JP2010212206A - Flat secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat secondary battery in which filling work of liquid or the like can be carried out efficiently and welding reliability at the ultrasonic welding part of a can (positive electrode can) on the positive electrode terminal side and a positive electrode lead can be secured, and furthermore, corrosion at the edge portion of the positive electrode can hardly occurs, while installation work of an insulting tape can be dispensed with. <P>SOLUTION: A positive electrode lead of aluminum foil integrated with each of positive electrode current collectors is led out from those of an electrode body to the side direction of the electrode body, and tip parts of these are welded to the inner face of a sealing can, and a negative electrode current collector is arranged at the end face on the opposing side to the inner face of an outer package can in the lamination direction of the electrode body, and is electrically connected to the inner face of the outer package can, thereby the sealing can is placed on the positive electrode side and the outer package can is placed on the negative electrode side. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a flat secondary battery in which a laminated electrode body and a nonaqueous electrolytic solution (hereinafter also simply referred to as “electrolytic solution”) are accommodated in a flat battery container. Applicable.

  As this type of flat secondary battery, for example, a coin-type secondary battery as described in Patent Document 1 is known. This is caulked and sealed by attaching a sealing can (sealing plate) to the opening of an outer can (battery can in the same document 1) via a gasket and tightening the peripheral edge of the opening from the outside to the inside. In the battery container, a laminated electrode body (electrode group) and a non-aqueous electrolyte are accommodated to form a 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 coating a negative electrode material such as a coke baked product with a separator alternately stacked, and a positive electrode lead made of an aluminum foil extended from the positive electrode current collector is attached to the outer can. Negative electrode leads made of copper foil extending from the electric body are electrically connected to the sealing cans.

Japanese Patent Laying-Open No. 2005-310577 (pages 5-7, FIGS. 1-4)

  In the coin-type secondary battery described above, in order to electrically connect the positive electrode lead extended from the positive electrode current collector to the outer can on the positive electrode terminal side (that is, for current collection), The positive electrode lead is ultrasonically welded to the inner surface. This is because the electrical resistance at the contact portion is larger than the case of welding and the current collection efficiency is poor only by bringing the positive electrode lead made of aluminum foil into contact with the outer can. However, in the case of a battery structure in which the outer can is used as the positive electrode side, that is, the positive electrode terminal side (positive electrode can), and the positive electrode lead extended from the positive electrode current collector of the electrode body is welded to the outer can. The following problems occur in the liquid injection process (step of injecting the electrolyte into the can constituting the battery container).

  That is, when injecting an electrolytic solution into a battery container composed of an outer can and a sealing can as described above, in general, a method of injecting an electrolytic solution into an opening of the outer can and facing upward, and a sealing It can be considered that the opening of the can faces upward and the electrolytic solution is injected into this. However, if the positive electrode lead of the electrode body is welded to the outer can, the electrode body is usually accommodated in the outer can. The method of injecting the electrolytic solution, that is, the former method must be taken. For this reason, when the sealing can is fitted into the opening of the outer can after the injection of the electrolytic solution, the electrolytic solution in the outer can overflows to the outside. Since it is necessary to work while paying attention so as not to generate waste as much as possible, there arises a problem that the work efficiency is lowered. It is also conceivable that the electrode body is temporarily fixed to the inner surface of the outer can by some method, and the outer can is covered with the sealing can into which the electrolytic solution has been injected. Therefore, it is inevitable that the electrolytic solution overflows to the outside by the volume excluded by the electrode body.

  In the coin-type secondary battery described in Patent Document 1, the positive electrode lead made of aluminum foil extended from the positive electrode current collector is ultrasonically welded to the inner surface of the outer can. If the outer can is made of different types of metals such as stainless steel, joining of aluminum and different types of metals such as stainless steel makes ultrasonic welding not easy and poor welding tends to occur. For this reason, the above coin-type secondary battery uses an outer can made of a clad made of aluminum on the inner surface and stainless steel on the outer surface, and an aluminum foil positive electrode lead is ultrasonically welded to the inner surface aluminum portion of the outer can. Doing what to do.

