Method for manufacturing an electrode

Abstract

Provided is a method for manufacturing an electrode that allows for a good state of adhesion between a protective layer and an electrode mixture layer and that allows for a reduction in the thickness of the protective layer. The present disclosure is a method for manufacturing an electrode that has an electrode mixture layer and a protective layer adjacent to the electrode mixture layer on a current collector. The manufacturing method includes a coating step of coating an electrode mixture paste and a paste for forming a protective layer on a current collector using a die having a spacer, and a drying step of drying the coated electrode mixture paste and the paste for forming a protective layer. The paste for forming a protective layer is die-coated simultaneously with the electrode mixture paste in a manner so as to be adjacent to the electrode mixture paste. The spacer has a discharge port for discharging the electrode mixture paste and a discharge port for discharging the paste for forming a protective layer. The ratio (B / A) of the opening width B of the discharge port for discharging the paste for forming a protective layer to the coating width A of the paste for forming a protective layer is 1.00 to 1.07.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing an electrode having an electrode paste layer and an adjacent protective layer on a current collector foil. Furthermore, this application claims priority based on Japanese Patent Application No. 2024-212526, filed on December 5, 2024, the entire contents of which are incorporated herein by reference. Background Technology

[0002] In recent years, lithium-ion secondary batteries and other secondary batteries have been suitable for use as portable power sources for personal computers, mobile terminals, electric vehicles (BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and other vehicle drive power sources.

[0003] As electrodes for secondary batteries such as lithium-ion batteries, electrodes with an electrode mixture layer and an adjacent protective layer on the current collector foil are known (see, for example, Patent Document 1). As a method for forming the electrode mixture layer and the protective layer on the current collector foil, for example, a method is known to use a coating apparatus as described in Patent Documents 1 and 2 to simultaneously coat the electrode mixture slurry and the protective layer forming slurry onto the current collector foil through a mold.

[0004] In the above-described coating apparatus, the die head has a gasket, on which flow paths for the electrode mixture slurry and the protective layer forming slurry are provided (see, for example, Patent Document 2). In addition, the gasket also has an outlet for the electrode mixture slurry and an outlet for the protective layer forming slurry. Typically, considering that the slurry will wet and spread after coating, the opening width of the outlet for the protective layer forming slurry on the gasket is set to be narrower than the coating width of the protective layer forming slurry.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2021-131988

[0006] Patent Document 2: Japanese Patent Application Publication No. 2021-120148

[0007] Here, the thinner the protective layer of the electrode, the better, while maintaining insulation. However, in existing methods, it is difficult to reduce the thickness of the protective layer while maintaining good contact between the protective layer and the electrode adhesive layer.

[0008] In view of the above, the purpose of this disclosure is to provide a method for manufacturing an electrode that can maintain a good adjacency between the protective layer and the electrode mixture layer and reduce the thickness of the protective layer. Summary of the Invention

[0009] This disclosure discloses a method for manufacturing an electrode having an electrode paste layer and an adjacent protective layer on a current collector foil. The manufacturing method includes: a coating step, in which an electrode paste slurry and a protective layer forming slurry are coated onto the current collector foil using a die with a gasket; and a drying step, in which the coated electrode paste slurry and the protective layer forming slurry are dried. The protective layer forming slurry is simultaneously die-coated with the electrode paste slurry in an adjacent manner. The gasket has a discharge port for discharging the electrode paste slurry and a discharge port for discharging the protective layer forming slurry. The ratio (B / A) of the opening width B of the discharge port for discharging the protective layer forming slurry to the coating width A of the protective layer forming slurry is 1.00 to 1.07.

[0010] Based on this configuration, a method for manufacturing an electrode can be provided that maintains a good adjacency between the protective layer and the electrode mixture layer and reduces the thickness of the protective layer. Attached Figure Description

[0011] Figure 1 This is a flowchart illustrating each step of a manufacturing method according to one embodiment of the present disclosure.

[0012] Figure 2 This is a schematic cross-sectional view of an example of a positive electrode obtained by a manufacturing method according to one embodiment of the present disclosure.

[0013] Figure 3 This is a schematic diagram showing an example of a positive electrode obtained by the manufacturing method according to one embodiment of the present disclosure, viewed from a direction perpendicular to the main surface.

[0014] Figure 4 This is a top view of the gasket of the die head used in the coating process of a manufacturing method according to one embodiment of this disclosure.

[0015] Figure 5 This is a schematic diagram illustrating the mold coating process in the coating step of a manufacturing method according to one embodiment of the present disclosure.

[0016] Figure 6 This is a schematic diagram illustrating the mold coating process in the coating step of a manufacturing method according to one embodiment of the present disclosure.

[0017] Figure 7 (A) to (C) are schematic cross-sectional views of the positive electrode used to illustrate the adjacency state of the positive electrode mixture layer and the protective layer.

[0018] Figure 8 It is a schematic diagram showing the existing coating pattern of a mold. Detailed Implementation

[0019] The embodiments of this disclosure will now be described with reference to the accompanying drawings. Furthermore, matters not mentioned in this specification that require implementation of this disclosure can be understood by those skilled in the art based on prior art. This disclosure can be implemented based on the content disclosed in this specification and common technical knowledge in the field. Additionally, in the following drawings, components and parts that perform the same function are labeled and described using the same reference numerals. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect actual dimensional relationships. Moreover, the numerical ranges represented as "A~B" in this specification include both A and B.

