Secondary battery, polyester film, laminated polyester film, resin current collector, monolaminated current collector, power storage element, electric vehicle,

Abstract

The present invention addresses the problem of providing: a film which is not susceptible to thermal damage when a thick layer comprising a metal and / or a metal-based compound is directly deposited by vapor deposition; a current collector which uses the film and which has excellent external stress resistance; and a secondary battery which uses the current collector and which has excellent pressure durability. [Solution] A secondary battery equipped with a current collector having a layer comprising a metal and / or a metal-based compound and having a thickness of 0.2-3.0 [mu] m (inclusive) on both surfaces of a polyester film that satisfies the following conditions (1) and (2). (1) The polyester film has a thickness of 1 [mu] m or more and 30 [mu] m or less. (2) The polyester film has a resin layer containing 0.1% by mass or more but less than 5.0% by mass of conductive particles.

Description

Technical Field

[0001] The present invention relates to a base film and a resin current collector for providing a thick metal layer. Background Art

[0002] In recent years, there has been an urgent need to reduce carbon dioxide emissions in order to protect the environment. In the automotive industry, there is a strong expectation that carbon dioxide emissions can be reduced by introducing electric vehicles (EVs) or hybrid electric vehicles (HEVs), and efforts are being made to develop secondary batteries for motor drives, which are key to their practical application. As secondary batteries, in addition to lithium-ion batteries that can achieve high energy density and high output density, other next-generation batteries such as lithium-ion batteries using metallic lithium negative electrodes, all-solid-state batteries, and air batteries can also be listed. In addition, in addition to automobiles, the development of next-generation mobile devices such as drones, flying cars, and flying communication base stations is also being promoted, and there is an urgent need for lightweight and high-energy-density secondary batteries.

[0003] In lithium-ion batteries and other secondary batteries, metal foil (metal collector foil) has traditionally been used as the current collector. However, in recent years, resin film collector foils made of resin films have been proposed as an alternative to metal foil. Compared to metal collector foils, resin film collector foils are lighter in weight and are expected to increase the battery's output per unit weight.

[0004] For example, Patent Documents 1 to 3 disclose a resin current collector material and a resin current collector including the film current collector material.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2021-182519

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2021-86782

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 2018-98206 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] Resin film collector foils primarily employ a structure in which a surface layer composed of metal and / or metal compounds (hereinafter sometimes referred to as a surface metal layer) is deposited on both sides of a resin film substrate through a vapor deposition process such as vacuum evaporation or sputtering. This vapor deposition process presents a problem: the high-temperature metal vapor can cause thermal damage to the resin film surface, degrading the film's mechanical properties (hereinafter sometimes referred to as thermal damage).

[0012] In order to suppress the thermal damage of film, usually the surface of resin film is charged by discharge treatment etc., and by applying high conveying tension, film and low-temperature cooling metal roller are tightly fitted and vapor deposition processing is carried out.But, when film is through thin filmization, the fold or the end when carrying that can produce suddenness is broken, because the cooling metal roller tight fitting caused thereby is bad and thermal damage is obvious.In order to eliminate the breakage of described fold or end, the method for improving conveying tension is arranged, but on the other hand, easily produce film fracture, in addition, in order to improve charging efficiency, the electric quantity of discharge treatment can be improved, but on the other hand, because of suddenness abnormal discharge and easily produce the defect of film surface, either method all has limit.In addition, along with making the metal vapor-deposited layer thick filmization, the thermal damage of film becomes many, therefore because of the slight tight fitting bad and cooling roller thermal damage becomes remarkable.

[0013] From the above circumstances, it is important to improve the adhesion with the cooling metal roll by utilizing the film properties in order to suppress the thermal damage of the film.

[0014] Patent Documents 1 to 3 disclose resin current collectors using conductive polyimide resin films or conductive polyolefin films. However, it has been shown that applying a thick metal layer to the surface of these substrate films through vapor deposition results in thermal damage, significantly degrading mechanical properties, and causing defects in the metal layer when stress is applied. Furthermore, when films with such surface metal layers are used as current collectors for secondary batteries, external stress can cause short circuits in the current collector, resulting in reduced battery performance.

[0015] The object of the present invention is to provide a film that is not easily damaged by heat when a thick film layer composed of metal and / or metal-based compound is directly evaporated, a collector with excellent external stress resistance using the film, and a secondary battery with excellent pressure durability using the collector.

[0016] Means of solving problems

[0017] In order to solve the above-mentioned problems, a preferred embodiment of the present invention adopts the following configuration.

[0018] [I] A secondary battery equipped with a current collector having a layer (hereinafter referred to as M layer) formed of a metal and / or a metal compound with a thickness of not less than 0.2 μm and not more than 3.0 μm on the surfaces of both sides of a polyester film that satisfies the following (1) and (2).

[0019] (1) The polyester film has a thickness of 1 μm or more and 30 μm or less.

[0020] (2) The polyester film has a resin layer containing 0.1% by mass or more and less than 5.0% by mass of conductive particles.

[0021] [II] The secondary battery according to [I], wherein the conductive particles contain 80% by mass or more and 100% by mass or less of at least one selected from furnace black, Ketjen black, carbon nanotubes, and acetylene black in total, based on 100% by mass of the conductive particles.

[0022] [III] The secondary battery according to [I] or [II], further comprising a current collector having an active material layer directly laminated on the surface of the M layer.

[0023] [IV] The secondary battery according to any one of [I] to [III], further comprising the current collector in which the M layer contains aluminum or copper.

[0024] [V] The secondary battery according to any one of [I] to [IV], comprising the current collector having a thickness of 4 μm to 7 μm.

[0025] [VI] The secondary battery described in any one of [I] to [V] has a structure in which the current collector is stacked in at least 45 layers and less than 80 layers with a stacked structure (hereinafter referred to as an active agent layer) including a positive electrode active material layer and a negative electrode active material layer.

[0026] [VII] A secondary battery as described in any one of [I] to [VI], having a structure in which the collectors are stacked in at least 45 layers and less than 80 layers, the stacked collectors having a joint with the electrode lead, the joint having a concave shape with a spacing of more than 0.3 mm and less than 0.8 mm and a depth of more than 0.1 mm and less than 1.0 mm.

[0027] [VIII] The secondary battery according to [VI], wherein the thickness of the current collector is 0.01 times or more and 0.04 times or less the thickness of the active agent layer.

[0028] [IX] A secondary battery as described in any one of [I] to [VIII], wherein when the thickness of the end of the collector is set to D1 (μm) and the thickness of the collector at a position 20 mm inside the end is set to D2 (μm), D1 / D2 is greater than 0.9 and less than 1.2.

[0029] [X] A secondary battery as described in any one of [I] to [IX], equipped with a collector, wherein the M layer contains aluminum element and a positive electrode active material layer with a thickness of not less than 90 μm and not more than 120 μm is stacked on the surface of the M layer containing the aluminum element.

[0030] [XI] The secondary battery as described in any one of [I] to [IX] is equipped with a collector, wherein the M layer contains copper element and a negative electrode active material layer with a thickness of 80 μm to 170 μm is stacked on the surface of the M layer containing the copper element.

[0031] [XII] The secondary battery according to [II], comprising an electrolyte solution containing furnace black and Ketjen black in a total amount of 0.001 mass ppm to 100 mass ppm.

[0032] [XIII] A polyester film that satisfies the following (3) and (4) and is used for directly depositing a layer (M layer) having a thickness of 0.2 μm to 3.0 μm inclusive, formed of a metal and / or a metal-based compound.

[0033] (3) The volume resistivity at 23°C and 65% RH is 1.0×10 8 Ω·cm or more and 9.0×10 16 Ω·cm or less.

[0034] (4) The polyester film has a thickness of 1 μm or more and 30 μm or less.

[0035] [XIV] The polyester film according to [XIII], wherein the M layer contains an aluminum element or a copper element.

[0036] [XV] The polyester film according to [XIII] or [XIV], comprising a resin layer (P1 layer) containing 0.1% by mass or more and less than 5.0% by mass of a carbon material.

[0037] [XVI] The polyester film according to [XV], wherein the carbon material contains 80% by mass or more and 100% by mass or less of at least one selected from furnace black, Ketjen black, carbon nanotubes, and acetylene black in total, based on 100% by mass of the carbon material.

[0038] [XVII] The polyester film as described in [XV], wherein a polyester resin layer (P2 layer) having a lower carbon material content than the P1 layer is provided on at least one side of the P1 layer, and when the carbon material content in the P1 layer is set to M P1 (mass %), the content of the carbon material in the P2 layer is M P2 (mass %), satisfying M P1 -M P2 ≥0.1.

[0039] [XVIII] The polyester film according to any one of [XIII] to [XVII], wherein the relative dielectric constant determined using a molecular orientation meter is 3.5 or more and 7.0 or less.

[0040] [XIX] A laminated polyester film, wherein a layer (M layer) composed of a metal and / or a metal-based compound having a thickness of 0.2 μm to 3.0 μm is directly laminated on both surfaces of a polyester film satisfying the following (5) and (6).

[0041] (5) The volume resistivity at 23°C and 65% RH is 1.0×10 8 Ω·cm or more and 9.0×10 16 Ω·cm or less.

[0042] (6) The thickness of the polyester film is 1 μm or more and 30 μm or less.

[0043] [XX] The laminated polyester film according to [XIX], wherein the elongation at break in at least one of the longitudinal direction and the width direction within the film plane is 50% or more and 120% or less.

[0044] [XXI] A resin current collector comprising the polyester film described in [XIII] or the laminated polyester film described in [XIX].

[0045] [XXII] A monopolar current collector having a layer (M layer) formed of a metal and / or a metal-based compound with a thickness of 0.2 μm to 3.0 μm on both surfaces of a polyester film satisfying the following (7) and (8).

[0046] (7) The polyester film has a thickness of 1 μm or more and 30 μm or less.

[0047] (8) A resin layer (P1' layer) containing 0.1 mass % or more and less than 5.0 mass % of conductive particles is included.

[0048] [XXIII] The monopolar current collector according to [XXII], wherein the conductive particles contain 80% by mass or more and 100% by mass or less of at least one selected from Ketjen black, carbon nanotubes, and acetylene black in total, based on 100% by mass of the conductive particles.

[0049] [XXIV] The monopolar current collector according to [XXII] or [XXIII], having a volume resistivity of 1.0×10 8 Ω·cm or more and 9.0×10 16 Polyester film with a thickness of Ω·cm or less.

[0050] [XXV] The monopolar current collector according to any one of [XXII] to [XXIV], wherein the M layer contains aluminum or copper.

[0051] [XXVI] The monopolar current collector according to any one of [XXII] to [XXV], wherein the elongation at break in at least one of the longitudinal direction and the width direction within the film surface is 50% or more and 120% or less.

[0052] [XXVII] The monopolar current collector according to any one of [XXII] to [XXVI], wherein the breaking strength in at least one of the longitudinal direction and the width direction within the film surface is 180 MPa or more and 300 MPa or less.

[0053] [XXVIII] The monopolar current collector according to any one of [XXII] to [XXVII], comprising an M layer in contact with the polyester film, wherein the M layer has an arithmetic mean height Sa of 15 nm to 60 nm.

[0054] [XXIX] The monopolar current collector as described in any one of [XXII] to [XXVIII], when the monopolar current collector is analyzed using inductively coupled plasma atomic emission spectrometry (inductively coupled plasma-atomic emission spectrometry (ICP-AES) method) under the following conditions, the silicon element content in the polyester film is greater than 0 mass ppm and less than 10 mass ppm.

[0055] <Analysis conditions>

[0056] Apparatus: ICP emission spectrometry (manufactured by Hitachi High-Tech Science Corporation) PS3520VDDII

[0057] Sample Preparation: The polyester film was weighed in a beaker and decomposed under pressure using sulfuric acid, followed by nitric acid, followed by heating to ash. The ash was dissolved in a mixed flux of sodium carbonate and boric acid and then dissolved in dilute nitric acid under heating to a constant volume of 10 mL. The solution diluted with dilute nitric acid was then analyzed for silicon content using inductively coupled plasma atomic emission spectrometry (ICP-AES). This was used as the silicon content in the polyester film.

[0058] (Measurement conditions)

[0059] Measurement wavelength: 251.6nm

[0060] High frequency output: 1.2kW

[0061] Plasma gas flow rate: 16L / min

[0062] Auxiliary gas flow rate: 0.5L / min

[0063] Carrier gas flow rate: 0.9L / min

[0064] Measuring height: 12mm

[0065] [XXX] The monopolar current collector according to any one of [XXII] to [XXIX], further comprising an active material layer on the surface of the M layer.

[0066] [XXXI] An electric storage device comprising the unipolar current collector according to [XXX].

[0067] [XXXII] The energy storage device according to [XXXI] has a structure in which at least two layers of current collectors are stacked with an active agent layer interposed therebetween.

[0068] [XXXIII] An electric vehicle equipped with the secondary battery described in [I].

[0069] [XXXIV] An electric flying vehicle equipped with the secondary battery described in [I].

[0070] [XXXV] A method for producing a laminated polyester film, comprising the step of directly vapor-depositing a layer (M layer) having a thickness of 0.2 μm or more and formed of a metal and / or a metal-based compound on a polyester film satisfying the following (9) and (10).

[0071] (1) The volume resistivity at 23°C and 65% RH is 1.0×10 8 Ω·cm or more and 9.0×10 16 Ω·cm or less.

[0072] (2) The polyester film has a thickness of 1 μm or more and 30 μm or less.

[0073] Effects of the Invention

[0074] The present invention can provide a film that is less susceptible to thermal damage when a thick layer composed of metal and / or metal-based compound is directly vapor-deposited, a current collector using the film that has excellent external stress resistance, and a secondary battery using the current collector that has excellent pressure durability. DETAILED DESCRIPTION

[0075] The present invention is described in detail below.

[0076] A preferred embodiment of the present invention is a polyester film that satisfies the following conditions (3) and (4) and is used for directly depositing an M layer having a thickness of 0.2 μm to 3.0 μm.

[0077] (3) The volume resistivity at 23°C and 65% RH is 1.0×10 8 Ω·cm or more and 9.0×10 16 Ω·cm or less.

[0078] (4) The polyester film has a thickness of 1 μm or more and 30 μm or less.

[0079] In addition, another preferred embodiment of the present invention is a laminated polyester film in which a layer formed of a metal and / or a metal compound having a thickness of 0.2 μm or more and 3.0 μm or less is directly laminated on the surfaces of both sides of a polyester film that satisfies the following conditions (5) and (6).

[0080] (5) The volume resistivity at 23°C and 65% RH is 1.0×10 8 Ω·cm or more and 9.0×10 16 Ω·cm or less.

[0081] (6) The film thickness is 1 μm or more and 30 μm or less.

