Support film for current collector for semi-solid battery

Abstract

A support film according to the present invention is a support film for a current collector for a semi-solid battery and includes: a substrate; and an adhesive layer disposed on one surface of the substrate. The adhesive strength A1 of the adhesive layer to a copper foil as measured by a peel test is 2 N / 15 mm or more. The adhesive strength A1 is greater than the adhesive strength A2 of the adhesive layer to the substrate as measured by a peel test. A semi-solid battery according to the present invention includes: an outer bag obtained by using the support film; and a plurality of power storage elements accommodated in the outer bag and provided adjacent to each other. The power storage elements respectively have a pair of electrodes each having a current collector, and a semi-solid electrolyte. The adhesive layer of the support film is bonded to the current collectors of the pairs of electrodes.

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] The support film must be in close contact with the current collector to protect it from moisture and other foreign matter. However, when an excessive load is applied to the battery, the support film may peel off from the current collector. If water or other foreign matter gets into the support film while it is peeled off from the current collector, the electrodes may short-circuit, potentially causing a fire or other problem.

[0006] Therefore, an object of the present disclosure is to provide a support film for a current collector for a semi-solid battery, which has excellent adhesion to the current collector and, even when the support film is peeled off, allows the adhesive layer of the support film to remain on the current collector, thereby suppressing the occurrence of a short circuit.

[0007] One aspect of the present disclosure includes, for example, the following invention. [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 the adhesive layer has an adhesion strength A1 to a copper foil of 2 N / 15 mm or more as measured in the following peel test, and the adhesion strength A1 is greater than the adhesion strength A2 of the adhesive layer to the substrate as measured in 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. According to 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 adhesive layer and the electrolytic copper foil are peeled at a 180° angle at a rate of 300 mm / min at the interface between the adhesive layer and the electrolytic copper foil. The peel strength is measured every 0.01 s from the maximum peak at the start of peeling for 4.00 seconds, and the average of the measured values ​​is defined as adhesion strength A1. The adhesive layer and the substrate are peeled at a 180° angle at a rate of 300 mm / min at the interface between the adhesive layer and the substrate. The peel strength is measured every 0.01 s from the maximum peak at the start of peeling for 4.00 seconds, and the average of the measured values ​​is defined as adhesion strength A2. [2] The support film according to [1], wherein, after the support film is adhered to the copper foil, peeling occurs at the interface between the substrate and the adhesive layer when the substrate is peeled. [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 thickness of the substrate is 4 to 100 μm. [6] The support film according to any one of [1] to [5], wherein the thickness of the adhesive layer is 2 to 30 μm. [7] The support film according to any one of [1] to [6], wherein the thickness of the adhesive layer is 2 to 5 μm.[8] The support film according to any one of [1] to [7], wherein the adhesion strength A1 is 6 N / 15 mm or more. [9] The support film according to any one of [1] to [8], wherein the adhesion strength A2 is 5 N / 15 mm or less.

[10] The support film according to any one of [1] to [9], wherein the difference between the adhesion strength A1 and the adhesion strength A2 (the adhesion strength A1 - the adhesion strength A2) is 0.4 N / 15 mm or more.

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

[10] , wherein a support film having an adhesive layer of thickness T1 and a support film having an adhesive layer of thickness T2 (where T2 > T1) are prepared, and when the adhesion strength of the adhesive layer of thickness T1 to the copper foil is X1 and the adhesion strength of the adhesive layer of thickness T2 to the copper foil is X2, as measured in the following peel test, (X2 - X1) / (T2 - T1) is 0.7 [(N / 15 mm) / μm] or less. <Peel Test> The adhesive layer (thickness T1 or T2) 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 between them. 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 X1 and X2.

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

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

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

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

[14] A semi-solid battery comprising: an outer bag obtained using a support film; and a plurality of electric storage elements housed in the outer bag and arranged adjacent to each other, wherein the electric 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 together.

