Method for manufacturing electrode and method for manufacturing secondary battery

Abstract

Provided is an electrode manufacturing method capable of suppressing fluctuation in the thickness of an electrode. This electrode manufacturing method is provided with a first active material layer formation step for forming a first active material layer on a first surface of a current collector, a first pressing step for pressing the first active material layer, and a second pressing step for pressing the first active material layer after the first pressing step, the ratio of the pressing line pressure P2 in the second pressing step to the pressing line pressure P1 in the first pressing step is 100% or more and 200% or less.

Description

Technical Field

[0001] The present application relates to a method for manufacturing an electrode and a method for manufacturing a secondary battery. Background Art

[0002] The electrode of the secondary battery is manufactured by forming an active material layer on a current collector and then pressing it at a predetermined pressure to adjust the density. For example, Patent Document 1 discloses a method for manufacturing a bipolar electrode, which forms a negative electrode active material layer on a first surface of a first metal foil, presses the negative electrode active material layer in a state where the first surface of a second metal foil is opposite to the second surface of the first metal foil, forms a positive electrode active material layer on a second surface of the second metal foil, and presses the positive electrode active material layer.

[0003] Prior art literature

[0004] Patent Document 1: Japanese Patent Application Publication No. 2021-82504 Summary of the invention

[0005] As described above, in order to adjust the density of the active material layer, the active material layer is pressed. However, after pressing, the residual stress during pressing is released over time, and the thickness of the active material layer increases. In other words, sometimes the active material layer rebounds. In this way, the thickness of the active material layer fluctuates, and thus the density of the active material layer changes, resulting in the problem of unstable electrode quality.

[0006] The inventors have found that even the method for manufacturing an electrode described in Patent Document 1, in which the negative electrode active material layer is pressed twice, cannot fully suppress the above-mentioned problem. It is believed that this is because the linear pressure of the second pressing is set smaller than the linear pressure of the first pressing. Usually, in the second pressing, the direction in which the surface pressure is applied is close to the vertical direction, so the transport direction component becomes smaller. In this way, in the second pressing, the amount of plastic deformation of the active material layer is insufficient, so the amount of rebound of the active material layer becomes larger. Therefore, the inventors have found that in the method for manufacturing an electrode described in Patent Document 1, it is not possible to fully suppress the fluctuation of the thickness of the active material layer.

[0007] Therefore, in view of the above circumstances, a main object of the present disclosure is to provide a method for manufacturing an electrode capable of suppressing fluctuation in electrode thickness.

[0008] The present disclosure provides at least the following aspects.

[0009] The first method is a method for manufacturing an electrode, comprising: a first active material layer forming step of forming a first active material layer on a first surface of a current collector; a first pressing step of pressing the first active material layer; and a second pressing step of pressing the first active material layer after the first pressing step, wherein a ratio of a pressing line pressure P2 in the second pressing step to a pressing line pressure P1 in the first pressing step is greater than 100% and less than 200%.

[0010] A second aspect is the method for producing an electrode according to the first aspect, wherein a ratio of the pressing linear pressure P2 in the second pressing step to the pressing linear pressure P1 in the first pressing step is 100% or more and 125% or less.

[0011] A third aspect is the method for producing an electrode according to the first aspect or the second aspect, further comprising a heating step of heating the first active material layer after the first pressing step and between the second pressing step.

[0012] A fourth aspect is the method for producing an electrode according to any one of the first to third aspects, further comprising a second active material layer forming step of forming a second active material layer on a second surface of the current collector after the first pressing step and between the second pressing step.

[0013] A fifth aspect is a method for manufacturing a secondary battery, comprising: an electrode manufacturing step of manufacturing an electrode by the electrode manufacturing method according to any one of the first to fourth aspects; and a secondary battery manufacturing step of manufacturing a secondary battery using the electrode.

[0014] According to the method for manufacturing an electrode of the present disclosure, it is possible to suppress the variation in electrode thickness. In addition, according to the method for manufacturing a secondary battery of the present disclosure, it is possible to improve the battery quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a flowchart of the first embodiment.