[0082] This form enables the production of a polyester film that is less susceptible to thermal damage when directly depositing a thick M layer. In particular, it is possible to suppress the degradation of mechanical properties of films formed by direct deposition of an M layer with a thickness of 0.2 μm to 3.0 μm. Furthermore, even in the event of deformation due to external stress, defects in the resin current collector are suppressed, resulting in improved mechanical strength of the resulting monopolar current collector and secondary battery.

[0083] (Polyester film)

[0084] The polyester film in the present invention preferably has a volume resistivity of 1.0×10 8 Ω·cm or more and 9.0×10 16 Ω·cm or less. The method for measuring volume resistivity will be described later. The volume resistivity of a polyester film is a value indicating how easily the charge imparted to the film surface (hereinafter sometimes referred to as charged charge) penetrates into the interior of the polyester film when the film is charged by discharge treatment.

[0085] In the step of directly depositing an M layer having a thickness of 0.2 μm or more on a polyester film having a film thickness of 1 μm or more and 30 μm or less, if the transport tension is increased to a level where film breakage during processing is not noticeable, wrinkles or edge breakage during the deposition process may become noticeable if the rigidity of the polyester film is insufficient. Therefore, by setting the volume resistivity of the polyester film at 23°C and 65% RH to 1.0×10 8 Ω·cm or more and 9.0×10 16 When the thickness is Ω·cm or less, the effect of suppressing heat damage can be preferably obtained as described later.

[0086] The volume resistivity of the polyester film of the present invention at 23°C and 65% RH is 9.0×10 16Ω·cm or less. When the M layer having a thickness of 0.2 μm or more is provided by direct vapor deposition, the adhesion to the cooling metal roller used in the vapor deposition process becomes good, and the decrease in the elongation at break of the film after vapor deposition (heat damage) can be suppressed. The reason is that the charge imparted to the polyester film by the charging treatment in the vapor deposition step moderately penetrates into the interior of the polyester film, thereby improving the electrostatic adhesion between the polyester film and the cooling metal roller, and sufficient cooling can be performed. From the same point of view, the volume resistivity is more preferably 7.0×10 16 Ω·cm or less, more preferably 5.0×10 15 Ω·cm or less.

[0087] The volume resistivity of the polyester film at 23°C and 65% RH is 1.0×10 8 Ω·cm or more. When the M layer having a thickness of 0.2 μm or more is formed by direct vapor deposition, good adhesion to the cooling metal roll can be achieved, and a decrease in the elongation at break of the mechanical properties of the laminated polyester film after the vapor deposition can be suppressed. This is because the charge imparted to the film by the charging treatment in the vapor deposition step does not flow through the film to the metal roll but is retained within the polyester film, thereby improving the electrostatic adhesion between the polyester film and the cooling metal roll. The volume resistivity at 23°C and 65% RH is more preferably 1.0×10 9 Ω·cm or more, more preferably 1.0×10 10 Ω·cm or more.

[0088] The volume resistivity of the polyester film of the present invention at 23°C and 65% RH can be controlled by incorporating a conductive material into the polyester film. The conductive material may be an inorganic material including a metal or a metal compound, or an organic material such as a carbon material or a conductive polymer.

[0089] Examples of the inorganic conductive material include single-substance particles of metal elements such as gold, silver, copper, zinc, lead, nickel, iron, aluminum, titanium, cobalt, manganese, cadmium, palladium, and platinum; metal particles composed of multiple metal elements such as stainless steel and nickel-indium alloys; and particles composed of metal compounds obtained by mixing the above metal elements with oxygen, nitrogen, fluorine, carbon, boron, chlorine, sulfur, and phosphorus.

[0090] Examples of the organic conductive material include carbon materials and conductive polymers.

[0091] The carbon material refers to a carbon material derived from a graphite structure (sp) in a so-called G band as measured by Raman spectroscopy. 2 Key) 1580cm -1 Nearby, and commonly referred to as the D band, originates from the diamond structure (sp 3 Key) 1350cm -1Materials in which a peak is observed near λ / λ. Specifically, furnace black, Ketjen black, acetylene black, carbon nanotubes (CNTs), graphene, fullerene, etc. can be exemplified.

[0092] Examples of the conductive polymer include polyacetylene resins, polythiophene resins, and particles having these as components.

[0093] The polyester film of the present invention preferably has a resin layer containing 0.1% by mass or more and less than 5.0% by mass of conductive particles. Examples of the conductive particles include metal particles, metal oxide particles, conductive resin particles, and the carbon material. The conductive particles preferably include at least one selected from the group consisting of metal particles, metal oxide particles, conductive resin particles, and the carbon material. More preferably, the conductive particles include the carbon material, and even more preferably, the conductive particles include a carbon material.

[0094] By setting the conductive particle content to 0.1% by mass or greater, the volume resistivity of the polyester film can be reduced, minimizing the decrease in elongation at break after vapor deposition of the M layer. This also allows for optimal battery durability when used in the production of resin current collectors. From a similar perspective, the conductive particle content is preferably 0.2% by mass or greater, and more preferably 1.1% by mass or greater.

[0095] By setting the conductive particle content to less than 5.0% by mass, excessive aggregation of the conductive particles can be suppressed, thereby reducing variations in volume resistivity during the casting step and stabilizing polyester film formation by electrostatic application (described later). Particularly when Ketjen black, carbon nanotubes, or acetylene black, which are highly conductive carbons, are included, the conductive particle content is more preferably 2.5% by mass or less, from the same perspective.

[0096] Examples of metal particles used as conductive particles include single-element particles of metal elements such as gold, silver, copper, zinc, lead, nickel, iron, aluminum, titanium, cobalt, manganese, cadmium, palladium, and platinum, and metal particles composed of multiple metal elements such as stainless steel and nickel-indium alloy.

[0097] Examples of metal oxide particles used as conductive particles include tin oxide and zinc oxide. Inorganic particles such as aluminum oxide, calcium carbonate, mica, talc, and glass having a coating layer formed from the metals listed above as examples of the metal particles and the metal oxides listed above as examples of the metal oxides on their surfaces can also be used.

[0098] Examples of conductive resin particles used as conductive particles include resins having a conjugated double bond structure in the main chain skeleton, such as polyacetylene, polyparaphenylene, polyfluorene, and polyparaphenylene vinylene; thiophene resins such as polyethylenedioxythiophene (PEDOT) / polystyrenesulfonic acid (PSS), polythiophene, and polythienylene vinylene; polyaniline; and polypyrrole.

[0099] When the polyester film of the present invention is used as a member facing a resin current collector for a lithium-ion battery, it is more preferable to include an organic conductive material in the polyester film to prevent conductive material from falling from the polyester film from causing a battery short circuit or heat generation due to an electrochemical reaction, which could lead to battery fire. Furthermore, to reduce the content of the conductive material relative to the polyester film raw material, it is more preferable for the polyester film to include a carbon material, and more preferably, at least one selected from furnace black, Ketjen black, carbon nanotubes, and acetylene black, which have high conductivity. It is particularly preferable to include at least one selected from Ketjen black, acetylene black, and carbon nanotubes (CNTs), which have even higher conductivity.

[0100] In the present invention, from the viewpoint of reducing the content of the conductive particles, it is preferred that 100 mass % of the conductive particles contain 80 mass % or more and 100 mass % or less of at least one selected from furnace black, Ketjen black, carbon nanotubes, and acetylene black in total.

[0101] Methods for obtaining a polyester film containing a conductive material or conductive particles include: a method in which the conductive material or conductive particles are directly mixed with a resin serving as a raw material for the polyester film, and the film is formed using the method described below in the "Method for Producing Biaxially Oriented Polyester Film"; or a method in which a masterbatch is prepared by preliminarily melt-kneading the conductive material or conductive particles with a resin serving as a raw material for the polyester film, the resin serving as a raw material for the polyester film and the masterbatch are mixed, and the film is formed using the method described below in the "Method for Producing Biaxially Oriented Polyester Film" From the perspective of uniformly dispersing the conductive material or conductive particles, the method using the masterbatch is preferred.

[0102] The polyester film in the present invention preferably has a relative dielectric constant of 3.5 or more and 7.0 or less, as determined using a molecular orientation meter. The so-called relative dielectric constant of the polyester film is an indicator of the ease of polarization of the resin molecules constituting the polyester film. The high relative dielectric constant of the polyester film allows for more electrons to be accumulated on the surface and inside the film during a charged treatment based on voltage application. The relative dielectric constant of the polyester film determined using a molecular orientation meter is 3.5 or more, and in the step of providing the M layer by direct vapor deposition, the adhesion to the cooled metal roller can be improved, and the thermal damage caused by vapor deposition can be further suppressed. Thus, the decrease in the mechanical strength of the laminated polyester film having the M layer can be suppressed, and when assembled into a battery, the mechanical properties of the battery can be improved.

[0103] The polyester film more preferably has a volume resistivity within the preferred range and a relative dielectric constant of 3.5 to 7.0. The relative dielectric constant of the polyester film determined using a molecular orientation meter is more preferably 4.0 or more, and even more preferably 4.5 or more.

[0104] Furthermore, by setting the relative dielectric constant to 7.0 or less, it is possible to prevent the charge imparted by the charging treatment from flowing out to the metal roll side due to excessive polarization of the polyester film, thereby deteriorating the adhesion to the cooled metal roll. The relative dielectric constant is more preferably 6.5 or less.

[0105] When the thickness of the polyester film in the present invention is set to T (μm), T is preferably set to 1 or more and 30 or less. When the thickness T (μm) of the polyester film is 1 or more, the polyester film does not break during the step of providing the M layer described later, making processing easier. The thickness T (μm) of the polyester film is more preferably 2 or more, further preferably 3 or more, and most preferably 4 or more. When the thickness T (μm) of the polyester film is 30 or less, even when used as a lithium-ion battery component, an increase in the weight or thickness of the battery itself can be suppressed. The thickness T (μm) of the polyester film is more preferably 20 or less, further preferably 15 or less, and most preferably 7 μm or less.

[0106] The resin constituting the polyester film of the present invention preferably contains a polyester resin as a main component. The main component herein means a component contained in an amount exceeding 50% by mass in 100% by mass of all components of the film.

[0107] The polyester resin in the present invention is a resin obtained by polycondensing a dicarboxylic acid component and a diol component. In this specification, the term "component" refers to the smallest unit obtainable by hydrolyzing the polyester resin.

[0108] Examples of the diol constituent components constituting the polyester resin include, but are not limited to, aliphatic diols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; alicyclic diols such as 1,4-cyclohexanedimethanol and spiroglycerol; and compounds formed by linking a plurality of these diols.

[0109] Examples of the dicarboxylic acid constituent component constituting the polyester resin include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, and 4,4′-diphenyletherdicarboxylic acid.

[0110] Examples of polyester resins containing the dicarboxylic acid constituent components and the diol constituent components include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polypropylene terephthalate (PTT), and polycyclohexanedimethylene terephthalate (PCT). From the viewpoint of excellent moldability, polyethylene terephthalate (PET) is preferably used.

[0111] These polyester resins may contain isophthalic acid or naphthalene dicarboxylic acid as part of the dicarboxylic acid constituent of the polyester, that is, copolymerize them, within a range not impairing the effects of the present application.

[0112] The polyester film in the present invention is preferably a film for directly vapor-depositing the M layer having a thickness of 0.2 μm or more and 3.0 μm or less described later. The direct vapor deposition described in the present invention means that the M layer described later is provided on the surface of the polyester film in the present invention (the surface of the P1 layer or P1' layer and / or the P2 layer described later), or that the polyester film surface (the surface of the P1 layer or P1' layer and / or the P2 layer described later) and the M layer described later are provided with a layer having a thickness of 0.0 μm or more and 0.1 μm or less interposed therebetween for the purpose of improving the adhesion between the two layers. Here, the so-called layer having an interposed thickness of 0.0 μm means that the polyester film surface (the surface of the P1 layer or P1' layer and / or the P2 layer described later) and the M layer described later are directly laminated.

[0113] The M layer in the present invention can be formed by metal vapor deposition or metal sputtering under vacuum conditions, which will be described in detail later.

[0114] (P1 layer: a resin layer containing 0.1% by mass or more and less than 5.0% by mass of a carbon material)

[0115] The polyester film in the present invention preferably has a resin layer (P1 layer) containing 0.1% by mass or more and less than 5.0% by mass of a carbon material.

[0116] By appropriately using the carbon materials listed above as the conductive materials, the volume resistivity of the polyester film of the present invention at 23°C and 65% RH can be controlled within a preferred range. The carbon material contained in the P1 layer preferably contains one or more highly conductive carbon materials selected from furnace black, Ketjen black, acetylene black, and carbon nanotubes (CNTs) from the perspective of achieving an effect even with a small amount.

[0117] By setting the carbon material content of the P1 layer in the present invention to 0.1% by mass or greater, the volume resistivity of the polyester film can be reduced, minimizing the decrease in elongation at break after vapor deposition of the M layer. This allows for optimal battery durability even when a resin current collector is used. From a similar perspective, the carbon material content of the P1 layer is preferably 0.2% by mass or greater, and more preferably 1.1% by mass or greater.

[0118] By setting the carbon material content of the P1 layer in the present invention to less than 5.0% by mass, excessive aggregation of the carbon material can be suppressed, thereby reducing variations in volume resistivity during the casting step and stabilizing polyester film formation by electrostatic application (described later). From the same perspective, the carbon material content of the P1 layer is more preferably 2.5% by mass or less.

[0119] The carbon material contained in the P1 layer in the present invention is preferably 80% by mass or more and 100% by mass or less of one or more selected from furnace black, acetylene black, carbon nanotubes, graphene, Ketjen black, fullerene, and graphite in 100% by mass of the carbon material. From the viewpoint of imparting conductivity by a small amount of addition, it is more preferred that 80% by mass or more and 100% by mass of at least one selected from furnace black, Ketjen black, carbon nanotubes, and acetylene black is contained in 100% by mass of the carbon material, and it is further preferred that 80% by mass or more and 100% by mass of at least one selected from acetylene black, carbon nanotubes, and Ketjen black is contained in 100% by mass of the carbon material.

[0120] (P2 layer: a resin layer containing less carbon material than the P1 layer)

[0121] The polyester film of the present invention preferably has a polyester resin layer (P2 layer) having a lower carbon material content than the P1 layer on at least one side of the P1 layer, and the carbon material content in the P1 layer is set to M. P1 (mass %), the content of the carbon material in the P2 layer is M P2 (mass %), satisfying M P1 -M P2 ≥0.1.

[0122] The reason is that in the casting step of film formation, co-extrusion is performed in a manner that the casting drum and the P2 layer are connected to form an unstretched film. Therefore, even if the carbon material content of the P1 layer is high and discharge disorder occurs, it can be prevented by the P2 layer, and the occurrence of uneven discharge can be suppressed.

