Electrode manufacturing method

Abstract

The present invention provides a method for manufacturing electrodes that allows for a reduction in the thickness of the protective layer while maintaining good proximity between the protective layer and the electrode composite layer. [Solution] This disclosure relates to a method for manufacturing an electrode comprising an electrode composite layer and a protective layer adjacent thereto on a current collector foil. The manufacturing method comprises the steps of: coating the current collector foil with an electrode composite slurry and a protective layer forming slurry using a die head equipped with a shim; and drying the coated electrode composite slurry and the protective layer forming slurry. The protective layer forming slurry is die-coated simultaneously with the electrode composite slurry so as to be adjacent to the electrode composite slurry. The shim comprises a discharge port for discharging the electrode composite 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.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing an electrode comprising an electrode composite layer and a protective layer adjacent thereto on a current collector foil. [Background technology]

[0002] In recent years, secondary batteries such as lithium-ion secondary batteries have been suitably used as portable power supplies for personal computers and mobile devices, as well as power supplies for vehicle propulsion systems such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] As electrodes for secondary batteries such as lithium-ion secondary batteries, electrodes comprising an electrode composite layer and an adjacent protective layer on a current collector foil are known (see, for example, Patent Document 1). As a method for forming the electrode composite layer and protective layer on the current collector foil, a method is known in which an electrode composite slurry and a protective layer forming slurry are simultaneously die-coated onto the current collector foil using a coating apparatus such as those described in Patent Documents 1 and 2.

[0004] In the coating apparatus described above, the die head has a shim provided with a flow path for the electrode mixture slurry and a flow path for the protective layer forming slurry (see, for example, Patent Document 2). In addition, the shim has an outlet for the electrode mixture slurry and an outlet for the protective layer forming slurry. Typically, the opening width of the outlet for the protective layer forming slurry of the shim is set to be narrower than the coating width of the protective layer forming slurry, taking into account that the slurry will spread after coating. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-131988 [Patent Document 2] Japanese Patent Publication No. 2021-120148 [Overview of the project] [Problems that the invention aims to solve]

[0006] Here, the thickness of the electrode protective layer is desirable to be as small as possible while maintaining insulation. However, with conventional methods, it is difficult to reduce the thickness of the protective layer while maintaining good proximity between the protective layer and the electrode composite layer.

[0007] In view of the above circumstances, the present disclosure aims to provide a method for manufacturing an electrode that can reduce the thickness of the protective layer while improving the adjacent condition between the protective layer and the electrode composite layer. [Means for solving the problem]

[0008] This disclosure relates to a method for manufacturing an electrode comprising an electrode composite layer and a protective layer adjacent thereto on a current collector foil. The manufacturing method comprises the steps of: coating the current collector foil with an electrode composite slurry and a protective layer forming slurry using a die head equipped with a shim; and drying the coated electrode composite slurry and the protective layer forming slurry. The protective layer forming slurry is die-coated simultaneously with the electrode composite slurry so as to be adjacent to the electrode composite slurry. The shim comprises a discharge port for discharging the electrode composite 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.

[0009] This configuration provides a method for manufacturing electrodes that allows for a reduction in the thickness of the protective layer while maintaining good proximity between the protective layer and the electrode composite layer. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a flowchart showing the steps of a manufacturing method according to one embodiment of the present disclosure. [Figure 2] Figure 2 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. [Figure 3] FIG. 3 is a schematic view of an example of a positive electrode obtained by the manufacturing method according to an embodiment of the present disclosure, as viewed from a direction perpendicular to the main surface. [Figure 4] FIG. 4 is a plan view of a shim of a die head used in the coating step of the manufacturing method according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a diagram schematically showing die coating in the coating step of the manufacturing method according to an embodiment of the present disclosure. [Figure 6] FIG. 6 is a diagram schematically showing the state of die coating in the coating step of the manufacturing method according to an embodiment of the present disclosure. [Figure 7] FIGS. 7A to 7C are schematic cross-sectional views of a positive electrode for explaining the adjacent state of a positive electrode composite layer and a protective layer. [Figure 8] FIG. 8 is a diagram schematically showing the state of conventional die coating.

MODE FOR CARRYING OUT THE INVENTION

[0011] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. Note that matters not mentioned in this specification but necessary for the implementation of the present disclosure can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The present disclosure can be implemented based on the content disclosed in this specification and the common technical knowledge in the relevant field. In the following drawings, members and parts having the same function are denoted by the same reference numerals for explanation. Also, the dimensional relationships (length, width, thickness, etc.) in each figure do not reflect the actual dimensional relationships. In this specification, the numerical range expressed as "A to B" includes A and B.

