Battery case and secondary battery including the battery case

Abstract

To improve the ease of assembly when attaching a sealing plate to an opening of a case body.SOLUTION: A battery case disclosed here includes a bottomed square case body 41a having a substantially rectangular opening 41a1, and a sealing plate attached to the opening. The opening 41a1 of the case body 41a has a long side 44a, a short side 46a, an R portion 47c, and a step 48b protruding from the inner surface of the short side 46a. The R portion 47c is provided with a gradually changing region 47c3 in which the shape of the step 48b gradually changes toward the shape of the inner surface of the long side 44a as it goes along the R portion 47c toward the long side 44a.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a battery case and a secondary battery including the battery case. [Background technology]

[0002] Japanese Patent Application Laid-Open Publication No. 2001-135282 discloses a sealed battery in which a lid is attached to the opening at the top of the battery can and sealed by welding. This publication proposes forming four-corner step portions into which the lid can fit at the four curved corners of the inner surface of the opening at the top of the battery can, and forming long-side step portions on the inner surface of at least the long sides of the opening that are connected to the four-corner step portions, and fitting the battery lid into the step portions and welding it. The technology proposed in this publication claims that by forming step portions not only at the four corners of the battery can but also on the long sides, the battery lid can be fitted into the desired position and reliably welded.

[0003] Japanese Patent Application Laid-Open Publication No. 2013-93119 discloses a battery case having a rectangular case body with sidewalls having long and short side portions, a bottom, and an opening, and a cover plate that seals the opening. This publication proposes forming a step on the short side of the case body and a tapered portion below the contact point between the long side and the cover plate. The technology proposed in this publication is said to be able to suppress penetration of laser light into the long side by forming a tapered portion at a predetermined location on the long side.

[0004] Japanese Patent Application Laid-Open Publication No. 2013-222705 discloses a secondary battery including a roughly rectangular parallelepiped case and a cap plate that covers the opening of the case. The publication proposes providing triangular prism-shaped support members at the four corners of the case. The technology proposed in the publication claims that by forming the support members over the corners, the thickness of the corners is increased, thereby reducing deformation of the case.

[0005] Japanese Patent Application Laid-Open Publication No. 2014-10936 discloses a prismatic battery including a battery case having a rectangular tubular body member with a bottom and a rectangular plate-shaped lid member. The body member has a pair of long and short sides, and four curved openings connecting the long and short sides. The publication proposes providing support protrusions and lower protrusions that protrude toward the inside of the case body. The support protrusions are provided over the entire curved openings. The lower protrusions are provided over the entire short sides of the opening at a lower level than the support protrusions. The lower protrusions do not come into contact with the lid member. The technology proposed in the publication is said to prevent an energy beam (such as a laser beam) from penetrating the body member and causing defects when the energy beam is irradiated to weld the battery case. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-135282 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-93119 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-222705 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-10936 Summary of the Invention [Problem to be solved by the invention]

[0007] It is desirable to improve the ease of assembly when attaching the sealing plate to the opening of the case body. [Means for solving the problem]

[0008] The battery case disclosed herein includes a rectangular case body with a bottom and a substantially rectangular opening on one side opposite the bottom, and a substantially rectangular sealing plate attached to the opening and having an outer diameter corresponding to the upper edge of the opening. The opening of the case body has a pair of opposing long sides, a pair of opposing short sides located at both ends of the pair of long sides, rounded portions provided at each of the four corners between the long sides and the short sides, and steps protruding from the inner surfaces of the pair of short sides. The rounded portions have a gradually changing region in which the shape of the steps gradually approaches the shape of the inner surfaces of the long sides as they move along the rounded portions toward the long sides.

[0009] With this configuration, when the sealing plate is attached to the opening of the case body, the gradually changing region creates a portion where the sealing plate comes into contact, making it easier to achieve a light press-fit, in which the sealing plate is pressed into the opening with light force. Achieving a light press-fit improves the ease of assembly when attaching the sealing plate to the opening of the case body.

[0010] The inner surfaces of the pair of opposing long sides may be tapered surfaces that slope inwardly downward. In the gradually changing region, the shape of the step may be configured to gradually change to approach the tapered surface toward the long sides. In this case, when the sealing plate is attached to the opening, a gap that widens toward the upper edge of the opening may be formed between the portion where the tapered surface is formed and the sealing plate.

[0011] Alternatively, the inner surfaces of the pair of opposing long sides may be flat. In this case, the gradually changing region may be configured so that the step shape gradually changes to approach a flat shape along the R portion toward the long sides.

