U.S. patent application number 14/549583 was filed with the patent office on 2017-04-06 for alkaline electrochemical cells with separator and electrolyte combination.
The applicant listed for this patent is DURACELL U.S. OPERATIONS, INC.. Invention is credited to James Joseph Cervera, Nikolai Nikolaevich Issaev, Michael Pozin.
Application Number | 20170098865 14/549583 |
Document ID | / |
Family ID | 56011118 |
Filed Date | 2017-04-06 |
United States Patent
Application |
20170098865 |
Kind Code |
A9 |
Issaev; Nikolai Nikolaevich ;
et al. |
April 6, 2017 |
ALKALINE ELECTROCHEMICAL CELLS WITH SEPARATOR AND ELECTROLYTE
COMBINATION
Abstract
An alkaline electrochemical cell having an anode including
electrochemically active anode material, a cathode including
electrochemically active cathode material, a separator between the
anode and the cathode, and an electrolyte. The electrolyte includes
a hydroxide dissolved in water. The separator in combination with
the electrolyte has an initial area-specific resistance between
about 100 mOhm-cm.sup.2 and about 220 mOhm-cm.sup.2.
Inventors: |
Issaev; Nikolai Nikolaevich;
(Woodbridge, CT) ; Cervera; James Joseph; (Sandy
Hook, CT) ; Pozin; Michael; (Brookfield, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DURACELL U.S. OPERATIONS, INC. |
Wilmington |
DE |
US |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20160149266 A1 |
May 26, 2016 |
|
|
Family ID: |
56011118 |
Appl. No.: |
14/549583 |
Filed: |
November 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13705400 |
Dec 5, 2012 |
8920969 |
|
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14549583 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/24 20130101; H01M
4/244 20130101; H01M 2004/027 20130101; H01M 4/42 20130101; H01M
4/06 20130101; Y02E 60/10 20130101; H01M 6/045 20130101; H01M 4/50
20130101; H01M 10/26 20130101 |
International
Class: |
H01M 10/26 20060101
H01M010/26; H01M 4/24 20060101 H01M004/24 |
Claims
1. A primary AA alkaline electrochemical cell comprising: an anode
including an electrochemically active anode material, the
electrochemically active anode material comprising zinc, zinc
alloys, or mixtures thereof; a cathode including an
electrochemically active cathode material, the electrochemically
active cathode material comprising manganese oxide, manganese
dioxide, electrolytic manganese dioxide (EMD), chemical manganese
dioxide (CMD), high power electrolytic manganese dioxide (HP EMD),
or mixtures thereof; a cathode loading of at least about 10.0 grams
of electrochemically active cathode material; a separator between
said anode and said cathode; and an electrolyte comprising an
ionically-conductive component dissolved in water, the separator in
combination with the electrolyte having an initial area-specific
resistance between about 100 mOhm-cm.sup.2 and about 220
mOhm-cm.sup.2.
2. The alkaline electrochemical cell of claim 1 wherein initial
area-specific resistance is between about 150 mOhm-cm.sup.2 and
about 200 mOhm-cm.sup.2.
3. The alkaline electrochemical cell of claim 1 having a final
area-specific resistance of less than about 500 mOhm-cm.sup.2.
4. The alkaline electrochemical cell of claim 1 having a final
area-specific resistance between about 200 mOhm-cm.sup.2 and about
500 mOhm-cm.sup.2.
5. The alkaline electrochemical cell of claim 1 having an ASR ratio
of less than about 1.9.
6. The alkaline electrochemical cell of claim 1 having an ASR ratio
from about 1.2 to about 1.65.
7. The alkaline electrochemical cell of claim 1 wherein the
ionically conductive component is selected from the group
consisting of sodium hydroxide, potassium hydroxide, lithium
hydroxide, cesium hydroxide, zinc chloride, ammonium chloride,
magnesium perchlorate, magnesium bromide, and mixtures thereof.
8. A primary AAA alkaline electrochemical cell comprising: an anode
including an electrochemically active anode material, the
electrochemically active anode material comprising zinc, zinc
alloys, or mixtures thereof; a cathode including an
electrochemically active cathode material, the electrochemically
active cathode material comprising manganese oxide, manganese
dioxide, electrolytic manganese dioxide (EMD), chemical manganese
dioxide (CMD), high power electrolytic manganese dioxide (HP EMD),
or mixtures thereof; a cathode loading of at least about 4.0 grams
of electrochemically active cathode material; a separator between
said anode and said cathode; and an electrolyte comprising an
ionically-conductive component dissolved in water, the separator in
combination with the electrolyte having an initial area-specific
resistance between about 100 mOhm-cm.sup.2 and about 220
mOhm-cm.sup.2.
9. The alkaline electrochemical cell of claim 8 wherein initial
area-specific resistance is between about 150 mOhm-cm.sup.2 and
about 200 mOhm-cm.sup.2.
10. The alkaline electrochemical cell of claim 8 having a final
area-specific resistance of less than about 500 mOhm-cm.sup.2.
11. The alkaline electrochemical cell of claim 8 having a final
area-specific resistance between about 200 mOhm-cm.sup.2 and about
500 mOhm-cm.sup.2.
12. The alkaline electrochemical cell of claim 8 having an ASR
ratio of less than about 1.9.
13. The alkaline electrochemical cell of claim 8 having an ASR
ratio from about 1.2 to about 1.65.
14. The alkaline electrochemical cell of claim 8 wherein the
ionically conductive component is selected from the group
consisting of sodium hydroxide, potassium hydroxide, lithium
hydroxide, cesium hydroxide, zinc chloride, ammonium chloride,
magnesium perchlorate, magnesium bromide, and mixtures thereof.