[0020] Furthermore, in this specification, "secondary battery" refers to an energy storage device capable of repeated charging and discharging. Additionally, in this specification, "lithium-ion secondary battery" refers to a secondary battery that uses lithium ions as charge carriers and achieves charging and discharging through the movement of charge between the positive and negative electrodes accompanied by lithium ions.

[0021] The electrode manufacturing method disclosed herein is a method for manufacturing an electrode having an electrode binder layer and an adjacent protective layer on a current collector foil. For example... Figure 1 As shown, the manufacturing method includes: a step (hereinafter also referred to as the "coating step") S101 of applying an electrode mixture slurry and a protective layer forming slurry to the current collector foil using a die head equipped with a gasket; and a step (hereinafter also referred to as the "drying step") S102 of drying the coated electrode mixture slurry and the protective layer forming slurry. The protective layer forming slurry is simultaneously die-coated with the electrode mixture slurry in an adjacent manner. The gasket has a discharge port for discharging the electrode mixture slurry and a discharge port for discharging the protective layer forming slurry. The ratio (B / A) of the opening width B of the discharge port for discharging the protective layer forming slurry to the coating width A of the protective layer forming slurry is 1.00 to 1.07.

[0022] Typically, the electrode obtained by the manufacturing method of this disclosure is the positive electrode of a lithium-ion secondary battery. Therefore, the following describes an embodiment for manufacturing a positive electrode of a lithium-ion secondary battery as an example of the manufacturing method of this disclosure. Furthermore, the electrode manufactured by the manufacturing method of this disclosure is not limited to the positive electrode of a lithium-ion secondary battery. As long as the current collector foil has an electrode binder layer and an adjacent protective layer, the electrode manufactured by the manufacturing method of this disclosure can be either the negative electrode of a lithium-ion secondary battery or an electrode other than a lithium-ion secondary battery.

[0023] [Positive electrode of lithium-ion secondary battery]

[0024] first, Figure 2 and Figure 3This describes one example of the positive electrode of a lithium-ion secondary battery obtained by the manufacturing method described in this embodiment. Figure 2 It is a cross-sectional view of the positive electrode along the width and thickness directions. Figure 3 This is a schematic diagram of the positive electrode viewed from the vertical direction of the main face.

[0025] In the illustrated example, the positive electrode 50 is configured as a long strip-shaped positive electrode plate. Figure 3 The image shows only a portion of the sample. However, the positive electrode can also be cut to specified dimensions, and therefore does not have to be a long strip. For example... Figure 2 and Figure 3 As shown, the positive electrode 50 includes a positive electrode current collector foil 52 and a positive electrode flux layer 54 formed on the positive electrode current collector foil 52. In the illustrated example, the positive electrode flux layer 54 is disposed on both sides of the positive electrode current collector foil 52. However, the positive electrode flux layer 54 may also be disposed on only one side of the positive electrode current collector foil 52.

[0026] The main surface of the positive electrode current collector foil 52 has a portion (positive electrode current collector foil exposed portion) 52a where the positive electrode binder layer 54 is not formed. In the illustrated example, the positive electrode current collector foil exposed portion 52a is provided at one end in the width direction of the positive electrode 50. However, the positive electrode current collector foil exposed portion 52a may also be provided at the end in the long side direction of the positive electrode 50. In addition, the positive electrode current collector foil exposed portion 52a may also be provided at two or more ends of the positive electrode 50.

[0027] The positive electrode 50 has a protective layer 56. The protective layer 56 is an insulating layer. The protective layer 56 prevents the exposed portion 52a of the positive electrode current collector foil of the positive electrode 50 from directly contacting the negative electrode, thereby suppressing short circuits between the positive electrode 50 and the negative electrode. In the illustrated example, the protective layer 56 is provided on both sides of the positive electrode current collector foil 52. However, the protective layer 56 may also be provided on only one side of the positive electrode current collector foil 52.

[0028] The protective layer 56 is adjacent to the positive electrode flux layer 54 and is located between the positive electrode flux layer 54 and the exposed positive electrode current collector foil 52a in the surface direction of the positive electrode sheet 50. In other words, the protective layer 56 is located at the boundary between the positive electrode flux layer 54 and the exposed positive electrode current collector foil 52a. By providing the protective layer 56 in this position, short circuits between the positive electrode 50 and the negative electrode 60 can be highly suppressed.

[0029] The positive electrode current collector foil 52 is a foil-like material made of metal such as aluminum or aluminum alloy. The positive electrode current collector foil 52 is preferably aluminum foil. The thickness of the positive electrode current collector foil 52 is not particularly limited, but is, for example, 5 μm or more and 35 μm or less, preferably 7 μm or more and 20 μm or less.

[0030] The positive electrode layer 54 contains a positive electrode active material. As the positive electrode active material, known positive electrode active materials used in lithium-ion secondary batteries can be used. Specifically, for example, lithium composite oxides, lithium transition metal phosphate compounds, etc., can be used as the positive electrode active material.

