Secondary battery

Abstract

The present invention provides a secondary battery which has higher reliability. A secondary battery according to one embodiment of the present disclosure is provided with: a battery element in which a first electrode and a second electrode are laminated via a separator and wound about a winding axis extending in a first direction; an external terminal; and a lead which includes a pair of end edge parts and connects the first electrode and the external terminal. The first electrode has: a first electrode current collector which includes a first end edge; and a first electrode active material layer which covers a part of the first electrode current collector. The lead is joined to the first electrode current collector in a state in which the pair of end edge parts are inclined with respect to the first end edge of the first electrode current collector.

Description

secondary battery

[0001] The present disclosure relates to secondary batteries.

[0002] Due to the widespread use of various electronic devices such as mobile phones, secondary batteries have been developed as power sources that are small, lightweight, and capable of achieving high energy density. These secondary batteries include a positive electrode, a negative electrode, and an electrolyte housed inside an exterior member, and various studies have been conducted on the configuration of such secondary batteries (see, for example, Patent Document 1).

[0003] For example, Patent Document 1 describes a sealed electricity storage device that includes an electrode body in which a positive electrode body and a negative electrode body are stacked or wound with a separator interposed therebetween, and an exterior case that houses the electrode body.

[0004] Japanese Patent Application Laid-Open No. 2019-46639

[0005] Various studies have been conducted to improve the performance of secondary batteries, but there is still room for improvement in the performance of secondary batteries.

[0006] Therefore, it is desirable to provide a secondary battery with higher reliability.

[0007] A secondary battery according to an embodiment of the present disclosure includes a battery element in which a first electrode and a second electrode are stacked with a separator interposed therebetween and wound around a winding axis extending in a first direction, an external connection terminal, and a lead including a pair of edges connecting the first electrode to the external connection terminal. The first electrode includes a first electrode current collector including a first edge and a first electrode active material layer covering a portion of the first electrode current collector. The lead is joined to the first electrode current collector with the pair of edges inclined relative to the first edge of the first electrode current collector.

[0008] In a secondary battery according to an embodiment of the present disclosure, the lead joined to the first electrode current collector includes a pair of edges that are inclined relative to the first edge of the first electrode current collector. This reduces stress applied to the joint between the first electrode current collector and the lead. This suppresses a decrease in the strength of the first electrode current collector and prevents cracks or breakage of the first electrode current collector. This allows the secondary battery according to an embodiment of the present disclosure to have high reliability.

[0009] Note that the effects of the present disclosure are not necessarily limited to the effects described here, but may be any of a series of effects related to the present technology described below.

[0010] FIG. 1 is a perspective view illustrating the configuration of a secondary battery according to an embodiment of the present disclosure. FIG. 2 is a vertical cross-sectional view illustrating the configuration of the secondary battery illustrated in FIG. 1. FIG. 3 is a cross-sectional view illustrating the configuration of a battery element illustrated in FIG. 2. FIG. 4A is a developed view schematically illustrating a positive electrode of the battery element illustrated in FIG. 3. FIG. 4B is a developed view schematically illustrating a negative electrode of the battery element illustrated in FIG. 3. FIG. 5 is a horizontal cross-sectional view illustrating the configuration of the secondary battery illustrated in FIG. 1. FIG. 6 is an enlarged plan view of the negative electrode lead and its vicinity illustrated in FIG. 4B. FIG. 7 is an exploded perspective view illustrating a manufacturing process of the secondary battery illustrated in FIG. 1. FIG. 8A is a partially enlarged cross-sectional view illustrating a portion of the battery element illustrated in FIG. 5. FIG. 8B is a partially enlarged cross-sectional view illustrating a portion of the battery element illustrated in FIG. 2. FIG. 9 is a partially enlarged plan view of a negative electrode of a first modified example. FIG. 10 is a partially enlarged plan view of a negative electrode of a second modified example. FIG. 11 is a partially enlarged plan view of a negative electrode of a third modified example. FIG. 12 is a partially enlarged plan view of a negative electrode of a fourth modified example. Fig. 13 is a partially enlarged plan view of the negative electrode of the fifth modified example. Fig. 14 is a partially enlarged plan view of the negative electrode of the comparative example.

[0011] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. The description will be given in the following order: 1. One embodiment 1-1. Configuration 1-2. Operation 1-3. Manufacturing method 1-4. Actions and effects 2. Modifications of one embodiment 2-1. First modification 2-2. Second modification 2-3. Third modification 2-4. Fourth modification 2-5. Fifth modification 3. Examples

[0012] 1. One Embodiment First, a secondary battery according to one embodiment of the present disclosure will be described.

[0013] The secondary battery described here has a flat, columnar, three-dimensional appearance and is referred to as a coin type or button type. As will be described later, this secondary battery has a pair of opposing bottoms and a sidewall portion located between the pair of bottoms. In this secondary battery, the height is smaller than the outer diameter. The "outer diameter" here refers to the maximum diameter (maximum outer diameter) of the bottoms. In this secondary battery, the maximum diameters of the pair of opposing bottoms are substantially equal to each other. Furthermore, the "height" here refers to the maximum distance from the upper surface of one bottom to the lower surface of the other bottom. In this embodiment, the direction in which the pair of bottoms face each other is defined as the height direction Z.

[0014] The charge / discharge principle of a secondary battery is not particularly limited, but the following description will be given of a case in which battery capacity is obtained by utilizing the absorption and desorption of an electrode reactant. This secondary battery includes a positive electrode, a negative electrode, and an electrolyte. In this secondary battery, the charge capacity of the negative electrode is greater than the discharge capacity of the positive electrode to prevent deposition of the electrode reactant on the surface of the negative electrode during charging. That is, the electrochemical capacity per unit area of ​​the negative electrode is set to be greater than the electrochemical capacity per unit area of ​​the positive electrode. Note that the secondary battery of this embodiment is a high-charge-voltage secondary battery that can exhibit good cycle characteristics without reducing energy density even when charged at a high voltage of 4.38 V or higher.

[0015] The type of electrode reactant is not particularly limited, but specifically includes light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, and alkaline earth metals include beryllium, magnesium, and calcium.

[0016] In the following, we will take the case where the electrode reactant is lithium as an example. A secondary battery that obtains battery capacity by utilizing the absorption and desorption of lithium is called a lithium ion secondary battery. In this lithium ion secondary battery, lithium is absorbed and desorbed in the ionic state.

[0017] (1-1. Structure) FIG. 1 shows a perspective structure of a secondary battery. FIG. 2 shows a cross-sectional structure of the secondary battery shown in FIG. 1. FIG. 3 shows a cross-sectional structure of the battery element 40 shown in FIG. 2 in an expanded state. Furthermore, FIG. 4A is an expanded view of a positive electrode 41 (described later) of the battery element 40, and is a schematic representation of the state before being wound. FIG. 4B is an expanded view of a negative electrode 42 (described later) of the battery element 40, and is a schematic representation of the state before being wound.

[0018] In the following description, for convenience, the upper side of each of the pages in FIGS. 1 and 2 will be referred to as the upper side of the secondary battery, and the lower side of each of the pages in FIGS. 1 and 2 will be referred to as the lower side of the secondary battery.

[0019] As shown in FIG. 1 , the secondary battery described here has a three-dimensional shape in which the height H is smaller than the outer diameter D, i.e., a flat and columnar three-dimensional shape. Here, the three-dimensional shape of the secondary battery is a flat and cylindrical (columnar) shape. In this embodiment, the vertical direction of the paper in each of FIGS. 1 and 2 is defined as the height direction Z. Therefore, the height H refers to the dimension of the secondary battery of this embodiment in the height direction Z. Furthermore, the outer diameter D refers to the dimension of the secondary battery of this embodiment in the direction perpendicular to the height direction Z.

[0020] The dimensions of the secondary battery are not particularly limited, but as an example, the outer diameter D is 3 mm to 30 mm and the height H is 0.5 mm to 70 mm. However, the ratio of the outer diameter D to the height H (D / H) is greater than 1. In other words, the outer diameter D is greater than the height H. The upper limit of this ratio (D / H) is not particularly limited, but is preferably 25 or less.

[0021] 1 to 3, this secondary battery includes an outer can 10, an external terminal 20, a battery element 40, and a positive electrode lead 51. In the configuration example shown in Fig. 2, the secondary battery further includes a gasket 30, a negative electrode lead 52, a sealant 61, and insulating films 62 and 63.

[0022] 1 and 2, the outer can 10 is a hollow outer casing member that houses the battery element 40 and the like. The outer can 10 is made of a conductive material. The outer can 10 is a specific example that corresponds to the "external connection terminal" of the present disclosure.

[0023] In the configuration example shown in FIG. 1 , the exterior can 10 has a flat, approximately cylindrical three-dimensional shape corresponding to the three-dimensional shape of the secondary battery, which is flat and cylindrical. Therefore, the exterior can 10 has a pair of bottoms M1 and M2 facing each other and a side wall M3 located between the bottoms M1 and M2. That is, the side wall M3 connects the bottoms M1 and M2 and surrounds the battery element 40. The upper end of the side wall M3 is connected to the bottom M1. The lower end of the side wall M3 is connected to the bottom M2. As described above, the exterior can 10 is approximately cylindrical. The planar shapes of the bottoms M1 and M2 are each circular, and the surface of the side wall M3 is a convex curved surface.

[0024] The exterior can 10 also includes a storage section 11 and a lid section 12 that are welded to each other. That is, the interior space of the exterior can 10 is sealed by welding the lid section 12 to the storage section 11. In this embodiment, the bottom section M1 forms the lid section 12, and the bottom section M2 and the side wall section M3 form the storage section 11 together. Therefore, the outer edge of the lid section 12 is welded to the upper end of the side wall section M3.

