Secondary battery and battery pack

Abstract

Provided is a secondary battery having excellent vibration resistance without degraded manufacturability. This secondary battery comprises an electrode wound body and a battery can. The electrode wound body is formed by stacking a positive electrode and a negative electrode with a separator therebetween and wound around a central axis. The battery can has a cylindrical outer shape having, as the height direction, a direction along the center axis and accommodates the electrode wound body. The battery can has a container and a lid part. The container has: a lower end section closed by a bottom section; and an upper end section which is located on the side opposite the lower end section in the height direction and includes an opening open so that the electrode wound body can be inserted therethrough. The lid part closes the opening of the container. Here, when the ratio of the maximum diameter of the electrode wound body to the minimum diameter of the electrode wound body is defined as the flatness of the electrode wound body, the flatness of at least a portion of an upper section of the electrode wound body is greater than the flatness of at least a portion of a lower section of the electrode wound body.

Description

Secondary batteries and 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 battery element 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 that employs a so-called tabless structure to reduce internal resistance and enable charging and discharging with a relatively large current.

[0004] International Publication No. 2021 / 020235

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

[0006] Therefore, a secondary battery having excellent vibration resistance without impairing manufacturability is desired.

[0007] A secondary battery according to an embodiment of the present disclosure includes an electrode winding and a battery can. The electrode winding is formed by stacking a positive electrode and a negative electrode with a separator interposed between them and winding them around a central axis. The battery can has a generally cylindrical outer shape with its height direction along the central axis and houses the electrode winding. The battery can includes a container and a lid. The container has a lower end portion closed by a bottom portion and an upper end portion located opposite the lower end portion in the height direction and including an opening through which the electrode winding can be inserted. The lid portion closes the opening of the container. Here, when the flatness of the electrode winding is defined as the ratio of the maximum diameter of the electrode winding to the minimum diameter of the electrode winding, the flatness of the upper portion of the electrode winding is greater than the flatness of the lower portion of the electrode winding.

[0008] According to the secondary battery of one embodiment of the present disclosure, the flatness of the upper part of the electrode winding is greater than the flatness of the lower part of the electrode winding. Because the flatness of the lower part of the electrode winding is relatively small, the electrode winding can be easily inserted into the battery can during assembly of the secondary battery. Furthermore, because the flatness of the upper part of the electrode winding is large, the electrode winding is less likely to move inside the battery can even when vibrations are applied to the secondary battery. As a result, damage to the electrode winding itself and to the connection between the positive electrode current collector plate joined to the electrode winding and the external terminal (lid) can be prevented. Therefore, according to the secondary battery of one embodiment of the present disclosure, excellent vibration resistance can be ensured without impairing manufacturability.

[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 vertical cross-sectional view illustrating an example configuration of the vertical 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 a plan view of the positive electrode current collector illustrated in FIG. 1. FIG. 6B is a plan view of the negative electrode current collector illustrated in FIG. 1. FIG. 7A is a horizontal cross-sectional view schematically illustrating the horizontal cross-sectional structure of the upper part of the electrode winding body illustrated in FIG. 1. FIG. 7B is a horizontal cross-sectional view schematically illustrating the horizontal cross-sectional structure of the lower part of the electrode winding body 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 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 this embodiment. The secondary battery 1 shown in Fig. 1 includes an outer can 11 having a cylindrical outer shape as a battery can, and an electrode wound body 20 as a battery element housed in the outer can 11. The cylindrical shape referred to here is not limited to a circular shape in cross section perpendicular to the height direction, but also includes a shape in cross section perpendicular to the height direction that is elliptical. Furthermore, the secondary battery 1 includes an outer tube 50 that covers the outer peripheral surface of the 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 in the Z-axis direction (height direction) and an open upper end. Therefore, the upper end of the external can 11 is an open end 11N, and the lower end of the external can 11 is closed by a substantially disc-shaped bottom 11B. Between the open end 11N and the bottom 11B is a side wall 11W that surrounds the electrode winding 20. The external can 11 is made of a material that 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 opposite each other in the Z-axis direction, sandwiching the electrode winding 20 therebetween. 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. An open end 11N of the outer can 11 is closed by a battery lid 14 (described later).

[0020] (Outer tube 50) The outer tube 50 surrounds the side surface 11WS1, which is the outer surface of the side wall portion 11W of the outer can 11. However, as shown in Fig. 1 , the outer tube 50 may also cover the folded portion 11P (described later) at the upper end of the outer can 11. The outer tube 50 may also cover a portion of the bottom surface 11BS, which is the outer surface of the bottom portion 11B of the outer can 11. The outer tube 50 is made of a heat-shrinkable insulating film containing, for example, a polyester-based resin, a polyamide-based resin, or a thermoplastic elastomer resin.