[0123] The carbon material contained in the P2 layer can be any of the carbon materials listed above as examples of the conductive material. The carbon material contained in the P2 layer is preferably one or more selected from furnace black, Ketjen black, acetylene black, and carbon nanotubes (CNTs). From the perspective of exhibiting conductivity when contained in a small amount, one or more selected from Ketjen black, acetylene black, and carbon nanotubes (CNTs) are more preferably used.

[0124] The laminated structure of the polyester film in the present invention may be a two-layer structure of P2 layer / P1 layer or a three-layer structure of P2 layer / P1 layer / P2 layer.

[0125] (Biaxially oriented polyester film)

[0126] From the perspective of improving the film's mechanical strength and thermal dimensional stability, the polyester film in the present invention is preferably biaxially oriented. Biaxial orientation improves the mechanical strength of the polyester film, thereby preventing wrinkles and curling, and also suppressing film breakage during the M layer processing step. Furthermore, by applying uniform tensile stress during the stretching step, the polyester film's thickness can be made uniform across both the width and length directions, preventing variations in the electrical properties of the resin current collector foil due to sudden thickness variations when used as a resin current collector.

[0127] The term "biaxial orientation" as used herein refers to an orientation that exhibits a biaxially oriented pattern in wide-angle X-ray diffraction. The biaxially oriented polyester film of the present invention can generally be obtained by stretching an unstretched thermoplastic resin sheet in the film forming machine axis direction (hereinafter sometimes referred to as the longitudinal direction) and the width direction of the sheet, and then subjecting the sheet to a heat treatment to complete the orientation crystallization.

[0128] In the polyester film of the present invention, the intrinsic viscosity (IV) of the entire polyester film is preferably 0.60 dl / g or greater, more preferably 0.70 dl / g or greater. An IV of 0.60 dl / g or greater shortens the polyester molecular chain, thereby suppressing breakage during the stretching step due to excessive crystallization, and enabling stable film formation.

[0129] In the case where the polyester film in the present invention has a laminated structure comprising the P1 layer and the P2 layer, there is no particular limitation on the method for laminating the P1 layer and the P2 layer, and the following methods may be used: the coextrusion method described later in which the resins of the respective layers are laminated and extruded in a molten state; or a method in which other resin layer raw materials are fed into an extruder and melt-extruded and extruded from a die while being laminated onto a film in the middle of film formation (melt lamination method); a method in which the films after film formation are laminated with each other via an adhesive layer, etc. Among them, the coextrusion method can be preferably used from the viewpoint of excellent lamination uniformity and difficulty in intrusion of interfering foreign matter between layers.

[0130] (Method for producing biaxially oriented polyester film)

[0131] Next, a method for producing a biaxially oriented film from the polyester film of the present invention will be described with reference to examples. However, the present invention is not to be construed as being limited to the products obtained by the examples described above.

[0132] The polyester resin can be obtained by conventional polymerization methods. For example, it can be obtained by subjecting the dicarboxylic acid component or its ester-forming derivative to a transesterification reaction or esterification reaction with the diol component or its ester-forming derivative using a known method, followed by melt polymerization. Alternatively, the polyester resin obtained by melt polymerization can be subjected to solid-phase polymerization at a temperature below the melting point of the polyester resin, if desired.

[0133] The polyester film of the present invention can be obtained by a conventionally known production method. Specifically, the polyester film of the present invention can be produced by, as needed, heating and melting the dried raw material in an extruder, and extruding it from a die onto a cooled casting drum to form a sheet (melt casting method). Alternatively, a method can be used in which the raw material is dissolved in a solvent, the solution is extruded from a die onto a support such as a casting drum or an endless belt to form a film, and then the solvent is dried and removed from the film layer to form a sheet (solution casting method).

[0134] When producing a polyester film of two or more layers by melt casting, a method (coextrusion method) is preferably used in which the raw materials of each layer constituting the biaxially oriented polyester film are melted using an extruder, and the raw materials are laminated in a molten state using a merging device provided between the extruder and the die. The molten raw materials are then introduced into the die, extruded from the die onto a casting drum cooled to a surface temperature of 20°C to 60°C, and processed into a sheet to form an unstretched film. In particular, by setting the casting drum temperature to 40°C or higher, the cooling of the resin is delayed, making it easier to temporarily adhere to the casting drum. The properties of the extruded resin can sometimes suppress the decrease in adhesion between the unstretched film and the casting drum due to the electrostatic application method described below.

[0135] As a method for making the unstretched film adhere to the casting drum, the following methods can be appropriately selected and used: an electrostatic application method in which the extruded polyester resin is charged using a charging treatment device accompanied by high voltage application to make it adhere to the casting drum; a method in which the polyester resin is clamped between the casting drum and a kneading roller to make it adhere to the casting drum; a method in which wind pressure is applied to press the resin to make it adhere to the casting drum, etc. From the perspective of achieving uniform adhesion in the width direction, the electrostatic application method is preferably used.

[0136] (Sequential biaxial stretching)

[0137] In the polyester film of the present invention, the following sequential biaxial stretching conditions are preferably used when biaxially stretching the unstretched film. Specifically, first, for longitudinal stretching, the unstretched film is preferably stretched in the longitudinal direction using a roll set heated to 70°C or higher, followed by cooling using a roll set set to a temperature of 20°C to 50°C. The lower limit of the heated roll temperature during longitudinal stretching is not particularly limited as long as it does not impair the stretchability of the sheet, but it is preferably higher than the glass transition temperature of the resin used. The longitudinal stretch ratio is preferably in the range of 2x to 5x, with a more preferred range of 2.5x to 4x. A longitudinal stretch ratio of 2x or higher promotes orientation crystallization and improves film strength. On the other hand, a stretch ratio of 5x or lower prevents excessive orientation crystallization of the polyester resin during stretching, which can lead to brittleness and cracking during film formation.

[0138] Next, the engineering film (uniaxially stretched film) stretched in the longitudinal direction is stretched in a direction perpendicular to the longitudinal direction (width direction). Preferably, the uniaxially stretched film is introduced into a tenter while being gripped at both ends with clips, and is stretched in a direction perpendicular to the longitudinal direction (width direction) by a factor of 2 to 5 in an environment heated to a temperature of 70°C to 160°C.

[0139] Afterwards, it is preferred to heat-treat the uniaxially stretched polyester film to stabilize the internal orientation structure. The thermal history temperature to which the polyester film is subjected during the heat treatment can be confirmed by the temperature of the small endothermic peak (sometimes referred to as Tmeta) that appears just below the melting point temperature measured by the differential scanning calorimeter (DSC) described later. However, as the setting temperature of the tenter device, when polyester (melting point 255°C) is the main component, it is preferred to set the maximum temperature in the tenter to 170°C or higher and 245°C or lower. When other thermoplastic resins are used as the main component, it is preferably set to the resin melting point (°C) - 45°C or higher and the resin melting point (°C) - 10°C or lower. By setting the heat treatment temperature to 170°C or higher, the dimensional stability of the biaxially oriented polyester film can be improved. In addition, by setting the heat treatment temperature to 245°C or lower, the occurrence of film rupture associated with the melting of the polyester film can be suppressed, and production can be performed with good productivity. From the same viewpoint, the heat treatment temperature is more preferably 220°C or higher and 235°C or lower.

[0140] Regarding the temperature range of Tmeta, which represents the thermal history temperature to which the polyester film is subjected during heat treatment, when the polyester resin is the main component, for the reasons described above, it is preferably 160°C to 235°C. From the same viewpoint, the temperature range of Tmeta is more preferably 210°C to 225°C.

[0141] In order to further impart dimensional stability after heat treatment, a relaxation treatment (relaxation treatment) may be performed within a range of 1% to 6%. By setting the relaxation treatment to 1% or more, the dimensional stability of the biaxially oriented polyester film when used in a high-temperature environment can be improved, while by setting the relaxation treatment to 6% or less, appropriate tension can be continuously applied to the biaxially oriented polyester film, thereby preventing the deterioration of thickness unevenness.

[0142] The stretch ratio in the longitudinal direction and the width direction is set to 2 times or more and 5 times or less, respectively. However, the area ratio (stretch ratio in the longitudinal direction × stretch ratio in the width direction) is preferably 4 times or more and 25 times or less, and more preferably 9 times or more and 20 times or less. By setting the area ratio to 4 times or more, the molecular orientation of the obtained biaxially oriented polyester film can be promoted and the durability can be improved. By setting the area ratio to 25 times or less, the occurrence of cracks during stretching can be suppressed.

[0143] (M layer: a layer formed of a metal and / or a metal compound)

[0144] In the present invention, it is preferred that the polyester film has a layer (M layer) formed of a metal and / or metal compound with a thickness of greater than or equal to 0.2 μm and less than or equal to 3.0 μm, more preferably, the surfaces on both sides of the polyester film have an M layer with a thickness of greater than or equal to 0.2 μm and less than or equal to 3.0 μm, and further preferably, the surfaces on both sides of the polyester film have an M layer with a thickness of greater than or equal to 0.2 μm and less than or equal to 3.0 μm directly laminated.

[0145] By setting the thickness of the M layer in the present invention to 0.2 μm or more, it is preferred that the decrease in electrical properties due to uneven thickness of the metal layer be suppressed when used as a resin current collector. The thickness of the M layer is more preferably 0.5 μm or more. In addition, by setting the thickness of the M layer to 3.0 μm or less, it is preferred that the increase in battery weight be reduced when used as a resin current collector for a battery. In addition, when manufacturing by vapor deposition, thermal damage during vapor deposition can be suppressed. The thickness of the M layer is more preferably 2.0 μm or less.

[0146] As a method for setting the M layer, the following method is preferred: using a method of setting it by metal evaporation, metal sputtering, or electroplating under vacuum conditions or reduced pressure conditions with an inert gas such as argon sealed in (hereinafter sometimes collectively referred to as evaporation method), to continuously form the M layer on the polyester film.

[0147] When using the vacuum evaporation method, the preferred form is to pre-set a polyester roll in a vacuum chamber, so that the rolled polyester film is tightly attached to the cooling roller, and the metal and / or metal compound that is heated and vaporized is solidified and attached to the surface of the polyester film. After the M layer is set, it is rolled up again as a film roll.

[0148] Here, a 9.0×10 -3 Pa or less, or fill with inert gas such as argon and reduce the pressure to 9.0×10 -3 Pa or more and 1×10 -1 Any of the conditions of Pa or less. Alternatively, the M layer may be formed by continuously performing two or more deposition steps, such as forming a first M layer by sputtering and then forming a second M layer by vacuum deposition.

[0149] Vacuum deposition methods include induction heating, resistance heating, laser beam, and electron beam. Among these, electron beam, laser beam, and induction heating are preferred, as they generate a high calorific value from the deposition source. The calorific value of the deposition source must be increased to form the desired thickness of the M layer. The substrate surface temperature must be sufficiently high, but this is difficult to measure. Therefore, sufficient heat is required to confirm that the M layer after deposition has reached the desired thickness.

[0150] Among them, if the calorific value of the evaporation source is increased to the required heat, then in the management of the cooling function of the usual vacuum evaporation method, the temperature of the polyester film rises and the mechanical properties of the polyester film decrease due to thermal damage, and then the polyester film is likely to melt. Therefore, during the evaporation process, it is necessary to manage the cooling function while performing evaporation in a manner that does not excessively increase the temperature and can evenly cool the polyester film. Specifically, it is necessary to utilize a cooling mechanism comprising a metal plate or a metal roller that is fully cooled by a refrigerant to evenly cool the back of the evaporation surface. In order to cool evenly, it is necessary to fit the polyester film and the cooling mechanism tightly without forming a gap. By improving the tightness, the thermal damage suffered by the surface of the polyester film can be reduced, and the mechanical properties of the polyester film can be suppressed from decreasing.

[0151] For example, if the metal roller of the cooling mechanism has a scratch, the scratch creates a gap, preventing the polyester film from cooling at the scratched area, and increasing thermal damage to the polyester film. Furthermore, if foreign matter enters between the polyester film and the metal roller of the cooling mechanism, the foreign matter prevents the polyester film from cooling, further increasing thermal damage. If the heating value of the deposition source is increased to the required level, the presence of scratches or foreign matter on the metal roller, which is permitted in conventional vacuum deposition methods, becomes a problem. Therefore, stricter management of scratches and foreign matter on the metal roller is required.

[0152] When the M layer in the present invention is set to the desired thickness, from the viewpoint of productivity, resistance characteristics, grade and quality, it is preferred to form it by a single vapor deposition method (the whole set of unwinding, vapor deposition and winding is defined as a single vapor deposition method). For example, a thin film vapor deposition method of forming a 50nm thick aluminum vapor deposition layer by a single vapor deposition method can be repeated 20 times (the said whole set is repeated 20 times) to form an aluminum metal layer with a total thickness of 1μm.

[0153] That is, a preferred form of the method for manufacturing a laminated polyester film in the present invention is a method for manufacturing a laminated polyester film, which has a step of directly vapor-depositing a layer formed of a metal and / or a metal-based compound with a thickness of 0.2 μm or more on a polyester film that satisfies the following (9) and (10).

[0154] (9) The volume resistivity at 23°C and 65% RH is 1.0×10 8 Ω·cm or more and 9.0×10 16 Ω·cm or less.

[0155] (10) The thickness of the polyester film is 1 μm or more and 30 μm or less.

[0156] To further enhance the effect of suppressing thermal damage to the polyester film of the present invention, it is preferable to perform the vapor deposition process using a roll-to-roll method using a roll of the polyester film of the present invention. Furthermore, a transport speed of 15 m / min or higher during the vapor deposition process can more clearly achieve the effect of suppressing thermal damage to the polyester film of the present invention, and the increased processing speed can reduce processing costs. A more preferred transport speed is 25 m / min or higher, and even more preferably 35 m / min or higher. On the other hand, excessively high transport speeds may deteriorate productivity or thermal damage, so the transport speed is preferably 500 m / min or lower.

[0157] Examples of metal elements constituting the M layer include gold, silver, copper, zinc, lead, nickel, iron, aluminum, titanium, cobalt, manganese, cadmium, and palladium. The M layer may be formed from a single substance of one of these metal elements, or may be formed from a metal compound obtained by mixing these metal elements with oxygen, nitrogen, fluorine, carbon, boron, chlorine, sulfur, or phosphorus. Furthermore, the metal element of the M layer directly formed on the polyester film may be the same or different on both sides.

[0158] When used as a resin current collector for lithium ion batteries, it is preferable that the M layer contains copper or aluminum. When used as a resin current collector for negative electrodes, it is more preferable that the M layer consists of copper.