[0012] In this specification, the "secondary battery" refers to a rechargeable power storage device. Also, in this specification, the "lithium ion secondary battery" refers to a secondary battery that uses lithium ions as charge carriers and realizes charge and discharge by the movement of charges associated with lithium ions between the positive and negative electrodes.

[0013] The electrode manufacturing method according to this disclosure is a method for manufacturing an electrode comprising an electrode composite layer and a protective layer adjacent thereto on a current collector foil. As shown in Figure 1, the manufacturing method comprises a step S101 of coating the current collector foil with an electrode composite slurry and a protective layer forming slurry using a die head equipped with a shim (hereinafter also referred to as the "coating step"), and a step S102 of drying the coated electrode composite slurry and the protective layer forming slurry (hereinafter also referred to as the "drying step"). The protective layer forming slurry is die-coated simultaneously with the electrode composite slurry so as to be adjacent to the electrode composite slurry. The shim is equipped with a discharge port for discharging the electrode composite 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.

[0014] The electrodes obtained by the manufacturing method according to this disclosure are typically positive electrodes for lithium-ion secondary batteries. Therefore, an embodiment for manufacturing a positive electrode for a lithium-ion secondary battery will be described below as an example of the manufacturing method according to this disclosure. However, the electrodes manufactured by the manufacturing method according to this disclosure are not limited to positive electrodes for lithium-ion secondary batteries. The electrodes manufactured by the manufacturing method according to this disclosure may be negative electrodes for lithium-ion secondary batteries, or electrodes for batteries other than lithium-ion secondary batteries, as long as they comprise an electrode composite layer and an adjacent protective layer on a current collector foil.

[0015] [Positive electrode of a lithium-ion secondary battery] First, Figures 2 and 3 show an example of a positive electrode of a lithium-ion secondary battery obtained by the manufacturing method according to this embodiment. Figure 2 is a cross-sectional view of the positive electrode along the width and thickness directions. Figure 3 is a schematic diagram of the positive electrode viewed from a direction perpendicular to the main surface.

[0016] The positive electrode 50 in the illustrated example is configured as a long positive electrode sheet, and only a portion of it is shown in Figure 3. However, the positive electrode may be cut to a predetermined size and therefore does not have to be long. As shown in Figures 2 and 3, the positive electrode 50 comprises a positive electrode current collector foil 52 and a positive electrode composite layer 54 formed on the positive electrode current collector foil 52. In the illustrated example, the positive electrode composite layer 54 is provided on both sides of the positive electrode current collector foil 52. However, the positive electrode composite layer 54 may be provided on only one side of the positive electrode current collector foil 52.

[0017] The main surface of the positive electrode current collector foil 52 has a portion (exposed positive electrode current collector foil portion) 52a where the positive electrode composite layer 54 is not formed and the positive electrode current collector foil 52 is exposed. In the illustrated example, the exposed positive electrode current collector foil portion 52a is provided at one end in the width direction of the positive electrode 50. However, the exposed positive electrode current collector foil portion 52a may also be provided at the longitudinal end of the positive electrode 50. Furthermore, the exposed positive electrode current collector foil portion 52a may be provided at two or more ends of the positive electrode 50.

[0018] The positive electrode 50 has a protective layer 56. The protective layer 56 is an insulating layer. The protective layer 56 prevents direct contact between the exposed portion 52a of the positive electrode current collector foil 50 and the negative electrode, thereby suppressing a short circuit 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 be provided on only one side of the positive electrode current collector foil 52.

[0019] The protective layer 56 is adjacent to the positive electrode composite layer 54 and is located between the positive electrode composite layer 54 and the exposed positive electrode current collector foil portion 52a in the planar direction of the positive electrode sheet 50. In other words, the protective layer 56 is located at the boundary between the positive electrode composite layer 54 and the exposed positive electrode current collector foil portion 52a. By providing the protective layer 56 at this position, short circuits between the positive electrode 50 and the negative electrode 60 can be suppressed to a high degree.

[0020] The positive electrode current collector foil 52 is a foil-like body made of metal such as aluminum or an aluminum alloy. The positive electrode current collector foil 52 is preferably an 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, and preferably 7 μm or more and 20 μm or less.

[0021] The positive electrode composite layer 54 contains a positive electrode active material. As the positive electrode active material, a known positive electrode active material used in lithium-ion secondary batteries may be used. Specifically, for example, lithium composite oxides, lithium transition metal phosphate compounds, etc., can be used as the positive electrode active material.

