Secondary batteries

Abstract

Provided is a secondary battery having a higher safety. This secondary battery comprises: a battery element formed by winding a laminated body including a first electrode and a second electrode about a winding axis extending in a first direction; an exterior member having a through hole that penetrates in the first direction and housing the battery element; and an external terminal attached to the exterior member via an insulating member at a position overlapping with the through hole of the exterior member in the first direction. The external terminal has a curved shape including a recessed surface or a protruded surface facing the battery element.

Description

[Technical Field]

[0001] The present disclosure relates to secondary batteries. [Background technology]

[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 these 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-046639 Summary of the Invention

[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 that has high safety.

[0007] A secondary battery according to an embodiment of the present disclosure includes a battery element formed by winding a laminate including a first electrode and a second electrode around a winding axis extending in a first direction, an exterior member having a through-hole penetrating in the first direction and housing the battery element, and an external terminal attached to the exterior member via an insulating member at a position overlapping the through-hole of the exterior member in the first direction. The external terminal has a curved shape including a concave or convex surface facing the battery element.

[0008] According to the secondary battery of one embodiment of the present disclosure, the external terminals have a curved shape, so that pressure inside the battery is applied to the external terminals more evenly, thereby achieving high safety.

[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 disclosure described below. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view illustrating a configuration example of a secondary battery according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view illustrating an example of the configuration of the secondary battery shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view illustrating an example of the configuration of the battery element shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view illustrating an example of the configuration of the external terminal shown in FIG. [Figure 5] FIG. 5 is a perspective view showing an example of the structure of an exterior can used in the manufacturing process of a secondary battery. [Figure 6] FIG. 6 is a cross-sectional view illustrating an example of the configuration of the secondary battery of the first modification. [Figure 7] FIG. 7 is a cross-sectional view illustrating a configuration example of a secondary battery according to the second modification. [Figure 8] FIG. 8 is a cross-sectional view illustrating a configuration example of a secondary battery according to the third modification. [Figure 9] FIG. 9 is a cross-sectional view showing the amount of bending of the external terminal of the example. [Figure 10A] FIG. 10A is a first explanatory diagram for explaining the seal tear strength test. [Figure 10B] FIG. 10B is a second explanatory diagram for explaining the seal split strength test. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. The description will be made in the following order. 1. Secondary battery 1-1.Configuration 1-2.Operation 1-3. Manufacturing method 1-4. Action and effects 2. Variations

[0012] <1. Secondary battery> First, a secondary battery according to an embodiment of the present disclosure will be described.

[0013] The secondary battery described here has a flat, columnar, three-dimensional shape and is called a coin type or a 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, and the height of this secondary battery is smaller than the outer diameter. The "outer diameter" here refers to the diameter (maximum diameter) of each of the pair of bottoms, and the "height" refers to the distance (maximum distance) from the surface of one bottom to the surface of the other bottom. In this embodiment, the direction connecting one bottom and the other bottom is defined as the height direction Z.

[0014] The charge / discharge principle of a secondary battery is not particularly limited, but the following description focuses on a case where battery capacity is obtained by utilizing the absorption / 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 larger than the discharge capacity of the positive electrode to prevent deposition of the electrode reactant on the surface of the negative electrode during charging. In other words, the electrochemical capacity per unit area of ​​the negative electrode is set to be larger than the electrochemical capacity per unit area of ​​the positive electrode.

[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.Configuration> Fig. 1 shows an example of a perspective configuration of a secondary battery. Fig. 2 shows an example of a cross-sectional configuration of the secondary battery shown in Fig. 1. Fig. 3 shows an example of a cross-sectional configuration of a battery element 40 shown in Fig. 2. However, Fig. 3 shows an enlarged view of only a portion of the cross-sectional configuration of the battery element 40.

[0018] In the following description, for convenience, the upper side in each of FIGS. 1 and 2 is the upper side of the secondary battery. 1 and 2 will be explained assuming that the lower side in each of FIGS. 1 and 2 is 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 flat and cylindrical (columnar). 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 means the dimension of the secondary battery of this embodiment in the height direction Z. Furthermore, the outer diameter D means 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. Here, the secondary battery further includes a gasket 30, a negative electrode lead 52, a sealant 61, and insulating films 62 and 63.

[0022] [Outer can] 1 and 2, the exterior can 10 is a hollow exterior member that houses the battery element 40 etc. The exterior can 10 is made of a conductive material.

[0023] Here, the exterior can 10 has a flat, 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, M2 facing each other and a side wall M3 located between the bottoms M1, 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, since the exterior can 10 is substantially cylindrical, the planar shapes of the bottoms M1, M2 are each substantially circular, and the surface of the side wall M3 is a convex, curved surface.

[0024] The outer can 10 also includes a storage section 11 and a lid section 12 that are welded to each other. That is, the internal space of the outer 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 are integrated to form the storage section 11. Therefore, the outer edge of the lid section 12 is welded to the end of the side wall section M3 opposite the bottom section M2, i.e., the upper end section of the side wall section M3.

[0025] The storage section 11 is a flat, cylindrical storage member that stores the battery element 40 and the like inside. 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 the upper end as an insertion port through which the battery element 40 can be inserted in the height direction Z.

[0026] As shown in FIG. 2, the lid 12 is a substantially disk-shaped lid member that closes the opening 11K of the storage section 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 outer edge of the lid 12 is welded to the opening 11K of the storage section 11. The external terminal 20 is attached to the lid 12 via a gasket 30. In other words, the lid 12 supports the external terminal 20 via the gasket 30. The external terminal 20 is disposed between the through-hole 12K of the lid 12 and the through-hole 12K of the lid 12 in the height direction Z. The external terminal 20 is attached to the lid 12 via a gasket 30 at a position where it overlaps the outer can 10. The external terminal 20 is electrically insulated from the outer can 10.

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

[0028] However, if the lid 12 is welded to the storage section 11, weld marks remain on the surface of the outer can 10, more specifically, on the boundary between the storage section 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 section 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 in the height direction Z toward the interior 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 penetrating in the height direction Z, a bottom portion 12HB surrounding the through-hole 12K along a horizontal plane perpendicular to the height direction Z, and a wall portion 12HW erected along the outer edge of the bottom portion 12HB. The portion of the lid portion 12 other than the recessed portion 12H forms a peripheral portion 12R. The peripheral portion 12R has an annular shape that surrounds the recessed portion 12H in a horizontal plane perpendicular to the height direction Z of the secondary battery. The peripheral portion 12R surrounds the periphery of the recessed portion 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 than the surface 12RS of the peripheral portion 12R toward the inside of the storage portion 11. That is, 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.

[0031] The planar shape of the recessed portion 12H, i.e., the shape defined by the outer edge of the recessed portion 12H when the secondary battery is viewed from above, is not particularly limited. Here, the planar shape of the recessed portion 12H is approximately circular. The inner diameter and depth of the recessed portion 12H are not particularly limited and can be set arbitrarily. However, the depth of the recessed portion 12H is set so that when the external terminal 20 is attached to the recessed portion 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.

[0032] 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 from each other, 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.

[0033] The exterior can 10, which is a welded can, is different from a crimp can formed using a caulking process and is a so-called crimpless can. 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 can be used to store the battery element 40.

