JP2009302019A - Sealed battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable sealed battery capable of restraining leak of fluid caused by corrosion of a member (valve) in the battery by infiltration of the liquid from outside toward inside the battery. <P>SOLUTION: The sealed battery comprises a power generation element, a battery case for housing the power generation element, and a sealing plate having a projected section projecting upward in the center as an electrode terminal part and sealing an opening of the battery case. The projected section has an exhaust port for discharging a gas in the battery to the outside at its side, an external package member for covering the exhaust port by fitting to the projected section is mounted on the sealing plate, and the external package member is covered by a heat-shrinking resin film together with the external surface of the battery case. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sealed battery, and more particularly to improvement of leakage resistance of the sealed battery.

  2. Description of the Related Art In recent years, electronic devices such as AV devices and personal computers have been rapidly becoming portable and cordless. As power sources for driving electronic devices, alkaline storage batteries and nonaqueous electrolyte secondary batteries represented by lithium secondary batteries are used. Such high-capacity sealed secondary batteries are widely used. As electronic devices become more sophisticated, there is an increasing expectation for improving the performance of non-aqueous electrolyte secondary batteries having high energy density and excellent load characteristics.

In a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte containing a non-aqueous solvent is used, and if the electrolyte leaks outside the battery, the electronic equipment may be corroded. In order to prevent the leakage of the battery, the battery case is securely sealed by the sealing member.
In a nonaqueous electrolyte secondary battery, for example, a battery composite lid in which an explosion-proof mechanism is added to a sealing plate is used as a sealing member of a battery case. The battery composite lid is composed of, for example, a composite member in which a sealing plate having a convex portion at the center as an electrode terminal portion, a valve body made of metal foil, and a conductive plate in contact with a part of the valve body are overlapped. . The battery case is sealed by caulking the open end of the battery case to the peripheral edge of the battery composite lid via a gasket. The valve body is usually made of an aluminum foil that has good electronic conductivity and can be deformed when the battery internal pressure increases.

Explosion-proof mechanisms are provided in non-aqueous electrolyte secondary batteries to prevent the battery from generating a large amount of gas when overcharged or short-circuited, resulting in a significant increase in battery internal pressure and damage to the battery. Yes.
Hereinafter, the operation of the explosion-proof mechanism will be described. When the battery internal pressure reaches a predetermined value, the valve body is deformed by the internal pressure and is pushed up in the direction opposite to the conductive plate. With this deformation, the valve body is separated from the contact portion of the conductive plate. In this way, the current is interrupted at the initial stage of occurrence during overcharge or short circuit. By the above operation, a significant increase in battery temperature and battery internal pressure during overcharge or short circuit is suppressed.

Further, the convex portion of the sealing plate is usually provided with an exhaust port for releasing the gas generated inside the battery to the outside of the battery when the internal pressure of the battery further increases and the valve body is broken.
However, when the electronic device is a portable device such as a portable device, a PC, an AV device, and a power tool, depending on the environment in which the device is used, an alkaline solution such as concrete water or ammonium solution from a pet is a battery. There is a possibility to adhere to. However, since the aluminum foil used for the valve body is weak in alkalinity, if an alkaline solution adheres to the valve body, there is a possibility that the valve body will have a hole due to corrosion and leak through the hole. In addition, in the case of a battery pack provided with a protection circuit that controls charging, if the electrolytic solution adheres to the protection circuit, electric leakage may occur and heat may be generated.

By the way, Patent Document 1 proposes that a PTFE (polytetrafluoroethylene) film is disposed between the power generation element and the battery composite lid. Based on this method, for example, as a means for preventing leakage due to corrosion of the valve body, it is conceivable to cover the valve body with a PTFE membrane.
JP-A-10-27596

However, after the valve body is welded to the sealing plate, the upper surface (exhaust port side surface) of the valve body is exposed inside the convex portion of the sealing plate, so it is difficult to cover the upper surface of the valve body with the PTFE film. Further, when the valve body is previously covered with a PTFE membrane, it is difficult to weld the valve body to the sealing plate.
Therefore, in order to solve the above-described conventional problems, the present invention provides a highly reliable sealed battery in which leakage due to corrosion of a member (valve element) in the battery due to penetration of liquid from the outside into the battery is suppressed. The purpose is to provide.

