Secondary battery, electronic device, and power tool

Abstract

A secondary battery in which a negative electrode has a covered portion covered by a negative electrode active material covered portion and a negative electrode active material uncovered portion on a negative electrode foil in a band shape, the negative electrode active material uncovered portion is joined to a negative electrode current collector plate at the other of the end portions of an electrode roll body, the electrode roll body has a flat surface formed by bending and overlapping either or both of the positive electrode active material uncovered portion and the negative electrode active material uncovered portion toward a center axis of a structure wound, and a first groove formed in the flat surface, the secondary battery has at least one C-shaped second groove in a can bottom of a battery can, the second groove is located at a position not overlapping a plate-shaped portion of the negative electrode current collector plate when viewed from a direction of the center axis, and all end portions of the second groove are located at positions overlapping the plate-shaped portion of the negative electrode current collector plate.

Description

Technical Field

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

[0002] Lithium-ion batteries are also being developed for applications requiring high output, such as power tools and automobiles. Batteries suitable for high output often have the following structure: a current collector is joined to a current-collecting foil exposed on the end face of a cylindrical electrode winding to allow for high current flow. In such batteries, the end face of the electrode winding is covered by the current collector. Therefore, when the battery overheats abnormally, the generated gas tends to be difficult to escape from the electrode winding.

[0003] For example, Patent Document 1 describes a secondary battery in which a groove is formed at the bottom of the battery can as an annular thin-walled portion.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2015-135822 Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] When the technology of Patent Document 1 is applied to a cylindrical battery having a flat negative electrode current collector plate on the end face of the electrode winding body, due to the positional relationship between the groove and the negative electrode current collector plate, there is a problem that the gas cannot be released smoothly when the internal pressure rises abnormally.

[0009] Therefore, one of the objectives of this invention is to provide a battery for high-rate discharge that can smoothly release gas when abnormally heated.

[0010] Means for solving technical problems

[0011] To solve the above-mentioned technical problems, the present invention relates to a secondary battery, wherein an electrode winding body, a positive electrode current collector, and a negative electrode current collector are housed in a battery can, and the electrode winding body has a structure in which a strip-shaped positive electrode and a strip-shaped negative electrode are stacked and wound together with a separator, wherein...

[0012] The positive electrode has a covered portion covered by the positive electrode active material and an uncovered portion on the strip-shaped positive electrode foil.

[0013] The negative electrode has a covered portion covered by the negative electrode active material and an uncovered portion on the strip-shaped negative electrode foil.

[0014] The uncovered portion of the positive electrode active material is bonded to the positive electrode current collector at one end of the electrode winding body.

[0015] The uncovered portion of the negative electrode active material is joined to the negative electrode current collector at another end of the electrode winding body.

[0016] The electrode winding body has:

[0017] A flat surface is formed by bending and aligning one or both of the uncovered portions of the positive and negative active materials toward the central axis of the wound structure; and

[0018] The first groove is formed on a flat surface.

[0019] The secondary battery has at least one C-shaped second groove at the bottom of the battery can.

[0020] When viewed from the direction of the central axis, the second groove is located in a position that does not overlap with the plate-shaped portion of the negative electrode current collector, and all ends of the second groove are located in positions that overlap with the plate-shaped portion of the negative electrode current collector.

[0021] Invention Effects

[0022] At least according to an embodiment of the present invention, when the internal pressure of the battery rises due to gas generated during abnormal heating, the bottom of the can will open (crack) starting from the groove with lower strength, thereby allowing the gas inside the battery to be discharged outside the battery. Furthermore, by configuring the portion of the end of the electrode winding that does not overlap with the plate-like portion of the negative electrode current collector and the end of the second groove so that they do not overlap when viewed from the central axis direction of the electrode winding, the opening (crack) of the bottom of the can can be smoothly induced when the internal pressure of the battery rises. Additionally, the content of the present invention is not to be interpreted as limited to the effects exemplified in this specification. Attached Figure Description

[0023] Figure 1 This is a cross-sectional view of a battery according to one embodiment.

[0024] Figure 2 This is a diagram illustrating an example of the arrangement of the positive electrode, negative electrode, and separator in an electrode winding.

[0025] Figure 3 A is a top view of the positive current collector. Figure 3 B is a top view of the negative current collector.

[0026] Figure 4 A to Figure 4 F is a diagram illustrating the battery assembly process according to one embodiment.

[0027] Figure 5 The figure is used in the description of Example 1.

[0028] Figure 6 The figure is used in the description of Example 2.

[0029] Figure 7 The figure is used in the description of Comparative Example 1.

[0030] Figure 8 The figure is used in the description of Comparative Example 2.

[0031] Figure 9 This is the diagram used in the description of Comparative Example 3.

[0032] Figure 10 The figure is used in the description of Comparative Example 4.

[0033] Figure 11 The figure is used in the description of Comparative Example 5.

[0034] Figure 12 This is the diagram used in the description of Comparative Example 6.

[0035] Figure 13 This is the diagram used in the description of Comparative Example 7.

