U.S. patent application number 10/113075 was filed with the patent office on 2002-10-24 for zinc electrode particle form.
This patent application is currently assigned to Duracell Inc., a Delaware corporation. Invention is credited to Durkot, Richard Edward, Harris, Peter Bayard, Lin, Lifun.
Application Number | 20020155352 10/113075 |
Document ID | / |
Family ID | 25420502 |
Filed Date | 2002-10-24 |
United States Patent
Application |
20020155352 |
Kind Code |
A1 |
Durkot, Richard Edward ; et
al. |
October 24, 2002 |
Zinc electrode particle form
Abstract
A primary electrochemical cell with an anode comprising zinc
alloy particles suspended in a fluid medium is disclosed. The zinc
alloy particles include at least about 10 percent, by weight, of
fines (particles of -200 mesh size) or dust (particles of -325 mesh
size). The zinc particles are preferably alloyed with indium or
bismuth and of acicular or flake form. The anode has a low
resistivity at low zinc loadings, and the cell demonstrates good
mechanical stability and overall performance.
Inventors: |
Durkot, Richard Edward;
(East Walpole, MA) ; Lin, Lifun; (Lincoln, MA)
; Harris, Peter Bayard; (Stow, MA) |
Correspondence
Address: |
ROBERT C. NABINGER
Fish & Richardson P.C.
225 Franklin Street
Boston
MA
02110-2804
US
|
Assignee: |
Duracell Inc., a Delaware
corporation
|
Family ID: |
25420502 |
Appl. No.: |
10/113075 |
Filed: |
April 1, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10113075 |
Apr 1, 2002 |
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09666704 |
Sep 21, 2000 |
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09666704 |
Sep 21, 2000 |
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08905254 |
Aug 1, 1997 |
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6284410 |
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Current U.S.
Class: |
429/229 ;
429/50 |
Current CPC
Class: |
B22F 1/05 20220101; Y02P
70/50 20151101; H01M 4/42 20130101; H01M 4/06 20130101; H01M 6/06
20130101; Y02E 60/10 20130101; H01M 4/244 20130101 |
Class at
Publication: |
429/229 ;
429/50 |
International
Class: |
H01M 004/42 |
Claims
What is claimed is:
1. A negative electrode for an electrochemical cell, comprising
zinc alloy particles suspended in a fluid medium, at least about 10
percent, by weight, of the zinc alloy particles being of -200 mesh
size or smaller.
2. The negative electrode of claim 1, wherein at least about 25
percent, by weight, of the zinc alloy particles are of -200 mesh
size or smaller.
3. The negative electrode of claim 2, wherein at least about 50
percent, by weight, of the zinc alloy particles are of -200 mesh
size or smaller.
4. The negative electrode of claim 3, wherein at least about 80
percent, by weight, of the zinc alloy particles are of -200 mesh
size or smaller.
5. The negative electrode of claim 1, wherein at least about 10
percent, by weight, of the zinc alloy particles are of -325 mesh
size or smaller.
6. The negative electrode of claim 5, wherein at least about 45
percent, by weight, of the zinc alloy particles are of -325 mesh
size or smaller.
7. The negative electrode of claim 6, wherein at least about 80
percent, by weight, of the zinc alloy particles are of -325 mesh
size or smaller.
8. The negative electrode of claim 1 further including a
surfactant.
9. The negative electrode of claim 1 wherein the fluid medium
comprises an electrolyte and a thickening agent.
10. The negative electrode of claim 9 wherein the zinc alloy
particles include a plating material from the group consisting of
indium and bismuth.
11. The negative electrode of claim 1 wherein at least about 25
percent, by weight, of the zinc alloy particles are between about
20 and 200 mesh size.
12. The negative electrode of claim 11 wherein at least about 50
percent, by weight, of the zinc alloy particles are between about
20 and 200 mesh size.
13. The negative electrode of claim 1 wherein the zinc alloy
particles are generally acicular, having a length along a major
axis at least two times a length along a minor axis.
14. The negative electrode of claim 1 wherein the zinc alloy
particles are generally flakes, each flake generally having a
thickness of no more than about 20 percent of the maximum linear
dimension of the particle.
