Method for manufacturing bipolar electrode, and bipolar electrode

Abstract

To reduce metal usage.SOLUTION: A method for manufacturing a bipolar electrode includes the steps of (a) forming a first carbon film on a sheet-like support material, (b) forming a conductive resin layer on the first carbon film, (c) forming a second carbon film on the conductive resin layer, (d) forming a second electrode layer on the second carbon film, (e) separating the support material from the first carbon film, and (f) forming a first electrode layer on the first carbon film to manufacture a bipolar electrode.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a bipolar electrode and a bipolar electrode.

Background Art

[0002] Japanese Patent Application Laid-Open No. 2023-053669 discloses a bipolar electrode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, the current collector of a bipolar electrode has been manufactured by laminating two types of metal foils. For example, from the viewpoint of effective utilization of resources and the like, reduction of the amount of metal used is desired.

[0005] An object of the present disclosure is to reduce the amount of metal used.

Means for Solving the Problems

[0006] 1. A method for manufacturing a bipolar electrode includes the following (a) to (f). (a) Form a first carbon film on a sheet-like support. (b) Form a conductive resin layer on the first carbon film. (c) Form a second carbon film on the conductive resin layer. (d) Form a second electrode layer on the second carbon film. (e) Separate the support from the first carbon film. (f) Manufacture a bipolar electrode by forming a first electrode layer on the first carbon film. The above (d), (e), and (f) are performed in this order.

[0007] By using a conductive resin layer as the current collector instead of a metal foil, the amount of metal used can be significantly reduced. However, generally, since the conductive resin layer is difficult to be a self-supporting layer, it is difficult to form an electrode layer on the conductive resin layer. Therefore, a support material is used. A conductive resin layer is formed on the support material. By forming one electrode layer on one side of the conductive resin layer, the conductive resin layer and the electrode layer can form a self-supporting layer as a whole. After the formation of the self-supporting layer, the support material is separated. After the separation of the support material, the other electrode layer is formed on the back surface of the conductive resin layer. The conductive resin layer can exhibit sufficient electron conductivity in the thickness direction. However, the conductive resin layer tends to be poor in electron conductivity in the plane direction. Therefore, by forming carbon films on both sides of the conductive resin layer, improvement in electron conductivity in the plane direction is expected.

[0008] 2. The method for manufacturing a bipolar electrode described in the above "1" may include, for example, the following configuration. The support material contains a fluororesin.

[0009] Fluororesins tend to have excellent releasability (non-stickiness). By the support material containing a fluororesin, it is expected that the separation of the support material becomes easy.

[0010] 3. The method for manufacturing a bipolar electrode described in the above "1" or "2" may include, for example, the following configuration. The first electrode layer is a positive electrode layer. The second electrode layer is a negative electrode layer.

[0011] Generally, the negative electrode layer has a larger area than the positive electrode layer. By forming the negative electrode layer first, for example, improvement in handleability is expected during the formation of the positive electrode layer.

[0012] 4. The bipolar electrode includes, in this order in the thickness direction, a positive electrode layer, a first carbon film, a conductive resin layer, a second carbon film, and a negative electrode layer.

[0013] 5. The bipolar electrode described in the above "4" may include, for example, the following configuration. The conductive resin layer has a larger area than each of the first electrode layer, the first carbon film, the second carbon film, and the second electrode layer. The conductive resin layer extends so as to cover the side surface of the first carbon film.

[0014] Since the conductive resin layer has the maximum area, in the bipolar battery, the conductive resin layer can be in direct contact with the sealing material. For example, compared with the case where the carbon film is interposed between the conductive resin layer and the sealing material, the direct contact of the conductive resin layer with the sealing material is expected to improve the sealing performance.

[0015] Hereinafter, embodiments of the present disclosure (hereinafter may be abbreviated as "the present embodiment"), and examples of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the present example do not limit the technical scope of the present disclosure. The present embodiment and the present example are illustrative in all respects. The present embodiment and the present example are non-limiting. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the description of the claims. For example, any configuration is extracted from the present embodiment and their arbitrary combinations are also initially planned.

[0016] Geometric terms (such as parallel, perpendicular, orthogonal, etc.) should not be construed in a strict sense. For example, "parallel" may deviate slightly from "parallel" in the strict sense. Geometric terms may include, for example, tolerances, errors, etc. in design, operation, manufacturing, etc. The dimensional relationships in each figure may not match the actual dimensional relationships. The dimensional relationships in each figure may be changed to assist the reader's understanding. For example, the length, width, thickness, etc. may be changed. Some configurations may be omitted.

