Secondary battery

Abstract

To provide a secondary battery capable of suppressing stress concentration on a local part of a separator arranged facing a positive electrode.SOLUTION: First and second positive electrode material layers 12B1 and 12B2 provided on both surfaces of the positive electrode current collector, and a first exposed portion 11X in which one surface of a local portion of the current collector is exposed and a second exposed portion 11Y in which the other surface is exposed, A first insulating member 31 covering the positive electrode tab 360 provided on one of the first and second exposed sections and the first positive electrode material layer 12B1 located on both sides of the first exposed section in the circumferential direction, and a second insulating member 32 covering the second positive electrode material layer 12B2 located on both sides of the second exposed section in the circumferential direction, in the secondary battery, the ends where the pair of exposed portions are located are shifted in the circumferential direction, and the dimensions of the first exposed portion and the second exposed portion are different from each other.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to secondary batteries. [Background technology]

[0002] Secondary batteries that can be repeatedly charged and discharged have been used for various purposes. For example, secondary batteries are used as power sources for electronic devices such as smartphones and laptop computers.

[0003] The secondary battery has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, and an electrolyte are housed in a housing. The positive electrode has a current collector and a positive electrode material layer containing a positive electrode active material provided on the current collector, and the negative electrode has a current collector and a negative electrode material layer containing a negative electrode active material provided on the current collector.

[0004] A secondary battery may use a wound electrode assembly in which the above-mentioned positive electrode, negative electrode, and separator are wound. In this case, a configuration may be adopted in which exposed portions are formed at predetermined locations in the circumferential direction of a strip-shaped electrode, particularly a strip-shaped positive electrode, in which both surfaces of the current collector are exposed so that they locally face each other, and a current collecting tab is connected to one of the exposed portions. Furthermore, since the current collector is exposed at these exposed portions, if an internal short circuit occurs at these exposed portions, a large current may flow at the short-circuited location, resulting in a large amount of heat generation. Therefore, insulating tape may be provided to cover the exposed portions locally provided on both surfaces of the current collector and the positive electrode material layers located on both sides of each exposed portion in the circumferential direction of the positive electrode. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-135298 [Patent Document 2] International Publication No. 2019 / 069890 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, when an external impact is applied to the secondary battery, the positive electrode of the wound electrode assembly, which is a component of the secondary battery, may also be affected by the external force accompanying the impact.

[0007] In particular, when the tape ends of the insulating tape are aligned in the thickness direction of the positive electrode, two stepped portions formed at the tape ends can be aligned in the thickness direction of the positive electrode. In addition, when the ends of the positive electrode material layers formed on both sides of the current collector are aligned in the thickness direction of the positive electrode, two stepped portions can be aligned in the thickness direction of the positive electrode at localized portions of the insulating tape covering the ends of the positive electrode material layers.

[0008] When the external force described above is applied to the positive electrode in the thickness direction with such a stepped portion, the presence of two aligned stepped portions in the thickness direction of the positive electrode tends to cause stress to concentrate in localized areas of the two separators arranged opposite each other on both sides of the positive electrode, which can result in the separators breaking and the occurrence of a short circuit.

[0009] The present disclosure has been devised in view of the above circumstances, and specifically, an object of the present disclosure is to provide a secondary battery capable of suppressing stress concentration in a local portion of a separator disposed opposite a positive electrode. [Means for solving the problem]

[0010] In order to achieve the above object, in one embodiment of the present disclosure, a wound electrode assembly in which a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode are wound together, and an electrolyte are sealed in an outer casing; the positive electrode comprises at least a wound current collector, first and second positive electrode material layers provided on both sides of the current collector, and a pair of exposed portions each including a first exposed portion exposing one surface of a local portion of the current collector and a second exposed portion exposing the other surface opposite to the first exposed portion in the thickness direction of the positive electrode; a positive electrode tab provided on one of the first exposed portion and the second exposed portion; a first insulating member that covers the first exposed portion and the first positive electrode material layers that are located on both sides of the first exposed portion in the circumferential direction of the positive electrode; a second insulating member covering the second exposed portion and the second positive electrode material layers located on both sides of the second exposed portion in the circumferential direction of the positive electrode; Further provided with In the wound electrode body, the first positive electrode material layer is located on the inner side of the winding and the second positive electrode material layer is located on the outer side of the winding, one end side of the first insulating member and one end side of the second insulating member are arranged to be offset from each other in a circumferential direction of the positive electrode, and the other end side of the first insulating member and the other end side of the second insulating member are arranged to be offset from each other in a circumferential direction of the positive electrode, a first end of the first positive electrode material layer and a first end of the second positive electrode material layer located on one side of the pair of exposed portions with respect to the circumferential direction of the positive electrode as a reference are disposed so as to be offset in the circumferential direction of the positive electrode, and a second end of the first positive electrode material layer and a second end of the second positive electrode material layer located on the other side of the pair of exposed portions are disposed so as to be offset in the circumferential direction of the positive electrode; A secondary battery is provided in which the first exposed portion and the second exposed portion have mutually different dimensions in the circumferential direction of the positive electrode. [Effects of the Invention]

[0011] According to a secondary battery according to an embodiment of the present disclosure, it is possible to suppress stress concentration on a local portion of the separator disposed opposite the positive electrode, and to suppress breakage of the separator. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a general configuration of a secondary battery. [Figure 2] FIG. 2 is a schematic partial cross-sectional view of a positive electrode with a positive electrode tab in the radial direction of a wound electrode assembly of a secondary battery according to an embodiment of the present disclosure. [Figure 3] FIG. 10 is a schematic partial cross-sectional view of a positive electrode with a positive electrode tab in the radial direction of a wound electrode assembly of a secondary battery according to another embodiment of the present disclosure. [Figure 4]FIG. 1 is a schematic partial cross-sectional view of a positive electrode with a positive electrode tab in the radial direction of a wound electrode assembly of a conventional secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a secondary battery according to an embodiment of the present disclosure will be described with reference to the drawings. The various elements in the drawings are merely shown schematically and illustratively to facilitate understanding of the present disclosure, and the appearance, dimensional ratio, etc. may differ from the actual ones.