[0031] Examples of lithium composite oxides include lithium-nickel composite oxides, lithium-cobalt composite oxides, lithium-manganese composite oxides, lithium-nickel-manganese composite oxides, lithium-nickel-cobalt-manganese composite oxides, lithium-nickel-cobalt-aluminum composite oxides, and lithium-iron-nickel-manganese composite oxides. Among these, lithium-nickel-cobalt-manganese composite oxides are preferred. Examples of lithium transition metal phosphate compounds include lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), and lithium manganese iron phosphate.

[0032] The average particle size of the positive electrode active material is not particularly limited, but is, for example, 0.05 μm or more and 25 μm or less, preferably 1 μm or more and 20 μm or less. Furthermore, in this specification, "average particle size" refers to the median particle size (D50). The average particle size (D50) can be determined using a known laser diffraction / scattering particle size distribution measuring device, etc.

[0033] The positive electrode binder layer 54 may also contain components other than the positive electrode active material, such as lithium triphosphate, conductive materials, and binders. As conductive materials, carbon black such as acetylene black (AB) and carbon materials such as carbon nanotubes may be suitable examples. As binders, polyvinylidene fluoride (PVDF) may be used, for example.

[0034] The content of the positive electrode active material in the positive electrode compound layer 54 (i.e., the content of the positive electrode active material relative to the total mass of the positive electrode compound layer 54) is not particularly limited, but is preferably 80% by mass or more, more preferably 90% by mass or more and 97.5% by mass or less. The content of trilithium phosphate in the positive electrode compound layer 54 is not particularly limited, but is preferably 1% by mass or more and 12% by mass or less, more preferably 3% by mass or more and 10% by mass or less. The content of conductive material in the positive electrode compound layer 54 is not particularly limited, but is preferably 1% by mass or more and 10% by mass or less, more preferably 1.5% by mass or more and 7% by mass or less. The content of binder in the positive electrode compound layer 54 is not particularly limited, but is preferably 1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 2.7% by mass or less.

[0035] The thickness of the positive electrode additive layer 54 is not particularly limited, but for example, it is 10 μm or more and 300 μm or less, preferably 20 μm or more and 200 μm or less.

[0036] The protective layer 56 is an insulating layer containing insulating filler. Examples of insulating fillers include ceramic particles, polymer particles, and organic-inorganic composite particles, with ceramic particles being preferred.

[0037] Examples of ceramic particles contained in the protective layer 56 include: oxide-based ceramic particles such as alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, and zinc oxide; nitride-based ceramic particles such as silicon nitride, titanium nitride, and boron nitride; hydroxide particles such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide; and clay mineral particles such as mica, talc, boehmite, zeolite, apatite, and kaolin. Preferably, the particles are alumina, boehmite, silicon dioxide, or magnesium oxide, and more preferably alumina or boehmite. Alumina and boehmite exhibit excellent heat resistance, mechanical strength, and durability.

[0038] The shape of the ceramic particles is not particularly limited and can be spherical or non-spherical. The average particle size (D50) of the ceramic particles is not particularly limited, for example, it is 0.01 μm or more and 10 μm or less, preferably 0.1 μm or more and 5 μm or less, and more preferably 0.2 μm or more and 2.0 μm or less.

[0039] The content of ceramic particles in the protective layer 56 is not particularly limited, but is, for example, 70% by mass or more, preferably 75% by mass or more, and more preferably 85% by mass or more.

[0040] The protective layer 56 may also contain an adhesive. Examples of adhesives contained in the protective layer 56 include acrylic adhesives, styrene-butadiene rubber (SBR), and polyolefin adhesives. Fluoropolymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) may also be used.

[0041] The content of adhesive in the protective layer 56 is not particularly limited, but for example, it is 1% or more and 25% or less by mass, preferably 3% or more and 20% or less by mass, and more preferably 3% or more and 10% or less by mass.

[0042] The protective layer 56 may also contain a carbon-based conductive material within a range that maintains insulation (i.e., within a range that suppresses short circuits between the positive and negative electrodes). When the protective layer 56 contains a carbon-based conductive material, the current collection capacity in the positive electrode 50 becomes higher.

[0043] Examples of carbon-based conductive materials contained in the protective layer 56 include acetylene black, furnace black, channel black, thermal cracking black, Ketjen black, and carbon nanotubes. During the current collector tab forming process described later, carbon black exhibits high performance in absorbing the heat during laser cutting, thus suppressing the peeling of the protective layer 56 from the positive electrode current collector foil 52, and is therefore preferred. Among carbon blacks, acetylene black is more preferred.

[0044] The content of carbon-based conductive material in the protective layer 56 is not particularly limited, but for example, it is 0.1% by mass or more and 5.0% by mass or less, preferably 0.2% by mass or more and 3.0% by mass or less, and more preferably 0.3% by mass or more and 1.0% by mass or less.

[0045] Alternatively, without impairing the effects of this disclosure, the positive electrode 50 may also have layers other than the positive electrode compound layer 54 and the protective layer 56.

