Method and apparatus for manufacturing battery electrode

Abstract

To produce a coated body having good characteristics.SOLUTION: A method for producing a battery electrode includes a step of applying a first coating liquid containing an electrode active material to a first surface of a substrate to form a first coating liquid layer, a step of spraying a second coating liquid containing an alkali silicate onto the first coating liquid layer to form a second coating liquid layer, and a step of drying the first coating liquid layer and the second coating liquid layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for manufacturing battery electrodes, and more particularly to a method and an apparatus for manufacturing battery electrodes used for battery separators and the like. [Background technology]

[0002] In recent years, the use of batteries such as lithium-ion batteries has become widespread in automobiles and infrastructure applications. In batteries such as lithium-ion batteries, the positive and negative electrode materials are separated by a porous film called a separator. The separator has, for example, multiple micropores large enough for lithium ions to pass through, allowing the lithium ions to move between the positive and negative electrode materials through these pores, enabling repeated charging and discharging. In this way, the separator serves to separate the positive and negative electrode materials and prevent short circuits.

[0003] Furthermore, if the temperature inside the battery becomes too high for some reason, the micropores in the separator close, stopping the movement of lithium ions and shutting down the battery (shutdown function).

[0004] In this way, the separator plays the role of a safety device for the battery, and it is therefore important to improve the mechanical strength and heat resistance of the separator.

[0005] For example, Patent Document 1 (JP 2016-183209 A) discloses a technique for forming a coating layer containing inorganic particles and a binder resin composition on at least one surface of a polyolefin resin porous film.

[0006] Furthermore, Patent Document 2 (JP 2019-72666 A) discloses a coating device for preventing multiple coating liquids from mixing together, which includes a first die that ejects a first coating liquid from a first outlet and applies the first coating liquid to a sheet in contact with a backup roll to form a first layer, and a second die that ejects a second coating liquid from a second outlet and applies the second coating liquid onto the first layer on a sheet in contact with a backup roll to form a second layer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-183209 [Patent Document 2] Japanese Patent Application Publication No. 2019-72666 Summary of the Invention [Problem to be solved by the invention]

[0008] The present inventors have been conducting research and development into coating techniques for forming a coating layer on the surface of a substrate in order to improve the properties of coated bodies such as battery separators.

[0009] During the research and development process, we discovered that when multiple coating layers are used, there is a problem of coating liquid mixing, and after extensive research into how to solve this problem, we have discovered an effective coating technology.

[0010] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0011] The method for manufacturing a battery electrode disclosed in the present application is characterized by comprising the steps of applying a first coating liquid containing an electrode active material to a first surface of a substrate to form a first coating liquid layer, spraying a second coating liquid containing an alkali silicate onto the first coating liquid layer to form a second coating liquid layer, and drying the first coating liquid layer and the second coating liquid layer.

[0012] The present application discloses a battery electrode manufacturing apparatus including a first coating unit that applies a first coating liquid containing an electrode active material to a first surface of the substrate to form a first coating liquid layer, a second coating unit that sprays a second coating liquid containing an alkali silicate onto the first coating liquid layer to form a second coating liquid layer, and a drying unit that dries the first coating liquid and the second coating liquid. The first coating liquid contains a first filler and a second filler, and the second coating unit has a nozzle that sprays the second coating liquid, and when spraying the second coating liquid, a voltage of 1 kV or more is applied between the nozzle and the substrate. [Effects of the Invention]

[0013] According to the method for producing a coated body disclosed in the present application, a coated body with good properties can be produced.