[0025] The storage section 11 is a flat, cylindrical storage member that stores the battery element 40 and other components therein. The storage section 11 has a hollow structure with an open upper end and a closed lower end. That is, the storage section 11 has an opening 11K (FIG. 2) at its upper end as an insertion port through which the battery element 40 can be inserted in the height direction Z.

[0026] The lid portion 12 is a substantially disk-shaped lid member that closes the opening 11K of the storage portion 11 and has a through-hole 12K. The through-hole 12K is used as a connection path for connecting the battery element 40 and the external terminal 20 to each other. As described above, the lid portion 12 is welded to the storage portion 11 at the opening 11K. The external terminal 20 is attached to the lid portion 12 via a gasket 30. That is, the lid portion 12 supports the external terminal 20 via the gasket 30. The external terminal 20 is attached to the lid portion 12 via the gasket 30 so as to close the through-hole 12K. The external terminal 20 is electrically insulated from the outer can 10.

[0027] As described above, in the completed secondary battery, the lid 12 is welded to the storage portion 11. As described above, the opening 11K is closed by the lid 12. Therefore, even if one looks at the exterior of the secondary battery, it may not be possible to determine whether the storage portion 11 had the opening 11K.

[0028] However, if the lid 12 is welded to the storage portion 11, weld marks remain on the surface of the outer can 10, more specifically, on the boundary between the storage portion 11 and the lid 12. Based on the presence or absence of the weld marks, it can be confirmed after the fact whether or not the storage portion 11 had the opening 11K.

[0029] That is, if there are weld marks remaining on the surface of the outer can 10, it means that the storage section 11 had an opening 11K. On the other hand, if there are no weld marks remaining on the surface of the outer can 10, it means that the storage section 11 did not have an opening 11K.

[0030] The lid portion 12 is bent so as to partially protrude along the height direction Z toward the inside of the storage portion 11, forming a recessed portion 12H. That is, when viewed from the outside of the outer can 10, the lid portion 12 has a shape that is partially recessed in the height direction Z toward the battery element 40 housed inside the outer can 10. The recessed portion 12H includes a through-hole 12K that penetrates in the height direction Z, a bottom portion 12HB that surrounds the through-hole 12K along a horizontal plane perpendicular to the height direction Z, and a wall portion 12HW that stands along the outer edge of the bottom portion 12HB.

[0031] The portion of the lid 12 other than the recess 12H constitutes a peripheral portion 12R. The peripheral portion 12R is annular and surrounds the recess 12H in a horizontal plane perpendicular to the height direction Z of the secondary battery. The peripheral portion 12R surrounds the recess 12H and protrudes away from the battery element 40 along the height direction Z. Therefore, in the height direction Z, the surface 12HS of the bottom 12HB of the recess 12H is located lower toward the interior of the storage section 11 than the surface 12RS of the peripheral portion 12R. In other words, in the height direction Z, the distance between the surface 12HS of the bottom 12HB of the recess 12H and the battery element 40 is shorter than the distance between the surface 12RS of the peripheral portion 12R and the battery element 40.

[0032] The planar shape of the recess 12H, i.e., the shape defined by the outer edge of the recess 12H when the secondary battery is viewed from above, is not particularly limited. Here, the planar shape of the recess 12H is approximately circular. The inner diameter and depth of the recess 12H are not particularly limited and can be set arbitrarily. However, the depth of the recess 12H is set so that, when the external terminal 20 is attached to the recess 12H via the gasket 30, the height position of the surface 20S of the external terminal 20 is lower than the height position of the surface 12RS of the peripheral portion 12R.

[0033] As described above, the outer can 10 is a so-called welded can in which the storage section 11 and the lid section 12, which were previously physically separate, are welded together. As a result, the outer can 10 after welding is a single, physically integrated member, and therefore cannot be separated into the storage section 11 and the lid section 12 later.

[0034] The exterior can 10, which is a welded can, is a so-called crimpless can, which is different from a crimp can formed using a caulking process. This is because the element space volume increases inside the exterior can 10, thereby increasing the energy density per unit volume. This "element space volume" refers to the volume (effective volume) of the internal space of the exterior can 10 that is available for housing the battery element 40.

[0035] Furthermore, the exterior can 10, which is a welded can, does not have any overlapping portions, nor does it have any portion where two or more members overlap each other.

[0036] "Having no overlapping parts" means that the outer can 10 is not processed (folded) so that parts thereof overlap each other. Also, "having no parts where two or more components overlap each other" means that the outer can 10 is physically a single component after the secondary battery is completed, and therefore the outer can 10 cannot be separated into two or more components afterward. In other words, the state of the outer can 10 in the completed secondary battery is not a state in which two or more components are combined while overlapping each other so that they can be separated afterward.

[0037] Here, the outer can 10 is conductive. More specifically, the storage portion 11 and the lid portion 12 are both conductive. The outer can 10 is electrically connected to the negative electrode 42 of the battery element 40 via the negative electrode lead 52. Therefore, the outer can 10 also serves as an external connection terminal for the negative electrode 42. Since the secondary battery of this embodiment does not need to include an external connection terminal for the negative electrode 42 separate from the outer can 10, a reduction in the element spatial volume due to the presence of the external connection terminal for the negative electrode 42 is suppressed. This increases the element spatial volume, thereby increasing the energy density per unit volume.

[0038] Specifically, the exterior can 10 is a metal can containing one or more conductive materials such as metal materials and alloy materials. The conductive materials constituting the metal can include iron, copper, nickel, stainless steel, iron alloys, copper alloys, and nickel alloys. The type of stainless steel is not particularly limited, but specific examples include SUS304 and SUS316. However, the materials forming the storage portion 11 and the lid portion 12 may be the same or different.

[0039] The lid 12 is insulated via a gasket 30 from an external terminal 20 serving as a terminal for external connection of the positive electrode 41. This is to prevent contact, i.e., a short circuit, between the outer can 10 serving as a terminal for external connection of the negative electrode 42 and the external terminal 20 serving as a terminal for external connection of the positive electrode 41.

[0040] 1 and 2, the external terminal 20 is a connection terminal that is connected to an electronic device when the secondary battery is mounted in the electronic device. As described above, the external terminal 20 is attached to and supported by the lid portion 12 of the outer can 10. The external terminal 20 is provided on the opposite side of the lid portion 12 from the bottom portion M2, at a position that overlaps with the through hole 12K in the height direction Z.

[0041] Here, the external terminal 20 is connected to the positive electrode 41 of the battery element 40 via the positive electrode lead 51. Therefore, the external terminal 20 functions as an external connection terminal for the positive electrode 41. As a result, when the secondary battery is in use, the secondary battery is connected to an electronic device via the external terminal 20 (external connection terminal for the positive electrode 41) and the outer casing 10 (external connection terminal for the negative electrode 42). Therefore, the electronic device can operate using the secondary battery as a power source.

[0042] The external terminal 20 is a flat, approximately plate-shaped member extending along a horizontal plane perpendicular to the height direction Z of the secondary battery. It is disposed within the recessed portion 12H via the gasket 30. The external terminal 20 is insulated from the lid portion 12 via the gasket 30. As shown in FIG. 2 , the surface 20S of the external terminal 20 is positioned lower toward the battery element 40 than the surface 12RS of the peripheral portion 12R of the outer can 10 in the height direction Z. That is, the external terminal 20 is housed within the recessed portion 12H so that its upper end, the surface 20S, is recessed toward the battery element 40 relative to the surface 12RS. In the secondary battery of this embodiment, the height of the secondary battery is reduced compared to when the external terminal 20 protrudes above the lid portion 12. This increases the energy density per unit volume of the secondary battery. Furthermore, it is possible to prevent short-circuiting between the outer can 10 and the external terminal 20 via other conductive members. In this embodiment, the peripheral portion of the external terminal 20 overlaps with the bottom portion 12HB of the recessed portion 12H in the height direction Z. Having an overlapping portion between the external terminal 20 and the lid portion 12 improves the mechanical strength of the secondary battery as a whole. Here, the length of the overlapping portion between the external terminal 20 and the peripheral portion along a horizontal plane perpendicular to the height direction Z is preferably greater than the thickness of the external terminal 20 and the thickness of the bottom portion 12HB.

[0043] The outer diameter of the external terminal 20 is smaller than the inner diameter of the recess 12H. Therefore, the outer edge 20T of the external terminal 20 is spaced apart from the lid 12. The gasket 30 is disposed only in a portion of the area between the external terminal 20 and the lid 12 (recess 12H). More specifically, the gasket 30 is disposed only in a location where the external terminal 20 and the lid 12 would come into contact with each other if the gasket 30 were not present. However, it is preferable that the gasket 30 is also disposed between the inner wall surface of the wall 12HW of the recess 12H and the outer edge 20T of the external terminal 20. It is also preferable that the lid 12 and the external terminal 20 are fixed together by the gasket 30.

[0044] The external terminal 20 includes one or more conductive materials such as metal materials and alloy materials, and the conductive materials include aluminum and aluminum alloys. However, the external terminal 20 may be formed of a clad material. This clad material includes an aluminum layer and a nickel layer, in that order from the side closest to the gasket 30, and the aluminum layer and the nickel layer are roll-bonded to each other in the clad material.

[0045] [Gasket] As shown in Fig. 2, the gasket 30 is an insulating member disposed between the outer can 10 (lid portion 12) and the external terminal 20. The external terminal 20 is fixed to the lid portion 12 via the gasket 30. The gasket 30 has a ring-shaped planar shape with a through hole at a position corresponding to the through hole 12K. The gasket 30 contains one or more insulating materials such as insulating polymer compounds, and the insulating materials are resins such as polypropylene and polyethylene.

