Flat battery

Abstract

To provide a flat battery that can have higher capacity.SOLUTION: A flat battery 1 includes an outer can 10, a sealing can 20, and an electrode body 40 accommodated between the outer can 10 and the sealing can 20. The electrode body 40 includes an electrode body main body 41, a positive electrode connection part 42, and a negative electrode connection part 43. The negative electrode connection part 43 is dispersed into a first negative electrode connection part 43a and a second negative electrode connection part 43b. The positive electrode connection part 42 is disposed between the first negative electrode connection part 43a and the second negative electrode connection part 43b and extends outward from a cutoff part 41a of the electrode body main body 41 together with the first negative electrode connection part 43a and the second negative electrode connection part 43b. The first negative electrode connection part 43a is formed by bundling a group of negative electrode leads 431 on the sealing can 20 side, and the second negative electrode connection part is formed by bundling another group of negative electrode leads 431 on the outer can 10 side.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to flat batteries such as coin batteries. [Background technology]

[0002] A flat battery is known that includes a cylindrical outer can with a bottom, a cylindrical outer can with a bottom and a sealed can that is disposed in an inverted dish shape relative to the outer can so that a space is formed between the outer can and the sealed can, and an electrode assembly disposed between the outer can and the sealed can. In such a flat battery, as in JP 2011-9118 A (Patent Document 1) or JP 2021-111590 A (Patent Document 2), for example, an electrode assembly formed by alternately stacking multiple positive electrodes and multiple negative electrodes is housed in the space formed by the outer can and the sealed can.

[0003] Patent Document 1 discloses a coin-type secondary battery having an electrode body in which multiple positive electrodes and negative electrodes are stacked. The coin-type secondary battery has multiple positive electrode leads extending to one side from the multiple positive electrodes of the electrode body, and multiple negative electrode leads extending to the other side from the multiple negative electrodes of the electrode body. The multiple positive electrode leads are bundled and bent in the stacking direction of the electrode body. The multiple negative electrode leads are bundled and bent in the stacking direction of the electrode body.

[0004] Patent Document 2 discloses a secondary battery having an electrode assembly, an exterior housing for housing the electrode assembly, a positive electrode current collecting tab extending from a positive electrode included in the electrode assembly, and a negative electrode current collecting tab extending from a negative electrode included in the electrode assembly. The positive and negative electrode bodies included in the electrode assembly have a planar shape with a partially cut-out circle, with a portion cut out from the circle. The positive and negative electrode current collecting tabs are arranged side by side along the cut-out portion of the electrode assembly. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-9118 [Patent Document 2] Patent Publication No. 2021-111590 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present disclosure is to provide a flat battery that can achieve high capacity. [Means for solving the problem]

[0007] To solve the above-mentioned problems, the flat battery of the present disclosure employs the following solution. Specifically, the flat battery of the present disclosure includes an outer can, a sealed can, and an electrode assembly housed between the outer can and the sealed can. The electrode assembly includes an electrode assembly main body formed by alternately stacking multiple positive electrodes and multiple negative electrodes, a positive electrode connection portion formed by bundling together the positive electrode leads extending outward from each of the positive electrodes, and a negative electrode connection portion formed by bundling together the negative electrode leads extending outward from each of the negative electrodes. The electrode assembly main body has a notched portion formed by cutting out a portion of its circular shape in a plan view and an arc portion. The negative electrode connection portion includes a first negative electrode connection portion formed by bundling together one group of the negative electrode leads and a second negative electrode connection portion formed by bundling together the other groups of the negative electrode leads. Each of the positive electrode connection portion, the first negative electrode connection portion, and the second negative electrode connection portion is arranged in the cutout portion so that the positive electrode connection portion is positioned between the first negative electrode connection portion and the second negative electrode connection portion in a planar view, and is bent in the stacking direction of the electrode body. [Effects of the Invention]

