Conductive resin film for current collector of secondary battery and method for producing same

Abstract

To provide a low-cost conductive resin film for a collector of a secondary battery and a method of producing the same, capable of preventing deterioration in charge / discharge cycle characteristics by improving chemical resistance, preventing the peeling of a collector of a secondary battery, and contributing to an improvement in conductivity and reduced weight.SOLUTION: Provided is a conductive resin film 5 for a collector of a secondary battery, which contains, in a composition mass ratio, 75 mass% or more and 97 mass% or less of a polyarylene ether ketone resin and 3 mass% or more and 25 mass% or less of a carbon-based conductive material, the conductive resin film 5 for a collector having a relative crystallinity of 80% or more. The conductive resin film 5 for a collector is produced by selecting a polyarylene ether ketone resin 2 that is excellent in reduced weight, mechanical properties, chemical resistance and heat resistance and low in water absorption, so that, even if the conductive resin film 5 for a collector is used as a collector, an electrolyte component does not permeate into the inside of the conductive resin film 5 for a collector, and the risk of deterioration in charge / discharge cycle characteristics can be eliminated.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a conductive resin film for a current collector of a secondary battery used in a lithium ion secondary battery, an all-solid-state battery, or the like, and a method for producing the same. [Background technology]

[0002] In recent years, high-performance rechargeable secondary batteries, such as nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium-ion secondary batteries, and all-solid-state batteries, have been attracting attention. Among these high-performance secondary batteries, lithium-ion secondary batteries and all-solid-state batteries have been attracting particular attention. Although not shown, lithium-ion secondary batteries are composed of a positive electrode, a negative electrode, a separator, an electrolyte, a container, and other components. The positive electrode (positive electrode plate) consists of a current collector plate and a positive electrode mixture containing a positive electrode active material formed on top of it. The positive electrode active material used for this positive electrode is lithium cobalt oxide, lithium manganese oxide, or the like.

[0003] In contrast, the negative electrode (negative electrode plate) is composed of a current collector plate and a negative electrode mixture formed on both sides of the current collector plate. The negative electrode active material used for this negative electrode is graphitic carbon such as natural graphite or artificial graphite. The current collectors for these positive and negative electrodes are generally aluminum foil for the positive electrode and metal foil such as copper foil for the negative electrode.

[0004] Such lithium-ion secondary batteries and all-solid-state batteries have excellent characteristics, such as high energy density, high operating voltage, long life cycle, and low self-discharge, and are therefore used in a variety of fields, including as power sources for mobile information devices such as mobile phones, multi-function mobile phones, and tablet terminals, electronic devices such as cameras, video cameras, and portable digital music players, automobiles such as electric vehicles (EVs), hybrid vehicles (HEVs), and plug-in hybrid vehicles (PHEVs), and aircraft.

[0005] Lithium-ion secondary batteries and all-solid-state batteries used in mobile information devices, automobiles, and the like are required to have high energy densities, and one way to achieve this is to reduce the weight of the battery. Various methods have been investigated for reducing the weight of batteries, one of which is the use of conductive resin films for current collectors. That is, as described above, metal foils are used for the current collectors of the positive and negative electrodes of lithium-ion secondary batteries. However, using conductive resin films, which have a lower specific gravity than metals, instead of the metal foils can contribute to reducing the weight of the battery.

[0006] Therefore, various conductive resin films have been investigated in order to reduce the weight of secondary batteries (see Patent Documents 1, 2, and 3). For example, Patent Document 1 proposes a conductive resin film made of a cyclic olefin resin, a conductive filler, and a conjugated diene rubber, or a cyclic olefin resin, a hydrogenated product of an aromatic vinyl-conjugated diene block copolymer, a conductive filler, and a conjugated diene rubber.

[0007] Patent Document 2 proposes a current collector for a secondary battery having a conductive resin layer containing at least one resin selected from the group consisting of polyether ether ketone and a tetrafluoroethylene-hexafluoropropylene copolymer, and at least one conductive filler selected from the group consisting of ketjen black and a multi-layer carbon tube. Patent Document 3 also discloses a current collector for a bipolar lithium-ion secondary battery, which comprises a conductive resin layer (first conductive layer) formed by adding a conductive filler to a substrate containing an imide group-containing resin, and a conductive resin layer (second conductive layer) formed by adding a conductive filler to a substrate containing a non-imide group-containing resin, and a metal layer. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-77236 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-248430 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-26192 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the conductive resin film described in Patent Document 1 has a problem with chemical resistance, and therefore, when such a conductive resin film is used as a current collector of a lithium-ion secondary battery, electrolyte components may penetrate into the conductive resin film, resulting in a deterioration in charge-discharge cycle characteristics.

[0010] Furthermore, in the case of the current collector for secondary batteries described in Patent Document 2, ketjen black and multi-walled carbon nanotubes are used as conductive filler components. When ketjen black is used as the conductive filler component, it is not possible to add a large amount of ketjen black to the resin, making it impossible to achieve high conductivity for the current collector for secondary batteries. Furthermore, because current collector plates containing ketjen black are brittle, there is a risk of breakage during application of positive or negative electrode active material or during assembly into a secondary battery.

[0011] Furthermore, conductive resin layers manufactured from a raw material mixture using multi-walled carbon nanotubes as a conductive filler have the problem that, although the multi-walled carbon nanotubes are oriented in the plane direction, they have excellent in-plane conductivity, but poor conductivity in the thickness direction. Furthermore, when tetrafluoroethylene-hexafluoropropylene copolymer is used as the resin component, the specific gravity of the resin is high, at 2.1 or more and 2.2 or less, which is problematic in that it does not contribute to reducing the weight of the current collector. Furthermore, because tetrafluoroethylene-hexafluoropropylene copolymer is a fluororesin, special steel materials and equipment are required for melt molding, resulting in increased costs for the current collector.

[0012] Furthermore, in the case of the current collector for a bipolar lithium-ion secondary battery described in Patent Document 3, the multilayer structure is made up of two different resins, and because the two resins have different linear expansion coefficients, the difference in the expansion rate of the conductive resins caused by heat generation during repeated charging and discharging may lead to peeling of the current collector between the first and second conductive layers. Furthermore, because the resins used in the first and second conductive layers have different water absorption rates, the current collector may curl due to the difference in expansion rate caused by water absorption after production, or the current collector may peel between the first and second conductive layers.

[0013] The present invention has been made in view of the above, and aims to provide an inexpensive conductive resin film for a current collector of a secondary battery, which can improve chemical resistance to prevent a decrease in charge / discharge cycle characteristics, prevent peeling of the current collector of the secondary battery, and contribute to improving conductivity and weight reduction, and a method for producing the same. [Means for solving the problem]

[0014] As a result of extensive research, the present inventors have focused on polyarylene ether ketone resin, which has the most heat resistance of all thermoplastic resin materials and also has excellent chemical resistance and mechanical properties, and on lightweight carbon-based conductive materials, which have the most excellent conductivity of all conductive materials, and have completed the present invention using these polyarylene ether ketone resin and carbon-based conductive material.

[0015] That is, in order to solve the above-mentioned problems, in the present invention, a polyarylene ether ketone resin is used in a composition mass ratio 78% by mass and 3% by mass or more and 25% by mass or less of a carbon-based conductive material. A conductive resin film for a current collector of a secondary battery, which is formed from a molding material containing the following, and has a relative crystallinity of 80% or more and 100% or less: The apparent shear viscosity of polyarylene ether ketone resin was measured with a flow tester using a die with a diameter of 1.0 mm and a length of 10 mm under the conditions of a temperature of 375°C and a load of 50 kgf. The apparent shear viscosity at 375°C was 1 x 10 1 Pa·s or more 1×10 4 Pa·s or less, The mass change rate when immersed in N-methyl-2-pyrrolidone and electrolyte is 0.0% to 2.0%, and the volume resistance value measured in accordance with JIS K 7194 is 10 Ω·cm to 100 Ω·cm. It is characterized by the following.

[0016] In addition, the thickness is 5 μm or more and 500 μm or less, It is preferable that the tensile elongation at break measured in accordance with JIS K 7127 is 10% or more and 500% or less, and the maximum tensile strength measured in accordance with JIS K 7127 is 70 MPa or more and 500 MPa or less. Also, The apparent shear viscosity of the molding material was measured with a flow tester using a die with a diameter of 1.0 mm and a length of 10 mm under the conditions of a temperature of 375°C and a load of 50 kgf, and the apparent shear viscosity at 375°C was 1 x 10 1 Pa·s or more 1×10 4 It is preferable that it is Pa·s or less.

[0017] In order to solve the above problems, the present invention provides a method for producing a conductive resin film for a current collector of a secondary battery according to claim 1, 2, or 3, comprising the steps of: Composition mass ratio: Polyarylene ether ketone resin 78% by mass or more A molding material consisting of 97% by mass or less and 3% by mass or more and 25% by mass or less of a carbon-based conductive material is melt-kneaded, and the molding material is extruded using a die to form a conductive resin film for a current collector, and the film is cooled by being sandwiched between a pressure roll and a cooling roll, thereby controlling the relative crystallinity of the conductive resin film for a current collector. Between 80% and 100% It is characterized by the fact that

[0019] The cooled conductive resin film for a current collector is then heat-compressed and molded, and the heating temperature of the conductive resin film for a current collector is set to a temperature equal to or higher than the melting point of the polyarylene ether ketone resin but lower than the thermal decomposition temperature. The pressure applied to the conductive resin film for a current collector is set to 0.5 kgf / cm with respect to the projected area of the conductive resin film for a current collector. 2 More than 100kgf / cm 2 It is preferable to do the following:

[0020] Here, the conductive resin film for a current collector in the claims may be any of a uniaxially stretched type, a biaxially stretched type, and a non-stretched type. This conductive resin film for a current collector includes not only a thin conductive resin film for a current collector but also a thick conductive resin sheet for a current collector. The molding material can be prepared into a conductive resin composition by stirring and mixing a polyarylene ether ketone resin and a carbon-based conductive material such as carbon nanotubes, followed by melt-kneading.

[0021] The polyarylene ether ketone resin and the carbon-based conductive material of the molding material can be melt-kneaded at a temperature equal to or higher than the melting point of the polyarylene ether ketone resin and lower than the thermal decomposition temperature of the polyarylene ether ketone resin. Furthermore, the secondary battery according to the present invention includes at least a nickel-cadmium storage battery, a nickel-metal hydride storage battery, a nickel-zinc storage battery, a lithium-ion secondary battery, a bipolar lithium-ion secondary battery, an all-solid-state battery, etc.

