Secondary battery, electronic device, and power tool

Abstract

A secondary battery includes a positive electrode having a covered portion and a positive active material non-covered portion on a strip-shaped positive electrode foil, the covered portion being covered with a positive active material layer, and a negative electrode having a covered portion and a first negative active material non-covered portion on a strip-shaped negative electrode foil, the covered portion being covered with a negative active material layer, the positive active material non-covered portion being joined to a positive current collector plate at one end of an electrode roll body, the first negative active material non-covered portion being joined to a negative current collector plate at the other end of the electrode roll body, the electrode roll body having a flat surface formed by bending and overlapping a center axis of a structure wound in either one or both of the positive active material non-covered portion and the first negative active material non-covered portion, and a groove formed in the flat surface, and the negative electrode having a second negative active material non-covered portion at an end of a lengthwise winding start side.

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 automobiles. One method to achieve high output is high-rate discharge, which involves a large current flowing through the battery. During high-rate discharge, the internal resistance of the battery becomes a problem due to the large current flowing through it.

[0003] For example, Patent Document 1 describes a battery with high current collection efficiency, which involves winding the overlapping positions of the positive and negative electrodes in a staggered manner in the width direction to create an electrode winding body, pressing a current collector plate onto the end of the electrode winding body, and joining the end and the current collector plate by laser welding.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2001-160387 Summary of the Invention

[0007] In the battery described in Patent Document 1, when the current collector is pressed onto the end of the electrode winding body, there is a problem that the negative electrode active material peels off from the active material covering part of the negative electrode, causing an internal short circuit due to the peeled active material.

[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 formed by stacking and winding strip-shaped positive and negative electrodes with a separator in between.

[0010] The positive electrode has a covered portion covered by a layer of positive electrode active material and a non-covered portion of positive electrode active material on a strip-shaped positive electrode foil.

[0011] The negative electrode has a covered portion covered by a layer of negative electrode active material and a non-covered portion of the first negative electrode active material on a 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 first 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] A flat surface formed by bending and coinciding the central axis of a structure wound in one or both directions through the uncovered portion of the positive electrode active material and the uncovered portion of the first negative electrode active material; and

[0016] Grooves formed on a flat surface

[0017] The negative electrode has a second negative electrode active material non-covered portion at the end of the winding start side in the length direction.

[0018] According to at least one embodiment of the present invention, a battery for high-rate discharge can be made to prevent internal short circuits. Furthermore, the initial capacity can be increased. 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

[0019] Figure 1 This is a cross-sectional view of a battery according to one embodiment.

[0020] Figure 2A This diagram shows the structure of the stacked positive electrode, negative electrode, and separator in Examples 1 and 2 before winding. Figure 2B This is a diagram showing the structure of Comparative Example 1 before winding, which consists of a stacked positive electrode, a negative electrode, and a separator.

[0021] Figure 3 A is a top view of the positive current collector. Figure 3 B is a top view of the negative current collector.

[0022] Figure 4 A to Figure 4 F is a diagram illustrating the battery assembly process according to one embodiment.

[0023] Figure 5 A is a top view and a front view of the positive and negative electrodes of Example 1 before winding. Figure 5 B is a cross-sectional view of the electrode winding body on the winding start side of Embodiment 1. Figure 5 C is a cross-sectional view of the electrode winding on the winding termination side of Example 1.

[0024] Figure 6 A is a top view and a front view of the positive and negative electrodes of Example 2 before winding. Figure 6 B is a cross-sectional view of the electrode winding body on the winding start side of Embodiment 2. Figure 6 C is a cross-sectional view of the electrode winding on the winding termination side of Example 2.

[0025] Figure 7 A is the top view and front view of the positive and negative electrodes of Comparative Example 1 before winding. Figure 7 B is a cross-sectional view of the electrode winding body on the winding start side of Comparative Example 1. Figure 7C is a cross-sectional view of the electrode winding on the winding termination side of Comparative Example 1.

[0026] Figure 8 This is a connection diagram illustrating a battery pack as an application example of the present invention.

[0027] Figure 9 This is a connection diagram illustrating an application example of the present invention using an electric tool.

[0028] Figure 10 This is a connection diagram used to illustrate an electric vehicle as an application example of the present invention. Detailed Implementation

[0029] 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.

