Manufacturing method of electrode

Abstract

To provide a manufacturing method of an electrode, capable of suppressing cracking of the electrode.SOLUTION: A manufacturing method of an electrode, includes: a coating step of coating collector foil with slurry obtained by scattering an electrode material in a solvent to obtain a coating film; and a dry step of drying the coating film while transporting the collector foil which is formed with the coating in a dry furnace inner part. The dry step irradiates the coating film with heat source at least one time. An irradiation range of the heat source radiated to the coating film includes two regions divided by a straight line for dividing a length in a transportation direction of the irradiation range into two. When a region arranged on an upstream side of the transportation direction is an upstream region and a region arranged on a downstream side of the transportation direction is a downstream region, a ratio of an energy density of the heat source radiated to the upstream region against the energy density of the heat source radiated to the downstream region is 1.2 or more and 3.0 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] 2. Description of the Related Art Conventionally, there has been known a method for producing an electrode, in which a slurry obtained by dispersing an electrode material in a solvent is applied onto 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, Patent Document 1 discloses a method for manufacturing an electrode, in which a slurry for forming an electrode composite layer is applied to a web-shaped current collecting foil, and then the current collecting foil coated with the slurry is sent in one direction in a drying furnace while applying hot air to the coating film to dry the coating film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-084383 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the drying process, a heat source (laser or hot air) is irradiated to the coating film, but the solvent evaporation rate on the downstream side of the heat source irradiation range in the transport direction is faster than the solvent evaporation rate on the upstream side, which causes cracks in the manufactured electrodes.

[0006] Therefore, a main object of the present disclosure is to provide a method for manufacturing an electrode that can suppress cracking of the electrode. [Means for solving the problem]

[0007] The present disclosure provides at least the following aspects.

[0008] The first aspect is a method for manufacturing an electrode, comprising: a coating step of coating a current collecting foil with a slurry obtained by dispersing an electrode material in a solvent to obtain a coating film; and a drying step of drying the coating film while transporting the current collecting foil on which the coating film has been formed inside a drying furnace, in which the drying step irradiates the coating film with a heat source at least once, and the irradiation range of the heat source irradiated to the coating film has two regions divided by a straight line that equally divides the length of the irradiation range in the transport direction, and in which the region located upstream in the transport direction is defined as the upstream region and the region located downstream in the transport 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 1.2 or more and 3.0 or less.

[0009] A second aspect is the method for producing an electrode according to the first aspect, wherein the heat source in the drying step is a laser and hot air.

[0010] In the third embodiment, the hot air includes upstream hot air irradiated to the upstream region and downstream hot air irradiated to the downstream region, and the wind speed of the upstream hot air is made faster than the wind speed of the downstream hot air. A method for producing the electrode according to the second aspect.

[0011] A fourth aspect includes an electrode production step of producing an electrode by the electrode production method according to any one of the first to third aspects, and a battery production step of assembling a battery using the electrode. A method for manufacturing a battery. Effect of the Invention

[0012] According to the electrode manufacturing method of the present disclosure, it is possible to suppress cracking of the electrode, and according to the battery manufacturing method of the present disclosure, it is possible to suppress deterioration of battery performance due to cracking of the electrode. [Brief description of the drawings]

[0013] [Figure 1] 2 is a cross-sectional view of the drying furnace 30 cut along the transport direction X of the current collector foil 10. FIG. [Diagram 2] 2 is a diagram illustrating an irradiation area A of a heat source irradiated onto a coating film 20. FIG. [Diagram 3]1A and 1B are views showing how lasers L1 and L2 are irradiated onto a coating film 20. (A) is a view of the coating film 20 observed from the side. (B) is a view of the coating film 20 observed from above. [Figure 4] 1A and 1B are views showing how a laser L and hot air streams W1 and W2 are irradiated onto a coating film 20. (A) is a view of the coating film 20 observed from the side. (B) is a view of the coating film 20 observed from above. [Diagram 5] FIG. 13 shows the results of an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] [Electrode manufacturing method] The method for producing an electrode according to the present disclosure will be described using one embodiment.

[0015] A manufacturing method of an electrode in one embodiment includes a coating step of coating a current collecting foil 10 with a slurry obtained by dispersing an electrode material in a solvent to obtain a coating film 20, and a drying step of drying the coating film 20 while transporting the current collecting foil 10 on which the coating film 20 has been formed inside a drying furnace 30.

