2.5 Electrochemical Double-Layer Supercapacitors
2.5.1 Structure and Capacitance
The structure of an electrochemical double-layer supercapacitor is similar
to that of a battery: two electrodes comprised of a carbon material as shown