Conductive aqueous primer coating, current collector for power storage device, electrode for power storage device, power storage device, and method for manufacturing current collector for power storage device

Abstract

This conductive aqueous primer coating is characterized by comprising a conductive filler, poly-N-vinylacetamide (hereinafter, PNVA), and a solvent, and is characterized in that the percentage content of the PNVA with respect to the conductive filler is 15-65 mass%, and the solvent contains water as a main component.

Description

Conductive water-based primer paint, current collector for electricity storage device, electrode for electricity storage device, electricity storage device, and method for manufacturing current collector for electricity storage device

[0001] The present disclosure relates to a conductive water-based primer paint, a current collector for an electricity storage device, an electrode for an electricity storage device, an electricity storage device, and a method for manufacturing a current collector for an electricity storage device.

[0002] Electrodes for power storage devices such as lithium-ion secondary batteries are generally produced by a wet method in which a slurry of an electrode mixture containing an active material, a binder, etc. is applied to the surface of a core material that is a metal foil, and the coating is dried and compressed. In recent years, a dry method has been considered in which a powder of the electrode mixture is stretched and formed into a sheet to produce a mixture sheet, and the sheet is then bonded to a core material to produce an electrode (e.g., Patent Document 1).

[0003] Incidentally, Patent Document 2 discloses that, in order to obtain a low-resistance electricity storage device, a current collector is used in which a coating liquid containing a powdered carbon material, acid-modified polyvinylidene fluoride, and polyvinylpyrrolidone in predetermined amounts, and containing N-methyl-2-pyrrolidone as a solvent, is applied onto a core material to form a coating layer on the core material.

[0004] JP 2019-512872 A International Publication No. 2020 / 053916

[0005] However, when attempting to join a composite sheet by a dry method using the current collector of Patent Document 2, the coating layer formed from the coating liquid of Patent Document 2 reduces the interfacial resistance between the current collector and the composite sheet, but the coating layer causes problems such as the composite sheet coming off (areas where the composite sheet does not adhere and the current collector is exposed in streaks) and reduced adhesion between the composite sheet and the current collector.

[0006] Therefore, an object of the present disclosure is to provide a conductive water-based primer paint (a coating liquid for forming a coating layer on a core material) that can suppress the loss of the composite sheet and the decrease in adhesion between the composite sheet and the current collector while keeping the interfacial resistance between the current collector and the composite sheet low, a current collector for an electricity storage device, and a method for manufacturing a current collector for an electricity storage device, and further to provide an electrode for an electricity storage device that includes the current collector for an electricity storage device, and an electricity storage device.

[0007] The conductive water-based primer paint according to the present disclosure comprises a conductive filler, poly-N-vinylacetamide (hereinafter, PNVA), and a solvent, wherein the content of the PNVA relative to the conductive filler is 15% by mass or more and 65% by mass or less, and the solvent is a solvent containing water as a main component.

[0008] The current collector for an electricity storage device according to the present disclosure is characterized by having a core material and a coating layer formed by applying the conductive water-based primer paint onto the core material.

[0009] The current collector for an electricity storage device according to the present disclosure has a core material and a coating layer disposed on the core material, the coating layer containing a conductive filler and PNVA, and the content of the PNVA relative to the conductive filler is 15 mass% or more and 65 mass% or less.

[0010] The electrode for an electricity storage device according to the present disclosure is characterized by having the current collector for an electricity storage device.

[0011] The electricity storage device according to the present disclosure is characterized by having the above-described electricity storage device electrode.

[0012] The method for manufacturing a current collector for an electricity storage device according to the present disclosure is characterized by including a step of spraying the conductive water-based primer paint onto a core material using a two-fluid nozzle to form a coating layer.

[0013] According to the present disclosure, it is possible to suppress the loss of the composite sheet and the decrease in adhesion between the composite sheet and the current collector while keeping the interface resistance between the current collector and the composite sheet low.

[0014] 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention; 2 is a schematic cross-sectional view showing an example of the configuration of an electrode for an electricity storage device according to an embodiment of the present invention; 3 is a view showing an example of a joining step of joining a current collector for an electricity storage device and a composite sheet according to an embodiment of the present invention;

[0015] The embodiments described below are merely examples, and the present disclosure is not limited to the following embodiments. The drawings referred to in the description of the embodiments are schematic, and the dimensional ratios of the components depicted in the drawings should be determined in consideration of the following description. Furthermore, configurations formed by selectively combining multiple embodiments and modified examples described below are included in the present disclosure.