[0016] <Coating process> The coating process is a process in which a slurry obtained by dispersing an electrode material in a solvent is applied onto the current collector foil 10 to obtain a coating film 20. Such coating processes are well known. A typical example will be described below, but the coating process is not limited to this form.

[0017] The current collector foil 10 is not particularly limited as long as it is a sheet-shaped conductive member. For example, the current collector foil 10 may be a metal foil made of a metal such as stainless steel, copper, aluminum, titanium, or nickel. The metal foil may be made of an alloy containing two or more of these metals. The metal foil may also be subjected to a surface treatment such as plating. The current collector foil 10 may be made of two or more sheets of metal foil. In this case, the metal foils may be joined by an adhesive or the like, or may be joined by pressing or the like.

[0018] The electrode material includes 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 may be appropriately selected from known materials depending on 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. An example of the composite oxide is olivine-type lithium iron phosphate (LiFePO4). The negative electrode active material is not particularly limited, and may be appropriately selected from known materials depending on the target battery performance. Examples include carbon such as graphite, artificial graphite, highly oriented graphite, mesocarbon microbeads, hard carbon, and soft carbon, metal compounds, elements or compounds thereof that can be alloyed with lithium, and boron-added carbon. Examples of elements that can be alloyed with lithium include silicon and tin.

[0019] When the electrode material contains a positive electrode active material, the final electrode is a positive electrode, whereas when the electrode material contains a negative electrode material, the final electrode is a negative electrode.

[0020] The electrode material may optionally contain a conductive assistant. The conductive assistant is not particularly limited and may be appropriately selected from known materials depending on the intended battery performance. Examples of the conductive assistant include acetylene black, carbon black, graphite, etc.

[0021] The electrode material may optionally contain a binder. The binder is not particularly limited and may be appropriately selected from known materials according to the intended battery performance. For example, fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluorine rubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, acrylic resins such as poly(meth)acrylic acid, styrene-butadiene rubber (SBR), carboxymethyl cellulose, alginates such as sodium alginate and ammonium alginate, water-soluble cellulose ester crosslinked bodies, and starch-acrylic acid graft polymers can be mentioned.

[0022] The electrode material may optionally contain a solid electrolyte. The solid electrolyte is not particularly limited and may be appropriately selected from known materials depending on the intended battery performance. For example, oxide solid electrolytes and sulfide solid electrolytes may be mentioned.

[0023] The solvent is not particularly limited as long as it can disperse the electrode material appropriately. For example, water and organic solvents can be used. Examples of organic solvents include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, methanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, and tetrahydrofuran. These solvents may be used alone or in combination of two or more.

[0024] The coating method is not particularly limited as long as the slurry can be applied in a thin film form to the current collector foil 10. For example, the slurry can be applied to the current collector foil 10 in any thickness using a known coating device.

[0025] <Drying process> The drying step is a step of drying the coating film 20 while transporting the current collector foil 10 on which the coating film 20 has been formed inside a drying furnace 30. An electrode is obtained by the drying step. A schematic diagram for explaining the drying step is shown in Fig. 1. Fig. 1 is a cross-sectional view of the drying furnace 30 cut along the transport direction X of the current collector foil 10.

[0026] 1, the current collector foil 10 on which the coating film 20 has been formed is transported using a plurality of transport rollers 31 installed inside a drying furnace 30. During this process, the coating film 20 is dried by a heat source device 32 installed above the coating film 20. Typically, a plurality of heat source devices 32 are installed along the transport direction of the current collector foil 10. The transport speed is not particularly limited, but is, for example, in the range of 1 to 10 m / sec.

[0027] The heat source device 32 is a device that irradiates a heat source to the coating film 20. In Fig. 1, multiple heat source devices 32 are installed in the drying furnace 30, so the coating film 20 is irradiated with the heat source multiple times. However, the number of heat source devices 32 may be changed appropriately depending on the purpose, and at least one is sufficient. In other words, the drying process requires that the heat source be irradiated to the coating film 20 at least once.

[0028] Here, we will explain the irradiation range of the heat source irradiated from the heat source device 32 to the coating film 20. A diagram explaining the irradiation range A is shown in Fig. 2. As shown in Fig. 2, the irradiation range A has two regions divided by a straight line that equally bisects the length of the irradiation range A in the transport direction X, with the region located on the upstream side of the transport direction X being the upstream region A1 and the region located on the downstream side of the transport direction X being the downstream region A2.