[0046] The installation range of the gasket 30 is not particularly limited and can be set arbitrarily. Here, the gasket 30 is disposed in the gap between the upper surface of the lid 12 and the lower surface of the external terminal 20 inside the recess 12H. However, as described above, the gasket 30 may also be provided between the inner wall surface of the wall 12HW of the recess 12H and the outer edge 20T of the external terminal 20. The lid 12 and the external terminal 20 may also be fixed by the gasket 30.

[0047] [Battery Element] The battery element 40 is a power generation element that causes charge / discharge reactions to proceed, and is housed inside the outer can 10 as shown in Figures 2 and 3. The battery element 40 includes a positive electrode 41 and a negative electrode 42. Here, the battery element 40 further includes a separator 43 and an electrolytic solution (not shown) that is a liquid electrolyte. The battery element 40 is a specific example corresponding to the "battery element" of the present disclosure.

[0048] 2 is a line segment corresponding to the center of the battery element 40 in the direction along the outer diameter D of the secondary battery (external can 10). In other words, the position P0 of the center line PC corresponds to the position of the center of the battery element 40.

[0049] The battery element 40 is a so-called wound electrode assembly. That is, in the battery element 40, for example, as shown in FIGS. 2 and 3 , a positive electrode 41 and a negative electrode 42 are stacked in a radial direction R with a separator 43 interposed therebetween. The radial direction R is the radial direction of the outer can 10. Furthermore, as shown in FIG. 5 , the stacked positive electrode 41, negative electrode 42, and separator 43 are wound around a center line PC as a winding axis. The positive electrode 41 and negative electrode 42 are wound while facing each other with the separator 43 interposed therebetween. Therefore, a winding central space 40K is formed at the center of the battery element 40. Note that FIG. 5 shows an example configuration along a horizontal cross section of the battery element 40 perpendicular to the height direction Z. However, the separator 43 is omitted from FIG. 5 to ensure visibility.

[0050] Here, the positive electrode 41, the negative electrode 42, and the separator 43 are wound such that the separator 43 is disposed at the outermost and innermost peripheries of the wound electrode body. The number of windings of the positive electrode 41, the negative electrode 42, and the separator 43 is not particularly limited and can be set arbitrarily. Furthermore, at the outermost periphery of the battery element 40, the negative electrode 42 is disposed outside the positive electrode 41. That is, as shown in FIG. 5 , the outermost positive electrode portion 41out of the positive electrode 41 included in the battery element 40 is disposed inside the outermost negative electrode portion 42out of the negative electrode 42 included in the battery element 40. Here, the positive electrode outermost portion 41out refers to the outermost portion of the positive electrode 41 in the battery element 40, which corresponds to one circumference. The negative electrode outermost portion 42out refers to the outermost portion of the negative electrode 42 in the battery element 40, which corresponds to one circumference. Meanwhile, at the innermost periphery of the battery element 40, the negative electrode 42 may be disposed inside the positive electrode 41. 5 , the negative electrode innermost circumferential portion 42in, which is located at the innermost periphery of the negative electrode 42 included in the battery element 40, may be located more inward than the positive electrode innermost circumferential portion 41in, which is located at the innermost periphery of the positive electrode 41 included in the battery element 40. Here, the positive electrode innermost circumferential portion 41in is the innermost portion of the positive electrode 41 in the battery element 40, which corresponds to one circumference. The negative electrode innermost circumferential portion 42in is the innermost portion of the negative electrode 42 in the battery element 40, which corresponds to one circumference.

[0051] The battery element 40 has a three-dimensional shape similar to that of the outer can 10. Specifically, the battery element 40 has a flat, approximately cylindrical three-dimensional shape. Compared to a case in which the battery element 40 has a three-dimensional shape different from that of the outer can 10, when the battery element 40 is housed inside the outer can 10, so-called dead space, specifically, a gap between the outer can 10 and the battery element 40, is less likely to occur. Therefore, the internal space of the outer can 10 is effectively utilized. As a result, the element space volume increases, and the energy density per unit volume of the secondary battery increases.

[0052] (Positive Electrode) The positive electrode 41 is a first electrode used to promote charge / discharge reactions. As shown in FIGS. 3 to 5, the positive electrode 41 includes a positive electrode current collector 41A, a positive electrode active material layer 41B, and a protective tape 41C. As shown in FIG. 4A, the positive electrode 41 has a generally rectangular planar shape with the height direction Z as its short side and the winding direction θ of the battery element 40 as its long side. That is, the positive electrode 41 is a strip-shaped member defined by an upper edge 41UT, an inner peripheral edge 41S, a lower edge 41BT, and an outer peripheral edge 41E. The upper edge 41UT is located at the top of the height direction Z and extends along the longitudinal direction (winding direction θ). The inner peripheral edge 41S is located on the innermost side of the winding direction θ and extends along the height direction Z. The lower edge 41BT is located on the lower side in the height direction Z and extends along the longitudinal direction (winding direction θ). The outer peripheral edge 41E is located on the outermost side in the winding direction θ and extends along the height direction Z.

[0053] The positive electrode current collector 41A has a pair of surfaces on which the positive electrode active material layer 41B is provided. More specifically, the positive electrode current collector 41A includes an inner surface facing the winding center of the battery element 40, i.e., position P0, and an outer surface facing the side opposite the winding center of the battery element 40, i.e., the outer surface opposite the inner surface. The positive electrode current collector 41A includes a conductive material such as a metal material. The positive electrode current collector 41A is, for example, a metal foil made of aluminum or an aluminum alloy.

[0054] The positive electrode active material layer 41B is provided, for example, on both a portion of the inner surface and a portion of the outer surface of the positive electrode current collector 41A. However, the positive electrode active material layer 41B may be provided on only one surface of the positive electrode current collector 41A. The positive electrode active material layer 41B contains one or more types of positive electrode active materials capable of absorbing and releasing lithium. The positive electrode active material layer 41B may further contain a positive electrode binder, a positive electrode conductive agent, and the like. The method for forming the positive electrode active material layer 41B is not particularly limited, but specifically includes a coating method, etc.

[0055] The positive electrode 41 has a positive electrode current collector-covered region 411 and a positive electrode current collector-exposed region 412. The positive electrode current collector-covered region 411 is a region of the positive electrode 41 where the positive electrode current collector 41A is covered with the positive electrode active material layer 41B. The positive electrode current collector-exposed region 412 is a region of the positive electrode 41 other than the positive electrode current collector-covered region 411. In other words, the positive electrode current collector-exposed region 412 is a region where the positive electrode current collector 41A is exposed and not covered with the positive electrode active material layer 41B. As shown in FIG. 4A , the positive electrode current collector-covered region 411 and the positive electrode current collector-exposed region 412 each extend from an upper edge 41UT of the positive electrode 41 to a lower edge 41BT of the positive electrode 41 along the height direction Z, which is the short-side direction of the positive electrode 41. Two positive electrode current collector exposed regions 412 are provided at both ends of the positive electrode 41 in the winding direction θ, which is the longitudinal direction of the positive electrode 41. One of the two positive electrode current collector exposed regions 412 includes the inner peripheral edge 41S of the innermost positive electrode portion 41in ( FIG. 5 ) of the positive electrode 41, and the other of the two positive electrode current collector exposed regions 412 includes the outer peripheral edge 41E of the outermost positive electrode portion 41out ( FIG. 5 ) of the positive electrode 41. The positive electrode current collector covered region 411 is disposed so as to be sandwiched between the two positive electrode current collector exposed regions 412 in the winding direction θ. In other words, the positive electrode active material layer 41B is not present at both ends of the positive electrode current collector 41A in the winding direction θ, which is the longitudinal direction of the positive electrode current collector 41A. The protective tape 41C is provided on a portion of the positive electrode current collector covered region 411. More specifically, it covers a portion of the positive electrode current collector 41A in the positive electrode current collector exposed region 412 that faces the negative electrode active material layer 42B (described later). A positive electrode lead 51 is attached to the positive electrode current collector 41A in the inner peripheral side positive electrode current collector exposed region 412. The positive electrode lead 51 is provided so that a portion of it protrudes upward from the upper edge 41UT of the positive electrode 41.

[0056] The positive electrode active material contains a lithium compound. This lithium compound is a general term for compounds containing lithium as a constituent element, and more specifically, compounds containing lithium and one or more transition metal elements as constituent elements. This is because a high energy density can be obtained. However, the lithium compound may further contain one or more other elements (excluding lithium and transition metal elements). The type of lithium compound is not particularly limited, but specific examples include oxides, phosphate compounds, silicate compounds, and borate compounds. Specific examples of oxides include LiNiO2, LiCoO2, and LiMn 2 O 4 Specific examples of the phosphate compound include LiFePO4 and LiMnPO4 4 And so on.

[0057] The positive electrode binder contains one or more of synthetic rubbers and polymeric compounds. The synthetic rubber is styrene-butadiene rubber, and the polymeric compound is polyvinylidene fluoride. The positive electrode conductor contains one or more of conductive materials such as carbon materials, and the carbon materials include graphite, carbon black, acetylene black, and ketjen black. However, the conductive material may also be a metal material or a polymeric compound.

