Electrode manufacturing method

Abstract

To provide an electrode manufacturing method that can suppress the occurrence of cracks.SOLUTION: An electrode manufacturing method includes a drying step of drying an electrode paste by a laser while transporting a workpiece having the electrode paste applied to at least one surface of a current collector, and the viscosity of the electrode paste, the film thickness of the electrode paste applied to the current collector, and the basis weight of the electrode paste applied to the current collector are obtained in advance before the drying step, and an output of the laser is adjusted in accordance with the basis weight in the drying step.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

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

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-029256 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional technology, when electrode paste is dried with a laser while being transported, there is variation in the basis weight of the applied electrode paste, and therefore, if the electrode paste is dried with a laser under uniform conditions, it is likely to become over-dried, which can cause cracks in the resulting electrode layer and reduce the peel strength of the electrode layer.

[0005] The present disclosure has been made in view of the above-described circumstances, and a main object of the present disclosure is to provide a method for manufacturing an electrode that can suppress the occurrence of cracks. [Means for solving the problem]

[0006] That is, the present disclosure includes the following aspects. <1> A method for manufacturing an electrode, comprising: a drying step of drying the electrode paste by a laser while transporting a workpiece having an electrode paste applied to at least one surface of a current collector; Before the drying step, the viscosity of the electrode paste, the film thickness of the electrode paste coated on the current collector, and the basis weight of the electrode paste coated on the current collector are obtained in advance, The method for manufacturing an electrode, wherein, in the drying step, an output of the laser is adjusted depending on the basis weight. [Effects of the Invention]

[0007] The electrode manufacturing method of the present disclosure can suppress the occurrence of cracks. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram for explaining a presumed mechanism by which an electrode layer cracks. [Figure 2] FIG. 2 is a graph showing the results of the relationship between the basis weight of the electrode paste and the time until cracking of the electrode layer (time to cracking). DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of electrodes that do not characterize the present disclosure) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships.

[0010] The present disclosure provides a method for manufacturing an electrode, comprising: a drying step of drying the electrode paste by a laser while transporting a workpiece having an electrode paste applied to at least one surface of a current collector; Before the drying step, the viscosity of the electrode paste, the film thickness of the electrode paste coated on the current collector, and the basis weight of the electrode paste coated on the current collector are obtained in advance, In the drying step, the output of the laser is adjusted depending on the basis weight.

[0011] Laser drying of the electrode paste can cause cracking of the resulting electrode layer. If the laser output is too high, water vapor will be generated suddenly inside the electrode layer, causing the internal pressure to rise and causing cracks. FIG. 1 is a schematic diagram for explaining a presumed mechanism by which an electrode layer cracks. The presumed mechanism by which the electrode layer cracks is as follows: As shown in Figure 1, electrode paste 2 applied to current collector 1 is dried from the surface side toward the current collector 1 side. However, electrode paste 2 contains moisture 3, and water vapor 4 is continuously generated during drying, causing the volume of the electrode layer obtained by drying to expand. This makes it difficult for water vapor 4 generated from the current collector 1 side to be released, and when the electrode layer can no longer withstand the expansion caused by the continuously generated water vapor 4, the electrode layer cracks. In the present disclosure, by adjusting the drying conditions according to the variation in the basis weight of the electrode paste applied in the actual field, it is possible to perform laser drying of the electrode paste under appropriate conditions without over-drying, thereby suppressing the occurrence of cracks in the electrode layer. In addition, realizing high-speed drying can reduce capital investment.

[0012] (drying process) The method for manufacturing an electrode according to the present disclosure includes a drying step. The drying step is a step of drying the electrode paste by a laser while transporting a workpiece having a current collector coated on at least one surface thereof. In the drying step, a laser device is used to dry the electrode paste. In addition to the laser device, a conventionally known device capable of drying the electrode paste, such as a hot air device or an IR (infrared) device, may be used as the drying device. In the drying step, the electrode paste may be completely dried until the moisture content is reduced to several hundred ppm or less. In the drying step, the electrode paste may be dried in a drying furnace. In the drying step, the workpiece may be transported on a transport body. The transport speed may be, for example, 30 m / min or more. The drying temperature of the electrode paste may be 100°C to 200°C. The drying time of the electrode paste is not particularly limited. The electrode paste becomes an electrode layer after a drying process, and an electrode including a current collector and an electrode layer formed on at least one surface of the current collector is obtained.

[0013] Before the drying process, the viscosity of the electrode paste, the film thickness of the electrode paste coated on the current collector, and the basis weight of the electrode paste coated on the current collector are obtained in advance, and in the drying process, the output of the laser is adjusted according to the basis weight. The laser output may be adjusted to the upper limit at which the electrode layer does not crack. The upper limit of the electrode layer before it cracks may be determined by the evaporation rate of water (amount of water vapor). The evaporation rate is determined by the viscosity and basis weight of the electrode paste. The viscosity of the electrode paste may be a non-volatile organic compound (NV) value, which is calculated by the following formula: NV (%) = (mass of electrode paste coating after drying) / (mass of electrode paste coating before drying) × 100 The viscosity of the electrode paste may be a value obtained for each lot of the electrode paste. The film thickness of the electrode paste applied to the current collector may be measured in real time using an infrared camera or the like. The basis weight of the electrode paste may be calculated by measuring at least one of the flow rate of the electrode paste from the coater and the film thickness of the electrode paste.