[0016] The electricity storage device according to the present disclosure is suitable for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, but can also be applied to batteries containing aqueous electrolytes, capacitors, etc. The conductive aqueous primer paint, electricity storage device current collector and manufacturing method therefor, and electricity storage device electrode according to the present disclosure may be applied to the negative electrode or positive electrode of an electricity storage device. Note that the following description will be given taking a non-aqueous electrolyte secondary battery as an example.

[0017] FIG. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment. The nonaqueous electrolyte secondary battery 10 shown in FIG. 1 includes a wound electrode assembly 14 formed by winding a positive electrode 11 and a negative electrode 12 with a separator 13 interposed therebetween, a nonaqueous electrolyte, insulating plates 18 and 19 disposed above and below the electrode assembly 14, respectively, and a battery case 15 for accommodating the above components. The battery case 15 is composed of a cylindrical case body 16 with a bottom and a sealing body 17 that closes the opening of the case body 16. Note that, instead of the wound electrode assembly 14, other electrode bodies may be used, such as a laminated electrode body formed by alternately stacking positive and negative electrodes with separators interposed therebetween. Examples of the battery case 15 include a cylindrical, prismatic, coin-shaped, or button-shaped metal case, and a resin case formed by laminating a resin sheet (a so-called laminate type).

[0018] The non-aqueous electrolyte has, for example, ion conductivity (for example, lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0019] The liquid electrolyte (electrolytic solution) contains, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0020] Furthermore, examples of the solid electrolyte that can be used include solid or gel polymer electrolytes, inorganic solid electrolytes, and the like. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. The matrix polymer is, for example, a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, and the like).

[0021] The case body 16 is, for example, a cylindrical metal container with a bottom. A gasket 28 is provided between the case body 16 and the sealing body 17 to ensure airtightness inside the battery. The case body 16 has, for example, a protruding portion 22, which is a portion of the side surface that protrudes inward and supports the sealing body 17. The protruding portion 22 is preferably formed in an annular shape along the circumferential direction of the case body 16, and supports the sealing body 17 on its upper surface.

[0022] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in this order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disk or ring shape, and all components except for the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the nonaqueous electrolyte secondary battery 10 increases due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0023] 1 , a positive electrode lead 20 attached to the positive electrode 11 passes through a through-hole in the insulating plate 18 and extends toward the sealing body 17, and a negative electrode lead 21 attached to the negative electrode 12 passes outside the insulating plate 19 and extends toward the bottom of the case body 16. The positive electrode lead 20 is connected by welding or the like to the underside of a filter 23, which is the bottom plate of the sealing body 17, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the filter 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected by welding or the like to the inner bottom surface of the case body 16, and the case body 16 serves as the negative electrode terminal.

[0024] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator.

[0025] The electrode for an electricity storage device of this embodiment is applied to at least one of the positive electrode 11 and the negative electrode 12. The electrode for an electricity storage device of this embodiment will be described below.

[0026] Fig. 2 is a schematic cross-sectional view showing an example of the configuration of an electrode for an electricity storage device according to this embodiment. As shown in Fig. 2, an electrode for an electricity storage device 30 has a current collector 32 for an electricity storage device and a composite sheet 34 disposed on the current collector 32 for an electricity storage device. The current collector 32 for an electricity storage device has a core material 32a and a coating layer 32b disposed on the core material 32a. The coating layer 32b may be disposed on both sides of the core material 32a, or may be disposed on one side as shown in Fig. 2. The composite sheet 34 is disposed on the coating layer 32b.

[0027] The composite sheet 34 includes an active material and a binder. The composite sheet 34 may also include a conductive material. In particular, in the case of a positive electrode, the composite sheet 34 preferably includes a conductive material. The thickness of the composite sheet 34 is, for example, 50 μm or more and 150 μm or less.

[0028] In the case of the positive electrode, for example, a lithium transition metal composite oxide is used as the active material. Metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Among these, it is preferable to contain at least one selected from Ni, Co, and Mn. In particular, the composition of the lithium transition metal composite oxide preferably contains Ni in an amount of 70% to 99% of the metal elements other than lithium, more preferably 80% to 95%. The content of the positive electrode active material in the composite sheet 34 is preferably, for example, 85% to 99% by mass, more preferably 90% to 98% by mass.

