Electrode manufacturing method and electrode manufacturing apparatus

Abstract

To provide a method for manufacturing an electrode that reduces energy consumption in electrode manufacturing without reducing battery capacity.SOLUTION: A method for manufacturing an electrode for a secondary battery includes a wet powder preparation step of adding a liquid in which the solubility of a non-aqueous binder is less than 1 g / 1 L at room temperature to coated powder of an active material, the surfaces of which are coated with a non-aqueous binder, to prepare a wet powder, a film formation step of forming the wet powder into a film, and a liquid removal step of removing the liquid from the film-like wet powder to form an electrode active material film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Secondary batteries such as lithium-ion secondary batteries are widely used as power sources for driving EVs because they are lightweight and have high energy density.

[0003] Electrodes constituting secondary batteries such as lithium-ion secondary batteries are generally produced by coating a mixture slurry, in which an active material, a binder, a conductive additive, etc. are dispersed in a predetermined solvent, on the surface of a current collector made of a metal foil or the like, and then drying the coating. Furthermore, various studies are being conducted on materials, manufacturing methods, etc. in order to further increase the weight and energy density of secondary batteries.

[0004] Most positive electrode active materials are metal oxides containing lithium ions, such as lithium cobalt oxide (LCO), nickel-cobalt-manganese oxide (NCM), nickel-cobalt-aluminum oxide (NCA), and lithium iron phosphate (LFP). Negative electrode active materials include graphite, lithium titanate (LTO), and silicon.

[0005] Conventionally, polyvinylidene fluoride (PVDF), which has excellent properties such as mechanical strength, adhesiveness, and oxidation resistance, has been widely used as a binder for positive electrodes.

[0006] However, because PVDF is insoluble in water, it must be dissolved in an organic solvent such as N-methyl-pyrrolidone (NMP) to create a slurry in which the active material is dispersed. The use of organic solvents requires a large amount of energy for drying, which increases the environmental impact. Furthermore, the drying process requires explosion-proof equipment and organic solvent recovery equipment. Therefore, in recent years, there has been a demand for the development of aqueous binders that can be dispersed in aqueous solvents with a lower environmental impact.

[0007] Carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) have been developed as aqueous binders for use in negative electrodes. However, when these aqueous binders are used directly in positive electrodes, they suffer from oxidative degradation in the positive electrode environment.

[0008] Patent Document 1 discloses a binder composed of an acrylic polymer as an aqueous binder used in a positive electrode. This aqueous binder does not dissolve in water, and is dispersed as suspended particles in an aqueous solvent to prepare a positive electrode slurry. When this positive electrode slurry is applied to a current collector and dried to prepare a positive electrode, the aqueous binder is unevenly distributed in the recesses between the positive electrode active material particles while maintaining its particle shape. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-091789 [Patent Document 2] Japanese Patent Publication No. 2022-115019 Summary of the Invention [Problem to be solved by the invention]

[0010] The aqueous binder disclosed in Patent Document 1 is effective in terms of its oxidation resistance, but because the positive electrode active material contains lithium, when this aqueous binder is dispersed in an aqueous solvent together with a positive electrode active material and a conductive additive to prepare a positive electrode slurry, or when it is dispersed in an aqueous solvent together with lithium titanate as a negative electrode active material to prepare a negative electrode slurry, the lithium in the positive electrode active material or negative electrode active material, lithium titanate, dissolves in the aqueous solvent, resulting in a decrease in the positive electrode capacity or negative electrode capacity. Furthermore, because the slurry contains a large amount of solvent, a large amount of energy is required to dry the slurry.

[0011] Furthermore, the aqueous binder disclosed in Patent Document 1 is unevenly distributed in the recesses between the positive electrode active materials, making it difficult to uniformly disperse the aqueous binder within the positive electrode. This weakens the binding between the positive electrode active materials and between the positive electrode active material and the current collector, resulting in a problem of reduced cycle characteristics of the secondary battery.

[0012] The present invention has been made in view of the above points, and an object of the present invention is to provide a method for manufacturing an electrode that reduces energy consumption in electrode manufacturing without reducing battery capacity. [Means for solving the problem]

[0013] The method for manufacturing an electrode of the present invention is a method for manufacturing an electrode for a secondary battery, and includes the steps of: a wet powder preparation step of adding a liquid in which the solubility of the non-aqueous binder is less than 1 g / 1 L at room temperature to coated powder in which the surfaces of active material powder are coated with a non-aqueous binder to prepare a wet powder; a film formation step of forming the wet powder into a film; and a liquid removal step of removing the liquid from the film-like wet powder to form an electrode active material film.