[0014] The term "secondary battery" as used herein refers to a battery capable of repeated charging and discharging. The term "secondary battery" is not limited to its name and may also encompass, for example, "energy storage devices." The term "cross-sectional view" as used herein refers to a state when viewed from a direction substantially perpendicular to the thickness direction based on the lamination direction of the electrode materials constituting the secondary battery. The terms "vertical direction" and "horizontal direction" used directly or indirectly in this specification correspond to the vertical direction and horizontal direction in the drawings, respectively. In a preferred embodiment, the vertical downward direction (i.e., the direction in which gravity acts) can be considered to correspond to the "downward direction," and the opposite direction can be considered to correspond to the "upward direction."

[0015] The various numerical ranges referred to in this specification are intended to include both the lower and upper limits. For example, a numerical range such as 1 to 10 can be interpreted as including the lower limit of "1" and the upper limit of "10."

[0016] [Basic structure of secondary batteries] First, the basic structure of a secondary battery will be described with reference to FIG. 1. A secondary battery 1000 has a structure in which an electrode assembly 100 and an electrolyte 20 are housed and sealed inside a predetermined housing 500. The electrode assembly 100 may include a positive electrode 10B, a negative electrode 10A, and a separator 50 disposed between the positive electrode 10B and the negative electrode 10A. In the present disclosure, the electrode assembly 100 may be a wound electrode assembly. A wound electrode assembly is formed by winding electrode constituent layers including a positive electrode, a negative electrode, and a separator.

[0017] (positive electrode / negative electrode) The positive electrode 10B is composed of at least a positive electrode material layer and a positive electrode current collector. The positive electrode material layer contains a positive electrode active material as an electrode active material. In the present disclosure, the positive electrode 10B in the battery assembly 100 has positive electrode material layers provided on both sides of the positive electrode current collector.

[0018] The negative electrode 10A is composed of at least a negative electrode material layer and a negative electrode current collector. The negative electrode material layer contains a negative electrode active material as an electrode active material. For example, each of the multiple negative electrodes 10A in the battery assembly 100 may have a negative electrode material layer provided on both sides of the negative electrode current collector, or may have a negative electrode material layer provided on only one side of the negative electrode current collector.

[0019] The electrode active materials contained in the positive electrode 10B and the negative electrode 10A, i.e., the positive electrode active material and the negative electrode active material, respectively, are materials directly involved in the transfer of electrons in the secondary battery and are the main materials of the positive and negative electrodes responsible for charge and discharge, i.e., the battery reaction. More specifically, the "positive electrode active material contained in the positive electrode material layer" and the "negative electrode active material contained in the negative electrode material layer" provide ions to the electrolyte, and these ions move between the positive electrode and the negative electrode, transferring electrons and causing charge and discharge. The positive electrode material layer and the negative electrode material layer may be layers capable of absorbing and desorbing lithium ions. In other words, the secondary battery according to the present disclosure may be a nonaqueous electrolyte secondary battery in which lithium ions move between the positive electrode and the negative electrode via a nonaqueous electrolyte to charge and discharge the battery. When lithium ions are involved in charge and discharge, the secondary battery according to the present disclosure corresponds to a so-called "lithium ion battery," having layers capable of absorbing and desorbing lithium ions as the positive electrode and the negative electrode.

[0020] In the case of a lithium-ion battery, the positive electrode active material may be a material that contributes to the absorption and desorption of lithium ions. That is, the positive electrode layer may contain one or more positive electrode materials that can absorb and desorb lithium. From this perspective, the positive electrode active material may be, for example, a lithium-containing compound. The type of lithium-containing compound is not particularly limited, but examples include lithium-containing composite oxides and lithium-containing phosphate compounds. This is because a high energy density can be easily obtained.

[0021] The lithium-containing composite oxide is a general term for oxides containing lithium and one or more other elements (elements other than lithium) as constituent elements, and may have, for example, a layered rock salt type or a spinel type crystal structure. The lithium-containing phosphate compound is a general term for phosphate compounds containing lithium and one or more other elements as constituent elements, and may have, for example, an olivine type crystal structure. The type of the other element is not particularly limited as long as it is one or more of any elements. In particular, the other element is preferably one or more of elements belonging to Groups 2 to 15 of the long-form periodic table. More specifically, the other element is, for example, nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), etc. This is because these added elements make it easier to obtain a high voltage.

[0022] The positive electrode layer may contain a binder. Furthermore, to facilitate the transfer of electrons that drive the battery reaction, the positive electrode layer may contain a positive electrode conductive agent. The positive electrode binder may contain, for example, one or more of synthetic rubbers and polymeric compounds. Examples of synthetic rubbers include styrene-butadiene rubbers, fluorine-containing rubbers, and ethylene propylene dienes. Examples of polymeric compounds include polyvinylidene fluoride and polyimides. The positive electrode conductive agent may contain, for example, one or more of carbon materials. Examples of carbon materials include graphite, carbon black, acetylene black, and ketjen black. However, the positive electrode conductive agent may also be a metal material or a conductive polymer, as long as it is a conductive material.

