U.S. patent application number 11/536069 was filed with the patent office on 2007-02-08 for preparation of epsilon-phase silver vanadium oxide from gamma-phase svo starting material.
This patent application is currently assigned to Greatbatch Ltd.. Invention is credited to Randolph Leising, Esther S. Takeuchi.
Application Number | 20070031731 11/536069 |
Document ID | / |
Family ID | 26673761 |
Filed Date | 2007-02-08 |
United States Patent
Application |
20070031731 |
Kind Code |
A1 |
Leising; Randolph ; et
al. |
February 8, 2007 |
Preparation Of Epsilon-Phase Silver Vanadium Oxide From Gamma-Phase
SVO Starting Material
Abstract
The current invention relates to the preparation of an improved
cathode active material for non-aqueous lithium electrochemical
cell. In particular, the cathode active material comprises
.epsilon.-phase silver vanadium oxide prepared by using a
.gamma.-phase silver vanadium oxide starting material. The reaction
of .gamma.-phase SVO with a silver salt produces the novel
.epsilon.-phase SVO possessing a lower surface area than
.epsilon.-phase SVO produces from vanadium oxide (V.sub.2O.sub.5)
and a similar silver salt as starting materials. Consequently, the
low surface area .epsilon.-phase SVO material provides an advantage
in greater long-term stability in pulse dischargeable cells.
Inventors: |
Leising; Randolph;
(Williamsville, NY) ; Takeuchi; Esther S.; (East
Amherst, NY) |
Correspondence
Address: |
GREATBATCH LTD
9645 WEHRLE DRIVE
CLARENCE
NY
14031
US
|
Assignee: |
Greatbatch Ltd.
Clarence
NY
|
Family ID: |
26673761 |
Appl. No.: |
11/536069 |
Filed: |
September 28, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10944661 |
Sep 17, 2004 |
7118829 |
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11536069 |
Sep 28, 2006 |
|
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|
10004995 |
Dec 5, 2001 |
6797017 |
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10944661 |
Sep 17, 2004 |
|
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60254918 |
Dec 12, 2000 |
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Current U.S.
Class: |
429/219 ;
423/594.8; 429/231.5 |
Current CPC
Class: |
C01P 2006/12 20130101;
C01G 31/00 20130101; C01P 2006/40 20130101; H01M 4/485 20130101;
Y02E 60/10 20130101; C01P 2002/54 20130101; C01G 45/006 20130101;
H01M 4/405 20130101; H01M 4/54 20130101; C01P 2002/50 20130101;
C01G 31/006 20130101; H01M 4/5825 20130101; H01M 6/16 20130101;
H01M 4/131 20130101 |
Class at
Publication: |
429/219 ;
429/231.5; 423/594.8 |
International
Class: |
H01M 4/54 20060101
H01M004/54; C01G 31/02 20060101 C01G031/02; C01G 5/00 20070101
C01G005/00 |
Claims
1. A cathode for an electrochemical cell, the cathode comprising an
.epsilon.-phase silver vanadium oxide characterized as prepared
from a mixture of .gamma.-phase silver vanadium oxide having the
formula Ag.sub.1.2V.sub.3O.sub.8.1 and a metal salt to form a
reaction mixture heated to at least one reaction temperature in an
oxidizing atmosphere to produce the .epsilon.-phase silver vanadium
oxide having the formula Ag.sub.2V.sub.4O.sub.11, wherein the metal
salt is selected from one of: Ag.sub.2O and the .epsilon.-phase
silver vanadium oxide has a BET surface area of about 0.54
m.sup.2/gram, and Ag.sub.2CO.sub.3 and the .epsilon.-phase silver
vanadium oxide has a BET surface area of about 0.44
m.sup.2/gram.
2. The cathode of claim 1 wherein the reaction mixture is heated to
the at least one reaction temperature in a range from about
300.degree. C. to about 550.degree. C.
3. The cathode of claim 1 wherein the reaction mixture is heated to
the at least one reaction temperature for about 5 hours to about 30
hours.
4. The cathode of claim 1 further comprising a binder and a
conductive material.
