Battery Cell

Abstract

To provide a battery cell excellent in impregnation of an electrolyte.SOLUTION: A battery cell includes an electrolyte and an electrode body including a separator. The electrode body is a wound electrode body or a laminated electrode body. The separator includes a base material layer and a functional layer formed on the base material layer. When the electrode body is the wound electrode body, a contact angle with the electrolyte on a surface of the separator becomes smaller from an area on an end side toward an area on a central part side in a direction parallel to a winding shaft. When the electrode body is the laminated electrode body, a contact angle with the electrolyte on a surface of the separator becomes smaller from an area on an end side toward an area on a central part side in plan view of the electrode body.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] The electrode assembly included in the battery cell has a laminate with a separator interposed between a positive electrode plate and a negative electrode plate. In order to impregnate the laminate with the electrolyte evenly, Patent Document 1 discloses that a space is provided in the adhesive layer between the electrode plate and the separator for the electrolyte to be impregnated. Patent Document 2 discloses that the affinity between the separator and the electrolyte can be improved by reducing the contact angle between the functional resin layer of the separator and the electrolyte in order to impregnate the laminate with the electrolyte sufficiently and improve the battery characteristics. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2021-163665 A [Patent Document 2] JP 2015-99801 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the invention disclosed in Patent Document 1, when the laminate is pressed, the compression state differs between the space portion and the other portion, resulting in a difference in the distance between the positive electrode plate and the negative electrode plate. When such a difference in distance occurs, metals such as lithium are likely to precipitate. In the invention disclosed in Patent Document 2, since the affinity between the separator and the electrolyte is good, the electrolyte is captured at the edge of the battery cell, and the electrolyte is unlikely to penetrate into the center part, which is located inside the edge of the battery cell.

[0005] An object of the present disclosure is to provide a battery cell with excellent electrolyte impregnation. [Means for solving the problem]

[0006] The present disclosure provides the following battery cell. [1] A battery cell comprising an electrode assembly including a separator and an electrolyte, The electrode body is a wound type electrode body or a laminated type electrode body, The separator has a base layer and a functional layer formed on the base layer, When the electrode body is a wound electrode body, a contact angle of the surface of the separator with the electrolyte decreases from an end region toward a center region in a direction parallel to a winding axis, A battery cell, wherein when the electrode body is a laminated electrode body, a contact angle between the surface of the separator and the electrolyte decreases from an end region toward a central region in a plan view of the electrode body. [2] The surface of the separator has two or more regions having different contact angles, The battery cell according to [1], wherein the absolute value of the difference in contact angle between two adjacent regions among the two or more regions is 4° or more at a temperature of 25°C. [3] The battery cell according to [2], wherein the surface of the separator has a region (a1) in which the contact angle at a temperature of 25° C. is 15° or more, and a region (b1) adjacent to the region (a1) in which the contact angle at a temperature of 25° C. is 20° or less. [4] The surface of the separator is A region (a2) in which the contact angle at a temperature of 25° C. is 15° or more; A region (b2) in which the contact angle at a temperature of 25° C. is 25° or less; and The battery cell according to [2], further comprising a region (c2) adjacent to the region (a2) and the region (b2), the contact angle being 15° or more and 25° or less at a temperature of 25°C. [5] The battery cell according to any one of [1] to [4], wherein the functional layer is an adhesive layer or a heat-resistant layer. [6] The electrode body has an electrode plate including an active material layer, When the electrode body is a wound electrode body, the length of a portion where the length of the active material layer is maximum in a direction parallel to the winding axis is 200 mm or more, The battery cell according to any one of [1] to [5], wherein when the electrode body is a laminated electrode body and the laminated electrode body has a rectangular shape in a planar view, the length of the active material layer in a direction parallel to a long side of the shape of the electrode body in a planar view is 200 mm or more. [7] The battery cell according to any one of [1] to [6], wherein the contact angle is a contact angle between the separator and the electrolyte on the surface of the functional layer. Effect of the Invention

