JP2007035576A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery in which gas generated in a battery is dispersed to a non-welding portion to reduce internal pressure of the battery. <P>SOLUTION: In the nonaqueous electrolyte secondary battery including a sealed sheet-shaped outer package 10 which houses a power generating element 1 having a positive electrode 4 and a negative electrode 3, the sealed portion of the outer package 10 includes a welding portion and a non-welding portion 12 surrounded by the welding portion. The welding portion is provided between the non-welding portion 12 and the power generating element 1. The width d of the welding portion between the non-welding portion 12 and the power generating element 1 is smaller than the width h of the welding portion not including the non-welding portion of the outer package 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery in which a power generation element is accommodated in a sheet-like exterior body and the exterior body is sealed.

  Lithium ion batteries are widely used as nonaqueous electrolyte secondary batteries. In recent years, reduction in size and weight of a battery has been strongly demanded, and a lithium ion battery in which a power generation element including a positive electrode and a negative electrode is housed in a sheet-shaped outer package is also used (see, for example, Patent Document 1).

4 and 5 are diagrams showing examples of lithium ion batteries using a sheet-shaped outer package. For example, in Patent Document 1, the square-shaped power generation element 1 is accommodated in a square-shaped recess formed on the half side of the sheet-shaped exterior body 10a, and the laminate film 10a is folded in half and covered. As shown to Fig.4 (a), the outer peripheral parts (hatching part) are heat-welded. And after welding, as shown in FIG. 5, the welding part on either side is bent.
JP 2001-155790 A

  However, the lithium ion battery has a problem that the electrolyte is decomposed during overcharging, the battery temperature rises, and gas is generated inside the battery. In particular, in a battery using a sheet-shaped exterior body, there is a problem that the power generation element is easily deformed due to an increase in battery internal pressure due to the generated gas. When the power generation element is deformed, an internal short circuit may occur, and in some cases, smoke may be generated.

  The present invention has been made in view of such circumstances, and the sealing portion of the exterior body includes a welded portion and a non-welded portion surrounded by the welded portion, and between the non-welded portion and the power generating element. By providing a welded portion, the width of the welded portion between the non-welded portion and the power generation element is smaller than the width of the sealing portion of the exterior body that does not include the non-welded portion. It aims at providing the nonaqueous electrolyte secondary battery which can disperse | distribute the generated gas to a non-welding part and can reduce an internal pressure.

  A non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery in which a power generation element is sealed in a sheet-shaped outer package, wherein the sealed portion of the outer package is surrounded by the weld and the weld. A welding portion is provided between the non-welding portion and the power generation element, and the width of the welding portion between the non-welding portion and the power generation element does not include the non-welding portion. It is smaller than the width | variety of the sealing part of an exterior body, It is characterized by the above-mentioned.

  In the present invention, the sealing portion of the exterior body includes a welded portion and a non-welded portion surrounded by the welded portion, and a welded portion is provided between the non-welded portion and the power generation element. Since the width of the welded portion between the welded portion and the power generation element is smaller than the width of the sealed portion of the exterior body that does not include the non-welded portion, the welded portion has a lower welding strength than the sealed portion. That is, when gas is generated inside the battery (inside the exterior body) and the internal pressure is increased, the welded portion is peeled off, and the inside of the battery and the non-welded portion can be connected. By connecting the inside of the battery and the non-welded portion, the gas inside the battery is dispersed to the non-welded portion, and the internal pressure can be reduced. When the width of the welded portion is larger than 2 mm, the weld strength is relatively high, and even if gas is generated inside the battery and the internal pressure increases, the welded portion is difficult to peel off. Therefore, the width of the welded portion is 2 mm or less. It is preferable to do. The width of the sealing portion of the exterior body that does not include the non-welded portion is, for example, the width of the welded portion that does not include the non-welded portion between the outer periphery of the exterior body and the power generation element. The width is set to have a welding strength that does not peel even when the pressure increases.

