JP7804536B2 - 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, but among these high-performance secondary batteries, lithium-ion secondary batteries and all-solid-state batteries in particular are attracting attention.

A lithium-ion secondary battery is composed of a positive electrode, a negative electrode, a separator, an electrolyte, a container, and other components (not shown). The positive electrode (positive plate) consists of a current collector plate and a positive electrode mixture containing a positive electrode active material formed on top of it. The positive electrode active material in this positive electrode mixture is lithium cobalt oxide or lithium manganese oxide, for example. In contrast, the negative electrode (negative plate) consists of a current collector plate and a negative electrode mixture formed on both sides of it. The negative electrode active material in this negative electrode mixture 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 the excellent characteristics of high energy density, high operating voltage, a long life cycle, and low self-discharge, and are therefore used in a wide variety of fields. For example, they are widely used as power sources in 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 positive and negative electrode current collectors 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-walled carbon nanotubes. 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. However, 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, current collector plates containing ketjen black are brittle and may be damaged when applying positive or negative electrode active materials or when assembling them into secondary batteries.

In addition, conductive resin layers manufactured from a raw material mixture using multi-walled carbon nanotubes as the conductive filler, rather than Ketjen black, have the problem that, because the multi-walled carbon nanotubes are oriented in the plane direction, they have excellent conductivity in the plane direction but poor conductivity in the thickness direction. Furthermore, if tetrafluoroethylene-hexafluoropropylene copolymer is used as the resin component, the specific gravity of the resin is high, at 2.1 or more and 2.2 or less, which may make it difficult to reduce 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 the problem of 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 polyether ether ketone resin, which has the highest heat resistance of all thermoplastic resin materials and also excels in chemical resistance and mechanical properties, and carbon-based conductive materials, which are lightweight and have excellent conductivity. They then completed the present invention using these polyether ether ketone resin and carbon-based conductive materials.

In other words, in order to solve the above-mentioned problems, the present invention is characterized by comprising 100 parts by mass of a polyether ether ketone resin composition containing at least multiple polyether ether ketone resins with different apparent melt viscosities, and 5 to 30 parts by mass of a carbon-based conductive material, and having a relative crystallinity of 80% or more.

Preferably, the thickness is 5 μm or more and 500 μm or less, 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 resistance value when measured while applying a pressure of 1 MPa in the thickness direction is 1 mΩ· ^cm2 or more and 1000 mΩ· ^cm2 or less.

The multiple polyether ether ketone resins include first and second polyether ether ketone resins, and the composition mass ratios of the first and second polyether ether ketone resins are 5% by mass or more and 60% by mass or less for the first polyether ether ketone resin and 40% by mass or more and 95% by mass or less for the second polyether ether ketone resin,
the first polyether ether ketone resin has an apparent melt viscosity of 50 Pa s or more and 500 Pa s or less under conditions of a temperature of 375°C and a load of 50 kgf;
The second polyether ether ketone resin preferably has an apparent melt viscosity of more than 500 Pa·s and not more than 2500 Pa·s under conditions of a temperature of 375° C. and a load of 50 kgf.

The apparent melt viscosity ratio of the first and second polyether ether ketone resins under the conditions of a temperature of 375°C and a load of 50 kgf is:
It is preferable that the apparent melt viscosity of the second polyether ether ketone resin/the apparent melt viscosity of the first polyether ether ketone resin be 3/1 or more and 15/1 or less.

In order to solve the above problems, the present invention provides a method for producing a conductive resin film for a current collector of a secondary battery according to claim 1 or 2, comprising the steps of:
A molding material comprising 100 parts by mass of a polyether ether ketone resin composition containing at least a plurality of polyether ether ketone resins having different apparent melt viscosities from each other and 5 parts by mass or more and 30 parts by mass or less of a carbon-based conductive material is melt-kneaded;
The molding material is extruded through a die into a conductive resin film for a current collector , and the extrusion is then cooled by sandwiching the extrusion material between a pressure roll and a cooling roll, both of which have temperatures equal to or higher than the glass transition temperature of the polyether ether ketone resin but lower than the melting point of the polyether ether ketone resin , thereby making the relative crystallinity of the conductive resin film for a current collector 80% or higher.

The apparent melt viscosity of the molding material at 375°C, measured with a flow tester using a die 1.0 mm in diameter and 10 mm in length under conditions of a temperature of 375°C and a load of 50 kgf, is preferably 50 Pa·s or more and 10,000 Pa·s or less.
Furthermore, the cooled conductive resin film for a current collector is preferably subjected to heat compression molding, and the heating temperature of the conductive resin film for a current collector is set to be equal to or higher than the melting point and lower than the thermal decomposition temperature of the polyether 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.

The polyetheretherketone (PEEK) resin composition and carbon-based conductive material in the claims can be melt-kneaded at a temperature equal to or higher than the melting point of the polyetheretherketone resin and lower than the thermal decomposition temperature of the polyetheretherketone resin. If necessary, polyarylene ether ketone resins such as polyetherketone (PEK) resin, polyetherketoneketone (PEKK) resin, polyetheretherketoneketone (PEEKK) resin, and polyetherketoneetherketoneketone (PEKEKK) resin can be added to the polyetheretherketone resin, as long as the properties of the present invention are not impaired.

The carbon-based conductive material includes at least carbon nanotubes. The conductive resin film for the current collector may be uniaxially oriented, biaxially oriented, or unoriented. The conductive resin film for the current collector includes not only thin conductive resin films for the current collector but also thick conductive resin sheets for the current collector. The molding material can be prepared by stirring and mixing multiple polyether ether ketone resin compositions with different apparent melt viscosities with the carbon-based conductive material, followed by melt-kneading.

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, all-solid-state batteries, etc. Furthermore, the conductive resin film for the current collector preferably has a specific gravity of 1.23 to 1.60, a maximum tensile strength of 60 MPa to 500 MPa, a tensile elongation at break of 10% to 500%, and a tensile modulus of elasticity of 2000 MPa to 10000 MPa.

According to the present invention, a conductive resin film for a current collector is manufactured using a polyether ether ketone resin composition containing multiple polyether ether ketone resins that are lightweight, excellent in mechanical strength, chemical resistance, etc., and have low water absorption and different apparent melt viscosities. Therefore, even when the conductive resin film for a current collector is used as a current collector, there is little penetration of electrolyte components into the conductive resin film for a current collector. 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 little 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.

The present invention has the effect of improving chemical resistance, preventing a decline in charge/discharge cycle characteristics, preventing peeling of the current collector of a secondary battery, and also contributing to improved conductivity and weight reduction.

According to the invention described in claim 2, the thickness of the conductive resin film for current collector is 5 μm or more and 500 μm or less, thereby preventing a decrease in the tensile strength of the conductive resin film for current collector and enabling a reduction in the weight of the current collector for secondary batteries. Furthermore, the conductive resin film for current collector exhibits a mass change rate of 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 current collector exhibits a low resistance value of 1 mΩ· ^cm2 or more and 1000 mΩ· ^cm2 when measured under a pressure of 1 MPa in the thickness direction, thereby preventing a decrease in energy density even when used as a current collector for secondary batteries.

According to the invention described in claim 3, the composition mass ratios of the first and second polyether ether ketone resins are 5% to 60% by mass for the first polyether ether ketone resin and 40% to 95% by mass for the second polyether ether ketone resin, making it possible to obtain a conductive resin film for current collectors with excellent conductivity and mechanical strength, and achieving excellent film formability. Furthermore, the apparent melt viscosity of the first polyether ether ketone resin at a temperature of 375°C and a load of 50 kgf is 50 Pa·s to 500 Pa·s, which is expected to improve the conductivity of the conductive resin film for current collectors and prevent a decrease in mechanical strength.

According to the invention described in claim 4, the apparent melt viscosity of the second polyether ether ketone resin/the apparent melt viscosity of the first polyether ether ketone resin is equal to or greater than 3/1 and equal to or less than 15/1, which prevents excessive similarity in the properties of the first and second polyether ether ketone resins and enables favorable improvement in conductivity. Furthermore, the first and second polyether ether ketone resins can be uniformly dispersed, eliminating the risk of fisheyes or holes.

According to the invention described in claim 5, the conductive resin film for the current collector is manufactured by melt extrusion molding, which is expected to improve the thickness accuracy, productivity, and handling properties of the conductive resin film for the current collector, as well as simplify the manufacturing equipment.

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

A preferred embodiment of the present invention will now be described with reference to the drawings. In this embodiment, the conductive resin film 6 for a current collector of a secondary battery is a conductive resin film with a relative crystallinity of 80% or more, formed from a molding material 1 containing a polyether ether ketone resin composition 2 containing at least a plurality of polyether ether ketone resins with different apparent melt viscosities, and a carbon-based conductive material 5 with excellent conductivity, as shown in Figures 1 to 3. The conductive resin film contributes to the achievement of Goal 9 of the SDGs (the United Nations' international goals for sustainable development, consisting of 17 global goals and 169 targets (achievement criteria)) adopted at the United Nations Summit.

