JP2011129451A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

An insulating sheet provided between an inner surface of a positive electrode can and a negative electrode current collector made of copper foil disposed so as to face the positive electrode can is prevented from peeling off in a non-aqueous electrolyte.
An adhesive made of an ionomer resin such as an ethylene-based ionomer resin is used as an adhesive means between one negative electrode current collector opposed to a positive electrode can and an insulating sheet.
[Selection] Figure 2

Description

  The present invention relates to a non-aqueous electrolyte secondary battery in which a laminated electrode body and a non-aqueous electrolyte are accommodated in a battery container, and is applied to a rechargeable ion secondary battery and the like.

  Conventionally, for example, a non-aqueous electrolyte secondary battery as described in Patent Document 1 is known. This is because an electrode having a laminated structure is installed in a battery container sealed by attaching a sealing plate (sealing can) to the opening of a battery can (exterior can) via a gasket and caulking the peripheral edge of the opening. And a non-aqueous electrolyte secondary battery having a coin-shaped appearance. The electrode body of the laminated structure in this battery is composed of a positive electrode obtained by coating a positive electrode material such as lithium cobaltate on both surfaces of a positive electrode current collector formed of an aluminum foil, and a negative electrode current collector formed of a copper foil. A negative electrode formed by applying a negative electrode material such as a coke fired product is alternately laminated via a separator, and the positive electrode is electrically connected to the battery can and the negative electrode is electrically connected to the sealing plate.

  In such a battery, a micro short circuit due to deposition of electrolyte (lithium in the rechargeable ion secondary battery) released from the positive electrode located in the vicinity of the positive electrode can (bottomed case in Patent Document 1, specifically, the battery can). From the viewpoint of prevention, the negative electrode current collector made of copper foil (in Patent Document 1, the negative electrode lead extended from the negative electrode current collector) is disposed at both ends in the stacking direction of the electrode bodies, respectively, A configuration is adopted in which the negative electrode current collector is positioned opposite to the positive electrode can, and the other negative electrode current collector is positioned opposite to the negative electrode can (a sealing case, specifically a sealing plate in Patent Document 1).

Japanese Patent Laying-Open No. 2005-310577

  In the non-aqueous electrolyte secondary battery as described above, in which the negative electrode current collector (including the case of the negative electrode lead) is disposed at both ends in the stacking direction of the electrode body having the multilayer structure, the negative electrode current collector positioned opposite to the negative electrode can The body is set in a state where it is electrically connected to the negative electrode can by bringing it into contact with the inner surface of the negative electrode can, but the negative electrode current collector located opposite the positive electrode can prevents short circuit due to contact between the two. In order to achieve this, it is set so as to face the inner surface of the positive electrode can in a state where an insulating sheet made of an electrically insulating plastic (for example, polyethylene terephthalate (PET)) is interposed between the positive electrode can and the positive electrode can. In that case, the negative electrode current collector made of copper foil and the insulating sheet are bonded in advance in consideration of workability. Conventionally, for example, hot melt made of ethylene-vinyl acetate resin (EVA) is used as the bonding means at that time. An adhesive was used.

  However, a non-aqueous electrolyte secondary battery in which a non-aqueous electrolyte containing ethylene carbonate (EC) and methyl ethyl carbonate (MEC), which is generally used in lithium ion secondary batteries, is contained in a battery container. In the above, the EVA hot melt adhesive as described above is used as an adhesive means between the negative electrode current collector made of copper foil and the insulating sheet. There was a problem of peeling off.

  In order to maintain insulation between the positive electrode can and the negative electrode current collector as described above, for example, an adhesive tape having an adhesive layer on the surface of a polyimide tape base material may be used. . However, when this type of adhesive tape is used, for example, conductive foreign matters (eg, graphite) floating in the air can easily adhere to the adhesive layer portion at the end of the tape, and a short circuit may occur at that portion. There is. On the other hand, in the case of a hot melt adhesive, since it has adhesiveness only when it is in a state of being heated to a predetermined use temperature or higher, it is difficult for foreign matter to cause a short circuit to occur. The reason why the hot melt adhesive is used in the insulating portion between the positive electrode can and the negative electrode current collector is as described above.