  However, when using an outer can made of a clad material whose inner surface is made of aluminum and the outer surface is made of stainless steel as described above, an aluminum unim on the inner surface is formed at the edge (edge portion) of the peripheral portion of the outer can in the assembled state as a battery container. The portion and the stainless steel portion on the outer surface side are exposed to the outside, or are located at a site that is susceptible to intrusion of water droplets or the like. If water droplets or the like adhere to the edge portion of such an outer can, a so-called local cell is formed, and the aluminum portion is easily corroded. When the corrosion further progresses, the electrolyte leaks from the corroded portion. There is a risk.

  By the way, in the flat type secondary battery having the laminated electrode body as described above, in order to electrically connect the negative electrodes of the respective stages (each layer) constituting the electrode body, it has been described above. A negative electrode lead integrated with the negative electrode current collector is led out from each negative electrode current collector in a direction opposite to the direction in which the positive electrode lead is led out, and these are integrated by welding on the side of the electrode body. When such a lead-out portion of the negative electrode lead comes into contact with the inner surface of the can on the positive electrode terminal side (battery can in the above-mentioned coin-type secondary battery), a short circuit occurs. It is necessary to take measures such as covering with insulating tape. However, if this type of insulating tape is attached to each battery, the work efficiency is low, and it is desirable to eliminate the need for attaching the insulating tape or the like in order to increase productivity as a whole.

  The present invention addresses the above-described problems in a flat secondary battery having a laminated electrode body, and the electrolyte solution is injected when the electrolyte solution is injected into the can constituting the battery container in the battery assembly process. A flat secondary battery with a structure that is easy to carry out liquid injection work and subsequent assembly work between the outer can and the sealing can. This is the first purpose. In addition to achieving the first object, the present invention can ensure welding reliability in the ultrasonic welded portion between the positive electrode terminal can (positive electrode can) and the positive electrode lead, and at the same time, corrosion at the edge of the positive electrode can. It is a second object to realize a flat secondary battery that is less likely to cause the problem. A third object of the present invention is to realize a flat secondary battery that can eliminate the above-described work of attaching an insulating tape after achieving these objects.

  In order to achieve the above object, the present invention attaches a sealing can to the opening of the outer can via a gasket (the outer can can be opened as a result of covering the opening edge of the sealing can via the gasket). Including a case in which a sealing can is attached to a part via a gasket) and tightening the peripheral edge of the opening from the outside to have a caulking-sealed battery container, and the battery container includes an aluminum foil A positive electrode in which a positive electrode active material layer is formed on both sides of a positive electrode current collector composed of a negative electrode and a negative electrode in which a negative electrode current collector is formed with a negative electrode active material layer are alternately stacked in multiple stages via a separator. A flat-type secondary battery in which a laminated electrode body and a non-aqueous electrolyte are accommodated is configured as follows.

  That is, from each positive electrode current collector, a positive electrode lead made of an aluminum foil integral with the positive electrode current collector is led out to the side of the electrode body, and the tip portion thereof is welded to the inner surface of the sealing can. Alternatively, from each positive electrode current collector, an aluminum foil positive electrode lead integrated with the positive electrode lead is directed toward the side of the electrode body, and the other positive electrode lead is welded to the specific positive electrode lead, and then the specific positive electrode The tip of the lead is welded to the inner surface of the sealed can. Then, a negative electrode current collector is disposed on the end surface facing the inner surface of the outer can in the stacking direction of the electrode bodies, and is electrically connected to the inner surface of the outer can. In this way, the sealing can constituting the battery container is the positive electrode side (positive electrode can) and the outer can is the negative electrode side (negative electrode can), in other words, the sealing can serves also as the positive electrode terminal, and the outer can serves as the negative electrode terminal. .

  Specifically, the sealing can is formed of a clad material made of other metal such as aluminum on the inner surface side and stainless steel on the outer surface side, and the positive electrode lead or the specific positive electrode is formed on the aluminum portion on the inner surface side. The lead tip is ultrasonically welded. In this case, it is desirable to form an insulating oxide film on the surface of the aluminum portion on the inner surface side of the sealing can by anodizing (so-called alumite treatment). The thickness of the insulating oxide film at this time is 50 μm or more and 100 μm or less as a range in which a short circuit can be prevented when the sealing can and the negative electrode side component (for example, the negative electrode lead derived from the negative electrode) are in contact with each other. It is preferable to do this.