Molding material 1 is prepared to contain 100 parts by mass of a polyether ether ketone resin composition containing multiple polyether ether ketone (PEEK) resins with different apparent melt viscosities, and 5 to 30 parts by mass of a carbon-based conductive material. The mass ratio of these components is preferably 5 to 30 parts by mass, preferably 8 to 25 parts by mass, and more preferably 10 to 20 parts by mass of the carbon-based conductive material 5 per 100 parts by mass of the polyether ether ketone resin composition.

This is because, if the amount of carbon-based conductive material 5 is less than 5 parts by mass, the resistance value measured by applying a pressure of 1 MPa in the thickness direction of the conductive resin film 6 for a current collector does not reach 1000 mΩ· ^cm² or less, and therefore sufficient conductivity cannot be imparted to the conductive resin film 6 for a current collector, making it difficult to use the film as a current collector for a secondary battery. On the other hand, if the amount of carbon-based conductive material 5 exceeds 30 parts by mass, the melt viscosity of the molding material 1 increases, resulting in a decrease in melt fluidity, and the processability of the conductive resin film 6 for a current collector decreases due to a decrease in melt elongation, resulting in the formation of holes in the conductive resin film 6 for a current collector. In addition, it becomes difficult to blend the carbon-based conductive material 5 into multiple polyether ether ketone resins.

Furthermore, if the amount of carbon-based conductive material 5 exceeds 30 parts by mass, the carbon-based conductive material 5 will separate from the current collector conductive resin film 6, causing the generation of die fill, which will result in a deterioration in the quality of the current collector conductive resin film 6. To explain this point in more detail, when the current collector conductive resin film 6 is molded into a film, a large amount of deposits known as die fill may adhere and accumulate at the exit (also called the die lip) of the molding die 33 shown in Figure 3. The accumulation of this die fill can cause die lines to appear in the current collector conductive resin film 6, or the die fill may leave the die exit and become mixed into the current collector conductive resin film 6, resulting in a deterioration in the quality of the current collector conductive resin film 6.

Furthermore, if the carbon-based conductive material 5 exceeds 30 parts by mass, in addition to the above, the toughness of the conductive resin film 6 for the current collector is lost, and the conductive resin film 6 for the current collector may crack during molding of the conductive resin film 6, during the coating process of the positive electrode active material or negative electrode active material, or during assembly of the secondary battery.

The polyetheretherketone resin composition 2 of the molding material 1 contains multiple polyetheretherketone resins, including a low-viscosity first polyetheretherketone resin 3 and a high-viscosity second polyetheretherketone resin 4. The composition mass ratios of these first and second polyetheretherketone resins 3 and 4 are adjusted to 5% to 60% by mass for the first polyetheretherketone resin and 40% to 95% by mass for the second polyetheretherketone resin, and the apparent melt viscosities of the first and second polyetheretherketone resins 3 and 4 are different from each other.

The polyether ether ketone resin composition 2 has an apparent melt viscosity of 50 Pa·s or more and 2500 Pa·s or less, preferably 75 Pa·s or more and 2000 Pa·s or less, more preferably 100 Pa·s or more and 1500 Pa·s or less, and even more preferably 100 Pa·s or more and 1200 Pa·s or less, at a temperature of 375°C and a load of 50 kgf. This is because if the apparent melt viscosity is less than 50 Pa·s, the polyether ether ketone resin will be in the oligomer region, which will not only fail to improve the conductivity of the conductive resin film 6 for the current collector, but may also result in a decrease in mechanical strength. On the other hand, if the apparent melt viscosity exceeds 2500 Pa·s, the carbon-based conductive material 5 will not be able to be uniformly dispersed in the polyether ether ketone resin composition 2.

The first and second polyether ether ketone resins 3 and 4 are crystalline thermoplastic resins composed of arylene groups, ether groups, and carbonyl groups. Examples of such resins include those described in Japanese Patent Nos. 5702283 and 5847522, or in the literature [Asahi Research Center Co., Ltd.: PEEK: A Super Engineering Plastic Growing in Cutting-Edge Applications (Part 1)], and are characterized by excellent mechanical strength, light weight, low dielectric properties, hydrolysis resistance, heat resistance, chemical resistance, etc.

Specific examples of the first and second polyether ether ketone resins 3 and 4 include polyether ether ketone resins having the chemical structural formula represented by chemical formula (1), which typically have a melting point of 320 to 360°C, preferably 335 to 345°C, and are typically used in a form suitable for molding, such as powder, granules, or pellets.

In order to improve mechanical properties, n in the structural formula of the first and second polyether ether ketone resins 3 and 4 is 10 or greater, preferably 20 or greater. The first and second polyether ether ketone resins 3 and 4 may be homopolymers consisting only of repeating units of chemical formula (1), but may also contain repeating units other than those of chemical formula (1). Furthermore, the proportion of the chemical structure of chemical formula (1) in the first and second polyether ether ketone resins 3 and 4, relative to 100 mol% of the polyether ether ketone resin, is preferably 50 mol% or greater, preferably 70 mol% or greater, and more preferably 80 mol% or greater. The first and second polyether ether ketone resins 3 and 4 may also be block copolymers, random copolymers, or modified products with other copolymerizable monomers, as long as the effects of the present invention are not impaired.

Examples of the first and second polyether ether ketone resins 3 and 4 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.

The methods for producing the first and second polyether ether ketone resins are not particularly limited, but a typical production method involves polycondensing an aromatic diol component and an aromatic dihalide component (wherein one of the components contains at least a carbonyl group) in the presence of an alkali metal salt and a solvent at a temperature ranging from 150°C to 400°C. Examples of aromatic diol components include hydroquinone, and examples of aromatic dihalide components include 4,4'-difluorobenzophenone. Examples of alkali metal salts include inorganic potassium carbonate, and examples of solvents include diphenyl sulfone. After the polycondensation reaction is complete, the resin may be pulverized, washed with acetone, methanol, ethanol, water, or the like, and then dried.

The first and second polyether ether ketone resins 3 and 4 may be used by appropriately adjusting the crystallization temperature by modifying the terminal groups (usually halogen atoms) with alkaline sulfonic acid groups (sodium sulfonate groups, potassium sulfonate groups, lithium sulfonate groups, etc.), but it is preferable to use them without modifying the terminal groups.

The composition mass ratio of the first and second polyetheretherketone resins 3 and 4 is 5% by mass or more and 60% by mass or less for the first polyetheretherketone resin and 40% by mass or more and 95% by mass or less for the second polyetheretherketone resin. However, the composition mass ratio of the first polyetheretherketone resin 3 is preferably 10% by mass or more and 50% by mass or less, more preferably 15% by mass or more and 40% by mass or less, and even more preferably 20% by mass or more and 40% by mass or less.

This is because, when the composition mass ratio of the first and second polyether ether ketone resins 3 and 4 is within the above range, a conductive resin film 6 for a current collector having excellent conductivity and mechanical strength can be obtained. It is also because a molding material 1 having excellent film formability can be obtained.

The first polyether ether ketone resin 3 has an apparent melt viscosity of 50 Pa·s or more and 500 Pa·s or less, preferably 75 Pa·s or more and 400 Pa·s or less, more preferably 90 Pa·s or more and 300 Pa·s or less, and even more preferably 100 Pa·s or more and 200 Pa·s or less, at a temperature of 375°C and a load of 50 kgf. This is because if the apparent melt viscosity is less than 50 Pa·s, the polyether ether ketone resin will be in the oligomer region, which will not only fail to improve the conductivity of the conductive resin film for current collector 6 but may also result in a decrease in mechanical strength. In contrast, if the apparent melt viscosity exceeds 500 Pa·s, improving conductivity will be hindered.

The apparent melt viscosity of the first polyether ether ketone resin 3 can be measured with a flow tester using a die with a diameter of 1.0 mm and a length of 10 mm under conditions of a temperature of 375°C and a load of 50 kgf.

The second polyether ether ketone resin 4 has an apparent melt viscosity of more than 500 Pa·s and 2500 Pa·s or less, preferably 700 Pa·s or more and 2000 Pa·s or less, more preferably 900 Pa·s or more and 1500 Pa·s or less, and even more preferably 900 Pa·s or more and 1200 Pa·s or less, at a temperature of 375°C and a load of 50 kgf. The apparent melt viscosity of the second polyether ether ketone resin 4 can also be measured with a flow tester using a die with a diameter of 1.0 mm and a length of 10 mm under conditions of a temperature of 375°C and a load of 50 kgf.

The apparent melt viscosity ratio of the first and second polyetheretherketone resins 3 and 4 at a temperature of 375°C and a load of 50 kgf should be in the range of (apparent melt viscosity of second polyetheretherketone resin 4)/(apparent melt viscosity of first polyetheretherketone resin 3)=3/1 or more and 15/1 or less, preferably 4/1 or more and 13/1 or less, more preferably 4.5/1 or more and 11/1 or less, and even more preferably 5/1 or more and 10/1 or less, because this can significantly improve the properties of the polyetheretherketone resins.

