Electrode manufacturing method

Abstract

To reduce deformation of a concave part when pressing an active material layer.SOLUTION: A first active material layer is formed on a front surface of a base material. By pressing the first active material layer, a second active material layer is formed. By forming a concave part onto the front surface of the second active material layer, a third active material layer is formed. By drying the third active material layer, a fourth active material layer is formed. By pressing the fourth active material layer, an electrode containing a fifth active material layer is manufactured. Each of the first active material layer, the second active material layer, and the third active material layer includes a solid content ratio that is 83% or more and less than 100% in a mass fraction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Japanese Patent Application Laid-Open No. 2002-015764 (Patent Document 1) discloses forming grooves in an active material layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-015764 Summary of the Invention [Problem to be solved by the invention]

[0004] It has been proposed to form recesses (grooves) on the surface of the active material layer. The recesses can serve as, for example, flow paths for the electrolyte. For example, the recesses can control the flow of the electrolyte, which is expected to improve battery performance. The recesses can be formed, for example, by embossing. That is, the recesses can be formed by pressing a convex mold against the surface of the active material layer.

[0005] The active material layer can be formed by applying a coating material to the surface of the substrate. The coating material contains a liquid component (dispersion medium). The liquid component can be removed from the active material layer by a drying operation. After drying, the active material layer can be pressed to adjust the density of the active material layer.

[0006] It is difficult to perform embossing on the active material layer after pressing because the active material layer hardens and is difficult to deform. Therefore, embossing is performed on the active material layer before pressing. Therefore, the active material layer is pressed after the recesses are formed.

[0007] If the compression ratio during pressing is high (if the density of the active material layer changes significantly before and after pressing), the material may flow. This flow of material may fill the recesses, meaning that the shape of the recesses may not be maintained.

[0008] An object of the present disclosure is to reduce deformation of recesses when pressing an active material layer. [Means for solving the problem]

[0009] The technical configuration and effects of the present disclosure will be described below. However, the mechanism of action in this specification includes speculation. The mechanism of action does not limit the technical scope of the present disclosure.

[0010] The method for producing the electrode includes the following steps (a) to (e). (a) A first active material layer is formed on the surface of a substrate. (b) The first active material layer is pressed to form a second active material layer. (c) A third active material layer is formed by forming recesses on the surface of the second active material layer. (d) The third active material layer is dried to form a fourth active material layer. (e) The fourth active material layer is pressed to produce an electrode including a fifth active material layer. Each of the first active material layer, the second active material layer and the third active material layer has a solid content of 83% or more and less than 100% by mass.

[0011] In the present disclosure, a pre-press is performed on an active material layer in a wet state (moist state). The pre-press can be performed within a range that does not excessively harden the active material layer so that it can be subsequently embossed. After the pre-press, the active material layer is embossed. After the embossing, the active material layer is subjected to a final press. By undergoing the pre-press, density changes during the final press can be reduced. That is, the amount of deformation (amount of crushing) of the active material layer during the final press can be reduced. Because the amount of deformation of the active material layer is small, it is thought that the material is less likely to flow. That is, it is thought that deformation of the recesses can be reduced. Therefore, it is thought that recesses of the desired shape can remain in the active material layer even after the final press.

[0012] However, the solid content of the active material layer must be 83% or more and less than 100% during the period from pre-pressing to embossing. When the solid content of the active material layer reaches 100% (when it is completely dry), the active material layer is fixed to the surface of the substrate. In other words, the active material layer restrains the surface of the substrate. As a result, slippage is less likely to occur at the interface between the active material layer and the substrate. During pressing, elongation occurs in both the substrate and the active material layer. The amount of elongation of the active material layer tends to be greater than the amount of elongation of the substrate. If pressing is performed in a state where slippage is less likely to occur, the substrate is stretched by the active material layer at the interface between the active material layer and the substrate. Because the amount of elongation is locally large at the surface of the substrate, the substrate attempts to eliminate the distortion by warping. As a result, unacceptable warping may occur.

[0013] On the other hand, the lower the solid content of the active material layer, the more likely the active material layer is to peel off. If the solid content of the active material layer is less than 83%, for example, the active material layer may peel off from the substrate during pre-pressing.

[0014] When the solid content of the active material layer is 83% or more and less than 100%, the preliminary pressing and embossing can be carried out smoothly.

