Secondary battery and battery pack

Abstract

A secondary battery with improved performance is provided. The secondary battery is provided with an electrode wound body, a first electrode current-collecting plate, a second electrode current-collecting plate, an electrolyte solution, and a battery can. The electrode wound body has a first end face and a second end face. The first electrode current-collecting plate is disposed to face the first end face. The second electrode current-collecting plate is disposed to face the second end face. The first electrode comprises: a first electrode coating portion in which the first electrode current collector is coated with a first electrode active material layer; and a first electrode exposed portion in which the first electrode current collector is not coated with the first electrode active material layer and is exposed, the first electrode exposed portion being bonded to the first electrode current-collecting plate and being located adjacent to the first electrode coating portion in a first direction. The number of bent portions of the first electrode current collector of the first electrode exposed portion in a central axis-side portion of the electrode wound body is greater than the number of bent portions of the first electrode current collector of the first electrode exposed portion in an outer peripheral-side portion of the electrode wound body.

Description

Secondary batteries, battery packs

[0001] The present disclosure relates to a secondary battery and a battery pack including the same.

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

[0003] Patent Document 1 proposes a secondary battery in which the electrode foil and the current collector plate are reliably welded to reduce internal resistance or achieve high output.

[0004] International Publication No. 2021 / 020237

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

[0006] Therefore, a secondary battery with better performance is desired.

[0007] A secondary battery and a battery pack according to an embodiment of the present disclosure include an electrode winding, a first electrode current collector, a second electrode current collector, an electrolyte, and a battery can. The electrode winding is formed by winding a laminate including a first electrode, a first separator, a second electrode, and a second separator in that order around a central axis extending in a first direction, and has a first end face and a second end face facing each other in the first direction. The first electrode current collector is disposed so as to face the first end face of the electrode winding. The second electrode current collector is disposed so as to face the second end face of the electrode winding. The battery can accommodates the electrode winding, the first electrode current collector, the second electrode current collector, and the electrolyte. The first electrode has a first electrode covered portion in which a first electrode current collector is covered with a first electrode active material layer, and a first electrode exposed portion in which the first electrode current collector is exposed without being covered with the first electrode active material layer and joined to the first electrode current collector plate, and adjacent to the first electrode covered portion in the first direction, wherein the number of bending points of the first electrode current collector of the first electrode exposed portion in the central axis side portion of the electrode winding is greater than the number of bending points of the first electrode current collector of the first electrode exposed portion in the outer circumferential side portion of the electrode winding.

[0008] In a secondary battery and a battery pack according to an embodiment of the present disclosure, the number of bends of the first electrode current collector in the first electrode exposed portion in the central axis side portion of the electrode winding is greater than the number of bends of the first electrode current collector in the first electrode exposed portion in the outer peripheral side portion of the electrode winding. This facilitates impregnation of the outer peripheral side portion of the electrode winding with electrolyte, making it less likely that elution of metal ions or deposition of metallic lithium will occur due to a local increase in the potential of the first electrode in the outer peripheral side portion of the electrode winding. As a result, internal short circuits between the first electrode and the second electrode can be prevented during high-temperature storage. Furthermore, excessive electrolyte impregnation in the central axis side portion of the electrode winding can be avoided, thereby mitigating deterioration of cycle characteristics. This results in higher reliability.

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

[0010] FIG. 1 is a cross-sectional view illustrating a configuration of a secondary battery according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram illustrating an example configuration of a laminate including the positive electrode, the negative electrode, and the separator illustrated in FIG. 1 . FIG. 3 is a cross-sectional view illustrating an example configuration of a cross-sectional structure of the electrode winding body illustrated in FIG. 1 . FIG. 4A is a developed view of the positive electrode illustrated in FIG. 1 . FIG. 4B is a cross-sectional view of the positive electrode illustrated in FIG. 1 . FIG. 5A is a developed view of the negative electrode illustrated in FIG. 1 . FIG. 5B is a cross-sectional view of the negative electrode illustrated in FIG. 1 . FIG. 6A is an enlarged cross-sectional view schematically illustrating an upper portion of the secondary battery illustrated in FIG. 1 . FIG. 6B is an enlarged cross-sectional view schematically illustrating a lower portion of the secondary battery illustrated in FIG. 1 . FIG. 7A is a plan view of a positive electrode current collector illustrated in FIG. 1 . FIG. 7B is a plan view of a negative electrode current collector illustrated in FIG. 1 . FIG. 8 is a perspective view illustrating a manufacturing process of the secondary battery illustrated in FIG. 1 . FIG. 9 is a block diagram illustrating a circuit configuration of a battery pack to which the secondary battery according to an embodiment of the present disclosure is applied.

[0011] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. The description will be made in the following order: 1. Secondary battery 1-1. Configuration 1-2. Operation 1-3. Manufacturing method 1-4. Actions and effects 2. Application examples 2-1. Battery pack 2-2. Power storage system

[0012] 1. Secondary Battery First, a secondary battery having a positive electrode according to an embodiment of the present disclosure will be described.

[0013] In this embodiment, a cylindrical lithium-ion secondary battery having a cylindrical external shape will be described as an example. However, the secondary battery of the present disclosure is not limited to a cylindrical lithium-ion secondary battery, and may be a lithium-ion secondary battery having an external shape other than a cylindrical shape, or may be a battery using an electrode reactant other than lithium.

[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 as described above, but specifically includes light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, and alkaline earth metals include beryllium, magnesium, and calcium.

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

[0017] [1-1. Configuration] (Lithium-ion secondary battery 1) Fig. 1 shows a cross-sectional configuration along the height direction of a lithium-ion secondary battery 1 (hereinafter simply referred to as secondary battery 1) according to the present embodiment. In the secondary battery 1 shown in Fig. 1, an electrode winding body 20 serving as a battery element is housed inside a cylindrical outer can 11.

[0018] Specifically, the secondary battery 1 includes, for example, a pair of insulating plates 12, 13, an electrode winding body 20, a positive electrode current collector 24, and a negative electrode current collector 25 inside an outer can 11. The electrode winding body 20 is a structure in which, for example, a positive electrode 21 and a negative electrode 22 are stacked and wound with a separator 23 interposed therebetween. The electrode winding body 20 is impregnated with an electrolytic solution, which is a liquid electrolyte. The secondary battery 1 may further include, inside the outer can 11, one or more of a positive temperature coefficient (PTC) element and a reinforcing member.

[0019] (External Can 11) The external can 11 has, for example, a hollow cylindrical structure with a closed lower end and an open upper end in the Z-axis direction (height direction). Therefore, the upper end of the external can 11 is an open end 11N. The constituent material of the external can 11 includes, for example, a metal material such as iron. However, the surface of the external can 11 may be plated with a metal material such as nickel. The insulating plates 12 and 13 are disposed, for example, facing each other in the Z-axis direction with the electrode winding body 20 sandwiched between them. Note that in this specification, the open end 11N and its vicinity in the Z-axis direction may be referred to as the upper part of the secondary battery 1, and the closed portion of the external can 11 and its vicinity may be referred to as the lower part of the secondary battery 1.

[0020] (Insulating Plates 12, 13) Each of the insulating plates 12, 13 is, for example, a dish-shaped plate having a surface perpendicular to the central axis CL of the electrode winding body 20, i.e., a surface perpendicular to the Z-axis in Fig. 1. The insulating plates 12, 13 are arranged so as to sandwich the electrode winding body 20 therebetween.

[0021] (Crimped structure 11R) At the open end 11N of the exterior can 11, for example, a structure in which the battery lid 14 and the safety valve mechanism 30 are crimped via a gasket 15, i.e., a crimped structure 11R, is formed. The battery lid 14 seals the exterior can 11 with the electrode wound body 20 and the like housed inside the exterior can 11. The crimped structure 11R is a so-called crimped structure and has a bent portion 11P as a so-called crimp portion.

[0022] (Battery lid 14) The battery lid 14 is a closing member that mainly closes the open end 11N when the electrode winding body 20 and the like are housed inside the exterior can 11. The battery lid 14 contains, for example, the same material as the material from which the exterior can 11 is formed. For example, the central region of the battery lid 14 protrudes upward (in the +Z direction). As a result, the peripheral region of the battery lid 14 other than the central region is in contact with, for example, the safety valve mechanism 30.

[0023] (Gasket 15) The gasket 15 is a sealing member interposed primarily between the folded portion 11P of the outer can 11 and the battery lid 14. The gasket 15 seals the gap between the folded portion 11P and the battery lid 14. However, the surface of the gasket 15 may be coated with, for example, asphalt. The gasket 15 contains, for example, one or more insulating materials. The type of insulating material is not particularly limited, but examples include polymeric materials such as polybutylene terephthalate (PBT) and polypropylene (PP). Among these, polybutylene terephthalate is preferred as the insulating material. This is because the gap between the folded portion 11P and the battery lid 14 is sufficiently sealed while electrically isolating the outer can 11 and the battery lid 14 from each other.

[0024] (Safety valve mechanism 30) The safety valve mechanism 30 is mainly configured to release the internal pressure of the outer can 11 by releasing the sealed state of the outer can 11 as necessary when the pressure inside the outer can 11 (internal pressure) increases. The internal pressure of the outer can 11 may increase, for example, due to gas generated by a decomposition reaction of the electrolyte during charging and discharging. The internal pressure of the outer can 11 may also increase due to external heating.

[0025] (Electrode Wound Body 20) The electrode wound body 20 is a power generating element that causes charge / discharge reactions to proceed, and is housed inside the outer can 11. The electrode wound body 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolytic solution that is a liquid electrolyte.

