Secondary battery and battery pack

Abstract

To provide a secondary battery with an excellent reliability.SOLUTION: A secondary battery comprises: an electrode winding body in which a lamination body containing a positive electrode, a negative electrode, and a separator is wound along a longitudinal direction of the lamination body, and includes a penetration hole penetrated to a width direction orthogonal to the longitudinal direction; and an outer casing that houses the electrode winding body. The positive electrode includes: a positive electrode active material layer that is expanded to both of the longitudinal direction and a width direction; and a positive electrode collector that contains a positive electrode coated region that is coated by the positive electrode active material layer, and a positive electrode exposure region that is extended to the width direction from the positive electrode active material layer. The positive electrode active material layer contains: a first thin film part; and a first film thickness part that includes a thickness larger than that of the first thin film part, and is adjacent to the first thin film part in the width direction.SELECTED DRAWING: Figure 4A

Description

[Technical field]

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

[0002] Due to the widespread use of various electronic devices such as mobile phones, secondary batteries have been developed as power sources that are small and lightweight and can obtain high energy density. These secondary batteries have a battery element housed inside an exterior member, and various studies have been conducted on the configuration of the secondary battery (for example, see 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 020237 Summary of the Invention [Problem to be solved by the invention]

[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 highly reliable secondary battery is desired. [Means for solving the problem]

[0007] A secondary battery according to an embodiment of the present disclosure includes an electrode winding body in which a laminate including a positive electrode, a negative electrode, and a separator is wound along the longitudinal direction of the laminate, and the electrode winding body has a through hole penetrating in a width direction perpendicular to the longitudinal direction, and an outer can housing the electrode winding body. The positive electrode has a positive electrode active material layer extending in both the longitudinal direction and the width direction, and a positive electrode current collector including a positive electrode covered region covered by the positive electrode active material layer and a positive electrode exposed region extending in the width direction from the positive electrode active material layer. The positive electrode active material layer includes a first thin portion and a first thick portion having a thickness greater than that of the first thin portion and adjacent to the first thin portion in the width direction. Effect of the Invention

[0008] According to the secondary battery of the embodiment of the present disclosure, the positive electrode active material layer includes the first thin portion, which can reduce stress concentration inside the outer can caused by the expansion of the negative electrode. Furthermore, the positive electrode active material layer includes the first thick portion adjacent to the first thin portion, which can effectively prevent the separator located between the positive electrode and the negative electrode from shifting in position. As a result, it is possible to prevent a short circuit between the positive electrode and the negative electrode, and ensure excellent reliability.

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

[0010] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of a vertical cross-sectional structure of a secondary battery according to an embodiment of the present disclosure taken along a height direction. [Diagram 2] FIG. 2 is a horizontal cross-sectional view showing one configuration example of an electrode winding body of the secondary battery shown in FIG. [Diagram 3] FIG. 3 is a cross-sectional view illustrating an example of a configuration of the electrode winding body illustrated in FIG. 2 in an expanded state. [Figure 4A] FIG. 4A is a plan view showing one configuration example of the positive electrode in a state in which the electrode winding body shown in FIG. 3 is developed. [Figure 4B]FIG. 4B is a plan view showing one configuration example of the negative electrode in a state in which the electrode winding body shown in FIG. 3 is unfolded. [Figure 5A] FIG. 5A is a first cross-sectional view of the positive electrode shown in FIG. 4A. [Figure 5B] FIG. 5B is a second cross-sectional view of the positive electrode shown in FIG. 4A. [Figure 6] FIG. 6 is a block diagram showing a circuit configuration of a battery pack to which the secondary battery according to an embodiment of the present disclosure is applied. [Figure 7] FIG. 7 is a cross-sectional view of a positive electrode according to a first modified example of the present disclosure. [Figure 8A] FIG. 8A is a cross-sectional view illustrating a first embodiment of a positive electrode according to a second modification of the present disclosure. [Figure 8B] FIG. 8B is a cross-sectional view showing a second embodiment of a positive electrode according to a second modification of the present disclosure. [Figure 8C] FIG. 8 is a cross-sectional view showing a third embodiment of a positive electrode according to the second modification of the present disclosure. [Figure 9A] FIG. 9A is a development view of a positive electrode according to a third modified example of the present disclosure. [Figure 9B] FIG. 9B is a cross-sectional view of the positive electrode shown in FIG. 9A. [Figure 10A] FIG. 10A is a development view showing the positive electrode of Example 1-2. [Figure 10B] FIG. 10B is a cross-sectional view showing the positive electrode of Example 1-2. [Figure 11A] FIG. 11A is a development view showing the positive electrode of Example 1-3. [Figure 11B] FIG. 11B is a cross-sectional view showing the positive electrode of Example 1-3. [Figure 12] FIG. 12 is a cross-sectional view showing the positive electrode of Example 3-1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. The description will be given in the following order. 1. Secondary battery 1-1. Overall composition 1-2.Detailed structure of the electrode winding body 1-3.Operation 1-4. Manufacturing method 1-5. Actions and Effects 2. Application Examples 3. Variations

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

[0013] The principle of charging and discharging the secondary battery described here is not particularly limited, but the following description will be given of a case where battery capacity is obtained by utilizing the occlusion and release of an electrode reactant.

[0014] A 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, that is, the electrochemical capacity per unit area of ​​the negative electrode is larger than the electrochemical capacity per unit area of ​​the positive electrode. This is to prevent deposition of electrode reactants on the surface of the negative electrode during charging.

[0015] The type of the electrode reactant is not particularly limited, but specifically, it is a light metal such as an alkali metal or an alkaline earth metal, etc. The alkali metal is lithium, sodium, potassium, etc., and the alkaline earth metal is beryllium, magnesium, calcium, etc.

[0016] In the following, an example will be given in which the electrode reactant is lithium. A secondary battery that obtains battery capacity by utilizing the absorption and release of lithium is a so-called lithium ion secondary battery. In this lithium ion secondary battery, lithium is absorbed and released in an ionic state.

[0017] <1-1. Overall composition> Fig. 1 shows a cross-sectional structure of a secondary battery. As shown in Fig. 1, this secondary battery is a so-called cylindrical secondary battery, in which an electrode winding body 20 as a battery element is housed inside a cylindrical battery can 11. The symbol CL represents the central axis of this secondary battery.

[0018] Hereinafter, the direction in which the electrode winding body 20 is housed inside the battery can 11, i.e., the height direction of the cylindrical battery can 11, is defined as the Z direction, and the radial direction of the cylindrical battery can 11 is defined as the R direction.

[0019] 1, for example, a pair of insulating plates 12, 13 and an electrode winding body 20 are housed inside a cylindrical battery can 11. The electrode winding body 20 is sandwiched between the insulating plates 12 and 13 in the Z direction. A safety valve mechanism 30 is attached to the battery can 11. The battery can 11 is sealed by, for example, a battery lid 14. However, the secondary battery may further include a positive thermal capacitance (PTC) element, a reinforcing member, and the like inside the battery can 11. The battery can 11 is a specific example that corresponds to an "external can" of the present disclosure.

[0020] [Battery can] The battery can 11 is a hollow container that extends in the Z direction and has one end in the Z direction closed and the other end in the Z direction open. One end of the battery can 11 in the Z direction is an open end 11N. The battery can 11 contains, for example, one or more types of metal materials such as iron, aluminum, and alloys thereof. The surface of the battery can 11 may be plated with, for example, one or more types of metal materials such as nickel.

[0021] [Insulating plate] The pair of insulating plates 12, 13 are disposed to sandwich the electrode winding body 20 in the Z direction and to extend along a plane perpendicular to the Z direction.

[0022] [Clamming structure] The battery lid 14 and the safety valve mechanism 30 are crimped to the open end 11N of the battery can 11 via a gasket 15. As a result, the battery can 11 is formed with a bent portion 11P that defines the open end 11N.

[0023] With the electrode winding body 20 and the like housed inside the battery can 11, the open end 11N of the battery can 11 is sealed by the battery lid 14. The battery can 11 has a crimping structure 11R formed in the vicinity of the open end 11N. The crimping structure 11R is a structure in which a bent portion 11P that defines the open end 11N, the battery lid 14, and the safety valve mechanism 30 are crimped together via a gasket 15. The bent portion 11P is a so-called crimp portion, and the crimping structure 11R is also called a so-called crimp structure.

[0024] [Battery cover] The battery lid 14 is a lid member that closes the open end 11N of the battery can 11. The battery lid 14 may be made of the same material as the material used to form the battery can 11. However, the battery lid 14 may contain a material different from the material used to form the battery can 11.

[0025] Among them, it is preferable that the battery lid 14 contains stainless steel. This is because the physical strength of the crimping structure 11R is ensured in accordance with the physical strength of the battery lid 14, and thus the battery lid 14 is prevented from falling off and the electrolyte is prevented from leaking even if the internal pressure of the battery can 11 increases. Specific examples of stainless steel include SUS304 and SUS430.

[0026] The central portion of the battery lid 14 is bent so as to protrude in the direction away from the electrode winding body 20 (the +Z direction).

[0027] [gasket] The gasket 15 is a sealing member that seals the gap between the bent portion 11P and the battery lid 14. The gasket 15 is interposed between the bent portion 11P of the battery can 11 and the battery lid 14.

[0028] The gasket 15 contains one or more kinds of insulating materials, and specific examples of the insulating materials are polymeric materials such as polybutylene terephthalate (PBT) and polypropylene (PP). Among them, it is preferable that the gasket 15 contains polypropylene, because this allows the battery can 11 and the battery lid 14 to be electrically isolated from each other while the gap between the bent portion 11P and the battery lid 14 is sufficiently sealed.

[0029] [Safety valve mechanism] The safety valve mechanism 30 is provided on the inside of the battery lid 14 in the Z direction. The safety valve mechanism 30 is a mechanism that releases the internal pressure by releasing the sealed state of the battery can 11 as necessary when the internal pressure of the battery can 11 increases. The internal pressure of the battery can 11 increases due to gas generated due to a decomposition reaction of the electrolyte during charging and discharging.

