Positive electrode, secondary battery, and battery pack

Abstract

To provide a highly reliable secondary battery.SOLUTION: A secondary battery includes an electrode wound 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 which has a through hole penetrating in a width direction orthogonal to a longitudinal direction. The positive electrode includes a positive electrode current collector 21A that spreads in both the longitudinal direction and the width direction, and a positive electrode active material layer that is stacked on the positive electrode current collector and includes a positive electrode active material 21BP and a positive electrode binder 21BB. The positive electrode active material layer includes a first thin-walled portion 61-1 and a first thick-walled portion 71-1 having a thickness larger than the thickness of the first thin-walled portion and located on a winding outer peripheral side of the electrode wound body when viewed from the first thin-walled portion in the longitudinal direction. A ratio of an abundance of the positive electrode binder to the abundance of the positive electrode active material in the first thin-walled portion is lower than a ratio of the abundance of the positive electrode binder to the abundance of the positive electrode active material in the first thick-walled portion.SELECTED DRAWING: Figure 4D

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode, and a secondary battery and a battery pack including the positive electrode. [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, lightweight, and capable of obtaining 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 these secondary batteries (see, for example, Patent Document 1).

[0003] Patent Document 1 proposes a secondary battery that employs a so-called tabless structure to reduce internal resistance and enable charging and discharging with a relatively large current. [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 one 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 has through-holes penetrating in a width direction perpendicular to the longitudinal direction. The positive electrode includes a positive electrode current collector extending in both the longitudinal and width directions, and a positive electrode active material layer laminated on the positive electrode current collector and including a positive electrode active material and a positive electrode binder. 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 positioned on the outer periphery of the electrode winding body in the longitudinal direction as viewed from the first thin portion. The ratio of the amount of positive electrode binder to the amount of positive electrode active material in the first thin portion is lower than the ratio of the amount of positive electrode binder to the amount of positive electrode active material in the first thick portion. [Effects of the Invention]

[0008] According to the secondary battery of one embodiment of the present disclosure, by reducing the amount of positive electrode binder present in the gaps between the positive electrode active material in the first thin-walled portion of the positive electrode active material layer, the positive electrode active material becomes more mobile, and the flexibility of the positive electrode active material layer is increased. This improves the flexibility of the positive electrode, thereby reducing stress concentration near the center of the winding of the electrode winding, for example. Therefore, the secondary battery of one embodiment of the present disclosure can achieve higher reliability.

[0009] Note that the effects of the present disclosure are not necessarily limited to the effects described here, but may be any of a series of effects related to the present disclosure described below. [Brief explanation 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. [Figure 2] FIG. 2 is a schematic diagram showing an example of the configuration of a laminate including the positive electrode, negative electrode, and separator shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view showing an example of the horizontal cross-sectional structure of the electrode winding body shown in FIG. [Figure 4A]FIG. 4A is a development view showing an example of the configuration of the positive electrode shown in FIG. [Figure 4B] FIG. 4B is a first cross-sectional view showing an example of the configuration of the positive electrode shown in FIG. [Figure 4C] FIG. 4C is a second cross-sectional view illustrating one configuration example of the positive electrode shown in FIG. [Figure 4D] FIG. 4D is a schematic cross-sectional view showing an enlarged portion of the cross section of the positive electrode shown in FIG. 4C. [Figure 5A] FIG. 5A is a development view showing an example of the configuration of the negative electrode shown in FIG. [Figure 5B] FIG. 5B is a cross-sectional view illustrating an example of the configuration of the negative electrode shown in FIG. [Figure 6A] FIG. 6A is a plan view illustrating an example of the configuration of the positive electrode current collector plate shown in FIG. [Figure 6B] FIG. 6B is a plan view illustrating an example of the configuration of the negative electrode current collector plate shown in FIG. [Figure 7] FIG. 7 is a perspective view illustrating a manufacturing process of the secondary battery shown in FIG. [Figure 8] FIG. 8 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 9] FIG. 9 is a cross-sectional view illustrating a configuration example of a positive electrode according to a first modification of the present disclosure. [Figure 10A] FIG. 10A is a cross-sectional view showing a first embodiment of a positive electrode according to a second modification of the present disclosure. [Figure 10B] FIG. 10B is a cross-sectional view showing a second embodiment of a positive electrode according to a second modification of the present disclosure. [Figure 10C] FIG. 10C is a cross-sectional view showing a third embodiment of a positive electrode according to the second modification of the present disclosure. [Figure 11A] FIG. 11A is a development view showing a configuration example of a positive electrode according to a third modified example of the present disclosure. [Figure 11B] FIG. 11B is a cross-sectional view illustrating an example of the configuration of the positive electrode shown in FIG. 11A. [Figure 12A] FIG. 12A is a development view showing a configuration example of a positive electrode according to a fourth modified example of the present disclosure. [Figure 12B] FIG. 12B is a cross-sectional view illustrating an example of the configuration of the positive electrode shown in FIG. 12A. [Figure 13] FIG. 13 is a development view showing a configuration example of a positive electrode according to a fifth modification of the present disclosure. [Figure 14] FIG. 14 is a cross-sectional view illustrating a configuration example of a vertical cross-sectional structure along the height direction of a secondary battery according to a sixth modified example of the present disclosure. [Figure 15A] FIG. 15A is a development view showing a configuration example of a positive electrode mounted on the secondary battery shown in FIG. [Figure 15B] FIG. 15B is a development view showing a configuration example of a negative electrode mounted on the secondary battery shown in FIG. [Figure 16A] FIG. 16A is a first cross-sectional view of the positive electrode shown in FIG. 15A. [Figure 16B] FIG. 16B is a second cross-sectional view of the positive electrode shown in FIG. 15A. [Figure 17] FIG. 17 is a schematic diagram showing a measuring device for measuring the maximum bending stress of the test piece in the examples. [Figure 18] FIG. 18 is a characteristic diagram showing the relationship between the area density of the positive electrode active material layer and the maximum bending stress. DETAILED DESCRIPTION OF THE INVENTION

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

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

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

[0014] The charge / discharge principle of a secondary battery is not particularly limited, but the following description focuses on a case where battery capacity is obtained by utilizing the absorption / desorption of an electrode reactant. This secondary battery includes a positive electrode, a negative electrode, and an electrolyte. In this secondary battery, the charge capacity of the negative electrode is larger than the discharge capacity of the positive electrode to prevent deposition of the electrode reactant on the surface of the negative electrode during charging. In other words, the electrochemical capacity per unit area of ​​the negative electrode is set to be larger than the electrochemical capacity per unit area of ​​the positive electrode.

[0015] The type of electrode reactant is not particularly limited as described above, but specifically includes light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, and alkaline earth metals include beryllium, magnesium, and calcium.

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

[0017] [1-1.Configuration] (Lithium-ion secondary battery 1) Fig. 1 shows a vertical cross-sectional configuration along the height direction of a lithium-ion secondary battery 1 (hereinafter simply referred to as secondary battery 1) according to this embodiment. The secondary battery 1 shown in Fig. 1 includes a substantially cylindrical outer can 11 and an electrode winding body 20 as a battery element housed in the outer can 11. Furthermore, the secondary battery 1 includes an outer tube 50 that covers the outer peripheral surface of the outer can 11. In this specification, the height direction of the secondary battery 1 is defined as the Z-axis direction.

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

[0019] (Outer can 11) The outer can 11 is a container that houses the positive electrode current collector 24, the negative electrode current collector 25, the electrode winding 20, and the like. The outer can 11 has a bottom 11B and a sidewall 11W. The bottom 11B also serves as a negative electrode terminal connected to the negative electrode 22 via the negative electrode current collector 25. The outer can 11 has, for example, a hollow cylindrical structure with a closed lower end in the Z-axis direction and an open upper end. Therefore, the upper end of the outer can 11 is an open end 11N, and the lower end of the outer can 11 is closed by the substantially disk-shaped bottom 11B. Between the open end 11N and the bottom 11B is a sidewall 11W that surrounds the electrode winding 20. The sidewall 11W is erected in the height direction along the outer edge of the bottom 11B to surround the electrode winding 20, and includes an open end 11N on the opposite side to the bottom 11B that is open and allows the electrode winding 20 to be inserted therethrough. The constituent material of the outer can 11 includes, for example, a metal material such as iron. However, the surface of the outer can 11 may be plated with a metal material such as nickel. The insulating plates 12 and 13 are disposed, for example, facing each other in the Z-axis direction with the electrode winding body 20 sandwiched between them. In this specification, in the Z-axis direction, the open end 11N and its vicinity may be referred to as the upper part of the secondary battery 1, and the portion where the outer can 11 is closed and its vicinity may be referred to as the lower part of the secondary battery 1.

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

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

[0022] (insulating plates 12, 13) Each of the insulating plates 12 and 13 is, for example, a dish-shaped plate having a surface perpendicular to the central axis CL of the wound electrode body 20, i.e., a surface perpendicular to the Z axis in Fig. 1. The insulating plates 12 and 13 are arranged so as to sandwich the wound electrode body 20 therebetween.

[0023] (Crimped structure 11R) An open end 11N of the outer can 11 has a structure in which, for example, the battery lid 14 and the safety valve mechanism 30 are crimped via a gasket 15, i.e., a crimped structure 11R. The battery lid 14 seals the outer can 11 with the electrode wound body 20 and other components housed inside. The crimped structure 11R has a bent portion 11P as a so-called crimp portion. In addition, a constricted portion 11S is provided between the bent portion 11P and the insulating plate 12, where a portion of the outer can 11 protrudes inward.

[0024] (Battery cover 14) The battery lid 14 is primarily a closing member that closes the open end 11N when the electrode winding body 20 and other components are housed inside the exterior can 11. The battery lid 14 is, for example, a conductor containing the same material as the material from which the exterior can 11 is formed. The battery lid 14 closes the open end 11N of the exterior can 11 and is connected to the positive electrode current collector 24. Therefore, the battery lid 14 also serves as a positive electrode terminal that is connected to the positive electrode 21 via the positive electrode current collector 24. A central region of the battery lid 14 protrudes upward (in the +Z direction), for example. As a result, the peripheral region of the battery lid 14 other than the central region is in contact with, for example, a safety valve mechanism 30.

[0025] (Gasket 15) The gasket 15 is a sealing member interposed mainly between the folded portion 11P of the outer can 11 and the battery lid 14. The gasket 15 seals the gap between the folded portion 11P and the battery lid 14. However, the surface of the gasket 15 may be coated with, for example, asphalt. The gasket 15 contains, for example, one or more types of insulating materials. The type of insulating material is not particularly limited, but examples include polymer materials such as polybutylene terephthalate (PBT) and polypropylene (PP). Among these, polybutylene terephthalate is preferable as the insulating material. This is because the gap between the folded portion 11P and the battery lid 14 is sufficiently sealed while electrically isolating the outer can 11 and the battery lid 14 from each other.

[0026] (Safety valve mechanism 30) The safety valve mechanism 30 is mainly configured to release the internal pressure of the outer can 11 by releasing the sealed state of the outer can 11 as necessary when the pressure inside the outer can 11 (internal pressure) increases. The internal pressure of the outer can 11 increases, for example, due to gas generated by a decomposition reaction of the electrolyte during charging and discharging. The internal pressure of the outer can 11 may also increase due to external heating.

[0027] (Electrode winding body 20) The electrode winding body 20 is disposed between a positive electrode current collector 24 and a negative electrode current collector 25. The electrode winding body 20 has an upper end face 41 that faces the positive electrode current collector 24 in the height direction, and a lower end face 42 that faces the negative electrode current collector 25 in the height direction. The electrode winding body 20 is a power generation element that causes charge / discharge reactions to proceed, and is housed inside an outer can 11. The electrode winding body 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolytic solution that is a liquid electrolyte.

[0028] FIG. 2 is a developed view of the electrode winding body 20. Specifically, FIG. 2 is a schematic representation of a portion of a laminate S20 in which the electrode winding body 20 is developed. The laminate S20 includes a positive electrode 21, a negative electrode 22, and a separator 23. In the laminate S20, the positive electrode 21 and the negative electrode 22 are stacked with the separator 23 interposed between them. The separator 23 has, for example, two base materials, namely, a first separator member 23A and a second separator member 23B. Therefore, the electrode winding body 20 has a four-layer laminate S20 in which the positive electrode 21, the first separator member 23A, the negative electrode 22, and the second separator member 23B are stacked in this order. The positive electrode 21, the first separator member 23A, the negative electrode 22, and the second separator member 23B are all substantially strip-shaped members with the W direction as the short side direction and the L direction as the long side direction.

