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Electrochemical Supercapacitor Design, Fabrication, and Operation
and composition. Over the years, research and development focused heavily on investigating carbons. In general, raw carbons are not favorable for
the development of significant capacitance. However, procedures involving
pyrolysis (carbonization) in a non-oxidizing environment introduce high
surface area and enhance porosity, increasing capacitance. As a result, in
the manufacturing of carbon-based ES cells, the choice of precursor material
and carbonization and activation techniques are critical to achieve a suitable
electroactive material for well performing devices.
5.3.2 Electrode Fabrication
Fabricating ES electrodes in commercial applications is proprietary information and normally not disclosed to the public domain. However, the laboratory and commercial techniques used for the fabrication of electrodes
are similar. The process involves mixing several ingredients, including the
electrode material such as a carbon powder (carbon black or CNT), conducting particles, and a fluorine-containing polymer (often PTFE) binding agent with a solvent to obtain a paste or slurry. This is followed by a
period of ball milling or ultrasonication to ensure a good dispersion of the
active material within a homogeneous composition. The paste or slurry
is then rolled, heat pressed, and dried to form an electrode layer film.
Alternatively, a spray deposition of the slurry or spreading of the paste
onto a substrate acting as the current collector can also be used to prepare
the electrode layer, followed by drying, annealing, and possibly press procedures to achieve the required film.
5.3.3 Electrolyte Preparation
Both aqueous electrolytes, including ionic liquids [e.g., 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF 4 )] and non-aqueous electrolytes
(e.g., Li or Na tetrafluoroborate, tetraethylammonium perchlorate dissolved
in acetonitrile, or propylene carbonate) can be used for saturation of the electrode layer and the separator. This process must be performed in a glove
box if a moisture-sensitive electrolyte, such as a non-aqueous electrolyte, is
used because any water inside a non-aqueous electrolyte will cause gas to
form during operating potentials intended to reach 2.5 to 3.5 V. Furthermore,
water contamination can disrupt the cell sealant during cycling and cause
higher internal resistance, lower power ratings, higher leakage current, and
loss of cycle life. To effectively maintain performance over the intended operating life, commercially available ESs are generally equipped with pressure
safety valves along the sides or ends of the cells to release any gas produced
by contamination or overheating.
Electrochemical Supercapacitor Design, Fabrication, and Operation
and composition. Over the years, research and development focused heavily on investigating carbons. In general, raw carbons are not favorable for
the development of significant capacitance. However, procedures involving
pyrolysis (carbonization) in a non-oxidizing environment introduce high
surface area and enhance porosity, increasing capacitance. As a result, in
the manufacturing of carbon-based ES cells, the choice of precursor material
and carbonization and activation techniques are critical to achieve a suitable
electroactive material for well performing devices.
5.3.2 Electrode Fabrication
Fabricating ES electrodes in commercial applications is proprietary information and normally not disclosed to the public domain. However, the laboratory and commercial techniques used for the fabrication of electrodes
are similar. The process involves mixing several ingredients, including the
electrode material such as a carbon powder (carbon black or CNT), conducting particles, and a fluorine-containing polymer (often PTFE) binding agent with a solvent to obtain a paste or slurry. This is followed by a
period of ball milling or ultrasonication to ensure a good dispersion of the
active material within a homogeneous composition. The paste or slurry
is then rolled, heat pressed, and dried to form an electrode layer film.
Alternatively, a spray deposition of the slurry or spreading of the paste
onto a substrate acting as the current collector can also be used to prepare
the electrode layer, followed by drying, annealing, and possibly press procedures to achieve the required film.
5.3.3 Electrolyte Preparation
Both aqueous electrolytes, including ionic liquids [e.g., 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF 4 )] and non-aqueous electrolytes
(e.g., Li or Na tetrafluoroborate, tetraethylammonium perchlorate dissolved
in acetonitrile, or propylene carbonate) can be used for saturation of the electrode layer and the separator. This process must be performed in a glove
box if a moisture-sensitive electrolyte, such as a non-aqueous electrolyte, is
used because any water inside a non-aqueous electrolyte will cause gas to
form during operating potentials intended to reach 2.5 to 3.5 V. Furthermore,
water contamination can disrupt the cell sealant during cycling and cause
higher internal resistance, lower power ratings, higher leakage current, and
loss of cycle life. To effectively maintain performance over the intended operating life, commercially available ESs are generally equipped with pressure
safety valves along the sides or ends of the cells to release any gas produced
by contamination or overheating.