[0023] Similarly, the negative electrode active material of the negative electrode layer may be a material that contributes to the absorption and desorption of lithium ions. That is, the negative electrode layer may contain one or more negative electrode materials that can absorb and desorb lithium. From this perspective, the negative electrode active material may be, for example, various carbon materials, metal materials, and / or other materials.

[0024] When a carbon material is used as the negative electrode active material, the change in the crystal structure during lithium absorption and desorption is very small, so a high energy density can be easily obtained stably. In addition, the carbon material also functions as a negative electrode conductive agent, so the conductivity of the negative electrode layer can be easily improved.

[0025] The term "metallic material" used as the negative electrode active material is a general term for materials containing one or more of metal elements and metalloid elements as constituent elements. When a carbon material is used as the negative electrode active material, a high energy density is easily obtained. The metallic material may be a simple substance, an alloy, a compound, or two or more of these, or may be a material containing at least one or more of these phases. However, alloys may include materials containing one or more metal elements and one or more metalloid elements in addition to materials consisting of two or more metal elements. Furthermore, alloys may also contain nonmetallic elements. The structure of this metallic material may be, for example, a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or a mixture of two or more of these.

[0026] Alternatively, the negative electrode material may be one or more of metal oxides and polymer compounds. Examples of metal oxides include iron oxide, ruthenium oxide, and molybdenum oxide. Examples of polymer compounds include polyacetylene, polyaniline, and polypyrrole.

[0027] The negative electrode layer may contain a binder. Furthermore, the negative electrode layer may contain a negative electrode conductive agent to facilitate the transfer of electrons that promote the battery reaction. The binder that may be contained in the negative electrode layer is not particularly limited, but may include at least one selected from the group consisting of styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyimide resins, and polyamide-imide resins. The negative electrode conductive agent that may be contained in the negative electrode layer is not particularly limited, but may include at least one selected from the group consisting of carbon blacks such as thermal black, furnace black, channel black, ketjen black, and acetylene black; carbon fibers such as graphite, carbon nanotubes, and vapor-grown carbon fibers; metal powders such as copper, nickel, aluminum, and silver; and polyphenylene derivatives. The negative electrode layer may also contain components derived from thickener components (e.g., carboxymethyl cellulose) used during battery fabrication.

[0028] The positive electrode current collector and negative electrode current collector used in the positive electrode 10B and negative electrode 10A are members that contribute to collecting and supplying electrons generated in the electrode active material due to the battery reaction. Such electrode current collectors may be sheet-shaped metal members. The electrode current collectors may be single-layer or multi-layer. Furthermore, the electrode current collectors may be porous or perforated. For example, the current collectors may be metal foil, punched metal, mesh, expanded metal, or the like. The positive electrode current collector used in the positive electrode may be made of, for example, a metal foil containing at least one selected from the group consisting of aluminum, nickel, stainless steel, and the like. On the other hand, the negative electrode current collector used in the negative electrode may be made of, for example, a metal foil containing at least one selected from the group consisting of copper, aluminum, nickel, stainless steel, and the like.

[0029] (separator) The separator 50 provided between the positive electrode 10B and the negative electrode 10A is a member provided from the viewpoint of preventing short circuits due to contact between the positive and negative electrodes and maintaining electrolyte retention. In other words, the separator 50 separates the positive electrode 10B from the negative electrode 10A, and is a member that allows ions (e.g., lithium ions) to pass through while preventing short circuits of current due to contact between the two electrodes. For example, the separator 50 may be a porous or microporous insulating member, and may have a membrane form due to its small thickness.

[0030] The separator 50 may be, for example, one or more types of porous membranes made of synthetic resins and / or ceramics, or may be a laminated membrane of two or more types of porous membranes. Examples of synthetic resins used for the separator 50 include polytetrafluoroethylene, polypropylene, and polyethylene. For example, the separator 50 may include a porous membrane (substrate layer) and a polymer compound layer provided on one or both sides of the substrate layer. This improves the adhesion of the separator 50 to the positive electrode and the negative electrode, thereby reducing distortion of the wound electrode assembly. The polymer compound layer may include, for example, one or more types of polymer compounds such as polyvinylidene fluoride. This improves physical strength and electrochemical stability. The polymer compound layer may also include, for example, one or more types of insulating particles, such as inorganic particles. The inorganic particles may be, for example, aluminum oxide and / or aluminum nitride. In the present disclosure, the separator 50 should not be limited to a particular name, and may be a solid electrolyte, a gel electrolyte, and / or insulating inorganic particles, etc., which have similar functions.

[0031] (electrolyte) The electrolyte 20 that can be used in the secondary battery of the present disclosure may be a so-called "nonaqueous" electrolyte. Typically, the electrolyte is an electrolytic solution containing a solvent and an electrolyte salt. The electrolytic solution may further contain one or more other materials, such as additives. In a preferred embodiment, the separator is impregnated with the electrolytic solution, and the positive electrode and / or the negative electrode may also be impregnated with the electrolytic solution.

[0032] The solvent may contain one or more non-aqueous solvents such as organic solvents. An electrolyte solution containing a non-aqueous solvent can be a so-called non-aqueous electrolyte solution. The non-aqueous solvent may be, for example, a cyclic carbonate ester, a chain carbonate ester, a lactone, a chain carboxylic acid ester, and / or a nitrile (e.g., mononitrile). This facilitates obtaining better battery capacity, cycle characteristics, and / or storage characteristics. The cyclic carbonate ester may be, for example, ethylene carbonate, propylene carbonate, and / or butylene carbonate. The chain carbonate ester may be, for example, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and / or methyl propyl carbonate. The lactone may be, for example, γ-butyrolactone and / or γ-valerolactone. The chain carboxylic acid ester may be, for example, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and / or ethyl trimethylacetate. The nitrile may be, for example, acetonitrile, methoxyacetonitrile, and / or 3-methoxypropionitrile, etc. In addition, the non-aqueous solvent may be, for example, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, N,N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N,N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethyl phosphate, and / or dimethyl sulfoxide, etc.