[0007] According to the present disclosure, it is possible to provide a battery cell with excellent electrolyte impregnation. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic plan view showing an example of a separator used in a wound electrode body. [Diagram 2] FIG. 11 is a schematic plan view showing another example of a separator used in a wound electrode body. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] (Battery cell) The battery cell of this embodiment includes an electrode assembly including a separator and an electrolyte. The battery cell may further include a case that contains the electrode assembly and the electrolyte. The battery cell may be used in non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. The electrode assembly is a wound type electrode assembly or a laminated type electrode assembly. The electrode assembly usually includes a positive electrode plate and a negative electrode plate, which are electrode plates in which an active material layer is formed on a current collector. The electrode assembly has a structure in which a separator is sandwiched between a positive electrode active material layer (described later) of the positive electrode plate and a negative electrode active material layer (described later) of the negative electrode plate. The separator has a substrate layer and a functional layer formed on the substrate layer.

[0010] The wound electrode body is a laminate formed by winding a long sheet-like electrode plate and a long sheet-like separator. The laminate is, for example, laminated so that the separator is sandwiched between the positive electrode active material layer of the positive electrode plate and the negative electrode active material layer of the negative electrode plate. The wound electrode body may be a cylindrical electrode body or a flat electrode body. In the wound electrode body, the length of the part where the length of the active material layer is maximum in the direction perpendicular to the direction x parallel to the winding axis (hereinafter also referred to as "winding axis direction x") is preferably 120 mm or less, more preferably 60 mm or more and 120 mm or less, even more preferably 80 mm or more and 110 mm or less, and particularly preferably 90 mm or more and 100 mm or less. In the wound electrode body, the length of the active material layer in the winding axis direction is preferably 150 mm or more, more preferably 200 mm or more, and even more preferably 200 mm or more and 350 mm or less. The length of the active material layer described above may be the length of the negative electrode active material layer or the length of the positive electrode active material layer.

[0011] The laminated electrode body is a laminate of sheet-like electrode plates and sheet-like separators alternately, and can be obtained by laminating a plurality of positive electrode plates, negative electrode plates, and separators, for example, so that the separator is sandwiched between the positive electrode active material layer and the negative electrode active material layer. The planar shape of the laminated electrode body is preferably a quadrangle, more preferably a rectangle or a square. In the laminated electrode body, when the planar shape of the laminated electrode body is a rectangle, the length of the active material layer in the direction parallel to the short side of the planar shape is preferably 120 mm or less, more preferably 60 mm or more and 120 mm or less, even more preferably 80 mm or more and 110 mm or less, and particularly preferably 90 mm or more and 100 mm or less. When the planar shape of the laminated electrode body is a rectangle, the length of the active material layer in the direction parallel to the long side of the planar shape is preferably 150 mm or more, more preferably 200 mm or more, and even more preferably 200 mm or more and 350 mm or less. The length of the active material layer described above may be the length of the negative electrode active material layer or the length of the positive electrode active material layer.

[0012] In a large battery cell having an electrode assembly of the above size, it takes time for the electrolyte to be impregnated. In a large battery cell, by improving the impregnation of the electrode assembly with the electrolyte as described below, the manufacturing efficiency of the battery cell can be further improved.

[0013] (Separator) 1 and 2 are schematic plan views showing an example of a separator used in a wound electrode body. The double-headed arrows shown in FIGS. 1 and 2 indicate the winding axis direction x. The separator 1 has a base layer and a functional layer 11 formed on the base layer. The functional layer 11 can be formed on one or both sides of the base layer. The functional layer 11 may be formed on the entire surface of one or both sides of the base layer, or may be formed on a part of one or both sides, or may be formed discretely. The separator shown in FIGS. 1 and 2 shows a case in which the functional layer 11 is provided on the entire surface of one side of the base layer.

[0014] The substrate layer may be a porous sheet, and is preferably a porous resin sheet. Examples of resin materials constituting the porous resin sheet include polyolefins such as polyethylene (PE) and polypropylene (PP); polyesters such as polyethylene terephthalate and polyethylene naphthalate; cellulose; and polyamide. The substrate layer may have a single-layer structure or a multi-layer structure of two or more layers.

