Secondary battery

Abstract

To provide a secondary battery with high reliability against expansion of an electrode body accompanying charge and discharge.SOLUTION: A secondary battery 100 includes an electrode body and a battery case 10 for housing the electrode body. The battery case 10 has a hexahedral battery case body 11 having an opening, and a sealing plate for sealing the opening of the battery case body 11. The battery case body 11 includes a pair of rectangular wide side surfaces facing each other and a pair of rectangular narrow side surfaces facing each other. The sealing plate 14 has a peripheral portion and a flat central portion surrounded by the peripheral portion. In the sealing plate 14, an end surface of a peripheral edge of the peripheral portion is joined to end surfaces of the pair of wide side surfaces and end surfaces of the pair of narrow side surfaces. The peripheral portion is curved over the entire periphery thereof from the central portion of the sealing plate 14 toward the end surface of the peripheral edge of the peripheral portion so that the battery outer surface side becomes a convex surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a secondary battery. [Background technology]

[0002] In secondary batteries such as lithium-ion secondary batteries, repeated charging and discharging can cause the electrode body to expand, which can damage the battery case. Therefore, research is being conducted on secondary batteries with an increased internal volume of the battery can in anticipation of the expansion of the electrode body. As an example of this type of technology, Patent Document 1 describes a secondary battery in which expansion of the electrode body is absorbed by a thin portion in the center of the battery case, thereby preventing damage to the battery case. Furthermore, Patent Document 2 describes a secondary battery in which a sealing plate is provided with a curved surface facing the height direction of the battery, thereby preventing damage to the battery case due to expansion of the electrode body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-338992 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-294012 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to increase the capacity of secondary batteries, development of secondary batteries using Si or Si compounds as the negative electrode active material is progressing. However, when Si or Si compounds are used as the negative electrode active material, the electrode body expands significantly during charging and discharging of the secondary battery compared to when other negative electrode active materials such as graphite are used. Therefore, there is a need for further improvement in the reliability of the electrode body against expansion of the secondary battery.

[0005] The present disclosure has been made in view of the above circumstances, and its main object is to provide a secondary battery that is highly reliable against expansion of an electrode assembly due to charging and discharging. [Means for solving the problem]

[0006] To solve the above-mentioned problems, the secondary battery disclosed herein includes an electrode assembly and a battery case that houses the electrode assembly. The battery case includes a hexagonal battery case body with an opening and a sealing plate that seals the opening of the battery case body. The battery case body includes a pair of mutually opposing rectangular wide side surfaces and a pair of mutually opposing rectangular narrow side surfaces. Each of the one or two sealing plates has a peripheral portion and a flat central portion surrounded by the peripheral portion, with peripheral end faces of the peripheral portion joined to end faces of the pair of wide side surfaces and end faces of the pair of narrow side surfaces, and the peripheral portion is curved around its entire periphery from the central portion to the peripheral end faces of the sealing plate so that the outer surface of the battery is convex.

[0007] In the secondary battery having the above configuration, the sealing plate has an R-shape (curved shape), which can reduce stress concentration at the joint between the battery case body and the sealing plate, where stress tends to concentrate when the electrode body expands, and can prevent damage to the battery case due to the expansion of the electrode body.

[0008] In a preferred embodiment of the secondary battery disclosed herein, the outer surfaces of the four side surfaces of the battery case body and at least one outer surface of the peripheral portion of the sealing plate adjacent to the end faces of the four side surfaces are joined to each other so as to be substantially flush with each other. This allows for better integration (equalization) of the battery case body and the sealing plate, thereby suppressing uneven distribution of stress concentration areas during expansion of the electrode body and making it possible to preferably prevent damage to the battery case.

[0009] One aspect of the secondary battery disclosed herein includes a six-sided battery case body having an opening on one side and a sealing plate that seals the opening of the battery case body, with the surface facing the opening being the bottom surface, thereby making it possible to effectively prevent damage to the battery case, in which the positive and negative terminals are attached to the sealing plate that faces the bottom surface of the battery case.