The present invention includes a power generation element, a battery case that houses the power generation element, and a sealing plate that has an upward protruding protrusion at the center as an electrode terminal portion and seals the opening of the battery case. A sealed battery,
The convex part has an exhaust port for releasing the gas in the battery to the outside on the side part,
On the sealing plate, an exterior member that fits the convex portion and covers the exhaust port is disposed,
The exterior member is covered with a heat-shrinkable resin film together with the outer surface of the battery case.

  The exterior member is preferably made of ethylene propylene diene rubber, fluoro rubber, or acrylic resin.

  According to the present invention, leakage due to corrosion of a member (valve element) in the battery due to intrusion of liquid from outside into the battery is suppressed, and a highly reliable sealed battery can be provided.

  The present invention includes a power generation element, a battery case that houses the power generation element, and a sealing plate that has a projecting portion protruding upward as an electrode terminal portion at the center and seals the opening of the battery case. Type battery. And the said convex part has the exhaust port for discharge | releasing the gas in the said battery to the exterior in a side part, has an opening part fitted to the said convex part on the said sealing board, The said exhaust port The exterior member which covers is arranged, The said exterior member is characterized by the point covered with the heat-shrinkable resin film with the said battery case outer surface.

As a result, liquid can be prevented from entering the battery from the outside when the battery is used, and leakage due to corrosion of the member (valve element) in the battery (leakage of electrolyte to the outside of the battery) is suppressed. Thus, a highly reliable sealed battery excellent in safety can be obtained. Even in the case of long-term storage, liquid can be reliably prevented from entering the battery from the outside, and the reliability for long-term storage is greatly improved.
On the sealing plate, the exterior member is covered with a heat-shrinkable resin film together with the outer surface of the battery case, with the opening of the exterior member fitted into the convex portion. For this reason, the exterior member can be fixed on the sealing plate in a stable state.

Hereinafter, although the structure of the cylindrical lithium ion secondary battery which is one Embodiment of the sealed battery of this invention is demonstrated, referring FIG. 1, this invention is not limited to the following embodiment. FIG. 1 is a schematic longitudinal sectional view of a cylindrical lithium ion secondary battery which is an embodiment of the sealed battery of the present invention.
An electrode group 4 is housed as a power generation element in a battery case 1 made of a bottomed cylindrical metal (for example, a steel plate having a surface plated with Ni). The bottom surface of the battery case serves as a negative electrode terminal portion. The electrode group 4 is constituted by winding a belt-like positive electrode 5, a belt-like negative electrode 6, and a belt-like separator 7 interposed between both electrodes. For the separator 7, for example, a microporous resin film having a thickness of 10 to 30 μm is used. Polypropylene or polyethylene is used for the resin film.

The positive electrode 5 has a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector. One end of the positive electrode lead 9 is connected to the positive electrode 5, and the other end of the positive electrode lead 9 is connected to the lower surface of the lower plate 15 in the battery composite lid 12 described later. The negative electrode 6 has a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. One end of the negative electrode lead 10 is connected to the negative electrode 6, and the other end of the negative electrode lead 10 is connected to the inner bottom surface of the battery case 1. For the negative electrode lead 10, for example, a nickel lead or a copper lead is used. An aluminum lead is used for the positive electrode lead 9.
Insulating rings 8a and 8b are disposed on the upper and lower portions of the electrode group 4, respectively. The opening of the battery case 1 is sealed by caulking the opening end of the battery case 1 to the peripheral edge of the battery composite lid 2 via a gasket 3 made of resin (for example, polypropylene).

