Field of Invention
The present invention generally relates to solid electrolytic
capacitors. More particularly, the present invention relates to anodes of solid
electrolytic capacitors featuring high electrical capacitance relative to their
physical size. Also, the present invention relates to a manufacturing process for
such solid electrolytic capacitor anodes.
Background of the Invention
There is a continuously growing demand in the market of
solid electrolytic capacitors for small case size capacitors featuring low manufacturing
costs and high electrical capacitance. Miniature 'chip' solid electrolytic capacitors
designed for surface mounting (SMT) applications are increasingly being used in
microelectronics and communication applications.
A solid electrolytic capacitor consists of a high surface
area porous sintered pellet, the anode, made from a capacitor grade powder, with
an embedded conductor wire or foil and a dielectric oxide layer, which is formed
by anodizing the surface of the pellet. The anodized porous body is then impregnated
and coated with a cathode material and connected to a cathode lead wire. Finally
the assembly is encapsulated.
Large capacitance is achieved with extremely thin dielectric
layers and very high surface area of the capacitor anode. The high surface area
of the porous pellet structure is the dominant feature that allows solid electrolytic
capacitors to have higher capacitance per unit volume than any other type of capacitor.
Anodes of solid electrolytic capacitors are typically made
from tantalum (Ta), niobium (Nb), aluminum (A1) or niobium oxide (NbO). The anode
morphology significantly influences the quality and electrical properties of the
In current industrial manufacturing processes, solid electrolytic
capacitors are made from large particle agglomerates and therefore can only partially
comply with demands for miniaturization and high electrical capacitance in small
In one production method known from the art, the powder
is first mixed with specific adhesive binders and then pressed to form a porous
'slug' named also 'green anode' having a density much lower than the bulk density
of the anode material.
The next production step is to sinter the green anode into
a porous rigid pellet with high open porosity and high mechanical strength that
acts as the capacitor anode. Sintering is done in vacuum or in a protective environment
at about 1300°C to 1500°C. This relatively high temperature is required
in order to produce capacitors with sufficient mechanical strength. If lower temperatures
are used the anode crumbles due to the large size of the powder agglomerates.
After sintering, a dielectric oxide layer is formed by
anodizing of the entire interconnected open porosity surface of the anode.
Next a cathode is formed on the surface of the dielectric
by impregnation of a cathode material, such as manganese oxide (MnO2),
or a conductive polymer.
The effective efficiency of a specific capacitor powder
is indicated by a single lumped parameter, the CV of the powder, which is the product
of the capacitance that can be carried by the powder and the dielectric formation
voltage per unit powder weight. CV has the physical units of Farads multiplied by
volts divided by grams. Different powders are compared by measuring the capacitance
of the sintered anode after formation and calculating from it the CV value of the
powder. By definition, since the capacitance is inversely proportional to the formation
voltage, CV is indifferent to the formation voltage and can be used as a measure
of the powder properties regardless of specific formation conditions.
To accommodate current production methods, industry uses
highly porous powders with large agglomerates and wide distribution of particle
sizes in order to facilitate handling of the powders.
For example, capacitor grade tantalum powder and a method
for making capacitor anode are described in
US Patent No. 5,986,877
US Patent No. 5,954,856
US Patent No. 6,765,786
discloses a niobium powder for producing niobium capacitors.
US Patents No. 6,527,937 B2
US Patent Application No. 2003/0170169 A1
describe a method for producing capacitor grade niobium monoxide powder.
Tantalum, Niobium and Niobium oxide powders with rated
CV ranging from 10,000 µF-V/g to 120,000 µF-V/g (also referred to as 10
KCV to 120 KCV) are standard and commercially available from various manufacturers.
Higher CV powders made from high surface area particle agglomerates are being developed.
Recently, ElectroPhoretic (EPD) method has been offered
as a means to manufacture solid electrolytic capacitor anodes from non-agglomerated,
non-granulated capacitor grade powder made from fine particles of materials such
as, but not limited to, tantalum, aluminum, niobium, or niobium monoxide.
EPD processes, capacitor anodes made by EPD, and capacitors
made thereof have been described in the art. A few examples are
PCT application IL/2002/00458
PCT application IL/2004/000865
Israeli patent application No. 168397 dated May 4, 2005
all by the applicant of the present application, the descriptions of which,
including references cited therein, are incorporated herein by reference in their
As described in the art, use of small particle size powders
with narrow and sharp particle size distribution would be advantageous for making
small size capacitors with high capacitance density and tight tolerance of electrical
It is, therefore, an object of the present invention to
obtain capacitor anodes having high capacitance that are produced at low sintering
It is another object of the current invention to provide
a manufacturing process using low sintering temperature to produce solid electrolyte
capacitor anodes and capacitors having high electrical capacitance in a small package
Other objects and advantages of the invention will become
apparent as the description proceeds.
