Secondary battery and battery pack

Abstract

Provided is a secondary battery that has excellent reliability. A secondary battery according to an embodiment of the present disclosure comprises an electrode winding body and an exterior can. In the electrode winding body, a laminate including a positive electrode, a negative electrode, and a separator is wound along a longitudinal direction of the laminate, and the electrode winding body has a through-hole penetrating in a width direction that is orthogonal to the longitudinal direction. The exterior can houses the electrode winding body. The positive electrode comprises a positive electrode current collector that extends in both the longitudinal direction and the width direction, and a positive electrode active material layer that is provided to the positive electrode current collector and that includes a thin portion and a thick portion having a thickness greater than the thickness of the thin portion. Positive electrode active material particles that include a deactivated portion in at least a portion thereof are present on the surface of the thin portion that is on the opposite side from the positive electrode current collector. The thickness of the deactivated portion is less than 6.1 μm.

Description

Secondary batteries and battery packs

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

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

[0003] Patent Document 1 proposes a secondary battery that employs a so-called tabless structure to reduce internal resistance and enable charging and discharging with a relatively large current.

[0004] International Publication No. 2021 / 020237

[0005] Various efforts have been made 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.

[0007] A secondary battery according to an embodiment of the present disclosure includes an electrode winding and an outer can. The electrode winding is formed by winding a laminate including a positive electrode, a negative electrode, and a separator along the longitudinal direction of the laminate, and has a through-hole extending in the width direction perpendicular to the longitudinal direction. The outer can houses the electrode winding. The positive electrode includes a positive electrode current collector extending in both the longitudinal and width directions, and a positive electrode active material layer disposed on the positive electrode current collector and including a thin portion and a thick portion having a thickness greater than that of the thin portion. Positive electrode active material particles including at least a deactivated portion are present on the surface of the thin portion opposite the positive electrode current collector. The thickness of the deactivated portion is less than 6.1 μm.

[0008] According to the secondary battery of one embodiment of the present disclosure, the positive electrode active material layer includes a thin portion, thereby alleviating stress concentration inside the outer can due to expansion of the negative electrode. Furthermore, the presence of a deactivated portion in the thin portion of the positive electrode active material layer can suppress release of electrode reactants from the thin portion of the positive electrode active material layer. As a result, stress concentration inside the outer can due to expansion of the negative electrode can be effectively alleviated. Therefore, short circuits between the positive electrode and the negative electrode can be prevented, ensuring excellent reliability.

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

[0010] FIG. 1 is a cross-sectional view illustrating an example of a vertical cross-sectional structure along the height direction of a secondary battery according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram illustrating an example of a laminate including a positive electrode, a negative electrode, and a separator illustrated in FIG. 1 . FIG. 3 is a cross-sectional view illustrating an example of a horizontal cross-sectional structure of an electrode winding body illustrated in FIG. 1 . FIG. 4A is a developed view of the positive electrode illustrated in FIG. 1 . FIG. 4B is a first cross-sectional view of the positive electrode illustrated in FIG. 1 . FIG. 4C is a second cross-sectional view of the positive electrode illustrated in FIG. 1 . FIG. 4D is a cross-sectional view schematically illustrating an enlarged portion of the positive electrode illustrated in FIG. 1 . FIG. 5A is a developed view of the negative electrode illustrated in FIG. 1 . FIG. 5B is a cross-sectional view of the negative electrode illustrated in FIG. 1 . FIG. 6A is a plan view of a positive electrode current collector plate illustrated in FIG. 1 . FIG. 6B is a plan view of a negative electrode current collector plate illustrated in FIG. 1 . FIG. 7 is a perspective view illustrating a manufacturing process of the secondary battery illustrated in FIG. 1 . FIG. 8 is a block diagram illustrating a circuit configuration of a battery pack to which the secondary battery according to an embodiment of the present disclosure is applied. FIG. 9A is a cross-sectional view showing a first embodiment of a positive electrode according to a first modified example of the present disclosure. FIG. 9B is a cross-sectional view showing a second embodiment of a positive electrode according to a first modified example of the present disclosure. FIG. 9C is a cross-sectional view showing a third embodiment of a positive electrode according to a first modified example of the present disclosure. FIG. 10A is a developed view of a positive electrode according to a second modified example of the present disclosure. FIG. 10B is a cross-sectional view of the positive electrode shown in FIG. 10A. FIG. 11A is a developed view of a positive electrode according to a third modified example of the present disclosure. FIG. 11B is a developed view of a negative electrode used together with the positive electrode shown in FIG. 11A. FIG. 12A is a first cross-sectional view of the positive electrode shown in FIG. 11A. FIG. 12B is a second cross-sectional view of the positive electrode shown in FIG. 11A. FIG. 13A is an SEM cross-sectional image showing a portion of the positive electrode of Example 1. FIG. 13B is an explanatory diagram showing the results of measuring the composition of the positive electrode active material layer of Example 1. FIG. 14 is a cross-sectional view showing an example of a vertical cross-sectional structure along the height direction of a secondary battery according to another modified example of the present disclosure.

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

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

[0019] (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 that is 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 a 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 side wall portion 11W extends in the height direction along the outer edge of the bottom portion 11B to surround the electrode winding body 20, and includes an open end portion 11N on the opposite side of the bottom portion 11B, which is open and allows the electrode winding body 20 to be inserted therethrough. The outer can 11 is made of 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 opposite each other in the Z-axis direction, for example, with the electrode winding body 20 sandwiched therebetween. In this specification, the open end portion 11N and its vicinity in the Z-axis direction may be referred to as the upper portion 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 portion 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 portion of the bottom surface 11BS, which is the outer surface of the bottom portion 11B of the outer can 11. The outer tube 50 is made of a heat-shrinkable insulating film containing, for example, a polyester-based resin, a polyamide-based resin, or a thermoplastic elastomer resin.

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

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

[0023] (Crimped structure 11R) The open end 11N of the exterior 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 exterior can 11 with the electrode wound body 20 and other components housed inside the exterior can 11. The crimped structure 11R has a folded portion 11P as a so-called crimp portion. In addition, a constricted portion 11S is provided between the folded portion 11P and the insulating plate 12, where a portion of the exterior can 11 protrudes inward.

[0024] (Battery Lid 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, the safety valve mechanism 30.

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

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

[0027] (Electrode winding body 20) The electrode winding body 20 is disposed between the positive electrode current collector plate 24 and the negative electrode current collector plate 25. The electrode winding body 20 has an upper end face 41 that faces the positive electrode current collector plate 24 in the height direction, and a lower end face 42 that faces the negative electrode current collector plate 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 the 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, and schematically illustrates a portion of a laminate S20 including a positive electrode 21, a negative electrode 22, and a separator 23. In the laminate S20 obtained by developing the electrode winding body 20, the positive electrode 21 and the negative electrode 22 are stacked with the separator 23 interposed therebetween. The separator 23 has, for example, two base materials, namely, a first separator member 23A and a second separator member 23B. Thus, the electrode winding body 20 has a four-layer laminate S20 in which the positive electrode 21, the first separator member 23A, the negative electrode 22, and the second separator member 23B are stacked in this order. The positive electrode 21, the first separator member 23A, the negative electrode 22, and the second separator member 23B are all substantially strip-shaped members with the W 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 a position in which the W direction roughly coincides with the Z-axis direction. Note that FIG. 3 illustrates an example of a 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 26 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 26.

[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 periphery portion 21out, which is located at the outermost periphery of the positive electrode 21 included in the electrode winding body 20, is disposed inside a negative electrode outermost periphery portion 22out, which is located at the outermost periphery of the negative electrode 22 included in the electrode winding body 20. Here, the positive electrode outermost periphery portion 21out is the outermost one-round portion of the positive electrode 21 in the electrode winding body 20. The negative electrode outermost periphery portion 22out is the outermost one-round 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 show a cross-sectional configuration of the positive electrode 21. Note that FIG. 4B shows a cross-section of the positive electrode 21 taken along line IVB-IVB in FIG. 4A . FIG. 4C shows a cross-section of the positive electrode 21 taken along line IVC-IVC in FIG. 4A . The positive electrode 21 includes a positive electrode current collector 21A, a positive electrode active material layer 21B, and an insulating layer 101. In FIGS. 4B and 4C , the stacking direction of the positive electrode current collector 21A and the positive electrode active material layer 21B is designated as the T direction. Note that, in this specification, the T direction may also be referred to as the thickness direction of the positive electrode 21. The positive electrode active material layer 21B may be provided, for example, on only one surface of the positive electrode current collector 21A, or on both surfaces of the positive electrode current collector 21A. FIG. 4B illustrates a case in which 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 central axis CL and a positive electrode current collector outer peripheral surface 21A2 opposite the positive electrode current collector inner peripheral surface 21A1. The positive electrode 21 includes, 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. The positive electrode active material layer 21B extends in both the L direction and the W direction perpendicular to the L direction. The L direction is the winding direction of the laminate S20, and the W direction substantially coincides with the central axis CL.

[0032] The positive electrode current collector 21A includes a positive electrode covering region 211 covered by the positive electrode active material layer 21B and a positive electrode exposed region 212 that is not covered by the positive electrode active material layer 21B and extends in the W direction. The insulating layer 101 extends in the L direction along a first edge 21BT1 of the positive electrode active material layer 21B located at the boundary K between the positive electrode covering region 211 and the positive electrode exposed region 212. In the positive electrode 21 of this 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. 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 thick portions 71 to 73. In the positive electrode 21 of the present embodiment, 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. However, in the positive electrode 21, 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 61 and the thick portions 71 to 73. 4B and 4C, 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. Also, as shown in FIG. 4C, the position in the L direction of the boundary 21B1K between the thin portion 61-1 and the thick portion 73-1 is different from the position in the L direction of the boundary 21B2K between the thin portion 61-2 and the thick portion 73-2. That is, the length L1 from the winding center side edge 21E1 to the position of the boundary 21B1K is different from the length L2 from the winding center side edge 21E1 to the position of the boundary 21B2K.

