Patent Description:
Japanese Patent Application <CIT> discloses a sealed battery in which a lid provided over the opening in an upper portion of a battery can is sealed by welding. This publication proposes that four corner steps are provided on the four curved corners of the inner surface of the opening in the upper portion of the battery can, and long side steps are formed on the inner surfaces of at least the long sides of the opening, and the battery lid is fitted and welded to the long side steps. In the technology proposed in the publication, steps are additionally provided in the long sides in addition to the four corner steps in the battery can, so that the battery lid can be reliably fitted and welded to a desired position.

<CIT> discloses a power storage device including a bottomed cylindrical metal case body having an opening and a metal lid closing the opening. The lid of the power storage device includes a lid body, an insertion portion, and a corner portion. The lid body is a portion which closes the opening and is supported by an opening end surface of the case body surrounding the opening. The insertion portion is a columnar portion protruding from the lid body toward the inside of the case body and extending along the inner peripheral surface of the case body. The corner portion is a rounded or chamfered portion at the leading edge of the insertion portion in the inserting direction.

The publication proposes that the lower limit of the chamfer in the corner portion is set to the average particle diameter of the material of the lid. In the publication, with such a configuration, when the insertion portion is inserted into the case body during the process of manufacturing the case, the tip edge of the insertion portion is substantially prevented from being cut by the inner peripheral surface of the case body, and generation of thread-like foreign matter is substantially prevented.

From <CIT>, a secondary battery is known which includes: an electrode assembly including: a first electrode plate; a second electrode plate; and a separator between the first electrode plate and the second electrode plate; a can comprising an opening formed on an end of the can to accommodate the electrode assembly; and a cap plate configured to seal the opening of the can, the cap plate including: a first surface; a second surface parallel to the first surface; a third surface coupling the first and second surfaces and having a constant height; and a chamfer at a portion of the first surface which contacts the third surface, wherein the chamfer has a varying tilt. Japanese Patent Application <CIT> discloses a battery case according to the preamble of claim <NUM>.

Formation of a gap between a case body and a sealing plate with the sealing plate attached to the opening of the case body is desirably reduced.

The battery case disclosed herein includes: a case body in bottomed rectangular parallelopiped shape having an opening in one side surface facing its bottom surface; and a substantially rectangular sealing plate attached to the opening and having a shape corresponding to an upper edge of the opening. The opening of the case body has steps protruding inward on inner surfaces of a pair of short sides facing each other. The sealing plate is a plate fitted into the opening, and has a pair of long side portions facing each other, a pair of short side portions located at both ends of the pair of long side portions and facing each other, and R portions provided at four corners between the long side portions and the short side portions. An edge of a lower surface of the sealing plate is chamfered. A chamfering amount of the pair of short side portions is greater than a chamfering amount of the pair of long side portions, and the R portions are each provided with a first region, a second region and a gradual change region, wherein the first region is a region adjacent to one of the short side portions, the second region is a region adj acent to one of the long side portions and the gradual change region is provided between the first region and the second region. A chamfering amount of the first region is equal to the chamfering amount of the short side portions, a chamfering amount of the second region is equal to the chamfering amount of the long side portions, and, in the gradual change region, a chamfering amount gradually decreases from a first end on a side of the short side portions toward a second end on a side of the long side portions where the first end is an endpoint of the first region and the second end is a starting point of the second region.

In the battery case with such a configuration, when the sealing plate is attached to the opening, the chamfering amount of the long side portions of the sealing plate is made smaller to improve fitting to the long sides of the opening. Further, each of the R portions is provided with a gradual change region, so that the chamfering amount of the short side portions gradually approaches the chamfering amount of the long side portions. This makes it difficult for a gap to be formed between the case body and the sealing plate in the battery case disclosed herein.

When a straight line connecting a center of each of the R portions and a boundary between each of the R portions and each of the short side portions is set as a reference, the gradual change region may be provided in a range from45° or more and less than <NUM>° from the center of each of the R portions, starting from the boundary between each of the R portions and each of the short side portions.

A secondary battery disclosed herein may include the battery case.

The following describes embodiments of the present disclosure. The embodiments described herein are naturally not intended to limit the present disclosure. Each drawing has been schematically illustrated and therefore may not necessarily reflect actual elements. The expression "A to B" indicating a numerical range means "A or more and B or less," and also means "above A and below B" unless otherwise specified. In the drawings described below, the same members/portions which exhibit the same action are denoted by the same reference numerals, and the duplicated descriptions may be omitted or simplified.

The "secondary battery" herein generally refers to an electricity storage device which causes a charging and discharging reaction by movement of charge carriers between a pair of electrodes (a positive electrode and a negative electrode) via an electrolyte. The "secondary battery" herein encompasses so-called secondary batteries such as a lithium-ion secondary battery, a nickel hydride battery and a nickel cadmium battery, and capacitors such as an electric double-layer capacitor The following describes the embodiments of the battery case and the secondary battery including the same disclosed herein, using a lithium-ion secondary battery as an example among secondary batteries. The disclosure herein is not limited to the lithium-ion secondary battery and can be applied to other secondary batteries, unless otherwise mentioned.

