Electrode sheet manufacturing method

Abstract

To provide a manufacturing method of an intermittent coating type electrode sheet in which variations in dimensions in a width direction and a transfer direction regarding an active material layer are reduced and a current collector foil is not damaged.SOLUTION: The present invention relates to a manufacturing method of an electrode sheet including an active material layer on a surface of a current collector foil in an intermittent manner. The manufacturing method includes: a masking layer forming step of sticking a masking material to a portion other than a formation portion of the active material layer on the surface of the current collector foil; a wet granulation preparing step of preparing a wet granulation containing an electrode active material, a binder, a conductive material and a solvent; an active material layer formation step of forming an active material layer by compression-molding the wet granulation; an active material layer disposing step of disposing the active material layer by supplying and compressing the active material layer on the masking layer and in a portion, which is not covered by the masking layer, on the surface of the current collector foil; and a removal step of removing the masking layer and the active material layer formed on the masking layer.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Known electrode sheets include those having an active material layer on the surface of a current collector foil. Examples of methods for manufacturing such electrode sheets include the method disclosed in Patent Document 1 (JP 2021-44096 A).

[0003] Patent Document 1 also discloses that protrusions that protrude outward in the width direction may be formed at both widthwise ends of the active material layer, but that by removing the protrusions with a scraping blade, it is possible to reduce the variation in the widthwise dimension of the active material layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-44096 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, intermittently coated electrode sheets, in which areas where an active material layer is formed (coated areas) and areas where it is not formed (uncoated areas) are alternately present on a current collector foil, are also known as electrode sheets that are often used in high-energy density batteries. However, the method described in Patent Document 1 cannot be applied to the production of intermittently coated electrode sheets. Another problem is that the scraping blade can damage the current collector foil.

[0006] Therefore, an object of the present disclosure is to provide a method for manufacturing an intermittently coated electrode sheet in which the dimensional variation in the width direction and conveyance direction of the active material layer is small and the current collector foil is not damaged. [Means for solving the problem]

[0007] [1] The present disclosure provides a method for producing an electrode sheet having an active material layer intermittently formed on the surface of a current collector foil, the method comprising: a masking layer forming step of applying a masking material to a portion of the surface of the current collecting foil other than the portion where the active material layer is formed; a wet granulation preparation step of preparing wet granulation containing an electrode active material, a binder, a conductive material, and a solvent; an active material layer forming step of forming an active material layer by compression-molding the wet granules; an active material layer disposing step of disposing the active material layer by supplying the active material layer onto the masking layer and onto a portion of the surface of the current collecting foil that is not covered by the masking layer and compressing the active material layer; and a removal step of removing the masking layer and the active material layer formed on the masking layer.

[0008] According to the manufacturing method [1] above, it is possible to produce an intermittently coated electrode sheet in which the dimensional variation in the width direction and conveyance direction of the active material layer is small and which does not damage the current collector foil.

[0009] That is, the portions of the surface of the current collector foil where the active material layer is not to be formed are masked. Next, a wet granule is prepared and compression-molded to form the active material layer. The active material layer is then applied to the entire masked surface of the current collector foil and compressed to form the active material layer. Finally, the masked portion is removed together with the active material layer formed on the masking layer. In this manner, an intermittently coated electrode sheet can be produced in which the dimensional variation of the active material layer in the width direction and conveyance direction is small, without damaging the current collector foil.

[0010] [2] In the manufacturing method of the electrode sheet of the present disclosure, the masking layer has a two-layer structure consisting of an upper layer and a lower layer, In the removing step, it is preferable to remove the active material layer formed on the upper layer and the masking layer.

[0011] In this case, the layer below the masking layer is not removed and remains on the current collector foil, thereby functioning as a protective layer for the current collector foil, such as improving short-circuit resistance when foreign matter gets mixed in. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a flowchart showing an outline of a method for producing an electrode sheet according to an embodiment. [Figure 2] FIG. 2 is a conceptual diagram showing an apparatus used to manufacture an electrode sheet in the embodiment. [Figure 3] FIG. 3 is a perspective view schematically illustrating an example of an electrode sheet manufactured by the electrode sheet manufacturing method of the embodiment. [Figure 4] FIG. 4 is a photograph of the end portion in the width direction of the active material layer of the example and the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present disclosure will be described. However, the present disclosure is not limited thereto. In this specification, the "positive electrode" and the "negative electrode" will be collectively referred to as "electrodes."

