Support film for current collector for semi-solid battery

Abstract

Provided is a support film for a current collector for a semi-solid battery, the support film comprising a base material and an adhesive layer that is provided on one surface of the base material. When the haze of a first test piece obtained by layering one and another of the support films such that the adhesive layers face is A1 and the haze of a second test piece obtained by thermocompression of the first test piece is A2, the haze rate of change (%) calculated from ((A1-A2) / A1)×100 is at least 25%.

Description

Support film for current collectors in semi-solid batteries

[0001] The present disclosure relates to a support film for a current collector for a semi-solid battery.

[0002] In recent years, semi-solid batteries have attracted attention because they are safer and can achieve higher energy densities than liquid batteries, which use liquid electrolytes. Semi-solid batteries have a gel, clay, or other electrolyte and electrodes (positive and negative electrodes), and the electrodes are composed of a positive electrode current collector, a positive electrode active material, a separator, a negative electrode active material, and a negative electrode current collector, in this order.

[0003] The electrodes are sealed with a support film to form a single pouch (unit cell), and in secondary batteries, multiple unit cells are stacked to form a battery assembly (stack cell) to improve battery capacity. The support film isolates the active material, current collector, etc. from the outside, protects them from moisture and other foreign matter, and prevents short-circuiting between adjacent electrodes. Such unit cells are fabricated, for example, by the method described in Patent Document 1.

[0004] Special Publication No. 2023-545410

[0005] In Patent Document 1, a current collector and the like are laminated to a support film by heat sealing. Insufficient adhesion between the support film and the current collector can cause poor adhesion, which can lead to the intrusion of foreign matter such as moisture or the risk of short-circuiting with adjacent cells.

[0006] Therefore, the inventors considered that by making it possible to visually identify defective parts when poor adhesion occurs, it would be easier to remove defective products during semi-solid battery manufacturing, and it would be possible to provide safe semi-solid batteries.

[0007] The present disclosure provides a support film that makes it easy to visually recognize poor adhesion.

[0008] One aspect of the present disclosure includes, for example, the following inventions. [1] A support film for a current collector for a semi-solid battery, comprising: a substrate; and an adhesive layer disposed on one surface of the substrate, wherein a haze change rate (unit: %) calculated by ((A1-A2) / A1) x 100 is 25% or more when a first test piece obtained by superposing the support films together with the adhesive layers facing each other has a haze of A1 and a second test piece obtained by thermocompression bonding the first test piece has a haze of A2. [2] The support film according to [1], wherein the A1 is 7% or more. [3] The support film according to [1] or [2], wherein the substrate contains polyester, and the adhesive layer contains a thermoplastic resin. [4] The support film according to [3], wherein the thermoplastic resin is an ethylene-vinyl acetate copolymer. [5] The support film according to any one of [1] to [4], wherein the arithmetic mean roughness Ra of the adhesive layer on the surface opposite the substrate is 0.4 μm or more. [6] The support film according to any one of [1] to [5], wherein the adhesive layer has an adhesion strength B1 to copper foil of 5 N / 15 mm or more, as measured by the following peel test. <Peel Test> The adhesive layer of the support film is superimposed on the shiny side of an electrolytic copper foil (thickness 18 μm, surface roughness 0.33 μm), a PET film is placed on the surface of the support film opposite the substrate, and the support film is sandwiched between them. Using a heat seal tester, heat is applied only from the adhesive layer side of the support film to perform thermocompression bonding. The compression conditions are 150°C, 0.2 MPa, and 1 second. [7] The support film according to any one of [1] to [6], wherein the arithmetic mean roughness Ra of the surface of the adhesive layer opposite the substrate is 0.2 μm or more, and the adhesion strength B1 of the adhesive layer to the copper foil measured by the following peel test is 1 N / 15 mm or more.<Peel Test> The adhesive layer of the support film was superimposed on the shiny side of an electrolytic copper foil (thickness 18 μm, surface roughness 0.33 μm), a PET film was placed on the surface of the support film opposite the substrate, and the support film was sandwiched. Using a heat seal tester, heat was applied only from the adhesive layer side of the support film to perform thermocompression bonding. The bonding conditions were 150°C, 0.2 MPa, and 1 second. In accordance with JIS K 6854-2, the thermocompression-bonded support film was adjusted to a width of 15 mm, and the end of the thermocompression-bonded support film was fixed to the grip of an autograph tester. The interface between the adhesive layer and the electrolytic copper foil was peeled at a speed of 300 mm / min at a 180° angle. The peel strength was measured every 0.01 second for 4.00 seconds from the maximum peak at the start of peeling, and the average of the measured values ​​was measured as adhesion strength B1. [8] The support film according to any one of [1] to [7], wherein the substrate has a thickness of 4 to 100 μm. [9] The support film according to any one of [1] to [8], wherein the adhesive layer contains an organic filler.