[0008] The flat battery of the present disclosure can achieve a high capacity. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a flat battery according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a plan view of the positive electrode and the positive electrode lead shown in FIG. [Figure 3] FIG. 3 is a plan view of the negative electrode and the negative electrode lead corresponding to the first negative electrode connecting portion shown in FIG. [Figure 4] FIG. 4 is a plan view of the negative electrode and negative electrode lead corresponding to the second negative electrode connecting portion shown in FIG. [Figure 5] FIG. 5 is a perspective view showing an electrode body of a flat battery according to the first embodiment of the present disclosure. [Figure 6] FIG. 6 is a schematic side view of an electrode body of a flat battery according to a second embodiment of the present disclosure. [Figure 7] FIG. 7 is a plan view showing the dimensions of the positive electrode according to the example. [Figure 8] FIG. 8 is a plan view showing the dimensions of the positive electrode according to Comparative Example 1. As shown in FIG. [Figure 9] FIG. 9 is a plan view showing the dimensions of the positive electrode according to Comparative Example 2. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] The inventors of the present invention have considered that, in order to increase the capacity of a flat battery, it is essential to effectively utilize the internal space of the flat battery formed by the outer can and the sealed can, i.e., to reduce the accommodation space for the positive electrode leads extending from each of the multiple positive electrodes and the negative electrode leads extending from each of the multiple negative electrodes, and to increase the area of ​​the electrode body in a planar view. In the coin-type secondary battery of the above-mentioned Patent Document 1, the electrode body is formed by cutting out one side of its circular shape in a planar view to accommodate the multiple positive electrode leads in the accommodation space, and also by cutting out the other side of the circular shape in a planar view to accommodate the multiple negative electrode leads. Therefore, one side and the other side of the electrode body are cut out. As a result, the area of ​​the electrode body in a planar view is reduced, making it difficult to increase the capacity of the flat battery.

[0011] In addition, in the secondary battery of Patent Document 2, the electrode assembly is notched on only one side. The positive electrode current collecting tab and the negative electrode current collecting tab are arranged side by side along the notched portion of the electrode assembly. This allows the accommodation space for the positive electrode current collecting tab and the negative electrode current collecting tab to be relatively small, and the area of ​​the electrode assembly in a plan view to be relatively large. However, the positive electrode current collecting tab and the negative electrode current collecting tab are each bundled and accommodated, which does not allow for effective use of the internal space of the secondary battery.

[0012] After extensive research, the inventors focused on the planar shape of the storage space for the positive electrode connection portion (multiple bundled positive electrode leads) and the negative electrode connection portion (multiple bundled negative electrode leads) formed between the electrode assembly and a cylindrical case consisting of an outer can and a sealed can in an electrode assembly having a notch cut out only on one side. They discovered that by storing the negative electrode connection portions in a dispersed manner, the storage space for the positive electrode connection portion and the negative electrode connection portion can be effectively utilized. That is, in the planar shape of the storage space formed between the electrode assembly and the case, the gap between the center of the notch and the case is relatively large, and the gap gradually decreases toward both ends of the notch. In such a planar shape of the storage space, by arranging a single, thick, bundled positive electrode connection portion near the center of the notch and arranging two, thin, bundled negative electrode connection portions dispersedly on both sides of the positive electrode connection portion, the storage space can be fully utilized and the area of ​​the electrode assembly in a planar view can be increased. Based on this finding, the inventors have completed a flat-type battery according to the present disclosure.

[0013] (Configuration 1) A flat battery according to an embodiment of the present disclosure includes an outer can, a sealable can, and an electrode assembly housed between the outer can and the sealable can. The electrode assembly includes an electrode assembly main body formed by alternately stacking multiple positive electrodes and multiple negative electrodes, a positive electrode connection portion formed by bundling the positive electrode leads extending outward from each of the positive electrodes, and a negative electrode connection portion formed by bundling the negative electrode leads extending outward from each of the negative electrodes. The electrode assembly main body has a notch formed by cutting out a portion of its circular shape in a planar view and an arc portion. The negative electrode connection portion has a first negative electrode connection portion formed by bundling one group of the negative electrode leads together, and a second negative electrode connection portion formed by bundling another group of the negative electrode leads together. The positive electrode connection portion, the first negative electrode connection portion, and the second negative electrode connection portion are each disposed in the notch and bent in the stacking direction of the electrode assembly so that the positive electrode connection portion is positioned between the first negative electrode connection portion and the second negative electrode connection portion in a planar view.