[0034] 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.

[0035] "Having no overlapping parts" means that the outer can 10 is not processed (folded) so that parts thereof are overlapping each other. Also, "having no overlapping parts of two or more components" 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.

[0036] 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. 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, and therefore 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.

[0037] 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 section 11 and the lid section 12 may be the same or different.

[0038] 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.

[0039] [External terminal] 1 and 2, the external terminals 20 are connection terminals that are connected to an electronic device when the secondary battery is mounted in the electronic device. As described above, the external terminals 20 are attached to and supported by the lid 12 of the outer can 10.

[0040] 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 also serves 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 as an external connection terminal for the positive electrode 41 and the outer casing 10 as an external connection terminal for the negative electrode 42. Therefore, the electronic device can operate using the secondary battery as a power source.

[0041] The external terminal 20 has a curved shape that is curved with respect to a horizontal plane perpendicular to the height direction Z of the secondary battery. Specifically, as shown in FIG. 2, the external terminal 20 has a convex surface that protrudes toward the battery element 40 and a curved surface CS that faces the battery element 40. The external terminal 20 is disposed inside the recessed portion 12H via the gasket 30. That is, the external terminal 20 is provided in a state where it is housed in the recessed portion 12H without protruding from the recessed portion 12H in the height direction Z. The curved surface CS is a convex surface that protrudes most and approaches the battery element 40 at the center position of the external terminal 20 in the radial direction r, and curves away from the battery element 40 as it moves from the center position of the external terminal 20 toward the outer edge 20T of the external terminal 20 in the radial direction r. The center position of the external terminal 20 coincides with the center line PC (described below) of the secondary battery.

[0042] The planar shape of the external terminal 20, i.e., the shape defined by the outer edge of the external terminal 20 when the secondary battery is viewed from above, is not particularly limited. In the secondary battery of this embodiment, the planar shape of the external terminal 20 is approximately circular.

[0043] The external terminal 20 includes one or more types of conductive materials such as metal materials and alloy materials. The external terminal 20 may be, for example, a laminate including two or more layers having different linear expansion coefficients. Specifically, as shown in FIG. 4, the external terminal 20 is a laminate including a first layer 21 made of Ni (nickel), a second layer 22 made of stainless steel such as SUS304, and a third layer 23 made of Al (aluminum). FIG. 4 is a cross-sectional view showing an example of the configuration of the external terminal 20. At room temperature (20°C), the linear expansion coefficient of nickel is 13.3×10 -6 / ℃], and the linear expansion coefficient of SUS304 is 17. 3[×10 -6 / ℃], and the linear expansion coefficient of aluminum is 23.9[×10 -6 / °C]. However, the external terminal 20 may be a single layer body.

[0044] The external terminal 20 is insulated from the lid 12 via a gasket 30. As shown in FIG. 2 , even the highest position of the surface 20S of the external terminal 20 in the height direction Z is lower toward the battery element 40 than the surface 12RS of the peripheral portion 12R of the outer can 10. In the secondary battery of this embodiment, the height of the secondary battery is smaller than when the external terminal 20 protrudes above the lid 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. The external terminal 20 has a central portion 20C and a peripheral portion 20R surrounding the central portion. The central portion 20C is a portion of the external terminal 20 that overlaps with the through-hole 12K of the lid 12. A positive electrode lead 51 is connected to the central portion 20C. The peripheral portion 20R overlaps with the bottom portion 12HB of the recessed portion 12H in the height direction Z. By providing an overlapping portion between the external terminal 20 and the lid portion 12, the mechanical strength of the secondary battery as a whole can be improved.

[0045] Since the outer diameter of the external terminal 20 is smaller than the inner diameter of the recess 12H, the external terminal 20 is spaced apart from the lid 12 on its periphery. As a result, the gasket 30 is disposed only in a part of the area between the external terminal 20 and the lid 12 (recess 12H), more specifically, 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, 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.

[0046] [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-like planar shape with a through hole at a position corresponding to the through hole 12K. The gasket 30 contains one or more types of insulating materials such as insulating polymer compounds, and the insulating materials are resins such as polypropylene and polyethylene.

[0047] 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 curved surface CS, which is the lower surface of the external terminal 20, inside the recess 12H. However, as described above, it is preferable that the gasket 30 is also provided 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.

[0048] The gasket 30 includes a thin portion 30A that is relatively thinner than other portions in the radial direction r along a horizontal plane perpendicular to the height direction Z. The thin portion 30A exists in a ring shape on the horizontal plane. That is, the gasket 30 is provided with the thin portion 30A isotropically centered on the horizontal center position of the secondary battery. In the secondary battery of this embodiment, the thin portion 30A is located near the edge 12T of the lid portion 12 that forms the through hole 12K. In the secondary battery of this embodiment, the thickness of the gasket 30 is thickest at a portion corresponding to the outer edge 20T of the external terminal 20 and gradually decreases toward the center line PC that passes through the horizontal center position of the secondary battery. This is because the bottom 12HB of the recessed portion 12H extends along the horizontal plane, while the curved surface CS of the external terminal 20 protrudes downward.

[0049] [Battery element] 2 and 3, the battery element 40 is a power generating element that causes charge / discharge reactions to proceed, and is housed inside the outer can 10. The battery element 40 includes a positive electrode 41 as a first electrode and a negative electrode 42 as a second electrode. Here, the battery element 40 further includes a separator 43 and an electrolytic solution that is a liquid electrolyte.

[0050] 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, position P of the center line PC corresponds to the position of the center of the battery element 40.

[0051] The battery element 40 is a so-called wound electrode body. That is, in the battery element 40, a positive electrode 41 and a negative electrode 42 are stacked one on top of the other with a separator 43 interposed therebetween. Furthermore, the stacked positive electrode 41, negative electrode 42, and separator 43 are wound around a center line PC, which is the winding axis. The positive electrode 41 and negative electrode 42 are wound while maintaining a state in which they face each other with the separator 43 interposed therebetween. Therefore, a winding center space 40K is formed as an internal space at the center of the battery element 40.

[0052] Here, the positive electrode 41, the negative electrode 42, and the separator 43 are wound so that the separator 43 is disposed on both 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.

[0053] The battery element 40 has a three-dimensional shape that matches the three-dimensional shape of the outer can 10. Specifically, the battery element 40 has a flat, cylindrical three-dimensional shape. Compared to a case where the battery element 40 has a three-dimensional shape that differs from the three-dimensional shape 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. This allows the internal space of the outer can 10 to be used effectively. As a result, the element space volume increases, and the energy density per unit volume of the secondary battery increases.

[0054] (positive electrode) The positive electrode 41 is a first electrode used to promote charge / discharge reactions, and as shown in FIG. 3, includes a positive electrode current collector 41A and a positive electrode active material layer 41B.

[0055] Positive electrode current collector 41A has a pair of surfaces on which positive electrode active material layers 41B are provided. Positive electrode current collector 41A contains a conductive material such as a metal material, and the metal material is aluminum or the like.

[0056] The positive electrode active material layer 41B is provided on both sides of the positive electrode current collector 41A and contains one or more types of positive electrode active materials capable of absorbing and releasing lithium. However, the positive electrode active material layer 41B may be provided on only one side of the positive electrode current collector 41A. 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.