[0159] In the laminated polyester film in which the polyester film of the present invention is provided with an M layer, the elongation at break in at least one direction of the length direction and the width direction within the film surface is preferably 20% or more. By setting the elongation at break in at least one direction to 20% or more, when the film laminated with the M layer is used for a resin current collector, even when deformed by external stress, defects in the resin current collector and a significant decrease in battery characteristics can be suppressed. In addition, when assembled into a secondary battery, the current collector can be destroyed due to deformation corresponding to external stress, battery characteristics can be reduced, or fire can be caused due to thermal runaway. As the elongation at break in at least one direction, it is more preferably 35% or more, further preferably 45% or more, particularly preferably 50% or more, and most preferably 70% or more. In addition, the elongation at break in at least one direction is preferably 120% or less.

[0160] When the elongation at break is 120% or less, the following problems can be suppressed:

[0161] When heat is applied to the polyester film, thermal crystallization of the polyester film proceeds, reducing the breaking strength. When used as a resin current collector or assembled into a secondary battery, the current collector is destroyed due to deformation corresponding to the external stress, the battery characteristics are reduced, or a fire is caused by thermal runaway.

[0162] The following structures can be exemplified as the laminated structure of the polyester film and the M layer in the present invention. When the polyester film is a single layer, the structure is preferably M layer / P1 layer / M layer, or M layer / P1 layer / M' layer having a layer (M' layer) composed of a "metal and / or metal-based compound composed of a metal element different from that of the M layer."

[0163] When the polyester film has two or more layers, the preferred structure is M layer / P1 layer / P2 layer / M layer, M layer / P1 layer / P2 layer / M' layer, or M layer / P2 layer / P1 layer / P2 layer / M layer, or M layer / P2 layer / P1 layer / P2 layer / M' layer.

[0164] Furthermore, in order to improve adhesion with the layer (M layer) formed of metal and / or metal-based compound, an anchor layer may be provided on the polyester film (P1 layer or P2 layer) of the present invention within a range that does not impair the effects of the present invention.

[0165] [Unipolar current collector]

[0166] A preferred form of the polyester film of the present invention when used as a monopolar current collector is a monopolar current collector having a layer formed of metal and / or metal compounds with a thickness of greater than 0.2 μm and less than 3.0 μm on the surfaces of both sides of the polyester film that satisfies the following (7) and (8).

[0167] (7) The polyester film has a thickness of 1 μm or more and 30 μm or less.

[0168] (8) A resin layer (P1' layer) containing 0.1 mass % or more and less than 5.0 mass % of conductive particles is included.

[0169] The monopolar current collector of the present invention preferably has a resin layer containing 0.1% by mass or more and less than 5.0% by mass of the conductive particles. Conductive particles contained in the polyester film can also be suitably used as the conductive particles.

[0170] The monopole current collector in the present invention preferably has a volume resistivity of 1.0×10 8 Ω·cm or more and 9.0×10 16 By setting the thickness within the above range, a decrease in mechanical properties due to the provision of the M layer can be suppressed, so that when incorporated into a secondary battery, the secondary battery can be made resistant to deformation caused by external impact.

[0171] That is, the monopole current collector of the present invention preferably has an elongation at break of 50% or more and 120% or less in at least one of the length direction and the width direction within the membrane surface. By having an elongation at break of 50% or more in at least one of the length direction and the width direction within the membrane surface of the monopole current collector, when assembled into a secondary battery, it is possible to suppress the destruction of the collector due to deformation corresponding to external stress, degradation of battery characteristics, or fire caused by thermal runaway. The elongation at break is more preferably 70% or more. In addition, by having an elongation at break of 120% or less in at least one of the length direction and the width direction within the membrane surface, the following situations can be suppressed:

[0172] When heat is applied to a polyester film, thermal crystallization of the polyester film proceeds, reducing its breaking strength. When incorporated into a secondary battery, the current collector may be destroyed due to deformation caused by external stress, resulting in reduced battery characteristics or fire caused by thermal runaway.

[0173] Similarly, the monopole current collector of the present invention preferably has a breaking strength of 180 MPa or more and 300 MPa or less in at least one of the length direction and the width direction within the film surface. By having a breaking strength of 180 MPa or more in at least one of the length direction and the width direction within the film surface, when assembled into a secondary battery, it is possible to suppress the current collector from being damaged due to deformation corresponding to external stress, the battery characteristics from being degraded, or the fire from being caused by thermal runaway. The breaking strength is more preferably 200 MPa or more. In addition, by having the elongation at break be 300% or less, it is possible to suppress the following situations: when assembled into a secondary battery due to excessive oriented crystallization within the polyester film, the current collector from being damaged due to deformation corresponding to external stress, the battery characteristics from being degraded, or the fire from being caused by thermal runaway.

[0174] In the monopolar current collector of the present invention, the M layer preferably contains aluminum as a main component in the case of a monopolar current collector facing the positive electrode, and copper as a main component in the case of a monopolar current collector facing the negative electrode, from the perspective of shifting the redox potential of the metal and / or metal-based compound from the range of the reaction potential within the battery. Furthermore, from the perspective of productivity, the M layer in the monopolar current collector of the present invention is preferably formed by direct vapor deposition on a polyester film.

[0175] In the monopole current collector of the present invention, the arithmetic mean height Sa of the M layer is preferably greater than or equal to 15 nm and less than or equal to 60 nm. By setting the arithmetic mean height Sa of the M layer to be greater than or equal to 15 nm, it is possible to suppress the occurrence of defects on the surface of the M layer due to friction with metal rollers when the polyester film provided with the M layer is transported, thereby reducing the performance of the assembled secondary battery. Furthermore, by setting the arithmetic mean height Sa to be less than or equal to 60 nm, it is possible to suppress the increase in resistance of the assembled secondary battery due to poor contact when the active material described later is provided on the surface of the M layer.

[0176] In the monopolar current collector of the present invention, lubricant particles comprising inorganic and / or organic particles may be added to the polyester film. The inclusion of lubricant particles can reduce friction during transport of the polyester film and improve process stability. The aforementioned metal compounds, metal oxides, and carbon materials can also be used as lubricant particles.

[0177] In the monopole current collector of the present invention, the silicon content is preferably greater than 0 mass ppm and less than 10 mass ppm. The method for determining the silicon content will be described later. In the manufacture of the polyester film, silicon can be introduced by using lubricant particles having silicon dioxide as the main component. By setting the silicon content to less than 10 mass ppm, the mechanical properties of the monopole current collector having the M layer can be suppressed from being reduced. The reason is that the thermal expansion coefficient of the silicon dioxide particles contained in the polyester film is low. Specifically, the reason is that when the vapor deposition process is performed, when the polyester film expands due to the heat it is subjected to, the difference in thermal expansion coefficient with the silicon dioxide particles becomes larger, thereby causing peeling at the interface between the polyester resin and the silicon dioxide particles and generating voids in the film. In addition, when the monopole current collector of the present invention is assembled into a lithium-ion battery, the silicon generated by the partial reduction of silicon dioxide in the polyester film can be suppressed from irreversibly reacting and combining with lithium ions, thereby reducing the battery characteristics.

[0178] [Electrical storage element]

[0179] The energy storage device of the present invention comprises an electrode assembly comprising a positive electrode and a negative electrode. It may also contain an electrolyte, in which case a separator is preferably interposed between the positive and negative electrodes. An energy storage device comprising a solid electrolyte that does not contain an electrolyte is also preferred. Furthermore, it may comprise a battery case for housing the electrode assembly.

[0180] Examples of such an electric storage element include primary batteries, secondary batteries, electric double layer capacitors, and aluminum electrolytic capacitors. However, in the present invention, the electric storage element refers to an electric storage element for a secondary battery.

[0181] Examples of the secondary battery include lithium secondary batteries, lead storage batteries, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-iron storage batteries, silver oxide-zinc storage batteries, manganese dioxide-lithium secondary batteries, lithium cobaltate-carbonate secondary batteries, and vanadium-lithium secondary batteries.

[0182] Among these, secondary batteries are preferred in terms of long-term use, and lithium secondary batteries that achieve high energy density by using an organic solvent are more preferred.

[0183] As the battery case, for example, an aluminum case, an iron case whose inner surface is nickel-plated, a case including an aluminum laminate film, or the like can be used.

[0184] Examples of the shape of the battery case include a pouch type, a cylindrical type, a square type, and a coin type. Among these, the pouch type is preferred because it can achieve high energy density and can be freely designed in shape at low cost.

[0185] The positive electrode is formed by laminating a positive electrode material containing an active material, a binder resin, and a conductive additive on a current collector. Examples of active materials include: layered lithium-containing transition metal oxides such as LiCoO2 (LCO), LiNiO2, LiNiCoMnO2 (NCM), and LiNiCoAlO2 (NCA); spinel-type manganese oxides such as LiMn2O4; iron-based compounds such as LiFePO4 (LFP) and LFMP in which a portion of the iron is replaced with magnesium; olivine-type compounds such as LiMnPO4 (LMP), LiCoPO4 (LCP), and LiNiPO4 (LNP); and sulfur-based compounds. As the binder resin, any resin with high oxidation resistance can be used. Specifically, fluorine-containing resins, acrylic resins, and styrene-butadiene resins can be used. As conductive additives, carbon blacks such as acetylene black and furnace black, and carbon materials such as graphite can be used.

[0186] As the current collector, a metal foil or a resin film having a metal layer can be used. In the case of metal foil, aluminum foil is particularly often used. It is particularly preferable to use the monopolar current collector of the present invention.

[0187] The negative electrode is formed by laminating a negative electrode material containing an active material and a binder resin on a current collector. Examples of active materials include carbon materials such as artificial graphite, natural graphite, hard carbon, and soft carbon, lithium alloy materials such as tin and silicon, metal materials such as lithium, and lithium titanate (Li4Ti5O 12 ) etc. Examples of the binder resin include fluorine-containing resins, acrylic resins, and styrene-butadiene resins. As the current collector, a resin film having a metal foil or a metal layer can be used. In the case of metal foil, copper foil is often used, but the monopolar current collector of the present invention is particularly preferably used.

[0188] When a liquid electrolyte (electrolyte) is used in a lithium ion battery or the like, an olefin-based membrane such as polyethylene or polypropylene may be used as a separator for the purpose of isolating the positive electrode from the negative electrode.

[0189] As the electrolyte of the electric storage element of the present invention, either an electrolytic solution or a solid electrolyte can be used.

[0190] When the energy storage device of the present invention contains an electrolyte, the electrolyte serves as a site for ion transfer between the positive electrode and the negative electrode in an electrochemical device such as a secondary battery, and has a structure in which an electrolyte is dissolved in an organic solvent.

[0191] Examples of the electrolyte include LiPF 6 , LiBF 4 , and LiClO 4 . From the viewpoint of solubility in organic solvents and ion conductivity, LiPF 6 is preferably used.

[0192] Examples of the organic solvent include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. These organic solvents may be used in combination of two or more.

[0193] When the storage element of the present invention contains a solid electrolyte, the solid electrolytes that can be used include: sulfide-based solid electrolytes that are crystalline or glassy and contain elements such as phosphorus, silicon, chlorine, and tin in addition to lithium and sulfur; and oxide-based solid electrolytes that are crystalline or glassy and contain elements such as lanthanum, titanium, aluminum, germanium, and zirconium in addition to lithium and oxygen.

[0194] Hereinafter, a method for producing a lithium secondary battery which is also preferably used as an electricity storage element will be described.

[0195] As a method for producing a lithium secondary battery, an active material and a conductive auxiliary agent are first dispersed in a binder resin solution to prepare an electrode coating liquid, the coating liquid is applied to a current collector, and the solvent is dried to obtain a positive electrode and a negative electrode, respectively. The film thickness of the dried coating film is preferably set to 50 μm or more and 500 μm or less. As a further preferred form, the positive electrode active material layer is preferably set to 90 μm or more and 120 μm or less. In addition, the negative electrode active material layer is preferably set to 100 μm or more and 170 μm or less. By setting the thickness of the active material layer of the positive electrode and the negative electrode to the above range, a high-capacity secondary battery can be produced. Here, since the polyester film and the monopole current collector in the present invention have excellent mechanical properties, even when the thickness of the active material layer becomes thicker, the heat required for drying increases, or high-pressure roller pressing is performed to increase the density of the active material layer, electrode processing can be carried out without problem.

[0196] Furthermore, it is preferable to apply pressure to the active material layer formed on the current collector by a method such as roll pressing to densify the layer and thereby thin the current collector.

[0197] A separator for a lithium secondary battery is arranged between the obtained positive electrode and negative electrode in contact with the active material layer of each electrode, and sealed in an outer packaging material such as an aluminum laminate film. After injecting the electrolyte, a negative electrode lead or a safety valve is installed, and the outer packaging material is sealed.

[0198] The lithium secondary battery element thus obtained has high adhesion to electrodes and excellent battery characteristics, and can be manufactured at low cost.

[0199] [Secondary battery]

[0200] Energy storage elements produced using the above methods and other methods are sometimes used as secondary batteries by connecting multiple elements in series to meet the specific application or required battery capacity. In such cases, it is preferable to use the secondary battery with voltage or temperature management and safety features. A preferred example is to connect the energy storage elements with tab wires (current extraction wires) and house them in a resin or metal module housing, thereby using the secondary battery.

[0201] A preferred form of the secondary battery of the present invention is a secondary battery equipped with a collector having a layer (hereinafter referred to as M layer) formed of a metal and / or metal-based compound with a thickness of greater than 0.2 μm and less than 3.0 μm on the surface of both sides of a polyester film that satisfies the following (1) and (2).

[0202] (1) The polyester film has a thickness of 1 μm or more and 30 μm or less

[0203] (2) The polyester film has a resin layer containing 0.1% by mass or more and less than 5.0% by mass of conductive particles.

[0204] In the secondary battery of the present invention, the thickness of the current collector is more preferably 4 μm or more and 7 μm or less. A current collector thickness of 4 μm or more can suppress a decrease in the mechanical properties of the battery, while a current collector thickness of 7 μm or less can reduce the weight of the battery.

[0205] The secondary battery of the present invention preferably has a structure in which the current collector is stacked in more than 45 layers and less than 80 layers, and more preferably has a structure in which the current collector is stacked in at least 45 layers and less than 80 layers with an active agent layer described later as a separator. By having the current collector having at least 45 layers and less than 80 layers in the secondary battery, the battery capacity can be increased, and by using the current collector in the present invention, the size of the secondary battery can be reduced. The stacked structure can be a structure in which the current collector is separated by a stacked structure (hereinafter referred to as an active agent layer) comprising a positive electrode active material layer and a negative electrode active material layer, and is stacked in more than 45 layers in a single sheet, or a structure in which an active agent layer is arranged between two sheets of the current collector and the active agent layer is wound, and more than 45 layers of the current collector are stacked from the center of the winding. Here, the so-called stacking number, whether it is a positive electrode or a negative electrode, refers to the number of sheets stacked with a current collector containing a polyester film and an M layer and an active agent layer. For example, if the structure is current collector / active agent layer / current collector, it is two layers, and if the structure is current collector / active agent layer / current collector / active agent layer / current collector, it is three layers. In addition, in the active agent layer structure, a separator may be provided between the positive electrode active material layer and the negative electrode active material layer. When the electrolyte is a solid electrolyte and the battery structure does not contain a separator, the active agent layer becomes a layer composed of the positive electrode active material layer and the negative electrode active material layer.

