Laminated separator sheet and wound secondary battery

Abstract

To provide a laminated separator sheet that, when incorporated into a wound secondary battery, is suppressed from thermally shrinking in the winding axis direction.SOLUTION: A laminated separator sheet according to the present disclosure includes a first microporous layer and a second microporous layer laminated on both main surfaces of the first microporous layer. The first microporous layer contains polyethylene. The second microporous layer contains polypropylene. The first microporous layer has a corrugated shape. The corrugated shape is undulating in a wave-like manner along the longitudinal direction of the laminated separator sheet.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a laminated separator sheet and a wound-type secondary battery. [Background technology]

[0002] Lithium secondary batteries (hereinafter also referred to as "secondary batteries") using non-aqueous electrolytes are used in vehicles, information and communication technology (for example, personal computers or smartphones), and power storage. A separator sheet is used in secondary batteries. The separator sheet prevents short circuits caused by contact between the positive and negative electrodes and allows electrolyte ions to pass through.

[0003] Patent Document 1 discloses a lithium ion secondary battery separator (hereinafter also referred to as a "laminated separator sheet"). The laminated separator sheet has a specific microporous separator. The microporous separator has a three-layer structure of polypropylene (PP) / polyethylene (PE) / polypropylene (PP). Specifically, as shown in FIG. 6, it discloses that the shape of the interface between the intermediate polyethylene layer and the outer polypropylene layer is flat. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-36543 Summary of the Invention [Problem to be solved by the invention]

[0005] A long laminated separator sheet is used in a wound secondary battery. The laminated separator sheet is incorporated into the wound secondary battery in a wound state. Typically, the laminated separator sheet is wound so that the winding axis direction and the short side direction (hereinafter also referred to as the "short side direction") of the laminated separator sheet are parallel (i.e., so that the long side direction (hereinafter also simply referred to as the "long side direction") is parallel to the winding direction). The ends of the wound laminated separator sheet in the winding direction (i.e., the long side ends) are fixed with a winding stopper.

[0006] Wound secondary batteries may be exposed to high-temperature environments during use. When a wound secondary battery is exposed to a high-temperature environment, the laminated separator sheet thermally shrinks only in the winding axis direction (short direction) where it is not fixed by the winding stopper. Therefore, to prevent the occurrence of short circuits, wound batteries are generally manufactured using laminated separator sheets with a margin in the winding axis direction. The "margin" means that the length is sufficiently longer than the length of thermal shrinkage in the winding axis direction. The margin reduces product competitiveness (for example, increases the cost of the laminated separator sheet, reduces cell energy density, etc.).

[0007] In the laminated separator sheet disclosed in Patent Document 1 (hereinafter also referred to as the "conventional sheet"), the interface between the intermediate polyethylene layer and the outer polypropylene layer has a flat shape. Therefore, when the conventional sheet is in an open state and not secured by a winding stopper, it is prone to thermal shrinkage in the longitudinal direction when heat is applied. On the other hand, when the conventional sheet is incorporated into a wound secondary battery, the fixed winding stopper prevents the conventional sheet from thermally shrinking in the winding direction (i.e., the longitudinal direction) even when exposed to a high-temperature environment. Therefore, strain occurs in the conventional sheet in the winding direction (i.e., the longitudinal direction). When strain occurs in the conventional sheet in the winding direction (i.e., the longitudinal direction), strain also occurs in the winding axis direction (i.e., the transverse direction) of the conventional sheet due to Poisson's ratio deformation. Due to this strain in the winding axis direction (i.e., the transverse direction) of the conventional sheet, the conventional sheet is prone to thermal shrinkage in the winding axis direction when incorporated into a wound secondary battery. In order to prevent a decline in product competitiveness, there is a demand for a laminated separator sheet that is inhibited from thermally shrinking in the winding axis direction when incorporated into a wound secondary battery.

[0008] The present disclosure has been made in consideration of the above circumstances. An object of one embodiment of the present disclosure is to provide a laminated separator sheet that is inhibited from thermally shrinking in the winding axis direction when incorporated into a wound secondary battery. Another problem to be solved by another embodiment of the present disclosure is to provide a wound secondary battery in which thermal shrinkage of the laminated separator sheet in the winding axis direction is suppressed. [Means for solving the problem]

[0009] The means for solving the above problems include the following embodiments. <1> A first microporous layer and a second microporous layer laminated on both main surfaces of the first microporous layer, the first microporous layer comprises polyethylene; the second microporous layer comprises polypropylene; A laminated separator sheet, wherein the first microporous layer has a corrugated shape that is undulating in a longitudinal direction of the laminated separator sheet. <2> The amplitude ratio is 6% to 27%. The peak-valley period is 10 μm to 50 μm, Except when the amplitude ratio is 6% to 13% and the peak-valley period is 50 μm, the amplitude ratio indicates a ratio (A / B) of an average value (B) of distances between adjacent peaks and valleys of the corrugated shape in the thickness direction of the laminated separator sheet to a thickness (A) of the laminated separator sheet, the peak-valley period indicates an average value of a plurality of intervals in the longitudinal direction between adjacent peak portions and a plurality of intervals in the longitudinal direction between adjacent valley portions; <1> 2. The laminated separator sheet according to claim 1. <3> Except when the amplitude ratio is 23% to 27% and the peak-valley period is 10 μm to 40 μm, <2> 2. The laminated separator sheet according to claim 1. <4> The amplitude ratio is 16% to 23%, The peak-valley period is 10 μm to 15 μm. <2> 2. The laminated separator sheet according to claim 1. <5> The wavy shape is undulating periodically along the longitudinal direction. <1> ~ <4> 10. The laminated separator sheet according to any one of the above items. <6> a wound electrode body; An electrolyte; an exterior body that accommodates the wound electrode body and the electrolyte; Equipped with the wound electrode body is formed by winding an electrode laminate around a widthwise direction of a laminated separator sheet as a winding axis, The electrode stack is <1> ~ <5> 1. A wound secondary battery comprising the laminated separator sheet according to any one of 1 to 8, one of a positive electrode sheet and a negative electrode sheet, and the laminated separator sheet and the other of a positive electrode sheet and a negative electrode sheet stacked in this order. [Effects of the Invention]

[0010] According to the present disclosure, there is provided a laminated separator sheet in which thermal shrinkage in the winding axis direction is suppressed when incorporated into a wound secondary battery. According to the present disclosure, there is provided a wound secondary battery in which thermal shrinkage of the laminated separator sheet in the winding axis direction is suppressed. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing the configuration of a wound secondary battery according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a front view of an electrode stack according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a front view of an electrode stack according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a scanning electron microscope photograph of a conventional lithium-ion secondary battery separator. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances unless otherwise specified.