<FIG> is a partial sectional view of a secondary battery <NUM>. <FIG> shows the state where the inside of the lithium-ion secondary battery <NUM> is exposed along one wider surface of a substantially cuboid battery case <NUM>. The secondary battery <NUM> shown in <FIG> is a so-called sealed battery where a battery case <NUM> housing an electrode body <NUM> is sealed. Up, down, left, right, front, and rear directions are represented by the U, D, L, R, F, and Rr arrows, respectively, in the drawings. Herein, a wide surface portion <NUM> (see <FIG> and <FIG>) facing a wide surface portion <NUM> of the secondary battery <NUM> is defined as "front (F)" (front surface), and the wide surface portion <NUM> is defined as "rear (Rr)," the sealing plate 41b side is defined as "upper (U)," the bottom portion <NUM> side is defined as "lower (D)," the narrow surfaces portion <NUM> side is defined as "left (L)," and the narrow surface portion <NUM> side is defined as "right (R).

As shown in <FIG>, the secondary battery <NUM> includes the electrode body <NUM> and the battery case <NUM>. The battery case <NUM> includes a case body 41a having an opening 41a1 and a sealing plate 41b blocking the opening 41a1 of the case body 41a. The case body 41a houses the electrode body <NUM>. Inner terminals <NUM> and <NUM> and external terminals <NUM> and <NUM> are attached to the sealing plate 41b via gaskets <NUM> and insulators <NUM>. In the embodiment, the inner terminal <NUM> is connected to a positive electrode current collector foil 21a of the electrode body <NUM>. The external terminal <NUM> is connected to the inner terminal <NUM> and constitutes a positive electrode terminal <NUM> outside the battery case <NUM>. The inner terminal <NUM> is connected to a negative electrode current collector foil 22a of the electrode body <NUM>. The external terminal <NUM> is connected to the inner terminal <NUM>, and constitutes a negative electrode terminal <NUM> outside the battery case <NUM>.

The electrode body <NUM> is housed in the battery case <NUM> with being covered with an insulation film (not shown) or the like. The electrode body <NUM> includes a positive electrode sheet <NUM> as a positive electrode member, a negative electrode sheet <NUM> as a negative electrode member, and separator sheets <NUM> and <NUM> as a separator. The positive electrode sheet <NUM>, the first separator sheet <NUM>, a negative electrode sheet <NUM>, and a second separator sheet <NUM> are each a long strip-like member.

In the positive electrode sheet <NUM>, positive electrode active material layers 21b are formed on both surfaces of a positive electrode current collector foil 21a (e.g., an aluminum foil) having a predetermined width and a predetermined thickness except for a portion 21a1 which is set to have a certain width at one end in the width direction. For lithium-ion secondary batteries, 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. For the positive electrode active material, various kinds besides the lithium transition metal composite material are generally proposed without particular limitations.

In the negative electrode sheet <NUM>, negative electrode active material layers 22b containing a negative electrode active material are formed on both surfaces of a negative electrode current collector foil 22a (here, a copper foil) having a predetermined width and a predetermined thickness except for a portion 22a1 which is set to have a certain width at one end in the width direction. For lithium-ion secondary batteries, the negative electrode active material is, for example, a material that absorbs lithium ions during charging and releases the absorbed lithium ions during discharging, such as natural graphite. For the negative electrode active material, various kinds besides the natural graphite are generally proposed without particular limitations.

The separator sheets <NUM> and <NUM> used may each be porous resin sheets through which an electrolyte with a desired heat resistance can pass. For the separator sheets <NUM> and <NUM>, various kinds are proposed without particular limitations.

The negative electrode active material layer 22b is formed to have a width greater than the width of the positive electrode active material layer 21b, for example. The widths of the separator sheets <NUM> and <NUM> are greater than that of the negative electrode active material layer 22b. The portion 21a1 where the positive electrode active material layer 21b is not formed and the portion 22a1 where the negative electrode active material layer 22b is not formed are disposed to face each other in the width direction. The positive electrode sheet <NUM>, the first separator sheet <NUM>, a negative electrode sheet <NUM>, and a second separator sheet <NUM> are aligned in the length direction, and are wound up in turn on top of each other. The negative electrode active material layer 22b covers the positive electrode active material layer 21b with the separator sheets <NUM> and <NUM> interposed therebetween. The negative electrode active material layer 22b is covered with the separator sheets <NUM> and <NUM>. The portion 21a1 protrudes from one side of the separator sheets <NUM> and <NUM> in the width direction. The portion 22a1 protrudes from the separator sheets <NUM> and <NUM> on the other side in the width direction.

As shown in <FIG>, the above-mentioned electrode body <NUM> is flat along one plane including the winding axis so as to be housed in the case body 41a of the battery case <NUM>. The portion 21a1 is disposed on one side, and the portion 22a1 is disposed on the other side, of the electrode body <NUM> along the winding axis.