[0029] As shown in FIG. 3 , the electrode winding body 20 is formed by winding the laminate S20 around a through-hole 26 along 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 laminate S20 is wound in an orientation in which the W direction roughly coincides with the Z-axis direction. Note that FIG. 3 shows an example of the configuration of the electrode winding body 20 along a horizontal cross section perpendicular to the Z-axis direction. However, in FIG. 3 , the separator 23 is omitted for improved visibility. The electrode winding body 20 has an overall substantially cylindrical appearance. The positive electrode 21 and the negative electrode 22 are wound while maintaining a state in which they face each other with the separator 23 interposed therebetween. A through-hole 26 is formed at the center of the electrode winding body 20 as an internal space. The through-hole 26 is a hole for inserting a winding core for assembling the electrode winding body 20 and an electrode rod for welding. The through-hole extends in the Z-axis direction along the central axis CL and penetrates the electrode winding body 20. Therefore, the laminate S20 is wound around the through-hole .

[0030] The positive electrode 21, the negative electrode 22, and the separator 23 are wound such that the separator 23 is disposed at the outermost and innermost peripheries of the electrode winding body 20, respectively. At the outermost periphery of the electrode winding body 20, the negative electrode 22 is disposed outside the positive electrode 21. That is, as shown in FIG. 3 , a positive electrode outermost portion 21out located at the outermost periphery of the positive electrode 21 included in the electrode winding body 20 is disposed inside a negative electrode outermost portion 22out located at the outermost periphery of the negative electrode 22 included in the electrode winding body 20. Here, the positive electrode outermost portion 21out is the outermost one-turn portion of the positive electrode 21 in the electrode winding body 20. The negative electrode outermost portion 22out is the outermost one-turn portion of the negative electrode 22 in the electrode winding body 20. Meanwhile, at the innermost periphery of the electrode winding body 20, the negative electrode 22 is disposed inside the positive electrode 21. That is, as shown in Fig. 3, the negative electrode innermost circumferential portion 22in, which is located at the innermost periphery of the negative electrode 22 included in the electrode winding body 20, is located inside the positive electrode innermost circumferential portion 21in, which is located at the innermost periphery of the positive electrode 21 included in the electrode winding body 20. Here, the positive electrode innermost circumferential portion 21in is the innermost one-circumferential portion of the positive electrode 21 in the electrode winding body 20. The negative electrode innermost circumferential portion 22in is the innermost one-circumferential portion of the negative electrode 22 in the electrode winding body 20. The number of windings of each of the positive electrode 21, the negative electrode 22, and the separator 23 is not particularly limited and can be set as desired.

[0031] FIG. 4A is a development view of the positive electrode 21, schematically illustrating the state before winding. FIGS. 4B and 4C each illustrate a cross-sectional configuration of the positive electrode 21. FIG. 4B illustrates a cross section taken along line IVB-IVB in FIG. 4A. FIG. 4C illustrates a cross section taken along line IVC-IVC in FIG. 4A. The positive electrode 21 includes, for example, a positive electrode current collector 21A and a positive electrode active material layer 21B that covers a portion of the positive electrode current collector 21A. The positive electrode active material layer 21B may be provided on only one side of the positive electrode current collector 21A, or on both sides of the positive electrode current collector 21A. FIGS. 4B and 4C illustrate the case where the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A. More specifically, the positive electrode current collector 21A includes a positive electrode current collector inner peripheral surface 21A1 facing the winding center of the electrode wound body 20, i.e., facing the central axis CL, and a positive electrode current collector outer peripheral surface 21A2 facing the side opposite the winding center of the electrode wound body 20, i.e., on the opposite side of the positive electrode current collector inner peripheral surface 21A1. The positive electrode 21 has, as the positive electrode active material layer 21B, a positive electrode inner peripheral side active material layer 21B1 covering at least a portion of the positive electrode current collector inner peripheral surface 21A1, and a positive electrode outer peripheral side active material layer 21B2 covering at least a portion of the positive electrode current collector outer peripheral surface 21A2. Note that, in this specification, the positive electrode inner peripheral side active material layer 21B1 and the positive electrode outer peripheral side active material layer 21B2 may be collectively referred to as the positive electrode active material layer 21B without distinction.

[0032] The positive electrode current collector 21A includes a positive electrode covering region 211 covered with the positive electrode active material layer 21B and a positive electrode exposed region 212 extending in the W direction 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 along the L direction, which is the longitudinal direction of the positive electrode 21, from an edge 21E1 on the winding center side of the positive electrode 21 to an edge 21E2 on the winding outer periphery side of the positive electrode 21. Here, the L direction corresponds to the winding direction of the electrode wound body 20. That is, in the positive electrode 21, the positive electrode active material layer 21B covers the positive electrode current collector 21A from the edge 21E1 on the winding center side of the positive electrode 21 to the edge 21E2 on the winding outer periphery side of the positive electrode 21 in the winding direction of the electrode wound body 20. The positive electrode covering region 211 and the positive electrode exposed region 212 are adjacent to each other in the W direction, which is the short-side direction of the positive electrode 21. The W direction substantially coincides with the central axis CL. The positive electrode active material layer 21B extends in both the L direction, which is the longitudinal direction of the positive electrode 21, and the W direction, which is the width direction perpendicular to the L direction. As shown in FIG. 2, in the electrode wound body 20, the edge 21E1 of the positive electrode innermost circumferential portion 21in on the winding center side is positioned more inward than the edge 22E1 of the negative electrode innermost circumferential portion 22in on the winding center side. The positive electrode 21 also has a lower edge 21E3 extending in the L direction at the lower side of the electrode wound body 20. Note that FIGS. 4A and 4B schematically depict the positive electrode current collector 21A extending linearly along the W direction. 1, the positive electrode edge 212E of the positive electrode exposed region 212 is bent toward the central axis CL and connected to the positive electrode current collector 24. That is, the end of the positive electrode exposed region 212 in the W direction forms the upper end surface 41 and is connected to the positive electrode current collector 24 (see FIG. 1). The upper end surface 41 is formed by bending the positive electrode edge 212E of the positive electrode exposed region 212 toward the through-hole 26 when the electrode winding body 20 is wound.

[0033] An insulating layer 101 may be provided in a region including the boundary K between the positive electrode covering region 211 and the positive electrode exposed region 212 and its vicinity. Similar to the positive electrode covering region 211 and the positive electrode exposed region 212, the insulating layer 101 may extend from the edge 21E1 on the winding center side of the electrode wound body 20 to the edge 21E2 on the winding outer periphery side. The insulating layer 101 may be bonded to at least one of the first separator member 23A and the second separator member 23B. This is because misalignment between the positive electrode 21 and the separator 23 can be prevented. The insulating layer 101 may contain a resin containing polyvinylidene fluoride (PVDF). The PVDF content of the insulating layer 101 allows the insulating layer 101 to swell with, for example, a solvent contained in the electrolyte solution, thereby achieving good adhesion to the separator 23.

[0034] In the positive electrode 21 of the present embodiment, as shown in FIG. 4B , the first edge 21BT1 of the positive electrode active material layer 21B is an inclined surface, and the insulating layer 101 is in contact with the first edge 21BT1 located at the boundary K. That is, the insulating layer 101 is formed so as to cover the first edge 21BT1 of the positive electrode active material layer 21B and its vicinity. The positive electrode active material layer 21B includes a thin portion 61 and a thick portion 71. The thin portion 61 is a specific example corresponding to a “first thin portion” as an embodiment of the present disclosure, and the thick portion 71 is a specific example corresponding to a “first thick portion” as an embodiment of the present disclosure. In the positive electrode 21 of the present embodiment, the thin portion 61 and the thick portion 71 are formed on both the positive electrode current collector inner peripheral surface 21A1 and the positive electrode current collector outer peripheral surface 21A2, respectively. That is, both the positive electrode inner periphery side active material layer 21B1 and the positive electrode outer periphery side active material layer 21B2 each include a thin portion 61 and a thick portion 71. However, in the positive electrode 21, it is sufficient that at least one of the positive electrode inner periphery side active material layer 21B1 and the positive electrode outer periphery side active material layer 21B2 includes a thin portion 61 and a thick portion 71. In Figures 4B and 4C, the thin portion 61 and the thick portion 71 constituting the positive electrode inner periphery side active material layer 21B1 are referred to as a thin portion 61-1 and a thick portion 71-1, respectively, and the thin portion 61 and the thick portion 71 constituting the positive electrode outer periphery side active material layer 21B2 are referred to as a thin portion 61-2 and a thick portion 71-2, respectively, for convenience. In the example shown in FIG. 4C, the position in the L direction of the boundary 21B1K between the thin portion 61-1 and the thick portion 71-1 substantially coincides with the position in the L direction of the boundary 21B2K between the thin portion 61-2 and the thick portion 71-2.

[0035] The thick portion 71 has a thickness greater than that of the thin portion 61. The thickness of the thin portion 61 can be, for example, approximately half the thickness of the thick portion 71. More specifically, as shown in FIGS. 4B and 4C, in the positive-electrode inner-periphery-side active material layer 21B1, the thickness T71-1 of the thick portion 71-1 is greater than the thickness T61-1 of the thin portion 61-1. Similarly, in the positive-electrode outer-periphery-side active material layer 21B2, the thickness T71-2 of the thick portion 71-2 is greater than the thickness T61-2 of the thin portion 61-2. The thickness T61-1 and the thickness T61-2 may be equal to or different from each other. Furthermore, the thickness T71-1 and the thickness T71-2 may be equal to or different from each other.

[0036] The thin portion 61 includes the edge 21E1 on the winding center side in the L direction of the positive electrode 21. The length of the thin portion 61 in the L direction may be, for example, approximately 1 to 5 revolutions around the electrode wound body 20, starting from the edge 21E1 on the winding center side. The thick portion 71 is adjacent to the thin portion 61 in the L direction. More specifically, the thick portion 71 is provided on the opposite side of the thin portion 61 in the L direction from the edge 21E1 on the winding center side.

[0037] (Positive electrode current collector 21A) The positive electrode current collector 21A contains a conductive material such as aluminum, etc. The positive electrode current collector 21A is, for example, a metal foil made of aluminum or an aluminum alloy.

[0038] (Positive electrode active material layer 21B) The positive electrode active material layer 21B contains, as a positive electrode active material, one or more types of positive electrode materials capable of absorbing and releasing lithium. However, the positive electrode active material layer 21B may further contain one or more types of other materials, such as a positive electrode binder and a positive electrode conductor. The positive electrode material is preferably a lithium-containing compound, more specifically, a lithium-containing composite oxide or a lithium-containing phosphate compound. The lithium-containing composite oxide is an oxide containing lithium and one or more other elements, i.e., elements other than lithium, as constituent elements. The lithium-containing composite oxide has, for example, a layered rock salt type or a spinel type crystal structure. The lithium-containing phosphate compound is a phosphate compound containing lithium and one or more other elements as main constituent elements, and has, for example, an olivine type crystal structure. Examples of the other elements include nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe). The positive electrode active material layer 21B preferably contains at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide as the positive electrode active material. The positive electrode binder includes, for example, one or more of synthetic rubber and polymer compounds. Examples of synthetic rubber include styrene butadiene rubber, fluorine-based rubber, and ethylene propylene diene. Examples of polymer compounds include polyvinylidene fluoride and polyimide. The positive electrode conductive agent includes, for example, one or more of carbon materials. Examples of carbon materials include graphite, carbon black, acetylene black, and ketjen black. However, the positive electrode conductive agent may also be a metal material or a conductive polymer, as long as it is a conductive material.

[0039] In the positive electrode active material layer 21B, the ratio of the amount of positive electrode binder present to the amount of positive electrode active material present in the thin portion 61 is lower than the ratio of the amount of positive electrode binder present to the amount of positive electrode active material present in the thick portion 71. The amounts of positive electrode active material present and positive electrode binder present in the thin portion 61 can be determined, for example, by using SEM-EDX to measure the atomic concentration of the elements contained as the positive electrode active material and the atomic concentration of the elements contained as the positive electrode binder. The same applies to the amounts of positive electrode active material present and positive electrode binder present in the thick portion 71.

[0040] FIG. 4D is an enlarged schematic cross-sectional view of the vicinity of the boundary 21B1K between the thin portion 61-1 and the thick portion 71-1 of the positive electrode inner periphery active material layer 21B1, specifically, the area IVD enclosed by the dashed line shown in FIG. 4C. As shown in FIG. 4D, each of the thin portion 61-1 and the thick portion 71-1 contains a plurality of positive electrode active material particles 21BP and a positive electrode binder 21BB present in the gaps between the plurality of positive electrode active material particles 21BP. The plurality of positive electrode active material particles 21BP contains the above-described positive electrode active material. The thin portion 61-1 includes a surface layer UL including a surface opposite to the surface facing the positive electrode current collector 21A, and a lower layer BL between the surface layer UL and the positive electrode current collector 21A. The ratio of the amount of positive electrode binder 21BB to the amount of positive electrode active material present in the surface layer UL is lower than, for example, the ratio of the amount of positive electrode binder 21BB to the amount of positive electrode active material present in the lower layer BL.