The battery composite lid 2 is made of a metal (for example, nickel) sealing plate 12 having a convex portion 12a protruding upward as a positive terminal portion and a metal foil (for example, an aluminum foil having a thickness of 10 to 30 μm). The valve body 13, the metal (for example, aluminum) conductive plate 14 electrically connected to a part of the valve body 13, and the periphery of the valve body 13 and the periphery of the conductive plate 14. A ring-shaped insulating plate 15 made of resin, and a lower plate 16 made of metal (for example, aluminum) arranged below the conductive plate 14. The conductive plate 14 and the lower plate 16 have openings for passing gas.
The convex part 12a of the sealing board 2 consists of a disk-shaped upper part provided so that the opening of the upper part of a cylindrical side part and a cylindrical side part may be plugged up. A plurality of exhaust ports 12b are provided on the cylindrical side portion of the convex portion 12a. The plurality of exhaust ports 12b are preferably provided at equal intervals along the circumferential direction of the cylindrical side portion in the vicinity of the central portion of the cylindrical side portion. The central portion of the conductive plate 14 has a shape that can contact the valve body 13, and the central portion of the conductive plate 14 is electrically connected to the central portion of the valve body 13 by welding.

On the sealing plate 12, an exterior ring 11 that covers the exhaust port 12 b is disposed between the convex portion 12 a and the caulked portion at the open end of the battery case 1. The convex part 12a fits into the opening provided in the center of the exterior ring 11, and the exterior ring 11 is fixed on the sealing plate 12 in a stable state by covering the exterior ring 11 with the heat-shrinkable resin film 17. ing. From the viewpoint of wearability, it is preferable that the outer diameter of the outer ring 11 (the diameter of the opening) is substantially the same as the outer diameter of the cylindrical side portion of the convex portion 12a.
Thereby, it can prevent that a liquid enters into the inside of a battery via an exhaust port from the exterior, and a liquid adheres to a valve body. As a result, it is possible to prevent the valve body from being perforated and the resulting leakage.

For the outer ring 11, it is preferable to use a material such as a resin or rubber having elasticity and excellent adhesion to a metal. Examples of such a material include ethylene propylene diene rubber (EPDM), fluorine rubber, and acrylic resin. These materials are excellent in alkali resistance.
From the viewpoints of heat shrinkability and workability, it is preferable to use a polyvinylidene chloride resin film (for example, Kureha Corporation, Kurehalon Film) as the heat shrinkable resin film 17. In consideration of the environment, a polyethylene terephthalate (PET) film is preferably used for the heat-shrinkable resin film 17.

When the battery internal pressure increases, the valve body 13 (explosion-proof mechanism) operates as follows. When the battery internal pressure rises and the battery internal pressure reaches a predetermined value, the valve body 13 is pushed upward by the gas pressure through the opening of the conductive plate 14 and deforms. With this deformation, the central portion of the valve body 13 is separated from the central portion of the conductive plate 14, thereby interrupting the current.
Further, when the battery internal pressure rises and the battery internal pressure reaches a predetermined value, the valve body 13 is further pushed upward, the valve body 13 is broken, the outer ring 11 is detached by the battery internal pressure, and the gas in the battery protrudes. It is discharged outside through the exhaust port 12b of the part 12a.

In the said embodiment, although the exterior ring is distribute | arranged inside the crimping part of the opening edge part of a battery, the shape of an exterior ring is not limited to this. For example, the outer ring may have a shape in which the outer peripheral edge extends to the upper part of the caulking part of the opening end of the battery and covers the upper part of the caulking part. In this case, the caulking part of the battery case is sealed. Short circuit due to contact with the plate can be prevented more reliably.
In the said embodiment, although the exterior ring is distribute | arranged so that between a convex part and a crimping | crimped part may be completely filled, the shape of an exterior ring is not limited to this. The exterior ring may have a shape that closes the exhaust port of the convex portion.
In the said embodiment, although a heat-shrinkable resin film covers the whole upper surface of an exterior ring, how to cover the exterior ring of a heat-shrinkable resin film is not limited to this. As long as the exterior ring can be fixed, it may be configured to cover a part of the upper surface of the exterior ring.
In the said embodiment, although the heat-shrinkable resin film has covered the whole side surface of the battery case, how to cover the battery case of a heat-shrinkable film is not limited to this. What is necessary is just to be able to cover an exterior ring stably.