15. A primary AAAA alkaline electrochemical cell comprising: an
anode including an electrochemically active anode material, the
electrochemically active anode material comprising zinc, zinc
alloys, or mixtures thereof; a cathode including an
electrochemically active cathode material, the electrochemically
active cathode material comprising manganese oxide, manganese
dioxide, electrolytic manganese dioxide (EMD), chemical manganese
dioxide (CMD), high power electrolytic manganese dioxide (HP EMD),
or mixtures thereof; a cathode loading of at least about 2.0 grams
of electrochemically active cathode material; a separator between
said anode and said cathode; and an electrolyte comprising an
ionically-conductive component dissolved in water, the separator in
combination with the electrolyte having an initial area-specific
resistance between about 100 mOhm-cm.sup.2 and about 220
mOhm-cm.sup.2.
16. The alkaline electrochemical cell of claim 15 wherein initial
area-specific resistance is between about 150 mOhm-cm.sup.2 and
about 200 mOhm-cm.sup.2.
17. The alkaline electrochemical cell of claim 15 having a final
area-specific resistance of less than about 500 mOhm-cm.sup.2.
18. The alkaline electrochemical cell of claim 15 having a final
area-specific resistance between about 200 mOhm-cm.sup.2 and about
500 mOhm-cm.sup.2.
19. The alkaline electrochemical cell of claim 15 having an ASR
ratio of less than about 1.9.
20. The alkaline electrochemical cell of claim 15 having an ASR
ratio from about 1.2 to about 1.65.
21. The alkaline electrochemical cell of claim 15 wherein the
ionically conductive component is selected from the group
consisting of sodium hydroxide, potassium hydroxide, lithium
hydroxide, cesium hydroxide, zinc chloride, ammonium chloride,
magnesium perchlorate, magnesium bromide, and mixtures thereof.
Description
FIELD OF THE INVENTION
[0001] The invention relates to an alkaline electrochemical
cell.
BACKGROUND OF THE INVENTION
[0002] Electrochemical cells, or batteries, are commonly used as
electrical energy sources. A battery contains a negative electrode,
typically called the anode, and a positive electrode, typically
called the cathode. The anode contains an active material that can
be oxidized. The cathode contains or consumes an active material
that can be reduced. The anode active material is capable of
reducing the cathode active material. A separator is disposed
between the anode and cathode. These components are disposed in a
metal can.
[0003] When a battery is used as an electrical energy source in a
device, electrical contact is made to the anode and the cathode,
allowing electrons to flow through the device and permitting the
respective oxidation and reduction reactions to occur to provide
electrical power. An electrolyte in contact with the anode and the
cathode contains ions that flow through the separator between the
electrodes to maintain charge balance throughout the battery during
discharge.
[0004] There is a growing need to make batteries better suitable to
power contemporary electronic devices such as toys; remote
controls; audio devices; flashlights; digital cameras and
peripheral photography equipment; electronic games; toothbrushes;
radios; and clocks. It is also desirable for batteries to have a
long service life. There exists a need to provide an alkaline
electrolyte solution and separator combination for use in a battery
to provide lower overall battery impedance to substantially
increase overall battery performance, such as power capability and
service life.
SUMMARY OF THE INVENTION
[0005] The invention is directed to an alkaline electrochemical
cell comprising an anode, a cathode, a separator between said anode
and said cathode, and an electrolyte. The anode comprises
electrochemically active anode material. The cathode comprises
electrochemically active cathode material. The electrolyte
comprises a hydroxide dissolved in water. The separator in
combination with the electrolyte has an initial area specific
resistance between about 100 mOhm-cm.sup.2 and about 220
mOhm-cm.sup.2.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] While the specification concludes with claims particularly
pointing out and distinctly claiming the subject matter, which is
regarded as forming the present invention, it is believed that the
invention will be better understood from the following description
taken in conjunction with the accompanying drawings.
[0007] FIG. 1 is a cross-section of an electrochemical cell of the
present invention.
[0008] FIG. 2 is another view of the electrochemical cell of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0009] Electrochemical cells, or batteries, may be primary or
secondary. Primary batteries are meant to be discharged, e.g., to
exhaustion, only once and then discarded. Primary batteries are
described, for example, in David Linden, Handbook of Batteries
(McGraw-Hill, 2d ed. 1995). Secondary batteries are intended to be
recharged. Secondary batteries may be discharged and then recharged
many, e.g., more than fifty times, a hundred times, or more, times.
Secondary batteries are described, e.g., in Falk & Salkind,
"Alkaline Storage Batteries", John Wiley & Sons, Inc. 1969;
U.S. Pat. No. 345,124; and French Patent No. 164,681, all hereby
incorporated by reference. Accordingly, batteries may include
various electrochemical couples and electrolyte combinations.
Although the description and examples provided herein are directed
towards primary alkaline electrochemical cells, batteries, it
should be appreciated that the invention applies to both primary
and secondary alkaline batteries and both primary and secondary
alkaline batteries, regardless of their embodiments, are within the
scope of this application. is not limited to such an
embodiment.
[0010] Referring to FIG. 1, an alkaline electrochemical cell, or
battery, 10 includes a cathode 12, an anode 14, a separator 16 and
a housing 18. Battery 10 also includes current collector 20, seal
22, and a negative metal end cap 24, which serves as the negative
terminal for the battery 10. A positive pip 26, which serves the
positive terminal of the cell, is at the opposite end of the
battery 10 from the negative metal end cap 24. An electrolytic
solution (not shown) is dispersed throughout the battery 10.
Battery 10 can be, for example, a AA, AAA, AAAA, C, or D alkaline
battery.