  In addition, about the above-mentioned "attaching a sealing can to the opening part of an exterior can via a gasket", what is necessary is just to become such an attachment state as a result. In other words, “attach the sealing can through the gasket to the opening of the outer can” attaches the gasket to the peripheral portion of the opening of the sealing can, and covers the outer can from the mounting as described above The gasket is attached to the peripheral portion of the opening of the sealed can, and the opening side of the sealed can with the gasket is fitted into the outer can with the opening facing downward. The case where such a wearing state is set is also included.

  In the flat secondary battery of the present invention, the tip of each positive electrode lead or the tip of a specific positive electrode lead is ultrasonically welded to a sealing can attached to the opening of the outer can via a gasket. Since the can is the positive electrode side, that is, the positive electrode can also serving as the positive electrode terminal, a sealing can (a gasket is attached in advance to the peripheral portion of the sealing can in the liquid injection step of injecting the non-aqueous electrolyte into the battery container. The electrolytic solution can be easily injected into the sealing can in a state where the opening is placed upward and the electrode body is accommodated therein.

  Then, after the injection, the sealing can filled with the electrode body and filled with the electrolyte is covered with the outer can with the opening facing downward, or the opening of the outer can with the facing downward is placed in the opening. By fitting the peripheral edge of the sealing can with the opening facing upward from the lower side, the sealing can and the outer can can be relatively easily made without causing any or almost overflowing of the electrolyte from the sealing can. Can be assembled in a predetermined state (a state in which caulking can be sealed in the next step). That is, when the sealing can is fitted in the opening of the outer can filled with the electrolytic solution, or when the outer can with the electrode body temporarily fixed is put on the sealing can filled with the electrolytic solution and assembled. The outer can and the sealed can are kept in a predetermined state (next) without causing a situation in which the electrolyte of the other can overflows due to the peripheral portion of the other can entering one can filled with the liquid. It is possible to efficiently assemble it in a caulking sealable state in the process. In addition, the outer can and the sealing can assembled in a predetermined state in this manner are caulked and sealed by tightening the peripheral edge of the outer can from the outside to the inside.

  Thus, according to the flat secondary battery of the present invention, the overflow of the electrolyte in the liquid injection process can be avoided or suppressed to a small amount, and the liquid injection operation and the subsequent assembly of the outer can and the sealing can can be performed. Work can be done easily. Therefore, not only can the loss due to the overflow of the electrolyte in the liquid injection process be reduced, but the working efficiency can be improved.

  Further, in the above-described flat secondary battery, the sealing can which is a positive electrode can is formed of a clad material made of other metal such as aluminum on the inner surface side and stainless steel on the outer surface side, and the aluminum portion on the inner surface side of the clad material When the tip of the positive electrode lead or the specific positive electrode lead is ultrasonically welded, the ultrasonic welding of the inner surface aluminum portion of the sealing can and the positive electrode lead made of aluminum foil is a welding of aluminum. For this reason, for example, the welding defect like the case where the positive electrode lead made of aluminum foil is ultrasonically welded to the inner surface of a stainless steel sealing can which is generally used is unlikely to occur.

  Moreover, in the state where the sealing can as the positive electrode can and the outer can as the negative electrode can are assembled into a battery as described above, the peripheral portion of the sealing can is located inside the peripheral portion of the outer can, and The edge part is covered with a gasket interposed between them and sealed so as to maintain an airtight and liquid tight state, so that external water droplets and the atmosphere do not touch the edge part of the sealing can. it can. Therefore, in this case, even though a sealing can as a positive electrode can is formed by a clad material in which the inner surface side is made of aluminum and the outer surface side is made of other kinds of metal such as stainless steel, local cells are formed at the edge portion. As a result, the occurrence and progression of corrosion accompanying the formation of such local cells can be prevented or suppressed.

  Thus, in the present invention, the sealing can which is a positive electrode can is formed of a clad material having an inner surface side made of aluminum and an outer surface side made of another metal such as stainless steel, and the positive electrode lead or When the tip of a specific positive electrode lead is ultrasonically welded, the welding reliability of the ultrasonic weld between the positive electrode terminal can (positive electrode can) and the positive electrode lead can be ensured, and at the same time, the positive electrode can It is possible to realize a flat secondary battery in which corrosion at the edge portion is less likely to occur.