[0036] Figure 14 This is a connection diagram used in the description of a battery pack, which is an application example of the present invention.

[0037] Figure 15 This is a connection diagram used in the description of a battery tool that serves as an application example of the present invention.

[0038] Figure 16 This is a connection diagram used in the description of an electric vehicle, which is an application example of the present invention. Detailed Implementation

[0039] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The descriptions will proceed in the following order.

[0040] <1. Implementation Method>

[0041] <2. Variations>

[0042] <3. Application Examples>

[0043] The embodiments described below are preferred examples of the present invention, and the content of the present invention is not limited to these embodiments.

[0044] In an embodiment of the present invention, a cylindrical lithium-ion battery will be used as an example of a secondary battery.

[0045] <1. Implementation Method>

[0046] First, let's explain the overall structure of a lithium-ion battery. Figure 1 This is a schematic cross-sectional view of lithium-ion battery 1. (As shown...) Figure 1As shown, the lithium-ion battery 1 is, for example, a cylindrical lithium-ion battery 1 in which an electrode winding body 20 is housed inside a battery can 11.

[0047] Specifically, the lithium-ion battery 1 may have a pair of insulating plates 12 and 13 and an electrode winding body 20 inside a cylindrical battery can 11. However, the lithium-ion battery 1 may also have one or more of the following inside the battery can 11: a thermistor (PTC) element and reinforcing components.

[0048] [Battery can]

[0049] The battery can 11 is primarily a component for housing the electrode winding 20. The battery can 11 is, for example, a cylindrical container with one open end and the other closed end. That is, the battery can 11 has an open end (open end 11N). The battery can 11 may contain, for example, any one or more of the following metallic materials: iron, aluminum, and their alloys. However, the surface of the battery can 11 may also be plated with, for example, any one or more of the following metallic materials: nickel.

[0050] A can bottom 51 is provided on the closed end face of the battery can 11. The can bottom 51 serves as the negative terminal of the battery 1. The can bottom 51 has a C-shaped groove 52 (second groove). The groove 52 refers to a thin-walled portion disposed on the inner surface of the battery can 11 on both sides of the can bottom 51. The groove 52 is, for example, a groove-shaped portion formed by an engraving process to thin the wall thickness of the can bottom 51. The groove 52 is C-shaped. In the case of having multiple grooves 52, for example, as Figure 5 As shown, two grooves are preferably provided on the same circumference. The circle passes through the center of the width of the groove 52, and the diameter of the circle is D1. Furthermore, it is preferable that the circle is concentric with the outer edge (diameter D2) of the bottom of the can 51. This is because by setting it to be concentric, leakage from the groove 52 is less likely to occur when the battery 1 falls. In this case, the width of the groove 52 is preferably 0.10 mm or more and 1.00 mm or less. This is because if the width of the groove 52 is less than 0.10 mm, there is a possibility that the battery 1 may break when abnormal heat is applied to the battery 1; if the width of the groove 52 is more than 1.00 mm, there is a possibility that the electrode winding body 20 may detach from the battery can 11 when the battery 1 falls.

[0051] Preferably, the diameter of the C-shaped groove 52 (hereinafter referred to as D1) is at least 44% of the outer diameter of the can bottom 51. This will be explained below. If abnormal heat is applied to the battery 1 from the outside, heat (flame) will be generated from the outer periphery of the electrode winding body 20. This heat (flame) has the effect of softening the groove 52 of the can bottom 51; the closer the groove 52 is to the outer periphery of the electrode winding body 20, the easier it is to soften. If D1 is at least 44% of the outer diameter of the can bottom, since the groove 52 is close to the outer periphery of the electrode winding body 20, if abnormal heat is applied to the battery from the outside, the groove 52 of the can bottom 51 will easily soften. Therefore, by generating gas, the gas pressure in the can bottom 51 increases, causing the groove 52 of the can bottom 51 to crack, thereby allowing the gas to escape to the outside. On the other hand, if D1 is less than 44% of the outer diameter of the bottom 51, the groove 52 is far from the outer periphery of the electrode winding body 20, making it difficult for the groove 52 to soften due to the heat generated during the combustion test. Therefore, even if the gas pressure in the bottom 51 increases due to the generation of gas, the bottom 51 cannot crack, and the gas cannot escape to the outside.

[0052] [Insulating board]

[0053] Insulating plates 12 and 13 are having a winding shaft relative to the electrode winding body 20. Figure 1 A disc-shaped plate with a plane approximately perpendicular to the Z-axis. In addition, insulating plates 12 and 13 are arranged, for example, to clamp the electrode winding 20 between each other.

[0054] [Riveting Structure]

[0055] At the open end face 11N of the battery can 11, the battery cover 14 and the safety valve mechanism 30 are riveted together with a gasket 15 to form a riveting structure 11R (press-fit structure). Thus, the battery can 11 is sealed with the electrode winding body 20 and the like housed inside the battery can 11.

[0056] [Battery cover]

[0057] The battery cover 14 is primarily a component that seals 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.