This is because if the apparent melt viscosity of the second polyetheretherketone resin 4 is less than three times the apparent melt viscosity of the first polyetheretherketone resin 3, the properties of the second polyetheretherketone resin 4 and the first polyetheretherketone resin 3 tend to be too similar, making it difficult to improve conductivity. In contrast, if the apparent melt viscosity of the second polyetheretherketone resin 4 is more than 15 times the apparent melt viscosity of the first polyetheretherketone resin 3, the difference in apparent melt viscosity is so great that uniform dispersion of the first and second polyetheretherketone resins 3 and 4 becomes difficult, and fisheyes and holes may occur.

Examples of the carbon-based conductive material 5 in the molding material 1 include carbon blacks such as furnace black (oil furnace black and gas furnace black), channel black, acetylene black, and thermal black; carbon fibers such as carbon nanotubes, carbon nanofibers, fullerenes, amorphous carbon, bread-based carbon fibers, and pitch-based carbon fibers; 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 and then heating it; expanded graphite obtained by heat-treating expanded graphite at high temperatures; and artificial graphite.

Among these carbon-based conductive materials 5, carbon nanotubes are optimal because they provide high conductivity in small amounts and can be used to form the conductive resin film 6 for the current collector without losing the mechanical strength of the current collector. Because these carbon nanotubes have a cylindrical hollow fiber structure, they are expected to contribute to weight reduction. Carbon nanotubes 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 other than single-walled and multi-walled carbon nanotubes include nanografibers, bamboo-shaped nanotubes, and stacked cup nanotubes, as described in "Introduction to Materials Chemistry of Carbon Nanotubes" (Corona Publishing, edited by Saito Yahachi, pp. 7-9). Also included are carbon nanotube analogs such as nanohorns, nanocones, microcoils, and nanocoils, as described in "Introduction to Materials Chemistry of Carbon Nanotubes" (Corona Publishing, edited by Saito Yahachi, pp. 9-11). Of these carbon nanotubes and their analogs, multi-walled carbon nanotubes are the most suitable from the perspective of cost reduction.

The fiber diameter (outer diameter) of the carbon nanotubes is not particularly limited, but is preferably 0.5 nm or more and 200 nm or less. These carbon nanotubes can be produced by known production methods. For example, they can be produced by (1) the arc discharge method, (2) the laser evaporation method, or (3) chemical vapor deposition methods (or pyrolysis methods) such as the substrate growth method, supported catalyst method, fluidized catalyst method, and HiPco method, as described in "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 carbon nanotube products include Supergrowth CNT (manufactured by the New Energy and Industrial Technology Development Organization), eDIPS-CNT (manufactured by the New Energy and Industrial Technology Development Organization), SWNT series (manufactured by Meijo Nanocarbon Co., Ltd.: product name), VGCF series (manufactured by Showa Denko K.K.: product name), FloTube series (manufactured by CNano Technology: product name), AMC (manufactured by Ube Industries, Ltd.: product name), Nanocyl NC7000 series (manufactured by Nanocyl: product name), Baytubes (manufactured by Bayer: product name), GRAPHISTRENGTH (manufactured by Arkema: product name), MWNT7 (manufactured by Hodogaya Chemical Co., Ltd.: product name), K-Nanos series (manufactured by Kumho), and Hyperion CNT (Hypeprion Examples include Catalysis International (product name).

Other metallic or carbon-based conductive materials may be added to carbon nanotubes 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 5 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 5 may contain, within a range that does not impair the properties of the conductive resin film 6 for current collector, a compound selected from the group consisting of silane coupling agents (vinyltrimethoxysilane, vinyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-aminopropylethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-ureidopropyltrialkoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-isocyanatepropyltriethoxysilane, 3-trimethoxysilylpropylsuccinic anhydride, imidazole silane, etc.), titanate coupling agents (isopropyl triisostearoyl titanate, isopropyl(diisopropyl)silane, etc.), octyl pyrophosphate) titanate, isopropyl tris(N-aminoethyl-aminoethyl) titanate, tetraoctyl bis(di-tridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(di-tridecyl)phosphite titanate, bis(dioctyl pyrophosphate) oxyacetate titanate, bis(dioctyl pyrophosphate) ethylene titanate, isopropyl trioctanoyl titanate, isopropyl Treatment can be performed with various coupling agents such as dimethacryl isostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, isopropyl isostearoyl diacryl titanate, isopropyl tri(dioctyl phosphate) titanate, isopropyl tricumylphenyl titanate, tetraisopropyl (dioctyl phosphite) titanate, and aluminate coupling agents such as acetoalkoxyaluminum diisopropylate.

The molding material 1 may include, in addition to the polyether ether ketone resin composition 2 and the carbon-based conductive material 5, 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, provided that the properties of the present invention are not impaired. Polyester resins such as polyester oils, polyimide resins such as 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, and polyamide 46 (PA46) resin, etc., polysulfone (PSU) ) resin, polysulfone resins such as polyethersulfone (PES) resin and polyphenylene sulfone (PPSU) resin, polyarylene sulfide resins such as polyphenylene sulfide (PPS) resin, polyphenylene sulfide ketone resin, polyphenylene sulfide sulfone resin and polyphenylene sulfide ketone sulfone resin, polytetrafluoroethylene (PTFE) resin, polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) resin, tetrafluoroethylene-hexafluoropropylene copolymer (TPE) resin, Fluororesins such as vinylidene fluoride copolymer (FEP) resin, 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), and aliphatic polyketone resin can be selectively added.

In addition to the polyether ether ketone resin composition 2, carbon-based conductive material 5, and the above-mentioned thermoplastic resin, certain additives can be selectively added to the molding material 1, as long as they do not impair the properties of the present invention. 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 apparent melt viscosity of molding material 1, measured at 375°C under conditions of a temperature of 375°C and a load of 50 kgf using a die with a diameter of 1.0 mm and a length of 10 mm using a flow tester, is preferably in the range of 50 Pa·s to 10,000 Pa·s, preferably 100 Pa·s to 5,000 Pa·s, and more preferably 500 Pa·s to 2,500 Pa·s.

This is because, if the apparent melt viscosity is within the range of 50 Pa·s or more and 10,000 Pa·s or less, the conductive resin film 6 for the current collector has excellent formability and can be expected to have sufficient mechanical strength. In contrast, if the apparent melt viscosity is less than 50 Pa·s, the apparent melt viscosity is low, resulting in a decrease in melt tension and making it difficult to form the conductive resin film 6 for the current collector. Furthermore, if the apparent melt viscosity exceeds 10,000 Pa·s, the melt viscosity is high and the melt elongation is reduced, which may cause holes to form in the conductive resin film 6 for the current collector and cause it to break, resulting in difficulties in forming the conductive resin film 6 for the current collector.

When producing the conductive resin film 6 for a current collector as described above, first prepare a polyether ether ketone resin composition 2 containing multiple polyether ether ketone resins with different apparent melt viscosities. This polyether ether ketone resin composition 2 and a carbon-based conductive material 5 are melt-kneaded for a predetermined period of time to prepare a molding material 1. Then, by feeding the molding material 1 into a melt extrusion molding machine 30 for molding a resin film, a conductive resin film 6 for a current collector having a thickness of 500 μm or less, for example, between 10 μm and 500 μm, can be produced by melt extrusion molding.

Methods for preparing polyether ether ketone resin composition 2 include: (1) a method in which first and second polyether ether ketone resins 3 and 4, which have different apparent melt viscosities, are charged into melt kneader 10 and melt-kneaded to prepare polyether ether ketone resin composition 2; and (2) a method in which first and second polyether ether ketone resins 3 and 4, which have different apparent melt viscosities, are stirred and mixed in a stirring mixer at room temperature (a temperature of approximately 0°C or higher and 50°C or lower) to prepare polyether ether ketone resin composition 2.

First, to explain preparation method (1) in detail, in this method, a specified melt kneader 10 as shown in Figure 1 is prepared, and the first and second polyether ether ketone resins 3 and 4 are simultaneously charged into this melt kneader 10 through the inlet 15, or the first polyether ether ketone resin 3 is charged through the inlet 15 and the second polyether ether ketone resin 4 is charged separately through the side feeder 16, and melt-kneaded to prepare the polyether ether ketone resin composition 2. Alternatively, the second polyether ether ketone resin 4 may be charged through the inlet 15, and the first polyether ether ketone resin 3 may be charged separately through the side feeder 16, and melt-kneaded.

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 first and second polyether ether ketone resins 3 and 4 and can remove moisture and volatile gases generated from them.

