Electrode sheet manufacturing method

Abstract

To reduce deterioration of an active material.SOLUTION: (a) A wet powder is made containing an active material and a volatile liquid. (b) An active material sheet is formed by spreading the wet powder. (c) An electrode sheet is produced by placing the active material sheet on the surface of the substrate. In at least one of (a) and (b), the ambient temperature of a workpiece is 15°C or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Japanese Patent Application Laid-Open Publication No. 2020-013681 (Patent Document 1) discloses a method for manufacturing an electrode plate, which includes rolling a particle aggregate in which wet particles are aggregated. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-013681 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, electrode sheets are produced by coating a slurry on the surface of a substrate and drying it. A large amount of solvent (volatile liquid) is consumed during the production of the slurry. A large amount of thermal energy is consumed during the drying of the slurry to volatilize the large amount of volatile liquid. From the viewpoints of production costs, environmental impact, etc., there is a demand for a reduction in the amount of volatile liquid.

[0005] A method for producing an electrode sheet by spreading a wet powder has been proposed. The wet powder has a higher solid content than a slurry. The use of a wet powder can reduce the amount of volatile liquid. However, the wet powder tends to cause the active material to deteriorate more easily than a slurry. The deterioration of the active material can lead to a decrease in battery capacity.

[0006] An object of the present disclosure is to reduce the degradation of active materials. [Means for solving the problem]

[0007] The technical configuration and effects of the present disclosure will be described below. However, the mechanism of action in this specification includes speculation. The mechanism of action does not limit the technical scope of the present disclosure.

[0008] 1. A method for producing an electrode sheet includes the following steps (a) to (c): (a) A wet powder containing an active material and a volatile liquid is prepared. (b) The wet powder is spread to form an active material sheet. (c) An electrode sheet is produced by disposing an active material sheet on the surface of a substrate. In at least one of the above (a) and (b), the ambient temperature of the workpiece is 15°C or less.

[0009] It is believed that the active material deteriorates due to a reaction between the active material and the volatile liquid. A slurry contains a larger amount of volatile liquid than a wet powder. It is believed that the contact opportunity between the active material and the volatile liquid in a slurry is greater than the contact opportunity between the active material and the volatile liquid in a wet powder. Therefore, it has been believed that the deterioration of the active material is less likely to progress in a wet powder than in a slurry. However, according to the new findings of the present disclosure, the deterioration of the active material tends to progress more easily in a wet powder.

[0010] It is believed that a large shear load is applied to the active material when the wet powder is prepared (mixed) and when it is spread. When the volatile liquid evaporates, the spreadability of the wet powder decreases, and the load applied to the surface of the active material increases. This causes the outermost layer of the active material to peel off, exposing a new surface. The new surface is active. The increased contact area between the new surface and the volatile liquid is believed to accelerate the deterioration of the active material.

[0011] According to the new findings of the present disclosure, degradation of the active material tends to be less likely to progress in an environment of 15°C or below. In an environment of 15°C or below, the saturated water vapor pressure of the volatile liquid is low, so the evaporation rate of the volatile liquid may be reduced. Therefore, it is thought that the decrease in spreadability due to the evaporation of the volatile liquid may be reduced. In other words, it is thought that the load applied to the surface of the active material may be reduced. It is expected that deterioration of the active material will be reduced by keeping the ambient temperature of the workpiece at 15°C or below during at least one of the preparation of the wet powder and the spreading of the wet powder.

[0012] 2. The volatile liquid may include, for example, water.

[0013] 3. In at least one of the above (a) and (b), for example, the ambient humidity of the workpiece may be 70% or higher.

[0014] By keeping the ambient humidity at 70% or higher, the evaporation rate of the volatile liquid can be reduced, which is thought to result in a reduction in the load on the surface of the active material.

[0015] 4. The electrode sheet manufacturing system may include, for example, a mixing device and a film-forming device. The mixing device is configured to mix an active material with a volatile liquid to produce a wet powder. The film-forming device is configured to spread the wet powder to form an active material sheet. The electrode sheet manufacturing system is configured so that the ambient temperature of the workpiece is 15°C or less in at least one of the mixing device and the film-forming device.

[0016] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic flowchart of a method for producing an electrode sheet in this embodiment. [Figure 2] FIG. 2 is a schematic diagram showing an example of a film forming apparatus. [Figure 3] FIG. 3 is a conceptual diagram of a manufacturing system for an electrode sheet according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] <Definitions of terms, etc.> In this specification, the terms "comprise," "include," "have," and variations thereof (e.g., "consisting of") are open-ended. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even in closed-ended terms, additional elements that are normally incidental impurities or unrelated to the disclosed technology are not excluded. The term "consisting essentially of..." is semi-closed. Semi-closed terms allow for the addition of elements that do not substantially affect the basic and novel characteristics of the disclosed technology.

