Coating method, slurry composition, and coating device

Abstract

To provide a coating method, a slurry composition, and a coating device capable of improving coatability during high-speed coating.SOLUTION: A coating method is a coating method of a slurry composition containing a positive electrode active material, a conductive additive agent, a binder, and a solvent. The coating method includes a step of applying the slurry composition to a base material by discharging the slurry composition from a discharge port while relatively moving the discharge member provided with the discharge port and the base material. A concentration of solids relative to a total amount of the slurry composition is in a range of 70 mass % to 90 mass %. When a value obtained by dividing a value obtained by multiplying a viscosity of the slurry composition by the coating speed of the slurry composition by a surface tension of the slurry composition is defined as the number of capillaries, the number of capillaries is in the range of 1 to 5. When a coating thickness of the slurry composition is defined as a coating thickness and a separation distance between the discharge port and the base material is defined as a bead gap, a value obtained by dividing the coating thickness by the bead gap is in a range of more than 2 / 3 and less than 1.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

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

[0003] In the manufacturing process of a secondary battery, an electrode is formed by applying a slurry containing an active material to a sheet-like substrate. The application of the slurry is performed using an intermittent coating device, as shown in Patent Document 1, for example. The intermittent coating device continuously transports the substrate and intermittently ejects the slurry toward the substrate. This allows the slurry to be applied to the substrate at intervals. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-038276 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when coating is performed at high speed, there is a concern that coating defects such as unevenness in the thickness of the coated slurry and irregularities in the coated surface may occur, and therefore there is room for improvement in terms of coatability during high-speed coating.

[0006] An object of the present invention is to provide a coating method, a slurry composition, and a coating device that can improve coatability during high-speed coating. [Means for solving the problem]

[0007] (1) The present invention provides a method for applying a slurry composition containing a positive electrode active material, a conductive additive, a binder, and a solvent, the method comprising the steps of: discharging the slurry composition from a discharge member having a discharge port for discharging the slurry composition while moving the discharge member and a substrate relative to each other; and applying the slurry composition to the substrate by discharging the slurry composition from the discharge port. The solid content of the slurry composition is in the range of 70% by mass to 90% by mass. The capillary number is calculated by multiplying the viscosity (Pa·s) of the slurry composition by the application speed (m / s) of the slurry composition and dividing the result by the surface tension (N·m) of the slurry composition, where the capillary number is in the range of 1 to 5. 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 bead gap. The value obtained by dividing the coating thickness by the bead gap is in the range of 2 / 3 to 1.

[0008] The coating method described in (1) can suppress coating defects such as uneven thickness of the slurry discharged from the coating device and irregularities on the coated surface, thereby providing a coating method that can improve coatability during high-speed coating.

[0009] (2) In the coating method described in (1) above, the bead gap may be in the range of more than 200 μm and less than 300 μm.

[0010] According to the coating method described in (2), it is possible to further improve the coatability during high-speed coating.

[0011] (3) In the coating method described in (1) or (2) above, the coating thickness may be in the range of 100 μm to 200 μm.

[0012] According to the coating method described in (3), it is possible to further improve the coatability during high-speed coating.

[0013] (4) In the coating method according to any one of the above (1) to (3), the coating speed of the slurry composition may be in the range of 0.83 m / s to 1.17 m / s.

[0014] According to the coating method described in (4), it is possible to further improve the coatability during high-speed coating.

[0015] (5) The present invention relates to the slurry composition used in the coating method according to any one of (1) to (4) above, which contains a solid electrolyte.

[0016] According to the slurry composition described in (5), it is possible to provide a slurry composition that can improve the coatability during high-speed coating.

[0017] (6) In the slurry composition described in (5) above, the content of the positive electrode active material may be in the range of 60% by mass to 85% by mass, the content of the conductive additive may be in the range of 1% by mass to 3% by mass, the content of the solid electrolyte may be in the range of 10% by mass to 38% by mass, and the content of the binder may be in the range of 0.5% by mass to 5% by mass, relative to the total amount of solids contained in the slurry composition.