[0021] (Washer 55) A washer 55 is provided in the gap between the exterior tube 50 and the bent portion 11P of the exterior can 11. The washer 55 is an insulating ring member having an opening 55K in the central region within a plane perpendicular to the height direction. The protrusion 14T in the central region of the battery lid 14 is inserted into the opening 55K. The washer 55 can be made of, for example, black modified polyphenylene ether.

[0022] (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.

[0023] (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.

[0024] (Battery lid 14) The battery lid 14 is mainly a closing member that 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, a convex portion 14T that protrudes upward (in the +Z direction) is provided in the central region of the battery lid 14. 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.

[0025] (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.

[0026] (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.

[0027] (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.

[0028] 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. In the laminate S20 obtained by developing the electrode winding body 20, the positive electrode 21 and the negative electrode 22 are stacked with the separator 23 interposed therebetween. The separator 23 has, for example, two base materials, namely, a first separator member 23A and a second separator member 23B. Thus, 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.

[0029] As shown in FIG. 3 , the electrode winding body 20 is formed by winding the laminate S20 around a central axis CL 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 in an orientation in which the W-axis direction roughly coincides 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 from illustration to improve visibility. The electrode winding body 20 has an overall substantially cylindrical appearance. The positive electrode 21 and the negative electrode 22 are wound while maintaining a state in which they face each other with the separator 23 interposed therebetween. A through-hole 26 is formed at the center of the electrode winding body 20 as an internal space. 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.

[0030] 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.

[0031] 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.

[0032] 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 central axis side edge 21E1 to the outer peripheral edge 21E2 of the positive electrode 21. 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 central axis side edge 21E1 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. As shown in FIG. 2 , in the electrode winding body 20, the central axis side edge 21E1 of the positive electrode innermost circumferential portion 21 in is located in a position receding inward from the central axis side edge 22E1 of the negative electrode innermost circumferential portion 22 in. The positive electrode 21 also has a lower edge 21E3 extending in the L-axis direction at the lower side of the electrode winding body 20.

[0033] 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 central axis side edge 21E1 to the outer peripheral side edge 21E2 of the electrode winding body 20. The insulating layer 101 may 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. The insulating layer 101 may contain a resin containing polyvinylidene fluoride (PVDF). The PVDF content of the insulating layer 101 allows the insulating layer 101 to swell with, for example, a solvent contained in the electrolyte solution, thereby enabling good adhesion to the separator 23. The detailed configuration of the positive electrode 21 will be described later.

[0034] 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.

[0035] 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 central axis side 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 central axis side 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 negative electrode 22 further has a lower edge 22E3 extending in the L-axis direction at the lower side of the electrode winding body 20. The first portion 222A is provided adjacent to the negative electrode cover portion 221 in the W-axis direction and extends in the L-axis direction from the central axis side edge 22E1 to the outer peripheral edge 22E2 of the negative electrode 22. The second portion 222B and the third portion 222C are provided to sandwich the negative electrode cover portion 221 in the L-axis direction. The first portion 222A is located near the lower edge 22E3 of the negative electrode 22. The second portion 222B is located near the central axis side 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. 5A and 5B schematically show the negative electrode current collector 22A extending linearly along the W-axis direction. However, in reality, the negative electrode edge portion 222E of the negative electrode exposed portion 222 is bent toward the central axis CL as shown in FIG. 1 and connected to the negative electrode current collector plate 25. The detailed configuration of the negative electrode 22 will be described later.

[0036] 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.

[0037] 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).