[0013] (1) Laminated separator sheet The laminated separator sheet of the present disclosure comprises a first microporous layer and a second microporous layer laminated on both main surfaces of the first microporous layer. The first microporous layer contains polyethylene. The second microporous layer contains polypropylene. The first microporous layer has a corrugated shape. The corrugated shape is undulating in a wave-like manner along the longitudinal direction of the laminated separator sheet (hereinafter simply referred to as the "longitudinal direction").

[0014] The term "microporous layer" refers to a layer having a plurality of micropores for use as a separator sheet in a lithium secondary battery using a nonaqueous electrolyte. The "wave shape" refers to a zigzag shape. Specifically, the wave shape has multiple peaks, multiple valleys, and multiple connection portions. The connection portions connect adjacent peaks and valleys. The peaks, connection portions, and valleys are formed in this order, continuously, periodically or aperiodically, along the longitudinal direction. Each of the multiple peaks, valleys, and connection portions extends along the short-side direction of the laminated separator sheet (hereinafter simply referred to as the "short-side direction").

[0015] Because the laminate separator sheet of the present disclosure has the above-described configuration, when incorporated into a wound secondary battery, thermal shrinkage in the winding axis direction is suppressed, and therefore the laminate separator sheet of the present disclosure can suppress a decrease in the product competitiveness of wound secondary batteries (for example, an increase in the cost of the laminate separator sheet, a decrease in cell energy density, etc.). This effect is presumably due to, but not limited to, the following reasons. In the present disclosure, the first microporous layer has a corrugated shape. Therefore, the laminate separator sheet of the present disclosure is less susceptible to thermal shrinkage in the longitudinal direction than conventional laminate separator sheets when in an open state (hereinafter simply referred to as the "open state") where it is not secured by a winding stopper. When the laminate separator sheet of the present disclosure is incorporated into a wound secondary battery so that its short side is parallel to the winding axis direction, distortion of the laminate separator sheet of the present disclosure in the winding direction (i.e., the longitudinal direction) is suppressed compared to that of a laminate separator sheet, even when exposed to a high-temperature environment. In other words, distortion of the laminate separator sheet of the present disclosure in the winding axis direction (i.e., the short side direction) due to Poisson's ratio deformation is also suppressed. As a result, it is presumed that the laminate separator sheet of the present disclosure is less susceptible to thermal shrinkage in the winding axis direction (i.e., the short side direction) than conventional laminate separator sheets when incorporated into a wound secondary battery.

[0016] The laminate separator sheet is a long sheet-like object, and the surface shape of both main surfaces of the laminate separator sheet may be flat.

[0017] The thickness (A) of the laminated separator sheet is not particularly limited and is appropriately selected depending on the intended use of the wound secondary battery.

[0018] The length of the laminated separator sheet in the longitudinal direction and the length of the laminated separator sheet in the lateral direction are not particularly limited, and are appropriately selected depending on the intended use of the wound secondary battery, etc.

[0019] The porosity of the laminated separator sheet is not particularly limited, and may be 45% or more, 50% or more, 53% or more, 60% or less, or 57% or less.

[0020] The laminated separator sheet includes a first microporous layer and a second microporous layer laminated on both major surfaces of the first microporous layer. In addition to the first and second microporous layers, the laminated separator sheet may also include another microporous layer different from the first and second microporous layers. The other microporous layer may be a known microporous layer.

[0021] (1.1) First microporous layer The first microporous layer has a shutdown function to prevent ignition of the wound secondary battery. The "shutdown function" refers to the function in which, when abnormal heat generation occurs in the wound secondary battery, the micropores in the first microporous layer are blocked by the molten resin of the first microporous layer, thereby stopping the battery reaction. The shutdown function is exhibited in the first microporous layer at a lower temperature than in the second microporous layer.

[0022] The first microporous layer may or may not be a layer made of nonwoven fabric. "Nonwoven fabric" refers to a flat fibrous assembly that has a predetermined level of structural strength achieved by physical and / or chemical methods, excluding weaving, knitting, and papermaking.

[0023] (1.1.1) Wave shape The first microporous layer has a corrugated shape that undulates in a wavy manner along the longitudinal direction.

[0024] The wave shape may be a periodic wave-like undulation along the longitudinal direction, or a non-periodic wave-like undulation along the longitudinal direction, and it is particularly preferable that the wave shape be a periodic wave-like undulation along the longitudinal direction. Because the wavy shape is periodically wavy along the longitudinal direction, the laminate separator sheet of the present disclosure is less likely to thermally shrink in the longitudinal direction in an open state than when the wavy shape is non-periodically wavy along the longitudinal direction. When the laminate separator sheet of the present disclosure is incorporated into a wound secondary battery so that the short side direction is parallel to the winding axis direction, distortion of the laminate separator sheet of the present disclosure in the winding direction (longitudinal direction) is further suppressed even when exposed to a high-temperature environment. In other words, distortion in the winding axis direction (short side direction) due to Poisson's ratio deformation is also further suppressed. As a result, the laminate separator sheet of the present disclosure is even less likely to thermally shrink in the winding axis direction (short side direction) when incorporated into a wound secondary battery.

[0025] The average value (B) of the distance between adjacent peaks and valleys of the corrugated shape in the thickness direction of the multiple laminated separator sheets (hereinafter also referred to as "amplitude") need only be smaller than the thickness (A) of the laminated separator sheet, and is appropriately selected depending on the intended use of the wound-type secondary battery, etc. The average value (B) of the amplitude may be 0.5 μm to 6 μm, 1 μm to 5 μm, 2.5 μm to 3.5 μm, or 3.5 μm to 4.5 μm. The method for measuring the average value (B) of the amplitude is the same as that described in the Examples. In addition, when the wave shape is undulating periodically along the longitudinal direction, each of the multiple amplitudes has the same numerical value. Therefore, when the wave shape is undulating periodically along the longitudinal direction, the average amplitude (B) is also called "amplitude (B)."