[0033] Among these, the nonaqueous solvent preferably contains one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate. This is because it is likely to result in higher battery capacity, better cycle characteristics, and / or better storage characteristics. Furthermore, the nonaqueous solvent may be, for example, an unsaturated cyclic carbonate, a halogenated carbonate, a sulfonate ester, an acid anhydride, a dicyano compound (dinitrile compound), a diisocyanate compound, a phosphate ester, and / or a chain compound having a carbon-carbon triple bond. This tends to improve the chemical stability of the electrolyte. The term "unsaturated cyclic carbonate" as used herein refers to a cyclic carbonate having one or more unsaturated bonds (carbon-carbon double bonds or carbon-carbon triple bonds). Examples of such unsaturated cyclic carbonates include vinylene carbonate, vinylethylene carbonate, and / or methyleneethylene carbonate. The term "halogenated carbonate" refers to a cyclic or chain carbonate containing one or more halogen elements as constituent elements. When the halogenated carbonate contains two or more halogens as constituent elements, the two or more halogens may be of one type or two or more types.

[0034] The electrolyte salt contained in the electrolyte solution may include, for example, one or more salts such as lithium salts. The electrolyte salt may include, for example, a salt other than lithium salt. Such salts other than lithium may be, for example, salts of light metals other than lithium. Examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium tetrachloroaluminate (LiAlCl4), dilithium hexafluorosilicate (Li2SiF6), lithium chloride (LiCl), and / or lithium bromide (LiBr). This is because it is easier to obtain better battery capacity, cycle characteristics, and / or storage characteristics. Among these, any one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium hexafluoroarsenate may be used.

[0035] (Storage section) The housing 500 used in the secondary battery corresponds to a member that encases the electrode assembly 100 including the positive electrode 10B, the negative electrode 10A, and the separator 50. Such a housing 500 can also be referred to as a battery can, for example. As an example, the housing 500 can be broadly divided into an exterior body 200 having an opening on one end side, a sealing body 300 that seals the opening, and a gasket 400 that functions as a sealant and an insulator between the exterior body 200 and the sealing body 300.

[0036] Gasket 400 is located between the inner surface of one end of side wall 220 of exterior body 200 and the outer edge of sealing body 300. Gasket 400 may be an insulating resin member. In this case, for example, a propylene-based resin member, an acrylic-based resin member, a silicone-based resin member, a urethane-based resin member, or the like may be used as gasket 400.

[0037] The exterior body 200 includes a side wall portion 220 that constitutes or forms the opening, and a bottom portion 210 that is continuous with the side wall portion 220. That is, the exterior body 200 may have a hollow structure. The sealing body 300 may include a positive electrode terminal 310 that may be located at the top of the battery can, and a sealing plate 320 that is provided inside the positive electrode terminal 310 and is capable of coming into contact with the terminal. The sealing plate 320 may function as a safety valve.

[0038] Furthermore, the exterior body 200 itself can function as a negative electrode terminal. The negative electrode 10A can be connected to this exterior body 200 via a conductive member on the negative electrode side. The constituent material of such a conductive member can include, for example, nickel.

[0039] The exterior body 200 may be a conductive metal member. For example, the exterior body 200 may include iron, copper, nickel, stainless steel, an iron alloy, a copper alloy, a nickel alloy, etc. Examples of stainless steel that can be used include SUS304 and SUS316.

[0040] The sealing plate 320 may include a first metal member 330, a second metal member 350, and an insulating member 340 located between the first metal member 330 and the second metal member 350, which are stacked in order from the installation location of the positive electrode terminal 310 located on the upper or outer side toward the lower or inner side.

[0041] In one example, the first metal member 330 is displaceable so as to be deformable and / or rupturable in response to the internal pressure in the battery can. The second metal member 350 is displaceable in response to an increase in the internal pressure in the battery can. The second metal member 350 and the positive electrode 10B of the electrode assembly 100 can be connected via a positive electrode tab 360. The positive electrode tab 360 can include one or more metal materials such as aluminum, titanium, platinum, and gold.

[0042] 1 shows the configuration under normal conditions when no gas or the like is generated inside the battery can, and the second metal member 350 has a central region 352 that is inside the location of the groove portion 351 and can come into contact with the first metal member 330. Also, as described above, the first metal member 330 can come into contact with the positive electrode terminal 310. As a result, the positive electrode 10B inside the battery can can be electrically connected to the positive electrode terminal 310.

[0043] The following describes the characteristic features of the present disclosure: The present disclosure is characterized by the configuration of a predetermined portion of the positive electrode 10B, which is a component of the wound-type electrode assembly 100, where the positive electrode tab 360 is arranged.

[0044] Specifically, in the present disclosure, the positive electrode 10B includes a wound current collector 11B and first and second positive electrode material layers 12B1, 12B2 provided on both sides of the current collector 11B. When the electrode assembly 100 is wound, the first positive electrode material layer 12B1 can be located on the inner side of the winding, and the second positive electrode material layer 12B2 can be located on the outer side of the winding.

[0045] The positive electrode 10B also has a pair of exposed portions, each of which includes a first exposed portion 11X where one surface of a localized portion of the current collector 11B is exposed, and a second exposed portion 11Y where the other surface facing the first surface in the thickness direction of the positive electrode 10B is exposed. That is, in this exposed portion, only the metal current collector is located, and no positive electrode material layer is provided on either side thereof.