  The present invention addresses such problems, an insulating sheet is provided between the inner surface of the positive electrode can and a negative electrode current collector made of copper foil disposed so as to face the positive electrode can, and ethylene In a non-aqueous electrolyte secondary battery in which a non-aqueous electrolyte containing carbonate (EC) and methyl ethyl carbonate (MEC) is used, the insulating sheet does not peel from the negative electrode current collector on the bonding partner side in the electrolyte The purpose is to do so.

  In order to achieve the above object, the present invention is configured as follows. That is, the nonaqueous electrolyte secondary battery of the present invention has a battery container that is sealed by attaching a sealing can to the opening of the outer can through a gasket and caulking the peripheral edge of the opening. In this battery container, a positive electrode formed by forming a positive electrode active material layer on both sides of a positive electrode current collector and a negative electrode formed by forming a negative electrode active material layer on a negative electrode current collector made of copper foil are interposed via a separator. A stacked electrode body formed by alternately stacking a plurality of stages and a nonaqueous electrolytic solution containing ethylene carbonate (EC) and methyl ethyl carbonate (MEC) are accommodated. The positive electrode in the electrode body is electrically connected to one of the outer can and the sealed can. The negative electrode current collectors made of copper foil are respectively disposed at both ends in the stacking direction of the electrode bodies, and one of the negative electrode current collectors of the outer cans or the sealed cans is placed through an insulating sheet. The positive electrode can is opposed to the other negative electrode current collector, and the other negative electrode current collector is opposed to the other can (negative electrode can). Then, an adhesive made of an ionomer resin is used for bonding between the negative electrode current collector facing the positive electrode can and the insulating sheet, and the negative electrode current collector is insulated through the adhesive made of the ionomer resin. The sheet is bonded to the sheet.

  As an adhesive made of an ionomer resin, for example, an ethylene ionomer resin is used, but not limited thereto, for example, a urethane ionomer resin, a styrene ionomer resin, or the like can be used.

  The insulating sheet is made of plastic having electrical insulation properties, but there are cases where terminal members are welded to the outer surface of the positive electrode can, and a certain degree of heat resistance is taken into account in view of the influence of welding heat at that time. What has is preferable and what is hard to receive to the influence of electrolyte solution is further preferable. Representative examples include polyethylene terephthalate (PET), but not limited thereto, polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyimide (PI), polyphenylene sulfide (PPS), polycarbonate (PC). Any of these can be used.

  In the non-aqueous electrolyte secondary battery of the present invention, an adhesive made of an ionomer resin is used for bonding the negative electrode current collector facing the positive electrode can and the insulating sheet. When such an adhesive made of an ionomer resin is used as an adhesive means between the negative electrode current collector and the insulating sheet, the insulating sheet can be used even in a non-aqueous electrolyte containing ethylene carbonate (EC) and methyl ethyl carbonate (MEC). Becomes difficult to peel from the negative electrode current collector. The reason why it is difficult to peel off is unclear at present, but the adhesive made of ionomer resin is ethylene carbonate (EC), which is a component of a non-aqueous electrolyte, compared to the EVA hot melt adhesive that has been used conventionally. It is also considered that it is less susceptible to the influence of methyl ethyl carbonate (MEC) and is less susceptible to deterioration and modification in the electrolysis solution.

It is a longitudinal cross-sectional view which shows the whole structure of the nonaqueous electrolyte secondary battery of this invention. It is a longitudinal cross-sectional view which shows the cross-sectional structure of the nonaqueous electrolyte secondary battery of this invention. It is an exploded view which shows the state before the assembly of a non-aqueous electrolyte secondary battery.

  1 to 3 show a non-aqueous electrolyte secondary battery according to an embodiment in which the present invention is applied to a coin-type lithium ion battery. As shown in FIGS. 1 and 2, the non-aqueous electrolyte secondary battery 1 has a configuration in which a laminated electrode body 3 and a non-aqueous electrolyte (not shown) are accommodated in a battery container 2. As the nonaqueous electrolytic solution, a solution obtained by dissolving LiPF6 in a solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) are mixed at a volume ratio of 1: 2 is used.

