Method for manufacturing an electrode sheet

Abstract

To provide a manufacturing method for an electrode sheet that can suppress scratches and foil breakage on a current collector foil and has excellent removability of protruding portions.SOLUTION: The manufacturing method for an electrode sheet includes a coating film forming step in which a coating film is formed on the surface of a second roll by passing an electrode mixture between a first roll and the second roll rotating opposite to each other, a removal step for removing a protrusion formed at the edge of the coating film in the width direction by pressing a blade against the coating film, and a transfer step of transferring the coating film onto the surface of the collector foil by passing the coating film and the collector foil conveyed by a third roll rotating opposite the second roll between the second and third rolls, after the removal step.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Conventionally, as an electrode sheet (a positive electrode sheet or a negative electrode sheet), an electrode sheet having an electrode mixture layer on the surface of a current collector foil is known. As a method for manufacturing the electrode sheet, the following method is known. First, an electrode mixture composed of a plurality of wet granules obtained by mixing an electrode active material, a binder, and a solvent and granulating is produced. Next, the electrode mixture is passed between a first roll and a second roll that rotate oppositely to form a film while compressing the electrode mixture, and the film-shaped electrode mixture is adhered to the surface of the second roll. Further, a current collector foil conveyed by a third roll that rotates oppositely to the second roll is passed through the gap between the second roll and the third roll, so that the film-shaped electrode mixture adhered to the surface of the second roll is brought into contact with the surface of the current collector foil while being pressurized, transferred to the surface of the current collector foil, and dried to obtain an electrode sheet.

[0003] As in the above method, the film-shaped electrode mixture transferred to the surface of the current collector foil may form protruding portions that protrude outward in the width direction at both ends in the width direction, and both ends in the width direction may have an uneven shape. In contrast, in the manufacturing method of Patent Document 1, it has been proposed to remove the protruding portions using a blade after transferring the film-shaped electrode mixture to the surface of the current collector foil and before drying.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The manufacturing method of Patent Document 1 requires precise adjustment of the surface pressure of the blade against the film-like electrode composite material. Specifically, when the surface pressure is set high, there is a possibility of damage, foil breakage, etc. occurring in the current collector foil, and when the surface pressure is set low, the removal of the protruding portion is not sufficient, and so-called doctor streaks may occur.

[0006] The problem to be solved by one embodiment of the present disclosure is to provide a manufacturing method of an electrode sheet that can suppress the occurrence of damage and foil breakage in the current collector foil and has excellent removability of the protruding portion.

Means for Solving the Problem

[0007] The means for solving the above problems include the following embodiments. <1> A coating film forming step of passing an electrode composite material between a first roll and a second roll that rotate oppositely and forming a coating film on the surface of the second roll, A removing step of removing a protruding portion formed at an end in the width direction of the coating film by pressing a blade against the coating film, After the removing step, a transfer step of passing a current collector foil conveyed by a third roll that rotates opposite to the second roll and the coating film between the second roll and the third roll and transferring the coating film onto the surface of the current collector foil. A manufacturing method of an electrode sheet including the above steps. <2> The manufacturing method of the electrode sheet according to <1> above, wherein an angle θ formed by a tangent line passing through a contact point between the blade and the second roll and the surface of the blade on the second roll side is 20° to 60°. <3> The manufacturing method of the electrode sheet according to <1> or <2> above, wherein the thickness of the blade is 0.3 mm to 2.0 mm. <4> The manufacturing method of the electrode sheet according to any one of <1> to <3> above, wherein the blade contains one or more resins selected from the group consisting of polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), and polypropylene (PP). <5> The surface pressure applied to the coating film by the blade is 100 MPa to 300 MPa, and the method for manufacturing the electrode sheet according to any one of <1> to <4> above.

