Method for manufacturing an electrode sheet

Abstract

The present disclosure provides a method for manufacturing an electrode sheet that is less likely to generate a film defect. The method for manufacturing an electrode sheet includes: preparing a wet powder containing an active material and a volatile liquid and having a BET specific surface area of 50 cm 2 / g or more; forming an active material sheet by extending the wet powder; and manufacturing an electrode sheet by disposing the active material sheet on a surface of a substrate.

Description

Technical Field

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

[0002] Japanese Patent Application Publication No. 2019-106311 discloses a method for manufacturing an electrode sheet, which uses a moistened powder containing a volatile liquid such as water or alcohol.

[0003] Furthermore, Japanese Patent Application Publication No. 2019-106311 discloses a method for obtaining an electrode sheet that is less prone to film-forming defects by controlling the liquid crosslinking force between the wet powder and the surfaces of each roller within an appropriate range when the electrode mixture composed of the wet powder passes through the gap between two opposing rollers. Film-forming defects refer to the formation of pores in the film of the electrode mixture. Electrode sheets with many film-forming defects are sometimes unsuitable for use as electrode sheets in battery construction. Summary of the Invention

[0004] In the fabrication of electrode sheets from wet powder, there is a need to further improve productivity. To increase electrode sheet productivity, it is desirable to further reduce the occurrence of film formation defects.

[0005] Therefore, this disclosure provides a method for manufacturing an electrode sheet that is less prone to film formation defects.

[0006] (1) A method for manufacturing an electrode sheet according to the present disclosure includes the following steps: preparing a moist powder, wherein the moist powder contains an active substance and a volatile liquid, and the Brunauer–Emmett–Teller (BET) specific surface area is 50 cm². 2 / g or more; forming an active material sheet by extending the wetted powder; and manufacturing an electrode sheet by disposing the active material sheet on the surface of a substrate.

[0007] It is believed that if the ductility of the wetted powder decreases with the evaporation of the volatile liquid contained in the wetted powder, film-forming defects are easily generated on the electrode mixture film. As a result, if the electrode mixture film cannot be properly used as an electrode sheet, the productivity of the electrode sheet may decrease. Furthermore, it is believed that if the ductility of the wetted powder decreases with the evaporation of the volatile liquid contained in the wetted powder, the load applied to the surface of the active material increases. This may also make the electrode mixture film more prone to film-forming defects.

[0008] According to one aspect of this disclosure, the BET specific surface area of ​​the moistened powder is set to 50 cm². 2 With a surface area of ​​ / g or higher, film-forming defects are difficult to occur. This is achieved by setting the BET specific surface area of ​​the wetted powder to 50 cm². 2At a concentration of / g or higher, it can suppress the decrease in the ductility of the wetted powder associated with the evaporation of volatile liquids contained in the wetted powder. Therefore, it is believed that film-forming defects in the electrode mixture film are difficult to form. In addition, it is also believed that it can reduce the load applied to the surface of the active material.

[0009] (2) The time interval between the preparation of the wet powder and the film formation of the active substance sheet can also be less than 5 minutes.

[0010] It is believed that by setting the time to less than 5 minutes, the volatilization of volatile liquids can be further suppressed, thus making it difficult to generate film defects on the electrode mixture film.

[0011] (3) Another method for manufacturing an electrode sheet according to this disclosure includes the following steps: preparing a moist powder containing an active substance and a volatile liquid; and compressing the moist powder to achieve a BET specific surface area of ​​20 cm². 2 / g or less; the BET specific surface area is 50cm² by crushing the moist powder. 2 / g or more; forming an active material sheet by extending the wetted powder; and manufacturing an electrode sheet by disposing the active material sheet on the surface of a substrate.

