Bipolar current collector, bipolar electrode, and bipolar secondary battery

Abstract

To provide a bipolar current collector and a bipolar electrode that achieve both electrical conductivity and adhesiveness without using a conductive material, and a bipolar secondary battery that is low in cost and has good battery characteristics.SOLUTION: A bipolar current collector includes a pair of metal foils and an adhesive layer disposed between opposing surfaces of the pair of metal foils, and at least one of the pair of metal foils has a surface roughness Rz on the opposing surface that is equal to or greater than the thickness of the adhesive layer, and a surface roughness RSm on the opposing surface that is in the range of 15 μm to 1400 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a bipolar current collector, a bipolar electrode, and a bipolar secondary battery. [Background technology]

[0002] A bipolar secondary battery has a structure in which a plurality of bipolar electrodes, each of which includes a current collector, a positive electrode formed on one side of the current collector, and a negative electrode formed on the other side, are stacked so that the negative electrode and the positive electrode face each other. The current collector may be a single conductive metal layer, or a laminate in which a negative electrode current collector and a positive electrode current collector are joined via a conductive adhesive layer.

[0003] Patent Document 1 discloses a bipolar electrode current collector that is laminated with a resin layer containing a conductive material and a polymer material and an ion-blocking layer that suppresses lithium ion permeation. In the bipolar electrode current collector disclosed in Patent Document 1, a particulate or fibrous conductive material that is thicker than the resin layer is used, thereby electrically connecting the resin layer and the ion-blocking layer and reducing electrical resistance in the perpendicular direction. Patent Document 2 also discloses that a negative electrode current collector and a positive electrode current collector are bonded via an adhesive layer, and the adhesive layer contains a conductive filler and a material having a PTC (Positive Temperature Coefficient) characteristic. Patent Document 3 also discloses a bonded assembly of a pair of metal substrates that can be used in lithium-ion batteries, which has a conductive adhesive layer between the pair of metal substrates. In the bonded assembly disclosed in Patent Document 3, the conductive adhesive layer contains a cured product of an acid-modified polyolefin resin having an acid value of less than 20.0 mgKOH / g and a glycidylamine-based epoxy resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-277862 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-317468 [Patent Document 3] Patent No. 7358670 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, when a metal foil used as a negative electrode current collector and a metal foil used as a positive electrode current collector are bonded with an adhesive layer to ensure electrical conductivity, the adhesive layer is made to contain a conductive material. Therefore, when a bipolar current collector is used in which a pair of metal foils are bonded with an adhesive layer, the increase in cost due to the conductive material becomes a problem.

[0006] In view of the above-described circumstances, an object of one embodiment of the present disclosure is to provide a bipolar current collector and a bipolar electrode that achieve both conductivity and adhesion without using a conductive material, and a bipolar secondary battery that is low in cost and has good battery characteristics. [Means for solving the problem]

[0007] The present disclosure, which achieves the above-mentioned objectives, includes the following. <1> A bipolar current collector comprising a pair of metal foils and an adhesive layer disposed between opposing surfaces of the pair of metal foils, wherein at least one of the pair of metal foils has a surface roughness Rz on the opposing surface that is equal to or greater than the thickness of the adhesive layer, and a surface roughness RSm on the opposing surface that is in the range of 15 μm to 1400 μm. <2> <1> a negative electrode active material layer disposed on one surface of the bipolar current collector; and a positive electrode active material layer disposed on the other surface of the bipolar current collector. <3> At least two or more <2> and an electrolyte layer disposed between a negative electrode active material layer of one of the adjacent bipolar electrodes and a positive electrode active material layer of the other of the adjacent bipolar electrodes. [Effects of the Invention]

[0008] In the bipolar current collector, bipolar electrode, and bipolar secondary battery according to an embodiment of the present disclosure, the metal foils are well bonded via an adhesive layer, and electrical conductivity between the pair of metal foils is ensured without using a conductive material, thereby reducing the cost of materials for the bipolar current collector, bipolar electrode, and bipolar secondary battery according to an embodiment of the present disclosure. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a main portion of a bipolar current collector according to an embodiment of the present disclosure. [Figure 2] 1 is a cross-sectional view of a main portion of a bipolar electrode according to an embodiment of the present disclosure. [Figure 3] 1 is a cross-sectional view of a main portion of a bipolar secondary battery according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described. The description is for illustrating the embodiments and is not intended to limit the scope of the present disclosure.