[0016] Figure 2 This is a schematic diagram of the first pressing step S12.

[0017] Figure 3 This is a flowchart of the second embodiment.

[0018] Figure 4 This is a schematic diagram of the second pressing step S25.

[0019] Description of Reference Numerals

[0020] 10 collector

[0021] 11 Page 1

[0022] 12 Page 2

[0023] 201st active material layer

[0024] 30 Second active material layer DETAILED DESCRIPTION

[0025] [Method for producing electrode]

[0026] The method for producing an electrode of the present disclosure will be described in detail using the first embodiment and the second embodiment.

[0027] <First Embodiment>

[0028] Figure 1 Flowchart showing the first embodiment. Figure 1 As shown, the first embodiment includes a first active material layer forming step S11, a first pressing step S12, a heating step S13, and a second pressing step S14. Each step will be described below.

[0029] (First Active Material Layer Forming Step S11)

[0030] The first active material layer forming step S11 is a step of forming the first active material layer 20 on the first surface 11 of the current collector 10 .

[0031] The current collector 10 is a sheet-shaped conductive member that is rectangular when viewed from above. The current collector 10 has a first surface 11 and a second surface 12 located on the opposite side of the first surface 11. The current collector 10 is composed of, for example, a metal foil or an alloy foil. As metal foil, for example, copper foil, aluminum foil, titanium foil, nickel foil, etc. can be cited. As alloy foil, for example, stainless steel foil, steel plate subjected to plating treatment, stainless steel plate subjected to plating treatment, etc. can be cited. The alloy foil can also be an alloy foil of the metal exemplified as the material of the above-mentioned metal foil. The current collector 10 can be formed by integrating or stacking a plurality of metal foils, or by plating other metals on the surface of the metal foil.

[0032] The first active material layer 20 is a sheet-shaped active material layer and contains a positive electrode active material or a negative electrode active material.

[0033] Examples of positive electrode active materials include composite oxides, metallic lithium, and sulfur. The composition of the composite oxide includes, for example, at least one of iron, manganese, titanium, nickel, cobalt, and aluminum, as well as lithium. Examples of the composite oxide include olivine-type lithium iron phosphate (LiFePO4), LiCoO2, and LiNiMnCoO2.

[0034] Examples of negative electrode active materials include graphite, artificial graphite, highly oriented graphite, mesocarbon microbeads, hard carbon, soft carbon and other carbons, metal compounds, elements capable of alloying with lithium or compounds of the elements, boron-added carbon, etc. Elements capable of alloying with lithium include silicon and tin.

[0035] The first active material layer 20 may optionally contain a conductive auxiliary agent. Examples of the conductive auxiliary agent include acetylene black, carbon black, and graphite.

[0036] The first active material layer 20 may also optionally contain a binder. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamide-imide, resins containing alkoxysilyl groups, acrylic resins containing monomer units such as acrylic acid or methacrylic acid, styrene-butadiene rubber (SBR), carboxymethyl cellulose, alginates such as sodium alginate and ammonium alginate, water-soluble cellulose ester crosslinked bodies, and starch-acrylic acid graft polymers.

[0037] The first active material layer 20 may optionally contain a solid electrolyte. Examples of the solid electrolyte include oxide solid electrolytes, sulfide solid electrolytes, and nitride solid electrolytes.

[0038] When the first active material layer 20 contains a positive electrode active material, the first active material layer 20 is a positive electrode active material layer. When the first active material layer 20 contains a negative electrode active material, the first active material layer 20 is a negative electrode active material layer. Therefore, the first active material layer 20 can be a positive electrode active material layer or a negative electrode active material layer. From the viewpoint of further suppressing the increase in electrode thickness caused by rebound, the first active material layer 20 can also be a negative electrode active material layer. This is because, typically, the density of the negative electrode active material layer is required to be higher than that of the positive electrode active material layer.

