Method for manufacturing electrode

Abstract

A method for manufacturing an electrode, the method comprising: a coating step for coating a current collector foil with a slurry obtained by dispersing an electrode material in a solvent to obtain a coating film; and a drying step for drying the coating film while conveying the collector foil on which the coating film is formed inside a drying furnace, the drying step irradiating the coating film with a heat source at least once, the irradiation range of the heat source irradiated to the coating film having two regions divided by a straight line bisecting the length of the irradiation range in the conveying direction, when a region disposed on the upstream side in the transport direction is defined as an upstream region and a region disposed on the downstream side in the transport direction is defined as a downstream region, the ratio of the energy density of the heat source irradiated to the upstream region to the energy density of the heat source irradiated to the downstream region is 1.2-3.0.

Description

Technical Field

[0001] The present application relates to a method for manufacturing an electrode. Background Art

[0002] Conventionally, there is known a method for producing an electrode, in which a slurry obtained by dispersing an electrode material in a solvent is applied on a current collector foil to obtain a coating film, and then the coating film is dried in a drying furnace to obtain an electrode.

[0003] For example, Japanese Patent Application Laid-Open No. 2013-084383 discloses a method for manufacturing an electrode, wherein after a mesh collector foil is coated with a slurry for forming an electrode composite material layer, the collector foil coated with the slurry is conveyed in one direction in a drying furnace while hot air is blown to dry the coating. Summary of the invention

[0004] In the drying process, the coating film is irradiated with a heat source (laser or hot air). However, the solvent evaporation rate on the downstream side of the conveying direction within the irradiation range of the heat source is faster than that on the upstream side. Therefore, there is a problem that cracks occur in the manufactured electrode.

[0005] Therefore, a main object of the present disclosure is to provide a method for manufacturing an electrode capable of suppressing breakage of the electrode.

[0006] The present disclosure provides at least the following aspects.

[0007] A method for manufacturing an electrode according to one embodiment of the present disclosure includes: a coating step of coating a slurry obtained by dispersing an electrode material in a solvent on the collector foil to obtain a coating film; and In the drying process, the current collector foil with the coating formed thereon is conveyed inside a drying furnace while the coating is dried. The drying process irradiates the coating with a heat source at least once. When the irradiation range of the heat source irradiated to the coating film has two regions divided by a straight line that divides the length of the irradiation range in the conveying direction into two equal parts, the region arranged on the upstream side in the conveying direction is defined as the upstream region, and the region arranged on the downstream side in the conveying direction is defined as the downstream region, The ratio of the energy density of the heat source irradiated to the upstream region to the energy density of the heat source irradiated to the downstream region is set to 1.2 or more and 3.0 or less.

[0008] In the above-mentioned method for manufacturing an electrode, it is also possible that: In the drying process, the heat sources are laser and hot air.

[0009] In the above-mentioned method for manufacturing an electrode, it is also possible that: The hot air includes the upstream hot air irradiated to the upstream area and the downstream hot air irradiated to the downstream area. The wind speed of the hot air on the upstream side is made faster than the wind speed of the hot air on the downstream side.

[0010] Another aspect of the present disclosure provides a method for manufacturing a battery. The method for manufacturing a battery comprises: An electrode manufacturing step, manufacturing the electrode by the above-mentioned electrode manufacturing method; and Battery manufacturing process, using electrodes to assemble batteries.

