U.S. patent application number 10/990379 was filed with the patent office on 2005-04-28 for electrolyte additive for non-aqueous electrochemical cells.
This patent application is currently assigned to The Gillette Company, a Delaware corporation. Invention is credited to Blasi, Jane A., Issaev, Nikolai N., Pozin, Michael.
Application Number | 20050089760 10/990379 |
Document ID | / |
Family ID | 21808824 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050089760 |
Kind Code |
A1 |
Blasi, Jane A. ; et
al. |
April 28, 2005 |
Electrolyte additive for non-aqueous electrochemical cells
Abstract
An electrochemical secondary cell is disclosed. The cell
includes a cathode, an anode, a current collector including
aluminum, and an electrolyte containing a perchlorate salt and a
second salt. The electrolyte is essentially free of LiPF.sub.6.
Inventors: |
Blasi, Jane A.; (South
Danbury, CT) ; Issaev, Nikolai N.; (Woodbridge,
CT) ; Pozin, Michael; (Brookfield, CT) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
225 FRANKLIN STREET
BOSTON
MA
02110
US
|
Assignee: |
The Gillette Company, a Delaware
corporation
|
Family ID: |
21808824 |
Appl. No.: |
10/990379 |
Filed: |
November 17, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10990379 |
Nov 17, 2004 |
|
|
|
10022289 |
Dec 14, 2001 |
|
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Current U.S.
Class: |
429/245 ;
429/176; 429/224; 429/324 |
Current CPC
Class: |
H01M 50/531 20210101;
H01M 4/661 20130101; H01M 4/502 20130101; H01M 50/116 20210101;
Y10T 29/49108 20150115; H01M 6/166 20130101 |
Class at
Publication: |
429/245 ;
429/324; 429/224; 429/176 |
International
Class: |
H01M 004/66; H01M
010/40; H01M 004/50; H01M 002/00 |
Claims
1-42. (canceled)
43. A method of inhibiting aluminum corrosion in an electrochemical
cell, the method comprising: (a) adding a lithium perchlorate salt
and a lithium salt selected from the group consisting of LiTFS,
LiTFSI, and LiPF.sub.6 to an electrolyte; and (b) placing the
electrolyte, an anode, a cathode, and an aluminum current collector
into a cell case to form the cell, wherein the cell is a primary
electrochemical cell.
44-47. (canceled)
48. The method of claim 43, wherein the anode contains lithium.
49. The method of claim 43, wherein the cathode contains
MnO.sub.2.
50. The method of claim 43, wherein the method comprises adding at
least 500 ppm by weight of the lithium perchlorate to the
electrolyte.
51. The method of claim 43, wherein the method comprises adding at
least 1000 ppm by weight of the lithium perchlorate to the
electrolyte.
52. The method of claim 43, wherein the method comprises adding at
least 1500 ppm by weight of the lithium perchlorate to the
electrolyte.
53. The method of claim 43, wherein the method comprises adding at
least 2500 ppm by weight of the lithium perchlorate to the
electrolyte.
54. The method of claim 43, wherein the method comprises adding
less than 20,000 ppm by weight of the lithium perchlorate to the
electrolyte.
55. The method of claim 43, wherein the cell case comprises
aluminum.
56. The method of claim 55, wherein the cell case consists
essentially of aluminum.
57. The method of claim 43, wherein the method comprises adding at
least 5000 ppm by weight of LiPF.sub.6 to the electrolyte.
58. The method of claim 43, wherein the method comprises adding at
least 10,000 ppm by weight of LiPF.sub.6 to the electrolyte.
59. The method of claim 43, wherein the method does not comprise
adding LiPF.sub.6 to the electrolyte, and the electrolyte is
essentially free of LiPF.sub.6.
Description
BACKGROUND
[0001] This invention relates to non-aqueous electrochemical cells
for batteries.
[0002] Batteries are commonly used 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.
[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] Aluminum can be used as a construction material in a
battery. However, aluminum can corrode because the electrode
potential of aluminum is lower than the normal operating potential
of the positive electrode of the battery. This corrosion increases
the internal impedance of a cell, leading to capacity loss and to a
decrease in specific energy. When aluminum is coupled with metals
of a different nature in the environment of an electrochemical
cell, the aluminum can also be susceptible to corrosion
degradation.
