JP7723587B2 - 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. While not shown, lithium-ion secondary batteries are composed of a positive electrode, a negative electrode, a separator, an electrolyte, a container, and other components. The positive electrode (positive electrode plate) consists of a current collector plate and a positive electrode mixture containing a positive electrode active material formed on top of it. Positive electrode active materials used for this positive electrode include lithium cobalt oxide and lithium manganese oxide.

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

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 for the current collector. As mentioned above, metal foil is used for the current collectors of the positive and negative electrodes of lithium-ion secondary batteries, but using a conductive resin film, which has a lower specific gravity than metal, instead of this metal foil 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.

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-layer carbon tubes. Patent Document 3 also discloses a current collector for a bipolar lithium-ion secondary battery, which comprises a conductive resin layer (first conductive layer) formed by adding a conductive filler to a substrate containing an imide group-containing resin, and a conductive resin layer 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.

Furthermore, in the case of the current collector for secondary batteries described in Patent Document 2, ketjen black and multi-walled carbon nanotubes are used as conductive filler components. When ketjen black is used as a conductive filler component, it is not possible to add a large amount of ketjen black to the resin, making it impossible to achieve high conductivity for the current collector for secondary batteries. Furthermore, due to their brittleness, current collector plates containing ketjen black may be damaged when applying positive or negative electrode active material or when assembling them into secondary batteries.

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 plane-oriented orientation of the multi-walled carbon nanotubes, they have poor conductivity in the thickness direction. Furthermore, when tetrafluoroethylene-hexafluoropropylene copolymer is used as the resin component, the resin has a high specific gravity of 2.1 or more and 2.2 or less, which poses the problem of not contributing 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 the current collector may curl due to differences in expansion rate caused by water absorption after manufacturing, or that the current collector may peel between the first and second conductive layers.

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, and contributes to improved conductivity and weight reduction, as well as a method for producing the same.

After extensive research, the inventors focused on polyarylene ether ketone resin, which has the highest heat resistance of all thermoplastic resin materials and also excels in chemical resistance and mechanical properties, and lightweight carbon-based conductive materials, which have the highest conductivity of all conductive materials. They then completed the present invention using this polyarylene ether ketone resin and carbon-based conductive material.

That is, in order to solve the above-mentioned problems, the present invention provides a conductive resin film for a current collector of a secondary battery, which is formed from a molding material containing, in terms of composition mass ratios , 78 mass % or more and 97 mass % or less of a polyarylene ether ketone resin and 3 mass % or more and 25 mass % or less of a carbon-based conductive material, and has a relative crystallinity of 80% or more and 100% or less,
the apparent shear viscosity of the polyarylene ether ketone resin is 1×10 1 Pa·s or more and 1×10 4 Pa·s or less at 375°C, as measured with a flow tester using a die having a diameter of 1.0 mm and a length of 10 mm under conditions of a temperature of 375°C and a ^load of 50 ^kgf ;
The electrode is characterized by 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, and a volume resistivity of 10 Ω cm or more and 100 Ω cm or less when measured in accordance with JIS K 7194 .

Preferably, the thickness is 5 μm or more and 500 μm or less, the tensile elongation at break measured in accordance with JIS K 7127 is 10% or more and 500% or less, and the maximum tensile strength measured in accordance with JIS K 7127 is 70 MPa or more and 500 MPa or less.
Furthermore, the apparent shear viscosity of the molding material is preferably 1 x 101 Pa·s or more and 1 x 104 Pa ·s or less at 375°C, as measured with a flow tester using a die having a diameter of 1.0 mm and a length of 10 mm under conditions of a temperature of ³⁷⁵ °C and a load of ⁵⁰ kgf.

In order to solve the above problems, the present invention provides a method for producing a conductive resin film for a current collector of a secondary battery according to claim 1, 2, or 3, comprising the steps of:
The molding material is melt-kneaded and composed of 78% by mass or more and 97% by mass or less of a polyarylene ether ketone resin and 3% by mass or more and 25% by mass or less of a carbon-based conductive material in terms of composition mass ratio, and this molding material is extruded using a die to form 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 and 100% or less .

Furthermore, 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 conductive resin film for current collectors in the claims may be uniaxially stretched, biaxially stretched, or unstretched. This conductive resin film for current collectors includes not only thin conductive resin films for current collectors but also thick conductive resin sheets for current collectors. The molding material can be prepared into a conductive resin composition by stirring and mixing polyarylene ether ketone resin and a carbon-based conductive material such as carbon nanotubes, followed by melt-kneading.

The polyarylene ether ketone resin and carbon-based conductive material used as molding materials can be melt-kneaded at a temperature equal to or higher than the melting point of the polyarylene ether ketone resin and lower than the thermal decomposition temperature of the polyarylene ether ketone resin. Furthermore, secondary batteries according to the present invention include at least nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium-ion secondary batteries, bipolar lithium-ion secondary batteries, and all-solid-state batteries.