[0041] The positive electrode inner periphery side active material layer 21B1 contains, for example, fluorine as a positive electrode binder 21BB. In this case, when the ratio of the amount of fluorine to the amount of positive electrode active material in the thick portion 71-1 is 1, the ratio of the amount of fluorine to the amount of positive electrode active material in the surface layer UL of the thin portion 61-1 is, for example, 0.62 or less.

[0042] The positive electrode inner periphery side active material layer 21B1 contains, for example, carbon as the positive electrode binder 21BB. In this case, when the ratio of the amount of carbon to the amount of positive electrode active material in the thick portion 71-1 is 1, the ratio of the amount of carbon to the amount of positive electrode active material in the surface layer UL of the thin portion 61-1 is, for example, 0.52 or less.

[0043] When the positive electrode inner periphery side active material layer 21B1 contains nickel (Ni) as the positive electrode active material and polyvinylidene fluoride (PVDF) as the positive electrode binder 21BB, the ratio of the number of fluorine (F) atoms to the number of nickel (Ni) atoms in the surface layer UL is, for example, 0.6 or less. Also, when the positive electrode inner periphery side active material layer 21B1 contains nickel (Ni) as the positive electrode active material and polyvinylidene fluoride (PVDF) as the positive electrode binder 21BB, the ratio of the number of carbon (C) atoms to the number of nickel (Ni) atoms in the surface layer UL is, for example, 0.6 or less.

[0044] The positive electrode outer periphery side active material layer 21B2 may have a configuration similar to that of the positive electrode inner periphery side active material layer 21B1. That is, the thin portion 61-2 may have a configuration similar to that of the thin portion 61-1, and the thick portion 71-2 may have a configuration similar to that of the thin portion 61-2.

[0045] FIG. 5A is a developed view of the negative electrode 22, schematically illustrating the state before winding. FIG. 5B illustrates a cross-sectional configuration of the negative electrode 22. Note that FIG. 5B illustrates a cross section taken along line VB-VB in FIG. 5A. The negative electrode 22 includes, for example, a negative electrode current collector 22A as a second electrode current collector and a negative electrode active material layer 22B that covers a portion of the negative electrode current collector 22A. The negative electrode active material layer 22B may be provided on only one surface of the negative electrode current collector 22A, or on both surfaces of the negative electrode current collector 22A. FIG. 5B illustrates a case in which the negative electrode active material layer 22B is provided on both surfaces of the negative electrode current collector 22A. More specifically, the negative electrode current collector 22A includes a negative electrode current collector inner peripheral surface 22A1 facing the central axis CL and a negative electrode current collector outer peripheral surface 22A2 opposite the negative electrode current collector inner peripheral surface 22A1. The negative electrode 22 includes, as the negative electrode active material layer 22B, a negative electrode inner peripheral side active material layer 22B1 covering at least a portion of the negative electrode current collector inner peripheral surface 22A1 and a negative electrode outer peripheral side active material layer 22B2 covering at least a portion of the negative electrode current collector outer peripheral surface 22A2. Note that, in this specification, the negative electrode inner peripheral side active material layer 22B1 and the negative electrode outer peripheral side active material layer 22B2 may be collectively referred to as the negative electrode active material layer 22B without distinction.

[0046] The negative electrode 22 has a negative electrode covering region 221 in which the negative electrode current collector 22A is covered with the negative electrode active material layer 22B, and a negative electrode exposed region 222 in which the negative electrode current collector 22A is exposed and not covered with the negative electrode active material layer 22B. As shown in FIG. 5A , the negative electrode covering region 221 and the negative electrode exposed region 222 each extend along the L direction. The negative electrode exposed region 222 extends in the winding direction of the electrode wound body 20 from an edge 22E1 on the winding center side of the negative electrode 22 to an edge 22E2 on the winding outer periphery side. In contrast, the negative electrode covering region 221 is not provided on the edge 22E1 on the winding center side or the edge 22E2 on the winding outer periphery side of the negative electrode 22. As shown in FIG. 5A , parts of the negative electrode exposed region 222 are formed to sandwich the negative electrode covering region 221 in the L direction. Specifically, the negative electrode exposed region 222 includes a first portion 222A, a second portion 222B, and a third portion 222C. The negative electrode 22 further has a lower edge 22E3 extending in the L direction at the lower side of the electrode winding 20. The first portion 222A is provided adjacent to the negative electrode covering region 221 in the W direction and extends in the L direction from an edge 22E1 on the winding center side of the negative electrode 22 to an edge 22E2 on the winding outer periphery side. That is, the first portion 222A is a region extending in the W direction from the negative electrode active material layer 22B. The second portion 222B and the third portion 222C are provided to sandwich the negative electrode covering region 221 in the L direction. The first portion 222A is located near the lower edge 22E3 of the negative electrode 22. The second portion 222B is located near the edge 22E1 of the negative electrode 22 on the winding center side, and the third portion 222C is located near the edge 22E2 of the negative electrode 22 on the winding outer periphery side. Note that FIGS. 5A and 5B schematically illustrate the negative electrode current collector 22A extending linearly along the W direction. However, in reality, the negative electrode edge 222E of the negative electrode exposed region 222 is bent toward the central axis CL as shown in FIG. 1 and connected to the negative electrode current collector 25. That is, the W-direction end of the negative electrode exposed region 222 forms the lower end surface 42 and is connected to the negative electrode current collector 25 (see FIG. 1). The lower end surface 42 is formed by bending the negative electrode edge 222E of the negative electrode exposed region 222 toward the through-hole 26 when the electrode winding body 20 is wound.

[0047] (Negative electrode current collector 22A) The negative electrode current collector 22A contains a conductive material such as copper. The negative electrode current collector 22A is a metal foil made of, for example, nickel, a nickel alloy, copper, or a copper alloy. The surface of the negative electrode current collector 22A is preferably roughened. This is because the so-called anchor effect improves the adhesion of the negative electrode active material layer 22B to the negative electrode current collector 22A. In this case, it is sufficient that the surface of the negative electrode current collector 22A is roughened at least in the region facing the negative electrode active material layer 22B. The roughening method may be, for example, a method of forming fine particles using an electrolytic process. In the electrolytic process, fine particles are formed on the surface of the negative electrode current collector 22A by electrolysis in an electrolytic bath, resulting in an uneven surface of the negative electrode current collector 22A. Copper foil produced by an electrolytic process is generally called electrolytic copper foil.

[0048] (Negative electrode active material layer 22B) The negative electrode active material layer 22B contains, as the negative electrode active material, one or more types of negative electrode materials capable of absorbing and releasing lithium. However, the negative electrode active material layer 22B may further contain one or more types of other materials, such as a negative electrode binder and a negative electrode conductor. The negative electrode material is, for example, a carbon material. This is because a high energy density can be stably obtained because the crystal structure changes very little during lithium absorption and release. In addition, the carbon material also functions as a negative electrode conductor, thereby improving the conductivity of the negative electrode active material layer 22B. Examples of carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite. However, the interplanar spacing of the (002) plane of non-graphitizable carbon is preferably 0.37 nm or more. The interplanar spacing of the (002) plane of graphite is preferably 0.34 nm or less. More specifically, carbon materials include, for example, pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound calcined bodies, activated carbon, and carbon blacks. Examples of cokes include pitch coke, needle coke, and petroleum coke. Organic polymer compound calcined bodies are obtained by calcining (carbonizing) polymer compounds such as phenolic resins and furan resins at an appropriate temperature. Alternatively, the carbon material may be low-crystalline carbon heat-treated at temperatures below approximately 1000°C, or amorphous carbon. The carbon material may be fibrous, spherical, granular, or flake-shaped. In the secondary battery 1, when the open-circuit voltage at full charge, i.e., the battery voltage, is 4.25 V or higher, the amount of lithium released per unit mass is greater than when the open-circuit voltage at full charge is 4.20 V, even when the same positive electrode active material is used. Therefore, the amounts of positive and negative electrode active materials are adjusted accordingly. This results in a high energy density.

[0049] Further, the negative electrode active material layer 22B may contain, as a negative electrode active material, a silicon-containing material containing at least one of silicon, silicon oxide, carbon-silicon compound, and silicon alloy. The silicon-containing material is a general term for materials containing silicon as a constituent element. However, the silicon-containing material may contain only silicon as a constituent element. Note that the type of the silicon-containing material may be only one type or two or more types. The silicon-containing material can form an alloy with lithium, and may be a single silicon, a silicon alloy, a silicon compound, a mixture of two or more of them, or a material containing one or two or more phases of them. Further, the silicon-containing material may be crystalline, amorphous, or may contain both a crystalline part and an amorphous part. However, since the single substance described here means a general single substance, it may contain a trace amount of impurities. That is, the purity of the single substance is not necessarily limited to 100%. The silicon alloy contains, for example, any one or two or more of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as constituent elements other than silicon. The silicon compound contains, for example, any one or two or more of carbon and oxygen as constituent elements other than silicon. Note that the silicon compound may contain any one or two or more of the series of constituent elements described for the silicon alloy as constituent elements other than silicon. Specifically, the silicon alloy and the silicon compound are, for example, SiB4, SiB6, Mg2Si, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu5Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSi2, ZnSi2, SiC, Si3N4, Si2N2O, and SiO v (0 < v ≤ 2) and the like. However, the range of v can be arbitrarily set, and for example, 0.2 < v < 1.4 may be used.

[0050] In the laminate S20 of the electrode winding body 20, the positive electrode 21 and the negative electrode 22 are laminated with the separator 23 interposed between them so that the positive electrode exposed region 212 and the first portion 222A of the negative electrode exposed region 222 face opposite each other along the width direction W. A fixing tape 46 is attached to a middle region of the side surface 45 of the electrode winding body 20. By attaching the fixing tape 46 to the middle region of the side surface 45 of the electrode winding body 20, the end of the separator 23 is fixed, preventing loosening of the winding.

[0051] In the secondary battery 1, as shown in FIG. 2 , when the width of the positive electrode exposed region 212 is A and the width of the first portion 222A of the negative electrode exposed region 222 is B, it is preferable that A>B. For example, when width A=7 (mm), width B=4 (mm). Furthermore, when the width of the portion of the positive electrode exposed region 212 that protrudes from the outer edge of the separator 23 in the width direction is C and the width of the portion of the first portion 222A of the negative electrode exposed region 222 that protrudes from the outer edge on the opposite side in the width direction of the separator 23 is D, it is preferable that C>D. For example, when width C=4.5 (mm), width D=3 (mm).

[0052] 1 , at the upper part of the secondary battery 1, a plurality of adjacent positive electrode edges 212E in the radial direction (direction R) of the electrode winding 20 in the positive electrode exposed region 212 wound around the central axis CL are bent toward the central axis CL so as to overlap with each other, thereby constituting an upper end surface 41 of the electrode winding 20. Similarly, at the lower part of the secondary battery 1, a plurality of adjacent negative electrode edges 222E in the radial direction (direction R) in the negative electrode exposed region 222 wound around the central axis CL are bent toward the central axis CL so as to overlap with each other, thereby constituting a lower end surface 42 of the electrode winding 20. Therefore, a plurality of positive electrode edges 212E of the positive electrode exposed region 212 are gathered at the upper end surface 41 of the electrode winding 20, and a plurality of negative electrode edges 222E of the negative electrode exposed region 222 are gathered at the lower end surface 42 of the electrode winding 20. To improve contact between the positive electrode current collector plate 24 for extracting current and the positive electrode edge portion 212E, the multiple positive electrode edge portions 212E are bent toward the central axis CL and have flat surfaces. Similarly, to improve contact between the negative electrode current collector plate 25 for extracting current and the negative electrode edge portion 222E, the multiple negative electrode edge portions 222E are bent toward the central axis CL and have flat surfaces. Note that the flat surface referred to here does not only include a completely flat surface, but also includes a surface that has some unevenness or surface roughness to the extent that the positive electrode exposed region 212 and the negative electrode exposed region 222 can be joined to the positive electrode current collector plate 24 and the negative electrode current collector plate 25, respectively.

[0053] As described above, the positive electrode current collector 21A is made of, for example, aluminum foil. Meanwhile, the negative electrode current collector 22A is made of, for example, copper foil. In this case, the positive electrode current collector 21A is softer than the negative electrode current collector 22A. That is, the Young's modulus of the positive electrode exposed region 212 is lower than that of the negative electrode exposed region 222. Therefore, in one embodiment, it is more preferable that the widths A to D satisfy the relationship A>B and C>D. In this case, when the positive electrode exposed region 212 and the negative electrode exposed region 222 are folded simultaneously from both electrode sides with the same pressure, the heights of the folded portions measured from the tip of the separator 23 may be approximately the same for the positive electrode 21 and the negative electrode 22. At this time, the multiple positive electrode edge portions 212E (FIG. 1) of the positive electrode exposed region 212 are folded and overlap each other to a moderate extent. This facilitates bonding of the positive electrode exposed region 212 and the positive electrode current collector 24. Similarly, the negative electrode edge portions 222E (FIG. 1) of the negative electrode exposed region 222 are folded and overlap each other to an appropriate degree. This facilitates joining of the negative electrode exposed region 222 and the negative electrode current collector plate 25. The joining here means joining by, for example, laser welding, but the joining method is not limited to laser welding.

