Method for manufacturing electrode sheets

Abstract

This invention provides a technology for suppressing uneven distribution of electrode density in electrode sheets. [Solution] The method for manufacturing an electrode sheet comprises the steps of: preparing an electrode composite mixture by mixing active material particles with at least a fibrillable binder; processing the electrode composite mixture into a plurality of particles; applying a mechanical impact force to the plurality of particles to make each of the plurality of particles spherical; and rolling the spherical plurality of particles with a pair of rollers to form a sheet.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a method for manufacturing an electrode sheet.

Background Art

[0002] Patent Document 1 describes a method for manufacturing an electrode sheet. This manufacturing method includes a step of preparing an electrode composite mixture by mixing at least a fibrillatable binder with active material particles, and a step of forming the electrode composite mixture into a sheet shape by rolling it with a pair of rollers.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The above-mentioned electrode composite mixture is in the form of flaky granules, having different shapes and / or different sizes. If the shape and / or size of the granules are non-uniform, the amount of granules drawn into the space between a pair of rollers per unit time will vary. As a result, in the electrode sheet formed by rolling, the density distribution may become non-uniform.

[0005] In view of the above situation, this specification provides a technology for manufacturing an electrode sheet having a uniform density.

Means for Solving the Problems

[0006] The technology disclosed herein is embodied in a method for manufacturing an electrode sheet. In a first embodiment, the manufacturing method comprises the steps of: preparing an electrode composite mixture by mixing active material particles with at least a fibrillable binder; processing the electrode composite mixture into a plurality of particles; applying a mechanical impact force to the plurality of particles to make each of the plurality of particles spherical; and rolling the spherical plurality of particles with a pair of rollers to form a sheet. Note that the spheroidization of particles as used herein means making the shape of the particles closer to a sphere, and does not mean making the shape of the particles perfectly spherical.

[0007] In the manufacturing method described above, the electrode composite mixture is processed into multiple particles, and these multiple particles are further shaped into spheres. The sphere-shaped multiple particles have a relatively uniform shape and size. Therefore, by rolling such multiple particles with a pair of rollers, an electrode sheet with a uniform density can be manufactured.

[0008] In a second embodiment, the step of processing the electrode mixture into multiple particles in the first embodiment may include a step of forming the electrode mixture into a columnar shape by extrusion molding, and a step of producing multiple particles by cutting the electrode mixture formed into a columnar shape. With such a configuration, the shape and size of the particles can be made relatively uniform when processing the electrode mixture into multiple particles. As a result, in the subsequent spheroidization, the multiple particles can be processed into a more uniform shape and size.

[0009] In a third embodiment, the following features may be further satisfied in the second embodiment. That is, in the step of forming a columnar shape, when the diameter of the electrode composite mixture formed into a columnar shape is r, and in the step of producing a plurality of particles, when the cutting length of the electrode composite mixture formed into a columnar shape is L, the relation L = 2r / 3 may be satisfied. With such a configuration, when the corners of each of the plurality of particles are rounded off, a sphere with diameter r is easily obtained. That is, further uniformity of the shape and size of the plurality of spherical particles can be achieved.

[0010] In a fourth embodiment, the following features may be further satisfied in the second or third embodiment: In the step of forming the electrode mixture into a columnar shape, let r be the diameter of the electrode mixture formed into a columnar shape, and in the step of forming it into a sheet shape, let G be the distance between a pair of rollers, then the relation r ≤ 40G may be satisfied. With such a configuration, in the step of forming it into a sheet shape, the jamming of multiple spherical particles between the pair of rollers is suppressed. As a result, an electrode sheet having electrodes can be produced in a quantity corresponding to the amount of electrode mixture drawn in by the rotation of the pair of rollers per unit time.

[0011] In the fifth embodiment, in any of the first to fourth embodiments, the spheroidization step may include a step of making each of the multiple particles spherical by causing the multiple particles to collide with each other. With such a configuration, the spheroidization of multiple particles can be easily carried out in a short time. [Brief explanation of the drawing]

[0012] [Figure 1] A schematic diagram showing the configuration of the electrode body 100 in which the electrode sheet 10 is used. [Figure 2] A flowchart illustrating the manufacturing method of the electrode sheet 10. [Figure 3] A diagram illustrating the process of preparing an electrode composite mixture 16 by mixing active material particles 12 with at least a fibrillable binder 14 using a mixer 104. [Figure 4] A diagram illustrating the process of processing an electrode composite mixture 16 into multiple particles 18 using an extrusion molding machine 110. [Figure 5] Enlarged view of section V in Figure 4. [Figure 6] A diagram illustrating the process of applying a mechanical impact force to multiple particles 18 using a disc rotating machine 122 to make each of the multiple particles 18 spherical. [Figure 7]A diagram illustrating the process of forming a sheet by rolling a plurality of spherical particles 18 with a pair of rollers 130 using a press device 128. [Figure 8] The results of measuring the density distribution of electrode sheets manufactured by the manufacturing method of the example are shown. [Figure 9] The results of measuring the density distribution of electrode sheets manufactured using the manufacturing method of the comparative example are shown. [Modes for carrying out the invention]