[10] The support film according to [9], wherein the organic filler has an average particle size of 1 to 100 μm.

[11] The support film according to any one of [1] to

[10] , wherein the adhesive layer has a thickness of 1 to 30 μm.

[12] The support film according to any one of [1] to

[11] , wherein the adhesive layer has a thickness of 2 to 5 μm.

[13] The support film according to any one of [1] to

[12] , wherein the adhesive layer is formed by a wet coating method.

[14] The support film according to any one of [1] to

[13] , wherein the support film is wound into a roll.

[15] A semi-solid battery comprising: an outer bag obtained by using a support film; and a plurality of storage elements housed in the outer bag and arranged adjacent to each other, wherein the storage elements have a pair of electrodes each having a current collector and a semi-solid electrolyte, the support film being the support film according to claim 1 or 2, and the adhesive layer of the support film and the current collectors of the pair of electrodes are bonded to each other.

[16] A method for producing a support film for a current collector for a semi-solid battery, comprising: forming an adhesive layer on one surface of a substrate; wherein when the haze of a first test piece obtained by superposing the support films together so that the adhesive layers face each other is A1, and the haze of a second test piece obtained by thermocompression bonding the first test pieces is A2, the haze change rate [unit: %] calculated by ((A1-A2) / A1) x 100 is 25% or more.

[0009] According to the present disclosure, a support film is provided in which poor adhesion can be easily recognized visually.

[0010] FIG. 1 is a schematic cross-sectional view of a support film for a current collector for a semi-solid battery according to one embodiment.

[0011] Hereinafter, embodiments of the present disclosure will be described in detail, but the present disclosure is not limited to the following embodiments.

[0012] In the numerical ranges described herein, the upper or lower limit of the numerical range may be replaced with a value shown in the examples. Furthermore, the lower and upper limits of a numerical range can be arbitrarily combined with the lower or upper limit of another numerical range. When a numerical range is described as "A to B," the values ​​A and B at both ends are included as the lower and upper limits of the numerical range, respectively. In this specification, for example, "10 or more" means 10 and a value greater than 10, and this also applies when the numerical values ​​differ. Furthermore, for example, "10 or less" means 10 and a value less than 10, and this also applies when the numerical values ​​differ. Furthermore, unless otherwise specified, each component and material exemplified herein may be used alone or in combination of two or more types. In this specification, when multiple substances corresponding to each component are present in the composition, the content of each component in the composition refers to the total amount of the multiple substances present in the composition, unless otherwise specified.

[0013] <Support Film> Figure 1 is a schematic cross-sectional view of a support film for a current collector for a semi-solid battery according to one embodiment. The support film 10 includes a substrate 1 and an adhesive layer 2 disposed on one surface of the substrate 1. When a first test piece obtained by overlapping two support films 10 with their adhesive layers 2 facing each other has a haze of A1 and a second test piece obtained by thermocompression bonding the first test piece has a haze of A2, the haze change rate (unit: %) calculated by ((A1-A2) / A1) x 100 is 25% or more.

[0014] From the viewpoint of making poor adhesion more easily visible, the haze change rate may be 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more. The haze change rate may be, for example, 99.9% or less. The haze change rate may be 30% or more and 99.9% or less, 40% or more and 99.9% or less, 50% or more and 99.9% or less, 60% or more and 99.9% or less, 70% or more and 99.9% or less, 80% or more and 99.9% or less, or 90% or more and 99.9% or less.

[0015] From the viewpoint that having a certain degree of haze before thermocompression bonding makes poor adhesion more easily visible, the above-mentioned A1 may be 7% or more, 10% or more, 20% or more, 30% or more, 40% or more, or 50% or more, and may be 80% or less, 60% or less, 50% or less, 40% or less, 30% or less, or 25% or less.

[0016] The A2 may be 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, 6% or more, or 7% or more, and may be 10% or less, 9% or less, or 8% or less.

[0017] Methods for controlling the haze change rate, A1, and A2 include a method for controlling the film formation of a granular resin in the adhesive layer, a method for adding a filler to the adhesive layer, a method for forming an uneven shape on the surface of the adhesive layer by shaping treatment, and a method for forming islands by adding a material with low compatibility to the adhesive layer.

[0018] The above-mentioned A1 is measured as follows. That is, a pair of support films 10 is prepared. The pair of support films 10 are overlapped with each other so that the adhesive layers 2 face each other to obtain a first test piece. Using a haze meter, the haze is measured in a state where the first test piece is fixed so that light entering an integrating sphere from a light source passes through the first test piece in the thickness direction. This allows the above-mentioned A1 to be measured.