  The battery container 2 is sealed by attaching a sealing can 6 to the opening of the outer can 4 via a gasket 5 and caulking the peripheral edge of the opening. That is, the battery container 2 includes a flat round dish-shaped outer can 4 whose peripheral edge 4a is bent upward in FIG. 1, and a flat round dish-shaped sealing can 6 whose peripheral edge 6a is bent downward in FIG. The outer can 4 and the sealing can 6 are configured to be caulked and sealed through a gasket 5 disposed between the peripheral portions 4a and 6a. The outermost peripheral portion (lower portion) of the peripheral edge portion 6a of the sealing can 6 is processed into an inner and outer double helix fold. The outer can 4 and the sealed can 6 are made of stainless steel. The gasket 5 is formed of a synthetic resin that is an insulator. The flat battery 1 in this example has an overall height of 3.5 mm and an outer diameter of 20 mm.

  The electrode body 3 has a configuration in which a plurality of substantially circular positive electrodes 7 and substantially circular negative electrodes 8 are alternately stacked in a vertical direction via a bag-shaped separator 9. Each separator 9 is made of a microporous thin film made of polyethylene having excellent insulating properties, and is capable of transmitting lithium ions. In the illustrated example, the number of stacked layers of the positive electrode 7 and the negative electrode 8 is drawn only for the sake of simplification, but in actuality, about 7 stacked layers are employed in the flat battery of the size described above. However, it is needless to say that the number of stages is not limited to this.

  Each positive electrode 7 is accommodated in a substantially circular flat bag-like separator 9. 2, each positive electrode 7 is provided with a positive electrode active material layer 72 containing a positive electrode active material such as lithium cobaltate on both surfaces of a positive electrode current collector 71 made of aluminum foil. It is a configuration. From each positive electrode current collector 71, a positive electrode lead 71a made of an aluminum foil integrated with the positive electrode current collector 71 is located on the other side of the electrode body 3 (on the left side in FIGS. 1 and 2 opposite to the direction in which the negative electrode lead 81a is led out). It is derived for each. These positive electrode leads 71a are electrically connected to the inner bottom surface of the outer can 4 in the illustrated nonaqueous electrolyte secondary battery, and the outer can 4 is a positive electrode can.

  That is, the inner surface of the outer can 4 located on the side of the electrode body 3 on the side from which the positive electrode lead 71a is led out, specifically, the inner surface of the can serving as an electrical connection between the positive electrode lead 71a and the outer can 4 The positive electrode lead 71a extending from the positive electrode current collector 71 to a portion (in the illustrated example, the inner bottom surface portion of the outer can 4 positioned between the side surface of the electrode body 3 on the side where the positive electrode lead 71a is led out and the gasket 5) A rectangular aluminum foil piece (in the illustrated example, the thickness of the aluminum foil piece is about 15 μm) 11 made of the same kind of aluminum foil is ultrasonically welded. The aluminum foil pieces are ultrasonically welded with the tip portions of the respective positive electrode leads 71a overlapped.

  Negative electrodes 8A and 8B are respectively disposed at both ends (upper and lower ends in FIG. 1) of the electrode body 3 in the stacking direction. Except for the negative electrodes 8A and 8B located at both upper and lower ends, the negative electrode 8 has a configuration in which a negative electrode active material layer 82 containing a negative electrode active material such as graphite is provided on both surfaces of a negative electrode current collector 81 made of copper foil. is there. In the negative electrode 8A located at the upper end of the electrode body 3 in the state of FIG. 1, the negative electrode active material layer 82 is provided only on the lower surface side of the negative electrode current collector 81 as shown in an enlarged view in FIG. The upper surface is in contact with the inner surface of the sealing can 6 in an exposed state. Similarly, in the negative electrode 8 </ b> B located at the lower end of the electrode body 3, the negative electrode active material layer 82 is provided only on the upper surface side of the negative electrode current collector 81.

