Battery

Abstract

A short circuit between a positive electrode and a negative electrode is suppressed when a separator is damaged by an external force. This battery is provided with an electrode assembly having a positive electrode, a negative electrode, and a film-like separator, the electrode assembly having a flat shape, and the separator having a thickness at least in a first direction and being provided at least between the positive electrode and the negative electrode in the first direction when the shortest direction of the electrode assembly is the first direction. The second direction is the direction in which the distance between the mutually facing sides of the diaphragm in plan view in the first direction is minimum, and the third direction is the direction perpendicular to the first direction and the second direction. The angle between the second direction and the direction in which the tensile strength of the diaphragm is minimized in plan view in the first direction is larger than the angle between the third direction and the direction in which the tensile strength of the diaphragm is minimized. In plan view in the first direction, the ratio of the length of the diaphragm in the third direction to the length of the diaphragm in the second direction is 2.0 or more.

Description

Technical Field

[0001] The present invention relates to a battery. Background Art

[0002] In a battery, a film-like separator formed by stretching in a uniaxial direction is sometimes provided between a positive electrode and a negative electrode. The film-like separator has a stretching direction (MD) (machine direction) and a direction perpendicular to the stretching direction (TD) (transverse direction).

[0003] Patent Document 1 illustrates a secondary battery in which the short side direction of the battery is the same as the TD of the separator.

[0004] Patent Document 2 discloses a secondary battery in which the TD of the separator is along the short side direction of the battery can when viewed in plan along the lamination direction of the separator in order to prevent the positive electrode and the negative electrode from contacting and short-circuiting due to thermal contraction of the separator.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2017-152199

[0008] Patent Document 2: Japanese Patent Application Publication No. 2016-58393 Summary of the invention

[0009] Technical problem to be solved by the invention

[0010] In the batteries described in Patent Documents 1 and 2, the short side direction of the battery is the same as the TD of the separator. Therefore, when the separator is damaged by external force, there is a possibility that the positive electrode and the negative electrode cannot be sufficiently prevented from short-circuiting.

[0011] Technical solutions for solving technical problems

[0012] A battery according to one aspect of the present invention comprises an electrode assembly, the electrode assembly having a positive electrode, a negative electrode and a film-like separator, the electrode assembly being flat, the separator having a thickness at least in the first direction when the shortest direction of the electrode assembly is set as a first direction, and being provided between the positive electrode and the negative electrode in at least the first direction, the direction in which the distance between mutually opposing sides of the separator becomes the smallest when viewed from above along the first direction is set as a second direction, and the direction perpendicular to the first direction and the second direction is set as a third direction, the angle formed by the direction in which the tensile strength of the separator becomes the smallest when viewed from above along the first direction and the second direction is larger than the angle formed by the direction in which the tensile strength of the separator becomes the smallest and the third direction, and the ratio of the length of the separator in the third direction to the length of the separator in the second direction when viewed from above along the first direction is 2.0 or more.

[0013] Effects of the Invention

[0014] According to the present invention, when the separator is damaged by external force, short circuit between the positive electrode and the negative electrode can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a cutaway perspective view showing an example of the battery according to the first embodiment.

[0016] Figure 2 It is an exploded plan view showing components of the electrode assembly according to the first embodiment.

[0017] Figure 3 It is a schematic diagram explaining the method of measuring the tensile strength of the separator.

[0018] Figure 4 This is a schematic plan view showing the electrode assembly according to the first embodiment when the separator is broken.

[0019] Figure 5 Yes means Figure 4 A schematic plan view of a comparative example of the electrode assembly.

[0020] Figure 6 It is a schematic plan view showing an electrode assembly according to a modified example of the battery according to the first embodiment.

[0021] Figure 7 Yes means Figure 6 A schematic plan view of a comparative example of the electrode assembly.

[0022] Figure 8 This is a partially cutaway view showing an example of a battery according to the second embodiment.

[0023] Fig. 9 It is along Figure 8 A schematic cross-sectional view of line IX-IX.

[0024] Fig.10 It is a schematic plan view showing an electrode assembly according to the second embodiment.

[0025] Fig.11 It is a perspective view showing an example of a battery according to the third embodiment.

[0026] Fig.12 It is along Fig.11 A cross-sectional view taken along line XII-XII.

[0027] Fig.13 It is a cross-sectional view showing a modified example of the battery according to the third embodiment.

[0028] Fig.14 It is a schematic plan view showing batteries according to Examples and Comparative Examples.

[0029] Fig.15 is a schematic cross-sectional view illustrating a puncture test.

[0030] Fig.16 This is a diagram showing the results of the tensile test of the separators according to Example 1 and Comparative Example 1.

[0031] Fig.17 This is a graph showing the temporal change in the potential difference of the battery during the puncture test according to Example 1.

[0032] Fig.18 This is an X-ray CT image of the battery after the puncture test according to Example 1.

[0033] Fig.19 This is a graph showing the temporal change in the potential difference of the battery during the puncture test according to Comparative Example 1.

[0034] Fig. 20 This is an X-ray CT image of the battery after the puncture test according to Comparative Example 1. DETAILED DESCRIPTION

[0035] The following describes an embodiment of the present invention. It should be noted that the present invention is not limited to the embodiment. Each embodiment is merely an example, and it is of course possible to partially replace or combine the structures shown in different embodiments.

[0036] (First Embodiment)

[0037] Figure 1 FIG. 1 is a cutaway perspective view showing an example of a battery according to the first embodiment. Figure 1As shown, the battery according to the first embodiment includes a positive electrode lead 11A, a negative electrode lead 12A, an electrode assembly 10A, an outer packaging member 21, and a sealing member 22. The battery 1A according to the first embodiment is a so-called laminated lithium ion secondary battery in which the electrode assembly 10A is housed in the outer packaging member 21.

[0038] The positive electrode lead 11A is a terminal extending from the electrode assembly 10A to the outside of the outer packaging member 21. That is, the positive electrode lead 11A is a terminal that becomes the positive electrode of the battery 1A. The positive electrode lead 11A is provided so as to extend in a direction perpendicular to the Z direction described later. The positive electrode lead 11A is composed of a conductor.

[0039] The negative electrode lead 12A is a terminal extending from the electrode assembly 10A to the outside of the outer packaging member 21. That is, the negative electrode lead 12A is a terminal that becomes the negative electrode of the battery 1A. The negative electrode lead 12A is provided so as to extend in a direction perpendicular to the Z direction described later. The negative electrode lead 12A is composed of a conductor.

