Battery case and secondary battery including 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] JP 2001-135282 A discloses a sealed battery in which a lid is provided on the opening at the top of the battery can and sealed by welding. The publication proposes forming four corner step parts into which the lid is fitted at the curved four corners of the inner surface of the opening at the top of the battery can, and forming long side step parts on the inner surface of at least the long sides of the opening that are connected to the four corner step parts, and fitting the battery lid into the step parts and welding it. The technology proposed in the publication is said to be able to fit the battery lid into the desired position and weld it reliably by forming step parts not only at the four corner step parts of the battery can but also on the long sides.

[0003] JP 2013-93119 A discloses a battery case having a rectangular case body having a sidewall with a long side portion and a short side portion, a bottom surface, and an opening, and a cover plate that seals the opening. The publication proposes forming a step portion on the short side portion of the case body and forming a tapered portion below the contact portion of the long side portion with the cover plate. The technology proposed in the publication is said to be able to suppress the penetration of laser light into the long side by forming a tapered portion at a predetermined portion of the long side.

[0004] JP 2013-222705 A discloses a secondary battery including a case formed into a roughly rectangular parallelepiped shape and a cap plate that covers the opening of the case. The publication proposes providing triangular prism-shaped support parts at the four corners of the case. The technology proposed in the publication is said to be able to reduce deformation of the case by forming support parts that hang over the corner parts, thereby increasing the thickness of the corner parts.

[0005] JP 2014-10936 A discloses a rectangular battery including a battery case having a rectangular opening, a bottomed rectangular tubular body member, and a rectangular plate-shaped lid member. The body member has a pair of opening long sides, a pair of opening short sides, and four opening R parts that are curved in an arc connecting the opening long sides and the opening short sides. The publication proposes providing a support protrusion and a low-level protrusion that protrude toward the inside of the case body. The support protrusion is a part that is provided over the entire opening R part. The low-level protrusion is a part that is provided lower than the support protrusion over the entire opening short side. The lid member does not come into contact with the low-level protrusion. The technology proposed in the publication is said to be able to prevent an energy beam (such as a laser beam) from penetrating into the body member and causing defects when the energy beam is irradiated for welding the battery case by the low-level protrusion. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2001-135282 A [Patent Document 2] JP 2013-93119 A [Patent Document 3] JP 2013-222705 A [Patent Document 4] JP 2014-10936 A 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 bottomed rectangular case body having a substantially rectangular opening on one side surface facing the bottom surface, and a substantially rectangular sealing plate attached to the opening and having an outer diameter shape corresponding to the upper edge of the opening. The opening of the case body has a pair of long sides facing each other, a pair of short sides facing each other and disposed at both ends of the pair of long sides, R parts provided at each of the four corners between the long sides and the short sides, and a step protruding from the inner side surface of the pair of short sides. The R parts are provided with a gradual change region in which the shape of the step gradually changes to approach the shape of the inner surface of the long side along the R parts toward the long side.

[0009] With this configuration, when the sealing plate is attached to the opening of the case body, a portion is generated in the gradually changing region where the sealing plate comes into contact, and light press-fitting of the sealing plate into the opening with light force is easily achieved. Achieving light press-fitting 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 are inclined inwardly toward the bottom. In the gradually changing region, the shape of the step may be configured to change so as to gradually 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 such that the shape of the step gradually changes to approach a flat shape along the R portion toward the long sides.

[0012] The gradually changing region may be provided within 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.

[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 gradual change region when the sealing plate is attached to the opening may be chamfered according to the shape of the gradual change region.

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

[0015] [Figure 1] FIG. 1 is a partial cross-sectional view of a secondary battery 10. As shown in FIG. [Diagram 2] FIG. 2 is a plan view of the case main body 41a. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III of FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. [Diagram 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 with sealing plate 41b attached. [Figure 12] FIG. 12 is a cross-sectional view of opening 41a1 with sealing plate 41b attached. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] An embodiment of the disclosure herein will be described below. The embodiments described herein are, of course, not intended to limit the disclosure. Each drawing is drawn diagrammatically and does not necessarily reflect the actual product. Furthermore, a notation such as "A~B" indicating a numerical range means "A or more and B or less" unless otherwise specified, and also includes the meaning of "greater than A and less than B". In the drawings described below, the same reference numerals are given to members and parts that perform the same function, and duplicated descriptions may be omitted or simplified.

