Inspection method, manufacturing method of laminate for secondary battery, and manufacturing method of secondary battery

Abstract

The purpose of the present invention is to provide a novel technology capable of sufficiently suppressing bonding failure by identifying poorly coated areas with a high degree of accuracy when producing a secondary battery laminate in which battery members are bonded to one another using an adhesive material. The testing method of the present invention is used when forming a dried material on a bonding surface by performing a step for applying a coating material onto the bonding surface of an electrode / and or a separator, and a step for forming an adhesive material by drying the coating material on the bonding surface. This testing method involves identifying a poorly coated area by measuring the displacement of the bonding surface to which the coating material was applied by using a laser displacement meter before performing the step for forming the adhesive material.

Description

[Technical Field]

[0001] The present invention relates to a method for inspecting the surface of a battery component for defective application of adhesive material, and a method for manufacturing a laminate for a secondary battery and a secondary battery through said inspection. [Background technology]

[0002] Secondary batteries such as lithium-ion secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications. Secondary batteries generally include battery components such as a positive electrode, a negative electrode, and a separator that separates the positive electrode from the negative electrode to prevent short-circuiting between the positive electrode and the negative electrode.

[0003] In the manufacturing process of a secondary battery, the electrodes and separators are pressure-bonded together before being immersed in an electrolyte solution to form a laminate (hereinafter, sometimes referred to as a "secondary battery laminate"), which may then be cut to a desired size, stacked, folded, or rolled as needed. During the cutting, stacking, folding, or rolling, the pressure-bonded electrodes and separators may become misaligned, resulting in problems such as defects and reduced productivity.

[0004] Therefore, in recent years, a technology has been studied for effectively bonding battery components together by using battery components having an adhesive material containing a binder on their surfaces.For example, in Patent Document 1, a separator having an adhesive material on its surface is produced by applying a coating containing a predetermined thermoplastic polymer to the separator and drying the coating to remove the solvent in the coating liquid. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-170281 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, when bonding battery components together using an adhesive material, there may be areas where the adhesive material is not applied unintentionally due to improper application of the paint (application imperfections). In order to identify such application imperfections and prevent bonding defects between battery components, the bonding surfaces on which the adhesive material has been dried may be inspected using a CCD camera or the like before bonding. However, the conventional inspection method is required to identify the defective coating portion with higher accuracy. In particular, in recent years, attempts have been made to reduce the amount of adhesive material that can become a resistance component in order to lower the internal resistance of secondary batteries and improve battery characteristics. However, the inventors' studies have revealed that when the amount of paint used is reduced to reduce the amount of adhesive material, the adhesive material formed after drying is buried in the unevenness of the bonding surfaces, making it difficult to identify the defective coating portion using the conventional inspection method.

[0007] Therefore, the present invention aims to provide a new technology that can sufficiently suppress bonding defects by identifying defective coating areas with high accuracy when manufacturing a laminate for a secondary battery in which battery components are bonded together via an adhesive material. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems. First, in the manufacturing process of a laminate in which battery components are bonded together via an adhesive material, the inventors focused on the paint applied to the bonding surfaces before drying, rather than the adhesive material that has been the subject of conventional inspection after drying. The inventors then discovered that by using a laser displacement meter to measure the displacement of the bonding surfaces to which the paint has been applied but before drying, it is possible to improve the accuracy of identifying coating defects, and thus completed the present invention.

[0009] That is, the present invention aims to advantageously solve the above-mentioned problems, and provides an inspection method that is used when forming an adhesive material on a bonding surface, through a step of applying a paint containing a binder and a solvent to the bonding surfaces of at least one of an electrode and a separator, and a step of drying the paint applied to the bonding surfaces to form an adhesive material, and is characterized by including a step of measuring the displacement of the bonding surfaces to which the paint has been applied using a laser displacement meter, prior to the step of forming the adhesive material, to identify areas of poor coating. Compared to adhesive materials formed after drying, paint before drying tends to have a larger displacement (height) from the bonded surface due to the solvent removed by drying. Therefore, by measuring the displacement of the bonded surface coated with paint using a laser displacement meter before drying, the difference in displacement between the coated area and the defective coating area can be clearly identified, allowing for the identification of the defective coating area with high accuracy. In other words, if such an inspection is performed, if a large number of defective coating areas are found, the production line can be immediately stopped, the cause of the defective coating areas (e.g., clogging of the coating nozzle) can be identified, and the cause can be quickly removed. As a result, the incidence of defective electrode and separator bonding can be reduced.

[0010] Furthermore, in the inspection method of the present invention, it is preferable that in the step of applying the paint, the average height of the paint from the bonding surface is 2 μm or more and 150 μm or less. If the average height of the paint applied to the bonding surface is within the above-mentioned range, the difference in displacement between the applied area and the area with poor coating becomes clearer, resulting in improved accuracy in identifying the areas with poor coating. In addition, the drying efficiency of the paint can be improved. In the present invention, the "average height of the paint from the bonding surface" of the paint can be calculated as the average value of the height of the paint at any 1000 points measured using a laser displacement meter or the like.

[0011] In the inspection method of the present invention, it is preferable that in the step of applying the adhesive material, the adhesive material is applied in the form of dots, and the average diameter of the adhesive material applied in the form of dots is 5 μm or more and 300 μm or less. If the average diameter of the dot-shaped adhesive material applied to the bonding surfaces is within the above-mentioned range, the electrodes and the separators can be bonded well. In the present invention, the "average diameter of the adhesive material formed in the form of dots" can be calculated as the average value of the maximum diameters (the maximum length of the line segments connecting two points on the outer edge of one dot) of any 1,000 dots in a planar image of the bonding surface obtained by observation using a laser microscope or the like.

[0012] In the inspection method of the present invention, it is preferable that the solid content of the paint in the paint application step is 20% by mass or less. Paint with a solid content of 20% by mass or less does not become excessively viscous and is easy to handle. Therefore, the occurrence of poorly applied areas can be sufficiently suppressed, and the incidence of poor bonding between the electrode and the separator can be reduced.

[0013] In the inspection method of the present invention, it is preferable that the coating is performed by an inkjet method in the step of applying the coating material, since the inkjet method offers excellent flexibility in the shape of the coating material (coating shape), and if the coating material is applied by the inkjet method, productivity of the laminate can be sufficiently ensured.

[0014] The present invention also aims to advantageously solve the above-mentioned problems. The present invention provides a method for manufacturing a secondary battery laminate comprising bonding electrodes and separators, the method comprising the steps of: inspecting the electrodes and separators according to any of the inspection methods described above; and, after the inspection, bonding the electrodes and separators together via the bonding surfaces on which the adhesive material is formed. By inspecting the electrodes and separators according to the inspection method described above, if a large number of coating defects are found, a rapid response is possible, such as immediately stopping the production line to resolve the problem. As a result, the incidence of bonding defects between electrodes and separators is reduced, and laminates can be manufactured efficiently.