SUMMARY
[0005] The invention relates to an electrochemical cell that
includes parts made from aluminum or an aluminum-based alloy; these
parts contact the electrolyte of the cell. The cell also includes
an additive to suppress aluminum corrosion.
[0006] In one aspect, the invention features a secondary
electrochemical cell including a cathode, an anode, a current
collector including aluminum, and an electrolyte containing a
perchlorate salt and a second salt that is different from the
perchlorate salt. Preferably, the second salt is not a perchlorate
salt. The electrolyte is essentially free of LiPF.sub.6. The
electrolyte can contain at least 5000 ppm by weight of the
perchlorate salt or at least 10,000 ppm by weight of the
perchlorate salt. An example of the second salt is LiTFS.
[0007] In another aspect, the invention features an electrochemical
cell including a cathode containing MnO.sub.2, an anode containing
lithium, and an electrolyte containing a perchlorate salt. The cell
includes an aluminum surface in electrical contact with a second
metal surface. Preferably, the surface is a portion of an object
having at least one dimension greater than 0.5 mm, 1 mm, or 2 mm.
An "aluminum surface" can be the surface of an object made of pure
aluminum, or a surface made of an aluminum-based alloy. The second
metal surface is different than the aluminum surface. The different
metal can be, e.g., steel, stainless steel, or nickel. The
different metal can also be a different alloy of aluminum. That is,
different alloys of aluminum are considered to be different
metals.
[0008] Because aluminum weighs less than other metals, such as
stainless steel, that are used in electrochemical cells, the cell
is relatively light. The cell also has low ohmic resistance under
polarization, because aluminum is very conductive. Furthermore,
aluminum is less expensive than stainless steel. The aluminum is
protected from corrosion by the addition of a perchlorate salt.
[0009] The cell can include a cathode current collector containing
aluminum. The electrolyte can contain about 500 to about 2500 ppm
by weight of a perchlorate salt. The perchlorate salt can be, e.g.,
LiClO.sub.4, Ca(ClO.sub.4).sub.2, Al(ClO.sub.4).sub.3, or
Ba(ClO.sub.4).sub.2. In some embodiments, the electrolyte is
essentially free of LiPF.sub.6.
[0010] In another aspect, the invention features an electrochemical
cell including a cathode containing an aluminum current collector,
an anode, and an electrolyte containing a lithium salt and a
perchlorate salt. The cell is a primary electrochemical cell.
Primary electrochemical cells are meant to be discharged to
exhaustion only once, and then discarded. Primary cells are not
meant to be recharged. The cathode can contain MnO.sub.2 and the
anode can contain lithium. The electrolyte can contain at least 500
ppm by weight of the perchlorate salt, or at least. 1000, 1500, or
2500 ppm by weight of the perchlorate salt. The electrolyte can
also contain less than 20,000 ppm by weight of the perchlorate
salt. The perchlorate salt can be, e.g., LiClO.sub.4,
Ca(ClO.sub.4).sub.2, Al(ClO.sub.4).sub.3, or Ba(ClO.sub.4).sub.2.
The electrolyte can also include LiPF.sub.6, e.g., at least 5000
ppm by weight LiPF.sub.6 or at least 10,000 ppm by weight
LiPF.sub.6. In other aspects, the electrolyte is essentially free
of LiPF.sub.6. The case of the cell can be aluminum, either in
whole or in part.
[0011] In another aspect, the invention features an electrochemical
cell comprising a cathode containing MnO.sub.2, an anode containing
lithium, and an electrolyte containing about 500 ppm to about 2000
ppm of a perchlorate salt. The perchlorate salt can be, e.g.,
LiClO.sub.4, Ca(ClO.sub.4).sub.2, Al(ClO.sub.4).sub.3, or
Ba(ClO.sub.4).sub.2.
[0012] In another aspect, the invention features an electrochemical
cell comprising a cathode containing MnO.sub.2, an anode containing
lithium, and an electrolyte containing a perchlorate salt; the cell
is a primary electrochemical cell and includes two pieces of
aluminum in electrical contact with each other. The two pieces can
be made of the same alloy of aluminum.
