Flat battery

Abstract

To provide a flat battery which secures excellent sealing property and furthermore enables the increase of the internal space thereof and therefore can be increased in the capacity.SOLUTION: A flat battery includes: an exterior can 2; a sealed can 3; and a gasket 5. The exterior can 2 includes: a bottom portion 21; and a cylindrical side wall portion 22. The sealed can 3 includes: an upper surface portion 31; and a peripheral wall portion 32. The peripheral wall portion 32 includes: a proximal end 32a on the upper surface portion 31 side; a cylinder portion 32b that is formed larger than an outer diameter of the proximal end 32a, and includes a distal end opposite to the bottom portion 21 of the exterior can 2; and a step portion 32c that is positioned between the proximal end 32a and the cylinder portion 32b. The cylinder portion 32b is inclined to a radial outside directed to the distal end of the cylinder portion 32b from an end portion on the step portion 32c side, and has an inclination angle at 0.5° to 4°toward an axial direction. The proximal end 32a is inclined to a radial inner direction toward the end portion on the step portion 32c side from the end portion on the upper surface portion 31 side, and includes the inclination angle at 0.5° to 5°with respect to the axial direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to flat batteries. [Background technology]

[0002] Conventionally, flat batteries such as coin- or button-type nonaqueous electrolyte batteries are generally constructed by housing a power generating element having a positive electrode and a negative electrode between an exterior can and a sealing can, each of which is generally made of a stainless steel plate. The exterior can has a bottom and a cylindrical side wall, and the sealing can faces the exterior can and has a top surface and a peripheral wall.

[0003] JP 2018-18797 A (Patent Document 1) discloses a coin-type lithium primary battery. The coin-type lithium primary battery includes a case having a bottom plate and a side portion rising from the periphery of the bottom plate, and a sealing plate having a top plate and a peripheral portion extending from the top plate to the inside of the side portion. The tip of the peripheral portion of the sealing plate is folded back toward the top plate so as to follow the outer circumferential surface of the peripheral portion.

[0004] WO 2012 / 132373 (Patent Document 2) discloses a coin-shaped battery. The coin-shaped battery has a cylindrical battery can having a bottom portion and a first side wall rising from the periphery of the bottom portion, and a sealing plate having a top plate portion and a second side wall extending from the periphery of the top plate to the inside of the first side wall. A bulge portion that bulges outward is formed on the second side wall. The second side wall of the sealing plate has a folded structure with its tip folded back.

[0005] Japanese Patent Laid-Open Publication No. 8-162075 (Patent Document 3) discloses a coin-type lithium battery. The coin-type lithium battery has a sealing plate whose periphery is not folded back into a U-shape, and a cylindrical positive electrode case with a bottom. The opening of the sealing plate is inclined toward the outer diameter with respect to the height direction of the positive electrode case. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2018-18797 A [Patent Document 2] International Publication No. 2012 / 132373 [Patent Document 3] Japanese Patent Application Publication No. 8-162075 Summary of the Invention [Problem to be solved by the invention]

[0007] In the coin-type lithium primary battery of Patent Document 1, the edge of the sealing plate is folded back to improve the sealing of the internal space of the battery. This increases the thickness of the sealing plate, restricts the internal volume of the battery, and prevents the battery from having a high capacity.

[0008] The coin battery of Patent Document 2 needs to have a relatively wide flange on the second side wall of the sealing plate to ensure leakage resistance. Therefore, even though the sealing plate has a bulge, this does not necessarily lead to an increase in the internal volume of the entire battery, which hinders the battery from having a high capacity.

[0009] Although the coin battery of Patent Document 3 can improve leakage resistance, there is no suggestion to increase the capacity of the battery.

[0010] Therefore, an object of the present disclosure is to provide a flat battery that can increase the internal volume while ensuring excellent sealing properties, thereby achieving a high capacity battery. [Means for solving the problem]

[0011] In order to solve the above problems, the present disclosure is configured as follows. That is, the flat battery according to the present disclosure includes an exterior can having a bottom and a cylindrical side wall, a sealing can having an upper surface and a peripheral wall and facing the exterior can, and a gasket arranged between the cylindrical side wall and the peripheral wall. The peripheral wall has a base end on the upper surface side, a cylindrical part formed larger than the outer diameter of the base end and having a tip facing the bottom of the exterior can, and a step part located between the base end and the cylindrical part. The cylindrical part is inclined radially outward from the end on the step part side toward the tip of the cylindrical part, and has an inclination angle of 0.5 to 4° with respect to the axial direction. The base end is inclined radially inward from the end on the upper surface side toward the end on the step part side, and has an inclination angle of 0.5 to 5° with respect to the axial direction. Effect of the Invention

