Manufacturing method of electrode sheet

Abstract

To provide a manufacturing method of an electrode sheet capable of transferring an intermittent coating film with excellent dimensional accuracy to a third roll.SOLUTION: A disclosed manufacturing method of an electrode sheet includes: a paint film forming step of forming a coating film on the surface of a second roll by passing the electrode mixture between the first and second rolls that rotate oppositely; a removal step of removing part of the coating film by bringing a linear member into contact with the second roll on which the coating film is formed, and subsequently, separating the linear member from the second roll and the coating film; and a transfer step of transferring the coating film on the surface of a current collector foil after the above removal step by passing the coating film and the current collector foil conveyed by the third roll that rotates opposite the second roll through between the second roll and the third roll.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, an electrode sheet having an electrode mixture layer on the surface of a current collector foil is known as an electrode sheet (positive electrode sheet or negative electrode sheet). The following method is known as a manufacturing method of an electrode sheet. First, an electrode mixture is prepared from a plurality of wet granules obtained by mixing and granulating an electrode active material, a binder, and a solvent. Next, the electrode mixture is compressed and made into a film by passing it between a first roll and a second roll rotating opposite to each other, and the film-like electrode mixture is attached to the surface of the second roll. Furthermore, the current collector foil conveyed by a third roll rotating opposite to the second roll is passed through the gap between the second roll and the third roll, so that the film-like electrode mixture attached to the surface of the second roll is brought into contact with the surface of the current collector foil while being pressed, and is transferred to the surface of the current collector foil and dried to obtain an electrode sheet.

[0003] Depending on the application, the film-like electrode mixture formed on the surface of the second roll is required to be an intermittent coating film rather than a continuous coating film. The intermittent coating film transferred to the surface of the current collecting foil is required to have linearity at the start and end of the coating (hereinafter also referred to as "dimensional accuracy"). As a method of forming such an intermittent coating film, Patent Document 1 discloses a method in which a roll having convex portions on its surface (hereinafter also referred to as a "convex roll") is brought into contact with the coating film formed on the surface of a second roll to remove part of the coating film, thereby forming an intermittent coating film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-17962 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one embodiment of the present disclosure is to provide a method for producing an electrode sheet that can transfer an intermittent coating film with excellent dimensional accuracy to a third roll. [Means for solving the problem]

[0006] Means for solving the above problems include the following embodiments. <1> a coating film forming step of passing an electrode mixture between a first roll and a second roll rotating opposite to each other to form a coating film on a surface of the second roll; a removing step of contacting a linear member with the second roll on which the coating film is formed, and then removing a portion of the coating film by separating the linear member from the second roll and the coating film; a transfer step of, after the removing step, passing the current collecting foil conveyed by a third roll rotating opposite to the second roll and the coating film between the second roll and the third roll to transfer the coating film onto a surface of the current collecting foil; A method for producing an electrode sheet comprising the steps of: <2> The linear member includes a wire having a thickness of 0.17 mm to 4 mm. <1> A method for producing the electrode sheet according to claim 1. <3> The tensile strength of the above wire is 21N / mm 2 ~2600N / mm 2 The above <2> A method for producing the electrode sheet according to claim 1. <4> The wire contains a fluororesin. <2> or <3> A method for producing the electrode sheet according to claim 1. <5> The second roll is brought into contact with the linear member at an angle of ±20° with respect to a direction perpendicular to a tangent line of the second roll. <1> ~ <4> 13. A method for producing the electrode sheet according to claim 12. Effect of the Invention

