Method for manufacturing electrode active material sheets

Abstract

This disclosure aims to reduce inter-particle friction during dry film formation of active material particles. [Solution] The present disclosure method for manufacturing an electrode active material sheet 300 comprises (a) providing an electrode mixture 100 comprising active material particles 120, a binder 140, and ethylene carbonate 160, and (b) pressing the electrode mixture 100 with a press member 200, wherein in step (b), the ethylene carbonate 160 is at least partially melted.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing an electrode active material sheet. [Background technology]

[0002] Electrode active material sheets are made by rolling or otherwise forming electrode composite materials into a sheet, and are used as the active material layer of electrodes.

[0003] For example, Patent Document 1 discloses an electrode comprising a core material and an electrode composite laminated on the surface of the core material, wherein the electrode composite contains an active material and PTFE, and in an image showing the composition distribution obtained when the surface of the electrode composite is measured using energy-dispersive X-ray analysis, the standard deviation of the area ratio of the PTFE in 30 adjacent sections of 150 μm × 133 μm size is 6% or less, and when the electrode composite is divided into three equal parts in the thickness direction, and the regions from the core material side are designated as the first region, the second region, and the third region, the PTFE content in the first region (a), the PTFE content in the second region (b), and the PTFE content in the third region (c) satisfy (ca) / (a+b+c)≦±10%. According to the electrode described in Patent Document 1, it is possible to improve tensile strength.

[0004] Furthermore, Patent Document 2 discloses an electrode for a secondary battery, characterized by comprising a dry electrode film consisting of an active material, a conductive material, and a fibrillated binder with an average particle size of 0.05 μm to 3 μm, and a current collector on which the electrode film is laminated. The electrode for a secondary battery described in Patent Document 2 is said to be an electrode for a secondary battery that includes a dry electrode film which is highly flexible and minimizes bending, while still containing an active material with small particle size. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2022 / 163186 [Patent Document 2] International Publication No. 2023 / 008803 [Overview of the project] [Problems that the invention aims to solve]

[0006] In dry film deposition using rolling, it is necessary to roll the electrode mixture while it has a high solid content concentration. During this rolling process, there is significant friction between the particles that make up the electrode mixture. Therefore, this rolling process requires the use of high-output press equipment, such as a large roll press (to increase the pressure supplied) or multiple roll presses (to increase the number of times pressure is supplied), which raises concerns about the need for larger equipment and increased investment.

[0007] Furthermore, while friction between particles can be suppressed by commonly used lubricants, drying of the lubricant is necessary, making it difficult to implement a film deposition method that does not involve a drying step, i.e., a dry film deposition method.

[0008] Therefore, this disclosure aims to reduce friction between particles during dry film formation of active material particles. [Means for solving the problem]

[0009] This disclosure aims to achieve the above objectives by the following means:

[0010] (Aspect 1) (a) To provide an electrode mixture containing active material particles, a binder, and ethylene carbonate, and (b) Pressing the electrode composite material with a press member, including and In step (b), the ethylene carbonate is melted at least partially. A method for manufacturing an electrode active material sheet. (Aspect 2) The method according to embodiment 1, wherein the temperature of the press member is at or above the melting point of ethylene carbonate. (Aspect 3) The method according to aspect 1 or 2, wherein the binder is polytetrafluoroethylene. (Aspect 4) The method according to any one of aspects 1 to 3, wherein the pressing member is a pressing roll. [Advantages of the Invention]

[0011] According to the above method, the friction between particles can be reduced during rolling of the active material particles. [Brief Description of the Drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram for explaining step (a). [Figure 2] FIG. 2 is a schematic diagram for explaining step (b). [Modes for Carrying Out the Invention]

[0013] ≪Method for Manufacturing an Electrode Active Material Sheet≫ The method of the present disclosure for manufacturing an electrode active material sheet is (a) providing an electrode mixture containing active material particles, a binder, and ethylene carbonate, and (b) pressing the electrode mixture with a pressing member, and in step (b), at least partially melting the ethylene carbonate.