[15] 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 surface of a substrate, wherein the adhesive layer has an adhesion strength A1 to a copper foil of 2 N / 15 mm or more as measured in the following peel test, and the adhesion strength A1 is greater than the adhesion strength A2 of the adhesive layer to the substrate as measured in the following peel test. <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) or a test substrate identical to the substrate, and a PET film was placed on the surface of the support film opposite the substrate to sandwich the support film, and heat was applied only from the adhesive layer side of the support film using a heat seal tester to perform thermocompression bonding under the conditions of 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. The average of the measured values ​​is defined as adhesion strength A1. The adhesive layer and the test substrate 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. The average of the measured values ​​is defined as adhesion strength A2.

[0008] According to the present disclosure, it is possible to provide a support film for a current collector for a semi-solid battery, which has excellent adhesion to the current collector, and even when the support film is peeled off, the adhesive layer of the support film remains on the current collector, thereby suppressing the occurrence of a short circuit.

[0009] 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.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail, but the present disclosure is not limited to the following embodiments.

[0011] 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.

[0012] 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.

[0013] (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.

[0014] 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.

[0015] (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.

[0016] 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.

[0017] Examples of the thermosetting resin include epoxy resin, phenol resin, polyurethane, polyisocyanate, polyisocyanurate, and polyvinyl ether.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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. In this specification, "average particle size" means the median diameter (D50) and can be measured using a laser diffraction particle size distribution analyzer.

[0024] 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.

[0025] 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.

[0026] 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, or 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 making the support film thinner, enabling a higher capacity, and suppressing a decrease in handleability due to curling of the support film. Note that, in the past, when the adhesive layer was thin (for example, 5 μm or less), there were cases where adhesion to the current collector was insufficient or where the adhesive layer of the support film remained on the current collector when the support film was peeled off, thereby suppressing the occurrence of a short circuit. However, when the adhesive layer has an adhesion strength A1 of 2 N / 15 mm or more and is greater than the adhesion strength A2, there is excellent adhesion to the current collector, and even when the support film is peeled off, the adhesive layer of the support film remains on the current collector, thereby suppressing the occurrence of a short circuit. 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.

[0027] The arithmetic mean roughness Ra of the surface of the adhesive layer 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 performing a shaping treatment on the surface of the adhesive layer or by adding a filler to the resin composition forming the adhesive layer.

[0028] 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.

[0029] The adhesive strength A1 of the adhesive layer to the copper foil is 2 N / 15 mm or more. The adhesive strength A1 can be measured by the following peel test. <Peel Test> The adhesive layer of the support film and the shiny side of an electrolytic copper foil (thickness 18 μm, surface roughness 0.33 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 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, the end of the thermocompression-bonded support film is fixed to the gripping portion of an autograph testing machine, and the interface between the adhesive layer and the electrolytic copper foil is peeled at an angle of 180° at a speed of 300 mm / min. 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 recorded as adhesion strength A1.

[0030] The adhesion strength A1 may be 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 adhesion strength A1 may be 10 N / 15 mm or less, 8 N / 15 mm or less, 6 N / 15 mm or less, or 4 N / 15 mm. The adhesion strength A1 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 adhesion strength A1 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.

[0031] The adhesion strength A1 is greater than the adhesion strength A2 of the adhesive layer to the substrate. The adhesion strength A2 can be measured by the following peel test. <Peel Test> The adhesive layer of the support film and a test substrate identical to the substrate are overlapped, 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 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 test substrate is peeled 180 degrees at a speed of 300 mm / min. 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 A2.

[0032] The adhesion strength A2 may be 8 N / 15 mm or less, 7 N / 15 mm or less, 6 N / 15 mm or less, 5 N / 15 mm or less, 4 N / 15 mm or less, 3 N / 15 mm or less, or 2 N / 15 mm or less, from the viewpoint that even when the support film is peeled off, the adhesive layer of the support film remains on the current collector and the occurrence of a short circuit is easily suppressed. The adhesion strength A2 may be 0.5 N / 15 mm or more, 1 N / 15 mm or more, 2 N / 15 mm or more, or 3 N / 15 mm or more, from the viewpoint of excellent adhesion to the substrate. The adhesion strength A2 can be adjusted by the type of binder resin, the type of filler, etc., contained in the resin composition that forms the adhesive layer.