[0206] In the secondary battery of the present invention, from the viewpoint of minimizing the internal resistance of the battery and improving the battery output, the current collector is preferably one in which the active material layer is directly laminated on the surface of the M layer.

[0207] In addition, the thickness of the current collector is preferably not less than 0.01 times and not more than 0.04 times the thickness of the active agent layer. By using the laminated polyester film with excellent mechanical properties of the present invention, a thick active material layer can be formed on a thin film, which can achieve both high capacity and mechanical strength. Here, the so-called active agent layer thickness refers to the distance between the nearest current collector stacked from a current collector with a positive electrode active material layer and a negative electrode active material layer interposed therebetween. Specifically, it is the thickness obtained by adding the total thickness of the positive electrode active material layer and the negative electrode active material layer, and the thickness of the separator when a separator is present between the positive electrode active material layer and the negative electrode active material layer. In addition, the thickness of the current collector is the total thickness of the polyester film and the metal layers on both sides. In the case where the thickness of the current collector is different in the positive electrode current collector and the negative electrode current collector, the average value of the thickness of the positive electrode current collector and the thickness of the negative electrode current collector is taken as the thickness of the current collector.

[0208] The secondary battery of the present invention preferably has a joint portion joined to the electrode lead in a structure in which the collector is stacked with more than 45 layers and less than 80 layers, and the joint portion has a concave shape with a spacing of more than 0.3 mm and less than 0.8 mm and a depth of more than 0.1 mm and less than 1.0 mm. As a method for setting the joint, known techniques such as resistance welding, laser welding, and ultrasonic bonding are used. In terms of minimizing the thermal damage to the membrane, ultrasonic bonding is preferably used. As the shape of the joint, it is preferably set to a concave shape with a spacing of more than 0.3 mm and less than 0.8 mm and a depth of more than 0.4 mm and less than 1.0 mm. By having a depth of more than 0.1 mm in the concave shape, the collector can be joined with at least 10 pieces at a time, and by having a depth of less than 1.0 mm in the concave shape, the electrode lead can be suppressed from breaking. In addition, by having a spacing of more than 0.3 mm in the concave shape, it is possible to suppress the situation where the concave shapes are close to each other and the concave shapes are connected to each other and the resin collector is broken. Furthermore, by setting the spacing between the recessed shapes in the current collector to 0.8 mm or less, it is possible to prevent an increase in resistance at the junction of the current collector and a decrease in battery characteristics of the assembled secondary battery. The number of recessed shapes is not particularly limited, but preferably, there are at least 16 recessed shapes at the junction with the electrode tab.

[0209] In the secondary battery of the present invention, the polyester film contains conductive particles, so that even if a small amount of polyester film remains when forming the concave shape of the joint, an increase in resistance of the joint can be suppressed, thereby allowing more current collectors to be joined to the electrode tabs at one time.

[0210] In the secondary battery of the present invention, it is preferred that when the thickness of the end of the collector is set to D1 (μm) and the thickness of the collector at a position 20 mm inside the end of the collector is set to D2 (μm), D1 / D2 is greater than or equal to 0.9 and less than or equal to 1.2. Here, the thickness of the end refers to the thickness of the collector 3 mm inside the end. D1 / D2, which is the ratio of the thickness, represents the thickness uniformity of the end of the collector. When D1 / D2 is greater than or equal to 0.9 and less than or equal to 1.2, due to the high uniformity of the end, the situation where the end specifically becomes thicker when multiple sheets are stacked can be suppressed. The high uniformity of the end can suppress the following situations: the situation where stress is concentrated on the end during the step of stacking and winding the collector and then pressing to form, or the situation where stress is concentrated on the end during bending as a durability test of the assembled secondary battery, and defects are generated in the collector. D1 / D2 is more preferably greater than or equal to 0.95 and less than or equal to 1.1. The method of controlling D1 / D2 within the above range is to control the breaking strength of the polyester film of the present invention within the above range. By controlling the breaking strength, deformation in the thickness direction can be suppressed, and the occurrence of end bulging during slit processing can be suppressed.

[0211] In the secondary battery of the present invention, from the viewpoint that the battery capacity of the assembled secondary battery can be increased by increasing the capacity of the positive electrode active material, it is preferred that the collector is a collector in which the M layer contains an aluminum element and a positive electrode active material layer with a thickness of greater than 90 μm and less than 120 μm is stacked on the surface of the M layer containing the aluminum element.

[0212] In addition, in the secondary battery of the present invention, from the viewpoint of increasing the battery capacity of the assembled secondary battery by increasing the capacity of the negative electrode active material, it is preferred that the collector is a collector in which the M layer contains a copper element and a negative electrode active material layer with a thickness of greater than or equal to 80 μm and less than or equal to 170 μm is stacked on the surface of the M layer containing the copper element.

[0213] In the secondary battery of the present invention, the content of furnace black and Ketjen black contained in the electrolyte is preferably 0.001 mass ppm or more and 100 mass ppm or less in total. The so-called content of 100 mass ppm or less indicates that the leakage of the carbon material contained in the polyester film into the electrolyte is suppressed. By including the furnace black and Ketjen black in the electrolyte, the decrease in battery capacity due to the obstruction of the movement of lithium ions moving in the electrolyte can be suppressed. In particular, when the carbon material in the polyester leaks over time due to being left in an environment exceeding 30°C for a long time, the decrease in battery capacity becomes non-negligible.

[0214] [Electric Vehicles]

[0215] The secondary battery produced by the method and the like has excellent battery characteristics and durability, so one of the preferred forms is to be mounted on an electric vehicle. The so-called electric vehicle refers to a car that is supplied with part or all of the driving energy required for driving by a secondary battery. As types of electric vehicles, there can be listed pure electric vehicles (BEVs) equipped only with secondary battery packs, hybrid electric vehicles HEV (Hybrid Electric Vehicle) equipped with both fossil fuels such as gasoline and secondary battery packs, and plug-in hybrid electric vehicles (PHEV). In any use, the secondary battery of the present invention can be suitably used.

[0216] [Electric Flying Vehicle]

[0217] Since the secondary battery produced by the above method has excellent battery characteristics and durability, one of the preferred forms is to be mounted on an electric flying object. The so-called electric flying object refers to a flying object that is supplied with part or all of the driving energy required for flight by a secondary battery. Specifically, electric aircraft represented by drones, stratospheric communication platform aircraft (high altitude platform (High Altitude Platform Station, HAPS)), air subways (airmetro), and air taxis (airtaxi) can be listed. In any use, the secondary battery of the present invention can be used well.

[0218] [Evaluation method of characteristics]

[0219] A. Polymer Properties

[0220] Regarding the polymer properties, the case of using a polyester resin has been exemplified, but the resin serving as the main component of the polyester film in the present invention is not limited thereto.

[0221] (i) Intrinsic viscosity (IV)

[0222] A sample (polyester resin (raw material) or the polyester film of the present invention) was dissolved in 100 ml of o-chlorophenol (solution concentration C (sample weight / solution volume) = 1.2 g / 100 ml), and the viscosity of the solution at 25°C was measured using an Ostwald viscometer. The viscosity of the solvent was also measured in the same manner. Using the obtained solution viscosity and solvent viscosity, [η] was calculated using the following formula (1), and the obtained value was used as the intrinsic viscosity (IV) of the entire polyester film.

[0223] ηsp / C=[η]+K[η] 2 ·C…(1)

[0224] (Here, ηsp = (solution viscosity / solvent viscosity) - 1, and K is the Huggins constant (set to 0.343))

[0225] When insoluble matter such as inorganic particles exists in the solution in which the measurement sample is dissolved, measurement is performed using the following method.

[0226] (1-1) A measurement sample was dissolved in 100 mL of o-chlorophenol to prepare a solution having a concentration higher than 1.2 g / 100 mL. Here, the weight of the measurement sample supplied to o-chlorophenol was defined as the measurement sample weight.

[0227] (1-2) Next, the solution containing the insoluble matter was filtered, and the weight of the insoluble matter and the volume of the filtrate after filtration were measured.

[0228] (1-3) Additional o-chlorophenol was added to the filtrate after filtration, and the concentration was adjusted so that (measured sample weight (g) - weight of insoluble matter (g)) / (volume of filtrate after filtration (mL) + volume of additional o-chlorophenol (mL)) was 1.2 g / 100 mL.

[0229] (For example, when a concentrated solution with a measurement sample weight of 2.0 g / solution volume of 100 mL is prepared, the weight of the insoluble matter when filtering the solution is 0.2 g, and the volume of the filtrate after filtration is 99 mL, an additional 51 mL of o-chlorophenol is added for adjustment. ((2.0 g - 0.2 g) / (99 mL + 51 mL) = 1.2 g / 100 mL))

[0230] (1-4) The solution obtained in (1-3) was used to measure the viscosity at 25°C using an Ostwald viscometer. The obtained solution viscosity and solvent viscosity were used to calculate [η] according to the above formula (1). The obtained value was used as the intrinsic viscosity (IV) of the entire polyester film. F ).

[0231] B. Film Formability Evaluation

[0232] (i) Evaluation of discharge stability during extrusion

[0233] In the polyester film production process of the present invention, an unstretched film is obtained by melt extrusion from a die, cooling using a casting drum and electrostatic application, and forming the film into a sheet. A 10-meter roll of the unstretched film obtained is collected. The longitudinal thickness unevenness of the 10-meter roll of the unstretched film produced by the above method is evaluated as follows. The thickness of the center of the 10-meter roll is measured at 50-cm intervals in the longitudinal direction. The percentage value of the value obtained by dividing the difference between the maximum and minimum values of the measured values by the average thickness of the center of the 10-meter roll is used as the thickness unevenness (%).

[0234] A: The thickness unevenness of the unstretched film is less than 10%

[0235] B: Unevenness in thickness of unstretched film is 10% or more and less than 20%

[0236] C: Uneven thickness of unstretched film is 20% or more

[0237] As for discharge stability, A and B were good, and A was the most excellent.

[0238] (ii) Evaluation of stretchability

[0239] The stretching during the production of the polyester film of the present invention was carried out by the method described in the section (Sequential Biaxial Stretching). The number of film breakages when 4000 m of the biaxially oriented polyester film produced by the above method was collected was evaluated as follows.

[0240] A: The number of membrane ruptures is less than 3 times

[0241] B: The number of membrane ruptures is 3 or more and less than 10 times

[0242] C: The membrane ruptures more than 10 times

[0243] As for stretchability, A and B were good, with A being the most excellent.

[0244] C. Film thickness

[0245] (i) Film thickness T

[0246] The total thickness of the polyester film was measured at five random locations using a dial gauge in accordance with the A-2 method of Japanese Industrial Standards (JIS) K7130 (1992) on ten films stacked together. The average value was divided by 10 to obtain the film thickness T (μm).

[0247] (ii) Stack thickness (T P1 、T P2 、T M )

[0248] The cross section of the polyester film or laminated polyester film of the present invention is cut out in a direction parallel to the width direction of the polyester film using a microtome. The cross section is subjected to a sputtering treatment using platinum palladium, and then observed using a scanning electron microscope (JSM-6700 manufactured by JEOL Ltd.) at an accelerating voltage of 3 kV at a magnification of 5000 to 20000 times to determine the thickness ratio of the layers (P1 layer, P2 layer) and the M layer constituting the laminated film. The thickness of each layer (T) is calculated based on the obtained stacking ratio and the film thickness of all layers obtained in item (i). P1 、T P2 、T M ).

[0249] (iii) Thickness D1 at the end of the current collector, thickness D2 at a position 20 mm from the end of the current collector

[0250] As in item (i) above, using a dial gauge in accordance with JIS K7130 (1992) A-2 method, measure the thickness of 10 current collectors at five random locations 3 mm inward from the ends, with the ends combined and overlapped. Divide the average value by 10 to obtain the thickness D1 (μm) at the end of the current collector. Similarly, measure the thickness of 5 random locations 20 mm inward from the ends, and divide the average value by 10 to obtain the thickness D2 (μm) at the position 20 mm inward from the end of the current collector.

[0251] D. Constituent elements of the layer containing metal and / or metal compound

[0252] After the surface of the laminated polyester film of the present invention was sputtered with platinum and palladium, the metal species of the metal layer provided on the surface of the laminated polyester film of the present invention were identified by energy dispersive X-ray spectroscopy (EDX). The EDX used in this analysis (Aztec Live Standard UltimMax 65, manufactured by Oxford Co., Ltd.) was attached to a scanning electron microscope (JSM-6700F, manufactured by JEOL Ltd.).

[0253] The acceleration voltage was varied within a range of 0.5 kV to 30 kV, and the detected elements were defined as the elements constituting the M layer. At this time, platinum and palladium were excluded, and if only platinum or palladium was detected through measurement at all acceleration voltages, these were defined as the elements constituting the metal and / or metal compound layer (M layer).

[0254] E. Determination of film volume resistivity

[0255] The volume resistivity of the polyester film in the present invention is measured using a high resistivity meter (Nittoseiko Analytech Co., Ltd. / high resistivity meter Hiresta UX). The electrode unit is measured using a J box X type according to the JIS K6911 method. The measurement mode is set to the volume resistivity measurement mode (unit: Ω·cm), and the film thickness of the sample is input into the low resistivity meter for measurement. According to the JIS K6911 method, the polyester film in the present invention is cut out into a square of 100 mm square as a sample. The applied voltage and the voltage application time are set to the values after maintaining the voltage applied for 1 minute in the 500V application state according to the JIS K6911 method, and the sample is changed 3 times for measurement, and the average value of these is used as the volume resistivity of the polyester film.

[0256] If the volume resistivity falls below the lower limit (under the specified voltage or application time), the applied voltage is changed to 10 V and held for 1 minute before measurement. Three measurements are performed using different samples, and the average value is used as the volume resistivity of the polyester film. Measurements are performed at 23°C and 65% RH.

[0257] F. Carbon material content

[0258] The P1 layer or P2 layer of the polyester film of the present invention is placed in 200 ml of hexafluoroisopropanol (HFIP) to dissolve the polyester resin. 200 ml of water is added to the solution after dissolution. The liquid is then placed in a centrifuge to settle the particles and the supernatant is removed. Water is further added to the particles, and the washing and centrifugation are repeated twice. The particles obtained in this way are dried and weighed to calculate the content (mass %) of particles contained in each layer. This operation is performed on three different parts of the polyester film of the present invention, and the content of the particles obtained is used as the concentration of the carbon material contained in the sample.

