Method for manufacturing electrode laminate and method for manufacturing battery

Abstract

The present disclosure provides a method for producing an electrode laminate capable of suppressing cracking of an electrode active material layer, and a method for producing a battery including such a method for producing an electrode laminate.SOLUTION: The method of the present disclosure for producing an electrode laminate comprises the following steps, and does not comprise a step of winding the laminate into a roll after step (c): (a) applying an electrode mixture slurry to a transfer sheet 20 and drying the applied electrode mixture slurry to form an electrode active material layer, (b) providing a current collector 30, and (c) transferring the electrode active material layer to at least one surface of the current collector to obtain a laminate. The method of the present disclosure for producing a battery includes producing an electrode laminate by the method of the present disclosure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] As disclosed in Patent Documents 1 to 3, techniques for producing electrode stacks for batteries have been developed.

[0003] Patent Document 1 discloses a method for drying an electrode material, comprising: a coating step of coating a secondary current collector with an electrode material containing a solvent; an intermediate heating step of heating the electrode material coated on the secondary current collector to a temperature at which the saturated vapor pressure is 100 mmHg or more and 500 mmHg or less; and a transfer step of transferring the electrode material dried in the intermediate heating step from the secondary current collector to a main current collector.

[0004] Furthermore, Patent Document 1 discloses that heating in the intermediate heating section causes a binder to segregate on the surface side of the electrode material applied to the secondary current collector, and then the electrode material is transferred from the secondary current collector to the primary current collector in the transfer section, so that the electrode material binds to the primary current collector at the surface where the binder has segregated on the surface side, thereby improving the binding strength between the electrode material and the primary current collector.

[0005] Patent Document 2 discloses a method for manufacturing a bipolar electrode (electrode laminate), which includes a fabrication step of fabricating a laminate having a current collector, a positive electrode layer disposed on one surface of the current collector, and a negative electrode layer disposed on the other surface of the current collector, and a pressing step of roll-pressing the laminate from both sides using opposing press rolls, wherein in the pressing step, the press roll disposed on one side has an embrace angle.

[0006] Patent Document 3 discloses a method for manufacturing a bipolar battery electrode using a double-sided coated electrode (electrode laminate) for a bipolar battery, characterized in that a crush-resistant active material is first applied to one side of a current collector and pressed, and then a crush-resistant active material is applied to the remaining side and pressed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-216227 [Patent Document 2] Japanese Patent Application Publication No. 2024-034047 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-128039 Summary of the Invention [Problem to be solved by the invention]

[0008] There is room for improvement in terms of suppressing cracking of the electrode active material layer during the production of the electrode laminate.

[0009] An object of the present disclosure is to provide a method for manufacturing an electrode stack that can suppress cracking of an electrode active material layer, and a method for manufacturing a battery that includes a method for manufacturing such an electrode stack. [Means for solving the problem]

[0010] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> A method for producing an electrode laminate, comprising the steps of: (a) applying an electrode mixture slurry to a transfer sheet and then drying the applied electrode mixture slurry to form an electrode active material layer; (b) providing a current collector; and (c) transferring the electrode active material layer onto at least one surface of the current collector to obtain the laminate; <Aspect 2> the step (c) comprising transferring a negative electrode active material layer as the electrode active material layer to one surface of the current collector, and transferring a positive electrode active material layer as the electrode active material layer to the other surface of the current collector. <Aspect 3> 3. The method of claim 2, wherein the negative electrode active material layer is larger in size than the positive electrode active material layer. <Aspect 4> The method of embodiment 3, further comprising, after step (a), pressing at least the negative electrode active material layer. <Aspect 5> A method for producing a battery, comprising producing an electrode stack by the method according to any one of aspects 1 to 4. [Effects of the Invention]

[0011] According to the method of the present disclosure, cracking of the electrode active material layer can be suppressed during the production of an electrode stack, and a battery including the electrode stack thus produced can be produced. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a method of the present disclosure for producing an electrode stack. [Figure 2] FIG. 2 is a schematic diagram illustrating an example of a method of the present disclosure for producing an electrode stack. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the present disclosure.

