JP2017183230A - Separator for power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a power storage device with excellent adhesion with an electrode.SOLUTION: A separator for a power storage device includes a polyolefin microporous film, and thermoplastic polymer applied on at least a part of at least one surface of the polyolefin microporous film. The thermoplastic polymer has a tensile elasticity of 300 MPa or more and 3000 MPa or less at 25°C in the swelling state. The thermoplastic polymer has a sulfonyl group.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a separator for an electricity storage device and a lithium ion battery using the separator.

  In recent years, development of non-aqueous electrolyte batteries centering on lithium ion secondary batteries has been actively conducted. Usually, in a nonaqueous electrolyte battery, a microporous membrane (separator) is provided between positive and negative electrodes. The separator has a function of preventing physical contact between the positive and negative electrodes and allowing ions to permeate through the electrolytic solution held in the microporous film.

  In recent years, with the reduction in size and thickness of portable devices, power storage devices such as lithium ion secondary batteries are also required to be reduced in size and thickness. On the other hand, in order to make it possible to carry the device for a long time, an increase in the capacity by increasing the volume energy density has been attempted.

  Here, the separator has a characteristic that the battery reaction is quickly stopped when it is abnormally heated (fuse characteristic) or a dangerous situation in which the positive electrode material and the negative electrode material react directly while maintaining the shape even at high temperatures. In addition to performance related to safety, such as performance to prevent (short-circuit characteristics), and the like, from the viewpoint of uniform charge / discharge current and suppression of lithium dendrite, improvement in adhesion to the electrode is required.

  By improving the close contact between the separator and the battery electrode, it becomes difficult to make the charge / discharge current non-uniform, and it becomes difficult for lithium dendrite to precipitate, resulting in a longer charge / discharge cycle life. Become.

  Under such circumstances, an attempt to apply an adhesive polymer to a polyolefin microporous film has been made as an attempt to give the separator an adhesive property (see, for example, Patent Documents 1 and 2). In Patent Document 1, for the purpose of providing a secondary battery excellent in discharge characteristics and safety, a porous film in which an adhesive is supported by applying a reactive polymer on a porous film and drying is proposed. Has been. In patent document 2, it is proposed to arrange | position resin which expresses adhesiveness by heating to the at least single side | surface of a separator base material from a viewpoint of a high temperature storage characteristic, charging / discharging cycling characteristics, a load characteristic, and productivity.

JP 2007-59271 A JP 2011-54502 A

  However, the separator described in Patent Document 1 has a problem that the adhesion between the reactive polymer and the porous film is not sufficient, and therefore, the adhesion with the electrode is not sufficient. The separator described in Patent Document 2 still has room for improvement in terms of adhesion with the electrode.

  This invention is made | formed in view of the said problem, Comprising: It aims at providing the separator for electrical storage devices which is excellent in adhesiveness with an electrode.

As a result of intensive studies to achieve the above object, the present inventors have found that the above-mentioned problems can be solved by disposing a specific thermoplastic polymer on at least a part of at least one side of the polyolefin microporous membrane. .
That is, the present invention is as follows.
[1]
A separator for an electricity storage device, wherein at least a part of at least one surface of a polyolefin microporous membrane is coated with a thermoplastic polymer having a sulfonyl group and a tensile elastic modulus at 25 ° C. in a swollen state of 300 MPa to 3000 MPa. .
[2]
The separator for an electricity storage device according to [1], wherein the polymer is polyphenylsulfone.
[3]
The separator for an electricity storage device according to [1] or [2], wherein the polymer is formed in a microporous film shape or a dot shape.
[4]
Coating basis weight of the resin layer containing the polymer is 0.05 g / ^{m 2} or more 5.0 g / ^{m 2} or less, [1] an electric storage device separator as claimed in any one of - [3].
[5]
The separator for an electricity storage device according to [4], wherein the total thickness of the polyolefin microporous membrane and the resin layer is 5 μm or more and 25 μm or less.
[6]
The separator for an electricity storage device according to any one of [1] to [5], wherein the air permeability is 40 seconds / 100 cc or more and 1000 seconds / 100 cc or less.
[7]
The lithium ion battery containing the separator for electrical storage devices of any one of [1]-[6].