[0259] The content of the carbon material contained in the electrolyte solution in the secondary battery of the present invention is also measured in the same manner as described above.

[0260] G. Identification of Carbon Species

[0261] The carbon material particles obtained in the above-mentioned F were analyzed by Raman spectroscopy for the so-called G band derived from the graphite structure (sp 2 Key) 1580cm -1 Nearby, and commonly referred to as the D band, originates from the diamond structure (sp 3 Key) 1350cm -1The peaks near the sample are observed and identified based on the ratio of these peak intensities. When performing the identification, the peak intensity data obtained by measuring the commercially available carbon materials are compared with the known Raman spectrum database. In addition, the carbon material obtained in the above-mentioned item (i) is observed at 50,000 to 500,000 times using a transmission electron microscope (TEM), and the obtained shape is observed. Combined with the Raman spectrum results, the type of carbon material present in the sample is identified. In the case where there are multiple carbon materials observed, the number of each carbon material observed by the TEM is converted into a volume ratio and the value thus obtained is used as the existence ratio of each carbon material.

[0262] H. Quantitative determination of silicon

[0263] The polyester film contained in the monopolar current collector of the present invention was measured by ICP emission spectroscopy. If a metal layer was laminated on the polyester film, the metal layer was removed by a known method such as acid treatment before quantitative measurement.

[0264] <Analysis conditions>

[0265] Apparatus: ICP emission spectrometry (manufactured by Hitachi High-Tech Sciences, Inc.) PS3520VDDII

[0266] Sample Preparation: The polyester film was weighed in a beaker and decomposed under pressure using sulfuric acid, followed by nitric acid, followed by heating to ash. The ash was dissolved in a mixed flux of sodium carbonate and boric acid and heated to dissolve in dilute nitric acid to a constant volume of 10 mL. The solution diluted with dilute nitric acid was then analyzed for silicon content using inductively coupled plasma atomic emission spectrometry (ICP-AES). This was used as the silicon content in the polyester film.

[0267] (Measurement conditions)

[0268] Measurement wavelength: 251.6nm

[0269] High frequency output: 1.2kW

[0270] Plasma gas flow rate: 16L / min

[0271] Auxiliary gas flow rate: 0.5L / min

[0272] Carrier gas flow rate: 0.9L / min

[0273] Photometric height: 12mm.

[0274] H. Quantitative analysis of resins constituting polyester films

[0275] A sample was collected from all layers, the P1 layer, and the P2 layer of the polyester film of the present invention. The sample was immersed in 1,1,1,2,2,2-hexafluoro-2-isopropanol (HFIP), and the soluble portion was separated by centrifugation. The supernatant was collected to extract the resin component contained in the polyester film. The extract was measured by matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS). The obtained mass spectrum was compared with the nuclear magnetic resonance method ( 1 H-NMR) spectroscopy to identify the structure of the compound.

[0276] 50 mg of all layers, P1 layer, or P2 layer of the polyester film of the present invention were measured, and 2.63 mg of octamethylcyclotetrasiloxane (OMTS) was added as an internal standard substance. 0.7 ml of deuterated 1,1,1,2,2,2-hexafluoro-2-isopropanol (HFIP-d2) was added to dissolve the soluble portion, and then centrifuged. The supernatant of the centrifuged solution was collected and analyzed by nuclear magnetic resonance (NMR). 1 The compounds contained in the sample are quantified based on the ratio of the NMR spectrum area of the added internal standard substance to the spectrum area of the extract.

[0277] ( 1 H-NMR measurement conditions)

[0278] Device used: ECA-400 (manufactured by JEOL RESONANCE)

[0279] Measurement method: single pulse

[0280] Observation frequency: 399.8MHz

[0281] Pulse width: 6.45s (45 pulses)

[0282] Lock solvent: HFIP-d2

[0283] Chemical shift standard: Deuterated solvent residual protons (4.41 ppm)

[0284] Observation width: about 8000Hz (about -2ppm to 18ppm)

[0285] Number of data points: 32768

[0286] Waiting time: 30 seconds

[0287] Cumulative number of times: 128 times

[0288] Measurement temperature: room temperature (21°C)

[0289] Sample rotation speed: 15Hz.

[0290] I.DSC measurement

[0291] The polyester film of the present invention or its raw material was measured using a Thermo Plus Evo2 series DSC Vesta manufactured by Rigaku Corporation as a differential scanning calorimeter (DSC). Approximately 5 mg of the sample was placed on an aluminum tray and heated from room temperature to 300°C at a heating rate of 20°C / minute and held there for 5 minutes (first-pass measurement). The temperature of the exothermic peak due to glass transition observed at this time was designated as the glass transition temperature (Tg), and the peak temperature of the endothermic peak due to melting was designated as the melting point (Tm). The average of three measurements was taken as the glass transition temperature (Tg) and melting point (Tm) of the sample.

[0292] If the DSC chart of the polyester film of the present invention is difficult to distinguish from the minor endothermic peak Tmeta that appears immediately before the melting point, the following measurement is performed in addition to the first run of measurement. The temperature is raised to 300°C at a rate of 20°C / min and held for 5 minutes, followed by rapid cooling with liquid nitrogen and then again raised to 300°C at a rate of 20°C / min (second run measurement). The number and temperature of the melting point peaks are confirmed, and peaks that disappear from the first run of measurement are considered to be the minor endothermic peak Tmeta that appears immediately before the melting point and are excluded from the first run of measurement data.

[0293] J. Relative dielectric constant

[0294] A sample was cut out of a polyester film with a length of 35 mm and a width of 35 mm. The cut sample was clamped in such a way that the length direction of the sample became the length direction of the sample holder, and the sample was measured using a molecular orientation meter (manufactured by Oji Measuring Instruments, MOR-7015). The measurement frequency was set to 15 GHz using a signal generator (manufactured by KEYSIGHT, E8257D). The measurement control software "MOR-7000" was used and the following measurement conditions and sample thickness were input to calculate the dielectric constant ε' and dielectric loss ε" in the directions where the measurement angles were 0° (sample length direction), 30°, 60°, 90°, 120°, and 150°. The average values of the dielectric constant ε' and dielectric loss ε" obtained in each measurement direction were respectively used as the dielectric constant ε' and dielectric loss ε" of the measured sample, and the relative dielectric constant ε was calculated according to the following formula (2) r .

[0295] ε r ={(ε')2 +(ε”) 2} 0.5 …Formula (2)

[0296] The above operation was performed on samples cut out from two different locations of the polyester film, and the average value of the obtained relative dielectric constants was defined as the relative dielectric constant of the polyester film.

[0297] (Measurement conditions)

[0298] Measurement mode: Dielectric constant model measurement

[0299] Measuring angle interval θ: 30°

[0300] [Evaluation method for application characteristics]

[0301] A. Vacuum evaporation processing

[0302] The polyester film roll of the present invention is set in a roll-to-roll vacuum evaporation device (EWC-060 manufactured by ULVAC), and the copper ingot or aluminum ingot is heated by the induction heating evaporation method using a carbon crucible under the conveying speed and output conditions so that the thickness of the metal layer becomes a specified value, thereby performing vacuum evaporation to form a metal layer. As a conveying speed, it is implemented at 20m / minute. Next, the roll of the polyester film with a metal layer on one side is again set in a roll-to-roll vacuum evaporation device (EWC-060 manufactured by ULVAC), and the copper ingot or aluminum ingot is heated by the induction heating evaporation method using a carbon crucible on the surface of the polyester film on the side opposite to the surface on which the metal layer is provided, thereby providing a metal layer by vacuum evaporation. At this time, the conveying speed and output conditions are adjusted in such a way that the metal layer becomes a specified thickness, and vacuum evaporation is performed.

[0303] B. Evaluation of Mechanical Properties of Laminated Polyester Films or Monopolar Current Collectors with Surface Metal Layers

[0304] The elongation at break of a laminated polyester film or a monopole current collector having a metal layer made by the vacuum evaporation processing method described in item A. on both sides is measured. From the laminated polyester film or the monopole current collector having the metal layer on both sides, a rectangular shape with a length of 150 mm and a width of 10 mm is cut out in the length direction as a sample. In accordance with the following method specified in the American Society for Testing Materials (ASTM)-D882, an Instrontype tensile testing machine (AMF / RTA-100 manufactured by Orientec) is used, a sample film with a width of 10 mm is set in a manner such that the length between the chucks becomes 50 mm, and a tensile test is performed at a tensile speed of 300 mm / min. The test is performed 5 times, and the average values of the elongation and strength at the breaking point obtained are respectively used as the elongation at break and the breaking strength possessed by the sample.

[0305] When the longitudinal and width directions of a laminated polyester film having the metal layer on both sides are unknown, the elongation at break and the breaking strength are measured in four directions, namely, a specific direction and directions rotated 45°, 90°, and 135° in-plane from the specific direction. The maximum value of the elongation at break and the breaking strength obtained in the four directions is defined as the elongation at break and the breaking strength of the laminated polyester film whose longitudinal and width directions are unknown.

[0306] C. Arithmetic mean height of the monopole current collector

[0307] The arithmetic mean height of the metal layer surface of a monopolar current collector having metal layers on both sides was measured (according to ISO 25178). A rectangular sample with a length of 60 mm and a width of 60 mm was cut out from the monopolar current collector along the longitudinal direction.

[0308] For the cut samples, a scanning white interference microscope (device: "VertScan" (registered trademark) VS1540 manufactured by Hitachi High-Tech Science Corporation) was used, and the measurement mode was set to the wave (WAVE) mode using a 50x objective lens. The sample surface was measured with 90 fields of view within a measurement area of 113μm×113μm. Regarding the sample setting, the sample was set on the stage in such a way that the Y-axis became the length direction of the sample for measurement. Furthermore, in the case of a sample with an unknown length direction, the measurement was performed in such a way that the Y-axis became any direction of the sample film, and then the measurement was performed in such a way that the direction became after being rotated 120 degrees, and then the measurement was performed in such a way that the direction became after being rotated 120 degrees, and the average value of each measurement result was used as the arithmetic mean height of the surface being measured. In addition, the sample to be measured was clamped between two metal frames equipped with rubber gaskets, thereby making the film in the frame a tensioned state (a state after removing the slack or curling of the sample), and the sample surface was measured.

[0309] The obtained microscope image was subjected to image processing under the following conditions using VS-Viewer Version 10.0.3.0, a surface analysis software built into the microscope, to determine the arithmetic mean height.

[0310] (Image processing conditions)

[0311] Image processing is performed in the following order.

[0312] Interpolation processing: Full interpolation

[0313] Filter processing: median (3×3 pixels)

[0314] Face correction: 4 times.

[0315] Scanning white interference microscopy measurements were performed on both sides of the monopolar current collector in 90 fields of view. For each measured image after image processing, the arithmetic mean height Sa (nm) was calculated by selecting the following analysis conditions and the numerical value set obtained by "Height Parameters" in the "ISO Parameters" analysis within the surface analysis software and outputting it to the parameter table. The average value of the 180 fields of view (90 fields of view x two surfaces) was used as the arithmetic mean height Sa (nm) of the measured surface.

[0316] (ISO parameter analysis conditions)

[0317] The ISO parameter analysis process was performed under the following conditions.

[0318] S-Filter: Automatic

[0319] Normal probability paper

[0320] Number of divisions: 300

[0321] Upper limit of calculation range: 3.000

[0322] Lower limit of calculation range: -3.000

[0323] Parameters: Select only "Height Parameters"

[0324] Output: Select "Parameter List"

[0325] (Parameter table output)

[0326] Select "Height Parameters" in the "ISO Parameters" window displayed by the ISO parameter analysis and click "Add to Parameter Table" to convert the "Sa [μm]" displayed in the "ISO Parameters" tab of the "Parameter Table" window into nm units for use.

[0327] (Base height: zero plane (average plane))

[0328] As the "zero plane (average plane)" in the setting of the reference height (height 0 nm), the plane of the "average height (Ave)" automatically calculated by the following formula in the measurement image (113 μm×113 μm) obtained by microscope observation using the method and performing the image processing is used.

[0329]

[0330] lx: The range length in the X direction of each measurement image after the image processing

[0331] ly: The range length in the Y direction of each measurement image after the image processing

[0332] h(x, y): The height of each image point (x, y) in the measured image after the image processing.

[0333] D. Evaluation of Resin Collectors

[0334] (i) Preparation of resin current collector

[0335] A laminated polyester film is produced by forming a metal layer on both sides of the polyester film of the present invention by the method described in section A. Vacuum Deposition Processing. A negative electrode resin current collector and a positive electrode resin current collector are produced. Copper is used as the metal species in the negative electrode resin current collector, and aluminum is used as the metal species in the positive electrode resin current collector.

[0336] (ii) Positive electrode active material, negative electrode active material

[0337] A positive electrode active material slurry was prepared by mixing 85% by mass of LiMn2O4 as a positive electrode active material, 5% by mass of acetylene black as a conductive additive, 10% by mass of polyvinylidene fluoride (PVDF) as a binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a slurry viscosity adjustment solvent.

[0338] 90 parts by mass of hard carbon as a negative electrode active material, 5 parts by mass of acetylene black as a conductive additive, 10 parts by mass of PVDF as a binder, and an appropriate amount of NMP as a slurry viscosity adjusting solvent were mixed to prepare a negative electrode active material slurry.

[0339] (iii) Preparation of battery evaluation unit

[0340] <Fabrication of a battery evaluation unit>

[0341] Two rectangular glass epoxy substrates (Nikko Chemical Co., Ltd., "Nikolyte" (registered trademark) NL-EG-23N) measuring 105 mm wide and 205 mm long were prepared. A hole was bored through the inside of each substrate, leaving a 15 mm wide outer perimeter. Heat-sealable film (Mitsui Chemicals, Inc., "Admer" (registered trademark) QE-060) with the same shape as the outer perimeter of the glass epoxy substrate was affixed to both sides. Next, a rectangular polyethylene (PE) separator (Celgard, Inc.) measuring 95 mm wide and 195 mm long was heat-sealed to one side of the glass epoxy substrate, thereby securing it. This produced a single cell frame member having a frame-shaped glass epoxy substrate affixed to one side of the separator.

[0342] The resin collector prepared in item (i) is cut into a rectangle with a width of 105 mm and a length of 205 mm. The active material prepared in item (ii) is applied to the surface of the resin collector on which the metal layer is formed using a scraper in the shape of a rectangle with a width of 66 mm and a length of 166 mm, with the outer periphery remaining.

[0343] A positive electrode active material layer was formed on the metal layer surface of the positive electrode resin current collector prepared in (i), and a negative electrode active material layer was formed on the metal layer surface of the negative electrode resin current collector. The NMP used as the adjustment solvent was dried to form a coating film, which was then pressed to form an active material layer with a thickness of 30 μm.

