JP7708033B2 - Manufacturing method of electrode sheet - Google Patents

Description

This disclosure relates to a method for manufacturing an electrode sheet.

Conventionally, an electrode sheet (positive electrode sheet or negative electrode sheet) having an electrode mixture layer on the surface of a current collector foil is known. The following method is known as a method for manufacturing 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 passed between a first roll and a second roll rotating opposite to each other, whereby the electrode mixture is compressed and made into a film, 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, whereby 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 then dried to obtain an electrode sheet.

In the above-described method, the film-like electrode composite material transferred to the surface of the current collecting foil may have protrusions at both ends in the width direction that protrude outward in the width direction, resulting in uneven shapes at both ends in the width direction.
In response to this, the manufacturing method disclosed in Patent Document 1 proposes removing the protruding portions with a blade after the film-like electrode mixture has been transferred to the surface of the current collector foil and before drying.

JP 2021-44096 A

The manufacturing method of Patent Document 1 requires strict adjustment of the surface pressure of the blade against the film-like electrode composite. Specifically, if the surface pressure is set too high, scratches and cuts in the current collecting foil may occur, while if the surface pressure is set too low, the protruding parts may not be sufficiently removed, resulting in so-called doctor marks.

The problem that one embodiment of the present disclosure aims to solve is to provide a method for manufacturing an electrode sheet that can prevent scratches and cuts in the current collecting foil and has excellent removability of protrusions.

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 removing protrusions formed at width direction ends of the coating film by pressing a blade against 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:
<2> The method for producing an electrode sheet according to <1>, wherein an angle θ formed between a tangent line passing through a contact point between the blade and the second roll and a surface of the blade facing the second roll is 20° to 60°.
<3> The method for producing an electrode sheet according to <1> or <2> above, wherein the blade has a thickness of 0.3 mm to 2.0 mm.
<4> The method for producing an 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 method for producing an electrode sheet according to any one of <1> to <4> above, wherein the surface pressure applied to the coating film by the blade is 100 MPa to 300 MPa.

According to one embodiment of the present disclosure, it is possible to provide a method for manufacturing an electrode sheet that can prevent scratches and cuts in the current collecting foil and has excellent removability of protrusions.

FIG. 1 is a schematic side view for explaining an angle θ formed between a tangent line passing through a contact point between a blade and a second roll and a surface of the blade facing the second roll. FIG. 2 is a schematic side view showing one embodiment of an electrode sheet manufacturing apparatus. FIG. 3 is an enlarged view seen from the X direction in FIG.

In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values before and after "to" 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 aspects are more preferred aspects.
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.

[Manufacturing method of electrode sheet]
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 removing protrusions formed at width direction ends of the coating film by pressing a blade against 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:

According to the manufacturing method of the electrode sheet of the present disclosure, it is possible to suppress the occurrence of scratches and foil breaks in the current collector foil, and the protrusions are easily removable. The reason why the above effects are achieved is not clear, but is presumed to be as follows.
In the electrode sheet manufacturing method of the present disclosure, the protrusions are removed before the coating film is transferred to the surface of the current collector foil, which is believed to prevent scratches and foil breaks from occurring in the current collector foil.
In addition, since the protrusions are removed before the coating is transferred to the surface of the current collector foil, the surface pressure of the blade against the coating can be set high, which is presumably why the protrusions can be removed sufficiently.

The manufacturing method of the electrode sheet disclosed herein can include a drying step for drying the coating film after the transfer step.

(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.

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.
The thickness of the coating film after passing between the second roll and the third roll is also preferably changed appropriately depending on the application, and can be, for example, 30 μm to 500 μm.

It is preferable that the rotation speed of the second roll is faster than that of the first roll. This allows the coating film to be easily formed 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, it is preferable that S2/S1 is 1.5 to 4.0.

-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 the present disclosure, the term "wet granules" refers to a mixture of at least a powder material and a solvent, and is present in a plurality of dispersed granules as discontinuous bodies in the form of powder, crumbs, or chunks (lumps larger than a powder).

The electrode mixture can be made of materials that have been commonly used as electrode materials for non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries.

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 oxide, lithium transition metal phosphate compound (e.g., LiFePO ₄ ), etc. can be preferably used. Examples of lithium transition metal composite oxides include lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel manganese composite oxide (e.g., LiNi _0.5 Mn _1.5 O ₄ ), lithium nickel manganese cobalt composite oxide (e.g., LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), etc. As the solvent, N-methyl-2-pyrrolidone, etc. can be used. As the conductive material, carbon black such as acetylene black (AB) and other carbon materials (e.g., graphite) can be suitably used. As the binder, for example, polyvinylidene fluoride (PVDF), etc. can be used.

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.

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.

(Removal process)
In the removing step, a blade is pressed against the coating film to remove the protrusions formed at the width direction ends of the coating film.
The blades are preferably provided at both ends in the width direction of the coating film to remove protrusions formed at both ends of the coating film.

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 protruding portion can be improved.
The thickness of the blade means the thickness at the portion where the blade has the maximum thickness.

The material of the blade is not particularly limited, and may be any known material such as resin, metal, etc. From the viewpoint of preventing contamination by foreign matter, resin is preferred.
Among the resins, a resin having high resistance to dissolution in a solvent that the electrode mixture may contain is preferred, and one or more resins selected from the group consisting of polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), and polypropylene (PP) are more preferred. The content of the resin relative to the total mass of the blade is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass.

