JP2024067800A - Secondary battery - Google Patents

Abstract

[Problem] To provide a secondary battery with higher safety. [Solution] This secondary battery includes a battery element, an exterior member, and an external terminal. The exterior member has a through hole penetrating in a first direction and houses the battery element. The external terminal is 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 exterior member has a lid portion provided with a through hole, a bottom portion facing the lid portion with the battery element in between in the first direction, a side wall portion connecting the lid portion and the bottom portion and surrounding the battery element, and a protrusion portion that protrudes from an intermediate portion of the side wall portion located between the battery element and the lid portion toward the inside of the exterior member and includes an overlapping portion that overlaps with the battery element in the first direction. [Selected Figure] Figure 2

Description

This disclosure relates to secondary batteries.

As various electronic devices such as mobile phones become widespread, secondary batteries are being developed as power sources that are small and lightweight and can provide high energy density. These secondary batteries have 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).

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.

JP 2019-046639 A

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

Therefore, it is desirable to provide a secondary battery that has a high level of safety.

The secondary battery of one embodiment of the present disclosure includes a battery element, an exterior member having a through hole penetrating in a 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. Here, the exterior member has a lid portion having a through hole, a bottom portion facing the lid portion with the battery element in between in the first direction, a side wall portion connecting the lid portion and the bottom portion and surrounding the battery element, and a protrusion portion that protrudes from an intermediate portion of the side wall portion located between the battery element and the lid portion toward the inside of the exterior member and includes an overlapping portion that overlaps with the battery element in the first direction.

According to the secondary battery of one embodiment of the present disclosure, a protrusion is provided on the side wall of the exterior member, so that the battery element housed in the exterior member can be stably held. Therefore, even if the secondary battery is subjected to vibration, the application of local stress to the battery element can be mitigated, and a high level of safety can be obtained.

Note that the effects of this disclosure are not necessarily limited to the effects described here, but may be any of a series of effects related to this disclosure described below.

1 is a perspective view illustrating a configuration example of a secondary battery according to an embodiment of the present disclosure. 2 is a cross-sectional view illustrating a configuration example of the secondary battery illustrated in FIG. 1. 3 is a cross-sectional view illustrating a configuration example of the battery element illustrated in FIG. 2. 1 is a perspective view illustrating an example of the configuration of an exterior can used in a manufacturing process of a secondary battery. 1 is a cross-sectional view illustrating a configuration example of a secondary battery according to a first modified example. FIG. 2 is a schematic cross-sectional view illustrating the dimensions of each portion of the secondary battery of Example 1. FIG. 11 is a schematic cross-sectional view illustrating the dimensions of each portion of the secondary battery of Example 2.

Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. The description will be given in the following order.

1. Secondary battery 1-1. Configuration 1-2. Operation 1-3. Manufacturing method 1-4. Actions and effects 2. Modifications

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

The secondary battery described here has a flat, columnar, three-dimensional shape, and is called a coin type or button type. As described below, this secondary battery has a pair of bottoms facing each other and a side wall 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.

The principle of charging and discharging a secondary battery is not particularly limited, but the following describes a case where battery capacity is obtained by utilizing the absorption and release of an electrode reactant. This secondary battery has 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 the electrode reactant from being deposited 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.

The type of electrode reactant is not particularly limited, but specifically, it is a light metal such as an alkali metal or an alkaline earth metal. Alkaline metals include lithium, sodium, and potassium, while alkaline earth metals include beryllium, magnesium, and calcium.

In the following, we will use an example where the electrode reactant is lithium. A secondary battery that obtains battery capacity by utilizing the absorption and release of lithium is known as a lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is absorbed and released in an ionic state.

<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, in Fig. 3, only a part of the cross-sectional configuration of the battery element 40 is enlarged.

For the sake of convenience, the upper side in each of Figures 1 and 2 will be described below as the upper side of the secondary battery, and the lower side in each of Figures 1 and 2 will be described below as the lower side of the secondary battery.

The secondary battery described here has a three-dimensional shape with a height H smaller than the outer diameter D, i.e., a flat and columnar three-dimensional shape, as shown in FIG. 1. Here, the three-dimensional shape of the secondary battery is flat and cylindrical. In this embodiment, the vertical direction of the paper in each of FIG. 1 and FIG. 2 is the height direction Z. Therefore, the height H means the dimension of the secondary battery of this embodiment in the height direction Z. In addition, the outer diameter D means the dimension of the secondary battery of this embodiment in the direction perpendicular to the height direction Z, i.e., in the horizontal plane.

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 it is preferably 25 or less.

As shown in Figures 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 an insulating film 63.

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

Here, the exterior can 10 has a flat, cylindrical three-dimensional shape in accordance with the three-dimensional shape of the secondary battery, which is flat and cylindrical. The exterior can 10 includes a storage section 11 and a lid section 12 that are welded together. That is, the internal space of the exterior can 10 is sealed by welding the lid section 12 to the storage section 11.

