U.S. patent number RE31,532 [Application Number 06/270,216] was granted by the patent office on 1984-03-06 for primary cells and iodine containing cathodes therefor.
This patent grant is currently assigned to Catalyst Research Corporation. Invention is credited to James R. Moser, Alan A. Schneider.
United States Patent |
RE31,532 |
Schneider , et al. |
March 6, 1984 |
**Please see images for:
( Certificate of Correction ) ** |
Primary cells and iodine containing cathodes therefor
Abstract
A mixture of iodine with a poly-2-vinylpyridine.I.sub.2 or a
poly-2-vinylquinoline.I.sub.2 charge transfer complex is an
improved cathode material of a plastic state and in conjunction
with a metal anode, for example lithium, provides primary cells
with improved capacity and performance characteristics.
Inventors: |
Schneider; Alan A. (Baltimore,
MD), Moser; James R. (Shrewsbury, PA) |
Assignee: |
Catalyst Research Corporation
(Baltimore, MD)
|
Family
ID: |
27365982 |
Appl.
No.: |
06/270,216 |
Filed: |
June 3, 1981 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
106657 |
Jan 15, 1971 |
03674562 |
Jul 4, 1972 |
|
|
Current U.S.
Class: |
429/310; 429/199;
429/213 |
Current CPC
Class: |
H01M
4/06 (20130101); H01M 4/36 (20130101); H01M
6/182 (20130101); H01M 4/661 (20130101); H01M
4/60 (20130101) |
Current International
Class: |
H01M
4/06 (20060101); H01M 4/36 (20060101); H01M
4/66 (20060101); H01M 4/60 (20060101); H01M
6/18 (20060101); H01M 006/18 () |
Field of
Search: |
;429/212,213,191,101,199,218 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Gutmann et al., J. Electrochem. Soc., 114, pp. 323-324,
(1967)..
|
Primary Examiner: Skapars; Anthony
Attorney, Agent or Firm: Pennie & Edmonds
Claims
We claim:
1. A plastic cathode consisting essentially of a mixture of iodine
and a charge transfer complex of iodine with an organic donor
component selected from the group consisting of
poly-2-vinylquinoline and poly-2-vinylpyridine the mixture
containing between about 2 and 15 molecules of iodine for each atom
of nitrogen.
2. A cathode according to claim 1 containing about 6 molecules of
iodine for each atom of nitrogen.
3. A primary cell comprising a metallic anode and a cathode
consisting essentially of a plastic mixture of iodine and a charge
transfer complex of iodine with an organic donor component selected
from the group consisting of organic donor component selected from
the group consisting poly-2-vinylquinoline and poly-2-vinylpyridine
containing between about 2 and 15 molecules of iodine for each atom
of nitrogen.
4. A cell according to claim 3 in which the anode is silver,
magnesium or lithium.
5. A cell according to claim 3 having a current collector in
contact with the cathode and made of a metal selected from the
group consisting of zirconium, platinum, nickel or alloys
thereof.
6. A cell according to claim 5 in which the anode is lithium and
the cathode current collector is zirconium.
7. A cell according to claim 6 in which the cathode contains
between about 2 and 6 molecules of iodine for each atom of
nitrogen.
8. A cell according to claim 6 in which the cathode is a mixture of
iodine and poly-2-vinylpyridine.
9. A cell according to claim 6 in which the cathode is a mixture of
iodine and poly-2-vinylquinoline.
10. A primary cell comprising laminae in intimate contact
sequentially arranged as follows: (1) a metallic anode, (2) an
electrolyte comprising an iodide of the anode metal, (3) a cathode
consisting essentially of a plastic mixture of iodine and a charge
transfer complex of iodine with an organic donor component selected
from the group consisting of poly-2-vinylquinoline and
poly-2-vinylpyridine containing between 2 and 15 molecules of
iodine for each atom of nitrogen and (4) a metal cathode current
collector inert to said cathode.
11. A cell according to claim 10 having a lithium anode and a
zirconium cathode current collector.