[0013] Referring to the drawings, the electrode sheet 10 and the electrode body 100 employing it will be described. The electrode body 100 is used, for example, as the negative electrode of a lithium-ion secondary battery. However, the electrode body 100 is not necessarily limited to the negative electrode of a lithium-ion secondary battery, but can also be used as the positive electrode of a lithium-ion secondary battery. Furthermore, this technology shows that the electrode body 100 is not limited to the electrode of a lithium-ion secondary battery, but can also be used as an electrode of any type of secondary battery or as an electrode of an all-solid-state battery.

[0014] As shown in Figure 1, the electrode body 100 comprises an electrode sheet 10 and a current collector 102. The current collector 102 is a conductive sheet. The current collector 102 is, for example, aluminum foil or copper foil. The thickness of the current collector 102 is, for example, 5 μm or more and 50 μm or less. The electrode sheet 10 is placed on the current collector 102. In this embodiment, the electrode sheet 10 is a self-supporting electrode sheet. A self-supporting electrode sheet, as used here, means an electrode sheet that is supported by itself without requiring a support such as the current collector 102. Therefore, the electrode body 100 does not necessarily need to include a current collector 102. That is, in another embodiment, the electrode sheet 10 may constitute the electrode body 100 by itself. The thickness of the electrode sheet 10 is, for example, 10 μm or more and 500 μm or less.

[0015] The electrode sheet 10 includes active material particles 12 and a binder 14 that binds the active material particles 12 to each other. At least a part of the binder 14 is fibrillated. As will be described later, the binder 14 is made of a material that can be fibrillated, such as polytetrafluoroethylene (PTFE). Note that a part of the binder 14 may be made of a material that cannot be fibrillated, such as polyvinylidene fluoride (PVdF). Further, the electrode sheet 10 may further contain a conductive assistant or the like.

[0016] The active material particles include negative electrode active material particles. Examples of the negative electrode active material particles include carbon materials such as graphite (graphite), hard carbon, and soft carbon, materials that form an alloy with lithium such as silicon (Si), and these lithium alloys (for example, Li ,

[0017] , 1 / 3 , 1 / 3 , 3 / 2 , 1 / 3 , 1 / 2 , M, where M is C, Si, Sn, Sb, Al, Mg, Ti, Bi, Ge, Pb, or P, etc., and X is a natural number). The negative electrode active material particles may be composed of a single type of material or a plurality of types of materials. When the electrode body 100 is used as the positive electrode of a lithium-ion secondary battery, the active material particles include positive electrode active material particles instead of negative electrode active material particles. Examples of the positive electrode active material particles include lithium nickel-based composite oxides, lithium cobalt-based composite oxides, lithium manganese-based composite oxides, lithium nickel manganese-based composite oxides (for example, LiNi 1 / 2 Mn 3 / 2 O4), lithium nickel manganese cobalt-based composite oxides (for example, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2), etc., rock salt layer-type active materials, spinel-type active materials such as lithium manganese oxide, and olivine-type active materials such as lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP).

[0017] As described above, the binder 14 is made of a fibrillatable material. A fibrillatable material is a material that can be fibrillated when a shearing force is applied. Examples of fibrillatable materials include polytetrafluoroethylene (PTFE), cellulose, acrylic resin, and ultra-high molecular weight polyethylene. A material that is one of these fibrillatable materials and can function as a binder is referred to herein as a fibrillatable binder. The fibrillatable binder may be composed of a single type of material or a plurality of types of materials.

[0018] Next, a method for manufacturing the electrode sheet 10 will be described with reference to FIGS. 2-7. In this manufacturing method, the electrode sheet 10 can be produced without using a solvent. That is, the manufacturing method is a so-called dry process.

[0019] As shown in FIG. 2, the manufacturing method includes a step (S10) of producing an electrode mixture 16 by mixing at least a fibrillatable binder  14 with the active material particles 12. In this step, as shown in FIG. 3, for example, a mixer 104 is used. The mixer 104 rotates the blade 106 to mix the active material particles 12 and the fibrillatable binder 14 introduced into the container 108. Thereby, the electrode mixture 16 is produced. The mixer 104 applies a shearing force to the fibrillatable binder 14 present between the blade 106 and the wall surface 108a of the container 108 by rotating the blade 106. Therefore, in the electrode mixture 16, the fibrillatable binder 14 is fibrillated. Note that in step S10, it is not always necessary to use the mixer 104. In other embodiments, a blender, a mill, a kneader, or the like may be used instead of the mixer 104.

