WO2024070819A1

WO2024070819A1 - Secondary battery positive electrode, secondary battery, and battery pack

Info

Publication number: WO2024070819A1
Application number: PCT/JP2023/033949
Authority: WO
Inventors: 彩松塚
Original assignee: 株式会社村田製作所
Priority date: 2022-09-29
Filing date: 2023-09-19
Publication date: 2024-04-04

Abstract

Provided is a secondary battery that has better performance. This secondary battery positive electrode includes: a positive electrode coating part in which a positive electrode active material layer is coated on a positive electrode current collector; a positive electrode current collector exposed part that is adjacent to the positive electrode coating part in a first direction and in which the positive electrode current collector is exposed without being covered by the positive electrode active material layer; and an insulating film covering both a portion of the positive electrode coating part and a portion of the positive electrode current collector exposed part over a boundary between the positive electrode coating part and the positive electrode current collector exposed part. The positive electrode active material layer includes a thickness decreasing portion where the thickness decreases approaching the boundary in the first direction, and a section of the thickness decreasing portion is covered by the insulating film.

Description

Positive electrodes for secondary batteries, secondary batteries, battery packs

This disclosure relates to a positive electrode for a secondary battery, and a secondary battery and a battery pack including the same.

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

Patent Document 1 proposes a secondary battery that addresses the problem of metal elements eluting due to a localized increase in potential during charging caused by the formation of thin layer regions at the ends of a mixture layer formed on a metal foil by giving the ends of the mixture layer a specific cross-sectional shape.

JP 2014-154363 A

As such, various studies are being conducted to improve the performance of secondary batteries. However, there is still room for improvement in the performance of secondary batteries.

Therefore, secondary batteries with better performance are desired.

The positive electrode for secondary batteries, secondary batteries, and battery packs of one embodiment of the present disclosure include a positive electrode covering portion in which a positive electrode collector is covered with a positive electrode active material layer, a positive electrode collector exposed portion in which the positive electrode collector is exposed without being covered by the positive electrode active material layer and adjacent to the positive electrode covering portion in the first direction, and an insulating film that straddles the boundary between the positive electrode covering portion and the positive electrode collector exposed portion and covers both a portion of the positive electrode covering portion and a portion of the positive electrode collector exposed portion. Here, the positive electrode active material layer includes a thickness reducing portion whose thickness decreases as it approaches the boundary in the first direction, and a portion of the thickness reducing portion is covered by the insulating film.

In one embodiment of the present disclosure, the positive electrode for a secondary battery, the secondary battery, and the battery pack have an insulating film that straddles the boundary between the positive electrode coating portion and the exposed portion of the positive electrode current collector and covers both a part of the positive electrode coating portion and a part of the exposed portion of the positive electrode current collector. Here, the positive electrode active material layer includes a thickness reduction portion whose thickness decreases as it approaches the boundary in the first direction, and a part of the thickness reduction portion is covered by the insulating film. This effectively suppresses the elution of metal ions contained in the positive electrode active material layer in the positive electrode coating portion. This makes it possible to obtain higher reliability.

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

FIG. 1 is a cross-sectional view illustrating a configuration of a secondary battery according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram showing an example of the configuration of a laminate including the positive electrode, the negative electrode, and the separator shown in FIG. FIG. 3 is a cross-sectional view showing one example of the cross-sectional structure of the electrode winding body shown in FIG. FIG. 4A is a development view of the positive electrode shown in FIG. FIG. 4B is a cross-sectional view of the positive electrode shown in FIG. FIG. 5A is a development view of the negative electrode shown in FIG. FIG. 5B is a cross-sectional view of the negative electrode shown in FIG. FIG. 6 is an explanatory diagram for explaining how to determine the covering length of the insulating film shown in FIG. 4B. FIG. 7A is a plan view of the positive electrode current collector plate shown in FIG. FIG. 7B is a plan view of the negative electrode current collector plate shown in FIG. FIG. 8 is a perspective view illustrating a manufacturing process of the secondary battery shown in FIG. FIG. 9 is a block diagram showing a circuit configuration of a battery pack to which the secondary battery according to one embodiment of the present disclosure is applied.

Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. The description will be given in the following order.

1. Secondary battery 1-1. Configuration 1-2. Operation 1-3. Manufacturing method 1-4. Actions and effects

2. Application examples 2-1. Battery pack 2-2. Energy storage system

<1. Secondary battery>
First, a secondary battery having a positive electrode according to an embodiment of the present disclosure will be described.

In this embodiment, a cylindrical lithium ion secondary battery having a cylindrical exterior shape will be described as an example. However, the secondary battery disclosed herein is not limited to a cylindrical lithium ion secondary battery, and may be a lithium ion secondary battery having an exterior shape other than cylindrical, or may be a battery using an electrode reactant other than lithium.

The principle of charging and discharging a secondary battery is not particularly limited, but below, a case will be described in which battery capacity is obtained by utilizing the absorption and release of electrode reactants. This secondary battery has a positive electrode, a negative electrode, and an electrolyte. In this secondary battery, in order to prevent the electrode reactants from depositing on the surface of the negative electrode during charging, the charge capacity of the negative electrode is larger than the discharge capacity of the positive electrode. 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.

As mentioned above, the type of electrode reactant is not particularly limited, but specifically, it is a light metal such as an alkali metal or an alkaline earth metal. Alkaline metals include lithium, sodium, and potassium, while alkaline earth metals include beryllium, magnesium, and calcium.

Below, we will use an example where the electrode reactant is lithium. A secondary battery that obtains battery capacity by utilizing the absorption and release of lithium is known as a lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is absorbed and released in an ionic state.

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

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, for example, a structure in which 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 electrolyte 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.

(Outer can 11)
The outer can 11 has a hollow cylindrical structure with a closed lower end and an open upper end in the Z-axis direction, which is the height direction. Therefore, the upper end of the outer can 11 is an open end 11N. The material of the outer can 11 includes, for example, a metal material such as iron. However, the surface of the outer can 11 may be plated with a metal material such as nickel. The insulating plate 12 and the insulating plate 13 are disposed, for example, facing each other in the Z-axis direction with the electrode winding body 20 sandwiched therebetween. In this specification, in the Z-axis direction, the open end 11N and its vicinity are sometimes referred to as the upper part of the secondary battery 1, and the part where the outer can 11 is closed and its vicinity are sometimes referred to as the lower part of the secondary battery 1.