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

As shown in FIG. 2, the storage section 11 has a bottom 11B, a side wall 11W, and a protruding portion 11P. The storage section 11 is a container in which the bottom 11B, the side wall 11W, and the protruding portion 11P are integrated. The upper end of the storage section 11, which is a container, i.e., the upper end (opening 11K) of the side wall M3, is fitted and welded to the outer edge 12T of the lid 12. The bottom 11B faces the lid 12 with the battery element 40 sandwiched between them in the height direction Z. The side wall 11W is a cylindrical portion having a central axis along the height direction Z. The side wall 11W connects the lid 12 and the bottom 11B and surrounds the battery element 40. The protruding portion 11P protrudes in the radial direction of the secondary battery from an intermediate portion of the side wall 11W located between the battery element 40 and the lid 12 toward the inside of the outer can 10. The protrusion 11P includes an overlapping portion OL that overlaps with the battery element 40 in the height direction Z. The protrusion 11P may include a tip portion 11AS having a rounded shape. The tip portion 11AS is also an opening edge that constitutes an opening 11PK that communicates with a through hole 12K (described later) of the lid portion 12. The protrusion 11P is an annular portion that is provided along the entire circumference along the inner surface of the side wall portion 11W and surrounds the battery element 40. The protrusion 11P includes an abutting surface 11US that abuts against the peripheral portion of the lower surface 12LS of the lid portion 12. Furthermore, the protrusion 11P includes an opposing surface 11LS that faces the upper surface of the battery element 40. As described above, since the exterior can 10 is approximately cylindrical, the planar shapes of the outer edges of the lid portion 12 and the bottom portion 11B are approximately circular, and the outer surface of the side wall portion 11W is a convex curved surface. In this way, the presence of the protrusion 11P makes it difficult for the battery element 40 to move inside the exterior can 10. Therefore, even if the secondary battery 1 is subjected to external forces such as vibration and impact, problems such as collapse of the wound electrode body of the battery element 40 can be suppressed.

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. The through hole 12K has an inner diameter φ12K. The inner diameter φ11PK of the tip portion 11AS, which is the opening edge that constitutes the opening 11PK of the protrusion 11P, can be larger than the inner diameter φ12K of the through hole 12K. However, the inner diameter φ11PK is smaller than the outer diameter φ40 of the battery element 40 (φ11PK<φ40). The outer edge 12T of the lid 12 is welded to the opening 11K of the storage section 11 as described above. The peripheral portion of the lower surface 12LS of the lid 12 abuts against the abutment surface 11US of the protrusion 11P as described above. The external terminal 20 is attached to the lower surface 12LS of the lid portion 12 via a gasket 30. That is, the lid portion 12 supports the external terminal 20 via the gasket 30. The external terminal 20 is attached to the lid portion 12 via the gasket 30 at a position overlapping the through hole 12K of the lid portion 12 in the height direction Z. The external terminal 20 is electrically insulated from the exterior can 10.

As described above, in the completed secondary battery, the lid 12 is welded to the storage section 11. As described above, the opening 11K is blocked by the lid 12. Therefore, even if one looks at the exterior of the secondary battery, it is considered impossible to determine whether the storage section 11 had an opening 11K or not.

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 is possible to confirm after the fact whether or not the storage section 11 had an opening 11K.

In other words, if there are weld marks remaining on the surface of the outer can 10, this 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, this means that the storage section 11 did not have an opening 11K.

As described above, the exterior can 10 is a can in which the storage section 11 and the lid section 12, which were previously physically separate, have been welded together, making it a so-called welded can. As a result, the exterior 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.

The exterior can 10, which is a welded can, is different from a crimp can formed using a crimping process and is a so-called crimpless can. This is because the element space volume increases inside the exterior can 10, and the energy density per unit volume increases. 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.

In addition, the exterior can 10, which is a welded can, does not have any parts that are folded over each other, and does not have any parts where two or more members overlap each other.

"Having no overlapping parts" means that no parts of the exterior can 10 have been processed (folded) so that they overlap each other. Also, "having no parts where two or more components overlap each other" means that after the secondary battery is completed, the exterior can 10 is physically one component, and therefore the exterior can 10 cannot be separated into two or more components later. In other words, the state of the exterior can 10 in the completed secondary battery is not in a state where two or more components are combined together while overlapping each other so that they can be separated later.

Here, the exterior can 10 is conductive. More specifically, the storage section 11 and the lid section 12 are each conductive. The exterior can 10 is electrically connected to the negative electrode 42 of the battery element 40 via the negative electrode lead 52. Therefore, the exterior can 10 also serves as an external connection terminal for the negative electrode 42. Since the secondary battery of this embodiment does not need to have an external connection terminal for the negative electrode 42 separate from the exterior can 10, a reduction in the element space volume caused by the presence of the external connection terminal for the negative electrode 42 is suppressed. This increases the element space volume, and therefore increases the energy density per unit volume.

Specifically, the exterior can 10 is a metal can containing one or more types of 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 material forming the storage section 11 and the material forming the lid section 12 may be the same as or different from each other.

The lid 12 is insulated via a gasket 30 from the external terminal 20, which serves as the external connection terminal for the positive electrode 41. This is to prevent contact, i.e., a short circuit, between the exterior can 10, which serves as the external connection terminal for the negative electrode 42, and the external terminal 20, which serves as the external connection terminal for the positive electrode 41.

[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 exterior can 10.

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 the external connection terminal for the positive electrode 41 and the exterior can 10 as the external connection terminal for the negative electrode 42. Therefore, the electronic device can operate using the secondary battery as a power source.

The external terminal 20 is a flat, approximately plate-shaped member that is disposed below the lid 12, i.e., inside the exterior can 10, via a gasket 30.

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.