[0030] <1. One implementation method>

[0031] <2. Variations>

[0032] <3. Application Examples>

[0033] The embodiments described below are preferred examples of the present invention, and the content of the present invention is not limited to these embodiments.

[0034] In an embodiment of the present invention, a cylindrical lithium-ion battery will be used as an example of a secondary battery.

[0035] <1. One implementation method>

[0036] 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.

[0037] Specifically, the lithium-ion battery 1 has a pair of insulating plates 12 and 13 and an electrode winding body 20 inside the cylindrical battery can 11. In addition, the lithium-ion battery 1 may also have any one or more of the following inside the battery can 11: a thermistor (PTC) element and reinforcing components.

[0038] [Battery can]

[0039] 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.

[0040] [Insulating board]

[0041] 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.

[0042] [Riveting Structure]

[0043] 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.

[0044] [Battery cover]

[0045] 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.

[0046] [washer]

[0047] 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.

[0048] 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.

[0049] [Safety Valve Mechanism]

[0050] 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.

[0051] [Electrode winding]

[0052] 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 positive electrode active material layer 21B 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 negative electrode active material layer 22B 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 thin film that electrically insulates the positive electrode 21 and the negative electrode 22 while allowing the movement of ions, electrolyte, and other substances.

[0053] The positive electrode 21 has portions of one and the other main surfaces of the positive electrode foil 21A covered by the positive electrode active material layer 21B, and portions not covered by the positive electrode active material layer 21B. The negative electrode 22 has portions of one and the other main surfaces of the negative electrode foil 22A covered by the negative electrode active material layer 22B, and portions not covered by the negative electrode active material layer 22B. Hereinafter, the portions not covered by the active material layers 21B and 22B will be appropriately referred to as the active material uncovered portions, and the portions covered by the active material layers 21B and 22B will be appropriately referred to as the active material covered portions. 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 a separator 23.

[0054] Figure 2A An example of the structure before winding is shown, in which the positive electrode 21, negative electrode 22, and separator 23 are stacked. The non-covered portion 21C of the active material of the positive electrode ( Figure 2A and Figure 2B The width of the upper part of the dotted portion is A, and the non-covered portion of the active material of the negative electrode is 22C. Figure 2A and Figure 2BThe 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).

[0055] The negative electrode 22 has an active material covered portion 22B and an active material uncovered portion 22C covered by a negative electrode active material layer on a strip-shaped negative electrode foil. On one main surface of the negative electrode 22, the active material uncovered portion 22C continuously exists on one long side and two short sides of its four perimeters. The portion where the boundary lines between the active material covered portion 22B and the active material uncovered portion 22C intersect (the area indicated by P) has a circular shape. The other main surface of the negative electrode 22 has the same structure.

[0056] Figure 2B An example of the structure before winding of the positive electrode 21, negative electrode 22, and separator 23 is shown. The portion (represented by Q) where the boundary line between the active material covered portion 22B and the active material uncovered portion 22C of the negative electrode intersects with the end of the negative electrode in the longitudinal direction is the part where the active material of the negative electrode is most easily peeled off. This is because the cut surface of the active material uncovered portion 22C of the negative electrode is exposed on the aforementioned boundary line.

[0057] The positive electrode foil 21A and the non-covered portion 21C of the positive electrode active material are made of, for example, aluminum, while the negative electrode foil 22A and the non-covered portion 22C of the negative electrode active material are made of, for example, copper. Therefore, generally speaking, the non-covered portion 21C of the positive electrode active material is softer (lower Young's modulus) than the non-covered portion 22C of the negative electrode active material. Therefore, in one embodiment, it is more preferable that A > B and C > D. In this case, when the non-covered portion 21C of the positive electrode and the non-covered portion 22C of the negative electrode active material are bent simultaneously from both electrode sides with the same pressure, the height of the bent portion measured from the front end of the diaphragm 23 is the same for both the positive electrode 21 and the negative electrode 22. At this time, since the non-covered portions 21C and 22C of the active material are bent and moderately overlapped, the non-covered portions 21C and 22C of the active material can be easily joined to the current collectors 24 and 25 by laser welding. In one embodiment, the joining refers to joining by laser welding, but the joining method is not limited to laser welding.

[0058] 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 2A and Figure 2BThe 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 impact 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.

[0059] A through hole 26 is provided on 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 collector plates 24 and 25 used to extract 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 winding 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.

