Manufacturing method for electrode

Abstract

To provide a manufacturing method for an electrode that can improve productivity.SOLUTION: A manufacturing method for an electrode includes a coating step of coating a base material with an electrode slurry, and a drying step of drying the electrode slurry. The drying step includes a first step of drying the electrode slurry at a constant rate under a first dew point after the coating step, a second step of drying the electrode slurry at a reduced rate under a second dew point after the first step, and a third step of drying the electrode slurry at a reduced rate under a third dew point after the second step. The second dew point is lower than the first dew point and the third dew point is lower than the second dew point.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing an electrode. [Background technology]

[0002] Various techniques have been proposed for producing electrodes such as those disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-145034 A Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional technology, in order to suppress springback of the electrode, which occurs when residual stress from press processing is released over time and the electrode thickness increases, the processes are performed in the order of coating and drying, pressing, and baking (bone drying).However, if pressing is performed when the workpiece temperature after coating and drying is high, electrode distortion will occur due to the difference in the linear expansion of the electrode composite and the linear expansion of the current collector. Therefore, it is necessary to lower the temperature once before pressing. Therefore, even though the temperature is raised in the coating and drying process, it is necessary to lower the temperature once and then raise it again in the baking process, which results in poor energy efficiency (low productivity).

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and has as its main object to provide a method for manufacturing an electrode that can improve productivity. [Means for solving the problem]

[0006] In a first embodiment of the present disclosure, there is provided a method for producing an electrode, comprising the steps of: A coating step of coating the electrode slurry on a substrate; A drying step of drying the electrode slurry, The drying step includes: A first step of drying the electrode slurry at a fixed rate below a first dew point after the coating step; A second step of drying the electrode slurry at a falling rate below a second dew point after the first step; A third step of drying the electrode slurry at a falling rate below a third dew point after the second step, The second dew point is lower than the first dew point, The third dew point is lower than the second dew point.

[0007] In the second embodiment of the present disclosure, in the first embodiment, the pressure in the first furnace in the first step is lower than the pressure in the second furnace in the second step; The pressure in the second furnace in the second step may be lower than the pressure in the third furnace in the third step.

[0008] In a third embodiment of the present disclosure, in the second embodiment, the temperature in the third furnace in the third step may be 65° C. or higher.

[0009] In a fourth embodiment of the present disclosure, in the second embodiment, the volume of the first furnace may be greater than the volumes of the second furnace and the third furnace.

[0010] In a fifth embodiment of the present disclosure, in the first embodiment, the third dew point may be −20° C. or lower. Effect of the Invention

[0011] The electrode manufacturing method of the present disclosure can improve productivity. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic diagram showing an example of a drying step according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present disclosure will be described. Note that matters other than those specifically mentioned in this specification and necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of the electrode that do not characterize the present disclosure) can be understood as design matters of a person skilled in the art based on the prior art in the field. The present disclosure can be implemented based on the contents disclosed in this specification and the technical common sense in the field. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships.

[0014] The present disclosure provides a method for producing an electrode, comprising the steps of: A coating step of coating the electrode slurry on a substrate; A drying step of drying the electrode slurry, The drying step includes: A first step of drying the electrode slurry at a fixed rate below a first dew point after the coating step; A second step of drying the electrode slurry at a falling rate below a second dew point after the first step; A third step of drying the electrode slurry at a falling rate below a third dew point after the second step, The second dew point is lower than the first dew point, The third dew point is lower than the second dew point.

[0015] Conventionally, the temperature was raised to about 100°C in the coating and drying process, then cooled to room temperature to suppress the occurrence of electrode distortion in the subsequent pressing process, and then raised again to about 200°C in the baking (absolute drying) process (to make the electrode absolutely dry before pouring). In this disclosure, by preventing the vapor from the electrode slurry from being brought into the baking process and directly connecting the conventional coating and drying process and baking process in reel-to-reel transport, cooling in the pressing process is no longer necessary, improving energy efficiency and productivity.

[0016] (1) Coating process The coating step is a step of coating the electrode slurry onto a substrate.

[0017] The substrate may be a current collector or the like. The current collector may be a negative electrode current collector, a positive electrode current collector, a bipolar current collector, or the like. Examples of materials for the current collector include metals such as aluminum, copper, SUS, and nickel. The thickness of the current collector is, for example, 0.1 μm or more and 100 μm or less. The shape of the current collector may be a sheet or the like.

[0018] The electrode slurry is applied to a first surface of a substrate. The electrode slurry may be applied only to the first surface of a current collector, or may be applied to the first surface of the current collector and a second surface opposite to the first surface. The electrode slurry can be prepared by mixing electrode materials including an active material, a binder, a conductive material, an electrolyte, a thickener, and the like, together with a solvent. The electrode slurry may be a positive electrode slurry or a negative electrode slurry. The electrode slurry may contain water of about 10,000 ppm or less.