[0014] In this way, the positive electrode connection part, the first negative electrode connection part, and the second negative electrode connection part are arranged so that they extend outward from the same cutout part in the electrode body main body, and the positive electrode connection part is positioned between the first negative electrode connection part and the second negative electrode connection part, and the negative electrode connection parts are distributed among the first negative electrode connection part and the second negative electrode connection part so that their thickness is relatively small. This makes it possible to effectively utilize the internal space between the outer can and the sealed can that house the positive electrode connection part and the negative electrode connection part, thereby increasing the area of ​​the electrode body main body in a plan view. As a result, it is possible to achieve a high capacity flat battery.

[0015] (Configuration 2) In the flat battery of Configuration 1, the first negative electrode connection part may be configured by bundling a group of negative electrode leads located on the sealing can side in the stacking direction of the electrode body. The second negative electrode connection part may be configured by bundling another group of negative electrode leads located on the outer can side in the stacking direction of the electrode body. This makes it easier to distribute and bundle the negative electrode connection parts to the first negative electrode connection part and the second negative electrode connection part.

[0016] (Configuration 3) In the flat battery of Configuration 1 or 2, the electrode assembly may have a negative electrode connector that connects, at an arc portion, any one of the plurality of negative electrodes connected to the first negative electrode connector and any one of the plurality of negative electrodes connected to the second negative electrode connector. This eliminates the need to bend either the first negative electrode connector or the second negative electrode connector so that it extends toward the sealing can or the outer can, thereby reducing the risk of a short circuit caused by either the first negative electrode connector or the second negative electrode connector coming into contact with the positive electrode connector or the like.

[0017] (Configuration 4) The flat battery of any one of Configurations 1 to 3 may have an insulating member housed between the outer can and the sealing can. The insulating member may be disposed at least one between the positive electrode connecting part and the first negative electrode connecting part, and between the positive electrode connecting part and the second negative electrode connecting part. This makes it possible to suppress short circuits caused by contact between the positive electrode connecting part and the negative electrode connecting part.

[0018] (Configuration 5) In the flat battery of any one of Configurations 1 to 4, the outer can may have an outer diameter of 3 to 15 mm or less. The flat battery of the present disclosure is particularly suitable for use in relatively small flat batteries, particularly those of 3 to 15 mm or less.

[0019] (First embodiment) A flat battery 1 according to a first embodiment of the present disclosure will be specifically described below with reference to Figures 1 to 4. Note that identical or corresponding components in the figures are denoted by the same reference numerals, and the same description will not be repeated. Note that, for ease of understanding, the drawings referred to below show simplified or schematic configurations, and some components are omitted.

[0020] As shown in Fig. 1, the flat battery 1 includes a cylindrical outer can 10 with a bottom, a seal can 20 that covers the opening of the outer can 10, a gasket 30 that is disposed between the outer periphery of the outer can 10 and the outer periphery of the seal can 20, and an electrode assembly 40 that is housed in the space formed between the outer can 10 and the seal can 20. Therefore, by combining the outer can 10 and the seal can 20, the flat battery 1 has a flat coin shape as a whole. In other words, the outer can 10 and the seal can 20 form a case with an internal space. In addition to the electrode assembly 40, a nonaqueous electrolyte (not shown) is also enclosed in the case space.

[0021] The outer can 10 is made of a metal material such as stainless steel, and is formed into a cylindrical shape with a bottom by press molding. The outer can 10 has a circular bottom 11 and a cylindrical peripheral wall 12 formed on the outer periphery of the bottom 11 and continuing from the bottom 11. This peripheral wall 12 is provided so as to extend almost perpendicularly from the outer peripheral edge of the bottom 11 in a vertical cross-sectional view (as shown in FIG. 1 ). As will be described later, the outer can 10 is crimped to the sealable can 20 with a gasket 30 sandwiched between it and the sealable can 20, with the open end of the peripheral wall 12 bent inward.