15. A negative electrode mixture for an electrochemical cell,
comprising zinc alloy particles suspended in a fluid medium with
the zinc alloy particles comprising less than about 55 percent of
the electrode mixture, by weight; the zinc alloy particles
including a sufficient proportion of particles of about -200 mesh
size or smaller to provide an electrode resistivity of less than
about 0.2 ohm-centimeters.
16. The negative electrode mixture of claim 15 wherein the zinc
alloy particles comprise less than about 45 percent, by weight, of
the electrode mixture.
17. The negative electrode mixture of claim 15, wherein at least
about 10 percent, by weight, of the zinc alloy particles are of
-200 mesh size or smaller.
18. The negative electrode mixture of claim 17, wherein at least
about 10 percent, by weight, of the zinc alloy particles are of
-325 mesh size or smaller.
19. The negative electrode mixture of claim 15 wherein at least
about 25 percent, by weight, of the zinc alloy particles are
between about 20 and 200 mesh size.
20. A primary electrochemical cell having a cathode, an anode
comprising zinc alloy particles suspended in a fluid medium, at
least 10 percent, by weight, of the zinc alloy particles being of
-200 mesh size or smaller, and a separator between the cathode and
the anode.
21. The primary electrochemical cell of claim 20, wherein at least
about 25 percent, by weight, of the zinc alloy particles are of
-200 mesh size or smaller.
22. The primary electrochemical cell of claim 21, wherein at least
about 50 percent, by weight, of the zinc alloy particles are of
-200 mesh size or smaller.
23. The primary electrochemical cell of claim 22, wherein at least
about 80 percent, by weight, of the zinc alloy particles are of
-200 mesh size or smaller.
24. The primary electrochemical cell of claim 20, wherein at least
about 10 percent, by weight, of the zinc alloy particles are of
-325 mesh size or smaller.
25. The primary electrochemical cell of claim 24, wherein at least
about 45 percent, by weight, of the zinc alloy particles are of
-325 mesh size or smaller.
26. The primary electrochemical cell of claim 25, wherein at least
about 80 percent, by weight, of the zinc alloy particles are of
-325 mesh size or smaller.
27. A negative electrode slurry for an electrochemical cell,
comprising zinc alloy particles suspended in a fluid medium
including an electrolyte, the slurry having a resistivity of less
than about 0.2 ohm-centimeters and the zinc alloy particles
comprising less than about 55 percent, by weight, of the
slurry.
28. A method of generating an electric current, comprising
accumulating ions on the surface of zinc alloy particles suspended
in a fluid medium containing an electolyte, at least about 10
percent, by weight, of the zinc alloy particles being of -200 mesh
size or smaller.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to improvements in
electrochemical cells, particularly cells having negative
electrodes comprising zinc (Zn) particles, such as in alkaline
batteries.
[0002] An electrochemical cell (i.e., a galvanic cell or battery)
has the following basic components: a negative electrode (sometimes
called an anode), a positive electrode (sometimes called a
cathode), and an ion-conductive solution (sometimes called an
electrolyte) providing a path for the transfer of charged ions
between the two electrodes when they are connected through an
external load.
[0003] Some alkaline cells have anodes with zinc as an active
element, and cathodes with manganese dioxide (MnO.sub.2) as an
active element. Anodes do not have to be solid; in fact,
conventional alkaline cells have a gelled zinc anode mixture. The
mixture contains individual zinc metal particles suspended in a
thickened liquid or gel containing a gelling agent, an alkaline
electrolyte such as potassium hydroxide (KOH), and minor amounts of
other additives, such as indium or bismuth (gassing inhibitors for
reducing the undesirable tendency for hydrogen gas to build up
inside the cell). The zinc particles are characterized by a
specific size range, commonly indicated by the standard mesh size
through which the particles pass. Typically, average anode particle
sizes fall in the range of about -50/+200 mesh, indicating
particles that pass through a 50 mesh screen and do not pass
through a 200 mesh screen (the larger the screen number, the
smaller the aperture size of the screen).
[0004] Common gelling agents used in anodes include
carboxymethycellulose, polyacrylic acid (e.g., Carbopol 940.TM.
from B.F. Goodrich in Brecksville, Ohio, or POLYGEL-4P.TM. from 3V
in Bergamo, Italy), sodium polyacrylate (e.g., CL-15.TM. from
Allied Colloids in Yorkshire, England), and salts. Non-limiting
examples of gassing inhibitors include inorganic additives such as
indium, bismuth, tin and lead and organic inhibitors such as
phosphate esters and anionic and non-ionic surfactants. See U.S.