(Insulating plates 12, 13)
Each of the insulating

plates

12 and 13 is, for example, a dish-shaped plate having a surface perpendicular to the central axis CL of the electrode winding body 20, i.e., a surface perpendicular to the Z-axis in Fig. 1. The insulating

plates

12 and 13 are arranged so as to sandwich the electrode winding body 20 therebetween.

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

(Battery cover 14)
The battery lid 14 is a closing member that mainly closes the open end 11N when the electrode winding body 20 and the like are housed inside the exterior can 11. The battery lid 14 contains, for example, the same material as the material from which the exterior can 11 is formed. The 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.

(Gasket 15)
The gasket 15 is a sealing member that is mainly interposed between the folded portion 11P of the outer can 11 and the battery lid 14. The gasket 15 seals the gap between the folded portion 11P and the battery lid 14. However, the surface of the gasket 15 may be coated with, for example, asphalt. The gasket 15 contains, for example, one or more types of insulating materials. The type of insulating material is not particularly limited, but may be, for example, a polymer material such as polybutylene terephthalate (PBT) and polypropylene (PP). Among them, the insulating material is preferably polybutylene terephthalate. 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.

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

(Electrode winding body 20)
The electrode winding body 20 is a power generating element that causes charge/discharge reactions to proceed, and is housed inside the exterior 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.

Figure 2 is an exploded view of the electrode winding 20, and is a schematic representation of a portion of the laminate S20 including the positive electrode 21, the negative electrode 22, and the separator 23. Figure 2 particularly shows the vicinity of the end of the innermost circumferential portion of the electrode winding 20. In the laminate S20 obtained by expanding the electrode winding 20, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with the separator 23 interposed therebetween. The separator 23 has, for example, two base materials, i.e., a first separator member 23A and a second separator member 23B. Thus, the electrode winding 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 order. The positive electrode 21, the first separator member 23A, the negative electrode 22, and the second separator member 23B are all substantially strip-shaped members with the W-axis direction as the short side direction and the L-axis direction as the long side direction. As shown in FIG. 3, the electrode winding body 20 is formed by winding the laminate S20 around a central axis CL (see FIG. 1) extending in the Z-axis direction so as to form a spiral shape in a horizontal cross section perpendicular to the Z-axis direction. At this time, the laminate S20 is wound in a position in which the W-axis direction is approximately aligned with the Z-axis direction. Note that FIG. 3 shows an example of a configuration along a horizontal cross section perpendicular to the Z-axis direction in the electrode winding body 20. However, in FIG. 3, the separator 23 is omitted from the illustration in order to improve visibility. The electrode winding body 20 has a substantially cylindrical appearance as a whole. The positive electrode 21 and the negative electrode 22 are wound while maintaining a state in which they face each other via the separator 23. A through hole 26 is formed as an internal space in the center of the electrode winding body 20. The through hole 26 is a hole for inserting the winding core for assembling the electrode winding body 20 and the electrode rod for welding.

The positive electrode 21, the negative electrode 22, and the separator 23 are wound so that the separator 23 is disposed at the outermost circumference of the electrode winding body 20 and the innermost circumference of the electrode winding body 20. In addition, the negative electrode 22 is disposed outside the positive electrode 21 at the outermost circumference of the electrode winding body 20. That is, as shown in FIG. 3, the positive electrode outermost portion 21out located at the outermost circumference of the positive electrode 21 included in the electrode winding body 20 is disposed inside the negative electrode outermost portion 22out located at the outermost circumference of the negative electrode 22 included in the electrode winding body 20. Here, the positive electrode outermost portion 21out is the outermost portion of the positive electrode 21 in the electrode winding body 20 for one revolution. The negative electrode outermost portion 22out is the outermost portion of the negative electrode 22 in the electrode winding body 20 for one revolution. On the other hand, the negative electrode 22 is disposed inside the positive electrode 21 at the innermost circumference of the electrode winding body 20. That is, as shown in FIG. 3, the negative electrode innermost portion 22in located at the innermost circumference of the negative electrode 22 included in the electrode winding body 20 is located inside the positive electrode innermost portion 21in located at the innermost circumference of the positive electrode 21 included in the electrode winding body 20. Here, the positive electrode innermost portion 21in is the innermost portion of the positive electrode 21 in the electrode winding body 20. The negative electrode innermost portion 22in is the innermost portion of the negative electrode 22 in the electrode winding body 20. The number of turns of each of the positive electrode 21, the negative electrode 22, and the separator 23 is not particularly limited and can be set arbitrarily.

FIG. 4A is an exploded view of the positive electrode 21, and is a schematic representation of the state before being wound. FIG. 4B shows the cross-sectional configuration of the positive electrode 21. Note that FIG. 4B shows a cross section taken along line IVB-IVB shown in FIG. 4A. The positive electrode 21 includes, for example, a positive electrode collector 21A and a positive electrode active material layer 21B provided on the positive electrode collector 21A. The positive electrode active material layer 21B may be provided on only one side of the positive electrode collector 21A, or on both sides of the positive electrode collector 21A. FIG. 4B shows the case where the positive electrode active material layer 21B is provided on both sides of the positive electrode collector 21A. More specifically, the positive electrode current collector 21A includes a positive electrode current collector inner peripheral surface 21A1 facing the winding center side of the electrode winding body 20, i.e., the central axis CL, and a positive electrode current collector outer peripheral surface 21A2 facing the opposite side to the winding center side of the electrode winding body 20, i.e., the opposite side of the positive electrode current collector inner peripheral surface 21A1. The positive electrode 21 has, as the positive electrode active material layer 21B, a positive electrode inner peripheral side active material layer 21B1 covering at least a part 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 part of the positive electrode current collector outer peripheral surface 21A2. In this specification, the positive electrode inner peripheral side active material layer 21B1 may be simply referred to as the positive electrode active material layer 21B1, and the positive electrode outer peripheral side active material layer 21B2 may be simply referred to as the positive electrode active material layer 21B2. Furthermore, in this specification, the positive electrode inner periphery side active material layer 21B1 and the positive electrode outer periphery side active material layer 21B2 may not be distinguished from each other and may be collectively referred to as the positive electrode active material layer 21B.