[0019] In this specification, expressions such as "may" and "can" are used in the permissive sense of "possibly" rather than the obligatory sense of "must."

[0020] In this specification, the order of execution of multiple steps, actions, operations, etc. included in various methods is not limited to the order described unless otherwise specified. For example, multiple steps may proceed simultaneously. For example, multiple steps may occur one after the other.

[0021] In this specification, unless otherwise specified, a numerical range such as "m to n%" includes both the upper and lower limits. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% and less than n%." Furthermore, a numerical value arbitrarily selected from within the numerical range may be set as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described elsewhere in this specification, in a table, a figure, or the like.

[0022] As used herein, "wet powder" refers to a dispersion system in which a liquid is dispersed in a powder, and "slurry" refers to a dispersion system in which a powder is dispersed in a liquid.

[0023] In this specification, the term "electrode" is a general term for a positive electrode or a negative electrode. The electrode may be a positive electrode or a negative electrode. The electrode may be used for any purpose. For example, the electrode may be used for a battery. In this specification, an electrode for a lithium ion battery will be described as an example.

[0024] As used herein, the term "volatile liquid" refers to a liquid having a boiling point of 50 to 240°C. The volatile liquid may have a boiling point of, for example, 75 to 150°C, or 75 to 125°C.

[0025] In this specification, the term "solid content" refers to the mass fraction of solid components in a paint, etc. (for example, a slurry, a wet powder, etc.) A solute dissolved in a solvent is considered to be a solid component.

[0026] In this specification, the term "workpiece" refers to an object to be processed. For example, when a wet powder is produced, the active material and the volatile liquid are the workpiece. For example, when an active material sheet is formed, the wet powder is the workpiece.

[0027] In this specification, "ambient temperature" refers to the ambient temperature around the workpiece. In this specification, "ambient humidity" refers to the ambient humidity around the workpiece. For example, if the workpiece and processing equipment are placed in a temperature-controlled room, the room temperature is considered to be the ambient temperature. For example, if the temperature inside the mixing tank of a mixing device is controlled, the set temperature of the mixing tank is considered to be the ambient temperature. The same applies to ambient humidity. In this specification, "humidity" refers to relative humidity.

[0028] In this specification, the D50 of an active material refers to the particle size at which the cumulative frequency of smaller particle sizes reaches 50% in a volumetric particle size distribution. The volumetric particle size distribution can be measured by a laser diffraction scattering method.

[0029] In this specification, D50 of a wet powder refers to the particle size at which the cumulative frequency of particles from the smallest particle size reaches 50% in a particle size distribution based on mass (number). The particle size distribution based on mass can be measured in accordance with "JIS Z 8815 General rules for sieving test methods."

[0030] <Electrode sheet manufacturing method> Fig. 1 is a schematic flowchart of a method for manufacturing an electrode sheet according to this embodiment. Hereinafter, the "method for manufacturing an electrode sheet according to this embodiment" may be abbreviated as "the present manufacturing method." The present manufacturing method includes "(a) preparation of a wet powder," "(b) formation of an active material sheet," and "(c) manufacturing of an electrode sheet."

[0031] In at least one of "(a) Preparation of Wet Powder" and "(b) Formation of an Active Material Sheet", the ambient temperature of the workpiece is 15°C or less. This can reduce deterioration of the active material. In either "(a) Preparation of Wet Powder" or "(b) Formation of an Active Material Sheet", the ambient temperature of the workpiece may be 15°C or less. In both "(a) Preparation of Wet Powder" and "(b) Formation of an Active Material Sheet", the ambient temperature of the workpiece may be 15°C or less. The ambient temperature of the workpiece may be, for example, 0 to 15°C, or 5 to 15°C.

[0032] In at least one of "(a) Preparation of Wet Powder" and "(b) Formation of an Active Material Sheet", the ambient humidity of the workpiece may be 70% or more. This can reduce film formation defects when forming an active material sheet. This is thought to be because an ambient humidity of 70% or more improves the spreadability of the wet powder. In either "(a) Preparation of Wet Powder" or "(b) Formation of an Active Material Sheet", the ambient humidity of the workpiece may be 70% or more. In both "(a) Preparation of Wet Powder" and "(b) Formation of an Active Material Sheet", the ambient humidity of the workpiece may be 70% or more. The ambient humidity of the workpiece may be, for example, 80% or more. The ambient humidity of the workpiece may be, for example, 70 to 100%, or 70 to 80%.

