136
Electrochemical Supercapacitors for Energy Storage and Delivery
4.1.2 Electrochemical Supercapacitors
Electrochemical supercapacitors (ESs) differ from traditional capacitors
because they have lower power densities, greater charge storage densities, and different material requirements. Electrical double-layer capacitors
(EDLCs) incorporate an electrolyte that allows charged ions to assemble on
porous electrode surfaces with much higher areas than traditional capacitors. The charge is separated by a solvent cage layer at the interface of only
5 to 10 angstroms [1,2]. A combination of high surface area and small charge
separation enables the generation of high energy density compared to traditional static capacitors.
Optimizing ES design involves the selection of appropriate electrodes,
electrolytes, separators, and sealants. Electrode materials must be conductive and highly porous to increase charge storage ability. Non-metal porous
electrodes are used in ECs rather than the metal plates of traditional capacitors; this creates a need for current collector plates to enhance the conduction
of electrons in the capacitor. Collectors must be in strong contact with the
electrode layer, remain stable during charge and discharge, and be highly
conductive to enhance electron transport.
Electrolyte materials require high ion mobility to provide ions to the double-layer quickly. Improved electrolyte performance also requires optimization of operating voltages, toxicity, corrosion, and safety. Separators must be
electronically insulating to prevent short circuits between the two electrode
layers, and allow high ionic mobility from the electrolyte to the electrode
surface. The separator choices in ES design include microporous or nonwoven polymers, glass, and cellulose derivatives. The most common ones
are polymer separators that include polyolefins such as polypropylene (PP),
polyethylene (PE), Teflon, PVdF, and PVC.
The chosen polymer and production method vary based on the electrolyte used.
Sealants must be non-conductive, prevent ion leakage between stacked
cells, and resist corrosion and degradation. Sealant use depends on cell type;
sealants are commonly made of low melting temperature PE material or viscous fast setting polymers such as epoxies. Sealants do not directly impact
performance; they help control safety and moisture. A seal that fails can lead
to short circuits within assembled cells.
Overall, careful selection and matching of ES materials can minimize
resistances, avoid short circuits, reduce safety issues, support high ion mobility, increase operating voltage, and enhance the charge storage capacity of
future ES devices [3].
Electrode materials in ESs fall into two categories based on storage mechanism: EDLC and pseudocapacitive materials. Each material in these categories presents its own benefits and challenges as this technology moves toward
the next generation of ES devices. EDLC materials are carbons that provide
physical charge storage at the interface between electrode and electrolyte.
Electrochemical Supercapacitors for Energy Storage and Delivery
4.1.2 Electrochemical Supercapacitors
Electrochemical supercapacitors (ESs) differ from traditional capacitors
because they have lower power densities, greater charge storage densities, and different material requirements. Electrical double-layer capacitors
(EDLCs) incorporate an electrolyte that allows charged ions to assemble on
porous electrode surfaces with much higher areas than traditional capacitors. The charge is separated by a solvent cage layer at the interface of only
5 to 10 angstroms [1,2]. A combination of high surface area and small charge
separation enables the generation of high energy density compared to traditional static capacitors.
Optimizing ES design involves the selection of appropriate electrodes,
electrolytes, separators, and sealants. Electrode materials must be conductive and highly porous to increase charge storage ability. Non-metal porous
electrodes are used in ECs rather than the metal plates of traditional capacitors; this creates a need for current collector plates to enhance the conduction
of electrons in the capacitor. Collectors must be in strong contact with the
electrode layer, remain stable during charge and discharge, and be highly
conductive to enhance electron transport.
Electrolyte materials require high ion mobility to provide ions to the double-layer quickly. Improved electrolyte performance also requires optimization of operating voltages, toxicity, corrosion, and safety. Separators must be
electronically insulating to prevent short circuits between the two electrode
layers, and allow high ionic mobility from the electrolyte to the electrode
surface. The separator choices in ES design include microporous or nonwoven polymers, glass, and cellulose derivatives. The most common ones
are polymer separators that include polyolefins such as polypropylene (PP),
polyethylene (PE), Teflon, PVdF, and PVC.
The chosen polymer and production method vary based on the electrolyte used.
Sealants must be non-conductive, prevent ion leakage between stacked
cells, and resist corrosion and degradation. Sealant use depends on cell type;
sealants are commonly made of low melting temperature PE material or viscous fast setting polymers such as epoxies. Sealants do not directly impact
performance; they help control safety and moisture. A seal that fails can lead
to short circuits within assembled cells.
Overall, careful selection and matching of ES materials can minimize
resistances, avoid short circuits, reduce safety issues, support high ion mobility, increase operating voltage, and enhance the charge storage capacity of
future ES devices [3].
Electrode materials in ESs fall into two categories based on storage mechanism: EDLC and pseudocapacitive materials. Each material in these categories presents its own benefits and challenges as this technology moves toward
the next generation of ES devices. EDLC materials are carbons that provide
physical charge storage at the interface between electrode and electrolyte.