U.S. patent application number 10/767875 was filed with the patent office on 2004-12-16 for method of preparing a negative electrode for a rechargeable lithium battery, method of fabricating a rechargeable lithium battery, and a rechargeable lithium battery.
Invention is credited to Kim, Young-Jun, Nah, Jae-Hou.
Application Number | 20040253517 10/767875 |
Document ID | / |
Family ID | 32960135 |
Filed Date | 2004-12-16 |
United States Patent
Application |
20040253517 |
Kind Code |
A1 |
Kim, Young-Jun ; et
al. |
December 16, 2004 |
Method of preparing a negative electrode for a rechargeable lithium
battery, method of fabricating a rechargeable lithium battery, and
a rechargeable lithium battery
Abstract
Disclosed is a method of preparing a negative electrode for a
rechargeable lithium battery. The steps include vacuum-drying a
negative electrode precursor, the negative electrode precursor
comprising a negative active material and an aqueous binder. The
steps may further include vacuum-drying a lithium cell battery that
includes a vacuum-dried negative electrode.
Inventors: |
Kim, Young-Jun;
(Daejeon-city, KR) ; Nah, Jae-Hou; (Cheonan-city,
KR) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
PO BOX 7068
PASADENA
CA
91109-7068
US
|
Family ID: |
32960135 |
Appl. No.: |
10/767875 |
Filed: |
January 29, 2004 |
Current U.S.
Class: |
429/231.95 ;
252/182.1; 34/406 |
Current CPC
Class: |
H01M 4/1393 20130101;
F26B 5/04 20130101; H01M 4/139 20130101; H01M 10/0525 20130101;
H01M 4/131 20130101; Y02E 60/10 20130101; H01M 2004/027 20130101;
Y10T 29/49108 20150115; H01M 4/04 20130101; H01M 4/0404
20130101 |
Class at
Publication: |
429/231.95 ;
252/182.1; 034/406 |
International
Class: |
H01M 004/58; F26B
005/04; H01M 004/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 29, 2003 |
KR |
2003-0005997 |
Claims
What is claimed is:
1. A method of preparing a negative electrode for a rechargeable
lithium battery, comprising: vacuum-drying a negative electrode
precursor, the negative electrode precursor comprising a negative
active material and an aqueous binder.
2. The method of claim 1, wherein the vacuum-drying is performed at
a temperature from 80 to 200.degree. C. under a pressure of 10 torr
or less for 1 to 72 hours.
3. The method of claim 2, wherein the vacuum-drying is performed at
a temperature from 90 to 150.degree. C. under a pressure of 10 torr
or less for 1 to 72 hours.
4. The method of claim 1, wherein the negative electrode is
prepared by coating a negative active material composition on a
current collector, the negative active material composition
comprising the negative active material and the aqueous binder.
5. A method of fabricating a rechargeable lithium battery
comprising: assembling a negative electrode, a positive electrode,
and an electrolyte to form a battery precursor; and vacuum-drying
the battery precursor.
6. The method of claim 5, wherein the vacuum-drying is performed at
a temperature of 100.degree. C. or less.
7. The method of claim 5, wherein the negative electrode is
prepared by vacuum-drying a negative electrode precursor including
a negative active material and an aqueous binder.
8. The method of claim 6, wherein the vacuum-drying is performed at
a temperature from 80 to 200.degree. C. under a pressure of 10 torr
or less for 1 to 72 hours.
9. The method of claim 8, wherein the vacuum-drying is performed at
a temperature from 90 to 150.degree. C. under a pressure of 10 torr
or less for 1 to 72 hours.
10. A rechargeable lithium battery in which a total amount of gas
is generated gas during initial charging, wherein the gas generated
has a CO content of 30 volume % or less.
11. The rechargeable lithium battery of claim 10, wherein the gas
generated has a H.sub.2 content of 0.2 volume % or less.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority of and is based on Korean
patent application No. 2003-5997 filed in the Korean Intellectual
Property Office on Jan. 29, 2003, the entire disclosure of which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of preparing a
negative electrode for a rechargeable lithium battery, a method of
fabricating a rechargeable lithium battery, and a rechargeable
lithium battery, and more particularly, to a rechargeable lithium
battery that generates a reduced amount of gas.