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 composed of a single layer, or may be a laminate including two or more layers having different linear expansion coefficients. Specifically, the external terminal 20 may be a laminate including a first layer made of Ni (nickel), a second layer made of stainless steel such as SUS304, and a third layer made of Al (aluminum).

[gasket]
2, the gasket 30 is an insulating member disposed between the exterior 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 having 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.

The installation range of the gasket 30 can be set arbitrarily. Here, the gasket 30 is placed in the gap between the lower surface 12LS of the lid 12 and the upper surface 20US of the external terminal 20. As shown in FIG. 2, the gasket 30 may also cover, for example, the inner edge of the through hole 12K of the lid 12, or the outer edge of the external terminal 20. Furthermore, it is preferable that the lid 12 and the external terminal 20 are fixed to each other by the gasket 30.

[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 exterior 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.

The center line PC shown in FIG. 2 is a line segment that corresponds to the center of the battery element 40 in the direction along the outer diameter D of the secondary battery (outer can 10). In other words, the position P of the center line PC corresponds to the position of the center of the battery element 40.

The battery element 40 is a so-called electrode winding body. That is, in the battery element 40, the positive electrode 41 and the negative electrode 42 are stacked on top of each 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 the 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.

Here, the positive electrode 41, the negative electrode 42, and the separator 43 are wound so that the separator 43 is disposed on the outermost circumference and the innermost circumference of the wound electrode body. The number of turns of the positive electrode 41, the negative electrode 42, and the separator 43 is not particularly limited and can be set arbitrarily.

The battery element 40 has a three-dimensional shape that conforms to 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 in which the battery element 40 has a three-dimensional shape different from that of the outer can 10, when the battery element 40 is housed inside the outer can 10, so-called dead space, specifically, a gap between the outer can 10 and the battery element 40, is less likely to occur. For this reason, the internal space of the outer can 10 is effectively utilized. As a result, the element space volume increases, and the energy density per unit volume of the secondary battery increases.

(Positive electrode)
The positive electrode 41 is a first electrode used for promoting charge/discharge reactions, and includes a positive electrode current collector 41A and a positive electrode active material layer 41B, as shown in FIG.

The positive electrode current collector 41A has a pair of surfaces on which the positive electrode active material layer 41B is provided. This positive electrode current collector 41A contains a conductive material such as a metal material, and the metal material is aluminum, for example.

The positive electrode active material layer 41B is provided on both sides of the positive electrode 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 collector 41A. The positive electrode active material layer 41B may further contain a positive electrode binder and a positive electrode conductive agent. The method of forming the positive electrode active material layer 41B is not particularly limited, but specifically includes a coating method.

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, it is a compound containing one or more transition metal elements as constituent elements together with lithium. This is because a high energy density can be obtained. However, the lithium compound may further contain any one or more of other elements (excluding lithium and transition metal elements). The type of lithium compound is not particularly limited, but specifically includes oxides, phosphate compounds, silicate compounds, and borate compounds. Specific examples of oxides include LiNiO ₂ , LiCoO ₂ , and LiMn ₂ O ₄ , and specific examples of phosphate compounds include LiFePO ₄ and LiMnPO ₄ .

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 conductive agent contains one or more of conductive materials such as carbon materials, and the carbon materials are graphite, carbon black, acetylene black, and ketjen black. However, the conductive material may also be a metal material and a polymer compound.

(Negative electrode)
The negative electrode 42 is a second electrode used for promoting charge/discharge reactions, and includes a negative electrode current collector 42A and a negative electrode active material layer 42B, as shown in FIG.

The negative electrode current collector 42A has a pair of surfaces on which the negative electrode active material layer 42B is provided. This negative electrode current collector 42A contains a conductive material such as a metal material, and the metal material is, for example, copper.

The negative electrode active material layer 42B is provided on both sides of the negative electrode 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 collector 42A. The negative electrode active material layer 42B may further contain a negative electrode binder and a negative electrode conductor. 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. The method of forming the negative electrode active material layer 42B is not particularly limited, but specifically, it is one or more types of a coating method, a gas phase method, a liquid phase method, a thermal spraying method, and a sintering method (sintering method).

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. The carbon material is graphitizable carbon, non-graphitizable carbon, graphite (natural graphite and artificial graphite), etc. The metal-based material is a material containing one or more of 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, etc. However, the metal-based material may be a single element, an alloy, a compound, a mixture of two or more of them, or a material containing two or more phases of them. Specific examples of metal-based materials are TiSi ₂ and SiO _x (0<x≦2, or 0.2<x<1.4), etc.

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 the lithium released from the positive electrode 41 from being precipitated. This "height" is the dimension corresponding to the height H of the secondary battery described above, that is, the vertical dimension in each of Figures 1 and 2. The definition of height described here will be the same hereinafter.

(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.

Here, the height of the separator 43 is greater than the height of the negative electrode 42. In other words, the separator 43 preferably protrudes upward from the negative electrode 42 and 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.

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

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

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 20LS of the external terminal 20 via a through hole 12K provided in the lid portion 12. The method of connecting the positive electrode lead 51 is not particularly limited, but specifically, it is one or more of welding methods such as resistance welding and laser welding. The details of the welding methods described here will be the same hereinafter.

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, a portion of the positive electrode lead 51 is covered with a sealant 61, so that the positive electrode lead 51 does not come into contact with the negative electrode 42 of the battery element 40.

