Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
2001-08-24
2004-01-20
Bell, Bruce F. (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S302000, C429S300000, C429S231900, C429S231950
Reexamination Certificate
active
06680147
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application Nos. 00-52364, filed Sep. 5, 2000 and 00-52365, filed Sep. 5, 2000, in the Korean Patent Office, the disclosures of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lithium battery, and more particularly, to a lithium battery having improved safety and reliability by using a gel electrolyte.
2. Description of the Related Art
Lithium secondary batteries generate electricity by lithium ions migrating between a cathode and an anode. The lithium secondary batteries have higher energy density per volume and have a higher voltage, than lithium cadmium batteries or nickel hydrogen batteries. Also, the lithium secondary batteries are lightweight, compared to lithium cadmium batteries or nickel hydrogen batteries, that is, approximately one half as heavy. Thus, the lithium secondary batteries are well adapted for miniaturization and long-time use in electronic appliances.
As described above, since the lithium secondary batteries have higher voltage characteristics and better charging/discharge cycle life than conventional nickel cadmium batteries or nickel hydrogen batteries, without causing environmental problems, much attention has been paid thereto as the most promising high-performance batteries. However, it is a critical issue to attain safety due to danger of explosion of a lithium secondary battery.
Lithium secondary batteries are classified according to the kind of electrolyte used, into lithium ion batteries and lithium ion polymer batteries. The lithium ion batteries generally use a cylindrical case or prismatic case as the case for sealing an electrode assembly. However, recently, a pouch has been in widespread use instead of such a case. The reason of using a pouch as a case is that the energy density per weight and volume increases, thin and lightweight batteries can be attained, and the material cost for the case can be reduced.
FIG. 1
is an exploded perspective view showing an example of a lithium ion battery using a pouch as a case.
Referring to
FIG. 1
, a lithium ion battery includes an electrode assembly
10
having a cathode
11
, an anode
12
and a separator
13
, and a case
14
surrounding and hermetically sealing the electrode assembly
10
. Here, the electrode assembly
10
is formed such that the separator
13
is interposed between the cathode
11
and the anode
12
and wound. A cathode tap
15
and an anode tap
15
′, serving as electrical passageways between the electrode assembly
10
and the outside, are drawn from the cathode
11
and the anode
12
, respectively, to form electrode terminals
16
and
16
′.
FIG. 2
is an exploded perspective view showing an example of a conventional lithium ion polymer battery.
Referring to
FIG. 2
, the lithium ion polymer battery includes an electrode assembly
21
having a cathode, an anode and a separator, and a case
22
surrounding and hermetically sealing the electrode assembly
21
. Electrode terminals (or lead wires)
24
and
24
′, serving as electrical passageways for inducing the current formed at the electrode assembly
21
to the outside, are connected to a cathode tap
23
and an anode tap
23
′ provided at the cathode and the anode, respectively, and are exposed outside the case
22
by a predetermined length.
As described above, in the lithium ion battery shown in FIG.
1
and the lithium ion polymer battery shown in
FIG. 2
, the electrode assemblies
10
and
21
are put into the cases
14
and
22
and an electrolytic solution is injected therein, with the electrode terminals
13
and
13
′ and
24
and
24
′ being partially exposed. Then, heat and pressure are applied so that the thermally adhesive materials in the edges of upper and lower case parts are adhered to be sealed, thereby completing the battery.
As described above, since the electrolytic solution is injected during a subsequent process to the one in which the electrode assemblies are put into the cases, in the case of using an organic solvent having a low melting point, the electrode assembly or pouch may swell, resulting in deterioration in the reliability and safety of the battery.
To solve the above-described problems, there have been proposed several methods of fabricating batteries such that plain batteries are cured by UV rays or electron beams, or electrode plates are coated with gel without separately injecting an electrolytic solution, as disclosed in U.S. Pat. Nos. 5,972,539, 5,279,910, 5,437,942 and 5,340,368. In practice, swelling of an electrode assembly or pouch can be somewhat mitigated, which is, however, not yet satisfactory.
SUMMARY OF THE INVENTION
To solve the above problems, it is a first object of the present invention to provide a polymeric gel electrolyte which can effectively suppress swelling of a battery due to an electrolytic solution.
It is another object of the present invention to provide a lithium battery which has improved reliability and safety by employing the polymeric gel electrolyte.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects, there is provided a polymeric gel electrolyte prepared by curing a composition comprising a polysiloxane compound represented by formula 1 or a polysiloxane-polyoxyalkylene compound represented by formula 2, a polyethylene glycol derivative represented by formula 3, and an organic solvent containing a lithium salt:
[Formula 1]
R
1
—O—(CH
2
)
m
—[Si(R
2
R
3
)—O]
n
—Si(R
2
R
3
)—(CH
2
)
n
—O—R
4
[Formula 2]
R
5
—O—(CH
2
)
m
—[Si(R
2
R
3
)—O]
n
—Si(R
2
R
3
)—(CH
2
)
m
—O—(CH
2
—CHR
6
—O—)
x
—R
7
[Formula 3]
H2C═C(R′)C(═O)(OCH2CH2)n-OR″
wherein R1 is —C(═O)CR
8
═CR
9
R
24
or —CR
10
R
11
R
25
, R
2
and R
3
are independently one selected from the group consisting of C
a
H
(2a+1)
in which a is an integer from 1 to 5, phenyl, benzyl and allyl, R
4
is one selected from the group consisting of —C(═O)CR
12
═CR
13
R
14
, —CR
15
R
16
R
17
and —C
a
H
(2a+1)
(here, a is an integer from 1 to 5), R
5
and R
7
are independently —C(O)CR
18
═C(R
19
R
20
) or —CR
21
(R
22
R
23
), R
6
is hydrogen or —C
a
H
(2a+1)
(here, a is an integer from 1 to 5), m is an integer from 1 to 5, n is an integer from 1 to 20, x is an integer from 1 to 15, and R
8
, R
9
, R
10
, R
11
, R
12
, R
13
, R
14
, R
15
, R
16
, R
17
, R
18
, R
19
, R
20
, R
21
, R
22
, R
23
, R
24
and R
25
are independently hydrogen or —C
b
H
(2b+1)
in which b is an integer from 1 to 5, R′ is hydrogen or CH
3
, and R″ is hydrogen, —C(═O)CH═CH
2
or —C(═O)C(CH
3
)═CH
2
.
The polyethylene glycol derivative represented by formula 3 is at least one selected from the group consisting of polyethylene glycol monomethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol monoacrylate and polyethylene glycol diacrylate. Also, the composition may further include ethoxylated trimethylolpropane triacrylate. In the composition, the content of the polysiloxane compound represented by formula 1 or the polysiloxane-polyoxyalkylene compound represented by formula 2 is preferably 0.1 to 10 parts by weight based on 100 parts by weight of the composition. The content of the polyethylene glycol derivative represented by formula 3 is preferably 0.4 to 50 parts by weight based on 100 parts by weight of the composition. The content of the ethoxylated trimethylolpropane triacrylate is greater than 0 parts by weight and less than or equal to 5 parts by weight based on 100 parts by weight of the composition.
To achieve the above and other objects of the present invention, there is provided a lithium battery including an electrode assembly having a cathode, an anode and a separato
Bell Bruce F.
Samsung SDI & Co., Ltd.
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