The positive electrode mixture layer includes, for example, a positive electrode active material, a binder, and a conductive material. As the positive electrode active material, for example, a lithium-containing composite oxide is used. Examples of the lithium-containing composite oxide include lithium cobaltate (LiCoO ₂ ), modified LiCoO ₂ , lithium nickelate (LiNiO ₂ ), modified LiNiO ₂ , lithium manganate (LiMnO ₂ ), or LiMnO ₂ . Examples include modified products. Examples of each modified body include those containing elements such as aluminum (Al) and magnesium (Mg). Further, examples of each modified body include those containing at least two of cobalt (Co), nickel (Ni), and manganese (Mn).

As the binder, for example, polytetrafluoroethylene (PTFE), modified acrylonitrile rubber particles (for example, BM-500B (trade name) manufactured by Nippon Zeon Co., Ltd.), or polyvinylidene fluoride (PVDF) is used. PTFE and modified acrylonitrile rubber particles are carboxymethylcellulose (CMC), polyethylene oxide (PEO), or modified acrylonitrile rubber (for example, BM-720H manufactured by Nippon Zeon Co., Ltd.) (product) It is preferable to use in combination with a thickener such as name)). PVDF functions as both a binder and a thickener.
As the conductive material, for example, carbon black such as acetylene black and ketjen black, or graphite material such as natural graphite and artificial graphite is used. These may be used alone or in combination of two or more.

  The negative electrode mixture layer includes, for example, a negative electrode active material and a binder. As the negative electrode active material, for example, natural graphite, artificial graphite, silicon-containing composite materials such as silicide, or alloy materials can be used. As the negative electrode binder, for example, PVDF or a modified product thereof is used.

The electrode group 4 includes a non-aqueous electrolyte. The non-aqueous electrolyte is composed of, for example, a non-aqueous solvent and a lithium salt that dissolves in the non-aqueous solvent. For example, lithium hexafluorophosphate (LiPF ₆ ) or lithium tetrafluoroborate (LiBF ₄ ) is used as the lithium salt. As the nonaqueous solvent, for example, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC) is used, and these may be used alone. Alternatively, two or more kinds may be used in combination. Further, vinylene carbonate (VC), cyclohexyl benzene (CHB), or a modified product thereof may be added to the nonaqueous electrolytic solution.

Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.
A cylindrical lithium ion secondary battery having the structure shown in FIG. 1 was produced according to the following procedure.
(1) Preparation of positive electrode Li ₂ CO ₃ , Co ₃ O ₄ , NiO, and MnO ₂ are mixed with an atomic ratio of Li: Ni: Mn: Co = 0.94: 0.35: 0.35: 0.35. Then, the mixture was calcined at 900 ° C. for 10 hours to obtain Li _0.94 Ni _0.35 Mn _0.35 Co _0.35 O ₂ as a positive electrode active material. To 100 parts by weight of the positive electrode active material, 2.5 parts by weight of acetylene black as a conductive material, 4 parts by weight of PTFE as a binder, and an appropriate amount of an aqueous carboxymethyl cellulose solution were added, and then stirred with a double-arm kneader. A positive electrode paste was obtained. This positive electrode paste was applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 30 μm, and then dried to form a positive electrode mixture layer on both surfaces of the positive electrode current collector to obtain a positive electrode. After the positive electrode was rolled so that the total thickness of the positive electrode combined with the positive electrode mixture layer and the positive electrode current collector was 115 μm, this was cut into a strip having a width of 52 mm and a length of 1350 mm to obtain the positive electrode 5. . The positive electrode current collector was exposed at the connecting portion with the positive electrode lead 9 without forming the positive electrode mixture layer.