Pat. Nos. 5,283,139, 5,168,018, 4,939,048, 4,500,614, 3,963,520,
4,963,447, 4,455,358, and 4,195,120 for examples of various anode
mixtures.
[0005] The gel anode is typically separated from the cathode by a
separator, such as a thin layer of non-woven material or paper,
that prohibits electronic conduction between the anode and the
cathode but allows ions to pass between them.
[0006] Alkaline Zn/MnO.sub.2 cells have been commercially available
for over 30 years, during which time their performance
characteristics have been incrementally optimized by the industry
in an attempt to provide the "longest lasting" battery (i.e., one
with the greatest overall capacity, measured in ampere-hours)
within the volume constraints imposed by the international size
standards (e.g., AAA, AA, C, D cylindrical and 9 volt prismatic
sizes). The volume within such standard cells, into which the
active materials are packed, is more or less fixed. The amount of
energy available from any given cell size (which is a function of
the total amount of the active elements in the cell) has a
theoretical upper limit which is defined by the internal cell
volume and the practical densities of the active components that
are employed.
[0007] In addition to trying to produce the "longest-lasting"
battery, battery manufacturers are also trying to increase the
maximum instantaneous rate of electrical current that can be
generated from a battery under a given load without the battery
voltage dropping below a minimum value. The motivation for
increasing this "maximum discharge rate" capability includes the
ongoing development of electronic products, such as cellular
phones, which require high currents from small packages. Some of
these new devices automatically test the voltage levels of their
batteries, and therefore may cause the premature disposal of
batteries which have remaining overall capacity, if the sensed
voltage dips excessively during a period of high current draw.
[0008] When a high current is being drawn from a battery, the
voltage of the battery may drop due to zinc particle surface
"passivation" or anode polarization which can indicate a localized
lack of sufficient hydroxide ions to sustain the chemical reaction
of the cell. It is believed that a certain amount of porosity is
necessary for the free supply of OH.sup.-ions coming from the
electrolyte and the free disposal of Zn(OH).sub.4.sup.=,
Zn(OH).sub.2 or ZnO reaction products back into the electrolyte. If
the zinc particles are too densely crowded, or if their surfaces
are inaccessible due to accumulation of reaction products, the
reaction cannot keep up with the rate of current draw. Batteries
with densely packed zinc in their anodes may perform acceptably
with very stable voltage levels while supplying low continuous
currents, but drop to very low, unacceptable voltages when a high
current is drawn due to zinc crowding (sometimes referred to as
"choking" or being "electrolyte starved").
[0009] In addition, too little electrolyte can starve the overall
chemical reaction of the cell or cause the battery to "dry out", as
water from the electrolyte is continuously consumed during
discharge. The net reaction inside the cell is:
Zn+2MnO.sub.2+H.sub.2O.fwdarw.ZnO+2MnOOH.
[0010] Thus, competing with the desire to pack as much zinc as
possible into the available anode volume to increase overall
capacity for "long life" is the need to provide a sufficient amount
of electrolyte to avoid "choking" during periods of high discharge
rate.
SUMMARY OF THE INVENTION
[0011] The invention is based upon the discovery that a high
proportion of very small zinc particles (i.e., fines or dust) among
the zinc particles of the anode of a Zn/MnO.sub.2 electrochemical
cell can provide good cell performance characteristics, especially
those characteristics related to high discharge rate
performance.
[0012] As used herein, "fines" are particles small enough to pass
through a standard 200 mesh screen in a normal sieving operation
(i.e., with the sieve shaken by hand). "Dust" consists of particles
small enough to pass through a standard 325 mesh screen in a normal
sieving operation.
[0013] According to one aspect of the invention, a negative
electrode for an electrochemical cell contains zinc alloy particles
suspended in a fluid medium, with at least about 10 percent, by
weight, of the zinc alloy particles being of -200 mesh size or
smaller. Even higher percentages (e.g., 25 percent, 50 percent and
even 80 percent or more) of zinc fines are preferable.