[0014] According to the coated body manufacturing apparatus disclosed in the present application, a coated body with good properties can be manufactured. [Brief explanation of the drawings]

[0015] [Figure 1] 1A to 1C are cross-sectional views showing a manufacturing process of a coated body according to a first embodiment. [Figure 2] 1 is a diagram schematically illustrating the configuration of a coated body manufacturing apparatus according to a first embodiment. [Figure 3] FIG. 2 is a cross-sectional view showing a gravure coating device. [Figure 4] FIG. 1 is a cross-sectional view showing a spray coating device. [Figure 5] FIG. 1 is a cross-sectional view showing a spray coating device. [Figure 6] FIG. 2 is a diagram schematically illustrating the configuration of a coated body manufacturing apparatus of a comparative example. [Figure 7] FIG. 1 is a diagram showing the configuration of a coated body manufacturing apparatus of a comparative example. [Figure 8] FIG. 1 is a cross-sectional view showing a spray coating device of Application Example 1. [Figure 9] FIG. 1 is a cross-sectional view showing a spray coating device of Application Example 1. [Figure 10] FIG. 1 is a cross-sectional view showing a spray coating device of Application Example 1. [Figure 11] FIG. 1 is a diagram showing the relationship between the movement of lithium ions (Li+) and charge / discharge. [Figure 12] FIG. 1 is a cross-sectional perspective view showing the configuration of a lithium ion battery. [Figure 13] FIG. 1 is a schematic diagram showing the configuration of a porous film manufacturing apparatus (system). [Figure 14] FIG. 10 is a diagram showing the precipitation state of cellulose (Ceolus) in the fourth embodiment. [Figure 15] FIG. 10 is a diagram showing the precipitation state of cellulose in the fifth embodiment. [Figure 16] FIG. 10 is a diagram showing the precipitation state of cellulose in the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, the embodiments will be described in detail with reference to examples and drawings. In all drawings for explaining the embodiments, the same reference numerals are used to designate components having the same functions, and repeated description thereof will be omitted.

[0017] (Embodiment 1) Fig. 1 is a cross-sectional view showing a manufacturing process of a coated body according to the present embodiment, and Fig. 2 is a diagram schematically showing the configuration of an apparatus for manufacturing a coated body according to the present embodiment.

[0018] First, the process of forming a coated body will be described with reference to FIG.

[0019] As shown in FIG. 1(A), a substrate 1 made of a porous film is prepared. The porous film serving as the substrate 1 is made of, for example, a polyolefin-based resin. The thickness of the substrate 1 is, for example, about 5 μm to 50 μm, and the width is, for example, about 100 mm to 3000 mm. The pore size distribution of the micropores is, for example, about 10 nm to 10 μm, and the average pore size is, for example, about 10 nm to 900 nm. The Gurley value of the substrate 1 is, for example, about 100 to 300 sec / 100 cc.

[0020] Next, as shown in FIG. 1(B), a first coating liquid is applied to the surface of the substrate 1 to form a first coating liquid layer 3a. The first coating liquid contains a filler and a dispersion medium. Examples of fillers that can be used include inorganic materials such as alumina, silica, aluminum hydroxide, and boehmite, as well as cellulose (including cellulose nanofibers), carbon fiber, carbon nanotubes, carbon nanofibers, graphene, fullerene, and aramid fiber. Cellulose in which the hydrophilic groups have been replaced with hydrophobic groups may also be used. Examples of dispersion mediums that can be used include aqueous and organic solvents. A binder may also be added. Examples of binders that can be used include side-chain or cyclic polymer resins, acrylic resins, and thermoplastic fluoropolymers. A gravure coating machine, for example, can be used as the coating device. Furthermore, in addition to the filler and binder, SBR (styrene-butadiene rubber) or a highly ionic conductive polymer may also be added.

[0021] Next, as shown in FIG. 1(C), a second coating liquid is applied to the surface of the substrate 1 to form a second coating liquid layer 4a. The second coating liquid contains water glass and a solvent. Water glass is an aqueous solution of silicate of an alkali metal or alkaline earth metal. For example, sodium silicate (sodium silicate, Na2O·nSiO2 (n=2-4)) or silicate (alkali silicate) containing Li, K, Rb, Ba, Ca, Mg, Sr, etc. instead of Na can be used. One type can be used alone, or two or more types can be used in combination. Aqueous solvents or organic solvents can be used as the solvent. A binder can also be added. Resins (fluorine-based resins) such as PVdF (polyvinylidene fluoride) can be used as the binder.

