Current collector, polyester film, current collector for negative electrode, power storage element, secondary battery, electric vehicle, and electric flying object

Abstract

The present invention addresses the problem of providing a current collector which, particularly when used in negative electrode applications, can suppress the generation of voids due to resin decomposition gas or the like caused by charging and discharging of a secondary battery or the like, and also provides a polyester film. The present invention addresses the problem of providing a current collector having a layer (M layer) containing a metal and / or a metal-based compound and a polyester film and having a maximum reduction current peak intensity of 0.000mA / cm2 or more and 0.050 mA / cm2 or less in CV measurement (0.01 V to 2.0 V, 10 cycles), in which the occurrence of voids due to decomposition gas or the like is reduced when the current collector is used as a current collector for a negative electrode and charge and discharge is performed, and a means for solving the problem is a current collector having a polyester film and a layer (M layer) containing a metal and / or a metal-based compound and having a maximum reduction current peak intensity of 0.000mA / cm2 or more and 0.050 mA / cm2 or less.

Description

Technical Field

[0001] The present invention relates to a current collector, a polyester film, a current collector for a negative electrode, a power storage element, a secondary battery, an electric vehicle, and an electric flying vehicle. Background Art

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

[0003] In secondary batteries such as lithium-ion batteries, metal foils (metal current collector foils) have been used as current collectors, but in recent years, resin film current collectors containing resin films have been proposed instead of metal foils. The resin film current collector is lighter in weight than the metal current collector foil, and an increase in the output per unit weight of the battery can be expected.

[0004] For example, in Patent Documents 1 to 3, a dispersant for a resin current collector, a material for a resin current collector containing a resin and a conductive filler, and a resin current collector having the material for a resin current collector are disclosed.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: International Publication No. 2015 / 005116

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2020-102386

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 2020-68085 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] However, although resin current collectors using polyolefin films are disclosed in Patent Documents 1 to 3, with reference thereto, a resin current collector using a polyester film was fabricated, and as a result, it was found that voids were generated due to decomposition gases of the resin or the like when used as a current collector of a secondary battery, and there were problems with battery durability.

[0012] An object of the present invention is to provide a current collector that can suppress the generation of voids caused by decomposition gases of the resin or the like due to charge and discharge of a secondary battery, etc., especially when used for a negative electrode application, and to provide a polyester film that generates few voids due to decomposition gases or the like, especially when used as a current collector for a negative electrode and subjected to charge and discharge.

[0013] Technical means for solving the problem

[0014] To solve the above problems, a preferred embodiment of the present invention adopts the following structure.

[0015] [I] A current collector having a layer (M layer) containing a metal and / or a metal-based compound and a polyester film, and the maximum reduction current peak intensity in cyclic voltammetry (CV) measurement (0.01 V to 2.0 V, 10 cycles) is 0.000 mA / cm 2 or more and 0.050 mA / cm 2 or less.

[0016] <CV measurement method>

[0017] CV measurement is performed using the following methods (i) to (iii), and the maximum reduction current peak intensity is obtained.

[0018] (i) Fabrication of 2032 coin cell

[0019] A sample having a copper metal layer provided on the surface of the current collector by sputtering is punched into a circle with a diameter of 16 mm. On the surface of the copper metal layer of the punched sample, a polyethylene separator with a diameter of 18 mm, a lithium metal foil with a diameter of 16.1 mm, and two stainless steel plates (SUS304) are sequentially laminated, and the following electrolyte is sealed to fabricate a 2032 coin cell. At this time, the surface of the current collector on the side opposite to the surface where the polyethylene separator is laminated is brought into contact with the outer package of the 2032 coin cell.

[0020] (Electrolyte composition)

[0021] · Electrolyte: 1 mol / L lithium hexafluorophosphate (LiPF6)

[0022] · Solvent: A 1:1 (volume %) mixture of ethylene carbonate (EC) and diethylenecarbonate (DEC)

[0023] · Blending environment: Conducted inside an argon circulation glove box with a dew point below -70°C and an oxygen concentration below 10 volume ppm.

[0024] (ii) CV measurement

[0025] Using the type 2032 coin cell obtained in item (i) above, cyclic voltammetry measurement using a VSP manufactured by Biologic is conducted under the following conditions. The current value (mA) observed through a potential sweep operation with the oxidation-reduction potential of lithium metal set as the reference 0 V is divided by the sample area (2.01 cm 2 ), thereby obtaining the current value per unit area (mA / cm 2 ).

[0026] (Measurement conditions)

[0027] · Test temperature: 25°C

[0028] · Potential sweep range: 0.01 V - 2.0 V (v.s. Li + / Li)

[0029] · Scanning speed: 1 mV / s

[0030] · Number of cycles: 10 cycles

[0031] (iii) Maximum reduction current peak intensity

[0032] Regarding the current value per unit area (mA / cm 2 ) obtained in item (ii) above, the current value with the largest absolute value is taken as the maximum reduction current peak intensity per unit area (mA / cm 2 ) for calculation.

[0033] [II] The current collector according to [I] has at least one layer mainly composed of a polyester resin (resin α) containing a dicarboxylic acid component and a diol component with 3 or more and 16 or less carbon atoms.

[0034] [III] The current collector according to [I] or [II] has M layers on both surfaces of the polyester film.

[0035] [IV] The current collector according to any one of [I] to [III] has M layers on both surfaces of the polyester film, and at least one of the M layers on the surface is a layer containing copper element.

[0036] [V] The current collector according to any one of [II] to [IV], wherein M layers are provided on both surfaces of the polyester film, and at least one of the layers on the M layers on the surfaces is a layer containing a copper element, and the layer containing a copper element is in contact with the layer containing the resin α as the main component.

[0037] [VI] The current collector according to [I], having at least one layer containing a polyester resin (resin β) containing a diol component and a dicarboxylic acid component having 9 or more and 16 or less carbon atoms as the main component.

[0038] [VII] The current collector according to [VI], wherein M layers are provided on both surfaces of the polyester film, and at least one of the layers on the M layers on the surfaces is a layer containing a copper element, and the layer containing a copper element is in contact with the layer containing the resin β as the main component.

[0039] [VIII] A current collector satisfying the following (1) and (2).

[0040] (1) The layer on at least one surface of the polyester film is a layer (P1 layer) containing a polyester resin (resin α) containing a dicarboxylic acid component and a diol component having 3 or more and 16 or less carbon atoms as the main component, or a layer containing a polyester resin (resin β) containing a diol component and a dicarboxylic acid component having 9 or more and 16 or less carbon atoms as the main component.

[0041] (2) Layers (M layers) containing a metal and / or a metal-based compound are provided on both surfaces of the polyester film.

[0042] [IX] The current collector according to [VIII], wherein at least one of the M layers is in contact with the P1 layer, and the M layer in contact with the P1 layer is a layer containing a copper element.

[0043] [X] The current collector according to any one of [I] to [VIII], wherein the thickness of the M layer is 0.1 μm or more and 5.0 μm or less.

[0044] [XI] The current collector according to any one of [VIII] to [X], wherein the main component of the polyester film is any one of polycyclohexylene dimethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate.

[0045] [XII] The current collector according to [XI], wherein the main component of the polyester film is polycyclohexylene dimethylene terephthalate or polybutylene terephthalate.

[0046] [XIII]The current collector according to [I] or [VIII], wherein the polyester film has a layer (P1 layer) mainly composed of a polyester resin (resin α) containing a dicarboxylic acid component and a diol component having 3 or more and 16 or less carbon atoms, or a polyester resin (resin β) containing a diol component and a dicarboxylic acid component having 9 or more and 16 or less carbon atoms, and has a resin layer (P2 layer) that does not have resin α or resin β as the main component.

[0047] [XIV]The current collector according to any one of [I] to [XIII], wherein M layers are provided on the surfaces on both sides of the polyester film, and the adhesion force between the surface of the polyester film and the M layer is 2 N / 15 mm or more and 5 N / 15 mm or less on both sides.

[0048] [XV]The current collector according to any one of [I] to [XIV], wherein the breaking strength in at least one of the long side direction and the width direction in the plane of the film is 150 MPa or more and 400 MPa or less.

[0049] [XVI]The current collector according to any one of [I] to [XV], wherein the elongation at break in at least one of the long side direction and the width direction in the plane of the film is 35% or more and 150% or less.

[0050] [XVII]The current collector according to any one of [I] to [XVI], wherein when the polyester film is analyzed under the following conditions using inductively coupled plasma optical emission spectrometry (Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) method), the silicon element content in the polyester film is 0 mass ppm or more and 10 mass ppm or less.

[0051] <Analysis conditions>

[0052] Apparatus: ICP optical emission analysis (manufactured by Hitachi High-Tech Science Corporation) PS3520VDDII

[0053] Preparation of sample: Weigh the current collector in a beaker, decompose it under pressure with sulfuric acid and then with nitric acid, and then heat and ashing. Dissolve the ash with a mixed flux of sodium carbonate and boric acid, dissolve it by heating with dilute nitric acid, and make the volume constant at 10 mL. Thereafter, the amount of silicon element in the solution diluted with dilute nitric acid is measured by inductively coupled plasma optical emission spectrometry, and used as the silicon element content in the polyester film.

[0054] (Measurement conditions)

[0055] Measurement wavelength: 251.6 nm

[0056] High-frequency output: 1.2 kW

[0057] Plasma gas flow rate: 16 L / min

[0058] Auxiliary gas flow rate: 0.5 L / min

[0059] Carrier gas flow rate: 0.9 L / min

[0060] Optical measurement height: 12 mm

[0061] [XVIII]

[0062] A polyester film, the maximum reduction current peak intensity in CV measurement (0.01 V to 2.0 V, 10 cycles) is 0.000 mA / cm 2 or more and 0.050 mA / cm 2 or less.

[0063] <CV measurement method>

[0064] Perform CV measurement using the following methods (i) to (iii) to obtain the maximum reduction current peak intensity.

[0065] (i) Fabrication of 2032 coin cell

[0066] Use sputtering method to set copper metal layers on the surfaces of both sides of the polyester film, and then punch it into a circular sample with a diameter of 16 mm. On the surface of the copper metal layer of the punched sample, stack a polyethylene separator with a diameter of 18 mm, a lithium metal foil with a diameter of 16.1 mm, and two stainless steel plates (made of SUS304) in sequence, and seal the following electrolyte to fabricate a 2032 coin cell. At this time, make the surface of the copper metal layer on the side opposite to the surface where the polyethylene separator is stacked contact with the removed outer package of the 2032 coin cell.

[0067] (Electrolyte composition)

[0068] · Electrolyte: 1 mol / L lithium hexafluorophosphate (LiPF6)

[0069] · Solvent: 1:1 (volume%) mixture of ethylene carbonate (EC) and diethyl carbonate (DEC)

[0070] · Blending environment: Conduct in an argon-circulating glove box with a dew point of -70°C or lower and an oxygen concentration of 10 volume ppm or lower.

[0071] (ii) CV measurement

[0072] Using the type 2032 coin cell obtained in item (i) above, cyclic voltammetry measurements were performed using a VSP manufactured by Biologic under the following conditions. The current value (mA) observed by the potential sweep operation with the redox potential of lithium metal set as the reference 0 V was divided by the sample area (2.01 cm 2 ), and the current value per unit area (mA / cm 2 ) was thus obtained.

[0073] (Measurement conditions)

[0074] · Test temperature: 25 °C

[0075] · Potential sweep range: 0.01 V - 2.0 V (v.s. Li + / Li)

[0076] · Scan rate: 1 mV / s

[0077] · Number of cycles: 10 cycles

[0078] (iii) Maximum reduction current peak intensity

[0079] The current value per unit area (mA / cm 2 ) obtained in item (ii) above, the current value with the largest absolute value among them was taken as the maximum reduction current peak intensity (mA / cm 2 ) to obtain.

[0080] [XIX]

[0081] The polyester film according to [XVIII] has at least one layer mainly composed of a polyester resin (resin α) containing a dicarboxylic acid component and a diol component having 3 or more and 16 or less carbon atoms.

[0082] [XX] The polyester film according to [XVIII] has at least one layer mainly composed of a polyester resin (resin β) containing a diol component and a dicarboxylic acid component having 9 or more and 16 or less carbon atoms.

[0083] [XXI] The polyester film according to [XVIII] or [XIX], wherein the thickness of the polyester film is 1 μm or more and 30 μm or less.

[0084] [XXII] A current collector for a negative electrode, which is the current collector according to any one of [I] to [XVII].

[0085] [XXIII] An electrical storage element, comprising the current collector according to any one of [I] to [XVII].

[0086] [XXIV]A power storage element having a negative electrode active material layer on at least one surface of the current collector for the negative electrode described in [XXII].

[0087] [XXV]A power storage element having a laminate in which the current collector for the negative electrode, an electrolyte, the current collector for the positive electrode, and an electrolyte described in [XXII] are arranged in sequence, and including a structure in which at least two or more of the laminates are laminated.

[0088] [XXVI]A secondary battery including the power storage element according to any one of [XXIII] to [XXV].

[0089] [XXVII]An electric vehicle equipped with the secondary battery according to [XXVI].

[0090] [XXVIII]An electric flying object equipped with the secondary battery according to [XXVI].

[0091] Effects of the Invention

[0092] According to the present invention, a current collector can be provided which, particularly when used for a negative electrode, can suppress the generation of voids caused by decomposition gases of the resin or the like due to charge and discharge of a secondary battery or the like, and a polyester film can be provided which, particularly when used as a current collector for a negative electrode and charged and discharged, generates few voids due to decomposition gases or the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Figure 1 is a diagram illustrating a curve obtained by plotting the current value with respect to the applied potential by CV measurement and the maximum reduction current peak intensity read therefrom. DETAILED DESCRIPTION

[0094] Hereinafter, the present invention will be described in detail.

[0095] A preferred embodiment of the present invention is a current collector having a layer (M layer) containing a metal and / or a metal-based compound and a polyester film, and the maximum reduction current peak intensity in the CV measurement (0.01 V to 2.0 V, 10 cycles) described later is 0.000 mA / cm 2 or more and 0.050 mA / cm 2 or less. By adopting this embodiment, a current collector that can suppress decomposition gases of the resin or the like due to charge and discharge of a secondary battery or the like can be produced.

[0096] ​The inventors, with reference to Patent Documents 1 to 3, made a resin current collector using a polyester film from the perspective of heat resistance and the like. As a result, it was found that there were problems with battery durability due to decomposition gases of the resin when used as a current collector for secondary batteries. As the main reasons, hydrolysis of the polyester film, release of dissolved gases in the polyester film, reaction between the catalyst in the polyester film and the electrolyte, etc. were also considered. However, the inventors conducted detailed research and found that the redox reaction of the polyester film caused by voltage application was a major factor in gas generation, thus achieving the present invention.