[0022] According to the present invention, a conductive resin film for a current collector is manufactured using a polyarylene ether ketone resin, which is lightweight, chemical-resistant, and has low water absorption, as a molding material. Therefore, even when the conductive resin film for a current collector is used as a current collector, electrolyte components are less likely to penetrate into the conductive resin film for a current collector, eliminating the risk of deterioration in charge-discharge cycle characteristics. Furthermore, since no special steel materials or equipment are required for molding, the cost of the current collector can be reduced. Furthermore, since there is no need to use two different resins, the risk of peeling of the current collector can be eliminated. Furthermore, there is also less risk of curling due to differences in expansion coefficients caused by water absorption after manufacturing, or peeling of the current collector between the first and second conductive layers. [Effects of the Invention]

[0023] The present invention has the advantages of improving the chemical resistance of the conductive resin film for a current collector, preventing a decrease in the charge-discharge cycle characteristics of the secondary battery, preventing peeling of the current collector of the secondary battery, and contributing to improved conductivity and weight reduction. Also, it has the advantage of being able to provide a secondary battery at low cost. Furthermore, since the relative crystallinity of the conductive resin film for a current collector is 80% or more and 100% or less, problems with the mechanical strength, heat resistance, chemical resistance, and solvent resistance of the conductive resin film for a current collector can be prevented, and the conductive resin film can be expected to have sufficient mechanical strength, heat resistance, and chemical resistance to be usable as a conductive resin film for a current collector. The apparent shear viscosity of the polyarylene ether ketone resin was measured with a flow tester using a die with a diameter of 1.0 mm and a length of 10 mm under the conditions of a temperature of 375°C and a load of 50 kgf, and was found to be 1 x 10 1 Pa·s or more 1×10 4 Because the melt tension is below Pa·s, it does not decrease, making it difficult to mold the molding material, and it also prevents an increase in melt viscosity and a decrease in melt elongation. Furthermore, when the conductive resin film for current collectors is immersed in N-methyl-2-pyrrolidone and an electrolyte, the mass change rate is between 0.0% and 2.0%, enabling excellent chemical resistance. Furthermore, because the volume resistivity of the conductive resin film for current collectors is low, between 10 Ω·cm and 100 Ω·cm, it is possible to prevent a decrease in energy density even when the conductive resin film for current collectors is used as a current collector in secondary batteries.

[0024] According to the invention described in claim 2, the thickness of the conductive resin film for the current collector is 5 μm or more and 500 μm or less, which prevents a decrease in the tensile strength of the conductive resin film for the current collector and is expected to lead to a reduction in the weight of the current collector of the secondary battery. Furthermore, the tensile elongation at break of the conductive resin film for current collector, measured in accordance with JIS K 7127, is 10% or more and 500% or less, which prevents the conductive resin film for current collector from becoming inferior in toughness and prevents the conductive resin film for current collector from stretching during the process of coating the conductive resin film for current collector with a positive electrode active material or a negative electrode active material. Furthermore, since the maximum tensile strength of the conductive resin film for a current collector is 70 MPa or more and 500 MPa or less when measured in accordance with JIS K 7127, the conductive resin film for a current collector can be prevented from having poor toughness and cracking during production of the conductive resin film for a current collector. In addition, since the cuttability of the conductive resin film for a current collector is not reduced during production, there is little risk of a decrease in the production speed of long conductive resin films for a current collector.

[0025] According to the invention of claim 3, the conductive resin film for current collector has excellent formability and is expected to have sufficient mechanical strength.

[0026] According to the invention of claim 4, the conductive resin film for current collector is produced by melt extrusion molding, which improves the thickness accuracy, productivity, and handling of the conductive resin film for current collector, and simplifies the production equipment. I'm looking forward to it.

[0027] Claim 5 According to the invention, the melt-extruded conductive resin film for a current collector is further heated and compressed to form a current collector. This makes it possible to lower the resistance value, increase the conductivity, and reduce the amount of carbon-based conductive material used, thereby reducing costs. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is an overall explanatory view schematically illustrating a melt-kneader in an embodiment of a conductive resin film for a current collector of a secondary battery and a method for producing the same according to the present invention. [Figure 2] 1 is an overall explanatory diagram schematically illustrating a melt extrusion molding apparatus in an embodiment of a conductive resin film for a current collector of a secondary battery and a method for producing the same according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] A preferred embodiment of the present invention will now be described with reference to the drawings. In this embodiment, a conductive resin film 5 for a current collector of a secondary battery is a resin film having a relative crystallinity of 80% or more, which is formed from a conductive molding material 1 containing, in terms of composition mass ratio, 75% by mass or more and 97% by mass or less of a polyarylene ether ketone resin 2 and 3% by mass or more and 25% by mass or less of a carbon-based conductive material 3, as shown in FIGS. 1 and 2 .

[0030] The composition mass ratio of the polyarylene ether ketone resin 2 in the molding material 1 is preferably 75% by mass or more and 97% by mass or less, preferably 78% by mass or more and 95% by mass or less, and more preferably 80% by mass or more and 90% by mass or less of the polyarylene ether ketone resin. This is because, if the composition mass ratio of the polyarylene ether ketone resin 2 is less than 75% by mass, the melt viscosity of the molding material 1 increases, resulting in a decrease in melt fluidity, and the processability of the conductive resin film 5 for a current collector decreases due to a decrease in melt elongation, resulting in the formation of holes in the conductive resin film 5 for a current collector. In addition, it becomes difficult to blend a conductive material into the polyarylene ether ketone resin.

[0031] Furthermore, if the composition mass ratio is less than 75 mass %, the carbon-based conductive material 3 separates from the conductive resin film 5 for a current collector, causing the generation of die fill, which leads to a deterioration in the quality of the conductive resin film 5 for a current collector. To explain this point in more detail, when the conductive resin film 5 for a current collector is molded into a film, a large amount of deposits called die fill may adhere and accumulate at the exit (also referred to as the die lip) of the molding die 23 shown in FIG. 2. The accumulation of such die fill may cause die lines to appear in the conductive resin film 5 for a current collector, or the die fill may move away from the exit of the die 23 and become mixed into the conductive resin film 5 for a current collector, resulting in a deterioration in the quality of the conductive resin film 5 for a current collector.

[0032] On the other hand, if the composition mass ratio of the polyarylene ether ketone resin 2 exceeds 97 mass %, the volume resistivity of the conductive resin film 5 for a current collector exceeds 100 Ω·cm, and the conductive resin film 5 for a current collector cannot be imparted with sufficient conductivity, making it difficult to use it as a current collector for a secondary battery.

[0033] Such molding material 1 may include, in addition to polyarylene ether ketone resin 2 and carbon-based conductive material 3, polyolefin resins such as polyethylene (PE) resin, polypropylene (PP) resin, polymethylpentene (PMP) resin, and polystyrene (PS) resin, acid-modified olefin resins such as maleic anhydride-modified polyethylene resin and maleic anhydride-modified polypropylene resin, polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, and polyethylene naphthalate (PEN) resin, within the range that does not impair the characteristics of the present invention. Polyamide resins such as polyester resins, polyimide (PI) resins, polyamideimide (PAI) resins, polyetherimide (PEI) resins, etc.; polyamide 4T (PA4T) resins, polyamide 6T (PA6T) resins, modified polyamide 6T (modified PA6T) resins, polyamide 9T (PA9T) resins, polyamide 10T (PA10T) resins, polyamide 11T (PA11T) resins, polyamide 6 (PA6) resins, polyamide 66 (PA66) resins, polyamide 46 (PA46) resins, etc.; polysulfone (PSU) resins; Polysulfone resins such as polyphenylene sulfone (PES) resin and polyphenylene sulfone (PPSU) resin, polyarylene sulfide resins such as polyphenylene sulfide (PPS) resin, polyphenylene sulfide ketone resin, polyphenylene sulfide sulfone resin and polyphenylene sulfide ketone sulfone resin, polytetrafluoroethylene (PTFE) resin, polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) resin, tetrafluoroethylene-hexafluoropropyl copolymer (FEP) resin, Fluororesins such as tetrafluoroethylene-ethylene copolymer (ETFE) resin, polychlorotrifluoroethylene (PCTFE) resin, polyvinylidene fluoride (PVdF) resin, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer resin, and acid-modified fluororesins, as well as thermoplastic resins such as polycarbonate (PC) resin, polyarylate (PAR) resin, polyacetal (POM) resin, liquid crystal polymer (LCP), aliphatic polyketone resin, polyimide resin, and polyamide-imide resin can be selectively added.

[0034] In addition to the polyarylene ether ketone resin 2, the carbon-based conductive material 3, and the thermoplastic resin, certain additives may be selectively added to the molding material 1, provided that the properties of the present invention are not impaired. Specifically, nucleating agents, impact modifiers, antioxidants, light stabilizers, ultraviolet absorbers, plasticizers, lubricants, flame retardants, heat resistance improvers, inorganic fillers, organic fillers, glass fibers, carbon fibers, etc. may be selectively added.

[0035] The polyarylene ether ketone resin 2 of the molding material 1 is a crystalline thermoplastic resin consisting of arylene groups, ether groups, and carbonyl groups, and examples thereof include the resins described in Japanese Patent No. 5709878 and Japanese Patent No. 5847522, or in the literature [Asahi Research Center Co., Ltd.: PEEK, a super engineering plastic growing in cutting-edge applications (Part 1)], and is characterized by excellent mechanical strength, light weight, low dielectric properties, hydrolysis resistance, heat resistance, chemical resistance, etc.

[0036] Specific examples of the polyarylene ether ketone resin 2 include, for example, polyether ether ketone (PEEK) resin having a chemical structure represented by chemical formula (1), polyether ketone (PEK) resin having a chemical structure represented by chemical formula (2), polyether ketone ketone (PEKK) resin having a chemical structure represented by chemical formula (3), polyether ether ketone ketone (PEEKK) resin having a chemical structure represented by chemical formula (4), and polyether ketone ether ketone ketone (PEKEKK) resin having a chemical structure represented by chemical formula (5).

[0037] [ka]

[0038] [ka]

[0039] [ka]

[0040] [ka]

[0041] [ka]

[0042] Among these polyarylene ether ketone resins 2, at least one of polyether ether ketone resins and polyether ketone ketone resins is preferred from the viewpoints of easy availability, cost, and formability of the conductive resin film 5 for current collector. Specific examples of polyether ether ketone resins include Victrex Powder series and Victrex Granules series manufactured by Victrex, Vestakeep series manufactured by Diesel-Evonik, and KetaSpire PEEK series manufactured by Solvay Specialty Polymers. Specific examples of polyether ketone ketone resins include KEPSTAN series manufactured by Arkema.

[0043] The polyarylene ether ketone resin 2 may be used alone or in combination of two or more. The polyarylene ether ketone resin 2 may also be a copolymer having two or more chemical structures represented by chemical formulas (1) to (5). The polyarylene ether ketone resin 2 is usually used in a form suitable for molding, such as powder, granules, or pellets. The method for producing the polyarylene ether ketone resin 2 is not particularly limited, and examples thereof include the method described in the literature [Asahi Research Center Co., Ltd.: PEEK, a super engineering plastic growing in cutting-edge applications (Vol. 1)].

[0044] The apparent shear viscosity of polyarylene ether ketone resin 2 at 375°C, measured with a flow tester using a die with a diameter of 1.0 mm and a length of 10 mm under the conditions of a temperature of 375°C and a load of 50 kgf, was set to 1 x 10 from the viewpoint of improving moldability. 1 Pa·s or more 1×104 Pa·s or less, preferably 5×10 1 Pa·s or more 5×10 3 Pa·s or less, preferably 1×10 2 Pa·s or more 2×10 3 Pa·s or less is good. This is 1×10 1 If the viscosity is less than Pa·s, the apparent shear viscosity will be low, which will lead to a decrease in melt tension and make it difficult to mold the molding material 1. Therefore, care must be taken. Also, if the apparent shear viscosity is less than 1×10 4 If the viscosity exceeds Pa·s, care must be taken as the melt viscosity will increase and the melt elongation will decrease, making it difficult to mold the molding material 1.