[0014] In some embodiments, the zinc alloy particles also include
at least about 25 percent (preferably at least about 50 percent),
by weight, of particles between about 20 and 200 mesh size.
[0015] Preferably, a substantial percentage (e.g., 10, 45 or 80
percent or more) of the zinc alloy particles are dust (of -325 mesh
size or smaller, as defined above).
[0016] The negative electrode may include a surfactant. The fluid
medium preferably includes both an electrolyte and a thickening
agent.
[0017] The zinc alloy particles can include a plating material,
such as indium and bismuth.
[0018] The zinc alloy particles are preferably either generally
acicular in shape (having a length along a major axis at least two
times a length along a minor axis) or of flake form (having a
thickness of no more than about 20 percent of their maximum linear
dimension).
[0019] According to another aspect, a negative electrode mixture
for an electrochemical cell contains zinc alloy particles suspended
in a fluid medium with the zinc alloy particles comprising less
than about 55 percent (preferably less than about 45 percent) of
the electrode mixture, by weight. The zinc alloy particles include
a sufficient proportion of particles of about -200 mesh size or
smaller to provide an electrode resistivity of less than about 0.2
ohm-centimeters. Preferably, at least about 10 percent, by weight,
of the zinc alloy particles are of -200 mesh size (more preferably,
of -325 mesh size) or smaller.
[0020] According to another aspect, the invention features a
primary electrochemical cell having a cathode, an anode with zinc
alloy particles suspended in a fluid medium, at least 10 percent,
by weight, of the zinc alloy particles being of -200 mesh size or
smaller, and a separator between the cathode and the anode.
[0021] The anode of the electrochemical cell may include other
features, such as zinc alloy particle sizes, mentioned above.
[0022] According to a further aspect, a negative electrode slurry
for an electrochemical cell contains zinc alloy particles suspended
in a fluid medium including an electrolyte. The slurry has a
resistivity of less than about 0.2 ohm-centimeters and the zinc
alloy particles comprise less than about 55 percent, by weight, of
the slurry.
[0023] According to another aspect of the invention, a method of
generating an electric current includes accumulating ions on the
surface of zinc alloy particles suspended in a fluid medium
containing an electolyte, at least about 10 percent, by weight, of
the zinc alloy particles being of -200 mesh size or smaller.,
[0024] Cells constructed according to the invention have displayed
high tolerance for mechanical shock. They have also demonstrated
high running voltages at high rate drains, low internal impedances
under load, and good overall performance under various pulsed rate
discharge loads.
[0025] In addition, the high proportion of zinc fines or dust can
enable the total amount of zinc to be reduced (i.e., the cell can
have a lower zinc "loading") while maintaining overall capacity on
practical drains and without the typical loss in mechanical
stability normally associated with a reduction in zinc loading.
This is believed to be due, in part, to a high efficiency of zinc
usage and good particle-to-particle connectivity.
[0026] By reducing the total zinc loading needed to achieve a given
performance level, water and alkaline electrolyte can be added
which may reduce the risk of anode choking.
[0027] Other advantages and features will become apparent from the
following description and claims.
BRIEF DESCRIPTION OF THE DRAWING
[0028] FIG. 1 is a cross sectional view through an alkaline
cell.
[0029] FIG. 2 illustrates zinc particle size distributions.
[0030] FIG. 3 shows acicular particles.
[0031] FIG. 4 shows flake particles.
[0032] FIG. 5 shows the effect of anode solids loading on anode
resistivity using different zinc particle size distributions.
[0033] FIGS. 6A and 6B show battery voltage traces taken during
pulse impedance tests of the cells of Example 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] Referring to FIG. 1, cylindrical cell 10 has a casing 12
closed at its open end by seal member 14 being crimped in place.
The cathode 16 is an annular structure with an outer surface in
electrical contact with the inner surface of the casing, which
serves as the positive external terminal of the cell. Cathode 16 is
formed by stacking multiple cathode pellets 16a, as shown. Each
cathode pellet is made from a mixture of MnO.sub.2, a conductive
agent, and electrolyte. Alternatively, the cathode may be formed
directly in the casing by pressure compaction, without stacking
individual pellets.
[0035] A separator 18 lines the inner surfaces of annular cathode
16 and electronically separates the cathode from the anode 20.
Separator 18 can be any of a number of well known separator
materials, such as cellulose or rayon.
