Positive electrode for secondary battery, secondary battery, and battery pack

Abstract

Provided are a positive electrode for a secondary battery, a secondary battery, and a battery pack having more excellent performance. The positive electrode for a secondary battery has: 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 portion in which the positive electrode current collector is exposed without being covered by the positive electrode active material layer, the positive electrode current collector exposed portion being adjacent to the positive electrode coating portion in the first direction; and an insulating film that covers both a part of the positive electrode coating part and a part of the positive electrode current collector exposed part across the boundary between the positive electrode coating part and the positive electrode current collector exposed part. The positive electrode active material layer includes a thickness-reduced portion, the thickness of which decreases as approaching the boundary in the first direction, a portion of which is covered by the insulating film.

Description

Technical Field

[0001] This disclosure relates to a positive electrode for secondary batteries, and to secondary batteries and battery packs having the same. Background Technology

[0002] Due to the widespread use of mobile phones and other electronic devices, secondary batteries are being developed as small, lightweight power sources capable of achieving high energy density. These secondary batteries include a positive electrode, a negative electrode, and an electrolyte housed within an outer packaging component. Various studies have been conducted regarding the structure of these secondary batteries (see, for example, Patent Document 1).

[0003] Patent document 1 proposes a secondary battery that addresses the problem of metal elements dissolving due to a localized potential rise during charging caused by a thin layer region formed at the end of the compound layer formed on the metal foil. The solution is to give the end of the compound layer a specific cross-sectional shape.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2014-154363 Utility Model Content

[0007] Various studies have been conducted to improve the performance of secondary batteries. However, there is still room for improvement in the performance of secondary batteries.

[0008] Therefore, there is a need for rechargeable batteries with superior performance.

[0009] A positive electrode for a secondary battery according to one embodiment of the present disclosure is characterized by having:

[0010] Positive electrode coating portion, wherein a positive electrode active material layer is coated on the positive electrode current collector;

[0011] A positive current collector exposed portion, wherein the positive current collector is not covered by the positive active material layer and is exposed, and the exposed portion is adjacent to the positive coating portion in a first direction; and

[0012] An insulating film extends across the boundary between the positive electrode covering portion and the exposed positive electrode current collector portion, covering both a portion of the positive electrode covering portion and a portion of the exposed positive electrode current collector portion.

[0013] The positive electrode active material layer includes a thickness-reducing portion, wherein the thickness of the thickness-reducing portion decreases as it approaches the boundary in the first direction.

[0014] A portion of the reduced thickness is covered by the insulating film.

[0015] In the positive electrode of the secondary battery

[0016] The ratio of the thickness of the positive electrode active material layer to the length of the coating portion covered by the insulating film in the positive electrode coating in the first direction is 92.5 or more.

[0017] In the positive electrode of the secondary battery

[0018] The coverage length is greater than 0 mm and less than 0.2 mm.

[0019] In the positive electrode of the secondary battery

[0020] The thickness of the insulating film is 0.0012 mm or more.

[0021] In the positive electrode of the secondary battery

[0022] The positive electrode active material layer contains a positive electrode active material, which contains at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0023] A secondary battery according to one embodiment of the present disclosure is characterized by comprising:

[0024] The electrode winding body is formed by winding a stack of layers, which sequentially includes the positive electrode, the first separator, the negative electrode and the second separator for the secondary battery, around a central axis extending along the first direction.

[0025] In the secondary battery,

[0026] The secondary battery also includes a positive electrode current collector and a negative electrode current collector.

[0027] The electrode winding has a first end face and a second end face that are opposed to each other in the first direction.

[0028] The positive current collector plate faces the first end face of the electrode winding body and is engaged with the exposed portion of the positive current collector of the positive electrode.

[0029] The negative electrode current collector is opposite to the second end face of the electrode winding and is connected to the negative electrode.

[0030] A battery pack according to one embodiment of the present disclosure is characterized by having:

[0031] The aforementioned secondary battery;

[0032] Control unit, controlling the secondary battery; and

[0033] The outer casing houses the aforementioned secondary battery.

[0034] In one embodiment of the present disclosure, a positive electrode for a secondary battery, a secondary battery, and a battery pack include an insulating film that spans the boundary between the positive electrode coating and the exposed positive electrode current collector, covering both a portion of the positive electrode coating and a portion of the exposed positive electrode current collector. Here, the positive electrode active material layer includes a thickness-reducing portion, which decreases in thickness towards the boundary in a first direction, and a portion of this thickness-reducing portion is covered by the insulating film. This effectively suppresses the dissolution of metal ions contained in the positive electrode active material layer within the positive electrode coating. Therefore, higher reliability can be achieved.

[0035] It should be noted that the effects of this disclosure are not necessarily limited to those described herein, but can also be any of the series of effects related to this disclosure as described below. Attached Figure Description

[0036] Figure 1 This is a cross-sectional view showing the configuration of a secondary battery in one embodiment of the present disclosure.

[0037] Figure 2 It means Figure 1 The diagram shown is a schematic representation of a composite material comprising a positive electrode, a negative electrode, and a separator.

[0038] Figure 3 It means Figure 1 A cross-sectional view of one configuration example of the cross-sectional structure of the electrode winding shown.

[0039] Figure 4A yes Figure 1 The diagram shown is a unfolded diagram of the positive electrode.

[0040] Figure 4B yes Figure 1 The cross-sectional view of the positive electrode is shown.

[0041] Figure 5A yes Figure 1 The diagram shown is a unfolded diagram of the negative electrode.

[0042] Figure 5B yes Figure 1 The cross-sectional view of the negative electrode is shown.

[0043] Figure 6 This is an explanation Figure 4B The diagram illustrates the method for determining the coverage length of the insulating film.

[0044] Figure 7A yes Figure 1 The top view of the positive current collector shown.

[0045] Figure 7B yes Figure 1 The top view of the negative current collector shown.

[0046] Figure 8 This is an explanation Figure 1 The diagram shows a three-dimensional representation of the manufacturing process of a secondary battery.

[0047] Figure 9 This is a block diagram showing the circuit configuration of a battery pack using a secondary battery according to an embodiment of the present disclosure. Detailed Implementation

[0048] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. It should be noted that the description is presented in the following order.

[0049] 1. Secondary battery

[0050] 1-1. Composition

[0051] 1-2. Actions

[0052] 1-3. Manufacturing Method

[0053] 1-4. Functions and Effects

[0054] 2. Application Examples

[0055] 2-1. Battery Pack

[0056] 2-2. Energy Storage System

[0057] <1. Secondary Battery>

[0058] First, a secondary battery having a positive electrode according to one embodiment of the present disclosure will be described.

[0059] In this embodiment, a cylindrical lithium-ion secondary battery with a cylindrical appearance is exemplarily described. However, the secondary battery of this disclosure is not limited to a cylindrical lithium-ion secondary battery, but may be a lithium-ion secondary battery with an appearance other than a cylindrical shape, or a battery using electrode reactants other than lithium.

[0060] The charging and discharging principle of a secondary battery is not particularly limited. The following explanation describes the case where battery capacity is obtained by utilizing the intercalation and deintercalation of electrode reactants. This secondary battery includes a positive electrode, a negative electrode, and an electrolyte. In this secondary battery, to prevent the deposition of electrode reactants on the surface of the negative electrode during charging, the charging capacity of the negative electrode is greater than the discharging capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is set to be greater than that of the positive electrode per unit area.

[0061] The types of substances used in the electrode reactions are not particularly limited as described above. Specifically, they are light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, while alkaline earth metals include beryllium, magnesium, and calcium.

[0062] The following example uses lithium as the electrode reactant. A secondary battery that utilizes the insertion and extraction of lithium to obtain battery capacity is called a lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is inserted and extracted in an ionic state.