[0057] 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 LiMn2O4, and specific examples of phosphate compounds include LiFePO4 and LiMnPO4.

[0058] The positive electrode binder contains one or more of synthetic rubber and polymer compounds. The synthetic rubber is styrene-butadiene rubber, and the polymer 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 polymer compound.

[0059] (Negative electrode) The negative electrode 42 is a second electrode used to promote charge / discharge reactions, and as shown in FIG. 3, includes a negative electrode current collector 42A and a negative electrode active material layer 42B.

[0060] The negative electrode current collector 42A has a pair of surfaces on which the negative electrode active material layer 42B is provided. The negative electrode current collector 42A contains a conductive material such as a metal material, and the metal material is copper or the like.

[0061] The negative electrode active material layer 42B is provided on both sides of the negative electrode current collector 42A and contains one or more types of negative electrode active materials capable of absorbing and releasing lithium. However, the negative electrode active material layer 42B may be provided on only one side of the negative electrode current collector 42A. The negative electrode active material layer 42B may further contain a negative electrode binder, a negative electrode conductor, and the like. Details regarding the negative electrode binder and the negative electrode conductor are the same as those regarding the positive electrode binder and the positive electrode conductor, respectively. The method for forming the negative electrode active material layer 42B is not particularly limited, but specifically includes one or more types of coating method, vapor phase method, liquid phase method, thermal spraying method, and firing method (sintering method).

[0062] 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). Metal-based materials are materials containing one or more metal elements and metalloid elements that can form an alloy with lithium as constituent elements, and the metal elements and metalloid elements are one or both of silicon and tin. 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 are TiSi2 and SiO x (0 <x≦2、または0.2<x<1.4)などである。

[0063] Here, the height of the negative electrode 42 is greater than the height of the positive electrode 41. That is, the negative electrode 42 protrudes upward from the positive electrode 41 and also protrudes downward from the positive electrode 41. This is to prevent lithium released from the positive electrode 41 from being deposited. This "height" is a dimension corresponding to the height H of the secondary battery described above, that is, the dimension in the vertical direction in each of FIGS. 1 and 2. The definition of height described here will also be applied hereinafter.

[0064] (separator) 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.

[0065] Here, the height of the separator 43 is greater than the height of the negative electrode 42. That is, the separator 43 preferably protrudes upward from the negative electrode 42 and also protrudes downward from the negative electrode 42. This is because the separator 43 is used to insulate the positive electrode lead 51 from the negative electrode 42.

[0066] (electrolyte) The electrolyte solution 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 solution 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.

[0067] [Positive lead] As shown in Fig. 2, the positive electrode lead 51 is housed inside the outer 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 has one positive electrode lead 51. However, the secondary battery may have two or more positive electrode leads 51.

[0068] The positive electrode lead 51 is connected to the upper end of the positive electrode 41. Specifically, the positive electrode lead 51 is connected to the upper end of the positive electrode current collector 41A. The positive electrode lead 51 is also connected to the lower surface of the external terminal 20 via a through hole 12K provided in the lid 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.

[0069] 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.

[0070] The first portion 511 and the second portion 512 are sandwiched between the battery element 40 and the protruding portion 12P of the lid portion 12 in the height direction Z of the secondary battery.

[0071] 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.

[0072] That is, a portion of the positive electrode lead 51 being 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, and therefore 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 suppressed.

[0073] The positive electrode lead 51 may be in a state of being pressed into the battery element 40 due to being pressed by the battery element 40. More specifically, since the height of the separator 43 is greater than the heights of the positive electrode 41 and the negative electrode 42, as described above, the positive electrode lead 51 may be in a state of being pressed into the upper end portion of the separator 43. In this case, a depression is formed in the upper end portion of the separator 43 due to the pressing of the positive electrode lead 51. Part or all of the positive electrode lead 51 is accommodated inside the depression, and the positive electrode lead 51 is held by the separator 43. Since the positive electrode lead 51 is less likely to move inside the outer can 10, the positive electrode lead 51 is less likely to be damaged.

[0074] Here, as described above, the lid portion 12 includes the protruding portion 12P, and a portion of the positive electrode lead 51 is sandwiched between the protruding portion 12P and the battery element 40. That is, a portion of the positive electrode lead 51 extends along the lower surface of the protruding portion 12P and the upper surface of the battery element 40, and is thereby held by the protruding portion 12P and the battery element 40. Since the positive electrode lead 51 is more easily held by utilizing the protruding portion 12P, the positive electrode lead 51 is less likely to be damaged.

[0075] 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 film 62, respectively.

[0076] 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.

[0077] 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.

[0078] Furthermore, 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.

[0079] Furthermore, an insulating film may also be disposed between the battery element 40 and the positive electrode lead 51 .

[0080] 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 41A. However, the materials for forming the positive electrode lead 51 and the positive electrode current collector 41A may be the same as or different from each other.

[0081] Here, the positive electrode lead 51 is connected to the positive electrode 41 in a region in front of the center line PC, i.e., a region to the right of the center line PC in FIG. 2 . The positive electrode lead 51 has a folded portion 513 on the way to the external terminal 20 in order to be connected to the external terminal 20. The folded portion 513 is located in a region behind the center line PC, i.e., a region to the left of the center line PC in FIG. 2 . The positive electrode lead 51 has a first portion 511 as a portion from the point where it is connected to the positive electrode 41, passing through the center position P, to the folded portion 513. The first portion 511 extends along the upper surface of the battery element 40 in a direction perpendicular to the height direction Z. Furthermore, the positive electrode lead 51 has a second portion 512 as a portion from the folded portion 513 to the point where it is connected to the external terminal 20. The second portion 512 extends along the upper surface of the battery element 40 in a direction perpendicular to the height direction Z so as to cover the first portion 511. In this way, a portion of the positive electrode lead 51 extends toward the external terminal 20 while being sandwiched between the lid portion 12 and the battery element 40 in both the region in front of the center line PC and the region behind the center line PC.

[0082] Here, as is clear from FIG. 2, when the battery element 40 is divided into two regions based on the center line PC in the direction along the outer diameter D, the "region in front of the center line PC" refers to one of the regions where the connection point of the positive electrode lead 51 to the positive electrode 41 is present. In FIG. 2, the "region in front of the center line PC" refers to the region to the right of the center line PC. In contrast, as is clear from FIG. 2, the "region behind the center line PC" refers to the other of the two regions, which is the region to the left of the center line PC in FIG. 2. In other words, when the battery element 40 is divided into two regions based on the center line PC in the direction along the outer diameter D, the "region behind the center line PC" refers to the other region where the connection point of the positive electrode lead 51 to the positive electrode 41 is not present.

[0083] 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, it is preferable that the positive electrode lead 51 be connected to the positive electrode 41 at a position closer to the inner periphery 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.

[0084] Here, the positive electrode lead 51 is folded back one or more times between the positive electrode 41 and the external terminal 20, and is therefore folded back one or more times. The number of times the positive electrode lead 51 is folded back is not particularly limited as long as it is folded back one or more times. The phrase "the positive electrode lead 51 is folded back" means that the extension direction of the positive electrode lead 51 changes midway so as to form an angle greater than 90°. The folded back portion of the positive electrode lead 51 may have a curved shape, like the folded back portion 513, without being bent. Although FIG. 2 illustrates an example in which the positive electrode lead 51 includes one folded back portion 513, the positive electrode lead 51 may include multiple folded back portions 513.