[0033] Furthermore, in "(c) Manufacturing of electrode sheets," the ambient temperature of the workpiece may be 15° C. or lower. In "(c) Manufacturing of electrode sheets," the ambient humidity of the workpiece may be 70% or higher.

[0034] (a) Preparation of wet powder The manufacturing method includes preparing a wet powder containing an active material and a volatile liquid. For example, the wet powder may be prepared by mixing the active material with the volatile liquid. For example, at least one selected from the group consisting of a conductive material, a solid electrolyte, and a binder may be mixed with the wet powder.

[0035] For example, the active material and the volatile liquid may be mixed using an agitation granulator. The wet powder may be crushed or sized. For example, a planetary mixer, a three-roll mill, or the like may be used. Mixing may be performed in one stage or in multiple stages. For example, the active material and the volatile liquid may be mixed in a planetary mixer to form a wet powder. The wet powder may be kneaded using a three-roll mill.

[0036] For example, air whose temperature and / or humidity are controlled may be supplied to the mixing vessel of the planetary mixer. The supply air temperature may be 15°C or lower. The supply air humidity may be 70% or higher.

[0037] For example, a three-roll mill may be used in a room where at least one of temperature and humidity is controlled. The room temperature may be 15° C. or lower, and the room humidity may be 70% or higher.

[0038] The wet powder may be made to have a solid content of, for example, 70% or more, 70 to 90% or 75 to 85%.

[0039] The wet powder may be in the form of granules, flakes, clay, etc. The properties of the wet powder can be adjusted, for example, by adjusting the solid content, mixing conditions, etc.

[0040] The wet powder may be made to have a D50 of, for example, 4 mm or less. The wet powder may be made to have a D50 of, for example, 0.1 to 4 mm, or 0.5 to 2 mm.

[0041] The active material may be, for example, in the form of particles. The active material may have a D50 of, for example, 0.5 to 50 μm, or may have a D50 of 1 to 10 μm.

[0042] The active material may include a positive electrode active material. The active material may include, for example, at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. For example, "(NiCoMn)" in "Li(NiCoMn)O2" indicates that the sum of the composition ratios in parentheses is 1. As long as the sum is 1, the amounts of the individual components are arbitrary. Li(NiCoMn)O2 may be, for example, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3)O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 The active material may include a negative electrode active material, such as graphite, soft carbon, hard carbon, silicon, silicon oxide, silicon-based alloys, tin, tin oxide, tin-based alloys, and Li4Ti5O. 12 It may contain at least one selected from the group consisting of:

[0043] The volatile liquid may contain, for example, at least one selected from the group consisting of water, N-methyl-2-pyrrolidone (NMP), alcohol (e.g., ethanol, propanol, etc.), and ester (e.g., butyl butyrate, etc.). From the viewpoint of thermal energy during drying, the volatile liquid may have a boiling point of 150°C or less. The amount of the volatile liquid to be added can be determined depending on the solid content of the wet powder.

[0044] The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of active material. The binder may contain any component. For example, the binder may contain at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyamideimide (PAI), and polyimide (PI).

[0045] The amount of conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the active material. The conductive material may include, for example, conductive carbon particles, conductive carbon fibers, etc. The conductive material may include, for example, at least one selected from the group consisting of carbon black, vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes. The carbon black may include, for example, at least one selected from the group consisting of acetylene black, Ketjen Black (registered trademark), furnace black, channel black, and thermal black.

[0046] The amount of the solid electrolyte may be, for example, 1 to 100 parts by volume per 100 parts by volume of the active material. The solid electrolyte may include, for example, at least one selected from the group consisting of Li2S-P2S5, LiI-Li2S-P2S5, LiBr-Li2S-P2S5, and LiI-LiBr-Li2S-P2S5.

[0047] (b) Formation of an active material sheet The method includes spreading a wet powder to form an active material sheet. The wet powder can be spread by any method. For example, the wet powder can be spread by roll molding.

[0048] 2 is a schematic diagram showing an example of a film forming apparatus. The film forming apparatus 200 may be placed in a room where at least one of the temperature and humidity is controlled. The room temperature may be 15°C or lower. The room humidity may be 70% or higher.

[0049] In the film-forming apparatus 200, the electrode sheet 10 can be manufactured by a roll-to-roll process. In the film-forming apparatus 200, roll forming and roll transfer can be performed.

