Electrode manufacturing method

Abstract

To provide an electrode manufacturing method capable of preventing edge cracks in coated areas.SOLUTION: The electrode manufacturing method includes: a first coating step of intermittently coating electrode composite slurry over a current collecting foil to form a first coated area in which an electrode composite layer is formed and an uncoated area where the electrode composite layer is not formed; a determination step of determining whether the surface area of the uncoated area exceeds a threshold value by measuring the surface area of the uncoated area; and a drying step of drying the electrode composite slurry. In the determination step, when the surface area of the uncoated area exceeds the threshold, a second coating step is also included, the second coating step forming a second coated area by applying the electrode composite slurry to the uncoated area so that the surface area of the uncoated area is below the threshold value, between the determination step and the drying step.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing an electrode. [Background technology]

[0002] Patent Document 1 (JP 2021-044096 A) discloses a method of processing the ends of an electrode sheet formed by wet powder deposition using a scraping blade installed on the transport path to form ends with high linearity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-044096 Summary of the Invention [Problem to be solved by the invention]

[0004] An intermittently coated electrode sheet, in which formed areas (coated areas) and unformed areas (uncoated areas) of the active material layer exist alternately on a current collector foil, is known as an electrode sheet that is often used in high energy density batteries.

[0005] However, in producing an intermittently coated electrode sheet, when the electrode mixture slurry coated on the current collector foil is dried, the temperature of the uncoated parts is likely to become high, which may cause cracks at the edges of the coated parts.

[0006] An object of the present disclosure is to suppress edge cracking of a coated portion in an intermittently coated electrode. [Means for solving the problem]

[0007] [1] a first coating step of intermittently coating an electrode mixture slurry on a current collector foil to form a first coated portion having an electrode mixture layer and an uncoated portion having no electrode mixture layer; a determination step of measuring a surface area of ​​the uncoated portion and determining whether or not the surface area of ​​the uncoated portion exceeds a threshold value; A drying step of drying the electrode mixture slurry, The method for manufacturing an electrode further includes a second coating step between the determination step and the drying step, in which, when the surface area of ​​the uncoated portion exceeds a threshold value in the determination step, the electrode mixture slurry is applied onto the uncoated portion to form a second coated portion so that the surface area of ​​the uncoated portion is equal to or less than the threshold value.

[0008] The inventors of the present disclosure have noticed that if the surface area of ​​the uncoated part is equal to or less than a certain value, it is possible to suppress the temperature rise of the uncoated part due to the latent heat of the coated part, and have discovered that by adjusting the surface area of ​​the uncoated part, it is possible to suppress edge cracking of the coated part. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a flow chart showing an outline of the method for producing an electrode in this embodiment. [Diagram 2] FIG. 2 is a conceptual diagram showing an example of an electrode in this embodiment. [Diagram 3] FIG. 3 is a conceptual diagram showing another example of the electrode in this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present embodiment") will be described. However, the present embodiment and the present embodiment do not limit the technical scope of the present disclosure. In this specification, the "positive electrode" and the "negative electrode" are collectively referred to as "electrodes".

[0011] <Electrode manufacturing method> Fig. 1 is a flow chart showing an outline of the method for producing an electrode in this embodiment. As shown in Fig. 1, the method for producing an electrode in this embodiment includes at least (a) a first coating step, (b) a determination step, and (c) a drying step, and may include (b') a second coating step between (b) the determination step and (c) the drying step. The method for producing an electrode in this embodiment may also include (d) a pressing step.

[0012] Fig. 2 is a conceptual diagram showing an example of an electrode in this embodiment, and Fig. 3 is a conceptual diagram showing another example of an electrode in this embodiment. Hereinafter, a method for producing an electrode in this embodiment will be described with reference to Figs. 2 and 3.

[0013] The electrode manufactured in this embodiment may be any of a positive electrode, a negative electrode, and a bipolar electrode. The electrode manufactured in this embodiment may be used in any of a liquid battery, a polymer battery, and an all-solid-state battery.

[0014] (a) First coating process In the first coating step, an electrode mixture slurry is intermittently coated onto a current collector foil to form a first coated portion 1 on which an electrode mixture layer is formed and an uncoated portion 2 on which no electrode mixture layer is formed.

[0015] (current collecting foil) The current collecting foil may have a thickness of, for example, 5 μm or more and 100 μm or less. The current collecting foil is conductive. Examples of the current collecting foil include aluminum (Al) foil, Al alloy foil, copper (Cu) foil, Cu alloy foil, nickel (Ni) foil, Ni alloy foil, titanium (Ti) foil, and Ti alloy foil. When the electrode is a positive electrode, the current collecting foil is, for example, an Al foil. When the electrode is a negative electrode, the current collecting foil is, for example, a Cu foil.