[0058] (Negative Electrode) The negative electrode 42 is a second electrode used to promote charge-discharge reactions. As shown in FIGS. 3 to 5 , the negative electrode 42 includes a negative electrode current collector 42A and a negative electrode active material layer 42B. As shown in FIG. 4B , the negative electrode 42 has a generally rectangular planar shape with the height direction Z as its short side and the winding direction θ of the battery element 40 as its long side. That is, the negative electrode 42 is a strip-shaped member defined by an upper edge 42UT, an inner peripheral edge 42S, a lower edge 42BT, and an outer peripheral edge 42E. The upper edge 42UT is located on the upper side of the height direction Z and extends along the longitudinal direction (winding direction θ). The inner peripheral edge 42S is located on the inner side of the winding direction θ and extends along the height direction Z. The lower edge 42BT is located on the lower side of the height direction Z and extends along the longitudinal direction (winding direction θ). The outer peripheral edge 42E is located on the outer peripheral side in the winding direction θ and extends along the height direction Z. The negative electrode 42 has a length H42 in the height direction Z.

[0059] The negative electrode current collector 42A has a pair of surfaces on which the negative electrode active material layer 42B is provided. More specifically, the negative electrode current collector 42A includes an inner surface 42A1 facing the winding center of the battery element 40, i.e., facing position P0, and an outer surface 42A2 facing the side opposite the winding center of the battery element 40, i.e., opposite the inner surface 42A1. The negative electrode current collector 42A is a metal foil made of, for example, nickel, a nickel alloy, copper, or a copper alloy.

[0060] The anode active material layer 42B is provided, for example, on both a portion of the inner surface and a portion of the outer surface of the anode current collector 42A. The anode active material layer 42B includes one or more anode active materials capable of absorbing and releasing lithium. However, the anode active material layer 42B may further include an anode binder, an anode conductor, and the like. Details regarding the anode binder and the anode conductor are the same as those regarding the positive electrode binder and the positive electrode conductor, respectively. The method for forming the anode active material layer 42B is not particularly limited, but may include one or more of a coating method, a vapor phase method, a liquid phase method, a thermal spraying method, and a firing method (sintering method).

[0061] As shown in FIG. 4B , the negative electrode 42 has a negative electrode current collector-covered region 421 and a negative electrode current collector-exposed region 422. The negative electrode current collector-covered region 421 is a region of the negative electrode 42 where the negative electrode current collector 42A is covered with the negative electrode active material layer 42B. The negative electrode current collector-exposed region 422 is a region of the negative electrode 42 other than the negative electrode current collector-covered region 421. That is, the negative electrode current collector-exposed region 422 is a region where the negative electrode current collector 42A is exposed and not covered with the negative electrode active material layer 42B. The negative electrode current collector-covered region 421 and the negative electrode current collector-exposed region 422 each extend from an upper edge 42UT to a lower edge 42BT of the negative electrode 42 along the height direction Z, which is the short-side direction of the negative electrode 42. Two negative electrode current collector exposed regions 422 are provided at both ends in the winding direction θ, which is the longitudinal direction of the negative electrode 42. One of the two negative electrode current collector exposed regions 422 includes the inner peripheral edge 42S of the innermost negative electrode portion 42in ( FIG. 5 ) of the negative electrode 42, and the other of the two negative electrode current collector exposed regions 422 includes the outer peripheral edge 42E of the outermost negative electrode portion 42out ( FIG. 5 ) of the negative electrode 42. The negative electrode current collector covered region 421 is disposed so as to be sandwiched between the two negative electrode current collector exposed regions 422 in the winding direction θ. In other words, the negative electrode active material layer 42B is not present at both ends in the winding direction θ, which is the longitudinal direction of the negative electrode current collector 42A.

[0062] As shown in FIGS. 3 to 5 , the negative electrode lead 52 is attached to the negative electrode current collector 42A in the negative electrode current collector exposed region 422. More specifically, the negative electrode lead 52 is attached to the inner surface 42A1 of the negative electrode current collector 42A in the outermost one of the two negative electrode current collector exposed regions 422. As shown in FIG. 4B , the negative electrode lead 52 is provided such that a portion thereof protrudes downward from the lower edge 42BT of the negative electrode 42. The negative electrode current collector 42A has a notch 42K formed in part of the lower edge 42BT. The notch 42K has an outline that is curved, for example, to describe an arc.

[0063] 4B , the length HWA in the height direction Z of the bonding region WA of the negative electrode current collector 42A, which includes the bonding portion WP to which the negative electrode lead 52 is bonded, is shorter than the length H42 in the height direction Z of the negative electrode current collector 42A in the negative electrode current collector covering region 421. In other words, the distance between the upper edge 42UT and the lower edge 42BT at the location of the negative electrode current collector 42A where the negative electrode lead 52 is attached is narrower than the distance between the upper edge 42UT and the lower edge 42BT in the negative electrode current collector covering region 421 of the negative electrode current collector 42A.

[0064] 4A, 4B, and 5, the protective tape 41C of the positive electrode 41 covers the entire region of the positive electrode current collector exposed region 412 of the positive electrode 41 that faces the negative electrode current collector covered region 421 of the negative electrode 42 with the separator 43 interposed therebetween. The protective tape 41C can effectively prevent an internal short circuit in the secondary battery, for example, when a foreign object enters between the negative electrode current collector covered region 421 and the positive electrode current collector exposed region 412. Furthermore, when an impact is applied to the secondary battery, the protective tape 41C absorbs the impact and can effectively prevent bending of the positive electrode current collector exposed region 412 and short circuiting between the positive electrode current collector exposed region 412 and the negative electrode 42. Furthermore, even if a local increase in potential occurs in the positive electrode collector covered region 411 near the boundary between the positive electrode collector covered region 411 and the positive electrode collector exposed region 412, the outflow of metal ions from the positive electrode active material layer 41B can be suppressed, and a short circuit between the positive electrode 41 and the negative electrode 42 can be prevented.

[0065] The negative electrode active material contains one or both of a carbon material and a metal-based material. This is because a high energy density can be obtained. Carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite (natural graphite and artificial graphite). The metal-based material is a material containing, as a constituent element, one or more of metal elements and metalloid elements that can form an alloy with lithium, and the metal element and metalloid element are one or both of silicon and tin, for example. However, the metal-based material may be a simple substance, an alloy, a compound, a mixture of two or more of these, or a material containing two or more of these phases. Specific examples of metal-based materials include TiSi 2 and SiOx (0<x≦2, or 0.2<x<1.4), etc.

[0066] Here, the height of the negative electrode 42 is greater than the height of the positive electrode 41. That is, as shown in FIG. 2 , the upper edge 42UT of the negative electrode 42 protrudes upward beyond the upper edge 41UT of the positive electrode 41, and the lower edge 42BT of the negative electrode 42 protrudes downward beyond the lower edge 41BT of the positive electrode 41. This is to prevent lithium released from the positive electrode 41 from being deposited. This "height" refers to the dimension corresponding to the height H of the secondary battery described above, i.e., the dimension in the vertical direction (height direction Z) in each of FIGS. 1 and 2 . The definition of height described here will also apply hereinafter.

[0067] 2 and 3, the separator 43 is an insulating porous film disposed between the positive electrode 41 and the negative electrode 42. The separator 43 allows lithium ions to pass through while preventing a short circuit between the positive electrode 41 and the negative electrode 42. The separator 43 contains a polymer compound such as polyethylene.

[0068] 2, the height of the separator 43 is greater than the height of the negative electrode 42. That is, the separator 43 preferably protrudes upward beyond the upper edge 42UT of the negative electrode 42 and downward beyond the lower edge 42BT of the negative electrode 42.

[0069] (Electrolyte) The electrolyte is impregnated into each of the positive electrode 41, the negative electrode 42, and the separator 43, and contains a solvent and an electrolyte salt. The solvent contains one or more of non-aqueous solvents (organic solvents) such as carbonate ester compounds, carboxylic acid ester compounds, and lactone compounds, and the electrolyte containing the non-aqueous solvent is a so-called non-aqueous electrolyte. The electrolyte salt contains one or more of light metal salts such as lithium salts.

[0070] [Positive Electrode Lead] As shown in Fig. 2 , the positive electrode lead 51 is housed inside the exterior can 10. The positive electrode lead 51 is a connecting wire connected to each of the positive electrode 41 and the external terminal 20. The secondary battery shown in Fig. 2 includes one positive electrode lead 51. However, the secondary battery may include two or more positive electrode leads 51.

[0071] As described above, the positive electrode lead 51 is connected to the positive electrode current collector 41A in the positive electrode current collector exposed region 412. The positive electrode lead 51 is also connected to a portion of the surface 20S of the external terminal 20 via a through hole 12K provided in the lid portion 12. The method for connecting the positive electrode lead 51 is not particularly limited, but specifically, it is any one or more of welding methods such as resistance welding and laser welding. The details of the welding methods described here also apply hereinafter.

[0072] A portion of the positive electrode lead 51 is electrically insulated from the lid portion 12 of the outer can 10 and the negative electrode 42 of the battery element 40, and is sandwiched between the lid portion 12 and the battery element 40 in the height direction of the secondary battery. As shown in FIG. 2 , the positive electrode lead 51 includes a first portion 511, a second portion 512, and a folded portion 513. The first portion 511 and the second portion 512 extend along a horizontal plane perpendicular to the height direction Z of the secondary battery. The first portion 511 and the second portion 512 overlap each other in the height direction Z of the secondary battery via the sealant 61. The folded portion 513 is curved to connect the first portion 511 and the second portion 512. The first portion 511 and the second portion 512 are sandwiched between the battery element 40 and the recessed portion 12H of the lid portion 12 in the height direction Z of the secondary battery.

[0073] In this way, a portion of the positive electrode lead 51 extends along the lower surface of the lid portion 12 and the upper surface of the battery element 40, and is thereby held by the lid portion 12 and the battery element 40. Therefore, the positive electrode lead 51 is fixed inside the outer can 10. Even if the secondary battery is subjected to external forces such as vibration and impact, the positive electrode lead 51 is less likely to move, and therefore the positive electrode lead 51 is less likely to be damaged. Damage to the positive electrode lead 51 here refers to the occurrence of cracks in the positive electrode lead 51, the positive electrode lead 51 being cut, the positive electrode lead 51 falling off from the positive electrode 41, etc.