[0029] The positive electrode active material is composed of, for example, secondary particles formed by aggregation of multiple primary particles. The volume-based median diameter (D50) of the positive electrode active material is preferably 3 μm or more and 30 μm or less. D50 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size, and is also called the median diameter. The particle size distribution of the positive electrode active material can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II manufactured by Microtrac-Bell Corporation) using water as a dispersion medium.

[0030] In the case of the negative electrode, the active material may be a carbon-based active material such as natural graphite, such as flake graphite, lump graphite, or amorphous graphite, or artificial graphite, such as massive artificial graphite (MAG) or graphitized mesophase carbon microbeads (MCMB). The negative electrode active material may contain an active material containing Si, Sn, or the like, which alloys with lithium. The content of the negative electrode active material may be the same as that of the positive electrode active material described above.

[0031] The binder may be, for example, a conventional binder used in nonaqueous electrolyte secondary batteries, such as fluorine-based resins such as polytetrafluoroethylene and polyvinylidene fluoride, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and styrene-butadiene rubber (SBR). In terms of the strength of the composite sheet produced by the dry method, the binder preferably contains polytetrafluoroethylene, and in particular, fibrous polytetrafluoroethylene. Fibrous polytetrafluoroethylene can be obtained, for example, by kneading polytetrafluoroethylene particles and applying shear force. The content of the binder in the composite sheet 34 may be, for example, 0.5% by mass or more and 5.0% by mass or less.

[0032] Examples of the conductive material include carbon black such as acetylene black and ketjen black, carbon nanotubes (CNT), graphite, and other carbon materials. The content of the conductive material in the composite sheet 34 may be, for example, 0.5 mass % or more and 5.0 mass % or less.

[0033] In the case of a positive electrode, the core material 32a constituting the electricity storage device current collector 32 is a foil of a metal that is stable in the potential range of the positive electrode, such as aluminum, an aluminum alloy, etc. In the case of a negative electrode, the core material 32a constituting the electricity storage device current collector 32 is a foil of a metal that is stable in the potential range of the negative electrode, such as copper, a copper alloy, etc. The thickness of the core material 32a is, for example, 5 μm or more and 20 μm or less.

[0034] The coating layer 32b constituting the current collector 32 for an electric storage device contains a conductive filler and poly-N-vinylacetamide (hereinafter, PNVA), with the PNVA content relative to the conductive filler being 15% by mass or more and 65% by mass or less. Using a current collector 32 for an electric storage device (hereinafter, sometimes referred to as the current collector 32) in which the coating layer 32b having the above-described configuration is disposed on a core material 32a can prevent the composite sheet 34 from coming off and the adhesion between the composite sheet 34 and the current collector 32 when bonding the composite sheet 34 to the current collector 32 by a dry method. It can also reduce the interfacial resistance between the current collector 32 and the composite sheet 34. The thickness of the coating layer 32b is preferably 3 μm or less, for example, to further reduce the interfacial resistance between the current collector 32 and the composite sheet 34. The lower limit of the thickness of the coating layer 32b may be, for example, 0.1 μm or more.

[0035] Examples of the conductive filler include metal materials such as aluminum metal, stainless steel (SUS), silver, gold, copper, and titanium, carbon blacks such as graphite, acetylene black, ketjen black, furnace black, channel black, and thermal lamp black, and carbon materials such as carbon nanotubes. Of these, carbon materials are preferred from the viewpoints of reducing the resistance of the coating layer 32b and keeping the interface resistance between the current collector 32 and the composite sheet 34 low.

[0036] The conductive filler is preferably composed of two or more types of conductive fillers having different average aspect ratios, for example, in order to reduce the resistance of the coating layer 32b and keep the interfacial resistance between the current collector 32 and the composite sheet 34 low. The conductive filler preferably includes, for example, a conductive filler A and a conductive filler B having an average aspect ratio larger than that of the conductive filler A. The average aspect ratio of the conductive filler B is preferably, for example, 10 or more and 40 or less, and more preferably 15 or more and 35 or less. The average aspect ratio of the conductive filler A is preferably, for example, 1 or more and 8 or less, and more preferably 2 or more and 6 or less.