[0017] A numerical range such as "from m to n%" includes the upper limit value and the lower limit value unless otherwise specified. "From m to n%" indicates a numerical range of "m% or more and n% or less". "m% or more and n% or less" includes "more than m% and less than n%".

Brief Description of the Drawings

[0018]

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Embodiments for Carrying Out the Invention

[0019] <Method for Manufacturing a Bipolar Electrode> Figure 1 is a schematic flowchart of the method for manufacturing a bipolar electrode according to the present embodiment. Hereinafter, the "method for manufacturing a bipolar electrode according to the present embodiment" may be abbreviated as the "present manufacturing method". The present manufacturing method includes "(a) formation of a first carbon film", "(b) formation of a conductive resin layer", "(c) formation of a second carbon film", "(d) formation of a second electrode layer", "(e) separation of a support material", and "(f) formation of a first electrode layer". (d) to (f) are performed in this order. Each step may be carried out, for example, by a roll-to-roll method. Unless otherwise specified, the order of each step is arbitrary. For example, the three steps (a), (b), and (c) may be performed simultaneously.

[0020] In the present manufacturing method, the terms "first" and "second" are simply used to distinguish two elements. The terms "first" and "second" do not include, for example, the concept of order. For example, "on the support material" means "on the surface of the support material". The term "on" has nothing to do with the up and down in the vertical direction.

[0021] ·(a) Formation of a first carbon film Figure 2 is a first schematic cross-sectional view showing the manufacturing process of the bipolar electrode. The present manufacturing method includes forming a first carbon film 11 on a sheet-like support material 5.

[0022] The support material 5 has an arbitrary thickness. The thickness of the support material 5 may be, for example, from 0.1 to 2 mm. The support material 5 may have releasability. The support material may contain, for example, a fluororesin or the like. The support material 5 may contain at least one selected from the group consisting of polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polyvinylidene difluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), and chlorotrifluoroethylene-ethylene copolymer (ECTFE).

[0023] The support 5 may have releasability throughout or may have releasability in part. For example, by coating a component having releasability on the surface of an arbitrary substrate, releasability may be imparted to the surface of the substrate. The component having releasability may contain, for example, silicone or the like.

[0024] For example, a first carbon film 11 may be formed by coating a first dispersion liquid on the surface of the support 5. The first dispersion liquid may contain, for example, a first carbon material, a binder, and a dispersion medium. The coating method is arbitrary. For example, a gravure coater, a die coater, or the like may be used. The coating film may be formed continuously or intermittently. In FIG. 2, as an example, the coating film is formed intermittently. For example, the coating film may be dried in a drying furnace. The same applies to the formation methods (coating method, drying method) of the subsequent second carbon film 12 and various layers.

[0025] The thickness of the first carbon film 11 may be, for example, from 0.1 to 3 μm. For example, the first carbon film 11 may contain, by mass fraction, 50% or more of the first carbon material and the balance of the binder. The mass fraction of the first carbon material may be, for example, from 75 to 99% or from 80 to 95%. The first carbon material has electronic conductivity. The first carbon material may contain at least one selected from the group consisting of acetylene black (AB), graphite, vapor-grown carbon fiber (VGCF), graphene flake (GF), carbon nanotube (CNT), carbon nanofiber (CNF), and carbon nanosphere (CNS). The binder may contain at least one selected from the group consisting of PVDF, PTFE, carboxymethyl cellulose (CMC), and polyacrylic acid (PAA).

[0026] ·(b) Formation of the conductive resin layer FIG. 3 is a second schematic cross-sectional view showing the manufacturing process of the bipolar electrode. This manufacturing method includes forming a conductive resin layer 10 on the first carbon film 11. For example, the conductive resin layer 10 may be formed by coating a conductive adhesive on the surface of the first carbon film 11. The conductive resin layer 10 may be continuously coated, for example. The conductive adhesive may be a one-component type or a two-component type. The conductive adhesive may include, for example, a main agent, a curing agent, and a conductive filler. The main agent may include, for example, an olefin-based resin or the like. The curing agent may include, for example, a compound having an isocyanate group or the like.

[0027] The thickness of the conductive resin layer 10 may be, for example, 1 to 100 μm, 1 to 50 μm, 1 to 30 μm, 1 to 10 μm, or 1 to 5 μm. The conductive resin layer 10 has electronic conductivity. The conductive resin layer 10 may include, for example, a resin material and a conductive filler. For example, the conductive resin layer 10 may include a conductive filler in a mass fraction of 1 to 99% and the balance of the resin material. The mass fraction of the conductive filler may be, for example, 5 to 50% or 10 to 30%.