[0033] Each of the thick portions 71 to 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 to 73. The thicknesses of the thick portions 71 to 73 may be the same as or different from one another. 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, 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. In the example shown in FIGS. 4B and 4C , the thickness T71-1 of the thick portion 71-1, the thickness T72-1 of the thick portion 72-1, and the thickness T73-1 of the thick portion 73-1 are all equal to one another. Similarly, in the positive electrode outer peripheral active material layer 21B2, the thickness T71-2 of the thick portion 71-2, the thickness T72-2 of the thick portion 72-2, and the thickness T73-2 of the thick portion 73-2 are greater than the thickness T61-2 of the thin portion 61-2. In the example shown in FIGS. 4B and 4C , the thickness T71-2 of the thick portion 71-2, the thickness T72-2 of the thick portion 72-2, and the thickness T73-2 of the thick portion 73-2 are all equal. The thicknesses T61-1 and T61-2 may be equal to or different from each other. The thicknesses T62-1 and T62-2 may be equal to or different from each other. Furthermore, the thicknesses T71-1, T72-1, and T73-1 may be equal to or different from the thicknesses T71-2, T72-2, and T73-2, respectively.

[0034] The thin portion 61 includes the winding center side edge 21E1 of the positive electrode 21 in the L direction. The length of the thin portion 61 in the L direction may be, for example, approximately one to five revolutions of the electrode winding body 20 starting from the winding center side edge 21E1. The thick portion 71 is adjacent to the thin portion 61 in the W direction. More specifically, the thick portion 71 is located between the thin portion 61 and the 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 72 includes a second edge 21BT2 located opposite the first edge 21BT1 in the W direction. The thick portion 73 is adjacent to the thin portion 61 in the L direction. The thick portion 73 is located on the opposite side of the winding center side edge 21E1 from the thin portion 61 in the L direction. The thick portions 71 to 73 may be separated from one another, or may be partly or entirely integrated.

[0035] As shown in FIG. 4A , the positive electrode covering region 211 and the positive electrode exposed region 212 each extend along the L direction from the winding center edge 21E1 of the positive electrode 21 to the winding outer edge 21E2. That is, in the positive electrode 21, the positive electrode active material layer 21B covers the positive electrode current collector 21A from the winding center edge 21E1 of the positive electrode 21 to the winding outer edge 21E2 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. Note that FIGS. 4A and 4B schematically illustrate the positive electrode current collector 21A extending linearly along the W direction. However, in reality, the positive electrode edge 212E of the positive electrode exposed region 212 is bent toward the central axis CL as shown in FIG. 1 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 an upper end surface 41 and is connected to the positive electrode current collector plate 24 (see FIG. 1 ). The upper end surface 41 is formed by bending the positive electrode edge portion 212E of the positive electrode exposed region 212 toward the through hole 26 in a rolled state.

[0036] An insulating layer 101 may be provided at and near the boundary K between the positive electrode covering region 211 and the positive electrode exposed region 212. Similar to the positive electrode covering region 211 and the positive electrode exposed region 212, the insulating layer 101 may extend from the winding center edge 21E1 to the winding outer peripheral edge 21E2 of the electrode wound body 20. The insulating layer 101 may be bonded to at least one of the first separator member 23A and the second separator member 23B. This is because misalignment between the positive electrode 21 and the separator 23 can be prevented. The insulating layer 101 may include a resin containing polyvinylidene fluoride (PVDF). The PVDF content of the insulating layer 101 allows the insulating layer 101 to swell with, for example, a solvent contained in the electrolyte solution, thereby enabling good adhesion to the separator 23.

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

[0039] FIG. 4D is a cross-sectional view further enlarging a portion of the positive electrode 21 shown in FIG. 4C , specifically illustrating the vicinity of the boundary 21B1K between the thin portion 61-1 and the thick portion 73-1. FIG. 4D depicts only a portion of the positive electrode current collector 21A and a portion of the positive electrode inner periphery active material layer 21B1 of the positive electrode 21, omitting the positive electrode outer periphery active material layer 21B2. As shown in FIG. 4D , the positive electrode inner periphery active material layer 21B1 contains a plurality of positive electrode active material particles 81 made of the above-described positive electrode material. The positive electrode inner periphery active material layer 21B1 further contains a plurality of positive electrode binders 82 and a plurality of positive electrode conductors 83. Some of the positive electrode active material particles 81 located on the surface of the thin portion 61-1 opposite the positive electrode current collector 21A include an active portion 811 and a deactivated portion 812 that covers at least a portion of the active portion 811. The effective portion 811 of the positive electrode active material particle 81 is a portion that can fully absorb and release lithium. In contrast, the deactivated portion 812 of the positive electrode active material particle 81 is a portion that has lost the ability to absorb and release lithium or has a weaker ability to absorb and release lithium compared to the effective portion 811. The oxygen mass concentration of the deactivated portion 812 of the positive electrode active material particle 81 is lower than the oxygen mass concentration of the effective portion 811 of the positive electrode active material particle 81 other than the deactivated portion 812. The deactivated portion 812 is discretely present on the surface of the thin portion 61-1. The average thickness of the deactivated portion 812 is, for example, 0.2 μm or more and 2.8 μm or less. Similar to the thin portion 61-1 described above, the thin portion 61-2 of the positive electrode outer peripheral active material layer 21B2 also includes the positive electrode active material particle 81 that includes the effective portion 811 and the deactivated portion 812 that covers at least a portion of the effective portion 811. The thickness of the deactivated portion 812 may be less than 6.1 μm.

[0040] 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 as viewed from the arrow direction. The negative electrode 22 includes, for example, a negative electrode current collector 22A and a negative electrode active material layer 22B 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 winding center of the electrode wound body 20, i.e., facing the central axis CL, and a negative electrode current collector outer peripheral surface 22A2 facing the side opposite the winding center of the electrode wound body 20, i.e., on the opposite side of the negative electrode current collector inner peripheral surface 22A1. The negative electrode 22 has, as the negative electrode active material layer 22B, a negative electrode inner peripheral side active material layer 22B1 covering at least a portion of the negative electrode current collector inner peripheral surface 22A1, and a negative electrode outer peripheral side active material layer 22B2 covering at least a portion of the negative electrode current collector outer peripheral surface 22A2. Note that in this specification, the negative electrode inner peripheral side active material layer 22B1 and the negative electrode outer peripheral side active material layer 22B2 may be collectively referred to as the negative electrode active material layer 22B without distinguishing between them.

[0041] 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, which is the longitudinal direction of the negative electrode 22. The negative electrode exposed region 222 extends from the central axis side edge 22E1 to the outer peripheral edge 22E2 of the negative electrode 22 in the winding direction of the electrode wound body 20. In contrast, the negative electrode covering region 221 is not provided on the central axis side edge 22E1 or the outer peripheral edge 22E2 of the negative electrode 22. As shown in FIG. 5A , parts of the negative electrode exposed region 222 are formed to sandwich the negative electrode covering region 221 in the L direction, which is the longitudinal direction of the negative electrode 22. 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 body 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 the central axis side edge 22E1 to the outer peripheral side edge 22E2 of the negative electrode 22. 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 central axis side edge 22E1 of the negative electrode 22, for example, and the third portion 222C is located near the outer peripheral side edge 22E2 of the negative electrode 22. 5A and 5B schematically illustrate the negative electrode current collector 22A extending linearly along the W direction. However, in reality, the negative electrode edge portion 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 end portion of the negative electrode exposed region 222 in the W direction 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 portion 222E of the negative electrode exposed region 222 toward the through-hole 26 in a wound state.

[0042] 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 therebetween 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. The electrode winding body 20 has the end of the separator 23 fixed by attaching a fixing tape 46 to a side surface portion 45 thereof, thereby preventing loosening of the winding.

[0043] 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 the width A = 7 (mm), the 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 the width C = 4.5 (mm), the width D = 3 (mm).

[0044] 1 , at the upper part of the secondary battery 1, of the positive electrode exposed region 212 wound around the central axis CL, multiple portions of the positive electrode edge portions 212E adjacent in the radial direction (direction R) of the electrode winding 20 are bent toward the central axis CL so as to overlap with each other, thereby constituting the upper end surface 41 of the electrode winding 20. Similarly, at the lower part of the secondary battery 1, of the negative electrode exposed region 222 wound around the central axis CL, multiple portions of the negative electrode edge portions 222E adjacent in the radial direction (direction R) are bent toward the central axis CL so as to overlap with each other, thereby constituting the lower end surface 42 of the electrode winding 20. Therefore, the multiple positive electrode edge portions 212E of the positive electrode exposed region 212 are gathered at the upper end surface 41 of the electrode winding 20, and the multiple negative electrode edge portions 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.

[0045] As described above, the positive electrode current collector 21A is made of, for example, aluminum foil. On the other hand, as described below, 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, multiple portions of the positive electrode edge portion 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, multiple portions of the negative electrode edge portion 222E ( FIG. 1 ) of the negative electrode exposed region 222 are folded and overlap each other to an appropriate degree, which facilitates joining of the negative electrode exposed region 222 and the negative electrode current collector plate 25. The term "joining" as used herein means joining by, for example, laser welding, but the joining method is not limited to laser welding.