[0037] The average aspect ratio of the conductive filler was determined by measuring the minor axis (x) and major axis (y) of 30 conductive fillers using a scanning electron microscope (SEM) and calculating the average value of the ratio of the major axis (y) to the minor axis (x) [major axis (y) / minor axis (x)].

[0038] The content of the conductive filler in the coating layer 32b is preferably, for example, 50% by mass or more and 90% by mass or less, and more preferably 60% by mass or more and 80% by mass or less, in order to reduce the resistance of the coating layer 32b and keep the interfacial resistance between the collector 32 and the composite sheet 34 low, for example.

[0039] PNVA is a binder that serves to bond materials such as conductive filler within coating layer 32b to each other and to bond coating layer 32b to other layers (composite sheet 34 and core material 32a). The PNVA content is 15% by mass or more and 65% by mass or less, preferably 20% by mass or more and 60% by mass or less, and more preferably 30% by mass or more and 60% by mass or less, relative to the total mass of the conductive filler. By setting the PNVA content within the above range, it is possible to suppress an increase in the resistance of coating layer 32b and to suppress loss of composite sheet 34 and a decrease in adhesion between composite sheet 34 and current collector 32.

[0040] Although the coating layer 32b is not limited to containing a binder other than PNVA, such as polyvinylidene fluoride, it is preferable that the coating layer 32b contain as few binders other than PNVA as possible. The content of binders other than PNVA in the coating layer 32b is preferably 3 mass % or less, more preferably 1 mass % or less, and even more preferably 0 mass %, relative to the total mass of the conductive filler.

[0041] The coating layer 32b preferably contains a dispersion material, which will be described later.

[0042] An example of a method for manufacturing the electricity storage device current collector 32 in this embodiment will be described.

[0043] A conductive water-based primer paint containing a conductive filler, PNVA, and a solvent, wherein the content of the PNVA relative to the conductive filler is 15% by mass or more and 65% by mass or less, and the solvent is a solvent mainly composed of water, is applied to a core material 32a to form a coating layer 32b, thereby obtaining a current collector 32 for an electricity storage device in which the coating layer 32b is formed on the core material 32a. By forming the coating layer 32b on the core material 32a using the conductive water-based primer paint having the above configuration, it is possible to prevent the composite sheet 34 from coming off and the adhesion between the composite sheet 34 and the current collector 32 from decreasing when the composite sheet 34 is bonded to the current collector 32 by a dry method, and it is also possible to keep the interfacial resistance between the current collector 32 and the composite sheet 34 low.

[0044] The conductive filler is as described above. The content of the conductive filler in the conductive water-based primer paint is, for example, preferably 20% by mass or more and 80% by mass or less, and more preferably 50% by mass or more and 80% by mass or less, of the solid content of the paint, from the viewpoint of, for example, reducing the resistance of the coating layer 32b and keeping the interface resistance between the current collector 32 and the composite sheet 34 low.

[0045] The content of PNVA relative to the conductive filler in the conductive water-based primer paint is as described above. As described above, the conductive water-based primer paint is not limited to containing binders other than PNVA, such as polyvinylidene fluoride, but it is preferable to contain as few binders other than PNVA as possible. The content of binders other than PNVA is as described above.

[0046] The solvent is primarily composed of water. "Mainly composed of water" means that water is the most abundant component of the solvent. The water content in the solvent is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 100% by mass, relative to the total amount of solvent, in order to reduce the viscosity of the conductive water-based primer paint and prevent uneven application of the conductive water-based primer paint. The solvent may contain an organic solvent, but preferably does not contain any, and the water content is preferably 5% by mass or less, and even more preferably 1% by mass or less, relative to the total amount of solvent.

[0047] The conductive water-based primer paint preferably contains a dispersant. The dispersant is a material for adjusting the viscosity of the conductive water-based primer paint and improving the dispersibility of the conductive filler. By using a conductive water-based primer paint containing a dispersant, the conductive filler can be highly dispersed in the coating layer 32b, which makes it possible to further reduce the resistance of the coating layer 32b and further reduce the interfacial resistance between the current collector 32 and the composite sheet 34. Examples of dispersants include carboxymethyl cellulose and methyl cellulose. In order to further improve the dispersibility of the conductive filler, the dispersant is preferably a 100 s solution of a 3% aqueous solution of the dispersant. －１ The viscosity is preferably 2 mPa·s or more and 200 mPa·s or less, and more preferably 20 mPa·s or more and 100 mPa·s or less. The content of the dispersant in the conductive water-based primer paint (and in the coating layer 32b) may be, for example, 5 mass% or more and 20 mass% or less with respect to the total mass of the conductive filler.