[0058] [Gasket]

[0059] The gasket 15 is a component that mainly seals the gap between the bend 11P and the battery cover 14 by being clamped between the battery can 11 (bent portion 11P) and the battery cover 14. However, the surface of the gasket 15 may also be coated with, for example, asphalt.

[0060] The gasket 15 may contain one or more insulating materials. The type of insulating material is not particularly limited; for example, it may be a polymer such as polybutylene terephthalate (PBT) and polypropylene (PP). Preferably, the insulating material is polybutylene terephthalate. This is because the battery canister 11 and the battery cover 14 are electrically separated, and the gap between the bent portion 11P and the battery cover 14 is adequately sealed.

[0061] [Safety Valve Mechanism]

[0062] The safety valve mechanism 30 mainly releases the internal pressure of the battery can 11 by releasing the seal of the battery can 11 as needed when the pressure (internal pressure) inside the battery can 11 rises. The cause of the rise in internal pressure of the battery can 11 may be, for example, gas generated by the decomposition reaction of the electrolyte during charging and discharging.

[0063] [Electrode winding]

[0064] In a cylindrical lithium-ion battery, a strip-shaped positive electrode 21 and a strip-shaped negative electrode 22 are wound into a vortex shape, sandwiching a separator 23, and stored in a battery can 11 while immersed in electrolyte. The positive electrode 21 has an active material covering portion 21B formed on one or both sides of the positive electrode foil 21A. The material of the positive electrode foil 21A is, for example, a metal foil made of aluminum or an aluminum alloy. The negative electrode 22 has an active material covering portion 22B formed on one or both sides of the negative electrode foil 22A. The material of the negative electrode foil 22A 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 membrane that electrically insulates the positive electrode 21 from the negative electrode 22 and allows the movement of substances such as ions and electrolyte.

[0065] 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 intentionally do not cover the periphery of one end located in the direction of the strip. The portion not covered by the active material layer will be appropriately referred to as the uncovered active material portion, and the portion covered by the active material layer will be appropriately referred to as the covered active material portion. In the cylindrical battery, the electrode winding body 20 is wound in an overlapping manner with the separator 23 such that the uncovered active material portion 21C of the positive electrode and the uncovered active material portion 22C of the negative electrode face opposite directions.

[0066] exist Figure 2 This shows an example of the structure before winding, in which a positive electrode 21, a negative electrode 22, and a separator 23 are stacked. The uncovered portion 21C of the active material of the positive electrode ( Figure 2 The width of the dotted portion on the upper side is A, and the portion 22C of the active material not covered by the negative electrode is... Figure 2The width of the lower dotted portion 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 positive electrode's uncovered active material 21C protruding from one end of the separator 23 in the width direction is C, and the length of the portion of the negative electrode's uncovered active material 22C protruding from the other end of the separator 23 in the width direction is D. In one embodiment, C > D is preferred, for example, C = 4.5 (mm) and D = 3 (mm).

[0067] Since the uncovered portion 21C of the positive electrode is made of, for example, aluminum, and the uncovered portion 22C of the negative electrode is made of, for example, copper, the uncovered portion 21C of the positive electrode is generally softer (has a smaller Young's modulus) than the uncovered 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 uncovered portions 21C of the positive electrode and 22C of the negative electrode are bent simultaneously from both electrode sides under the same pressure, the heights measured from the front end of the separator 23 of the bent portion are sometimes approximately the same for both the positive electrode 21 and the negative electrode 22. At this time, since the uncovered portions 21C of the positive electrode and 22C of the negative electrode are bent and appropriately overlapped, laser welding of the uncovered portions 21C of the positive electrode and 22C of the negative electrode to the current collectors 24 and 25 can be easily performed. In one embodiment, the joining refers to connection by laser welding, but the joining method is not limited to laser welding.

[0068] For the positive electrode 21, a 3mm wide area, including the boundary between the uncovered active material portion 21C and the covered active material portion 21B of the positive electrode, is covered by the insulating layer 101. Figure 2 The gray area is covered. Furthermore, the entire area of ​​the uncovered 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 has the effect of reliably preventing an internal short circuit in the battery 1 when a foreign object enters between the active material covered portion 22B of the negative electrode and the uncovered active material portion 21C of the positive electrode. In addition, the insulating layer 101 has the effect of absorbing the impact when the battery 1 is subjected to an impact, and reliably preventing the uncovered active material portion 21C of the positive electrode from bending or short-circuiting with the negative electrode 22.