[0046] [Coating process S101]

[0047] The coating process S101 will be explained. First, the positive electrode slurry and the protective layer forming slurry, which are used as electrode slurry, will be explained.

[0048] The positive electrode slurry comprises the components of the positive electrode layer 54 described above (i.e., the positive electrode active material and any binder, conductive material, etc.) and a dispersion medium. N-methylpyrrolidone (NMP) or similar materials can be suitably used as the dispersion medium. The positive electrode slurry can be prepared by stirring or kneading the components of the positive electrode layer 54 with the dispersion medium according to known methods.

[0049] The protective layer forming slurry comprises the components of the protective layer 56 described above (i.e., insulating fillers and any binders, carbon-based conductive materials, etc.) and a dispersion medium. N-methylpyrrolidone (NMP) or similar materials can be suitably used as the dispersion medium. The protective layer forming slurry can be prepared by stirring or kneading the components of the protective layer 56 with the dispersion medium according to known methods.

[0050] The solid content concentration of the positive electrode mixture slurry is not particularly limited, but is preferably 70% to 85% by mass, more preferably 80% to 85% by mass. Furthermore, the solid content concentration of the protective layer forming slurry is not particularly limited, but is preferably 15% to 25% by mass. When the solid content concentrations of both the positive electrode mixture slurry and the protective layer forming slurry are within the above ranges, the adjacency between the protective layer 56 and the positive electrode mixture layer 54 is particularly good.

[0051] Viscosity η of positive electrode mixture slurry A Not specifically limited, but the viscosity η of the positive electrode mixture slurry A For example, the viscosity is 2.5 Pa·s to 5.0 Pa·s, preferably 4.0 Pa·s to 4.5 Pa·s. Additionally, the viscosity η of the slurry used to form the protective layer... B Not particularly limited, but for example 0.9 Pa·s to 1.5 Pa·s, preferably 1.0 Pa·s to 1.31 Pa·s. Furthermore, the viscosity η of the positive electrode mixture slurry... Aand the viscosity η of the slurry used to form the protective layer B It can be used with a commercially available rotary viscometer at 25°C and a shear rate of 100 s. －1 The viscosity value is determined under the given conditions.

[0052] Viscosity η of positive electrode mixture slurry A The viscosity η of the slurry used to form the protective layer B The ratio (η) A / η B The value is not particularly limited, but is preferably 3.05 to 4.5. When this ratio (η) A / η B Within this range, the adjacency between the protective layer 56 and the positive electrode agent layer 54 is particularly good.

[0053] Furthermore, in this specification, "slurry" refers to a mixture in which some or all of the solid components are dispersed in a solvent, including so-called "paste," "ink," etc.

[0054] Next, the die coating in coating process S101 will be described. In coating process S101, a coating apparatus is prepared, which includes a die head and a gasket. The die head is, for example, the same as the prior art described above, having a pair of die blocks and a gasket fixed between the pair of die blocks.

[0055] The gasket is a component that restricts the flow path of the electrode mixture slurry and the protective layer forming slurry. It also includes a discharge port for discharging the electrode mixture slurry and a discharge port for discharging the protective layer forming slurry. Figure 4 The image shows one example of a gasket. Figure 4 This is a top view of an example gasket.

[0056] Figure 4 The gasket 10 shown has a flow path 12 for the positive electrode mixture slurry in the center. Additionally, the gasket 10 has a pair of flow paths 14 for the protective layer forming slurry on both sides of the positive electrode mixture slurry flow path 12. Using such a gasket 10, protective layers 56 can be formed at both ends of the positive electrode mixture layer 54. By cutting the sheet with protective layers 56 formed at both ends of the positive electrode mixture layer 54 at its central portion in the width direction, two sheets can be manufactured. Figure 2 , 3 The positive electrode 50 shown in the diagram is advantageous for its manufacturability. Furthermore, the gasket 10 can also be configured such that a protective layer forming slurry flow path 14 is provided on one side of the positive electrode mixture slurry flow path 12. In this case, it is possible to directly obtain a protective layer 56 formed at one end of the positive electrode mixture layer 54. Figure 2 , 3 The positive electrode 50 is shown in the diagram.

[0057] The flow path 12 of the positive electrode mixture slurry has a terminal opening, thereby the gasket 10 has a discharge port 12a for discharging the positive electrode mixture slurry. The flow path 14 of the protective layer forming slurry has a terminal opening, thereby the gasket 10 has a discharge port 14a for discharging the protective layer forming slurry.

[0058] To prevent the positive electrode slurry and the protective layer forming slurry from mixing before coating, the flow path 12 of the positive electrode slurry and the flow path 14 of the protective layer forming slurry are separated. To ensure contact between the positive electrode slurry and the protective layer forming slurry during mold coating, the flow path 14 of the protective layer forming slurry is configured to be close to the flow path 12 of the positive electrode slurry near the outlet 14a of the protective layer forming slurry. Thus, the protective layer forming slurry is discharged from the outlet 14a towards the positive electrode slurry, allowing contact between the positive electrode slurry and the protective layer forming slurry during mold coating.