[0040] The outer packaging component 21 is a shell that accommodates the electrode assembly 10A. The outer packaging component 21 has an insulating layer, a metal layer and an outermost layer. The outer packaging component 21 has a structure in which an insulating layer, a metal layer, and an outermost layer are stacked in sequence from the inside, that is, the side where the electrode assembly 10A is provided, and are bonded by lamination. The insulating layer of the outer packaging component 21 is composed of resins such as polyethylene, polypropylene, modified polyethylene, modified polypropylene, polyolefin resin containing ethylene or propylene as monomers. As a result, the outer packaging component 21 can reduce the moisture permeability of the battery 1A and improve the airtightness. The metal layer of the outer packaging component 21 is a metal plate or foil such as aluminum, stainless steel, nickel, and iron. The outermost layer can be any material, for example, it is preferably composed of a high-strength material such as the same resin as the insulating layer, nylon, etc. As a result, the outer packaging component 21 can improve the strength against rupture, puncture, etc.

[0041] The sealing member 22 is a member that makes the outer package 21 airtight. The sealing member 22 is arranged in a manner that surrounds the positive lead 11A and the negative lead 12A, and seals the positive lead 11A and the negative lead 12A with the outer package 21. The material of the sealing member 22 preferably has tightness relative to the positive lead 11A and the negative lead 12A. For example, when the positive lead 11A and the negative lead 12A are composed of a metal material, the sealing member 22 uses a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, and modified polypropylene. Thus, since the gap between the outer package 21 and the positive lead 11A and the negative lead 12A can be sealed, the outer package 21 can be made airtight.

[0042] Figure 21 is an exploded plan view showing the components of the electrode assembly according to the first embodiment. The electrode assembly 10A includes a positive electrode, a negative electrode, and a separator 17A. Figure 2 As shown, the electrode assembly 10A involved in the first embodiment is an electrode stack formed by alternately stacking positive electrodes and negative electrodes with separators 17A therebetween. The electrode assembly 10A is flat and has a roughly plate-like shape. The electrode assembly 10A is roughly rectangular. That is, the length of the electrode assembly 10A in one direction is shorter than that in other directions.

[0043] In the following description, the shortest direction of the electrode assembly 10A is set as the Z direction for description. In addition, the direction in which the distance between the mutually opposing sides of the separator 17A described later becomes the smallest when viewed from above along the Z direction is set as the Y direction, and the direction perpendicular to the Y direction and the Z direction is set as the X direction for description. That is, the electrode assembly 10A becomes a flat shape having a width in the YZ direction. In the first embodiment, in the electrode assembly 10A, the positive electrode and the negative electrode are stacked in the Z direction. In addition, the separator 17A has a thickness in the Z direction, and when viewed from above along the Z direction, the length in the X direction is greater than the length in the Y direction. The details of the shape of the separator 17A will be described below.

[0044] (positive electrode)

[0045] The positive electrode includes a positive electrode current collector layer 13A and a positive electrode active material layer 14A. Figure 2 As shown, the positive electrode is a stacked body in which positive electrode active material layers 14A are stacked on both sides of a positive electrode collector layer 13A in the Z direction.

[0046] The positive electrode current collector layer 13A is a sheet-shaped conductor foil, such as aluminum foil. In the first embodiment, the positive electrode current collector layer 13A has a rectangular shape having a rectangular protrusion 13Aa when viewed in plan along the Z direction. The protrusion 13Aa of the positive electrode current collector layer 13A is connected to the positive electrode lead 11A.

[0047] The positive electrode active material layer 14A is a layer containing a positive electrode active material. The positive electrode active material layer 14A is stacked in a manner that sandwiches the positive electrode collector layer 13A. The positive electrode active material layer 14A contains a positive electrode active material, a conductive agent, and a binder. In the first embodiment, when viewed from above along the Z direction, the shape of the positive electrode active material layer 14A is rectangular. It should be noted that the contents of the positive electrode active material layer 14A are not limited to the substances listed above, and for example, a dispersant may also be contained.

[0048] The positive electrode active material is preferably a lithium-containing compound such as a lithium-containing composite oxide or a lithium-containing phosphate compound. A lithium-containing composite oxide is an oxide containing lithium and one or more elements other than lithium as constituent elements. The lithium-containing composite oxide has, for example, a layered rock salt type or spinel type crystal structure. A lithium-containing phosphate compound is a phosphate compound containing lithium and one or more elements other than lithium as constituent elements. The lithium-containing phosphate compound has, for example, an olivine type crystal structure.

[0049] The binder contained in the positive electrode active material layer 14A may be any material, for example, any one or more of synthetic rubber and polymer compounds, etc. Synthetic rubber is, for example, styrene-butadiene rubber, fluorine rubber, EPDM rubber, etc. Polymer compounds are, for example, polyvinylidene fluoride, polyimide, etc.

[0050] The conductive agent included in the positive electrode active material layer 14A may be any material, for example, carbon. Examples of carbon include graphite, carbon black, acetylene black, Ketjen black, etc. In addition, the positive electrode conductive agent may be any material having conductivity, and is not limited thereto, and may also be a metal material, a conductive polymer, etc.

[0051] (negative electrode)

[0052] The negative electrode includes a negative electrode current collector layer 15A and a negative electrode active material layer 16A. Figure 2 As shown, the negative electrode is a stacked body in which two negative electrode active material layers 16A are stacked on both sides of a negative electrode collector layer 15A in the Z direction.

[0053] The negative electrode current collector layer 15A is a sheet-shaped conductor foil, such as copper foil. In the first embodiment, the negative electrode current collector layer 15A has a rectangular shape having a rectangular protrusion 15Aa when viewed in plan along the Z direction. The protrusion 15Aa of the negative electrode current collector layer 15A is connected to the negative electrode lead 12A.

[0054] The negative electrode active material layer 16A is a layer containing a negative electrode active material. The negative electrode active material layer 16A may further contain a conductive agent and a binder similar to those of the positive electrode active material layer 14A.

[0055] The negative electrode active material includes, for example, a material capable of absorbing and releasing lithium (Li), such as a carbon material, a metal, a semimetal, an alloy or compound of silicon (Si), or an alloy or compound of tin (Sn).

[0056] Carbon materials that can be used as negative electrode active materials include, for example, graphite, difficult-graphitization carbon, and easy-graphitization carbon. More specifically, carbon materials include, for example, pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound sintered bodies, activated carbon, and carbon blacks. Cokes include pitch coke, needle coke, and petroleum coke. Here, the organic polymer compound sintered body is formed by sintering and carbonizing a polymer compound such as a phenolic resin or a furan resin at an appropriate temperature.