[0026] The amplitude ratio of the waveform (hereinafter also referred to as "amplitude ratio (A / B)") is not particularly limited, and may be 6% to 27%, 23% to 27%, or 16% to 23%. "Amplitude ratio" refers to the ratio (A / B) of the average value (B) of the distance (i.e., amplitude) between adjacent peaks and valleys of the wave-like shape in the thickness direction of multiple laminated separator sheets to the thickness (A) of the laminated separator sheet.

[0027] The peak-valley period of the waveform is not particularly limited and may be 5 μm to 55 μm, 10 μm to 50 μm, 5 μm to 35 μm, 5 μm to 25 μm, 5 μm to 15 μm, or 15 μm to 25 μm. The "peak-valley period" refers to the average value of the distance between the plurality of adjacent peak portions in the longitudinal direction and the distance between the plurality of adjacent valley portions in the longitudinal direction. In addition, when the wavy shape is undulating periodically along the longitudinal direction, the longitudinal spacing between adjacent peak portions and the longitudinal spacing between adjacent valley portions are each the same numerical value.

[0028] The laminated separator sheet of the present disclosure preferably satisfies the first condition, which indicates that the amplitude ratio is 6% to 27% and the peak-valley period is 10 μm to 50 μm, excluding the case where the amplitude ratio is 6% to 13% and the peak-valley period is 50 μm. When the laminate separator sheet of the present disclosure satisfies the first condition, the laminate separator sheet of the present disclosure is less likely to thermally shrink in the lateral direction in an open state than when the laminate separator sheet of the present disclosure does not satisfy condition 1. When the laminate separator sheet of the present disclosure is incorporated into a wound secondary battery so that the lateral direction is parallel to the winding axis direction, the laminate separator sheet of the present disclosure is less likely to thermally shrink in the winding axis direction (lateral direction) even when exposed to a high-temperature environment. That is, when incorporated into a wound secondary battery, the thermal shrinkage of the laminate separator sheet in the winding axis direction includes a first thermal shrinkage caused by distortion in the winding direction (longitudinal direction) of the laminate separator sheet of the present disclosure, and a second thermal shrinkage in the winding axis direction (transverse direction) of the laminate separator sheet of the present disclosure itself. When the laminate separator sheet of the present disclosure satisfies the first condition, the second thermal shrinkage is suppressed in addition to the first thermal shrinkage.

[0029] When the laminate separator sheet of the present disclosure satisfies the first condition, it preferably further satisfies the second condition, excluding the cases where the amplitude ratio is 23% to 27% and the peak-valley period is 10 μm to 40 μm. When the laminate separator sheet of the present disclosure satisfies the first and second conditions, the thickness variation (MD) of the laminate separator sheet of the present disclosure is suppressed compared to when the laminate separator sheet of the present disclosure does not satisfy the first and second conditions, and therefore the laminate separator sheet of the present disclosure can suppress the occurrence of defects (e.g., the occurrence of lithium dendrites and shortened lifespan due to differences in the progress of the battery reaction).

[0030] When the laminate separator sheet of the present disclosure satisfies the first condition, it preferably further satisfies the third condition, which indicates that the amplitude ratio is 16% to 23%, and the peak-valley period is 10 μm to 15 μm. When the laminate separator sheet of the present disclosure satisfies the first and third conditions, the laminate separator sheet of the present disclosure is less likely to thermally shrink in the longitudinal and lateral directions in an open state, and thickness variation (MD) is suppressed, compared to when the laminate separator sheet of the present disclosure does not satisfy the first and third conditions. Therefore, when the laminate separator sheet of the present disclosure is incorporated into a wound secondary battery so that the lateral direction is parallel to the winding axis direction, the laminate separator sheet of the present disclosure is less likely to thermally shrink in the winding axis direction (lateral direction) even when exposed to a high-temperature environment. In addition, the laminate separator sheet of the present disclosure can suppress the occurrence of defects (e.g., the occurrence of lithium dendrites and shortened life due to differences in the progress of the battery reaction).

[0031] (1.1.2) Material The first microporous layer contains polyethylene. The main component of the first microporous layer may be polyethylene. "The main component of the first microporous layer" means that the content of polyethylene relative to the total amount of the first microporous layer is 50% by mass or more. The content of polyethylene relative to the total amount of the first microporous layer may be 80% by mass or more, 90% by mass or more, 95% by mass or more, or 100% by mass.

[0032] The Young's modulus of polyethylene is not particularly limited and may be 0.8 GPa to 1.5 GPa.The Poisson's ratio of polyethylene is not particularly limited and may be 0.3 to 0.6.

[0033] Examples of polyethylene include ultra-high molecular weight polyethylene (UHMW-PE), high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), etc. These polyethylenes may be used alone or in combination of two or more.

[0034] The first microporous layer may contain a resin other than polyethylene. Examples of the other resin include polypropylene, poly-1-butene, poly-1-pentene, poly-1-hexene, poly-4-methyl-1-pentene, poly-1-octene, polyvinyl acetate, polymethyl methacrylate, polystyrene, polyvinylidene fluoride, and polytetrafluoroethylene. These other resins may be used alone or in combination of two or more.

[0035] (1.2) Second microporous layer The second microporous layer has a function of imparting mechanical strength and thermal strength to the first microporous layer, and also has a shutdown function.

[0036] The second microporous layer is laminated on both major surfaces of the first microporous layer, and the second microporous layer may be welded to both major surfaces of the first microporous layer.

[0037] The second microporous layer may or may not be a layer made of nonwoven fabric.

[0038] (1.2.1) Shape etc. The shape of the second microporous layer may be any shape that allows the laminated separator sheet to be formed into a sheet-like product, and is appropriately selected depending on the corrugated shape of the first microporous layer. The size of the second microporous layer is appropriately selected depending on the sizes of the laminated separator sheet and the first microporous layer.

[0039] (1.2.2) Material The second microporous layer contains polypropylene. The main component of the second microporous layer may be polypropylene. "The main component of the second microporous layer" means that the content of polypropylene relative to the total amount of the second microporous layer is 50% by mass or more. The content of polypropylene relative to the total amount of the second microporous layer may be 80% by mass or more, 90% by mass or more, 95% by mass or more, or 100% by mass.

[0040] The Young's modulus of polypropylene is not particularly limited and may be 1.4 GPa to 2.1 GPa.The Poisson's ratio of polypropylene is not particularly limited and may be 0.3 to 0.6.