[0014] According to the above method, the friction between particles can be reduced during rolling of the active material particles.

[0015] In dry film deposition using rolling, it is necessary to roll the electrode mixture while it has a high solid content concentration. During this rolling process, the friction between the particles constituting the electrode mixture is large, so it is necessary to use a press with high output. For example, this rolling process requires the use of a large roll press (to increase the pressure supplied) or multiple roll presses (to increase the number of times pressure is supplied), which raises concerns about the size of the equipment and the increase in investment.

[0016] In contrast, according to this disclosure, by using an electrode mixture containing ethylene carbonate and rolling the electrode mixture while the ethylene carbonate is molten, the ethylene carbonate in the electrode mixture can be used as a lubricant, thereby reducing the load during rolling and solving the above problem.

[0017] Furthermore, since ethylene carbonate is a solid at room temperature (25°C) and is an electrolyte component, it is unnecessary to dry and remove the ethylene carbonate after film formation. Therefore, the method disclosed herein can be used even when the entire film formation process is carried out as a dry film formation process.

[0018] The embodiments of this disclosure will be described in detail below. However, this disclosure is not limited to the embodiments described below, and can be implemented in various ways within the scope of the gist of this disclosure. Furthermore, in the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0019] <Process (a)> The present disclosure provides a method for manufacturing an electrode active material sheet, first providing an electrode mixture comprising active material particles, a binder, and ethylene carbonate.

[0020] Figure 1 shows, but is not limited to, one embodiment of the present disclosure. The electrode mixture 100 contains active material particles 120, a binder 140, and ethylene carbonate 160. By pre-shearing the active material particles 120 and the binder 140, the binder 140 is fibrillated, and then ethylene carbonate is added to this mixture to obtain an electrode mixture containing active material particles, a binder entangled with the active material particles, and ethylene carbonate, as shown in Figure 1.

[0021] (electrode composite material) In this disclosure, the electrode mixture comprises at least active material particles, a binder, and ethylene carbonate, and can be obtained, for example, by shear-mixing the active material particles and the binder, adding ethylene carbonate, and then mixing. The electrode mixture may further contain a conductive additive such as carbon nanotubes (CNTs).

[0022] (active material particles) In this disclosure, the active material particles are included in the electrode mixture. In this disclosure, the "active material particles" may be either "positive electrode active material particles" or "negative electrode active material particles."

[0023] The content of active material particles in the electrode mixture of this disclosure is not particularly limited, but may be 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more, and may be 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, or 30% by mass or less.

[0024] The material of the positive electrode active material particles is not particularly limited. Examples of positive electrode active material particles include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), and nickel-cobalt-lithium manganese oxide (NCM:LiCO2). 1 / 3 Ni 1 / 3 Mn 1 / 3 O2), lithium nickel-cobalt aluminum oxide (LiNi 0.8 (CoAl) 0.2O2), Li 1+x Mn 2-x-y M y It may be, but is not limited to, a heterogeneously element-substituted Li-Mn spinel or the like having a composition represented by O4 (M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, and Zn).

[0025] The positive electrode active material particles may have any shape, and may be, for example, spherical, ellipsoidal, flaky, fibrous, or the like.

[0026] The particle diameter D of the positive electrode active material particles 50 may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Note that the particle diameter D 50 is the particle diameter (median diameter) at 50% of the integrated value in the volume-based particle size distribution determined by the laser diffraction / scattering method.

[0027] The material of the negative electrode active material particles is not particularly limited, and may be metallic lithium or a material capable of occluding and releasing metal ions such as lithium ions. Examples of the material capable of occluding and releasing metal ions such as lithium ions include, but are not limited to, alloy-based negative electrode active materials, carbon materials, lithium titanate (Li4Ti5O 12 ), etc.