[0015] The present invention also aims to advantageously solve the above-mentioned problems, and provides a method for manufacturing a secondary battery comprising a laminate for a secondary battery formed by bonding together electrodes and a separator, the method comprising the steps of: manufacturing the laminate for a secondary battery using the above-described method for manufacturing a laminate for a secondary battery; and assembling a secondary battery using the laminate for a secondary battery and an electrolyte solution. The laminate manufactured according to the above-described method for manufacturing a laminate has a reduced incidence of bonding defects between the electrodes and the separator, and therefore, by using the laminate, secondary batteries with excellent battery characteristics can be efficiently manufactured. [Effects of the Invention]

[0016] According to the inspection method of the present invention, when manufacturing a stack for a secondary battery in which battery components are bonded together via an adhesive material, it is possible to identify defective coating locations with high accuracy. Furthermore, according to the method for producing a laminate for a secondary battery of the present invention, the rate of occurrence of defective bonding between electrodes and separators can be reduced, and laminates for a secondary battery can be produced efficiently. According to the method for producing a secondary battery of the present invention, a secondary battery having excellent battery characteristics can be produced efficiently. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is an explanatory diagram showing a schematic configuration of an example of an apparatus for manufacturing a laminate for a secondary battery. [Figure 2] FIG. 2 is a plan view showing an example of a coating pattern of paint. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail. Here, the inspection method of the present invention can be used to identify defective coating locations on the bonding surfaces of electrodes and / or separators when manufacturing a laminate for a secondary battery by bonding electrodes (positive electrode and / or negative electrode) and separators together. Furthermore, the method for manufacturing a secondary battery stack of the present invention is a method for manufacturing a secondary battery stack through inspection according to the above-described inspection method of the present invention, and is particularly suitable for use when continuously manufacturing secondary battery stacks. The method for manufacturing a secondary battery of the present invention can be used to manufacture a secondary battery such as a non-aqueous secondary battery (e.g., a lithium ion secondary battery) using the laminate for a secondary battery manufactured according to the method for manufacturing a laminate for a secondary battery of the present invention described above.

[0019] (Testing method) As described above, the inspection method of the present invention is used in the process of manufacturing a stack for a secondary battery. Specifically, the manufacturing process of a stack for a secondary battery in which the inspection method of the present invention is implemented includes at least the following steps: a step of applying a coating material containing a binder and a solvent to at least one of the bonding surfaces of the electrode and the separator (application step); After the coating process, a step (inspection step) of measuring the displacement of the bonded surfaces on which the coating has been applied using a laser displacement meter to identify coating defects; After the inspection step, a step of drying the paint applied to the bonding surface to form an adhesive material (drying step); a step of bonding the electrode and the separator together via the bonding surface on which the adhesive material is formed (a bonding step) after the drying step; Equipped with.

[0020] In the manufacturing process of a laminate, which involves coating, drying, and bonding steps, if an inspection step is performed prior to the drying step to measure the displacement of the bonding surface using a laser displacement meter, coating defects can be identified with high accuracy. As a result, the occurrence of bonding defects between the electrode and separator can be suppressed, and laminates can be manufactured efficiently. Furthermore, this manufacturing process allows the laminate to be manufactured in-line, with the coating, inspection, drying, and lamination processes all carried out on a single line, eliminating problems such as adhesive material falling off or blocking that occur when winding and slitting to transport battery components in conventional manufacturing processes.

[0021] <Laminate for secondary battery> The laminate is formed by bonding an electrode and a separator together via their bonding surfaces. Here, the electrode bonded to the separator to form the laminate may be only a positive electrode, only a negative electrode, or both a positive electrode and a negative electrode. Furthermore, when both a positive electrode and a negative electrode are bonded to a separator to form a laminate, the number of positive electrodes, negative electrodes, and separators in the laminate may each be one, or two or more. That is, the structure of the laminate may be any one of the following (1) to (6). (1) Positive electrode / separator (2) Negative electrode / separator (3) Positive electrode / separator / negative electrode (4) Positive electrode / separator / negative electrode / separator (5) Separator / positive electrode / separator / negative electrode (6) A structure in which multiple positive and negative electrodes are alternately stacked with separators in between (e.g., "separator / negative electrode / separator / positive electrode / separator / negative electrode... / separator / positive electrode") A laminate having a plurality of electrodes and / or separators can be manufactured by, for example, repeatedly carrying out the above-mentioned coating step, inspection step, drying step, and lamination step.

[0022] <Electrode> Here, the electrode is not particularly limited, and for example, an electrode made of an electrode base material in which an electrode mixture layer is formed on one or both sides of a current collector, or an electrode in which a porous membrane layer is further formed on the electrode mixture layer of an electrode base material can be used. The current collector, electrode mixture layer, and porous membrane layer are not particularly limited, and any current collector, electrode mixture layer, and porous membrane layer that can be used in the field of secondary batteries, such as those described in JP 2013-145763 A, can be used. Here, the porous membrane layer refers to a layer containing non-conductive particles, such as those described in JP 2013-145763 A. The electrodes used to manufacture the laminate may be wound in a roll shape or may be pre-cut. The thickness of the electrode is not particularly limited, but is preferably 30 μm or more and 250 μm or less.

[0023] <Separator> The separator is not particularly limited, and for example, a separator made of a separator substrate or a separator made of a separator substrate with a porous membrane layer formed on one or both sides thereof can be used. The separator substrate and the porous membrane layer are not particularly limited, and any separator substrate and porous membrane layer that can be used in the field of secondary batteries, such as those described in JP-A-2012-204303 and JP-A-2013-145763, can be used. The separator used in the production of the laminate may be wound in a roll shape or may be pre-cut. In particular, from the viewpoint of efficient and continuous production of the laminate, it is preferable to use a separator wound in a roll shape. Here, the thickness of the separator is not particularly limited, but is preferably 1 μm or more and 30 μm or less.

[0024] <Coating process> In the coating step, a coating material is applied to the bonding surfaces of the electrodes and / or separators.

[0025] <<Paint>> The coating material is a component that can form an adhesive material by drying on the bonding surfaces, and includes a binder and a solvent, and optionally includes components other than the binder and the solvent, such as non-conductive particles.

[0026] [Binding material] The binder is not particularly limited as long as it can bond the electrodes and the separator and does not inhibit the battery reaction, and any binder used in the field of secondary batteries can be used. In particular, from the viewpoint of good adhesion between the electrodes and the separator, it is preferable to use a binder made of a polymer. The binder may be made of only one type of polymer, or two or more types of polymers.

