JP7803105B2 - Electrode manufacturing method - Google Patents

Description

This disclosure relates to a method for manufacturing an electrode.

A known electrode manufacturing method involves preparing granules containing an electrode mixture, molding the granules, and then disposing an electrode mixture layer on an electrode current collector (a granule molding method) to produce sheet-like electrodes for use in lithium-ion secondary batteries, etc.

Here, an intermittently coated electrode sheet, in which formed areas (coated areas) and unformed areas (uncoated areas) of the electrode composite layer alternate on the electrode current collector, is known as an electrode sheet that is often used in high-energy density batteries.

Patent Document 1 (JP 2021-44096 A) discloses a method for reducing the variation in the widthwise dimension of an electrode mixture layer by removing protrusions that protrude outward in the widthwise direction from both widthwise ends of the electrode mixture layer using a chipping blade.

Japanese Patent Application Laid-Open No. 2021-44096

To manufacture an intermittently coated electrode sheet, it is possible to form uncoated portions of the intermittently coated electrode sheet by chipping off the electrode mixture layer with a blade or the like, as described in Patent Document 1. However, in this case, there is a risk that the chipping blade may damage the electrode current collector (metal foil, etc.).

Therefore, the object of the present disclosure is to provide a method for manufacturing an electrode that can produce an intermittently coated electrode sheet without damaging the electrode current collector in the uncoated areas of the intermittently coated electrode sheet.

[1] The method for manufacturing an electrode according to the present disclosure includes:
preparing granules containing an electrode active material, a binder, and a solvent;
supplying the granules to a first gap between a first roll and a second roll, and compressing and molding the granules to form an electrode mixture layer;
and a step of supplying the electrode mixture layer transported on the second roll and the electrode current collector transported on the third roll into a second gap between the second roll and the third roll, thereby arranging the electrode mixture layer on the electrode current collector.
the electrode current collector has a substrate intermittently provided on a surface facing the third roll,
The electrode mixture layer is disposed only on a portion of the surface of the electrode current collector on the second roll side that corresponds to the substrate.

According to the manufacturing method [1] above, it is possible to provide a method for manufacturing an electrode that can manufacture an intermittently coated electrode sheet without damaging the electrode current collector in the uncoated parts of the intermittently coated electrode sheet.
That is, by providing the substrate 14 intermittently on the surface of the electrode current collector 13 facing the third roll 33 (the surface opposite to the surface on which the electrode mixture layer 12 is provided), the electrode mixture layer 12 is pressed against the electrode current collector 13 only at positions corresponding to the substrate 14, and the electrode mixture layer 12 is disposed on the electrode current collector 13. Therefore, the electrode mixture layer 12 is disposed only in the portion of the surface of the electrode current collector 13 facing the second roll 32 that corresponds to the substrate 14. Therefore, according to the manufacturing method of the present disclosure, there is no risk of the electrode current collector (metal foil or the like) being damaged by the notching blade, as in the method disclosed in Patent Document 1 above.

1 is a flowchart showing an outline of a method for manufacturing an electrode according to an embodiment. FIG. 2 is a conceptual diagram showing an apparatus used to manufacture an electrode in the embodiment. FIG. 2 is a schematic perspective view showing an apparatus used to manufacture an electrode in the embodiment. FIG. 2 is a schematic diagram illustrating an example of an electrode sheet. FIG. 1 is a conceptual diagram showing an apparatus used in the manufacture of electrodes in the prior art.

One embodiment of the present disclosure will be described below. However, the present disclosure is not limited to this. In this specification, "positive electrode" and "negative electrode" will be collectively referred to as "electrodes."

Figure 1 is a flowchart showing an outline of the electrode manufacturing method of this embodiment. As shown in Figure 1, the electrode manufacturing method of this embodiment includes at least a granule preparation process (S10), an electrode mixture layer formation process (S20), and an arrangement process (S30).

The electrode manufactured in this embodiment is, for example, a sheet-shaped electrode (electrode sheet) for a lithium-ion secondary battery. The electrode may be either a positive electrode or a negative electrode.

Granule Preparation Step (S10)
In the granule preparation step, granules (wet granules) containing an electrode active material, a binder, and a solvent are prepared. The granules are an aggregate of a plurality of granulated particles (composite particles) containing the electrode active material, the binder, and the solvent.

Granules can be produced, for example, by mixing (granulating) electrode active material, binder, solvent, etc. The granulation method can be, for example, agitation granulation. Examples of granulation procedures used in the granule production process include agitation granulation, fluidized bed granulation, and tumbling granulation. Various granulation devices, such as agitation mixers, can be used for these granulation procedures. When the agitation mixer has an agitation blade (rotor blade), the rotation speed of the agitation blade is, for example, approximately 10 to 5,000 rpm.