[0060] 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 "voids" 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 wrinkles or voids, a groove 43 is pre-formed in the radial direction from the through hole 26 (for example, see reference). Figure 4B). 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 at the beginning of winding of the positive electrode 21 and negative electrode 22, near the through hole 26. This is to prevent the through hole 26 from being 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.

[0061] 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.

[0062] [Cold Collector]

[0063] In conventional lithium-ion batteries, leads for extracting current are welded to the positive and negative electrodes, respectively. However, this results in a 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 multiple points are welded 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 the low resistance.

[0064] Figure 3 A and Figure 3 B represents an example of a collector plate. Figure 3 A is the positive current collector 24. Figure 3 B 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 portion 31 with a rectangular strip 32. A hole 35 is provided near the center of the fan-shaped portion 31, and the position of the hole 35 corresponds to that of the through hole 26.

[0065] Figure 3The 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.

[0066] 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 fan-shaped portion 33, the position of which corresponds to the through hole 26. Since the fan-shaped portions 31 of the positive current collector plate 24 and 33 of the negative current collector plate 25 are fan-shaped, they cover 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.

[0067] [positive electrode]

[0068] 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.

[0069] 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.

[0070] 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.

[0071] [negative electrode]

[0072] To improve adhesion to the negative electrode active material layer, the surface of the negative electrode current collector 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.

[0073] 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.

[0074] 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).

[0075] For the active material covering portion 22B of the negative electrode, as shown in the following manufacturing method, when the end of a thin plate (e.g., 0.5 mm thick) is pressed perpendicularly relative to the end faces 41 and 42 (becoming...) Figure 4 In state B), at the winding start side of the electrode winding body 20 (the end side of the positive or negative electrode along the length direction of the innermost circumference of the electrode winding body 20), the negative electrode active material sometimes peels off from the active material covering portion 22B of the negative electrode. This peeling can be attributed to the stress generated when pressing the end face 42. Therefore, for example, when there is a non-covered portion 22C of the active material of the negative electrode on the end face 42 side of the negative electrode at the winding start side, it is possible to prevent the negative electrode active material from peeling off from the active material covering portion 22B of the negative electrode. The negative electrode may also have a non-covered portion 22C of the active material of the negative electrode at the end of the winding stop side along the length direction (the end side of the positive electrode 21 or negative electrode 22 along the length direction of the outermost circumference of the electrode winding body 20).

[0076] On the winding termination side of the electrode winding 20, the negative electrode 22 may have a region of the negative electrode active material non-covered portion 22C on the main surface of the side not facing the positive electrode active material covering portion 21B. This is because even if there is a negative electrode active material covering portion 22B on the main surface not facing the positive electrode active material covering portion 21B, its contribution to charging and discharging is very small. The region of the negative electrode active material non-covered portion 22C is preferably more than 3 / 4 turn and less than 5 / 4 turn of the electrode winding. At this time, since there is no negative electrode active material covering portion 22B that contributes very little to charging and discharging, the initial capacity can be increased relative to the same volume of the electrode winding 20.

[0077] [Septum]

[0078] 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.

[0079] 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.

[0080] Electrolyte

[0081] 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.

[0082] 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.

[0083] [Methods for manufacturing lithium-ion batteries]

[0084] Reference Figure 4 A to Figure 4F. 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, which corresponds to the starting point 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, and wound into a spiral shape with a through hole 26 formed on the central axis and the cuts made are arranged near the central axis. Figure 4 Electrode winding body 20, like A.

[0085] Next, as Figure 4 As shown in Figure B, the groove 43 is created by pressing the end of a thin plate (e.g., 0.5 mm thick) perpendicularly relative to the end faces 41 and 42, thereby partially bending the end faces 41 and 42. The groove 43 extends radially from the through hole 26 toward the central axis using 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, etc., by overlapping and bending the uncovered active material portions on end faces 41 and 42 towards the through hole 26. Then, the fan-shaped portion 31 of the positive electrode current collector plate 24 is laser-welded to end face 41, and the fan-shaped portion 33 of the negative electrode current collector plate 25 is laser-welded to end face 42.

[0086] 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 Figure F, the battery is sealed using gasket 15 and battery cover 14.

[0087] Example

[0088] The present invention will now be specifically described using a lithium-ion battery 1 manufactured as described above, based on an embodiment comparing internal short-circuit rate and initial capacity. It should be noted that the present invention is not limited to the embodiments described below.