[0046] 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 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 via the separator 23. The insulating layer 101 can effectively prevent an internal short circuit in the secondary battery 1, for example, when a foreign object enters between the negative electrode covering 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 short circuiting between the positive electrode exposed region 212 and the negative electrode 22.

[0047] (Insulating Tapes 53, 54) The secondary battery 1 may further include insulating tapes 53, 54 in the gap between the outer can 11 and the electrode winding body 20. The positive electrode exposed 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 24 facing the upper end face 41 comes close to the outer can 11, a short circuit may also occur. For this reason, it is preferable to provide insulating tapes 53, 54 as insulating members. The insulating tapes 53, 54 are, for example, adhesive tapes whose base layer is made of one of polypropylene, polyethylene terephthalate, and polyimide and whose base layer has an adhesive layer on one surface. In order to prevent the installation of the insulating tapes 53 and 54 from reducing the volume of the electrode winding body 20, the insulating tapes 53 and 54 are positioned so as not to overlap with the fixing tape 46 attached to the side portion 45, and the thickness of the insulating tapes 53 and 54 is set to be equal to or less than the thickness of the fixing tape 46.

[0048] (Positive Electrode Current Collector 24 and Negative Electrode Current Collector 25) In a typical lithium-ion secondary battery, for example, a lead for current extraction is welded to each of the positive and negative electrodes. However, this increases the internal resistance of the lithium-ion secondary battery and causes the lithium-ion secondary battery to heat up and reach high temperatures during discharge, making it unsuitable for high-rate discharge. Therefore, in the secondary battery 1 of this embodiment, the positive 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 electrode current collector 24 is electrically connected to the battery lid 14 via, for example, a safety valve mechanism 30. The negative electrode current collector 25 is provided between the bottom 11B and the lower end surface 42 of the outer can 11. The negative electrode 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 electrode current collector 24. FIG. 6B is a developed view showing an example of the configuration of the negative electrode current collector 25. The positive electrode current collector 24 is a metal plate made of, for example, aluminum or an aluminum alloy, or a composite material thereof. The negative electrode current collector 25 is a metal plate made of, for example, nickel, a nickel alloy, copper, or a copper alloy, or a composite material of two or more of these.

[0049] As shown in FIG. 6A , the positive current collector 24 has a substantially sector-shaped sector portion 31 and a substantially rectangular strip 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 portion 32 folded relative to the sector portion 31, as shown in FIG. 1 . FIG. 6A shows the positive current collector 24 in an unfolded state. The sector portion 31 is a facing portion that faces and is connected to the upper end surface 41. The sector 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 portion 31. FIG. 6A illustrates a case in which the opening 35 has a circular planar shape in a horizontal plane perpendicular to the Z-axis direction. The strip portion 32 is connected to, for example, a straight portion of the outer edge of the sector 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.

[0050] 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 insulating tape is attached or 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 of 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 widening the width between the positive electrode 21 and the negative electrode 22 by an amount corresponding to the thickness of the insulating portion 32A.

[0051] 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 band portion 34. However, the shape of the negative electrode current collector 25 is not limited to the shape shown in FIG. 6B 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 band 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 band portion 34 is connected to, for example, the straight portion of the outer edge of the fan portion 33. The band 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. Similar to 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.

[0052] 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. The sector-shaped portions 31 and 33 do not cover the entire upper end surface 41 and the entire lower end surface 42, for example, for the following two reasons. 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 toward the center of the winding 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 an overcharged state.

[0053] (Negative Electrode Current Collector 22A) The negative electrode current collector 22A contains a conductive material such as copper. The negative electrode current collector 22A is a metal foil made of, for example, nickel, a nickel alloy, copper, or a copper alloy. The surface of the negative electrode current collector 22A is preferably roughened. This is because the so-called anchor effect improves adhesion of the negative electrode active material layer 22B to the negative electrode current collector 22A. In this case, it is sufficient that the surface of the negative electrode current collector 22A is roughened at least in the region facing the negative electrode active material layer 22B. The roughening method may be, for example, a method of forming fine particles using an electrolytic process. In the electrolytic process, fine particles are formed on the surface of the negative electrode current collector 22A by electrolysis in an electrolytic bath, resulting in an uneven surface of the negative electrode current collector 22A. Copper foil produced by an electrolytic process is generally called electrolytic copper foil.

[0054] (Negative Electrode Active Material Layer 22B) The negative electrode active material layer 22B contains, as the negative electrode active material, one or more negative electrode materials capable of absorbing and releasing lithium. However, the negative electrode active material layer 22B may further contain one or more other materials, such as a negative electrode binder and a negative electrode conductor. The negative electrode material is, for example, a carbon material. This is because the crystal structure undergoes minimal change upon lithium absorption and desorption, thereby enabling a stable high energy density. Furthermore, the carbon material also functions as a negative electrode conductor, thereby improving the conductivity of the negative electrode active material layer 22B. Examples of carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite. However, the interplanar spacing of the (002) plane of non-graphitizable carbon is preferably 0.37 nm or more. The interplanar spacing of the (002) plane of graphite is preferably 0.34 nm or less. More specifically, the carbon material may be, for example, pyrolytic carbon, cokes, glassy carbon fiber, organic polymer compound calcined bodies, activated carbon, or carbon black. Examples of the cokes include pitch coke, needle coke, and petroleum coke. The organic polymer compound calcined bodies are formed by calcining (carbonizing) polymer compounds such as phenolic resin and furan resin at an appropriate temperature. Alternatively, the carbon material may be low-crystalline carbon heat-treated at temperatures below approximately 1000°C, or amorphous carbon. The carbon material may be fibrous, spherical, granular, or flake-shaped. In the secondary battery 1, when the open-circuit voltage at full charge, i.e., the battery voltage, is 4.25 V or higher, the amount of lithium released per unit mass is greater than when the open-circuit voltage at full charge is 4.20 V, even when the same positive electrode active material is used. Therefore, the amounts of the positive electrode active material and the negative electrode active material are adjusted accordingly. This results in a high energy density.

[0055] The negative electrode active material layer 22B may also contain a silicon-containing material containing at least one of silicon, silicon oxide, carbon-silicon compound, and silicon alloy as the negative electrode active material. A silicon-containing material is a general term for materials containing silicon as a constituent element. However, a silicon-containing material may contain only silicon as a constituent element. The silicon-containing material may be of one type or two or more types. The silicon-containing material is capable of forming an alloy with lithium and may be silicon itself, a silicon alloy, a silicon compound, a mixture of two or more of these, or a material containing one or more of these phases. The silicon-containing material may be crystalline, amorphous, or contain both crystalline and amorphous portions. However, the element described here refers to a general element and may contain trace amounts of impurities. In other words, the purity of the element is not necessarily limited to 100%. Silicon alloys contain, for example, one or more of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, chromium, etc. as constituent elements other than silicon. Silicon compounds contain, for example, one or more of carbon, oxygen, etc. as constituent elements other than silicon. Note that silicon compounds may contain, for example, one or more of the series of constituent elements described for silicon alloys as constituent elements other than silicon. Specifically, silicon alloys and silicon compounds include, for example, SiB 4 , SiB 6 , Mg 2 Si, Ni 2 Si, TiSi 2 , MoSi 2 , CoSi 2 , NiSi 2 , CaSi 2 , CrSi 2 , Cu 5 Si, FeSi 2 , MnSi 2 , NbSi 2 , TaSi 2 , VSi 2 , WSi 2 , ZnSi2 , SiC, Si 3 N 4 , Si 2 N 2 O and SiO v (0<v≦2), etc. However, the range of v can be set arbitrarily, and may be, for example, 0.2<v<1.4.

[0056] (Separator 23) The separator 23 is interposed between the positive electrode 21 and the negative electrode 22. The separator 23 allows lithium ions to pass through while preventing current short-circuiting due to contact between the positive electrode 21 and the negative electrode 22. The separator 23 may be made of one or more types of porous membranes, such as synthetic resins and ceramics, or may be a laminate 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. By making the single-layer porous membrane made of polyolefin 10 μm or more thick, internal short-circuiting can be sufficiently avoided. If the thickness of the single-layer porous film made of polyolefin is 15 μm or less, better discharge capacity characteristics can be obtained. In addition, the surface density of the porous film is, for example, 6.3 g / m ２ 8.3g / m or more ２ The surface density of the single-layer porous film made of polyolefin is preferably 6.3 g / m or less. ２ If the surface density of the single-layer porous film made of polyolefin is 8.3 g / m or more, internal short circuits can be sufficiently avoided. ２ If the content is less than this, better discharge capacity characteristics can be obtained.

[0057] 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 into the substrate, thereby making it less likely for resistance to increase even with repeated charge and discharge, and suppressing battery swelling. The polymer compound layer includes, for example, a polymer compound such as polyvinylidene fluoride. This is because it has excellent physical strength and is electrochemically stable. However, the polymer compound may be other than polyvinylidene fluoride. To form this polymer compound layer, for example, a solution in which the polymer compound is dissolved in an organic solvent or the like is applied to the substrate, and the substrate is then dried. Alternatively, the substrate 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.

[0058] (Electrolyte) The electrolyte contains a solvent and an electrolyte salt. However, the electrolyte may further contain one or more other materials, such as additives. The solvent contains one or more non-aqueous solvents, such as organic solvents. An electrolyte containing a non-aqueous solvent is a so-called non-aqueous electrolyte. The non-aqueous solvent contains, for example, a fluorine compound and a dinitrile compound. The fluorine compound may include, for example, at least one of fluorinated ethylene carbonate, trifluorocarbonate, trifluoroethyl methyl carbonate, fluorinated carboxylic acid ester, and fluorinated ether. The non-aqueous solvent may also contain at least one nitrile compound other than the dinitrile compound, such as a mononitrile compound or a trinitrile compound. The dinitrile compound is preferably succinonitrile (SN). However, the dinitrile compound is not limited to succinonitrile and may be other dinitrile compounds, such as adiponitrile.

