Electrode and secondary battery

Abstract

In a positive electrode as an example of an embodiment, a positive electrode mixture layer (31A) has a trailing region (33A) formed by a plurality of trailing portions (34A) extending in the longitudinal direction of a positive electrode core (30) from one edge of a core exposed portion (32A). The positive electrode mixture layer (31B) has a trailing region (33B) formed by a plurality of trailing portions (34B) extending in the longitudinal direction of the positive electrode core (30) from one edge of the core exposed portion (32B). The positive electrode mixture layers (31A, 31B) are formed such that at least the trailing tip regions (37A, 37B) do not overlap in the thickness direction of the positive electrode core (30).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an electrode and a secondary battery provided with the electrode. BACKGROUND

[0002] Generally, an electrode for a secondary battery, which is manufactured by applying slurry of an agent containing active material particles to both faces of a core body composed of a metal foil, drying and compressing the applied film, has an agent layer formed on both faces of the core body. In this case, there is a case where a core body exposed portion where the surface of the core body is exposed is provided by intermittently applying the agent slurry. The core body exposed portion is, for example, a portion to which an electrode lead is connected and is provided in the middle of the length direction of the electrode.

[0003] In the case where the core body exposed portion is provided by intermittently applying the agent slurry, a tailing portion is formed at the terminal end of the application of the agent slurry. The tailing portion is a thin line-shaped portion that extends long in the application direction of the agent slurry, and particularly, the tip end portion thereof is in a state where active material particles are dispersed. Therefore, when pressure is applied to the electrode, the portion where the core body is pinched by the tailing portion is sometimes strongly compressed, and the active material particles intrude into the core body, resulting in partial thinning of the thickness of the core body.

[0004] Conventionally, a technique of forming a protective layer at a predetermined portion to be cut for the purpose of suppressing burrs generated in the cutting process of the electrode due to the tailing portion is known (see Patent Literature 1). In Patent Literature 1, it is described that the generation of burrs in the cutting process is suppressed by providing the protective layer at the portion where the tailing portion is formed.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: International Publication No. 2019 / 077943 SUMMARY

[0008] The tailing portion is formed in multiple from one edge of the core body exposed portion, but according to the research results of the present inventors and others, it is known that the core body is damaged due to the tailing portion when the charge and discharge of the secondary battery are repeated. In the case where the cracks of the core body become large and the core body is broken, problems such as an increase in resistance and a decrease in capacity occur, and therefore, it is an important issue to suppress the damage of the core body caused by the tailing portion.

[0009] An electrode according to one embodiment of the present disclosure includes a long strip-shaped core body including a first end and a second end in a length direction, and a first binder layer and a second binder layer disposed on both surfaces of the core body, respectively, a first core body exposed portion and a second core body exposed portion being provided in a middle portion in the length direction of the core body so as to overlap in a thickness direction of the core body, the first binder layer has a first tail region in which a plurality of first tail portions extending in the length direction of the core body from an edge of the first end side of the first core body exposed portion are formed, the second binder layer has a second tail region in which a plurality of second tail portions extending in the length direction of the core body from an edge of the first end side of the second core body exposed portion are formed, in each of the first tail region and the second tail region, a range from a leading end of a tail portion located on the first end side to a leading end of a tail portion located on the first end side is defined as a first tail leading end region and a second tail leading end region, respectively, and the first binder layer and the second binder layer are formed so that the first tail leading end region and the second tail leading end region do not overlap in the thickness direction of the core body.

[0010] An electrode according to another embodiment of the present disclosure includes a long strip-shaped core body including a first end and a second end in a length direction, and a first binder layer and a second binder layer disposed on both surfaces of the core body, respectively, a first core body exposed portion and a second core body exposed portion being provided in a middle portion in the length direction of the core body so as to overlap in a thickness direction of the core body, the first binder layer has a first tail region in which a plurality of first tail portions extending in the length direction of the core body from an edge of the first end side of the first core body exposed portion are formed, the second binder layer has a second tail region in which a plurality of second tail portions extending in the length direction of the core body from an edge of the first end side of the second core body exposed portion are formed, and the first tail region and the second tail region are formed so that a range of more than 50% of a length of each region in the length direction of the core body does not overlap in the thickness direction of the core body.

[0011] A secondary battery according to the present disclosure includes a jelly-roll type electrode body including a positive electrode, a negative electrode, and a separator, and the electrode according to the present disclosure is applied to the positive electrode.

[0012] According to the electrode according to the present disclosure, damage to the core body caused by the tail portions can be effectively suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is an axial cross-sectional view of a cylindrical battery as one example of an embodiment.

[0014] Figure 2This is a front view of a portion of the positive electrode, representing an example of an implementation method.

[0015] Figure 3 yes Figure 2 The AA line cross-section diagram.

[0016] Figure 4 This is a magnified view of the tail section of the positive electrode and its surrounding area. Figure 4 (a) represents the first surface of the positive electrode (front view). Figure 4 (b) represents the second side of the positive electrode (rear view).