[0074] That is, "a portion of the positive electrode lead 51 is sandwiched between the outer can 10 and the battery element 40" means that the positive electrode lead 51 is held from above and below by the outer can 10 and the battery element 40 while being insulated from each other, so that the positive electrode lead 51 is unlikely to move inside the outer can 10 even if the secondary battery is subjected to external forces such as vibration and impact. The fact that the positive electrode lead 51 is unlikely to move inside the outer can 10 means that the battery element 40 is also unlikely to move inside the outer can 10. Therefore, when the secondary battery is subjected to vibration or impact, problems such as collapse of the battery element 40, which is a wound electrode body, can be avoided.

[0075] As described above, the lid portion 12 includes the recessed portion 12H, and a portion of the positive electrode lead 51 is sandwiched between the recessed portion 12H and the battery element 40. That is, a portion of the positive electrode lead 51 extends along the lower surface of the recessed portion 12H and the upper surface of the battery element 40, and is thereby held by the recessed portion 12H and the battery element 40. Since the positive electrode lead 51 is more easily held by utilizing the recessed portion 12H, the positive electrode lead 51 is less likely to be damaged.

[0076] Furthermore, a portion of the positive electrode lead 51 is insulated from the lid portion 12 and the negative electrode 42 via the separator 43 , the sealant 61 , and the insulating films 62 and 63 , respectively.

[0077] Specifically, as described above, the height of the separator 43 is greater than the height of the negative electrode 42. As a result, a portion of the positive electrode lead 51 is separated from the negative electrode 42 via the separator 43, and is therefore insulated from the negative electrode 42 via the separator 43. This is because a short circuit between the positive electrode lead 51 and the negative electrode 42 is prevented.

[0078] The positive electrode lead 51 is also coated with an insulating sealant 61. As a result, a portion of the positive electrode lead 51 is insulated from the lid portion 12 and the negative electrode 42 via the sealant 61. This is because a short circuit between the positive electrode lead 51 and the lid portion 12 is prevented, and a short circuit between the positive electrode lead 51 and the negative electrode 42 is also prevented.

[0079] An insulating film 62 is disposed between the lid portion 12 and the positive electrode lead 51. As a result, a portion of the positive electrode lead 51 is insulated from the lid portion 12 via the insulating film 62. This is because a short circuit between the positive electrode lead 51 and the lid portion 12 is prevented.

[0080] Furthermore, an insulating film 63 is disposed between the battery element 40 and the positive electrode lead 51. As a result, a portion of the positive electrode lead 51 is insulated from the negative electrode 42 via the insulating film 63. This is because a short circuit between the positive electrode lead 51 and the negative electrode 42 is prevented.

[0081] The details regarding the material for forming the positive electrode lead 51 are the same as the details regarding the material for forming the positive electrode current collector 41 A. However, the materials for forming the positive electrode lead 51 and the positive electrode current collector 41 A may be the same as or different from each other.

[0082] The connection position of the positive electrode lead 51 to the positive electrode 41 is not particularly limited and can be set arbitrarily. In particular, the positive electrode lead 51 is preferably connected to the positive electrode 41 at a position more inward than the outermost periphery of the positive electrode 41. This is because, unlike when the positive electrode lead 51 is connected to the positive electrode 41 at the outermost periphery of the positive electrode 41, corrosion of the outer can 10 due to creeping up of the electrolyte is prevented. This "creeping up of the electrolyte" refers to the electrolyte in the battery element 40 creeping up the positive electrode lead 51 and reaching the inner wall surface of the outer can 10 when the positive electrode lead 51 is disposed close to the inner wall surface of the outer can 10. When the electrolyte comes into contact with the outer can 10 due to "creeping up of the electrolyte," a phenomenon occurs in which the outer can 10 dissolves or discolors.

[0083] The positive electrode lead 51 is provided as a separate body from the positive electrode current collector 41A. However, since the positive electrode lead 51 is physically continuous with the positive electrode current collector 41A, the positive electrode lead 51 may be integrated with the positive electrode current collector 41A.

[0084] [Negative Electrode Lead] As shown in FIG. 2 , the negative electrode lead 52 is housed inside the outer can 10. The negative electrode lead 52 electrically connects the negative electrode 42 and the outer can 10 (storage section 11). Therefore, the storage section 11 (bottom M2) is electrically connected to the negative electrode 42 via the negative electrode lead 52. Here, the secondary battery includes one negative electrode lead 52. However, the secondary battery may include two or more negative electrode leads 52. The negative electrode lead 52 is a specific example corresponding to "lead" in the present disclosure.

[0085] As described above, the negative electrode lead 52 is connected to the negative electrode current collector 42A so as to protrude from the lower edge 42BT of the negative electrode 42. The negative electrode lead 52 is further connected to the bottom surface of the storage section 11. There are no particular limitations on the method for connecting the negative electrode lead 52, and specific examples include one or more welding methods such as resistance welding and laser welding.

[0086] The details regarding the material for forming the negative electrode lead 52 are the same as the details regarding the material for forming the negative electrode current collector 42A. However, the material for forming the negative electrode lead 52 and the material for forming the negative electrode current collector 42A may be the same as or different from each other. An example of the material for forming the negative electrode lead 52 is nickel.

[0087] The connection position of the negative electrode lead 52 to the negative electrode 42 is not particularly limited and can be set arbitrarily. Here, the negative electrode lead 52 is connected to the outermost peripheral portion of the negative electrode 42 that constitutes the wound electrode body.

[0088] The negative electrode lead 52 is provided as a separate body from the negative electrode current collector 42A. However, since the negative electrode lead 52 is physically continuous with the negative electrode current collector 42A, the negative electrode lead 52 may be integrated with the negative electrode current collector 42A.

[0089] FIG. 6 is an enlarged plan view of the negative electrode lead 52 and its vicinity shown in FIG. 4B . The negative electrode lead 52 includes a pair of edges 52T1 and 52T2, which are both end edges in the width direction (winding direction θ) perpendicular to the extension direction (height direction Z). As described above, the negative electrode current collector 42A has a notch 42K, and the negative electrode lead 52 is joined so as to overlap the notch 42K in the radial direction R. Therefore, the negative electrode lead 52 is joined to the negative electrode current collector 42A with the pair of edges 52T1 and 52T2 inclined relative to the lower edge 42BT. Here, the inclination of the pair of edges 52T1 and 52T2 relative to the lower edge 42BT means that the angle at which the lower edge 42BT intersects with the edge 52T1 and the angle at which the lower edge 42BT intersects with the edge 52T2 are other than 90°. Furthermore, the length W42K of the notch 42K in the winding direction θ of the negative electrode current collector 42A may be longer than the length W52 of the negative electrode lead 52 in the winding direction θ. In the configuration example shown in FIG. 6 , the length W42K of the notch 42K in the winding direction θ is longer than the length H42K of the notch 42K in the height direction Z. The joint portion of the negative electrode lead 52 with the negative electrode current collector 42A extends, for example, in the height direction Z. However, the portion of the negative electrode lead 52 that protrudes downward from the lower edge 42BT is bent so as to be along a horizontal plane perpendicular to the height direction Z, as shown in FIG. 2 . Because the notch 42K is provided in the lower edge 42BT of the negative electrode current collector 42A, the stress applied to the lower edge 42BT due to the bending of the negative electrode lead 52 is alleviated.

[0090] 2 , the sealant 61 is a first insulating member that covers the periphery of the positive electrode lead 51, and is formed by attaching two pieces of insulating tape to the front and back surfaces of the positive electrode lead 51. Here, the sealant 61 covers the periphery of the middle portion of the positive electrode lead 51 in order to connect the positive electrode lead 51 to the positive electrode 41 and the external terminal 20, respectively. Note that the sealant 61 is not limited to having a tape-like structure, and may have, for example, a tube-like structure.

[0091] The sealant 61 contains one or more insulating materials such as insulating polymer compounds, and the insulating material is polyimide or the like.

[0092] 2, the insulating film 62 is an insulating member disposed between the lid portion 12 and the battery element 40 in the height direction Z. Here, the insulating film 62 has a ring-shaped planar shape having an opening 62K at a position corresponding to the through hole 12K in the height direction Z.

[0093] Here, the insulating film 62 may be adhered to the lid portion 12 via an adhesive layer.

[0094] The insulating film 62 may contain one or more insulating materials such as insulating polymer compounds, etc. The insulating material contained in the insulating film 62 is polyimide, etc.

[0095] 2, the insulating film 63 is an insulating member disposed between the battery element 40 and the positive electrode lead 51. Here, the insulating film 63 has a flat plate-like shape. The insulating film 63 is disposed so as to shield the winding center space 40K and to cover the battery element 40 around the winding center space 40K.

[0096] The details regarding the material for forming the insulating film 63 are the same as the details regarding the material for forming the insulating film 62. However, the materials for forming the insulating film 63 and the insulating film 62 may be the same as or different from each other.

[0097] [Others] The secondary battery may further include one or more other components. Specifically, the secondary battery includes a safety valve mechanism. This safety valve mechanism is configured to cut off the electrical connection between the outer can 10 and the battery element 40 when the internal pressure of the outer can 10 reaches a certain level or higher. Causes of the internal pressure of the outer can 10 reaching a certain level or higher include the occurrence of a short circuit inside the secondary battery and the secondary battery being heated from the outside. The location of the safety valve mechanism is not particularly limited, but it is preferable that the safety valve mechanism be provided on either the bottom portion M1 or M2, and it is more preferable that the safety valve mechanism be provided on the bottom portion M2 to which the external terminal 20 is not attached.