[0057] Examples of metals and semimetals that can be used as negative electrode active materials include tin, lead (Pb), aluminum, indium (In), silicon, zinc (Zn), antimony (Sb), bismuth (Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) and hafnium (Hf). Among them, silicon, germanium, tin and lead are preferred. In addition, silicon and tin are more preferred because they have high ability to insert and remove lithium and can obtain high energy density.

[0058] As an alloy of silicon that can be used as a negative electrode active material, for example, an alloy containing at least one of the group consisting of tin, nickel, copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc, indium, silver, titanium (Ti), germanium, bismuth, antimony and chromium (Cr) as a second constituent element other than silicon can be listed. In addition, as a compound of silicon that can be used as a negative electrode active material, for example, a compound containing oxygen (O) or carbon (C) can be listed, and in addition to silicon, the above-mentioned second constituent element can also be contained.

[0059] As the alloy of tin that can be used as the negative electrode active material, for example, there can be listed an alloy containing at least one of the group consisting of silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium as a second constituent element other than tin. In addition, as the compound of tin that can be used as the negative electrode active material, for example, there can be listed a compound containing oxygen or carbon, which can contain the above-mentioned second constituent element in addition to tin.

[0060] (Electrolytes)

[0061] The electrolyte is filled in the outer packaging member 21. The electrolyte includes an electrolyte salt and a solvent that dissolves the electrolyte salt. The electrolyte salt includes, for example, lithium perchlorate (LiClO 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO 2 CF 3 ) 2 ), lithium bis(pentafluoroethanesulfonyl)imide (LiN(SO 2C 2 F 5 ) 2 ) lithium hexafluoroarsenate (LiAsF 6 ) and other lithium salts. The solvent includes, for example, lactone solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone, carbonate solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, ether solvents such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran, nitrile solvents such as acetonitrile, sulfolane solvents, phosphoric acid, phosphate ester solvents, and non-aqueous solvents such as pyrrolidones.

[0062] (Diaphragm)

[0063] The separator 17A insulates the positive electrode from the negative electrode. The separator 17A is provided so that the positive electrode and the negative electrode do not directly contact each other, and in the electrode assembly 10A, the separator 17A is stacked between the positive electrode and the negative electrode in the Z direction. Figure 2 As shown, in the first embodiment, a plurality of diaphragms 17A are provided, and each diaphragm 17A has a thickness in the Z direction.

[0064] In the first embodiment, the diaphragm 17A is rectangular when viewed from above along the Z direction. That is, the diaphragm 17A has a short side parallel to the Y direction and a long side parallel to the X direction and longer than the short side when viewed from above along the Z direction. In the following, the length of the diaphragm 17A in the X direction is sometimes referred to as a, and the length in the Y direction is referred to as b. It should be noted that Figure 2 The diaphragm 17A shown has a right-angled apex when viewed in a plan view along the Z direction, but this is only an example, and the apex may be rounded.

[0065] In the first embodiment, the length a of the separator 17A in the X direction is 2.0 times or more of the length b in the Y direction. By setting it within this range, when the separator 17A is damaged by external force, the cracks generated in the separator 17A can reach the long side, so that the positive electrode and the negative electrode can be suppressed from shorting. The short-circuit suppression effect caused by the cracks generated in the separator 17A will be described below.

[0066] The separator 17A is made of a material that is electrically stable, chemically stable to the positive electrode active material, the negative electrode active material, and the electrolyte, and has insulating properties. The separator 17A can use, for example, a layer made of a polymer non-woven fabric, a porous film, glass, or ceramic fiber. In addition, the separator 17A can be a separator formed by stacking multiple layers, or a separator formed by compounding a porous polyolefin film and a heat-resistant film containing polyimide, glass, or ceramic fibers. In addition, the separator 17A can also be a separator with particles such as ceramic particles coated on the surface of the film, but is not limited to this.

[0067] The separator 17A uses a film synthesized by a uniaxial stretching method or a biaxial stretching method. The separator 17A is preferably composed of a film synthesized by a uniaxial stretching method. Thus, the cost can be suppressed. When a film synthesized by a uniaxial stretching method is used as the separator 17A, the separator 17A is more preferably synthesized by a dry stretching method. Thus, the cost can be further suppressed.

[0068] The separator 17A has MD (machine direction: longitudinal direction) and TD (transverse direction: transverse direction). MD refers to the flow direction of the film, that is, the direction in which the film travels during manufacturing. TD refers to the direction perpendicular to MD when viewed from above along the transverse direction of the film of the separator 17A, that is, the thickness direction. In the uniaxial stretching method, the film is stretched only in MD. On the other hand, in the biaxial stretching method, the film is stretched not only in MD but also in TD.

[0069] The MD and TD of the separator 17A can be inspected by SEM (Scanning Electron Microscope) etc. Specifically, in the SEM observation image of the separator 17A, the direction in which the fibrous structures are oriented can be defined as MD, and the direction perpendicular to the orientation direction and the thickness direction can be defined as TD.

[0070] The tensile strength of the diaphragm 17A in MD is different from that in TD, and it has anisotropy in tensile strength. This is because, when the diaphragm 17A is manufactured, the orientation of the molecules constituting the diaphragm 17A is tilted in MD due to stretching in MD. Here, the tensile strength of the diaphragm 17A refers to the maximum tensile stress that the diaphragm 17A can withstand. In the first embodiment, the tensile strength of the diaphragm 17A in MD is the maximum, and the tensile strength in TD is the minimum. That is, in the first embodiment, the direction in which the tensile strength of the diaphragm 17A is the minimum is TD. The anisotropy of the tensile strength of the diaphragm 17A is stronger in a film manufactured by a uniaxial stretching method than in a film manufactured by a biaxial stretching method.

[0071] Figure 3 Schematic diagram for explaining the method of measuring the tensile strength of the separator. Figure 3 As shown, the tensile strength of the diaphragm 17A can be measured using an INSTRON universal material testing machine. Specifically, the two ends of the test piece 17T of the diaphragm 17A can be fixed by using the tensile fixtures J1 and J2, and the tensile test can be performed under the following conditions to measure. Here, the test piece 17T of the diaphragm 17A is a film used in the diaphragm 17A or a test piece cut out from the diaphragm 17A. In addition, the width w of the test piece 17T refers to the maximum length in the direction perpendicular to the tensile direction of the test piece 17T at the beginning of the test.

