Coating method, slurry composition, and coating device

Abstract

Provided are a coating method, a slurry composition, and a coating device with which coating properties during high-speed coating can be improved. The coating method is a coating method of a slurry composition, and the slurry composition comprises a positive electrode active material, a conductive auxiliary agent, a binder and a solvent. The coating method includes a step of discharging a slurry composition from a discharge port while moving a discharge member provided with the discharge port and a substrate relative to each other to coat the slurry composition on the substrate. The concentration of the solid component relative to the total amount of the slurry composition is in the range of 70-90 mass%. When the value obtained by multiplying the viscosity of the slurry composition by the coating speed of the slurry composition and dividing the value by the surface tension of the slurry composition is defined as the number of capillaries, the number of capillaries is in the range of 1-5. When the coating thickness of the slurry composition is defined as the coating thickness and the spacing distance between the ejection port and the base material is defined as the flow path gap, the value obtained by dividing the coating thickness by the flow path gap is in the range of more than 2 / 3 and less than 1.

Description

Technical Field

[0001] The present invention relates to a coating method, a slurry composition and a coating device. Background Art

[0002] In recent years, research and development of secondary batteries that contribute to improving energy efficiency have been underway to ensure that more people have access to affordable, reliable, sustainable, and advanced energy.

[0003] In the manufacturing process of secondary batteries, a slurry containing an active material is applied to a sheet-like substrate to form an electrode. For example, as shown in Patent Document 1, an intermittent coating device is used for slurry application. The intermittent coating device continuously transports the substrate and intermittently sprays the slurry onto the substrate. This allows the slurry to be applied to the substrate at intervals.

[0004] [Prior Art Literature]

[0005] (Patent Document)

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-038276 Summary of the Invention

[0007] [Problems to be solved by the invention]

[0008] However, when coating is performed at high speed, coating defects such as uneven thickness of the applied slurry or a messy coated surface may occur. Therefore, there is still room for improvement in the coating properties during high-speed coating.

[0009] An object of the present invention is to provide a coating method, a slurry composition, and a coating device capable of improving coating properties during high-speed coating.

[0010] [Technical means to solve the problem]

[0011] (1) The present invention is a coating method, which is a coating method for a slurry composition, wherein the slurry composition includes a positive electrode active material, a conductive additive, a binder and a solvent, and the coating method includes the following steps: while moving a discharge member provided with a discharge port for discharging the slurry composition relative to a substrate, discharging the slurry composition from the discharge port to coat the slurry composition on the substrate; and the concentration of the solid content relative to the total amount of the slurry composition is in the range of 70% by mass to 90% by mass, when the capillary number is a value obtained by multiplying the viscosity (Pa.s) of the slurry composition by the coating speed (m / s) of the slurry composition and dividing it by the surface tension (Nm) of the slurry composition, the capillary number is in the range of 1 to 5, and when the coating thickness of the slurry composition is defined as the coating thickness and the distance between the discharge port and the substrate is defined as the flow channel gap, the value obtained by dividing the coating thickness by the flow channel gap is in the range of greater than 2 / 3 and less than 1.

[0012] According to the coating method described in (1), coating defects such as uneven thickness of the slurry discharged from the coating device and disordered coating surface can be suppressed. Therefore, a coating method capable of improving coating properties during high-speed coating can be provided.

[0013] (2) The coating method according to (1) above, wherein the flow channel gap may be within a range of greater than 200 μm and less than 300 μm.

[0014] According to the coating method described in (2), the coating properties during high-speed coating can be further improved.

[0015] (3) The coating method according to (1) or (2) above, wherein the coating thickness is within a range of 100 μm to 200 μm.

[0016] According to the coating method described in (3), the coating properties during high-speed coating can be further improved.

[0017] (4) The coating method according to any one of (1) to (3) above, wherein the coating speed of the slurry composition is within a range of 0.83 m / s to 1.17 m / s.

[0018] According to the coating method described in (4), the coating properties during high-speed coating can be further improved.

[0019] (5) The present invention is a slurry composition used in the coating method described in any one of (1) to (4) above, and includes a solid electrolyte.