[0019] The active material may be a positive electrode active material. Examples of the positive electrode active material include oxide active materials. Examples of the oxide active material include LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., rock salt layered active materials, LiMn2O4, Li(Ni 0.5 Mn 1.5 )O4 and the like; and olivine type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCuPO4.

[0020] The active material may be a negative electrode active material. Examples of the negative electrode active material include carbon active materials, oxide active materials, and metal active materials. Examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Examples of the oxide active material include Nb2O5, Li4Ti5O 12 and SiO. Examples of the metal active material include In, Al, Si, Sn, and the like.

[0021] Examples of the binder include fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubber-based binders such as butadiene rubber, and acrylic-based binders.

[0022] Examples of conductive materials include carbon materials, metal particles, conductive polymers, etc. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0023] Examples of thickeners include polysaccharides such as carboxymethylcellulose and methylcellulose.

[0024] Examples of the electrolyte include solid electrolytes such as sulfide solid electrolytes and oxide solid electrolytes. Examples of the sulfide solid electrolyte include solid electrolytes containing Li, X (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and halogen elements. Examples of the halogen elements include F, Cl, Br, and I.

[0025] Examples of oxide solid electrolytes include Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li 1.3 Al 0.3 Ti 0.7 (PO4)3, Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 S 0.6 P 0.4 O4, Li4SiO4, Li3PO4, Li3PO 4-3 / 2x N x (x≦1).

[0026] Examples of the solvent include aqueous solvents and organic solvents. The aqueous solvent means water or a mixed solvent containing water and a polar organic solvent. For example, an appropriate dispersion medium can be selected depending on the types of active material, binder, etc. As the aqueous solvent, water is preferably used because of its ease of handling. Examples of polar organic solvents that can be used in the mixed solvent include alcohols such as methanol, ethanol, and isopropyl alcohol, ketones such as acetone, and ethers such as tetrahydrofuran. An example of the organic solvent is N-methyl-2-pyrrolidone (NMP).

[0027] (2) Drying process The drying step is a step of drying the electrode slurry. In general, in the drying step, a drying device is used to dry the electrode slurry. The drying device may be a conventional device capable of drying the electrode slurry, such as a hot air device, a laser device, or an IR (infrared) device. In the drying step, the electrode slurry may be completely dried until the moisture content is reduced to several hundred ppm or less. The electrode slurry becomes an electrode layer through a drying process.

[0028] The drying process includes a first step, a second step, and a third step. The first step is a step of drying the electrode slurry at a fixed rate below a first dew point after the coating step. The second step is a step of drying the electrode slurry at a falling rate below a second dew point after the first step. The third step is a step of drying the electrode slurry at a falling rate below a third dew point after the second step. In the first step, the electrode slurry may be dried in a first furnace, in the second step, the electrode slurry may be dried in a second furnace, and in the third step, the electrode slurry may be dried in a third furnace. In the drying step, the substrate and the workpiece including the electrode slurry applied on the substrate may be placed on a carrier and transported in the order of the first furnace, the second furnace, and the third furnace. Also, the workpiece may be placed on a carrier and transported in the order of the coating step and the drying step. The transport speed may be, for example, 30 m / min or more.

[0029] The second dew point is lower than the first dew point, and the third dew point is lower than the second dew point. The first dew point may be -20° C. or higher, or may be -10° C. or higher. The second dew point may be lower than the first dew point and higher than the third dew point, for example, -10° C. or lower. The third dew point may be -20° C. or lower.

[0030] The pressure in the first furnace in the first step may be lower than the pressure in the second furnace in the second step, and the pressure in the second furnace in the second step may be lower than the pressure in the third furnace in the third step. This makes it possible to suppress the generation of an airflow from the first furnace to the second furnace and to suppress the generation of an airflow from the second furnace to the third furnace, thereby maintaining the dew points of the second and third furnaces lower than the dew point of the first furnace. The pressure in the first furnace in the first step may be negative relative to the pressure outside the drying process system, and may also be negative relative to the pressure in the second furnace in the second step. The pressure in the second furnace in the second step may be a positive pressure relative to the pressure in the first furnace in the first step, and may be a negative pressure relative to the pressure in the third furnace in the third step. The pressure in the third furnace in the third step may be negative with respect to the outside of the drying process system, and may be positive with respect to the pressure in the second furnace in the second step.