[0048] Here, 100s of a 3% aqueous solution of the dispersant －１ The viscosity is determined by dissolving 3.0 g of dispersant in 100 g of ion-exchanged water at a shear rate of 100 s －１ The viscosity was measured at 25° C. A cone-plate type rotational viscometer (jig radius 24 mm, angle 1.34°) (TV25 type viscometer manufactured by Toki Sangyo Co., Ltd.) was used to measure the viscosity.

[0049] For example, a gravure coater, roll coater, blade coater, dip coater, spray coater, spin coater, or die coater can be used to apply the conductive water-based primer paint to the core material 32a. Among these, a spray coater is preferred to spray the conductive water-based primer paint onto the core material 32a to form the coating layer 32b, as it can form a thin coating layer 32b in a short time. A two-fluid nozzle is preferred as the nozzle used for the spray coater. A two-fluid nozzle is a spray nozzle that atomizes and sprays the conductive water-based primer paint using a high-speed airflow. By spraying the conductive water-based primer paint onto the core material 32a using a two-fluid nozzle, the solid content of the paint increases when it reaches the core material, allowing the paint to dry more quickly, thereby enabling the coating layer 32b to be formed in a shorter time.

[0050] After the conductive water-based primer paint is applied to the core material 32a, it is preferably dried at a temperature of, for example, 80° C. or higher and 120° C. or lower. The drying time may be, for example, 3 minutes or higher and 20 minutes or lower, depending on the application method.

[0051] An example of a method for producing the power storage device electrode 30 in this embodiment will be described.

[0052] The electrode 30 for the energy storage device of this embodiment is produced by placing a composite sheet 34 prepared by a dry process on the coating layer 32b of the current collector 32 for the energy storage device of this embodiment described above, and joining the current collector 32 and the composite sheet 34.

[0053] The method for producing the composite sheet 34 by a dry process includes, for example, a kneading step in which an active material, a binder, a conductive material, etc. are kneaded to produce electrode composite particles having a solid content concentration of substantially 100%, and a rolling step in which the electrode composite particles are rolled to form them into a sheet.

[0054] In the kneading step, raw materials such as the active material, binder, conductive material, etc. can be kneaded using, for example, a conventionally known mechanical stirring mixer. Suitable mixers include devices capable of applying mechanical shearing force, such as a cutter mill, a pin mill, a bead mill, a microparticle compounding device (a device in which shearing force is generated between a specially shaped rotor rotating at high speed inside a tank and an impact plate), a granulator, a twin-screw extrusion kneader, and a planetary mixer, and among these, a cutter mill, a microparticle compounding device, a granulator, and a twin-screw extrusion kneader are preferred.

[0055] The active material, binder, and conductive material are materials that constitute the composite sheet 34. In terms of the strength of the composite sheet 34, the binder preferably contains a binder that is turned into fibers in the kneading step, and specifically, it preferably contains PTFE particles.

[0056] In the rolling step, for example, a pair of rolls is used to roll the electrode mixture particles having a solid content concentration of substantially 100% obtained in the kneading step and form them into a sheet. The pair of rolls is arranged with a predetermined gap between them and rotates in the same direction. The electrode mixture particles are supplied to the gap between the pair of rolls, where they are compressed by the two rolls and stretched into a sheet. The resulting mixture sheet may be passed through the gap between the pair of rolls multiple times, or may be stretched one or more times using other rolls with different roll diameters, peripheral speeds, gaps, etc. Alternatively, the rolls may be heated to heat-press the electrode mixture particles.

[0057] 3 is a diagram showing an example of a joining step for joining a current collector for an electricity storage device and a composite sheet in this embodiment. As shown in FIG. 3 , in the joining step, for example, a composite sheet 34 obtained by the dry process described above and the current collector for an electricity storage device 32 in this embodiment are passed between a pair of rolls 36, thereby joining the composite sheet 34 and the current collector for an electricity storage device 32 (joining step). Specifically, the composite sheet 34 is joined onto the coating layer 32b of the current collector 32. In this manner, an electrode for an electricity storage device 30 is obtained.