[0069] 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 winding core used for assembling the electrode winding body 20 and the electrode rod used for welding. For the electrode winding body 20, since the active material uncovered portion 21C of the positive electrode and the active material uncovered portion 22C of the negative electrode are overlapped in opposite directions when the winding body is wound, the active material uncovered portion 21C of the positive electrode is gathered on one end face (end face 41) of the electrode winding body, and the active material uncovered portion 22C of the negative electrode is gathered on the other end face (end face 42) of the electrode winding body 20. In order to improve the contact with the current collector plates 24 and 25 used for drawing out the current, the active material uncovered portion 21C of the positive electrode and the active material uncovered portion 22C of the negative electrode are bent so that the end faces 41 and 42 become flat surfaces. The bending direction is from the outer edges 27 and 28 of the end faces 41 and 42 toward the through hole 26, and the uncovered active material portions on adjacent loops overlap and bend with each other in the wound state. In addition, in this specification, "flat surface" includes not only a completely flat surface, but also a surface with slight unevenness or surface roughness to the extent that the uncovered active material portion can engage with the current collector plate.

[0070] By bending the uncovered active material portion 21C of the positive electrode and the uncovered active material portion 22C of the negative electrode in an overlapping manner, it appears at first glance that the end faces 41 and 42 can be made into 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 "gap" refer to the parts where the uncovered active material portion 21C of the positive electrode and the uncovered active material portion 22C of the negative electrode are deflected during bending, preventing the end faces 41 and 42 from becoming flat surfaces. In order to prevent the formation of the above-mentioned wrinkles or gaps, a groove 43 (first groove, for example, see reference) is pre-formed in the radial direction from the through hole 26. 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. There are gaps at the uncovered active material portions 21C of the positive electrode and 22C of the negative electrode at the beginning of the winding of the positive electrode 21 and the negative electrode, which are located near the through hole 26. This is to prevent the through hole 26 from being blocked when bending towards it. Even after bending the uncovered active material portions 21C of the positive electrode and 22C of the negative electrode, the groove 43 remains in the flat surface, and the portion without the groove 43 is joined (welded, etc.) to the positive electrode current collector 24 or the negative electrode current collector 25. In addition, not only the flat surface, the groove 43 can also be joined to a portion of the current collectors 24 and 25.

[0071] The detailed structure of the electrode winding 20, namely the positive electrode 21, the negative electrode 22, the separator 23, and the electrolyte, will be described later.

[0072] [Cold Collector]

[0073] In conventional lithium-ion batteries, for example, although current-leading pins are welded at both the positive and negative electrodes, the internal resistance of the battery increases at these points. During discharge, the lithium-ion battery heats up and becomes very hot, making it unsuitable for high-rate discharge. Therefore, in one embodiment of the lithium-ion battery, the positive electrode current collector 24 and the negative electrode current collector 25 are disposed on end faces 41 and 42, and the internal resistance of the battery is suppressed to a low level by welding the uncovered active material portions 21C of the positive electrode and 22C of the negative electrode at multiple points on end faces 41 and 42. Bending the end faces 41 and 42 to make them flat also contributes to lower resistance.

[0074] exist Figure 3 A and Figure 3 Example of a current collector is shown in B. 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 with a rectangular strip 32 at a flat, fan-shaped plate portion 31. A hole 35 is provided near the center of the plate portion 31, and the position of the hole 35 corresponds to that of the through hole 26.

[0075] Figure 3 The part indicated by the dotted portion (A) is the insulating portion 32A where an insulating tape or insulating material is adhered to the strip portion 32. The portion below the dotted portion in the attached drawing is the connecting portion 32B facing the sealing plate, which also serves as an external terminal. Furthermore, in a battery structure without a metal center pin (not shown) at the through hole 26, the likelihood of the strip portion 32 contacting the negative electrode potential is low; therefore, the insulating portion 32A can be omitted. In this case, the widths of the positive electrode 21 and the negative electrode 22 can be increased by an amount equivalent to the thickness of the insulating portion 32A to increase the charge / discharge capacity.

[0076] The negative current collector 25 has a shape that is roughly the same as that of the positive current collector 24, but the strip section is different. Figure 3The strip portion 34 of the negative current collector plate 24 is shorter than the strip portion 32 of the positive current collector plate and does not have a portion equivalent to the insulating portion 32A. A circular protrusion (raised portion) 37, indicated by multiple circle markings, exists at the strip portion 34. During resistance welding, the current concentrates on the protrusion, which melts and welds the strip portion 34 to the bottom of the battery canister 11. Similar to the positive current collector plate 24, a hole 36 is provided near the center of the plate portion 33 in the negative current collector plate 25, the hole 36 being positioned corresponding to the through hole 26. 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, thus covering a portion of the end faces 41 and 42. The reason for not covering the entire surface is to allow the electrolyte to smoothly penetrate the electrode winding during battery assembly, or to release gases generated when the battery reaches an abnormally high temperature or overcharged state to the outside of the battery.

[0077] [positive electrode]

[0078] The positive electrode active material layer contains at least a positive electrode material (positive electrode active material) capable of absorbing and releasing lithium, and may also contain 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, lithium-containing composite oxides have a layered rock salt or spinel-type crystal structure. Lithium-containing phosphate compounds have, for example, an olivine-type crystal structure.

[0079] The positive electrode binder contains synthetic rubber or polymeric compounds. Synthetic rubbers include styrene-butadiene rubbers, fluorinated rubbers, and ethylene propylene diene, etc. Polymeric compounds include polyvinylidene fluoride (PVdF) and polyimide, etc.