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

According to the present invention, the chemical resistance of the conductive resin film for a current collector is improved to prevent a decrease in the charge/discharge cycle characteristics of the secondary battery, and further, peeling of the current collector of the secondary battery is prevented, contributing to improved conductivity and weight reduction. Furthermore, the present invention has the effect of enabling the provision of a secondary battery at low cost. Furthermore, since the relative crystallinity of the conductive resin film for a current collector is 80% or more and 100% or less, problems with the mechanical strength, heat resistance, chemical resistance, and solvent resistance of the conductive resin film for a current collector can be prevented, and the mechanical strength, heat resistance, and chemical resistance sufficient for use as a conductive resin film for a current collector can be expected.
The apparent shear viscosity of the polyarylene ether ketone resin, measured with a flow tester using a die having a diameter of 1.0 mm and a length of 10 mm under a load of 50 kgf at 375°C, is 1 x 101 ^Pa ·s or more and 1 x 104 ^Pa ·s or less. This prevents a decrease in melt tension, which makes molding of the molding material difficult, and also prevents an increase in melt viscosity and a decrease in melt elongation. Furthermore, the conductive resin film for a current collector exhibits a mass change of 0.0% or more and 2.0% or less when immersed in N-methyl-2-pyrrolidone and an electrolyte solution, thereby achieving excellent chemical resistance. Furthermore, the conductive resin film for a current collector has a low volume resistivity of 10 Ω·cm or more and 100 Ω·cm or less, which prevents a decrease in energy density even when used as a current collector for a secondary battery.

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

According to the third aspect of the present invention, the conductive resin film for current collector has excellent formability and can be expected to have sufficient mechanical strength.

According to the invention of claim 4, the conductive resin film for a current collector is produced by melt extrusion molding, which is expected to improve the thickness accuracy, productivity, and handling properties of the conductive resin film for a current collector, and to simplify the production equipment.

According to the invention of claim 5 , the melt-extruded conductive resin film for a current collector is further subjected to heat compression molding, which makes it possible to lower the resistance value, increase the conductivity, and reduce the amount of carbon-based conductive material used, thereby reducing costs.

1 is an overall explanatory view schematically illustrating a melt-kneader in an embodiment of a conductive resin film for a current collector of a secondary battery and a method for producing the same according to the present invention. 1 is an overall explanatory diagram schematically illustrating a melt extrusion molding apparatus in an embodiment of a conductive resin film for a current collector of a secondary battery and a method for producing the same according to the present invention.

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

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

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

In contrast, if the composition mass ratio of polyarylene ether ketone resin 2 exceeds 97 mass%, the volume resistivity of conductive resin film 5 for current collector exceeds 100 Ω·cm, making it impossible to impart sufficient conductivity to conductive resin film 5 for current collector, making it difficult to use as a current collector for a secondary battery.

Such molding material 1 may include, in addition to polyarylene ether ketone resin 2 and carbon-based conductive material 3, polyolefin resins such as polyethylene (PE) resin, polypropylene (PP) resin, polymethylpentene (PMP) resin, and polystyrene (PS) resin, acid-modified olefin resins such as maleic anhydride-modified polyethylene resin and maleic anhydride-modified polypropylene resin, polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, and polyethylene naphthalate (PEN) resin, as long as the properties of the present invention are not impaired. Polyimide resins such as polyester resins, polyimide (PI) resin, polyamideimide (PAI) resin, polyetherimide (PEI) resin, etc.; polyamide resins such as 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.; polysulfone (PSU) resin; polysulfone resins such as teresulfone (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, and tetrafluoroethylene-hexafluoropropyl copolymer (FEP) resin; Fluororesins such as tetrafluoroethylene-ethylene copolymer (ETFE) resin, polychlorotrifluoroethylene (PCTFE) resin, polyvinylidene fluoride (PVdF) resin, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer resin, and acid-modified fluororesins, as well as thermoplastic resins such as polycarbonate (PC) resin, polyarylate (PAR) resin, polyacetal (POM) resin, liquid crystal polymer (LCP), aliphatic polyketone resin, polyimide resin, and polyamide-imide resin can be selectively added.

In addition to the polyarylene ether ketone resin 2, carbon-based 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, 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 5 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 composition mass ratio of the carbon-based conductive material 3 in the molding material 1 is preferably 3% by mass or more and 25% by mass or less, preferably 5% by mass or more and 22% by mass or less, and more preferably 10% by mass or more and 20% by mass or less. Examples of this carbon-based conductive material 3 include carbon blacks such as furnace black (oil furnace black and gas furnace black), channel black, acetylene black, and thermal black; carbon nanotubes 4, carbon nanofibers, fullerenes, amorphous carbon, carbon fibers such as bread-based carbon fiber and pitch-based carbon fiber; and graphites such as flake graphite, lump graphite, earthy graphite, expanded graphite obtained by chemically treating flake graphite with concentrated sulfuric acid or the like followed by heating; expanded graphite obtained by heat-treating expanded graphite at high temperatures; and artificial graphite.