[0030] [Electrode winding body] Fig. 2 is a horizontal cross-sectional view taken along a cross section perpendicular to the Z direction, showing one configuration example of the electrode winding body 20. However, Fig. 2 also shows the battery can 11. The electrode winding body 20 is housed inside the battery can 11, and contains an electrolytic solution, which is a liquid electrolyte, together with a positive electrode 21 and a negative electrode 22. The electrode winding body 20 further includes a positive electrode lead 25 (see Fig. 1) and a negative electrode lead 26.

[0031] The electrode winding body 20 is formed by winding a laminate S20 in which a positive electrode 21 and a negative electrode 22 are laminated with a separator 23 interposed therebetween. More specifically, as shown in FIG. 2, 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. The electrode winding body 20 has an overall appearance of a substantially cylindrical shape. 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. The positive electrode 21, the negative electrode 22, and the separator 23 are each impregnated with an electrolyte. Note that the separator 23 and the positive electrode lead 25 are not shown in FIG. 2.

[0032] At the center of the electrode winding body 20, a space is formed when the positive electrode 21, the negative electrode 22, and the separator 23 are wound, that is, a through-hole 20C is formed.

[0033] The positive electrode 21, the negative electrode 22, and the separator 23 are wound so that the separator 23 is disposed at the outermost circumference and the innermost circumference of the electrode winding body 20. In addition, the negative electrode 22 is disposed outside the positive electrode 21 at the outermost circumference of the electrode winding body 20. That is, as shown in FIG. 2, the positive electrode outermost circumference part 21out located at the outermost circumference of the positive electrode 21 included in the electrode winding body 20 is disposed inside the negative electrode outermost circumference part 22out located at the outermost circumference of the negative electrode 22 included in the electrode winding body 20. Here, the positive electrode outermost circumference part 21out is the outermost one-turn part of the positive electrode 21 in the electrode winding body 20. The negative electrode outermost circumference part 22out is the outermost one-turn part of the negative electrode 22 in the electrode winding body 20. On the other hand, the negative electrode 22 is disposed inside the positive electrode 21 at the innermost circumference of the electrode winding body 20. That is, as shown in Fig. 2, the negative electrode innermost circumferential portion 22in 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 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-turn portion of the positive electrode 21 in the electrode winding body 20. The negative electrode innermost circumferential portion 22in is the innermost one-turn portion of the negative electrode 22 in the electrode winding body 20. The number of turns of each of the positive electrode 21, the negative electrode 22, and the separator 23 is not particularly limited and can be set arbitrarily.

[0034] A positive electrode lead 25 is connected to the positive electrode 21. A negative electrode lead 26 is connected to the negative electrode 22. The positive electrode lead 25 includes one or more types of conductive materials such as metal materials. A specific example of the metal material constituting the positive electrode lead 25 is aluminum. The positive electrode lead 25 is electrically connected to the battery cover 14 via a safety valve mechanism 30. The negative electrode lead 26 includes one or more types of conductive materials such as metal materials. A specific example of the metal material constituting the negative electrode lead 26 is nickel. The negative electrode lead 26 is electrically connected to the battery can 11. The detailed configuration of the electrode winding body 20, that is, the detailed configurations of the positive electrode 21, the negative electrode 22, the separator 23, and the electrolyte will be described below.

[0035] <1-2. Detailed structure of the electrode winding body> 3 shows a cross-sectional configuration of the laminate S20 in a state where the electrode winding body 20 is unfolded. FIG. 4A is a plan view showing an example of the configuration of the positive electrode 21 in a state where the electrode winding body 20 is unfolded. FIG. 4B is a plan view showing an example of the configuration of the negative electrode 22 in a state where the electrode winding body 20 shown in FIG. 3 is unfolded. Note that FIG. 3 shows a cross section taken along line III-III shown in each of FIG. 4A and FIG. 4B as viewed from the arrow direction. As shown in FIG. 3, the positive electrode 21, the separator 23, the negative electrode 22, and the separator 23 are laminated in the R direction, which is the radial direction of the electrode winding body 20 and the radial direction of the battery can 11.

[0036] [Positive electrode] As shown in FIGS. 2, 3, and 4A, the positive electrode 21 includes a positive electrode current collector 21A, a positive electrode active material layer 21B, and a protective tape 21C.

[0037] The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. The positive electrode current collector 21A contains a conductive material such as a metal material. The positive electrode current collector 21A is, for example, a metal foil made of aluminum or an aluminum alloy.

[0038] In the example shown in FIG. 2 and FIG. 3, the positive electrode active material layer 21B is provided on both sides of the positive electrode collector 21A. The positive electrode active material layer 21B contains one or more types of positive electrode active materials capable of absorbing and releasing lithium. However, the positive electrode active material layer 21B may be provided on only one side of the positive electrode collector 21A on the side where the positive electrode 21 faces the negative electrode 22. The positive electrode active material layer 21B may further contain a positive electrode binder, a positive electrode conductive agent, and the like. The method of forming the positive electrode active material layer 21B is not particularly limited, but specifically includes a coating method, etc.

[0039] The positive electrode active material layer 21B covers a part of the surface of the positive electrode collector 21A. The positive electrode 21 has a positive electrode covering region 211 and a positive electrode exposed region 212. The positive electrode covering region 211 is a region of the positive electrode 21 where the positive electrode collector 21A is covered with the positive electrode active material layer 21B. The positive electrode exposed region 212 is a region of the positive electrode 21 other than the positive electrode covering region 211. That is, the positive electrode exposed region 212 is a region where the positive electrode collector 21A is exposed without being covered with the positive electrode active material layer 21B. As shown in FIG. 4A, the positive electrode covering region 211 and the positive electrode exposed region 212 each extend from the upper end edge 21UT of the positive electrode 21 to the lower end edge 21BT of the positive electrode 21 along the Z direction, which is the short side direction of the positive electrode 21. In addition, two positive electrode exposed regions 212 are provided at both ends in the L direction, which is the longitudinal direction of the positive electrode 21. Here, the L direction corresponds to the winding direction of the electrode winding body 20. One of the two positive electrode exposed regions 212 includes the inner periphery side positive electrode edge 21S of the positive electrode innermost periphery part 21in (FIG. 2) of the positive electrode 21, and the other of the two positive electrode exposed regions 212 includes the outer periphery side edge 21E of the positive electrode outermost periphery part 21out (FIG. 2) of the positive electrode 21. The positive electrode covering region 211 is disposed so as to be sandwiched between the two positive electrode exposed regions 212 in the L direction. That is, the positive electrode active material layer 21B does not exist at both ends in the L direction, which is the longitudinal direction of the positive electrode current collector 21A. The protective tape 21C is provided in a part of the positive electrode exposed region 212. More specifically, it covers a portion of the positive electrode current collector 21A in the positive electrode exposed region 212 that faces the negative electrode active material layer 22B (described later). The protective tape 21C may also cover a portion of the thin portion and the thick portion 74, 75. In the configuration example of FIG. 4A, the protective tape 21C is provided on the outer positive electrode exposed region 212 of the two positive electrode exposed regions 212, but it may also be provided on the inner positive electrode exposed region 212. A positive electrode lead 25 is attached to the positive electrode current collector 21A in the inner positive electrode exposed region 212.

[0040] The positive electrode active material contains a lithium compound. This lithium compound is a compound containing lithium as a constituent element, more specifically, a compound containing lithium and one or more transition metal elements as constituent elements. This is because a high energy density can be obtained. However, the lithium compound may further contain other elements, that is, one or more elements other than lithium and transition metal elements.

[0041] The type of lithium compound is not particularly limited, but specific examples include lithium composite oxides having a layered rock-salt crystal structure, lithium composite oxides having a spinel crystal structure, and lithium phosphate compounds having an olivine crystal structure. A specific example of a lithium composite oxide having a layered rock-salt crystal structure is LiNiO 2 、 LiNi 0.8 Co 0.15 Al 0.05 and LiCoO2. A specific example of the lithium composite oxide having a spinel crystal structure is LiMn2O4. A specific example of the lithium phosphate compound having an olivine crystal structure is LiFePO4 and LiMnPO4.

[0042] Among them, the positive electrode active material preferably contains a lithium phosphate compound having an olivine crystal structure. This is because the crystal structure of the lithium phosphate compound having an olivine crystal structure is thermally stable, so that thermal runaway caused by overcharging and internal short circuit is unlikely to occur in the secondary battery. In addition, the crystal structure of the lithium phosphate compound having an olivine crystal structure is strong, so that the battery capacity is unlikely to decrease even if the secondary battery is repeatedly charged and discharged.

[0043] The positive electrode binder contains one or more of synthetic rubber and polymeric compounds, etc. The synthetic rubber is styrene-butadiene rubber, etc., and the polymeric compound is polyvinylidene fluoride, etc.

[0044] The positive electrode conductive agent contains one or more conductive materials such as carbon materials, and the carbon materials are graphite, carbon black, acetylene black, ketjen black, etc. However, the conductive material may also be a metal material, a polymer compound, etc.

[0045] The protective tape 21C is preferably adhered to the separator 23. This is because it is possible to prevent misalignment between the positive electrode 21 and the separator 23. The protective tape 21C is preferably made of a material that does not swell. This is because it is possible to prevent damage to the negative electrode due to swelling. The protective tape 21C is preferably made of a resin that contains, for example, polyimide (PI).