[0031] The volume of the first furnace may be larger than the volumes of the second furnace and the third furnace. By making the volumes of the second furnace and the third furnace smaller than the volume of the first furnace, the dew point of the air can be lowered after the second step. The volumes of the second furnace and the third furnace may be the same or different.

[0032] In the first step, the electrode slurry may be heated using a hot air device, a laser device, an IR device, or the like. In the first step, outside air may be supplied into the first furnace, or air with a dew point of -20°C or more and 25°C or less and a temperature of 65°C or more may be supplied as hot air to set the temperature in the first furnace to 65°C or more. In the first step, taking advantage of the fact that the pressure in the first furnace is smaller than the pressure in the second furnace, hot air may be supplied into the second furnace, an air flow may be generated so that the hot air flows from the second furnace into the first furnace, and the hot air supplied into the second furnace may be supplied into the first furnace. This makes it possible to suppress an increase in the dew point in the second furnace. In the first step, radiant heat may be used. In the first step, the electrode slurry may be heated to the maximum temperature required for drying the electrode slurry, and the heating temperature of the electrode slurry may be 100°C to 200°C. The drying time of the electrode slurry in the first step is not particularly limited as long as it is within the constant rate drying period of the electrode slurry. The constant rate drying period is a period during which the surface and center temperatures of the material are kept the same and the moisture content decreases linearly with time. The drying time of the electrode slurry in the first step can be appropriately set depending on the dew point and temperature in the first furnace, the heating temperature of the electrode slurry, and the like. In the first step, the electrode slurry may be dried using a laser, IR, or the like under conditions of a temperature of 100° C. to 200° C. and a time period of 10 to 15 seconds.

[0033] In the second step, for example, air with a dew point of -10°C or less and a temperature of 65°C or more may be supplied as hot air into the second furnace, and the temperature in the second furnace may be set to 65°C or more. In the second step, the pressure in the first furnace is lower than the pressure in the second furnace, and the pressure in the second furnace is lower than the pressure in the third furnace, so that hot air is supplied into the third furnace, an air flow is generated so that hot air flows from the third furnace into the second furnace and the first furnace, and the hot air supplied into the third furnace is supplied into the second furnace and the first furnace. This makes it possible to suppress an increase in the dew point in the third furnace. In the second step, by providing the second furnace, the first furnace and the third furnace can be isolated, and the third furnace can be maintained at a low dew point. The drying time of the electrode slurry in the second step is not particularly limited as long as it is within the falling-rate drying period of the electrode slurry. The falling-rate drying period is the period from when the surface temperature starts to rise rapidly, when the central temperature also rises following the surface temperature, until the surface temperature and central temperature of the material approach the heat source temperature.

[0034] In the third step, air having a dew point of -20°C or less and a temperature of 65°C or more may be supplied as hot air into the third furnace, and the temperature in the third furnace may be set to 65°C or more. In the third step, the electrode slurry may be heated using a hot air device, a laser device, an IR device, or the like. In the third step, radiant heat may be used. The electrode slurry may be heated to a temperature of 100°C to 200°C in the third step. The temperature of the hot air supplied into the third furnace in the third step may be the same as or higher than the temperature of the hot air supplied into the first furnace in the first step, from the viewpoint of suppressing a decrease in the temperature of the electrode slurry, and may be a temperature higher than the temperature reached by the electrode slurry. The drying time of the electrode slurry in the third step is not particularly limited as long as it is within the falling rate drying period of the electrode slurry. In the third step, the electrode slurry may be dried using a laser, IR, or the like under conditions of a temperature of 100° C. to 200° C. and a time period of 10 to 15 seconds.

[0035] The dew point at the outlet of the third furnace in the third step may be -20°C or less. The area on the outlet side after leaving the third furnace may be in a dry air atmosphere. In the third step, moisture is removed from the electrode slurry until the moisture is reduced to several hundred ppm or less, for example, 500 ppm or less, and an electrode layer is formed on the substrate. After the third step, the electrode including the substrate and the electrode layer may be subjected to a press treatment.

[0036] The dew point varies when outside air flows into the furnace or when the moisture in the electrode slurry itself dries. Therefore, in the drying process, a dew point meter may be provided to appropriately adjust the dew point of the air, the amount of hot air supplied, and the temperature of the hot air according to the dew point actually measured in an environment in which air is supplied as hot air. Specifically, the dew point meter may be provided in the exhaust pipe in the third furnace. The dew point of the exhaust pipe may be fed back to the intake air side, and the dew point of the air, the amount of intake hot air, and the temperature of the hot air may be adjusted so that the dew point value becomes a predetermined dew point. Even if the environment inside the furnace fluctuates due to evaporation of water in the electrode slurry, etc., the electrode slurry can be stably dried by adjusting the dew point, hot air supply amount, hot air temperature, etc. to follow the changes. Rather than adjusting the dew point, hot air supply amount, hot air temperature, etc. for all of the first to third furnaces, the electrode slurry can be most efficiently dried by observing and controlling the dew point of the third furnace, which is the final zone. The amount of hot air supplied may be adjusted using an auto-damper or the like whose opening / closing and opening degree can be controlled according to the dew point.