[0097] In addition, in the present invention, the CV (Cyclic Voltammetry) measurement is carried out using the following evaluation method.

[0098] <CV Measurement Method>

[0099] The CV measurement is carried out using the following methods (i) to (iii) to obtain the maximum reduction current peak intensity.

[0100] (i) Fabrication of 2032 coin cell

[0101] A sample with a copper metal layer provided on the surface of the current collector by sputtering is punched into a circle with a diameter of 16 mm. On the surface of the copper metal layer of the punched sample, a polyethylene separator with a diameter of 18 mm, a lithium metal foil with a diameter of 16.1 mm, and two stainless steel plates (made of SUS304) are sequentially laminated, and the following electrolyte is sealed to fabricate a 2032 coin cell. At this time, the surface of the current collector on the side opposite to the surface where the polyethylene separator is laminated is brought into contact with the outer package of the 2032 coin cell. In addition, in the present invention, the polyethylene separator used in the CV measurement is a polyethylene separator with a thickness of 4 μm or more and 20 μm or less and an air permeability of 500 seconds or less.

[0102] (Electrolyte composition)

[0103] · Electrolyte: 1 mol / L lithium hexafluorophosphate (LiPF6)

[0104] · Solvent: A 1:1 (volume %) mixture of ethylene carbonate (EC) and diethyl carbonate (DEC)

[0105] · Blending environment: In an argon circulation type glove box with a dew point of -70°C or lower and an oxygen concentration of 10 volume ppm or lower.

[0106] (ii) CV measurement

[0107] Using the type 2032 coin cell obtained in item (i) above, cyclic voltammetry measurements were performed using a VSP manufactured by Biologic under the following conditions. The current value (mA) observed by a potential sweep operation with the redox potential of lithium metal set as 0 V as a reference was divided by the sample area (2.01 cm 2 ), and the current value per unit area (mA / cm 2 ) was thus obtained.

[0108] (Measurement conditions)

[0109] · Test temperature: 25 °C

[0110] · Potential sweep range: 0.01 V - 2.0 V (v.s. Li + / Li)

[0111] · Sweep rate: 1 mV / s

[0112] · Number of cycles: 10 cycles

[0113] (iii) Maximum reduction current peak intensity

[0114] The current value per unit area (mA / cm 2 ) obtained in item (ii) above, in which the absolute value is the largest, was taken as the maximum reduction current peak intensity per unit area (mA / cm 2 ) for calculation.

[0115] In addition, in the case where the current collector is a current collector having M layers laminated on the surface layers on both sides of the polyester film, a copper metal layer was provided on any one surface of the current collector by sputtering, and then punched into a circle with a diameter of 16 mm. The copper metal layer, a polyethylene separator with a diameter of 18 mm, a lithium metal foil with a diameter of 16.1 mm, and two stainless steel plates (made of SUS304) were sequentially arranged, and the electrolyte was sealed to fabricate a type 2032 coin cell. In the case where the current collector is a current collector having M layers laminated on one surface of the polyester film, a copper metal layer was provided on the surface side without the M layer by sputtering, and then the evaluation was carried out in the same manner.

[0116] The above potential sweep operation was performed to evaluate the maximum reduction current peak intensity. In the case where the current collector has M layers on the surfaces on both sides of the polyester film, the coin cell was fabricated and the potential sweep operation was performed on both sides respectively, the reduction current peak was evaluated, and the maximum value of these was used.

[0117] In the above CV measurement, the current value observed during the potential sweep with the redox potential of lithium metal set as 0 V as a reference, with the area of the sample (2.01 cm 2)The standardized maximum reduction current peak intensity is 0.050 mA / cm 2 The following indicates that no current due to oxidation-reduction reaction was observed at the interface between the polyester film and the M layer. When the observed current value shows a positive value, it indicates that an oxidation reaction occurred at the interface between the polyester film and the M layer. When the current value shows a negative value, it indicates that a reduction reaction occurred at the interface between the polyester film and the M layer.

[0118] In particular, when the minimum value of the observed current value is -0.050 mA / cm 2 or more and less than 0.000 mA / cm 2 it shows that even when the M layer laminated on the polyester film undergoes an oxidation reaction due to the potential sweep operation and functions as the negative electrode in the coin cell, it is not easy to undergo reductive decomposition at the interface between the M layer and the polyester film. A more preferable range of the maximum reduction current peak intensity is 0.000 mA / cm 2 or more and 0.010 mA / cm 2 or less. As the current value, it is preferably that the minimum value is -0.010 mA / cm 2 or more and less than 0.000 mA / cm 2 . The most preferable range of the maximum reduction current peak intensity is 0.000 mA / cm 2 or more and 0.006 mA / cm 2 or less. As the current value, it is preferably that the minimum value is -0.006 mA / cm 2 or more and less than 0.000 mA / cm 2 . In addition, although the current collector has two surfaces, as long as the maximum reduction current peak intensity in the CV measurement is 0.000 mA / cm 2 or more and 0.050 mA / cm 2 or less in at least one surface. It is more preferably that the maximum reduction current peak intensity in the CV measurement is 0.000 mA / cm 2 or more and 0.050 mA / cm 2 or less in both surfaces.

[0119] Generally, it is known that an ester bond connecting the molecular chains of polyester reacts with water molecules or hydrogen ions, and a reaction in which the bond is cleaved and decomposed, so-called hydrolysis reaction, occurs.

[0120] Therefore, although the reaction path of the polyester film during voltage application is not clear, it is considered that water molecules remaining in trace amounts in the polyester film or hydrogen ions ionized from hydrogen atoms present at the ends of polyester molecular chains, i.e., carboxyl groups, undergo an ester bond cleavage decomposition reaction in the same way as hydrolysis. Therefore, in the polyester film, suppressing the reduction reaction is important for suppressing the generation of decomposition gases.

[0121] The polyester film described in the present invention refers to a film having a polyester resin as the main component. Here, the main component described in the present invention refers to a component contained in an amount exceeding 50% by mass in all 100% by mass of the components of the film. In addition, regarding each of the following preferred forms, compared with the form having a specific resin as the main component, a form containing 85% by mass or more of the specific resin is more preferred, and a form containing 93% by mass or more of the specific resin is further preferred.

[0122] The polyester resin described in the present invention is a resin obtained by polycondensing a dicarboxylic acid component and a diol component. In addition, in this specification, the so-called component refers to the smallest unit that can be obtained by hydrolyzing the polyester. In addition, in the present application, a polyester resin obtained by polycondensing a dicarboxylic acid component and a diol component is sometimes referred to as a polyester resin containing a dicarboxylic acid component and a diol component.

[0123] A preferred form of the polyester film of the present invention is that the maximum reduction current peak intensity in the CV measurement (0.01 V to 2.0 V, 10 cycles) is 0.050 mA / cm 2 The following polyester film. When performing CV measurement on the polyester film, a copper metal layer is provided on the surfaces of both sides of the polyester film by sputtering, and then it is punched into a circular sample with a diameter of 16 mm, and then the measurement is performed by the same method as described above.

[0124] In the present invention, as a method for making the maximum reduction current peak intensity during the CV measurement (0.01 V to 2.0 V, 10 cycles) be 0.050 mA / cm 2 The following methods can be preferably cited, for example: the resin layer in contact with the copper metal layer during the CV measurement is a layer (P1 layer) having a polyester resin containing a dicarboxylic acid component and a diol component having 3 or more and 16 or less carbon atoms (resin α) as the main component, or a polyester resin containing a diol component and a dicarboxylic acid component having 9 or more and 16 or less carbon atoms (resin β) as the main component, and in 100 mol% of the diol component in the P1 layer, 85 mol% or more of the diol component having 3 or more and 16 or less carbon atoms is contained, or in 100 mol% of the dicarboxylic acid component in the P1 layer, 85 mol% or more of the dicarboxylic acid component having 9 or more and 16 or less carbon atoms is contained, the inherent viscosity (Inherent Viscosity, IV) of the P1 layer is 0.60 dl / g or more, and the water content rate of the P1 layer is set to 3000 mass ppm or less. In addition, a more preferred method is that the P1 layer has resin α as the main component, and in 100 mol% of the diol component in the P1 layer, 85 mol% or more of the diol component having 3 or more and 16 or less carbon atoms is contained.

[0125] In the present invention, the polyester film preferably has at least one layer containing a polyester resin (resin α) mainly composed of a dicarboxylic acid component and a diol component having 3 or more and 16 or less carbon atoms, or has at least one layer containing a polyester resin (resin β) mainly composed of a diol component and a dicarboxylic acid component having 9 or more and 16 or less carbon atoms. Further, the polyester film in the present invention more preferably has at least one layer containing a polyester resin (resin α) mainly composed of a dicarboxylic acid component and a diol component having 3 or more and 16 or less carbon atoms.

[0126] By using a diol component having 3 or more and 16 or less carbon atoms or a dicarboxylic acid component having 9 or more and 16 or less carbon atoms, the molecular mobility around the ester bond is reduced, thereby suppressing the approach of water molecules or hydrogen ions to the ester bond and reacting. Therefore, the reduction reaction of the polyester film during voltage application can be suppressed, and the generation of decomposition gas can be suppressed.

[0127] Examples of the diol constituent components constituting resin α include: aliphatic diols such as 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, etc., alicyclic diols such as 1,4-cyclohexanedimethanol and spiroglycol, aromatic diols such as bisphenol A, and substances formed by connecting a plurality of the above diols.

[0128] Aliphatic diols are preferred because the molecular interaction between the diol components is enhanced and a high-density and large molecular structure similar to the crystalline structure is formed around the ester bond, and more preferably linear aliphatic diols such as 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol.

[0129] In addition, when using alicyclic diols, the approach of water molecules or hydrogen ions can be suppressed because of the presence of low-mobility and sterically large cyclic molecules around the ester bond, so it is preferred.

[0130] Examples of the dicarboxylic acid constituent components constituting resin α 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'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, or their ester derivatives.

[0131] Examples of the resin α include polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polycyclohexylene dimethylene terephthalate (PCT), etc. Preferably, the main component of the polyester film is any one of polycyclohexylene dimethylene terephthalate and polybutylene terephthalate, and more preferably, the main component of the polyester film is polycyclohexylene dimethylene terephthalate. For these polyester resins, preferably, within the range not affecting the effects of the present application, for the purpose of improving the extensibility of the polyester film, isophthalic acid or naphthalene dicarboxylic acid is copolymerized with a part of the dicarboxylic acid component of the polyester. The reason is that by introducing a copolymer component with a different structure, it is possible to suppress the excessive progress of the orientation crystallization of the resin during the stretching process and prevent breakage during the film-forming process. The addition amount of the copolymer component as the dicarboxylic acid component is preferably 1.5 mol% or more and 15 mol% or less. By setting it to 15 mol% or less, it is possible to suppress the case where the resin does not orient and the mechanical properties deteriorate.

[0132] By setting the carbon number of the glycol component to 16 or less, the polymerization reaction can be carried out without the glycol components aggregating with each other in the polyester polymerization process, and a polyester resin with an appropriate molecular weight for the film can be produced. A more preferable range for the carbon number of the glycol component is 12 or less, and further preferably 9 or less.

[0133] Examples of the glycol constituent component constituting the resin β include aliphatic glycols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, etc., alicyclic glycols such as 1,4-cyclohexanedimethanol and spiroglycerol, and substances formed by connecting multiple of the above-mentioned glycols.

[0134] Examples of the dicarboxylic acid constituent component constituting the resin β include aromatic dicarboxylic acids such as 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, and 4,4'-diphenyletherdicarboxylic acid.

[0135] By using a dicarboxylic acid component having a carbon number of 9 or more and 16 or less, the molecular mobility around the ester bond that can be the decomposition point of the polyester resin can be reduced. Thereby, it is possible to prevent molecules such as decomposition ester bonds of the electrolyte, electrolyte, and additive existing in the vicinity from approaching the ester bond of the polyester resin.

[0136] Particularly in the case of using an aromatic dicarboxylic acid component having 9 or more and 16 or less carbon atoms or an aliphatic dicarboxylic acid component having 9 or more and 16 or less carbon atoms, the dicarboxylic acid components self-aggregate with each other, whereby the molecular chains of the polyester resin are densely packed, and intrusion of molecules such as those that decompose ester bonds into the intermolecular spaces of the polyester resin molecular chains can be inhibited.

[0137] By setting the carbon number of the dicarboxylic acid component to 16 or less, a polymerization reaction can be carried out without agglomeration of the dicarboxylic acid components in the polyester polymerization step, and a polyester resin having an appropriate molecular weight for the film can be produced. The carbon number of the dicarboxylic acid component is more preferably 14 or less.

[0138] Examples of resin β include polyethylene 2,6-naphthalate (hereinafter referred to as PEN). For these polyester resins, isophthalic acid or naphthalenedicarboxylic acid can be copolymerized with a part of the dicarboxylic acid component of the polyester, and polyethylene glycol can be copolymerized with a part of the glycol component, within the range that does not affect the effects of the present application.

[0139] In addition, the polyester resin containing a dicarboxylic acid component having 9 or more and 16 or less carbon atoms and a glycol component having 3 or more and 16 or less carbon atoms, as exemplified above, can also be suitably used.

[0140] The layer on at least one side surface of the polyester film in the present invention is preferably a layer (P1 layer) containing resin α as the main component or resin β as the main component. By adopting this form, reduction reaction of the polyester film during voltage application, which is likely to occur especially on the surface of the polyester film, can be inhibited, and generation of decomposition gas can be further inhibited. In addition, it is more preferably that M layers are provided on both side surfaces of the polyester film in the present invention. By adopting this form, it can be suitably used as a current collector for a bipolar battery. Furthermore, it is further preferred that at least one side M layer is in contact with the P1 layer, and the M layer in contact with the P1 layer is a layer containing a copper element. By adopting this form, while the electrical properties of copper are exerted, the situation where copper promotes the reduction reaction of the polyester film during voltage application can be inhibited by the P1 layer. From the same viewpoint, the P1 layer in contact with the M layer containing a copper element is particularly preferably a layer containing resin α as the main component.

[0141] In addition, when M layers are provided on both sides of the polyester film in the present invention, a structure in which layers containing resin α as the main component of the same or different types are provided on the M layers on both sides is preferred.