A portion of the positive electrode lead 51 extends along the lower surface 20LS of the external terminal 20 and the upper surface of the battery element 40, and is thereby held by the external terminal 20 and the battery element 40. Therefore, the positive electrode lead 51 is fixed inside the exterior 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.

That is, a part of the positive electrode lead 51 is sandwiched between the outer can 10 and the battery element 40 means that the positive electrode lead 51 is insulated from the outer can 10 and the battery element 40, while being held from above and below by the outer can 10 and the battery element 40, so that the positive electrode lead 51 is in a state in which it is difficult 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 in a state in which it is difficult to move inside the outer can 10 means that the battery element 40 is also in a state in which it is difficult to move inside the outer can 10. Therefore, when the secondary battery is subjected to vibration or impact, it is also possible to suppress problems such as collapse of the winding of the battery element 40, which is a wound electrode body.

As described above, the secondary battery of this embodiment includes a protrusion 11P that protrudes radially from the side wall 11W toward the inside of the storage section 11. Therefore, the battery element 40 is stably held in the space between the bottom 11B and the protrusion 11P in the internal space of the storage section 11, and is in a state where it is difficult to move. Therefore, the positive electrode lead 51 sandwiched between the external terminal 20 fixed to the lid section 12 via the gasket 30 and the battery element 40 is stably held by the external terminal 20 and the battery element 40. Therefore, the positive electrode lead 51 is less likely to be damaged.

In addition, a portion of the positive electrode lead 51 is insulated from the negative electrode 42 via the separator 43, the sealant 61, and the insulating film 63.

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.

The positive electrode lead 51 is also covered with an insulating sealant 61. This insulates a portion of the positive electrode lead 51 from the negative electrode 42 via the sealant 61. This is because a short circuit between the positive electrode lead 51 and the negative electrode 42 is prevented.

An insulating film 63 is disposed between the battery element 402 and the positive electrode lead 51. As a result, a portion of the positive electrode lead 51 is insulated from the battery element 40 via the insulating film 63.

The details regarding the material for the positive electrode lead 51 are similar to the details regarding the material for the positive electrode collector 41A. However, the material for the positive electrode lead 51 and the material for the positive electrode collector 41A may be the same as or different from each other.

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 is connected to the positive electrode 41 on the inner side of the outermost circumference of the positive electrode 41. This is because, unlike the case where the positive electrode lead 51 is connected to the positive electrode 41 at the outermost circumference of the positive electrode 41, corrosion of the outer can 10 caused by the electrolyte creeping up is prevented. This "electrolyte creeping up" 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 the "electrolyte creeping up", the outer can 10 dissolves or discolors.

Here, the positive electrode lead 51 may be folded back one or more times between the positive electrode 41 and the external terminal 20, and overlapped one or more times. The number of times the positive electrode lead 51 is folded back is not particularly limited. This "positive electrode lead 51 is folded back" means that the extension direction of the positive electrode lead 51 changes so as to form an angle of more than 90° midway. The folded back portion of the positive electrode lead 51 may have a curved shape without bending.

The connection range of the positive electrode lead 51 to the external terminal 20 is not particularly limited. In particular, it is preferable that the connection range of the positive electrode lead 51 to the external terminal 20 is sufficiently wide so that the positive electrode lead 51 is unlikely to fall off the external terminal 20, and is sufficiently narrow so that a length margin of the positive electrode lead 51 is obtained. The reason why it is preferable that the connection range of the positive electrode lead 51 to the external terminal 20 is 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 of the positive electrode lead 51 becomes sufficiently large.

The positive electrode lead 51 is provided separately from the positive electrode collector 41A. However, since the positive electrode lead 51 is physically continuous with the positive electrode collector 41A, it may be integrated with the positive electrode collector 41A.

[Negative lead]
As shown in Fig. 2, the negative electrode lead 52 is stored inside the exterior can 10. The negative electrode lead 52 is connected to both the negative electrode 42 and the exterior can 10 (storage 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.

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 regarding the method of connecting the negative electrode lead 52 are the same as the details regarding the method of connecting the positive electrode lead 51.

The details regarding the material for the negative electrode lead 52 are similar to the details regarding the material for the negative electrode current collector 42A. However, the material for the negative electrode lead 52 and the material for the negative electrode current collector 42A may be the same as or different from each other.

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.

The negative electrode lead 52 is provided separately from the negative electrode current collector 42A. However, since the negative electrode lead 52 is physically continuous with the negative electrode current collector 42A, it may be integrated with the negative electrode current collector 42A.

[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, respectively. Here, the sealant 61 covers the periphery of the middle part of the positive electrode lead 51 in order to connect the positive electrode lead 51 to the positive electrode 41 and the external terminal 20, respectively. Note that the sealant 61 is not limited to having a tape-like structure, and may have, for example, a tube-like structure.

The sealant 61 contains one or more insulating materials, such as insulating polymer compounds, such as polyimide.

[Insulating film]
2, the insulating film 63 is disposed between the battery element 40 and the positive electrode lead 51. Here, the insulating film 63 has a flat plate 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.

The insulating film 63 may contain one or more insulating materials such as insulating polymer compounds. The insulating material contained in the insulating film 63 is polyimide, for example.