[0022] Examples of lithium composite oxides include lithium nickel-based composite oxides, lithium cobalt-based composite oxides, lithium manganese-based composite oxides, lithium nickel-manganese-based composite oxides, lithium nickel-cobalt-manganese-based composite oxides, lithium nickel-cobalt-aluminum-based composite oxides, and lithium iron-nickel-manganese-based composite oxides. Among these, lithium nickel-cobalt-manganese-based composite oxides are preferred. Examples of lithium transition metal phosphate compounds include lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), and lithium iron manganese phosphate.

[0023] The average particle diameter 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. In this specification, "average particle diameter" refers to the median diameter (D50). The average particle diameter (D50) can be determined using a known laser diffraction / scattering type particle size distribution analyzer or the like.

[0024] The positive electrode composite layer 54 may contain components other than the positive electrode active material, such as trilithium phosphate, a conductive material, a binder, etc. Suitable conductive materials include carbon black such as acetylene black (AB) and carbon materials such as carbon nanotubes. Suitable binders include polyvinylidene fluoride (PVDF), etc.

[0025] The content of positive electrode active material in the positive electrode composite layer 54 (i.e., the content of positive electrode active material relative to the total mass of the positive electrode composite layer 54) is not particularly limited, but is preferably 80% by mass or more, and more preferably 90% by mass or more and 97.5% by mass or less. The content of trilithium phosphate in the positive electrode composite layer 54 is not particularly limited, but is preferably 1% by mass or more and 12% by mass or less, and more preferably 3% by mass or more and 10% by mass or less. The content of conductive material in the positive electrode composite layer 54 is not particularly limited, but is preferably 1% by mass or more and 10% by mass or less, and more preferably 1.5% by mass or more and 7% by mass or less. The content of binder in the positive electrode composite layer 54 is not particularly limited, but is preferably 1% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 2.7% by mass or less.

[0026] The thickness of the positive electrode composite layer 54 is not particularly limited, but is, for example, 10 μm or more and 300 μm or less, and preferably 20 μm or more and 200 μm or less.

[0027] The protective layer 56 contains insulating fillers for insulating purposes. Examples of insulating fillers include ceramic particles, polymer particles, and organic-inorganic composite particles, with ceramic particles being particularly preferred.

[0028] Examples of ceramic particles included in the protective layer 56 include oxide ceramic particles such as alumina, silica, titania, zirconia, magnesia, ceria, and zinc oxide; nitride 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. Among these, alumina particles, boehmite particles, silica particles, or magnesia particles are preferred, with alumina particles or boehmite particles being more preferred. Alumina and boehmite have excellent heat resistance, mechanical strength, and durability.

[0029] The shape of the ceramic particles is not particularly limited and may be spherical or non-spherical. The average particle diameter (D50) of the ceramic particles is not particularly limited and is, for example, 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.

[0030] 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.

[0031] The protective layer 56 may contain a binder. Examples of binders that can be contained in the protective layer 56 include acrylic binders, styrene-butadiene rubber (SBR), polyolefin binders, and fluorine-based polymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) can also be used.

[0032] There are no particular restrictions on the binder content in the protective layer 56, but for example, it is 1% by mass or more and 25% by mass or less, preferably 3% by mass or more and 20% by mass or less, and more preferably 3% by mass or more and 10% by mass or less.

[0033] The protective layer 56 may contain a carbon-based conductive material within a range that maintains insulating properties (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 performance at the positive electrode 50 is improved.

[0034] Examples of carbon-based conductive materials included in the protective layer 56 include carbon blacks such as acetylene black, furnace black, channel black, thermal black, and Ketjen black, as well as carbon nanotubes. When performing the current collector tab formation process described later, carbon black is preferred because it has high heat absorption properties during laser cutting and can suppress delamination between the protective layer 56 and the positive electrode current collector foil 52. Among carbon blacks, acetylene black is more preferred.

[0035] The content of the 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.

[0036] The positive electrode 50 may further comprise layers other than the positive electrode composite layer 54 and the protective layer 56, to the extent that they do not impede the effects of the present disclosure.

[0037] [Coating process S101] The coating process S101 will now be explained. First, the cathode mixture slurry and the protective layer formation slurry, which are electrode mixture slurry, will be explained.

[0038] The positive electrode mixture slurry contains the components of the positive electrode mixture layer 54 (i.e., positive electrode active material, an arbitrary binder, conductive material, etc.) and a dispersion medium. N-methylpyrrolidone (NMP) or the like can be suitably used as the dispersion medium. The positive electrode mixture slurry can be prepared by stirring, mixing, or kneading the components of the positive electrode mixture layer 54 and the dispersion medium according to a known method.

