JP7816626B2 - Manufacturing method of electrode mixture layer - Google Patents

Description

This disclosure relates to a method for manufacturing an electrode.

Patent Document 1 (JP 2020-149862 A) discloses a method for manufacturing electrodes in which an electrode mixture material containing an active material and a binder is attached to a magnetic carrier, which is then transported by a magnet roll. A potential difference is generated between the magnet roll and a backup roll carrying a current collector foil, and only the electrode mixture material is attached to the current collector foil by electrostatic force.

Japanese Patent Application Laid-Open No. 2020-149862

Conventionally, electrodes have been manufactured using a wet method, in which an active material and additives such as a binder are dissolved in a solvent to prepare a coating solution, which is then applied to the surface of a current collector foil and dried to form an active material layer on the surface of the current collector foil. However, a dry method is also known in which the active material and additives are kneaded together without using a solvent, and then compression molded.

The dry method has the advantage of requiring less energy because it does not require a drying process. However, because no solvent is used, it is difficult to disperse the binder, reducing the contact area between the active material and the binder. Furthermore, unlike the wet method, when the solvent evaporates due to drying, the binder does not segregate on the surface of the active material, so adhesion is not achieved. As such, the dry method has the disadvantage of low peel strength.

Therefore, the object of the present disclosure is to provide a method for manufacturing electrodes with improved peel strength.

[1] A step of preparing a first composite material by mixing an active material and a binder by a dry method;
preparing a second composite material by dry mixing the first composite material and a conductive material;
forming an electrode mixture layer by applying the second composite material to a surface of a current collecting foil;
and compressing the electrode mixture layer to form an electrode.

By pre-mixing the active material and binder before adding the conductive material, the binder adheres to the surface of the active material. This increases the contact area between the active material and the binder, which is thought to improve peel strength.

[2] The electrode manufacturing method described in [1], wherein the first composite material and the second composite material are combined by mechanochemical treatment.

[3] The electrode manufacturing method described in [1] or [2], wherein the second composite material is applied by electrostatic screen printing.

[4] preparing a first composite material by mixing an active material and a binder by a dry method;
preparing a second composite material by dry mixing the first composite material and a conductive material;
forming an electrode mixture layer by applying the second composite material to a surface of a current collecting foil;
and compressing the electrode mixture layer to form an electrode.
the first composite material and the second composite material are combined by a mechanochemical treatment,
The method for manufacturing an electrode, wherein the application of the second composite material is performed by electrostatic screen printing.

FIG. 1 is a flowchart showing an outline of the method for manufacturing an electrode according to this embodiment. FIG. 2 is a conceptual diagram showing an example of a method for applying the second composite material. FIG. 3 is a schematic diagram showing the distribution of the binder and the conductive material on the surface of the active material for the examples and the comparative examples. FIG. 4 is a bar graph showing the peel strength for the Examples and Comparative Examples.

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 first composite material preparation process (S10), a second composite material preparation process (S20), an electrode mixture layer formation process (S30), and an electrode formation process (S40).

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.

<<First Composite Material Preparation Step (S10)>>
In the first composite material preparation step, the active material and binder are mixed by a dry method to prepare the first composite material. As will be described later, by mixing the conductive material in a separate step, the amount of binder present on the surface of the active material increases, and it is expected that the peel strength will be improved. Here, the "dry method" refers to a mixing method in which the solid content of the paint is 90% or more. The solid content of the paint in the dry method may be 95 to 100%.

For example, the first composite material may be prepared by mixing the active material powder and the binder using a simple dry process. For example, the active material powder and the binder may be composited using a mechanochemical process.

"Mechanochemical processing" refers to a process in which mechanical energy such as shear force, collision force, and friction force is continuously applied to the target material, causing mechanochemical reactions that cause materials to react with each other or change the physicochemical properties of the material. Examples of equipment that can be used for mechanochemical processing include planetary ball mills, bead mills, jet mills, dispersers, planetary mixers, and homogenizers.

(active material)
The active material may be a positive electrode active material or a negative electrode active material. The active material may be in a particulate form, or may be porous active material particles formed by aggregation of primary particles made of the 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 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.

