U.S. patent application number 15/092128 was filed with the patent office on 2016-07-28 for double layer capacitors.
The applicant listed for this patent is CALGON CARBON CORPORATION. Invention is credited to Joseph M. KLINVEX, Robert P. O'BRIEN, Walter G. TRAMPOSCH, Robert H. VAUGHN.
Application Number | 20160217938 15/092128 |
Document ID | / |
Family ID | 48613283 |
Filed Date | 2016-07-28 |
United States Patent
Application |
20160217938 |
Kind Code |
A1 |
KLINVEX; Joseph M. ; et
al. |
July 28, 2016 |
DOUBLE LAYER CAPACITORS
Abstract
Activated carbons having improved volumetric capacitance and
double layer capacitors including these activated carbons are
described herein.
Inventors: |
KLINVEX; Joseph M.;
(Sewickley, PA) ; TRAMPOSCH; Walter G.; (Moon
Township, PA) ; VAUGHN; Robert H.; (Bethel Park,
PA) ; O'BRIEN; Robert P.; (Bethel Park, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CALGON CARBON CORPORATION |
Moon Township |
PA |
US |
|
|
Family ID: |
48613283 |
Appl. No.: |
15/092128 |
Filed: |
April 6, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13717497 |
Dec 17, 2012 |
9312077 |
|
|
15092128 |
|
|
|
|
61576597 |
Dec 16, 2011 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01G 11/60 20130101;
H01G 11/32 20130101; H01G 11/84 20130101; Y02E 60/13 20130101; H01G
11/34 20130101; H01G 11/24 20130101; H01G 11/58 20130101; H01G
11/62 20130101 |
International
Class: |
H01G 11/84 20060101
H01G011/84; H01G 11/60 20060101 H01G011/60; H01G 11/62 20060101
H01G011/62; H01G 11/34 20060101 H01G011/34 |
Claims
1. A method for making an activated carbon for use in an
electrochemical double layer capacitor comprising: heating a
carbonaceous material to a temperature of from about 1600.degree.
F. to about 2200.degree. F. for a time period sufficient to produce
a volumetric surface are of about 400 m.sup.2/cc to about 800
m.sup.2/cc; and contacting the carbonaceous material with an
electrolyte.
2. The method of claim 1, further comprising pulverizing the
carbonaceous material.
3. The method of claim 1, further comprising contacting the
carbonaceous material with an activating gas.
4. The method of claim 1, wherein the activating gas is comprises
steam or carbon dioxide (CO.sub.2).
5. The method of claim 1, wherein the volumetric surface area is
from about 500 m.sup.2/cc to about 700 m.sup.2/cc.
6. The method of claim 1, wherein the carbonaceous material
comprises a carbonaceous char derived from coconut shell, babassu
nut shell, macadamia nut shell, dende nut shell, walnut shell,
peach pit, cherry pit, olive pit, and combinations thereof.
7. The method of claim 1, wherein the carbonaceous material
comprises a carbonaceous char derived from nut shells, pits, coal,
wood, petroleum, petroleum by-products, polymers, resins, and
combinations thereof.
8. The method of claim 1, wherein the electrolyte comprises an
organic solvent or water.
9. The method of claim 1, wherein the organic solvent is selected
from the group consisting of propylene carbonate (PC),
y-butyrolactone, acetonitrile (AN), dimethylformamide,
1,2-dimethoxyethane, sulfolane, nitromethane acetonitrile (ACN), or
combinations thereof.
10. The method of claim 1, wherein the electrolyte comprises an
organic solvent and one or more alkali metal salt, amine salts,
tetraalkylammonium salts, tetraalkylphosphonium salts, and
combinations thereof.
11. The method of claim 1, wherein the electrolyte comprises an
aqueous electrolyte comprising a solution of water and an inorganic
acid, sulfuric acid, tetrafluoroboric acid, an inorganic base,
potassium hydroxide, sodium hydroxide, or inorganic salts, or
combinations thereof.
12. The method of claim 1, wherein the time period is from about 2
hours to about 10 hours.