[0011] In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0012] In this specification, when an embodiment is described with reference to drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of components in each drawing are conceptual, and the relative size relationships between components are not limited to these.

[0013] In this specification, each component may contain a plurality of corresponding substances. When referring to the amount of each component in the composition in this embodiment, if a plurality of substances corresponding to each component are present in the composition, the amount refers to the total amount of the plurality of substances present in the composition unless otherwise specified.

[0014] The bipolar current collector of the present disclosure comprises a pair of metal foils and an adhesive layer disposed between opposing surfaces of the pair of metal foils, wherein at least one of the pair of metal foils has a surface roughness Rz on the opposing surface that is equal to or greater than the thickness of the adhesive layer, and a surface roughness RSm on the opposing surface that is in the range of 15 μm to 1400 μm.

[0015] In the bipolar current collector of the present disclosure, the metal foils are bonded well via the adhesive layer without using a conductive material in the adhesive layer, while ensuring conductivity between the pair of metal foils, i.e., in the direction perpendicular to the surfaces of the pair of metal foils. Therefore, the bipolar current collector of the present disclosure can be manufactured at low cost because it does not use a conductive material. The "direction perpendicular to the surfaces" refers to the direction normal to the surfaces of the pair of metal foils. In other words, the "direction perpendicular to the surfaces" can also be referred to as the stacking direction in a laminate in which one metal foil, an adhesive layer, and the other metal foil are stacked in this order, or the thickness direction of the laminate.

[0016] Fig. 1 shows a schematic cross section of a main part of a bipolar current collector according to the present disclosure. As shown in Fig. 1, the bipolar current collector shown as one embodiment includes a pair of metal foils 1a and 1b and an adhesive layer 2 disposed between the pair of metal foils 1a and 1b. In the bipolar current collector shown in this embodiment, the surface roughness Rz of the metal foil 1a on the surface facing the metal foil 1b is equal to or greater than the thickness of the adhesive layer 2, and the surface roughness RSm on the facing surface satisfies the requirements of 15 µm to 1400 µm.

[0017] Here, the surface roughness Rz is the maximum height roughness in accordance with JIS B0601 (2013). Specifically, for metal foils, the surface roughness Rz was measured using a laser microscope (Keyence, VK-X3000) as a measuring device at an arbitrary location on the surface of the metal foil, and the value obtained from the measurement was used. Furthermore, the surface roughness RSm is the element mean length in accordance with JIS B0601 (2013). Specifically, for metal foils, the surface roughness RSm was measured using a laser microscope (Keyence, VK-X3000) as a measuring device at an arbitrary location on the surface of the metal foil, and the value obtained from the measurement was used. The surface roughness Rz and surface roughness RSm of the metal foil can be adjusted to desired values ​​by shot blasting, laser processing, or mechanical processing using a grinder, sander, or the like.

[0018] In the embodiment shown in FIG. 1, the metal foil 1a satisfies the requirements that the surface roughness Rz on the opposing surface is equal to or greater than the thickness of the adhesive layer 2 and that the surface roughness RSm on the opposing surface is 15 μm to 1400 μm. However, like the metal foil 1a, the surface roughness Rz on the opposing surface of the metal foil 1b may also be equal to or greater than the thickness of the adhesive layer 2. However, if the surface roughness Rz on the opposing surface of both the metal foils 1a and 1b is equal to or greater than the thickness of the adhesive layer 2, the profile elements are considered to be located on one of the metal foils 1a and 1b, and the average length of the profile elements in this case is taken as the surface roughness RSm. Even in this case, the metal foil 1a or the metal foil 1b is considered to fall within the requirement that the surface roughness RSm be in the range of 15 μm to 1400 μm.