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

(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.

<<Second Composite Material Preparation Step (S20)>>
In the second composite material preparation step, the first composite material and the conductive material are mixed by a dry method to prepare the second composite material.

For example, the second composite material may be produced by mixing the first composite material and the conductive material using a simple dry process. For example, the first composite material and the conductive material may be combined using a mechanochemical process.

(Conductive material)
Examples of the conductive material include carbon black such as acetylene black (AB), thermal black, furnace black, etc. The conductive material may be used alone or in combination of two or more.

The active material content in the second composite material is, for example, approximately 90 to 99% by mass. The binder content in the second composite material is, for example, approximately 0.5 to 5% by mass. The conductive material content in the second composite material is, for example, approximately 0.5 to 5% by mass.

《Electrode composite material layer formation step (S30)》
In the electrode mixture layer forming step, the electrode mixture layer is formed on the current collecting foil. For example, the electrode mixture layer is formed on the current collecting foil by adhering the second composite material to the surface of the current collecting foil. For example, electrostatic printing, electrostatic painting, or similar techniques may be used.

Figure 2 is a conceptual diagram showing an example of a method for applying the second composite material. For example, the second composite material 10 may be applied by electrostatic screen printing. The second composite material 10 is placed on a screen 101. The screen 101 is conductive. A plurality of through holes are formed in the screen 101. A current collector foil 11 is placed below the screen 101. A power source 102 applies a DC voltage between the current collector foil 11 and the screen 101. This creates an electric field between the screen 101 and the current collector foil 11. An electric charge is injected from the screen 101 into the second composite material 10. In other words, the second composite material 10 is charged. A printing brush 103 smooths the second composite material 10, introducing the second composite material 10 into the electric field. In the electric field, an electrostatic force acts on the second composite material 10. The electrostatic force can cause the second composite material 10 to adhere to the surface of the current collector foil 11. For example, the application pattern can be controlled by the pattern of through holes in the screen 101. In other words, the desired scattering state can be created.

The electrode mixture layer may have a thickness of, for example, 10 to 500 μm, or 50 to 200 μm.

《Electrode formation step (S40)》
In the electrode formation process, the electrode mixture layer is compressed to fix the electrode mixture layer to the current collector foil, thereby forming an electrode. Fixing the electrode mixture layer to the current collector foil is expected to improve peel strength.

The pressure can be adjusted depending on, for example, the target thickness, the target density, etc. of the electrode mixture layer. For example, a pressure of 1 to 10 t/cm ² may be applied to the electrode mixture layer.

Heat may be applied in this process. Heat may be applied separately from pressure, or may be applied substantially simultaneously. For example, the electrode mixture layer may be heated using a heat roll, a heat plate, or the like. The heating temperature may be, for example, a temperature near the melting point of the binder. The heating temperature may be, for example, 50 to 200°C.

The electrode can be manufactured in this manner. This electrode may be cut into a specified planar shape according to the battery specifications.

Electrodes obtained by the manufacturing method of the present disclosure can be used, for example, as electrodes for secondary batteries such as lithium-ion secondary batteries (nonaqueous electrolyte secondary batteries). Secondary batteries such as 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, 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 present embodiment will be explained below using examples, but the present embodiment is not limited to these.

Example 1
The electrode (positive electrode) of Example 1 was produced as follows.

<<First composite material production process>>
NCM (nickel cobalt manganese oxide lithium) (manufactured by Hunan Ruixiang) was prepared as the positive electrode active material, and PVdF (Kynar 301F, manufactured by Arkema K.K.) was prepared as the binder. An "MP Mixer" manufactured by Nippon Coke & Engineering Co., Ltd. was prepared as an apparatus for mechanochemical treatment. The positive electrode active material and the binder were charged into the apparatus, and treatment was carried out at 10,000 rpm for 10 minutes, to produce a first composite material.