[0020] As shown in Figure 2, the manufacturing method further comprises a step (S12) of processing the electrode mixture 16 into a plurality of particles 18. In this step, as shown in Figure 4, an extrusion molding machine 110 is used, for example. In the extrusion molding machine 110, the electrode mixture 16 that has been fed into the hopper 112 is supplied into the cylinder 114. A screw 116 rotates inside the cylinder 114, and the electrode mixture 16 is sent to a die 118 connected to the tip of the cylinder 114. The die 118 has a plurality of discharge holes 118a. The electrode mixture 16 is extruded from the plurality of discharge holes 118a and formed into a plurality of columnar shapes. The electrode mixture 16 formed into columnar shapes is cut by a cutting blade 120 and processed into a plurality of particles 18.

[0021] Thus, the process of processing into multiple particles 18 (S12) includes the steps of forming the electrode mixture 16 into a columnar shape by extrusion molding and producing multiple particles 18 by cutting the electrode mixture 16 formed into a columnar shape. Furthermore, when the diameter of the electrode mixture 16 formed into a columnar shape is r in the process of forming into a columnar shape, and the cutting length of the electrode mixture 16 formed into a columnar shape is L in the process of producing multiple particles 18, the relationship L = 2r / 3 is satisfied. As an example, in the die 118 of this embodiment, each of the multiple discharge holes 118a has a circular shape, and the electrode mixture 16 is formed into a cylindrical shape. In this case, as shown in Figure 5, each of the multiple particles 18 produced by step S12 has a cylindrical shape with a diameter of r and an axial length of L (i.e., 2r / 3). Therefore, the multiple particles 18 produced by step S12 have approximately the same shape and size. However, the shape in which the electrode mixture 16 is formed by extrusion molding is not necessarily limited to a cylindrical shape, but may also be a polygonal prism shape, etc. When the electrode mixture 16 is formed into a polygonal prism shape, it is preferable to set the diameter of the circumscribed circle of the polygon to the aforementioned r.

[0022] As shown in Figure 2, the manufacturing method further comprises a step (S14) in which a mechanical impact force is applied to a plurality of particles 18 to make each of the plurality of particles 18 spherical. In this step, as shown in Figure 6, for example, a disc rotating machine 122 is used. The disc rotating machine 122 causes the plurality of particles 18 on the disc 126 to collide with each other by rotating the disc 126 inside the container 124. As a result, each of the plurality of particles 18 is made spherical. Note that the sphericalization of particles here means making the shape of the particles closer to a sphere, and does not mean making the shape of the particles perfectly spherical. The disc 126 has grooves arranged in a grid pattern, although this is not particularly limited. The rotational speed on the outer circumference of the disc 126 is, for example, a peripheral speed of 400 m / min.

[0023] As shown in Figure 2, the manufacturing method further comprises a step (S16) in which a plurality of spherical particles 18 are rolled by a pair of rollers 130 to form a sheet. In this step, as shown in Figure 7, for example, a press device 128 is used. The press device 128 is equipped with a pair of rollers 130 and is configured to roll the plurality of particles 18 passing between the pair of rollers 130. As a result, the plurality of spherical particles 18 are rolled by the pair of rollers 130 to form a sheet. The electrode sheet 10 is produced by cutting the formed sheet to predetermined dimensions. As mentioned above, in the step of forming into a columnar shape, if the diameter of the electrode composite mixture 16 formed into a columnar shape is r, then in the step of forming into a sheet (S16), if the distance between the pair of rollers 130 is G, then the relationship r ≤ 40G is satisfied. In this embodiment, the thickness of the electrode sheet 10 is approximately equal to the distance between the pair of rollers 130.

[0024] In the manufacturing method described above, the electrode composite mixture 16 is processed into a plurality of particles 18, and these particles 18 are further shaped into spheres. The sphered particles 18 have a relatively uniform shape and size. The shape and / or size of the particles 18 greatly affects the density distribution of the electrode sheet 10. For example, if the shape and / or size of the particles 18 are non-uniform, the amount of particles 18 drawn between the pair of rollers 18 per unit time will fluctuate. As a result, the density distribution of the electrode sheet 18 formed by rolling will be non-uniform. In contrast, if the sphered particles 18 have a relatively uniform shape and size, when they are rolled by the pair of rollers 130, an electrode sheet 10 with a uniform density can be manufactured.