[0038] 1 , at the upper part of the secondary battery 1, a plurality of adjacent positive electrode edge portions 212E in the radial direction (direction R) of the electrode wound body 20 of the positive electrode exposed portion 212 wound around the central axis CL are bent toward the central axis CL so as to overlap with each other, thereby constituting an upper end surface 41 of the electrode wound body 20. Similarly, at the lower part of the secondary battery 1, a plurality of adjacent negative electrode edge portions 222E in the radial direction (direction R) of the negative electrode exposed portion 222 wound around the central axis CL are bent toward the central axis CL so as to overlap with each other, thereby constituting a lower end surface 42 of the electrode wound body 20. Therefore, a plurality of positive electrode edge portions 212E of the positive electrode exposed portion 212 are gathered at the upper end surface 41 of the electrode wound body 20, and a plurality of negative electrode edge portions 222E of the negative electrode exposed portion 222 are gathered at the lower end surface 42 of the electrode wound body 20. In order to improve contact between the positive electrode current collector plate 24 for extracting current and the positive electrode edge portion 212E, the multiple positive electrode edge portions 212E are bent toward the central axis CL and have flat surfaces. Similarly, in order to improve contact between the negative electrode current collector plate 25 for extracting current and the negative electrode edge portion 222E, the multiple negative electrode edge portions 222E are bent toward the central axis CL and have flat surfaces. Note that the flat surface referred to here does not only include a completely flat surface, but also includes a surface that has some unevenness or surface roughness to the extent that the positive electrode exposed portion 212 and the negative electrode exposed portion 222 can be joined to the positive electrode current collector plate 24 and the negative electrode current collector plate 25, respectively.

[0039] 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 positive electrode 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 negative electrode 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 joining here means joining by, for example, laser welding, but the joining method is not limited to laser welding.

[0040] 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 bending of the positive electrode exposed portion 212 and short circuiting between the positive electrode exposed portion 212 and the negative electrode 22.

[0041] (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 body 20. The positive electrode exposed portion 212 and the negative electrode exposed portion 222, which are gathered at the upper end surface 41 and the lower end surface 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 upper end surface 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 one of polypropylene, polyethylene terephthalate, and 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.

[0042] (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 the upper end face 41 and the negative current collector 25 is positioned opposite the lower end face 42. The positive electrode cover 211 at the upper end face 41 is welded to the positive electrode cover 24 at multiple points, and the negative electrode cover 221 at the lower end face 42 is welded to the negative electrode cover 25 at multiple points. This reduces the internal resistance of the secondary battery 1. The flat surfaces of the upper end face 41 and the lower end face 42, as described above, also contribute to the low resistance. The positive electrode current collector 24 is electrically connected to the battery lid 14 via, for example, a safety valve mechanism 30. The negative electrode current collector 25 is electrically connected to, for example, the outer can 11. FIG. 6A is a schematic diagram showing an example of the configuration of the positive electrode current collector 24. FIG. 6B 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.

[0043] As shown in FIG. 6A , 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 fan-shaped portion 31. A through-hole 35 is formed near the center of the fan-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. 6A 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.

[0044] The shape of the negative current collector 25 shown in FIG. 6B is almost the same as the shape of the positive current collector 24 shown in FIG. 6A . 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.

[0045] Due to its planar shape, the sector-shaped portion 31 of the positive current collector plate 24 covers only a portion of the upper 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 lower end surface 42. The sector-shaped portions 31 and 33 do not cover the entire upper end surface 41 and the entire lower end surface 42 for the following two reasons. First, this is to allow the electrolyte to smoothly penetrate into the electrode winding body 20 when assembling the secondary battery 1, for example. 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.

[0046] (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.

[0047] (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.

[0048] (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.

[0049] (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.

[0050] 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.

[0051] (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.

[0052] 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.

[0053] (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.

[0054] 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.

[0055] (Horizontal Cross-Sectional Shape of Secondary Battery) Both Fig. 7A and Fig. 7B schematically show the structure of a horizontal cross section perpendicular to the central axis CL of the secondary battery 1. Note that Fig. 7A and Fig. 7B only show the electrode winding body 20 and the outer can 11, and other components are omitted. Furthermore, Fig. 7A and Fig. 7B do not show the detailed configuration of the electrode winding body 20, but only show the outer shape of the electrode winding body 20 so that it can be recognized. In particular, Fig. 7A shows a horizontal cross section of the upper part of the electrode winding body 20 in the height direction Z. In contrast, Fig. 7B shows a horizontal cross section of the lower part of the electrode winding body 20 in the height direction Z. Here, the upper part of the electrode winding body 20 in the height direction Z refers to any location in the portion above the center point CP ( Fig. 1 ) of the electrode winding body 20 in the height direction Z. Furthermore, the lower part of the electrode winding body 20 in the height direction Z refers to any location within the portion below the center point CP ( FIG. 1 ) of the electrode winding body 20 in the height direction Z. In detail, FIG. 7A shows a horizontal cross section at a height position Lv1 indicated by an arrow in FIG. 1 . Meanwhile, FIG. 7B shows a horizontal cross section at a height position Lv2 indicated by an arrow in FIG. 1 . Here, the height position Lv1 corresponds to the height position of the upper edge of the electrode winding body 20 in the height direction Z. Furthermore, the height position Lv2 corresponds to the height position of the lower edge of the electrode winding body 20 in the height direction Z.