[0012] The gradually changing region may be provided in a range of 45 degrees or more and 90 degrees or less from the center of the rounded portion, starting from the boundary between the rounded portion and the short side portion.

[0013] The edge of the lower surface of the sealing plate may be chamfered. In this case, the edge of the lower surface, in a region that overlaps with the gradually changing region when the sealing plate is attached to the opening, may be chamfered according to the shape of the gradually changing region.

[0014] The battery case can be applied to a secondary battery. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a partial cross-sectional view of a secondary battery 10. As shown in FIG. [Figure 2] FIG. 2 is a plan view of the case body 41a. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a partially enlarged view of FIG. [Figure 6] FIG. 6 is a view taken along the arrow A in FIG. [Figure 7] FIG. 7 is a cross-sectional view of the gradually changing region 47c3. [Figure 8] FIG. 8 is a cross-sectional view of the gradually changing region 47c3. [Figure 9] FIG. 9 is a plan view of the secondary battery 10 with the sealing plate 41b attached. [Figure 10] FIG. 10 is a rear view of the sealing plate 41b. [Figure 11] FIG. 11 is a cross-sectional view of opening 41a1 to which sealing plate 41b is attached. [Figure 12] FIG. 12 is a cross-sectional view of opening 41a1 to which sealing plate 41b is attached. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the disclosure herein will be described below. The embodiments described herein are, of course, not intended to limit the disclosure. The drawings are schematic and do not necessarily reflect the actual product. Furthermore, a notation such as "A to B" indicating a numerical range means "greater than A and less than B" unless otherwise specified, and also encompasses the meaning of "greater than A and less than B." In the drawings described below, components and parts that perform the same function are designated by the same reference numerals, and redundant explanations may be omitted or simplified.

[0017] In this specification, the term "secondary battery" refers generally to an electricity storage device in which charge carriers move between a pair of electrodes (positive and negative electrodes) via an electrolyte, resulting in a charge-discharge reaction. Such secondary batteries include so-called storage batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, as well as capacitors such as electric double-layer capacitors. Below, we will explain embodiments of the battery case disclosed herein and a secondary battery including the battery case, taking a lithium-ion secondary battery as an example of the secondary batteries described above. Unless otherwise specified, the disclosure herein is not limited to lithium-ion secondary batteries and may also be applied to other secondary batteries.

[0018] First Embodiment <Secondary battery 10> FIG. 1 is a partial cross-sectional view of a secondary battery 10. FIG. 1 illustrates a state in which the interior is exposed along one wide surface of a substantially rectangular parallelepiped battery case 41. The secondary battery 10 illustrated in FIG. 1 is a so-called sealed battery in which the battery case 41 containing the electrode assembly 20 is sealed. The directions of up, down, left, right, front, and rear are indicated by arrows U, D, L, R, F, and Rr in the drawing, respectively. In this specification, the wide surface 44 (see FIGS. 1 and 2 ) facing the wide surface 43 of the secondary battery 10 is defined as the “front (F)” (front face), the wide surface 43 is defined as the “rear (Rr),” the sealing plate 41b side is defined as the “top (U),” the bottom 42 side is defined as the “bottom (D),” the narrow surface 45 side is defined as the “left (L),” and the narrow surface 46 side is defined as the “right (R).”

[0019] As shown in FIG. 1 , the secondary battery 10 includes an electrode assembly 20 and a battery case 41. The battery case 41 includes a case body 41a having an opening 41a1 and a sealing plate 41b that closes the opening 41a1 of the case body 41a. The case body 41a accommodates the electrode assembly 20. Internal terminals 55, 65 and external terminals 51, 61 are attached to the sealing plate 41b via a gasket 70 and an insulator 80. In this embodiment, the internal terminal 55 is connected to the positive current collector foil 21a of the electrode assembly 20. The external terminal 51 is connected to the internal terminal 55 and constitutes the positive terminal 50 outside the battery case 41. The internal terminal 65 is connected to the negative current collector foil 22a of the electrode assembly 20. The external terminal 61 is connected to the internal terminal 65 and constitutes the negative terminal 60 outside the battery case 41.

[0020] <Electrode body 20> The electrode assembly 20 is housed in a battery case 41 while being covered with an insulating film (not shown) or the like. The electrode assembly 20 includes a positive electrode sheet 21 as a positive electrode element, a negative electrode sheet 22 as a negative electrode element, and separator sheets 31 and 32 as separators. The positive electrode sheet 21, the first separator sheet 31, the negative electrode sheet 22, and the second separator sheet 32 ​​are each a long, strip-shaped member.