[0013] In yet another aspect, the invention features a method of
inhibiting aluminum corrosion in a primary electrochemical cell.
The method includes: (a) adding a perchlorate salt to the
electrolyte of the cell; and (b) placing the electrolyte, an anode
containing Li, and a cathode containing MnO.sub.2 and an aluminum
current collector into a cell case. The perchlorate salt can be,
e.g., LiClO.sub.4, Ca(ClO.sub.4).sub.2, Al(ClO.sub.4).sub.3, or
Ba(ClO.sub.4).sub.2.
[0014] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a sectional view of a nonaqueous electrochemical
cell.
[0016] FIG. 2 is a graph showing current density vs. potential of
the aluminum in an electrode exposed to LiTFS, DME:EC:PC
electrolytes containing different amounts of LiClO.sub.4.
[0017] FIG. 3 is a graph showing current density vs. time of the
aluminum in an electrode exposed to LiTFS, DME:EC:PC electrolytes
containing different amounts of LiClO.sub.4.
[0018] FIG. 4 is a graph showing current density vs. time of the
aluminum in an electrode exposed to a LiTFS, DME:EC:PC electrolyte
containing LiClO.sub.4.
[0019] FIG. 5 is a graph showing current density vs. potential of
the aluminum in an electrode exposed to LiTFS+LiTFSI, DME:EC:PC
electrolytes containing different amounts of LiClO.sub.4.
[0020] FIG. 6 is a graph showing current density vs. time of the
aluminum in an electrode exposed to LiTFS+LiTFSI, DME:EC:PC
electrolytes containing different amounts of LiClO.sub.4.
[0021] FIG. 7 is a graph showing current density vs. potential of
the aluminum in an electrode exposed to LiTFS+LiPF.sub.6, DME:EC:PC
electrolytes containing different amounts of LiClO.sub.4.
[0022] FIG. 8 is a graph showing current density vs. time of the
aluminum in an electrode exposed to LiTFS+LiPF.sub.6, DME:EC:PC
electrolytes containing different amounts of LiClO.sub.4.
[0023] FIG. 9 is a graph showing current density vs. potential of
the aluminum in an electrode exposed to a LiTFS, DME:EC:PC
electrolyte containing different amounts of LiClO.sub.4 and
different amounts of Al(ClO.sub.4).sub.3.
[0024] FIG. 10 is a graph showing current density vs. potential of
the aluminum in an electrode exposed to a LiTFS, DME:EC:PC
electrolyte containing different amounts of LiClO.sub.4 and
different amounts of Ba(ClO.sub.4).sub.2.
DETAILED DESCRIPTION
[0025] Referring to FIG. 1, an electrochemical cell 10 includes an
anode 12 in electrical contact with a negative lead 14, a cathode
16 in electrical contact with a positive lead 18, a separator 20
and an electrolytic solution. Anode 12, cathode 16, separator 20
and the electrolytic solution are contained within a case 22. The
electrolytic solution includes a solvent system and a salt that is
at least partially dissolved in the solvent system.
[0026] Cathode 16 includes an active cathode material, which is
generally coated on the cathode current collector. The current
collector is generally titanium, stainless steel, nickel, aluminum,
or an aluminum alloy, e.g., aluminum foil. The active material can
be, e.g., a metal oxide, halide, or chalcogenide; alternatively,
the active material can be sulfur, an organosulfur polymer, or a
conducting polymer. Specific examples include MnO.sub.2,
V.sub.2O.sub.5, CoF.sub.3, MoS.sub.2, FeS.sub.2, SOCl.sub.2,
MoO.sub.3, S, (C.sub.6H.sub.5N).sub.n, (S.sub.3N.sub.2).sub.n,
where n is at least 2. The active material can also be a carbon
monofluoride. An example is a compound having the formula CF.sub.x,
where x is 0.5 to 1.0. The active material can be mixed with a
conductive material such as carbon and a binder such as
polytetrafluoroethylene (PTFE). An example of a cathode is one that
includes aluminum foil coated with MnO.sub.2. The cathode can be
prepared as described in U.S. Pat. No. 4,279,972.