[0142] Regarding the same view, in the present invention, it is more preferable that the glycol component in 100 mol% of the glycol component of the polyester film contains 51 mol% or more of a glycol component having 3 or more and 16 or less carbon atoms, or the dicarboxylic acid component in 100 mol% of the dicarboxylic acid component of the polyester film contains 51 mol% or more of a dicarboxylic acid component having 9 or more and 16 or less carbon atoms. More preferably, the glycol component in 100 mol% of the glycol component of the polyester film contains 85 mol% or more of a glycol component having 3 or more and 16 or less carbon atoms, or the dicarboxylic acid component in 100 mol% of the dicarboxylic acid component of the polyester film contains 85 mol% or more of a dicarboxylic acid component having 9 or more and 16 or less carbon atoms. Among them, it is preferable that the glycol component in 100 mol% of the glycol component of the polyester film contains 51 mol% or more of 1,4-cyclohexanedimethanol component or 1,4-butanediol, more preferably contains 51 mol% or more of 1,4-cyclohexanedimethanol component, and further preferably contains 85 mol% or more of 1,4-cyclohexanedimethanol component.

[0143] In addition, regarding the same view, in at least one layer of the polyester film in the present invention, it is more preferable that the glycol component in 100 mol% of the glycol component of the layer contains 51 mol% or more of a glycol component having 3 or more and 16 or less carbon atoms, or the dicarboxylic acid component in 100 mol% of the dicarboxylic acid component of the layer contains 51 mol% or more of a dicarboxylic acid component having 9 or more and 16 or less carbon atoms. More preferably, the glycol component in 100 mol% of the glycol component of the layer contains 85 mol% or more of a glycol component having 3 or more and 16 or less carbon atoms, or the dicarboxylic acid component in 100 mol% of the dicarboxylic acid component of the layer contains 85 mol% or more of a dicarboxylic acid component having 9 or more and 16 or less carbon atoms. Among them, it is preferable that the glycol component in 100 mol% of the glycol component of the layer contains 51 mol% or more of 1,4-cyclohexanedimethanol component or 1,4-butanediol, more preferably contains 51 mol% or more of 1,4-cyclohexanedimethanol component, and further preferably contains 85 mol% or more of 1,4-cyclohexanedimethanol component. In addition, the qualitative and quantitative analysis of the components of the polyester resin is carried out by the method described below. In addition, as a more preferable form of the layer, a form the same as the preferable form of the P1 layer can be preferably adopted.

[0144] The intrinsic viscosity (IV) of the resin α is preferably 0.60 dl / g or more. Since the intrinsic viscosity (IV) of the resin α is 0.60 dl / g or more, the polyester molecular chains constituting the resin α become longer, and the number of polyester molecular chain ends per unit weight contributing to the decomposition reaction of the P1 layer in the CV measurement decreases, whereby it is easier to further suppress the decomposition reaction of the P1 layer caused by hydrogen ions or the like in the CV measurement.

[0145] A more preferred range of the intrinsic viscosity (IV) of the resin α is 0.70 dl / g or more, more preferably 0.75 dl / g or more, and most preferably 0.80 dl / g or more. The same applies to the intrinsic viscosity (IV) of the resin β.

[0146] In addition, the water content rate of the resin α is preferably 3000 mass ppm or less. By setting the water content rate of the resin α to 3000 mass ppm or less, the decomposition reaction of the polyester film caused by water molecules in the CV measurement can be suppressed. As the water content rate of the resin α, it is more preferably 2500 mass ppm or less, and still more preferably 2000 mass ppm or less. The same applies to the intrinsic viscosity (IV) of the resin β.

[0147] In the present invention, as a more preferred structure for achieving a maximum reduction current peak intensity of 0.050 mA / cm² when performing the CV measurement (0.01 V to 2.0 V, 10 cycles) 2 preferably, the P1 layer contains the resin α as a main component, and the intrinsic viscosity (IV) of the P1 layer is 0.60 dl / g or more. By setting the intrinsic viscosity (IV) of the P1 layer to 0.60 dl / g or more, the polyester molecular chains constituting the P1 layer become longer, and the number of polyester molecular chain ends per unit weight contributing to the decomposition reaction decreases, thereby more easily suppressing the decomposition reaction of the P1 layer caused by hydrogen ions or the like in the CV measurement.

[0148] A more preferred range of the intrinsic viscosity (IV) of the P1 layer is 0.70 dl / g or more, more preferably 0.75 dl / g or more, and most preferably 0.80 dl / g or more.

[0149] In addition, the water content rate of the P1 layer is preferably 3000 mass ppm or less. By setting the water content rate of the P1 layer to 3000 mass ppm or less, the decomposition reaction of the P1 layer caused by water molecules or the like in the CV measurement can be suppressed. As the water content rate of the P1 layer, it is more preferably 2500 mass ppm or less, and still more preferably 2000 mass ppm or less.

[0150] The polyester film in the present invention is more preferably biaxially stretched. The reason is that: by making a biaxially stretched film, the molecular mobility around the ester bond is reduced due to stretching orientation, and decomposition caused by the reduction reaction can be further suppressed. Furthermore, from the viewpoints of improving the mechanical strength of the film, being less likely to wrinkle, and improving the thermal dimensional stability, it is also preferred. The biaxial orientation described here refers to an orientation that shows a biaxial orientation pattern in wide-angle X-ray diffraction. A biaxially oriented polyester film can generally be obtained by stretching an unstretched thermoplastic resin film in the machine direction of the film (hereinafter, sometimes referred to as the long side direction) and the width direction, and then performing heat treatment to complete orientation crystallization. The details will be described later.

[0151] In addition, from the viewpoint of improving the stretchability of the polyester film, the P1 layer is preferably mainly composed of resin α or resin β, and may have an intermediate layer P11 layer that does not contact the M layer. As the laminated structure, it is preferably P1 layer / P11 layer / P1 layer.

[0152] For the purpose of improving the interfacial adhesion between the P1 layer and the P2 layer described later, the P1 layer preferably contains 1.5 mol% or more and 15 mol% or less of the glycol component and / or dicarboxylic acid component of the polyester resin that is the main component of the P2 layer. Specifically, when the P1 layer is mainly composed of cyclohexanedimethylene terephthalate resin and the P2 layer is mainly composed of polyethylene terephthalate resin, the P1 layer preferably contains 1.5 mol% or more and 15 mol% or less of ethylene glycol component as the glycol component. In addition, when the P1 layer is mainly composed of polyethylene naphthalate resin and the P2 layer is mainly composed of polyethylene terephthalate resin, the P1 layer preferably contains 1.5 mol% or more and 15 mol% or less of terephthalic acid component as the dicarboxylic acid component. By the P1 layer containing 1.5 mol% or more of the glycol component and / or dicarboxylic acid component of the polyester resin that is the main component of the P2 layer, the interfacial adhesion between the P1 layer and the P2 layer can be improved. In addition, by the P1 layer containing 15 mol% or less of the glycol component and / or dicarboxylic acid component of the polyester resin that is the main component of the P2 layer, the current value observed in the CV measurement can be set within a preferred range.

[0153] (P2 layer)

[0154] In the present invention, since the polyester film has a structure in which there is a resin layer P2 that is independent of the P1 layer and does not use resin α or resin β as the main component, a polyester film having mechanical properties superior to those of resin α or resin β is laminated, so the mechanical properties of the entire polyester film can be improved.

[0155] As the polyester resin constituting the P2 layer, polyethylene terephthalate (PET) etc. can be used.

[0156] As the laminated structure of the P1 layer and the P2 layer, it can be a two-layer structure of P1 layer / P2 layer, or a three-layer structure of P1 layer / P2 layer / P1 layer. However, in the case of providing the M layer containing a copper element, it is preferably configured such that the M layer containing a copper element is in contact with only the P1 layer.

[0157] When the main components of the resins of the P1 layer and the P2 layer are different, for the purpose of improving the interfacial adhesion between the P1 layer and the P2 layer, the P2 layer preferably contains 1.5 mol% or more and 15 mol% or less of the glycol component and / or the dicarboxylic acid component of the polyester resin that is the main component of the P1 layer. Specifically, when the P1 layer has polycyclohexanedimethylene terephthalate resin as the main component and the P2 layer has polyethylene terephthalate resin as the main component, the P2 layer preferably contains 1.5 mol% or more and 15 mol% or less of the cyclohexanedimethanol component as the glycol component. Additionally, when the P1 layer has polyethylene naphthalate resin as the main component and the P2 layer has polyethylene terephthalate resin as the main component, the P2 layer preferably contains 1.5 mol% or more and 15 mol% or less of the 2,6-naphthalenedicarboxylic acid component as the dicarboxylic acid component. By the P2 layer containing 1.5 mol% or more of the glycol component and / or the dicarboxylic acid component of the polyester resin that is the main component of the P1 layer, the interfacial adhesion between the P1 layer and the P2 layer can be improved. Additionally, by the P2 layer containing 15 mol% or less of the glycol component and / or the dicarboxylic acid component of the polyester resin that is the main component of the P1 layer, a decrease in mechanical strength during the production of the biaxially stretched polyester film can be suppressed.

[0158] The P1 layer and the P2 layer in the present invention may also contain particles within the range that does not impair the effects of the present invention. Regarding the added particles, either inorganic particles or organic particles can be used, or two or more types of particles can be used in combination. From the perspective of imparting slipperiness to the surface of the polyester film by controlling the surface roughness of the polyester film, examples of inorganic particles include: calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide, cerium oxide, magnesium oxide, barium sulfate, zinc sulfide, calcium phosphate, alumina (α-alumina, β-alumina, γ-alumina, δ-alumina), mica, mica titanate, zeolite, talc, clay, kaolin, lithium fluoride, calcium fluoride, montmorillonite, zirconia, wet silica, dry silica, colloidal silica, etc. Examples of organic particles include organic particles having acrylic resin, styrene resin, silicone resin, polyimide resin, etc. as constituent components, core-shell type organic particles, etc.

[0159] Additionally, from the perspective of controlling the volume resistivity of the polyester film in the present invention and imparting conductivity for the purpose of improving the electrical characteristics of the resin current collector foil, inorganic metal particles such as gold, silver, and copper or carbon particles can also be added.

[0160] (Polyester film)

[0161] When the thickness of the polyester film in the present invention is set to T (μm), T is preferably 1 or more and 30 or less. When the thickness T (μm) of the polyester film is 1 or more, processing can be performed without film breakage in the step of providing the M layer described later. T is more preferably 3 or more, and further preferably 3.5 or more. In addition, when the thickness T (μm) of the polyester film is 30 or less, even when used as a lithium ion battery member, an increase in the weight or thickness of the battery itself can be suppressed. T is more preferably 20 or less, and further preferably 15 or less.

[0162] In the polyester film of the present invention, the intrinsic viscosity (IV) of the entire polyester film is preferably 0.60 dl / g or more. By setting the IV to 0.60 dl / g or more, the length of the polyester molecular chain is appropriate, so that excessive crystallization can be suppressed and breakage during the stretching process can be prevented, and stable film formation can be performed. In addition, as the polyester molecular chain becomes longer, the number of polyester molecular chain ends per unit weight contributing to the decomposition reaction decreases, so that it is easier to further suppress the decomposition reaction of the polyester film caused by hydrogen ions or the like in the CV measurement. A more preferable range of the intrinsic viscosity (IV) of the entire polyester film is 0.70 dl / g or more, further preferably 0.75 dl / g or more, and most preferably 0.80 dl / g or more.

[0163] The water content of the polyester film in the present invention is preferably 3000 mass ppm or less. When the water content of the polyester film is 3000 mass ppm or less, the decomposition reaction of the polyester film caused by water molecules or the like in the CV measurement can be suppressed. As the water content of the polyester film, it is more preferably 2500 mass ppm or less, and further preferably 2000 mass ppm or less.

[0164] (Biaxially oriented polyester film)

[0165] The polyester film in the present invention is preferably biaxially oriented. By performing biaxial orientation, the mechanical strength of the film is improved, so that the generation of wrinkles or curls can be suppressed, and the generation of film breakage can also be suppressed in the processing step of providing the M layer described later. In addition, by applying uniform stretching stress in the stretching process, the thickness in the width direction and the long side direction of the polyester film can be made uniform, and the deviation of the electrical characteristics of the resin current collector foil due to sudden thickness unevenness when used as a resin current collector can be suppressed.

[0166] When the polyester film in the present invention has a laminated structure including the P1 layer and the P2 layer, there is no particular limitation on the method of laminating the P1 layer and the P2 layer. The following methods can be used: the co-extrusion method in which the resins of each layer are laminated and extruded in a molten state as described later; or a method in which other resin layer raw materials are put into an extruder, melted and extruded, and extruded from a die, and at the same time laminated onto a film in the middle of film formation (molten lamination method); a method in which the films after film formation are laminated via an adhesive layer, etc. Among them, from the viewpoint of excellent lamination uniformity and difficulty for foreign matter to enter between layers, the co-extrusion method can be preferably used.

[0167] The elongation at break of the polyester film in the present invention is preferably such that the elongation at break in at least one of the long side direction and the width direction in the film plane is 35% or more and 150% or less. By setting the elongation at break in at least one direction in the plane to 35% or more, when the polyester film in the present invention is incorporated into a power storage element as a current collector, it is possible to suppress the power storage element from thermally expanding and deforming due to the heat generated by the driving of the power storage element, and the incorporated polyester film breaks, resulting in a decrease in the performance of the power storage element. In addition, it is resistant to stretching or bending, and even when deformation occurs during processing into a battery component, it is possible to suppress a significant decrease in battery characteristics due to the breakage of the polyester film. In addition, by setting the elongation at break in at least one of the long side direction and the width direction in the film plane to 150% or less, the polyester film in the present invention has low crystallinity, and when incorporated into a power storage element, it is possible to suppress the crystallization of the polyester film from proceeding over time due to the heat generated during charging and discharging of the power storage element and breaking due to slight deformation, resulting in a decrease in battery characteristics.

[0168] A more preferable range of the elongation at break in at least one of the long side direction and the width direction in the film plane is 65% or more, and more preferably 90% or more. In addition, a more preferable range of the elongation at break in at least one direction in the plane is 140% or less, and more preferably 130% or less.

[0169] As the elongation at break of the polyester film in the present invention, when the unwinding direction of the polyester film roll is set as the long side direction and the direction rotated 90° in the plane with respect to the long side direction is set as the width direction of the polyester film, it is more preferable that the elongation at break in at least one of the long side direction and the width direction satisfies the above-mentioned preferable range. In addition, it is further preferable that any elongation at break in the long side direction and the width direction satisfies the above-mentioned preferable range.

[0170] As the breaking strength of the polyester film in the present invention, preferably, the breaking strength in at least one of the long side direction and the width direction in the film plane is 150 MPa or more and 400 MPa or less. By setting the breaking strength to 150 MPa or more, when the polyester film in the present invention is incorporated into a power storage element as a current collector, it is possible to suppress the breakage of the polyester film when a slight impact is applied during the handling of the power storage element, and thus the performance degradation of the power storage element. As a more preferable range of the breaking strength in at least one of the long side direction and the width direction in the film plane, it is 180 MPa or more in at least one direction in the plane, and more preferably 200 MPa or more in at least one direction in the plane.