[0029] The ratio (E1 / E2) of the energy density E1 of the heat source irradiated to the upstream region A1 to the energy density E2 of the heat source irradiated to the downstream region A2 is set to 1.2 or more and 3.0 or less. This makes it possible to suppress cracking of the resulting electrode. From the viewpoint of further enhancing the effect, E1 / E2 may be set to 1.5 or more and 2.0 or less. If E1 / E2 is less than 1.2, the temperature of the coating film 20 in the downstream region A2 becomes high (the solvent evaporation rate becomes high), and electrode cracking may not be suppressed. If E1 / E2 exceeds 3.0, the temperature of the coating film 20 in the upstream region A1 becomes high (the solvent evaporation rate becomes high), and electrode cracking may not be suppressed.

[0030] The reason for setting E1 / E2 within a predetermined range in this way will be explained. In the heat source irradiation area A, when the upstream area A1 and the downstream area A2 are both irradiated with a heat source having the same energy density, the temperature of the coating film 20 is higher in the downstream area A2 than in the upstream area A1. This is because the irradiation time of the heat source is longer for the coating film 20 in the downstream area A2 than for the coating film 20 in the upstream area A1. The evaporation rate of the solvent in the coating film 20 increases as the temperature of the coating film 20 increases. If the evaporation rate of the solvent is too fast, the electrode is more likely to crack or break. Therefore, the coating film 20 (the electrode to be manufactured) is more likely to crack in the downstream area A2 where the temperature is high.

[0031] Therefore, in the drying process of one embodiment, the energy density of the heat source irradiated to the upstream region A1 is set to be greater than the energy density of the heat source irradiated to the downstream region A2, so that the evaporation rate of the solvent in the upstream region A1 is increased and the evaporation rate of the solvent in the downstream region A2 is decreased, thereby making it possible to suppress cracking of the electrode.

[0032] The length of the irradiation area A in the width direction Y is not particularly limited, but is usually set to be the same as the width direction length of the coating film 20. The length of the irradiation area A in the transport 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.

[0033] The energy density E1 of the heat source irradiated to the upstream region A1 is, for example, not less than 1 and not more than 5. The energy density E2 of the heat source irradiated to the downstream region A2 is, for example, not less than 0.33 and not more than 4.2.

[0034] The heat source irradiated from the heat source device 32 is a laser or hot air. In order to set the energy densities E1 and E2 to different values, a combination of multiple heat sources is usually used. For example, there are (1) a heat source including two types of lasers with different energy densities and (2) a heat source including a combination of a laser and hot air.

[0035] Examples of the laser include a fiber laser, a direct laser, and a VCSFL laser. The laser may be a laser with high light-focusing properties. The frequency of laser irradiation in the transport direction may be pulsed or continuous. Since the laser has a higher energy density than hot air, it has the advantage of being able to impart a higher energy density to the coating film 20.

[0036] The temperature of the hot air is not particularly limited, but is, for example, in the range of 100° C. to 160° C. The wind speed of the hot air is not particularly limited, but is, for example, more than 0 m / s and not more than 15 m / s. Although the energy density of the hot air is not as high as that of a laser, it can expel the evaporated solvent to the outside of the drying furnace 30, and therefore can promote the drying of the coating film 20.

[0037] The energy density of the laser and hot air is calculated as follows. (Laser energy density) = Laser irradiation power (W) / Laser irradiation area (cm 2 ) (Hot air energy density) = Energy required to dry the coating film 20 (J / cm 2 ) / hot air drying time (s)

[0038] (1) A further explanation will be given of the case where two types of lasers with different energy densities are used as heat sources. When two types of lasers with different energy densities are used as heat sources, laser L1 is irradiated to the upstream region A1, and laser L2 is irradiated to the downstream region. In this case, the energy density of each laser is set so that E1 / E2 falls within a predetermined range. Figure 3 shows how lasers L1 and L2 are irradiated onto a coating film 20. (A) is a view of the coating film 20 observed from the side, and (B) is a view of the coating film 20 observed from above.

[0039] When using two types of lasers with different energy densities, a heat source device 132 (FIG. 3) may be used, which is an example of the heat source device 32. That is, the heat source device 132 includes an upstream laser irradiation section 133 capable of irradiating the upstream region A1 with a laser L1 and a downstream laser irradiation section 134 capable of irradiating the downstream region A2 with a laser L2.