[0010] In a preferred embodiment of the secondary battery disclosed herein, the bottom surface has a bottom peripheral portion and a flat bottom central portion surrounded by the bottom peripheral portion. The bottom peripheral portion is curved around its entire periphery so as to rise upward in the case height direction, which is the vertical direction from the bottom central portion, and is configured to be continuous with the pair of wide side surfaces and the pair of narrow side surfaces. This more effectively prevents damage to the battery case, in which the positive and negative terminals are attached to a sealing plate facing the bottom surface of the battery case.

[0011] In a preferred embodiment of the secondary battery disclosed herein, the battery case includes a hexagonal battery case body with two openings on each side and two sealing plates that seal the two openings of the battery case body. One of the sealing plates has a positive electrode terminal attached to its center, electrically connected to the positive electrode of the electrode assembly via a positive electrode current collector, and the other has a negative electrode terminal attached to its center, electrically connected to the negative electrode of the electrode assembly via a negative electrode current collector. This effectively prevents damage to a secondary battery in which the positive and negative electrode terminals are attached perpendicular to the stacking direction of the electrode assembly.

[0012] In a preferred embodiment of the secondary battery disclosed herein, the electrode assembly contains Si or a Si compound as the negative electrode active material. From the viewpoint of increasing the capacity of batteries, it is desirable to use Si or Si compounds (hereinafter sometimes collectively referred to as "Si-based negative electrode active materials"), which have a larger capacity per unit volume than conventional graphite-based negative electrode active materials, but the high expansion rate during charge and discharge has been an issue. As described above, the secondary battery disclosed herein has high resistance to expansion of the battery case, so that Si-based negative electrode active materials can be suitably used as the negative electrode active material. Therefore, the technology disclosed herein can provide a high-performance secondary battery. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a perspective view schematically illustrating a secondary battery according to a first embodiment. [Figure 2] FIG. 2 is a side view schematically showing a battery case of the secondary battery according to the first embodiment. [Figure 3] FIG. 2 is a partially enlarged view of a battery case of the secondary battery according to the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view schematically showing the vicinity of the bottom surface of a secondary battery according to a second embodiment. [Figure 5] FIG. 10 is a cross-sectional view schematically showing a side surface of a secondary battery 100 according to a third embodiment. [Figure 6] FIG. 2 is a diagram schematically illustrating the configuration of an electrode body (wound electrode body) of a secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of the technology disclosed herein are described below. Matters necessary for implementing the technology disclosed herein, other than those specifically mentioned in this specification, can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. Furthermore, in the drawings described in this specification, components and parts that perform the same function are denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Furthermore, the dimensional relationships (length, width, thickness, etc.) in each drawing do not necessarily reflect the actual dimensional relationships.

[0015] In this specification, the term "secondary battery" refers to a general term for an electricity storage device that can be repeatedly charged and discharged with the movement of charge carriers between positive and negative electrodes, and is a concept that encompasses so-called storage batteries (chemical batteries) such as lithium ion secondary batteries and sodium ion secondary batteries, and capacitors (physical batteries) such as lithium ion capacitors (LIC). Below, each of the main constituent materials of the secondary battery according to the present disclosure will be described. It should be noted that conventionally known materials can be used for constituent materials of secondary batteries not described here.

[0016] 1. Overall structure of secondary battery 1 is a perspective view of a secondary battery (lithium ion secondary battery) 100 according to the first embodiment. The secondary battery 100 according to the first embodiment is composed of a battery case 10 and an electrode assembly 20 (not shown) housed inside the battery case 10. The battery case 10 has a six-sided box-shaped battery case body 11 with one or two sides as openings, and one or two sealing plates 14 that seal the one or two openings of the battery case body 11, respectively. At least one corner 12 is characterized by being rounded. The sealing plate 14 is provided with a liquid inlet 15, a sealing portion 16, a gas release valve 17, and two terminal extraction holes (not shown). The liquid inlet 15 is for injecting the electrolyte. The liquid inlet 15 is sealed with a sealing member 16. The gas release valve 17 is configured to break when the pressure inside the box-shaped battery case 10 reaches or exceeds a predetermined value, thereby releasing gas inside the battery case 10 to the outside. The two terminal holes are formed at both ends of the battery case 10 in the long side direction Y. The terminal holes penetrate the sealing plate 14 in the up-down direction Z. The terminal holes each have an inner diameter large enough to allow the positive electrode terminal 30 and the negative electrode terminal 40 to pass through before they are attached to the sealing plate 14 (before crimping).

