JP7756046B2 - Conductive resin film for current collector of secondary battery and method for producing same - Google Patents

Description

The present invention relates to a conductive resin film for use as a current collector in secondary batteries such as lithium-ion secondary batteries and all-solid-state batteries, and a method for producing the same.

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 are particularly noteworthy. A lithium-ion secondary battery is composed of a positive electrode, a negative electrode, a separator, an electrolyte, a container, and other components (not shown). Of these components, the positive electrode (positive electrode plate) is formed from a current collector plate and a positive electrode mixture containing a positive electrode active material formed on the top of the current collector plate. In contrast, the negative electrode (negative electrode plate) is formed from a current collector plate and a negative electrode mixture formed on both sides of the current collector plate.

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 wide range of fields. For example, they are used in a wide range of applications as power sources for mobile information devices such as mobile phones, multi-function mobile phones, and tablet devices, 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.

Lithium-ion secondary batteries and all-solid-state batteries used in mobile information devices, automobiles, etc. require high energy density, and one way to achieve this is to reduce the battery's weight. Various methods are being considered for reducing the battery's weight, one of which is the use of conductive resin film. While metal foil is used as the current collector for the positive and negative electrodes of lithium-ion secondary batteries, replacing this metal foil with a conductive resin film, which has a lower specific gravity than metal, can contribute to reducing the battery's weight.

In light of this, 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 conjugated diene rubber, or a cyclic olefin resin, a hydrogenated product of an aromatic vinyl-conjugated diene block copolymer, a conductive filler, and conjugated diene rubber.

Furthermore, 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 tetrafluoroethylene-hexafluoropropylene copolymer, and at least one conductive filler selected from the group consisting of ketjen black and multi-walled carbon nanotubes. Furthermore, Patent Document 3 discloses a current collector for a bipolar lithium-ion secondary battery comprising 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 and a metal layer (second conductive layer) formed by adding a conductive filler to a substrate containing a non-imide group-containing resin.

JP 2010-77236 A JP 2012-248430 A JP 2013-26192 A

However, the conductive resin film described in Patent Document 1 has problems with chemical resistance, and when such a conductive resin film is used as a current collector in a lithium-ion secondary battery, electrolyte components may penetrate into the conductive resin film, resulting in a decrease in charge-discharge cycle performance.

In addition, 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. However, 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 difficult to achieve high conductivity in the current collector for secondary batteries. Furthermore, current collector plates containing ketjen black are brittle, and may be damaged when applying the positive or negative electrode active material or when assembling them into a secondary battery.

In addition, conductive resin layers manufactured from a raw material mixture using multi-walled carbon nanotubes as a conductive filler have the problem that, although they have excellent in-plane conductivity due to the multi-walled carbon nanotubes being oriented in the plane direction, they have poor conductivity in the thickness direction. Furthermore, if tetrafluoroethylene-hexafluoropropylene copolymer is used as the resin component, the specific gravity of the resin becomes high, at 2.1 or more and 2.2 or less, which poses a major problem 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.

Furthermore, the current collector for a bipolar lithium-ion secondary battery described in Patent Document 3 has a multilayer structure composed of two different types of resin, and because the two types of resin have different linear expansion coefficients, there is a risk that the difference in the expansion rate of the conductive resin 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, there is a risk that such a current collector may curl due to differences in expansion rate caused by water absorption after manufacturing, or that the first and second conductive layers may peel.

The present invention has been developed in light of the above, and aims to provide an inexpensive conductive resin film for secondary battery current collectors that improves chemical resistance, prevents deterioration of charge/discharge cycle characteristics, prevents peeling of secondary battery current collectors, improves conductivity in the thickness direction, and contributes to weight reduction, as well as a method for producing the same.

After extensive research, the inventors focused on mixing polyarylene ether ketone resin, which has the highest heat resistance of all thermoplastic resins and also excels in chemical resistance and mechanical properties, with lightweight carbon nanotubes, which have the highest conductivity of all conductive materials, and a conductive material other than carbon nanotubes. They discovered that when a conductive resin film is molded using a molding material containing carbon nanotubes, the carbon nanotubes are oriented in the extrusion direction, preventing good conductivity from being achieved through the thickness of the resin film. However, they discovered that adding a conductive material other than carbon nanotubes can improve conductivity through the thickness, leading to the completion of this invention.

That is, in order to solve the above-mentioned problems, the present invention provides a conductive resin film for a current collector having a relative crystallinity of 80% or more, which is formed from a molding material containing 100 parts by mass of a polyarylene ether ketone resin and 5 parts by mass or more and 35 parts by mass or less of a conductive material,
the conductive material is composed of, in terms of composition mass ratio, 30% by mass or more and 99% by mass or less of carbon nanotubes and 1% by mass or more and 70% by mass or less of a conductive material other than carbon nanotubes;
The conductive material other than carbon nanotubes is a metal-based or carbon-based conductive material, has a shape of either a polyhedron, a sphere, or an ellipsoid, and has an average particle diameter of 0.1 μm or more and 10.0 μm or less;
The conductive resin film for a current collector is characterized in that the resistance value measured by applying a pressure of 1 MPa in the thickness direction thereof is 1 mΩ·cm ² or more and 800 mΩ·cm ² or less.

Preferably, the thickness is 10 μm or more and 500 μm or less, the specific gravity measured in accordance with JIS K 7112 Method A is 1.25 or more and 1.60 or less, and the mass change rate when immersed in N-methyl-2-pyrrolidone and an electrolyte solution is 2.0% or less.

The conductive resin film for a current collector may also have a thickness of 25 μm or more and 353 μm or less, a specific gravity of 1.33 or more and 1.38 or less when measured in accordance with JIS K 7112 Method A, a resistance of 97 mΩ cm or ^more and 732 mΩ cm ^or less when measured while applying a pressure of 1 MPa in the thickness direction of the conductive resin film for a current collector, and a mass change rate of 0.0% or more and 2.0% or less when immersed in N-methyl-2-pyrrolidone and an electrolyte solution.

It is also preferable that the polyarylene ether ketone resin is at least one of polyether ether ketone resin and polyether ketone ketone resin.

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 or 2, comprising the steps of:
a molding material containing 100 parts by mass of polyarylene ether ketone resin and 5 parts by mass or more and 35 parts by mass or less of a conductive material, the conductive material being composed of, in terms of composition mass ratio, 30% by mass or more and 99% by mass or less of carbon nanotubes and 1% by mass or more and 70% by mass or less of a conductive material other than carbon nanotubes;
The molding material is extruded through a die into a conductive resin film for a current collector, and then the film is cooled by being sandwiched 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.

It is preferable that the cooled conductive resin film for a current collector is heated and compression molded, the heating temperature of the conductive resin film for a current collector is equal to or higher than the melting point and lower than the thermal decomposition temperature of the polyarylene ether ketone resin, and the pressure applied to the conductive resin film for a current collector is equal to or higher than 0.5 kgf/ ^cm2 and equal to or lower than 100 kgf/ ^cm2 relative to the projected area of the conductive resin film for a current collector.

The molding material in the claims can be prepared by melt-kneading a conductive material consisting of a polyarylene ether ketone resin and a mixture of carbon nanotubes and a conductive material other than carbon nanotubes. The molding material and polyarylene ether ketone resin can be melt-kneaded at a temperature above the melting point of the polyarylene ether ketone resin and below the thermal decomposition temperature of the polyarylene ether ketone resin. Furthermore, to take advantage of the properties of carbon nanotubes, multiple types with different outer diameters and lengths may be mixed and used.

The conductive resin film for the current collector may be uniaxially stretched, biaxially stretched, or unstretched. This conductive resin film for the current collector includes not only thin conductive resin films for the current collector but also thick conductive resin sheets for the current collector. Furthermore, the secondary battery according to the present invention includes at least nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium-ion secondary batteries, bipolar lithium-ion secondary batteries, all-solid-state batteries, etc.

According to the present invention, a conductive resin film for a current collector is manufactured using a polyarylene ether ketone resin as a molding material, which has excellent mechanical strength, light weight, chemical resistance, and low water absorption. 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 a deterioration in charge-discharge cycle characteristics. Furthermore, because the molding material uses carbon nanotubes as well as conductive materials other than carbon nanotubes, the conductivity of the conductive resin film for a current collector in the thickness direction is improved.

According to the present invention, it is possible to improve the chemical resistance of a conductive resin film for a current collector and prevent a decrease in charge-discharge cycle characteristics. Furthermore, it is possible to prevent peeling of a current collector of a secondary battery, improve conductivity in the thickness direction, and contribute to weight reduction, and it is possible to provide a conductive resin film for a current collector at low cost. Furthermore, since the conductive material other than carbon nanotubes has a polyhedral, spherical, or ellipsoidal shape, it is expected that conductivity in the thickness direction will be improved.
Furthermore, since the particle diameter of the conductive material other than carbon nanotubes is 0.1 μm or more and 10.0 μm or less in average particle diameter, poor dispersion is not caused, uniform conductivity in the thickness direction is obtained, and a thin conductive resin film for a current collector can be obtained. In addition, it is possible to prevent a decrease in mechanical strength, which would otherwise cause breakage, cracking, or holes in the conductive resin film for a current collector. Furthermore, since the resistance value of the conductive resin film for a current collector measured under a pressure of 1 MPa in the thickness direction is 1 mΩ· ^cm2 or more and 800 mΩ·cm2 or ^less , it is possible to suppress a decrease in energy density and prevent the conductive resin film for a current collector from becoming brittle.