[0046] Each of FIG. 5A and FIG. 5B shows a cross-sectional configuration of the positive electrode 21. FIG. 5A shows a cross section in the direction of the arrows along the line VA-VA shown in FIG. 4A. FIG. 5B shows a cross section in the direction of the arrows along the line VB-VB shown in FIG. 4A. FIG. 5A and FIG. 5B show a case where the positive electrode active material layer 21B is provided on both sides of the positive electrode collector 21A. More specifically, the positive electrode collector 21A includes a positive electrode collector inner peripheral surface 21A1 facing the central axis CL and a positive electrode collector outer peripheral surface 21A2 opposite to the positive electrode 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 part of the positive electrode collector inner peripheral surface 21A1 and a positive electrode outer peripheral side active material layer 21B2 covering at least a part of the positive electrode collector outer peripheral surface 21A2. In this specification, the positive electrode inner periphery side active material layer 21B1 and the positive electrode outer periphery side active material layer 21B2 may not be distinguished from each other and may be collectively referred to as the positive electrode active material layer 21B. The positive electrode active material layer 21B extends in both the L direction and the W direction perpendicular to the L direction. The L direction is the winding direction of the laminate S20. The W direction substantially coincides with the central axis CL.

[0047] As described above, the positive electrode collector 21A includes the positive electrode covered region 211 covered by the positive electrode active material layer 21B, and the positive electrode exposed region 212 not covered by the positive electrode active material layer 21B. The positive electrode active material layer 21B includes a thin portion 61 and thick portions 71-73. In the positive electrode 21 of this embodiment, the thin portion 61 and the thick portions 71-73 are formed on both the positive electrode collector inner peripheral surface 21A1 and the positive electrode collector outer peripheral surface 21A2. That is, both the positive electrode inner peripheral side active material layer 21B1 and the positive electrode outer peripheral side active material layer 21B2 include the thin portion 61 and the thick portions 71-73, respectively. However, in the positive electrode 21, at least one of the positive electrode inner peripheral side active material layer 21B1 and the positive electrode outer peripheral side active material layer 21B2 may include the thin portion 61 and the thick portions 71-73. 5A and 5B, the thin portion 61 and the thick portions 71, 72, and 73 constituting the positive electrode inner periphery side active material layer 21B1 are described as the thin portion 61-1 and the thick portions 71-1, 72-1, and 73-1, respectively, for convenience, and the thin portion 61 and the thick portions 71, 72, and 73 constituting the positive electrode outer periphery side active material layer 21B2 are described as the thin portion 61-2 and the thick portions 71-2, 72-2, and 73-2, respectively, for convenience. In the example shown in FIG. 5B, the position in the L direction of the boundary 21B1K between the thin portion 61-1 and the thick portion 73-1 substantially coincides with the position in the L direction of the boundary 21B2K between the thin portion 61-2 and the thick portion 73-2.

[0048] Each of the thick portions 71 to 73 has a thickness larger than that of the thin portion 61. The thickness of the thin portion 61 can be, for example, about half the thickness of each of the thick portions 71 to 73. The thicknesses of the thick portions 71 to 73 may be the same as each other or may be different from each other. In detail, as shown in FIG. 5A and FIG. 5B, in the positive electrode inner periphery side active material layer 21B1, the thickness T71-1 of the thick portion 71-1, the thickness T72-1 of the thick portion 72-1, and the thickness T73-1 of the thick portion 73-1 are larger than the thickness T61-1 of the thin portion 61-1. In the example shown in FIG. 5A and FIG. 5B, the thickness T71-1 of the thick portion 71-1, the thickness T72-1 of the thick portion 72-1, and the thickness T73-1 of the thick portion 73-1 are equal to each other. Similarly, in the positive electrode outer peripheral side active material layer 21B2, the thickness T71-2 of the thick portion 71-2, the thickness T72-2 of the thick portion 72-2, and the thickness T73-2 of the thick portion 73-2 are greater than the thickness T61-2 of the thin portion 61-2. In the example shown in FIG. 5A and FIG. 5B, the thickness T71-2 of the thick portion 71-2, the thickness T72-2 of the thick portion 72-2, and the thickness T73-2 of the thick portion 73-2 are equal to each other. The thickness T61-1 and the thickness T61-2 may be equal to each other or may be different from each other. In addition, the thickness T71-1, the thickness T72-1, and the thickness T73-1 may be equal to the thickness T71-2, the thickness T72-2, and the thickness T73-2, respectively, or may be different from each other.

[0049] The thin portion 61 includes the winding center side positive electrode active material layer edge (inner circumference side positive electrode active material layer edge) 21BS of the positive electrode active material layer 21B in the L direction. The thin portion 61 may extend in the L direction, for example, from the winding center side positive electrode active material layer edge 21BS as a starting point, over a range of about 1 to 5 turns of the electrode wound body 20. The thick portion 71 is adjacent to the thin portion 61 in the W direction. More specifically, the thick portion 71 is located between the thin portion 61 and the upper end edge 21UT in the W direction. The thick portion 71 includes a first end face 21BT1. The thick portion 72 is located on the opposite side to the thick portion 71 as viewed from the thin portion 61 in the W direction. That is, the thick portion 72 is located between the thin portion 61 and the lower end edge 21BT located opposite to the upper end edge 21UT in the W direction. The thick portion 72 includes the lower end edge 21BT. The thick portion 73 is provided on the opposite side of the inner circumferential positive electrode end edge 21S from the thin portion 61 in the L direction. The thick portions 71 to 73 may be separated from each other, or may be partially or entirely integrated.

[0050] [Negative electrode] As shown in FIGS. 2, 3, and 4B, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

[0051] The negative electrode current collector 22A has a pair of surfaces on which the negative electrode active material layer 22B is provided. The negative electrode current collector 22A contains a conductive material such as a metal material. The negative electrode current collector 22A is a metal foil made of, for example, nickel, a nickel alloy, copper, or a copper alloy.

[0052] In the example shown in FIG. 2 and FIG. 3, the negative electrode active material layer 22B is provided on both sides of the negative electrode collector 22A. The negative electrode active material layer 22B contains one or more types of negative electrode active materials capable of absorbing and releasing lithium. However, the negative electrode active material layer 22B may be provided only on one side of the negative electrode collector 22A on the side where the negative electrode 22 faces the positive electrode 21. The negative electrode active material layer 22B may further contain a negative electrode binder, a negative electrode conductor, and the like. Details regarding the negative electrode binder and the negative electrode conductor are the same as those regarding the positive electrode binder and the positive electrode conductor. The method of forming the negative electrode active material layer 22B is not particularly limited, but specifically, it is one or more types of a coating method, a gas phase method, a liquid phase method, a thermal spraying method, a baking method (sintering method), and the like.

[0053] The negative electrode active material contains one or both of a carbon material and a metal-based material. This is because a high energy density can be obtained. Carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite (natural graphite and artificial graphite). Metal-based materials are materials that contain, as constituent elements, one or more of metal elements and semi-metal elements that can form an alloy with lithium, and specific examples of the metal elements and semi-metal elements include one or both of silicon and tin. However, the metal-based material may be a single element, an alloy, a compound, a mixture of two or more of them, or a material containing two or more of them. Specific examples of metal-based materials are TiSi2 and SiO x (0 <x≦2または0.2<x<1.4)などである。

[0054] The negative electrode active material layer 22B covers a part of each of the pair of surfaces 22Aout, 22Ain of the negative electrode collector 22A. The negative electrode 22 has a negative electrode covering region 221 and a negative electrode exposed region 222. The negative electrode covering region 221 is a region of the negative electrode 22 where the negative electrode collector 22A is covered with the negative electrode active material layer 22B. The negative electrode exposed region 222 is a region of the negative electrode 22 other than the negative electrode covering region 221. That is, the negative electrode exposed region 222 is a region where the negative electrode collector 22A is exposed without being covered with the negative electrode active material layer 22B. As shown in FIG. 4B, the negative electrode covering region 221 and the negative electrode exposed region 222 each extend from the upper end edge 22UT of the negative electrode 22 to the lower end edge 22BT of the negative electrode 22 along the Z direction, which is the short side direction of the negative electrode 22. In addition, two negative electrode exposed regions 222 are provided at both ends in the θ direction, which is the longitudinal direction of the negative electrode 22. One of the two negative electrode exposed regions 222 includes the inner peripheral edge 22S of the negative electrode innermost peripheral portion 22in (FIG. 2) of the negative electrode 22, and the other of the two negative electrode exposed regions 222 includes the outer peripheral edge 22E of the negative electrode outermost peripheral portion 22out (FIG. 2) of the negative electrode 22. The negative electrode covering region 221 is disposed so as to be sandwiched between the two negative electrode exposed regions 222 in the L direction. That is, the negative electrode active material layer 22B does not exist at both ends in the L direction, which is the longitudinal direction of the negative electrode current collector 22A. The size and position of the region of the negative electrode active material layer 22B covering the surface 22Aout may be different from or may be the same as each other.

[0055] The negative electrode lead 26 is attached to the negative electrode current collector 22A in the negative electrode exposed region 222. More specifically, the negative electrode lead 26 is attached to the negative electrode current collector 22A in the negative electrode exposed region 222 on the outer periphery of the two negative electrode exposed regions 222. The negative electrode lead 26 is provided so that a part of the negative electrode lead 26 protrudes downward from the lower end edge 22BT of the negative electrode 22. In the configuration example shown in FIG. 2, the negative electrode lead 26 is attached to a portion of the negative electrode current collector 22A where the negative electrode active material layer 22B is not provided on either of the pair of surfaces 22Aout, 22Ain of the negative electrode current collector 22A. In the configuration example shown in FIG. 2, the negative electrode lead 26 is attached to the outer surface 22Aout of the pair of surfaces 22Aout, 22Ain of the negative electrode current collector 22A, that is, the surface facing the inner surface of the battery can 11.