[0019] As described above, in the bipolar current collector of the present disclosure, the surface roughness Rz of the opposing surface of at least one of the metal foils 1a is equal to or greater than the thickness of the adhesive layer 2, and the surface roughness RSm of the opposing surface is in the range of 15 μm to 1400 μm. Therefore, the pair of metal foils 1a and 1b are electrically connected through the adhesive layer 2, and the pair of metal foils 1a and 1b can be firmly bonded by the adhesive layer 2. If the surface roughness Rz of both of the metal foils 1a and 1b is less than the thickness of the adhesive layer 2, electrical connection between the pair of metal foils 1a and 1b cannot be achieved. Furthermore, even if the surface roughness Rz of one of the metal foils 1a and 1b is equal to or greater than the thickness of the adhesive layer 2, if the surface roughness RSm exceeds 1400 μm, sufficient electrical connection between the pair of metal foils 1a and 1b cannot be achieved. Furthermore, even if the surface roughness Rz of either of the metal foils 1a and 1b is greater than or equal to the thickness of the adhesive layer 2, if the surface roughness RSm is less than 15 μm, the adhesive area between the pair of metal foils 1a and 1b becomes small and sufficient adhesive strength cannot be maintained. For the same reasons as above, RSm is preferably 15 μm to 500 μm, more preferably 15 μm to 300 μm, and even more preferably 15 μm to 200 μm.

[0020] Hereinafter, in the bipolar current collector of the present disclosure, the pair of metal foils 1a and 1b will be referred to as the negative electrode current collector and the positive electrode current collector, respectively, and will be described in further detail.

[0021] [Negative electrode current collector] The negative electrode current collector constituting the bipolar current collector of the present disclosure is not particularly limited, and any negative electrode current collector conventionally used in producing negative electrodes can be used. The material of the negative electrode current collector is not particularly limited, and examples thereof include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel, with Cu being particularly preferred. The thickness of the negative electrode current collector is not particularly limited, and can be, for example, in the range of 0.1 μm to 1 mm. The negative electrode current collector can also be in the form of a strip, such as a foil, a perforated foil, or a mesh.

[0022] [Positive electrode current collector] The positive electrode current collector constituting the bipolar current collector of the present disclosure is not particularly limited, and a positive electrode current collector conventionally used in producing positive electrodes can be used. The material of the negative electrode current collector is not particularly limited, and examples thereof include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel, with Al being particularly preferred. The thickness of the positive electrode current collector is not particularly limited, and can be, for example, in the range of 0.1 μm to 1 mm. The positive electrode current collector can also be in the form of a strip, such as a foil, a perforated foil, or a mesh.

[0023] [Adhesive layer] The adhesive layer constituting the bipolar current collector of the present disclosure is not particularly limited as long as it can bond the negative electrode current collector and the positive electrode current collector, and examples of the adhesive layer include epoxy resin, acrylic resin, cyanoacrylate resin, polyurethane resin, silicone resin, phenolic resin, polyimide resin, vinyl resin, melamine resin, alkyd resin, etc. Furthermore, polyolefin resin and polyester resin having a polar group introduced therein can also be used as the adhesive layer.

[0024] The thickness of the adhesive layer is set to be smaller than the larger of the surface roughness Rz of the negative electrode current collector and the surface roughness Rz of the positive electrode current collector. This allows the negative electrode current collector and the positive electrode current collector to be bonded while being electrically connected. The thickness of the adhesive layer can be, for example, 95% or less, 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, or 65% or less of the larger of the surface roughness Rz of the negative electrode current collector and the surface roughness Rz of the positive electrode current collector. By setting the upper limit of the adhesive layer thickness within this range, the electrical connection between the negative electrode current collector and the positive electrode current collector can be ensured. On the other hand, the thickness of the adhesive layer can be, for example, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, or 80% or more of the larger of the surface roughness Rz of the negative electrode current collector and the surface roughness Rz of the positive electrode current collector. By setting the lower limit of the adhesive layer thickness within this range, the negative electrode current collector and the positive electrode current collector can be more firmly bonded to each other. The thickness of the adhesive layer is preferably 1 μm to 10 μm, and more preferably 1 μm to 5 μm.

[0025] [Bipolar electrode] One embodiment of the bipolar electrode of the present disclosure is shown schematically in Figure 2. As shown in Figure 2, the bipolar electrode of the present disclosure includes a bipolar current collector 5 of the present disclosure, a negative electrode active material layer 6 disposed on one surface of the bipolar current collector 5, and a positive electrode active material layer 7 disposed on the other surface of the bipolar current collector 5.