The battery case <NUM> houses the electrode body <NUM>. The battery case <NUM> includes a case body 41a and a sealing plate 41b. The case body 41a is a bottomed member with an opening 41a1 on one side opposite to the bottom surface. In the present embodiment, the case body 41a has an opening in one side surface and a substantially cuboid square shape. The sealing plate 41b is a plate material which is attached to the opening 41a1 of the case body 41a. In this embodiment, the case body 41a and the sealing plate 41b are formed of aluminum or an aluminum alloy mainly containing aluminum in order to reduce weight and ensure the required rigidity. In the embodiment shown in <FIG>, a wound electrode body <NUM> is shown as an example, but the structure of the electrode body <NUM> is not limited thereto. The structure of the electrode body <NUM> may have, for example, a lamination structure in which the positive electrode sheet and the negative electrode sheet are stacked alternately with separators interposed therebetween. The battery case <NUM> may house a plurality of electrode bodies <NUM>.

The battery case <NUM> may house an electrolyte (not shown) together with the electrode body <NUM>. The electrolyte used may be a nonaqueous electrolyte obtained by dissolving a supporting electrolyte in a nonaqueous solvent. Examples of the nonaqueous solvent include carbonate-based solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of the supporting electrolyte include fluorine-containing lithium salts such as LiPF<NUM>.

<FIG> is a plan view of a case body 41a. The case body 41a is a member in bottomed rectangular parallelopiped shape with an opening 41a1 on one side opposite to the bottom surface. In the present embodiment, the case body 41a has an opening in one side surface and a substantially cuboid square shape. As shown in <FIG> and <FIG>, the case body 41a has a bottom portion <NUM> forming a substantially rectangular bottom surface, a pair of wide surface portions <NUM> and <NUM>, and a pair of narrow surface portions <NUM> and <NUM>. The wide surface portions <NUM> and <NUM> in pair are each standing from the long side of the bottom portion <NUM>. The narrow surface portions <NUM> and <NUM> in pair are each standing from the short side of the bottom portion <NUM>. In one side surface of the case body 41a, an opening 41a1 surrounded by the pair of wide surface portions <NUM> and <NUM> and the pair of narrow surface portions <NUM> and <NUM> is formed. As shown in <FIG>, the opening 41a1 of the case body 41a is a substantially rectangular opening having curved portions 47a to 47d each having an arc shape.

As shown in <FIG>, the opening 41a1 of the case body 41a has a pair of long sides 43a and 44a facing each other, a pair of short sides 45a and 46a facing each other, and four curved portions 47a to 47d. The long sides 43a and 44a are upper edges of the wide surface portions <NUM> and <NUM>. The short sides 45a and 46a are upper edges of the narrow surface portions <NUM> and <NUM>. The short sides 45a and 46a are located at both ends of the pair of long sides 43a and 44a. The curved portions 47a to 47d are upper edges of outwardly bulging curved surfaces connecting the wide surface portions <NUM> and <NUM> and the narrow surface portions <NUM> and <NUM>. The curved portions 47a to 47d are provided at the four corners of the opening 41a1 of the case body 41a, along the curved lines connecting the long sides and the short sides. In the embodiment, the opening 41a1 of the case body 41a is molded 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, short side portions <NUM> and <NUM> (see <FIG> and <FIG>) of the sealing plate 41b are placed on steps 48a and 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 opening 41a1 of the case body 41a is clamped by the long sides 43a and 44a. As a result, this holds the sealing plate 41b between the long sides 43a and 44a of the opening 41a1 of the case body 41a. The sealing plate 41b and the case body 41a are welded together by laser irradiation and scanning in the circumferential direction at the boundary site between the sealing plate 41b and the case body 41a. As a result, the opening 41a1 of the case body 41a is sealed by the sealing plate 41b.

<FIG> is a sectional view taken along line III-III of <FIG>. As shown in <FIG> and <FIG>, the opening 41a1 of the case body 41a has steps 48a and 48b on the inner surfaces of the short sides 45a and 46a in pair facing each other. The steps 48a and 48b are portions that support the sealing plate 41b attached to the opening 41a1 of the case body 41a. The steps 48a and 48b are located at predetermined positions from the upper edges of the short sides 45a and 46a. In this embodiment, the positions of the steps 48a and 48b on the inner surfaces of the short sides 45a and 46a are defined such that the height of the upper edge of the opening 41a1 of the case body 41a and the height of 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, the steps 48a and 48b are provided at a height corresponding to the thickness of the sealing plate 41b from the upper edges of the short sides 45a and 46a. In this embodiment, the short sides 45a and 46a of the case body 41a have a thickness below the steps 48a and 48b that is higher than a thickness at the upper edge. When viewed from the upper edges of the short sides 45a and 46a of the case body 41a, the steps 48a and 48b protrude inward of the case from the upper edge of the case body 41a. In the embodiment shown in <FIG>, the steps 48a and 48b each have a tapered surface inclined inward toward the bottom portion <NUM>. The taper angle may be <NUM>° to <NUM>°. The steps 48a and 48b of the short sides 45a and 46a are continuous to part of the curved portions 47a to 47d. In this embodiment, the edge of a lower surface 41b2 of the sealing plate 41b is chamfered, and the tapered surfaces of the steps 48a and 48b of the short sides 45a and 46a are set, as appropriate, according to the angle of the chamfer.