Summary of the Invention
In one aspect, the present invention is a high capacitance
capacitor anode that is manufactured by creating a green anode body from particles
of a dielectric oxide film-forming electrical conducting non-agglomerated powder,
sintering the green anode body, and anodizing the sintered body. The non-agglomerated
powder comprises fine particles having a small average particle size and a narrow
size distribution. The selection of particle size results in an anode having a morphology
comprised of a multitude of solid particles of powder substantially uniformly dispersed
throughout its volume with voids interspersed between the particles forming a network
of interconnecting channels. This morphology allows the green anode body to be sintered
at temperatures significantly lower than that recommended by the manufacturer of
the powder. The sintering temperature is lower than 1200°C and, in some embodiments,
at a temperature in the range from 900°C to 1000°C. After anodizing, the
measured CV of the anodized, sintered anode of the invention is significantly higher
than the CV determined for the powder by the manufacturer.
The powder is preferably made from particles of one of
the materials selected from the following group: tantalum, aluminum, magnesium,
titanium, niobium, zinc, zirconium, and niobium monoxide. In preferred embodiments
of the invention the non-agglomerated powder particle size is characterized by D10
in the range from 0.2 micron to 2 microns, D50 in the range from 0.5
micron to 5 microns and D90 in the range from 1.2 microns to 12 microns.
In more preferred embodiments the non-agglomerated powder particle size is characterized
by D10 in the range from 0.4 micron to 0.8 micron, D50 in
the range from 0.8 micron to 3 microns and D90 in the range from 1.5
microns to 6 microns. In order to obtain the preferred particle distributions, the
powder may be treated before being formed into a green anode body such that the
fine particles have the desired small maximum particle size and narrow size distribution.
In preferred embodiments of the invention, the green anode
body is formed by depositing the fine particles from a suspension by an EPD process.
In another aspect, the invention is a method of producing
the high capacitance capacitor anodes. The method comprises the steps of:
- a. selecting a capacitor grade powder;
- b. treating the powder to produce non-agglomerated powder comprising fine particles
having a small maximum particle size and a narrow size distribution;
- c. preparing a green anode;
- d. sintering the green anode; and
- e. oxidizing the entire inner and outer surface of the sintered anode.
In preferred embodiments of the method of the invention,
the green anode body is formed by depositing fine particles from a suspension by
an EPD process. In these embodiments the method may comprise the additional step,
between step a and step b, of preparing a stable suspension of the capacitor grade
powder that is suitable for the EPD deposition process and treating the stable suspension
by sedimentation and decantation, thereby reducing agglomerate size and narrowing
the size distribution of the dispersed particles in the EPD suspension. Alternatively
a milling technique can be used to achieve the required particle size distribution.
In preferred embodiments of the method the sintering temperature is between 900°C
The powder used to carry out the method of the invention
is preferably made from particles of one of the materials selected from the following
group: tantalum, aluminum, magnesium, titanium, niobium, zinc, zirconium, and niobium
monoxide. The non-agglomerated powder particle size is preferably characterized
by D10 ranging from 0.2 micron to 2 microns, D50 ranging from
0.5 micron to 5 microns and D90 ranging from 1.2 microns to 12 microns.
More preferably the non-agglomerated powder particle size is characterized by D10
ranging from 0.4 micron to 0.8 micron, D50 ranging from 0.8 micron to
3 microns and D90 ranging from 1.5 microns to 6 microns.
In another aspect the invention is a solid electrolyte
capacitor comprising a high capacitance capacitor anode of the invention or comprising
a high capacitance capacitor anode produced according to the method of the invention.
Brief Description of the Drawings
Detailed Description of the Preferred Embodiments
- Fig. 1 shows the particle size distribution of capacitor grade 80,000 CV NbO
powder as received from the manufacturer and after being adapted to EPD;
- Fig. 2 is a photograph of a green NbO anode made by EPD on Ta wire;
- Fig. 3 is a cross section photograph of the anode of Fig. 2 showing the fine
morphological structure of anodes made by EPD;
- Fig. 4 is a cross section SEM of a typical prior art pressed anode showing typical
defects in the anode morphology;
- Fig 5 shows CV values of anodes made from various powders and at several dielectric
formation voltages, as a function of the sintering temperature;
- Fig 6 shows the dependence of direct current leakage (DCL) on sintering temperature;
- Fig. 7 shows an unencapsulated capacitor made from an anode produced by the
method of the invention.