[0041] The second microporous layer may contain a resin other than polypropylene. Examples of the other resin include polyethylene, poly-1-butene, poly-1-pentene, poly-1-hexene, poly-4-methyl-1-pentene, poly-1-octene, polyvinyl acetate, polymethyl methacrylate, polystyrene, polyvinylidene fluoride, and polytetrafluoroethylene. These other resins may be used alone or in combination of two or more.

[0042] (2)Wound secondary battery The wound secondary battery of the present disclosure includes a wound electrode assembly, an electrolyte, and an exterior housing containing the wound electrode assembly and the electrolyte. The wound electrode assembly is formed by winding an electrode stack around the short-side direction of a laminated separator sheet. The electrode stack is formed by stacking, in this order, a laminated separator sheet of the present disclosure, one of a positive electrode sheet and a negative electrode sheet, a laminated separator sheet of the present disclosure, and the other of a positive electrode sheet and a negative electrode sheet.

[0043] The wound secondary battery of the present disclosure has the above-described configuration, which suppresses thermal shrinkage of the laminated separator sheet in the winding axis direction, thereby preventing a decrease in product competitiveness (e.g., an increase in the cost of the laminated separator sheet, a decrease in cell energy density, etc.).

[0044] (2.1) Wound electrode body The wound electrode body is formed by winding an electrode laminate around the widthwise direction of the laminated separator sheet as the winding axis.

[0045] The electrode laminate is formed by laminating one of a positive electrode sheet and a negative electrode sheet, a laminate separator sheet of the present disclosure, the other of the positive electrode sheet and the negative electrode sheet, and the laminate separator sheet in this order.

[0046] (2.1.1) Positive electrode sheet The positive electrode sheet is a long sheet-like object and may be a known positive electrode sheet used in wound secondary batteries.

[0047] The positive electrode sheet may include a positive electrode current collector and positive electrode active material layers laminated on both main surfaces of the positive electrode current collector.

[0048] The positive electrode current collector supplies current to the positive electrode active material layer during discharge or charge of the wound secondary battery. The positive electrode current collector may be a metal foil. Examples of metal foils include aluminum foil, copper foil, nickel foil, titanium foil, and stainless steel foil. A coating layer may be formed on the surface of the positive electrode current collector. The coating layer may be formed by a known method (e.g., plating, spray coating, etc.). The thickness of the positive electrode current collector may be 1 μm to 100 μm.

[0049] The positive electrode active material layer contains a positive electrode layer active material capable of absorbing and releasing charge carriers (for example, a lithium composite metal oxide having a layered rock salt structure, a metal oxide having a spinel structure, a polyanion compound, etc.) The thickness of the positive electrode active material layer may be 2 μm to 500 μm. The positive electrode active material layer may further contain, as necessary, a conductive additive for improving electronic conductivity, a binder, an electrolyte supporting salt (lithium salt) for improving ionic conductivity, a polymer electrolyte, or an additive (e.g., trifluoropropylene carbonate, a filler as a reinforcing material, etc.). Examples of conductive additives include carbon nanofibers, acetylene black, carbon black, and graphite. Examples of binders include fluorine-containing resins (e.g., polyvinylidene fluoride, polytetrafluoroethylene, fluororubber, etc.), thermoplastic resins (e.g., polypropylene, polyethylene, etc.), imide resins (e.g., polyimide, polyamideimide, etc.), alkoxysilyl group-containing resins, acrylic resins (e.g., acrylic acid, methacrylic acid, etc.), styrene-butadiene rubber (SBR), carboxymethyl cellulose, alginates (e.g., sodium alginate, ammonium alginate, etc.), water-soluble cellulose ester crosslinked bodies, and starch-acrylic acid graft polymers. These binders may be used alone or in combination of two or more.

[0050] (2.1.2) Negative electrode sheet The negative electrode sheet is a long sheet-like object and may be a known negative electrode sheet used in wound-type secondary batteries.

[0051] The negative electrode sheet may include a negative electrode current collector and negative electrode active material layers laminated on both main surfaces of the negative electrode current collector.

[0052] The negative electrode current collector supplies current to the negative electrode active material layer during discharge or charge of the wound secondary battery. The negative electrode current collector may be a metal foil. Examples of negative electrode foil include aluminum foil, copper foil, nickel foil, titanium foil, and stainless steel foil. A coating layer may be formed on the surface of the negative electrode current collector. The coating layer may be formed by a known method (e.g., plating, spray coating, etc.). The thickness of the negative electrode current collector may be 1 μm to 100 μm.

[0053] The negative electrode active material layer contains a negative electrode active material (e.g., carbon, a compound alloyable with lithium, etc.) capable of absorbing and releasing charge carriers. Examples of carbon include natural graphite, artificial graphite, hard carbon (non-graphitizable carbon), and soft carbon (easily graphitizable carbon). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. Examples of elements alloyable with lithium include silicon and tin. The thickness (length in the Z-axis direction) of the negative electrode active material layer may be 2 μm to 500 μm. The negative electrode active material layer may further contain, as necessary, a conductive additive for improving electronic conductivity, a binder, an electrolyte supporting salt (lithium salt) for improving ionic conductivity, a polymer electrolyte, or an additive (e.g., trifluoropropylene carbonate, a filler as a reinforcing material, etc.). Examples of conductive additives include carbon nanofibers, acetylene black, carbon black, and graphite. Examples of binders include fluorine-containing resins (e.g., polyvinylidene fluoride, polytetrafluoroethylene, fluororubber, etc.), thermoplastic resins (e.g., polypropylene, polyethylene, etc.), imide resins (e.g., polyimide, polyamideimide, etc.), alkoxysilyl group-containing resins, acrylic resins (e.g., acrylic acid, methacrylic acid, etc.), styrene-butadiene rubber (SBR), carboxymethyl cellulose, alginates (e.g., sodium alginate, ammonium alginate, etc.), water-soluble cellulose ester crosslinked bodies, and starch-acrylic acid graft polymers. These binders may be used alone or in combination.

[0054] (2.2) Electrolyte The electrolyte solution is not particularly limited. As the electrolyte solution, a liquid electrolyte, a gel polymer electrolyte, or an ionic liquid electrolyte may be used. The electrolyte solution may be any known electrolyte solution.