[0080] The positive electrode conductive agent is a carbon material such as graphite, carbon black, acetylene black, or Ketjen black. However, the positive electrode conductive agent can also be a metallic material or a conductive polymer.

[0081] [negative electrode]

[0082] To improve adhesion to the negative electrode active material layer, it is preferable to roughen the surface of the negative electrode foil 22A. The negative electrode active material layer contains at least a negative electrode material (negative electrode active material) capable of absorbing and releasing lithium, and may also contain a negative electrode binder and a negative electrode conductive agent, etc.

[0083] 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 carbon materials can be fibrous, spherical, granular, or flake-like.

[0084] Furthermore, negative electrode materials may include metallic materials. Examples of metallic materials include Li (lithium), Si (silicon), Sn (tin), Al (aluminum), Zn (zinc), and Ti (titanium). Metallic elements may form compounds, mixtures, or alloys with other elements; an example is silicon oxide (SiO₂).x where \(0 < x\leq2\)), silicon carbide (SiC), or an alloy of carbon and silicon, lithium titanate (LTO).

[0085] [Separator]

[0086] The separator 23 is a porous membrane containing resin, or may be a laminated membrane of two or more porous membranes. The resin is polypropylene, polyethylene, etc. The separator 23 may also use a porous membrane as a base layer and include a resin layer on one or both sides of the base layer. This is because, by improving the adhesion of the separator 23 to each of the positive electrode 21 and the negative electrode 22, deformation of the electrode winding body 20 is suppressed.

[0087] The resin layer contains a resin such as PVdF. In the case of forming this resin layer, a solution in which the resin is dissolved in an organic solvent is coated on the base layer, and then the base layer is dried. Alternatively, the base layer may be impregnated with the solution and then dried. From the viewpoints of improving heat resistance and battery safety, the resin layer preferably contains inorganic particles or organic particles. Examples of the inorganic particles include alumina, aluminum nitride, aluminum hydroxide, magnesium hydroxide, boehmite, talc, silica, mica, etc. In addition, a surface layer mainly composed of inorganic particles formed by a sputtering method, an ALD (atomic layer deposition) method, etc. may be used instead of the resin layer.

[0088] [Electrolyte solution]

[0089] The electrolyte solution contains a solvent and an electrolyte salt, and may also contain additives, etc. as required. The solvent is a non-aqueous solvent such as an organic solvent or water. An electrolyte solution containing a non-aqueous solvent is called a non-aqueous electrolyte solution. The non-aqueous solvent includes cyclic carbonates, chain carbonates, lactones, chain carboxylic acid esters, or nitriles (mononitriles), etc.

[0090] Representative examples of the electrolyte salt are lithium salts, but salts other than lithium salts may also be included. Examples of the lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), dilithium hexafluorosilicate (Li2SF6), etc. These salts can be used in combination, and among them, from the viewpoint of improving battery characteristics, it is preferable to use LiPF6 and LiBF4 in combination. 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.

[0091] [Method for manufacturing a lithium-ion battery]

[0092] Refer to 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 onto the surface of a strip of positive electrode foil 21A to serve as a cover portion of the positive electrode 21, and a negative electrode active material is coated onto the surface of a strip of negative electrode foil 22A to serve as a cover portion of the negative electrode 22. At this time, at one end of the short side direction of the positive electrode 21 and at one end of the short side direction of the negative electrode 22, an uncovered active material portion 21C of the positive electrode and an uncovered active material portion 22C of the negative electrode, where no positive or negative electrode active material is coated, are formed. A notch is formed in a portion of the uncovered active material portion 21C of the positive electrode and a portion of the uncovered active material portion 22C of the negative electrode, that is, at the starting point of winding during winding. The positive electrode 21 and the negative electrode 22 are then subjected to drying processes, etc. Then, the uncovered active material portion 21C of the positive electrode and the uncovered active material portion 22C of the negative electrode are overlapped in opposite directions, separated by the separator 23, and wound into a vortex shape with a through hole 26 formed at the central axis and the notch disposed near the central axis, thereby producing... Figure 4 Electrode winding body 20, like A.

[0093] Next, as Figure 4 As shown in B, the end faces 41 and 42 are partially bent to form a groove 43 by pressing the end face 41 and 42 perpendicularly relative to the end face 41 and 42. The groove 43 extends radially from the through hole 26 toward the central axis in this way. Figure 4 The number or configuration of slots 43 shown in B is just one example. Then, as Figure 4 As shown in Figure C, the same pressure is applied simultaneously to end faces 41 and 42 from both pole sides in a substantially perpendicular direction, bending the uncovered active material portion 21C of the positive electrode and the uncovered active material portion 22C of the negative electrode, so that end faces 41 and 42 are formed into flat surfaces. At this time, a load is applied through the plate surface, etc., by bending the uncovered active material portions of end faces 41 and 42 in an overlapping manner toward the through hole 26. 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 to end face 42.