[0027] Anode 12 can consist of an active anode material, usually in
the form of an alkali metal, e.g., Li, Na, K, or an alkaline earth
metal, e.g., Ca, Mg. The anode can also consist of alloys of alkali
metals and alkaline earth metals or alloys of alkali metals and Al.
The anode can be used with or without a substrate. The anode also
can consist of an active anode material and a binder. In this case
an active anode material can include carbon, graphite, an
acetylenic mesophase carbon, coke, a metal oxide and/or a lithiated
metal oxide. The binder can be, for example, PTFE. The active anode
material and binder can be mixed to form a paste which can be
applied to the substrate of anode 12.
[0028] Separator 20 can be formed of any of the standard separator
materials used in nonaqueous electrochemical cells. For example,
separator 20 can be formed of polypropylene, (e.g., nonwoven
polypropylene or microporous polypropylene), polyethylene, and/or a
polysulfone.
[0029] The electrolyte can be in liquid, solid or gel (polymer)
form. The electrolyte can contain an organic solvent such as
propylene carbonate (PC), ethylene carbonate (EC), dimethoxyethane
(DME), dioxolane (DO), tetrahydrofuran (THF), acetonitrile
(CH.sub.3CN), gamma-butyrolactone, diethyl carbonate (DEC),
dimethyl carbonate (DMC), ethyl methyl carbonate (EMC)
dimethylsulfoxide (DMSO) methyl acetate (MA), methyl formiate (MF),
sulfolane or combinations thereof. The electrolyte can
alternatively contain an inorganic solvent such as SO.sub.2 or
SOCl.sub.2. The electrolyte also contains a lithium salt such as
lithium trifluoromethanesulfonate (LiTFS) or lithium
trifluoromethanesulfonimide (LiTFSI), or a combination thereof.
Additional lithium salts that can be included are listed in U.S.
Pat. No. 5,595,841, which is hereby incorporated by reference in
its entirety. In some embodiments, the electrolyte may contain
LiPF.sub.6; in other embodiments, the electrolyte is essentially
free of LiPF.sub.6. The electrolyte also contains a perchlorate
salt, which inhibits corrosion in the cell. Examples of suitable
salts include lithium, barium, calcium, aluminum, sodium,
potassium, magnesium, copper, zinc, ammonium, and
tetrabutylammonium perchlorates. Generally, at least 500 ppm by
weight of the perchlorate salt is used; this ensures that there is
enough salt to suppress corrosion. In addition, less than about
20,000 by weight of the perchlorate salt is generally used. If too
much perchlorate salt is used, the cell can be internally shorted
under certain conditions during use.
[0030] To assemble the cell, separator 20 can be cut into pieces of
a similar size as anode 12 and cathode 16 and placed therebetween
as shown in FIG. 1. Anode 12, cathode 16, and separator 20 are then
placed within case 22, which can be made of a metal such as nickel,
nickel plated steel, stainless steel, or aluminum, or a plastic
such as polyvinyl chloride, polypropylene, polysulfone, ABS or a
polyamide. Case 22 is then filled with the electrolytic solution
and sealed. One end of case 22 is closed with a cap 24 and an
annular insulating gasket 26 that can provide a gas-tight and
fluid-tight seal. Positive lead 18, which can be made of aluminum,
connects cathode 16 to cap 24. Cap 24 may also be made of aluminum.
A safety valve 28 is disposed in the inner side of cap 24 and is
configured to decrease the pressure within battery 10 when the
pressure exceeds some predetermined value. Additional methods for
assembling the cell are described in U.S. Pat. Nos. 4,279,972;
4,401,735; and 4,526,846.
[0031] Other configurations of battery 10 can also be used,
including, e.g., the coin cell configuration. The batteries can be
of different voltages, e.g., 1.5V, 3.0V, or 4.0V.
[0032] The invention is further described in the following
examples, which do not limit the scope of the invention described
in the claims.