[0026] FIG. 2 is a developed view of the electrode winding body 20, and schematically illustrates a portion of a laminate S20 including a positive electrode 21, a negative electrode 22, and a separator 23. FIG. 2 particularly illustrates the vicinity of the end of the innermost circumferential portion of the electrode winding body 20. In the laminate S20 obtained by developing the electrode winding body 20, the positive electrode 21 and the negative electrode 22 are stacked together with the separator 23 interposed therebetween. The separator 23 has, for example, two base materials, i.e., a first separator member 23A and a second separator member 23B. Therefore, the electrode winding body 20 has a four-layer laminate S20 in which the positive electrode 21, the first separator member 23A, the negative electrode 22, and the second separator member 23B are stacked in this order. The positive electrode 21, the first separator member 23A, the negative electrode 22, and the second separator member 23B are all substantially strip-shaped members with the W-axis direction as the short side direction and the L-axis direction as the long side direction. As shown in FIG. 3 , the electrode winding body 20 is formed by winding the laminate S20 around a central axis CL (see FIG. 1 ) extending in the Z-axis direction so as to form a spiral shape in a horizontal cross section perpendicular to the Z-axis direction. At this time, the laminate S20 is wound with the W-axis direction roughly aligned with the Z-axis direction. Note that FIG. 3 illustrates an example configuration of the electrode winding body 20 along a horizontal cross section perpendicular to the Z-axis direction. However, in FIG. 3 , the separator 23 is omitted for improved visibility. The electrode winding body 20 has a substantially cylindrical appearance overall. The positive electrode 21 and the negative electrode 22 are wound while facing each other via the separator 23. A through hole 26 serving as an internal space is formed in the center of the electrode winding body 20. The through hole 26 is a hole for inserting a winding core for assembling the electrode winding body 20 and an electrode rod for welding.

[0027] The positive electrode 21, the negative electrode 22, and the separator 23 are wound such that the separator 23 is disposed at the outermost and innermost peripheries of the electrode winding body 20, respectively. At the outermost periphery of the electrode winding body 20, the negative electrode 22 is disposed outside the positive electrode 21. That is, as shown in FIG. 3 , a positive electrode outermost portion 21out located at the outermost periphery of the positive electrode 21 included in the electrode winding body 20 is disposed inside a negative electrode outermost portion 22out located at the outermost periphery of the negative electrode 22 included in the electrode winding body 20. Here, the positive electrode outermost portion 21out refers to the outermost portion of the positive electrode 21 in the electrode winding body 20, which corresponds to one circumference. The negative electrode outermost portion 22out refers to the outermost portion of the negative electrode 22 in the electrode winding body 20, which corresponds to one circumference. Meanwhile, at the innermost periphery of the electrode winding body 20, the negative electrode 22 is disposed inside the positive electrode 21. That is, as shown in Fig. 3, the negative electrode innermost circumferential portion 22in, which is located at the innermost periphery of the negative electrode 22 included in the electrode winding body 20, is located inside the positive electrode innermost circumferential portion 21in, which is located at the innermost periphery of the positive electrode 21 included in the electrode winding body 20. Here, the positive electrode innermost circumferential portion 21in is the innermost one-circumferential portion of the positive electrode 21 in the electrode winding body 20. The negative electrode innermost circumferential portion 22in is the innermost one-circumferential portion of the negative electrode 22 in the electrode winding body 20. The number of windings of each of the positive electrode 21, the negative electrode 22, and the separator 23 is not particularly limited and can be set as desired.

[0028] FIG. 4A is a developed view of the positive electrode 21, and schematically shows the state before winding. FIG. 4B shows a cross-sectional configuration of the positive electrode 21. Note that FIG. 4B shows a cross section taken along line IVB-IVB in FIG. 4A as viewed from the arrow direction. The positive electrode 21 includes, for example, a positive electrode current collector 21A and a positive electrode active material layer 21B provided on the positive electrode current collector 21A. The positive electrode active material layer 21B may be provided on only one side of the positive electrode current collector 21A, or on both sides of the positive electrode current collector 21A. FIG. 4B shows a case where the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A. More specifically, the positive electrode current collector 21A includes a positive electrode current collector inner peripheral surface 21A1 facing the winding center of the electrode wound body 20, i.e., facing the central axis CL, and a positive electrode current collector outer peripheral surface 21A2 facing the side opposite the winding center of the electrode wound body 20, i.e., on the opposite side of the positive electrode current collector inner peripheral surface 21A1. The positive electrode 21 has, as the positive electrode active material layer 21B, a positive electrode inner peripheral side active material layer 21B1 covering at least a portion of the positive electrode current collector inner peripheral surface 21A1, and a positive electrode outer peripheral side active material layer 21B2 covering at least a portion of the positive electrode current collector outer peripheral surface 21A2. Note that in this specification, the positive electrode inner peripheral side active material layer 21B1 and the positive electrode outer peripheral side active material layer 21B2 may be collectively referred to as the positive electrode active material layer 21B without distinguishing between them.

[0029] The positive electrode 21 has a positive electrode covering portion 211 in which a positive electrode active material layer 21B is covering a positive electrode current collector 21A, and a positive electrode exposed portion 212 in which the positive electrode current collector 21A is exposed without being covered by the positive electrode active material layer 21B. As shown in FIG. 4A , the positive electrode covering portion 211 and the positive electrode exposed portion 212 each extend along the L-axis direction, which is the longitudinal direction of the positive electrode 21, from the inner peripheral edge 21E1 to the outer peripheral edge 21E2 of the electrode wound body 20. Here, the L-axis direction corresponds to the winding direction of the electrode wound body 20. That is, in the positive electrode 21, the positive electrode active material layer 21B covers the positive electrode current collector 21A from the inner peripheral edge 21E1 of the positive electrode 21 to the outer peripheral edge 21E2 of the positive electrode 21 in the winding direction of the electrode wound body 20. The positive electrode covering portion 211 and the positive electrode exposed portion 212 are adjacent to each other in the W-axis direction, which is the short-side direction of the positive electrode 21. The W-axis direction substantially coincides with the central axis CL. The first edge portion 212E of the positive electrode exposed portion 212 is connected to the positive electrode current collector plate 24 as shown in FIG. 1 . An insulating layer 101 may be provided near the boundary between the positive electrode covering portion 211 and the positive electrode exposed portion 212. Similar to the positive electrode covering portion 211 and the positive electrode exposed portion 212, the insulating layer 101 may extend from the inner peripheral edge 21E1 to the outer peripheral edge 21E2 of the electrode winding body 20. The insulating layer 101 may also be bonded to at least one of the first separator member 23A and the second separator member 23B. This is because misalignment between the positive electrode 21 and the separator 23 can be prevented. Furthermore, the insulating layer 101 preferably contains a resin containing polyvinylidene fluoride (PVDF). When the insulating layer 101 contains PVDF, the insulating layer 101 swells due to, for example, a solvent contained in the electrolyte solution, and can be well bonded to the separator 23. The detailed configuration of the positive electrode 21 will be described later.

[0030] FIG. 5A is a developed view of the negative electrode 22, and schematically shows the state before winding. FIG. 5B shows a cross-sectional configuration of the negative electrode 22. Note that FIG. 5B shows a cross section taken along line VB-VB in FIG. 5A as viewed from the arrow direction. The negative electrode 22 includes, for example, a negative electrode current collector 22A and a negative electrode active material layer 22B provided on the negative electrode current collector 22A. The negative electrode active material layer 22B may be provided on only one surface of the negative electrode current collector 22A, or on both surfaces of the negative electrode current collector 22A. FIG. 5B shows a case where the negative electrode active material layer 22B is provided on both surfaces of the negative electrode current collector 22A. More specifically, the negative electrode current collector 22A includes a negative electrode current collector inner peripheral surface 22A1 facing the winding center of the electrode wound body 20, i.e., facing the central axis CL, and a negative electrode current collector outer peripheral surface 22A2 facing the side opposite the winding center of the electrode wound body 20, i.e., on the opposite side of the negative electrode current collector inner peripheral surface 22A1. The negative electrode 22 has, as the negative electrode active material layer 22B, a negative electrode inner peripheral side active material layer 22B1 covering at least a portion of the negative electrode current collector inner peripheral surface 22A1, and a negative electrode outer peripheral side active material layer 22B2 covering at least a portion of the negative electrode current collector outer peripheral surface 22A2. Note that in this specification, the negative electrode inner peripheral side active material layer 22B1 and the negative electrode outer peripheral side active material layer 22B2 may be collectively referred to as the negative electrode active material layer 22B without distinguishing between them.

[0031] The negative electrode 22 has a negative electrode covering portion 221 in which a negative electrode active material layer 22B is covering a negative electrode current collector 22A, and a negative electrode exposed portion 222 in which the negative electrode current collector 22A is exposed without being covered by the negative electrode active material layer 22B. As shown in FIG. 5A , the negative electrode covering portion 221 and the negative electrode exposed portion 222 each extend along the L-axis direction, which is the longitudinal direction of the negative electrode 22. The negative electrode exposed portion 222 extends from the inner peripheral edge 22E1 to the outer peripheral edge 22E2 of the negative electrode 22 in the winding direction of the electrode wound body 20. In contrast, the negative electrode covering portion 221 is not provided on the inner peripheral edge 22E1 or the outer peripheral edge 22E2 of the negative electrode 22. As shown in FIG. 5A , parts of the negative electrode exposed portion 222 are formed to sandwich the negative electrode covering portion 221 in the L-axis direction, which is the longitudinal direction of the negative electrode 22. Specifically, the negative electrode exposed portion 222 includes a first portion 222A, a second portion 222B, and a third portion 222C. The first portion 222A is adjacent to the negative electrode cover portion 221 in the W-axis direction and extends in the L-axis direction from the inner peripheral edge 22E1 to the outer peripheral edge 22E2 of the negative electrode 22. The second portion 222B and the third portion 222C are arranged to sandwich the negative electrode cover portion 221 in the L-axis direction. The second portion 222B is located near the inner peripheral edge 22E1 of the negative electrode 22, for example, and the third portion 222C is located near the outer peripheral edge 22E2 of the negative electrode 22. As shown in FIG. 1 , the second edge 222E of the negative electrode exposed portion 222 is connected to the negative electrode current collector plate 25. The detailed configuration of the negative electrode 22 will be described later.