[0171] By setting the breaking strength in at least one of the long side direction and the width direction in the film plane to 400 MPa or less, when the polyester film in the present invention is incorporated into a power storage element as a current collector, crystallization in the polyester film proceeds moderately, thereby increasing the strength. On the other hand, it is possible to suppress the breakage of the polyester film due to the accumulation of slight volume changes in the battery components during charging and discharging of the power storage element due to the reduced durability against deformation, and thus the performance degradation of the power storage element. As the upper limit value of the breaking strength, it is more preferably 350 MPa or less.

[0172] As the breaking strength of the polyester film in the present invention, when the unwinding direction of the polyester film roll is set as the long side direction and the direction rotated 90° in the plane with respect to the long side direction is set as the width direction of the polyester film, it is more preferably that the breaking strength in at least one of the long side direction and the width direction satisfies the above-mentioned preferable range. Further preferably, any breaking strength in the long side direction and the width direction satisfies the above-mentioned preferable range.

[0173] The polyester film in the present invention preferably has a silicon element content of 0 mass ppm or more and 10 mass ppm or less. By setting the silicon element content to 10 mass ppm or less, when incorporated into a lithium-ion secondary battery, during the charge and discharge process, the lithium ions moving in the battery are bonded to the silicon in the polyester film and the movement is restricted, so it is possible to suppress the decrease in the discharge capacity of the lithium-ion secondary battery. In addition, through the above reaction path, the silicon in the polyester film introduces lithium ions into the polyester film, thereby proceeding with the decomposition reaction of the polyester film in the negative electrode. The reason is considered to be that the lithium ions are coordinated to the oxygen atoms of the ester bonds of the polyester resin, thereby inducing the polarization of the ester bonds and promoting the reaction with the hydrogen ions formed by the ionization with the water molecules slightly remaining in the polyester film or the hydrogen atoms in the carboxyl groups at the ends of the polyester molecular chains.

[0174] As the content of the silicon element, it is preferably 5 mass ppm or less, and more preferably 1 mass ppm or less. In addition, the content of the silicon element is determined by the method described in the examples.

[0175] (Method for manufacturing biaxially oriented polyester film)

[0176] Next, the manufacturing method for forming the polyester film in the present invention into a biaxially stretched film will be exemplified. However, the present invention is not construed restrictively as an article obtained only through the said example.

[0177] As a method for obtaining the polyester film used in the present invention, a polymerization method based on a conventional method can be adopted. For example, it can be obtained by the following means: performing a transesterification reaction or an esterification reaction on the dicarboxylic acid component or its ester-forming derivative and the diol component or its ester-forming derivative using a known method, and then performing a melt polymerization reaction. Additionally, if necessary, a solid-phase polymerization reaction can also be performed on the polyester resin obtained through the melt polymerization reaction at a temperature below the melting point temperature of the polyester resin.

[0178] The manufacturing method of the polyester film in the present invention can preferably adopt an existing well-known manufacturing method. Specifically, for the polyester film in the present invention, if necessary, a method of heating and melting the dried raw material in an extruder and extruding it from a die onto a cooled casting drum to process it into a sheet (melt casting method) can be used. As another method, a method can also be used, that is, dissolving the raw material in a solvent, extruding the solution from a die onto a support such as a casting drum or an endless belt to form a film, and then drying and removing the solvent from the film layer to process it into a sheet (solution casting method), etc.

[0179] Regarding the drying of the polyester resin used as the raw material of the polyester film, it is preferably carried out at a temperature of 100 °C or higher, which is the boiling point of water, under reduced pressure because trace amounts of water present in the raw material of the polyester film can be removed. More preferably, it is carried out at a drying temperature of 120 °C or higher under reduced pressure. From the perspective of improving the drying efficiency of the polyester resin used as the raw material of the polyester film, it is further preferably to put the resin raw material into a rotating metal container and carry out drying at a drying temperature of 120 °C or higher under reduced pressure.

[0180] In addition, in the process of melt-extruding the polyester resin used as the raw material of the polyester film, it is also a preferred method to carry out the melting of the polyester resin and the removal of the contained water simultaneously by reducing the pressure in the extruder.

[0181] By removing water through the drying of the said raw material and / or extrusion under reduced pressure conditions, the water content rate of the P1 layer and the polyester film can be controlled within a preferred range.

[0182] When manufacturing a polyester film having two or more layers by the melt casting method, the following method can be suitably used. That is, an extruder is used for each layer constituting the biaxially oriented polyester film to melt the raw materials of each layer, and these are laminated in a molten state by a merging device provided between the extrusion device and the die opening, then introduced into the die opening, and extruded from the die opening onto a casting drum cooled to a surface temperature of 20°C or higher and 60°C or lower to be processed into a sheet to form an unstretched film (co-extrusion method).

[0183] (Sequential biaxial stretching)

[0184] Regarding the stretching conditions when biaxially stretching the unstretched film, in the case where the polyester film in the present invention has a polyester resin as the main component, for stretching in the long side direction, it is preferably to stretch the unstretched film in the long side direction using a set of rolls heated to 70°C or higher and cool it using a set of rolls set at a temperature of 20°C or higher and 50°C or lower. Regarding the lower limit of the temperature of the heating rolls in the stretching in the long side direction, as long as the stretchability of the sheet is not impaired, there is no particular limitation, and it is preferably higher than the glass transition temperature of the polyester resin used. In addition, the preferable range of the stretching ratio in the long side direction is 2 times or more and 5 times or less. As a more preferable range, it is 3 times or more and 4 times or less. If the stretching ratio in the long side direction is 2 times or more, orientation crystallization can be carried out to improve the film strength. On the other hand, by setting the stretching ratio to 5 times or less, it is possible to suppress the excessive progress of the orientation crystallization of the polyester resin accompanying stretching and becoming brittle and causing breakage during film formation.

[0185] Subsequently, the engineered film (uniaxially stretched film) stretched in the long side direction is stretched in the direction perpendicular to the long side direction (width direction). It is preferably to hold both ends of the uniaxially stretched film with clips and introduce it into a tenter, and stretch it 2 times or more and 5 times or less in the direction perpendicular to the long side direction (width direction) in an environment heated to a temperature of 70°C or higher and 160°C or lower.

[0186] Thereafter, it is preferable to perform heat treatment on the stretched film to stabilize the internal orientation structure. Regarding the temperature of the heat history received by the film during heat treatment, it can be confirmed by the temperature of the minute endothermic peak (sometimes referred to as Tmeta) that appears directly below the melting point temperature measured by a differential scanning calorimeter (DSC) described later. However, as the set temperature of the tenter device, when polyester (melting point: 280°C) is the main component, it is preferable to set the maximum temperature in the tenter to 150°C or higher and 270°C or lower. When other thermoplastic resins are the main component, it is preferable to set it to resin melting point (°C) - 70°C or higher and resin melting point (°C) - 10°C or lower. By setting the heat treatment temperature to 150°C or higher, the dimensional stability of the biaxially oriented polyester film after biaxial orientation can be improved. In addition, by setting the heat treatment temperature to 270°C or lower, the generation of film breakage accompanied by the melting of the polyester film can be suppressed, and manufacturing can be carried out with good productivity. As a more preferable range of the heat treatment temperature, it is more preferably 180°C or higher, and furthermore, more preferably 250°C or lower.

[0187] As the temperature range of Tmeta representing the temperature of the heat history received by the film during heat treatment, when polyester resin is the main component, for the reasons described above, it is preferably 200°C or higher and 260°C or lower. As a more preferable temperature range of Tmeta, it is more preferably 210°C or higher, and more preferably 240°C or lower.

[0188] For the purpose of further imparting dimensional stability after heat treatment, relaxation treatment can also be performed in the range of 1% or more and 6% or less. By setting the relaxation treatment to 1% or more, the dimensional stability when using the biaxially oriented polyester film in a high-temperature environment can be improved. By setting it to 6% or less, an appropriate tension can be continuously applied to the biaxially oriented polyester film, preventing deterioration of thickness unevenness.

[0189] The stretching ratio is preferably set to 2 times or more and 5 times or less in the longitudinal direction and the width direction, respectively. However, its area ratio (stretching ratio in the longitudinal direction × stretching ratio in the width direction) is preferably 4 times or more and 22 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 22 times or less, breakage during stretching can be suppressed.

[0190] (M layer: layer containing metal and / or metal-based compound)

[0191] In terms of improving battery characteristics by reducing the resistance when incorporated into a secondary battery, it is preferable to provide a layer (M layer) containing a metal and / or a metal compound on the surfaces of both sides of the polyester film in the present invention. In terms of the viewpoint of particularly suppressing gas generation when applied to a current collector for a negative electrode of a secondary battery, it is more preferable that at least one side layer of the M layer on the surface is a layer containing a copper element.

[0192] As a method for providing the M layer in the present invention, there is no particular limitation, and a method of providing it by vapor deposition, sputtering, or electroplating under vacuum conditions or reduced pressure conditions in which an inert gas such as argon is enclosed (hereinafter, sometimes collectively referred to as a vapor deposition method), a method of directly or via an adhesive layer laminating a metal foil or a metal compound foil with a polyester film, or a method of using a solution containing a metal salt and setting a metal layer by an electrochemical reaction (electrolytic plating method, electroless plating method) can be used. Among them, in terms of the viewpoint of continuously forming the M layer on the polyester film roll, it is preferable to use the vapor deposition method.

[0193] As the sputtering method, a high-frequency sputtering method, a magnetron sputtering method, a diode sputtering method, a direct current (DC) sputtering method, a reactive sputtering method, etc. can be cited. In terms of the viewpoint of simple equipment, being able to provide a metal layer to an insulator sample, and less damage to the sample, it is preferable to use the high-frequency sputtering method.

[0194] In the case of using the vacuum vapor deposition method, a preferable form is to previously set a polyester film roll in a vacuum chamber, while bringing the unrolled film into close contact with a cooling roll, while solidifying and adhering the heated and vaporized metal and / or metal compound to the surface of the polyester film, and after providing the M layer, winding it up again as a film roll.

[0195] Here, in the vacuum chamber, a vacuum condition of 9.0×10 -3 Pa or less, or a condition of enclosing an inert gas such as argon and reducing the pressure to 9.0×10 -3 Pa or more and 1×10 -1 Pa or less can be appropriately used. In addition, the M layer can also be formed by continuously performing two or more vapor deposition steps such as setting a first M layer by sputtering and then setting a second M layer by vacuum vapor deposition.

[0196] The vacuum vapor deposition method includes an induction heating vapor deposition method, a resistance heating vapor deposition method, a laser beam vapor deposition method, an electron beam vapor deposition method, etc. Among them, the electron beam vapor deposition method, the laser beam vapor deposition method, and the induction heating vapor deposition method with a large calorific value of the vapor deposition source can be preferably used. The calorific value of the vapor deposition source needs to be increased until the M layer of the desired thickness is formed, and the surface temperature of the substrate needs to be sufficiently high. However, since it is difficult to actually measure, the M layer after vapor deposition is confirmed to be of the desired thickness to judge whether the heat is sufficient.

[0197] Among them, if the calorific value of the evaporation source is increased to the required heat, in the management of the cooling function of the ordinary vacuum evaporation method, the temperature of the resin film rises and the mechanical properties of the resin film are reduced due to thermal damage, and further the resin film may melt. Therefore, during the evaporation process, it is preferably carried out while managing the cooling function in such a way that the temperature does not rise excessively and the film can be cooled evenly. Specifically, it is preferably cooled evenly from the back of the evaporation surface by a cooling mechanism including a metal plate or a metal roller that is sufficiently cooled by a refrigerant.

[0198] When the M layer of the present invention is set to the desired metal layer thickness, from the viewpoints of productivity, resistance characteristics, grade, and quality, a method of forming by single evaporation (defining a set of unwinding, evaporation, and winding as single evaporation) is preferred. For example, the thin film evaporation of forming a 50 nm thick aluminum evaporation layer by single evaporation can be repeated 20 times (repeating the set 20 times) to form an aluminum metal layer with a total thickness of 1 μm, etc. In addition, when the M layer is provided on the surface of the polyester film in the present invention, for the purpose of improving the adhesion between the M layer and the polyester film, the surface of the polyester film can also be modified by vacuum plasma treatment, atmospheric pressure plasma treatment, etc.

[0199] Examples of the metal element constituting the M layer include gold, silver, copper, zinc, lead, nickel, iron, aluminum, titanium, cobalt, manganese, cadmium, palladium. It can be a metal layer containing the simple substance of the metal element, or a layer containing a metal compound formed by mixing the metal element with oxygen, nitrogen, fluorine, carbon, boron, chlorine, sulfur, or phosphorus. In addition, the metal elements of the M layer provided on the polyester film can be the same or different on both sides.

[0200] When used as a resin current collector for a lithium-ion battery, a preferred form is that the M layer contains a metal and / or a metal-based compound using copper or aluminum elements. When used as a resin current collector for a negative electrode, it is further preferred that the M layer containing copper elements is laminated on the P1 layer.

[0201] As a preferred laminated structure of the polyester film (P1 layer, P2 layer) and the M layer in the present invention, it is preferred that the P1 layer is the outermost layer containing resin on at least one side of the polyester film, and the M layer is directly laminated on the P1 layer. Specifically, the following structure is preferred. When the polyester film is single-layer, a structure of M layer / P1 layer / M layer is preferred, or a structure having a layer, that is, an M layer / P1 layer / M' layer including a layer (M' layer) containing a metal and / or a metal-based compound containing a metal element different from the M layer is provided.

[0202] When there are two or more layers of polyester film, it is preferably an M layer / P1 layer / P2 layer / M layer, M layer / P1 layer / P2 layer / M' layer, or M layer / P1 layer / P2 layer / P1 layer / M layer, M layer / P1 layer / P2 layer / P1 layer / M' layer. In particular, when the M' layer is a layer containing a metal and / or a metal-based compound containing an aluminum element and is used as the positive electrode in the resin current collector, the structure of M layer / P1 layer / P2 layer / M' layer can be used.