[0063] [1-1. Composition]

[0064] (Lithium-ion secondary battery 1)

[0065] Figure 1 This diagram shows the cross-sectional configuration along the height direction of the lithium-ion secondary battery 1 (hereinafter referred to as "secondary battery 1") according to this embodiment. Figure 1 In the secondary battery 1 shown, an electrode winding body 20, which serves as a battery element, is housed inside a cylindrical outer casing 11.

[0066] Specifically, the secondary battery 1, for example, includes a pair of insulating plates 12 and 13, an electrode winding body 20, a positive current collector 24, and a negative current collector 25 inside the outer casing 11. The electrode winding body 20 is, for example, a structure formed by stacking and winding a positive electrode 21 and a negative electrode 22 with a separator 23 in between. An electrolyte, which is a liquid electrolyte, is impregnated in the electrode winding body 20. It should be noted that the secondary battery 1 may further include one or more of a thermistor (PTC) element and reinforcing components inside the outer casing 11.

[0067] (Outer packaging tank 11)

[0068] The outer can 11 has, for example, a hollow cylindrical structure that is closed at the lower end and open at the upper end in the Z-axis direction (height direction). Therefore, the upper end of the outer can 11 is called the open end 11N. The outer can 11 is made of, for example, a metallic material such as iron. However, a metallic material such as nickel may also be plated on the surface of the outer can 11. The insulating plate 12 and the insulating plate 13 are arranged opposite each other, for example, in such a way that the electrode winding body 20 is sandwiched between them in the Z-axis direction. It should be noted that, 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 closed portion of the outer can 11 and its vicinity are referred to as the lower part of the secondary battery 1.

[0069] (Insulation boards 12 and 13)

[0070] Insulating plates 12 and 13, for example, have surfaces perpendicular to the central axis CL of the electrode winding body 20, i.e., perpendicular to... Figure 1 The plate is a disc-shaped plate perpendicular to the Z-axis. In addition, insulating plates 12 and 13 are configured to sandwich the electrode winding body 20.

[0071] (Riveted structure 11R)

[0072] At the open end 11N of the outer can 11, for example, a structure is formed by riveting the battery cover 14 and the safety valve mechanism 30 together via a gasket 15, namely, a riveting structure 11R. With the electrode winding body 20 and the like housed inside the outer can 11, the outer can 11 is sealed by the battery cover 14. The riveting structure 11R, also known as a coiled structure, has a bent portion 11P as a coiled section.

[0073] (Battery cover 14)

[0074] The battery cover 14 is primarily a sealing component that closes the open end 11N when the electrode winding body 20 and the like are housed inside the outer can 11. The battery cover 14, for example, is made of the same material as the outer can 11. The central region of the battery cover 14 protrudes upward (in the +Z direction), for example. As a result, the area outside the central region of the battery cover 14, i.e., the peripheral region, comes into contact with the safety valve mechanism 30, for example.

[0075] (Washer 15)

[0076] The gasket 15 is primarily a sealing component located between the bend 11P of the outer can 11 and the battery cover 14. The gasket 15 seals the gap between the bend 11P and the battery cover 14. However, a coating such as asphalt can also be applied to the surface of the gasket 15. The gasket 15 may contain one or more insulating materials. The type of insulating material is not particularly limited; for example, it may be a polymer such as polybutylene terephthalate (PBT) and polypropylene (PP). Polybutylene terephthalate is preferred as the insulating material. This is because, while electrically separating the outer can 11 from the battery cover 14, the gap between the bend 11P and the battery cover 14 is adequately sealed.

[0077] (Safety valve mechanism 30)

[0078] The safety valve mechanism 30 is mainly used to release the internal pressure of the outer tank 11 when the internal pressure rises, thereby releasing the sealed state of the outer tank 11. The increase in internal pressure of the outer tank 11 can be caused by, for example, gases generated during the decomposition reaction of the electrolyte during charging and discharging. Additionally, there is a possibility that the internal pressure of the outer tank 11 may increase due to external heating.

[0079] (Electrode winding 20)

[0080] The electrode winding 20 is a power generation element that enables the charging and discharging reaction, and it is housed inside the outer casing 11. The electrode winding 20 includes a positive electrode 21, a negative electrode 22, a diaphragm 23, and an electrolyte as a liquid electrolyte.

[0081] Figure 2This is an unfolded view of the electrode winding body 20, and a diagram schematically showing a portion of the laminate S20 including the positive electrode 21, the negative electrode 22, and the separator 23. Figure 2 Specifically, this refers to the area near the end of the innermost circumferential portion of the electrode winding 20. In the laminated body S20 after the electrode winding 20 is unwound, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with a separator 23 in between. The separator 23 has, for example, two substrates, namely a first separator component 23A and a second separator component 23B. Therefore, the electrode winding 20 has a four-layer laminated body S20 consisting of the positive electrode 21, the first separator component 23A, the negative electrode 22, and the second separator component 23B stacked sequentially. The positive electrode 21, the first separator component 23A, the negative electrode 22, and the second separator component 23B are all generally strip-shaped components with the W-axis as the short side and the L-axis as the long side. Figure 3 As shown, the electrode winding body 20 is a laminated body S20 that presents a spiral shape in a horizontal cross section orthogonal to the Z-axis direction with a central axis CL extending in the Z-axis direction (refer to...). Figure 1 It is formed by winding around a central point. At this point, the laminate S20 is wound in an orientation where the W-axis direction is roughly aligned with the Z-axis direction. It should be noted that... Figure 3 This represents an example of the configuration of a horizontal cross-section orthogonal to the Z-axis in the electrode winding 20. However, in Figure 3 To improve visual clarity, the diaphragm 23 is omitted from the illustration. The electrode winding body 20 has a generally cylindrical shape. The positive electrode 21 and the negative electrode 22 are wound together while maintaining their opposing positions with the diaphragm 23 in between. A through hole 26, serving as an internal space, is formed in the center of the electrode winding body 20. The through hole 26 is used to insert the assembly core of the electrode winding body 20 and the electrode rod for welding.

[0082] The positive electrode 21, negative electrode 22, and separator 23 are wound such that the separator 23 is disposed at the outermost periphery and the innermost periphery of the electrode winding body 20, respectively. Furthermore, at the outermost periphery of the electrode winding body 20, the negative electrode 22 is disposed further outward than the positive electrode 21. That is, as... Figure 3 As shown, the outermost positive electrode portion 21out of the positive electrode 21 included in the electrode winding 20 is located further inward than the outermost negative electrode portion 22out of the negative electrode 22 included in the electrode winding 20. Here, the outermost positive electrode portion 21out refers to the portion around the outermost edge of the positive electrode 21 in the electrode winding 20. The outermost negative electrode portion 22out refers to the portion around the outermost edge of the negative electrode 22 in the electrode winding 20. On the other hand, at the innermost edge of the electrode winding 20, the negative electrode 22 is positioned further inward than the positive electrode 21. That is, as... Figure 3As shown, the innermost circumferential portion 22in of the negative electrode 22 in the electrode winding body 20 is located further inward than the innermost circumferential portion 21in of the positive electrode 21 in the electrode winding body 20. Here, the innermost circumferential portion 21in of the positive electrode refers to the portion around the innermost edge of the positive electrode 21 in the electrode winding body 20. The innermost circumferential portion 22in of the negative electrode refers to the portion around the innermost edge of the negative electrode 22 in the electrode winding body 20. The number of turns of the positive electrode 21, the negative electrode 22, and the separator 23 is not particularly limited and can be arbitrarily set.