[0022] The sealing can 20 is made of a metal material such as stainless steel and is formed into a cylindrical shape with a bottom by press molding. The sealing can 20 has a cylindrical peripheral wall portion 22 that is smaller in outer diameter than the peripheral wall portion 12 of the outer can 10, and a circular flat portion 21 that closes one opening of the peripheral wall portion 22. The peripheral wall portion 22 is provided so as to extend substantially perpendicular to the flat portion 21 in a vertical cross-sectional view.

[0023] The peripheral wall 22 of the sealable can 20 is formed with an expanded diameter portion 22b whose diameter is stepped larger than that of the base end portion 22a on the flat portion 21 side. That is, the peripheral wall 22 is formed with a step portion 22c between the base end portion 22a and the expanded diameter portion 22b. As shown in FIG. 1 , the opening end side of the peripheral wall 12 of the outer can 10 is bent and crimped relative to the step portion 22c. That is, the opening end side of the peripheral wall 12 of the outer can 10 is fitted into the step portion 22c of the sealable can 20.

[0024] The gasket 30 is made of polypropylene (PP). The gasket 30 is disposed between the peripheral wall 22 of the sealable can 20 and the peripheral wall 12 of the outer can 10 so as to be sandwiched between them. The material of the gasket 30 is not limited to PP, and may be a resin composition containing an olefin-based elastomer in polyphenylene sulfide (PPS), polytetrafluoroethylene (PFA), polyamide-based resin, or the like.

[0025] The electrode body 40 has an electrode body main body 41 , a positive electrode connecting portion 42 , and a negative electrode connecting portion 43 .

[0026] The electrode body main body 41 has a substantially disc-shaped positive electrode 411, a substantially disc-shaped negative electrode 412, and a negative electrode connector 45, all of which are housed in a bag-shaped separator 44. The electrode body main body 41 has a substantially cylindrical shape with a notched portion 41a and an arc portion 41b, formed by stacking a plurality of positive electrodes 411 and negative electrodes 412 (described later) alternately in the thickness direction.

[0027] Although not shown, the positive electrode 411 is formed by disposing positive electrode active material layers containing a positive electrode active material such as lithium cobalt oxide on both sides of a positive electrode current collector made of a metal foil such as aluminum. As shown in FIG. 2, the positive electrode 411 has a shape with a portion cut out of a circular plate. That is, the positive electrode 411 has a cutout portion 411a formed by cutting out a portion of the circular shape in a plan view. The positive electrode lead 421 extends outward from the positive electrode current collector near the center of the cutout portion 411a. The positive electrode connection portion 42 is formed by bundling the positive electrode leads 421 extending outward from the multiple positive electrodes 411 while bending them. The positive electrode connection portion 42 is connected to the positive electrode foil 46 via an insulating sheet 47 disposed between the electrode assembly 40 and the bottom 11 of the outer can 10. The positive electrode foil 46 is in contact with the bottom 11 of the outer can 10. Therefore, in this embodiment, the outer can 10 functions as a positive electrode can. The positive electrode foil 46 is made of a metal such as an aluminum alloy.

[0028] Although not particularly shown, the negative electrode 412 is formed by disposing a negative electrode active material layer containing a negative electrode active material such as graphite on both sides of a negative electrode current collector made of a metal foil such as copper. As shown in Fig. 1, the negative electrode 412 closest to the flat surface portion 21 of the sealing can 20 has a negative electrode active material layer formed on only one surface of the negative electrode current collector so that the negative electrode current collector faces the flat surface portion 21.

[0029] 3 and 4, the negative electrode 412 has a shape in which a part of a circular plate is cut out. That is, the negative electrode 412 has a cutout portion 412a in which a part of the circular shape in a plan view is cut out.

[0030] 1, the negative electrode connection portion 43 has a first negative electrode connection portion 43a and a second negative electrode connection portion 43b. The first negative electrode connection portion 43a is formed by bundling a group of negative electrode leads 431 extending outward from one group of the negative electrodes 412 among the plurality of negative electrodes 412 while bending the same. The second negative electrode connection portion 43b is formed by bundling another group of negative electrode leads 431 extending outward from another group of the negative electrodes 412 among the plurality of negative electrodes 412 while bending the same.