Capacitor anodes made by EPD from non-agglomerated powders
are characterized by fine morphology and open porosity. The basis of the present
invention is the confirmation by the inventors of the observation that by reducing
the maximum agglomerate size and narrowing the size distribution of the commercially
supplied particles used in the EPD suspension, significantly lower sintering temperature
can be used then if the suspension comprises particles of the size distribution
provided by the manufacturer. It has been found that the anodes obtained according
to the method of this invention demonstrate robustness, high surface area, and CV
values which are much higher than the CV of the powder as rated by the supplier.
In addition to providing capacitors having much higher capacitance per unit volume
than prior art solid electrolytic capacitors, the lower sintering temperatures used
in the present invention provide a significant economic advantage to the method
of the invention.
The anode production in the present invention includes
the steps of:
- a. selection of capacitor grade powder for the production of a solid electrolytic
- b. treatment of the powder to reduce agglomerate size and narrow the size distribution
of the particles;
- c. preparing a stable suspension suitable for EPD deposition process;
- d. deposition by EPD of a green anode;
- e. sintering the green anode; and
- f. oxidizing the entire inner and outer surface of the sintered anode.
In a preferred embodiment of the invention, steps b and
c are interchanged and, after the stable EPD suspension is prepared, it is treated
by sedimentation and decantation, thereby reducing agglomerate size and narrowing
the size distribution of the dispersed particles in the EPD suspension.
The size distributions of some commercially available powders
used for the production of solid electrolyte capacitors are given in the Table 1.
The examples are high CV niobium oxide powders of Hermann C. Starck (Germany) and
Ningxia OTIC (China). Particle size distribution (PSD) of the powders was measured
by dispersing powder in ethanol and measuring the sizes of the dispersed particles
and agglomerates using a Malvern Zetasizer 2000 (United Kingdom). The parameters
D10, D50 and D90 in the table are defined as follows: 10% by volume of the dispersion
particles have particle size smaller than D10, 50% by volume of the dispersion particles
have particle size smaller than D50, and 90% by volume of the dispersion particles
have particle size smaller than D90. For example, a particle dispersion with D10
= 1.2 microns means that the total volume of the particles having size 1.2 microns
and less is equal to 10% of the total volume of all of the particles.
Batch / Manufacturer
209-1-3 / 4 HCS
The rated CV of the powders listed in Table 1 is provided
by the manufacturers based upon anodes that have been optimally pressed and sintered
(recommended sintering temperature of pressed anodes for the above Ningxia OTIC
80KCV powder being 1300 to 1350°C). As can be seen in Table 1, typical capacitor
grade powders are made from agglomerates of particles featuring wide particle size
distribution. According to this invention, the capacitor grade powder used in this
invention should comprise fine, non-agglomerated particles of the selected materials.
In order to narrow the particle size distribution in a preferred embodiment of the
invention agglomerates are eliminated from the powder after forming the EPD suspension
by a process of sedimentation of large particles and agglomerates followed by decantation
of the suspension. Other methods, for example a milling technique, are known in
the art and could be used for preparing the required particle size distribution.
Example 1: Production of NbO green anode
60000-80000µFV/g capacitor niobium oxide powder supplied
by Ningxia OTIC is typically applied to high quality DIP type or CHIP niobium oxide
electrolytic capacitors. It provides high specific capacitance and low leakage current.
Some of the parameters supplied by OTIC for batch 209-2-1 80KCV NbO powder are:
- Powder surface area: BET = 1.48 m2/g
- Recommended sintering temperature (pressed anodes): 1300 to 1350°C
- Oxygen by weight: 15%
- chemical impurity (ppm)
An EPD suspension for the deposition of niobium oxide green
anodes was produced as described hereinbelow wherein the niobium oxide suspension
for EPD was composed of the following materials:
Niobium Oxide powder (NbO)
Polyethylenimine (PEI 17%)
The equipment used for preparation of the suspension and
its characterization and measurements was as follows:
Used for particle dispersion by sonic energy
550 Sonic dismembrator
Measurement of particle size distribution
Sedimentation/ decantation tool
Pyrex beaker with dimensions: height=6.5cm diameter= 11cm
The preparation procedure of the EPD suspension was as
- add 15 grams NbO powder to 300 ml IPA
- sonication for 5 minutes
- add 240 µl PEI 17%
- sonication for 1 minute
- Stir while cooling.