[0019] The above A2 is measured as follows. That is, a pair of support films 10 is prepared. The pair of support films 10 is overlapped with each other so that the adhesive layers 2 face each other to obtain a first test piece. The first test piece is thermocompression bonded using a hot stamping device to obtain a second test piece in which the support films are in close contact with each other. The thermocompression bonding conditions are a temperature of 140°C on the contact surface of the member in contact with the first test piece of the hot stamping device, a diameter of the contact surface of 2 cm, 300 kgf, and a time of 3 seconds. Using a haze meter, the haze is measured in a state in which the second test piece is fixed so that light entering an integrating sphere from a light source passes through the second test piece in the thickness direction. This allows the above A2 to be measured.

[0020] (Substrate) The substrate may be a resin substrate (resin film). Examples of resins constituting the substrate include polyolefins (LLDPE, PP, COP, CPP, etc.), polyesters (PET, etc.), fluororesins (PTFE, ETFE, EFEP, PFA, FEP, PCTFE, etc.), PVC, PVA, acrylic resins, epoxy resins, polyamides, polyimides, etc. The substrate is transparent, making it easier to check the contents (e.g., current collectors) and to detect any abnormalities. The substrate may be a laminate of multiple substrates.

[0021] The thickness of the substrate may be 4 μm or more, 5 μm or more, or 6 μm or more from the viewpoint of easily preventing a short circuit when an overvoltage is applied, and may be 100 μm or less, 50 μm or less, or 25 μm or less from the viewpoint of improving loading efficiency and enabling a high capacity by making the support film thinner. From these viewpoints, the thickness of the substrate may be 4 to 100 μm, 5 to 50 μm, or 6 to 25 μm.

[0022] (Adhesive Layer) The adhesive layer is a layer formed from a resin composition containing a binder resin and a liquid medium that dissolves and disperses the binder resin. The binder resin may be a thermoplastic resin, a thermosetting resin, or a mixture thereof.

[0023] Examples of thermoplastic resins include polyolefins such as polypropylene, polyethylene, polybutene, and polypentene; modified polyolefins, polyesters, polystyrenes, acrylonitrile-butadiene-styrene copolymers, methyl methacrylate-butadiene-styrene copolymers, ethylene-vinyl acetate copolymers, ethylene-propylene copolymers, ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, polycarbonates, polyphenylene ethers, acrylic copolymers, polyamides, polyvinyl chloride, polyvinyl alcohol (PVA), polyvinyl acetal, and ionomers. From the viewpoints of achieving better adhesion to the current collector, allowing the adhesive layer of the support film to remain on the current collector, and further suppressing the occurrence of short circuits, the adhesive layer may be formed from a resin composition containing at least one selected from the group consisting of modified polyolefins, polyesters, ethylene-vinyl acetate copolymers, ethylene-methacrylic acid copolymers, and ionomers.

[0024] Examples of the thermosetting resin include epoxy resin, phenol resin, polyurethane, polyisocyanate, polyisocyanurate, and polyvinyl ether.

[0025] The liquid medium may be an organic solvent, such as a water-soluble solvent, including alcohols such as methanol, ethanol, isopropyl alcohol, and n-propyl alcohol; ketones such as acetone and methyl ethyl ketone; glycols such as ethylene glycol and diethylene glycol; and glycol ethers such as N-methylpyrrolidone (NMP), tetrahydrofuran, and butyl cellosolve.

[0026] The resin composition may further contain other components in addition to the binder resin and the liquid medium, such as a curing agent, a filler, a lubricant, a UV absorber, a matting agent, a flexibility imparting agent, a surfactant, etc.

[0027] The resin composition may further contain a filler from the viewpoint of suppressing the occurrence of blocking when the support film is wound into a roll. The filler may be an organic filler or an inorganic filler.

[0028] Examples of organic fillers include fillers made of thermoplastic resins. A filler made of a thermoplastic resin means a filler in which the proportion of the thermoplastic resin in the filler is 90 mass % or more. When the filler is made of a thermoplastic resin, the filler made of the thermoplastic resin melts when the support film and the current collector are bonded by heating and / or pressure, which makes it easier to achieve excellent adhesion to the current collector while suppressing the occurrence of blocking.

[0029] When the organic filler is a filler made of a thermoplastic resin, the thermoplastic resin may be a polyolefin resin or an acid-modified polyolefin resin from the viewpoint of achieving better adhesion to the current collector.

[0030] The particle size of the filler is not particularly limited as long as it is within a range that provides a blocking suppression effect in the adhesive layer, and can be appropriately adjusted depending on the type of thermoplastic resin used in the adhesive layer and the film thickness of the adhesive layer. The average particle size of the filler may be 1 μm or more, 3 μm or more, or 5 μm or more from the viewpoint of providing a sufficient blocking suppression effect in the adhesive layer, and may be 100 μm or less, 30 μm or less, or 20 μm or less from the viewpoint of providing better adhesion to the current collector. From these viewpoints, the average particle size of the filler may be 1 to 100 μm, 3 to 30 μm, or 5 to 20 μm. In this specification, "average particle size" refers to the median diameter (D50) and can be measured using a laser diffraction particle size distribution analyzer.