[0028] In the conductive resin layer 10, the resin material forms a continuous phase. The resin material may have resistance to the electrolytic solution. The resin material may be insoluble in the electrolytic solution. The resin material may include, for example, at least one selected from the group consisting of an olefin-based resin, a urethane-based resin, a polyamide-based resin, a cellulose-based resin, a polyether-based resin, an acrylic-based resin, an epoxy-based resin, and a polyester-based resin. The resin material may have, for example, a hydroxyl group. When the resin material has a hydroxyl group, a hydrogen bond can be formed with the sealing material 40 described later. The formation of the hydrogen bond is expected to improve the sealing performance.

[0029] In the conductive resin layer 10, the conductive filler forms a dispersed phase. The conductive filler is a conductive component. The conductive filler may include, for example, carbon particles, metal particles, metal-plated particles, etc. The core of the metal-plated particles may be solid or hollow resin particles. The conductive filler may include at least one selected from the group consisting of, for example, AB, graphite, VGCF, CNT, CNF, CNS, Ni particles, Ni-plated particles, Cu particles, and Cu-plated particles. The particle shape of the conductive filler is arbitrary. The conductive filler may be, for example, spherical, flaky, rod-shaped, needle-shaped, fibrous, etc. The particle diameter of the conductive filler may be, for example, from 0.1 to 10 μm, from 0.5 to 5 μm, or from 1 to 3 μm. The "particle diameter" indicates the average value of the maximum Feret diameter in the particle image. The average value is calculated from the measurement results of 10 times or more.

[0030] ·(c) Formation of the second carbon film FIG. 4 is a third schematic cross-sectional view showing the manufacturing process of the bipolar electrode. This manufacturing method includes forming a second carbon film 12 on the conductive resin layer 10. The second carbon film 12 can be formed in the same manner as the first carbon film 11. The composition and dimensions may be the same or different between the second carbon film 12 and the first carbon film 11. The composition and dimensions of the second carbon film 12 may be selected and adjusted, for example, within the range of the description given above as the composition and dimensions of the first carbon film 11.

[0031] ·(d) Formation of the second electrode layer FIG. 5 is a fourth schematic cross-sectional view showing the manufacturing process of the bipolar electrode. This manufacturing method includes forming a second electrode layer 22 on the second carbon film 12. For example, the second electrode layer 22 can be formed by coating a second electrode composite paste on the surface of the second carbon film 12. The second electrode composite paste may include, for example, a second electrode composite and a dispersion medium. After the formation of the second electrode layer 22 (after drying of the second electrode composite paste), the whole workpiece may be compressed. The compression of the workpiece may also be after the formation of the first electrode layer 21 described later.

[0032] ·(e) Separation of the support material FIG. 6 is a fifth schematic cross-sectional view showing the manufacturing process of the bipolar electrode. This manufacturing method includes separating the support material 5 from the first carbon film 11. The support material 5 may be peeled off by an external force, for example. In order to form a trigger for peeling, a jig such as a scraper may be used, for example. Since the support material 5 has releasability, it is expected that the peeling of the support material 5 is promoted. The recovered support material 5 can be reused.

[0033] ·(f) Formation of the first electrode layer FIG. 7 is a sixth schematic cross-sectional view showing the manufacturing process of the bipolar electrode. This manufacturing method includes manufacturing the bipolar electrode 20 by forming the first electrode layer 21 on the first carbon film 11. For example, the first electrode layer 21 can be formed by coating the surface of the first carbon film 11 with the first electrode composite paste. The first electrode composite paste may include, for example, a first electrode composite and a dispersion medium.

[0034] The first electrode layer 21 may be formed to have a smaller area than the second electrode layer 22. The first electrode layer 21 has a different polarity from the second electrode layer 22. For example, the first electrode layer 21 may be a positive electrode layer and the second electrode layer 22 may be a negative electrode layer. For example, the first electrode layer 21 may be a negative electrode layer and the second electrode layer 22 may be a positive electrode layer. The positive electrode layer contains a positive electrode active material. The positive electrode active material may include, for example, lithium nickel composite oxide, lithium iron phosphate, etc. The negative electrode layer contains a negative electrode active material. The negative electrode active material may include, for example, graphite, silicon oxide, silicon, etc. Each of the positive electrode layer and the negative electrode layer may further include a conductive material and a binder. The positive electrode layer and the negative electrode layer may independently include AB, PVDF, CMC, SBR, etc.