[0056] As shown in FIG. 2, the protective tape 21C of the positive electrode 21 covers the entire area of ​​the positive electrode exposed area 212 of the positive electrode 21 that faces the negative electrode covering area 221 of the negative electrode 22 via the separator 23. The protective tape 21C can effectively prevent an internal short circuit of the secondary battery 1 when, for example, a foreign object enters between the negative electrode covering area 221 and the positive electrode exposed area 212. In addition, when an impact is applied to the secondary battery 1, the protective tape 21C can absorb the impact and effectively prevent the occurrence of bending of the positive electrode exposed area 212 and the occurrence of a short circuit between the positive electrode exposed area 212 and the negative electrode 22. Furthermore, even if a local increase in potential occurs in the positive electrode covered area 211 near the boundary between the positive electrode covered area 211 and the positive electrode exposed area 212, the outflow of metal ions from the positive electrode active material layer 21B can be suppressed, and a short circuit between the positive electrode 21 and the negative electrode 22 can be suppressed.

[0057] In the electrode winding body 20, the entire overlapping region in which the negative electrode lead 26 and the negative electrode current collector 22A are joined and overlapped in the stacking direction (R direction) of the positive electrode 21 and the negative electrode 22 overlaps with the protective tape 21C in the R direction. That is, the entire portion of the negative electrode current collector 22A to which the negative electrode lead 26 is attached is located at a position corresponding to the protective tape 21C in the R direction.

[0058] [Separator] The separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22. The separator 23 allows lithium ions to pass through while preventing a short circuit between the positive electrode 21 and the negative electrode 22. The separator 23 contains a polymer compound such as polyethylene.

[0059] [Electrolyte] The electrolyte solution contains a solvent and an electrolyte salt. The solvent contains one or more of non-aqueous solvents (organic solvents) such as carbonate ester compounds, carboxylate ester compounds, and lactone compounds, and the electrolyte solution containing the non-aqueous solvent is a so-called non-aqueous electrolyte solution. However, the solvent may be an aqueous solvent. The electrolyte salt contains one or more of light metal salts such as lithium salts. 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. This is because high ionic conductivity can be obtained.

[0060] <1-3. Operation> In the secondary battery of the present embodiment, for example, during charging, lithium ions are released from the positive electrode 21 and are absorbed in 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 in the positive electrode 21 via the electrolyte.

[0061] <1-4. Manufacturing method> Next, a method for manufacturing the secondary battery according to this embodiment will be described.

[0062] [Preparation of positive electrode] First, a positive electrode active material and, if necessary, a positive electrode binder and a positive electrode conductive agent are mixed together to form a positive electrode mixture. Then, the positive electrode mixture is dispersed in a solvent to form a paste-like positive electrode mixture slurry. The type of the solvent is not particularly limited, and may be an aqueous solvent or a non-aqueous solvent (organic solvent). Then, the positive electrode mixture slurry is applied to both sides of the positive electrode collector 21A to form a positive electrode active material layer 21B. Then, the positive electrode active material layer 21B is compression molded using a roll press or the like. In this case, the positive electrode active material layer 21B may be heated, or the compression molding of the positive electrode active material layer 21B may be repeated multiple times. Furthermore, a predetermined region of the positive electrode active material layer 21B is dug down by, for example, laser ablation to form a thin portion 61. As a result, the positive electrode active material layer 21B including the thin portion 61 and the thick portions 71 to 73 is formed on both sides of the positive electrode collector 21A. Finally, protective tape 21C is attached to a predetermined position of positive electrode current collector 21A, thereby completing positive electrode 21.

[0063] [Preparation of negative electrode] The negative electrode active material layer 22B is formed on both sides of the negative electrode current collector 22A by the same procedure as the positive electrode 21 described above. Specifically, the negative electrode active material, the negative electrode binder, the negative electrode conductor, and the like are mixed together to form a negative electrode mixture. Then, the negative electrode mixture is dispersed in a solvent to form a paste-like negative electrode mixture slurry. Details regarding the solvent are as described above. Next, the negative electrode mixture slurry is applied to both sides of the negative electrode current collector 22A to form the negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B is compression molded using a roll press machine or the like. Details regarding the compression molding are as described above. As a result, the negative electrode active material layer 22B is formed on both sides of the negative electrode current collector 22A, and the negative electrode 22 is produced.

[0064] [Secondary battery assembly] First, the positive electrode lead 25 is connected to the positive electrode current collector 21A of the positive electrode 21 by welding or the like. Similarly, the negative electrode lead 26 is connected to the negative electrode current collector 22A of the negative electrode 22 by welding or the like. Next, the positive electrode 21 and the negative electrode 22 are stacked on each other via the separator 23 to form a laminate, and then the resulting laminate is wound to form a wound body having a through hole 20C. When preparing the wound body, the positive electrode 21 and the negative electrode 22 are aligned so that the entire overlapping area between the negative electrode lead 26 and the negative electrode current collector 22A in the stacking direction of the positive electrode 21 and the negative electrode 22 overlaps with the protective tape 21C in the stacking direction. This wound body has a configuration similar to that of the electrode wound body 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with the electrolyte.

[0065] Next, after preparing the battery can 11, the insulating plates 12 and 13 are placed opposite each other via the wound body, and the wound body is housed inside the battery can 11 together with the insulating plates 12 and 13. In this case, the positive electrode lead 25 is connected to the safety valve mechanism 30 by welding or the like, and the negative electrode lead 26 is connected to the battery can 11 by welding or the like.

[0066] Next, the wound body is impregnated with the electrolyte by injecting the electrolyte into the battery can 11. As a result, the electrolyte is impregnated into each of the positive electrode 21, the negative electrode 22, and the separator 23, and the electrode wound body 20 is produced. Next, the battery lid 14 and the safety valve mechanism 30 are housed inside the battery can 11 together with the gasket 15.

[0067] 1, the open end 11N of the battery can 11 is crimped to the battery lid 14 and the safety valve mechanism 30 via the gasket 15. This forms the bent portion 11P and the crimped structure 11R. This causes the battery can 11 to be closed by the battery lid 14, completing the assembly of the secondary battery.

[0068] [Stabilization of secondary batteries] The assembled secondary battery is charged and discharged. Various conditions such as the ambient temperature, the number of charge / discharge cycles (number of cycles), and the charge / discharge conditions can be set as desired. As a result, a coating is formed on the surface of the negative electrode 22, etc., and the state of the secondary battery is electrochemically stabilized. As a result, a cylindrical secondary battery is completed with the electrode winding body 20 and the like enclosed inside the battery can 11.

[0069] <1-5. Actions and Effects> In this manner, in the secondary battery 1 of the present embodiment, the thin portion 61 and the thick portion 71 are provided adjacent to each other in the W direction perpendicular to the winding direction (L direction) in the positive electrode active material layer 21B. By providing the thin portion 61 having a small thickness in a part of the positive electrode active material layer 21B in this manner, stress concentration inside the electrode winding body 20 accommodated in the battery can 11 can be alleviated. Specifically, when the negative electrode 22 expands inside the electrode winding body 20 due to charging and discharging, it is possible to prevent the occurrence of large deformation such as buckling (bending) of the positive electrode current collector 21A. This is because the amount of electrode reactant (e.g., lithium ions) supplied to a part of the negative electrode active material layer 22B facing the thin portion 61 is reduced, thereby suppressing the expansion and contraction of the part of the negative electrode active material layer 22B facing the thin portion 61. As a result, the stress applied to the separator 23 separating the positive electrode 21 and the negative electrode 22 is also alleviated, and even if the thickness of the separator 23 is reduced, the separator 23 can be prevented from breaking, and the occurrence of a short circuit between the positive electrode 21 and the negative electrode 22 can be prevented. That is, the separator 23 can be made thinner. As a result, the gap between the positive electrode 21 and the negative electrode 22 can be narrowed, the internal resistance of the electrode winding body 20 can be reduced, and the charge / discharge rate characteristics can be improved and the capacity of the secondary battery 1 can be increased. On the other hand, since the positive electrode active material layer 21B includes the thick portion 71 at a position adjacent to the thin portion 61 in the W direction, the separator 23 disposed between the positive electrode active material layer 21B and the negative electrode active material layer 22B can be firmly held. As a result, the electrode winding body 20 is less likely to collapse when the electrode winding body 20 expands and contracts, and the separator 23 can be prevented from shifting from a predetermined position. As a result, it is possible to prevent a short circuit from occurring between the positive electrode 21 and the negative electrode 22. Therefore, according to the secondary battery 1 of the present embodiment, excellent reliability can be ensured.

[0070] In the secondary battery 1 of the present embodiment, the thin portion 61 includes the positive electrode active material layer edge 21BS of the positive electrode active material layer 21B on the winding center side in the L direction. That is, the thin portion 61 is provided at a position of the positive electrode active material layer 21 closest to the winding center. This makes it possible to effectively reduce stress concentration in the vicinity of the center of the electrode wound body 20, where stress concentration is likely to occur significantly, within the inside of the electrode wound body 20.

[0071] Furthermore, in the secondary battery 1 of the present embodiment, the positive electrode active material layer 21B further includes a thick portion 72 including the lower edge 21BT located opposite the upper edge 21UT in the W direction, so that the separator 23 arranged between the positive electrode active material layer 21B and the negative electrode active material layer 22B can be more firmly held.

[0072] In the secondary battery 1 of the present embodiment, the positive electrode active material layer 21B further includes a thick portion 73 provided on the opposite side of the winding center side positive electrode active material layer edge 21BS in the L direction as viewed from the thin portion 61. This is advantageous in ensuring a predetermined battery capacity while mitigating stress concentration in the vicinity of the winding center of the electrode winding body 20.

[0073] In the secondary battery 1 of the present embodiment, both the positive electrode inner periphery side active material layer 21B1 and the positive electrode outer periphery side active material layer 21B2 include the thin portion 61 and the thick portions 71-73, so that it is possible to more effectively alleviate stress concentration in the vicinity of the winding center of the electrode wound body 20. In the secondary battery 1 of the present embodiment, the thin portion 61 is provided in a region including the center in the W direction, which is the width direction of the positive electrode 21, so that it is possible to effectively alleviate stress concentration inside the electrode wound body 20.