[0007] According to one embodiment of the present disclosure, it is possible to provide a manufacturing method for an electrode sheet, which is capable of transferring an intermittent coating film with excellent dimensional accuracy to a third roll. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic side view showing one embodiment of an electrode sheet manufacturing apparatus. [Diagram 2] FIG. 2 is a schematic side view showing one embodiment of an electrode sheet manufacturing apparatus. [Diagram 3] FIG. 3 is a schematic side view showing one embodiment of an electrode sheet manufacturing apparatus. [Figure 4] FIG. 4 is a schematic side view showing one embodiment of an electrode sheet manufacturing apparatus. [Diagram 5] FIG. 5 is a schematic perspective view showing one embodiment of a linear member. [Figure 6] FIG. 6 is a schematic side view for explaining the contact angle θ between the linear member and the second roll. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In the present disclosure, a numerical range indicated using "~" means a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in the present disclosure. In the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. In the present disclosure, the term "process" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In the present disclosure, combinations of two or more preferred embodiments are more preferred embodiments. In the present disclosure, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances, unless otherwise specified. When an embodiment of the present disclosure is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. In addition, the size of the members in each drawing is conceptual, and the relative relationship between the sizes of the members is not limited to this.

[0010] [Manufacturing method of electrode sheet] The method for producing an electrode sheet according to the present disclosure includes a coating film forming step of passing an electrode mixture between a first roll and a second roll rotating opposite to each other to form a coating film on a surface of the second roll; a removing step of contacting a linear member with the second roll on which the coating film is formed, and then removing a portion of the coating film by separating the linear member from the second roll and the coating film; After the removing step, the method includes a transfer step of passing the current collecting foil, which is conveyed by a third roll rotating 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.

[0011] According to the manufacturing method of the electrode sheet of the present disclosure, an intermittent coating film with excellent dimensional accuracy can be transferred to the third roll. Although the reason why the above effect is achieved is not clear, it is presumed as follows. When a portion of a coating film is removed using a conventional convex roll, the gap between the convex roll and the second roll may vary. When the gap becomes small, the coating start and end may be stretched, which may reduce dimensional accuracy. It is presumed that the electrode sheet manufacturing method of the present disclosure can transfer an intermittent coating film with excellent dimensional accuracy to the third roll without causing such fluctuation in the roll gap. In addition, when a conventional convex roll was used, the removed coating film was torn off from the continuous coating film by the convex roll, and the linearity of the coating start and end was not sufficient. In the manufacturing method of the electrode sheet of the present disclosure, a linear member is used to cut and remove a part of the coating film from the continuous coating film, and it is presumed that an intermittent coating film with excellent dimensional accuracy can be transferred to the third roll.

[0012] The manufacturing method of the electrode sheet of the present disclosure can include a drying step of drying the coating film after the transfer step.

[0013] (Coating film formation process) In the coating film forming step, the electrode mixture is passed between a first roll and a second roll which rotate in an opposing manner, and a coating film is formed on the surface of the second roll.

[0014] The thickness of the coating film to be formed is preferably appropriately changed depending on the application, and can be, for example, 50 μm to 600 μm. It is preferable that the thickness of the coating film after passing between the second roll and the third roll is also appropriately changed depending on the application, and can be, for example, 30 μm to 500 μm.

[0015] The rotation speed of the second roll is preferably faster than that of the first roll. This allows easy formation of a coating film on the surface of the second roll. When the rotation speed of the first roll (rpm: revolutions per minute) is S1 and the rotation speed of the second roll is S2, the ratio S2 / S1 is preferably 1.5 to 4.0.

[0016] -Electrode composite material- The electrode mixture may be in the form of a paste, a slurry, or a granule. Among these, a granule, particularly a wet granule, is preferred. In this disclosure, the term "wet granules" refers to a mixture of at least a powder material and a solvent, and is present in multiple dispersed form as discontinuous bodies in the form of powder, crumbs, or chunks (lumps larger than a powder).

[0017] As the electrode mixture, there can be used those which have been conventionally used as electrode materials for non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries.