[0022] Next, as shown in Figure 1(D), the first coating fluid layer 3a and the second coating fluid layer 4a on the substrate 1 are dried using a heater 10 or the like to form a laminated film of coating films 3b and 4b. Through the above steps, a coated body (separator) 5 consisting of the substrate (porous film) 1 and coating films 3b and 4b can be formed. Coating films 3b and 4b are breathable, and the Gurley value (air permeability, [sec / 100cc]) of coating body 5 is 10 or more and 3000 or less, ensuring breathability.

[0023] The case where the coating layer is formed using the apparatus (system) shown in FIG. 2 will be described below.

[0024] As shown in FIG. 2, the coated body manufacturing apparatus has an unwinding section (discharge section) UW that unwinds the substrate 1 and a winding section WD that winds the substrate 1. The substrate 1 is continuously arranged from the unwinding section UW to the winding section WD, and between the unwinding section UW and the winding section WD, coating films 3b and 4b are formed on the surface (first surface) of the substrate 1, completing the coated body 5. This coated body manufacturing apparatus can continuously process the substrate 1 in a roll shape (wound strip shape), allowing for efficient formation of the coated body. Note that in this specification, the unwinding section UW side may be referred to as the upstream side, and the winding section (carry-in section) WD may be referred to as the downstream side.

[0025] Specifically, a first coating processing section (20), a second coating processing section (30), and a drying processing section (40) are arranged between the unwinding section UW and the winding section WD. The substrate 1 is guided by a plurality of rolls (guide rolls) R and processed in each processing section, and a coating film 3b and a coating film 4b are formed on the surface of the substrate 1. These sections are described in detail below.

[0026] The substrate 1 unwound from the unwinding section UW is guided by a roll R and transported to the first coating section (20). A gravure coating device is disposed in the first coating section (20), and a first coating liquid is applied (coated) onto a first surface of the substrate 1 to form a first coating liquid layer 3a.

[0027] The substrate 1 on which the first coating fluid layer 3a has been formed is guided by a roll R and transported to the second coating processing section (30). A spray coating device is disposed in the second coating processing section (30), and a second coating fluid is applied (coated) onto the first coating fluid layer 3a on the first surface of the substrate 1, thereby forming a second coating fluid layer 4a.

[0028] The substrate 1 having the first coating fluid layer 3a and the second coating fluid layer 4a formed thereon is transported to a drying section (40). A drying oven (conveyor-type drying oven) 40 is disposed in the drying section (40), and the liquid components of the first coating fluid layer 3a and the second coating fluid layer 4a on the substrate 1 transported by the rolls R are vaporized to form coating films 3b and 4b. For example, the drying oven has a drying chamber (cover), into which heated air is introduced from a nozzle (not shown). The temperature of the heated air is controlled by a heating section (such as a heater) (not shown).

[0029] In this manner, the belt-shaped substrate 1 is treated in each treatment section while being guided by a plurality of rolls (guide rolls) R, and a coated body 5 is formed.

[0030] In this embodiment, a gravure coating device is used in the first coating processing section (20) to perform contact coating processing, and a spray coating device is used in the second coating processing section (30) to perform non-contact coating processing, thereby enabling the first coating fluid layer 3a and the second coating fluid layer 4a to be formed with high precision.

[0031] FIG. 3 is a cross-sectional view of a gravure coating device. The gravure coating device shown in FIG. 3 is a vertical coating device in which a chamber (tank) 20b is arranged vertically (parallel to the direction of gravity). This device includes a chamber (tank) 20b for storing a coating liquid 20a, a coating roll (gravure roll) CR that is partially immersed in the chamber (tank) 20b, a first blade 20c for preventing the coating liquid 20a from splashing and adjusting the amount of liquid on the roll surface, and a second blade 20c for preventing the coating liquid from leaking from the gap between the coating liquid in the chamber (tank) 20b and the coating roll (gravure roll). The first blade 20c is arranged on the rotational direction side of the coating roll CR so that the angle and pressing pressure of the first blade 20c can be adjusted to adjust the amount of coating liquid 20a attached to the surface of the coating roll CR. Then, the first coating liquid layer 3a is formed by transferring the coating liquid 20a attached to the surface of the coating roll CR to the surface of the substrate 1. The gravure coating device shown in Fig. 3 may be either a vertical type or a horizontal type. In the case of a horizontal type, the second blade for preventing leakage of the coating liquid is not required, and only the first blade 20c for preventing scattering of the coating liquid 20a and adjusting the amount of liquid on the roll surface is provided.