[0021] The positive electrode sheet 21 has a positive electrode current collector foil 21a (e.g., aluminum foil) of a predetermined width and thickness, and a positive electrode active material layer 21b containing a positive electrode active material formed on both sides thereof, except for an unformed portion 21a1 set at one end of the width direction with a fixed width. In a lithium-ion secondary battery, the positive electrode active material is, for example, a material that can release lithium ions during charging and absorb lithium ions during discharging, such as a lithium transition metal composite material. Generally, various positive electrode active materials have been proposed in addition to lithium transition metal composite materials, and there is no particular limitation to the positive electrode active material.

[0022] The negative electrode sheet 22 has a negative electrode current collector foil 22a (copper foil in this case) of a predetermined width and thickness, and a negative electrode active material layer 22b containing a negative electrode active material formed on both sides thereof, except for an unformed portion 22a1 set at a fixed width on one edge in the width direction. In a lithium-ion secondary battery, the negative electrode active material is, for example, a material such as natural graphite that can absorb lithium ions during charging and release the absorbed lithium ions during discharging. Generally, various negative electrode active materials other than natural graphite have been proposed, and there is no particular limitation.

[0023] For example, a porous resin sheet having required heat resistance and allowing the electrolyte to pass through is used for the separator sheets 31 and 32. Various separator sheets 31 and 32 have been proposed, and there is no particular limitation.

[0024] Here, the width of the negative electrode active material layer 22b is formed to be wider than that of the positive electrode active material layer 21b, for example. The width of the separator sheets 31 and 32 is wider than that of the negative electrode active material layer 22b. The unformed portion 21a1 of the positive electrode current collector foil 21a and the unformed portion 22a1 of the negative electrode current collector foil 22a are oriented on opposite sides of each other in the width direction. The positive electrode sheet 21, the first separator sheet 31, the negative electrode sheet 22, and the second separator sheet 32 ​​are aligned in the length direction and are stacked and wound in this order. The negative electrode active material layer 22b covers the positive electrode active material layer 21b with the separator sheets 31 and 32 interposed therebetween. The negative electrode active material layer 22b is covered by the separator sheets 31 and 32. The unformed portion 21a1 of the positive electrode current collector foil 21a protrudes from one widthwise side of the separator sheets 31 and 32. The unformed portion 22a1 of the negative electrode current collector foil 22a protrudes from the separator sheets 31 and 32 on the opposite widthwise side.

[0025] 1, the electrode body 20 described above is flattened along a plane including the winding axis so that it can be housed in the case body 41a of the battery case 41. Then, along the winding axis of the electrode body 20, the unformed portion 21a1 of the positive electrode current collector foil 21a is arranged on one side, and the unformed portion 22a1 of the negative electrode current collector foil 22a is arranged on the other side.

[0026] <Battery Case 41> The battery case 41 accommodates the electrode assembly 20. The battery case 41 includes a case body 41a and a sealing plate 41b. The case body 41a is a bottomed member having an opening 41a1 on one side opposite the bottom. In this embodiment, the case body 41a has a substantially rectangular parallelepiped shape with one side open. The sealing plate 41b is a plate material attached to the opening 41a1 of the case body 41a. In this embodiment, the case body 41a and the sealing plate 41b are each formed of aluminum or an aluminum alloy primarily containing aluminum to ensure weight reduction and required rigidity. Note that, although the embodiment shown in FIG. 1 illustrates a wound-type electrode assembly 20, the structure of the electrode assembly 20 is not limited to this form. The electrode assembly 20 may have a laminated structure in which positive electrode sheets and negative electrode sheets are alternately stacked with separator sheets interposed therebetween. Furthermore, the battery case 41 may accommodate multiple electrode assemblies 20.

[0027] The battery case 41 may house an electrolyte (not shown) together with the electrode assembly 20. A non-aqueous electrolyte in which a supporting salt is dissolved in a non-aqueous solvent can be used as the electrolyte. Examples of non-aqueous solvents include carbonate-based solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of supporting salts include fluorine-containing lithium salts such as LiPF6.