<FIG> is a sectional view taken along line IV-IV of <FIG>. In the form shown in <FIG> and <FIG>, the inner surfaces of the long sides 43a and 44a in pair facing each other are provided with tapered surfaces 49c inclined inward toward their lower portions. The angle of each of the tapered surfaces 49c may be set such that when the sealing plate 41b is attached to the opening 41a1 of the case body 41a, it is pushed with light force, i.e., lightly press-fitted. In this embodiment, the tapered surface 49c is inclined at an angle θ1 from the upper edge of each of the long sides 43a, 44a with respect to the direction orthogonal to the opening 41a1 of the case body 41a. The angle θ1 may be <NUM>° to <NUM>° (e.g., about <NUM>°).

<FIG> is a partially enlarged view of <FIG>. <FIG> shows a partially enlarged curved portion 47c of <FIG>. As shown in <FIG>, the curved portion 47c is provided with a gradual change section 47c3 where the shape of the step 48b changes to be gradually close to the shape of the inner surface of the long side 44a toward the long side 44a along the curved portion 47c. The curved portions 47a, 47b, and 47d have the same configuration as the curved portion 47c; thus, illustration and description thereof may be omitted.

The gradual change section 47c3 may be superimposed on a gradual change region (described later) of the sealing plate 41b. In this embodiment, the gradual change portion 47c3 is provided in the range from <NUM>° to <NUM>° from the center Rc1 of the curved portion 47c, starting from the boundary B1 between the curved portion 47c and the short side 46a. As shown in <FIG>, when the straight line L1 connecting the center Rc1 and the boundary B1 is set as a reference (<NUM>°), the gradual change section 47c3 may be located in the range from <NUM>° or more and less than <NUM>° (e.g., <NUM>° to <NUM>°) from the straight line L1 with the center Rc1 as the center. In <FIG>, the gradual change section 47c3 is a portion sandwiched between straight lines La and Lb. Although not particularly limited thereto, the angle α formed between the straight lines La and Lb may be set to, for example, <NUM>° to <NUM>°.

In the form shown in <FIG>, the curved portion 47c has a first section 47c1, a second section 47c2, and a gradual change section 47c3. The first section 47c1 is adjacent to the short side 46a. In <FIG>, the first section 47c1 is a section sandwiched between straight lines L1 and La. In this embodiment, the first section 47c1 overlaps a first region (described later) of the sealing plate 41b. The second section 47c2 is adjacent to the long side 44a. In <FIG>, the second section 47c2 is a section sandwiched between straight lines Lb and L2. In this embodiment, the second section 47c2 overlaps a second region (described later) of the sealing plate 41b. The straight line L2 is a straight line L2 connecting the center Rc1 and a boundary B2 between the curved portion 47c and the long side 44a.

As shown in <FIG>, the first section 47c1 is provided with the step 48b. The step 48b is provided from the short side 46a to the first section 47c1. As shown in <FIG>, the second section 47c2 is provided with the tapered surface 49c. In this embodiment, the tapered surface 49c is provided from the second section 47c2 to the long side 44a. In the form shown in <FIG>, the gradual change section 47c3 is provided between the first section 47c1 and the second section 47c2. In the gradual change section 47c3, the shape of the step 48b in the first section 47c1 may be configured to change so as to be gradually close to the tapered surface 49c from the second section 47c2 and the long side 44a along the curved portion 47c.

<FIG> is a view seen from the arrow A in <FIG>. <FIG> are sectional views of the gradual change section 47c3. The gradual change section 47c3 is a region where the shape of the inner surface changes. Thus, the sectional shape of the gradual change section 47c3 is not defined. <FIG> is a view of the curved portion 47c seen from the inside of the case body 41a. <FIG> show the process of changing the shape of the inner surface from the step 48b of the first section 47c1 toward the tapered surface 49c of the second section 47c2 in the gradual change section 47c3.

In this embodiment, the gradual change section 47c3 has two tapered surfaces. For example, the shape of the two tapered surfaces 49c gradually change from the first section 47c1 toward the second section 47c2, so that the step 48b and the tapered surfaces 49c are continuous. In this embodiment, the two tapered surfaces 47t include the tapered surface of the step 48b and the tapered surface 47t. The shape of the tapered surface 47t changes from the endpoint E1 of the first section 47c1 toward the starting point E2 of the second section 47c2, for example. As shown in <FIG>, the tapered surface 47t is inclined inward toward its lower portion. As shown in <FIG>, the tapered surface 47t gradually increases in size from the endpoint E1 of the first section 47c1 toward the starting point E2 of the second section 47c2, becoming a tapered surface 49c at the starting point E2. Further, the tapered surface of the step 48b gradually decreases in size from the endpoint E1 toward the starting point E2, and is absorbed by the tapered surface 49c at the starting point E2.