[0045] The composition mass ratio of the carbon-based conductive material 3 in the molding material 1 is preferably 3% by mass or more and 25% by mass or less, preferably 5% by mass or more and 22% by mass or less, and more preferably 10% by mass or more and 20% by mass or less. Examples of the carbon-based conductive material 3 include carbon blacks such as furnace black (oil furnace black and gas furnace black), channel black, acetylene black, and thermal black; carbon nanotubes 4, carbon nanofibers, fullerenes, amorphous carbon, carbon fibers such as bread-based carbon fibers and pitch-based carbon fibers; and graphite such as flake graphite, lump graphite, amorphous graphite, expanded graphite obtained by chemically treating flake graphite with concentrated sulfuric acid or the like and then heating it; expanded graphite obtained by heat-treating expanded graphite at high temperatures; and artificial graphite.

[0046] Among these carbon-based conductive materials 3, carbon nanotubes 4 are optimal because they can provide high conductivity with a small amount and can be molded into a conductive resin film 5 for a current collector without losing the mechanical strength of the current collector. These carbon nanotubes 4 have a cylindrical hollow fiber structure, and are therefore expected to contribute to weight reduction. Carbon nanotubes 4 include single-walled carbon nanotubes, which have a structure in which one surface of graphite is wrapped around them, and multi-walled carbon nanotubes, which have two or more layers wrapped around them, but are not particularly limited.

[0047] Carbon nanotubes 4 other than these single-walled carbon nanotubes and multi-walled carbon nanotubes include nanografibers, bamboo-shaped nanotubes, and cup-stacked nanotubes, which are described in "Introduction to Materials Chemistry of Carbon Nanotubes" (Corona Publishing, edited by Yahachi Saito, pp. 7-9). Also included are analogs of carbon nanotubes 4, such as nanohorns, nanocoils, microcoils, and nanocoils, which are described in "Introduction to Materials Chemistry of Carbon Nanotubes" (Corona Publishing, edited by Yahachi Saito, pp. 9-11). Among these carbon nanotubes 4 and analogs thereof, multi-walled carbon nanotubes are the most advantageous in terms of cost reduction.

[0048] The fiber diameter (outer diameter) of the carbon nanotubes 4 is not particularly limited, but is preferably 0.5 nm or more and 200 nm or less. Such carbon nanotubes 4 can be produced by known production methods. For example, they can be produced by (1) the arc discharge method, (2) the laser evaporation method, or (3) a chemical vapor deposition method (or pyrolysis method) such as the substrate growth method, supported catalyst method, fluidized catalyst method, or HiPco method, as described in "Introduction to Materials Chemistry of Carbon Nanotubes" (Corona Publishing, edited by Yahachi Saito, pp. 11-12). They can also be produced by the eDPIS method, the supergloss method, or the like.

[0049] Examples of carbon nanotube 4 products include supergrowth CNT (manufactured by the New Energy and Industrial Technology Development Organization), eDIPS-CNT (manufactured by the New Energy and Industrial Technology Development Organization), SWNT series (manufactured by Meijo Nanocarbon Co., Ltd.: product name), VGCF series (manufactured by Showa Denko K.K.: product name), FloTube series (manufactured by CNano Technology: product name), AMC (manufactured by Ube Industries, Ltd.: product name), Nanocyl NC7000 series (manufactured by Nanocyl: product name), Baytubes (manufactured by BAYER: product name), GRAPHISTRENGTH (manufactured by Arkema: product name), MWNT7 (manufactured by Hodogaya Chemical Co., Ltd.: product name), K-Nanos series (manufactured by Kumho), and Hyperion CNT (manufactured by Hypeprion Catalysis International: product name).

[0050] As long as the characteristics of the present invention are not impaired, other metallic or carbon-based conductive materials may be added to the carbon nanotubes 4. Examples of metallic conductive materials include gold, silver, copper, nickel, iron, aluminum, chromium, niobium, titanium, tin, vanadium, and alloys containing two or more of these, metal oxides, metal carbides, and metal nitrides.

[0051] The carbonaceous conductive material 3 may be in any form, such as powder, granules, lumps, fibers, etc. One type may be used alone, or two or more types may be used in combination. Furthermore, the carbon-based conductive material 3 can be treated with various coupling agents, such as silane coupling agents (3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-aminopropylethoxysilane, imidazole silane, etc.), titanate-based coupling agents (isopropyl triisostearoyl titanate, tetraoctyl bis(dioctyl phosphite) titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, tetraisopropyl bis(dioctyl phosphite) titanate, isopropyl tri(N-amitoethyl aminoethyl) titanate, etc.), and aluminate-based coupling agents (acetoalkoxyaluminum diisopropylate, etc.), within the range that does not impair the properties of the conductive resin film 5 for current collector.

[0052] The apparent shear viscosity of molding material 1 was measured with a flow tester using a die with a diameter of 1.0 mm and a length of 10 mm under the conditions of a temperature of 375°C and a load of 50 kgf. The apparent shear viscosity at a temperature of 375°C was 1 x 10 1 Pa·s or more 1×10 4 Pa·s or less, preferably 1×10 2 Pa·s or more 5×10 3 Pa·s or less, preferably 5×10 2 Pa·s or more 2×10 3 A value in the Pa·s range or less is preferable.

[0053] This is because the apparent shear viscosity is 1×101 Pa·s or more 1×10 4 If the apparent shear viscosity is within the range of 1×10 s or less, the conductive resin film 5 for current collector can be expected to have excellent formability and sufficient mechanical strength. 1 If the viscosity is less than Pa·s, the apparent shear viscosity will be low and the melt tension will be reduced, making it difficult to form the conductive resin film 5 for current collector. 4 If the viscosity exceeds Pa·s, the melt viscosity will be high and the melt elongation will be low, which may cause holes to form in the conductive resin film 5 for a current collector and cause it to break, resulting in problems with molding the conductive resin film 5 for a current collector.

[0054] In the above, when producing the conductive resin film 5 for a current collector, first, a polyarylene ether ketone resin 2 and carbon nanotubes 4, which are a carbon-based conductive material 3, are melt-kneaded for a predetermined time to prepare a molding material 1, and this molding material 1 is fed into a melt extrusion molding machine 20 for resin film molding to produce a conductive resin film 5 for a current collector having a thickness of 500 μm or less, for example, 5 μm or more and 500 μm or less.

[0055] Methods for preparing the molding material 1 include: (1) a method in which carbon nanotubes 4 are introduced into a melt mixer 10 for the molding material 1 and melt-kneaded with the molten polyarylene ether ketone resin 2 to prepare the molding material 1; and (2) a method in which the polyarylene ether ketone resin 2 and the carbon nanotubes 4 are stirred and mixed at room temperature (a temperature of about 0°C or higher and 50°C or lower) using a stirring mixer, and then melt-extruded and kneaded in the melt mixer 10 to prepare the molding material 1.

[0056] First, the preparation method (1) will be explained in detail. In this method, a predetermined melt kneader 10 shown in FIG. 1 is prepared, and a polyarylene ether ketone resin 2 is introduced into the melt kneader 10 and melted. After that, carbon nanotubes 4 are newly introduced into the melt kneader 10 by a side feeder method or the like and melt-kneaded with the already melted polyarylene ether ketone resin 2 to prepare a molding material 1.

[0057] Examples of the melt kneader 10 include a Banbury mixer, a mixing roll, a pressure kneader, and a multi-screw extruder consisting of a single-screw extruder, a twin-screw extruder, a triple-screw extruder, a four-screw extruder, or an eight-screw extruder. Among these, it is preferable to use a vent-type multi-screw extruder, which is expected to achieve good kneading and dispersion of the polyarylene ether ketone resin 2 and the carbon nanotubes 4 and can remove moisture and volatile gases generated from them.

[0058] As shown in Figure 1, melt mixer 10, which is a multi-screw extruder, is composed of a cylinder 12 installed on base 11, a screw 13 that is built into and supported by a motor and rotates to melt and mix polyarylene ether ketone resin 2 and carbon nanotubes 4, and extrudes strands or the like from a die 14 at the tip, an inlet 15 for polyarylene ether ketone resin 2 connected to the upstream part of cylinder 12, a side feeder 16 for introducing carbon nanotubes 4 connected to the downstream part of cylinder 12, and a rotatable cutter 17 that cuts the strands (rod-shaped) or the like extruded from die 14 of cylinder 12 and cooled by air or water to obtain molding material 1.

[0059] The inlet 15 and side feeder 16 of the melt kneader 10 are such that the inlet 15 is installed as a hopper on the upper upstream side of the cylinder 12, and the side feeder 16 has a screw structure and is mounted on the upper downstream side of the cylinder 12. By feeding fine powder carbon nanotubes 4 from the side into the side feeder 16, which is located downstream of the inlet 15, the carbon nanotubes 4 are injected into the molten polyarylene ether ketone resin 2, improving the uniform dispersion of the molding material 1. Furthermore, since the time required to knead the carbon nanotubes 4 with the polyarylene ether ketone resin 2 is shortened, decomposition can also be prevented.

[0060] The melting temperature when melt-kneading the polyarylene ether ketone resin 2 and the carbon nanotubes 4 is not particularly limited as long as it is a temperature that allows melt-kneading and dispersion and does not cause decomposition of the polyarylene ether ketone resin 2, but is in the range of not less than the melting point of the polyarylene ether ketone resin 2 and not more than the thermal decomposition temperature of the polyarylene ether ketone resin 2. Specifically, the range is not less than the melting point of the polyarylene ether ketone resin +10°C and not more than the polyarylene ether ketone resin +100°C, preferably not less than the polyarylene ether ketone resin +20°C and not more than the polyarylene ether ketone resin +80°C, more preferably not less than the polyarylene ether ketone resin +30°C and not more than the polyarylene ether ketone resin +60°C, and even more preferably not less than the melting point of the polyarylene ether ketone +30°C and not more than the melting point of the polyarylene ether ketone +50°C.

[0061] This is because, if the temperature is lower than the melting point of the polyarylene ether ketone resin 2, it is not possible to melt-knead and disperse the polyarylene ether ketone resin 2 and the carbon nanotubes 4. Conversely, if the temperature is higher than the thermal decomposition temperature, it is not preferable because it will lead to decomposition of the polyarylene ether ketone resin 2.

[0062] The melt-kneaded polyarylene ether ketone resin 2 and carbon nanotubes 4 are extruded from a die 14 as strands to prepare strand molding material 1, but after being extruded from the die 14 as a crystalline thermoplastic resin film, they may be prepared into powder, granules, flakes, or pellets as molding material 1. When preparing molding material 1, either the polyarylene ether ketone resin 2 or the carbon nanotubes 4 may be dispersed in a predetermined amount or more to form a masterbatch.

[0063] Next, the preparation method (2) will be described in detail. When the polyarylene ether ketone resin 2 and the carbon nanotubes 4 are stirred and mixed at room temperature in this method, a stirring mixer such as a tumbler mixer, a Henschel mixer, a V-type mixer, a Nauta mixer, a ribbon blender, or a universal stirring mixer is used. In this case, the polyarylene ether ketone resin 2 is preferably in the form of powder so that it can be more uniformly dispersed with the carbon nanotubes 4. Methods for pulverizing into powder include, for example, shear pulverization, impact pulverization, collision pulverization, freeze pulverization, and solution pulverization.