[0203] A more preferable structure is M layer / P1 layer / P2 layer / P1 layer / M layer, M layer / P1 layer / P2 layer / P1 layer / M' layer in which both sides of the layer containing a metal and / or a metal-based compound are in contact with the P1 layer. When the thickness of the M layer in the present invention is 0.1 μm or more, it is preferable because it can suppress the decrease in electrical characteristics corresponding to the thickness unevenness of the metal layer, especially the increase in the resistance value when incorporated into a battery cell. The thickness of the M layer is more preferably 0.2 μm or more. In addition, by setting the thickness of the M layer to 5.0 μm or less, the increase in battery weight can be reduced when used as a battery resin current collector, so it is preferable. The thickness of the M layer is more preferably 3.0 μm or less. In addition, it is further preferable that the thicknesses of the M layers on both sides of the polyester film are both 0.2 μm or more. In addition, it is further preferable that the thicknesses of the M layers on both sides of the polyester film are 3.0 μm or less.

[0204] From the viewpoint of suppressing the peeling of the M layer and short-circuiting of the battery when the current collector of the present invention is incorporated into a battery, it is preferable that the current collector of the present invention has M layers on the surfaces on both sides of the polyester film, and the adhesion between the polyester film surface and the M layer is 2 N / 15 mm or more and 5 N / 15 mm or less on both sides. As a method thereof, a method of previously providing a metal layer having good affinity with the M layer on the surface of the polyester film by sputtering treatment or the like can be preferably cited. The preferable range of the adhesion between the polyester film surface and the M layer is 2.5 N / 15 mm or more and 5 N / 15 mm or less.

[0205] [Power storage element]

[0206] The power storage element of the present invention includes an electrode assembly including a positive electrode and a negative electrode. It may also contain an electrolyte, and in that case, it is preferably provided with a separator between the positive electrode and the negative electrode. A power storage element containing a solid electrolyte without an electrolyte can also be preferably exemplified. In addition, it may include a battery case for housing the electrode assembly.

[0207] As such a power storage element, for example, a primary battery, a secondary battery, an electric double layer capacitor, an aluminum electrolytic capacitor, etc. can be cited, but in the present invention, it refers to a secondary battery.

[0208] As secondary batteries, for example, there may be mentioned: lithium secondary batteries, lead storage batteries, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-iron storage batteries, silver oxide-zinc storage batteries, manganese dioxide-lithium secondary batteries, lithium cobaltate-carbonate secondary batteries, vanadium-lithium secondary batteries, etc.

[0209] Among these, in terms of long-term utilization, secondary batteries are preferred, and lithium secondary batteries that achieve high energy density by using an organic solvent are more preferred.

[0210] As the battery case, for example, an aluminum case, an iron case with a nickel-plated inner surface, a case including an aluminum laminate film, etc. may be used. Examples of the shape of the battery case include: pouch type, cylindrical type, square type, coin type, etc. Among these, in terms of achieving high energy density and being able to freely design the shape at low cost, the pouch type is preferred.

[0211] The positive electrode is a positive electrode formed by laminating a positive electrode material containing an active material, a binder resin, and a conductive aid on a current collector. As the active material, there may be mentioned: layered structure lithium-containing transition metal oxides such as LiCoO2, LiNiO2, Li(NiCoMn)O2, spinel type manganese oxides such as LiMn2O4, and iron-based compounds such as LiFePO4, etc. As the binder resin, a resin with high oxidation resistance may be used. Specifically, there may be mentioned fluororesins, acrylic resins, styrene-butadiene resins, etc. As the conductive aid, carbon materials such as carbon black and graphite may be mentioned. As the current collector, a metal foil is suitable, and in particular, aluminum foil is mostly used.

[0212] The negative electrode is a negative electrode formed by laminating a negative electrode material containing an active material and a binder resin on a current collector. As the active material, there may be mentioned: carbon materials such as artificial graphite, natural graphite, hard carbon, and soft carbon, lithium alloy-based materials such as tin and silicon, metal materials such as lithium, and lithium titanate (Li4Ti5O 12 ) etc. As the binder resin, there may be mentioned: fluororesins, acrylic resins, styrene-butadiene resins, etc. As the current collector, a metal foil is suitable, and in particular, aluminum foil is mostly used, but it is particularly preferred to use the current collector of the present invention.

[0213] When the power storage element of the present invention contains an electrolytic solution, the electrolytic solution becomes a place where ions move between the positive electrode and the negative electrode in an electrochemical element such as a secondary battery, and preferably has a structure in which an electrolyte is dissolved in an organic solvent.

[0214] As the electrolyte, there may be mentioned LiPF6, LiBF4, LiClO4, etc. From the viewpoints of solubility in an organic solvent and ionic conductivity, LiPF6 can be suitably used.

[0215] Examples of the organic solvent include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc., and two or more of these organic solvents can be used in combination.

[0216] Hereinafter, an example of a method for manufacturing a lithium secondary battery, which is also preferably used in the power storage element, will be described.

[0217] As a method for manufacturing a lithium secondary battery, first, an active material and a conductive assistant are dispersed in a binder resin solution to prepare a coating liquid for an electrode. 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 be 50 μm or more and 500 μm or less. Further, it is preferable to apply pressure to the active material layer formed on the current collector by a method such as a roll pressing method to densify it, thereby thinning the current collector.

[0218] Between the obtained positive electrode and negative electrode, a separator for a lithium secondary battery is disposed in contact with the active material layer of each electrode, and it is sealed in an outer packaging material such as an aluminum laminated film. After injecting an electrolyte, a negative electrode lead or a safety valve is provided, and the outer packaging material is sealed.

[0219] Regarding the lithium secondary battery element thus obtained, it has high adhesion to the electrode, excellent battery characteristics, and can be manufactured at low cost.

[0220] [Secondary battery]

[0221] In some cases, in order to meet the use of the power storage element or the required battery capacity, the power storage elements manufactured by the above method or the like are connected in series and used as a secondary battery. In such a case, it is preferable to manufacture a secondary battery including voltage management, temperature management, and a safety device. Examples thereof include connecting the power storage elements to each other with tab lead wires (current extraction wires) and housing them in a resin or metal module case, and using them as a secondary battery.

[0222] [Electric vehicle]

[0223] The secondary battery manufactured by the above method etc. has excellent battery characteristics and durability, and has a polyester film with a specific gravity lower than that of metal in its structure. Therefore, it is lightweight and has an increased weight energy density. Thus, one of the preferred forms is to be mounted on an electric vehicle. An electric vehicle refers to a vehicle that is supplied with part or all of the driving energy required during driving by a secondary battery. As types of electric vehicles, there can be listed a battery electric vehicle (BEV) equipped only with a secondary battery pack, a hybrid electric vehicle (HEV) equipped with both a fossil fuel such as gasoline and a secondary battery pack, and a plug-in hybrid electric vehicle (PHEV). In any application, the secondary battery of the present invention can be suitably used.

[0224] [Electric flying vehicle]

[0225] The secondary battery manufactured by the above method etc. has excellent battery characteristics and durability, and has a polyester film with a specific gravity lower than that of metal in its structure. Therefore, it is lightweight and has an increased weight energy density. Thus, one of the preferred forms is to be mounted on an electric flying vehicle. An electric flying vehicle refers to a flying vehicle that is supplied with part or all of the driving energy required during flight by a secondary battery. Specifically, there can be listed electric aircraft such as drones, aircraft for stratospheric communication platforms (high altitude platform station (HAPS)), air metros, and air taxis. In any application, the secondary battery of the present invention can be suitably used.

[0226] [Evaluation method of characteristics]

[0227] A. Polymer characteristics

[0228] (i) Intrinsic viscosity (IV)

[0229] Dissolve the test sample (polyester resin (raw material) or polyester film) in 100 ml of o-chlorophenol (solution concentration C (weight of test sample / volume of solution) = 1.2 g / 100 ml), and use an Ostwald viscometer to measure the viscosity of the solution at 25°C. Additionally, measure the viscosity of the solvent in the same way. Using the obtained solution viscosity and solvent viscosity, calculate [η] by the following formula (1), and take the obtained value as the intrinsic viscosity (IV) of the entire polyester film.

[0230] ηsp / C = [η] + K[η] 2 ·C…(1)

[0231] (Here, ηsp = (solution viscosity / solvent viscosity) - 1, and K is the Huggins constant (assumed to be 0.343))

[0232] In addition, in the case where insoluble substances such as inorganic particles are present in the solution in which the test sample is dissolved, the following method is used for measurement.

[0233] (1 - 1) Dissolve the test sample in 100 mL of o - chlorophenol to prepare a solution with a concentration ratio of more than 1.2 g / 100 mL. Here, the weight of the test sample supplied to the o - chlorophenol is defined as the weight of the test sample.

[0234] (1 - 2) Next, filter the solution containing insoluble substances, and measure the weight of the insoluble substances and the volume of the filtrate after filtration.

[0235] (1 - 3) Add o - chlorophenol to the filtrate after filtration, and adjust it so that (weight of test sample (g) - weight of insoluble substances (g)) / (volume of filtrate after filtration (mL)+volume of added o - chlorophenol (mL)) becomes 1.2 g / 100 mL.

[0236] (For example, when preparing a concentrated solution with a test sample weight of 2.0 g / 100 mL of solution volume, if the weight of insoluble substances during filtration of the solution is 0.2 g and the volume of the filtrate after filtration is 99 mL, an adjustment of adding 51 mL of o - chlorophenol is carried out. ((2.0 g - 0.2 g) / (99 mL + 51 mL)=1.2 g / 100 mL))

[0237] (1 - 4) Using the solution obtained in (1 - 3), measure the viscosity at 25 °C using an Ostwald viscometer. Using the obtained solution viscosity and solvent viscosity, calculate [η] through the above formula (1), and take the obtained value as the inherent viscosity (IV). The inherent viscosity of the polyester film obtained according to the above (1 - 1) to (1 - 4) is defined as IV F (dl / g).

[0238] In addition, only take out the surface layer (layer A) and the intermediate layer (layer B) of the polyester film, and the inherent viscosities of layer A and layer B obtained according to the above (1 - 1) to (1 - 4) are defined as IV A (dl / g) and IV B (dl / g).

[0239] B. Film thickness

[0240] (i) Polyester film thickness T

[0241] Regarding the total thickness of the polyester film, using a dial gauge, in accordance with Japanese Industrial Standards (JIS) K7130 (1992) Method A-2, measure the thickness at any 5 locations in the state where 10 films are overlapped. Divide the average value by 10 to obtain the polyester film thickness T (μm).

[0242] (ii) Laminated thickness (T A 、T B 、T M )

[0243] Use a microtome to cut a cross-section of the polyester film in a direction parallel to the film width direction. Observe the cross-section with a scanning electron microscope at a magnification of 5000 times to 20000 times, and obtain the thickness ratios of the layers (Layer A, Layer B) and the M layer that make up the laminated polyester film. Based on the obtained lamination ratio and the film thickness of all layers obtained in item (i) above, calculate the thickness of each layer (T A 、T B 、T M ).

[0244] C. Formation of the metal layer based on vacuum sputtering processing

[0245] Under the following conditions, use a high-frequency sputtering device to form a copper metal layer with a thickness of 1 μm on the surface of Layer A of the polyester film.

[0246] Sputtering environment: Under vacuum (9.0×10 -3 Pa or less)

[0247] Target metal: Copper

[0248] Power output: 500W.

[0249] D. Constituent elements of the M layer

[0250] After performing sputtering treatment using platinum-palladium on the surface of the laminated polyester film, use a scanning electron microscope (manufactured by JEOL Ltd., JSM-6700) and the included Energy Dispersive X-ray Spectroscopy (EDX) detector (manufactured by Oxford Instruments plc, AztecLive Standard UltimMax65) to identify the metal elements.

[0251] The measurement is carried out by changing the acceleration voltage within the range of 0.5 kV to 30 kV, and the detected elements are taken as the elements constituting the M layer. At this time, except for platinum and palladium, when only platinum or palladium is detected through the measurements at all acceleration voltages, these are taken as the elements constituting the M layer.

[0252] E. Evaluation of the reduction current based on cyclic voltammetry (CV) measurement

[0253] (i) Fabrication of 2032 coin cells

[0254] The sample with a copper metal layer provided on the surface of layer A of the polyester film by the method described in item C above is punched into a circle with a diameter of 16 mm. On the surface of the copper metal layer of the punched sample, a polyethylene separator with a diameter of 18 mm, a lithium metal foil with a diameter of 16.1 mm, and two stainless steel (SUS) plates are sequentially laminated, and the following electrolyte is sealed to fabricate 2032 coin cells. In addition, the polyethylene separator used is a polyethylene separator with a thickness of 4 μm or more and 20 μm or less and an air permeability of 500 seconds or less.

[0255] (Electrolyte composition)

[0256] · Electrolyte: 1 mol / L lithium hexafluorophosphate (LiPF6)

[0257] · Solvent: A 1:1 (volume %) mixture of ethylene carbonate (EC) and diethyl carbonate (DEC)

[0258] · Blending environment: Conducted inside an argon circulation type glove box with a dew point of -70 °C or lower and an oxygen concentration of 10 volume ppm or lower.

[0259] (ii) CV measurement

[0260] Using the 2032 coin cells obtained in item (i) above, cyclic voltammetry measurement using a VSP manufactured by BioLogic is carried out under the following conditions. The current value (mA) observed through the potential sweep operation is divided by the sample area used (2.01 cm 2 ), and thereby the current value per unit area (mA / cm 2 ) is obtained.

[0261] (Measurement conditions)

[0262] · Test temperature: 25 °C

[0263] · Potential sweep range: 0.01 V - 2.0 V (v.s. Li + / Li)

[0264] · Sweep rate: 1 mV / s

[0265] · Number of cycles: 10 cycles

[0266] (iii) Peak intensity of the maximum reduction current per unit area

[0267] Regarding the current value per unit area (mA / cm 2 ) obtained in item (ii) above, the current value with the largest absolute value is taken as the peak intensity of the maximum reduction current (mA / cm 2 ) for calculation.

[0268] E-2. Moisture content (W F )

[0269] The moisture content of the polyester film and the polyester resin is measured using a moisture measuring device (Aquacounter AQ-7) and a moisture vaporization device (Evaporator Unit EV-6) manufactured by Hiranuma Co., Ltd., and by the Karl Fischer coulometric titration method. The measured moisture content is divided by the mass of the polyester film as the sample, and the obtained ratio is converted to parts per million, and the value thus obtained is taken as the moisture content W F (ppm by mass).

[0270] As the reagent for coulometric titration, "Aqualyte" (registered trademark) RS-A (manufactured by Hiranuma Co., Ltd.) is used in the generation liquid layer, and "Aqualyte" (registered trademark) CN (manufactured by Hiranuma Co., Ltd.) is used in the counter electrode liquid phase.

[0271] In the polyester resin used as the raw material of the polyester film, the moisture content is also calculated by the same method.

[0272] In addition, only layers A and B of the polyester film are taken out, and the moisture contents of layers A and B obtained according to the above method are respectively set as W A (ppm by mass) and W B (ppm by mass).