[0014] The wet powder or granule is preferably in any one of the pendular, funicular and capillary regions.

[0015] In the film-forming step, the wet powder or granule is formed into a film on the side surface or flat surface of a cylinder, and in the liquid-removing step, the liquid is removed from the side surface or flat surface of the cylinder and dried, and the method may further include a peeling step in which the dried electrode active material film is peeled off from the side surface or flat surface of the cylinder after the liquid-removing step.

[0016] The method may further include a step of placing the electrode active material film on a metal foil as a current collector and applying pressure to make the film adhere to the metal foil.

[0017] In the film-forming step, the wet powder may be formed into a film on a metal foil that serves as a current collector.

[0018] The electrode manufacturing apparatus of the present invention is an apparatus for manufacturing an electrode for a secondary battery, and includes a film forming section that forms a wet powder into a film by adding a liquid in which the solubility of the non-aqueous binder is less than 1 g / 1 L at room temperature to a coated powder in which the surface of an active material powder is coated with a non-aqueous binder, and a liquid removal section that removes the liquid from the wet powder film to form an electrode active material film.

[0019] The film forming section may have a cylindrical member or a planar member, and the wet powder or granular material may be placed on the side surface of the cylindrical member or on the planar member to form a film.

[0020] The liquid removal section may remove and dry the liquid on the side surface of the cylindrical member or on the planar member.

[0021] The electrode active material film may further have an adhesion section where the electrode active material film is placed on a metal foil as a current collector and pressed to adhere to the metal foil.

[0022] The film forming section may be formed into a film by placing the wet powder on a metal foil that is a current collector. [Effects of the Invention]

[0023] A liquid in which the binder is hardly dissolved is added to powder particles of an active material coated with a non-aqueous binder to form a wet powder particle, and the wet powder particle is formed into a film and the liquid is removed to form an electrode active material film, so that the electrode active material film can be formed with little energy. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 2 is a schematic diagram showing an electrode manufacturing apparatus according to an embodiment. [Figure 2] FIG. 10 is a schematic diagram showing an electrode manufacturing apparatus according to another embodiment. [Figure 3] FIG. 10 is a schematic diagram showing an electrode manufacturing apparatus according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses. In the following drawings, for the sake of simplicity, components having substantially the same functions are designated by the same reference numerals.

[0026] (Embodiment 1) In the manufacturing of the electrode according to the first embodiment, the manufacturing of a positive electrode will be described, but the manufacturing of a negative electrode can also be performed in a similar manner. That is, in this embodiment, a positive electrode is manufactured using a powdered active material of the positive electrode, a binder, and a liquid, but a negative electrode can also be manufactured using a powdered active material of the negative electrode, a binder, and a liquid. The binder and liquid used for the positive electrode and the negative electrode may be the same or different.

[0027] The secondary battery to which the positive electrode of this embodiment is applied includes a lithium ion secondary battery, a lithium sulfur secondary battery, etc. In addition, the positive electrode active material is, for example, LiCoO2, LiNiO2, LiNi 0.8 Co 0.2 The positive electrode active material preferably includes lithium-containing composite oxides such as LiMnO2 and LiMnO4. The positive electrode active material preferably includes two or more positive electrode active materials having different particle sizes. The positive electrode active material having a small particle size can be formed, for example, by a flux method.

[0028] Active materials are generally distributed as powders, but in this embodiment, they are referred to as granular powders, as explained below. In powder engineering, a collection of solid particles is called a powder, and typically refers to a collection of particles in which interparticle interactions, such as adhesive forces, are greater than the gravity of a single particle. When such interactions are smaller than gravity, they are called granular, and when such granular materials are intentionally included, they are called granular. However, the distinction between these is not necessarily clearly defined. Although powders are solid, they have fluid-like properties, meaning they flow in response to external forces, and are often treated as a material form distinct from solids, liquids, and gases.

[0029] In the manufacturing of the positive electrode according to this embodiment, a coating step is first performed in which the surface of the powder of the positive electrode active material is coated with a non-aqueous binder. Specifically, the non-aqueous binder is made of a fluorine-based resin that is substantially insoluble in aqueous solvents such as water but soluble in certain non-aqueous solvents such as organic solvents. Representative examples include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine-based rubber, etc. Note that "substantially insoluble in aqueous solvents" refers to the fact that when the non-aqueous binder is added to an aqueous solvent (liquid), the solubility of the non-aqueous binder in the liquid is less than 1 g / 1 L at room temperature. Since a solvent is something that dissolves a solute, in this embodiment, a solvent that does not dissolve a solute will simply be referred to as a liquid.