[0017] In the secondary battery 100, various insulating members are attached between any components to prevent conduction between the components. The material of the insulating members is not particularly limited as long as it has a predetermined insulating property. For example, synthetic resin materials such as polyolefin resins (e.g., polypropylene (PP), polyethylene (PE)), fluorine-based resins (e.g., perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE)), etc. can be used.

[0018] 1.1 Box-type battery case FIG. 2 is a side view schematically illustrating the battery case of the secondary battery according to the first embodiment. In this embodiment, the surface facing the opening 11h is the bottom surface 11a. The material of the battery case 10 may be the same as that conventionally used, and is not particularly limited. The box-shaped battery case 10 is preferably made of metal, and more preferably made of, for example, aluminum, aluminum alloy, iron, iron alloy, or the like.

[0019] As shown in this figure, the box-shaped battery case body 11 has a pair of mutually opposing rectangular wide side surfaces 11d and a pair of mutually opposing rectangular narrow side surfaces 11e. The wide side surfaces 11d have a relatively larger area than the narrow side surfaces 11e. In this specification, the direction in which the wide side surfaces 11d face each other is the thickness direction of the battery (x direction in FIG. 1), the direction in which the narrow side surfaces 11e face each other is the width direction of the battery (y direction in FIG. 1), and the direction in which the side surfaces 11d, 11e rise from the bottom surface 11a of the battery case body 10 is the height direction of the battery (z direction in FIG. 1).

[0020] In this embodiment, one or two sealing plates 14 to be joined to the battery case body 11 to construct the battery case 10 each have a peripheral portion 14a and a flat central portion 14b surrounded by the peripheral portion 14a. The two terminal lead-out holes are formed at both ends of the sealing plate 14 in the long side direction Y. The terminal lead-out holes penetrate the sealing plate 14 in the up-down direction Z. The terminal lead-out holes each have an inner diameter large enough to allow the positive electrode terminal 30 and the negative electrode terminal 40 to be inserted therethrough before they are attached to the sealing plate 14 (before they are crimped).

[0021] The sealing plate 14 has the peripheral edge of the peripheral portion 14a joined to the edge of the pair of wide side surfaces 11d and the edge of the pair of narrow side surfaces 11e. The sealing plate 14 is joined (for example, welded) to the peripheral edge of the opening 11h of the box-shaped battery case body 11, thereby forming an integrated structure. The battery case 10 is hermetically sealed (sealed). The peripheral portion 14a of the sealing plate 14 is curved all around from the central portion 14b of the sealing plate 14 toward the edge of the periphery so that the outer surface of the battery is convex.

[0022] Fig. 3 is a partially enlarged view of the battery case of the secondary battery according to the first embodiment. In the secondary battery according to this embodiment, as shown in Fig. 3, the outer surfaces of the four side surfaces of the battery case body 11 and at least one of the outer surfaces of the peripheral portion 14a covering the central portion 14b of the sealing plate 14 adjacent to the end faces of the four side surfaces 11d and 11e (not shown) are joined to each other so as to be substantially flush with each other. This makes it possible to suppress breakage of the battery case according to the present disclosure, as will be described later.