EXAMPLE 1
Al Corrosion in Different Electrolytes with Addition of
LiClO.sub.4
[0033] Glass Cell Experimentation
[0034] An electrochemical glass cell was constructed having an Al
working electrode, a Li reference electrode, and two Li auxiliary
electrodes. The working electrode was fabricated from a 99.999% Al
rod inserted into a Teflon sleeve to provide a planar electrode
area of 0.33 cm.sup.2. The native oxide layer was removed by first
polishing the planar working surface with 3 .mu.m aluminum oxide
paper under an argon atmosphere, followed by thorough rinsing of
the Al electrode in electrolyte. All experiments were performed
under an Ar atmosphere.
Cyclic Voltammetry
[0035] Corrosion current measurements were made according to a
modified procedure generally described in X. Wang et al.,
Electrochemica Acta, vol. 45, pp. 2677-2684 (2000). The corrosion
potential of Al was determined by continuous cyclic voltammetry. In
each cycle, the potential was initially set to an open circuit
potential, then anodically scanned to +4.5 V and reversed to an
open circuit potential. A scan rate of 50 mV/s was selected, at
which good reproducibility of the corrosion potential of aluminum
was obtained. The corrosion potential of aluminum was defined as
the potential at which the anodic current density reached 10.sup.-5
A/cm.sup.2 at the first cycle.
Chronoamperometry
[0036] Corrosion current measurements were made according to the
procedure described in EP 0 852 072. The aluminum electrode was
polarized at various potentials vs. a Li reference electrode while
the current was recorded vs. time. Current vs. time measurements
were taken during a 30-minute period. The area under current vs.
time curve was used as a measure of the amount of aluminum
corrosion occurring. The experiment also could be terminated in
case the current density reached 3 mA/cm.sup.2 before the 30 minute
time period elapsed and no corrosion suppression occurred.
Corrosion suppression occurred when the resulting current density
was observed in the range of 10.sup.-6 A/cm.sup.2.
[0037] Referring to FIG. 2, cyclic voltammograms taken in the
electrolyte containing LiTFS and DME:EC:PC showed significant
shifts in the corrosion potential of the Al electrode. The addition
of LiClO.sub.4 to the electrolyte shifted the potential of aluminum
in the positive direction, which indicates corrosion
suppression.
[0038] Curves "a" and "a'" in FIG. 2 show the corrosion potential
of the aluminum in the electrolyte containing no LiClO.sub.4. The
addition of 500 ppm of LiClO.sub.4 to the electrolyte shifted the
potential of the aluminum 150 mV in the positive direction (curves
"b" and "b'"); the addition of 1000 ppm of LiClO.sub.4 to the
electrolyte shifted the potential 300 mV (curves "c" and "c'"); and
the addition of 2500 ppm of LiClO.sub.4 to the electrolyte shifted
the potential 600 mV (curves "d" and "d'"). These results
demonstrate that the addition of increasing amounts of LiClO.sub.4
to the electrolyte containing LiTFS salt and mixture of DME:EC:PC
results in increasing degrees of corrosion protection of the
aluminum electrode.
[0039] Referring to FIG. 3, curve "a" shows a potentiostatic
dependence (chronoamperogram) of the aluminum electrode exposed to
the electrolyte containing LiTFS, DME:EC:PC with the addition of
500 ppm LiClO.sub.4; curve "b" shows the chronoamperogram taken in
the same electrolyte with addition of 1000 ppm LiClO.sub.4; curve
"c" shows the chronoamperogram taken in the electrolyte containing
LiTFS, DME:EC:PC, and 2500 ppm LiClO.sub.4. As shown in FIG. 3, at
a LiClO.sub.4 concentration of 2500 ppm, the aluminum corrosion at
+3.6 V (vs. a Li reference electrode) is effectively suppressed,
and the corrosion current is less than 10.sup.-6 A/cm.sup.2 after
30 minutes of measurement.
[0040] Referring to FIG. 4, the electrochemical window of Al
stability can be extended as high as +4.2 V (vs. a Li reference
electrode) by increasing the concentration of LiClO.sub.4 to 1%
(10,000 ppm). At a LiClO.sub.4 concentration of 1%, aluminum
corrosion is effectively suppressed at 4.2 V. The corrosion current
after 30 minutes is 8-10 .mu.A/cm.sup.2, and the current continues
to fall over time. The falling current indicates passivation of the
Al surface. The increased level of the resulting current (10
.mu.A/cm.sup.2 vs. 1 .mu.A/cm.sup.2 after 30 minutes of experiment)
is due to the increased background current at these potentials.