(electrode active material)
The electrode active material may be a positive electrode active material or a negative electrode active material.

Examples of the positive electrode active material include lithium-containing metal oxides and lithium-containing phosphates. Examples of lithium-containing metal oxides include LiCoO ₂ , LiNiO ₂ , compounds represented by the general formula LiNi _a Co _b O ₂ (wherein a + b = 1, 0 < a < 1, 0 < b < 1), LiMnO ₂ , LiMn ₂ O ₄ , compounds represented by the general formula LiNi _a Co _b Mn _c O ₂ (wherein a + b + c = 1, 0 < a < 1, 0 < b < 1, 0 < c < 1), and LiFePO ₄ . Examples of the compound represented by the general formula LiNi _a Co _b Mn _c O ₂ include LiNi _1/3 Co _1/3 Mn _1/3 O ₂ . Examples of lithium-containing phosphates include _LiFePO4 .

The average particle size of the positive electrode active material may be, for example, approximately 0.1 to 25 μm. Note that "average particle size" here refers to the particle size at 50% cumulative value (D50) in the volume-based particle size distribution measured by laser diffraction/scattering.

Anode active materials include, for example, carbon-based anode active materials such as graphite, graphitizable carbon, and non-graphitizable carbon, as well as alloy-based anode active materials containing silicon (Si), tin (Sn), etc. The average particle size (D50) of the anode active material may be, for example, approximately 1 to 25 μm.

The blending ratio of the electrode active material to the total amount of solids in the granules (i.e., the content of the electrode active material in the electrode mixture layer) is, for example, approximately 94 to 99.7% by mass.

(binder)
Examples of binders include carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), etc. One type of binder may be used alone, or two or more types may be used in combination.

The binder content relative to the total amount of solids in the granules (i.e., the binder content in the electrode mixture layer) is, for example, approximately 0.3 to 6% by mass.

(solvent)
Examples of the solvent include an aqueous solvent, an organic solvent, etc. An aqueous solvent means water or a mixed solvent containing water and a polar organic solvent.

Water is a suitable aqueous solvent due to its ease of handling. Examples of polar organic solvents that can be used in the mixed solvent include alcohols such as methanol, ethanol, and isopropyl alcohol, ketones such as acetone, and ethers such as tetrahydrofuran. Aqueous solvents are also suitable for use as solvents for producing negative electrodes.

Examples of organic solvents include N-methyl-2-pyrrolidone (NMP). Organic solvents can be suitably used as solvents for manufacturing positive electrodes.

The amount of solvent used is not particularly limited, but may be adjusted so that the solid content (non-volatile content) of the granules is 70% by mass or more but less than 100% by mass, preferably 70 to 90% by mass, and more preferably 70 to 80% by mass. In this case, in the disposing step (S30) described below, when the electrode mixture layer 12 is pressed against the electrode current collector 13 at a position corresponding to the substrate 14 of the electrode current collector 13, the electrode mixture layer 12 is more reliably disposed (fixed) to the electrode current collector 13. On the other hand, when the electrode mixture layer 12 is not pressed against the electrode current collector 13 at a position where the substrate 14 is not present, the electrode mixture layer 12 is not disposed (fixed) to the electrode current collector 13. Therefore, the electrode mixture layer 12 is more reliably disposed (fixed) only to the portion of the surface of the electrode current collector 13 facing the second roll 32 that corresponds to the substrate 14. Therefore, the desired intermittently coated electrode sheet can be more reliably produced.
If the solid content of the granules is less than 70% by mass, the amount of solvent is large, which may make it difficult to produce the granules. Note that the "solid content" refers to the ratio of the mass of components other than the solvent (non-volatile components) to the total mass of all raw materials including the solvent.

(Other ingredients)
The granules may contain other components than those mentioned above, such as a conductive material. Examples of the conductive material include carbon black such as acetylene black (AB), thermal black, and furnace black, and carbon nanotubes (CNT). The conductive material is expected to improve electronic conductivity.

《Electrode composite material layer formation step (S20)》
In the electrode mixture layer forming step, granules 10 are supplied to a first gap between first roll 31 and second roll 32 and are compression-molded to form electrode mixture layer 12 .

The electrode manufacturing method of this embodiment uses an electrode manufacturing apparatus 3 as shown in Figures 2 and 3. The electrode manufacturing apparatus 3 includes a feeder 2 and three rolls (a first roll 31, a second roll 32, and a third roll 33). The diameter of each of the first roll 31, second roll 32, and third roll 33 is, for example, 10 to 1000 mm, and the length in the axial direction of each is, for example, 100 to 2000 mm.