[0344] The positive electrode active material layer is housed inside the frame-shaped glass epoxy substrate of the cell frame member with the separator in contact with the active material layer, and the negative electrode active material layer is arranged with the separator interposed therebetween so that the active material layers face each other.

[0345] Before housing the positive electrode active material layer, an electrolyte solution is injected into the inner surface of the frame-shaped glass epoxy substrate of the cell frame. The electrolyte is a 1 mol / L solution of lithium hexafluorophosphate (LiPF6) in a mixture of equal volumes of ethylene carbonate and diethyl carbonate (EC:DEC = 1:1 by volume).

[0346] A single cell is produced by heat-sealing the overlapping portion of the resin collector on the positive electrode side / glass epoxy substrate / resin collector on the negative electrode side. Eight single cells are stacked in a direction where the resin collector on the positive electrode side is in contact with the resin collector on the negative electrode side to produce a stacked battery. The cells are housed in a laminated container and sealed to produce a cell for battery evaluation.

[0347] (iv) Battery Characteristics Evaluation (External Stress Resistance)

[0348] According to the descriptions of (i), (ii), and (iii), 10 battery evaluation units were prepared. As a bending test, each battery evaluation unit was bent along a cylindrical surface having the following curvature, and the presence or absence of short circuits as an electrical characteristic of the battery evaluation unit was confirmed. The bending test was carried out in the order of R250 (mm), R90 (mm), R70 (mm), and R30 (mm), and the external stress resistance as a characteristic of the battery using a resin collector was evaluated based on the curvature at which short circuits occurred. 10 battery evaluation units were used for evaluation, and the external stress resistance was evaluated as follows using the curvature with the largest number of short circuits.

[0349] AA: No short circuit occurred after the bending test using R30.

[0350] A: A short circuit occurred after the bending test using R30.

[0351] B: Short circuit occurred after the bending test using R70.

[0352] C: Short circuit occurred after the bending test using R90.

[0353] D: Short circuit occurred after the bending test using R250.

[0354] As for external stress resistance, AA to C are good, and AA is the most excellent.

[0355] E. Evaluation of stacked secondary batteries

[0356] (i) Preparation of a monopolar resin current collector

[0357] In the same manner as in item (i) of the above-mentioned section D., a negative electrode monopolar resin current collector having a copper layer on both surfaces of the polyester film of the present invention and a positive electrode monopolar resin current collector having an aluminum layer were obtained.

[0358] (ii) Fabrication of laminated secondary batteries

[0359] The active material layers shown below were applied to both surfaces of the monopolar current collector obtained in (i), dried, and roll-pressed to obtain a positive electrode and a negative electrode containing a resin current collector each having a predetermined thickness.

[0360] A positive electrode containing the resin current collector, a separator, a negative electrode containing the resin current collector, and a separator were stacked in this order. Ultrasonic welding was used to join the ends of the stacked resin current collectors to the electrode tabs in units of 30 sheets. After joining, the resistance between the electrode tab and each joined current collector was measured. If the resistance exceeded 60 mΩ, the number of sheets was reduced and welding was repeated.

[0361] (Positive electrode member)

[0362] Active material: LiFePO4 (LFP) 85 mass%

[0363] Conductive additive: acetylene black 5% by mass

[0364] Binder: Polyvinylidene fluoride (PVDF) 10% by mass

[0365] ·Slurry viscosity adjustment solvent: N-methyl-2-pyrrolidone (NMP) in appropriate amount

[0366] The above ingredients are mixed to prepare positive electrode active material slurry.

[0367] (Negative electrode member)

[0368] Active material: Graphite 85% by mass

[0369] Conductive additive: acetylene black 5% by mass

[0370] Binder: Carboxymethyl cellulose (CMC) 5% by mass / Styrene butadiene rubber (SBR) 5% by mass

[0371] ·Slurry viscosity adjustment solvent: water in appropriate amount

[0372] The above ingredients are mixed to prepare positive electrode active material slurry.

[0373] (Partition)

[0374] A 10 μm porous polyethylene film was used.

[0375] The stacked body was placed in an aluminum bag. The electrode leads were extended outside the bag. A positive electrode containing a resin current collector, a separator, a negative electrode containing a resin current collector, and a separator were stacked in this order as an electrolyte. Ultrasonic welding was used to join the ends of the stacked resin current collector to the electrode leads.

[0376] The aluminum pouch was filled with the following electrolyte solution and the pouch was sealed to obtain a laminated secondary battery.

[0377] (Electrolyte)

[0378] Electrolyte: lithium hexafluorophosphate (LiPF6) 1 mol / L

[0379] Solvent: a mixed solution of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC).

[0380] Mixing ratio: EC:EMC:DMC=30:40:30 (volume ratio)

[0381] (iii) Pressure durability test

[0382] According to the preceding item (ii), five stacked battery cells were made and a pressure durability test was performed. First, each stacked battery cell was placed on a metal plate, and a metal round rod with a diameter of 15.8 mm was pressed from the upper surface with a pressure of 13 kN. The voltage of the battery was measured at the time point of pressing 1 cm at a speed of 3 m / min, and the rate of reduction relative to the initial voltage was calculated. The average value of the voltage reduction rate of the five stacked secondary batteries was used as the rate of reduction of the voltage of the stacked secondary battery sample, and the evaluation was performed as follows.

[0383] A: The voltage reduction rate after the pressure endurance test is 10% or less.

[0384] B: The voltage reduction rate after the pressure endurance test is more than 10% and 25% or less.

[0385] C: The voltage reduction rate after the pressure endurance test is more than 25% and 50% or less.

[0386] D: The voltage reduction rate after the pressure endurance test exceeds 50%, or a fire occurs during the test.

[0387] As for the pressure durability test evaluation, A to C were good, and A was the most excellent.

[0388] (iv) Long-term storage evaluation

[0389] According to the previous item (ii), five stacked secondary batteries were placed in an environment of 35°C and 50% RH for 100 hours. The capacity during charging was then determined, and the retention of the charge capacity before and after long-term storage was evaluated as follows. The average of the capacity retention rates of the five stacked secondary batteries was used as the capacity retention rate of the stacked secondary battery sample, and the evaluation was performed as follows.

[0390] A: The capacity retention rate after long-term storage is 98% or more.

[0391] B: The capacity retention rate after long-term storage is 95% or more and less than 98%.

[0392] C: The capacity retention rate after long-term storage is 90% or more and less than 95%.

[0393] D: The capacity retention rate after long-term storage is less than 90%.

[0394] As for the long-term storage evaluation, A to C were good, and A was the most excellent.

[0395] (v) Electrode lead bonding

[0396] According to the preceding item (ii), the resistance values of the electrode tabs and the 30 current collectors bonded to the electrode tabs were measured for the electrode tab joints of five stacked secondary batteries. The current collector closest to the electrode tab was designated as the first tab, and the number of tabs where the resistance first exceeded 60 mΩ was determined. The same evaluation was performed on all five stacked secondary batteries, and the average value was used as the electrode tab bondability of the stacked secondary battery sample.

[0397] A: The number of current collectors satisfying a resistance value of 60 mΩ or less is 25 or more among 30 pieces.

[0398] B: The number of current collectors satisfying a resistance value of 60 mΩ or less is 20 or more and 24 or less among 30 current collectors.

[0399] C: The number of current collectors satisfying a resistance value of 60 mΩ or less is 15 or more and 19 or less among 30 current collectors.

[0400] D: The number of current collectors satisfying a resistance value of 60 mΩ or less is 14 or less among 30 pieces.

[0401] Example

[0402] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0403] [Manufacture of Polyester-1]

[0404] 1.9 mol of ethylene glycol was added to 1 mol of dimethyl terephthalate (DMT), and 0.05 parts by mass of magnesium acetate tetrahydrate and 0.015 parts by mass of phosphoric acid were added to 100 parts by mass of DMT, followed by heat transesterification. Subsequently, 0.025 parts by mass of antimony trioxide was added, and the mixture was heated and polycondensed under high reduced pressure to obtain polyester-1 pellets substantially free of particles. Polyester-1 has a glass transition temperature of 81°C, a melting point of 255°C, and an intrinsic viscosity of 0.70 dl / g.

[0405] [Manufacture of Polyester-2]

[0406] 1.9 mol of ethylene glycol was added to 1 mol of DMT, and 0.05 parts by mass of magnesium acetate tetrahydrate and 0.015 parts by mass of phosphoric acid were added to 100 parts by mass of DMT, followed by heat transesterification. 0.01% by mass of silica with an average particle size of 1 μm was added, followed by the addition of 0.025 parts by mass of antimony trioxide. The mixture was heated and polycondensed under high reduced pressure to produce polyester-2 pellets containing silica particles. Polyester-2 has a glass transition temperature of 81°C, a melting point of 255°C, and an intrinsic viscosity of 0.70 dl / g.

[0407] (Method for producing carbon material masterbatch)

[0408] [Production of Carbon-1]

[0409] The polyester-1 and Ketjen black were kneaded and extruded using a twin-screw kneader set to gradually increase the temperature within a range of 230° C. to 270° C. to obtain a masterbatch, Carbon-1, containing 5% by mass of Ketjen black.

[0410] [Production of Carbon-2]

[0411] The polyester-1 and carbon nanotubes were kneaded and extruded using a biaxial kneader set to gradually increase the temperature within a range of 230° C. to 270° C. to obtain master batches of carbon-2 containing 5% by mass of carbon nanotubes.

[0412] [Production of Carbon-3]

[0413] The polyester-1 and acetylene black were kneaded and extruded using a twin-screw kneader set to gradually increase the temperature within a range of 230° C. to 270° C. to obtain master batches containing 10% by mass of acetylene black, namely, carbon-3.

[0414] [Manufacturing of Carbon-4]

[0415] The polyester-1 and furnace black were kneaded and extruded using a twin-screw kneader set to gradually increase the temperature within a range of 230° C. to 270° C. to obtain master batches containing 20% by mass of furnace black, namely, carbon-4.

[0416] [Manufacturing of Carbon-5]

[0417] The polyester-1 is mixed and extruded with furnace black and silica particles with an average particle size of 1 μm using a twin-screw mixer set to gradually increase the temperature within a range of 230°C to 270°C to obtain a masterbatch, namely carbon-5, containing 20% by mass of furnace black and 0.01% by mass of silica particles with an average particle size of 1 μm.

[0418] (Example 1)

[0419] After drying polyester-1 and carbon-1 under reduced pressure at 180°C and 150°C for 2.5 hours, respectively, the raw materials were blended to the concentrations listed in the table. The resulting materials were fed into an extruder, melt-extruded, and filtered. The resulting materials were then electrostatically cast through a T-die onto a cooled casting roll maintained at 50°C and cooled to solidify, yielding unstretched films. This unstretched film was first introduced longitudinally onto a set of stretching rolls heated to 60°C to 120°C according to the film production conditions listed in the table, where it was stretched at a ratio of 3.0. The uniaxially stretched film was then introduced into a tenter frame, preheated to 90°C, stretched 3.0 times in the width direction at 100°C to 130°C, heat treated at 230°C while maintaining a fixed length, and relaxed by 4% in the width direction to yield a biaxially oriented polyester film with a thickness of 5 μm. The evaluation results are listed in the table.

[0420] Positive and negative electrode resin current collectors were produced by applying an M layer to the polyester film of the present invention using the vacuum deposition method described in the "Method for Evaluating Application Characteristics" above, using the metal type and metal layer thickness as specified in the table. The evaluation results are shown in the table.

[0421] To evaluate the resin current collector, battery evaluation cells using the positive and negative electrode resin current collectors were prepared according to the method described in the [Evaluation Method for Application Characteristics], and battery characteristics were evaluated. As shown in the table, the polyester film exhibited excellent resistance to external stress.

[0422] (Example 2)

[0423] A polyester film was obtained in the same manner as in Example 1 except that the amount of Ketjen Black added was reduced compared with Example 1 as shown in the table, and various evaluations were performed.

[0424] The elongation at break in the longitudinal direction after copper deposition decreased because the volume resistivity increased compared to Example 1. The external stress resistance of the resin current collector evaluated was worse than that of Example 1, but was within a practical range.

[0425] (Example 3)

[0426] A polyester film was obtained in the same manner as in Example 1 except that Carbon-2 was used as a masterbatch and the carbon material was changed to carbon nanotubes (CNTs) and the addition amount was increased as described in the table, and various evaluations were performed.

[0427] (Example 4)

[0428] A polyester film was obtained in the same manner as in Example 1 except that the film thickness was made thinner than that in Example 1 as described in the table, and each evaluation was performed.

[0429] Since the film thickness was thinner than that in Example 1, the elongation at break in the longitudinal direction after copper deposition decreased, and the external stress resistance of the resin current collector deteriorated compared to Example 1, but both were within the practical range.

[0430] (Example 5)

[0431] A polyester film was obtained in the same manner as in Example 3 except that the structure of the polyester film was set to a three-layer structure having a P2 layer using polyester-1 as a raw material as shown in the table, and various evaluations were performed.

[0432] The three-layer structure including the P2 layer containing no carbon material resulted in a higher volume resistivity than in Example 3. The elongation at break in the longitudinal direction after copper deposition increased, and the external stress resistance of the resin current collector was improved compared to that in Example 3.

[0433] (Examples 6 to 8, Example 11)

[0434] In Examples 6 and 7, except that carbon-4 was used as the masterbatch, furnace black as the conductive particle was changed as described in the table, and the film formation conditions were changed as described in the table, polyester films having a thickness of 4.5 μm were obtained in the same manner as in Example 1, and the various evaluations were performed. In Examples 8 and 11, except that Ketjen black was changed as described in the table, and the film formation conditions were changed as described in the table, polyester films having a thickness of 4.5 μm were obtained in the same manner as in Example 1, and the various evaluations were performed.

[0435] (Example 9)

[0436] As the raw material of the lubricant particles, polyester-2 or carbon-5 was used, except that the changes were made as described in the table, and the film forming conditions were changed as described in the table. A polyester film with a thickness of 4.5 μm was obtained in the same manner as in Example 1, and various evaluations were performed.

[0437] Because the film contained silica particles, voids derived from the silica particles were generated in the film during the vapor deposition step, resulting in a decrease in mechanical properties. The external stress resistance decreased compared to Example 1, but was within a practical range.

[0438] (Example 10)

[0439] A resin current collector was obtained and evaluated in the same manner as in Example 8, except that a 3 μm metal layer was provided on a 4.5 μm-thick polyester film as described in the table. The increased thickness of the metal layer increased the amount of heat applied to the film during the vapor deposition step, resulting in decreased mechanical properties. While external stress resistance decreased compared to Example 1, it remained within a practical range.

[0440] (Comparative Example 1)

[0441] A polyester film was obtained in the same manner as in Example 1 except that the constituent components of the polyester film did not contain a carbon material as shown in the table, and various evaluations were performed.

