U.S. patent application number 10/020685 was filed with the patent office on 2003-06-19 for oxazoline surfactant anode additive for alkaline electrochemical cells.
Invention is credited to Ndzebet, Ernest.
Application Number | 20030113623 10/020685 |
Document ID | / |
Family ID | 21799985 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030113623 |
Kind Code |
A1 |
Ndzebet, Ernest |
June 19, 2003 |
Oxazoline surfactant anode additive for alkaline electrochemical
cells
Abstract
According to the present invention an alkaline electrochemical
cell can contain an anode having an anode active material, an
alkaline electrolyte, a gelling agent and an oxazoline surfactant
additive. The invention relates to an anode mix, to an anode
containing the mix, and to an electrochemical cell containing the
anode and to methods for making the anode mix, the anode and the
cell. Performance improvements can be realized when the oxazoline
surfactant is provided in the anode, which can include increased
operating voltage, good high rate pulse capability, elimination of
initial potential dip, good shelf life and reduced sensitivity to
open circuit rest.
Inventors: |
Ndzebet, Ernest; (Middleton,
WI) |
Correspondence
Address: |
Bennett J. Berson
Quarles & Brady LLP
1 South Pinckney Street
P O Box 2113
Madison
WI
53701-2113
US
|
Family ID: |
21799985 |
Appl. No.: |
10/020685 |
Filed: |
December 14, 2001 |
Current U.S.
Class: |
429/212 ;
429/229 |
Current CPC
Class: |
H01M 4/02 20130101; H01M
4/628 20130101; H01M 4/42 20130101; H01M 2300/0014 20130101; H01M
12/06 20130101; H01M 4/62 20130101; H01M 4/06 20130101 |
Class at
Publication: |
429/212 ;
429/229 |
International
Class: |
H01M 004/62; H01M
004/42 |
Claims
I claim:
1. An anode mix comprising an alkaline electrolyte, an anode active
material, a gelling agent and an oxazoline surfactant.
2. The anode mix of claim 1 wherein the oxazoline surfactant
comprises a fatty side chain.
3. The anode mix of claim 2 wherein the oxazoline surfactant is
ethanol, 2,2'-[(2-heptadecyl-4(5H)-oxazolydine) bis
(methyleneoxy-2,1 -ethanedyloxy]bis.
4. The anode mix of claim 2 wherein the oxazoline surfactant
comprising the fatty side chain is Alkaterge T-IV.
5. The anode mix of claim 1, wherein the alkaline electrolyte is
potassium hydroxide.
6. The anode mix of claim 1, wherein the anode active material is
particulate zinc powder.
7. The anode mix of claim 1, wherein the surfactant coats at least
a portion of the anode active material.
8. An anode for use in an electrochemical cell, the anode
comprising the anode mix of any of claims 1-7.
9. An alkaline electrochemical cell comprising a cathode, an anode,
and an alkaline electrolyte in electrical contact with the anode
and the cathode, the anode comprising an anode active material, a
gelling agent and an oxazoline surfactant.
10. The alkaline electrochemical cell of claim 9 wherein the
oxazoline surfactant comprises a fatty side chain.
11. The alkaline electrochemical cell of claim 10 wherein the
oxazoline surfactant is ethanol,
2,2'-[(2-heptadecyl-4(5H)-oxazolydine) bis
(methyleneoxy-2,1-ethanedyloxy]bis.
12. The alkaline electrochemical cell of claim 10 wherein the
oxazoline surfactant comprising the fatty side chain is Alkaterge
T-IV.
13. The alkaline electrochemical cell of claim 9 wherein the
alkaline electrolyte is potassium hydroxide.
14. The alkaline electrochemical cell of claim 9 wherein the anode
active material is particulate zinc powder.