[0012] The flat battery according to the present disclosure can increase the internal volume while ensuring excellent sealing properties, thereby achieving a high capacity battery. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view showing the structure of a flat battery according to this embodiment. [Diagram 2] FIG. 2 is an enlarged cross-sectional view showing the structure of the flat battery shown in FIG. [Diagram 3] FIG. 3 is an enlarged cross-sectional view showing the structure of a flat battery according to an embodiment. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing the structure of a flat battery according to a comparative example. [Diagram 5] FIG. 5 is an enlarged cross-sectional view showing the structure of a flat battery according to an embodiment. [Figure 6] FIG. 6 is an enlarged cross-sectional view showing the structure of a flat battery according to a comparative example. [Figure 7] FIG. 7 is a graph showing the change in the surface pressure of the gasket in contact with the sealing can. [Figure 8] FIG. 8 is a graph showing the change in the surface pressure of the gasket in contact with the sealing can. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The flat battery according to the embodiment includes an exterior can having a bottom and a cylindrical side wall, a sealing can having an upper surface and a peripheral wall and facing the exterior can, and a gasket disposed between the cylindrical side wall and the peripheral wall. The peripheral wall has a base end on the upper surface side, a cylindrical portion having a tip formed larger than the outer diameter of the base end and facing the bottom of the exterior can, and a step portion located between the base end and the cylindrical portion. The cylindrical portion is inclined radially outward from the end on the step portion side toward the tip of the cylindrical portion, and has an inclination angle of 0.5 to 4° with respect to the axial direction. The base end is inclined radially inward from the end on the upper surface side toward the end on the step portion side, and has an inclination angle of 0.5 to 5° with respect to the axial direction. This allows the internal volume to be increased while ensuring excellent sealing properties, thereby increasing the capacity of the battery. In addition, the peripheral wall portion of the sealing can preferably has a thickness of 0.185 to 0.215 mm. This makes it easier to form an inclined structure of the cylindrical portion and the base end. The cylindrical side wall of the outer can preferably has a thickness of 92 to 108% of the thickness of the peripheral wall, which makes it easier to ensure excellent sealing properties and increase the internal volume.

[0015] The sealing can is preferably made of a cold-rolled steel sheet, which is particularly suitable for use since it is easy to form the above-mentioned gradient structure and has a relatively low strength within the above-mentioned range of thickness of the peripheral wall.

[0016] The outer can is preferably made of a stainless steel plate, which can reduce costs.

[0017] Hereinafter, the flat battery 1 of the present embodiment according to the present disclosure will be specifically described with reference to FIG. 1. The flat battery according to the present embodiment is a non-aqueous electrolyte battery. First, as shown in FIG. 1, the flat battery 1 is composed of an outer can 2, a sealing can 3, a positive electrode 41, a negative electrode 42, a separator 43, and a gasket 5. The positive electrode 41, the negative electrode 42, the separator 43, and a non-aqueous electrolyte (not shown) are filled in the internal space between the outer can 2 and the sealing can 3 as power generating elements. The power generating elements may be those used in general non-aqueous electrolyte batteries. Therefore, detailed description of the power generating elements will be omitted. The flat battery 1 is not limited to a non-aqueous electrolyte battery, and may be a flat all-solid-state battery using a solid electrolyte.