  According to the present invention, the adhesion between the separator and the electrode can be improved, thereby improving the cycle characteristics of the electricity storage device.

FIG. 1 shows a surface SEM image of the separator obtained in Example 1.

  Hereinafter, the best mode for carrying out the present invention (hereinafter abbreviated as “this embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

  The separator for an electricity storage device according to the present embodiment (hereinafter simply abbreviated as “separator”) includes a polyolefin microporous membrane and a swollen swelling that is immersed in an electrolyte solution on at least a part of at least one surface of the polyolefin microporous membrane. The room temperature tensile elastic modulus in the state is 300 MPa or more and 3000 MPa or less, and a thermoplastic polymer having a sulfonyl group is applied.

  The structure of the separator according to this embodiment that can improve the adhesion with the electrode and the cycle characteristics of the electricity storage device is the tensile elasticity of 300 MPa to 3000 MPa in the swollen state of the thermoplastic polymer disposed on the polyolefin microporous film. Specified by the rate and the sulfonyl group.

<Swelled state>
In the present embodiment, a state in which the thermoplastic polymer is immersed and swelled in the electrolytic solution of the electricity storage device is hereinafter abbreviated as “swelled state”. The electrolyte solution for the electricity storage device (hereinafter abbreviated as “electrolyte solution”) is not particularly limited, but a non-aqueous electrolyte solution in which an electrolyte is dissolved in an organic solvent can be used. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ , propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Moreover, a trace amount additive may be contained in the said electrolyte solution, As an additive, vinylene carbonate is mentioned, for example.

  The swollen state of the present embodiment means that the polymer of the present embodiment is immersed in the electrolyte solution and undergoes a certain heat history applied to develop adhesive force in the battery manufacturing process, and the shape change further occurs. This refers to the state of disappearance, for example, a state in which a non-porous membrane of polyphenylsulfone described later is immersed in an electrolyte at 25 ° C. for 24 hours or more.

<Thermoplastic polymer>
The thermoplastic polymer of this embodiment has a sulfonyl group. Since the sulfonyl group is a polar functional group having a strong interaction with the active material of the lithium ion battery, the adhesive strength at the interface between the electrode and the thermoplastic polymer layer is high. In addition, since the thermoplastic polymer of the present embodiment has a high tensile elastic modulus of 300 MPa to 3000 MPa in the swollen state, it can prevent cohesive failure of the polymer layer. Thereby, high adhesive peeling strength with respect to an electrode is realizable.
From the above viewpoint, the tensile elastic modulus at room temperature of the swelled thermoplastic polymer is preferably 400 MPa to 2900 MPa, more preferably 800 MPa to 2800 MPa. The method for obtaining the tensile elastic modulus and adhesive peel strength will be described in the examples described later.

As the thermoplastic polymer, a polysulfone resin is preferable, and the following formula:
The polyphenyl sulfone represented by these is more preferable.

  The molecular weight of the thermoplastic polymer is not particularly limited, but it is preferable that the weight average molecular weight is 100,000 or more and 1,000,000 or less from the viewpoint of solubility in a polymer solvent and film formability. The molecular weight can be measured by the method shown in Examples described later.

<Polyolefin microporous membrane>
The polyolefin microporous membrane according to this embodiment will be described. Although it does not specifically limit as a polyolefin microporous film of this embodiment, For example, the porous film comprised from the polyolefin resin composition containing polyolefin is mentioned, It is preferable that it is a porous film which has polyolefin resin as a main component. . In the present embodiment, the polyolefin microporous membrane is not particularly limited with respect to the content of the polyolefin resin, but from the viewpoint of shutdown performance when used as a separator for an electricity storage device, the mass fraction of all components constituting the porous membrane A porous film made of a polyolefin resin composition in which a polyolefin resin accounts for 50% or more and 100% or less is preferable. The proportion of the polyolefin resin is more preferably 60% or more and 100% or less, and still more preferably 70% or more and 100% or less.