[0017] In this specification, the term "secondary battery" refers to a general electricity storage device in which a charge / discharge reaction occurs by the movement of charge carriers between a pair of electrodes (positive and negative electrodes) via an electrolyte. Such secondary batteries include so-called storage batteries such as lithium ion secondary batteries, nickel hydrogen batteries, and nickel cadmium batteries, as well as capacitors such as electric double layer capacitors. In the following, among the above-mentioned secondary batteries, an embodiment of the battery case disclosed herein and a secondary battery including the battery case will be described using a lithium ion secondary battery as an example. 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. In FIG. 1, the inside of a battery case 41, which is a substantially rectangular parallelepiped, is exposed along one wide surface. The secondary battery 10 shown in FIG. 1 is a so-called sealed battery in which the battery case 41 in which the electrode body 20 is accommodated is sealed. The directions of up, down, left, right, front, and rear are respectively indicated by arrows U, D, L, R, F, and Rr in the drawing. In this specification, the wide surface portion 44 (see FIGS. 1 and 2) facing the wide surface portion 43 of the secondary battery 10 is defined as the "front (F)" (front face), the wide surface portion 43 is defined as the "rear (Rr)", the sealing plate 41b side is defined as the "upper (U)", the bottom portion 42 side is defined as the "lower (D)", the narrow surface portion 45 side is defined as the "left (L)", and the narrow surface portion 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. The sealing plate 41b is provided with internal terminals 55, 65 and external terminals 51, 61 attached thereto via a gasket 70 and an insulator 80. In this embodiment, the internal terminal 55 is connected to the positive electrode current collector foil 21a of the electrode assembly 20. The external terminal 51 is connected to the internal terminal 55, and constitutes the positive electrode terminal 50 outside the battery case 41. The internal terminal 65 is connected to the negative electrode current collector foil 22a of the electrode assembly 20. The external terminal 61 is connected to the internal terminal 65, and constitutes the negative electrode terminal 60 outside the battery case 41.

[0020] <Electrode body 20> The electrode body 20 is housed in a battery case 41 while being covered with an insulating film (not shown) or the like. The electrode body 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 is a positive electrode current collector foil 21a (e.g., aluminum foil) having a predetermined width and thickness, on both sides of which a positive electrode active material layer 21b containing a positive electrode active material is formed, except for an unformed portion 21a1 set at a certain width at one end of the width direction. For example, in a lithium ion secondary battery, the positive electrode active material is a material that can release lithium ions during charging and absorb lithium ions during discharging, such as a lithium transition metal composite material. In general, various positive electrode active materials have been proposed other than lithium transition metal composite materials, and there is no particular limitation.

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

[0023] For example, a porous resin sheet having a required heat resistance and through which an electrolyte can pass is used for the separator sheets 31 and 32. Various types of 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 in opposite directions 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 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 with the separator sheets 31 and 32. The unformed portion 21a1 of the positive current collector foil 21a protrudes from one widthwise side of the separator sheets 31, 32. The unformed portion 22a1 of the negative current collector foil 22a protrudes from the separator sheets 31, 32 on the opposite widthwise side.

[0025] 1, the electrode body 20 described above is in a flat state along one 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 opposite side.

[0026] <Battery case 41> The battery case 41 houses the electrode body 20. The battery case 41 has a case body 41a and a sealing plate 41b. The case body 41a is a bottomed member having an opening 41a1 on one side surface facing the bottom surface. In this embodiment, the case body 41a has a substantially rectangular parallelepiped shape with one side surface 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 mainly containing aluminum, from the viewpoint of ensuring weight reduction and required rigidity. In the embodiment shown in FIG. 1, a wound type electrode body 20 is exemplified, but the structure of the electrode body 20 is not limited to such a form. The structure of the electrode body 20 may be, for example, a laminated structure in which a positive electrode sheet and a negative electrode sheet are alternately laminated with a separator sheet interposed therebetween. In addition, a plurality of electrode bodies 20 may be housed in the battery case 41.