[0032] Figures 4 and 5 are cross-sectional views showing a spray coating device. The spray coating device shown in Figures 4 and 5 is a solution coating device that utilizes the electrospray phenomenon.

[0033] As shown in FIG. 4, the spray coating device sprays the second coating liquid supplied from the liquid supply device LS onto the substrate (first coating liquid layer 3a) 1 from a nozzle N together with a gas. The nozzle N extends, for example, in the depth direction of the paper, and the nozzle hole has a rectangular shape with its long side in the depth direction of the paper. The gas may be one or more types of gas selected from an inert gas, oxygen, and air. The moisture content (humidity) of this gas is preferably 0 to 90%.

[0034] As shown in FIG. 5, a high voltage HV is applied between the nozzle N and the substrate 1. Instead of the substrate 1, the high voltage HV may be applied between the nozzle N and a roller R with which the substrate 1 is in contact or a conveyor belt (not shown) disposed between the substrate 1 and the roller R. When a high voltage HV (1 kV or higher) is applied, a strong electric field is generated at the nozzle tip, charging the solution surface at the nozzle tip. This results in the formation of a conical meniscus called a Taylor cone due to the interaction between the charged solution surface and the electric field. Further increasing the electric field causes the electrostatic repulsion at the liquid surface to exceed the surface tension, resulting in the ejection of fine droplets from the tip of the Taylor cone. The solvent evaporates from these fine droplets in a short time, increasing the charge density of the droplets. This causes electrostatic fragmentation of the droplets, further reducing their size, and they adhere to the opposing substrate 1 (electrode), forming a second coating liquid layer 4a. For example, the diameter of the droplets on the coating surface is 0.01 to 60 μm.

[0035] In this way, by using a spray coating device that utilizes the electrospray phenomenon, the second coating fluid layer 4a can be formed uniformly with good controllability.

[0036] Fig. 6 is a diagram schematically illustrating the configuration of a coating material manufacturing apparatus according to a comparative example. As shown in Fig. 6, it is possible to form the first coating fluid layer 3a and the second coating fluid layer 4a using a coating apparatus having two gravure coating units (20A, 20B). However, because gravure coating is a contact coating process, when applying the second coating fluid, the roll CR comes into contact with the first coating fluid layer 3a, disturbing the first coating fluid layer 3a and possibly creating an undesirable mixed layer of the coating fluids.

[0037] Fig. 7 is a diagram showing a schematic configuration of a coating body manufacturing apparatus of a comparative example. As a coating apparatus capable of non-contact coating processing, a coating apparatus using a rotating disk (rotor) 90 as shown in Fig. 7 can be used. However, in this case, it is difficult to control multiple rotating disks and to control the size reduction of droplets, making it difficult to form a coating liquid layer with good controllability.

[0038] In contrast, in the present embodiment, a spray coating device utilizing the electrospray phenomenon is used as the coating device in the subsequent stage, thereby enabling the second coating fluid layer 4a to be formed uniformly and with good controllability. For example, it is possible to form a thin second coating fluid layer 4a (a layer with a thickness of about 0.01 to 10 μm).