  The polyolefin resin is not particularly limited, but refers to a polyolefin resin used for normal extrusion, injection, inflation, blow molding and the like, such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1 -Homopolymers and copolymers such as octene and multistage polymers can be used. In addition, polyolefins selected from the group consisting of these homopolymers and copolymers and multistage polymers can be used alone or in admixture.

  Representative examples of the polyolefin resin are not particularly limited, but for example, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene Random copolymer, polybutene, ethylene propylene rubber and the like can be mentioned.

  When the separator according to this embodiment is used as a battery separator, it is preferable to use a resin mainly composed of high-density polyethylene because of its low melting point and high strength.

  Moreover, it is more preferable to use the porous film which consists of a resin composition containing polypropylene and polyolefin resins other than a polypropylene from a viewpoint of the heat resistance improvement of a porous film.

  Here, the three-dimensional structure of polypropylene is not limited, and any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene may be used.

The ratio of polypropylene to the total polyolefin in the polyolefin resin composition is not particularly limited, but is preferably 1 to 35% by mass, more preferably 3 to 20% by mass from the viewpoint of achieving both heat resistance and a good shutdown function. %, More preferably 4 to 10% by mass.
In this case, the polyolefin resin other than polypropylene is not limited, and examples thereof include homopolymers or copolymers of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Specifically, examples of the polyolefin resin other than polypropylene include polyethylene, polybutene, and ethylene-propylene random copolymer.
From the viewpoint of shutdown characteristics that the pores of the microporous membrane are blocked by heat melting, polyolefins other than polypropylene include polyethylene such as low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, and ultra high molecular weight polyethylene. It is preferable to use it. Among these, from the viewpoint of strength, it is more preferable to use polyethylene having a density measured according to JIS K 7112 of 0.93 g / cm ³ or more.

  The viscosity average molecular weight of the polyolefin resin constituting the polyolefin microporous membrane is not particularly limited, but is preferably 30,000 or more and 12 million or less, more preferably 50,000 or more and less than 2 million, and still more preferably 100,000 or more and 1,000,000. Is less than. A viscosity average molecular weight of 30,000 or more is preferable because the melt tension during melt molding increases, moldability is improved, and the strength tends to increase due to entanglement between polymers. On the other hand, a viscosity average molecular weight of 12 million or less is preferable because uniform melt kneading is facilitated and the formability of the sheet, particularly thickness stability, tends to be excellent. Furthermore, when the viscosity average molecular weight is less than 1,000,000, it is preferable because the pores are likely to be blocked when the temperature rises and a good shutdown function tends to be obtained. For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000, the viscosity average molecular weight being less than 1 million Mixtures may be used.

  The polyolefin microporous membrane used in the present embodiment can contain any additive. The additive is not particularly limited, and examples thereof include polymers other than polyolefins; inorganic particles; antioxidants such as phenols, phosphoruss, and sulfurs; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; Examples thereof include a light stabilizer; an antistatic agent; an antifogging agent; and a coloring pigment.

  The total content of these additives is preferably 0.001 part by mass or more and 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass with respect to 100 parts by mass of the polyolefin resin composition. It is below mass parts.

<Coating layer>
The thermoplastic polymer of the present embodiment is coated on a polyolefin microporous film to form a microporous film-like or dot-like resin layer. By forming a microporous film-like or dot-like resin layer, high adhesive peel strength can be realized while ensuring an appropriate air permeability. From their point of view, the coating basis weight, it is preferably at 0.05 g / ^{m 2} or more 5.0 g / ^{m 2} or less, the total thickness of the polyolefin microporous film and the resin layer is 5μm or more 25μm or less preferable.

  An appropriate air permeability of the separator for the electricity storage device is important for ensuring ion conductivity in the lithium ion battery, but may be in the range of 40 (seconds / 100 cc) to 1000 (seconds / 100 cc). preferable. The air permeability can be measured by the method shown in Examples described later.

  The coating layer of a present Example may contain the filler comprised with an organic substance and / or an inorganic substance.