BACKGROUND OF THE INVENTION
[0003] An electrode for a rechargeable lithium battery is produced
by coating an active material composition on a current collector
and drying it to form an active mass layer on the current
collector. The active material composition includes an active
material, a binder, optionally a conductive binder, and an organic
solvent.
[0004] The active mass layer should be firmly maintained without
separation from the current collector during initial charging in
order to guarantee high capacity and good cycle life
characteristics. Good adhesion between the active mass layer and
the current collector depends on the choice of suitable binders.
The binder is required to render a physical binding strength to the
electrode in only a small amount, which leads to provision of a
positive electrode with a high energy density. The binder must also
be unreactive with the electrolyte solution and must maintain a
stable form within the battery operating temperature range.
[0005] Binders satisfying such requirements include aqueous binders
such as styrene rubber and carboxymethyl cellulose. However, the
aqueous binders generate gas caused by moisture in the electrode,
and carboxymethyl cellulose decomposes or forms thin layers on the
negative electrode, thereby expanding the volume of the
battery.
SUMMARY OF THE INVENTION
[0006] It is an aspect of the present invention to provide a method
of preparing a negative electrode for a rechargeable lithium
battery which generates less gas during the initial charging.
[0007] It is another aspect to provide a method of fabricating a
rechargeable lithium battery that generates less gas during the
initial charging.
[0008] It is still another aspect to provide a method of
fabricating a rechargeable lithium battery that generates less gas
during charging and where the composition of the gas can be
controlled.
[0009] It is still another aspect to provide a rechargeable lithium
battery including a negative electrode fabricated by the
method.
[0010] These and other aspects may be achieved by a method of
preparing a negative electrode for a rechargeable lithium battery
including vacuum-drying a negative electrode precursor, wherein the
negative electrode precursor includes a negative active material
and an aqueous binder.
[0011] In order to achieve these aspects and others, the present
invention further provides a method of fabricating a rechargeable
lithium battery including assembling a negative electrode, a
positive electrode, and an electrolyte to form a battery precursor,
and vacuum-drying the battery precursor.
[0012] The present invention further includes a rechargeable
lithium battery that generates gas containing less than 30 volume %
CO based on the total amount of gas generated during an initial
charging.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] A more complete appreciation of the invention, and many of
the attendant advantages thereof, will be readily apparent as the
same becomes better understood by reference to the following
detailed description when considered in conjunction with the
accompanying drawings, wherein:
[0014] FIG. 1 is a graph showing the amounts of generated gas in
rechargeable lithium batteries during initial charging, according
to Example 1 of the present invention and Comparative Example
1;
[0015] FIG. 2 is a graph showing the thicknesses of the
rechargeable lithium batteries after initial charging, according to
Example 1 of the present invention and Comparative Example 1;
and
[0016] FIG. 3 is a battery according to the present invention.
DETAILED DESCRIPTION
[0017] In order to firmly adhere an active material on a current
collector, aqueous binders such as styrene-butadiene rubber and
carboxylmethyl cellulose are widely used. However, the binders
cause gas generation which results in safety problems such as
explosion of the battery, and deterioration of the cycle life
characteristics. Thus, the amount of generated gas should be
controlled and reduced, but it is generally impossible to control
the amount of the generated gas after assembly of the battery.
According to the present invention, the amount of gas generated can
be controlled by either vacuum-drying an electrode, or removing gas
during the battery fabrication.
[0018] One embodiment of the invention for controlling the amount
of gas generated includes vacuum-drying a negative electrode
precursor. The vacuum-drying is performed at 80 to 200.degree. C.,
and preferably 90 to 150.degree. C. under a pressure of 10 torr or
less for from 1 to 72 hours. The negative electrode precursor
includes a negative active material and an aqueous binder. The
vacuum-drying step can remove the atmospheric gas which may be
present in the electrode. Thus, it can reduce the generation of
gas.