Effect of the Invention

[0008] According to one embodiment of the present disclosure, it is possible to provide a method for manufacturing an electrode sheet that can suppress the occurrence of scratches and foil breakage on the current collector foil and has excellent removability of protrusions.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0010] In the present disclosure, a numerical range indicated by using "~" means a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. In the numerical ranges described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples. In the present disclosure, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, unless otherwise specified, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances.

[0011] [Method for manufacturing an electrode sheet] A coating film forming step of passing an electrode mixture through between a first roll and a second roll that rotate facing each other, and forming a coating film on the surface of the second roll; A removing step of removing protrusions formed at both end portions in the width direction of the coating film by pressing a blade against the coating film; After the removing step, a transfer step of passing a current collecting foil conveyed by a third roll that rotates facing the second roll and the coating film through between the second roll and the third roll, and transferring the coating film onto the surface of the current collecting foil; A method for manufacturing an electrode sheet, including the above steps.

[0012] According to the method for manufacturing an electrode sheet of the present disclosure, it is possible to suppress the occurrence of damage and foil breakage on the current collecting foil, and the removability of protrusions is excellent. Although the reason for achieving the above effects is not clear, it is presumed as follows. In the method for manufacturing an electrode sheet of the present disclosure, the protrusions are removed before transferring the coating film onto the surface of the current collecting foil. It is presumed that this can suppress the occurrence of damage and foil breakage on the current collecting foil. In addition, since the protrusions are removed before transferring the coating film onto the surface of the current collecting foil, the surface pressure of the blade against the coating film can be set high. Therefore, it is presumed that the protrusions can be sufficiently removed.

[0013] The method for manufacturing an electrode sheet of the present disclosure may include a drying step of drying the coating film after the transfer step.

[0014] (Coating film forming step) In the coating film forming step, an electrode mixture is passed through between a first roll and a second roll that rotate facing each other, and a coating film is formed on the surface of the second roll.

[0015] The thickness of the formed coating film is preferably appropriately changed according to the application, and for example, it can be set to 50 μm to 600 μm. Regarding the thickness of the coating film after passing between the second roll and the third roll as well, it is preferably appropriately changed according to the application, and for example, it can be set to 30 μm to 500 μm.

[0016] The rotational speed of the second roll is preferably greater than the rotational speed of the first roll. The formation of the coating film on the surface of the second roll can be easily performed. When the rotational speed of the first roll (rpm: revolutions per minute) is S1 and the rotational speed of the second roll is S2, S2 / S1 is preferably 1.5 to 4.0.

[0017] - Electrode mixture - The electrode mixture may be in any form of paste, slurry, and granulated bodies. Among them, granulated bodies, particularly granulated bodies in a wet state, are preferable. In the present disclosure, the "granulated body in a wet state" refers to a mixture of at least a powder material and a solvent, and is a granulated body that is dispersed in a plurality of discontinuous forms such as powder form, flaky form, and chunk form (a relatively large lump compared to the powder form).

[0018] As the electrode mixture, those generally used as electrode materials for non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, can be used.

[0019] When manufacturing the positive electrode sheet, the electrode mixture contains a positive electrode active material and a solvent. Further, the electrode mixture can contain a conductive material, a binder, and the like. As the positive electrode active material, a lithium transition metal composite oxide, a lithium transition metal phosphate compound (for example, LiFePO4), etc. can be preferably used. Examples of the lithium transition metal composite oxide include a lithium nickel-based composite oxide, a lithium cobalt-based composite oxide, a lithium manganese-based composite oxide, a lithium nickel manganese-based composite oxide (for example, LiNi 0.5 Mn 1.5O4), lithium nickel manganese cobalt composite oxide (for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), etc. can be mentioned. As the solvent, N-methyl-2-pyrrolidone or the like can be used. As the conductive material, carbon black such as acetylene black (AB) and other carbon materials (such as graphite) can be preferably used. As the binder, for example, polyvinylidene fluoride (PVDF) or the like can be used.