[0089] In all the following embodiments and comparative examples, the battery size is 21700 (diameter 21 mm, height 70 mm), the width of the positive electrode active material covering portion 21B is 59 mm, the width of the negative electrode active material covering portion 22B is 62 mm, and the width of the separator 23 is 64 mm. The separator 23 is overlapped to cover the entire extent of the positive electrode active material covering portion 21B and the negative electrode active material covering portion 22B. The width of the non-covered portion of the positive electrode active material is 7 mm, and the width of the non-covered portion of the negative electrode active material (the width of the first non-covered portion of the negative electrode active material) is 4 mm. In Embodiment 1, Embodiment 2, and Comparative Example 1, the number of slots 43 is set to 8, and they are arranged at approximately equal angular intervals.

[0090] Figure 5 B~ Figure 7 B is contained within the manufactured battery ( Figure 1 A cross-sectional view (along a plane perpendicular to the winding axis) of the electrode winding body in its winding state. Figure 5 C~ Figure 7 C is contained within the manufactured battery ( Figure 1 A cross-sectional view of the winding termination side of the electrode winding in the state of (and) Figure 1 (A cross-sectional view of a plane perpendicular to the Z-axis), in which the positive and negative electrodes are simply shown in any one of the figures, without showing other details such as the diaphragm.

[0091] Hereinafter, the length of the non-covered portion 21C of the active material at both ends of the positive electrode in the longitudinal direction of the positive electrode 21, starting from the end on the winding start side or starting from the end on the winding end side, shall be appropriately referred to as the blank length, and the length of the non-covered portion 22C of the active material at both ends of the negative electrode in the longitudinal direction of the negative electrode 22, starting from the end on the winding start side (length of the second non-covered portion of the active material) or starting from the end on the winding end side (length of the third non-covered portion of the active material) shall be appropriately referred to as the blank length.

[0092] [Example 1]

[0093] The length of the active material covering portion 21B of the positive electrode is set to 1650 mm on both main surfaces, and the length of the active material covering portion 22B of the negative electrode is set to 1703 mm on one main surface (referred to as surface A) and 1701 mm on the other main surface (referred to as surface B). For example... Figure 2A and Figure 5As shown in Figure A, non-covered portions 22C of the active material of the negative electrode are formed at both ends along the length of the negative electrode 22. The blank length of surface A of the negative electrode 22 is set to 1 mm on both the winding start and winding end sides. The blank length of surface B of the negative electrode 22 is set to 2 mm on both the winding start and winding end sides. At both ends along the length of the positive electrode 21, the non-covered portions 21C of the active material of the positive electrode are not formed on either of the two main surfaces. The blank length of both main surfaces of the positive electrode 21 is set to 0 mm on both the winding start and winding end sides. On the winding start side of the electrode winding body 20, as shown in Figure A... Figure 5 As shown in Figure B, the positive electrode 21 and the negative electrode 22 are configured such that the active material covering portion 21B of the positive electrode, which is opposite to the active material covering portion 22B of the negative electrode, is located within the range of the active material covering portion 22B of the negative electrode. The same applies to the winding termination side of the electrode winding body 20. Figure 5 As shown in C, the positive electrode 21 and the negative electrode 22 are configured such that the active material covering portion 21B of the positive electrode, which is opposite to the active material covering portion 22B of the negative electrode, is located within the range of the active material covering portion 22B of the negative electrode.

[0094] [Example 2]