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

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 exterior can 10 and the battery element 40 when the internal pressure of the exterior can 10 reaches a certain level or higher. Causes of the internal pressure of the exterior can 10 reaching a certain level or higher include a short circuit occurring inside the secondary battery and the secondary battery being heated from the outside. There are no particular limitations on the location where the safety valve mechanism is installed. However, it is preferable that the safety valve mechanism be installed in either the lid portion 12 or the bottom portion 11B, and it is more preferable that the safety valve mechanism be installed in the bottom portion 11B to which the external terminal 20 is not attached.

The secondary battery may also have an insulator between the exterior can 10 and the battery element 40. This insulator includes one or more types of insulating film and insulating sheet, 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.

The outer can 10 is provided with a row opening valve. This row opening 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 of the row opening valve, but as with the location of the safety valve mechanism described above, it is preferable to install the row opening valve on either the lid 12 or the bottom 11B, and more preferably on the bottom 11B.

<1-2. Operation>
When the secondary battery is charged, lithium is released from the positive electrode 41 in the battery element 40, and the lithium is absorbed in the negative electrode 42 via the electrolyte. Lithium is released from the negative electrode 42 and is absorbed into the positive electrode 41 via the electrolyte. During these charge and discharge operations, lithium is absorbed and released in an ionic state.

<1-3. Manufacturing method>
FIG. 4 shows a perspective view of an exterior can 10 used in the manufacturing process of a secondary battery, and corresponds to FIG.

Figure 4 shows the state in which the lid portion 12 is separated from the storage portion 11 before the lid portion 12 is welded to the storage portion 11.

In the following explanation, reference will be made to Figures 1 to 3, which have already been described, as well as Figure 4.

To form the exterior can 10, as shown in FIG. 4, a storage section 11 and a lid section 12 that are physically separated from each other are prepared. The storage section 11 is a roughly container-shaped member in which a bottom section 11B and a side wall section 11W are integrated with each other, and has an opening section 11K. However, the bottom section 11B and the side wall section 11W that are physically separated from each other may be prepared, and the storage section 11 may be formed by welding the side wall section 11W to the bottom section 11B. A protrusion 11P is provided on the inside of the side wall section 11W. The protrusion 11P is, for example, formed integrally with the side wall section 11W. Alternatively, the protrusion 11P formed separately from the side wall section 11W may be attached to the inside of the side wall section 11W.

The lid 12 is a generally plate-shaped member that corresponds to the bottom M1, and as described below, the external terminal 20 is attached in advance to the underside of the lid 12 via a gasket 30 (not shown in FIG. 4).

[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 put into an organic solvent or the like to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is applied to both sides of the 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 way, the positive electrode 41 is prepared.

[Preparation of negative electrode]
The negative electrode 42 is produced by the same procedure as the positive electrode 41. Specifically, after preparing the negative electrode collector 42A, a negative electrode mixture obtained by mixing 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 collector 42A has both ends in the width direction 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 collector 42A to form a negative electrode active material layer 42B. After this, the negative electrode active material layer 42B is compression molded using a roll press or the like. This produces the negative electrode 42.

[Preparation of electrolyte solution]
An electrolyte salt is added to a solvent, whereby the electrolyte salt is dispersed or dissolved in the solvent, and an electrolyte solution is prepared.

[Assembly of secondary battery]
First, using a welding method such as resistance welding, the positive electrode lead 51, whose periphery 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).

Next, the positive electrode 41 and the negative electrode 42 are stacked with the separator 43 interposed therebetween, and then the stack including the positive electrode 41, the negative electrode 42, and the separator 43 is wound to produce the wound body 40Z as shown in FIG. 4. At that time, the outer diameter φ40Z of the wound body 40Z is made slightly smaller than the inner diameter φ11PK of the opening 11PK of the protruding portion 11P (φ40Z<φ11PK). This is to make it possible to store the wound body 40Z inside the storage section 11. 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 the electrolyte. Note that in FIG. 4, the positive electrode lead 51 and the negative electrode lead 52 are not shown.

Then, the wound body 40Z to which the positive electrode lead 51 and the negative electrode lead 52 are connected is stored inside the storage section 11 through the opening 11K. At this time, the wound body 40Z is stored in the space below the convex portion 11P, that is, in the space between the convex portion 11P and the bottom portion 11B in the height direction Z. In this case, the negative electrode lead 52 is connected to the storage section 11 using a welding method such as resistance welding. Next, an insulating film 63 is placed on the wound body 40Z.

Next, after preparing the lid 12 to which the external terminal 20 is attached via the gasket 30, 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.

As a result, the wound body 40Z (positive electrode 41) stored inside the storage section 11 and the external terminal 20 attached to the lid section 12 are connected to each other via the positive electrode lead 51.

Then, the electrolyte is injected 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 through the positive electrode lead 51 as described above, the lid 12 does not close the opening 11K, so that the electrolyte can be easily injected 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, and the battery element 40, which is a wound electrode body, is produced.

Then, the lid 12 is tilted down so as to approach the storage section 11, and the opening 11K is closed 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 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 stored inside the outer can 10, completing the assembly of the secondary battery.

[Stabilization of secondary battery]
The assembled secondary battery is charged and discharged. Various conditions such as the environmental temperature, the number of charge/discharge cycles (number of cycles), and the charge/discharge conditions can be set arbitrarily. As a result, a coating is formed on the surface of the negative electrode 42, etc., and the state of the secondary battery is electrochemically stabilized. Thus, the secondary battery is completed. Since the battery element 40 expands after charging and discharging, its outer diameter φ40 becomes larger than the inner diameter φ11PK of the opening 11PK of the protruding portion 11P.