[0059] The electrolyte salt may include one or more salts, such as lithium salts. However, the electrolyte salt may also include salts other than lithium salts, such as salts of light metals other than lithium. Examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium tetraphenylborate (LiB(C(H)), lithium methanesulfonate (LiCHSO), lithium trifluoromethanesulfonate (LiCFSO), lithium tetrachloroaluminate (LiAlCl), dilithium hexafluorosilicate (LiSiF), lithium chloride (LiCl), and lithium bromide (LiBr). Among these, one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium hexafluoroarsenate are preferred, with lithium hexafluorophosphate being more preferred. The content of the electrolyte salt is not particularly limited, but is preferably 0.3 mol / kg to 3 mol / kg relative to the solvent. When the electrolyte solution contains LiPF as the electrolyte salt, ６ When the electrolyte contains LiPF ６ The concentration of the electrolyte salt is preferably 1.25 mol / kg or more and 1.45 mol / kg or less. This is because it is possible to prevent cycle deterioration due to salt consumption (decomposition) during high-load rate charging, thereby improving high-load cycle characteristics. ６ In addition to LiBF ４ When further containing LiBF in the electrolyte ４ The concentration of salt is preferably 0.001% by weight or more and 0.1% by weight or less, because this more effectively prevents cycle deterioration due to salt consumption (decomposition) during high-load rate charging, thereby further improving high-load cycle characteristics.

[0060] [1-2. Operation] In the secondary battery 1 of this embodiment, for example, during charging, lithium ions are released from the positive electrode 21 and are absorbed into the negative electrode 22 via the electrolyte. In addition, in the secondary battery 1, for example, during discharging, lithium ions are released from the negative electrode 22 and are absorbed into the positive electrode 21 via the electrolyte.

[0061] 1-3. Manufacturing Method] A method for manufacturing the secondary battery 1 will be described with reference to Fig. 7 in addition to Fig. 1 to Fig. 6B. Fig. 7 is a perspective view illustrating the manufacturing process of the secondary battery 1 shown in Fig. 1.

[0062] 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 dug down by, for example, laser ablation, i.e., a portion of the positive electrode active material layer 21B in the thickness direction is removed to form a thin portion 61. Then, by subjecting the predetermined region of the positive electrode active material layer 21B to laser ablation, a deactivated portion 812 is formed in the positive electrode active material particle 81. The positive electrode 21 is obtained by the above operations.

[0063] 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.

[0064] Next, as shown in Fig. 7B , the edge of a flat plate having a thickness of, for example, 0.5 mm is pressed perpendicularly against the upper end surface 41 and the lower end surface 42 of the electrode winding body 20, i.e., in the Z-axis direction, thereby locally bending a portion of the upper end surface 41 and a portion of the lower end surface 42. As a result, grooves 43 are formed extending radially from the through-holes 26 in the radial direction (direction R). Note that the number and arrangement of grooves 43 shown in Fig. 7B are merely examples and the present disclosure is not limited thereto.

[0065] Next, as shown in FIG. 7C , 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. At this time, a rod-shaped jig, for example, is inserted into the through-hole 26. This bends the positive electrode exposed region 212 and the first portion 222A of the negative electrode exposed region 222, respectively, so that the upper end face 41 and the lower end face 42 each become flat. At this time, it is preferable that adjacent portions of the positive electrode edge 212E of the positive electrode exposed region 212 on the upper end face 41 in the radial direction of the electrode winding 20 bend toward the through-hole 26 so as to overlap each other. Similarly, it is preferable that adjacent portions of the negative electrode edge 222E of the negative electrode exposed region 222 on the lower end face 42 in the radial direction of the electrode winding 20 bend toward the through-hole 26 so as to overlap each other. 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.

[0066] Next, insulating tapes 53 and 54 are attached to predetermined positions of the electrode winding body 20. Thereafter, as shown in Fig. 7D, the strip portion 32 of the positive current collector plate 24 is bent and inserted into the hole 12H of the insulating plate 12. Also, the strip portion 34 of the negative current collector plate 25 is bent and inserted into the hole 13H of the insulating plate 13.

[0067] Next, the electrode winding body 20 assembled as described above is inserted into the outer can 11 shown in Figure 7(E), and the bottom 11B of the outer can 11 is welded to the negative electrode current collector 25. After that, a constricted portion 11S is formed near the open end 11N of the outer can 11. Furthermore, after the electrolyte is poured into the outer can 11, the strip portion 32 of the positive electrode current collector 24 is welded to the safety valve mechanism 30.

[0068] 7(F), the outer can 11 is sealed with 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, so that the outer tube 50 is tightly attached to the outer surface of the outer can 11. With the above steps, the secondary battery 1 of this embodiment is completed.

[0069] [1-4. Actions and Effects] As described above, in the secondary battery 1 of the present embodiment, the cathode active material layer 21B includes the thin portion 61, thereby reducing stress concentration inside the outer can 11 due to expansion of the anode 22. Specifically, when expansion of the anode 22 occurs inside the electrode wound body 20 due to charge and discharge, significant deformation, such as buckling (bending) of the cathode 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 anode active material layer 22B facing the thin portion 61 reduces expansion and contraction of the portion of the anode active material layer 22B facing the thin portion 61. As a result, stress applied to the separator 23 separating the cathode 21 and the anode 22 is also reduced, preventing breakage of the separator 23 even when the thickness of the separator 23 is reduced, and preventing short-circuiting between the cathode 21 and the anode 22. That is, the separator 23 can be made thinner. As a result, the gap between the positive electrode 21 and the negative electrode 22 can be narrowed, the internal resistance of the electrode winding body 20 can be reduced, and the charge / discharge rate characteristics and capacity of the secondary battery 1 can be improved. Meanwhile, because the positive electrode active material layer 21B includes the thick portion 71 at a position adjacent to the thin portion 61 in the W direction, the separator 23 disposed between the positive electrode active material layer 21B and the negative electrode active material layer 22B can be firmly held. As a result, the electrode winding body 20 is less likely to collapse during expansion and contraction of the electrode winding body 20, and the separator 23 can be prevented from shifting from its predetermined position. As a result, short-circuiting between the positive electrode 21 and the negative electrode 22 can be prevented. Therefore, the secondary battery 1 of this embodiment can achieve excellent reliability.

[0070] Furthermore, cathode active material particles 81 including at least a portion of a deactivated portion 812 are present on the surface of the thin portion 61 opposite to the cathode current collector 21A. The presence of the deactivated portion 812 can inhibit the migration of an electrode reactant (e.g., lithium ions) from the thin portion 61 of the cathode active material layer 21B to the anode active material layer 22B. As a result, expansion of the anode 22 is alleviated, and stress concentration inside the outer can 11 due to the expansion of the anode 22 can be effectively alleviated. Therefore, short circuits between the cathode 21 and the anode 22 can be prevented, and excellent reliability can be achieved.

[0071] Furthermore, in the secondary battery 1 of this embodiment, 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 periphery surface 21A1 of the positive electrode current collector due to expansion of the negative electrode 22 is misaligned with the location where stress concentrates on the outer periphery 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, with the secondary battery 1 including the electrode wound body 20 having the positive electrode 21, stress concentration inside the electrode wound body 20 due to expansion and contraction can be further alleviated compared to when the L-direction position of the boundary 21B1K and the L-direction position of the boundary 21B2K are substantially aligned.

[0072] In the secondary battery 1 of the present embodiment, the thin portion 61 includes the edge 21E1 of the positive electrode 21 that is closest to the winding center in the L direction. That is, the thin portion 61 is provided in the positive electrode active material layer 21B at a position that is closest to the winding center. This makes it possible to effectively reduce stress concentration in the center of the electrode wound body 20 and in its vicinity, where stress concentration is likely to occur significantly.

[0073] Furthermore, in the secondary battery 1 of the present embodiment, the thick portion 71 is provided between the thin portion 61 and the insulating layer 101. This ensures a sufficient thickness for the insulating layer 101, thereby improving the insulating performance of the insulating layer 101. Furthermore, by making the thick portion 71 contact the insulating layer 101, the insulating layer 101 is less likely to fall off the positive electrode current collector 21A and the positive electrode active material layer 21B.

[0074] Furthermore, in the secondary battery 1 of this embodiment, the positive electrode active material layer 21B further includes a thick portion 72 including the second edge 21BT2 located on the opposite side of the first edge 21BT1 in the W direction, so that the separator 23 arranged between the positive electrode active material layer 21B and the negative electrode active material layer 22B can be more firmly held.

[0075] Furthermore, in the secondary battery 1 of the present embodiment, the positive electrode active material layer 21B further includes a thick portion 73 provided on the opposite side of the winding center-side edge 21E1 in the L direction as viewed from the thin portion 61. This is advantageous for ensuring a predetermined battery capacity while mitigating stress concentration at and near the winding center of the electrode winding body 20.

[0076] Furthermore, in the secondary battery 1 of this embodiment, both the positive electrode inner periphery side active material layer 21B1 and the positive electrode outer periphery side active material layer 21B2 include the thin portion 61 and the thick portions 71-73, which makes it possible to more effectively alleviate stress concentration at and near the winding center of the electrode wound body 20. Furthermore, in the secondary battery 1 of this embodiment, the thin portion 61 is provided in a region including the center in the W direction, which is the width direction of the positive electrode 21, so it is possible to effectively alleviate stress concentration inside the electrode wound body 20.

