Battery unit and wiring unit for batteries

Abstract

Provided is a battery unit which has high reliability, while being suited to downsizing. The battery unit comprises a battery and a wiring unit. The battery has a first electrode terminal and a second electrode terminal. The wiring unit has flexible wiring boards which are respectively provided with a first connection terminal that is to be bonded to the first electrode terminal and a second connection terminal that is to be bonded to the second electrode terminal. At least one of the first connection terminal and the second connection terminal has a conductive member and a solder layer. The conductive member includes a first surface, a second surface, and a through hole penetrating therethrough from the first surface toward the second surface. The solder layer includes a first portion that covers at least a part of the first surface of the conductive member, a second portion that covers at least a part of the second surface of the conductive member, and a connection portion that passes through the through hole and connects the first portion and the second portion to each other.

Description

Battery unit and battery wiring unit

[0001] The present disclosure relates to a battery unit and a battery wiring unit used therein.

[0002] A battery unit including a battery having a positive terminal and a negative terminal and a flexible wiring board having wiring connected to the battery has been known. Various studies have been conducted on the configuration of such a battery unit (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a battery unit that includes, for example, a battery having a positive terminal and a negative terminal, a flexible substrate having a plurality of contact terminals that respectively contact the positive terminal and the negative terminal, and a fixing member that fixes the flexible substrate onto the battery, in which the flexible substrate is arranged to cover at least a portion of the battery and is fixed by the fixing member without being joined to the battery.

[0004] Japanese Patent Application Laid-Open No. 2014-022122

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

[0006] Therefore, there is a demand for a battery unit that is highly reliable while being compatible with miniaturization.

[0007] A battery unit according to one embodiment of the present disclosure includes a battery and a wiring unit. The battery has a first electrode terminal and a second electrode terminal. The wiring unit includes a flexible wiring substrate provided with a first connection terminal joined to the first electrode terminal and a second connection terminal joined to the second electrode terminal. At least one of the first connection terminal and the second connection terminal includes a conductive member and a solder layer. The conductive member includes a first surface, a second surface, and a through hole extending from the first surface to the second surface. The solder layer includes a first portion covering at least a portion of the first surface of the conductive member, a second portion covering at least a portion of the second surface of the conductive member, and a connection portion passing through the through hole and connecting the first portion and the second portion.

[0008] According to the battery unit of an embodiment of the present disclosure, high reliability can be achieved while also being able to accommodate miniaturization.

[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.

[0010] FIG. 1A is a perspective view illustrating an example of the overall configuration of a battery unit according to an embodiment of the present disclosure. FIG. 1B is a perspective view illustrating the appearance of a secondary battery shown in FIG. 1A. FIG. 2 is an exploded perspective view illustrating an example of the configuration of the battery unit shown in FIG. 1A. FIG. 3A is a cross-sectional view illustrating an example of the cross-sectional configuration of the battery unit shown in FIG. 1A. FIG. 3B is an enlarged cross-sectional view illustrating an example of the cross-sectional configuration of a portion of the battery unit shown in FIG. 3A. FIG. 3C is an enlarged cross-sectional view illustrating an example of the cross-sectional configuration of a portion of the battery unit shown in FIG. 3A. FIG. 4 is a cross-sectional view illustrating an example of a detailed configuration of the secondary battery shown in FIG. 1A. FIG. 5 is a cross-sectional view illustrating an example of the configuration of a battery element shown in FIG. 4. FIG. 6 is a perspective view illustrating an example of the configuration of an outer can used in a manufacturing process of a secondary battery. FIG. 7 is an exploded perspective view illustrating an example of the configuration of a battery unit according to a first modified example of an embodiment of the present disclosure. FIG. 8A is a perspective view illustrating an example of the overall configuration of a battery unit according to a second modified example of an embodiment of the present disclosure. FIG. 8B is an exploded perspective view illustrating an example of the overall configuration of a battery unit according to a second modified example of an embodiment of the present disclosure. FIG. 9 is a perspective view illustrating an example of the configuration of a battery unit according to a modified example of the present disclosure. FIG. 10 is an exploded perspective view showing an example of the structure of the wiring unit shown in FIG. 9 in an expanded state.

[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. Battery unit 1-1. Configuration 1-2. Operation of secondary battery 1-3. Manufacturing method 1-4. Actions and effects 2. Modified examples

[0012] 1. Battery Unit <1-1. Configuration> Fig. 1A is a perspective view showing an example of the overall configuration of a battery unit according to one embodiment of the present disclosure. As shown in Fig. 1A, this battery unit includes a secondary battery 1 and a wiring unit 2 attached to the secondary battery 1. It is preferable that this battery unit does not include a circuit. The circuit here refers to, for example, a control circuit for controlling the charging operation of the secondary battery 1. However, the battery unit according to the present disclosure is not limited to one that does not include such a control circuit, and may instead include, for example, an electronic component including a control circuit provided in the wiring unit.

[0013] (1-1-1. Configuration of Secondary Battery) The secondary battery described here has a flat, columnar, three-dimensional shape and is called a coin type or button type. As will be described later, this secondary battery has a pair of opposing bottoms and a sidewall portion located between the pair of bottoms, 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] Fig. 1B is a perspective view showing the appearance of the secondary battery 1 shown in Fig. 1A. For convenience, the upper side of the paper in Fig. 1B will be referred to as the upper side of the secondary battery, and the lower side of the paper in Fig. 1B will be referred to as the lower side of the secondary battery.

[0018] As shown in FIG. 1B , the secondary battery 1 described here has a three-dimensional shape in which the height H is smaller than the outer diameter D, i.e., a flat, columnar three-dimensional shape. Here, the three-dimensional shape of the secondary battery 1 is a flat, cylindrical (columnar) shape. In this embodiment, the vertical direction of the paper in FIG. 1B is defined as the height direction Z. Therefore, the height H refers to the dimension of the secondary battery 1 in the height direction Z. Furthermore, the outer diameter D refers to the dimension of the secondary battery 1 in the direction perpendicular to the height direction Z, i.e., in the horizontal plane.

[0019] The dimensions of the secondary battery 1 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.

