Electrode manufacturing method

Abstract

To provide an electrode manufacturing method that reduces cracking around the outer periphery of an electrode mix layer.SOLUTION: An electrode manufacturing method includes the steps of: applying an electrode mixture to one or both surfaces of a current collector and drying the applied electrode mixture to form an electrode mix layer; pressing the electrode mix layer formed on the current collector to form an electrode; and removing a solvent contained in the electrode mix layer after the pressing step. Therein the removing step includes: covering an electrode mixture uncoated portion of the current collector with an insulating material; creating an inert gas atmosphere inside a space isolated by the insulating material; and then drying the electrode mix layer by laser irradiation.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] In a conventional method for manufacturing a secondary battery, a technique is known in which an electrode is manufactured by coating a current collector with an electrode mixture layer, drying the coated electrode mixture layer, and pressing the electrode mixture layer onto the current collector. When manufacturing an electrode in this manner, a step of further drying the pressed electrode may be added in order to remove the solvent contained in the electrode mixture layer.

[0003] Patent Document 1 discloses a method in which a coating film is irradiated with far-infrared rays having a wavelength that is highly absorbed by organic solvents, thereby evaporating the organic solvent from the entire coating film and bringing the coating film to a dry state. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 06-063495 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when laser drying is applied to drying an electrode mixture, the foil (current collector) in the uncoated portion of the electrode mixture on the periphery of the electrode mixture layer may become overheated during drying, causing the periphery of the electrode mixture layer to dry rapidly, which may result in cracks on the periphery of the electrode mixture layer.

[0006] An object of one embodiment of the present disclosure is to provide a method for manufacturing an electrode that suppresses cracks in the outer periphery of the electrode mixture layer. [Means for solving the problem]

[0007] The means for solving the above problems include the following aspects. <1> a step of applying an electrode mixture to one or both surfaces of a current collector and drying the applied mixture to form an electrode mixture layer; a step of applying pressure to the electrode mixture layer formed on the current collector to form an electrode; and a step of removing a solvent contained in the electrode mixture layer after the pressure application step, The removing step includes covering the electrode mixture uncoated portion of the current collector with an isolating material, creating an inert gas atmosphere inside the space isolated by the isolating material, and then drying the electrode mixture layer by laser irradiation. [Effects of the Invention]

[0008] According to one embodiment of the present disclosure, there is provided a method for manufacturing an electrode that suppresses cracking in the outer periphery of an electrode mixture layer. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic perspective view (separator not shown) showing an example of the removal step in the method for producing an electrode according to the present disclosure. [Figure 2] FIG. 2 is a schematic perspective view (laser irradiator not shown) of an example of the removal step of the electrode manufacturing method of the present disclosure, viewed from the electrode transport direction side. [Figure 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] The method for manufacturing the electrode of the present disclosure will be described below.

[0011] The electrode according to the electrode manufacturing method of the present disclosure can be used, for example, in nonaqueous electrolyte secondary batteries in which the electrolyte layer does not contain a solid electrolyte but does contain a liquid electrolyte, solid secondary batteries in which the electrolyte layer does not contain a liquid electrolyte but contains a solid electrolyte, and quasi-solid secondary batteries in which the electrolyte layer contains both a liquid electrolyte and a solid electrolyte. When the electrolyte layer contains a liquid electrolyte, the electrolyte layer preferably has a separator for retaining the liquid electrolyte and preventing contact between the positive electrode layer and the negative electrode layer. Examples of secondary batteries include lithium-ion secondary batteries and nickel-metal hydride secondary batteries. Secondary batteries are used, for example, in batteries for various vehicles such as forklifts, hybrid vehicles, and electric vehicles. The secondary battery is, for example, a flat laminated battery, specifically composed of a plurality of stacked electrodes, as described below.

[0012] The electrode has a current collector formed of a metal plate and an electrode mixture layer provided on one side of the current collector. In the present disclosure, an embodiment in which the electrode mixture layer is provided on one side will be described below, but the present disclosure is not limited to this and can also be applied to an embodiment in which the electrode mixture layer is provided on both sides.