15. The alkaline electrochemical cell of claim 9 wherein the
surfactant coats at least a portion of the anode active material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
BACKGROUND OF THE INVENTION
[0003] The demand for very small electrochemical cells has
increased with increased use of small, electrically-powered
devices, and alkaline and alkaline metal-air electrochemical cells
are an increasingly popular choice for powering such devices as
hearing appliances and computers. Metal air cells contain an anode
and an oxygen cathode, with the oxygen usually obtained from
ambient air. The oxygen cathode catalytically promotes the reaction
of oxygen with an aqueous neutral or alkaline electrolyte and is
not consumed or changed during discharge. As the cathode is
extremely compact yet has essentially unlimited capacity, very high
energy densities are achieved, resulting from the increased
available volume for the anode active material. Consequently, a
metal-air cell can provide more watt-hours of electromotive force
than a so-called "two-electrode cell" of similar cell size, mass
and anode composition that contains both anode- and cathode-active
materials inside the cell structure. Metal-air cells have an
advantageous watt-hour capacity/mass ratio without regard to size
or configuration, which can be, e.g., button cells as in, for
example, U.S. Pat. No. 5,721,065 ("the '065 patent"), or
cylindrical cells as in, for example, U.S. Pat. No. 6,210,827 (the
'827 patent"), each incorporated by reference in its entirety as if
set forth herein.
[0004] A typical metal air cell such as a zinc air cell contains an
anode that includes a zinc alloy powder, a carbon-based air cathode
and an alkaline electrolyte with a gelling agent to prevent the
electrolyte from creeping through the cell seals. For efficient
operation, the anode of a zinc air cell should participate only
during current-generating reaction periods. In reality, though,
corrosive shelf-discharge side reactions in the alkaline
electrolyte can reduce both service and shelf life of alkaline
electrochemical systems that use zinc as the anode active material.
Much effort has been directed to improving electrochemical reaction
efficiency and cell output. Previously, mercury was added to cell
anodes to improve corrosion resistance. In recent years, mercury
has been replaced by substances that conform to environmental
requirements. Small amounts of metals such as lead, indium, and
bismuth, and combinations thereof, can effectively improve
corrosion behavior of anodic zinc. Certain organic surfactants can
provide effective corrosion-inhibiting effect at the metal surface
while making the anode sufficiently available for electrochemical
oxidation that the cell output can be maintained under heavy cell
loading. Surfactants can, like mercury, improve discharge capacity,
service life and shelf life, without substantial adverse
environmental impact. U.S. Pat. No. 4,857,424 ("the '424 patent")
incorporated by reference herein as if set forth in its entirety,
discloses reduced-mercury or mercury-free zinc-manganese dioxide
cells containing an organosiliconate type surfactant. Also, the
'065 patent discloses a button cell having an anode mix containing
zinc metal powder, indium or other compounds, optionally a low
level of mercury, a gelling agent and preferably a
hydroxyethylcellulose surfactant. The anode disclosed therein
sustains longer periods of power production at a relative steady
voltage of at least 1.1 volts while protecting the anode metal from
corrosion in the alkaline environment.
[0005] Similarly, the '827 patent discloses a cylindrical cell
having an anode mix containing electrolyte, a gelling agent,
particulate zinc, zinc oxide, additives and an organic surfactant
comprising hydroxyethylcellulose.
[0006] Japanese Patent No. JP10083812 to Toshiba Battery Co. Ltd.
discloses providing a high performance zinc alkaline battery
containing 0.5-100 ppm of a fluorine-containing surfactant in a
non-amalgamated-zinc-alloy-based gelled anode having a viscosity of
100,000 to 300,000 cPs at 25.degree. C.
[0007] U.S. Pat. No. 5,382,482 concerns suppressing dendrites and
shape change in an alkaline cell by disposing a cross-linked
polymer film layer in close proximity to the anode active material,
where the polymer film layer can contain, among other polymers,
polyoxazoline. The patent does not describe including an oxazoline
surfactant in the anode mix of the cell.
[0008] Further improvements in performance, such as increased
operating voltage, improved discharge profile and reduced
sensitivity to open circuit rest in alkaline electrochemical cells,
preferably without sacrificing known benefits, are welcome and
desired.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention discloses that an alkaline
electrochemical cell having superior discharge performance and
corrosion resistance includes an oxazoline surfactant additive in
the cell anode. In one aspect, the present invention relates to an
anode for use in a alkaline electrochemical cell, where the anode
contains a metal anode active material, an anode electrolyte and an
oxazoline surfactant. Optionally, the anode of the invention can
include additional components known in the manufacture of alkaline
electrochemical cells and anodes for same. In a related aspect, the
invention relates to an alkaline electrochemical cell containing an
anode of the invention. In another aspect, the present invention
relates to methods for making an anode of the invention, or for
making a cell containing the anode, as are detailed below.