[0019] The negative electrode precursor is prepared by a
conventional procedure in which a negative active material
composition is coated on a current collector. The negative active
material composition includes the negative active material and the
aqueous binder. The negative active material may be any
carbonaceous material as long as it can be generally used as the
negative active material for rechargeable lithium batteries.
Exemplary materials are materials in which electrochemical redox
reactions occur, and in which lithium ions reversibly intercalate
and deintercalate. Examples thereof are amorphous carbon or
crystalline carbon. Examples of amorphous carbon materials are soft
or hard carbon, mesophase pitch carbides, and sintered coke.
Examples of crystalline carbon materials are shapeless, plate,
flake, circular, or fiber types of natural graphite or artificial
graphite.
[0020] The aqueous binder may be a mixture of butadiene-based
rubbers such as styrene-butyrene rubber, acrylonitrile rubber, or
acrylonitrile-butadiene-styrene rubber; and a cellulose-based
compound such as carboxymethyl cellulose or hydroxypropylmethyl
cellulose.
[0021] Another embodiment of the invention for controlling the
amount of gas generated by a battery includes assembling a battery
using a conventional negative electrode and vacuum-drying the
assembled battery. The vacuum-drying is performed at a temperature
not exceeding 100.degree. C. for at least 10 minutes.
[0022] Another embodiment of the present invention includes
assembling the battery with a vacuum-dried negative electrode, and
again vacuum-drying the assembled battery. This procedure is quite
effective at reducing the amount of gas generated.
[0023] The resulting rechargeable lithium battery generates gas
with a CO content of 50% or less based on the total gas generated
during the initial charging. In this application, "initial
charging" means that the battery is charged at a 0.1 to 1.0C rate
for 1 to 5 cycles. Generally, gases including H.sub.2, N.sub.2,
O.sub.2, CO, CO.sub.2, CH.sub.4 and C.sub.2H.sub.4 are generated
during the initial charging. The hydrogen gas is mainly derived
from the decomposition of the atmosphere, and the CO gas is mainly
derived from the decomposition of carboxymethyl cellulose, with a
smaller amount derived from the formation of a thin layer on a
surface of the negative electrode. Controlling the content of CO
gas is critical for controlling the thickness of the battery. A
battery made according to the present invention generates gas with
a combined CO and CO.sub.2 content of 30 volume % or less based on
the total amount of gas, and 50 volume % or less based on the
nitrogen gas. If the amount of the CO and the CO.sub.2 gases
combined is more than 30 volume % based on the total gas, the
volume of the battery increases to cause possible safety problems
and a swelling phenomenon.
[0024] In addition, the amount of hydrogen gas generated preferably
does not exceed 0.2 volume % based on the total amount of gas
generated.
[0025] An example of a rechargeable lithium battery according to
the invention is shown in FIG. 3. The lithium-sulfur battery 1
includes a positive electrode 3, a negative electrode 4, and a
separator 2 interposed between the positive electrode 3 and the
negative electrode 4. The positive electrode 3, the negative
electrode 4, and the separator 2 are contained in a battery case 5.
The electrolyte is present between the positive electrode 3 and the
negative electrode 4.
[0026] The following examples further illustrate the present
invention in detail, but are not to be construed to limit the scope
thereof.
EXAMPLE 1
[0027] 96 g of graphite, 2 g of carboxymethyl cellulose and 2 g of
styrene-butadiene rubber were mixed in water to prepare a negative
active material slurry. The negative active material slurry was
coated on a Cu foil and dried followed by pressing, thereby
obtaining a negative electrode.
[0028] The negative electrode was vacuum-dried at 90.degree. C. for
1 hour. Using the vacuum-dried negative electrode, a LiCoO.sub.2
positive electrode, and an electrolyte including 1 M LiPF.sub.6 in
a mixed solvent of ethylene carbonate and methylene carbonate (1:1
volume ratio), a rechargeable lithium cell was fabricated.
EXAMPLE 2
[0029] A rechargeable lithium cell was fabricated by the same
procedure as in Example 1 except that the vacuum-drying step was
performed at 120.degree. C. for 1 hour.