[0046] The positive electrode tab 360 described above is provided on one of the first exposed portion 11X and the second exposed portion 11Y. Furthermore, a first insulating member 31 is provided to cover the first exposed portion 11X and portions of the first positive electrode material layer 12B1 located on both sides of the first exposed portion 11X in the circumferential direction of the positive electrode. In this case, the first insulating member 31 may cover the portion of the first positive electrode material layer 12B1 by 1.0 mm or more. A second insulating member 32 is provided to cover the second exposed portion 11Y and portions of the second positive electrode material layer 12B2 located on both sides of the second exposed portion 11Y in the circumferential direction of the positive electrode. In this case, the second insulating member 32 may cover the portion of the second positive electrode material layer 12B2 by 1.0 mm or more.

[0047] In this case, in the present disclosure, one end 31X side of the first insulating member 31 and one end 32X side of the second insulating member 32 are arranged offset in the circumferential direction of the positive electrode, and further, the other end 31Y side of the first insulating member 31 and the other end 32Y side of the second insulating member 32 are arranged offset.

[0048] Furthermore, first end 12B11 of first positive electrode material layer 12B1 and first end 12B21 of second positive electrode material layer 12B2, which are located on one side of a pair of exposed portions (first exposed portion 11X and second exposed portion 11Y) with respect to the circumferential direction of the positive electrode, are shifted in the circumferential direction of the positive electrode. Furthermore, second end 12B12 of first positive electrode material layer 12B1 and second end 12B22 of second positive electrode material layer 12B2, which are located on the other side of the pair of exposed portions (first exposed portion 11X and second exposed portion 11Y) with respect to the circumferential direction of the positive electrode, are shifted in the circumferential direction of the positive electrode.

[0049] According to the above configuration, one end 31X of the first insulating member 31 is misaligned with one end 32X of the second insulating member 32 in the circumferential direction of the positive electrode, and the other end 31Y of the first insulating member 31 is misaligned with the other end 32Y of the second insulating member 32. Furthermore, the first end 12B11 of the first positive electrode material layer 12B1 and the first end 12B21 of the second positive electrode material layer 12B2, and the second end 12B12 of the first positive electrode material layer 12B1 and the second end 12B22 of the second positive electrode material layer 12B2 are each misaligned in the circumferential direction of the positive electrode.

[0050] When the end of the first insulating member and the end of the second insulating member are aligned in the thickness direction of the positive electrode, and the end of the first positive electrode material layer and the end of the second positive electrode material layer are aligned (see FIG. 4), as in the past, the number of step portions that can be formed in the local portions of the insulating tape covering the end of the insulating member and the end of the positive electrode material layer can each be two.

[0051] In contrast, in the present disclosure, the number of step portions that can be formed in the end of the insulating member and in the local portion of the insulating tape covering the end of the positive electrode material layer, which can be aligned in the thickness direction of the positive electrode, can be reduced from two to one.

[0052] Since the step portion may have a bent portion due to its shape, stress tends to be concentrated in a local portion of the separator 50 positioned opposite this step portion. However, as described above, the number of step portions that can be aligned in the thickness direction at a predetermined location on the positive electrode can be reduced from two to one.

[0053] From a similar perspective, it is preferable that the first end 12B11 of the first positive electrode material layer 12B1 and one end 32X of the second insulating member 32 are arranged so as to be offset from each other in the circumferential direction of the positive electrode. This reduces the number of stress concentration points in the thickness direction of a given location on the positive electrode, making it possible to disperse stress acting on the separators 50 arranged opposite each other on both sides of the positive electrode. As a result, breakage of the separators 50 that may be arranged on both sides of the positive electrode is suppressed, and the occurrence of short circuits can be suitably suppressed.

[0054] In the present disclosure, the dimension (1) of the first exposed portion 11X and the dimension (2) of the second exposed portion 11Y are different from each other in the circumferential direction of the positive electrode. In one example, as shown in FIG. 2, the dimension (1) is larger than the dimension (2). In another example, as shown in FIG. 3, the dimension (2) is larger than the dimension (1).

[0055] When the dimension (1) of the first exposed portion 11X and the dimension (2) of the second exposed portion 11Y are different from each other in the circumferential direction of the positive electrode, the adhesion between the separators 50 located on both sides of the positive electrode 10B can be improved compared to when the dimensions (1) and (2) of both are the same. Such improved adhesion can contribute to an improvement in the energy density of the secondary battery.

[0056] In particular, considering that the curvature of the inner and outer sides of the electrode may differ (the curvature of the inner side is greater than that of the outer side), it is preferable that the dimension (2) of the second exposed portion 11Y is smaller than the dimension (1) of the first exposed portion 11X. In other words, it is preferable that the dimension (1) of the first exposed portion 11X is larger than the dimension (2) of the second exposed portion 11Y. In this case, the incidence of short circuits in the battery can be reduced.

[0057] From another perspective, the first end 12B21 of the second positive electrode material layer 12B2 on the outside of the positive electrode winding is located closer to the positive electrode tab 360 than the first end 12B11 of the first positive electrode material layer 12B1 on the inside of the winding. Also, the second end 12B22 of the second positive electrode material layer 12B2 on the outside of the positive electrode winding is located closer to the positive electrode tab 360 than the second end 12B12 of the first positive electrode material layer 12B1 on the inside of the winding.

[0058] Furthermore, in the present disclosure, when the distance (3) between one end 31X of the first insulating member 31 and one end 32X of the second insulating member 32 and the distance (4) between the first end 12B11 of the first positive electrode material layer 12B1 and the first end 12B21 of the second positive electrode material layer 12B2 in the longitudinal direction of the positive electrode (before winding) are each within a specific range, the incidence of short circuits in the battery can be suitably reduced (see FIG. 2).