[0083] Figure 4A This is a diagram showing the unfolded state of the positive electrode 21, schematically representing its state before winding. Figure 4B This indicates the cross-sectional structure of the positive electrode 21. It should be noted that... Figure 4B Indicates along Figure 4A The cross-section shown is a view of the IVB-IVB line. The positive electrode 21 includes, for example, a positive current collector 21A and a positive active material layer 21B disposed on the positive current collector 21A. The positive active material layer 21B may be disposed on only one side of the positive current collector 21A, or it may be disposed on both sides of the positive current collector 21A. Figure 4B The diagram shows the positive electrode active material layer 21B disposed on both sides of the positive electrode current collector 21A. More specifically, the positive electrode current collector 21A includes an inner peripheral surface 21A1 and an outer peripheral surface 21A2 opposite to the inner peripheral surface 21A1. The inner peripheral surface 21A1 faces the winding center side of the electrode winding body 20, i.e., the central axis CL, while the outer peripheral surface 21A2 faces the side opposite to the winding center side of the electrode winding body 20. The positive electrode 21 has an inner peripheral active material layer 21B1 and an outer peripheral active material layer 21B2 as the positive electrode active material layer 21B. The inner peripheral active material layer 21B1 covers at least a portion of the inner peripheral surface 21A1, and the outer peripheral active material layer 21B2 covers at least a portion of the outer peripheral surface 21A2. It should be noted that, in this specification, the inner peripheral active material layer 21B1 of the positive electrode is sometimes simply referred to as the positive electrode active material layer 21B1, and the outer peripheral active material layer 21B2 of the positive electrode is sometimes simply referred to as the positive electrode active material layer 21B2. Furthermore, in this specification, the inner peripheral active material layer 21B1 and the outer peripheral active material layer 21B2 of the positive electrode are sometimes collectively referred to as the positive electrode active material layer 21B, without distinguishing between them.

[0084] The positive electrode 21 has a positive electrode covering portion 211 on the positive electrode current collector 21A covered by a positive electrode active material layer 21B, and a positive electrode current collector exposed portion 212 on the positive electrode current collector 21A that is not covered by the positive electrode active material layer 21B. For example... Figure 4AAs shown, the positive electrode coating portion 211 and the positive electrode current collector exposed portion 212 extend from the inner peripheral end edge 21E1 to the outer peripheral end edge 21E2 of the electrode winding body 20 along the L-axis direction, which is the long side direction of the positive electrode 21. Here, the L-axis direction corresponds to the winding direction of the electrode winding body 20. That is, in the positive electrode 21, from the inner peripheral end edge 21E1 to the outer peripheral end edge 21E2 of the positive electrode 21, the positive electrode current collector 21A is coated with a positive electrode active material layer 21B in the winding direction of the electrode winding body 20. The positive electrode coating 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 is substantially aligned with the central axis CL. In addition, as Figure 2 As shown, in the electrode winding body 20, the inner peripheral edge 21E1 of the innermost peripheral portion 21in of the positive electrode is located further inward and backward than the inner peripheral edge 22E1 of the innermost peripheral portion 22in of the negative electrode.

[0085] like Figure 1 As shown, the first edge 212E of the exposed positive electrode current collector 212 is connected to the positive electrode current collector plate 24. An insulating film 101 is provided near the boundary between the positive electrode covering portion 211 and the exposed positive electrode current collector 212. Similar to the positive electrode covering portion 211 and the exposed positive electrode current collector 212, the insulating film 101 extends from the inner peripheral edge 21E1 to the outer peripheral edge 21E2 of the electrode winding body 20. Furthermore, the insulating film 101 is bonded to at least one of the first separator component 23A and the second separator component 23B. This is because it prevents positional misalignment between the positive electrode 21 and the separator 23. Additionally, the insulating film 101 can be a film containing a resin containing polyvinylidene fluoride (PVDF). This is because by containing PVDF in the insulating film 101, for example, the insulating film 101 swells due to the solvent contained in the electrolyte, enabling good adhesion to the separator 23. It should be noted that the detailed composition of the positive electrode 21 will be described below.

[0086] Figure 5A This is the unfolded diagram of negative electrode 22, which schematically represents the state before winding. Figure 5B This indicates the cross-sectional structure of the negative electrode 22. It should be noted that... Figure 5B Indicates along Figure 5A The cross-section of the VB-VB line shown is in the viewing direction. The negative electrode 22 includes, for example, a negative electrode current collector 22A and a negative electrode active material layer 22B disposed on the negative electrode current collector 22A. The negative electrode active material layer 22B may be disposed on only one side of the negative electrode current collector 22A, or it may be disposed on both sides of the negative electrode current collector 22A. Figure 5BThe diagram shows the negative electrode active material layer 22B disposed on both sides of the negative electrode current collector 22A. More specifically, the negative electrode current collector 22A includes an inner peripheral surface 22A1 and an outer peripheral surface 22A2 opposite to the inner peripheral surface 22A1. The inner peripheral surface 22A1 faces the winding center side of the electrode winding body 20, i.e., the central axis CL, while the outer peripheral surface 22A2 faces the side opposite to the winding center side of the electrode winding body 20. The negative electrode 22 has an inner peripheral active material layer 22B1 and an outer peripheral active material layer 22B2 as the negative electrode active material layer 22B. The inner peripheral active material layer 22B1 covers at least a portion of the inner peripheral surface 22A1, and the outer peripheral active material layer 22B2 covers at least a portion of the outer peripheral surface 22A2. It should be noted that in this specification, the inner peripheral active material layer 22B1 and the outer peripheral active material layer 22B2 of the negative electrode are sometimes collectively referred to as the negative electrode active material layer 22B without distinguishing between them.

[0087] The negative electrode 22 has a negative electrode covered portion 221 on the negative electrode current collector 22A covered by a negative electrode active material layer 22B, and a negative electrode exposed portion 222 on the negative electrode current collector 22A that is not covered by the negative electrode active material layer 22B. For example... Figure 5A As shown, the negative electrode covering portion 221 and the negative electrode exposed portion 222 extend along the L-axis direction, which serves as the long side 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. Figure 5A As shown, a portion of the exposed negative electrode portion 222 is formed such that a negative electrode covering portion 221 is sandwiched in the L-axis direction, which is the long side direction of the negative electrode 22. Specifically, the exposed negative electrode portion 222 includes a first portion 222A, a second portion 222B, and a third portion 222C. The first portion 222A is arranged adjacent to the negative electrode covering portion 221 in the W-axis direction and extends from the inner peripheral edge 22E1 to the outer peripheral edge 22E2 of the negative electrode 22 in the L-axis direction. The second portion 222B and the third portion 222C are arranged 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. It should be noted that, as Figure 1 As shown, the second edge portion 222E in the exposed negative electrode portion 222 is connected to the negative electrode current collector 25. The detailed structure of the negative electrode 22 will be described below.

[0088] In the stacked body S20 of the electrode winding body 20, the positive electrode 21 and the negative electrode 22 are stacked with the diaphragm 23 in a manner in which the first portions 222A of the positive electrode current collector exposure 212 and the negative electrode exposure 222 are opposite to each other along the W-axis direction, which is the width direction. The electrode winding body 20 fixes the end of the diaphragm 23 by attaching a fixing strap 46 to its side portion 45 to prevent the winding from becoming loose.

[0089] In secondary battery 1, such as Figure 2 As shown, when the width of the exposed positive current collector 212 is set as A, and the width of the first portion 222A of the exposed negative electrode 222 is set as 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 exposed positive current collector 212 that protrudes from the outer edge of the diaphragm 23 in the width direction is set as C, and the length of the portion of the first portion 222A of the exposed negative electrode 222 that protrudes from the outer edge on the opposite side of the diaphragm 23 in the width direction is set as D, it is preferable that C > D. For example, when the width C = 4.5 (mm), the width D = 3 (mm).