[0013] Examples of electrodes include a positive electrode having a positive electrode mixture layer provided on one or both sides of a current collector, a negative electrode having a negative electrode mixture layer provided on one or both sides of a current collector, and a bipolar electrode having a positive electrode mixture layer on one side of a current collector and a negative electrode mixture layer on the other side. In the present disclosure, both the positive electrode mixture layer and the negative electrode mixture layer correspond to the "electrode mixture layer" in the present disclosure.

[0014] The current collector is formed of a rectangular metal plate made of a metal such as aluminum, stainless steel, nickel, copper, etc. The current collector may be a foil whose metal surface is coated with aluminum, copper, etc. In the electrode manufacturing method of the present disclosure, for example, the edge of the current collector is an uncoated portion that is not coated with an electrode mixture layer.

[0015] The electrode mixture layer is formed by applying an electrode mixture to a current collector.

[0016] The positive electrode mixture layer is formed by coating a current collector with a positive electrode mixture. The positive electrode mixture contains a positive electrode active material. Examples of the positive electrode active material include lithium composite oxides such as lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), lithium manganese oxide (LiMnO), nickel cobalt lithium aluminum oxide (NCA), nickel cobalt lithium manganese oxide (NCM), and lithium iron phosphate (LiFePO).

[0017] The negative electrode mixture layer is formed by coating a negative electrode mixture on a current collector. The negative electrode mixture contains a negative electrode active material. Examples of the negative electrode active material include carbon-based negative electrode active materials such as natural graphite, artificial graphite, and graphite; lithium titanate (e.g., Li4Ti5O 12 and Si-based negative electrode active materials such as simple Si.

[0018] In the electrode manufacturing method of the present disclosure, first, in a general environment, solid components including an active material are dissolved in a solvent and kneaded to prepare a slurry (kneading step). Here, "solid components" refers to components other than the solvent contained in the slurry. In addition, in the present disclosure, a non-aqueous solvent is used as the "solvent." Examples of non-aqueous solvents include N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO).

[0019] Next, the slurry is applied to a current collector and dried to form an electrode mixture layer (film formation step). Specifically, for example, the current collector is in a roll shape, and a slurry (electrode mixture) containing an active material is applied to one side of a sheet-like current collector unwound from the roll-shaped current collector and then dried. The film formation method in the film formation step is not particularly limited, and any known method can be used.

[0020] Next, the electrode mixture layer formed on the current collector is compressed by applying pressure, and the electrode mixture layer is adjusted to a target density or thickness to form an electrode (pressing step). The pressing method in the pressing step is not particularly limited, and known methods such as pressing with a pressure plate or pressing with a press can be used.

[0021] In the electrode manufacturing method of the present disclosure, after the pressing step, the solvent contained in the electrode mixture layer is removed in a dry environment (removal step). At this time, the electrode mixture layer is completely dried to remove water to the order of several hundred ppm (parts per million).

[0022] Next, in a dry environment, the sheet-like electrode is cut to a predetermined size (cutting step). The cutting method in the cutting step is not particularly limited, and any known method can be used. In this way, a rectangular electrode as shown in FIG. 1 is produced.

[0023] The above-mentioned removal step will be described in detail below.

[0024] FIG. 1 is a schematic perspective view showing an example of a removal step in the method for producing an electrode according to the present disclosure. The removing step in the manufacturing method of an electrode according to the present disclosure can be performed using a drying device 100, as shown in Fig. 1. In Fig. 1, the drying device 100 includes a drying furnace 20 that uses a laser and a control device (not shown). Also in Fig. 1, the drying furnace 20 includes a laser irradiator 21 and a radiation thermometer 22. As shown in Fig. 1, before the cutting step, a plurality of electrode mixture layers 10 are continuously provided on an electrode mixture uncoated portion 11A of a current collector 11. These are transported at a desired speed by a known transport device (not shown).