[0016] The surface of the current collector foil may be coated with carbon (C-coat treatment). The carbon is not particularly limited, and examples thereof include graphite, graphitizable carbon, and non-graphitizable carbon.

[0017] (Electrode mixture slurry) The electrode mixture slurry contains an electrode active material. The electrode active material may be a positive electrode active material or a negative electrode active material. When the electrode active material is a positive electrode active material, the electrode material is a positive electrode material. When the electrode active material is a negative electrode active material, the electrode material is a negative electrode material.

[0018] Examples of the positive electrode active material include lithium-containing metal oxides and lithium-containing phosphates. Examples of the lithium-containing metal oxides include Li(NiCoMn)O2 and Li(NiCoAl)O2. Examples of the lithium-containing phosphates include LiFePO4.

[0019] Examples of the negative electrode active material include carbon-based negative electrode active materials such as graphite, graphitizable carbon, and non-graphitizable carbon, and alloy-based negative electrode active materials containing silicon (Si), tin (Sn), and the like.

[0020] The electrode mixture slurry contains a solvent. Examples of the solvent include an aqueous solvent, an organic solvent, etc. The aqueous solvent refers to water or a mixed solvent containing water and a polar organic solvent.

[0021] Examples of the aqueous solvent include water (ion-exchanged water). Examples of the polar organic solvent that can be used in the mixed solvent include alcohols such as methanol, ethanol, and isopropyl alcohol, ketones such as acetone, and ethers such as tetrahydrofuran. Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP).

[0022] The electrode mixture slurry may further contain a conductive material, such as acetylene black (AB), vapor grown carbon fiber (VGCF), carbon nanotube (CNT), etc.

[0023] The electrode material may further contain a binder, such as carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), etc.

[0024] The blending amount of the conductive material and the binder may be, for example, 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the electrode active material.

[0025] (Coating) In this step, the electrode mixture slurry is applied to the surface of the current collecting foil by an arbitrary coating device. For example, a die coater, a roll coater, or the like may be used as the coating device. The electrode mixture slurry may be applied to only one side of the current collecting foil. The electrode mixture slurry may be applied to both the front and back sides of the current collecting foil. The electrode mixture slurry is intermittently applied to the current collecting foil.

[0026] 《(b) Judgment process》 In the determination step, the surface area of ​​the uncoated portion 2 is measured, and it is determined whether or not the surface area of ​​the uncoated portion 2 exceeds a threshold value. If the surface area of ​​the uncoated portion 2 is equal to or less than the threshold value (see FIG. 2), the drying step (c) described below is carried out. If the surface area of ​​the uncoated portion 2 exceeds the threshold value (see FIG. 3), the second coating step (b') described below and the drying step (c) are carried out in that order. If the surface area of ​​the uncoated portion 2 exceeds the threshold value, the temperature of the uncoated portion 2 becomes higher than the temperature of the first coated portion 1 in the drying step (c), and there is a risk of cracks (edge ​​cracks of the first coated portion 1) occurring at the boundary between the first coated portion 1 and the uncoated portion 2. On the other hand, if the surface area of ​​the uncoated portion 2 is equal to or less than the threshold value, it is possible to cool the uncoated portion 2 by the latent heat of the first coated portion 1. This makes it possible to suppress the temperature rise of the uncoated portion 2 and suppress edge cracks of the first coated portion 1.

[0027] Here, the "threshold" is a value obtained in advance by correlating the surface area of ​​the uncoated portion with the temperature of the uncoated portion, and is set empirically. The threshold varies depending on, for example, the size of the electrode and the material contained in the electrode mixture slurry.

[0028] 《(b') Second coating process》 As shown in Fig. 3, in the second coating step, if the surface area of ​​the uncoated portion 2 exceeds a threshold value in the determination step, the electrode mixture slurry is coated onto the uncoated portion 2 so that the surface area of ​​the uncoated portion 2 is equal to or less than the threshold value, thereby forming a second coated portion 3. The second coated portion 3 may be formed so that the surface area of ​​the uncoated portion 2 is equal to or less than the threshold value. The second coated portion 3 may be formed, for example, in an approximately central portion of the uncoated portion 2 in the conveyance direction, as shown in Fig. 3.

[0029] 《(c) Drying process》 In the drying step, the electrode mixture slurry applied onto the current collector foil is dried. For example, the electrode mixture slurry may be dried in a hot air drying oven or by laser irradiation. From the viewpoint of carbon dioxide emission, drying by laser irradiation is preferred.