5. A nonaqueous electrochemical cell, comprising: a) an anode; b) a
cathode containing an electrode active material characterized as
having been prepared from a mixture of .gamma.-phase silver
vanadium oxide having the formula Ag.sub.1.2V.sub.3O.sub.8.1 and a
metal salt forming a reaction mixture heated to at least one
reaction temperature in an oxidizing atmosphere to produce the
electrode active material selected from one of: i)
Ag.sub.2V.sub.4O.sub.11 having a BET surface area of about 0.54
m.sup.2/gram with the metal salt having been Ag.sub.2O; and ii)
Ag.sub.2V.sub.4O.sub.11 having a BET surface area of about 0.44
m.sup.2/gram with the metal salt having been Ag.sub.2CO.sub.3; and
c) a non-aqueous electrolyte activating the anode and the cathode;
and d) a separator material electrically insulating the anode from
the cathode, and of a porosity to allow for electrolyte flow.
6. The electrochemical cell of claim 5 wherein the anode is
comprised of lithium.
7. The electrochemical cell of claim 5 wherein the reaction mixture
is heated to the at least one reaction temperature in a range from
about 300.degree. C. to about 550.degree. C.
8. The electrochemical cell of claim 5 wherein the reaction mixture
is heated to the at least one reaction temperature for about 5
hours to about 30 hours.
9. A cathode for an electrochemical cell, the cathode comprising an
electrode active material characterized as prepared from
.gamma.-phase silver vanadium oxide having the formula
Ag.sub.1.2V.sub.3O.sub.8.1 mixed with a metal salt compound to form
a reaction mixture heated to at least one reaction temperature in
an oxidizing atmosphere to produce the electrode active material
selected from the group consisting of
Mn.sub.0.2Ag.sub.0.8V.sub.2O.sub.5.8, and
Mg.sub.0.2Ag.sub.0.8V.sub.2O.sub.5.6.
10. The cathode of claim 9 wherein the metal salt is selected from
the group consisting of manganese carbonate, manganese oxide,
magnesium carbonate, magnesium oxide, and combinations and mixtures
thereof.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of application Ser. No.
10/944,661, now U.S. Pat. No. 7,118,829 to Leising et al., which is
continuation-in-part of application Ser. No. 10/004,995, now U.S.
Pat. No. 6,797,017 to Leising et al., which claims priority on
provisional application Ser. No. 60/254,918, filed Dec. 12,
2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to the conversion of chemical energy
to electrical energy. More particularly, this invention relates to
the preparation of an improved cathode active material for
non-aqueous lithium electrochemical cells, and still more
particularly, a cathode active .epsilon.-phase silver vanadium
oxide (SVO, Ag.sub.2V.sub.4O.sub.11) prepared using a .gamma.-phase
silver vanadium oxide (Ag.sub.1.2V.sub.3O.sub.8.1) starting
material. The product cathode active material can be used in an
implantable electrochemical cell, for example of the type powering
a cardiac defibrillator, where the cell may run under a light load
for significant periods interrupted from time to time by high rate
pulse discharges.
[0004] The reaction of .gamma.-phase SVO with a source of silver
produces .epsilon.-phase SVO that possesses a lower surface area
than SVO produced from other vanadium-containing starting
materials. The relatively low surface area of this new
.epsilon.-phase SVO material results in greater long-term stability
for the cathode active material in comparison to other forms of SVO
with higher specific surfaces areas.
[0005] 2. Prior Art
[0006] The prior art discloses many processes for manufacturing
SVO; however, they result in a product with greater surface area
than the material prepared by the current invention.
[0007] Specifically, U.S. Pat. Nos. 4,310,609 and 4,391,729, both
to Liang et al., disclose the preparation of silver vanadium oxide
by a thermal decomposition reaction of silver nitrate with vanadium
oxide conducted under an air atmosphere. This decomposition
reaction is further detailed in the publication: Leising, R. A.;
Takeuchi, E. S. Chem. Mater. 1993, 5, 738-742, where the synthesis
of SVO from silver nitrates and vanadium oxide under an air
atmosphere is presented as a function of temperature. In another
reference: Leising, R. A.; Takeuchi, E. S. Chem. Mater. 1994, 6,
489-495, the synthesis of SVO from different silver precursor
materials (silver nitrate, silver nitrite, silver oxide, silver
vanadate, and silver carbonate) is described. The product active
materials of this latter publication are consistent with the
formation of a mixture of SVO phases prepared under argon, which is
not solely .epsilon.-phase Ag.sub.2V.sub.4O.sub.11.