The positive electrode 21 has a positive electrode covering portion 211 in which the positive electrode collector 21A is covered with the positive electrode active material layer 21B, and a positive electrode collector exposed portion 212 in which the positive electrode collector 21A is exposed without being covered with the positive electrode active material layer 21B. As shown in FIG. 4A, the positive electrode covering portion 211 and the positive electrode collector exposed portion 212 each extend along the L-axis direction, which is the longitudinal direction of the positive electrode 21, from the inner peripheral edge 21E1 of the electrode winding body 20 to the outer peripheral edge 21E2 of the electrode winding body 20. Here, the L-axis direction corresponds to the winding direction of the electrode winding body 20. That is, in the positive electrode 21, the positive electrode collector 21A is covered with the positive electrode active material layer 21B from the inner peripheral edge 21E1 of the positive electrode 21 to the outer peripheral edge 21E2 of the positive electrode 21 in the winding direction of the electrode winding body 20. The positive electrode covering portion 211 and the positive electrode current collector exposed portion 212 are adjacent to each other in the W-axis direction, which is the short side direction of the positive electrode 21. The W-axis direction substantially coincides with the central axis CL. Also, as shown in FIG. 2, in the electrode winding body 20, the inner peripheral edge 21E1 of the innermost peripheral portion 21in of the positive electrode is located in a position recessed inward from the inner peripheral edge 22E1 of the innermost peripheral portion 22in of the negative electrode.

The first edge 212E of the positive electrode collector exposed portion 212 is connected to the positive electrode collector plate 24 as shown in FIG. 1. An insulating film 101 may be provided near the boundary between the positive electrode covering portion 211 and the positive electrode collector exposed portion 212. The insulating film 101 may extend from the inner peripheral edge 21E1 to the outer peripheral edge 21E2 of the electrode winding body 20, similar to the positive electrode covering portion 211 and the positive electrode collector exposed portion 212. The insulating film 101 may be bonded to at least one of the first separator member 23A and the second separator member 23B. This is because it is possible to prevent misalignment between the positive electrode 21 and the separator 23. The insulating film 101 may include a resin containing polyvinylidene fluoride (PVDF). This is because the insulating film 101 contains PVDF, and the insulating film 101 swells due to, for example, a solvent contained in the electrolyte solution, and can be well adhered to the separator 23. The detailed configuration of the positive electrode 21 will be described later.

FIG. 5A is an exploded view of the negative electrode 22, and is a schematic representation of the state before being wound. FIG. 5B shows the cross-sectional configuration of the negative electrode 22. Note that FIG. 5B shows a cross section taken along line VB-VB shown in FIG. 5A. The negative electrode 22 includes, for example, a negative electrode collector 22A and a negative electrode active material layer 22B provided on the negative electrode collector 22A. The negative electrode active material layer 22B may be provided on only one side of the negative electrode collector 22A, or on both sides of the negative electrode collector 22A. FIG. 5B shows the case where the negative electrode active material layer 22B is provided on both sides of the negative electrode collector 22A. More specifically, the negative electrode current collector 22A includes a negative electrode current collector inner peripheral surface 22A1 facing the winding center side of the electrode winding body 20, i.e., the central axis CL, and a negative electrode current collector outer peripheral surface 22A2 facing the opposite side of the winding center side of the electrode winding body 20, i.e., 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 part 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 part of the negative electrode current collector outer peripheral surface 22A2. 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.

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

In the laminate S20 of the electrode winding body 20, the positive electrode 21 and the negative electrode 22 are laminated via the separator 23 so that the positive electrode collector exposed portion 212 and the first portion 222A of the negative electrode exposed portion 222 are oriented in opposite directions along the W-axis direction, which is the width direction. The end of the separator 23 of the electrode winding body 20 is fixed by attaching a fixing tape 46 to the side portion 45, so that the winding does not become loose.

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

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

The positive electrode collector 21A is made of, for example, aluminum foil, as described later. On the other hand, the negative electrode collector 22A is made of, for example, copper foil, as described later. In this case, the positive electrode collector 21A is softer than the negative electrode collector 22A. That is, the Young's modulus of the positive electrode collector exposed portion 212 is lower than that of the negative electrode exposed portion 222. For this reason, in one embodiment, it is more preferable that the widths A to D have a relationship of A>B and C>D. In that case, when the positive electrode collector exposed portion 212 and the negative electrode exposed portion 222 are folded simultaneously from both electrode sides with the same pressure, the heights measured from the tip of the separator 23 at the folded portions may be approximately the same for the positive electrode 21 and the negative electrode 22. At this time, the multiple first edge portions 212E (FIG. 1) of the positive electrode collector exposed portion 212 are folded and overlap moderately. Therefore, the joining of the positive electrode collector exposed portion 212 and the positive electrode collector plate 24 can be easily performed. Similarly, the multiple second edges 222E (FIG. 1) of the negative electrode exposed portion 222 are folded and overlap each other to a certain extent. This allows the negative electrode exposed portion 222 and the negative electrode current collector plate 25 to be easily joined. The joining here means that they are joined together by, for example, laser welding, but the joining method is not limited to laser welding.