[0074] Furthermore, if the secondary battery is a lithium ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium, so that higher operational reliability can be obtained.

[0075] <3. Application Examples> The uses of the secondary battery according to one embodiment of the present disclosure are, for example, as described below.

[0076] [3-1. Battery pack] 6 is a block diagram showing an example of a circuit configuration in which a battery according to an embodiment of the present invention (hereinafter, appropriately 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.

[0077] The battery pack 300 includes a positive terminal 321 and a negative terminal 322, and during 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 the electronic device is in use, 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.

[0078] The battery pack 301 is formed by connecting a plurality of secondary batteries 301a in series or parallel. The secondary battery 1 described above can be used as the secondary batteries 301a. Note that, although Fig. 7 shows an example in which six secondary batteries 301a are connected in 2 parallel 3 series (2P3S), any other connection method such as n parallel m series (n and m are integers) may be used.

[0079] Switch unit 304 includes charge control switch 302a and diode 302b, as well as discharge control switch 303a and diode 303b, and is controlled by control unit 310. Diode 302b has a polarity in the reverse direction to the charge current flowing from positive terminal 321 to battery pack 301, and a polarity in the forward direction to the discharge current flowing from negative terminal 322 to battery pack 301. Diode 303b has a polarity in the forward direction to the charge current, and a polarity in the reverse direction to the discharge current. Although switch unit 304 is provided on the + side in FIG. 7, it may be provided on the - side.

[0080] 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 the charging current does not flow in the current path of the assembled battery 301. After the charge control switch 302a is turned off, only discharging is possible through the diode 302b. In addition, 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 flowing in the current path of the assembled battery 301 is interrupted. 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 the discharging current does not flow in the current path of the assembled battery 301. After the discharge control switch 303a is turned off, only charging is possible through the diode 303b. In addition, 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 flowing in the current path of the assembled battery 301 is interrupted.

[0081] Temperature detection element 308 is, for example, a thermistor that is provided near battery pack 301 and measures the temperature of battery pack 301 and supplies the measured temperature to control unit 310. Voltage detection unit 311 measures the voltage of battery pack 301 and each secondary battery 301a that constitutes it, A / D converts the measured voltage, and supplies it to control unit 310. Current measurement unit 313 measures the current using current detection resistor 307, and supplies this measured current to control unit 310. Switch control unit 314 controls charge control switch 302a and discharge control switch 303a of switch unit 304 based on the voltage and current input from voltage detection unit 311 and current measurement unit 313.

[0082] 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 and discharging. Here, for example, if the secondary battery is a lithium ion secondary battery, the overcharge detection voltage is set to, for example, 4.20V±0.05V, and the overdischarge detection voltage is set to, for example, 2.4V±0.1V.

[0083] The charge / discharge switch may be a semiconductor switch such as a MOSFET. In this case, the parasitic diode of the MOSFET functions as the diodes 302b and 303b. When a P-channel FET is used as the charge / discharge switch, the switch control section 314 supplies control signals DO and CO to the gates of the charge control switch 302a and the discharge control switch 303a, respectively. When the charge control switch 302a and the discharge control switch 303a are P-channel types, they are turned on by a gate potential that is lower than the source potential by a predetermined value or more. That is, in normal charge and discharge operations, the control signals CO and DO are at a low level, and the charge control switch 302a and the discharge control switch 303a are turned on.

[0084] For example, in the event of overcharging or overdischarging, the control signals CO and DO are set to a high level, and the charge control switch 302a and the discharge control switch 303a are set to an OFF state.

[0085] The memory 317 is made up of RAM and ROM, such as a non-volatile memory such as EPROM (Erasable Programmable Read Only Memory). In the memory 317, numerical values ​​calculated by the control unit 310 and the internal resistance value of each secondary battery 301a in the initial state measured during the manufacturing process are stored in advance, and can be rewritten as necessary. In addition, by storing the full charge capacity of the secondary battery 301a, it is possible to calculate, for example, the remaining capacity together with the control unit 310.

[0086] The temperature detection unit 318 measures the temperature using the temperature detection element 308, and performs charge / discharge control in the event of abnormal heat generation, and performs correction in the calculation of remaining capacity.

[0087] [3-2. Energy storage system] The secondary battery according to the embodiment of the present disclosure described above can be mounted on devices such as electronic devices, power tools, electric vehicles, electric aircraft, and power storage devices, or can be used to supply power.

[0088] 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.

[0089] Examples of electric vehicles include railroad cars, golf carts, electric carts, electric cars (including hybrid cars), and the like, and the device is used as a driving power source or auxiliary power source for these vehicles. Examples of power storage devices include power sources for storing electricity in buildings such as houses, or power generation facilities.

[0090] <3. Modifications> (First Modification) Next, a description will be given of a positive electrode 21-1 as a first modified example applied to secondary battery 1 of the above embodiment. Fig. 7 shows a cross-sectional configuration of positive electrode 21-1, and corresponds to Fig. 5B showing positive electrode 21 of the above embodiment.

[0091] 7, in the positive electrode 21-1 as the first modified example, the position of the boundary 21B1K in the L direction is different from the position of the boundary 21B2K in the L direction. That is, the length L1 from the winding center side positive electrode active material layer edge 21BS to the position of the boundary 21B1K is different from the length L2 from the winding center side positive electrode active material layer edge 21BS to the position of the boundary 21B2K. Except for this point, the configuration of the positive electrode 21-1 is substantially the same as the configuration of the positive electrode 21 of the above embodiment.

[0092] Thus, in the positive electrode 21-1, the position of the boundary 21B1K in the L direction is different from the position of the boundary 21B2K in the L direction. That is, the position of the step in the positive electrode inner periphery side active material layer 21B1 in the L direction is different from the position of the step in the positive electrode outer periphery side active material layer 21B2 in the L direction. Therefore, the location where stress is concentrated on the inner periphery surface 21A1 of the positive electrode collector caused by the expansion of the negative electrode 22 and the location where stress is concentrated on the outer periphery surface 21A2 of the positive electrode collector caused by the expansion of the negative electrode 22 are shifted. Therefore, the stress applied to the positive electrode collector 21A is dispersed. Therefore, according to the secondary battery 1 including the electrode wound body 20 having the positive electrode 21-1 as the first modification, the stress concentration inside the electrode wound body 20 caused by the expansion and contraction can be further alleviated compared to the case where the positive electrode 21 of the above embodiment is used.

[0093] (Second Modification) Next, a description will be given of a positive electrode 21-2 (21-2A to 21-2C) as a second modified example applied to secondary battery 1 of the above embodiment. Figures 8A to 8C show cross-sectional configurations of positive electrodes 21-2A to 21-2C, respectively, and correspond to Figure 5B showing positive electrode 21 of the above embodiment.

[0094] As shown in FIGS. 8A to 8C, in the positive electrodes 21-2A to 21-2C as the second modified example, the positive electrode inner periphery side active material layer 21B1 further includes a groove portion U1 between the thick portion 73-1 and the thin portion 61-1, and the positive electrode outer periphery side active material layer 21B2 further includes a groove portion U2 between the thick portion 73-2 and the thin portion 61-2. The groove portions U1 and U2 both extend in the W direction. The groove portion U1 has a thickness smaller than the thickness T61-1 of the thin portion 61-1 of the positive electrode inner periphery side active material layer 21B1. Similarly, the groove portion U2 has a thickness smaller than the thickness T61-2 of the thin portion 61-2 of the positive electrode outer periphery side active material layer 21B2. In the positive electrode 21-2A of Fig. 8A, the cross-sectional shape of the groove portions U1 and U2 is approximately rectangular, in the positive electrode 21-2B of Fig. 8B, the cross-sectional shape of the groove portions U1 and U2 is approximately V-shaped, and in the positive electrode 21-2C of Fig. 8C, the cross-sectional shape of the groove portions U1 and U2 is approximately U-shaped. However, the cross-sectional shapes of the groove portions U1 and U2 are not limited to the shapes shown in Figs. 8A to 8C, and can be selected arbitrarily.

[0095] In the positive electrodes 21-2A to 21-2C, the width of the groove portion U1 and the width of the groove portion U2 may be the same in the L direction, or the width of the groove portion U1 and the width of the groove portion U2 may be different. The width of the groove portion U1 is the length in the L direction from the position of the boundary 73U1 between the thick portion 73-1 and the groove portion U1 to the position of the boundary 61U1 between the thin portion 61-1 and the groove portion U1. The width of the groove portion U2 is the length in the L direction from the position of the boundary 73U2 between the thick portion 73-2 and the groove portion U2 to the position of the boundary 61U2 between the thin portion 61-2 and the groove portion U2. The width of the groove portion U1 and the width of the groove portion U2 are, for example, about 150 μm.

[0096] Furthermore, in each of the configuration examples of the positive electrodes 21-2A to 21-2C shown in FIGS. 8A to 8C, the L-direction position of the boundary 73U1 is different from the L-direction position of the boundary 73U2, and the L-direction position of the boundary 61U1 is different from the L-direction position of the boundary 61U2. However, in the present disclosure, the L-direction position of the boundary 73U1 may be the same as the L-direction position of the boundary 73U2. Also, the L-direction position of the boundary 61U1 may be the same as the L-direction position of the boundary 61U2. Alternatively, the L-direction position of the boundary 73U1 may be the same as the L-direction position of the boundary 73U2, and ...

[0097] 8A to 8C, the positive electrode inner periphery side active material layer 21B1 includes the groove portion U1 and the positive electrode outer periphery side active material layer 21B2 includes the groove portion U2, but only one of the groove portion U1 and the groove portion U2 may be included. Furthermore, the positive electrodes 21-2A to 21-2C may have only one of the positive electrode inner periphery side active material layer 21B1 and the positive electrode outer periphery side active material layer 21B2.

