Manufacturing method of electrode mixture layer

Abstract

To provide a manufacturing method of an electrode having improved peel strength.SOLUTION: A manufacturing method of an electrode mixture layer includes the steps of: preparing a first composite material by mixing an active material and a binder by a dry method; preparing a second composite material by mixing the first composite material and a conductive material by a dry method; and forming the electrode mixture layer by applying the second composite material to a surface of a current collector foil. An application of the second composite material is performed by electrostatic screen printing, and the binder is composed of at least one selected from a group consisting of carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, and polyacrylic acid.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Patent Document 1 (JP 2020-149862 A) discloses a method for manufacturing an electrode in which an electrode composite material containing an active material and a binder is attached to a magnetic carrier, transported by a magnet roll, a potential difference is generated between the magnet roll and a backup roll carrying a current collecting foil, and only the electrode composite material is attached to the current collecting foil by electrostatic force. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-149862 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, a wet method has been used to manufacture electrodes, 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. On the other hand, a dry method is also known in which an active material and additives are kneaded together without using a solvent, and then compression-molded.

[0005] 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 during drying, the binder does not segregate on the surface of the active material, resulting in poor adhesion. Thus, the dry method has the disadvantage of low peel strength.

[0006] It is therefore an object of the present disclosure to provide a method for manufacturing an electrode with improved peel strength. [Means for solving the problem]

[0007] [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.

[0008] By premixing the active material and binder before adding the conductive material, the binder adheres to the surface of the active material, which is thought to increase the contact area between the active material and the binder and improve the peel strength.

[0009] [2] The method for manufacturing an electrode according to [1], wherein the first composite material and the second composite material are combined by mechanochemical treatment.

[0010] [3] The method for manufacturing an electrode according to [1] or [2], wherein the second composite material is applied by electrostatic screen printing.

[0011] [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. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a flowchart showing an outline of the method for producing an electrode according to this embodiment. [Figure 2] FIG. 2 is a conceptual diagram showing an example of a method for applying the second composite material. [Figure 3] 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. [Figure 4] FIG. 4 is a bar graph showing the peel strength for the Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present disclosure will be described. However, the present disclosure is not limited thereto. In this specification, the "positive electrode" and the "negative electrode" will be collectively referred to as "electrodes."

[0014] Fig. 1 is a flowchart showing an outline of the method for producing an electrode according to the present embodiment. As shown in Fig. 1, the method for producing an electrode according to the present embodiment includes at least a first composite material preparation step (S10), a second composite material preparation step (S20), an electrode mixture layer formation step (S30), and an electrode formation step (S40).

[0015] 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.

[0016] First composite material preparation step (S10) In the first composite material manufacturing process, the first composite material is produced by mixing the active material and the binder by a dry method. As described later, by mixing the conductive material in a separate process, it is expected that the amount of the binder present on the surface of the active material will increase and the peel strength will be improved. Here, the "dry method" means a mixing method in which the solid content ratio of the paint is 90% or more. The solid content ratio of the paint in the dry method may be 95 to 100%.

[0017] For example, the first composite material may be produced by simply mixing the active material powder and the binder by a dry method. For example, the active material powder and the binder may be compounded by a mechanochemical treatment.

[0018] The "mechanochemical treatment" means a treatment that causes a mechanochemical reaction in which materials react with each other or the physicochemical properties of the materials are changed by continuously applying mechanical energy such as shear force, impact force, and frictional force to the target materials. Examples of the apparatus for performing the mechanochemical treatment include a planetary ball mill, a bead mill, a jet mill, a disper, a planetary mixer, a homogenizer, and the like.

[0019] (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 composed of the active material.

[0020] Examples of the positive electrode active material include lithium-containing metal oxides, lithium-containing phosphates, and the like. Examples of the lithium-containing metal oxide include LiCoO2, LiNiO2, and the compound represented by the general formula LiNi a Co b O2 (where a + b = 1, 0 < a < 1, 0 < b < 1).), LiMnO2, LiMn2O4, and the general formula LiNi a Co b Mn cCompounds represented by O2 (where a + b + c = 1, 0 < a < 1, 0 < b < 1, 0 < c < 1), such as LiFePO4, etc. Here, the general formula LiNi a Co b Mn c Examples of the compound represented by O2 include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. Examples of lithium-containing phosphates include LiFePO4, etc.

[0021] The average particle size of the positive electrode active material may be, for example, about 1 to 25 μm. Here, the "average particle size" means the particle size (D50) at an integrated value of 50% in the volume-based particle size distribution measured by the laser diffraction / scattering method.