[0090] like Figure 1 As shown, in the upper part of the secondary battery 1, the plurality of adjacent first edge portions 212E in the radial direction (R direction) of the electrode winding body 20 of the positive electrode current collector exposed portion 212 wound around the central axis CL are bent toward the central axis CL in a manner that they overlap with each other. Similarly, in the lower part of the secondary battery 1, the plurality of adjacent second edge portions 222E in the radial direction (R direction) of the negative electrode exposed portion 222 wound around the central axis CL are bent toward the central axis CL in a manner that they overlap with each other. Therefore, the plurality of first edge portions 212E of the positive electrode current collector exposed portion 212 are gathered on the upper end face 41 of the electrode winding body 20, and the plurality of second edge portions 222E of the negative electrode exposed portion 222 are gathered on the lower end face 42 of the electrode winding body 20. In order to improve the contact between the positive electrode current collector plate 24 used for extracting current and the first edge portions 212E, the plurality of first edge portions 212E bent toward the central axis CL are made into flat surfaces. Similarly, in order to improve the contact between the negative current collector 25 used for current extraction and the second edge portion 222E, the plurality of second edge portions 222E bent towards the central axis CL become flat surfaces. It should be noted that the flat surfaces referred to here include not only completely flat surfaces, but also surfaces with some unevenness and surface roughness to the extent that the exposed positive current collector portion 212 and the exposed negative current collector portion 222 can engage with the positive current collector 24 and the negative current collector 25, respectively.

[0091] The positive current collector 21A is, for example, made of aluminum foil, as described below. On the other hand, the negative current collector 22A is, for example, made of copper foil, as described below. In this case, the positive current collector 21A is softer than the negative current collector 22A. That is, the Young's modulus of the exposed portion 212 of the positive current collector is lower than that of the exposed portion 222 of the negative current collector. Therefore, in one embodiment, it is more preferable that the widths A to D have a relationship of A>B and C>D. In this case, when the exposed portion 212 of the positive current collector and the exposed portion 222 of the negative current collector are bent simultaneously from both electrode sides with the same pressure, the height of the bent portion measured from the front end of the diaphragm 23 is sometimes approximately the same for the positive electrode 21 and the negative electrode 22. At this time, the plurality of first edge portions 212E of the exposed portion 212 of the positive current collector ( Figure 1 The positive current collector exposed portion 212 and the positive current collector plate 24 are bent and appropriately overlapped. This allows for easy joining of the positive current collector exposed portion 212 and the positive current collector plate 24. Similarly, the plurality of second edge portions 222E of the negative current collector exposed portion 222... Figure 1 The electrodes are bent and overlapped appropriately. This allows for easy joining of the exposed negative electrode portion 222 to the negative electrode current collector 25. The joining method described here refers, for example, to joining by laser welding, but is not limited to laser welding.

[0092] like Figure 2 , Figure 4A , Figure 4B As shown, the portion of the positive electrode 21's exposed positive current collector 212, which contains the separator 23 and faces the negative electrode 22, is covered by an insulating film 101. The insulating film 101 is, for example, made of polyvinylidene fluoride. The insulating film 101 has, for example, a width of 3 mm in the W-axis direction. It is configured to span the boundary K(…) between the positive electrode covering portion 211 and the exposed positive current collector 212. Figure 4A , Figure 4BThe insulating film 101 covers both a portion of the positive electrode coating and a portion of the positive electrode current collector exposed portion 212. However, the insulating film 101 completely covers the area in the positive electrode current collector exposed portion 212 of the positive electrode 21 that is opposite the negative electrode coating 221 of the negative electrode 22, separated by the separator 23. Boundary K indicates the position of the positive electrode active material layer 21B provided on the positive electrode current collector 21A closest to the positive electrode current collector exposed portion 212. For example, when a foreign object enters between the negative electrode coating 221 and the positive electrode current collector exposed portion 212, the insulating film 101 can effectively prevent an internal short circuit in the secondary battery 1. 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 potential rise occurs in the positive electrode coating 211 near the boundary K between the positive electrode coating 211 and the positive electrode current collector exposed portion 212, it is possible to suppress the outflow of metal ions from the positive electrode active material layer 21B and to suppress the short circuit between the positive electrode 21 and the negative electrode 22.

[0093] like Figure 4B As shown, the positive electrode active material layers 21B1 and 21B2 include flat portions 21B1F and 21B2F with substantially constant thickness and thickness-reducing portions 21B1S and 21B2S whose thickness decreases as they approach the boundary K in the W-axis direction. Here, only a portion of the thickness-reducing portions 21B1S and 21B2S is covered by the insulating film 101. The flat portions 21B1F and 21B2F are not covered by the insulating film 101. This is because when the insulating film 101 covers the flat portions 21B1F and 21B2F, the movement of lithium ions in and out of the flat portions 21B1F and 21B2F is hindered, which may lead to a decrease in capacity.

[0094] Furthermore, in the positive electrode 21, the ratio of the thickness T21B of the positive electrode active material layers 21B1 and 21B2 to the coverage length W101 in the W-axis direction of the portion covered by the insulating film 101 in the positive electrode coating portion 211, i.e., the portion covered by the insulating film 101 in the thickness reduction portions 21B1S and 21B2S, is 92.5 or more. Here, the coverage length W101 is, for example, greater than 0 mm and less than 0.2 mm. In addition, the thickness of the insulating film 101 is, for example, 0.0012 mm or more. The coverage length W101 and the thickness T21B can be measured, for example, based on SEM images. If the positive electrode 21 is included in the finished secondary battery 1, the cross-section of the end of the positive electrode 21 taken out after disassembling the secondary battery 1 is measured based on SEM images. In this case, the coating length W101 is measured starting from the point where the virtual line orthogonal to the positive current collector 21A intersects with the outermost positive active material particle among the positive active material particles covered by the insulating film 101. For example... Figure 6 As shown, the horizontal axis is set to the position along the W-axis, and the vertical axis is set to the thickness of the positive electrode 21 to plot and create a graph of the measured data. It should be noted that... Figure 6 This is an explanatory diagram illustrating the method for determining the coverage length W101. Figure 6 In the diagram, the plotted portion 212 of the positive current collector represents the thickness of the positive current collector 21A in the positive electrode 21, and the plotted portion 211 of the positive electrode represents the thickness of the entire positive electrode 21, including the positive current collector 21A and the positive active material layer 21B. The position P0 of the boundary K is taken as the starting point SP of the coating length W101. Furthermore, based on three values ​​of the position in the thickness direction of the positive electrode 21 measured at positions P10, P20, and P30 at points 10 mm, 20 mm, and 30 mm from this starting point SP, an approximate straight line AL is calculated. The point closest to the boundary K among the intersections of this approximate straight line AL and the graph of the measured data is taken as the ending point EP of the coating length W101. The difference between the ending point EP and the starting point SP in the W-axis direction on the graph thus calculated is taken as the coating length W101. Regarding the thickness T21B, measurements are taken at ten points within a 50 mm range in the central portion of the positive active material layer 21B in the W-axis direction, and the average value is calculated.

[0095] (Insulating tapes 53 and 54)

[0096] The secondary battery 1 may further have insulating tape 53, 54 at the gap between the outer can 11 and the electrode winding body 20. The positive electrode current collector exposed portion 212 and the negative electrode exposed portion 222 gathered on the end faces 41, 42 are exposed conductive materials such as bare metal foil. Therefore, when the positive electrode current collector exposed portion 212 and the negative electrode exposed portion 222 are close to the outer can 11, a short circuit may occur between the positive electrode 21 and the negative electrode 22 through the outer can 11. In addition, a short circuit may also occur when the positive electrode current collector plate 24 located on the end face 41 is close to the outer can 11. For this reason, insulating tape 53, 54 can be provided as insulating components. The insulating tape 53, 54 is, for example, an adhesive tape whose substrate layer is made of any one of polypropylene, polyethylene terephthalate, or polyimide and has an adhesive layer on one side of the substrate layer. In order to prevent the volume of the electrode winding body 20 from being reduced due to the installation of insulating tapes 53 and 54, the insulating tapes 53 and 54 are configured not to overlap with the fixing tape 46 pasted on the side portion 45, and the thickness of the insulating tapes 53 and 54 is set to be less than or equal to the thickness of the fixing tape 46.