[0094] After that, 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, which has been assembled as described above, is then inserted into... Figure 4 The battery can 11, as shown in Figure E, is then filled with electrolyte, and 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, the battery is sealed using a gasket 15 and a battery cover 14.

[0095] Example

[0096] The present invention will now be specifically described based on an example of comparing the number of defects in burner tests using a lithium-ion battery 1 manufactured as described above. However, the present invention is not limited to the examples described below.

[0097] In all the following embodiments and comparative examples, the battery size is set to 21700 (diameter 21mm, length 70mm). The width of the positive electrode active material covering portion 21B is set to 59mm, the width of the negative electrode active material covering portion 22B is set to 62mm, and the width of the separator 23 is set to 64mm. The separator 23 overlaps 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 uncovered portion of the positive electrode active material is set to 7mm, and the width of the uncovered portion of the negative electrode active material is set to 4mm. The number of slots 43 is set to 8, and they are arranged at approximately equal angular intervals.

[0098] by Figure 5 For example, the number of grooves 52 in the bottom of the tank 51 and the number of end portions 53 of the grooves that do not overlap with the plate-shaped portion 33 of the negative electrode current collector will be explained. Figure 5 From the central axis direction of the electrode winding body ( Figure 1 This is a schematic diagram drawn by overlapping the outer edge of the bottom 51 of the battery can 11 with the slot 52 and the plate-shaped portion 33 of the negative electrode current collector 25 when viewed in the Z-axis direction. In the embodiment or comparative example, the slot 52 is C-shaped or O-shaped. The number of slots 52 refers to the number of C-shaped or O-shaped slots. Figure 5 In the example, the number of slots 52 is 2.

[0099] End 53 of groove 52 refers to the front end portion of the C-shaped groove. Furthermore, for one C-shaped groove, end 53 is counted as two. Figure 5 In the middle, as the negative electrode current collector 25, a plate-shaped portion 33 and a hole 36 in the plate-shaped portion are shown. At the negative electrode current collector 25, apart from the hole 36 in the plate-shaped portion, there are no notches or holes. The number of ends of the grooves that do not overlap with the plate-shaped portion of the negative electrode current collector refers to: from the central axis direction of the electrode winding body 20 (… Figure 1 When viewed along the Z-axis, this refers to the number of ends 53 of the grooves 52 present in the bottom 51 of the can that do not overlap with the plate-like portion 33. Figure 5 In the example, all the ends 53 of the groove 52 overlap with the plate-shaped portion 33, therefore, the number of ends 53 of the groove 52 that do not overlap with the plate-shaped portion 33 is 0.

[0100] [Example 1]

[0101] like Figure 5As shown, the number of slots at the bottom of the tank is set to 2, and the number of the ends of the slots that do not overlap with the plate-shaped part of the negative electrode current collector is set to 0.

[0102] [Example 2]

[0103] like Figure 6 As shown, the number of slots at the bottom of the tank is set to 1, and the number of the ends of the slots that do not overlap with the plate-shaped part of the negative electrode current collector is set to 0.

[0104] [Comparative Example 1]

[0105] like Figure 7 As shown, the number of slots at the bottom of the tank is set to 2, and the number of the ends of the slots that do not overlap with the plate-shaped part of the negative electrode current collector is set to 2.

[0106] [Comparative Example 2]

[0107] like Figure 8 As shown, the number of slots at the bottom of the tank is set to 1, and the number of the ends of the slots that do not overlap with the plate-shaped part of the negative electrode current collector is set to 2.

[0108] [Comparative Example 3]

[0109] like Figure 9 As shown, the number of slots at the bottom of the tank is set to 2, and the number of the ends of the slots that do not overlap with the plate-shaped part of the negative electrode current collector is set to 1.

[0110] [Comparative Example 4]

[0111] like Figure 10 As shown, the number of slots at the bottom of the tank is set to 1, and the number of the ends of the slots that do not overlap with the plate-shaped part of the negative electrode current collector is set to 1.

[0112] [Comparative Example 5]

[0113] like Figure 11 As shown, the number of slots at the bottom of the tank is set to 1, and the number of the ends of the slots that do not overlap with the plate-shaped part of the negative electrode current collector is set to 0.

[0114] [Comparative Example 6]

[0115] like Figure 12 As shown, the number of slots at the bottom of the tank is set to 0, and the number of the ends of the slots that do not overlap with the plate-shaped part of the negative electrode current collector is set to 0.

[0116] [Comparative Example 7]

[0117] like Figure 13 As shown, the number of slots at the bottom of the tank is set to 1, and the number of the ends of the slots that do not overlap with the plate-shaped part of the negative electrode current collector is set to 0.