[0039] The slurry for forming the protective layer comprises the components of the protective layer 56 (i.e., an insulating filler, an arbitrary binder, a carbon-based conductive material, etc.) and a dispersion medium. N-methylpyrrolidone (NMP) or the like can be suitably used as the dispersion medium. The slurry for forming the protective layer can be prepared by stirring and mixing or kneading the components of the protective layer 56 and the dispersion medium according to a known method.

[0040] The solid content concentration of the positive electrode mixture slurry is not particularly limited, but is preferably 70% to 85% by mass, and more preferably 80% to 85% by mass. The solid content concentration of the protective layer forming slurry is also not particularly limited, but is preferably 15% to 25% by mass. When the solid content concentration of 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.

[0041] Viscosity η of the positive electrode composite slurry A is not particularly limited, but the viscosity η of the positive electrode composite slurry A is, for example, 2.5 Pa·s to 5.0 Pa·s, preferably 4.0 Pa·s to 4.5 Pa·s. Also, the viscosity η of the slurry for forming the protective layer B is not particularly limited, but is, for example, 0.9 Pa·s to 1.5 Pa·s, preferably 1.0 Pa·s to 1.31 Pa·s. The viscosity η of the positive electrode composite slurry A and the viscosity η of the slurry for forming the protective layer B can be determined as the viscosity value at a shear rate of 100 s at 25°C using a commercially available rotational viscometer -1 .

[0042] The ratio (η B of the viscosity η of the positive electrode composite slurry to the viscosity η of the slurry for forming the protective layer A is not particularly limited, but is preferably 3.05 to 4.5. When the ratio (η A / η B ) is within this range, the adjacent state between the protective layer 5 and the positive electrode composite layer 54 becomes particularly good A / η B ).

[0043] In this specification, "slurry" refers to a mixture in which part or all of the solid content is dispersed in a solvent, and includes so-called "paste", "ink", etc

[0044] Next, die coating in the coating step S101 will be described. In the coating step S101, a coating apparatus having a die head equipped with a shim is prepared. This die head has, for example, a pair of die blocks and a shim fixed between the pair of die blocks, similar to the above-mentioned prior art

[0045] A shim is a component that restricts the flow path of electrode mixture slurry and protective layer forming slurry, and also includes an outlet for discharging electrode mixture slurry and an outlet for discharging protective layer forming slurry. An example of a shim is shown in Figure 4. Figure 4 is a plan view of an example of a shim.

[0046] The shim 10 shown in Figure 4 has a channel 12 for the positive electrode mixture slurry in the center. The shim 10 also has a pair of channels 14 for protective layer formation slurry on either side of the channel 12 for the positive electrode mixture slurry. When such a shim 10 is used, protective layers 56 can be formed on both ends of the positive electrode mixture layer 54, and by cutting the sheet with protective layers 56 formed on both ends of the positive electrode mixture layer 54 in the center in the width direction, two positive electrodes 50 in the form shown in Figures 2 and 3 can be manufactured, which is advantageous in terms of the productivity of the positive electrode 50. Alternatively, the shim 10 may have a form in which one channel 14 for protective layer formation slurry is located next to the channel 12 for the positive electrode mixture slurry. In this case, a positive electrode 50 in the form shown in Figures 2 and 3, with a protective layer 56 formed on one end of the positive electrode mixture layer 54, can be obtained directly.

[0047] The end of the channel 12 for the positive electrode mixture slurry is open, so that the shim 10 has a discharge port 12a for discharging the positive electrode mixture slurry. The end of the channel 14 for the protective layer forming slurry is open, so that the shim 10 has a discharge port 14a for discharging the protective layer forming slurry.

[0048] To prevent the positive electrode mixture slurry and the protective layer forming slurry from mixing before coating, the flow path 12 for the positive electrode mixture slurry and the flow path 14 for the protective layer forming slurry are separated. To ensure that the positive electrode mixture slurry and the protective layer forming slurry come into contact during die coating, the flow path 14 for the protective layer forming slurry is configured to approach the flow path 12 for the positive electrode mixture slurry near the discharge port 14a of the protective layer forming slurry. As a result, the protective layer forming slurry is discharged from the discharge port 14a in the direction of the positive electrode mixture slurry, allowing the positive electrode mixture slurry and the protective layer forming slurry to come into contact during die coating.