<1-4. Actions and Effects>
Thus, according to the secondary battery of the present embodiment, the exterior can 10 has the lid portion 12 provided with the through hole 12K, the bottom portion 11B facing the lid portion 12 with the battery element 40 in the height direction Z, the side wall portion 11W connecting the lid portion 12 and the bottom portion 11B and surrounding the battery element 40, and the protrusion portion 11P protruding from an intermediate portion of the side wall portion 11W located between the battery element 40 and the lid portion 12 toward the inside of the exterior can 10. Here, the protrusion portion 11P includes an overlapping portion OL that overlaps with the battery element 40 in the height direction Z. Therefore, the battery element 40 can be stably held by the protrusion portion 11P, the bottom portion 11B, and the side wall portion 11W. Therefore, even if vibration is applied to the secondary battery, the application of local stress to the battery element 40 can be alleviated, and high safety can be obtained.

In particular, in the secondary battery of this embodiment, the protrusion 11P is provided in an annular shape around the entire circumference of the side wall portion 11W so as to surround the battery element. Therefore, the secondary battery of this embodiment can hold the battery element 40 more stably and ensure higher safety compared to a case in which the protrusion 11P is provided only on a portion of the circumference surrounding the center line PC.

In addition, in the secondary battery of this embodiment, the tip portion 11AS of the protrusion 11P has a rounded shape. Therefore, even if the protrusion 11P comes into contact with the battery element 40 due to the application of vibration or the expansion and contraction of the battery element 40, damage to the battery element 40 can be sufficiently avoided. Therefore, an even higher level of safety can be ensured.

In addition, in the secondary battery of this embodiment, the lid portion 12 and the external terminal 20 are fixed with a gasket 30 made of insulating resin. This increases the mechanical strength against vibration. Furthermore, it is possible to prevent short circuits caused by foreign matter entering the gap between the lid portion 12 and the external terminal 20.

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

The secondary battery of this embodiment, which is called a coin type or 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.

In this respect, in the secondary battery of this embodiment, the movement of the positive electrode lead 51 inside the outer can 10 is sufficiently suppressed, so that 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 coming off the external terminal 20 or breaking is extremely low. Therefore, according to the secondary battery of this embodiment, even if it is subjected to an external force such as vibration or impact, it is possible to maintain a good electrical connection state between the external terminal 20 and the positive electrode lead 51. Therefore, according to the secondary battery of this embodiment, it is possible to achieve high physical durability even when it is miniaturized.

In addition, in the secondary battery of this embodiment, which is provided with 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 exterior 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 to the external terminal 20 sufficiently small and to place the positive electrode lead 51 sufficiently far from the lid 12.

In this respect, in the secondary battery of this embodiment, the movement of the positive electrode lead 51 inside the outer can 10 is sufficiently suppressed, so that 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 coming off from the external terminal 20 or the positive electrode lead 51 breaking is extremely low. Therefore, according to the secondary battery of this embodiment, even if it is subjected to an external force such as vibration or impact, it is possible to maintain a good electrical connection state between the external terminal 20 and the positive electrode lead 51. Therefore, according to the secondary battery of this embodiment, even if it is miniaturized, it is possible to realize high physical durability while preventing a short circuit between the lid portion 12 and the external terminal 20.

In addition, 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, resulting in higher reliability.

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 caused by the electrolyte creeping up can be prevented. This makes it possible to obtain even higher reliability.

In addition, 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, resulting in higher reliability.

In this case, particularly when the periphery of the positive electrode lead 51 is covered with the sealant 61, the following action and effect 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 positive electrode lead 51 is easily held by the outer can 10 and the battery element 40 by utilizing the gripping force supplied to the positive electrode lead 51 via the sealant 61. Therefore, the positive electrode lead 51 is insulated from the outer can 10 and the negative electrode 42 via the sealant 61. In addition, the sealant 61 makes it easier to fix the positive electrode lead 51 inside the outer can 10, thereby obtaining even higher physical durability.

In addition, if an 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. This makes it possible to obtain higher reliability.

In addition, if the secondary battery is flat and columnar, i.e., the secondary battery is a type called a coin type or button type, 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 a greater effect can be obtained in terms of physical durability.

In addition, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium.

2. Modified Examples
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.

[Modification 1]
Fig. 5 shows a cross-sectional structure of a secondary battery as a first modified example of the above embodiment. In the secondary battery of Fig. 2, the external terminal 20 is provided inside the exterior can 10, i.e., on the lower surface 12LS of the lid portion 12 via a gasket 30. However, in the secondary battery of the present disclosure, as shown in Fig. 5, the external terminal 20 may be provided outside the exterior can 10, i.e., on the upper surface 12US of the lid portion 12 via a gasket 30. In this case, the same effects as those of the secondary battery of the above embodiment can be obtained.

An example of this technology will be explained.

After producing the secondary batteries of the present disclosure described in the above embodiment and modified example, the battery characteristics of those secondary batteries were evaluated. In addition, a secondary battery was produced as a comparative example, and the battery characteristics of that secondary battery were also evaluated.

[Preparation of secondary battery]
Example 1
First, as Example 1, the secondary battery shown in FIG. 2 was fabricated in the following manner.