(2) Production of Negative Electrode Mesophase spherules were graphitized at a high temperature of 2800 ° C. to obtain mesophase graphite as a negative electrode active material. To 100 parts by weight of the negative electrode active material, 2.5 parts by weight of an acrylic acid-modified product of SBR (styrene / butadiene rubber), 1 part by weight of carboxymethyl cellulose, and an appropriate amount of water were added, and then a double-arm kneader. To obtain a negative electrode paste. This negative electrode paste was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 0.02 mm, and then dried to form a negative electrode mixture layer on both sides of the negative electrode current collector to obtain a negative electrode. The negative electrode was rolled so that the total thickness of the negative electrode combined with the negative electrode mixture layer and the negative electrode current collector was 120 μm and the negative electrode mixture layer had a porosity of 35%, and then cut into a strip having a width of 57 mm and a length of 1570 mm. A negative electrode 6 was obtained. The negative electrode current collector was exposed at the connecting portion with the negative electrode lead without forming the negative electrode mixture layer.

(3) Battery assembly The positive electrode 5, the negative electrode 6, and the separator 7 that separates the two electrodes were wound to form the electrode group 4. The electrode group 4 was housed in a bottomed cylindrical battery case 1 (diameter 26.0 mm, height 65 mm). As the separator 7, a polyethylene film having a thickness of 20 μm was used. After providing an annular stepped portion for placing the battery composite lid 2 on the battery case 1, a bronze agent was applied to the stepped portion and dried. 13 g of non-aqueous electrolyte was injected into the battery case 1 in which the electrode group 4 was housed. As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ as a lithium salt at a concentration of 1.4 mol / L in a non-aqueous solvent in which EC, EMC, and DMC are mixed at a volume ratio of 15:15:70 is used. It was. After the battery composite lid 2 including the aluminum valve body 13 and the nickel sealing plate 12 is placed on the upper part of the stepped portion, the opening end of the battery case 1 is connected to the battery composite lid 2 via the gasket 3. The opening of the battery case 1 was sealed by crimping on the peripheral edge.

An outer ring 11 (inner diameter) made of EPDM is formed in an annular recess portion surrounded by the gasket 3 exposed at the caulked portion of the opening end portion of the battery case 1 and the convex portion 12b of the sealing plate 12 at the upper portion of the sealing plate 12. 11.9 mm, outer diameter 25.9 mm, and height 1.5 mm) were mounted, and the exhaust port 12 b of the sealing plate 12 was covered with the exterior ring 11.
After covering the outer surface of the battery case 1 together with the outer ring 11 (except for the negative electrode terminal portion on the outer bottom surface of the battery case 1) with the heat-shrinkable resin film 17, the heat-shrinkable resin film 17 is heat-shrinked, and the battery Fixed to the surface. As the heat-shrinkable resin film 17, a polyvinylidene chloride resin film (thickness 80 μm) was used.
Six exhaust ports 12b (width 3.4 mm, height 1.0 mm) of the sealing plate 12 were provided at equal intervals along the circumferential direction of the side surface 1 mm below the top surface of the convex portion 12a. The convex portion 12a of the sealing plate 12 had an outer diameter of 11.8 mm and a height of 2.1 mm.

Example 2
A battery was produced in the same manner as in Example 1 except that the material of the exterior ring was changed to fluororubber.

Example 3
A battery was produced in the same manner as in Example 1 except that the material of the exterior ring was changed to urethane rubber.

<< Comparative Example 1 >>
A cylindrical lithium ion secondary battery having the conventional configuration shown in FIG. 2 was produced. Specifically, it was produced as follows. The exterior ring was not installed. A heat-shrinkable resin film was not used. Moreover, the position of the exhaust port provided in the convex part of a sealing board was changed into the corner | angular part of a convex part. A battery was fabricated in the same manner as in Example 1 except for the above.