13. A method for making an activated carbon for use in an
electrochemical double layer capacitors comprising: identifying an
activation time for a carbon source that provides a maximum
volumetric capacitance; and activating carbon from the carbon
source for the activation time identified to produce activated
carbon.
14. The method of claim 13, wherein the activation time is
sufficient to produce an activated carbon having a volumetric
surface area of about 400 m.sup.2/cc to about 800 m.sup.2/cc.
15. The method of claim 13, wherein the activation time is
sufficient to produce an activated carbon having a volumetric
surface area of from about 500 m.sup.2/cc to about 700
m.sup.2/cc.
16. The method of claim 13, wherein the carbon source is coconut
shell, babassu nut shell, macadamia nut shell, dende nut shell,
walnut shell peach pit, cherry pit, olive pit, and combinations
thereof.
17. The method of claim 13, wherein the carbon source is nut
shells, pits, coal, wood, petroleum, petroleum by-products,
polymers, resins, and combinations thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 13/717,497 filed on Dec. 17, 2012, which
claims the benefit of U.S. Provisional Application No. 61/576,597,
filed Dec. 16, 2011, each of which are hereby incorporated herein
by reference in their entireties.
GOVERNMENT INTERESTS
[0002] Not applicable
PARTIES TO A JOINT RESEARCH AGREEMENT
[0003] Not applicable
INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT
DISC
[0004] Not applicable
BACKGROUND
[0005] Not Applicable
BRIEF SUMMARY OF THE INVENTION
[0006] Not Applicable.
DESCRIPTION OF DRAWINGS
[0007] For a fuller understanding of the nature and advantages of
the present invention, reference should be made to the following
detailed description taken in connection with the accompanying
drawings, in which:
[0008] FIG. 1 is a graph showing gravimetric capacitance versus
gravimetric surface area for activated carbons prepared from
different materials.
[0009] FIG. 2 is a graph showing volumetric capacitance versus
volumetric surface area for activated carbons prepared from
different materials.
[0010] FIG. 3 is a graph showing volumetric capacitance versus
apparent density for activated carbons prepared from three
different materials and having varying degrees of activation.
DETAILED DESCRIPTION
[0011] It must be noted that, as used herein, and in the appended
claims, the singular forms "a," "an," and "the" include plural
reference unless the context clearly dictates otherwise. Unless
defined otherwise, all technical and scientific terms used herein
have the same meanings as commonly understood by one of ordinary
skill in the art. Although any methods similar or equivalent to
those described herein can be used in the practice or testing of
embodiments of the present invention, the preferred methods are now
described. All publications and references mentioned herein are
incorporated by reference. Nothing herein is to be construed as an
admission that the invention is not entitled to antedate such
disclosure by virtue of prior invention.
[0012] As used herein, the term "about" means plus or minus 10% of
the numerical value of the number with which it is being used.
Therefore, about 50% means in the range of 45%-55%.
[0013] "Optional" or "optionally" may be taken to mean that the
subsequently described structure, event or circumstance may or may
not occur, and that the description includes instances where the
event occurs and instances where it does not.
[0014] Activated carbon is widely used in the food industry,
chemical industry, pharmaceutical industry and various other
industries. In recent years, activated carbon has been used in the
electrodes in electrical double layer capacitors. Electrical double
layer capacitors that use activated carbon in the electrodes
generally exhibit superior electrostatic capacitance, which has
made them desirable for use in electronics, electronic device
electrode applications, and more recently back-up power supplies in
which high-capacitance products are used in the auxiliary power
supplies of motors and various regenerative energy storage
applications and the like.
[0015] Double layer capacitors rely on the formation of an ionic
double layer at each of two electrodes when a potential is applied
and the capacitor is charged. The total capacitance achievable in
the device is related to the surface area of the electrodes by
equation 1:
C = eS d ( 1 ) ##EQU00001##
Where C is capacitance of the device; S is the surface area of the
electrode; e is the dielectric constant; and d is the double layer
thickness.
[0016] In this equation, e and d are properties of the electrolyte,
and S is a property of the material that serves as the electrode.