[0054] As shown in FIG. 2 , the portion of the positive electrode exposed region 212 of the positive electrode 21 that faces the negative electrode 22 across the separator 23 is covered with an insulating layer 101. The insulating layer 101 has a width of, for example, 3 mm in the W-axis direction. The insulating layer 101 covers the entire region of the positive electrode exposed region 212 of the positive electrode 21 that faces the negative electrode covering region 221 of the negative electrode 22 with the separator 23 interposed therebetween. The insulating layer 101 can effectively prevent an internal short circuit in the secondary battery 1, for example, when a foreign object enters between the negative electrode covering region 221 and the positive electrode exposed region 212. Furthermore, when an impact is applied to the secondary battery 1, the insulating layer 101 absorbs the impact and can effectively prevent bending of the positive electrode exposed region 212 and a short circuit between the positive electrode exposed region 212 and the negative electrode 22.

[0055] (insulating members 53, 54) The secondary battery 1 further includes insulating members 53 and 54 in the gap between the outer can 11 and the electrode wound body 20. The positive electrode exposed region 212 and the negative electrode exposed region 222, which are concentrated on the upper end face 41 and the lower end face 42, are conductors such as bare metal foil. Therefore, if the positive electrode exposed region 212 and the negative electrode exposed region 222 are in close proximity to the outer can 11, a short circuit may occur between the positive electrode 21 and the negative electrode 22 through the outer can 11. Furthermore, if the positive electrode current collector plate 24, which forms the upper end face 41, is in close proximity to the outer can 11, a short circuit may also occur. For this reason, it is preferable to provide the insulating members 53 and 54 as insulating members. Furthermore, providing the insulating members 53 and 54 can protect the electrode wound body 20 when inserting the electrode wound body 20 into the outer can 11 or when attaching the safety valve mechanism 30 during the manufacturing process described below. Furthermore, by providing the insulating members 53, 54, when the electrode wound body 20 expands due to charging, it is possible to prevent the electrode wound body 20 from coming into contact with other components of the secondary battery 1 and protect the electrode wound body 20. The insulating members 53, 54 are, for example, adhesive tapes whose base layer is made of one of polypropylene, polyethylene terephthalate, and polyimide and which have an adhesive layer on one surface of the base layer. To prevent the installation of the insulating members 53, 54 from reducing the volume of the electrode wound body 20, the insulating members 53, 54 are arranged so as not to overlap with the fixing tape 46 attached to the side surface 45, and the thickness of the insulating members 53, 54 is set to be equal to or less than the thickness of the fixing tape 46.

[0056] (Positive electrode current collector 24 and negative electrode current collector 25) In a typical lithium-ion secondary battery, for example, one lead for current extraction is welded to each of the positive and negative electrodes. However, this increases the internal resistance of the lithium-ion secondary battery and causes the lithium-ion secondary battery to heat up and reach high temperatures during discharge, making it unsuitable for high-rate discharge. Therefore, in the secondary battery 1 of this embodiment, the positive electrode current collector 24 is positioned opposite the upper end face 41, and the negative electrode current collector 25 is positioned opposite the lower end face 42. The positive electrode exposed region 212 at the upper end face 41 is welded to the positive electrode current collector 24 at multiple points, and the negative electrode exposed region 222 at the lower end face 42 is welded to the negative electrode current collector 25 at multiple points. This reduces the internal resistance of the secondary battery 1. The flat surfaces of the upper end face 41 and the lower end face 42, as described above, also contribute to the low resistance. The positive electrode current collector 24 is located between the battery cover 14 and the upper end face 41. The positive current collector 24 is electrically connected to the battery lid 14 via, for example, a safety valve mechanism 30. The negative current collector 25 is provided between the bottom 11B and the lower end surface 42 of the outer can 11. The negative current collector 25 is electrically connected to, for example, the inner surface of the bottom 11B of the outer can 11. FIG. 6A is a developed view showing an example of the configuration of the positive current collector 24. FIG. 6B is a developed view showing an example of the configuration of the negative current collector 25. The positive current collector 24 is a metal plate made of, for example, aluminum or an aluminum alloy, or a composite material thereof. The negative current collector 25 is a metal plate made of, for example, nickel, a nickel alloy, copper, or a copper alloy, or a composite material of two or more of these.

[0057] As shown in FIG. 6A , the positive current collector 24 has a sector-shaped portion 31 and a substantially rectangular strip-shaped portion 32. However, the shape of the positive current collector 24 is not limited to the shape shown in FIG. 6A and can be selected arbitrarily. In the secondary battery 1, the positive current collector 24 is housed in the outer can 11 with the strip-shaped portion 32 folded relative to the sector-shaped portion 31, as shown in FIG. 1 . FIG. 7A shows the positive current collector 24 in an unfolded state. The sector-shaped portion 31 is a facing portion that faces and is connected to the upper end face 41. The sector-shaped portion 31 has an outer edge that includes, for example, a straight portion and a curved portion. An opening 35 is formed near the center of the sector-shaped portion 31. FIG. 7A illustrates an example in which the opening 35 has a circular planar shape in a horizontal plane perpendicular to the Z-axis direction. The strip-shaped portion 32 is connected to, for example, a straight portion of the outer edge of the sector-shaped portion 31. The strip-shaped portion 32 extends in a direction intersecting the straight portion of the sector-shaped portion 31. As shown in Fig. 1, in the secondary battery 1, the positive electrode current collector plate 24 is provided so that the opening 35 overlaps with the through-hole 26 in the Z-axis direction. That is, the opening 35 is provided at a position that overlaps with a part of the upper end surface 41 on the winding center side in the Z-axis direction.

[0058] The shaded portion in FIG. 6A is the insulating portion 32A of the strip portion 32. The insulating portion 32A is a portion of the strip portion 32 to which an insulating member is attached or to which an insulating material is applied. The portion of the strip portion 32 below the insulating portion 32A is a connection portion 32B to the sealing plate, which also serves as an external terminal. The sealing plate is electrically connected to the battery cover 14. Note that, as shown in FIG. 1, if the secondary battery 1 has a battery structure without a metal center pin in the through hole 26, the strip portion 32 is unlikely to come into contact with a portion at the negative electrode potential. Therefore, the positive electrode current collector 24 may not have the insulating portion 32A. If the positive electrode current collector 24 does not have the insulating portion 32A, the charge / discharge capacity can be increased by increasing the width between the positive electrode 21 and the negative electrode 22 by an amount corresponding to the thickness of the insulating portion 32A.

[0059] The shape of the negative electrode current collector 25 shown in FIG. 6B is almost the same as the shape of the positive electrode current collector 24 shown in FIG. 6A. The negative electrode current collector 25 has a substantially sector-shaped fan portion 33 and a substantially rectangular strip portion 34. However, the shape of the negative electrode current collector 25 is not limited to the shape shown in FIG. 7B and can be selected arbitrarily. In the secondary battery 1, the negative electrode current collector 25 is housed in the outer can 11 with the strip portion 34 folded relative to the fan portion 33, as shown in FIG. 1. FIG. 6B shows the negative electrode current collector 25 in an unfolded state. The fan portion 33 is a facing portion that faces and is connected to the lower end surface 42. The fan portion 33 has an outer edge that includes, for example, a straight portion and a curved portion. The strip portion 34 is connected to, for example, the straight portion of the outer edge of the fan portion 33. The strip portion 34 extends in a direction that intersects with the straight portion of the fan portion 33. The strip portion 34 of the negative current collector 25 is shorter than the strip portion 32 of the positive current collector 24 and does not have a portion corresponding to the insulating portion 32A of the positive current collector 24. The strip portion 34 has a plurality of circular protrusions 37 indicated by circles. At least some of the protrusions 37 are welded to the bottom 11B of the outer can 11. During resistance welding, current concentrates on the protrusions 37, melting the protrusions 37 and welding the strip portion 34 to the bottom 11B of the outer can 11. Like the positive current collector 24, the negative current collector 25 has an opening 36 formed near the center of the sector portion 33. In the secondary battery 1, the negative current collector 25 is provided with the opening 36 overlapping the through-hole 26 in the Z-axis direction. FIG. 6B illustrates an example in which the opening 36 has a circular planar shape in a horizontal plane perpendicular to the Z-axis direction.

[0060] Due to its planar shape, the sector-shaped portion 31 of the positive current collector 24 covers only a portion of the upper end surface 41. Similarly, due to its planar shape, the sector-shaped portion 33 of the negative current collector 25 covers only a portion of the lower end surface 42. There are two reasons why the sector-shaped portions 31 and 33 do not cover the entire upper end surface 41 and the entire lower end surface 42. The first reason is to allow the electrolyte to smoothly penetrate into the electrode winding 20, for example, when assembling the secondary battery 1. In particular, in the secondary battery 1 of this embodiment, the positive current collector 24 is provided so that the opening 35 overlaps with a portion of the upper end surface 41 on the winding center side in the Z-axis direction. Therefore, a portion of the positive edge portion 212E constituting the upper end surface 41 is not covered by the sector-shaped portion 31 of the positive current collector 24 and is exposed to the opening 35. Therefore, the secondary battery 1 has a structure that allows the electrolyte to penetrate into the electrode winding 20 more quickly. The second reason is to facilitate the release of gas generated when the lithium ion secondary battery is in an abnormally high temperature state or is overcharged.

[0061] (Separator 23) The separator 23 is interposed between the positive electrode 21 and the negative electrode 22. The separator 23 allows lithium ions to pass through while preventing current short-circuiting due to contact between the positive electrode 21 and the negative electrode 22. The separator 23 is made of, for example, one or more types of porous membranes, such as synthetic resins and ceramics, or may be a laminated membrane of two or more types of porous membranes. Examples of synthetic resins include polytetrafluoroethylene, polypropylene, and polyethylene. However, the separator 23 preferably has a substrate made of a single-layer polyolefin porous membrane containing polyethylene. This is because better high-output characteristics can be obtained compared to laminated membranes. When the first separator member 23A and the second separator member 23B constituting the separator 23 are each a single-layer porous membrane made of polyolefin, the thickness of the porous membrane may be, for example, 10 μm or more and 15 μm or less. When the single-layer porous membrane made of polyolefin has a thickness of 10 μm or more, internal short-circuiting can be sufficiently avoided. If the thickness of the single-layer porous film made of polyolefin is 15 μm or less, better discharge capacity characteristics can be obtained. In addition, the surface density of the porous film is, for example, 6.3 g / m 2 More than 8.3g / m 2 The surface density of the single-layer porous film made of polyolefin is preferably 6.3 g / m or less. 2 If the surface density of the single-layer porous film made of polyolefin is 8.3 g / m or more, internal short circuits can be sufficiently avoided. 2 If the content is less than this, better discharge capacity characteristics can be obtained.

[0062] In particular, the separator 23 may include, for example, the porous membrane substrate described above and a polymer compound layer provided on one or both sides of the substrate. This is because the separator 23 improves adhesion to each of the positive electrode 21 and the negative electrode 22, thereby suppressing distortion of the electrode winding body 20. This suppresses decomposition reactions of the electrolyte and also suppresses leakage of the electrolyte impregnated in the substrate layer, thereby making it difficult for resistance to increase even with repeated charge / discharge and suppressing battery swelling. The polymer compound layer includes, for example, a polymer compound such as polyvinylidene fluoride. This is because it has excellent physical strength and is electrochemically stable. However, the polymer compound may be other than polyvinylidene fluoride. To form this polymer compound layer, for example, a solution in which a polymer compound is dissolved in an organic solvent or the like is applied to the substrate layer, and the substrate layer is then dried. Alternatively, the substrate layer may be immersed in the solution and then dried. The polymer compound layer may contain one or more types of insulating particles such as inorganic particles, for example, aluminum oxide and aluminum nitride.

[0063] (electrolyte) The electrolyte solution contains a solvent and an electrolyte salt. However, the electrolyte solution may further contain one or more other materials such as additives. The solvent contains one or more non-aqueous solvents such as organic solvents. An electrolyte solution containing a non-aqueous solvent is a so-called non-aqueous electrolyte solution. The non-aqueous solvent contains, for example, a fluorine compound and a dinitrile compound. The fluorine compound includes, for example, at least one of fluorinated ethylene carbonate, trifluorocarbonate, trifluoroethyl methyl carbonate, fluorinated carboxylic acid ester, and fluorinated ether. The non-aqueous solvent may further contain a nitrile compound other than the dinitrile compound, such as at least one of a mononitrile compound and a trinitrile compound. As the dinitrile compound, succinonitrile (SN) is preferable. However, the dinitrile compound is not limited to succinonitrile, and may be other dinitrile compounds such as adiponitrile.