EXAMPLE 3
[0030] 96 g of graphite, 2 g of carboxymethyl cellulose, and 2 g of
styrene-butadiene rubber were mixed in water to prepare a negative
active material slurry. The negative active material slurry was
coated on a Cu foil and dried followed by pressing, thereby
obtaining a negative electrode.
[0031] Using the negative electrode, a LiCoO.sub.2 positive
electrode, and an electrolyte including 1 M LiPF.sub.6 in a mixed
solvent of ethylene carbonate and methylene carbonate (1:1 volume
ratio), a rechargeable lithium cell was fabricated.
EXAMPLE 4
[0032] 96 g of graphite, 1 g of carboxymethyl cellulose and 1 g of
styrene-butadiene rubber were mixed in water to prepare a negative
active material slurry. The negative active material slurry was
coated on a Cu foil and dried followed by pressing, thereby
obtaining a negative electrode.
[0033] The negative electrode was vacuum-dried at 90.degree. C. for
1 hour. Using the vacuum-dried negative electrode, a LiCoO.sub.2
positive electrode, and an electrolyte including 1 M LiPF.sub.6 in
a mixed solvent of ethylene carbonate and methylene carbonate (1:1
volume ratio), a rechargeable lithium cell was fabricated. The
lithium cell was again vacuum-dried at 100.degree. C.
COMPARATIVE EXAMPLE 1
[0034] A rechargeable lithium cell was fabricated by the same
procedure as in Example 1, except that the vacuum-drying step was
not performed.
[0035] The rechargeable lithium cells according to Examples 1 to 2,
and Comparative Example 1 were initially-charged (formation). At
this time, the generated gas was gathered and the composition was
analyzed. The results are presented in Tables 1 and 2. The results
in Table 1 indicate the relative volume as a percent of the total,
and those in Table 2 indicate the volume of each component as a
percentage based on N.sub.2 which was added from atmosphere. The
analysis was performed by injecting 0.1 cc of the gathered gas into
a column and using a gas chromatography (column: Heyasep column)
procedure.
1 TABLE 1 Comparative Example 1 Example 1 Example 2 H.sub.2 0.3
Trace amount Trace amount N.sub.2 47.2 63.5 74.7 O.sub.2 12.0 10.7
12.2 CO 37.6 23.7 11.2 CH.sub.4 1.6 1.5 1.4 C.sub.2H.sub.4 1.3 0.5
0.3
[0036]
2 TABLE 2 Comparative Example 1 Example 1 Example 2 H.sub.2 0.6
Trace amount Trace amount N.sub.2 100 100 100 O.sub.2 25.4 16.9
16.3 CO 79.7 37.3 15.0 CH.sub.4 3.4 2.4 1.9 C.sub.2H.sub.4 2.8 0.8
0.4
[0037] Amount of Gas Generated
[0038] The amounts of gas generated in the cells according to
Example 1 and Comparative Example 1 are shown in FIG. 1. It is
evident from FIG. 1 that the amount of generated gas is very much
smaller for Example 1, the cell with the vacuum-dried negative
electrode, than for Comparative Example 1, the cell with the
non-vacuum-dried negative electrode.
[0039] Thickness Variation
[0040] The initial thicknesses of the cells according to Examples 1
and 2 and Comparative Example 1 were measured to be 4.2 mm. After
the initial charging, the thickness of the cells according to
Examples 1 and 2, and Comparative Example 1 were again measured,
and the results are presented in FIG. 2. FIG. 2 indicates that a
much more severe thickness variation occurred in the cell with the
non-vacuum-dried negative electrode according to Comparative
Example 1 compared to Example 1, and as the vacuum-drying
temperature increases from 90.degree. C. as was done in Example 1,
to 120.degree. C. as was done in Example 2, the thickness variation
was reduced further.
[0041] While the present invention has been described in detail
with reference to the preferred embodiments, those skilled in the
art will appreciate that various modifications and substitutions
can be made thereto without departing from the spirit and scope of
the present invention as set forth in the appended claims.
* * * * *