As shown in <FIG>, an 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 <FIG>, from the endpoint E1 to the starting point E2, the upper end X1 is provided from the upper end of the step 48b at the endpoint E1 gradually toward the opening 41a1, and reaches the upper edge of the opening 41a1 at the starting point E2. As shown in <FIG>, from the endpoint E1 toward the starting point E2, a lower end X2 of the tapered surface 47t is provided from the upper end of the step 48b at the endpoint E1 gradually toward the bottom portion <NUM> (see <FIG>), and reaches the lower end of the tapered surface 49c at the starting point E2.

Further, in this embodiment, the tapered surface 47t is inclined at an angle θ2 with respect to the direction orthogonal to the opening 41a1. The angle θ2 may be, for example, <NUM>° to <NUM>°. In the gradual change section 47c3, for example, the angle θ2 gradually changes from the endpoint E1 toward the starting point E2 in the range from <NUM>° to <NUM>°, so that the step 48b and the tapered surface 49c are continuous.

<FIG> is a plan view of the secondary battery <NUM> with a sealing plate 41b attached. As shown in <FIG> and <FIG>, the sealing plate 41b is a substantially rectangular plate member attached to the opening 41a1 of the case body 41a and having a shape corresponding to an upper edge of the opening 41a1. In this embodiment, the sealing plate 41b is attached to the inner side of the opening 41a1 along the inner surface of the opening 41a1 of the case body 41a.

In this embodiment, the sealing plate 41b is provided with a liquid injection hole 40a and a safety valve 40b. A sealing member is attached to the liquid injection hole 40a after the sealing plate 41b is attached to the opening 41a1 of the case body 41a and an electrolyte is injected into the case body 41a. <FIG> shows the state where the sealing plate 41b is assembled and welded to the opening 41a1 of the case body 41a. In <FIG>, the sealing member is not attached to the sealing plate 41b. The safety valve 40b is a thin portion which breaks when the pressure inside the battery case <NUM> reaches a pressure larger than a predetermined pressure.

A positive electrode terminal <NUM> and a negative electrode terminal <NUM> are attached to an upper surface 41b1 of the sealing plate 41b. The sealing plate 41b includes terminal attachment holes <NUM> and <NUM> to which a positive electrode terminal <NUM> and a negative electrode terminal <NUM> are attached (see <FIG>). As shown in <FIG> and <FIG>, the positive electrode terminal <NUM> includes an external terminal <NUM> and an inner terminal <NUM>. The negative electrode terminal <NUM> includes an external terminal <NUM> and an inner terminal <NUM>. The inner terminals <NUM> and <NUM> are attached to the inner side of the sealing plate 41b via an insulator <NUM>. The external terminals <NUM> and <NUM> are attached to the outer side of the sealing plate 41b via a gasket <NUM>. The inner terminals <NUM> and <NUM> extend into the case body 41a. A portion 21a1 of the positive electrode current collector foil 21a in the electrode body <NUM> and a portion 22a1 of the negative electrode current collector foil 22a in the electrode body <NUM> are attached respectively to the inner terminals <NUM> and <NUM> attached to both sides of sealing plate 41b in the longitudinal direction.

The sealing plate 41b is a rectangular plate fitted to the opening 41a1 of the case body 41a. As shown in <FIG>, the sealing plate 41b includes a pair of long side portions <NUM> and <NUM>, a pair of short side portions <NUM> and <NUM>, and R portions <NUM> to <NUM> provided at four corners. The long side portions <NUM> and <NUM> in pair face each other. The short side portions <NUM> and <NUM> in pair are located at both ends of the long side portions <NUM> and <NUM> in pair and face each other. The R portions <NUM> to <NUM> are provided at four corners between the long side portions <NUM> and <NUM> and the short side portions <NUM> and <NUM>. As shown in <FIG>, the R portions <NUM> to <NUM> are provided between the long side portions <NUM> and <NUM> and the short side portions <NUM> and <NUM>, and are curved to bulge outward of the sealing plate 41b.

As shown in <FIG> and <FIG>, when the sealing plate 41b is attached to the case body 41a, the upper surface 41b1 of the sealing plate 41b is positioned to face outside of the secondary battery <NUM>. As shown in <FIG>, the lower surface 41b2 of the sealing plate 41b is positioned to face inside of the secondary battery <NUM>. The upper surface 41b1 is, for example, a surface which faces outside of the case body 41a when attached to the opening 41a1 of the case body 41a. The lower surface 41b2 is, for example a surface which faces inside of the case body 41a when attached to the opening 41a1 of the case body 41a.

<FIG> is a back surface view of the sealing plate 41b. <FIG> is a sectional view of a long side portion <NUM>. <FIG> is a sectional view of a short side portion <NUM>. As shown in <FIG>, the edge of the lower surface 41b2 of the sealing plate 41b comprises a chamfered portion 41c. In this embodiment, the chamfered portion 41c has a first chamfered portion 91c provided in the long side portions <NUM> and <NUM>, and a second chamfered portion 94c provided in the short side portions <NUM> and <NUM>. As shown in <FIG>, the first chamfered portion 91c is provided in the long side portion <NUM>. As shown in <FIG>, the second chamfered portion 94c is provided in the short side portion <NUM>. In this embodiment, both the first chamfered portion 91c and the second chamfered portion 94c are formed.

