U.S. patent number 5,620,811 [Application Number 08/452,935] was granted by the patent office on 1997-04-15 for lithium polymer electrochemical cells.
This patent grant is currently assigned to Motorola, Inc.. Invention is credited to Anaba Anani, Ganesh Venugopal, Jinshan Zhang.
United States Patent |
5,620,811 |
Zhang , et al. |
April 15, 1997 |
Lithium polymer electrochemical cells
Abstract
A secondary lithium electrochemical charge storage device, such
as a battery (10) is taught. The battery (10) includes a first
composite electrode (20), and electrolyte layer (40), and a second
composite electrode (30). The composite electrodes include at least
an active material, and a polymer or polymer blend for lending
ionic conductivity and mechanical strength. The electrolyte may
also include a polymer as well as an electrolyte active material.
The polymer from which the composite electrode is fabricated may be
the same as or different than the polymer from which the
electrolyte layer is fabricated.
Inventors: |
Zhang; Jinshan (Coral Springs,
FL), Venugopal; Ganesh (Plantation, FL), Anani; Anaba
(Lauderhill, FL) |
Assignee: |
Motorola, Inc. (Schaumburg,
IL)
|
Family
ID: |
23798568 |
Appl.
No.: |
08/452,935 |
Filed: |
May 30, 1995 |
Current U.S.
Class: |
429/212; 429/217;
429/224; 429/223 |
Current CPC
Class: |
H01M
4/623 (20130101); H01M 4/131 (20130101); H01M
10/0565 (20130101); H01M 4/621 (20130101); H01M
10/052 (20130101); H01M 6/22 (20130101); Y02E
60/10 (20130101) |
Current International
Class: |
H01M
4/62 (20060101); H01M 6/00 (20060101); H01M
10/36 (20060101); H01M 6/22 (20060101); H01M
10/40 (20060101); H01M 006/16 (); H01M 006/14 ();
H01M 004/62 (); H01M 004/50 () |
Field of
Search: |
;429/192,194,218,223,224,217 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Poly(Dimethylsiloxane)-Poly(Ethylene Oxide) Based Polyurethane
Networks Used as Electrolytes . . . 15(1985), 233-240
North-Holland, Amsterdam by A. Bouridah, et al Apr. 11, 1983. .
Ionic Conductivity of Polyether . . . Macromolecules, 1984, 17,
63-66 by Killis, et al. .
Mechanism High Ionic Conductivity in Elastomeric Networks, Journal
of Power Sources, 9(1983) 389-395 by Gandini, et al. .
Polyaniline/Polyurethane, LiClO.sub.4 Conducting Polymer Composite
British Polymer Journal 23 (1990) 151-155, 1990, by Yi-Rui, et al.
.
Carbonxylate and Sulfonate Polyaddition Polymers, Polymer Research
Laboratories, NHK Spring Company, Ltd. Dept. of Research, Yokohama,
Japan. .
Cycloaliphatic Epoxide-Base Photocured Gelled Electrolytes for
Secondary Lithium Battery Applications . . . Nagasubramanian, et
al, J. Electrochem Soc. vol. 141, No. 6, Jun. 1994..
|
Primary Examiner: Valentine; Donald R.
Attorney, Agent or Firm: Massaroni; Kenneth M.
Claims
What is claimed is:
1. A lithium polymer secondary electrochemical cell comprising:
a first composite electrode including an electrode active material
and a first polymer, said polymer being
poly(tetrafluoroethylene);
a polymer electrolyte including an electrolyte active material and
a second polymer different than said first polymer, said second
polymer being poly(urethane); and
a second electrode.
2. A lithium polymer secondary electrochemical cell as in claim 1,
wherein said first composite electrode active material is selected
from the group consisting of LiCoO.sub.2, LiNiO.sub.2, LiMnO.sub.2,
V.sub.6 O.sub.13, V.sub.2 O.sub.5, and combinations thereof.
3. A lithium polymer secondary electrochemical cell as in claim 1,
wherein said electrolyte active material is a liquid
electrolyte.
4. A lithium polymer secondary electrochemical cell as in claim 4,
wherein said liquid electrolyte is a solution of a lithium salt
dissolved in an aprotic organic solvent.
5. A lithium polymer secondary electrochemical cell as in claim 1,
wherein said second electrode is a composite electrode including an
electrode active material and a third polymer, said third polymer
being different than at least one of said first polymer or said
second polymer.
6. A lithium polymer secondary electrochemical cell as in claim 5,
wherein said second composite electrode active material is selected
from the group of carbon, activated carbon, graphite, lithium
alloys and combinations thereof.