[0035] After the formation of the first electrode layer 21, the bipolar electrode 20 may be compressed. After compression, the thicknesses of the first electrode layer 21 and the second electrode layer 22 may be, for example, 10 to 500 μm, 50 to 300 μm, or 100 to 200 μm, respectively. The bipolar electrode 20 (original sheet) may be cut according to the battery specifications. The dashed-dotted line in FIG. 7 is an example of a cutting line.

[0036] <Bipolar electrode> FIG. 8 is a first schematic cross-sectional view showing an example of the bipolar electrode in the present embodiment. The bipolar electrode 20 has a thickness direction (Z direction). The bipolar electrode 20 includes, in the thickness direction, a first electrode layer 21, a first carbon film 11, a conductive resin layer 10, a second carbon film 12, and a second electrode layer 22 in this order. The conductive resin layer 10 functions as an electrode current collector. The conductive resin layer 10 may have a larger area than each of the first electrode layer 21, the first carbon film 11, the second carbon film 12, and the second electrode layer 22. The conductive resin layer 10 may have an area that is, for example, 1.01 to 1.5 times, 1.05 to 1.25 times, or 1.1 to 1.2 times the area of each of the other components (such as the first electrode layer 21, etc.).

[0037] The conductive resin layer 10 may extend so as to cover the side surface of the first carbon film 11. In the XY plane, the conductive resin layer 10 may include a peripheral portion 10a that extends outside each film and each layer. The peripheral portion 10a may be flush with the first carbon film 11. For example, the bipolar electrode 20 in FIG. 8 can be formed by forming the first carbon film 11, etc. by intermittent coating.

[0038] FIG. 9 is a second schematic cross-sectional view showing an example of the bipolar electrode in the present embodiment. For example, each of the first carbon film 11 and the second carbon film 12 may extend so as to cover the peripheral portion 10a of the conductive resin layer 10. For example, the bipolar electrode 20 in FIG. 9 can be formed by forming the first carbon film 11 and the second carbon film 12 by continuous coating.

[0039] In the bipolar electrode 20, the resistance of the components other than the first electrode layer 21 and the second electrode layer 22 when electrons flow in the thickness direction can also be referred to as "through - resistance". For example, in FIG. 9, the through - resistance is the resistance between the first carbon film 11 and the second carbon film 12. The through - resistance may be, for example, 150 mΩ or less. The through - resistance may be, for example, 100 mΩ or less, or 80 mΩ or less. The through - resistance may be, for example, 10 mΩ or more, or 50 mΩ or more.

[0040] <Bipolar battery> FIG. 10 is a schematic cross - sectional view showing an example of the bipolar battery in the present embodiment. The bipolar battery 100 includes a plurality of bipolar electrodes 20, an electrolyte (not shown), and a sealing material 40. The bipolar battery 100 may include, for example, an exterior body (not shown). The exterior body may house the bipolar electrodes 20 and the electrolyte. The exterior body may be, for example, a pouch made of a metal foil laminate film, a metal case, or the like.

[0041] The electrolyte is a liquid electrolyte. The electrolyte may include, for example, a supporting salt and a solvent. The supporting salt may include, for example, LiPF6 or the like. The solvent may include, for example, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, or the like. The electrolyte may further include an arbitrary additive.

[0042] The plurality of bipolar electrodes 20 are laminated in the thickness direction (Z - direction). The bipolar battery 100 may further include a separator 30. The separator 30 is disposed between the first electrode layer 21 and the second electrode layer 22. The separator 30 separates the first electrode layer 21 from the second electrode layer 22. The separator 30 may include, for example, a porous film made of resin or the like.

[0043] At the peripheral portion 10a of the bipolar electrode 20, the sealing material 40 seals between two adjacent conductive resin layers 10. The conductive resin layer 10 may be in direct contact with the sealing material 40. For example, by using the bipolar electrode 20 of FIG. 8, the conductive resin layer 10 can be in direct contact with the sealing material 40. When the conductive resin layer 10 is in direct contact with the sealing material 40, for example, an improvement in sealing performance is expected.

[0044] In the XY plane, the sealing material 40 surrounds the periphery of the first electrode layer 21 and the second electrode layer 22. The sealing material 40 may include, for example, a first sealing material 41 (primary sealing) and a second sealing material 42 (secondary sealing). The first sealing material 41 may seal between adjacent conductive resin layers 10. The second sealing material 42 may further seal the outside of the first sealing material 41. The sealing material 40 includes, for example, a resin material. The sealing material may include, for example, at least one selected from the group consisting of polypropylene, polyphenylene sulfide, and modified polyphenylene ether. The second sealing material 42 may be the same material as the first sealing material 41 or a different material.