[0014] <<Electrode sheet manufacturing method>> Fig. 1 is a flowchart showing an outline of the electrode sheet manufacturing method of this embodiment. As shown in Fig. 1, the electrode sheet manufacturing method of this embodiment includes at least a masking layer forming step (S10), a wet granule preparing step (S20), an active material layer forming step (S30), an active material layer arranging step (S40), and a removal step (S50).

[0015] The electrode sheet manufactured in this embodiment is, for example, an electrode sheet for a lithium ion secondary battery. The electrode sheet may be either a positive electrode sheet or a negative electrode sheet.

[0016] <Masking layer forming step (S10)> In the masking layer forming step, a masking material is applied to the surface of the current collector foil in an area other than the area where the active material layer is to be formed, thereby forming a masking layer.

[0017] (Masking layer) The masking layer is made of a masking material. In this embodiment, this masking layer formation step can be performed by applying the masking material to the current collector foil using a roll, a coating machine, or the like. Note that, to prevent the masking material from being applied to the portion of the surface of the current collector foil where the active material layer is to be formed, for example, an opening of a size corresponding to the active material layer can be provided in that portion.

[0018] The masking material forming the masking layer must be a material that does not react with the current collector foil or the material constituting the wet granules described below, and examples of such a material include metals and resins. Examples of metals include stainless steel (SUS), chromium, tungsten, molybdenum, and titanium. Examples of resins include polyimide resins, polyester resins, polyacetal resins, and fluororesins.

[0019] The masking layer may consist of one layer or two layers. When the masking layer consists of one layer, the masking material forming the masking layer is preferably a resin. When the masking layer consists of one layer, the masking layer may have a thickness of, for example, 10 μm or more and 50 μm or less, or 80 μm or more and 400 μm or less.

[0020] When the masking layer consists of two layers, it has an upper layer and a lower layer. The upper layer is located opposite the surface of the lower layer that contacts the current collecting foil and is preferably made of the above-mentioned metal or resin. The lower layer is the layer that contacts the current collecting foil and is preferably made of the above-mentioned resin. When the masking layer consists of two layers, the masking layer may have a thickness of, for example, 20 μm or more and 70 μm or less, or may have a thickness of 90 μm or more and 420 μm or less.

[0021] When the masking layer is made up of two layers, it is sufficient to apply it so that the lower layer is in contact with the current collecting foil.

[0022] (current collecting foil) The current collecting foil is a support for the active material layer. The current collecting foil may be, for example, in the form of a sheet or a strip. Examples of current collecting foils include aluminum (Al) foil, Al alloy foil, copper (Cu) foil, Cu alloy foil, nickel (Ni) foil, Ni alloy foil, titanium (Ti) foil, and Ti alloy foil. When the electrode is a positive electrode, the current collecting foil is, for example, Al foil. When the electrode is a negative electrode, the current collecting foil is, for example, Cu foil. The current collecting foil may have a thickness of, for example, 5 μm to 50 μm, or 5 μm to 20 μm.

[0023] <Wet granule preparation step (S20)> In the wet granule preparation step, wet granules containing an electrode active material, a binder, a conductive material, and a solvent are prepared.

[0024] (Wet granules) The wet granules can be produced, for example, by mixing (granulating) an electrode active material, a binder, a conductive material, a solvent, and the like. As a granulation method, for example, an agitation granulation method can be used. Examples of various granulation procedures include agitation granulation, fluidized bed granulation, and rolling granulation. Various granulation devices such as an agitation mixer can be used for these granulation procedures. The granulation procedure may be carried out in one stage or in multiple stages.

[0025] The wet granules may be further kneaded. For the kneading, a roll mill equipped with three rolls arranged horizontally or the like may be used. The kneading may be carried out once, or may be carried out two or more times.

[0026] (electrode active material) The electrode active material may be a positive electrode active material or a negative electrode active material.