[0020] The secondary battery 1 has a top surface 1US, a bottom surface 1LS opposite the top surface 1US, and a side surface 1SS connecting the top surface 1US and the bottom surface 1LS. An external terminal 20 serving as a first electrode terminal (positive electrode terminal) is exposed on the top surface 1US. A bottom portion M2 of the outer can 10 serving as a second electrode terminal (negative electrode terminal) is exposed on the bottom surface 1LS. The outer can 10 has a storage portion 11 and a lid portion 12, and extends from the bottom surface 1LS through the side surface 1SS to the outer edge of the top surface 1US. The external terminal 20 is surrounded on the top surface 1US by a peripheral portion 12R (described below) of the lid portion 12, which is part of the outer can 10. The detailed configuration of the secondary battery 1 will be described later.

[0021] 2 is an exploded perspective view showing an example of the configuration of a battery unit according to this embodiment. The battery unit according to this embodiment further includes an insulating sheet 3 between the secondary battery 1 and the wiring unit 2. The insulating sheet 3 is an annular insulating paper with an opening 3K in its central region. The battery unit according to this embodiment may further include an insulating sheet 4 located on the opposite side of the wiring unit 2 from the secondary battery 1, and an insulating sheet 5 located on the opposite side of the wiring unit 2 from the secondary battery 1.

[0022] (1-1-2. Wiring Unit) The wiring unit 2 has a flexible wiring board 21 on which a first connection terminal 31 and a second connection terminal 34 are respectively provided. Fig. 3A shows an example of the cross-sectional configuration of the battery unit. Fig. 3B is an enlarged cross-sectional view of the first connection terminal 31 and its vicinity. Fig. 3C is an enlarged cross-sectional view of the second connection terminal 34 and its vicinity.

[0023] [First Connection Terminal and Second Connection Terminal] The first connection terminal 31 is a conductive member that is disposed opposite the external terminal 20 of the secondary battery 1 and is electrically joined to the external terminal 20. The second connection terminal 34 is disposed opposite the bottom M2 of the outer can 10 that serves as the negative electrode terminal of the secondary battery 1 and is a conductive member that is electrically joined to the bottom M2.

[0024] The first connection terminal 31 is electrically connected to the external terminal 20 by solder. As shown in FIGS. 3A and 3B , the first connection terminal 31 includes a conductive member 32 and a solder layer 33. The conductive member 32 is an annular thin plate or foil made of a conductive material. Specifically, the conductive member 32 may be made of, for example, copper foil. As shown in FIG. 3B , the conductive member 32 includes an upper surface 32U, a lower surface 32L, and an end surface 32T connecting the upper surface 32U and the lower surface 32L. The lower surface 32L faces the upper surface of the external terminal 20. The conductive member 32 includes a through hole 32K in its central region, penetrating from the upper surface 32U to the lower surface 32L. The end surface 32T is the inner wall surface of the through hole 32K. The solder layer 33 is a conductive layer including a first portion 331 covering at least a portion of the upper surface 32U of the conductive member 32, a second portion 332 covering at least a portion of the lower surface 32L of the conductive member 32, and a connection portion 333 connecting the first portion 331 and the second portion 332 through the through hole 32K. The second portion 332 is sandwiched between the lower surface 32L of the conductive member 32 and the upper surface of the external terminal 20 to firmly connect them electrically and mechanically. Here, the external terminal 20 and the first connection terminal 31 are soldered together through the opening 3K in the insulating sheet 3. That is, at least a portion of the opposing region between the external terminal 20 and the first connection terminal 31 overlaps with the opening 3K in the height direction Z.

[0025] The second connection terminal 34 is electrically connected to the bottom M2 of the outer can 10 by solder. As shown in FIGS. 3A and 3C , the second connection terminal 34 includes a conductive member 35 and a solder layer 36. The conductive member 35 is an annular thin plate or foil made of a conductive material. Specifically, the conductive member 35 may be made of, for example, copper foil. As shown in FIG. 3C , the conductive member 35 includes an upper surface 35U, a lower surface 35L, and an end surface 35T connecting the upper surface 35U and the lower surface 35L. The upper surface 35U faces the lower surface of the bottom M2 of the outer can 10, i.e., the lower surface 1LS of the secondary battery 1. The conductive member 35 includes a through-hole 35K in its central region, penetrating from the upper surface 35U to the lower surface 35L. The end surface 35T is the inner wall surface of the through-hole 35K. The solder layer 36 is a conductive layer including a first portion 361 covering at least a portion of the upper surface 35U of the conductive member 35, a second portion 362 covering at least a portion of the lower surface 35L of the conductive member 35, and a connection portion 363 connecting the first portion 361 and the second portion 362 through the through-hole 35K. The first portion 361 is sandwiched between the lower surface of the bottom portion M2 and the upper surface 35U of the conductive member 35, and firmly connects them electrically and mechanically.

[0026] [Flexible Wiring Board] As shown in FIG. 2 , the flexible wiring board 21 has a first support portion 21U, a second support portion 21L, an intermediate portion 21M, and an output terminal portion 21C. The first support portion 21U is a portion that supports the first connection terminal 31. The first support portion 21U is arranged to face the upper surface 1US of the secondary battery 1. The second support portion 21L is a portion that supports the second connection terminal 34. The second support portion 21L is arranged to face the lower surface 1LS of the secondary battery 1. The intermediate portion 21M is a portion that connects the first support portion 21U and the second support portion 21L. The intermediate portion 21M is provided along the side surface 1SS of the secondary battery 1. The output terminal portion 21C has a first output terminal 24 and a second output terminal 27 for outputting the electromotive force of the secondary battery 1 to the outside. In the example of wiring unit 2 shown in Fig. 2, output terminal portion 21C is provided on the opposite side of intermediate portion 21M from first support portion 21U. Note that in Figs. 2A and 2B, flexible wiring board 21 is unfolded so that first support portion 21U, second support portion 21L, intermediate portion 21M, and output terminal portion 21C all extend along the same plane, but in the battery unit according to an embodiment of the present disclosure, the flexible wiring board is bent substantially perpendicularly at the boundary between first support portion 21U and intermediate portion 21M, and is bent substantially perpendicularly at the boundary between second support portion 21L and intermediate portion 21M.

[0027] 2, the flexible wiring board 21 further includes a first wiring W1 extending from the first connection terminal 31 to the first output terminal 24, and a second wiring W2 extending from the second connection terminal 34, passing through the intermediate portion 21M and the first support portion 21U in this order, to the second output terminal 27. The first wiring W1 and the second wiring W2 are printed wiring made of a highly conductive material such as copper. The first wiring W1 and the second wiring W2 are sandwiched between, for example, two flexible insulating films (a first layer F1 and a second layer F2, which will be described later).