[0011] According to the method for producing an electrode of the present disclosure, it is possible to suppress cracking of the electrode. In addition, according to the method for producing a battery of the present disclosure, it is possible to suppress a decrease in battery performance due to cracking of the electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements. Figure 1 is a cross-sectional view obtained by cutting the drying furnace 30 along the conveying direction X of the collector foil 10; Figure 2 2 is a diagram for explaining an irradiation range A of a heat source irradiated to the coating film 20; Figure 3A 1 is a diagram showing a state where the coating film 20 is irradiated with lasers L1 and L2, and is a diagram obtained by observing the coating film 20 from the side; Figure 3B 1 is a diagram showing a state where the coating film 20 is irradiated with laser light L1 and L2, and is a diagram obtained by observing the coating film 20 from above; Figure 4A 2 is a diagram showing a state where the coating film 20 is irradiated with the laser light L and the hot air W1 and W2, and is a diagram obtained by observing the coating film 20 from the side; Figure 4B 2 is a diagram showing a state where the coating film 20 is irradiated with the laser light L and the hot air W1 and W2, and is a diagram obtained by observing the coating film 20 from above; Figure 5 It is a figure which shows the result of Example. DETAILED DESCRIPTION Electrode manufacturing method

[0013] The method for producing an electrode of the present disclosure will be described using one embodiment.

[0014] The electrode manufacturing method according to one embodiment includes: a coating step of coating a slurry obtained by dispersing an electrode material in a solvent on a collector foil 10 to obtain a coating film 20 ; and a drying step of drying the coating film 20 while conveying the collector foil 10 formed with the coating film 20 inside a drying furnace 30 . Coating process

[0015] The coating step is a step of coating the current collector foil 10 with a slurry obtained by dispersing an electrode material in a solvent to obtain a coating film 20. Such a coating step is well known. A typical example will be described below, but the coating step is not limited to this embodiment.

[0016] The collector foil 10 can be a sheet-shaped conductive component without any particular limitation. For example, the collector foil 10 can be a metal foil made of metals such as stainless steel, copper, aluminum, titanium, and nickel. The metal foil can also be made of an alloy containing two or more of these metals. In addition, the metal foil can also be subjected to surface treatments such as plating. The collector foil 10 can also be made of two or more metal foils. In this case, the metal foils can be joined by adhesives or the like, or by stamping or the like.

[0017] The electrode material contains at least an active material. The active material is a positive electrode active material or a negative electrode active material. The positive electrode active material is not particularly limited and can be appropriately selected from known materials according to the target battery performance. Examples include composite oxides, metallic lithium and sulfur. The composition of the composite oxide includes, for example, at least one of iron, manganese, titanium, nickel, cobalt and aluminum and lithium. As an example of a composite oxide, olivine lithium iron phosphate (LiFePO4) can be mentioned. The negative electrode active material is not particularly limited and can be appropriately selected from known materials according to the target battery performance. Examples include graphite, artificial graphite, highly oriented graphite, secondary carbon microbeads, hard carbon, soft carbon and other carbon, metal compounds, elements or compounds thereof that can be alloyed with lithium, boron-added carbon, etc. As examples of elements that can be alloyed with lithium, silicon and tin can be mentioned.

[0018] When the electrode material contains a positive electrode active material, the final electrode becomes a positive electrode. On the contrary, when the electrode material contains a negative electrode material, the final electrode becomes a negative electrode.

[0019] The electrode material may optionally contain a conductive aid. The conductive aid is not particularly limited and may be appropriately selected from known materials according to the target battery performance. Examples thereof include acetylene black, carbon black, graphite, and the like.

[0020] The electrode material may arbitrarily include a binder. The binder is not particularly limited and can be appropriately selected from known materials according to the target battery performance. For example, polyvinylidene fluoride, polytetrafluoroethylene, fluorine-containing resins such as fluorine rubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamide-imide, alkoxysilyl-containing resins, acrylic resins such as poly(meth)acrylic acid, styrene-butadiene rubber (SBR), carboxymethyl cellulose, sodium alginate, alginate such as ammonium alginate, water-soluble cellulose ester crosslinked products, starch-acrylic acid graft polymers, etc. can be cited.

[0021] The electrode material may arbitrarily include a solid electrolyte. The solid electrolyte is not particularly limited and may be appropriately selected from known materials according to the target battery performance. Examples thereof include oxide solid electrolytes, sulfide solid electrolytes, and the like.

[0022] The solvent is not particularly limited as long as it can properly disperse the electrode material. Examples include water and organic solvents. Examples of organic solvents include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, methanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, tetrahydrofuran, etc. These solvents may be used alone or in combination of two or more.

