304
Electrochemical Supercapacitors for Energy Storage and Delivery
double-layer capacitance that has a value of ~0.1 F.cm –2 , consistent with the
values obtained by both CV and CDC measurements of a similar electrode
layer. Therefore, the EIS measurement and the proposed EC in Figure 7.14
should be reasonable.
7.6 Physical Characterization of Supercapacitor Materials
7.6.1 Scanning Electron Microscopy (SEM)
The SEM technique utilizes electron beams to scan the surface of a sample
specimen, as shown in Figure 7.15. The specimen is irradiated by a focused
electron beam and the signals produced create useful images describing the
surface morphology of the specimen. Samples must be electronically conductive to prevent charging effects that can blur image quality at higher resolutions. To avoid this, some insulating samples are gold sputtered to provide a
nanometer-thick conductive surface layer.
When the incident electron strikes the specimen surface, instead of bouncing off immediately, it penetrates for some distance before it collides with a
surface atom and a region of primary excitation where signals are produced
is created [12]. The most common signals used for imaging are secondary
electrons, backscattered electrons, and characteristic X-rays. In normal conditions, the secondary electrons created from inelastic surface scattering can
reach the detector in greater numbers, depending on incidence angle, and
generate topographic information.
The backscattered electrons are higher energy electrons deflected elastically or scattered back to the detector. This backscattering provides specimen
composition data because heavier elements produce greater backscattering
intensity, resulting in brighter images than those produced by lighter elements [12,13]. Characteristic x-rays can reveal the distribution of chemical
elements. Drawbacks of SEM include the requirement for a sample to be in
a solid state and stable inside a vacuum. Normally, materials saturated with
hydrocarbons, wet samples, and moisture-containing organic materials and
clays are not compatible with SEM until they are lyophilized [14].
In the study of supercapacitors, SEM can provide important information
about the material surface morphologies of cell components, specifically
when analyzing separator membrane porosity and electrode morphology
[15]. Images of the material surface can be collected before and after certain chemical or physical modifications or treatments to investigate their
effects on material phases and morphologies. For example, SEM is used to
examine the structural breakdown of single wall nanotube (SWNT) forests
after the addition of liquid (stability within electrolyte), or investigating the
layer interactions of graphene sheets in a transparent film [16]. SEM can also
Electrochemical Supercapacitors for Energy Storage and Delivery
double-layer capacitance that has a value of ~0.1 F.cm –2 , consistent with the
values obtained by both CV and CDC measurements of a similar electrode
layer. Therefore, the EIS measurement and the proposed EC in Figure 7.14
should be reasonable.
7.6 Physical Characterization of Supercapacitor Materials
7.6.1 Scanning Electron Microscopy (SEM)
The SEM technique utilizes electron beams to scan the surface of a sample
specimen, as shown in Figure 7.15. The specimen is irradiated by a focused
electron beam and the signals produced create useful images describing the
surface morphology of the specimen. Samples must be electronically conductive to prevent charging effects that can blur image quality at higher resolutions. To avoid this, some insulating samples are gold sputtered to provide a
nanometer-thick conductive surface layer.
When the incident electron strikes the specimen surface, instead of bouncing off immediately, it penetrates for some distance before it collides with a
surface atom and a region of primary excitation where signals are produced
is created [12]. The most common signals used for imaging are secondary
electrons, backscattered electrons, and characteristic X-rays. In normal conditions, the secondary electrons created from inelastic surface scattering can
reach the detector in greater numbers, depending on incidence angle, and
generate topographic information.
The backscattered electrons are higher energy electrons deflected elastically or scattered back to the detector. This backscattering provides specimen
composition data because heavier elements produce greater backscattering
intensity, resulting in brighter images than those produced by lighter elements [12,13]. Characteristic x-rays can reveal the distribution of chemical
elements. Drawbacks of SEM include the requirement for a sample to be in
a solid state and stable inside a vacuum. Normally, materials saturated with
hydrocarbons, wet samples, and moisture-containing organic materials and
clays are not compatible with SEM until they are lyophilized [14].
In the study of supercapacitors, SEM can provide important information
about the material surface morphologies of cell components, specifically
when analyzing separator membrane porosity and electrode morphology
[15]. Images of the material surface can be collected before and after certain chemical or physical modifications or treatments to investigate their
effects on material phases and morphologies. For example, SEM is used to
examine the structural breakdown of single wall nanotube (SWNT) forests
after the addition of liquid (stability within electrolyte), or investigating the
layer interactions of graphene sheets in a transparent film [16]. SEM can also