7. A lithium polymer secondary electrochemical cell as in claim 5,
wherein said third polymer is poly(tetrafluoroethylene).
8. A lithium polymer secondary electrochemical cell as in claim 1,
wherein said first polymer is a polymer blend of at least two
polymers.
9. A lithium polymer secondary electrochemical cell as in claim 8,
wherein said polymer blend includes at least poly(urethane) or
polyvinylidene fluoride, or poly(tetrafluoroethylene).
10. A lithium polymer secondary electrochemical cell as in claim 8,
wherein said polymer blend includes poly(urethane) and
poly(vinylidene fluoride).
11. A lithium polymer secondary electrochemical cell
comprising:
a first composite electrode including an electrode active material
selected from the group of LiCoO.sub.2, LiNiO.sub.2, LiMnO.sub.2,
V.sub.6 O.sub.13, V.sub.2 O.sub.5, and combinations thereof, and a
first polymer consisting of poly(tetrafluoroethylene);
a polymer electrolyte including a liquid electrolyte solution
comprising a lithium salt dissolved in an aprotic organic solvent,
and a second polymer including at least poly(urethane); and
a second composite electrode including a second composite electrode
active material and a third polymer, said third polymer being
different than at least one of said first polymer or said second
polymer.
12. A lithium polymer secondary electrochemical cell as in claim
11, wherein said second composite electrode active material is
selected from the group of carbon, activated carbon, graphite,
lithium alloys and combinations thereof.
13. A lithium polymer secondary electrochemical cell as in claim
11, wherein said third polymer is poly(tetrafluoroethylene).
14. A lithium polymer secondary electrochemical cell
comprising:
a first composite electrode including an electrode active material
selected from the group of LiCoO.sub.2, LiNiO.sub.2, LiMnO.sub.2,
V.sub.6 O.sub.13, V.sub.2 O.sub.5, and combinations thereof, and a
first polymer consisting of poly(urethane);
a polymer electrolyte including a liquid electrolyte solution
comprising a lithium salt dissolved in an aprotic organic solvent,
and a second polymer including at least poly(urethane); and
a second composite electrode, including a second composite
electrode active material and a third polymer, including at least
poly(urethane).
15. A lithium polymer secondary electrochemical cell as in claim
14, wherein said second composite electrode active material is
selected from the group of carbon, activated carbon, graphite,
lithium alloys and combinations thereof.
16. A lithium polymer secondary electrochemical cell as in claim
14, wherein said third polymer further includes
poly(tetrafluoroethylene).
17. A lithium polymer secondary electrochemical cell
comprising:
a first composite electrode including an electrode active material
and a first polymer;
a polymer electrolyte including an electrolyte active material and
a second polymer different than said first polymer; and
a second composite electrode including an electrode active material
and a third polymer, said third polymer being different than at
least one of said first polymer or said second polymer.
18. A lithium polymer secondary electrochemical cell as in claim
17, wherein said first composite electrode active material is
selected from the group consisting of LiCoO.sub.2, LiNiO.sub.2,
LiMnO.sub.2, V.sub.6 O.sub.13, V.sub.2 O.sub.5, and combinations
thereof.
19. A lithium polymer secondary electrochemical cell as in claim
17, wherein said first polymer is poly(tetrafluoroethylene).
20. A lithium polymer secondary electrochemical cell as in claim
17, wherein said electrolyte active material is a liquid
electrolyte.
21. A lithium polymer secondary electrochemical cell as in claim
20, wherein said liquid electrolyte is a solution of a lithium salt
dissolved in an aprotic organic solvent.
22. A lithium polymer secondary electrochemical cell as in claim
17, wherein said second polymer is poly(urethane).
23. A lithium polymer secondary electrochemical cell as in claim
12, wherein said second composite electrode active material is
selected from the group of carbon, activated carbon, graphite,
lithium alloys and combinations thereof.
24. A lithium polymer secondary electrochemical cell as in claim
17, wherein said third polymer is poly(tetrafluoroethylene).
25. A lithium polymer secondary electrochemical cell as in claim
17, wherein said first polymer is a polymer blend of at least two
polymers.
26. A lithium polymer secondary electrochemical cell as in claim
25, wherein said polymer blend includes at least poly(urethane) or
polyvinylidene fluoride, or poly(tetrafluoroethylene).
27. A lithium polymer secondary electrochemical cell as in claim
25, wherein said polymer blend includes poly(urethane) and
poly(vinylidene fluoride).
Description
TECHNICAL FIELD
This invention relates in general to secondary lithium
electrochemical cells and more particularly to lithium batteries
having composite electrodes.