[0018] According to the slurry composition described in (6), the solid content ratio in such a configuration can make the rheological properties of the slurry composition favorable. As a result, the slurry composition can be cured immediately after being discharged from the coating device. When the viscosity of the slurry composition is high, it becomes difficult for the slurry composition to scatter. Therefore, the occurrence of drag at the end of coating can be favorably suppressed. Therefore, it is possible to provide a slurry composition that can improve the coatability in high-speed coating.

[0019] (7) In the slurry composition described in (5) or (6) above, the viscosity of the slurry composition may be in the range of 0.2 Pa·s to 3 Pa·s when the shear rate of the slurry composition is 1000 / s, and may change from the range of 0.2 Pa·s to 3 Pa·s to the range of 10 Pa·s to 1000 Pa·s when the shear rate of the slurry composition is changed from 1000 / s to 0.1 / s.

[0020] According to the slurry composition described in (7), the slurry composition can be more preferably cured immediately after being discharged, and therefore the occurrence of drag at the end of the coating can be more preferably suppressed. Therefore, the coatability in high-speed coating can be further improved. In addition, the slurry composition can be more smoothly discharged during high-speed coating.

[0021] (8) The present invention provides a coating device for coating a substrate with a slurry composition by the coating method according to any one of (1) to (4), comprising: a conveying member for conveying the substrate; and a discharge member having a discharge port for discharging the slurry composition toward the substrate, wherein the direction in which the shortest line connecting the discharge member and the substrate extends is defined as a first direction; the direction in which the substrate is conveyed among directions 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, and the dimension of the discharge port in the third direction is within a range of 100 mm to 600 mm.

[0022] The coating device described in (8) can suppress coating defects such as uneven thickness of the slurry discharged from the coating device and irregularities on the coated surface, thereby providing a coating device that can improve coating performance during high-speed coating.

[0023] (9) In the coating device described in (8) above, the dimension of the discharge port in the second direction may be in the range of 1 mm to 10 mm.

[0024] According to the coating device described in (9), the coating properties during high-speed coating can be further improved. [Effects of the Invention]

[0025] According to the present invention, it is possible to provide a coating method, a slurry composition, and a coating device that can improve the coatability during high-speed coating. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 2 is a conceptual diagram for explaining a method for applying a slurry composition according to an embodiment. [Figure 2] FIG. 2 is a diagram showing a state in which a slurry composition is applied onto a substrate. [Figure 3] FIG. 2 is a diagram showing the periphery of a discharge port of a coating device. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments of the present invention will be described. However, the embodiments described below are merely examples of the present invention, and the present invention is not limited to the following.

[0028] <Composition of Slurry Composition> The slurry composition of the present embodiment is a slurry composition used for manufacturing a positive electrode of a secondary battery such as a lithium ion battery, etc. The slurry composition contains a positive electrode active material, a conductive additive, a binder, and a solvent.

[0029] Examples of the positive electrode active material include a layered active material containing lithium, a spinel type active material, and an olivine type active material.

[0030] Examples of the conductive additive include acetylene black, carbon nanotubes, graphene, and graphite particles.

[0031] Examples of binders include polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyethylene oxide (PEO), polypropylene oxide (PPO), and polyethylene oxide-propylene oxide copolymer (PEO-PPO).

[0032] Examples of the solvent include ester solvents such as butyl butyrate.

[0033] The slurry composition preferably contains a solid electrolyte.

[0034] The solid electrolyte is not particularly limited as long as it has charge transfer medium conductivity, i.e., ion conductivity, and examples thereof include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes.

[0035] However, the positive electrode active material, conductive additive, solid electrolyte, binder, and solvent are not limited to those described above, and may be, for example, the same as those used in the positive electrode of a general solid-state battery.

[0036] The concentration of solids in the slurry composition relative to the total amount of the slurry composition (sometimes simply referred to as "solids 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.

[0037] This can improve the coatability during high-speed coating.

[0038] It is preferable that, relative to the total amount of solids 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.

[0039] With respect to the total amount of solids contained in the slurry composition, the content of the positive electrode active material 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.

[0040] In this case, the coatability during high-speed coating can be further improved.