[0031] As shown in Fig. 3, in the first negative electrode connecting portion 43a, each negative electrode lead 431 extending outward from one group of negative electrodes 412 is connected to the above-mentioned negative electrode current collector near the end of the notch 412a. On the other hand, as shown in Fig. 4, in the second negative electrode connecting portion 43b, each negative electrode lead 431 extending outward from another group of negative electrodes 412 is connected to the above-mentioned negative electrode current collector near the end of the notch 412a on the opposite side from the group of negative electrode leads 431. The first negative electrode connecting portion 43a and the second negative electrode connecting portion 43b are connected to the negative electrode current collector of the negative electrode 412 that is closest to the flat surface portion 21 of the sealing can 20. Therefore, in this embodiment, the sealing can 20 functions as a negative electrode can.

[0032] The negative electrode connector 45 connects one of the multiple negative electrodes 412 connected to the first negative electrode connector 43a and one of the multiple negative electrodes 412 connected to the second negative electrode connector 43b at the arc portion 41b of the electrode body main body 41. This connects the first negative electrode connector 43a and the second negative electrode connector 43b to each other. Therefore, by connecting the first negative electrode connector 43a to the negative electrode current collector of the negative electrode 412 closest to the flat portion 21 of the sealing can 20, it is not necessary to directly connect the second negative electrode connector 43b to the negative electrode current collector of the negative electrode 412 closest to the flat portion 21. Therefore, it is not necessary to bend the second negative electrode connector 43b so that it extends toward the sealing can 20. As a result, it is possible to reduce the risk of a short circuit caused by the second negative electrode connector 43b coming into contact with the positive electrode connector 42, etc.

[0033] The separator 44 is a bag-shaped member that is circular in plan view and is sized to accommodate the positive electrode 411 and the base end of the positive electrode lead 421 on the positive electrode 411 side. The separator 44 is made of a microporous thin film made of polyethylene, which has excellent insulating properties. By making the separator 44 from a microporous thin film in this way, lithium ions can pass through the separator 44. The separator 44 is formed by sandwiching the positive electrode 411 and a portion of the positive electrode lead 421 closer to the positive electrode 411 between two rectangular microporous thin film sheets, bonding the overlapping portions of the two sheets, i.e., the outer portion of the peripheral edge of the positive electrode 411 and the outer portion of a portion of the positive electrode lead 421, by heat welding or the like, and punching out the bonded portion along the outer shapes of the positive electrode 411 and the positive electrode lead 421.

[0034] 1 and 5, the positive electrode connection portion 42, the first negative electrode connection portion 43a, and the second negative electrode connection portion 43b extend in the same direction from the cutout portion 41a of the electrode body main body 41 in a plan view. As described above, in a plan view, the positive electrode connection portion 42 extends from near the center of the cutout portion 41a. The first negative electrode connection portion 43a extends from near the end of the cutout portion 41a (to the left in FIG. 5). The second negative electrode connection portion 43b extends from near the end opposite to the first negative electrode connection portion 42a (to the right in FIG. 5). Therefore, the positive electrode connection portion 42 is positioned between the first negative electrode connection portion 43a and the second negative electrode connection portion 43b in a plan view. The first negative electrode connection portion 43a is formed by bundling a group of negative electrode leads 431 of the plurality of negative electrodes 412 that are located on the upper side in the stacking direction of the electrode body main body 41, i.e., on the flat surface portion 21 side of the sealing can 20. The second negative electrode connection portion 43b is formed by bundling another group of negative electrode leads 431 of the plurality of negative electrodes 412 that are located on the lower side in the stacking direction of the electrode body main body 41, i.e., on the bottom 11 side of the outer can 10. By bundling the first negative electrode connection portion 43a and the second negative electrode connection portion 43b on the upper and lower sides in this manner, it becomes easier to bundle the first negative electrode connection portion 43a and the second negative electrode connection portion 43b into a single bundle. Note that the number of stacked positive electrodes 411 and negative electrodes 412 shown in FIG. 1 is different from the number of stacked positive electrodes 411 and negative electrodes 412 shown in FIG. 5. The electrode body 40 may have various numbers of stacked positive electrodes 411 and negative electrodes 412 depending on the size or shape of the flat battery 1. In this embodiment, the cutout portion 41a is formed linearly in a plan view, but the cutout shape of the cutout portion 41a can be variously changed depending on the size or shape of the flat battery 1.