[0039] The method for forming the first active material layer 20 on the first surface 11 of the current collector 10 is not particularly limited, and a known method can be appropriately used. For example, roll coating, die coating, dip coating, blade coating, spray coating, curtain coating, etc. can be cited. Specifically, after the electrode material constituting the first active material layer is mixed with a solvent to obtain a slurry, the slurry is applied to the first surface 11 of the current collector 10 and dried, thereby forming the first active material layer. The solvent is, for example, N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water.

[0040] (First Pressing Step S12)

[0041] The first pressing step S12 is performed after the first active material layer forming step S11, and is a step of pressing the first active material layer 20. The pressing may be performed using a roll press. Figure 2 A schematic diagram of the first pressing step S12 is shown.

[0042] The pressing line pressure P1 in the first pressing step S12 is not particularly limited, and can be set to, for example, 3 kN / cm or more and 5 kN / cm or less. However, the pressing line pressure P1 in the first pressing step S12 is set to be less than the pressing line pressure P2 in the second pressing step S14. Details will be described later.

[0043] (Heating Step S13)

[0044] The heating step S13 is performed between the first pressing step S12 and the second pressing step S14, and is a step for heating the first active material layer 20. By performing the heating step S13, the residual stress of the first active material layer 20 is released. Therefore, by performing the heating step S13, the thickness fluctuation of the electrode can be further suppressed. However, the heating step S13 is an optional step and may not be performed.

[0045] The heating step S13 can be implemented in an air atmosphere or in an inert gas atmosphere. The heating temperature is not particularly limited, and is, for example, 120° C. or more and 150° C. or less. If the heating temperature is lower than 120° C., the residual stress of the first active material layer 20 cannot be fully released. If the heating temperature exceeds 150° C., the first active material layer 20 may be degraded. The heating time is not particularly limited, and is, for example, 1 minute or more and 5 minutes or less. If the heating time is less than 1 minute, the residual stress of the first active material layer 20 cannot be fully released. If the heating time is more than 5 minutes, the first active material layer 20 may be degraded.

[0046] (Second Pressing Step S14)

[0047] The second pressing step S14 is performed after the heating step S13 and is a step of pressing the first active material layer 20. When the heating step S13 is not performed, the second pressing step S14 is performed after the first pressing step S12.

[0048] The pressing method can also be carried out by using a roller press (see Figure 2 ). The pressing line pressure P2 in the second pressing step S14 is not particularly limited, and can be set to, for example, 4 kN / cm or more and 6 kN / cm or less.

[0049] Here, the first embodiment is characterized in that a ratio (P2 / P1) of the pressing line pressure P2 in the second pressing step S14 to the pressing line pressure P1 in the first pressing step S11 is 100% or more and 200% or less.

[0050] Typically, the first active material layer 20 is pressed to adjust the density. However, the residual stress during pressing is released over time, and the thickness of the first active material layer 20 increases. That is, rebound occurs in the first active material layer 20. In this way, since the thickness of the first active material layer 20 fluctuates, the density of the first active material layer 20 changes, and there is a problem of unstable electrode quality. In contrast, in the first embodiment, the first active material layer 20 is pressed at least twice. In addition, it is characterized in that the ratio (P2 / P1) of the pressing line pressure P2 in the second pressing step S14 to the pressing line pressure P1 in the first pressing step S11 is 100% or more and 200% or less. As a result, the fluidity of the particles constituting the first active material layer 20 is increased, the residual stress is dispersed, and the amount of plastic deformation (the conveying direction component of the pressing surface pressure) can be increased, so that the increase in the thickness of the first active material layer caused by rebound can be reduced. Therefore, according to the first embodiment, the thickness fluctuation of the electrode can be reduced.

[0051] If the ratio (P2 / P1) is less than 100%, the plastic deformation of the first active material layer 20 is small, and the increase in thickness of the first active material layer caused by the rebound cannot be sufficiently reduced. If the ratio (P2 / P1) exceeds 200%, the vertical component of the pressing surface pressure becomes larger, and the rebound caused by the elastic deformation of the active material layer becomes larger, and the increase in thickness of the first active material layer cannot be sufficiently reduced. From the viewpoint of further improving the effect, the ratio (P2 / P1) can be greater than 100% and less than 125%, or it can be greater than 100% and less than 125%.