[0028] The first support portion 21U has a first insulating member 23 that holds the first connection terminal 31. As shown in FIGS. 3A and 3B , the first insulating member 23 has a laminated structure of a first layer F1 and a second layer F2. A wiring layer 22 including a first wiring W1 and the like is provided between the first layer F1 and the second layer F2. The first layer F1 and the second layer F2 are flexible insulating films such as polyimide films. The outer diameter of the first support portion 21U, particularly the outer diameter of the first insulating member 23, is preferably substantially equal to or slightly smaller than the outer diameter D of the secondary battery 1.

[0029] The intermediate portion 21M is a portion that connects the first support portion 21U and the second support portion 21L. The intermediate portion 21M is integrated with the first support portion 21U and the second support portion 21L and has a laminated structure of a first layer F1 and a second layer F2. A wiring layer 22 including second wiring W2 is disposed between the first layer F1 and the second layer F2. The intermediate portion 21M is provided along the side surface 1SS of the side wall portion M3 of the secondary battery 1.

[0030] The second support portion 21L has a second insulating member 26 that holds the second connection terminal 34. As shown in Figures 3A and 3C, the second insulating member 26 has a laminated structure of a first layer F1 and a second layer F2, similar to the first insulating member 23. A wiring layer 22 including a second wiring W2 is provided between the first layer F1 and the second layer F2. The outer diameter of the second support portion 21L, particularly the outer diameter of the second insulating member 26, is preferably substantially equal to or slightly smaller than the outer diameter D of the secondary battery 1.

[0031] (1-1-3. Detailed Structure of Secondary Battery) Fig. 4 is a cross-sectional view showing a detailed structure example of the secondary battery 1. As shown in Fig. 4, the secondary battery 1 includes an outer can 10, an external terminal 20, a gasket 30, a battery element 40, a positive electrode lead 51, a negative electrode lead 52, a sealant 61, and insulating films 62 and 63.

[0032] [Outer Can] The outer can 10 is a hollow outer casing member that houses the battery element 40 etc. The outer can 10 is made of a conductive material such as metal.

[0033] 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. The exterior can 10 has a pair of bottoms M1 and M2 facing each other and a side wall M3 located between the bottoms M1 and M2. That is, the side wall M3 connects the bottoms M1 and M2 and surrounds the battery element 40. The upper end of the side wall M3 is connected to the bottom M1. The lower end of the side wall M3 is connected to the bottom M2. As described above, since the exterior can 10 is approximately cylindrical, the planar shapes of the bottoms M1 and M2 are each approximately circular, and the surface of the side wall M3 is a convex, curved surface.

[0034] The outer can 10 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.

[0035] The storage section 11 is a flat, cylindrical storage member that stores the battery element 40 and other components therein. The storage section 11 has a hollow structure with an open upper end and a closed lower end. That is, the storage section 11 has an opening 11K at its upper end as an insertion port through which the battery element 40 can be inserted in the height direction Z.

[0036] As shown in FIG. 4 , 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. That is, the lid 12 supports the external terminal 20 via the gasket 30. The external terminal 20 is attached to the lid 12 via the gasket 30 at a position that overlaps the through-hole 12K of the lid 12 in the height direction Z. The external terminal 20 is electrically insulated from the outer can 10.

[0037] As described above, in the completed secondary battery, the lid 12 is welded to the storage portion 11. As described above, the opening 11K is closed by the lid 12. Therefore, even if one looks at the exterior of the secondary battery, it may not be possible to determine whether the storage portion 11 had the opening 11K.

[0038] As described above, in the completed secondary battery, the lid 12 is welded to the storage portion 11. As described above, the opening 11K is closed by the lid 12. Therefore, even if one looks at the exterior of the secondary battery, it may not be possible to determine whether the storage portion 11 had the opening 11K.

[0039] However, if the lid 12 is welded to the storage portion 11, weld marks remain on the surface of the outer can 10, more specifically, on the boundary between the storage portion 11 and the lid 12. Based on the presence or absence of the weld marks, it can be confirmed after the fact whether or not the storage portion 11 had the opening 11K.

[0040] 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.

[0041] 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 exterior 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 exterior 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 toward the inside of the storage section 11 than the surface 12RS of the peripheral section 12R. 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 section 12R and the battery element 40.

[0042] The planar shape of the recess 12H, i.e., the shape defined by the outer edge of the recess 12H when the secondary battery is viewed from above, is not particularly limited. Here, the planar shape of the recess 12H is approximately circular. The inner diameter D12H and depth of the recess 12H are not particularly limited and can be set arbitrarily. However, the depth of the recess 12H is set so that, when the external terminal 20 is attached to the recess 12H via the gasket 30, the height position of the surface 20S of the external terminal 20 is lower than the height position of the surface 12RS of the peripheral portion 12R. Furthermore, the inner diameter D12H of the recess 12H is set to be larger than the outer diameter D20 of the external terminal 20.

[0043] As described above, the outer can 10 is a so-called welded can in which the storage section 11 and the lid section 12, which were previously physically separate, are welded together. As a result, the outer can 10 after welding is a single, physically integrated member, and therefore cannot be separated into the storage section 11 and the lid section 12 later.

[0044] The exterior can 10, which is a welded can, is a so-called crimpless can, which is different from a crimp can formed using a caulking process. This is because the element space volume increases inside the exterior can 10, thereby increasing the energy density per unit volume. This "element space volume" refers to the volume (effective volume) of the internal space of the exterior can 10 that is available for housing the battery element 40.

[0045] 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.

[0046] "Having no overlapping parts" means that the outer can 10 is not processed (folded) so that parts thereof overlap each other. Also, "having no parts where two or more components overlap each other" means that the outer can 10 is physically a single component after the secondary battery is completed, and therefore the outer can 10 cannot be separated into two or more components afterward. In other words, the state of the outer can 10 in the completed secondary battery is not a state in which two or more components are combined while overlapping each other so that they can be separated afterward.

[0047] 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 1 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.