As shown in <FIG>, a chamfering amount C2 of the short side portions <NUM> and <NUM> in pair is larger than a chamfering amount C1 of the long side portions <NUM> and <NUM> in pair. Herein, "the chamfering amount C1 of the long side portions <NUM> and <NUM>" refers to a value obtained by subtracting the thickness T2 of the sealing plate 41b at the edges of the long side portions <NUM> and <NUM> from the thickness T1 of the sealing plate 41b (the chamfering amount C1 = the thickness T1 - the thickness T2 (see <FIG>). The thickness T1 may be defined by the shortest distance from the upper surface 41b1 to the lower surface 41b2, for example. Thickness T2 is the thickness of the sealing plate 41b at the edge of the long side portion <NUM> in <FIG>. Herein, "the chamfering amount C2 of short side portions <NUM> and <NUM>" refers to a value obtained by subtracting the thickness T3 of the sealing plate 41b at the edges of short side portions <NUM> and <NUM> from the thickness T1 of the sealing plate 41b (the chamfering amount C2 = the thickness T1 - the thickness T3 (see <FIG>). The thickness T3 is the thickness of the sealing plate 41b at the edge of the short side portion <NUM> in <FIG>. In this embodiment, the chamfering amount C1 of the long side portions <NUM> and <NUM> and the chamfering amount C2 of the short side portions <NUM> and <NUM> may be defined by chamfer dimensions.

In this embodiment, the ratio (C1/C2) of the chamfering amount C1 of the long side portions <NUM> and <NUM> to the chamfering amount C2 of the short side portions <NUM> and <NUM> is set in the range from <NUM>/<NUM> to <NUM>/<NUM> (preferably from <NUM>/<NUM> to <NUM>/<NUM>).

In this embodiment, the ratio (C1/T1) of the chamfering amount C1 to the thickness T1 is, for example, set in the range from <NUM>/<NUM> to <NUM>/<NUM>. The ratio (C2/T1) of the chamfering amount C2 to the thickness T1 is, for example, set in the range from <NUM>/<NUM> to <NUM>/<NUM>. In one preferred aspect, when the thickness T1 is <NUM> to <NUM>, the chamfering amount C1 is greater than <NUM> and less than <NUM>, and the chamfering amount C2 is <NUM> to <NUM>.

<FIG> is a partially enlarged view of <FIG>. <FIG> shows a partially enlarged portion in the vicinity of the R portion <NUM> of <FIG>. As shown in <FIG>, the R portion <NUM> is provided with a gradual change region <NUM>. In the gradual change region <NUM>, the chamfering amount gradually decreases from the first end P1 on the short side portion <NUM> side toward the second end P2 on the long side portion <NUM> side.

In this embodiment, the gradual change region <NUM> is provided in the range from <NUM>° or more and less than <NUM>° from the center Rc2 of the R portion <NUM>, starting from the boundary B3 between the R portion <NUM> and the short side portion <NUM>. As shown in <FIG>, when the straight line L3 connecting the center Rc2 and the boundary B3 is set as a reference (<NUM>°), the gradual change region <NUM> may be located in the range from <NUM>° or more and less than <NUM>° (e.g., <NUM>° to <NUM>°) from the straight line L3 with the center Rc2 as the center. In <FIG>, the gradual change region <NUM> is a portion sandwiched between straight lines Lc and Ld. Although not particularly limited thereto, the angle β formed between the straight lines Lc and Ls may be set to, for example, <NUM>° to <NUM>°.

In the form shown in <FIG>, the R portion <NUM> has a first region <NUM>, a second region <NUM>, and a gradual change region <NUM>. The first region <NUM> is a region adjacent to the short side portion <NUM>. In <FIG>, the first region <NUM> is a region sandwiched between the straight lines L3 and Lc. The second region <NUM> is a region adjacent to the long side portion <NUM>. In <FIG>, the second region <NUM> is a region sandwiched between the straight lines Ld and L4. The straight line L4 is a straight line connecting the center Rc2 and the boundary B4 between the R portion <NUM> and the long side portion <NUM>. In the form shown in <FIG>, the gradual change region <NUM> is provided between the first region <NUM> and the second region <NUM>.

In this embodiment, the chamfering amount of the first region <NUM> is equal to the chamfering amount of the short side portion <NUM>. The chamfering amount of the second region <NUM> is equal to the chamfering amount of the long side portion <NUM>. In this case, as shown in <FIG>, the first region <NUM> and the second chamfer 94c suitably have second chamfers 94c. The second region <NUM> and the long side portion <NUM> suitably have first chamfers 91c.

In the gradual change region <NUM>, the chamfering amount of the first region <NUM> may change to gradually approach the chamfering amount of the second region <NUM> toward the second region <NUM> along the R portion <NUM>. For example, the chamfering amount gradually decreases from the endpoint (the first end P1 in <FIG>) of the first region <NUM> toward the starting point (the second end P2 in <FIG>) of the second region <NUM>.