[0020] When manufacturing the negative electrode sheet, the electrode mixture contains a negative electrode active material and a solvent. Further, the electrode mixture can contain a binder, a binding material, etc. As the negative electrode active material, carbon materials such as graphite, hard carbon, soft carbon, and carbon nanotubes can be preferably used. As the solvent, water or the like can be used. As the binder, styrene-butadiene rubber (SBR) or the like can be used. As the binding material, carboxymethyl cellulose (CMC) or the like can be used.

[0021] The electrode mixture can be prepared by putting the above materials into a known stirring granulator and mixing and granulating them. Also, commercially available ones can be used as the electrode mixture.

[0022] (Removal step) In the removal step, by pressing a blade against the coating film, the protrusions formed at the widthwise ends of the coating film are removed. The blade is preferably provided at both widthwise ends of the coating film to remove the protrusions formed at both ends of the coating film.

[0023] The thickness of the blade is preferably 0.3 mm to 2.0 mm, and more preferably 0.5 mm to 1.5 mm. When the thickness of the blade is 0.3 mm or more, the strength of the blade can be improved. When the thickness of the blade is 2.0 mm or less, a decrease in the surface pressure applied to the coating film can be suppressed, and the removability of the protrusions can be improved. Note that the blade thickness means the thickness at the part where the blade thickness is maximum.

[0024] The material of the blade is not particularly limited, and conventionally known materials can be used, such as resins and metals. From the viewpoint of suppressing foreign matter contamination, it is preferably a resin. Among the resins, a resin with high solubility resistance to the solvent that the electrode composite material may contain is preferable, and it is more preferably one or more resins selected from the group consisting of polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), and polypropylene (PP). The content rate of the resin with respect to the total mass of the blade is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass.

[0025] The shape of the blade is not particularly limited, and for example, it can be plate-shaped.

[0026] As shown in FIG. 1, the angle θ formed by the tangent line passing through the contact point between the blade 10 and the second roll 11 and the surface of the blade 10 on the second roll side is preferably 20° to 60°, more preferably 25° to 55°, and still more preferably 30° to 40°. When the angle θ is 20° or more, it is possible to suppress the electrode composite material from entering between the worn blade and the second roll, and improve the removability of the protrusion. When the angle θ is 60° or less, it is possible to suppress the blade from deforming when the blade is pressed against the coating film, and improve the removability of the protrusion. The rotation direction of the second roll 11 is indicated by an arrow in FIG. 1.

[0027] From the viewpoint of the removability of the protrusion, the surface pressure applied to the coating film by the blade is preferably 100 MPa to 300 MPa, more preferably 150 MPa to 250 MPa, and still more preferably 180 MPa to 220 MPa. The above surface pressure is measured as follows. After the blade is brought into contact with the roll surface with a pressure-sensitive film (for example, Prescale HHS manufactured by Fujifilm) attached thereto, the blade is separated from the roll, the pressure-sensitive film is recovered, and the pressure-sensitive film is read by a scanner and subjected to image analysis (using, for example, FPD-8010J manufactured by Fujifilm, etc.).

[0028] The removed protrusions are preferably recovered by a recovery device. Thereby, it is possible to suppress the protrusions from depositing on the surface of the blade and the removability of the protrusions from deteriorating. As the recovery device, a conventionally known dust collector can be used. The recovery device is preferably provided at both ends in the width direction of the coating film.

[0029] (Transfer process) The transfer process is performed after the removal process, and the current collector foil conveyed by the third roll that rotates opposite to the second roll and the coating film formed on the surface of the second roll are passed between the second roll and the third roll, and the coating film is transferred onto the surface of the current collector foil.

[0030] The minimum gap dimension between the second roll and the third roll is preferably smaller than the total thickness of the coating film and the current collector foil. Thereby, pressure is applied to the coating film and the current collector foil by the second roll and the third roll, and the coating film is transferred onto the surface of the current collector foil. The minimum gap dimension is preferably 30 μm or more smaller than the total thickness of the coating film and the current collector foil, and more preferably 50 μm or more smaller.