[0012] As described above, if the ductility of the wetted powder decreases with the evaporation of the volatile liquid contained in the wetted powder, film-forming defects are easily generated on the electrode mixture film. Therefore, to suppress the formation of film-forming defects on the electrode mixture film, it is considered to suppress the evaporation of the volatile liquid. As a method to suppress the evaporation of the volatile liquid, reducing the specific surface area of ​​the wetted powder is considered. However, if the specific surface area of ​​the wetted powder is reduced, unevenness may occur at the ends of the electrode mixture in the width direction during film formation. In addition, if film formation itself becomes more difficult, productivity may decrease.

[0013] According to another aspect of this disclosure, after preparing a moist powder containing active substances and volatile liquids, the moist powder is compressed to achieve a BET specific surface area of ​​20 cm². 2 Below a certain value (g), the volatile liquid becomes difficult to volatilize. Then, the BET specific surface area is reduced to 50 cm² by breaking down the wet powder. 2 / g or more, as mentioned above, makes it difficult to generate film-forming defects on the electrode mixture film.

[0014] (4) The time interval between the crushing of the wet powder and the film formation of the active material sheet can also be less than 5 minutes.

[0015] (5) It may also include a step of storing the moist powder between the compression of the moist powder and the crushing of the moist powder.

[0016] (6) The volatile liquid may also contain water, for example. Attached Figure Description

[0017] Hereinafter, the features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings, wherein like reference numerals denote like elements.

[0018] Figure 1 This is a schematic flowchart of the method for manufacturing the electrode sheet according to Embodiment 1.

[0019] Figure 2 This is a schematic flowchart of the method for manufacturing the electrode sheet according to Embodiment 2.

[0020] Figure 3 This is a schematic diagram illustrating an example of a film-forming apparatus.

[0021] Figure 4 This is a conceptual diagram of an electrode sheet manufacturing system. Detailed Implementation

[0022] The embodiments of this disclosure (hereinafter referred to as "this embodiment") and the examples of this disclosure (hereinafter referred to as "this example") will be described below. However, this embodiment and this example do not limit the technical scope of this disclosure.

[0023] Definitions of terms, etc.

[0024] In this specification, the terms "possessing," "comprises," "have," and variations thereof (e.g., "consisting of," etc.) are open-ended. An open-ended description may include additional requirements in addition to essential requirements, or it may not include additional requirements. The description "composed of," is closed-ended. However, even in a closed-ended description, impurities and additional requirements unrelated to the present disclosure are not excluded. The description "substantially composed of," is semi-closed-ended. In a semi-closed-ended description, it is permissible to add requirements that do not substantially affect the essential or novel characteristics of the present disclosure.

[0025] In this specification, expressions such as "may also" and "may" are not used in a sense of obligation ("must do so"), but rather in a sense of permission ("has such a possibility").

[0026] In this specification, numerical ranges such as "m~n%" include both upper and lower limits unless otherwise specified. That is, "m~n%" represents a numerical range "above m% and below n%". Furthermore, "above m% and below n%" includes "more than m% but less than n%". Moreover, any value arbitrarily selected from the numerical range can also be used as a new upper or lower limit. For example, a new numerical range can be set by arbitrarily combining values ​​within the numerical range with values ​​recorded in other parts of this specification, tables, and figures.

[0027] In this specification, "wet powder" refers to a dispersion system in which liquid is dispersed in the powder.

[0028] In this manual, "electrode" is a general term for either a positive or negative electrode. An electrode can be either positive or negative. Electrodes can be used for any purpose. For example, electrodes can also be used in batteries. This manual describes an electrode used in a lithium-ion battery as an example.

[0029] In this specification, "volatile liquid" refers to a liquid with a boiling point of 50 to 240°C. For example, a volatile liquid may have a boiling point of 75 to 150°C or a boiling point of 75 to 125°C.

[0030] The term "solid composition percentage" in this specification refers to the mass fraction of solid components in the wetted powder. Furthermore, the solute dissolved in the solvent is considered as solid component.