[0072] Width w of test piece 17T: 12.5 mm

[0073] · Distance c between tensile fixtures J1 and J2 of test piece 17T: 30 mm

[0074] ·Stretching speed: 50mm per minute

[0075] Here, the direction in which the tensile strength of the diaphragm 17A becomes the minimum refers to the direction in which the tensile strength of the diaphragm 17A becomes the minimum in the direction perpendicular to the thickness direction of the diaphragm 17A. The direction in which the tensile strength of the diaphragm 17A becomes the minimum can be determined by setting the direction perpendicular to the thickness direction of the diaphragm 17A as the tensile direction and performing the aforementioned tensile test. More specifically, the tensile test can be performed by setting multiple directions perpendicular to the thickness direction of the diaphragm 17A as tensile directions, and as a result, the direction in which the tensile strength becomes the minimum is set as the direction in which the tensile strength of the diaphragm 17A becomes the minimum. Here, the multiple directions perpendicular to the thickness direction of the diaphragm 17A as the tensile direction in the tensile test include one direction selected from the direction perpendicular to the thickness direction of the diaphragm 17A, a direction perpendicular to the first direction, and multiple directions rotated every 5° from the one direction to the perpendicular direction. In other words, the tensile test can be performed by changing the tensile direction of the diaphragm 17A at 5° scales to determine the direction in which the tensile strength of the diaphragm 17A becomes the minimum.

[0076] In the first embodiment, the tensile strength of the separator 17A in MD is 1.05 times or more of the tensile strength in TD. By setting it within this range, when the separator 17A is damaged by external force, cracks are generated in a certain direction on the separator 17A, so that the positive electrode and the negative electrode can be reliably suppressed from short-circuiting. The details of the direction of the cracks generated in the separator 17A will be described below.

[0077] In the first embodiment, the direction in which the tensile strength of the separator 17A becomes the smallest, that is, the TD of the separator 17A is the direction along the X direction. Here, the direction along the X direction includes a direction completely parallel to the X direction and a direction substantially parallel to the X direction. Two directions being substantially parallel means, for example, that the angle formed by the two directions is greater than 0° and less than 10°. Thus, when the separator 17A is damaged by external force, a short circuit between the positive electrode and the negative electrode can be suppressed. Figure 4 as well as Figure 5 This point will be explained in detail.

[0078] Figure 4 FIG. 1 is a schematic top view showing the electrode assembly according to the first embodiment when the separator is broken. Figure 4 In the electrode assembly 10A1, the TD direction is the same as the X direction. Figure 4As shown, when an external force is applied to the electrode assembly 10A1 in a manner of piercing in the Z direction, a crack T1 is generated in the separator 17A1. The crack T1 expands depending on the anisotropy of the tensile strength of the separator 17A1, so the crack T1 expands in the MD in a manner that the separator 17A1 is split in the TD where the tensile strength is weak. At this time, since the crack T1 expands in the short side direction, that is, the Y direction, the end E1 of the crack T1 reaches the long side of the separator 17A1. As a result, the positive electrode and the negative electrode are broken together with the separator 17A1 before they come into contact in the Z direction, so when the separator 17A1 is damaged by an external force, the positive electrode and the negative electrode can be suppressed from short-circuiting.

[0079] Figure 5 Yes means Figure 4 A schematic top view of a comparative example of the electrode assembly involved. Figure 5 In the electrode assembly 10A2, the TD direction is the same as the Y direction. Figure 5 As shown in FIG. 1 , when an external force is applied to the electrode assembly 10A2 so as to penetrate the electrode assembly 10A2 in the Z direction, a crack T2 is generated in the separator 17A2. Figure 4 Similarly, the crack T2 expands in the MD so that the separator 17A2 is split in the TD where the tensile strength is weak. At this time, since the crack T2 expands in the long side direction, that is, the X direction, the end E2 of the crack T2 does not reach the short side of the separator 17A2. As a result, the electrode assembly 10A2 is compressed in a ground manner, so that the positive electrode and the negative electrode contact in the Z direction and short-circuit.

[0080] In a first embodiment, if Figure 2 As shown, the TD of the separator 17A, that is, the direction in which the tensile strength is the smallest, is the same in the plurality of separators 17A. Thus, when the separator 17A is damaged by external force, cracks easily extend in the Y direction, thereby preventing the positive electrode and the negative electrode from short-circuiting.

[0081] In the first embodiment, the separators 17A are not welded to each other. Therefore, when the separator 17A is damaged by external force, the cracks are easily extended in the Y direction, so that the positive electrode and the negative electrode can be prevented from short-circuiting.

[0082] The battery 1A according to the first embodiment has been described above, but the battery according to the first embodiment is not limited to Figure 1 The battery shown is 1A.

[0083] Figure 6 FIG. 1 is a schematic plan view showing an electrode assembly according to a modified example of the battery according to the first embodiment. Figure 6As shown, in the electrode assembly 10A3, when viewed from above along the Z direction, the TD of the separator 17A3 may not be along the X direction, as long as the angle β3 formed by the TD of the separator 17A3 and the Y direction is greater than the angle α3 formed by the TD of the separator 17A3 and the X direction. Even in this case, when the separator 17A3 is damaged by external force, the cracks easily reach the long sides of the separator 17A3, and the positive electrode and the negative electrode are broken together with the separator 17A3 before they come into contact in the Z direction, so that the positive electrode and the negative electrode can be prevented from short-circuiting.

[0084] Figure 7 Yes means Figure 6 A schematic top view of a comparative example of the electrode assembly involved. Figure 7 As shown, in the electrode assembly 10A4, when viewed from above along the Z direction, when the angle β4 formed by the TD of the separator 17A4 and the Y direction is less than the angle α4 formed by the TD of the separator 17A4 and the X direction, the crack is unlikely to reach the long side of the separator 17A4. Therefore, when the separator 17A4 is damaged by external force, the electrode assembly 10A4 is compressed in a grinding manner, so that the positive electrode and the negative electrode may contact in the Z direction and short-circuit.

[0085] In addition, in the electrode assembly, a gel-like electrolyte layer composed of a polymer compound that retains the electrolyte may also be provided to replace the electrolyte. In this case, the electrolyte layer is provided between the separator 17a and the positive electrode or the negative electrode. The polymer compound constituting the gel of the electrolyte layer is not particularly limited as long as it absorbs a solvent and gels. The polymer compound constituting the gel of the electrolyte layer can be, for example, fluorine-based polymer compounds such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, ether-based polymer compounds containing polyethylene oxide or a crosslinked body of polyethylene oxide, and polymer compounds containing polyacrylonitrile, polypropylene oxide or polymethyl methacrylate as monomers. From the viewpoint of stability to redox reactions, the polymer compound constituting the gel of the electrolyte layer is preferably a fluorine-based polymer compound, more preferably a copolymer containing vinylidene fluoride and hexafluoropropylene as components. It should be noted that the copolymer may also contain monoesters of unsaturated dibasic acids such as monomethyl maleate, halogenated vinyl such as trifluoroethylene, cyclic carbonates of unsaturated compounds such as vinyl carbonate, and acrylic vinyl monomers containing epoxy groups as components. Thus, high cycle characteristics can be obtained.

