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Electrochemical Supercapacitors for Energy Storage and Delivery
4.2.2 Introducing Electrode Requirements for
Electrochemical Supercapacitors
Static storage mechanisms in EDLCs efficiently store charges upon the electrodes at high rates. Unlike rechargeable batteries, ESs involve no chemical breakdown or redeposition of electrode materials during operation. This
lowers the risk of electrode phase changes during operation and enables long
electrode cycle lives. The static charge storage in EDLCs enables the anode
and cathode to be interchangeable. Unlike specific electrode requirements
seen in many batteries, the anode and cathode of an EDLC are composed of
the same material. If the positive and negative current collector terminals
and cell casing are also made of similar materials, theoretically the EDLC
has no true polarity [8]. The important requirements for the optimization of
electrode materials include:
• Long and stable cycle life (>10 5 )
• Minimal irreversible redox processes
• High specific surface area
• Thermodynamic stability for a large potential window of operation
• Ability to control morphology, pore size, particle size, and material distribution
• Surface wettability
• High electrical conductivity
• Sufficient thermal conductivity to reduce heat build-up within cell
• Strong mechanical properties
Expanding upon the EDLC mechanism, pseudocapacitive materials used in
ESs can be used to store more charge and energy. Pseudocapacitive materials undergo reversible redox reactions that are faster than those in batteries.
Multiple redox states are available and each reaction will occur at a specific
voltage as the device charges and discharges. The fast redox rate allows an
increase in energy density while maintaining a large portion of the power
density available in EDLC electrodes.
The main drawback is that pseudocapacitive materials suffer from poor
cycle lives compared to EDLC devices. This knowledge can be utilized to
design composite electrodes where pseudocapacitive materials can be deposited onto an EDLC support to provide highly porous structure. Further, in
asymmetric (also known as hybrid) cells, pseudocapacitive material can
be used at one electrode while EDLC materials can be used on the other.
Hybrid designs are meant to optimize energy density while maintaining the
power density available to EDLC-based capacitors. Both pseudocapacitive
and EDLC contributions can be significantly altered by key factors such as
surface area, structure, conductivity, and interaction with functional groups
on the material surface.
Electrochemical Supercapacitors for Energy Storage and Delivery
4.2.2 Introducing Electrode Requirements for
Electrochemical Supercapacitors
Static storage mechanisms in EDLCs efficiently store charges upon the electrodes at high rates. Unlike rechargeable batteries, ESs involve no chemical breakdown or redeposition of electrode materials during operation. This
lowers the risk of electrode phase changes during operation and enables long
electrode cycle lives. The static charge storage in EDLCs enables the anode
and cathode to be interchangeable. Unlike specific electrode requirements
seen in many batteries, the anode and cathode of an EDLC are composed of
the same material. If the positive and negative current collector terminals
and cell casing are also made of similar materials, theoretically the EDLC
has no true polarity [8]. The important requirements for the optimization of
electrode materials include:
• Long and stable cycle life (>10 5 )
• Minimal irreversible redox processes
• High specific surface area
• Thermodynamic stability for a large potential window of operation
• Ability to control morphology, pore size, particle size, and material distribution
• Surface wettability
• High electrical conductivity
• Sufficient thermal conductivity to reduce heat build-up within cell
• Strong mechanical properties
Expanding upon the EDLC mechanism, pseudocapacitive materials used in
ESs can be used to store more charge and energy. Pseudocapacitive materials undergo reversible redox reactions that are faster than those in batteries.
Multiple redox states are available and each reaction will occur at a specific
voltage as the device charges and discharges. The fast redox rate allows an
increase in energy density while maintaining a large portion of the power
density available in EDLC electrodes.
The main drawback is that pseudocapacitive materials suffer from poor
cycle lives compared to EDLC devices. This knowledge can be utilized to
design composite electrodes where pseudocapacitive materials can be deposited onto an EDLC support to provide highly porous structure. Further, in
asymmetric (also known as hybrid) cells, pseudocapacitive material can
be used at one electrode while EDLC materials can be used on the other.
Hybrid designs are meant to optimize energy density while maintaining the
power density available to EDLC-based capacitors. Both pseudocapacitive
and EDLC contributions can be significantly altered by key factors such as
surface area, structure, conductivity, and interaction with functional groups
on the material surface.