[0023] The coating method is not particularly limited, and any method is sufficient as long as the slurry can be coated in a thin film on the collector foil 10. For example, the slurry can be coated on the collector foil 10 in an arbitrary thickness using a known coating device. Drying process

[0024] The drying step is a step of drying the coating film 20 while conveying the current collector foil 10 on which the coating film 20 is formed inside the drying furnace 30. The electrode is obtained through the drying step. Figure 1 A schematic diagram illustrating the drying process is shown in FIG. Figure 1 This is a cross-sectional view obtained by cutting the drying furnace 30 along the conveyance direction X of the collector foil 10 .

[0025] like Figure 1 As shown, the collector foil 10 formed with the coating film 20 is conveyed using a plurality of conveying rollers 31 provided inside a drying furnace 30. At this time, the coating film 20 is dried by a heat source device 32 provided on the upper portion of the coating film 20. Typically, a plurality of heat source devices 32 are provided along the conveying direction of the collector foil 10. The conveying speed is not particularly limited, and is, for example, in the range of 1 m / sec to 10 m / sec.

[0026] The heat source device 32 is a device for irradiating the coating film 20 with a heat source. Figure 1 In the drying process, a plurality of heat source devices 32 are provided in the drying furnace 30, so the coating film 20 is irradiated with the heat source multiple times. However, the number of the heat source devices 32 can be appropriately changed according to the target, and at least one is sufficient. That is, the coating film 20 is irradiated with the heat source at least once in the drying process.

[0027] Here, the irradiation range of the heat source irradiated from the heat source device 32 to the coating film 20 will be described. Figure 2 A diagram illustrating the irradiation range A is shown in FIG. Figure 2 As shown, the irradiation range A has two regions divided by a straight line that divides the length of the irradiation range A in the conveying direction X into two equal parts. The region arranged on the upstream side in the conveying direction X is referred to as the upstream region A1. The region arranged on the downstream side in the conveying direction X is referred to as the downstream region A2.

[0028] Furthermore, the ratio (E1 / E2) of the energy density E1 of the heat source irradiated to the upstream area A1 to the energy density E2 of the heat source irradiated to the downstream area A2 is set to be greater than 1.2 and less than 3.0. Thus, the rupture of the obtained electrode can be suppressed. From the perspective of further improving the effect, E1 / E2 can be greater than 1.5 and less than 2.0. If E1 / E2 is less than 1.2, the temperature of the coating film 20 in the downstream area A2 becomes higher (the solvent evaporation rate becomes faster), and there is a situation where the electrode rupture cannot be suppressed. If E1 / E2 exceeds 3.0, the temperature of the coating film 20 in the upstream area A1 becomes higher (the solvent evaporation rate becomes faster), and there is a situation where the electrode rupture cannot be suppressed.

[0029] The reason for setting E1 / E2 to a specified range is described below. In the irradiation area A of the heat source, when the heat source of the same energy density is irradiated to both the upstream area A1 and the downstream area A2, the temperature of the coating 20 is higher in the downstream area A2 than in the upstream area A1. This is because, in terms of the irradiation time of the heat source, the coating 20 in the downstream area A2 is longer than the coating 20 in the upstream area A1. The higher the temperature of the coating 20, the faster the evaporation rate of the solvent in the coating 20. In addition, if the evaporation rate of the solvent is too fast, the electrode is prone to rupture and cracking. Therefore, ruptures are likely to occur in the coating 20 (manufactured electrode) in the downstream area A2 where the temperature is high.

[0030] Therefore, in the drying process of one embodiment, the energy density of the heat source irradiated to the upstream area A1 is set to be greater than the energy density of the heat source irradiated to the downstream area A2. The evaporation rate of the solvent in the upstream area A1 is accelerated, and the evaporation rate of the solvent in the downstream area A2 is slowed down. As a result, the cracking of the electrode can be suppressed.