[0085] The positive electrode lead 51 is folded back at a folding back portion 513 midway from the positive electrode 41 to the external terminal 20. Specifically, as shown in FIG. 2 , the first portion 511 extends, in a horizontal plane perpendicular to the height direction of the secondary battery, from a first position P1 other than the center position P of the outer casing 10 to a second position P2 on the opposite side of the first position P1 as seen from the center position. The second portion 512 extends from the second position P2 toward the center position P. In the positive electrode lead 51, the overlapping portion of the first portion 511 and the second portion 512 is a surplus portion. In other words, it can be said that the positive electrode lead 51 has a length margin in its longitudinal direction.

[0086] This provides room for changing the orientation of the lid portion 12 relative to the housing portion 11 when forming the outer can 10 using the housing portion 11 and the lid portion 12 in the manufacturing process of the secondary battery, as will be described later. Also, when the secondary battery is subjected to external forces such as vibration and impact, the external forces are alleviated by utilizing the length margin of the positive electrode lead 51, making the positive electrode lead 51 less likely to be damaged. Furthermore, by utilizing the length margin of the positive electrode lead 51, the connection position of the positive electrode lead 51 relative to the positive electrode 41 can be changed as desired without changing the length of the positive electrode lead 51.

[0087] In this case, the length of the positive electrode lead 51 (total length including a length margin) is not particularly limited and can be set arbitrarily. In particular, the length of the positive electrode lead 51 is preferably equal to or greater than half the outer diameter D of the outer can 10. This is because the length of the positive electrode lead 51 ensures a length margin for standing the lid part 12 upright relative to the storage part 11, making it easier to stand the lid part 12 upright relative to the storage part 11.

[0088] The connection range of the positive electrode lead 51 to the external terminal 20 is not particularly limited. In particular, the connection range of the positive electrode lead 51 to the external terminal 20 is preferably sufficiently wide so that the positive electrode lead 51 is unlikely to fall off the external terminal 20, and is also preferably sufficiently narrow so that a length margin for the positive electrode lead 51 is obtained. The reason why the connection range of the positive electrode lead 51 to the external terminal 20 is preferably sufficiently narrow is that the portion of the positive electrode lead 51 that is not connected to the external terminal 20 becomes the length margin, and therefore the length margin for the positive electrode lead 51 becomes sufficiently large.

[0089] 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.

[0090] [Negative lead] As shown in Fig. 2, the negative electrode lead 52 is housed inside the outer can 10. The negative electrode lead 52 is connected to both the negative electrode 42 and the outer can 10 (housing portion 11). Here, the secondary battery includes one negative electrode lead 52. However, the secondary battery may include two or more negative electrode leads 52.

[0091] The negative electrode lead 52 is connected to the lower end of the negative electrode 42, more specifically, to the lower end of the negative electrode current collector 42A. The negative electrode lead 52 is also connected to the bottom surface of the storage section 11. Details of the connection method of the negative electrode lead 52 are the same as the details of the connection method of the positive electrode lead 51.

[0092] 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 materials for forming the negative electrode lead 52 and the negative electrode current collector 42A may be the same as or different from each other.

[0093] 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.

[0094] 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.

[0095] [Sealant] 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 tubular structure.

[0096] The sealant 61 contains one or more kinds of insulating materials such as insulating polymer compounds, and the insulating material is polyimide or the like.

[0097] [Insulating film] 2, the insulating film 62 is disposed between the lid portion 12 and the positive electrode lead 51 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.

[0098] The insulating film 62 may have an adhesive layer (not shown) on one surface and be adhered to either the lid portion 12 or the positive electrode lead 51 via the adhesive layer. Alternatively, the insulating film 62 may have adhesive layers on both surfaces and be adhered to both the lid portion 12 and the positive electrode lead 51 via the adhesive layers.

[0099] Furthermore, 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.

[0100] 2, the insulating film 63 is a third 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.

[0101] 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.

[0102] [others] The secondary battery may further include one or more other components.

[0103] Specifically, the secondary battery is equipped with 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 or exceeds a certain level. Causes of the internal pressure of the outer can 10 reaching or exceeding a certain level include the occurrence of a short circuit inside the secondary battery and the secondary battery being heated from the outside. There are no particular restrictions on the location where the safety valve mechanism is installed, but it is preferable that the safety valve mechanism be installed on either the bottom portion M1 or M2, and more preferably on the bottom portion M2 to which the external terminal 20 is not attached.

[0104] The secondary battery may also include an insulator between the exterior can 10 and the battery element 40. This insulator includes one or more types of insulating film, 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 arbitrarily.

[0105] 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 more preferred.

[0106] <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 cycles, lithium is absorbed and released in an ionic state.

[0107] <1-3. Manufacturing method> FIG. 5 shows a perspective view of an exterior can 10 used in the manufacturing process of a secondary battery, and corresponds to FIG.

[0108] FIG. 5 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.

[0109] In the following description, reference will be made to FIG. 5 as well as to FIGS. 1 to 4, which have already been described.

[0110] 5, 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 container-shaped member in which a bottom portion M2 and a side wall portion M3 are integrated with each other, and has an opening portion 11K. The lid portion 12 is a roughly plate-shaped member corresponding to the bottom portion M1, and an external terminal 20 is attached in advance to a recessed portion 12H provided in the lid portion 12 via a gasket 30.

[0111] 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.

[0112] [Preparation 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 a positive electrode current collector 41A to form a 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 prepared.

[0113] [Preparation of negative electrode] The negative electrode 42 is fabricated using the same procedure as that for fabricating the positive electrode 41. Specifically, after preparing the negative electrode current collector 42A, a negative electrode mixture, which is a mixture of a negative electrode active material, a negative electrode binder, a negative electrode conductive agent, etc., is poured into an organic solvent to prepare a paste-like negative electrode mixture slurry. The negative electrode current collector 42A has both widthwise ends slightly bent in the same direction to form an upper end 42U and a lower end 42L. Next, the negative electrode mixture slurry is applied to both sides of the negative electrode current collector 42A. This forms the negative electrode active material layer 42B. Thereafter, the negative electrode active material layer 42B is compression molded using a roll press or the like. In this way, the negative electrode 42 is produced.

[0114] [Preparation of electrolyte] An electrolyte salt is added to a solvent, whereby the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing an electrolytic solution.

[0115] [Secondary battery assembly] First, using a welding method such as resistance welding, the positive electrode lead 51, which is covered with a 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).

[0116] Next, the positive electrode 41 and the negative electrode 42 are stacked with a 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. 4. 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. 4.

[0117] 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.

[0118] Next, after preparing a lid 12 to which the external terminal 20 is attached via the gasket 30 and on which the insulating film 62 is provided in advance, 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. When a laminate including two or more layers having different linear expansion coefficients is used as the external terminal 20, a curved shape such as that shown in FIG. 4 can be easily formed when connecting the positive electrode lead 51 to the external terminal 20 by welding. This is because the layers exhibit different expansion coefficients due to heat applied to the external terminal 20 during welding.