[0030] The laser may be a semiconductor laser. A semiconductor laser has the features of a large irradiation area, small equipment size, and high conversion efficiency, and therefore can be suitably used for laser drying of a slurry. The wavelength of the semiconductor laser may be, for example, 800 to 1000 nm.

[0031] When the surface of the current collecting foil is C-coated, the absorption by the semiconductor laser is increased, and therefore it is suitable for use. For example, the absorptance of the C-coated current collecting foil to the semiconductor laser (wavelength: 800 to 1000 nm) is 30 to 100%.

[0032] The output of the laser is not particularly limited as long as it can evaporate the solvent without causing deterioration of the constituent material (solid content) of the active material layer contained in the electrode mixture slurry. The output of the laser is, for example, 0.5 W or more and 1000 W or less. The drying time is determined by the laser output density (W / cm 2 For example, the temperature of the electrode (slurry) surface may be monitored by a radiation thermometer and the laser output may be adjusted while performing laser drying.

[0033] The laser may be a continuous wave (CW) laser or a pulsed laser.

[0034] The temperature of the slurry during laser drying is, for example, 20 to 100° C. During laser drying, air may or may not be blown. When air is blown, the temperature of the air is, for example, 80 to 120° C., and the air speed is, for example, 1 to 20 m / s.

[0035] (d) Pressing process In the pressing step, the first coated portion 1 dried in the drying step is pressed to form an active material layer. That is, an electrode is produced in which an active material layer is formed on a current collector foil. The pressure can be appropriately adjusted depending on the thickness of the active material layer after pressing. EXAMPLES

[0036] The present embodiment will be described below using examples, but the present embodiment is not limited to these.

[0037] Example 1 A C-coated current collector foil and an electrode mixture slurry were prepared. The electrode mixture slurry was intermittently applied to the surface of the current collector foil to form a first coated portion and an uncoated portion. After coating, the surface area of ​​the uncoated portion was measured. The surface area was equal to or less than the threshold value. The first coated portion and the uncoated portion were dried for 60 seconds by a semiconductor laser. After drying, the electrode of Example 1 was manufactured by pressing. Note that the threshold value in Examples 1 to 2 and Comparative Example 1 was a value calculated in advance from the surface area of ​​the uncoated portion and the temperature of the uncoated portion.

[0038] Example 2 The same material as in Example 1 was prepared. The electrode mixture slurry was intermittently applied to the surface of the current collector foil to form a first coated portion and an uncoated portion. After application, the surface area of ​​the uncoated portion was measured. The surface area exceeded a threshold value. The electrode mixture slurry was applied to the uncoated portion so that the surface area of ​​the uncoated portion was equal to or less than the threshold value to form a second coated portion. The uncoated portion on which the first coated portion and the second coated portion were formed was dried for 60 seconds by a semiconductor laser. After drying, the electrode was pressed to produce the electrode of Example 2.

[0039] Comparative Example 1 In Comparative Example 1, the second coating step was not performed. That is, the same material as in Example 1 was prepared. The electrode mixture slurry was intermittently coated on the surface of the current collector foil to form a first coated portion and an uncoated portion. After coating, the surface area of ​​the uncoated portion was measured. The surface area exceeded the threshold value. The first coated portion and the uncoated portion were dried for 60 seconds by a semiconductor laser. After drying, the electrode of Comparative Example 1 was manufactured by pressing.

[0040] <Evaluation> In the above-mentioned Examples 1 and 2 and Comparative Example 1, edge cracks in the first coated portion of each electrode were visually confirmed.

[0041] <Result> No edge cracking was observed in the first coated portion in Examples 1 and 2. On the other hand, in Comparative Example 1, edge cracking was observed in the first coated portion.

[0042] The embodiments and examples disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the scope and meaning equivalent to the claims. [Explanation of symbols]

[0043] 1 First coated section, 2 Uncoated section, 3 Second coated section.

Claims

[Claim 1] a first coating step of intermittently coating an electrode mixture slurry onto a current collector foil to form a first coated portion having an electrode mixture layer formed thereon and an uncoated portion having no electrode mixture layer formed thereon; a determination step of measuring a surface area of ​​the uncoated portion and determining whether or not the surface area of ​​the uncoated portion exceeds a threshold value; A drying step of drying the electrode mixture slurry, The method for manufacturing an electrode further includes a second coating step between the determination step and the drying step, in which, when the surface area of ​​the uncoated portion exceeds a threshold value in the determination step, the electrode mixture slurry is applied onto the uncoated portion to form a second coated portion so that the surface area of ​​the uncoated portion is equal to or less than the threshold value.

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