[0064] The polyarylene ether ketone resin 2 and the carbon nanotubes 4 are stirred and mixed, and then melt-kneaded and dispersed using a melt kneader such as a Banbury mixer, a mixing roll, a pressure kneader, a single-screw extruder, or a multi-screw extruder consisting of a twin-screw extruder, a triple-screw extruder, a four-screw extruder, or an eight-screw extruder, to prepare the molding material 1. The melt kneader is preferably a vent-type multi-screw extruder, which is expected to achieve good kneading and dispersion of the polyarylene ether ketone resin 2 and the carbon nanotubes 4 and can degas the moisture and volatile gases generated therefrom. Furthermore, when preparing the molding material 1, either the polyarylene ether ketone resin 2 or the carbon nanotubes 4 can be dispersed in a predetermined amount or more to form a masterbatch.

[0065] The moisture content (water content) of the molding material 1 before melt extrusion molding is adjusted to 2000 ppm or less, preferably 1000 ppm or less, and more preferably 500 ppm or less using a hot air dryer or the like, because if the moisture content exceeds 2000 ppm, foaming of the conductive resin film 5 for current collector may occur.

[0066] The molding material 1 is preferably heated and dried to reduce the moisture content before melt-kneading. Examples of heat-drying methods include known methods such as hot air circulation drying, dehumidified hot air drying, heated vacuum drying, and microwave drying. The heating and drying temperature for the molding material 1 is between −50°C and +50°C of the glass transition point of the polyarylene ether ketone resin 2, preferably between −30°C and +30°C of the glass transition point of the polyarylene ether ketone resin 2, and more preferably between −20°C and +20°C of the glass transition point of the polyarylene ether ketone resin 2.

[0067] The heat drying time for the molding material 1 is 2 hours or more, preferably 4 hours or more, and more preferably 8 hours or more. There is no particular upper limit to the heat drying time, but 24 hours or less is appropriate.

[0068] Once the molding material 1 is prepared, the conductive resin film 5 for a current collector is manufactured using this molding material 1. As a manufacturing method, a melt extrusion method, a calendar molding method, a casting method, or the like can be adopted. Among these manufacturing methods, the melt extrusion method in which the conductive resin film 5 for a current collector is continuously extruded into a strip shape is optimal from the viewpoints of improving the thickness accuracy, productivity, and handleability of the conductive resin film 5 for a current collector, and simplifying the equipment.

[0069] The melt extrusion molding method is a method for producing a conductive resin film 5 for a current collector by melt-kneading a molding material 1 using a melt extruder 20 and continuously extruding the conductive resin film 5 for a current collector from a die 23, such as a T-die or a round die, connected to the tip of the melt extruder 20 (see FIG. 2). As shown in FIG. 2, the melt extruder 20 is, for example, a single-screw extruder or a twin-screw extruder, and has a raw material inlet 21 for the molding material 1 at the upper rear. This raw material inlet 21 is connected to an inert gas supply pipe 22 that supplies an inert gas such as helium gas, neon gas, argon gas, krypton gas, or nitrogen gas as needed. The supply of the inert gas from the inert gas supply pipe 22 effectively prevents oxidative degradation, oxygen crosslinking, and thermal crosslinking of the molding material 1.

[0070] The melting temperature during melt-kneading in the melt extrusion molding machine 20 is not particularly limited as long as it is a temperature at which melt-kneading dispersion is possible and decomposition of the polyarylene ether ketone resin 2 does not occur, but it is preferably in the range of not less than the melting point of the polyarylene ether ketone resin 2 but less than the thermal decomposition temperature of the polyarylene ether ketone resin 2.

[0071] Specifically, the temperature range is from the melting point of the polyarylene ether ketone resin +10°C to the melting point of the polyarylene ether ketone resin +100°C, preferably from the melting point of the polyarylene ether ketone resin +20°C to the melting point of the polyarylene ether ketone resin +80°C, more preferably from the melting point of the polyarylene ether ketone resin +30°C to the melting point of the polyarylene ether ketone resin +60°C, and even more preferably from the melting point of the polyarylene ether ketone +30°C to the melting point of the polyarylene ether ketone resin +50°C.

[0072] This is because, if the temperature is lower than the melting point of the polyarylene ether ketone resin 2, it is not possible to melt-knead and disperse the polyarylene ether ketone resin 2 and the carbon nanotubes 4. Conversely, if the temperature is higher than the thermal decomposition temperature, it is undesirable because it will lead to decomposition of the polyarylene ether ketone resin 2.

[0073] The die 23 is connected to the tip of the melt extruder 20 via a connecting pipe 24, and functions to continuously extrude downward a strip-shaped conductive resin film for current collector 5. This die 23 is preferably a T-die, which is capable of obtaining a conductive resin film for current collector 5 with excellent thickness precision. A gear pump 25 is preferably attached to the connecting pipe 24 upstream of the die 23. This gear pump 25 functions to transfer the molding material 1 melt-kneaded by the melt extruder 20 to the downstream die 23 at a constant flow rate and with high precision.

[0074] The temperature during extrusion of the die 23 is in the range of not less than the melting point of the polyarylene ether ketone resin 2 but less than the thermal decomposition temperature of the polyarylene ether ketone resin 2, specifically, not less than the melting point of the polyarylene ether ketone resin 2 +10°C but not more than the melting point of the polyarylene ether ketone resin 2 +100°C, preferably not less than the melting point of the polyarylene ether ketone resin 2 +20°C but not more than the melting point of the polyarylene ether ketone resin 2 +80°C, more preferably not less than the melting point of the polyarylene ether ketone resin 2 +30°C but not more than the melting point of the polyarylene ether ketone resin 2 +60°C, and even more preferably not less than the melting point of the polyarylene ether ketone resin 2 +30°C but not more than the melting point of the polyarylene ether ketone resin 2 +50°C.

[0075] This is because, if the temperature is lower than the melting point of the polyarylene ether ketone resin 2, it is not possible to melt-knead and disperse the polyarylene ether ketone resin 2 and the carbon nanotubes 4. Conversely, if the temperature is higher than the thermal decomposition temperature, it is not preferable because it will lead to decomposition of the polyarylene ether ketone resin 2.

[0076] Below the die 23, a pair of pressure rolls 26 facing each other at a distance are rotatably supported, and between the pair of pressure rolls 26, a plurality of cooling rolls 27 arranged in a row and in sliding contact with each other are rotatably supported, and of the plurality of cooling rolls 27, the upstream cooling roll 27 and the downstream cooling roll 27 each slide against the circumferential surface of the pressure roll 26. Each pressure roll 26 and each cooling roll 27 is configured so that the pressure roll 26 has a reduced diameter and the cooling roll 27 has an expanded diameter.

[0077] Of the pair of pressure rolls 26, a winder 28 is installed downstream of the downstream pressure roll 26, which winds up the conductive resin film 5 for a current collector onto a rotatable winding tube 29. A slit blade 30 is arranged between this winder 28 and the downstream pressure roll 26 so as to be able to move up and down, and a required number of rotatable tension rolls 31 are supported between this slit blade 30 and the winder 28 to apply tension to the conductive resin film 5 for smooth winding.

[0078] Each pressure roller 26 is adjusted to a temperature of 50°C or higher but lower than the melting point of the polyarylene ether ketone resin 2, preferably 100°C or higher (melting point of polyarylene ether ketone resin - 50°C) or lower, more preferably 130°C or higher (melting point of polyarylene ether ketone resin - 100°C) or lower, and even more preferably 150°C or higher (melting point of polyarylene ether ketone resin - 100°C) or lower, and brings the conductive resin film 5 for current collector into sliding contact with the film and presses it against the cooling roller 27.

[0079] The reason why the temperature of the pressure roller 26 is within this range is because, if the temperature is below 50°C, condensation will form on the pressure roller 26. Conversely, if the temperature exceeds the melting point, the conductive resin film 5 for current collector may stick to the peripheral surface of the pressure roller 26 and break, or the strength of the conductive resin film 5 for current collector may decrease, leading to breakage. Methods for adjusting the temperature of the pressure roller 26 include, for example, a method using a heat medium such as air, water, or oil, a method using an electric heater, and a method using induction heating.

[0080] The peripheral surface of each pressure roll 26 is coated as needed with a rubber layer such as at least natural rubber, isoprene rubber, butadiene rubber, norbornene rubber, acrylonitrile butadiene rubber, nitrile rubber, urethane rubber, silicone rubber, or fluororubber, from the viewpoint of improving the adhesion between the conductive resin film 5 for current collector and the cooling roll 27. An inorganic compound such as silica or alumina is selectively added to this rubber layer. Of these, silicone rubber and fluororubber, which have excellent heat resistance, are preferably selected.

[0081] As the pressure roll 26, a metal elastic roll with a metal surface may be used as needed. When this metal elastic roll is used, it is possible to form a conductive resin film 5 for a current collector with an excellent surface smoothness. Specific examples of this metal elastic roll include a metal sleeve roll, an air roll (product name manufactured by Dymco Corporation), and a UF roll (product name manufactured by Hitachi Zosen Corporation). It is also possible to use a pressure roll 26 whose surface is coated with a fluororesin film such as polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) resin or tetrafluoroethylene-hexafluoropyrene copolymer (FEP) resin.

[0082] The multiple cooling rolls 27 are, for example, metal rolls with a larger diameter than the pressure-bonding roll 26, and are rotatably supported below the die 23 to sandwich the extruded conductive resin film 5 for the current collector between themselves and the peripheral surface of the pressure-bonding roll 26, and function to cool the conductive resin film 5 for the current collector together with the pressure-bonding roll 26 while controlling its thickness within a predetermined range.

[0083] For the same reasons as for the pressure roll 26, each cooling roll 27 is adjusted to a temperature of 50°C or higher but lower than the melting point of the polyarylene ether ketone resin 2, preferably 100°C or higher (melting point of polyarylene ether ketone resin - 50°C), more preferably 130°C or higher (melting point of polyarylene ether ketone resin - 100°C), and even more preferably 150°C or higher (melting point of polyarylene ether ketone resin - 100°C), and is brought into sliding contact with the conductive resin film 5 for current collector and pressure-welded to the cooling roll 27. Methods for adjusting the temperature of the cooling roll 27 include, for example, a method using a heat medium such as air, water, or oil, a method using an electric heater, and a method utilizing induction heating.

[0084] After the molding material 1 is extrusion-molded into a strip-shaped conductive resin film 5 for a current collector, this conductive resin film 5 for a current collector is wound around a pair of pressure-bonding rolls 26, a cooling roll 27, a tension roll 31, and a take-up tube 29 of a winder 28, and both side portions of the conductive resin film 5 for a current collector are cut in the longitudinal direction with a slit blade 30, and the film is sequentially wound around the take-up tube 29 of the winder 28, thereby producing a long conductive resin film 5 for a current collector.

[0085] The thickness of the conductive resin film 5 for a current collector produced by cooling with the cooling roll 27 is preferably 5 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 200 μm or less, and even more preferably 20 μm or more and 100 μm or less. This is because if the thickness of the conductive resin film 5 for a current collector is less than 5 μm, the tensile strength of the conductive resin film 5 for a current collector will be significantly reduced, making it difficult to produce the conductive resin film 5 for a current collector.

[0086] Conversely, if the thickness of the conductive resin film 5 for current collector exceeds 500 μm, it will hinder weight reduction when used as a current collector for a secondary battery such as a lithium ion secondary battery, a bipolar lithium ion secondary battery, or an all-solid-state battery. The thickness of this conductive resin film 5 for current collector can be measured using various contact thickness gauges. Alternatively, the thickness can be measured by averaging multiple measured values.