[0119] 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.

[0120] Next, the electrolyte solution is poured into the storage section 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 section 12 does not close the opening 11K, so the electrolyte solution can be easily poured into the storage section 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.

[0121] 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 point 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.

[0122] [Secondary battery stabilization] 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.

[0123] <1-4. Actions and Effects> As described above, in the secondary battery of this embodiment, the external terminal 20 has a curved shape including a curved surface CS, which is a convex surface facing the battery element 40. By having the external terminal 20 have such a curved shape, the external terminal 20 can seal the battery element 40 inside the outer can 10 during normal use, while quickly separating from the lid portion 12 (i.e., opening the valve) when the pressure inside the secondary battery increases, thereby reducing the internal pressure. This is because the curved shape of the external terminal 20 allows the pressure inside the battery to be applied more evenly to the external terminal 20. Therefore, it is possible to reduce variations in the pressure value inside the battery when the external terminal 20 opens. In other words, the external terminal 20 opens more reliably when a substantially constant pressure value is reached. Therefore, high safety can be achieved.

[0124] Furthermore, in the secondary battery of this embodiment, if the external terminal 20 is a laminate including two or more layers having different linear expansion coefficients, the desired curved shape can be easily formed when connecting the positive electrode lead 51 to the external terminal 20 by a welding method.

[0125] Furthermore, in the secondary battery of this embodiment, the external terminal 20 is accommodated in the recess 12H without protruding from the recess 12H in the height direction Z, which allows the height of the secondary battery to be reduced compared to when the external terminal 20 protrudes above the lid 12. This increases the energy density per unit volume of the secondary battery. Furthermore, it is possible to prevent a short circuit between the outer can 10 and the external terminal 20 via another conductive member.

[0126] Furthermore, in the secondary battery of this embodiment, the gasket 30 includes a thin portion 30A that is relatively thinner than other portions in the radial direction r along a horizontal plane perpendicular to the height direction Z. This makes it easier for the external terminal 20 to stably open, starting from the thin portion 30A, when the pressure inside the battery increases. In particular, if the thin portion 30A is arranged in a circular ring shape centered on the center line PC in the horizontal plane, the valve can be opened with better reproducibility when the pressure inside the battery reaches a predetermined pressure value.

[0127] Furthermore, in the secondary battery of this embodiment, the recessed portion 12H includes a through-hole 12K penetrating in the height direction Z and a bottom portion 12HB surrounding the through-hole 12K along a horizontal plane perpendicular to the height direction Z, and a portion of the external terminal 20 overlaps with the bottom portion 12HB of the recessed portion 12H in the height direction Z. In this way, the secondary battery of this embodiment has an overlapping portion between the external terminal 20 and the lid portion 12, thereby improving the mechanical strength of the secondary battery as a whole. In particular, when the length of the overlapping portion between the external terminal 20 and the bottom portion 12HB along the horizontal plane perpendicular to the height direction Z is greater than the thickness of the external terminal 20 and the thickness of the bottom portion 12HB, the mechanical strength is further improved.

[0128] Furthermore, in the secondary battery of this embodiment, a gasket 30 made of insulating resin is also provided between the inner wall surface of the recessed portion 12H and the outer edge 20T of the external terminal 20. This prevents foreign matter from entering the gap between the inner wall surface of the recessed portion 12H and the outer edge 20T of the external terminal 20, and makes it possible to sufficiently avoid a short circuit between the lid portion 12 and the external terminal 20.

[0129] In the secondary battery of this embodiment, the lid portion 12 and the external terminal 20 are fixed together by the gasket 30 made of insulating resin. This increases the mechanical strength against vibration. This can prevent short circuits caused by foreign matter entering the gap between the recessed portion 12H and the external terminal 20.

[0130] Furthermore, in the secondary battery of this embodiment, the folded portion 513 is located at the peripheral portion 12R of the lid portion 12, and the first portion 511 and the second portion 512 extend radially from the center of the secondary battery toward the peripheral portion 12R. Specifically, the first portion 511 extends, in a horizontal plane perpendicular to the height direction Z of the secondary battery, from a first position P1 other than the center position P of the outer can 10 to a second position P2 on the opposite side of the first position P1 as viewed from the center position P. The second portion 512 extends from the second position P2 toward the center position. Furthermore, the overlapping portion of the first portion 511 and the second portion 512 is sandwiched between the protruding portion 12P and the battery element 40. This allows for a larger contact area between the first portion 511 and the battery element 40 via the sealant 61, and a larger contact area between the second portion 512 and the recessed portion 12H directly or via the sealant 61. This sufficiently limits the movement of the positive electrode lead 51 and the battery element 40 inside the exterior can 10. Therefore, even if the secondary battery is subjected to impact or vibration, problems such as damage to the positive electrode lead 51 or collapse of the battery element 40 are unlikely to occur. Therefore, the secondary battery of this embodiment can achieve excellent physical durability.

[0131] In particular, the secondary battery of this embodiment provides the above-mentioned functions and effects for the reasons explained below.

[0132] The secondary battery of this embodiment, which is called a coin type or a button type, i.e., a secondary battery having a flat and columnar three-dimensional shape, is provided with a small external terminal 20 that functions as an external connection terminal for the positive electrode 41, as is clear from FIGS. 1 and 2 . In this case, since the size of the external terminal 20 is small, the connection area of ​​the positive electrode lead 51 to the external terminal 20 is small. Therefore, in order to maintain the electrical connection between the external terminal 20 and the positive electrode lead 51, it is necessary to sufficiently fix the positive electrode lead 51 inside the outer can 10.

[0133] In this regard, in the secondary battery of this embodiment, movement of the positive electrode lead 51 inside the outer can 10 is sufficiently suppressed, so even if the connection area of ​​the positive electrode lead 51 to the external terminal 20 is small, the possibility of the positive electrode lead 51 becoming detached from the external terminal 20 or breaking is extremely low. Therefore, with the secondary battery of this embodiment, even when subjected to external forces such as vibrations or impacts, the electrical connection state between the external terminal 20 and the positive electrode lead 51 can be maintained favorably. Therefore, with the secondary battery of this embodiment, high physical durability can be achieved even when it is miniaturized.

[0134] In addition, in the secondary battery of this embodiment, which includes a small external terminal 20 that is an external connection terminal for the positive electrode 41, as is clear from FIG. 2 , the lid 12 of the outer can 10 that functions as an external connection terminal for the negative electrode 42 is disposed close to the external terminal 20. That is, the lid 12 and the external terminal 20, which are two external connection terminals having different polarities, are close to each other. Therefore, in order to prevent a short circuit between the lid 12 and the external terminal 20, it is desirable to make the connection area of ​​the positive electrode lead 51 with respect to the external terminal 20 sufficiently small and to place the positive electrode lead 51 sufficiently far from the lid 12.

[0135] In this regard, in the secondary battery of this embodiment, movement of the positive electrode lead 51 inside the outer can 10 is sufficiently suppressed, so even if the connection area of ​​the positive electrode lead 51 to the external terminal 20 is small, the possibility of the positive electrode lead 51 becoming detached from the external terminal 20 or breaking is extremely low. Therefore, with the secondary battery of this embodiment, even when subjected to external forces such as vibrations or impacts, it is possible to maintain a good electrical connection between the external terminal 20 and the positive electrode lead 51. Therefore, with the secondary battery of this embodiment, even when miniaturized, it is possible to prevent short-circuiting between the lid portion 12 and the external terminal 20 and achieve high physical durability.