[0015] The functional layer 11 may be an adhesive layer or a heat-resistant layer. The functional layer 11 can be formed, for example, by applying a coating liquid containing a material for forming the functional layer 11 onto a base layer and drying the coating liquid.

[0016] Examples of the adhesive for forming the adhesive layer include hot melt adhesives, ultraviolet curing adhesives, and thermosetting adhesives. Examples of the base resin of the adhesive include one or more resins selected from the group consisting of acrylic resins, urethane resins, ethylene vinyl acetate resins, epoxy resins, and fluororesins. The adhesive layer may be formed of a pressure-bonding adhesive that can be bonded by applying pressure. Since the functional layer 11 is an adhesive layer, the adhesive penetrates into at least one of the base material layer, active material layer, and positive electrode active material layer (anchor effect) by pressing during the manufacture of the electrode body, and the layers constituting the electrode body can be pressure-bonded between each other.

[0017] The heat-resistant layer includes a filler and may further include a binder. Examples of the filler include ceramic particles that are one or more types selected from the group consisting of alumina, boehmite, aluminum hydroxide, silica, magnesia, titania, silicon nitride, and titanium nitride. Examples of the binder include one or more types selected from the group consisting of acrylic binders such as acrylic resins, fluoropolymer binders such as polyvinylidene fluoride, and styrene-butadiene rubber (SBR).

[0018] When the battery cell includes a wound electrode body, the contact angle of the separator 1 surface with the electrolyte (hereinafter also referred to as "contact angle A of the separator 1 surface") decreases from the end region toward the center region in the winding axis direction x. Specifically, the separator 1 surface is divided into two or more regions on the same surface by dividing the side in the winding axis direction x, and the contact angle A of the separator 1 surface in each divided region is constant (the same), and the contact angle A of the separator 1 surface between at least two different adjacent regions is relatively large in the end region and relatively small in the center region. In this way, the contact angle A of the separator 1 surface may be decreased stepwise from the end side toward the center in the winding axis direction x by sufficiently increasing the width of the region divided into two or more, or may be decreased continuously by reducing the width of the region divided into two or more. The end in the winding axis direction x is usually the position where impregnation of the electrolyte begins during the manufacture of the battery cell.

[0019] When the battery cell includes a laminated electrode body, the contact angle A of the separator 1 surface is smaller from the end region toward the center region in the plan view of the electrode body. In the laminated electrode body, the surface of the separator 1 is divided into a plurality of sections from any end toward the center in the plan view of the laminated electrode body, and the contact angle A of the separator 1 surface in each divided section is constant (same). At least the contact angle A of the separator 1 surface between two different adjacent regions is relatively large in the end region and relatively small in the center region. As described in the separator of the wound electrode body, the contact angle A of the separator 1 surface may be decreased stepwise or continuously from the end side toward the center side. In the laminated electrode body, the end where the contact angle A of the separator 1 surface is larger than that of the center side is preferably the end located at the position where the impregnation of the electrolyte begins during the manufacture of the battery cell.

[0020] The contact angle A on the surface of the separator 1 in each of the above-mentioned regions is a value measured at the same temperature, and may be a value measured at a temperature of, for example, 25°C.

[0021] It can be said that the smaller the contact angle A of the separator 1 surface, the better the affinity between the separator 1 surface and the electrolyte. Therefore, in the above-mentioned battery cell, it can be said that the affinity between the separator 1 and the electrolyte is relatively small at the ends, and relatively large at the center. In the battery cell, the electrolyte is injected into a case containing the electrode body, so that the electrolyte is impregnated from the ends of the electrode body. By making the contact angle A of the separator 1 surface smaller from the end side region toward the center side region, the electrolyte that has entered from the ends easily permeates into the center side. This promotes the penetration of the supporting salt and additives contained in the electrolyte into the electrode body, making it possible to provide a battery cell with excellent electrolyte impregnation, and improves the manufacturing efficiency of the battery cell.