[0031] The filler content may be 1 mass% or more, 2 mass% or more, or 3 mass% or more relative to the total mass of the thermoplastic resin, from the viewpoint of providing the adhesive layer with a sufficient blocking suppression effect, and may be less than 30 mass%, 20 mass% or less, or 10 mass% or less, from the viewpoint of excellent formability of the adhesive layer.

[0032] The adhesive layer may be a single layer or may be composed of multiple layers. When the adhesive layer is composed of multiple layers, each adhesive layer may be formed based on the description regarding the resin composition described above.

[0033] The thickness of the adhesive layer may be 1 μm or more, 1.5 μm or more, or 2 μm or more from the viewpoint of providing better adhesion to the current collector and allowing the adhesive layer of the support film to remain on the current collector even when the support film is peeled off, thereby further suppressing the occurrence of a short circuit. Furthermore, the thickness of the adhesive layer may be 50 μm or less, 30 μm or less, 10 μm or less, 8 μm or less, 6 μm or less, or 5 μm or less from the viewpoint of improving loading efficiency by thinning the support film, enabling a high capacity, and suppressing a decrease in handleability due to curling of the support film. Conventionally, when the adhesive layer is thin (e.g., 5 μm or less), poor adhesion with the current collector tends to occur, so it is required that the occurrence of poor adhesion be easily visually confirmed. However, by setting the haze change rate of the support film to 25% or more, even when the adhesive layer is thin (e.g., 5 μm or less), defective parts can be easily visually confirmed when poor adhesion occurs. This makes it easier to remove defective products during semi-solid battery production, thereby enabling the provision of safe semi-solid batteries. From these perspectives, the thickness of the adhesive layer may be 1 to 50 μm, 1 to 30 μm, 1.5 to 30 μm, 2 to 30 μm, 2 to 10 μm, 2 to 8 μm, 2 to 6 μm, or 2 to 5 μm.

[0034] The arithmetic mean roughness Ra of the surface of the adhesive layer (the surface opposite the substrate) may be 0.2 μm or more, 0.4 μm or more, 0.6 μm or more, 0.8 μm or more, or 1 μm or more, from the viewpoint of sufficiently imparting a blocking suppression effect to the adhesive layer. The arithmetic mean roughness Ra of the surface of the adhesive layer may be 2.0 μm or less, or 1.5 μm or less, from the viewpoint of better adhesion to the current collector, allowing the adhesive layer of the support film to remain on the current collector, and further suppressing the occurrence of short circuits. The arithmetic mean roughness Ra of the surface of the adhesive layer can be measured using a contact surface roughness meter (e.g., Mitutoyo, model number: SJ-210) in accordance with JIS B 0601 and JIS B 0031. The arithmetic mean roughness Ra of the surface of the adhesive layer can be adjusted, for example, by subjecting the surface of the adhesive layer to a shaping treatment, or by adding a filler to the resin composition forming the adhesive layer.

[0035] The surface of the adhesive layer may have an uneven shape. The uneven shape may be formed by a shaping treatment, and by performing the shaping treatment, it is possible to suppress blocking with the surface of the substrate on which the adhesive layer is not provided when the film is formed into a roll shape. The formation of the uneven shape by the shaping treatment can be confirmed using an optical microscope or a laser microscope, a surface roughness meter, a white light interference microscope, or the like. The uneven shape may also be formed by the resin composition forming the adhesive layer containing a filler, and the filler protruding from the surface of the adhesive layer. When the filler is made of a thermoplastic resin, the formation of an uneven shape on the surface of the adhesive layer by the filler suppresses blocking, and when the support film and the current collector are bonded by heating and / or pressure, the filler made of a thermoplastic resin melts, making it easier to achieve excellent adhesion to the current collector.

[0036] The adhesive strength B1 of the adhesive layer to the copper foil (hereinafter also simply referred to as "adhesion strength B1") may be 2 N / 15 mm or more, 3 N / 15 mm or more, 4 N / 15 mm or more, 5 N / 15 mm or more, 6 N / 15 mm or more, 7 N / 15 mm or more, or 8 N / 15 mm or more, from the viewpoint of achieving better adhesion to the current collector, allowing the adhesive layer of the support film to remain on the current collector, and further suppressing the occurrence of short circuits. The adhesive strength B1 may be 20 N / 15 mm or less, 15 N / 15 mm or less, or 10 N / 15 mm or less. The adhesive strength B1 can be adjusted by the type of binder resin and the type of filler contained in the resin composition forming the adhesive layer. For example, the adhesive strength B1 can be increased by increasing the acid value, lowering the melting point, using a filler with a small particle size, using a heat-fusible filler, etc.