The temperature during melt-kneading in the melt-kneader 10 is not particularly limited as long as it allows melt-kneading and dispersion without decomposing the first and second polyetheretherketone resins 3 and 4. It is preferably in the range of from the melting point to the thermal decomposition temperature of the first and second polyetheretherketone resins 3 and 4. Specifically, it is in the range of from 360°C to 450°C, preferably from 360°C to 420°C, and more preferably from 370°C to 400°C. This is because if the temperature during melt-kneading in the melt-kneader 10 is below the melting points of the first and second polyetheretherketone resins 3 and 4, the first and second polyetheretherketone resins 3 and 4 will not melt and will not be able to be kneaded and dispersed together. Furthermore, if the temperature of the melt kneader 10 exceeds the thermal decomposition temperature of the first and second polyether ether ketone resins 3 and 4, the first and second polyether ether ketone resins 3 and 4 will decompose violently, which is undesirable.

As shown in Figure 1, the melt mixer 10, which is a multi-screw extruder, is equipped with a cylinder 12 mounted on a base 11, a screw 13 that is built into the cylinder 12 and rotates by a motor to melt and mix the first and second polyether ether ketone resins 3 and 4 together and extrude strands (rod-shaped) or the like from a die 14 at the tip, an inlet 15 for the first polyether ether ketone resin 3 consisting of a hopper connected to the upstream side of the cylinder 12, a side feeder 16 for feeding the second polyether ether ketone resin 4 connected to the downstream side of the cylinder 12, and a rotatable cutter 17 that cuts the strands or the like extruded from the die 14 of the cylinder 12 and cooled by air or water to produce the polyether ether ketone resin composition 2.

When kneading and dispersing a polyetheretherketone resin composition 2 using such a melt kneader 10, the first polyetheretherketone resin 3 is introduced into the inlet 15 of the melt kneader 10, and then the second polyetheretherketone resin 4 is introduced laterally into the side feeder 16 of the cylinder 12, which has a screw structure. This allows the second polyetheretherketone resin 4 to be injected into the molten first polyetheretherketone resin 3, thereby allowing the first and second polyetheretherketone resins 3 and 4, which have different apparent melt viscosities, to be appropriately kneaded and dispersed together. This shortens the melt kneading time, which is expected to prevent thermal decomposition and crosslinking of the first and second polyetheretherketone resins 3 and 4. Alternatively, the second polyetheretherketone resin 4 may be introduced into the inlet 15 of the melt kneader 10, and then the first polyetheretherketone resin 3 may be introduced laterally into the side feeder 16 of the cylinder 12.

The kneaded and dispersed first and second polyether ether ketone resins 3 and 4 are extruded from the die 14 in the form of strands to form the polyether ether ketone resin composition 2. However, after being extruded from the die 14 as a polyether ether ketone resin film, the resin may be processed into powder, granules, flakes, or pellets to prepare the polyether ether ketone resin composition 2.

Next, the preparation method (2) will be described in detail. In this method, first and second polyether ether ketone resins 3 and 4, which have different apparent melt viscosities, can be prepared by stirring and mixing them at room temperature. When stirring and mixing the first and second polyether ether ketone resins 3 and 4 together at room temperature, a stirring and mixing machine such as a tumbler mixer, Henschel mixer, V-type mixer, Nauta mixer, ribbon blender, or universal stirring mixer is used. In this case, the first and second polyether ether ketone resins 3 and 4 are preferably in a powder form, which contributes to uniform dispersion. Methods for pulverizing them into a powder form include, for example, shear pulverization, impact pulverization, collision pulverization, freeze pulverization, and solution pulverization.

Next, a method for preparing molding material 1 using polyether ether ketone resin composition 2 will be described. Examples of methods for preparing molding material 1 include: (1) a method in which carbon-based conductive material 5 is introduced into a melt kneader 20 for molding material 1 and melt-kneaded with the molten polyether ether ketone resin composition 2 to prepare molding material 1; and (2) a method in which polyether ether ketone resin composition 2 and carbon-based conductive material 5 are stirred and mixed at room temperature (a temperature of approximately 0°C or higher and 50°C or lower) using a stirring mixer, and then melt-extruded and kneaded in the melt kneader 20 to prepare molding material 1.

First, to explain preparation method (1) in detail, in this method, a specified melt kneader 20 as shown in Figure 2 is prepared, and a polyether ether ketone resin composition 2 is introduced into this melt kneader 20 and melted. After that, a carbon-based conductive material 5 is newly introduced into the melt kneader 20 using a side feeder method or the like, and melt-kneaded with the already-molten polyether ether ketone resin composition 2 to prepare molding material 1.

Examples of the melt kneader 20 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 polyether ether ketone resin composition 2 and the carbon-based conductive material 5 and can remove moisture and volatile gases generated from them.

As shown in Figure 2, the melt kneader 20, which is a multi-screw extruder, is composed of a cylinder 22 mounted on a base 21, a screw 23 built into the cylinder 22 and supported by a shaft, which rotates by a motor to melt and knead the polyether ether ketone resin composition 2 and the carbon-based conductive material 5 and extrudes strands or the like from a die 24 at the tip, an inlet 25 for the polyether ether ketone resin composition 2 consisting of a hopper connected to the upstream side of the cylinder 22, a side feeder 26 for the carbon-based conductive material 5 connected to the downstream side of the cylinder 22, and a rotatable cutter 27 that cuts the strands or the like extruded from the die 24 of the cylinder 22 and cooled with air or water to produce the molding material 1.

When using such a melt kneader 20 to knead and disperse the polyether ether ketone resin composition 2 and the carbon-based conductive material 5, the polyether ether ketone resin composition 2 is introduced into the inlet 25 of the melt kneader 20, and then the finely powdered carbon-based conductive material 5 is introduced laterally using the screw-structured side feeder 26 of the cylinder 22. This injects the carbon-based conductive material 5 into the molten polyether ether ketone resin composition 2, allowing the polyether ether ketone resin composition 2 and the carbon-based conductive material 5 to be uniformly and appropriately kneaded and dispersed. Since the kneading time can be shortened in this process, decomposition of the polyether ether ketone resin composition 2 can be prevented.

The melting temperature when melt-kneading the polyether ether ketone resin composition 2 and the carbon-based conductive material 5 is not particularly limited as long as it is a temperature at which melt-kneading dispersion is possible and the polyether ether ketone resin composition 2 does not decompose. However, it is preferably in the range of from the melting point of the polyether ether ketone resin to the thermal decomposition temperature of the polyether ether ketone resin. Specifically, it is in the range of from 360°C to 450°C, preferably from 360°C to 420°C, and more preferably from 370°C to 400°C.

This is because if the temperature during melt-kneading in the melt-kneader 20 is below the melting point of the polyether ether ketone resin, the polyether ether ketone resin composition 2 will not melt, and the polyether ether ketone resin composition 2 and the carbon-based conductive material 5 will not be uniformly dispersed. Conversely, if the temperature of the melt-kneader 20 exceeds the thermal decomposition temperature of the polyether ether ketone resin composition 2, the polyether ether ketone resin composition 2 will decompose violently, which is preferable.

The melt-kneaded polyether ether ketone resin composition 2 and carbon-based conductive material 5 are extruded through a die 24 as strands to prepare strand molding material 1. However, after being extruded through the die 24 as a 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 the polyether ether ketone resin composition 2 or the carbon-based conductive material 5 can be dispersed to form a masterbatch.

Next, the preparation method (2) will be described in detail. When this method is used to stir and mix the polyether ether ketone resin composition 2 and the carbon-based conductive material 5 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 polyether ether ketone resin composition 2 is preferably in the form of a powder that can be more uniformly dispersed with the carbon-based conductive material 5. Methods for pulverizing into this powder include, for example, shear pulverization, impact pulverization, collision pulverization, freeze pulverization, and solution pulverization.

After stirring and mixing, the polyether ether ketone resin composition 2 and the carbon-based conductive material 5 are melt-kneaded and dispersed in a melt kneader 20, such as a Banbury mixer, mixing roll, pressure kneader, single-screw extruder, or a multi-screw extruder consisting of a twin-screw extruder, a triple-screw extruder, a four-screw extruder, or an eight-screw extruder, to prepare molding material 1. The melt kneader 20 is preferably a vented multi-screw extruder, which is expected to achieve good kneading and dispersion of the polyether ether ketone resin composition 2 and the carbon-based conductive material 5 and can degas the moisture and volatile gases generated by them. When preparing molding material 1, a masterbatch can be prepared by dispersing a predetermined amount or more of either the polyether ether ketone resin composition 2 or the carbon-based conductive material 5.

Before preparation, the moisture content (water content) of molding material 1 is adjusted to 2000 ppm or less, preferably 1000 ppm or less, and more preferably 500 ppm or less, using a hot air dryer or similar device. This is because a moisture content above 2000 ppm may cause foaming of the conductive resin film 6 for current collector. To achieve such a low moisture content, molding material 1 is preferably heated and dried before preparation. Examples of heat-drying methods include known methods such as hot air circulation drying, dehumidified hot air drying, heated vacuum drying, and microwave drying.

