Manufacturing method of electrode sheet

Abstract

To provide a manufacturing method for an electrode sheet that reduces a transfer defect of an electrode material layer to a base material.SOLUTION: A manufacturing method of an electrode sheet includes: a preparation step of preparing a wet granule containing an electrode material and a solvent; a film forming step of passing the wet granules through a gap between a first roll and a second roll having a solvent absorbing portion on the outer peripheral surface to form an electrode material layer on the outer peripheral surface of the second roll; and a transfer step of transferring the electrode material layer onto a base material.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] 2. Description of the Related Art In recent years, secondary batteries such as lithium-ion secondary batteries have been suitably used as portable power sources for personal computers, mobile terminals, and the like, and as power sources for driving vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs), among others.

[0003] In a secondary battery, an electrode sheet is generally used as an electrode, in which an electrode material layer containing an electrode material (eg, an active material) is provided on a substrate (eg, a current collecting foil). In a production line for an electrode sheet, generally, a wet granulated material containing an electrode material and a solvent is passed through a gap between a pair of rolls, and an electrode material layer is formed on the outer peripheral surface of one of the pair of rolls, and then this electrode material layer is transferred onto a substrate to obtain an electrode sheet (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-106311 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the conventional electrode sheet manufacturing method, when the electrode material layer formed on the outer peripheral surface of the roll using the wet granules is transferred onto the substrate, the solvent component contained in the wet granules may seep out from the formed electrode material layer. When the solvent component seeps out, the electrode material layer becomes difficult to peel off from the roll, and transfer failure of the electrode material layer onto the substrate may occur. Patent Document 1 discloses the use of a specific wet granule to prevent the film of the electrode material layer transferred onto the surface of the current collector foil, which is the substrate, from becoming see-through, but does not disclose transfer failure of the electrode material layer caused by the seepage of the solvent component contained in the wet granules onto the roll, and a new method for manufacturing an electrode sheet is required. In view of the above circumstances, an object of the present disclosure is to provide a manufacturing method for an electrode sheet that reduces transfer defects of an electrode material layer onto a substrate. [Means for solving the problem]

[0006] Means for solving the above problems include the following means. <1> A preparation step of preparing a wet granule containing an electrode material and a solvent; a film-forming step of passing the wet granules through a gap between a first roll and a second roll having a solvent absorbing portion on an outer circumferential surface of the second roll to form an electrode material layer on the outer circumferential surface of the second roll; a transfer step of transferring the electrode material layer onto a substrate; A method for producing an electrode sheet comprising the steps of: <2> The solvent absorbing portion is a porous material. <1> A method for producing the electrode sheet according to claim 1. <3> The porous material has a porosity of 5% to 30% and a pore size of 0.1 μm to 3.2 mm. <2> A method for producing the electrode sheet according to claim 1. <4> The wet granules have a solid content of 75.96% by mass to 80.31% by mass. <1> ~ <3> 13. A method for producing the electrode sheet according to claim 12. <5> The method further includes a roll drying step of drying the second roll before the film forming step. <1> ~ <4> 13. A method for producing the electrode sheet according to claim 12. Effect of the Invention

[0007] According to the present disclosure, there is provided a method for manufacturing an electrode sheet that reduces transfer defects of an electrode material layer onto a substrate. [Brief description of the drawings]

[0008] [Figure 1] 3A to 3C are schematic diagrams illustrating an example of a film-forming step and a transfer step in the manufacturing method of the electrode sheet according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In the present disclosure, in the ranges of numerical values ​​described stepwise, the upper limit or lower limit of one numerical range may be replaced with the upper limit or lower limit of another numerical range of numerical values ​​described stepwise. In addition, in the ranges of numerical values ​​described in the present disclosure, the upper limit or lower limit of the numerical range may be replaced with a value shown in the examples. In the present disclosure, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified. In the present disclosure, the term "step" refers not only to an independent step, but also to a step that cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved.

[0010] Hereinafter, an embodiment that is an example of the present disclosure will be described. These descriptions and examples are merely illustrative of the embodiment, and do not limit the scope of the invention.