According to the invention described in claim 2, the thickness of the conductive resin film for the current collector is 10 μm or more and 500 μm or less, which prevents a significant decrease in the tensile strength of the conductive resin film for the current collector, and does not hinder weight reduction when the conductive resin film for the current collector is used as a current collector for a secondary battery. Furthermore, the specific gravity of the conductive resin film for the current collector, measured in accordance with JIS K 7112 Method A, is 1.25 or more and 1.60 or less, which eliminates the risk of voids or cracks occurring in the conductive resin film for the current collector and contributes to weight reduction.

Furthermore, the mass change rate when immersed in N-methyl-2-pyrrolidone and an electrolyte is 2.0% or less, so that excellent chemical resistance can be obtained.

According to the invention described in claim 3, the polyarylene ether ketone resin is at least one of polyether ether ketone resin and polyether ketone ketone resin, which not only provides excellent mechanical strength, light weight, hydrolysis resistance, heat resistance, chemical resistance, etc., but also makes it easier to obtain, reduces manufacturing costs, and improves the formability of the conductive resin film for current collectors.

According to the invention described in claim 4, the conductive resin film for the current collector is manufactured by melt extrusion molding, which improves the thickness accuracy, productivity, and handling of the conductive resin film for the current collector, and is expected to simplify manufacturing equipment. Furthermore, since no special steel materials or equipment are required to mold the conductive resin film for the current collector, reductions in the manufacturing costs of the current collector can be expected.

According to the invention described in claim 5, the conductive resin film for the current collector is subjected to heat compression molding, which reduces the resistance value of the conductive resin film for the current collector, improves conductivity, and reduces the amount of conductive material used, thereby reducing costs.

FIG. 1 is an explanatory view schematically showing a melt kneader in an embodiment of a method for producing a conductive resin film for a current collector of a secondary battery according to the present invention. 1 is an explanatory diagram schematically illustrating a manufacturing apparatus in an embodiment of a conductive resin film for a current collector of a secondary battery according to the present invention and a manufacturing method thereof. 1A and 1B are cross-sectional explanatory views schematically illustrating measurement states of the conductivity of conductive resin films for current collectors in examples and comparative examples of the method for producing a conductive resin film for current collectors of secondary batteries according to the present invention. FIG. 2 is a partial plan view illustrating a schematic diagram of the measurement state of the conductivity of a conductive resin film for a current collector in an example and a comparative example of the method for producing a conductive resin film for a current collector of a secondary battery according to the present invention.

A preferred embodiment of the present invention will now be described with reference to the drawings. In this embodiment, as shown in FIGS. 1 to 4, the conductive resin film 4 for a current collector of a secondary battery is formed into a conductive resin film with a relative crystallinity of 80% or more using a molding material 1 containing a polyarylene ether ketone resin 2 and a conductive material 3, and the conductive material 3 is composed of carbon nanotubes that contribute to conductivity in the planar direction and a conductive material other than carbon nanotubes that contributes to conductivity in the thickness direction, thereby contributing to the achievement of Goal 9 of the SDGs (the United Nations' international goals for sustainable development, consisting of 17 global goals and 169 targets (achievement criteria)) adopted at the United Nations Summit.

Molding material 1 is prepared by adding 5 to 35 parts by mass, preferably 8 to 30 parts by mass, and more preferably 10 to 25 parts by mass of conductive material 3 to 100 parts by mass of polyarylene ether ketone resin. This is because if the amount of conductive material 3 added is less than 5 parts by mass, it will be impossible to obtain a conductivity of 1000 mΩ ^cm2 or less when measured by applying a pressure of 1 MPa in the thickness direction of conductive resin film 4 for current collector, and therefore sufficient conductivity cannot be imparted to conductive resin film 4 for current collector, making it difficult to use the film as a current collector for secondary batteries.

In contrast, if the amount of conductive material 3 added exceeds 35 parts by mass, the melt viscosity of molding material 1 increases, resulting in a decrease in melt fluidity, and the processability of conductive resin film 4 for current collector decreases due to a decrease in melt elongation, resulting in the formation of holes. In addition, it becomes difficult to blend conductive material 3 into polyarylene ether ketone resin 2. Furthermore, if the amount of conductive material 3 added exceeds 35 parts by mass, conductive material 3 will separate from conductive resin film 4 for current collector, causing the generation of resin buildup and resulting in a decrease in the quality of conductive resin film 4 for current collector.

To explain this point in more detail, when the conductive resin film 4 for the current collector is molded into a film, a large amount of deposits called "pitting resin" can adhere and accumulate at the exit (also called the die lip) of the molding die 23 shown in Figure 2. When such pitting resin accumulates, die lines can appear in the conductive resin film 4 for the current collector, or the pitting resin can leave the die exit and become mixed into the conductive resin film 4 for the current collector, resulting in a deterioration in the quality of the conductive resin film 4 for the current collector.

The conductive material 3 is prepared as a mixture of carbon nanotubes and a conductive material other than the carbon nanotubes, with the conductive material other than the carbon nanotubes functioning to improve the conductivity of the conductive resin film for a current collector 4 in the thickness direction. The composition mass ratio of the carbon nanotubes and the material other than the carbon nanotubes is 30% by mass or more and 99% by mass or less of the carbon nanotubes, and 1% by mass or more and 70% by mass or less of the conductive material other than the carbon nanotubes, preferably 40% by mass or more and 95% by mass or less of the carbon nanotubes, more preferably 50% by mass or more and 90% by mass or less, and even more preferably 60% by mass or more and 80% by mass or less of the carbon nanotubes. This composition mass range allows for high conductivity in the thickness direction of the conductive resin film for a current collector 4 without reducing the chemical resistance of the conductive resin film for a current collector 4.

The reason why the composition weight ratio of carbon nanotubes is 30% by mass or more is that if it is less than 30% by mass, sufficient conductivity cannot be imparted to the conductive resin film 4 for current collector, making it difficult to use it as a current collector for a secondary battery. On the other hand, the reason why the composition weight ratio of carbon nanotubes is 99% by mass or ^less is that if it exceeds 99% by mass, the carbon nanotubes will be oriented in the extrusion direction, and the resistance value measured by applying a pressure of 1 MPa in the thickness direction will exceed 1000 mΩ cm2, making it difficult to impart sufficient conductivity to the conductive resin film 4 for current collector, making it difficult to use it as a current collector for a secondary battery.

Such molding material 1 may include, in addition to polyarylene ether ketone resin 2 and 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 polypropylene, polyester resins such as polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, and polyethylene naphthalate (PEN) resin, and polyolefin resins such as olefins, as long as the properties of the present invention are not impaired. polyimide resins such as polyimide (PI) resin, polyamideimide (PAI) resin, polyetherimide (PEI) resin, etc.; polyamide 4T (PA4T) resin, polyamide 6T (PA6T) resin, modified polyamide 6T (modified PA6T) resin, polyamide 9T (PA9T) resin, polyamide 10T (PA10T) resin, polyamide 11T (PA11T) resin, polyamide 6 (PA6) resin, polyamide 66 (PA66) resin, polyamide 46 (PA46) resin, etc.; polyamide resins such as polysulfone (PSU) resin, poly Polysulfone resins such as ether 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-hexafluoropropylene copolymer (TPE) resin, Fluororesins such as polyvinylidene fluoride copolymer (FEP) resin, tetrafluoroethylene-ethylene copolymer (ETFE) resin, polychlorotrifluoroethylene (PCTFE) resin, polyvinylidene fluoride (PVdF) resin, and vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer resin, and thermoplastic resins such as polycarbonate (PC) resin, polyarylate (PAR) resin, polyacetal (POM) resin, liquid crystal polymer (LCP), and aliphatic polyketone resin can be selectively added.

In addition to the polyarylene ether ketone resin 2, conductive material 3, and the above-mentioned thermoplastic resin, certain additives can 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, UV absorbers, plasticizers, lubricants, flame retardants, heat resistance improvers, inorganic fillers, organic fillers, glass fibers, carbon fibers, nanofibers, etc. can be selectively added.

The polyarylene ether ketone resin 2 of the molding material 1 is a crystalline thermoplastic resin composed of arylene groups, ether groups, and carbonyl groups. Examples include resins described in Patent Publication Nos. 5709878 and 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.

Specific examples of polyarylene ether ketone resin 2 include 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).

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 4 for the current collector. Specific examples of polyether ether ketone resins include the Victrex Powder series and Victrex Granules series manufactured by Victrex, the Vestakeep series manufactured by Diesel-Evonik, and the KetaSpire PEEK series manufactured by Solvay Specialty Polymers. Specific examples of polyether ketone ketone resins include the KEPSTAN series manufactured by Arkema.

Polyarylene ether ketone resin 2 may be used alone or in a mixture of two or more types. Polyarylene ether ketone resin 2 may also be a copolymer having two or more chemical structures represented by chemical formulas (1) to (5). Polyarylene ether ketone resin 2 is typically used in a form suitable for molding, such as powder, granules, or pellets. The method for producing polyarylene ether ketone resin 2 is not particularly limited, but examples include the method described in the literature [Asahi Research Center Co., Ltd.: PEEK, a Super Engineering Plastic Growing in Cutting-Edge Applications (Vol. 1)].

The apparent shear viscosity of the polyarylene ether ketone resin 2 at 375°C, 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, is preferably ^1x101 Pa·s or more ^{and 1x104} Pa·s or less, preferably ^5x101 Pa·s or more and ^5x103 Pa·s or less, and more preferably ^1x102 Pa·s or more and ^2x103 Pa·s or less, from the viewpoint of improving moldability. This is because care must be taken when the apparent shear viscosity is less than ^1x101 Pa·s, as this reduces the apparent shear viscosity, leading to a decrease in melt tension and making it difficult to mold the molding material 1. Furthermore, care must be taken when the apparent shear viscosity exceeds ^1x104 Pa·s, as the melt viscosity increases and the melt elongation decreases, making it difficult to mold the molding material 1.