[0031] The rotational speed of the third roll is preferably greater than the rotational speed of the second roll. The transfer of the coating film onto the surface of the current collector foil can be easily performed. When the rotational speed of the third roll is S3 and the rotational speed of the second roll is S2, S3 / S2 is preferably 1.5 to 4.0.

[0032] -Current collector foil- As the current collector foil, those conventionally known can be used. When manufacturing the positive electrode sheet, an aluminum foil can be used as the current collector foil. When manufacturing the negative electrode sheet, a copper foil can be used as the current collector foil. The thickness of the current collector foil is preferably appropriately changed according to the application, and for example, it can be set to 6 μm to 50 μm.

[0033] (Drying process) The method for manufacturing the electrode sheet of the present disclosure can include a drying process of drying the coating film after the transfer process. The drying method is not particularly limited. For example, there is a method in which a laminate of the current collector foil and the coating film is conveyed into a drying device by a third roll and passed through it.

[0034] (Other processes) The electrode sheet of the present disclosure may include a second coating film forming process of further forming a coating film of the electrode composite material on the surface opposite to the surface on which the coating film of the current collector foil is formed. Specifically, after the transfer process or the drying process, the electrode composite material and the laminate of the current collector foil and the coating film are passed between the fourth roll and the fifth roll that rotate oppositely, and a second coating film is formed on the surface opposite to the surface on which the coating film of the current collector foil is formed. After the second coating film forming process, a second drying process of drying the coating film may be included.

[0035] Hereinafter, with reference to FIGS. 2 and 3, an embodiment of the method for manufacturing the electrode sheet of the present disclosure will be described. Note that the method for manufacturing the electrode sheet of the present disclosure is not limited thereto. FIG. 2 is a schematic side view showing an embodiment of an electrode sheet manufacturing apparatus that can be used in the method for manufacturing the electrode sheet of the present disclosure. FIG. 3 is an enlarged view seen from the X direction of FIG. 2. The electrode sheet manufacturing apparatus 20 shown in FIG. 2 includes a first roll 21, a second roll 22, a third roll 23, a blade 24, a recovery device 25, and a partition plate 26. The electrode sheet manufacturing apparatus may include a drying device 29 and a winding roll (not shown) downstream of the third roll. In FIGS. 2 and 3, the transport direction of the coating film, current collector foil, etc. is indicated by the symbol CD. Also, in FIGS. 2 and 3, the electrode mixture is indicated by the symbol 27, and the current collector foil is indicated by the symbol 28.

[0036] First, the electrode mixture 27 is supplied from above the partition plate 26 that is spaced apart in the width direction of the first roll 21 and the second roll 22, passes between the first roll 21 and the second roll 22 that rotate facing each other, and a coating film 27A is formed on the surface of the second roll 22 (coating film forming step). The formed coating film 27A is transported by the rotation of the second roll 22. The rotation directions of the first roll 21 and the second roll 22 are indicated by arrows in FIG. 2.

[0037] Next, as shown in FIG. 3, by pressing the blades 24 arranged at both ends in the width direction of the coating film 27A against the coating film 27A, the protruding portions 27a formed at both ends in the width direction of the coating film 27A are removed (removing step). The removed protruding portions 27a are recovered by the recovery device 25.

[0038] Next, the current collector foil 28 and the coating film 27A transported by the third roll 23 that rotates facing the second roll 22 are passed between the second roll 22 and the third roll 23, and the coating film 27A is transferred onto the surface of the current collector foil 28.

[0039] Next, the laminate of the current collector foil 28 and the coating film 27A is transported to the drying device 29 by the third roll 23 and passed through it to dry the coating film 27A.

[0040] Next, the laminate (electrode sheet) is wound up by a winding roll (not shown).

[0041] The electrode sheet obtained by the method for manufacturing an electrode sheet of the present disclosure can be used as a positive electrode sheet or a negative electrode sheet of a lithium-ion secondary battery.