[0098] The secondary battery may also have an insulator other than the insulating films 62, 64 between the exterior can 10 and the battery element 40. This insulator includes one or more types of insulating film and insulating sheet, etc., and prevents short-circuiting between the exterior can 10 and the battery element 40. The installation range of the insulator is not particularly limited and can be set as desired.

[0099] The outer can 10 is provided with a series valve. This series valve bursts when the internal pressure of the outer can 10 reaches a certain level or higher, thereby releasing the internal pressure. There are no particular limitations on the location where the series valve is to be installed, but, similar to the location where the safety valve mechanism is installed, either of the bottoms M1 and M2 is preferred, and the bottom M2 is particularly preferred.

[0100] (1-2. Operation) When the secondary battery is charged, lithium is released from the positive electrode 41 in the battery element 40 and is absorbed in the negative electrode 42 via the electrolyte. On the other hand, when the secondary battery is discharged, lithium is released from the negative electrode 42 in the battery element 40 and is absorbed in the positive electrode 41 via the electrolyte. During these charge and discharge operations, lithium is absorbed and released in an ionic state.

[0101] (1-3. Manufacturing Method) FIG. 7 shows a perspective view of the exterior can 10 used in the manufacturing process of the secondary battery, and corresponds to FIG.

[0102] FIG. 7 shows the state in which the cover 12 is separated from the storage section 11 before the cover 12 is welded to the storage section 11.

[0103] In the following description, reference will be made to FIG. 7 as well as to FIGS. 1 to 6, which have already been described.

[0104] 7, to form the exterior can 10, a housing portion 11 and a lid portion 12, which are physically separated from each other, are prepared. The housing portion 11 is a roughly bowl-shaped member in which a bottom portion M2 and a side wall portion M3 are integrated with each other, and has an opening 11K. The lid portion 12 is a roughly plate-shaped member corresponding to the bottom portion M1, and the external terminals 20 are attached in advance to recess portions 12H provided in the lid portion 12 via gaskets 30.

[0105] However, the storage section 11 may be formed by preparing the bottom section M2 and the side wall section M3 which are physically separated from each other, and welding the side wall section M3 to the bottom section M2.

[0106] [Fabrication of Positive Electrode] First, a positive electrode mixture is prepared by mixing a positive electrode active material, a positive electrode binder, a positive electrode conductive agent, and the like. Next, the prepared positive electrode mixture is poured into an organic solvent or the like to prepare a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry is applied to both sides of the positive electrode current collector 41A to form the positive electrode active material layer 41B. Finally, the positive electrode active material layer 41B is compression-molded using a roll press or the like. In this case, the positive electrode active material layer 41B may be heated, or the compression molding may be repeated multiple times. In this manner, the positive electrode 41 is fabricated.

[0107] [Fabrication of Negative Electrode] The negative electrode 42 is fabricated using the same procedure as that for fabricating the positive electrode 41. Specifically, a negative electrode mixture, which is a mixture of a negative electrode active material, a negative electrode binder, a negative electrode conductive agent, and the like, is poured into an organic solvent to prepare a paste-like negative electrode mixture slurry, and then the negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector 42A to form the negative electrode active material layer 42B. The negative electrode active material layer 42B is then compression-molded using a roll press or the like. This completes the fabrication of the negative electrode 42.

[0108] [Preparation of Electrolyte Solution] An electrolyte salt is added to a solvent, whereby the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing an electrolyte solution.

[0109] [Assembly of Secondary Battery] First, using a welding method such as resistance welding, the positive electrode lead 51, the periphery of which is covered with the sealant 61, is connected to the positive electrode 41 (positive electrode current collector 41A), and the negative electrode lead 52 is connected to the negative electrode 42 (negative electrode current collector 42A).

[0110] Next, the positive electrode 41 and the negative electrode 42 are stacked with the separator 43 interposed therebetween, and the stack including the positive electrode 41, the negative electrode 42, and the separator 43 is wound to produce a wound body 40Z as shown in Fig. 7. The wound body 40Z has a configuration similar to that of the battery element 40, except that the positive electrode 41, the negative electrode 42, and the separator 43 are not impregnated with an electrolyte. Note that the positive electrode lead 51 and the negative electrode lead 52 are not shown in Fig. 7.

[0111] Next, the wound body 40Z, to which the positive electrode lead 51 and the negative electrode lead 52 are respectively connected, is accommodated inside the accommodation section 11 through the opening 11K. In this case, the negative electrode lead 52 is connected to the accommodation section 11 using a welding method such as resistance welding. Next, an insulating film 63 is placed on the wound body 40Z.

[0112] Next, after preparing the lid portion 12 to which the external terminal 20 is attached via the gasket 30 and on which the insulating film 62 is already provided, the positive electrode lead 51 is connected to the external terminal 20 via the through hole 12K using a welding method such as resistance welding.

[0113] As a result, the wound body 40Z (positive electrode 41) housed inside the housing portion 11 and the external terminal 20 attached to the lid portion 12 are connected to each other via the positive electrode lead 51.

[0114] Next, the electrolyte solution is injected into the storage portion 11 through the opening 11K. In this case, even if the battery element 40 and the external terminal 20 are connected to each other via the positive electrode lead 51 as described above, the lid portion 12 does not close the opening 11K, so the electrolyte solution can be easily injected into the storage portion 11 through the opening 11K. As a result, the wound body 40Z including the positive electrode 41, the negative electrode 42, and the separator 43 is impregnated with the electrolyte solution, and the battery element 40, which is a wound electrode body, is produced.

[0115] Next, the lid 12 is tilted down so as to approach the storage section 11, thereby closing the opening 11K with the lid 12, and then the lid 12 is welded to the storage section 11 using a welding method such as laser welding. In this case, as shown in Fig. 2 , a part of the positive electrode lead 51 is sandwiched between the lid 12 and the battery element 40, and a curved folded-back portion 513 is formed in the positive electrode lead 51 before the connection location to the external terminal 20. In this way, the outer can 10 is formed, and the battery element 40 and the like are housed inside the outer can 10, completing the assembly of the secondary battery.

[0116] [Stabilization of Secondary Battery] The assembled secondary battery is charged and discharged. Various conditions, such as the ambient temperature, the number of charge / discharge cycles (number of cycles), and the charge / discharge conditions, can be set as desired. This forms a coating on the surface of the negative electrode 42, etc., which electrochemically stabilizes the state of the secondary battery. This completes the secondary battery.

[0117] (1-4. Actions and Effects) As described above, in the secondary battery of the present embodiment, the negative electrode lead 52 is joined to the negative electrode current collector 42A in a state in which the pair of edges 52T1, 52T2 of the negative electrode 42 of the battery element 40 are inclined relative to the lower edge 42BT. Specifically, a notch 42K is provided in a portion of the lower edge 42BT of the negative electrode current collector 42A, and the negative electrode lead 52 is joined to a portion of the negative electrode current collector 42A that overlaps with the notch 42K. This suppresses a decrease in the strength of the negative electrode current collector 42A and prevents cracks or breakage from occurring in the first electrode current collector. This is because the stress applied by the negative electrode lead 52 to the negative electrode current collector 42A is alleviated even when the negative electrode lead 52 is bent.

[0118] The effects of the secondary battery of this embodiment will be described in more detail with reference to FIGS. 8A and 8B . FIG. 8A is a partially enlarged cross-sectional view of a portion of the battery element 40 shown in FIG. 5 . FIG. 8B is a partially enlarged cross-sectional view of a portion of the battery element 40 shown in FIG. 2 . FIG. 8B is a cross-sectional view taken along line VIII-VIII in FIG. 8A . For example, as shown in FIG. 8A , in a horizontal cross-section perpendicular to the height direction Z, the joint portion 52A of the negative electrode lead 52 joined to the negative electrode current collector 42A is curved to conform to the shape of the negative electrode current collector 42A wound around the center line PC as the winding axis. As shown in FIG. 8B , near the lower edge 42BT of the negative electrode current collector 42A to which the negative electrode lead 52 is attached, the drawn-out portion 52B of the negative electrode lead 52 protruding from the lower edge 42BT is bent at a substantially right angle to the joint portion 52A joined to the negative electrode current collector 42A. That is, the joint portion 52A extends in the height direction Z, while the lead portion 52B extends in the radial direction R. Therefore, the lead portion 52B, particularly the portion near the lower edge 42BT, tends to deform linearly. Therefore, the pair of edges 52T1, 52T2 of the lead portion 52B of the negative electrode lead 52 applies stress to the negative electrode current collector 42A in the directions indicated by arrows SS1, SS2 in FIG. 8A . Therefore, compressive stress or tensile stress is locally applied near the lower edge 42BT of the negative electrode current collector 42A. Therefore, in the secondary battery of this embodiment, the cutout 42K is provided, and the negative electrode lead 52 is joined to the negative electrode current collector 42A with the pair of edges 52T1, 52T2 inclined relative to the lower edge 42BT, thereby dispersing the compressive stress and tensile stress applied to the lower edge 42BT around the lower edge 42BT and preventing stress from concentrating on the lower edge 42BT. As a result, sufficient strength of the negative electrode current collector 42A is maintained, and the secondary battery of this embodiment can have high reliability.

[0119] In contrast, when the pair of edges 52T1 and 52T2 are perpendicular to the lower edge 42BT, stress tends to concentrate at the contact position between the lower edge 42BT and the edge 52T1, and at the contact position between the lower edge 42BT and the edge 52T1, unlike the secondary battery of the present embodiment, which may result in a decrease in the strength of the negative electrode current collector compared to the secondary battery of the present embodiment.