<FIG> is a sectional view of a first region <NUM> attached to an opening 41a1. <FIG> is a sectional view of a second region <NUM> attached to the opening 41a1. As shown in <FIG>, <FIG>, <FIG>, and <FIG>, when the sealing plate 41b is attached to the opening 41a1 of the case body 41a, the R portion <NUM> is superimposed on the curved portion 47d. As shown in <FIG>, the second chamfer 94c is superimposed on the step 48b (here, a first section of the curved portion 47d). As shown in <FIG>, the first chamfer 91c is fitted into a portion (here, a second section of the curved portion 47d) where the tapered surface 49c is formed in the curved portion 47d.

In the battery case <NUM> disclosed herein, the steps 48a and 48b protruding inward are provided in the inner surfaces of the short sides 45a and 46a of the opening 41a1 in the case body 41a. The edge of the lower surface 41b2 of the sealing plate 41b is chamfered. The chamfering amount C2 of the short side portions <NUM> and <NUM> is greater than the chamfering amount C1 of the long side portions <NUM> and <NUM>. As mentioned above, when the sealing plate 41b is attached to the opening 41a1, the long sides 43a and 44a of the opening 41a1 are superimposed on the long side portions <NUM> and <NUM>, which is then clamped. Thus, by making the chamfering amount C1 of the long side portions <NUM> and <NUM> smaller, the fitting to the long sides 43a and 44a can be improved. Further, in the battery case <NUM>, the R portions <NUM> to <NUM> are each provided with a gradual change region where the chamfering amount gradually decreases from the first end P1 on the short side portion <NUM> side toward the second end P2 on the long side portion <NUM> side. In other words, in the battery case <NUM>, R portions <NUM> to <NUM> are each provided with a gradual change region, so that the chamfering amount of the short side portions <NUM> and <NUM> gradually approaches the chamfering amount of the long side portions <NUM> and <NUM>. In this case, the chamfering amount of the short side portions <NUM> and <NUM> gradually decreases toward the long side portions <NUM> and <NUM>. This can make it difficult for a gap to be formed between the case body 41a and the sealing plate 41b in the R portions <NUM> to <NUM>. In particular, the clamping can suitably reduce formation of the gap in an area where a pressure is relatively difficult to be applied (e.g., an area in the vicinity of the boundaries between the R portions <NUM> to <NUM> and the long side portions <NUM> and <NUM>). In addition, this can make it easier for a molten pool to be formed, so that welding between the case body 41a and the sealing plate 41b can be realized more suitably.

In this embodiment, the gradual change region <NUM> is provided in the range from <NUM>° and more and less than <NUM>° from the center Rc2, starting from the boundary B3 between the R portion <NUM> and the short side portion <NUM>. When the sealing plate 41b is attached to the opening 41a1, the gradual change region <NUM> and a region where the chamfering amount is smaller than that of the short side portion <NUM> can be formed in a region where a gap is lively to be generated between the sealing plate 41b and the opening 41a1. This can allow the effect of preventing formation of the gap to be exhibited more suitably.

In this embodiment, the gradual change region <NUM> of the R portion <NUM> is provided between the first region <NUM> and the second region <NUM>. Further, the chamfering amount of the first region <NUM> is equal to the chamfering amount of the short side portion <NUM>, and the chamfering amount of the second region <NUM> is equal to the chamfering amount of the long side portion <NUM>. In the R portion <NUM>, the chamfering amount of a region (second region <NUM>) adjacent to the long side portion <NUM> can be smaller. This can allow the effect of preventing formation of the gap to be exhibited more suitably.

The secondary battery <NUM> includes a battery case <NUM>. In the battery case <NUM>, as mentioned above, welding between the case body 41a and the sealing plate 41b substantially prevents formation of the gap between the case body 41a and the sealing plate 41b attached to each other. Thus, in the secondary battery <NUM> including the battery case <NUM>, sealing is achieved more suitably.

In the case body 41a, the curved portions 47a to 47d are each provided with a gradual change section where the shape of the step 48a, 48b changes to be gradually close to the shape of the inner surface of the long side 43a, 44a. In other words, in the battery case <NUM>, the curved portions 47a to 47d are provided with gradual change sections so that the shapes of the steps 48a and 48b of the short sides 45a and 46a become gradually close to the shapes of the inner surfaces of the long sides 43a and 44a. In this case, when the sealing plate 41b is attached to the opening 41a1 of the case body 41a, portions in contact with the sealing plate 41b are generated in the gradual change sections of the curved portions 47a to 47d of the opening 41a1 of the case body 41a, and the sealing plate 41b can be lightly press-fitted into the opening 41a1 of the case body 41a. This can make it difficult for the sealing plate 41b to slide out of place and easier to attach the sealing plate 41b to the opening 41a1 of the case body 41a when the sealing plate 41b is attached to the opening 41a1 of the case body 41a. Further, the gradual change sections provided in the curved portions 47a to 47d can allow for structural light press-fitting. Thus, the dimensional accuracy of the opening 41a1 of the case body 41a and the sealing plate 41b can be relaxed, and light press-fitting can be achieved within the range of dimensional error. This facilitates dimensional control of the sealing plate 41b and the case body 41a. Accordingly, operability is improved when the sealing plate 41b is attached to the opening 41a1 of the case body 41a. Further, the gap generated between the opening 41a1 of the case body 41a and the sealing plate 41b becomes smaller, making it difficult for the laser to escape.