[0027] The battery case 41 may house an electrolyte (not shown) together with the electrode body 20. As the electrolyte, a non-aqueous electrolyte in which a supporting salt is dissolved in a non-aqueous solvent can be used. Examples of the non-aqueous solvent include carbonate-based solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of the supporting salt 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 surface facing the bottom surface. In this embodiment, the case body 41a has a substantially rectangular parallelepiped shape with one side surface open. As shown in FIG. 1 and FIG. 2, the case body 41a has a bottom portion 42 constituting a substantially rectangular bottom surface, a pair of wide surface portions 43, 44, and a pair of narrow surface portions 45, 46. The pair of wide surface portions 43, 44 rise from the long sides of the bottom portion 42, respectively. The pair of narrow surface portions 45, 46 rise from the short sides of the bottom portion 42, respectively. An opening 41a1 surrounded by the pair of wide surface portions 43, 44 and the pair of narrow surface portions 45, 46 is formed on one side surface 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 side portions 43a, 44a, a pair of opposing short side portions 45a, 46a, and R portions 47a to 47d at the four corners. The long side portions 43a, 44a are the upper edges of the wide surface portions 43, 44. The short side portions 45a, 46a are the upper edges of the narrow surface portions 45, 46. The short side portions 45a, 46a are disposed at both ends of the pair of long side portions 43a, 44a. The R portions 47a to 47d are the upper edges of curved surfaces that bulge outward and connect the wide surface portions 43, 44 and the narrow surface portions 45, 46. The R portions 47a to 47d are provided along curved lines that connect the long side portions and the short side portions at the four corners of the opening 41a1 of the case body 41a. In this embodiment, the opening 41a1 of the case body 41a is formed such that the long side portions 43a, 44a of the opening 41a1 bulge outward slightly before the sealing plate 41b is attached. When the sealing plate 41b is attached to the opening 41a1, the short side portions 93, 94 (see FIGS. 9 and 10) of the sealing plate 41b are placed on the steps 48a, 48b of the opening 41a1. As a result, the opening 41a1 of the case body 41a is closed by the sealing plate 41b. In this state, the long side portions 43a, 44a of the opening 41a1 of the case body 41a are clamped. As a result, the sealing plate 41b is held in a state in which it is sandwiched between the long side portions 43a, 44a of the opening 41a1 of the case body 41a. A boundary portion between sealing plate 41b and case body 41a is irradiated with a laser in the circumferential direction and scanned, thereby welding sealing plate 41b and case body 41a together, whereby opening 41a1 of case body 41a is sealed by sealing plate 41b.

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

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

[0032] Fig. 5 is a partially enlarged view of Fig. 2. Fig. 5 shows a partially enlarged view of the R portion 47c of Fig. 2. As shown in Fig. 5, the R portion 47c is provided with a gradually changing region 47c3 in which the shape of the step 48b gradually changes to approach the shape of the inner surface of the long side portion 44a along the R portion 47c. Note that the R portions 47a, 47b, and 47d have the same configuration as the R portion 47c, and therefore illustrations and descriptions thereof may be omitted.

[0033] 2, 4, and 5, the inner surfaces of the pair of opposing long side portions 43a, 44a are tapered surfaces 49c that are inclined inwardly as they extend 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 as it approaches the long side portion 44a along the R portion 47c.

[0034] In this embodiment, the gradually changing region 47c3 is provided in a range of 45 degrees to 90 degrees from the center Rc of the R portion 47c, starting from the boundary B1 between the R 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 in a range of 45 degrees to 90 degrees (for example, 50 degrees to 70 degrees) from the straight line L1 with the center Rc as the center. In Fig. 5, the gradually changing region 47c3 is a region sandwiched between the straight lines La and Lb. Although not particularly limited, the angle α formed by the straight lines La and Lb can be set to, for example, 3 degrees to 10 degrees.