[0011] <Electrode manufacturing method> The electrode manufacturing method of the present disclosure is a method for manufacturing an electrode sheet, including a preparation step of preparing a wet granulation containing an electrode material and a solvent, a film formation step of passing the wet granulation through a gap between a first roll and a second roll having a solvent absorbing portion on its outer peripheral surface to form an electrode material layer on the outer peripheral surface of the second roll, and a transfer step of transferring the electrode material layer onto a substrate. In the manufacturing method of the electrode sheet of the present disclosure, the second roll has a solvent absorbing portion on the outer peripheral surface. Therefore, for example, the solvent component contained in the wet granule is easily absorbed by the outer peripheral surface of the second roll when the electrode material layer is formed. Therefore, even in the subsequent transfer step, the seepage of the solvent component from the electrode material layer is reduced, and the peelability of the electrode material layer from the roll is improved. As a result, transfer failure of the electrode material layer to the substrate is reduced.

[0012] An example of the manufacturing method of the electrode sheet of the present disclosure will be described with reference to the drawings. Fig. 1 is a schematic diagram showing an example of the film forming step and the transfer step in the manufacturing method of the electrode sheet of the present disclosure.

[0013] The manufacturing method of the electrode sheet shown in Fig. 1 uses a manufacturing apparatus including a container P containing a wet granulated material 10, a first roll 1, a second roll 2, and a third roll 3. The second roll 2 has a solvent absorbing portion over the entire area of ​​its outer circumferential surface. Although not shown, the manufacturing apparatus includes a substrate 30 provided on the outer circumferential surface of a transfer belt stretched by the third roll 3. Although not shown, the manufacturing apparatus includes a heat source device that heats and dries the outer circumferential surface of the second roll 2 on the side of the region of the second roll 2 on which the electrode material layer 20 is not formed. In the manufacturing method of the electrode sheet shown in FIG. 1, before passing the wet granule 10 through the gap between the first roll 1 and the second roll (i.e., before the film-forming step), the outer peripheral surface of the second roll 2 is dried by a heat source device to improve the solvent absorption of the solvent absorbing portion of the second roll 2 in advance (roll drying step). Then, the wet granule 10 is passed through the gap between the first roll 1 and the second roll. The wet granule 10 that has passed through the gap is formed into a film on the outer peripheral surface of the second roll 2 to become the electrode material layer 20 (film-forming step). At this time, at least a part of the solvent component contained in the wet granule 10 is absorbed by the solvent absorbing portion provided on the outer peripheral surface of the second roll 2. Then, the electrode material layer 20 passes through the gap between the second roll 2 and the third roll 3 and is transferred to the substrate 30 provided in contact with the outer peripheral surface of the third roll 3 (transfer step). Although not shown, in the manufacturing method of the electrode sheet shown in FIG. 1, the substrate 30 onto which the electrode material layer 20 has been transferred is dried from the side on which the electrode material layer 20 is provided, and is pressed and cut as necessary to obtain the final electrode sheet.

[0014] The first roll 1, the second roll 2, and the third roll 3 rotate in the direction of the arrows shown in Fig. 1. Although not shown, in the manufacturing method of the electrode sheet shown in Fig. 1, from the viewpoint of roll-selective formation of the electrode material layer and from the viewpoint of improving transferability, the rotation speed is adjusted so that it becomes faster in the order of the third roll>the second roll>the first roll. Note that the roll-selective layer formation and transferability may be controlled by adjusting the releasability to be higher in the order of the first roll>the second roll>the third roll by selecting the material of each outer peripheral surface of the first roll, the second roll, and the third roll.

[0015] Hereinafter, the manufacturing method of the electrode sheet according to the present disclosure will be described in detail for each step, where reference numerals will be omitted.

[0016] [Preparation process] In the preparation step, a wet granule containing an electrode material and a solvent is prepared. The wet granules may be commercially available or may be appropriately designed and manufactured from known material compositions depending on the type of electrode sheet desired. The wet granules of the present disclosure also conceptually include those called electrode slurries and electrode pastes for all-solid-state batteries. As the electrode material, for example, known materials contained in electrodes, such as an electrode active material, a binder, an electrolyte, a solvent, a thickener, a conductive material, AB, CNT, graphene, etc., can be used. As the solvent, for example, known solvents that can be used for wet granules, such as water and N-methyl-2-pyrrolidone (NMP), can be used.

[0017] The solid content of the wet granules may be 75.80% by mass to 83.50% by mass, 75.96% by mass to 80.80% by mass, 75.96% by mass to 80.31% by mass, or 78.66% by mass to 80.31% by mass. In the conventional electrode sheet manufacturing method, when the solid content rate of the wet granule is high, the solvent component is more likely to bleed out from the electrode material layer in the transfer step described below, and the peelability of the electrode material layer from the roll is reduced, and as a result, transfer failure of the electrode material layer to the substrate tends to occur more easily. In contrast, in the electrode sheet manufacturing method of the present disclosure, even if the solid content rate is within the above range, the solvent component tends to be absorbed in the solvent absorbing portion on the outer peripheral surface of the second roll, so that transfer failure of the electrode material layer to the substrate is reduced. The solid content is determined by the following measurement method: The wet granules are vacuum-dried at 100° C. or higher, and the weight of the resulting dry powder is divided by the total mass of the wet granules and multiplied by 100 to obtain the solid content.