The heat-drying temperature for molding material 1 should be between -50°C and +50°C below the glass transition point of the polyether ether ketone resin. Specifically, it should be between 80°C and 210°C, preferably between 110°C and 190°C, more preferably between 130°C and 180°C, and even more preferably between 150°C and 170°C. The glass transition point of polyether ether ketone resin is typically between 130°C and 160°C (test method: differential scanning calorimetry), preferably between 135°C and 155°C, and more preferably between 140°C and 150°C. Furthermore, 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 this heat-drying time, but 24 hours or less is appropriate.

Once molding material 1 is prepared, conductive resin film 6 for current collectors is manufactured using this molding material 1. Manufacturing methods that can be used include melt extrusion, calendar molding, and casting. Of these manufacturing methods, melt extrusion, which allows for continuous extrusion molding of conductive resin film 6 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 6 for current collectors, and simplifying the equipment required.

The melt extrusion molding method involves melt-kneading molding material 1 using a melt extruder 30, and continuously extruding conductive resin film 6 for a current collector from a die 33, such as a T-die or a round die, connected to the tip of the melt extruder 30, thereby producing conductive resin film 6 for a current collector (see Figure 3). As shown in Figure 3, the melt extruder 30 may be, for example, a single-screw or twin-screw extruder. At the upper rear, a raw material inlet 31 for molding material 1 is installed. Connected to this raw material inlet 31 is an inert gas supply pipe 32, 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 32 effectively prevents oxidative degradation, oxygen crosslinking, and thermal crosslinking of molding material 1.

The melting temperature during melt-kneading in the melt extruder 30 is not particularly limited, as long as it is a temperature that allows melt-kneading and dispersion and does not decompose the polyether ether ketone resin composition 2. However, it is preferably in the range of the melting point of the polyether ether ketone resin to less than the thermal decomposition temperature of the polyether ether ketone resin. Specifically, it is in the range of 360°C to 450°C, preferably 360°C to 420°C, and more preferably 370°C to 400°C. This is because if the temperature during melt-kneading in the melt extruder 30 is below the melting point of the polyether ketone resin, the polyether ether ketone resin and the carbon-based conductive material 5 cannot be melt-kneaded and dispersed. Conversely, if the temperature is above the thermal decomposition temperature, the polyether ether ketone resin will decompose.

The die 33 is connected to the tip of the melt extruder 30 via a connecting pipe 34 and functions to continuously extrude a strip-shaped conductive resin film 6 for a current collector downward. This die 33 is preferably a T-die, which is capable of producing a conductive resin film 6 for a current collector with excellent thickness precision. A gear pump 35 is preferably attached to the connecting pipe 34 upstream of the die 33. This gear pump 35 functions to transfer the molding material 1 melt-kneaded by the melt extruder 30 to the downstream die 33 at a constant flow rate and with high precision.

The temperature during extrusion of the die 33 is in the range of above the melting point of the polyether ether ketone resin and below the thermal decomposition temperature of the polyether ether ketone resin. Specifically, it is in the range of 360°C to 450°C, preferably 360°C to 420°C, and more preferably 370°C to 400°C. This is because, if the temperature is below the melting point of the polyether ether ketone resin, it will be impossible to melt-knead the polyether ether ketone resin composition 2 and the carbon-based conductive material 5 and disperse the carbon-based conductive material 5. Conversely, if the temperature is above the thermal decomposition temperature, it will lead to decomposition of the polyether ether ketone resin, which is undesirable.

Below the die 33, a pair of opposing pressure rolls 36 are rotatably supported at a distance from each other, and between these pair of pressure rolls 36, a number of cooling rolls 37 are rotatably supported in a row so that they slide against each other. Of these cooling rolls 37, the upstream cooling roll 37 and the downstream cooling roll 37 slide against the circumferential surface of the pressure roll 36. Each pressure roll 36 is configured with a narrower diameter, and each cooling roll 37 is configured with a wider diameter than the pressure roll 36.

Of the pair of pressure rolls 36, a winder 39 is installed downstream of the downstream pressure roll 36, which winds the collector conductive resin film 6 onto a rotatable winding tube 38. Between the downstream pressure roll 36 and the winder 39, a slit blade 40 is positioned so that it can be raised and lowered, forming a slit in the longitudinal direction of the side of the collector conductive resin film 6. Between this slit blade 40 and the winder 39, the required number of rotatable tension rolls 41 are supported on shafts to apply tension to the collector conductive resin film 6 for smooth winding.

The temperature of each pressure roller 36 is equal to or higher than the glass transition temperature of the polyether ether ketone resin and lower than the melting point of the polyether ether ketone resin, specifically, 140°C or higher and lower than 340°C, preferably 180°C or higher and 300°C or lower, more preferably 200°C or higher and 280°C or lower, and even more preferably 210°C or higher and 240°C or lower.

The reason why the temperature of the pressure roller 36 is within this range is that if the temperature is below the glass transition point of the polyether ether ketone resin, the relative crystallinity of the current collector conductive resin film 6 cannot be 80% or more. Conversely, if the temperature exceeds the melting point, the current collector conductive resin film 6 may stick to the circumferential surface of the pressure roller 36 and break, or the strength of the current collector conductive resin film 6 may decrease, leading to breakage. Methods for adjusting the temperature of the pressure roller 36 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 6 for the current collector and the cooling roll 37, the peripheral surface of each pressure roll 36 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 36, a metal elastic roll with a metal surface can be used if necessary. When this metal elastic roll is used, it is possible to form a conductive resin film 6 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). It is also possible to use a pressure roll 36 whose surface is coated with a fluororesin film such as polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) resin or tetrafluoroethylene-hexafluoropyrene copolymer (FEP) resin.

The multiple cooling rolls 37 are, for example, metal rolls with a larger diameter than the pressure roll 36. They are rotatably supported below the die 33 and sandwich the extruded current collector conductive resin film 6 between them and the pressure roll 36. Together with the pressure roll 36, they cool the current collector conductive resin film 6 while controlling its thickness within a predetermined range. Like the pressure roll 36, the cooling roll 37 is adjusted to a temperature above the glass transition temperature of the polyether ether ketone resin and below its melting point, specifically, 140°C to 340°C, preferably 180°C to 300°C, more preferably 200°C to 280°C, and even more preferably 210°C to 240°C, and comes into sliding contact with the current collector conductive resin film 6.

The cooling roll 37 is adjusted to a temperature above the glass transition temperature of the polyether ether ketone resin but below its melting point because, if the temperature is below the glass transition temperature of the polyether ether ketone resin, the relative crystallinity of the current collector conductive resin film 6 cannot be 80% or higher. Conversely, if the temperature exceeds the melting point, the current collector conductive resin film 6 may stick to the circumferential surface of the pressure roll 36 and break, or the strength of the current collector conductive resin film 6 may decrease, leading to breakage. Methods for adjusting the temperature and cooling the cooling roll 37 include methods using a heat medium such as air, water, or oil, or an electric heater or induction heating.

After the molding material 1 is extruded into a strip-shaped conductive resin film 6 for the current collector, this conductive resin film 6 for the current collector is wound around a pair of pressure rolls 36, multiple cooling rolls 37, a tension roll 41, and a take-up tube 38 of a winder 39. Both sides of the conductive resin film 6 for the current collector are cut longitudinally with a slit blade 40, and the film is sequentially wound around the take-up tube 38 of the winder 39, thereby producing a long conductive resin film 6 for the current collector.

The thickness of the conductive resin film 6 for current collectors produced by cooling with the cooling roll 37 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 6 for current collectors is less than 5 μm, the tensile strength of the conductive resin film 6 for current collectors will be significantly reduced, making it difficult to produce the conductive resin film 6 for current collectors.

Conversely, if the thickness of the conductive resin film 6 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 6 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 6 for the current collector should be 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 1.33 to 1.41. This is because if the specific gravity of the conductive resin film 6 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 6 for the current collector, which would result in a decrease in mechanical strength and is therefore undesirable.

On the other hand, if the specific gravity of the conductive resin film 6 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 6 for current collector can be measured, for example, using a specific gravity measurement method in accordance with JIS K 7112 Method A.

The relative crystallinity of the conductive resin film 6 for the current collector is optimally 80% or more, preferably 90% or more, more preferably 95% or more, and even more preferably 100%. This is because if the relative crystallinity of the conductive resin film 6 for the current collector is less than 80%, problems will arise with the mechanical strength, heat resistance, chemical resistance, and solvent resistance of the conductive resin film 6 for the current collector. In contrast, if the relative crystallinity is greater than 80%, the conductive resin film 6 can be expected to have the mechanical strength, heat resistance, and chemical resistance sufficient for use as a conductive resin film for the current collector.

The crystallinity of the conductive resin film 6 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 6 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 6 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 for practical purposes, a value of 10,000 MPa or less is preferable.

This is because if the tensile modulus is less than 2000 MPa, when the current collector conductive resin film 6 is used as a current collector for a secondary battery, the current collector conductive resin film 6 will have poor rigidity, and there is a risk that the current collector conductive resin film 6 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 6 will be too rigid and will not be able to be wound up.