[0031] The term "BET specific surface area" in this specification refers to the specific surface area calculated using the Brunol-Emmett-Taylor (BET) multipoint method within an adsorption isotherm determined by gas adsorption. The adsorbed gas is nitrogen. For a single test object, the BET specific surface area is measured at least three times. The arithmetic mean of the results from these three or more measurements is considered the BET specific surface area of ​​the test object.

[0032] In this specification, the D50 of an active substance represents the particle size at which the cumulative frequency from the smallest particle size side reaches 50% in a volume-based particle size distribution. The volume-based particle size distribution can be determined using laser diffraction scattering.

[0033] In this specification, D50 of wet powder refers to the particle size that, in the particle size distribution based on mass (number), accumulates to 50% of the frequency from the smallest particle size side. The particle size distribution based on mass can be determined according to "JIS Z8815 General Rules for Sieve Analysis".

[0034] In this manual, "State of Charge (SOC)" refers to the percentage of the charging capacity relative to the full charge capacity at that moment.

[0035] Implementation Method 1

[0036] Figure 1 This is a schematic flowchart of the electrode sheet manufacturing method according to this embodiment. Hereinafter, "the electrode sheet manufacturing method in this embodiment" may be simply referred to as "this manufacturing method". This manufacturing method includes "the preparation of wet powder (S10)", "the formation of an active material sheet (S20)" and "the manufacturing of the electrode sheet (S30)".

[0037] Preparation of moist powder (S10)

[0038] This manufacturing method includes preparing a liquid containing active substances and volatile liquids, with a BET specific surface area of ​​50 cm². 2 The process involves producing a wet powder with a surface area of ​​50 cm² or more. 2 With a concentration of 60 g or more, film-forming defects are unlikely to occur during the film formation of active material sheets. The preferred BET specific surface area of ​​the wetted powder is 60 cm². 2 / g or more.

[0039] For example, a wetted powder can be prepared by mixing an active material with a volatile liquid. For example, at least one selected from conductive materials, solid electrolytes, and binders can be mixed with the wetted powder.

[0040] For example, active substances and volatile liquids can be mixed using a mixing granulator. In the production of moist powders, planetary mixers, three-roll mills, etc., can be used, for example. One-stage mixing or multi-stage mixing can be performed. For example, moist powders can be formed by mixing active substances and volatile liquids in a planetary mixer. Moist powders can also be kneaded using a three-roll mill, for example.

[0041] The moist powder obtained by mixing or kneading using the above method can be further crushed, for example, by using a high-speed mixer, ball mill, hammer mill, etc. This treatment can further increase the BET specific surface area.

[0042] For example, the moistened powder can be formulated to have a solid content of 70% or more. For example, the moistened powder can be formulated to have a solid content of 70% to 90%. For example, the moistened powder can be formulated to have a solid content of 75% to 85%.

[0043] Moistened powders can be granular, flake-like, clay-like, etc. The properties of moistened powders can be adjusted, for example, by adjusting the solid content and mixing conditions.

[0044] For example, the wetted powder can be made to have a D50 of less than 4 mm. The wetted powder can be made to have a D50 of 0.1 to 4 mm, or it can be made to have a D50 of 0.5 to 2 mm.

[0045] The active substance may also be in particulate form. The active substance may have a D50 of 0.5 to 50 μm or a D50 of 1 to 10 μm.

[0046] The active material may include a positive electrode active material. For example, the active material may contain at least one selected from LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. For example, "(NiCoMn)" in "Li(NiCoMn)O2" indicates that the total proportions within the parentheses are 1. As long as the total is 1, the amounts of each component are arbitrary. Li(NiCoMn)O2 may contain, 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 O2, etc. The active material may contain a negative electrode active material. The active material may contain, for example, materials selected from graphite, soft carbon, hard carbon, silicon, silicon oxide, silicon-based alloys, tin, tin oxide, tin-based alloys, and Li4Ti5O. 12 At least one of them.