[0059] Specifically, it is preferable that distance (3) is 0.5 mm or more and less than 2.0 mm, and distance (4) is 0.5 mm or more and 5 mm or less. In particular, when distance (3) is 1.0 mm or more and 1.5 mm or less, and distance (4) is 3 mm, the incidence of short circuits in the battery can be more suitably reduced.

[0060] Hereinafter, a method for producing a secondary battery according to an embodiment of the present disclosure will be described.

[0061] First, a positive electrode mixture containing a positive electrode active material is formed, and the positive electrode mixture is dispersed in an organic solvent to obtain a paste-like positive electrode mixture slurry. After ensuring space for forming exposed portions of the current collector for providing electrode tabs (described later) on both sides of the main surface of a metal foil serving as a positive electrode current collector, the positive electrode mixture slurry is applied, and the positive electrode mixture slurry is dried to produce a positive electrode. Then, the positive electrode is compressed using a roll press.

[0062] Similarly, a negative electrode mixture containing a negative electrode active material is formed, and the negative electrode mixture is dispersed in an organic solvent to obtain a paste-like negative electrode mixture slurry. After ensuring space for forming an exposed portion of the current collector for providing an electrode tab (described later) on both sides of the main surface of a metal foil serving as a negative electrode current collector, the negative electrode mixture slurry is applied, and the negative electrode mixture slurry is dried to produce a negative electrode. Then, the negative electrode is compressed using a roll press.

[0063] Then, a positive electrode tab is connected to one of the exposed portions formed on both sides of the metal foil serving as a positive electrode current collector. Also, a negative electrode tab is connected to one of the exposed portions formed on both sides of the metal foil serving as a negative electrode current collector. After connecting the electrode tabs, insulating tape (insulating member) is applied so as to cover the exposed portions and parts of the electrode material layer located on both sides of each exposed portion in the longitudinal direction of the current collector foil.

[0064] At this time, alignment is performed so that the following configuration is realized. At least in the positive electrode, one end of the first insulating member and one end of the second insulating member are displaced from each other in the thickness direction of the positive electrode, and the other end of the first insulating member and the other end of the second insulating member are displaced from each other. A first end of the first positive electrode material layer and a first end of the second positive electrode material layer located on one side of the pair of exposed portions are displaced in the thickness direction of the positive electrode relative to the longitudinal direction of the positive electrode, and a second end of the first positive electrode material layer and a second end of the second positive electrode material layer located on the other side of the pair of exposed portions are displaced in the thickness direction of the positive electrode. The dimensions of the first exposed portion and the second exposed portion are made different from each other in the longitudinal direction of the positive electrode.

[0065] Next, the positive and negative electrodes formed with a separator interposed therebetween are stacked, and the positive and negative electrodes and separator are wound to form an electrode assembly. Next, the electrode assembly 100 is housed inside the exterior body 200, and one end of the positive electrode tab 360 is connected to the second metal member 350 of the sealing plate 320 by welding, and one end of the negative electrode tab is connected to the inner surface of the exterior body 200 in a similar manner. Next, an electrolyte solution is injected into the interior of the exterior body 200, and the electrolyte solution is impregnated into the electrode assembly. Next, the side wall portion 220 of the exterior body 200 is crimped using a crimping member so that one end side of the side wall portion 220 of the exterior body 200 is positioned above the outer edge of the sealing body 300.

[0066] In this manner, the secondary battery 1000 of the present disclosure can be fabricated.

[0067] Although the embodiments of the present disclosure have been described above, they are merely typical examples. Those skilled in the art will readily understand that the present disclosure is not limited thereto, and that various modifications are possible within the scope of the present disclosure. [Example]

[0068] Examples will be described below.

[0069] Example First, in the positive electrode fabrication process, a positive electrode mixture containing a positive electrode active material was formed, and the positive electrode mixture was dispersed in an organic solvent to obtain a paste-like positive electrode mixture slurry. After ensuring space for forming exposed portions of the current collector for providing electrode tabs (described later) on both sides of the main surface of a metal foil serving as a positive electrode current collector, the positive electrode mixture slurry was applied, and the positive electrode mixture slurry was dried to fabricate a positive electrode. In this case, after providing the electrode tabs (described later), the positive electrode was pressed using a roll press.

[0070] Similarly, in the negative electrode preparation process, a negative electrode mixture containing a negative electrode active material was formed, and the negative electrode mixture was dispersed in an organic solvent to obtain a paste-like negative electrode mixture slurry. After ensuring space for forming exposed portions of the current collector for providing electrode tabs (described later) on both sides of the main surface of a metal foil serving as a negative electrode current collector, the negative electrode mixture slurry was applied, and the negative electrode mixture slurry was dried to prepare a negative electrode. The negative electrode was then pressed using a roll press. A positive electrode was then connected to the exposed portion of the metal foil serving as a positive electrode current collector, and a negative electrode tab was connected to the exposed portion of the metal foil serving as a negative electrode current collector.

[0071] After connecting the electrode tabs, insulating tape (insulating member) was attached so as to cover the exposed portions and portions of the electrode material layer located on both sides of each exposed portion in the longitudinal direction of the current collector foil. In particular, when forming the positive electrode, the alignment was adjusted so that the exposed portions, insulating tape, and positive electrode material formed on both sides of the metal foil had the following configuration. At least in the positive electrode, one end of the first insulating member and one end of the second insulating member are displaced from each other in the thickness direction of the positive electrode, and the other end of the first insulating member and the other end of the second insulating member are displaced from each other. A first end of the first positive electrode material layer and a first end of the second positive electrode material layer located on one side of the pair of exposed portions are displaced in the thickness direction of the positive electrode relative to the longitudinal direction of the positive electrode, and a second end of the first positive electrode material layer and a second end of the second positive electrode material layer located on the other side of the pair of exposed portions are displaced in the thickness direction of the positive electrode. The dimensions of the first exposed portion and the second exposed portion are made different from each other in the longitudinal direction of the positive electrode.