[0041] Referring to FIG. 5, curves "a", "a'", and "a"" show the
corrosion potential of an aluminum electrode subjected to an
electrolyte containing a mixture of LiTFS and LiTFSI salts,
DME:EC:PC, and no LiClO.sub.4. The addition of 500 ppm of
LiClO.sub.4 to this electrolyte shifted the corrosion potential of
the aluminum 150 mV in the positive direction (curves "b" and
"b'"); the addition of 1000 ppm of LiClO.sub.4 to the electrolyte
shifted the potential 280 mV (curves "c" and "c'"); and the
addition of 2500 ppm of LiClO.sub.4 to the electrolyte shifted
potential 460 mV (curves "d" and "d'"). These results demonstrate
that the addition of increasing amounts of LiClO.sub.4 to the
electrolyte containing the mixture of LiTFS and LiTFSI salts and
DME:EC:PC results in increasing degrees of corrosion protection of
the aluminum electrode.
[0042] Referring to FIG. 6, curve "a" shows the chronoamperogram of
the aluminum electrode exposed to the electrolyte containing a
mixture of LiTFS and LiTFSI salts, DME:EC:PC, and 1000 ppm
LiClO.sub.4; and curve "b" shows the chronoamperogram of the
aluminum electrode exposed to the same electrolyte containing 2500
ppm LiClO.sub.4. As shown in FIG. 5, at a LiClO.sub.4 concentration
of 2500 ppm in LiTFS, LiTFSI, DME:EC:PC electrolyte, the aluminum
corrosion at +3.6 V is effectively suppressed, and resulting
corrosion current of the Al electrode is about 10.sup.-6 A/cm.sup.2
after 30 minutes.
[0043] Referring to FIG. 7, curve "a" shows the corrosion potential
of the aluminum subjected to an electrolyte containing a mixture of
LiTFS and LiPF.sub.6 salts, DME:EC:PC, and no LiClO.sub.4. The
addition of 500 ppm of LiClO.sub.4 to this electrolyte shifted the
corrosion potential of the aluminum 125 mV in the positive
direction (curve "b"); the addition of 2500 ppm of LiClO.sub.4 to
the electrolyte shifted the potential 425 mV (curve "c"); and the
addition of 5000 ppm of LiClO.sub.4 to the electrolyte shifted the
potential 635 mV (curve "d"). These results demonstrate that the
addition of increasing amounts of LiClO.sub.4 to the electrolyte
containing the mixture of LiTFS, LiPF.sub.6 salts, and DME:EC:PC
results in increasing degrees of corrosion protection of the
aluminum electrode.
[0044] Referring to FIG. 8, curve "a" shows a chronoamperogram of
the aluminum electrode exposed to the electrolyte containing LiTFS,
LiPF.sub.6, DME:EC:PC with no LiClO.sub.4; curve "b" shows a
chronoamperogram taken in the same electrolyte with 2500 ppm
LiClO.sub.4 added; curve "c" shows a chronoamperogram taken in the
electrolyte containing LiTFS, LiPF.sub.6, DME:EC:PC, and 5000 ppm
LiClO.sub.4. As shown in FIG. 8, at a LiClO.sub.4 concentration of
5000 ppm, the aluminum corrosion at +3.6 V (vs. a Li reference
electrode) is effectively suppressed, and the corrosion current is
less than 10.sup.-6 A/cm.sup.2 after 30 minutes of measurement.
EXAMPLE 2
Al Corrosion in Electrolytes Containing LiTFS, DME:EC:PC, with the
Addition of Different Perchlorates
[0045] Electrochemical glass cells were constructed as described in
Example 1. Cyclic voltammetry and chromoamperometry were performed
as described in Example 1.