[0048] Specifically, the exterior can 10 is a metal can containing one or more conductive materials such as metal materials and alloy materials. The conductive materials constituting the metal can include iron, copper, nickel, stainless steel, iron alloys, copper alloys, and nickel alloys. The type of stainless steel is not particularly limited, but specific examples include SUS304 and SUS316. However, the materials forming the storage portion 11 and the lid portion 12 may be the same or different.

[0049] 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.

[0050] 1B, 3, and 4, the external terminals 20 are connection terminals that are connected to an electronic device via the wiring unit 2 when the secondary battery 1 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.

[0051] 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 1 is in use, 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 are connected to an electronic device via the wiring unit 2. Therefore, the electronic device can operate using the secondary battery 1 as a power source.

[0052] The external terminal 20 is a flat, approximately plate-like member extending along a horizontal plane perpendicular to the height direction Z of the secondary battery. 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 1 of this embodiment, the planar shape of the external terminal 20 is approximately circular. The external terminal 20 is disposed within the recess 12H via the gasket 30. That is, the external terminal 20 is accommodated within the recess 12H without protruding from the recess 12H in the height direction Z. Therefore, as shown in FIG. 3 , in a cross section taken along the height direction Z, the outer diameter D20 of the external terminal 20 is smaller than the inner diameter D12H of the recess 12H. Similarly, the outer diameter D31 of the first connection terminal 31 of the wiring unit 2 is also smaller than the inner diameter D12H of the recess 12H. Furthermore, the center position of the negative external terminal 20 preferably coincides with the center line PC (described below) of the secondary battery.

[0053] The external terminal 20 is insulated from the lid 12 via a gasket 30. As shown in FIG. 4 , the highest position of the surface 20FS 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 1 of this embodiment, the height of the secondary battery 1 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 1. Furthermore, it is possible to prevent short circuits 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 the 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 back surface 20BS of 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 having 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.

[0054] 2, the outer diameter D20 of the external terminal 20 is smaller than the inner diameter D12H of the recess 12H (D20<D12H), and therefore the outer edge 20T of the external terminal 20 is spaced apart from the lid 12 as shown in FIG. 4. As a result, the gasket 30 is disposed only in a portion of the area between the external terminal 20 and the lid 12 (recess 12H). More specifically, the gasket 30 is disposed only in a location where the external terminal 20 and the lid 12 would come into contact with each other if the gasket 30 were not present. However, 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.

[0055] The external terminal 20 includes one or more conductive materials such as metal materials and alloy materials. The external terminal 20 may be configured with 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).

[0056] [Gasket] As shown in Fig. 2, the gasket 30 is an insulating member disposed between the outer can 10 (lid portion 12) and the external terminal 20. The external terminal 20 is fixed to the lid portion 12 via the gasket 30. The gasket 30 has a ring-shaped planar shape with a through hole at a position corresponding to the through hole 12K. The gasket 30 contains one or more insulating materials such as insulating polymer compounds, and the insulating materials are resins such as polypropylene and polyethylene.

[0057] The installation range of the gasket 30 can be set arbitrarily. Here, the gasket 30 is disposed in the gap between the surface 12HS of the bottom 12HB of the recess 12H and the back surface 20BS of the external terminal 20. However, as described above, the gasket 30 may also be provided between the inner wall surface of the wall 12HW of the recess 12H and the outer edge 20T of the external terminal 20. In addition, the lid 12 and the external terminal 20 may be fixed by the gasket 30.

[0058] [Battery Element] The battery element 40 is a power generating element that causes charge / discharge reactions to proceed, and is housed inside the exterior can 10 as shown in Figures 3 and 4. As shown in Figure 4, 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.

[0059] 4 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 (outer can 10 thereof). In other words, the position P of the center line PC corresponds to the position of the center of the battery element 40.

[0060] The battery element 40 is a so-called electrode winding 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.

[0061] 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.

[0062] 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 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. Therefore, the internal space of the outer can 10 is effectively utilized. As a result, the element space volume increases, and the energy density per unit volume of the secondary battery increases.

[0063] (Positive Electrode) Fig. 5 is a cross-sectional view showing a configuration example of a portion of the battery element 40. The positive electrode 41 is a first electrode used to promote charge / discharge reactions, and includes a positive electrode current collector 41A and a positive electrode active material layer 41B, as shown in Fig. 5.

[0064] The positive electrode current collector 41A has a pair of surfaces on which the positive electrode active material layers 41B are provided. The positive electrode current collector 41A contains a conductive material such as a metal material, and the metal material is aluminum or the like.

[0065] 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.

[0066] 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 of 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 LiNiO 2 , LiCoO 2 and LiMn 2 O 4 Specific examples of the phosphate compound include LiFePO 4 and LiMnPO 4 And so on.

[0067] The positive electrode binder contains one or more of synthetic rubbers and polymeric compounds. The synthetic rubber is styrene-butadiene rubber, and the polymeric compound is polyvinylidene fluoride. The positive electrode conductor contains one or more of conductive materials such as carbon materials, and the carbon materials include graphite, carbon black, acetylene black, and ketjen black. However, the conductive material may also be a metal material or a polymeric compound.

[0068] (Negative Electrode) The negative electrode 42 is a second electrode used to promote charge / discharge reactions, and includes a negative electrode current collector 42A and a negative electrode active material layer 42B, as shown in FIG.

[0069] 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.

[0070] The anode active material layer 42B is provided on both sides of the anode current collector 42A and contains one or more anode active materials capable of absorbing and releasing lithium. However, the anode active material layer 42B may be provided on only one side of the anode current collector 42A. The anode active material layer 42B may further contain an anode binder, an anode conductor, and the like. Details regarding the anode binder and the anode conductor are the same as those regarding the positive electrode binder and the positive electrode conductor, respectively. The method for forming the anode active material layer 42B is not particularly limited, but may be one or more of a coating method, a vapor phase method, a liquid phase method, a thermal spraying method, and a firing method (sintering method).

[0071] The negative electrode active material contains one or both of a carbon material and a metal-based material. This is because a high energy density can be obtained. Carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite (natural graphite and artificial graphite). The metal-based material is a material containing, as a constituent element, one or more of metal elements and metalloid elements that can form an alloy with lithium, and the metal element and metalloid element are one or both of silicon and tin, for example. However, the metal-based material may be a simple substance, an alloy, a compound, a mixture of two or more of these, or a material containing two or more of these phases. Specific examples of metal-based materials include TiSi 2 and SiO x (0<x≦2, or 0.2<x<1.4), etc.