Among these carbon-based conductive materials 3, carbon nanotubes 4 are optimal because they can provide high conductivity with a small amount and can be used to form the conductive resin film 5 for the current collector without losing the mechanical strength of the current collector. Because these carbon nanotubes 4 have a cylindrical hollow fiber structure, they are expected to contribute to weight reduction. Carbon nanotubes 4 include single-walled carbon nanotubes, which have a structure in which one surface of graphite is wrapped around them, and multi-walled carbon nanotubes, which have two or more layers wrapped around them, but there are no particular limitations.

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

The fiber diameter (outer diameter) of the carbon nanotubes 4 is not particularly limited, but is preferably 0.5 nm or more and 200 nm or less. Such carbon nanotubes 4 can be produced by known production methods. For example, they can be produced by (1) the arc discharge method, (2) the laser evaporation method, or (3) 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 "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.

Examples of products of the carbon nanotubes 4 include, for example, 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 (Hyperion Examples include Catalysis International (product name).

Other metallic or carbon-based conductive materials may be added to the carbon nanotubes 4 as long as the properties of the present invention are not impaired. 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.

The carbon-based conductive material 3 may be in any form, such as powder, granules, lumps, fibers, etc. One type may be used alone, or two or more types may be used in combination. Furthermore, the carbon-based conductive material 3 can be treated with various coupling agents, such as silane coupling agents (3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-aminopropylethoxysilane, imidazole silane, etc.), titanate coupling agents (isopropyl triisostearoyl titanate, tetraoctylbis(dioctylphosphite)titanate, bis(dioctylpyrophosphate)oxyacetate titanate, tetraisopropylbis(dioctylphosphite)titanate, isopropyltri(N-amitoethylaminoethyl)titanate, etc.), and aluminate coupling agents (acetoalkoxyaluminum diisopropylate, etc.), as long as the properties of the collector conductive resin film 5 are not impaired.

The apparent shear viscosity of molding material 1 is measured using a flow tester with 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, and is preferably in the range of 1 x ¹⁰¹ Pa·s or more and 1 x ¹⁰⁴ Pa·s or less, preferably 1 x ¹⁰² Pa·s or more and 5 x ¹⁰³ Pa·s or less, and more preferably 5 x ¹⁰² Pa·s or more and 2 x ¹⁰³ Pa·s or less.

This is because, when the apparent shear viscosity is in the range of 1×10 ¹ Pa·s or more and 1×10 ⁴ Pa·s or less, the conductive resin film 5 for a current collector has excellent formability and can be expected to have sufficient mechanical strength. On the other hand, when the apparent shear viscosity is less than 1×10 ¹ Pa·s, the apparent shear viscosity becomes low and the melt tension decreases, making it difficult to form the conductive resin film 5 for a current collector. On the other hand, when the apparent shear viscosity exceeds 1×10 ⁴ Pa·s, the melt viscosity becomes high and the melt elongation decreases, which may cause holes to form in the conductive resin film 5 for a current collector and cause rupture, resulting in difficulties in forming the conductive resin film 5 for a current collector.

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

Methods for preparing molding material 1 include: (1) a method in which carbon nanotubes 4 are introduced into a melt mixer 10 for molding material 1 and 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 and carbon nanotubes 4 are agitated and mixed at room temperature (a temperature of approximately 0°C or higher and 50°C or lower) using an agitator mixer, followed by melt-extrusion kneading in melt mixer 10 to prepare molding material 1.

First, to explain the preparation method (1) in detail, in this method, a specified melt kneader 10 as shown in Figure 1 is prepared, polyarylene ether ketone resin 2 is introduced into this melt kneader 10 and melted, and then carbon nanotubes 4 are newly introduced into the melt kneader 10 using a side feeder method or the like and melt-kneaded with the already melted 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 multi-screw extruder consisting of a twin-screw extruder, triple-screw extruder, quadruple-screw extruder, or 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 and the carbon nanotubes 4 and can remove moisture and the volatile gases generated from them.

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

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 is mounted at the upper downstream side of the cylinder 12. By feeding finely powdered carbon nanotubes 4 laterally into the side feeder 16, which is located downstream of the inlet 15, the carbon nanotubes 4 are injected into the molten polyarylene ether ketone resin 2, improving the uniform dispersion of the molding material 1. Furthermore, since the kneading time of the carbon nanotubes 4 with the polyarylene ether ketone resin 2 is shortened, decomposition can also be prevented.

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

This is because, if the temperature is below the melting point of the polyarylene ether ketone resin 2, the polyarylene ether ketone resin 2 and the carbon nanotubes 4 cannot be melt-kneaded and dispersed. 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 and carbon nanotubes 4 are extruded from a die 14 as strands to prepare strand molding material 1. However, after being extruded from the die 14 as a crystalline thermoplastic resin film, molding material 1 may be prepared in powder, granules, flakes, or pellets. Furthermore, when preparing molding material 1, a predetermined amount or more of either polyarylene ether ketone resin 2 or carbon nanotubes 4 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 the polyarylene ether ketone resin 2 and carbon nanotubes 4 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 that can be more uniformly dispersed with the carbon nanotubes 4. Methods for pulverizing into a powder include, for example, shear pulverization, impact pulverization, collision pulverization, freeze pulverization, and solution pulverization.