[0033] The difference between the adhesion force A1 and the adhesion force A2 (adhesion force A1 - adhesion force A2) may be 0.4 N / 15 mm or more, 0.8 N / 15 mm or more, 1 N / 15 mm or more, 1.2 N / 15 mm or more, 1.4 N / 15 mm or more, 1.6 N / 15 mm or more, 1.8 N / 15 mm or more, or 2 N / 15 mm or more, from the viewpoint that even when the support film is peeled off, the adhesive layer of the support film remains on the current collector and the occurrence of a short circuit is easily suppressed. The difference between the adhesion force A1 and the adhesion force A2 (adhesion force A1 - adhesion force A2) may be 5 N / 15 mm or less, 4 N / 15 mm or less, 3 N / 15 mm or less, or 2 N / 15 mm or less.

[0034] When a support film having an adhesive layer with a thickness T1 and a support film having an adhesive layer with a thickness T2 (where T2 > T1) are prepared, and the adhesion strength of the adhesive layer with thickness T1 to the copper foil is X1 and the adhesion strength of the adhesive layer with thickness T2 to the copper foil as measured in the following peel test is X2, (X2 - X1) / (T2 - T1) may be 0.7 [(N / 15 mm) / μm] or less. When (X2 - X1) / (T2 - T1) is small to a certain extent, adhesion failure during thermocompression bonding with the current collector is less likely to occur. The reason for this is that the larger the (X2 - X1) / (T2 - T1) ratio, the greater the variation in adhesion strength relative to the thickness of the adhesive layer, making localized adhesion failure within the surface of the adhesive layer more likely to occur. However, when (X2 - X1) / (T2 - T1) ratio is small, the adhesion strength of the entire adhesive layer becomes uniform, making adhesion failure less likely to occur. <Peel Test> The adhesive layer (thickness T1 or T2) of a support film was superimposed on the glossy 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 edge 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 each measurement value was measured as adhesion strength X1 and X2.

[0035] From the viewpoint of making poor adhesion less likely to occur during thermocompression bonding with the current collector, (X2-X1) / (T2-T1) may be 0.6 (N / 15 mm) / μm or less, 0.5 (N / 15 mm) / μm or less, 0.4 (N / 15 mm) / μm or less, 0.3 (N / 15 mm) / μm or less, 0.2 (N / 15 mm) / μm or less, or 0.1 (N / 15 mm) / μm or less.

[0036] The support film described above may have a standard deviation α of the adhesive layer thickness calculated by the following calculation method, which may be less than 1.0 μm. <Method for Calculating Standard Deviation α of Adhesive Layer Thickness> The method for calculating the standard deviation α of the adhesive layer thickness is performed by the following steps (1) to (6). (1) When a test piece obtained by cutting a support film into a rectangle is viewed in plan from the adhesive layer side, the rectangular area defined between a pair of short sides of the adhesive layer is divided into 30 equal parts along a direction perpendicular to the pair of short sides, and the thickness A1a (μm) of the test piece is measured in each of the 30 divided areas. (2) When the test piece is viewed in plan from the adhesive layer side, the rectangular area defined between a pair of long sides of the adhesive layer is divided into 30 equal parts along a direction perpendicular to the pair of long sides, and the thickness A1b (μm) of the test piece is measured in each of the 30 divided areas. (3) The thickness of the substrate is measured at five locations, and the average of the measured thicknesses is calculated as the average thickness A2a (μm) of the substrate. (4) The thicknesses A3a (μm) and A3b (μm) of the adhesive layer in the 30 divided regions are calculated based on the following formulas (F1) and (F2): A3a = A1a - A2a ... (F1) A3b = A1b - A2a ... (F2) (5) The average values ​​of the adhesive layer thicknesses A3a and A3b in (4) are determined as the average adhesive layer thicknesses A4a and A4b, respectively. (6) The first standard deviation of the adhesive layer thickness is calculated from the average adhesive layer thickness A4a and the adhesive layer thickness A3a, and the second standard deviation of the adhesive layer thickness is calculated from the average adhesive layer thickness A4b and the adhesive layer thickness A3b. The larger of the first and second standard deviations is designated as the standard deviation α of the adhesive layer thickness.