[0059] Figure 5 This is a schematic diagram of an example of die coating in coating process S101. The coating apparatus in the illustrated example includes a die head 20 and a back support roller 30. In the die head 20, as... Figure 5 As shown, the gasket 10 is held by a pair of die blocks 22. Additionally, the coating apparatus includes a slurry supply unit (not shown). The slurry supply unit can be any known type. Positive electrode slurry and protective layer forming slurry are supplied from the slurry supply unit to the die head 20. On the other hand, the elongated positive electrode current collector foil 52 is conveyed by the rotation of the back support roller 30. The conveying speed of the positive electrode current collector foil 52 is not particularly limited, but is, for example, 20 m / min to 80 m / min, preferably 30 m / min to 60 m / min.

[0060] Towards the positive electrode current collector foil 52, positive electrode slurry and protective layer forming slurry are discharged from the die head 20 through the discharge port 12a of the positive electrode slurry and the discharge port 14a of the protective layer forming slurry, respectively. Thus, the positive electrode slurry and the protective layer forming slurry are simultaneously coated onto the positive electrode current collector foil 52 in an adjacent manner. In this way, a coating film 42 of the positive electrode slurry and a coating film 44 of the protective layer forming slurry are formed on the positive electrode current collector foil 52. The discharge amounts of the positive electrode slurry and the protective layer forming slurry are not particularly limited and can be appropriately determined according to the design values ​​of the thickness and width of the positive electrode slurry layer 54 and the thickness and width of the protective layer 56. The discharge amount of the protective layer forming slurry is, for example, 10 mL / min to 25 mL / min, preferably 15 mL / min to 20 mL / min.

[0061] Here, the opening width of the outlet 14a of the gasket used to discharge the slurry for forming the protective layer is set as B (refer to...). Figure 4 Furthermore, the coating width of the protective layer forming slurry is set as A. Additionally, the coating width A of the protective layer forming slurry is... Figure 5The dimension of the coating 44 of the protective layer forming slurry shown is in the width direction (i.e., the direction perpendicular to the long side direction). This width direction is perpendicular to the transport direction of the positive electrode current collector foil 52. In this disclosure, the ratio (B / A) of the opening width B of the discharge port of the protective layer forming slurry to the coating width A of the protective layer forming slurry is 1.00 to 1.07.

[0062] exist Figure 8 The image schematically illustrates what a conventional mold coating method looks like. Figure 8 In the die head 820, flow paths 814 for a protective layer forming slurry are formed on both sides of the flow path 812 of the positive electrode mixture slurry in the gasket. The die head 820 is separated from the positive electrode current collector foil 52 by a predetermined gap. The flow path 814 of the protective layer forming slurry has a discharge port 814a for the protective layer forming slurry. The positive electrode mixture slurry and the protective layer forming slurry pass through these flow paths and are discharged from the discharge port, thereby being coated onto the positive electrode current collector foil 52. At this time, as Figure 8 As shown, typically, the protective layer forming slurry is wetted and diffused on the positive electrode current collector foil 52. Therefore, taking this into consideration, conventionally, the opening width B of the outlet 814a of the protective layer forming slurry is set to be narrower than the coating width A of the protective layer forming slurry. Specifically, conventionally, the ratio (B / A) is set to be less than 1, particularly 0.95 or less.

[0063] Therefore, in this disclosure, the outlet of the gasket is designed to make the aforementioned ratio (B / A) larger than conventionally. Figure 6 The diagram schematically illustrates the mold coating method of this embodiment. In this case, the opening width B of the discharge port 14a of the gasket 10 for discharging the protective layer forming slurry is increased, such that the size of the opening of the discharge port 14a is greater than or equal to the coating width A of the protective layer forming slurry. Furthermore, since the discharge volume is reduced to achieve thin film formation, the protective layer forming slurry diffuses more within the discharge port than usual before being discharged, resulting in a lower flow rate than usual. The discharged protective layer forming slurry is pulled by the speed difference with the conveyed current collector foil, thereby preventing diffusion on the current collector foil and coating it in a narrower state than the opening width B (see reference). Figure 6 As a result, the slurry for forming the protective layer can maintain the same coating width A as before, but is coated thinner than before, and a protective layer 56 with a thinner thickness than before can be formed. In addition, the adjacency state between the formed positive electrode agent layer 54 and the formed protective layer 56 also becomes better.

[0064] Furthermore, compared to the condition where the protective layer forming slurry discharged from the outlet 14a is coated onto the positive electrode current collector foil 52 while maintaining its thickness and width, it is preferable to reduce the discharge amount of the protective layer forming slurry and increase the conveying speed of the positive electrode current collector foil 52. Thus, the protective layer forming slurry discharged from the outlet 14a is coated onto the positive electrode current collector foil 52 with at least one of its width and thickness reduced after discharge. For example, when the discharge amount of the protective layer forming slurry is 10 mL / min to 25 mL / min, it is preferable that the conveying speed of the positive electrode current collector foil 52 is 20 m / min to 80 m / min.

[0065] Preferably, the ratio (B / A) is 1.03 to 1.07. In this case, the thickness of the final protective layer can be reduced, and the adjacency between the protective layer and the electrode mixture layer is particularly good.

[0066] The coating width A of the protective layer 56 is not particularly limited, but is, for example, 3 mm to 10 mm, preferably 4 mm to 8 mm.