After stirring and mixing, the polyarylene ether ketone resin 2 and the carbon nanotubes 4 are melt-kneaded and dispersed in a melt kneader 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 molding material 1. A vent-type multi-screw extruder is preferred as the melt kneader, as this is expected to achieve good kneading and dispersion of the polyarylene ether ketone resin 2 and the carbon nanotubes 4 and can degas the moisture and volatile gases generated by them. Furthermore, when preparing molding material 1, either the polyarylene ether ketone resin 2 or the carbon nanotubes 4 can be dispersed in a predetermined amount or more to form a masterbatch.

The moisture content (water content) of molding material 1 before melt extrusion is adjusted using a hot air dryer or similar to 2000 ppm or less, preferably 1000 ppm or less, and more preferably 500 ppm or less. This is because a moisture content exceeding 2000 ppm may cause foaming of the conductive resin film 5 for current collector.

It is preferable that molding material 1 be heated and dried to reduce its moisture content before melt-kneading. Heat-drying methods include known methods such as hot air circulation drying, dehumidified hot air drying, heated vacuum drying, and microwave drying. The heating and drying temperature for 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 heat drying time for molding material 1 should be at least 2 hours, preferably at least 4 hours, and more preferably at least 8 hours. There is no particular upper limit to the heat drying time, but 24 hours or less is appropriate.

Once molding material 1 is prepared, conductive resin film 5 for current collectors is manufactured using this molding material 1. Manufacturing methods that can be used include melt extrusion, calendar molding, and casting. Among these manufacturing methods, melt extrusion, which continuously extrudes conductive resin film 5 for current collectors into a strip, is optimal from the standpoints of improving the thickness accuracy, productivity, and ease of handling of conductive resin film 5 for current collectors, and simplifying the equipment.

The melt extrusion molding method involves melt-kneading molding material 1 using a melt extruder 20, continuously extruding conductive resin film 5 for a current collector from a die 23, such as a T-die or a round die, connected to the tip of the melt extruder 20, thereby producing conductive resin film 5 for a current collector (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 molding material 1 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 the polyarylene ether ketone resin +10°C to the melting point of the polyarylene ether ketone resin +100°C, preferably from the melting point of the polyarylene ether ketone resin +20°C to the melting point of the polyarylene ether ketone resin +80°C, more preferably from the melting point of the polyarylene ether ketone resin +30°C to the melting point of the polyarylene ether ketone resin +60°C, and even more preferably from the melting point of the polyarylene ether ketone resin +30°C to the melting point of the polyarylene ether ketone resin +50°C.

This is because, if the temperature is below the melting point of the polyarylene ether ketone resin 2, the polyarylene ether ketone resin 2 and the carbon nanotubes 4 cannot be melt-kneaded and dispersed. Conversely, if the temperature is above the thermal decomposition temperature, this undesirably leads to decomposition of the polyarylene ether ketone resin 2.

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

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

This is because, if the temperature is below the melting point of the polyarylene ether ketone resin 2, the polyarylene ether ketone resin 2 and the carbon nanotubes 4 cannot be melt-kneaded and dispersed. 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.

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 so that they slide against each other. Of these cooling rolls 27, the upstream cooling roll 27 and the downstream cooling roll 27 slide against the circumferential surface of the pressure roll 26, respectively. Each pressure roll 26 and each cooling roll 27 is configured so that the pressure roll 26 has a reduced diameter and the cooling roll 27 has an expanded diameter.

A winder 28 is installed downstream of the downstream pressure roll 26 of the pair of pressure rolls 26, winding the collector conductive resin film 5 onto a rotatable winding tube 29. Between this winder 28 and the downstream pressure roll 26, a slit blade 30 is positioned so that it can move up and down, forming a slit in the longitudinal direction of the side of the collector conductive resin film 5. 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 collector conductive resin film 5 for smooth winding.

Each pressure roll 26 is adjusted to a temperature of 50°C or higher but lower than the melting point of the polyarylene ether ketone resin 2, preferably 100°C or higher (melting point of polyarylene ether ketone resin - 50°C) or lower, more preferably 130°C or higher (melting point of polyarylene ether ketone resin - 100°C) or lower, and even more preferably 150°C or higher (melting point of polyarylene ether ketone resin - 100°C) or lower, and slides against the conductive resin film 5 for the current collector, pressing it against the cooling roll 27.