[0018] The outer can 2 has a circular bottom 21 and a cylindrical side wall 22 formed continuously from the outer periphery of the bottom 21. The cylindrical side wall 22 is provided so as to extend substantially perpendicularly to the bottom 21 in a vertical cross-sectional view. The outer can 2 can be made of a stainless steel plate such as an austenitic stainless steel such as SUS301, SUS304, or SUS316, an austenitic-ferritic stainless steel such as SUS329J1, SUS329J3L, or SUS329J4L, or a ferritic stainless steel such as SUS430 or SUS444. The surface of the outer can 2 may be plated with an anticorrosive plating such as Ni plating, or the cost can be reduced by not plating with an anticorrosive plating. The shape of the outer can 2 is not limited to a cylindrical shape with a circular bottom 21. For example, the shape of the exterior can 2 may be variously changed according to the size and shape of the flat battery 1, with the bottom 21 being formed into a polygonal shape such as a square shape or an elliptical shape, and the cylindrical side wall 22 being formed into a polygonal shape such as a square cylinder or an elliptical cylinder that matches the shape of the bottom 21. Therefore, the shape of the cylindrical side wall 22 includes not only a cylindrical shape but also a polygonal shape such as a square cylinder or an elliptical cylinder. The bottom 21 of the exterior can 2 may or may not be flat. For example, the bottom 21 of the exterior can 2 may be shaped to protrude downward at the position where the power generating element is arranged so as to accommodate a part of the positive electrode 41 side of the power generating element.

[0019] The sealing can 3 has a circular upper surface portion 31 and a cylindrical peripheral wall portion 32 formed continuously from the outer periphery of the upper surface portion 31. The opening of the sealing can 3 faces the opening of the outer can 2. The sealing can 3 can be made of the above-mentioned stainless steel plate or cold-rolled steel plate (SPCD, SPCE, SPCF, etc.). The surface of the sealing can 3 is provided with an anti-corrosion plating. The anti-corrosion plating is, for example, Ni plating. The shape of the sealing can 3 is not limited to a cylindrical shape with a circular upper surface portion 31. For example, the shape of the sealing can 3 may be such that the upper surface portion 31 is formed into a polygonal shape such as a square shape or an elliptical shape, and the peripheral wall portion 32 is formed into a polygonal shape such as a square cylinder or an elliptical cylinder that matches the shape of the upper surface portion 31, and can be variously changed according to the size and shape of the flat battery 1. Therefore, the shape of the peripheral wall portion 32 includes not only a cylindrical shape but also a polygonal shape such as a square cylinder or an elliptical cylinder. The upper surface 31 of the sealing can 3 may or may not have a flat shape. For example, the upper surface 31 of the sealing can 3 may have a shape including a curved surface, such as a slight inclination from the outer periphery toward the center.

[0020] The peripheral wall 32 of the sealing can 3 has a base end 32a on the top surface 31 side, a cylindrical portion 32b formed to be larger in outer diameter than the base end 32a, and a step 32c between the base end 32a and the cylindrical portion 32b. Therefore, the peripheral wall 32 is formed in a step shape such that the cylindrical portion 32b is wider outward than the base end 32a. The tip of the cylindrical portion 32b faces the bottom 21 of the outer can 2. In other words, the cylindrical portion 32b is not folded back so as to fit along the outer circumferential surface of the peripheral wall 32.

[0021] The gasket 5 is made of a low moisture permeable resin such as polypropylene resin, polyphenylene sulfide resin, or PFA resin (tetrafluoroethylene-perfluoroalkoxyethylene copolymer). The gasket 5 is formed in a cylindrical shape that fits along the inner peripheral surface of the cylindrical side wall portion 22 of the outer can 2, and is disposed between the cylindrical side wall portion 22 of the outer can 2 and the peripheral wall portion 32 of the sealable can 3. The gasket 5 is not particularly limited as long as it can insulate the outer can 2 and the sealable can 3, but from the viewpoints of moisture permeability and heat resistance, a fluororesin such as polyphenylene sulfide resin or PFA resin is preferably used.

[0022] After the power generating element is accommodated in the internal space of the outer can 2 and the sealing can 3, the outer can 2 and the sealing can 3 are crimped together with a gasket 5 between the cylindrical side wall 22 of the outer can 2 and the peripheral wall 32 of the sealing can 3. Specifically, the outer can 2 and the sealing can 3 are crimped together with the gasket 5 between the cylindrical side wall 22 and the peripheral wall 32 after the openings of the outer can 2 and the sealing can 3 are opposed to each other and the peripheral wall 32 of the sealing can 3 is inserted inside the cylindrical side wall 22 of the outer can 2. The edge of the cylindrical side wall 22 is crimped so as to face inward toward the step 32c of the peripheral wall 32.