[0067] use Figure 7 (A) ~ Figure 7 (C) describes the adjacency state between the formed protective layer and the electrode mixture layer. Figure 7 (A) ~ Figure 7 (C) is a schematic cross-sectional view of the positive electrode along its width and thickness directions. Because the slurry is a fluid, the ends of the slurry coating are curved surfaces. Figure 7 In the example shown in (A), the shape of the end of the positive electrode mixture layer is close to the natural shape when the positive electrode mixture slurry is coated. Therefore, the outline of the end of the positive electrode mixture layer 54 is a curve that is close to an elliptical arc, and the protective layer 56 contacts the end of the positive electrode mixture layer 54. Figure 7 In the example shown in (A), the adjacency state between the positive electrode compound layer 54 and the protective layer 56 is particularly good because the functions of the positive electrode compound layer 54 and the protective layer 56 are fully utilized. Figure 7 In the example shown in (B), the protective layer 56 extends into the lower part of the positive electrode binder layer 54. Figure 7 In the example shown in (B), the positive electrode binder layer 54 and the protective layer 56 are in good contact state because the protective layer 56 functions fully. On the other hand, in Figure 7 In the example shown in (C), the protective layer 56 is separated from the positive electrode binder layer 54. Figure 7 In the example shown in (C), there is a possibility of a short circuit in the gap between the positive electrode compound layer 54 and the protective layer 56, and the adjacency state between the positive electrode compound layer 54 and the protective layer 56 is not ideal.

[0068] [Drying process S102]

[0069] Next, the drying process S102 will be described. This drying process S102 can be carried out according to known methods.

[0070] For example, the drying process S102 can be performed by using a known drying device such as a drying oven to remove the dispersion medium of the positive electrode current collector foil 52 coated with the positive electrode mixture slurry and the protective layer forming slurry.

[0071] The drying temperature and drying time can be appropriately determined based on the boiling point and amount of the dispersion medium contained in the positive electrode mixture slurry and the slurry for forming the protective layer, and are not particularly limited. The drying temperature is, for example, 70°C to 200°C, preferably 110°C to 180°C. The drying time is, for example, 20 seconds to 120 minutes, preferably 30 seconds to 20 minutes.

[0072] A positive electrode flux layer 54 and a protective layer 56 can be formed on the positive electrode current collector foil 52 through the drying process S102. As a result, a positive electrode 50 having a positive electrode flux layer 54 and an adjacent protective layer 56 on the positive electrode current collector foil 52 can be obtained.

[0073] In the resulting positive electrode 50, the positive electrode flux layer 54 and the protective layer 56 have good adjacency. Furthermore, the protective layer 56 has a small thickness. Specifically, the thickness of the protective layer 56 can be 20 μm or less, 15 μm or less, or 12 μm or less. Alternatively, the thickness of the protective layer 56 can be 3 μm or more, 5 μm or more, or 7 μm or more. Moreover, the thickness of the protective layer 56 is not particularly limited as long as it is less than or equal to the thickness of the positive electrode flux layer 54.

[0074] [Any process]

[0075] Hereinafter, any step of the manufacturing method of this disclosure will be described. The manufacturing method according to this embodiment may also include a step of stamping the formed positive electrode mixture layer 54 after the drying step S102 (hereinafter also referred to as the "stamping process").

[0076] The stamping process can be performed using known methods (e.g., by rolling the positive electrode flux layer 54). This stamping process can increase the density of the positive electrode flux layer 54, thereby increasing the energy density and capacity of the lithium-ion secondary battery.

[0077] In addition, such as Figure 5As shown, when the protective layer 56 is formed at both ends of the positive electrode mixture layer 54, the manufacturing method according to this embodiment may also include, after the drying step S102, a step of cutting the central portion of the positive electrode current collector foil 52 along with the positive electrode mixture layer 54 to divide the resulting sheet into two positive electrodes (hereinafter also referred to as the "division step"). This division step can be performed according to known methods. As a result, two positive electrodes 50 can be manufactured efficiently.

[0078] Furthermore, the manufacturing method according to this embodiment may also include, after the drying step S102, a step of forming a collector tab by laser cutting a portion of the exposed portion 52a of the positive electrode current collector foil (hereinafter also referred to as the "collector tab forming step"). When laser cutting is performed, a portion of the protective layer 56 may also be cut along with the positive electrode current collector foil 52. The collector tab forming step can be performed according to known methods.

[0079] Furthermore, when performing two or more of the following processes—stamping, cutting, and collector tab forming—the order is not particularly important. Any of them can be performed in any order.

[0080] The positive electrode 50 obtained above can be used in lithium-ion secondary batteries according to known methods. Therefore, the electrode manufacturing method according to this embodiment is suitable for manufacturing the positive electrode of a lithium-ion secondary battery.

[0081] In the above description, the manufacturing of the positive electrode of a lithium-ion secondary battery was used as an example; however, the electrode obtained by the manufacturing method of this disclosure can be an electrode other than the positive electrode of a lithium-ion secondary battery. The electrode obtained by the manufacturing method of this disclosure is suitable for use as an electrode in a secondary battery.