[0011] The housing 18 can be of any conventional type commonly used
in primary alkaline batteries and can be made of any suitable
material, such as, e.g., nickel-plated cold-rolled steel or
plastic. The seal 22 may be made of, for example, a polyamide
(Nylon). The housing 18 may have a conventional cylindrical
shape--or may have any other suitable non-cylindrical, e.g.,
prismatic, shape. Interior walls of the housing 18 may be treated
with a material that has low electrical-contact resistance to an
electrode. The interior walls of the housing 18 may be plated,
e.g., with nickel, cobalt, or painted with a carbon-loaded
paint.
[0012] The current collector 20 may be made of metal, e.g., zinc,
copper, brass, or any other suitable material. The current
collector 20 may be optionally plated with tin, zinc, bismuth,
indium, or another suitable material presenting a low
electrical-contact resistance between the current collector 20 and,
for example, the anode 14.
[0013] Cathode 12 includes one or more electrochemically active
cathode materials. The electrochemically active cathode material
may include manganese oxide, manganese dioxide, electrolytic
manganese dioxide (EMD), chemical manganese dioxide (CMD), high
power electrolytic manganese dioxide (HP EMD), lambda manganese
dioxide, and mixtures thereof. Other electrochemically active
cathode materials include, but are not limited to, silver oxide,
nickel oxide, nickel oxyhydroxide, copper oxide, bismuth oxide,
high-valence nickel, alloys thereof, and mixtures thereof. The
nickel oxide can include nickel oxyhydroxide, cobalt
oxyhydroxide-coated nickel oxyhydroxide, delithiated layered
lithium nickel oxide, and combinations thereof. The nickel
oxyhydroxide can include beta-nickel oxyhydroxide, gamma-nickel
oxyhydroxide, and/or intergrowths of beta-nickel oxyhydroxide
and/or gamma-nickel oxyhydroxide. The cobalt oxyhydroxide-coated
nickel oxyhydroxide can include cobalt oxyhydroxide-coated
beta-nickel oxyhydroxide, cobalt oxyhydroxide-coated gamma-nickel
oxyhydroxide, and/or cobalt oxyhydroxide-coated intergrowths of
beta-nickel Oxyhydroxide and gamma-nickel oxyhydroxide. The nickel
oxide can include a partially delithiated layered nickel oxide
having the general chemical formula Li.sub.1-xH.sub.yNi0.sub.2,
wherein 0.1.ltoreq.x.ltoreq.0.9 and 0.1.ltoreq.y.ltoreq.0.9. The
high-valence nickel may, for example, include tetravalent
nickel.
[0014] A preferred electrochemically active cathode material is
manganese dioxide, having a purity of at least about 91 percent by
weight. Electrolytic manganese dioxide (EMD) is a preferred form of
manganese dioxide for electrochemical cells because of its high
density and since it is conveniently obtained at high purity by
electrolytic methods. Chemical manganese dioxide (CMD), a
chemically synthesized manganese dioxide, has also been used as
electrochemically active cathode material in electrochemical cells
including alkaline cells and heavy-duty cells.
[0015] EMD is typically manufactured from direct electrolysis of a
bath of manganese sulfate and sulfuric acid. Processes for the
manufacture of EMD and its properties appear in Batteries, edited
by Karl V. Kordesch, Marcel Dekker, Inc., New York, Vol. 1, (1974),
p. 433-488. CMD is typically made by a process known in the art as
the "Sedema process," a chemical process disclosed by U.S. Pat. No.
2,956,860 (Welsh). Battery-grade MnO.sub.2 may be produced via the
Sedema process by employing the reaction mixture of MnSO.sub.4 and
an alkali metal chlorate, preferably NaClO.sub.3. Distributors of
manganese dioxides include Tronox, Erachem, Tosoh, Delta Manganese,
and Xiangtan.
[0016] In batteries where very low or no cell distortion is
required, high power (HP) EMD may be used. Preferably, the HP EMD
has an open circuit voltage (OCV) of at least 1.635. A suitable HP
EMD is commercially available from Tronox, under the trade name
High Drain.
[0017] The cathode 12 may also include carbon particles and a
binder. The cathode 12 may also include other additives. The
cathode 12 will have a porosity. The cathode porosity is preferably
between about 22% and about 31%. The cathode porosity is calculated
at the time of manufacturing by the following formula:
% Cathode Porosity=(1-(cathode solids volume/cathode
volume)).times.100
The porosity of the cathode is typically calculated at the time of
manufacturing since the porosity will change over time due to
cathode swelling associated with electrolyte wetting of the cathode
and battery discharge.
[0018] The carbon particles are included in the cathode to allow
the electrons to flow through the cathode. The carbon particles may
be graphite, such as expanded graphite and natural graphite. It is
preferred that the amount of carbon particles in the cathode is
relatively low, e.g., less than 3.75%, or even less than 3.5%, for
example 2.0% to 3.5%. A lower carbon level enables inclusion of a
higher level of active material within the cathode without
increasing the volume of the cell or reducing the void volume
(which must be maintained at or above a certain level to prevent
internal pressure from rising too high as gas is generated within
the cell). A suitable expanded graphite can be obtained, for
example, from Timcal.
[0019] Some preferred cells contain from about 2% to about 3.5%
expanded graphite by weight. In some implementations, this allows
the level of EMD to be from about 89% to 91% by weight as supplied.
(EMD contains about 1-1.5% moisture as supplied, so this range
equates to about 88% to 90% pure EMD.) Preferably, the ratio of
cathode active material to expanded graphite is greater than 25,
and more preferably greater than 26 or even greater than 27. In
some implementations, the ratio is between 25 and 33, e.g., between
27 and 30. These ratios are determined by analysis, ignoring any
water.