The tensile elongation at break of the conductive resin film 6 for the current collector, as measured in accordance with JIS K 7127, is preferably 10% or more, preferably 15% or more, more preferably 20% or more, and even more preferably 25% or more. This is because if the tensile elongation at break of the conductive resin film 6 for the current collector is less than 10%, the conductive resin film 6 for the current collector will have poor toughness and will crack during its manufacture. Furthermore, this is because the conductive resin film 6 for the current collector will crack during the coating process of the positive or negative electrode active material for the conductive resin film 6 for the current collector. 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 6 for the current collector will stretch during the coating process of the positive or negative electrode active material for the conductive resin film 6 for the current collector.

The maximum tensile strength of the conductive resin film 6 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 6 for the current collector is less than 60 MPa, the conductive resin film 6 for the current collector will have poor toughness and will crack during its manufacture. Furthermore, the conductive resin film 6 for the current collector will crack during the coating process of the positive electrode active material or negative electrode active material for the conductive resin film 6 for the current collector.

The upper limit of the tensile elongation at break is not particularly limited, but is preferably 500 MPa or less. This is because if it exceeds 500 MPa, the cutting ability with the slit blade 40 will decrease during the production of the conductive resin film 6 for current collectors, which is undesirable as it will slow down the production speed of long conductive resin film 6 for current collectors.

The conductivity of the conductive resin film 6 for current collector can be evaluated by the resistance value measured when a pressure of 1 MPa is applied in the thickness direction. The resistance value when a pressure of 1 MPa is applied in the thickness direction is optimally 1000 mΩ· ^cm² or less, preferably 800 mΩ· ^cm² or less, more preferably 600 mΩ· ^cm² or less, and even more preferably 500 mΩ· ^cm² or less. There are no particular restrictions on the lower limit of the resistance value when measured when a pressure of 1 MPa is applied in the thickness direction, but in practice it is 1 mΩ· ^cm² or more.

This is because, if the resistance value of the conductive resin film 6 for current collector exceeds 1000 mΩ· ^cm2 , the energy density will decrease when used as a current collector for a secondary battery. Conversely, if the resistance value is less than 1 mΩ· ^cm2 , a large amount of carbon-based conductive material 5 must be added, making the resulting conductive resin film 6 for current collector brittle, which can cause the conductive resin film 6 for current collector to crack during assembly of the secondary battery.

The chemical resistance of the conductive resin film 6 for the current collector can be evaluated by immersing the conductive resin film 6 for the current collector in N-methyl-2-pyrrolidone and an electrolyte solution 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 6 for the current collector is immersed in N-methyl-2-pyrrolidone and an electrolyte solution 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 electrolyte solution in which a lithium salt is dissolved as a solute in an organic solvent. Examples of organic solvents for this 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 6 for current collectors, current collector plates using the conductive resin film 6 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 6 for current collectors can be used as is, or it can be further heat-compression molded. Heat-compression molding the conductive resin film 6 for current collectors can lower the resistance value, increase conductivity, and reduce the amount of carbon-based conductive material 5 used, thereby reducing costs.

When the conductive resin film 6 for a current collector is subjected to heat compression molding, the conductive resin film 6 for a current collector is sandwiched between a plurality of metal plates, metal rolls, or metal belts that have been heated to a temperature that is equal to or higher than the melting point of the polyetheretherketone resin and lower than the thermal decomposition temperature of the polyetheretherketone resin, specifically, a temperature that is higher than the melting point of the polyetheretherketone resin by 10°C and higher than the melting point of the polyetheretherketone resin by 100°C, preferably higher than the melting point of the polyetheretherketone resin by 20°C and higher than the melting point of the polyetheretherketone resin by 80°C, more preferably higher than the melting point of the polyetheretherketone resin by 30°C and higher than the melting point of the polyetheretherketone resin by 60°C, and even more preferably higher than the melting point of the polyetheretherketone resin by 30°C and higher than the melting point of the polyetheretherketone resin by 50°C, and a pressure of 0.5 kgf/cm2 or higher and 100 kgf/cm2 or higher is applied to the projected area of the conductive resin film ⁶ for a current collector. The resin is then immediately cooled to a temperature below the glass transition point of the polyether ether ketone resin, after which a pressure of ² or less is applied and maintained for 0.5 to 300 seconds.

As described above, polyether ether ketone resin, which has excellent lightness, mechanical properties, chemical resistance, and heat resistance, as well as low water absorption, is selected as the thermoplastic resin for molding material 1 to manufacture current collector conductive resin film 6. Therefore, even if current collector conductive resin film 6 is used as a current collector, electrolyte components do not penetrate into the current collector conductive resin film 6, effectively eliminating the risk of a deterioration in charge/discharge cycle characteristics. Furthermore, because polyether ether ketone resin 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, by using first and second polyether ether ketone resins 3 and 4 with different apparent melt viscosities, there is no need to use two different types of resin, eliminating the risk of peeling of the current collector. 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 5 is carbon nanotubes, it is not only chemically stable, but also enables further weight reduction of secondary batteries. Furthermore, because the thickness of the conductive resin film 6 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 6 for the current collector is prevented, and significant weight reduction of the current collector for secondary batteries can be expected.

Furthermore, since the specific gravity of the conductive resin film 6 for a current collector is 1.60 or less, this contributes to a significant weight reduction of the secondary battery and the current collector. Furthermore, since the resistance value of the conductive resin film 6 for a current collector, measured by applying a pressure of 1 MPa in the thickness direction, is low, at 1 mΩ ^cm2 or more and 1000 mΩ ^cm2 or less, it is possible to prevent a decrease in energy density even when the conductive resin film 6 for a current collector is used as a current collector of a secondary battery.

The shape of the polyether ketone resin in the above embodiment is not particularly limited and may be powder, granules, blocks, powder, pellets, etc. The conductive resin film 6 for a current collector may have a specific gravity of 1.33 to 1.41 as measured in accordance with JIS K7112 Method A, a relative crystallinity of 95% to 100%, a tensile modulus of 3683 MPa to 5274 MPa as measured in accordance with JIS K 7127, a tensile elongation at break of 24% to 45% as measured in accordance with JIS K 7127, a maximum tensile strength of 94 MPa to 126 MPa as measured in accordance with JIS K 7127, and a resistance of 107 mΩ·cm ² to 227 mΩ·cm ² as measured under a pressure of 1 MPa in the thickness direction.

In addition, to take advantage of the properties of carbon nanotubes, multiple types of carbon nanotubes with different outer diameters and lengths may be mixed and used. Furthermore, a single cooling roll 37 may be rotatably supported between a pair of pressure rolls 36.

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, in order to prepare a polyether ether ketone resin composition comprising a plurality of polyether ether ketone resins having different apparent melt viscosities, a commercially available polyether ether ketone resin (manufactured by Victrex, product name: Victrex Granules 90G, hereinafter abbreviated as "90G") was prepared as the first polyether ether ketone resin, and a commercially available polyether ether ketone resin (manufactured by Victrex, product name: Victrex Granules 381G, hereinafter abbreviated as "381G") was prepared as the second polyether ether ketone resin.

The first and second polyether ether ketone resins were each pulverized using a freeze-pulverization method. The pulverized first and second polyether ether ketone resins were weighed out in the composition mass ratios shown in Table 1 and charged into a stirring mixer. Polyether ether ketone resin compositions with different apparent melt viscosities were prepared by stirring and mixing. Hereinafter, polyether ether ketone resins will be abbreviated as "PEEK resin."

The apparent melt viscosity of PEEK resin was measured using a flow tester (Shimadzu Flow Tester CFT-500D, manufactured by Shimadzu Corporation). Specifically, the PEEK resin was pre-dried in a hot air dryer at 160°C for 12 hours, and 1.5 ^cm3 of 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 temperature reached 375°C, it was preheated for 5 minutes. Immediately after preheating, a load of 50 kgf was applied to melt and flow the PEEK resin, and its apparent melt viscosity was measured. The apparent melt viscosity was measured using the same method below. The apparent melt viscosity at 90 G was 109 Pa·s, and at 381 G was 879 Pa·s.

Once the PEEK resin composition was prepared, the PEEK resin composition and multi-walled carbon nanotubes, a carbon-based conductive material, were weighed out to the mass ratio shown in Table 1. The PEEK resin and multi-walled carbon nanotubes were then placed in a mixer to prepare a stirred mixture. NC7000 (product name, manufactured by Nanosil Co., Ltd., hereafter abbreviated as "NC7000") was used as the multi-walled carbon nanotubes.