[0023] 4 is a cross-sectional view schematically showing the vicinity of the bottom surface of a secondary battery according to the second embodiment. In this figure, only the vicinity of the bottom surface of the secondary battery, which is a characteristic part of this embodiment, is depicted, and other parts are omitted because they have the same configuration as the battery of the first embodiment described above. 4, the bottom surface 11a of the battery case body 11 has a bottom peripheral portion 11b and a flat bottom central portion 11c surrounded by the bottom peripheral portion 11b, and the bottom peripheral portion 11b curves upward in the case height direction from the bottom central portion 11c along its entire periphery and is configured to be continuous with the pair of wide side surfaces 11d and the pair of narrow side surfaces 11e. This makes it possible to effectively suppress breakage of the battery case according to the present disclosure, as will be described later.

[0024] Fig. 5 is a cross-sectional view schematically illustrating the side of a secondary battery 100 according to a third embodiment. As shown in Fig. 5, the battery case 10 includes a hexagonal box-shaped battery case body 11 having openings 11h on two sides, and two sealing plates 14 that seal the two openings 11h of the battery case body 11. A positive electrode terminal 30 is attached to the center portion 14b of one of the sealing plates 14, and is electrically connected to the positive electrode 22 of the electrode assembly 20 via a positive electrode current collector 32. A negative electrode terminal 40 is attached to the other sealing plate 14, and is electrically connected to the negative electrode 24 of the electrode assembly 20 via a negative electrode current collector 42. This effectively prevents damage to a secondary battery in which the positive electrode terminal and negative electrode terminal are attached perpendicular to the stacking direction of the electrode assembly.

[0025] 1.2 Electrode body FIG. 6 is a schematic diagram showing the configuration of an electrode assembly 20. The electrode assembly 20 has a positive electrode 22 and a negative electrode 24. Here, the electrode assembly 20 is a flat wound electrode assembly formed by stacking a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 with a strip-shaped separator 26 interposed therebetween and winding the stack around a winding axis WL. However, the electrode assembly 20 may also be a laminated electrode assembly formed by stacking multiple square-shaped (typically rectangular) positive electrodes and multiple square-shaped (typically rectangular) negative electrodes in an insulated state. In this specification, the "thickness direction of the electrode assembly" refers to the stacking direction in which the electrode plates are stacked. In the electrode assembly 20 of this embodiment, the direction in which the wide surfaces perpendicular to the stacking end faces oppose each other (the X direction in FIG. 4) is referred to as the thickness direction of the electrode assembly. In this embodiment, the thickness direction of the battery and the thickness direction of the electrode assembly coincide.

[0026] As shown in FIG. 6, the positive electrode 22 has a positive electrode core 22c and a positive electrode active material layer 22a formed on at least one surface (both surfaces in this case) of the positive electrode core 22c.

[0027] The positive electrode core 22c is strip-shaped and made of a conductive metal such as aluminum, an aluminum alloy, or stainless steel. The positive electrode core 22c is a metal foil, specifically an aluminum foil, in this example.

[0028] As shown in FIG. 6, the positive electrode active material layer 22a is provided in a strip-like shape along the longitudinal direction of the strip-shaped positive electrode substrate 22c. The positive electrode active material layer 22a contains a positive electrode active material capable of reversibly absorbing and releasing charge carriers. The positive electrode active material preferably contains at least one of Ni, Co, and Mn. For example, a lithium transition metal composite oxide such as a lithium nickel cobalt manganese composite oxide may be used. When the total solid content of the positive electrode active material layer 22a is taken as 100% by mass, the positive electrode active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The positive electrode active material layer 22a may contain optional components other than the positive electrode active material, such as a conductive material, a binder, various additives, etc. Examples of the conductive material include carbon materials such as carbon black (e.g., acetylene black (AB)). Examples of the binder include PVdF.

[0029] As shown in Fig. 6, the positive electrode tabs 22t protrude from the end of the electrode assembly 20 in the long side direction Y. The positive electrode tabs 22t are provided at intervals along the longitudinal direction of the strip-shaped positive electrode 22. The tabs are rectangular in this example, but may have various other shapes (e.g., trapezoidal). In at least a portion of the positive electrode tab 22t, a region is formed in which the positive electrode active material layer 22a is not formed and the positive electrode core 22c is exposed.