[0047] The volatile liquid may contain at least one selected from water, N-methyl-2-pyrrolidone (NMP), alcohols (e.g., ethanol, propanol, etc.), and esters (e.g., butyl butyrate, etc.). From the viewpoint of thermal energy during drying, the volatile liquid may have a boiling point below 150°C. The amount of volatile liquid incorporated can be determined based on the solid content of the wetted powder.

[0048] The amount of adhesive incorporated relative to 100 parts by weight of active material can be, for example, 0.1 to 10 parts by weight. The adhesive may contain optional components. For example, the adhesive may contain at least one selected from polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyamide-imide (PAI), and polyimide (PI).

[0049] The amount of conductive material relative to 100 parts by mass of active material can be, for example, 0.1 to 10 parts by mass. The conductive material may contain, for example, conductive carbon particles, conductive carbon fibers, etc. For example, the conductive material may contain at least one selected from carbon black, vapor-grown carbon fibers (VGCF), carbon nanotubes (CNTs), and graphene sheets. The carbon black may contain, for example, at least one selected from acetylene black, Ketjen black (registered trademark), furnace black, channel black, and thermal cracking black.

[0050] The amount of solid electrolyte relative to 100 parts by volume of active material can be, for example, 1 to 100 parts by volume. The solid electrolyte may contain, for example, at least one selected from Li₂S-P₂S₅, LiI-Li₂S-P₂S₅, LiBr-Li₂S-P₂S₅, and LiI-LiBr-Li₂S-P₂S₅.

[0051] Film formation of active substance sheets (S20)

[0052] This manufacturing method includes a step of forming an active material sheet by stretching a moistened powder. The moistened powder can be stretched using any method. For example, the moistened powder can be stretched by roll forming.

[0053] Figure 3 This is a schematic diagram illustrating an example of a film-forming apparatus. In the film-forming apparatus 200, electrode sheets 10 can be manufactured using a roll-to-roll process. Roll forming and roll transfer printing can be performed in the film-forming apparatus 200.

[0054] The film-forming apparatus 200 includes a first roller 201, a second roller 202, and a third roller 203. Each roller rotates in the direction of the arrow. The rotation axes of each roller are parallel. When the rotation speed of the first roller 201 is ω1, the rotation speed of the second roller 202 is ω2, and the rotation speed of the third roller 203 is ω3, for example, the relationship "ω1 < ω2 < ω3" can be satisfied.

[0055] A gap AB is formed between the first roller 201 and the second roller 202. Wet powder 5 is fed into the gap AB. Within the gap AB, the wet powder 5 is compressed and extended, thereby forming an active material sheet 12. The active material sheet 12 may have a thickness of, for example, 10–500 μm, or 50–200 μm.

[0056] Furthermore, the interval between S10 and S20 is preferably 5 minutes or less. This setting further suppresses the evaporation of the volatile liquid, making it difficult for film-forming defects to form on the electrode mixture film. More preferably, the interval between S10 and S20 is 3 minutes or less.

[0057] Electrode fabrication (S30)

[0058] This manufacturing method includes a step of manufacturing an electrode sheet 10 by disposing an active material sheet 12 on the surface of a substrate 11. The processing can then be performed in a film-forming apparatus 200. A gap BC is formed between a second roller 202 and a third roller 203. The second roller 202 conveys the active material sheet 12 to the gap BC (see reference). Figure 3 The third roller 203 conveys the substrate 11 to the gap BC.

[0059] Within the gap BC, the active material sheet 12 comes into contact with the surface of the substrate 11. Thus, the active material sheet 12 adheres to the surface of the substrate 11. The electrode sheet 10 is manufactured by attaching the active material sheet 12 to the substrate 11.

[0060] The active material sheet 12 can be disposed on only one side of the substrate 11, or on both sides of the substrate 11. The electrode sheet 10 can be dried. The electrode sheet 10 can be compressed. The electrode sheet 10 can also be cut, for example, to fit the battery design.