[0028] <Case body 41a> FIG. 2 is a plan view of the case body 41a. The case body 41a is a bottomed, rectangular member having an opening 41a1 on one side opposite the bottom. In this embodiment, the case body 41a has a generally rectangular parallelepiped shape with one side open. As shown in FIGS. 1 and 2, the case body 41a has a bottom 42 constituting a generally rectangular bottom surface, a pair of wide side portions 43 and 44, and a pair of narrow side portions 45 and 46. The pair of wide side portions 43 and 44 each rise from a long side of the bottom 42. The pair of narrow side portions 45 and 46 each rise from a short side of the bottom 42. An opening 41a1 surrounded by the pair of wide side portions 43 and 44 and the pair of narrow side portions 45 and 46 is formed on one side of the case body 41a. As shown in FIG. 2, opening 41a1 of case body 41a is a substantially rectangular opening with rounded portions 47a to 47d each having an arc shape.

[0029] As shown in FIG. 2, the opening 41a1 of the case body 41a has a pair of opposing long sides 43a, 44a, a pair of opposing short sides 45a, 46a, and rounded portions 47a to 47d at the four corners. The long sides 43a, 44a are the upper edges of the wide side portions 43, 44. The short sides 45a, 46a are the upper edges of the narrow side portions 45, 46. The short sides 45a, 46a are located at both ends of the pair of long sides 43a, 44a. The rounded portions 47a to 47d are the upper edges of curved surfaces that bulge outward and connect the wide side portions 43, 44 and the narrow side portions 45, 46. The rounded portions 47a to 47d are provided at the four corners of the opening 41a1 of the case body 41a along curves that connect the long and short sides. In this embodiment, the opening 41a1 of the case body 41a is formed so that the long sides 43a and 44a of the opening 41a1 bulge slightly outward before the sealing plate 41b is attached. When the sealing plate 41b is attached to the opening 41a1, the short sides 93 and 94 (see FIGS. 9 and 10) of the sealing plate 41b rest on the steps 48a and 48b of the opening 41a1. This closes the opening 41a1 of the case body 41a. In this state, the long sides 43a and 44a of the opening 41a1 of the case body 41a are clamped. This holds the sealing plate 41b in a sandwiched state between the long sides 43a and 44a of the opening 41a1 of the case body 41a. A laser is irradiated and scanned in the circumferential direction at the boundary between sealing plate 41b and case body 41a, thereby welding sealing plate 41b and case body 41a, thereby sealing opening 41a1 of case body 41a with sealing plate 41b.

[0030] FIG. 3 is a cross-sectional view taken along the line III-III of FIG. 2. As shown in FIGS. 2 and 3, opening 41a1 of case body 41a has steps 48a and 48b on the inner surfaces of a pair of opposing short sides 45a and 46a. Steps 48a and 48b are portions that support sealing plate 41b to be attached to opening 41a1 of case body 41a. Steps 48a and 48b are provided at predetermined positions from the upper edges of short sides 45a and 46a. In this embodiment, the positions at which steps 48a and 48b are provided on the inner surfaces of short sides 45a and 46a are determined so that, when sealing plate 41b is attached to opening 41a1 of case body 41a, the height of the upper edge of opening 41a1 of case body 41a and the height of the top surface of sealing plate 41b are aligned. Specifically, steps 48a, 48b are provided from the upper edges of the short sides 45a, 46a at heights corresponding to the thickness of the sealing plate 41b. In this embodiment, the short sides 45a, 46a of the case body 41a are thicker below the steps 48a, 48b than on the upper edge side. When the short sides 45a, 46a of the case body 41a are viewed from the upper edge side, the steps 48a, 48b protrude from the upper edge of the case body 41a toward the inside of the case. In the embodiment shown in FIG. 3, the steps 48a, 48b have tapered surfaces that slope inward toward the bottom 42. The taper angle may be 40 degrees to 55 degrees. The steps 48a, 48b of the short sides 45a, 46a continue to parts of the rounded portions 47a to 47d. In this embodiment, a C-surface is provided on the edge of the lower surface 41b2 of the sealing plate 41b. The tapered surfaces of the steps 48a, 48b of the short side portions 45a, 46a may be aligned with the angle of the chamfered portion.

[0031] 4 is a cross-sectional view taken along line IV-IV of FIG. 2. In the embodiment shown in FIGS. 2 and 4, tapered surfaces 49c are provided on the inner surfaces of a pair of opposing long side portions 43a, 44a, inclining inward as they extend downward. The angle of tapered surfaces 49c is preferably set so that sealing plate 41b can be pressed into the opening of case body 41a with a light force, resulting in a light press-fit. In this embodiment, the long side portions 43a, 44a are inclined at an angle θ1 from the upper edges thereof relative to the vertical direction of the opening of case body 41a. The angle θ1 may be 5 to 20 degrees (for example, approximately 15 degrees).