[0049] Figure 5 is a schematic diagram of an example of die coating in coating process S101. The coating apparatus in the illustrated example comprises a die head 20 and a backup roll 30. In the die head 20, the shim 10 is held between a pair of die blocks 22, as shown in Figure 5. The coating apparatus also has a slurry supply unit (not shown). The slurry supply unit may be a known type. The slurry supply unit supplies positive electrode composite slurry and protective layer forming slurry to the die head 20. Meanwhile, the backup roll 30 rotates to transport the elongated positive electrode current collector foil 52. The transport 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.

[0050] From the die head 20, the positive electrode composite slurry and the protective layer forming slurry are discharged toward the positive electrode current collector foil 52 via the discharge port 12a for the positive electrode composite slurry and the discharge port 14a for the protective layer forming slurry, respectively. As a result, the positive electrode composite slurry and the protective layer forming slurry are simultaneously coated onto the positive electrode current collector foil 52 so that they are adjacent to each other. In this way, a coating film 42 of the positive electrode composite 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 composite slurry and the protective layer forming slurry are not particularly limited and may be appropriately determined according to the design values ​​of the thickness and width of the positive electrode composite 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.

[0051] Here, let B be the opening width of the discharge port 14a of the shim for discharging the protective layer forming slurry (see Figure 4). Also, let A be the coating width of the protective layer forming slurry. The coating width A of the protective layer forming slurry is the dimension in the width direction (i.e., the direction perpendicular to the longitudinal direction) of the coating film 44 of the protective layer forming slurry shown in Figure 5. This width direction is perpendicular to the transport direction of the positive electrode current collector foil 52. In this disclosure, the ratio 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 (B / A) is 1.00 to 1.07.

[0052] Figure 8 schematically shows a conventional die coating method. In Figure 8, in the shim inside the die head 820, channels 814 for protective layer forming slurry are formed on both sides of the channel 812 for positive electrode composite slurry. The die head 820 and the positive electrode current collector foil 52 are separated by a predetermined gap. The channel 814 for protective layer forming slurry has a discharge port 814a for protective layer forming slurry. The protective layer forming slurry and protective layer forming slurry pass through these channels and are discharged from the discharge port and coated onto the positive electrode current collector foil 52. At this time, as shown in Figure 8, typically the coated protective layer forming slurry wets and spreads on the positive electrode current collector foil 52. Therefore, taking this into consideration, conventionally, the opening width B of the discharge port 814a for protective layer forming slurry was set to be narrower than the coating width A of the protective layer forming slurry. Specifically, conventionally, the above ratio (B / A) was set to less than 1, particularly 0.95 or less.

[0053] Therefore, in this disclosure, the shim discharge port is designed so that the value of the above ratio (B / A) is larger than in the conventional method. Figure 6 schematically shows the die coating method in this embodiment. In this case, the opening width B of the discharge port 14a for discharging the slurry for forming the protective layer of the shim 10 is widened so that the dimensions of the opening of the discharge port 14a are greater than or equal to the coating width A of the slurry for forming the protective layer. Furthermore, in order to reduce the discharge amount for thinning, the slurry for forming the protective layer is wider than in the conventional method within the discharge port before being discharged, and the flow velocity is lower than in the conventional method. The discharged protective layer slurry is pulled by the speed difference with the transported current collector foil, and is coated on the current collector foil without spreading out, in a state narrower than the opening width B (see Figure 6). As a result, the slurry for forming the protective layer is coated thinner than in the conventional method while maintaining the same coating width A as in the conventional method, making it possible to form a protective layer 56 with less thickness than in the conventional method. In addition, the adjacency between the formed positive electrode composite layer 54 and the formed protective layer 56 is also improved.

[0054] Furthermore, it is preferable to reduce the amount of protective layer forming slurry discharged from the discharge port 14a and increase the transport speed of the positive electrode current collector foil 52, to a degree that would allow the protective layer forming slurry discharged from the discharge port 14a to be applied to the positive electrode current collector foil 52 while maintaining its thickness and width. This ensures that the protective layer forming slurry discharged from the discharge port 14a is applied to the positive electrode current collector foil 52 with at least one of its width and thickness reduced from its discharged state. For example, if the discharge amount of protective layer forming slurry is 10 mL / min to 25 mL / min, it is preferable that the transport speed of the positive electrode current collector foil 52 be 20 m / min to 80 m / min.

[0055] The above ratio (B / A) is preferably 1.03 to 1.07. In this case, the thickness of the final protective layer can be reduced while particularly improving the proximity between the protective layer and the electrode composite layer.

[0056] The coating width A of the protective layer 56 is not particularly limited, and is, for example, 3 mm to 10 mm, preferably 4 mm to 8 mm.