[0030] The coating process includes dissolving a non-aqueous binder powder in a non-aqueous solvent, dispersing a positive electrode active material powder in the non-aqueous solvent, and heating and evaporating the non-aqueous solvent to coat the surfaces of the positive electrode active material powder with the non-aqueous binder. The coating process produces coated powder particles. The non-aqueous solvent may be dried by vacuum drying at room temperature without heating. While the non-aqueous binder may coat at least a portion of the surface of the positive electrode active material powder, it is preferable that the entire surface be coated. Coating the surface of the positive electrode active material powder with the non-aqueous binder prevents lithium ions in the positive electrode active material from leaching into the liquid even when the coated powder comes into contact with an aqueous liquid, thereby preventing a decrease in electrode capacity. Coating the entire surface with the non-aqueous binder significantly suppresses the decrease in electrode capacity. The non-aqueous solvent is made of a material in which the powder of the non-aqueous binder can be dissolved, and includes an organic solvent such as N-methyl-2-pyrrolidone (NMP).

[0031] Next, a wet powder preparation step is carried out in which a liquid in which the non-aqueous binder is substantially insoluble (i.e., the solubility of the non-aqueous binder is less than 1 g / 1 L at room temperature) is added to the coated powder to prepare a wet powder. In this step, a conductive additive or an additive that can be generally added to electrodes may also be added to prepare the wet powder. Such a liquid may be an aqueous liquid such as water. The wet powder will be described below.

[0032] The state of solid particles, liquid, and gas in wet granular materials (packing state) can be classified into four regions: the "pendular region," the "funicular region," the "capillary region," and the "slurry region."

[0033] The "pendular region" is a state in which the solid phase is continuous, meaning that solid particles are in contact with each other, and the gas phase is also continuous, but the liquid phase is small, forming a discontinuous phase. It is a state in which a liquid (liquid phase) exists discontinuously, bridging the active material particle granules (solid phase), and the active material particle granules can exist in a connected (continuous) state. The liquid content is relatively low, and many of the voids (gas phase) in the wet granules exist continuously, forming interconnected pores that lead to the outside. Liquid is present in patches on the surface of the granules (solid phase), giving the granules a "dry" appearance. A characteristic of the pendular region is that, when observed under an electron microscope (SEM), no continuous solvent layer is observed across the entire outer surface of the wet granules.

[0034] The "funicular region" is a state in which the liquid content in wet granular materials is relatively higher than in the pendular region, and liquid exists continuously around the granular materials (solid phase). However, because the amount of liquid is still small, the granular materials exist in a connected (continuous) state. Among the voids (gas phase) present in wet granular materials, the proportion of interconnected pores that lead to the outside decreases slightly, and the proportion of discontinuous, isolated pores increases. Funicular I is a packed state in which the solid phase is continuous, in the sense that the solid particles are in contact with each other, and the liquid and gas phases are also continuous. Furthermore, a state in which the amount of liquid increases and the number of interconnected pores leading to the gas outside becomes very few is called Funicular II. Both states can be considered as states in which the liquid evenly coats the solid.

[0035] In the "capillary region," the liquid content in the wet powder / granules increases to the point where the liquid is close to saturation, separating the solid particles with the liquid, making the solid phase discontinuous. The gas phase exists as small, isolated voids or is almost non-existent, so only the liquid phase is continuous. In other words, the voids in the powder / granule layer are almost entirely filled with liquid.

[0036] The "slurry region" contains a larger proportion of liquid than the capillary region, there is almost no gas phase, and the powder or granules in the solid phase are suspended in the liquid.

[0037] In this embodiment, an electrode is formed using wet powder or granules in any of the pendular, funicular, and capillary regions, rather than in the slurry region. Specifically, the positive electrode (electrode) is formed through a film-forming process in which the wet powder or granules are formed into a film, and a liquid-removing process in which the liquid is removed from the film-like wet powder or granules to form a positive electrode active material film (electrode active material film).

[0038] In the electrode manufacturing apparatus of this embodiment shown in Figure 1, a wet powder or granule is applied from an application member 30 to the side surface of a cylindrical member 2. The cylindrical member 10 rotates (clockwise in Figure 1) around a central axis parallel to its side surface, and the wet powder or granule extruded from the application member 30 forms a wet powder or granule film 2 on the side surface of the cylindrical member 10 as it rotates (clockwise). In other words, the film forming unit has the application member 30 and the cylindrical member 10. The wet powder or granule is supplied to the application member 30 by a supply member 31.