[0273] F. Evaluation of the mechanical properties of the polyester film

[0274] The elongation at break and tensile strength of the polyester film were measured. The unwinding direction of the roll was taken as the long side direction of the polyester film, and a sample was cut out from the polyester film in a rectangular shape with a length of 150 mm and a width of 10 mm such that the long side direction became the long side. According to the following method specified in American Society for Testing Materials (ASTM)-D882, using an Instron-type tensile tester (AMF / RTA-100 manufactured by Orientec Co., Ltd.), a sample film with a width of 10 mm was set such that the length between the chucks became 50 mm, and a tensile test was carried out at a tensile speed of 300 mm / minute, and the elongation at break (elongation at break) and strength (tensile strength) at the time of sample fracture were read. The measurement was carried out 5 times, and the average value of these was taken as the elongation at break and tensile strength in the long side direction of the polyester film.

[0275] In the same manner as the measurement in the long side direction, the direction after rotating the long side direction of the polyester film 90° in the plane was taken as the width direction, and a sample was cut out in a rectangular shape with a length of 150 mm and a width of 10 mm such that the width direction became the long side, and the elongation at break and tensile strength of the sample were measured. The measurement was carried out 5 times, and the average value of these was taken as the elongation at break and tensile strength in the width direction of the polyester film.

[0276] In the case where the long side direction and width direction of the polyester film are not clear, the elongation at break and tensile strength were measured for a total of four directions: a specific direction and the directions rotated 45°, 90°, and 135° in the in-plane direction from the specific direction. The maximum values of the elongation at break and tensile strength in the four obtained directions were taken as the elongation at break and tensile strength of the polyester film with unclear long side direction and width direction.

[0277] Adhesion of the G.M layer to the polyester film

[0278] A sample provided with the M layer formed on the surface of the polyester film was cut out in a rectangular shape with a width of 15 mm × a length of 80 mm. A cellophane tape No. 29 (tape width 15 mm wide) manufactured by Nitto was adhered to the M layer of the cut-out sample as a peeling tape, and it was made to adhere closely using a 2 kg rubber roller and conditioned for 1 day at 23°C and 65% RH.

[0279] The 180° peel test was carried out on the conditioned sample using the Adhesion-Film Peel Analysis Device (VPA-2) manufactured by Kyowa Interface Science Co., Ltd. After fixing the side of the conditioned sample opposite to the tape-attached surface to the device, the end of the peeling tape was fixed to the load cell of the device for measurement.

[0280] (Peel test conditions)

[0281] · Peel angle: 180°

[0282] · Tape width: 15 mm

[0283] · Peel speed: 25 mm / min

[0284] · Initial peel force: 0 N

[0285] · Measurement distance: 50 mm

[0286] The average value of the peel force (N / 15 mm) in the range of 15 mm to 35 mm of the moving distance in the obtained peel force waveform was calculated. For three different samples, the peel force was measured, and the average value of these was taken as the adhesion between the M layer and the polyester film.

[0287] H. Quantitative determination of silicon element

[0288] The polyester film was measured by ICP emission spectrometry. In the case where the polyester film has a metal layer, the quantitative determination was carried out after removing the metal layer.

[0289] <Analysis conditions>

[0290] Device: ICP emission spectrometry (manufactured by Hitachi High-Tech Science Corporation) PS3520VDDII

[0291] Preparation of sample: Weigh the polyester film in a beaker, decompose it under pressure using sulfuric acid and then nitric acid, and then heat it to ashing. Dissolve the ash with a mixed flux of sodium carbonate and boric acid, dissolve it by heating with dilute nitric acid, and make the volume constant at 10 mL. Subsequently, the amount of silicon element in the solution diluted with dilute nitric acid was measured by inductively coupled plasma emission spectrometry as the content of silicon element in the polyester film.

[0292] (Measurement conditions)

[0293] Measurement wavelength: 251.6 nm

[0294] RF output: 1.2 kW

[0295] Plasma gas flow rate: 16 L / min

[0296] Auxiliary gas flow rate: 0.5 L / min

[0297] Carrier gas flow rate: 0.9 L / min

[0298] Photometric height: 12 mm

[0299] G-2. Quantitative analysis of the components of the resin constituting the polyester film

[0300] Measurement samples are collected from all layers, layer A, and layer B of the polyester film of the present invention. The measurement samples are immersed in 1,1,1,2,2,2-hexafluoro-2-isopropanol (HFIP), and the soluble part is separated by centrifugation. The supernatant is collected, and thus the resin components contained in the polyester film are extracted. The extract is measured by matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS). According to the obtained mass spectrum and the spectrum of the nuclear magnetic resonance method ( 1 H-Nuclear Magnetic Resonance, 1 H-NMR) described below, the structure of the components containing the resin is identified.

[0301] Weigh 50 mg of all layers, layer A, or layer B of the polyester film of the present invention, and add 2.63 mg of octamethylcyclotetrasiloxane (OMTS) as an internal standard substance. After adding 0.7 ml of deuterated 1,1,1,2,2,2-hexafluoro-2-isopropanol (HFIP-d2) to dissolve the soluble part, centrifugation is performed. The supernatant of the centrifugation is collected and measured by nuclear magnetic resonance method ( 1 H-NMR). According to the ratio of the NMR spectral area of the added internal standard substance to the spectral area of the extract, the components of the resin contained in the sample are quantified.

[0302] ( 1 H-NMR measurement conditions)

[0303] Device used: ECA-400 (manufactured by JEOL RESONANCE)

[0304] Measurement method: single pulse

[0305] Observation frequency: 399.8 MHz

[0306] Pulse width: 6.45 s (45 pulses)

[0307] Locked solvent: HFIP-d2

[0308] Chemical shift reference: Residual protons of deuterated solvent (4.41 ppm)

[0309] Observation width: Approximately 8000 Hz (approximately -2 ppm to 18 ppm)

[0310] Number of data points: 32768

[0311] Waiting time: 30 seconds

[0312] Number of accumulations: 128 times

[0313] Measurement temperature: Room temperature (21 °C)

[0314] Sample rotation speed: 15 Hz.

[0315] G-3.DSC measurement

[0316] For the polyester film of the present invention or its raw materials, using a differential scanning calorimeter (DSC), Thermo Plus Evo2 series DSC Vesta manufactured by Rigaku Corporation, about 5 mg of the sample is heated from room temperature to 300 °C at a heating rate of 20 °C / minute on an aluminum tray and held for 5 minutes (first round (1st Run) measurement). The temperature of the heat generation peak originating from the glass transition observed at this time is taken as the glass transition temperature (Tg), the peak temperature of the endothermic peak of melting is taken as the melting point (Tm), and the average value of three measurements is taken as the glass transition temperature (Tg) and melting point (Tm) of the sample.

[0317] In the DSC chart of the polyester film of the present invention, in the case where it is difficult to distinguish from the small endothermic peak Tmeta that appears immediately before the melting point temperature, in addition to performing the first round of measurement, the following measurement is also performed. After heating to 300 °C at a heating rate of 20 °C / minute and holding for 5 minutes, rapid cooling is performed using liquid nitrogen, and then it is heated to 300 °C again at a heating rate of 20 °C / minute (second round (2nd Run) measurement). Confirm the number and temperature of the melting point peaks, and take the peak that disappears from the first round of measurement as the small endothermic peak Tmeta that appears immediately before the melting point temperature, and exclude it from the first round of measurement data.

[0318] [Evaluation method of use characteristics]

[0319] A. Evaporation processability

[0320] On the surface of layer A of the polyester film, vacuum sputtering using metallic copper is carried out in the same manner as described in item 『C. Formation of a metal layer by vacuum sputtering process』. Vacuum sputtering is carried out on 10 films with a length of 29.7 cm in the long side direction and a width of 21.0 cm. According to whether there are wrinkles on the surface of the polyester film with a metal layer, the sputtering processability is evaluated as follows.

[0321] A: Wrinkles occur in 2 or fewer out of 10 films.

[0322] B: Wrinkles occur in 3 or more and 5 or fewer out of 10 films.

[0323] C: Wrinkles occur in 6 or more and 8 or fewer out of 10 films.

[0324] D: Wrinkles occur in 9 or more out of 10 films.

[0325] As an evaluation of the sputtering processability, A to C are good, and among them, A is the most excellent.

[0326] B. Evaluation of the resin current collector

[0327] (i) Fabrication of the resin current collector

[0328] A film with an aluminum metal layer or a copper metal layer provided on both sides of the polyester film by vacuum evaporation is fabricated, and thus a positive electrode resin current collector and a negative electrode resin current collector are fabricated respectively.

[0329] Specifically, a roll stock of the polyester film is placed in a roll-type vacuum evaporation apparatus (EWC-060 manufactured by ULVAC), and an aluminum ingot is heated by an induction heating evaporation method using a carbon crucible, and thus an aluminum metal layer is provided by the vacuum evaporation method. At this time, the conveyance speed and output conditions are adjusted so that the aluminum metal layer has a thickness of 1 μm to carry out vacuum evaporation. Subsequently, the roll of the polyester film having an aluminum metal layer provided on one side is placed again in a roll-type vacuum evaporation apparatus (EWC-060 manufactured by ULVAC), and on the surface of the polyester film on the side opposite to the surface on which the aluminum metal layer is provided, an aluminum ingot is heated by an induction heating evaporation method using a carbon crucible, and thus an aluminum metal layer is provided by the vacuum evaporation method. At this time, the conveyance speed and output conditions are adjusted so that the aluminum metal layer has a thickness of 1 μm to carry out vacuum evaporation. Through the above operations, a positive electrode resin current collector having aluminum metal layers provided on both sides of the polyester film is fabricated.

[0330] In addition, the metal ingot used is changed to a copper ingot, and the same operations as above are carried out, and thus a negative electrode resin current collector having copper metal layers provided on both sides of the polyester film is fabricated.

[0331] (ii) Fabrication of the positive electrode

[0332] Mix 94 parts by mass of nickel-cobalt-manganese composite oxide NMC (Ni:Co:Mn = 6:2:2 (element ratio)) as the positive electrode active material, 3 parts by mass of carbon black as the conductive material, and 3 parts by mass of polyvinylidene fluoride (PVDF) as the resin binder in the said ratio, disperse these in N-Methylpyrrolidone (NMP) to prepare a slurry. Uniformly coat the said slurry on one side of an aluminum foil with a thickness of 20 μm as the positive electrode current collector and dry it, then perform compression molding using a roll press. At this time, make the single-sided coating amount of the positive electrode mixture be 170 g / m 2 , and the density be 3.0 g / cm 3 . After manufacturing in this way, cut it out to 28 mm × 44 mm. Among them, 28 mm × 5 mm on one side is the uncoated part for connecting the tab, and the coated part of the slurry is 28 mm × 39 mm. Bond an aluminum positive electrode tab to the uncoated part by ultrasonic welding.

[0333] (iii) Fabrication of the negative electrode

[0334] Mix 97 parts by mass of artificial graphite as the negative electrode active material, 1 part by mass of carboxymethyl cellulose as the resin binder, and 2 parts by mass of styrene-butadiene copolymer latex in the said ratio, disperse these in purified water to prepare a slurry. Uniformly coat the said slurry on one side of a copper foil with a thickness of 10 μm as the negative electrode current collector, or a resin current collector for the negative electrode, and dry it, then perform compression molding using a roll press. At this time, make the single-sided coating amount of the negative electrode mixture be 100 g / m 2 , and the density be 1.5 g / cm 3 . After manufacturing in this way, cut it out to 30 mm × 46 mm. Among them, 30 mm × 5 mm on one side is the uncoated part for connecting the tab, and the coated part of the slurry is 30 mm × 41 mm. Bond a copper negative electrode tab to the uncoated part by ultrasonic welding.

[0335] (iv) Polyolefin microporous membrane

[0336] The manufacturing method of the polyolefin microporous membrane is not particularly limited, and a known manufacturing method of the polyolefin microporous membrane can be used. In this embodiment, the polyolefin microporous membrane is fabricated with reference to the method described in Japanese Patent No. 4460028. Cut out the fabricated microporous membrane to 38 mm × 49 mm.

[0337] (v) Non-aqueous electrolyte

[0338] In a mixed solvent of ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate = 3:3:4 (volume ratio), LiPF6 as a solute is dissolved to a concentration of 1.0 mol / L. 1 part by mass of vinylene carbonate is added to 100 parts by mass of the solution to prepare a non-aqueous electrolyte.

[0339] (vi) Fabrication of the evaluation battery

[0340] The positive electrode and the negative electrode are stacked in the order of positive electrode / microporous polyethylene film / negative electrode to fabricate a laminated electrode body. The laminated electrode body is sandwiched by an aluminum laminated film, with a part left as an opening and then sealed. After drying it in a vacuum oven at 80 °C for 6 hours, the non-aqueous electrolyte is injected and sealed with a vacuum sealer. Subsequently, in an environment at 35 °C, constant current charging is carried out at a current value of 6 mA until the battery voltage reaches 4.2 V, and then constant voltage charging is carried out at 4.2 V until the current value becomes 3 mA. After pausing for 30 minutes, constant current discharging is carried out at a current value of 6 mA until the battery voltage reaches 2.5 V, and then paused for 30 minutes. The above charge and discharge cycles are implemented 3 times to fabricate a laminated battery with a battery capacity of 30 mAh.

[0341] (vii) Initial resistance value of the evaluation battery

[0342] For the evaluation battery fabricated in (vi) above, in an environment at 25 °C, using a battery tester (Battery HiTester) BT3561 manufactured by Hioki E.E. Corporation, resistance measurement is carried out under the condition that the AC frequency is 1 kHz.

[0343] In the same manner as in (i) to (vi) above, an evaluation battery is fabricated with an aluminum foil of 15 μm thickness for the positive electrode and a copper foil of 15 μm thickness for the negative electrode, and the initial resistance value is measured in the same way.

[0344] Let the initial resistance value of the evaluation battery using the metal foil be R0, and the initial resistance value of the evaluation battery using the polyester film in the present invention be R1. Use R1 / R0 (%) which represents the relative ratio of the two in percentage and evaluate as follows. The closer R1 / R0 is to 100%, the smaller the initial resistance value of the current collector using the polyester film. Five evaluation batteries are evaluated, and the average value of these is taken as the initial resistance value of the sample.

[0345] A: R1 / R0 is 103% or less.

[0346] B: R1 / R0 exceeds 103% and is 110% or less.

[0347] C: R1 / R0 exceeds 110% and is 200% or less.

[0348] D: R1 / R0 exceeds 200%.

[0349] As the initial resistance evaluation, A to C are good, with A being the best.