(Preparation of Positive Electrode)
First, 91 parts by mass of a positive electrode active material (LiCoO ₂ ), 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. Next, the positive electrode mixture was added to an organic solvent (N-methyl-2-pyrrolidone), and the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector 41A (a strip-shaped aluminum foil having a thickness of 12 μm) using a coating device, and then the positive electrode mixture slurry was 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 machine. As a result, a positive electrode 41 (width = 3.3 mm) was produced.

(Preparation of negative electrode)
First, 95 parts by mass of the negative electrode active material (graphite) and 5 parts by mass of the negative electrode binder (polyvinylidene fluoride) were mixed to prepare a negative electrode mixture. Next, the negative electrode mixture was added to an organic solvent (N-methyl-2-pyrrolidone), and the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of the negative electrode current collector 42A (a strip-shaped copper foil having a thickness of 15 μm) using a coating device, and then the negative electrode mixture slurry was dried to form the negative electrode active material layer 42B. Finally, the negative electrode active material layer 42B was compression molded using a roll press machine. This produced the negative electrode 42 (width = 3.8 mm).

(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 solvent was ethylene carbonate:diethyl carbonate=30:70, and the content of the electrolyte salt was 1 mol/kg relative to the solvent. As a result, the electrolyte salt was dissolved or dispersed in the solvent, and an electrolyte solution was prepared.

(Assembly of secondary batteries)
First, a positive electrode lead 51 (thickness = 0.1 mm, width = 2.0 mm, protruding length from the positive electrode 41 = 11.7 mm) made of aluminum, the periphery of which was partially covered 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) by using a resistance welding method. In addition, a negative electrode lead 52 (thickness = 0.1 mm, width = 2.0 mm, protruding length from the negative electrode 42 = 6.0 mm) made of nickel was welded to the negative electrode 42 (negative electrode current collector 42A) by 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 in the middle of winding the positive electrode 41.

Then, the positive electrode 41 and the negative electrode 42 were stacked on top of each other with a separator 43 (a microporous polyethylene film having a thickness of 25 μm and a width of 4.0 mm) interposed therebetween, and the positive electrode 41, the negative electrode 42, and the separator 43 were wound to produce a cylindrical wound body 40Z (outer diameter = 8.99 mm) having a central space 40K (inner diameter = 2.0 mm).

Next, a ring-shaped insulating film (polyimide film, outer diameter = 11.6 mm, inner diameter = 2.2 mm, thickness = 0.05 mm) for underlay was placed inside the 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 using resistance welding.

Next, a disk-shaped external terminal 20 (thickness = 0.3 mm, outer diameter = 7.2 mm) made of aluminum with a through hole 12K (inner diameter = 3.0 mm) was prepared. A disk-shaped lid 12 (thickness = 0.15 mm, outer diameter = 11.7 mm) made of stainless steel (SUS316) was also prepared. After applying an insulating resin to the lower surface 12LS of the lid 12, 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 placed and pressurized, and the insulating resin was cooled. As a result, the external terminal 20 was welded to the lid 12 by the gasket 30 made of the cooled insulating resin.

Next, the positive electrode lead 51 was welded to the center of the external terminal 20 attached to the lid 12 via the gasket 30 using resistance welding.

Next, with the lid 12 standing upright on the storage section 11, the electrolyte was injected 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 (outer diameter = 9.08 mm) was produced.

Finally, the opening 11K was closed with the lid 12, and the lid 12 was welded to the storage section 11 using a laser welding method. At that time, 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 enclosed inside the outer can 10, and a secondary battery (outer diameter D1 = 9.50 mm, height H1 = 4.00 mm) was assembled.

(Stabilization of secondary batteries)
The assembled secondary battery was charged and discharged for one 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 charged at a constant voltage of 4.2 V until the current reached 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 at which the battery capacity (theoretical capacity) is fully discharged in 10 hours, and 0.05 C is the current value at which the battery capacity is fully discharged in 20 hours.

As a result, a coating was formed on the surface of the negative electrode 42 and other parts, and the state of the secondary battery was electrochemically stabilized. Thus, the secondary battery of Example 1 was completed. The dimensions of each part of the secondary battery of Example 1 (see FIG. 6), i.e., the inner diameter D2 of the outer can 10, the inner diameter φ11PK of the opening 11PK, the inner height H2 of the outer can 10, the height H11P of the protruding part, the outer diameter φ40 of the wound body 40Z before charging and discharging, the outer diameter φ40 of the battery element 40, the height H40 of the battery element 40, and the thickness T20 of the external terminal 20, are as shown in Table 1 below. FIG. 6 is a schematic diagram illustrating the dimensions of each part of the secondary battery of Example 1.

Example 2
Next, a secondary battery shown in Fig. 5 was fabricated as Example 2. The fabrication conditions for the secondary battery of Example 2 were the same as those for the secondary battery of Example 1, except that the external terminal 20 was provided outside the exterior can 10, i.e., on the upper surface 12US of the lid portion 12 via a gasket 30. The dimensions of each part of the secondary battery of Example 2 (see Fig. 7) are as shown in Table 1. Fig. 7 is a schematic diagram illustrating the dimensions of each part of the secondary battery of Example 2.

<Comparative Example 1>
Next, as Comparative Example 1, a secondary battery was fabricated in which the storage section 11 of the outer can 10 did not include the convex portion 11P. Except for the fact that the storage section 11 did not include the convex portion 11P, the fabrication conditions for the secondary battery of Comparative Example 1 were the same as those for the secondary battery of Example 1.