The pH of the above suspension was 8.37 and its conductivity
was 0.7µS/cm at 25.2°C.
Particle size distribution was analyzed for the above dispersion.
As said above, in the preferred embodiment of this invention, the particle size
of the EPD suspension is made smaller and more uniform by sedimentation of agglomerates
and decantation of the suspension prior to carrying out the electrophoretic deposition
process of the green anode. The smaller and more uniform particle size used in the
EPD process according to the invention allows the production of a green anode having
fine morphology with uniform pore structure. This allows the production of robust
anodes even when the green anode is sintered at significantly lower temperatures
than in conventional production techniques based on pressed pellets.
A one hour sedimentation process was then performed, removing
particle agglomerates from the dispersion. The particle size distribution measurement
was then repeated. The results are shown in Fig. 1 and summarized in table 2. Fig.
1 shows two particle size distributions (the graph shows the differential distribution
of the particle size that is derived from the cumulative distribution given in table
2). Curve a is the distribution for the NbO powder in the EPD suspension prepared
according to the above method and curve b is the distribution after a one hour sedimentation
process followed by decantation.
NbO powder in ethanol
As-prepared EPD suspension (curve a)
After sedimentation process (curve b)
As can be seen, the sedimentation process successfully
removed particle agglomerates, thereby narrowing the dispersion particle size distribution
and reducing average particle size.
For the purpose of example only, a procedure for electrophoretic
deposition of green niobium oxide anodes from the above suspension is as follows:
- a. insert into a beaker a Platinum foil that serves as the anode;
- b. insert tantalum wire as the cathode with the length of tantalum wire exposed
to the EPD suspension about 0.8 mm; and
- c. apply 100V for 50 seconds.
The mass of the anode deposited by this procedure is 0.7
An example of niobium oxide green anode morphology achieved
by this process is shown by the photomicrograph of Fig. 2 and a longitudinal cross
section photomicrograph in Fig. 3. The anode length is 900 microns and the diameter
is 500 microns. These may be compared with the coarser and more defective morphology
of a typical tantalum anode produced by standard pressing technology as shown in
the SEM cross section photo of Fig. 4 (TAJ capacitor of AVX Corporation, Myrtle
Beach SC USA).
Example 2: Production of NbO anode and calculation of CV
Preparation of NbO green anode body by EPD
An EPD suspension was prepared by dispersing 5 g capacitor
grade niobium oxide powder of 80,000 CV rating into 100 ml of 2-Propanol. The niobium
oxide powder, designated 209-1-3, was supplied by Hermann C. Starck of Germany.
The suspension was subjected to ultrasonic treatment in a Fisher Scientific Sonic
Dismembrator 550 at 20 KHz and a power level of 550 Watts for 5 minutes in pulse
regime, 2 sec pulse on and 2 sec pulse off. 150 µl of Polyethylenimine 17 wt%
aqueous solution was added to the suspension and pulsed sonification repeated for
1 minute. The suspension was further stirred for 20 minutes. Large particles and
agglomerates were allowed to sediment for one hour and the suspension was decanted.
A suspension pH in the range of 9 to 10 and conductivity of 1 µS/cm were obtained.
A 0.2 mm diameter tantalum wire with a length of 2 cm acted
as cathode in the EPD process. When an external voltage of 80 volts was applied
between the cathode and a platinum counter-electrode in the presence of the suspension,
positively charged NbO particles were deposited on the surface of the tantalum wire.
The deposition time was 40 seconds. The green anode had a length of 1.5 mm and outer
diameter of 550 micron. A total of 20 green anodes were produced.
Sintering of the EPD green anode
Sintering was done in a vacuum furnace at a pressure of
5X10-5 millibar and a temperature of 1050 degrees Celsius. The sintering
cycle included heating from room temperature to 150 degrees Celsius, at a rate of
50 degrees Celsius per minute and then continued heating at a rate of 100 degrees
Celsius per minute to the final sintering temperature. The dwell time at the final
sintering temperature was 20 minutes, after which the furnace was switched off and
filled with helium gas (600 millibar) to speed the cooling rate. As the temperature
in the furnace approached room temperature, the furnace was pumped again to 5X10-5
millibar and then filled with 50 millibar of air for an additional 20 minutes. The
pressure was again raised to 100 millibar of air for an additional 20 minutes. Finally
air was admitted to reach atmospheric pressure and the furnace opened.