[0032] In the laminate S20 of the electrode winding body 20, the positive electrode 21 and the negative electrode 22 are laminated with the separator 23 interposed between them so that the positive electrode exposed portion 212 and the first portion 222A of the negative electrode exposed portion 222 face opposite each other along the W-axis direction, which is the width direction. The electrode winding body 20 has the end of the separator 23 fixed by attaching a fixing tape 46 to the side surface portion 45 thereof, preventing loosening of the winding.

[0033] In the secondary battery 1, as shown in FIG. 2 , when the width of the positive electrode exposed portion 212 is A and the width of the first portion 222A of the negative electrode exposed portion 222 is B, it is preferable that A > B. For example, when the width A = 7 (mm), the width B = 4 (mm). Furthermore, when the width of the portion of the positive electrode exposed portion 212 that protrudes from the outer edge of the separator 23 in the width direction is C and the length of the first portion 222A of the negative electrode exposed portion 222 that protrudes from the outer edge on the opposite side in the width direction of the separator 23 is D, it is preferable that C > D. For example, when the width C = 4.5 (mm), the width D = 3 (mm).

[0034] As shown in FIG. 1 , at the upper part of the secondary battery 1, among the positive electrode exposed portion 212 wound around the central axis CL, multiple first edges 212E adjacent in the radial direction (R direction) of the electrode winding body 20 are inclined toward the central axis CL so as to overlap with each other. Similarly, at the lower part of the secondary battery 1, among the negative electrode exposed portion 222 wound around the central axis CL, multiple second edges 222E adjacent in the radial direction (R direction) are inclined toward the central axis CL so as to overlap with each other. Therefore, the multiple first edges 212E of the positive electrode exposed portion 212 are gathered at the upper end surface 41 of the electrode winding body 20, and the multiple second edges 222E of the negative electrode exposed portion 222 are gathered at the lower end surface 42 of the electrode winding body 20. To improve contact between the positive electrode current collector plate 24 and the first edges 212E for extracting current, the multiple first edges 212E bent toward the central axis CL are flat. Similarly, in order to improve contact between negative electrode current collector plate 25 and second edge portion 222E for extracting current, multiple second edge portions 222E bent toward central axis CL have flat surfaces. Note that the flat surface here does not only mean a completely flat surface, but also includes a surface having some unevenness or surface roughness to the extent that positive electrode exposed portion 212 and negative electrode exposed portion 222 can be joined to positive electrode current collector plate 24 and negative electrode current collector plate 25, respectively.

[0035] The positive electrode current collector 21A is made of, for example, aluminum foil, as described below. On the other hand, the negative electrode current collector 22A is made of, for example, copper foil, as described below. In this case, the positive electrode current collector 21A is softer than the negative electrode current collector 22A. That is, the Young's modulus of the positive electrode exposed portion 212 is lower than that of the negative electrode exposed portion 222. Therefore, in one embodiment, it is more preferable that the widths A to D satisfy the relationship A > B and C > D. In this case, when the positive electrode exposed portion 212 and the negative electrode exposed portion 222 are folded simultaneously from both electrode sides with the same pressure, the heights of the folded portions measured from the tip of the separator 23 may be approximately the same for the positive electrode 21 and the negative electrode 22. At this time, the multiple first edge portions 212E (FIG. 1) of the positive electrode exposed portion 212 are folded and overlap each other to a moderate extent. This facilitates joining of the positive electrode exposed portion 212 and the positive electrode current collector 24. Similarly, the plurality of second edge portions 222E ( FIG. 1 ) of the negative electrode exposed portion 222 are folded and overlap each other to an appropriate degree, which facilitates joining of the negative electrode exposed portion 222 and the negative electrode current collector plate 25. The term "joining" as used herein means joining them together by, for example, laser welding, but the joining method is not limited to laser welding.

[0036] As shown in FIG. 2 , the portion of the positive electrode exposed portion 212 of the positive electrode 21 that faces the negative electrode 22 across the separator 23 is covered with an insulating layer 101. The insulating layer 101 has a width of, for example, 3 mm in the W-axis direction. The insulating layer 101 covers the entire area of ​​the positive electrode exposed portion 212 of the positive electrode 21 that faces the negative electrode covering portion 221 of the negative electrode 22 via the separator 23. The insulating layer 101 can effectively prevent an internal short circuit in the secondary battery 1, for example, when a foreign object enters between the negative electrode covering portion 221 and the positive electrode exposed portion 212. Furthermore, when an impact is applied to the secondary battery 1, the insulating layer 101 absorbs the impact and can effectively prevent deformation of the positive electrode exposed portion 212 and a short circuit between the positive electrode exposed portion 212 and the negative electrode 22.

[0037] FIG. 6A is an enlarged cross-sectional view showing an upper portion of the secondary battery 1, mainly illustrating the details of the positive electrode exposed portion 212. Note that the separator 23 is omitted from FIG. 6A . As shown in FIG. 6A , the positive electrode current collector 21A of the positive electrode exposed portion 212 has multiple bent portions K21A in a range from the boundary K21 between the positive electrode covering portion 211 and the positive electrode exposed portion 212 to the first edge portion 212E. Each bent portion K21A may be a bent portion where the positive electrode current collector 21A is bent, or may be a curved portion where the positive electrode current collector 21A is curved. In the configuration example of FIG. 6A , the number of bent portions K21A of the positive electrode current collector 21A in each of the three wound portions in the outer peripheral portion 20out is six, and the number of bent portions K21A of the positive electrode current collector 21A in each of the three wound portions in the central axis side portion 20in is 11 to 17. The number of bending points K21A in the outer peripheral portion 20out and the number of bending points K21A in the central axis side portion 20in are not limited to the numbers shown in FIG. 6A and can be set arbitrarily. However, in the secondary battery 1 of the present embodiment, the number of bending points K21A in the positive electrode current collector 21A in the central axis side portion 20in (referred to as number N21in for convenience of explanation) is greater than the number of bending points K21A in the positive electrode current collector 21A in the outer peripheral portion 20out (referred to as number N21out for convenience of explanation). The number N21out of bending points K21A in the positive electrode current collector 21A in the outer peripheral portion 20out and the number N21in of bending points K21A in the positive electrode current collector 21A in the central axis side portion 20in can be compared, for example, as follows. First, among the multiple windings included in the outer peripheral portion 20out, the number of bent points K21A of the positive electrode current collector 21A in the positive electrode exposed portion 212 of any three windings is counted, and the average value is calculated and defined as the number N21out of bent points K21A of the positive electrode current collector 21A in the outer peripheral portion 20out. Next, among the multiple windings included in the central axis side portion 20in, the number K21A of the positive electrode current collector 21A in the positive electrode exposed portion 212 of any three windings is counted, and the average value is calculated and defined as the number N21in of bent points K21A of the positive electrode current collector 21A in the central axis side portion 20in. Then, the number N21out and the number N21in are compared.Here, as shown in FIG. 1 , the outer peripheral portion 20out is a portion of the electrode winding 20 located closer to the outer periphery in the radial direction R than the intermediate position IP. As shown in FIG. 1 , the central axis side portion 20in is a portion of the electrode winding 20 located closer to the central axis CL in the radial direction R than the intermediate position IP. The intermediate position IP is a midpoint between the outer edge OE of the electrode winding 20 in the radial direction R and the inner edge IE of the electrode winding 20 in the radial direction R (see FIG. 1 ). While FIG. 6A illustrates an example in which the bent portion K21A is present only in the positive electrode exposed portion 212 of the positive electrode current collector 21A that is not covered by the positive electrode active material layer 21B, the present disclosure is not limited thereto. For example, the bent portion K21A may be present in the positive electrode covering portion 211 of the positive electrode current collector 21A.

[0038] 6A , in the electrode winding 20 of the secondary battery 1, the maximum spacing W21out between the multiple winding portions of the positive electrode current collector 21A that constitutes the outer periphery portion 20out of the electrode winding 20 is preferably larger than the maximum spacing W21in between the multiple winding portions of the positive electrode current collector 21A that constitutes the central axis portion 20in of the electrode winding 20. The maximum spacing W21out and the maximum spacing W21in are each the maximum values ​​of the dimensions of the gap along the radial direction (R direction) between the multiple winding portions of the positive electrode current collector 21A that are adjacent in the radial direction (R direction).

[0039] FIG. 6B is an enlarged cross-sectional view showing a lower portion of the secondary battery 1, mainly illustrating the details of the negative electrode exposed portion 222. Note that the separator 23 is omitted from FIG. 6B . As shown in FIG. 6B , the negative electrode current collector 22A of the negative electrode exposed portion 222 has multiple bent portions K22A in a range from the boundary K22 between the negative electrode covering portion 221 and the negative electrode exposed portion 222 to the second edge portion 222E. Each bent portion K22A may be a bent portion where the negative electrode current collector 22A is bent, or may be a curved portion where the negative electrode current collector 22A is curved. In the configuration example of FIG. 6B , the number of bent portions K22A of the negative electrode current collector 22A in each of the three winding portions in the outer peripheral portion 20 out is six, and the number of bent portions K22A of the negative electrode current collector 22A in each of the three winding portions in the central axis side portion 20 in is 11 to 17. The number of bending points K22A in the outer peripheral portion 20out and the number of bending points K22A in the central axis side portion 20in are not limited to the numbers shown in Figure 6B and can be set arbitrarily. However, in the secondary battery 1 of this embodiment, the number of bending points K22A in the negative electrode current collector 22A in the central axis side portion 20in (referred to as number N22in for convenience of explanation) is greater than the number of bending points K22A in the negative electrode current collector 22A in the outer peripheral portion 20out (referred to as number N22out for convenience of explanation). The number N22out and the number N22in are compared, for example, as follows. First, among the multiple winding portions included in the outer peripheral portion 20out, the number of bent points K22A of the negative electrode current collector 22A in the negative electrode exposed portion 222 of any three winding portions is counted, and the average value is calculated and defined as the number N22out of bent points K22A of the negative electrode current collector 22A in the outer peripheral portion 20out. Next, among the multiple winding portions included in the central axis side portion 20in, the number K22A of the bent points K22A of the negative electrode current collector 22A in the negative electrode exposed portion 222 of any three winding portions is counted, and the average value is calculated and defined as the number N22in of bent points K22A of the negative electrode current collector 22A in the central axis side portion 20in. Then, the number N22out and the number N22in are compared.6B illustrates an example in which the bent portion K22A is provided only in the negative electrode exposed portion 222 of the negative electrode current collector 22A that is not covered with the negative electrode active material layer 22B, but the present disclosure is not limited to this. For example, the bent portion K22A may be provided in the negative electrode current collector 22A in the negative electrode covering portion 221.