[0032] Fig. 5 is a partially enlarged view of Fig. 2. Fig. 5 shows a partially enlarged view of R portion 47c of Fig. 2. As shown in Fig. 5, R portion 47c is provided with a gradually changing region 47c3 in which the shape of step 48b gradually changes to match the shape of the inner surface of long side portion 44a along R portion 47c. Note that R portions 47a, 47b, and 47d have the same configuration as R portion 47c, and therefore may not be illustrated or described.

[0033] 2, 4, and 5, the inner surfaces of the pair of opposing long side portions 43a, 44a are tapered surfaces 49c that slope inwardly downward. In this case, in the gradually changing region 47c3, the shape of the step 48b may be configured to gradually change so as to approach the tapered surface 49c along the rounded portion 47c toward the long side portion 44a.

[0034] In this embodiment, the gradually changing region 47c3 is provided within a range of 45 degrees to 90 degrees from the center Rc of the rounded portion 47c, starting from the boundary B1 between the rounded portion 47c and the short side portion 46a. As shown in FIG. 5, when a straight line L1 connecting the center Rc and the boundary B1 is set as a reference (0 degrees), the gradually changing region 47c3 can be arranged within a range of 45 degrees to 90 degrees (e.g., 50 degrees to 70 degrees) from the line L1, centered at the center Rc. In FIG. 5, the gradually changing region 47c3 is a region sandwiched between the lines La and Lb. Although not particularly limited, the angle α formed by the lines La and Lb can be set to, for example, 3 degrees to 10 degrees.

[0035] In the embodiment shown in FIG. 5, the rounded portion 47c includes a first region 47c1, a second region 47c2, and a gradually changing region 47c3. The first region 47c1 is adjacent to the short side 46a. In FIG. 5, the first region 47c1 is the region sandwiched between lines L1 and La. The second region 47c2 is the region adjacent to the long side 44a. In FIG. 5, the second region 47c2 is the region sandwiched between lines Lb and L2. The line L2 is a line connecting the center Rc and the boundary B2 between the rounded portion 47c and the long side 44a. As shown in FIG. 5, a step 48b is provided in the first region 47c1. The step 48b is provided from the short side 46a to the first region 47c1.

[0036] As shown in Fig. 5, the second region 47c2 has a tapered surface 49c. In this embodiment, the tapered surface 49c is provided from the second region 47c2 to the long side portion 44a. In the embodiment shown in Fig. 5, the gradually changing region 47c3 is provided between the first region 47c1 and the second region 47c2. Here, the gradually changing region 47c3 may be configured so that the shape of the step 48b in the first region 47c1 gradually changes to approach the tapered surface 49c as it moves along the rounded portion 47c toward the second region 47c2 and the long side portion 44a.

[0037] FIG. 6 is a view taken along the arrow A in FIG. 5. FIGS. 7 and 8 are cross-sectional views of the gradually changing region 47c3. The gradually changing region 47c3 is a region where the shape of the inner surface changes. Therefore, the cross-sectional shape of the gradually changing region 47c3 is not fixed. FIG. 6 shows the curved portion 47c as seen from the inside of the case body 41a. FIGS. 6 to 8 show the process in which the shape of the inner surface changes in the gradually changing region 47c3 from the step 48b of the first region 47c1 toward the tapered surface 49c of the second region 47c2.

[0038] In this embodiment, the gradually changing region 47c3 has two tapered surfaces. For example, the shapes of the two tapered surfaces gradually change from the first region 47c1 to the second region 47c2, thereby connecting the step 48b and the tapered surface 49c. In this embodiment, the two tapered surfaces are composed of the tapered surface of the step 48b and a tapered surface 47t. The shape of the tapered surface 47t changes, for example, from the end E1 of the first region 47c1 to the start E2 of the second region. As shown in FIGS. 7 and 8, the tapered surface 47t slopes inward as it extends downward. As shown in FIG. 6, the tapered surface 47t gradually becomes larger from the end E1 of the first region 47c1 to the start E2 of the second region 47c2, becoming a tapered surface 49c at the start E2. The tapered surface of the step 48b gradually becomes smaller from the end E1 toward the start E2, and is absorbed into the tapered surface 49c at the start E2.