[0010] It is an object of the invention to improve discharge
performance and corrosion resistance without sacrificing the known
benefits of adding surfactants to alkaline cell anodes.
[0011] It is a feature of the invention that the anode, and an
electrochemical cell containing the anode, contain an oxazoline
surfactant that can coat at least a portion of the particles of the
anode active material.
[0012] It is an advantage of the present invention can maintain
known benefits of anode surfactants, and can provide additional
benefits that can include improved discharge efficiency at low and
high rates, high operating voltage, lack of initial potential dip,
and reduced sensitivity to open circuit rest.
[0013] Other objects, features and advantages of the present
invention will become apparent in view of the following detailed
description of the invention and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 compares the discharge profiles of cells of the
invention containing an oxazoline surfactant and cells containing
an organosiliconate surfactant. Discharge was at 374 Ohm for 16
hours/day at 70.degree. F., 50 % relative humidity, after one month
storage at 70.degree. F.
[0015] FIG. 2 compares the discharge profiles of cells of the
invention containing an oxazoline surfactant and cells containing
an organosiliconate surfactant. Discharge was at 620 Ohm for 16
hours/day at 70.degree. F. 50 % relative humidity, after 20 days
storage at 140.degree. F.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present invention relates to using an oxazoline-type
surfactant, which can be a fatty oxazoline surfactant, as an
additive for an alkaline electrochemical cell anode. Cells
comprising the anode can exhibit improved electrical discharge
performance, including higher operating voltage, good high rate
pulse capability, no initial potential dip and reduced sensitivity
to open circuit rest in comparison to cells that use other
surfactants.
[0017] Oxazoline-type surfactants can be added to anode materials
of any alkaline metal-anode electrochemical cells to improve
discharge performance and to improve discharge capacity,
service-life, and shelf life. While the invention was exemplified
with metal-air anodes and cells, more particularly in zinc-air
cells, the invention can be employed in metal-containing anodes
generally, more particularly in zinc anodes, and in cells
containing same. Suitable chemistries include, but are not limited
to, zinc-air, zinc-manganese dioxide, zinc/AgO and zinc/Ag.sub.2O
systems, without regard to size or configuration. Preferable cells
are of standard configurations, such as button cells, cylindrical
cells and prismatic cells, which are available in a variety of
standard sizes. For example, oxazoline type-surfactants can be
substituted for the surfactants described in incorporated U.S. Pat.
Nos. 4,857,424, 5,721,065 and 6,210,827. The anode materials to
which an oxazoline surfactant is added contain a metal powder, a
gelling agent, and an electrolyte. The anode materials can also
include other components including but not limited to mercury,
indium, gallium, aluminum, lead, bismuth and calcium compounds, and
combinations thereof, as disclosed, for example, in the '065 patent
and in U.S. Pat. No. 5,721,072, also incorporated herein by
reference as if set forth in its entirety.
[0018] In one aspect, the present invention relates to an anode mix
that includes a metal powder suitable for an anode of an alkaline
electrochemical cell, an electrolyte compatible with the anode
metal, an oxazoline surfactant and a gelling agent. In another
aspect, the present invention relates to an anode that includes the
composition described above in a container for receiving the
composition of matter. In still another aspect, the present
invention relates to an alkaline electrochemical cell that contains
the anode. The cell has a discharge voltage of at least 0.7 volts,
preferably 1.0 volts, more preferably 1.1 volts and still more
preferably 1.2 volts, during its service life.
[0019] In preferred embodiments, the metal powder is preferably
about 55% to about 73% by weight of the anode, the electrolyte is
about 27% to about 45% (by weight) in an aqueous solution, and the
oxazoline surfactant is about 0.001% to about 5% (by weight), based
on the weight of the particles of metal powder. The anode material
generally also contains about 0.1% to about 0.5% of gelling agent,
by weight based on the weight of active material, and between about
1% to about 4%, preferably about 2% of zinc oxide, by weight based
on the weight of the electrolyte. In more preferred embodiments,
the metal powder is a particulate zinc alloy powder and the
electrolyte is potassium hydroxide.