[0037] FIG. 1 is a schematic diagram showing an example of the drying step of the present disclosure. In the drying process shown in Figure 1, the workpiece 1 is transported in the transport direction, and in the first process, the workpiece 1 is heated by the laser device 11 in the first furnace 10, in the second process, hot air 50 is supplied into the second furnace 20 by the hot air device 21, and in the third process, hot air 50 is supplied into the third furnace 30 by the hot air device 32, and the workpiece 1 is heated by the laser device 31 in the third furnace 30. In the first step, hot air 50 may be supplied from a hot air device into the first furnace 10. In the first step, instead of the laser device 11, a hot air device, an IR device, or the like may be used. In the second step, a partition may be provided to separate the first furnace 10 and the third furnace 30. In the second step, the hot air 50 supplied from the hot air device 21 may have a dew point of -10°C or lower and a temperature of 65°C or higher. In the third step, the hot air 50 supplied from the hot air device 32 may have a dew point of -20°C or lower and a temperature of 65°C or higher. The volumes of the second furnace 20 and the third furnace 30 are smaller than the volume of the first furnace 10. Since the pressure in the first furnace 10 is smaller than the pressure in the second furnace 20, an airflow is generated such that the hot air 50 supplied to the second furnace 20 flows from the second furnace 20 into the first furnace 10, and the second dew point in the second furnace 20 is maintained lower than the first dew point in the first furnace 10. Since the pressure in the second furnace 20 is lower than the pressure in the third furnace 30, an air current is generated such that the hot air 50 supplied into the third furnace 30 flows from the third furnace 30 into the second furnace 20, and the third dew point in the third furnace 30 is maintained lower than the second dew point in the second furnace 20. The area on the outlet side of the third furnace 30 after the third step may be in a dry air atmosphere. After the third step, the workpiece 1 is subjected to a press process.

[0038] The electrode obtained by the production method of the present disclosure comprises an electrode layer and a current collector. The electrode layer may be a positive electrode layer or a negative electrode layer. The electrode layer may contain one of a positive electrode active material and a negative electrode active material, and may further contain a binder, a conductive material, an electrolyte, etc. These materials are as described above. The current collector may be a negative electrode current collector, a positive electrode current collector, a bipolar current collector, etc. The material of the current collector, the thickness of the current collector, and the shape of the current collector are as described above.

[0039] The electrodes of the present disclosure are typically used in the manufacture of batteries. The electrodes may be positive or negative electrodes. The type of battery in which the electrode is used is not particularly limited, and may be, for example, a lithium ion secondary battery. The battery may be a liquid battery using an electrolytic solution as an electrolyte, or a solid battery using a solid electrolyte as an electrolyte. Examples of uses of the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline automobiles, and diesel automobiles. In particular, the battery may be used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The battery may also be used as a power source for moving objects other than vehicles (for example, railways, ships, and aircraft), and may be used as a power source for electrical products such as information processing devices. [Explanation of symbols]

[0040] 1. Work 10.First furnace 11. Laser equipment 20.Second Furnace 21.Hot air device 30. No. 3 furnace 31. Laser equipment 32.Hot air device 50. Hot air

Claims

1. A method for manufacturing an electrode, comprising the steps of: A coating step of coating an electrode slurry on a substrate; A drying step of drying the electrode slurry, The drying step includes: A first step of drying the electrode slurry at a fixed rate under a first dew point after the coating step; A second step of drying the electrode slurry at a falling rate below a second dew point after the first step; A third step of drying the electrode slurry at a falling rate below a third dew point after the second step, The second dew point is lower than the first dew point, The method for producing an electrode, wherein the third dew point is lower than the second dew point.

2. the pressure in the first furnace in the first step is lower than the pressure in the second furnace in the second step; 2. The method for producing an electrode according to claim 1, wherein a pressure in the second furnace in the second step is lower than a pressure in the third furnace in the third step.

3. The method for producing an electrode according to claim 2 , wherein a temperature in the third furnace in the third step is 65° C. or higher.

4. The method for manufacturing an electrode according to claim 2 , wherein a volume of the first furnace is greater than volumes of the second furnace and the third furnace.

5. The method for producing an electrode according to claim 1 , wherein the third dew point is −20° C. or lower.

Images