[0118] [evaluate]

[0119] A burner test was performed on the assembled and charged battery 1 of the above example. The burner test was based on the UL 1642 projectile test. Prior to the burner test, the battery was fully charged under CC / CV charging conditions of 4.2V / 2A and 100mAcut. In the burner test, a gas burner was used to burn the battery on an octagonal aluminum mesh (Φ0.25mm, 16-18 wires / inch) with a diagonal distance of 61cm and a height of 30.5cm. A screen (20 openings / inch, Φ0.43mm wire) on an operating stand with a 102mm hole in the center was placed 38mm above the edge of the burner opening. The gas flow rate of the burner was set to 500ml / min (methane) and 150~175ml / min (propane). The battery was placed on the screen (not fixed unless moved to the end) and burned when the flame of the burner turned bright blue and the screen turned red. In the burner test, 100 tests were conducted. Any instance where battery 1 or a portion of battery 1 penetrated the outer casing (metal cage) was considered a defect. The number of defective units was counted to determine the total number of defects in the burner test. The results are shown below.

[0120] [Table 1]

[0121]

[0122] In Examples 1 and 2, the number of defects occurring in the burner test was relatively small, less than 5 each, compared to more than 10 in Comparative Example 7 of Comparative Example 1. During the burner test, the battery 1 was heated, causing an increase in internal pressure due to gas generated from the electrode winding 20 of the battery 1. We then assume that the bottom of the can is opened (cracked) starting from the slot 52 with lower strength, allowing gas to escape from the battery. In Examples 1 and 2, the area where the end face of the electrode winding 20 is not blocked, i.e., the area where the plate-shaped portion 33 of the negative electrode current collector 25 is absent, becomes the main gas passage. Since the slot 52 exists in this area and the slot 52 does not have an end 53, we assume that the bottom of the can is opened (cracked) smoothly, thereby safely venting the gas.

[0123] In Comparative Examples 1 to 4, the configuration was such that, when viewed from the central axis direction of the electrode winding body 20, the end 53 of the groove 52 overlapped with the area where the plate-shaped portion 33 of the negative electrode current collector 25 did not exist. Therefore, we believe that since the end 53 of the groove 52 is present in the area where the plate-shaped portion 33 of the negative electrode current collector 25 does not exist, the bottom of the can 51 will not open (crack) smoothly. That is, since the end 53 of the groove 52 is present in the area that becomes the main channel for gas, it is difficult to expel gas. In Comparative Examples 5 and 6, since the groove 52 of the bottom of the can 51 is not present in the area that does not overlap with the plate-shaped portion 33 of the negative electrode current collector 25, i.e., the area that becomes the main channel for gas, it is difficult to expel gas. In Comparative Example 7, since the shape of the groove 52 is not C-shaped but O-shaped, the contents of the battery 1 flew out and penetrated the outer casing (metal cage), therefore, we believe that the number of defects is relatively large.

[0124] Based on the above results and investigation, it can be determined that: the bottom 51 of the battery can 11 has at least one C-shaped groove 52, and when viewed from the central axis direction of the electrode winding body 20, the groove 52 exists at a position that does not overlap with the plate-shaped portion 33 of the negative electrode current collector 25, and the ends 53 of the groove are all located at positions that overlap with the plate-shaped portion 33 of the negative electrode current collector 25. When the internal pressure of the battery 1 rises, the bottom of the can will open smoothly (crack), and the gas can be safely discharged to the outside of the battery.

[0125] <2. Variations>

[0126] 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.

[0127] In the embodiments and comparative examples, the number of slots 43 is set to 8, but other numbers may also be used. The battery size is set to 21700, but it may also be 18650 or other sizes.

[0128] Although the positive current collector 24 and the negative current collector 25 have fan-shaped plate portions 31 and 33, they can also be other shapes.

[0129] Without departing from the spirit of the invention, this invention can also be applied to batteries other than lithium-ion batteries, or batteries other than cylindrical shapes (e.g., stacked 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.

[0130] <3. Application Examples>

[0131] (1) Battery pack

[0132] Figure 14 This is a block diagram illustrating a circuit configuration example when a 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 equipped with a charging control switch 302a and a discharging control switch 303a; a current sensing resistor 307; a temperature sensing element 308; and a control unit 310. The control unit 310 can control various devices, perform charge / discharge control in case of abnormal heat generation, or calculate or correct 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.

[0133] Battery pack 301 is formed by connecting multiple secondary batteries 301a in series and / or parallel. Figure 14 The example shown is a case where six secondary batteries 301a are connected in a two-in-parallel-three-in-series (2P3S) configuration.

[0134] Temperature detection unit 318 is connected to temperature detection element 308 (e.g., a thermistor) to measure the temperature of battery pack 301 or battery stack 300 and supply 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 supplies it to control unit 310. Current measurement unit 313 uses current detection resistor 307 to measure current and supplies the measured current to control unit 310.

[0135] 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. The switch control unit 314 sends a disconnect control signal to the switch unit 304 when the secondary battery 301a is above the overcharge detection voltage (e.g., 4.20V ± 0.05V) or below the over-discharge detection voltage (2.4V ± 0.1V). This prevents overcharging or over-discharging.

[0136] After the charging control switch 302a or the discharging control switch 303a is turned off, charging or discharging can only be achieved via diode 302b or diode 303b. A semiconductor switch such as a MOSFET can be used as the aforementioned charging and discharging switch. Furthermore, although in Figure 14 In the middle, the switch part 304 is set on the + side, but it can also be set on the - side.