[0023] As shown in FIG. 2, the peripheral wall portion 32 preferably has a relatively small thickness t1 of 0.185 to 0.215 mm. If the thickness t1 of the peripheral wall portion 32 is too small, the strength of the peripheral wall portion 32 decreases, and the sealing performance of the internal space of the flat battery 1 decreases. Therefore, the thickness t1 is preferably 0.185 mm or more, more preferably 0.190 mm or more, and particularly preferably 0.195 mm or more. If the thickness t1 is too large, the internal volume of the flat battery 1 is limited, which hinders the flat battery 1 from having a high capacity. Therefore, the thickness t1 is preferably 0.215 mm or less, more preferably 0.210 mm or less, and particularly preferably 0.205 mm or less. When the metal material of the sealing can 3 is a cold-rolled steel plate with a relatively low strength, it is particularly suitable for the thickness t1 of the peripheral wall portion 32 to be in the above-mentioned range. By specifying the thickness of the peripheral wall portion 32 in this manner, when the exterior can 2 and the sealing can 3 are crimped together, the cylindrical portion 32b and the base end portion 32a are easily deformed to have an inclined structure, which will be described later, and excellent sealing properties can be ensured. In addition, the internal volume can be increased, thereby enabling the battery to have a high capacity.

[0024] The cylindrical portion 32b of the peripheral wall portion 32 is inclined radially outward from the end portion on the step portion 32c side toward the tip of the cylindrical portion 32b. That is, when the outer can 2 and the sealing can 3 are crimped together, the base end portion 32a of the peripheral wall portion 32 is pressed radially inward by the tip of the cylindrical side wall portion 22 of the outer can 2, and the step portion 32c is pressed downward and inward. At this time, the cylindrical portion 32b side of the base end portion 32a is deformed so as to be inclined radially inward, and accordingly, the cylindrical portion 32b is deformed so that its tip appears to open outward, that is, to be inclined radially outward. When the cylindrical side wall portion 22 of the outer can 2 is crimped, the cylindrical portion 32b inclined radially outward improves the adhesion with the gasket 5, and appropriately presses the gasket 5 radially outward and is pushed back radially inward by the gasket 5. This makes it possible to improve the contact pressure between the gasket 5 and the outer peripheral surface of the cylindrical portion 32b, suppress the occurrence of gaps between the gasket 5 and the cylindrical portion 32b, and increase the contact area therebetween. Increasing the contact pressure and contact area between the gasket 5 and the outer peripheral surface of the cylindrical portion 32b in this way makes it possible to further improve the sealing of the internal space of the flat battery 1.

[0025] The inclination angle θ1 of the cylindrical portion 32b with respect to the axial direction may be set to 0.5 to 4°. If the inclination angle θ1 is too small, the contact pressure between the gasket 5 and the outer circumferential surface of the cylindrical portion 32b or the contact pressure between the gasket 5 and the cylindrical side wall portion 22 decreases, resulting in poor sealing performance. On the other hand, if the inclination angle θ1 is too large, the contact pressure between the gasket 5 and the cylindrical portion 32b or the bottom portion 21 of the outer can 2 decreases, resulting in poor sealing performance. The inclination angle θ1 is preferably 1° or more, and more preferably 2° or more.

[0026] The base end 32a of the peripheral wall portion 32 is inclined radially inward from the end on the upper surface portion 31 side toward the end on the step portion 32c side. When the outer can 2 and the sealing can 3 are crimped together, the base end 32a is deformed so as to be inclined radially inward by the downward inward pressing force of the cylindrical side wall portion 22. As a result, when the outer can 2 and the sealing can 3 are crimped together, the edge of the cylindrical side wall portion 22 is more likely to press the gasket 5 downward, improving the adhesion between the gasket 5 and the cylindrical portion 32b. In addition, the tip of the cylindrical portion 32b is more likely to press the gasket 5 toward the bottom portion 21 of the outer can 2. This further improves the sealing of the internal space of the flat battery 1. From the viewpoint of increasing the capacity of the internal volume of the flat battery 1, the inclination width of the base end 32a is preferably smaller than the thickness t1 of the peripheral wall portion 32 of the sealing can 3, and more preferably is 50% or less of t1. The inclined width is the radial width from the end of the base end 32a on the upper surface portion 31 side to the end of the step portion 32c side, and corresponds to the length displaced in the radial direction from the position where the inclination angle θ2 of the base end 32a with respect to the axial direction is 0°. Such an inclined shape of the base end 32a may be formed in advance during press molding of the sealing can 3, or may be formed by pressing with the edge of the cylindrical side wall portion 22 during the above-mentioned crimping.