The reason why the temperature of the pressure roll 26 is within this range is because condensation will form on the pressure roll 26 if the temperature is below 50°C. Conversely, if the temperature exceeds the melting point, the conductive resin film 5 for the current collector may stick to the circumferential surface of the pressure roll 26 and break, or the strength of the conductive resin film 5 for the current collector may decrease, leading to breakage. Methods for adjusting the temperature of the pressure roll 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 5 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 5 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 5 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 5 and control 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 - 50°C), more preferably 130°C or higher (melting point of polyarylene ether ketone resin - 100°C), and even more preferably 150°C or higher (melting point of polyarylene ether ketone resin - 100°C). The cooling roll 27 slides against the collector conductive resin film 5 and presses it against the 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 5 for a current collector, this conductive resin film 5 for a current collector is wound around a pair of pressure rolls 26, a cooling roll 27, a tension roll 31, and a take-up tube 29 of a winder 28. Both sides of the conductive resin film 5 for a current collector are cut longitudinally with a slit blade 30, and the film is sequentially wound around the take-up tube 29 of the winder 28, thereby producing a long conductive resin film 5 for a current collector.

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

Conversely, if the thickness of the conductive resin film 5 for current collectors exceeds 500 μm, 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 thickness of this conductive resin film 5 for current collectors can be measured using various contact thickness gauges. Alternatively, the thickness can be determined by averaging multiple measurements.

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

On the other hand, if the specific gravity of the conductive resin film 5 for current collector exceeds 1.60, it will hinder weight reduction when used as a current collector for 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 5 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 5 for current collectors is optimally 80% or higher, preferably 90% or higher, more preferably 95% or higher, and even more preferably 100%. This is because if the relative crystallinity of the conductive resin film 5 for current collectors is less than 80%, problems will arise with the mechanical strength, heat resistance, chemical resistance, and solvent resistance of the conductive resin film 5 for current collectors. In contrast, if the relative crystallinity is greater than 80%, the conductive resin film 5 can be expected to have sufficient mechanical strength, heat resistance, and chemical resistance to be usable as a conductive resin film for current collectors.

The crystallinity of the conductive resin film 5 for a current collector can be expressed by a relative crystallinity, which is calculated by the following formula based on the results of thermal analysis measured at a temperature rise 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 mechanical properties of the conductive resin film 5 for current collectors can be expressed in terms of tensile modulus, tensile elongation at break, and maximum tensile strength. When measured in accordance with JIS K 7127, the tensile modulus of the conductive resin film 5 for current collectors is 2000 MPa or more, preferably 3000 MPa or more, more preferably 3500 MPa or more, and even more preferably 4000 MPa or more. There are no particular restrictions on the upper limit of this tensile modulus, but it is preferably 10,000 MPa or less.

This is because if the tensile modulus is less than 2000 MPa, when the current collector conductive resin film 5 is used as a current collector for a secondary battery, the current collector conductive resin film 5 will have poor rigidity, and there is a risk that the current collector conductive resin film 5 will deform during the coating process of the positive electrode active material or negative electrode active material, or during assembly of the secondary battery. In contrast, if the tensile modulus exceeds 10,000 MPa, the current collector conductive resin film 5 will be too rigid and will not be able to be wound up.

The tensile elongation at break of the conductive resin film 5 for current collectors, as measured in accordance with JIS K 7127, is preferably 10% or more, preferably 15% or more, more preferably 20% or more, and even more preferably 25% or more. This is because if the tensile elongation at break of the conductive resin film 5 for current collectors is less than 10%, the conductive resin film 5 for current collectors will have poor toughness and will crack during its manufacture. Furthermore, this is because the conductive resin film 5 for current collectors will crack during the process of applying the positive or negative electrode active material to the conductive resin film 5 for current collectors. While there are no particular restrictions on the upper limit of this tensile elongation at break, it is preferable that it be 500% or less. This is because if it exceeds 500%, the conductive resin film 5 for current collectors will stretch during the process of applying the positive or negative electrode active material to the conductive resin film 5 for current collectors.

The maximum tensile strength of the conductive resin film 5 for the current collector, as measured in accordance with JIS K 7127, should be 60 MPa or more, preferably 70 MPa or more, more preferably 90 MPa or more, and even more preferably 100 MPa or more. This is because if the maximum tensile strength of the conductive resin film 5 for the current collector is less than 60 MPa, the conductive resin film 5 for the current collector will have poor toughness and may crack during its manufacture. Also, the conductive resin film 5 for the current collector may crack during the process of coating the positive electrode active material or negative electrode active material of the conductive resin film 5 for the current collector.

There are no particular restrictions on the upper limit of the maximum tensile strength, but it is preferably 500 MPa or less. This is because if it exceeds 500 MPa, the cutting ability with the slit blade 30 will decrease during the production of the conductive resin film 5 for current collectors, which is undesirable as it will slow down the production speed of long conductive resin film 5 for current collectors.

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

The chemical resistance of the conductive resin film 5 for current collectors can be evaluated by immersing the conductive resin film 5 for current collectors 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 rate of mass change when the conductive resin film 5 for current collectors 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 for current collector 5, current collector plates using conductive resin film for current collector 5 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 plate, reducing the charge/discharge cycle.

The molded conductive resin film 5 for current collectors can be used as is, or it can be further heat-compression molded. Heat-compression molding the conductive resin film 5 for current collectors can lower the resistance value, increase conductivity, and reduce the amount of carbon-based conductive material 3 used, thereby reducing costs.