[0035] The difference in thickness between the first negative electrode connecting portion 43a and the second negative electrode connecting portion 43b is preferably small. In addition, the thickness of the larger of the first negative electrode connecting portion 43a and the second negative electrode connecting portion 43b is preferably 0.4 times or less the thickness of the positive electrode connecting portion 42.

[0036] In this way, the positive electrode connection portion 42, the first negative electrode connection portion 43a, and the second negative electrode connection portion 43b are arranged to extend outward from the same cutout portion 41a of the electrode body main body 41, and the negative electrode connection portion 43 is distributed across the first negative electrode connection portion 43a and the second negative electrode connection portion 43b, arranging them so that their thickness is relatively small. This makes it possible to effectively utilize the storage space within the case for the positive electrode connection portion 42 and the negative electrode connection portion 43, and thereby increase the area of ​​the electrode body main body 41 in a plan view. As a result, the capacity of the flat battery 1 can be increased.

[0037] Although not specifically shown, the flat battery 1 may also have an insulating member housed between the outer can 10 and the sealing can 20. The insulating member may be disposed between the positive electrode connection portion 42 and the first negative electrode connection portion 43a and / or between the positive electrode connection portion 42 and the second negative electrode connection portion 43b. This prevents short circuits caused by contact between the positive electrode connection portion 42 and the negative electrode connection portion 43. The insulating member may be, for example, insulating tape. By wrapping the insulating tape around the positive electrode connection portion 42, the positive electrode connection portion 42 and the negative electrode connection portion 43 can be insulated from each other. The insulating member may also be an insulating partition member disposed between the positive electrode connection portion 42 and the first negative electrode connection portion 43a and / or between the positive electrode connection portion 42 and the second negative electrode connection portion 43b. The insulating member is not particularly limited as long as it can insulate at least one of the positive electrode connecting portion 42 and the first negative electrode connecting portion 43a, and the positive electrode connecting portion 42 and the second negative electrode connecting portion 43b.

[0038] As shown in FIG. 1 , the outer can 10 has an outer diameter D of 3 to 15 mm. If the outer diameter D of the outer can 10 is too small, the thicknesses of the positive electrode connecting portion 42 and the negative electrode connecting portion 43 will be relatively large compared to the size of the flat battery 1. As a result, a relatively large portion of the electrode body main body 41 may be cut away to form the cutout 41a, making it difficult to efficiently achieve the effect of increasing the area of ​​the electrode body main body 41 in a planar view. On the other hand, if the outer diameter D of the outer can 10 is too large, the radius of curvature of the inner circumferential surfaces of the outer can 10 and the sealing can 20 facing the cutout 41a in a planar view will be large, making it difficult to efficiently achieve the effect of effectively utilizing the storage space by arranging the relatively thick positive electrode connecting portion 42 between the relatively thin first negative electrode connecting portion 43a and second negative electrode connecting portion 43b. Therefore, from the viewpoint of efficiently utilizing the accommodation space of the positive electrode connecting portion 42 and the negative electrode connecting portion 43 to increase the capacity of the flat battery 1, it is preferable that the outer diameter D of the outer can 10 be 3 to 15 mm, which will result in a relatively small flat battery 1.

[0039] (Second embodiment) Next, the flat battery 1 according to the second embodiment will be described in detail using Figure 6. Note that a description of the same configuration as the flat battery 1 of the first embodiment will be omitted, and the configuration that differs from the flat battery 1 of the first example will be described.