[0046] Referring to FIG. 9, curves "a", "b", and "c" show the
corrosion potential of an aluminum electrode exposed to the
electrolyte LiTFS, DME:EC:PC containing 0, 1000 and 2500 ppm of
LiClO.sub.4, respectively. Curves "a'", "b'," and "c'" show the
corrosion potential of an aluminum electrode exposed to the
electrolyte LiTFS, DME:EC:PC containing 0, 1000 and 2500 ppm of
Al(ClO.sub.4).sub.3, respectively. These results demonstrate that
the addition of Al(ClO.sub.4).sub.3 salt, like the addition of
LiClO.sub.4 salt, suppressed the corrosion of Al.
[0047] Referring to FIG. 10, curves "a", "b", and "c" show the
corrosion potential of an aluminum electrode exposed to the
electrolyte LiTFS, DME:EC:PC containing 0, 1000 and 2500 ppm of
LiClO.sub.4, respectively. Curves "a'", "b'" and "c'" show the
corrosion potential of an aluminum electrode exposed to the
electrolyte LiTFS, DME:EC:PC containing 0, 1000 and 2500 ppm of
Ba(ClO.sub.4).sub.2, respectively. These results demonstrate that
the addition of Ba(ClO.sub.4).sub.2 salt, like the addition of
LiClO.sub.4 salt, suppressed the corrosion of Al.
[0048] The shifts in the corrosion potential that result from the
addition of LiClO.sub.4, Al(ClO.sub.4).sub.3, and
Ba(ClO.sub.4).sub.2 to an electrolyte containing LiTFS and
DME:EC:PC are summarized below in Table 1.
1 TABLE 1 Anodic shift of corrosion potential (mV) Additive 0 ppm
1000 ppm 2500 ppm Al(ClO.sub.4).sub.3 0 170 450 Ba(ClO.sub.4).sub.2
0 170 400 LiClO.sub.4 0 300 600
Example 3
Al Corrosion in Electrolyte Containing LiTFS, DME:EC:PC, (Vial
Storage Test)
[0049] The following test conditions were used:
[0050] Electrodes: EMD (electrochemically synthesized manganese
dioxide) based cathodes applied on the Al current collector
[0051] Electrolyte (10 mL per sample): LiTFS, DME:EC:PC with and
without addition of LiClO.sub.4 salt
[0052] Aging conditions: 60.degree. C. for 20 days
[0053] Direct determination of Al corrosion was performed in one of
two ways:
[0054] Analytical determination of Al ions in the electrolyte after
aging (ICP method)
[0055] Direct observation of the Al surface (optical microscopy)
after aging
[0056] Measurements of Al corrosion were performed by measuring the
Al ions in the electrolyte after aging of the EMD based cathodes
with an Al current collector. Analytical results (ICP) are
summarized in Table 2.
2TABLE 2 Al concentration Sample Electrolyte after storage (ppm)
None LiTFS, DME:EC:PC 1.94 .+-. 0.20 EMD based cathode on LiTFS,
DME:EC:PC 21.55 .+-. 1.58 Al current collector EMD based cathode on
LiTFS, DME:EC:PC + 2.16 .+-. 0.18 Al current collector 2500 ppm
LiClO.sub.4
[0057] The level of Al ions in the electrolyte indicates the rate
of Al corrosion. As shown above, the background level of Al ions in
solution is about 2 ppm. As referred to herein, the corrosion of a
metal is said to be suppressed when, after the test described above
is performed, the concentration of metal ions in the electrolyte is
less than about 3 ppm, which is just above the background
level.
[0058] The Al concentration in the electrolyte without LiClO.sub.4
addition is high (the range is 19.4-23 ppm). Thus, part of the Al
substrate has dissolved (corroded) under the potential of the
applied active cathode material.
[0059] On the other hand, the samples which were stored in the
electrolytes with added LiClO.sub.4 did not show any corrosion (the
resulting Al concentration in the electrolyte is at the background
level 1.9-2.3 ppm). These data confirm results of the
electrochemical measurements in a glass cell: 2500 ppm of
LiClO.sub.4 completely suppresses the corrosion of Al at the
potential of the EMD cathode.
[0060] The analytical data were confirmed by the direct observation
of Al surface after aging (under an optical microscope, at a
magnification of 60.times.). The electrodes stored in the
electrolyte without LiClO.sub.4 exhibited substantial corrosion, as
viewed under the optical microscope. The section stored in the
electrolyte with added LiClO.sub.4 showed virtually no
corrosion.