[0018] [Film formation process] In the film-forming step, the wet granules are passed through a gap between a first roll and a second roll having a solvent absorbing portion on the outer circumferential surface of the second roll to form an electrode material layer on the outer circumferential surface of the second roll. The material of the first roll is not particularly limited.

[0019] The second roll is not particularly limited as long as it has a solvent absorbing portion on its outer circumferential surface. The solvent absorption section may be provided over the entire outer peripheral surface of the second roll or may be provided locally, but from the viewpoint of efficiently absorbing the solvent components and further reducing transfer defects, it is preferable that it be provided over the entire outer peripheral surface of the second roll.

[0020] The solvent absorbing portion is preferably made of a porous material from the viewpoint of efficiently absorbing the solvent component and further reducing transfer defects. From the viewpoint of efficiently absorbing the solvent component and further reducing transfer defects, the porous material preferably has a porosity of 5% to 30%, more preferably 8% to 25%, and even more preferably 10% to 20%. The porosity is determined by the following method: The pore volume of the porous material formed on the outer peripheral surface of the second roll is measured with a mercury porosimeter, and the percentage value is calculated by dividing the volume of the measured object.

[0021] From the viewpoint of efficiently absorbing the solvent component and further reducing transfer defects, the porous material preferably has a pore size of 0.1 μm to 3.2 mm, more preferably 1 μm to 1 mm, and even more preferably 100 μm to 500 μm. The pore size is determined by the following method: The pore volume of the porous material formed on the outer peripheral surface of the second roll is measured with a mercury porosimeter, and the percentage value obtained by dividing the volume of the measured object is the porosity of the porous material.

[0022] The porosity and pore size of the porous material can be adjusted, for example, by machining the roll base material, forming a sleeve structure, performing surface treatment, or the like.

[0023] In one embodiment, from the viewpoint of efficiently absorbing the solvent component and further reducing transfer defects, the porous material preferably has a porosity of 5% to 30% and a pore diameter of 0.1 μm to 3.2 mm, more preferably has a porosity of 8% to 25% and a pore diameter of 1 μm to 1 mm, and further preferably has a porosity of 10% to 20% and a pore diameter of 100 μm to 500 μm.

[0024] Examples of the material for the solvent absorbing portion include ceramics, resins, and metals. The material of the solvent absorbing portion may be used alone or in combination of two or more kinds. Examples of the ceramics include known fine ceramics such as alumina, zirconia, silicon carbide, boron carbide, silicon nitride, and aluminum nitride. Examples of the resin include nylon resin, fluorine-based resin (for example, vinylidene fluoride resin), polyester resin, polyethylene resin, polystyrene resin, and polyether ether ketone resin. Examples of the metal include iron, manganese, nickel, chromium, molybdenum, magnesium, silicon, aluminum, titanium, and alloys thereof. Among the above, from the viewpoint of efficiently absorbing the solvent component as a porous material and further reducing transfer defects, the material of the solvent absorbing portion preferably contains a ceramic material, and more preferably contains alumina.

[0025] [Transfer process] In the transfer step, the electrode material layer is transferred onto a substrate, thereby obtaining an electrode sheet in which the electrode material layer is provided on the substrate. As the substrate, for example, a known substrate for an electrode such as a current collecting foil can be used. The transfer means is not particularly limited, and may be either a transfer belt or a transfer roll. The transfer step may be, for example, a step of conveying a substrate provided on a transfer belt stretched by a stretch roll while rotating a stretch roll (e.g., the third roll shown in FIG. 1 ), and transferring the electrode material layer to the substrate while pressing the substrate in the gap between the stretch roll and the second roll.

[0026] [Roller drying process] From the viewpoint of efficiently absorbing the solvent component and further reducing transfer defects even when the electrode sheet is repeatedly manufactured, the electrode sheet manufacturing method according to the present embodiment preferably further includes a roll drying step of drying the second roll before the film formation step. In the roll drying step, the second roll is dried before the film formation step. The drying means is not particularly limited, and may be any of heating and drying using hot air, infrared rays, microwaves, electromagnetic waves, or the like; heating and drying using light rays such as laser; and the like. The roll drying process may be, for example, a process in which the outer peripheral surface of the second roll is heated to 40°C or higher while checking the temperature of the outer peripheral surface of the second roll with a temperature sensor such as a thermocouple, from the viewpoint of efficiently drying the outer peripheral surface of the second roll.