[0022] The contact angle A of the separator 1 surface may be the contact angle of the electrolyte on the surface of the functional layer 11 of the separator 1. For example, in a separator in which the functional layer 11 is formed on the entire surface of the substrate layer, the contact angle A of the separator 1 surface is the contact angle of the electrolyte on the surface of the functional layer 11. In a separator in which the functional layer 11 is partially provided on the substrate layer, the contact angle A of the separator 1 surface is the contact angle of the electrolyte on the substrate layer surface or the functional layer 11 surface.

[0023] The surface of the separator 1 preferably has two or more regions with different contact angles A. The absolute value of the difference in the contact angle A on the separator 1 surface between two adjacent regions among the two or more regions is preferably 4° or more, more preferably 5° or more, may be 6° or more, and is usually 20° or less, at a temperature of 25°C. By making the absolute value of the difference in the contact angle A on the separator 1 surface 4° or more, the electrolyte can be efficiently permeated from the region with the relatively large contact angle A to the region with the relatively small contact angle A. The separator 1 may include one or more adjacent regions on the same surface in which the difference in the contact angle A is within the above range, and may include two or more. The contact angle A on the separator 1 surface is calculated by the θ / 2 method using an automatic contact angle meter to determine the angle between the droplet on the separator 1 and the separator 1 surface one second after a droplet of electrolyte is dropped on the separator 1 surface.

[0024] The surface of the separator 1 may have a region (a1) in which the absolute value of the difference in contact angle A between two adjacent regions is 4° or more at a temperature of 25° C., and the contact angle A (hereinafter also referred to as “contact angle A(25)”) of the surface of the separator 1 at a temperature of 25° C. is 15° or more, and a region (b1) adjacent to the region (a1) and in which the contact angle A(25) is 25° or less. The contact angle A(25) of the region (a1) may be 16° or more, 18° or more, or 20° or more. The contact angle A(25) of the region (b1) may be 22° or less, 20° or less, or 18° or less. In this case, the region (a1) is a region closer to the end of the electrode body than the region (b1). Since the absolute value of the difference in contact angle A(25) between the region (a1) and the region (b1) is 4° or more, the electrolyte can be efficiently permeated from the region (a1) to the region (b1). When the surface of the separator 1 has a combination of the region (a1) and the region (b1), the surface may have one or more of such combinations. When the surface of the separator 1 has two or more of such combinations, the combinations of the contact angles A(25) of the respective combinations may be the same or different from each other.

[0025] The surface of the separator 1 may have a region (a2) in which the absolute value of the difference in contact angle A(25) between two adjacent regions is 4° or more, and the contact angle A(25) is 15° or more, a region (b2) in which the contact angle A(25) is 25° or less, and a region (c2) adjacent to the regions (a2) and (b2) and in which the contact angle A(25) is 15° or more and 25° or less. The contact angle A(25) of the region (a2) may be 18° or more, 20° or more, or 25° or more. The contact angle A(25) of the region (b2) may be 20° or less, 16° or less, or 14° or less. The contact angle A(25) of the region (c2) may be 16° or more and 23° or less, 17° or more and 22° or less, or 18° or more and 21° or less. In this case, the region (a2), the region (c2), and the region (b2) are arranged in this order from the end side to the center side of the electrode body. Since the absolute value of the difference in contact angle A (25) between each region is 4° or more, the electrolyte can efficiently permeate from the region (a2) through the region (c2) to the region (b2). When the surface of the separator 1 has a combination of the region (a2), the region (c2), and the region (b2), it may have one set of the combination, or two or more sets. When it has two or more sets of the combination, the combinations of the contact angles A (25) of each set may be the same or different from each other.

[0026] For example, in a wound electrode body, it is preferable to make the contact angle A of the separator 1 surface relatively large in the regions at both ends of the winding axis, and to make the contact angle A of the separator 1 surface relatively small toward the central region between these end regions. Specifically, as shown in Figures 1 and 2, it is preferable to divide the separator 1 surface into four (Figure 1) or five (Figure 2) along the winding axis direction x, and to make the contact angle A of the separator 1 surface smaller from the regions at both ends toward the central region along the winding axis direction x. Each region may be equally divided or unequal divided along the winding axis direction x.