  Furthermore, in the above-described flat secondary battery, when an anodizing treatment (so-called anodized treatment) is performed on the surface of the aluminum portion on the inner surface side of the sealing can serving as a positive electrode can, an electrically insulating oxide film is formed. Even if the negative electrode side component such as the negative electrode lead contacts the inner surface of the sealing can (positive electrode can), the short circuit can be prevented by the presence of the electrically insulating oxide film formed on the inner surface. Therefore, in order to prevent this type of short circuit, it is not necessary to perform an operation such as covering the negative electrode lead or the like with an insulating tape for each battery during battery assembly. On the other hand, the anodizing treatment on the inner surface aluminum portion of the sealing can is continuously performed in the flow operation at the stage of a single sealing can before being assembled as a battery or at the stage of a plate-like work before being formed on the sealing can. Or a large number of them can be performed together, so that the work efficiency is far better than the above-described work of attaching the insulating tape.

  In addition, if the thickness of the insulating oxide film is 50 μm or more, it is possible to prevent a short circuit when a sealing can and a constituent member on the negative electrode side (for example, a negative electrode lead led out from the negative electrode) contact each other.

It is a longitudinal cross-sectional view which shows the whole structure of the flat battery which concerns on 1st Example of this invention. FIG. 3 is an enlarged longitudinal sectional view showing a periphery of a welded portion of a positive electrode lead in the flat battery according to the first embodiment of the present invention. It is an exploded view which shows the state before the assembly of the flat battery which concerns on 1st Example of this invention. It is an exploded view which shows the state before the assembly of the flat battery which concerns on 2nd Example of this invention. It is a longitudinal cross-sectional view which shows only a part of flat battery which concerns on the modification of this invention.

First Embodiment FIGS. 1 to 3 show a flat secondary battery according to a first embodiment in which the present invention is applied to a coin-type lithium ion battery. As shown in FIGS. 1 and 2, the flat 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.

  The battery container 2 is caulked and sealed by attaching a sealing can 6 to the opening of the outer can 4 via a gasket 5 and tightening the peripheral edge of the opening of the outer can 4 from the outside to the inside. That is, the battery container 2 includes a flat round dish-shaped outer can 4 whose peripheral edge 4a is bent downward in FIG. 1, and a flat round dish-shaped sealing can 6 whose peripheral edge 6a is bent upward 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 (upper portion in FIG. 1) of the peripheral edge portion 6 a of the sealing can 6 is processed into an inner and outer double-folded fold, and its end (edge portion) 6 b is completely sealed by the gasket 5. Liquid-tight and air-tight. The outer can 4 is 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 shown only for the sake of simplicity, but in actuality, the number of stacked layers of about 7 to 10 is used 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.

  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 (direction orthogonal to the stacking surface). Except for the negative electrodes 8A and 8B located at both upper and lower ends, the negative electrode 8 is provided with a negative electrode active material layer 82 containing a negative electrode active material such as graphite on both surfaces of a negative electrode current collector 81 made of a metal foil such as copper. It is a configuration. In the negative electrode 8A located at the upper end of the electrode body 3 in the state of FIGS. 1 and 2, the negative electrode active material layer 82 is provided only on the lower surface side of the negative electrode current collector 81, and the upper surface on the opposite side is exposed. It is in contact with the inner surface 4b of the facing outer can 4. 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. 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 6 c of the sealing can 6, an insulating seal 10 for preventing a short circuit is disposed. The insulating seal 10 is made of an insulating tape made of polyethylene or polypropylene.

  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 in which their tip portions are grouped together. In this state, as described above, the negative electrode current collector 81 of the negative electrode 8A located at the upper end of the electrode body 3 is in contact with the inner surface 4b of the outer can 4 facing the negative electrode 8A. 8A and 8B are electrically connected to the outer can 4, and the outer can 4 is a negative electrode side, that is, a can also serving as a negative electrode terminal (negative electrode can).

  Each positive electrode 7 is accommodated in a substantially circular flat bag-like separator 9. Each positive electrode 7 has a configuration in which a positive electrode active material layer 72 containing a positive electrode active material such as lithium cobaltate is provided on both surfaces of a positive electrode current collector 71 formed of an aluminum foil. 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.