[0017] Figure 5 This is a cross-sectional view showing an existing example of an electrode. Detailed Implementation

[0018] As described above, when the core is exposed by intermittently applying the slurry, a trailing portion is formed at the end of the slurry application. The slurry is applied, for example, by a die coater, but it is difficult to stop the application of the slurry so that the position of the slurry end along the edge of the core exposure is a straight line. At the end of the application, the slurry is applied from the die head in a trailing manner, forming multiple trailing portions.

[0019] exist Figure 5 The diagram schematically illustrates a cross-section of an electrode plate cut along the length of its tail in a conventional electrode. For example... Figure 5 As shown, the active material particles are dispersed, especially near the leading edge of the tail section. For example, if the negative electrode swells during the charging and discharging of the secondary battery, the dispersed active material particles exert large local pressure on the core. As a result, sometimes the active material particles penetrate the core, causing the core thickness to become locally thinner.

[0020] According to the research results of the inventors, during repeated charging and discharging of secondary batteries, damage such as cracking occurs in the portion of the core containing the trailing portion. Furthermore, it was discovered that by offsetting the trailing portions on the surface and back of the electrode plates so that the leading edge regions of the trailing portions do not overlap in the thickness direction of the core, or by offsetting the trailing portions on the surface and back so that more than 50% of the length of the trailing portion does not overlap in the thickness direction of the core, damage to the core can be effectively suppressed.

[0021] Hereinafter, an example of an embodiment of the electrode and secondary battery of the present disclosure will be described in detail with reference to the accompanying drawings. The embodiment described below is merely an example, and the present disclosure is not limited to the following embodiment. Furthermore, the present disclosure includes the selective combination of the constituent elements of the embodiment described below.

[0022] Hereinafter, as an example of an embodiment of the secondary battery of the present disclosure, a cylindrical battery 10 in which a wound electrode body 14 is housed in a bottomed cylindrical outer can 16 is illustrated. However, the outer can of the battery is not limited to a cylindrical outer can. The secondary battery of the present disclosure may also be, for example, a square battery with a square outer can, or a pouch-type battery with an outer can composed of a laminate containing a metal layer and a resin layer.

[0023] Figure 1 This is a schematic diagram showing an axial cross-section of a cylindrical battery 10 as an example of an embodiment. Figure 1 As shown, the cylindrical battery 10 includes an electrode body 14, an electrolyte, and a bottomed cylindrical outer container 16 for housing the electrode body 14 and the electrolyte. The electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and has a structure in which the positive electrode 11 and the negative electrode 12 are wound into a spiral shape with the separator 13 in between. The outer container 16 is a bottomed cylindrical metal container with an opening on one axial side, and the opening of the outer container 16 is closed by a sealing body 17. Hereinafter, for ease of explanation, the sealing body 17 side of the cylindrical battery 10 will be described as upper, and the bottom side of the outer container 16 will be described as lower.

[0024] The electrolyte can be an aqueous electrolyte, but a non-aqueous electrolyte is used in this embodiment. The non-aqueous electrolyte has lithium-ion conductivity. The non-aqueous electrolyte can be a liquid electrolyte (electrolyte) or a solid electrolyte. The cylindrical battery 10 is, for example, a non-aqueous electrolyte secondary battery, wherein a lithium-ion battery is preferred.

[0025] Liquid electrolytes (electrolytes) comprise a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Non-aqueous solvents can include, for example, esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may contain halogen-substituted derivatives (e.g., fluoroethylene carbonate) formed by replacing at least a portion of the hydrogen atoms in these solvents with halogen atoms such as fluorine. The electrolyte salt is, for example, a lithium salt such as LiPF6.

[0026] As a solid electrolyte, examples include solid or gel-like polymer electrolytes and inorganic solid electrolytes. As an inorganic solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. Polymer electrolytes, for example, comprise lithium salts and matrix polymers, or non-aqueous solvents, lithium salts, and matrix polymers. As a matrix polymer, for example, a polymer material that absorbs non-aqueous solvents and gels. Examples of polymer materials include fluoropolymers, acrylic resins, and polyether resins.

[0027] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode body 14 are all strip-shaped elongated bodies, which are alternately stacked in the radial direction of the electrode body 14 by being wound into a spiral. To prevent lithium deposition, the negative electrode 12 is formed to be one size larger than the positive electrode 11. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the length and width directions (short side direction). The separator 13 is formed to be at least one size larger than the positive electrode 11, and two sheets are arranged to sandwich the positive electrode 11. The cylindrical battery 10 has insulating plates 18 and 19 respectively disposed on the upper and lower parts of the electrode body 14.

[0028] The electrode body 14 has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like. In this embodiment, the positive electrode lead 20 is connected to the central portion of the positive electrode 11 in the longitudinal direction, and the negative electrode lead 21 is connected to the end of the negative electrode 12 located on the outer side of the electrode body 14 in the longitudinal direction. The positive electrode lead 20 is connected to the lower surface of the bottom plate of the sealing body 17, i.e., the inner terminal plate 23, and the negative electrode lead 21 is connected to the inner surface of the bottom of the outer packaging can 16. Therefore, the sealing body 17 becomes the external terminal of the positive electrode, and the outer packaging can 16 becomes the external terminal of the negative electrode.