[Evaluation]
Next, the following evaluation tests were carried out on the batteries of Examples 1 and 2 of the present invention and the batteries of conventional Comparative Examples 1 and 2.

(1) Battery leakage test A battery was impregnated with ammonium chloride water having a pH of about 9 for 10 seconds. Thereafter, the battery was allowed to stand for 1 month in an atmosphere of a temperature of 40 ° C. and a humidity of 95%, and the occurrence of rust on the valve body and the presence or absence of leakage were confirmed. The number of tests for each battery was 10.

(2) Battery Pack Leakage Test A battery pack with a protection circuit in which four of the batteries (single cells) were connected in series was prepared, and the battery pack was impregnated with ammonium chloride water having a pH of about 9 for 10 seconds. Thereafter, the battery pack was left for 1 month in an atmosphere of a temperature of 40 ° C. and a humidity of 95%, and it was confirmed whether or not the protection circuit generated heat due to leakage. Using a thermocouple, the temperature of the protection circuit was measured, and when the temperature was 100 ° C. or higher, it was determined that heat was generated (leak was present). The number of tests for each battery pack was five.

(3) Battery heating test The battery was heated with a burner to check for damage to the battery. The number of tests for each battery was 10. The results of the above test are shown in Table 1.

  In the batteries of Examples 1 to 3 of the present invention, the liquid leakage resistance was improved as compared with the battery of Comparative Example 1. Also, in the battery pack using the batteries of Examples 1 to 3, leakage resistance was improved as compared with the battery pack using the battery of Comparative Example 1. In particular, in the batteries of Examples 1 and 2 of the present invention using the outer ring made of EPDM, which is an alkali-resistant resin, and a fluororesin, none of the batteries was corroded and leaked by the valve body, which was excellent. Liquid leakage resistance and high reliability were obtained. Even in the case of the battery pack using the batteries of Examples 1 and 2, excellent liquid leakage resistance and high reliability were obtained.

  On the other hand, in the conventional battery of Comparative Example 1, all the batteries leaked. Also in the battery pack leakage test, in Comparative Example 1, there was a battery pack that generated heat in the protection circuit due to the influence of the leakage. Further, when the leaked battery of Example 3 was examined, it was confirmed that a part of the outer ring made of urethane rubber was dissolved by the alkaline solution.

  For the battery heating test, none of the batteries were damaged. Even when the exhaust port of the sealing plate was closed with the exterior ring, the internal pressure of the battery increased and the valve element was actuated (broken), the external ring was removed by the internal pressure of the battery, and gas was released from the exhaust port.

  The sealed battery of the present invention is suitably used as a power source for electronic devices such as portable devices or information devices.

It is a schematic longitudinal cross-sectional view of the cylindrical lithium ion secondary battery which is one Embodiment of the sealed battery of this invention. It is a schematic longitudinal cross-sectional view of the cylindrical lithium ion secondary battery of the conventional comparative example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery case 2 Battery compound cover 3 Gasket 4 Electrode group 5 Positive electrode 6 Negative electrode 7 Separator 8a, 8b Insulating ring 9 Positive electrode lead 10 Negative electrode lead 11 Insulating ring 12 Sealing plate 12a Protruding part 12b Exhaust port 13 Valve body 14 Conductive plate 15 Insulating plate 16 Lower plate 17 Heat shrinkable resin film

Claims (2)

Power generation elements,
A battery case for storing the power generation element;
A sealed battery having a convex part protruding upward as an electrode terminal part in the center, and a sealing plate for sealing the opening of the battery case,
The convex part has an exhaust port for releasing the gas in the battery to the outside on the side part,
On the sealing plate, an exterior member that fits the convex portion and covers the exhaust port is disposed,
The sealed battery, wherein the exterior member is covered with a heat-shrinkable resin film together with the outer surface of the battery case.   The sealed battery according to claim 1, wherein the exterior member is made of ethylene propylene diene rubber, fluorine rubber, or acrylic resin.

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