[0018] When producing a positive electrode sheet, the electrode mixture contains a positive electrode active material and a solvent. The electrode mixture may also contain a conductive material, a binder, and the like. As the positive electrode active material, lithium transition metal composite oxides, lithium transition metal phosphate compounds (e.g., LiFePO4), etc. can be preferably used. Examples of the lithium transition metal composite oxides include lithium nickel composite oxides, lithium cobalt composite oxides, lithium manganese composite oxides, and lithium nickel manganese composite oxides (e.g., LiNi 0.5 Mn 1.5 O4), lithium nickel manganese cobalt complex oxides (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2) and the like. As the solvent, N-methyl-2-pyrrolidone and 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 suitably used. As the binder, for example, polyvinylidene fluoride (PVDF) and the like can be used.

[0019] When a negative electrode sheet is produced, the electrode mixture contains a negative electrode active material and a solvent. The electrode mixture may also contain a binder, a binding material, and the like. As the negative electrode active material, carbon materials such as graphite, hard carbon, soft carbon, and carbon nanotubes can be suitably 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.

[0020] The electrode mixture can be prepared by putting the above materials into a known agitation granulator, mixing and granulating them. Alternatively, a commercially available electrode mixture may be used.

[0021] (Removal process) In the removing step, the linear member is brought into contact with the second roll on which the coating film is formed, and then the linear member is separated from the second roll and the coating film to remove a portion of the coating film. The coating film that has passed the position of the linear member is removed during the period from when the linear member comes into contact with the second roll to when the linear member is separated from the second roll and the coating film. The contact of the linear member with the second roll cuts the continuous coating film, forming the end of the intermittent coating film, and the removal of the linear member from the second roll and the coating film cuts the continuous coating film, forming the start of the intermittent coating film.

[0022] The removal step may be carried out once or may be carried out two or more times. The interval of the removal step is preferably adjusted appropriately depending on the required size of the coating film. For example, the removal step can be carried out so that the interval of the intermittent coating film is 1 mm or more.

[0023] In one embodiment, the linear member may include a wire, and the linear member may include a holding portion for holding the wire. The cross-sectional shape of the wire may be a circle, a wire in which circles are bundled in parallel or spiral form, or a square, and among these, a circle is preferred.

[0024] From the viewpoint of dimensional accuracy, the wire thickness is preferably 0.17 mm to 4.00 mm, more preferably 0.20 mm to 1.00 mm, and even more preferably 0.25 mm to 0.50 mm. Furthermore, by setting the wire thickness within the above numerical range, adhesion of the coating film to the wire can be prevented, and a decrease in removability of the coating film can be suppressed. Also, a blower may be applied to the wire to prevent the coating from adhering to the wire. The wire thickness means the maximum length when a straight line is drawn on the cross section of the wire. The wire thickness can be measured, for example, by a Mitutoyo caliper.

[0025] The tensile strength of the wire is preferably from 21 MPa to 2600 MPa, more preferably from 50 MPa to 500 MPa, and further preferably from 50 MPa to 200 MPa. In this disclosure, tensile strength is measured by Zwick Roell's AllroundLine.

[0026] The wire may contain resin, metal, etc. From the viewpoint of preventing adhesion of the coating film to the wire, it is preferable that the wire contains resin.

[0027] Examples of the resin include fluororesin, nylon resin, fluorocarbon resin, polyester resin, polyolefin resin, polystyrene resin, and polyether ketone ketone resin. Among the above, from the viewpoint of dimensional accuracy, one or more resins selected from fluororesin, polyolefin resin, and polyolefin resin are preferred, fluororesin is preferred, one or more resins selected from polyvinylidene fluoride and Teflon resin are more preferred, and polyvinylidene fluoride is even more preferred. From the viewpoint of chemical resistance, polyolefin resins are preferred, and polypropylene resins are more preferred. Furthermore, by making the wire contain a fluororesin, adhesion of the coating film to the wire can be prevented, and a decrease in removability of the coating film can be suppressed. When the wire contains resin, the content of the resin relative to the total mass of the wire is not particularly limited, and can be, for example, 50% by mass to 100% by mass, 60% by mass to 100% by mass, or 70% by mass to 100% by mass.