The carbon nanotubes in the molding material 1 are configured in a cylindrical hollow fiber structure, and function to improve the conductivity in the plane direction of the conductive resin film 4 for the current collector and contribute to weight reduction. These carbon nanotubes come in two varieties: 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. To make the most of their properties, multiple types of carbon nanotubes with different outer diameters and lengths can be mixed and used.

Carbon nanotubes other than single-walled and multi-walled carbon nanotubes include nanografibers, bamboo-shaped nanotubes, and stacked cup nanotubes, as described in Non-Patent Document 1 [Introduction to the Materials Chemistry of Carbon Nanotubes, Corona Publishing, edited by Saito Yahachi, pp. 7-9]. Also included are carbon nanotube analogs such as nanohorns, nanocones, microcoils, and nanocoils, as described in Non-Patent Document 1 [Introduction to the Materials Chemistry of Carbon Nanotubes, Corona Publishing, edited by Saito Yahachi, pp. 9-11]. Of these carbon nanotubes and their analogs, multi-walled carbon nanotubes are the most suitable from a cost perspective.

The fiber diameter (outer diameter) of the carbon nanotubes is not particularly limited, but is preferably 0.5 nm or more and 200 nm or less. Such carbon nanotubes 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) chemical vapor deposition methods (or pyrolysis methods) such as the substrate growth method, supported catalyst method, fluidized catalyst method, and HiPco method, as described in Non-Patent Document 1 [Introduction to Materials Chemistry of Carbon Nanotubes, Corona Publishing, edited by Saito Yahachi, pp. 11-12]. They can also be produced by the eDPIS method, the Supergloss method, etc.

Specific examples of carbon nanotubes 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 (Hypeprion Examples include Catalysis International (product name).

The conductive material other than carbon nanotubes in molding material 1 is a metallic or carbon-based conductive material, and functions to improve the conductivity of the collector conductive resin film 4 in the thickness direction. 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.

Examples of carbon-based conductive materials include carbon blacks such as furnace black (oil furnace black and gas furnace black), channel black, acetylene black, and thermal black; carbon fibers such as carbon nanofibers, fullerenes, amorphous carbon, bread-based carbon fibers, and pitch-based carbon fibers; and graphite such as flake graphite, lump graphite, earthy 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.

The shape of the conductive material other than carbon nanotubes may be any shape, such as plate-like, scale-like, polyhedral, spherical, or ellipsoidal, but polyhedral, spherical, or ellipsoidal shapes are preferred because they improve conductivity in the thickness direction. Powder, granular, block, fibrous, or other shapes are also not particularly important. One type may be used alone, or two or more types may be used in combination.

The particle size of the conductive material other than carbon nanotubes should be an average particle size of 0.1 μm to 10.0 μm, preferably 0.5 μm to 8.0 μm, and more preferably 1.0 μm to 8.0 μm. This is because an average particle size of less than 0.1 μm results in severe secondary aggregation of the conductive material, leading to poor dispersion and making it impossible to achieve uniform conductivity through the thickness. Furthermore, the melt viscosity of the molding material 1 increases, making it impossible to obtain a thin conductive resin film 4 for the current collector. In contrast, an average particle size of the conductive material exceeding 10.0 μm results in the generation of resin buildup and a decrease in mechanical strength, leading to breaks, cracks, and holes in the conductive resin film 4 for the current collector, making it difficult to manufacture the conductive resin film 4 for the current collector.

Furthermore, the conductive material 3 may contain, to the extent that it does not impair the properties of the collector conductive resin film 4, for example, a silane coupling agent [vinyltrimethoxysilane, vinyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-aminopropylethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-ureidopropyltrialkoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-isocyanatopropyltriethoxysilane, 3-trimethoxysilylpropylsuccinic anhydride, imidazole silane, etc.], a titanate coupling agent [isopropyl triisostearoyl titanate, isopropyl(dioctyl)silane, etc.], bis(dioctyl pyrophosphate) titanate, isopropyl tris(N-aminoethyl-aminoethyl) titanate, tetraoctyl bis(di-tridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(di-tridecyl)phosphite titanate, bis(dioctyl pyrophosphate) oxyacetate titanate, bis(dioctyl pyrophosphate) ethylene titanate, isopropyl trioctanoyl titanate, isopropyl di Treatment can be performed with various coupling agents such as methacrylic isostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, isopropyl isostearoyl diacryl titanate, isopropyl tri(dioctyl phosphate) titanate, isopropyl tricumylphenyl titanate, tetraisopropyl (dioctyl phosphite) titanate, and aluminate coupling agents such as acetoalkoxyaluminum diisopropylate.

The apparent shear viscosity of the molding material 1, measured at 375°C using a die 1.0 mm in diameter and 10 mm in length under conditions of a temperature of 375°C and a load of 50 kgf, is preferably in the range of 1× ¹⁰ Pa s to 1× ¹⁰ Pa s, preferably 1× ¹⁰ Pa s to 5× ¹⁰ Pa s, and more preferably 5× ¹⁰ Pa s to 2× ¹⁰ Pa s. This is because, if the apparent shear viscosity is in the range of 1× ¹⁰ Pa s to 1× ¹⁰ Pa s, the conductive resin film 4 for current collector will have excellent formability and sufficient mechanical strength.

On the other hand, if the apparent shear viscosity is less than 1×10 ¹ Pa·s, the apparent shear viscosity is low, which leads to a decrease in melt tension and makes it difficult to form the conductive resin film 4 for a current collector. If the apparent shear viscosity exceeds 1×10 ⁴ Pa·s, the melt viscosity is high and the melt elongation is reduced, which may cause holes to form in the conductive resin film 4 for a current collector and cause it to break, resulting in problems in forming the conductive resin film 4 for a current collector.

In the above, when producing the conductive resin film 4 for the current collector, the polyarylene ether ketone resin 2, the conductive material 3 (carbon nanotubes), and a conductive material other than carbon nanotubes are melt-kneaded for a predetermined period of time to prepare the molding material 1, and this molding material 1 is then fed into a melt extruder 20 for resin film molding and melt-extruded to produce the conductive resin film 4 for the current collector having a thickness of 500 μm or less, for example, 10 μm to 500 μm.

Methods for preparing molding material 1 include: (1) a method in which carbon nanotubes and a conductive material other than carbon nanotubes are simultaneously or separately charged into a melt kneader 10 for molding materials, and then melt-kneaded with molten polyarylene ether ketone resin 2 to prepare molding material 1; and (2) a method in which polyarylene ether ketone resin 2, carbon nanotubes, and a conductive material other than carbon nanotubes are stirred and mixed at room temperature (a temperature of approximately 0°C to 50°C) using a stirring mixer, and then melt-kneaded in melt kneader 10 to prepare molding material 1.

First, to explain the preparation method (1) in detail, in this method, for example, a predetermined melt kneader 10 as shown in FIG. 1 is prepared, and after polyarylene ether ketone resin 2 is charged into this melt kneader 10, a stirred mixture of carbon nanotubes and a conductive material other than the carbon nanotubes is newly charged using a side feeder method or the like, and melt-kneaded with the already molten polyarylene ether ketone resin 2 to prepare molding material 1. Alternatively, for example, polyarylene ether ketone resin 2 is charged into melt kneader 10 and melted, and after carbon nanotubes and a conductive material other than the carbon nanotubes are separately charged into melt kneader 10 using a third feeder method or the like, and melt-kneaded with the already molten polyarylene ether ketone resin 2 to prepare molding material 1.

Examples of the melt kneader 10 include a Banbury mixer, mixing roll, pressure kneader, 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. Among these, a vent-type multi-screw extruder is preferred, as it is expected to achieve good mixing and dispersion of the polyarylene ether ketone resin 2 with the carbon nanotubes and conductive materials other than carbon nanotubes, and is capable of degassing the moisture and volatile gases generated from these materials.

As shown in FIG. 1, the melt mixer 10, which is a multi-screw extruder, is comprised of a cylinder 12 mounted on a base 11, a screw 13 built into the cylinder 12 and supported by a shaft. The screw 13 is rotated by a motor to melt and mix polyarylene ether ketone resin 2, carbon nanotubes, and other conductive materials, and extrudes strands (rod-shaped) or the like from a die 14 at the tip of the screw 13, an inlet 15 for polyarylene ether ketone resin 2 connected to the upstream end of the cylinder 12, a side feeder 16 connected to the downstream end of the cylinder 12 for adding carbon nanotubes and other conductive materials, and a rotatable cutter 17 for cutting the strands extruded from the die 14 of the cylinder 12 and cooled with air or water to produce the molding material 1. The side feeder 16 may be used singularly or in plural, depending on the method of adding carbon nanotubes and other conductive materials.

The inlet 15 and side feeder 16 of the melt kneader 10 are as follows: the inlet 15 is installed as a hopper at the upper upstream side of the cylinder 12, and the side feeder 16 is configured as a screw structure and mounted at the upper downstream side of the cylinder 12. Finely powdered carbon nanotubes and conductive materials other than carbon nanotubes are simultaneously or separately fed from the side into the side feeder 16, which is located downstream of the inlet 15. By injecting the carbon nanotubes and conductive materials other than carbon nanotubes into the molten polyarylene ether ketone resin 2, the uniform dispersion of the molding material 1 is improved. Furthermore, the kneading time of the carbon nanotubes and conductive materials other than carbon nanotubes in the polyarylene ether ketone resin 2 is shortened, which is expected to prevent decomposition.