[0020] In a related aspect, the present invention is a method of
making an anode mix for use in the anode and in the cells of the
invention, the method involving the steps of mixing a metal powder,
a gelling agent, an oxazoline surfactant, and an electrolyte in the
above-mentioned proportions. The order in which the components are
combined is not critical, except insofar as when mixing the
oxazoline surfactant with a liquid (namely, the electrolyte or the
gelled electrolyte), the surfactant is preferably a state (e.g.,
melted). Alternatively, if the surfactant is mixed first with the
metal powder or other dry component, it can be a solid. In one
embodiment of the method, the gelling agent and the alkaline
electrolyte are combined first to form a gelled electrolyte. Then,
the oxazoline surfactant is added to the gelled electrolyte with
agitation. Finally, the metal powder is combined with the
surfactant-containing alkaline electrolyte to form the gelled zinc
anode material which can be incorporated into the receiving
container.
[0021] In another related aspect, the present invention is a method
of making an alkaline electrochemical cell involving the step of
incorporating the aforementioned inventive anode into an
electrochemical cell, the process for making the cell being, apart
from the composition of the anode, conventional as is shown, for
example in U.S. Pat. No. 4,617,242, incorporated herein by
reference as if set forth in its entirety.
[0022] A suitable oxazoline surfactant can be solubilized in an
anode-compatible electrolyte and is a liquid or can be liquefied
under the anode processing conditions. U.S. Pat. No. 3,389,145,
incorporated by reference herein as if set forth in its entirety,
discloses structures of one suitable set of oxazolines and
processes for making same. Also suitable for use in the anode of
the invention are substituted oxazoline surfactants having the
structures shown in U.S. Pat. No. 3,336,145, in U.S. Pat. No.
4,536,300, in U.S. Pat. No. 5,758,374 and in U.S. Pat. No.
5,407,500, each incorporated by reference herein as if set forth in
its entirety, and mixtures of any of the foregoing. A most
preferred oxazoline surfactant, ethanol,
2,2'-[(2-heptadecyl-4(5H)-oxazolydine) bis
(methyleneoxy-2,1-ethanedyloxy]bis, has a structure shown as
Formula (I-2) in incorporated U.S. Pat. No. 5,407,500. This
compound is commercially available from Angus Chemical (Northbrook,
Ill.) as Alkaterge T-IV.
EXAMPLE
[0023] Zinc air cells according to the invention were built with an
anode as described in incorporated U.S. Pat. No. 4,617,242. except
that the oxazoline surfactant was substituted at 0.3%, relative to
the alkaline electrolyte in test cells in place of the
organosiliconate surfactant of the prior anode composition. The
structure of the test and control cells was as described in
incorporated U.S. Pat. No. 5,721,065.
[0024] The discharge characteristics of 13 size zinc air cells of
the present invention containing Alkaterge T-IV were compared
against otherwise identical commercial cells having an
organosiliconate surfactant in the anode. FIG. 1 illustrates the
discharge curve at 374 Ohm after 1 month storage of cells at
70.degree. F.; FIG. 2 shows the discharge curve at 620 Ohm after 20
days storage at 140.degree. F. As shown in FIGS. 1 and 2, cells
containing oxazoline-type surfactant-based exhibited operating
voltage at least 5-10 mV higher than prior art cells during most of
their usable lives. In addition, the test cells did not exhibit an
initial potential dip and were less sensitive to open circuit rest
than otherwise comparable cells containing the organosiliconate
type-surfactant.
[0025] Further, Table 1 shows discharge capacity values at 374 Ohm
of test cells containing Alkaterge T-IV surfactant. The capacity of
these cells was comparable to that of organosiliconate type
surfactant-based cells before and after storage for one month at
70.degree. F., 50% relative humidity, although discharge capacity
before storage was comparatively lower in cells that contained
Alkaterge T-IV.
1TABLE 1 Discharge Capacity (mAh) at 1.1 Volt Control Alkaterge
T-IV Alkaterge T Alkaterge E No Delay 251 244 247 N/A One month 252
252 198 N/A
[0026] Additionally, cells containing Alkaterge T-IV and control
cells were also stored for twenty days at 140.degree. F., 50%
relative humidity and were tested at 620 Ohm for 16 hours/day at
70.degree. F., 50% relative humidity. Results of the two cell types
were comparable (258 mAh v. 254 mAh, respectively).
[0027] Taken together these results demonstrate that oxazoline-type
surfactants can effectively maintain cell capacity. Also,
oxazoline-type surfactant based cells exhibited good high rate
pulse capability as compared to the control cells.
* * * * *