2, 4A, 4B, etc., the part of the positive electrode collector exposed portion 212 of the positive electrode 21 facing the negative electrode 22 across the separator 23 is covered with an insulating film 101. The insulating film 101 is made of, for example, polyvinylidene fluoride. The insulating film 101 has a width of, for example, 3 mm in the W-axis direction. It is provided so as to cover both a part of the positive electrode covering portion and a part of the positive electrode collector exposed portion 212 across the boundary K (FIGS. 4A, 4B) between the positive electrode covering portion 211 and the positive electrode collector exposed portion 212. However, the insulating film 101 covers the entire region of the positive electrode collector exposed portion 212 of the positive electrode 21 that faces the negative electrode covering portion 221 of the negative electrode 22 through the separator 23. The boundary K indicates the position of the positive electrode active material layer 21B provided on the positive electrode collector 21A that is closest to the positive electrode collector exposed portion 212. The insulating film 101 can effectively prevent an internal short circuit of the secondary battery 1, for example, when a foreign object enters between the negative electrode covering portion 221 and the positive electrode current collector exposed portion 212. In addition, when an impact is applied to the secondary battery 1, the insulating film 101 can absorb the impact and effectively prevent bending of the positive electrode current collector exposed portion 212 and short circuit between the positive electrode current collector exposed portion 212 and the negative electrode 22. Furthermore, even if a local increase in potential occurs in the positive electrode covering portion 211 near the boundary K between the positive electrode covering portion 211 and the positive electrode current collector exposed portion 212, the outflow of metal ions from the positive electrode active material layer 21B can be suppressed, and a short circuit between the positive electrode 21 and the negative electrode 22 can be suppressed.

As shown in FIG. 4B, the positive electrode active material layers 21B1, 21B2 include flat portions 21B1F, 21B2F having a substantially constant thickness, and thickness-reducing portions 21B1S, 21B2S whose thickness decreases toward the boundary K in the W-axis direction. Here, only a portion of the thickness-reducing portions 21B1S, 21B2S is covered by the insulating film 101. The flat portions 21B1F, 21B2F are not covered by the insulating film 101. If the insulating film 101 covers the flat portions 21B1F, 21B2F, the movement of lithium ions in and out of the flat portions 21B1F, 21B2F may be hindered, possibly resulting in a decrease in capacity.

Furthermore, in the positive electrode 21, the ratio of the thickness T21B of the positive electrode active material layer 21B1, 21B2 to the covering length W101 in the W-axis direction of the covering portion of the positive electrode covering portion 211 covered by the insulating film 101, i.e., the portion of the thickness-reduced portions 21B1S, 21B2S covered by the insulating film 101, is, for example, 92.5 or more. Here, the covering length W101 is, for example, more than 0 mm and 0.2 mm or less. Also, the thickness of the insulating film 101 is, for example, 0.0012 mm or more. The covering length W101 and the thickness T21B can be measured, for example, based on SEM images. In the case of the positive electrode 21 included in the completed secondary battery 1, the secondary battery 1 is disassembled and the cross section of the end of the positive electrode 21 taken out is measured based on SEM images. In this case, the covering length W101 is measured starting from the point where a virtual line perpendicular to the positive electrode collector 21A intersects with the outermost positive electrode active material particle among the positive electrode active material particles covered by the insulating film 101. As shown in FIG. 6, the measurement data is plotted and a graph is drawn with the horizontal axis representing the position in the W axis direction and the vertical axis representing the thickness of the positive electrode 21. Note that FIG. 6 is an explanatory diagram for explaining how to obtain the covering length W101. In FIG. 6, the plot included in the positive electrode collector exposed portion 212 represents the thickness of the positive electrode collector 21A of the positive electrode 21, and the plot included in the positive electrode covering portion 211 represents the overall thickness of the positive electrode 21 including the positive electrode collector 21A and the positive electrode active material layer 21B. The position P0 of the boundary K is set as the starting point SP of the covering length W101. Furthermore, an approximate straight line AL is calculated based on the three values of the positions in the thickness direction of the positive electrode 21 measured at positions P10, P20, and P30, which are 10 mm, 20 mm, and 30 mm from the starting point SP, and the point closest to the boundary K among the intersections of the approximate straight line AL and the graph of the measurement data is determined as the end point EP of the coating length W101. The difference in the W-axis direction between the end point EP and the starting point SP on the graph calculated in this way is determined as the coating length W101. For the thickness T21B, measurements are taken at 10 locations within a 50 mm range in the central part of the positive electrode active material layer 21B in the W-axis direction, and the average value is calculated.

(Insulating tapes 53, 54)
The secondary battery 1 may further include insulating

tapes

53, 54 in the gap between the exterior can 11 and the electrode winding body 20. The positive electrode collector exposed portion 212 and the negative electrode exposed portion 222 gathered on the end faces 41, 42 are conductors such as bare metal foil. Therefore, if the positive electrode collector exposed portion 212 and the negative electrode exposed portion 222 are close to the exterior can 11, a short circuit may occur between the positive electrode 21 and the negative electrode 22 through the exterior can 11. In addition, there is a possibility of a short circuit when the positive electrode collector plate 24 on the end face 41 and the exterior can 11 are close to each other. Therefore, it is preferable that the insulating

tapes

53, 54 are provided as insulating members. The insulating

tapes

53, 54 are, for example, adhesive tapes whose base layer is made of any one of polypropylene, polyethylene terephthalate, and polyimide, and whose base layer has an adhesive layer on one side. In order to prevent the installation of the insulating

tapes

53, 54 from reducing the volume of the electrode winding body 20, the insulating

tapes

53, 54 are positioned so as not to overlap with the fixing tape 46 attached to the side portion 45, and the thickness of the insulating

tapes

53, 54 is set to be equal to or less than the thickness of the fixing tape 46.

(Positive electrode current collector 24 and negative electrode current collector 25)
In a normal lithium ion secondary battery, for example, a lead for current extraction is welded to each of the positive and negative electrodes. However, this is not suitable for high-rate discharge because the internal resistance of the lithium ion secondary battery is large and the lithium ion secondary battery generates heat and becomes hot during discharge. Therefore, in the secondary battery 1 of this embodiment, the positive electrode current collector 24 is arranged to face the end face 41, and the negative electrode current collector 25 is arranged to face the end face 42, and the positive electrode covering portion 211 present on the end face 41 and the positive electrode current collector 24 are welded at multiple points, and the negative electrode covering portion 221 present on the end face 42 and the negative electrode current collector 25 are welded at multiple points. In this way, the internal resistance of the secondary battery 1 is reduced. The end faces 41 and 42 being flat as described above also contribute to the reduction in resistance. The positive electrode current collector 24 is electrically connected to the battery cover 14, for example, via the safety valve mechanism 30. The negative electrode current collector 25 is electrically connected to the exterior can 11, for example. Fig. 7A is a schematic diagram showing an example of the configuration of the positive electrode current collector 24. Fig. 7B is a schematic diagram showing an example of the configuration of the negative electrode current collector 25. The positive electrode current collector 24 is a metal plate made of, for example, aluminum or an aluminum alloy, or a composite material thereof. The negative electrode current collector 25 is a metal plate made of, for example, nickel, a nickel alloy, copper, or a copper alloy, or a composite material of two or more of these.