[0077] Furthermore, if the secondary battery is a lithium ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the absorption and desorption of lithium, thereby achieving higher operational reliability.

[0078] 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 that houses the battery pack 301, a switch unit 304 having 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.

[0079] The battery pack 300 includes a positive terminal 321 and a negative terminal 322. When charging, the positive terminal 321 and the negative terminal 322 are connected to the positive terminal and the negative terminal of a charger, respectively, for charging. When using the electronic device, the positive terminal 321 and the negative terminal 322 are connected to the positive terminal and the negative terminal of the electronic device, respectively, for discharging.

[0080] The battery pack 301 is formed by connecting a plurality of secondary batteries 301a in series or parallel. The secondary batteries 301a can be the secondary batteries 1 described above. While Fig. 8 shows an example in which six secondary batteries 301a are connected in a 2-parallel-3-series (2P3S) configuration, any other connection method may be used, such as n-parallel or m-series (n and m are integers).

[0081] The switch unit 304 includes a charge control switch 302a and a diode 302b, as well as a discharge control switch 303a and a diode 303b, and is controlled by the control unit 310. The diode 302b has a polarity opposite to the charge current flowing from the positive terminal 321 to the battery pack 301, and a polarity forward to the discharge current flowing from the negative terminal 322 to the battery pack 301. The diode 303b has a polarity forward to the charge current and opposite to the polarity of the discharge current. Although the switch unit 304 is provided on the + side in FIG. 8, it may also be provided on the - side.

[0082] 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.

[0083] The temperature detection element 308 is, for example, a thermistor, and is provided near the battery pack 301. It measures the temperature of the battery pack 301 and supplies the measured temperature data to the control unit 310. The voltage detection unit 311 measures the voltage of the battery pack 301 and each of the secondary batteries 301a that make up the battery pack 301, A / D converts this measured voltage data, and supplies it to the control unit 310. The current measurement unit 313 measures the current using the current detection resistor 307, and supplies this measured current data to the control unit 310. The switch control unit 314 controls the charge control switch 302a and the discharge control switch 303a of the switch unit 304 based on the voltage data and current data input from the voltage detection unit 311 and the current measurement unit 313.

[0084] When the voltage of any of the multiple secondary batteries 301a falls below the overcharge detection voltage or the overdischarge detection voltage, or when a large current suddenly flows, the switch control unit 314 sends a control signal to the switch unit 304 to prevent overcharging, overdischarging, and overcurrent charging / discharging. Here, for example, if the secondary battery is a lithium-ion secondary battery, the overcharge detection voltage is set to, for example, 4.20 V±0.05 V, and the overdischarge detection voltage is set to, for example, 2.4 V±0.1 V.

[0085] The charge / discharge control switch can be a semiconductor switch such as a MOSFET. In this case, the parasitic diode of the MOSFET functions as diodes 302b and 303b. When a P-channel FET is used as the charge / discharge control switch, switch control unit 314 supplies control signals DO and CO to the gates of charge control switch 302a and discharge control switch 303a, respectively. When charge control switch 302a and discharge control switch 303a are P-channel, they are turned ON by a gate potential that is lower than the source potential by a predetermined value or more. That is, during normal charge and discharge operations, control signals CO and DO are set to a low level, and charge control switch 302a and discharge control switch 303a are turned ON.

[0086] 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.

[0087] The memory 317 is made up of RAM or ROM, such as non-volatile memory such as EPROM (Erasable Programmable Read Only Memory). Numerical values ​​calculated by the control unit 310 and the internal resistance values ​​of the secondary batteries 301a in their initial states measured during the manufacturing process are stored in advance in the memory 317, and the memory 317 can be rewritten as needed. Furthermore, by storing the full charge capacity of the secondary batteries 301a in the memory 317, the control unit 310 can calculate, for example, the remaining capacity.

[0088] 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.

[0089] [2-2. Power Storage System] The secondary battery according to the embodiment of the present disclosure described above can be mounted on devices such as electronic devices, electric vehicles, electric aircraft, and power storage devices, or can be used to supply power.

[0090] Examples of electronic devices include notebook computers, smartphones, tablet devices, PDAs as portable information terminals, 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.

[0091] Examples of electric vehicles include railcars, golf carts, electric carts, electric vehicles (including hybrid vehicles), and the like, and the device is used as a driving power source or auxiliary power source for these. Examples of power storage devices include power storage power sources for buildings such as homes, or for power generation facilities.

[0092] 3. Modifications (First Modification) Next, a description will be given of a positive electrode 21-1 (21-1A to 21-1C) as a first modification applied to the secondary battery 1 of the above embodiment. Figures 9A to 9C show cross-sectional configurations of the positive electrodes 21-1A to 21-1C, respectively, and correspond to Figure 4C showing the positive electrode 21 of the above embodiment.

[0093] As shown in FIGS. 9A to 9C , in the positive electrodes 21-1A to 21-1C as the first modified example, the positive-electrode inner-periphery-side active material layer 21B1 further includes a groove portion U1 between the thick portion 73-1 and the thin portion 61-1, and the positive-electrode outer-periphery-side active material layer 21B2 further includes a groove portion U2 between the thick portion 73-2 and the thin portion 61-2. Both groove portions U1 and U2 extend in the W 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 21-1A of Fig. 9A, the cross-sectional shape of the groove portions U1 and U2 is approximately rectangular, in the positive electrode 21-1B of Fig. 9B, the cross-sectional shape of the groove portions U1 and U2 is approximately V-shaped, and in the positive electrode 21-1C of Fig. 9C, the cross-sectional shape of the groove portions U1 and U2 is approximately U-shaped. However, the cross-sectional shapes of the groove portions U1 and U2 are not limited to the shapes shown in Figs. 9A to 9C, and can be selected arbitrarily.

[0094] In the positive electrodes 21-2A to 21-2C, the width of the groove portion U1 and the width of the groove portion U2 may be the same in the L direction, or may be different. More specifically, the width of the groove portion U1 and the width of the groove portion U2 may be equal to each other, or may be different from each other. The width of the groove portion U1 is the length in the L direction from the boundary 73U1 between the thick portion 73-1 and the groove portion U1 to the boundary 61U1 between the thin portion 61 and the groove portion U1. The width of the groove portion U2 is the length in the L direction from the boundary 73U2 between the thick portion 73-2 and the groove portion U2 to the boundary 61U2 between the thin portion 61-2 and the groove portion U2. The widths of the groove portions U1 and U2 are, for example, approximately 150 μm.

[0095] In each of the configuration examples of the positive electrodes 21-1A to 21-1C shown in Figures 9A to 9C, the L-direction positions of the boundary 73U1 and the boundary 73U2 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 73U1 and the L-direction positions of the boundary 73U2 may coincide. Alternatively, the L-direction positions of the boundary 61U1 and the L-direction positions of the boundary 61U2 may coincide.

[0096] In each of the configuration examples of the positive electrodes 21-1A to 21-1C shown in FIGS. 9A to 9C, 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 it is also possible for only one of the groove portion U1 and the groove portion U2 to be included.

[0097] In this way, the positive electrodes 21-1A to 21-1C as the first 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 electrodes 21-1A to 21-1C and the negative electrode 22. This is because, 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 electrodes 21-1A to 21-1C 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 21-1A to 21-1C, short-circuiting between the positive electrodes 21-1A to 21-1C and the negative electrode 22 can be effectively prevented, and superior reliability can be achieved.

[0098] (Second Modification) Next, with reference to Figures 10A and 10B, a positive electrode 21-2 as a second modification applied to the secondary battery 1 of the above embodiment will be described. Figure 10A is an exploded view of the positive electrode 21-2 and corresponds to Figure 4A, which shows the positive electrode 21 of the above embodiment. Figure 10B is an exploded view of the positive electrode 21-2 and corresponds to Figure 4C, which shows the positive electrode 21 of the above embodiment. Note that Figure 10B shows a cross section taken along line XB-XB in Figure 10A as viewed in the direction of the arrows.

[0099] As shown in FIGS. 10A and 10B , in the positive electrode 21-2, 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 73 from the thin portion 61. The thickness of the thin portion 62 is thinner than the thickness of the thick portion 73. The thin portion 62 includes the outer peripheral winding edge 21E2 in the L direction of the positive electrode 21-2. 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 outer peripheral winding edge 21E2. 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 the 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.

[0100] In the positive electrode 21-2 as the second 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. Note that in FIG. 10B , 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 for convenience, 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 for convenience. Also, as shown in FIG. 10B , in the positive electrode 21-2, the position in the L direction of the boundary 21B1K1 between the thin portion 61-1 and the thick portion 73-1 is different from the position in the L direction of the boundary 21B2K1 between the thin portion 61-2 and the thick portion 73-2. Furthermore, in the positive electrode 21-2, the position in the L direction of a boundary 21B1K2 between the thin portion 62-1 and the thick portion 73-1 is different from the position in the L direction of a boundary 21B2K2 between the thin portion 62-2 and the thick portion 73-2.

[0101] Thus, in the positive electrode 21-2 of the second modified example, in addition to the thin portion 61, a thin portion 62 is also provided on the outer periphery of the wound electrode body 20. Therefore, the step between the portion where the positive electrode 21 is present and the portion where the positive electrode 21 is not present on the outer periphery of the wound electrode body 20 can be made smaller than 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 edge 21E2. Therefore, even when the thickness of the separator 23 is reduced, breakage of the separator 23 can be avoided, and short-circuiting between the positive electrode 21 and the negative electrode 22 can be prevented. 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 can be improved and the capacity of the secondary battery 1 can be increased.