[0028] Examples of the metal include iron, manganese, nickel, chromium, molybdenum, magnesium, silicon, aluminum, titanium, and alloys thereof. When the wire contains a metal, the metal content relative to the total mass of the wire is not particularly limited, and can be, for example, 50% by mass to 100% by mass, 60% by mass to 100% by mass, or 70% by mass to 100% by mass.

[0029] The contact of the linear member with the second roll and the separation of the linear member from the second roll and the coating film may be performed manually or by using a drive device or the like.

[0030] The removed coating film is preferably collected by a collection device. This makes it possible to prevent the coating film from accumulating on the linear member and reducing the removability of the coating film. As the collection device, a conventionally known dust collector can be used.

[0031] (Transfer process) The transfer step is carried out after the removal step, in which the current collector foil conveyed by the third roll rotating opposite to the second roll and the coating film formed on the surface of the second roll and conveyed are passed between the second roll and the third roll to transfer the coating film onto the surface of the current collector foil. The coating film to be transferred has been partially removed in the removal step, making it an intermittent coating film.

[0032] The minimum gap dimension between the second roll and the third roll is preferably smaller than the sum of the thicknesses of the coating film and the current collector foil, so that the second roll and the third roll apply pressure to the coating film and the current collector foil, transferring the coating film to the surface of the current collector foil. The above-mentioned minimum gap dimension is preferably at least 30 μm smaller than the total thickness of the coating film and the current collecting foil, and more preferably at least 50 μm smaller.

[0033] The rotation speed of the third roll is preferably faster than that of the second roll. This allows the coating film to be easily transferred to the surface of the current collector foil. When the rotation speed of the third roll is S3 and the rotation speed of the second roll is S2, the ratio S3 / S2 is preferably 1.5 to 4.0.

[0034] -Current collecting foil- The current collector foil may be a conventionally known one. When a positive electrode sheet is produced, an aluminum foil may be used as the current collector foil. When a negative electrode sheet is produced, a copper foil may be used as the current collector foil. The thickness of the current collector foil is preferably changed appropriately depending on the application, and can be, for example, 6 μm to 50 μm.

[0035] (drying process) The manufacturing method of the electrode sheet of the present disclosure can include a drying step of drying the coating film after the transfer step. The drying method is not particularly limited, and may be, for example, a method in which the laminate of the current collector foil and the coating film is conveyed by a third roll into a drying device and passed through the device.

[0036] (Other processes) The electrode sheet of the present disclosure may include a second coating film formation step of further forming a coating film of an electrode mixture on the surface of the current collector foil opposite to the surface on which the coating film is formed. Specifically, after the transfer step or the drying step, the electrode mixture and the laminate of the current collector foil and the coating film are passed between a fourth roll and a fifth roll rotating opposite to each other, and a second coating film is formed on the surface of the current collector foil opposite to the surface on which the coating film is formed. After the second coating film forming step, a second drying step of drying the coating film may be included. Furthermore, the second coating film may be subjected to the above-mentioned removal step, if necessary.

[0037] Hereinafter, one embodiment of the manufacturing method of the electrode sheet of the present disclosure will be described with reference to Figures 1 to 6. However, the manufacturing method of the electrode sheet of the present disclosure is not limited to this. 1 to 4 are schematic side views showing one embodiment of an electrode sheet manufacturing apparatus that can be used in the electrode sheet manufacturing method of the present disclosure. 1 includes a first roll 11, a second roll 12, a third roll 13, a linear member 14, and a partition plate 15. In one embodiment, the two partition plates 15, together with the first roll 11 and the second roll 12, form a supply section for the electrode mixture. The electrode sheet manufacturing apparatus may include a drying device (indicated by reference numeral 18 in FIG. 4) and a take-up roll (not shown) downstream of the third roll. In FIG. 1, the conveying direction of the coating film, current collecting foil, etc. is indicated by the symbol CD. 1 to 4, the electrode mixture is indicated by reference numeral 16, and the current collecting foil is indicated by reference numeral 17. As shown in FIG.