[0040] In the flat battery 1 of the first embodiment, the first negative electrode connection portion 43a is arranged on the upper side in the stacking direction, and the second negative electrode connection portion 43b is arranged on the lower side in the stacking direction. However, in the flat battery 1 of the second embodiment, as shown in FIG. 6, the first negative electrode connection portion 43a and the second negative electrode connection portion 43b are formed by bundling together multiple negative electrode leads 431 extending from multiple stacked negative electrodes 412 in a staggered manner.

[0041] In this way, in the first negative electrode connection portion 43a and the second negative electrode connection portion 43b, the group of negative electrode leads 431 and the other group of negative electrode leads 431 bundled from the multiple negative electrode leads 431 are not limited to the upper and lower sides, but may be in any form as long as the first negative electrode connection portion 43a and the second negative electrode connection portion 43b can be bundled in a distributed manner.

[0042] The negative electrode connector 45 connects one of the multiple negative electrodes 412 connected to the first negative electrode connector 43a and one of the multiple negative electrodes 412 connected to the second negative electrode connector 43b at the arc portion 41b of the electrode body main body 41. From the viewpoint of preventing short circuits, the negative electrode connector 45 preferably connects the nearest negative electrodes 412 to each other at the first negative electrode connector 43a and the second negative electrode connector 43b.

[0043] In the first and second embodiments described above, the outer can 10 functions as a positive electrode can and the sealing can 20 functions as a negative electrode can, but conversely, the sealing can may be the positive electrode can and the outer can may be the negative electrode can.

[0044] Although the embodiments have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0045] Furthermore, the present invention can contribute to the achievement of Goal 7 "Ensure access to affordable, reliable, sustainable and modern energy for all" and Goal 12 "Ensure sustainable consumption and production patterns" of the Sustainable Development Goals (SDGs) advocated by the United Nations. [Example]

[0046] Flat batteries of the examples and comparative examples shown in Table 1 below were fabricated, and the area of ​​the positive electrode that could be housed in a case of the same size and shape for each flat battery was compared to confirm whether the flat batteries of the examples had a higher capacity.

[0047] [Table 1]

[0048] (Example) In the flat batteries of the example, each electrode body was fabricated by stacking 10 positive electrodes and 11 negative electrodes housed in a pouch-shaped separator, as in the flat battery of the first embodiment described above. Each of the 10 positive electrodes had a positive electrode lead extending outward, and each of the 11 negative electrodes had a negative electrode lead extending outward. As in the flat battery of the first embodiment, the 11 negative electrode leads were distributed and bundled into a first negative electrode connection portion (corresponding to six negative electrodes) located on the upper side and a second negative electrode connection portion (corresponding to five negative electrodes) located on the lower side, and each was folded. As described above, the negative electrode located on the outermost side of each electrode body, i.e., the negative electrode closest to the flat portion of the sealed can and the negative electrode closest to the bottom of the outer can, had a negative electrode active material provided only on one side of the negative electrode current collector. This electrode assembly was housed in a case to prepare a flat battery of this example having an outer diameter of 6.8 mm and a height of 4.0 mm.

[0049] (Comparative Example 1) For the flat battery of the comparative example, an electrode assembly was prepared, similar to the coin-type secondary battery of Patent Document 1, with a cutout in the electrode assembly body and another cutout formed on the opposite side, with a positive electrode connector and a negative electrode connector disposed in each cutout. The electrode assembly was fabricated by stacking 10 positive electrodes and 11 negative electrodes housed in a pouch-shaped separator. The negative electrodes closest to the flat surface of the sealed can and the negative electrodes closest to the bottom of the outer can had negative electrode active material provided only on one surface of the negative electrode current collector. This electrode assembly was housed in a case to fabricate a flat battery of Comparative Example 1 having an outer diameter of 6.8 mm and a height of 4.0 mm.