[0039] As shown in Figures 6 to 8, the upper end X1 of the tapered surface 47t is located between the step 48b and the upper edge of the opening 41a1. As shown in Figures 3 to 8, from the end E1 to the start E2, the upper end X1 gradually moves from the upper end of the step 48b at the end E1 toward the opening 41a1 side, and reaches the upper edge of the opening 41a1 at the start E2. On the other hand, as shown in Figures 3 to 7, from the end E1 to the start E2, the lower end X2 of the tapered surface 47t gradually moves from the upper end of the step 48b at the end E1 toward the bottom 42 side (see Figure 1) and reaches the lower end of the tapered surface 49c at the start E2.

[0040] In this embodiment, the tapered surface 47t is inclined at an angle θ2 relative to the vertical direction of the opening 41a1. The angle θ2 may be, for example, 5 to 30 degrees. In the gradually changing region 47c3, the angle θ2 gradually changes within a range of 5 to 30 degrees from the end point E1 to the start point E2, and the step 48b and the tapered surface 49c are continuous.

[0041] In the gradually changing region 47c3, the shapes of the two tapered surfaces (tapered surface 47t and the tapered surface of step 48b) gradually change as described above, and step 48b and tapered surface 49c are continuous, thereby suppressing partial excessive interference and improving ease of assembly.

[0042] <Sealing plate 41b> 9 is a plan view of the secondary battery 10 with the sealing plate 41b attached. As shown in FIGS. 1 and 9, the sealing plate 41b is attached to the opening 41a1 of the case body 41a and is a substantially rectangular plate having an outer diameter corresponding to the upper edge of the opening 41a1. In this embodiment, the sealing plate 41b is attached to the inside of the opening 41a1 of the case body 41a along the inner side surface of the opening 41a1, sealing the opening 41a1.

[0043] In this embodiment, the sealing plate 41b is provided with a liquid inlet 40a and a safety valve 40b. The liquid inlet 40a is closed by attaching a sealing member after the sealing plate 41b is attached to the opening 41a1 of the case body 41a and electrolyte is injected into the case body 41a. Note that FIG. 9 shows the sealing plate 41b assembled to the opening 41a1 of the case body 41a and welded. In FIG. 9, no sealing member is attached to the sealing plate 41b. The safety valve 40b is thin-walled and breaks when the pressure inside the battery case 41 exceeds a predetermined value.

[0044] A positive electrode terminal 50 and a negative electrode terminal 60 are attached to the upper surface 41b1 of the sealing plate 41b. The sealing plate 41b has terminal attachment holes 5 and 6 for attaching the positive electrode terminal 50 and the negative electrode terminal 60, respectively (see FIG. 10). As shown in FIGS. 1 and 9, the positive electrode terminal 50 has an external terminal 51 and an internal terminal 55. The negative electrode terminal 60 has an external terminal 61 and an internal terminal 65. The internal terminals 55 and 65 are each attached to the inside of the sealing plate 41b via an insulator 80. The external terminals 51 and 61 are each attached to the outside of the sealing plate 41b via a gasket 70. The internal terminals 55 and 65 each extend into the inside of the case body 41a. The unformed portion 21a1 of the positive electrode current collector foil 21a of the electrode body 20 and the unformed portion 22a1 of the negative electrode current collector foil 22a are attached to internal terminals 55, 65 attached to both sides of the sealing plate 41b in the long side direction, respectively.

[0045] In this embodiment, as shown in Fig. 9, the sealing plate 41b has a pair of long sides 91, 92, a pair of short sides 93, 94, and rounded portions 95-98 provided at the four corners. The pair of long sides 91, 92 face each other. The pair of short sides 93, 94 are located at both ends of the pair of long sides 91, 92 and face each other. The rounded portions 95-98 are provided at the four corners between the long sides 91, 92 and the short sides 93, 94, respectively. As shown in Fig. 9, the rounded portions 95-98 are provided between the long sides 91, 92 and the short sides 93, 94, respectively, and are curved so as to bulge outward from the sealing plate 41b.

[0046] 1 and 9, when the sealing plate 41b is attached to the case body 41a, the upper surface 41b1 of the sealing plate 41b is arranged to face the outside of the secondary battery 10. As shown in FIG. 1, the lower surface 41b2 of the sealing plate 41b is arranged to face the inside of the secondary battery 10. For example, the upper surface 41b1 is the surface that faces the outside of the case body 41a when attached to the opening 41a1 of the case body 41a. For example, the lower surface 41b2 is the surface that faces the inside of the case body 41a when attached to the opening 41a1 of the case body 41a.