[0064] The electrolyte salt includes, for example, one or more salts such as lithium salts. However, the electrolyte salt may include, for example, a salt other than lithium salt. The salt other than lithium salt may be, for example, a salt of a light metal other than lithium. Examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium tetrachloroaluminate (LiAlCl4), dilithium hexafluorosilicate (Li2SF6), lithium chloride (LiCl), and lithium bromide (LiBr). Among these, one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium hexafluoroarsenate are preferred, with lithium hexafluorophosphate being more preferred. The content of the electrolyte salt is not particularly limited, but is preferably 0.3 mol / kg to 3 mol / kg relative to the solvent. When the electrolyte solution contains LiPF6 as the electrolyte salt, the LiPF6 concentration in the electrolyte solution is preferably 1.25 mol / kg to 1.45 mol / kg. This is because cycle deterioration due to salt consumption (decomposition) during high-load rate charging can be prevented, thereby improving high-load cycle performance. When the electrolyte salt further contains LiBF4 in addition to LiPF6, the LiBF4 concentration in the electrolyte solution is preferably 0.001 wt% to 0.1 wt%. This is because cycle deterioration due to salt consumption (decomposition) during high-load rate charging can be more effectively prevented, thereby further improving high-load cycle performance.

[0065] [1-2. Operation] In the secondary battery 1 of the present embodiment, for example, during charging, lithium ions are released from the positive electrode 21 and are absorbed into the negative electrode 22 via the electrolyte. In addition, in the secondary battery 1, for example, during discharging, lithium ions are released from the negative electrode 22 and are absorbed into the positive electrode 21 via the electrolyte.

[0066] [1-3. Manufacturing method] 1 to 6B, and also with reference to Fig. 7, a method for manufacturing the secondary battery 1 will be described. Fig. 7 is a perspective view illustrating the manufacturing process of the secondary battery 1 shown in Fig. 1.

[0067] First, a positive electrode current collector 21A is prepared, and a positive electrode active material layer 21B is selectively formed on the surface of the positive electrode current collector 21A. Then, an insulating layer 101 is formed on the surface of the positive electrode current collector 21A along a first edge 21BT1 of the positive electrode active material layer 21B. Furthermore, a predetermined region of the positive electrode active material layer 21B is partially excavated by, for example, laser ablation to form a thinned portion 61. At this time, more of the positive electrode binder 21BB is removed than the positive electrode active material in the surface layer UL of the thinned portion 61 irradiated with the laser. As a result, the ratio of the amount of the positive electrode binder 21BB to the amount of the positive electrode active material in the surface layer UL becomes lower than the ratio of the amount of the positive electrode binder 21BB to the amount of the positive electrode active material in the lower layer BL. The positive electrode 21 is obtained through the above operations. Next, a negative electrode current collector 22A is prepared, and a negative electrode active material layer 22B is selectively formed on the surface of the negative electrode current collector 22A to form a negative electrode 22 having a negative electrode covering region 221 and a negative electrode exposed region 222. A drying process may be performed on the positive electrode 21 and the negative electrode 22. Subsequently, the positive electrode 21 and the negative electrode 22 are stacked with the first separator member 23A and the second separator member 23B interposed therebetween so that the positive electrode exposed region 212 and the first portion 222A of the negative electrode exposed region 222 are opposite each other in the W direction, thereby producing a laminate S20. Thereafter, the laminate S20 is spirally wound so as to form through-holes 26. For example, a cylindrical winding core is used as a jig, and the laminate S20 is wound around the cylindrical winding core. Furthermore, a fixing tape 46 is attached to the outermost periphery of the spirally wound laminate S20, and then the winding core is removed. As a result, an electrode winding body 20 is obtained as shown in FIG. 7(A).

[0068] Next, for example, the tip of a plate-like member having a wedge-shaped cross section is pressed perpendicularly against the upper end face 41 and the lower end face 42 of the electrode winding body 20, i.e., in the Z-axis direction, to locally bend a part of the upper end face 41 and a part of the lower end face 42 (first press). As a result, as shown in FIG. 7B, a plurality of grooves 43 extending radially from the through-holes 26 in the radial direction (R direction) are created in each of the upper end face 41 and the lower end face 42. Note that the number and arrangement of the grooves 43 shown in FIG. 7B are merely examples and the present disclosure is not limited thereto.

[0069] Next, substantially the same pressure is applied substantially simultaneously from above and below the electrode winding 20 to the upper end face 41 and the lower end face 42 in a direction approximately perpendicular to the electrode winding 20 (secondary pressing). At this time, a rod-shaped jig, for example, is inserted into the through-hole 26. By doing so, as shown in FIG. 7C , the positive electrode exposed region 212 and the first portion 222A of the negative electrode exposed region 222 are each bent, making the upper end face 41 and the lower end face 42 each flat. At this time, it is preferable that multiple adjacent portions of the positive electrode edge portion 212E of the positive electrode exposed region 212 on the upper end face 41 bend toward the through-hole 26 so as to overlap with each other in the radial direction of the electrode winding 20. Similarly, it is preferable that multiple adjacent portions of the negative electrode edge portion 222E of the negative electrode exposed region 222 on the lower end face 42 bend toward the through-hole 26 so as to overlap with each other in the radial direction of the electrode winding 20. Thereafter, the sectorial portion 31 of the positive current collector plate 24 is joined to the upper end face 41 by laser welding or the like, and the sectorial portion 33 of the negative current collector plate 25 is joined to the lower end face 42 by laser welding or the like.

[0070] 7(D), insulating members 53 and 54 are attached to predetermined positions of the electrode winding body 20. Thereafter, the strip portion 32 of the positive current collector plate 24 is bent and inserted into the hole 12H of the insulating plate 12. In addition, the strip portion 34 of the negative current collector plate 25 is bent and inserted into the hole 13H of the insulating plate 13.

[0071] 7(E), the electrode winding body 20 assembled as described above is inserted into the outer can 11, and then the bottom 11B of the outer can 11 is welded to the negative electrode current collector plate 25. After that, a constricted portion 11S (FIG. 1) is formed near the open end 11N of the outer can 11. Furthermore, after the electrolyte is poured into the outer can 11, the strip portion 32 of the positive electrode current collector plate 24 is welded to the safety valve mechanism 30.

[0072] 7(F), the outer can 11 is sealed using the gasket 15, the safety valve mechanism 30, and the battery lid 14, utilizing the constricted portion 11S. Finally, the outer can 11, with the washer 55 attached to the battery lid 14, is covered with the outer tube 50, and the outer tube 50 is heated and shrunk, for example, by applying hot air to the outer tube 50, and the outer tube 50 is brought into close contact with the outer surface of the outer can 11.

[0073] Through the above steps, the secondary battery 1 of this embodiment is completed.

[0074] [1-4. Actions and Effects] As described above, in the secondary battery 1 of the present embodiment, the thin portion 61 is provided in a portion of the positive electrode active material layer 21B, thereby reducing stress concentration inside the electrode winding body 20 housed in the outer can 11. Specifically, when expansion of the negative electrode 22 occurs inside the electrode winding body 20 due to charge and discharge, large deformation such as buckling (bending) of the positive electrode current collector 21A can be prevented. This is because reducing the amount of electrode reactant (e.g., lithium ions) supplied to a portion of the negative electrode active material layer 22B facing the thin portion 61 reduces expansion and contraction of the portion of the negative electrode active material layer 22B facing the thin portion 61. As a result, stress applied to the separator 23 separating the positive electrode 21 and the negative electrode 22 is also reduced. This prevents breakage of the separator 23 even when the thickness of the separator 23 is reduced, thereby preventing short-circuiting between the positive electrode 21 and the negative electrode 22. In other words, the separator 23 can be made thinner. As a result, the distance 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 and the capacity of the secondary battery 1 can be improved.

[0075] Furthermore, in the secondary battery 1 of this embodiment, the ratio of the amount of the positive electrode binder 21BB present in the thin portion 61 to the amount of the positive electrode active material present in the thick portion 71 is set lower than the ratio of the amount of the positive electrode binder 21BB present in the gaps between the plurality of positive electrode active material particles 21BP, each containing a positive electrode active material, in the thin portion 61 of the positive electrode active material layer 21B is set lower than the amount of the positive electrode binder 21BB present in the gaps between the plurality of positive electrode active material particles 21BP, each containing a positive electrode active material, in the thick portion 71. This facilitates the movement of the plurality of positive electrode active material particles 21BP, thereby increasing the flexibility of the positive electrode active material layer 21B. This improves the flexibility of the positive electrode 21, thereby improving the processability when fabricating the electrode wound body 20, i.e., the workability when winding the laminate S20. Furthermore, cracking and detachment of the positive electrode active material layer 21B when fabricating the electrode wound body 20 can be prevented.

[0076] In particular, in the secondary battery 1 of the present embodiment, the ratio of the amount of the positive electrode binder 21BB to the amount of the positive electrode active material in the surface layer UL of the thin portion 61 is lower than the ratio of the amount of the positive electrode binder 21BB to the amount of the positive electrode active material in the lower layer BL of the thin portion 61. Therefore, when producing the electrode wound body 20, the operation of winding the sheet-like laminate S20 becomes easier, and stress concentration near the winding center of the electrode wound body 20 can be alleviated.

[0077] Furthermore, in the secondary battery 1 of this embodiment, the thin portion 61 includes the edge 21E1 of the positive electrode 21 on the winding center side in the L direction. This increases the flexibility of the region of the positive electrode 21 near the edge 21E1 on the winding center side. This prevents the radius of curvature of the electrode wound body 20 from increasing near the winding center. Meanwhile, the positive electrode active material layer 21B includes the thick portion 71 provided on the opposite side of the edge 21E1 on the winding center side in the L direction from the thin portion 61. This is advantageous for ensuring a predetermined battery capacity while mitigating stress concentration near the winding center of the electrode wound body 20. That is, the secondary battery 1 can achieve a high capacity density while ensuring reliability.

[0078] In the positive electrode 21 of the secondary battery 1 of this embodiment, the thin portion 61 and the thick portion 71 are formed on both the positive electrode current collector inner surface 21A1 and the positive electrode current collector outer surface 21A2, respectively. This further improves processability when fabricating the electrode wound body 20. Furthermore, cracking and falling off of the positive electrode active material layer 21B when fabricating the electrode wound body 20 can be further prevented.

[0079] 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, and therefore higher battery performance can be obtained.

[0080] <2. Application Examples> The secondary battery 1 according to the embodiment of the present disclosure can be used, for example, as described below.

[0081] [2-1. Battery pack] 8 is a block diagram showing an example of a circuit configuration when a battery according to an embodiment of the present invention (hereinafter referred to as a secondary battery) is applied to a battery pack 300. The battery pack 300 includes a battery pack 301, an exterior body 305, 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.

[0082] The battery pack 300 includes a positive terminal 321 and a negative terminal 322. When charging, the positive terminal 321 and the negative terminal 322 are connected to the positive terminal and the negative terminal of a charger, respectively, for charging. When using an electronic device, the positive terminal 321 and the negative terminal 322 are connected to the positive terminal and the negative terminal of the electronic device, respectively, for discharging.

[0083] The battery pack 301 is made up of a plurality of secondary batteries 301a connected in series or parallel. The secondary batteries 301a can be the above-described secondary battery 1. Note that, although Fig. 8 shows an example in which six secondary batteries 301a are connected in 2-parallel-3-series (2P3S) configuration, any other connection method may be used, such as n-parallel-m-series (n and m are integers).

[0084] 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 opposite to the charge current flowing from positive terminal 321 to battery pack 301 and a polarity forward to the discharge current flowing from negative terminal 322 to battery pack 301. Diode 303b has a polarity forward to the charge current and opposite to the polarity of the discharge current. Although switch unit 304 is provided on the + side in FIG. 8, it may also be provided on the - side.

[0085] The charge control switch 302a is controlled by the charge / discharge control unit so that it is turned off when the battery voltage reaches the overcharge detection voltage and so that no charging current flows in the current path of the battery pack 301. After the charge control switch 302a is turned off, only discharging is possible via the diode 302b. Furthermore, the control unit 310 controls the switch so that it is turned off when a large current flows during charging and so that the charging current flows in the current path of the battery pack 301. The discharge control switch 303a is controlled by the control unit 310 so that it is turned off when the battery voltage reaches the overdischarge detection voltage and so that no discharging current flows in the current path of the battery pack 301. After the discharge control switch 303a is turned off, only charging is possible via the diode 303b. Furthermore, the control unit 310 controls the switch so that it is turned off when a large current flows during discharging and so that the discharging current flows in the current path of the battery pack 301.