[0058] 3, the composite sheet 34 is bonded to only one surface of the electricity storage device current collector 32, but it may be bonded to both surfaces of the electricity storage device current collector 32. In this case, it is preferable that a coating layer 32b is provided on both surfaces of a core material 32a constituting the electricity storage device current collector 32.

[0059] At least one of the pair of rolls 36 may be heated. The temperature of these rolls is preferably from room temperature to 300° C. or less, more preferably from room temperature to 200° C. The linear pressure between the pair of rolls 36 is, for example, from 0.1 t / cm to 2 t / cm.

[0060] Furthermore, a compression step may be carried out on the electricity storage device electrode 30 obtained in this manner, as necessary. Specifically, the electricity storage device electrode 30 may be transported to a predetermined gap provided between a pair of opposing rolls and compressed by the gap. The linear pressure between the pair of rolls compressing the electricity storage device electrode 30 is, for example, 1 t / cm or more and 3 t / cm or less.

[0061] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0062] Example 1 Preparation of Positive Electrode Current Collector A conductive filler A was 15 parts by mass of graphite particles (average aspect ratio 18), conductive filler B was 5 parts by mass of acetylene black (average aspect ratio 1.5), 3 parts by mass of PNVA, and 100 parts by mass of ion-exchanged water. A conductive water-based primer paint containing 15% by mass of PNVA relative to the total mass of the conductive filler was prepared. Using a spray coater with a two-fluid nozzle (manufactured by Musashi Engineering Co., Ltd., two-fluid spray valve SV-6), the conductive water-based primer paint was sprayed onto a positive electrode core material made of aluminum foil, and then dried at 100 ° C. for 30 seconds. This resulted in a positive electrode current collector having a coating layer formed on the positive electrode core material.

[0063] [Preparation of Positive Electrode Composite Sheet] Using NOB300-Nobilta (registered trademark) manufactured by Hosokawa Micron Corporation, 99.1 parts by mass of a lithium transition metal composite oxide as the positive electrode active material and 0.9 parts by mass of acetylene black as the conductive material were mixed for 20 minutes to perform a composite treatment, thereby preparing a composite material in which acetylene black was adhered to the particle surfaces of the positive electrode active material.

[0064] Next, this composite material and polytetrafluoroethylene (PTFE) were added to a Wonder Crusher manufactured by Osaka Chemical Co., Ltd. in a mass ratio of 100:1.0 and mixed for 2 minutes at room temperature and 8,400 rpm. The PTFE particles were fibrous by the mixing process, resulting in a cathode composite containing the composite material (cathode active material and conductive material) and fibrous PTFE. The solids concentration of this cathode composite was 100%.

[0065] The above-mentioned positive electrode composite was passed through a pair of rolls and rolled to prepare a positive electrode composite sheet. At this time, the peripheral speed ratio of the pair of rolls was set to 1:1, and the linear pressure between the pair of rolls was set to 0.1 t / cm. This positive electrode composite sheet was passed through the pair of rolls and repeatedly stretched until a desired film thickness was reached, thereby obtaining a positive electrode composite sheet used in the examples.

[0066] [Fabrication of Positive Electrode] The positive electrode composite sheet was placed on the coating layer of the positive electrode current collector, and the laminate of the positive electrode composite sheet and the positive electrode current collector was pressed (linear pressure: 1 t / cm) using a pair of rolls, thereby obtaining a positive electrode in which the positive electrode composite sheet was joined onto the coating layer of the positive electrode current collector.

[0067] Example 2 A positive electrode was obtained in the same manner as in Example 1, except that a conductive water-based primer paint containing 7.5 parts by mass of graphite particles, 2.5 parts by mass of acetylene black, 3 parts by mass of PNVA, and 100 parts by mass of ion-exchanged water was used, in which the content of PNVA was 30% by mass relative to the total mass of the conductive filler.

[0068] Example 3 A positive electrode was obtained in the same manner as in Example 1, except that a conductive water-based primer paint containing 5 parts by mass of graphite particles, 5 parts by mass of acetylene black, 6.5 parts by mass of PNVA, and 100 parts by mass of ion-exchanged water was used, in which the content of PNVA was 65% by mass relative to the total mass of the conductive filler.