Once the stirred mixture was prepared, it was fed into a co-rotating twin-screw extruder equipped with a vacuum pump and melt-kneaded under reduced pressure. The melt-kneaded mixture was extruded into a rod shape from the die at the tip of the co-rotating twin-screw extruder, cooled with water, and cut to prepare pellet-shaped molding material. The co-rotating twin-screw extruder used was a φ25 mm, L/D=41 type. The stirred mixture was melt-kneaded to prepare the molding material under conditions of a cylinder temperature of 300-370°C and a die temperature of 370°C, with the vent on the raw material inlet side of the co-rotating twin-screw extruder open and the vent on the die side degassed under reduced pressure. The temperature during melt-kneading was measured by measuring the temperature of the molten molding material immediately after extrusion from the die, and was measured to be 376°C. Once the molding material was prepared, the apparent melt viscosity of the molding material was measured using the same method as above.

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 of conductive resin film for current collectors with a relative crystallinity of 100%. 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 molding materials 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, and the temperature of the connecting pipe connecting the single-screw extruder to the T-die to 395°C. The temperature of the molten molding material was measured from the resin temperature at the T-die inlet and found to be 398°C. When feeding the molding material into the single-screw extruder, nitrogen gas was supplied at a rate of 15 L/min.

Once the conductive resin film for the current collector was formed, it was sequentially wound around a pair of silicone rubber pressure rolls (210°C) and a cooling roll (220°C) made of silicone rubber, as shown in Figure 3, and the take-up tube of a 6-inch take-up machine located downstream of these, while being sandwiched between the pressure roll and a metal roll. The continuous conductive resin film for the current collector was then sequentially wound up around the take-up tube, producing a conductive resin film for the current collector measuring 100 m in length and 150 mm in width.

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, chemical resistance, and conductivity 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, chemical resistance was evaluated by the change in mass before and after immersion in N-methyl-2-pyrrolidone and electrolyte, and conductivity was evaluated by the conductivity of the conductive film before and after immersion in electrolyte.

- 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 mass change. To evaluate the mass change of the conductive resin film for current collector, the conductive resin film for current collector was cut into a size of MD: 5.5 cm x TD: 5.5 cm and weighed [W ₀ ]. This conductive resin film for current collector and 5 g of NMP or 5 g of electrolyte solution were placed in a PET/AL/PE flat bag (manufactured by Nippon Seisaku Co., Ltd.: trade name Lamizip) and sealed by heat sealing. The electrolyte solution used was an electrolyte solution for lithium primary/secondary/polymer batteries and lithium ion capacitors (manufactured by Kishida Chemical Co., Ltd.: trade name electrolyte LiPF ₆ , molar concentration 1 mol/L, solvent EC:DEC (3:7) V/V %).

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

Conductivity of Conductive Resin Film for Current Collector The conductivity of the conductive resin film for current collector was evaluated by the resistance value in the thickness direction. The resistance value in the thickness direction [Rc] was calculated by cutting the conductive resin film for current collector to a size of 5.5 cm in MD × 5.5 cm in TD to prepare a test piece, sandwiching the conductive resin film for current collector between a pair of carbon papers each measuring 5.0 cm × 5.0 cm, and then sandwiching the pair of carbon papers between a pair of gold-plated electrodes. A direct current was passed through the test piece, and a pressure of 1 MPa was applied from above. The resistance value [ _R0 ] after 1 minute was measured with a resistance meter, and then the resistance value was calculated using the following formula:

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

The carbon paper used was a SIGRACET Gas Diffusion Media type GDL24B (manufactured by SGL. GROUP, product name). The resistance meter used was a Milliohm HiTester 3540 (manufactured by Hioki E.E. Corporation, product name). The through-thickness resistance (Rc) was measured before and after a chemical resistance test using a conductive resin film and an electrolyte for lithium primary and secondary polymer batteries and lithium ion capacitors (manufactured by Kishida Chemical Co., Ltd., product name: electrolyte LiPF6, molar concentration 1 mol/L, solvent EC:DEC (3:7) V/V%). Measurements were taken in an environment with a temperature of 23°C ± 2°C and a relative humidity of 50 RH ± 5% RH.

Example 2
The composition mass ratio of the pulverized first and second PEEK resins of Example 1, which had different apparent melt viscosities, was changed as shown in Table 1, and PEEK resin compositions were prepared in the same manner as in Example 1. After the PEEK resin composition was prepared, this PEEK resin composition and multi-walled carbon nanotubes, which are carbon-based conductive materials, were weighed out to achieve the mass ratio shown in Table 1, and then the PEEK resin and multi-walled carbon nanotubes were charged into a mixer to prepare a stirred mixture. After preparing the stirred mixture, a pellet-shaped molding material was prepared in the same manner as in Example 1.

The temperature during melt-kneading was measured by measuring the temperature of the molten molding material immediately after extrusion from the die, and was found to be 375°C. The multi-walled carbon nanotubes used were the NC7000 used in Example 1. Once the molding material was prepared, the apparent melt 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 was manufactured in the same manner as in Example 1, and the generation of die buildup during the manufacturing of this conductive resin film for a current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, chemical resistance, and conductivity of this conductive resin film for a current collector were evaluated and the results are summarized in Table 1.

Example 3
The procedure was basically the same as in Example 1, except that the PEEK resin composition was changed to Victrex Granules 151G (product name of Victrex Corporation; hereinafter abbreviated as "151G"), which was prepared by pre-freezing and grinding the 90G PEEK resin used in Example 1. 151G and the 381G used in Example 1 were weighed out in the composition mass ratio shown in Table 1, charged into a stirring mixer, and stirred and mixed to prepare PEEK resin compositions with different apparent melt viscosities. The apparent melt viscosity of 151G was measured using the same method as in Example 1 and was found to be 192 Pa s.

After preparing the PEEK resin composition, the PEEK resin composition and multi-walled carbon nanotubes, a carbon-based conductive material, were weighed out to obtain the mass ratio shown in Table 1. The PEEK resin and multi-walled carbon nanotubes were then placed in a mixer to prepare a stirred mixture. The multi-walled carbon nanotubes used were the NC7000 used in Example 1. After preparing the molding material, the apparent melt viscosity of the molding material was measured using the same method as in Example 1.

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

Next, the prepared molding material was used to mold a conductive resin film for a current collector into a strip shape 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 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, chemical resistance, and conductivity of the conductive resin film for a current collector were evaluated and the results are summarized in Table 1.

Example 4
The process was basically the same as in Example 1, but PEEK resin compositions with different apparent melt viscosities were prepared by weighing out 151G, which was the PEEK resin used in Example 3, and 381G, which was used in Example 1, in the composition mass ratios shown in Table 1, charging them into a stirring mixer, and stirring and mixing them.

After preparing the PEEK resin composition, the PEEK resin composition and multi-walled carbon nanotubes, a carbon-based conductive material, were weighed out to achieve the mass ratio shown in Table 1. The PEEK resin and multi-walled carbon nanotubes were then placed in a mixer to prepare a stirred mixture. The multi-walled carbon nanotubes used in Example 1 were changed from NC7000 to FloTube 9000 (manufactured by CNano Technology, Inc.; product name, hereinafter abbreviated as "9000"). The PEEK resin composition and multi-walled carbon nanotubes were weighed out to achieve the composition mass ratio shown in Table 1, and a stirred mixture was prepared.

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 melt 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 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, chemical resistance, and conductivity of the conductive resin film for a current collector were evaluated and the results are summarized in Table 1.

Example 5
The process was basically the same as in Example 1, except that the PEEK resin 381G used in Example 1 was replaced with pre-frozen and crushed Victrex Granules 450G (product name by Victrex, hereinafter abbreviated as "450"), which was weighed out to achieve the composition mass ratio shown in Table 2 with the 90G used in Example 1, and then charged into a stirring mixer and stirred and mixed to prepare PEEK resin compositions with different apparent melt viscosities. The apparent melt viscosity of 450G was measured in the same manner as in Example 1 and was found to be 1067 Pa s.

Once the PEEK resin composition was prepared, the PEEK resin composition and multi-walled carbon nanotubes, a carbon-based conductive material, were weighed out to the mass ratio shown in Table 2. The PEEK resin and multi-walled carbon nanotubes were then placed in a mixer to prepare a stirred mixture. The multi-walled carbon nanotubes used were the NC7000 used in Example 1.

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 melt 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 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, chemical resistance, and conductivity of the conductive resin film for a current collector were evaluated and are listed in Table 2.

Example 6
The process was basically the same as in Example 1, but the 90G used in Example 1 and the 450G used in Example 5 were weighed out to achieve the composition mass ratio shown in Table 2, and then charged into a stirring mixer and stirred and mixed to prepare PEEK resin compositions with different apparent melt viscosities. After preparing the PEEK resin composition, this PEEK resin composition and multi-walled carbon nanotubes, which are a carbon-based conductive material, were weighed out to achieve the mass ratio shown in Table 2, and then the PEEK resin and multi-walled carbon nanotubes were charged into the mixer to prepare a stirred mixture. The multi-walled carbon nanotubes used were NC7000, the same as in Example 1.

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 melt 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 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, chemical resistance, and conductivity of the conductive resin film for a current collector were evaluated and are listed in Table 2.