[0061] The substrate 11 may have a thickness of 5 to 50 μm. The substrate 11 may also be conductive. The substrate 11 may also contain, for example, metal foil. The substrate 11 may contain at least one selected from aluminum (Al) foil, Al alloy foil, copper (Cu) foil, Cu alloy foil, titanium (Ti) foil, stainless steel (SUS) foil, nickel-plated (Ni) SUS foil, and Ni foil.

[0062] Implementation Method 2

[0063] Figure 2 This is a schematic flowchart of the electrode sheet manufacturing method according to Embodiment 2. This manufacturing method includes "preparation of moist powder (S110)," "compression of moist powder (S120)," "crushing of moist powder (S130)," "film formation of active material sheet (S140)," and "manufacturing of electrode sheet (S150)." Furthermore, descriptions that are repeated in Embodiment 1 are omitted.

[0064] Compression of moist powder (S120)

[0065] This manufacturing method involves compressing wetted powder to achieve a BET specific surface area of ​​20 cm². 2 The process involves steps below / g. This treatment makes it difficult for volatile liquids to evaporate. The preferred BET specific surface area of ​​the moistened powder is 15 cm². 2 / g or less.

[0066] The shape of the compressed wet powder is not particularly limited; examples include spheres, ellipsoids, cylinders, elliptical cylinders, prisms, and discs. The maximum diameter of the compressed wet powder is, for example, 4–10 mm. Compression can be performed using granulators, pelletizing machines, tablet presses, and other compression forming machines.

[0067] Crushing of moist powder (S130)

[0068] This manufacturing method involves crushing compressed, moistened powder to achieve a BET specific surface area of ​​50 cm². 2 Processes involving grains of 100g or more. Crushing can be performed using high-speed mixers, ball mills, hammer mills, etc.

[0069] Preservation of moist powder

[0070] This manufacturing method may also include a step of preserving the compressed, moistened powder between steps S120 and S130. This is because the BET specific surface area of ​​the compressed, moistened powder is 20 cm². 2 The concentration is below 0.5 g / g, so even volatile liquids are unlikely to evaporate during storage. There is no particular limitation on the storage time; it can be 30 minutes, 60 minutes, 120 minutes, or 180 minutes.

[0071] Implementation Method 3

[0072] Figure 4 This is a conceptual diagram of the electrode sheet manufacturing system according to this embodiment. Hereinafter, "the electrode sheet manufacturing system of this embodiment" may be simply referred to as "this manufacturing system". This manufacturing system 1000 includes a mixing device 100 and a film-forming device 200. This manufacturing system 1000 may also include a compression forming device 300 and a crushing device 400. This manufacturing system 1000 may also include, for example, a conveying device, a drying device (e.g., a hot air drying oven), a cutting device (e.g., a rotary cutter), etc.

[0073] The mixing device 100 is configured to produce a wetted powder by mixing an active substance and a volatile liquid. The wetted powder is supplied to the film-forming device 200. For example, a conveying device may also convey the wetted powder to the film-forming device 200. The film-forming device 200 is configured to form a film of the active substance by stretching the wetted powder.

[0074] Alternatively, the wet powder produced by the mixing device 100 can also be fed into the compression forming device 300. The compression forming device 300 compresses and forms the wet powder. The compressed and formed wet powder can also be fed into the crushing device 400. The crushing device 400 crushes the compressed and formed wet powder. The crushed wet powder is then fed into the film forming device 200.

[0075] Electrode sheet manufacturing

[0076] Electrode sheets No.1 and No.2 are manufactured as described below. Hereinafter, for example, "electrode sheet No.1" may be simply referred to as "No.1".

[0077] No.1

[0078] Prepare the following electrode materials.

[0079] Active material: LiFePO4 (particle surface coated with carbon)

[0080] Volatile liquids: water

[0081] Conductive material: Carbon nanotubes (CNTs)

[0082] Adhesives: Carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR)

[0083] Prepare a planetary mixer and a three-roll mill. Use the planetary mixer and three-roll mill to knead the electrode materials in the specified proportions, thereby producing a moist powder. The solid content of the moist powder is above 75%.