[0020] According to the slurry composition described in (5), a slurry composition capable of improving coating properties during high-speed coating can be provided.

[0021] (6) The slurry composition according to (5) above, wherein, relative to the total amount of solid components contained in the slurry composition, the content of the positive electrode active material can be in the range of 60% by mass to 85% by mass, the content of the conductive additive can be in the range of 1% by mass to 3% by mass, the content of the solid electrolyte can be in the range of 10% by mass to 38% by mass, and the content of the binder can be in the range of 0.5% by mass to 5% by mass.

[0022] According to the slurry composition described in (6), the rheological properties of the slurry composition can be made appropriate according to the composition ratio of the solid components in the composition. As a result, the slurry composition can solidify immediately after being ejected from the coating device. If the viscosity of the slurry composition is high, it is difficult to scatter. Therefore, the occurrence of drag at the coating terminal can be appropriately suppressed. Therefore, a slurry composition that can improve the coating properties during high-speed coating can be provided.

[0023] (7) The slurry composition according to (5) or (6) above, wherein when the shear rate of the slurry composition is set to 1000 / s, the viscosity of the slurry composition can be in the range of 0.2 Pa.s to 3 Pa.s, and when the shear rate of the slurry composition is changed from 1000 / s to 0.1 / s, the viscosity of the slurry composition can be changed from the range of 0.2 Pa.s to 3 Pa.s to the range of 10 Pa.s to 1000 Pa.s.

[0024] According to the slurry composition described in (7), it is more preferred that the slurry composition can be solidified immediately after being ejected, so that the occurrence of drag at the coating terminal can be more appropriately suppressed. Therefore, the coating property during high-speed coating can be further improved. In addition, the slurry composition can be ejected more smoothly during high-speed coating.

[0025] (8) The present invention is a coating device that coats a slurry composition on a substrate using the coating method described in any one of (1) to (4), and includes: a conveying member for conveying the aforementioned substrate; and a spraying member provided with a spraying port for spraying the aforementioned slurry composition toward the aforementioned substrate; and, if the extension direction of the shortest line connecting the aforementioned spraying member and the aforementioned substrate is set as a first direction, the direction of conveying the aforementioned substrate in a direction orthogonal to the aforementioned first direction is set as a second direction, and the direction orthogonal to the aforementioned first direction and the aforementioned second direction is set as a third direction, then the size of the aforementioned spraying port in the aforementioned third direction is in the range of 100 mm to 600 mm.

[0026] According to the coating apparatus described in (8), it is possible to suppress coating defects such as uneven thickness of the slurry discharged from the coating apparatus or disordered coating surface, thereby providing a coating apparatus capable of improving coating properties during high-speed coating.

[0027] (9) The coating device according to (8) above, wherein the size of the ejection port in the second direction may be in the range of 1 mm to 10 mm.

[0028] According to the coating device described in (9), the coating performance during high-speed coating can be further improved.

[0029] (Effects of the Invention)

[0030] According to the present invention, a coating method, a slurry composition, and a coating apparatus capable of improving coating properties during high-speed coating can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a conceptual diagram for explaining a method for applying a slurry composition according to an embodiment.

[0032] Figure 2 It is a figure which shows the state which coated the slurry composition on a base material.

[0033] Figure 3 It is a figure which shows the area around the discharge outlet of the coating device. DETAILED DESCRIPTION

[0034] The following describes embodiments of the present invention. However, the following embodiments are merely examples of the present invention, and the present invention is not limited to the following.

[0035] <Composition of slurry composition>

[0036] The slurry composition of this embodiment is a slurry composition for producing a positive electrode of a secondary battery such as a lithium ion battery. The slurry composition includes a positive electrode active material, a conductive additive, a binder, and a solvent.

[0037] Examples of the positive electrode active material include a lithium-containing layered active material, a spinel-type active material, and an olivine-type active material.

[0038] Examples of the conductive auxiliary agent include acetylene black, carbon nanotubes, graphene, and graphite particles.

[0039] Examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl dichloride (PVDC), polyethylene oxide (PEO), polypropylene oxide (PPO), and polyethylene oxide-propylene oxide copolymer (PEO-PPO).