[0055] The liquid electrolyte functions as a carrier of lithium ions and may include an organic solvent and a lithium salt dissolved in the organic solvent, or may further include an additive in addition to the organic solvent and the lithium salt. Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, etc. One type of organic solvent may be used alone, or two or more types may be used in combination. Examples of the lithium salt include Li(C2F5SO2)2N, LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, etc. One type of lithium salt may be used alone, or two or more types may be used in combination. Examples of additives include vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, etc. These additives may be used alone or in combination of two or more.

[0056] The gel polymer electrolyte may include a matrix polymer (host polymer) made of an ion-conductive polymer, and the liquid electrolyte injected into the matrix polymer. Examples of matrix polymers (host polymers) include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene (PVdF-HEP), polymethyl methacrylate (PMMA), and copolymers thereof.

[0057] The ionic liquid electrolyte may contain an ionic liquid and the lithium salt dissolved in the ionic liquid, or may further contain the additive in addition to the ionic liquid and lithium salt. "Ionic liquid" refers to a series of compounds that are salts composed only of cations and anions and are liquid at room temperature. The cationic component constituting the ionic liquid is preferably at least one selected from the group consisting of imidazolium ions, pyridinium ions, pyrrolium ions, pyrazolium ions, pyrrolinium ions, pyrrolidinium ions, piperidinium ions, triazinium ions, and ammonium ions. These cationic components may be substituted or unsubstituted. The anion components that make up ionic liquids include halide ions and nitrate ions (NO3 - ), tetrafluoroborate ion (BF4 - ), hexafluorophosphate ion (PF6 - ), (FSO2)2N - , AlCl3 - , lactate ion, etc. The ionic liquid may be used alone or in combination of two or more kinds.

[0058] (2.3) Exterior body The exterior housing accommodates the wound electrode assembly and the electrolyte.

[0059] The exterior body is not particularly limited, and examples thereof include a laminate film (for example, an aluminum sheet), a battery can (for example, a cylindrical, rectangular, or coin-shaped battery can), etc. The exterior body may be a known exterior body.

[0060] (3) Implementation form Hereinafter, embodiments of the laminated separator sheet and the wound secondary battery of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0061] As shown in Fig. 1, the wound secondary battery 1 includes a wound electrode body 10, an electrolyte (not shown), a cylindrical exterior body 20, and current collecting tabs 30A and 30B. The wound electrode body 10 is formed by winding a rectangular electrode stack 10a (see Fig. 2) around a winding axis R. The wound electrode body 10 is cylindrical. The current collecting tabs 30A and 30B electrically connect the wound electrode body 10 and the exterior body 20. The exterior body 20 houses the wound electrode body 10, the electrolyte, and the current collecting tabs 30A and 30B.

[0062] In this embodiment, the longitudinal direction of the rectangular electrode stack 10a is defined as the X-axis direction. The lateral direction of the rectangular electrode stack 10a is defined as the Y-axis direction. The thickness direction of the rectangular electrode stack 10a is defined as the Z-axis direction. The X-axis, Y-axis, and Z-axis are perpendicular to each other. Note that these directions do not limit the orientation of the wound secondary battery of the present disclosure during use.

[0063] The applications of the wound secondary battery 1 include, for example, in-vehicle applications, information and communication technology (for example, personal computers or smartphones), power storage, etc. A plurality of wound secondary batteries 1 are suitably used in the form of a battery module.

[0064] (3.1) Wound electrode body 2, the wound electrode body 10 is formed by winding a rectangular electrode stack 10a around a winding axis R. The axial direction of the winding axis R and the Y-axis direction are parallel to each other.

[0065] The wound electrode body 10 may be housed in an insulating bag before being housed in the exterior body 20. The insulating bag is made of a resin (for example, polyethylene, polypropylene, or the like).

[0066] The size and number of windings of the wound electrode body 10 are selected appropriately depending on the application of the wound secondary battery 1 and other factors.

[0067] The electrode laminate 10a is a sheet-like object, and both main surfaces of the electrode laminate 10a are flat.

[0068] As shown in FIG. 3, the electrode stack 10a is formed by stacking a stacked separator sheet 11, a negative electrode sheet 12, a stacked separator sheet 11, and a positive electrode sheet 13 in this order along the negative direction of the Z axis.

[0069] (3.1.1) Laminated separator sheet The laminated separator sheet 11 is a long sheet-like object as shown in Figures 4 and 5. The surface shape of both main surfaces of the laminated separator sheet is flat.

[0070] The laminated separator sheet 11 includes a first microporous layer 111 and a second microporous layer 112 laminated on a first main surface S111A and a second main surface S111B of the first microporous layer 111.

[0071] (3.1.1.1) First microporous layer The first microporous layer 111 has a corrugated shape. The corrugated shape is undulating periodically along the X-axis direction (longitudinal direction). Specifically, as shown in FIG. 4, the corrugated shape has a plurality of peak portions 11M, a plurality of valley bottom portions 11V, and a plurality of connection portions 11C. The connection portions 11C connect adjacent peak portions 11M and valley bottom portions 11V. The peak portions 11M, connection portions 11C, and valley bottom portions 11V are formed successively in this order and periodically repeated along the X-axis direction (longitudinal direction). Each of the plurality of peak portions 11M, the plurality of valley bottom portions 11V, and the plurality of connection portions 11C extends along the Y-axis direction (transverse direction).

[0072] It is preferable that the laminated separator sheet 11 satisfy the first condition, which indicates that the amplitude ratio (A / B) is 6% to 27% and the peak-valley period L3 is 10 μm to 50 μm, excluding the case where the amplitude ratio (A / B) is 6% to 13% and the peak-valley period L3 is 50 μm. The "amplitude ratio (A / B)" refers to the ratio (A / B) of the average value (B) of the spacing L2 (see FIG. 5) between adjacent peak portions 11M and valley portions 11V of the wave-like shape in the thickness direction of the laminated separator sheet to the thickness (A) L1 (see FIG. 5) of the laminated separator sheet 11. In this embodiment, the average value (B) of the spacing L2 (see FIG. 5) is also referred to as the "amplitude (B) L2." The "peak-valley period" refers to the average value of the intervals L3 (see FIGS. 4 and 5) between adjacent peak portions 11M in the X-axis direction (longitudinal direction) and the intervals L3 (see FIGS. 4 and 5) between adjacent valley portions 11V in the X-axis direction (longitudinal direction). In this embodiment, the "peak-valley period" is also referred to as the "peak-valley period L3."

