Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Cell enclosure structure – e.g. – housing – casing – container,...
Reexamination Certificate
1999-08-30
2001-06-05
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Cell enclosure structure, e.g., housing, casing, container,...
C429S163000, C429S176000
Reexamination Certificate
active
06242131
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lithium secondary battery, and more particularly, to the case of a lithium secondary battery which hermetically seals and surrounds a battery body generating a current.
2. Description of the Related Art
As electronic devices such as camcorders, cellular phones or notebook type computers have been made smaller in size and lighter in weight, there has been considerable demand for small and lightweight secondary batteries with high energy density which can be used for these electronic devices. As such, a lithium secondary battery has been attracting attention as a high energy density battery. According to the kind of electrolyte used, a lithium secondary battery can be classified into a lithium ion battery which uses a liquid electrolyte and a lithium ion polymer battery which uses a solid electrolyte.
The lithium ion polymer battery includes a battery body for generating current, which is made by stacking a cathode, an anode and a separator. An electrode terminal serving as an electrical path to the outside is connected to the battery body. Parts of the battery body and the electrode terminal are hermetically sealed in an insulating case. The case of the lithium ion polymer battery hermetically seals the battery body such that thermal adhesive material layers, an innermost layer of the battery body, are adhered to each other.
FIG. 1
is an exploded perspective view showing an example of a conventional lithium ion polymer battery. Referring to
FIG. 1
, the lithium ion polymer battery includes a battery body
11
having a cathode plate, an anode plate and a separator, and a case
12
surrounding the battery body
11
, heretically sealing the body. Electrode tabs
14
and
14
′ serving as an electrode path for inducing the current generated in the battery body
11
to the outside are installed such that a predetermined length of them is exposed outside the case material
12
.
The case
12
is made of an outer material such as an insulating film having a stacked structure, as shown in FIG.
2
.
Referring to
FIG. 2
, the outer material is formed such that a thermal adhesive material layer
21
, an innermost layer of a battery body
20
, has an aluminum (Al) layer
22
, a polyethylene layer
23
, and a polyester layer
24
sequentially deposited thereon. Here, the thermal adhesive material layer
21
is formed of SURLYN (Dupont Inc.) obtained by adding Na, K, Mg or Zn to poly(ethylene-co-acrylic acid). The Al layer
22
on the thermal adhesive material layer
21
prevents permeation of moisture and loss of an electrolytic solution. The polyethylene layer
23
strengthens the functions of an outermost layer and improves adhesiveness. The polyester layer
24
, the outermost layer, protects the battery against external shock.
The case
12
formed of the above-described outer material hermetically seals the battery such that the battery body
11
is inserted into the case
12
, with only parts of the electrode taps
14
and
14
′ being exposed, and then the case is folded in half. Then, heat and pressure are applied to the case
12
to hermetically seal the battery such that thermally adhesive materials of the edges in the upper and lower portions of the case
12
are adhered to each other.
As described above, the case is bonded by thermally adhering parts of the innermost layer surrounding the battery body
20
. However, since the outer material of the conventional lithium secondary battery is relatively thin and the Al layer
22
is particularly thin, that is, about 9 &mgr;m, it is not easy to fabricate the outer material of the conventional lithium secondary battery. Also, the polyester layer
24
, the outermost layer, is susceptible to defects during molding, such as cracking.
Further, in the outer material of the conventional lithium secondary battery, when the innermost layer is thermally adhered, the adhesion efficiency may be poor, depending on a slight change in processing conditions including pressure, temperature and time, which causes leakage of the electrolytic solution in the lithium secondary battery.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide a case of a lithium secondary battery having an improved reliability by enhancing its moldability.
To accomplish the above objective, the present invention provides a case of a lithium secondary battery for surrounding and hermetically sealing a battery body which generates current, comprising:
a first copolymer layer which is the innermost layer for surrounding and hermetically sealing the battery body and is formed of poly(ethylene-co-acrylic acid) (EAA);
an aluminum (Al) layer formed on the first copolymer layer; and
a first nylon layer which is the outermost layer formed on the Al layer.
Here, the Al layer has a thickness of at least 50 &mgr;m. Also, a second nylon layer is further formed between the first copolymer layer and the Al layer.
According to another aspect of the present invention, a first polyethylene layer is formed between the first copolymer layer and the Al layer and a second polyethylene layer is formed between the Al layer and the first nylon layer.
According to still another aspect of the present invention, a polyethylene layer, a second nylon layer and an EAA layer are sequentially deposited between the first copolymer layer and the Al layer.
Also, the objective of the present invention can be accomplished by a case of a lithium secondary battery for surrounding and hermetically sealing a battery body which generates current, comprising:
a polypropylene layer which is the innermost layer for surrounding and hermetically sealing the battery body;
an Al layer formed on the polypropylene layer; and
a polyester layer which is the outermost layer formed on the Al layer.
The case of the lithium secondary battery having the above-described layer structure employs a solid electrolyte, which obviate a possibility of electrolytic solution leakage. Thus, the case is useful for a battery which does not need to be molded.
The Al layer preferably has a thickness of 30 &mgr;m or more. An Al layer having a thickness of less than 50 &mgr;m is not preferred because the moldability of the Al layer is poor.
REFERENCES:
patent: 4759972 (1988-07-01), Yoshiga
patent: 59-173944 (1984-10-01), None
patent: 2000123800 (2000-04-01), None
Kalafut Stephen
Leydig , Voit & Mayer, Ltd.
Ruthkosky Mark
Samsung SDI & Co., Ltd.
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