Electrode manufacturing method and secondary battery manufacturing method

Abstract

To provide a method for manufacturing an electrode capable of suppressing variation in thickness of the electrode.SOLUTION: A method for manufacturing an electrode includes a first active material layer forming step of forming a first active material layer on a first surface of a current collector, a first press step of pressing the first active material layer, and a second press step of pressing the first active material layer after the first press step, and a ratio of a press line pressure P2 in the second press step to a press line pressure P1 in the first press step is 100% or more and 200% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] An electrode provided in a secondary battery is produced by forming an active material layer on a current collector, and then pressing the active material layer at a predetermined pressure to adjust the density. For example, Patent Document 1 discloses a method for producing a bipolar electrode, which includes forming a negative electrode active material layer on a first surface of a first metal foil, pressing the negative electrode active material layer with the first surface of a second metal foil facing the second surface of the first metal foil, forming a positive electrode active material layer on the second surface of the second metal foil, and pressing the positive electrode active material layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-82504 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, the active material layer is pressed to adjust the density of the active material layer. However, after pressing, the residual stress from the pressing is released over time, and the thickness of the active material layer may increase. That is, springback may occur in the active material layer. This causes variation in the thickness of the active material layer, which changes the density of the active material layer and causes a problem of unstable quality of the electrode.

[0005] The present inventors have found that the above problem cannot be sufficiently suppressed even in the electrode manufacturing method described in Patent Document 1, in which two presses are performed on the negative electrode active material layer. This is thought to be because the second press line pressure is set to be smaller than the first press line pressure. Usually, in the second press, the direction of surface pressure application approaches the vertical direction, so that the conveying direction component becomes smaller. Then, in the second press, the amount of plastic deformation of the active material layer is insufficient, and therefore the amount of springback of the active material layer becomes large. Therefore, the present inventors have found that the electrode manufacturing method described in Patent Document 1 cannot sufficiently suppress the occurrence of variations in the thickness of the active material layer.

[0006] In view of the above circumstances, a main object of the present disclosure is to provide a method for manufacturing an electrode that can suppress variation in thickness of the electrode. [Means for solving the problem]

[0007] The present disclosure provides at least the following aspects.

[0008] The first aspect is a method for manufacturing an electrode, comprising a first active material layer formation step of forming a first active material layer on a first surface of a current collector, a first press step of pressing the first active material layer, and a second press step of pressing the first active material layer after the first press step, wherein a ratio of a press line pressure P2 in the second press step to a press line pressure P1 in the first press step is 100% or more and 200% or less.

[0009] A second aspect is the method for producing an electrode according to the first aspect, in which the ratio of the press line pressure P2 in the second press step to the press line pressure P1 in the first press step is 100% or more and 125% or less.

[0010] A third aspect is a method for producing an electrode according to the first or 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.

[0011] A fourth aspect is a 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 press step and between the second press step.

[0012] A fifth aspect is a method for producing a secondary battery, comprising: an electrode production step of producing an electrode by the electrode production method according to any one of the first to fourth aspects; and a secondary battery production step of producing a secondary battery by using the electrode. Effect of the Invention

[0013] According to the method for producing an electrode of the present disclosure, it is possible to suppress variation in thickness of the electrode, and according to the method for producing a secondary battery of the present disclosure, it is possible to improve battery quality. [Brief description of the drawings]

[0014] [Figure 1] 2 is a flowchart of the first embodiment. [Diagram 2] FIG. 1 is a schematic diagram of a first pressing step S12. [Diagram 3] 11 is a flowchart of a second embodiment. [Figure 4] FIG. 11 is a schematic diagram of a second pressing step S25. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [Electrode manufacturing method] The method for producing an electrode according to the present disclosure will be described in detail using a first embodiment and a second embodiment.

[0016] First Embodiment A flow chart of the first embodiment is shown in Fig. 1. As shown in Fig. 1, 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.

[0017] (First active material layer forming step S11) The first active material layer forming step S11 is a step of forming a first active material layer 20 on the first surface 11 of the current collector 10.

[0018] The current collector 10 is a rectangular sheet-like conductive member in a plan view. 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 made of, for example, a metal foil or an alloy foil. Examples of the metal foil include copper foil, aluminum foil, titanium foil, and nickel foil. Examples of the alloy foil include stainless steel foil, plated steel sheet, and plated stainless steel sheet. The alloy foil may be an alloy foil of the metals exemplified as the materials for the metal foil. The current collector 10 may be formed by integrating or laminating a plurality of metal foils, or may be formed by plating the surface of a metal foil with another metal.

[0019] The first active material layer 20 is a sheet-shaped active material layer. The first active material layer 20 contains a positive electrode active material or a negative electrode active material.