[0015] 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 example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic flowchart of a method for producing an electrode according to this embodiment. [Figure 2] FIG. 2 is a manufacturing flow diagram according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] <Definitions of terms, etc.> In this specification, the terms "comprise," "include," "have," and variations thereof (e.g., "consisting of") are open-ended. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even in closed-ended terms, additional elements that are normally associated with the technology or that are unrelated to the technology disclosed herein are not excluded. The term "consisting essentially of..." is semi-closed. Semi-closed terms allow for the addition of elements that do not substantially affect the basic and novel characteristics of the technology disclosed herein.

[0018] In this specification, expressions such as "may" and "can" are used in the permissive sense of "possibly" rather than the obligatory sense of "must."

[0019] In this specification, unless otherwise specified, a numerical range such as "m to n%" includes both the upper and lower limits. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% and less than n%." Furthermore, a numerical value arbitrarily selected from within the numerical range may be set as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described elsewhere in this specification, in a table, a figure, or the like.

[0020] In this specification, the order of execution of multiple steps, actions, operations, etc. included in various methods is not limited to the order described unless otherwise specified. For example, multiple steps may proceed simultaneously. For example, multiple steps may occur one after the other.

[0021] In this specification, the term "solid content" refers to the total mass fraction of components other than the liquid. For example, when an active material layer contains a dispersion medium (liquid), a binder (solute), a conductive material (dispersoid), and an active material (dispersoid), the solid content of the active material layer refers to the total mass fraction of the binder, conductive material, and active material relative to the mass of the active material layer. The solid content may be abbreviated as "NV (Nonvolatile Content)."

[0022] In this specification, "electrode" is a general term for a positive electrode and a negative electrode. The electrode may be a positive electrode or a negative electrode. The use of the electrode is arbitrary. In this specification, an electrode for a lithium ion battery is described as an example. The use of the electrode is not limited to lithium ion batteries.

[0023] In this specification, the terms "preliminary pressing" and "main pressing" are used to distinguish between the two pressings. "Preliminary pressing" and "main pressing" may be alternatively referred to as "first pressing" and "second pressing," for example. In this embodiment, as long as at least two pressings are performed, for example, a third and a fourth pressing may also be performed.

[0024] <Electrode manufacturing method> Fig. 1 is a schematic flowchart of a method for producing an electrode in this embodiment. Fig. 2 is a production flow diagram of this embodiment. Hereinafter, the "method for producing an electrode in this embodiment" may be abbreviated as "this production method." This production method includes "(a) formation of an active material layer," "(b) pre-pressing," "(c) formation of recesses," "(d) drying," and "(e) final pressing."

[0025] (a) Formation of Active Material Layer The manufacturing method includes forming a first active material layer 11 on the surface of a substrate 10 (see FIG. 2). The first active material layer 11 is formed so as to have a solid content of 83% or more and less than 100%.

[0026] The substrate 10 may be, for example, in the form of a sheet. The substrate 10 may be, for example, conductive. The substrate 10 may include, for example, a metal foil. The substrate 10 may include, for example, an aluminum foil, a copper foil, or the like. The substrate 10 may have a thickness of, for example, 5 to 100 μm, or may have a thickness of 10 to 50 μm.

[0027] For example, a slurry may be prepared by mixing an active material, a conductive material, a binder, and a dispersion medium. The slurry may have a solid content of, for example, 50 to 80%. The slurry may be applied to the surface of the substrate 10 using, for example, a die coater. A coating layer (coating film) may be formed by applying the slurry. The coating layer may be dried using a dryer. The first active material layer 11 may be formed by drying the coating layer to a solid content of 83% or more. The dryer may include, for example, a hot air drying oven, an infrared heater, or the like.

[0028] For example, a wet powder may be produced by mixing an active material, a conductive material, a binder, and a solvent. The wet powder may have a solid content of, for example, 70 to 90%. For example, the wet powder may be applied to the surface of the substrate 10 using a roll coater or the like. A coating layer may be formed by applying the wet powder. If the solid content of the wet powder is less than 83%, the coating layer may be dried to a solid content of 83% or more, thereby forming the first active material layer 11. If the solid content of the wet powder is initially 83% or more, the coating layer may be considered to be the first active material layer 11.