To achieve the highest device capacitance, previous work has
focused on maximizing the surface area of the electrode material to
attain the highest gravimetric capacitance (F/g) resulting in the
highest gravimetric device capacitance. The electrode material has
thus been chosen from materials that have a large surface area, and
preferred materials have generally been carbon-based materials such
as activated carbons, carbon nanotubes, graphenes, and the like
because of their high surface areas and chemical stability, which
provides stability in the electrolyte system at the voltages
applied.
[0017] Like electrodes may be used in pairs to produce devices
which behave as capacitors and are generally referred to as
symmetric double layer capacitors. A single carbon electrode can
also be coupled in combination with a faradaic and/or
electrochemically active electrode using for example but not
limited to containing nickel, lead, lithium, or manganese and their
salts to produce devices known as asymmetric capacitors, pseudo
capacitors, or hybrid batteries. Carbon electrodes may also be used
in split electrode configurations or added to electrodes rather
than used alone as an electrode material. The term "capacitor," as
used herein, and in the appended claims refers to symmetric
capacitors, asymmetric capacitors, pseudo capacitors, hybrid
batteries, advanced batteries, and split electrode electrochemical
devices.
[0018] Embodiments of the invention are directed to activated
carbon materials and methods for preparing activated carbon
materials for use in double layer capacitors in both symmetric and
asymmetric devices. The activated carbons of the invention exhibit
a maximum volumetric capacitance (F/cc) and provide improved
capacitance at lower surface areas than previously described
activated carbon materials used in double layer capacitors.
[0019] The activation process relies upon the gasification of the
carbonaceous precursor, which leads to increased surface area of
the resultant activated carbon. Gasification also results in a
reduction in the bulk density of the activated carbon commonly
known as the apparent density ("AD") in g/cc. The increase in the
surface area leads to an increase in the capacitance of the device
as provided in equation (1) given a fixed weight of carbon;
however, the accompanied decrease in activated carbon density would
require a larger volume of activated carbon to maintain a constant
device capacitance based on the gravimetric capacitance (F/g). .
According to equation (1), increasing the surface area of the
activated carbon should result in an increase in device size to
accommodate the larger volume of activated carbon. FIG. 1 is a
graph showing the relationship of gravimetric surface area
(m.sup.2/g) to gravimetric capacitance (F/g). As expected, as the
BET surface area increases the gravimetric capacitance also
increases for all of the materials tested.
[0020] The same relationship would be expected to be evident
regardless of the means for determining the surface area of the
activated carbon. However, as illustrated in FIG. 2 the linear
relationship exhibited when gravimetric surface area (m.sup.2/g) is
plotted in relation to gravimetric capacitance (F/g) is not
apparent. Rather, the volumetric capacitance (F/cc) appears to peak
at particular volumetric surface areas (m.sup.2/cc), and these
peaks appear to vary somewhat depending on the material used to
make the activated carbon. "Volumetric surface area" as used herein
is defined as the product of the gravimetric surface area in
m.sup.2/g and the apparent density (AD) in g/cc.
[0021] Table 1 shows the surface area of activated carbon materials
prepared from various precursors as measured by standard nitrogen
adsorption as a function of AD. In general, the lower the AD, the
higher the degree of activation and the higher the surface area. As
indicated by the BET surface area in m.sup.2/g for the three
materials also presented Table 1, an increase in the surface area
is observed as the material is activated at least for the
bituminous and coconut based materials. The anthracite-based
material exhibits an increase in surface area followed by a
decrease as the material is further activated. This type of
behavior is well known to those skilled in the art for materials
that are difficult to activate, such as anthracite precursors as
they will generally reach a plateau in surface area at a relatively
low value and then decline upon further activation. Table 1 also
provides the volumetric capacitance (F/cc) as a function of
apparent density (AD) of the activated carbon materials in double
layer electrodes fabricated using a solvent of propylene carbonate
(PC) and acetonitrile (AN) along with a salt.