[0027] Examples of the positive electrode active material include lithium-containing metal oxides, lithium-containing phosphates, etc. Examples of lithium-containing metal oxides include LiCoO2, LiNiO2, and lithium phosphates of the general formula LiNi aCo b A compound represented by O2 (where a + b = 1, 0 < a < 1, 0 < b < 1), LiMnO2, LiMn2O4, general formula LiNi a Co b Mn c O2 (where a + b + c = 1, 0 < a < 1, 0 < b < 1, 0 < c < 1), compounds such as LiFePO4 can be mentioned. Here, for the compound represented by the general formula LiNi a Co b Mn c O2, examples include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and the like. Examples of lithium-containing phosphates include LiFePO4 and the like.

[0028] The average particle size of the positive electrode active material may be, for example, about 0.1 to 25 μm. Here, the "average particle size" means the particle size (D50) at the integrated value of 50% in the volume-based particle size distribution measured by the laser diffraction / scattering method.

[0029] Examples of the negative electrode active material include carbon-based negative electrode active materials such as graphite, easily graphitizable carbon, and difficult-to-graphitize carbon, and alloy-based negative electrode active materials containing silicon (Si), tin (Sn), etc. The average particle size (D50) of the negative electrode active material may be, for example, about 1 to 25 μm.

[0030] The blending ratio of the electrode active material with respect to the total amount of the solid content of the wet granule (that is, the content rate of the electrode active material in the active material layer) is, for example, about 94 to 99.7 mass%.

[0031] (Binder) Examples of the binder include carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), etc. The binder may be used alone or in combination of two or more.

[0032] The blending ratio of the binder to the total amount of solids in the wet granules (ie, the content of the binder in the active material layer) is, for example, about 0.3 to 6 mass %.

[0033] (Conductive material) Examples of conductive materials include carbon black, carbon nanotubes, vapor-grown carbon fibers, graphene flakes, etc. The conductive material is expected to improve electronic conductivity.

[0034] The blending ratio of the conductive material to the total amount of solids in the wet granules (ie, the content of the conductive material in the active material layer) is, for example, about 0.3 to 6 mass %.

[0035] (solvent) Examples of the solvent include an aqueous solvent, an organic solvent, etc. An aqueous solvent means water or a mixed solvent containing water and a polar organic solvent.

[0036] As the aqueous solvent, water (ion-exchanged water) is preferably used because of its ease of handling. Examples of polar organic solvents that can be used in the mixed solvent include alcohols such as methanol, ethanol, and isopropyl alcohol, ketones such as acetone, and ethers such as tetrahydrofuran. The aqueous solvent is preferably used as a solvent for producing the negative electrode.

[0037] Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP), etc. The organic solvent can be suitably used as a solvent for producing a positive electrode.

[0038] The amount of solvent used is not particularly limited, but may be adjusted so that the solid content (NV) of the wet granules is 70% by mass or more but less than 100% by mass, preferably 70 to 90% by mass. If the NV of the wet granules is less than 70% by mass, the amount of solvent is large, which may make it difficult to produce the wet granules. The "solid content" refers to the ratio of the mass of components other than the solvent (non-volatile components) to the total mass of all raw materials including the solvent.

[0039] <Active material layer formation process (S30)> In the active material layer forming step, the wet granules are compression molded to form an active material layer.

[0040] The active material layer forming step and the active material layer arranging step described later may be performed using, for example, a roll-type film forming apparatus 10 as shown in Fig. 2. A method using the roll-type film forming apparatus 10 will be described below, but is merely an example.

[0041] The roll-type film forming apparatus 10 includes three rolls: a first roll 1, a second roll 2, and a third roll 3. The first roll 1 and the second roll 2 are arranged side by side in the horizontal direction (the left-right direction in FIG. 2). Meanwhile, the second roll 2 and the third roll 3 are arranged side by side in the vertical direction (the up-down direction in FIG. 2). The first roll 1 and the second roll 2 face each other (opposite each other) with a small gap (first gap) between them. Similarly, the second roll 2 and the third roll 3 face each other (opposite each other) with a small gap (second gap) between them. Furthermore, above the first gap, a pair of partition plates 4 are arranged spaced apart in the width direction of the rolls (the axial direction, the direction perpendicular to the paper surface in FIG. 2).