12. A cell according to claim 11 having a metallic anode current
collector lamina in intimate contact with the anode.
Description
The invention herein described was made in the course of or under a
contract or subcontract thereunder with The Department of the
Army.
This invention relates to primary cells having charge transfer
complex cathodes and more particularly to new and improved
iodine-containing cathode material and to cells having a metal
anode and a cathode of the new cathode material.
Cells utilizing iodine-containing charge transfer complexes as
cathodes and having anodes of certain divalent metals or silver
have been disclosed by Gutman et al., J. Electrochem. Soc. 114, 323
(1967) and ibid. 115, 359 (1968). In the copending application of
James R. Moser, Ser. No. 41,801 filed June 1, 1970, there are as
disclosed high voltage, high energy density batteries having a
lithium anode and iodine-containing cathodes, including
organic-iodine charge transfer complexes.
It is an object of this invention to provide a new and improved
iodine-containing cathode composition that has a high proportion of
electrochemically available iodine and a high electronic
conductivity over a wide range of iodine content. Another object is
to provide such cathode compositions in a solid, plastic state.
Another object is to provide cells and batteries having a metal
anode and a cathode of the new compositions. Still another object
is to provide a stable, long-lived, high energy density, high
voltage battery especially useful for long life, low current drain
applications. Another object is to provide such a battery having a
lithium anode and a cathode of the new composition. Other objects
will be apparent from the following description and claims.
In the accompanying drawings:
FIG. 1 is a plan view of a preferred battery construction in
accordance with this invention; and
FIG. 2 is a vertical section, greatly enlarged, taken on line
II--II of FIG. 1; and
FIG. 3 is a chart showing discharge characteristics of cells made
in accordance with FIG. 1.
The new cathode materials of this invention are pliable, putty-like
solids containing iodine and a charge transfer complex of iodine
and poly-2-vinylpyridine or poly-2-vinylquinoline. The term
"plastic" used in relation to the cathode materials will refer to
the pliable, putty-like physical state. The cathode materials
contain from about 2 to 15 moles of I.sub.2 for each atom of N.
Cells or batteries utilizing the iodine-containing cathodes of this
invention have an anode reaction, ##EQU1## and a cathode reaction
I.sub.2 +2e.fwdarw.2I-giving an overall reaction where M is a metal
electrochemically reactive with iodine, and n is the valence of the
metal. In these cells, the electrolyte is solid state metal iodide,
preferably the iodide of the cathode metal, which may be formed in
situ by contacting the anode and cathode surfaces. The cathode is
preferably contacted against an inert current collector, suitably
carbon or metal inert to the cathode. We have discovered that
zirconium, platinum or alloys thereof are the most desirable
materials for cathode collectors as they exhibit no apparent
reaction or deterioration. Nichrome, nickle and other high nickel
alloys are suitable for shorter life batteries, e.g. 4-6
months.
In the conventional preparation of charge transfer complexes of
iodine with poly-2-vinylpyridine or poly-2-vinylquinoline one
molecule of I.sub.2 coordinates with each N atom resulting in a
solid having an iodine content of about 71% by weight in the case
of the poly-2-vinylpyridine complex and about 62% in the case of
the poly-2-vinylquinoline complex. The new cathode compositions of
the invention are a mixture of iodine and the solid
poly-2-vinylpyridine.multidot.I.sub.2 or
poly-2-vinylquinoline.multidot.I.sub.2 charge transfer complex in
the desired proportions. (Throughout the specification the cathode
materials may be designated by the formulas P2VP.multidot.nI.sub.2
and P2VQ.multidot.nI.sub.2, where P2VP is poly-2-vinylpyridine,
P2VQ is poly-2-vinylquinoline and n is the number of moles of
I.sub.2 for each atom of N. For example, the charge transfer
complex with one mole of I.sub.2 per N atom is designated as
P2VP.multidot.I.sub.2 ; if four moles of I.sub.2 per N atom are
added, the mixture is designated P2 VP.multidot.51.sub.2.)