[0095] The length of the active material covering portion 21B of the positive electrode is set to 1675 mm in both main planes, and the length of the active material covering portion 22B of the negative electrode is set to 1726 mm in one main plane (referred to as plane A) and 1662 mm in the other main plane (referred to as plane B). For example... Figure 2A and Figure 6 As shown in Figure A, the active material non-covered portions 22C of the negative electrode 22 are formed at both ends along the length direction of the negative electrode 22. The blank length of surface A of the negative electrode 22 is set to 1 mm on both the winding start side and the winding end side. The blank length of surface B of the negative electrode 22 is set to 2 mm on the winding start side and 64 mm on the winding end side. At both ends along the length direction of the positive electrode 21, the active material non-covered portions 21C of the positive electrode are not formed on either of the two main surfaces. The blank length of both main surfaces of the positive electrode 21 is set to 0 mm on both the winding start side and the winding end side. On the winding start side of the electrode winding body 20, as shown in Figure A... Figure 6 As shown in Figure B, the positive electrode 21 and the negative electrode 22 are configured such that the active material covering portion 21B of the positive electrode, which is opposite to the active material covering portion 22B of the negative electrode, is located within the range of the active material covering portion 22B of the negative electrode. The same applies to the winding termination side of the electrode winding body 20. Figure 6 As shown in Figure C, the positive electrode 21 and the negative electrode 22 are configured such that the active material covering portion 21B of the positive electrode, which is opposite to the active material covering portion 22B of the negative electrode, is located within the range of the active material covering portion 22B of the negative electrode. For example... Figure 6As shown in Figure C, approximately one circumference of the outer surface side (surface B) of the negative electrode 22, i.e., the winding termination side, is not opposite to the positive electrode 21. An active material covering portion 22B, having a negative electrode only on the inner surface side (surface A) of the negative electrode 22, is provided on the winding termination side. Even with the formation of the negative electrode active material covering portion 22B, this region cannot undergo a charge-discharge reaction. In Example 2, by providing this approximately one-circumference region, the length of the positive electrode active material covering portion 21B can be greater than in Example 1. The length of this region is preferably more than 3 / 4 circumference and less than 5 / 4 circumference of the electrode winding. This is because, if this range is exceeded, a useless electrode region that does not contribute to the battery reaction will be created.

[0096] [Comparative Example 1]

[0097] The length of the active material covering portion 21B of the positive electrode is set to 1650 mm on both main surfaces, and the length of the active material covering portion 22B of the negative electrode is set to 1710 mm on both main surfaces. For example... Figure 2B and Figure 7 As shown in Figure A, at both ends of the positive electrode 21 along its length, neither of the two main surfaces has an uncovered portion 21C of the active material. The blank length of the two main surfaces of the positive electrode 21 is 0 mm at both the winding start and winding end sides. At both ends of the negative electrode 22 along its length, neither of the two main surfaces has an uncovered portion 22C of the active material. The blank length of the two main surfaces of the negative electrode 22 is 0 mm at both the winding start and winding end sides. Figure 7 As shown in Figure B, the positive electrode 21 and the negative electrode 22 are configured such that the active material covering portion 21B of the positive electrode, which is opposite to the active material covering portion 22B of the negative electrode, is located within the range of the active material covering portion 22B of the negative electrode. The same applies to the winding termination side of the electrode winding body 20. Figure 7 As shown in C, the positive electrode 21 and the negative electrode 22 are configured such that the active material covering portion 21B of the positive electrode, which is opposite to the active material covering portion 22B of the negative electrode, is located within the range of the active material covering portion 22B of the negative electrode.

[0098] [evaluate]

[0099] For the battery 1 assembled in the above example and charged, the internal short-circuit rate and initial capacity were calculated and evaluated. Battery 1 was assembled and charged to 4.20V, then stored at 25±3℃ for 5 days. The voltage of the stored battery 1 was measured, and the number of batteries whose voltage dropped by more than 50mV (below 4.15V) was counted, and this proportion was used as the internal short-circuit rate. 100 batteries were used per example in the internal short-circuit rate test. The initial capacity value was set to 100% of the value in Example 1.

[0100] [Table 1]

[0101]

[0102] The internal short-circuit rate in Examples 1 and 2 was 0%, while the internal short-circuit rate in Comparative Example 1 was a high value of 6%. It can be assumed that the internal short circuit occurred in the battery of Comparative Example 1 because when the non-covered portion 22C of the active material of the negative electrode is bent to form the end face 42, the active material of the negative electrode peels off from the covered portion 22B of the active material of the negative electrode at both ends in the length direction of the negative electrode 22. As shown in Examples 1 and 2, when the active material non-covered portion 22C of the negative electrode is present at both ends in the length direction of the negative electrode 22, the battery 1 did not experience an internal short circuit. It can be assumed that the reason why no internal short circuit occurred in the batteries of Examples 1 and 2 is because the active material non-covered portion 22C of the negative electrode is present at both ends in the length direction of the negative electrode 22, making it difficult to peel off the active material of the negative electrode. As can be seen from the results in Table 1, when the active material of the negative electrode is not covered by the end of the winding start side in the length direction of the negative electrode 22 and the active material of the negative electrode is not covered by the end of the winding end side in the length direction, the battery 1 will not cause an internal short circuit.