[0036] Anode 20 is of gel form, having a desired amount of zinc
metal, in particulate form, suspended in a mixture of alkaline
electrolyte and a gelling agent. Gassing inhibitors, such as those
described above, are preferably added to the anode gel or as a
coating on the zinc particles. Generally, the zinc and alkaline
electrolyte together make up about 96%, and more preferably about
98%, by weight, of the anode.
[0037] Anode collector 22 passes through seal member 14 and extends
into anode 20. The upper end of anode collector 22 electrically
contacts a negative end cap 24, which serves as the negative
external terminal of the cell. Upon assembly, additional liquid
alkaline electrolyte is added to the cell and becomes distributed
throughout the anode, cathode, and separator.
[0038] The zinc particles in the anode include a significant
proportion of fines, at least 10% by weight, preferably at least
50% by weight, and more preferably at least 80% by weight. High
performance has also been noticed, as described more fully below,
when there is a significant proportion of zinc dust in the
anode.
[0039] The desired distribution of particle sizes can be produced
by several processes. For instance, standard mesh sieves can be
employed to sort zinc particles produced by centrifugal
atomization, gas atomization, or any other known method. Once
sorted, by sieving or air classification, for instance, various
size ranges of particles can be mixed in proper proportions to
produce the desired size distribution. Alternatively, the average
size of the particles, as produced, can be controlled, along with
the distribution of particle sizes about a mean, to produce a
statistical distribution having a significant proportion of fines
and dust. Once formed, the particles can be mixed with surfactants,
gassing inhibitors, gelling agents, electrolyte and other additives
by standard processes.
[0040] FIG. 2 illustrates some of the distributions of zinc
particles that have been tested in anode 20. The distributions are
shown as a function of effective particle diameter as measured with
the particle diameter measurement technique described below. As a
rough correspondence between mesh sizes and effective particle
diameters, it should be noted that spherical particles with a
diameter of 74 microns, for instance, will just sift through a 200
mesh screen, and spherical particles with a diameter of 44 microns
will just sift through a 325 mesh screen. This correspondence is
less accurate for particles of other shapes. Distribution 32 is of
centrifugally atomized zinc particles that were sifted through a
325 mesh screen (i.e., zinc dust), and has a peak at an effective
particle diameter of about 57 microns. Distribution 34 is of gas
atomized particles. Distributions 36 and 38 are of centrifugally
atomized particles of -20/+200 and -200 mesh size, respectively.
Distribution 40 is a combination of 50%, by weight, of the zinc
dust of distribution 34 and 50%, by weight, of the particles of
distribution 36.
[0041] One of the effects of including significant proportions of
very small zinc particles is an increase in the bulk surface area
(i.e., the aggregate surface area) of the zinc particles in the
anode. This is due to the inherent relationship between particle
surface area and volume: namely that, for particles of similar
shape, decreasing the particle size increases the surface area to
volume ratio of the particle. High bulk surface area for a given
particle mass is offered as a possible explanation of some of the
high performance demonstrated by batteries with zinc fines.
[0042] Particle surface area can be further enhanced by controlling
the production or subsequent processing of the zinc particles to
produce particles with extended, non-spherical shapes, such as
flakes or acicular particles. Acicular shapes (see particle 42 in
FIG. 3, for instance) having a length L.sub.1 along a major axis at
least two times a length L.sub.2 along a minor axis are considered
to be appropriate. Flakes, such as particle 44 in FIG. 4, have a
thin cross-section and two broad, opposite sides (such as a wafer
or potato chip). Preferably, such a flake-form particle has an
average thickness between its broad sides of no more than about 20%
of the maximum dimension of the particle, to have a very low volume
to surface area ratio.
[0043] One plausible theory for the mechanism that results in the
good performance characteristics of batteries with anodes having
high proportions of zinc dust or fines concerns
particle-to-particle connectivity. This theory is only offered as a
possible explanation of the observed results, and is not intended
to limit the scope of the invention. In effect, it is believed that
the additional fines form a mechanical network, particularly under
electrical load and at low zinc loadings. This theory is supported
by slurry resistivity measurements taken at various zinc loadings,
as plotted in FIG. 5. In this figure, the solid line is of an anode
mixture with zinc particles of -20/+200 mesh size and the dashed
line is of an anode mixture with zinc particles of -200 mesh size.