The mixture is at ordinary ambient room temperatures a putty-like,
pliable solid that is sufficiently plastic to be spread on a solid
substrate, such as a sheet of anode metal. The materials are
useable as cathodes in solid state cells at temperatures up to the
point where softening causes loss of dimensional stability; this
point may range from 20.degree. to 75.degree. C., or higher,
depending on the degree of polymerization of the organic component
of the charge transfer complex. It is believed that the plastic
state of the cathode materials permits excellent atomic bonding of
the cathode materials to the anode and to the cathode current
collector resulting in greater outputs from a cell.
The following examples are illustrative of the preparation of the
new cathode compositions, it being recognized that any methods of
preparing the charge transfer complex my be used, variations in
which may modify the molecular weight of the polymer component of
the complex. In general, the most satisfactory cathode materials
are obtained using a charge transfer complex precipitated from
organic solution.
EXAMPLE I
Poly-2-vinylquinoline is prepared by the conventional method of
polymerizing a benzene solution of 2-vinylquinoline using
n-butylithium polymerization initiator, suitably by adding 11.3 g.
of initiator (15-22% by weight in hexane) to a solution of 100 g.
of 2-vinylquinoline in 1500 cc. of benzene (the solution at
45.degree. C.) and stirring for about 10 minutes. A solution of
iodine in benzene, is added in excess of stoichiometric to the
poly-2-vinylquinoline solution to precipitate P2VQ.multidot.I.sub.2
charge transfer complex. The presence of an excess of iodine is
readily determinable by a red coloration of the mixed solutions.
The precipitate is filtered, vacuum dried and mixed with between
about 1 and 17 molecular weights of I.sub.2 for each atomic weight
of N in the complex to form a plastic, pliable solid.
EXAMPLE II
Example I is repeated except that 2-vinylpyridine is used in place
of the 2-vinylquinoline. The resultant materials having the formula
P2VP.multidot.nI.sub.2 when n is between about 2and 7, are
plastic.
It will be recognized that solutions of poly-2-vinylquinoline and
poly-2-vinylpyridine may be prepared using a variety of organic
solvents or conventional catalysts, such as for example the
solvents toluene and hexane and the catalysts sodium metal and
potassium metal. The polymers may also be prepared from aqueous
solution using catalysts such as acetyl peroxide, lauroyl peroxide
or methyl ethyl ketone peroxide with a cobalt naphthenate
accelerator. .[.EXAMPLE III.]..[.2-vinylpyridine was thermally
polymerized by heating to about 80.degree. for 8 hours. The
resultant red thermoplastic material was cooled, ground to a
powder, and mixed with from 20 to 40 parts of poly-2-vinylpyridine
to form a plastic, pliable solid..].
The new compositions of the invention are particularly suitable as
iodine-containing cathode materials because, in addition to their
putty-like physical state, they exhibit a low and relatively
constant electronic resistance over a wide range of iodine content
and have a comparatively low electronic resistance even at
extremely high iodine contents.
With proportions of between about 3 and 7 moles of I.sub.2 per atom
of nitrogen (or monomer unit) the electrical resistance of the new
cathode material is low and substantially constant. For example,
the specific resistance of P2VP.multidot.3I.sub.2 prepared by the
method of Example 1 is about 1400 ohm-cm.; P2VP.multidot.4I.sub.2
is 1000 ohm-cm.; P2VP.multidot.5I.sub.2 is 100 ohm-cm;
P2VP.multidot.6I.sub.2 is 930 ohm-cm; P2VP.multidot.7I.sub.2 os
1400 ohm-cm. With lower iodine content, the resistance rapidly
increases; for example, P2VP.multidot.2I.sub.2 has a specific
resistance of about 40,000 ohm-cm. With increasing iodine content
above about 7 moles of I.sub.2 per monomer unit, the resistance
also increases; for example, the specific resistance of
P2VP.multidot.8I.sub.2 is 2600 ohm-cm. Thus the new cathode
materials are especially advantageous in that they can provide a
large amount of iodine for electrochemical reaction without greatly
increasing the cell resistance because of change in the cathode
composition resulting from consumption of iodine; this results in
longer lived cells with higher power and energy outputs. For high
current drain batteries it is preferred to use cathodes containing
about 6 moles of iodine per monomer unit, as about 4 moles of
iodine are available for reaction at the lowest resistance level.