  According to the present invention, when gas is generated inside the battery (inside the exterior body) and the internal pressure increases, the inside of the battery and the non-welded part can be connected, and the gas generated inside the battery is dispersed to the non-welded part. In addition, the battery internal pressure can be reduced. The deformation of the power generation element due to the increase in the battery internal pressure can be suppressed.

Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
Example 1
FIG.1 and FIG.2 is a figure which shows the example of the lithium ion battery (nonaqueous electrolyte secondary battery) based on this invention. As shown in FIG. 1, the lithium ion battery accommodates a square power generation element 1 in a sheet-like exterior body 10 in which a square-shaped recess is formed on the half side, and the remaining half of the exterior body 10. The outer peripheral parts of the outer package 10 are sealed by heat welding (hatched part in FIG. 1A). Further, as shown in FIG. 2, the left and right sides of the exterior body 10 are bent.

  For example, the power generation element 1 is formed by winding a negative electrode plate 3 in which a negative electrode mixture is applied to a copper current collector and a positive electrode plate 4 in which a positive electrode mixture is applied to an aluminum current collector in a flat winding shape through a separator. It is accommodated in the sheet-like exterior body 10 together with the nonaqueous electrolytic solution (electrolyte).

For the positive electrode plate 4, for example, a positive electrode mixture in which 97% by mass of lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, 1% by mass of acetylene black as a conductive agent, and 2% by mass of polyvinylidene fluoride as a binder is mixed. Then, an appropriate amount of N-methyl-2-pyrrolidone as a solvent was added and stirred to prepare a positive electrode paste, and this positive electrode paste was applied to both sides of an aluminum foil current collector and dried.

  For the negative electrode plate 3, for example, an appropriate amount of N-methyl-2-pyrrolidone is added to a negative electrode mixture in which 90% by mass of graphite as a negative electrode active material and 10% by mass of polyvinylidene fluoride as a binder are mixed, to prepare a negative electrode paste, This negative electrode paste was applied to both sides of a copper foil current collector and dried.

For the separator, for example, a polyethylene microporous film was used. As the electrolytic solution, for example, a solution obtained by dissolving 1 mol / l of LiPF _{6 in} a mixed solvent of ethylene carbonate: diethyl carbonate = 3: 7 (volume ratio) was used. The size of the power generation element 1 is 5 mm in thickness, 40 mm in width, 60 mm in height, and the battery capacity is 1000 mAh.

  For the outer package 10, for example, a resin layer (lamination layer) such as PET or nylon is provided on the upper layer of a metal layer such as aluminum, and a resin layer (welding layer) such as polyethylene or polypropylene is provided on the lower layer of the metal layer. Is used. The back surfaces can be heat-welded by bringing the back surfaces (welding layers) of the outer package 10 into contact with each other and applying heat.

  In the present invention, the non-thermally welded portion 12 is provided in the sealed portion of the exterior body 10 by thermal welding. The non-thermally welded portions 12 are linearly provided along the vertical direction on the left and right sides of the exterior body 10. The non-welded portion 12 is surrounded by the welded portion, and the width d of the welded portion between the non-welded portion 12 and the power generation element 1 housing portion (rectangular recess) is 0.5 mm. Further, the width e of the non-welded portion 12 is 2 mm, for example, and the length is substantially the same as the height of the power generation element 1. In addition, the width g of the welded portion outside the left and right non-welded portions 12 of the outer package 10 (the welded portion not including the non-welded portion between the power generation element 1 housing portion and the outer periphery of the outer package 10) is 5 mm. The width h of the welded portion above the body 10 (the welded portion not including the non-welded portion between the power generation element 1 housing portion and the outer periphery of the exterior body 10) is 2.5 mm (<width g). As shown in FIG. 2, the left and right bends of the exterior body 10 are bent outside the non-welded portion 12.

  As a method of providing the non-welded portion 12 when the outer peripheral portions of the exterior body 10 are heat-welded, for example, heat is applied only to other welded portions without applying heat to the non-welded portion 12, or to the non-welded portion 12 The applied heat is made lower than the other welded portions, the time for applying heat to the non-welded portion 12 is made shorter than the other welded portions, or the non-welded portion 12 of the exterior body 10 is made difficult to be thermally welded. There are methods.