[0052] <Second Embodiment>

[0053] Figure 3 Flowchart showing the second embodiment. Figure 3 As shown, the second embodiment includes a first active material layer forming step S21, a first pressing step S22, a second active material layer forming step S23, a heating step S24, and a second pressing step S25. The second embodiment is different from the first embodiment mainly in that it includes a second active material layer forming step S23. Each step is described below.

[0054] The first active material layer forming step S21 and the first pressing step S22 are the same as the first active material layer forming step S11 and the first pressing step S12 of the first embodiment, and thus description thereof is omitted here.

[0055] (Second Active Material Layer Formation Step S23)

[0056] The second active material forming step S23 is performed between the first pressing step S22 and the heating step S24 , and is a step of forming the second active material layer 30 on the second surface 12 of the current collector 10 .

[0057] The second active material layer 30 may be a positive electrode active material layer or a negative electrode active material layer. In addition, the second active material layer 30 may be an active material layer of the same type as the first active material layer 20 or an active material layer of a different type. Typically, in the case of a single-pole secondary battery, the second active material layer 30 is an active material layer of the same type as the first active material layer. In the case of a bipolar secondary battery, the second active material layer 30 is an active material layer of a different type from the first active material layer. Typically, the density of the negative electrode active material layer is made higher than that of the positive electrode active material layer. From this point of view, the first active material layer 20 can be used as a negative electrode active material layer, and the second active material layer 30 can be used as a positive electrode active material layer.

[0058] The material constituting the second active material layer 30 can be appropriately selected from the materials constituting the first active material layer 20 . The method for forming the second active material layer 30 can be appropriately selected from the method for forming the first active material layer 20 .

[0059] (Heating Step S24)

[0060] The heating step S24 is implemented between the second active material forming step S23 and the second pressing step S25, and is a step for heating the first active material layer 20 and the second active material layer 30. The heating step S24 is different from the heating step S13 of the first embodiment in that the second active material layer 30 is heated in addition to the first active material layer 20, but the heating method is the same as that of the heating step S13. Therefore, detailed description is omitted. However, the heating step S24 is an optional step and may not be implemented.

[0061] (Second Pressing Step S25)

[0062] The second pressing step S25 is performed after the heating step S24 and is a step of pressing the first active material layer 20 and the second active material layer 30. When the heating step S24 is not performed, the second pressing step S25 is performed after the first pressing step S22. The second pressing step S25 is different from the second pressing step S14 of the first embodiment in that the second active material layer 30 is pressed in addition to the first active material layer 20, but the pressing method is the same as that of the second pressing step S14. Figure 4 A schematic diagram of the second pressing step S25 is shown.

[0063] Here, the second embodiment is the same as the first embodiment, and is characterized in that the ratio (P2 / P1) of the pressing line pressure P2 in the second pressing step S25 to the pressing line pressure P1 in the first pressing step S21 is 100% or more and 200% or less. From the viewpoint of improving the effect, the ratio (P2 / P1) may be 100% or more and 125% or less, or may be greater than 100% and 125% or less.

[0064] Since the second embodiment has the above-mentioned features, the increase in thickness of the first active material layer due to springback can be reduced, similarly to the first embodiment. Therefore, according to the second embodiment, the thickness variation of the electrode can be reduced.

[0065] The method for manufacturing an electrode disclosed in the present invention has been described above using the first embodiment and the second embodiment. The method for manufacturing an electrode disclosed in the present invention suppresses the increase in electrode thickness caused by springback. Therefore, according to the method for manufacturing an electrode disclosed in the present invention, it is possible to suppress the thickness fluctuation of the electrode.

[0066] [Method for producing secondary battery]

[0067] The manufacturing method of the secondary battery of the present disclosure is described using one embodiment. One embodiment includes: an electrode manufacturing process of manufacturing an electrode by the above-mentioned electrode manufacturing method, and a secondary battery manufacturing process of manufacturing a secondary battery using the electrode. In addition, since the electrode manufacturing process is as described above, the description thereof is omitted here.