[0072] The positive and negative electrodes were then stacked with a separator between them, and the positive and negative electrodes and separator were wound together to form an electrode assembly. A crash test was conducted on a secondary battery including the electrode assembly. The thickness of the positive electrode layer was 110-120 μm, and the thickness of the metal foil was 12 μm.

[0073] In the first embodiment, under the above conditions, the length of one end 32X of the second insulating member 32 was set to be 1.5 mm longer than the length of one end 31X of the first insulating member 31 in the longitudinal direction of the positive electrode (before winding). In the second embodiment, under the above conditions, the length of one end 32X of the second insulating member 32 was set to be 1.0 mm longer than the length of one end 31X of the first insulating member 31 in the longitudinal direction of the positive electrode (before winding).

[0074] Furthermore, in addition to the above two conditions, the distance between the first end 12B11 of the first positive electrode material layer 12B1 and the first end 12B21 of the second positive electrode material layer 12B2 in the longitudinal direction of the positive electrode (before winding) was set to 1.0 mm, 3.0 mm, and 5.0 mm.

[0075] The above crash test is based on the UL1642_Ed.6 standard. Specifically, the crash test is carried out in the following basic form: Charge the test sample (prepared cell) to 4.25V at room temperature. Place the test sample on a flat surface. Place a 15.8 ± 0.1 mm (5 / 8 ± 0.004 in) diameter rod across the center of the sample. A weight of 9.1 ± 0.46 kg (20 ± 1 lb) is dropped from a height of 610 ± 25 mm (24 ± 1 in) directly onto the sample. A cylindrical, pouch, or prismatic cell is placed with its long axis parallel to a flat surface and impacted perpendicular to the long axis by a 15.8 mm (5 / 8 inch) diameter curved surface placed across the center of the test sample. Prismatic cells are rotated 90 degrees around their long axis so that both the wide and narrow sides receive the impact. Each sample is subjected to only one impact. Use separate samples for each test.

[0076] Comparative Example 1 The following describes Comparative Example 1. In Comparative Example 1, in order to avoid duplication with the contents of the Examples, the following mainly describes the differences from the contents of the Examples.

[0077] In the comparative example, unlike the above examples, the configuration of the exposed portions formed on both sides of the metal foil, the insulating tape, and the positive electrode material in the obtained positive electrode was as follows, without performing the alignment adjustment as in the examples. At least in the positive electrode, one end of the first insulating member and one end of the second insulating member are arranged on the same line in the thickness direction of the positive electrode, and the other end of the first insulating member and the other end of the second insulating member are arranged on the same line. With the longitudinal direction of the positive electrode as the reference, a first end of the first positive electrode material layer and a first end of the second positive electrode material layer located on one side of a pair of exposed portions are aligned in the thickness direction of the positive electrode, and a second end of the first positive electrode material layer and a second end of the second positive electrode material layer located on the other side of the pair of exposed portions are aligned in the thickness direction of the positive electrode.

[0078] Comparative Example 2 Comparative Example 2 will be described below. Furthermore, in Comparative Example 2, compared to the Examples, the lengths, in the longitudinal direction of the positive electrode (before winding), of one end 32X of the second insulating member 32 were set to be 3.0 mm, 2.5 mm, and 2.0 mm longer than the length, in the longitudinal direction, of one end 31X of the first insulating member 31. In addition to these conditions, the distances, in the longitudinal direction of the positive electrode (before winding), between the first end 12B11 of the first positive electrode material layer 12B1 and the first end 12B21 of the second positive electrode material layer 12B2 were also set to be 1.0 mm, 3.0 mm, 5.0 mm, and 7.0 mm.

[0079] The short circuit occurrence rate for each positive electrode was then measured. As a result, it was found that, compared to Comparative Examples 1 and 2, in the Example, the short circuit occurrence rate of the battery can be suitably reduced when the distance (3) between one end 31X of the first insulating member 31 and one end 32X of the second insulating member 32, and the distance (4) between the first end 12B11 of the first positive electrode material layer 12B1 and the first end 12B21 of the second positive electrode material layer 12B2 in the longitudinal direction of the positive electrode (before winding) are each within the following specific ranges.

[0080] Specifically, it was found that the short circuit occurrence rate is reduced when distance (3) is 0.5 mm or more and less than 2.0 mm, and distance (4) is 0.5 mm or more and 5 mm or less. It was found that the short circuit occurrence rate of the battery is particularly reduced when distance (3) is 1.0 mm or more and 1.5 mm or less, and distance (4) is 3 mm.