[0087] The specific gravity of the conductive resin film 5 for a current collector is 1.60 or less, preferably 1.23 to 1.60, more preferably 1.26 to 1.55, even more preferably 1.28 to 1.50, and even more preferably 1.30 to 1.45. This is because if the specific gravity of the conductive resin film 5 for a current collector is 1.60 or less, particularly less than 1.23, there is a risk of voids or cracks occurring in the conductive resin film 5 for a current collector, which causes a problem of reduced mechanical strength, and is therefore undesirable.

[0088] On the other hand, if the specific gravity of the conductive resin film 5 for current collector exceeds 1.60, it will hinder weight reduction when used as a current collector for a secondary battery such as a lithium ion secondary battery, a bipolar lithium ion secondary battery, or an all-solid-state battery. The specific gravity of the conductive resin film 5 for current collector can be measured using a specific gravity measuring device or the like in accordance with JIS K 7112 Method A, for example.

[0089] The relative crystallinity of the conductive resin film 5 for a current collector is optimally 80% or more, preferably 90% or more, more preferably 95% or more, and even more preferably 100%. This is because if the relative crystallinity of the conductive resin film 5 for a current collector is less than 80%, problems arise in the mechanical strength, heat resistance, chemical resistance, and solvent resistance of the conductive resin film 5 for a current collector. In contrast, if the relative crystallinity is more than 80%, the conductive resin film 5 for a current collector can be expected to have sufficient mechanical strength, heat resistance, and chemical resistance to be usable as a conductive resin film 5 for a current collector.

[0090] The crystallinity of the conductive resin film 5 for a current collector can be expressed as a relative crystallinity, which is calculated by the following formula based on the results of thermal analysis measured at a heating rate of 10°C / min using a differential scanning calorimeter. Relative crystallinity (%) = {1-(ΔHc / ΔHm)} × 100 ΔHc: Heat quantity at the recrystallization peak of the conductive resin film for the current collector (J / g) ΔHm: Heat of melting peak of conductive resin film for current collector (J / g)

[0091] The mechanical properties of the conductive resin film 5 for current collector can be expressed by the tensile modulus, tensile elongation at break, and maximum tensile strength. The tensile modulus of the conductive resin film 5 for current collector, as measured in accordance with JIS K 7127, is preferably 2000 MPa or more, preferably 3000 MPa or more, more preferably 3500 MPa or more, and even more preferably 4000 MPa or more. There are no particular restrictions on the upper limit of this tensile modulus, but it is preferably 10000 MPa or less.

[0092] This is because if the tensile modulus is less than 2000 MPa, when the conductive resin film 5 for current collectors is used as a current collector of a secondary battery, the conductive resin film 5 for current collectors will have poor rigidity, and may be deformed during the coating process of the positive electrode active material or the negative electrode active material, or during assembly of the secondary battery. On the other hand, if the tensile modulus exceeds 10000 MPa, the conductive resin film 5 for current collectors will have too great rigidity and will not be able to be wound up.

[0093] The tensile elongation at break of the conductive resin film 5 for current collector, as measured in accordance with JIS K 7127, is preferably 10% or more, preferably 15% or more, more preferably 20% or more, and even more preferably 25% or more. This is because if the tensile elongation at break of the conductive resin film 5 for current collector is less than 10%, the conductive resin film 5 for current collector has poor toughness and may crack during its manufacture. This is also because the conductive resin film 5 for current collector may crack during the process of applying a positive electrode active material or a negative electrode active material to the conductive resin film 5 for current collector. The upper limit of the tensile elongation at break is not particularly limited, but is preferably 500% or less. This is because if the tensile elongation at break exceeds 500%, the conductive resin film 5 for current collector may stretch during the process of applying a positive electrode active material or a negative electrode active material to the conductive resin film 5 for current collector.

[0094] The maximum tensile strength of the conductive resin film 5 for a current collector, as measured in accordance with JIS K 7127, is preferably 60 MPa or more, preferably 70 MPa or more, more preferably 90 MPa or more, and even more preferably 100 MPa or more. This is because if the maximum tensile strength of the conductive resin film 5 for a current collector is less than 60 MPa, the conductive resin film 5 for a current collector will have poor toughness and will crack during production of the conductive resin film 5 for a current collector. Another reason is that the conductive resin film 5 for a current collector will crack during the step of coating the conductive resin film 5 with a positive electrode active material or a negative electrode active material.

[0095] Although there are no particular restrictions on the upper limit of the maximum tensile strength, it is preferably 500 MPa or less. This is because if the strength exceeds 500 MPa, the cutting ability with the slit blade 30 decreases during the production of the conductive resin film 5 for a current collector, which undesirably reduces the production speed of the long conductive resin film 5 for a current collector.

[0096] The conductivity of the conductive resin film 5 for current collectors can be evaluated by its volume resistivity. When measured using a four-point, four-probe method in accordance with JIS K 7194, the optimal volume resistivity is 1 Ω·cm to 100 Ω·cm, preferably 10 Ω·cm to 75 Ω·cm, more preferably 20 Ω·cm to 50 Ω·cm, and even more preferably 20 Ω·cm to 25 Ω·cm. This is because if the volume resistivity of the conductive resin film 5 for current collectors exceeds 100 mΩ·cm, the energy density will decrease when used as a current collector for a secondary battery. Conversely, if the volume resistivity is less than 1 Ω·cm, a large amount of carbon nanotubes 4 must be added, making the resulting conductive resin film 5 for current collectors brittle and potentially causing cracking during secondary battery assembly.

[0097] The chemical resistance of the conductive resin film 5 for a current collector can be evaluated by immersing the conductive resin film 5 for a current collector in N-methyl-2-pyrrolidone and an electrolyte and measuring the mass change. From the viewpoint of improving chemical resistance and solvent resistance, the mass change rate when the conductive resin film 5 for a current collector is immersed in N-methyl-2-pyrrolidone and an electrolyte is optimally 2.0% or less, preferably 0.0% to 2.0%, more preferably 0.0% to 1.0%, and even more preferably 0.0% to 0.1%.

[0098] The electrolyte is an organic electrolytic solution containing a lithium salt dissolved in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), linear carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), cyclic ethers such as tetrahydrofuran (THF) and 1,3-dioxolane (DOXL), linear ethers such as 1,2-dimethoxyethane (DEM) and 1,2-diethoxyethane (DEE), cyclic esters such as gamma-butyrolactone (GBL), and linear esters such as methyl acetate (MA).

[0099] Examples of lithium salts include lithium perchlorate (LiClO4), lithium borofluoride (LiBF4), lithium hexafluorophosphate (LiPF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), and lithium tris(trifluoromethanesulfonyl)methide (LiC(CF3SO2)3).

[0100] If N-methyl-2-pyrrolidone or the electrolyte remains in the conductive resin film for current collector 5, the N-methyl-2-pyrrolidone or the electrolyte may seep into the secondary battery during operation, causing problems, so care must be taken. Also, care must be taken because the electrolyte of the secondary battery may seep into the current collector, reducing the charge / discharge cycle.

[0101] The molded conductive resin film 5 for a current collector may be used as is, or may be further subjected to heat compression molding. Heat compression molding of the conductive resin film 5 for a current collector can lower the resistance value and increase the conductivity, and can reduce the amount of carbon-based conductive material 3 used, thereby reducing costs.

[0102] When the conductive resin film 5 for a current collector is subjected to heat compression molding, the conductive resin film 5 for a current collector is sandwiched between a plurality of metal plates, metal rolls, or metal belts that have been heated to a temperature not lower than the melting point of the polyarylene ether ketone resin 2 but lower than the thermal decomposition temperature of the polyarylene ether ketone resin 2, specifically, a temperature not lower than the melting point of the polyarylene ether ketone resin +10°C and not higher than the thermal decomposition temperature of the polyarylene ether ketone resin 2, preferably not lower than the melting point of the polyarylene ether ketone resin +20°C and not higher than the melting point of the polyarylene ether ketone resin +80°C, more preferably not lower than the melting point of the polyarylene ether ketone resin +30°C and not higher than the melting point of the polyarylene ether ketone resin +60°C, and even more preferably not lower than the melting point of the polyarylene ether ketone resin +30°C and not higher than the melting point of the polyarylene ether ketone resin +50°C, and a pressure of 0.5 kgf / cm against the projected area of the conductive resin film 5 for a current collector is applied. 2 More than 100kgf / cm 2 The pressure is applied to the polyarylene ether ketone resin 2, and the pressure is maintained for 0.5 seconds to 300 seconds, and the polyarylene ether ketone resin 2 is immediately cooled to a temperature below the glass transition point.

[0103] According to the above, the polyarylene ether ketone resin 2, which is lightweight, excellent in mechanical properties, chemical resistance, and heat resistance, and has low water absorption, is selected as the thermoplastic resin of the molding material 1 to produce the conductive resin film 5 for a current collector, so that even when the conductive resin film 5 for a current collector is used as a current collector, electrolyte components do not penetrate into the conductive resin film 5 for a current collector, effectively eliminating the risk of a decrease in charge-discharge cycle characteristics. Furthermore, because the polyarylene ether ketone resin 2 is used instead of a fluororesin, no special steel material or equipment is required for molding, and significant cost reductions in the current collector can be expected.

[0104] Furthermore, since there is no need to use two different types of resin, the risk of peeling of the current collector can be effectively eliminated. In addition, there is no risk of curling due to differences in expansion coefficients caused by water absorption after production, or peeling of the current collector between the first and second conductive layers. Furthermore, when the carbon-based conductive material 3 is carbon nanotubes 4, not only is it chemically stable, but it can also further reduce the weight of secondary batteries. Furthermore, since the thickness of the conductive resin film 5 for current collector is 5 μm or more and 500 μm or less, a decrease in the tensile strength of the conductive resin film 5 for current collector is prevented, and significant weight reduction of the current collector for secondary batteries can be expected.

[0105] In addition, since the specific gravity of the current collector conductive resin film 5 is 1.60 or less, it can contribute to significantly reducing the weight of secondary batteries and current collectors. Furthermore, since the volume resistivity of the current collector conductive resin film 5 is low, at 1 Ω·cm or more and 100 Ω·cm or less, a decrease in energy density can be prevented even when the current collector conductive resin film 5 is used as a current collector for secondary batteries.

[0106] The polyarylene ether ketone resin 2 in the above embodiment may be used alone, or two or more may be alloyed or blended. The polyarylene ether ketone resin 2 may be in any form, including powder, granules, lumps, powder, and pellets. The conductive resin film 5 for a current collector may have a specific gravity of 1.23 to 1.60 as measured in accordance with JIS K7112 Method A, a relative crystallinity of 95% to 100%, a tensile modulus of 3500 MPa to 5300 MPa as measured in accordance with JIS K7127, a tensile elongation at break of 10% to 65%, and a volume resistivity of 1 Ω·cm to 100 Ω·cm as measured in accordance with JIS K7194.

[0107] Furthermore, in order to utilize the properties of the carbon nanotubes 4, a mixture of multiple types of carbon nanotubes 4 having different outer diameters and lengths may be used. Furthermore, a single cooling roll 27 may be rotatably supported between a pair of pressure bonding rolls 26. [Example]

[0108] EXAMPLES Hereinafter, examples of a conductive resin film for a current collector of a secondary battery according to the present invention and a method for producing the same will be described together with comparative examples. Example 1 First, to prepare the molding material, a commercially available polyether ether ketone resin (manufactured by Solvay Specialty Polymers, product name: KetaSpire PEEK KT-851NL SP, hereinafter abbreviated as "KT-851NL SP") was prepared as the polyarylene ether ketone resin and pulverized by freeze-grinding. Hereinafter, the polyether ether ketone resin will be abbreviated as "PEEK resin."