[0008] Also, the preparation of SVO from silver oxide and vanadium
oxide is well documented in the literature. In the publications:
Fleury, P.; Kohlmuller, R. C. R. Acad. Sci. Paris 1966, 262C,
475-477, and Casalot, A.; Pouchard, M. Bull Soc. Chim. Fr. 1967,
3817-3820, the reaction of silver oxide with vanadium oxide is
described. Wenda, E. J. Thermal Anal. 1985, 30, 89-887, present the
phase diagram of the V.sub.2O.sub.5-Ag.sub.2O system in which the
starting materials are heated under oxygen to form SVO, among other
materials. Thus, Fleury and Kohlmuller teach that the heat
treatment of starting materials under a non-oxidizing atmosphere
(such as argon) results in the formation of SVO with a reduced
silver content.
[0009] U.S. Pat. Nos. 5,955,218 and 6,130,005, both to Crespi et
al., relate to heat-treating silver vanadium oxide materials, for
example, .gamma.-phase SVO to form decomposition-produced SVO
(dSVO). In these patents, thermal decomposition SVO prepared
according to the previously discussed U.S. Pat. Nos. 4,310,609 and
4,391,729 is heated under an air atmosphere at a somewhat lower
temperature of 360.degree. C. However, the '218 and '005 patents to
Crespi et al. demonstrate that adding a second heat treatment step
increases the crystallinity of the resulting active material. The
present invention is concerned with the product active material's
surface area, and not necessarily its crystallinity.
[0010] U.S. Pat. No. 5,221,453 to Crespi teaches a method for
making an electrochemical cell containing SVO, in which the cathode
active material is prepared by a chemical addition reaction of an
admixed 2:1 mole ratio of AgVO.sub.3 and V.sub.2O.sub.5 heated in
the range of 300.degree. C. to 700.degree. C. for a period of 5 to
24 hours. Crespi does not discuss .gamma.-phase SVO in the context
of this invention. Therefore, this process could not manufacture
the .epsilon.-phase material described by the current
invention.
[0011] Also, U.S. Pat. No. 5,895,733 to Crespi et al. shows a
method for synthesizing SVO by using AgO and a vanadium oxide as
starting materials. However, the result is not a low surface area
.epsilon.-phase SVO cathode material, as disclosed in the current
invention.
[0012] U.S. Pat. No. 5,545,497 to Takeuchi et al. teaches cathode
materials having the general formula of Ag.sub.xV.sub.2O.sub.y.
Suitable materials comprise a .beta.-phase SVO having in the
general formula x=0.35 and y=5.18 and a .gamma.-phase SVO having
x=0.74 and y=5.37, or a mixture of the phases thereof. Such SVO
materials are produced by the thermal decomposition of a silver
salt in the presence of vanadium pentoxide. In addition, U.S. Pat.
No. 6,171,729 to Gan et al. shows exemplary alkali metal/solid
cathode electrochemical cells in which the cathode may be an SVO of
.beta.-, .gamma.- or .epsilon.-phase materials. However, none of
Gan et al.'s methods are capable of producing a low surface area
.epsilon.-phase cathode material, as per the current invention.
[0013] Therefore, based on the prior art, there is a need to
develop a process for the synthesis of mixed metal oxides,
including silver vanadium oxide, having a relatively low surface
area. An example is a low surface area SVO prepared using a
silver-containing compound and .gamma.-phase SVO as starting
materials. The product .epsilon.-phase SVO is a cathode active
material useful for non-aqueous electrochemical cells having
enhanced characteristics, including the high pulse capability
necessary for use with cardiac defibrillators.