As shown in FIG. 7A, the positive electrode current collector 24 has a shape in which a substantially rectangular band-shaped portion 32 is connected to a substantially fan-shaped sector portion 31. A through hole 35 is formed near the center of the sector portion 31. In the secondary battery 1, the positive electrode current collector 24 is provided so that the through hole 35 overlaps with the through hole 26 in the Z-axis direction. The portion indicated by diagonal lines in FIG. 7A is the insulating portion 32A of the band-shaped portion 32. The insulating portion 32A is a part of the band-shaped portion 32 to which an insulating tape is attached or an insulating material is applied. The portion of the band-shaped portion 32 below the insulating portion 32A is the connection portion 32B to the sealing plate, which also serves as an external terminal. Note that, as shown in FIG. 1, when the secondary battery 1 has a battery structure in which the through hole 26 does not have a metal center pin, the band-shaped portion 32 is less likely to come into contact with the portion of the negative electrode potential. Therefore, the positive electrode current collector 24 does not need to have the insulating portion 32A. If the positive electrode current collector 24 does not have an 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 equivalent to the thickness of the insulating portion 32A.

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

The sectorial portion 31 of the positive electrode current collector 24 is configured to cover only a portion of the end face 41 due to its planar shape. Similarly, the sectorial portion 33 of the negative electrode current collector 25 is configured to cover only a portion of the end face 42 due to its planar shape. There are, for example, two reasons why the

sectorial portions

31 and 33 do not cover the entire end faces 41 and 42. First, this is to allow the electrolyte to smoothly penetrate the electrode winding body 20 when, for example, assembling the secondary battery 1. Second, this is to make it easier to release gas generated when the lithium-ion secondary battery is in an abnormally high temperature state or overcharged state to the outside.

(Positive electrode 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.

(Positive electrode active material layer 21B)
The positive electrode active material layer 21B contains, as a positive electrode active material, any one or more of positive electrode materials capable of absorbing and releasing lithium. However, the positive electrode active material layer 21B may further contain any one or more of other materials such as a positive electrode binder and a positive electrode conductor. The positive electrode material is preferably a lithium-containing compound, more specifically, a lithium-containing composite oxide and 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, any one of a layered rock salt type and 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 may contain, in particular, at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide as a positive electrode active material. The positive electrode binder contains, for example, one or more of synthetic rubber and polymer compounds. The synthetic rubber is, for example, styrene butadiene rubber, fluorine rubber, and ethylene propylene diene. The polymer compound is, for example, polyvinylidene fluoride and polyimide. The positive electrode conductive agent contains, for example, one or more of carbon materials. The carbon materials are, for example, graphite, carbon black, acetylene black, and ketjen black. However, the positive electrode conductive agent may be a metal material, a conductive polymer, or the like, as long as it is a material having conductivity.

(Negative electrode current collector 22A)
The negative electrode collector 22A includes a conductive material such as copper. The negative electrode collector 22A is a metal foil made of nickel, a nickel alloy, copper, or a copper alloy. The surface of the negative electrode collector 22A is preferably roughened. This is because the adhesion of the negative electrode active material layer 22B to the negative electrode collector 22A is improved by the so-called anchor effect. In this case, it is sufficient that the surface of the negative electrode collector 22A is roughened at least in the region facing the negative electrode active material layer 22B. The roughening method is, 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 collector 22A by an electrolytic method in an electrolytic bath, so that the surface of the negative electrode collector 22A is provided with unevenness. Copper foil produced by an electrolytic method is generally called electrolytic copper foil.

(Negative electrode active material layer 22B)
The negative electrode active material layer 22B contains, as the negative electrode active material, any one or more of negative electrode materials capable of absorbing and releasing lithium. However, the negative electrode active material layer 22B may further contain any one or more of other materials such as a negative electrode binder and a negative electrode conductor. The negative electrode material is, for example, a carbon material. This is because a high energy density can be stably obtained because the change in the crystal structure during the absorption and release of lithium is very small. In addition, the carbon material also functions as a negative electrode conductor, so that the conductivity of the negative electrode active material layer 22B is improved. The carbon material is, for example, graphitizable carbon, non-graphitizable carbon, graphite, etc. However, the plane spacing of the (002) plane in the non-graphitizable carbon is preferably 0.37 nm or more. The plane spacing of the (002) plane in graphite is preferably 0.34 nm or less. More specifically, the carbon material is, for example, pyrolytic carbon, cokes, glassy carbon fiber, organic polymer compound calcined body, activated carbon, and carbon black. The cokes include pitch coke, needle coke, and petroleum coke. The organic polymer compound calcined body is a product of calcining (carbonizing) a polymer compound such as a phenolic resin and a furan resin at an appropriate temperature. In addition, the carbon material may be low-crystalline carbon heat-treated at a temperature of about 1000° C. or less, or amorphous carbon. The shape of the carbon material may be any of fibrous, spherical, granular, and scaly. In the secondary battery 1, when the open circuit voltage at the time of full charge, i.e., the battery voltage, is 4.25 V or more, the amount of lithium released per unit mass is greater even if the same positive electrode active material is used, compared to when the open circuit voltage at the time of full charge is 4.20 V. For this reason, the amounts of the positive electrode active material and the negative electrode active material are adjusted accordingly. This allows a high energy density to be obtained.