[0098] In this way, the positive electrodes 21-2A to 21-2C as the second modified example include at least one of the groove portion U1 and the groove portion U2, and therefore when used in the secondary battery 1, the separator 23 can be more firmly held between the positive electrode 21-2 and the negative electrode 22. When a part of the separator 23 fits into at least one of the groove portion U1 and the groove portion U2, the separator 23 sandwiched between the positive electrode 21-2 and the negative electrode 22 is less likely to be displaced or come off from a predetermined position. As a result, in the secondary battery 1 using the positive electrodes 21-2A to 21-2C, it is possible to effectively prevent a short circuit between the positive electrode 21 and the negative electrode 22, and to ensure better reliability.

[0099] (Third Modification) Next, with reference to Figs. 9A and 9B, a positive electrode 21-3 as a third modified example applied to the secondary battery 1 of the above embodiment will be described. Fig. 9A is a development view of the positive electrode 21-3, and corresponds to Fig. 4A showing the positive electrode 21 of the above embodiment. Fig. 9B is a development view of the positive electrode 21-3, and corresponds to Fig. 5B showing the positive electrode 21 of the above embodiment. Fig. 9B shows a cross section taken along line IXB-IXB shown in Fig. 9A in the direction of the arrows. Fig. 9B omits the illustration of the positive electrode lead 25 and the protective tape 21C.

[0100] As shown in FIG. 9A and FIG. 9B, in the positive electrode 21-3, the positive electrode active material layer 21B further includes a thin portion 62. The thin portion 62 is provided on the opposite side of the thick portion 73 from the thin portion 61. The thickness of the thin portion 62 is thinner than the thickness of the thick portion 73. The thin portion 62 includes the outer peripheral winding edge 21BE in the L direction of the positive electrode active material layer 21B. The positive electrode active material layer 21B further includes a thick portion 74 adjacent to the thin portion 62 in the W direction. More specifically, the thick portion 74 is located between the thin portion 62 and the upper edge 21UT in the W direction. The thick portion 74 includes the upper edge 21UT. The positive electrode active material layer 21B further includes a thick portion 75. The thick portion 75 includes the lower edge 21BT.

[0101] In the positive electrode 21-3 as the third modified example, the thin portion 62 is formed on both the positive electrode current collector inner peripheral surface 21A1 and the positive electrode current collector outer peripheral surface 21A2. That is, both the positive electrode inner peripheral side active material layer 21B1 and the positive electrode outer peripheral side active material layer 21B2 each include the thin portion 62. However, in the positive electrode 21-3, it is sufficient that at least one of the positive electrode inner peripheral side active material layer 21B1 and the positive electrode outer peripheral side active material layer 21B2 includes the thin portion 62. In FIG. 9B, the thin portion 62 included in the positive electrode inner peripheral side active material layer 21B1 is described as the thin portion 62-1 for convenience, and the thin portion 62 included in the positive electrode outer peripheral side active material layer 21B2 is described as the thin portion 62-2 for convenience. In the example shown in Fig. 9B, the position in the L direction of the boundary 21B1K1 between the thin portion 61-1 and the thick portion 73-1 substantially coincides with the position in the L direction of the boundary 21B2K1 between the thin portion 61-2 and the thick portion 73-2. In the example shown in Fig. 9B, the position in the L direction of the boundary 21B1K2 between the thin portion 62-1 and the thick portion 73-1 substantially coincides with the position in the L direction of the boundary 21B2K2 between the thin portion 62-2 and the thick portion 73-2.

[0102] In this way, in the positive electrode 21-3 as the third modified example, in addition to the thin portion 61, the thin portion 62 is also provided on the outer periphery of the electrode winding body 20. Therefore, the step between the portion where the positive electrode 21 is present and the portion where the positive electrode 21 is not present on the outer periphery of the electrode winding body 20 can be made smaller than when the positive electrode 21 does not have the thin portion 62. Therefore, the stress concentration on the portion of the separator 23 that overlaps with the outer periphery of the winding edge 21BE can be alleviated. Therefore, even if the thickness of the separator 23 is reduced, the breakage of the separator 23 can be avoided, and the occurrence of a short circuit between the positive electrode 21 and the negative electrode 22 can be prevented. That is, the separator 23 can be made thinner. As a result, the gap between the positive electrode 21 and the negative electrode 22 can be narrowed, the internal resistance of the electrode winding body 20 can be reduced, and the charge / discharge rate characteristics can be improved and the capacity of the secondary battery 1 can be increased. EXAMPLES

[0103] An embodiment of the present disclosure will be described.

[0104] (Example 1-1) A plurality of secondary batteries as Example 1-1 were fabricated in the following manner, and the battery characteristics of these secondary batteries were evaluated.

[0105] [Preparation of secondary battery] A cylindrical lithium ion secondary battery (diameter=outer diameter 18 mm and length 65 mm) shown in FIG. 1 was fabricated by the procedure described below.

[0106] (Preparation of positive electrode) First, the positive electrode active material (LiNi 0.8 Co 0.15 Al 0.0594 parts by mass of ethylenediaminetetraacetate (ethylenediaminetetraacetate), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 3 parts by mass of a positive electrode conductive agent (graphite) were mixed together to prepare a positive electrode mixture. Next, the positive electrode mixture was added to a solvent (N-methyl-2-pyrrolidone, an organic solvent), and the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector 21A (a strip-shaped aluminum foil having a thickness of 15 μm) using a coating device, and then the positive electrode mixture slurry was dried to form a positive electrode active material layer 21B. Next, the positive electrode active material layer 21B was compression-molded using a roll press machine. Furthermore, a predetermined region of the positive electrode active material layer 21B was dug down by laser ablation to form a thin portion 61. At that time, as shown in FIG. 4A and FIG. 5A, thick portions 71 (71-1, 71-2) and thick portions 72 (72-1, 72-2) were formed by leaving a part of the positive electrode active material layer 21B. In Example 1-1, the width in the W direction of each of the thick portions 71, 72 was set to 6 mm, which corresponds to 10% of the total width of 60 mm in the W direction of the positive electrode covering region 211. In Example 1-1, the position, dimensions, and shape of the thin portion 61-1 and the positions, dimensions, and shapes of the thick portions 71-1 to 73-1 in the positive electrode inner periphery side active material layer 21B1 were substantially the same as the position, dimensions, and shapes of the thin portion 61-2 and the positions, dimensions, and shapes of the thick portions 71-2 to 73-2 in the positive electrode outer periphery side active material layer 21B2. Here, the length of the thin portion 61 in the L direction, i.e., the length from the end edge 21BS of the positive electrode active material layer on the winding center side to the boundaries 21B1K, 21B2K, was set to 30 mm. In this manner, the positive electrode active material layer 21B including the thin portion 61 and the thick portions 71-73 was formed on both sides of the positive electrode current collector 21A. Finally, the protective tape 21C was attached to a predetermined position of the positive electrode current collector 21A to obtain the positive electrode 21.

[0107] (Preparation of negative electrode) First, 95 parts by mass of the negative electrode active material (graphite), 3 parts by mass of the negative electrode binder (styrene butadiene rubber (SBR)), and 2 parts by mass of the negative electrode conductive agent (carbon black) were mixed together to prepare a negative electrode mixture. Next, the negative electrode mixture was added to a solvent (water), and the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of the negative electrode current collector 22A (strip-shaped copper foil with a thickness of 15 μm) using a coating device, and then the negative electrode mixture slurry was dried to form the negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B was compression molded using a roll press machine.

[0108] (Preparation of electrolyte) After adding the electrolyte salt (LiPF6) to the solvent (ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate), the solvent was stirred. In this case, the mixing ratio (weight ratio) of the solvent was ethylene carbonate:ethyl methyl carbonate:dimethyl carbonate = 20:20:60, and the content of the electrolyte salt was 1 mol / kg relative to the solvent.

[0109] (Secondary battery assembly) First, an aluminum positive electrode lead 25 was welded to the positive electrode 21 (positive electrode current collector 21A), and a nickel negative electrode lead 26 was welded to the negative electrode 22 (negative electrode current collector 22A). Next, the positive electrode 21 and the negative electrode 22 were laminated with each other via a separator 23 (a porous polyethylene film having a thickness of 16 μm), and then the positive electrode 21, the negative electrode 22, and the separator 23 were wound to produce a wound body having a through hole 20C. When producing this wound body, the positive electrode 21 and the negative electrode 22 were aligned so that the entire overlapping region between the negative electrode lead 26 and the negative electrode current collector 22A in the lamination direction of the positive electrode 21 and the negative electrode 22 was overlapped with the protective tape 21C in the lamination direction.

[0110] Next, the wound body was housed inside a nickel-plated iron battery can 11 together with a pair of insulating plates 12, 13. The positive electrode lead 25 was welded to a safety valve mechanism 30, and the negative electrode lead 26 was welded to the battery can 11. Next, an electrolyte was injected into the battery can 11 using a reduced pressure method, and the electrolyte was impregnated into the wound body.

[0111] Next, asphalt was added to a solvent (ethylcyclohexane, an organic solvent) and the solvent was stirred to prepare a coating solution, which was then applied to a polypropylene gasket 15.

[0112] Finally, the open end 11N of the battery can 11, the battery lid 14 and the safety valve mechanism 30 were crimped together via a polypropylene gasket 15 to form a crimped structure 11R.

[0113] As a result, the open end 11N of the battery can 11 was closed by the battery lid 14, and the battery element and the like were housed inside the battery can 11, so that a cylindrical lithium ion secondary battery was assembled.

[0114] (Stabilization of secondary batteries) The secondary battery was charged and discharged for one cycle in a room temperature environment (temperature = 23°C). During charging, the battery was charged at a constant current of 0.1C until the voltage reached 4.2V, and then charged at a constant voltage of 4.2V until the current reached 0.05C. During discharging, the battery was discharged at a constant current of 0.1C until the voltage reached 3.0V. 0.1C is the current value at which a battery capacity (theoretical capacity) of 4000mAh is fully discharged in 10 hours, and 0.05C is the current value at which a battery capacity of 4000mAh is fully discharged in 20 hours.