[0038] First, an electrode mixture 16 is supplied from above a partition plate 15 arranged at a distance in the width direction of the first roll 11 and the second roll 12, and passed between the first roll 11 and the second roll 12 rotating oppositely to form a coating film 16A on the surface of the second roll 12 (coating film forming step). The formed coating film 16A is transported by the rotation of the second roll 12. The rotation directions of the first roll 11 and the second roll 12 are indicated by arrows in FIG. 1.

[0039] Next, the linear member 14 is moved in the direction of the arrow shown in FIG. 1, and the linear member 14 and the second roll 12 are brought into contact with each other as shown in FIG. Next, the linear member 14 is moved in the direction of the arrow shown in Fig. 2, and as shown in Fig. 3, the linear member 14 is separated from the second roll 12 and the coating film 16A, and a part of the coating film 16A is removed (removal step). In this way, the coating film 16A that has passed the position where the linear member 14 is placed during the time from when the linear member 14 comes into contact with the second roll 12 until when it is separated from the second roll 12 is removed. The removed coating film 16A is preferably collected by a collection device (not shown). Although Figs. 1 to 4 show an electrode sheet manufacturing apparatus having one linear member, the present invention is not limited to this and may have a plurality of linear members.

[0040] In one embodiment, as shown in FIG. 5, the linear member 14 preferably includes a wire holding portion 14A and a wire 14B held by the wire holding portion. From the viewpoint of dimensional accuracy, the contact between the second roll 12 and the linear member 14 is preferably at an angle of ±20°, more preferably ±10°, relative to the direction L perpendicular to the tangent line l of the second roll 12. In Fig. 6, the above angle is indicated by θ.

[0041] Next, as shown in FIG. 4 , the current collecting foil 17 and coating film 16A transported by the third roll 13 rotating opposite to the second roll 12 are passed between the second roll 12 and the third roll 13, and the coating film 16A is transferred to the surface of the current collecting foil 17. Here, by repeatedly carrying out the above-mentioned removing step, it is possible to form an intermittent coating film, rather than a continuous coating film, as shown in FIG. 4, and this can be transferred to the surface of the current collecting foil.

[0042] Next, the laminate of the current collector foil 17 and the coating film 16A is transported by the third roll 13 to a drying device 18, and is passed through to dry the coating film 16A.

[0043] Next, the laminate (electrode sheet) is wound up by a winding roll (not shown).

[0044] The electrode sheet obtained by the electrode sheet manufacturing method of the present disclosure can be used as a positive electrode sheet or a negative electrode sheet of a lithium ion secondary battery. EXAMPLES

[0045] The present disclosure will be described in more detail below with reference to examples, but the invention of the present disclosure is not limited to these examples.

[0046] <Example 1> An electrode sheet manufacturing apparatus as shown in FIG. 1 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 linear member was made of polyvinylidene fluoride, and was a wire (cross-sectional shape: circular) with a thickness of 0.30 mm held by the wire holder shown in Fig. 5. The tensile strength of the wire was 66.5 MPa.

[0047] The electrode mixture was prepared by mixing 97.3% by mass of lithium nickel manganese composite oxide (positive electrode active material), 1.5% by mass of carbon nanotubes (conductive material), and 1.2% by mass of polyvinylidene fluoride (binder), and then mixing with N-methyl-2-pyrrolidone (solvent) to obtain an electrode mixture (solid content concentration 89% by mass). The electrode mixture was a wet granule.

[0048] First, an electrode mixture was supplied from above a partition plate arranged at a distance in the width direction of the first roll and the second roll, and passed between the first roll and the second roll rotating opposite to each other to form a coating film having a thickness of 200 μm on the surface of the second roll (coating film forming step). The formed coating film was transported by the rotation of the second roll.