The negative electrode active material layer 22B may 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. The silicon-containing material is a general term for materials containing silicon as a constituent element. However, the silicon-containing material may contain only silicon as a constituent element. The type of silicon-containing material may be only one type or two or more types. The silicon-containing material can form an alloy with lithium, and may be a simple substance of silicon, a silicon alloy, a silicon compound, a mixture of two or more types thereof, or a material containing one or more types of phases thereof. The silicon-containing material may be crystalline or amorphous, or may contain both a crystalline portion and an amorphous portion. However, the simple substance described here means a general simple substance, and may contain a trace amount of impurities. In other words, the purity of the simple substance is not necessarily limited to 100%. The silicon alloy contains, for example, one or more of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as a constituent element other than silicon. The silicon compound contains, for example, one or more of carbon and oxygen as a constituent element other than silicon. The silicon compound may contain, for example, one or more of the series of constituent elements described for the silicon alloy as a constituent element other than silicon. Specifically, examples of silicon alloys and silicon compounds include _SiB4 , _SiB6 , _Mg2Si , Ni2Si, _TiSi2 , _MoSi2 , CoSi2 _, _NiSi2 , _CaSi2 , _CrSi2 , _Cu5Si , FeSi2, _MnSi2 , _NbSi2 , _TaSi2 , _VSi2 , _WSi2 , _ZnSi2 , _SiC , _Si3N4 , _Si2N2O , and _SiOv (0<v≦ ₂ ), etc. However, the range of v can be set arbitrarily, _and may be, for example, _0.2 <v<1.4.

(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 while preventing a short circuit of current caused by contact between the positive electrode 21 and the negative electrode 22. The separator 23 is, for example, one or more of porous films such as synthetic resins and ceramics, and may be a laminated film of two or more types of porous films. The synthetic resin is, for example, polytetrafluoroethylene, polypropylene, and polyethylene. However, the separator 23 may have a base material made of a single-layer polyolefin porous film containing polyethylene. This is because good high-output characteristics can be obtained compared to a laminated film. When the first separator member 23A and the second separator member constituting the separator 23 are each a single-layer porous film made of polyolefin, the thickness of the porous film may be, for example, 10 μm or more and 15 μm or less. By having a single-layer porous film made of polyolefin having a thickness of 10 μm or more, internal short circuits can be sufficiently avoided. If the thickness of the single-layered 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 may be, for example, 6.3 g/m ² or more and 8.3 g/m ² or less. If the surface density of the single-layered porous film made of polyolefin is 6.3 g/m ² or more, internal short circuit can be sufficiently avoided. If the surface density of the single-layered porous film made of polyolefin is 8.3 g/m ² or less, better discharge capacity characteristics can be obtained.

In particular, the separator 23 may include, for example, the porous film as the substrate described above and a polymer compound layer provided on one or both sides of the substrate layer. This is because the adhesiveness of the separator 23 to each of the positive electrode 21 and the negative electrode 22 is improved, thereby suppressing distortion of the electrode winding body 20. This suppresses the decomposition reaction of the electrolyte and also suppresses leakage of the electrolyte impregnated in the substrate layer, so that the resistance is less likely to increase even when charging and discharging is repeated, and battery swelling is suppressed. 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. When forming this polymer compound layer, for example, a solution in which a polymer compound is dissolved in an organic solvent or the like is applied to the substrate layer, and then the substrate layer is dried. Note that the substrate layer may be immersed in the solution and then dried. This polymer compound layer may contain, for example, one or more types of insulating particles such as inorganic particles. Types of inorganic particles include, for example, aluminum oxide and aluminum nitride.

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

The electrolyte salt includes, for example, one or more of salts such as lithium salts. However, the electrolyte salt may include, for example, a salt other than lithium salt. The salt other than lithium is, for example, a salt of a light metal other than lithium. The lithium salt is, for example, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium tetraphenylborate (LiB(C ₆ H ₅ ) ₄ ), lithium methanesulfonate (LiCH ₃ SO ₃ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium tetrachloroaluminate (LiAlCl ₄ ), dilithium hexafluorosilicate (Li ₂ SF ₆ ), lithium chloride (LiCl), lithium bromide (LiBr), etc. Among them, any one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium hexafluoroarsenate are preferred, and lithium hexafluorophosphate is 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 contains LiPF ₆ as the electrolyte salt, the concentration of LiPF ₆ in the electrolyte is preferably 1.25 mol/kg or more and 1.45 mol/kg or less. This is because cycle deterioration due to consumption (decomposition) of salt during high-load rate charging can be prevented, and high-load cycle characteristics are improved. When the electrolyte salt further contains LiBF ₄ in addition to LiPF ₆ , the concentration of LiBF ₄ in the electrolyte is preferably 0.001 (wt%) or more and 0.1 (wt%) or less. This is because cycle deterioration due to consumption (decomposition) of salt during high-load rate charging can be more effectively prevented, and high-load cycle characteristics are further improved.

[1-2. motion]
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 the present embodiment, for example, during discharge, lithium ions are released from the negative electrode 22 and are absorbed into the positive electrode 21 via the electrolyte.

[1-3. Production method]
A method for manufacturing the secondary battery 1 will be described with reference to Fig. 8 in addition to Figs. 1 to 5B. Fig. 8 is a perspective view for explaining the manufacturing process of the secondary battery shown in Fig. 1.

First, a positive electrode collector 21A is prepared, and a positive electrode active material layer 21B and an insulating film 101 are selectively formed on the surface of the positive electrode collector 21A to form a positive electrode 21 having a positive electrode coating portion 211 and a positive electrode collector exposed portion 212. Next, a negative electrode collector 22A is prepared, and a negative electrode active material layer 22B is selectively formed on the surface of the negative electrode collector 22A to form a negative electrode 22 having a negative electrode coating portion 221 and a negative electrode exposed portion 222. A drying process may be performed on the positive electrode 21 and the negative electrode 22. Next, the positive electrode 21 and the negative electrode 22 are stacked via the first separator member 23A and the second separator member 23B so that the positive electrode collector exposed portion 212 and the first portion 222A of the negative electrode exposed portion 222 are opposite each other in the W-axis direction, to produce a laminate S20. When preparing the laminate S20, the inner peripheral end 23A1 of the first separator member 23A and the inner peripheral end 23B1 of the second separator member are folded back so that the inner peripheral end 23A1 and the inner peripheral end 23B1 are sandwiched between the inner peripheral edge 21E1 of the positive electrode 21 and the negative electrode 22. The laminate S20 is then spirally wound so that the through holes 26 are formed. Furthermore, a fixing tape 46 is attached to the outermost circumference of the spirally wound laminate S20. This results in the electrode winding body 20, as shown in FIG. 8A.