[0115] This electrochemically stabilized the state of the secondary battery, resulting in the creation of a cylindrical lithium-ion secondary battery.

[0116] (Example 1-2) When forming the thin portion 61 by laser ablation, as shown in FIG. 10A and FIG. 10B, a part of the positive electrode active material layer 21B is left to form the thick portion 71 (71-1, 71-2), while the thick portion 72 (72-1, 72-2) is not formed. FIG. 10A is a development view of the positive electrode 21 representing Example 1-2, and FIG. 10B is a cross-sectional view of the positive electrode 21 representing Example 1-2. Except for this point, the secondary battery of Example 1-2 was fabricated in the same manner as in Example 1-1. In Example 1-2, the width of the thick portion 71 in the W direction was set to 6 mm, which corresponds to 10% of the total width of 60 mm in the W direction of the positive electrode covering region 211.

[0117] (Examples 1-3) When forming the thin portion 61 by laser ablation, as shown in FIG. 11A and FIG. 11B, a part of the positive electrode active material layer 21B is left to form the thick portion 72 (72-1, 72-2), while the thick portion 71 (71-1, 71-2) is not formed. FIG. 11A is a development view of the positive electrode 21 representing Example 1-3, and FIG. 11B is a cross-sectional view of the positive electrode 21 representing Example 1-3. Except for this point, the secondary battery of Example 1-3 was fabricated in the same manner as in Example 1-1. In Example 1-3, the width of the thick portion 72 in the W direction was set to 6 mm, which corresponds to 10% of the total width of 60 mm in the W direction of the positive electrode covering region 211.

[0118] (Example 2-1) A secondary battery of Example 2-1 was produced in the same manner as in Example 1-1, except that a positive electrode 21-1 (FIG. 7) was used instead of the positive electrode 21. That is, when forming a thin portion 61 by digging down a part of the positive electrode active material layer 21B by laser ablation, the position in the L direction of a boundary 21B1K in the positive electrode inner periphery side active material layer 21B1 was made to differ from the position in the L direction of a boundary 21B2K in the positive electrode outer periphery side active material layer 21B2.

[0119] (Example 2-2) When forming the thin portion 61 by laser ablation, as shown in Fig. 10A and Fig. 10B, a part of the positive electrode active material layer 21B is left to form the thick portion 71 (71-1, 71-2), but the thick portion 72 (72-1, 72-2) is not formed. Except for this point, the secondary battery of Example 2-2 was fabricated in the same manner as in Example 2-1. In Example 2-2, the width of the thick portion 71 in the W direction was set to 6 mm, which corresponds to 10% of the total width of 60 mm in the W direction of the positive electrode covering region 211.

[0120] (Example 2-3) When forming the thin portion 61 by laser ablation, as shown in Fig. 11A and Fig. 11B, a part of the positive electrode active material layer 21B is left to form the thick portion 72 (72-1, 72-2), but the thick portion 71 (71-1, 71-2) is not formed. Except for this point, the secondary battery of Example 2-3 was fabricated in the same manner as in Example 2-1. In Example 2-3, the width of the thick portion 72 in the W direction was set to 6 mm, which corresponds to 10% of the total width of 60 mm in the W direction of the positive electrode covering region 211.

[0121] (Example 3-1) A secondary battery of Example 3-1 was fabricated in the same manner as in Example 1-1, except that a positive electrode 21-2D (FIG. 12) was used instead of the positive electrode 21. That is, when forming the thin portion 61 by digging down a part of the positive electrode active material layer 21B by laser ablation, groove portions U1 and U2 were formed between the thin portion 61 (61-1, 61-2) and the thick portion 73 (73-1, 73-2). At that time, the position of the groove portion U1 in the L direction was made to coincide with the position of the groove portion U2 in the L direction.

[0122] (Example 3-2) When forming the thin portion 61 by laser ablation, as shown in Fig. 10A and Fig. 10B, a part of the positive electrode active material layer 21B is left to form the thick portion 71 (71-1, 71-2), but the thick portion 72 (72-1, 72-2) is not formed. Except for this point, the secondary battery of Example 3-2 was fabricated in the same manner as in Example 3-1. In Example 3-2, the width of the thick portion 71 in the W direction was set to 6 mm, which corresponds to 10% of the total axial width of the positive electrode covering region 211, 60 mm.

[0123] (Example 3-3) When forming the thin portion 61 by laser ablation, as shown in Fig. 11A and Fig. 11B, a part of the positive electrode active material layer 21B is left to form the thick portion 72 (72-1, 72-2), but the thick portion 71 (71-1, 71-2) is not formed. Except for this point, the secondary battery of Example 3-3 was fabricated in the same manner as in Example 3-1. In Example 3-3, the width of the thick portion 72 in the W direction was set to 6 mm, which corresponds to 10% of the total width of 60 mm in the W direction of the positive electrode covering region 211.

[0124] (Example 4-1) A secondary battery of Example 4-1 was fabricated in the same manner as in Example 1-1, except that a positive electrode 21-2C (FIG. 8C) was used instead of the positive electrode 21. That is, when forming the thin portion 61 including the central axis side edge 21E1 by digging down a part of the positive electrode active material layer 21B by laser ablation, groove portions U1 and U2 were formed between the thin portion 61 (61-1, 61-2) and the thick portion 73 (73-1, 73-2). At that time, the position of the groove portion U1 in the L direction was made different from the position of the groove portion U2 in the L direction.

[0125] (Example 4-2) When forming the thin portion 61 by laser ablation, as shown in Fig. 10A and Fig. 10B, a part of the positive electrode active material layer 21B is left to form the thick portion 71 (71-1, 71-2), but the thick portion 72 (72-1, 72-2) is not formed. Except for this point, the secondary battery of Example 4-2 was fabricated in the same manner as in Example 4-1. In Example 4-2, the width of the thick portion 71 in the W direction was set to 6 mm, which corresponds to 10% of the total width of 60 mm in the W direction of the positive electrode covering region 211.

[0126] (Example 4-3) When forming the thin portion 61 by laser ablation, as shown in Fig. 11A and Fig. 11B, a part of the positive electrode active material layer 21B is left to form the thick portion 72 (72-1, 72-2), while the thick portion 71 (71-1, 71-2) is not formed. Except for this point, the secondary battery of Example 4-3 was fabricated in the same manner as in Example 4-1. In Example 4-3, the width of the thick portion 72 in the W direction was set to 6 mm, which corresponds to 10% of the total width of 60 mm in the W direction of the positive electrode covering region 211.

[0127] (Example 5-1) Of the positive electrode inner circumference side active material layer 21B1 and the positive electrode outer circumference side active material layer 21B2 respectively provided on the positive electrode current collector 21A, only the positive electrode inner circumference side active material layer 21B1 provided on the positive electrode current collector inner circumference surface 21A1 was provided with a thin portion 61. That is, in Example 5-1, the positive electrode outer circumference side active material layer 21B2 provided on the positive electrode current collector outer circumference surface 21A2 was not formed with a thin portion 61, and the positive electrode outer circumference side active material layer 21B2 had a uniform thickness throughout. Except for this point, the secondary battery of Example 5-1 was fabricated in the same manner as in Example 1-1.

[0128] (Example 5-2) Of the positive electrode inner circumference side active material layer 21B1 and the positive electrode outer circumference side active material layer 21B2 respectively provided on the positive electrode current collector 21A, only the positive electrode inner circumference side active material layer 21B1 provided on the positive electrode current collector inner circumference surface 21A1 was provided with a thin portion 61. That is, in Example 5-2, the positive electrode outer circumference side active material layer 21B2 provided on the positive electrode current collector outer circumference surface 21A2 was not formed with a thin portion 61, and the positive electrode outer circumference side active material layer 21B2 had a uniform thickness throughout. Except for this point, the secondary battery of Example 5-2 was fabricated in the same manner as in Example 3-1.

[0129] Comparative Example 1 The positive electrode inner periphery side active material layer 21B1 and the positive electrode outer periphery side active material layer 21B2 provided on the positive electrode current collector 21A were not formed with the thin portion 61, and both the positive electrode inner periphery side active material layer 21B1 and the positive electrode outer periphery side active material layer 21B2 had a uniform thickness throughout. Except for this point, the secondary battery of Comparative Example 1 was fabricated in the same manner as in Example 1-1.

[0130] Comparative Example 2 For both the positive electrode inner periphery side active material layer 21B1 and the positive electrode outer periphery side active material layer 21B2 provided on the positive electrode current collector 21A, a thin portion 61 was formed so as to extend over the entire W direction of the positive electrode covering region 211. In other words, no thick portions 71, 72 were provided. Except for this point, the secondary battery of Comparative Example 2 was produced in the same manner as in Example 1-1.

[0131] [Evaluation of battery characteristics] The secondary batteries of Examples 1-1 to 1-3, 2-1 to 2-3, 3-1 to 3-3, 4-1 to 4-3, 5-1 to 5-2 and Comparative Examples 1 and 2 were examined for the presence or absence of winding defects, the incidence of short circuits after the first charge and discharge, the amount of deformation of the positive electrode after charge and discharge cycles, and the incidence of short circuits after charge and discharge cycles. The results are shown in Table 1.

[0132] [Table 1]

[0133] (Whether or not winding is defective) The electrode windings of each secondary battery were evaluated for the presence or absence of physical shorts when electrolyte was not injected. Specifically, HPT (high potential test) was performed. At that time, the insulation resistance was set at 0.2 kV as the reference value. The number of samples was 10,000.

[0134] (Short circuit occurrence rate after first charge / discharge) The presence or absence of short circuits caused by the inclusion of conductive powder such as metal was judged by the presence or absence of heat generation after the initial charge and discharge. The number of samples was 10,000.