[0020] Examples of the positive electrode active material include composite oxides, metallic lithium, and sulfur. The composition of the composite oxide includes at least one of iron, manganese, titanium, nickel, cobalt, and aluminum, and lithium. Examples of the composite oxide include olivine-type lithium iron phosphate (LiFePO4), LiCoO2, and LiNiMnCoO2.

[0021] Examples of the negative electrode active material include graphite, artificial graphite, highly oriented graphite, mesocarbon microbeads, hard carbon, soft carbon, and other carbon, metal compounds, elements capable of being alloyed with lithium or compounds of such elements, boron-added carbon, etc. Examples of elements capable of being alloyed with lithium include silicon and tin.

[0022] The first active material layer 20 may optionally contain a conductive additive. Examples of the conductive additive include acetylene black, carbon black, and graphite.

[0023] The first active material layer 20 may optionally contain a binder. Examples of binders include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluorine rubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, acrylic resins containing monomer units such as acrylic acid and 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.

[0024] The first active material layer 20 may optionally contain a solid electrolyte. Examples of the solid electrolyte include an oxide solid electrolyte, a sulfide solid electrolyte, and a nitride solid electrolyte.

[0025] 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 may be a positive electrode active material layer or a negative electrode active material layer. From the viewpoint of further suppressing an increase in the electrode thickness due to springback, the first active material layer 20 may be a negative electrode active material layer. This is because a higher density is typically required for the negative electrode active material layer than for the positive electrode active material layer.

[0026] 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 may be appropriately adopted. Examples of the method include roll coating, die coating, dip coating, doctor blade, spray coating, and curtain coating. Specifically, the electrode material constituting the first active material layer is mixed with a solvent to obtain a slurry, and then the slurry is applied to the first surface 11 of the current collector 10 and dried to form the first active material layer. The solvent is, for example, N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, or water.

[0027] (First pressing process S12) The first pressing step S12 is carried out 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 by a roll press. A schematic diagram of the first pressing step S12 is shown in FIG.

[0028] The press line pressure P1 in the first press step S12 is not particularly limited, but may be, for example, 3 kN / cm or more and 5 kN / cm or less. However, the press line pressure P1 in the first press step S12 is equal to or less than the press line pressure P2 in the second press step S14. Details will be described later.

[0029] (Heating process S13) The heating step S13 is carried out between the first pressing step S12 and the second pressing step S14, and is a step of heating the first active material layer 20. By carrying out the heating step S13, residual stress in the first active material layer 20 is released. Therefore, by carrying out the heating step S13, it is possible to further suppress variations in the thickness of the electrode. However, the heating step S13 is an optional step and does not have to be carried out.

[0030] The heating step S13 may be performed in an air atmosphere or an inert gas atmosphere. The heating temperature is not particularly limited, but is, for example, 120°C or more and 150°C or less. If the heating temperature is less than 120°C, the residual stress of the first active material layer 20 cannot be sufficiently released. If the heating temperature exceeds 150°C, there is a risk of deteriorating the first active material layer 20. The heating time is not particularly limited, but 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 sufficiently released. If the heating time is 5 minutes or more, there is a risk of deteriorating the first active material layer 20.

[0031] (Second pressing process S14) 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.

[0032] The pressing may be performed by a roll press (see FIG. 2). The press line pressure P2 in the second pressing step S14 is not particularly limited, but may be, for example, 4 kN / cm or more and 6 kN / cm or less.

[0033] Here, the first embodiment is characterized in that the ratio (P2 / P1) of the press line pressure P2 in the second press step S14 to the press line pressure P1 in the first press step S11 is 100% or more and 200% or less.

[0034] 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, springback occurs in the first active material layer 20. As a result, the thickness of the first active material layer 20 varies, and the density of the first active material layer 20 changes, resulting in a problem of unstable quality of the electrode. In contrast, in the first embodiment, the first active material layer 20 is pressed at least twice. In addition, the ratio (P2 / P1) of the press line pressure P2 in the second press step S14 to the press line pressure P1 in the first press step S11 is 100% or more and 200% or less. This increases the fluidity of the particles constituting the first active material layer 20, disperses the residual stress, and increases the amount of plastic deformation (the component of the press surface pressure in the conveying direction), thereby reducing the increase in the thickness of the first active material layer due to springback. Therefore, according to the first embodiment, the variation in the thickness of the electrode can be reduced.

[0035] If the ratio (P2 / P1) is less than 100%, the amount of plastic deformation of the first active material layer 20 is small, and the increase in thickness of the first active material layer due to springback cannot be sufficiently reduced. If the ratio (P2 / P1) exceeds 200%, the vertical component of the press surface pressure becomes large, and the amount of springback due to elastic deformation of the active material layer becomes large, and the increase in thickness of the first active material layer cannot be sufficiently reduced. From the viewpoint of further enhancing the effect, the ratio (P2 / P1) may be 100% or more and 125% or less, or may be more than 100% and 125% or less.