[0102] (Third Modification) Next, with reference to FIGS. 11A and 11B, a positive electrode 21-3 and a negative electrode 22-3 as a third modification applied to the secondary battery 1 of the above embodiment will be described. FIG. 11A is an exploded view of the positive electrode 21-3, corresponding to FIG. 4A showing the positive electrode 21 of the above embodiment. FIG. 11B is an exploded view of the negative electrode 22-3, corresponding to FIG. 5A showing the negative electrode 22 of the above embodiment. In the above embodiment, the secondary battery 1 including the positive electrode 21 and the negative electrode 22 of 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 also include a positive electrode 21-3 with a tabbed structure having a positive electrode lead 28 as shown in FIG. 11A, and a negative electrode 22-3 with a tabbed structure having a negative electrode lead 27 as shown in FIG. 11B.

[0103] As shown in FIG. 11A , the positive electrode 21-3 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. 11A , 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 21-3, from the upper edge 21UT of the positive electrode 21-3 to the lower edge 21BT of the positive electrode 21-3. In addition, two positive electrode exposed regions 212 are provided at both ends of the positive electrode 21-3 in the L direction, which is the longitudinal direction. One of the two positive electrode exposed regions 212 includes the inner peripheral edge 21S of the innermost positive electrode portion 21in ( FIG. 3 ) of the positive electrode 21, and the other of the two positive electrode exposed regions 212 includes the outer peripheral edge 21E of the outermost positive electrode portion 21out ( FIG. 3 ) of the positive electrode 21. 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 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. 11A , the positive electrode lead 28 is provided in the outermost positive electrode exposed region 212 of the two positive electrode exposed regions 212, but it may also be provided in 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.

[0104] The protective tape 21C is preferably adhered to the separator 23, since this can prevent misalignment between the positive electrode 21 and the separator 23. The protective tape 21C is preferably made of a material that does not swell, since 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).

[0105] As shown in FIG. 11B , the negative electrode 22-3 includes a negative electrode current collector 22A and a negative electrode active material layer 22B. The negative electrode active material layer 22B is provided on both sides of the negative electrode current collector 22A. The negative electrode 22-3 has a negative electrode covering region 221 and a negative electrode exposed region 222. As shown in FIG. 11B , 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, from the upper edge 22UT of the negative electrode 22 to the lower edge 22BT of the negative electrode 22. In addition, two negative electrode exposed regions 222 are provided at both ends of the negative electrode 22 in the L direction, which is the longitudinal direction of the negative electrode 22. One of the two negative electrode exposed regions 222 includes the inner peripheral edge 22S of the innermost negative electrode portion 22in ( FIG. 2 ) of the negative electrode 22, and the other of the two negative electrode exposed regions 222 includes the outer peripheral edge 22E of the outermost negative electrode portion 22out ( FIG. 2 ) of the negative electrode 22. The negative electrode covering region 221 is disposed so as to be sandwiched between the two negative electrode exposed regions 222 in the L direction. That is, the negative electrode active material layer 22B is not present at both ends in the L direction, which is the longitudinal direction of the negative electrode current collector 22A. The size and position of the region of the negative electrode active material layer 22B covering the surface 22Aout may be different from or may match each other.

[0106] The negative electrode lead 27 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 27 is provided such that a part of it protrudes downward from the lower end edge 22BT of the negative electrode 22.

[0107] 12A and 12B each show a cross-sectional configuration of the positive electrode 21-3. Fig. 12A shows a cross section taken along line XIIA-XIIA in Fig. 11A. Fig. 12B shows a cross section taken along line XIIB-XIIB in Fig. 11A.

[0108] The positive electrode active material layer 21B includes a thin portion 61 and thick portions 71 to 73. In the positive electrode 21 of the present embodiment, 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. 12A and 12B, 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. 12B, the position in the L direction of the boundary 21B1K between the thin portion 61-1 and the thick portion 73-1 is different from the position in the L direction of the boundary 21B2K between the thin portion 61-2 and the thick portion 73-2.

[0109] The thin portion 61 includes the edge 21BS (inner peripheral edge) of the positive electrode active material layer 21B that is closer to the center of winding in the L direction. The thin portion 61 may extend, for example, from the inner peripheral edge 21BS in the L direction over a range of approximately one to five turns of the electrode wound body 20. The thick portion 71 is adjacent to the thin portion 61 in the W direction. More specifically, the thick portion 71 is located between the thin portion 61 and the upper edge 21UT in the W direction. The thick portion 71 includes the first edge 21BT1. The thick portion 72 is located on the opposite side of the thick portion 71 from the thin portion 61 in the W direction. That is, the thick portion 72 is located between the thin portion 61 and the lower edge 21BT, which is located opposite the upper edge 21UT in the W direction. The thick portion 72 includes the lower edge 21BT. The thick portion 73 is provided on the opposite side of the inner peripheral edge 21S in the L direction from the thin portion 61. The thick portions 71 to 73 may be separated from one another, or may be partly or entirely integrated.

[0110] In the secondary battery having the positive electrode 21-3 and the negative electrode 22-3 as the third modified example, the position of the boundary 21B1K in the L direction is different from the position of the boundary 21B2K in the L direction, so that the same effect as in the above embodiment can be expected.

[0111] An embodiment of the present disclosure will be described.

[0112] Example 1 Fabrication of Positive Electrode As will be described below, the positive electrode 21 shown in FIGS. 4A to 4D was fabricated.

[0113] First, a 10 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 the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to predetermined areas on both sides of the positive electrode current collector 21A using a coating device, and the positive electrode mixture slurry was then dried to form the positive electrode active material layer 21B. The thickness of each of the two positive electrode active material layers 21B formed on both sides of the positive electrode current collector 21A was 95 μm. 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 then 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. Furthermore, a portion of the thickness direction of the positive electrode active material layer 21B in a predetermined region was selectively removed by laser ablation to form a thin portion 61 including the winding center-side edge 21E1. The laser irradiation conditions used for laser ablation were a pulse width of 30 nsec, a frequency of 270 Hz, and an energy density of 2 J / cm, as shown in Table 1. ２The laser output was set to 200 W, the scanning speed was set to 3000 mm / sec, and the number of scans was set to one.

[0114]

[0115] The cathode 21 fabricated as described above was cut in the thickness direction (T direction) to form a cross section along the thickness direction of the cathode active material layer 21B. The cross section was observed using a scanning electron microscope (SEM) "S-4800 (Hitachi, Ltd.)," resulting in the cross-sectional image shown in FIG. 13A . The cross-sectional image in FIG. 13A confirmed the presence of cathode active material particles 81 including active portions 811 and deactivated portions 812. Furthermore, using the cross-sectional image obtained using the scanning electron microscope, elemental analysis was performed using an energy dispersive X-ray analyzer (EDX) "EMAX (Horiba, Ltd.)" to determine the abundance ratios [%] of Ni and O elements in the cathode active material layer 21B. The EDX elemental analysis was performed using point EDX, an acceleration voltage of 5 kV, a magnification of 40 K, and three repetitions. The results are shown in FIG. 13B . As shown in FIG. 13B , the oxygen concentration in the effective portion 811 was 37.29% and the nickel concentration was 61.71%, whereas the oxygen concentration in the effective portion 811 was 27.04% and the nickel concentration was 71.43%. Thus, it was confirmed that the oxygen concentration in the deactivated portion 812 of the positive electrode active material particle 81 was lower than the oxygen concentration in the effective portion 811. The thickness of the deactivated portion 812 was also determined from the cross-sectional image of FIG. 13A . The thickness of the deactivated portion 812 was calculated as the average of the measurements taken at five arbitrary points. The results are shown in Table 1.

[0116] Furthermore, the thickness of the thin portion 61 of the positive electrode active material layer 21B was determined by observing a cross section along the thickness direction of the positive electrode 21 fabricated as described above. The thickness of the thin portion 61 was determined as the average value of measurements taken at five arbitrary points. The results are shown in Table 1.

[0117] [Fabrication of Negative Electrode] Furthermore, the negative electrode 22 shown in Figures 5A and 5B was fabricated as follows. Specifically, first, an 8-μm-thick copper foil was prepared as the negative electrode current collector 22A. Next, a negative electrode active material, which was a mixture of a carbon material made of graphite and SiO, a negative electrode binder made of polyvinylidene fluoride, and a conductive additive, which was a mixture of carbon black, acetylene black, and ketjen black, was mixed to obtain a negative electrode mixture. The mixing ratio of the negative electrode active material, the negative electrode binder, and the conductive additive was 96.1:2.9:1.0. Furthermore, the mixing ratio of graphite to SiO in the negative electrode active material was 95:5. Next, the negative electrode mixture was introduced into an organic solvent (N-methyl-2-pyrrolidone), and the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. Next, a coating device was used to apply the anode mixture slurry to predetermined regions on both sides of the anode current collector 22A, and the anode mixture slurry was then dried to form the anode active material layer 22B. The anode active material layer 22B was then compression-molded using a roll press. This resulted in a anode 22 having a anode covering region 221 and a anode exposed region 222. The anode 22 was then sheared to set the width of the anode covering region 221 in the W direction to 62 mm, and the width of the first portion 222A of the anode exposed region 222 in the W direction to 4 mm. The length of the anode 22 in the L direction was 1760 mm. Each of the two anode active material layers 22B formed on both sides of the anode current collector 22A had a thickness of 80 μm.