[0041] 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 1000 / s, and changes from the range of 0.2 Pa·s to 3 Pa·s to the range of 10 Pa·s to 1000 Pa·s when the shear rate of the slurry composition is changed from 1000 / s to 0.1 / s.

[0042] In this case, the coatability during high-speed coating can be further improved.

[0043] <Coating equipment> The slurry composition of this embodiment is applied onto a substrate 2, for example, using a coating device 10. The coating device 10 will be described below. The slurry composition 1 is the slurry composition of this embodiment. The substrate 2 is in the form of a sheet. The substrate 2 is a positive electrode current collector, and is, for example, aluminum foil.

[0044] The coating device 10 is a device that performs intermittent coating. As shown in Fig. 1, 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.

[0045] The transport roller 11 is a roller that transports the substrate 2. The transport roller 11 is connected to, for example, a motor (not shown) and rotates by the driving force of the motor. When the transport roller 11 is in contact with the substrate 2 and the transport roller 11 is rotated, the substrate 2 is transported. It is preferable 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. The transport roller 11 corresponds to a transport member. In Figures 1 and 3, the rotation direction of the transport roller is indicated by a thick arrow.

[0046] The storage tank 12 is a tank for storing the slurry composition.

[0047] The supply line 13 is a pipe for supplying the slurry composition and is connected to the storage tank 12.

[0048] The shutoff valve 14 is a switching valve. The shutoff valve 14 is provided in the middle of the supply path 13. The shutoff valve 14 can be in an allowable state in which the slurry composition 1 can pass through the supply path 13, and in a blocked state in which the slurry composition 1 cannot pass through the supply path 13. The state of the shutoff valve 14 can be switched between the allowable state and the blocked state.

[0049] The die head 15 is connected to a supply path 13. The storage tank 12 and the die head 15 are connected by the supply path 13. The die head 15 and the conveying roller 11 face each other with a gap therebetween. While the substrate 2 is being conveyed by the conveying roller 11, a gap is formed between the die head 15 and the substrate 2. When the substrate 2 is conveyed by the conveying roller 11, the die head 15 and the substrate 2 move relative to each other.

[0050] The die head 15 has a flow path 16. One end of the flow path 16 is connected to the supply path 13. The other end of the flow path 16 opens toward the conveying roller 11. The opening at the other end of the flow path 16 is referred to as the "discharge port 16a." The die head 15 corresponds to a discharge member.

[0051] The direction in which the shortest line connecting the die head 15 and the substrate 2 extends is referred to as the "first direction D1." The direction in which the substrate 2 is transported, among directions perpendicular to the first direction D1, is referred to as the "second direction D2." The direction perpendicular to the first direction D1 and the second direction D2 is referred to as the "third direction D3" (see FIG. 3).

[0052] <Coating method> Next, a method for applying the slurry composition of this embodiment will be described.

[0053] The coating method of this embodiment includes a step of discharging the slurry composition 1 from the discharge port 16a while moving the die head 15, which has a discharge port 16a for discharging the slurry composition, relative to the substrate 2, and applying the slurry composition 1 to the substrate 2.

[0054] More specifically, the conveying roller 11 is rotated while the conveying roller 11 and the substrate 2 are in contact with each other. This allows the substrate 2 to be continuously conveyed. The die head 15 and the substrate 2 move relative to each other.

[0055] When the shutoff valve 14 is set to the permitted state, the slurry composition 1 is supplied from the storage tank 12 to the die head 15 through the supply path 13 and discharged from the discharge port 16a. Therefore, while the shutoff valve 14 is in the permitted state, the slurry composition 1 is intermittently discharged from the discharge port 16a onto the substrate 2. At this time, since the die head 15 and the substrate 2 are moving relative to each other, a section on the substrate 2 where the slurry composition 1 is applied is continuously formed in the direction of the relative movement of the die head 15 and the substrate 2.

[0056] When shutoff valve 14 is shut off, slurry composition 1 cannot pass through supply path 13 and is not supplied to die head 15. Therefore, while shutoff valve 14 is shut off, discharge of slurry composition 1 from die head 15 stops. At this time, since die head 15 and substrate 2 are moving relative to each other, a section where slurry composition 1 is not placed is continuously formed on the surface of substrate 2 in the direction of relative movement of die head 15 and substrate 2.