[0027] Here, polymers that can be used as binders are not particularly limited, and examples thereof include fluorine-based polymers such as polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer; conjugated diene-based polymers such as styrene-butadiene copolymer (SBR) and acrylonitrile-butadiene copolymer (NBR); hydrogenated conjugated diene-based polymers; polymers containing (meth)acrylic acid alkyl ester monomer units (acrylic polymers); and polyvinyl alcohol-based polymers such as polyvinyl alcohol (PVA). In the present invention, the term "(meth)acrylic acid" means acrylic acid and / or methacrylic acid.

[0028] The shape of the polymer binder is not particularly limited, and may be particulate, non-particulate, or a combination of particulate and non-particulate forms. When the polymer binder is particulate, the particulate binder may be a particle with a single phase structure formed from a single polymer, or a particle with a heterogeneous phase structure formed by physically or chemically bonding two or more different polymers. Specific examples of heterogeneous phase structures include a core-shell structure in which spherical particles have a central portion (core portion) and an outer shell portion (shell portion) formed from different polymers; and a side-by-side structure in which two or more polymers are juxtaposed. In the present invention, the term "core-shell structure" includes not only a structure in which the shell portion completely covers the outer surface of the core portion, but also a structure in which the shell portion partially covers the outer surface of the core portion. Even if the outer surface of the core portion appears to be completely covered by the shell portion, the shell portion is considered to partially cover the outer surface of the core portion if pores communicating the inside and outside of the shell portion are formed.

[0029] Furthermore, when the polymer binder is particulate, the volume average particle diameter of the particulate binder is preferably 0.1 μm or more, more preferably 0.15 μm or more, and even more preferably 0.18 μm or more, and is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 6 μm or less. If the volume average particle diameter of the particulate binder is 0.1 μm or more, the adhesive strength between the electrode and the separator can be increased. Furthermore, if the volume average particle diameter of the particulate binder is 10 μm or less, the energy density of a secondary battery produced using the laminate can be increased. In the present invention, the term "volume average particle size" refers to the particle size at which the cumulative volume calculated from the smallest diameter side is 50% in the volume-based particle size distribution measured by laser diffraction. Furthermore, when the particulate binder contains a polymer having a core-shell structure, the volume average particle diameter of the polymer having a core-shell structure is preferably 0.1 μm or more, more preferably 0.15 μm or more, even more preferably 0.2 μm or more, and preferably 8 μm or less, more preferably 6 μm or less, and even more preferably 4 μm or less. If the volume average particle diameter of the binder made of a polymer having a core-shell structure is 0.1 μm or more, the adhesive strength between the electrode and the separator can be increased. Furthermore, if the volume average particle diameter of the binder made of a polymer having a core-shell structure is 8 μm or less, the energy density of a secondary battery produced using the laminate can be increased.

[0030] Furthermore, when the particulate binder contains a polymer having a core-shell structure, the diameter of the core portion of the polymer having a core-shell structure is preferably 5% or more and less than 100%, more preferably 10% or more and less than 100%, and even more preferably 20% or more and less than 100%, of the volume average particle diameter of the polymer having a core-shell structure (100%). If the diameter of the core portion is equal to or more than the above lower limit, the particle shape can be maintained in a good condition even after being supplied to the bonding surface and dried, and the electrode and separator can be well bonded.

[0031] Furthermore, when the binder is made of a polymer, the polymer constituting the binder preferably contains a low Tg polymer with a glass transition temperature of 25°C or lower. If the polymer constituting the binder contains a low Tg polymer, the adhesive strength between the electrode and the separator can be increased. The glass transition temperature of the low Tg polymer is preferably -120°C or higher. In the present invention, the glass transition temperature can be measured by the following procedure using a differential thermal analyzer. First, a differential scanning calorimetry (DSC) measurement system (SII NanoTechnology, product name: EXSTAR DSC6220) was used. 10 mg of the dried polymer sample was weighed into an aluminum pan, and an empty aluminum pan was used as a reference. The DSC curve was measured at room temperature and humidity with a temperature increase rate of 10°C / min between -120°C and 200°C. During this temperature increase, the glass transition temperature (Tg) was calculated as the intersection of the baseline just before the endothermic peak of the DSC curve, where the differential signal (DDSC) is 0.05 mW / min / mg or higher, and the tangent to the DSC curve at the first inflection point after the endothermic peak. When the polymer has a core-shell structure described below and the core polymer or the shell polymer is used as the measurement sample, the monomer composition used in preparing each of the core polymer and the shell polymer is used to prepare an aqueous dispersion containing the polymer to be used as the measurement sample under polymerization conditions similar to those of the polymer, and the aqueous dispersion is dried to obtain the polymer to be used as the measurement sample.

[0032] When the binder contains a polymer having a core-shell structure, the polymer having a core-shell structure preferably has a shell portion with a higher glass transition temperature than the core portion. If the shell portion has a higher glass transition temperature than the core portion, fusion of the particulate polymers after bonding the battery components together can be prevented, thereby suppressing an increase in resistance. The glass transition temperature of the core portion of the polymer having a core-shell structure is preferably -40°C or higher and 200°C or lower, more preferably -40°C or higher and 100°C or lower, and even more preferably -40°C or higher and 70°C or lower. If the glass transition temperature of the core portion is -40°C or higher, the battery components can be more firmly bonded to each other via the adhesive material. Furthermore, if the glass transition temperature of the core portion is 100°C or lower, the polymerization stability of the particulate polymer can be ensured. The glass transition temperature of the shell portion of the polymer having a core-shell structure is preferably 10°C or higher, more preferably 20°C or higher, and even more preferably 30°C or higher, and is preferably 130°C or lower, and more preferably 120°C or lower. If the glass transition temperature of the shell portion is 10°C or higher, the particle shape can be maintained in good condition even after being supplied to the bonding surface. If the glass transition temperature of the shell portion is 130°C or lower, the electrode and separator can be well bonded. Here, the polymer having a core-shell structure preferably has at least one glass transition temperature of 25° C. or less.

[0033] [solvent] The solvent is not particularly limited, and examples thereof include water, organic solvents, and mixtures thereof. Examples of the organic solvent include, but are not limited to, alicyclic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone and cyclohexanone; esters such as ethyl acetate, butyl acetate, γ-butyrolactone, and ε-caprolactone; nitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether; and alcohols such as methanol, ethanol, isopropanol, ethylene glycol, and ethylene glycol monomethyl ether. Among the above, from the viewpoint of efficiently producing the laminate, water and alcohol are preferred as the solvent, and water is more preferred.

