280
Electrochemical Supercapacitors for Energy Storage and Delivery
geometry. The pressure from the stainless steel plates can be directly transferred to the ESEA through stainless steel coins placed on the back of each
Teflon plate of the internal cell
Before testing, the whole test cell is placed into a beaker filled with electrolyte solution for electrolyte intake, after which the cell is placed in a vacuum
oven at 60°C for at least 30 min to remove trapped air inside the cell. Note
that some test cells include a reference electrode to measure the individual
electrode potentials, similar to the three-electrode measurement discussed
above. However, locating this reference electrode inside the thin layer electrolyte (separator) is a challenge.
For the preparation of the electrode sheet, an active material is mixed with
conducting carbon powders, formed into a paste using a solvent, and then
manipulated by repeatedly folding, pressing, and rolling into a thin electrode sheet. For example, in the work by Tsay et al. [1], an electrode active
carbon (BP 2000) and a conducting carbon were mixed for 30 min to form a
uniform powder. The powder was then transferred to a beaker containing
both PTFE binder and ethanol solution under constant stirring to form a
powder suspension. By heating this suspension to remove most of the ethanol, a paste was formed. The paste was then manipulated by repeatedly folding and pressing using a spatula until sufficient mechanical strengthen was
achieved. The next step was rolling the paste into a thin electrode sheet of
the required thickness with a rolling press. Finally, the electrode sheet was
placed into a vacuum oven at 90°C for at least 12 hr. The dry electrode sheet
was then cut into two 2 × 2 cm2 electrode layer squares that were sandwiched
into the two-electrode test cell for examination.
7.2.3 Differences between Three- and Two-Electrode
Cell Supercapacitor Characterizations
One primary difference must be understood in characterizing supercapacitors using the three- and two-electrode cells. The information obtained using
the former technique comes solely from the target electrode process without
interference from the other electrode. With the latter technique, the information obtained is the sum of contributions from both electrodes. Interference
from the second electrode must be subtracted to determine the sole contribution of the target electrode. The information obtained from the threecell technique is ex situ and does not necessarily reflect the real situation.
However, it is commonly used for fast screening because it does not require
an entire supercapacitor assembly The information obtained from the twocell method is considered in situ or close to the real operating conditions.
For symmetric supercapacitor systems in which the two electrodes are
identical, the information obtained using the two-electrode cell can be easily
separated. For example, the obtained capacitance from the whole cell represents only half of the targeted electrode because the entire capacitance can
be treated as two identical capacitances connected in series, as described in
Electrochemical Supercapacitors for Energy Storage and Delivery
geometry. The pressure from the stainless steel plates can be directly transferred to the ESEA through stainless steel coins placed on the back of each
Teflon plate of the internal cell
Before testing, the whole test cell is placed into a beaker filled with electrolyte solution for electrolyte intake, after which the cell is placed in a vacuum
oven at 60°C for at least 30 min to remove trapped air inside the cell. Note
that some test cells include a reference electrode to measure the individual
electrode potentials, similar to the three-electrode measurement discussed
above. However, locating this reference electrode inside the thin layer electrolyte (separator) is a challenge.
For the preparation of the electrode sheet, an active material is mixed with
conducting carbon powders, formed into a paste using a solvent, and then
manipulated by repeatedly folding, pressing, and rolling into a thin electrode sheet. For example, in the work by Tsay et al. [1], an electrode active
carbon (BP 2000) and a conducting carbon were mixed for 30 min to form a
uniform powder. The powder was then transferred to a beaker containing
both PTFE binder and ethanol solution under constant stirring to form a
powder suspension. By heating this suspension to remove most of the ethanol, a paste was formed. The paste was then manipulated by repeatedly folding and pressing using a spatula until sufficient mechanical strengthen was
achieved. The next step was rolling the paste into a thin electrode sheet of
the required thickness with a rolling press. Finally, the electrode sheet was
placed into a vacuum oven at 90°C for at least 12 hr. The dry electrode sheet
was then cut into two 2 × 2 cm2 electrode layer squares that were sandwiched
into the two-electrode test cell for examination.
7.2.3 Differences between Three- and Two-Electrode
Cell Supercapacitor Characterizations
One primary difference must be understood in characterizing supercapacitors using the three- and two-electrode cells. The information obtained using
the former technique comes solely from the target electrode process without
interference from the other electrode. With the latter technique, the information obtained is the sum of contributions from both electrodes. Interference
from the second electrode must be subtracted to determine the sole contribution of the target electrode. The information obtained from the threecell technique is ex situ and does not necessarily reflect the real situation.
However, it is commonly used for fast screening because it does not require
an entire supercapacitor assembly The information obtained from the twocell method is considered in situ or close to the real operating conditions.
For symmetric supercapacitor systems in which the two electrodes are
identical, the information obtained using the two-electrode cell can be easily
separated. For example, the obtained capacitance from the whole cell represents only half of the targeted electrode because the entire capacitance can
be treated as two identical capacitances connected in series, as described in