SUMMARY OF THE INVENTION
[0014] The current invention relates to the preparation of an
improved cathode active material for non-aqueous lithium
electrochemical cells, and in particular, a cathode active material
that contains .epsilon.-phase SVO prepared using a .gamma.-phase
SVO starting material. The reaction of .gamma.-phase SVO with a
source of silver produces .epsilon.-phase SVO possessing a lower
surface area than .epsilon.-phase SVO produced from other
vanadium-containing starting materials. The present synthesis
technique is not, however, limited to silver salts since salts of
copper, magnesium and manganese can be used to produce relatively
low surface are metal oxide active materials as well. The
relatively low surface area of the .epsilon.-phase SVO material
provides an advantage in greater long-term stability when used as
an active cathode material compared to SVO with a higher specific
surface area.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The current invention discloses that reacting a
.gamma.-phase SVO material with a source of silver, or other
suitable metal salt, produces pure .epsilon.-phase SVO
(Ag.sub.2V.sub.4O.sub.11). This product material possesses a
relatively lower surface area in comparison to active materials
synthesized by a thermal decomposition reaction under an oxidizing
atmosphere. Decreased surface area is an unexpected result.
[0016] The thermal reaction of silver nitrate with vanadium oxide
under an air atmosphere is a typical example of the preparation of
silver vanadium oxide by a decomposition reaction. This reaction is
set forth below in Equation 1:
2AgNO.sub.3+2V.sub.2O.sub.5.fwdarw.Ag.sub.2V.sub.4O.sub.11+2NO.sub.x
(1)
[0017] The physical characteristics of SVO material (i.e. particle
morphology, surface area, crystallinity, etc.) produced by this
reaction are dependent on the temperature and time of reaction. In
addition, the reaction environment has a dramatic effect on the
product material. The same reaction of silver nitrate with vanadium
oxide conducted under an argon atmosphere is depicted below in
Equation 2:
2AgNO.sub.3+2V.sub.2O.sub.5.fwdarw.AgVO.sub.3+Ag.sub.1.2V.sub.3O.sub.8+2N-
O.sub.x (2)
[0018] Thus, the synthesis of SVO under an inert atmosphere results
in the formation of a mixture of silver vanadate (AgVO.sub.3) and
.gamma.-phase SVO (Ag.sub.1.2V.sub.3O.sub.8). This is described in
the above-referenced publication by Leising, R. A.; Takeuchi, E. S.
Chem. Mater. 1994, 6, 489-495. As reported by Leising et al., a
mixture of material phases is less suitable than a single
.epsilon.-phase SVO (Ag.sub.2V.sub.4O.sub.11) as a cathode active
material for lithium electrochemical cells. For this reason, argon
is typically not preferred for synthesis of SVO cathode active
material.
[0019] A more benign preparation technique for producing
.epsilon.-phase SVO from vanadium oxide and silver carbonate
(Ag.sub.2CO.sub.3) according to Equation 3 below, results in the
release of CO.sub.2 gas, which is a nontoxic byproduct. However,
the specific surface area of the product SVO is also higher than
the surface area of SVO prepared from silver nitrate. This is shown
below in Table 1.
Ag.sub.2CO.sub.3+2V.sub.2O.sub.5.fwdarw.Ag.sub.2V.sub.4O.sub.11+CO.sub.2
(3)
[0020] Thus, a synthesis technique for SVO using vanadium oxide and
either silver oxide or silver carbonate, or other preferred metal
salts, while eliminating the formation of toxic NO.sub.x byproduct,
results in an SVO material with a higher specific surface area than
SVO produced from vanadium oxide and silver nitrate. TABLE-US-00001
TABLE 1 Specific Surface Area of .epsilon.-Phase SVO Synthesis BET
Surface Starting Materials Temperature Area V.sub.2O.sub.5 +
AgNO.sub.3 500.degree. C. 0.42 m.sup.2/gram V.sub.2O.sub.5 +
0.5Ag.sub.2O 500.degree. C. 0.64 m.sup.2/gram V.sub.2O.sub.5 +
0.5Ag.sub.2CO.sub.3 500.degree. C. 0.81 m.sup.2/gram
Ag.sub.1.2V.sub.3O.sub.8.1 + 0.15Ag.sub.2O 500.degree. C. 0.54
m.sup.2/gram Ag.sub.1.2V.sub.3O.sub.8.1 + 0.15Ag.sub.2CO.sub.3
500.degree. C. 0.44 m.sup.2/gram
[0021] The present invention is an alternate preparation synthesis
that does not produce noxious by-products, such as NO.sub.x and,
additionally, results in an active material with a desirable
relatively low surface area. Benefits attributed to the present
synthesis process for the formation of a cathode active material
are illustrated in the following examples.