[0014] <<Method for manufacturing electrode stack>> The disclosed method for producing an electrode stack includes the following steps and does not include a step of winding the stack into a roll after step (c): (a) applying an electrode mixture to a transfer sheet and then drying the applied electrode mixture to form an electrode active material layer; (b) providing a current collector; and (c) Transferring an electrode active material layer onto at least one surface of a current collector to obtain a laminate.

[0015] The present inventors have found that, as disclosed in Patent Document 1, when an electrode mixture slurry is applied onto a transfer sheet, and then an electrode active material layer is formed on the transfer sheet by segregating a binder contained in the electrode mixture slurry near the surface by heating, and then the electrode active material layer is transferred from the transfer sheet to a current collector, cracks may occur in the electrode active material layer.

[0016] The present inventors have considered that one of the causes of cracks in the electrode active material layer is a low binder density near the surface of the electrode active material layer after transfer. Specifically, without intending to be bound by any theory, this is presumed as follows. That is, while the binder segregates near the surface of the electrode active material layer before transfer, the binder density near the surface of the electrode active material layer is thought to be low after transfer. In such cases, the electrode active material layer has low flexibility near the surface, and the electrode active material layer is thought to crack when, for example, bending stress is applied to the electrode active material layer. Here, examples of when bending stress is applied to the electrode active material layer include when an electrode laminate is manufactured by a roll-to-roll process, i.e., when a laminate including the electrode active material layer is wound into a roll after the electrode active material layer is transferred.

[0017] In this regard, the present inventors have found that cracking of the electrode active material layer can be suppressed by not including a step of winding up a laminate including an electrode active material layer into a roll when producing an electrode laminate by transferring an electrode active material layer to a current collector. Without intending to be bound by any theory, the reason for this is thought to be that, since a step of winding up a laminate including an electrode active material layer into a roll is not included, it is possible to prevent bending stress from being applied to the electrode active material layer, and as a result, it is possible to suppress cracking of the electrode active material layer.

[0018] In the present disclosure, the term "electrode laminate" refers to a laminate of an electrode active material layer and a current collector, and is a component capable of passing a current. The term "electrode laminate" may be a negative electrode laminate or a positive electrode laminate. For example, when the term "electrode laminate" refers to a negative electrode laminate, the negative electrode laminate is a laminate of a negative electrode active material layer and a negative electrode current collector. When the term "electrode laminate" refers to a positive electrode laminate, the positive electrode laminate is a laminate of a positive electrode active material layer and a positive electrode current collector.

[0019] The method of manufacturing an electrode according to the present disclosure will be described below with reference to the drawings, in which the dimensional relationships do not reflect the actual dimensional relationships.

[0020] <Formation of electrode active material layer> As illustrated in FIG. 1( a), the method of the present disclosure for producing an electrode laminate 100 includes (a) applying an electrode mixture slurry to a transfer sheet 20 and drying the applied electrode mixture slurry to form an electrode active material layer 10.

[0021] The method for applying the electrode mixture slurry to the transfer sheet is not particularly limited, and any conventional method can be used.

[0022] The method for drying the electrode mixture slurry is not particularly limited, and any conventional method can be used.

[0023] The method for drying the electrode mixture slurry and the drying conditions such as drying time and drying temperature can be appropriately set depending on the ease of binder segregation and the like.

[0024] <Provision of current collectors> As illustrated in FIG. 1( b ), the disclosed method of manufacturing the electrode stack 100 includes (b) providing a current collector 30 .

[0025] The method for providing the current collector is not particularly limited, and for example, a commercially available product of a material that functions as a current collector may be used, or one prepared by a conventional method may be used. Furthermore, the current collector provided may be one that has been previously wound into a roll, unwound, and cut to a predetermined size.