[0056] As shown in FIGS. 7A and 7B , in the secondary battery 1, the horizontal cross-sectional shape of the outer can 11 is approximately circular. Therefore, the inner diameter D11 of the outer can 11 is substantially constant. In contrast, as shown in FIG. 7A , the horizontal cross-sectional shape of the electrode winding body 20 at the upper part of the secondary battery 1 is approximately elliptical. Here, the first radial direction in which the outer diameter of the electrode winding body 20 is maximum in the horizontal cross-section is defined as the radial direction R1. In FIG. 7A , the radial direction R1 is defined as the up-down direction on the paper. The electrode winding body 20 has a maximum diameter D20max1 along the radial direction R1 at the height position Lv1. Furthermore, the electrode winding body 20 has a minimum diameter D20min1 along the radial direction R2 (the left-right direction on the paper) perpendicular to the radial direction R1 at the height position Lv1. (D20max1 - D20min1) / D20max1 is referred to as the flatness FT1 of the electrode winding body 20 at the height position Lv1.

[0057] As shown in FIG. 7B , the horizontal cross-sectional shape of the electrode winding body 20 is also substantially elliptical at the lower part of the secondary battery 1. However, the flatness FT2 of the horizontal cross-sectional shape of the electrode winding body 20 at the height position Lv2 is smaller than the flatness FT1 of the horizontal cross-sectional shape of the electrode winding body 20 at the height position Lv1. That is, the flatness FT1 of the horizontal cross-sectional shape of the electrode winding body 20 at the height position Lv1 is larger than the flatness FT2 of the horizontal cross-sectional shape of the electrode winding body 20 at the height position Lv2 (FT1 > FT2). The electrode winding body 20 has a maximum diameter D20max2 along the radial direction R1 at the height position Lv2. The maximum diameter D20max2 at the height position Lv2 is smaller than the maximum diameter D20max1 at the height position Lv1. Furthermore, the electrode winding body 20 has a minimum diameter D20min2 along the radial direction R2 at the height position Lv2. The flatness FT2 of the electrode winding 20 at the height position Lv2 is expressed as (D20max2-D20min2) / D20max2. The maximum diameter at the center point CP of the electrode winding 20 in the height direction Z is smaller than the maximum diameter D20max1 at the upper edge of the electrode winding 20 in the height direction Z and is larger than the maximum diameter D20max2 at the lower edge of the electrode winding 20 in the height direction Z.

[0058] 7A , at the height position Lv1, a part of the outer peripheral surface 20S of the electrode winding body 20 may be in contact with the inner surface 11WS2 of the side wall portion 11W of the outer can 11. In this case, the maximum diameter D20max1 of the electrode winding body 20 substantially coincides with the inner diameter D11 of the outer can 11. In contrast, as shown in FIG. 7B , at the height position Lv2, the outer peripheral surface 20S of the electrode winding body 20 is spaced from the inner surface 11WS2 of the side wall portion 11W of the outer can 11. In other words, the maximum diameter D20max2 of the electrode winding body 20 is smaller than the inner diameter D11 of the outer can 11.

[0059] [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.

[0060] 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.

[0061] First, a positive electrode current collector 21A is prepared, and a positive electrode active material layer 21B is selectively formed on the surface of the positive electrode current collector 21A to form a positive electrode 21 having a positive electrode coating 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 coating 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 so 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. Thereafter, the stack S20 is spirally wound to form through-holes 26. In this process, for example, a cylindrical winding core whose cross-sectional shape gradually changes from ellipse to circle along the height direction is used as a jig, and the laminate S20 is wound around the cylindrical winding core. Furthermore, a fixing tape 46 is attached to the outermost periphery of the spirally wound laminate S20, and then the winding core is removed. This results in the electrode winding body 20 as shown in FIG. 8A . Alternatively, the laminate S20 may be wound around a cylindrical winding core whose cross-sectional shape is circular, and after the winding core is removed, light pressure may be applied to a portion of the wound laminate S20 in the height direction using a jig such as a clamp, thereby obtaining the electrode winding body 20 having the predetermined flatnesses FT1 and FT2.

[0062] Next, as shown in Fig. 8B , the edge of a flat plate having a thickness of, for example, 0.5 mm is pressed perpendicularly against the upper end surface 41 and the lower end surface 42 of the electrode winding body 20, i.e., in the Z-axis direction, thereby locally bending a portion of the upper end surface 41 and a portion of the lower end surface 42. As a result, grooves 43 are formed extending radially from the through-holes 26 in the radial direction (direction R). Note that the number and arrangement of grooves 43 shown in Fig. 8B are merely examples and the present disclosure is not limited thereto.