Higher proportions of iodine, up to 15 moles of iodine per monomer
unit, are advantageously used in low current drain batteries, as a
much higher energy capacity is obtained and at low current drains
the polarization (IR drop) is not objectionably large.
Referring to FIG. 1 and FIG. 2, a preferred cell is enclosed in a
plastic or metal housing 2, suitably a plastic envelope of
polyvinyl chloride or Teflon, or a potted housing of polyester or
epoxy, or a metal enclosure made from zirconium or nickel or other
hermetically sealed housing that is impervious to iodine and
ordinary atmospheres; that is, oxygen, nitrogen and water vapor. A
thin metallic anode current collector 4, suitably nickel foil or a
nickel plate deposited in the plastic housing by vacuum deposition
or electroless plating, abuts a lithium electrode 6; a metal lead 8
is connected to the anode current collector for external circuit
connection. The lithium is most conveniently in the form of a foil,
but it may also be deposited on the current collector by vacuum
deposition, electroplating or other conventional methods. When
using anodes of metals with more structural strength than lithium,
such as silver, magnesium or the like, the anode lead 8 may be
connected directly to the anode, eliminating the anode current
collector. An initial film of metal iodide electrolyte 10 may be
formed spontaneously when the anode surface is brought into contact
with the cathode material 12. The plastic cathode material is
preferably directly applied to the cathode current collector 14,
which laminate is then brought into contact with the anode. The
cathode material may be also heated to melting and be applied by
brushing or spraying, or be applied as a solution in
tetrahydrofuran and then evaporating the solvent. If desired the
cathode can be applied directly onto the anode. The cathode current
collector is preferably a thin metal sheet or foil of zirconium or
platinum or a coating of the metal deposited on the plastic housing
although other electronic conducting material is substantially
inert to the cathode may be used. Metal cathode lead 16 is
connected to the cathode current collector for making external
circuit connections. The stacked cell components are compressed to
provide good adhesion and contact between the layers; only small
pressures on the order of 25 lb./in..sup.2 are necessary to insure
adhesion between layers that is maintained during storage and
discharge without external force.
The cells may be made in a variety of forms, and completely
encapsulated flexible cells have been made as thin as 0.020 inch,
allowing batteries to be formed in almost any configuration; for
example, a battery can be wrapped around electronic circuitry for
efficient use of available space. When flexibility is not needed,
cells can be encapsulated in rigid plastic or sealed in metal cans.
Longer capacities per unit electrode area can be obtained by
increasing the thickness of the anode and cathode, suitably to give
cells having a thickness as much as 0.5 inch, or more. Batteries of
low internal impedance are formed by stacking cells in series and
parallel.
Batteries having a lithium anode and utilizing our new cathode
material have exceptional storage stability, long life, high
voltage output and high energy density making them especially
suitable for long life, low current drain applications, such as
power supplies for implanted prosthetic devices like heart pacers.
The cell has a theoretical energy density of 213 w.h./lb. or 19.2
w.h./in..sup.3 ; actual energy densities of 136 w.h./lb. and 11.5
w.h./in..sup.3 have been measured during discharge of cells at room
temperature.
Open circuit voltage for the cell is 2.87 volts. Since impedance is
a function of electrolyte conductivity, a plot of cell voltage vs.
current shows a linear decrease in voltage with increasing current
until short circuit current is reached. Short circuit current
densities as high as 20 ma./cm..sup.2 have been measured
immediately after construction. At room temperature after 20 days
the short circuit current decreases to 1 ma./cm..sup.2 and to 0.5
ma./cm..sup.2 after 110 days.