[0442] Since the carbon material was not contained, the volume resistivity increased compared to Example 1, and the elongation at break in the longitudinal direction after copper deposition decreased. Therefore, the external stress resistance of the resin current collector of the polyester film was significantly inferior to that of Example 1.

[0443] (Comparative Example 2)

[0444] A polyester film was obtained in the same manner as in Example 1 except that Carbon-3 was used as a raw material and acetylene black was used as the carbon material and the content was greatly increased compared with Example 1 as shown in the table, and various evaluations were performed.

[0445] (Laminated secondary battery)

[0446] (Example 12)

[0447] Using the metal-layered polyester film obtained in Example 6 as a current collector, a laminated secondary battery was prepared by laminating multiple current collectors according to the "D. Evaluation of Laminated Secondary Batteries" section. The structure of the laminated secondary battery is shown in the table, and the evaluation results of the resulting laminated secondary battery (pressure durability evaluation, long-term storage evaluation, and electrode tab bonding evaluation) are also shown in the table.

[0448] (Example 13)

[0449] Using the metal-layered polyester film obtained in Example 2 as a current collector, a stacked secondary battery was prepared by stacking multiple current collectors in accordance with the "D. Evaluation of Stacked Secondary Batteries" section. The structure of the stacked secondary battery is shown in the table, and the evaluation results of the resulting stacked secondary battery (pressure durability evaluation, long-term storage evaluation, and electrode tab bonding evaluation) are also shown in the table.

[0450] Since the mechanical properties of the laminated polyester film of Example 2 were inferior to those of Example 6, the pressure resistance evaluation was poor. In addition, the volume resistivity of the polyester film was high, resulting in a slightly poor electrode tab bonding evaluation. However, both were within the practical range.

[0451] (Example 14)

[0452] Using the metal-layered polyester film obtained in Example 7 as a current collector, a laminated secondary battery was prepared by laminating multiple current collectors in accordance with the "D. Evaluation of Laminated Secondary Batteries" section. The structure of the laminated secondary battery is shown in the table, and the evaluation results of the resulting laminated secondary battery (pressure durability evaluation, long-term storage evaluation, and electrode tab bonding evaluation) are also shown in the table.

[0453] The mechanical properties of the laminated polyester film of Example 7 were comparable to those of Example 6. However, the increased edge thickness ratio resulted in stress concentration at the laminated edges during the pressure durability test, resulting in a decrease in the pressure durability rating compared to Example 12, but remaining within a practical range. Furthermore, the amount of furnace black leaking into the electrolyte within the secondary battery was greater than in Example 12, resulting in a poor long-term storage rating, but remaining within a practical range.

[0454] (Example 15, Example 16, Example 18)

[0455] In Examples 15 and 16, the metal-layered polyester film obtained in Example 8 was used as the current collector. According to the "D. Evaluation of Laminated Secondary Batteries," laminated secondary batteries were prepared by laminating multiple current collectors. The structure of the laminated secondary battery is shown in the table, and the evaluations of the resulting laminated secondary batteries (pressure durability evaluation, long-term storage evaluation, and electrode tab bonding evaluation) are shown in the table.

[0456] In Example 18, the metal-layered polyester film obtained in Example 11 was used as a current collector. A laminated secondary battery was prepared by laminating multiple current collectors in accordance with the procedure described in "D. Evaluation of Laminated Secondary Batteries." The structure of the laminated secondary battery is shown in the table, and the evaluations of the resulting laminated secondary battery (pressure durability evaluation, long-term storage evaluation, and electrode tab bonding evaluation) are also shown in the table.

[0457] (Example 17)

[0458] Using the metal-layered polyester film obtained in Example 9 as a current collector, a stacked secondary battery was prepared by stacking multiple current collectors in accordance with the "D. Evaluation of Stacked Secondary Batteries" section. The structure of the stacked secondary battery is shown in the table, and the evaluation results of the resulting stacked secondary battery (pressure durability evaluation, long-term storage evaluation, and electrode tab bonding evaluation) are shown in the table.

[0459] The silica particles contained in the laminated polyester film of Example 9 caused a decrease in mechanical properties, and the pressure durability evaluation was lower than that of Example 12, but it was within a practical range.

[0460] (Comparative Example 3)

[0461] Using the metal-layered polyester film obtained in Comparative Example 1 as a current collector, a stacked secondary battery was prepared by stacking multiple current collectors according to the "D. Evaluation of Stacked Secondary Batteries" section. The structure of the stacked secondary battery is shown in the table, and the evaluation results of the resulting stacked secondary battery (pressure durability evaluation, long-term storage evaluation, and electrode tab bonding evaluation) are also shown in the table.

[0462] Since the laminated polyester film of Comparative Example 1 had significantly inferior mechanical properties, the pressure durability evaluation was significantly lower than that of Example 12. Furthermore, since the polyester film of Comparative Example 1 had poor volume resistivity, the secondary battery had significantly inferior electrode tab bonding performance compared to Example 12.

[0463] (Comparative Example 4)

[0464] Using the metal-layered polyester film obtained in Comparative Example 2 as a current collector, a stacked secondary battery was prepared by stacking multiple current collectors according to the "D. Evaluation of Stacked Secondary Batteries" section. The structure of the stacked secondary battery is shown in the table, and the evaluation results of the resulting stacked secondary battery (pressure durability evaluation, long-term storage evaluation, and electrode tab bonding evaluation) are shown in the table.

[0465] Since the laminated polyester film of Comparative Example 2 had significantly inferior mechanical properties, the pressure durability evaluation was significantly lower than that of Example 12. In addition, the secondary battery was significantly inferior to that of Example 12 in the long-term storage evaluation due to a large amount of acetylene black leakage into the electrolyte.

[0466] (Comparative Example 5)

[0467] A laminated secondary battery was prepared by laminating multiple current collectors using 10 μm thick aluminum foil as a positive electrode current collector and 10 μm thick copper foil as a negative electrode current collector according to the above-mentioned "D. Evaluation of laminated secondary batteries".

[0468] Here, the aluminum foil had an elongation at break of 2% and a strength at break of 110 MPa, as measured in "B. Mechanical Property Evaluation of Laminated Polyester Film or Monopolar Current Collector with Surface Metal Layer" described above. The copper foil had an elongation at break of 10% and a strength at break of 300 MPa.

[0469] The structure of the laminated secondary battery is shown in the table, and the evaluations of the obtained laminated secondary battery (pressure durability evaluation, long-term storage evaluation, and electrode tab bonding evaluation) are shown in the table.

[0470] Compared with Example 12, the secondary battery was significantly inferior in the pressure durability evaluation.

[0471]

[0472]

[0473]

[0474]

[0475] Table 5

[0476]

[0477]

[0478] Table 7

[0479]

[0480] Table 8

[0481]

Claims

1. A secondary battery comprising a current collector having a layer composed of a metal and / or a metal-based compound having a thickness of 0.2 μm or more and 3.0 μm or less on both surfaces of a polyester film satisfying the following conditions (1) and (2), wherein the layer is hereinafter referred to as an M layer. (1) The polyester film has a thickness of 1 μm or more and 30 μm or less; (2) The polyester film has a resin layer containing 0.1% by mass or more and less than 5.0% by mass of conductive particles. 2 . The secondary battery according to claim 1 , wherein 100 mass % of the conductive particles contain 80 mass % or more and 100 mass % or less of at least one selected from furnace black, Ketjen black, carbon nanotubes, and acetylene black in total. 3 . The secondary battery according to claim 1 , further comprising a current collector in which an active material layer is directly laminated on a surface of the M layer. 4 . The secondary battery according to claim 1 , further comprising the current collector in which the M layer contains aluminum or copper. 5 . The secondary battery according to claim 1 , comprising the current collector having a thickness of 4 μm to 7 μm.

6. The secondary battery according to claim 1 or 2 has a structure in which the current collector is stacked in at least 45 layers and not more than 80 layers via a stacked structure including a positive electrode active material layer and a negative electrode active material layer, wherein the stacked structure is hereinafter referred to as an active agent layer.

7. The secondary battery according to claim 1 or 2 has a structure in which the current collectors are stacked in at least 45 layers and less than 80 layers, the stacked current collectors having a joint portion joined to an electrode lead, the joint portion having a concave shape with a depth of 0.1 mm to 1.0 mm at intervals of 0.3 mm to 0.8 mm. 8 . The secondary battery according to claim 6 , wherein the thickness of the current collector is not less than 0.01 times and not more than 0.04 times the thickness of the active agent layer.

9. The secondary battery according to claim 1 or 2, wherein when the thickness of the end portion of the current collector is set to D1 μm and the thickness of the current collector at a position 20 mm inside the end portion is set to D2 μm, D1 / D2 is greater than or equal to 0.9 and less than or equal to 1.

2. 10 . The secondary battery according to claim 1 , comprising a current collector in which the M layer contains aluminum and a positive electrode active material layer having a thickness of 90 μm to 120 μm is stacked on a surface of the M layer containing aluminum. 11 . The secondary battery according to claim 1 , comprising a current collector in which the M layer contains copper and a negative electrode active material layer having a thickness of 80 μm to 170 μm is stacked on a surface of the M layer containing copper. 12 . The secondary battery according to claim 1 , comprising an electrolyte solution containing furnace black and Ketjen black in a total amount of 0.001 ppm by mass or more and 100 ppm by mass or less.

13. A polyester film satisfying the following conditions (3) and (4), for directly depositing a layer composed of a metal and / or a metal-based compound having a thickness of 0.2 μm to 3.0 μm, hereinafter referred to as an M layer, (3) The volume resistivity at 23°C and 65% RH is 1.0×10 8 Ω·cm or more and 9.0×10 16 Ω·cm or less; (4) The polyester film has a thickness of 1 μm or more and 30 μm or less. The polyester film according to claim 13 , wherein the M layer comprises aluminum or copper. The polyester film according to claim 13 or 14, comprising a P1 layer, wherein the P1 layer is a resin layer containing 0.1% by mass or more and less than 5.0% by mass of a carbon material. The polyester film according to claim 15 , wherein the carbon material contains 80% by mass or more and 100% by mass or less of at least one selected from furnace black, Ketjen black, carbon nanotubes, and acetylene black in total, based on 100% by mass of the carbon material.

17. The polyester film according to claim 15, further comprising a polyester resin layer (P2 layer) having a lower carbon material content than that of the P1 layer on at least one side of the P1 layer, wherein the carbon material content in the P1 layer is M P1 , the content of the carbon material in the P2 layer is set to M P2 When M P1 -M P2 ≥0.1, the M P1 and M P2 The unit is mass %. The polyester film according to claim 13 or 14, wherein the relative dielectric constant determined using a molecular orientation meter is 3.5 to 7.

0.

19. A laminated polyester film comprising a layer composed of a metal and / or a metal-based compound having a thickness of 0.2 μm to 3.0 μm, hereinafter referred to as an M layer, directly laminated on both surfaces of a polyester film satisfying the following conditions (5) and (6). (5) The volume resistivity at 23°C and 65% RH is 1.0×10 8 Ω·cm or more and 9.0×10 16 Ω·cm or less; (6) The thickness of the polyester film is 1 μm or more and 30 μm or less. 20 . The laminated polyester film according to claim 19 , wherein the elongation at break in at least one of the longitudinal direction and the width direction within the film plane is 50% or more and 120% or less. 21 . A resin current collector comprising the polyester film according to claim 13 or the laminated polyester film according to claim 19 .

22. A monopolar current collector comprising a layer of metal and / or metal-based compound having a thickness of 0.2 μm to 3.0 μm on both surfaces of a polyester film satisfying the following conditions (7) and (8), wherein the layer is hereinafter referred to as an M layer. (7) The thickness of the polyester film is 1 μm or more and 30 μm or less; (8) A P1′ layer is provided, wherein the P1′ layer is a resin layer containing 0.1% by mass or more and less than 5.0% by mass of conductive particles. 23 . The monopolar current collector according to claim 22 , wherein the conductive particles contain 80% to 100% by mass of at least one selected from Ketjen black, carbon nanotubes, and acetylene black in a total amount.

24. The monopolar current collector according to claim 22 or 23, having a volume resistivity of 1.0×10 8 Ω·cm or more and 9.0×10 16 Polyester film with a thickness of Ω·cm or less. 25 . The monopolar current collector according to claim 22 , wherein the M layer comprises aluminum or copper. 26 . The monopolar current collector according to claim 22 , wherein the elongation at break in at least one of the longitudinal direction and the width direction within the film surface is 50% or more and 120% or less. 27 . The monopolar current collector according to claim 22 , wherein the breaking strength in at least one of the longitudinal direction and the width direction within the film surface is 180 MPa or more and 300 MPa or less. 28 . The monopolar current collector according to claim 22 , comprising an M layer in contact with the polyester film, wherein an arithmetic mean height Sa of the M layer is not less than 15 nm and not more than 60 nm.

29. The monopolar current collector according to claim 22, wherein the content of silicon in the polyester film is 0 mass ppm or more and 10 mass ppm or less when the monopolar current collector is analyzed using inductively coupled plasma atomic emission spectrometry (ICP-AES) under the following conditions: Analysis conditions: Equipment: ICP emission spectrometer PS3520VDDII manufactured by Hitachi High-Tech Science Corporation Sample preparation: The polyester film was weighed in a beaker and decomposed under pressure using sulfuric acid, then nitric acid, followed by heating and ashing. The ash was dissolved in a mixed flux of sodium carbonate and boric acid to a constant volume of 10 mL. The solution, diluted with dilute nitric acid, was then analyzed for silicon content using inductively coupled plasma atomic emission spectrometry (ICP-AES). This was used as the silicon content in the polyester film. Measurement conditions: Measurement wavelength: 251.6nm High frequency output: 1.2kW Plasma gas flow rate: 16L / min Auxiliary gas flow rate: 0.5L / min Carrier gas flow rate: 0.9L / min Photometric height: 12mm. 30 . The monopolar current collector according to claim 22 , further comprising an active material layer on a surface of the M layer. 31 . An electric storage device comprising the monopolar current collector according to claim 30 .

32. The energy storage device according to claim 31, having a structure in which at least two layers of current collectors are stacked with an active agent layer interposed therebetween.

33. An electric vehicle equipped with the secondary battery according to claim 1.

34. An electric flying object equipped with the secondary battery according to claim 1.

35. A method for producing a laminated polyester film, comprising the steps of directly vapor-depositing a layer of metal and / or metal-based compound having a thickness of 0.2 μm or more on a polyester film satisfying the following conditions (9) and (10), wherein the layer is hereinafter referred to as the M layer, and (1) the volume resistivity at 23°C and 65% RH is 1.0×10 8 Ω·cm or more and 9.0×10 16 Ω·cm or less; (2) The polyester film has a thickness of 1 μm or more and 30 μm or less.

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