[0135] (Deformation of the positive electrode after charge / discharge cycles) The CT images were used to measure the radial protrusions of the electrode winding body 20 occurring in the positive electrode at the middle portion of the electrode winding body 20 (near the boundaries 21B1K, 21B2K between the thin portion 61 and the thick portion 73) and near the central axis side edge 21E1 of the electrode winding body 20. The number of samples was 100. Specifically, the cycle test was performed under the following test conditions.

[0136] (Cycle test conditions) (1) Environmental temperature: 23°C. (2) Charging conditions: constant current constant voltage (CC-CV) charging was performed. The battery was charged at a constant current of 10 A up to a voltage of 4.2 V, and then charged at a constant voltage of 4.2 V. The cutoff current was 1 A. (3) Rest time after charging: 60 minutes. (4) Discharge conditions: Constant current (CC) discharge was performed at a constant current of 50 A. The cut-off voltage was set to 2 V. Discharge was stopped when the temperature reached 85° C. (5) Rest after discharge: The battery was rested until the surface temperature of the battery was below 50°C. . (6) Number of cycles: 100 cycles.

[0137] (Short circuit occurrence rate after charge / discharge cycles) After carrying out the cycle test under the above test conditions, the battery was stored in an environment of 25°C for one week. If a voltage drop of 4.1 V or more was observed, it was determined that a short circuit had occurred.

[0138] As shown in Table 1, in all of Examples 1-1 to 1-3, 2-1 to 2-3, 3-1 to 3-3, 4-1 to 4-3, and 5-1 to 5-2, no winding defects, no short circuits after the initial charge / discharge, and no short circuits after the charge / discharge cycle occurred. In contrast, in Comparative Example 1, short circuits after the charge / discharge cycle occurred at a rate of 4% (4 out of 100 samples). In Comparative Example 2, winding defects occurred at a rate of 200 ppm, and short circuits after the charge / discharge cycle occurred at a rate of 2% (2 out of 100 samples).

[0139] From the above results, it was confirmed that the secondary battery of the present disclosure can ensure superior safety.

[0140] Although the present disclosure has been described above with reference to one embodiment and some modified examples, the configuration of the present disclosure is not limited to the configuration described in the above embodiment and some modified examples, and can be modified in various ways. For example, in the above embodiment, the thin portion 61 as the first thin portion is provided at a position in contact with the winding center side positive electrode active material layer edge 21BS of the positive electrode active material layer 21B, but the present disclosure is not limited to this. The first thin portion (thin portion 61) may be provided at a location away from the winding center side positive electrode active material layer edge 21BS of the positive electrode active material layer 21B. Similarly, the thin portion 62 as the second thin portion is not limited to a location in contact with the winding outer periphery side edge 21BE of the positive electrode active material layer 21B. The second thin portion (thin portion 62) may be provided at a location away from the winding outer periphery side edge 21BE of the positive electrode active material layer 21B.

[0141] In the above embodiment and examples, 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.

[0142] 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.

[0143] The present disclosure may take the following forms. <1> a laminate including a positive electrode, a negative electrode, and a separator, wound along a longitudinal direction of the laminate, the laminate having a through hole penetrating in a width direction perpendicular to the longitudinal direction; an exterior can that houses the electrode winding body; Equipped with The positive electrode is a positive electrode active material layer extending in both the longitudinal direction and the width direction; a positive electrode current collector including a positive electrode covered region covered with the positive electrode active material layer and a positive electrode exposed region extending in the width direction from the positive electrode active material layer; having The positive electrode active material layer includes a first thin portion and a first thick portion having a thickness greater than a thickness of the first thin portion and adjacent to the first thin portion in the width direction. Secondary battery. <2> The first thin portion includes an end edge of the positive electrode active material layer on a side closer to the center of winding in the longitudinal direction. the above <1> The secondary battery described herein. <3> the positive electrode active material layer further has a second thick portion located on an opposite side of the first thick portion from the first thin portion in the width direction, The thickness of the second thick portion is greater than the thickness of the first thin portion. the above <1> or <2> The secondary battery described herein. <4> the positive electrode active material layer further includes a third thick portion provided on a side opposite to the end edge of the positive electrode active material layer on the winding center side as viewed from the first thin portion in the longitudinal direction, The thickness of the third thick portion is greater than the thickness of the first thin portion. the above <1> The secondary battery described herein. <5> the positive electrode current collector includes a positive electrode current collector inner peripheral surface (21A1) facing the winding center side of the electrode winding body, and a positive electrode current collector outer peripheral surface (21A2) facing the outside opposite to the winding center side of the electrode winding body, The first thick portion and the first thin portion are formed on both the inner peripheral surface and the outer peripheral surface of the positive electrode current collector, respectively. the above <1> from <4> 13. The secondary battery according to claim 12, <6> the positive electrode current collector includes an inner peripheral surface of the positive electrode current collector facing the winding center side of the electrode winding body, and an outer peripheral surface of the positive electrode current collector facing the outside opposite to the winding center side of the electrode winding body, the positive electrode active material layer includes a first positive electrode active material layer provided on an inner peripheral surface of the positive electrode current collector, and a second positive electrode active material layer provided on an outer peripheral surface of the positive electrode current collector, each of the first positive electrode active material layer and the second positive electrode active material layer includes the first thin portion, the first thick portion, and the third thick portion; a first length from an end edge of the positive electrode active material layer on a winding center side in the longitudinal direction to a position of a first boundary between the first thin portion of the first positive electrode active material layer and the third thick portion of the first positive electrode active material layer, and a second length from an end edge of the positive electrode active material layer on a winding center side in the longitudinal direction to a position of a second boundary between the first thin portion of the second positive electrode active material layer and the third thick portion of the second positive electrode active material layer are different. the above <4> The secondary battery described herein. <7> The positive electrode active material layer further includes a groove portion between the third thick portion and the first thin portion. the above <4> or <6> The secondary battery described herein. <8> the positive electrode active material layer further has a second thin portion on an opposite side of the third thick portion to the first thin portion, The second thin portion has a thickness smaller than the thickness of the third thick portion. the above <4> , <6> or <7> The secondary battery according to claim 1. <9> the above <1> from <8> A secondary battery according to any one of the above items, A control unit that controls the secondary battery; An exterior body that encapsulates the secondary battery; A battery pack having [Explanation of symbols]

[0144] 11...battery can, 11N...open end, 11P...folded portion, 11R...crimping structure, 12, 13...insulating plate, 14...battery lid, 15...gasket, 20...electrode winding body, 20C...through hole, 21...positive electrode, 21A...positive electrode current collector, 21B...positive electrode active material layer, 21C...protective tape, 211...positive electrode coating region, 212...positive electrode exposed region, 22...negative electrode, 22A...negative electrode current collector, 22B...negative electrode active material layer, 221...negative electrode coating region, 222...negative electrode exposed region, 23...separator, 25...positive electrode lead, 26...negative electrode lead, 30...safety valve mechanism.

Claims

1. an electrode winding body in which a laminate including a positive electrode, a negative electrode, and a separator is wound along a longitudinal direction of the laminate and has a through hole penetrating in a width direction perpendicular to the longitudinal direction; an exterior can that houses the electrode winding body; Equipped with The positive electrode is a positive electrode active material layer extending in both the longitudinal direction and the width direction; a positive electrode current collector including a positive electrode covered region covered with the positive electrode active material layer and a positive electrode exposed region extending in the width direction from the positive electrode active material layer; having The positive electrode active material layer includes a first thin portion and a first thick portion having a thickness greater than a thickness of the first thin portion and adjacent to the first thin portion in the width direction. Secondary battery.

2. The first thin portion includes an end edge of the positive electrode active material layer on a winding center side in the longitudinal direction. The secondary battery according to claim 1 .

3. the positive electrode active material layer further has a second thick portion located on an opposite side of the first thick portion from the first thin portion in the width direction, The thickness of the second thick portion is greater than the thickness of the first thin portion. The secondary battery according to claim 1 .

4. the positive electrode active material layer further includes a third thick portion provided on a side opposite to the end edge of the positive electrode active material layer on a winding center side as viewed from the first thin portion in the longitudinal direction, The thickness of the third thick portion is greater than the thickness of the first thin portion. The secondary battery according to claim 2.

5. the positive electrode current collector includes an inner peripheral surface of the positive electrode current collector facing the winding center side of the electrode winding body, and an outer peripheral surface of the positive electrode current collector facing the outside opposite to the winding center side of the electrode winding body, The first thick portion and the first thin portion are formed on both the inner peripheral surface of the positive electrode current collector and the outer peripheral surface of the positive electrode current collector, respectively. The secondary battery according to claim 1 .

6. the positive electrode current collector includes an inner peripheral surface of the positive electrode current collector facing the winding center side of the electrode winding body, and an outer peripheral surface of the positive electrode current collector facing the outside opposite to the winding center side of the electrode winding body, the positive electrode active material layer includes a first positive electrode active material layer provided on an inner peripheral surface of the positive electrode current collector, and a second positive electrode active material layer provided on an outer peripheral surface of the positive electrode current collector, each of the first positive electrode active material layer and the second positive electrode active material layer includes the first thin portion, the first thick portion, and the third thick portion; A first length from an end edge of the positive electrode active material layer on a winding center side in the longitudinal direction to a position of a first boundary between the first thin portion of the first positive electrode active material layer and the third thick portion of the first positive electrode active material layer is different from a second length from an end edge of the positive electrode active material layer on a winding center side in the longitudinal direction to a position of a second boundary between the first thin portion of the second positive electrode active material layer and the third thick portion of the second positive electrode active material layer. The secondary battery according to claim 4.

7. The positive electrode active material layer further includes a groove portion between the third thick portion and the first thin portion. The secondary battery according to claim 4.

8. the positive electrode active material layer further has a second thin portion on an opposite side of the third thick portion to the first thin portion, The second thin portion has a thickness smaller than the thickness of the third thick portion. The secondary battery according to claim 4.

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

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