[0029] It should be noted that the negative electrode 12 can also be arranged on the outer peripheral surface of the electrode body 14, so that the exposed part of the negative electrode core contacts the inner peripheral surface of the outer can 16, thereby electrically connecting the negative electrode 12 to the outer can 16. Alternatively, a negative electrode lead can be connected to the center of the negative electrode 12 along its length.

[0030] The positive electrode 11 has a positive electrode core and a positive electrode binder layer disposed on the positive electrode core. The positive electrode core can be a foil of a metal stable within the potential range of the positive electrode 11, such as aluminum, aluminum alloy, stainless steel, or titanium, or a film having a surface layer made of these metals. The thickness of the positive electrode core is preferably 5 μm or more and 25 μm or less, more preferably 10 μm or more and 20 μm or less. The positive electrode binder layer comprises a positive electrode active material, a conductive agent, and a binder, and is preferably disposed on both sides of the positive electrode core. The thickness of the positive electrode binder layer is greater than the thickness of the positive electrode core; on one side of the positive electrode core, the thickness of the positive electrode binder layer is, for example, 60 μm or more and 120 μm or less.

[0031] The positive electrode active material can be a lithium transition metal composite oxide containing transition metal elements such as Ni, Co, and Mn. Examples of metal elements contained in lithium transition metal composite oxides include Ni, Co, Mn, Al, Be, B, Na, Mg, Si, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ta, W, Pb, and Bi. Preferably, it contains at least one of Ni, Co, and Mn. A single lithium transition metal composite oxide can be used, or multiple oxides can be used in combination.

[0032] The positive electrode active material is a particle with a median particle size (D50) on a volume basis, for example, 10 μm or more and 30 μm or less, preferably 15 μm or more and 25 μm or less. D50 refers to the particle size in the volume-based particle size distribution where the cumulative frequency from the smallest particle size accounts for 50%. The particle size distribution of lithium transition metal composite oxides can be measured using a laser diffraction-type particle size distribution measuring device (e.g., Microtrac BEL Co., Ltd., MT3000II) with water as the dispersion medium. Alternatively, the particle size distribution can be measured using an image-based particle size distribution measuring device (e.g., Microtrac BEL Co., Ltd., CAMSIZER X2) with water as the dispersion medium.

[0033] The thickness of the positive electrode core can be greater than the D50 of the positive electrode active material particles, but from the viewpoint of high capacity, it is preferable that the D50 of the active material particles is less than or equal to that of the core. However, if the particle size of the active material becomes larger relative to the thickness of the core, damage to the core caused by tailing is more likely to occur. Details will be described later. By applying a configuration that staggers the tailing regions on the surface and back of the electrode plate to the positive electrode 11, damage to the positive electrode core can be effectively suppressed even under such circumstances.

[0034] Examples of conductive agents contained in the positive electrode binder layer include acetylene black, carbon black such as Ketjen black, graphite, carbon nanotubes (CNTs), carbon nanofibers, graphene, metal fibers, metal powders, and conductive whiskers. Examples of binders include fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymers, and ethylene-propylene-butadiene copolymers, polyacrylonitrile (PAN), polyimide, polyamide, and acrylic resins such as ethylene-acrylic acid copolymers. Furthermore, these resins can be used in combination with carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0035] The positive electrode 11 is manufactured by coating a positive electrode slurry containing a positive electrode active material, a conductive agent, and a binder onto a positive electrode core, drying the coating, and then compressing it to form a positive electrode slurry layer on both sides of the positive electrode core. The positive electrode 11, with the core exposed portion connected to the positive electrode lead 20 located in the middle of its length, is manufactured by intermittently coating the positive electrode slurry and temporarily stopping the coating process midway; the uncoated portion becomes the core exposed portion. The dispersion medium for the positive electrode slurry is, for example, N-methyl-2-pyrrolidone (NMP).

[0036] The negative electrode 12 has a negative electrode core and a negative electrode binder layer disposed on the negative electrode core. The negative electrode core can be made of foil of metals stable within the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, or nickel alloy, or a film having a surface layer made of these metals. The negative electrode binder layer contains a negative electrode active material and a binder, and is preferably disposed on both sides of the negative electrode core. Similar to the positive electrode 11, the negative electrode 12 can be manufactured by coating the negative electrode core with a negative electrode binder slurry, drying the coating, and then compressing it to form a negative electrode binder layer on both sides of the negative electrode core. It should be noted that lithium metal foil can also be used as the negative electrode 12. Alternatively, the negative electrode 12 can also be composed only of a negative electrode core, with lithium metal deposited on the surface of the core during battery charging.