The melting temperature when melt-kneading polyarylene ether ketone resin 2 with carbon nanotubes and conductive material 3 other than carbon nanotubes is not particularly limited as long as it is a temperature at which melt-kneading dispersion is possible and polyarylene ether ketone resin 2 does not decompose, but is in the range of from the melting point of polyarylene ether ketone resin 2 to less than the thermal decomposition temperature of polyarylene ether ketone resin 2.

Specifically, the temperature is in the range of not less than 10°C above the melting point of polyarylene ether ketone resin 2 but not more than 100°C above the melting point of polyarylene ether ketone resin 2, preferably not less than 20°C above the melting point of polyarylene ether ketone resin 2 but not more than 80°C above the melting point of polyarylene ether ketone resin 2, more preferably not less than 30°C above the melting point of polyarylene ether ketone resin 2 but not more than 60°C above the melting point of polyarylene ether ketone resin 2, and even more preferably not less than 30°C above the melting point of polyarylene ether ketone but not more than 50°C above the melting point of polyarylene ether ketone resin 2.

This is because, if the temperature is below 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 with the carbon nanotubes and the conductive material 3 other than carbon nanotubes. Conversely, if the temperature is above the thermal decomposition temperature, this is undesirable as it will lead to decomposition of the polyarylene ether ketone resin 2.

The melt-kneaded polyarylene ether ketone resin 2, carbon nanotubes, and conductive materials other than carbon nanotubes are extruded as strands through a die 14 to prepare molding material 1. However, after being extruded as a conductive resin film through the die 14, molding material 1 may be prepared in the form of powder, granules, flakes, or pellets. Furthermore, when preparing molding material 1, a predetermined amount or more of polyarylene ether ketone resin 2, carbon nanotubes, and conductive materials other than carbon nanotubes may be dispersed and formed into a masterbatch.

Next, the preparation method (2) will be described in detail. When this method is used to stir and mix polyarylene ether ketone resin 2 with carbon nanotubes and a conductive material other than carbon nanotubes 3 at room temperature, a stirring mixer such as a tumbler mixer, Henschel mixer, V-type mixer, Nauta mixer, ribbon blender, or universal stirring mixer is used. In this case, the polyarylene ether ketone resin 2 is preferably in the form of a powder, which allows for more uniform dispersion of the carbon nanotubes and the conductive material other than carbon nanotubes. Methods for pulverizing into a powder include, for example, shear pulverization, impact pulverization, collision pulverization, freeze pulverization, and solution pulverization.

The polyarylene ether ketone resin 2, carbon nanotubes, and conductive materials other than the carbon nanotubes are stirred and mixed, and then melt-kneaded and dispersed in a melt-kneader 10 such as a Banbury mixer, mixing roll, pressure kneader, single-screw extruder, or a multi-screw extruder consisting of a twin-screw extruder, triple-screw extruder, four-screw extruder, or eight-screw extruder, to prepare the molding material 1.

The melt kneader 10 is preferably a vented multi-screw extruder that can be expected to achieve good mixing and dispersion of the polyarylene ether ketone resin 2, carbon nanotubes, and conductive materials other than carbon nanotubes, and can degas the moisture and volatile gases generated from them. When preparing the molding material 1 using this melt kneader 10, a predetermined amount or more of the polyarylene ether ketone resin 2, carbon nanotubes, and conductive materials other than carbon nanotubes 3 can be dispersed and turned into a masterbatch.

The moisture content (water content) of molding material 1 before melt extrusion is adjusted by heat drying to 2000 ppm or less, preferably 1000 ppm or less, and more preferably 500 ppm or less. This is because a moisture content above 2000 ppm may cause foaming of the conductive resin film 4 for current collector. Therefore, molding material 1 is preferably heat dried to reduce the moisture content before melt kneading.

Methods for heating and drying molding material 1 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 molding material 1 is between the glass transition point of polyarylene ether ketone resin 2 -50°C and the glass transition point of polyarylene ether ketone resin 2 +50°C, preferably between the glass transition point of polyarylene ether ketone resin 2 -30°C and the glass transition point of polyarylene ether ketone resin 2 +30°C, and more preferably between the glass transition point of polyarylene ether ketone resin 2 -20°C and the glass transition point of polyarylene ether ketone resin 2 +20°C. The heating and drying time for molding material 1 is at least 2 hours, preferably at least 4 hours, and more preferably at least 8 hours. There is no particular upper limit to this heating and drying time, but 24 hours or less is appropriate.

Once molding material 1 is prepared, conductive resin film 4 for current collectors is manufactured using this molding material 1. This manufacturing method can be a melt extrusion method, a calendar molding method, a casting method, or the like. Of these manufacturing methods, melt extrusion molding, which allows conductive resin film 4 for current collectors to be continuously extruded into a strip, is optimal from the standpoints of improving the thickness accuracy, productivity, and ease of handling of conductive resin film 4 for current collectors, and simplifying the equipment.

The melt extrusion molding method involves melt-kneading molding material 1 using a melt extruder 20 and continuously extruding conductive resin film 4 for a current collector from a die 23, such as a T-die or round die, connected to the tip of the melt extruder 20 (see Figure 2). As shown in Figure 2, the melt extruder 20 may be, for example, a single-screw or twin-screw extruder. At the upper rear, a raw material inlet 21 for the molding material is installed. Connected to this raw material inlet 21 is an inert gas supply pipe 22, which supplies an inert gas such as helium gas, neon gas, argon gas, krypton gas, or nitrogen gas as needed. The supply of inert gas from this inert gas supply pipe 22 effectively prevents oxidative degradation, oxygen crosslinking, and thermal crosslinking of molding material 1.

The melting temperature during melt-kneading in the melt extruder 20 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 it is preferably in the range of the melting point of the polyarylene ether ketone resin 2 or higher and lower than the thermal decomposition temperature of the polyarylene ether ketone resin 2.

Specifically, the temperature range is from the melting point of polyarylene ether ketone resin 2 + 10°C to polyarylene ether ketone resin 2 + 100°C, preferably from polyarylene ether ketone resin 2 + 20°C to polyarylene ether ketone resin 2 + 80°C, more preferably from polyarylene ether ketone resin 2 + 30°C to polyarylene ether ketone resin 2 + 60°C, and even more preferably from the melting point of polyarylene ether ketone + 30°C to polyarylene ether ketone resin 2 + 50°C. This is because, if the temperature is below the melting point of polyarylene ether ketone resin 2, melt extrusion molding of molding material 1 becomes difficult, and conversely, if the temperature exceeds the thermal decomposition temperature, polyarylene ether ketone resin 2 may decompose violently.

The die 23 is connected to the tip of the melt extruder 20 via a connecting pipe 24 and functions to continuously extrude a strip-shaped conductive resin film 4 for a current collector downward. A T-die is suitable for this die 23, as it is capable of producing a conductive resin film 4 for a current collector with excellent thickness accuracy. A gear pump 25 is preferably attached to the connecting pipe 24 upstream of the die 23. Using this gear pump 25, the molding material 1 melted and kneaded by the melt extruder 20 can be transferred to the downstream die 23 at a constant flow rate and with high precision.

The temperature during extrusion of the die 23 should be in the range of not less than the melting point of the polyarylene ether ketone resin 2 but not more 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 and 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 and 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 and 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 + 30°C and not more than the melting point of the polyarylene ether ketone resin 2 + 50°C.

This is because if the temperature is below the melting point of polyarylene ether ketone resin 2, it becomes difficult to melt extrude molding of molding material 1, and conversely, if the temperature exceeds the thermal decomposition temperature, polyarylene ether ketone resin 2 may decompose violently.

Below the die 23, a pair of opposing pressure rolls 26 are rotatably supported at a distance from each other, and between these pair of pressure rolls 26, a number of cooling rolls 27 are rotatably supported in a row and in sliding contact with each other. Of these 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. The pair of pressure rolls 26 and the multiple cooling rolls 27 are configured so that the pressure roll 26 has a reduced diameter and the cooling rolls 27 have an expanded diameter.

Of the pair of pressure rolls 26, a winder 28 is installed downstream of the downstream pressure roll 26, which winds the current collector conductive resin film 4 onto a rotatable winding tube 29. Between the downstream pressure roll 26 and the winder 28, a slit blade 30 is arranged to be able to move up and down, forming a slit in the longitudinal direction of the side of the current collector conductive resin film 4. Between this slit blade 30 and the winder 28, the required number of rotatable tension rolls 31 are supported on shafts to apply tension to the current collector conductive resin film 4 for smooth winding.

Each pressure roll 26 is adjusted to a temperature of 50°C or higher but lower than the melting point of polyarylene ether ketone resin 2, preferably 100°C or higher (melting point of polyarylene ether ketone resin 2 - 50°C) or lower, more preferably 130°C or higher (melting point of polyarylene ether ketone resin 2 - 100°C) or lower, and even more preferably 150°C or higher (polyarylene ether ketone resin 2 - 100°C) or lower, and slides against the collector conductive resin film 4, pressing it against the cooling roll 27.

The reason why the temperature of the pressure roller 26 is within this range is because condensation will form on the pressure roller 26 if the temperature is below 50°C. Conversely, if the temperature exceeds the melting point, the conductive resin film 4 for the current collector may stick to the circumferential surface of the pressure roller 26 and break, or the strength of the conductive resin film 4 for the current collector may decrease, leading to breakage. Methods for adjusting the temperature of the pressure roller 26 include, for example, using a heat medium such as air, water, or oil, using an electric heater, or using induction heating.