[0020] It is generally preferred that the cathode be substantially
free of unexpanded graphite. While unexpanded graphite particles
provide lubricity to the cathode forming equipment, this type of
graphite is significantly less conductive than expanded graphite,
and thus it is necessary to use more in order to obtain the same
cathode conductivity. While not preferred, the cathode may include
low levels of unexpanded graphite, however this will compromise the
reduction in graphite concentration that can be obtained while
maintaining a particular cathode conductivity.
[0021] The cathode may be provided in the form of pressed pellets.
For optimal processing, it is generally preferred that the cathode
have a moisture level in the range of about 2.5% to about 5%, more
preferably about 2.8% to about 4.6%. It is also generally preferred
that the cathode have a porosity of from about 22% to about 31%,
for a good balance of manufacturability, energy density, and
integrity of the cathode.
[0022] Examples of binders that may be used in the cathode include
polyethylene, polyacrylic acid, or a fluorocarbon resin, such as
PVDF or PTFE. An example of a polyethylene binder is sold under the
trade name COATHYLENE HA-1681 (available from Hoechst or
DuPont).
[0023] Examples of other cathode additives are described in, for
example, U.S. Pat. Nos. 5,698,315, 5,919,598, and 5,997,775 and
U.S. application Ser. No. 10/765,569.
[0024] The amount of electrochemically active cathode material
within the cathode 12 may be referred to as the cathode loading.
The loading of the cathode 12 may vary depending upon the
electrochemically active cathode material used within, and the cell
size of the battery 10. For example, AA batteries with a manganese
dioxide electrochemically active cathode material may have a
cathode loading of at least 10.0 grams of manganese dioxide. The
cathode loading may be, for example, at least about 10.5 grams of
manganese dioxide. The cathode loading may be, for example, between
about 10.7 grams and about 11.5 grams of manganese dioxide. The
cathode loading may be from about 10.7 grams and about 11.0 grams
of manganese dioxide. The cathode loading may be from about 10.8
grams and about 11.2 grams of manganese dioxide. The cathode
loading may be from about 10.9 grams and about 11.5 grams of
manganese dioxide. For a AAA battery, the cathode loading may be
from about 4.0 grams and about 6.0 grams of manganese dioxide. For
a AAAA battery, the cathode loading may be from about 2.0 grams and
about 3.0 grams of manganese dioxide. For a C battery, the cathode
loading may be from about 25.0 grams and about 29.0 grams of
manganese dioxide. For a D battery, the cathode loading may be from
about 54.0 grams and about 70.0 grams of manganese dioxide.
[0025] Anode 14 can be formed of at least one electrochemically
active anode material, a gelling agent, and minor amounts of
additives, such as gassing inhibitor. The electrochemically active
anode material may include zinc; cadmium; iron; metal hydride, such
as AB.sub.5, AB.sub.2, and A.sub.2B.sub.7; alloys thereof; and
mixtures thereof.
[0026] The amount of electrochemically active anode material within
the anode 14 may be referred to as the anode loading. The loading
of the anode 14 may vary depending upon the electrochemically
active anode material used within, and the cell size of the battery
10. For example, AA batteries with a zinc electrochemically active
anode material may have an anode loading of at least about 3.3
grams of zinc. The anode loading may be, for example, at least
about 4.0, about 4.3, about 4.6 grams, about 5.0 grams, or about
5.5 grams of zinc. AAA batteries, for example, with a zinc
electrochemically active anode material may have an anode loading
of at least about 1.9 grams of zinc. For example, the anode loading
may have at least about 2.0 or about 2.1 grams of zinc. AAAA
batteries, for example, with a zinc electrochemically active anode
material may have an anode loading of at least about 0.6 grams of
zinc. For example, the anode loading may have at least about 0.7 to
about 1.0 grams of zinc. C batteries, for example, with a zinc
electrochemically active anode material may have an anode loading
of at least about 9.5 grams of zinc. For example, the anode loading
may have at least about 10.0 to about 15.0 grams of zinc. D
batteries, for example, with a zinc electrochemically active anode
material may have an anode loading of at least about 19.5 grams of
zinc. For example, the anode loading may have at least about 20.0
to about 30.0 grams of zinc.
[0027] Examples of a gelling agent that may be used include a
polyacrylic acid; a grafted starch material; a salt of a
polyacrylic acid; a carboxymethylcellulose; a salt of a
carboxymethylcellulose (e.g., sodium carboxymethylcellulose); or
combinations thereof. The anode may include a gassing inhibitor
that may include an inorganic material, such as bismuth, tin, or
indium. Alternatively, the gassing inhibitor can include an organic
compound, such as a phosphate ester, an ionic surfactant or a
nonionic surfactant.
[0028] An electrolyte may be dispersed throughout the cathode 12,
the anode 14 and the separator 16. The electrolyte comprises an
ionically conductive component in an aqueous solution. The
ionically conductive component may be a hydroxide. The hydroxide
may be, for example, sodium hydroxide, potassium hydroxide, lithium
hydroxide, cesium hydroxide, and mixtures thereof. The ionically
conductive component may also include a salt. The salt may be, for
example, zinc chloride, ammonium chloride, magnesium perchlorate,
magnesium bromide, and mixtures thereof. The concentration of the
ionically conductive component may be selected depending on the
battery design and its desired performance. An aqueous alkaline
electrolyte may include a hydroxide, as the ionically conductive
component, in a solution with water. The concentration of the
hydroxide within the electrolyte may be from about 0.25 to about
0.35, or from about 25% to about 35%, on a total weight basis of
the electrolyte. For example, the hydroxide concentration of the
electrolyte may be from about 0.25 to about 0.32, or from about 25%
to about 32%, on a total weight basis of the electrolyte.