[0026] <Transfer of electrode active material layer> As illustrated in FIG. 1(c), the method of the present disclosure for producing an electrode laminate 100 includes (c) transferring an electrode active material layer 10 to at least one surface of a current collector 30. The method of the present disclosure does not include a step of winding the laminate into a roll after step (c). In particular, the method of the present disclosure does not include a step of curving the laminate during or after the transfer in step (c). As described above, this configuration is believed to prevent bending stress from being applied to the electrode active material layer, thereby suppressing cracking of the electrode active material layer. In the present disclosure, the "curved" state of the electrode active material layer refers to a state in which the radius of curvature of the electrode active material layer is 100 cm or less, 90 cm or less, 80 cm or less, 70 cm or less, 60 cm or less, or 50 cm or less.

[0027] When manufacturing an electrode laminate, for example, a roll-to-roll process may be used, which may include a step of winding a laminate including an electrode active material layer into a roll. In the method of the present disclosure, for example, by not using the roll-to-roll process, it is possible to avoid the step of winding a laminate including an electrode laminate into a roll, particularly the step of curving the electrode active material layer during and after the transfer in step (c). Specifically, for example, by providing a current collector of a predetermined size that makes it inappropriate to use the roll-to-roll process, it is possible to avoid the step of curving the electrode active material layer.

[0028] The "predetermined size" of the current collector may refer to a size that can be used to manufacture a battery using an electrode laminate manufactured by the method of the present disclosure, for example, after step (c), without cutting the electrode laminate, or by cutting the electrode laminate so that the area of ​​the electrode laminate is reduced by 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less. In this case, the electrode active material layer may also be formed in step (a) to a size that can be used to manufacture a battery, similar to the electrode laminate. This configuration not only prevents cracking of the electrode active material layer, but also reduces the number of steps required after step (c) when manufacturing a battery, which is advantageous in terms of manufacturing.

[0029] The method for transferring the electrode active material layer onto at least one surface of the current collector is not particularly limited, and examples thereof include a method in which the electrode active material layer is pressed onto the current collector.

[0030] As illustrated in Fig. 2, the method of the present disclosure may include, in step (c), transferring a negative electrode active material layer 11 as an electrode active material layer 10 to one surface of a current collector 30, and transferring a positive electrode active material layer 12 as an electrode active material layer 10 to the other surface of the current collector 30. That is, the method of the present disclosure may be a method for producing a bipolar electrode laminate. Note that Fig. 2(a) shows the step of forming an electrode active material layer, Fig. 2(c) shows the step of providing a current collector, and Fig. 2(d) shows the step of transferring an electrode active material layer.

[0031] When the method of the present disclosure is a method for producing a bipolar electrode laminate, the size of the negative electrode active material layer 11 may be larger than the size of the positive electrode active material layer 12, as illustrated in FIGS. 2(a), 2(b), and 2(d). In this case, as illustrated in FIG. 2(b), the method may further include pressing at least the negative electrode active material layer 11 after step (a). If the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer, pressing the obtained bipolar electrode laminate after step (c) may not properly press the portion 11a of the negative electrode active material layer extending from the positive electrode active material layer in the planar direction (hereinafter, the extension portion), resulting in the extension portion being thicker than the other portions. As a result, cracks are more likely to occur due to bending stress. In this regard, the present inventors have discovered that pressing at least the negative electrode active material layer after step (a) can suppress cracks due to bending stress. The reason for this is thought to be that, without intending to be bound by any theory, pressing can be performed so that the thickness of the negative electrode active material layer becomes uniform.