[0072] 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. 1B and 2. The definition of height described here will also be applied hereinafter.

[0073] 4 and 5, 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.

[0074] 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.

[0075] (Electrolyte) The electrolyte is impregnated into each of the positive electrode 41, the negative electrode 42, and the separator 43, and contains a solvent and an electrolyte salt. The solvent contains one or more of non-aqueous solvents (organic solvents) such as carbonate ester compounds, carboxylic acid ester compounds, and lactone compounds, and the electrolyte containing the non-aqueous solvent is a so-called non-aqueous electrolyte. The electrolyte salt contains one or more of light metal salts such as lithium salts.

[0076] [Positive Electrode Lead] As shown in Fig. 4 , the positive electrode lead 51 is housed inside the exterior can 10. The positive electrode lead 51 is a connecting wire connected to each of the positive electrode 41 and the external terminal 20. The secondary battery shown in Fig. 2 includes one positive electrode lead 51. However, the secondary battery may include two or more positive electrode leads 51.

[0077] 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 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 will also apply hereinafter.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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 recess is formed in the upper end portion of the separator 43 due to the pressing of the positive electrode lead 51. A part or all of the positive electrode lead 51 is accommodated inside the recess, 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] Furthermore, an insulating film may also be disposed between the battery element 40 and the positive electrode lead 51 .

[0089] The details regarding the material for forming the positive electrode lead 51 are the same as the details regarding the material for forming the positive electrode current collector 41 A. However, the materials for forming the positive electrode lead 51 and the positive electrode current collector 41 A may be the same as or different from each other.

[0090] 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. 4 . 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. 4 . 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 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.

[0091] Here, as is clear from FIG. 4 , when the battery element 40 is divided into two regions with the center line PC as a reference 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. 4 , 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. 4 , 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. 4 . In other words, 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 when the battery element 40 is divided into two regions with the center line PC as a reference in the direction along the outer diameter D.

[0092] The connection position of the positive electrode lead 51 to the positive electrode 41 is not particularly limited and can be set arbitrarily. In particular, the positive electrode lead 51 is preferably connected to the positive electrode 41 at a position more inward than the outermost periphery of the positive electrode 41. This is because, unlike when the positive electrode lead 51 is connected to the positive electrode 41 at the outermost periphery of the positive electrode 41, corrosion of the outer can 10 due to creeping up of the electrolyte is prevented. This "creeping up of the electrolyte" refers to the electrolyte in the battery element 40 creeping up the positive electrode lead 51 and reaching the inner wall surface of the outer can 10 when the positive electrode lead 51 is disposed close to the inner wall surface of the outer can 10. When the electrolyte comes into contact with the outer can 10 due to "creeping up of the electrolyte," a phenomenon occurs in which the outer can 10 dissolves or discolors.

[0093] 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. This "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 without bending, like the folded back portion 513. Furthermore, while FIG. 4 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.

[0094] The positive electrode lead 51 is folded back at a folded 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 viewed 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.

[0095] As a result, as will be described later, when the outer can 10 is formed using the housing 11 and the lid 12 in the manufacturing process of the secondary battery, there is a margin for changing the attitude of the lid 12 relative to the housing 11. Furthermore, 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, it is possible to arbitrarily change the connection position of the positive electrode lead 51 relative to the positive electrode 41 without changing the length of the positive electrode lead 51.

[0096] 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.

[0097] 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 preferably sufficiently narrow so that a length margin of 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 of the positive electrode lead 51 becomes sufficiently large.

[0098] 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.

[0099] [Negative Electrode Lead] As shown in Fig. 4 , 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] [Sealant] As shown in Fig. 4 , the sealant 61 is a first insulating member that covers the periphery of the positive electrode lead 51, and is formed by attaching two pieces of insulating tape to the front and back surfaces of the positive electrode lead 51. Here, the sealant 61 covers the periphery of the middle portion of the positive electrode lead 51 in order to connect the positive electrode lead 51 to the positive electrode 41 and the external terminal 20, respectively. Note that the sealant 61 is not limited to having a tape-like structure, and may have, for example, a tube-like structure.

[0105] The sealant 61 contains one or more insulating materials such as insulating polymer compounds, and the insulating material is polyimide or the like.

[0106] 4, 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.

[0107] 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.

[0108] 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.

[0109] 4, 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.

[0110] 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.

[0111] [Others] The secondary battery 1 may further include one or more other components.

[0112] Specifically, the secondary battery 1 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 1 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.

[0113] The secondary battery 1 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 as desired.

[0114] 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.

[0115] <1-2. Operation> When the secondary battery 1 is charged, lithium is released from the positive electrode 41 in the battery element 40 and is absorbed into 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 into the positive electrode 41 via the electrolyte. During these charge and discharge cycles, lithium is absorbed and released in an ionic state.

[0116] <1-3. Manufacturing Method> Next, a method for manufacturing the battery unit will be described.

[0117] (1-3-1. Method for Manufacturing Secondary Battery) First, a description will be given of a method for manufacturing the secondary battery 1. Fig. 6 shows a perspective view of the exterior can 10 used in the manufacturing process of the secondary battery 1, and corresponds to Fig. 1B.

[0118] 6 shows a 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 description, reference will be made to the already described FIGS. 1A to 5 as well as FIG. 6.

[0119] Here, to form the outer can 10, a storage section 11 and a lid section 12 that are physically separated from each other are prepared as shown in FIG. 6 . 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 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 inner side of the side wall section 11W. For example, the protrusion 11P may be formed integrally with the side wall section 11W. Alternatively, the protrusion 11P may be formed separately from the side wall section 11W and attached to the inner side of the side wall section 11W.

[0120] The lid 12 is a substantially plate-shaped member that corresponds to the bottom M1, and as will be described later, the external terminals 20 are attached in advance to the underside of the lid 12 via a gasket 30 (not shown in FIG. 6).

[0121] [Fabrication of Positive Electrode] First, a positive electrode mixture is prepared by mixing a positive electrode active material, a positive electrode binder, a positive electrode conductive agent, and the like. Next, the prepared positive electrode mixture is poured into an organic solvent or the like to prepare a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry is applied to both sides of the positive electrode current collector 41A to form the positive electrode active material layer 41B. Finally, the positive electrode active material layer 41B is compression-molded using a roll press or the like. In this case, the positive electrode active material layer 41B may be heated, or the compression molding may be repeated multiple times. In this manner, the positive electrode 41 is fabricated.