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

[0036] As shown in Fig. 5, the second region 47c2 is provided with 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 addition, 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, in the gradually changing region 47c3, the shape of the step 48b in the first region 47c1 may be configured to gradually change to approach the tapered surface 49c as it moves along the R 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 side surface changes. Therefore, the cross-sectional shape of the gradually changing region 47c3 is not fixed. FIG. 6 shows the R portion 47c as viewed from the inside of the case body 41a. FIGS. 6 to 8 show the process in which the shape of the inner side 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 shape of the two tapered surfaces gradually changes from the first region 47c1 to the second region 47c2, so that the step 48b and the tapered surface 49c are continuous. 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 Figures 7 and 8, the tapered surface 47t is inclined inward as it goes downward. As shown in Figure 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, and becomes the tapered surface 49c at the start E2. Further, the tapered surface of the step 48b gradually becomes smaller from the end E1 toward the starting end E2, and is absorbed into the tapered surface 49c at the starting end E2.

[0039] As shown in Figures 6 to 8, the upper end X1 of the tapered surface 47t is provided 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 is gradually provided 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 is gradually provided 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 to the vertical direction of the opening 41a1. The angle θ2 may be, for example, 5 degrees to 30 degrees. In the gradually changing region 47c3, for example, the angle θ2 gradually changes in a range of 5 degrees 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 with each other. This makes it possible to suppress partial excessive interference and improve the ease of assembly.

[0042] <Sealing plate 41b> Fig. 9 is a plan view of the secondary battery 10 with the sealing plate 41b attached. As shown in Fig. 1 and Fig. 9, the sealing plate 41b is attached to the opening 41a1 of the case body 41a, and is a substantially rectangular plate material having an outer diameter shape 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 along the inner side surface of the opening 41a1 of the case body 41a, and seals 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 the electrolyte is injected into the case body 41a. Note that FIG. 9 shows the state in which the sealing plate 41b is 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 is a portion that breaks when the pressure inside the battery case 41 becomes greater than a predetermined pressure.

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

[0045] In this embodiment, as shown in FIG. 9, the sealing plate 41b has a pair of long side portions 91, 92, a pair of short side portions 93, 94, and R portions 95-98 provided at the four corners. The pair of long side portions 91, 92 face each other. The pair of short side portions 93, 94 are disposed at both ends of the pair of long side portions 91, 92 and face each other. The R portions 95-98 are provided at the four corners between the long side portions 91, 92 and the short side portions 93, 94, respectively. As shown in FIG. 9, the R portions 95-98 are provided between the long side portions 91, 92 and the short side portions 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, an upper surface 41b1 of the sealing plate 41b is arranged facing the outside of the secondary battery 10. As shown in FIG. 1, a lower surface 41b2 of the sealing plate 41b is arranged facing the inside of the secondary battery 10. The upper surface 41b1 is, for example, a surface that faces the outside of the case body 41a when the sealing plate 41b is attached to the opening 41a1 of the case body 41a. The lower surface 41b2 is, for example, a surface that faces the inside of the case body 41a when the sealing plate 41b is attached to the opening 41a1 of the case body 41a.

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

[0048] Although not shown, it is preferable that a region of the lower surface 41b2 that overlaps with the gradual change region 47c3 when the sealing plate 41b is attached to the opening 41a1 is chamfered according to the shape of the gradual change region 47c3.

[0049] 11 and 12 are cross-sectional views of the opening 41a1 to which the sealing plate 41b is attached. Both of FIGS. 11 and 12 show partial cross-sectional views of the opening 41a1 of the case body 41a in a state in which the sealing plate 41b is attached. FIG. 11 is a cross-sectional view of a portion of the case body 41a where the step 48b is formed (for example, 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 at that portion is supported by the step 48b. As shown in FIG. 11, the C surface 41c of the sealing plate 41b is disposed on the step 48b.