[0081] It should be noted that the embodiment of the present disclosure as described above includes the following preferred aspects. <1> a wound electrode assembly in which a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode are wound together, and an electrolyte are sealed in an outer casing; the positive electrode comprises at least a wound current collector, first and second positive electrode material layers provided on both sides of the current collector, and a pair of exposed portions each including a first exposed portion exposing one surface of a local portion of the current collector and a second exposed portion exposing the other surface opposite to the first exposed portion in the thickness direction of the positive electrode; a positive electrode tab provided on one of the first exposed portion and the second exposed portion; a first insulating member that covers the first exposed portion and the first positive electrode material layers that are located on both sides of the first exposed portion in the circumferential direction of the positive electrode; a second insulating member covering the second exposed portion and the second positive electrode material layers located on both sides of the second exposed portion in the circumferential direction of the positive electrode; Further provided with In the wound electrode body, the first positive electrode material layer is located on the inner side of the winding and the second positive electrode material layer is located on the outer side of the winding, one end side of the first insulating member and one end side of the second insulating member are arranged to be offset from each other in a circumferential direction of the positive electrode, and the other end side of the first insulating member and the other end side of the second insulating member are arranged to be offset from each other in a circumferential direction of the positive electrode, a first end of the first positive electrode material layer and a first end of the second positive electrode material layer located on one side of the pair of exposed portions with respect to the circumferential direction of the positive electrode as a reference are disposed so as to be offset in the circumferential direction of the positive electrode, and a second end of the first positive electrode material layer and a second end of the second positive electrode material layer located on the other side of the pair of exposed portions are disposed so as to be offset in the circumferential direction of the positive electrode; The secondary battery has dimensions of the first exposed portion and the second exposed portion that are different from each other in the circumferential direction of the positive electrode. <2> a dimension of the first exposed portion in the circumferential direction of the positive electrode is larger than a dimension of the second exposed portion; <1> The secondary battery according to claim 1. <3> In the longitudinal direction of the positive electrode, the distance between one end side of the first insulating member and one end side of the second insulating member is 0.5 mm or more and less than 2.0 mm, and the distance between a first end side of the first positive electrode material layer and a first end side of the second positive electrode material layer is 0.5 mm or more and 5 mm or less. <1> or <2> The secondary battery according to claim 1. <4> a first end of the first positive electrode material layer and one end of the second insulating member are arranged to be offset from each other in the circumferential direction of the positive electrode; <1> ~ <3> 1. The secondary battery according to claim 1 , [Industrial Applicability]

[0082] The secondary battery according to the present disclosure can be used in applications that typically require the use of electrical energy. For example, the secondary battery according to the present disclosure can be used in various fields where power storage is expected. By way of example only, the battery of the present disclosure can be used in the electrical, information, and communications fields where electrical and electronic devices are used (for example, the electrical and electronic device fields or mobile device fields including mobile phones, smartphones, laptop computers and digital cameras, activity monitors, arm computers, electronic paper, wearable devices, and small electronic devices such as RFID tags, card-type electronic money, and smart watches), household and small industrial applications (for example, power tools, golf carts, and household, nursing care, and industrial robots), large industrial applications (for example, forklifts, elevators, and port cranes), transportation systems (for example, hybrid cars, electric cars, buses, trains, electrically assisted bicycles, and electric motorcycles), power system applications (for example, various power generation systems, road conditioners, smart grids, and general household-installed power storage systems), medical applications (for medical devices such as earphone hearing aids), pharmaceutical applications (for example, medication management systems), as well as the IoT field and space and deep-sea applications (for example, space probes, submersible research vessels, and the like). [Explanation of symbols]

[0083] 100 battery assembly 10B positive electrode 10A negative pole 20 Electrolytes 50 Separator 200 exterior body 210 Bottom of exterior body 220 Side wall of exterior body 300 Sealing body 310 Positive terminal 320 Sealing plate 330 First metal member 340 Insulating materials 350 Second metal member 360 Positive tab 400 gaskets 500 storage compartment 1000 secondary battery

Claims

1. a wound electrode assembly in which a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode are wound together, and an electrolyte are sealed in an outer casing; the positive electrode comprises at least a wound current collector, first and second positive electrode material layers provided on both sides of the current collector, and a pair of exposed portions each including a first exposed portion exposing one surface of a local portion of the current collector and a second exposed portion exposing the other surface opposite to the first exposed portion in the thickness direction of the positive electrode; a positive electrode tab provided on one of the first exposed portion and the second exposed portion; a first insulating member that covers the first exposed portion and the first positive electrode material layers that are located on both sides of the first exposed portion in the circumferential direction of the positive electrode; a second insulating member covering the second exposed portion and the second positive electrode material layer located on both sides of the second exposed portion in the circumferential direction of the positive electrode; Further provided with In the wound electrode body, the first positive electrode material layer is located on an inner side of the winding and the second positive electrode material layer is located on an outer side of the winding, one end side of the first insulating member and one end side of the second insulating member are arranged to be offset from each other in a circumferential direction of the positive electrode, and the other end side of the first insulating member and the other end side of the second insulating member are arranged to be offset from each other in a circumferential direction of the positive electrode, a first end of the first positive electrode material layer and a first end of the second positive electrode material layer located on one side of the pair of exposed portions with respect to the circumferential direction of the positive electrode as a reference are disposed so as to be offset in the circumferential direction of the positive electrode, and a second end of the first positive electrode material layer and a second end of the second positive electrode material layer located on the other side of the pair of exposed portions are disposed so as to be offset in the circumferential direction of the positive electrode; a secondary battery in which the first exposed portion and the second exposed portion have different dimensions in the circumferential direction of the positive electrode;

2. The secondary battery according to claim 1 , wherein a dimension of the first exposed portion is larger than a dimension of the second exposed portion in the circumferential direction of the positive electrode.

3. 2. The secondary battery according to claim 1, wherein, in the longitudinal direction of the positive electrode, a distance between one end side of the first insulating member and one end side of the second insulating member is 0.5 mm or more and less than 2.0 mm, and a distance between a first end of the first positive electrode material layer and a first end of the second positive electrode material layer is 0.5 mm or more and 5 mm or less.

4. The secondary battery according to claim 1 , wherein a first end of the first positive electrode material layer and one end of the second insulating member are arranged to be offset from each other in the circumferential direction of the positive electrode.

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