  In the flat secondary battery of the present invention, the end on the lead-out side, that is, the front end of the positive electrode lead 71a is electrically connected to the inner bottom surface 6c of the sealing can 6, so that the sealing can 6 is The can is also used as the positive electrode side, that is, the positive electrode terminal (positive electrode can). More specifically, the sealing can 6 in this embodiment is formed of a clad material whose inner surface side is aluminum 6d and whose outer surface side is stainless steel 6e. Among these, the surface of the aluminum 6d portion on the inner surface side is subjected to anodizing treatment (alumite treatment), so that an aluminum oxide film having electrical insulation (in this embodiment, the film thickness t is about 50 μm). (See a partially enlarged view in FIG. 3) 6f is formed. The tip 71b of each positive electrode lead 71a described above is ultrasonically welded to the inner bottom surface 6c of the sealing can 6, that is, the surface of the aluminum 6d portion on which the oxide film 6f is formed. And the sealing can 6 are electrically connected to each other so that the sealing can 6 has a polarity opposite to that of the conventional flat secondary battery. Here, when ultrasonic welding is difficult due to the presence of the oxide film 6f, the oxide film 6f at the place to be welded may be formed thinner than the other parts.

  As shown in FIG. 3, the flat secondary battery 1 is assembled with the flat round dish-shaped sealing can 6 facing down (in other words, with the opening of the sealing can 6 facing upward). (1) Ultrasonic welding of the positive electrode lead 71a in the electrode body 3 → (2) Mounting of the gasket 5 → (3) Injection of a non-aqueous electrolyte (not shown) → (4) Assembly of the outer can 4 → (5 ) Perform in the order of caulking. Specifically, this is performed as follows. Although the order of (1) and (2) may be reversed, here, the case where they are performed in the above order will be described.

  First, with the opening portion of the sealing can 6 facing up, the laminated electrode body 3 is temporarily fixed to the inner bottom surface 6 c via the insulating seal 10. The electrode body 3 is temporarily fixed by, for example, providing an adhesive layer on both surfaces of the insulating seal 10 in advance, and the negative electrode current collector 81 and the inner bottom surface of the sealing can 6 in the negative electrode 8B located on the outermost layer of the electrode body 3. It can be performed by interposing the insulating seal 10 between 6c. Further, each positive electrode lead 71a of the electrode body 3 is electrically connected to a predetermined portion of the inner bottom surface 6c of the sealing can 6 by ultrasonic welding in a state where these tip portions are overlapped. In this case, the inner surface side of the sealing can 6 is made of aluminum 6d, and each positive electrode lead 71a is made of aluminum foil. Therefore, ultrasonic welding can be performed relatively easily by joining aluminum. An oxide film 6f by anodization is formed on the surface of the inner surface aluminum portion 6d of the sealing can 6, and the film thickness t is about 50 μm.

Next, after mounting the gasket 5 on the peripheral edge 6 a of the sealing can 6, a predetermined amount of nonaqueous electrolyte is injected into the sealing can 6. After this liquid injection is completed, the outer can 4 with the opening facing downward is fitted into the outer side of the gasket 5, and the peripheral edge 4 a of the outer can 4 is tightened from the outer side to the inner side to seal it with caulking. At this time, the gasket 5 is compressed, and the gap between the outer can 4 and the sealing can 6 is sealed in an airtight / liquidtight state by the gasket 5. Thus, the outer can 4 and the sealing can 6 are caulked and sealed with the gasket 5 interposed therebetween, and the flat secondary battery 1 of the present invention shown in FIG. 1 is obtained. As the non-aqueous electrolyte solution, for example, it can be used those obtained by dissolving LiPF ₆ in a solvent mixture of ethylene carbonate and methyl ethyl carbonate.

  The flat secondary battery 1 of the present invention is assembled as described above, and in the process, as described above, the operation of injecting the non-aqueous electrolyte into the sealing can 6 and the subsequent assembly of the outer can 4 Is done. In that case, when the positive electrode lead 71a of the electrode body 3 is welded to the outer can 4 and the outer can 4 is a positive electrode can as in the past, the outer can 4 is assembled to the sealing can 6 from above. When the sealing can 6 is assembled to the outer can 4 from the lower side, the electrode body 3 is stored in the sealing can 6 containing the electrolytic solution. Only the problem that the electrolyte overflows from the sealed can 6 arises.