[0034] [Non-conductive particles] The non-conductive particles that can be optionally contained in the coating material are particles that do not dissolve in the coating material solvent or the secondary battery electrolyte and maintain their shape even in these solvents. By using a coating material that contains non-conductive particles in addition to the binder and solvent described above, the non-conductive particles can be incorporated into the adhesive material formed after drying. Such non-conductive particles can contribute to improving the heat shrinkage resistance of the laminate and preventing short circuits in the secondary battery.

[0035] As the non-conductive particles, for example, various inorganic fine particles or organic fine particles can be used. Specifically, the non-conductive particles may be either inorganic fine particles or organic fine particles made of a polymer other than the binder described above, but inorganic fine particles are usually used. Among these, the non-conductive particles are preferably made of a material that is stable in the environment in which the secondary battery is used and is electrochemically stable. From this viewpoint, preferred examples of non-conductive particles include oxide particles such as aluminum oxide (alumina), aluminum oxide hydrate (boehmite (AlOOH), gibbsite (Al(OH)), silicon oxide, magnesium oxide (magnesia), calcium oxide, titanium oxide (titania), barium titanate (BaTiO), ZrO, and alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystalline particles such as silicon and diamond; sparingly soluble ionic crystalline particles such as barium sulfate, calcium fluoride, and barium fluoride; and clay fine particles such as talc and montmorillonite. Furthermore, these particles may be subjected to element substitution, surface treatment, solid solution formation, etc., as necessary. Among these, barium sulfate particles and alumina particles are preferred as non-conductive particles. The non-conductive particles may be used alone or in combination of two or more kinds.

[0036] The volume average particle size of the non-conductive particles is not particularly limited, but is preferably, for example, 0.1 μm or more and 2.0 μm or less. The amount of the non-conductive particles used is not particularly limited, and can be determined appropriately within the range of a normal amount used.

[0037] [Paint properties] The solids concentration of the coating material is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 20% by mass or less, even more preferably 15% by mass or less, and particularly preferably 10% by mass or less. A solids concentration of 50% by mass or less allows the coating material to have a sufficient average height at the bonding surface, facilitating detection using a laser displacement meter. Furthermore, a coating material with a solids concentration of 20% by mass or less does not become excessively viscous and is easy to handle. This effectively prevents the occurrence of coating defects, thereby reducing the incidence of bonding defects between electrodes and separators. Although there is no particular lower limit for the solid content of the paint, from the viewpoint of ensuring drying efficiency, the solid content is preferably 1% by mass or more, and more preferably 5% by mass or more.

[0038] The viscosity of the coating material is preferably 1 mPa·s or more and 50 mPa·s or less, more preferably 1 mPa·s or more and 40 mPa·s or less, and even more preferably 1 mPa·s or more and 30 mPa·s or less. Coating materials with viscosities within the above ranges are easy to handle. Therefore, coating defects can be sufficiently suppressed, reducing the incidence of poor bonding between the electrode and separator. In the present invention, the "viscosity" can be measured in accordance with JIS Z8803. Specifically, the "viscosity" value can be the viscosity value measured at a temperature of 25°C using a coaxial double cylindrical rotational viscometer.

[0039] <<Application method>> The coating material may be applied to the bonding surfaces by any method, including, for example, an inkjet method, a spray method, a dispenser method, a gravure coating method, a screen printing method, etc. Among these, from the viewpoints of productivity and a high degree of freedom in the shape of the coating material, the inkjet method is preferred.

[0040] The paint may be applied to the entire bonding surface or only a portion of the bonding surface. When the paint is applied to only a portion of the bonding surface, the paint may be applied to any shape in a plan view, such as a stripe shape, a dot shape, or a grid shape, without any particular limitation. In particular, from the viewpoint of improving the injectability of an electrolyte solution when a secondary battery is manufactured using the laminate, it is preferable to apply the paint in a dot shape. The dot-shaped paint may be uniformly arranged (applied) over the entire bonding surface, or may be arranged (applied) in a predetermined pattern, such as a stripe shape, a dot shape, or a grid shape. When fine dot-shaped paint is arranged in a predetermined pattern, it is preferable to apply the paint in the desired pattern by an inkjet method, from the viewpoint of ease of forming and arranging the paint.

[0041] The average height of the paint applied to the bonding surfaces is preferably 2 μm or more, preferably 150 μm or less, and more preferably 125 μm or less. If the average height of the paint is 2 μm or more, the difference in displacement between the applied area and the imperfectly applied area becomes clearer, resulting in improved accuracy in identifying the imperfectly applied area. On the other hand, if the average height of the paint is 150 μm or less, the drying efficiency of the paint in the drying process described below can be improved.

[0042] In addition, the surface roughness Sa of the bonding surface to which the coating material is applied in the electrode and / or separator is not particularly limited, but is preferably 0.2 μm or more and 1.0 μm or less in the case of the electrode, and 0.1 μm or more and 1.0 μm or less in the case of the separator. According to the inspection method of the present invention, in which the bonding surface to which the solvent-containing coating material is applied and before drying is inspected using a laser displacement meter, it is possible to ensure sufficient accuracy in identifying coating defects even when the bonding surface has a surface roughness Sa within the above-mentioned range. In the present invention, the "surface roughness Sa" of the bonding surface can be calculated by measuring 10 arbitrary 100 μm square areas on the bonding surface using a laser displacement meter microscope (manufactured by Keyence, model: VK-X1000).

[0043] <Inspection process> In the inspection step, the displacement of the bonding surface to which the paint has been applied in the coating step is measured by a laser displacement meter to identify areas of coating defects.

[0044] Here, the laser displacement meter is not particularly limited as long as it is an inspection device that can measure the displacement of a measurement surface without contact using laser light, and any known laser displacement meter can be used. By using a laser displacement meter as an inspection device, it is possible to precisely measure the displacement of the bonding surface. In addition, a laser displacement meter has the advantage that it can detect paint even if it is a dilute liquid with high light transmittance.

[0045] In the inspection process, the number and locations of coating defects can be identified from data on the displacement of the bonding surface measured by the laser displacement meter. For example, in the coating process described above, if dot-shaped paint is applied to the bonding surface in a desired pattern, by comparing the desired pattern with the actually formed pattern identified from displacement data measured by a laser displacement meter, it is possible to easily identify the number of defective coating areas, etc., during the process of continuously (in-line) manufacturing the laminate. If a large number of defective coating areas are found during the inspection process, for example exceeding a predetermined standard value, a quick response can be taken, such as immediately stopping the production line to solve the problem. As a result, the rate of defective bonding between the electrode and separator can be reduced. The measurement conditions (inspection conditions) using the laser displacement meter can be set appropriately depending on the material of the battery components that have the bonding surfaces and the properties of the paint on the bonding surfaces.

[0046] <Drying process> In the drying step, after the inspection step, the paint applied to the bonding surfaces is dried to form an adhesive material.