[0030] As shown in FIG. 6, the negative electrode 24 has a negative electrode core 24c and a negative electrode active material layer 24a formed on at least one surface (both surfaces in this case) of the negative electrode core 24c.

[0031] The negative electrode core 24c is strip-shaped and made of a conductive metal such as copper, a copper alloy, nickel, stainless steel, etc. Here, the negative electrode core 24c is a metal foil, specifically a copper foil.

[0032] The negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction of the strip-shaped negative electrode core 24c. The negative electrode active material layer 24a contains a negative electrode active material (for example, a carbon material such as graphite, Si, Si compounds such as SiO) that can reversibly occlude and release charge carriers. As the Si compound, SiO x silicon oxide represented by (0.05 < x < 1.95), Li x Si y O z lithium silicon oxide represented by (x, y, z independently satisfy 0 ≤ x, y, z ≤ 1), Li 21 a lithium-containing lithium-silicon alloy represented by LiSi5, etc. may be used. When the total solid content of the negative electrode active material layer 24a is 100% by mass, the negative electrode active material may occupy approximately 80% by mass or more, typically 90% by mass or more, for example 95% by mass or more. The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, for example, a binder, a dispersant, various additive components, etc. As the binder, for example, rubbers such as styrene butadiene rubber (SBR) may be used. As the dispersant, for example, celluloses such as carboxymethyl cellulose (CMC) may be used.

[0033] When Si or a Si compound is particularly used as the above negative electrode active material, since the amount of insertion / desorption of charge carriers (such as lithium ions) per unit area is large, it becomes possible to provide a high-performance secondary battery that realizes high capacity. When Si or a Si compound is used as the negative electrode active material, since the volume change accompanying the insertion / desorption of charge carriers (such as lithium ions) is large, the expansion of the electrode body during charge and discharge occurs significantly, and as a result, the battery case is likely to be damaged. However, the secondary battery according to the present disclosure can preferably prevent the damage of the battery case accompanying the expansion of the electrode body during charge and discharge, and thus Si or a Si compound can be used as the negative electrode active material.

[0034] As shown in Fig. 6, the negative electrode tabs 24t protrude from the end of the electrode body 20 in the long side direction Y. The negative electrode tabs 24t are provided at intervals along the longitudinal direction of the strip-shaped negative electrode 24. The tabs are rectangular in shape here, but may also have various other shapes (e.g., trapezoidal). In at least a portion of the negative electrode tab 24t, a region is formed in which the negative electrode active material layer 24a is not formed and the negative electrode core 24c is exposed.

[0035] The separator 26 is a member that insulates the positive electrode active material layer 22a of the positive electrode 22 from the negative electrode active material layer 24a of the negative electrode 24. A porous resin sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) is suitable for the separator 26. The separator 26 may have a heat resistance layer (HRL) containing an inorganic filler provided on the surface of the resin sheet. Examples of inorganic fillers that can be used include alumina, boehmite, aluminum hydroxide, and titania. An adhesive layer is preferably provided on one or both surfaces of the separator 26. The adhesive layer improves adhesion to the contacting positive electrode active material layer or negative electrode active material layer. The adhesive layer contains, for example, polyvinylidene fluoride (PVdF) as an adhesive component. The adhesive layer may also contain inorganic particles such as alumina and boehmite. The adhesive layer may be provided on the surface of the resin sheet or on the surface of the HRL.

[0036] 2.Prevention of electrode expansion and damage to the battery case As described above, in this type of secondary battery, the electrode body housed inside the battery case may expand during charging and discharging. Excessive expansion of the electrode body may cause damage to the battery case. In particular, when Si or a Si compound is used as the negative electrode active material, the volume change associated with the insertion / extraction of charge carriers (such as lithium ions) is large, so excessive expansion of the electrode body during charging and discharging of the secondary battery is more likely to occur than when other types of negative electrode active materials (e.g., graphite) are used. Therefore, the battery case used in the secondary battery disclosed herein is devised as described below.