[0039] The cylindrical member 10 has an internal heating mechanism, and the wet powder / granular film 2 is heated by the cylindrical member 10 to remove the liquid and dry (liquid removing step). In other words, the cylindrical member 10 also serves as a liquid removing section.

[0040] The liquid is removed from the wet granular film 2 by the cylindrical member 10, and the wet granular film 2 becomes an electrode active material film 2a, which is then peeled off from the cylindrical member 10 by a peeling member 25 (peeling step).

[0041] The peeled electrode active material film 2a is bonded to a metal foil 4, which is a current collector, to form an electrode (positive electrode) 100. Specifically, a supply roll 40 that supplies the metal foil 4 and a pressure roll 50 overlap the metal foil 4 and the electrode active material film 2a and apply pressure, thereby closely adhering the metal foil 4 and the electrode active material film 2a to each other.

[0042] In this manner, the electrode 100 in this embodiment is manufactured.

[0043] In most conventional electrode manufacturing methods, electrodes are manufactured by applying a slurry to a current collector. However, Patent Document 2 discloses the use of a wet powder in the pendular or funicular I region to sufficiently increase the surface area of ​​the electrode active material by press molding. However, in Patent Document 2, a solvent in which the binder dissolves is added to a mixture of the electrode active material and binder to form the wet powder. Without the use of such a solvent, the binder would not be uniformly distributed and the electrode active material would not bond sufficiently to itself. Therefore, as described in the examples of Patent Document 2, when a non-aqueous binder is used, a non-aqueous solvent in which the binder dissolves is used.

[0044] In this embodiment, a wet powder is produced by applying an aqueous liquid to coated powder (active material) coated with a non-aqueous binder. This reduces the energy required for drying in terms of both the quality and quantity of the liquid, shortens the drying time, and eliminates the need for environmental measures that would be required if an organic solvent were used. While organic solvents require costs for recovery and recycling of the removed solvent, using water as the liquid eliminates the need for recovery, significantly reducing costs. Furthermore, the conventional drying ovens used for organic solvents are no longer required, significantly reducing manufacturing costs.

[0045] The smaller the amount of liquid in the wet powder / granules, the less energy is required for drying. On the other hand, if the amount of liquid is large, the state approaches the conventional slurry region, and the electrode characteristics become almost the same as those produced by conventional manufacturing methods. Therefore, if you want to reduce the drying energy and increase the production speed to lower production costs, it is preferable to use wet powder / granules in the pendular region or funicular I region. If you want to obtain electrode characteristics similar to those of electrodes produced by conventional slurry manufacturing methods, it is preferable to use wet powder / granules in the capillary region.

[0046] (Embodiment 2) The second embodiment differs from the first embodiment in the film forming section and the liquid removing section, and the differences from the first embodiment will be mainly explained below.

[0047] As shown in Fig. 2, in the electrode manufacturing apparatus according to the second embodiment, a wet powder-granular material is applied onto a flat belt 20 by an application member 30 to form a wet powder-granular material film 2 (film-forming step). The belt 20 is driven by two rollers 15 and 16, and moves from left to right in the upper part of the figure and from right to left in the lower part of the figure. The wet powder-granular material film 2 is transported by the belt 20 and placed in a drying furnace 80 where the liquid is removed (liquid removing step).

[0048] The electrode active material film 2a from which the liquid has been removed is peeled off from the belt 20 by a peeling member 26. The electrode active material film 2a after peeling is adhered to and bonded to a metal foil 4 using the same process and equipment as in the first embodiment to form an electrode (positive electrode) 100.

[0049] In the second embodiment, the cost of the manufacturing apparatus is higher than that of the first embodiment because it is equipped with the drying oven 80, but the manufacturing speed can be increased and the manufacturing cost can be reduced by lengthening the drying zone of the drying oven 80. Other aspects and effects are the same as those of the first embodiment.

[0050] (Embodiment 3) In the third embodiment, an electrode is manufactured using a manufacturing apparatus similar to that of the second embodiment. However, the third embodiment differs from the second embodiment in that a wet powder / granular film is formed on a metal foil and that the metal foil and the electrode active material film are pressed together on a belt to form a tight bond. Therefore, the differences from the second embodiment will be mainly explained below.