[0097] (Positive current collector 24 and negative current collector 25)

[0098] In conventional lithium-ion secondary batteries, for example, leads for current extraction are welded at both the positive and negative electrodes. However, this increases the internal resistance of the lithium-ion secondary battery, causing it 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 end face 41, and the negative electrode current collector 25 is positioned opposite the end face 42. The positive electrode covering portion 211 and the positive electrode current collector 24, which are located on the end face 41, are welded at multiple points, and the negative electrode covering portion 221 and the negative electrode current collector 25, which are located on the end face 42, are also welded at multiple points. This reduces the internal resistance of the secondary battery 1. The flatness of the end faces 41 and 42, as described above, also contributes to lower resistance. The positive electrode current collector 24 is electrically connected to the battery cover 14, for example, via a safety valve mechanism 30. The negative electrode current collector 25 is electrically connected to the outer casing 11, for example. Figure 7A This is a schematic diagram showing one configuration example of the positive current collector 24. Figure 7B This is a schematic diagram illustrating one configuration example of the negative current collector 25. The positive current collector 24 is, for example, a metal plate made of elemental aluminum or aluminum alloy, or a composite material thereof. The negative current collector 25 is, for example, a metal plate made of elemental nickel, nickel alloy, copper or copper alloy, or a composite material thereof.

[0099] like Figure 7A As shown, the positive electrode current collector 24 has a shape in which a generally fan-shaped portion 31 is connected to a generally rectangular strip portion 32. A through hole 35 is formed near the center of the fan-shaped portion 31. In the secondary battery 1, the positive electrode current collector 24 is configured such that the through hole 35 and the through hole 26 coincide in the Z-axis direction. Figure 7A The section indicated by the diagonal line is the insulating portion 32A within the strip-shaped portion 32. The insulating portion 32A is a part of the strip-shaped portion 32 and is the portion to which insulating tape is adhered or coated with insulating material. The lower part of the insulating portion 32A within the strip-shaped portion 32 is the connecting portion 32B, which also serves as an external terminal to the sealing plate. It should be noted that, as... Figure 1 As shown, when the secondary battery 1 has a battery structure in which there is no metal center lead in the through hole 26, the possibility of the strip portion 32 coming into contact with the negative electrode potential is low. Therefore, the positive electrode current collector 24 may not have an insulating portion 32A. When the positive electrode current collector 24 does not have an insulating portion 32A, the charge and discharge capacity can be increased by increasing the width of the positive electrode 21 and the negative electrode 22 by an amount equivalent to the thickness of the insulating portion 32A.

[0100] Figure 7B The shape of the negative current collector 25 shown is similar to Figure 7AThe positive current collector plate 24 shown has almost the same shape. However, the strip portion 34 of the negative current collector plate 25 is different from the strip portion 32 of the positive current collector plate 24. The strip portion 34 of the negative current collector plate 25 is shorter than the strip portion 32 of the positive current collector plate 24, and does not have a portion equivalent to the insulating portion 32A of the positive current collector plate 24. A plurality of circular protrusions 37, indicated by circular marks, are provided on the strip portion 34. During resistance welding, the current is concentrated on the protrusions 37, and the protrusions 37 melt to weld the strip portion 34 to the bottom of the outer can 11. Similar to the positive current collector plate 24, a through hole 36 is formed near the center of the fan-shaped portion 33 on the negative current collector plate 25. In the secondary battery 1, the negative current collector plate 25 is configured such that the through hole 36 and the through hole 26 coincide in the Z-axis direction.

[0101] The fan-shaped portion 31 of the positive electrode current collector 24 only covers a portion of the end face 41 due to its planar shape. Similarly, the fan-shaped portion 33 of the negative electrode current collector 25 only covers a portion of the end face 42 due to its planar shape. The reasons why the fan-shaped portions 31 and 33 do not completely cover the end faces 41 and 42 are, for example, twofold. First, to allow the electrolyte to smoothly penetrate into the electrode winding body 20, for example, during the assembly of the secondary battery 1. Second, to facilitate the release of gases generated when the lithium-ion secondary battery is under abnormally high temperatures or overcharged conditions.

[0102] (Positive current collector 21A)

[0103] The positive current collector 21A may contain conductive materials such as aluminum. The positive current collector 21A may be a metal foil made of aluminum or an aluminum alloy.

[0104] (Positive electrode active material layer 21B)

[0105] The positive electrode active material layer 21B comprises any one or more positive electrode materials capable of lithium intercalation and deintercalation as positive electrode active materials. However, the positive electrode active material layer 21B may further comprise any one or more other materials such as a positive electrode binder and a positive electrode conductive agent. The positive electrode material is preferably a lithium-containing compound, and more specifically, preferably a lithium-containing composite oxide and a lithium-containing phosphate compound. The lithium-containing composite oxide is an oxide comprising lithium and one or more other elements, i.e., elements other than lithium, as constituent elements. The lithium-containing composite oxide may have, for example, any one of layered rock salt type and spinel type crystal structures. The lithium-containing phosphate compound is a phosphate compound comprising lithium and one or more other elements as constituent elements, for example, having a olivine type crystal structure. The positive electrode active material layer 21B particularly comprises at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide as positive electrode active materials. The positive electrode binder may comprise, for example, any one or more of synthetic rubber and polymer compounds. Synthetic rubbers include, for example, styrene-butadiene rubber, fluoropolymers, and ethylene-propylene-diene rubber. Polymer compounds include, for example, polyvinylidene fluoride and polyimide. Positive electrode conductive agents include, for example, any one or more carbon materials. These carbon materials include, for example, graphite, carbon black, acetylene black, and Ketjen black. However, the positive electrode conductive agent can be any conductive material, and can also be a metallic material or a conductive polymer.

[0106] (Negative current collector 22A)

[0107] The negative current collector 22A contains, for example, a conductive material such as copper. The negative current collector 22A is, for example, a metal foil made of nickel, a nickel alloy, copper, or a copper alloy. The surface of the negative current collector 22A is preferably roughened. This is because, through the so-called anchoring effect, the adhesion of the negative active material layer 22B to the negative current collector 22A is improved. In this case, at least in the region opposite to the negative active material layer 22B, the surface of the negative current collector 22A needs to be roughened. The roughening method can be, for example, a method of forming microparticles using electrolytic processing. In electrolytic processing, since microparticles are formed on the surface of the negative current collector 22A by electrolysis in an electrolytic cell, unevenness is provided on the surface of the negative current collector 22A. Copper foil produced by electrolysis is generally called electrolytic copper foil.

[0108] (Negative electrode active material layer 22B)

[0109] The negative electrode active material layer 22B contains one or more negative electrode materials capable of lithium insertion and extraction as the negative electrode active material. 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 conductive agent. The negative electrode material is, for example, a carbon material. This is because the crystal structure changes very little during lithium insertion and extraction, thus a high energy density can be stably obtained. Also, because the carbon material also acts as a negative electrode conductive agent, the conductivity of the negative electrode active material layer 22B is improved. The carbon material is, for example, easily graphitized carbon, difficult-to-graphitized carbon, and graphite. However, the interplanar spacing of the (002) facets in difficult-to-graphitized carbon is preferably 0.37 nm or more. The interplanar spacing of the (002) facets in graphite is preferably 0.34 nm or less. More specifically, the carbon material is, for example, pyrolytic carbon, coke, glassy carbon fibers, sintered organic polymer compounds, activated carbon, and carbon black. This type of coke includes pitch coke, needle coke, and petroleum coke. The sintered organic polymer compound is obtained by sintering (carbonizing) polymer compounds such as phenolic resin and furan resin at an appropriate temperature. Furthermore, the carbon material can be low-crystallinity carbon that has undergone heat treatment at a temperature below approximately 1000°C, or it can be amorphous carbon. It should be noted that the shape of the carbon material can be fibrous, spherical, granular, or flake-like. In the secondary battery 1, when the open-circuit voltage during full charging, i.e., the battery voltage, is 4.25V or higher, compared to the case where the open-circuit voltage during full charging is 4.20V, even using the same positive electrode active material, the lithium extraction / intercalation per unit mass increases. Therefore, the amounts of the positive and negative electrode active materials are adjusted accordingly. This results in a high energy density.