[0109] The melting point (also called melting temperature) of PEEK resin was measured using a differential scanning calorimeter (SII NanoTechnology, product name: High Sensitivity Differential Scanning Calorimeter X-DSC7000) at a heating rate of 10°C / min in accordance with JIS K 7121. The melting point of KT-851NLSP was measured to be 340°C.

[0110] After crushing the PEEK resin, the crushed PEEK resin and multi-walled carbon nanotubes, a carbon-based conductive material, were weighed out so that the composition mass ratio was 95% PEEK resin and 5% carbon nanotubes, and then the PEEK resin and carbon nanotubes were placed in a mixer and stirred to prepare a stirred mixture. The carbon nanotubes used were NC7000 (product name, manufactured by Nanosil Co., Ltd., hereinafter abbreviated as "NC7000").

[0111] The apparent shear viscosity of the PEEK resin was measured using a flow tester (Shimadzu Corporation, product name: Shimadzu Flow Tester CFT-500D). Specifically, the PEEK resin was dried in advance in a hot air dryer at 160°C for 12 hours, and 1.5 cm of the PEEK resin was 3 The mixture was packed into a cylinder at 375°C equipped with a die (diameter: 1 mm, length: 10 mm), and a 1.0 cm2 area was placed on the top of the cylinder. 2 A plunger was attached, and when the temperature of the cylinder reached 375°C, it was preheated for 5 minutes, and immediately after this preheating, a load of 50 kgf was applied to melt and flow out the PEEK resin, and its apparent shear viscosity was measured. The apparent shear viscosity was measured in the same manner as below.

[0112] Once the stirred mixture was prepared, it was fed into a high-speed twin-screw extruder equipped with a vacuum pump and melt-kneaded under reduced pressure. The melt-kneaded mixture was extruded into a rod shape from the die at the tip of the high-speed twin-screw extruder, air-cooled, and cut to prepare pellet-shaped molding material. The high-speed twin-screw extruder used was a φ42 mm, L / D=38 type. The stirred mixture was melt-kneaded under conditions of a cylinder temperature of 350-375°C and a die temperature of 375°C, with the vent on the raw material inlet side of the high-speed twin-screw extruder open and the vent on the die side degassed under reduced pressure to prepare the molding material. The temperature during melt-kneading was measured by measuring the temperature of the molten molding material immediately after extrusion from the die, and was measured to be 376°C.

[0113] After preparing the molding material, the apparent shear viscosity of this molding material was measured. The apparent shear viscosity of this molding material was measured using a flow tester (Shimadzu Corporation, product name: Shimadzu Flow Tester CFT-500D). Specifically, the molding material was dried in a hot air dryer at 160°C for 12 hours, and then 1.5 cm of the molding material was dried. 3 The mixture was packed into a cylinder at 375°C equipped with a die (diameter: 1 mm, length: 10 mm), and a 1.0 cm2 area was placed on the top of the cylinder. 2The plunger was attached, and when the temperature of the cylinder reached 375°C, it was preheated for 5 minutes, and immediately after this preheating, a load of 50 kgf was applied to melt and flow out the molding material, and its apparent shear viscosity was measured. The apparent shear viscosity was measured in the same manner as below.

[0114] The prepared molding material was then placed in a dehumidifying hot air dryer heated to 160°C and dried for at least 12 hours. After confirming that the moisture content of the dried molding material was 300 ppm or less, the molding material was placed in a φ40 mm single-screw extruder and continuously extruded through a 900 mm wide T-die to form a strip-shaped conductive resin film for a current collector. The moisture content of the molding material was confirmed by Karl Fischer titration using a trace moisture analyzer (Mitsubishi Chemical Corporation, product name: CA-100). The moisture content of the molding material was subsequently measured in the same manner.

[0115] The single-screw extruder had an L / D ratio of 25, a compression ratio of 2.5, and a full-flight screw. The temperature of the single-screw extruder was adjusted to 360-395°C, the temperature of the T-die to 395°C, the temperature of the connecting pipe connecting the single-screw extruder to the T-die to 395°C, and the gear pump to 395°C. The temperature of the molten molding material was measured from the resin temperature at the inlet of the T-die and found to be 398°C. When the molding material was introduced into this single-screw extruder, nitrogen gas was supplied at a rate of 15 L / min.

[0116] After the conductive resin film for current collector was formed, it was sequentially wound around a pair of 210°C pressure rolls made of silicone rubber, multiple 210°C cooling rolls, and a 6-inch take-up tube located downstream of these, as shown in Figure 2, and sandwiched between the pressure rolls and cooling rolls, and both sides of the continuous conductive resin film for current collector were cut with a slit blade and sequentially taken up onto the take-up tube, thereby producing a conductive resin film for current collector with a length of 100 m and a width of 650 mm. A slit blade that cuts both sides of the conductive resin film for current collector was positioned between the pressure rolls and the take-up tube so that it could be raised and lowered, and a tension roll that applies tension to the conductive resin film for current collector was rotatably supported between the take-up tube and the slit blade.

[0117] Once the conductive resin film for current collectors was manufactured, the presence or absence of die buildup during manufacturing of the conductive resin film for current collectors, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of the conductive resin film for current collectors were evaluated, and the results are summarized in Table 1. The mechanical properties of the conductive resin film for current collectors were evaluated by the tensile modulus, tensile elongation at break, and maximum tensile strength, the electrical conductivity was evaluated by the volume resistivity of the conductive film before and after immersion in electrolyte, the chemical resistance was evaluated by the change in mass before and after immersion in N-methyl-2-pyrrolidone and electrolyte, and the heat resistance was evaluated by the dimensional change upon heating.

[0118] -Film used in the current collector is made of conductive resin. Regarding the occurrence of die resin during the production of conductive resin film for current collector, after producing 100 m of conductive resin film for current collector, the vicinity of the lip of the T-die was visually observed.

[0119] Thickness of conductive resin film for current collector The thickness of the conductive resin film for the current collector was measured using a micrometer (Mitutoyo Corporation, product name: Coolant-proof micrometer, model number MDC-25PJ). Measurements were taken at 10 random locations in the width direction (the direction perpendicular to the extrusion direction (hereinafter abbreviated as "TD")) of the conductive resin film for the current collector, and the average value was taken as the film thickness.

[0120] Specific gravity of conductive resin film for current collector The specific gravity of the conductive resin film for current collector was measured in an environment of 23°C in accordance with the standard of JIS K 7112 Method A.

[0121] Relative crystallinity of conductive resin film for current collector The relative crystallinity of the conductive resin film for current collectors was measured by weighing out approximately 5 mg of a measurement sample from the conductive resin film for current collectors and using a differential scanning calorimeter (manufactured by SII Nanotechnologies, Inc., product name: EXSTAR7000 series X-DSC7000) at a heating rate of 10°C / min over a measurement temperature range of 20°C to 380°C. The heat quantity (J / g) of the melting peak and the heat quantity (J / g) of the recrystallization peak obtained at this time were used to calculate the crystallinity using the following formula.

[0122] Relative crystallinity (%) = {1-(ΔHc / ΔHm)} × 100 ΔHc: Heat quantity at the recrystallization peak of the conductive resin film for the current collector (J / g) ΔHm: Heat of melting peak of conductive resin film for current collector (J / g)

[0123] ·Mechanical properties of conductive resin film for current collectors The mechanical properties of the conductive resin film for current collector were evaluated in terms of tensile modulus, elongation at break, and maximum tensile strength at 23°C. The mechanical properties were measured in the extrusion direction (hereinafter abbreviated as "MD") and TD. The measurements were performed in accordance with JIS K 7127 under conditions of a pulling speed of 50 mm / min, a temperature of 23°C ± 2°C, and a relative humidity of 50 RH ± 5% RH.

[0124] Chemical resistance of conductive resin film for current collectors The chemical resistance of the conductive resin film for current collector was evaluated by immersing it in N-methyl-2-pyrrolidone (hereinafter abbreviated as "NMP") and an electrolyte solution and measuring the change in mass.

[0125] To evaluate the mass change of the conductive resin film for the current collector, the conductive resin film for the current collector was cut into a size of 50 mm MD x 80 mm TD and weighed [W0]. This conductive resin film for the current collector and 5 g of NMP or 5 g of electrolyte were placed in a PET / AL / PE flat bag (manufactured by Nippon Seisaku Co., Ltd.: product name Lamizip) and heat-sealed. The electrolyte used was an electrolyte for lithium primary / secondary / polymer batteries and lithium ion capacitors (manufactured by Kishida Chemical Co., Ltd.: product name LiPF6, molarity 1 mol / L, solvent EC:DEC (3:7) V / V%).

[0126] After sealing with heat sealing, the PET / AL / PE flat bag was left to stand in a hot air oven heated to 50°C for 15 days. After leaving it to stand, the conductive resin film for the current collector was removed from the PET / AL / PE flat bag and washed with ethanol. This conductive resin film for the current collector was left to stand in a hot air oven heated to 50°C for 24 hours, and after leaving it to stand, it was left to stand in a glass desiccator containing a desiccant (manufactured by Ozone Chemical Co., Ltd.: product name OZO-C) in an environment of 23°C for 24 hours. Thereafter, the conductive resin film for the current collector was weighed [W1], and the mass change rate was calculated using the following formula and evaluated as A to F.

[0127] Mass change rate (%) = {(W1-W0) / W0} x 100 W0: Initial mass of conductive resin film for current collector [g] W1: Mass of the conductive resin film for the current collector after immersion in NMP or electrolyte [g] A: When the mass change rate is between 0.0% and 0.1% B: Mass change rate is over 0.1% and 1.0% or less C: Mass change rate is over 1.0% and 2.0% or less D: Mass change rate is over 2.0% and 5.0% or less E: Mass change rate is over 5.0% and 10% or less F: Mass change rate is over 10% and 20% or less

[0128] Conductivity of conductive resin film for current collector The conductivity of the conductive resin film for current collector was evaluated by the volume resistivity, which was measured before and after immersion in NMP and the electrolyte.

[0129] The volume resistivity was measured by the four-terminal four-probe method (a method conforming to JIS K 7194:1994). The measurement was carried out using a low resistivity meter (manufactured by Mitsubishi Chemical Analytech Co., Ltd.: trade name Loresta GP MCP-610). The volume resistivity of the conductive resin film for current collector was also measured before and after the chemical resistance evaluation. The measurement was carried out in an environment of a temperature of 23°C ± 2°C and a relative humidity of 50 RH ± 5% RH.

[0130] -Heat resistance of conductive resin film for current collectors The heat resistance of the conductive resin film for current collector was evaluated by the change in dimension due to heating. The dimensional change due to heating was measured in both MD and TD. This measurement was in accordance with JIS K 7133, where the sample was heated at 250°C for 10 minutes, and the dimensional change rate was evaluated based on the change rate before and after heating. The dimensional change rate was calculated using the following formula: Dimensional change rate (%) = {(L1-L0) / L0} x 100 L0: Dimensions of the conductive resin film for the current collector before heating [mm] L1: Dimensions of conductive resin film for current collector and after heating [mm]

[0131] Example 2 The composition mass ratio of the pulverized polyarylene ether ketone resin of Example 1 to the carbon nanotubes was changed as shown in Table 1, and pellet-shaped molding materials were prepared in the same manner as in Example 1. After the molding materials were prepared, the apparent shear viscosity of the molding materials was measured in the same manner as in Example 1.