Example

[0042] Hereinafter, the present disclosure will be described in more detail with reference to examples, but the invention of the present disclosure is not limited to these examples only.

[0043] <Example 1> An electrode sheet manufacturing apparatus shown in FIG. 2 was prepared. The minimum gap dimension between the first roll and the second roll was 220 μm, and the minimum gap dimension between the second roll and the third roll was 130 μm. The rotation speed of the first roll was 0.75 rpm, the rotation speed of the second roll was 2 rpm, and the rotation speed of the third roll was 5 rpm. The blade was made of polyetheretherketone and was a plate-shaped one with a thickness of 0.8 mm, and was provided at both ends in the width direction of the coating film.

[0044] As an electrode mixture, 97.3% by mass of a lithium nickel manganese-based composite oxide (positive electrode active material), 1.5% by mass of carbon nanotubes (conductive material), and 1.2% by mass of polyvinylidene fluoride (binder) were mixed, and further N-methyl-2-pyrrolidone (solvent) was mixed to obtain an electrode mixture (solid content concentration: 89% by mass). The electrode mixture was a granule in a wet state.

[0045] First, the electrode mixture was supplied from above a partition plate disposed apart in the width direction of the first roll and the second roll, passed between the first roll and the second roll rotating oppositely, and a coating film with a thickness of 200 μm was formed on the surface of the second roll (coating film forming step). The formed coating film was conveyed by the rotation of the second roll.

[0046] Next, as shown in FIG. 3, by pressing the blades disposed at both ends in the width direction of the coating film against the coating film, the protrusions formed at both ends in the width direction of the coating film were removed (removing step). The angle θ formed by the tangent line passing through the contact point between the blade and the second roll and the surface of the blade on the second roll side was set to 30°. Also, the surface pressure applied to the coating film by the blade was 200 MPa. The removed protrusions were recovered by a recovery device.

[0047] Next, the current collector foil and the coating film conveyed by the third roll rotating opposite to the second roll were passed between the second roll and the third roll, and the coating film was transferred onto the surface of the current collector foil. An aluminum foil with a thickness of 30 μm was used as the current collector foil. Also, the thickness of the coating film that passed between the second roll and the third roll was 100 μm.

[0048] Next, the third roll conveyed the laminate of the current collector foil and the coating film to the drying device and passed it through to dry the coating film.

[0049] Next, the laminate (electrode sheet) was wound up by a winding roll (not shown).

[0050] When the obtained electrode sheet was visually observed, it was confirmed that there were no scratches or foil breaks on the current collector foil, and the protrusions were satisfactorily removed.

Explanation of Reference Numerals

[0051] 10: Blade, 11: Second roll, 20: Electrode sheet manufacturing apparatus, 21: First roll, 22: Second roll, 23: Third roll, 24: Blade, 25: Recovery device, 26: Partition plate, 27: Electrode composite material, 27A: Coating film, 27a: Protrusion, 28: Current collector foil, 29: Drying device

Claims

1. A coating film forming step of passing an electrode mixture between a first roll and a second roll that rotate in opposite directions, and forming a coating film on the surface of the second roll; A removing step of removing the protruding portions formed at the widthwise ends of the coating film by pressing a blade against the coating film; After the removing step, a transfer step of passing a current collecting foil conveyed by a third roll that rotates opposite to the second roll and the coating film between the second roll and the third roll, and transferring the coating film onto the surface of the current collecting foil; comprising: an angle θ formed between a tangent on the rotation direction side of the second roll passing through the contact point between the blade and the second roll and the surface of the blade on the second roll side is 20° to 60°; a surface pressure applied to the coating film by the blade is 100 MPa to 300 MPa, A method for manufacturing an electrode sheet.

2. The method for manufacturing an electrode sheet according to Claim 1, wherein the thickness of the blade is 0.3 mm to 2.0 mm.

3. The method for manufacturing an electrode sheet according to Claim 1, wherein the blade contains one or more resins selected from the group consisting of polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), and polypropylene (PP).

Images