To improve adhesion between the conductive resin film 4 for the current collector and the cooling roll 27, the peripheral surface of each pressure roll 26 is coated 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, as needed. Inorganic compounds such as silica or alumina are optionally added to this rubber layer. Among these, silicone rubber and fluororubber are preferred due to their excellent heat resistance.

As the pressure roll 26, a metal elastic roll with a metal surface may be used if necessary. When this metal elastic roll is used, it is possible to form a conductive resin film 4 for the 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). Pressure rolls 26 whose surfaces are coated with a fluororesin film such as polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) resin or tetrafluoroethylene-hexafluoropyrene copolymer (FEP) resin can also be used.

The multiple cooling rolls 27 are, for example, metal rolls with a larger diameter than the pressure roll 26, and are rotatably supported below the die 23. They clamp the extruded current collector conductive resin film 4 between themselves and the circumferential surface of the pressure roll 26, and function together with the pressure roll 26 to cool the current collector conductive resin film 4 while controlling its thickness within a predetermined range.

For the same reasons as 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 2 - 50°C), more preferably 130°C or higher (melting point of polyarylene ether ketone resin 2 - 100°C), and even more preferably 150°C or higher (polyarylene ether ketone resin 2 - 100°C). The cooling roll 27 slides against the conductive resin film 4 for current collector and presses it against the opposing cooling roll 27. Methods for adjusting the temperature of the cooling roll 27 include, for example, using a heat medium such as air, water, or oil, using an electric heater, or using induction heating.

After the molding material 1 is extruded into a strip-shaped conductive resin film 4 for a current collector, this conductive resin film 4 for a current collector is wound around a pair of pressure rolls 26, multiple cooling rolls 27, a tension roll 31, and a winder 28. Both sides of the conductive resin film 4 for a current collector are cut longitudinally with a slit blade 30, and the film is sequentially wound around a winding tube 29 of the winder 28, thereby producing a long conductive resin film 4 for a current collector.

The thickness of the conductive resin film 4 for the current collector, produced by cooling with the cooling roll 27, is preferably 10 μm to 500 μm, more preferably 15 μm to 350 μm, more preferably 20 μm to 200 μm, and even more preferably 25 μm to 100 μm. This is because if the thickness of the conductive resin film 4 for the current collector is less than 10 μm, the tensile strength of the conductive resin film 4 for the current collector is significantly reduced, making it difficult to manufacture. Conversely, if the thickness of the conductive resin film 4 for the current collector exceeds 500 μm, it will hinder weight reduction when used as a current collector for lithium-ion secondary batteries, bipolar lithium-ion secondary batteries, and all-solid-state batteries. The thickness of the conductive resin film 4 for the current collector can be measured using various contact thickness gauges.

The specific gravity of the conductive resin film 4 for the current collector, as measured in accordance with JIS K 7112 Method A, should be 1.25 or more and 1.60 or less, preferably 1.30 or more and 1.50 or less, more preferably 1.31 or more and 1.45 or less, and even more preferably 1.32 or more and 1.40 or less. This is because if the specific gravity of the conductive resin film 4 for the current collector is less than 1.25, voids or cracks may occur in the conductive resin film 4 for the current collector, which would result in a decrease in mechanical strength, and is therefore undesirable.

On the other hand, if the specific gravity of the conductive resin film 4 for current collector exceeds 1.60, it will hinder weight reduction when used as a current collector for secondary batteries such as lithium ion secondary batteries, bipolar lithium ion secondary batteries, and all-solid-state batteries. The specific gravity of the conductive resin film 4 for current collector can be measured, for example, using a specific gravity measuring device conforming to JIS K 7112 Method A.

The relative crystallinity of the conductive resin film 4 for the 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 4 for the current collector is less than 80%, problems will arise with the mechanical strength, heat resistance, chemical resistance, and solvent resistance of the conductive resin film 4 for the current collector. In contrast, if the relative crystallinity is greater than 80%, the conductive resin film 4 can be expected to have sufficient mechanical strength, heat resistance, and chemical resistance to be usable as a conductive resin film for the current collector.

The crystallinity of the conductive resin film 4 for the current collector can be expressed as the relative crystallinity. The relative crystallinity of the conductive resin film 4 for the current collector is calculated using 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 (J/g) of the recrystallization peak of the conductive resin film for current collector
ΔHm: heat quantity (J/g) of the melting peak of the conductive resin film for current collector
The conductivity of the conductive resin film 4 for current collector can be evaluated by the resistance value measured when a pressure of 1 MPa is applied in the thickness direction. The resistance value measured when a pressure of 1 MPa is applied in the thickness direction is 1000 mΩ·cm2 or less, preferably 1 mΩ· ^cm2 or more and 1000 mΩ· ^cm2 or less, more preferably 1 mΩ·cm2 or ^more and 800 mΩ· ^cm2 or ^less , even more preferably 50 mΩ· ^cm2 or more and 600 mΩ· ^cm2 or less, and even more preferably 90 mΩ· ^cm2 or more and 500 mΩ· ^cm2 or less.

This is because if the resistance value of the conductive resin film 4 for current collector, measured by applying a pressure of 1 MPa in the thickness direction, exceeds 1000 mΩ ^cm2 , its use as a current collector for a secondary battery will result in a decrease in energy density. Conversely, if the resistance value is less than ¹ mΩ cm2, a large amount of conductive material 3 must be added, making the resulting conductive resin film 4 for current collector brittle, which can cause the conductive resin film 4 for current collector to crack during assembly of a secondary battery.

The chemical resistance of the conductive resin film 4 for the current collector can be evaluated by immersing the conductive resin film 4 for the current collector in N-methyl-2-pyrrolidone and an electrolyte and measuring the change in mass. From the perspective of improving chemical resistance and solvent resistance, the mass change rate when the conductive resin film 4 for the 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%.

The electrolyte is an organic electrolytic solution in which a lithium salt is dissolved as a solute in an organic solvent. Examples of organic solvents for the electrolyte include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC); chain 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); chain ethers such as 1,2-dimethoxyethane (DEM) and 1,2-diethoxyethane (DEE); cyclic esters such as gamma-butyrolactone (GBL); and chain esters such as methyl acetate (MA).

Examples of lithium salts include lithium perchlorate [LiClO ₄ ], lithium borofluoride [LiBF ₄ ], lithium hexafluorophosphate [LiPF ₆ ], lithium trifluoromethanesulfonate [LiCF ₃ SO ₃ ], lithium bis(trifluoromethanesulfonyl)imide [LiN(CF ₃ SO ₂ ) ₂ ], and lithium tris(trifluoromethanesulfonyl)methide [LiC(CF ₃ SO ₂ ) ₃ ].

However, if N-methyl-2-pyrrolidone or electrolyte remains in the conductive resin film 4 for current collectors, current collectors using conductive resin film 4 may cause problems when the N-methyl-2-pyrrolidone or electrolyte seeps into the secondary battery while the secondary battery is in operation, so care must be taken. Also, care must be taken because the secondary battery's electrolyte may seep into the current collector, reducing the charge/discharge cycle.

The molded conductive resin film 4 for current collectors can be used as is, or it can be further heat-compression molded. Heat-compression molding the conductive resin film 4 for current collectors can lower the resistance value, increase conductivity, and reduce the amount of conductive material 3 used, thereby reducing costs.

When the conductive resin film 4 for a current collector is subjected to heat compression molding, the conductive resin film 4 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, not lower than the melting point of the polyarylene ether ketone resin 2 + 10°C and not higher than the melting point of the polyarylene ether ketone resin 2 + 100°C, preferably not lower than the melting point of the polyarylene ether ketone resin 2 + 20°C and not higher than the melting point of the polyarylene ether ketone resin 2 + 80°C, more preferably not lower than the melting point of the polyarylene ether ketone resin 2 + 30°C and not higher than the melting point of the polyarylene ether ketone resin 2 + 60°C, and even more preferably not lower than the melting point of the polyarylene ether ketone resin 2 + 30°C and not higher than the melting point of the polyarylene ether ketone resin ² + 50°C, and a pressure of 0.5 kgf/cm2 or more and 100 kgf/cm2 is applied to the projected area of the conductive resin film 4 for a current collector. ² or less is applied and maintained for 0.5 seconds to 300 seconds, and then immediately cooled to a temperature below the glass transition point of the polyarylene ether ketone resin 2.

As described above, polyarylene ether ketone resin 2, which has excellent lightness, mechanical properties, chemical resistance, and heat resistance, and low water absorption, is selected as the thermoplastic resin for molding material 1 to manufacture current collector conductive resin film 4. Therefore, even if current collector conductive resin film 4 is used as a current collector, electrolyte components do not penetrate into the current collector conductive resin film 4, effectively eliminating the risk of a deterioration in charge/discharge cycle characteristics. Furthermore, because polyarylene ether ketone resin 2 is used instead of fluororesin, no special steel materials or equipment are required for molding, and significant cost reductions in current collectors can be expected.

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 rate 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 is carbon nanotubes, it is not only chemically stable, but also makes it possible to further reduce the weight of the secondary battery. Furthermore, since conductive materials other than carbon nanotubes are also used, significant improvements in the conductivity of the conductive resin film 4 for the current collector in the thickness direction can be expected.