[0025] FIG. 2 is a schematic perspective view (laser irradiator not shown) of an example of a removal step in the electrode manufacturing method of the present disclosure, as viewed from the electrode transport direction side. As shown in FIG. 2, the electrode mixture uncoated portion 11A of the current collector 11 is covered with a separator 30 with low laser transparency, and the space separated by the separator 30 is filled with argon gas, an example of an inert gas. The separator 30 is provided with an intake / exhaust duct 40 for supplying or exhausting the inert gas. As shown in FIG. 3 (a cross-sectional view along line AA in FIG. 2), the electrode mixture layer 10 formed in the film-forming step is irradiated with a laser from a laser irradiator positioned vertically above the electrode mixture layer, but the electrode mixture uncoated portion 11A of the current collector 11 is not irradiated with the laser because it is covered with the separator 30. Therefore, the current collector is not excessively heated by the laser irradiation, and cracking of the outer periphery of the electrode mixture layer is suppressed.

[0026] In the removal step of the electrode manufacturing method of the present disclosure, first, the electrode mixture uncoated portion of the current collector is covered with a separator 30. The separator 30 is not particularly limited as long as it can absorb and block the laser of the irradiated wavelength. From the viewpoints of heat resistance and prevention of foreign matter contamination, the separator is preferably made of metal (e.g., SUS). As described above, by covering the electrode mixture uncoated portion of the current collector with a separator, the electrode mixture layer is not irradiated with the laser and the temperature of the current collector is not excessively raised, thereby suppressing cracking of the outer periphery of the electrode mixture layer.

[0027] Next, in the drying step of the electrode manufacturing method of the present disclosure, the inside of the separator is filled with an inert gas to create an inert gas atmosphere, which may be nitrogen gas (N), helium gas (He), argon gas (Ar), or the like.

[0028] By creating an inert gas atmosphere inside the separator, the current collector does not oxidize and deteriorate even when heated. This eliminates one of the factors that can reduce battery performance. Furthermore, by adjusting the temperature of the inert gas to a low temperature, the temperature rise in the vicinity of the uncoated portion of the current collector can be suppressed, further suppressing cracking around the outer periphery of the electrode mixture layer.

[0029] Next, in the removal step of the electrode manufacturing method of the present disclosure, the electrode mixture layer is dried by laser irradiation. In FIG. 1, a laser irradiator 21 irradiates a laser. Examples of the laser include a fiber laser and a semiconductor laser (diode laser). From the viewpoint of output, it is preferable to use a semiconductor laser. By using a high-output semiconductor laser, the solvent contained in the electrode mixture layer can be efficiently evaporated, and the electrode mixture can be dried.

[0030] The wavelength of the laser irradiation is not particularly limited as long as the effects of the present disclosure can be obtained, but from the viewpoint of evaporating the general-purpose solvent used in the manufacture of the electrode and drying the electrode mixture, it is preferably in the far-infrared region of 900 nm to 1100 nm.

[0031] The laser irradiation time is not particularly limited as long as the effects of the present disclosure can be obtained, and the laser output is also not particularly limited as long as the effects of the present disclosure can be obtained.

[0032] According to the above method, cracks in the outer periphery of the electrode mixture layer can be suppressed.

[0033] The radiation thermometer 22 is a thermometer that measures temperature by detecting infrared rays, and uses a thermometer that has a detection range that is outside the wavelength of the laser irradiated by the laser irradiator 21 so as not to detect the wavelength originating from the laser irradiator 21. In the present disclosure, the radiation thermometer 22 measures the radiation temperature from the surface of the electrode mixture layer 10. [Explanation of symbols]

[0034] 100 drying device, 10 electrode mixture layer, 11 current collector, 11A current collector (electrode mixture uncoated portion), 20 drying oven, 21 laser irradiator, 22 radiation thermometer, 30 isolation material, 40 intake and exhaust duct, L laser

Claims

[Claim 1] a step of applying an electrode mixture to one or both surfaces of a current collector and drying the applied mixture to form an electrode mixture layer; a step of pressing the electrode mixture layer formed on the current collector to form an electrode; a step of removing a solvent contained in the electrode mixture layer after the pressurizing step; Including, The removing step includes covering an uncoated portion provided on the outer periphery of the electrode mixture of the current collector with an isolating material, supplying an inert gas to or exhausting the inert gas from an intake / exhaust duct provided in the isolating material to create an inert gas atmosphere inside the space isolated by the isolating material, and then drying the electrode mixture layer by laser irradiation. Electrode manufacturing method.

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