[0082] Batteries made using electrodes obtained by the manufacturing method described in this embodiment, particularly lithium-ion secondary batteries, can be used for various applications. Suitable applications include batteries used as drive power supplies for vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs), as well as batteries for small energy storage devices.

[0083] The following describes test examples related to this disclosure, but it is not intended to limit this disclosure to the situations shown in the test examples.

[0084] [Experimental Example 1]

[0085] A positive electrode slurry (1) was prepared by mixing lithium nickel cobalt manganese composite oxide, polyvinylidene fluoride (PVDF) as a binder, and acetylene black (AB) as a conductive material in N-methylpyrrolidone. The positive electrode slurry (1) had a solid content concentration of 77.5% by mass and a viscosity of 4.0 Pa·s.

[0086] In addition, a protective layer forming slurry (1) was prepared by mixing alumina as ceramic particles, polyvinylidene fluoride (PVDF) as a binder, and acetylene black (AB) as a carbon-based conductive material in N-methylpyrrolidone. The solid content concentration of the protective layer forming slurry (1) was 24.5% by mass, and the viscosity was 1.31 Pa·s.

[0087] Furthermore, the viscosities of the positive electrode slurry (1) and the protective layer forming slurry (1) were determined as follows. At room temperature (25°C), the viscosity was measured using an MCR rheometer manufactured by Anton-Paar at a shear rate of 0.01 s⁻¹. －1 ~10,000s －1 Viscosity measurements were performed at a shear rate of 100 s⁻¹. －1 The viscosity below is the viscosity of the positive electrode mixture slurry (1) and the protective layer forming slurry (1).

[0088] Prepared Figure 4 The gasket shown has a flow path and an outlet for the positive electrode slurry, and a flow path and an outlet for the protective layer forming slurry. Here, five gaskets with opening widths (B) of 5.7 mm, 6.0 mm, 6.2 mm, 6.4 mm, and 6.6 mm for the outlet of the protective layer forming slurry are prepared. A die coating apparatus equipped with these gaskets is also prepared.

[0089] The positive electrode slurry (1) and the protective layer forming slurry (1) were simultaneously applied to an aluminum foil with a thickness of 13 μm, serving as a current collector, through a mold, with the two materials placed adjacent to each other. The aluminum foil was conveyed at a speed of 45 m / min, and the coating width (A) of the protective layer forming slurry (1) was 6 mm. The discharge rate of the protective layer forming slurry (1) was as shown in Table 1. After drying, the positive electrode slurry layer and the protective layer were formed. Thus, the positive electrode was obtained.

[0090] The thicknesses of the flux layer and protective layer of the obtained positive electrode were measured using a thickness gauge. Furthermore, the boundary between the flux layer and the protective layer in a cross-section of the positive electrode was observed using a microscope. Here, it will be as follows... Figure 7 The case illustrated in (A) where the protective layer does not extend into the end of the positive electrode compound layer but is adjacent to it is judged as "excellent". Figure 7 The condition where the end of the protective layer, as illustrated in (B), enters the lower part of the end of the positive electrode compound layer is judged as "good," and will be as follows: Figure 7 The separation of the positive electrode binder layer from the protective layer, as illustrated in (C), was judged as "unacceptable." Furthermore, "excellent" and "good" were judged as acceptable. The results are shown in Table 1.

[0091]

[0092] [Experimental Example 2]

[0093] A positive electrode slurry (2) was prepared in the same manner as in Test Example 1, with a solid content concentration of 80% by mass and a viscosity of 4.5 Pa·s. A protective layer forming slurry (2) was also prepared in the same manner as in Test Example 1, with a solid content concentration of 15% by mass and a viscosity of 1.0 Pa·s.

[0094] Using the same coating apparatus as in Test Example 1, the positive electrode mixture slurry (2) and the protective layer forming slurry (2) were simultaneously coated onto a 13 μm thick aluminum foil, which served as the current collector foil, in the same manner as in Test Example 1, with them adjacent to each other. The coating width (A) of the protective layer forming slurry (2) was 6 mm. After drying, the positive electrode mixture layer and the protective layer were formed. Thus, the positive electrode was obtained.

[0095] Similar to Example 1, the thicknesses of the flux layer and protective layer of the obtained positive electrode were measured, and the adjacency status between the flux layer and the protective layer was evaluated. The results are shown in Table 2.

[0096]

[0097] As shown in Tables 1 and 2, when the ratio (B / A) of the opening width B of the discharge port for discharging the protective layer slurry to the coating width A of the protective layer slurry is in the range of 1.00 to 1.07, the adjacency state between the positive electrode mixture layer and the protective layer is good, and the thickness of the positive electrode mixture layer is reduced.

[0098] In summary, the electrode manufacturing method disclosed herein can achieve good contact between the protective layer and the electrode mixture layer, and can reduce the thickness of the protective layer.

[0099] The specific examples of this disclosure have been described in detail above, but they are merely illustrative and do not limit the scope of protection. The technology described in the technical solutions includes various modifications and alterations to the specific examples illustrated above.

[0100] That is, the method of manufacturing the electrode involved in this disclosure is as follows [1] to [6].

