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Electrochemical Supercapacitors for Energy Storage and Delivery
good contact between the current collector and active material layer must be
maintained to minimize internal resistance. They must be pressed together
uniformly to avoid pressing out a critical volume of electrolyte.
5.3.5.1 Coin Cells
Coin cells provide good media for small capacitance devices. The casing of a
coin cell is made from conductive metal end caps and the fitting is designed
to be crimped under high pressure. The top plate sits in a hydrophobic insulating rubber or Teflon gasket seal that prevents water moisture from entering the device and disrupting performance. However, the result is a thin
device with a low mass of active material. To create larger capacitors, it is
important to better utilize cell volume and produce larger cells. Rolled cells
are used in larger capacitance devices where the electrode material can be
synthesized in long sheets and spirally wound into rolls. A high level of compression is needed for good contact with the aluminum support. However it
is important not to remove electrolyte to a level that will limit ion availability.
If too little electrolyte is present within a soaked separator, ion saturation
will occur and performance will suffer. The presence of an aluminum collector allows for strong conduction. The external contact tabs are soldered onto
the collector foil during the rolling process. Rolled cells provide uniform
rolling and compression on a large scale. However, they exhibit poor space
optimization and the thick nature of the cell makes designing of efficient
heat sink and cooling designs difficult.
5.3.5.2 Cylindrical Cells
Alternatively, a roll can be wound to fit a prismatic case as commonly found
in lithium ion batteries. The roll is placed in a fitted conductive metal casing that has a Teflon or rubber gasket seal separating the outer can and top
button contact. The cylindrical metal rod around which the film is wound
becomes the internal contact. Contacts are ensured by soldering and then
electrolyte is injected into the cell followed by a curable polymer sealant.
The top of the casing is fitted with a vent, gasket layer, and top contact plate.
To seal the device, the top of the can is mechanically crimped and the outer
metal casing acts as the other contact and provides mechanical stability and
rupture resistance.
To prevent discharge and ensure safety, an external sealant or insulator
must be applied to the electrode as a solid casing or as a shrink wrap to finish the manufacture. In stiff metal cases for which gas evolution is a concern,
a one-way safety vent must be incorporated into the device. The safety vent
prevents moisture from entering but will rupture and release gas if the capacitor enters a regime in which pressure or heat build-up is a concern. Another
assembly concern for organic electrolytes in commercial devices is contamination via penetration of water moisture into the electrolyte. Cells made with
Electrochemical Supercapacitors for Energy Storage and Delivery
good contact between the current collector and active material layer must be
maintained to minimize internal resistance. They must be pressed together
uniformly to avoid pressing out a critical volume of electrolyte.
5.3.5.1 Coin Cells
Coin cells provide good media for small capacitance devices. The casing of a
coin cell is made from conductive metal end caps and the fitting is designed
to be crimped under high pressure. The top plate sits in a hydrophobic insulating rubber or Teflon gasket seal that prevents water moisture from entering the device and disrupting performance. However, the result is a thin
device with a low mass of active material. To create larger capacitors, it is
important to better utilize cell volume and produce larger cells. Rolled cells
are used in larger capacitance devices where the electrode material can be
synthesized in long sheets and spirally wound into rolls. A high level of compression is needed for good contact with the aluminum support. However it
is important not to remove electrolyte to a level that will limit ion availability.
If too little electrolyte is present within a soaked separator, ion saturation
will occur and performance will suffer. The presence of an aluminum collector allows for strong conduction. The external contact tabs are soldered onto
the collector foil during the rolling process. Rolled cells provide uniform
rolling and compression on a large scale. However, they exhibit poor space
optimization and the thick nature of the cell makes designing of efficient
heat sink and cooling designs difficult.
5.3.5.2 Cylindrical Cells
Alternatively, a roll can be wound to fit a prismatic case as commonly found
in lithium ion batteries. The roll is placed in a fitted conductive metal casing that has a Teflon or rubber gasket seal separating the outer can and top
button contact. The cylindrical metal rod around which the film is wound
becomes the internal contact. Contacts are ensured by soldering and then
electrolyte is injected into the cell followed by a curable polymer sealant.
The top of the casing is fitted with a vent, gasket layer, and top contact plate.
To seal the device, the top of the can is mechanically crimped and the outer
metal casing acts as the other contact and provides mechanical stability and
rupture resistance.
To prevent discharge and ensure safety, an external sealant or insulator
must be applied to the electrode as a solid casing or as a shrink wrap to finish the manufacture. In stiff metal cases for which gas evolution is a concern,
a one-way safety vent must be incorporated into the device. The safety vent
prevents moisture from entering but will rupture and release gas if the capacitor enters a regime in which pressure or heat build-up is a concern. Another
assembly concern for organic electrolytes in commercial devices is contamination via penetration of water moisture into the electrolyte. Cells made with