It is believed that improved connectivity between large particles,
fines and dust results in higher conductivity at loadings down to
50% or less. As a result, more electrolyte may be added to the
mixture to increase zinc utilization (i.e., increase zinc
volumetric usage efficiency) while maintaining low anode
resistance. This improvement in connectivity, if the above theory
is correct, would also tend to account for the high slurry
viscosity, as well as good tolerance for mechanical shock (e.g.,
tap load voltage stability and drop voltage stability, as described
below) of anodes with high proportions of fines and dust.
[0044] Continuous 3.9 Ohm Load Test
[0045] This test simulates constant discharge in medium current
draw applications, such as in some toys. A 3.9 ohm load is applied
across the battery terminals and the battery is continuously
discharged through the load. The amount of time from the
application of the load to when the battery voltage drops to a
cut-off voltage is recorded.
[0046] One Watt Continuous Load Test
[0047] In this test power is discharged from the battery at a
constant rate of one watt, with the load automatically adjusted to
account for changing battery voltage. This test is generally
considered to be a more strenuous test than the 3.9 ohm continuous
test, especially toward the end of the test as the battery voltage
nears the cutoff value. The amount of time from the application of
the load to when the battery voltage drops to a cut-off voltage is
recorded.
[0048] Pulse Impedance Test
[0049] This test is a measure of the maximum dip in voltage that
occurs when a fixed load is rapidly applied to the cell, and is an
indication of the lag between voltage and current that can be
exacerbated by the use of organic corrosion inhibitors to reduce
gassing. Though of short duration, instantaneous drops in voltage
can have significant consequences, as in devices which monitor
instantaneous battery voltage and signal that the battery should be
replaced if a low voltage is measured. A 3.9 ohm load is applied to
the cell through a fast-acting relay, and the cell voltage is
monitored on an oscilloscope. The load is maintained for 400
milliseconds. The minimum voltage during the test, which occurs
upon application of the load, is measured.
[0050] High Current Pulse Test
[0051] This test was designed to simulate the performance of a
battery in a camera application. A controlled 1.1 amp current is
intermittently drawn from the battery in a series of pulses, each
of 10 seconds duration with a 50 second pause in between each
pulse. The pulse series is continued for one hour each day until
the battery voltage drops to a predetermined cut-off level, at
which point the total number of pulses is recorded. This test is
also performed on cells that have been stored for two weeks at
55.degree. C. to determine how storage at elevated temperatures
affects high discharge rate performance.
[0052] Anode AC Bulk Resistivity
[0053] This test measures how well the anode performs as an
electrical conductor. A small alternating current, oscillating at
about 1000 Hz, is applied to a volume of prepared anode mixture
(with proper proportions of zinc particles, gelling agent,
electrolyte and additives for use in an electrochemical cell), and
the bulk resistivity of the mixture is measured.
[0054] Tap Load Voltage Instability
[0055] This test is a measure of the mechanical stability of the
anode during a physical bump or shock. It is common for the voltage
of batteries to dip under load during a bump (such as when they are
tapped against a hard surface). This test measures the magnitude of
such undesirable voltage dips. A constant 3.9 ohm load is applied
to the battery, and the battery is struck once with an automated
hammer (with a force of about 50-60 pounds, inducing an effective
peak acceleration of about 20-50 kilometers/second/second with high
attenuation) once every 60 seconds, while monitoring the battery
voltage. Generally, when the battery reaches about a 25 percent
discharge, the magnitude of the voltage dips reaches a maximum
value, decreasing as the battery continues to discharge. The
severity of the maximum voltage drop is used as a measure of cell
performance.
[0056] Particle Diameter Measurement
[0057] The data in FIG. 2 were generated by analyzing dry zinc
alloy particles, in bulk. A representative amount of sample powder
to be analyzed was transferred into the funnel of a RODOS-VIBRI.TM.
Sample Dispersion unit, available from Sympatec, which dispersed
the powder into a stream of air to form an aerosol. The aerosol of
the zinc powder is then passed through a HELOS.TM. Particle Size
Analyzer, also available from Sympatec, which measures the
intensity and distribution of light diffused through the aerosol of
spinning particles. Various optical lenses with different focal
lengths are used, in accordance with manufacturer's
recommendations, with particles of different size ranges.