EXAMPLE 1
[0022] In contrast to the prior art syntheses described above, SVO
of the present invention is prepared using .gamma.-phase SVO
(Ag.sub.1.2V.sub.3O.sub.8.1) as a starting material instead of
V.sub.2O.sub.5. In particular, a 12.90-gram sample of
Ag.sub.1.2V.sub.3O.sub.8.1 was combined with a 1.09-gram sample of
Ag.sub.2O, and heated to 500.degree. C. under a flowing air
atmosphere for about 16 hours. The sample was then cooled, mixed
and reheated under a flowing air atmosphere at about 500.degree. C.
for about 24 hours. At this point, the material was cooled and
analyzed by x-ray powder diffraction and BET surface area
measurements. The x-ray powder diffraction data confirmed the
formation of .epsilon.-phase SVO (Ag.sub.2V.sub.4O.sub.11). The
material displayed a BET surface area of 0.54 m.sup.2/gram.
COMPARATIVE EXAMPLE 1
[0023] As a comparison, SVO was prepared by a prior art combination
reaction. In particular, a 9.00-gram sample of V.sub.2O.sub.5 was
combined with a 5.73-gram sample of Ag.sub.2O, and heated to about
500.degree. C. under a flowing air atmosphere for about 16 hours.
The sample was then cooled, mixed and reheated under a flowing air
atmosphere at about 500.degree. C. for about 24 hours. At this
point the material was cooled and analyzed by x-ray powder
diffraction and BET surface area measurements. The material
displayed a BET surface area of 0.64 m.sup.2/gram, which is
significantly higher than the specific surface area of the material
prepared in Example 1.
EXAMPLE 2
[0024] Epsilon-phase SVO according to the present invention was
also prepared using a .gamma.-phase SVO starting material in
combination with silver carbonate. In particular, a 5.00-gram
sample of Ag.sub.1.2V.sub.3O.sub.8.1 was combined with a 0.50-gram
sample of Ag.sub.2CO.sub.3, and heated to about 500.degree. C.
under a flowing air atmosphere for about 16 hours. The sample was
then cooled, mixed and reheated under a flowing air atmosphere at
about 500.degree. C. for about 24 hours. At this point, the
material was cooled and analyzed by x-ray powder diffraction and
BET surface area measurements. The x-ray powder diffraction data
confirmed the formation of .epsilon.-phase SVO
(Ag.sub.2V.sub.4O.sub.11), while the material displayed a BET
surface area of 0.44 m.sup.2/gram.
COMPARATIVE EXAMPLE 2
[0025] As a comparison to Example 2, SVO was prepared using
V.sub.2O.sub.5 and Ag.sub.2CO.sub.3. In particular, a 15.00-gram
sample of V.sub.2O.sub.5 was combined with an 11.37-gram sample of
Ag.sub.2CO.sub.3, and heated to about 450.degree. C. under a
flowing air atmosphere for about 16 hours. The sample was then
cooled, mixed and reheated under a flowing air atmosphere at about
500.degree. C. for about 24 hours. At this point the material was
cooled and analyzed by x-ray powder diffraction and BET surface
area measurements. The material displayed a BET surface area of
0.81 m.sup.2/gram, which is nearly twice the specific surface area
of the material prepared in Example 2.
EXAMPLE 3
[0026] Copper silver vanadium oxide or CSVO
(Cu.sub.0.2Ag.sub.0.8V.sub.2O.sub.5.6) was prepared according to
the present invention using .gamma.-phase SVO as a starting
material in combination with copper(II) oxide. In particular, a
1.80-gram sample of Ag.sub.1.2V.sub.3O.sub.8.1 was combined with a
0.10-gram sample of CuO, and heated to about 450.degree. C. under a
flowing air atmosphere for about 16 hours. The sample was then
cooled, mixed and reheated under a flowing air atmosphere at about
500.degree. C. for about 24 hours. At this point, the material was
cooled and analyzed by BET surface area measurements. The material
displayed a BET surface area of 0.31 m.sup.2/gram.