When the conductive resin film 5 for a current collector is subjected to heat compression molding, the conductive resin film 5 for a current collector is sandwiched between a plurality of metal plates, metal rolls, or metal belts that have been heated to a temperature not lower than the melting point of the polyarylene ether ketone resin 2 but lower than the thermal decomposition temperature of the polyarylene ether ketone resin 2, specifically, a temperature not lower than the melting point of the polyarylene ether ketone resin + 10°C and not higher than the melting point of the polyarylene ether ketone resin + 100°C, preferably not lower than the melting point of the polyarylene ether ketone resin + 20°C and not higher than the melting point of the polyarylene ether ketone resin + 80°C, more preferably not lower than the melting point of the polyarylene ether ketone resin + 30°C and not higher than the melting point of the polyarylene ether ketone resin + 60°C, and even more preferably not lower than the melting point of the polyarylene ether ketone resin + 30°C and not higher than the melting point of the polyarylene ether ketone resin + 50°C, and a pressure of 0.5 kgf/cm2 or ^more and 100 kgf/cm2 is applied to the projected area of the conductive resin film 5 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 5. Therefore, even if current collector conductive resin film 5 is used as a current collector, electrolyte components do not penetrate into the current collector conductive resin film 5, 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 coefficients caused by water absorption after production, or peeling of the current collector between the first and second conductive layers. Furthermore, when the carbon-based conductive material 3 is carbon nanotubes 4, it is not only chemically stable but also further improves the weight reduction of secondary batteries. Furthermore, since the thickness of the conductive resin film 5 for the current collector is 5 μm or more and 500 μm or less, a decrease in the tensile strength of the conductive resin film 5 for the current collector is prevented, and significant weight reduction of the current collector for secondary batteries can be expected.

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

In the above embodiment, the polyarylene ether ketone resin 2 may be used singly or in the form of an alloy or blend of two or more types. The polyarylene ether ketone resin 2 may be in any form, including powder, granules, lumps, powder, and pellets. The conductive resin film 5 for the current collector may have a specific gravity of 1.23 to 1.60 as measured in accordance with JIS K7112 Method A, a relative crystallinity of 95% to 100%, a tensile modulus of 3500 MPa to 5300 MPa as measured in accordance with JIS K 7127, a tensile elongation at break of 10% to 65%, and a volume resistivity of 1 Ω·cm to 100 Ω·cm as measured in accordance with JIS K 7194.

In addition, in order to take advantage of the characteristics of the carbon nanotubes 4, multiple types of carbon nanotubes 4 with different outer diameters and lengths may be mixed and used. 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 the molding material, a commercially available polyether ether ketone resin (manufactured by Solvay Specialty Polymers, product name: KetaSpire PEEK KT-851NL SP, hereinafter abbreviated as "KT-851NL SP") was prepared as the polyarylene ether ketone resin, and this polyether ether ketone resin was pulverized by a freeze-pulverization method. Hereinafter, this polyether ether ketone resin will be abbreviated as "PEEK resin."

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

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

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 pre-dried at 160°C for 12 hours in a hot air dryer, and 1.5 ^cm3 of the PEEK resin was filled into a 375°C cylinder equipped with 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 a temperature of 375°C, it was preheated for 5 minutes. Immediately after preheating, a load of 50 kgf was applied, causing the PEEK resin to melt and flow out, and its apparent shear viscosity was measured. The apparent shear viscosity was measured in the same manner below.

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

Once the molding material was prepared, the apparent shear viscosity of this molding material was measured. The apparent shear viscosity of this molding material was measured using a flow tester (Shimadzu Corporation, product name: Shimadzu Flow Tester CFT-500D). Specifically, the molding material was dried in a hot air dryer at 160°C for 12 hours, and then 1.5 ^cm3 of the molding material was filled into a 375°C cylinder equipped with 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, it was preheated for 5 minutes. Immediately after this preheating, a load of 50 kgf was applied, causing the molding material to melt and flow out, and its apparent shear viscosity was measured. The apparent shear viscosity was measured using the same method below.

The prepared molding material was then placed in a dehumidifying hot air dryer heated to 160°C and dried for at least 12 hours. After confirming that the moisture content of the dried molding material was 300 ppm or less, the molding material was placed in a φ40 mm single-screw extruder and continuously extruded through a 900 mm wide T-die to form a strip-shaped conductive resin film for the current collector. The 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. The temperature of the single-screw extruder was adjusted to 360-395°C, the temperature of the T-die to 395°C, the temperature of the connecting pipe connecting the single-screw extruder to the T-die to 395°C, and the gear pump to 395°C. The temperature of the molten molding material was measured from the resin temperature at the 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 210°C pressure rolls made of silicone rubber, multiple 210°C cooling rolls, and a 6-inch take-up tube located downstream of these, as shown in Figure 2, and sandwiched between the pressure rolls and cooling rolls. Both sides of the continuous conductive resin film for the current collector were cut with a slit blade and sequentially wound onto the take-up tube, producing a conductive resin film for the current collector measuring 100 m in length and 650 mm in width. A slit blade that cuts both sides of the conductive resin film for the current collector was positioned between the pressure rolls and the take-up tube and was capable of moving up and down, and a tension roll that applies tension to the conductive resin film for the current collector was rotatably supported between the take-up tube and the slit blade.