Next, as shown in FIG. 8B, the end of a flat plate having a thickness of, for example, 0.5 mm is pressed perpendicularly against the end faces 41, 42 of the electrode winding body 20, i.e., in the Z-axis direction, to locally bend the end faces 41, 42. As a result, grooves 43 are created that extend radially from the through holes 26 in the radial direction (R direction). Note that the number and arrangement of the grooves 43 shown in FIG. 8B are examples, and the present disclosure is not limited thereto.

Next, as shown in FIG. 8C, substantially the same pressure is applied from above and below the electrode winding body 20 substantially simultaneously in a direction substantially perpendicular to the end faces 41 and 42. At this time, for example, a rod-shaped jig is inserted into the through hole 26. By doing so, the positive electrode collector exposed portion 212 and the first part 222A of the negative electrode exposed portion 222 are bent so that the end faces 41 and 42 are flat. At this time, the first edge portion 212E of the positive electrode collector exposed portion 212 and the second edge portion 222E of the negative electrode exposed portion 222 at the end faces 41 and 42 are bent while overlapping toward the through hole 26. After that, the fan-shaped portion 31 of the positive electrode collector plate 24 is joined to the end face 41 by laser welding or the like, and the fan-shaped portion 33 of the negative electrode collector plate 25 is joined to the end face 42 by laser welding or the like.

Next, insulating

tapes

53, 54 are attached to predetermined positions of the electrode winding body 20. After that, as shown in FIG. 8 (D), the strip portion 32 of the positive electrode current collector 24 is folded and the strip portion 32 is inserted into the hole 12H of the insulating plate 12. In addition, the strip portion 34 of the negative electrode current collector 25 is folded and the strip portion 34 is inserted into the hole 13H of the insulating plate 13.

Next, the electrode winding body 20 assembled as described above is inserted into the exterior can 11 shown in FIG. 8(E), and the bottom of the exterior can 11 is welded to the negative electrode current collector 25. Then, a narrowed portion 11S is formed near the open end 11N of the exterior can 11. Furthermore, electrolyte is injected into the exterior can 11, and the strip portion 32 of the positive electrode current collector 24 is welded to the safety valve mechanism 30.

Next, as shown in FIG. 8(F), the gasket 15, the safety valve mechanism 30, and the battery cover 14 are used to seal the narrowed portion 11S.

The above completes the secondary battery 1 of this embodiment.

[1-4. Actions and Effects]
In this manner, the secondary battery 1 of the present embodiment has the insulating film 101 that covers both a part of the positive electrode covering portion 211 and a part of the positive electrode current collector exposed portion 212 across the boundary K between the positive electrode covering portion 211 and the positive electrode current collector exposed portion 212. This effectively suppresses the elution of metal ions contained in the positive electrode active material layer 21B in the positive electrode covering portion 211. Specifically, even if a local increase in potential occurs in the thickness-reduced portions 21B1S, 21B2S near the boundary K, the outflow of metal ions from the positive electrode active material layer 21B can be suppressed, and a short circuit between the positive electrode 21 and the negative electrode 22 can be prevented. This allows for higher reliability to be obtained. In the secondary battery 1, in particular, by setting the ratio of the thickness T21B of the positive electrode active material layers 21B1, 21B2 to the covering length W101 in the W-axis direction of the covered portion of the positive electrode covering portion 211 that is covered with the insulating film 101, i.e., the portion of the thickness-reduced portions 21B1S, 21B2S that is covered with the insulating film 101, to 92.5 or more, the outflow of metal ions from the positive electrode active material layer 21B can be more effectively suppressed.

In addition, by providing the insulating film 101, when the positive electrode active material layer 21B is formed by a coating method, the insulating film 101 acts as a stopper to prevent the positive electrode active material layer 21B from spreading to the positive electrode current collector exposed portion 212. This makes it possible to make the area occupied by the thickness-reduced portions 21B1S, 21B2S in the positive electrode active material layer 21B relatively small compared to the area occupied by the flat portions 21B1F, 21B2F. This is therefore suitable for realizing a secondary battery 1 with a higher capacity.

＜2. Application Examples＞
The use of the secondary battery 1 according to the embodiment of the present disclosure is, for example, as described below.

[2-1. Battery pack]
9 is a block diagram showing an example of a circuit configuration in which a battery according to an embodiment of the present invention (hereinafter, referred to as a secondary battery) is applied to a battery pack 300. The battery pack 300 includes a battery pack 301, an exterior, a switch unit 304 including a charge control switch 302a and a discharge control switch 303a, a current detection resistor 307, a temperature detection element 308, and a control unit 310.

The battery pack 300 has a positive terminal 321 and a negative terminal 322, and when charging, the positive terminal 321 and the negative terminal 322 are connected to the positive terminal and the negative terminal of the charger, respectively, and charging is performed. When the electronic device is in use, the positive terminal 321 and the negative terminal 322 are connected to the positive terminal and the negative terminal of the electronic device, respectively, and discharging is performed.

The battery pack 301 is made up of multiple secondary batteries 301a connected in series or parallel. The secondary batteries 1 described above can be used as the secondary batteries 301a. Note that while FIG. 9 shows an example in which six secondary batteries 301a are connected in 2 parallel and 3 series (2P3S), any other connection method may be used, such as n parallel and m series (n and m are integers).

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 reverse polarity to the charge current flowing from the positive terminal 321 to the battery pack 301, and a forward polarity to the discharge current flowing from the negative terminal 322 to the battery pack 301. The diode 303b has a forward polarity to the charge current and a reverse polarity to the discharge current. Note that although the switch unit 304 is provided on the + side in FIG. 9, it may be provided on the - side.