[0039] Furthermore, the spray coating device of this embodiment shown in Figure 4 has a spray area AS where ultrafine droplets (mist) are sprayed, an air curtain area A1 located upstream of this spray area AS, and an air curtain area A1 located downstream of the spray area AS. In the air curtain area A1, air is sprayed in the direction a of the spray area AS (nozzle N). In other words, an air nozzle is arranged tilted toward the spray area AS (nozzle N), and air is sprayed through this air nozzle toward the spray area AS. The angle (θ) between the direction perpendicular to the substrate 1 and the direction a, or in other words, the angle (θ) between the direction perpendicular to the substrate 1 and the nozzle, is 0.1° or more and 90° or less. In other words, the angle (θ) between the arrangement direction of the nozzle N (vertical direction) and the tilt direction of the air nozzle is 0.1° or more and 90° or less. As the transport speed of the substrate 1 changes, the amount of accompanying flow flowing into the air curtain area A1 located upstream of the spray area AS, the amount of accompanying flow flowing into the spray area AS, and the amount of accompanying flow flowing into the air curtain area A1 located downstream of the spray area AS change, so it is desirable to be able to arbitrarily change the tip position of the air nozzle and the nozzle angle (θ).

[0040] In this way, by providing the air curtain area A1, it is possible to prevent mist from leaking upstream or downstream of the spray area AS. In particular, the substrate 1 is transported through openings (windows, gaps, substrate inlets, substrate outlets) provided below the walls separating each area (each chamber A1, AS, A1). As the substrate 1 is transported, an accompanying flow, which is wind flowing in the transport direction (travel direction) of the substrate 1, is generated. Because the mist leaks on this accompanying flow, it is particularly preferable to provide the air curtain area A1 downstream of the spray area AS.

[0041] As mentioned above, in the apparatus shown in Fig. 4, the air curtain areas A1 are provided on both the upstream and downstream sides of the spray area AS, but it may be provided only on the downstream side. Also, in the apparatus shown in Fig. 5, the air is blown obliquely, but it may also be perpendicular (θ=90°) to the substrate 1.

[0042] (Embodiment 2) In this embodiment, an application example of the coated body manufacturing apparatus of the first embodiment will be described.

[0043] (Application example 1) Figures 8 to 10 are cross-sectional views showing the spray coating device of this application example. Z indicates an accompanying flow, with Figure 9 showing the upstream side and Figure 10 showing the downstream side. In the first embodiment (Figure 4), the air blowing directions in the air curtain areas A1 upstream and downstream of the spray area AS were symmetrical (the angle θ was the same), but as shown in Figures 8 to 10, the air blowing angle θb on the downstream side may be greater than the air blowing angle θa on the upstream side (θb > θa).

[0044] In this way, by increasing the air blowing angle θb on the downstream side, it is possible to improve the effect of preventing leakage on the downstream side where mist is likely to leak due to the accompanying flow Z.

[0045] Furthermore, when adjusting the air blowing angle (θa, θb) on the upstream and downstream sides as described above, it becomes easier to tilt the air nozzle by making the length B of the air curtain area A1 on the downstream side greater than the length A of the air curtain area A1 on the upstream side (B>A) in terms of the length (A, B) of the air curtain area A1 in the conveying direction of the substrate 1.

[0046] (Application example 2) The air volume of the air nozzle may be increased in the downstream air curtain area A1, which is more susceptible to the influence of the accompanying flow. The air volume is the amount of air (m 3 For example, the air volume of the air nozzles in the downstream air curtain area A1 may be set to be greater than the air volume of the air nozzles in the upstream air curtain area A1.

[0047] (Application example 3) The number of air nozzles may be increased in the downstream air curtain area A1, which is more susceptible to the influence of accompanying flows. For example, in the downstream air curtain area A1, multiple air nozzles may be arranged in the depth direction of the paper in Figure 4, and the number of air nozzles may be greater than the number of air nozzles in the upstream air curtain area A1. In this case, if the air volume per air nozzle is the same, the air volume of the air nozzles in the downstream air curtain area A1 will be greater than the air volume of the air nozzles in the upstream air curtain area A1.

[0048] The plurality of air nozzles is referred to as an air nozzle group. The plurality of air nozzles in the air nozzle group are arranged, for example, in a direction perpendicular to the conveying direction. The air blower used for the air nozzle group may be a single blower for the plurality of nozzles (with a constant air volume for all nozzles). Alternatively, a system in which one blower is connected to one nozzle may be used. In this case, the air volume can be changed for each nozzle, further suppressing the outflow of accompanying flows.