[0103] In both the battery of Example 1 and the battery of Example 2, although the same size battery canister 11 was used, the initial capacity of the battery of Example 2 was 1.5% larger than that of the battery of Example 1. In Example 2, as... Figure 6 As shown in Figure C, an area of ​​approximately one circumference of active material covering portion 22B, which has a negative electrode only on the inner surface side (A-side) of the negative electrode 22, is provided on the winding termination side. This reduces the useless area of ​​the negative electrode active material covering portion that does not contribute to the battery reaction, and the length of the positive electrode active material covering portion 21B is greater than that in Example 1. As a result, it can be considered that the battery of Example 2 can increase the initial capacity compared to the battery of Example 1. As can be seen from the results in Table 1, when the end of the negative electrode 22 at the winding start side in the length direction has a negative electrode active material non-covered portion 22C, and the end of the winding termination side in the length direction has an area of ​​approximately one circumference of active material covering portion 22B, which has a negative electrode only on the inner surface side (A-side) of the negative electrode 22, the battery 1 does not experience an internal short circuit and can obtain a larger initial capacity.

[0104] <2. Variations>

[0105] 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.

[0106] 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, but it can also be 18650 or other sizes.

[0107] The positive current collector 24 and the negative current collector 25 have fan-shaped portions 31 and 33, but they can also be other shapes.

[0108] 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.

[0109] <3. Application Examples>

[0110] (1) Battery pack

[0111] Figure 8 This is a block diagram illustrating a circuit structure example when the secondary battery according to 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.

[0112] The battery pack 301 is constructed by connecting multiple secondary batteries 301a in series and / or parallel. Figure 8 The example shown is a case where six secondary batteries 301a are connected in a 2-in-parallel and 3-in-series (2P3S) configuration.

[0113] 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.

[0114] 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.

[0115] 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 8 In the middle, the switch part 304 is provided on the + side, but it can also be provided on the - side.

[0116] 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.

[0117] (2) Electronic devices

[0118] The secondary batteries described in the above-described embodiments or examples of the present invention can be mounted in electronic devices, electric conveying equipment, energy storage devices, or other equipment to supply power.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] (3) Power tools

[0123] Reference Figure 9 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, as described in 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.

[0124] 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.

[0125] (4) Energy storage system for electric vehicles

[0126] As an example of applying the present invention to an energy storage system for electric vehicles, Figure 10 The diagram schematically illustrates a configuration 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.

[0127] 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 secondary batteries of this invention.

[0128] 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.

[0129] 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).

[0130] 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.

[0131] 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.

[0132] Symbol Explanation

[0133] 1…Lithium-ion battery, 12…Insulating plate, 21…Positive electrode, 21A…Positive electrode foil, 21B…Positive electrode active material layer, 21C…Active material non-covered portion of positive electrode, 22…Negative electrode, 22A…Negative electrode foil, 22B…Negative electrode active material layer, 22C…Active material non-covered portion of negative electrode, 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 formed by stacking and winding strip-shaped positive and negative electrodes with a separator in between. The positive electrode has a covered portion covered by a layer of positive electrode active material and a non-covered portion of positive electrode active material on a strip-shaped positive electrode foil. The negative electrode has a covered portion covered by a layer of negative electrode active material and a first negative electrode 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 first 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: A flat surface is formed by bending and coinciding the central axis of the wound structure in either or both directions of the uncovered portion of the positive electrode active material and the uncovered portion of the first negative electrode active material; and Grooves formed on the flat surface The negative electrode has a second negative electrode active material non-covered portion at its end on the winding start side in the length direction. The portion of the negative electrode active material covering part that intersects the boundary line between the first non-covered portion of the negative electrode active material and the covered portion of the negative electrode active material, and the portion where the boundary line between the second non-covered portion of the negative electrode active material and the covered portion of the negative electrode active material intersects, has a circular shape.

2. The secondary battery according to claim 1, wherein, The negative electrode also has a third negative electrode active material non-covered portion at the end on the winding termination side in the length direction.

3. The secondary battery according to claim 2, wherein, The negative electrode has a negative electrode active material layer formed only on one main surface region on the winding termination side.

4. The secondary battery according to claim 3, wherein, The region is between 3 / 4 and 5 / 4 of the electrode winding.

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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