EXAMPLE 4
Al Current Collector Coupled with Other Metals, (Vial Storage
Test)
[0061] The same cathodes on the Al substrate as described above
were used in this experiment. In this case, the Al substrates were
welded to stainless steel (SS) or nickel (Ni) tabs. A description
of the samples and analytical results is presented in Table 3.
3TABLE 3 Ni Al Fe Sample Electrolyte (ppm) (ppm) (ppm) None LiTFS,
DME:EC:PC <1.0 <1.0 <1.0 Cathode (Al cur. LiTFS, DME:EC:PC
<1.0 24.4 5.3 collector with welded SS tab) Cathode (Al cur.
LiTFS, DME:EC:PC 90.9 20.5 <1.0 collector with welded Ni tab)
Cathode (Al cur. LiTFS, DME:EC:PC + <1.0 <1.0 <1.0
collector with 2500 ppm LiClO.sub.4 welded SS tab) Cathode (Al cur.
LiTFS, DME:EC:PC + <1.0 <1.0 <1.0 collector with 2500 ppm
LiClO.sub.4 welded Ni tab)
[0062] The highest corrosion rate was observed on the sample welded
to the SS tab and stored in the electrolyte without added
LiClO.sub.4 (the resulting solution contains the residue colored as
a rust, and the SS tab is separated from the Al substrate). The
presence of iron (5.3 ppm of Fe ions in the resulting electrolyte)
indicates a high rate of SS corrosion as well as Al corrosion (24.4
ppm of the Al in the resulting electrolyte).
[0063] A high concentration of Ni (90.9 ppm) in the resulting
electrolyte (Al current collector with welded Ni tab, electrolyte
without LiClO.sub.4) indicates the severe corrosion of the Ni tab
coupled with Al (the Al corroded as well, as indicated by the
presence of 20.5 ppm Al).
[0064] On the other hand, the samples stored in the electrolytes
with added LiClO.sub.4 did not show any corrosion (the resulting
Al, Ni, Fe concentrations in the electrolyte were at the background
level of <1 ppm).
EXAMPLE 5
Al Corrosion in Electrolyte Containing LiTFS, DME:EC:PC and 2500
ppm of LiClO.sub.4, (2/3A Cell Tests)
[0065] Cells were assembled with investigated parts and
electrolytes according to the standard procedure with Al current
foil applied as the cathode substrate.
[0066] The assembled cells (2/3A size) were stored 20 days at
60.degree. C. Electrolyte removed from the cells after storage was
submitted for ICP analysis. The electrolyte did not show any traces
of Al, Fe, or Ni (the concentrations were at the background
level).
EXAMPLE 6
Corrosion Tests Using Different Aluminum Alloys, (Vial Storage
Test)
[0067] Two cathodes were prepared by coating aluminum foil
substrates (1145 Al) with MnO.sub.2. Pieces of aluminum foil (3003
Al) were welded to the aluminum foil of each of the cathodes. One
cathode was stored for 20 days at 60.degree. C. over LiTFS,
DME:EC:PC electrolyte containing 2500 ppm of LiClO.sub.4. The
second cathode was stored for 20 days at 60.degree. C. over LiTFS,
DME:EC:PC electrolyte containing no LiClO.sub.4. After the 20-day
period, the electrolytes were analyzed by ICP. The first
electrolyte (2500 ppm LiClO.sub.4 in the electrolyte) contained
less than 1 ppm Al, while the second electrolyte (no LiClO.sub.4 in
the electrolyte) contained 18 ppm Al. These results indicate that
the presence of LiClO.sub.4 can suppress corrosion when two
different alloys of aluminum are in electrical contact in the
presence of electrolyte.
[0068] All publications, patents, and patent applications mentioned
in this application are herein incorporated by reference to the
same extent as if each individual publication, patent, or patent
application was specifically and individually indicated to be
incorporated by reference.
OTHER EMBODIMENTS
[0069] A number of embodiments of the invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. For example, although the examples
described above relate to batteries, the invention can be used to
suppress aluminum corrosion in systems other than batteries, in
which an aluminum-metal couple occurs. Other embodiments are within
the scope of the following claims.
* * * * *