Dielectric formation and measurement thereof on a sintered anode
A dielectric layer, Nb2O5, was formed
by anodization using a solution of 63% nitric acid in deionized water. The solution
had a conductivity of 2 mS/cm. The anodic oxidation process was performed at constant
electrical current of 0.1 mA per anode. Five anodes were anodized at each of four
formation voltages: 7V, 14V, 21V and 30V. A standard 'wet-check' procedure was performed
to validate and demonstrate the ability to achieve exceptionally high CV in these
fine morphology anodes produced by EPD process and low sintering temperature, the
subject matter of this invention. An electrolytic bath was filled with 10 molar
ammonium nitrate water solution (300 mS/cm) with the sintered capacitor anode body
as anode and a cylindrical platinum foil as cathode.
Table 3 shows results of electrical capacitance at each
of the four formation voltages, where the table entries are total anode mass and
total anode capacitance for the five anodes at each formation voltage. The average
CV value calculated from these data demonstrates a 42.5% improvement over the niobium
oxide powder rated CV.
Example 3: Sintering and measurement of powder CV
Dielectric Formation Voltage
Total Anode Mass, mg
Total Anode Capacitance, µF
Powder CV (Cap*V/mass, µF-V/g)
To further demonstrate the results that can be obtained
by using the method of the invention, green anodes deposited by EPD from various
high CV niobium oxide powders were sintered over a range of temperatures, anodized
(dielectric formation), and measured for capacitance. Powder CV was then calculated
from the product of the dielectric formation voltage with the ratio of anode capacitance
to anode weight for the anodes produced using the low temperature sintering process
of the invention and compared to the rated CV of the powder. The basic sintering
process used for all of the anodes used in this example is described as follows,
where the peak sintering temperature is as presented in the table.
Sintering was done in a vacuum furnace at a pressure of
5X10-5 millibar and at peak temperatures as shown in the following table.
The sintering cycle included heating from room temperature to 150 degrees Celsius
at a rate of 50 degrees Celsius per minute and then continued heating at a rate
of 100 degrees Celsius per minute to the final sintering temperature. The dwell
time at the final sintering temperature was 20 minutes, after which the furnace
was switched off and filled with helium gas (600 millibar) to speed the cooling
rate. As the temperature in the furnace approached room temperature, the furnace
was pumped again to 5X10-5 millibar and then filled with 50 millibar
of air for an additional 20 minutes. The pressure was again raised to 100 millibar
of air for an additional 20 minutes. Finally air was admitted to reach atmospheric
pressure and the furnace opened. After anodization of the sintered anodes, anode
capacitance was measured and powder CV was calculated. The results are presented
in table 4 in which the third column shows the KCV of the powder as determined by
the manufacturer based on the recommended prior art manufacturing process and the
following columns list the KCV determined from the anodes produced according to
the method of the invention.
POWDER KCV, CALCULATED
H. C. Starck, Germany
H. C. Starck, Germany
Ningxia OTIC, China
By starting with an EPD process to make green anodes of
fine morphology with uniform small pore structure, an optimal sintering temperature
was then discovered for each powder that is hundreds of degrees lower than the generally
accepted sintering temperature. Optimal sintering temperatures (maximum KCV) achieved
for these examples are: 1000°C (148 KCV) for the H. C. Starck 80 KCV rated
powder; 1000°C (184 KCV) for the H. C. Starck 120 KCV rated powder; and 950°C
(165 KCV) for the Ningxia OTIC 80 KCV rated powder, where this innovation achieved.
For the Ningxia OTIC powder, the capacitance achieved from the powder is more than
double its rating, where this was achieved by using a sintering temperature for
the EPD deposited green anode that is about 375°C lower than the manufacturer's
recommended optimum sintering temperature.