[0063] 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 upper end face 41 and the lower end face 42. At this time, for example, a rod-shaped jig is inserted into the through-hole 26. By doing so, the positive electrode exposed portion 212 and the first portion 222A of the negative electrode exposed portion 222 are bent so that the upper end face 41 and the lower end face 42 become flat surfaces. At this time, the positive electrode edge portion 212E of the positive electrode exposed portion 212 and the negative electrode edge portion 222E of the negative electrode exposed portion 222 at the upper end face 41 and the lower end face 42 are bent while overlapping toward the through-hole 26. Thereafter, the sector-shaped portion 31 of the positive electrode current collector 24 is joined to the upper end face 41 by laser welding or the like, and the sector-shaped portion 33 of the negative electrode current collector 25 is joined to the lower end face 42 by laser welding or the like.

[0064] 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.

[0065] 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.

[0066] 8(F), the outer can 11 is sealed using the gasket 15, the safety valve mechanism 30, and the battery lid 14, utilizing the constricted portion 11S. Finally, the outer can 11, with the washer 55 attached to the battery lid 14, is covered with the outer tube 50, and the outer tube 50 is heated and shrunk by applying hot air to the outer tube 50, for example, and the outer tube 50 is then tightly attached to the outer surface of the outer can 11.

[0067] In this way, the secondary battery 1 of this embodiment is completed.

[0068] [1-4. Actions and Effects] As described above, in the secondary battery 1 of the present embodiment, the flatness FT1 of the horizontal cross-sectional shape of the upper part of the electrode winding body 20 is larger than the flatness FT2 of the horizontal cross-sectional shape of the lower part of the electrode winding body 20 (FT1>FT2). As described above, the flatness FT2 of the lower part of the electrode winding body 20 is smaller than the flatness FT1 of the upper part, which makes it easier to insert the electrode winding body 20 into the outer casing 11 during the assembly of the secondary battery 1. That is, by reducing the flatness FT2 of the lower part of the electrode winding body 20 so that the cross-sectional shape approaches a perfect circle, the electrode winding body 20 can be easily accommodated inside the outer casing 11 without interfering with the outer circumferential surface 20S of the electrode winding body 20 and the upper end of the outer casing 11. On the other hand, because the flatness FT1 of the upper part of the electrode winding body 20 is greater than the flatness FT2 of the lower part of the electrode winding body 20, the outer peripheral surface 20S of the upper part of the electrode winding body 20 housed inside the exterior can 11 comes into contact with the inner surface 11WS2 of the exterior can 11. For this reason, even if the secondary battery 1 is subjected to vibration or impact, the electrode winding body 20 is less likely to move inside the exterior can 11. As a result, damage to the electrode winding body 20 itself and to the connection between the positive electrode current collector plate 24 joined to the electrode winding body 20 and the battery lid 14 can be prevented. Therefore, the secondary battery 1 can ensure excellent vibration resistance without impairing manufacturability.

[0069] In particular, the secondary battery 1 employs a so-called tabless structure in which the electrode winding body 20 does not have an electrode tab extending in the height direction Z. For this reason, the electrode winding body 20 is soft and easily deformed, making it easy to adjust the flatness of the electrode winding body 20. This is therefore suitable for realizing an electrode winding body 20 in which the horizontal cross-sectional shape of the upper part in the height direction Z differs from the horizontal cross-sectional shape of the lower part. Furthermore, the electrode winding body 20 does not have a winding core at its center, and has a through-hole 26, so in this respect too, it is suitable for realizing an electrode winding body 20 in which the horizontal cross-sectional shape of the upper part in the height direction Z differs from the horizontal cross-sectional shape of the lower part.

[0070] 2. Application Examples The secondary battery 1 according to the embodiment of the present disclosure can be used in the following applications, for example.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] [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, electric vehicles, electric aircraft, and power storage devices, or can be used to supply power.

[0083] 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.

[0084] 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.

[0085] An embodiment of the present disclosure will be described.

[0086] (Examples 1-1 to 1-4, Comparative Examples 1-1 to 1-4) As described below, the cylindrical secondary batteries shown in Fig. 1 etc. were fabricated, and then the dimensions of the fabricated secondary batteries were measured. Here, lithium ion secondary batteries having nominal dimensions of 21 mm in diameter and 70 mm in length were fabricated.