[0032] When the method of the present disclosure is a method for producing a bipolar electrode stack, the method may further include pressing both the negative electrode active material layer 11 and the positive electrode active material layer 12 after step (a), as illustrated in FIG. 2(b). When the entire electrode stack including the positive electrode active material layer is pressed after step (c), excessive stress may be applied near the boundary between the extension portion 11a of the negative electrode active material layer and other portions, which may result in cracks occurring near the boundary in the negative electrode active material layer. In this regard, pressing both the negative electrode active material layer and the positive electrode active material layer after step (a) can prevent the application of such stress, thereby preventing cracks near the boundary in the negative electrode active material layer.

[0033] The pressing method is not particularly limited, and a conventional method can be used.

[0034] The elements that make up the method of the present disclosure are described below.

[0035] <Transfer sheet> The transfer sheet is not particularly limited as long as it allows the formed electrode active material layer to be peeled off. The material of the transfer sheet may be, for example, a resin, a metal, or the like.

[0036] The transfer sheet may have a release property on its surface. Examples of such a transfer sheet include sheets containing fluororesins such as polytetrafluoroethylene, silicone, etc. Also, examples include sheets whose surfaces are treated with a release agent, such as resin or metal.

[0037] <Electrode mixture slurry> The electrode mixture slurry contains an electrode active material, a binder, and a dispersion medium. The electrode mixture slurry may optionally contain a conductive aid and other components.

[0038] In the present disclosure, a "composite" refers to a composition that can constitute an electrode active material layer, etc., either as it is or by further containing other components. Also, in the present disclosure, a "composite slurry" refers to a slurry that contains a dispersion medium in addition to a "composite" and can be applied and dried to form an electrode active material layer, etc.

[0039] <Electrode active material> The electrode active material is not particularly limited. In the present disclosure, the "electrode active material" can be used as both a "negative electrode active material" and a "positive electrode active material."

[0040] The negative electrode active material is not particularly limited as long as it has a lower potential than the positive electrode active material. When the electrode laminate of the present disclosure is an electrode laminate for a lithium ion secondary battery, examples of the negative electrode active material include carbonaceous materials such as graphite (artificial graphite, natural graphite), resin carbon, carbon fiber, activated carbon, hard carbon, and soft carbon; metal-based materials mainly composed of tin, tin alloys, silicon, silicon alloys, gallium, gallium alloys, indium, indium alloys, aluminum, and aluminum alloys; conductive polymers such as polyacene, polyacetylene, and polypyrrole; metallic lithium; and Li4Ti5O 12and lithium alloys such as Li-Si alloys, Li-Sn alloys, Li-Al alloys, Li-Ga alloys, Li-Mg alloys, and Li-In alloys. These negative electrode active materials may be used singly or in combination of two or more.

[0041] The content of the negative electrode active material in the negative electrode mixture as the electrode mixture is not particularly limited, but may be 50 mass % or more, 70 mass % or more, 90 mass % or more, or 95 mass % or more.

[0042] The negative electrode active material may be in the form of particles, for example.

[0043] The positive electrode active material is not particularly limited as long as it has a more noble potential than the negative electrode active material. When the electrode laminate of the present disclosure is an electrode laminate for a lithium ion secondary battery, examples of the positive electrode active material include lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), lithium manganese oxide (LiMnO), solid solution oxide (LiMnO-LiMO (M=Co, Ni, etc.)), lithium nickel manganese oxide (LiNi 1 / 2 Mn 1 / 2 O2), lithium nickel cobalt manganese oxide (LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 Examples of the cathode active materials that can be used include composite oxides such as lithium phosphate oxide (LiFePO4), olivine-type lithium phosphate oxide (LiFePO4), and conductive polymers such as polyaniline and polypyrrole; sulfide-based cathode active materials such as LiS, CuS, Li-Cu-S compounds, TiS2, FeS, MoS2, Li-Mo-S compounds, Li-Ti-S compounds, and Li-VS compounds; and sulfur-based active materials such as sulfur-impregnated acetylene black, sulfur-impregnated porous carbon, and mixed powders of sulfur and carbon. These cathode active materials may be used alone or in combination of two or more.