TABLE-US-00001 TABLE 1 Gravi- metric Volumetric Volumetric
Volumetric Surface Surface Capacitance Capacitance AD Area Area in
PC (F/cc) in AN (F/cc) (g/cc) (m.sup.2/g) (m.sup.2/cc) Bituminous-
based 3346-45F 2 3 0.825 209 172 3346-45G 52 66 0.650 960 624
3346-45H 47 48 0.584 1192 696 3346-45J 54 55 0.480 1381 663
Anthracite- based 3359-79A 35 40 0.780 564 440 3359-79D 46 51 0.640
814 521 3359-79E 46 49 0.595 978 582 3359-79C-1 31 31 0.511 473 242
Coconut- based 3366-39-1 11 15 0.603 859 518 3366-40-4 52 71 0.564
875 494 3366-39-3 62 76 0.514 1236 635 3366-39-2 57 59 0.456 1591
725 3366-39-4 57 58 0.397 1754 696
[0022] The data in Table 1 is graphically provided in FIG. 3. As
discussed above, the increase in surface area associated with
increased activation would generally be expected to result in an
increase in the volumetric capacitance (see equation (1)). However,
as indicated in Table 1 and FIG. 1, this does not appear to be the
case. Rather, the volumetric capacitance appears to maximize at
some intermediate surface area and not at the greatest surface area
achieved for each of the three materials tested. Both PC and AN
show similar results indicating the effect is not dependent on the
electrolyte solvent used. It is therefore reasonable to assume that
the effect would be seen for other electrolyte solvents and salts
in various combinations. Notably, the degree of the increase in the
volumetric capacitance and the area at which the maximum is reached
in terms of the AD or activation is also dependent on the material
that is activated.
[0023] The activated carbon materials described above permit the
fabrication of improved high capacitance electrodes including
carbonaceous materials that have an optimum degree of activation
rather than merely the highest surface area. As discussed above, we
show that high surface area materials do not appear to produce the
highest capacitance devices when actually reduced to electrodes.
This is quite surprising given that one skilled in the art would
expect that electrodes manufactured from high surface area
materials would also produce the highest capacitance devices. The
capacitance provided by the electrodes manufactured with these
optimized materials exhibit higher overall capacitance per unit
volume. Therefore, these lower surface area materials may allow for
the fabrication of reduced volume electrodes and capacitor devices
that can be made smaller while retaining excellent capacitance. In
addition, the electrodes and capacitor devices of various
embodiments may be produced from lower cost raw materials with
equivalent capacitance because a high degree of activation is not
required and the processing costs of these materials (and others)
is greatly reduced since the yields of lower surface area (higher
AD) materials is much higher.
[0024] Based on the foregoing, various embodiments of the invention
are directed to methods for preparing activated carbon having
surface areas that exhibit a maximum volumetric capacitance (F/cc),
and capacitors including an activated carbon material having
maximum volumetric capacitance. For example, the capacitors
prepared using such activated carbons having optimized gravimetric
(e.g., BET) surface area and AD may generally exhibit a volumetric
capacitance of from about 40 F/cc to about 80 F/cc, and in some
embodiments, from about 45 F/cc to about 75 F/cc.
[0025] The activated carbon of such embodiments may be prepared
from any precursor carbonaceous material known in the art
including, but not limited to bituminous coal, sub-bituminous coal,
lignite coal, anthracite coal, peat, nut shells, pits, coconut,
babassu nut, macadamia nut, dende nut, peach pit, cherry pit, olive
pit, walnut shell, wood, polymers, resins, petroleum pitches, and
any other carbonaceous material or combinations thereof.
Additionally, activated carbons produced from various precursors
which have been in-use and subsequently reactivated and/or
regenerated may be used. As indicated in Table 1, the surface area
of activated carbon materials having maximum volumetric capacity
may vary depending on the precursor material used to prepare the
activated carbon. For example, in some embodiments, the activated
carbon may have a gravimetric surface area of from about 300
m.sup.2/g to about 2100 m.sup.2/g as measured using either the
Langmuir, multipoint, or BET methods, and in other embodiments,
activated carbon may have a gravimetric surface area of from about
700 m.sup.2/g to about 1300 m.sup.2/g or about 800 m.sup.2/g to
about 1100 m.sup.2/g using such methods.