[0136] Furthermore, if the height of the insulating separator 43 is greater than the height of the negative electrode 42 and a portion of the positive electrode lead 51 is insulated from the negative electrode 42 via the separator 43, a short circuit between the positive electrode lead 51 and the negative electrode 42 is prevented, thereby achieving higher reliability.

[0137] In this case, if the positive electrode 41 and the negative electrode 42 are wound facing each other with the separator 43 interposed therebetween and the positive electrode lead 51 is connected to the positive electrode 41 on the inner side of the outermost periphery of the positive electrode 41, corrosion of the outer can 10 due to creeping up of the electrolyte can be prevented, thereby achieving even higher reliability.

[0138] Furthermore, if the sealant 61 covers the periphery of the positive electrode lead 51 and a portion of the positive electrode lead 51 is insulated from the outer can 10 and the negative electrode 42 via the sealant 61, a short circuit between the positive electrode lead 51 and the outer can 10 is prevented, and a short circuit between the positive electrode lead 51 and the negative electrode 42 is also prevented, thereby achieving higher reliability.

[0139] In this case, particularly when the periphery of the positive electrode lead 51 is covered with the sealant 61, the following advantageous effects can be obtained. That is, when the positive electrode lead 51 is sandwiched between the outer can 10 and the battery element 40 via the sealant 61, a gripping force is generated between the outer can 10 and the sealant 61, and a gripping force is also generated between the battery element 40 and the sealant 61. As a result, the gripping force supplied to the positive electrode lead 51 via the sealant 61 is utilized to make it easier for the positive electrode lead 51 to be held by the outer can 10 and the battery element 40. Therefore, the positive electrode lead 51 is insulated from the outer can 10 and the negative electrode 42 via the sealant 61. Furthermore, the sealant 61 makes it easier for the positive electrode lead 51 to be fixed inside the outer can 10, thereby achieving even higher physical durability.

[0140] Furthermore, if the insulating film 62 is disposed between the outer can 10 and the positive electrode lead 51 and a portion of the positive electrode lead 51 is insulated from the outer can 10 via the insulating film 62, a short circuit between the positive electrode lead 51 and the outer can 10 is prevented, thereby achieving higher reliability.

[0141] Furthermore, if the insulating film 63 is disposed between the battery element 40 and the positive electrode lead 51 and a portion of the positive electrode lead 51 is insulated from the negative electrode 42 via the insulating film 63, a short circuit between the positive electrode lead 51 and the negative electrode 42 is prevented, thereby achieving higher reliability.

[0142] Furthermore, since the outer can 10 includes the storage section 11 and the lid section 12 that are welded together, and the positive electrode lead 51 is folded back one or more times, a length margin for the positive electrode lead 51 is obtained. Therefore, during the manufacturing process of the secondary battery, particularly during the process of forming the outer can 10, it becomes possible to stand the lid section 12 upright relative to the storage section 11. This not only makes it easier to inject the electrolyte, but also makes it possible to arbitrarily change the connection position of the positive electrode lead 51 relative to the positive electrode 41, thereby achieving greater ease of manufacturing.

[0143] Furthermore, if the secondary battery is flat and columnar, that is, if the secondary battery is a type called a coin-type or button-type secondary battery, the positive electrode lead 51 is less likely to be damaged even in small secondary batteries that are subject to significant size restrictions, and therefore greater effectiveness can be achieved in terms of physical durability.

[0144] 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.

[0145] <2. Modifications> The configuration of the secondary battery described above can be modified as appropriate, as described below, although any two or more of the series of modifications described below may be combined with each other.

[0146] [Variation 1] Fig. 6 shows a cross-sectional configuration of a secondary battery as Modification 1 of the above embodiment. In the secondary battery of Fig. 2, the curved surface CS of the external terminal 20 that faces the battery element 40 is convex. However, in the secondary battery of the present disclosure, the curved surface CS of the external terminal 20 that faces the battery element 40 may be concave, as shown in Fig. 6. In this case, the same effects as those of the secondary battery of the above embodiment can be obtained.

[0147] In the first modification, as shown in Fig. 6, the height of the secondary battery can be reduced by accommodating the external terminal 20 in the recess 12H without protruding from the recess 12H in the height direction Z. In this case, the energy density per unit volume of the secondary battery increases. Also, it is possible to prevent a short circuit between the outer can 10 and the external terminal 20 via another conductive member.

[0148] [Variation 2] FIG. 7 shows a cross-sectional configuration of a secondary battery according to a second modification of the embodiment. In the secondary battery of FIG. 2, the bottom portion 12HB, which serves as an overlapping portion that overlaps the peripheral portion 20R of the external terminal 20 via the gasket 30, extends along a horizontal plane. In contrast, in the secondary battery of the second modification, the bottom portion 12HB is inclined relative to the horizontal plane to conform to the curved shape of the external terminal 20. Therefore, in the secondary battery of the second modification, the distance in the height direction Z between the external terminal 20 and the bottom portion 12HB is substantially constant. As a result, the thickness of the gasket 30 is also maintained substantially constant from the outer edge 20T of the external terminal 20 toward the center line PC. Except for the above points, the configuration of the secondary battery of the second modification is substantially the same as the configuration of the secondary battery shown in FIG. 2.

[0149] In the secondary battery of Modification 2, the external terminal 20 also has a curved shape including a curved surface CS that is a convex surface facing the battery element 40, so that the pressure inside the battery is applied more evenly to the external terminal 20. This reduces the variation in the pressure value inside the battery when the external terminal 20 opens. In other words, the external terminal 20 opens more reliably when a substantially constant pressure value is reached. This provides high safety.

[0150] [Variation 3] FIG. 8 shows a cross-sectional configuration of a secondary battery according to Modification 3 of the above-described embodiment. In the secondary battery according to Modification 1 of FIG. 6, the bottom portion 12HB, which serves as an overlapping portion that overlaps the peripheral portion 20R of the external terminal 20 via the gasket 30, extends along a horizontal plane. In contrast, in the secondary battery according to Modification 3, the bottom portion 12HB is inclined relative to the horizontal plane to conform to the curved shape of the external terminal 20. Therefore, in the secondary battery according to Modification 3, the distance in the height direction Z between the external terminal 20 and the bottom portion 12HB is substantially constant. As a result, the thickness of the gasket 30 is also maintained substantially constant from the outer edge 20T of the external terminal 20 toward the center line PC. Except for the above points, the configuration of the secondary battery according to Modification 3 is substantially the same as the configuration of the secondary battery according to Modification 1 shown in FIG. 6.

[0151] In the secondary battery of Modification 3, the external terminal 20 also has a curved shape including a curved surface CS that is a concave surface facing the battery element 40, so that the pressure inside the battery is applied more evenly to the external terminal 20. This reduces the variation in the pressure value inside the battery when the external terminal 20 opens. In other words, the external terminal 20 opens more reliably when a substantially constant pressure value is reached. This provides high safety. [Example]

[0152] An embodiment of the present technology will be described.