COMPARATIVE EXAMPLE 3
[0027] As a comparison to the product of Example 3, CSVO was
prepared via the prior art decomposition method using
V.sub.2O.sub.5, Cu(NO.sub.3).sub.2 and AgNO.sub.3. In particular, a
1.36 gram sample of V.sub.2O.sub.5 was combined with a 0.99 gram
sample of AgNO.sub.3 and a 0.34 gram sample of
Cu(NO.sub.3).sub.2.2.5H.sub.2O, and heated to about 400.degree. C.
under a flowing air atmosphere for about 16 hours. The sample was
then cooled, mixed and reheated under a flowing air atmosphere at
about 500.degree. C. for about 44 hours. At this point, the product
material was cooled and analyzed by BET surface area measurement.
The material displayed a BET surface area of 0.45 m.sup.2/gram,
which is significantly higher than the specific surface area of the
CSVO material prepared in Example 3. Thus, in addition to the toxic
implications of released NO.sub.x gas, the preparation of CSVO by
the prior art method provides a material with a higher specific
surface area than the new preparation technique.
[0028] The above detailed description and examples are intended for
the purpose of illustrating the invention, and are not to be
construed as limiting. For example, starting materials other than
silver oxide and silver carbonate are reacted with .gamma.-phase
silver vanadium oxide to form .epsilon.-phase silver vanadium
compounds. The list includes: silver lactate
(AgC.sub.3H.sub.5O.sub.3, T.sub.m 120.degree. C.), silver triflate
(AgCF.sub.3SO.sub.3, T.sub.m 286.degree. C.), silver
pentafluoropropionate (AgC.sub.3F.sub.5O.sub.2, T.sub.m 242.degree.
C.), silver laurate (AgC.sub.12H.sub.23O.sub.2, T.sub.m 212.degree.
C.), silver myristate (AgC.sub.14H.sub.27O.sub.2, T.sub.m
211.degree. C.), silver palmitate (AgC.sub.16H.sub.31O.sub.2,
T.sub.m 209.degree. C.), silver stearate
(AgC.sub.18H.sub.35O.sub.2, T.sub.m 205.degree. C.), silver
vanadate (AgVO.sub.3, T.sub.m 465.degree. C.), copper oxide (CuO,
T.sub.m 1,446.degree. C.), copper carbonate (Cu.sub.2Co.sub.3),
manganese carbonate (MnCO.sub.3), manganese oxide (MnO, T.sub.m
1,650.degree. C.), magnesium carbonate (MgCO.sub.3, T.sub.d
350.degree. C.), magnesium oxide (MgO, T.sub.m 2,826.degree. C.),
and combinations and mixtures thereof.
[0029] While the starting materials are described as being heated
to a preferred temperature of about 500.degree. C., it is
contemplated by the scope of the present invention that suitable
heating temperatures range from about 300.degree. C. to about
550.degree. C., depending on the specific starting materials. Also,
heating times for both the first and second heating steps range
from about 5 hours to about 30 hours. Longer heating times are
required for lower heating temperatures. Further, while the present
invention has been described in the examples as requiring two
heating events with an ambient mixing in between, that is not
necessarily imperative. Some synthesis protocols according to the
present invention may require one heating step with periodic
mixing, or multiple heating events with periodic ambient
mixing.
[0030] The product mixed metal oxides according to the present
invention include: .epsilon.-phase SVO (Ag.sub.2V.sub.4O.sub.11)
CSVO (Cu.sub.0.2Ag.sub.0.8V.sub.2O.sub.5.6), MnSVO
(Mn.sub.0.2Ag.sub.0.8V.sub.2O.sub.5.8), and MgSVO
(Mg.sub.0.2Ag.sub.0.8V.sub.2O.sub.5.6). The use of the above mixed
metal oxides as a cathode active material provides an
electrochemical cell that possesses sufficient energy density and
discharge capacity required to meet the vigorous requirements of
implantable medical devices. These types of cells comprise an anode
of a metal selected from Groups IA, IIA and IIIB of the Periodic
Table of the Elements. Such anode active materials include lithium,
sodium, potassium, etc., and their alloys and intermetallic
compounds including, for example, Li--Mg, Li--Si, Li--Al, Li--B and
Li--Si--B alloys and intermetallic compounds. The preferred anode
comprises lithium. An alternate anode comprises a lithium alloy
such as a lithium-aluminum alloy. The greater the amounts of
aluminum present by weight in the alloy, however, the lower the
energy density of the cell.