[0057] The adjacency state between the formed protective layer and the electrode composite layer will be explained using Figures 7A to 7C. Figures 7A to 7C are schematic cross-sectional views along the width and thickness directions of the positive electrode. Since the slurry is a fluid, the edges of the slurry coating are curved. In the example shown in Figure 7A, the shape of the edge of the positive electrode composite layer is close to the natural shape when the positive electrode composite slurry is coated. Therefore, the contour of the edge of the positive electrode composite layer 54 is a curve close to an elliptical arc, and the protective layer 56 is in contact with the edge of the positive electrode composite layer 54. In the example shown in Figure 7A, the functions of the positive electrode composite layer 54 and the protective layer 56 are fully performed, so the adjacency state between the positive electrode composite layer 54 and the protective layer 56 is particularly good. In the example shown in Figure 7B, the protective layer 56 extends below the positive electrode composite layer 54. In the example shown in Figure 7B, the protective layer 56 functions well, so the adjacency state between the positive electrode composite layer 54 and the protective layer 56 is good. On the other hand, in the example shown in Figure 7C, the protective layer 56 is separated from the positive electrode composite layer 54. In the example shown in Figure 7C, there is a possibility of a short circuit occurring in the gap between the positive electrode composite layer 54 and the protective layer 56, and the proximity of the positive electrode composite layer 54 and the protective layer 56 is not good.

[0058] [Drying process S102] Next, the drying process S102 will be described. This drying process S102 can be carried out according to a known method.

[0059] For example, the drying step S102 can be carried out by removing the dispersion medium of the positive electrode mixture slurry and protective layer forming slurry from the positive electrode current collector foil 52 coated with the positive electrode mixture slurry and protective layer forming slurry using a known drying apparatus such as a drying oven.

[0060] The drying temperature and drying time can be appropriately determined according to the boiling point and amount of the dispersion medium contained in the positive electrode mixture slurry and the protective layer forming slurry, 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.

[0061] By performing the drying process S102, a positive electrode composite layer 54 and a protective layer 56 can be formed on the positive electrode current collector foil 52. This makes it possible to obtain a positive electrode 50 on the positive electrode current collector foil 52 that comprises a positive electrode composite layer 54 and an adjacent protective layer 56.

[0062] In the resulting positive electrode 50, the adjacency between the positive electrode composite layer 54 and the protective layer 56 is good. Furthermore, the thickness of the protective layer 56 is small. Specifically, the thickness of the protective layer 56 can be 20 μm or less, 15 μm or less, or 12 μm or less. The thickness of the protective layer 56 can also be 3 μm or more, 5 μm or more, or 7 μm or more. However, 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 composite layer 54.

[0063] [Optional steps] The following describes an optional step of the manufacturing method of the present disclosure. The manufacturing method according to this embodiment may further include a step of pressing the formed positive electrode composite layer 54 after the drying step S102 (hereinafter also referred to as the "pressing step").

[0064] The pressing process can be carried out according to a known method (for example, by applying a roll press treatment to the positive electrode composite layer 54). This pressing process can increase the density of the positive electrode composite layer 54, thereby increasing the energy density and capacity of the lithium-ion secondary battery.

[0065] Furthermore, as shown in Figure 5, when protective layers 56 are formed on both ends of the positive electrode composite layer 54, the manufacturing method according to this embodiment may further include a step (hereinafter also referred to as the "dividing step") in which the central part in the width direction of the positive electrode current collector foil 52 is cut together with the positive electrode composite layer 54 after the drying step S102, thereby dividing the resulting sheet into two positive electrodes. This dividing step can be carried out according to a known method. This makes it possible to efficiently manufacture two positive electrodes 50.

[0066] Furthermore, the manufacturing method according to this embodiment may further include a step of forming a current collector tab by laser cutting a portion of the exposed portion 52a of the positive electrode current collector foil after the drying step S102 (hereinafter also referred to as the "current collector tab forming step"). During laser cutting, a portion of the protective layer 56 may be cut together with the positive electrode current collector foil 52. The current collector tab forming step can be carried out according to a known method.

[0067] Furthermore, when performing two or more of the pressing process, the splitting process, and the current collection tab forming process, the order in which they are performed is not particularly limited. They may be performed in any order.

[0068] The positive electrode 50 obtained by the above method can be used in a lithium-ion secondary battery according to a known method. Therefore, the electrode manufacturing method according to this embodiment is preferably a method for manufacturing a positive electrode of a lithium-ion secondary battery.

[0069] Although the above describes the manufacturing of a positive electrode for a lithium-ion secondary battery as an example, the electrode obtained by the manufacturing method of this disclosure may be an electrode other than the positive electrode of a lithium-ion secondary battery. Preferably, the electrode obtained by the manufacturing method of this disclosure is an electrode for a secondary battery.