Example 7
The process was basically the same as in Example 1, but the 151G used in Example 3 and the 450G used in Example 5 were weighed out to achieve the composition mass ratio shown in Table 2, and then charged into a stirring mixer and stirred and mixed to prepare PEEK resin compositions with different apparent melt viscosities. After preparing the PEEK resin composition, this PEEK resin composition and multi-walled carbon nanotubes, which are a carbon-based conductive material, were weighed out to achieve the mass ratio shown in Table 2, and then the PEEK resin and multi-walled carbon nanotubes were charged into the mixer to prepare a stirred mixture. The 9000 multi-walled carbon nanotubes used in Example 4 were used.

The molding material was then 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 376°C. Once the molding material was prepared, the apparent melt 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 398°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, chemical resistance, and conductivity of the conductive resin film for a current collector were evaluated and are listed in Table 2.

Example 8
The process was basically the same as in Example 1, except that the 151G used in Example 3 and the 450G used in Example 5 were weighed out to achieve the composition mass ratio shown in Table 2, charged into a stirring mixer, and stirred and mixed to prepare PEEK resin compositions with different apparent melt viscosities. After preparing the PEEK resin composition, this PEEK resin composition and multi-walled carbon nanotubes, a carbon-based conductive material, were weighed out to achieve the mass ratio shown in Table 2, and then the PEEK resin and multi-walled carbon nanotubes were charged into a mixer to prepare a stirred mixture. The 9000 multi-walled carbon nanotubes used in Example 4 were used. After preparing the molding material, the apparent melt viscosity of this molding material was measured using the same method as in Example 1.

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.

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 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, chemical resistance, and conductivity of the conductive resin film for a current collector were evaluated and are listed in Table 2.

Comparative Example 1
The process was basically the same as in Example 1, but the first and second PEEK resins used in Example 1, which had different apparent melt viscosities, were weighed out at composition mass ratios outside the range of the present invention shown in Table 3, and then charged into a stirring mixer and stirred and mixed to prepare a plurality of PEEK resin compositions having different apparent melt viscosities.

Next, the PEEK resin composition was prepared into a molding material using the same method as in Example 1. That is, the PEEK resin composition and multi-walled carbon nanotubes were weighed out in the composition mass ratio shown in Table 3 and charged into a stirring mixer to prepare a stirred mixture. This stirred mixture was then prepared into a pellet-shaped molding material in the same manner as in Example 1. The temperature during melt-kneading was measured by measuring the temperature of the molten molding material immediately after extrusion from the die, and was found to be 376°C. Once the molding material was prepared, the apparent melt viscosity of this molding material was measured using the same method as in Example 1.

Next, using the prepared molding material, a conductive resin film for a current collector with a relative crystallinity of 100% was molded into a strip shape using the same method as in Example 1. The temperature of the molten molding material was measured from the resin temperature at the entrance of the T-die and was found to be 398°C. After molding, the conductive resin film for a current collector was manufactured using the same method 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, chemical resistance, and conductivity of this conductive resin film for a current collector were evaluated and the results are summarized in Table 3.

Comparative Example 2
First, the PEEK resin used in Example 3 and the PEEK resin used in Example 1 were weighed out in a composition mass ratio outside the range of the present invention shown in Table 3, and then charged into a stirring mixer and stirred and mixed to prepare a plurality of PEEK resin compositions with different apparent melt viscosities. At the same time, this PEEK resin composition and multi-walled carbon nanotubes were weighed out in the composition mass ratio 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 by 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 melt 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 397°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, chemical resistance, and conductivity of the conductive resin film for a current collector were evaluated and the results are summarized in Table 3.

Comparative Example 3
The PEEK resin composition used in Example 5 and the multi-walled 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 by 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 measured to be 375°C. After the molding material was prepared, the apparent melt 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 396°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, chemical resistance, and conductivity of the conductive resin film for a current collector were evaluated and the results are summarized in Table 3.

Comparative Example 4
The PEEK resin composition used in Example 7 and the multi-walled carbon nanotubes used in Example 4 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 by 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 measured to be 381°C. After the molding material was prepared, the apparent melt 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 396°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, chemical resistance, and conductivity of the conductive resin film for a current collector were evaluated and the results are summarized in Table 3.

Comparative Example 5
A conductive resin film for a current collector having a relative crystallinity of 35% was molded using a molding material comprising the polyether ether ketone resin composition and multi-walled carbon nanotubes used in Example 1. The molding of the conductive resin film for a current collector was carried out in the same manner as in Example 1. However, the temperatures of the pressure roll and the chill roll were changed from 220°C for the pressure roll and 210°C for the chill roll in Example 1 to 100°C for the pressure roll and 100°C for the chill roll in Comparative Example 5, and the conductive resin film for a current collector was molded into a strip shape. 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, the generation of die deposits during the production of the conductive resin film for the current collector, as well as the thickness, specific gravity, relative crystallinity, mechanical properties, chemical resistance, and conductivity of the conductive resin film for the current collector were evaluated and the results are listed in Table 3.

〔evaluation〕
In Examples 1 to 7, good results were obtained in terms of the mechanical properties, chemical resistance, and conductivity of the conductive resin film for current collector. In Example 8, the chemical resistance of the conductive resin film for current collector was slightly reduced, but practically sufficient results were obtained.

In contrast, in Comparative Example 1, the composition mass ratio of the first PEEK resin was outside the range of the present invention, resulting in a significant deterioration in the conductivity of the conductive resin film for the current collector. Furthermore, in Comparative Example 2, the composition mass ratio of the second PEEK resin was outside the range of the present invention, resulting in a significant deterioration in the tensile elongation at break of the conductive resin film for the current collector. In Comparative Example 3, the amount of carbon-based conductive material added was outside the range of the present invention, resulting in a significant deterioration in the conductivity of the conductive resin film for the current collector. Furthermore, in Comparative Example 4, the amount of carbon-based conductive material added was outside the range of the present invention, resulting in a deterioration in the chemical resistance as well as the tensile elongation at break of the conductive resin film for the current collector. Furthermore, in Comparative Example 5, the relative crystallinity was outside the range of the present invention, resulting in a significant deterioration in the chemical resistance of the conductive resin film for the current collector, raising doubts about its practical utility.

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, including 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 Polyether ether ketone resin composition 3 First polyether ether ketone resin 4 Second polyether ether ketone resin 5 Carbon-based conductive material 6 Conductive resin film for current collector 10 Melt kneader 20 Melt kneader 30 Melt extrusion molding machine 33 Die 36 Pressure roll 37 Cooling roll 38 Winding tube 39 Winding machine

Claims (5)

A conductive resin film for a current collector of a secondary battery, characterized by comprising 100 parts by mass of a polyether ether ketone resin composition containing at least multiple polyether ether ketone resins with different apparent melt viscosities, and 5 to 30 parts by mass of a carbon-based conductive material, and having a relative crystallinity of 80% or more. 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 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 resistance value of 1 mΩ· ^cm2 or more and 1000 mΩ· ^cm2 or less when measured while applying a pressure of 1 MPa in the thickness direction. the plurality of polyether ether ketone resins include first and second polyether ether ketone resins, and the composition mass ratios of the first and second polyether ether ketone resins are 5% by mass or more and 60% by mass or less for the first polyether ether ketone resin and 40% by mass or more and 95% by mass or less for the second polyether ether ketone resin;
the first polyether ether ketone resin has an apparent melt viscosity of 50 Pa s or more and 500 Pa s or less under conditions of a temperature of 375°C and a load of 50 kgf;
3. The conductive resin film for a current collector of a secondary battery according to claim 1, wherein the second polyether ether ketone resin has an apparent melt viscosity of more than 500 Pa·s and not more than 2500 Pa·s under conditions of a temperature of 375°C and a load of 50 kgf. The apparent melt viscosity ratio of the first and second polyether ether ketone resins under the conditions of a temperature of 375°C and a load of 50 kgf is:
4. The conductive resin film for a current collector of a secondary battery according to claim 3, wherein the apparent melt viscosity of the second polyether ether ketone resin/the apparent melt viscosity of the first polyether ether ketone resin is equal to or greater than 3/1 and equal to or less than 15/1. A method for producing the conductive resin film for a current collector of a secondary battery according to claim 1 or 2, comprising:
A molding material comprising 100 parts by mass of a polyether ether ketone resin composition containing at least a plurality of polyether ether ketone resins having different apparent melt viscosities from each other and 5 parts by mass or more and 30 parts by mass or less of a carbon-based conductive material is melt-kneaded;
A method for producing a conductive resin film for a current collector of a secondary battery, comprising extruding a molding material through a die into a conductive resin film for a current collector, and then cooling the film by sandwiching the film between a pressure roll and a cooling roll, both of which have temperatures equal to or higher than the glass transition temperature of the polyether ether ketone resin but lower than the melting point of the polyether ether ketone resin, to thereby produce a conductive resin film for a current collector having a relative crystallinity of 80% or higher.