193
Components and Materials for Electrochemical Supercapacitors
increases self discharge and reduces device efficiency. A poor seal will break
over time and cause degradation and short circuiting [2].
Rolled cells can contain separate sealant materials. The internal seal is a
curable polymer placed onto the top of the metal casing before it is closed
and mechanically crimped shut. Curable polymer sealants are also used
to prevent short circuits across multiple layers in bipolar stacks (tops and
bottoms of roll edges). The curable material composed of a thermosetting
polymer, epoxy, polyurethane, polyester, polyacrylate creates a moistureresistant and mechanically strong seal [130]. A second type is an insulating
shrink wrap that seals the outer casing electrode, offers an external moisture barrier, and prevents unplanned discharges that create safety issues.
Shrink wrap seals are made from loosely fitting preformed bags composed
of polyolefins (PP, PE, reinforced PE) that surround the metal casing. Heat is
then applied to cause the plastic to shrink and tightly seal around the casing
insulating the cell.
Pouch cells have no metal casings. A multilayer polymer is placed around
the cell and laminated on a production line to bind and seal the device
between the bag layers. Before electrolyte infusion and bagging, the devices
undergo a nitrogen purge of the environment. A vacuum is applied, then the
electrolyte is fed through the bagging enclosure system under vacuum to
create a tight seal. The vacuum applies even pressure along the contents of
the film and drives the correct amount of electrolyte resin into the cells. The
excess is removed and collected for reuse [131].
The process lends itself to lamination on a large scale. Many cells can be
processed at one time within a single vacuum bag by careful arrangement
and spacing to minimize wasted bagging material. After lamination, the
laminated sheet can be cut into individual devices.
In smaller scale research applications, a polymer-coated foil bag (polybag)
can be vacuumed and the edges heat-sealed by hand [47]. An ideal sealant
bag is thermally conductive, electronically insulating, moisture resistant,
and has a one-way gas permeability membrane to vent gases generated from
the system.
Safety dictates that a seal must be strongly electronically insulating and
be puncture resistant. While optimizing these properties, it is also desirable
to minimize bag weight. The polybag used by Ioxus ESs is a patented laminate design [132]. LDPE sealant material is used as a first layer that re-forms
at 120°C, insulates, and binds the cell surface to the packaging. A copper
non-reactive foil layer provides moisture resistance and thermal conductivity away from the cell. The copper is sandwiched between another LDPE
layer that provides further electrical insulation and binds an outer punctureresistant layer of PET or Mylar® (biaxially aligned PET) that is mechanically
strong. After aligning the films, they are laminated in production and sent
to module assembly.
Components and Materials for Electrochemical Supercapacitors
increases self discharge and reduces device efficiency. A poor seal will break
over time and cause degradation and short circuiting [2].
Rolled cells can contain separate sealant materials. The internal seal is a
curable polymer placed onto the top of the metal casing before it is closed
and mechanically crimped shut. Curable polymer sealants are also used
to prevent short circuits across multiple layers in bipolar stacks (tops and
bottoms of roll edges). The curable material composed of a thermosetting
polymer, epoxy, polyurethane, polyester, polyacrylate creates a moistureresistant and mechanically strong seal [130]. A second type is an insulating
shrink wrap that seals the outer casing electrode, offers an external moisture barrier, and prevents unplanned discharges that create safety issues.
Shrink wrap seals are made from loosely fitting preformed bags composed
of polyolefins (PP, PE, reinforced PE) that surround the metal casing. Heat is
then applied to cause the plastic to shrink and tightly seal around the casing
insulating the cell.
Pouch cells have no metal casings. A multilayer polymer is placed around
the cell and laminated on a production line to bind and seal the device
between the bag layers. Before electrolyte infusion and bagging, the devices
undergo a nitrogen purge of the environment. A vacuum is applied, then the
electrolyte is fed through the bagging enclosure system under vacuum to
create a tight seal. The vacuum applies even pressure along the contents of
the film and drives the correct amount of electrolyte resin into the cells. The
excess is removed and collected for reuse [131].
The process lends itself to lamination on a large scale. Many cells can be
processed at one time within a single vacuum bag by careful arrangement
and spacing to minimize wasted bagging material. After lamination, the
laminated sheet can be cut into individual devices.
In smaller scale research applications, a polymer-coated foil bag (polybag)
can be vacuumed and the edges heat-sealed by hand [47]. An ideal sealant
bag is thermally conductive, electronically insulating, moisture resistant,
and has a one-way gas permeability membrane to vent gases generated from
the system.
Safety dictates that a seal must be strongly electronically insulating and
be puncture resistant. While optimizing these properties, it is also desirable
to minimize bag weight. The polybag used by Ioxus ESs is a patented laminate design [132]. LDPE sealant material is used as a first layer that re-forms
at 120°C, insulates, and binds the cell surface to the packaging. A copper
non-reactive foil layer provides moisture resistance and thermal conductivity away from the cell. The copper is sandwiched between another LDPE
layer that provides further electrical insulation and binds an outer punctureresistant layer of PET or Mylar® (biaxially aligned PET) that is mechanically
strong. After aligning the films, they are laminated in production and sent
to module assembly.