[0037] The adhesion strength B1 can be measured by the following peel test. <Peel Test> The adhesive layer of the support film is superimposed on the shiny side of copper foil (electrolytic copper foil, thickness 18 μm, surface roughness 0.33 μm), and heat is applied only from the copper foil side of the support film using a heat seal tester to perform thermocompression bonding. The bonding conditions are 150°C, 0.2 MPa, and 1 second. In accordance with JIS K 6854-2, the thermocompression-bonded support film is adjusted to a width of 15 mm, the end of the thermocompression-bonded support film is fixed to the grip of an autograph tester, and the interface between the adhesive layer and the copper foil is peeled at a rate of 300 mm / min at a 180° angle. The peel strength is measured every 0.01 second for 4.00 seconds from the maximum peak at the start of peeling, and the average of the measured values ​​is measured as adhesion strength B1.

[0038] The adhesion strength B2 of the adhesive layer to the aluminum foil (hereinafter also simply referred to as "adhesion strength B2") may be 2 N / 15 mm or more, 3 N / 15 mm or more, 4 N / 15 mm or more, or 5 N / 15 mm or more, from the viewpoint of achieving better adhesion to the current collector, allowing the adhesive layer of the support film to remain on the current collector, and further suppressing the occurrence of short circuits. The adhesion strength B2 may be 10 N / 15 mm or less, 8 N / 15 mm or less, 7 N / 15 mm or less, or 4 N / 15 mm. The adhesion strength B2 can be adjusted by the type of binder resin contained in the resin composition forming the adhesive layer, the type of filler, etc. For example, the adhesion strength B2 can be increased by increasing the acid value, lowering the melting point, using a filler with a small particle size, or using a heat-fusible filler.

[0039] The adhesive layer may have an arithmetic mean roughness Ra of 0.2 μm or more on the surface opposite to the substrate, and an adhesion strength B1 of the adhesive layer to the copper foil measured in a peel test of 1 N / 15 mm or more. Such an adhesive layer has excellent adhesion to the current collector and can suppress the occurrence of blocking.

[0040] The adhesion strength B2 can be measured by the following peel test. <Peel Test> The adhesive layer of the support film and the glossy side of aluminum foil (thickness 7 μm, surface roughness 0.98 μm) are overlapped, a PET film is placed on the surface of the support film opposite the substrate, and the support film is sandwiched. Using a heat seal tester, heat is applied only from the adhesive layer side (aluminum foil side) of the support film to perform thermocompression bonding. The bonding conditions are 150 ° C, 0.2 MPa, and 1 second. In accordance with JIS K 6854-2, the thermocompression-bonded support film is adjusted to a width of 15 mm, the end of the thermocompression-bonded support film is fixed to the grip of an autograph tester, and the interface between the adhesive layer and the aluminum foil is peeled at a speed of 300 mm / min at a 180 ° peel angle. The peel strength is measured every 0.01 s for 4.00 seconds from the maximum peak at the start of peeling, and the average value of each measurement value is measured as adhesion strength B2.

[0041] The self-adhesion strength of the adhesive layer may be 2 N / 15 mm or more, 3 N / 15 mm or more, 4 N / 15 mm or more, or 5 N / 15 mm or more from the viewpoint of suppressing the intrusion of foreign matter such as moisture and the occurrence of short circuits. The self-adhesion strength may be 10 N / 15 mm or less, 8 N / 15 mm or less, 7 N / 15 mm or less, or 4 N / 15 mm. The self-adhesion strength can be adjusted by the type of binder resin, the type of filler, etc. contained in the resin composition that forms the adhesive layer.

[0042] The self-adhesion strength can be measured by the following peel test. <Peel Test> A pair of support films are overlapped with their respective adhesive layers facing each other, and a heat seal tester is used to apply heat only to one of the support films to perform thermocompression bonding. The bonding conditions are 150°C, 0.2 MPa, and 1 second. In accordance with JIS K 6854-2, the thermocompression-bonded support film is adjusted to a width of 15 mm, the end of the thermocompression-bonded support film is fixed to the grip of an autograph tester, and the interface between the adhesive layers is peeled at a rate of 300 mm / min at a 180° angle. The peel strength is measured every 0.01 second for 4.00 seconds from the maximum peak at the start of peeling, and the average of the measured values ​​is measured as the self-adhesion strength.

[0043] The adhesive layer can be formed by known methods. For example, the adhesive layer can be formed by applying a resin composition to a substrate, forming a coating film, and then drying the coating. The resin composition can be applied by a wet coating method, which facilitates uniform thickness of the adhesive layer, thereby preventing localized peeling of the adhesive layer of the support film from the current collector and further suppressing the occurrence of short circuits. That is, the above-mentioned support film can be obtained by a manufacturing method including a step of forming an adhesive layer on one side of the substrate. If the adhesive layer is formed by extrusion lamination, it is difficult to control the thickness of the adhesive layer, and differences in the in-plane thickness may result in localized reduced adhesion. Examples of wet coating methods include gravure coating, comma coating, dip coating, curtain coating, spin coating, sponge roll coating, and die coating. The coating film can be dried, for example, at 60 to 100°C for 0.5 to 2 minutes.