[0031] The length of the irradiation range A in the width direction Y is not particularly limited, and is usually set to be the same as the length in the width direction of the coating film 20. The length of the irradiation range A in the conveying direction X is not particularly limited, and varies depending on the configuration of the heat source device 32. For example, it is 100 mm or more and 2000 mm or less.

[0032] The energy density E1 of the heat source irradiated to the upstream area A1 is set to, for example, 1 to 5. The energy density E2 of the heat source irradiated to the downstream area A2 is set to, for example, 0.33 to 4.2.

[0033] The heat source irradiated from the heat source device 32 is a laser or hot air. From the perspective of setting the energy densities E1 and E2 to different values, the heat source is usually a combination of multiple heat sources. For example, (1) a heat source including two lasers with different energy densities, and (2) a heat source composed of a combination of laser and hot air can be cited.

[0034] As the laser, there can be cited fiber laser, direct laser, VCSFL laser, etc. The laser can use a laser with high light focusing property. In addition, the irradiation frequency of the laser can be pulse irradiation for the conveying direction or continuous irradiation. Laser has a higher energy density than hot air, so it has the advantage of being able to impart high energy density to the coating film 20.

[0035] The temperature of the hot air is not particularly limited, and is, for example, in the range of 100° C. to 160° C. The wind speed of the hot air is not particularly limited, and is, for example, greater than 0 m / s and less than 15 m / s. The energy density of the hot air is not as high as that of the laser, but the evaporated solvent can be discharged outside the drying furnace 30, so the drying of the coating film 20 can be promoted.

[0036] The energy density of laser light and hot air was calculated as follows. (Laser energy density) = Laser irradiation output power (W) / Laser irradiation area (cm 2 ) (hot air energy density) = energy required for drying the coating film 20 (J / cm 2 ) / Drying time under hot air (s)

[0037] The case of (1) using two lasers with different energy densities as heat sources is further described. When two lasers with different energy densities are used as heat sources, the upstream area A1 is irradiated with laser L1, and the downstream area is irradiated with laser L2. At this time, the energy density of each laser is set so that E1 / E2 is within a specified range. Figure 3A and Figure 3B 2 shows a state where the coating film 20 is irradiated with the laser beams L1 and L2. Figure 3A This is a diagram obtained by observing the coating film 20 from the side. Figure 3B This is a diagram of the coating film 20 observed from above.

[0038] When two lasers with different energy densities are used, a heat source device 132 ( Figure 3A and Figure 3B ). That is, the heat source device 132 includes an upstream laser irradiation unit 133 capable of irradiating the upstream area A1 with the laser light L1 and a downstream laser irradiation unit 134 capable of irradiating the downstream area A2 with the laser light L2.

[0039] In addition to the two lasers with different energy densities, hot air can also be used as a heat source. Thus, a large amount of evaporated solvent can be discharged outside the drying furnace 30, so the drying of the coating 20 can be promoted. In this case, the heat source device has a hot air irradiation unit in addition to the upstream laser irradiation unit and the downstream laser irradiation unit. In addition, three or more lasers can also be used as heat sources.

[0040] (2) The case of using laser and hot air as the heat source is described below. When using laser and hot air as the heat source, while irradiating the entire irradiation area A with laser L, the upstream area A1 is irradiated with upstream hot air W1, and the downstream area A2 is irradiated with downstream hot air W2. In this case, the energy density E1 becomes the sum of the energy density of the laser L and the energy density of the upstream hot air W1, and the energy density E2 becomes the sum of the energy density of the laser L1 and the energy density of the downstream hot air W2. Figure 4A and Figure 4B 2 shows a state where the coating film 20 is irradiated with the laser light L and the hot air W1 and W2. Figure 4A This is a diagram obtained by observing the coating film 20 from the side. Figure 4B This is a diagram of the coating film 20 observed from above.