[0047] Drying can be performed using a heating device such as a heater, dryer, or heat roller, without any particular limitation. The temperature at which the electrodes and / or separators coated with the coating material are dried is preferably 0°C or higher, more preferably 10°C or higher, even more preferably 15°C or higher, and preferably 200°C or lower, more preferably 150°C or lower, and even more preferably 100°C or lower. If the drying temperature is 10°C or higher, the drying rate can be sufficiently increased, allowing the laminate to be produced efficiently. Furthermore, if the drying temperature is 200°C or lower, the adhesive material formed by drying the coating material has a good shape, allowing the electrodes and separators to be well bonded.

[0048] Here, the adhesive material formed by drying the paint is preferably in the form of dots. The average diameter of the adhesive material formed in the form of dots is preferably 5 μm or more, preferably 300 μm or less, and more preferably 250 μm or less. If the average diameter of the adhesive material dots formed on the bonding surface is within the above-mentioned range, the electrode and the separator can be bonded well.

[0049] The amount of adhesive material applied to the bonding surfaces is 0.01 g / m 2 More than 100g / m 2 Preferably, it is 0.01 g / m or less. 2 More than 50g / m 2 More preferably, it is 0.01 g / m or less. 2 More than 10g / m 2 More preferably, it is 0.01 g / m or less. 2 More than 1g / m 2 It is particularly preferable that the amount of adhesive material formed is 0.01 g / m or less. 2 If the amount of adhesive material formed is 100 g / m or more, the electrodes and the separator can be sufficiently bonded. 2 If the above ratio is less than 1, the laminate can be efficiently produced.

[0050] The cross-sectional shape of the adhesive material is not particularly limited and may be a convex shape, a concave shape, or a concave shape, and among these, a concave shape is preferable from the viewpoint of further improving adhesion between the electrode and the separator. Note that the cross-sectional shape of the adhesive material can be changed, for example, by adjusting the drying conditions when drying the paint to form the adhesive material. When the adhesive material is formed at one or more locations, preferably at two or more locations, on the bonding surface, the area of ​​the adhesive material formed on the bonding surface is 15 μm per location. 2 It is preferable that the thickness is 25 μm or more. 2 More preferably, it is 50 μm or more. 2 More preferably, it is 150,000 μm or more. 2 Preferably, it is 100,000 μm or less. 2 More preferably, it is 80,000 μm or less. 2 It is more preferable that the area of ​​the adhesive material formed per one location is 15 μm or less. 2 If the thickness is more than 150,000 μm, the electrode and the separator can be sufficiently bonded. 2 If the above ratio is less than 1, the laminate can be efficiently produced. The formation area can be adjusted by changing the amount, shape, and range of the paint applied to the bonding surfaces. Specifically, when the paint is applied to the bonding surfaces by an inkjet method, the formation area can be adjusted by changing the gradation of the paint ejection from the nozzles of the inkjet head (the number of times the paint is ejected onto the same point).

[0051] <Laminating process> In the lamination step, after the drying step, the electrode and the separator are laminated together via the lamination surfaces on which the adhesive material has been formed. The lamination method is not particularly limited, and can be performed, for example, by applying pressure and / or heat to a laminate of the electrode and the separator that have been laminated together via the lamination surfaces.

[0052] The pressure applied to the laminate in the lamination step, the temperature when laminating the electrodes and the separator, and the time for pressurizing and / or heating the laminate can be adjusted appropriately depending on the type and amount of the binder (including the adhesive material) used, etc.

[0053] (Method of manufacturing laminate for secondary battery) The method of manufacturing a stack for a secondary battery of the present invention is a method of manufacturing a stack for a secondary battery formed by bonding together electrodes and separators, and includes a step of carrying out an inspection according to the above-described inspection method of the present invention. Specifically, one embodiment of the method for manufacturing a secondary battery laminate of the present invention includes at least the coating step, inspection step, drying step, and lamination step described in the "Inspection Method" section. Furthermore, by using the method for manufacturing a secondary battery laminate of the present invention, it is possible to identify coating defects with high accuracy in the inspection step, and if a large number of coating defects occur, it is possible to quickly address the problem by immediately stopping the production line. As a result, by using the method for manufacturing a secondary battery laminate of the present invention, the rate of occurrence of bonding defects between electrodes and separators is reduced, and secondary battery laminates can be produced efficiently.

[0054] (An example of a manufacturing apparatus for a laminate for a secondary battery) The manufacturing of a secondary battery stack using the inspection method of the present invention and the manufacturing method of a secondary battery stack of the present invention is not particularly limited, and can be carried out using, for example, a manufacturing apparatus 100 as shown in FIG. 1.

[0055] 1 is an apparatus for manufacturing a secondary battery stack 200 in which electrodes (positive and negative electrodes) and separators are stacked from top to bottom in the order of "positive electrode / separator / negative electrode / separator." In addition, in this manufacturing apparatus 100, the obtained secondary battery stack 200 is cut to an appropriate size, and then stacked again before being used to manufacture a secondary battery.

[0056] The manufacturing apparatus 100 includes a negative electrode roll 10 formed by winding up a negative electrode 11 in a roll shape, a first separator roll 20 and a second separator roll 30 formed by winding up separators 21, 31 in a roll shape, and a positive electrode stocker 40 that stores pre-cut positive electrodes 41. The manufacturing apparatus 100 also includes a plurality of (eleven in the illustrated example) conveying rollers 1, a plurality of (three pairs of) press rollers 2, a plurality of (six in the illustrated example) coating machines 60A, 60B, 60C, 60D, 60E, and 60F, a plurality of (six in the illustrated example) laser displacement meters 70A, 70B, 70C, 70D, 70E, and 70F, and a cutting machine 50.

[0057] In this manufacturing apparatus 100, first, a coating machine 60A applies a coating material 61 to the bonding surface of a negative electrode 11, which is unwound from a negative electrode roll 10 and conveyed via a conveying roller 1, so as to form a coating pattern, for example, a diagonal stripe pattern as shown in FIG. 2 (coating process). Next, a laser displacement meter 70A measures the displacement of the bonding surface of the negative electrode 11 to which the coating material 61 has been applied, and the number of coating defects on the bonding surface is identified (inspection process). For example, if the number of coating defects exceeds a predetermined threshold, a prompt response can be taken, such as immediately stopping the production line to resolve the problem (the same applies to the "inspection process" below). Then, the negative electrode 11 that has undergone inspection using the laser displacement meter 70A is heated by a conveying roller 1 positioned between the laser displacement meter 70A and a press roller 2, which serves as a heat roller. This heating dries the coating material 61, forming an adhesive material on the bonding surface of the negative electrode 11 (drying process). Then, the negative electrode 11 on which the adhesive material is formed and the separator 21 unwound from the first separator roll 20 are bonded together by the press roller 2 (bonding step).