[0037] A small standard deviation α of the adhesive layer thickness reduces the surface irregularities of the adhesive layer, and therefore, even if a current collector and an active material layer are sequentially formed on top of the adhesive layer, the surface of the active material layer formed on top of the current collector and the active material layer will also be smoother. This reduces the likelihood of poor contact between the semi-solid electrolyte and the active material layer, and reduces the increase in contact resistance. As a result, localized heat generation is reduced, which can suppress deterioration of the energy storage element and the resulting degradation of the performance of the semi-solid battery. The value of the standard deviation α of the adhesive layer thickness serves as an indicator of the degree of variation in the adhesive layer thickness; the smaller the value of the standard deviation α of the adhesive layer thickness, the smaller the variation in the adhesive layer thickness. The larger the value of the standard deviation α of the adhesive layer thickness, the greater the variation in the adhesive layer thickness.

[0038] The value of the standard deviation α of the adhesive layer thickness may be 0.90 or less, or 0.80 or less. When the value of the standard deviation α of the adhesive layer thickness is 0.90 or less, short circuits between adjacent energy storage elements can be further suppressed, and deterioration of the performance of the semi-solid battery due to deterioration of the energy storage elements can be further suppressed. The value of the standard deviation α of the adhesive layer thickness may be 0.10 or more, 0.15 or more, or 0.20 or more. Note that the value of the standard deviation α of the adhesive layer thickness increases as the thickness of the adhesive layer increases and decreases as the thickness of the adhesive layer decreases, and therefore, can be adjusted by adjusting the thickness of the adhesive layer.

[0039] The size of the test piece used to determine the standard deviation α of the adhesive layer thickness can be, for example, 100 mm x 270 mm.

[0040] The support film may be one that peels off at the interface between the substrate and the adhesive layer when the substrate is peeled off after the support film is adhered to copper foil (the copper foil used in measuring adhesion strength A1). That is, the support film may be one that does not peel off at the interface between the adhesive layer and the copper foil when the substrate is peeled off after the support film is adhered to copper foil (the copper foil used in measuring adhesion strength A1). If the support film is one that peels off at the interface between the substrate and the adhesive layer when the substrate is peeled off after the support film is adhered to copper foil (the copper foil used in measuring adhesion strength A1), the adhesive layer of the support film remains on the current collector even when the support film is peeled off from the current collector, thereby further suppressing the occurrence of a short circuit.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] The present disclosure will be specifically described below with reference to examples, but the present disclosure is not limited to the following examples.

[0048] Example 1 Chemipearl S300 (ethylene-unsaturated carboxylic acid copolymer, manufactured by Mitsui Chemicals, Inc.) was applied to a PET substrate (manufactured by Toray Industries, Inc., product name: P60, thickness: 12 μm) using a bar coater. After coating, the coating was dried at 100° C. for 1 minute to produce a support film having an adhesive layer of 8.5 μm thickness on the substrate.

[0049] (Example 2) A support film was produced in the same manner as in Example 1, except that Arrowbase SE-1030N (acid-modified olefin, manufactured by Unitika Ltd.) was used instead of Chemipearl S300, and the thickness of the adhesive layer after drying was 3.5 μm.

[0050] (Example 3) A support film was prepared in the same manner as in Example 1, except that Aquatex EC1700 (ethylene vinyl acetate copolymer, manufactured by Japan Coating Resins Co., Ltd.) was used instead of Chemipearl S300, and the thickness of the adhesive layer after drying was 2.0 μm.

[0051] Example 4 A support film was prepared in the same manner as in Example 3, except that the thickness of the adhesive layer after drying was 3.6 μm.

[0052] Example 5 A support film was prepared in the same manner as in Example 3, except that the thickness of the adhesive layer after drying was 5.0 μm.

[0053] (Example 6) A support film was prepared in the same manner as in Example 1, except that Aquatex AC3100 (ethylene methacrylic acid copolymer, manufactured by Japan Coating Resins Co., Ltd.) was used instead of Chemipearl S300, and the thickness of the adhesive layer after drying was 4.0 μm.