[0042] The rotation directions of these three rolls are set so that the rotation directions of two adjacent (facing) rolls are opposite to each other, i.e., so that the two facing rolls rotate in the same direction as each other, as shown by the arrows in Figure 2. The first gap is set so that the surfaces of these rolls move downward as they rotate. The second gap is set so that the surfaces of these rolls move rightward as they rotate. Regarding the rotation speed, the speed at which the roll surfaces move due to rotation is set to be the slowest for the first roll 1, the fastest for the third roll 3, and intermediate between them for the second roll 2.

[0043] In such a roll-type film forming apparatus 10, wet granules 5 are introduced into the storage space between the partition plates 4 located above the first gap. The introduced wet granules 5 are supplied into the first gap and compressed and molded by the first roll 1 and the second roll 2 to form a sheet-like active material layer 7. At this time, since the rotation speed of the second roll 2 is faster than that of the first roll 1, the sheet-like active material layer 7 is supported on the surface of the second roll 2.

[0044] <Active material layer arrangement process (S40)> In the active material layer disposing step, the active material layer is supplied onto the masking layer and onto the portion of the surface of the current collector foil that is not covered by the masking layer, and then compressed to dispose the active material layer. As in the active material layer forming step described above, a method using the roll-type film forming apparatus 10 is exemplified below.

[0045] The sheet-like active material layer 7 carried on the second roll 2 is transported through the second gap to the third roll 3 as the second roll 2 rotates. A current collector foil 8 having a masking layer formed thereon (hereinafter also referred to as "current collector foil 6 with a masking layer") is also transported to the third roll 3. This current collector foil 6 with a masking layer is transported through the second gap from the lower left to the upper right of the third roll 3 as the third roll 3 rotates.

[0046] The surface of the masking layer-attached current collector foil 6 and the sheet-like active material layer 7 are sandwiched in the second gap. The dimension of the second gap (minimum gap dimension) is set to be smaller than the sum of the thickness of the masking layer-attached current collector foil 6 and the thickness of the film-like sheet-like active material layer 7.

[0047] Therefore, when the masking layer-equipped current collector foil 6 and the sheet-like active material layer 7 are sandwiched in the second gap, a pressing load is applied to the sheet-like active material layer 7 from the surface of the second roll 2 toward the surface of the masking layer-equipped current collector foil 6. This allows the sheet-like active material layer 7 attached to the surface of the second roll 2 to be brought into contact with the surface of the masking layer-equipped current collector foil 6 while being pressed against it, so that the sheet-like active material layer 7 is transferred from the second roll 2 onto the surface of the masking layer-equipped current collector foil 6 that is rotating together with the third roll 3, thereby forming the active material layer 7 on the masking layer-equipped current collector foil 6. Furthermore, by forming the active material layer using the roll-type film-forming apparatus 10 equipped with three rolls, the basis weight of the active material layer can be made more uniform.

[0048] <Removal process (S50)> In the removal step, the masking layer and the active material layer formed on the masking layer are removed. In this embodiment, this removal step may be performed by winding up the masking layer and the active material layer formed on the masking layer from the current collector foil using a roll or the like, or by sucking the masking layer and the active material layer formed on the masking layer from the current collector foil using a suction device.

[0049] When the masking layer consists of one layer, the masking layer and the active material layer formed on the masking layer are removed together with the masking layer.

[0050] When the masking layer is composed of two layers, it is preferable to remove the upper layer and the active material layer formed on the masking layer. By removing only the upper layer and leaving the lower layer on the current collector foil, the lower layer can function as a protective layer for the current collector foil, such as improving short-circuit resistance when foreign matter is mixed in.

[0051] In this way, the sheet-like active material layers 7 can be intermittently disposed only at predetermined positions on the current collector foil 8. This makes it possible to manufacture an intermittently coated electrode sheet 9. Note that the intermittently coated electrode sheet 9 is an electrode sheet 9 having exposed portions of the current collector foil 8 between the active material layers 7, as shown in FIG. 3, for example.

[0052] After the active material layer 7 is dried, the electrode sheet 9 may be cut to a predetermined size using, for example, a slitter.

[0053] <Lithium-ion secondary battery> The electrode sheet obtained by the manufacturing method of the present disclosure can be used, for example, as an electrode sheet for a lithium ion secondary battery (nonaqueous electrolyte secondary battery). The lithium ion secondary battery can be used, for example, as a power source for a hybrid vehicle (HV), an electric vehicle (EV), a plug-in hybrid vehicle (PHV), etc. However, the electrode sheet obtained by the manufacturing method of the present disclosure is not limited to such in-vehicle applications and can be used for a variety of applications.