[0027] The inclination angle θ2 of the base end 32a with respect to the axial direction may be 0.5 to 5°. If the inclination angle θ2 is too small, the edge of the cylindrical side wall portion 22 is less likely to press the cylindrical portion 32b downward, and the sealing performance is reduced. On the other hand, if the inclination angle θ2 is too large, the contact pressure between the gasket 5 and the base end 32a or the contact pressure between the gasket 5 and the step portion 32c is reduced, and the sealing performance is reduced. The inclination angle θ2 is preferably 1° or more, more preferably 2° or more, and particularly preferably 3° or more. In addition, when the base end 32a does not include a straight portion as shown in FIG. 2 and is composed only of curved lines, the inclination angle θ2 may be the angle at which the angle that the tangent to the curve and the axial direction forms with the largest angle.

[0028] The thickness t2 of the cylindrical side wall portion 22 of the exterior can 2 is preferably 92 to 108% of the thickness t1 of the peripheral wall portion 32 of the sealing can 3. If the thickness t2 of the cylindrical side wall portion 22 is too small, the cylindrical side wall portion 22 may be deformed radially outward due to the elastic force generated radially outward of the peripheral wall portion 32 after crimping, particularly the elastic force of the cylindrical portion 32b. Therefore, the thickness t2 is preferably 92% or more of the thickness t1, more preferably 95% or more, and particularly preferably 98% or more. If the thickness t2 is too large, the internal volume of the flat battery 1 is limited, which hinders the flat battery 1 from having a high capacity. Therefore, the thickness t2 is preferably 108% or less of the thickness t1, more preferably 105% or less, and particularly preferably 102% or less.

[0029] 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.

[0030] (Example) The contact pressure (surface pressure) between the sealing can and the gasket, and the contact pressure (surface pressure) between the exterior can and the gasket were calculated using structural analysis software, and the sealing properties of the examples and comparative examples were simulated. In this structural analysis, the general-purpose structural analysis software "LS-DYNA" made by Livermore Software Technology was used. In this structural analysis, the exterior can was SUS430, the sealing can was cold-rolled steel plate (SPCD), the gasket was made of polypropylene resin, and the tensile modulus of elasticity of the gasket was 1372 MPa.

[0031] First, a flat battery 1 of Example 1 in which the cylindrical portion 32b of the sealing can 3 shown in FIG. 3 is not folded back, the thickness of the entire sealing can 3 including the peripheral wall portion 32 is 0.2 mm, and the thickness of the entire exterior can 2 including the cylindrical side wall portion 22 is 0.2 mm was compared with a flat battery 100 of Comparative Example 1 in which the open end side of the peripheral wall portion 332 of the sealing can 300 shown in FIG. 4 is folded back along its outer periphery. In FIG. 4, the reference numeral 200 denotes the exterior can, and the reference numeral 500 denotes the gasket. Each of FIGS. 3 and 4 shows a flat battery before the sealing can and the exterior can are crimped. The above-mentioned structural analysis was performed on the surface pressure when the sealing can and the exterior can shown in FIG. 3 and FIG. 4 were crimped. As shown in FIG. 5, the surface pressure of the gasket 5 in contact with the surface of the sealing can 3 from the start point S to the end point T in the example was calculated. 2, the inclination angle θ1 of the cylindrical portion 32b relative to the axial direction and the inclination angle θ2 of the base end portion 32a relative to the axial direction of the peripheral wall portion 32 of the sealing can 3 were determined, and the inclination angle θ1 was about 3° and the inclination angle θ2 was about 4°. Furthermore, as shown in FIG. 6, in Comparative Example 1, the contact pressure of the surface of the gasket 500 in contact with the surface of the sealing can 300 was measured at positions corresponding to the start point S and the end point. The measurement results are shown in the graph of FIG. 7. In the graph of FIG. 7, the horizontal axis is the distance from the start point S toward the end point T, the solid line shows the change in contact pressure in Example 1, and the dashed line shows the change in contact pressure in Comparative Example 1.

[0032] 7, the sealing performance on the sealing can side was evaluated from the sum of the areas of the surface pressure in Example 1 and Comparative Example 1. When the area of ​​the surface pressure graph in Comparative Example 1 was taken as 100%, the value in the Example was 130%, indicating that the sealing performance on the sealing can side was improved.