[0070] Batteries, particularly lithium-ion secondary batteries, manufactured using electrodes obtained by the manufacturing method according to this embodiment can be used for various applications. Suitable applications include power supplies for vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs); and storage batteries for small-scale power storage devices.

[0071] The following describes test examples relating to the present invention, but the present invention is not intended to be limited to those shown in these test examples.

[0072] [Test Example 1] A cathode composite slurry (1) was prepared by mixing a lithium nickel-cobalt-manganese composite oxide, polyvinylidene fluoride (PVDF) as a binder, and acetylene black (AB) as a conductive material in N-methylpyrrolidone. The solid content concentration of this cathode composite slurry (1) was 77.5% by mass, and the viscosity was 4.0 Pa·s.

[0073] Furthermore, alumina as ceramic particles, polyvinylidene fluoride (PVDF) as a binder, and acetylene black (AB) as a carbon-based conductive material were mixed in N-methylpyrrolidone to prepare a slurry (1) for forming a protective layer. The solid content concentration of this slurry (1) was 24.5% by mass, and its viscosity was 1.31 Pa·s.

[0074] The viscosity of the positive electrode composite slurry (1) and the protective layer forming slurry (1) was determined as follows: At room temperature (25°C), an Anton-Paar MCR rheometer was used to measure the viscosity at a shear rate of 0.01 s². -1 ~10,000s -1 Viscosity measurements were performed at a shear rate of 100 s. -1 The viscosity at this point was defined as the viscosity of the positive electrode mixture slurry (1) and the protective layer forming slurry (1).

[0075] As shown in Figure 4, a shim was prepared having a flow path and discharge port for the positive electrode mixture slurry, and a flow path and discharge port for the protective layer forming slurry. Five types of shims were prepared, with opening widths (B) of the protective layer forming slurry discharge port being 5.7 mm, 6.0 mm, 6.2 mm, 6.4 mm, and 6.6 mm, respectively. A die head coating apparatus equipped with these shims was prepared.

[0076] A 13 μm thick aluminum foil, used as a current collector foil, was simultaneously die-coated with a positive electrode mixture slurry (1) and a protective layer forming slurry (1) adjacent to each other. The transport speed of the aluminum foil was 45 m / min, and the coating width (A) of the protective layer forming slurry (1) was 6 mm. The discharge volume of the protective layer forming slurry (1) was as shown in Table 1. After drying, the positive electrode mixture layer and protective layer were formed. This obtained a positive electrode.

[0077] The thickness of the composite layer and protective layer of the obtained positive electrode was measured using a thickness gauge. In addition, the boundary between the positive electrode composite layer and the protective layer in the cross-section of the positive electrode was observed using a microscope. Here, as exemplified in Figure 7A, when the protective layer was adjacent to the positive electrode composite layer without encroaching on its edge, it was judged as "excellent"; as exemplified in Figure 7B, when the edge of the protective layer was encroaching below the edge of the positive electrode composite layer, it was judged as "good"; and as exemplified in Figure 7C, when the positive electrode composite layer and the protective layer were separated, it was judged as "unacceptable". "Excellent" and "good" were judged as passing. The results are shown in Table 1.

[0078] [Table 1]

[0079] [Test Example 2] A cathode composite slurry (2) was prepared in the same manner as in Test Example 1, except that the solid content concentration was changed to 80% by mass and the viscosity to 4.5 Pa·s. Similarly, a protective layer forming slurry (2) was prepared in the same manner as in Test Example 1, except that the solid content concentration was changed to 15% by mass and the viscosity to 1.0 Pa·s.

[0080] 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 die-coated onto a 13 μm thick aluminum foil, which served as the current collector foil, in the same manner as in Test Example 1, so that they were adjacent to each other. The coating width (A) of the protective layer forming slurry (2) at this time was 6 mm. After that, drying was performed to form the positive electrode mixture layer and the protective layer. This obtained a positive electrode.

[0081] The thickness of the composite layer and protective layer of the obtained positive electrode were measured, and the adjacency of the positive electrode composite layer and protective layer was evaluated in the same manner as in Test Example 1. The results are shown in Table 2.

[0082] [Table 2]

[0083] As shown in the results in Tables 1 and 2, when the ratio 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 (B / A) is within the range of 1.00 to 1.07, the adjacency between the positive electrode mixture layer and the protective layer is good, and the thickness of the positive electrode mixture layer is reduced.

