204
Electrochemical Supercapacitors for Energy Storage and Delivery
This chapter incorporates academic literature, conference proceedings,
and seminar publications issued over the past 10 years to provide up-to-date
information about electrochemical supercapacitor design, fabrication, and
operation. A review of publicly accessible patents is also presented, along
with information made available by manufacturers.
5.2 Design Considerations
In general, the first consideration in designing any device, including an
electrochemical supercapacitor (ES), is the intended application. An ES is
used for energy storage and delivery across a wide range of applications.
The important design considerations include: (1) cell voltage, (2) frequency
response, (3) lifetime and cycle charging, (4) polarity, (5) heat and temperature effects, and (6) humidity. For cell voltage considerations, an ES must be
suitable for low voltage, high voltage, or both types of applications. Since
the application systems require immediate high power (supplied within less
than a millisecond to a few seconds) or delaying the desired power for longer
periods ranging from a few seconds to minutes, the operational voltage and
its frequency response must be considered.
Other factors such as cycle life, cell polarity, and heat management must
combine to achieve synergy and optimization to ensure adequate performance and efficiency. All these factors can also be governed by additional
intrinsic and extrinsic aspects of cell materials and their manufacturing processes. This section will discuss each design factor along with material and
manufacturing requirements and implementation methods. It is important
to note that these considerations are general guidelines for carbon-based
electric double-layer ESs.
5.2.1 Cell Voltage
As discussed in Chapter 3, the operating voltage of a single cell ES is largely
limited by the electrolyte used. According to the equation of ES energy density (E = ½CV 2 ), the energy density is proportional to the square of the cell
voltage, determined mainly by the electrolyte voltage window. Therefore,
electrolyte selection has a direct impact on energy storage capabilities and
the number of single-stacked cells to achieve a rated operating voltage. In
commercial manufacturing, some organic electrolytes are preferred due to
their wider voltage windows compared to aqueous electrolytes. For example,
tetraethylammonium tetrafluoroborate (Et 4 NBF 4 ) as the electrolyte salt dissolved in an acetonitrile or propylene carbonate solvent is the most popular choice to attain high operating potentials near 3V. A typical ES stack for
applications requiring high load operating potentials, such as uninterrupted
Electrochemical Supercapacitors for Energy Storage and Delivery
This chapter incorporates academic literature, conference proceedings,
and seminar publications issued over the past 10 years to provide up-to-date
information about electrochemical supercapacitor design, fabrication, and
operation. A review of publicly accessible patents is also presented, along
with information made available by manufacturers.
5.2 Design Considerations
In general, the first consideration in designing any device, including an
electrochemical supercapacitor (ES), is the intended application. An ES is
used for energy storage and delivery across a wide range of applications.
The important design considerations include: (1) cell voltage, (2) frequency
response, (3) lifetime and cycle charging, (4) polarity, (5) heat and temperature effects, and (6) humidity. For cell voltage considerations, an ES must be
suitable for low voltage, high voltage, or both types of applications. Since
the application systems require immediate high power (supplied within less
than a millisecond to a few seconds) or delaying the desired power for longer
periods ranging from a few seconds to minutes, the operational voltage and
its frequency response must be considered.
Other factors such as cycle life, cell polarity, and heat management must
combine to achieve synergy and optimization to ensure adequate performance and efficiency. All these factors can also be governed by additional
intrinsic and extrinsic aspects of cell materials and their manufacturing processes. This section will discuss each design factor along with material and
manufacturing requirements and implementation methods. It is important
to note that these considerations are general guidelines for carbon-based
electric double-layer ESs.
5.2.1 Cell Voltage
As discussed in Chapter 3, the operating voltage of a single cell ES is largely
limited by the electrolyte used. According to the equation of ES energy density (E = ½CV 2 ), the energy density is proportional to the square of the cell
voltage, determined mainly by the electrolyte voltage window. Therefore,
electrolyte selection has a direct impact on energy storage capabilities and
the number of single-stacked cells to achieve a rated operating voltage. In
commercial manufacturing, some organic electrolytes are preferred due to
their wider voltage windows compared to aqueous electrolytes. For example,
tetraethylammonium tetrafluoroborate (Et 4 NBF 4 ) as the electrolyte salt dissolved in an acetonitrile or propylene carbonate solvent is the most popular choice to attain high operating potentials near 3V. A typical ES stack for
applications requiring high load operating potentials, such as uninterrupted