[0050] The film forming apparatus 200 includes a first roll 201, a second roll 202, and a third roll 203. Each roll rotates in the direction of the arrow. The rotation axes of the rolls are parallel to each other. When the rotation speed of the first roll 201 is ω1, the rotation speed of the second roll 202 is ω2, and the rotation speed of the third roll 203 is ω3, the relationship "ω1<ω2<ω3" may be satisfied, for example.

[0051] A gap AB is formed between a first roll 201 and a second roll 202. Wet powder 5 is supplied to the gap AB. In the gap AB, the wet powder 5 is consolidated and spread to form an active material sheet 12. The active material sheet 12 may have a thickness of, for example, 10 to 500 μm, or may have a thickness of 50 to 200 μm.

[0052] (c) Manufacturing of electrode sheets This manufacturing method includes manufacturing an electrode sheet 10 by placing an active material sheet 12 on the surface of a substrate 11. Subsequently, processing can be performed in a film-forming apparatus 200. A gap BC is formed between a second roll 202 and a third roll 203. The second roll 202 transports the active material sheet 12 into the gap BC (see FIG. 2). The third roll 203 transports the substrate 11 into the gap BC.

[0053] In the gap BC, the active material sheet 12 is rubbed against the surface of the substrate 11. This causes the active material sheet 12 to adhere to the surface of the substrate 11. By adhering the active material sheet 12 to the substrate 11, the electrode sheet 10 is produced.

[0054] The active material sheet 12 may be disposed on only one side of the substrate 11, or on both the front and back sides of the substrate 11. The electrode sheet 10 may be dried. The electrode sheet 10 may be compressed. The electrode sheet 10 may be cut to fit, for example, the battery design.

[0055] The substrate may have a thickness of, for example, 5 to 50 μm. The substrate may be conductive. The substrate may include, for example, a metal foil. The substrate may include at least one selected from the group consisting of aluminum (Al) foil, Al alloy foil, copper (Cu) foil, Cu alloy foil, titanium (Ti) foil, stainless steel (SUS) foil, nickel (Ni)-plated SUS foil, and Ni foil.

[0056] <Electrode sheet manufacturing system> 3 is a conceptual diagram of a manufacturing system for an electrode sheet according to this embodiment. Hereinafter, the "manufacturing system for an electrode sheet according to this embodiment" may be abbreviated as "the manufacturing system of this embodiment." The manufacturing system 1000 includes a mixing device 100 and a film-forming device 200. The manufacturing system 1000 may further include, for example, a conveying device, a compression device (e.g., a roll press), a drying device (e.g., a hot-air drying oven), a cutting device (e.g., a rotary slitter), and the like.

[0057] The mixing device 100 is configured to mix an active material with a volatile liquid to produce a wet powder. The wet powder is supplied to the film-forming device 200. For example, a conveying device may convey the wet powder to the film-forming device 200. The film-forming device 200 is configured to spread the wet powder to form an active material sheet.

[0058] The manufacturing system 1000 is configured so that the ambient temperature of the workpiece is 15° C. or less in at least one of the mixing apparatus 100 and the film forming apparatus 200. For example, at least one of the mixing apparatus 100 and the film forming apparatus 200 may be placed in a temperature-controlled room.

[0059] The manufacturing system 1000 may be configured so that the ambient humidity of the workpiece is 70% or higher in at least one of the mixing apparatus 100 and the film forming apparatus 200. For example, at least one of the mixing apparatus 100 and the film forming apparatus 200 may be placed in a humidity-controlled room. [Example]

[0060] <Experiment 1> <<Manufacturing of electrode sheets>> Electrode sheets Nos. 1 to 7 were produced as follows. Hereinafter, for example, "electrode sheet No. 1" may be abbreviated as "No. 1."

[0061] No. 1 The following electrode materials were prepared: Active material: LiFePO4 (particle surface coated with carbon) Volatile liquid: Water Conductive material: CNT Binder: CMC and SBR

[0062] A planetary mixer, a three-roll mill, and a film-forming apparatus 200 (see FIG. 2) were placed in a room. The room temperature was adjusted to 25°C. The room humidity was adjusted to 50%. The temperature and humidity were adjusted by a precision air conditioning system (manufactured by Orion Machinery Co., Ltd.).

[0063] The electrode materials were mixed in a planetary mixer and a three-roll mill to produce a wet powder with a solid content of 75% or more.