[0058] It is sufficient that an adhesive material is formed on at least one of the bonding surfaces of the negative electrode 11 and the separator 21. That is, the adhesive material may be formed in the above-described manner only on the bonding surface of the negative electrode 11, only on the bonding surface of the separator 21, or on both the bonding surfaces of the negative electrode 11 and the separator 21. Here, when forming an adhesive material on the bonding surface of separator 21, coating machine 60B applies paint 61 to the bonding surface of separator 21, which is transported from first separator roll 20 via transport roller 1, so as to form a coating pattern, for example, a diagonal stripe pattern as shown in Figure 2 (coating process), and the displacement of the bonding surface of separator 21 to which paint 61 has been applied is measured by laser displacement meter 70B to identify the number of coating defects on the bonding surface (inspection process).Then, transport roller 1, located between laser displacement meter 70B and press roller 2, is used as a heat roller, and the adhesive material is formed on the bonding surface of separator 21 by heating with this heat roller (drying process).

[0059] In the manufacturing apparatus 100, a coating material 61 is supplied from a coating machine 60C to the surface of the negative electrode 11 side of a laminate of a negative electrode 11 and a separator 21 bonded together using an adhesive material, so as to form a coating pattern of, for example, a diagonal stripe shape as shown in FIG. 2 . Next, the displacement of the bonding surface of the negative electrode 11 coated with the coating material 61 is measured using a laser displacement meter 70C, and the number of coating defects on the bonding surface is identified (inspection process). Then, the laminate inspected using the laser displacement meter 70C is heated by a heat roller, which is a conveying roller 1 positioned between the laser displacement meter 70C and a press roller 2. This heating dries the coating material 61, and an adhesive material is formed on the bonding surface of the negative electrode 11 in the laminate (drying process). Then, the laminate including the negative electrode 11 on which the adhesive material is formed and the separator 31 unwound from the second separator roll 30 are bonded together using the press roller 2 (bonding process).

[0060] It is sufficient that an adhesive material is formed on the bonding surface of at least one of the negative electrode 11 and the separator 31 that constitute the laminate. That is, the adhesive material may be formed in the above-described manner only on the bonding surface of the negative electrode 11, only on the bonding surface of the separator 31, or on the bonding surfaces of both the negative electrode 11 and the separator 31. Here, when forming an adhesive material on the bonding surface of separator 31, coating machine 60D supplies paint 61 to the bonding surface of separator 31, which is transported from second separator roll 30 via transport roller 1, so as to form a coating pattern, for example, a diagonal stripe pattern as shown in Figure 2 (coating process), and the displacement of the bonding surface of separator 31 to which paint 61 has been applied is measured using laser displacement meter 70D to identify the number of coating defects on the bonding surface (inspection process).Then, transport roller 1, located between laser displacement meter 70D and press roller 2, is used as a heat roller, and the adhesive material is formed on the bonding surface of separator 31 by heating with this heat roller (drying process).

[0061] Furthermore, in the manufacturing apparatus 100, a coating machine 60E supplies paint 61 to the surface of the separator 31 side of the laminate of the negative electrode 11 and separators 21 and 31 bonded together using an adhesive material, so as to form a coating pattern, for example, a diagonal stripe pattern similar to that shown in FIG. 2 . Next, the displacement of the bonded surface of the separator 31 to which the paint 61 has been applied is measured using a laser displacement meter 70E, and the number of coating defects on the bonded surface is identified (inspection process). Then, the laminate inspected using the laser displacement meter 70E is heated by a heat roller, which is a conveying roller 1 positioned between the laser displacement meter 70E and a press roller 2. This heating dries the paint 61, and an adhesive material is formed on the bonded surface of the separator 31 in the laminate (drying process). Then, the laminate including the separator 31 on which the adhesive material has been applied is bonded to a positive electrode 41 supplied from a positive electrode stocker 40 using a press roller 2 (bonding process).

[0062] Additionally, in the manufacturing apparatus 100, a coating material 61 is supplied from a coating machine 60F to the surface of the positive electrode side of the secondary battery laminate 200, which is laminated from top to bottom in the order of "positive electrode / separator / negative electrode / separator," so as to form a coating pattern of, for example, a diagonal stripe shape similar to that shown in FIG. 2 , and inspection is performed using a laser displacement meter 70F. After that, if necessary, the conveying roller 1 is used as a heat roller for drying, and the secondary battery laminate 200 is cut by a cutting machine 50. The laminates (cut pieces) obtained by cutting the secondary battery laminate 200 with the cutting machine 50 are further stacked and then used to manufacture a secondary battery.

[0063] (Secondary battery manufacturing method) The method for manufacturing a secondary battery of the present invention includes a step of manufacturing a laminate for a secondary battery using the method for manufacturing a laminate for a secondary battery of the present invention described above, and a step (assembly step) of assembling a secondary battery using the laminate for a secondary battery and an electrolyte solution. By using the method for manufacturing a secondary battery of the present invention, the rate of occurrence of defective bonding between the electrodes and the separator during the production of the laminate is reduced, making it possible to efficiently manufacture secondary batteries with excellent battery characteristics.

[0064] <Assembly process> Here, the electrolyte solution is typically an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent. For example, when the secondary battery is a lithium ion secondary battery, a lithium salt is used as the supporting electrolyte. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, CF4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. Among these, LiPF6, LiClO4, and CF3SO3Li are preferred, with LiPF6 being particularly preferred, because they are easily soluble in solvents and exhibit a high degree of dissociation. Note that one type of electrolyte may be used alone, or two or more types may be used in combination at any ratio. Typically, the use of a supporting electrolyte with a higher degree of dissociation tends to result in higher lithium ion conductivity, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0065] Furthermore, the organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide are preferably used. Mixtures of these solvents may also be used. Among these, carbonates are preferred because of their high dielectric constant and wide stable potential range. Generally, the lower the viscosity of the solvent used, the higher the lithium ion conductivity, so the lithium ion conductivity can be adjusted by the type of solvent. The concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate. Known additives may also be added to the electrolytic solution.

[0066] A secondary battery can be assembled by further laminating additional battery components (such as electrodes and / or separators) as needed on the laminate for a secondary battery manufactured according to the manufacturing method for a laminate for a secondary battery of the present invention, then rolling or folding the resulting laminate as needed according to the battery shape and placing it in a battery container, injecting an electrolyte into the battery container, and sealing it. Note that, to prevent internal pressure increases, overcharge / discharge, and the like, fuses, overcurrent protection elements such as PTC elements, expanded metal, lead plates, and the like may be provided as needed. The shape of the secondary battery may be any type, such as a coin type, button type, sheet type, cylindrical type, prismatic type, or flat type. [Example]

[0067] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified.