BACKGROUND OF THE INVENTION
Secondary lithium electrochemical cells, and particularly lithium
batteries, using an intercalation compound as the positive
electrode have been studied intensively during the past decade.
Heretofore, the cathode material used in these batteries was
typically a lithiated cobalt oxide, nickel oxide, or manganese
oxide. The earliest reports of rechargeable lithium batteries
occurred more than a decade ago, and are shown in, for example,
U.S. Pat. Nos. 4,302,518 and 4,357,215 to Goodenough, et al.
Secondary lithium batteries using polymer electrolytes offer
substantial advantages over lithium ion batteries with liquid
electrolytes as are currently known in the field. Among these
advantages are enhanced safety, long-cycle life, high energy
density, and flexibility. Most of all, secondary lithium batteries
using polymer electrolyte holds great promise to be manufactured
with ease, since thin film processes in the polymer industry can be
used or adapted to the production of secondary lithium batteries.
One of the key issues in making secondary lithium polymer batteries
is the preparation of composite electrodes which possess good
mechanical strength and high conductivity, both in terms of ionic
conductivity and electronic conductivity. High conductivity, both
ionic and electronic, is essential for high rate operation of the
lithium battery. Good mechanical strength is also necessary for
large scale processing.
Composite electrodes used in secondary lithium polymer batteries
typically contain an electrode material providing active mass and
polymer electrolyte providing mechanical integrity and ionic
conductivity. The polymer electrolyte used in the composite
electrodes of the prior art are identical to the polymer used in
the electrolyte layer of the device, and have, heretofore been
fabricated of, for example, poly(ethylene oxide) or poly(vinylidene
fluoride).
Examples of this electrochemical device configuration can be found
in, for example, U.S. Pat. No. 5,296,318 to Gozdz, et al., in which
poly(vinylidene fluoride) copolymer was used in the composite
electrode and as the electrolyte layer. Other polymers which were
used in the same fashion include polyethylene oxide and
poly(acrylonitrile).
These devices, while acceptable, did not demonstrate the high
levels of ionic conductivity and the high performance rate
characteristics required to make lithium polymer batteries
successful in the marketplace. Moreover, due to inherent
limitations with the polymer itself, mechanical integrity, and
hence cycle life of the material were compromised.
Accordingly, there exists a need for a method of preparing
composite electrodes, having high ionic and electronic
conductivity, as well as mechanical strength which enables easy and
inexpensive production of secondary lithium polymer batteries.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a representation of an electrochemical cell including a
composite electrode in accordance with the instant invention;
FIG. 2 is a charge/discharge profile of a half cell reaction
employing a composite electrode cycled between 3.40 and 4.25 volts
in accordance with the instant invention;
FIG. 3 illustrates the charge/discharge profile of a half cell
using a composite electrode in accordance with the instant
invention; and
FIG. 4 shows the charge and discharge profile of a half-cell using
a composite electrode in accordance with the instant invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
While the specification concludes with claims defining the features
of the invention that are regarded as novel, it is believed that
the invention will be better understood from a consideration of the
following description in conjunction with the drawing figures, in
which like reference numerals are carried forward.
Referring now to FIG. 1, there is illustrated therein a
representation of an electrochemical cell 10 including a composite
electrode in accordance with the instant invention. The
electrochemical cell includes a positive electrode 20 and a
negative electrode 30 and a polymer electrolyte 40 disposed between
said electrodes. Either one of, or both, electrodes 20 and 30 may
be composite electrodes as are taught herein. As used herein and as
is generally accepted in the industry, a composite electrode refers
to an electrode which includes at least an electrode active
material as well as a polymeric material which serves as both
binder and to improve conductivity.
Using this definition of a composite electrode, a first electrode,
such as the positive electrode 20 or cathode may be fabricated
including a electrode active material selected from the group of
LiCoO.sub.2, LiMnO.sub.2, LiNiO.sub.2, V.sub.6 O.sub.13, V.sub.2
O.sub.5, and combinations thereof. The polymeric material used may
be either a single polymer or a blend of polymers which provide the
desired mechanical strength and high ionic conductivity. The
polymer may be selected from the group of, but not limited to,
polyesters, polyethers, poly(urethane), poly(ethyloxide),
poly(vinylidine fluoride), poly(acrylonitrile),
poly(tetrafluoroethylene), and combinations thereof. In this
regard, and in a first preferred embodiment, the polymer used in
the composite electrode is poly(tetrafluoroethylene). In another
preferred embodiment, the polymer used in the composite electrode
is a polymer blend which comprises at least about 90%
poly(urethane) and the balance being poly(vinylidene fluoride). In
a composite electrode, the polymer or polymer blend may comprise up
to 60% of the composite electrode, and typically comprises between
five and forty percent of the composite electrode.