[0029] The concentration of the ionic ally conductive component may
be determined by collecting the total amount of electrolyte from
within an assembled alkaline cell, for example a AA or a AAA
alkaline cell. Removing the separator, cathode, and anode
components and dissolving these components within a hydrochloric
solution may generally accomplish this. Hydrogen peroxide may be
added in a drop-wise manner to aid in the dissolving process. The
dissolved solution may then be diluted to a specific volume to
provide an analyte. The analyte may then be analyzed via an
inductively coupled plasma (ICP) emission spectrometer, such as a
JY Ultratrace or its equivalent, to determine the total positive
ion concentration of the ionically conductive component within the
analyte, for example potassium (K.sup.+) concentration in ppm. The
total positive ion concentration determined via ICP from the
analyte may be used to mathematically determine the total weight of
the positive ion, for example potassium (K.sup.+) in grams, and
subsequently the total weight of ionically conductive component,
for example potassium hydroxide (KOH) in grams, within the
electrolyte solution of the sampled alkaline cell. The
concentration of the ionically conductive component of the
electrolyte, for example potassium hydroxide (KOH), on a weight
basis of the electrolyte may be determined by dividing the total
weight of the ionically conductive component by the analyte
weight.
[0030] The aqueous alkaline electrolyte may also include zinc oxide
(ZnO). The ZnO may serve to suppress zinc corrosion within the
anode. The concentration of ZnO included within the electrolyte may
be less than about 3% by weight of the electrolyte. The ZnO
concentration, for example, may be less than about 2% by weight of
the electrolyte.
[0031] The total weight of the aqueous alkaline electrolyte within
a AA alkaline battery, for example, may be from about 3.0 grams to
about 4.0 grams. The weight of the electrolyte within a AA battery
preferably may be, for example, from about 3.3 grams to about 3.8
grams. The weight of the electrolyte within a AA battery may be
more preferably, for example, from about 3.4 grams to about 3.6
grams. The total weight of the aqueous alkaline electrolyte within
a AAA alkaline battery, for example, may be from about 1.0 grams to
about 2.0 grams. The weight of the electrolyte within a AAA battery
preferably may be, for example, from about 1.2 grams to about 1.8
grams. The weight of the electrolyte within a AA battery may be
more preferably, for example, from about 1.4 grams to about 1.6
grams.
[0032] It has been found that in addition to the electrolyte a low
resistance separator may facilitate optimal discharge performance
of an assembled alkaline electrochemical cell. Separator 16
comprises a material that is wettable or wetted by the electrolyte.
A material is said to be wetted by a liquid when the contact angle
between the liquid and the surface is less than 90.degree. or when
the liquid tends to spread spontaneously across the surface; both
conditions normally coexist. Separator 16 may comprise woven or
nonwoven paper or fabric. Separator 16 may include a layer of, for
example, cellophane combined with a layer of non-woven material.
The separator also can include an additional layer of non-woven
material. The separator material may be thin. The separator, for
example, may have a dry thickness of less than 150 micrometers
(microns). The separator, for example, may have a dry thickness of
less than 100 microns. The separator preferably has a dry thickness
from about 70 microns to about 90 microns, more preferably from
about 70 microns to about 75 microns. The separator has a basis
weight of 40 g/m.sup.2 or less. The separator preferably has a
basis weight from about, 15 g/m.sup.2 to about 40 g/m.sup.2, and
more preferably from about 20 g/m.sup.2 to about 30 g/m.sup.2.
[0033] Separator 16 may have an air permeability value. The air
permeability value of a separator may be characterized by the Sodim
air permeability tester, as defined in ISO 2965. The Sodim air
permeability tester is designed to measure the air permeability of
papers and non-woven materials. The tester measures the volume of
gas that passes, at a pressure of 1 kPa, through a predetermined
cross-section of the material during one minute. The air
permeability value of Separator 16 may be from about 2000
cm.sup.3/cm.sup.2min @ 1 kPa to about 5000 cm.sup.3/cm.sup.2min @ 1
kPa. The air permeability value of Separator 16 may be from about
3000 cm.sup.3/cm.sup.2min @ 1 kPa to about 4000 cm.sup./cm.sup.2min
@ 1 kPa. The air permeability value of Separator 16 may be from
about 3500 cm.sup.3/cm.sup.2min @ 1 kPa to about 3800
cm.sup.3/cm.sup.2min @ 1 kPa.
[0034] The overall chemical reaction for the reduction of the anode
and oxidation of the cathode in the primary alkaline
electrochemical cell, or battery, may be represented by Reaction
(I) below.
Zn+2MnO.sub.2+H.sub.2O.fwdarw.ZnO+2MnOOH (I)
Although the manganese compound is shown as MnO.sub.2, as is
conventional, it is well understood by those skilled in the art
that manganese dioxide is non-stoichiometric, and the actual
chemical formula for manganese dioxide is approximately
MnO.sub.1.96. Accordingly, the actual number of electrons involved
in this reaction is approximately 0.925. This is referred to
herein, as is also conventional, as the 1-electron step.
[0035] The 1-electron step, as represented by Reaction (I) above,
is not necessarily the only reaction to occur. The 1-electron step
may be followed by a second electron reaction, referred to as the
2.sup.nd-electron step, where the MnOOH is converted to
Mn(OH).sub.2. This second reaction is usually only significant
where a battery has been discharged to a significant degree. The
2.sup.nd-electron step appears to have very little, or no,
contribution on the overall discharge of the battery. Thus, for the
calculations herein, only the 1-electron step is taken into
account. Any references herein to the "point of completion" mean
the point at which the 1-electron step, or 0.925 electrons in
stoichiometric terms, has gone to completion (i.e., Mn.sup.+3.925
is reduced to) Mn.sup.+3.0).