[0037] The negative electrode active material only needs to reversibly absorb, store, and release lithium ions; there are no particular restrictions, and carbon materials such as graphite are commonly used. Alternatively, elements alloyed with Li, such as Si and Sn, or materials containing these elements can be used as negative electrode active materials. Silicon-containing materials containing Si are preferred. Furthermore, lithium titanate, which has a higher charge / discharge potential relative to metallic lithium than carbon materials, can also be used as a negative electrode active material. A single negative electrode active material can be used, or multiple materials can be used in combination.

[0038] Similar to the case of positive electrode 11, the binder contained in the negative electrode binder layer can also be fluoropolymer, olefin resin, PAN, polyimide, polyamide, acrylic resin, etc., and can also be polyvinyl acetate, styrene-butadiene rubber (SBR), etc. SBR is preferred. A single binder can be used, or multiple binders can be used in combination. Furthermore, the negative electrode binder layer preferably contains CMC or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc. It should be noted that the negative electrode binder layer may also contain conductive agents such as CNTs.

[0039] The diaphragm 13 can be a porous sheet with ion permeability and insulation. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. Polyolefins such as polyethylene and polypropylene, and cellulose are suitable materials for the diaphragm 13. The diaphragm 13 can be a single-layer structure or a multi-layer structure. Alternatively, a resin layer with high heat resistance, such as an aromatic polyamide resin, can be formed on the surface of the diaphragm 13. A filler layer containing inorganic fillers can be formed at the interface between the diaphragm 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0040] As described above, the outer can 16 is a bottomed cylindrical metal container with an axial opening on one side. A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the airtightness of the battery interior and the insulation between the outer can 16 and the sealing body 17. A groove 22 is formed in the outer can 16, with a portion of its side protruding inward. The groove 22 is preferably formed in a ring shape along the circumference of the outer can 16, and the sealing body 17 is supported on its upper surface. The sealing body 17 is fixed to the upper part of the outer can 16 by the groove 22 and the open end of the outer can 16 that is crimped to the sealing body 17.

[0041] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cover 27 are stacked sequentially from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a circular or annular shape, and all components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and the insulating member 25 is sandwiched between their respective peripheral portions. If the battery malfunctions and the internal pressure rises, the lower valve body 24 deforms and breaks by pushing the upper valve body 26 upwards towards the cover 27, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 breaks, and gas is discharged from the opening of the cover 27.

[0042] The following is for reference Figures 2 to 4 The composition of the positive electrode 11 will be explained in more detail. Figure 2 This is a front view of the positive electrode 11, showing the exposed core portion 32A and its vicinity. It should be noted that... Figure 2 In the middle, the protective strip 29 is represented by an imaginary line. Figure 3 yes Figure 2 AA line cross-section diagram, Figure 4 (a) is an enlarged view of the trailing region 33A and its vicinity. Figure 4 (b) is an enlarged view of the trailing region 33B and its vicinity.

[0043] like Figures 2 to 4As shown, the positive electrode 11 includes an elongated positive electrode core 30, a first positive electrode compound layer 31A disposed on a first surface of the positive electrode core 30, and a second positive electrode compound layer 31B disposed on a second surface of the positive electrode core 30. It has a structure in which core exposed portions 32A and 32B are provided at the middle of the positive electrode core 30 along its length. The first surface of the positive electrode core 30 can face either the outer or inner surface of the electrode body 14. In this embodiment, the first surface is the outer surface (surface) facing the outer surface of the electrode body 14, and the second surface is the inner surface (back surface) facing the inner surface. The positive electrode lead 20 is bonded to the core exposed portion 32A on the first surface. The positive electrode lead 20 is configured, for example, not to overlap with the positive electrode compound layer 31A, and is ultrasonically welded to the positive electrode core 30.

[0044] The positive electrode core 30 is preferably composed of a strip-shaped metal foil comprising a first end and a second end along its length. Figure 2 and Figure 4 In the diagram, X represents the length direction of the positive electrode core 30, and Y represents the width direction. The X-direction side is designated as the first end side of the positive electrode core 30 along its length. The first end of the positive electrode core 30 is, for example, located on the winding start side of the positive electrode 11. Core exposure portions 32A and 32B can be formed at substantially equal distances from the first and second ends of the positive electrode core 30. Furthermore, the core exposure portions 32A and 32B are arranged to overlap in the thickness direction of the positive electrode core 30.

[0045] In this embodiment, one core exposure portion is formed on both the surface and the back surface of the positive electrode 11, but multiple core exposure portions may also be formed at intervals along the length direction (X direction) of the positive electrode 11. When multiple core exposure portions are formed along the length direction of the positive electrode 11, it is preferable to apply the configuration of the trailing regions 33A and 33B described later in all core exposure portions.

[0046] The exposed core portion 32A has dimensions that allow for the placement of the positive electrode lead 20 without overlapping with the positive electrode coating layer 31A. The exposed core portion 32A is longer in the Y direction than in the X direction, and is formed across the entire width of the positive electrode core 30. It should be noted that the exposed core portion may not be formed to a length extending from one end to the other in the width direction of the positive electrode core 30. The width (X-direction length) of the exposed core portion 32A is preferably 1.1 times or more and 2.0 times or less, more preferably 1.2 times or more and 1.5 times or less, of the width of the positive electrode lead 20. The width of the exposed core portion 32A refers to the length along the X direction from the coating start end portion 35A to the coating end portion 36A (refer to...). Figure 4Multiple trailing portions 34A are formed at the coating terminal portion 36A, and the position corresponding to the coating terminal portion 36A is set as the edge of the winding start side (the first end side of the positive electrode core 30) of the core exposure portion 32A. Similarly, the width of the core exposure portion 32B refers to the length along the X direction from the coating start portion 35B to the coating terminal portion 36B, and the position corresponding to the coating terminal portion 36B is set as the edge of the winding start side of the core exposure portion 32B. Details will be described later. The core exposure portion 32B is formed to be wider than the core exposure portion 32A.

[0047] A protective tape 29 is attached to the surface and back of the positive electrode 11, covering the positive electrode lead 20 and the exposed core portions 32A, 32B. The protective tape 29 is, for example, an insulating tape comprising a tape substrate and an adhesive layer formed on one side of the substrate. Examples of resins constituting the tape substrate include polyester, polypropylene, polyimide, polyphenylene sulfide, polyetherimide, and polyamide. The thickness of the tape substrate is, for example, 10 μm or more and 30 μm or less. The width of the protective tape 29 is larger than the width of the exposed core portions 32A, 32B, and the protective tape 29 covers the entire exposed core portions 32A, 32B. Furthermore, the protective tape 29 is preferably attached to the surface and back of the positive electrode 11 in such a way that it covers the entire trailing regions 33A, 33B.

[0048] Tail regions 33A and 33B, comprising multiple tail portions 34A and 34B, are formed on the surface and back side of the positive electrode 11, respectively. In this embodiment, the X direction is the coating direction of the positive electrode slurry, and the tail portions 34A and 34B extend along the X direction. The tail portion 34A is a thin line-shaped portion of the positive electrode slurry layer 31A, with a sharp decrease in thickness towards the leading edge of the tail portion 34A. In the region outside the tail portion 34A, multiple positive electrode active material particles are stacked in the thickness direction of the layer to form the region outside the tail portion 34A of the positive electrode slurry layer 31A. The leading edge of the tail portion 34A has a monolayer structure in which active material particles are dispersed (see reference). Figure 5 ).

[0049] The first trailing portions 34A have the same length and width, but their dimensions are not constant. For example, the length of the trailing portion 34A is more than 1 mm and less than 5 mm, and the width of the trailing portion 34A is less than 30% of its length. The trailing portions 34A have a tapered shape that gradually decreases in thickness and width from the root towards the front end. It should be noted that the second trailing portion 34B has the same shape and dimensions as the first trailing portion 34A.

[0050] The first trailing region 33A is formed along the edge of the first core exposed portion 32A on the winding start side (the edge of the first end side of the positive electrode core 30). Similarly, the second trailing region 33B is formed along the edge of the second core exposed portion 32B on the winding start side. Since the trailing regions 33A and 33B are formed at the coating terminal of the positive electrode slurry, in this embodiment, the positive electrode slurry is coated from the first end side of the positive electrode core 30. Furthermore, since the positive electrode slurry layers 31A and 31B are formed throughout the entire width of the positive electrode core 30, the trailing regions 33A and 33B are also formed throughout the entire width of the positive electrode core 30.

[0051] The trailing regions 33A and 33B formed at the edges of the core exposed portions 32A and 32B on the winding start side are configured such that at least their front ends do not overlap in the thickness direction of the positive electrode core 30. On the other hand, the edges of the core exposed portions 32A and 32B on the winding end side (the edges on the second end side of the positive electrode core 30) overlap in the thickness direction of the positive electrode core 30. The coating start points 35A and 35B, located at positions corresponding to the edges of the core exposed portions 32A and 32B on the winding end side, extend in a straight line when viewed from the front and overlap each other in the thickness direction of the positive electrode core 30. No trailing portion is formed at the coating start point of the positive electrode slurry.

[0052] The coating start points 35A and 35B can be substantially overlapped. The positions of the coating start points 35A and 35B can be offset within a range considered to be substantially overlapping (e.g., about 1 mm in the X direction). Alternatively, the position of the coating start point 35B can be moved closer to the winding start side than the position of the coating start point 35A, but in this case, aligning the core exposed portions 32A and 32B becomes difficult, resulting in a need to increase the width of the core exposed portions 32A and 32B. By aligning the positions of the coating start points 35A and 35B on both the surface and back of the positive electrode 11, the core exposed portions 32A and 32B can be formed with the required minimum width, contributing to higher battery capacity.

[0053] In this embodiment, the range from the front end P1 located at the second end closest to the positive electrode core 30 to the front end P2 located at the first end closest to the positive electrode core 30 among the plurality of trailing portions 34A is defined as the first trailing front end region 37A. Similarly, the range from the front end P1 located at the second end closest to the positive electrode core 30 to the front end P2 located at the first end closest to the positive electrode core 30 among the plurality of trailing portions 34B is defined as the second trailing front end region 37B. Furthermore, the positive electrode binder layers 31A and 31B are formed such that the trailing front end regions 37A and 37B do not overlap in the thickness direction of the positive electrode core 30.

[0054] The trailing front region 37A is the length range along the X direction from the front end P1 of the trailing portion 34A to the front end P2 of the trailing portion 34A, and is a region with a certain width along the Y direction (the same applies to the trailing front region 37B). The X-direction lengths of the trailing front regions 37A and 37B may differ from each other, but may be substantially the same, for example. The X-direction length of the front region 37A is less than 50% of the average length of the trailing portion 34A, for example, more than 3% and less than 30%.

[0055] As described above, the thickness and width of the trailing portions 34A and 34B decrease from the coating terminal portions 36A and 36B, which serve as the root, toward the front end. In particular, in the trailing front end regions 37A and 37B, the active material particles are easily dispersed. According to the research results of the inventors, when the negative electrode 12 expands due to repeated charge-discharge cycles, when the front end of the trailing portion overlaps on the surface and back of the core, the core is locally compressed and becomes thinner. In contrast, when the trailing portion exists only on one side of the core, the thinning of the core that would lead to damage such as cracking (foil breakage) does not occur.

[0056] The trailing regions 33A and 33B can also be configured such that a length of more than 50% of each region along the X direction does not overlap in the thickness direction of the positive electrode core 30. Positive electrode binder layers 31A and 31B are formed such that a length of more than 50% of the longest trailing portion 34A of the trailing region 33A does not overlap with the trailing region 33B, and a length of more than 50% of the longest trailing portion 34B of the trailing region 33B does not overlap with the trailing region 33A.

[0057] The trailing regions 33A and 33B can be further configured such that the entirety of each region does not overlap in the thickness direction of the positive electrode core 30. In this embodiment, the trailing regions 33A and 33B are completely staggered on the surface and back side of the positive electrode 11, and the width of the core exposed portion 32B is greater than the width of the trailing region 33A by the same amount as the core exposed portion 32A.

[0058] As described above, the positive electrode 11, which has exposed core portions 32A and 32B in the middle of the length direction of the electrode plate, is manufactured by intermittently coating the positive electrode slurry, where the coating of the positive electrode slurry is temporarily stopped midway. At this time, the portion without positive electrode slurry coating becomes the exposed core portions 32A and 32B, and the coating terminal portions 36A and 36B where the coating of the slurry has stopped form tailing regions 33A and 33B. In this embodiment, from the viewpoint of coating thickness stability and productivity improvement, the coating of the first positive electrode slurry layer 31A is formed before the coating of the second positive electrode slurry layer 31B. The coating of the positive electrode slurry layer 31B is formed on the surface and back of the positive electrode 11 such that the tailing front portions 37A and 37B do not overlap with each other, and the length range of the tailing regions 33A and 33B in the X direction does not overlap with each other, thus offsetting the position of the coating terminal portions.

[0059] Example

[0060] The present disclosure is further illustrated below by way of examples, but the present disclosure is not limited to these examples.

[0061] <Example 1>

[0062] [The production of the positive electrode]

[0063] Lithium-nickel composite oxide with a D50 of 10 μm was used as the positive electrode active material. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed at a solid content mass ratio of 97:2:1, and N-methyl-2-pyrrolidone (NMP) was used as the dispersion medium to prepare the positive electrode slurry. This slurry was coated onto both sides of a positive electrode core consisting of a 15 μm thick aluminum foil using a die-coating machine. After drying, the coating was compressed using calendering rollers. Then, it was cut to the specified electrode size, resulting in a positive electrode with a positive electrode slurry layer formed on both sides of the positive electrode core. The core exposed portion, serving as the connection part for the positive electrode lead, is formed in the middle of the positive electrode along its length.

[0064] The positive electrode slurry is applied using a controlled die coater so that the first exposed portion of the positive electrode core on its first surface is approximately 10 mm wide (length in the X direction). At this time, the first trailing region formed at the end of the slurry coating is approximately 3 mm wide (length in the X direction). It should be noted that the first exposed portion of the core extends from the front end of the first trailing region (the front end of the longest trailing portion) to the starting point of the next slurry coating. The amount of slurry applied can be controlled by changing the spacing between the positive electrode core and the die head, with this spacing set such that the thickness of the positive electrode slurry layer is 50 μm.

[0065] After the first coating film formed on the first surface of the positive electrode core is dried, a positive electrode slurry is intermittently applied to the second surface (back side) to form a second coating film, creating a second core exposure area that is wider than the first core exposure area. The starting point of the second coating film is aligned with the starting point of the first coating film. Conversely, the positions of the coating termination points are staggered so that the overlap between the second tail area formed at the coating termination point and the first tail area does not exceed 50% of the length of the first tail area. Specifically, the positive electrode slurry is applied using a die-coating machine such that the second core exposure area is approximately 11.5 mm wide. At this time, the second tail area formed at the coating termination point is approximately 3 mm wide (length in the X direction).

[0066] In the positive electrode of Example 1, the X-direction length of the first trailing tip region is shorter than 50% of the length of the trailing portion located closest to the second end of the positive electrode core (the same applies to the X-direction length of the second trailing tip region). The first and second trailing tip regions do not overlap in the thickness direction of the core. It should be noted that aluminum positive electrode leads are ultrasonically welded to the exposed portion of the first core, and protective strips are attached to the surface and back of the positive electrode to cover the positive electrode leads and the entire exposed portion of each core.

[0067] [Making the negative electrode]

[0068] Graphite was used as the negative electrode active material. The negative electrode active material, a dispersion of styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed at a solid component mass ratio of 98:1:1, using water as the dispersion medium to prepare a negative electrode slurry. This slurry was then coated onto both sides of a negative electrode core consisting of long strips of copper foil with a thickness of 8 μm using a die-coating machine. After drying, the coating was compressed using calendering rollers. Finally, it was cut to the specified electrode size, resulting in a negative electrode with a negative electrode slurry layer formed on both sides of the negative electrode core.

[0069] It should be noted that a portion of the negative electrode core remains exposed at its longitudinal end. A negative electrode adhesive layer is formed over the entire area of ​​the negative electrode core, excluding this exposed portion. Nickel-coated negative electrode leads are ultrasonically welded to the exposed portion of the core, and a protective tape is then attached to cover the negative electrode leads.

[0070] [Fabrication of Electrodes]

[0071] The positive electrode, the negative electrode, and the polyethylene diaphragm are wound into a spiral shape using a cylindrical core member, and an anti-winding tape is attached to the outermost circumferential surface to obtain a wound electrode body. At this time, the negative electrode is positioned with the negative electrode lead located on the outside of the wound electrode body. After forming the wound structure of the electrode body, the core member is removed, resulting in a wound electrode body with a cavity formed in the core portion.

[0072] [Preparation of non-aqueous electrolytes]

[0073] A non-aqueous electrolyte was prepared by adding 5 parts by mass of vinylene carbonate (VC) to 100 parts by mass of a mixed solvent prepared by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:3 (25°C) and dissolving 1.5 mol / L of LiPF6.

[0074] [Making of Cylindrical Batteries]

[0075] After placing insulating plates on the top and bottom of the aforementioned electrode body, the negative electrode lead is soldered to the inner surface of the bottom of the bottom cylindrical outer can, and the positive electrode lead is soldered to the internal terminal plate of the sealing body. The electrode body is then housed inside the outer can. A non-aqueous electrolyte is then injected into the outer can under reduced pressure, and the opening of the outer can is sealed with the sealing body through a gasket, thus obtaining a cylindrical battery.

[0076] <Example 2>

[0077] The width of the exposed portion of the second core is set to approximately 15 mm. Positive electrode slurry is intermittently applied to the second surface of the positive electrode core so that the entire second tail area does not overlap with the first tail area. Otherwise, the positive electrode and cylindrical battery are manufactured in the same manner as in Example 1.

[0078] <Comparative Example 1>

[0079] The coating terminal of the slurry is positioned on both the front and back sides so that the second tail region overlaps with the first tail region. Otherwise, the positive electrode and cylindrical battery are produced in the same manner as in Example 1.

[0080] [Cyclic Test]

[0081] The batteries of the examples and comparative examples were charged at a constant current of 1C at 25°C until the battery voltage reached 4.4V, and then discharged at a constant current of 1C until the battery voltage reached 2.5V. This charge-discharge cycle was performed 250 times. The batteries were then disassembled to remove the positive electrode, and the exposed core was visually inspected for cracks (foil breakage). The evaluation results are shown in Table 1. The denominator of the evaluation results refers to the number of batteries evaluated, and the numerator refers to the number of batteries where foil breakage was confirmed.

[0082] [Table 1]

[0083]

[0084] As shown in Table 1, in the comparative example batteries, foil breakage was observed at the exposed core portion in both batteries that underwent cycle testing (2 / 2), but no foil breakage was observed in the example battery (0 / 4). That is, by forming a positive electrode binder layer in a manner where at least 50% of the length of the tail portion does not overlap on the surface and back of the positive electrode, core damage caused by the tail portion is specifically suppressed. It should be noted that since the active material particles are dispersed at the leading edge of the tail portion, if the negative electrode swells due to charge-discharge cycles, the portion of the positive electrode core sandwiched between the active material particles is locally compressed, resulting in a thinner wall. Therefore, it is believed that by ensuring that the leading edge regions of the tail portion do not overlap on the surface and back of the positive electrode, foil breakage is sufficiently suppressed.

[0085] In the above embodiments, an example is shown where the configuration in which the surface and back tail of the electrode plate are offset in the X direction is applied to the positive electrode, but this configuration can also be applied to the negative electrode.

[0086] This disclosure is further illustrated by the following embodiments.

[0087] Configuration 1: An electrode comprising: an elongated core including a first end and a second end in the length direction; and a first adhesive layer and a second adhesive layer respectively disposed on both sides of the core; a first core exposed portion and a second core exposed portion overlapping in the thickness direction are provided at the middle portion in the length direction of the core; the first adhesive layer has a first tail region; the first tail region is formed with a plurality of first tail portions extending along the length direction of the core from the edge of the first end side of the first core exposed portion; the second adhesive layer has a second tail. The second trailing region is formed with a plurality of second trailing portions extending along the length direction of the core from the edge of the first end side of the exposed portion of the second core. In each region of the first trailing region and the second trailing region, the first and second front end regions are respectively defined as the range from the front end of the trailing portion closest to the second end side to the front end of the trailing portion closest to the first end side. The first and second compound layers are formed in such a way that the first and second front end regions do not overlap in the thickness direction of the core.

[0088] Configuration 2: An electrode comprising: an elongated core including a first end and a second end in the length direction, and a first adhesive layer and a second adhesive layer respectively disposed on both sides of the core; a first core exposed portion and a second core exposed portion overlapping in the thickness direction are provided at the middle portion in the length direction of the core; the first adhesive layer has a first trailing region, the first trailing region having a plurality of first trailing portions extending from the edge of the first end side of the first core exposed portion along the length direction of the core; the second adhesive layer has a second trailing region, the second trailing region having a plurality of second trailing portions extending from the edge of the first end side of the second core exposed portion along the length direction of the core; the first trailing region and the second trailing region are formed in such a way that at least 50% of the length of each region along the length direction of the core does not overlap in the thickness direction of the core.

[0089] Configuration 3: According to the electrode described in Configuration 1 or 2, the edges of the first core exposed portion and the second end side of the second core exposed portion overlap in the thickness direction of the core.

[0090] Configuration 4: The electrode according to any one of configurations 1 to 3, wherein the first trailing region and the second trailing region are arranged in such a way that the entirety of each region does not overlap in the thickness direction of the core.

[0091] Configuration 5: The electrode described in any one of configurations 1 to 4, wherein the thickness of the core is less than or equal to the median particle size (D50) of the active material particles contained in the first and second compound layers.

[0092] Configuration 6: A secondary battery having a wound electrode body comprising a positive electrode, a negative electrode and a separator, wherein the positive electrode is an electrode described in any one of configurations 1 to 5.

[0093] Explanation of reference numerals in the attached figures

[0094] 10 Cylindrical battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive lead, 21 Negative lead, 22 Inlet section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating component, 26 Upper valve body, 27 Cover, 28 Gasket, 29 Protective strip, 30 Positive electrode core, 31A, 31B Positive electrode compound layer, 32A, 32B Core exposed part, 33A, 33B Trailing area, 34A, 34B Trailing part, 35A, 35B Coating start end, 36A, 36B Coating end, 37A, 37B Trailing front end area, P1, P2 Front end.

Claims

1. An electrode comprising: a strip-shaped core having a first end and a second end in the length direction; and a first adhesive layer and a second adhesive layer respectively disposed on both sides of the core; wherein a first core protrusion and a second core protrusion overlapping in the thickness direction are provided at the middle portion of the core in the length direction. The first compound layer has a first trailing region, which is formed with a plurality of first trailing portions extending along the length direction of the core from the edge of the first end side of the exposed portion of the first core. The second compound layer has a second trailing region, which is formed with a plurality of second trailing portions extending along the length direction of the core from the edge of the first end side of the exposed portion of the second core. In each of the first and second trailing regions, the first and second composite layers are formed such that the range from the front end of the trailing portion closest to the second end to the front end of the trailing portion closest to the first end is defined as the first trailing front end region and the second trailing front end region, respectively.

2. An electrode comprising: a strip-shaped core having a first end and a second end in the length direction; and a first adhesive layer and a second adhesive layer respectively disposed on both sides of the core; wherein a first core exposed portion and a second core exposed portion overlapping in the thickness direction are provided at the middle portion of the core in the length direction. The first compound layer has a first trailing region, which is formed with a plurality of first trailing portions extending along the length direction of the core from the edge of the first end side of the exposed portion of the first core. The second compound layer has a second trailing region, which is formed with a plurality of second trailing portions extending along the length direction of the core from the edge of the first end side of the exposed portion of the second core. The first trailing region and the second trailing region are formed in such a way that more than 50% of the length of each region along the length direction of the core does not overlap in the thickness direction of the core.

3. The electrode according to claim 1 or 2, wherein, The edges of the first exposed core portion and the second exposed core portion overlap in the thickness direction of the core.

4. The electrode according to claim 1 or 2, wherein, The first trailing region and the second trailing region are configured such that the entirety of each region does not overlap in the thickness direction of the core.

5. The electrode according to claim 1 or 2, wherein, The thickness of the core is less than or equal to the median particle size D50 of the active material particles contained in the first and second compound layers, based on their volume.

6. A secondary battery comprising a wound electrode body including a positive electrode, a negative electrode, and a separator. The electrode according to claim 1 or 2 is used in the positive electrode.

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