<<Second composite material production process>>
AB (Li100, manufactured by Denka Co., Ltd.) was prepared as the conductive material. The first composite material and the conductive material were placed in the above-mentioned device and treated at 10,000 rpm for 10 minutes to produce a second composite material. The mixing ratio (mass ratio) of the positive electrode active material, binder, and conductive material in the second composite material was 95.5:3.0:1.5.

《Electrode composite layer formation process》
An Al foil (thickness: 12 μm) was prepared as a current collector foil. A tabletop manual electrostatic screen printer "T-1" manufactured by Berg Industries Co., Ltd. was prepared as a device for forming an electrode mixture layer. Using this device, an electrode mixture layer made of the second composite material was formed on the surface of the Al foil by electrostatic screen printing. The formation conditions were a voltage of 1.5 kV and a distance of 1 cm between the screen and the current collector foil.

《Electrode formation process》
The electrode mixture layer was fixed to the current collector foil by compressing and heating. An apparatus equipped with an upper plate and a lower plate was prepared as an electrode forming apparatus. The upper plate was heated to 160°C, and the lower plate was heated to 80°C. The current collector foil on which the electrode mixture layer was formed was placed between the upper plate and the lower plate, and a load of 5 t/ ^cm2 was applied for 60 seconds to produce the electrode (positive electrode) of Example 1.

Comparative Example 1
In Comparative Example 1, the order of mixing the binder and conductive material was reversed. That is, the same positive electrode active material and conductive material as in Example 1 were added to the above-mentioned device and treated at 10,000 rpm for 10 minutes. Next, the same binder as in Example 1 was further added to the above mixture and treated at 10,000 rpm for 10 minutes. Except for these points, the electrode of Comparative Example 1 was produced in the same manner as in Example 1.

Comparative Example 2
In Comparative Example 2, the positive electrode active material, binder, and conductive material were simultaneously mixed. That is, the same positive electrode active material, binder, and conductive material as in Example 1 were placed in the above-described apparatus and treated at 10,000 rpm for 10 minutes. Except for this, the electrode of Comparative Example 2 was fabricated in the same manner as in Example 1.

<Evaluation>
For the electrodes of Example 1 and Comparative Examples 1 and 2, the peel strength between the electrode mixture layer and the current collector foil was measured by a 90-degree peel test. A sample piece was taken from each electrode using a punch. The sample piece was circular. The diameter of the sample piece was 11.28 mm. A "MODEL-2257" manufactured by Aiko Engineering Co., Ltd. was used for the measurement. The results are shown in Figure 4.

The results shown in Figure 4 show that the electrode of Example 1 has improved peel strength compared to the electrodes of Comparative Examples 1 and 2.

Figure 3 is a schematic diagram showing the distribution of binder and conductive material on the surface of the active material in Example 1 and Comparative Examples 1 and 2. As shown in Figure 3(a), in Example 1, by mixing active material 1 and binder 2 to prepare the first composite material, the amount of binder present on the surface of the active material increased, which is thought to have improved the peel strength.

On the other hand, as shown in Figure 3(b), in Comparative Example 1, active material 1 and conductive material 3 were mixed first, so binder 2 was not present on the active material surface, and it is thought that this is why peel strength did not improve. Also, as shown in Figure 3(c), in Comparative Example 2, active material 1, binder 2, and conductive material 3 were mixed simultaneously, so the amount of binder present on the active material surface did not increase compared to Example 1, and it is thought that peel strength did not improve compared to Example 1.

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.

1 Active material, 2 Binder, 3 Conductive material, 10 Second composite material, 11 Current collecting foil, 101 Screen, 102 Power supply, 103 Printing brush.

Claims (2)

preparing a first composite material by dry mixing an active material and a binder;
preparing a second composite material by dry mixing the first composite material and a conductive material;
forming an electrode mixture layer by applying the second composite material to a surface of a current collecting foil;
Equipped with
applying the second composite material by electrostatic screen printing;
The method for producing an electrode mixture layer, wherein the binder comprises at least one selected from the group consisting of carboxymethyl cellulose, styrene butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, and polyacrylic acid. The method for manufacturing an electrode mixture layer according to claim 1 , wherein the first composite material and the second composite material are combined by a mechanochemical treatment.