Furthermore, since the thickness of the conductive resin film 4 for a current collector is 10 μm or more and 500 μm or less, a decrease in the tensile strength of the conductive resin film 4 for a current collector is prevented, and a significant reduction in the weight of the current collector of a secondary battery can be expected. Furthermore, since the specific gravity of the conductive resin film 4 for a current collector is 1.60 or less, it is possible to contribute to a significant reduction in the weight of the secondary battery and the current collector. Furthermore, since the resistance value measured by applying a pressure of 1 MPa in the thickness direction of the conductive resin film 4 is as low as 1000 mΩ· ^cm2 or less, a decrease in energy density can be prevented even when the conductive resin film 4 for a current collector is used as a current collector of a secondary battery.

The shape of the polyarylene ether ketone resin 2 of the molding material 1 in the above embodiment may be powder, granules, blocks, powder, pellets, etc. The conductive resin film 4 for a current collector may have a relative crystallinity of 95% or more and 100% or less, and a resistance value of 1 mΩ· ^cm2 or more and 1000 mΩ· ^cm2 or less when measured under a pressure of 1 MPa in the thickness direction. Furthermore, a single cooling roll 27 may be rotatably supported between a pair of pressure rolls 26.

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 a 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 a polyarylene ether ketone resin, and this polyether ether ketone resin was pulverized by a freeze-pulverization method.

The melting point (also referred to as melting temperature) of polyether ether ketone resin (hereinafter referred to as PEEK resin) was measured using a differential scanning calorimeter (manufactured by 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 measured melting point of KT-851NLSP was 340°C.

After the PEEK resin was pulverized, a conductive material consisting of a mixture of the pulverized PEEK resin, carbon nanotubes, and a conductive material other than the carbon nanotubes, which had been previously stirred and mixed in a mixer, was weighed out so that 8 parts by mass of the conductive material was used for 100 parts by mass of PEEK resin, as shown in Table 1.The PEEK resin and conductive material were then placed in a mixer and stirred and mixed to prepare a stirred mixture.

The carbon nanotubes used were NC7000 (manufactured by Nanosil Co., Ltd.: product name: (hereinafter abbreviated as "NC7000")), and the conductive material other than carbon nanotubes was spherical amorphous carbon, Bellpearl C2000SR (manufactured by Air Water Bellpearl Co., Ltd.: product name, average particle size: 8 μm (catalog value), (hereinafter abbreviated as "C2000SR")). The carbon nanotubes and conductive materials other than carbon nanotubes were weighed out so that the ratio was 95% by mass of carbon nanotubes and 5% by mass of conductive materials other than carbon nanotubes, as shown in Table 1. The carbon nanotubes and amorphous carbon were then placed in a mixer and mixed with stirring to prepare a stirred mixture.

The apparent shear viscosity of the PEEK resin was measured using a flow tester (Shimadzu Flow Tester CFT-500D, manufactured by Shimadzu Corporation). Specifically, the PEEK resin was dried in a hot air dryer at 160°C for 12 hours, and then 1.5 ^cm3 of the PEEK resin was filled into a 375°C cylinder attached to a die (diameter: 1 mm, length: 10 mm). A plunger with an area of 1.0 ^cm2 was attached to the top of the cylinder. Once the cylinder reached 375°C, it was preheated for 5 minutes. Immediately after preheating, a load of 50 kgf was applied to melt and flow the PEEK resin, and its apparent shear viscosity was measured. The apparent shear viscosity was measured using the same method below.

Once the stirred mixture was prepared, it was fed into a co-rotating twin-screw extruder equipped with a vacuum pump and melt-kneaded under reduced pressure. The melt-kneaded stirred mixture was extruded into a rod shape from the die at the tip of the co-rotating twin-screw extruder, cooled with water, and cut to prepare pellet-shaped molding material. The co-rotating twin-screw extruder used was a φ25mm, L/D=41 type. The stirred mixture was melt-kneaded to prepare the molding material under conditions of a cylinder temperature of 300°C to 370°C and a die temperature of 370°C, with the vent on the raw material inlet side of the co-rotating twin-screw extruder open and the vent on the die side degassed under reduced pressure. 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 372°C.

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 φ20 mm single-screw extruder and continuously extruded through a 150 mm wide T-die to form a strip-shaped conductive resin film for the current collector. The moisture content of the molding material was confirmed by Karl Fischer titration using a trace moisture analyzer (product name: CA-100, manufactured by Mitsubishi Chemical Corporation). Thereafter, the moisture content of the molding material was measured using the same method.

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

Once the conductive resin film for the current collector was formed, it was sequentially wound around a pair of silicone rubber pressure rolls (210°C) and cooling rolls (220°C) made of silicone rubber, as shown in Figure 2, and a 6-inch take-up tube of a winder located downstream of these. The continuous conductive resin film for the current collector was sandwiched between the pressure rolls and cooling roll, and sequentially wound around the take-up tube to produce a conductive resin film for the current collector measuring 10 m in length and 150 mm in width.

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, chemical resistance, and conductivity of the conductive resin film for current collector were evaluated, and the results are summarized in Table 1. The chemical resistance of the conductive film for current collector was evaluated based on the weight change before and after immersion in NMP and an electrolyte. The conductivity of the conductive film for current collector was evaluated based on the resistance value in the thickness direction before and after immersion in an electrolyte.
- Presence or absence of die buildup occurring during the production of conductive resin film for current collector Regarding the presence or absence of die buildup occurring during the production of conductive resin film for current collector, after producing 10 m of conductive resin film for current collector, the vicinity of the T-die lip was visually observed.

- Film Thickness of Conductive Resin Film for Current Collector The film thickness of the conductive resin film for current collector was measured using a micrometer (Mitutoyo Corporation, product name: Coolant Proof Micrometer, code MDC-25PJ). Measurements were taken at 10 arbitrary points in the extrusion direction (hereinafter abbreviated as "MD") at the center of the width direction (direction perpendicular to the extrusion direction (hereinafter abbreviated as "TD")) of the conductive resin film for current collector, and the average value was taken as the film thickness.

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 K7112 Method A.

Relative Crystallinity of Conductive Resin Film for Current Collector The relative crystallinity of the conductive resin film for current collector was measured by weighing about 5 mg of a measurement sample from the conductive resin film for current collector and using a differential scanning calorimeter (manufactured by SII Nanotechnologies, Inc., product name: High Sensitivity Differential Scanning Calorimeter X-DSC7000) at a heating rate of 10°C/min over a measurement temperature range of 20°C to 380°C. The crystallinity was calculated using the following formula from the calorific value (J/g) of the melting peak and the calorific value (J/g) of the recrystallization peak obtained at this time.

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

Chemical Resistance of Conductive Resin Film for Current Collector 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 weight change. To evaluate this weight change, the conductive resin film for current collector was cut into a size of MD: 55 mm x TD: 55 mm and weighed [W ₀ ]. This conductive resin film and 5 g of NMP or 5 g of electrolyte solution were placed in a PET/AL/PE flat bag (manufactured by Nippon Seisaku Co., Ltd.: trade name Lamizip) and sealed by heat sealing. The electrolyte solution used was an electrolyte solution for lithium primary/secondary/polymer batteries and lithium ion capacitors (manufactured by Kishida Chemical Co., Ltd.: trade name electrolyte LiPF ₆ , molar concentration 1 mol/L, solvent EC:DEC (3:7) V/V %).

After sealing by heat sealing, the PET/AL/PE flat bag was left standing in a hot air oven heated to 50°C for 15 days. After leaving it standing, the conductive resin film for a current collector was removed from the PET/AL/PE flat bag and washed with ethanol. This conductive resin film for a current collector was left standing in a hot air oven heated to 50°C for 24 hours, and after leaving it standing, it was left standing in a glass desiccator containing a desiccant (manufactured by Ozone Chemical Co., Ltd.: product name OZO-C) in an environment of 24°C for 24 hours. Thereafter, the conductive resin film for a current collector was weighed [ _W1 ] and evaluated by calculating the weight change rate using the following formula.

Weight change rate (%)={(W ₁ −W ₀ )×100}/W ₀
W ₀ : Initial weight of the conductive resin film for the current collector [g]
W ₁ : Weight [g] of the conductive resin film for current collector after immersion in NMP or electrolyte
A: When the weight change rate is 0.0% or more and 0.1% or less B: When the weight change rate is more than 0.1% and 1.0% or less C: When the weight change rate is more than 1.0% and 2.0% or less D: When the weight change rate is more than 2.0% and 5.0% or less E: When the weight change rate is more than 5.0% and 10% or less F: When the weight change rate is more than 10% and 20% or less

Conductivity of Conductive Resin Film for Current Collector The conductivity of the conductive resin film for current collector was evaluated by the resistance value in the thickness direction. The resistance value in the thickness direction [Rc] was calculated by cutting the conductive resin film for current collector to a size of 5.5 cm × 5.5 cm to prepare a test piece, sandwiching this test piece between a pair of upper and lower carbon papers each having a size of 5.0 cm × 5.0 cm, and then sandwiching this pair of carbon papers between a pair of upper and lower gold-plated electrodes, passing a direct current, applying a pressure of 1 MPa from above, and measuring the resistance value [R0] after 1 minute with a resistance meter, and then calculating the resistance value in the thickness direction [ _Rc ] from the following formula:

Rc = _R1 x S
R ₁ = R ₀ - (resistance value of two sheets of a pair of carbon paper)
S: Area of carbon paper

The carbon paper used was a SIGRACET Gas Diffusion Media type GDL24B (product name, manufactured by SGL GROUP). The resistance meter used was a Milliohm HiTester 3540 (product name, manufactured by Hioki E.E.).

The through-thickness resistance value [Rc] was measured before and after a chemical resistance test using the conductive resin film for the current collector and an electrolyte for lithium primary and secondary polymer batteries and lithium ion capacitors (manufactured by Kishida Chemical Co., Ltd., product name: electrolyte LiPF6, molar concentration 1 mol/L, solvent EC:DEC (3:7) V/V%). The measurement was performed in an environment with a temperature of 23°C ± 2°C and a relative humidity of 50 RH ± 5% RH.