[0120] In the secondary battery of the present embodiment, the negative electrode lead 52 is joined to the inner surface 42A1 of the negative electrode current collector 42A. Therefore, when the negative electrode lead 52 is present at the outermost periphery of the negative electrode current collector 42A, the ease of insertion into the storage portion 11 of the outer can 10 is improved compared to when the negative electrode lead 52 is joined to the outer surface 42A2 of the negative electrode current collector 42A.

[0121] Furthermore, if the secondary battery is a lithium ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the absorption and desorption of lithium.

[0122] 2. Modifications of One Embodiment (First Modification) Next, a negative electrode 42-1 as a first modification of one embodiment of the present disclosure will be described with reference to FIG. 9 . FIG. 9 is a partially enlarged plan view of the negative electrode 42-1 as the first modification, corresponding to FIG. 6 , which shows a partially enlarged view of the negative electrode 42 of the above-described embodiment. The negative electrode current collector 42-1A of the negative electrode 42-1 has a notch 42-1K at the lower edge 42BT of the negative electrode current collector exposed region 422. The notch 42-1K has a substantially triangular planar shape including two straight line segments. Except for the above points, the configuration of the negative electrode 42-1 as the first modification is substantially the same as the configuration of the negative electrode 42 of the above-described embodiment. A secondary battery including the negative electrode 42-1 of this modification can be expected to have the same effects as a secondary battery including the negative electrode 42 of the above-described embodiment.

[0123] (Second Modification) Next, a negative electrode 42-2 as a second modification of an embodiment of the present disclosure will be described with reference to FIG. 10 . FIG. 10 is a partially enlarged plan view of a negative electrode 42-2 as the second modification, and corresponds to FIG. 6 , which shows a partially enlarged view of the negative electrode 42 of the embodiment. The negative electrode current collector 42-2A of the negative electrode 42-2 has a notch 42-2K at the lower edge 42BT of the negative electrode current collector exposed region 422. The notch 42-2K has a substantially rectangular planar shape including three straight line segments. Except for the above points, the configuration of the negative electrode 42-2 as the second modification is substantially the same as the configuration of the negative electrode 42 of the embodiment. A secondary battery including the negative electrode 42-2 of this modification can be expected to have the same effects as a secondary battery including the negative electrode 42 of the embodiment.

[0124] (Third Modification) Next, a negative electrode 42-3 as a third modification of an embodiment of the present disclosure will be described with reference to FIG. 11 . FIG. 11 is a partially enlarged plan view of a negative electrode 42-3 as a third modification, corresponding to FIG. 6 , which shows a partially enlarged view of the negative electrode 42 of the embodiment. The negative electrode current collector 42-3A of the negative electrode 42-3 has a notch 42-3K at the lower edge 42BT of the negative electrode current collector exposed region 422. The notch 42-3K has a substantially trapezoidal planar shape including three straight line segments. Except for the above points, the configuration of the negative electrode 42-3 as the third modification is substantially the same as the configuration of the negative electrode 42 of the embodiment. A secondary battery including the negative electrode 42-3 of this modification can be expected to have the same effects as a secondary battery including the negative electrode 42 of the embodiment.

[0125] (Fourth Modification) Next, a negative electrode 42-4 as a fourth modification of an embodiment of the present disclosure will be described with reference to FIG. 12 . FIG. 12 is a partially enlarged plan view of a negative electrode 42-4 as the fourth modification, and corresponds to FIG. 6 , which shows a partially enlarged view of the negative electrode 42 of the embodiment. The negative electrode current collector 42-4A of the negative electrode 42-4 has a notch 42-4K at the lower edge 42BT of the negative electrode current collector exposed region 422. The notch 42-4K has a semi-elliptical planar shape including a curved portion. The length H42K of the notch 42-4K is longer than half the length W42K. Note that the length H42K may be equal to half the length W42K. The configuration of the negative electrode 42-4 as the fourth modification is substantially the same as the configuration of the negative electrode 42 of the embodiment, except for the above points. The secondary battery including the negative electrode 42-4 of this modified example is also expected to have the same effects as the secondary battery including the negative electrode 42 of the above embodiment.

[0126] (Fifth Modification) Next, a negative electrode 42-5 as a fifth modification of an embodiment of the present disclosure will be described with reference to FIG. 13 . FIG. 13 is a partially enlarged plan view of a negative electrode 42-5 as a fifth modification, corresponding to FIG. 6 , which shows a partially enlarged view of the negative electrode 42 of the embodiment. The negative electrode current collector 42-5A of the negative electrode 42-5 has a stepped notch 42-5K at the lower edge 42BT of the negative electrode current collector exposed region 422. The notch 42-5K includes an inclined portion 42-5K1 and an inclined portion 42-5K2 at the locations where the notch 42-5K intersects with the edge 52T1 and the edge 52T2 of the negative electrode lead 52, respectively. Except for the above points, the configuration of the negative electrode 42-5 as the fifth modification is substantially the same as the configuration of the negative electrode 42 of the embodiment. A secondary battery including the negative electrode 42-5 of this modification can be expected to have the same effects as a secondary battery including the negative electrode 42 of the embodiment.

[0127] 4. Examples Examples of the present disclosure will be described.

[0128] 1 to 6 were fabricated. Specifically, coin-type secondary batteries including a negative electrode 42 having a notch 42K formed therein were fabricated as follows.

[0129] (Preparation of Positive Electrode) First, a positive electrode active material (LiCoO 2 A positive electrode mixture was prepared by mixing 91 parts by weight of ethylenediamine fluoride (Eu), 3 parts by weight of a positive electrode binder (polyvinylidene fluoride), and 6 parts by weight of a positive electrode conductive agent (graphite). Subsequently, the positive electrode mixture was added to an organic solvent (N-methyl-2-pyrrolidone), and the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector 41A (a strip-shaped aluminum foil having a thickness of 12 μm) using a coating device, and the positive electrode mixture slurry was then dried to form a positive electrode active material layer 41B. Finally, the positive electrode active material layer 41B was compression-molded using a roll press. This resulted in a positive electrode 41 (width = 3.3 mm). The thicknesses of the positive electrode inner active material layer 41B1 and the positive electrode outer active material layer 41B2 after compression molding were each 0.037 mm.

[0130] (Negative Electrode Fabrication) First, 95 parts by mass of negative electrode active material (graphite) and 5 parts by mass of negative electrode binder (polyvinylidene fluoride) were mixed to prepare a negative electrode mixture. Subsequently, the negative electrode mixture was added to an organic solvent (N-methyl-2-pyrrolidone), and the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. Next, a strip of copper foil having a thickness of 15 μm was prepared, and a notch 42K was formed by punching out a portion of its outer edge to prepare a negative electrode current collector 42A. Next, the positive electrode mixture slurry was applied to both sides of the negative electrode current collector 42A using a coating device, and the negative electrode mixture slurry was then dried to form a negative electrode active material layer 42B. Finally, the negative electrode active material layer 42B was compression-molded using a roll press. This resulted in the production of a negative electrode 42 (width = 3.8 mm).

[0131] (Preparation of Electrolyte Solution) After adding electrolyte salt (LiPF6) to a solvent (ethylene carbonate and diethyl carbonate), the solvent was stirred. In this case, the mixing ratio (weight ratio) of the solvents was ethylene carbonate:diethyl carbonate = 30:70, and the content of the electrolyte salt was 1 mol / kg relative to the solvent. As a result, the electrolyte salt was dissolved or dispersed in the solvent, and an electrolyte solution was prepared.

[0132] (Assembly of Secondary Battery) First, an aluminum positive electrode lead 51 (thickness = 0.1 mm, width = 2.0 mm, protruding length from the positive electrode 41 = 11.7 mm) partially coated with a tubular sealant 61 (polypropylene film, outer diameter = 9.0 mm, inner diameter = 3.0 mm) was welded to the positive electrode 41 (positive electrode current collector 41A) using a resistance welding method. Also, a nickel negative electrode lead 52 (thickness = 0.1 mm, width = 2.0 mm, protruding length from the negative electrode 42 = 6.0 mm) was welded to the negative electrode 42 (negative electrode current collector 42A) using a resistance welding method.

[0133] Next, the positive electrode 41 and the negative electrode 42 were stacked on top of each other with a separator 43 (a microporous polyethylene film having a thickness of 25 μm and a width of 4.0 mm) interposed therebetween, and then the positive electrode 41, the negative electrode 42, and the separator 43 were wound together to produce a cylindrical wound body 40Z (outer diameter = 11.6 mm) having a winding center space 40K (inner diameter = 1.5 mm).

[0134] Subsequently, a ring-shaped insulating film (polyimide film, outer diameter = 11.6 mm, inner diameter = 2.2 mm, thickness = 0.05 mm) for underlay was placed inside a cylindrical storage portion 11 (wall thickness = 0.15 mm, outer diameter = 12.0 mm, height = 5.0 mm) made of stainless steel (SUS316) through the opening 11K, and then the wound body 40Z was placed inside the storage portion 11. The negative electrode lead 52 was welded to the storage portion 11 by resistance welding. Subsequently, the positive electrode lead 51 was welded by resistance welding to the external terminal 20 of the disk-shaped lid portion 12 (wall thickness = 0.15 mm, outer diameter 11.7 mm) made of stainless steel (SUS316), which has a recessed portion 12H (inner diameter = 9.0 mm, step height = 0.3 mm) with a through hole 12K (inner diameter = 3.0 mm) provided therein, and to which the disk-shaped external terminal 20 (wall thickness = 0.3 mm, outer diameter = 7.2 mm) made of aluminum is attached via a gasket 30 (polyimide film, outer diameter = 9.2 mm, inner diameter = 3.2 mm).