[0054] (Example 7) A support film was prepared in the same manner as in Example 1, except that Superchlorine 930 (acid-modified chlorinated olefin, manufactured by Nippon Paper Industries Co., Ltd.) was used instead of Chemipearl S300, the drying conditions were 80°C for 1 minute, and the thickness of the adhesive layer after drying was 2.0 μm.

[0055] Example 8 A support film was prepared in the same manner as in Example 7, except that the thickness of the adhesive layer after drying was 5.0 μm.

[0056] Example 9 A support film was produced in the same manner as in Example 1, except that a mixed solution of 100 parts by mass of Superchlorine 930 (acid-modified chlorinated olefin, manufactured by Nippon Paper Industries Co., Ltd., solid content 20 parts by mass) and 3 parts by mass (solid content) of Unistall E-200EM (acid-modified polyolefin particles, dispersed in an organic solvent at a solid content of 15% by mass, median diameter (D50) 17 μm, manufactured by Mitsui Chemicals, Inc.) was used instead of Chemipearl S300, the drying conditions were 80° C. for 1 minute, and the thickness of the adhesive layer after drying was 2.0 μm.

[0057] (Comparative Example 1) A support film was prepared in the same manner as in Example 1, except that Elitel UE9800 (polyester resin, manufactured by Unitika Ltd.) was used instead of Chemipearl S300, the drying conditions were 80°C for 1 minute, and the thickness of the adhesive layer after drying was 2.5 μm.

[0058] Comparative Example 2 A support film was produced in the same manner as in Example 1, except that NeoCryl A1125 (manufactured by Covestro Corporation) was used instead of Chemipearl S300, and the thickness of the adhesive layer after drying was 2.0 μm.

[0059] (Comparative Example 3) A support film was produced in the same manner as in Example 1, except that UNISTOL XP04 (acid-modified olefin, manufactured by Mitsui Chemicals, Inc.) was used instead of CHEMIPEARL S300, the drying conditions were 80°C for 1 minute, and the thickness of the adhesive layer after drying was 3.0 µm.

[0060] <Thermocompression bonding> (Thermocompression bonding with copper foil) The adhesive layer of the prepared support film was superimposed on the shiny side of an electrolytic copper foil (thickness 18 μm, surface roughness 0.33 μm, product name: 4-1592-02, manufactured by AS ONE), and the support film was sandwiched between PET films (thickness 25 μm, product name: Lumirror S10, manufactured by Toray) in the following order: PET film / electrolytic copper foil / support film / PET film. Thermocompression bonding was performed by applying heat only from the electrolytic copper foil side using a heat seal tester (product name: TP-701-B, manufactured by Tester Sangyo Co., Ltd.). The bonding conditions were 150°C, 0.2 MPa, and 1 second.

[0061] (Thermocompression bonding with substrate) The adhesive layer of the prepared support film and a test PET substrate (manufactured by Toray Industries, Inc., trade name: P60, thickness: 12 μm) were superimposed, and the support film was sandwiched using a PET film (thickness 25 μm, trade name: Lumirror S10, manufactured by Toray) in the order PET film / test PET substrate / support film / PET film, and thermocompression bonding was performed by applying heat only from the test PET substrate side using a heat seal tester (trade name: TP-701-B, manufactured by Tester Sangyo Co., Ltd.). The compression bonding conditions were 150°C, 0.2 MPa, and 1 second.

[0062] <Peel Test> In accordance with JIS K 6854-2, a thermocompression-bonded support film was adjusted to a width of 15 mm, and the edge of the support film was fixed to the grip of an autograph testing machine (product name: AGS-X, manufactured by Shimadzu Corporation). The adhesive layer was peeled at a speed of 300 mm / min at a 180° angle at the interface between the adhesive layer and the electrolytic copper foil or the test PET substrate. 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 the measured values ​​was taken as the adhesion strength. The adhesion strength to the copper foil was designated A1, and the adhesion strength to the test PET substrate was designated A2. The measurement results are shown in Tables 1 and 2.

