WO 2005/006467 PCT/KR2004/001691
SECONDARY BATTERY WITH AN IMPROVED SAFETY
Technical Field
The present invention relates to a secondary battery enclosed in a new battery package structure which provides an improvement in the safety of the battery. More particularly, the inventive package can be used in lithium secondary batteries, particularly lithium polymer batteries.
Background Art
Recently, lithium secondary batteries using non-aqueous electrolyte are increasingly used as a power source for portable electronic devices due to high voltage, high capacity, high output and low weight. However, such lithium secondary batteries have a safety problem and thus attempts to solve this problem are being made. When lithium secondary battery is overcharged, excess lithium flows out from a positive electrode and is inserted into a negative electrode, while very highly reactive lithium metal is deposited on the negative electrode surface,. and the positive electrode becomes thermally unstable. This results in rapid exothermic reactions due to the decomposition reaction of an organic solvent used as electrolyte, thus causing safety problems, such as battery fire and explosion.
Furthermore, when conductive materials, such as nails, penetrate the battery, the electrochemical energy within the battery is converted into thermal energy while generating heat rapidly. The generated heat causes rapid exothermic reactions by the chemical reaction of the positive or negative electrode materials, resulting in safety problems,
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such as battery fire and explosion.
Moreover, the nail penetration, compression, impact and high temperature exposure of the battery lead to a local short circuit within the positive and negative electrodes of the battery. At this time, excessive currents locally flow to generate heat. As the magnitude of a short circuit current caused by the local short circuit is inversely proportional to resistance, the short circuit current flows toward portions with low resistance, mainly through a metal foil used as a current collector. The calculation of heat generation in this case indicates that a very high heat generation locally occurs centering a part into which a nail penetrated, as described in Fig 1.
If heat generation occurs within the battery, the positive and negative electrodes and the electrolyte included in the battery will either react with each other or combust, and eventually the battery will catch fire or explode, since this reaction is a very high exothermic reaction. For this reason, care is required to make sure that rapid heat generation within the battery does not occur.
If the battery is pressed with a heavy object, subj ected to strong impact or exposed to high temperature, such a safety problem will also occur. This safety problem will be more serious, as the capacity of lithium secondary batteries increases, leading to an increase in energy density.
Generally, lithium secondary batteries use a lithium-containing transition metal oxide as a positive active material, which is one or more selected from the group consisting of, for example, LiCo02, LiNiO2r LiMn2O4, LiMnO2 and
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LiNi1-xCox2 (O2, LiMnsOt, LiMnO2 LiNii-xCox02 (02, or a combination thereof, may also be used.
Furthermore, examples of the porous separator include a porous polyolefin separator.
The lithium ion secondary battery according to the present invention can be fabricated by placing the porous separator between the positive and negative electrodes and adding the non-aqueous electrolyte containing a lithium salt, such as LiPFg, and additives, according to a conventional method.
The secondary battery package according to the present invention can be used in pouch-type batteries made of an aluminum-laminated film.
Hereafter, the present invention will be described in detail by the following exaroples. It is to be understood, however, that these examples are for illustrative purpose only and not intended to limit the scope of the present
