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Electrochemical Supercapacitor Design, Fabrication, and Operation
vacuums, a product should be used within 6 months of opening the vacuum
seal to prevent the soldered leads from oxidizing.
The Coulombic efficiency of ESs, defined as the ratio of the discharge
current to the charging current, can be expected to approach 100% even
at high currents. In practical use, the charge and discharge current values
are controlled to be the same, so the Columbic efficiency equals 100%. This
efficiency applies to the current, and does not directly correspond to high
energy efficiency.
5.2.4 Polarity
Electric double-layer ESs are commonly designed to be symmetrical, with
both the anode and cathode using the same materials such as high surface
carbon particles. Therefore, they do not have a theoretical polarity. However
some manufacturers use stainless steel casings that indicate the intended
polarity for use. Labeling is used to avoid the reverse corrosion potential of
the stainless steel that leads to subsequent loss of life. Manufacturers recommend that users maintain the polarity, but no catastrophic failure will occur
if an ES is reverse charged. However, if the EC has been conditioned for
charge in a certain direction and the direction is changed, the lifetime of the
device will be reduced.
The lifetime of an EC will be shortened considerably when the cell connected to the positively marked terminal is connected to the negative terminal of the charging source. Reversing the voltage may not show any ill effects
on performance, but the cell will show degraded lifetime and performance
characteristics after it is reconnected correctly. The negative effects on lifetime and performance can be avoided if cells are properly connected based
on their polarities.
For asymmetric ESs, as discussed in Chapter 2, polarity is very important because the anode material is different from the cathode material.
Particularly, if an electrochemically active material is used as the electrode
material, the corresponding electrochemical reaction or process on that electrode may be different from the activities of the other electrode, resulting in
different electrode potentials and different polarities. Therefore, the polarity
must be marked on each electrode in an asymmetric ES to indicate how each
material should perform within a specific operating potential.
5.2.5 Heat and Temperature Effects
The ability of ESs to operate at temperature ranges from –40 to 65°C is favorable for increasing their applications across different environments. This
range, in particular temperatures below ice point, favor organic rather than
aqueous electrolytes because of water’s freezing point. However, ES performance can be affected by heat generated from its proximate operating
Electrochemical Supercapacitor Design, Fabrication, and Operation
vacuums, a product should be used within 6 months of opening the vacuum
seal to prevent the soldered leads from oxidizing.
The Coulombic efficiency of ESs, defined as the ratio of the discharge
current to the charging current, can be expected to approach 100% even
at high currents. In practical use, the charge and discharge current values
are controlled to be the same, so the Columbic efficiency equals 100%. This
efficiency applies to the current, and does not directly correspond to high
energy efficiency.
5.2.4 Polarity
Electric double-layer ESs are commonly designed to be symmetrical, with
both the anode and cathode using the same materials such as high surface
carbon particles. Therefore, they do not have a theoretical polarity. However
some manufacturers use stainless steel casings that indicate the intended
polarity for use. Labeling is used to avoid the reverse corrosion potential of
the stainless steel that leads to subsequent loss of life. Manufacturers recommend that users maintain the polarity, but no catastrophic failure will occur
if an ES is reverse charged. However, if the EC has been conditioned for
charge in a certain direction and the direction is changed, the lifetime of the
device will be reduced.
The lifetime of an EC will be shortened considerably when the cell connected to the positively marked terminal is connected to the negative terminal of the charging source. Reversing the voltage may not show any ill effects
on performance, but the cell will show degraded lifetime and performance
characteristics after it is reconnected correctly. The negative effects on lifetime and performance can be avoided if cells are properly connected based
on their polarities.
For asymmetric ESs, as discussed in Chapter 2, polarity is very important because the anode material is different from the cathode material.
Particularly, if an electrochemically active material is used as the electrode
material, the corresponding electrochemical reaction or process on that electrode may be different from the activities of the other electrode, resulting in
different electrode potentials and different polarities. Therefore, the polarity
must be marked on each electrode in an asymmetric ES to indicate how each
material should perform within a specific operating potential.
5.2.5 Heat and Temperature Effects
The ability of ESs to operate at temperature ranges from –40 to 65°C is favorable for increasing their applications across different environments. This
range, in particular temperatures below ice point, favor organic rather than
aqueous electrolytes because of water’s freezing point. However, ES performance can be affected by heat generated from its proximate operating