[0029] The active material may include, for example, lithium cobalt oxide, graphite, etc. The conductive material may include, for example, carbon black, etc. The amount of conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of active material. The binder may include, for example, polyvinylidene fluoride, styrene butadiene rubber, carboxymethyl cellulose, etc. The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of active material. The dispersion medium or solvent may include, for example, water, N-methyl-2-pyrrolidone, etc.

[0030] The solid content of first active material layer 11 may be, for example, 86% or more, 89% or more, or 93% or more. The solid content of first active material layer 11 may be, for example, 99% or less, 95% or less, or 93% or less.

[0031] The first active material layer 11 may have a thickness of, for example, 50 to 2000 μm, 100 to 1500 μm, or 500 to 1000 μm.

[0032] (b) Pre-press This manufacturing method includes pressing a first active material layer 11 to form a second active material layer 12 (see FIG. 2). The second active material layer 12 also has a solid content of 83% or more and less than 100%.

[0033] For example, the second active material layer 12 and the substrate 10 are pressed by a roll press. The roll linear pressure may be, for example, 0.5 to 2 t / cm. The roll gap may be, for example, 300 to 1000 μm. The second active material layer 12 is pressed at a pressure of, for example, 1.35 to 1.88 g / cm. 3 and may have a density of 1.51 to 1.74 g / cm 3 The density may be

[0034] (c) Formation of a recess This manufacturing method includes forming recesses 5 on the surface of the second active material layer 12 to form a third active material layer 13. The third active material layer 13 also has a solid content of 83% or more and less than 100%.

[0035] For example, the recesses 5 may be formed by pressing a convex mold against the surface of the second active material layer 12. For example, an embossing roll may be used. The embossing roll may have a plurality of convex molds on its surface. On the surface of the third active material layer 13, the recesses 5 may extend, for example, linearly or curvedly. A single recess 5 may be formed, or a plurality of recesses 5 may be formed. The recesses 5 may have any planar pattern on the surface of the third active material layer 13. The planar pattern of the recesses 5 may be, for example, a lattice pattern or a line pattern. The width of the recesses 5 may be, for example, 10 to 500 μm. The depth of the recesses 5 may be, for example, 10 to 90% of the thickness of the third active material layer 13. The cross-sectional shape of the recesses 5 is arbitrary. The cross-sectional shape of the recesses 5 may be, for example, rectangular, V-shaped, or U-shaped.

[0036] 《(d) Drying》 This manufacturing method includes drying the third active material layer 13 to form a fourth active material layer 14. The third active material layer 13 can be dried by any method. The fourth active material layer 14 may have a solid content of, for example, 100%. Recesses 5 are also formed on the surface of the fourth active material layer 14.

[0037] (e) This Press The present manufacturing method includes pressing the fourth active material layer 14 to form a fifth active material layer 15. The electrode 100 is completed by forming the fifth active material layer 15. That is, the present manufacturing method includes producing an electrode 100 including the fifth active material layer 15. Recesses 5 remain on the surface of the fifth active material layer 15. The fifth active material layer 15 may have a solid content of, for example, 100%.

[0038] For example, the fourth active material layer 14 may be pressed using a roll press. The main pressing may be performed so as to increase the density of the active material layer. The roll linear pressure may be, for example, 0.5 to 2 t / cm. The linear pressure of the main pressing may be, for example, equal to or greater than the linear pressure of the preliminary pressing. The roll gap may be, for example, 300 to 1000 μm. The roll gap of the main pressing may be equal to or smaller than the roll gap of the preliminary pressing.

[0039] The fifth active material layer 15 has a density of, for example, 1.5 to 3.0 g / cm 3 and may have a density of 1.8 to 2.5 g / cm 3 and may have a density of 1.8 to 2.0 g / cm 3 The density ratio indicates the ratio of the density of the fifth active material layer 15 (after main pressing) to the density of the second active material layer 12 (after pre-pressing). The density ratio may be, for example, 1.03 to 1.42, 1.03 to 1.28, or 1.03 to 1.11. It is believed that the smaller the density ratio, the more likely deformation of the recesses 5 (flow of material) can be reduced.

[0040] In the fifth active material layer 15, the recesses 5 may have a width of, for example, 5 to 250 μm. The depth of the recesses 5 may be, for example, 10 to 90% of the thickness of the fifth active material layer 15.