[0069] Comparative Example 1 A positive electrode was obtained in the same manner as in Example 1, except that a conductive water-based primer paint containing 15 parts by mass of graphite particles, 5 parts by mass of acetylene black, 2 parts by mass of PNVA, and 100 parts by mass of ion-exchanged water was used, in which the content of PNVA was 10% by mass relative to the total mass of the conductive filler.

[0070] Comparative Example 2 A positive electrode was obtained in the same manner as in Example 1, except that a conductive water-based primer paint containing 5 parts by mass of graphite particles, 5 parts by mass of acetylene black, 7 parts by mass of PNVA, and 100 parts by mass of ion-exchanged water was used, in which the content of PNVA was 70% by mass relative to the total mass of the conductive filler.

[0071] Comparative Example 3 A positive electrode was obtained in the same manner as in Example 1, except that a conductive water-based primer paint containing 7.5 parts by mass of graphite particles, 2.5 parts by mass of acetylene black, 3 parts by mass of PVDF, and 100 parts by mass of N-methyl-2-pyrrolidone, which did not contain PNVA, and in which the PVDF content was 30% by mass relative to the total mass of the conductive filler, was used.

[0072] [Evaluation 1: Loss of Positive Electrode Composite Sheet] The obtained positive electrodes of each Example and Comparative Example were visually observed, and were evaluated as ◯ when no loss of the positive electrode composite sheet was observed, and as × when loss of the positive electrode composite sheet was observed.

[0073] [Evaluation 2: Interface Resistance Between Positive Electrode Composite Sheet and Positive Electrode Current Collector] Using an electrode resistance measuring device (manufactured by Hioki E.E. Corporation, product name: XF057-012), the interface resistance between the positive electrode composite sheet and the positive electrode current collector was measured under the conditions of applied current value: 1 mA, voltage range: 0.2 V, and measurement speed: Normal. The measured interface resistance was evaluated according to the following criteria. ◯: Interface resistance value was 0.08 Ω cm ２ x: The interface resistance is less than 0.08 Ω cm ２ That's all.

[0074] [Evaluation 3: Peel strength between positive electrode composite sheet and positive electrode current collector] A 100 mm x 25 mm positive electrode composite sheet surface of each Example or Comparative Example was attached to a 120 mm x 30 mm acrylic plate via double-sided tape (Nichiban Co., Ltd., Nicetack NW-20). A compact benchtop testing machine (FGS-TV and FGP-5) manufactured by Nidec-Shimpo Corporation was used to measure the peel strength between the positive electrode composite sheet and the positive electrode current collector, at a measurement temperature of 25°C and a tensile speed of 50 mm / min. The measured peel strength was evaluated according to the following criteria. ◯: The peel strength was 12 N / m or more, indicating good adhesion between the positive electrode composite sheet and the positive electrode current collector. △: The peel strength was 10 N / m or more but less than 12 N / m, indicating that the adhesion between the positive electrode composite sheet and the positive electrode current collector was at a level that would not pose a problem in the manufacture of the positive electrode. x: The peel strength is less than 10 N / m, and the adhesion between the positive electrode mixture sheet and the positive electrode current collector is at a level that interferes with the production of the positive electrode.

[0075] Table 1 summarizes the results of evaluations 1 to 3 of the positive electrodes in each example and each comparative example.

[0076]

[0077] As can be seen from the results of the examples and comparative examples, by forming a coating layer on a core material using a conductive water-based primer paint containing a conductive filler, PNVA, and a solvent, wherein the PNVA content relative to the conductive filler is 15% by mass or more and 65% by mass or less, and the solvent is a solvent whose main component is water, it becomes possible to suppress the loss of the composite sheet and the decrease in adhesion between the composite sheet and the current collector when producing an electrode by a dry method, and it also becomes possible to keep the interfacial resistance between the current collector and the composite sheet low in the produced electrode.