  From the negative electrode current collector 81 of each of the negative electrodes 8, 8 A, and 8 B, a negative electrode lead 81 a integrated therewith is led out toward one side (right side in FIG. 1) of the electrode body 3. These negative electrode leads 81a are connected to each other by ultrasonic welding or the like in a state where their tips are grouped together. As described above, the negative electrode current collector 81 of the negative electrode 8 </ b> A located at the upper end of the electrode body 3 is in contact with the inner surface of the sealing can 6, and thus each negative electrode 8, 8 </ b> A, 8 </ b> B is electrically connected to the sealing can 6. That is, the sealing can 6 is a negative electrode can.

  Between the negative electrode current collector 81 of the negative electrode 8 </ b> B located at the lower end of the electrode body 3 and the inner bottom surface 4 b of the outer can 4, an insulating sheet 10 for preventing a short circuit is disposed. In the illustrated battery, the insulating sheet 10 is made of polyethylene terephthalate (PET), and is more in place than the negative electrode current collector 81 in order to reliably prevent a short circuit at the periphery of the negative electrode current collector 81 of the negative electrode 8B. Larger areas are used for quantitative purposes.

  The surface on the inner bottom surface 4 b side of the outer can of the insulating sheet 10 is merely in contact with the inner bottom surface 4 b, but the surface on the negative electrode current collector 81 side of the negative electrode 8 B is bonded to the negative electrode current collector 81. . As the means for adhering the insulating sheet 10 to the negative electrode current collector 81, in the battery of this example, an adhesive made of an ethylene ionomer resin is used as an adhesive made of an ionomer resin. An adhesive layer (hereinafter also simply referred to as an adhesive layer) 12 is interposed between the negative electrode current collector 81 and the insulating sheet 10. In the battery of this example, for the purpose of improving the adhesion between the insulating sheet 10 made of PET and the adhesive layer 12, a layer made of polyethylene (PE) (hereinafter also simply referred to as a PE layer) is provided between them. .) 13 is interposed. When the thickness of each layer in this case is illustrated, the insulating sheet 10 is 50 μm, the PE layer 13 is 25 μm, and the adhesive layer 12 is 25 μm.

  According to such a configuration, as long as the insulating sheet 10 exists between the outer can 4 serving as the positive electrode can and the negative electrode current collector 81 positioned opposite to the outer can 4, a short circuit between the two can be performed by the insulating sheet 10. However, if the insulating sheet 10 adhered to the negative electrode current collector 8 is peeled off, a displacement occurs between the negative electrode current collector 81 and the insulating sheet 10, and as a result, the negative electrode current collector A short circuit occurs when the electric body 81 comes into contact with the outer can 4. However, in the battery of this example, as described above, an adhesive made of an ionomer resin is used as an adhesive means between the insulating sheet 10 and the negative electrode current collector 81, and these include the adhesive layer 12 and the insulating sheet 10. Since it is bonded through the PE layer 13 used for the purpose of improving the adhesiveness of ethylene carbonate (EC) and methyl as compared with the conventional one using an EVA-based hot melt adhesive Insulating sheet 10 becomes difficult to exfoliate in nonaqueous electrolyte containing ethyl carbonate (MEC). Therefore, it is possible to reliably prevent a short circuit due to contact between the outer can 4 serving as the positive electrode can and the negative electrode current collector 81 positioned opposite thereto.

  In order to investigate the adhesive effect when used in a non-aqueous electrolyte containing ethylene carbonate (EC) and methyl ethyl carbonate (MEC), an adhesive composed of the above ionomer resin and a conventional EVA hot melt are used. The following tests were performed on the adhesive. That is, using these adhesives, an electrode body sample was prepared by bonding the above-mentioned PET insulating sheet to the negative electrode current collector 81 made of copper foil at the end, and these were prepared at room temperature (25 ° C.) for 24 hours. After being immersed in the electrolytic solution, it was taken out and examined for changes in the adhesion state. As a result, in the case of using the EVA hot melt adhesive, there was a case where the insulating sheet (PET layer) was peeled off at the time of taking out, but in the case of using the adhesive made of an ionomer resin. There was no one that caused delamination.