[0110] In addition, the negative electrode active material layer 22B may be a layer containing a silicon-containing material as the negative electrode active material, and the silicon-containing material contains at least one of silicon, silicon oxide, silicon carbide compound, and silicon alloy. The silicon-containing material is a general term for materials containing silicon as a constituent element. However, the silicon-containing material may also contain only silicon as a constituent element. It should be noted that the type of the silicon-containing material may be only one kind, or two or more kinds. The silicon-containing material can form an alloy with lithium, and can be elemental silicon, a silicon alloy, a silicon compound, a mixture of two or more of them, or a material containing one or two or more of their phases. In addition, the silicon-containing material can be crystalline, amorphous, or include both a crystalline part and an amorphous part. However, the elemental substance described here only refers to the elemental substance in the general sense, so it may also contain trace amounts of impurities. That is, the purity of the elemental substance is not necessarily limited to 100%. The silicon alloy contains, for example, any one or two or more of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as constituent elements other than silicon. The silicon compound contains, for example, any one or two or more of carbon and oxygen as constituent elements other than silicon. It should be noted that the silicon compound may also contain, for example, any one or two or more of the series of constituent elements described for the silicon alloy as constituent elements other than silicon. Specifically, the silicon alloy and the silicon compound are, for example, SiB4, SiB6, Mg2Si, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu5Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSiL, ZnSi2, SiC, Si3N4, Si2N2O, and SiO v (0 < v ≤ 2), etc. However, the range of v can be set arbitrarily, for example, it can be 0.2 < v < 1.4.

[0111] (Separator 23)

[0112] A separator 23 is located between the positive electrode 21 and the negative electrode 22. The separator 23 allows lithium ions to pass through and prevents short circuits caused by contact between the positive electrode 21 and the negative electrode 22. The separator 23 can be any one or more porous membranes such as synthetic resins and ceramics, or it can be a laminate of two or more porous membranes. Synthetic resins include, for example, polytetrafluoroethylene, polypropylene, and polyethylene. However, the separator 23 can have a substrate made of a single-layer polyolefin porous membrane containing polyethylene. This is because, compared to laminated membranes, it provides better high-output characteristics. When the first separator component 23A and the second separator component 23B constituting the separator 23 are both single-layer porous membranes made of polyolefin, the thickness of the porous membrane can be, for example, 10 μm or more and 15 μm or less. By having a thickness of 10 μm or more for the single-layer porous membrane made of polyolefin, internal short circuits can be sufficiently avoided. If the thickness of the single-layer porous membrane made of polyolefin is 15 μm or less, even better discharge capacity characteristics can be obtained. In addition, the areal density of this porous membrane is, for example, 6.3 g / m³. 2 And above 8.3g / m 2 The following is sufficient. If the areal density of a single-layer porous membrane made of polyolefin is 6.3 g / m³, then... 2 The above measures can effectively prevent internal short circuits. If the areal density of a single-layer porous membrane made of polyolefin is 8.3 g / m³... 2 The following approach will yield better discharge capacity characteristics.

[0113] In particular, the separator 23 may include, for example, a porous membrane serving as the substrate and a polymer compound layer disposed on one or both sides of the substrate layer. This is because the separator 23 improves the adhesion to both the positive electrode 21 and the negative electrode 22, thereby suppressing the deformation of the electrode winding 20. This suppresses the decomposition reaction of the electrolyte and also suppresses leakage of the electrolyte impregnated into the substrate layer. Therefore, even with repeated charging and discharging, the resistance does not easily increase, and battery swelling is suppressed. The polymer compound layer may, for example, contain a polymer compound such as polyvinylidene fluoride (PVDF). This is because it has excellent physical strength and is electrochemically stable. However, the polymer compound may also be a compound other than PVDF. When forming this polymer compound layer, for example, a solution in which the polymer compound is dissolved in an organic solvent is coated onto the substrate layer, and then the substrate layer is dried. It should be noted that the substrate layer may also be dried after being immersed in the solution. The polymer compound layer may also contain, for example, any one or more of insulating particles such as inorganic particles. Inorganic particles include, for example, aluminum oxide and aluminum nitride.

[0114] (electrolyte)

[0115] The electrolyte comprises a solvent and an electrolyte salt. However, the electrolyte may further comprise one or more other materials, such as additives. The solvent comprises one or more non-aqueous solvents, such as organic solvents. An electrolyte comprising a non-aqueous solvent is called a non-aqueous electrolyte. The non-aqueous solvent may, for example, contain a fluorinated compound and a dinitrile compound. The fluorinated compound may, for example, be a compound comprising at least one of fluorinated ethylene carbonate, trifluorocarbonate, methyltrifluoroethyl carbonate, fluorinated carboxylic acid ester, and fluoroether. Furthermore, the non-aqueous solvent may further comprise a nitrile compound other than a dinitrile compound, such as at least one of a mononitrile compound or a trinitrile compound. As a dinitrile compound, butadionitrile (SN) is preferred, for example. However, the dinitrile compound is not limited to butadionitrile; other dinitrile compounds, such as adiponitrile, may also be used.

[0116] The electrolyte salt may contain one or more of the following: lithium salts. However, the electrolyte salt may also contain salts other than lithium salts. These other salts may be salts of light metals other than lithium. Examples of lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium tetrachloroaluminate (LiAlCl4), dilithium hexafluorosilicate (Li2SF6), lithium chloride (LiCl), and lithium bromide (LiBr). 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 it is preferably from 0.3 mol / kg to 3 mol / kg relative to the solvent. When the electrolyte contains LiPF6 as the electrolyte salt, the concentration of LiPF6 in the electrolyte should be 1.25 mol / kg or higher and 1.45 mol / kg or lower. This is because it can prevent cycle degradation caused by salt consumption (decomposition) during high-load charging, thus improving high-load cycle characteristics. When LiBF4 is also included as the electrolyte salt in addition to LiPF6, the concentration of LiBF4 in the electrolyte should be 0.001% (wt%) or higher and 0.1% (wt%) or lower. This is because it can more effectively prevent cycle degradation caused by salt consumption (decomposition) during high-load charging, thus further improving high-load cycle characteristics.

[0117] [1-2. Actions]

[0118] In the secondary battery 1 of this embodiment, for example, during charging, lithium ions are deintercalated from the positive electrode 21 and intercalated into the negative electrode 22 via the electrolyte. Additionally, in the secondary battery 1, for example, during discharging, lithium ions are deintercalated from the negative electrode 22 and intercalated into the positive electrode 21 via the electrolyte.

[0119] [1-3. Manufacturing Method]

[0120] Apart from Figures 1 to 5B In addition, refer to Figure 8 The manufacturing method of secondary battery 1 is described. Figure 8 This is an explanation Figure 1 The diagram shows a three-dimensional representation of the manufacturing process of a secondary battery.

[0121] First, a positive current collector 21A is prepared, and a positive active material layer 21B and an insulating film 101 are selectively formed on the surface of the positive current collector 21A to form a positive electrode 21 having a positive electrode covering portion 211 and a positive current collector exposed portion 212. Next, a negative current collector 22A is prepared, and a negative active material layer 22B is selectively formed on the surface of the negative current collector 22A to form a negative electrode 22 having a negative electrode covering portion 221 and a negative electrode exposed portion 222. The positive electrode 21 and the negative electrode 22 may also be dried. Subsequently, the positive electrode 21 and the negative electrode 22 are overlapped with a first separator member 23A and a second separator member 23B in such a way that the first portions 222A of the positive current collector exposed portion 212 and the negative electrode exposed portion 222 are opposite to each other in the W-axis direction, thereby creating a laminate S20. When fabricating the laminate S20, the inner peripheral end 23A1 of the first diaphragm component 23A and the inner peripheral end 23B1 of the second diaphragm component 23B are folded back, and the inner peripheral end 23A1 and the inner peripheral end 23B1 are sandwiched between the inner peripheral end edge 21E1 of the positive electrode 21 and the negative electrode 22. Then, the laminate S20 is wound into a spiral shape to form a through hole 26. Furthermore, a fixing tape 46 is attached to the outermost periphery of the spirally wound laminate S20. Thus, as... Figure 8 As shown in (A), electrode winding body 20 is obtained.