[0027] As shown in Fig. 1, for example, in the surface of the functional layer 11 formed on the entire surface of the base material layer, two regions located at both ends of the winding axis may be defined as regions (a1), and two central regions adjacent to each region (a1) may be defined as regions (b1). The contact angle A of the separator 1 surface of the two regions (a1) and the contact angle A of the separator 1 surface of the two regions (b1) may be the same or different. When the contact angle A of the separator 1 surface of the two regions (b1) is the same, the two adjacent regions (b1) are not distinguished from each other by the difference in the contact angle A of the separator 1 surface, and therefore the surface of the functional layer 11 is divided into three regions (two regions (a1) and one region (b1)).

[0028] 2, for example, on the surface of functional layer 11 formed on the entire surface of the base layer, two regions located at both ends of the winding axis may be region (a2), one region located at the center in the winding axis direction x may be region (b2), and the (two) regions between region (a2) and region (b2) may be region (c2). The contact angle A of the separator 1 surface of the two regions (a2) and the contact angle A of the separator 1 surface of the two regions (c2) may be the same or different.

[0029] The separator included in the wound electrode body has been described above, but the separator included in the laminated electrode body may also be divided into two or more regions on the surface of the separator 1 from the end region including a pair of opposing sides in a plan view of the electrode body toward the center region. Each region may be equally divided or unequal. The number of regions on the surface of the separator 1 formed so that the contact angle A of the separator 1 surface differs between adjacent regions may be two or more, and may be three, four, or five as described based on Figures 1 and 2, or may be six or more.

[0030] The contact angle A of the separator 1 surface can be adjusted by, for example, one or more of the following: the type of base layer, surface modification of the base layer by corona discharge treatment or the like, the type and polymerization degree of the resin such as the adhesive or binder contained in the functional layer 11, the diameter and packing density of the filler, surface modification of the functional layer 11 by corona discharge treatment or the like, and the type of electrolyte. When impregnating the electrode body with the electrolyte, the separator may be heated. This reduces the viscosity of the electrolyte in contact with the separator and reduces the contact angle between the surface of the functional layer 11 and the electrolyte, thereby improving the impregnation of the electrolyte into the electrode body.

[0031] (electrolyte) The electrolyte may be a non-aqueous electrolyte, for example, a non-aqueous solvent such as an organic solvent containing a supporting salt. The electrolyte may further contain one or more additives selected from the group consisting of vinylene carbonate (VC), cyclohexylbenzene (CHB), and modified forms of CHB, in order to form a good coating on the surface of the negative electrode active material layer and / or the positive electrode active material layer, or to ensure stability during overcharging.

[0032] Examples of the non-aqueous solvent include one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), γ-butyrolactone (γ-BL), sulfolane, acetonitrile, 1,2-dimethoxyethane (DME), 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0033] Examples of supporting salts include one or more selected from the group consisting of lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium borofluoride (LiBF4), lithium arsenic hexafluoride (LiAsF6), lithium trifluoromethansulfonate (LiCF3SO3), and lithium bistrifluoromethylsulfonylimide [LiN(CF3SO2)2].

[0034] (Positive plate) The positive electrode plate usually has a positive electrode current collector and a positive electrode active material layer (active material layer) formed on the positive electrode current collector. The positive electrode current collector is, for example, a metal foil made of an aluminum material such as aluminum or an aluminum alloy. The positive electrode active material layer contains a positive electrode active material, and may further contain a binder and a conductive assistant.

[0035] Known materials can be used as the positive electrode active material, and lithium transition metal oxides such as layered or spinel-based oxides (e.g., LiNiCoMnO2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 O4, LiCrMnO4, LiFePO4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2) are examples.

[0036] Examples of the binder include styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE). Examples of the conductive assistant include carbon materials such as fibrous carbon, carbon black (acetylene black, ketjen black, etc.), coke, and activated carbon. Examples of the fibrous carbon include carbon nanotubes (hereinafter also referred to as "CNTs"). The CNTs may be single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes such as double-walled carbon tubes (DWCNTs).