[0040] Examples of the solvent include ester solvents such as butyl butyrate.

[0041] Furthermore, the slurry composition preferably includes a solid electrolyte.

[0042] The solid electrolyte is not particularly limited as long as it has charge transfer medium conductivity, that is, ion conductivity, and examples thereof include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes.

[0043] However, the positive electrode active material, conductive additive, solid electrolyte, binder and solvent are not limited to the above. As the positive electrode active material, conductive additive, solid electrolyte, binder and solvent, for example, the same materials as those used for the positive electrode of a general solid battery can be used.

[0044] The concentration of the solid content in the slurry composition relative to the total amount of the slurry composition (sometimes simply referred to as "solid content concentration") is in the range of 70% by mass to 90% by mass, and preferably in the range of 75% by mass to 80% by mass.

[0045] This can improve coating properties during high-speed coating.

[0046] Relative to the total amount of solid components contained in the slurry composition, the content of the positive electrode active material is preferably in the range of 60% by mass to 85% by mass, the content of the conductive additive is preferably in the range of 1% by mass to 3% by mass, the content of the solid electrolyte is preferably in the range of 10% by mass to 38% by mass, and the content of the binder is preferably in the range of 0.5% by mass to 5% by mass.

[0047] The content of the positive electrode active material relative to the total amount of solid components contained in the slurry composition is more preferably in the range of 70% by mass to 85% by mass, the content of the conductive additive is more preferably in the range of 1.5% by mass to 3% by mass, the content of the solid electrolyte is more preferably in the range of 10% by mass to 25% by mass, and the content of the binder is more preferably in the range of 0.5% by mass to 3% by mass.

[0048] In this case, the coating properties during high-speed coating can be further improved.

[0049] When the shear rate of the slurry composition is set to 1000 / s, the viscosity of the slurry composition is preferably in the range of 0.2 Pa.s to 3 Pa.s. When the shear rate of the slurry composition is changed from 1000 / s to 0.1 / s, the viscosity of the slurry composition is preferably changed from the range of 0.2 Pa.s to 3 Pa.s to the range of 10 Pa.s to 1000 Pa.s.

[0050] In this case, the coating properties during high-speed coating can be further improved.

[0051] <Coating device>

[0052] The slurry composition of this embodiment is applied to substrate 2 using, for example, a coating apparatus 10. Coating apparatus 10 is described below. Slurry composition 1 is the slurry composition of this embodiment. Substrate 2 is in a sheet form. Substrate 2 is a positive electrode current collector, such as aluminum foil.

[0053] The coating device 10 is a device for performing intermittent coating. Figure 1 As shown, the coating device 10 includes a conveying roller 11 , a storage tank 12 , a supply path 13 , a shutoff valve 14 , and a die head 15 .

[0054] The transport roller 11 is a roller that transports the substrate 2. The transport roller 11 is connected to a motor (not shown), for example, and is rotated by the driving force of the motor. If the transport roller 11 is set to a rotating state while the transport roller 11 is in contact with the substrate 2, the substrate 2 is transported. In addition, it is preferred that the rotation speed of the transport roller 11 (i.e., the rotation speed of the motor) is adjustable. In this case, the transport speed of the substrate 2 can be adjusted by adjusting the rotation speed of the transport roller 11. In addition, the transport roller 11 is equivalent to a transport member. Figure 1 and Figure 3 In FIG, the rotation direction of the transport roller is indicated by a thick arrow.

[0055] The storage tank 12 is a tank for storing the slurry composition.

[0056] The supply path 13 is a pipe for supplying the slurry composition and is connected to the storage tank 12 .

[0057] The stop valve 14 is a switching valve. The stop valve 14 is provided in the middle portion of the supply path 13. The stop valve 14 can be in a state of allowing the slurry composition 1 to pass through the supply path 13, and a state of blocking the slurry composition 1 from passing through the supply path 13. The state of the stop valve 14 can be switched between the state of allowing and the state of blocking.