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

[0051] In the battery case 41 disclosed herein, steps 48a, 48b are provided on the inner surfaces of the short side portions 45a, 46a. In addition, the R portions 47a to 47d are provided with gradually changing regions in which the shape of the steps 48a, 48b gradually changes to the shape of the inner surfaces of the long side portions 43a, 44a along the R portions. In other words, in the battery case 41, the R portions 47a to 47d are provided with gradually changing regions, so that the shape of the steps 48a, 48b of the short side portions 45a, 46a gradually approaches the shape of the inner surfaces of the long side portions 43a, 44a. In this case, when the sealing plate 41b is attached to the opening 41a1 of the case body 41a, a portion where the sealing plate 41b comes into contact is generated in the gradually changing regions of the R portions 47a to 47d of the opening 41a1 of the case body 41a. By creating such a contact portion, the sealing plate 41b can be pressed into the opening 41a1 of the case body 41a with a light force (light press-in). Therefore, when the sealing plate 41b is attached to the opening 41a1 of the case body 41a, the sealing plate 41b is less likely to shift, and the assembly quality can be improved. In this way, the gradually changing region is provided in the R parts 47a to 47d, so that the above-mentioned light press-in can be realized even if the dimensions of the opening 41a1 of the case body 41a and the sealing plate 41b vary. In addition, the dimensional accuracy of the opening 41a1 of the case body 41a and the sealing plate 41b for realizing the light press-in can be relaxed, so that the dimensional control of the sealing plate 41b and the case body 41a becomes easier. Furthermore, when there is a gradually changing region, the gap generated between the opening 41a1 of the case body 41a and the sealing plate 41b is smaller than when there is no gradually changing region. Therefore, laser leakage is less likely to occur.

[0052] In this embodiment, the inner surface of the long side portion 44a is a tapered surface 49c. By having the inner surface of the long side portion 44a be the tapered surface 49c, the inner surface of the portion of the long side portion 44a adjacent to the R portion 47c can be a tapered surface. Therefore, in addition to the gradually changing region 47c3, the adjacent portion can also be lightly press-fitted. 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. When the gap S is formed, the sealing plate 41b can be more easily press-fitted. Therefore, with such a configuration, the above-mentioned effect of improving the assembling property can be better achieved, and dimensional control can be made easier.

[0053] In this embodiment, the gradually changing region 47c3 is provided in a range of 45 degrees or more and 90 degrees or less from the center Rc, starting from the boundary B1 between the R portion 47c and the short side portion 46a. The gradually changing region 47c3 can be formed in an area where it is difficult to control the dimensions when attaching the sealing plate 41b. This allows light press-fitting in the area, and the above-mentioned effect of improving the assembling property can be better achieved. In addition, the step 48b is provided in a range of at least less than 45 degrees from the center Rc. Therefore, even if a gap occurs in a range of at least less than 45 degrees from the center Rc of the R portion 47c due to the dimensional accuracy of the sealing plate 41b, laser leakage can be suppressed in a range of at least less than 45 degrees from the center Rc of the R portion 47c.

[0054] In this embodiment, the edge of the lower surface 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 lower surface 41b2 of the sealing plate 41b is smaller than the upper edge of the opening 41a1 of the case body 41a. Therefore, the sealing plate 41b has a shape that makes it easy to fit into the opening 41a1 of the case body 41a. In addition, since a light press fit is realized in the opening 41a1 of the case body 41a, interference between the two components is unlikely to occur when the sealing plate 41b is attached to the opening 41a1. Therefore, in the battery case 41, a configuration in which the sealing plate 41b is easily fitted into the case body 41a can be realized.

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

[0056] Moreover, the secondary battery 10 includes the battery case 41. As described above, the battery case 41 improves the ease of assembly 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 favorable dimensional accuracy.

[0057] Second Embodiment In the first embodiment, the inner side surfaces of the long side portions 43a, 44a are tapered surfaces 49c. However, this is not limited thereto. Although not shown, the inner side 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 approach a flat shape along the R 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 the assembling property can be realized. Although not particularly limited thereto, the tapered surface 49c may be provided in the second region 47c2 of the R portion 47c as necessary.

[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-surface. Instead of the C-surface, for example, an R-surface may be formed.

[0059] Although 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 changes to 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 part 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 having 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; having 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 is inclined inwardly as it extends downward, the gradually changing region is provided between the first region and the second region, The battery case, wherein in the gradual-changing region, a shape of the step gradually approaches a 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 sides are flat. The battery case according to claim 1 .

4. The battery case according to any one of claims 1 to 3, wherein the gradual change 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. The battery case according to any one of claims 1 to 4, wherein the edge of the lower surface of the sealing plate is chamfered.

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 a 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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