[0040] 6B , in the electrode winding 20 of the secondary battery 1, the maximum spacing W22out between the multiple winding portions of the negative electrode current collector 22A that constitutes the outer periphery side portion 20out of the electrode winding 20 is preferably larger than the maximum spacing W22in between the multiple winding portions of the negative electrode current collector 22A that constitutes the central axis side portion 20in of the electrode winding 20. The maximum spacing W22out and the maximum spacing W22in are each the maximum values ​​of the dimensions of the gap along the radial direction (R direction) between the multiple winding portions of the negative electrode current collector 22A that are adjacent in the radial direction (R direction).

[0041] The number of bending points K22A of the negative electrode current collector 22A of the negative electrode exposed portion 222 in the central axis side portion 20 in of the electrode winding 20 is preferably greater than the number of bending points K21A of the positive electrode current collector 21A of the positive electrode exposed portion 212 in the central axis side portion 20 in of the electrode winding 20. This is because the upper portion of the electrode winding 20, which is more likely to be deficient in electrolyte compared to the lower portion of the electrode winding 20, is more likely to be impregnated with electrolyte.

[0042] (Insulating Tapes 53, 54) The secondary battery 1 may further include insulating tapes 53, 54 in the gap between the outer can 11 and the electrode winding 20. The positive electrode exposed portion 212 and the negative electrode exposed portion 222, which are gathered on the end faces 41, 42, are conductors such as bare metal foil. Therefore, if the positive electrode exposed portion 212 and the negative electrode exposed portion 222 are close to the outer can 11, a short circuit may occur between the positive electrode 21 and the negative electrode 22 through the outer can 11. Furthermore, if the positive electrode current collector 24 on the end face 41 comes close to the outer can 11, a short circuit may also occur. For this reason, it is preferable to provide insulating tapes 53, 54 as insulating members. The insulating tapes 53, 54 are, for example, adhesive tapes whose base layer is made of polypropylene, polyethylene terephthalate, or polyimide and whose base layer has an adhesive layer on one surface. In order to prevent the installation of the insulating tapes 53, 54 from reducing the volume of the electrode winding body 20, the insulating tapes 53, 54 are positioned so as not to overlap with the fixing tape 46 attached to the side portion 45, and the thickness of the insulating tapes 53, 54 is set to be equal to or less than the thickness of the fixing tape 46.

[0043] (Positive Current Collector 24 and Negative Current Collector 25) In a typical lithium-ion secondary battery, for example, a lead for current extraction is welded to each of the positive and negative electrodes. However, this increases the internal resistance of the lithium-ion secondary battery and causes the lithium-ion secondary battery to heat up and reach high temperatures during discharge, making it unsuitable for high-rate discharge. Therefore, in the secondary battery 1 of this embodiment, the positive current collector 24 is positioned opposite end face 41, and the negative current collector 25 is positioned opposite end face 42. The positive electrode coating 211 on end face 41 is welded to the positive electrode collector 24 at multiple points, and the negative electrode coating 221 on end face 42 is welded to the negative electrode collector 25 at multiple points. This reduces the internal resistance of the secondary battery 1. The flat surfaces of end faces 41 and 42, as described above, also contribute to the low resistance. The positive current collector 24 is electrically connected to the battery lid 14, for example, via a safety valve mechanism 30. The negative electrode current collector 25 is electrically connected to, for example, the outer can 11. Fig. 7A is a schematic diagram showing an example of the configuration of the positive electrode current collector 24. Fig. 7B is a schematic diagram showing an example of the configuration of the negative electrode current collector 25. The positive electrode current collector 24 is a metal plate made of, for example, aluminum or an aluminum alloy, or a composite material thereof. The negative electrode current collector 25 is a metal plate made of, for example, nickel, a nickel alloy, copper, or a copper alloy, or a composite material of two or more of these.

[0044] As shown in FIG. 7A , the positive electrode current collector 24 has a shape in which a substantially rectangular strip-shaped portion 32 is connected to a substantially sector-shaped sector portion 31. A through-hole 35 is formed near the center of the sector-shaped portion 31. In the secondary battery 1, the positive electrode current collector 24 is provided such that the through-hole 35 overlaps the through-hole 26 in the Z-axis direction. The hatched portion in FIG. 7A is an insulating portion 32A of the strip-shaped portion 32. The insulating portion 32A is a portion of the strip-shaped portion 32 to which insulating tape is attached or an insulating material is applied. The portion of the strip-shaped portion 32 below the insulating portion 32A is a connection portion 32B to the sealing plate, which also serves as an external terminal. Note that, as shown in FIG. 1 , if the secondary battery 1 has a battery structure in which the through-hole 26 does not have a metal center pin, the strip-shaped portion 32 is unlikely to come into contact with a portion of the negative electrode potential. Therefore, the positive electrode current collector 24 does not need to have the insulating portion 32A. When the positive electrode current collector 24 does not have the insulating portion 32A, the charge / discharge capacity can be increased by widening the width between the positive electrode 21 and the negative electrode 22 by an amount corresponding to the thickness of the insulating portion 32A.

[0045] The shape of the negative current collector 25 shown in FIG. 7B is almost the same as the shape of the positive current collector 24 shown in FIG. 7A . However, the strip portion 34 of the negative current collector 25 is different from the strip portion 32 of the positive current collector 24. The strip portion 34 of the negative current collector 25 is shorter than the strip portion 32 of the positive current collector 24 and does not have a portion corresponding to the insulating portion 32A of the positive current collector 24. The strip portion 34 has round protrusions 37 indicated by multiple circles. During resistance welding, current concentrates on the protrusions 37, melting the protrusions 37 and welding the strip portion 34 to the bottom of the outer can 11. Like the positive current collector 24, the negative current collector 25 has a through hole 36 formed near the center of the sector portion 33. In the secondary battery 1, the negative current collector 25 is provided so that the through hole 36 overlaps with the through hole 26 in the Z-axis direction.

[0046] Due to its planar shape, the sector-shaped portion 31 of the positive current collector plate 24 covers only a portion of the end surface 41. Similarly, due to its planar shape, the sector-shaped portion 33 of the negative current collector plate 25 covers only a portion of the end surface 42. The reasons why the sector-shaped portions 31 and 33 do not cover the entire end surface 41 and the end surface 42 are, for example, as follows: First, this is to allow the electrolyte to smoothly penetrate into the electrode winding body 20 when, for example, assembling the secondary battery 1. Second, this is to facilitate the release of gas generated when the lithium-ion secondary battery is subjected to an abnormally high temperature or is overcharged.

[0047] (Positive Electrode Current Collector 21A) The positive electrode current collector 21A contains a conductive material such as aluminum, etc. The positive electrode current collector 21A is, for example, a metal foil made of aluminum or an aluminum alloy.

[0048] (Positive Electrode Active Material Layer 21B) The positive electrode active material layer 21B contains, as the positive electrode active material, one or more positive electrode materials capable of absorbing and releasing lithium. However, the positive electrode active material layer 21B may further contain one or more other materials, such as a positive electrode binder and a positive electrode conductor. The positive electrode material is preferably a lithium-containing compound, more specifically, a lithium-containing composite oxide or a lithium-containing phosphate compound. The lithium-containing composite oxide is an oxide containing lithium and one or more other elements, i.e., elements other than lithium, as constituent elements. The lithium-containing composite oxide has, for example, a layered rock salt type or a spinel type crystal structure. The lithium-containing phosphate compound is a phosphate compound containing lithium and one or more other elements as constituent elements, and has, for example, an olivine type crystal structure. The positive electrode active material layer 21B preferably contains at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide as the positive electrode active material. The positive electrode binder includes, for example, one or more of synthetic rubber and polymer compounds. Examples of synthetic rubber include styrene butadiene rubber, fluorine-based rubber, and ethylene propylene diene. Examples of polymer compounds include polyvinylidene fluoride and polyimide. The positive electrode conductive agent includes, for example, one or more of carbon materials. Examples of carbon materials include graphite, carbon black, acetylene black, and ketjen black. However, the positive electrode conductive agent may also be a metal material or a conductive polymer, as long as it is a conductive material.

[0049] (Negative Electrode Current Collector 22A) The negative electrode current collector 22A contains a conductive material such as copper. The negative electrode current collector 22A is a metal foil made of, for example, nickel, a nickel alloy, copper, or a copper alloy. The surface of the negative electrode current collector 22A is preferably roughened. This is because the so-called anchor effect improves adhesion of the negative electrode active material layer 22B to the negative electrode current collector 22A. In this case, it is sufficient that the surface of the negative electrode current collector 22A is roughened at least in the region facing the negative electrode active material layer 22B. The roughening method may be, for example, a method of forming fine particles using an electrolytic process. In the electrolytic process, fine particles are formed on the surface of the negative electrode current collector 22A by electrolysis in an electrolytic bath, resulting in an uneven surface of the negative electrode current collector 22A. Copper foil produced by an electrolytic process is generally called electrolytic copper foil.