[0036] <Second embodiment> A flow chart of the second embodiment is shown in Fig. 3. As shown in Fig. 3, 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 differs from the first embodiment mainly in that it includes a second active material layer forming step S23. Each step will be described below.

[0037] The first active material layer forming step S21 and the first pressing step S22 are similar to the first active material layer forming step S11 and the first pressing step S12 in the first embodiment, and therefore a description thereof will be omitted here.

[0038] (Second active material layer forming step S23) The second active material forming step S23 is carried out between the first pressing step S22 and the heating step S24, and is a step of forming a second active material layer 30 on the second surface 12 of the current collector 10.

[0039] The second active material layer 30 may be a positive electrode active material layer or a negative electrode active material layer. The second active material layer 30 may be the same type of active material layer as the first active material layer 20 or a different type of active material layer. Typically, when a monopolar secondary battery is intended, the second active material layer 30 is the same type of active material layer as the first active material layer. When a bipolar secondary battery is intended, the second active material layer 30 is the different type of active material layer from the first active material layer. Typically, the density of the negative electrode active material layer is made higher than the density of the positive electrode active material layer. From this viewpoint, the first active material layer 20 may be the negative electrode active material layer, and the second active material layer 30 may be the positive electrode active material layer.

[0040] The material constituting the second active material layer 30 may be appropriately selected from the materials constituting the first active material layer 20. The method for forming the second active material layer 30 may be appropriately selected from the methods for forming the first active material layer 20.

[0041] (Heating process S24) The heating step S24 is carried out between the second active material forming step S23 and the second pressing step S25, and is a step of heating the first active material layer 20 and the second active material layer 30. The heating step S24 differs 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, a detailed description will be omitted. However, the heating step S24 is an optional step and does not have to be carried out.

[0042] (Second pressing process S25) 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. If 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 differs 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. A schematic diagram of the second pressing step S25 is shown in FIG. 4.

[0043] Here, like the first embodiment, the second embodiment is characterized in that the ratio (P2 / P1) of the press line pressure P2 in the second press step S25 to the press line pressure P1 in the first press step S21 is 100% or more and 200% or less. From the viewpoint of enhancing the effect, the ratio (P2 / P1) may be 100% or more and 125% or less, or may be more than 100% and 125% or less.

[0044] The second embodiment has the above-mentioned features, and thus can reduce the increase in thickness of the first active material layer due to spring back, similar to the first embodiment, and therefore can reduce the variation in thickness of the electrode.

[0045] The electrode manufacturing method of the present disclosure has been described above using the first and second embodiments. The electrode manufacturing method of the present disclosure suppresses an increase in the thickness of the electrode due to springback. Therefore, according to the electrode manufacturing method of the present disclosure, it is possible to suppress the variation in the thickness of the electrode.

[0046] [Secondary battery manufacturing method] The method for producing a secondary battery according to the present disclosure will be described using one embodiment. The embodiment includes an electrode production process for producing an electrode by the above-mentioned electrode production process, and a secondary battery production process for producing a secondary battery using the electrode. Note that the electrode production process has been described above, so a description thereof will be omitted here.

[0047] <Secondary battery manufacturing process> The secondary battery manufacturing process is a process of manufacturing a secondary battery using the electrode obtained in the electrode manufacturing process. Such a secondary battery manufacturing process is known. The secondary battery manufacturing process will be described below using a typical example, but is not limited to this form.

[0048] When the electrode obtained in the electrode preparation process is a positive electrode, a secondary battery is prepared using a separately prepared negative electrode and electrolyte layer. When the electrode obtained in the electrode preparation process is a negative electrode, a secondary battery is prepared using a separately prepared positive electrode and electrolyte layer. For example, a secondary battery (monopolar secondary battery) can be obtained by disposing an electrolyte layer between the positive electrode and the negative electrode.

[0049] When the electrode obtained in the electrode preparation step is a bipolar electrode, a secondary battery is prepared using the bipolar electrode and an electrolyte layer. For example, a secondary battery (bipolar secondary battery) can be obtained by disposing an electrolyte layer between bipolar electrodes.

[0050] When the electrolyte layer is a liquid electrolyte layer, a separator is placed between the electrodes, and then an electrolyte solution is supplied to the separator to obtain the electrolyte layer. The separator is mainly a polyolefin-based porous sheet. The electrolyte solution is a non-aqueous solvent in which a supporting salt is dissolved. Examples of the non-aqueous solvent include carbonates, ethers, and esters. Examples of the supporting salt include LiPF6, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethane)sulfonimide (LiTFSI).