[0101] [1]

[0102] A method for manufacturing an electrode, wherein the electrode has an electrode flux layer and a protective layer adjacent to the electrode flux layer on a current collector foil, wherein...

[0103] The manufacturing method of the above-mentioned electrode includes:

[0104] In the coating process, an electrode mixture slurry and a protective layer forming slurry are applied to the aforementioned current collector foil using a die equipped with a gasket; and

[0105] The drying process involves drying the coated electrode mixture slurry and the protective layer forming slurry.

[0106] The protective layer forming slurry is applied simultaneously with the electrode mixture slurry in a manner adjacent to the electrode mixture slurry in a mold coating process.

[0107] The aforementioned gasket has a discharge port for discharging the aforementioned electrode mixture slurry and a discharge port for discharging the aforementioned protective layer forming slurry.

[0108] The ratio of the opening width B of the outlet for discharging the slurry for forming the protective layer to the coating width A of the slurry for forming the protective layer, i.e., B / A, is 1.00 to 1.07.

[0109] [2]

[0110] In the manufacturing method described in item [1], the ratio of the opening width B of the outlet for discharging the slurry for forming the protective layer to the coating width A of the slurry for forming the protective layer, i.e., B / A, is 1.03 to 1.07.

[0111] [3]

[0112] In the manufacturing method described in item [1] or [2], the solid content concentration of the positive electrode slurry is 70% to 85% by mass, and the solid content concentration of the protective layer forming slurry is 15% to 25% by mass.

[0113] [4]

[0114] In any of the manufacturing methods described in items [1] to [3], the above-mentioned positive electrode slurry is manufactured at 25°C and a shear rate of 100 s. －1 The viscosity η below A The shear strength is 4.0 Pa·s to 4.5 Pa·s, and the slurry used to form the protective layer is prepared at 25°C and a shear rate of 100 s. －1 The viscosity η below B The value ranges from 1.0 Pa·s to 1.31 Pa·s.

[0115] [5]

[0116] In any of the manufacturing methods described in items [1] to [4], the above-mentioned positive electrode slurry is manufactured at 25°C and a shear rate of 100 s. －1 viscosity η A Compared to the above-mentioned protective layer forming slurry at 25°C and a shear rate of 100s, －1 viscosity ηB The ratio, i.e., η A / η B It ranges from 3.05 to 4.5.

[0117] [6]

[0118] In any of the manufacturing methods described in items [1] to [5], the discharge rate of the slurry for forming the protective layer is 10 mL / min to 25 mL / min, and the conveying speed of the current collector foil is 20 m / min to 80 m / min.

[0119] [7]

[0120] In any of the manufacturing methods described in items [1] to [6], the electrode is the positive electrode of a lithium-ion secondary battery.

Claims

1. A method for manufacturing an electrode, wherein the electrode has an electrode flux layer and a protective layer adjacent to the electrode flux layer on a current collector foil. The method for manufacturing the electrode is characterized by comprising: In the coating process, an electrode mixture slurry and a protective layer forming slurry are applied to the current collector foil using a die with a gasket. as well as The drying process involves drying the coated electrode mixture slurry and the protective layer forming slurry. The protective layer forming slurry is applied simultaneously with the electrode mixture slurry in a manner adjacent to the electrode mixture slurry using a mold coating. The gasket has an outlet for discharging the electrode mixture slurry and an outlet for discharging the protective layer forming slurry. The ratio of the opening width B of the outlet for discharging the slurry for forming the protective layer to the coating width A of the slurry for forming the protective layer, i.e., B / A, is 1.00 to 1.

07.

2. The method for manufacturing the electrode according to claim 1, characterized in that, The ratio of the opening width B of the outlet for discharging the slurry for forming the protective layer to the coating width A of the slurry for forming the protective layer, i.e., B / A, is 1.03 to 1.

07.

3. The method for manufacturing the electrode according to claim 1, characterized in that, The solid content concentration of the positive electrode slurry is 70% to 85% by mass, and the solid content concentration of the protective layer forming slurry is 15% to 25% by mass.

4. The method for manufacturing an electrode according to claim 1, characterized in that, The positive electrode slurry was subjected to a shear rate of 100 s at 25°C. －1 viscosity η A The shear strength is 4.0 Pa·s to 4.5 Pa·s, and the slurry for forming the protective layer is prepared at 25°C with a shear rate of 100 s. －1 viscosity η B The value ranges from 1.0 Pa·s to 1.31 Pa·s.

5. The method for manufacturing an electrode according to claim 1, characterized in that, The positive electrode slurry was subjected to a shear rate of 100 s at 25°C. －1 viscosity η A The protective layer forming slurry is prepared at 25°C and a shear rate of 100 s. －1 viscosity η B The ratio, i.e., η A / η B It ranges from 3.05 to 4.

5.

6. The method for manufacturing an electrode according to claim 1, characterized in that, The discharge rate of the slurry for forming the protective layer is 10 mL / min to 25 mL / min, and the conveying speed of the current collector foil is 20 m / min to 80 m / min.

7. The method for manufacturing an electrode according to claim 1, characterized in that, The electrode is the positive electrode of a lithium-ion secondary battery.

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