[0137] The memory 317 is composed of RAM (random access memory) or ROM (read-only memory) and stores and rewrites battery characteristic values, fully charged capacity, remaining capacity, etc., calculated by the control unit 310.

[0138] (2) Electronic equipment

[0139] The secondary battery described above according to the embodiments or examples of the present invention can be mounted on devices such as electronic devices, electric conveying devices or energy storage devices to supply power.

[0140] Examples of electronic devices include laptops, smartphones, tablets, PDAs (mobile 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. Furthermore, 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.

[0141] 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. Furthermore, electric passenger aircraft or electric unmanned aerial vehicles (UAVs) for transport are also included. The secondary battery according to the present invention can be used not only as a power source for driving the aforementioned devices, but also as an auxiliary power source, a power source for energy regeneration, etc.

[0142] Examples of energy storage devices include commercial or residential energy storage modules, or power storage devices for buildings such as residences, buildings or offices, or power generation equipment.

[0143] (3) Power tools

[0144] Reference Figure 15 A brief description will be given of an example of an electric screwdriver, which is an electric tool to which the present invention can be applied. The electric screwdriver 431 is provided with a motor 433 that transmits rotational power to a shaft 434; and a user-operated trigger switch 432. A battery pack 430 and a 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 easily attached to or detached from the electric screwdriver 431.

[0145] The battery pack 430 and the motor control unit 435 each have a microcomputer (not shown), and can also be configured to communicate the charging and discharging information of the battery pack 430. 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.

[0146] (4) Energy storage system for electric vehicles

[0147] As an example of applying the present invention to an energy storage system for electric vehicles, Figure 16The 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 powered by an engine, or electricity temporarily stored in a battery, and operates using an electric drive conversion device.

[0148] The hybrid vehicle 600 is equipped with: 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 the present invention or a storage module equipped with multiple batteries 1 of the present invention.

[0149] The motor 603 is powered by electricity from battery 608, and the rotational force of motor 603 is transmitted to drive wheels 604a and 604b. Electricity generated by generator 602 under the rotational force of engine 601 is stored in battery 608. Various sensors 610 control engine speed or the opening of a throttle valve (not shown) via vehicle control unit 609.

[0150] 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 power 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. This type of HV vehicle is called a plug-in hybrid electric vehicle (PHV or PHEV).

[0151] In addition, the secondary battery according to the present invention can be applied to a miniaturized primary battery and used as a power source for a tire pressure monitoring system (TPMS) built into wheels 604 and 605.

[0152] The above explanation uses a series hybrid vehicle as an example, but the invention can also be applied to hybrid vehicles that combine an engine and an electric motor in a parallel configuration, or a combination of series and parallel configurations. Furthermore, the invention can also be applied to electric vehicles (EVs or BEVs) or fuel cell vehicles (FCVs) that do not use an engine and are driven solely by a drive motor.

[0153] Explanation of reference numerals in the attached figures

[0154] 1: Lithium-ion battery; 12: Insulating plate; 21: Positive electrode; 21A: Positive electrode foil; 21B: Active material covered part of the positive electrode; 21C: Active material uncovered part of the positive electrode; 22: Negative electrode; 22A: Negative electrode foil; 22B: Active material covered part of the negative electrode; 22C: Active material uncovered part of the 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: Groove.

Claims

1. A secondary battery comprising an electrode winding body, a positive electrode current collector, and a negative electrode current collector housed in a battery can, wherein the electrode winding body has a structure formed by stacking and winding strip-shaped positive and negative electrodes separated by a separator, and the negative electrode current collector is disposed on the bottom side of the battery can, wherein... 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 the strip-shaped negative electrode foil. 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. The uncovered 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: A flat surface is formed by bending and aligning one or both of the uncovered portions of the positive and negative active materials toward the central axis of the wound structure; and The first groove is formed on the flat surface. The secondary battery has at least one second groove that is C-shaped when viewed from the central axis direction at the bottom of the battery can. When viewed from the direction of the central axis, the second groove is located in a position that does not overlap with the plate-shaped portion of the negative electrode current collector, and all ends of the second groove are located in positions that overlap with the plate-shaped portion of the negative electrode current collector.

2. The secondary battery according to claim 1, wherein, The width of the second groove is greater than 0.10 mm and less than 1.00 mm.

3. The secondary battery according to claim 1 or 2, wherein, The second slot is disposed on the inner side of the battery can, one of the two sides of the bottom of the can.

4. The secondary battery according to claim 1 or 2, wherein, The negative electrode current collector is made of nickel, nickel alloy, copper, or a single copper alloy or a composite material thereof.

5. The secondary battery according to claim 1 or 2, wherein, The secondary battery includes a safety valve that releases gas when gas is generated inside the battery canister.

6. An electronic device comprising a secondary battery according to any one of claims 1 to 5.

7. An electric tool having a secondary battery according to any one of claims 1 to 5.

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