[0037] (Negative plate) A negative electrode plate usually has a negative electrode active material layer (active material layer) on one or both sides of a negative electrode current collector. The negative electrode current collector is, for example, a metal foil made of a copper material such as copper or a copper alloy. The negative electrode active material layer contains a negative electrode active material and may further contain a binder, a conductive assistant, and the like.

[0038] The negative electrode active material may be a known material, and examples of the material include graphite such as artificial graphite or natural graphite, amorphous coated graphite obtained by coating the graphite with amorphous carbon, hard carbon, soft carbon, and other carbon-based active materials containing carbon (C) atoms; and metal-based active materials containing metal elements such as metal simple substances or metal oxides containing elements selected from the group consisting of silicon (Si), tin (Sn), antimony (Sb), bismuth (Bi), titanium (Ti), and germanium (Ge). Examples of the Si-based active materials containing silicon elements include silicon simple substance, SiOx, LixSiyOz, and the like.

[0039] Examples of the binder include cellulose-based binders such as carboxymethyl cellulose (CMC), methyl cellulose (MC), and hydroxypropyl cellulose; styrene butadiene rubber (SBR), polyacrylic acid (PAA), acrylonitrile butadiene rubber (NBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE). CMC and PAA may be in the form of an acid or a salt.

[0040] Examples of the conductive assistant include carbon materials such as fibrous carbon, carbon black (for example, acetylene black, ketjen black), coke, activated carbon, etc. Examples of the fibrous carbon include those described above. EXAMPLES

[0041] The present disclosure will be described more specifically below with reference to examples and comparative examples. [Comparative Examples 1 to 4, Examples 1 to 7] (Preparation of separator) Each separator had a size of 10 cm in length and 20 cm in width, and a functional layer was formed on the entire surface of the substrate layer.

[0042] In Comparative Examples 1 to 3, a functional layer was formed on the entire surface of the substrate layer so that the contact angle with the electrolyte on the separator surface was a value shown in category (1) in Table 1, to prepare a separator.

[0043] In Comparative Example 4 and Examples 1 to 4, separators were prepared by forming a functional layer on the same surface of the base layer so that the contact angle with the electrolyte on the separator surface had the values ​​shown in sections (1) and (2) in Table 1. The separators in Comparative Example 4 and Examples 1 to 4 had sections (1) and (2) that divided their lateral length in half, and the magnitude of the contact angle changed stepwise in this order.

[0044] In Examples 5 to 7, separators were prepared by forming a functional layer on the same surface of the substrate layer so that the contact angle with the electrolyte on the separator surface was the value shown in sections (1) to (3) in Table 1. The separator of Example 5 had sections (1) to (3) that divided its horizontal length into three equal parts, but because sections (2) and (3) had the same contact angle, the contact angle did not change between sections (2) and (3), and the contact angle changed stepwise between sections (1) and (2). The separators of Examples 6 and 7 had sections (1) to (3) that divided its horizontal length into three equal parts, and the contact angle changed stepwise in this order.

[0045] (Preparation of electrode body) A stack was obtained by stacking separator / positive plate / separator / negative plate / separator / positive plate / separator / negative plate / separator in this order using positive and negative plate and separator with a length of 10 cm and a width of 20 cm and the separator prepared above. The stack was pressed with a pressure of 100 kN to obtain a sample electrode body.

[0046] (Preparation of electrolyte) An electrolyte solution was prepared by adding 1.1 mol / kg of lithium hexafluorophosphate (LiPF6) as a supporting salt to a non-aqueous solvent mixture of ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 3: 3: 4 (volume ratio).

[0047] [Contact angle measurement] One second after a droplet of the electrolyte prepared above was dropped onto the separator surface (functional layer surface), the angle between the droplet on the separator surface and the separator surface was calculated by the θ / 2 method using an automatic contact angle meter (manufactured by Kyowa Interface Science Co., Ltd.), and this was taken as the contact angle. The results are shown in Table 1.