[0031] The form of the anode may vary, but preferably the anode is
a thin metal sheet or foil of the anode metal, pressed or rolled on
a metallic anode current collector, i.e., preferably comprising
titanium, titanium alloy or nickel, to form an anode component.
Copper, tungsten and tantalum are also suitable materials for the
anode current collector. In the exemplary cell of the present
invention, the anode component has an extended tab or lead of the
same material as the anode current collector, i.e., preferably
nickel or titanium, integrally formed therewith such as by welding
and contacted by a weld to a cell case of conductive metal in a
case-negative electrical configuration. Alternatively, the anode
may be formed in some other geometry, such as a bobbin shape,
cylinder or pellet to allow an alternate low surface cell
design.
[0032] Before the previously described .epsilon.-phase active
materials are fabrication into a cathode electrode for
incorporation into an electrochemical cell, they are preferably
mixed with a binder material, such as a powdered fluoro-polymer,
more preferably powdered polytetrafluoro-ethylene or powdered
polyvinylidene fluoride, present at about 1 to about 5 weight
percent of the cathode mixture. Further, up to about 10 weight
percent of a conductive diluent is preferably added to the cathode
mixture to improve conductivity. Suitable materials for this
purpose include acetylene black, carbon black and/or graphite or a
metallic powder such as of nickel, aluminum, titanium and stainless
steel. The preferred cathode active mixture thus includes a
powdered fluoro-polymer binder present at about 3 weight percent, a
conductive diluent present at about 3 weight percent and about 94
weight percent of the cathode active material. For example,
depending on the application of the electrochemical cell, the range
of cathode compositions is from about 99% to about 80%, by weight,
.epsilon.-phase silver vanadium oxide mixed with carbon graphite
and PTFE.
[0033] Cathode components for incorporation into an electrochemical
cell according to the present invention may be prepared by rolling,
spreading or pressing the cathode active materials onto a suitable
current collector selected from the group consisting of stainless
steel, titanium, tantalum, platinum, gold, aluminum, cobalt-nickel
alloys, nickel-containing alloys, highly alloyed ferritic stainless
steel containing molybdenum and chromium, and nickel-, chromium-
and molybdenum-containing alloys. The preferred current collector
material is titanium and, most preferably, the titanium cathode
current collector has a thin layer of graphite/carbon material,
iridium, iridium oxide or platinum applied thereto. Cathodes
prepared as described above may be in the form of one or more
plates operatively associated with at least one or more plates of
anode material, or in the form of a strip wound with a
corresponding strip of anode material in a structure similar to a
"jellyroll".
[0034] In order to prevent internal short circuit conditions, the
cathode is separated from the Group IA, IIA or IIIB anode by a
suitable separator material. The separator is of electrically
insulative material, and the separator material also is chemically
unreactive with the anode and cathode active materials and both
chemically unreactive with and insoluble in the electrolyte. In
addition, the separator material has a degree of porosity
sufficient to allow flow there through of the electrolyte during
the electrochemical reaction of the cell. Illustrative separator
materials include fabrics woven from fluoropolymeric fibers
including polyvinylidine fluoride, polyethylenetetrafluoroethylene,
and polyethylenechlorotrifluoroethylene used either alone or
laminated with a fluoropolymeric microporous film, non-woven glass,
polypropylene, polyethylene, glass fiber materials, ceramics, a
polytetrafluoroethylene membrane commercially available under the
designation ZITEX (Chemplast Inc.), a polypropylene membrane
commercially available under the designation CELGARD (Celanese
Plastic Company, Inc.) and a membrane commercially available under
the designation DEXIGLAS (C. H. Dexter, Div., Dexter Corp.).