[0132] Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape in the same manner as in Example 1. The temperature of the molten molding material was measured from the resin temperature at the entrance of a T-die and was found to be 398°C. After molding the conductive resin film for a current collector in this manner, a conductive resin film for a current collector was produced in the same manner as in Example 1. The generation of die boogers during the production of this conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and the results are summarized in Table 1.

[0133] Example 3 The process was basically the same as in Example 1, except that the molding material, PEEK resin, a polyarylene ether ketone resin, used in Example 1 was changed from KT-851NL SP to Victrex Granules 381G (Victrex; product name, hereinafter abbreviated as "381GG"), which had been previously pulverized using the method of Example 1. The carbon nanotubes used in Example 1 were weighed to obtain the composition and mass shown in Table 1, and a stirred mixture was prepared. The apparent shear viscosity of 381G was measured using the same method as in Example 1. The melting point of 381G was measured using the same method as in Example 1, and was found to be 343°C.

[0134] Next, a molding material was prepared in the same manner as in Example 1. The temperature during melt-kneading was measured by measuring the temperature of the molten molding material immediately after extrusion from the die, and was found to be 375° C. After the molding material was prepared, the apparent shear viscosity of this molding material was measured in the same manner as in Example 1.

[0135] Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape in the same manner as in Example 1. The temperature of the molten molding material was measured from the resin temperature at the entrance of a T-die and was found to be 398°C. After molding the conductive resin film for a current collector in this manner, another conductive resin film for a current collector was produced in the same manner as in Example 1, and the generation of die boogers during the production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and the results are summarized in Table 1.

[0136] Example 4 The procedure was basically the same as in Example 1, except that the PEEK resin, which is a polyarylene ether ketone resin, was changed from KT-851NL SP to Victrex Granules 450G (Victrex Corporation; product name, hereinafter abbreviated as "450G"), which had been previously pulverized by the method of Example 1.

[0137] The carbon nanotubes used in Example 1 were changed from NC7000 to FloTube 9000 (manufactured by CNano Technology). The PEEK resin and carbon nanotubes were weighed to have the composition mass ratio shown in Table 2, and a stirred mixture was prepared. The apparent shear viscosity of 450G was measured in the same manner as in Example 1. The melting point of 450G was measured in the same manner as in Example 1 and was found to be 341°C.

[0138] Next, a molding material was prepared in the same manner as in Example 1. The temperature during melt-kneading was measured by measuring the temperature of the molten molding material immediately after extrusion from the die, and the measurement was 380° C. After the molding material was prepared, the apparent shear viscosity of this molding material was measured in the same manner as in Example 1.

[0139] Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape in the same manner as in Example 1. The temperature of the molten molding material was measured from the resin temperature at the entrance of a T-die and was found to be 400°C. After molding, a conductive resin film for a current collector was produced in the same manner as in Example 1, and the generation of die boogers during the production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and are shown in Table 2.

[0140] Example 5 The procedure was basically the same as in Example 1, except that the molding material, PEEK resin, a polyarylene ether ketone resin, used in Example 1 was changed from KT-851NL SP to Victrex Granules 151G (Victrex Corporation; product name, hereinafter abbreviated as "151G"), which had been previously pulverized using the method of Example 1. The components were weighed out to obtain the composition and mass shown in Table 2, and a stirred mixture was prepared. The apparent shear viscosity of 151G was measured using the same method as in Example 1. The melting point of 151G was measured using the same method as in Example 1, and was found to be 341°C.

[0141] Next, a molding material was prepared in the same manner as in Example 1. The temperature during melt-kneading was measured by measuring the temperature of the molten molding material immediately after extrusion from the die, and was found to be 375° C. After the molding material was prepared, the apparent shear viscosity of this molding material was measured in the same manner as in Example 1.

[0142] Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape in the same manner as in Example 1. The temperature of the molten molding material was measured from the resin temperature at the entrance of a T-die and was found to be 395°C. After molding, a conductive resin film for a current collector was produced in the same manner as in Example 1, and the generation of die boogers during the production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and are shown in Table 2.

[0143] Example 6 First, to prepare the molding material, a commercially available polyarylene ether ketone resin (manufactured by Arkema, product name: KEPSTAN 8003PF ST, hereinafter abbreviated as "8003") was prepared. This polyether ketone ketone resin and the carbon nanotubes used in Example 1 were weighed out to achieve the composition mass ratio shown in Table 2. The polyether ketone ketone resin and carbon nanotubes were then placed in a mixer and stirred to prepare a stirred mixture. The melting point of the polyether ketone ketone resin was measured using the same method as in Example 1 and was found to be 361°C. Hereinafter, the polyether ketone ketone resin will be referred to as "PEKK resin."

[0144] The apparent shear viscosity of 8003 was measured using a flow tester (Shimadzu Corporation, product name: Shimadzu Flow Tester CFT-500D). Specifically, 8003 was dried in a hot air dryer at 160°C for 12 hours, and then dried at 1.5cm 3 The 8003 was filled into a cylinder at 375°C attached to a die (diameter: 1 mm, length: 10 mm), and a 1.0 cm2 cylinder was placed on top of the cylinder. 2 A plunger was attached, and when the temperature of the cylinder reached 375°C, it was preheated for 5 minutes, and immediately after this preheating, a load of 50 kgf was applied, causing the PEKK resin to melt and flow out, and its apparent shear viscosity was measured.

[0145] Next, a molding material was prepared in the same manner as in Example 1. The temperature during melt-kneading was measured by measuring the temperature of the molten molding material immediately after extrusion from the die, and was found to be 375° C. After the molding material was prepared, the apparent shear viscosity of this molding material was measured in the same manner as in Example 1.

[0146] Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape in the same manner as in Example 1. The temperature of the molten molding material was measured from the resin temperature at the entrance of a T-die and was found to be 395°C. After molding, a conductive resin film for a current collector was produced in the same manner as in Example 1, and the generation of die boogers during the production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and are shown in Table 2.

[0147] [Table 1]

[0148] [Table 2]

[0149] Comparative Example 1 First, the polyarylene ether ketone resin and carbon nanotubes used in Example 1 were weighed out in a composition mass ratio outside the range of the present invention shown in Table 3 and charged into a stirring mixer to prepare a stirred mixture, and this stirred mixture was prepared into a pellet-shaped molding material in the same manner as in Example 1. The temperature during melt kneading was measured by measuring the temperature of the molten molding material immediately after extrusion from the die, and was measured to be 376°C. After preparing the molding material, the apparent shear viscosity of this molding material was measured by the same method as in Example 1.

[0150] Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape in the same manner as in Example 1. The temperature of the molten molding material was measured from the resin temperature at the entrance of a T-die and was found to be 398°C. After molding the conductive resin film for a current collector in this manner, another conductive resin film for a current collector was produced in the same manner as in Example 1, and the generation of die boogers during the production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of the conductive resin film for a current collector were evaluated and the results are summarized in Table 3.

[0151] Comparative Example 2 First, the polyarylene ether ketone resin and carbon nanotubes used in Example 1 were weighed out in a composition mass ratio outside the range of the present invention shown in Table 3 and charged into a stirring mixer to prepare a stirred mixture, and this stirred mixture was prepared into a pellet-shaped molding material in the same manner as in Example 1. After preparing the molding material, the apparent shear viscosity of this molding material was measured by the same method as in Example 1. The temperature during melt-kneading was measured by measuring the temperature of the molding material in a molten state immediately after extrusion from the die, and the measured value was 389°C.

[0152] Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape in the same manner as in Example 1. The temperature of the molten molding material was measured from the resin temperature at the entrance of a T-die and was found to be 403°C. After molding the conductive resin film for a current collector in this manner, another conductive resin film for a current collector was produced in the same manner as in Example 1, and the generation of die boogers during the production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and the results are summarized in Table 3.

[0153] Comparative Example 3 First, a conductive resin film for a current collector was molded using the molding material composed of the polyarylene ether ketone resin and carbon nanotubes used in Example 3. The molding of the conductive resin film for a current collector was carried out in the same manner as in Example 1. However, while the temperatures of the pressure roll and the chill roll were 220°C and 210°C, respectively, in Example 1, the temperatures of the pressure roll and the chill roll were 100°C and 100°C, respectively, in Comparative Example 3, the conductive resin film for a current collector was molded into a strip shape at 100°C and 100°C, respectively. The temperature of the molten molding material was measured from the resin temperature at the entrance of the T-die and was found to be 398°C.

[0154] After forming the conductive resin film for a current collector in this manner, another conductive resin film for a current collector was produced in the same manner as in Example 1, and the generation of die buildup during the production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of the conductive resin film for a current collector were evaluated and the results are summarized in Table 3.

[0155] Comparative Example 4 First, to prepare the molding material, Genestar N1000A-M42NA (product name, manufactured by Kuraray Co., Ltd., hereinafter abbreviated as "N1000A") was selected as the polyamide 9T resin and pulverized by freeze-pulverization. Hereinafter, polyamide 9T resin will be abbreviated as PA9T resin.

[0156] The melting point (also called melting temperature) of N1000A resin was measured using a differential scanning calorimeter (SII NanoTechnology, product name: High Sensitivity Differential Scanning Calorimeter X-DSC7000) in accordance with JIS K7121 at a heating rate of 10°C / min. The melting point of N1000A was measured to be 300°C.

[0157] The apparent shear viscosity of N1000A was measured using a flow tester (Shimadzu Corporation, product name: Shimadzu Flow Tester CFT-500D). Specifically, PA9T resin was dried in a hot air dryer at 160°C for 12 hours, and then 1.5 cm of PA9T resin was dried. 3 The mixture was packed into a 360°C cylinder attached to a die (diameter: 1 mm, length: 10 mm), and a 1.0 cm2 cylinder was placed on top of the cylinder. 2 A plunger was attached, and when the cylinder temperature reached 360°C, it was preheated for 5 minutes. Immediately after this preheating, a load of 50 kgf was applied, causing the PA9T resin to melt and flow out, and its apparent shear viscosity was measured. After pulverizing the PA9T resin, this PA9T resin and FloTube 9000, the carbon nanotubes used in Example 4, were stirred and mixed in the composition mass ratio shown in Table 4 to prepare a stirred mixture.

[0158] Once the stirred mixture was prepared, it was fed into a high-speed twin-screw extruder equipped with a vacuum pump and melt-kneaded under reduced pressure. It was then extruded into a rod shape from the die at the tip of the high-speed twin-screw extruder, air-cooled, and cut to prepare pellet-shaped molding material. The stirred mixture was melt-kneaded under conditions of a cylinder temperature of 330-360°C, an adapter temperature of 360°C, and a die temperature of 360°C. The temperature during melt-kneading was measured by measuring the temperature of the molten molding material immediately after extrusion from the die, and was found to be 361°C.

[0159] After preparing the molding material, the apparent shear viscosity of this molding material was measured in the same manner as in Example 1. The apparent shear viscosity of this molding material was measured using a flow tester (Shimadzu Flow Tester CFT-500D, manufactured by Shimadzu Corporation). Specifically, the molding material was dried in advance in a hot air dryer at 160°C for 12 hours, and then 1.5 cm of the molding material was dried. 3 The mixture was packed into a 360°C cylinder attached to a die (diameter: 1 mm, length: 10 mm), and a 1.0 cm2 cylinder was placed on top of the cylinder. 2 A plunger was attached, and when the temperature of the cylinder reached 360°C, it was preheated for 5 minutes, and immediately after this preheating, a load of 50 kgf was applied to melt and flow out N1000A, and its apparent shear viscosity was measured.