[0078] The present disclosure is further described by the following embodiments. Configuration 1: A conductive water-based primer paint comprising a conductive filler, poly-N-vinylacetamide (hereinafter, PNVA), and a solvent, wherein the content of the PNVA relative to the conductive filler is 15% by mass or more and 65% by mass or less, and the solvent is a solvent mainly composed of water. Configuration 2: The conductive water-based primer paint according to Configuration 1, which comprises a dispersant. Configuration 3: The conductive water-based primer paint according to Configuration 1 or 2, wherein the conductive filler includes a conductive filler A and a conductive filler B having an average aspect ratio larger than that of the conductive filler A. Configuration 4: The conductive water-based primer paint according to any one of Configurations 1 to 3, wherein the content of the conductive filler in the conductive water-based primer paint is 20% by mass or more and 80% by mass or less. Configuration 5: The conductive water-based primer paint according to any one of Configurations 1 to 4, wherein the conductive filler is a carbon material. Configuration 6: The conductive water-based primer paint according to Configuration 3, wherein the conductive filler B has an average aspect ratio of 10 or more and 40 or less. Configuration 7: The conductive water-based primer paint according to Configuration 2, wherein the dispersing agent contains carboxymethyl cellulose. Configuration 8: A 100s solution of a 3% aqueous solution of the dispersing agent －１The conductive water-based primer paint according to Configuration 2 or 7, having a viscosity of 2 mPa·s or more and 200 mPa·s or less. Configuration 9: A current collector for an electricity storage device, comprising a core material and a coating layer formed by applying the conductive water-based primer paint according to any one of Configurations 1 to 8 onto the core material. Configuration 10: A current collector for an electricity storage device, comprising a core material and a coating layer disposed on the core material, the coating layer containing a conductive filler and PNVA, and the content of the PNVA relative to the conductive filler is 15 mass% or more and 65 mass% or less. Configuration 11: The current collector for an electricity storage device according to Configuration 10, wherein the thickness of the coating layer is 3 μm or less. Configuration 12: An electrode for an electricity storage device, comprising the current collector for an electricity storage device according to Configuration 10 or 11. Configuration 13: An electricity storage device, comprising the electrode for an electricity storage device according to Configuration 12. Configuration 14. A method for producing a current collector for an electricity storage device, comprising the step of spraying the conductive water-based primer paint according to any one of Configurations 1 to 9 onto a core material using a two-fluid nozzle to form a coating layer.

[0079] REFERENCE SIGNS LIST 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Case body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Protruding portion, 23 Filter, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Electrode for electricity storage device, 32 Current collector for electricity storage device, 32a Core material, 32b Coating layer, 34 Composite sheet, 36 Roll.

Claims

1. A conductive water-based primer paint comprising a conductive filler, poly-N-vinylacetamide (hereinafter referred to as PNVA), and a solvent, wherein the content of the PNVA relative to the conductive filler is 15% by mass or more and 65% by mass or less, and the solvent is a solvent whose main component is water.

2. The conductive water-based primer paint according to claim 1, which contains a dispersing agent.

3. The conductive water-based primer paint according to claim 1 or 2, wherein the conductive filler comprises a conductive filler A and a conductive filler B having an average aspect ratio larger than that of the conductive filler A.

4. The conductive water-based primer paint according to claim 1 or 2, wherein the content of the conductive filler relative to the solid content in the conductive water-based primer paint is 20 mass % or more and 80 mass % or less.

5. The conductive water-based primer paint according to claim 1 or 2, wherein the conductive filler is a carbon material.

6. The conductive water-based primer paint according to claim 3, wherein the conductive filler B has an average aspect ratio of 10 or more and 40 or less.

7. The conductive water-based primer paint according to claim 2, wherein the dispersing agent comprises carboxymethyl cellulose.

8. 100s of a 3% aqueous solution of the dispersion material －１ The conductive water-based primer paint according to claim 2 or 7, having a viscosity of 2 mPa·s or more and 200 mPa·s or less.

9. A current collector for an electricity storage device, comprising a core material and a coating layer formed by applying the conductive water-based primer coating according to claim 1 or 2 onto the core material.

10. A current collector for an electricity storage device, comprising a core material and a coating layer disposed on the core material, wherein the coating layer contains a conductive filler and PNVA, and the content of the PNVA relative to the conductive filler is 15% by mass or more and 65% by mass or less.

11. The current collector for an electricity storage device according to claim 10, wherein the coating layer has a thickness of 3 μm or less.

12. An electrode for an electricity storage device, comprising the current collector for an electricity storage device according to claim 10 or 11.

13. An electricity storage device comprising the electricity storage device electrode according to claim 12.

14. A method for producing a collector for an electricity storage device, comprising the step of spraying the conductive water-based primer paint according to claim 1 or 2 onto a core material using a two-fluid nozzle to form a coating layer.

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