[0122] Next, as Figure 8 As shown in (B), by pressing, for example, the end faces 41 and 42 of a plate with a thickness of 0.5 mm perpendicular to the end faces 41 and 42 of the electrode winding body 20, i.e., along the Z-axis direction, the end faces 41 and 42 are partially bent. As a result, a groove 43 extending radially (in the R direction) from the through hole 26 is created. It should be noted that... Figure 8 The number and configuration of slots 43 shown in (B) are exemplary and this disclosure is not limited thereto.

[0123] Subsequently, as Figure 8As shown in (C), substantially the same pressure is applied simultaneously from above and below the electrode winding body 20 in a direction substantially perpendicular to end faces 41 and 42. At this time, a rod-shaped clamp is inserted, for example, into the through hole 26. This causes the first portions 222A of the positive current collector exposed portion 212 and the negative current collector exposed portion 222 to be bent, making end faces 41 and 42 flat. Then, the first edge portion 212E of the positive current collector exposed portion 212 and the second edge portion 222E of the negative current collector exposed portion 222, located on end faces 41 and 42, are bent so that one side overlaps with the through hole 26. Afterward, the fan-shaped portion 31 of the positive current 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 current collector plate 25 is joined to the end face 42 by laser welding or the like.

[0124] Next, insulating tapes 53 and 54 are applied to the designated positions on the electrode winding body 20. Afterwards, as... Figure 8 As shown in (D), the strip portion 32 of the positive current collector plate 24 is bent so that the strip portion 32 is inserted into the hole 12H of the insulating plate 12. Similarly, the strip portion 34 of the negative current collector plate 25 is bent so that the strip portion 34 is inserted into the hole 13H of the insulating plate 13.

[0125] Next, the electrode winding body 20, assembled as described above, is inserted into... Figure 8 The outer can 11, as shown in (E), is then filled with electrolyte, and the bottom of the outer can 11 is welded to the negative current collector plate 25. Afterwards, a recessed portion 11S is formed near the open end 11N of the outer can 11. Then, electrolyte is injected into the outer can 11, and the strip portion 32 of the positive current collector plate 24 and the safety valve mechanism 30 are welded together.

[0126] Next, as Figure 8 As shown in (F), the recessed portion 11S is sealed by a gasket 15, a safety valve mechanism 30, and a battery cover 14.

[0127] Through the above, the secondary battery 1 of this embodiment is completed.

[0128] [1-4. Functions and Effects]

[0129] In this embodiment, the secondary battery 1 includes an insulating film 101 that spans the boundary K between the positive electrode coating 211 and the exposed positive current collector 212, covering both a portion of the positive electrode coating 211 and a portion of the exposed positive current collector 212. This effectively suppresses the dissolution of metal ions contained in the positive electrode active material layer 21B within the positive electrode coating 211. Specifically, even if a localized potential rise occurs in the thickness reduction portions 21B1S and 21B2S near the boundary K, the outflow of metal ions from the positive electrode active material layer 21B can be suppressed, and short circuits between the positive electrode 21 and the negative electrode 22 can be prevented. Therefore, higher reliability can be achieved. In the secondary battery 1, in particular, by setting the ratio of the thickness T21B of the positive electrode active material layers 21B1 and 21B2 to the coverage length W101 in the W-axis direction of the portion covered by the insulating film 101 in the positive electrode covering portion 211, i.e., the portion covered by the insulating film 101 in the reduced thickness portions 21B1S and 21B2S, to 92.5 or more, it is possible to more effectively suppress the outflow of metal ions from the positive electrode active material layer 21B.

[0130] Furthermore, by providing the insulating film 101, during the formation of the positive electrode active material layer 21B by coating, the insulating film 101 acts as a barrier, thereby suppressing the diffusion of the positive electrode active material layer 21B to the exposed portion 212 of the positive electrode current collector. Therefore, the area occupied by the thickness-reduced portions 21B1S and 21B2S of the positive electrode active material layer 21B relative to the area occupied by the flat portions 21B1F and 21B2F can be relatively reduced. Thus, it is suitable to realize a secondary battery 1 with higher capacity.

[0131] <2. Application Examples>

[0132] The use of the secondary battery 1, as an embodiment of the present disclosure described above, is as follows.

[0133] [2-1. Battery Pack]

[0134] Figure 9 This is a block diagram illustrating a circuit configuration example when a battery (hereinafter appropriately referred to as a secondary battery) according to an embodiment of the present invention is applied to a battery pack 300. The battery pack 300 includes a battery group 301, an outer casing, a switch unit 304 equipped with a charging control switch 302a and a discharging control switch 303a, a current sensing resistor 307, a temperature sensing element 308, and a control unit 310.

[0135] The battery pack 300 has a positive terminal 321 and a negative terminal 322. During charging, the positive terminal 321 and the negative terminal 322 are connected to the positive and negative terminals of the charger, respectively, for charging. In addition, when the electronic device is in use, the positive terminal 321 and the negative terminal 322 are connected to the positive and negative terminals of the electronic device, respectively, for discharging.

[0136] The battery pack 301 is formed by connecting multiple secondary batteries 301a in series or parallel. The secondary battery 1 described above can be used as the secondary battery 301a. It should be noted that... Figure 9 The example shown is six secondary batteries 301a connected in a 2-parallel, 3-series (2P3S) configuration, but any other connection method is possible, such as n in parallel and m in series (n and m are integers).

[0137] The switching unit 304 includes a charging control switch 302a and a diode 302b, as well as a discharging control switch 303a and a diode 303b, and is controlled by the control unit 310. Diode 302b has a polarity that is reversed relative to the charging current flowing from the positive terminal 321 to the battery pack 301 and forward relative to the discharging current flowing from the negative terminal 322 to the battery pack 301. Diode 303b has a polarity that is forward relative to the charging current and reverse relative to the discharging current. It should be noted that... Figure 9 In this case, the switch part 304 is located on the + side, but it can also be located on the - side.

[0138] The charging control switch 302a is controlled by the charging / discharging control unit to turn off when the battery voltage reaches the overcharge detection voltage, so that no charging current flows through the current path of the battery pack 301. After the charging control switch 302a is turned off, discharge can only be performed using diode 302b. Additionally, it is controlled by the control unit 310 to turn off when a large current flows during charging, thereby cutting off the charging current flowing through the current path of the battery pack 301. The discharging control switch 303a is controlled by the control unit 310 to turn off when the battery voltage reaches the over-discharge detection voltage, so that no discharging current flows through the current path of the battery pack 301. After the discharging control switch 303a is turned off, charging can only be performed using diode 303b. Additionally, it is controlled by the control unit 310 to turn off when a large current flows during discharging, thereby cutting off the discharging current flowing through the current path of the battery pack 301.

[0139] Temperature sensing element 308, such as a thermistor, is disposed near battery pack 301, measures the temperature of battery pack 301, and supplies the measured temperature to control unit 310. Voltage sensing unit 311 measures the voltage of battery pack 301 and each secondary battery 301a constituting it, performs A / D conversion on the measured voltage, and supplies it to control unit 310. Current sensing unit 313 measures the current using current sensing resistor 307 and supplies the measured current to control unit 310. Switch control unit 314 controls charging control switch 302a and discharging control switch 303a of switch unit 304 based on the voltage and current input from voltage sensing unit 311 and current sensing unit 313.

[0140] When the voltage of any one of the multiple secondary batteries 301a falls below the overcharge detection voltage or the over-discharge detection voltage, and when a large current flows rapidly, the switch control unit 314 prevents overcharging, over-discharging, and overcurrent charging / discharging by sending a control signal to the switch unit 304. Here, for example, in the case of a lithium-ion secondary battery, the overcharge detection voltage is set to, for example, 4.20V ± 0.05V, and the over-discharge detection voltage is set to, for example, 2.4V ± 0.1V.