[Evaluation of Battery Characteristics]
A drop test (at two drop heights, 1.9 m and 3.0 m) was conducted on each of the secondary batteries of Examples 1 and 2 and Comparative Example 1, and an evaluation was conducted as to whether or not cracks or breakage occurred in the positive electrode lead 51. The results are shown in Table 1. The number of samples for each Example and Comparative Example was 20. In the drop test, the batteries were allowed to freely drop onto a concrete floor from a height of 1.9 m or 3.0 m, and visual confirmation was performed as to whether or not cracks or breakage occurred in the positive electrode lead 51.

[Discussion]
As shown in Table 1, in the drop test with a drop height of 1.9 m, no cracks or breaks occurred in the positive electrode lead 51 in any of Examples 1 and 2 and Comparative Example 1, and the pass rate was 100%. However, in the drop test with a drop height of 3.0 m, cracks or breaks occurred in the positive electrode lead 51 with a probability of 25% in Comparative Example 1 (pass rate was 75%). In contrast, in Examples 1 and 2, no cracks or breaks occurred in the positive electrode lead 51 even in the drop test with a drop height of 3.0 m, and the pass rate was 100%.

[summary]
From the results shown in Table 1, it can be seen that the secondary battery of the present disclosure has a convex portion 11P including an overlapping portion OL that overlaps with the battery element 40 in the height direction Z, and therefore the battery element 40 can be stably held even when vibration is applied to the secondary battery, thereby achieving high safety.

The present disclosure has been described above with reference to one embodiment and examples, but the configuration of the present disclosure is not limited to the configuration described in the embodiment and examples, and can be modified in various ways.

Specifically, the case where the outer can is a welded can (crimpless can) has been described, but the configuration of the outer can is not particularly limited, and it may be a crimped can that has been crimped. In this crimped can, the storage section and the lid section, which are separated from each other, are crimped together via a gasket.

Furthermore, although the electrode reactant has been described as being 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.

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

Furthermore, the present disclosure may take the following aspects.
<1>
A battery element;
an exterior member having a through hole penetrating in a first direction and housing 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,
The exterior member is
A lid portion having the through hole;
a bottom portion facing the lid portion with the battery element interposed therebetween in the first direction;
a sidewall portion connecting the lid portion and the bottom portion and surrounding the battery element;
a protrusion protruding from an intermediate portion of the side wall portion located between the battery element and the lid portion toward the inside of the exterior member and including an overlapping portion overlapping with the battery element in the first direction.
＜2＞
The secondary battery according to <1> above, wherein the protrusion includes an opening edge that constitutes an opening communicating with the through hole.
＜3＞
The secondary battery according to <1> or <2> above, wherein the protrusion includes a contact surface that contacts the lid.
＜4＞
the battery element has an upper surface facing the lid portion in the first direction, a lower surface facing the bottom portion in the first direction, and a side surface facing the side wall portion,
The secondary battery according to any one of <1> to <3>, wherein the protrusion includes an opposing surface that faces the upper surface of the battery element.
＜5＞
the bottom and the sidewall are an integral container,
The secondary battery according to any one of <1> to <4> above, wherein an outer edge of the lid and an upper end of the container are fitted together.
＜6＞
The secondary battery according to any one of <1> to <5> above, wherein the protrusion includes a tip portion having a rounded shape.
＜７＞
The secondary battery according to any one of <1> to <6> above, wherein the protrusion is an annular portion provided around the entire periphery of the side wall portion and surrounding the battery element.

10...outer can, 11...storage section, 11B...bottom, 11W...side wall section, 11P...projection section, 11K...opening section, 12...lid section, 12K...through hole, 20...external terminal, 30...gasket, 40...battery element, 41...positive electrode, 41A...positive electrode current collector, 41B...positive electrode active material layer, 42...negative electrode, 42A...negative electrode current collector, 42B...negative electrode active material layer, 43...separator, 40K...winding center space, 51...positive electrode lead, 52...negative electrode lead, 61...sealant, 63...insulating film, PC...center line.

Claims (7)

A battery element;
an exterior member having a through hole penetrating in a first direction and housing 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,
The exterior member is
A lid portion having the through hole;
a bottom portion facing the lid portion with the battery element interposed therebetween in the first direction;
a sidewall portion connecting the lid portion and the bottom portion and surrounding the battery element;
a protrusion protruding from an intermediate portion of the side wall portion located between the battery element and the lid portion toward the inside of the exterior member and including an overlapping portion overlapping with the battery element in the first direction. The secondary battery according to claim 1 , wherein the protrusion includes an opening edge that defines an opening communicating with the through hole. The secondary battery according to claim 1 , wherein the protrusion includes a contact surface that contacts the lid. the battery element has an upper surface facing the lid portion in the first direction, a lower surface facing the bottom portion in the first direction, and a side surface facing the side wall portion,
The secondary battery according to claim 1 , wherein the protrusion includes an opposing surface that faces the upper surface of the battery element. the bottom and the sidewall are an integral container,
The secondary battery according to claim 1 , wherein an outer edge of the lid is fitted into an upper end of the container. The secondary battery according to claim 1 , wherein the protrusion includes a tip portion having a rounded shape. The secondary battery according to claim 1 , wherein the protrusion is an annular portion provided around the entire periphery of the side wall portion and surrounding the battery element.

Images