[0037] (1) Shape of the corners (R parts) of the box-type battery case In the secondary battery according to the first embodiment, at least one of the corners 12 of the battery case 10 is curved, i.e., R-shaped, as shown in Fig. 1. This reduces stress concentration on the corners 12 of the battery case 10 when the electrode body 20 (not shown) expands, and can prevent the battery case 10 from being damaged. In the secondary battery according to the second embodiment, the corners 12 on the bottom surface 11a side of the battery case 10 are rounded as shown in Fig. 4. This allows the above-mentioned effect to be achieved also on the bottom surface 11a side of the battery case 10, and more preferably prevents the battery case 10 from being damaged. In the secondary battery according to the third embodiment, similarly to the secondary battery according to the second embodiment, damage to the battery case 10 can be suppressed on two surfaces of the battery case 10. The secondary battery according to the third embodiment differs from the secondary battery according to the second embodiment in the surfaces on which the positive and negative terminals are attached. Here, the degree of R shape (degree of curvature) is not particularly limited depending on the size of the battery, but R5 or more is appropriate, R8 or more is preferable, and R10 or more is more preferable. On the other hand, a curve that is too gentle may not achieve the effects disclosed herein, so R50 or less is appropriate, R40 or less is preferable, and R30 or less (e.g., R20±5) is more preferable. Here, the number following R indicates the radius of R (mm).

[0038] In some conventional secondary batteries, the corners of the battery case are formed as vertices. Such a configuration is outside the scope of the technical concept of the battery case according to the present disclosure. When the electrode assembly expands, stress is concentrated at the corners of the battery case, which can easily damage the battery case.

[0039] (2) Position of the battery case joint 3, in a preferred embodiment of the secondary battery according to the present disclosure, the exterior body 11 and the sealing plate 14 are joined together so that the outer surface of the battery case body 11 (wide side surface 11d in this figure) and the outer surface of the peripheral portion 14a of the sealing plate 14 are substantially flush with each other. This allows for better integration (equalization) of the battery case body and the sealing plate, which in turn suppresses uneven distribution of stress concentration areas when the electrode assembly expands, and can prevent damage to the battery case 10.

[0040] On the other hand, in some conventional secondary batteries, the joints between the exterior body and the sealing plate are all formed at positions corresponding to the corners of the battery case. Such configurations are outside the scope of the technical concept of the box-shaped battery case according to the present disclosure. When the electrode assembly expands, stress is concentrated at the joints of the battery case, which can easily damage the battery case.

[0041] In the secondary battery according to the present disclosure, by independently or in combination of the above (1) the shape of the corners of the battery case and the above (2) the joining manner between the battery case body and the sealing plate, damage to the battery case 10 due to expansion of the electrode body 20 can be effectively suppressed.

[0042] Although the present invention has been described in detail above using specific embodiments, these 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 above-described embodiments.

[0043] As described above, this specification includes the disclosures set forth in the following sections. Section 1: A secondary battery comprising an electrode assembly and a battery case that houses the electrode assembly, the battery case includes a hexagonal battery case body having an opening, and a sealing plate that seals the opening of the battery case body, The battery case body is A pair of mutually opposing rectangular wide side surfaces; A pair of mutually opposing rectangular narrow side surfaces; It is equipped with each of the one or two sealing plates has a peripheral portion and a flat central portion surrounded by the peripheral portion; the sealing plate is formed such that an end surface of the peripheral edge of the peripheral portion is joined to end surfaces of the pair of wide side surfaces and end surfaces of the pair of narrow side surfaces, the peripheral portion is curved along the entire periphery from the central portion of the sealing plate toward the edge of the peripheral edge so that the outer surface of the battery is convex, Secondary battery.

[0044] Section 2: Item 2. The secondary battery according to item 1, wherein the outer surfaces of the four side surfaces of the battery case and at least one outer surface of the peripheral portion of the sealing plate adjacent to the end faces of the four side surfaces are joined to each other so as to be approximately flush with each other.