[0028] The alloy-based negative electrode active materials are not particularly limited, and examples thereof include Si alloy-based negative electrode active materials and Sn alloy-based negative electrode active materials. The Si alloy-based negative electrode active materials include silicon, silicon oxides, silicon carbides, silicon nitrides, etc., or solid solutions thereof. Further, the Si alloy-based negative electrode active materials may contain metal elements other than silicon, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, Ti, etc. The Sn alloy-based negative electrode active materials include tin, tin oxides, tin nitrides, etc., or solid solutions thereof. Further, the Sn alloy-based negative electrode active materials may contain metal elements other than tin, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, Si, etc.

[0029] The carbon material is not particularly limited and examples include hard carbon, soft carbon, and graphite.

[0030] The shape of the negative electrode active material particles is not particularly limited and may be spherical, ellipsoidal, flake-shaped, or fibrous, for example. Particle size D of the negative electrode active material 50 For example, the particle size D may be 1 nm or more, 5 nm or more, or 10 nm or more, and may also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. 50 This is the particle diameter (median diameter) at 50% of the integrated value in the volume-based particle size distribution determined by laser diffraction and scattering.

[0031] (binder) In this disclosure, the binder is included in the electrode mixture.

[0032] Examples of binders include, but are not limited to, carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA). Binders may be used individually or in combination of two or more types.

[0033] The binder content in the electrode composite material of this disclosure is not particularly limited, but may be 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 3% by mass or more, or 5% by mass or more, and may be 10% by mass or less, 8% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less.

[0034] (Ethylene carbonate) In this disclosure, ethylene carbonate is included in the electrode mixture. When manufacturing an electrode mixture layer by coating and rolling the electrode mixture in layers, heating at least a portion of the electrode mixture layer with a rolling member causes at least a portion of the ethylene carbonate contained in the electrode mixture layer to melt, thereby reducing friction between the active material particles contained in the electrode mixture layer.

[0035] The ethylene carbonate content in the electrode mixture of this disclosure is not particularly limited, but may be 1% by mass or more, 3% by mass or more, 5% by mass or more, 7% by mass or more, or 10% by mass or more, and may be 20% by mass or less, 17% by mass or less, 15% by mass or less, 10% by mass or less, or 7% by mass or less.

[0036] <Process (b)> In the method for manufacturing an electrode active material sheet according to this disclosure, the electrode composite is then pressed with a pressing member, preferably a roll press. In this disclosure, pressing means rolling to form a film.

[0037] In this disclosure, in step (b), the ethylene carbonate is melted at least partially.

[0038] Figure 2 shows, but is not limited to, one embodiment of the present disclosure. An electrode active material sheet 300 can be manufactured by rolling an electrode mixture 100 containing active material particles 120, a binder 140, and ethylene carbonate 160 using a press member 200. At this time, the temperature of the press member 200 is above the melting point of ethylene carbonate 160 (36.4°C). This allows the ethylene carbonate 160 to be melted at least partially during pressing.

[0039] In this disclosure, step (b) may be performed after coating the electrode mixture onto a substrate or the like.

[0040] In this disclosure, the pressing pressure is not particularly limited, but may be 0.5 kN / cm or more, 1.0 kN / cm or more, 2.0 kN / cm or more, 5.0 kN / cm or more, or 10.0 kN / cm or more, and may be 100.0 kN / cm or less, 80.0 kN / cm or less, 60.0 kN / cm or less, 40.0 kN / cm or less, 20.0 kN / cm or less, or 15.0 kN / cm or less.

[0041] (Pressed parts) In this disclosure, the electrode composite material is pressed by a pressing member.

[0042] The material of the press member is not particularly limited, but examples include metal, resin, etc. The press member may be a press roll, and the electrode composite material may be pressed by rotating the press roll.