[0033] In addition, in Example 1 and Comparative Example 1, the same structural analysis was performed on the contact pressure (surface pressure) of the gasket in contact with the surface of each outer can. Although not shown in particular, a graph similar to that in FIG. 7 was created, and the sealing property on the outer can side was evaluated from the sum of the areas of the graphs of each surface pressure. In addition, in calculating the surface pressure, the starting point S is the radially innermost position of the gasket surface facing the bottom of the outer can, and the ending point T is the uppermost position of the gasket surface facing the cylindrical side wall of the outer can. Then, when the area of ​​the graph of surface pressure in Comparative Example 1 is taken as 100%, the value in Example 1 is 86%, and it was found that the sealing property on the outer can side is higher in Comparative Example 1.

[0034] Considering these results, the sealing properties of the entire flat battery in Example 1 and Comparative Example 1 were evaluated by comparing the sum of the area of ​​the graph of the surface pressure of the gasket in contact with the sealing can and the area of ​​the graph of the surface pressure of the gasket in contact with the exterior can. As a result, the value of Example 1 was 95% of the value of Comparative Example 1, and it was found that Example 1 and Comparative Example 1 obtained almost the same level of sealing properties. This is considered to be because in Example 1, the improvement of the sealing properties on the sealing can side compensated for the decrease in the sealing properties on the exterior can side. Thus, in Example 1, even when the overall thickness of the peripheral wall part of the sealing can was made relatively thin so as not to fold back the cylindrical part of the sealing can, it was found that excellent sealing properties could be secured as in the case of folding back the cylindrical part of the sealing can, and further, by not folding back the cylindrical part of the sealing can, the internal volume of the flat battery could be increased to achieve a high capacity. Note that, as shown in FIG. 6, a relatively large gap was formed between the peripheral wall part 332 and the gasket 500, and the contact area between the peripheral wall part 332 and the gasket 500 was reduced. This is believed to be because the gasket 500 that comes into contact with the tip of the folded-back peripheral wall portion 332 is spread outward in the radial direction.

[0035] A 2032 size flat battery was assembled using a 0.2 mm thick SUS430 exterior can, a 0.2 mm thick cold rolled steel (SPCD) sealing can, and a polypropylene gasket. The battery was then cut in the height direction and the cross section was observed. The inclination angle θ1 of the peripheral wall of the sealing can relative to the axial direction of the cylindrical part was 3°, and the inclination angle θ2 of the base end relative to the axial direction was 4°, confirming that the same results as those obtained from the structural analysis were obtained.

[0036] Next, the flat battery of Example 1 and the flat batteries of Comparative Examples 2 and 3 were subjected to the same structural analysis to evaluate the sealing property of each. In the flat batteries of Comparative Examples 2 and 3, the cylindrical part of the sealing can is not folded back along the outer peripheral surface of the cylindrical part, as in Example 1. In addition, the structural analysis was performed with the thickness t of the sealing can (circumferential wall part) in Comparative Example 2 set to 0.15 mm, and the thickness t of the sealing can (circumferential wall part) in Comparative Example 3 set to 0.25 mm. The sealing cans of Example 1, Comparative Example 2, and Comparative Example 3 were each made of a cold-rolled steel plate (SPCD).

[0037] The surface pressure of the gasket in contact with the surface of the sealing can in Example 1, Comparative Example 2, and Comparative Example 3 is shown in the graph of Fig. 8. In the graph shown in Fig. 8, the horizontal axis is the distance from the starting point S toward the end point T, and the solid line (t = 0.2 mm) shows the change in surface pressure in Example 1, the relatively fine dashed line (t = 0.15 mm) shows the change in surface pressure in Comparative Example 2, and the relatively coarse dashed line (t = 0.25 mm) shows the change in surface pressure in Comparative Example 3. In Comparative Example 2, the inclination angle θ1 exceeded 4° and the inclination angle θ2 exceeded 5°, whereas the inclination angles θ1 and θ2 in Comparative Example 3 were both approximately 0° (less than 0.5°).