[0073] When the laminated separator sheet 11 satisfies the first condition, it preferably further satisfies the second condition. The second condition excludes cases where the amplitude ratio (A / B) is 23% to 27% and the peak-valley period L3 is 10 μm to 40 μm.

[0074] When the laminated separator sheet 11 satisfies the first condition, it preferably further satisfies the third condition. The third condition indicates that the amplitude ratio (A / B) is 16% to 23%, and the peak-valley period L3 is 10 μm to 15 μm.

[0075] The first microporous layer 111 is made of polyethylene.

[0076] (3.1.1.2) Second microporous layer As shown in FIG. 5, the second microporous layer 112 has a wave shape on the contact surface with the first microporous layer 111 that follows the wave shape of the first microporous layer 111.

[0077] The second microporous layer 112 is made of polypropylene.

[0078] (3.1.2) Negative electrode sheet The negative electrode sheet 12 includes a negative electrode current collector and negative electrode active material layers laminated on both main surfaces of the negative electrode current collector. That is, the negative electrode active material layers, the negative electrode current collector, and the negative electrode active material layers are laminated in this order along the Z-axis direction.

[0079] (3.1.3) Positive electrode sheet The negative electrode sheet 12 may include a negative electrode current collector and negative electrode active material layers laminated on both main surfaces of the negative electrode current collector. That is, the positive electrode active material layer, positive electrode current collector, and positive electrode active material layer are laminated in this order along the Z-axis direction.

[0080] (3.2) Electrolyte The electrolyte is a liquid electrolyte, a gel polymer electrolyte, or an ionic liquid electrolyte.

[0081] (3.3) Exterior body The exterior body 20 accommodates and seals the wound electrode body 10, the electrolyte, and the current collecting tabs 30A and 30B.

[0082] 1, the exterior body 20 includes a main body 21, a lid 22, and a sealing member 23. The main body 21 houses the wound electrode body 10, the electrolyte, the shaft, and the current collecting tabs 30A and 30B.

[0083] The main body 21 is cylindrical. The main body 21 has an opening that is open to the positive Y-axis direction. The lid 22 closes the opening of the main body 21. The lid 22 is disk-shaped. In this embodiment, the main body 21 and the lid 22 are made of metal, such as iron, copper, nickel, gold, silver, platinum, cobalt, zinc, lead, tin, titanium, chromium, aluminum, magnesium, manganese, and alloys thereof (stainless steel, brass, phosphor bronze, etc.).

[0084] The sealing member 23 electrically insulates the main body 21 from the lid 22 and fills the gap between the main body 21 and the lid 22 . The material of the sealing member 23 may be a known elastomer. "Elastomer" refers to a resin having a tensile modulus of elasticity of less than 6.0 × 10 Pa at 25°C. Examples of elastomers include urethane-based thermoplastic elastomers, amide-based thermoplastic elastomers, olefin-based thermoplastic elastomers, styrene-based thermoplastic elastomers, and polyester-based thermoplastic elastomers.

[0085] (3.4) Current collecting tab In this embodiment, one end of the current collecting tab 30A is electrically connected to the positive electrode current collector located at the outermost periphery on the positive side of the Y axis of the wound electrode body 10. The other end of the current collecting tab 30A is electrically connected to the lid portion 22 of the exterior body 20. One end of the current collecting tab 30B is electrically connected to the negative electrode current collector located at the innermost periphery on the negative Y-axis direction side of the wound electrode body 10. The other end of the current collecting tab 30B is electrically connected to the main body 21 of the exterior body 20.

[0086] (3.5) Action and Effect As described with reference to Figs. 1 to 5, laminated separator sheet 11 includes first microporous layer 111 and second microporous layer 112 laminated on both main surfaces S111A, S111B of first microporous layer 111. First microporous layer 111 contains polyethylene. Second microporous layer 112 contains polypropylene. First microporous layer 111 has a wavy shape that is undulating along the X-axis direction (longitudinal direction). As a result, the laminate separator sheet 11 is less likely to thermally shrink in the X-axis direction (longitudinal direction) in an open state than conventional laminate separator sheets. When the laminate separator sheet 11 is incorporated into a wound secondary battery 1 so that the Y-axis direction (transverse direction) is parallel to the winding axis direction, distortion of the laminate separator sheet 11 in the winding direction (i.e., longitudinal direction) is suppressed more than that of a laminate separator sheet, even when exposed to a high-temperature environment. In other words, distortion of the laminate separator sheet 11 in the winding axis direction (i.e., transverse direction) due to Poisson's ratio deformation is also suppressed. As a result, the laminate separator sheet 11 is less likely to thermally shrink in the winding axis direction (i.e., transverse direction) in a state incorporated into a wound secondary battery 1 than conventional laminate separator sheets.

[0087] 1 to 5, it is preferable that the laminated separator sheet 11 satisfy the first condition, which indicates that the amplitude ratio (A / B) is 6% to 27% and the peak-valley period L3 is 10 μm to 50 μm, excluding the case where the amplitude ratio (A / B) is 6% to 13% and the peak-valley period L3 is 50 μm. When the laminate separator sheet 11 satisfies the first condition, the laminate separator sheet 11 is less likely to thermally shrink in the Y-axis direction (short side direction) in an open state than when the laminate separator sheet 11 does not satisfy the first condition. When the laminate separator sheet 11 is incorporated into the wound secondary battery 1 so that the Y-axis direction (short side direction) is parallel to the winding axis direction, the laminate separator sheet 11 is less likely to thermally shrink in the winding axis direction (short side direction) even when exposed to a high-temperature environment. That is, when incorporated into the wound secondary battery 1, the thermal shrinkage of the laminated separator sheet 11 in the winding axis direction includes a first thermal shrinkage caused by distortion in the winding direction (longitudinal direction) of the laminated separator sheet 11, and a second thermal shrinkage in the winding axis direction (transverse direction) of the laminated separator sheet 11 itself. When the laminated separator sheet 11 satisfies the first condition, the second thermal shrinkage is suppressed in addition to the first thermal shrinkage.