[0047] Fig. 10 is a rear view of sealing plate 41b. As shown in Fig. 10, the edge of lower surface 41b2 of sealing plate 41b is chamfered. In this embodiment, C-surface 41c is formed on the edge of lower surface 41b2 of sealing plate 41b.

[0048] Although not shown, the area of ​​the lower surface 41b2 that overlaps with the gradually changing region 47c3 when the sealing plate 41b is attached to the opening 41a1 may be chamfered according to the shape of the gradually changing region 47c3.

[0049] 11 and 12 are cross-sectional views of the opening 41a1 to which the sealing plate 41b is attached. Both FIGS. 11 and 12 show partial cross-sectional views of the opening 41a1 of the case body 41a with the sealing plate 41b attached. FIG. 11 is a cross-sectional view of a portion of the case body 41a where the step 48b is formed (e.g., the short side portion 46a or the first region 47c1). In this embodiment, the sealing plate 41b attached to the opening 41a1 of the case body 41a in this portion is supported by the step 48b. As shown in FIG. 11, the C-face 41c of the sealing plate 41b is positioned on the step 48b.

[0050] 12 is a cross-sectional view of a portion of case body 41a where tapered surface 49c is formed (for example, long side portion 44a or second region 47c2). As shown in FIG. 12, a gap S is formed between the portion where tapered surface 49c is formed and sealing plate 41b. Gap S widens toward the upper edge of opening 41a1 of case body 41a.

[0051] In the battery case 41 disclosed herein, steps 48a, 48b are provided on the inner surfaces of the short sides 45a, 46a. Furthermore, the curved portions 47a-47d are provided with gradually changing regions in which the shape of the steps 48a, 48b gradually changes to match the shape of the inner surfaces of the long sides 43a, 44a along the curved portions. In other words, the curved portions 47a-47d of the battery case 41 allow the shape of the steps 48a, 48b on the short sides 45a, 46a to gradually match the shape of the inner surfaces of the long sides 43a, 44a. In this case, when the sealing plate 41b is attached to the opening 41a1 of the case body 41a, the gradually changing regions of the curved portions 47a-47d of the opening 41a1 of the case body 41a will produce areas where the sealing plate 41b will come into contact. The presence of such a contact area allows the sealing plate 41b to be press-fitted into the opening 41a1 of the case body 41a with a light force (light press-fit). Therefore, when attaching the sealing plate 41b to the opening 41a1 of the case body 41a, the sealing plate 41b is less likely to shift, improving assembly quality. The provision of the gradually changing regions in the curved portions 47a-47d allows the above-mentioned light press-fitting to be achieved even when the dimensions of the opening 41a1 of the case body 41a and the sealing plate 41b vary. Furthermore, the dimensional accuracy requirements for the opening 41a1 of the case body 41a and the sealing plate 41b required for the light press-fitting can be relaxed, making it easier to control the dimensions of the sealing plate 41b relative to the case body 41a. Furthermore, the presence of the gradually changing regions reduces the gap between the opening 41a1 of the case body 41a and the sealing plate 41b compared to when the gradually changing regions are not present. This reduces the likelihood of laser leakage.

[0052] In this embodiment, the inner surface of the long side portion 44a is a tapered surface 49c. The tapered surface 49c on the inner surface of the long side portion 44a can form a tapered surface on the inner surface of the portion of the long side portion 44a adjacent to the rounded portion 47c. Therefore, in addition to the gradually changing region 47c3, light press-fitting is possible in the adjacent region as well. Furthermore, when the sealing plate 41b is attached to the opening 41a1 having such a configuration, a gap S is formed between the portion where the tapered surface 49c is formed and the sealing plate 41b. The formation of the gap S makes it easier to lightly press-fit the sealing plate 41b. Therefore, this configuration can more effectively achieve the effect of improving the ease of assembly and also facilitate dimensional control.

[0053] In this embodiment, the gradually-changing region 47c3 is formed in a range of 45 degrees to 90 degrees from the center Rc, starting from the boundary B1 between the rounded portion 47c and the short side portion 46a. The gradually-changing region 47c3 can be formed in a region where dimensional control is difficult when attaching the sealing plate 41b. This allows for a light press-fit in this region, further improving the ease of assembly. Additionally, the step 48b is formed in a range of at least less than 45 degrees from the center Rc. Therefore, even if the dimensional accuracy of the sealing plate 41b results in a gap occurring in a range of at least less than 45 degrees from the center Rc of the rounded portion 47c, laser leakage can be prevented in a range of at least less than 45 degrees from the center Rc of the rounded portion 47c.