[0038] In the graph of Fig. 8, the sealing property on the sealing can side was evaluated from the sum of the areas of the surface pressure in each of Comparative Example 2 and Comparative Example 3. When the area of ​​the surface pressure graph in Comparative Example 1 shown in Fig. 7 described above was taken as 100%, the value in Comparative Example 2 in Fig. 8 was 101%, and the value in Comparative Example 3 was 104%. As described above, since the value in Example 1 was 130% of Comparative Example 1, it was confirmed that the flat battery of Example 1, in which the inclination angle θ1 was in the range of 0.5° to 4° and the inclination angle θ2 was in the range of 0.5° to 5°, had the best sealing property on the sealing can side.

[0039] In addition, in the same manner as described above, the contact pressure (surface pressure) of the gasket in contact with the surface of the outer can was calculated, and the sealing property on the outer can side was evaluated from the sum of the areas of each surface pressure. Then, when the area of ​​the graph of the surface pressure in Comparative Example 1 was taken as 100%, the value in Comparative Example 2 was 80%, and the value in Comparative Example 3 was 84%. Since the value in Example 1 was 86% of Comparative Example 1, it was confirmed that the flat battery of Example 1, in which the inclination angle θ1 was in the range of 0.5° to 4° and the inclination angle θ2 was in the range of 0.5° to 5°, had superior sealing property on the outer can side compared to Comparative Example 2 and Comparative Example 3. Based on these results, the sealing property of the entire flat batteries of Comparative Example 2 and Comparative Example 3 was evaluated in the same manner as described above, and as a result, the sealing property of Comparative Example 2 was 84% ​​of Comparative Example 1, and the sealing property of Comparative Example 3 was 88%. Therefore, it was found that the flat battery of Example 1, which has a sealing property of 95% of Comparative Example 1, has superior sealing property to the flat batteries of Comparative Example 2 and Comparative Example 3.

[0040] In this way, the flat battery according to the Example was able to obtain a stronger contact pressure (surface pressure) and improved sealing performance compared to the batteries of Comparative Examples 2 and 3 by appropriately deforming the peripheral wall 32 of the sealing can 3 during crimping. Therefore, it is presumed that if the inclination angle θ1 of the cylindrical portion 32b with respect to the axial direction is set in the range of 0.5 to 4° and the inclination angle θ2 of the base end portion 32a with respect to the axial direction is set in the range of 0.5 to 5° in the peripheral wall 32 of the sealing can 3, it is possible to increase the internal volume and achieve a higher capacity while ensuring excellent sealing performance comparable to that of Comparative Example 1. [Explanation of symbols]

[0041] 1 Flat battery 2 outer can, 21 bottom, 22 cylindrical side wall 3 Sealing can, 31 Top part, 32 Peripheral wall part, 32a Base end part, 32b Cylindrical part 32c Stepped section 41 positive electrode, 42 negative electrode, 43 separator 5 Gasket θ1 tilt angle, θ2 tilt angle t1 thickness, t2 thickness

Claims

1. an outer can having a bottom and a cylindrical side wall; a sealing can having a top surface portion and a peripheral wall portion and facing the outer can; a gasket disposed between the cylindrical side wall portion and the peripheral wall portion; the peripheral wall portion has a base end portion on the upper surface portion side, a cylindrical portion formed larger in outer diameter than the base end portion and having a tip portion facing the bottom portion of the outer can, and a step portion located between the base end portion and the cylindrical portion, the cylindrical portion is inclined radially outward from the end portion on the step portion side toward the tip of the cylindrical portion, and has an inclination angle of 0.5° to 4° with respect to the axial direction, The base end portion is inclined radially inward from the end portion on the upper surface side toward the end portion on the stepped portion side, and has an inclination angle of 0.5° to 5° with respect to the axial direction.

2. The flat battery according to claim 1, The flat battery has a peripheral wall of the sealing can having a thickness of 0.185 to 0.215 mm.

3. The flat battery according to claim 2, The cylindrical side wall of the outer can has a thickness that is 92 to 108% of the thickness of the peripheral wall.

4. The flat battery according to claim 1, The flat battery, wherein the sealing can is made of a cold-rolled steel plate.

5. The flat battery according to claim 1, The flat battery, wherein the outer can is made of a stainless steel plate.

6. A flat battery according to claim 1, The tip of the cylindrical portion of the sealing can is not folded back and faces the bottom of the outer can.

7. A flat battery according to claim 1, The flat battery, wherein the gasket is formed from polypropylene resin, polyphenylene sulfide resin, or PFA resin.

8. A flat battery according to claim 1, The flat battery has a cylindrical outer can shape with a circular bottom.

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