  However, in the flat secondary battery 1 of the present invention, the positive electrode lead 71a of the electrode body 3 is ultrasonically welded to the inner bottom surface 6c of the sealing can 6, and the sealing can 6 serves as a positive electrode can also serving as a positive electrode terminal. . Therefore, as described above, in the state where the electrode body 3 is accommodated in the sealing can 6 and the electrolytic solution is injected, the outer can 4 is covered with the opening portion facing downward, or the outer can 4 facing downward. By fitting the peripheral edge of the sealing can 6 with the opening facing upward from the lower side into the opening of the sealing can 6, there is little or no overflow of the electrolyte from the sealing can 6 and relatively easily The sealed can 6 and the outer can 4 can be assembled in a predetermined state. Thus, according to the flat secondary battery 1 of the present invention, the overflow of the electrolyte in the liquid injection process can be avoided or suppressed to a small amount, and the liquid injection work and the subsequent outer can 4 and the sealing can 6 can be performed. Can be easily assembled. That is, not only can the loss due to overflow of the electrolyte in the liquid injection process be reduced, but also the work efficiency can be improved.

  Moreover, in the state assembled as a battery in this way, as shown in an enlarged view in FIG. 2, the peripheral portion 6a of the sealing can 6 is covered with the outer can 4 and is positioned inside the peripheral portion 4a. In addition, since the edge portion 6b is covered by the gasket 5 interposed therebetween and sealed so as to maintain an airtight / liquid-tight state, external water droplets and the air are sealed. Contact with the edge portion 6b of the can 6 can be prevented. For this reason, in the flat secondary battery 1 of the present embodiment, the sealing can 6 that is a positive electrode can has an edge that is formed by a clad material of aluminum 6d on the inner surface side and stainless steel 6e on the outer surface side. The formation of local cells in the portion 6b can be avoided, and as a result, the occurrence and progression of corrosion associated with the formation of such local cells can be prevented or suppressed.

  In addition, in the flat secondary battery 1 described above, an electrically insulating oxide film 6f is formed on the surface of the aluminum 6d portion on the inner surface side of the sealing can 6 serving as a positive electrode can by anodizing treatment (so-called alumite treatment). Therefore, even if the weld joint portion of the negative electrode lead 81a led out from the negative electrode 8 contacts the inner surface of the sealing can (positive electrode can) 6, a short circuit is caused by the presence of the electrically insulating oxide film 6f. Will not occur. Accordingly, in order to prevent such a short circuit, an operation such as covering the negative electrode lead or the like with an insulating tape for each individual battery at the time of battery assembly becomes unnecessary. On the other hand, the anodic oxidation treatment as described above is performed continuously in the flow operation at the stage of the single sealed can 6 before being assembled as a battery or at the stage of the plate-like work before being formed on the sealed can 6 or Since a large number can be performed together, the working efficiency is far better than the above-described work of attaching the insulating tape for preventing the short circuit. In this case, the thickness of the insulating oxide film 6f formed by the anodizing process is about 50 μm.

(Second Example) In the above example, as shown in FIG. 1 and FIG. 2, the positive electrode lead 71a led out from each positive electrode current collector 71 is sealed in the sealed can 6 in a state in which the tip parts 71b are overlapped. In the inside, the inner bottom surface 6c located on the side of the electrode body 3 is connected by ultrasonic welding, but the connection structure between the positive electrode lead 71a and the sealing can 6 is not limited to this. For example, like the flat secondary battery according to the second embodiment shown in FIG. 4, the positive electrode lead 71 a made of aluminum foil integrated with the positive electrode current collector 71 in the electrode body 3 is connected to the side of the electrode body 3. Of the positive electrode lead (a positive electrode lead 71c derived from the uppermost positive electrode current collector as the positive electrode current collector 71 in FIG. 4 and longer than the other positive electrode leads 71a). The other positive electrode lead 71a is welded to the formed one), and the tip 71d of the specific positive electrode lead 71c is positioned below a predetermined portion of the inner bottom surface 6c of the sealing can 6 (in the illustrated example, below the insulating sheet 10). It is good also as a structure which ultrasonically welds to the center part which carries out. Other configurations are the same as in the case of the first embodiment, so the corresponding parts are denoted by the same reference numerals and description thereof is omitted.

  According to such a configuration, by welding the other positive electrode lead 71a to the specific positive electrode lead 71c in advance, only the tip 71d of the specific positive electrode lead 71c is connected to the inner bottom surface 6c of the sealing can 6 at the time of battery assembly. Therefore, the welding operation is facilitated as compared with the case where the plurality of positive electrode leads 71a are superposed on the inner bottom surface 6c of the sealing can 6 and ultrasonically welded (in the case of the first embodiment).