[0068] Example 1 <Preparation of first binder> 100 parts of ion-exchanged water and 0.3 parts of ammonium persulfate were fed into a reactor equipped with a stirrer, the gas phase was replaced with nitrogen gas, and the temperature was raised to 80 °C. Meanwhile, in a separate vessel, 40 parts of ion-exchanged water, 0.2 parts of sodium dodecylbenzenesulfonate as an emulsifier, 40.3 parts of styrene as an aromatic monovinyl monomer, 27.3 parts of 2-ethylhexyl acrylate as a monofunctional (meth)acrylic acid ester monomer, 2.1 parts of methacrylic acid as an acidic group-containing monomer, and 0.3 parts of ethylene glycol dimethacrylate as a crosslinkable monomer were mixed to obtain a core-forming monomer composition. This core-forming monomer composition was continuously added to the reactor over 3 hours and subjected to a polymerization reaction at 80 °C. The polymerization was continued until the polymerization conversion reached 95%, yielding an aqueous dispersion containing the particulate polymer that constitutes the core. Next, a monomer composition for forming a shell portion, which contained 29.7 parts of styrene as an aromatic monovinyl monomer and 0.3 parts of methacrylic acid as an acidic group-containing monomer, was continuously fed to this aqueous dispersion over 60 minutes to continue polymerization. When the polymerization conversion rate reached 98%, the reaction was stopped by cooling to prepare an aqueous dispersion of a first binder (a particulate polymer having a core-shell structure, volume average particle diameter: 0.7 μm). <Preparation of second binder> 90 parts of ion-exchanged water and 0.5 parts of ammonium persulfate were fed into a reactor equipped with a stirrer, the gas phase was replaced with nitrogen gas, and the temperature was raised to 80°C. Meanwhile, in a separate vessel, 15 parts of ion-exchanged water, 1.0 part of Neopelex G15 (Kao Chemical Corporation) as an emulsifier, 70.0 parts of 2-ethylhexyl acrylate as a monofunctional (meth)acrylic acid ester monomer, 25.0 parts of styrene as an aromatic monovinyl monomer, 1.7 parts of allyl glycidyl ether and 0.3 parts of allyl methacrylate as crosslinkable monomers, and 3.0 parts of acrylic acid as an acidic group-containing monomer were mixed to obtain a monomer composition. This monomer composition was continuously added to the reactor over 4 hours to carry out polymerization. During the continuous addition, the reaction was carried out at a temperature of 80°C. After the continuous addition was completed, the mixture was stirred at 80°C for an additional 3 hours to terminate the reaction. The obtained aqueous dispersion was cooled to a temperature of 25°C, and then an aqueous sodium hydroxide solution was added thereto to adjust the pH to 8.0. Thereafter, steam was introduced to remove unreacted monomers, thereby preparing an aqueous dispersion of a second binder (a particulate polymer not having a core-shell structure, volume average particle diameter: 0.2 µm). <Paint preparation> The aqueous dispersion of the first binder and the aqueous dispersion of the second binder were mixed so that the mass ratio of the solid content was first binder:second binder = 100:10, and ion-exchanged water was further added to dilute the mixture so that the solid content concentration was 10.5%. Propylene glycol was further added to the resulting mixture to adjust the solid content concentration to 10%, thereby obtaining a coating material. <Preparing the separator> A separator made of polypropylene (PP) (product name "Celgard 2500", surface roughness Sa: 0.1 μm) was prepared as the application body. <Application, inspection, and drying> The separator unwound from the separator roll was conveyed at a speed of 10 m / min, while the coating material was applied to one surface of the separator from the inkjet head of an inkjet coating machine (Konica Corporation, "KM1024 (shear mode type)") in such a way that dots of the coating material (diameter: 5 μm) were placed 500 μm apart from each other. Then, while the separator was being transported, the displacement of the coated surface (bonding surface) was measured using a laser displacement meter (Keyence Corporation, "LJ-V7060") to determine the number of defective coating areas (areas where dots of paint were not placed based on the desired pattern) along 10 m of the separator. The average height of the paint from the bonding surface was calculated from the measurement results using the laser displacement meter. The results are shown in Table 1. After the above inspection, the paint on the separator was dried using a heat roller on part of the conveying roller (drying temperature: 70°C, drying time: 1 second), forming an adhesive material on the separator. The average diameter of the dots of adhesive material was calculated from the results of measurements using a laser microscope (Keyence Corporation, "VR-3100"). The results are shown in Table 1. <Evaluation of the accuracy of identifying defective coating areas> The separator with the adhesive material formed on one side was sampled in a 100m length. The adhesive material-formed surface of the sampled separator was observed with a laser microscope (Keyence Corporation, "VR-3100") to determine the number of defective coating locations for the 100m separator. The difference between the number of defective coating areas identified with a laser microscope after drying (N1) and the number of defective coating areas identified with a laser displacement meter before drying (N2), i.e., the difference in the number of defective coating areas identified (N1 - N2), was calculated and evaluated according to the following criteria. The results are shown in Table 1. It can be said that the smaller the difference in the number of defective coating areas identified, the more accurately it is possible to identify defective coating areas on the separator surface during transport. A: The difference in the number of defective coating locations is less than 10 B: The difference in the number of specific coating defects is 10 or more but less than 50 C: The difference in the number of specific coating defects is 50 or more but less than 300 D: The difference in the number of specific coating defects is 300 or more

[0069] Examples 2 to 4 Paint and separators were prepared in the same manner as in Example 1. Then, the diameters of the dots of paint applied to the separator were changed to 40 μm (Example 2), 100 μm (Example 3), and 250 μm (Example 4), respectively. The application, inspection, and drying were carried out in the same manner as in Example 1, and the accuracy of identifying defective coating locations was evaluated. The results are shown in Table 1.