[0054] The lithium ion secondary battery may include, for example, a case. The case may be, for example, a metal container or a pouch made of a metal foil laminate film. The case houses an electrode group and an electrolyte.

[0055] The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is disposed between the positive electrode sheet and the negative electrode sheet. An electrolyte is present in the voids within the electrode assembly.

[0056] (separator) The separator is porous. The separator is electrically insulating. The separator may be, for example, a porous film made of polyethylene (PE), polypropylene (PP), or the like. The separator may have a thickness of, for example, 10 μm or more and 50 μm or less.

[0057] The separator may have a single layer structure. The separator may be formed, for example, from only a porous PE film. The separator may have a multilayer structure. For example, the separator may be formed by laminating a porous PP film, a porous PE film, and a porous PP film in this order.

[0058] (electrolyte) The electrolyte solution includes a solvent and a supporting electrolyte. The solvent is aprotic. The solvent may include any component. The solvent may be, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), or the like. One type of solvent may be used alone, or two or more types of solvents may be used in combination.

[0059] The supporting electrolyte is dissolved in a solvent. The supporting electrolyte may be, for example, LiPF, LiBF, LiN(FSO), or the like. One type of supporting electrolyte may be used alone, or two or more types of supporting electrolytes may be used in combination. The supporting electrolyte may have a molar concentration of, for example, 0.5 mol / L or more and 2 mol / L or less.

[0060] The electrolyte may further contain an optional additive. The electrolyte may contain, for example, 0.1% to 5% by mass of the additive. The additive may be, for example, vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2), lithium fluorosulfonate (FSO3Li), lithium bis(oxalato)borate (LiBOB), or the like. One type of additive may be used alone, or two or more types of additives may be used in combination. [Example]

[0061] The present embodiment will be described below using examples, but the present embodiment is not limited to these.

[0062] <Test 1> Example 1 In Example 1, an electrode (positive electrode for a lithium ion secondary battery) sheet is produced as follows.

[0063] Masking layer formation process In Example 1, the following materials were first prepared: A plurality of openings, each 1168 mm wide and 1492 mm long, were formed in the area on the surface of the current collector foil where the active material layer was to be formed.

[0064] Masking material: Polyimide resin (Toray DuPont Co., Ltd., Kapton (registered trademark), width: 1183 mm) Current collecting foil: Al foil (thickness: 12 μm, width: 1200 mm) The polyimide resin and the Al foil with openings were placed in a roll press device (masking layer forming device) equipped with two rolls, and a masking layer (hereinafter also referred to as "Al foil with masking layer") was formed on the Al foil.

[0065] <<Wet granule production process>> Next, the following materials were prepared: SBR was dissolved in ion-exchanged water to give an SBR suspension with NV of 48% by mass.

[0066] Cathode active material: LiFePO4 (average particle size (D50): 1.1μm) Binder: Carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR) Conductive material: Carbon nanotubes (CNTs) (diameter 5-20 nm) Solvent: Ion-exchanged water First, CMC and CNT were added to a planetary mixer and mixed at 10 rpm for 2 minutes to obtain a first mixture. The blending ratios of CMC and CNT were adjusted so that the mass ratio of CMC was 1.2 mass% and the mass ratio of CNT was 2.0 mass% in the wet granules.

[0067] Next, the first mixture, SBR suspension, and ion-exchanged water were added to a planetary mixer and mixed at 10 rpm for 2 minutes, followed by 20 minutes at 90 rpm to obtain a second mixture. The blending ratio of the SBR suspension was adjusted so that the mass ratio of SBR in the wet granules was 1.3 mass%. Furthermore, ion-exchanged water was added so that the NV of the second mixture was 30 mass%.

[0068] The second mixture, LiFePO4, and ion-exchanged water were then added to a planetary mixer and mixed at 10 rpm for 2 minutes, followed by 20 minutes at 90 rpm to obtain wet granules. The LiFePO4 content was adjusted so that the mass ratio of LiFePO4 in the wet granules was 95.5 mass%. The ion-exchanged water was added so that the NV of the wet granules was 80 mass%.