The composite electrode, in this case, the positive electrode 20
may further include or be wetted with a liquid electrolyte, such as
that used in polymer electrolyte 40. In one preferred embodiment,
the liquid electrolyte is a solution of a lithium salt, or a
combination of salts, dissolved in an aprotic organic solvent, or
combination of solvents. Lithium salts include, but are not limited
to, salts, having the formula Li.sup.+ X.sup.-, where X.sup.- is an
anion such as Cl.sup.-, Br.sup.-, I.sup.-, ClO.sub.4.sup.-,
BF.sub.4.sup.-, PF.sub.5.sup.-, AsF.sub.6.sup.-, CH.sub.3
CO.sub.2.sup.-, CF.sub.3 SO.sub.3.sup.-, (CF.sub.3 SO.sub.2).sub.2
N.sup.-, (CF.sub.3 SO.sub.2).sub.3C.sup.-. Aprotic organic solvents
include, but are not limited to, propylene carbonate ("PC"),
ethylene carbonate ("EC"), diethyl carbonate, dimethyl carbonate,
dipropyl carbonate, dimethyl sulfoxide, acrylonitrile, and
combinations thereof.
A second electrode, such as negative electrode 30 or anode of the
cell 10 may also be fabricated as a composite electrode. In this
case, the composite electrode forming negative electrode 30
includes a polymer or polymer blend as described hereinabove with
respect to electrode 20. The composite electrode 30 further
includes a negative electrode active material selected from the
group of materials consisting of carbon, activated carbon,
graphite, petroleum coke, lithium alloys, such as LiAl, low voltage
lithium intercalation compounds, such as TiS.sub.2 and MoS.sub.2
and combinations thereof. Once again, the polymer or polymer blend
comprises between 5 and 40 percent of the total electrode.
Disposed between the positive and negative electrodes is the
polymer electrolyte 40 which consists of a polymer matrix and an
electrolyte active material. The electrolyte active material may be
a liquid species such as that described hereinabove, and includes,
in one preferred embodiment, EC, PC, and LiBF.sub.4. The material
from which the polymer matrix is fabricated may likewise be
selected from the polymer materials described hereinabove with
respect to the first and second composite electrodes. In one
preferred embodiment of the instant invention, the first composite
electrode is fabricated of an appropriate active material and a
polymer. The first composite electrode polymer in this preferred
embodiment is poly(tetrafluoroethylene), while the polymer matrix
from which the electrolyte layer is fabricated is of a different
polymer material. Hence, the polymer used in the electrolyte matrix
may be, for example, poly(urethane). Thereafter, the second
composite electrode may be fabricated so as to have a polymer
material either different than or the same as the polymer from
which the electrolyte layer is fabricated. Thus, in constructing a
lithium polymer secondary battery in accordance with the instant
invention, the polymer used in the composite electrode is different
than that used in the electrolyte. This is in sharp contrast to the
prior art in which the polymer used is the same for both
electrolyte and the composite electrode.
It thus may be appreciated that in an electrochemical cell, such as
a secondary lithium battery, fabricated according to this
invention, the polymer used in the first electrode may be different
than that used in the electrolyte. The polymer used in the second
electrode may likewise be different than both the first electrode
and the electrolyte. Alternatively, it may be the same as either
the first electrode or the electrolyte.
Alternatively, at least the first electrode and the electrolyte may
be fabricated so as to have a similar or the same polymer, if that
polymer is poly(urethane). The use of poly(urethane) as the
electrolyte polymer is disclosed in U.S. patent application Ser.
No. 08/279,131, filed Jul. 22, 1991, now U.S. Pat. No. 5,549,987 in
the names of Venugopal, et al, and assigned of record to Motorola,
Inc., the disclosure of which is incorporated herein by
reference.
Accordingly, a cell may be manufactured with a poly(urethane)
composite first electrode and a poly(urethane) electrolyte layer.
The second electrode may also be a composite electrode, and as such
may also be fabricated with a poly(urethane) polymer incorporated
therein.
The instant invention may be better understood from the perusal of
the examples which follow hereinbelow.
EXAMPLES
Example I
A first composite cathode was fabricated by mixing 90 parts of
LiMnO.sub.2, an electrode material, with 10 parts of carbon black,
a conductivity enhancing material. To this mixture was added 100
parts of a poly(urethane) electrolyte solution. The poly(urethane)
electrolyte solution contained 1 part of poly(urethane), 4 parts of
1M LiBF.sub.4 solution in an equal parts mixture of PC/EC, and 95
parts of tetrahydrofuran. Also added was 5 parts of poly(vinylidene
fluoride) which was added to the composite cathode to enhance the
mechanical strength of the film. The mixture was well blended and
pressed into a composite cathode pellet at 100.degree. C. under
10,000 pounds of pressure. The resulting composite electrode
contained 80 wt % of active mass of LiMnO.sub.2,.