[0026] The apparent density (AD) of the activated carbon used in
the capacitors of various embodiments may also vary and may vary
depending on the precursor used to prepare the activated carbon. In
general, the activated carbon of embodiments may have an AD of 0.20
g/cc to about 0.80 g/cc. For example, in embodiments in which the
activated carbon is prepared from a precursor derived from coal
such as, for example, bituminous, sub-bituminous, lignite, and
anthracite coal, the AD of the activated carbon may be from about
0.70 g/cc to about 0.55 g/cc, and in some embodiments, from about
0.65 g/cc to about 0.50 g/cc. In embodiments in which the activated
carbon is prepared from a precursor derived from a plant material
char such as, for example, coconuts, babassu nuts, peach pits,
walnuts, cherry pits, or the like, the AD of the activated carbon
may be from about 0.40 g/cc to about 0.60 g/cc and in some
embodiments, from about 0.45 g/cc to about 0.55 g/cc.
[0027] In particular embodiments, the surface area of the activated
carbon used in the capacitors of the invention may be determined by
volumetric methods. For example, the activated carbon may have a
volumetric surface area of from about 400 m.sup.2/cc to about 800
m.sup.2/cc or, in other embodiments, from about 500 m.sup.2/cc to
about 700 m.sup.2/cc. In still other embodiments, the volumetric
surface area may be from about 450 m.sup.2/cc to about 800
m.sup.2/cc, about 500 m.sup.2/cc to about 800 m.sup.2/cc, about 550
m.sup.2/cc to about 800 m.sup.2/cc, about 600 m.sup.2/cc to about
800 m.sup.2/cc, about 400 m.sup.2/cc to about 700 m.sup.2/cc, about
450 m.sup.2/cc to about 700 m.sup.2/cc, about 500 m.sup.2/cc to
about 700 m.sup.2/cc, about 550 m.sup.2/cc to about 700 m.sup.2/cc,
about 400 m.sup.2/cc to about 650 m.sup.2/cc, about 450 m2/cc to
about 650 m.sup.2/cc, about 500 m.sup.2/cc to about 650 m.sup.2/cc,
about 400 m.sup.2/cc to about 600 m.sup.2/cc, about 450 m.sup.2/cc
to about 600 m.sup.2/cc, about 500 m.sup.2/cc to about 600
m.sup.2/cc, or any value or range within these ranged. Without
wishing to be bound by theory, the volumetric surface area may be
more directly related to the maximum capacitance of devices
including activated carbon than either gravimetric surface area or
apparent or actual density of the activated carbon. Thus, activated
carbon made from any precursor that has a volumetric surface area
within the ranges identified above may exhibit higher capacitance
than lower or higher volumetric surface area activated carbons made
from the same materials.
[0028] The activated carbon of various embodiments may be of any
size appropriate for use in a capacitor. For example, in some
embodiments, the activated carbon may have a mean particle diameter
of about 20 .mu.m or less, about 10 .mu.m or less, about 5 .mu.m or
less, and in certain embodiments, from about 0.1 .mu.m to about 20
.mu.m or about 0.1 .mu.m to about 10 .mu.m. In other applications
that require thicker electrodes, for example, asymmetric capacitors
or hybrid batteries, larger particle sized materials may be
preferred
[0029] The capacitors of such embodiments may be configured or
designed in any way known in the art. For example, in some
embodiments, the capacitors may be symmetric double-layer
capacitors having two like electrically-conductive electrodes
impregnated with an electrolyte and separated by an ion permeable
material, wherein the electrically-conductive electrodes include at
least one carbonaceous material having an optimized capacitance. In
other embodiments, only one electrode or a portion of one electrode
would include a carbonaceous material having an optimized
capacitance. These devices are known as asymmetric capacitors,
hybrid batteries and advanced batteries as previously described.
Other embodiments may include mixtures or combinations of optimized
capacitance materials with various components such as other
capacitive materials, binders, conductivity enhancers,
electrochemically active materials, and/or faradaic materials.
[0030] The electrolyte may be any electrolyte known in the art.
Examples of such electrolytes include such electrochemically stable
salts such alkali metal salt, amine salts, tetraalkylammonium
salts, tetraalkylphosphonium salts, and the like dissolved in an
organic solvent such as propylene carbonate (PC),
.gamma.-butyrolactone, acetonitrile (AN), dimethylformamide,
1,2-dimethoxyethane, sulfolane, nitromethane, and the like. In
other embodiments, the electrolyte may be an aqueous electrolyte
containing a solution of water and inorganic acids such as, but not
limited to, sulfuric acid or tetrafluoroboric acid, inorganic bases
such as, but not limited to, potassium hydroxide or sodium
hydroxide, or inorganic salts. In particular embodiments, the
electrolyte may be propylene carbonate (PC) or acetoniltrile (AN)
containing tetraethylammoniumtetrafluoroborate (TEATFB) salt.
[0031] The ion permeable material between the electrodes can be
made of any commercially available materials. Films or membranes of
porous polymeric dielectric material can be used which, when coated
or impregnated with an electrolyte, permit movement of ions across
them. For example, porous membranes, including woven and non-woven
forms, of polyethylene, polypropylene, polyethersulfone,
fluoropolymers, fiberglass, and the like, can be used, and are
selected according to their stability and compatibility with the
electrolyte of the capacitor. Polyethersulfone, for instance, is
stable in an alkaline aqueous electrolyte, but cannot be used in an
acidic aqueous electrolyte. Preferably, the separator membranes are
thin, 200 micrometers or less thick, more preferably in the range
of 10 to 100 micrometers thick. The membrane resistance in an
electrolyte should be in the range 0.1 to 2.0 ohm-cm.
[0032] The activated carbon of the various embodiments may be
utilized to produce volumetrically smaller devices. For example,
optimized volumetric capacitance materials may be used to produce
smaller electrodes which would result in the manufacture of smaller
capacitor devices.
[0033] The activated carbon of various embodiments can be prepared
by any method known in the art. In general, such methods may
include high temperature treatment of a carbonaceous material to
produce highly porous activated carbon and may be performed in a
number of different manners including the use of steam, carbon
dioxide, or other activating gases known to those skilled in the
art. In particular embodiments, carbonaceous precursor materials
may be activated by steam at temperatures of from about
1000.degree. F. to about 2200.degree. F., and in particular
embodiments, carbonaceous precursor materials may be activated by
steam at a temperature of from about 1600.degree. F. to about
2000.degree. F. In particular embodiments, the carbonaceous
precursor may be activated by steam at a temperature of about
1750.degree. F.
[0034] The duration of the activation may be varied to produce
activated carbons of various activities and apparent densities. For
example, in some embodiments, the carbonaceous precursor may be
activated for from about 20 minutes to about 90 minutes, and in
other embodiments, the carbonaceous precursor may be activated for
from about 10 minutes to about 120 minutes.
[0035] In some embodiments, the activated carbon may be sized by
milling. Any means for milling activated carbon such as, for
example jet milling, may be used in various embodiments of the
invention, and milling may be continued until the activated carbon
has reached an appropriate size. For example, in some embodiments,
activated carbon may be milled to a mean particle diameter of about
20 .mu.m or less, about 10 .mu.m or less, about 5 .mu.m or less,
and in certain embodiments, from about 0.1 .mu.m to about 20 .mu.m
or about 0.1 .mu.m to about 10 .mu.m.
[0036] In some embodiments, the carbon electrode can be prepared
with the use of a binder. Any means can be used to prepare the
carbon based electrode including but not limited to solvent based
deposition, extrusion or other forming methods produce to
appropriately sized electrodes required for the various
electrochemical applications.
[0037] Further embodiments, are directed to a method for
determining the optimal volumetric capacitance of a carbonaceous
material for use in capacitors such as those described above. Such
embodiments may include the steps of preparing two or more sets of
activated carbon materials having different surface areas,
different apparent densities, and combinations thereof, and
determining the volumetric capacity for each of the sets of
activated carbon materials. In some embodiments, the method may
further include the step of comparing the volumetric capacities of
the sets of activated materials and identifying the surface area
and/or apparent density at which the volumetric capacity is
highest. In certain embodiments, the step of comparing may be
carried out by compiling the volumetric capacities for each of the
sets of activated carbon materials in a table and/or plotting the
volumetric capacities for each of the sets of activated carbon
materials on a graph. The means by which the volumetric capacity is
determined may vary among embodiments. For example, in some
embodiments, the activated carbon material may be incorporated into
a capacitor cell which is used to test the volumetric capacitance.
Thus, in certain embodiments, the method may further include the
step of preparing an electrode from the each set of activate carbon
materials, and in other embodiments, the method may further include
the step of preparing capacitor cells from each group of the
activated carbon materials.
EXAMPLES
[0038] Although the present invention has been described in
considerable detail with reference to certain preferred embodiments
thereof, other versions are possible. Therefore the spirit and
scope of the appended claims should not be limited to the
description and the preferred versions contained within this
specification. Various aspects of the present invention will be
illustrated with reference to the following non-limiting
examples.
Example 1
[0039] Three different carbonaceous precursors were activated at
1750.degree. F. for various times using steam as the activating gas
to provide a representative comparison of the effect of treatment
on various materials. Coconut-based materials were produced by
activation of a coconut based char, anthracite based material was
activated by activation of a sized anthracite coal, and bituminous
material was prepared from a reagglomerated bituminous material
which had been previously been carbonized to a maximum of
850.degree. F. for 7 hours in air. In other embodiments, the
materials may be carbonized at 500.degree. F. to 900.degree. F. for
a period of 1 to 10 hours.
[0040] The activated carbon materials were pulverized in a ball
mill prior to use. The activated carbon materials were dried at
60.degree. C. for 1 hour, and then mixed with a Teflon binder at
3.0% by weight. This mixture was thoroughly blended and formed into
sheets. Sheets were rolled to 0.002'' thick and punched using a
steel die to make discs 0.625'' in diameter for testing in
symmetric electrochemical capacitor cells. The electrodes to be
used in the symmetric cells were dried under vacuum conditions
(mechanical roughing pump) at 195.degree. C. for 18 hours. After
cooling, the vacuum container holding the electrodes (still under
vacuum) was transferred into the drybox, and all subsequent
assembly work was performed in the drybox.
[0041] The electrode materials were fabricated using an electrolyte
of propylene carbonate (PC) or acetoniltrile (AN) that contained
1.0 M of tetraethylammoniumtetrafluoroborate (TEATFB) salt. Two
different electrolyte solvents were chosen to determine any that
may be solvent specific.
[0042] For each cell, electrode discs were placed on specially
treated aluminum face-plates and soaked in the organic electrolyte
for 10 minutes. A .about.0.001'' thick disk of NKK separator
material was sandwiched between the electrodes and the cell was
sealed around the edges using a thermoplastic edge seal material
and an impulse heat sealer located directly within the drybox. The
aluminum faceplates were specially treated to reduce contact
resistance and the thermoplastic heat seal material was selected
for electrolyte compatibility and low moisture permeability.
[0043] Capacitor cells were conditioned at 1.0 V for ten minutes,
measured for properties, then conditioned at 2.0 V for 10 minutes
and measured for properties. Charging capacitance was measured at
2.0 V with a 500 ohm series resistance. The measured properties and
resulting capacitance are provided in Table 1, above, and FIG.
1.
[0044] Gravimetric capacitance (F/g) was determined by dividing the
capacitance of constructed cell by the measured weight of the dried
carbon electrodes minus any current collector. Volumetric
capacitance (F/cc) was determined by dividing the capacitance of
the cell by the volume of the carbon electrodes which was
determined by measuring the thickness and diameter of the dried
carbon electrode minus the current collector and calculating the
volume.
* * * * *