[0063]

[0064]

[0065] The support films produced in Examples 1 to 9 had an adhesion strength A1 of 2 N / 15 mm or more, and had a relationship of adhesion strength A1 > adhesion strength A2. On the other hand, in Comparative Examples 1 and 2, the adhesion strength A1 was less than 2 N / 15 mm, making it difficult to use them as support films for current collectors for semi-solid batteries. In Comparative Example 3, although the adhesion strength A1 was 2 N / 15 mm or more, the relationship of adhesion strength A1 < adhesion strength A2 was satisfied, and when the support film was peeled off from the current collector, the current collector was exposed, which could cause a short circuit.

[0066] <Evaluation of Adhesion Variation> Support films prepared in Examples 1, 4, and 6 were prepared with only the thickness of the adhesive layer varied. A peel test was conducted to evaluate the adhesion to the copper foil. The adhesion A1 at thickness T1 was designated X1, and the adhesion A1 at thickness T2 (T2 > T1) was designated X2. Furthermore, a peel test was conducted to evaluate the adhesion to the copper foil using the thinner support film (thickness T1) of the two support films. The maximum convex peak value M (excluding the maximum peak at the start of peeling) and the minimum concave peak value m were measured, and the adhesion variation (M-m) / adhesion X1 x 100 (%) was evaluated. The measurement results are shown in Table 3. Note that the greater the adhesion variation, the greater the possibility of in-plane adhesion failure during thermocompression bonding of the current collector and support film.

[0067]

[0068] When the thickness of the support film produced in Examples 1, 4, and 6 was changed, the smaller the (X2-X1) / (T2-T1), the smaller the variation in the adhesion strength within the surface of the adhesive layer, and it was confirmed that poor adhesion was less likely to occur.

[0069] 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 the adhesive layer has an adhesion strength A1 to copper foil of 2 N / 15 mm or greater as measured in the following peel test, and the adhesion strength A1 is greater than the adhesion strength A2 of the adhesive layer to the substrate as measured in 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) or a test substrate identical to the substrate, 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. The average of the measured values ​​is defined as adhesion strength A1. The adhesive layer and the test substrate 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. The average of the measured values ​​is defined as adhesion strength A2.

2. The support film according to claim 1, wherein after the support film is adhered to the copper foil, when the substrate is peeled off, the peeling occurs at the interface between the substrate and the adhesive layer.

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

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

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

8. A support film according to claim 1 or 2, wherein the adhesive strength A1 is 6 N / 15 mm or more.

9. A support film according to claim 1 or 2, wherein the adhesive strength A2 is 5 N / 15 mm or less.

10. A support film according to claim 1 or 2, wherein the difference between the adhesion force A1 and the adhesion force A2 (the adhesion force A1 - the adhesion force A2) is 0.4 N / 15 mm or more.

11. The support film according to claim 1 or 2, wherein, when a support film having an adhesive layer with a thickness T1 and a support film having an adhesive layer with a thickness T2 (where T2 > T1) are prepared, and the adhesion strength of the adhesive layer with thickness T1 to the copper foil is X1 and the adhesion strength of the adhesive layer with thickness T2 to the copper foil is X2, the ratio (X2 - X1) / (T2 - T1) is 0.7 [(N / 15 mm) / μm] or less. <Peel Test> The adhesive layer (thickness T1 or T2) 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 ends of the thermocompression-bonded support film are fixed to gripping portions 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 values ​​of the measured values ​​are taken as adhesion strengths X1 and X2.

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

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

14. 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.

15. A method for manufacturing a support film for a current collector for a semi-solid battery, comprising the step of forming an adhesive layer on one surface of a substrate, wherein the adhesive layer's adhesion strength A1 to copper foil, as measured in the following peel test, is 2 N / 15 mm or greater, and the adhesion strength A1 is greater than the adhesive strength A2 to the substrate, as measured in the following peel test. <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) or a test substrate identical to the substrate, 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. The average of the measured values ​​is defined as adhesion strength A1. The adhesive layer and the test substrate 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. The average of the measured values ​​is defined as adhesion strength A2.

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