[0122] [Fabrication of Negative Electrode] The negative electrode 42 is fabricated using a procedure similar to that for fabricating the positive electrode 41. Specifically, after preparing a 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, and the like, 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 to form a negative electrode active material layer 42B. The negative electrode active material layer 42B is then compression-molded using a roll press or the like. This completes the fabrication of the negative electrode 42.

[0123] [Preparation of Electrolyte Solution] An electrolyte salt is added to a solvent, whereby the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing an electrolyte solution.

[0124] [Assembly of Secondary Battery] First, using a welding method such as resistance welding, the positive electrode lead 51, the periphery of which is covered with the sealant 61, is connected to the positive electrode 41 (positive electrode current collector 41A), and the negative electrode lead 52 is connected to the negative electrode 42 (negative electrode current collector 42A).

[0125] Next, the positive electrode 41 and the negative electrode 42 are stacked with the separator 43 interposed therebetween, and the stack including the positive electrode 41, the negative electrode 42, and the separator 43 is wound to produce a wound body 40Z as shown in Fig. 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.

[0126] 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. At this time, the wound body 40Z is accommodated in the space below the convex portion 11P, i.e., 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 accommodation section 11 using a welding method such as resistance welding. Next, an insulating film 63 is placed on the wound body 40Z.

[0127] Next, after preparing the lid portion 12 to which the external terminal 20 is attached via the gasket 30 and on which the insulating film 62 is already provided, the positive electrode lead 51 is connected to the external terminal 20 via the through hole 12K using a welding method such as resistance welding.

[0128] 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.

[0129] Next, the electrolyte solution is injected into the storage portion 11 through the opening 11K. In this case, even if the battery element 40 and the external terminal 20 are connected to each other via the positive electrode lead 51 as described above, the lid portion 12 does not close the opening 11K, so the electrolyte solution can be easily injected into the storage portion 11 through the opening 11K. As a result, the wound body 40Z including the positive electrode 41, the negative electrode 42, and the separator 43 is impregnated with the electrolyte solution, and the battery element 40, which is a wound electrode body, is produced.

[0130] 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 1.

[0131] [Stabilization of Secondary Battery] The assembled secondary battery 1 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 causes a coating to form on the surface of the negative electrode 42, etc., which electrochemically stabilizes the state of the secondary battery 1. Thus, the secondary battery 1 is completed.

[0132] (1-3-2. Method for Manufacturing the Wiring Unit) Next, a method for manufacturing the wiring unit 2 will be described with reference to FIG. 2 and FIGS. 3A to 3C.

[0133] First, the flexible wiring board 21 is fabricated. Specifically, two sheets of flexible insulating film are punched into a predetermined shape to obtain the first layer F1 and the second layer F2. Next, a conductive member 32 is attached to the area of ​​the second layer F2 that will become the first insulating member 23, and a conductive member 35 is attached to the area of ​​the second layer F2 that will become the second insulating member 26. Furthermore, the first wiring W1 and the second wiring W2 are formed in predetermined areas of the second layer F2 by printing or the like. The first layer F1 is then superimposed on the second layer F2 so that the conductive member 32, the conductive member 35, the first wiring W1, and the second wiring W2 are sandwiched between the first layer F1 and the second layer F2. Furthermore, a first output terminal 24 to which the first wiring W1 is connected and a second output terminal 27 to which the second wiring W2 is connected are formed at the ends of the second layer F2.

[0134] Next, a solder layer 33 is applied to the upper surface 32U and the lower surface 32L of the conductive member 32, and a solder layer 36 is applied to the upper surface 35U and the lower surface 35L of the conductive member 35.

[0135] Through the above operations, the wiring unit 2 is completed.

[0136] (1-3-3. Manufacturing Method of Battery Unit) Next, the first connection terminal 31 of the wiring unit 2 is brought into contact with the surface 20FS of the external terminal 20 of the secondary battery 1, and then the solder layer 33 is melted to electrically and mechanically solder-join the first connection terminal 31 and the external terminal 20. Furthermore, the second connection terminal 34 of the wiring unit 2 is brought into contact with the underside 1LS of the bottom M2 of the exterior can 10 of the secondary battery 1, and then the solder layer 36 is melted to electrically and mechanically solder-join the second connection terminal 34 and the underside 1LS of the bottom M2.

[0137] Through the above operations, the battery unit according to one embodiment of the present disclosure is completed.

[0138] <1-4. Actions and Effects> As described above, in the battery unit according to one embodiment of the present disclosure, the wiring unit 2 is provided in the secondary battery 1, and therefore the flexible wiring board 21 in the wiring unit 2 can electrically connect the external terminal 20 serving as the positive electrode terminal of the secondary battery 1 and the outer casing 10 serving as the negative electrode terminal to an external device. Here, the flexible wiring board 21 is employed, which has a structure in which the first wiring W1 and the second wiring W2 are sandwiched between the first layer F1 and the second layer F2, which are two flexible insulating films. This makes it possible to avoid electrical short circuits between the positive electrode 41 and the negative electrode 42, while realizing a wiring layout with a relatively high degree of freedom.

[0139] Furthermore, in the battery unit according to an embodiment of the present disclosure, the first connection terminal 31 is solder-joined to the external terminal 20 by a solder layer 33. The solder layer 33 has an integrated structure including a first portion 331, a second portion 332, and a connecting portion 333 that are continuous from the upper surface 32U of the conductive member 32, past the end surface 32T, to the lower surface 32L. This allows the wiring unit 2 to be thin, yet provide a strong electrical and mechanical connection between the first connection terminal 31 and the external terminal 20. Similarly, the solder layer 36 that solder-joins the second connection terminal 34 to the bottom portion M2 of the outer can 10 has an integrated structure including a first portion 361, a second portion 362, and a connecting portion 363 that are continuous from the upper surface 35U of the conductive member 35, past the end surface 35T, to the lower surface 35L. This allows the wiring unit 2 to be thin, yet provide a strong electrical and mechanical connection between the second connection terminal 34 and the bottom portion M2. This prevents poor connections between the first connection terminal 31 and the external terminal 20 and between the second connection terminal 34 and the bottom portion M2 due to external factors such as shocks or vibrations applied from outside the battery unit. Furthermore, because the battery unit of this embodiment does not include circuits in the wiring unit 2, there is no need to consider the effects on circuits of heat generated during soldering. Therefore, the battery unit of this embodiment can be made compact while achieving high reliability.