[0026] In the present disclosure, the negative electrode active material is not particularly limited, and conventionally known materials can be used as appropriate. Examples of the negative electrode active material include carbon materials. Examples of carbon materials include cokes such as petroleum coke, pitch coke, and coal coke; carbon blacks such as carbides of organic compounds, carbon fiber, and acetylene black; and graphites such as artificial graphite and natural graphite. Other examples of the negative electrode active material include conductive polymers, lithium titanate, silicon, and silicon compounds. The above-mentioned materials may be used alone or in combination as the negative electrode active material.

[0027] In the present disclosure, the positive electrode active material may be any of conventionally known materials. Examples of the positive electrode active material include LiCoO, lithium nickel-containing composite oxides, LiMnO, olivine-type lithium iron phosphate, TiS, MnO, MoO, and VO. The positive electrode active material may contain any one of these compounds alone or multiple types.

[0028] The negative electrode active material layer 6 and the positive electrode active material layer 7 can be produced by applying a slurry containing the above-described negative electrode active material and a slurry containing the above-described positive electrode active material to one surface and the other surface, respectively, of the above-described bipolar current collector 5. Each slurry contains a binder, a solvent, and other components in addition to the negative electrode active material or the positive electrode active material.

[0029] [Bipolar secondary battery] A bipolar secondary battery according to the present disclosure includes at least two bipolar electrodes according to the present disclosure and an electrolyte layer disposed between the negative electrode active material layer of one of the adjacent bipolar electrodes and the positive electrode active material layer of the other. As an example, FIG. 3 schematically shows an embodiment of a bipolar secondary battery using the bipolar electrodes shown in FIG. 2. As shown in FIG. 3, the bipolar secondary battery shown as this embodiment includes a plurality of bipolar electrodes 10 each formed by stacking a bipolar current collector 5, a negative electrode active material layer 6, and a positive electrode active material layer 7. In the bipolar secondary battery, the negative electrode active material layer 6 of one bipolar electrode 10 faces the positive electrode active material layer 7 of the other bipolar electrode 10, and an electrolyte layer 11 is disposed between the opposing negative electrode active material layer 6 and positive electrode active material layer 7. In a bipolar secondary battery, as shown in FIG. 3, a plurality of cells are formed by a negative electrode active material layer 6 in one bipolar electrode 10, a positive electrode active material layer 7 in the other bipolar electrode 10, and an electrolyte layer 11 disposed between the negative electrode active material layer 6 and the positive electrode active material layer 7.

[0030] Here, the electrolyte layer 11 contains a solid electrolyte and / or a liquid electrolyte. When the electrolyte layer 11 does not contain a solid electrolyte but contains a liquid electrolyte, the electrolyte layer 11 includes a separator to prevent a short circuit between the negative electrode active material layer 6 and the positive electrode active material layer 7.

[0031] Examples of solid electrolytes include lithium lanthanum zirconate, LiPON, and Li 1+X Al X Ge 2-X Examples of oxide solid electrolytes include (PO4)3, Li-SiO-based glass, and Li-Al-SO-based glass; and sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Si2S-P2S5, Li2S-P2S5-LiI-LiBr, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, and Li2S-P2S5-GeS2.

[0032] Examples of liquid electrolytes include those obtained by dissolving electrolytes such as LiPF6, LiBF4, LiAsF6, Li(CF3SO2)2N, Li(C2F5SO2)2N, LiTaF6, LiClO4, and LiCF3SO3 in a solvent. Examples of solvents include cyclic carbonate solvents such as ethylene carbonate (EC) and propylene carbonate (PC); and chain carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Examples of separators include resin sheets such as polyethylene (PE) and polypropylene (PP). [Example]

[0033] The present disclosure will be described in more detail below using examples, but the technical scope of the present disclosure is not limited to the following examples.

[0034] [Example 1] <Fabrication of bipolar current collector> In this example, a bipolar current collector as shown in Figure 1 was fabricated. First, aluminum foil and copper foil with surface roughnesses of Rz = 4.1 μm and RSm = 197 μm were prepared. The aluminum foil used in this example had its surface roughness altered by processing it with a short-wavelength pulsed laser. The copper foil used in this example was YB foil manufactured by Nippon Denkai Co., Ltd.