It can be seen from the results shown in table 4 (and also
from Fig. 5) that when sintering at temperatures above 1050C the CV decreases significantly
below the manufacture's rated value, i.e. the anode is over-sintered. This illustrates
the motivation of the present invention. For standard anodes built from agglomerated
powder high temperature is required in order to get the large agglomerates to stick
together to form a robust anode; however, such a temperature causes oversintering
of the small particles within the agglomerate, causing a loss of surface area and
The same anodization process was used to produce the above
anodes, with various peak formation voltages used for each anode set The anodization
process is summarized as follows:
- a. add 500µl of 63% nitric acid to 100 ml deionized water, obtaining solution
conductivity of about 2000 µS/cm and pH 3.0-3.5 at 21°C;
- b. insert platinum foil in the beaker as a cathode;
- c. insert the green NbO pellet as an anode;
- d. apply constant current of 0.1 mA and allow the voltage to rise linearly until
a preset voltage limit is reached (voltage limits used herein for evaluating the
powder CV achieved by the low sintering temperatures of this invention are 7V, 14V,
21 V, and 30V); and
- e. allow the current to decrease after the voltage limit is reached until the
process is ended when no apparent change in the current is evident (dI/dt ≤
As an example of the order of magnitude of the time involved
for the anodization process, for a voltage limit of 21V it takes about 10 minutes
for the voltage to rise to the limit and the overall process takes about 80-90 minutes.
A high conductivity electrolyte of 10 molar ammonium nitrate
water solution (300 mS/cm) was used for measuring capacitance and leakage current
of the anodized, sintered anodes.
The KCV results listed in table 4 are also presented in
graphical form in Fig. 5. Several anodes were measured for each data point on this
graph and the points shown on the graph are the average for each powder and sintering
temperature. On the graph the data for the H. C. Starck 80KCV powder is represented
by the diamonds, H. C. Starck 120KCV by squares, and Ningxia 80KCV by triangles.
The fine morphology of the EPD deposited anodes also provided
for low leakage current of anodes that were sintered at the low sintering temperatures
of this invention. This is shown in Fig. 6 where, for example, anode leakage current
at 1050°C sintering temperature is generally lower than achieved at 1200°C
and where the scatter of the leakage current data between anodes is dramatically
reduced. In Fig. 7 the leakage current DCL is plotted on the vertical axis and the
sintering temperature on the horizontal axis. The dashed horizontal line at DCL=
0.02µA/µF-V represents the maximum value of DCL listed in the AVX catalog
(AVX is the only manufacturer today with significant commercial production of niobium
oxide capacitors) for CV's above 50 µF-V. In Fig 6, two batches of Hermann
C. Starck 80 KCV material are represented by the diamonds and squares, Starck 120
KCV material is represented by the triangles, and Ningxia OTIC 80 KCV material is
represented by the x's.
The capacitor grade powder used in the present invention
can be made from any anodic dielectric oxide film-forming electrical conductive
material. According to preferred embodiments of the present invention, the powder
is made from, but is not limited to, particles of one of the following materials:
tantalum, aluminum, magnesium, titanium, niobium, zinc, zirconium or niobium monoxide.
According to the present invention, suitable powder particle
size is characterized by D10 ranging from 0.2 micron to 2 microns, D50
ranging from 0.5 micron to 5 microns and D90 ranging from 1.2 microns
to 12 microns. According to preferred embodiments of the present invention, the
powder particle size is characterized by D10 ranging from 0.4 micron
to 0.8 micron, D50 ranging from 0.8 micron to 3 microns and D90
ranging from 1.5 microns to 6 microns.
Example 5: Production of capacitors
Very high capacitance solid electrolytic capacitors can
be made from the high CV anodes produced by the invention. After formation of dielectric
within the sintered anode, the anodized porous body is subsequently impregnated
and coated with a cathode material, coated with carbon and silver paste and then
connected to a cathode lead wire, lead frame or other manner of electrical contact.
The final assembly is encapsulated in epoxy or other resin. The cathode material
may be composed, for example, of manganese dioxide or conducting polymer. By way
of example only, anode capacitance that is twice the rated CV of the capacitor powder,
has been achieved by the invention, thereby providing a capacitor having double
the capacitance of a prior art capacitor for given dimensions of the solid electrolytic
In Fig. 7 is shown an unencapsulated capacitor made from
an anode produced by EPD from Hermann C. Starck 80KCV NbO powder, sintered at 1050°C,
and with dielectric coating formed at 7V, according to the procedure of example
2. The sintered anode was then impregnated with a manganese dioxide cathode and
coated with carbon and silver layers in order to complete the (unencapsulated) capacitor.
Measured parameters of the capacitor shown in Fig. 5 are listed in table 5.
While some embodiments of the invention have been described
by way of illustration, it will be apparent that the invention can be applied in
practice with many modifications, variations and adaptations, and with the use of
numerous equivalent or alternative solutions that are within the capacity of persons
skilled in the art, without the exceeding the scope of the invention.