[0153] Several secondary batteries according to the present disclosure described in the above embodiments and modifications were fabricated, and the battery characteristics of these secondary batteries were evaluated. Additionally, several secondary batteries were fabricated as comparative examples, and the battery characteristics of these secondary batteries were evaluated.

[0154] [Secondary battery production] Example 1 First, as Example 1, the secondary battery shown in FIG. 2 was fabricated in the following manner.

[0155] (Preparation of positive electrode) First, 91 parts by mass of a positive electrode active material (LiCoO), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 6 parts by mass of a positive electrode conductive agent (graphite) were mixed to prepare a positive electrode mixture. The positive electrode mixture was then added to an organic solvent (N-methyl-2-pyrrolidone), and the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. The positive electrode mixture slurry was then applied to both sides of a positive electrode current collector 41A (a strip-shaped aluminum foil with 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 the production of a positive electrode 41 (width = 3.3 mm).

[0156] (Preparation of negative electrode) First, 95 parts by mass of a negative electrode active material (graphite) and 5 parts by mass of a negative electrode binder (polyvinylidene fluoride) were mixed to prepare a negative electrode mixture. The negative electrode mixture was then added to an organic solvent (N-methyl-2-pyrrolidone), and the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. The positive electrode mixture slurry was then applied to both sides of a negative electrode current collector 42A (a strip-shaped copper foil having a thickness of 15 μm) 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 produced a negative electrode 42 (width = 3.8 mm).

[0157] (Preparation of Electrolyte) After adding the electrolyte salt (LiPF6) to the 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 electrolytic solution was prepared.

[0158] (Secondary battery assembly) 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. In this case, the welding position of the positive electrode lead 51 was adjusted so that the welding position of the positive electrode lead 51 was midway through the winding of the positive electrode 41.

[0159] Next, the positive electrode 41 and the negative electrode 42 were stacked together 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 = 2.0 mm).

[0160] Subsequently, a ring-shaped insulating film (polyimide film, outer diameter = 11.6 mm, inner diameter = 2.2 mm, thickness = 0.05 mm) for use as an underlay was placed inside a cylindrical storage section 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 section 11. In this case, the negative electrode lead 52 was welded to the storage section 11 by resistance welding.

[0161] Next, a disk-shaped external terminal 20 (thickness = 0.3 mm, outer diameter = 7.2 mm) made of aluminum was prepared. The external terminal 20 had a recessed portion 12H (inner diameter = 9.0 mm, step height = 0.3 mm) with a through hole 12K (inner diameter = 3.0 mm). The external terminal 20 was deformed by applying pressure to adjust the curvature to +0.01 mm. A disk-shaped lid portion 12 (thickness = 0.15 mm, outer diameter = 11.7 mm) made of stainless steel (SUS316) was also prepared. An insulating resin was applied to the surface 12HS of the bottom portion 10HB of the lid portion 12, and then the external terminal 20 was placed on the insulating resin. Polyimide was used as the insulating resin. Next, the insulating resin was heated and melted, while the external terminal 20 was pressed downward with pressure, and the insulating resin was then cooled. As a result, the external terminals 20 were welded to the lid portion 12 by the gasket 30 made of cooled insulating resin.

[0162] Next, using a resistance welding method, the positive electrode lead 51 was welded to the central portion 20C of the external terminal 20 attached to the lid portion 12 via the gasket 30. The amount of curvature of the external terminal 20 here refers to the protrusion height 20H, which is the difference between a position CS1 on the curved surface CS that is closest to the battery element 40 in the height direction Z and a position CS2 that is farthest from the battery element 40 in the height direction Z, as schematically shown in FIG. 9 . A positive amount of curvature of the external terminal 20 means that the central portion 20C of the external terminal 20 protrudes more toward the battery element 40 than the peripheral portion 20R. In other words, this means that the curved surface CS is convex toward the battery element 40.

[0163] 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 (positive electrode 41, negative electrode 42, and separator 43) was impregnated with the electrolyte, and the battery element 40 was produced.

[0164] Finally, the opening 11K was closed with 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 form a curved shape. In addition, a ring-shaped insulating film 62 (polyimide film, outer diameter = 9.2 mm, inner diameter = 3.2 mm) was placed 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 placed between the battery element 40 and the positive electrode lead 51. As a result, the storage section 11 and the lid 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).

[0165] (Stabilization of secondary batteries) The assembled secondary battery was subjected to one charge / discharge cycle 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 at that voltage of 4.2 V, it was charged at a constant voltage of 0.05 C. 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 that fully discharges the battery capacity (theoretical capacity) in 10 hours, and 0.05 C is the current value that fully discharges the battery capacity in 20 hours.

[0166] As a result, a coating was formed on the surface of the negative electrode 42 etc., and the state of the secondary battery was electrochemically stabilized. Thus, the secondary battery of Example 1 was completed.

[0167] <Example 2> Next, a secondary battery was fabricated as Example 2. Here, the amount of curvature of the external terminal 20 was set to +0.02 mm. Except for this, the fabrication conditions for the secondary battery of Example 2 were the same as those for the secondary battery of Example 1.

[0168] Example 3 Next, a secondary battery was fabricated as Example 3. Here, the amount of curvature of the external terminal 20 was set to +0.03 mm. Except for this, the fabrication conditions for the secondary battery of Example 3 were the same as those for the secondary battery of Example 1.

[0169] Example 4 Next, as Example 4, the secondary battery shown in FIG. 7 was fabricated. Here, as shown in FIG. 7, the bottom 12HB was inclined with respect to the horizontal plane in accordance with the curved shape of the external terminal 20. In addition, the amount of curvature of the external terminal 20 was set to +0.03 mm. Except for these points, the fabrication conditions for the secondary battery of Example 4 were the same as those for the secondary battery of Example 1.

[0170] <Example 5> Next, as Example 5, a secondary battery shown in FIG. 6 was fabricated. Here, as shown in FIG. 6, the external terminal 20 was curved so that the curved surface CS facing the battery element 40 was concave. In addition, the amount of curvature of the external terminal 20 was set to −0.01 mm. Except for these points, the fabrication conditions for the secondary battery of Example 4 were the same as those for the secondary battery of Example 1.

[0171] Example 6 Next, a secondary battery was fabricated as Example 6. Here, the amount of curvature of the external terminal 20 was set to −0.02 mm. Except for this, the fabrication conditions for the secondary battery of Example 6 were the same as those for the secondary battery of Example 5.

[0172] Example 7 Next, a secondary battery was fabricated as Example 7. Here, the amount of curvature of the external terminal 20 was set to −0.03 mm. Except for this, the fabrication conditions for the secondary battery of Example 7 were the same as those for the secondary battery of Example 5.

[0173] Example 8 Next, as Example 8, a secondary battery shown in FIG. 8 was fabricated. Here, as shown in FIG. 8, the bottom 12HB was inclined with respect to the horizontal plane in accordance with the curved shape of the external terminal 20. In addition, the amount of curvature of the external terminal 20 was set to −0.03 mm. Except for these points, the fabrication conditions for the secondary battery of Example 8 were the same as those for the secondary battery of Example 5.