<Polymer dissolution method>
In this embodiment, the thermoplastic polymer is dissolved in a solvent prior to coating. The dissolution method is not particularly limited, but when preparing a polymer solution of polyphenylsulfone, the polymer and solvent are put in a predetermined container and dissolved while stirring. If the polymer does not dissolve at room temperature, the polymer is dissolved by heating.

  The type of the solvent is not particularly limited as long as the thermoplastic polymer is a soluble solvent. For example, when the polymer is polyphenylsulfone, specifically, N-methyl-2-pyrrolidone (hereinafter referred to as “N-methyl-2-pyrrolidone”) is used. N-alkylpyrrolidones such as “NMP”); and chains such as N, N-dimethylacetamide (hereinafter abbreviated as “DMAc”) and N, N-dimethylformamide (hereinafter abbreviated as “DMF”) And at least one solvent selected from the group of amide solvents. Among these, N-methyl-2-pyrrolidone is preferable from the viewpoint of solubility and industrial handling properties.

  The dissolution temperature varies depending on the type of solvent used or the ratio of the polymer, but is usually 10 ° C. or higher and 100 ° C. or lower, preferably 20 ° C. or higher and 30 ° C. or lower.

  The dissolution time varies depending on the type of solvent, the ratio of the polymer, or the dissolution temperature, but is usually in the range of 1 hour to 24 hours.

<Coating method>
In the present embodiment, the method for applying the thermoplastic polymer to the polyolefin microporous film is not particularly limited as long as it is a method capable of realizing a preferred basis weight, thickness, and / or air permeability in the present embodiment. Coating methods include, for example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method Squeeze coater method, cast coater method, die coater method, screen printing method, spray coating method, spray coater coating method, and ink jet coating. Among these, the gravure coater method or the spray coating method is preferable in that the degree of freedom of the coating shape of the thermoplastic polymer is high and a preferable area ratio can be easily obtained.

  The method for removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the porous film, but the coating film is immersed in a poor solvent for the thermoplastic polymer to solidify the thermoplastic polymer. At the same time, a method of extracting the solvent can be mentioned.

<Poor solvent>
The poor solvent varies depending on the type of the solvent used in the polymer solution or the type of the polymer, but is an alcohol solvent such as methanol, ethanol, 1-propanol, or 2-propanol; water or the like, and particularly from the viewpoint of industrial handling properties. Therefore, water is preferable.

  Further, from the viewpoint of the uniformity of the coated film after solidification, the poor solvent is preferably a solvent that is uniformly mixed with the solvent of the polymer solution. Here, “uniformly mixed” means that an interface does not appear even when two or more solvents are mixed and allowed to stand for one day. For example, for NMP, it can be cited as a solvent in which water is uniformly mixed.

  The poor solvent may be a single solvent or a mixture of two or more solvents as long as it is uniformly mixed with the solvent used for polymer dissolution. From the viewpoint of film uniformity, it is preferable to use water or a mixed solvent of water and NMP.

  The separator according to the present embodiment produced by the method described above is excellent in adhesion with the electrode and handling properties, and can be suitably used as a separator for an electricity storage device.

<Peel strength>
The separator according to this embodiment is laminated with an electrode in the presence of an electrolytic solution, and develops an adhesive force with the electrode by applying a predetermined temperature and pressure. The 90 ° peel strength after pressurizing the separator with the positive electrode and the negative electrode for 2 minutes at a temperature of 100 ° C. and a pressure of 10 MPa is preferably 3 gf / cm or more. Moreover, it is preferable that an electrode active material transfers to the separator surface after a 90 degree peeling test, and it adheres 10% or more in conversion of an area ratio. The 90 ° peel strength can be measured by the method described in the examples.

  A separator having a peel strength in the above range is preferable in terms of excellent adhesion between the electrode and the separator when applied to an electricity storage device described later.

<Coating weight>
Basis weight of the resin layer of the separator for an electricity storage device, from the viewpoint of adhesion peel strength and ionic conductivity, preferably 0.05 g / ^{m 2} or more 5.0 g / ^{m 2} or less, more preferably 0.1 g / ^{m 2} or more It is 2.0 g / m ² or less, more preferably 0.5 g / m ² or more and 1.5 g / m ² or less.