[0041] The rate of change in the width of the recessed portions 5 before and after the main pressing may be, for example, −90 to −10%, −70 to −30%, or −60 to −40%.

[0042] The rate of change is calculated by the following formula: ΔW=(W1-W0) / W0×100 ΔW: Rate of change (%) W0: Width of the recess before final pressing W1: Width of the recess after final pressing [Example]

[0043] <Consideration of preliminary pressing> Active material layers having various solid content ratios were formed on the surface of the substrate. The thickness of the substrate was 37 μm. The thickness of the active material layer (before pressing) was 700 μm. The coating weight (mass per unit area) of the active material layer was 74.2 mg / cm. 2 It was.

[0044] The active material layer was compressed using a roll press. In Table 1 below, the numerical values ​​written in the cells indicate the density of the active material layer after pressing. In Table 1 below, "NG1" indicates that the active material layer peeled off from the substrate. In Table 1 below, "NG2" indicates that the electrode warped significantly. When the solid content of the active material layer is less than 100%, warping tends to be small. When the solid content of the active material layer is 83% or more, peel strength tends to be good. Therefore, the solid content at the time of pre-pressing is 83% or more and less than 100%.

[0045] [Table 1]

[0046] <Electrode manufacturing> 《First manufacturing example》 An active material layer was formed. The active material layer had a solid content of 83% or more and less than 100%. The active material layer had a density of 1.3 g / cm 3 The active material layer had a density of 1.96 g / cm. The protruding mold formed recesses on the surface of the active material layer. The recesses had a width of 130 μm. The active material layer was dried. After drying, the active material layer had a solid content of 100%. After drying, main pressing was carried out. In this way, an electrode was produced. After main pressing, the active material layer had a density of 1.96 g / cm. 3The width of the recesses was reduced to 2 μm. This is thought to be due to the material flowing during the main pressing.

[0047] 《Second manufacturing example》 An active material layer was formed. The active material layer had a solid content of 83% or more and less than 100%. The active material layer had a density of 1.3 g / cm 3 After pre-pressing, the active material layer had a density of 1.74 g / cm. 3 The active material layer had a density of 1.93 g / cm. The protruding mold formed recesses on the surface of the active material layer. The recesses had a width of 98 μm. The active material layer was dried. After drying, the active material layer had a solid content of 100%. After drying, main pressing was carried out. In this way, an electrode was produced. After main pressing, the active material layer had a density of 1.93 g / cm. 3 The width of the recesses was reduced to 47 μm. Table 2 below shows the results of the first and second production examples.

[0048] [Table 2]

[0049] In the second manufacturing example, the difference in density before and after the main pressing is reduced by performing the preliminary pressing. That is, the amount of deformation of the active material layer is small during the main pressing. Since the amount of deformation of the active material layer is small, it is thought that the material is less likely to flow, and deformation (reduced width) of the recesses can be reduced.

[0050] The present embodiment and examples are illustrative in all respects. The present embodiment and examples are not limiting. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is also intended from the beginning that any configuration may be extracted from the present embodiment and examples and that they may be combined in any desired manner. [Explanation of symbols]

[0051] 5 Recess, 10 Substrate, 11 First active material layer, 12 Second active material layer, 13 Third active material layer, 14 Fourth active material layer, 15 Fifth active material layer, 100 Electrode.

Claims

1. (a) forming a first active material layer on a surface of a substrate; (b) pressing the first active material layer to form a second active material layer; (c) forming a third active material layer by forming recesses in the surface of the second active material layer; (d) drying the third active material layer to form a fourth active material layer; and (e) pressing the fourth active material layer to produce an electrode including a fifth active material layer; Including, each of the first active material layer, the second active material layer, and the third active material layer has a solid content of 83% or more and less than 100% by mass; In (e), the rate of change in width of the recess is −60% or more and −40% or less; The rate of change is calculated by the formula: ΔW=(W 1 - W 0 ) / W 0 ×100 It is found by In the above formula, ΔW indicates the rate of change, W 0 represents the width of the recess in the fourth active material layer; and W 1 represents the width of the recess in the fifth active material layer; Electrode manufacturing method.

2. The ratio of the density of the fifth active material layer to the density of the second active material layer is 1.03 or more and 1.11 or less. A method for manufacturing the electrode according to claim 1 .

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