[0049] Next, the linear member was brought into contact with the second roll from a direction perpendicular to the tangent line of the second roll, and after advancing 13 mm, the linear member was separated from the second roll and the coating film, and a part of the coating film was removed (removal step). After advancing 300 mm from the completion of the separation of the linear member, the removal step was carried out again, and this was repeated. The removed coating film was collected by a collection device.

[0050] Next, the current collector foil and 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 to the surface of the current collector foil. The current collector foil was an aluminum foil with a thickness of 30 μm. The thickness of the coating film that passed between the second roll and the third roll was 100 μm.

[0051] Next, the laminate of the current collector foil and the coating film was transported to a drying device by a third roll, and the coating film was dried by passing through the device.

[0052] Next, the laminate (electrode sheet) was wound up by a winding roll (not shown).

[0053] The two corners in the width direction on the starting end side of the intermittent coating film of the obtained electrode sheet were connected by a straight line (L1-L1'), and the absolute value of the amount of protrusion from this straight line was measured and found to be 1 mm. In addition, the two corners in the width direction on the end side of the intermittent coating film were connected by a straight line (L2-L2'), and the absolute value of the amount of protrusion from this line was measured and found to be 1 mm.

[0054] <Comparative Example 1> An electrode sheet was obtained in the same manner as in Example 1, except that the linear member was changed to a scraping portion. The scraping unit includes a scraping blade and a moving unit that reciprocates the scraping blade. The moving unit is capable of moving the scraping blade up and down in the direction of gravity.

[0055] The two corners in the width direction on the starting end side of the intermittent coating film of the obtained electrode sheet were connected by a straight line (L1-L1'), and the absolute value of the amount of protrusion from this straight line was measured and found to be 10 mm. In addition, the two corners in the width direction on the end side of the intermittent coating film were connected by a straight line (L2-L2'), and the absolute value of the amount of protrusion from this line was measured and found to be 4 mm.

[0056] From the above results, it can be seen that the electrode sheet manufacturing method of the embodiment in which linear members are used and the coating film is removed can produce an electrode sheet having an intermittent coating film with excellent linearity at the beginning and end. [Explanation of symbols]

[0057] 10: electrode sheet manufacturing device, 11: first roll, 12: second roll, 13: third roll, 14: linear member, 14A: wire holding portion, 14B: wire, 15: partition plate, 16: electrode mixture, 16A: coating film, 17: current collecting foil, 18: drying device, l: tangent line of second roll, L: direction perpendicular to tangent line of second roll

Claims

1. a coating film forming step of passing an electrode mixture between a first roll and a second roll rotating opposite to each other to form a coating film on a surface of the second roll; a removing step of contacting a linear member with the second roll on which the coating film has been formed, and then separating the linear member from the second roll and the coating film, thereby removing a portion of the coating film on the surface of the second roll from the position where the linear member contacted the second roll to the position where the linear member was separated; a transfer step of, after the removing step, passing the current collecting foil conveyed by a third roll rotating opposite to the second roll and the coating film between the second roll and the third roll to transfer the coating film onto a surface of the current collecting foil; A method for producing an electrode sheet, comprising:

2. The wire according to claim 1, wherein the linear member comprises a wire having a thickness of 0.17 mm to 4.00 mm. A method for manufacturing the above-mentioned electrode sheet.

3. The method for producing an electrode sheet according to claim 2, wherein the tensile strength of the wire is from 21 MPa to 2600 MPa.

4. The method for producing an electrode sheet according to claim 2 or 3, wherein the wire comprises a fluororesin.

5. 3. The method for producing an electrode sheet according to claim 1, wherein the second roll is brought into contact with the linear member at an angle of ±20° relative to a direction perpendicular to a tangent line of the second roll.

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