[0014] The workpiece includes a current collector and an electrode paste applied to at least one surface of the current collector. The workpiece may be for a bipolar electrode in which electrode paste is applied to both sides of a current collector, where the electrode paste applied to one side of the current collector is a positive electrode paste and the electrode paste applied to the other side of the current collector is a negative electrode paste.

[0015] 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.

[0016] The electrode paste is applied to at least one of the surfaces of the current collector, that is, a first surface. The electrode paste may be applied only to the first surface of the current collector, or may be applied to both the first surface and a second surface opposite to the first surface of the current collector. The method for applying the electrode paste is not particularly limited, and any conventionally known method can be used. The electrode paste can be prepared by mixing a mixture containing an active material, a binder, a conductive material, an electrolyte, a thickener, etc. with a solvent. The electrode paste may be a positive electrode paste or a negative electrode paste. The electrode paste may contain water of about 10,000 ppm or less. The film width of the electrode paste is not particularly limited and may be 1000 mm or more.

[0017] The active material may be a positive electrode active material. Examples of the positive electrode active material include oxide active materials. Examples of oxide active materials 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 olivine type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCuPO4.

[0018] 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 graphite, 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, and Sn.

[0019] Examples of binders include fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubber-based binders such as styrene-butadiene rubber (SBR), and acrylic binders.

[0020] 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).

[0021] Examples of thickeners include polysaccharides such as carboxymethyl cellulose (CMC) and methyl cellulose.

[0022] 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 a halogen element. Examples of the halogen element include F, Cl, Br, and I.

[0023] Examples of oxide solid electrolytes include Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, and Li 1.3 Al 0.3 Ti 0.7 (PO4)3, Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 Si 0.6 P 0.4 O4, Li4SiO4, Li3PO4, Li3PO 4-3 / 2x N x (x≦1).

[0024] Examples of the solvent include aqueous solvents and organic solvents. An aqueous solvent refers to water or a mixed solvent containing water and a polar organic solvent. For example, an appropriate solvent 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. The organic solvent may, for example, be N-methyl-2-pyrrolidone (NMP).

[0025] The electrode obtained by the manufacturing method of the present disclosure includes a current collector and an electrode layer formed by drying an electrode paste applied to at least one surface of the 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, as well as 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.

[0026] The electrodes of the present disclosure are typically used in the manufacture of batteries. The electrodes may be positive electrodes, negative electrodes, or bipolar electrodes. A bipolar electrode comprises a positive electrode layer on one side of a current collector and a negative electrode layer on the other side of the current collector. The type of battery in which the electrode is used is not particularly limited, and examples thereof include lithium-ion secondary batteries. The battery may be a liquid battery using an electrolytic solution as the electrolyte, or a solid battery using a solid electrolyte as the 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-powered vehicles, and diesel-powered vehicles. 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 mobile objects other than vehicles (for example, railways, ships, and aircraft), and as a power source for electrical appliances such as information processing devices. [Example]

[0027] (Reference examples 1~3) The electrode paste used was a negative electrode paste containing graphite as a negative electrode active material, CMC as a thickener, and SBR as a binder. The viscosity of the electrode paste was determined by calculating the amount of water from the weight of the electrode paste before and after drying, and this was regarded as the viscosity. The basis weight of the electrode paste was calculated by measuring at least one of the flow rate of the electrode paste from the coater and the film thickness of the electrode paste. In each reference example, a workpiece was prepared by applying electrode paste to one side of a current collector so that the electrode paste had the viscosity and basis weight shown in Table 1, and then irradiating the workpiece with a laser of a predetermined output power to dry the electrode paste. The time until the resulting electrode layer cracked was measured. The results are shown in Table 1.

[0028] [Table 1]

[0029] FIG. 2 is a graph showing the results of the relationship between the basis weight of the electrode paste and the time until cracking of the electrode layer (time to cracking). As shown in Figure 2 and Table 1, it can be seen that as the basis weight increases, the time until cracks occur in the electrode layer increases. It can also be seen that as the water evaporation rate increases, the time until cracks occur in the electrode layer decreases. From the above results, it can be seen that by adjusting the laser output according to at least one of the basis weight and the evaporation rate of water, it is possible to prevent the electrode layer from being over-dried and to prevent cracks from occurring. For example, in Reference Example 1, the time until cracks occur in the electrode layer is 53 seconds, so the laser output may be adjusted to relatively increase the laser output to shorten the drying time. In Reference Example 2, the time until cracks occur in the electrode layer is 38 seconds, so the laser output may be adjusted to relatively equal the average laser output. In Reference Example 3, the time until cracks occur in the electrode layer is 32 seconds, so the laser output may be adjusted to relatively decrease the laser output to prevent cracks from occurring. [Explanation of symbols]

[0030] 1. Current collector 2. Electrode paste 3. Moisture 4. Water vapor

Claims

1. A method for manufacturing an electrode, comprising: a drying step of drying the electrode paste by a laser while transporting a workpiece having an electrode paste applied to at least one surface of a current collector; In the drying step, an output of the laser is adjusted according to a basis weight of the electrode paste.

2. The manufacturing method according to claim 1 , wherein the basis weight is calculated from at least one of a flow rate of the electrode paste from a coater and a film thickness of the electrode paste.

3. The manufacturing method according to claim 1 , wherein the output is determined from the basis weight and a non-volatile organic compound (NV) value of the electrode paste.

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