The first roll 31, second roll 32, and third roll 33 have their respective rotation axes fixed so that they are parallel to one another. The distance (width) of the first gap between the first roll 31 and the second roll 32 is maintained constant. The distance of the second gap between the second roll 32 and the third roll 33 is also maintained constant. The first roll 31, second roll 32, and third roll 33 are each driven to rotate. In Figures 2 and 3, the curved arrows drawn on each roll indicate the direction of rotation of each roll.

The first roll 31 and the second roll 32 are driven to rotate in opposite directions. Granulated material is supplied between this pair of rolls (first roll 31 and second roll 32), and the granulated material is compressed and molded by the pair of rolls to form a sheet-like electrode mixture layer.

The first gap distance between the first roll 31 and the second roll 32 is, for example, approximately 50 μm to 10 mm. Note that the first gap distance is the linear distance between the first roll 31 and the second roll 32 at the position where the first roll 31 and the second roll 32 are closest to each other.

Feeder 2 is positioned directly above the gap (first gap) between first roll 31 and second roll 32. In this process, granules are first supplied to feeder 2. Feeder 2 supplies granules 10 to the first gap between first roll 31 and second roll 32.

The electrode manufacturing apparatus 3 further includes a pair of regulating plates 24 arranged parallel to each other at a predetermined distance in the axial direction of the first roll 31 and the second roll 32. The pair of regulating plates 24 regulate the width of the granules 10 supplied to the gap (first gap) between the first roll 31 and the second roll 32. As the first roll 31 and the second roll 32 rotate (in the direction of the arrow in the figure), the granules are pulled downward through the first gap and pass through the first gap. This allows the weight (mass per unit area) of the electrode mixture layer 12 to be adjusted. The pair of regulating plates 24 also allows exposed portions 13b, where no electrode mixture layer 12 is located, to be formed at both ends of the electrode current collector 13 in the width direction (Figure 4). The weight of the electrode mixture layer 12 can also be adjusted by the distance of the first gap.

It is preferable that the rotation speed of the second roll 32 is faster than that of the first roll 31. For example, the rotation speed of the second roll 32 is approximately three to five times faster than that of the first roll 31. By making the rotation speed of the second roll 32 faster than that of the first roll 31, as shown in FIG. 2, the granules are stretched more on the surface of the second roll 32 than on the surface of the first roll 31, and the area of the liquid-bridged portion of the granules in contact with the surface of the second roll 32 becomes larger than the area in contact with the surface of the first roll 31. As a result, the granules 10 (electrode mixture layer 12) after rolling adhere to the second roll 32 side and are transported by the second roll 32.

《Placement process (S30)》
In the placement process, the electrode composite layer 12 transported on the second roll 32 and the electrode current collector 13 transported on the third roll 33 are supplied to the second gap between the second roll 32 and the third roll 33, thereby placing the electrode composite layer 12 on the electrode current collector 13.

For example, the sheet-like electrode mixture layer 12 produced in the electrode mixture layer formation step (S20) is transferred to the electrode current collector 13 (negative electrode current collector), thereby disposing the electrode mixture layer 12 on the electrode current collector 13.

Specifically, the electrode current collector 13 is transported on the third roll 33 and supplied to the gap (second gap) between the second roll 32 and the third roll 33. After leaving the gap (first gap) between the first roll 31 and the second roll 32, the electrode mixture layer 12 is transported on the second roll 32 and supplied to the gap between the second roll 32 and the third roll 33. The second roll 32 and the third roll 33 are driven to rotate in opposite directions (see the curved arrows in Figures 2 and 3).

Here, substrates 14 are intermittently provided on the surface of the electrode current collector 13 facing the third roll 33 (the surface that faces the third roll 33 in the placement process). As a result, the electrode mixture layer 12 is placed only on the portions of the surface of the electrode current collector 13 facing the second roll 32 (the surface that faces the third roll 33 in the placement process) that correspond to the substrates 14.

That is, the electrode mixture layer 12 is pressed against the electrode current collector 13 at a position corresponding to the substrate 14 of the electrode current collector 13, and the electrode mixture layer 12 is separated from the second roll 32 and pressed against the electrode current collector 13. That is, the electrode mixture layer 12 is transferred from the second roll 32 to the electrode current collector 13.

On the other hand, in areas of the electrode current collector 13 where there is no substrate 14, the electrode mixture layer 12 is not pressed against the electrode current collector 13, so the electrode mixture layer 12a does not separate from the second roll 32 and is further transported over the second roll 32.