[0087] [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 positive electrode 21 was then sheared to set the width of the positive electrode covering portion 211 in the W-axis direction to 60 mm, and the width of the positive electrode exposed portion 212 in the W-axis direction to 7 mm. The length of the positive electrode 21 in the L-axis direction was set to 1,700 mm.

[0088] 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 a anode exposed portion 222. The anode 22 was then sheared to set the width of the anode covering portion 221 in the W-axis direction to 62 mm and the width of the first portion 222A of the anode exposed portion 222 in the W-axis direction to 4 mm. The length of the anode 22 in the L-axis direction was 1,760 mm.

[0089] 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. As shown in Table 1 below, the laminate S20 was produced so that the first distance L1 and the second distance L2 were each 3 mm. 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. The laminate S20 was then spirally wound to form through-holes 26, and a fixing tape 46 was attached to the outermost periphery of the wound laminate S20. This produced an electrode roll 20. Pressure was applied to the widthwise ends of the obtained electrode winding body 20 from the outer surface of the electrode winding body 20 toward the winding center of the electrode winding body 20, thereby adjusting the electrode winding body 20 to have the predetermined flatnesses FT1 and FT2.

[0090] Next, the edges of a 0.5 mm thick flat plate were pressed against the upper end face 41 and the lower end face 42 of the electrode winding body 20 in the Z-axis direction, thereby locally bending the upper end face 41 and the lower end face 42, and creating grooves 43 extending radially from the through hole 26 in the radial direction (R direction).

[0091] Subsequently, substantially the same pressure was applied to the upper end face 41 and the lower end face 42 from above and below the electrode winding body 20 substantially simultaneously and in a direction approximately perpendicular to the upper end face 41 and the lower end face 42. As a result, the positive electrode exposed portion 212 and the first portion 222A of the negative electrode exposed portion 222 were each folded, making the upper end face 41 and the lower end face 42 each flat. At this time, the positive electrode edge portion 212E of the positive electrode exposed portion 212 and the negative electrode edge portion 222E of the negative electrode exposed portion 222 at the upper end face 41 and the lower end face 42 were folded while overlapping toward the through hole 26. Thereafter, the sector-shaped portion 31 of the positive electrode current collector plate 24 was joined to the upper end face 41 by laser welding, and the sector-shaped portion 33 of the negative electrode current collector plate 25 was joined to the lower end face 42 by laser welding.

[0092] 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.

[0093] 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. The inner diameter D11 of the outer can 11 used was 20.80±0.05 mm. Thereafter, 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.

[0094] 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.

[0095] Next, the gasket 15, the safety valve mechanism 30, and the battery lid 14 were used to seal the battery lid 14. Finally, the exterior can 11 with the washer 55 attached to the battery lid 14 was covered with the exterior tube 50, and then the exterior tube 50 was heated and shrunk by applying hot air to the exterior tube 50, for example, and the exterior tube 50 was tightly attached to the outer surface of the exterior can 11.

[0096] As a result of the above, secondary batteries were obtained as Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-4.

[0097] [Evaluation of Battery Characteristics] For each of the secondary batteries of Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-4 obtained as described above, the outer diameters of the upper and lower parts of the electrode wound body 20 were measured, and the ease of inserting the electrode wound body 20 into the outer can 11 and the vibration resistance were evaluated. The results are summarized in Table 1.

[0098]

[0099] (Measurement of Outer Diameter) The maximum diameter D20max1 and minimum diameter D20min1 of the upper part of the electrode winding body 20, and the maximum diameter D20max2 and minimum diameter D20min2 of the lower part of the electrode winding body 20 were measured. Specifically, the outer diameter of a two-dimensionally projected image of the electrode winding body 20 was measured using a two-dimensional projection type outer diameter measuring instrument while the electrode winding body 20 was rotated about its central axis as the axis of rotation. Here, the maximum diameter D20max1 and minimum diameter D20min1 were defined as the maximum diameter and minimum diameter, respectively, in the horizontal cross section of the electrode winding body 20 at the height position Lv1 shown in FIG. 1. The maximum diameter and minimum diameter D20max2 and minimum diameter D20min2 were defined as the maximum diameter and minimum diameter, respectively, in the horizontal cross section of the electrode winding body 20 at the height position Lv2 shown in FIG. 1. For Examples 1-1 to 1-4 and Comparative Examples 1-2 and 1-4, the outer diameter of the electrode winding body 20 was measured after the secondary battery was disassembled and removed. The reason why the maximum diameter D20max1 of the upper portion of Example 1-3 is larger than the diameter D11 without the outer can 11 is because the negative electrode active material layer 22B expands due to charging and discharging. The maximum diameter D11 without the outer can 11 of Example 1-3 also increases accordingly.