Under constant current discharge at relatively high current
densities, voltage decay is linear with time. This behavior is
illustrated in FIG. 3 for cells made in accordance with FIG. 1
having a lithium anode, a P2VP.multidot.5I.sub.2 cathode and
zirconium cathode collector which cell had been stored at room
temperature for one week. In FIG. 3, the cell voltage is plotted
against time of discharge at the indicated constant current density
and various temperatures for several cells of different thickness,
which is selected to provide the desired cell capacity. The cell
thickness range from 0.03 cm. to 0.25 cm., the anode being about
20% and the cathode being about 80% of the cell thickness. The
discharge curves generally obey the equation
where .tau. is polarization, C is a constant dependent on cell
construction, i/A is the current density, and t is time of
discharge. The value 8650 calories/mole agrees with published data
for the activation energy of ionic conduction in LiI. The constant
C is typically 1.25.times.10.sup.-4 ohm.multidot.cm..sup.4 /amp.
sec. using our new cathode material.
Discharging cells at smaller current densities results in a marked
decrease in polarization. For example, if the 0.13 cm. cell in FIG.
3 was discharged (at 25.degree. C.) at 25 .mu.a./cm..sup.2 rather
than 50 .mu.a./cm..sup.2, cell voltage at 1000 hours would be
increased from 0.24 to 2.16 volts. At 10 .mu.a./cm..sup.2,
polarization increase per thousand hours amounts to less than 100
mv. and cell life is increased by about a factor of five.
As current density is decreased, allowing cells to run for longer
periods, small deviations from linearity are evident in the
discharge curves, especially at higher temperatures, which are the
result of self discharge.
Self discharge for the cells involves diffusion of iodine from the
cathode through the electrolyte to the anode where additional
electrolyte is then generated. Resistance increase resulting from
this accumulation has been found to be governed by the
relationship
Thus, for example, a cell only 4.45 cm..times.3.50 cm..times.0.93
cm., to be discharged at 30 .mu.a. with a voltage of at least 2.3
volts at 370.degree. C. for use in a prosthetic device has a
projected life of at least 10 years. Even after long periods of
storage, cells can be operated at microamphere drains for many
years over a wide temperature range. In designing for very long
storage period, e.g.10 years, cell thickness is increased to
accomodate increased self discharge. Similar performance is
obtained when using either P2VP.multidot.nI.sub.2 or
P2VQ.multidot.nI.sub.2.
Although the foregoing description has been directed primarily to
cells having a lithium anode, the new cathode material can be used
to advantage with anodes of other metals that are reactive with
iodine, for example silver or magnesium. To illustrate, a sintered
silver anode 11/2".times.11/2".times.0.020" (about 50% porous) was
filled with 0.036 in..sup.3 of P2VP.multidot.5I.sub.2 to form a
cell 0.026" thick. Contact with the cathode was effected using a
zirconium cathode collector. The cell had an open circuit voltage
of 0.67 volt. After 170 hours of discharge at 1450 .mu.a. (at
24.degree. C.) the cell voltage had dropped only to about 0.52
volt; on further discharge at the same current, the voltage dropped
to zero at about 200 hours. The silver anode in this instance was a
sintered mat of 0.005".times.0.009".times.0.125" silver needles
weighing 3.7 grams. Other forms of electrodes may be used, e.g.
foil, screen or electroplates, but best performance is obtained
from sinters. A group of 6 cells having a silver foil anode and a
P2VQ.multidot.5I.sub.2 cathode, had when freshly prepared, an
average life of 976 hours when discharged at 10 .mu.a./cm..sup.2
and 25.degree. C.; 6 identical cells after thirty days storage had
an average life of 841 hours under the same discharge conditions.
In contrast to the lithium cells, only about one third of the
theoretical electrochemical capacity is realized in silver
batteries; this is the result of the inability of the silver to
conform to the growing silver iodide electrolyte causing a loss of
physical contact between the anode and electrolyte.
In another example, a cell having stacked laminae of magnesium
anode, P2VP.multidot.5I.sub.2 cathode and zirconium cathode
collector has an open circuit voltage of 0.95 volt and a short
circuit current of 2 ma./cm..sup.2. When discharged at a current
density of 10 .mu.a./cm..sup.2 the cells have a life of about 50
hours.
* * * * *