[0140] 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.

[0141] Specifically, the layout of the flexible wiring board of the wiring unit is not limited to the flexible wiring board 21 described in the above embodiment. FIG. 7 is an exploded perspective view illustrating a battery unit 100A according to a first modified example of an embodiment of the present disclosure. The battery unit 100A of FIG. 7 includes a wiring unit 2A. The wiring unit 2A includes a flexible wiring board 21A. Similar to the flexible wiring board 21 shown in FIG. 2 , the flexible wiring board 21A includes a first support portion 21U, a second support portion 21L, an intermediate portion 21M, and an output terminal portion 21C. However, in the flexible wiring board 21A, the intermediate portion 21M includes a connecting portion 28 connecting the first support portion 21U and the second support portion 21L, and a lead-out portion 29 branching from the connecting portion 28. The output terminal portion 21C is provided at the end of the lead-out portion 29 opposite the connecting portion 28. The connecting portion 28 and the lead-out portion 29 are integrated and have a laminated structure of a first layer F1 and a second layer F2, similar to the first insulating member 23. The connecting portion 28 and the lead-out portion 29 are provided with a first wiring W1 and a second wiring W2 sandwiched between the first layer F1 and the second layer F2. In the example of the wiring unit 2A shown in FIG. 7 , the first wiring W1 extends from the first connection terminal 31 via the connecting portion 28 and the lead-out portion 29 to the first output terminal 24. The second wiring W2 extends from the second connection terminal 34 via the connecting portion 28 and the lead-out portion 29 to the second output terminal 27.

[0142] Furthermore, in the battery unit 100 of the above embodiment, the first connection terminal 31 of the wiring unit 2 is joined to the upper surface 1US of the secondary battery 1, and the second connection terminal 34 of the wiring unit 2 is joined to the lower surface 1LS of the secondary battery 1. However, the present disclosure is not limited to this. For example, as shown in FIGS. 8A and 8B , as in a battery unit 100B of a second modified embodiment of the present disclosure, the first connection terminal 31 of the wiring unit 2B may be joined to the upper surface 1US of the secondary battery 1, and the second connection terminal 34 of the wiring unit 2B may be joined to the side surface 1SS of the secondary battery 1. Even in this case, the battery unit 100B can achieve the same effects as the battery unit 100 of the above embodiment. Note that FIG. 8A is a perspective view illustrating an example of the overall configuration of a battery unit 100B as a second modified embodiment of the present disclosure. FIG. 8B is an exploded perspective view illustrating an example of the overall configuration of the battery unit 100B. The battery unit 100B includes a wiring unit 2B. The wiring unit 2B has a flexible wiring board 21B including, for example, a substantially L-shaped stem portion 25. A second connection terminal 34 is provided at a first end of the stem portion 25, and an output terminal portion 21C is provided at a second end of the stem portion 25. A first insulating member 23 is connected via a connecting portion 28 to the region of the stem portion 25 between the second connection terminal 34 and the output terminal portion 21C. The first insulating member 23 supports a first connection terminal 31. The wiring unit 2B is configured such that the boundary between the first insulating member 23 and the connecting portion 28 and the boundary between the connecting portion 28 and the stem portion 25 are each bent substantially perpendicularly, so that the first connection terminal 31 faces the top surface 1US of the secondary battery 1 and the second connection terminal 34 faces the side surface 1SS of the secondary battery 1.

[0143] In addition, in the battery unit of the above embodiment, the outer can 10 is described as a welded can (crimpless can), but the configuration of the outer can is not particularly limited, and it may be a crimped can that is crimped. In this crimped can, the storage section and the lid section, which are separated from each other, are crimped together via a gasket.

[0144] 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.

[0145] Furthermore, while the battery unit of the above embodiment has been described as including a secondary battery as the battery, the present disclosure is not limited thereto and may include a primary battery. Fig. 9 is a perspective view showing an example configuration of a battery unit 100C as a modified example of the present disclosure, which includes a primary battery 9 instead of the secondary battery 1. The battery unit of the above embodiment includes a secondary battery 1 and a wiring unit 2 having a flexible wiring board 21 on which a first connection terminal 31 and a second connection terminal 34 are respectively provided. In contrast, the battery unit 100C of Fig. 9 includes a wiring unit 90 instead of the wiring unit 2.

[0146] 10 is an exploded perspective view showing an example of the configuration of the wiring unit 90 shown in FIG. 9 in an unfolded state. The wiring unit 90 has a flexible wiring board 91 provided with, for example, a first connection terminal 81 and a second connection terminal 84. The first connection terminal 81 is disposed opposite the positive terminal 9A of the primary battery 9 and is a conductive member electrically joined to the positive terminal 9A by soldering or the like. The second connection terminal 84 is disposed opposite the bottom surface 9B of the outer can serving as the negative terminal of the primary battery 9 and is a conductive member electrically joined to the bottom surface 9B of the outer can by soldering or the like. The flexible wiring board 91 has a first support portion 91U, a second support portion 91L, an intermediate portion 91M, and an output terminal portion 91C.

[0147] The first support portion 91U is a portion that supports the first connection terminal 81. The first support portion 91U is provided so as to face the positive electrode terminal 9A exposed on the surface of the primary battery 9. The second support portion 91L is a portion that supports the second connection terminal 84. The second support portion 91L is provided so as to face the bottom surface 9B of the primary battery 9. The intermediate portion 91M is a portion that connects the first support portion 91U and the second support portion 91L. The intermediate portion 91M is provided along the side surface of the primary battery 9. Note that in FIG. 10 , the flexible wiring board 91 is unfolded so that the first support portion 91U, the second support portion 91L, and the intermediate portion 91M all extend along the same plane. However, in the battery unit 100C, the flexible wiring board 91 is bent substantially vertically at the boundary between the first support portion 91U and the intermediate portion 91M, and is also bent substantially vertically at the boundary between the second support portion 91L and the intermediate portion 91M. The primary battery 9 has a height H1 that is shorter than the height H of the secondary battery 1. Therefore, in the battery unit 100C that includes the primary battery 9, the length of the intermediate portion 91M of the flexible wiring board 91 is shorter than the length of the intermediate portion 21M of the flexible wiring board 21 (FIG. 2).