[0035] Next, a 3-μm thick polyolefin adhesive was applied to one main surface of the aluminum foil (surface with a surface roughness of 4.1 μm and 197 μm), and the aluminum foil was bonded to the copper foil using a hot roll press. The penetration resistance and peel strength of the bipolar current collector thus obtained were measured. <Penetration resistance> The penetration resistance was measured as follows: The obtained bipolar current collector was punched out to a diameter of 18 mm, and the top and bottom were sandwiched between copper terminals of a resistance measuring instrument to measure the penetration resistance. <Peel strength> The peel strength was measured as follows: The obtained bipolar current collector was cut into a 15 mm width, including the part without the adhesive layer where the aluminum foil and copper foil were not bonded together, and the unbonded aluminum foil and copper foil were gripped from above and below using a T-peel tester, and then pulled up and down to measure the peel strength.

[0036] [Example 2] A bipolar current collector was produced in the same manner as in Example 1 except that an aluminum foil with Rz=4.1 μm and RSm=1393 μm was used, and the penetration resistance and peel strength were measured.

[0037] [Example 3] A bipolar current collector was produced in the same manner as in Example 1 except that an aluminum foil with Rz=4.1 μm and RSm=18 μm was used, and the penetration resistance and peel strength were measured.

[0038] [Comparative Example 1] A bipolar current collector was produced in the same manner as in Example 1 except that an aluminum foil with Rz=1.9 μm and RSm=188 μm was used, and the penetration resistance and peel strength were measured.

[0039] Comparative Example 2 A bipolar current collector was produced in the same manner as in Example 1 except that an aluminum foil with Rz=4.1 μm and RSm=1526 μm was used, and the penetration resistance and peel strength were measured.

[0040] Comparative Example 3 A bipolar current collector was produced in the same manner as in Example 1 except that an aluminum foil with Rz=4.1 μm and RSm=13 μm was used, and the penetration resistance and peel strength were measured.

[0041] [result] The results for Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1. The penetration resistance [%] and peel strength [%] in Table 1 are shown as relative values, with the measured value for Comparative Example 2 being set at 100%.

[0042] [Table 1]

[0043] When the penetration resistance of the bipolar current collector of Comparative Example 1 was measured, the resistance value was so high that it was impossible to measure. Comparing the results of Comparative Example 1 and Example 1, it became clear that conductivity can be ensured by making the surface roughness Rz of at least one of the pair of metal foils equal to or greater than the thickness of the adhesive layer. Furthermore, it became clear that when the surface roughness RSm of at least one of the pair of metal foils is in the range of 15 μm to 1400 μm while ensuring conductivity in this manner, it is possible to achieve extremely low penetration resistance while also achieving excellent peel strength. This can be understood from the fact that Comparative Example 2, in which the surface roughness RSm exceeds 1400 μm, exhibits a high value of penetration resistance, and Comparative Example 3, in which the surface roughness RSm is less than 15 μm, exhibits insufficient peel strength. [Explanation of symbols]

[0044] 1a, 1b...metal foil, 2...adhesive layer, 5...bipolar current collector, 6...negative electrode active material layer, 7...positive electrode active material layer, 10...bipolar electrode, 11...electrolyte layer, 20...cell

Claims

1. A pair of metal foils; an adhesive layer disposed between the opposing surfaces of the pair of metal foils; A bipolar current collector, wherein at least one of the pair of metal foils has a surface roughness Rz on the opposing surface that is equal to or greater than the thickness of the adhesive layer, and a surface roughness RSm on the opposing surface that is in the range of 15 μm to 1400 μm.

2. The bipolar current collector according to claim 1; a negative electrode active material layer disposed on one surface of the bipolar current collector; a positive electrode active material layer disposed on the other surface of the bipolar current collector.

3. At least two or more bipolar electrodes according to claim 2; a bipolar secondary battery comprising: an electrolyte layer disposed between a negative electrode active material layer of one of the adjacent bipolar electrodes and a positive electrode active material layer of the other of the adjacent bipolar electrodes;

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