[0049] (Embodiment 3) In this embodiment, a description will be given of an application example of the coated body described in Embodiment 1. A coated body formed using the coated body manufacturing apparatus described in Embodiment 1 can be applied as a separator to, for example, a lithium ion battery.

[0050] Figure 11 shows the lithium ion (Li +) and the relationship between charge and discharge. FIG. 12 is a cross-sectional perspective view showing the configuration of a lithium-ion battery. The lithium-ion battery shown in FIG. 12 has a cylindrical can 106, which houses an electrode group in which strip-shaped positive electrode material 101 and negative electrode material 103 are wound with a coating (separator) 5 interposed therebetween. A positive electrode current collector tab on the upper end surface of the electrode group is joined to a positive electrode cap. A negative electrode current collector tab on the lower end surface of the electrode group is joined to the bottom of the can 106. An insulating coating (not shown) is provided on the outer periphery of the can 106. An electrolyte (not shown) is poured into the can 106. Although a cylindrical battery has been described as an example here, there are no limitations on the battery configuration, and the battery may be, for example, a prismatic or laminated type.

[0051] As described above, the lithium-ion battery includes a positive electrode material 101, a negative electrode material 103, a coating (separator) 5, and an electrolyte solution, with the coating (separator) 5 disposed between the positive electrode material 101 and the negative electrode material 103. The coating (separator) 5 has many micropores. For example, during charging, i.e., when a charger is connected between the positive electrode (positive electrode cap) and the negative electrode (bottom of the can 106), lithium ions inserted into the positive electrode active material are desorbed and released into the electrolyte solution. The lithium ions released into the electrolyte solution move through the electrolyte solution, pass through the micropores in the separator, and reach the negative electrode. The lithium ions that reach the negative electrode are inserted into the negative electrode active material that constitutes the negative electrode.

[0052] In this way, lithium ions move between the positive and negative electrode materials (between electrodes E1 and E2) through micropores (not shown) provided in the coated body (separator) 5, allowing repeated charging and discharging (see also FIG. 11). In particular, when the thickness of the coated body (separator) 5 shown in FIG. 11 is large, the resistance when lithium ions pass through the membrane increases, resulting in a decrease in battery output characteristics. Furthermore, the amount of lithium ion movement decreases, resulting in a decrease in the amount of electron movement, resulting in a decrease in battery capacity. In contrast, by using a spray coater utilizing the electrospray phenomenon as the subsequent coater described in the first embodiment, etc., even very thin films (e.g., films with a thickness of approximately 0.01 to 10 μm) can be formed uniformly and with good controllability, thereby improving battery characteristics (output characteristics, capacity, etc.).

[0053] Next, a method for producing the substrate (porous film) onto which the coating liquid is applied will be described. The substrate (porous film) can be produced, for example, by the following steps.

[0054] Fig. 13 is a schematic diagram showing the configuration of a porous film manufacturing apparatus (system). For example, a plasticizer (liquid paraffin) and a polyolefin (e.g., polyethylene) are fed into the raw material supply section of the twin-screw kneading extruder (S1) in Fig. 13, and the plasticizer and polyolefin are kneaded in the kneading section. The kneading conditions are, for example, 180°C, 12 minutes, and a shaft rotation speed of 100 rpm.

[0055] The kneaded material (molten resin) is conveyed from the discharge section to the T-die S2, and the molten resin is extruded from the slit of the T-die S2 while being cooled in the raw material cooling device S3, thereby forming a thin-film resin molded body.

[0056] Next, the thin-film resin molded body is stretched in the longitudinal direction by a first stretching device S4, and further stretched in the transverse direction by a second stretching device S5.

[0057] The stretched thin film is then immersed in an organic solvent (e.g., methylene chloride) in extraction tank S6. In the stretched thin film, the polyolefin (e.g., polyethylene) and the plasticizer (paraffin) are phase-separated. Specifically, the plasticizer (paraffin) forms nano-sized islands. This nano-sized plasticizer (paraffin) is removed (degreased) by the organic solvent (e.g., methylene chloride) in extraction tank S6. This allows the formation of a porous film.