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

- Die resin generated during production of conductive resin film for current collector Regarding die resin generated during production of conductive resin film for current collector, after producing 100 m of conductive resin film for current collector, the vicinity of the lip of the T-die was visually observed.

The 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 random locations in 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 K 7112 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 out 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: EXSTAR7000 series 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

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

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 change in mass.

To evaluate the mass change of the conductive resin film for a current collector, the conductive resin film for a current collector was cut into a size of MD: 50 mm × TD: 80 mm and weighed [W0 _] . This conductive resin film for a current collector and 5 g of NMP or 5 g of electrolyte were placed in a PET/AL/PE flat bag [manufactured by Nippon Seisaku Co., Ltd.: product name Lamizip] and sealed by heat sealing. The electrolyte used was an electrolyte for lithium primary/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 %].

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 23°C for 24 hours. Thereafter, the conductive resin film for a current collector was weighed [W ₁ ], and the mass change rate was calculated using the following formula and evaluated as A to F.

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

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

Heat Resistance of Conductive Resin Film for Current Collector The heat resistance of the conductive resin film for current collector was evaluated by the change in dimension due to heating.
The dimensional change upon heating was measured in both MD and TD. This measurement was performed in accordance with JIS K 7133, where the sample was heated at 250°C for 10 minutes, and the dimensional change rate before and after heating was evaluated. The dimensional change rate was calculated and evaluated using the following formula:
Dimensional change rate (%)={(L ₁ −L ₀ )/L ₀ }×100
L ₀ : Dimension of the conductive resin film for current collector before heating [mm]
_L1 : Dimensions of the conductive resin film for current collector and after heating [mm]

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

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

Example 3
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 381G (product name of Victrex Corporation; hereinafter abbreviated as "381GG"), which had been previously pulverized by the method of Example 1, and the carbon nanotubes used in Example 1 were weighed to obtain the composition and mass shown in Table 1, to prepare a stirred mixture. The apparent shear viscosity of 381G was measured by the same method as in Example 1. The melting point of 381G was measured by 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 375°C. Once the molding material was prepared, the apparent shear viscosity of this molding material was measured using the same method as in Example 1.

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, another conductive resin film for a current collector was produced in the same manner 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, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and the results are summarized in Table 1.

Example 4
The experiment 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 (product name of Victrex Co., Ltd., hereinafter abbreviated as "450G") which had been pulverized in advance by the method of Example 1.

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

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

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 400°C. After molding, the conductive resin film for a current collector was produced in the same manner as in Example 1, and the generation of die buildup during the production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and are listed 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 previously pulverized by the method of Example 1, and the components were weighed out to obtain the composition and mass shown in Table 2 to prepare a stirred mixture. The apparent shear viscosity of 151G was measured by the same method as in Example 1. The melting point of 151G was measured by the same method as in Example 1 and was found to be 341°C.

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

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 395°C. After molding, the conductive resin film for a current collector was produced in the same manner as in Example 1, and the generation of die buildup during the production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and are listed in Table 2.

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

The apparent shear viscosity of 8003 was measured using a flow tester (Shimadzu Flow Tester CFT-500D, manufactured by Shimadzu Corporation). Specifically, 8003 was first dried in a hot air dryer at 160°C for 12 hours, and then 1.5 ^cm3 of 8003 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 out the PEKK resin, and its apparent shear viscosity was measured.

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

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 395°C. After molding, the conductive resin film for a current collector was produced in the same manner as in Example 1, and the generation of die buildup during the production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and are listed in Table 2.

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

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, another conductive resin film for a current collector was produced in the same manner 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, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and the results are summarized in Table 3.

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

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 403°C. After molding the conductive resin film for a current collector in this manner, another conductive resin film for a current collector was produced in the same manner as in Example 1. The generation of die buildup during the production of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and the results are summarized in Table 3.

Comparative Example 3
First, a conductive resin film for a current collector was molded using the molding material composed of the polyarylene ether ketone resin and carbon nanotubes used in Example 3. The molding of the conductive resin film for a current collector was carried out in the same manner as in Example 1. However, while the temperatures of the pressure roll and the chill roll were 220°C and 210°C 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 3. 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 way, 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, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for the current collector were evaluated and the results are summarized in Table 3.

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

The melting point (also known as melting temperature) of N1000A resin was measured using a differential scanning calorimeter (manufactured by SII Nanotechnology Inc., 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 N1000A was measured using a flow tester (Shimadzu Flow Tester CFT-500D, manufactured by Shimadzu Corporation). Specifically, PA9T resin was dried in a hot air dryer at 160°C for 12 hours, and then 1.5 ^cm3 of 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, it was preheated for 5 minutes. Immediately after preheating, a load of 50 kgf was applied, causing the PA9T resin to melt and flow out, and its apparent shear viscosity was measured. After pulverizing the PA9T resin, this PA9T resin was stirred and mixed with FloTube 9000, the carbon nanotubes used in Example 4, in the compositional mass ratios shown in Table 4 to prepare a stirred mixture.