[0045] Section 3: the battery case includes a six-sided battery case body, one of whose faces is an opening, and a sealing plate that seals the one opening of the battery case body; The surface facing the opening is a bottom surface. Item 1 or 2. The secondary battery according to item 1 or 2.

[0046] Section 4: the bottom surface has a bottom surface peripheral portion and a flat bottom surface central portion surrounded by the bottom surface peripheral portion, The bottom peripheral portion is curved along its entire periphery so as to rise upward in the case height direction, which is a vertical direction from the center of the bottom surface, and is configured to be continuous with the pair of wide side surfaces and the pair of narrow side surfaces. Item 3. The secondary battery according to item 3.

[0047] Section 5: the battery case includes a hexagonal battery case body having two openings on its two sides, and two sealing plates that seal the two openings of the battery case body; a positive electrode terminal electrically connected to the positive electrode of the electrode body via a positive electrode current collector is attached to a central portion of one of the sealing plates, and a negative electrode terminal electrically connected to the negative electrode of the electrode body via a negative electrode current collector is attached to a central portion of the other of the sealing plates. Item 1 or 2. The secondary battery according to item 1 or 2.

[0048] Item 6: Item 6. The secondary battery according to any one of items 1 to 5, wherein the electrode assembly contains Si or a Si compound as a negative electrode active material. [Explanation of symbols]

[0049] 10 Battery case 11 Battery case body 11a Bottom 11b Bottom periphery 11c Bottom center part 11d wide side 11e narrow side 12 Corner 14 Sealing plate 14a Periphery 14b Central part 20 Electrode body 22 Positive electrode 22a Cathode active material layer 22c positive electrode core 22t Positive electrode tab 24 Negative electrode 24a Negative electrode active material layer 24c negative electrode core 24t negative electrode tab 26 Separator 30 Positive terminal 40 Negative terminal 100 Secondary battery

Claims

1. A secondary battery comprising an electrode assembly and a battery case that houses the electrode assembly, the battery case includes a hexagonal battery case body having an opening, and a sealing plate that seals the opening of the battery case body; The battery case body is A pair of mutually opposing rectangular wide side surfaces; A pair of mutually opposing rectangular narrow side surfaces; It is equipped with each of the one or two sealing plates has a peripheral portion and a flat central portion surrounded by the peripheral portion; the sealing plate is formed such that an end surface of the peripheral edge of the peripheral portion is joined to end surfaces of the pair of wide side surfaces and end surfaces of the pair of narrow side surfaces, the peripheral portion is curved along the entire periphery from the central portion of the sealing plate toward the edge of the peripheral edge so that the outer surface of the battery is convex, Secondary battery.

2. 2. The secondary battery according to claim 1, wherein outer surfaces of the four side surfaces of the battery case body and at least one outer surface of the peripheral portion of the sealing plate adjacent to the end faces of the four side surfaces are joined to each other so as to be approximately flush with each other.

3. the battery case includes a six-sided battery case body, one of whose faces is an opening, and a sealing plate that seals the one opening of the battery case body; The surface facing the opening is the bottom surface. The secondary battery according to claim 1 or 2.

4. the bottom surface has a bottom peripheral portion and a flat bottom central portion surrounded by the bottom peripheral portion, The bottom peripheral portion is curved along its entire periphery so as to rise upward in the case height direction, which is a vertical direction from the center of the bottom surface, and is configured to be continuous with the pair of wide side surfaces and the pair of narrow side surfaces. The secondary battery according to claim 3 .

5. the battery case includes a hexagonal battery case body having two openings on its two sides, and two sealing plates that seal the two openings of the battery case body; a positive electrode terminal electrically connected to the positive electrode of the electrode body via a positive electrode current collector is attached to a central portion of one of the sealing plates, and a negative electrode terminal electrically connected to the negative electrode of the electrode body via a negative electrode current collector is attached to a central portion of the other of the sealing plates. The secondary battery according to claim 1 or 2.

6. 3. The secondary battery according to claim 1, wherein the electrode assembly contains Si or a Si compound as a negative electrode active material.

Images