[0044] The content of the positive electrode active material in the positive electrode mixture as the electrode mixture is not particularly limited, but may be 50 mass % or more, 70 mass % or more, 90 mass % or more, or 95 mass % or more.

[0045] The positive electrode active material may be in the form of particles, for example.

[0046] <Binder> In the present disclosure, the binder may segregate on the surface of the electrode active material layer during drying in step (a), and as a result, may have the function of facilitating peeling of the transfer sheet and the electrode active material layer during transfer in step (c), and may further have the function of improving the binding strength between the electrode active material layer and the current collector after transfer in step (c).

[0047] The binder is not particularly limited, but when the bipolar battery of the present disclosure is a lithium ion secondary battery, examples of the binder include polyvinylidene fluoride (PVdF), polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyvinyl alcohol, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, polyhexafluoropropylene, styrene-butadiene rubber, carboxymethyl cellulose, etc. These binders may be used alone or in combination of two or more.

[0048] The content of the binder in the electrode mixture is not particularly limited, and can be set appropriately depending on the desired binding properties, etc.

[0049] (dispersion medium) Examples of the dispersion medium include non-polar solvents, polar solvents, and combinations thereof. Examples of non-polar solvents include heptane, xylene, toluene, and combinations thereof. Examples of polar solvents include water, tertiary amine solvents such as triethylamine, ether solvents such as cyclopentyl methyl ether, thiol solvents such as ethane mercaptan, ester solvents such as butyl butyrate, and combinations thereof.

[0050] (Conductive additive) The conductive additive is not particularly limited, but when the bipolar battery of the present disclosure is a lithium ion secondary battery, examples include graphites such as natural graphite and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; carbon fibers such as carbon nanotubes, conductive fibers such as metal fibers; metal powders such as aluminum powder; conductive whiskers such as zinc oxide whiskers and conductive potassium titanate whiskers; conductive metal oxides such as titanium oxide; organic conductive materials such as phenylene derivatives; etc. These conductive additives may be used alone or in combination of two or more.

[0051] The content of the conductive auxiliary agent in the electrode mixture is not particularly limited and can be set appropriately depending on the desired conductivity, etc.

[0052] (Other ingredients) The electrode mixture may contain components other than those described above. Examples of such components include dispersants. Examples of dispersants include carboxymethyl cellulose.

[0053] <Current collector> The current collector may be any known electrode current collector, such as copper foil, copper alloy foil, nickel foil, aluminum foil, aluminum alloy foil, stainless steel foil, or carbon sheet.

[0054] In particular, when the method of the present disclosure is a method for producing a bipolar electrode laminate, the current collectors may have two different types of current collectors. In this case, the current collectors may be bonded to each other via a conductive adhesive layer or may be joined by pressing or the like. For example, the current collector on the negative electrode active material layer side may be copper foil, and the current collector on the positive electrode active material layer side may be aluminum foil.

[0055] The thickness of the current collector is not particularly limited, but may be 1 μm to 300 μm, 5 μm to 200 μm, or 10 μm to 100 μm. When the current collector has two types of current collectors bonded to each other via a conductive adhesive layer, the total thickness of the layers may be in the above range.

[0056] The size of the current collector is not particularly limited, but as described above, from the viewpoint of facilitating the production of an electrode laminate without including a step of winding the laminate into a roll after step (c), the current collector may be of a predetermined size, in particular a size that can be used directly in the production of a battery.

[0057] The planar shape of the current collector is not particularly limited, but may be, for example, a quadrangle such as a rectangle.

[0058] <Conductive adhesive layer> When the current collector has two different types of current collectors, the current collectors may be bonded to each other by a conductive adhesive layer interposed between the current collectors.

[0059] The material of the conductive adhesive layer is not particularly limited. The conductive adhesive layer may be made of a conductive adhesive, that is, for example, a mixture of an adhesive and a conductive component.