[0036] It can be seen from the above Reaction (I) that there must
be sufficient water present to allow the reaction to go
sufficiently to completion to be considered full discharge. The
aqueous alkaline electrolyte is the source of water within the
battery prior to discharge. The concentration of the hydroxide
within the electrolyte prior to discharge, which may be referred to
as the initial hydroxide concentration, must be sufficient to
support Reaction (I). In addition, the concentration of the
hydroxide within the electrolyte will change with the discharge of
the battery. The concentration of the hydroxide within the
electrolyte at the end of discharge may be referred to as the final
hydroxide concentration. The final hydroxide concentration may be
calculated for a given battery design based on the weight of
manganese dioxide within the cathode; the initial hydroxide
concentration; and the volume of electrolyte under the assumption
that at the end of 1-electron discharge electrolyte is saturated by
zincate ions. The values of zincate concentration in saturated
electrolyte solutions may be found within, for example, The Primary
Battery, George W. Heise and N. Corey Cahoon, Eds., John Wiley
& Sons, Inc. (1971).
[0037] In practice, calculating the final KOH concentration, based
on this principle, means that it is neither necessary to discharge
a cell by 1-electron, nor to measure final KOH concentration,
whether in the anode, cathode, or both. Accordingly, preferred
cells can be designed and manufactured with considerable ease, as
starting amounts of active materials are readily assembled and
adjusted to yield a suitable, final, calculated concentration of
KOH at 1-electron discharge.
[0038] Similar considerations also apply to the concentration of
KOH at the beginning, before the cell has been discharged. Reaction
(I) shows that the electrode reaction consumes one molecule of
water for every two molecules of manganese dioxide consumed.
However, a different reaction applies much below about 36% KOH and
the reaction scheme changes to:
Zn+2MnO.sub.2+2H.sub.2O.fwdarw.Zn(OH).sub.2+2MnOOH (II)
The final KOH concentration (i.e., at the end of the 1-electron
discharge) is calculated based on the assumption that all of the
MnO.sub.2 is discharged to MnOOH.
[0039] The overall primary alkaline battery reaction that applies
is dependent on the average initial KOH concentration within the
electrolyte:
Zn+2MnO.sub.2+H.sub.2O.fwdarw.ZnO+2MnOOH (I)
Zn+2MnO.sub.2+2H.sub.2O.fwdarw.Zn(OH).sub.2+2MnOOH (II)
The calculations herein assume only Reaction (I) will occur when
the alkaline electrolyte has an initial normality that is greater
than or equal to 8N. The calculations also assume that only
Reaction II will occur when the alkaline electrolyte has an initial
normality of less than or equal to 6N. It is also assumed that the
change from Reaction (I) to Reaction (II) occurs linearly for the
alkaline electrolyte solution with a normality between 6N and 8N.
It will also be appreciated that the exact initial KOH
concentration upon which the 8N and 6N calculations are based will
depend on any additives dissolved within the electrolyte, such as
ZnO.
[0040] The initial hydroxide concentration of the electrolyte may
be from about 0.25 to about 0.35, or from about 25% to about 35%,
on a total weight basis of the electrolyte. For example, the
initial hydroxide concentration of the electrolyte may be from
about 0.25 to about 0.32, or from about 25% to about 32%, on a
total weight basis of the electrolyte. The final hydroxide
concentration of the electrolyte may be from about 0.40 to about
0.55, or from about 40% to about 55%, on a total weight basis of
the electrolyte. For example, the final hydroxide concentration of
the electrolyte may be from about 0.46 to about 0.54, or from about
46% to about 54%, on a total weight basis of the electrolyte. For
example, the final hydroxide concentration of the electrolyte may
be from about 0.40 to about 0.49, or from about 40% to about 49%,
on a total weight basis of the electrolyte.
[0041] Area-specific resistance is a measured property of the
combined separator and electrolyte that is influenced by separator
properties, such as composition, thickness, air permeability, basis
weight, and wettability, along with electrolyte properties, such as
hydroxide and zincate concentration. The area-specific resistance
value may be the best parameter to correlate with predictable
alkaline electrochemical cell performance.
[0042] The area-specific resistance of an alkaline electrochemical
cell may be determined both before and after the electron discharge
step. The area-specific resistance of the cell prior to the
1-electron discharge may be referred to as the initial
area-specific resistance. The cell with desired discharge
performance characteristics may have an initial area-specific
resistance value from about 100 mOhm-cm.sup.2 to about 220
mOhm-cm.sup.2. The initial area-specific resistance may be from
about 150 mOhm-cm.sup.2 to about 200 mOhm-cm.sup.2.
[0043] The area-specific resistance of an alkaline battery after
the 1-electron discharge may be referred to as the final
area-specific resistance. An alkaline electrochemical cell with
desired discharge performance characteristics may have a final
area-specific resistance value of less than about 500
mOhm-cm.sup.2. The final area-specific resistance may be from about
200 mOhm-cm.sup.2 to about 500 mOhm-cm.sup.2. The final
area-specific resistance may be from about 250 mOhm-cm.sup.2 to
about 350 mOhm-cm.sup.2. The final area-specific resistance may be
from about 280 mOhm-cm.sup.2 to about 340 mOhm-cm.sup.2. The final
area-specific resistance may be from about 300 mOhm-cm.sup.2 to
about 330 mOhm-cm.sup.2.