[0043] The temperature of the press member is not particularly limited. The temperature of the press member may be 10°C or higher, 20°C or higher, 30°C or higher, 40°C or higher, or 50°C or higher, and may also be 100°C or lower, 90°C or lower, 80°C or lower, 70°C or lower, 60°C or lower, or 50°C or lower. In this disclosure, the temperature of the press member may preferably be above the melting point of ethylene carbonate (36.4°C). This allows the ethylene carbonate to be at least partially melted during pressing.

[0044] The present disclosure will be further described with reference to the following embodiments, but the scope of the present disclosure is not limited to these embodiments. [Examples]

[0045] <<Evaluation of the density of electrode active material sheets>> The density of the electrode active material sheets prepared in Comparative Examples 1 and 2, and Examples 1 to 4, was evaluated.

[0046] <Comparative Example 1> (preparation) The following materials were prepared. Positive electrode active material: Lithium nickel-cobalt manganese oxide (NCM) Conductive additive: Carbon nanotubes (CNTs) Binder: Polytetrafluoroethylene (PTFE)

[0047] (mixture) A positive electrode active material, a conductive additive, and a binder were mixed to obtain an electrode composite material.

[0048] (rolling) Using a rolling mill as the rolling member, the electrode composite was rolled and formed into a film to obtain the electrode active material sheet of Comparative Example 1. The rolling and film formation conditions are as shown in Table 1 below.

[0049] <Comparative Example 2> A sheet of electrode active material for Comparative Example 2 was obtained in the same manner as for Comparative Example 1, except that the pressure during rolling was set to 2.0 kN / cm. The conditions for rolling were as shown in Table 1 below.

[0050] <Example 1> An electrode active material sheet of Example 1 was obtained in the same manner as in Comparative Example 1, except that the electrode mixture further contained 6.0% by mass of ethylene carbonate (EC) in the total electrode mixture. The rolling film formation conditions are as shown in Table 1 below.

[0051] <Example 2> An electrode active material sheet of Example 2 was obtained in the same manner as in Comparative Example 2, except that the electrode mixture further contained 6.0% by mass of ethylene carbonate in the total electrode mixture. The rolling film formation conditions are as shown in Table 1 below.

[0052] <Example 3> An electrode active material sheet for Example 3 was obtained in the same manner as in Example 1, except that the temperature during rolling was set to 60°C. The rolling conditions are as shown in Table 1 below.

[0053] <Example 4> An electrode active material sheet for Example 4 was obtained in the same manner as in Example 1, except that the temperature during rolling and film formation was set to 70°C. The conditions for rolling and film formation are as shown in Table 1 below.

[0054] <Rating> The densities of the electrode active material sheets in Comparative Examples 1 and 2, and Examples 1 to 4, are shown in Table 1 below. A comparison of Comparative Examples 1 and 2 and Examples 1 and 2 shows that the density of the electrode active material sheet after film formation increased when the electrode mixture contained ethylene carbonate. Furthermore, a comparison of Examples 1, 3, and 4 shows that increasing the temperature of the rolling film formation conditions increased the density of the electrode active material sheet after film formation. Therefore, by containing ethylene carbonate in the electrode mixture and rolling while at least partially melting the ethylene carbonate, it was possible to reduce friction between particles.

[0055] [Table 1] [Explanation of Symbols]

[0056] 100 Electrode mixture 120 Active material particles 140 Binder 160 Ethylene carbonate 200 Pressed parts 300 Electrode Active Material Sheets

Claims

1. (a) To provide an electrode mixture containing active material particles, a binder, and ethylene carbonate, and (b) Pressing the electrode composite material with a press member, including and A method for producing an electrode active material sheet, wherein in step (b), the ethylene carbonate is at least partially melted.

2. The method according to claim 1, wherein the temperature of the press member is at or above the melting point of ethylene carbonate.

3. The method according to claim 1 or 2, wherein the binder is polytetrafluoroethylene.

4. The method according to claim 1 or 2, wherein the pressing member is a pressing roll.

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