[0064] The wet powder 5 was supplied to the film-forming apparatus 200 to form an active material sheet 12. The active material sheet 12 was then placed on the surface of the substrate 11, thereby producing the electrode sheet 10.

[0065] No. 2-7 Electrode sheets were prepared in the same manner as No. 1, except that the temperature and humidity were changed as shown in Table 1 below.

[0066] "evaluation" <Film Defects> The presence or absence of film formation defects was confirmed by visual inspection on the surface of the electrode sheet 10 (active material sheet 12). The results are shown in Table 1 below.

[0067] <Specific capacity> The electrode sheet was cut to a predetermined size. A small battery containing the electrode sheet was manufactured. The initial charge capacity of the small battery was measured by a constant current charge / discharge test. The specific capacity of the active material was calculated by dividing the initial charge capacity by the mass of the active material. The results are shown in Table 1 below. In this example, if the specific capacity is 162 mAh / g or more, it is considered that the deterioration of the active material is reduced.

[0068] [Table 1]

[0069] "result" When the ambient temperature is 15°C or lower, deterioration of the active material tends to be reduced. When the ambient humidity is 70% or higher, film formation defects tend to be reduced.

[0070] <Experiment 2> <Paint manufacturing> No. 1 The active material, volatile liquid, conductive material, and binder were mixed together to form a slurry. The slurry was allowed to stand for 1 hour at an ambient temperature of 25°C. After standing, the slurry was applied to the surface of a substrate to produce an electrode sheet.

[0071] <No.2, 3> As shown in Table 2 below, electrode sheets were produced in the same manner as No. 1, except that the standing time of the slurry was changed.

[0072] No.4 The active material, volatile liquid, conductive material, and binder were kneaded to produce a wet powder. The wet powder was allowed to stand for 1 hour at an ambient temperature of 25°C. After standing, an electrode sheet 10 was produced using a film-forming apparatus 200 (see FIG. 2).

[0073] <No.5, 6> As shown in Table 2 below, electrode sheets were produced in the same manner as No. 1, except that the standing time of the wet powder was changed.

[0074] "evaluation" As in Experiment 1, a small battery including the electrode sheet was fabricated. The specific capacity of the active material was measured by a constant current charge / discharge test of the small battery. The results are shown in Table 2 below.

[0075] [Table 2]

[0076] "result" The wet powders (Nos. 4 to 6) tend to have smaller specific capacities than the slurries (Nos. 1 to 3). In other words, the wet powders (Nos. 4 to 6) tend to be more susceptible to deterioration of the active material than the slurries (Nos. 1 to 3).

[0077] The active material was recovered from the electrode sheet. The surface of the active material was analyzed by Raman spectroscopy. It was confirmed that the composition of the outermost layer of the active material in the wet powders (Nos. 4 to 6) was significantly different from that in the slurries (Nos. 1 to 3). It is thought that the outermost layer (carbon coating) of the active material in the wet powders (Nos. 4 to 6) may have peeled off due to shear loads during film formation. Peeling of the outermost layer may expose a new surface. The increased contact area between the new surface and the volatile liquid may have accelerated the deterioration of the active material.

[0078] The present embodiment and examples are illustrative in all respects. The present embodiment and examples are not limiting. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is also intended from the beginning that any configuration may be extracted from the present embodiment and examples and that they may be combined in any desired manner. [Explanation of symbols]

[0079] 5 Wet powder, 10 Electrode sheet, 11 Substrate, 12 Active material sheet, 100 Mixing device, 200 Film forming device, 201 First roll, 202 Second roll, 203 Third roll, 1000 Manufacturing system.

Claims

1. (a) forming a wet powder comprising an active material and a volatile liquid; (b) spreading the wet powder to form an active material sheet; and (c) disposing the active material sheet on a surface of a substrate to produce an electrode sheet; Including, the volatile liquid comprises water; the active material has a property of being deteriorated by reaction with the volatile liquid, In at least one of (a) and (b), the ambient temperature of the workpiece is 15°C or less; A manufacturing method for electrode sheets for lithium-ion batteries.

2. The wet powder is a dispersion system in which a liquid is dispersed in a powder. The method for producing the electrode sheet for a lithium ion battery according to claim 1.

3. The ambient temperature is 0 to 15°C. The method for producing the electrode sheet for a lithium ion battery according to claim 1 or 2.

4. The active material is a positive electrode active material. The method for producing the electrode sheet for a lithium ion battery according to any one of claims 1 to 3.

5. The active material is at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. The method for producing the electrode sheet for a lithium ion battery according to claim 4.

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