[0141] The charge / discharge switch can be a semiconductor switch such as a MOSFET. In this case, the parasitic diodes of the MOSFET function as diodes 302b and 303b. When using a P-channel FET as the charge / discharge switch, the switch control unit 314 supplies control signals DO and CO to the gates of the charge control switch 302a and the discharge control switch 303a, respectively. When the charge control switch 302a and the discharge control switch 303a are P-channel type, they are turned on by a gate potential that is more than a predetermined value lower than the source potential. That is, during normal charging and discharging operations, the control signals CO and DO are set to a low level, and the charge control switch 302a and the discharge control switch 303a are turned on.

[0142] For example, during overcharging or over-discharging, control signals CO and DO are set to high level, and charging control switch 302a and discharging control switch 303a are set to the off state.

[0143] The memory 317 is composed of RAM and ROM, such as EPROM (Erasable Programmable Read Only Memory), which is a non-volatile memory. The memory 317 stores values ​​calculated by the control unit 310, the internal resistance values ​​of each secondary battery 301a in its initial state measured during the manufacturing process, and can also be rewritten as needed. Furthermore, by storing the full charge capacity of the secondary battery 301a, the remaining capacity can be calculated, for example, together with the control unit 310.

[0144] In the temperature detection unit 318, the temperature is measured using the temperature detection element 308, and charging and discharging control is performed when abnormal heating occurs, or correction is performed during the calculation of remaining capacity.

[0145] [2-2. Energy Storage System]

[0146] The secondary battery described in one embodiment of the present disclosure can be installed in devices such as electronic devices, power tools, electric vehicles, electric aircraft, and energy storage devices, or used to supply electricity.

[0147] Examples of electronic devices include laptops, smartphones, tablets, PDAs (portable information terminals), mobile phones, wearable devices, cordless phone extensions, camcorders, 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, stereo systems, water heaters, microwave ovens, dishwashers, washing machines, dryers, lighting equipment, toys, medical devices, robots, road regulators, and traffic lights.

[0148] In addition, examples of electric vehicles include railway vehicles, golf carts, electric trolleys, and electric vehicles (including hybrid vehicles), which are used as power sources for their propulsion or auxiliary power. Examples of energy storage devices include power sources for storing electricity in buildings, primarily residential buildings, or for power generation equipment.

[0149] The present disclosure has been described above with an example of one embodiment, but the configuration of the present disclosure is not limited to the configuration described in one embodiment, and various modifications can be made. 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 in the thickness direction of the positive electrode 21, but they may also be different from each other.

[0150] Furthermore, while the above-described embodiment and examples describe the use of lithium as the electrode reactant, this electrode reactant is not particularly limited. Therefore, as mentioned above, the electrode reactant can be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. Additionally, the electrode reactant can also be other light metals such as aluminum.

[0151] The effects described in this specification are merely illustrative, and the effects of this disclosure are not limited to those described in this specification. Therefore, other effects can also be obtained with respect to this disclosure.

[0152] Therefore, this disclosure can be made in the following ways.

[0153] <1>

[0154] A positive electrode for a secondary battery has the following characteristics:

[0155] Positive electrode coating portion, wherein a positive electrode active material layer is coated on the positive electrode current collector;

[0156] A positive current collector exposed portion, wherein the positive current collector is not covered by the positive active material layer and is exposed, and the exposed portion is adjacent to the positive electrode coating portion in a first direction; and

[0157] An insulating film extends across the boundary between the positive electrode covering portion and the exposed positive electrode current collector portion, covering both a portion of the positive electrode covering portion and a portion of the exposed positive electrode current collector portion.

[0158] The positive electrode active material layer includes a thickness-reducing portion, wherein the thickness of the thickness-reducing portion decreases as it approaches the boundary in the first direction.

[0159] A portion of the reduced thickness is covered by the insulating film.

[0160] <2>

[0161] According to the above <1> The positive electrode for the aforementioned secondary battery, wherein,

[0162] The ratio of the thickness of the positive electrode active material layer to the length of the coating portion covered by the insulating film in the positive electrode coating in the first direction is 92.5 or more.

[0163] <3>

[0164] According to the above <2> The positive electrode for the aforementioned secondary battery, wherein,

[0165] The coverage length is greater than 0 mm and less than 0.2 mm.

[0166] <4>

[0167] According to the above <2> or <3> The positive electrode for the aforementioned secondary battery, wherein,

[0168] The thickness of the insulating film is 0.0012 mm or more.

[0169] <5>

[0170] According to the above <1> to <4> The positive electrode for the secondary battery described in any one of the following statements, wherein,

[0171] The positive electrode active material layer contains a positive electrode active material, which contains at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0172] <6>

[0173] A secondary battery, comprising:

[0174] An electrode winding body, wherein the electrode winding body is formed by winding a laminated body around a central axis extending along the first direction, the laminated body comprising the above-mentioned components in sequence. <1> to <5> The positive electrode, the first diaphragm, the negative electrode, and the second diaphragm as described in any one of the following.

[0175] <7>

[0176] According to the above <6> The aforementioned secondary battery, wherein,

[0177] The secondary battery also includes a positive electrode current collector and a negative electrode current collector.

[0178] The electrode winding has a first end face and a second end face that are opposed to each other in the first direction.

[0179] The positive current collector plate faces the first end face of the electrode winding body and is engaged with the exposed portion of the positive current collector of the positive electrode.

[0180] The negative electrode current collector is opposite to the second end face of the electrode winding and is connected to the negative electrode.

[0181] <8>

[0182] A battery pack having:

[0183] The above <6> or <7> The secondary battery; a control unit for controlling the secondary battery; and an outer casing housing the secondary battery.

Claims

1. A positive electrode for a secondary battery, characterized in that, has: a positive electrode coating portion in which a positive electrode active material layer is coated on a positive electrode current collector; a positive electrode current collector exposed portion in which the positive electrode current collector is exposed without being covered by the positive electrode active material layer, the positive electrode current collector exposed portion being adjacent to the positive electrode coating portion in a first direction; and an insulating film covering both a portion of the positive electrode coating portion and a portion of the positive electrode current collector exposed portion across a boundary between the positive electrode coating portion and the positive electrode current collector exposed portion, the positive electrode active material layer includes a thickness reduction portion that reduces in thickness as it approaches the boundary in the first direction, a portion of the thickness reduction portion is covered by the insulating film.

2. The positive electrode for a secondary battery according to claim 1, characterized in that a ratio of a thickness of the positive electrode active material layer to a coating length of a coated portion in the positive electrode coating portion that is covered by the insulating film in the first direction is 92.5 or greater.

3. The positive electrode for a secondary battery according to claim 2, characterized in that the coating length is greater than 0 mm and 0.2 mm or less.

4. The positive electrode for a secondary battery according to claim 2 or 3, characterized in that a thickness of the insulating film is 0.0012 mm or greater.

5. The positive electrode for a secondary battery according to any one of claims 1 to 3, characterized by the positive electrode active material layer contains a positive electrode active material that contains at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

6. A secondary battery characterized by comprising: provided with: an electrode roll body that is a laminate including the positive electrode for a secondary battery according to any one of claims 1 to 5, a first separator, a negative electrode, and a second separator in this order, and is wound around a center axis extending in the first direction.

7. The secondary battery according to claim 6, characterized in that the secondary battery is further provided with a positive electrode current collector plate and a negative electrode current collector plate, the electrode roll body has a first end surface and a second end surface that face each other in the first direction, the positive electrode current collector plate faces the first end surface of the electrode roll body and is joined to the positive electrode current collector exposed portion of the positive electrode, the negative electrode current collector plate faces the second end surface of the electrode roll body and is connected to the negative electrode.

8. A battery pack, characterized by, provided with: the secondary battery according to claim 6 or 7; a control portion that controls the secondary battery; and an exterior body in which the secondary battery is built.

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