The electrode mixture layer 12a that is not placed on the electrode current collector 13 can be scraped off by the blade 4 and reused as material for the granules 10. In this way, it is preferable to reuse the electrode mixture layer 12a that is not placed on the electrode current collector 13 in the placement process. In this case, the material of the electrode mixture layer can be used effectively, reducing material costs.

In this way, the sheet-like electrode mixture layer 12 can be intermittently placed only at predetermined positions on the electrode current collector 13. Therefore, an intermittently coated electrode sheet can be manufactured. An intermittently coated electrode sheet 11 is, for example, an electrode sheet 11 having exposed portions 13a of the electrode current collector 13 between the electrode mixture layers 12, as shown in Figure 4.

The substrate 14 can be, for example, a positive electrode composite layer, a negative electrode composite layer, a carbon coating layer, or a metal sheet (such as a stainless steel sheet).

The thickness of the substrate 14 is preferably 10 μm to 100 mm, more preferably 30 μm to 1 mm, for example, 50 μm.
In this case, the electrode mixture layer 12 is pressed against the electrode current collector 13 at positions corresponding to the substrate 14 of the electrode current collector 13, and is not pressed against the electrode current collector 13 at positions where the substrate 14 is not present, so that the electrode mixture layer 12 is more reliably disposed (fixed) only in the portions corresponding to the substrate 14 on the surface of the electrode current collector 13 facing the second roll 32. Therefore, the desired intermittently coated electrode sheet can be more reliably manufactured.

When the substrate 14 remaining on the side of the electrode current collector 13 opposite the electrode mixture layer 12 is not required as a constituent member of the electrode (electrode sheet) (for example, when the substrate 14 is a metal sheet), it can be peeled off from the electrode current collector 13 before or after drying the electrode mixture layer 12. The substrate 14 can be mechanically peeled off by, for example, fixing the substrate 14 using a vacuum suction device, an electromagnetic suction device, or the like, and then winding up the electrode current collector 13 with the electrode mixture layer 12 on a roll or the like.
On the other hand, when the substrate 14 is a positive electrode composite layer, a negative electrode composite layer, a carbon coating layer, or the like, and is a necessary component of the electrode (electrode sheet), the substrate 14 does not need to be peeled off.

The substrate 14 and the electrode current collector 13 are bonded together with, for example, an adhesive sheet (double-sided tape). The thickness of the adhesive sheet is preferably 10 μm to 100 mm, more preferably 30 μm to 1 mm, for example, 50 μm. The peel strength between the substrate 14 and the electrode current collector 13 is preferably 1 to 100 N/10 mm as measured in a 90° peel test.
The 90° peel test can be carried out in accordance with "JIS Z 0237: Test method for adhesive tapes and adhesive sheets."

After the electrode mixture layer 12 has dried, the electrode sheet 11 may be cut to a predetermined size using, for example, a slitter.

The electrodes obtained by the manufacturing method of the present disclosure can be used, for example, as electrodes for lithium-ion secondary batteries (nonaqueous electrolyte secondary batteries). These lithium-ion secondary batteries can be used as power sources for hybrid vehicles (HVs), electric vehicles (EVs), plug-in hybrid vehicles (PHVs), and the like. However, the electrodes obtained by the manufacturing method of the present disclosure are not limited to such in-vehicle applications and can be used for a variety of applications.

The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present disclosure is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

10 Granules, 12, 12a Electrode mixture layer, 13 Electrode current collector, 13a, 13b Exposed portion, 14 Substrate, 2 Feeder, 24 Regulating plate, 3 Electrode manufacturing device, 31 First roll, 32 Second roll, 33 Third roll, 4 Blade.

Claims (3)

preparing granules containing an electrode active material, a binder, and a solvent;
supplying the granules to a first gap between a first roll and a second roll, and compressing and molding the granules to form an electrode mixture layer;
and supplying the electrode mixture layer transported on the second roll and the electrode current collector transported on the third roll into a second gap between the second roll and the third roll, thereby disposing the electrode mixture layer on the electrode current collector,
the electrode current collector has a substrate intermittently provided on a surface facing the third roll,
the electrode mixture layer is disposed only on a portion of the surface of the electrode current collector facing the second roll, the portion corresponding to the substrate;
The second roll and the third roll are driven to rotate in opposite directions.
Electrode manufacturing method. The method for manufacturing an electrode according to claim 1 , wherein the electrode mixture layer on the second roll that has passed through the second gap and has not been placed on the electrode current collector is scraped off by a blade. The method for manufacturing an electrode according to claim 1 or 2, wherein the substrate is a positive electrode mixture layer, a negative electrode mixture layer, or a carbon coating layer.