[0041] exist Figure 4A and Figure 4B In the embodiment, the upstream hot air W1 is irradiated toward the downstream side of the conveying direction, and the downstream hot air W2 is irradiated toward the upstream side of the conveying direction. However, this is not limited to this method. The upstream hot air W1 may also be irradiated toward the upstream side of the conveying direction, and the downstream hot air W2 may also be irradiated toward the downstream side of the conveying direction. The upstream hot air W1 and the downstream hot air W2 may be irradiated toward the upstream side of the conveying direction. Figure 4A and Figure 4B In that way, you can irradiate in different directions or in the same direction.

[0042] Here, usually, the wind speed of the upstream hot air W1 can be made faster than the wind speed of the downstream hot air W2. As a result, the solvent evaporated in the upstream area A1 can be discharged to the outside of the drying furnace 30, so the solvent evaporation rate in the upstream area A1 can be accelerated, and the electrode crack suppression effect can be improved. The wind speed of the upstream hot air W1 can be set to, for example, 3 m / s or more and 15 m / s or less. The wind speed of the downstream hot air W2 can be set to, for example, more than 0 m / s and less than 3 m / s.

[0043] When laser or hot air is used as a heat source, a heat source device 232 ( Figure 4A and Figure 4B That is, the heat source device 232 includes an irradiation unit 233 capable of irradiating the entire irradiation area A with the laser light L, an upstream hot air irradiation unit 234 capable of irradiating the upstream hot air W1 to the upstream area A1, and a downstream hot air irradiation unit 235 capable of irradiating the downstream hot air W2 to the downstream area A2.

[0044] As described above, the hot air may include the upstream hot air W1 irradiated to the upstream area A1 and the downstream hot air W2 irradiated to the downstream area A2, but the hot air may also be only the upstream hot air W1 irradiated to the upstream area A1 (the wind speed of the downstream hot air W2 is 0). Even so, as long as E1 / E2 can be set to a specified range, the rupture of the electrode can be suppressed.

[0045] The method for producing an electrode of the present disclosure has been described above using one embodiment. According to the method for producing an electrode of the present disclosure, it is possible to suppress the electrode from peeling off from the current collector foil. Battery manufacturing method

[0046] The method for manufacturing the battery of the present disclosure will be described using one embodiment.

[0047] One embodiment is a method for manufacturing a battery, comprising: an electrode manufacturing step, using the electrode manufacturing method to obtain an electrode; and a battery manufacturing step, using the obtained electrode to assemble a battery. The electrode manufacturing step has been described above, so the battery manufacturing step will be described below.

[0048] The battery manufacturing process is a process of assembling a battery using the electrode obtained in the electrode manufacturing process. Such a battery manufacturing process is well known. A typical example in which the electrode obtained in the electrode manufacturing process is a positive electrode is described below, but the present invention is not limited to this mode.

[0049] When the electrode obtained in the electrode production step is a positive electrode, a battery is produced using a separately produced negative electrode and an electrolyte layer.

[0050] When the electrolyte is a liquid electrolyte, a battery can be made by disposing a spacer between the positive electrode and the negative electrode and then supplying an electrolyte to the spacer. The spacer is mainly a porous sheet of a polyolefin system. The electrolyte is formed by dissolving a supporting salt in a non-aqueous solvent. As non-aqueous solvents, carbonates, ethers, esters, etc. can be cited. Support salts can include, for example, LiPF6, LiBF4, lithium bis(trifluoromethane)sulfonyl imide (LiFSI), lithium bis(trifluoromethane)sulfonyl imide (LiTFSI), etc.

[0051] When the electrolyte is a solid electrolyte, a battery can be made by configuring a solid electrolyte layer between the positive electrode and the negative electrode. The solid electrolyte layer contains a solid electrolyte. In addition, the solid electrolyte layer may also contain a binder. The solid electrolyte and the binder can be appropriately selected from the above-mentioned solid electrolytes and binders.