[0022] Examples of the negative electrode active material include carbon-based negative electrode active materials such as graphite, easily graphitizable carbon, and difficultly graphitizable carbon, 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, about 1 to 25 μm.

[0023] (Binder) Examples of the binder include carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), etc. The binder may be used alone or in combination of two or more.

[0024] 《Second Composite Material Preparation Step (S20)》 In the second composite material preparation step, the second composite material is prepared by mixing the first composite material and the conductive material by a dry method.

[0025] For example, the second composite material may be prepared by simply mixing the first composite material and the conductive material by a dry method. For example, the first composite material and the conductive material may be compounded by mechanochemical treatment.

[0026] (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.

[0027] The content of the active material in the second composite material is, for example, about 90 to 99 mass %, the content of the binder in the second composite material is, for example, about 0.5 to 5 mass %, and the content of the conductive material in the second composite material is, for example, about 0.5 to 5 mass %.

[0028] 《Electrode composite material layer formation process (S30)》 In the electrode mixture layer forming step, the electrode mixture layer is formed on the current collector foil. For example, the electrode mixture layer is formed on the current collector foil by adhering the second composite material to the surface of the current collector foil. For example, electrostatic printing, electrostatic painting, or similar techniques may be used.

[0029] FIG. 2 is a conceptual diagram illustrating 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, thereby 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. That is, a desired scattering state can be formed.

[0030] The electrode mixture layer may have a thickness of, for example, 10 to 500 μm, or 50 to 200 μm.

[0031] 《Electrode formation process (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.

[0032] The pressure can be adjusted depending on the target thickness and target density of the electrode mixture layer, for example, 1 to 10 t / cm 2 may be applied to the electrode mixture layer.

[0033] In this step, heat may be applied. Heat may be applied separately from pressure, or may be applied substantially simultaneously. For example, the electrode mixture layer may be heated by 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.

[0034] The electrode can be manufactured as described above. The electrode may be cut into a predetermined planar shape according to the specifications of the battery.

[0035] An electrode obtained by the manufacturing method of the present disclosure can be used as an electrode for a secondary battery such as a lithium ion secondary battery (nonaqueous electrolyte secondary battery). A secondary battery such as a lithium ion secondary battery can be used as a power source for a hybrid vehicle (HV), an electric vehicle (EV), a plug-in hybrid vehicle (PHV), etc. However, the electrode obtained by the manufacturing method of the present disclosure is not limited to such in-vehicle applications and can be applied to a variety of applications. [Example]

[0036] The present embodiment will be described below using examples, but the present embodiment is not limited to these.

[0037] Example 1 The electrode (positive electrode) of Example 1 was produced as follows.

[0038] <<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 a device for mechanochemical treatment. The positive electrode active material and the binder were placed in the device and treated at 10,000 rpm for 10 minutes, to produce a first composite material.

[0039] <<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.

[0040] 《Electrode composite material layer formation process》 An Al foil (thickness: 12 μm) was prepared as the current collecting foil. A tabletop manual electrostatic screen printing machine "T-1" manufactured by Berg Industries Co., Ltd. was prepared as the device for forming the 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 collecting foil.

[0041] 《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 to 80°C. The current collector foil on which the electrode mixture layer was formed was placed between the upper and lower plates, and the electrode mixture layer was fixed to the current collector foil at a density of 5 t / cm. 2 A load of this magnitude was applied for 60 seconds to prepare an electrode (positive electrode) of Example 1.

[0042] 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.

[0043] 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-mentioned device and treated at 10,000 rpm for 10 minutes. Except for this, the electrode of Comparative Example 2 was produced in the same manner as in Example 1.

[0044] <Evaluation> For the electrodes of Example 1 and Comparative Examples 1 and 2, the peel strength between the electrode composite layer and the current collecting 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.

[0045] From the results shown in FIG. 4, it can be seen that the electrode of Example 1 has improved peel strength compared to the electrodes of Comparative Examples 1 and 2.

[0046] Fig. 3 is a schematic diagram showing the distribution of the binder and conductive material on the surface of the active materials of Example 1 and Comparative Examples 1 and 2. As shown in Fig. 3(a), in Example 1, the amount of binder present on the surface of the active material increased by mixing active material 1 and binder 2 to prepare the first composite material, which is thought to have improved the peel strength.

[0047] On the other hand, as shown in Figure 3(b), in Comparative Example 1, the active material 1 and the conductive material 3 were mixed first, so the binder 2 was not present on the active material surface, and it is thought that this is why the peel strength was not improved. Also, as shown in Figure 3(c), in Comparative Example 2, the active material 1, the binder 2, and the 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 the peel strength was not improved compared to Example 1.

[0048] The embodiments and examples disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0049] 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

1. 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.

2. 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.

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