[0058] The die head 15 is connected to the supply path 13. The storage tank 12 and the die head 15 are connected via the supply path 13. The die head 15 and the conveying roller 11 are spaced apart from each other and face each other. While the conveying roller 11 conveys the substrate 2, a gap is formed between the die head 15 and the substrate 2. When the conveying roller 11 conveys the substrate 2, the die head 15 and the substrate 2 move relative to each other.

[0059] The die head 15 has a flow channel 16. One end of the flow channel 16 is connected to the supply path 13. The other end of the flow channel 16 opens to the conveying roller 11. The opening at the other end of the flow channel 16 is referred to as a "discharge port 16a." The die head 15 corresponds to a discharge member.

[0060] In addition, the direction of the shortest line connecting the die head 15 and the substrate 2 is defined as the "first direction D1". The direction in which the substrate 2 is conveyed in the direction perpendicular to the first direction D1 is defined as the "second direction D2". The direction perpendicular to the first direction D1 and the second direction D2 is defined as the "third direction D3" (refer to Figure 3 ).

[0061] <Coating method>

[0062] Next, a method for applying the slurry composition according to the present embodiment will be described.

[0063] The coating method of this embodiment includes the steps of discharging the slurry composition 1 from the discharge port 16 a while relatively moving the die head 15 provided with the discharge port 16 a for discharging the slurry composition and the substrate 2 to coat the substrate 2 with the slurry composition 1 .

[0064] More specifically, the transport roller 11 is rotated while being in contact with the substrate 2. This continuously transports the substrate 2. The die head 15 and the substrate 2 move relative to each other.

[0065] When the stop valve 14 is in the enabling state, the slurry composition 1 is supplied from the storage tank 12 to the die head 15 through the supply path 13 and ejected from the ejection port 16a. Therefore, while the stop valve 14 is in the enabling state, the slurry composition 1 is intermittently ejected from the ejection port 16a onto the substrate 2. At this time, since the die head 15 and the substrate 2 move relative to each other, the area on the substrate 2 where the slurry composition 1 is applied is continuously formed along the direction of relative movement of the die head 15 and the substrate 2.

[0066] If the stop valve 14 is blocked, the slurry composition 1 cannot pass through the supply path 13 and cannot be supplied to the die head 15. Therefore, while the stop valve 14 is blocked, the discharge of the slurry composition 1 from the die head 15 is stopped. At this time, since the die head 15 and the substrate 2 move relative to each other, a section on the surface of the substrate 2 where the slurry composition 1 is not disposed is continuously formed along the direction of relative movement of the die head 15 and the substrate 2.

[0067] While the transport roller 11 transports the substrate 2, the state of the shutoff valve 14 is alternately switched between a permitted state and a blocked state. As a result, on the surface of the substrate 2, sections where the slurry composition 1 is disposed and sections where the slurry composition 1 is not disposed are alternately formed side by side along the direction of relative movement between the die head 15 and the substrate 2. In other words, the slurry composition 1 can be intermittently applied to the substrate 2.

[0068] like Figure 2 As shown, on the surface of the substrate 2 coated with the slurry composition 1, a plurality of slurry compositions 1 are arranged at intervals. In the direction parallel to the surface of the substrate 2, the direction in which each slurry composition 1 is arranged is set as the "length direction L", and the direction orthogonal to the length direction L is set as the "width direction W". The length direction L is the second direction D2 during coating, and the width direction W is the third direction D3 during coating. Each slurry composition 1 is rectangular. The size of each slurry composition 1 in the width direction W is substantially the same as the size of the discharge port 16a in the second direction D2.

[0069] The slurry composition 1 is dried to form a positive electrode. Although detailed description is omitted, the substrate 2 coated with the slurry composition 1 is further processed to form an electrode sheet for a secondary battery.

[0070] The conveying speed of the substrate is the coating speed of the slurry composition. The coating speed of the slurry composition is not particularly limited, but is preferably higher from the viewpoint of increasing the speed of production of the secondary battery.

[0071] However, if the slurry is applied at high speed, coating defects may occur, such as uneven thickness of the slurry ejected from the coating device or a messy coating surface. Furthermore, slurry may accumulate (sometimes referred to as "beading") at the tip of the die head 15 in a position opposite to the direction of substrate transport. The formation of beading on the die head 15 can easily lead to coating defects.