[0086] As described above, the battery 1A according to the first embodiment is a battery including an electrode assembly 10A, the electrode assembly 10A including a positive electrode, a negative electrode, and a film-like separator 17A, the electrode assembly 10A being flat, the separator 17A having a thickness in at least the first direction when the shortest direction of the electrode assembly 10A is the first direction, and being provided between the positive electrode and the negative electrode in at least the first direction, the direction in which the distance between the mutually opposing sides of the separator 17A becomes the smallest when viewed in plan along the first direction being the second direction, and the direction perpendicular to the first direction and the second direction being the third direction, the angle formed by the direction (TD) in which the tensile strength of the separator 17A becomes the smallest when viewed in plan along the first direction and the second direction is larger than the angle formed by the direction in which the tensile strength of the separator 17A becomes the smallest and the third direction. When viewed in plan along the first direction, the ratio of the length of the separator 17A in the third direction to the length of the separator 17A in the second direction is 2.0 or more.

[0087] Thus, when an external force is applied, when viewed from above along the first direction, the crack T1 expands in a direction (MD) perpendicular to the direction in which the tensile strength is minimized, so that the separator 17A is split in the direction in which the tensile strength is minimized. The angle formed by the direction in which the tensile strength of the separator 17A is minimized (TD) and the second direction is greater than the angle formed by the direction in which the tensile strength of the separator 17A is minimized and the third direction, so that the end E1 of the crack T1 is more likely to reach the long side of the separator 17A than to reach the short side of the separator 17A. Thus, the positive electrode and the negative electrode are broken together with the separator 17A before they come into contact in the Z direction, so that the positive electrode and the negative electrode can be suppressed from short-circuiting.

[0088] As a preferred mode, the direction in which the tensile strength of the separator 17A becomes the smallest is the direction along the third direction. Therefore, when an external force is applied, when viewed from the first direction, the crack T1 expands in the short side direction, so that the end E1 of the crack T1 more reliably reaches the long side of the separator 17A. As a result, the short circuit between the positive electrode and the negative electrode can be more reliably suppressed.

[0089] In addition, when viewed from above along the first direction, the separator 17A has a short side parallel to the second direction and a long side parallel to the third direction and longer than the short side. Even in this case, since the positive electrode and the negative electrode are broken together with the separator 17A before contacting in the Z direction, it is possible to suppress the positive electrode and the negative electrode from short-circuiting when the separator 17A is damaged by external force.

[0090] In addition, the electrode assembly 10A is an electrode stack in which the positive electrode and the negative electrode are stacked in the first direction via the separator 17A. Even in this case, since the positive electrode and the negative electrode are broken together with the separator 17A before contacting in the Z direction, it is possible to suppress the positive electrode and the negative electrode from short-circuiting when the separator 17A is damaged by external force.

[0091] As a preferred embodiment, the electrode stack has a plurality of separators 17A, and the directions in which the tensile strength of the plurality of separators 17A is minimized are all the same. Thus, when the separator 17A is damaged by external force, cracks tend to expand in a direction perpendicular to the direction in which the tensile strength is minimized, thereby further suppressing the positive and negative electrodes from short-circuiting.

[0092] As a preferred embodiment, the ratio of the tensile strength of the separator 17A in the direction perpendicular to the direction in which the tensile strength of the separator 17A is the smallest to the tensile strength of the separator 17A in the direction in which the tensile strength of the separator 17A is the smallest is 1.05 or more. Thus, when the separator 17A is damaged by an external force, cracks are generated in a certain direction on the separator 17A, so that the short circuit between the positive electrode and the negative electrode can be further suppressed.

[0093] (Second Embodiment)

[0094] Figure 8 FIG. 2 is a partial cutaway view showing an example of a battery according to the second embodiment. Figure 8 As shown, the battery 1B according to the second embodiment is different from the first embodiment in that the electrode assembly 10B is an electrode winding body. The battery 1B according to the second embodiment will be described below using the drawings. It should be noted that the description of the same structure as the first embodiment will be omitted.

[0095] Fig. 9 It is along Figure 8 A schematic cross-sectional view of line IX-IX of FIG. Fig. 9 As shown, the electrode assembly 10B according to the second embodiment includes: a positive electrode including a positive electrode current collector layer 13B and a positive electrode active material layer 14B; a negative electrode including a negative electrode current collector layer 15B and a negative electrode active material layer 16B; a separator 17B; and a protective member 18. Fig. 9 As shown, the electrode assembly 10B is an electrode winding body in which a stacked body is wound, and the stacked body is formed by stacking the positive electrode and the negative electrode with a separator 17B interposed therebetween, with the positive electrode lead 11B and the negative electrode lead 12B extending in a direction perpendicular to the Z direction as the center. Fig. 9 In the example shown, the stacked body including the positive electrode, the negative electrode, and the separator 17B involved in the electrode assembly 10B is wound in a direction perpendicular to the X direction. That is, it can be said that in the electrode assembly 10B, the positive electrode, the negative electrode, and the separator 17B are stacked at least in a direction parallel to the Z direction, and the separator 17B has a thickness at least in a direction parallel to the Z direction. It should be noted that Fig. 9 The winding direction of the electrode assembly 10B shown is just an example, and the electrode assembly 10B may be wound in a direction perpendicular to the Y direction.

[0096] The electrode assembly 10B is the same as the electrode assembly 10A involved in the first embodiment, and is a flat shape. That is, the electrode assembly 10B is a plate-like shape whose length in the Z direction is shorter than that in the X direction and the Y direction. In other words, since the length in the direction perpendicular to the winding axis of the electrode assembly 10B is not fixed, the battery 1B is not a so-called cylindrical battery. In a cylindrical battery, since the surface perpendicular to the Z direction is a curved surface, even if an external force is applied by puncturing in the Z direction, the cracks in the separator will not expand in the MD direction, so the positive electrode and the negative electrode may be short-circuited.

[0097] The electrode assembly 10B has a structure in which the negative electrode collector layer 15B, the negative electrode active material layer 16B, the separator 17B, the positive electrode active material layer 14B, the positive electrode collector layer 13B, the positive electrode active material layer 14B, the separator 17B, and the negative electrode active material layer 16B are stacked in order from the outside (i.e., from the side of the protective member 18). The electrode assembly 10B does not have any layer other than the negative electrode collector layer 15B, the separator 17B, and the positive electrode collector layer 13B near the positive electrode lead 11B and the negative electrode lead 12B. With this structure, the positive electrode collector layer 13B is connected to the positive electrode lead 11B, and the negative electrode collector layer 15B is connected to the negative electrode lead 12B.