[0086] Temperature detection element 308 is, for example, a thermistor that is provided near battery pack 301 and measures the temperature of battery pack 301, supplying 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 the result to control unit 310. Current measurement unit 313 measures the current using current detection resistor 307 and supplies the 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.

[0087] When the voltage of any of the multiple secondary batteries 301a falls below the overcharge detection voltage or the overdischarge detection voltage, or when a large current suddenly flows, the switch control unit 314 sends a control signal to the switch unit 304 to prevent overcharging, overdischarging, and overcurrent charging / discharging. Here, for example, if the secondary battery is a lithium-ion secondary battery, the overcharge detection voltage is set to, for example, 4.20V±0.05V, and the overdischarge detection voltage is set to, for example, 2.4V±0.1V.

[0088] The charge / discharge switches can be semiconductor switches such as MOSFETs. In this case, the parasitic diodes of the MOSFETs function as diodes 302b and 303b. When P-channel FETs are used as the charge / discharge switches, switch control unit 314 supplies control signals DO and CO to the gates of charge control switch 302a and discharge control switch 303a, respectively. When charge control switch 302a and discharge control switch 303a are P-channel, they are turned on by a gate potential that is lower than the source potential by a predetermined value or more. That is, in normal charge and discharge operations, control signals CO and DO are set to low level, and charge control switch 302a and discharge control switch 303a are turned on.

[0089] For example, in the event of overcharging or overdischarging, the control signals CO and DO are set to high level, and the charge control switch 302a and the discharge control switch 303a are set to the OFF state.

[0090] The memory 317 is made up of RAM and ROM, such as non-volatile memory such as EPROM (Erasable Programmable Read Only Memory). The memory 317 stores in advance values ​​calculated by the control unit 310 and the internal resistance value of each secondary battery 301a in its initial state measured during the manufacturing process, and can be rewritten as needed. Furthermore, 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.

[0091] The temperature detection unit 318 measures the temperature using the temperature detection element 308, and controls charging and discharging when abnormal heat is generated, and corrects the calculation of the remaining capacity.

[0092] [2-2. 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, electric vehicles, electric aircraft, and power storage devices, or can be used to supply power.

[0093] 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.

[0094] Examples of electric vehicles include railcars, 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. Examples of power storage devices include power storage power sources for buildings such as homes, or for power generation facilities.

[0095] <3. Modifications> (First Modification) Next, a description will be given of a positive electrode 21-1 as a first modified example that is applied to secondary battery 1 of the above embodiment. Fig. 9 shows a cross-sectional configuration of positive electrode 21-1, and corresponds to Fig. 4C that shows positive electrode 21 of the above embodiment.

[0096] 9, in positive electrode 21-1 as the first modified example, the position of boundary 21B1K in the L direction is different from the position of boundary 21B2K in the L direction. That is, length L1 from edge 21E1 on the winding center side to the position of boundary 21B1K is different from length L2 from edge 21E1 on the winding center side to the position of boundary 21B2K. Except for this point, the configuration of positive electrode 21-1 is substantially the same as the configuration of positive electrode 21 of the above embodiment.

[0097] As described above, in the positive electrode 21-1, the L-direction position of the boundary 21B1K is different from the L-direction position of the boundary 21B2K. That is, the L-direction position of the step in the positive-electrode inner-periphery-side active material layer 21B1 is different from the L-direction position of the step in the positive-electrode outer-periphery-side active material layer 21B2. As a result, the location where stress concentrates on the inner peripheral surface 21A1 of the positive electrode current collector due to expansion of the negative electrode 22 is shifted from the location where stress concentrates on the outer peripheral surface 21A2 of the positive electrode current collector due to expansion of the negative electrode 22. Therefore, the stress applied to the positive electrode current collector 21A is dispersed. Therefore, the secondary battery 1 including the electrode wound body 20 having the positive electrode 21-1 of the first modified example can further reduce stress concentration inside the electrode wound body 20 due to expansion and contraction compared to the case where the positive electrode 21 of the above embodiment is used.

[0098] (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 10A to 10C show cross-sectional configurations of positive electrodes 21-2A to 21-2C, respectively, and correspond to Figure 4C showing positive electrode 21 of the above embodiment.

[0099] As shown in FIGS. 10A to 10C, in positive electrodes 21-2A to 21-2C as second modified examples, the positive-electrode inner-periphery-side active material layer 21B1 further includes a groove portion U1 between the thick portion 71-1 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 71-2 and the thin portion 61-2. Both groove portions U1 and U2 extend in the W-axis direction. The groove portion U1 has a thickness that is thinner than the thickness T61-1 of the thin portion 61-1 in the positive-electrode inner-periphery-side active material layer 21B1. Similarly, the groove portion U2 has a thickness that is thinner than the thickness T61-2 of the thin portion 61-2 in the positive-electrode outer-periphery-side active material layer 21B2. In the positive electrode 21-2A of Fig. 10A, the cross-sectional shape of the groove portions U1 and U2 is generally rectangular, in the positive electrode 21-2B of Fig. 10B, the cross-sectional shape of the groove portions U1 and U2 is generally V-shaped, and in the positive electrode 21-2C of Fig. 10C, the cross-sectional shape of the groove portions U1 and U2 is generally U-shaped. However, the cross-sectional shapes of the groove portions U1 and U2 are not limited to the shapes shown in Figs. 10A to 10C and can be selected arbitrarily.

[0100] In positive electrodes 21-2A to 21-2C, the width of groove portion U1 and the width of groove portion U2 may be the same in the L direction, or may be different. The width of groove portion U1 is the length in the L direction from the position of boundary 71U1 between thick portion 71-1 and groove portion U1 to the position of boundary 61U1 between thin portion 61-1 and groove portion U1. The width of groove portion U2 is the length in the L direction from the position of boundary 71U2 between thick portion 71-2 and groove portion U2 to the position of boundary 61U2 between thin portion 61-2 and groove portion U2. The width of groove portion U1 and the width of groove portion U2 are, for example, approximately 150 μm.

[0101] Furthermore, in each of the configuration examples of the positive electrodes 21-2A to 21-2C shown in FIGS. 10A to 10C, the L-direction positions of the boundary 71U1 and the boundary 71U2 are different, and the L-direction positions of the boundary 61U1 and the boundary 61U2 are different. However, in the present disclosure, the L-direction positions of the boundary 71U1 and the boundary 71U2 may coincide. Furthermore, the L-direction positions of the boundary 61U1 and the boundary 61U2 may coincide. Alternatively, the L-direction positions of the boundary 71U1 and the boundary 71U2 may coincide, and the L-direction positions of the boundary 61U1 and the boundary 61U2 may coincide.

[0102] 10A to 10C, 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.

[0103] 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 21-2A and the negative electrode 22. By having a portion of the separator 23 fit into at least one of the groove portion U1 and the groove portion U2, the separator 23 sandwiched between the positive electrode 21-2A and the negative electrode 22 is less likely to be displaced or come off from its predetermined position. As a result, in the secondary battery 1 using the positive electrodes 21-2A to 21-2C, short-circuiting between the positive electrode 21 and the negative electrode 22 can be effectively prevented, ensuring better reliability.

[0104] (Third Modification) Next, a positive electrode 21-3 as a third modified example applied to the secondary battery 1 of the above embodiment will be described with reference to FIGS. 11A and 11B. FIG. 11A is a development view of the positive electrode 21-3, corresponding to FIG. 4A showing the positive electrode 21 of the above embodiment. FIG. 11B is a cross-sectional view of the positive electrode 21-3, corresponding to FIG. 4B showing the positive electrode 21 of the above embodiment. FIG. 11B shows a cross section taken along line XIB-XIB in FIG. 11A as viewed in the direction of the arrows.

[0105] As shown in FIGS. 11A and 11B , in the positive electrode 21-3, the positive electrode active material layer 21B further includes thick portions 72 and 73 in addition to the thin portion 61 and the thick portion 71. Except for this point, the configuration of the positive electrode 21-3 is substantially the same as the configuration of the positive electrode 21 of the above-described embodiment. The thick portion 72 is a specific example corresponding to the "second thin portion" according to an embodiment of the present disclosure, and the thick portion 73 is a specific example corresponding to the "third thin portion" according to an embodiment of the present disclosure. In the positive electrode 21-3, the thin portion 61 and the thick portions 71 to 73 are 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 include the thin portion 61 and the thick portions 71 to 73, respectively. However, in the positive electrode 21-3, it is sufficient that at least one of the positive electrode inner periphery side active material layer 21B1 and the positive electrode outer periphery side active material layer 21B2 includes the thin portion 61 and the thick portions 71 to 73. Note that in Figures 11B and 11B, the thin portion 61 and the thick portions 71, 72, and 73 constituting the positive electrode inner periphery side active material layer 21B1 are referred to 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 referred to as the thin portion 61-2 and the thick portions 71-2, 72-2, and 73-2, respectively, for convenience. 11B, the position in the L direction of boundary 21B1K between thin portion 61-1 and thick portion 71-1 substantially coincides with the position in the L direction of boundary 21B2K between thin portion 61-2 and thick portion 71-2. However, the position in the L direction of boundary 21B1K and the position in the L direction of boundary 21B2K may be different.

[0106] Each of the thick portions 71-73 has a thickness greater than that of the thin portion 61. The thickness of the thin portion 61 can be, for example, approximately half the thickness of each of the thick portions 71-73. The thicknesses of the thick portions 71-73 may be the same as or different from one another. Specifically, as shown in FIG. 11B , in the positive-electrode inner-periphery-side active material layer 21B1, the thickness T72-1 of the thick portion 72-1 and the thickness T73-1 of the thick portion 73-1 are greater than the thickness T61-1 of the thin portion 61-1. Similarly, in the positive-electrode outer-periphery-side active material layer 21B2, 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. Note that thickness T71-1 (see FIG. 4C), thickness T72-1, and thickness T73-1 may be equal to or different from thickness T71-2 (see FIG. 4C), thickness T72-2, and thickness T73-2, respectively. In addition, in the width direction of positive electrode 21, the length of thick portion 71 is longer than the length of thick portion 72 and the length of thick portion 73.

[0107] The thick portion 72 is adjacent to the thin portion 61 in the W direction. More specifically, the thick portion 72 is located between the thin portion 61 and the insulating layer 101 in the W direction. The thick portion 71 includes a first edge 21BT1 and may be in contact with the insulating layer 101. The thick portion 73 includes a second edge 21BT2 located on the opposite side of the first edge 21BT1 in the W direction. The thick portions 71 to 73 may be separated from each other, or may be partially or entirely integrated. The thick portions 71 and 72 include the edge of the positive electrode 21 on the winding center side in the L direction.

[0108] As described above, in the positive electrode 21-3 as the third modified example, the positive electrode active material layer 21B includes the thick portion 72 and the thick portion 73 so as to sandwich the thin portion 61 in the W direction. This allows the separator 23, which is disposed between the positive electrode active material layer 21B and the negative electrode active material layer 22B, to be firmly held. As a result, the electrode wound body 20 is less likely to collapse when the electrode wound body 20 expands and contracts, and the separator 23 can be prevented from shifting from its predetermined position. This prevents a short circuit between the positive electrode 21-3 and the negative electrode 22. In other words, a secondary battery 1 including the positive electrode 21-3 instead of the positive electrode 21 can ensure excellent reliability.

[0109] (Fourth Modification) Next, a positive electrode 21-4 as a fourth modified example that is applied to the secondary battery 1 of the above embodiment will be described with reference to FIGS. 12A and 12B. FIG. 12A is a developed view of the positive electrode 21-4 and corresponds to FIG. 4A, which shows the positive electrode 21 of the above embodiment. FIG. 12B is a developed view of the positive electrode 21-4 and corresponds to FIG. 4C, which shows the positive electrode 21 of the above embodiment. FIG. 12B shows a cross section taken along line XIIB-XIIB in FIG. 12A, as viewed in the direction of the arrows.

[0110] As shown in FIGS. 12A and 12B , in the positive electrode 21-4, the positive electrode active material layer 21B further includes a thin portion 62. The thin portion 62 is located on the opposite side of the thick portion 71 from the thin portion 61. The thin portion 62 is a specific example corresponding to a “second thin portion” according to an embodiment of the present disclosure. The thin portion 62 is thinner than the thick portion 71. The thin portion 62 includes the edge 21E2 on the outer periphery of the winding in the L direction of the positive electrode 21-4. The length of the thin portion 62 in the L direction may be, for example, approximately half a circumference of the electrode wound body 20, starting from the edge 21E2 on the outer periphery of the winding. 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 insulating layer 101 in the W direction. The thick portion 74 includes a first edge 21BT1 and may be in contact with the insulating layer 101. The positive electrode active material layer 21B further includes a thick portion 75. The thick portion 75 includes a second edge 21BT2.