Example 2
The polyarylene ether ketone resin and conductive material of Example 1 were weighed as shown in Table 1, and a pellet-shaped 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 371°C. The conductive material used was the carbon nanotubes used in Example 1, and amorphous carbon as a conductive material other than carbon nanotubes, with the amounts added being changed. The carbon nanotubes and amorphous carbon were weighed to have the composition mass ratio shown in Table 1, and then charged into a mixer and stirred and mixed to prepare a conductive material.

Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape using the same method as in Example 1. 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. After molding the conductive resin film for a current collector in this way, it was produced using the same method as in Example 1. The generation of die buildup during production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, chemical resistance, and conductivity of the conductive resin film for a current collector were each evaluated using the same methods as in the examples and the results are summarized in Table 1.

Example 3
The process was basically the same as in Example 1, except that the PEEK resin, which was a polyarylene ether ketone resin used in Example 1, was changed from KT-851NL SP to Victrex Granules 381G (product name of Victrex Co., Ltd. (hereinafter abbreviated as "381G"), which had been pulverized in advance by the method of Example 1, as the molding material, and the PEEK resin and conductive material were weighed to obtain the mass ratio shown in Table 1, to prepare a stirred mixture.

The conductive materials used were the same as in Example 1, with amorphous carbon used as a conductive material other than carbon nanotubes, but the amounts added were changed. The carbon nanotubes and amorphous carbon were weighed out to achieve the composition mass ratio shown in Table 1, and then the carbon nanotubes and amorphous carbon were placed in a mixer and stirred and mixed to prepare the conductive material. The apparent shear viscosity of 381G was measured using the same method as in Example 1. The melting point of 381G was also measured using the same method as in Example 1, and was found to be 343°C.

Next, a molding material was prepared using the same method 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 372°C.

Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape using the same method as in Example 1. 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. After molding the conductive resin film for a current collector in this manner, a conductive resin film for a current collector was produced using the same method as in Example 1. 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, chemical resistance, and conductivity of this conductive resin film for a current collector were each evaluated using the same methods as in Example 1 and the results are summarized in Table 1.

Example 4
The example 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 (manufactured by Victrex KGaA; product name (hereinafter abbreviated as "450G")) which had been pulverized in advance by the method of Example 1. This PEEK resin and conductive material were weighed out so as to obtain the mass ratio shown in Table 2, and a stirred mixture was prepared.

The carbon nanotubes used in Example 1 were changed from NC7000 to FloTube 9000 (product name, manufactured by CNano Technology). Furthermore, the conductive material other than the carbon nanotubes was changed from the amorphous carbon C2000SR used in Example 1 to amorphous carbon with spherical particle shape, Bellpearl CR1-2000 (product name, manufactured by Air Water Bellpearl Inc., average particle diameter: 1.2 μm (catalog value), hereafter abbreviated as "CR1-2000")

The conductive material was prepared by weighing carbon nanotubes and amorphous carbon to achieve the composition mass ratio shown in Table 2, adding them to a mixer, and stirring and mixing. The apparent shear viscosity of 450G was measured using the same method as in Example 1. The melting point of 450G was also measured using the same method as in Example 1, and was found to be 341°C.

Next, a molding material was prepared using the same method 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 373°C.

Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape using the same method as in Example 1. 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 396°C. After molding the conductive resin film for a current collector in this manner, another conductive resin film for a current collector was produced using the same method as in Example 1. The generation of die buildup during production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, chemical resistance, and conductivity of this conductive resin film for a current collector were each evaluated using the methods of Example 1 and the results are summarized in Table 2.

Example 5
The process was basically the same as in Example 1, except that the molding material, PEEK resin, which is a polyarylene ether ketone resin, used in Example 1 was changed from KT-851NL SP to Victrex Granules 151G (product name of Victrex Co., Ltd. (hereinafter abbreviated as "151G") which had been pulverized in advance by the method of Example 1, and the PEEK resin and the conductive material were weighed to obtain the mass ratio shown in Table 2, to prepare a stirred mixture.

The apparent shear viscosity of 151G was measured using the same method as in Example 1. The melting point of 151G was also measured using the same method as in Example 1, and was found to be 341°C. The conductive material was prepared by weighing out the carbon nanotubes and amorphous carbon used in Example 4 to achieve the composition mass ratio shown in Table 2, adding them to a mixer, and stirring and mixing them.

Next, a molding material was prepared using the same method 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.

Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape using the same method as in Example 1. 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 395°C. After molding the conductive resin film for a current collector in this way, a conductive resin film was produced using the same method as in Example 1. 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, chemical resistance, and conductivity of this conductive resin film for a current collector were each evaluated using the same methods as in Example 1 and the results are summarized in Table 2.

Example 6
First, to prepare the molding material, a polyether ketone ketone resin [manufactured by Arkema, product name: KEPSTAN 8003PF ST (hereinafter abbreviated as "8003PF")] was prepared as a commercially available polyarylene ether ketone resin, and this polyether ketone ketone resin (hereinafter abbreviated as PEKK resin) and the conductive material used in Example 1 were weighed out to obtain the mass ratio shown in Table 2. Thereafter, the PEKK resin and the conductive material were charged into a mixer and stirred and mixed to prepare a stirred mixture.

The conductive materials used were the carbon nanotubes used in Example 1 and amorphous carbon, a conductive material other than carbon nanotubes. The conductive materials were weighed out to achieve the composition weight ratio shown in Table 2, and then added to a mixer and stirred to prepare the material. Furthermore, the melting point of 8003PF was measured using the same method as in Example 1 and found to be 361°C.

The apparent shear viscosity of 8003PF was measured using a flow tester (Shimadzu Flow Tester CFT-500D, manufactured by Shimadzu Corporation). Specifically, 8003PF was dried in advance in a hot air dryer at 160°C for 12 hours, and then 1.5 ^cm3 of 8003PF was filled into a 375°C cylinder attached to a die (diameter: 1 mm, length: 10 mm). A plunger with an area of 1.0 ^cm2 was attached to the top of this cylinder, and when the cylinder temperature reached 375°C, it was preheated for 5 minutes. Immediately after this preheating, a load of 50 kgf was applied to melt and flow the PEKK resin, and its apparent shear viscosity was measured.

Next, a molding material was prepared using the same method 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.

Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape using the same method as in Example 1. 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 397°C. After molding the conductive resin film for a current collector in this manner, a conductive resin film for a current collector was produced using the same method as in Example 1. The generation of die buildup during production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, chemical resistance, and conductivity of this conductive resin film for a current collector were each evaluated using the same methods as in Example 1 and the results are summarized in Table 2.

Comparative Example 1
First, the polyarylene ether ketone resin and conductive material used in Example 1 were weighed out in a 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 found to be 371°C.

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 the 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 buildup during production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, chemical resistance, and conductivity of this conductive resin film for a current collector were each evaluated in the same manner as in Example 1 and are listed in Table 3. As a result, the conductivity of the conductive resin film for a current collector was significantly reduced.

Comparative Example 2
First, the polyarylene ether ketone resin and conductive material used in Example 1 were weighed out in a 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 found to be 379°C.

Next, the prepared molding material was used to mold a 450 μm thick strip of conductive resin film for current collectors using the same method as in Example 1. The temperature of the molten molding material was measured from the resin temperature at the entrance of the T-die and found to be 403°C. After molding the conductive resin film for current collectors in this manner, a conductive resin film for current collectors was produced using the same method as in Example 1. The generation of die buildup during production of the conductive resin film for current collectors, as well as the thickness, specific gravity, relative crystallinity, chemical resistance, and conductivity of this conductive resin film for current collectors were each evaluated using the same methods as in Example 1 and are listed in Table 3. As a result, the chemical resistance of the conductive resin film for current collectors deteriorated.

Comparative Example 3
First, the polyarylene ether ketone resin used in Example 1 and the carbon nanotubes used in Example 4 were weighed out in a mass ratio outside the range of the present invention shown in Table 3, and charged into a stirring mixer to prepare a mixture. In this Comparative Example 3, no conductive material other than the carbon nanotubes was used. After preparing the mixture, this mixture was processed 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 found to be 372°C.

Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape using the same method as in Example 1. 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 393°C. After molding the conductive resin film for a current collector in this manner, a conductive resin film for a current collector was produced using the same method as in Example 1. The generation of die buildup during production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, chemical resistance, and conductivity of this conductive resin film for a current collector were each evaluated using the same methods as in Example 1 and are listed in Table 3. As a result, the conductivity of the conductive resin film for a current collector deteriorated.

Comparative Example 4
First, the carbon nanotubes and amorphous carbon 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 conductive material. After the conductive material was prepared in this manner, the conductive material and the polyarylene ether ketone resin used in Example 1 were weighed out in a mass ratio within 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 371°C.

Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape using the same method as in Example 1. 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 393°C. After molding the conductive resin film for a current collector in this manner, a conductive resin film for a current collector was produced using the same method as in Example 1. The generation of die buildup during production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, chemical resistance, and conductivity of this conductive resin film for a current collector were each evaluated using the same methods as in Example 1 and are listed in Table 4. As a result, the conductivity of the conductive resin film for a current collector deteriorated.

Comparative Example 5
First, a conductive resin film for a current collector having a relative crystallinity of 37% was molded in the same manner as in Example 1 using the molding material composed of the polyarylene ether ketone resin and conductive material used in Example 3. However, while the temperatures of the pressure roll and the chill roll were 210°C and 220°C in Example 1, the conductive resin film for a current collector was molded into a strip shape at 100°C and 100°C in Comparative Example 5. 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.