[0048] [Measurement of electrolyte soaking time] Both sides (separator sides) of the electrode sample were sandwiched between acrylic plates to obtain a laminated structure. The laminated structure was placed in a case placed on a flat surface so that the separator faces were perpendicular to the plane and the long side of the sample in plan view was parallel to the plane. The electrolyte prepared above was dripped at a drip rate of 5 cc / sec for 10 seconds along the side of the case at the end (short side in plan view of the sample) of the laminated structure where the separator (functional layer) surface in Table 1 is located. The moment the electrolyte contacted the sample was defined as the impregnation start time (0 seconds), and the time until the electrolyte reached a position 20 cm from the end in the horizontal direction of the sample was measured, and this was defined as the electrolyte impregnation time [seconds]. The results are shown in Table 1.

[0049] [Table 1] [Explanation of symbols]

[0050] 1 separator, 11 functional layers.

Claims

1. A battery cell including an electrode assembly including a separator and an electrolyte, The electrode body is a wound type electrode body or a laminated type electrode body, The separator has a base layer and a functional layer formed on the base layer, When the electrode body is a wound electrode body, a contact angle of the surface of the separator with the electrolyte decreases from an end region toward a center region in a direction parallel to a winding axis, When the electrode body is a laminated electrode body, a contact angle of the surface of the separator with the electrolyte decreases from an end region at a position where impregnation of the electrolyte starts toward a center region in a plan view of the electrode body, the surface of the separator has two or more regions having different contact angles, an absolute value of the difference in contact angle between two adjacent regions among the two or more regions is 4° or more at a temperature of 25° C.; the surface of the separator has a region (a1) in which the contact angle at a temperature of 25° C. is 15° or more, and a region (b1) adjacent to the region (a1) in which the contact angle at a temperature of 25° C. is 25° or less, A battery cell, wherein the contact angle is a contact angle between the electrolyte and the surface of the functional layer of the separator.

2. A battery cell including an electrode assembly including a separator and an electrolyte, The electrode body is a wound type electrode body or a laminated type electrode body, The separator has a base layer and a functional layer formed on the base layer, When the electrode body is a wound electrode body, a contact angle of the surface of the separator with the electrolyte decreases from an end region toward a center region in a direction parallel to a winding axis, When the electrode body is a laminated electrode body, a contact angle of the surface of the separator with the electrolyte decreases from an end region at a position where impregnation of the electrolyte starts toward a center region in a plan view of the electrode body, the surface of the separator has two or more regions having different contact angles, an absolute value of the difference in contact angle between two adjacent regions among the two or more regions is 4° or more at a temperature of 25° C.; The surface of the separator is A region (a2) in which the contact angle at a temperature of 25° C. is 15° or more; A region (b2) in which the contact angle at a temperature of 25° C. is 25° or less; and The battery cell has a region (c2) adjacent to the region (a2) and the region (b2), and the contact angle at a temperature of 25° C. is 15° or more and 25° or less.

3. The battery cell according to claim 2 , wherein the contact angle is a contact angle between the separator and the electrolyte on the surface of the functional layer.

4. The battery cell according to claim 1 , wherein the functional layer is an adhesive layer or a heat-resistant layer.

5. The electrode assembly has an electrode plate including an active material layer, When the electrode body is a wound electrode body, the length of a portion where the length of the active material layer is maximum in a direction parallel to the winding axis is 200 mm or more, The battery cell according to any one of claims 1 to 3, wherein when the electrode body is a laminated electrode body and the laminated electrode body has a rectangular shape in a planar view, a length of the active material layer in a direction parallel to a long side of the shape of the electrode body in a planar view is 200 mm or more.

6. The electrode assembly has an electrode plate including an active material layer, When the electrode body is a wound electrode body, the length of a portion where the length of the active material layer is maximum in a direction parallel to the winding axis is 200 mm or more, 5. The battery cell according to claim 4, wherein when the electrode body is a laminated electrode body and the laminated electrode body has a rectangular shape in a planar view, the length of the active material layer in a direction parallel to a long side of the planar shape of the electrode body is 200 mm or more.

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