[0100] (Evaluation of Insertability of Electrode Wound Body) Regarding the evaluation of the insertability of the electrode wound body 20 into the outer can 11, when the electrode wound body 20 could not be inserted into the outer can 11 because the outer peripheral surface 20S of the electrode wound body 20 came into contact with the open end 11N, for example, it was judged as being defective, and this was marked with "F" in Table 1. On the other hand, when the electrode wound body 20 could be inserted into the outer can 11, it was judged as being good, and this was marked with "P" in Table 1. Note that for Comparative Example 1-1 and Comparative Example 1-3, in which the electrode wound body 20 could not be inserted into the outer can 11, the maximum diameter D20max1 and minimum diameter D20min1 of the upper part of the electrode wound body 20, and the maximum diameter D20max2 and minimum diameter D20min2 of the lower part of the electrode wound body 20 were measured before insertion into the outer can 11.

[0101] (Evaluation of Vibration Resistance) Six secondary batteries were fabricated for each example and comparative example, and the vibration resistance was evaluated as described below. A drum test was conducted to measure the change in impedance. Specifically, the batteries were adjusted to an output voltage of 4.2 V, placed in a hexagonal steel tube with an inscribed circle diameter φ of 190 mm and a length of 200 mm in a hexagonal drum rotation test device, and rotated at an angular velocity of 60 rpm (2π rad / s) to apply mechanical vibration. Each secondary battery was then removed, and its open circuit voltage (OCV) and impedance were measured. The vibration test was continued until the impedance value after vibration significantly exceeded the initial impedance and the battery was deemed unacceptable. Generally, vibration gradually separates the joint between the lid and the positive electrode current collector, increasing the impedance. Therefore, the longer the vibration duration until the impedance increases, the higher the vibration resistance can be evaluated.

[0102] As shown in Table 1, in Examples 1-1 to 1-4, since the flatness FT1 is greater than the flatness FT2, i.e., (FT1 / FT2) > 1 is satisfied, the insertion performance was evaluated as "good" and it was found that a vibration resistance of at least 100 minutes was obtained in the drum test. In contrast, in Comparative Examples 1-1 and 1-3, where the flatness FT1 is smaller than the flatness FT2, i.e., (FT1 / FT2) ≦ 1, the insertion performance was evaluated as "poor" and further measurement was not possible. Furthermore, in Comparative Examples 1-2 and 1-4, the insertion performance was "good," but sufficient vibration resistance was not obtained.

[0103] From the above results, it was confirmed that the secondary battery of the present disclosure can ensure excellent vibration resistance without impairing manufacturability.

[0104] While the present disclosure has been described above with reference to an embodiment and examples, the configuration of the present disclosure is not limited to the configuration described in the embodiment and examples and can be modified in various ways. For example, while the above embodiment and examples have been described using a secondary battery with a so-called tab-less structure as an example, the secondary battery of the present disclosure is not limited thereto and can also be applied to a secondary battery with a so-called tab structure.

[0105] For example, in the above embodiment and example, the electrode reactant is lithium, but 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.

[0106] 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.