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 assembled battery 301. After the charge control switch 302a is turned off, only discharging is possible through the diode 302b. In addition, it is controlled by the control unit 310 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 assembled battery 301 is cut off. 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 assembled battery 301. After the discharge control switch 303a is turned off, only charging is possible through the diode 303b. In addition, it is controlled by the control unit 310 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 assembled battery 301 is cut off.

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

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

The charge and discharge switches can be semiconductor switches such as MOSFETs. In this case, the parasitic diodes of the MOSFETs function as diodes 302b and 303b. When a P-channel FET is used as the charge and discharge switch, switch control section 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 types, they are turned ON by a gate potential that is lower than the source potential by a predetermined value or more. That is, in normal charge and discharge operations, control signals CO and DO are at a low level, and charge control switch 302a and discharge control switch 303a are turned ON.

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

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 control unit 310 and the internal resistance value of each secondary battery 301a in its initial state measured during the manufacturing process are stored in memory 317 in advance, and can also be rewritten as appropriate. In addition, by storing the fully charged capacity of secondary battery 301a, it is possible to calculate, for example, the remaining capacity together with control unit 310.

The temperature detection unit 318 measures the temperature using the temperature detection element 308, and performs charge/discharge control in the event of abnormal heat generation, and performs corrections when calculating the remaining capacity.

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

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

Furthermore, examples of electric vehicles include railroad cars, golf carts, electric carts, and electric cars (including hybrid cars), and the device is used as a driving power source or auxiliary power source for these vehicles. Examples of power storage devices include power storage sources for buildings such as homes, or for power generation facilities.

The present disclosure has been described above with reference to one embodiment, but the configuration of the present disclosure is not limited to the configuration described in the embodiment, and can be modified in various ways. For example, in the above embodiment, the position of the boundary K of the positive electrode active material layer 21B1 and the position of the boundary K of the positive electrode active material layer 21B2 are aligned with each other in the thickness direction of the positive electrode 21, but they may be different from each other.

In addition, in the above embodiment and example, the electrode reactant is lithium, but the electrode reactant is not particularly limited. Therefore, as described above, the electrode reactant may be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium and calcium. In addition, the electrode reactant may be other light metals such as aluminum.

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

Furthermore, the present disclosure may take the following aspects.
＜1＞
a positive electrode covering portion in which a positive electrode current collector is covered with a positive electrode active material layer;
a positive electrode current collector exposed portion that is not covered by the positive electrode active material layer and is adjacent to the positive electrode covering portion in a first direction;
an insulating film that covers both a part of the positive electrode covering portion and a part of the positive electrode current collector exposed portion across a boundary between the positive electrode covering portion and the positive electrode current collector exposed portion,
the positive electrode active material layer includes a thickness reducing portion whose thickness decreases toward the boundary in the first direction,
a part of the reduced thickness portion is covered with the insulating film.
＜2＞
The secondary battery according to <1> above, wherein a ratio of a thickness of the positive electrode active material layer to a covering length in the first direction of a covered portion of the positive electrode covering portion that is covered with the insulating film is 92.5 or more.
＜3＞
The secondary battery according to <2> above, wherein the coating length is greater than 0 mm and is not greater than 0.2 mm.
＜4＞
The secondary battery according to the above item <2> or <3>, wherein the insulating film has a thickness of 0.0012 mm or more.
＜5＞
The secondary battery according to any one of <1> to <4> above, wherein the positive electrode active material layer includes a positive electrode active material containing at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.
＜6＞
A secondary battery comprising: an electrode winding body formed by winding a laminate including, in order, the positive electrode, a first separator, a negative electrode, and a second separator according to any one of <1> to <5> above, around a central axis extending in the first direction.
＜７＞
Further comprising a positive electrode current collector and a negative electrode current collector,
the electrode winding body has a first end surface and a second end surface opposed to each other in the first direction,
the positive electrode current collector is joined to the positive electrode current collector exposed portion of the positive electrode while facing the first end surface of the electrode winding body,
The secondary battery according to <6> above, wherein the negative electrode current collector plate faces the second end surface of the electrode winding body and is connected to the negative electrode.
＜8＞
The secondary battery according to <6> or <7> above,
A control unit that controls the secondary battery;
and an exterior housing that houses the secondary battery.

Claims

a positive electrode covering portion in which a positive electrode current collector is covered with a positive electrode active material layer;
a positive electrode current collector exposed portion that is not covered by the positive electrode active material layer and is adjacent to the positive electrode covering portion in a first direction;
an insulating film that covers both a part of the positive electrode covering portion and a part of the positive electrode current collector exposed portion across a boundary between the positive electrode covering portion and the positive electrode current collector exposed portion,
the positive electrode active material layer includes a thickness reducing portion whose thickness decreases toward the boundary in the first direction,
a part of the reduced thickness portion is covered with the insulating film.
2 . The positive electrode for a secondary battery according to claim 1 , wherein a ratio of a thickness of the positive electrode active material layer to a covering length in the first direction of a portion of the positive electrode covering portion that is covered with the insulating film is 92.5 or more.
The positive electrode for a secondary battery according to claim 2 , wherein the coating length is more than 0 mm and 0.2 mm or less.
4. The positive electrode for a secondary battery according to claim 2, wherein the insulating film has a thickness of 0.0012 mm or more.
5. The positive electrode for a secondary battery according to claim 1, wherein the positive electrode active material layer contains a positive electrode active material containing at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.
6. A secondary battery comprising: an electrode winding body formed by winding a laminate including, in order, the positive electrode for a secondary battery according to claim 1, a first separator, a negative electrode, and a second separator, about a central axis extending in the first direction.
Further comprising a positive electrode current collector and a negative electrode current collector,
the electrode winding body has a first end surface and a second end surface opposed to each other in the first direction,
the positive electrode current collector is joined to the positive electrode current collector exposed portion of the positive electrode while facing the first end surface of the electrode winding body,
The secondary battery according to claim 6 , wherein the negative electrode current collector plate faces the second end face of the electrode winding body and is connected to the negative electrode.
The secondary battery according to claim 6 or 7,
A control unit that controls the secondary battery;
and an exterior housing that houses the secondary battery.