[0051] 3, in the electrode manufacturing apparatus according to the third embodiment, a supply roll 40 is disposed ahead of the coating member 30 in the direction of movement of the upper side of the belt 20, and a metal foil 4 is supplied from the supply roll 40 onto the belt 20. The coating member 30 coats the metal foil 4 with a wet powder or granular material to form a wet powder or granular film 2. As the belt 20 moves, the wet powder or granular film 2 on the metal foil 4 is placed in a drying furnace 80, where the liquid is removed.

[0052] The electrode active material film 2a from which the liquid has been removed from the wet powder / granular film 2 is subjected to pressure by a pressure roll 50 on a transport roller 16 that transports the belt 20 after coming out of the drying furnace 80. This causes the metal foil 4 and the electrode active material film 2a to adhere to each other to form an electrode (positive electrode) 100.

[0053] In the third embodiment, the wet granular film 2 is directly applied onto the metal foil 4, so a peeling step is not required. Other aspects and effects are the same as those of the second embodiment.

[0054] (Other embodiments) The above-described embodiments are merely examples of the present invention, and the present invention is not limited to these examples. These examples may be combined with well-known, commonly used, or publicly known technologies, or may be partially replaced. Modified inventions that would be easily conceived by a person skilled in the art are also included in the present invention.

[0055] In the first embodiment, a liquid removal device (drying device) that uses heating, infrared radiation, or the like may be provided on the surface of the wet powder / granular material film formed on the cylindrical member, opposite the cylindrical member.

[0056] In the above embodiment, an electrode active material film may also be provided on the surface of the metal foil on the side where no electrode active material film is provided.

[0057] In the first embodiment, a metal foil may be wrapped around the cylindrical member to form a wet powder / granule film on the metal foil.

[0058] The positive electrode and negative electrode produced in the above embodiment are wound with a separator interposed therebetween to produce an electrode assembly, which is then housed in a battery case together with a non-aqueous electrolyte to produce a lithium ion secondary battery. [Explanation of symbols]

[0059] 2. Wet powder film 2a Electrode active material film 10 Cylinder 20 Belt (flat body) 30 Coating material 40 supply rolls 50 Pressing Roll 80 Drying oven 100 electrodes

Claims

1. A method for manufacturing an electrode for a secondary battery, comprising: a wet powder preparation step of adding a liquid in which the solubility of the non-aqueous binder is less than 1 g / 1 L at room temperature to the coated powder, in which the surfaces of powder and granules of an active material are coated with a non-aqueous binder, to prepare a wet powder and granule; a film-forming step of forming the wet powder or granule into a film; a liquid removing step of removing the liquid from the film-like wet powder or granule to form an electrode active material film; A method for manufacturing an electrode, comprising:

2. 2. The method for manufacturing an electrode according to claim 1, wherein the wet powder or granule is in a state of any one of a pendular region, a funicular region, and a capillary region.

3. In the film-forming step, the wet powder or granule is formed into a film on a side surface or a flat surface of a cylinder, In the liquid removing step, the liquid is removed from the side surface or the flat surface of the cylinder to perform drying; The method for producing an electrode according to claim 1 or 2, further comprising a peeling step of peeling off the electrode active material film dried after the liquid removing step from the side surface or the flat surface of the cylinder.

4. The method for producing an electrode according to claim 1 or 2, further comprising the step of placing the electrode active material film on a metal foil as a current collector and applying pressure to make the film adhere to the metal foil.

5. The method for manufacturing an electrode according to claim 1 or 2, wherein the film-forming step comprises forming the wet powder into a film on a metal foil serving as a current collector.

6. An apparatus for manufacturing electrodes for secondary batteries, comprising: a film forming unit that forms a wet powder or granule into a film by adding a liquid in which the solubility of the non-aqueous binder is less than 1 g / 1 L at room temperature to the coated powder or granule, the surface of which is coated with a non-aqueous binder; a liquid removal section that removes the liquid from the wet powder / granule film to form an electrode active material film; The electrode manufacturing apparatus comprises:

7. 7. The electrode manufacturing apparatus according to claim 6, wherein the film forming section has a cylindrical member or a planar member, and the wet powder or granular material is placed on a side surface of the cylindrical member or on the planar member to form a film.

8. The electrode manufacturing apparatus according to claim 7 , wherein the liquid removal unit removes and dries the liquid on the side surface of the cylindrical member or on the planar member.

9. 8. The electrode manufacturing apparatus according to claim 6, further comprising a contact section for placing the electrode active material film on a metal foil serving as a current collector and applying pressure to bring the film into close contact with the metal foil.

10. 7. The electrode manufacturing apparatus according to claim 6, wherein the film forming section forms a film by placing the wet powder on a metal foil that is a current collector.

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