[0044] The support film may further include layers other than the substrate and the adhesive layer. For example, the support film may include a release layer on the surface of the adhesive layer opposite the substrate.

[0045] The support film described above may or may not be wound into a roll, but is preferably wound into a roll. In this case, the support film can be processed to any size as needed. Furthermore, continuous adhesion to the current collector becomes possible, improving efficiency in terms of storage. In particular, when the width of the adhesive layer (the length perpendicular to the thickness) is 600 mm or more, the support film is preferably wound into a roll.

[0046] The support film can be used as a support film for a current collector for a semi-solid battery. The support film can be adhered to the current collector for a semi-solid battery by applying heat and / or pressure to the current collector for a semi-solid battery.

[0047] The current collector for a semi-solid battery is, for example, a substrate, sheet, or foil containing a conductive material. The current collector for a semi-solid battery may contain aluminum, copper, lithium, nickel, stainless steel, tantalum, titanium, tungsten, vanadium, or an alloy of these metals. The current collector for a semi-solid battery may contain a non-metallic material such as carbon, carbon nanotubes, or a metal oxide. The current collector for a semi-solid battery may also be a mixture of these. From the viewpoint of enabling high capacity, the current collector for a semi-solid battery is preferably thin, and may be, for example, 20 μm or less.

[0048] An outer bag for a semi-solid battery can be obtained using the support film described above. That is, another embodiment of the present disclosure is a semi-solid battery including an outer bag obtained using the support film described above and a plurality of energy storage elements housed in the outer bag and arranged adjacent to each other, the energy storage elements including a pair of electrodes each having a current collector and a semi-solid electrolyte, and the adhesive layer of the support film and the current collectors of the pair of electrodes are bonded to each other.

[0049] The present disclosure will be specifically described below with reference to examples, but the present disclosure is not limited to the following examples.

[0050] <Preparation of Support Film> (Example 1) Aquatex EC-1700 (manufactured by Japan Coating Resins, EVA) was applied as an adhesive composition onto a PET substrate (manufactured by Toray Industries, Inc., thickness: 12 μm) using a bar coater so that the thickness after drying would be 2 μm. After coating, the coating was dried at 100° C. for 1 minute to prepare a support film.

[0051] (Example 2) A support film was prepared in the same manner as in Example 1, except that the following composition 1 was used as the adhesive layer composition and composition 1 was applied so that the adhesive layer had a thickness of 4.5 μm after drying.

[0052] ((Composition 1)) Superchlorine 930 (manufactured by Nippon Paper Industries Co., Ltd., acid-modified chlorinated olefin) 100 parts by mass Unistall E200EM (manufactured by Mitsui Chemicals Co., Ltd., acid-modified olefin filler) 1 part by mass

[0053] (Example 3) A support film was prepared in the same manner as in Example 1, except that the following composition 2 was used as the adhesive layer composition and composition 2 was applied so that the adhesive layer had a thickness of 2.5 μm after drying.

[0054] ((Composition 2)) Superchlorine 930 (manufactured by Nippon Paper Industries Co., Ltd., acid-modified chlorinated olefin) 100 parts by mass (solid content 20 parts by mass) Unistall E200EM (manufactured by Mitsui Chemicals Co., Ltd., acid-modified olefin filler, dispersed in organic solvent at 15% by mass of solid content, median diameter (D50) 17 μm) 3 parts by mass

[0055] (Example 4) A support film was prepared in the same manner as in Example 1, except that the following composition 3 was used as the adhesive layer composition and composition 3 was applied so that the adhesive layer had a thickness of 8.5 μm after drying.

[0056] ((Composition 3)) 100 parts by mass of UNISTOLE XP04 (manufactured by Mitsui Chemicals, acid-modified olefin) 5 parts by mass of UNISTOLE E200EM (manufactured by Mitsui Chemicals, acid-modified olefin filler)

[0057] (Comparative Example 1) A support film was prepared in the same manner as in Example 1, except that Aquatex AC3100 (manufactured by Japan Coating Resins, EMAA) was used as the adhesive layer composition and the composition was applied so that the adhesive layer would have a thickness of 4 μm after drying.

[0058] (Comparative Example 2) A support film was produced in the same manner as in Example 1, except that Arrowbase SE-1030N (manufactured by Unitika, acid-modified olefin) was used as the adhesive layer composition, and the composition was applied so that the adhesive layer had a thickness of 3.5 μm after drying.