[0060] The adhesive may contain a curable resin. Examples of the curable resin include a thermosetting resin and a photocurable resin. More specifically, examples of the curable resin include an olefin-based resin and an acrylic-based resin.

[0061] The conductive adhesive layer may contain a water-based adhesive as the adhesive. When the adhesive in the conductive adhesive layer is a water-based adhesive, moisture is likely to remain in the conductive adhesive layer during the manufacturing process, and therefore, application of the water-based adhesive to the bipolar battery current collector of the present disclosure is more advantageous. The water-based adhesive is not particularly limited, but examples thereof include water-based curable resins, and examples of water-based curable resins include water-dispersible olefin resins.

[0062] The conductive component is not particularly limited as long as it has a higher conductivity than the adhesive, and examples thereof include metal particles such as gold, silver, platinum, zinc, stainless steel, nickel, copper, cobalt, molybdenum, antimony, iron, and chromium; alloy particles such as aluminum-magnesium alloys and aluminum-nickel alloys; metal oxide particles such as tin oxide and indium oxide; particles of metal particles such as nickel coated with precious metals such as gold, silver, and platinum; particles of non-conductive particles such as glass, ceramic, and plastic coated with precious metals such as gold, silver, and platinum, or particles of non-conductive particles such as plastic plated with metals such as nickel; graphites such as natural graphite and artificial graphite; and carbon particles such as carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black.

[0063] <Electrode active material layer> The electrode active material layer can be produced by drying an electrode mixture slurry applied to a transfer sheet.

[0064] The thickness of the electrode active material layer is not particularly limited. The thickness of the electrode active material layer before pressing may be 100 μm to 1000 μm, 200 μm to 750 μm, or 300 μm to 500 μm. The thickness of the electrode active material layer after pressing may be 10 μm to 500 μm, 100 μm to 450 μm, or 200 μm to 400 μm.

[0065] The size of the electrode active material layer is not particularly limited, but as described above, from the viewpoint of facilitating the production of an electrode laminate without including a step of winding the laminate into a roll after step (c), the size of the electrode active material layer may be a predetermined size, in particular a size that can be used directly for the production of a battery.

[0066] The planar shape of the electrode active material layer is not particularly limited, but may be, for example, a quadrangle such as a rectangle.

[0067] <Battery manufacturing method> The disclosed method of manufacturing a battery includes manufacturing an electrode stack by the disclosed method.

[0068] The battery produced by the method of the present disclosure may further include an electrolyte layer. In this case, for example, the battery can be produced by laminating the electrode stack produced by the method of the present disclosure and the electrolyte layer.

[0069] When the electrode stack produced by the method of the present disclosure is not a bipolar electrode stack, one of the negative electrode stack and the positive electrode stack may be an electrode stack produced by the method of the present disclosure, or both the negative electrode stack and the positive electrode stack may be electrode stacks produced by the method of the present disclosure.

[0070] The battery produced by the method of the present disclosure may be a secondary battery, and in particular a lithium ion secondary battery.

[0071] The battery manufactured by the method of the present disclosure may be a liquid-based battery or a solid-state battery. In the context of the present disclosure, a "solid-state battery" refers to a battery that uses at least a solid electrolyte as an electrolyte. Therefore, a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. Alternatively, the solid-state battery of the present disclosure may be an all-solid-state battery, i.e., a battery that uses only a solid electrolyte as an electrolyte. [Example]

[0072] Example <Production of Electrode Stack> (Preparation of electrode mixture slurry) A negative electrode mixture slurry containing artificial graphite as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a dispersion medium, and water as a dispersion medium was prepared by a conventional method.

[0073] A positive electrode mixture slurry containing lithium iron phosphate and lithium nickel cobalt manganese oxide as positive electrode active materials, SBR as a binder, carboxymethyl cellulose CMC as a dispersion medium, and water as a dispersion medium was prepared by a conventional method.