[0068] <Secondary Battery Manufacturing Process>

[0069] The secondary battery manufacturing process is a process for manufacturing a secondary battery using the electrode obtained in the electrode manufacturing process. Such a secondary battery manufacturing process is well known. The secondary battery manufacturing process is described below using a typical example, but is not limited to this method.

[0070] In the case where the electrode obtained in the electrode manufacturing process is a positive electrode, a secondary battery is made using a separately made negative electrode and an electrolyte layer. In the case where the electrode obtained in the electrode manufacturing process is a negative electrode, a secondary battery is made using a separately made positive electrode and an electrolyte layer. For example, an electrolyte layer can be arranged between the positive electrode and the negative electrode to obtain a secondary battery (monopolar secondary battery).

[0071] When the electrode obtained in the electrode production step is a bipolar electrode, a secondary battery is produced using the bipolar electrode and the electrolyte layer. For example, a secondary battery (bipolar secondary battery) can be obtained by arranging an electrolyte layer between bipolar electrodes.

[0072] When the electrolyte layer is a liquid electrolyte layer, a separator is arranged between the electrodes, and then an electrolyte is supplied to the separator to obtain an electrolyte layer. The separator is mainly a polyolefin-based porous sheet. The electrolyte is an electrolyte in which a supporting salt is dissolved in a non-aqueous solvent. As non-aqueous solvents, carbonates, ethers, esters, etc. can be cited. Support salts include, for example, LiPF6, LiBF4, lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethane) sulfonyl imide (LiSI), etc.

[0073] When the electrolyte layer is a solid electrolyte layer, the battery can be made by configuring the solid electrolyte layer between the electrodes. The solid electrolyte layer contains a solid electrolyte. In addition, the solid electrolyte layer may also contain a binder. The solid electrolyte and the binder can be appropriately selected from the above-mentioned solid electrolytes and binders.

[0074] The above describes the manufacturing method of the secondary battery disclosed in the present invention using one embodiment. The manufacturing method of the secondary battery disclosed in the present invention manufactures the electrode based on the above-mentioned electrode manufacturing method, thereby suppressing the thickness fluctuation of the electrode. Therefore, according to the manufacturing method of the secondary battery disclosed in the present invention, the battery quality can be improved.

[0075] [Example]

[0076] The present disclosure will be further described using the embodiments. Based on Table 1, each electrode was pressed. The following describes each embodiment and comparative example.

[0077] <Comparative Example 1>

[0078] On metal foil with a unit area weight of 36 mg / cm 2 A slurry containing a negative electrode material was applied, and then the applied slurry was dried at 100° C. for 10 minutes to form a negative electrode active material layer. Next, the negative electrode active material layer was roll-pressed to obtain a negative electrode of Comparative Example 1.

[0079] Here, a combination foil of aluminum and copper is used as the metal foil. Graphite is used as the negative electrode material. In addition, the negative electrode material contains a conductive material and / or a binder, etc. As the solvent used in the slurry, ion exchange water is used.

[0080] <Comparative Example 2, Examples 1 to 3>

[0081] A negative electrode active material layer was formed on the metal foil in the same manner as in Comparative Example 1. Next, the negative electrode active material layer was roll-pressed twice to obtain negative electrodes of Comparative Example 2 and Examples 1 to 3.

[0082] <Example 4>

[0083] A negative electrode active material layer was formed on the metal foil in the same manner as in Comparative Example 1. Next, the negative electrode active material layer was subjected to the first roll pressing, and then heated. The heating conditions were a temperature of 120° C. and 1 minute. Then, the negative electrode active material layer was subjected to the second roll pressing, and the negative electrode of Example 4 was obtained.

[0084] <Comparative Example 3>

[0085] On the first side of the metal foil, the weight per unit area is 36 mg / cm 2 Apply the slurry containing the negative electrode material on the second surface with a unit area weight of 72 mg / cm 2 A slurry containing a positive electrode material was applied, and then the applied slurry was dried at 100° C. for 10 minutes to form a negative electrode active material layer and a positive electrode active material layer. Next, the negative electrode active material layer and the positive electrode active material layer were roll-pressed to obtain a bipolar electrode of Comparative Example 1.