<Film thickness>
The film thickness of the separator for the electricity storage device is preferably 5 μm or more and 25 μm or less, more preferably 8 μm or more and 20 μm or less, and further preferably 10 μm or more and 15 μm or less from the viewpoint of securing the film strength and ionic conductivity. This film thickness may be the total value of the maximum thickness of the olefin microporous film and the maximum thickness of the resin layer when the separator is composed of the polyolefin microporous film described above and the resin layer described above. When the layer includes a layer other than the polyolefin microporous membrane and the resin layer, the maximum thickness of the separator may be sufficient.

<Air permeability>
The air permeability of the electricity storage device separator is preferably 1000 (seconds / 100 cc) or less from the viewpoint of ion conductivity. The lower limit value of the air permeability is not particularly limited, but 40 (seconds / 100 cc) or more is preferable from the viewpoint of the film thickness to ensure the minimum film strength. The air permeability is more preferably 40 (seconds / 100 cc) to 300 (seconds / 100 cc), and still more preferably 40 (seconds / 100 cc) to 250 (seconds / 100 cc).

<Laminated body>
The laminate according to this embodiment is a laminate of the separator and the electrode. The separator according to the present embodiment can be used as a laminate by adhering to an electrode. Here, “adhesion” means that the 90 ° C. peel strength between the separator and the electrode is 3 gf / cm or more.

  The laminate is excellent in handling property at the time of winding and rate characteristics of the electricity storage device, and further excellent in adhesion and permeability between the thermoplastic polymer and the polyolefin microporous film. Therefore, the use of the laminate is not particularly limited, but can be suitably used for, for example, a battery such as a non-aqueous electrolyte secondary battery, or an electric storage device such as a capacitor and a capacitor.

  As an electrode used for the laminated body according to the present embodiment, an electrode described in an item of an electricity storage device described later can be used.

  The method for producing a laminate using the separator according to the present embodiment is not particularly limited. For example, the separator and the electrode according to the present embodiment may be stacked and heated and pressurized as necessary. it can. Moreover, it can also manufacture by heating and pressurizing with respect to the winding body obtained by winding up an electrode and a separator and winding in a circular or flat spiral shape.

  Moreover, a laminated body can also be manufactured by laminating | stacking in the shape of a flat plate in order of a positive electrode-separator-negative electrode-separator, or a negative electrode-separator-positive electrode-separator, and heating and / or pressing as needed.

  More specifically, the separator according to this embodiment is prepared as a vertically long separator having a width of 10 mm to 500 mm (preferably 80 mm to 500 mm) and a length of 200 m to 4000 m (preferably 1000 m to 4000 m). Can be manufactured by stacking in the order of positive electrode-separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator, and heating and pressurizing as necessary.

  The heating temperature of the laminate or the wound body is preferably 40 ° C to 120 ° C. The heating time of the laminate or the wound body is preferably 5 seconds to 30 minutes. The pressure applied to the laminate or the wound body is preferably 1 MPa to 30 MPa. The pressurization time of the laminate or wound body is preferably 5 seconds to 30 minutes.

<Power storage device>
The separator according to the present embodiment can be used for a separator in a battery, a capacitor, a capacitor, or the like, or a substance separation. In particular, when the separator is used for a non-aqueous electrolyte battery, it is possible to impart adhesion to the electrode and excellent battery performance.

  Hereinafter, a suitable mode in the case where the electricity storage device is a non-aqueous electrolyte secondary battery will be described.

  When manufacturing a non-aqueous electrolyte secondary battery using the separator according to this embodiment, the positive electrode, the negative electrode, and the non-aqueous electrolyte are not limited, and known ones can be used.

<Electrode>
The positive electrode material of the nonaqueous electrolyte secondary battery is not particularly limited, and examples thereof include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO ₄ .

  The negative electrode material is not particularly limited, and examples thereof include carbon materials such as graphite, non-graphitizable carbonaceous, graphitizable carbonaceous, and composite carbon bodies; silicon, tin, metallic lithium, various alloy materials, and the like.