[0059] <Thermocompression bonding 1> A pair of support films from each Example and Comparative Example was overlapped with each other with the adhesive layers facing each other to obtain a first test piece. The first test piece was thermocompression bonded using a hot stamping device (NAVITAS V10) to obtain a second test piece in which the support films were in close contact with each other. The thermocompression bonding conditions were as follows: the temperature of the contact surface of the member in contact with the first test piece in the hot stamping device was 140°C (the set temperature of the hot stamping device was 150°C), the diameter of the contact surface was 2 cm, and the pressure was 300 kgf for 3 seconds.

[0060] <Haze Measurement> A pair of support films in each Example and Comparative Example was overlaid on each other with the adhesive layers facing each other to obtain a first test piece. The haze (unit: %) was measured using a haze meter (BYK-Gardner Haze-Guard Plus, manufactured by BYK) with the first test piece fixed so that light entering an integrating sphere from a light source passed through the first test piece in the thickness direction.

[0061] In addition, a second test piece in which the support films were closely attached to each other was obtained by thermocompression bonding the first test piece using a hot stamping machine (NAVITAS V10). The thermocompression bonding conditions were: the temperature of the contact surface of the member in contact with the first test piece of the hot stamping machine was 140 ° C (the set temperature of the hot stamping machine was 150 ° C), the diameter of the contact surface was 2 cm, 300 kgf, and 3 seconds. The haze of the second test piece was also measured in the same manner as the first test piece. The haze of the first test piece was designated A1, and the haze of the second test piece was designated A2, and these are shown in Table 1. The haze change rate was calculated as ((A1 - A2) / A1) x 100. When the haze change rate was 25% or more, it was determined that the visibility in the event of poor adhesion was high and the result was good, and it was given an "A" rating. When the haze change rate was less than 25%, it was determined that the visibility in the event of poor adhesion was low and the result was poor, and it was given a "B" rating. The results are shown in Table 1.

[0062] <Thermocompression bonding 2> The adhesive layer side of the support film and copper foil (thickness 18 μm, surface roughness 0.33 μm) were overlapped, and a PET film was placed on the surface of the support film opposite the substrate, sandwiching the support film. A heat seal tester TP-701-B (Tester Sangyo) was used to apply heat only from the copper foil side (the adhesive layer side of the support film) for compression bonding. The compression bonding conditions were 150 ° C, 0.2 MPa, and 1 second. A third test piece was obtained. A fourth test piece was obtained in the same manner as the third test piece, except that aluminum foil was used instead of copper foil. For each of the pair of support films in each example and comparative example, the adhesive layers were overlapped with each other, and compression bonding was performed by applying heat from one of the support film sides using a heat seal tester TP-701-B (Tester Sangyo). The compression bonding conditions were the same as for the third test piece. A fifth test piece was obtained in this manner.

[0063] <Peel Strength Test> The adhesion strength of the third test piece was measured in accordance with JIS K 6854-2. Specifically, each test piece was adjusted to a width of 15 mm, the end of the support film was fixed to the grip of an autograph tester (trade name: AGS-X, manufactured by Shimadzu Corporation), and peeled at a speed of 300 mm / min at a 180° angle. The peel strength was measured every 0.01 s for 4.00 seconds from the maximum peak at the start of peeling, and the average value of each measured value was taken as the adhesion strength with the copper foil. In addition, for the fourth test piece, the peel strength was measured every 0.01 s for 4.00 seconds from the maximum peak at the start of peeling, as in the case of the third test piece, and the average value of each measured value was taken as the adhesion strength with the aluminum foil. The adhesion strength with the copper foil was designated B1, and the adhesion strength with the aluminum foil was designated B2. Similarly to the third test piece, the peel strength of the fifth test piece was measured every 0.01 s for 4.00 seconds from the maximum peak at the start of peeling, and the average of the measured values ​​was calculated as the self-adhesion strength. The results are shown in Table 1.

[0064] <Measurement of arithmetic mean roughness Ra> The arithmetic mean roughness Ra of the surface of the adhesive layer of each support film (the surface opposite to the PET substrate) was measured using a contact surface roughness meter (manufactured by Mitutoyo, model number: SJ-210) in accordance with JIS B 0601 and JIS B 0031. Ra was measured at five different points on the surface of the adhesive layer, and the average was taken as the surface roughness of the adhesive layer. The results are shown in Table 1.

[0065]

[0066] The support films of Examples 1 to 4 had a haze A1 of 7 or more and a haze change rate of 25% or more, which resulted in high visibility in the event of poor adhesion, and were therefore favorable results. Furthermore, all of them had high metal adhesion, making them suitable for use as support films for semi-solid batteries. On the other hand, Comparative Examples 1 and 2 had low haze change rates, making poor adhesion difficult to detect.