[0058] Thereafter, the porous film is further stretched in the transverse direction in the third stretching device S7, while drying and heat-setting the thin film to relieve the internal stress generated during stretching. Next, the porous film transported from the third stretching device S7 is wound up by the winding device S8.

[0059] In this manner, the porous film (the substrate of the first embodiment) can be produced.

[0060] For example, a roll of porous film wound by a winding device S8 can be set in the unwinding section UW of embodiment 1 (Figure 2), and the first coating liquid layer 3a and the second coating liquid layer 4a can be formed sequentially on its surface.

[0061] Furthermore, for example, the device of embodiment 1 (FIG. 2) may be installed between the third stretching device S7 and the winding device S8. That is, the first coating liquid layer 3a and the second coating liquid layer 4a may be sequentially formed on the surface of the porous film transported from the third stretching device S7. In this case, the winding device S8 corresponds to the winding section WD in FIG. 2.

[0062] In this way, the coated body may be formed using a continuous device (system) from the formation of the porous film to the formation of the coating layer.

[0063] (Fourth embodiment) Figure 14 shows the precipitation state of cellulose (CEOLUS) in embodiment 4. Equal amounts of cellulose alone (untreated cellulose) and cellulose whose surface hydrophobic groups have been chemically modified (semi-esterified (SA)) were added to water and left for 24 hours (Figure 14). The amount added was 10 g. SA conversion refers to esterifying cellulose with an additive (succinic anhydride) and then removing unreacted additive.

[0064] As shown in Figure 14, after 24 hours, the SA-treated cellulose exhibited less sedimentation than untreated cellulose. This is thought to be due to the electrostatic repulsion effect of the hydrophobic groups modified on the surface of the cellulose molecules. Therefore, by adding this semi-esterified cellulose to the liquid being sprayed in the spray area AS, the electrostatic repulsion at the liquid surface was further increased, allowing finer droplets to be ejected from the tip of the Taylor cone.

[0065] In this way, by chemically modifying the surface of a filler such as cellulose, the electrostatic repulsion of the filler can be enhanced, allowing finer droplets to be applied.

[0066] (Embodiment 5) Figures 15 and 16 show the precipitation state of cellulose in the fifth embodiment. Cellulose with hydrophobic groups chemically modified on the surface (semi-esterified (SA)) or SA-modified cellulose with the hydrophobic groups secondarily chemically modified with propylene oxide (SAPO-modified) was added to water in equal amounts. Figure 15 shows the state immediately after addition. Figure 16 shows the state 24 hours later. As shown in Figure 16, comparing the precipitation states 24 hours after the addition of SA-modified or SAPO-modified cellulose, it was confirmed that SAPO-modified cellulose suppressed precipitation more than SA-modified cellulose. This is thought to be because the increased number of hydrophobic groups modified on the cellulose molecule surface enhanced electrostatic repulsion compared to SA-modified cellulose. Therefore, by adding not only SA-modified cellulose as described in the fourth embodiment but also SAPO-modified cellulose to the liquid being sprayed in the spray area AS, electrostatic repulsion at the liquid surface was greatly enhanced, enabling fine droplets to be ejected from the tip of the Taylor cone.

[0067] In this way, by chemically modifying the surface of a filler such as cellulose, the electrostatic repulsion of the filler can be enhanced, allowing finer droplets to be applied.

[0068] The invention made by the inventor has been specifically described above based on the embodiments and examples, but it goes without saying that the present invention is not limited to the above embodiments or examples, and various modifications are possible within the scope of the gist of the invention.

[0069] For example, in embodiment 1, a separator having a coating layer (coating film 3b and coating film 4b) on a substrate made of a porous film was described as an example, but the coating technique described in embodiment 1, etc. may also be applied to an electrode having a coating layer on a metal foil substrate.