[0074] (Formation of electrode active material layer) The negative electrode composite slurry and the positive electrode composite slurry were intermittently coated onto a polytetrafluoroethylene sheet used as a transfer sheet. The coatings were then dried to obtain a negative electrode active material layer and a positive electrode active material layer as electrode active material layers. The resulting electrode active material layers were then pressed. The thickness of the negative electrode active material layer before pressing was 350 μm, and the thickness of the coating of the positive electrode active material layer was 320 μm. The thickness of the negative electrode active material layer after pressing was 300 μm, and the thickness of the positive electrode active material layer was 300 μm. The coating width of the negative electrode active material layer was 1250 mm and the coating length was 1500 mm, and the coating width of the positive electrode active material layer was 1200 mm and the coating length was 1500 mm. That is, the difference in the coating widths of both electrode active material layers, i.e., the length of the extended portions, was 50 mm in total (25 mm on each side).

[0075] (Provision of current collectors) Copper foil and aluminum foil were prepared as different types of current collectors. The copper foil and aluminum foil were bonded together using a conductive adhesive made of a water-dispersible olefin resin (NZ-1015, manufactured by Toyobo MC Co., Ltd.) with nickel-plated particles dispersed therein. The bonded metal foil was then cut into a size suitable for use in battery production to provide a current collector.

[0076] (Transfer of electrode active material layer) The negative electrode active material layer was transferred onto the copper foil side of the provided current collector, and the positive electrode active material layer was transferred onto the aluminum foil side, thereby obtaining an electrode laminate of the example.

[0077] Comparative Example Each electrode active material layer was formed in the same manner as in the Examples, except that pressing was not performed in the electrode active material layer formation step. Then, each electrode active material layer was transferred to a current collector prepared by bonding copper foil and aluminum foil in the same manner as in the Examples, to obtain a laminate. Then, in the subsequent transport process, the laminate was pressed and wound into a roll. That is, the laminate was manufactured by a roll-to-roll method. The obtained laminate was unwound from the roll and cut. This resulted in an electrode laminate of the comparative example.

[0078] "evaluation" The electrode laminates of the examples and comparative examples were checked for the migration index on the current collector side of the negative electrode active material layer and for the presence or absence of cracks in the electrode active material layer. The "migration index" is an index for evaluating the binder distribution in the thickness direction of the electrode active material layer, and this value approaches 1.0 when the binder is uniformly distributed.

[0079] As a result, the migration index on the current collector side of the negative electrode active material layer was 0.67 in the example and 0.7 in the comparative example, which means that binder segregation was confirmed in both negative electrode active material layers.

[0080] On the other hand, no cracks were found in any of the electrode active material layers in the Examples, whereas cracks were found in the extending portions of the negative electrode active material layer in the Comparative Examples. [Explanation of symbols]

[0081] 100 Electrode laminate 10 Electrode active material layer 11 Negative electrode active material layer 11a Extension 12 Cathode active material layer 20 Transfer sheet 30 Current collector

Claims

1. A method for producing an electrode laminate, comprising the steps of: (a) applying an electrode mixture slurry to a transfer sheet and drying the applied electrode mixture slurry to form an electrode active material layer; (b) providing a current collector; and (c) transferring the electrode active material layer onto at least one surface of the current collector to obtain the laminate;

2. 2. The method according to claim 1, wherein in step (c), a negative electrode active material layer serving as the electrode active material layer is transferred to one surface of the current collector, and a positive electrode active material layer serving as the electrode active material layer is transferred to the other surface of the current collector.

3. The method according to claim 2 , wherein the negative electrode active material layer is larger in size than the positive electrode active material layer.

4. The method of claim 3 , further comprising pressing at least the negative electrode active material layer after step (a).

5. A method for producing a battery, comprising producing an electrode stack by the method according to any one of claims 1 to 4.

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