[0069] Finally, the wet granules were kneaded three times using a roll mill equipped with three rolls arranged horizontally.

[0070] 《Active material layer formation process》 In this step, the wet granules 5 were compression-molded using the roll film-forming apparatus 10 shown in FIG. 2, as in the above-described embodiment, to form a sheet-like active material layer 7.

[0071] In the roll-type film forming apparatus 10, the distance between the first roll 1 and the second roll 2 (first gap distance) was 70 μm or more and 80 μm or less, and the distance between the second roll 2 and the third roll 3 (second gap distance) was 20 μm or more and 30 μm or less. The rotation speed of the first roll 1 was 1.5 rpm, the rotation speed of the second roll 2 was 4 rpm, and the rotation speed of the third roll 3 was 12 rpm.

[0072] 《Active material layer arrangement process》 In this process, as in the above-described embodiment, a roll-type film-forming apparatus 10 shown in FIG. 2 was used to supply the sheet-shaped active material layer 7 onto the masking layer and onto the Al foil not covered by the masking layer, and then compress and arrange the active material layer 7.

[0073] 《Removal process》 In this step, the masking layer of the masking-layer-attached Al foil on which the active material layer was disposed and the active material layer formed on the masking layer were removed using a roll press device (masking layer removal device) equipped with two rolls. The active material layer on the Al foil was dried to produce the electrode (positive electrode) sheet of Example 1.

[0074] Comparative Example 1 In Comparative Example 1, an active material layer was formed using the same wet granules as in Example 1 and placed on an Al foil, but no masking layer was formed on the Al foil. Specifically, a sheet-like active material layer similar to that in Example 1 was placed on an Al foil with an opening and no masking layer formed on it. The active material layer provided in the opening was then dried to produce the electrode sheet of Comparative Example 1.

[0075] Comparative Example 2 In Comparative Example 2, a sheet-like active material layer was disposed on an Al foil in the same manner as in Comparative Example 1, but the subsequent process was different. Specifically, in order to remove protrusions protruding outward in the width direction from both widthwise ends of the Al foil, a scraper for scraping off the protrusions and a dust collector for collecting the removed protrusions were disposed downstream of the roll-type film-forming device 10. The scraper was made of PTFE, and the pressing pressure was 3 kPa. Then, the active material layer on the Al foil from which the protrusions had been scraped off was dried to produce the electrode sheet of Comparative Example 2.

[0076] "evaluation" In the above-mentioned Example 1, Comparative Example 1, and Comparative Example 2, each electrode sheet was cut to a predetermined size. The widthwise edges of the active material layer of the cut electrode sheets were observed using an optical microscope at 200x magnification to check for dimensional variation and the presence or absence of damage (scratches, dents, etc.) on the current collector foil. The results are shown in Table 1. A dimensional variation of 0.5 mm or less and no damage on the current collector foil was deemed good. Note that the dimensional variation was measured at three locations on the widthwise edges of different active material layers, and the arithmetic average of the three measurements was used. The presence or absence of damage on the current collector foil was also checked at three locations, and a case where there were no defects on the current collector foil in any of the cases was deemed good.

[0077] [Table 1]

[0078] (result) As shown in Table 1, the dimensional variation was a good 0.4 mm in Example 1. In addition, as can be seen from Figure 4(a), there was no damage to the current collecting foil.

[0079] On the other hand, in Comparative Example 1, as can be seen from Figure 4(b), there was no damage to the current collecting foil, but the dimensional variation was 2.4 mm.In Comparative Example 2, the dimensional variation was good at 0.3 mm, but there was damage to the current collecting foil, as can be seen from Figure 4(c).

[0080] <Test 2> [Production Example 1] The positive electrode sheet was produced using the same materials and by the same method as in Example 1. In this production example, the size of the material was adjusted so that the active material layer had a width of 45 mm and a length of 47 mm.

[0081] The following materials were prepared:

[0082] Active material particles: graphite Binder: CMC, SBR Dispersion medium: water Current collecting foil: Cu foil (thickness: 8 μm) A negative electrode sheet was produced in the same manner as the positive electrode sheet, using 96% by mass of graphite, 2% by mass of CMC, and 2% by mass of SBR. In this production example, the size of the material was adjusted so that the active material layer was 47 mm wide and 49 mm long.