[0070] (Examples 5 to 8) A coating material was prepared in the same manner as in Example 1. Then, coating, inspection, and drying were carried out in the same manner as in Examples 1 to 4, except that a negative electrode prepared as described below was used as the coating body instead of a separator, and the accuracy of identifying coating defects was evaluated. The results are shown in Table 1. The coating was carried out on the surface of the negative electrode composite layer of the negative electrode. <Preparation of negative electrode> A 5 MPa pressure vessel equipped with a stirrer was charged with 33 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 63.5 parts of styrene, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator. After thorough stirring, the mixture was heated to 50 °C to initiate polymerization. When the polymerization conversion reached 96%, the reaction was stopped by cooling, yielding a mixture containing a binder (SBR) for the negative electrode composite layer. A 5% aqueous sodium hydroxide solution was added to the mixture containing the binder for the negative electrode composite layer, adjusting the pH to 8, and then the unreacted monomer was removed by heated vacuum distillation. The mixture was then cooled to 30 °C or below to obtain an aqueous dispersion containing the desired binder for the negative electrode composite layer. Next, 100 parts of artificial graphite (volume average particle diameter: 15.6 μm) as the negative electrode active material, 1 part (solids equivalent) of a 2% aqueous solution of carboxymethylcellulose sodium salt (manufactured by Nippon Paper Industries Co., Ltd., product name "MAC350HC") as a viscosity modifier, and ion-exchanged water were mixed to adjust the solids concentration to 68%, and then further mixed at a temperature of 25°C for 60 minutes. The solids concentration was further adjusted to 62% with ion-exchanged water, and then further mixed at a temperature of 25°C for 15 minutes. To the resulting mixture, 1.5 parts (solids equivalent) of the aqueous dispersion containing the binder for the negative electrode composite layer and ion-exchanged water were added, and the final solids concentration was adjusted to 52%, and then further mixed for 10 minutes. This mixture was degassed under reduced pressure to obtain a slurry composition for secondary battery negative electrodes with good fluidity. The obtained slurry composition for secondary battery negative electrodes was applied to both sides of a 20 μm-thick copper foil current collector using a comma coater so that the dried film thickness was approximately 150 μm, and then dried. This drying was performed by conveying the copper foil at a speed of 0.5 m / min through an oven at a temperature of 60°C for 2 minutes. Thereafter, the copper foil was heat-treated at a temperature of 120°C for 2 minutes to obtain a pre-press negative electrode blank. This pre-press negative electrode blank was rolled using a roll press to obtain a negative electrode (thickness of negative electrode composite layer: 80 μm, surface roughness Sa of negative electrode composite layer: 0.3 μm).

[0071] Examples 9 to 12 A coating material and a separator were prepared in the same manner as in Example 1. Then, instead of using an inkjet coating machine, a gravure printing machine and a gravure roll with a gravure printing plate that would produce the desired dot shape were used to apply the coating material to the separator. The dot diameters were set to 20 μm (Example 9), 40 μm (Example 10), 100 μm (Example 11), and 250 μm (Example 12). Inspection and drying were performed in the same manner as in Example 1, and the accuracy of identifying defective coating locations was evaluated. The results are shown in Table 1.

[0072] (Comparative Examples 1 to 8) The accuracy of identifying the defective coating areas was evaluated in the same manner as in Examples 1 to 8, except that the inspection was carried out after drying (i.e., the "number of defective coating areas (N2)" was determined by inspecting the bonded surfaces with a laser displacement meter after drying, not before drying). The results are shown in Table 1.

[0073] (Comparative Examples 9 to 12) The inspection was carried out in the same manner as in Comparative Examples 1 to 4, except that a CCD camera was used as the inspection device instead of the laser displacement meter, and the accuracy of identifying the defective coating locations was evaluated. The results are shown in Table 1.

[0074] [Table 1]

[0075] It can be seen from Table 1 that defective coating locations on the separator or electrode can be identified with high accuracy in Examples 1 to 12. Furthermore, by using such an inspection method, the rate of defective bonding between the electrode and separator can be reduced, and a laminate can be produced efficiently. On the other hand, it is clear from Table 1 that in Comparative Examples 1 to 12, the defective coating locations on the separator or electrode could not be identified with high accuracy. [Industrial Applicability]

[0076] According to the inspection method of the present invention, when manufacturing a stack for a secondary battery in which battery components are bonded together via an adhesive material, it is possible to identify defective coating locations with high accuracy. Furthermore, according to the method for producing a laminate for a secondary battery of the present invention, the rate of occurrence of defective bonding between electrodes and separators can be reduced, and laminates for a secondary battery can be produced efficiently. According to the method for producing a secondary battery of the present invention, a secondary battery having excellent battery characteristics can be produced efficiently. [Explanation of symbols]

[0077] 1 Conveyor roller 2 press rollers 10. Negative electrode roll 11 Negative electrode 20 First separator roll 30 Second separator roll 21,31 Separator 40 Positive electrode stocker 41 Positive electrode 50 cutting machine 60A, 60B, 60C, 60D, 60E, 60F Coating Machine 61 Paint 70A, 70B, 70C, 70D, 70E Laser Displacement Meter 100 Manufacturing equipment 200 Laminate for secondary battery T Transport direction

Claims

1. applying a coating material containing a binder and a solvent to at least one of the bonding surfaces of the electrode and the separator; and a step of forming an adhesive material by drying the paint applied to the bonding surfaces, the inspection method being used when forming the adhesive material on the bonding surfaces, a step of measuring a displacement of the bonding surface to which the coating material is applied by a laser displacement meter and identifying a coating defect location prior to the step of forming the adhesive material; The electrode is an electrode made of an electrode base material in which an electrode mixture layer is formed on one or both sides of a current collector, or an electrode in which a porous membrane layer is further formed on the electrode mixture layer of the electrode base material.

2. 2. The inspection method according to claim 1, wherein in the step of applying the paint, the average height of the paint from the bonding surface is 2 μm or more and 150 μm or less.

3. A process of applying a coating material containing a binder and a solvent to at least one of the bonding surfaces of the electrode and the separator; and a step of forming an adhesive material by drying the paint applied to the bonding surfaces, the inspection method being used when forming the adhesive material on the bonding surfaces, a step of measuring a displacement of the bonding surface to which the coating material is applied by a laser displacement meter and identifying a coating defect location prior to the step of forming the adhesive material; In the step of forming the adhesive material, the adhesive material is formed in a dot shape, and an average diameter of the adhesive material formed in the dot shape is 5 μm or more and 300 μm or less.

4. 4. The inspection method according to claim 1, wherein in the step of applying the paint, the solid content of the paint is 20 mass % or less.

5. A process of applying a coating material containing a binder and a solvent to at least one of the bonding surfaces of the electrode and the separator; and a step of forming an adhesive material by drying the paint applied to the bonding surfaces, the inspection method being used when forming the adhesive material on the bonding surfaces, a step of measuring a displacement of the bonding surface to which the coating material is applied by a laser displacement meter and identifying a coating defect location prior to the step of forming the adhesive material; In the step of applying the paint, the application is performed by an inkjet method.

6. A method for manufacturing a laminate for a secondary battery formed by bonding an electrode and a separator, A step of carrying out an inspection according to the inspection method of any one of claims 1 to 5; a step of bonding the electrode and the separator together via the bonding surface on which the adhesive material is formed, after the inspection; A method for producing a laminate for a secondary battery, comprising:

7. A method for manufacturing a secondary battery including a laminate for a secondary battery formed by bonding together an electrode and a separator, a step of manufacturing a stack for a secondary battery using the manufacturing method for a stack for a secondary battery according to claim 6; and assembling a secondary battery using the laminate for a secondary battery and an electrolyte solution.

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