[0044] The ratio of the initial area-specific resistance to the
final area-specific resistance may be referred to as the ASR ratio
and is useful in predicting overall battery performance including a
separator and electrolyte combination. A separator and electrolyte
combination may have an acceptable initial ASR value that may
mistakenly indicate a battery including such a separator and
electrolyte combination would perform acceptably. As discussed
above, the concentration of the hydroxide within the electrolyte
will be dynamic during the discharge of the battery. The separator
and electrolyte combination must also have an acceptable ASR value
at the end of discharge. It is conceivable that a separator and
electrolyte combination with a low initial area-specific resistance
may have a high area-specific resistance value at the end of
discharge. The ASR ratio may help to better select a separator and
electrolyte combination for an alkaline electrochemical cell. An
alkaline electrochemical cell with desired discharge performance
characteristics may have an ASR ratio of less than about 1.9. For
example, the ASR ratio may be less than about 1.7. For example, the
ASR ratio may be from about 1.2 to about 1.65.
[0045] Referring to FIG. 2, a battery 10 is shown including a label
34 that has a voltage indicator, or tester, 36 incorporated within
it. The label 34 may be a laminated multi-layer film with a
transparent or translucent layer bearing the label graphics and
text. The label 34 may be made from polyvinyl chloride (PVC),
polyethylene terephthalate (PET), and other similar polymer
materials. Known types of voltage testers that are placed on
batteries may include thermochromic and electrochromic indicators.
In a thermochromic battery tester the indicator may be placed
between the anode and cathode electrodes of the battery. The
consumer activates the indicator by manually depressing a switch.
Once the switch is depressed, the consumer has connected an anode
of the battery to a cathode of the battery through the
thermochromic tester. The thermochromic tester may include a silver
conductor that has a variable width so that the resistance of the
conductor also varies along its length. The current generates heat
that changes the color of a thermochromic ink display that is over
the silver conductor as the current travels through the silver
conductor. The thermochromic ink display may be arranged as a gauge
to indicate the relative capacity of the battery. The higher the
current the more heat is generated and the more the gauge will
change to indicate that the battery is good.
Experimental Testing
Resistivity Cell Measurements
[0046] Resistance measurements are conducted in a resistivity cell
at room temperature, e.g., about 21.degree. C. The resistivity cell
consists of two stainless steel electrodes encased in Teflon.RTM..
The lower electrode is constructed such that a small reservoir of
electrolyte may be maintained in the cell. The top electrode
assembly is removable and is aligned to the bottom assembly via two
metal pins. The top electrode assembly is spring loaded so that
that force may be applied (approximately 4 to 5 lbs.) to the top of
a material sample being analyzed. The lower electrode assembly is
screwed to a fixture base and electrical leads are attached to each
electrode. The leads are then attached to the leads of an impedance
analyzer, such as a Solartron Impedance Analyzer, that is used to
complete impedance sweeps to determine resistances of the cell or
sample materials.
[0047] The background resistance of the resistivity cell is
determined by running an impedance sweep on the fixture filled with
electrolyte when its electrodes are shorted. The sweep starts at
100,000 kHz and finishes at 100 Hz using a 10 mV amplitude, using
the software program ZPlot by Scribner Instruments to control the
instrumentation. The resistance of the fixture (R.sub.CELL) may
have typical values between about 10 and 150 m.OMEGA. depending
upon the condition of the stainless steel electrodes. Several
sweeps may be completed to ensure the value obtained is relatively
constant.
[0048] The resistance of the separator and electrolyte combination
is determined by running an impedance sweep on a separator sample.
The fixture includes a center disk upon which the separator sample
may be placed. Electrolyte is placed within the cavity of the
resistivity cell to a level that ensures the separator sample is
well-wetted on both sides for 1 minute. The same impedance sweep as
described above is run. Again, several sweeps may be completed to
ensure the value obtained is relatively consistent. The data
obtained from the sweeps is plotted on a Nyquist plot. The ohmic
resistance (R.sub.REAL) of the separator and electrolyte
combination is determined at the Z''=0 point on the Nyquist plot.
However, this value includes the resistance of the resistivity
cell. By subtracting the resistance value of the resistivity cell
(R.sub.CELL) from the resistance determined for the separator and
electrolyte combination sample that includes resistivity cell
impedance (R.sub.REAL), one can calculate the adjusted resistance
value for the separator and electrolyte combination
[R.sub.REAL(ADJ)].
[0049] The area-specific resistance (ASR) of the
separator/electrolyte combination is determined by multiplying the
geometrical surface area of the resistivity cell's working
electrode by the adjusted separator-electrolyte combination's
resistance value. The working electrode surface area of resistivity
cell used in these experiments is 3.83 cm.sup.2. The units of ASR
are mOhmcm.sup.2.
[0050] The initial KOH concentration of the aqueous alkaline
electrolyte is selected to be 31% by weight of electrolyte and 2%
of ZnO by weight of the electrolyte are dissolved in water. The
initial weight of the electrolyte is about 3.532 grams. The cathode
may include 10.918 grams of manganese dioxide. The final KOH
concentration is calculated, as discussed above, to be 50.4% by
weight electrolyte with a saturated ZnO content of 9.7%.
[0051] Three potential separators for use within an improved
alkaline electrochemical cell design are each combined with
potassium hydroxide electrolyte solutions at the initial and final
KOH concentrations above for ASR screening.
[0052] Separator 1--PDM PAC623, a nonwoven material separator with
a basis weight of about 23 g/m.sup.2 and thickness of about 75
microns (dry).
[0053] Separator 2--PDM PAK628, a nonwoven material separator with
a basis weight of about 28 g/m.sup.2 and thickness of about 88
microns (dry).