[0051] When the electrolyte layer is a solid electrolyte layer, a battery can be fabricated by disposing the solid electrolyte layer between the electrodes. The solid electrolyte layer includes a solid electrolyte. The solid electrolyte layer may also include a binder. The solid electrolyte and the binder may be appropriately selected from the solid electrolytes and binders described above.

[0052] The method for manufacturing a secondary battery according to the present disclosure has been described above using one embodiment. Since the method for manufacturing a secondary battery according to the present disclosure manufactures electrodes based on the above-mentioned electrode manufacturing method, the variation in thickness of the electrodes is suppressed. Therefore, the method for manufacturing a secondary battery according to the present disclosure can improve battery quality. EXAMPLES

[0053] The present disclosure will be further described using embodiments. Pressing was performed on each electrode based on Table 1. Each example and comparative example will be described below.

[0054] <Comparative Example 1> A slurry containing negative electrode material was applied to the metal foil at a weight of 36 mg / cm 2 The coated slurry was then dried at 100° C. for 10 minutes to form a negative electrode active material layer. The negative electrode active material layer was then subjected to roll pressing to obtain a negative electrode of Comparative Example 1.

[0055] Here, a laminated foil of aluminum and copper was used as the metal foil, graphite was used as the negative electrode material, and a conductive material, a binder, etc. were included in the negative electrode material, and ion-exchanged water was used as the solvent for the slurry.

[0056] <Comparative Example 2, Examples 1 to 3> A negative electrode active material layer was formed on the metal foil in the same manner as in Comparative Example 1. Then, the negative electrode active material layer was roll-pressed twice to obtain negative electrodes of Comparative Example 2 and Examples 1-3.

[0057] <Example 4> 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 a first roll press, and then the negative electrode active material layer was heated. The heating conditions were a temperature of 120° C. and 1 minute. Then, the negative electrode active material layer was subjected to a second roll press to obtain a negative electrode of Example 4.

[0058] <Comparative Example 3> A slurry containing the negative electrode material was applied to the first surface of the metal foil at a basis weight of 36 mg / cm. 2 On the second surface, a slurry containing the positive electrode material was applied at a coating weight of 72 mg / cm 2 The coated slurry was then dried at 100° C. for 10 minutes to form a negative electrode active material layer and a positive electrode active material layer. The negative electrode active material layer and the positive electrode active material layer were then roll pressed to obtain a bipolar electrode of Comparative Example 1.

[0059] The negative electrode material was the same as that of Comparative Example 1. The positive electrode material was lithium iron phosphate. The positive electrode material contained a conductive material, a binder, etc. The solvent used for the slurry was the same as that of Comparative Example 1.

[0060] <Comparative Example 4, Example 5> A slurry containing the negative electrode material was applied to the first surface of the metal foil at a basis weight of 36 mg / cm. 2 The negative electrode active material layer was then subjected to roll pressing (first time). Next, a slurry containing a positive electrode material was applied to the second surface of the metal foil in a coating amount of 72 mg / cm2. 2 The mixture was then coated with a mixture of 0.1% by weight 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 (for the 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 used in Comparative Example 3.

[0061] <Example 6> A slurry containing the negative electrode material was applied to the first surface of the metal foil at a basis weight of 36 mg / cm. 2The negative electrode active material layer was then subjected to roll pressing (first time). Next, a slurry containing a positive electrode material was applied to the second surface of the metal foil in a coating amount of 72 mg / cm2. 2 The mixture was applied to the negative electrode active material layer 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 heated. The heating conditions were a temperature of 120°C and 1 minute. Then, the negative electrode active material layer and the positive electrode active material layer were roll pressed (for the second time) to obtain a bipolar electrode of Example 6. The negative electrode material, the positive electrode material, and the solvent used were the same as those used in Comparative Example 3.

[0062] [Table 1]

[0063] The "springback amount" shown in Table 1 was obtained by the following method. First, each electrode was heated at 120°C for 1 minute to cause the negative electrode active material layer to spring back. The springback amount was calculated from 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 springback was measured. The obtained density is shown in the "density of the negative electrode active material layer after pressing (g / cm3)" in Table 1. 3 )" in the second column.

[0064] <Result> The amount of springback was reduced in Examples 1 to 6 compared to Comparative Examples 1 to 4. This result was the same regardless of whether the electrode was a negative electrode or a bipolar electrode. From this, it can be understood that in order to reduce the amount of springback, it is important that the press line pressure ratio (P2 / P1) is 100% or more. In particular, when the press line pressure ratio (P2 / P1) is 100% or more and 125% or less, the amount of springback was further reduced. [Explanation of symbols]

[0065] 10 Current collector 11 Page 1 12 Side 2 20 First active material layer 30 The second active material layer

Claims

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

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

3. The method for producing an electrode according to claim 1 , further comprising a heating step of heating the first active material layer after the first pressing step and between the second pressing step.

4. The method for producing an electrode according to claim 1 , 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.

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

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