[0050] (Comparative Example 2) For the flat battery of Comparative Example 2, an electrode assembly was prepared, similar to the secondary battery of Patent Document 2, having a positive electrode connector and a negative electrode connector, each consisting of multiple positive electrode leads and multiple negative electrode leads extending from a notch in the electrode assembly body and bundled together. The electrode assembly was fabricated by stacking 10 positive electrodes and 11 negative electrodes housed in a bag-shaped separator. The negative electrodes closest to the flat surface of the sealed can and the negative electrodes closest to the bottom of the outer can had negative electrode active material provided only on one surface of the negative electrode current collector. This electrode assembly was housed in a case, and a flat battery of Comparative Example 2 with an outer diameter of 6.8 mm and a height of 4.0 mm was fabricated.

[0051] (Comparison results) The dimensions shown in Table 1 are the dimensions of each positive electrode shown in Figures 7 to 9. Figure 7 shows the dimensions of each part of the positive electrode of the example, Figure 8 shows the dimensions of each part in Comparative Example 1, and Figure 9 shows the dimensions of each part in Comparative Example 2.

[0052] As shown in Table 1, when the area of ​​the positive electrode of the example is compared with the area of ​​the positive electrode of Comparative Example 1, the area of ​​the positive electrode of the example is 0.64 mm 2 That is, the flat battery of the example was able to improve the battery capacity by 3.6% compared to the flat battery of the comparative example 1.

[0053] Comparing the dimensions of the positive electrode of the Example with those of the Comparative Example 2, the dimension of r2 in the positive electrode of the Example could be made larger than the dimension of the positive electrode of Comparative Example 2, and the dimension of the notch could be made smaller accordingly. As a result, the area of ​​the positive electrode of the Example was larger than that of Comparative Example 2, and the battery capacity could be improved by 1.2% compared to the flat battery of Comparative Example 1. [Explanation of symbols]

[0054] 1: Flat battery, 10: Outer can, 20: Sealing can, 30: Gasket, 40: Electrode body, 41: Electrode body main body, 41a: Notch, 41b: Arc portion, 42: Positive electrode connecting portion, 43: Negative electrode connecting portion, 43a: First negative electrode connecting portion, 43b: Second negative electrode connecting portion, 44: Separator, 411: Positive electrode, 412: Negative electrode, 421: Positive electrode lead, 431: Negative electrode lead, 411a: Notch, 45: Negative electrode connecting body

Claims

1. An outer can; A sealed can and an electrode assembly housed between the exterior can and the sealing can; The electrode body has an electrode body main body formed by alternately stacking a plurality of positive electrodes and a plurality of negative electrodes, a positive electrode connection part formed by bundling together positive electrode leads extending outward from each of the positive electrodes, and a negative electrode connection part formed by bundling together negative electrode leads extending outward from each of the negative electrodes, The electrode body has a notch formed by cutting out a part of a circular shape in a plan view and an arc portion, the negative electrode connection portion has a first negative electrode connection portion formed by bundling together one group of the negative electrode leads, and a second negative electrode connection portion formed by bundling together another group of the negative electrode leads, a flat battery in which each of the positive electrode connection portion, the first negative electrode connection portion, and the second negative electrode connection portion is arranged in the cutout portion so that the positive electrode connection portion is positioned between the first negative electrode connection portion and the second negative electrode connection portion in a planar view, and is bent in the stacking direction of the electrode body.

2. The flat battery according to claim 1, the first negative electrode connection portion is formed by bundling a group of the negative electrode leads located on the sealing can side in the stacking direction of the electrode body, The second negative electrode connection portion is formed by bundling together another group of the negative electrode leads located on the outer can side in the stacking direction of the electrode body.

3. The flat battery according to claim 1, The electrode body has a negative electrode connector that connects, at the arc portion, any one of the plurality of negative electrodes connected to the first negative electrode connection portion and any one of the plurality of negative electrodes connected to the second negative electrode connection portion.

4. The flat battery according to claim 1, further comprising: an insulating member accommodated between the exterior can and the sealing can; The flat battery, wherein the insulating member is disposed at least either between the positive electrode connection portion and the first negative electrode connection portion or between the positive electrode connection portion and the second negative electrode connection portion.

5. The flat battery according to claim 1, The outer can has an outer diameter of 3 to 15 mm.

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