[0111] In a positive electrode 21-4 as a fourth 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 21-4, 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. Note that in FIG. 12B , for convenience, the thin portion 62 included in the positive electrode inner peripheral side active material layer 21B1 is referred to as the thin portion 62-1, and the thin portion 62 included in the positive electrode outer peripheral side active material layer 21B2 is referred to as the thin portion 62-2. 12B, the position in the L direction of boundary 21B1K1 between thin portion 61-1 and thick portion 71-1 substantially coincides with the position in the L direction of boundary 21B2K1 between thin portion 61-2 and thick portion 71-2. In the example shown in FIG. 12B, the position in the L direction of boundary 21B1K2 between thin portion 62-1 and thick portion 71-1 substantially coincides with the position in the L direction of boundary 21B2K2 between thin portion 62-2 and thick portion 71-2.

[0112] Thus, in the positive electrode 21-4 as the fourth modification, in addition to the thin portion 61, a thin portion 62 is also provided on the outer periphery of the wound electrode body 20. This further enhances the flexibility of the positive electrode 21. Furthermore, by providing the thin portion 62, the difference in level 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 wound electrode body 20 can be reduced compared to when a positive electrode 21 without the thin portion 62 is used. This reduces stress concentration at the portion of the separator 23 that overlaps with the outer periphery of the wound electrode body 20, the breakage of the separator 23, and the occurrence of a short circuit between the positive electrode 21 and the negative electrode 22. In other words, 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 wound electrode body 20 can be reduced, and the charge / discharge rate characteristics and the capacity of the secondary battery 1 can be improved.

[0113] (Fifth Modification) FIG. 13 is a development view of a positive electrode 21-5 as a fifth modified example that can be applied to the secondary battery 1 of the embodiment described above, corresponding to FIG. 4A , which illustrates the positive electrode 21 of the embodiment described above. In the positive electrode 21-5 as the fifth modified example, the positive electrode active material layer 21B further includes a thin portion 62, similar to the positive electrode 21-4 as the fourth modified example described above. The thin portion 62 is located on the opposite side of the thick portion 71 from the thin portion 61 and includes the outer peripheral edge 21E2 of the wound electrode. However, in the positive electrode 21-5, the positive electrode active material layer 21B does not include the thick portions 72-75, and each of the thin portions 61 and 62 extends in the W direction from the first edge 21BT1 to the second edge 21BT2 of the positive electrode active material layer 21B. Except for this point, the configuration of the positive electrode 21-5 is substantially the same as the configuration of the positive electrode 21-4. Therefore, with the positive electrode 21-5 as the fifth modified example, the same effects as those of the positive electrode 21-4 described above due to the provision of the thin-walled portion 62 can be expected.

[0114] (Sixth Modification) In the above embodiment, a secondary battery 1 including a positive electrode 21 and a negative electrode 22 with a so-called tabless structure has been described as an example, but the present disclosure is not limited thereto. The secondary battery of the present disclosure may be, for example, the secondary battery 2 shown in FIG. 14 . A secondary battery 2 according to a sixth modification of the present disclosure includes a positive electrode 21-6 with a tabbed structure having a positive electrode lead 28 shown in FIG. 15A and a negative electrode 22-6 with a tabbed structure having a negative electrode lead 29 shown in FIG. 15B. FIG. 15A is a developed view of the positive electrode 21-6, corresponding to FIG. 4A, which illustrates the positive electrode 21 of the above embodiment. FIG. 15B is a developed view of the negative electrode 22-6, corresponding to FIG. 5A, which illustrates the negative electrode 22 of the above embodiment. Each of FIGS. 16A and 16B illustrates a cross-sectional configuration of the positive electrode 21-6. FIG. 16A illustrates a cross section taken along line XVIA-XVIA in FIG. 15A. FIG. 16B shows a cross section taken along line XVIB-XVIB in FIG. 15A.

[0115] 14, similar to the secondary battery 1, the secondary battery 2 includes an electrode winding body 20 housed in an outer can 11. The secondary battery 2 further includes insulating plates 12 and 13, a battery lid 14, a gasket 15, and a safety valve mechanism 30. The electrode winding body 20 of the secondary battery 2 is formed by winding a laminate in which a positive electrode 21-6 and a negative electrode 22-6 are stacked with a separator 23 interposed therebetween.

[0116] As shown in FIG. 15A, the positive electrode 21-6 includes a positive electrode current collector 21A, a positive electrode active material layer 21B, and a protective tape 21C. The positive electrode active material layer 21B covers a portion of the surface of the positive electrode current collector 21A. As shown in FIG. 15A, the positive electrode covering region 211 and the positive electrode exposed region 212 each extend along the W direction, which is the short-side direction of the positive electrode 21-6, from the upper edge 21UT of the positive electrode 21-6 to the lower edge 21BT of the positive electrode 21-6. In addition, two positive electrode exposed regions 212 are provided at both ends of the positive electrode 21-6 in the L direction, which is the longitudinal direction. One of the two positive electrode exposed regions 212 includes an inner peripheral edge 21S of the innermost positive electrode portion of the positive electrode 21-6, and the other of the two positive electrode exposed regions 212 includes an outer peripheral edge 21E of the outermost positive electrode portion of the positive electrode 21-6. The positive electrode covered 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 is not present 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 on a part of the positive electrode exposed region 212. More specifically, the protective tape 21C covers a portion of the positive electrode exposed region 212 of the positive electrode current collector 21A that faces the negative electrode active material layer 22B. 15A , the protective tape 21C is provided on the outermost positive electrode exposed region 212 of the two positive electrode exposed regions 212, but the protective tape 21C may also be provided on the innermost positive electrode exposed region 212. A positive electrode lead 28 is attached to the positive electrode current collector 21A in the innermost positive electrode exposed region 212.

[0117] The protective tape 21C is preferably adhered to the separator 23, as this can prevent misalignment between the positive electrode 21-6 and the separator 23. The protective tape 21C is preferably made of a material that does not swell, as this can prevent damage to the negative electrode due to swelling. The protective tape 21C is preferably made of a resin containing, for example, polyimide (PI).

[0118] As shown in FIG. 15B, the negative electrode 22-6 includes a negative electrode current collector 22A and a negative electrode active material layer 22B. The negative electrode active material layer 22B is provided, for example, on both sides of the negative electrode current collector 22A. The negative electrode 22-6 has a negative electrode covering region 221 and a negative electrode exposed region 222. As shown in FIG. 15B, the negative electrode covering region 221 and the negative electrode exposed region 222 each extend along the W direction, which is the short-side direction of the negative electrode 22-6, from the upper edge 22UT of the negative electrode 22-6 to the lower edge 22BT of the negative electrode 22-6. In addition, two negative electrode exposed regions 222 are provided at both ends of the negative electrode 22-6 in the L direction, which is the longitudinal direction. One of the two negative electrode exposed regions 222 includes the inner peripheral edge 22S of the innermost negative electrode portion of the negative electrode 22-6, and the other of the two negative electrode exposed regions 222 includes the outer peripheral edge 22-6E of the outermost negative electrode portion of the negative electrode 22-6. The negative electrode covered region 221 is disposed so as to be sandwiched between the two negative electrode exposed regions 222 in the L direction. In other words, the negative electrode active material layer 22B is not present at both ends in the L direction, which is the longitudinal direction of the negative electrode current collector 22A.

[0119] The negative electrode lead 29 is attached to the negative electrode current collector 22A in the negative electrode exposed region 222. More specifically, it is attached to the negative electrode current collector 22A in the outermost negative electrode exposed region 222 of the two negative electrode exposed regions 222. The negative electrode lead 29 is provided such that a part of it protrudes downward from the lower end edge 22BT of the negative electrode 22.

[0120] The positive electrode active material layer 21B includes a thin portion 61 and thick portions 71 to 73. In the positive electrode 21-6, the thin portion 61 and the thick portions 71 to 73 are formed on both the positive electrode current collector inner surface 21A1 and the positive electrode current collector outer surface 21A2. That is, both the positive electrode inner circumference side active material layer 21B1 and the positive electrode outer circumference side active material layer 21B2 include the thin portion 61 and the thick portions 71 to 73, respectively. 16A and 16B, the thin portion 61 and the thick portions 71, 72, and 73 constituting the positive-electrode inner-periphery-side active material layer 21B1 are referred to 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 referred to as the thin portion 61-2 and the thick portions 71-2, 72-2, and 73-2, respectively. In the example shown in FIG. 16B, the position in the L direction of the boundary 21B1K between the thin portion 61-1 and the thick portion 71-1 coincides with the position in the L direction of the boundary 21B2K between the thin portion 61-2 and the thick portion 71-2, but these positions may be different from each other.

[0121] The thin portion 61 includes the edge 21BS of the positive electrode active material layer 21B on the winding center side in the L direction (inner peripheral edge) thereof. The thin portion 61 may extend in the L direction, for example, from the inner peripheral edge 21BS as a starting point, over a range of approximately one to five revolutions of the electrode wound body 20. The thick portion 71 is provided on the opposite side of the inner peripheral edge 21S from the thin portion 61 in the L direction. The thick portion 72 is adjacent to the thin portion 61 in the W direction. More specifically, the thick portion 72 is located between the thin portion 61 and the upper edge 21UT in the W direction. The thick portion 72 includes the upper edge 21UT. The thick portion 73 is located on the opposite side of the thick portion 72 from the thin portion 61 in the W direction. That is, the thick portion 73 is located between the lower edge 21BT located on the opposite side of the upper edge 21UT in the W direction and the thin portion 61. The thick portion 73 includes the lower edge 21BT. The thick portions 71 to 73 may be separated from one another, or may be partially or entirely integrated.

[0122] The secondary battery 2 as the sixth modified example equipped with the positive electrode 21-6 also has the thin portion 61, and therefore the same effects as those of the above embodiment can be expected. [Example]

[0123] An embodiment of the present disclosure will be described.

[0124] Example 1 [Production method] As will be described below, a positive electrode 21 to be applied to the cylindrical secondary battery 1 (FIG. 1) described in the above embodiment was fabricated.

[0125] First, a 12 μm-thick aluminum foil was prepared as the positive electrode current collector 21A. Next, a layered lithium oxide having a Ni ratio of 85% or more in lithium nickel cobalt aluminum oxide (NCA) was used as the positive electrode active material. A positive electrode binder made of polyvinylidene fluoride was mixed with a conductive additive containing carbon black, acetylene black, and ketjen black to obtain a positive electrode mixture. The mixture ratio of the positive electrode active material, positive electrode binder, and conductive additive was 96.4:2:1.6. Next, the positive electrode mixture was added to an organic solvent (N-methyl-2-pyrrolidone) and stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to a predetermined area on one side of the positive electrode current collector 21A using a coating device, and the positive electrode mixture slurry was then dried to form the positive electrode active material layer 21B. Furthermore, a coating material containing polyvinylidene fluoride (PVDF) was applied to the surface of the positive electrode exposed region 212 adjacent to the positive electrode coated region 211, and the coating material was dried to form an insulating layer 101 having a width of 3 mm and a thickness of 8 μm. The positive electrode active material layer 21B was then compression-molded using a roll press. The thickness of the compressed positive electrode active material layer 21B (corresponding to the thickness of the "unprocessed portion" in Table 1 below) was 32 μm. Furthermore, a portion of the positive electrode active material layer 21B was hollowed out by laser ablation to form a thin portion 61 including an edge 21E1 on the winding center side. The thickness T61 of the thin portion 61 (corresponding to the thickness of the "processed portion" in Table 1 below) was 19 mm. The length of the thin portion 61 in the L direction, i.e., the length from the edge 21E1 on the winding center side to the boundary between the thin portion 61 and the thick portion 71, was 30 mm. In this way, a positive electrode 21 having a positive electrode covering region 211 and a positive electrode exposed region 212 was obtained.

[0126] [evaluation] (Measurement of basis weight of positive electrode active material layer) The weight of the positive electrode active material layer 21B attached to the positive electrode current collector 21A of the prepared positive electrode 21 was measured to determine the weight per unit area of ​​the positive electrode active material layer 21B, i.e., the area density (mg / cm 2 The results are shown in Table 1.

[0127] (Measurement of composition ratio of positive electrode active material layer) The atomic concentration of the major elements in the surface layer of each of the thin portion 61 and thick portion 71 of the fabricated positive electrode 21 was determined by SEM-EDX. The results are shown in Table 1. The equipment used was a scanning electron microscope S-4800 (manufactured by Hitachi, Ltd.) and an energy dispersive X-ray analyzer EMAX (manufactured by Horiba, Ltd.). The acceleration voltage was 5 kV, the magnification was 500x (viewing area 200 μm square), and the average value of two measurements was calculated. The elements to be detected were carbon (C) and fluorine (F) contained in the positive electrode binder, and nickel (Ni) as the positive electrode active material.