[0045] The "primary sealing performance" indicates the peel strength between the first sealing material 41 and the conductive resin layer 10 (or carbon film). The peel strength can be measured by a 90-degree peel test (ISO29862:2007). The primary sealing performance of the bipolar battery 100 may be, for example, 0.5 N / mm or more. The primary sealing performance may be, for example, 0.8 N / mm or more, or 1.0 N / mm or more.

[0046] The "electrolyte resistance" indicates the primary sealing performance after being immersed in the electrolyte for 1000 hours. The electrolyte resistance of the bipolar battery 100 may be, for example, 0.5 N / mm or more. The electrolyte resistance may be, for example, 0.8 N / mm or more, or 1.0 N / mm or more.

Examples

[0047] <Preparation of Samples> ·No.1 A support material (PTFE sheet) was set in a web handling and conveying device. A first dispersion liquid was continuously coated on the surface of the support material and dried, whereby a first carbon film was formed. A conductive adhesive was prepared by mixing a main agent (olefin resin), a curing agent (isocyanate compound), and a conductive filler (Ni-plated particles). The conductive adhesive was continuously coated on the surface of the first carbon film and dried, whereby a conductive resin layer was formed. A second dispersion liquid was continuously coated on the surface of the conductive resin layer and dried, whereby a second carbon film was formed. The second carbon film had substantially the same composition and the same dimensions as the first carbon film. A negative electrode composite paste was continuously coated on the surface of the second carbon film and dried, whereby a negative electrode layer was formed. After the formation of the negative electrode layer, the support material was peeled off from the workpiece and wound up. After the peeling of the support material, a positive electrode composite paste was continuously coated on the surface of the first carbon film and dried, whereby a positive electrode layer was formed. Thus, a bipolar electrode was manufactured. Note that various coating films and coating layers were dried by a drying furnace. The drying conditions were all as follows.

[0048] Line speed: 15 m / min Drying furnace temperature: 150 °C

[0049] ·No.2 A conductive adhesive was coated on one side of an aluminum (Al) foil, whereby an adhesive layer was formed. The conductive adhesive was the same as that prepared in No.1. A copper (Cu) foil was attached to the adhesive layer, whereby an electrode current collector was manufactured. Carbon films were formed on both sides of the electrode current collector. After the formation of the carbon films, a negative electrode layer was formed on the Cu foil side. Further, a positive electrode layer was formed on the Al foil side. Thus, a bipolar electrode was manufactured. No.2 corresponds to a conventional bipolar electrode.

[0050] <Evaluation> FIG. 11 is a table showing the evaluation results. The "standard" in FIG. 11 is the value for the sample of this experiment. In this experiment, the primary sealing property and the electrolyte resistance indicate the sealing property between the carbon film and the sealing material. In each item of through resistance, primary sealing property, and electrolyte resistance, No. 1 showed performance equivalent to that of No. 2. Therefore, No. 1 (metal foil-free) is considered to be practical.

Explanation of symbols

[0051] 5 Support material, 10 Conductive resin layer, 10a Peripheral part, 11 First carbon film, 12 Second carbon film, 20 Bipolar electrode, 21 First electrode layer, 22 Second electrode layer, 30 Separator, 40 Sealing material, 41 First sealing material, 42 Second sealing material, 100 Bipolar battery.

Claims

1. (a) forming a first carbon film on a sheet-like support; (b) forming a conductive resin layer on the first carbon film; (c) forming a second carbon film on the conductive resin layer; (d) forming a second electrode layer on the second carbon film; (e) separating the support from the first carbon film; and (f) forming a first electrode layer on the first carbon film to manufacture a bipolar electrode, comprising, wherein (d), (e) and (f) are performed in this order, A method for manufacturing a bipolar electrode.

2. The support contains a fluororesin, The method for manufacturing a bipolar electrode according to Claim 1.

3. The first electrode layer is a positive electrode layer, and The second electrode layer is a negative electrode layer, The method for manufacturing a bipolar electrode according to Claim 1 or Claim 2.

4. In the thickness direction, a first electrode layer, a first carbon film, a conductive resin layer, a second carbon film, and a second electrode layer, are included in this order, A bipolar electrode.

5. The conductive resin layer has a larger area than each of the first electrode layer, the first carbon film, the second carbon film and the second electrode layer, and The conductive resin layer extends so as to cover the side surface of the first carbon film, The bipolar electrode according to Claim 4.

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