A three-electrode electrochemical cell was constructed with the
LiMnO.sub.2 composite film as cathode, metallic lithium as counter
and reference electrode and a poly(urethane) gel film containing 2
parts of poly(urethane) and 8 parts of the 1M LiBF.sub.4 PC/EC
solution as electrolyte. The initial discharge capacity obtained
for the LiMnO.sub.2 composite cathode fabricated according to this
Example I was 104 mAh/g.
Referring now to FIG. 2, there is illustrated therein the
charge/discharge profile for the composite electrode described in
this example. The electrode was cycled between about 3.4 and 4.25
volts with a current density of about 0.2 A/cm.sup.2. As may be
appreciated from a perusal of FIG. 2, the first 15 cycles of the
cell were illustrated and demonstrate the efficacy of the composite
cathode fabricated according to this Example I.
Example II
A mixture of 45 parts of LiMnO.sub.2, 5 parts of carbon black and 4
parts of the poly(urethane) electrolyte solution described in
Example I was stirred at ambient temperatures for about four hours.
The resulting slurry was then poured onto a substrate sheet,
specifically a piece of Kapton, and cast into a thin film. After
approximately 15 minutes at ambient temperature, a thin film was
formed as a result of tetrahydrofuran evaporation. The film so
fabricated had a thickness of between 25 to 50 microns, though it
is to be understood that other thicknesses could be made by
changing viscosity of the slurry before casting, or by hot pressing
multiple layers of the thin film after casting at approximately
100.degree. C. The composite cathode was then soaked in a liquid
electrolyte of 1M LiBF.sub.4 solution in an equal parts mixture of
PC/EC for 1 hour at ambient temperature. The composite cathode
gained approximately 30% weight in the process due to absorption of
the liquid electrolyte. The composite cathode film made according
to this Example II demonstrated a rubbery characteristic with high
mechanical integrity. The conductivity of the composite film was
measured to be approximately 10.sup.-3 S/cm.
A piece of the composite film was used as cathode in a
three-electrode electrochemical cell with metallic lithium as
counter and reference electrode, and a poly(urethane) gel film as
electrolyte. The initial discharge capacity obtained for the
Li.sub.2 MnO.sub.4 composite cathode fabricated according to this
Example II was 100 mAh/g. Referring now to FIG. 3, there is
illustrated therein the charge/discharge profile for a composite
electrode in accordance with this invention. As may be appreciated
from a perusal of FIG. 3, the first 15 cycles of the cell were
illustrated and demonstrate the efficacy of the composite cathode
fabricated according to this Example II. Specifically, the
electrode was cycled between about 3.4 and 4.25 volts with a
current density of about 0.2 A/cm.sup.2. The electrode showed
relatively good capacity, about 95 mAh/g, without substantial
capacity fade over the test.
Example III
A composite cathode was fabricated using 85 parts of LiMnO.sub.2,
10 parts of carbon black, and 5 parts of poly(tetrafluoroethylene).
The polymer used herein did not include poly(urethane) or any other
polymer. Upon continuous grounding in a mortar, the well-blended
mixture of LiMnO.sub.2, carbon black and poly(tetrafluoroethylene)
formed a rubbery film. The film could be made thinner using a
conventional roller assembly. The thickness of the film was
adjusted by how much force was applied to, and how many times the
film was passed through the roller assembly. The resulting film did
not include electrolyte active material incorporated therein. The
cathode film was paired with a thin film of the poly(urethane) gel
electrolyte and assembled into a three-electrode electrochemical
cell as described hereinabove in Example I. Referring now to FIG.
4, there is illustrated therein the charge/discharge profile of the
composite LiMnO.sub.2, cathode cycled against the lithium anode.
The initial capacity of the LiMnO.sub.2 electrode was 110 mAh/g.
The electrode was cycled between about 3.4 and 4.25 volts, with a
current density of about 0.2 A/cm.sup.2. As may be appreciated from
FIG. 4, the electrode demonstrated good capacity without
performance degradation over the test. The result was deemed
surprising by the inventors because the composite electrode did not
contain electrolyte active material as is common in the prior
art.
While the preferred embodiments of the invention have been
illustrated and described, it will be clear that the invention is
not so limited. Numerous modifications, changes, variations,
substitutions and equivalents will occur to those skilled in the
art without departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *