Secondary battery, electronic device, and power tool

Abstract

A secondary battery in which a positive active material non-covered portion is joined to a positive current collector plate at one end of an electrode roll body, a negative active material non-covered portion is joined to a negative current collector plate at the other end of the electrode roll body, the electrode roll body has a flat surface formed by bending and overlapping at least the positive active material non-covered portion toward the center axis of the wound structure, a groove is formed in the flat surface, and an inner peripheral portion is formed of only a separator located inward of the innermost periphery of the positive electrode and the negative electrode, the length E of the portion of the positive active material non-covered portion protruding from one end in the width direction of the separator is greater than the length F of the portion of the separator protruding from one end in the width direction of the negative electrode, the number of layers of the separator in the inner peripheral portion is m, the thickness is t, and Z = t x m, and formula (1) is satisfied. Formula (1): 80 ≤ Z ≤ 196.

Description

Technical Field

[0001] This invention relates to secondary batteries, electronic devices, and power tools. Background Technology

[0002] Lithium-ion batteries have also been developed for applications requiring high output, such as power tools and electric vehicles. One method to achieve high output is high-rate discharge, which involves a relatively large current flowing through the battery. However, for lithium-ion batteries, not only high-rate discharge, the deformation of the electrodes during charging and discharging can shorten the battery's lifespan.

[0003] For example, Patent Document 1 describes a battery in which the resistance of the central portion to deformation caused by electrode expansion is improved by increasing the number of empty windings of the separator or by winding an inert material together with the separator at the beginning of winding, thereby increasing the cycle life.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2004-356047 Summary of the Invention

[0007] Patent Document 1 relates to a conventional battery that uses leads as extraction electrodes. If this technology is directly applied to a battery for high-rate discharge, the following problem exists: the non-covered portion of the bent active material enters the inner periphery, punctures the separator, and may cause an internal short circuit.

[0008] Therefore, one of the objectives of this invention is to provide a battery for high-speed discharge that does not cause internal short circuits.

[0009] To address the aforementioned issues, the present invention provides a secondary battery in which an electrode winding body, a positive electrode current collector, and a negative electrode current collector are housed within a battery can. The electrode winding body has a structure consisting of a strip-shaped positive electrode and a strip-shaped negative electrode stacked with a separator and wound around a central axis.

[0010] The positive electrode has a positive active material covered portion and a positive active material uncovered portion on the strip-shaped positive electrode foil.

[0011] The negative electrode has a negative active material covered portion and a negative active material uncovered portion on the strip-shaped negative electrode foil.

[0012] The uncovered portion of the positive electrode active material is joined to the positive electrode current collector at one end of the electrode winding body.

[0013] The non-covered portion of the negative electrode active material is joined to the negative electrode current collector at the other end of the electrode winding body.

[0014] The electrode winding body has:

[0015] At least the non-covered portion of the positive electrode active material bends toward the central axis of the wound structure and overlaps to form a flat surface;

[0016] Grooves formed on flat surfaces; and

[0017] The inner periphery consists only of a diaphragm located on the innermost side of the periphery, compared to the positive and negative electrodes.

[0018] The length E of the portion of the positive electrode active material that protrudes from one end of the membrane in the width direction is greater than the length F of the portion of the membrane that protrudes from one end of the negative electrode in the width direction.

[0019] When the number of diaphragm layers in the inner periphery is set to m, the thickness is set to t, and Z = t × m, equation (1) is satisfied.

[0020] Equation (1): 80≤Z≤196

[0021] According to at least one embodiment of the present invention, a battery that does not experience internal short circuits or poor welding and can maintain its initial capacity to a high degree can be provided. It should be noted that the content of the present invention should not be construed as limiting the effects illustrated in this specification. Attached Figure Description

[0022] Figure 1 This is a cross-sectional view of a battery according to one embodiment.

[0023] Figure 2 This is a diagram illustrating an example of the configuration relationship between the positive electrode, negative electrode, and diaphragm in an electrode winding.

[0024] Figure 3 A is a top view of the positive current collector. Figure 3 B is a top view of the negative current collector.

[0025] Figure 4 A to Figure 4 F is a diagram illustrating the battery assembly process according to one embodiment.

[0026] Figure 5 A and Figure 5 B is a diagram used to illustrate Example 1.

[0027] Figure 6 A and Figure 6 B is a diagram used to illustrate the number of membrane layers, m.

[0028] Figure 7 A and Figure 7 B is a diagram used to illustrate Comparative Example 1.

[0029] Figure 8 A and Figure 8 B is a diagram used to illustrate comparative example 2.

[0030] Figure 9 A and Figure 9 B is a diagram used to illustrate comparative example 3.

[0031] Figure 10 This is a connection diagram illustrating a battery pack as an application example of the present invention.

[0032] Figure 11 This is a connection diagram illustrating an application example of the present invention using an electric tool.

[0033] Figure 12 This is a connection diagram used to illustrate an electric vehicle as an application example of the present invention. Detailed Implementation

[0034] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the descriptions will proceed in the following order.

[0035] <1. One implementation method>

[0036] <2. Variations>

[0037] <3. Application Examples>

[0038] The embodiments described below are preferred examples of the present invention, and the content of the present invention is not limited to these embodiments.

[0039] In an embodiment of the present invention, a cylindrical lithium-ion battery will be used as an example of a secondary battery.

[0040] <1. One implementation method>

[0041] First, the overall structure of a lithium-ion battery will be explained. Figure 1 This is a schematic cross-sectional view of lithium-ion battery 1. For example, as shown... Figure 1 As shown, the lithium-ion battery 1 is a cylindrical lithium-ion battery 1, wherein the electrode winding body 20 is housed inside the battery can 11.

[0042] Specifically, the lithium-ion battery 1 may include, for example, a pair of insulating plates 12 and 13 and an electrode winding 20 inside a cylindrical battery can 11. Additionally, the lithium-ion battery 1 may also include, for example, any one or more of the following inside the battery can 11: a thermistor (PTC) element and reinforcing components.

[0043] [Battery can]

[0044] The battery canister 11 is the main component for housing the electrode winding 20. The battery canister 11 is, for example, a cylindrical container with one open end and the other closed end. That is, the battery canister 11 has an open end (open end 11N). The battery canister 11 contains, for example, any one or more of the following metallic materials: iron, aluminum, and their alloys. Additionally, the surface of the battery canister 11 may be plated with, for example, any one or more of the following metallic materials: nickel.

[0045] [Insulating board]

[0046] Insulating plates 12 and 13 have a winding shaft that is approximately perpendicular to the electrode winding body 20. Figure 1 A disc-shaped plate (within the Z-axis). In addition, insulating plates 12 and 13 are configured, for example, to sandwich the electrode winding 20 between each other.

[0047] [Riveting Structure]

[0048] At the open end face 11N of the battery can 11, the battery cover 14 and the safety valve mechanism 30 are riveted together via gaskets 15, thereby forming a riveting structure 11R (curled structure). Thus, the battery can 11 is sealed with the electrode winding body 20 and the like housed inside it.

[0049] [Battery cover]

[0050] The battery cover 14 is primarily a component that closes the open end face 11N of the battery can 11 when the electrode winding body 20 and the like are housed inside the battery can 11. The battery cover 14, for example, is made of the same material as the battery can 11. The central region of the battery cover 14 protrudes, for example, in the +Z direction. Therefore, the area outside the central region of the battery cover 14 (the peripheral region) comes into contact with, for example, the safety valve mechanism 30.

[0051] [washer]

[0052] The gasket 15 is a component that seals the gap between the bent portion 11P and the battery cover 14 by being located between the battery canister 11 (bent portion 11P) and the battery cover 14. In addition, the surface of the gasket 15 may be coated with asphalt, for example.

[0053] The gasket 15 may contain one or more insulating materials. The type of insulating material is not particularly limited, and may include polymers such as polybutylene terephthalate (PBT) and polypropylene (PP). Preferably, the insulating material is polybutylene terephthalate. This is because the gap between the bent portion 11P and the battery cover 14 can be adequately sealed while the battery canister 11 and battery cover 14 are electrically separated from each other.

[0054] [Safety Valve Mechanism]

[0055] When the internal pressure inside the battery can 11 rises, the safety valve mechanism 30 releases the internal pressure primarily by releasing the seal of the battery can 11 as needed. The rise in internal pressure in the battery can 11 can be caused by, for example, gases generated during charging and discharging due to the decomposition reaction of the electrolyte.

[0056] [Electrode winding]

[0057] In a cylindrical lithium-ion battery, a strip-shaped positive electrode 21 and a strip-shaped negative electrode 22 are wound into a spiral shape with a separator 23 in between, and stored in a battery can 11 while immersed in electrolyte. The positive electrode 21 is formed by forming a layer of positive active material on one or both sides of a positive electrode foil 21A, the material of which is, for example, a metal foil made of aluminum or an aluminum alloy. The negative electrode 22 is formed by forming a layer of negative active material on one or both sides of a negative electrode foil 22A, the material of which is, for example, a metal foil made of nickel, a nickel alloy, copper, or a copper alloy. The separator 23 is a porous and insulating film that electrically insulates the positive electrode 21 and the negative electrode 22 while allowing the movement of ions, electrolyte, and other substances.

[0058] The positive electrode active material layer and the negative electrode active material layer cover most of the positive electrode foil 21A and the negative electrode foil 22A, respectively, but neither intentionally covers the periphery of the short side of the strip. Hereinafter, the portions not covered by the active material layer will be appropriately referred to as active material uncovered portions 21C and 22C, and the portions covered by the active material layer will be appropriately referred to as active material covered portions 21B and 22B. In the cylindrical battery, the electrode winding body 20 is wound in an overlapping manner with the active material uncovered portions 21C of the positive electrode and the active material uncovered portions 22C of the negative electrode facing opposite directions, separated by the separator 23.

[0059] Figure 2 An example of the structure before winding is shown, with the positive electrode 21, negative electrode 22, and separator 23 stacked together. The non-covered portion 21C of the active material of the positive electrode ( Figure 2 The width of the dotted portion on the upper side of the negative electrode is A, and the non-covered portion 22C of the active material of the negative electrode is... Figure 2 The width of the lower dotted portion of the membrane 23 is B. In one embodiment, A > B is preferred, for example, A = 7 (mm) and B = 4 (mm). The length of the portion of the non-covered active material portion 21C of the positive electrode protruding from one end of the membrane 23 in the width direction is C, and the length of the portion of the non-covered active material portion 22C of the negative electrode protruding from the other end of the membrane 23 in the width direction is D. In one embodiment, C > D is preferred, for example, C = 4.5 (mm) and D = 3 (mm).

[0060] The non-covered portion 21C of the positive electrode is made of, for example, aluminum, while the non-covered portion 22C of the negative electrode is made of, for example, copper. Therefore, generally speaking, the non-covered portion 21C of the positive electrode is softer (lower Young's modulus) than the non-covered portion 22C of the negative electrode. Therefore, in one embodiment, it is more preferable that A > B and C > D. In this case, when the non-covered portions 21C and 22C of the positive and negative electrodes are simultaneously bent with the same pressure from both electrode sides, the height of the bent portion measured from the front end of the diaphragm 23 is the same for both the positive and negative electrodes. At this time, since the non-covered portions 21C and 22C are bent and moderately overlap, they can be easily joined to the current collectors 24 and 25 by laser welding. In one embodiment, joining refers to joining by laser welding, but the joining method is not limited to laser welding.

[0061] In the positive electrode 21, a 3 mm wide area including the boundary between the non-covered portion 21C and the covered portion 21B of the active material is covered by an insulating layer 101. Figure 2 The gray area in the image is covered. Furthermore, the entire area of ​​the non-covered active material portion 21C of the positive electrode, which is opposite the active material covered portion 22B of the negative electrode via a separator, is covered by the insulating layer 101. The insulating layer 101 reliably prevents internal short circuits in the battery 1 when foreign objects intrude between the active material covered portion 22B of the negative electrode and the non-covered active material portion 21C of the positive electrode. Additionally, the insulating layer 101 absorbs impacts when the battery 1 is subjected to an impact, reliably preventing the non-covered active material portion 21C of the positive electrode from bending or short-circuiting with the negative electrode 22.

[0062] A through hole 26 is provided in the region containing the central axis of the electrode winding body 20. The through hole 26 is a hole for inserting the assembly core of the electrode winding body 20 and the welding electrode rod. The electrode winding body 20 is wound with the active material uncovered portion 21C of the positive electrode and the active material uncovered portion 22C of the negative electrode facing opposite directions. Therefore, the active material uncovered portion 21C of the positive electrode is concentrated on one end face (end face 41) of the electrode winding body, and the active material uncovered portion 22C of the negative electrode is concentrated on the other end face (end face 42) of the electrode winding body 20. In order to make good contact with the current collectors 24 and 25 for extracting current, the active material uncovered portions 21C and 22C are bent, and the end faces 41 and 42 become flat surfaces. The bending direction is from the outer edge portion 27 and 28 of the end faces 41 and 42 toward the through hole 26, and the adjacent peripheral active material uncovered portions overlap and bend each other in the wound state. It should be noted that, in this specification, "flat surface" includes not only a completely flat surface, but also a surface with some unevenness or surface roughness to the extent that the non-covered part of the active material and the current collector can be joined.

[0063] By bending the non-covered portions 21C and 22C of the active material respectively, it might seem at first glance that the end faces 41 and 42 can become flat surfaces. However, if no processing is performed before bending, wrinkles or gaps (voids, spaces) will be generated on the end faces 41 and 42 during bending, and the end faces 41 and 42 will not become flat surfaces. Here, "wrinkles" and "gaps" refer to the parts on the non-covered portions 21C and 22C of the active material that are offset during bending, and the end faces 41 and 42 will not become flat surfaces. In order to prevent the formation of such wrinkles or gaps, a groove 43 is pre-formed in the radial direction from the through hole 26 (for example, see reference). Figure 4 B). The groove 43 extends from the outer edges 27 and 28 of the end faces 41 and 42 to the through hole 26. The through hole 26 is located at the center of the electrode winding body 20 and is used as a hole for inserting welding tools during the assembly process of the lithium-ion battery 1. Cutouts are made in the non-covered portions 21C and 22C of the active material near the through hole 26, where the winding of the positive electrode 21 and negative electrode 22 begins. This is to prevent the through hole 26 from becoming blocked when bending towards it. The groove 43 remains within the flat surface after bending the non-covered portions 21C and 22C of the active material; the portion without the groove 43 is joined (welded, etc.) to the positive electrode current collector 24 or the negative electrode current collector 25. It should be noted that not only the flat surface, but also a portion of the current collector 24 and 25 can be joined.

[0064] The detailed structure of the electrode winding 20, namely the detailed structure of the positive electrode 21, the negative electrode 22, the diaphragm 23, and the electrolyte, will be described later.

[0065] [Cold Collector]

[0066] In conventional lithium-ion batteries, leads for extracting current are welded to the positive and negative electrodes, respectively. However, this results in high internal resistance, causing the lithium-ion battery to heat up during discharge, making it unsuitable for high-rate discharge. Therefore, in one embodiment of the lithium-ion battery, a positive current collector 24 and a negative current collector 25 are disposed on end faces 41 and 42, and welded at multiple points to the uncovered portions 21C and 22C of the active material on the end faces 41 and 42, thereby reducing the internal resistance of the battery. The curvature of the end faces 41 and 42 to become flat surfaces also contributes to low resistance.

[0067] Figure 3 A and Figure 3 B represents an example of a collector plate. Figure 3 A is the positive current collector 24. Figure 3B is the negative current collector 25. The positive current collector 24 is made of, for example, a metal plate made of aluminum or aluminum alloy monomers or composite materials, and the negative current collector 25 is made of, for example, a metal plate made of nickel, nickel alloy, copper, or copper alloy monomers or composite materials. Figure 3 As shown in Figure A, the positive current collector 24 has a shape consisting of a flat, fan-shaped plate 31 with a rectangular strip 32. A hole 35 is provided near the center of the plate 31, and the position of the hole 35 corresponds to that of the through hole 26.

[0068] Figure 3 The dotted portion A is the insulating portion 32A on the strip 32 where insulating tape is attached or coated with insulating material. The portion below the dot in the attached drawing is the connecting portion 32B, which connects to the sealing plate that also serves as an external terminal. It should be noted that in a battery structure where the through-hole 26 does not have a metal center pin (not shown), the strip 32 is less likely to come into contact with the negative electrode potential, therefore the insulating portion 32A may be omitted. In this case, by increasing the width of the positive electrode 21 and the negative electrode 22 by an amount corresponding to the thickness of the insulating portion 32A, the charge / discharge capacity can be increased.

[0069] The negative current collector 25 has a shape that is almost identical to that of the positive current collector 24, but the strip section is different. Figure 3 The strip portion 34 of the negative current collector plate B is shorter than the strip portion 32 of the positive current collector plate and lacks a portion equivalent to the insulating portion 32A. The strip portion 34 has circular protrusions (protrusions) 37, indicated by multiple circular markings. During resistance welding, the current concentrates on the protrusions, causing them to melt, and the strip portion 34 is welded to the bottom of the battery canister 11. Similar to the positive current collector plate 24, the negative current collector plate 25 has a hole 36 near the center of the plate portion 33, the position of which corresponds to the through hole 26. Since the plate portion 31 of the positive current collector plate 24 and the plate portion 33 of the negative current collector plate 25 are fan-shaped, they cover only a portion of the end faces 41 and 42. The reason for not covering them entirely is to allow the electrolyte to smoothly penetrate the electrode winding body during battery assembly, or to facilitate the venting of gases generated when the battery is in an abnormally high temperature or overcharged state.

[0070] [positive electrode]

[0071] The positive electrode active material layer includes at least a positive electrode material (positive electrode active material) capable of lithium insertion and extraction, and may also include a positive electrode binder and a positive electrode conductive agent. The positive electrode material is preferably a lithium-containing composite oxide or a lithium-containing phosphate compound. For example, the lithium-containing composite oxide has a layered rock salt type or spinel type crystal structure. For example, the lithium-containing phosphate compound has an olivine type crystal structure.

[0072] The positive electrode binder contains synthetic rubber or polymeric compounds. Synthetic rubbers include styrene-butadiene rubber, fluorinated rubber, and ethylene propylene diene monomer (EPDM) rubber, etc. Polymeric compounds include polyvinylidene fluoride (PVdF) and polyimide, etc.

[0073] The positive electrode conductive agent is a carbon material such as graphite, carbon black, acetylene black, or Ketjen black. Alternatively, the positive electrode conductive agent can also be a metallic material or a conductive polymer.

[0074] The thickness of the positive electrode foil 21A is preferably 5 μm or more and 20 μm or less. This is because by setting the thickness of the positive electrode foil 21A to 5 μm or more, it is possible to manufacture the positive electrode 21 without breaking it when the positive electrode 21, negative electrode 22, and separator 23 are overlapped and wound. This is because by setting the thickness of the positive electrode foil 21A to 20 μm or less, it is possible to prevent a decrease in the energy density of the battery 1, and the opposing area of ​​the positive electrode 21 and negative electrode 22 is increased, enabling the manufacture of a battery 1 with a large output.

[0075] [negative electrode]

[0076] To improve adhesion to the negative electrode active material layer, the surface of the negative electrode foil 22A is preferably roughened. The negative electrode active material layer includes at least a negative electrode material (negative electrode active material) capable of lithium insertion and extraction, and may also include a negative electrode binder and a negative electrode conductive agent, etc.

[0077] Anode materials may include carbon materials. These carbon materials can be easily graphitized carbon, difficult-to-graphitize carbon, graphite, low-crystallinity carbon, or amorphous carbon. The shapes of carbon materials can be fibrous, spherical, granular, or flake-like.

[0078] Furthermore, negative electrode materials may include, for example, metallic materials. Examples of metallic materials include Li (lithium), Si (silicon), Sn (tin), Al (aluminum), Zr (zinc), and Ti (titanium). Metallic elements form compounds, mixtures, or alloys with other elements; examples include silicon oxide (SiO₂). x (0<x≤2)), silicon carbide (SiC) or an alloy of carbon and silicon, lithium titanate (LTO).

[0079] The thickness of the negative electrode foil 22A is preferably 5 μm or more and 20 μm or less. This is because by setting the thickness of the negative electrode foil 22A to 5 μm or more, it is possible to manufacture the negative electrode 22 without breaking it when the positive electrode 21, negative electrode 22, and separator 23 are overlapped and wound. This is because by setting the thickness of the negative electrode foil 22A to 20 μm or less, it is possible to prevent a decrease in the energy density of the battery 1, and the opposing area of ​​the positive electrode 21 and negative electrode 22 is increased, enabling the manufacture of a battery 1 with a large output.

[0080] [Septum]

[0081] The separator 23 is a porous membrane containing resin, or it can be a laminate of two or more porous membranes. The resin is polypropylene or polyethylene, etc. The separator 23 can use a porous membrane as a substrate layer, with a resin layer on one or both sides of the substrate layer. This is because it can improve the adhesion of the separator 23 to the positive electrode 21 and the negative electrode 22, respectively, thereby preventing deformation of the electrode winding body 20.

[0082] The resin layer contains resins such as PVdF. When forming this resin layer, a solution containing the resin dissolved in an organic solvent is applied to the substrate layer, and then the substrate layer is dried. It should be noted that the substrate layer can also be dried after being immersed in the solution. From the viewpoint of improving heat resistance and battery safety, it is preferable that the resin layer contains inorganic or organic particles. Types of inorganic particles include alumina, aluminum nitride, aluminum hydroxide, magnesium hydroxide, boehmite, talc, silica, mica, etc. Alternatively, a surface layer mainly composed of inorganic particles formed by sputtering, ALD (atomic layer deposition), or similar methods can be used instead of the resin layer.

[0083] The thickness of the separator 23 is preferably 4 μm or more and 30 μm or less. By setting the thickness of the separator to 4 μm or more, internal short circuits caused by contact between the positive electrode 21 and the negative electrode 22 separated by the separator 23 can be prevented. By making the thickness of the separator 23 30 μm or less, lithium ions or electrolyte can easily pass through the separator 23, and the electrode density of the positive electrode 21 and the negative electrode 22 can be increased during winding.

[0084] Electrolyte

[0085] Electrolytes contain solvents and electrolyte salts, and may also contain additives as needed. Solvents can be non-aqueous solvents such as organic solvents or water. Electrolytes containing non-aqueous solvents are called non-aqueous electrolytes. Non-aqueous solvents include cyclic carbonates, chain carbonates, lactones, chain carboxylic esters, or nitrile (mononitrile), etc.

[0086] Representative examples of electrolyte salts are lithium salts, but other salts may also be included. Lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), and dilithium hexafluorosilicate (Li2SF6). These salts can also be used in combination; from the viewpoint of improving battery performance, a combination of LiPF6 and LiBF4 is preferred. The content of the electrolyte salt is not particularly limited, but it is preferably 0.3 mol / kg to 3 mol / kg relative to the solvent.

[0087] [Methods for manufacturing lithium-ion batteries]

[0088] Reference Figure 4 A to Figure 4 F. A method for manufacturing a lithium-ion battery 1 according to one embodiment will be described. First, a positive electrode active material is coated on the surface of a strip of positive electrode foil 21A, which is used as a cover portion of the positive electrode 21. A negative electrode active material is coated on the surface of a strip of negative electrode foil 22A, which is used as a cover portion of the negative electrode 22. At this time, active material non-cover portions 21C and 22C, which are not coated with positive and negative electrode active materials, are made at one end of the short side direction of the positive electrode 21 and one end of the short side direction of the negative electrode 22. A cut is made in a portion of the active material non-cover portions 21C and 22C, that is, at the part corresponding to the beginning of winding during winding. The positive electrode 21 and the negative electrode 22 are dried. Then, the active material non-cover portions 21C of the positive electrode and 22C of the negative electrode are overlapped with the separator 23 in opposite directions, so as to form a through hole 26 in the center and to be wound into a spiral shape with the cuts made near the central axis, thus manufacturing a battery. Figure 4 Electrode winding body 20, like A.

[0089] Next, as Figure 4 As shown in Figure B, a groove 43 is formed on a portion of end faces 41 and 42 by pressing the end of a thin plate (e.g., 0.5 mm thick) perpendicularly relative to end faces 41 and 42. The groove 43 extends radially from the through hole 26 by this method. Figure 4 The number and configuration of slots 43 shown in B are just one example. Then, as... Figure 4 As shown in Figure C, the same pressure is applied simultaneously from both poles in a direction approximately perpendicular to end faces 41 and 42, bending the uncovered active material portion 21C of the positive electrode and the uncovered active material portion 22C of the negative electrode, making end faces 41 and 42 flat. At this time, a load is applied to the surface of the flat plate by bending the uncovered active material portions of end faces 41 and 42 towards the central axis and aligning them. Then, the plate-shaped portion 31 of the positive electrode current collector plate 24 is laser-welded to end face 41, and the plate-shaped portion 33 of the negative electrode current collector plate 25 is laser-welded and joined to end face 42.

[0090] Then, as Figure 4 As shown in Figure D, the strip-shaped portions 32 and 34 of the current collector plates 24 and 25 are bent, and the insulating plates 12 and 13 (or insulating tape) are pasted onto the positive current collector plate 24 and the negative current collector plate 25. The electrode winding body 20 assembled as described above is then inserted. Figure 4 Inside the battery can 11 shown in Figure E, the bottom of the battery can 11 is welded. After the electrolyte is injected into the battery can 11, as shown in Figure E... Figure 4 As shown in F, it is sealed with gasket 15 and battery cover 14.

[0091] Example

[0092] The present invention will now be specifically described using a lithium-ion battery 1 manufactured as described above, and based on an example comparing the open-circuit voltage failure rate, initial capacity, and soldering failure rate. It should be noted that the present invention is not limited to the embodiments described below.

[0093] In all the following embodiments and comparative examples, the battery size is set to 21700 (diameter 21 mm, height 70 mm), and the separator 23 is overlapped in such a way that it covers the entire range of the active material covering portion 21B of the positive electrode and the active material covering portion 22B of the negative electrode. Figure 5 A is the electrode winding 20 before the non-covered portion 21C of the positive electrode active material at end face 41 (see reference). Figure 4 A) A partial sectional view. For example... Figure 5 As shown in Figure A, along the central axis direction of the electrode winding body 20 ( Figure 1 In the Z-axis direction, the length of the portion of the non-covered part 21C of the positive electrode protruding from one end of the separator 23 in the width direction is E, and the length of the portion of the separator 23 protruding from one end of the negative electrode 22 in the width direction is F.

[0094] Let the thickness of the diaphragm 23 be t, and let multiple layers of diaphragms 23 be arranged in the inner circumference of the electrode winding body 20. Let the number of layers in the inner circumference diaphragm 23 be m, and let Z = t × m. Here, as Figure 5 As shown in Figure A, the inner periphery refers to the portion inside the innermost layer of the positive electrode 21 and the negative electrode 22 in the electrode winding body. The outer periphery of the electrode winding body 20 refers to the circumferential surface of the electrode winding body 20. Figure 6 A is a cross-sectional view showing an example of an electrode winding, with the diaphragm 23 omitted. Figure 6 B is from Figure 6 An enlarged view of the portion enclosed by line L1 of A. Figure 6 B shows a dashed line L2 extending from the end of the negative electrode 22 at the beginning of winding (the inner circumferential side of the electrode winding body) to the central axis of the electrode winding body 20. The value of the number of layers m of the inner circumferential diaphragm 23 is related to... Figure 6 The number of layers of diaphragm 23 intersected by the single-dotted line L2 depicted in B. Figure 6 In example B, m = 4.

[0095] There are eight grooves 43, arranged at approximately equal angular intervals. The distance between adjacent uncovered active material portions 21C of the positive electrode and the distance between adjacent uncovered active material portions 22C of the negative electrode are 0.2 mm. In the embodiments other than Comparative Example 3 and in the comparative examples, a structure is formed in which the uncovered active material portions 21C of the positive electrode overlap each other; in Comparative Example 3, a structure is formed in which the uncovered active material portions 21C of the positive electrode do not overlap each other.

[0096] Figure 5 A and Figure 7 A to Figure 9 A is the electrode winding 20 before the non-covered portion of the active material of the bent positive electrode 21C (refer to...). Figure 4 A) Partial sectional view, Figure 5 B and Figure 7 B to Figure 9 B is the electrode winding 20 after the non-covered portion 21C of the active material of the bent positive electrode (see reference). Figure 4 C) Partial cross-sectional view. The right side of the figure shows the inner circumference of the electrode winding 20, and the left side shows the outer circumference of the electrode winding 20. Although not specifically illustrated, the blank area adjacent to the right of the diaphragm 23 at the right end of the figure is the through hole 26 of the electrode winding 20. Figure 5 A~ Figure 9 A and Figure 5 B~ Figure 9 In B, the right side of the through hole 26 of the electrode winding body is omitted.

[0097] [Example 1]

[0098] like Figure 5 As shown in Figure A, E = 4.5 mm, F = 1 mm, E > F, as... Figure 5 As shown in Figure B, when the uncovered portion 21C of the active material of the positive electrode is bent, the uncovered portions 21C of the active material of the positive electrode overlap each other. t = 14 μm, m = 6, Z = 84.

[0099] [Comparative Example 1]

[0100] like Figure 7 As shown in Figure A, E = 4.5 mm, F = 1 mm, E > F, as... Figure 7 As shown in Figure B, when the uncovered portion 21C of the active material of the positive electrode is bent, the uncovered portions 21C of the active material of the positive electrode overlap each other. t = 14 μm, m = 4, Z = 56.

[0101] [Comparative Example 2]

[0102] like Figure 8 As shown in Figure A, E = 4.5 mm, F = 4.5 mm, E ≤ F, as... Figure 8 As shown in Figure B, when the uncovered portion 21C of the active material of the positive electrode is bent, the uncovered portions 21C of the active material of the positive electrode overlap each other. t = 14 μm, m = 6, Z = 84.

[0103] [Comparative Example 3]

[0104] like Figure 9 As shown in Figure A, E = 0.2 mm, F = 0.15 mm, E > F, as... Figure 9As shown in Figure B, when the uncovered portion 21C of the active material of the positive electrode is bent, the uncovered portions 21C of the active material of the positive electrode do not overlap with each other. t = 14 μm, m = 6, Z = 84.

[0105] [evaluate]

[0106] For batteries 1 in Example 1 and Comparative Examples 1 to 3, the open-circuit voltage failure rate, initial capacity, and welding failure rate were determined. The open-circuit voltage failure rate was determined as follows: At an ambient temperature of 25°C, the batteries were charged at a constant current and constant voltage of 500mA. The voltage of battery 1 immediately after reaching 4.2V (within 1 hour) was set as V1, and the voltage of battery 1 after being stored for two weeks was set as V2. At this point, batteries 1 with V1-V2 ≥ 50mV were considered to have open-circuit voltage failures. The number of these batteries was counted, and the proportion relative to the total was calculated. The initial capacity was calculated by discharging batteries 1 without open-circuit voltage failures at a constant current of 500mA until the voltage reached 3V. The initial capacity was calculated as the product of the discharge current and the time. The value for Example 1 was set to 100%. The welding failure rate was determined by laser welding of the positive electrode current collector 24 and the uncoated portion 21C of the positive electrode active material. The number of batteries with welding defects such as openings or sputtering was counted, and the proportion relative to the total was calculated. The number of tests was 25 for each battery. The results are shown in Table 1.

[0107] [Table 1]

[0108]

[0109] In Example 1, the open-circuit voltage defect rate was low, at 0%, and the soldering defect rate was low, at 0%. This is because, as... Figure 5 As shown in Figure B, because E is relatively large, the non-covered portion 21C of the active material of the bent positive electrode overlaps appropriately. Because the value of m is relatively large, the non-covered portion 21C of the active material of the bent positive electrode does not puncture the inner circumferential diaphragm 23. In Comparative Example 1, the open-circuit voltage failure rate is relatively high. This can be attributed to factors such as... Figure 7 As shown in B, because the value of m is relatively small, the non-covered portion 21C of the active material of the bent positive electrode punctures the inner peripheral diaphragm 23, causing an internal short circuit. In Comparative Example 2, the initial capacity is relatively low. This can be attributed to the fact that, as... Figure 8 A and Figure 8 As shown in B, the same size battery canister 11 is used in all examples, and the value of F is relatively large. Therefore, the width of the active material covering portion 21B of the positive electrode and the width of the active material covering portion 22B of the negative electrode are smaller than in other examples.

[0110] In Comparative Example 3, the open-circuit voltage failure rate was relatively high. This can be attributed to factors such as... Figure 9As shown in Figure B, the non-covered portions 21C of the active material of the bent positive electrode do not overlap, therefore, the metal powder generated during the bending of the non-covered portions 21C of the active material of the positive electrode mixes into the interior of the electrode winding body 20. Furthermore, in Comparative Example 3, the soldering defect rate is relatively high. This can be attributed to factors such as... Figure 9 As shown in B, since the value of E is relatively small, the thickness of the non-covered portion 21C of the active material of the bent positive electrode is insufficient relative to the thickness of the positive electrode current collector 24. Table 1 shows that in Example 1 (E > F, m = 6 (Z = 84), where there is overlap of the non-covered portion 21C of the active material of the positive electrode), no internal short circuit or poor welding occurs in battery 1, and the initial capacity of battery 1 can be maintained to a high degree.

[0111] Next, for the battery of Example 1, the values ​​of t and m were changed, and the acceptable range of Z values ​​was investigated.

[0112] [Example 2]

[0113] With E = 4.5 mm and F = 1 mm, and E > F, the uncovered portions 21C of the active material of the positive electrode overlap each other when the active material uncovered portions 21C of the positive electrode are bent. t = 10 μm, m = 8, Z = 80.

[0114] [Example 3]

[0115] Except for setting t = 8 μm, m = 10, and Z = 80, it is the same as in Example 2.

[0116] [Example 4]

[0117] Except for setting t = 14 μm, m = 14, and Z = 196, it is the same as in Example 2.

[0118] [Comparative Example 4]

[0119] Except for setting t = 8 μm, m = 8, and Z = 64, it is the same as in Example 2.

[0120] [Comparative Example 5]

[0121] Except for setting t = 12 μm, m = 6, and Z = 72, it is the same as in Example 2.

[0122] [Comparative Example 6]

[0123] Except for setting t = 20 μm, m = 10, and Z = 200, it is the same as in Example 2.

[0124] [evaluate]

[0125] For batteries 1 from Examples 2 to 4 and Comparative Examples 4 to 6, the open-circuit voltage failure rate, initial capacity, and soldering failure rate were calculated in the same manner as described above. Similarly, the number of tests was 25 for each example. The results are shown in Table 2.

[0126] [Table 2]

[0127]

[0128] In Examples 2 to 4, the open-circuit voltage failure rate was low (0%), the initial capacity was high (100%), and the soldering failure rate was low (0%). In contrast, in Comparative Examples 4 to 6, the initial capacity was high (100%), the soldering failure rate was low (0%), and the open-circuit voltage failure rate was relatively high (4% or more). In this case, the range of Z for Examples 2 to 4 was 80 or more and 196 or less.

[0129] Table 2 shows that when 80≤Z≤196, battery 1 will not experience internal short circuits or poor welding, and can maintain its initial capacity to a high extent.

[0130] <2. Variations>

[0131] The above describes one embodiment of the present invention in detail, but the content of the present invention is not limited to the above embodiment, and various modifications can be made based on the technical concept of the present invention.

[0132] In the embodiments and comparative examples, the number of slots 43 is 8, but it can also be any other number. The battery size is 21700 (diameter 21mm, height 70mm), but it can also be 18650 (diameter 18mm, height 65mm) or other sizes.

[0133] The positive current collector 24 and the negative current collector 25 have fan-shaped plate portions 31 and 33, but may also have other shapes.

[0134] As long as it does not depart from the spirit of the invention, the invention can also be applied to batteries other than lithium-ion batteries, and batteries other than cylindrical shapes (e.g., laminated batteries, prismatic batteries, coin-shaped batteries, button batteries). In this case, the shape of the "end face of the electrode winding" can be not only cylindrical, but also elliptical or flat, etc.

[0135] <3. Application Examples>

[0136] (1) Battery pack

[0137] Figure 10This is a block diagram illustrating a circuit structure example when the battery 1 of an embodiment or example of the present invention is applied to a battery pack 300. The battery pack 300 includes a battery assembly 301, a switch unit 304 including 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. The control unit 310 controls each device, thereby enabling charging and discharging control in case of abnormal heat generation, or calculating and correcting the remaining capacity of the battery pack 300. The positive terminal 321 and negative terminal 322 of the battery pack 300 are connected to a charger or electronic device for charging and discharging.

[0138] The battery pack 301 is constructed by connecting multiple secondary batteries 301a in series and / or parallel. Figure 10 The example shown is a case where six secondary batteries 301a are connected in a 2-in-parallel and 3-in-series (2P3S) configuration.

[0139] Temperature detection unit 318 is connected to temperature detection element 308 (e.g., thermistor) to measure the temperature of battery pack 301 or battery stack 300, and provides the measured temperature to control unit 310. Voltage detection unit 311 measures the voltage of battery pack 301 and each secondary battery 301a constituting battery pack 301, performs A / D conversion on the measured voltage, and provides it to control unit 310. Current detection unit 313 measures the current using current detection resistor 307, and provides the measured current to control unit 310.

[0140] The switch control unit 314 controls the charging control switch 302a and the discharging control switch 303a of the switch unit 304 based on the voltage and current input from the voltage detection unit 311 and the current measurement unit 313. When the secondary battery 301a reaches an overcharge detection voltage (e.g., 4.20V ± 0.05V) or an over-discharge detection voltage (2.4V ± 0.1V) or below, the switch control unit 314 sends a shut-off control signal to the switch unit 304, thereby preventing overcharging or over-discharging.

[0141] After the charging control switch 302a or the discharging control switch 303a is turned off, charging or discharging can be performed solely through diode 302b or diode 303b. These charging and discharging switches can utilize semiconductor switches such as MOSFETs. It should be noted that... Figure 10 In the middle, the switch part 304 is provided on the + side, but it can also be provided on the - side.

[0142] The memory 317 consists of RAM and ROM, and stores and rewrites the values ​​of battery characteristics, full charge capacity, remaining capacity, etc. calculated by the control unit 310.

[0143] (2) Electronic devices

[0144] The battery 1 described in the above-described embodiments or examples of the present invention can be mounted in electronic devices, electric conveying devices, energy storage devices, or other equipment to supply power.

[0145] Examples of electronic devices include laptop computers, smartphones, tablets, PDAs (portable information terminals), mobile phones, wearable devices, digital cameras, e-books, music players, game consoles, hearing aids, power tools, televisions, lighting equipment, toys, medical devices, and robots. Additionally, electrically powered transmission equipment, energy storage devices, power tools, and electrically powered unmanned aerial vehicles (UAVs) described later can also be broadly included in the category of electronic devices.

[0146] Examples of electric conveying equipment include electric vehicles (including hybrid vehicles), electric motorcycles, electric-assisted bicycles, electric buses, electric trolleys, automated guided vehicles (AGVs), and railway vehicles. Additionally, electric passenger aircraft and electric unmanned aerial vehicles (UAVs) for transportation are also included. The secondary battery involved in this invention can be used not only as a power source for driving these devices, but also as an auxiliary power source, a power source for energy regeneration, etc.

[0147] As energy storage devices, examples include energy storage modules for commercial or residential use, and power storage devices for use in buildings such as residences, high-rises, and offices, or for power generation equipment.

[0148] (3) Power tools

[0149] Reference Figure 11 A brief description will be given of an example of an electric screwdriver that is a power tool to which the present invention can be applied. The electric screwdriver 431 is equipped with a motor 433 that transmits rotational power to a shaft 434 and a user-operated trigger switch 432. The battery pack 430 and motor control unit 435 according to the present invention are housed within the lower housing of the handle of the electric screwdriver 431. The battery pack 430 is either built into the electric screwdriver 431 or can be freely installed and removed. The battery 1 of the present invention can be used in the batteries constituting the battery pack 430.

[0150] The battery pack 430 and the motor control unit 435 each have a microcomputer (not shown), and the charging and discharging information of the battery pack 430 can communicate with each other. The motor control unit 435 can control the operation of the motor 433 and cut off the power supply to the motor 433 in case of abnormalities such as over-discharge.

[0151] (4) Energy storage system for electric vehicles

[0152] As an example of applying the present invention to an energy storage system for electric vehicles, Figure 12The diagram schematically illustrates a structural example of a hybrid vehicle (HV) employing a series hybrid system. A series hybrid system is a vehicle that uses electricity generated by a generator that powers the engine, or electricity temporarily stored in a battery, to drive the vehicle via an electric drive conversion device.

[0153] The hybrid vehicle 600 includes an engine 601, a generator 602, an electric drive power conversion device 603 (DC motor or AC motor, hereinafter referred to as "motor 603"), drive wheels 604a and 604b, wheels 605a and 605b, a battery 608, a vehicle control device 609, various sensors 610, and a charging port 611. The battery 608 can be the battery pack 300 of this invention or a storage module equipped with multiple batteries 1 of this invention.

[0154] The motor 603 operates powered by the battery 608, and its rotational force is transmitted to the drive wheels 604a and 604b. The rotational force generated by the engine 601 allows the electricity generated by the generator 602 to be stored in the battery 608. Various sensors 610 control the engine speed or the opening of a throttle valve (not shown) via the vehicle control unit 609.

[0155] When the hybrid vehicle 600 is decelerated by a braking mechanism (not shown), the resistance during deceleration is applied as a rotational force to the motor 603, and the regenerative electricity generated by this rotational force is stored in the battery 608. The battery 608 can be charged by connecting to an external power source via the charging port 611 of the hybrid vehicle 600. Such an HV vehicle is called a plug-in hybrid electric vehicle (PHV or PHEV).

[0156] It should be noted that the secondary battery involved in this invention can also be applied to miniaturized primary batteries and used as a power source for the tire pressure monitoring system (TPMS) built into wheels 604 and 605.

[0157] The above explanation uses a series hybrid vehicle as an example, but the present invention can also be applied to hybrid vehicles that use a parallel connection of the engine and motor, or a combination of series and parallel connections. Furthermore, the present invention can also be applied to electric vehicles (EVs or BEVs) and fuel cell vehicles (FCVs) that operate solely on a drive motor without an engine.

[0158] Symbol Explanation

[0159] 1…Lithium-ion battery, 12…Insulating plate, 21…Positive electrode, 21A…Positive electrode foil, 21B…Positive electrode active material covering part, 21C…Positive electrode active material non-covering part, 22…Negative electrode, 22A…Negative electrode foil, 22B…Negative electrode active material covering part, 22C…Negative electrode active material non-covering part, 23…Separator, 24…Positive electrode current collector, 25…Negative electrode current collector, 26…Through hole, 27, 28…Outer edge, 41, 42…End face, 43…Slot.

Claims

1. A secondary battery, The secondary battery houses the electrode winding body, the positive electrode current collector, and the negative electrode current collector in a battery can. The electrode winding body has a structure in which strip-shaped positive and strip-shaped negative electrodes are stacked with a separator and wound around a central axis. The positive electrode has a positive active material covered portion and a positive active material uncovered portion on a strip-shaped positive electrode foil. The negative electrode has a negative active material covered portion and a negative active material uncovered portion on a strip-shaped negative electrode foil. The non-covered portion of the positive electrode active material is joined to the positive electrode current collector at one end of the electrode winding body. The non-covered portion of the negative electrode active material is joined to the negative electrode current collector at the other end of the electrode winding body. The electrode winding body has: At least the non-covered portion of the positive electrode active material bends toward the central axis of the wound structure to form a flat surface; The groove formed on the flat surface; and The inner peripheral portion is formed solely by the diaphragm located at a position further inward than the innermost periphery of the positive and negative electrodes. The length E of the portion of the positive electrode active material that protrudes from one end of the membrane in the width direction is greater than the length F of the portion of the membrane that protrudes from one end of the negative electrode in the width direction. When the number of diaphragm layers in the inner periphery is set to m, the thickness is set to t, and Z = t × m, equation (1) is satisfied. Equation (1): 80≤Z≤196, The number m of the diaphragm layers in the inner peripheral portion is an integer not equal to 1. The unit of Z is μm.

2. The secondary battery according to claim 1, wherein, The thickness of the diaphragm is greater than 4 μm and less than 30 μm.

3. The secondary battery according to claim 1 or 2, wherein, The thickness of the positive electrode foil is 5 μm or more and 20 μm or less, and the thickness of the negative electrode foil is 5 μm or more and 20 μm or less.

4. The secondary battery according to claim 1 or 2, wherein, The electrode winding body has: The flat surface formed by the non-covered portion of the negative electrode active material bending towards and overlapping the central axis of the wound structure; and A groove formed on the flat surface.

5. An electronic device, A secondary battery having any one of claims 1 to 4.

6. A power tool, A secondary battery having any one of claims 1 to 4.

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