[0088] 1 to 5, when the laminate separator sheet 11 satisfies the first condition, it preferably also satisfies the second condition. The second condition excludes cases where the amplitude ratio (A / B) is 23% to 27% and the peak-valley period L3 is 10 μm to 40 μm. When the laminate separator sheet 11 satisfies the first and second conditions, the thickness variation (MD) of the laminate separator sheet 11 is suppressed more than when the laminate separator sheet 11 does not satisfy the first and second conditions. Therefore, the laminate separator sheet 11 can suppress the occurrence of defects (for example, the occurrence of lithium dendrites and shortened life due to differences in the degree of progress of the battery reaction).

[0089] 1 to 5, when the laminate separator sheet 11 satisfies the first condition, it preferably further satisfies the third condition, which indicates that the amplitude ratio (A / B) is 16% to 23%, and the peak-valley period L3 is 10 μm to 15 μm. When the laminate separator sheet 11 satisfies the first and third conditions, the laminate separator sheet 11 is less likely to thermally shrink in the longitudinal and lateral directions in an open state, and thickness variation (MD) is suppressed, compared to when the laminate separator sheet 11 does not satisfy the first and third conditions. Therefore, when the laminate separator sheet 11 is incorporated into a wound secondary battery 1 so that the Y-axis direction (lateral direction) is parallel to the winding axis direction, the laminate separator sheet 11 is less likely to thermally shrink in the winding axis direction (lateral direction) even when exposed to a high-temperature environment. In addition, the laminate separator sheet 11 can suppress the occurrence of defects (e.g., the occurrence of lithium dendrites and shortened life due to differences in the progress of the battery reaction).

[0090] As described with reference to FIGS. 1 to 5, the wave shape is undulating periodically along the X-axis direction (longitudinal direction). Because the waves are periodically undulating along the X-axis direction (longitudinal direction), the laminate separator sheet 11 is less likely to thermally shrink in the X-axis direction (longitudinal direction) in an open state than when the waves are non-periodically undulating along the X-axis direction (longitudinal direction). When the laminate separator sheet 11 is incorporated into a wound secondary battery 1 so that the Y-axis direction (transverse direction) is parallel to the winding axis direction, distortion of the laminate separator sheet 11 in the winding direction (longitudinal direction) is further suppressed even when exposed to a high-temperature environment. In other words, distortion in the winding axis direction (transverse direction) due to Poisson's ratio deformation is also further suppressed. As a result, the laminate separator sheet 11 is even less likely to thermally shrink in the winding axis direction (transverse direction) when incorporated into a wound secondary battery 1.

[0091] As explained with reference to Figures 1 to 5, the wound secondary battery 1 includes a wound electrode body 10, an electrolyte, and an exterior body 20. The wound electrode body 10 is formed by winding an electrode laminate 10a around the Y-axis direction (short-side direction) of a laminated separator sheet 11 as a winding axis R. The electrode laminate 10a is formed by stacking the laminated separator sheet 11, a negative electrode sheet 12, a laminated separator sheet, and a positive electrode sheet 13 in this order. This suppresses thermal shrinkage in the winding axis direction of the laminated separator sheet 11 in the wound secondary battery 1. Therefore, the wound secondary battery 1 can suppress a decrease in product competitiveness (for example, an increase in the cost of the laminated separator sheet, a decrease in cell energy density, etc.). [Example]

[0092] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to the following examples. The materials, amounts used, ratios, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present disclosure. Unless otherwise specified, "parts" means "parts by mass."

[0093] [1] Examples and Comparative Examples Polyethylene (Young's modulus: 1.01 GPa, Poisson's ratio: 0.40) was prepared as the raw material for the first microporous layer, and polypropylene (Young's modulus: 1.75 GPa, Poisson's ratio: 0.45) was prepared as the raw material for the second microporous layer.

[0094] [1.1] Comparative Example 1 The raw materials for the first microporous layer were fed into the first extruder. The raw materials for the second microporous layer were fed into the second extruder. The raw materials for the second microporous layer were fed into the third extruder. A resin melt was extruded from the nozzles of the first extruder, the second extruder, and the third extruder to obtain a sheet molded body. The sheet molded body was stretched in the X-axis direction (longitudinal direction) using a roll stretching machine to form multiple micropores in the sheet molded body. This produced a long laminate separator sheet. The structure, thickness (A) L1, amplitude (B) L2, peak-valley period L3, maximum PP thickness L4, minimum PP thickness L5, PE thickness L6, and porosity of the laminate separator sheet are shown in Table 1.

[0095] [1.2] Examples 1 to 14 A long laminate separator sheet 11 shown in Figures 4 and 5 was produced in the same manner as in Comparative Example 1, except that the extrusion rate from the nozzle of the first extruder was periodically varied to achieve the amplitude (B) and peak-valley period shown in Table 1. The resin melt was extruded while continuously increasing and decreasing the thickness of the two second microporous layers 112 in the X-axis direction (longitudinal direction) while maintaining the thickness of the first microporous layer 111 at a constant 5 µm. While periodically varying the position of the interface between the first microporous layer 111 and the second microporous layer 112 in the X-axis direction (longitudinal direction), the thickness (A) L1 in the X-axis direction (longitudinal direction) was adjusted to be 15 µm. The structure, thickness (A) L1, amplitude (B) L2, peak-valley period L3, maximum PP thickness L4, minimum PP thickness L5, PE thickness L6, and porosity of the laminate separator sheet 11 are shown in Table 1.

[0096] [2]Measurement method [2.1] Thickness (A) L1 etc. The laminate separator sheet 11 was cut in a plane perpendicular to the Y-axis direction (short direction) of the laminate separator sheet 11 (along the longitudinal direction of the laminate separator sheet 11). From the cross section of the laminate separator sheet 11, the thickness (A) L1 of the laminate separator sheet 11, the amplitude (B) L2 of the first microporous layer, the peak-valley period L3 of the first microporous layer, the maximum PP thickness L4, the minimum PP thickness L5, and the PE thickness L6 were measured. As shown in FIG. 5, the "maximum PP thickness L4" indicates the maximum value of the distance in the Z-axis direction (thickness direction) between the first microporous layer 111 and the surface of the laminate separator sheet 11. As shown in FIG. 5, the "maximum PP thickness L5" indicates the minimum value of the distance in the Z-axis direction (thickness direction) between the first microporous layer 111 and the surface of the laminate separator sheet 11. The "PE thickness L6" indicates the length of the first microporous layer 111 in the Z-axis direction (thickness direction).