[0067] <Blocking test> Two sheets of the support films produced in Examples 2, 3, and 6, cut to 50 mm x 50 mm, were stacked and sandwiched in a hydraulic molding machine (product name: TT-5-2, manufactured by Toho International), and a blocking test was carried out at 70°C and 60 kgf for 1 minute. No sticking between the support films produced in Examples 2, 3, and 6 was observed, and blocking was suppressed.

[0068] 1...substrate, 2...adhesive layer, 10...support film

Claims

1. A support film for a current collector for a semi-solid battery, comprising a substrate and an adhesive layer disposed on one surface of the substrate, wherein when the haze of a first test piece obtained by overlapping the support films with the adhesive layers facing each other is A1 and the haze of a second test piece obtained by thermocompression bonding the first test piece is A2, the haze change rate (unit: %) calculated as ((A1-A2) / A1) x 100 is 25% or more.

2. The support film according to claim 1, wherein A1 is 7% or more.

3. The support film according to claim 1 or 2, wherein the substrate contains polyester and the adhesive layer contains a thermoplastic resin.

4. The support film of claim 3, wherein the thermoplastic resin is an ethylene-vinyl acetate copolymer.

5. A support film according to claim 1 or 2, wherein the adhesive layer has an arithmetic mean roughness Ra of 0.4 μm or more on the surface opposite to the substrate.

6. The support film according to claim 1 or 2, wherein the adhesive strength B1 of the adhesive layer to the copper foil measured by the following peel test is 5 N / 15 mm or more. <Peel Test> The adhesive layer of the support film is superimposed on the shiny side of an electrolytic copper foil (thickness 18 μm, surface roughness 0.33 μm), a PET film is placed on the surface of the support film opposite the substrate, and the support film is sandwiched between them. Using a heat seal tester, heat is applied only from the adhesive layer side of the support film to perform thermocompression bonding. The compression conditions are 150°C, 0.2 MPa, and 1 second. In accordance with JIS K 6854-2, the thermocompression-bonded support film is adjusted to a width of 15 mm, and the end of the thermocompression-bonded support film is fixed to the gripping portion of an autograph testing machine. The adhesive layer and the electrolytic copper foil are peeled at an angle of 180° at a speed of 300 mm / min at the interface between them, and the peel strength is measured every 0.01 s for 4.00 seconds from the maximum peak at the start of peeling, and the average value of the measured values ​​is measured as adhesion strength B1.

7. The support film according to claim 1 or 2, wherein the arithmetic mean roughness Ra of the adhesive layer on the surface opposite the substrate is 0.2 μm or more, and the adhesive strength B1 of the adhesive layer to copper foil measured in the following peel test is 1 N / 15 mm or more. <Peel Test> The adhesive layer of the support film is superimposed on the shiny side of electrolytic copper foil (thickness 18 μm, surface roughness 0.33 μm), a PET film is placed on the surface of the support film opposite the substrate, and the support film is sandwiched between them. Using a heat seal tester, heat is applied only from the adhesive layer side of the support film to perform thermocompression bonding. The compression conditions are 150°C, 0.2 MPa, and 1 second. In accordance with JIS K 6854-2, the thermocompression-bonded support film is adjusted to a width of 15 mm, and the end of the thermocompression-bonded support film is fixed to the gripping portion of an autograph testing machine. The adhesive layer and the electrolytic copper foil are peeled at an angle of 180° at a speed of 300 mm / min at the interface between them, and the peel strength is measured every 0.01 s for 4.00 seconds from the maximum peak at the start of peeling, and the average value of the measured values ​​is measured as adhesion strength B1.

8. The support film according to claim 1 or 2, wherein the thickness of the substrate is 4 to 100 μm.

9. The support film of claim 1 or 2, wherein the adhesive layer comprises an organic filler.

10. The support film according to claim 9, wherein the organic filler has an average particle size of 1 to 100 μm.

11. The support film according to claim 1 or 2, wherein the adhesive layer has a thickness of 1 to 30 μm.

12. The support film according to claim 1 or 2, wherein the adhesive layer has a thickness of 2 to 5 μm.

13. The support film according to claim 1 or 2, wherein the adhesive layer is formed by a wet coating method.

14. The support film according to claim 1 or 2, which is wound into a roll.

15. A semi-solid battery comprising: an outer bag obtained by using a support film; and a plurality of storage elements housed in the outer bag and arranged adjacent to each other, wherein the storage elements have a pair of electrodes each having a current collector, and a semi-solid electrolyte, the support film being the support film defined in claim 1 or 2, and the adhesive layer of the support film being bonded to the current collectors of the pair of electrodes.

16. A method for manufacturing a support film for a current collector for a semi-solid battery, comprising a step of forming an adhesive layer on one side of a substrate, wherein when the haze of a first test piece obtained by overlapping the support films with the adhesive layers facing each other is A1 and the haze of a second test piece obtained by thermocompression bonding the first test piece is A2, the haze change rate (unit: %) calculated as ((A1-A2) / A1) x 100 is 25% or more.

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