[0128] (Flexibility assessment) A test specimen SS was cut from the fabricated positive electrode 21, and the maximum bending stress (MPa) of the test specimen SS was measured. The measurement device 100 shown in FIG. 17 was used to measure the maximum bending stress. The measurement device 100 in FIG. 17 includes a force gauge 110 and a stand 102. The stand 102 has a base 103 on which the test specimen SS is placed and a support 104 that supports the force gauge 110 so that it can be raised and lowered. The base 103 has a 6 mm wide slit 103S. The force gauge 110 has an aluminum plate 105 that is abutted against the test specimen SS to apply a biasing force to the test specimen SS. The test specimen SS was prepared by shearing the positive electrode 21 into a strip with a width of 25 mm and a length of 30 mm. The test specimen SS was placed so that the longitudinal center of the test specimen SS coincided with the center of the slit 103S in the base 103. In the measuring device 100, the force gauge 110 was lowered at a speed of 10 mm / min, while measuring the maximum bending stress of the test piece SS with the force gauge 110. The results are shown in Table 1 and Fig. 18. Fig. 18 is a characteristic diagram showing the relationship between the area density of the positive electrode active material layer 21B and the maximum bending stress.

[0129] (Examples 2 and 3) Positive electrodes 21 of Examples 2 to 4 were produced in the same manner as in Example 1, except that the thickness of the positive electrode active material layer 21B after compression (corresponding to the thickness of the "unprocessed portion" in Table 1 below) and the thickness T61 of the thin-walled portion 61 subjected to laser ablation (the thickness of the "processed portion" in Table 1 below) were set to the values ​​shown in Table 1. The obtained positive electrodes 21 of Examples 2 to 3 were each evaluated in the same manner as in Example 1. The results are also shown in Table 1.

[0130] (Comparative Examples 1 to 3) Positive electrodes 21 of Comparative Examples 1 to 3 were produced in the same manner as in Example 1, except that no thin portion 61 was provided in the positive electrode active material layer 21B and the thickness of the positive electrode active material layer 21B was set to the values ​​shown in Table 1. The obtained positive electrodes 21 of Comparative Examples 1 to 3 were each evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0131] [Table 1]

[0132] As shown in Table 1 and FIG. 18, when Examples 1 to 3 are compared with Comparative Examples 1 to 3, it is confirmed that, at the same area density, Examples 1 to 3, in which thin-walled portions are provided by laser ablation, are able to reduce the maximum bending stress more than Comparative Examples 1 to 3, in which thin-walled portions are not provided.

[0133] From the above results, it was confirmed that a secondary battery including a positive electrode according to the present disclosure can achieve higher reliability by increasing the flexibility of the positive electrode active material layer, thereby improving the flexibility of the positive electrode, and thereby alleviating stress concentration near the winding center of the electrode winding body, for example.

[0134] While the present disclosure has been described above with reference to one embodiment and several examples, the configuration of the present disclosure is not limited to the configuration described in the above embodiment and several examples and can be modified in various ways. For example, while the above embodiment illustrates an electrode wound body having a cylindrical appearance with a circular horizontal cross section, the present disclosure is not limited thereto. The electrode wound body of the present disclosure may also have an elliptical cylindrical appearance with an elliptical horizontal cross section, for example.

[0135] In addition, although the above embodiment and examples have been described with reference to a case where the electrode reactant is lithium, the electrode reactant is not particularly limited. Therefore, as described above, the electrode reactant may be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be other light metals such as aluminum.

[0136] 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.

[0137] The present disclosure may take the following forms. <1> a positive electrode current collector extending in both the longitudinal and transverse directions; a positive electrode active material layer laminated on the positive electrode current collector and containing a positive electrode active material and a positive electrode binder; and the positive electrode active material layer includes a first thin portion and a first thick portion that has a thickness greater than a thickness of the first thin portion and is located on an outer circumferential side of the electrode winding body as viewed from the first thin portion in the longitudinal direction, The ratio of the amount of the positive electrode binder to the amount of the positive electrode active material in the first thin portion is lower than the ratio of the amount of the positive electrode binder to the amount of the positive electrode active material in the first thick portion. Positive electrode. <2> the first thin portion includes a surface layer including a surface opposite to a surface facing the positive electrode current collector, and a lower layer between the surface layer and the positive electrode current collector, The ratio of the amount of the positive electrode binder to the amount of the positive electrode active material in the surface layer is lower than the ratio of the amount of the positive electrode binder to the amount of the positive electrode active material in the lower layer. the above <1> The positive electrode described. <3> the positive electrode active material layer contains fluorine, When the ratio of the amount of fluorine present to the amount of the positive electrode active material present in the first thick portion is 1, the ratio of the amount of fluorine present to the amount of the positive electrode active material present in the surface layer is 0.62 or less. the above <2> The positive electrode described. <4> the positive electrode active material layer contains carbon, When the ratio of the amount of carbon present to the amount of the positive electrode active material present in the first thick portion is 1, the ratio of the amount of carbon present to the amount of the plurality of positive electrode active materials present in the surface layer is 0.52 or less. the above <2> or <3> The positive electrode described. <5> the positive electrode active material layer contains nickel (Ni) as the positive electrode active material, the positive electrode active material layer contains polyvinylidene fluoride (PVDF) as the positive electrode binder, In the surface layer, the ratio of the number of fluorine (F) atoms to the number of nickel (Ni) atoms is 0.6 or less. the above <2> from <4> 10. The positive electrode according to any one of the above items. <6> the positive electrode active material layer contains nickel (Ni) as the positive electrode active material, the positive electrode active material layer contains polyvinylidene fluoride (PVDF) as the positive electrode binder, In the surface layer, the ratio of the number of carbon (C) atoms to the number of nickel (Ni) atoms is 0.6 or less. the above <2> from <5> 10. The positive electrode according to any one of the above items. <7> The first thin portion includes an edge of the positive electrode on the winding center side in the longitudinal direction. the above <1> from <6> 10. The positive electrode according to any one of the above items. <8> the positive electrode current collector includes an inner peripheral surface of the positive electrode current collector facing the winding center of the electrode winding body, and an outer peripheral surface of the positive electrode current collector facing outward, opposite to the winding center 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 <7> 10. The positive electrode according to any one of the above items. <9> the positive electrode current collector includes an inner peripheral surface of the positive electrode current collector facing the winding center of the electrode winding body, and an outer peripheral surface of the positive electrode current collector facing outward, opposite to the winding center 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 and the first thick portion; a first length from an end edge of the positive electrode on the side of the winding center 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 first thick portion of the first positive electrode active material layer, and a second length from an end edge of the positive electrode on the side of the winding center 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 first thick portion of the second positive electrode active material layer are different from each other. the above <1> from <8> 10. The positive electrode according to any one of the above items. <10> the positive electrode active material layer further includes a second thick portion adjacent to 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> from <9> 10. The positive electrode according to any one of the above items. <11> the positive electrode active material layer further includes a third thick portion located on the opposite side to the second thick portion in the width direction, The thickness of the third thick portion is greater than the thickness of the first thin portion. the above <10> The positive electrode described. <12> the positive electrode active material layer further includes a second thin portion on a side opposite to the first thin portion as viewed from the first thick portion, The thickness of the second thin portion is thinner than the thickness of the first thick portion. the above <1> from <11> 10. The positive electrode according to any one of the above items. <13> the above <1> from <12> a laminate including the positive electrode, the negative electrode, and the separator according to any one of the preceding claims wound along the longitudinal direction and having a through-hole penetrating in the width direction; Secondary battery. <14> the above <13> a secondary battery according to the above; a control unit that controls the secondary battery; an exterior body that houses the secondary battery; A battery pack having [Explanation of symbols]

[0138] 1...lithium ion secondary battery, 11...outer can, 11B...bottom, 11N...open end, 11W...side wall, 12, 13...insulating plate, 14...battery lid, 15...gasket, 20...electrode winding body, S20...laminated body, 21...positive electrode, 21A...positive electrode current collector, 21B...positive electrode active material layer, 21BB...positive electrode binder, 21BP...positive electrode active material particles, 21BT1...first edge, 211...positive electrode covering region, 212...positive electrode exposed region, 22...negative electrode, 22A...negative electrode current collector, 22B...negative electrode active material layer, 221...negative electrode covering region, 222...negative electrode exposed region, 23...separator , 23A...first separator member, 23B...second separator member, 24...positive electrode current collector plate, 25...negative electrode current collector plate, 26...through hole, 30...safety valve mechanism, 31, 33...fan-shaped portion, 32, 34...strip-shaped portion, 35, 36...opening, 37...protrusion, 41...upper end surface, 42...lower end surface, 45...side surface, 45T...upper end region, 45B...lower end region, 45M...middle region, 46...fixing tape, 50...outer tube, 53, 54...insulating member, 55...washer, 61...thin portion, 71...thick portion, 101...insulating layer, BL...lower layer, CL...center axis, UL...surface layer.

Claims

1. a positive electrode current collector extending in both the longitudinal and transverse directions; a positive electrode active material layer laminated on the positive electrode current collector and containing a positive electrode active material and a positive electrode binder; and the positive electrode active material layer includes a first thin portion and a first thick portion that has a thickness greater than a thickness of the first thin portion and is located on an outer circumferential side of the electrode winding body as viewed from the first thin portion in the longitudinal direction, The ratio of the amount of the positive electrode binder to the amount of the positive electrode active material in the first thin portion is lower than the ratio of the amount of the positive electrode binder to the amount of the positive electrode active material in the first thick portion. Positive electrode.

2. the first thin portion includes a surface layer including a surface opposite to a surface facing the positive electrode current collector, and a lower layer between the surface layer and the positive electrode current collector, The ratio of the amount of the positive electrode binder to the amount of the positive electrode active material in the surface layer is lower than the ratio of the amount of the positive electrode binder to the amount of the positive electrode active material in the lower layer. The positive electrode according to claim 1 .

3. the positive electrode active material layer contains fluorine, When the ratio of the amount of fluorine present to the amount of the positive electrode active material present in the first thick portion is 1, the ratio of the amount of fluorine present to the amount of the positive electrode active material present in the surface layer is 0.62 or less. The positive electrode according to claim 2.

4. the positive electrode active material layer contains carbon, When the ratio of the amount of carbon present to the amount of the positive electrode active material present in the first thick portion is 1, the ratio of the amount of carbon present to the amount of the plurality of positive electrode active materials present in the surface layer is 0.52 or less. The positive electrode according to claim 2.

5. the positive electrode active material layer contains nickel (Ni) as the positive electrode active material, the positive electrode active material layer contains polyvinylidene fluoride (PVDF) as the positive electrode binder, In the surface layer, the ratio of the number of fluorine (F) atoms to the number of nickel (Ni) atoms is 0.6 or less. The positive electrode according to claim 2.

6. the positive electrode active material layer contains nickel (Ni) as the positive electrode active material, the positive electrode active material layer contains polyvinylidene fluoride (PVDF) as the positive electrode binder, In the surface layer, the ratio of the number of carbon (C) atoms to the number of nickel (Ni) atoms is 0.6 or less. The positive electrode according to claim 2.

7. The first thin portion includes an edge of the positive electrode on the winding center side in the longitudinal direction. The positive electrode according to claim 1 .

8. the positive electrode current collector includes an inner peripheral surface of the positive electrode current collector facing the winding center of the electrode winding body, and an outer peripheral surface of the positive electrode current collector facing outward, opposite to the winding center 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 positive electrode according to claim 1 .

9. the positive electrode current collector includes an inner peripheral surface of the positive electrode current collector facing the winding center of the electrode winding body, and an outer peripheral surface of the positive electrode current collector facing outward, opposite to the winding center 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 and the first thick portion; a first length from an end edge of the positive electrode on the side of the winding center 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 first thick portion of the first positive electrode active material layer, and a second length from an end edge of the positive electrode on the side of the winding center 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 first thick portion of the second positive electrode active material layer are different from each other; The positive electrode according to claim 1 .

10. the positive electrode active material layer further includes a second thick portion adjacent to 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 .

11. the positive electrode active material layer further includes a third thick portion located on the opposite side to the second thick portion in the width direction, The thickness of the third thick portion is greater than the thickness of the first thin portion. The positive electrode according to claim 10.

12. the positive electrode active material layer further includes a second thin portion on an opposite side of the first thin portion from the first thick portion, The thickness of the second thin portion is thinner than the thickness of the first thick portion. The positive electrode according to claim 1 .

13. a laminate including the positive electrode, the negative electrode, and the separator according to any one of claims 1 to 12, wound along the longitudinal direction and including an electrode winding body having a through-hole penetrating in the width direction; Secondary battery.

14. The secondary battery according to claim 13; a control unit that controls the secondary battery; an exterior body that encloses the secondary battery; A battery pack having

Images