[0025] As an example, Figure 8 shows the results of measuring the density distribution of electrode sheets 10 manufactured by the manufacturing method of this embodiment. In this measurement, the density was measured at 10 arbitrary locations in a series of electrode sheets 10 manufactured by the manufacturing method of this embodiment. As a result, the standard deviation of the density at these 10 locations was 1.1%, confirming that electrode sheets 10 with uniform density were manufactured. This can be said to be equivalent to the uniformity of electrode sheets manufactured by a wet process using a solvent. On the other hand, Figure 9 shows the results of measuring the density distribution of electrode sheets manufactured by the manufacturing method of the comparative example. In this measurement as well, the density was measured at 10 arbitrary locations in a series of electrode sheets manufactured by the manufacturing method of the comparative example. The manufacturing method of the comparative example is the manufacturing method of this embodiment shown in Figure 2, with steps 12 and 14 omitted. In the electrode sheets of the comparative example, the standard deviation of the density at these 10 locations was 5.5%, confirming the usefulness of the manufacturing method of this embodiment.

[0026] In the manufacturing method described above, the step of processing the material into multiple particles 18 (S12) includes the steps of forming the electrode mixture 16 into a columnar shape by extrusion molding and producing multiple particles 18 by cutting the columnar electrode mixture 16. With this configuration, the shape and size of the particles can be made relatively uniform when processing the electrode mixture into multiple particles 18. As a result, in the subsequent spheroidization, the multiple particles 18 can be processed into a more uniform shape and size.

[0027] In the manufacturing method described above, when the diameter of the electrode composite mixture 16 formed into a columnar shape is denoted as r in the process of forming it into a columnar shape, and the cutting length of the electrode composite mixture 16 formed into a columnar shape is denoted as L in the process of producing multiple particles 18, the relationship L = 2r / 3 is satisfied. With this configuration, when the corners of each of the multiple particles 18 are rounded off, a spherical shape with a diameter of r is easily obtained. That is, further uniformity of the shape and size of the multiple spherical particles can be achieved. However, the aforementioned relationship L = 2r / 3 does not necessarily have to be satisfied.

[0028] In the manufacturing method described above, when the diameter of the electrode composite mixture 16 formed into a columnar shape is r in the process of forming it into a columnar shape, and the distance between the pair of rollers 130 is G in the process of forming it into a sheet shape (S16), the relation r ≤ 40G is satisfied. With this configuration, the clogging of the spherical particles 18 between the pair of rollers 130 in the process of forming it into a sheet shape (S16) is suppressed. As a result, an electrode sheet 10 having a density corresponding to the amount of particles 18 drawn in by the rotation of the pair of rollers 130 per unit time can be produced. However, the aforementioned relation r ≤ 40G does not necessarily have to be satisfied.

[0029] In the manufacturing method described above, the spheroidizing step (S14) includes a step of making each of the multiple particles 18 spherical by causing them to collide with each other. With this configuration, the spheroidizing of the multiple particles 18 can be easily done in a short time. Alternatively, the spheroidizing step (S14) may include a step of applying a mechanical impact force to the multiple particles 18 by causing them to collide with a wall or the like, instead of causing the multiple particles 18 to collide with each other, thereby making each of the multiple particles 18 spherical.

[0030] Although several specific examples have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or in the drawings exhibit technical usefulness individually or in combination. [Explanation of Symbols]

[0031] 10: Electrode sheet, 12: Active material particles, 14: Binder, 16: Electrode mixture, 18: Particles, 100: Electrode body, 102: Current collector, 104: Mixer, 106: Blade, 108: Container, 110: Extrusion molding machine, 112: Hopper, 114: Cylinder, 116: Screw, 118: Die, 118a: Discharge hole, 120: Cutting blade, 122: Disc rotating machine, 124: Container, 126: Disc, 128: Pressing device, 130: Roller

Claims

1. A method for manufacturing an electrode sheet, A step of preparing an electrode composite mixture by mixing active material particles with at least a binder capable of fibrillation, A step of processing the electrode composite mixture into multiple particles, A step of applying a mechanical impact force to the plurality of particles to make each of the plurality of particles spherical, A process of forming the spherical particles into a sheet by rolling them with a pair of rollers, A manufacturing method that includes the following features.

2. The process of processing the aforementioned plurality of particles is, A step of forming the electrode composite mixture into a columnar shape by extrusion molding, A step of producing the plurality of particles by cutting the electrode composite mixture that has been formed into a columnar shape, The manufacturing method according to claim 1, including

3. In the process of forming the columnar shape, the diameter of the electrode composite mixture formed into the columnar shape is r. In the process of producing the plurality of particles, when the cutting length of the electrode composite mixture formed into the columnar shape is L, The manufacturing method according to claim 2, wherein the relation L = 2r / 3 is satisfied.

4. In the process of forming the columnar shape, the diameter of the electrode composite mixture formed into the columnar shape is r. In the process of forming the sheet, when the distance between the pair of rollers is G, The manufacturing method according to claim 2 or 3, wherein the relation r ≤ 40G is satisfied.

5. The manufacturing method according to claim 1, wherein the step of spheroidizing includes a step of making each of the plurality of particles spherical by causing them to collide with each other.

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