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invention.
Example 1
1M LiPFg solution having an EC: EMC ratio of 1: 2 was used as an electrolyte, artificial graphite as a negative electrode, and LiCoO2 as a positive electrode. Then, a 383562-type lithium polymer battery was fabricated by a conventional method, and enclosed in an aluminum-laminated package. In this packing step, in order to connect the aluminum layer of the package with the positive terminal, a portion of a terminal film covering the positive terminal was removed, after which an aluminum metal piece was inserted into the removed portion and subjected to thermal melting. In this way, a battery was fabricated.
Example 2
A battery was fabricated in the same manner as in Example 1 except that a nickel metal piece was inserted to connect the negative terminal with the aluminum layer of the package.
Example 3
1M LiPFs solution, having an EC: EMC ratio of 1: 2 was used as an electrolyte, artificial graphite as a negative electrode, and L1C0O2 as a positive electrode. Then, a 383562-type lithium polymer battery was fabricated by a conventional method, and enclosed in an aluminum-1 aminat ed package. In this packing step, a portion of the outer polymer layer of the package was removed to expose the aluminum layer to the outside, after which each of the exposed aluminum layer and the positive terminal was welded to aluminum piece such that they were electrically connected with each other. In this way, a battery was fabricated.
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Example 4
A battery was fabricated in the same manner as in Example 3 except that each of the negative terminal and the aluminum layer of the package was welded to aluminum piece such that they were electrically connected with each other.
Example 5
1M LiPF6 solution having an EC: EMC ratio of 1: 2 was used as an electrolyte, artificial graphite as a negative electrode, and LiCoQ? as a positive electrode. Then, a 383562-type lithium polymer battery was fabricated by a conventional method, and enclosed in an aluminum-laminated package. In this packing step, each of two aluminum foil was attached to each of both outer surfaces of the package and connected with the positive terminal by ultrasonic welding. In this way, a battery was fabricated.
Example 6
A battery was fabricated in the same manner as in Example 5 except that each of two copper foil was attached to each of both outer surfaces of the package and connected with the negative terminal.
Example 7
A battery was fabricated in the same manner as in Example 5 except that an aluminum foil and a copper foil were attached to each of both outer surfaces of the package and connected with the positive and negative terminals, respectively. At this time, an electrically non-conductive ■ material like a separator was interposed between the two foils to prevent short circuits.
Comparative Example 1
A battery was fabricated in the same manner as in
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Example 1 except that the aluminum layer of the package was not connected with either of the positive and negative terminals, and also the metal foil was not attached to the outside of the package.
Mail penetration test
The batteries fabricated in Examples 1-7 and Comparative Example 1 were provided in a fully charged state. The central portion of the batteries fabricated as described above was penetrated with a 2.5-mm diameter iron nail using a nail penetration tester. Since the safety of the batteries varies depending on the penetration speed of the nail, a device capable of adjusting the penetration speed was used so that the nail could penetrate at various speeds. To examine the safety of the batteries, the test was performed at varying penetration speeds of the nail. The battery of Comparative Example 1 did catch fire even when the nail penetrated at a ■ speed of 1 cm/second, but the batteries of Examples 1-7 did not catch fire even when the nail penetrated at a speed of 10 cm/second.
The results of the nail penetration test are summarized in Table 1 below.
Table 1