[0058] The above-described test provides an indication of the bulk
distribution of particle size over a range, with the particle size
classified by an effective diameter somewhere between the maximum
and minimum linear particle dimensions. This measurement cannot,
therefore, be directly correlated to a particle mesh size.
EXAMPLE 1
[0059] Cylindrical alkaline batteries of Type AA were built with
gel anodes having the following two compositions to test the effect
of zinc fines (the composition values listed are in percent by
weight):
1 Composition 1A 1B Zinc alloy particles 67.97 67.97 Indium acetate
0.03 0.03 (42% Indium) Phosphate ester 0.06 0.06 (6% concentration)
Polyacrylic acid 0.53 0.53 Sodium polyacrylate 0.38 0.38 Acetic
acid 0.09 0.09 (2.5% concentration) Electrolyte solution 30.94
30.94 (2% ZnO, 35% KOH) Total: 100.00 100.00 Zinc particle sieve
size -20/+200 -200
[0060] The above compositions were prepared by first mixing the
indium acetate powder with the dry zinc alloy particles. Next, the
acetic acid and phosphate ester were applied, followed by the
polyacrylic acid and sodium polyacrylate. After blending and
crushing any lumps, the electrolyte solution was added and the
mixture was blended until uniform.
[0061] In each of the following tests, four individual batteries
were tested.
2 Example 1 test results: 1A 1B Continuous 3.9 ohm load test Hours
to 1.0 volts 1.51 1.57 Hours to 0.9 volts 1.70 1.86 Hours to 0.8
volts 1.73 2.01 One watt continuous load test Hours to 1.0 volts
0.58 0.51 Hours to 0.9 volts 0.74 0.66 Hours to 0.8 volts 0.84 0.77
High current pulse test Pulses to 1.0 volts 174 221 Pulses to 0.9
volts 233 337 Pulses to 0.8 volts 306 421 Pulse impedance test
Actual voltage trace FIG. 6B
[0062] Note that in the pulse impedance tests the peak voltage dip
50 of build 1A (FIG. 6A) is much more pronounced than the voltage
dip 52 of build 1B (FIG. 6B).
EXAMPLE 2
[0063] Cylindrical alkaline batteries of Type AA were built with
gel anodes having the following two compositions (the composition
values listed are in percent by weight):
3 Composition 2A 2B 2C Zinc alloy particles 69.80.sup.1 69.80.sup.2
69.80.sup.3 Indium acetate 0.04 0.04 0.04 (42% Indium) Phosphate
ester 0.06 0.06 0.06 (6% concentration) Polyacrylic acid 0.51 0.45
0.45 (Carbopol 940) Acetic acid 1.12 1.12 1.12 (2.5% concentration)
Electrolyte solution 28.47 28.53 28.53 (2% ZnO, 35% KOH) Total:
100.00 100.00 100.00 .sup.1Alloy includes 150 ppm In, 200 ppm Bi;
particles sieved to -20/+200 mesh size (mean effective particle
diameter of 317 micron; distribution 36, FIG. 2) .sup.2Alloy
includes 150 ppm In, 200 ppm Bi; particles sieved to -325 mesh size
(mean effective particle diameter of 57 micron; distribution 32,
FIG. 2) .sup.3An equal mixture, by weight, of particles as in build
2A and gas atomized zinc particles alloyed with 500 ppm In and 500
ppm Bi. The gas atomized particles had a mean effective particle
diameter of about 41 micron (distribution 34, FIG. 2). The particle
mixture corresponds to distribution 40.
[0064] For each of the following tests, at least four individual
batteries of each composition were tested. The results of the
individual batteries are averaged.
4 Example 2 test results: 2A 2B 2C High current pulse test to 1.0 V
Pulses as built 226 293 299 Pulses after storage 217 278 244 Tap
load voltage instability (max voltage drop, mV) 374 112 71
[0065] Very small zinc particles, such as zinc fines and dust, tend
to be more unstable in oxygen-rich environments than larger
particles and must therefore be processed with due care. Such
issues, together with physical bulk handling issues of powders and
fines, may need to be considered when determining the absolute
minimum practical particle size for production anodes.
[0066] Other embodiments are also within the scope of the following
claims.
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