[0035] The electrochemical cell of the present invention further
includes a nonaqueous, ionically conductive electrolyte that serves
as a medium for migration of ions between the anode and the cathode
electrodes during the electrochemical reactions of the cell. The
electrochemical reaction at the electrodes involves conversion of
ions in atomic or molecular forms that migrate from the anode to
the cathode. Thus, nonaqueous electrolytes suitable for the present
invention are substantially inert to the anode and cathode
materials, and they exhibit those physical properties necessary for
ionic transport, namely, low viscosity, low surface tension and
wettability.
[0036] A suitable electrolyte has an inorganic, ionically
conductive salt dissolved in a nonaqueous solvent, and more
preferably, the electrolyte includes an ionizable alkali metal salt
dissolved in a mixture of aprotic organic solvents comprising a low
viscosity solvent and a high permittivity solvent. The inorganic,
ionically conductive salt serves as the vehicle for migration of
the anode ions to intercalate or react with the cathode active
material. Preferably, the ion forming alkali metal salt is similar
to the alkali metal comprising the anode.
[0037] In the case of an anode comprising lithium, the alkali metal
salt of the electrolyte is a lithium based salt. Known lithium
salts that are useful as a vehicle for transport of alkali metal
ions from the anode to the cathode include LiPF.sub.6, LiBF.sub.4,
LiAsF.sub.6, LiSbF.sub.6, LiClO.sub.4, LiO.sub.2, LiAlCl.sub.4,
LiGaCl.sub.4, LiC(SO.sub.2CF.sub.3).sub.3,
LiN(SO.sub.2CF.sub.3).sub.2, LiSCN, LiO.sub.3SCF.sub.3,
LiC.sub.6F.sub.5SO.sub.3, LiO.sub.2CCF.sub.3, LiSO.sub.6F,
LiB(C.sub.6H.sub.5).sub.4, LiCF.sub.3SO.sub.3, and mixtures
thereof.
[0038] Low viscosity solvents useful with the present invention
include esters, linear and cyclic ethers and dialkyl carbonates
such as tetrahydrofuran (THF), methyl acetate (MA), diglyme,
trigylme, tetragylme, dimethyl carbonate (DMC), 1,2-dimethoxyethane
(DME), 1,2-diethoxyethane (DEE), 1-ethoxy,2-methoxyethane (EME),
ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl
carbonate, diethyl carbonate, dipropyl carbonate, and mixtures
thereof. Suitable high permittivity solvents include cyclic
carbonates, cyclic esters and cyclic amides such as propylene
carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC),
acetonitrile, dimethyl sulfoxide, dimethyl, formamide, dimethyl
acetamide, .gamma.-valerolactone, .gamma.-butyrolactone (GBL),
N-methyl-pyrolidinone (NMP), and mixtures thereof. In the present
invention, the preferred anode is lithium metal and the preferred
electrolyte is 0.8M to 1.5M LiAsF.sub.6 or LiPF.sub.6 dissolved in
a 50:50 mixture, by volume, of propylene carbonate as the preferred
high permittivity solvent and 1,2-dimethoxyethane as the preferred
low viscosity solvent.
[0039] The preferred form of a primary alkali metal/solid cathode
electrochemical cell is a case-negative design wherein the anode is
in contact with a conductive metal casing and the cathode contacted
to a current collector is the positive terminal. The cathode
current collector is in contact with a positive terminal pin via a
lead of the same material as the current collector. The lead is
welded to both the current collector and the positive terminal pin
for electrical contact.
[0040] A preferred material for the casing is titanium although
stainless steel, mild steel, nickel-plated mild steel and aluminum
are also suitable. The casing header comprises a metallic lid
having an opening to accommodate the glass-to-metal seal/terminal
pin feedthrough for the cathode electrode. The anode electrode is
preferably connected to the case or the lid. An additional opening
is provided for electrolyte filling. The casing header comprises
elements having compatibility with the other components of the
electrochemical cell and is resistant to corrosion. The cell is
thereafter filled with the electrolyte solution described
hereinabove and hermetically sealed such as by close-welding a
titanium plug over the fill hole, but not limited thereto. The cell
of the present invention can also be constructed in a case-positive
design.
[0041] It is appreciated that various modifications to the
inventive concepts described herein may be apparent to those of
ordinary skill in the art without departing from the spirit and
scope of the present invention as defined by the appended
claims.
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