[0118] [Fabrication of Secondary Battery] The secondary battery 1 shown in FIG. 1 was fabricated using the positive electrode 21 and negative electrode 22 fabricated as described above. First, the positive electrode 21 and negative electrode 22 were dried. Subsequently, the positive electrode 21 and negative electrode 22 were stacked with the first separator member 23A and the second separator member 23B interposed therebetween so that the positive electrode exposed region 212 and the first portion 222A of the negative electrode exposed region 222 were opposite each other in the W direction, thereby fabricating a laminate S20. The laminate S20 was fabricated so that the positive electrode active material layer 21B did not protrude from the negative electrode active material layer 22B in the W direction. Polyethylene sheets having a width of 65 mm and a thickness of 5 μm were used as the first separator member 23A and the second separator member 23B. The laminate S20 was then spirally wound to form through-holes 26, and a fixing tape 46 was attached to the outermost periphery of the wound laminate S20.

[0119] Next, the edges of a 0.5 mm thick flat plate were pressed against the upper end face 41 and the lower end face 42 of the electrode winding body 20 in the Z-axis direction, thereby locally bending the upper end face 41 and the lower end face 42, and creating grooves 43 extending radially from the through hole 26 in the radial direction (R direction).

[0120] Next, substantially the same pressure was applied from above and below the electrode winding body 20 in a direction substantially perpendicular to the upper end surface 41 and the lower end surface 42 at substantially the same time. This caused the positive electrode exposed region 212 and the first portion 222A of the negative electrode exposed region 222 to bend, respectively, to form flat surfaces on the upper end surface 41 and the lower end surface 42. At this time, the positive electrode edge portion 212E of the positive electrode exposed region 212 and the negative electrode edge portion 222E of the negative electrode exposed region 222 at the upper end surface 41 and the lower end surface 42 were folded while overlapping toward the through-holes 26. Thereafter, the sector-shaped portion 31 of the positive electrode current collector 24 was joined to the upper end surface 41 by laser welding, and the sector-shaped portion 33 of the negative electrode current collector 25 was joined to the lower end surface 42 by laser welding. The positive electrode current collector 24 used had a sector-shaped portion 31 with an opening 35 having an inner diameter D35 of 4.0 mm.

[0121] Next, insulating tapes 53, 54 were attached to predetermined positions of the electrode winding body 20, and then the belt-shaped portion 32 of the positive current collector plate 24 was bent to insert the belt-shaped portion 32 into the hole 12H of the insulating plate 12, and the belt-shaped portion 34 of the negative current collector plate 25 was bent to insert the belt-shaped portion 34 into the hole 13H of the insulating plate 13. At this time, the belt-shaped portion 34 was bent while holding the flat region 34B of the belt-shaped portion 34, not the protruding region 34A, with a predetermined jig.

[0122] Next, the electrode winding body 20 assembled as described above was inserted into the outer can 11, and then the bottom 11B of the outer can 11 was welded to the negative electrode current collector plate 25. The inner diameter D11 of the outer can 11 used was 20.80±0.05 mm.

[0123] Thereafter, a constricted portion 11S was formed near the open end 11N of the outer can 11. Furthermore, after the electrolyte was poured into the outer can 11, the strip portion 32 of the positive electrode current collector plate 24 and the safety valve mechanism 30 were welded together.

[0124] The electrolyte used was a solvent containing ethylene carbonate (EC) and dimethyl carbonate (DMC) as the main solvent, to which fluoroethylene carbonate (FEC) and succinonitrile (SN) were added, and LiBF4 and LiPF6 were used as electrolyte salts. In the lithium-ion secondary battery of this example, the respective contents (by weight) of EC, DMC, FEC, SN, LiBF4, and LiPF6 in the electrolyte were 12.7:56.2:12.0:1.0:1.0:17.1.

[0125] Thereafter, the gasket 15, the safety valve mechanism 30, and the battery lid 14 were used to seal the battery lid 14. Finally, the exterior can 11 with the washer 55 attached to the battery lid 14 was covered with the exterior tube 50, and the exterior tube 50 was heated and shrunk by applying hot air to the exterior tube 50, for example, and the exterior tube 50 was tightly attached to the outer surface of the exterior can 11.

[0126] In this manner, the secondary battery 1 of Example 1 was obtained.

[0127] (Example 2) The laser irradiation conditions for forming the thinned portion 61 by laser ablation were as shown in Table 1, with a pulse width of 50 nsec, a frequency of 160 Hz, and an energy density of 3.5 J / cm ２ Except for this, secondary battery 1 of Example 2 was fabricated in the same manner as in Example 1. The thickness of deactivated portion 812 and the thickness of thin portion 61 in the obtained positive electrode 21 are as shown in Table 1.

[0128] (Example 3) The laser irradiation conditions for forming the thinned portion 61 by laser ablation were as shown in Table 1, with a pulse width of 80 nsec, a frequency of 100 Hz, and an energy density of 5.3 J / cm ２ Except for this, secondary battery 1 of Example 2 was fabricated in the same manner as in Example 1. The thickness of deactivated portion 812 and the thickness of thin portion 61 in the obtained positive electrode 21 are as shown in Table 1.

[0129] (Example 4) The laser irradiation conditions for forming the thinned portion 61 by laser ablation were as shown in Table 1, with a pulse width of 200 nsec, a frequency of 40 Hz, and an energy density of 13.3 J / cm ２ Except for this, secondary battery 1 of Example 2 was fabricated in the same manner as in Example 1. The thickness of deactivated portion 812 and the thickness of thin portion 61 in the obtained positive electrode 21 are as shown in Table 1.

[0130] (Example 5) The laser irradiation conditions for forming the thinned portion 61 by laser ablation were as shown in Table 1, with a pulse width of 300 nsec, a frequency of 25 Hz, and an energy density of 20.0 J / cm ２ Except for this, secondary battery 1 of Example 2 was fabricated in the same manner as in Example 1. The thickness of deactivated portion 812 and the thickness of thin portion 61 in the obtained positive electrode 21 are as shown in Table 1.

[0131] (Example 6) The laser irradiation conditions for forming the thinned portion 61 by laser ablation were as shown in Table 1, with a pulse width of 500 nsec, a frequency of 16 Hz, and an energy density of 35.0 J / cm ２Except for this, secondary battery 1 of Example 2 was fabricated in the same manner as in Example 1. The thickness of deactivated portion 812 and the thickness of thin portion 61 in the obtained positive electrode 21 are as shown in Table 1.

[0132] (Comparative Example 1) A secondary battery of Comparative Example 1 was fabricated in the same manner as in Example 1, except that no thin portions were formed by laser ablation, and only thick portions were used as the positive electrode. No deactivated portions were present in the obtained positive electrode, and the thickness of the thick portions was as shown in Table 1.

[0133] Comparative Example 2 The laser irradiation conditions for forming the thinned portion 61 by laser ablation were as shown in Table 1, with a pulse width of 800 nsec, a frequency of 10 Hz, and an energy density of 55.0 J / cm ２ Except for this, secondary battery 1 of Example 2 was fabricated in the same manner as in Example 1. The thickness of deactivated portion 812 and the thickness of thin portion 61 in the obtained positive electrode 21 are as shown in Table 1.

[0134] [Evaluation of Battery Characteristics] A charge-discharge cycle test was performed on each of the secondary batteries 1 of Examples 1 to 7 obtained as described above, and the incidence of short circuits after the charge-discharge cycle test was examined. In addition, each secondary battery 1 after the charge-discharge cycle test was disassembled, the negative electrode 22 was removed, and the expansion rate of the negative electrode 22 and the amount of Ni precipitation were measured. The results are also shown in Table 1.

[0135] The test conditions for the charge-discharge cycle test were as follows.

[0136] ((Cycle test conditions)) (1) Environmental temperature: 23°C. (2) Charging conditions: Constant current constant voltage (CC-CV) charging was performed. After charging at a constant current of 5 A to a voltage of 4.2 V or 4.3 V, charging was performed at a constant voltage of 4.2 V or 4.3 V. The cut-off current was 100 mA. (3) Rest time after charging: 60 minutes. (4) Discharge conditions: Constant current (CC) discharge was performed at a constant current of 30 A. The cut-off voltage was 2.5 V. Alternatively, discharging was stopped when the temperature reached 85°C. (5): (2) to (4) constitute one cycle, and the cycle was repeated until the capacity was 50% or less of the initial discharge capacity.

[0137] ((Rate of occurrence of short circuit after charge / discharge cycle)) After carrying out the cycle test under the above test conditions, the battery was stored for one week in an environment of 25±5°C, and it was determined that a short circuit had occurred if the charge voltage was less than 4.1 V. The rate of occurrence of short circuit was measured when the charge voltage was set to 4.2 V and when the charge voltage was set to 4.3 V. The number of samples was 50 for each case.

[0138] The amount of precipitated Ni was determined using an ICP (Inductively Coupled Plasma) mass spectrometer.

[0139] As shown in Table 1, when charging was performed at a normal charging voltage of 4.2 V (hereinafter referred to as 4.2 V charging), no short circuits occurred after charge-discharge cycles in any of Examples 1 to 6. On the other hand, in Comparative Example 2, the short circuit occurrence rate after charge-discharge cycles when charging at 4.2 V was 10%. The reason for this is thought to be that in Comparative Example 2, the thickness of deactivated portion 812 was 6.1 μm, and therefore a large amount of Ni element precipitated on the surface of negative electrode 22, making short circuits more likely to occur due to Ni element eluted from positive electrode active material layer 21B.