[0083] The following materials were prepared:

[0084] Separator: PE porous film (single layer structure, thickness: 20 μm) The positive electrode sheet, the separator, and the negative electrode sheet were stacked so that the positive electrode sheet and the negative electrode sheet faced each other with the separator sandwiched therebetween, thereby forming an electrode group.

[0085] The following materials were prepared:

[0086] Metallic foreign matter: Iron (Fe) fine particles (average particle size: 50 μm) The foreign metal object was fixedly placed on the current collector foil at a position in contact with the edge of the active material layer of the positive electrode sheet and at approximately the center of the current collector foil in the width direction.

[0087] A pouch made of an Al laminate film was prepared as the case, and the electrode group was housed in it so that the above-mentioned metal foreign matter was located between the case and the electrode group.

[0088] An electrolyte (electrolytic solution) having the following composition was prepared.

[0089] Supporting salt: LiPF6 (1 mol / l) Solvent: [EC:DMC:EMC = 3:4:3 (volume ratio)] The electrolyte was placed in the case. The case was then sealed. In this manner, the battery of Production Example 1 was assembled.

[0090] [Production Example 2] As a masking material, SUS foil was prepared in addition to the polyimide resin used in Example 1. The SUS foil was set as the upper layer and the polyimide resin as the lower layer in a masking layer forming device similar to that used in Example 1, and an Al foil with a masking layer was formed. Thereafter, a wet granule was prepared in the same manner as in Example 1, and an active material layer was formed and arranged.

[0091] Next, the active material layer formed on the upper layer and the masking layer was removed using the same masking layer removal device as in Example 1. The active material layer and the lower layer on the Al foil were dried to produce a positive electrode sheet. Otherwise, the battery of Production Example 2 was assembled in the same manner as in Production Example 1.

[0092] "evaluation" The batteries of Production Examples 1 and 2 were initially charged, and then aged under the following conditions.

[0093] Temperature: 60℃ Hours: 24 hours The voltage after aging and the value obtained by subtracting the discharge capacity after aging from the charge capacity before aging (self-discharge amount) were measured to evaluate short-circuit resistance against foreign matter. The results are shown in Table 2. A voltage of 3.25 V or higher after aging was considered good, and a voltage of less than 3.25 V was considered short-circuited. A self-discharge amount of 5.24 mV or less was considered good. In both Production Examples 1 and 2, four batteries (Production Examples 1-1 to 1-4, 2-1 to 2-4) were fabricated and measured.

[0094] [Table 2]

[0095] (result) As shown in Table 2, in Production Example 2, all voltages after aging were 3.25 V or higher, and the self-discharge amounts were good at 5.24 mV or lower.

[0096] On the other hand, in Production Example 1, all voltages after aging were less than 3.25 V, and the self-discharge amount could not be measured.

[0097] Tests 1 and 2 showed that when the masking layer consisted of one layer, the dimensional variation in the width direction and conveyance direction of the active material layer was small and no damage was caused to the current collecting foil. However, by using two masking layers and leaving the lower layer intact, the short-circuit resistance against foreign matter was further improved.

[0098] The embodiments and examples disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0099] 1 first roll, 2 second roll, 3 third roll, 4 partition plate, 5 wet granules, 6 current collector foil with masking layer, 7 active material layer, 8 current collector foil, 9 electrode sheet, 10 roll film forming device.

Claims

[Claim 1] A method for manufacturing an electrode sheet having an active material layer intermittently formed on a surface of a current collector foil, comprising: a masking layer forming step of applying a masking material to a portion of the surface of the current collecting foil other than the portion where the active material layer is formed; a wet granulation preparation step of preparing wet granulation containing an electrode active material, a binder, a conductive material, and a solvent; an active material layer forming step of forming the active material layer by compression-molding the wet granules; an active material layer disposing step of disposing the active material layer by supplying the active material layer onto the masking layer and onto a portion of the surface of the current collecting foil that is not covered by the masking layer and compressing the active material layer; a removal step of removing the masking layer and the active material layer formed on the masking layer, the masking layer has a two-layer structure consisting of an upper layer and a lower layer, In the removing step, the active material layer formed on the upper layer and the masking layer is removed.

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