The shape of the blade is not particularly limited, but can be, for example, plate-shaped.

As shown in Fig. 1, the angle θ between 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 even more preferably 30° to 40°. When the angle θ is 20° or more, it is possible to suppress the electrode mixture from entering between the worn blade and the second roll, and it is possible to 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 it is possible to improve the removability of the protrusion.
The rotation direction of the second roll 11 is indicated by an arrow in FIG.

From the viewpoint of removability of the protrusions, the surface pressure applied by the blade to the coating film is preferably 100 MPa to 300 MPa, more preferably 150 MPa to 250 MPa, and even more preferably 180 MPa to 220 MPa.
The surface pressure is measured as follows.
A blade is brought into contact with the roll surface with a pressure-sensitive film (e.g., Fujifilm's Prescale HHS) attached to it, and then the blade is separated from the roll to recover the pressure-sensitive film. The pressure-sensitive film is scanned with a scanner (e.g., Fujifilm's FPD-8010J) and subjected to image analysis.

The removed protrusions are preferably collected by a collection device. This prevents the protrusions from accumulating on the surface of the blade, which reduces the removability of the protrusions. A conventionally known dust collector can be used as the collection device. The collection device is preferably provided at both ends of the coating film in the width direction.

(Transfer process)
The transfer process is carried out after the removal process, in which the current collecting foil transported by a third roll rotating opposite the second roll and the coating film formed on the surface of the second roll and transported are passed between the second roll and the third roll, and the coating film is transferred to the surface of the current collecting foil.

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, and the coating film is transferred to the surface of the current collector foil.
The 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.

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, it is preferable that S3/S2 is 1.5 to 4.0.

- 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.

(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.

(Other processes)
The electrode sheet of the present disclosure may include a second coating film forming 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 in an opposed manner, and the 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.

Hereinafter, an embodiment of the manufacturing method of the electrode sheet of the present disclosure will be described with reference to Fig. 2 and Fig. 3. Note that the manufacturing method of 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 electrode sheet manufacturing method of the present disclosure. Fig. 3 is an enlarged view seen from the X direction in 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 take-up roll (not shown) downstream of the third roll.
2 and 3, the conveying direction of the coating film, current collecting foil, etc. is indicated by the symbol CD.
2 and 3, the electrode mixture is indicated by reference numeral 27, and the current collecting foil is indicated by reference numeral 28.

First, an electrode mixture 27 is supplied from above a partition plate 26 arranged at a distance in the width direction of the first roll 21 and the second roll 22, and passed between the first roll 21 and the second roll 22 rotating opposite to each other to form a coating film 27A on the surface of the second roll 22 (coating film forming process). 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.

Next, as shown in FIG. 3, the blades 24 arranged at both widthwise ends of the coating film 27A are pressed against the coating film 27A to remove the protrusions 27a formed at both widthwise ends of the coating film 27A (removal process).
The removed protrusion 27 a is collected by the collection device 25 .

Next, the current collector foil 28 and coating film 27A transported by the third roll 23 rotating opposite the second roll 22 are passed between the second roll 22 and the third roll 23, and the coating film 27A is transferred to the surface of the current collector foil 28.

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

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

The electrode sheet obtained by the electrode sheet manufacturing method disclosed herein can be used as a positive electrode sheet or a negative electrode sheet for a lithium ion secondary battery.

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

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 blades were made of polyether ether ketone and had a plate shape with a thickness of 0.8 mm, and were provided at both ends in the width direction of the coating film.

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 (solids concentration 89% by mass). The electrode mixture was a wet granule.

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 each other, forming a coating film with a thickness of 200 μm on the surface of the second roll (coating film forming process). The formed coating film was transported by the rotation of the second roll.

Next, as shown in FIG. 3, blades arranged at both ends in the width direction of the coating film were pressed against the coating film to remove the protrusions formed at both ends in the width direction of the coating film (removal step).
The angle θ between the tangent line passing through the contact point between the blade and the second roll and the surface of the blade facing the second roll was set to 30°. The surface pressure applied by the blade to the coating film was set to 200 MPa.
The removed protrusion was collected by a collection device.

Then, the current collector foil and coating film transported by the third roll rotating opposite 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.

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

The laminate (electrode sheet) was then wound up by a winding roll (not shown).

Visual inspection of the resulting electrode sheet confirmed that there were no scratches or cuts in the current collecting foil and that the protruding parts had been successfully removed.

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

Claims (3)

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 removing protrusions formed at width direction ends of the coating film by pressing a blade against 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;
Including,
an angle θ formed between a tangent line passing through a contact point between the blade and the second roll on the rotation direction side of the second roll and a surface of the blade facing the second roll is 20° to 60°;
The surface pressure applied to the coating film by the blade is 100 MPa to 300 MPa.
A method for manufacturing an electrode sheet. The method for producing an electrode sheet according to claim 1 , wherein the blade has a thickness of 0.3 mm to 2.0 mm. The method for producing an electrode sheet according to claim 1 , wherein the blade contains one or more resins selected from the group consisting of polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), and polypropylene (PP).