[0027] [Other steps] The manufacturing method of the electrode sheet of the present disclosure may further include other steps other than the preparation step, the film-forming step, the transfer step, and the roll drying step. The other steps include, for example, 1) a trimming step of trimming the formed electrode material layer with a laser, a scraper, or the like after the film-forming step; 2) a drying step of drying the electrode material layer after the transfer step; 3) a pressing step of pressing the electrode sheet with a roll press, or the like after the transfer step; and 4) a cutting step of cutting the electrode sheet to a desired size or number (for example, cutting into sheets) after the transfer step. EXAMPLES

[0028] <Example> A positive electrode sheet for a lithium ion battery was manufactured using the manufacturing apparatus shown in FIG. 1. Specifically, first, the wet granule described in JP 2018-45840 A was prepared and placed in a container P (preparation step). The solid content value of the wet granule was set to the specification shown in Table 1. Before the electrode material layer was formed, the outer peripheral surface of the second roll was heated and dried while confirming with a thermocouple that the temperature of the outer peripheral surface of the second roll was 40° C. or higher (roll drying step). Then, the wet granule was passed through the gap between the first roll and the second roll, and the electrode material layer was formed on the outer peripheral surface of the second roll (film formation step). The second roll has a solvent absorbing portion made of alumina, which is a porous material (porosity 10%, average pore diameter 400 μm), over the entire outer peripheral surface. Next, in the gap between the second roll and the third roll (i.e., the tension roll), the substrate (current collector foil, material: aluminum) provided on the transfer belt tensioned by the third roll was pressed against the electrode material layer, and the electrode material layer was transferred onto the substrate (transfer process). Next, the electrode material layer was heated and dried at 100°C for 3 minutes using a heater, and pressed with a roll press device to increase density. The electrode sheet was then cut to a predetermined size to produce the electrode sheet.

[0029] <Comparative Example> In the comparative example, an electrode sheet was produced in the same manner as in the example, except that the second roll was a stainless steel roll having no solvent absorbing portion on its outer circumferential surface. The solid content of the wet granules was as shown in Table 1.

[0030] <Evaluation of transferability> When the electrode sheet was manufactured by the manufacturing method of each example, the outer peripheral surface area of ​​the second roll on which the electrode material layer was provided after the transfer step was visually observed. The electrode sheet obtained by the manufacturing method of each example was visually observed. Then, the outer peripheral surface area of ​​the second roll and the electrode sheet were evaluated for transfer defects according to the following evaluation criteria. The results are shown in Table 1.

[0031] G1: No residue of the electrode material layer was found on the outer peripheral surface of the second roll. Furthermore, no transfer defects were observed in the electrode material layer transferred onto the substrate. G2: Residue of the electrode material layer was partially observed on the outer peripheral surface of the second roll. In addition, some areas of the electrode material layer transferred onto the substrate were chipped. G3: Residues of the electrode material layer were found in multiple places on the outer peripheral surface of the second roll. Furthermore, transfer defects were observed in multiple locations in the electrode material layer transferred onto the substrate.

[0032] [Table 1]

[0033] As described above, the electrode sheets obtained by the manufacturing methods of the Examples had reduced transfer defects of the electrode material layer onto the substrate, compared to the electrode sheets obtained by the manufacturing methods of the Comparative Examples. [Explanation of symbols]

[0034] 1 first roll, 2 second roll, 3 third roll, P container, 10 wet granules, 20 electrode material layer, 30 substrate

Claims

1. A preparation step of preparing a wet granule containing an electrode material and a solvent; a film-forming step of passing the wet granules through a gap between a first roll and a second roll having a solvent absorbing portion on an outer circumferential surface of the second roll to form an electrode material layer on the outer circumferential surface of the second roll; a transfer step of transferring the electrode material layer onto a substrate; wherein the solvent absorbing portion is a porous material having a porosity of 8% to 25% and a pore diameter of 1 μm to 1 mm.

2. The method for producing an electrode sheet according to claim 1, wherein the wet granules have a solids content of 75.96% by mass to 80.31% by mass.

3. The method for producing an electrode sheet according to claim 1 , further comprising a roll drying step of drying the second roll before the film forming step.

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