(Modification) In the first embodiment, as shown in FIGS. 1 and 2, the negative electrode current collector 81 of the negative electrode 8A located at the upper end directly contacts the inner surface of the outer can 4 facing the negative electrode current collector 81. However, as shown in FIG. 5, a conductive compression spring member (in the illustrated example in plan view) is provided between the negative electrode current collector 81 in the negative electrode 8A located at the upper end and the inner surface of the outer can 4 facing the negative electrode current collector 81. A cross-shaped disc spring) 20 may be mounted in a compressed state, and the negative electrode current collector 81 and the inner surface 4b of the outer can 4 opposed thereto may be electrically connected via the compression spring member 20. . In this case, even if there is a slight change between the negative electrode current collector 81 and the inner surface 4b of the outer can 4 opposed to the negative electrode current collector 81, the compression spring member 20 follows these and deforms in the expansion / expansion direction. The electric body 81 and the inner surface 4b of the outer can 4 opposed to the electric body 81 are always maintained in an electrically connected state.

DESCRIPTION OF SYMBOLS 1 Flat secondary battery 2 Battery container 3 Stacked type electrode body 4 Outer can 4a Peripheral part 5 of outer can 5 Gasket 6 Sealing can 6d Aluminum 6e on the inner surface side of the sealing can Oxide film 7 positive electrode 71 positive electrode current collector 72 positive electrode active material layer 71a positive electrode lead 71c specific positive electrode lead 8 negative electrode 81 negative electrode current collector 82 negative electrode active material layer 9 separator t thickness of electrically insulating oxide film

Claims (5)

It has a battery container that is caulked and sealed by attaching a sealing can to the opening of the outer can through a gasket and tightening the periphery of the opening from the outside,
In the battery container, a positive electrode in which a positive electrode active material layer is formed on both sides of a positive electrode current collector made of aluminum foil and a negative electrode in which a negative electrode current collector is formed with a negative electrode active material layer are interposed via a separator. A flat-type secondary battery in which a stacked electrode body formed by alternately stacking a plurality of layers and a nonaqueous electrolyte solution are housed,
From each positive electrode current collector, a positive electrode lead made of an aluminum foil integral with this is led out to the side of the electrode body, and their tips are welded to the inner surface of the sealing can,
The negative electrode current collector is disposed on the end surface on the side facing the inner surface of the outer can in the stacking direction of the electrode body, and is electrically connected to the inner surface of the outer can.
A flat secondary battery characterized in that the sealing can is on the positive electrode side and the outer can is on the negative electrode side. It has a battery container that is caulked and sealed by attaching a sealing can to the opening of the outer can through a gasket and tightening the periphery of the opening from the outside,
In the battery container, a positive electrode formed by forming a positive electrode active material layer on both sides of a positive electrode current collector made of aluminum foil and a negative electrode formed by forming a negative electrode active material layer on the negative electrode current collector are interposed via a separator. A flat-type secondary battery in which a stacked electrode body formed by alternately stacking a plurality of layers and a nonaqueous electrolyte solution are housed,
From each positive electrode current collector, a positive electrode lead made of an aluminum foil integral with the positive electrode lead is led out to the side of the electrode body, and the other positive electrode lead is welded to the specific positive electrode lead, and then the specific positive electrode While the tip of the lead is welded to the inner surface of the sealing can,
The negative electrode current collector is disposed on the end surface facing the inner surface of the outer can in the stacking direction of the electrode body, and is electrically connected to the inner surface of the outer can.
A flat secondary battery characterized in that the sealing can is on the positive electrode side and the outer can is on the negative electrode side.   The sealing can is formed of a clad material whose inner surface is made of aluminum and whose outer surface is made of another kind of metal, and the tip portion of the positive electrode lead is ultrasonically welded to the aluminum portion of the inner surface. The flat secondary battery according to claim 1 or 2.   The flat secondary battery according to claim 3, wherein an insulating oxide film is formed on the surface of the aluminum portion on the inner surface side of the sealing can by anodizing.   The flat secondary battery according to claim 4, wherein the insulating oxide film has a thickness of 50 to 100 μm.

Images