[0084] A high-speed mixer was prepared. The wet powder was crushed using the high-speed mixer. The BET specific surface area of ​​the crushed wet powder was 70.0 cm². 2 / g. The BET specific surface area was determined using a gas adsorption capacity measuring device (Shimadzu Corporation, 3Flex) (the same applies to No. 2 below). The crushed, moistened powder was stored for 120 minutes.

[0085] A film-forming device 200 (refer to) was prepared. Figure 3 The active material sheet 12 is formed by feeding the broken, wet powder 5 into the film-forming apparatus 200. Furthermore, the electrode sheet 10 is manufactured by disposing the active material sheet 12 on the surface of the substrate 11.

[0086] No.2

[0087] Prepare the same electrode material as No.1. Using the same method as No.1, knead the electrode material in the specified proportions together through a planetary mixer and a three-roll mill to produce a moist powder. The solid content of the moist powder is 75% or higher.

[0088] A tablet press was prepared. The wet powder was compressed into shape using the tablet press. The BET specific surface area of ​​the compressed wet powder was 11.2 cm². 2 / g. The compressed, moistened powder was stored for 120 minutes.

[0089] Similar to No. 1, the wet powder was crushed using a high-speed mixer. The BET specific surface area of ​​the crushed wet powder was 68.4 cm². 2 / g.

[0090] Similar to No. 1, the active material sheet 12 is formed by feeding the crushed wet powder 5 into the film-forming apparatus 200. The time from the crushing of the wet powder 5 to its supply to the film-forming apparatus 200 is 3 minutes. Furthermore, the electrode sheet 10 is manufactured by disposing the active material sheet 12 on the surface of the substrate 11.

[0091] evaluate

[0092] Film formation defects

[0093] Visually inspect the surface of electrode sheet 10 (active material sheet 12) to confirm whether there are any film-forming defects. The results are shown in Table 1 below under "Film-forming Defects".

[0094] Output performance

[0095] The electrode sheet was cut to a specified size. A small battery incorporating this electrode sheet was manufactured. The output was measured through a constant current charge-discharge test. In this test, the SOC of each small battery was adjusted to 80%, and 1500mW was used as the target output value. The results are shown in "Output Values ​​(mW)" in Table 1 below.

[0096] Table 1

[0097]

[0098] result

[0099] Film-forming defects were confirmed in the electrode sheet (active material sheet) of No.1. Furthermore, the output of the No.1 battery was lower than the target of 1500mW.

[0100] On the other hand, no film-forming defects were found in the electrode sheet (active material sheet) of No.2. Furthermore, the output of the No.2 battery exceeded the target of 1500mW.

[0101] The embodiments and examples disclosed herein should be considered illustrative rather than restrictive in all respects. The scope of this disclosure is not defined by the foregoing description, but by the scope of the patent claim, including all modifications within the scope of the claim.

Claims

1. A method of manufacturing an electrode sheet, characterized by, comprising the following steps: wet powder containing an active material and a volatile liquid is produced by kneading with a three-roll mill; The wet powder is compressed by a compression molding machine to have a BET specific surface area of 20 cm 2 / g or less, and a maximum diameter of 4 to 10 mm. by crushing the wetted powder to a BET specific surface area of 50 cm 2 / g or more; film formation of active material pieces is performed by extending the wet powder within 5 minutes from the time interval between the crushing of the wet powder; and an electrode sheet is manufactured by disposing the active material pieces on a substrate surface.

2. The electrode sheet manufacturing method according to claim 1, further comprising: storage of the wet powder, the storage of the wet powder is performed between the compression of the wet powder and the crushing of the wet powder.

3. The electrode sheet manufacturing method according to claim 1 or 2, wherein: the volatile liquid is water.

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