[0098] The protective member 18 is a member for protecting the inside of the electrode assembly 10B. The protective member 18 is provided so as to be wound around the electrode assembly 10B. The protective member 18 is, for example, an insulating tape.

[0099] Fig.10 is a schematic top view showing an electrode assembly according to the second embodiment. Fig.10 As shown in the figure, in the second embodiment, the direction in which the tensile strength of the separator 17B becomes the smallest, that is, TD, is the direction along the X direction. Therefore, when the separator 17B is damaged by external force, the cracks generated in the electrode assembly 10B extend in the short side direction, that is, the Y direction, regardless of the winding direction, so that the ends of the cracks reach the long sides of the separator 17B. Therefore, the positive electrode and the negative electrode are broken together with the separator 17B before they come into contact in the Z direction, so when the separator 17B is damaged by external force, it is possible to suppress the positive electrode and the negative electrode from short-circuiting.

[0100] The battery 1B according to the second embodiment has been described above, but the battery according to the second embodiment is not limited to Figure 8 For example, in the battery 1B according to the second embodiment, the electrolyte is filled into the outer packaging member 21 in the same manner as in the first embodiment, but the present invention is not limited thereto, and a gel electrolyte layer composed of a polymer compound that retains an electrolyte solution may be provided instead. That is, an electrolyte layer may be provided between the separator 17B and the positive electrode or the negative electrode instead of the electrolyte.

[0101] As described above, in the battery according to the second embodiment, the electrode assembly 10B is an electrode winding body in which the positive electrode and the negative electrode are stacked and wound with the separator 17B interposed therebetween. Even in this case, since the positive electrode and the negative electrode are broken together with the separator 17B before they come into contact in the Z direction, it is possible to suppress a short circuit between the positive electrode and the negative electrode when the separator 17B is broken by an external force.

[0102] (Third Embodiment)

[0103] Fig.11 It is a perspective view showing an example of a battery according to the third embodiment. Fig.12 It is along Fig.11 The cross-sectional view of the XII-XII line. Fig.11 as well as Fig.12 As shown, the battery 1C involved in the third embodiment is different from the first embodiment in that the electrode assembly 10C is accommodated in the battery tank 31. That is, the battery 1C involved in the third embodiment is a so-called square lithium-ion secondary battery. The battery 1C involved in the third embodiment is described below using the accompanying drawings. It should be noted that the description of the same structure as the first embodiment and the second embodiment is omitted.

[0104] The battery 1C includes an electrode assembly 10C, a battery can 31 , electrodes 32 and 33 , and seals 34 , 35 , and 36 .

[0105] The battery tank 31 is a tank for housing the electrode assembly 10C. The battery tank 31 is a flat rectangular parallelepiped tank made of a conductor.

[0106] The electrode 32 is a terminal drawn out from the inside of the battery tank 31 to the outside. The electrode 32 is a terminal that becomes the positive electrode of the battery 1C. The electrode 32 is made of a conductor. The electrode 32 is connected to the protrusion 13Ca of the positive electrode collector of the electrode assembly 10C.

[0107] The electrode 33 is a terminal drawn out from the inside of the battery tank 31 to the outside. The electrode 33 is a terminal that becomes the negative electrode of the battery 1C. The electrode 33 is made of a conductor. The electrode 33 is connected to the protrusion 15Ca of the negative electrode collector of the electrode assembly 10C.

[0108] The seal 34 is provided so as to surround the electrode 32 and seal the inside of the battery tank 31. The seal 34 is made of an insulator. Thus, the conduction between the battery tank 31 and the electrode 32 can be suppressed.

[0109] The seal 35 is provided so as to surround the electrode 33 and seal the inside of the battery tank 31. The seal 35 is made of an insulator. Thus, the conduction between the battery tank 31 and the electrode 33 can be suppressed.

[0110] The seal 36 is provided so as to cover the interior of the battery tank 31. The seal 35 is made of an insulator. Thus, the conduction between the electrode assembly 10C and the battery tank 31 can be suppressed.

[0111] The electrode assembly 10C is an electrode stack in which positive electrodes and negative electrodes are alternately stacked with separators interposed therebetween. The electrode assembly 10C is the same electrode stack as the electrode assembly 10A according to the first embodiment.

[0112] As in the first embodiment, the separator 17C according to the third embodiment has the direction in which the tensile strength is minimum, that is, TD, along the X direction when viewed in plan along the Z direction. This can prevent the positive and negative electrodes from short-circuiting when the separator is damaged by external force.

[0113] The battery 1C according to the third embodiment has been described above, but the battery according to the third embodiment is not limited to Fig.12 The battery 1C concerned may be, for example, an electrode assembly in the form of a wound electrode body.

[0114] Fig.13 : is a cross-sectional view showing a modification of the battery according to the third embodiment. In the battery 1D according to the modification of the third embodiment, the electrode assembly 10D is an electrode winding body wound around a positive electrode lead 11D and a negative electrode lead 12D extending in a direction perpendicular to the Z direction. The positive electrode lead 11D and the negative electrode lead 12D are connected to electrodes 32 and 33, respectively. The electrode assembly 10D is an electrode winding body having the same structure as the electrode assembly 10B according to the second embodiment. Fig.13 In the example shown, the stacked body having the positive electrode, the negative electrode and the separator involved in the electrode assembly 10D is wound in a direction perpendicular to the X direction. That is, it can be said that in the electrode assembly 10D, the positive electrode, the negative electrode and the separator are stacked in a direction at least parallel to the Z direction, and the separator 17B has a thickness in a direction at least parallel to the Z direction. In the electrode assembly 10D, as in the first embodiment, the tensile strength of the separator is the smallest in the direction, that is, TD is the direction along the X direction when viewed from above in the Z direction. Therefore, even in this case, when the separator is damaged by external force, the short circuit between the positive and negative electrodes can be suppressed. It should be noted that Fig.13 The winding direction of the electrode assembly 10B shown is just an example, and the electrode assembly 10B may be wound in a direction perpendicular to the Y direction.

[0115] (Example)

[0116] Hereinafter, examples will be described. It should be noted that the present invention is not limited to the examples described below.

[0117] Fig.14It is a schematic plan view showing batteries according to Examples and Comparative Examples. Fig.15 is a schematic cross-sectional view illustrating a puncture test. Fig.14 The battery 1E involved is Fig.15 Along the Fig.14 The cross section of the XV-XV line is shown. Fig.14 as well as Fig.15 The battery 1E shown in FIG. 1E is a laminated type battery. That is, Fig.14 as well as Fig.15 As shown, the battery 1E includes a positive electrode lead 11E, a negative electrode lead 12E, an electrode assembly 10E, an outer packaging member 21E, and a sealing member 22. The electrode assembly 10E is accommodated in the outer packaging member 21E. Here, the electrode assembly 10E has a structure in which a positive electrode including a positive electrode collector layer 13E and a positive electrode active material layer 14E and a negative electrode including a negative electrode collector layer 15E and a negative electrode active material layer 16E are stacked via a separator 17E.