[0050] (Negative Electrode Active Material Layer 22B) The negative electrode active material layer 22B contains, as the negative electrode active material, one or more negative electrode materials capable of absorbing and releasing lithium. However, the negative electrode active material layer 22B may further contain one or more other materials, such as a negative electrode binder and a negative electrode conductor. The negative electrode material is, for example, a carbon material. This is because the crystal structure undergoes minimal change upon lithium absorption and desorption, thereby enabling a stable high energy density. Furthermore, the carbon material also functions as a negative electrode conductor, thereby improving the conductivity of the negative electrode active material layer 22B. Examples of carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite. However, the interplanar spacing of the (002) plane of non-graphitizable carbon is preferably 0.37 nm or more. The interplanar spacing of the (002) plane of graphite is preferably 0.34 nm or less. More specifically, the carbon material may be, for example, pyrolytic carbon, cokes, glassy carbon fiber, organic polymer compound calcined bodies, activated carbon, or carbon black. Examples of the cokes include pitch coke, needle coke, and petroleum coke. The organic polymer compound calcined bodies are formed by calcining (carbonizing) polymer compounds such as phenolic resin and furan resin at an appropriate temperature. Alternatively, the carbon material may be low-crystalline carbon heat-treated at temperatures below approximately 1000°C, or amorphous carbon. The carbon material may be fibrous, spherical, granular, or flake-shaped. In the secondary battery 1, when the open-circuit voltage at full charge, i.e., the battery voltage, is 4.25 V or higher, the amount of lithium released per unit mass is greater than when the open-circuit voltage at full charge is 4.20 V, even when the same positive electrode active material is used. Therefore, the amounts of the positive electrode active material and the negative electrode active material are adjusted accordingly. This results in a high energy density.

[0051] The negative electrode active material layer 22B may also contain a silicon-containing material containing at least one of silicon, silicon oxide, carbon-silicon compound, and silicon alloy as the negative electrode active material. A silicon-containing material is a general term for materials containing silicon as a constituent element. However, a silicon-containing material may contain only silicon as a constituent element. The silicon-containing material may be of one type or two or more types. The silicon-containing material is capable of forming an alloy with lithium and may be silicon itself, a silicon alloy, a silicon compound, a mixture of two or more of these, or a material containing one or more of these phases. The silicon-containing material may be crystalline, amorphous, or contain both crystalline and amorphous portions. However, the element described here refers to a general element and may contain trace amounts of impurities. In other words, the purity of the element is not necessarily limited to 100%. Silicon alloys contain, for example, one or more of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, chromium, etc. as constituent elements other than silicon. Silicon compounds contain, for example, one or more of carbon, oxygen, etc. as constituent elements other than silicon. Note that silicon compounds may contain, for example, one or more of the series of constituent elements described for silicon alloys as constituent elements other than silicon. Specifically, silicon alloys and silicon compounds include, for example, SiB 4 , SiB 6 , Mg 2 Si, Ni 2 Si, TiSi 2 , MoSi 2 , CoSi 2 , NiSi 2 , CaSi 2 , CrSi 2 , Cu 5 Si, FeSi 2 , MnSi 2 , NbSi 2 , TaSi 2 , VSi 2 , WSi 2 , ZnSi2 , SiC, Si 3 N 4 , Si 2 N 2 O and SiO v (0<v≦2), etc. However, the range of v can be set arbitrarily, and may be, for example, 0.2<v<1.4.

[0052] (Separator 23) The separator 23 is interposed between the positive electrode 21 and the negative electrode 22. The separator 23 allows lithium ions to pass through while preventing current short-circuiting due to contact between the positive electrode 21 and the negative electrode 22. The separator 23 may be made of one or more types of porous membranes, such as synthetic resins and ceramics, or may be a laminated membrane of two or more types of porous membranes. Examples of synthetic resins include polytetrafluoroethylene, polypropylene, and polyethylene. However, the separator 23 preferably has a substrate made of a single-layer polyolefin porous membrane containing polyethylene. This is because better high-output characteristics can be obtained compared to laminated membranes. When the first separator member 23A and the second separator member constituting the separator 23 are each a single-layer porous membrane made of polyolefin, the thickness of the porous membrane may be, for example, 10 μm or more and 15 μm or less. By making the single-layer porous membrane made of polyolefin 10 μm or more thick, internal short-circuiting can be sufficiently avoided. If the thickness of the single-layer porous film made of polyolefin is 15 μm or less, better discharge capacity characteristics can be obtained. In addition, the surface density of the porous film is, for example, 6.3 g / m ２ 8.3g / m or more ２ The surface density of the single-layer porous film made of polyolefin is preferably 6.3 g / m or less. ２ If the surface density of the single-layer porous film made of polyolefin is 8.3 g / m or more, internal short circuits can be sufficiently avoided. ２ If the content is less than this, better discharge capacity characteristics can be obtained.

[0053] In particular, the separator 23 may include, for example, the porous membrane as the substrate described above and a polymer compound layer provided on one or both sides of the substrate layer. This is because the adhesion of the separator 23 to each of the positive electrode 21 and the negative electrode 22 is improved, thereby suppressing distortion of the electrode winding body 20. This suppresses decomposition reactions of the electrolyte and also suppresses leakage of the electrolyte impregnated in the substrate layer, thereby making it difficult for resistance to increase even with repeated charge and discharge, and suppressing battery swelling. The polymer compound layer includes, for example, a polymer compound such as polyvinylidene fluoride. This is because it has excellent physical strength and is electrochemically stable. However, the polymer compound may be other than polyvinylidene fluoride. To form this polymer compound layer, for example, a solution in which a polymer compound is dissolved in an organic solvent or the like is applied to the substrate layer, and the substrate layer is then dried. Alternatively, the substrate layer may be immersed in the solution and then dried. The polymer compound layer may contain one or more types of insulating particles such as inorganic particles, for example, aluminum oxide and aluminum nitride.

[0054] (Electrolyte) The electrolyte contains a solvent and an electrolyte salt. However, the electrolyte may further contain one or more other materials, such as additives. The solvent contains one or more non-aqueous solvents, such as organic solvents. An electrolyte containing a non-aqueous solvent is a so-called non-aqueous electrolyte. The non-aqueous solvent contains, for example, a fluorine compound and a dinitrile compound. The fluorine compound may include, for example, at least one of fluorinated ethylene carbonate, trifluorocarbonate, trifluoroethyl methyl carbonate, fluorinated carboxylic acid ester, and fluorinated ether. The non-aqueous solvent may also contain a nitrile compound other than a dinitrile compound, such as at least one of a mononitrile compound or a tritolyl compound. As the dinitrile compound, succinonitrile (SN) is preferable. However, the dinitrile compound is not limited to succinonitrile, and may be other dinitrile compounds, such as adiponitrile.

[0055] The electrolyte salt may include one or more salts, such as a lithium salt. However, the electrolyte salt may include a salt other than a lithium salt. The salt other than lithium may be, for example, a salt of a light metal other than lithium. Examples of the lithium salt include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium tetrachloroaluminate (LiAlCl4), dilithium hexafluorosilicate (Li2SF6), lithium chloride (LiCl), and lithium bromide (LiBr). Among these, one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium hexafluoroarsenate are preferred, with lithium hexafluorophosphate being more preferred. The content of the electrolyte salt is not particularly limited, but is preferably 0.3 mol / kg to 3 mol / kg relative to the solvent. When the electrolyte solution contains LiPF as the electrolyte salt, ６ When the electrolyte contains LiPF ６ The concentration of the electrolyte salt is preferably 1.25 mol / kg or more and 1.45 mol / kg or less. This is because it is possible to prevent cycle deterioration due to salt consumption (decomposition) during high-load rate charging, thereby improving high-load cycle characteristics. ６ In addition to LiBF ４ When further containing LiBF in the electrolyte ４ The concentration of salt is preferably 0.001 (wt %) or more and 0.1 (wt %) or less, because this more effectively prevents cycle deterioration due to salt consumption (decomposition) during high-load rate charging, thereby further improving high-load cycle characteristics.

[0056] [1-2. Operation] In the secondary battery 1 of this embodiment, for example, during charging, lithium ions are released from the positive electrode 21 and are absorbed into the negative electrode 22 via the electrolyte. In addition, in the secondary battery 1, for example, during discharging, lithium ions are released from the negative electrode 22 and are absorbed into the positive electrode 21 via the electrolyte.

[0057] 1-3. Manufacturing Method] A method for manufacturing the secondary battery 1 will be described with reference to Fig. 8 in addition to Fig. 1 to Fig. 7B. Fig. 8 is a perspective view illustrating the manufacturing process of the secondary battery shown in Fig. 1.

[0058] First, a positive electrode current collector 21A is prepared, and a positive electrode active material layer 21B and an insulating layer 101 are selectively formed on the surface of the positive electrode current collector 21A to form a positive electrode 21 having a positive electrode covering portion 211 and a positive electrode exposed portion 212. Next, a negative electrode current collector 22A is prepared, and a negative electrode active material layer 22B is selectively formed on the surface of the negative electrode current collector 22A to form a negative electrode 22 having a negative electrode covering portion 221 and a negative electrode exposed portion 222. A drying process may be performed on the positive electrode 21 and the negative electrode 22. Next, a stack S20 is produced by stacking the positive electrode 21 and the negative electrode 22 with the first separator member 23A and the second separator member 23B interposed between them such that the positive electrode exposed portion 212 and the first portion 222A of the negative electrode exposed portion 222 are opposite each other in the W-axis direction. When fabricating the laminate S20, the inner peripheral end portion of the first separator member 23A and the inner peripheral end portion of the second separator member are folded back, and each of the folded back inner peripheral end portions is sandwiched between the inner peripheral edge 21E1 of the positive electrode 21 and the negative electrode 22. The laminate S20 is then spirally wound so as to form through-holes 26. Furthermore, a fixing tape 46 is attached to the outermost periphery of the spirally wound laminate S20. As a result, the electrode roll 20 is obtained as shown in FIG. 8A .

[0059] Next, as shown in Fig. 8B , the end faces 41, 42 are locally bent by pressing the edge of a flat plate, for example, 0.5 mm thick, perpendicularly against the end faces 41, 42 of the electrode winding body 20, i.e., in the Z-axis direction. As a result, grooves 43 are formed that extend radially from the through-holes 26 in the radial direction (R direction). Note that the number and arrangement of grooves 43 shown in Fig. 8B are merely examples and the present disclosure is not limited thereto.

[0060] Next, as shown in FIG. 8C , substantially the same pressure is applied substantially simultaneously from above and below the electrode winding body 20 in a direction approximately perpendicular to the end faces 41 and 42. At this time, a rod-shaped jig, for example, is inserted into the through hole 26. With this jig inserted, a flat jig is pressed against the part of the positive electrode exposed portion 212 and the first part 222A of the negative electrode exposed portion 222 that are locally bent toward the through hole 26 by the groove formed in FIG. 8B . This bends the part of the positive electrode exposed portion 212 and the first part 222A of the negative electrode exposed portion 222, respectively, so that the end faces 41 and 42 become flat surfaces. At this time, the first edge 212E of the positive electrode exposed portion 212 and the second edge 222E of the negative electrode exposed portion 222, which are located at the end faces 41 and 42, respectively, are bent while overlapping toward the through hole 26. The rod-shaped jig inserted into the through-hole 26 suppresses bending portions on the central axis side, making it possible to make the number of bending portions on the central axis side of the electrode winding body 20 greater than the number of bending portions on the outer periphery side of the electrode winding body. Thereafter, the fan-shaped portion 31 of the positive current collector plate 24 is joined to the end face 41 by laser welding or the like, and the fan-shaped portion 33 of the negative current collector plate 25 is joined to the end face 42 by laser welding or the like.

[0061] Next, insulating tapes 53 and 54 are attached to predetermined positions of the electrode winding body 20. Thereafter, as shown in Fig. 8(D), the strip portion 32 of the positive current collector plate 24 is bent and inserted into the hole 12H of the insulating plate 12. Also, the strip portion 34 of the negative current collector plate 25 is bent and inserted into the hole 13H of the insulating plate 13.

[0062] Next, the electrode winding body 20 assembled as described above is inserted into the outer can 11 shown in Figure 8(E), and then the bottom of the outer can 11 is welded to the negative electrode current collector plate 25. After that, a constricted portion 11S is formed near the open end 11N of the outer can 11. Furthermore, after the electrolyte is poured into the outer can 11, the strip portion 32 of the positive electrode current collector plate 24 is welded to the safety valve mechanism 30.

[0063] Next, as shown in FIG. 8(F), the gasket 15, the safety valve mechanism 30, and the battery lid 14 are sealed using the constricted portion 11S.

[0064] In this way, the secondary battery 1 of this embodiment is completed.

[0065] [1-4. Actions and Effects] As described above, in the secondary battery 1 of the present embodiment, the number N21in of bending points K21A of the positive electrode current collector 21A in the central axis side portion 20in of the electrode winding 20 is greater than the number N21out of bending points K21A of the positive electrode current collector 21A in the outer peripheral side portion 20out of the electrode winding 20. Furthermore, the number N22in of bending points K22A of the negative electrode current collector 22A in the central axis side portion 20in is greater than the number N22out of bending points K22A of the negative electrode current collector 22A in the outer peripheral side portion 20out. Therefore, the electrolyte is more likely to be impregnated into the outer peripheral side portion 20out of the electrode winding 20, which is relatively more difficult to be impregnated with the electrolyte than the central axis side portion 20in. Therefore, elution of metal ions and deposition of metallic lithium due to a local increase in potential of the positive electrode 21 in the outer peripheral side portion 20out of the electrode winding 20 are less likely to occur. As a result, it is possible to prevent an internal short circuit between the positive electrode 21 and the negative electrode 22 during high-temperature storage. Also, it is possible to avoid excessive impregnation of the central axis side portion 20 in of the electrode winding body 20 with the electrolyte, thereby mitigating deterioration of the cycle characteristics. Therefore, higher reliability can be obtained.

[0066] In the secondary battery 1 of this embodiment, by making the maximum spacing W21out between the multiple wound portions of the positive electrode current collector 21A constituting the outer peripheral portion 20out larger than the maximum spacing W21in between the multiple wound portions of the positive electrode current collector 21A constituting the central axis side portion 20in, impregnation of the outer peripheral portion 20out with the electrolyte can be further promoted. The same is true when the maximum spacing W22out between the multiple wound portions of the negative electrode current collector 22A constituting the outer peripheral portion 20out is made larger than the maximum spacing W22in between the multiple wound portions of the negative electrode current collector 22A constituting the central axis side portion 20in. As a result, internal short circuits between the positive electrode 21 and the negative electrode 22 during high-temperature storage can be more effectively prevented, resulting in even higher reliability.

[0067] 2. Application Examples The secondary battery 1 according to the embodiment of the present disclosure can be used in the following applications, for example.

[0068] 9 is a block diagram showing an example of a circuit configuration when a battery according to an embodiment of the present invention (hereinafter referred to as a secondary battery) is applied to a battery pack 300. The battery pack 300 includes a battery pack 301, an exterior, a switch unit 304 including a charge control switch 302a and a discharge control switch 303a, a current detection resistor 307, a temperature detection element 308, and a control unit 310.

[0069] The battery pack 300 includes a positive terminal 321 and a negative terminal 322. When charging, the positive terminal 321 and the negative terminal 322 are connected to the positive terminal and the negative terminal of a charger, respectively, for charging. When using the electronic device, the positive terminal 321 and the negative terminal 322 are connected to the positive terminal and the negative terminal of the electronic device, respectively, for discharging.

[0070] The battery pack 301 is formed by connecting a plurality of secondary batteries 301a in series or parallel. The secondary batteries 301a can be the secondary batteries 1 described above. While Fig. 9 shows an example in which six secondary batteries 301a are connected in a 2-parallel-3-series (2P3S) configuration, any other connection method, such as n-parallel or m-series (n and m are integers), is also acceptable.

[0071] The switch unit 304 includes a charge control switch 302a and a diode 302b, and a discharge control switch 303a and a diode 303b, and is controlled by the control unit 310. The diode 302b has a polarity opposite to the charge current flowing from the positive terminal 321 to the battery pack 301, and a polarity forward to the discharge current flowing from the negative terminal 322 to the battery pack 301. The diode 303b has a polarity forward to the charge current and opposite to the polarity of the discharge current. Although the switch unit 304 is provided on the + side in FIG. 9, it may also be provided on the - side.

[0072] The charge control switch 302a is controlled by the charge / discharge control unit so that it is turned off when the battery voltage reaches the overcharge detection voltage and so that no charging current flows in the current path of the battery pack 301. After the charge control switch 302a is turned off, only discharging is possible via the diode 302b. Furthermore, the control unit 310 controls the switch so that it is turned off when a large current flows during charging and so that the charging current flows in the current path of the battery pack 301. The discharge control switch 303a is controlled by the control unit 310 so that it is turned off when the battery voltage reaches the overdischarge detection voltage and so that no discharging current flows in the current path of the battery pack 301. After the discharge control switch 303a is turned off, only charging is possible via the diode 303b. Furthermore, the control unit 310 controls the switch so that it is turned off when a large current flows during discharging and so that the discharging current flows in the current path of the battery pack 301.

[0073] The temperature detection element 308 is, for example, a thermistor, and is provided near the battery pack 301. It measures the temperature of the battery pack 301 and supplies the measured temperature to the control unit 310. The voltage detection unit 311 measures the voltage of the battery pack 301 and each of the secondary batteries 301a that make up the battery pack 301, A / D converts the measured voltage, and supplies it to the control unit 310. The current measurement unit 313 measures the current using the current detection resistor 307 and supplies this measured current to the control unit 310. The switch control unit 314 controls the charge control switch 302a and the discharge control switch 303a of the switch unit 304 based on the voltage and current input from the voltage detection unit 311 and the current measurement unit 313.

[0074] When the voltage of any of the multiple secondary batteries 301a falls below the overcharge detection voltage or the overdischarge detection voltage, or when a large current suddenly flows, the switch control unit 314 sends a control signal to the switch unit 304 to prevent overcharging, overdischarging, and overcurrent charging / discharging. Here, for example, if the secondary battery is a lithium-ion secondary battery, the overcharge detection voltage is set to, for example, 4.20 V±0.05 V, and the overdischarge detection voltage is set to, for example, 2.4 V±0.1 V.

[0075] The charge / discharge switches can be semiconductor switches such as MOSFETs. In this case, the parasitic diodes of the MOSFETs function as diodes 302b and 303b. When P-channel FETs are used as the charge / discharge switches, switch control unit 314 supplies control signals DO and CO to the gates of charge control switch 302a and discharge control switch 303a, respectively. When charge control switch 302a and discharge control switch 303a are P-channel, they are turned ON by a gate potential that is lower than the source potential by a predetermined value or more. That is, during normal charge and discharge operations, control signals CO and DO are set to a low level, and charge control switch 302a and discharge control switch 303a are turned ON.

[0076] For example, in the event of overcharging or overdischarging, the control signals CO and DO are set to high level, and the charge control switch 302a and the discharge control switch 303a are set to the OFF state.

[0077] The memory 317 is made up of RAM or ROM, such as a non-volatile memory such as an erasable programmable read-only memory (EPROM). Numerical values ​​calculated by the control unit 310 and the internal resistance values ​​of the secondary batteries 301a in their initial states measured during the manufacturing process are stored in advance in the memory 317, and the memory 317 can be rewritten as needed. Furthermore, by storing the full charge capacity of the secondary batteries 301a, the remaining capacity can be calculated together with the control unit 310.

[0078] The temperature detection unit 318 measures the temperature using the temperature detection element 308, and controls charging and discharging when abnormal heat is generated, and corrects the calculation of the remaining capacity.

[0079] [2-2. Power Storage System] The secondary battery according to the embodiment of the present disclosure described above can be mounted on devices such as electronic devices, power tools, motor vehicles, electric aircraft, and power storage devices, or can be used to supply power.

[0080] Examples of electronic devices include notebook computers, smartphones, tablet devices, PDAs (personal digital assistants), mobile phones, wearable devices, cordless phone handsets, video movie players, digital still cameras, e-books, electronic dictionaries, music players, radios, headphones, game consoles, navigation systems, memory cards, pacemakers, hearing aids, power tools, electric shavers, refrigerators, air conditioners, televisions, stereos, water heaters, microwave ovens, dishwashers, washing machines, dryers, lighting equipment, toys, medical equipment, robots, road conditioners, and traffic lights.

[0081] Examples of electric vehicles include railcars, golf carts, electric carts, electric vehicles (including hybrid vehicles), and the like, and the device is used as a driving power source or auxiliary power source for these. Examples of power storage devices include power storage power sources for buildings such as homes, or for power generation facilities.

[0082] An embodiment of the present disclosure will be described.

[0083] Example 1 As described below, a cylindrical secondary battery 1 shown in Fig. 1 was fabricated, and then its battery characteristics were evaluated. Here, a secondary battery 1 having dimensions of 21 mm in diameter and 70 mm in length was fabricated.

[0084] [Fabrication Method] First, a 12 μm thick aluminum foil was prepared as the positive electrode current collector 21A. Next, a layered lithium oxide (lithium nickel cobalt aluminum oxide (NCA) with a Ni ratio of 85% or more) was mixed as the positive electrode active material, a positive electrode binder made of polyvinylidene fluoride, and a conductive additive containing a mixture of carbon black, acetylene black, and ketjen black to obtain a positive electrode mixture. The mixture ratio of the positive electrode active material, positive electrode binder, and conductive additive was 96.4:2:1.6. Next, the positive electrode mixture was added to an organic solvent (N-methyl-2-pyrrolidone) and stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to predetermined regions on both sides of the positive electrode current collector 21A using a coating device, and the positive electrode mixture slurry was then dried to form the positive electrode active material layer 21B. Furthermore, a coating material containing polyvinylidene fluoride (PVDF) was applied to the surface of the positive electrode exposed portion 212 adjacent to the positive electrode covering portion 211, and the coating material was dried to form an insulating layer 101 having a width of 3 mm and a thickness of 8 μm. The positive electrode active material layer 21B was then compression molded using a roll press. This resulted in a positive electrode 21 having the positive electrode covering portion 211 and the positive electrode exposed portion 212. The width of the positive electrode covering portion 211 in the W-axis direction was 60 mm, and the width of the positive electrode exposed portion 212 in the W-axis direction was 7 mm. The length of the positive electrode 21 in the L-axis direction was 1700 mm. In the obtained positive electrode 21, the area density of the positive electrode active material layer 21B was 22.0 mg / cm. ２ The volume density of the positive electrode active material layer 21B is 3.55 g / cm ３ The thickness T1 of the positive electrode covering portion 211 was 74.3 μm.

[0085] Additionally, an 8 μm thick copper foil was prepared as the negative electrode current collector 22A. Next, a negative electrode active material consisting of a mixture of a carbon material made of graphite and SiO was prepared. A negative electrode binder consisting of polyvinylidene fluoride was mixed with a conductive additive consisting of a mixture of carbon black, acetylene black, and ketjen black to obtain a negative electrode mixture. The mixing ratio of the negative electrode active material, the negative electrode binder, and the conductive additive was 96.1:2.9:1.0. Furthermore, the mixing ratio of graphite to SiO in the negative electrode active material was 95:5. Subsequently, the negative electrode mixture was introduced into an organic solvent (N-methyl-2-pyrrolidone), and the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. Next, a coating device was used to apply the anode mixture slurry to predetermined regions on both sides of the anode current collector 22A, and the anode mixture slurry was then dried to form the anode active material layer 22B. The anode active material layer 22B was then compression-molded using a roll press. This resulted in a anode 22 having a anode covering portion 221 and anode exposed portion 222. The width of the anode covering portion 221 in the W-axis direction was 62 mm, and the width of the first portion 222A of the anode exposed portion 222 in the W-axis direction was 4 mm. The length of the anode 22 in the L-axis direction was 1760 mm. In the resulting anode 22, the area density of the anode active material layer 22B was 10.83 mg / cm. ２ The volume density of the negative electrode active material layer 22B is 1.65 g / cm ３ The thickness of the negative electrode covering portion 221 was 80.2 μm.

[0086] Next, the positive electrode 21 and the negative electrode 22 were stacked with the first separator member 23A and the second separator member 23B interposed therebetween so that the positive electrode exposed portion 212 and the first portion 222A of the negative electrode exposed portion 222 were on opposite sides of each other in the W-axis direction, thereby producing a laminate S20. The laminate S20 was produced so that the positive electrode active material layer 21B did not protrude beyond the negative electrode active material layer 22B in the W-axis direction. Polyethylene sheets having a width of 65 mm and a thickness of 14 μm were used as the first separator member 23A and the second separator member 23B. After producing the laminate S20, the laminate S20 was spirally wound so that the through-holes 26 were formed and the notch was positioned near the central axis CL, and a fixing tape 46 was attached to the outermost periphery of the wound laminate S20. This produced an electrode roll 20. When fabricating the electrode winding body 20, the number N21in of bending points K21A of the positive electrode current collector 21A in the central axis side portion 20in was set to be greater than the number N21out of bending points K21A of the positive electrode current collector 21A in the outer peripheral side portion 20out (N21out < N21in). Furthermore, the maximum spacing W21out was set to be greater than the maximum spacing W21in (W21out > W21in). Similarly, when fabricating the electrode winding body 20, the number N22in of bending points K22A of the negative electrode current collector 22A in the central axis side portion 20in was set to be greater than the number N22out of bending points K22A of the negative electrode current collector 22A in the outer peripheral side portion 20out (N22out < N22in). Furthermore, the maximum spacing W22out was set to be greater than the maximum spacing W22in (W22out > W22in).

[0087] Next, the ends of a 0.5 mm thick flat plate were pressed against the end faces 41 and 42 of the electrode winding body 20 in the Z-axis direction, thereby locally bending the end faces 41 and 42 and creating grooves 43 extending radially from the through hole 26 in the radial direction (R direction).

[0088] Next, substantially the same pressure was applied to end face 41 and end face 42 from above and below electrode winding body 20 substantially simultaneously and in a direction approximately perpendicular to end face 41 and end face 42, thereby bending positive electrode exposed portion 212 and first portion 222A of negative electrode exposed portion 222, respectively, to make end face 41 and end face 42 flat. At this time, first edge 212E of positive electrode exposed portion 212 and second edge 222E of negative electrode exposed portion 222 on end face 41 and end face 42 were bent while overlapping toward through hole 26. Thereafter, sector-shaped portion 31 of positive electrode current collector plate 24 was joined to end face 41 by laser welding, and sector-shaped portion 33 of negative electrode current collector plate 25 was joined to end face 42 by laser welding.

[0089] Next, insulating tapes 53, 54 were attached to predetermined positions of the electrode winding body 20, and then the strip portion 32 of the positive electrode current collector 24 was bent to insert the strip portion 32 into the hole 12H of the insulating plate 12, and the strip portion 34 of the negative electrode current collector 25 was bent to insert the strip portion 34 into the hole 13H of the insulating plate 13.

[0090] Next, the electrode winding body 20 assembled as described above was inserted into the outer can 11, and the bottom of the outer can 11 was welded to the negative electrode current collector 25. After that, a constricted portion 11S was formed near the open end 11N of the outer can 11. Furthermore, an electrolyte was poured into the outer can 11, and the strip portion 32 of the positive electrode current collector 24 was welded to the safety valve mechanism 30.

[0091] The electrolyte used was a solvent containing ethylene carbonate (EC) and dimethyl carbonate (DMC) as the main solvent, to which fluoroethylene carbonate (FEC) and succinonitrile (SN) were added, and LiBF4 and LiPF6 were used as electrolyte salts. In the lithium-ion secondary battery of this example, the respective contents (by weight) of EC, DMC, FEC, SN, LiBF4, and LiPF6 in the electrolyte were 12.7:56.2:12.0:1.0:1.0:17.1.

[0092] Finally, the gasket 15, the safety valve mechanism 30, and the battery lid 14 were used to seal the necked portion 11S.

[0093] In this manner, a secondary battery 1 was obtained as Example 1-1.

[0094] [Evaluation of Battery Characteristics] The battery characteristics of the secondary battery 1 (number of samples n=50) as Example 1 obtained as described above were evaluated, and the results shown in Table 1 were obtained. The evaluation items were the cycle capacity retention rate and the remaining capacity after a high-temperature storage test.

[0095] Specifically, a cycle test was conducted under the following test conditions, and then the cycle capacity retention rate was investigated. The test conditions for the cycle test were as follows: <Cycle Test Conditions> (1) Environmental temperature: 25°C. (2) Charging conditions: Constant current constant voltage (CC-CV) charging was performed. After charging at a constant current of 1 C to a voltage of 4.2 V, charging was performed at a constant voltage of 4.2 V. The cut-off time was 2.5 hours. (3) Rest time after charging: 30 minutes. (4) Discharge conditions: Constant current (CC) discharge was performed at a constant current of 5 C. The cut-off voltage was 2.5 V. (5) Rest time after discharging: 30 minutes. (6) Number of cycles: 500 cycles.

[0096] Specifically, a high-temperature storage test was conducted under the following test conditions, and then the remaining capacity was investigated. The test method for the high-temperature storage test was as follows. <High-Temperature Storage Test Conditions> (1) Charging: First, constant-current constant-voltage (CC-CV) charging was conducted in a room temperature (25°C) environment. Specifically, charging was conducted at a constant current of 1 C to a voltage of 4.2 V, and then charging was conducted at a constant voltage of 4.2 V. The cut-off time was set to 2.5 hours. (2) Discharging: Constant-current (CC) discharging was conducted at a constant current of 0.2 C. The cut-off voltage was set to 2.0 V. The discharge capacity at this time was measured and used as the initial capacity. (3) Full Charging: Next, constant-current constant-voltage (CC-CV) charging was conducted in a room temperature (25°C) environment. Specifically, charging was conducted at a constant current of 1 C to a voltage of 4.2 V, and then charging was conducted at a constant voltage of 4.2 V. The cut-off time was set to 2.5 hours. (4) High-temperature storage: The secondary battery was stored in a thermostatic chamber at 60°C for one month. (5) Discharge: After high-temperature storage, the secondary battery was subjected to constant current (CC) discharge at a constant current of 0.2 C in a room temperature (25°C) environment. The cut-off voltage was set to 2.0 V. The discharge capacity at this time was measured and used as the remaining capacity. (6) The remaining capacity / initial capacity was calculated as the high-temperature storage capacity retention rate.

[0097]

[0098] Comparative Example 1 When fabricating the electrode winding 20, the number N21out of bending points K21A of the positive electrode current collector 21A in the outer peripheral portion 20out was set to be greater than the number N21in of bending points K21A of the positive electrode current collector 21A in the central axis side portion 20in (N21out > N21in). Furthermore, the maximum spacing W21in was set to be greater than the maximum spacing W21out (W21out < W21in). Similarly, when fabricating the electrode winding 20, the number N22out of bending points K22A of the negative electrode current collector 22A in the outer peripheral portion 20out was set to be greater than the number N22in of bending points K22A of the negative electrode current collector 22A in the central axis side portion 20in (N22out > N22in). Furthermore, the maximum spacing W22in was set to be greater than the maximum spacing W22out (W22out < W22in). Except for the above, a secondary battery of Comparative Example 1 was fabricated in the same manner as in Example 1, and the battery characteristics were evaluated in the same manner as in Example 1 (number of samples n=50). The results are also shown in Table 1.

[0099] Comparative Example 2 When fabricating the electrode winding 20, the number N21out of bending points K21A of the positive electrode current collector 21A in the outer peripheral portion 20out was set to be substantially equal to the number N21in of bending points K21A of the positive electrode current collector 21A in the central axis side portion 20in (N21out ≈ N21in). Furthermore, the maximum spacing W21out and the maximum spacing W21in were set to be substantially equal (W21out ≈ W21in). Similarly, when fabricating the electrode winding 20, the number N22out of bending points K22A of the negative electrode current collector 22A in the outer peripheral portion 20out was set to be substantially equal to the number N22in of bending points K22A of the negative electrode current collector 22A in the central axis side portion 20in (N22out ≈ N22in). The maximum spacing W22out and the maximum spacing W22in were set to be substantially equal (W22out ≈ W22in). Except for the above, a secondary battery of Comparative Example 2 was fabricated in the same manner as in Example 1, and the battery characteristics were evaluated in the same manner as in Example 1 (number of samples n = 50). The results are also shown in Table 1.

[0100] [Discussion] As shown in Table 1, Example 1 exhibited higher values ​​for both the high-temperature storage capacity retention rate and the cycle capacity retention rate than Comparative Examples 1 and 2. This is because, in Example 1, the number N21in of bending points K21A in the central axis side portion 20in was greater than the number N21out of bending points K21A in the outer peripheral side portion 20out, and the number N22in of bending points K22A in the central axis side portion 20in was greater than the number N22out of bending points K22A in the outer peripheral side portion 20out. That is, it was confirmed that, in Example 1, impregnation of the outer peripheral side portion 20out of the electrode winding body 20 with an appropriate amount of electrolyte can prevent an internal short circuit between the positive electrode 21 and the negative electrode 22 during high-temperature storage, and that avoiding excessive impregnation of the central axis side portion 20in of the electrode winding body 20 with electrolyte can mitigate deterioration of cycle characteristics.

[0101] Although the present disclosure has been described above with reference to one embodiment, the configuration of the present disclosure is not limited to the configuration described in the one embodiment and can be modified in various ways. For example, in the above embodiment, the number N21in of bending points K21A in the central axis side portion 20in is greater than the number N21out of bending points K21A in the outer peripheral side portion 20out at the upper part of the outer can 11, and the number N22in of bending points K22A in the central axis side portion 20in is greater than the number N22out of bending points K22A in the outer peripheral side portion 20out. However, the present disclosure is not limited to this. For example, the number N21in may be greater than the number N21out, while the numbers N22out and N22in may be equal, or the number N22out may be greater than the number N22in. Alternatively, the number N22in may be greater than the number N22out, while the number N21out and the number N21in may be equal, or the number N21out may be greater than the number N21in.

[0102] Furthermore, in the above embodiment, an example was given in which the maximum interval W21out is larger than the maximum interval W21in, but in the present disclosure, the maximum interval W21out may be substantially equal to the maximum interval W21in, or the maximum interval W21out may be smaller than the maximum interval W21in. Furthermore, in the above embodiment, an example was given in which the maximum interval W22out is larger than the maximum interval W22in, but in the present disclosure, the maximum interval W22out may be substantially equal to the maximum interval W22in, or the maximum interval W22out may be smaller than the maximum interval W22in.

[0103] In addition, although the above embodiment and examples have been described with reference to a case where the electrode reactant is 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.

[0104] The effects described in this specification are merely examples, and the effects of the present disclosure are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present disclosure.

[0105] Furthermore, the present disclosure may take the following forms: <1> A battery comprising: an electrode wound body formed by winding a laminate including, in order, a first electrode, a first separator, a second electrode, and a second separator around a central axis extending in a first direction, the electrode wound body having a first end face and a second end face facing each other in the first direction, a first electrode current collector disposed so as to face the first end face of the electrode wound body, a second electrode current collector disposed so as to face the second end face of the electrode wound body, an electrolyte, and a battery can accommodating the electrode wound body, the first electrode current collector, the second electrode current collector, and the electrolyte, wherein the first electrode has a first electrode covering portion in which a first electrode current collector is covered with a first electrode active material layer, and a first electrode exposed portion in which the first electrode current collector is exposed without being covered by the first electrode active material layer and joined to the first electrode current collector, and adjacent to the first electrode covering portion in the first direction, The secondary battery according to claim 1, wherein the number of bends of the first electrode current collector of the first electrode exposed portion in the outer circumferential portion of the electrode winding is greater than the number of bends of the first electrode current collector of the first electrode exposed portion in the outer circumferential portion of the electrode winding. <3> The secondary battery according to <1> or <2> above, wherein the second electrode has a second electrode covered portion in which a second electrode current collector is covered with a second electrode active material layer, and a second electrode exposed portion in which the second electrode current collector is exposed without being covered with the second electrode active material layer, joined to the second electrode current collector, and adjacent to the second electrode covered portion in the first direction, and wherein the number of bending points of the second electrode current collector in the second electrode exposed portion at the central axis side portion of the electrode winding is greater than the number of bending points of the second electrode current collector in the second electrode exposed portion at the outer circumferential side portion of the electrode winding.<4> The secondary battery according to <3>, wherein the maximum spacing between the multiple wound portions of the second electrode current collector that constitutes the outer circumferential portion of the electrode winding is larger than the maximum spacing between the multiple wound portions of the second electrode current collector that constitutes the central axis side portion of the electrode winding. <5> The battery can includes a bottom and a wall portion erected on an outer edge of the bottom, wherein the second electrode exposed portion is located between the bottom and the second electrode covering portion, and the first electrode exposed portion is located on the opposite side of the bottom from the first electrode covering portion, and the number of bends of the second electrode current collector in the second electrode exposed portion at the central axis side portion of the electrode winding is greater than the number of bends of the first electrode current collector in the first electrode exposed portion at the central axis side portion of the electrode winding. <6> The secondary battery according to any one of <1> to <5>, wherein the first electrode is a positive electrode and the second electrode is a negative electrode. <7> A battery pack including: the secondary battery according to any one of <1> to <6> above; a control unit that controls the secondary battery; and an exterior body that encapsulates the secondary battery.

Claims

1. an electrode winding body formed by winding a laminate including a first electrode, a first separator, a second electrode, and a second separator in that order around a central axis extending in a first direction, the electrode winding body having a first end face and a second end face opposed to each other in the first direction; a first electrode current collector disposed to face the first end surface of the electrode winding body; a second electrode current collector arranged to face the second end surface of the electrode winding body; An electrolyte; a battery can that accommodates the electrode winding body, the first electrode current collector, the second electrode current collector, and the electrolyte; Equipped with the first electrode has a first electrode covering portion in which a first electrode collector is covered with a first electrode active material layer, and a first electrode exposed portion in which the first electrode collector is exposed without being covered with the first electrode active material layer, is joined to the first electrode collector, and is adjacent to the first electrode covering portion in the first direction; The number of bent points of the first electrode current collector of the first electrode exposed portion in a central axis side portion of the electrode winding is greater than the number of bent points of the first electrode current collector of the first electrode exposed portion in an outer circumferential side portion of the electrode winding. Secondary battery.

2. The maximum distance between the plurality of winding portions of the first electrode current collector constituting the outer periphery side portion of the electrode winding body is larger than the maximum distance between the plurality of winding portions of the first electrode current collector constituting the central axis side portion of the electrode winding body. The secondary battery according to claim 1 .

3. the second electrode has a second electrode covering portion in which a second electrode collector is covered with a second electrode active material layer, and a second electrode exposed portion in which the second electrode collector is exposed without being covered with the second electrode active material layer, is joined to the second electrode collector, and is adjacent to the second electrode covering portion in the first direction, the number of bent points of the second electrode current collector of the second electrode exposed portion in the central axis side portion of the electrode winding is greater than the number of bent points of the second electrode current collector of the second electrode exposed portion in the outer circumferential side portion of the electrode winding The secondary battery according to claim 1 .

4. The maximum distance between the multiple winding portions of the second electrode current collector that constitutes the outer periphery side portion of the electrode winding body is larger than the maximum distance between the multiple winding portions of the second electrode current collector that constitutes the central axis side portion of the electrode winding body. The secondary battery according to claim 3.

5. The battery can includes a bottom and a wall portion extending from an outer edge of the bottom, the second electrode exposed portion is located between the bottom portion and the second electrode covered portion, the first electrode exposed portion is located on the opposite side of the bottom portion from the first electrode covered portion, The number of bent points of the second electrode current collector of the second electrode exposed portion in the central axis side portion of the electrode winding is greater than the number of bent points of the first electrode current collector of the first electrode exposed portion in the central axis side portion of the electrode winding. The secondary battery according to claim 3.

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

7. The secondary battery according to any one of claims 1 to 5, A control unit that controls the secondary battery; an exterior body that encapsulates the secondary battery; A battery pack having