[0070] For example, the first coating liquid may be a mixture liquid 1 made by mixing an organic solvent and hydrophobic cellulose nanofibers (CeNF) dispersed in water, to which graphite and nano-Si are added as negative electrode active materials, and a mixture liquid 2 may be added further by adding, for example, CNT (carbon nanotube) or acetylene black as a conductive material. In addition to nano-Si, other negative electrode active materials include graphite, hard carbon (non-graphitizable carbon), soft carbon (easily graphitizable carbon), and lithium titanate (Li4Ti5O 12 ) or other widely used conductive materials may be used. Furthermore, other conductive materials besides CNT and acetylene black, such as Ketjen black and carbon nanofiber, may also be used. As the second coating liquid, the above-mentioned coating liquid may be used, and the first coating liquid layer 3a and the second coating liquid layer 4a may be formed on the metal foil as described above, followed by drying using a heater 10 or the like to form a laminated film (negative electrode) of the coating film 3b and the coating film 4b.

[0071] Alternatively, the first coating fluid may be a composite slurry obtained by suspending a positive electrode active material such as NCM, NCA, LiNiO2, Li2MnO3-LiMO2, or Li2MSiO4, a conductive material, or a binder such as PVDF in a mixture 3 containing hydrophobic cellulose nanofibers (CeNF) dispersed in an organic solvent and water. The second coating fluid may be the same as above, and a first coating fluid layer 3a and a second coating fluid layer 4a may be formed on a metal foil as described above, followed by drying with a heater 10 or the like to form a laminated film (positive electrode) of coating films 3b and 4b.

[0072] In this way, the first coating liquid containing the electrode active material and the second coating liquid may be applied sequentially onto the metal foil as described in the above embodiment.

[0073] The substrate may have two or more coating layers. That is, when a lower coating layer is already formed on the substrate and an upper coating layer is formed, the effects described in embodiment 1 and the like can be achieved by performing spray coating, which is a non-contact coating process, as described in embodiment 1 and the like. For example, a further coating film may be formed on coating film 3b and coating film 4b by spray coating, which is a non-contact coating process.

[0074] Furthermore, the method for forming the lower coating layer (e.g., coating film 3b) may be gravure coating, which is a contact coating process, or coating using a bar coater. Also, die coater coating may be used. Thus, the method for forming the lower coating layer (e.g., coating film 3b) may be contact coating or non-contact coating. For example, a three-layer coating film may be formed by contact coating → non-contact coating → non-contact coating. Alternatively, a three-layer coating film may be formed by non-contact coating → non-contact coating → non-contact coating. [Explanation of symbols]

[0075] 1 Base material 3a First coating liquid layer 3b Coating film 4a 2nd coating liquid layer 4b Coating film 5 Coated body 10. Heater 20 First coating processing section 20a Coating liquid 20A Gravure Coating Section 20b Chamber (tank) 20B Gravure Coating Department 20c blade 30 Second coating processing section 40 Drying processing section 90 Turntable 101 Cathode material 103 Anode materials 106 cans

Claims

1. A method for manufacturing a battery electrode, comprising: applying a first coating liquid containing an electrode active material to a first surface of a substrate to form a first coating liquid layer; spraying a second coating liquid containing an alkali silicate onto the first coating liquid layer to form a second coating liquid layer; drying the first coating liquid layer and the second coating liquid layer; The present invention is characterized by having the following.

2. 2. The method for manufacturing a battery electrode according to claim 1, The first coating liquid contains a first filler and a second filler.

3. 3. The method for manufacturing a battery electrode according to claim 1, When the second coating liquid is sprayed, a voltage of 1 kV or more is applied between the nozzle and the substrate.

4. a first coating section that applies a first coating liquid containing an electrode active material to a first surface of the substrate to form a first coating liquid layer; a second coating section that sprays a second coating liquid containing an alkali silicate onto the first coating liquid layer to form a second coating liquid layer; a drying section that dries the first coating liquid and the second coating liquid; Equipped with the first coating liquid includes a first filler and a second filler, the second coating unit has a nozzle that sprays the second coating liquid, a voltage of 1 kV or more is applied between the nozzle and the substrate when the second coating liquid is sprayed.

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