[0174] <Comparative Example 1> Next, a secondary battery having external terminals with a flat shape along a horizontal plane (not curved shape) was fabricated as Comparative Example 1. Except for the use of flat external terminals, the fabrication conditions for the secondary battery of Comparative Example 1 were the same as those for the secondary battery of Example 1.

[0175] [Evaluation of battery characteristics] Each secondary battery of Examples 1 to 8 and Comparative Example 1 was subjected to a seal tear strength test at room temperature and a heating test in accordance with UL1642 testing, and performance evaluations were performed. The results are shown in Table 1. The number of samples for each Example and Comparative Example was 10.

[0176] In the seal tear strength test, the presence or absence of tearing of the gasket 30, which is the seal, was determined. Specifically, as shown in FIG. 10A, a member in which the lid portion 12 and the external terminal 20 were joined via the gasket 30 was taken out from each of the secondary batteries of Examples 1 to 8 and Comparative Example 1, and a pressing member PM was moved at a constant speed of 10 mm / min to apply pressure from below to above to the surface opposite to the surface 20S of the central portion 20C of the external terminal 20. The pressing member PM is a cylindrical rigid body with a circle having a diameter of 3 mm as its base. Therefore, the area of ​​the contact surface between the pressing member PM and the central portion 20C of the external terminal 20 is 2.25×π mm 2 The maximum load applied to the external terminal 20 by the pressing member PM was set to 15 kg, and it was observed whether or not the gasket 30 was torn as shown in Fig. 10B, for example.

[0177] In the heating test conforming to UL1642, the temperature was raised from 20±5°C to 130±2°C at a rate of 5±2°C / min, and then held at 130±2°C for 10 minutes, after which it was determined whether the external terminal opened.

[0178] [Table 1]

[0179] [Consideration] As shown in Table 1, in Examples 1 to 8 and Comparative Example 1, no cleavage occurred in any of the 10 samples in the cleavage strength test. Furthermore, in the heating test, the external terminal did not open in four of the 10 samples in Comparative Example 1, whereas in Examples 1 to 8, the number of samples in which the external terminal did not open was reduced to three out of ten. In particular, in Examples 2 to 4, the external terminal opened in all of the 10 samples.

[0180] [summary] From the results shown in Table 1, it was confirmed that the secondary battery of the present disclosure has a curved external terminal, which makes it easier for the external terminal to open when the pressure inside the battery reaches a predetermined pressure value, thereby providing greater safety.

[0181] The present disclosure has been described above with reference to an embodiment and examples, but the configuration of the present disclosure is not limited to the configuration described in the embodiment and examples, and various modifications are possible.

[0182] 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 lid section, which are separated from each other, are crimped together via a gasket.

[0183] 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.

[0184] The effects described in this specification are merely examples, and the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

[0185] <1> a battery element formed by winding a laminate including a first electrode and a second electrode around a winding axis extending in a first direction; an exterior member having a through-hole penetrating in the first direction and accommodating the battery element; an external terminal attached to the exterior member via an insulating member at a position overlapping the through hole of the exterior member in the first direction; Equipped with The external terminals have a curved shape including a concave or convex surface facing the battery element. Secondary battery. <2> The external terminal is a laminate including two or more layers having different linear expansion coefficients. the above <1> The secondary battery described. <3> The external terminal is a laminate of a first layer made of Ni (nickel), a second layer made of stainless steel, and a third layer made of Al (aluminum). the above <1> The secondary battery described. <4> The exterior member is a lid portion provided with the through hole; a bottom portion facing the lid portion across the battery element in the first direction; a sidewall portion that connects the lid portion and the bottom portion and surrounds the battery element; the above <1> from <3> 10. The secondary battery according to claim 9, wherein the second battery is a battery having a capacitance of 100.degree. <5> the lid portion has a recessed portion recessed toward the battery element along the first direction, the through-hole is provided in the recess of the lid, The external terminal is accommodated in the recess without protruding from the recess in the first direction. the above <4> The secondary battery described. <6> the recessed portion includes an overlapping portion that overlaps a peripheral portion of the external terminal with the insulating member sandwiched therebetween in the first direction, The overlapping portion is inclined with respect to a plane perpendicular to the first direction in accordance with the curved shape of the external terminal. the above <5> The secondary battery described. <7> The insulating member includes a thin portion having a small thickness in a radial direction along a plane perpendicular to the first direction. the above <1> from <6> 10. The secondary battery according to claim 9, wherein the second battery is a battery having a capacitance of 100.degree. <8> The thin-walled portion is present in a circular ring shape on the plane. the above <7> The secondary battery described. <9> the external terminal is electrically connected to the first electrode, The exterior member is electrically connected to the second electrode. the above <1> from <8> 10. The secondary battery according to claim 9, wherein the second battery is a battery having a capacitance of 100.degree.

Claims

1. a battery element formed by winding a laminate including a first electrode and a second electrode around a winding axis extending in a first direction; an exterior member having a through-hole penetrating in the first direction and accommodating the battery element; an external terminal attached to the exterior member via an insulating member at a position overlapping the through hole of the exterior member in the first direction; Equipped with the external terminal has a curved shape including a concave or convex surface facing the battery element; the exterior member has a lid portion provided with the through hole, a bottom portion facing the lid portion with the battery element interposed therebetween in the first direction, and a sidewall portion connecting the lid portion and the bottom portion and surrounding the battery element, the lid portion has a recessed portion recessed toward the battery element along the first direction, the through-hole is provided in the recess of the lid, The external terminal is accommodated in the recess without protruding from the recess in the first direction. Secondary battery.

2. A battery element comprising a laminate including a first electrode and a second electrode wound around a winding axis extending in a first direction; an exterior member having a through-hole penetrating in the first direction and accommodating the battery element; an external terminal attached to the exterior member via an insulating member at a position overlapping the through hole of the exterior member in the first direction; Equipped with the external terminal has a curved shape including a concave or convex surface facing the battery element; The insulating member includes a thin portion having a small thickness in a radial direction along a plane perpendicular to the first direction. Secondary battery.

3. The external terminal is a laminate including two or more layers having different linear expansion coefficients.

3. The secondary battery according to claim 1.

4. The external terminal is a laminate of a first layer made of Ni (nickel), a second layer made of stainless steel, and a third layer made of Al (aluminum).

3. The secondary battery according to claim 1.

5. The exterior member is a lid portion provided with the through hole; a bottom portion facing the lid portion across the battery element in the first direction; a sidewall portion that connects the lid portion and the bottom portion and surrounds the battery element; The secondary battery according to claim 2.

6. the lid portion has a recessed portion recessed toward the battery element along the first direction, the through-hole is provided in the recess of the lid, The external terminal is accommodated in the recess without protruding from the recess in the first direction. The secondary battery according to claim 5.

7. the recessed portion includes an overlapping portion that overlaps a peripheral portion of the external terminal with the insulating member sandwiched therebetween in the first direction, The overlapping portion is inclined with respect to a plane perpendicular to the first direction, following the curved shape of the external terminal. The secondary battery according to claim 1 or 6.

8. The thin-walled portion is present in a circular ring shape on the plane. The secondary battery according to claim 2.

9. the external terminal is electrically connected to the first electrode, The exterior member is electrically connected to the second electrode.

3. The secondary battery according to claim 1.

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