[0084] From the above, it can be seen that the electrode manufacturing method according to this disclosure allows for good proximity between the protective layer and the electrode composite layer, while also reducing the thickness of the protective layer.

[0085] The specific examples of this disclosure have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples described above.

[0086] In other words, the method for manufacturing electrodes according to this disclosure is as described in the following sections [1] to [6]. [1] A method for manufacturing an electrode comprising an electrode composite layer and an adjacent protective layer on a current collector foil, A step of coating the current collector foil with an electrode mixture slurry and a protective layer forming slurry using a die head equipped with a shim, The process includes a step of drying the coated electrode mixture slurry and the protective layer forming slurry, The protective layer forming slurry is die-coated simultaneously with the electrode mixture slurry so as to be adjacent to the electrode mixture slurry. The shim comprises a discharge port for discharging the electrode mixture slurry and a discharge port for discharging the protective layer forming slurry. A manufacturing method wherein 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. [2] The manufacturing method according to item [1], wherein 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 1.03 to 1.07. [3] The solid content concentration of the positive electrode mixture slurry is 70% by mass to 85% by mass, and The aforementioned The manufacturing method according to item [1] or [2], wherein the solid content concentration of the slurry for forming the protective layer is 15% by mass to 25% by mass. [4] The cathode composite slurry at 25°C and a shear rate of 100 s -1 viscosity η A However, the pressure is 4.0 Pa·s to 4.5 Pa·s, and the slurry for forming the protective layer is at 25°C and a shear rate of 100 s. -1 viscosity η B The manufacturing method according to any one of items [1] to [3], wherein the pressure is between 1.0 Pa·s and 1.31 Pa·s. [5] The slurry for forming the protective layer was measured at 25°C and a shear rate of 100 s. -1 viscosity η B The cathode composite slurry was tested at 25°C with a shear rate of 100 s. -1 viscosity η A The ratio (η A / η B The manufacturing method according to any one of the items [1] to [4], wherein the coefficient of the product is 3.05 to 4.5. [6] The manufacturing method according to any one of items [1] to [5], wherein the discharge volume of the slurry for forming the protective layer is 10 mL / min to 25 mL / min, and the transport speed of the current collector foil is 20 m / min to 80 m / min. [7] The manufacturing method according to any one of items [1] to [6], wherein the electrode is the positive electrode of a lithium-ion secondary battery. [Explanation of symbols]

[0087] 10 Sims 12 Flow path of positive electrode composite slurry 12a Outlet of positive electrode mixture slurry 14 Flow channel for slurry for protective layer formation 14a Discharge port for slurry for forming protective layer 20 Die Heads 50 Positive electrode sheets (positive electrode) 52 Positive electrode current collector foil 52a Exposed portion of positive electrode current collector foil 54 Positive electrode composite layer 56 Protective layer

Claims

1. A method for manufacturing an electrode comprising an electrode composite layer and an adjacent protective layer on a current collector foil, A step of coating the current collector foil with an electrode mixture slurry and a protective layer forming slurry using a die head equipped with a shim, The process includes a step of drying the coated electrode mixture slurry and the protective layer forming slurry, The protective layer forming slurry is die-coated simultaneously with the electrode mixture slurry so as to be adjacent to the electrode mixture slurry. The shim comprises a discharge port for discharging the electrode mixture slurry and a discharge port for discharging the protective layer forming slurry. A manufacturing method wherein 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.

2. The manufacturing method according to claim 1, wherein 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 1.03 to 1.

07.

3. The manufacturing method according to claim 1, wherein the solid content concentration of the positive electrode mixture 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 aforementioned cathode composite slurry was measured at 25°C and a shear rate of 100 s. －１ viscosity η Ａ However, the pressure is 4.0 Pa·s to 4.5 Pa·s, and the temperature of the slurry for forming the protective layer is 25°C and the shear rate is 100 s. －１ viscosity η Ｂ The manufacturing method according to claim 1, wherein the pressure is between 1.0 Pa·s and 1.31 Pa·s.

5. The viscosity η of the slurry for forming the protective layer at 25°C and a shear rate of 100 s －１ and the viscosity η of the positive electrode composite slurry at 25°C and a shear rate of 100 s Ｂ The ratio (η －１ / η Ａ is 3.05 to 4.

5. The manufacturing method according to claim 1 Ａ Ｂ ​​

6. The manufacturing method according to claim 1, wherein the discharge volume of the slurry for forming the protective layer is 10 mL / min to 25 mL / min, and the transport speed of the current collector foil is 20 m / min to 80 m / min.

7. The manufacturing method according to claim 1, wherein the electrode is the positive electrode of a lithium-ion secondary battery.

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