[0054] In this embodiment, the edge of the underside 41b2 of the sealing plate 41b is chamfered. As a result, even if the sealing plate 41b has a shape that fits the opening 41a1 of the case body 41a, the shape of the underside 41b2 of the sealing plate 41b is smaller than the upper edge of the opening 41a1 of the case body 41a. This shape makes it easy to fit the sealing plate 41b into the opening 41a1 of the case body 41a. Furthermore, because a light press fit is achieved in the opening 41a1 of the case body 41a, interference between the two components is less likely to occur when the sealing plate 41b is attached to the opening 41a1. This allows the battery case 41 to be configured so that the sealing plate 41b is easily fitted into the case body 41a.

[0055] In this embodiment, the edge of the lower surface 41b2 of the sealing plate 41b, which is to be overlapped with the gradually changing region 47c3 after installation, is chamfered according to the shape of the gradually changing region 47c3, which makes it easier to fit the sealing plate 41b into the opening 41a1.

[0056] The secondary battery 10 also includes a battery case 41. As described above, the battery case 41 has improved assembly properties when attaching the sealing plate 41b to the opening 41a1 of the case body 41a. Therefore, the secondary battery 10 including the battery case 41 has desirable dimensional accuracy.

[0057] Second Embodiment In the first embodiment, the inner surfaces of the long side portions 43a, 44a are tapered surfaces 49c. However, this is not limited thereto. Although not shown, the inner surfaces of the pair of opposing long side portions 43a, 44a may be flat surfaces without steps or tapers. In this case, the gradually changing region 47c3 is configured so that the shape of the steps 48a, 48b gradually changes to a flat shape along the rounded portions 47a to 47d toward the long side portions 43a, 44a. Even if the long side portions 43a, 44a are flat, the above-mentioned effect of improving assembly can be achieved. Note that, although not particularly limited thereto, the tapered surface 49c may be provided in the second region 47c2 of the rounded portion 47c as needed.

[0058] Other Embodiments Furthermore, for example, the chamfered shape of the edge of the lower surface 41b2 of the sealing plate 41b is not limited to a C-shaped chamfer. Instead of the C-shaped chamfer, for example, an R-shaped chamfer may be formed.

[0059] While specific embodiments of the technology disclosed herein have been described above, these embodiments are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Explanation of symbols]

[0060] 10 Secondary battery 20 Electrode body 21 Positive electrode sheet 22 Negative electrode sheet 31,32 Separator sheet 41 Battery case 41a Case body 41a1 opening 41b Sealing plate 43a, 44a Long side 45a, 46a Short side 47a~47d R section 49c tapered surface 47c1 1st area 47c2 2nd area 47c3 Gradually changing region 48a, 48b steps 50 Positive terminal 60 Negative terminal 70 Gasket 80 insulator

Claims

1. a rectangular case body with a bottom and a substantially rectangular opening on one side surface facing the bottom surface; a substantially rectangular sealing plate attached to the opening and having an outer diameter corresponding to an upper edge of the opening; Equipped with The opening of the case body is a pair of long side portions facing each other; a pair of short side portions disposed at both ends of the pair of long side portions and facing each other; R portions provided at four corners between the long side portion and the short side portion; a step protruding from an inner surface of the pair of short side portions; and The R portion includes a first region, a second region, and a gradually changing region, the first region is adjacent to the short side portion and has the step; the second region is adjacent to the long side portion and has a tapered surface that slopes inward as it extends downward, the gradually changing region is provided between the first region and the second region, In the gradually changing region, the shape of the step gradually approaches the shape of the second region along the R portion.

2. The inner surfaces of the pair of opposing long side portions are the tapered surfaces. The battery case according to claim 1 .

3. The inner surfaces of the pair of opposing long side portions are flat. The battery case according to claim 1 .

4. The battery case according to any one of claims 1 to 3, wherein the gradually changing region is provided in a range of 45 degrees or more and 90 degrees or less from the center of the R portion, starting from the boundary between the R portion and the short side portion.

5. 5. The battery case according to claim 1, wherein the edge of the lower surface of the sealing plate is chamfered.

6. 6. The battery case according to claim 5, wherein an area of ​​the edge of the lower surface that overlaps with the gradually changing area when the sealing plate is attached to the opening is chamfered according to the shape of the gradually changing area.

7. A secondary battery comprising the battery case according to any one of claims 1 to 6.

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