[0118] The separator 17E involved in Example 1 and Comparative Example 1 is a porous polyolefin film manufactured by a uniaxial stretching method. The separator 17E is rectangular when viewed from above in the Z direction, and the length a in the X direction is 25 mm, and the length b in the Y direction of the separator 17E is 7 mm. That is, in Example 1 and Comparative Example 1, the length a in the X direction of the separator 17E is 3.5 times the length b in the Y direction of the separator 17E.

[0119] Here, a tensile test was performed under the following conditions on the membranes used in the separators 17E according to Example 1 and Comparative Example 1. The tensile test was performed in the air.

[0120] ·Measurement device: INSTRON universal material testing machine 5564 (INSTRON)

[0121] ·Test piece width w: 12.5 mm

[0122] · Distance c between tensile fixtures of the test piece: 30 mm

[0123] ·Stretching speed: 50mm per minute

[0124] ·Stretch direction: MD or TD

[0125] Fig.16 : is a graph showing the results of the tensile test of the diaphragms involved in Example 1 and Comparative Example 1. As a result of the tensile test, Fig.16 The load displacement curve is shown in Fig.16 In the load-displacement curve, the maximum value of the load is the tensile strength, so it can be seen that the tensile strength of the diaphragm 17E in MD is 14 times the tensile strength in TD.

[0126] In the battery 1E, a press plate K is further provided on both sides of the electrode assembly 10E in the Z direction. The press plate K is provided in the outer packaging member 21E. A circular depression Ka with a diameter of 6 mm is provided at the center in the X direction when viewed from above in the Z direction on the press plate K. The depression Ka is a depression for guiding the lead L used for the puncture test to the electrode assembly 10E in the puncture test.

[0127] The battery 1E involved in the above-described embodiment and comparative example was subjected to a puncture test. Fig.15 As shown, in the puncture test, the pin L was directed toward the depression Ka of the pressure plate K of the battery 1E on the seat M, and punctured in the Z direction at a speed of 200 mm per second. Here, the tip of the pin L was a ball with a diameter of 3 mm. At this time, the time change of the potential difference between the positive lead 11E and the negative lead 12E was measured before and after the puncture, thereby investigating the presence or absence of a short circuit between the positive and negative electrodes in the battery 1E. Then, the battery 1E was subjected to X-ray CT (Computed Tomography) to observe the cracks generated in the electrode assembly 10E.

[0128] In the battery according to Example 1, the TD of all the separators was the same direction as the X direction. That is, the TD of all the separators in the battery according to Example 1 was parallel to the long sides of the separators.

[0129] Fig.17 : is a graph showing the time change of the potential difference of the battery during the penetration test involved in Example 1. In the penetration test involved in Example 1, the pin L was in contact with the electrode assembly at 3110ms, and the pin L penetrated the electrode assembly at 3132ms. Fig.17 As shown, in the battery of Example 1, the potential difference hardly changes before and after the puncture. Therefore, it can be seen that in the battery of Example 1, even if an external force is applied in the Z direction, the positive electrode and the negative electrode will not be short-circuited.

[0130] Fig.18 This is an X-ray CT image of the battery after the puncture test according to Example 1. Fig.18 The X-ray CT image is an image of the electrode assembly after the puncture test in Example 1 viewed from above along the Z direction. Fig.18 As shown, it can be seen that the cracks generated in the electrode assembly by the puncture test reach both ends of the electrode assembly in the Y direction. It can be considered that during puncture, the positive electrode and the negative electrode of the electrode assembly are broken together with the separator before contacting in the Z direction, so the positive electrode and the negative electrode will not be short-circuited.

[0131] In the battery 1E according to Comparative Example 1, the TD of all the separators is the same direction as the Y direction. That is, the TD of all the separators in the battery 1E according to the example is parallel to the short side of the separator.

[0132] Fig.19 : is a graph showing the time change of the potential difference of the battery during the penetration test involved in Comparative Example 1. In the penetration test involved in Comparative Example 1, the pin L contacts the electrode assembly at 2332ms, and the pin L penetrates the electrode assembly at 2350ms. Fig.19 As shown, in the battery according to Comparative Example 1, the potential difference decreases after the electrode assembly penetrates. Therefore, it is known that in the battery according to Comparative Example 1, when an external force is applied in the Z direction, the positive electrode and the negative electrode are short-circuited.

[0133] Fig. 20 This is an X-ray CT image of the battery after the puncture test according to Comparative Example 1. Fig. 20 The X-ray CT image is an image of the electrode assembly after the puncture test in Comparative Example 1 viewed from above along the Z direction. Fig. 20 As shown, it can be seen that the cracks generated in the electrode assembly by the puncture test did not reach both ends of the electrode assembly in the X direction. It can be considered that during the puncture, the electrode assembly was compressed in a grinding manner, so the positive electrode and the negative electrode contacted in the Z direction, and the positive electrode and the negative electrode were short-circuited.

[0134] In Example 2, a battery 1E was manufactured in the same manner as in Example 1, except that the length b of the diaphragm 17E in the Y direction was set to 12 mm, and a puncture test was performed. That is, in the battery 1E involved in Example 2, the TD of the diaphragm is all in the same direction as the X direction and is parallel to the long side of the diaphragm. In addition, in Example 2, the length a of the diaphragm 17E in the X direction is 2.1 times the length b of the diaphragm 17E in the Y direction. In the battery involved in Example 2, the potential difference hardly changes before and after the puncture. Therefore, it can be seen that in the battery involved in Example 2, even if an external force is applied in the Z direction, the positive electrode and the negative electrode will not be short-circuited.

[0135] In Comparative Example 2, a battery 1E was manufactured in the same manner as in Comparative Example 1, except that the length b of the diaphragm 17E in the Y direction was 12 mm, and a puncture test was performed. That is, in the battery 1E involved in Comparative Example 2, the TD of the diaphragm is all in the same direction as the Y direction and is parallel to the short side of the diaphragm. In addition, in Comparative Example 2, the length a of the diaphragm 17E in the X direction is 2.1 times the length b of the diaphragm 17E in the Y direction. The potential difference of the battery involved in Comparative Example 2 decreased after the puncture test. Therefore, it can be seen that in the battery involved in Comparative Example 2, when an external force is applied along the Z direction, the positive electrode and the negative electrode are short-circuited.