Once the conductive resin film for the current collector was formed in this manner, it was manufactured in the same manner as in Example 1. The generation of die deposits during the manufacturing of the conductive resin film for the current collector, as well as the thickness, specific gravity, relative crystallinity, chemical resistance, and conductivity of this conductive resin film for the current collector were evaluated in the same manner as in Example 1, and the results are shown in Table 4. As a result, the chemical resistance of the conductive resin film for the current collector was deteriorated.

Comparative Example 6
To prepare the molding material, the polyarylene ether ketone resin was changed to polyamide 9T resin. Genestar N1000A-M42NA (product name, manufactured by Kuraray Co., Ltd., hereinafter abbreviated as "N1000A") was selected as the polyamide 9T resin, and this polyamide 9T resin (hereinafter abbreviated as PA9T resin) was pulverized by a freeze-pulverization method. This PA9T resin and the conductive material used in Example 1 were stirred and mixed in the mass ratios shown in Table 5 to prepare a stirred mixture.

The melting point 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 measured melting point of N1000A was 300°C.

The apparent shear viscosity of the PA9T resin was measured using a flow tester (Shimadzu Flow Tester CFT-500D, manufactured by Shimadzu Corporation). Specifically, the PA9T resin was dried in advance in a hot air dryer at 160°C for 12 hours, and then 1.5 ^cm3 of the PA9T resin was filled into a 360°C cylinder attached to a die (diameter: 1 mm, length: 10 mm). A plunger with an area of 1.0 ^cm2 was attached to the top of the cylinder. When the cylinder temperature reached 360°C, the cylinder was preheated for 5 minutes. Immediately after preheating, a load of 50 kgf was applied to melt and flow out the PA9T resin, and its apparent shear viscosity was measured.

Once the stirred mixture was prepared, it was fed into the co-rotating twin-screw extruder equipped with a vacuum pump used in Example 1, where it was melt-kneaded under reduced pressure, extruded into a rod shape from the die at the tip of the co-rotating twin-screw extruder, cooled with water, and cut to prepare a pellet-shaped molding material. The stirred mixture was melt-kneaded under conditions of a cylinder temperature of 330°C to 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 363°C.

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 φ20 mm single-screw extruder equipped with a 150 mm-wide T-die, as used in Example 1, and continuously extruded through the 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 (manufactured by Mitsubishi Chemical Corporation, product name: CA-100). The single-screw extruder was the same type as used in Example 1, with 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 340°C to 360°C, the temperature of the T-die to 360°C, and the temperature of the connecting pipe connecting the single-screw extruder to the T-die to 360°C. Furthermore, the temperature of the molten molding material was measured from the resin temperature at the T-die inlet, and was found to be 363°C. When feeding the molding material into this single-screw extruder, nitrogen gas was supplied at a rate of 15 L/min.

Once the conductive resin film for the current collector was manufactured, the presence or absence of die buildup during the manufacturing process, as well as the thickness, specific gravity, relative crystallinity, chemical resistance, and conductivity of the conductive resin film for the current collector were evaluated using the same methods as in Example 1, and the results are summarized in Table 5. When the conductive resin film for the current collector was immersed in NMP and electrolyte and then observed, it was found to have been deformed, making it impossible to fully evaluate its conductivity.

Comparative Example 7
To prepare a molding material, the polyarylene ether ketone resin was changed to a polyetherimide resin [polycondensate of 4,4'-[isopropylidenebis(p-phenyloxy)diphthalic dianhydride and m-phenylenediamine], manufactured by SABIC Corporation, product name: ULTEM 1010-1000-NB [product name manufactured by SABIC Corporation, (hereinafter abbreviated as "1010")]], and this polyetherimide resin (hereinafter abbreviated as PEI resin) was pulverized by a freeze-pulverization method.

To measure the melting point (also known as melting temperature) of 1010, a differential scanning calorimeter (manufactured by SII Nanotechnology Inc., product name: High-sensitivity Differential Scanning Calorimeter X-DSC7000) was used in accordance with JIS K7121 at a heating rate of 10°C/min, but no melting point was detected.

The apparent shear viscosity of the PEI resin was measured using a flow tester (Shimadzu Flow Tester CFT-500D, manufactured by Shimadzu Corporation). Specifically, the PEI resin was dried in a hot air dryer at 160°C for 12 hours, and then 1.5 ^cm3 of the PEI resin was filled into a 375°C cylinder attached to a die (diameter: 1 mm, length: 10 mm). A plunger with an area of 1.0 ^cm2 was attached to the top of the cylinder. When the cylinder temperature reached 375°C, the cylinder was preheated for 5 minutes. Immediately after preheating, a load of 50 kgf was applied to melt and flow the PEI resin, and its apparent shear viscosity was measured.

After the PEI resin was crushed, the PEI resin was stirred and mixed with the conductive material used in Example 1 in the mass ratio shown in Table 4 to prepare a stirred mixture. This stirred mixture was then fed into the co-rotating twin-screw extruder equipped with a vacuum pump used in Example 1, melt-kneaded under reduced pressure, and extruded into a rod shape from the die at the tip of the co-rotating twin-screw extruder. The rod was then cooled with water and cut to prepare a pellet-shaped molding material. The stirred mixture was melt-kneaded under conditions of a cylinder temperature of 350°C to 380°C, an adapter temperature of 380°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 383°C.

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 the φ20 mm single-screw extruder used in Example 1 and continuously extruded through a 150 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 (manufactured by Mitsubishi Chemical Corporation, product name: CA-100). The molding material was continuously extruded through a 150 mm wide T-die to form a strip-shaped conductive resin film for a current collector.

The single-screw extruder was the same type as used in Example 1, with 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 350°C to 380°C, the T-die temperature to 360°C, the temperature of the connecting pipe connecting the single-screw extruder and 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 T-die inlet and found to be 384°C. When the molding material was introduced into this single-screw extruder, nitrogen gas was supplied at a rate of 15 L/min.

Once the conductive resin film for the current collector was manufactured, the presence or absence of die buildup during the manufacturing process, as well as the thickness, specific gravity, chemical resistance, and conductivity of the conductive resin film for the current collector were evaluated using the same methods as in Example 1, and the results are summarized in Table 5.

Since the melting point of the conductive resin film for the current collector could not be determined, the relative crystallinity could not be calculated. Furthermore, when the conductive resin film for the current collector was immersed in NMP and electrolyte, the conductive resin film for the current collector dissolved, raising doubts about its practical use.

The conductive resin film for secondary battery current collectors and its manufacturing method according to the present invention are used in the manufacturing of various secondary batteries.

REFERENCE SIGNS LIST 1 Molding material 2 Polyarylene ether ketone resin 3 Conductive material 4 Conductive resin film for current collector 10 Melt kneader 12 Cylinder 13 Screw 14 Die 20 Melt extrusion molding machine 23 Die 26 Pressure roll 27 Cooling roll 28 Winder 29 Winding tube

Claims (5)

A conductive resin film for a current collector having a relative crystallinity of 80% or more is formed from a molding material containing 100 parts by mass of a polyarylene ether ketone resin and 5 parts by mass or more and 35 parts by mass or less of a conductive material,
the conductive material is composed of, in terms of composition mass ratio, 30% by mass or more and 99% by mass or less of carbon nanotubes and 1% by mass or more and 70% by mass or less of a conductive material other than carbon nanotubes;
The conductive material other than carbon nanotubes is a metal-based or carbon-based conductive material, has a shape of either a polyhedron, a sphere, or an ellipsoid, and has an average particle diameter of 0.1 μm or more and 10.0 μm or less;
A conductive resin film for a current collector of a secondary battery, characterized in that the resistance value measured by applying a pressure of 1 MPa to the conductive resin film for a current collector in the thickness direction is 1 mΩ· ^cm2 or more and 800 mΩ· ^cm2 or less. The conductive resin film for a current collector of a secondary battery according to claim 1, having a thickness of 10 μm or more and 500 μm or less, a specific gravity of 1.25 or more and 1.60 or less when measured in accordance with JIS K 7112 Method A, and a mass change rate of 2.0% or less when immersed in N-methyl-2-pyrrolidone and an electrolyte solution. The conductive resin film for a current collector of a secondary battery according to claim 1 or 2, wherein the polyarylene ether ketone resin is at least one of a polyether ether ketone resin and a polyether ketone ketone resin. A method for producing the conductive resin film for a current collector of a secondary battery according to claim 1 or 2, comprising:
a molding material containing 100 parts by mass of polyarylene ether ketone resin and 5 parts by mass or more and 35 parts by mass or less of a conductive material, the conductive material being composed of, in terms of composition mass ratio, 30% by mass or more and 99% by mass or less of carbon nanotubes and 1% by mass or more and 70% by mass or less of a conductive material other than carbon nanotubes;
A method for producing a conductive resin film for a current collector of a secondary battery, comprising extruding a molding material through a die into a conductive resin film for a current collector, and then cooling the film by sandwiching the film 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. 5. The method for producing a conductive resin film for a current collector of a secondary battery according to claim 4, wherein the cooled conductive resin film for a current collector is heat-compression molded, 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 and lower than the thermal decomposition temperature of the polyarylene ether ketone resin, and the pressure applied to the conductive resin film for a current collector is set to be equal to or higher than ^0.5 kgf/ ^cm2 and equal to or lower than 100 kgf/cm2 relative to the projected area of the conductive resin film for a current collector.