  FIG. 3A is a schematic diagram showing an example of heat welding. In the example of the figure, a groove having a width e corresponding to the non-welded portion 12 is provided in a flat portion of the heater 20 that comes into contact with the exterior body 10. Since heat is applied to the portion, the non-welded portion 12 is formed. FIG. 3B is a schematic diagram illustrating an example of the exterior body 10. In the example of the figure, the exterior body 10 has a resin welding layer 10c, a metal layer 10b, and a resin lamination layer 10a laminated from the lower layer side, and the welding layer 10c has a width corresponding to the non-welded portion 12. A notch e is provided, and the notched portion is not welded, and the non-welded portion 12 is formed.

(Example 2)
The width d of the welded portion between the non-welded portion 12 of the outer package 10 and the power generation element 1 housing portion (square-shaped recess) was 1.0 mm, and a battery similar to that of Example 1 was manufactured.

(Example 3)
The width d of the welded portion between the non-welded portion 12 of the outer package 10 and the power generation element 1 housing portion was 1.5 mm, and the battery was manufactured in the same manner as in Example 1 except that.

Example 4
The width d of the welded portion between the non-welded portion 12 of the outer package 10 and the power generation element 1 housing portion was 2.0 mm, and the battery was manufactured in the same manner as in Example 1 except that.

(Example 5)
The width d of the welded portion between the non-welded portion 12 of the exterior body 10 and the power generation element 1 accommodating portion is 0.5 mm, and the welded portion (the power generation element 1 accommodating portion and the outer periphery of the exterior body 10 are positioned above the exterior body 10. The width h of the welded portion not including the non-welded portion is 3.0 mm (<width g), and a battery similar to that of Example 1 is manufactured.

(Example 6)
The width d of the welded portion between the non-welded portion 12 of the exterior body 10 and the power generation element 1 housing portion is 1.0 mm, the width h of the welded portion above the exterior body 10 is 3.0 mm, and the others A battery similar to that of Example 1 was produced.

(Example 7)
The width d of the welded portion between the non-welded portion 12 of the exterior body 10 and the power generation element 1 housing portion is 1.5 mm, the width h of the welded portion above the exterior body 10 is 3.0 mm, and the others A battery similar to that of Example 1 was produced.

(Example 8)
The width d of the welded portion between the non-welded portion 12 of the exterior body 10 and the power generation element 1 housing portion is 2.0 mm, the width h of the welded portion above the exterior body 10 is 3.0 mm, and the others A battery similar to that of Example 1 was produced.

Example 9
The width d of the welded portion between the non-welded portion 12 of the exterior body 10 and the power generation element 1 housing portion is 2.5 mm, the width h of the welded portion above the exterior body 10 is 3.0 mm, and the others A battery similar to that of Example 1 was produced.

(Comparative Example 1)
The width d of the welded portion between the non-welded portion 12 of the outer package 10 and the power generation element 1 housing portion was 2.5 mm, and the battery was manufactured in the same manner as in Example 1 except that.

(Comparative Example 2)
The width d of the welded portion between the non-welded portion 12 of the outer package 10 and the power generation element 1 housing portion was 3.0 mm, and the battery was manufactured in the same manner as in Example 1 except that.

(Comparative Example 3)
A non-welded portion 12 was not provided in the sealed portion of the outer package 10, and welding was performed in the same manner as in the past (FIG. 4A), and a battery similar to that in Example 1 was manufactured.

(Comparative Example 4)
The width d of the welded portion between the non-welded portion 12 of the exterior body 10 and the power generation element 1 housing portion is 3.0 mm, and the width h of the welded portion above the exterior body 10 is 3.0 mm (<width g). Otherwise, a battery similar to that of Example 1 was produced.