Penetatkaispeed ofnail (an/sec) Occurrence of fiie Peak temperature (°Q
Comparative Example 1 10 Yes _

1 Yes _
Example 1 10 No 78

1 No 83
Example 2 10 No SI

1 No 89
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Example3 10 No 76
1 No 83
Example4 10 No 81

1 No 89
Example 5 10 No

1 No
Example 6 10 No
I No
Example 7 10 No

1 No
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Claims
1. A secondary battery comprising a battery package
which encloses the outer perimeter of the secondary battery
and covers the entire outer surface of positive and negative
electrodes and a portion of each terminal of the positive and
negative electrodes, wherein the battery package is formed of
a laminate film comprising an outer polymer layer, an inner
aluminum layer and an adhesive layer formed on a portion of
the inner surface of the aluminum 1 ayer, the aluminum 1 ayer
of the battery package being electrically connected with
either of the positive and negative terminals.
2. The secondary battery of Claim 1, wherein the
aluminum layer of the battery package and the positive or
negative electrode is connected directly with each other or
connected with each other by an electrically conductive
material.
3. The secondary battery of Claim 2, wherein the direct
connection between the aluminum layer and either of the two
terminals is made by any one of the following methods: a
method of making the connection between the aluminum layer
and the terminal by surrounding the outer surface of the
battery with the battery package and more strongly pressing
and thermally melting a package portion adjacent to the
corresponding terminal than that of other portions; a method
of making the connection by removing a portion of the
adhesive layer of the battery package; if the corresponding
terminal is coated with the terminal film, a method of making
the connection by removing a portion of the terminal film;
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and a method of making the connection by removing a portion of the adhesive layer of the battery package and a portion of the terminal film covering the terminal, which corresponds to the removed portion of the adhesive layer.
4. The secondary battery of Claim 2, wherein the
connection between the aluminum layer and either of the two
terminals by the electrically conductive material is made by
any one of the following methods: a method of making the
connection between the aluminum layer and the terminal by
removing the a portion of the adhesive layer of the battery
package, which is adjacent to the corresponding terminal, and
then inserting a piece made of an electrically conductive
material into the removed portion; and a method of making the
connection by removing at least a portion of the outer
polymer layer of the battery package and inserting an
electrically conductive material piece between the removed
portion and the corresponding terminal.
5. The secondary battery of Claim 2, wherein the
electrically conductive material is at least one selected
from the group consisting of aluminum, copper and nickel.
6. The secondary battery of any one of Claims 1 to 5,
which is a lithium secondary battery.
7. The secondary battery of any one of Claims 1 to 5,
which further comprises an electrically conductive metal foil
on at least one of the outer upper and lower surfaces of the
battery package, in which the electrically conductive metal
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foil is electrically connected with either of the positive and negative terminals.
8. A battery package formed of a laminate film
comprising an outer polymer layer, an inner aluminum layer
and an adhesive layer formed on a portion of the inner
surface of the aluminum layer, wherein a portion of the
adhesive layer to be contacted with a positive or negative
terminal is removed and a piece made of an electrically
conductive material is inserted into the removed portion.
9. A battery package formed of a laminate film
comprising an outer polymer layer, an inner aluminum layer
and an adhesive layer formed on a portion of the inner
surface of the aluminum layer, wherein at least a portion of
the outer polymer layer of the battery package is removed and
a piece made of an electrically conductive material is
inserted into the removed portion.
10. A secondary battery comprising a battery package
which encloses the outer perimeter of the secondary battery
and covers the entire outer surface of positive and negative
electrodes and a portion of each terminal of the positive and
negative electrodes, wherein the battery package is formed of
a laminate film comprising an outer polymer layerr an inner
aluminum layer and an adhesive layer formed on a portion of
the inner surface of the aluminum layer, and further
comprises at least one electrically conductive metal foil on
at least one of the outer upper and lower surfaces thereof,
and each of the electrically conductive metal foil is
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electrically connected with either of the positive and negative terminals.
11. The secondary battery of Claim 10, wherein the
metal foil is made of a material selected from the group
consisting of electrically conductive metals, and oxides and
alloys thereof.
12. The secondary battery of Claim 10, wherein the
metal foil additionally has thermal conductivity.

13. The secondary battery of Claim 10, wherein two more
metal foils are placed on the outer surfaces of the battery
package, and a separator made of an electrically non-
conductive material is inserted between the metal foils.
14. The secondary battery of any one of Claims 10 to
13, which is a lithium secondary battery.
15. A battery package formed of a laminate film
comprising an outer polymer layer, an inner aluminum layer
and an adhesive. layer formed on a portion of the inner
surface of the aluminum layer, the battery package further
comprising at least one electrically conductive metal foil on
at least one of the oute:r upper and lower surfaces thereof.
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The present invention provides a secondary battery comprising a battery package which encloses the outer perimeter of the secondary battery and covers the entire outer surface of positive and negative electrodes and a portion of each terminal of the positive and negative electrodes, wherein the battery package is formed of a laminate film comprising an outer polymer layer, an inner aluminum layer and an adhesive layer formed on a portion of the inner surface of the aluminum layer, the aluminum layer of the battery package being electrically connected with either of the positive and negative terminals. In another aspect, the invention provides a secondary battery comprising a battery package which encloses the outer perimeter of the secondary battery and covers the entire outer surface of positive and negative electrodes and a portion of each terminal of the positive and negative electrodes, wherein the battery package is formed of a laminate film comprising an outer polymer layer, an inner aluminum layer and an adhesive layer formed on a portion of the inner surface of the aluminum layer, and further comprises at least one electrically conductive metal foil on at least one of the outer upper and lower surfaces thereof, and each of the electrically conductive metal foil is electrically connected with either of the positive and negative terminals. In the inventive secondary battery, current occurring in conditions such as nail penetration can flow to either the aluminum layer of the package or the metal foil outside the package so as to inhibit heat generation inside the battery, thus improving the safety of the battery.