[0057] While the substrate 2 is being conveyed by the conveying roller 11, the state of the shutoff valve 14 is alternately switched between an enabling state and a blocking 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 in the direction in which the die head 15 and the substrate 2 move relative to each other. In other words, the slurry composition 1 can be intermittently applied onto the substrate 2.

[0058] As shown in FIG. 2, a plurality of slurry compositions 1 are arranged at intervals on the surface of the substrate 2 to which the slurry composition 1 has been applied. Of the directions parallel to the surface of the substrate 2, the direction in which the slurry compositions 1 are arranged is referred to as the "length direction L," and the direction perpendicular to the length direction L is referred to 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 has a rectangular shape. The dimension of each slurry composition 1 in the width direction W is approximately the same as the dimension of the discharge port 16a in the second direction D2.

[0059] The slurry composition 1 becomes a positive electrode when dried. Although a detailed explanation is omitted, the substrate 2 coated with the slurry composition 1 is further processed into an electrode sheet for a secondary battery.

[0060] 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 in order to increase the speed of secondary battery production.

[0061] However, when the slurry is applied at high speed, there is a concern that coating defects may occur, such as uneven thickness of the slurry discharged from the coating device or irregularities in the coated surface. Furthermore, accumulations of slurry (sometimes called "droplets") may occur at the tip of the die head 15 on the side opposite the substrate conveyance direction. The formation of droplets on the die head 15 makes coating defects more likely to occur.

[0062] Therefore, the capillary number Ca is calculated by multiplying the viscosity of the slurry composition (Pa·s, referred to as "μ") by the application speed of the slurry composition (m / s, referred to as "U") and dividing the result by the surface tension of the slurry composition (N·m, referred to as "σ"). In other words, the capillary number Ca = μ × U / σ.

[0063] The capillary number Ca is in the range of 1-5.

[0064] 3, the coating thickness (mm) of the slurry composition 1 is defined as "coating thickness t." The distance (mm) between the die head 15 and the substrate 2 is defined as "bead gap G."

[0065] The value obtained by dividing the coating thickness t by the bead gap G is in the range of greater than 2 / 3 and less than 1.

[0066] By applying the slurry composition of the present embodiment using this coating method, it is possible to suppress coating defects such as uneven thickness of the slurry discharged from the coating device and irregularities on the coated surface, thereby improving the coatability during high-speed coating.

[0067] The bead gap G is preferably in the range of greater than 200 μm and less than 300 μm.

[0068] The coating thickness t is preferably in the range of 100 μm to 200 μm.

[0069] It is preferable that U is in the range of 0.83 m / s to 1.17 m / s.

[0070] In these cases, the coatability during high-speed coating can be further improved.

[0071] In the coating device 10, the discharge port 16a is, for example, a slit-shaped opening with the second direction D2 as the 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.

[0072] The dimension of the outlet 16a in the second direction D2 is preferably within a range of 1 mm to 10 mm.

[0073] In these cases, the coatability during high-speed coating can be further improved. [Example]

[0074] Next, an example of the present invention will be described, but the present invention is not limited to this example.

[0075] <Preparation of Slurry Composition> Slurry compositions of the above embodiments were prepared as samples for Examples 1 and 2 and Comparative Examples 1 to 6. The same samples were used in all Examples and Comparative Examples.

[0076] A mixture of the positive electrode active material, the conductive additive, the solid electrolyte, the binder, and the solvent was kneaded in a kneader to prepare a slurry composition.

[0077] The positive electrode active material is a ternary positive electrode material. The content of the positive electrode active material relative to the total amount of solids contained in the slurry composition is 60 to 85 mass %, more specifically 80.0 mass %. The conductive additive is acetylene black. The content of the conductive additive relative to the total amount of solids contained in the slurry composition is 1 to 3 mass %, more specifically 1.92 mass %. The solid electrolyte is a sulfide solid electrolyte.