[0350] (viii) Electrolysis resistance

[0351] Perform the following charge and hold treatment on the evaluation battery fabricated in (vi) above. In an environment of 35 °C, perform constant current charging on the evaluation battery at a current value of 30 mA until the battery voltage reaches 4.2 V. Subsequently, maintain the constant voltage charging state of 4.2 V for 2 weeks (336 hours), and then pause for 30 minutes. Thereafter, perform low current discharge at a current value of 30 mA until the battery voltage reaches 2.5 V, and pause for 30 minutes.

[0352] Fabricate 10 evaluation batteries in accordance with the descriptions in (ii) to (vi) above. Disassemble the evaluation batteries that have undergone the above treatment, and for each cross-section of the positive electrode resin current collector and the negative electrode resin current collector, observe using an optical microscope to confirm whether voids with a circle equivalent diameter of 1 μm or more have occurred in the polyester film used in the resin current collector.

[0353] For the positive electrode resin current collector and the negative electrode resin current collector of 10 evaluation batteries, respectively confirm whether voids have occurred, and evaluate as follows.

[0354] A: Among 10, there are 3 or fewer evaluation batteries in which voids occurred after the 2-week charge and hold treatment.

[0355] B: Among 10, there are 4 or more and 6 or fewer evaluation batteries in which voids occurred after the 2-week charge and hold treatment.

[0356] C: Among 10, there are 7 or more and 8 or fewer evaluation batteries in which voids occurred after the 2-week charge and hold treatment.

[0357] D: Among 10, there are 9 or more evaluation batteries in which voids occurred after the 2-week charge and hold treatment.

[0358] As the electrolysis resistance, A to C are good, with A being the best.

[0359] (ix) Discharge capacity retention rate after 500 charge and discharge cycles

[0360] Perform the following charge and discharge operations on the evaluation battery fabricated in (vi) above.

[0361] (Charge and discharge operations)

[0362] Constant current charging is carried out at a current value of 30 mA in an environment of 35 °C until the battery voltage reaches 4.2 V. Then, constant voltage charging is carried out at 4.2 V until the current value becomes 6 mA, and charging is paused for 30 minutes. Thereafter, low current discharging is carried out at a current value of 30 mA until the battery voltage reaches 2.5 V, and discharging is paused for 30 minutes. The above operations are regarded as one cycle.

[0363] The above charge and discharge operations are carried out 500 cycles, and the discharge capacity in the initial state and after 500 charge and discharge cycle tests is obtained. The relative amount of the discharge capacity after 500 charge and discharge cycle tests with respect to the initial discharge capacity is regarded as the discharge capacity retention rate (%) and is evaluated as follows.

[0364] A: The discharge capacity retention rate after 500 charge and discharge cycle tests is 90% or more.

[0365] B: The discharge capacity retention rate after 500 charge and discharge cycle tests is 85% or more and less than 90%.

[0366] C: The discharge capacity retention rate after 500 charge and discharge cycle tests is 80% or more and less than 85%.

[0367] D: The discharge capacity retention rate after 500 charge and discharge cycle tests is less than 80%.

[0368] (x) Battery shock durability of 500 charge and discharge cycle tests

[0369] Sampling is carried out from 10 different parts of a polyester film having metal layers on both sides, and 10 evaluation batteries are manufactured according to the items (i) to (vi) above. Thereafter, the 500 charge and discharge cycle tests described in the item (ix) are carried out.

[0370] Subsequently, according to the impact test described in JIS8715-2 (2019), 10 evaluation batteries are placed on a flat concrete floor in a state where they are discharged to 50% of the rated capacity. A SUS316 round bar with a diameter of 15.8 mm and longer than the maximum size of the evaluation battery is set so as to straddle the center of the evaluation battery, and a heavy object with a mass of 9.1 kg is dropped from a height of 610 mm onto the round bar. The discharge capacity of 10 evaluation batteries is measured, and the average value thereof is obtained. The discharge capacity retention rate before and after the impact test obtained by dividing the average value of the discharge capacity after the impact test by the average value of the discharge capacity before the impact test is evaluated according to the following conditions.

[0371] A: The discharge capacity retention rate before and after the impact test is 90% or more.

[0372] B: The discharge capacity retention rate before and after the impact test is 70% or more and less than 90%.

[0373] C: The discharge capacity retention rate before and after the collision test is 50% or more and less than 70%.

[0374] D: The discharge capacity retention rate before and after the collision test is less than 50%.

[0375] As for the battery shock durability, A to C are good, and among them, A is the most excellent.

[0376] (xi) Battery heating deformation durability of 500 charge and discharge cycle tests

[0377] Samples are taken from 10 different parts of the laminated polyester film having metal layers on both sides, and 10 evaluation batteries are manufactured according to the items (i) to (vi) above. Thereafter, the 500 charge and discharge cycle test described in the item (ix) is carried out.

[0378] Subsequently, according to the heating test described in JIS8715-2 (2019), for the 10 evaluation batteries in a fully charged state, in a wind circulation type constant temperature bath, the temperature is raised from 25 °C to 85 °C at a rate of 5 °C per minute. After the evaluation batteries are held for 3 hours, they are taken out from the constant temperature bath, the discharge capacity of the 10 evaluation batteries is measured, and the average value thereof is obtained. The discharge capacity retention rate before and after the heating test, which is obtained by dividing the average value of the discharge capacity after the heating test by the average value of the discharge capacity before the heating test, is evaluated according to the following states.

[0379] A: The discharge capacity retention rate before and after the heating test is 90% or more.

[0380] B: The discharge capacity retention rate before and after the heating test is 70% or more and less than 90%.

[0381] C: The discharge capacity retention rate before and after the heating test is 50% or more and less than 70%.

[0382] D: The discharge capacity retention rate before and after the heating test is less than 50%.

[0383] As for the battery heating deformation durability, A to C are good, and among them, A is the most excellent.

[0384] Examples

[0385] Hereinafter, examples are given to illustrate the present invention, but the present invention is not necessarily limited to these examples.

[0386] [Manufacture of Polyester-1]

[0387] With respect to 1 mol of a dicarboxylic acid component containing 0.95 mol of dimethyl terephthalate (DMT) and 0.05 mol of dimethyl isophthalate, 1.9 mol of cyclohexanedimethanol was added, and with respect to 100 parts by mass of the dicarboxylic acid component, 0.05 part by mass of magnesium acetate tetrahydrate and 0.015 part by mass of phosphoric acid were added, followed by heating for transesterification. Subsequently, 0.025 part by mass of antimony trioxide was added, and the temperature was raised by heating, and polycondensation was carried out under a high vacuum state to obtain particles of a copolycyclohexanedimethylene terephthalate resin substantially free of particles, i.e., polyester-1. The glass transition temperature of polyester-1 was 92 °C, the melting peak temperature was 285 °C, the intrinsic viscosity was 0.95 dl / g, and the water content was 1900 mass ppm.

[0388] [Manufacture of Polyester-2]

[0389] With respect to 1 mol of dimethyl terephthalate (DMT), 1.9 mol of ethylene glycol was added, and with respect to 100 parts by mass of dimethyl terephthalate (DMT), 0.05 part by mass of magnesium acetate tetrahydrate and 0.015 part by mass of phosphoric acid were added, followed by heating for transesterification. Subsequently, 0.025 part by mass of antimony trioxide was added, and the temperature was raised by heating, and polycondensation was carried out under a high vacuum state to obtain particles of polyethylene terephthalate resin substantially free of particles, i.e., polyester-2. The glass transition temperature of polyester-2 was 78 °C, the melting peak temperature was 255 °C, the intrinsic viscosity was 0.70 dl / g, and the water content was 4300 mass ppm.

[0390] [Manufacture of Polyester-3]

[0391] With respect to 1 mol of a dicarboxylic acid component containing 0.95 mol of dimethyl terephthalate (DMT) and 0.05 mol of dimethyl isophthalate, 1.24 mol of cyclohexanedimethanol and 0.66 mol of ethylene glycol were added, and with respect to 100 parts by mass of the dicarboxylic acid component, 0.05 part by mass of magnesium acetate tetrahydrate and 0.015 part by mass of phosphoric acid were added, followed by heating for transesterification. Subsequently, 0.025 part by mass of antimony trioxide was added, and the temperature was raised by heating, and polycondensation was carried out under a high vacuum state to obtain particles of polyester-3. Polyester-3 is a copolycyclohexanedimethylene terephthalate (PCT) resin having 67 mol% of cyclohexanedimethanol component and 33 mol% of ethylene glycol component as the glycol component. The glass transition temperature of polyester-3 obtained by adjusting the polymerization time was 84 °C, the melting peak temperatures were 167 °C and 215 °C, the intrinsic viscosity was 0.75 dl / g, and the water content was 2100 mass ppm.

[0392] [Manufacture of Polyester-4]

[0393] With respect to 1 mole of dimethyl terephthalate (DMT), 1.9 moles of ethylene glycol were added, and with respect to 100 parts by mass of dimethyl terephthalate (DMT), 0.05 part by mass of magnesium acetate tetrahydrate and 0.015 part by mass of phosphoric acid were added, and transesterification was carried out by heating. Subsequently, 0.025 part by mass of antimony trioxide was added, the temperature was raised by heating, and polycondensation was carried out under a high vacuum state to obtain particles of polyester-4 substantially free of particles. The glass transition temperature of polyester-4 obtained by adjusting the polymerization time was 78 °C, the melting peak temperature was 255 °C, the intrinsic viscosity was 0.83 dl / g, and the water content was 4300 mass ppm.

[0394] [Production of Polyester-5]

[0395] With respect to 1 mole of a dicarboxylic acid component containing 0.95 mole of dimethyl terephthalate (DMT) and 0.05 mole of dimethyl isophthalate, 0.66 mole of cyclohexanedimethanol and 1.24 moles of ethylene glycol were added, and with respect to 100 parts by mass of the dicarboxylic acid component, 0.05 part by mass of magnesium acetate tetrahydrate and 0.015 part by mass of phosphoric acid were added, and transesterification was carried out by heating. Subsequently, 0.025 part by mass of antimony trioxide was added, the temperature was raised by heating, and polycondensation was carried out under a high vacuum state to obtain particles of polyester-5 substantially free of particles. Polyester-5 is a copolyethylene terephthalate resin having 33 mol% of a cyclohexanedimethanol component and 67 mol% of an ethylene glycol component as the glycol component. The glass transition temperature of polyester-5 obtained by adjusting the polymerization time was 81 °C, the melting peak temperature was 250 °C, the intrinsic viscosity was 0.75 dl / g, and the water content was 3900 mass ppm.

[0396] [Production of Polyester-6]

[0397] As a polyester polymerization catalyst, a polymerization catalyst described in Example 1 of Japanese Patent Laid-Open No. 2006-299222, which is a product obtained by reacting a silicon compound, a phosphorus compound and a titanium compound, was used. Except for this, in the same manner as in the above polyester-1, a copolycyclohexanedimethylene terephthalate resin containing a silicon element, that is, polyester-6, was obtained. The glass transition temperature of polyester-6 was 83 °C, the melting peak temperature was 280 °C, the intrinsic viscosity was 0.95 dl / g, and the water content was 1900 mass ppm.

[0398] [Production of Polyester-7]

[0399] With respect to 1 mole of dimethyl 2,6-naphthalenedicarboxylate (2,6-dimethyl naphthalate, 2,6DMN), 1.9 moles of ethylene glycol was added. Other than that, particles-free polyethylene naphthalate resin, i.e., polyester-7 particles, were obtained in the same manner as polyester-2. The glass transition temperature of polyester-7 obtained by adjusting the polymerization time was 115 °C, the melting peak temperature was 265 °C, the intrinsic viscosity was 0.86 dl / g, and the water content was 2200 mass ppm.

[0400] [Manufacture of Polyester-8]

[0401] With respect to a mixture of 0.66 moles of dimethyl 2,6-naphthalenedicarboxylate (2,6DMN) and 0.33 moles of dimethyl terephthalate (DMT), 1.9 moles of ethylene glycol was added. Other than that, particles-free polyester-8 particles were obtained in the same manner as polyester-7. Here, polyester-8 is a copolyethylene naphthalate resin having 67 mol% of 2,6-naphthalenedicarboxylic acid component and 33 mol% of terephthalic acid component as the dicarboxylic acid component. The glass transition temperature of polyester-8 was 110 °C, the melting peak temperature was 260 °C, the intrinsic viscosity was 0.75 dl / g, and the water content was 2400 mass ppm.

[0402] [Manufacture of Polyester-9]

[0403] With respect to a mixture of 0.33 moles of dimethyl 2,6-naphthalenedicarboxylate (2,6DMN) and 0.66 moles of dimethyl terephthalate (DMT), 1.9 moles of ethylene glycol was added. Other than that, particles-free polyester-9 particles were obtained in the same manner as polyester-7. Here, polyester-9 is a copolyethylene terephthalate resin having 33 mol% of 2,6-naphthalenedicarboxylic acid component and 67 mol% of terephthalic acid component as the dicarboxylic acid component. The glass transition temperature of polyester-9 was 89 °C, the melting peak temperature was 258 °C, the intrinsic viscosity was 0.70 dl / g, and the water content was 4000 mass ppm.

[0404] [Manufacture of Polyester-10]

[0405] Relative to 1 mole of a dicarboxylic acid component containing 0.67 moles of dimethyl terephthalate (DMT) and 0.33 moles of dimethyl isophthalate, 1.9 moles of cyclohexanedimethanol was added, and relative to 100 parts by mass of the dicarboxylic acid component, 0.05 part by mass of magnesium acetate tetrahydrate and 0.015 part by mass of phosphoric acid were added, and transesterification was carried out by heating. Subsequently, 0.025 part by mass of antimony trioxide was added, the temperature was raised by heating, and polycondensation was carried out under a high vacuum state to obtain particles of a copolycyclohexanedimethylene terephthalate resin, namely polyester-10, which is substantially free of particles and has a higher amount of isophthalic acid modification than polyester-1. Polyester-10 is an amorphous resin, having a glass transition temperature of 86 °C, an inherent viscosity of 0.72 dl / g, and a moisture content of 1800 mass ppm.

[0406] (Example 1)

[0407] As described in the table, after polyester-1 was dried under reduced pressure at 180 °C for 2 hours and 30 minutes, it was supplied to an extruder, melt-extruded and filtered using a filter, and then wound around a cooling casting roll maintained at 25 °C by electrostatic application casting method via a T-die and cooled and solidified to obtain an unoriented film. For the unoriented film, according to the film-forming conditions in the table, it was first introduced in the longitudinal direction into a set of stretching rolls heated to 60 °C to 120 °C and stretched 3.0 times by stretching operation. Thereafter, the uniaxially stretched film was introduced into a tenter, preheated at 90 °C, and then stretched 3.5 times in the width direction at a temperature of 100 °C to 130 °C, heat-treated at 230 °C at a fixed length, and relaxed 4% in the width direction, thereby obtaining a biaxially oriented polyester film with a thickness of 5 μm. The results of the evaluation are as described in the table.