[0140] In contrast, when charging was performed at an overcharge voltage of 4.3 V (hereinafter referred to as 4.3 V charging), no short circuits occurred after charge-discharge cycles in Examples 2 to 4, but some samples in Examples 1, 5, and 6 experienced short circuits after charge-discharge cycles. The reason for the short circuit in Example 1 is thought to be that the thickness of the deactivated portion 812 in Example 1 was as thin as 0.4 μm, which weakened the effect of inhibiting the migration of lithium ions, an electrode reactant, from the thin portion 61 to the negative electrode active material layer 22B compared to Examples 2 to 4. The reason for the short circuit in Examples 5 and 6 is thought to be that a larger amount of Ni element precipitated on the surface of the negative electrode 22 in Examples 5 and 6 compared to Examples 2 to 4, making short circuits more likely to occur due to Ni element eluted from the positive electrode active material layer 21B. However, the short circuit occurrence rate after charge-discharge cycles at 4.3 V charging in Examples 1 to 6 was lower than the short circuit occurrence rate after charge-discharge cycles at 4.3 V charging in Comparative Examples 1 and 2. From the above results, it was found that by providing a thin portion in the positive electrode active material layer and forming a deactivated portion of a predetermined thickness in that thin portion, the incidence of short circuits after charge-discharge cycling can be reduced both when charging to 4.2 V and when charging to 4.3 V.

[0141] The present disclosure has been described above with reference to one embodiment and several modified examples. However, the configuration of the present disclosure is not limited to the configuration described in the above embodiment and several modified examples and can be modified in various ways. For example, in the above embodiment, the thin portion 61 as the first thin portion is provided at a position contacting the winding center side edge 21E1 of the positive electrode 21, but the present disclosure is not limited to this. The first thin portion (thin portion 61) may be provided at a location of the positive electrode 21 away from the winding center side edge 21E1. Similarly, the thin portion 62 as the second thin portion is not limited to being provided at a position contacting the winding outer peripheral side edge 21E2 of the positive electrode 21. The second thin portion (thin portion 62) may be provided at a location of the positive electrode 21 away from the winding outer peripheral side edge 21E2.

[0142] In the secondary battery of the above embodiment, the position of the first boundary of the first positive electrode active material layer and the position of the second boundary of the second positive electrode active material layer are different in the longitudinal direction of the electrode winding body, but the present disclosure is not limited to this. In the secondary battery of the present disclosure, the position of the first boundary and the position of the second boundary may be substantially the same.

[0143] In the secondary battery of the above embodiment, a positive electrode active material layer is provided on each side of the positive electrode current collector, but in the present disclosure, a positive electrode active material layer may be provided on only one side of the positive electrode current collector.Similarly, in the present disclosure, a negative electrode active material layer may be provided on only one side of the negative electrode current collector.

[0144] Furthermore, the secondary battery of the present disclosure is not limited to the secondary battery of FIG. 1 described in the above embodiment. The secondary battery of the present disclosure may be, for example, the secondary battery shown in FIG. 14 . In the secondary battery shown in FIG. 14 , for example, a pair of insulating plates 12, 13 and an electrode winding 20 are housed inside a cylindrical outer can 11. The electrode winding 20 is sandwiched between the insulating plates 12 and 13 in the Z direction. A safety valve mechanism 30 is attached to the outer can 11. The outer can 11 is sealed by, for example, a battery lid 14. However, this secondary battery may further include a thermosensitive resistor (PTC) element, a reinforcing member, and the like inside the outer can 11. The safety valve mechanism 30 is provided inside the battery lid 14 in the Z direction. The safety valve mechanism 30 is a mechanism that releases the internal pressure of the outer can 11 by releasing the sealed state of the outer can 11 as necessary when the internal pressure of the outer can 11 increases. The internal pressure of the exterior can 11 increases due to gas generated by the decomposition reaction of the electrolyte during charging and discharging.

[0145] 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.

[0146] 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.

[0147] The present disclosure may take the following forms. <1> A secondary battery comprising: an electrode winding body formed by winding a laminate including a positive electrode, a negative electrode, and a separator along the longitudinal direction of the laminate and having through holes penetrating in a width direction perpendicular to the longitudinal direction; and an outer can housing the electrode winding body, wherein the positive electrode has: a positive electrode current collector extending in both the longitudinal direction and the width direction; and a positive electrode active material layer provided on the positive electrode current collector and including a thin portion and a thick portion having a thickness greater than that of the thin portion, wherein positive electrode active material particles including at least a deactivated portion are present on a surface of the thin portion opposite the positive electrode current collector, and the deactivated portion has a thickness of less than 6.1 μm. <2> The secondary battery according to <1> above, wherein the oxygen mass concentration of the deactivated portion is lower than the oxygen mass concentration of an effective portion of the positive electrode active material particles other than the deactivated portion. <3> The secondary battery according to <1> or <2> above, wherein the deactivated portion is present discretely on the surface of the thin portion. <4> The secondary battery according to any one of <1> to <3> above, wherein the thin portion and the thick portion are adjacent to each other in the width direction. <5> The secondary battery according to any one of <1> to <4> above, wherein the thin portion includes an edge of the positive electrode closer to the center of winding in the longitudinal direction. <6> The secondary battery according to any one of <1> to <5> above, wherein the positive electrode further has an insulating layer, wherein the positive electrode current collector includes a positive electrode covered region covered with the positive electrode active material layer and a positive electrode exposed region extending from the positive electrode active material layer in the width direction, and wherein the insulating layer extends in the longitudinal direction along a first edge of the positive electrode active material layer located at a boundary between the positive electrode covered region and the positive electrode exposed region. <7> The secondary battery according to any one of <1> to <3> above, wherein the thin portion and the thick portion are adjacent to each other in the longitudinal direction. <8> The secondary battery according to any one of <1> to <7> above, wherein the positive electrode current collector includes an inner peripheral surface of the positive electrode current collector facing a 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, and the thick portion and the thin portion are formed on both the inner peripheral surface of the positive electrode current collector and the outer peripheral surface of the positive electrode current collector.<9> The positive electrode current collector includes an inner peripheral surface of the positive electrode current collector facing the winding center side of the electrode winding body and an outer peripheral surface of the positive electrode current collector facing outward, opposite to the winding center side of the electrode winding body, and the positive electrode active material layer has a first positive electrode active material layer provided on the inner peripheral surface of the positive electrode current collector and a second positive electrode active material layer provided on the outer peripheral surface of the positive electrode current collector, and the first positive electrode active material layer and the second positive electrode active material layer each include the thin portion and the thick portion, and a first length from an edge of the positive electrode closer to the winding center in the longitudinal direction to a first boundary position between the thin portion of the first positive electrode active material layer and the thick portion of the first positive electrode active material layer is different from a second length from an edge of the positive electrode closer to the winding center in the longitudinal direction to a second boundary position between the thin portion of the second positive electrode active material layer and the thick portion of the second positive electrode active material layer. The secondary battery according to the above <7>. <10> The secondary battery according to the above <7>. <11> A battery pack comprising: the secondary battery according to any one of the above <1> to <10>; a control unit that controls the secondary battery; and an exterior body that encapsulates the secondary battery.

Claims

1. A secondary battery comprising: 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; and an exterior can housing the electrode winding body, wherein the positive electrode has: a positive electrode current collector extending in both the longitudinal direction and the width direction; and a positive electrode active material layer provided on the positive electrode current collector and including a thin portion and a thick portion having a thickness greater than that of the thin portion, wherein positive electrode active material particles including at least a deactivated portion are present on a surface of the thin portion opposite the positive electrode current collector, and the thickness of the deactivated portion is less than 6.1 μm.

2. The secondary battery according to claim 1, wherein the oxygen mass concentration in the deactivated portion is lower than the oxygen mass concentration in an effective portion of the positive electrode active material particle other than the deactivated portion.

3. The secondary battery according to claim 1 or 2, wherein the deactivated portion is present discretely on the surface of the thin portion.

4. A secondary battery according to any one of claims 1 to 3, wherein the thin portion and the thick portion are adjacent to each other in the width direction.

5. The secondary battery according to any one of claims 1 to 4, wherein the thin portion includes an end edge of the positive electrode on the side closer to the center of winding in the longitudinal direction.

6. The secondary battery according to any one of claims 1 to 5, wherein the positive electrode further has an insulating layer, the positive electrode current collector includes a positive electrode covered region covered with the positive electrode active material layer and a positive electrode exposed region extending in the width direction from the positive electrode active material layer, and the insulating layer extends in the longitudinal direction along a first edge of the positive electrode active material layer located at the boundary between the positive electrode covered region and the positive electrode exposed region.

7. A secondary battery according to any one of claims 1 to 3, wherein the thin portion and the thick portion are adjacent to each other in the longitudinal direction.

8. The secondary battery according to any one of claims 1 to 7, wherein 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 outwardly opposite the winding center of the electrode winding body, and the thick portion and the thin portion are each formed on both the inner peripheral surface of the positive electrode current collector and the outer peripheral surface of the positive electrode current collector.

9. The positive electrode current collector includes an inner peripheral surface of the positive electrode current collector facing the winding center side of the electrode winding body, and an outer peripheral surface of the positive electrode current collector facing the outside opposite to the winding center side of the electrode winding body, the positive electrode active material layer has a first positive electrode active material layer provided on the inner peripheral surface of the positive electrode current collector, and a second positive electrode active material layer provided on the 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 thin portion and the thick portion, and a first length from an end edge of the positive electrode on the winding center side in the longitudinal direction to a first boundary position between the thin portion of the first positive electrode active material layer and the thick portion of the first positive electrode active material layer is different from a second length from an end edge of the positive electrode on the winding center side in the longitudinal direction to a second boundary position between the thin portion of the second positive electrode active material layer and the thick portion of the second positive electrode active material layer. The secondary battery according to claim 7.

10. The secondary battery according to claim 7, wherein the positive electrode active material layer further includes a groove portion between the thick portion and the thin portion.

11. A battery pack comprising: a secondary battery according to any one of claims 1 to 10; a control unit for controlling the secondary battery; and an exterior body for enclosing the secondary battery.

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