[0148] 10 , the flexible wiring board 91 further includes a first wiring W1 extending from the first connection terminal 81 through the intermediate portion 91M and the second support portion 91L to the first output terminal 97, and a second wiring W2 extending from the second connection terminal 84 to the second output terminal 94. The first wiring W1 and the second wiring W2 are printed wiring made of a highly conductive material such as copper. The first wiring W1 and the second wiring W2 are sandwiched between, for example, two flexible insulating films (e.g., polyimide films).

[0149] The first support portion 91U has a first insulating member 93 that holds the first connection terminal 81. The middle portion 91M is a portion that connects the first support portion 91U and the second support portion 91L. The middle portion 91M is integrated with the first support portion 91U and the second support portion 91L. The middle portion 91M is provided along the side surface of the secondary battery 1. The second support portion 91L has a second insulating member 96 that holds the second connection terminal 84.

[0150] In the battery unit 100C shown in FIGS. 9 and 10, the electromotive force of the primary battery 9 can be extracted from the output terminal portion 91C.

[0151] 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.

[0152] The present disclosure may further take the following forms. <1> A battery unit comprising: a battery having a first electrode terminal and a second electrode terminal; and a wiring unit having a flexible wiring substrate on which a first connection terminal joined to the first electrode terminal and a second connection terminal joined to the second electrode terminal are respectively provided, wherein at least one of the first connection terminal and the second connection terminal has a conductive member and a solder layer, the conductive member includes a first surface, a second surface, and a through hole penetrating from the first surface to the second surface, and the solder layer includes a first portion covering at least a portion of the first surface of the conductive member, a second portion covering at least a portion of the second surface of the conductive member, and a connection portion passing through the through hole and connecting the first portion and the second portion. <2> The battery unit according to <1> above, wherein the battery includes: an external terminal as the first electrode terminal; and an outer can as the second electrode terminal, the outer can including a bottom portion facing the external terminal and a sidewall portion standing along an outer edge of the bottom. <3> The battery unit according to <2> above, further comprising an insulating layer provided between the external terminal and the wiring unit, wherein the external terminal is surrounded by an upper end of the side wall portion, the insulating layer includes an opening, and the external terminal and the first connection terminal are solder-bonded via the opening. <4> The battery unit according to any one of <1> to <3> above, wherein the flexible wiring board includes: a first support portion that supports the first connection terminal, a second support portion that supports the second connection terminal, an intermediate portion that connects the first support portion and the second support portion, a first wiring that extends from the first connection terminal to the intermediate portion via the intermediate portion, and a second wiring that extends from the second connection terminal to the intermediate portion via the intermediate portion. <5> The battery unit according to any one of <1> to <4> above, wherein the battery has a lid portion that holds the first electrode terminal, and a housing member serving as the second electrode terminal, the housing member including a bottom portion that faces the lid portion and a side wall portion that stands along an outer edge of the bottom portion, and the intermediate portion is provided along the side wall portion of the battery.<6> A battery wiring unit attachable to a battery having a first electrode terminal and a second electrode terminal, the battery unit having a flexible wiring board including a first connection terminal joined to the first electrode terminal and a second connection terminal joined to the second electrode terminal, at least one of the first connection terminal and the second connection terminal having a conductive member and a solder layer, the conductive member including a first surface, a second surface, and a through hole penetrating from the first surface to the second surface, the solder layer including a first portion covering at least a portion of the first surface of the conductive member, a second portion covering at least a portion of the second surface of the conductive member, and a connection portion passing through the through hole and connecting the first portion and the second portion.

Claims

1. A battery having a first electrode terminal and a second electrode terminal, a flexible wiring board, a first connection terminal provided on the flexible wiring board and joined to the first electrode terminal, and a second connection terminal provided on the flexible wiring board and joined to the second electrode terminal, and at least one of the first connection terminal and the second connection terminal has a conductive member and a solder layer, the conductive member includes a first surface, a second surface, and a through hole penetrating from the first surface toward the second surface, the solder layer includes a first portion covering at least a part of the first surface of the conductive member, a second portion covering at least a part of the second surface of the conductive member, and a connection portion connecting the first portion and the second portion through the through hole a battery unit.

2. The battery has an external terminal as the first electrode terminal and an exterior can as the second electrode terminal including a bottom portion facing the external terminal and a side wall portion standing along an outer edge of the bottom portion. The battery unit according to claim 1.

3. The battery unit further includes an insulating layer provided between the external terminal and the wiring unit, the external terminal is surrounded by an upper end portion of the side wall portion, the insulating layer includes an opening, and the external terminal and the first connection terminal are solder-joined through the opening. The battery unit according to claim 2.

4. The flexible wiring board has a first support portion supporting the first connection terminal, a second support portion supporting the second connection terminal, an intermediate portion connecting the first support portion and the second support portion, an output terminal portion having a first output terminal and a second output terminal, a first wiring extending from the first connection terminal through the intermediate portion to the first output terminal, and a second wiring extending from the second connection terminal through the intermediate portion and the first support portion in sequence to the second output terminal. The battery unit according to any one of claims 1 to 3.

5. The battery has a lid portion holding the first electrode terminal and a housing member as the second electrode terminal including a bottom portion facing the lid portion and a side wall portion standing along an outer edge of the bottom portion, and the intermediate portion is provided along the side wall portion of the battery. The battery unit according to claim 4.

6. A battery wiring unit attachable to a battery having a first electrode terminal and a second electrode terminal, the battery wiring unit including a flexible wiring board ​ A first connection terminal provided on the flexible wiring board and joined to the first electrode terminal, A second connection terminal provided on the flexible wiring board and joined to the second electrode terminal and having, A flexible wiring board including a first connection terminal joined to the first electrode terminal and a second connection terminal joined to the second electrode terminal, At least one of the first connection terminal and the second connection terminal has a conductive member and a solder layer, The conductive member includes a first surface, a second surface, and a through hole penetrating from the first surface toward the second surface, The solder layer includes a first portion covering at least a part of the first surface of the conductive member, a second portion covering at least a part of the second surface of the conductive member, and a connection portion connecting the first portion and the second portion through the through hole Wiring unit for a battery.