[0054] Separator 3--DT225, a separator including a cellophane
laminated to a nonwoven material with a basis weight of about 57
g/m.sup.2 and a thickness of about 90 microns (dry).
[0055] Electrolyte A--A mixture of 31% by weight potassium
hydroxide (KOH) and 2% by weight zinc oxide (ZnO) in water.
[0056] Electrolyte B--A mixture of 50.4% by weight potassium
hydroxide (KOH) and 9.7% by weight zinc oxide (ZnO) in water.
[0057] The impedance of the resistivity cell, at room temperature,
is first determined with each specific electrolyte as described
above. The impedance of the separator/electrolyte combination, at
room temperature, is then determined with each specific
electrolyte. The adjusted separator/electrolyte combination
resistance is then determined and used in the calculation of the
ASR. The results are included within Table 1. The
separator/electrolyte combinations that have the lowest initial ASR
values, final ASR values, and ASR ratios may provide lower overall
cell impedance and potentially improved discharge performance.
TABLE-US-00001 TABLE 1 Area-specific resistance (ASR) for
separator/electrolyte combinations. ASR (mOhm cm.sup.2) ASR
SEPARATOR Electrolyte A Electrolyte B Ratio 1 191.96 305.94 1.594 2
188.77 321.51 1.703 3 260.63 2178.83 8.360
Performance Testing of Assembled AA Alkaline Primary Batteries
[0058] An exemplary battery is assembled to evaluate the effects of
the present invention on battery discharge performance. The anode
includes an anode slurry containing 4.8 grams of zinc; 1.843 grams
of a potassium hydroxide alkaline electrolyte with about 31% KOH by
weight and 2% by ZnO dissolved in water; 0.027 grams of polyacrylic
acid gellant; and 0.02 grams of corrosion inhibitor. The cathode
includes a blend of EMD, graphite, and potassium hydroxide aqueous
electrolyte solution. The cathode includes a loading of 10.918
grams of EMD, a loading of 0.4 grams Timcal BNB-90 graphite, and
0.613 grams of electrolyte. A separator is interposed between the
anode and cathode. The anode, cathode, and separator are inserted
in a housing that is cylindrical in shape. The housing is then
sealed to finish off the battery assembly process. The resulting
battery is typically referred to as a AA battery.
[0059] Performance testing includes discharge performance testing
that may be referred to as the ANSI/IEC Motorized Toys Test (Toy
Test). The Toy Test protocol includes applying a constant load of
3.9 Ohms for 1 hour. The battery then rests for a period of 23
hours. This cycle is repeated until the cutoff voltage of 0.8 volts
is reached.
[0060] Performance testing also includes discharge performance
testing that may be referred to as the ANSI/IEC Remote Controls
Test (Remote Controls Test). The Remote Controls Test protocol
includes applying a constant load of 24 Ohms for 15 seconds per
minute for 8 hours. The battery then rests for a period of 16
hours. This cycle is repeated until the cutoff voltage of 1.0 volts
is reached.
[0061] Performance testing also includes discharge performance
testing that may be referred to as the ANSI/IEC Clock/Radio Test
(Clock/Radio Test). The Clock/Radio Test protocol includes applying
a constant load of 43 Ohms for 4 hours. The battery then rests for
a period of 20 hours. This cycle is repeated until the cutoff
voltage of 0.9 volts is reached.
Performance Testing
[0062] A size AA battery is assembled that includes the combination
of Separator 1 and Electrolyte A with an initial ASR of 191.96
mOhmcm.sup.2, final ASR of 305.94 mOhmcm.sup.2, and an ASR ratio of
1.594. The battery is stored at room temperature, e.g., at about
21.degree. C., and then the Remote Control Test is performed on the
battery. The battery is stored at room temperature, e.g., at about
21.degree. C., and then the Clock/Radio Test is performed on the
battery. The battery is stored at a temperature that cycles from a
temperature of 25.degree. C. to 55.degree. C. over a 24-hour period
that is repeated for a duration of two weeks and then the Toy Test
is performed on the battery.
[0063] The battery exhibits an average performance of 8.71 service
hours on the Toy Test, an average of 55.2 service hours on the
Remote Controls Test, and an average of 105.1 service hours on the
Clock/Radio Test. The battery exhibits Toy Test, Remote Controls
Test, and Clock/Radio Test performance improvements of about 3.2%,
about 4.0%, and about 4.3% respectively, versus a comparative
battery that includes a separator/electrolyte combination that has
an initial ASR of about 260.63 mOhmcm.sup.2, a final ASR of about
2178.83 mOhmcm.sup.2, and an ASR ratio of 8.36.
[0064] The dimensions and values disclosed herein are not to be
understood as being strictly limited to the exact numerical values
recited. Instead, unless otherwise specified, each such dimension
is intended to mean both the recited value and a functionally
equivalent range surrounding that value. For example, a dimension
disclosed as "40 mm" is intended to mean "about 40 mm."
[0065] Every document cited herein, including any cross referenced
or related patent or application and any patent application or
patent to which this application claims priority or benefit
thereof, is hereby incorporated herein by reference in its entirety
unless expressly excluded or otherwise limited. The citation of any
document is not an admission that it is prior art with respect to
any invention disclosed or claimed herein or that it alone, or in
any combination with any other reference or references, teaches,
suggests or discloses any such invention. Further, to the extent
that any meaning or definition of a term in this document conflicts
with any meaning or definition of the same term in a document
incorporated by reference, the meaning or definition assigned to
that term in this document shall govern.
[0066] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the
invention. It is therefore intended to cover in the appended claims
all such changes and modifications that are within the scope of
this invention.
* * * * *