[0136] In Comparative Example 3, a battery 1E was manufactured in the same manner as in Example 1, except that the length b of the diaphragm 17E in the Y direction was 17 mm, and a puncture test was performed. That is, in the battery 1E involved in Example 3, the TD of the diaphragm is all in the same direction as the X direction and is parallel to the long side of the diaphragm. In addition, in Comparative Example 3, the length a of the diaphragm 17E in the X direction is 1.5 times the length b of the diaphragm 17E in the Y direction. The potential difference of the battery involved in Comparative Example 3 decreased after the puncture test. Therefore, it can be seen that in the battery involved in Comparative Example 3, when an external force is applied in the Z direction, the positive electrode and the negative electrode are short-circuited.

[0137] Based on the above results, it can be seen that the batteries involved in Examples 1 and 2 in which the length a of the diaphragm 17E in the X direction is set to be more than 2.0 times the length b of the diaphragm 17E in the Y direction can suppress the short circuit between the positive electrode and the negative electrode compared with the battery involved in Comparative Example 3 in which the length a of the diaphragm 17E in the X direction is less than 2.0 times the length b of the diaphragm 17E in the Y direction.

[0138] It should be noted that the above-mentioned embodiments are for easy understanding of the present invention and are not intended to limit the interpretation of the present invention. The present invention can be modified / improved without departing from the gist thereof, and its equivalents are also included in the present disclosure.

[0139] Regarding the description of claims, the present disclosure can adopt the following aspects.

[0140] (1) a battery,

[0141] The battery comprises an electrode assembly having a positive electrode, a negative electrode, and a film-like separator.

[0142] The electrode assembly is in a flat shape.

[0143] When the shortest direction of the electrode assembly is a first direction, the separator has a thickness at least in the first direction and is provided between the positive electrode and the negative electrode at least in the first direction.

[0144] When the direction in which the distance between the mutually opposing sides of the diaphragm becomes the smallest when viewed from above along the first direction is set as the second direction, and the direction perpendicular to the first direction and the second direction is set as the third direction, the angle formed by the direction in which the tensile strength of the diaphragm becomes the smallest when viewed from above along the first direction and the second direction is larger than the angle formed by the direction in which the tensile strength of the diaphragm becomes the smallest and the third direction,

[0145] When viewed in plan along the first direction, a ratio of a length of the diaphragm in the third direction to a length of the diaphragm in the second direction is greater than or equal to 2.0.

[0146] (2) According to the battery described in (1) above, a direction in which the tensile strength of the separator becomes minimum is a direction along the third direction.

[0147] (3) The battery according to (1) or (2) above, wherein the separator has short sides parallel to the second direction and long sides parallel to the third direction and longer than the short sides when viewed in plan along the first direction.

[0148] (4) In the battery according to any one of (1) to (3) above, the electrode assembly is an electrode stack in which the positive electrode and the negative electrode are stacked in the first direction with the separator interposed therebetween.

[0149] (5) The battery according to (4) above,

[0150] The electrode stack has a plurality of separators.

[0151] The directions in which the tensile strengths of the plurality of separators become minimum are all the same.

[0152] (6) The battery according to any one of (1) to (3) above,

[0153] The electrode assembly is an electrode winding body in which the positive electrode and the negative electrode are stacked and wound with the separator interposed therebetween.

[0154] (7) The battery according to any one of (1) to (6) above,

[0155] A ratio of the tensile strength of the separator in a direction perpendicular to the direction in which the tensile strength of the separator becomes minimum to the tensile strength of the separator in the direction in which the tensile strength of the separator becomes minimum is 1.05 or more.

[0156] Description of Reference Numerals

[0157] 1A to 1E: battery; 10A to 10E, 10A1 to 10A4: electrode assembly; 11A, 11B, 11D, 11E: positive electrode lead; 12A, 12B, 12D, 12E: negative electrode lead; 13A, 13B, 13E: positive electrode collector layer; 13Aa, 13Ca: protrusion; 14A, 14B, 14E: positive electrode active material layer; 15A, 15B, 15E: negative electrode collector layer; 15Aa, 15Ca: protrusion; 16A, 16B, 16 E: negative electrode active material layer; 17A, 17B, 17C, 17E, 17A1~17A4: diaphragm; 17T: test piece; 18: protective part; 21, 21E: outer packaging part; 22: sealing part; 31: battery tank; 32, 33: electrodes; 34, 35, 36: sealing part; E1, E2: end; J1, J2: stretching fixture; K: pressing plate; Ka: depression; L: pin; M: seat; T1, T2: crack; w: width; α3, α4, β3, β4: angle.

Claims

1. A battery comprising an electrode assembly, wherein the electrode assembly comprises a positive electrode, a negative electrode and a film-like separator, The electrode assembly is in a flat shape. When the shortest direction of the electrode assembly is a first direction, the separator has a thickness at least in the first direction and is provided between the positive electrode and the negative electrode at least in the first direction. When the direction in which the distance between the mutually opposing sides of the diaphragm becomes the smallest when viewed from above along the first direction is set as the second direction, and the direction perpendicular to the first direction and the second direction is set as the third direction, the angle formed by the direction in which the tensile strength of the diaphragm becomes the smallest when viewed from above along the first direction and the second direction is larger than the angle formed by the direction in which the tensile strength of the diaphragm becomes the smallest and the third direction, When viewed in plan along the first direction, a ratio of a length of the diaphragm in the third direction to a length of the diaphragm in the second direction is greater than or equal to 2.

0.

2. The battery according to claim 1, wherein The direction in which the tensile strength of the separator becomes minimum is the direction along the third direction.

3. The battery according to claim 1 or 2, wherein: The diaphragm has a short side parallel to the second direction and a long side parallel to the third direction and longer than the short side when viewed in plan along the first direction.

4. The battery according to any one of claims 1 to 3, wherein The electrode assembly is an electrode stack in which the positive electrode and the negative electrode are stacked in the first direction with the separator interposed therebetween.

5. The battery according to claim 4, wherein The electrode stack has a plurality of separators. The directions in which the tensile strengths of the plurality of separators become minimum are all the same.

6. The battery according to any one of claims 1 to 3, wherein The electrode assembly is an electrode winding body in which the positive electrode and the negative electrode are stacked and wound with the separator interposed therebetween.

7. The battery according to any one of claims 1 to 6, wherein A ratio of the tensile strength of the separator in a direction perpendicular to the direction in which the tensile strength of the separator becomes minimum to the tensile strength of the separator in the direction in which the tensile strength of the separator becomes minimum is 1.05 or more.

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