  Finally, assembly of the non-aqueous electrolyte secondary battery 1 will be described. When the non-aqueous electrolyte secondary battery 1 is assembled, the flat circular dish-shaped sealing can 6 is placed on the lower side (in other words, the opening of the sealing can 6 is directed upward), contrary to the state of FIG. In this order, the gasket 5 is attached, a non-aqueous electrolyte (not shown) is injected, the outer can 4 with the electrode body 3 previously attached in a predetermined state is assembled, and the caulking sealing is performed. Specifically, this is performed as follows.

  First, with the opening of the sealing can 6 facing upward, the gasket 5 is attached to the peripheral edge 6a. On the other hand, for the outer can 4, an aluminum foil piece 11 is ultrasonically welded in advance to a predetermined position near the peripheral edge 4 a of the inner bottom surface 4 b. Further, the insulating sheet 10 is bonded to the surface of the negative electrode current collector 81 in the negative electrode 8B located in the outermost layer of the electrode body 3 through the hot melt layer 12 and the PE layer 13. And the positive electrode lead 71a of the electrode body 3 and the armored can 4 are electrically connected by ultrasonic welding in the state which accumulated the front end side of the positive electrode lead 71a of the electrode body 3 on the said aluminum foil piece 11. FIG.

  Next, after injecting a non-aqueous electrolyte into the sealing can 6 equipped with the gasket 5, the negative electrode current collector 81 in the negative electrode 8B is formed on the outer bottom surface of the gasket 5 with the opening facing downward and the inner bottom surface 4b. After the outer can 4 is fitted with the insulating sheet 10 facing each other, the peripheral edge 4a of the outer can 4 is crimped inward. With this caulking process, the gasket 11 is compressed, and the gap between the outer can 4 and the sealing can 6 is sealed by the gasket 11. Thus, the outer can 4 and the sealing can 6 are caulked and sealed with the gasket 11 interposed therebetween, and the nonaqueous electrolyte battery 1 as shown in FIG. 1 is obtained.

  In the illustrated non-aqueous electrolyte secondary battery 1, the stainless steel outer can 4 is used, but the same configuration can be used when an iron outer can is used. In addition, the nonaqueous electrolyte secondary battery 1 in the illustrated example is one when the outer can 4 is on the positive electrode side, but when the sealing can 6 is on the positive electrode side, that is, the positive electrode lead 71a is made of stainless steel or iron. Needless to say, the present invention can also be applied to a secondary battery electrically connected to a sealing can.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Battery container 3 Stacked-type electrode body 4 Outer can 4a Peripheral part 4c of outer can The inner bottom part (outer bottom part of can) of outer can
DESCRIPTION OF SYMBOLS 5 Gasket 6 Sealing can 7 Positive electrode 71 Positive electrode collector 72 Positive electrode active material layer 71a Positive electrode lead 8 Negative electrode 81 Negative electrode collector 82 made of copper foil Negative electrode active material layer 9 Separator 10 Insulation sheet 11 Aluminum foil piece 12 Adhesive layer

Claims (3)

A battery container sealed by attaching a sealing can to the opening of the outer can via a gasket and caulking the peripheral edge of the opening,
In the battery container, a positive electrode formed by forming a positive electrode active material layer on both surfaces of the positive electrode current collector and a negative electrode formed by forming a negative electrode active material layer on the negative electrode current collector made of copper foil are alternately arranged via separators. And a non-aqueous electrolyte containing ethylene carbonate and methyl ethyl carbonate are housed in a multi-layer laminated body.
While the positive electrode in the electrode body is electrically connected to one of the outer can or the sealed can,
The negative electrode current collectors made of copper foil are respectively disposed at both ends in the stacking direction of the electrode bodies, and one of the negative electrode current collectors is an outer can or a sealed can through an insulating sheet. The other negative electrode current collector is in a position facing the other can (negative electrode can),
The non-aqueous electrolyte secondary battery, wherein the one negative electrode current collector and the insulating sheet are bonded via an adhesive made of an ionomer resin.   The non-aqueous electrolyte secondary battery according to claim 1, wherein any one of ethylene ionomer resin, urethane ionomer resin, and styrene ionomer resin is used as the adhesive made of ionomer resin.   The insulating sheet is made of any one of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyimide (PI), polyphenylene sulfide (PPS), and polycarbonate (PC). Or the nonaqueous electrolyte secondary battery of 2.

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