190
Electrochemical Supercapacitors for Energy Storage and Delivery
FIGURE 4.32
Appearances and forms of polyolefin separators. (Source: Arora, P. and Z. J. Zhang. 2004.
Chemical Reviews, 104, 4419–4462. With permission.)
[114]. Polyolefins continue to see increased utilization in aqueous systems as
well. The problem with polyolefins for aqueous electrolytes is that they are
hydrophobic and cannot be effectively wetted by an electrolyte. However,
treatment of polyolefin films by graft polymerization enables modification
of surface properties to increase surface hydrophilicity [114].
Separator structures fall into four main categories: microporous films,
nonwovens, gel polymers, and solid polymers. Microporous films contain
small pores (5 to 10 nm in diameter) and are often used for low temperature
applications. They are made from nonwoven fibers such as cotton, polyester,
glass, polyolefins (PP and PE), PTFE, and PVC. Microporous separators are
commonly used with organic electrolytes and in acidic systems. Nonwovens
are manufactured as mats of fibers and bind through frictional forces. They
exhibit consistent weight, thickness, and degradation resistance but they
show inadequate pore order and are difficult to make thinner than 25 μm.
Nonwovens are generally made from cellulose, PTFE, PVC, PVdF, or a combination of polyolefins and receive preference in alkaline systems [114].
4.5 Current Collectors
Current collectors are used in ES devices to gather and feed electrical charges
stored within the active capacitive material. In most cases, the conduction of
charge throughout the active material of an electrode is insufficient and provides a large amount of resistance that can ruin performance characteristics
of an otherwise acceptable ES material. Efficient contacts and additives are
needed to effectively transport charge current and provide a system with
sufficient power.
Typically metal and metal alloys with high electrical conductivities are
used to move energy to a common ground for the capacitor stack. Metals of
Electrochemical Supercapacitors for Energy Storage and Delivery
FIGURE 4.32
Appearances and forms of polyolefin separators. (Source: Arora, P. and Z. J. Zhang. 2004.
Chemical Reviews, 104, 4419–4462. With permission.)
[114]. Polyolefins continue to see increased utilization in aqueous systems as
well. The problem with polyolefins for aqueous electrolytes is that they are
hydrophobic and cannot be effectively wetted by an electrolyte. However,
treatment of polyolefin films by graft polymerization enables modification
of surface properties to increase surface hydrophilicity [114].
Separator structures fall into four main categories: microporous films,
nonwovens, gel polymers, and solid polymers. Microporous films contain
small pores (5 to 10 nm in diameter) and are often used for low temperature
applications. They are made from nonwoven fibers such as cotton, polyester,
glass, polyolefins (PP and PE), PTFE, and PVC. Microporous separators are
commonly used with organic electrolytes and in acidic systems. Nonwovens
are manufactured as mats of fibers and bind through frictional forces. They
exhibit consistent weight, thickness, and degradation resistance but they
show inadequate pore order and are difficult to make thinner than 25 μm.
Nonwovens are generally made from cellulose, PTFE, PVC, PVdF, or a combination of polyolefins and receive preference in alkaline systems [114].
4.5 Current Collectors
Current collectors are used in ES devices to gather and feed electrical charges
stored within the active capacitive material. In most cases, the conduction of
charge throughout the active material of an electrode is insufficient and provides a large amount of resistance that can ruin performance characteristics
of an otherwise acceptable ES material. Efficient contacts and additives are
needed to effectively transport charge current and provide a system with
sufficient power.
Typically metal and metal alloys with high electrical conductivities are
used to move energy to a common ground for the capacitor stack. Metals of