[0086] The negative electrode material used was the same material as in Comparative Example 1. The positive electrode material used was lithium iron phosphate. The positive electrode material contained a conductive material and / or a binder, etc. The solvent used in the slurry was the same solvent as in Comparative Example 1.

[0087] <Comparative Example 4, Example 5>

[0088] On the first side of the metal foil, the weight per unit area is 36 mg / cm 2 The slurry containing the negative electrode material was applied and dried at 100°C for 10 minutes to form a negative electrode active material layer. Next, the negative electrode active material layer was roll-pressed (first time). Next, the second side of the metal foil was rolled with a unit area weight of 72 mg / cm 2 The slurry containing the positive electrode material was applied and dried at 100°C for 10 minutes to form a positive electrode active material layer. Next, the negative electrode active material layer and the positive electrode active material layer were roll-pressed (second time) to obtain bipolar electrodes of Comparative Example 4 and Example 5. The negative electrode material, positive electrode material, and solvent used were the same as those of Comparative Example 3.

[0089] <Example 6>

[0090] On the first side of the metal foil, the weight per unit area is 36 mg / cm 2 The slurry containing the negative electrode material was applied and dried at 100°C for 10 minutes to form a negative electrode active material layer. Next, the negative electrode active material layer was roll-pressed (first time). Next, the second side of the metal foil was rolled with a unit area weight of 72 mg / cm 2A slurry containing a positive electrode material is applied and dried at 100°C for 10 minutes to form a positive electrode active material layer. Next, the negative electrode active material layer and the positive electrode active material layer are heated. The heating conditions are a temperature of 120°C and 1 minute. Then, the negative electrode active material layer and the positive electrode active material layer are roll-pressed (for the second time) to obtain the bipolar electrode of Example 6. In addition, the negative electrode material, the positive electrode material, and the solvent use the same materials as those in Comparative Example 3.

[0091] Table 1

[0092]

[0093] Here, the "rebound amount" recorded in Table 1 is obtained by the following method. First, each electrode is heated at 120°C for 1 minute to make the negative electrode active material layer rebound. Then, the rebound amount is calculated based on the difference in thickness of the negative electrode active material layer before and after heating. In addition, the density of the negative electrode active material layer after rebound is measured. The obtained density is recorded in Table 1 "Density of negative electrode active material layer after pressing (g / cm 3 )" in the second column.

[0094] <Results>

[0095] Compared with Comparative Examples 1 to 4, the springback amount of Examples 1 to 6 is reduced. This result is the same regardless of the negative electrode and the bipolar electrode. It can be understood that in order to reduce the springback amount, it is important to make the pressing line pressure ratio (P2 / P1) 100% or more. Among them, if the pressing line pressure ratio (P2 / P1) is 100% or more and 125% or less, the springback amount is further reduced.

Claims

1. A method for manufacturing an electrode, comprising: a first active material layer forming step of forming a first active material layer on a first surface of the current collector; a first pressing step of pressing the first active material layer; and a second pressing step of pressing the first active material layer after the first pressing step, The ratio of the pressing line pressure P2 in the second pressing step to the pressing line pressure P1 in the first pressing step is 100% or more and 200% or less.

2. The method for producing an electrode according to claim 1, The ratio of the pressing line pressure P2 in the second pressing step to the pressing line pressure P1 in the first pressing step is 100% or more and 125% or less.

3. The method for manufacturing an electrode according to claim 1, A heating step of heating the first active material layer is provided after the first pressing step and between the second pressing step.

4. The method for manufacturing an electrode according to claim 1, A second active material layer forming step of forming a second active material layer on a second surface of the current collector is provided after the first pressing step and between the second pressing step.

5. A method for manufacturing a secondary battery, comprising: An electrode manufacturing step of manufacturing an electrode by the electrode manufacturing method according to any one of claims 1 to 4; and A secondary battery manufacturing process for manufacturing a secondary battery using the electrode.

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