[0040] In addition to the two types of lasers with different energy densities, hot air may also be used as a heat source. This allows a large amount of evaporated solvent to be discharged outside the drying furnace 30, accelerating the drying of the coating film 20. In this case, the heat source device includes a hot air irradiation section in addition to an upstream laser irradiation section and a downstream laser irradiation section. Also, three or more types of lasers may be used as a heat source.

[0041] (2) A case where a laser and hot air are used as a heat source will be described. When a laser and hot air are used as a heat source, the entire irradiation area A is irradiated with a laser L, while 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 is 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 is the sum of the energy density of the laser L1 and the energy density of the downstream hot air W2. Figure 4 shows how the laser L and the hot air W1 and W2 are irradiated to the coating film 20. (A) is a view of the coating film 20 observed from the side, and (B) is a view of the coating film 20 observed from above.

[0042] In Figure 4, the upstream hot air W1 is irradiated toward the downstream side in the transport direction, and the downstream hot air W2 is irradiated toward the upstream side in the transport direction. However, this is not limited to this form. The upstream hot air W1 may be irradiated toward the upstream side in the transport direction, and the downstream hot air W2 may be irradiated toward the downstream side in the transport direction. The upstream hot air W1 and the downstream hot air W2 may be irradiated in different directions as shown in Figure 4, or may be irradiated in the same direction.

[0043] Here, the wind speed of the upstream hot air W1 may be typically set to be faster than the wind speed of the downstream hot air W2. This can promote the discharge of the solvent evaporated in the upstream region A1 to the outside of the drying furnace 30, thereby increasing the solvent evaporation rate in the upstream region A1 and enhancing the effect of suppressing electrode cracking. The wind speed of the upstream hot air W1 may be, for example, 3 m / s or more and 15 m / s or less. The wind speed of the downstream hot air W2 may be, for example, more than 0 m / s and 3 m / s or less.

[0044] When a laser and hot air are used as the heat source, a heat source device 232 (FIG. 4) may be used, which is an example of the heat source device 32. That is, the heat source device 232 includes an irradiation section 233 capable of irradiating the entire irradiation area A with a laser L, an upstream hot air irradiation section 234 capable of irradiating the upstream area A1 with upstream hot air W1, and a downstream hot air irradiation section 235 capable of irradiating the downstream area A2 with downstream hot air W2.

[0045] As described above, the hot air may include the upstream hot air W1 irradiated to the upstream region A1 and the downstream hot air W2 irradiated to the downstream region A2, but the hot air may be only the upstream hot air W1 irradiated to the upstream region A1 (the wind speed of the downstream hot air W2 is 0). Even in this case, if E1 / E2 can be set within a predetermined range, cracking of the electrode can be suppressed.

[0046] The method for manufacturing an electrode according to the present disclosure has been described above using one embodiment. According to the method for manufacturing an electrode according to the present disclosure, peeling of the electrode from the current collecting foil can be suppressed.

[0047] [Battery manufacturing method] The manufacturing method of the battery of the present disclosure will be described using one embodiment.

[0048] One embodiment is a method for producing a battery, comprising: an electrode production step of obtaining an electrode by using the above-mentioned electrode production method; and a battery production step of assembling a battery using the obtained electrode. Since the electrode production step has been described above, the battery production step will be described below.

[0049] The battery preparation process is a process of assembling a battery using the electrode obtained in the electrode preparation process. Such a battery preparation process is publicly known. Below, a typical example in which the electrode obtained in the electrode preparation process is a positive electrode will be described, but the present invention is not limited to this form.

[0050] When the electrode obtained in the electrode preparation step is a positive electrode, a battery is prepared using a separately prepared negative electrode and electrolyte layer.

[0051] When the electrolyte is a liquid electrolyte, a separator is placed between the positive electrode and the negative electrode, and then an electrolytic solution is supplied to the separator to fabricate a battery. The separator is mainly a polyolefin-based porous sheet. The electrolytic solution is a non-aqueous solvent in which a supporting salt is dissolved. Examples of the non-aqueous solvent include carbonates, ethers, and esters. Examples of the supporting salt include LiPF6, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethane)sulfonimide (LiTFSI).