[0072] Therefore, the capillary number Ca is the value obtained by multiplying the viscosity of the slurry composition (Pa.s, denoted as "μ") by the coating speed of the slurry composition (m / s, denoted as "U") by the surface tension of the slurry composition (Nm, denoted as "σ"). In other words, the capillary number Ca = μ × U / σ.

[0073] The capillary number Ca is in the range of 1-5.

[0074] like Figure 3 As shown, the coating thickness (mm) of the slurry composition 1 is referred to as “coating thickness t.” The distance (mm) between the die head 15 and the substrate 2 is referred to as “flow channel gap G.”

[0075] The value obtained by dividing the coating thickness t by the flow channel gap G is within a range of greater than 2 / 3 and less than 1.

[0076] By applying the slurry composition of this embodiment using this coating method, coating defects such as uneven thickness of the slurry discharged from the coating device or disordered coating surface can be suppressed, thereby improving coating properties during high-speed coating.

[0077] The flow channel gap G is preferably within a range of greater than 200 μm and less than 300 μm.

[0078] The coating thickness t is preferably in the range of 100 μm to 200 μm.

[0079] U is preferably in the range of 0.83 m / s to 1.17 m / s.

[0080] In these cases, the coating properties during high-speed coating can be further improved.

[0081] In the coating device 10, the discharge port 16a is formed as a slit-shaped opening having the second direction D2 as its longitudinal direction. The dimension of the discharge port 16a in the third direction D3 is preferably within a range of 100 mm to 600 mm.

[0082] The dimension of the ejection port 16a in the second direction D2 is preferably within a range of 1 mm to 10 mm.

[0083] In these cases, the coating properties during high-speed coating can be further improved.

[0084] [Example]

[0085] Next, examples of the present invention will be described, but the present invention is not limited to these examples.

[0086] <Preparation of slurry composition>

[0087] The slurry composition of the above embodiment was prepared as samples of Examples 1 and 2 and Comparative Examples 1 to 6. The same sample was used in all the Examples and Comparative Examples.

[0088] A mixture of a positive electrode active material, a conductive additive, a solid electrolyte, a binder, and a solvent is kneaded in a kneader to prepare a slurry composition.

[0089] The positive electrode active material is a ternary positive electrode material. The content of the positive electrode active material relative to the total solid content in the slurry composition is 60-85% by mass, more specifically 80.0% by mass. The conductive additive is acetylene black. The content of the conductive additive relative to the total solid content in the slurry composition is 1-3% by mass, more specifically 1.92% by mass. The solid electrolyte is a sulfide solid electrolyte.

[0090] The solid electrolyte content relative to the total solid content in the slurry composition is 10 to 38% by mass, more specifically 15.5% by mass. The binder is polyvinylidene fluoride (PVDF). The binder content relative to the total solid content in the slurry composition is 0.5 to 5% by mass, more specifically 2.56% by mass.

[0091] The solvent was butyl butyrate, and the solid content concentration was 70 to 90% by mass, more specifically 79.4% by mass.

[0092] <Test method>

[0093] The slurry composition was printed using the coating apparatus 10 of the above embodiment. The slurry composition applied to the substrate 2 had a width W dimension (i.e., the dimension of the ejection port 16a in the second direction D2) of 500 mm. The slurry composition was applied at a speed of 60 m / min. The slurry application speed was set assuming so-called high-speed coating.

[0094] For the Examples and Comparative Examples, the value obtained by dividing the coating thickness t by the flow channel gap G and the capillary number Ca were changed. The values ​​of the coating thickness t, the flow channel gap G, the value obtained by dividing the coating thickness t by the flow channel gap G, and the capillary number Ca for the Examples and Comparative Examples are shown in Table 1.

[0095] The coating properties of the Examples and Comparative Examples were evaluated. When no defects were observed during application of the slurry composition, the evaluation was "good," and when some defects were observed, the evaluation was "poor." Examples of defects during application include a disordered coating surface of the slurry composition, a fractured coating surface of the slurry composition, and the formation of beads in the die head 15. The evaluation results for the Examples and Comparative Examples are shown in Table 1.