[0078] The content of the solid electrolyte relative to the total amount of solids contained in the slurry composition is 10 to 38 mass%, more specifically 15.5 mass%. The binder is polyvinylidene fluoride (PVDF). The content of the binder relative to the total amount of solids contained in the slurry composition is 0.5 to 5 mass%, more specifically 2.56 mass%.

[0079] The solvent is butyl butyrate, and the solid content is 70 to 90 mass %, more specifically, 79.4 mass %.

[0080] <Test Method> The slurry composition was printed using the coating device 10 of the above embodiment. The dimension in the width direction W of the slurry composition applied onto the substrate 2 (i.e., the dimension in the second direction D2 of the discharge port 16a) was 500 mm. The coating speed of the slurry composition was 60 m / min. The coating speed of the slurry was set assuming so-called high-speed coating.

[0081] The value obtained by dividing the coating thickness t by the bead gap G and the capillary number Ca were changed for each example and comparative example. The values ​​of the coating thickness t, the bead gap G, the value obtained by dividing the coating thickness t by the bead gap G, and the capillary number Ca for each example and comparative example are as shown in Table 1.

[0082] The coatability was evaluated for each example and comparative example. If no defects were observed during coating of the slurry composition, it was rated as "good," and if any defects occurred, it was rated as "poor." Examples of defects during coating include irregularities in the coated surface of the slurry composition, cutting of the coated surface of the slurry composition, and the occurrence of droplets on the die head 15. The evaluation results for each example and comparative example are shown in Table 1.

[0083] [Table 1]

[0084] <Result> In Examples 1 and 2, no irregularities in the coated surface, no breakage in the coated surface, and no formation of droplets were observed. In Comparative Examples 1 and 2, formation of droplets was observed. In Comparative Examples 3 and 4, irregularities in the coated surface were observed. In Comparative Examples 5 and 6, breakage in the coated surface was observed. In the cases of Examples 1 and 2, it was confirmed that the coatability during high-speed coating was good. In the cases of Comparative Examples 1 to 6, it was confirmed that the coatability during high-speed coating was not good. [Explanation of symbols]

[0085] 1: slurry composition, 10: coating device, 11: conveying roller as a conveying member, 15: die head as a discharging member, 16a: discharge port.

Claims

1. A method for applying a slurry composition containing a positive electrode active material, a conductive additive, a binder, and a solvent, comprising: a step of discharging the slurry composition from a discharge member provided with a discharge port for discharging the slurry composition and a substrate while moving the discharge member and a substrate relatively to each other, thereby coating the slurry composition on the substrate; 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 value obtained by multiplying the viscosity (Pa s) of the slurry composition by the coating speed (m / s) of the slurry composition and dividing the result by the surface tension (N m) of the slurry composition is defined as the capillary number, the number of capillaries 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 discharge port and the substrate is defined as the bead gap, A coating method, wherein a value obtained by dividing the coating thickness by the bead gap is in the range of greater than 2 / 3 and less than 1.

2. The coating method according to claim 1 , wherein the bead gap is in the range of more than 200 μm and less than 300 μm.

3. 2. The coating method according to claim 1, wherein the coating thickness is in the range of 100 μm to 200 μm.

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

5. The slurry composition used in the coating method according to claim 1, A slurry composition comprising a solid electrolyte.

6. 6. The slurry composition according to claim 5, wherein 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, relative to the total amount of solids contained in the slurry composition.

7. 7. The slurry composition according to claim 6, wherein 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 1000 / s, and when the shear rate of the slurry composition is changed from 1000 / s to 0.1 / s, the viscosity 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 apparatus for coating a substrate with a slurry composition by the coating method according to claim 1, comprising: a conveying member that conveys the substrate; a discharge member provided with a discharge port for discharging the slurry composition toward the substrate; Equipped with Let us assume that the direction in which the shortest line connecting the discharge member and the substrate extends is a first direction, the direction in which the substrate is transported among directions perpendicular to the first direction is a second direction, and the direction perpendicular to the first direction and the second direction is a third direction. A coating device, wherein the dimension of the discharge port in the third direction is within a range of 100 mm to 600 mm.

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

Images