[0135] Next, with the lid 12 standing upright on the storage section 11, the electrolyte was poured into the storage section 11 through the opening 11K. As a result, the wound body 40Z (the positive electrode 41, the negative electrode 42, and the separator 43) was impregnated with the electrolyte, and the battery element 40 was produced.

[0136] Finally, the opening 11K was closed using the lid 12, and then the lid 12 was welded to the storage section 11 using a laser welding method. When the opening 11K was closed with the lid 12, a folded portion 513 was formed in a part of the positive electrode lead 51 so as to have a curved shape, and the folded portion 513 was positioned in the peripheral portion 12R. Specifically, the distance between the folded portion 513 and the inner surface of the side wall portion M3 was adjusted to be 0.5 mm. In addition, a ring-shaped insulating film 62 (polyimide film, outer diameter = 9.2 mm, inner diameter = 3.2 mm) was disposed between the lid 12 and the positive electrode lead 51, and a disk-shaped insulating film 63 (polyimide film, outer diameter = 3.2 mm) was disposed between the battery element 40 and the positive electrode lead 51. As a result, the housing portion 11 and the lid portion 12 formed the outer can 10, and the battery element 40 was sealed inside the outer can 10, thereby assembling a secondary battery (outer diameter = 12.0 mm, height = 5.0 mm).

[0137] (Stabilization of Secondary Battery) The assembled secondary battery was subjected to one cycle of charge and discharge in a room temperature environment (temperature = 23°C). During charging, the battery was charged at a constant current of 0.1 C until the voltage reached 4.2 V, and then charged at a constant voltage of 0.05 C at the same voltage of 4.2 V. During discharging, the battery was discharged at a constant current of 0.1 C until the voltage reached 3.0 V. 0.1 C is the current value at which the battery capacity (theoretical capacity) is fully discharged in 10 hours, and 0.05 C is the current value at which the battery capacity is fully discharged in 20 hours.

[0138] As a result, a coating was formed on the surface of the negative electrode 42 and the like, which electrochemically stabilized the state of the secondary battery. Thus, the secondary battery was completed.

[0139] Next, the performance of the secondary batteries prepared as described above was evaluated. Specifically, 100 secondary batteries prepared as described above and subjected to one cycle of charge / discharge operation under the above conditions were all disassembled, and the presence or absence of damage (cracks or fractures) in the negative electrode current collector was visually confirmed. The results are shown in Table 1.

[0140]

[0141] 9 were fabricated, and then these secondary batteries were evaluated in the same manner as the secondary battery of Example 1. The results are also shown in Table 1.

[0142] 10 were fabricated, and then the secondary batteries were evaluated in the same manner as the secondary battery of Example 1. The results are also shown in Table 1.

[0143] 11 were fabricated, and then these secondary batteries were evaluated in the same manner as the secondary battery of Example 1. The results are also shown in Table 1.

[0144] 12 were fabricated, and then these secondary batteries were evaluated in the same manner as the secondary battery of Example 1. The results are also shown in Table 1.

[0145] 13 were fabricated, and then these secondary batteries were evaluated in the same manner as the secondary battery of Example 1. The results are also shown in Table 1.

[0146] [Comparative Example 1] One hundred secondary batteries having the negative electrode 142 shown in Figure 14 were fabricated, and then these secondary batteries were evaluated in the same manner as the evaluation of the secondary battery of Example 1. The results are also shown in Table 1. The negative electrode 142 has a negative electrode current collector 142A that does not include a notch. Except for the above points, the configuration of the negative electrode 142 of Comparative Example 1 is substantially the same as the configuration of the negative electrode 42 of the above embodiment.

[0147] As shown in Table 1, in Examples 1 to 6, no cracks or breaks occurred in the negative electrode current collector. In contrast, in Comparative Example 1, cracks and breaks were observed in the negative electrode current collector in 20 of the 100 secondary batteries. From these results, it is presumed that in Comparative Example 1, the lower edge 42BT intersecting with the negative electrode lead 52 is perpendicular to the edges 52T1 and 52T2 of the negative electrode lead 52, and therefore, due to the expansion and contraction of the battery element 40 associated with charge and discharge, local stress is applied to the portion of the negative electrode current collector 42A where the negative electrode lead 52 is provided, causing that portion to be stretched. In contrast, in Examples 1 to 6, the lower edge 42BT intersecting with the negative electrode lead 52 is designed to intersect obliquely with the edges 52T1 and 52T2 of the negative electrode lead 52, which is thought to have reduced the load on the negative electrode current collector 42A.

[0148] Although the present technology has been described above with reference to an embodiment and examples, the configuration of the present technology is not limited to the configuration described in the embodiment and examples, and various modifications are possible.

[0149] Specifically, the case where the outer can is a welded can (crimpless can) has been described, but the configuration of the outer can is not particularly limited, and it may be a crimped can that has been crimped. In this crimped can, the storage section and the lid section, which are separated from each other, are crimped together via a gasket. Furthermore, the configuration of the secondary battery described in the above embodiment is one example, and the present disclosure is not limited to that configuration.

[0150] In the above embodiment, a case where a notch is provided in a part of the negative electrode current collector has been described as an example, but the present disclosure is not limited to this. For example, a notch may be provided in the positive electrode current collector at a position where the positive electrode lead is joined.

[0151] In the above embodiment, the case where the outer can housing the battery element also serves as an external connection terminal to be connected to the lead has been described as an example, but the present disclosure is not limited to this. For example, an external connection terminal may be provided separately from the outer can. In the above embodiment, the negative electrode lead has been described as an example of the lead, but the lead of the present disclosure may be a positive electrode lead 51 connecting the external terminal 20 and the positive electrode 41.

[0152] Furthermore, although the electrode reactant is described as lithium, the electrode reactant is not particularly limited. Therefore, as described above, the electrode reactant may be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be other light metals such as aluminum.

[0153] The effects described in this specification are merely examples, and the effects of the present disclosure are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present disclosure.

[0154] Furthermore, the present disclosure may take the following forms. <1> A secondary battery comprising: a battery element in which a first electrode and a second electrode are stacked with a separator interposed between them and wound around a winding axis extending in a first direction; an external connection terminal; and a lead including a pair of edges and connecting the first electrode to the external connection terminal, wherein the first electrode has a first electrode current collector including a first edge and a first electrode active material layer covering a portion of the first electrode current collector, and the lead is joined to the first electrode current collector with the pair of edges inclined with respect to the first edge. <2> The secondary battery according to <1> above, wherein the first electrode current collector has a notch in the first edge. <3> The secondary battery according to <1> or <2>, wherein the first electrode includes a first electrode current collector-covered region in which the first electrode current collector is covered with the first electrode active material layer, and a first electrode current collector-exposed region in which the first electrode current collector is exposed and not covered by the first electrode active material layer, and the lead is joined to a part of the first electrode current collector in the first electrode current collector-exposed region. <4> The secondary battery according to <3>, wherein a length in the first direction of a joining region of the first electrode current collector, including a joining portion to which the lead is joined, is shorter than a length in the first direction of the first electrode current collector in the first electrode current collector-covered region. <5> The secondary battery according to any one of <1> to <4>, wherein the first electrode current collector includes a first electrode inner surface facing the winding axis and a first electrode outer surface opposite the first electrode inner surface, and the lead is joined to the first electrode inner surface. <6> The secondary battery according to any one of <1> to <5> above, wherein a joint portion of the lead with the first electrode current collector extends in the first direction. <7> The secondary battery according to any one of <1> to <6> above, wherein the first edge is curved. <8> The secondary battery according to any one of <1> to <7> above, wherein the first electrode is a negative electrode and the second electrode is a positive electrode. <9> The secondary battery according to any one of <1> to <8> above, further comprising an exterior can that houses the battery element, wherein the exterior can also serves as the external connection terminal.

Claims

1. A battery element in which a first electrode and a second electrode are laminated via a separator and wound around a winding axis extending in a first direction, an external connection terminal, a lead including a pair of edges and connecting the first electrode and the external connection terminal, and comprising: The first electrode has a first electrode current collector including a first edge, and a first electrode active material layer covering a part of the first electrode current collector, The lead is joined to the first electrode current collector with the pair of edges inclined with respect to the first edge, A secondary battery.

2. The first electrode current collector has a notch at the first edge, The secondary battery according to claim 1.

3. The first electrode includes a first electrode current collector covering region in which the first electrode current collector is covered by the first electrode active material layer, and a first electrode current collector exposed region in which the first electrode current collector is exposed without being covered by the first electrode active material layer, The lead is joined to a part of the first electrode current collector in the first electrode current collector exposed region, The secondary battery according to claim 1.

4. The length of the joining region including the joining portion to which the lead is joined in the first direction of the first electrode current collector is shorter than the length of the first electrode current collector in the first direction in the first electrode current collector covering region, The secondary battery according to claim 3.

5. The first electrode current collector includes a first electrode inner surface facing the winding axis side and a first electrode outer surface on the side opposite to the first electrode inner surface, The lead is joined to the first electrode inner surface, The secondary battery according to claim 1.

6. The joining portion of the lead with the first electrode current collector extends in the first direction, The secondary battery according to claim 1.

7. The first edge is curved, The secondary battery according to claim 1.

8. The first electrode is a negative electrode and the second electrode is a positive electrode, The secondary battery according to claim 1.

9. Further comprising an outer can for housing the battery element, The outer can also serves as the external connection terminal, The secondary battery according to any one of claims 1 to 8.