(Comparative Example 5)
The sealing part of the outer package 10 is not provided with the non-welded portion 12 and is welded in the same manner as in the past (FIG. 4A), and the width h of the welded portion above the outer package 10 is 3.0 mm. Otherwise, a battery similar to that of Example 1 was produced.

  An overcharge test was performed on each of the above-described Examples and Comparative Examples. In the overcharge test, each battery in a discharged state was overcharged at 1 A and 12 V for 3 hours to examine whether there was an abnormality such as smoke. The test results are shown in Table 1.

  About Examples 1-9, abnormality, such as smoke, has not arisen. This is because the non-welded portion 12 of the exterior body 10 is applied when a force is applied so that the pressure inside the exterior body 10 increases due to the gas generated inside the battery (inside the exterior body 10) due to overcharging, and the exterior body 10 swells. And the power generation element 1 housing portion are peeled off from the welded portion having the width d, and the power generating element 1 housing portion and the non-welded portion 12 are connected to each other. This is because the power generation element 1 can be prevented from being deformed.

  On the other hand, in Comparative Examples 3 and 5, abnormalities such as smoke are generated. This is because the pressure inside the outer package 10 is increased by the gas generated inside the battery due to overcharging, and the power generation element 1 is deformed. Also, in Comparative Examples 1, 2, and 4, abnormalities such as smoke are generated. Even if this is a case where the pressure generated inside the battery due to overcharge increases the pressure inside the exterior body 10 and a force acts so that the exterior body 10 swells, the non-welded portion 12 of the exterior body 10 and the power generation element This is because the welded portion having the width d between the first housing portion and the housing portion is not peeled off, and the power generating element 1 is deformed. As described above, when the width d of the welded portion between the non-welded portion 12 of the outer package 10 and the power generation element 1 housing portion is wide, the welding strength is high, and the non-welded portion 12 does not function effectively. The width d is preferably 2 mm or less. In addition, in the case of width d ≧ width h in FIG. 1, when the welding portion of width d is peeled off and the power generation element 1 housing portion and the non-welding portion 12 are connected, there is a high possibility that the welding portion of width h is also peeled off, Since there is a possibility that the electrolyte in the outer package 10 leaks to the outside, the width d of the welded portion between the non-welded portion 12 of the outer package 10 and the power generation element 1 housing portion is the welded portion above the outer package 10 ( It is necessary to make it smaller than the width h of the welded portion that does not include the non-welded portion between the power generation element 1 housing portion and the outer periphery of the exterior body 10.

  In each of the above-described embodiments, the non-welded portion 12 is filled with, for example, a substance that suppresses the generation of gas, for example, is filled with a substance that suppresses temperature rise, or is filled with, for example, a substance that prevents smoke generation It is also possible to keep it. Further, the size (width e or length) of the non-welded portion 12 is arbitrary.

It is a figure which shows the example of the lithium ion battery which concerns on this invention, (a) is a top view which shows a sealing part typically, (b) is xx sectional view taken on the line of (a). It is a figure which shows the example of the lithium ion battery which concerns on this invention, (a) is a top view which shows a sealing part typically, (b) is xx sectional view taken on the line of (a). (A) is a schematic diagram which shows the example of heat welding, (b) is a schematic diagram which shows the example of an exterior body. It is a figure which shows the example of the conventional lithium ion battery, (a) is a top view which shows typically a sealing part, (b) is xx sectional view taken on the line of (a). It is a figure which shows the example of the conventional lithium ion battery, (a) is a top view which shows typically a sealing part, (b) is xx sectional view taken on the line of (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power generation element 3 Negative electrode 4 Positive electrode 10 Exterior body 12 Non-welding part

Claims (1)

In a non-aqueous electrolyte secondary battery in which a power generation element is sealed in a sheet-shaped exterior body,
The sealing portion of the exterior body includes a welded portion and a non-welded portion surrounded by the welded portion,
A welded portion is provided between the non-welded portion and the power generation element;
A nonaqueous electrolyte secondary battery, wherein a width of a welded portion between the non-welded portion and the power generation element is smaller than a width of a sealing portion of an exterior body that does not include the non-welded portion.

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