[0052] When the electrolyte is a solid electrolyte, a battery can be fabricated by disposing a solid electrolyte layer between a positive electrode and a negative electrode. The solid electrolyte layer includes a solid electrolyte. The solid electrolyte layer may also include a binder. The solid electrolyte and the binder may be appropriately selected from the solid electrolytes and binders described above.

[0053] The manufacturing method of the battery of the present disclosure has been described above using one embodiment. Since the manufacturing method of the battery of the present disclosure manufactures the electrodes based on the manufacturing method of the electrodes, peeling of the electrodes from the current collecting foil is suppressed. Therefore, the manufacturing method of the battery of the present disclosure can suppress the deterioration of the battery performance due to the peeling of the electrodes. EXAMPLES

[0054] A slurry obtained by dispersing the electrode material in a solvent (water) was applied onto the current collector foil to obtain a coating film, and the current collector foil with the coating film formed thereon was introduced into a drying furnace to dry the coating film. The width of the coating film was adjusted to 1160 mm.

[0055] The heat source device of the drying furnace was constructed following the configuration of Figures 1 and 4. That is, a laser L (energy density: 1.0 W / cm) was irradiated to the entire irradiation area A. 2 ), and upstream hot air W1 (energy density: 0.38 W / cm 2 The upstream hot air irradiation section and downstream area A2 can irradiate hot air W2 (energy density: 0.05 W / cm 2A heat source device equipped with a downstream hot air irradiation section capable of irradiating 1000 W of heat from the downstream region A2 was used. The irradiation area A was set to a width direction length of 1160 mm and a transport direction length of 900 mm. The upstream hot air W1 was set to a temperature of 120°C and a wind speed of 15 m / s. The downstream hot air W2 was set to 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 region A1 to the energy density E2 of the heat source irradiated to the downstream region A2 was 1.31.

[0056] The results are shown in Figure 5. The electrode temperature (coating temperature) was measured on the electrode surface using a radiation thermometer. The moisture content was calculated from the amount of moisture loss obtained by successively observing the amount of mass loss while drying the electrode placed on a balance. The comparative example was an electrode with an energy density of 1.5 W / cm. 2 This is an example of constant irradiation of a heat source.

[0057] 5, in the comparative example, the electrode temperature rose at a constant rate in the irradiation area A, and the rate of decrease in moisture content was gentle in the upstream area A1 and rapid in the downstream area A2. Therefore, in the comparative example, there was a risk of cracks occurring in the electrode in the downstream area A2.

[0058] In contrast, in the Example, the electrode temperature (coating temperature) was almost constant in the irradiation area A, and the rate of decrease in moisture content was also almost constant. Comparing the Example and the Comparative Example, the rate of decrease in moisture content in the upstream area A1 was faster in the Example, and the rate of decrease in moisture content in the downstream area A2 was slower in the Example. Thus, in the Example, the electrode temperature and the solvent evaporation rate could be adjusted by adjusting E1 / E2 using a laser and hot air as heat sources. This makes it possible to suppress cracking of the electrode. [Explanation of symbols]

[0059] 10 Current collecting foil 20 Coating 30 Drying oven 31 Transport roller 32, 132, 232 Heat source equipment 133 Upstream laser irradiation section 134 Downstream laser irradiation section 233 Laser irradiation unit 234 Upstream hot air irradiation section 235 Downstream hot air irradiation section

Claims

1. a coating step of coating a slurry obtained by dispersing an electrode material in a solvent onto a current collector foil to obtain a coating film; a drying step of drying the coating film while transporting the current collecting foil on which the coating film has been formed in a drying furnace, The drying step comprises irradiating the coating with a heat source at least once, 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 transport direction into two equal parts, and when the region arranged on the upstream side in the transport direction is defined as an upstream region and the region arranged on the downstream side in the transport direction is defined as a downstream region, A 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. A method for manufacturing an electrode.

2. The method for manufacturing an electrode according to claim 1 , wherein in the drying step, the heat source is a laser and hot air.

3. The hot air includes upstream hot air irradiated to the upstream region and downstream hot air irradiated to the downstream region, The wind speed of the upstream hot air is made faster than the wind speed of the downstream hot air. A method for producing the electrode according to claim 2.

4. An electrode production step of producing an electrode by the electrode production method according to any one of claims 1 to 3; A battery fabrication step of assembling a battery using the electrode. How batteries are manufactured.

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