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

After preparing the molding material, the apparent shear viscosity of this molding material was measured in the same manner as in Example 1. The apparent shear viscosity of this molding material was measured using a flow tester (Shimadzu Flow Tester CFT-500D, manufactured by Shimadzu Corporation). Specifically, the molding material was dried in a hot air dryer at 160°C for 12 hours, and then 1.5 ^cm3 of the molding material 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, it was preheated for 5 minutes. Immediately after preheating, a load of 50 kgf was applied, causing the N1000A to melt and flow out, and its apparent shear viscosity was measured.

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

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

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

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

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

The apparent shear viscosity of 1010 was measured using a flow tester (Shimadzu Flow Tester CFT-500D, manufactured by Shimadzu Corporation). Specifically, the PEI resin was dried in advance in a hot air dryer at 160°C for 12 hours, and then 1.5 ^cm3 of 1010 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 temperature of the cylinder reached 375°C, it was preheated for 5 minutes. Immediately after this preheating, a load of 50 kgf was applied, causing the 1010 to melt and flow out, and its apparent shear viscosity was measured.

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

After preparing the molding material, the apparent shear viscosity of this molding material was measured in the same manner as in Example 1. The apparent shear viscosity of this molding material was measured using a flow tester (Shimadzu Flow Tester CFT-500D, manufactured by Shimadzu Corporation). Specifically, the molding material was dried in a hot air dryer at 160°C for 12 hours, and then 1.5 ^cm3 of the molding material 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. Once the cylinder temperature reached 360°C, the cylinder was preheated for 5 minutes. Immediately after preheating, a load of 50 kgf was applied, causing the PEI resin to melt and flow out, and its apparent shear viscosity was measured.

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

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

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

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

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

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 403°C. After molding, the conductive resin film for a current collector was manufactured in the same manner as in Example 1, and the generation of die buildup during the manufacturing of the conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, electrical conductivity, chemical resistance, and heat resistance of this conductive resin film for a current collector were evaluated and are listed in Table 4.

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

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

The conductive resin film for a current collector of a secondary battery and its manufacturing method according to the present invention are used in the manufacturing of secondary batteries such as nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium-ion secondary batteries, and all-solid-state batteries.

REFERENCE SIGNS LIST 1 Molding material 2 Polyarylene ether ketone resin 3 Carbon-based conductive material 4 Carbon nanotubes 5 Conductive resin film for current collector 10 Melt kneader 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 of a secondary battery, which is formed from a molding material containing, in terms of composition mass ratios , 78 % by mass or more and 97% by mass or less of a polyarylene ether ketone resin and 3% by mass or more and 25 % by mass or less of a carbon-based conductive material, and has a relative crystallinity of 80% or more and 100% or less,
the apparent shear viscosity of the polyarylene ether ketone resin is 1×10 1 Pa·s or more and 1×10 4 Pa·s or less at 375°C, as measured with a flow tester using a die having a diameter of 1.0 mm and a length of 10 mm under conditions of a temperature of 375°C and a ^load of 50 ^kgf ;
A conductive resin film for a current collector of a secondary battery, characterized in that the mass change rate when immersed in N-methyl-2-pyrrolidone and an electrolyte solution is 0.0% or more and 2.0% or less, and the volume resistivity when measured in accordance with JIS K 7194 is 10 Ω cm or more and 100 Ω cm or less . 2. The conductive resin film for a current collector of a secondary battery according to claim 1, which has a thickness of 5 μm or more and 500 μm or less, a tensile elongation at break measured in accordance with JIS K 7127 of 10% or more and 500% or less, and a maximum tensile strength measured in accordance with JIS K 7127 of 70 MPa or more and 500 MPa or less . 3. The conductive resin film for a current collector of a secondary battery according to claim 1 or 2, wherein the apparent shear viscosity of the molding material is 1 x 10 ¹ Pa·s or more and 1 x 10 ⁴ Pa·s or less at 375°C, as measured with a flow tester using a die having a diameter of 1.0 mm and a length of 10 mm under conditions of a temperature of 375°C and a load of 50 kgf. A method for producing the conductive resin film for a current collector of a secondary battery according to claim 1, 2, or 3, comprising the steps of:
A method for producing a conductive resin film for a current collector of a secondary battery, comprising melt-kneading a molding material composed of, in mass ratios of 78% by mass or more and 97% by mass or less, a polyarylene ether ketone resin and 3% by mass or more and 25% by mass or less, a carbon-based conductive material, and extruding the molding material through a die to form a conductive resin film for a current collector, and then cooling the film by sandwiching it between a pressure roll and a cooling roll, thereby making the relative crystallinity of the conductive resin film for a current collector 80% or more and 100% or less . 5. The 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, 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.