[0096] [Table 1]

[0097] Comparative Example 1 Comparative Example 2 Example 1 Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Coating thickness t(mm) 200 200 200 200 200 200 200 200 Flow channel gap G(mm) 200 200 250 250 300 300 400 500 Coating thickness t / flow channel gap G 1 1 4 / 5 4 / 5 2 / 3 2 / 3 1 / 2 2 / 5 Capillary number Ca 2 5 2 5 2 5 2 5 evaluate bad bad good good bad bad bad bad

[0098] Results

[0099] In Examples 1 and 2, no coating surface disorder, coating surface cracking, or beading was observed. Beading was observed in Comparative Examples 1 and 2. Coating surface disorder was observed in Comparative Examples 3 and 4. Coating surface cracking was observed in Comparative Examples 5 and 6. In Examples 1 and 2, good coating properties were confirmed during high-speed coating. In Comparative Examples 1 to 6, poor coating properties were confirmed during high-speed coating.

[0100] Reference numerals

[0101] 1. Slurry composition

[0102] 10 coating device

[0103] 11 Conveying roller as conveying member

[0104] 15 die head as ejection member

[0105] 16a ejection port

Claims

1. A coating method is a coating method for a slurry composition, wherein the slurry composition includes a positive electrode active material, a conductive additive, a binder, and a solvent, and the coating method includes the following steps: While relatively moving a discharge member provided with a discharge port for discharging the slurry composition and a substrate, the slurry composition is discharged from the discharge port to apply the slurry composition on the substrate; and The concentration of the solid content relative to the total amount of the slurry composition is in the range of 70% by mass to 90% by mass, When the capillary number is defined as the value obtained by multiplying the viscosity (Pa.s) of the slurry composition by the coating speed (m / s) of the slurry composition and dividing it by the surface tension (Nm) of the slurry composition, The capillary number is in the range of 1 to 5. When the coating thickness of the slurry composition is defined as the coating thickness and the distance between the ejection port and the substrate is defined as the flow channel gap, The value obtained by dividing the coating thickness by the flow channel gap is within a range of greater than 2 / 3 and less than 1.

2. The coating method according to claim 1, wherein The aforementioned flow channel gap is in a range of greater than 200 μm and less than 300 μm.

3. The coating method according to claim 1, wherein The coating thickness is within a range of 100 μm to 200 μm.

4. The coating method according to claim 1, wherein The coating speed of the slurry composition is within a range of 0.83 m / s to 1.17 m / s.

5. A slurry composition, which is the slurry composition used in the coating method according to claim 1, and Including solid electrolytes.

6. The slurry composition according to claim 5, wherein Relative to the total amount of solid components contained in the slurry composition, the content of the positive electrode active material is in the range of 60% by mass to 85% by mass, the content of the conductive additive is in the range of 1% by mass to 3% by mass, the content of the solid electrolyte is in the range of 10% by mass to 38% by mass, and the content of the binder is in the range of 0.5% by mass to 5% by mass.

7. The slurry composition according to claim 6, wherein When the shear rate of the slurry composition is set to 1000 / s, the viscosity of the slurry composition is in the range of 0.2 Pa.s to 3 Pa.s. When the shear rate of the slurry composition is changed from 1000 / s to 0.1 / s, the viscosity of the slurry composition changes from the range of 0.2 Pa.s to 3 Pa.s to the range of 10 Pa.s to 1000 Pa.s.

8. A coating device for coating a slurry composition on a substrate using the coating method according to claim 1, comprising: Conveying member, conveying the aforementioned base material; and, a spraying member having a spraying port for spraying the slurry composition toward the substrate; and, If the extending direction of the shortest line connecting the ejection member and the substrate is defined as a first direction, the direction in which the substrate is conveyed in a direction perpendicular to the first direction is defined as a second direction, and the direction perpendicular to the first direction and the second direction is defined as a third direction, then A dimension of the ejection port in the third direction is within a range of 100 mm to 600 mm.

9. The coating device according to claim 8, wherein: A dimension of the ejection port in the second direction is in a range of 1 mm to 10 mm.

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