[0107] The present disclosure may take the following forms. <1> A secondary battery comprising: an electrode winding body formed by stacking a positive electrode and a negative electrode with a separator interposed between them and winding them around a central axis; and a battery can having a cylindrical outer shape with a height direction along the central axis and housing the electrode winding body, wherein the battery can has: a container having a lower end closed by a bottom, and an upper end located opposite the lower end in the height direction and including an opening through which the electrode winding body can be inserted; and a lid that closes the opening of the container, wherein, when the ratio of the maximum diameter of the electrode winding body to the minimum diameter of the electrode winding body is defined as the flatness of the electrode winding body, the flatness of at least a portion of an upper part of the electrode winding body is greater than the flatness of at least a portion of a lower part of the electrode winding body. <2> The secondary battery according to <1> above, wherein the flatness of an upper edge of the electrode winding body in the height direction is greater than the flatness of a lower edge of the electrode winding body in the height direction. <3> The secondary battery according to <1> or <2> above, wherein the maximum diameter of the electrode winding body substantially coincides with the inner diameter of the battery can. <4> The secondary battery according to any one of <1> to <3> above, wherein the maximum diameter of the electrode winding body at a center point in the height direction is smaller than the maximum diameter at an upper edge of the electrode winding body in the height direction and larger than the maximum diameter at a lower edge of the electrode winding body in the height direction. <5> The secondary battery according to any one of <1> to <4> above, wherein a through-hole is provided in a center of the electrode winding body. <6> The secondary battery according to any one of <1> to <5> above, wherein a part of an upper part of the electrode winding body is in contact with the inner surface of the case. <7> The secondary battery according to any one of <1> to <6> above, wherein the maximum diameter of an upper part of the electrode winding body is larger than the maximum diameter of a lower part of the electrode winding body.<8> The electrode winding further includes: a positive electrode current collector plate disposed to face a first end face in the height direction of the electrode winding body; and a negative electrode current collector plate disposed to face a second end face of the electrode winding body opposite to the first end face in the height direction, wherein the positive electrode has a positive electrode covering portion in which a positive electrode active material layer is covered on a positive electrode current collector, and a positive electrode exposed portion in which the positive electrode current collector is not covered by the positive electrode active material layer and is joined to the positive electrode current collector, and the negative electrode has a negative electrode covering portion in which a negative electrode active material layer is covered on a negative electrode current collector, and a negative electrode exposed portion in which the negative electrode current collector is not covered by the negative electrode active material layer and is joined to the negative electrode current collector, The secondary battery according to any one of <1> to <7>, wherein at least one of a plurality of first edge portions of the positive electrode exposed portion wound around the central axis and a plurality of second edge portions of the negative electrode exposed portion wound around the central axis and adjacent in the radial direction of the electrode winding body is bent toward the central axis so as to overlap with each other. <9> A battery pack comprising: the secondary battery according to any one of <1> to <8>, a control unit that controls the secondary battery, and an exterior body that encapsulates the secondary battery.

Claims

1. an electrode winding body in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween and wound around a central axis; a battery can having a cylindrical outer shape with a height direction along the central axis and housing the electrode winding body; Equipped with The battery can is a container having a lower end portion closed by a bottom portion, and an upper end portion located on the opposite side to the lower end portion in the height direction and including an opening through which the electrode winding body can be inserted; A lid portion that closes the opening of the container; having When the ratio of the maximum diameter of the electrode winding body to the minimum diameter of the electrode winding body is defined as the flatness of the electrode winding body, the flatness of at least a part of an upper portion of the electrode winding body is greater than the flatness of at least a part of a lower portion of the electrode winding body. Secondary battery.

2. The flatness of the upper end edge of the electrode winding body in the height direction is greater than the flatness of the lower end edge of the electrode winding body in the height direction. The secondary battery according to claim 1 .

3. The maximum diameter of the electrode winding body is substantially equal to the inner diameter of the battery can. The secondary battery according to claim 1 .

4. The maximum diameter of the electrode winding body at the center point in the height direction is smaller than the maximum diameter at the upper end edge of the electrode winding body in the height direction and is larger than the maximum diameter at the lower end edge of the electrode winding body in the height direction. The secondary battery according to claim 1 .

5. A through hole is provided in the center of the electrode winding body. The secondary battery according to claim 1 .

6. A portion of the upper portion of the electrode winding body is in contact with the inner surface of the container. The secondary battery according to claim 1 .

7. The maximum diameter of an upper portion of the electrode winding body is larger than the maximum diameter of a lower portion of the electrode winding body The secondary battery according to claim 1 .

8. a positive electrode current collector plate disposed to face a first end surface in the height direction of the electrode winding body; a negative electrode current collector plate disposed to face a second end surface of the electrode winding body opposite to the first end surface in the height direction; Further equipped with the positive electrode has a positive electrode covering portion in which a positive electrode current collector is covered with a positive electrode active material layer, and a positive electrode exposed portion in which the positive electrode current collector is not covered with the positive electrode active material layer and is joined to the positive electrode current collector, the negative electrode has a negative electrode covering portion in which a negative electrode current collector is covered with a negative electrode active material layer, and a negative electrode exposed portion in which the negative electrode current collector is not covered with the negative electrode active material layer and is joined to the negative electrode current collector, At least one of a plurality of first edge portions adjacent in the radial direction of the electrode winding body of the positive electrode exposed portion wound around the central axis and a plurality of second edge portions adjacent in the radial direction of the negative electrode exposed portion wound around the central axis is bent toward the central axis so as to overlap with each other. The secondary battery according to claim 1 .

9. The secondary battery according to any one of claims 1 to 8, A control unit that controls the secondary battery; an exterior body that encapsulates the secondary battery; A battery pack having