[0052] The above is a description of the manufacturing method of the battery disclosed in the present invention using one embodiment. The manufacturing method of the battery disclosed in the present invention manufactures the electrode based on the above-mentioned electrode manufacturing method, so the electrode is prevented from peeling off from the collector foil. Therefore, according to the manufacturing method of the battery disclosed in the present invention, the reduction of battery performance caused by the peeling off of the electrode can be suppressed.

[0053] After applying a slurry obtained by dispersing an electrode material in a solvent (water) on the collector foil to obtain a coating film, the collector foil with the coating film formed thereon was introduced into a drying furnace to dry the coating film. The length of the coating film in the width direction was adjusted to 1160 mm.

[0054] The heat source device of the drying furnace is modeled after Figure 1 , Figure 4A , Figure 4B That is, a laser beam L (energy density: 1.0 W / cm 2 ) can irradiate the upstream area A1 with upstream hot air W1 (energy density: 0.38 W / cm 2 ) and can irradiate the downstream area A2 with downstream hot air W2 (energy density: 0.05 W / cm 2 ). The irradiation area A is set to have a length of 1160 mm in the width direction and a length of 900 mm in the conveying direction. The upstream hot air W1 is set to have a temperature of 120°C and a wind speed of 15 m / s. The downstream hot air W2 is set to have a temperature of 120°C and a wind speed of 2 m / s. The ratio (E1 / E2) of the energy density E1 of the heat source irradiated to the upstream area A1 to the energy density E2 of the heat source irradiated to the downstream area A2 is 1.31.

[0055] The results are shown in Figure 5 The electrode temperature (film temperature) is the value obtained by measuring the electrode surface using a radiation thermometer. The mass reduction obtained by successively observing the mass reduction while drying the electrode on a balance is defined as the water reduction, and the moisture content is calculated based on the water reduction. The comparative example is a constant irradiation energy density of 1.5 W / cm 2 Examples of heat sources.

[0056] according to Figure 5 In the comparative example, the electrode temperature rises at a constant rate in the irradiated area A, and the rate of decrease of the moisture content is slow in the upstream area A1 and rapid in the downstream area A2. Therefore, in the comparative example, the electrode may be cracked in the downstream area A2.

[0057] In contrast, in the embodiment, the electrode temperature (film temperature) in the irradiated area A is almost constant, and the rate of decrease in the moisture content is also almost constant. Comparing the embodiment and the comparative example, the rate of decrease in the moisture content in the upstream area A1 is faster in the embodiment, and the rate of decrease in the moisture content in the downstream area A2 is slower in the embodiment. As such, in the embodiment, by using laser and hot air as heat sources and adjusting E1 / E2, the electrode temperature and the solvent evaporation rate can be adjusted. Thus, the cracking of the electrode can be suppressed.

Claims

1. A method for manufacturing an electrode, comprising: a coating step of coating a slurry obtained by dispersing an electrode material in a solvent on the collector foil to obtain a coating film; and a drying step of drying the coating film while conveying the collector foil having the coating film formed thereon in a drying furnace; In the drying step, the coating film is irradiated with a heat source at least once. When the irradiation range of the heat source irradiated to the coating film has two regions divided by a straight line that divides the length of the irradiation range in the conveying direction into two equal parts, the region arranged on the upstream side in the conveying direction is set as the upstream region, and the region arranged on the downstream side in the conveying direction is set as the downstream region, The ratio of the energy density of the heat source irradiated to the upstream region to the energy density of the heat source irradiated to the downstream region is set to 1.2 or more and 3.0 or less.

2. The method for manufacturing an electrode according to claim 1, wherein: In the drying process, the heat source is laser and hot air.

3. The method for manufacturing an electrode according to claim 2, wherein: The hot air includes upstream hot air irradiated toward the upstream area and downstream hot air irradiated toward the downstream area. The wind speed of the upstream hot air is made faster than the wind speed of the downstream hot air.

4. A method for manufacturing a battery, comprising: an electrode manufacturing step, manufacturing the electrode by the electrode manufacturing method according to any one of claims 1 to 3; and The battery manufacturing process uses the electrodes to assemble the battery.

Images