[0408]

[0409] [Table 1-2] [Table 1-2]

[0410]

[0411]

[0412] [Table 2-2] [Table 2-2]

[0413]

[0414]

[0415] [Table 4-1] [Table 4-1]

[0416]

[0417] [Table 4-2] [Table 4-2]

[0418]

[0419]

[0420] The metal layers are provided on the surfaces of both sides of the obtained polyester film by vacuum evaporation such that the thickness of the metal layer becomes the thickness described in the table, and the metal type is set as described in the table, thereby manufacturing a resin current collector for the positive electrode and a resin current collector for the negative electrode. The results obtained by performing the above evaluation are as described in the table.

[0421]

[0422]

[0423] (Example 2)

[0424] The thickness of the polyester film is made thinner than that in Example 1 as described in the table. Except for this, the polyester film is obtained in the same manner as in Example 1, and the evaluation is performed in the same manner.

[0425] (Example 3)

[0426] Regarding the structure of the polyester film, it is set to have a three-layer structure with a layer B using PET, i.e., polyester-2, as a raw material as described in the table. Except for this, the polyester film is obtained in the same manner as in Example 1, and the evaluation is performed in the same manner.

[0427] (Example 4)

[0428] Regarding the structure of the polyester film, it is set to have a three-layer structure formed according to the film-forming conditions described in the table using PET, i.e., polyester-2, a copolymerized PCT component, i.e., polyester-3, and a copolymerized PET component, i.e., polyester-4, as raw materials. Except for this, the polyester film is obtained in the same manner as in Example 3, and the evaluation is performed in the same manner.

[0429] (Examples 5 and 6)

[0430] Regarding the structure of the polyester film, it is set to have a three-layer structure formed according to the film-forming conditions described in the table using PET, i.e., polyester-2, copolymerized PCT, i.e., polyester-3, and copolymerized PET, i.e., polyester-4, as raw materials and by changing the blending amounts. Except for this, the polyester film is obtained in the same manner as in Example 4, and the evaluation is performed in the same manner.

[0431] (Example 7)

[0432] A polyester film identical to that in Example 1 is formed, and the thickness of the metal layer provided on layer A is increased to 2 μm as described in the table. The evaluation is performed in the same manner.

[0433] (Example 8)

[0434] Regarding the structure of the polyester film, as shown in the table, PCT resin (i.e., polyester - 6) produced using a silicon catalyst was used as the raw material. Except for this, a polyester film was obtained in the same manner as in Example 1 and evaluated in the same manner.

[0435] (Examples 9 and 10)

[0436] In Example 9, regarding the structure of the polyester film, as shown in the table, PEN resin (i.e., polyester - 7) was used as the raw material, and the film - forming conditions recorded in the table were set. Except for this, a polyester film was obtained in the same manner as in Example 1 and evaluated in the same manner. Additionally, in Example 10, regarding the structure of the polyester film, as shown in the table, polyester - 8 was used as the raw material in layer A, and polyester - 2 and polyester - 9 were used as the raw materials in layer B. The longitudinal stretching temperature was appropriately adjusted within the range of 100°C to 145°C, and the transverse stretching temperature was appropriately adjusted within the range of 100°C to 140°C, and the film - forming conditions recorded in the table were set. Except for this, a polyester film was obtained in the same manner as in Example 1 and evaluated in the same manner.

[0437] (Example 11)

[0438] In Example 11, regarding the structure of the polyester film, as shown in the table, it was set to have a structure including layer A and layer B, and the film - forming conditions recorded in the table were set. Except for this, a polyester film was obtained in the same manner as in Example 1 and evaluated in the same manner. Layer A has PCT resin (i.e., polyester - 1) as the main component, and layer B has PCT resin with a higher isophthalic acid component ratio than layer A by mixing polyester - 1 and polyester - 10 as the main component.

[0439] (Comparative Example 1)

[0440] Regarding the constituent components of the polyester film, as shown in the table, PET (i.e., polyester - 2) was used as the raw material. Except for this, a polyester film was obtained in the same manner as in Example 1 and evaluated in the same manner.

[0441] Explanation of the reference numerals in the drawings

[0442] 1. The vertical axis reflecting the current value per unit area observed in the CV measurement

[0443] 2. The horizontal axis reflecting the applied potential with the redox potential of lithium metal in the CV measurement set as 0V as a reference

[0444] 3. The curve obtained by plotting the current value per unit area with respect to the applied potential obtained through the CV measurement

[0445] 4. The current - value peak where the current value observed in the CV measurement becomes the minimum

[0446] 5. The current - value peak in the region where the current value observed in the CV measurement becomes the maximum

[0447] 6. The absolute value in the current value observed in the CV measurement becomes the maximum value (maximum reduction current peak intensity).

Claims

1. A current collector having a layer (M layer) containing a metal and / or a metal-based compound and a polyester film, and the maximum reduction current peak intensity in cyclic voltammetry measurement (0.01 V to 2.0 V, 10 cycles) is 0.000 mA / cm 2 or more and 0.050 mA / cm 2 or less <Cyclic Voltammetry Measurement Method> The cyclic voltammetry measurement is carried out by the following methods (i) to (iii) to obtain the peak intensity of the maximum reduction current; (i) Fabrication of 2032 coin cell A sample with a copper metal layer provided on the surface of the current collector by sputtering is punched into a circle with a diameter of 16 mm; on the surface of the copper metal layer of the punched sample, a polyethylene separator with a diameter of 18 mm, a lithium metal foil with a diameter of 16.1 mm, and two stainless steel plates (SUS304) are sequentially laminated, and the following electrolyte is sealed to fabricate a 2032 coin cell; at this time, the surface of the current collector on the side opposite to the surface where the polyethylene separator is laminated is brought into contact with the outer package of the 2032 coin cell; (Electrolyte composition) · Electrolyte: 1 mol / L lithium hexafluorophosphate (LiPF6) · Solvent: A 1:1 (volume%) mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) · Blending environment: Conducted in an argon circulation type glove box with a dew point of -70°C or lower and an oxygen concentration of 10 volume ppm or lower; (ii) Cyclic voltammetry measurement Using the type 2032 coin cell obtained in item (i) above, cyclic voltammetry measurements using a VSP manufactured by Biologic were carried out under the following conditions; the current value (mA) observed by a potential sweep operation in which the redox potential of lithium metal was set to 0 V as a reference was divided by the sample area (2.01 cm 2 ), and thereby the current value per unit area (mA / cm 2 ) was obtained; (Measurement conditions) · Test temperature: 25°C ·Potential scanning range: 0.01V - 2.0V (v.s. Li + / Li) · Scanning rate: 1 mV / s · Number of cycles: 10 cycles (iii) Peak intensity of the maximum reduction current Take the current value per unit area (mA / cm 2 ) obtained in the above item (ii) whose absolute value is the largest as the maximum reduction current peak intensity per unit area (mA / cm 2 ) for calculation.

2. The current collector according to claim 1, having at least one layer mainly composed of a polyester resin (resin α) containing a dicarboxylic acid component and a diol component having 3 or more and 16 or less carbon atoms.

3. The current collector according to claim 1 or 2, wherein M layers are provided on the surfaces on both sides of the polyester film.

4. The current collector according to claim 1 or 2, wherein M layers are provided on the surfaces on both sides of the polyester film, and at least one of the layers on one side of the surface M layer is a layer containing copper element.

5. The current collector according to claim 2, wherein M layers are provided on the surfaces on both sides of the polyester film, at least one of the layers on one side of the surface M layer is a layer containing copper element, and the layer containing copper element is in contact with the layer mainly composed of the resin α.

6. The current collector according to claim 1, having at least one layer mainly composed of a polyester resin (resin β) containing a diol component and a dicarboxylic acid component having 9 or more and 16 or less carbon atoms.

7. The current collector according to claim 6, wherein M layers are provided on the surfaces on both sides of the polyester film, at least one of the layers on one side of the surface M layer is a layer containing copper element, and the layer containing copper element is in contact with the layer mainly composed of the resin β.

8. A current collector satisfying the following (1) and (2), (1) The layer on at least one side surface of the polyester film is a layer (P1 layer) mainly composed of a polyester resin (resin α) containing a dicarboxylic acid component and a diol component having 3 or more and 16 or less carbon atoms, or a layer mainly composed of a polyester resin (resin β) containing a diol component and a dicarboxylic acid component having 9 or more and 16 or less carbon atoms; (2) Layers (M layers) containing a metal and / or a metal-based compound are provided on the surfaces on both sides of the polyester film.

9. The current collector according to claim 8, wherein the M layer on at least one side is in contact with the P1 layer, and the M layer in contact with the P1 layer is a layer containing copper element.

10. The current collector according to claim 1 or 8, wherein the thickness of the M layer is 0.1 μm or more and 5.0 μm or less.

11. The current collector according to claim 1 or 8, wherein the main component of the polyester film is any one of cyclohexanedimethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate.

12. The current collector according to claim 11, wherein the main component of the polyester film is cyclohexanedimethylene terephthalate or polybutylene terephthalate.

13. The current collector according to claim 1 or 8, wherein the polyester film has a layer (P1 layer) mainly composed of a polyester resin (resin α) containing a dicarboxylic acid component and a glycol component having 3 or more and 16 or less carbon atoms, or a polyester resin (resin β) containing a glycol component and a dicarboxylic acid component having 9 or more and 16 or less carbon atoms, and has a resin layer (P2 layer) not mainly composed of resin α or resin β.

14. The current collector according to claim 1 or 8, wherein M layers are provided on both surfaces of the polyester film, and the adhesion force between the surface of the polyester film and the M layer is 2 N / 15 mm or more and 5 N / 15 mm or less on both sides.

15. The current collector according to claim 1 or 8, wherein the breaking strength in at least one of the long side direction and the width direction in the plane of the film is 150 MPa or more and 400 MPa or less.

16. The current collector according to claim 1 or 8, wherein the elongation at break in at least one of the long side direction and the width direction in the plane of the film is 35% or more and 150% or less.

17. The current collector according to claim 1 or 8, wherein when the polyester film is analyzed under the following conditions using inductively coupled plasma optical emission spectrometry (inductively coupled plasma-atomic emission spectrometry), the silicon element content in the polyester film is 0 mass ppm or more and 10 mass ppm or less, <Analysis conditions> Apparatus: Inductively coupled plasma optical emission analysis (manufactured by Hitachi High-Technologies Science Corporation) PS3520VDDII Preparation of sample: Weigh the current collector in a beaker, decompose it under pressure with sulfuric acid and then with nitric acid, and then heat it to ashing; dissolve the ash with a mixed flux of sodium carbonate and boric acid, dissolve it by heating with dilute nitric acid, and make the volume constant at 10 mL; thereafter, for the solution diluted with dilute nitric acid, measure the amount of silicon element by inductively coupled plasma optical emission spectrometry as the silicon element content in the polyester film; (Measurement conditions) Measurement wavelength: 251.6 nm High-frequency output: 1.2 kW Plasma gas flow rate: 16 L / min Auxiliary gas flow rate: 0.5 L / min Carrier gas flow rate: 0.9 L / min Optical measurement height: 12 mm.

18. A polyester film, the maximum reduction current peak intensity in cyclic voltammetry measurement (0.01 V to 2.0 V, 10 cycles) is 0.000 mA / cm 2 or more and 0.050 mA / cm 2 or less. <Cyclic voltammetry measurement method> Perform cyclic voltammetry measurement by the following methods (i) to (iii) to obtain the maximum reduction current peak intensity; (i) Fabrication of CR2032 coin cell A copper metal layer is deposited on the surfaces of both sides of a polyester film by sputtering method, and then punched into a circular sample with a diameter of 16 mm. On the surface of the copper metal layer of the punched sample, a polyethylene separator with a diameter of 18 mm, a lithium metal foil with a diameter of 16.1 mm, and two stainless steel plates (made of SUS304) are sequentially laminated, and the following electrolyte is sealed to fabricate a CR2032 coin cell. At this time, the surface of the copper metal layer on the side opposite to the surface where the polyethylene separator is laminated is brought into contact with the outer package of the CR2032 coin cell. (Electrolyte composition) · Electrolyte: 1 mol / L lithium hexafluorophosphate (LiPF6) · Solvent: A 1:1 (volume %) mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) · Blending environment: Conducted in an argon circulation type glove box with a dew point of -70 °C or lower and an oxygen concentration of 10 volume ppm or lower. (ii) Cyclic voltammetry measurement Using the type 2032 coin cell obtained in item (i) above, cyclic voltammetry measurements were performed using a VSP manufactured by Biologic under the following conditions; the current value (mA) observed by the potential sweep operation with the redox potential of lithium metal set as the reference 0 V was divided by the sample area (2.01 cm 2 ), and the current value per unit area (mA / cm 2 ) was thus obtained; (Measurement conditions) · Test temperature: 25 °C ·Potential scanning range: 0.01V - 2.0V (v.s. Li + / Li) · Scanning rate: 1 mV / s · Number of cycles: 10 cycles (iii) Maximum reduction current peak intensity The current value per unit area (mA / cm 2 ) obtained in the item (ii) is taken as the current value with the largest absolute value among them as the maximum reduction current peak intensity (mA / cm 2 ) for calculation.

19. The polyester film according to claim 18 has at least one layer mainly composed of a polyester resin (resin α) containing a dicarboxylic acid component and a diol component having 3 or more and 16 or less carbon atoms.

20. The polyester film according to claim 18 has at least one layer mainly composed of a polyester resin (resin β) containing a diol component and a dicarboxylic acid component having 9 or more and 16 or less carbon atoms.

21. The polyester film according to claim 18 or 19, wherein the thickness of the polyester film is 1 μm or more and 30 μm or less.

22. A current collector for a negative electrode, which is the current collector according to claim 1 or 8.

23. An energy storage element, comprising the current collector according to claim 1 or 8.

24. An energy storage element having a negative electrode active material layer on at least one surface of the current collector for a negative electrode according to claim 22.

25. An energy storage element having a laminate in which the current collector for a negative electrode, an electrolyte, a current collector for a positive electrode, and an electrolyte according to claim 22 are arranged in sequence, and comprising a structure in which at least the laminate is laminated two or more layers.

26. A secondary battery, comprising the energy storage element according to claim 23.

27. An electric vehicle, equipped with the secondary battery according to claim 26.

28. An electric flying vehicle, equipped with the secondary battery according to claim 26.

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