Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-10-12
2004-05-18
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S233000, C429S242000
Reexamination Certificate
active
06737196
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lithium (Li) polymer battery, and more particularly, to a Li polymer battery having an improved negative plate structure.
2. Description of the Related Art
A rechargeable secondary battery is widely used in portable wireless electric apparatus such as camcorders, cellular phones and lap-top computers. There are various secondary batteries including a nickel-cadmium (Ni—Cd) battery, a lead acid battery, a nickel metal hydride (Ni—MH) battery, a lithium (Li) ion battery, a Li polymer battery, a metal Li secondary battery and the like.
In particular, the metal Li secondary battery has a driving voltage of 3.6 V, a life span longer than that of the Ni—Cd battery or the Ni—MH battery, and high energy density to weight ratio, so its use is gradually expanding.
The Li secondary battery is classified into a Li-ion battery using a liquid electrolyte and a Li polymer battery using a polymer solid electrolyte, according to the type of electrolyte. The Li polymer battery can be embodied into various shapes as opposed to the Li-ion battery, and has merits of high stability and light-weight.
FIGS. 1A and 1B
shows the structure of a Bellcore Li polymer battery, a type of a Li polymer battery. Referring to
FIGS. 1A and 1B
a positive plate
11
and a negative plate
12
are stacked with a separator
13
interposed therebetween, each having a multilayered structure. The positive plate
11
consists of a positive collector
11
a
having a plurality of openings h
1
, and positive sheets
11
b
attached to both surfaces of the positive collector
11
a
. Also, the negative plate
12
consists of a negative collector
12
a
having a plurality of openings h
2
and negative sheets
12
b
attached to both surfaces of the negative collector
12
a
. The positive and negative collectors
11
a
and
12
a
are formed of expanded metal.
A manufacturing process of the Bellcore Li polymer battery having the above structure will be described.
First, acetone as a solvent, a positive or negative active material, a binder, a conductive material and a plasticizer are mixed to prepare a slurry. Then the slurry is deposited on a polyethylene (PET) base film with a doctor blade to form a thin sheet, the PET base film is removed to produce an electrode sheet of the corresponding active material. Then, the electrode sheets are laminated to both surfaces of each collector at a high temperature by applying pressure, and then cut to a predetermined size.
The resulting positive and negative plates
11
and
12
are combined with the separator
13
interposed therebetween, and the stacked structure is further laminated at a high temperature by applying pressure, thereby resulting in a bi-cell structure. Then, the bi-cell structure is soaked in ether to extract the plasticizer. Then, an electrode assembly is formed by stacking 9 of the bi-cells. Then, positive and negative terminals are welded onto the assembly, and electrolyte is infiltrated into the empty space from which the plasticizer has been extracted. Finally, a case is formed around the resulting product.
In the conventional Li polymer battery completed by the above method, the positive and negative collectors
11
a
and
12
a
require the openings h
1
and h
2
through which the plasticizer is extracted, so manufacturing the positive and negative collectors
11
a
and
12
a
is complicated. Also, adhesive forces between the positive collector
11
a
and the positive sheets
11
b
and between the negative collector
12
a
and the negative sheets
12
b
become weak due to burr generated during the formation of the openings h
1
and h
2
. In addition, the thicknesses of the positive and negative plates
11
and
12
are nonuniform.
Also, when attaching the electrode sheets
11
b
and
12
b
to the positive and negative collectors
11
a
and
12
a
, respectively, bubbles may form in the spaces between the sheet and collector due to the openings h
1
and h
2
, thereby lowering conductivity of the positive and negative collectors
11
a
and
12
a.
Also, the expanded metal forming the positive and negative collectors
11
a
and
12
a
is supplied in a roll having a width of less than 300 mm. The expanded metal has the property of being extendible in a longitudinal direction by force. Thus, it is difficult to manufacture the positive and negative collectors
11
a
and
12
a
through a continuous process by applying tensile strength.
In general, the material of the collectors determine the cost of the battery. Thus, using the expanded metal as a material for the collectors increases the cost of the battery, compared to using punched metal.
Also, as the expanded metal is mechanically processed, the metal itself is subject to stress. That is, when the expanded metal is cut in a predetermined size, fine powder of arsenic acid is separated from the collector made of the expanded metal. Also, because the collector made of the expanded metal is in the form of a mesh, a burr is generated due to expansion of strands in the mesh, thereby causing an electrical short circuit.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a lithium (Li) polymer battery in which a negative collector is a foil without openings, thereby improving the performance of plates and the productivity of the battery.
Accordingly, to achieve the above object, there is provided a lithium (Li) polymer battery comprising: a positive plate including a positive collector having a plurality of openings and a positive active material layer on at least one surface of the positive collector; a negative plate including a negative collector in a foil form, and a negative active material layer on at least on surface of the negative collector; and a separator between the positive and negative plates, for insulating the positive and negative plates.
Preferably, the negative collector is a copper (Cu) foil.
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patent: 6096455 (2000-08-01), Satake et al.
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Linden. Handbook of Batteries, 2nd ed., pp. 36.37-36.42, 1995 (no month).*
Linden. Handbook of Batteries, 2d, p. 15.26, 1995 (no month).*
Printout of Class 429 Definitions (p. 7). Nov. 13, 2001.
Chang Youn-han
Kim Jung-ho
Brouillette Gabrielle
Dove Tracy
Samsung Display Devices Co. Ltd.
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