[0097] [2.2] Presence or absence of wavy shape and periodicity The laminate separator sheet 11 was cut in a plane perpendicular to the Y-axis direction (short direction) of the laminate separator sheet 11 (along the longitudinal direction of the laminate separator sheet 11). The cross section of the laminate separator sheet 11 was visually observed to determine whether the first microporous layer 111 had a wavy shape and whether the wavy shape was cyclically undulating along the longitudinal direction. The results are shown in Tables 1 and 2.

[0098] [2.3] Heat shrinkage (MD) and heat shrinkage (TD) The laminated separator sheet 11 was subjected to a heat treatment. The heating temperature for the heat treatment was 105°C. The heating time for the heat treatment was 2 hours. Next, the laminated separator sheet 11 after the heat treatment was subjected to a cooling treatment. In the cooling treatment, the laminated separator sheet 11 after the heat treatment was left in the air atmosphere to cool to room temperature (23°C). The thermal shrinkage (MD) was calculated using the following formula (i). The thermal shrinkage (TD) was calculated using the following formula (ii). The results are shown in Tables 1 and 2. The acceptable range of thermal shrinkage (MD) is less than 4.65%.

[0099] Formula (i): Thermal shrinkage (MD) = [(La1 - La2) / La1] × 100 In formula (i), La1 represents the length in the X-axis direction (longitudinal direction) of the laminated separator sheet 11 before the heat treatment, and La2 represents the length in the X-axis direction (longitudinal direction) of the laminated separator sheet 11 after the cooling treatment.

[0100] Formula (ii): Thermal shrinkage (TD) = [(Lb1 - Lb2) / Lb1] × 100 In formula (ii), Lb1 represents the length in the Y-axis direction (short side direction) of the laminated separator sheet 11 before the heat treatment, and Lb2 represents the length in the Y-axis direction (short side direction) of the laminated separator sheet 11 after the cooling treatment.

[0101] [2.4] Thickness variation (MD) The laminate separator sheet 11 was cut in a plane perpendicular to the Y-axis direction (short direction) of the laminate separator sheet 11 (along the longitudinal direction of the laminate separator sheet 11). The thickness (A)L1 of the laminate separator sheet 11 was measured at five arbitrary positions in the X-axis direction (longitudinal direction) of the laminate separator sheet 11. The thickness variation (MD) was measured using the following formula (iii). The results are shown in Tables 1 and 2.

[0102] Formula (iii): Thickness variation (MD) = [(Lc3 - Lc2) / Lc1] × 100 In formula (iii), Lc1 represents the length of the laminate separator sheet 11 in the Z-axis direction (thickness direction) before the heat treatment. Since no thermal shrinkage occurs before the heat treatment, Lc1 is constant. After the heat treatment, thermal shrinkage occurs in the thickness direction, resulting in thickness fluctuations. Lc2 represents the minimum length of the laminate separator sheet 11 in the Z-axis direction (thickness direction) after the cooling treatment. Lc3 represents the maximum length of the laminate separator sheet 11 in the Z-axis direction (thickness direction) after the cooling treatment.

[0103] [Table 1]

[0104] [Table 2]

[0105] In Tables 1 and 2, "PP / PE / PP" indicates a three-layer structure in which a second microporous layer 112 containing polypropylene, a first microporous layer 111 containing polyethylene, and a second microporous layer 112 containing polypropylene are laminated in this order.

[0106] [3] Results In Examples 1 to 14, the first microporous layer 111 had a corrugated shape that was undulating along the X-axis direction (longitudinal direction) of the laminate separator sheet 11. Therefore, the thermal shrinkage (MD) of Examples 1 to 14 was less than 4.65%. This indicates that the laminate separator sheet 11, in an open state, is less susceptible to thermal shrinkage in the X-axis direction (longitudinal direction) than conventional laminate separator sheets. Therefore, when the laminate separator sheet 11 is incorporated into a wound secondary battery 1 so that the Y-axis direction (transverse direction) is parallel to the winding axis direction, distortion of the laminate separator sheet 11 in the winding direction (i.e., longitudinal direction) is suppressed compared to the laminate separator sheet 11, even when exposed to a high-temperature environment. In other words, distortion of the laminate separator sheet 11 in the winding axis direction (i.e., transverse direction) due to Poisson's ratio deformation is also suppressed. As a result, it was found that the laminated separator sheets 11 of Examples 1 to 14 were "laminated separator sheets in which thermal shrinkage in the winding axis direction was suppressed when incorporated into a wound secondary battery."

Claims

1. a first microporous layer and a second microporous layer laminated on both main surfaces of the first microporous layer, the first microporous layer comprises polyethylene; the second microporous layer comprises polypropylene; The laminated separator sheet, wherein the first microporous layer has a wavy shape that is undulating in a longitudinal direction of the laminated separator sheet.

2. The amplitude ratio is 6% to 27%; The peak-valley period is 10 μm to 50 μm, Except when the amplitude ratio is 6% to 13% and the peak-valley period is 50 μm, the amplitude ratio indicates a ratio (A / B) of an average value (B) of distances between adjacent peaks and valleys of the corrugated shape in the thickness direction of the laminated separator sheet to a thickness (A) of the laminated separator sheet, 2. The laminate separator sheet according to claim 1, wherein the peak-valley period represents an average value of a plurality of intervals in the longitudinal direction between adjacent peak portions and a plurality of intervals in the longitudinal direction between adjacent valley portions.

3. The laminated separator sheet according to claim 2, except for the case where the amplitude ratio is 23% to 27% and the peak-valley period is 10 μm to 40 μm.

4. The amplitude ratio is 16% to 23%, 3. The laminated separator sheet according to claim 2, wherein the peak-valley period is 10 μm to 15 μm.

5. The laminate separator sheet according to claim 1 , wherein the wavy shape is a periodic wavy undulation along the longitudinal direction.

6. a wound electrode body; An electrolyte; an exterior body that accommodates the wound electrode body and the electrolyte; Equipped with the wound electrode body is formed by winding an electrode laminate around a widthwise direction of a laminated separator sheet as a winding axis, 6. A wound secondary battery, wherein the electrode laminate is formed by stacking the laminate separator sheet according to claim 1, one of a positive electrode sheet and a negative electrode sheet, the laminate separator sheet, and the other of the positive electrode sheet and the negative electrode sheet in this order.

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