[0160] The prepared molding material was then placed in a dehumidifying hot air dryer heated to 160°C and dried for at least 12 hours. After confirming that the moisture content of the dried molding material was 300 ppm or less, the molding material was placed in a φ40 mm single-screw extruder and continuously extruded through a 900 mm wide T-die to form a strip-shaped conductive resin film for the current collector. The single-screw extruder had an L / D of 25, a compression ratio of 2.5, and a full-flight screw.

[0161] The temperature of the single-screw extruder was adjusted to 340-360°C, the temperature of the T-die to 360°C, the temperature of the connecting pipe connecting the single-screw extruder to the T-die to 360°C, and the gear pump to 395°C. The temperature of the molten molding material was measured from the resin temperature at the inlet of the T-die and was found to be 360°C. When the molding material was introduced into this single-screw extruder, nitrogen gas was supplied at a rate of 15 L / min.

[0162] After the conductive resin film for current collectors was manufactured, the presence or absence of die buildup during manufacturing of the conductive resin film for current collectors, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of the conductive resin film for current collectors were evaluated, and the results are shown in Table 4. However, when measuring the volume resistance, which is a mechanical property of the conductive resin film for current collectors, the conductive resin film for current collectors was immersed in NMP and an electrolyte, and it deformed, making it impossible to measure the volume resistance.

[0163] Comparative Example 5 First, to prepare the molding material, a polyetherimide resin (a polycondensate of 4,4'-isopropylidenebis(p-phenyloxy)diphthalic dianhydride and m-phenylenediamine, manufactured by SABIC, product name: ULTEM 1010-1000-NB (SABIC product name, hereinafter abbreviated as "1010")) was selected and pulverized by freeze-pulverization. Hereinafter, polyetherimide resin will be abbreviated as PEI resin.

[0164] The melting point (also called melting temperature) of 1010 was measured using a differential scanning calorimeter (SII NanoTechnology, product name: High Sensitivity Differential Scanning Calorimeter X-DSC7000) in accordance with JIS K7121 at a heating rate of 10°C / min. However, no melting point was observed.

[0165] The apparent shear viscosity of 1010 was measured using a flow tester (Shimadzu Corporation, product name: Shimadzu Flow Tester CFT-500D). Specifically, the PEI resin was dried in a hot air dryer at 160°C for 12 hours, and then the apparent shear viscosity of 1010, 1.5 cm 3The mixture was packed into a cylinder at 375°C attached to a die (diameter: 1 mm, length: 10 mm), and a 1.0 cm2 cylinder was placed on top of the cylinder. 2 A plunger was attached, and when the temperature of the cylinder reached 375°C, it was preheated for 5 minutes, and immediately after this preheating, a load of 50 kgf was applied, causing 1010 to melt and flow out, and its apparent shear viscosity was measured.

[0166] After crushing the PEI resin, this PEI resin and NC7000, the carbon nanotubes used in Example 4, were stirred and mixed in the composition mass ratio shown in Table 4 to prepare a stirred mixture. After preparing the stirred mixture, this stirred mixture was fed into a high-speed twin-screw extruder equipped with a vacuum pump, melt-kneaded under reduced pressure, and extruded into a rod shape from the die at the tip of the high-speed twin-screw extruder. After air cooling, the extruded material was cut into pellets to prepare a molding material. The stirred mixture was melt-kneaded under conditions of a cylinder temperature of 350 to 380°C, an adapter temperature of 380°C, and a die temperature of 375°C. The temperature during melt-kneading was measured by measuring the temperature of the molten molding material immediately after extrusion from the die, and was found to be 383°C.

[0167] After preparing the molding material, the apparent shear viscosity of this molding material was measured in the same manner as in Example 1. The apparent shear viscosity of this molding material was measured using a flow tester (Shimadzu Flow Tester CFT-500D, manufactured by Shimadzu Corporation). Specifically, the molding material was dried in advance in a hot air dryer at 160°C for 12 hours, and then 1.5 cm of the molding material was dried. 3 The mixture was packed into a 360°C cylinder attached to a die (diameter: 1 mm, length: 10 mm), and a 1.0 cm2 cylinder was placed on top of the cylinder. 2 A plunger was attached, and when the temperature of the cylinder reached 360°C, it was preheated for 5 minutes. Immediately after this preheating, a load of 50 kgf was applied to melt and flow out the PEI resin, and its apparent shear viscosity was measured.

[0168] The prepared molding material was then placed in a dehumidifying hot air dryer heated to 160°C and dried for at least 12 hours. After confirming that the moisture content of the dried molding material was 300 ppm or less, the molding material was placed in a φ40 mm single-screw extruder and continuously extruded through a 900 mm wide T-die to form a strip-shaped conductive resin film for the current collector. The single-screw extruder had an L / D of 25, a compression ratio of 2.5, and a full-flight screw.

[0169] The temperature of the single-screw extruder was adjusted to 350-380°C, the temperature of the T-die to 360°C, the temperature of the connecting pipe connecting the single-screw extruder to the T-die to 380°C, and the gear pump to 380°C. The temperature of the molten molding material was measured from the resin temperature at the inlet of the T-die and found to be 384°C. When the molding material was introduced into the single-screw extruder, nitrogen gas was supplied at a rate of 15 L / min.

[0170] After the conductive resin film for current collector was produced, the presence or absence of die buildup during production of the conductive resin film for current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, conductivity, chemical resistance, and heat resistance of the conductive resin film for current collector were evaluated and are shown in Table 4. However, when the conductive resin film for current collector was immersed in NMP in an attempt to measure the chemical resistance of the conductive resin film for current collector, the conductive resin film for current collector dissolved, making it impossible to measure the chemical resistance.

[0171] Comparative Example 6 First, to prepare the molding material, KT-851NLSP, which was used in Example 1, was selected as the PEEK resin. This PEEK resin and Ketjenblack EC600JB (a product name manufactured by Lion Specialty Chemicals Corporation, hereinafter abbreviated as "EC600JD"), a carbon black, were added to a mixer in the composition mass ratios shown in Table 4, and the mixture was stirred and mixed to prepare a stirred mixture.

[0172] After preparing the stirred mixture, the stirred mixture was fed to a high-speed twin-screw extruder equipped with a vacuum pump, melt-kneaded under reduced pressure, and extruded into a rod shape from a die at the tip of the high-speed twin-screw extruder. The rod was air-cooled and cut to prepare a pellet-shaped molding material. The temperature during melt-kneading was measured by measuring the temperature of the molten molding material immediately after extrusion from the die, and was found to be 383°C. Furthermore, after preparing the molding material, the apparent shear viscosity of the molding material was measured in the same manner as in Example 1.

[0173] Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape in the same manner as in Example 1. The temperature of the molten molding material was measured from the resin temperature at the entrance of a T-die and was found to be 403°C. After molding, a conductive resin film for a current collector was produced in the same manner as in Example 1, and the generation of die boogers during the production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and are shown in Table 4.

[0174] [Table 3]

[0175] [Table 4]

[0176] 〔evaluation〕 In the case of the conductive resin films for current collectors of each Example, no burrs were generated during production, and excellent mechanical properties, conductivity, chemical resistance, and heat resistance were obtained. These Examples demonstrate that the conductive resin films for current collectors of each Example are suitable for use as current collectors in secondary batteries.

[0177] In contrast, the conductive resin film for a current collector of Comparative Example 1 contained a large amount of polyarylene ether ketone resin outside the range of the present invention, resulting in poor mechanical properties and raising doubts about its suitability for use as a current collector for a secondary battery. Furthermore, the conductive resin films for a current collector of Comparative Examples 2, 4, 5, and 6 generated burrs during production, raising doubts about the quality of the conductive resin film for a current collector. The conductive resin film for a current collector of Comparative Example 3 did not generate burrs during production, but its chemical resistance deteriorated, raising doubts about its suitability for use as a current collector for a secondary battery. Furthermore, the conductive resin film for a current collector of Comparative Example 5 did not contain polyarylene ether ketone resin, resulting in the conductive resin film for a current collector dissolving and significantly deteriorating its chemical resistance, raising doubts about its suitability for use as a current collector for a secondary battery. [Industrial Applicability]

[0178] The conductive resin film for a current collector of a secondary battery and the method for producing the same according to the present invention can be used in the field of producing secondary batteries such as nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium ion secondary batteries, and all-solid-state batteries. [Explanation of symbols]

[0179] 1 Molding material 2 Polyarylene ether ketone resin 3 Carbon-based conductive materials 4. Carbon nanotubes 5. Conductive resin film for current collectors 10 Melt kneader 14 dice 20 Melt extrusion molding machine 23 Dice 26 Crimping roll 27 Cooling roll 28 Winder 29 Winding tube

Claims

1. A conductive resin film for a current collector of a secondary battery, which is formed from a molding material containing, in terms of composition mass ratios, 78% by mass or more and 97% by mass or less of a polyarylene ether ketone resin and 3% by mass or more and 25% by mass or less of a carbon-based conductive material, and has a relative crystallinity of 80% or more and 100% or less, the apparent shear viscosity of the polyarylene ether ketone resin is 1×10 1 Pa·s or more and 1×10 4 Pa·s or less at 375°C, as measured with a flow tester using a die having a diameter of 1.0 mm and a length of 10 mm under conditions of a temperature of 375°C and a load of 50 kgf; A conductive resin film for a current collector of a secondary battery, characterized in that the mass change rate when immersed in N-methyl-2-pyrrolidone and an electrolyte solution is 0.0% or more and 2.0% or less, and the volume resistivity when measured in accordance with JIS K 7194 is 10 Ω cm or more and 100 Ω cm or less.

2. 2. The conductive resin film for a current collector of a secondary battery according to claim 1, which has a thickness of 5 μm or more and 500 μm or less, a tensile elongation at break measured in accordance with JIS K 7127 of 10% or more and 500% or less, and a maximum tensile strength measured in accordance with JIS K 7127 of 70 MPa or more and 500 MPa or less.

3. A conductive resin film for a collector of a secondary battery as described in claim 1 or 2, wherein the apparent shear viscosity of the molding material is 1 x 101 Pa·s or more and 1 x 104 Pa·s or less at a temperature of 375°C, measured with a flow tester using a die with a diameter of 1.0 mm and a length of 10 mm under conditions of a temperature of 375°C and a load of 50 kgf.

4. A method for producing the conductive resin film for a current collector of a secondary battery according to claim 1, 2, or 3, comprising the steps of: A method for producing a conductive resin film for a current collector of a secondary battery, comprising melt-kneading a molding material composed of, in mass ratios of 78% by mass or more and 97% by mass or less, a polyarylene ether ketone resin and 3% by mass or more and 25% by mass or less, a carbon-based conductive material, and extruding the molding material through a die to form a conductive resin film for a current collector, and then cooling the film by sandwiching it between a pressure roll and a cooling roll, thereby making the relative crystallinity of the conductive resin film for a current collector 80% or more and 100% or less.

5. The cooled conductive resin film for a current collector is subjected to heat compression molding, and the heating temperature of the conductive resin film for a current collector is set to be equal to or higher than the melting point of the polyarylene ether ketone resin but lower than the thermal decomposition temperature, and the pressure applied to the conductive resin film for a current collector is set to be 0.5 kgf / cm with respect to the projected area of the conductive resin film for a current collector. ２ More than 100kgf / cm ２ 5. The method for producing a conductive resin film for a current collector of a secondary battery according to claim 4, wherein the following is performed:

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