The inner surface of the long side 44a is a tapered surface 49c. When the inner surface of the long side 44a is a tapered surface 49c, the inner surface of a portion of the long side 44a adjacent to the curved portion 47c may be a tapered surface. Therefore, light press-fitting can be achieved in the portion adjacent to the curved portion 47c in addition to the gradual change section 47c3. When the sealing plate is attached to the opening 41a1 with such a configuration, a gap is formed between the portion where the tapered surface 49c is formed and the sealing plate 41b. Such a gap can make it easier for the sealing plate 41b to be lightly press-fitted. Therefore, the configuration can allow the effect of improving the operability to be achieved more suitably, and the dimensional control to be conducted more easily.

The gradual change portion 47c3 is provided in the range from <NUM>° or more and less than <NUM>° from the center Rc1, starting from the boundary B1 between the curved portion 47c and the short side 46a. When the sealing plate 41b is attached, the gradual change section 47c3 can be formed in a region which is difficult to be dimensionally controlled. Thus, light press-fitting is achieved in the section, and the operability can be achieved more effectively. In addition, the step 48b can be provided in the range of at least less than <NUM>° from the center Rc1, making it easier to support the sealing plate 41b.

The following describes other embodiments of the technology disclosed herein. The matters other than those mentioned in the following embodiment are the same as those described in the above embodiment; thus, duplicated explanations are omitted.

In the first embodiment, the inner surfaces of the long sides 43a and 44a are each a tapered surface 49c. However, the present disclosure is not limited thereto. For example, the inner surfaces of the long sides 43a and 44a may each be a flat surface without any step or tapered portion except for the area in the vicinity of the boundaries with the curved portions 47a to 47d. In this case, for example, the second section 47c2 of the curved portion 47c and the portion in the vicinity of the curved portion 47c shown in <FIG> may each be provided with the tapered surface 49c. In this embodiment, the clamping substantially prevents formation of the gap in a portion where pressure is relatively difficult to be applied. Thus, when the sealing plate 41b is attached to the opening 41a1, formation of the gap between the sealing plate 41b and the opening 41a1 is substantially prevented. The portions in the vicinity of the curved portions 47a to 47d in the long sides 43a and 44a refer to, for example, portions from <NUM>% to <NUM>% of the lengths of the long sides 43a and 44a at both ends of the long sides 43a and 44a.

Claim 1:
A battery case (<NUM>) comprising:
a case body (41a) in bottomed rectangular parallelopiped shape having an opening (41a1) in one side surface facing a bottom surface (<NUM>); and
a substantially rectangular sealing plate (41b) attached to the opening (41a1) and having a shape corresponding to an upper edge of the opening (41a1),
wherein
the opening (41a1) of the case body (41a) comprises steps (48a, 48b) protruding inward, on inner surfaces of a pair of short sides (45a, 46a) facing each other,
the sealing plate (41b) which is a plate fitted into the opening (41a1) comprises:
a pair of long side portions (<NUM>, <NUM>) facing each other;
a pair of short side portions (<NUM>, <NUM>) located at both ends of the pair of long side portions (<NUM>, <NUM>) and facing each other; and
R portions (<NUM> - <NUM>) provided at four corners between the long side portions (<NUM>, <NUM>) and the short side portions (<NUM>, <NUM>),
an edge of a lower surface (41b2) of the sealing plate (41b) is chamfered,
characterized in that
a chamfering amount of the pair of short side portions (<NUM>, <NUM>) is greater than a chamfering amount of the pair of long side portions (<NUM>, <NUM>), and
each of the R portions (<NUM> - <NUM>) comprises a first region (<NUM>), a second region (<NUM>) and a gradual change region (<NUM>),
the first region (<NUM>) is a region adjacent to one of the short side portions (<NUM>, <NUM>),
the second region (<NUM>) is a region adj acent to one of the long side portions (<NUM>, <NUM>), and
the gradual change region (<NUM>) is provided between the first region (<NUM>) and the second region (<NUM>),
wherein :
a chamfering amount of the first region (<NUM>) is equal to the chamfering amount of the short side portions (<NUM>, <NUM>),
a chamfering amount of the second region (<NUM>) is equal to the chamfering amount of the long side portions (<NUM>, <NUM>), and
in the gradual change region (<NUM>), a chamfering amount gradually decreases from a first end (P1) on a side of the short side portions (<NUM>, <NUM>) toward a second end (P2) on a side of the long side portions (<NUM>, <NUM>),
the first end (P1) is an endpoint of the first region (<NUM>), and
the second end (P2) is a starting point of the second region (<NUM>).