The nonaqueous electrolytic solution is not particularly limited, but an electrolytic solution in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

  A method for manufacturing an electricity storage device using the separator according to the present embodiment is not particularly limited. However, when the electricity storage device is a secondary battery, for example, the separator according to the embodiment is 10 mm to 500 mm wide (preferably 80 mm to 500 mm). ), Prepared as a vertically long separator having a length of 200 m to 4000 m (preferably 1000 m to 4000 m). It can be manufactured by winding into a circular or flat spiral shape to obtain a wound body, storing the obtained wound body in a battery can, and further injecting an electrolyte. Under the present circumstances, you may form the above-mentioned laminated body by heating and pressurizing with respect to a winding body. Moreover, it can also manufacture using what wound the above-mentioned laminated body in the shape of a circle or a flat spiral as said winding body. In addition, the electricity storage device is obtained by laminating a positive electrode-separator-negative electrode-separator, or a negative electrode-separator-positive electrode-separator in the order of a flat plate, or laminating the above laminate with a bag-like film, and injecting an electrolytic solution. It can also be manufactured through a process and optionally a process of heating and / or pressing. The step of performing the above heating and / or pressing can be performed before and / or after the step of injecting the electrolytic solution.

  In addition, about the measured value of various parameters mentioned above, unless there is particular notice, it is a value measured according to the measuring method in the Example mentioned later.

Hereinafter, examples and comparative examples will be described. In addition, this embodiment is not limited to a following example, unless the summary is exceeded.
In addition, the physical property in an Example was measured with the following method.

(1) Viscosity average molecular weight (Mv)
Based on ASTM-D4020, the intrinsic viscosity [η] at 135 ° C. in a decalin solvent was determined, and Mv of polyethylene was calculated by the following equation.
[Η] = 6.77 × 10 ⁻⁴ × Mv ^0.67
Mv of polypropylene was calculated from the following formula.
[Η] = 1.10 × 10 ⁻⁴ Mv ^0.80

(2) Weight average molecular weight (Mw)
The weight average molecular weight (Mw) of the thermoplastic polymer was measured under the following conditions using gel permeation chromatography (GPC).
Solvent: 24.8 mmol / L lithium bromide monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) immediately before the measurement with respect to N, N-dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd., for high performance liquid chromatograph) Purity 99.5%) and 63.2 mmol / L phosphoric acid (manufactured by Wako Pure Chemical Industries, Ltd., for high performance liquid chromatography) Calibration curve: prepared using standard polystyrene (manufactured by Tosoh Corporation) Column: TSK-GEL SUPER HM-H
Flow rate: 0.5 ml / min Column temperature: 40 ° C
Pump: PU-2080 (manufactured by JASCO)
Detector: RI-2031Plus (RI: differential refractometer, manufactured by JASCO) and UV-2075Plus (UV-VIS: UV-visible absorptiometer, manufactured by JASCO)

(3) Film thickness (μm)
A 10 cm × 10 cm sample was cut out from the separator, nine locations (3 points × 3 points) were selected in a lattice shape, and the film thickness was measured at room temperature 23 ± 2 using a microthickness meter (Toyo Seiki Seisakusho Type KBM). Measured at ° C. The average value of the measured values at 9 locations was taken as the film thickness (μm) of the separator.

(4) Air permeability (sec / 100cc)
It was measured with Oken type air resistance meter EGO2 (Asahi Seiko Co., Ltd.) based on JIS P-8117.

(5) 90 ° peel strength (gf / mm)
a. Preparation of positive electrode 92.2% by mass of lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 2.3% by mass of flake graphite and acetylene black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder A slurry was prepared by dispersing 3.2% by mass in N-methylpyrrolidone (NMP). This slurry was applied to one side of a 20 μm thick aluminum foil serving as a positive electrode current collector with a die coater, dried at 130 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material application amount of the positive electrode was 250 g / m ² , and the bulk density of the active material was 3.00 g / cm ³ .

b. Preparation of Negative Electrode 96.9% by mass of artificial graphite as a negative electrode active material, and 1.4% by mass of ammonium salt of carboxymethyl cellulose and 1.7% by mass of styrene-butadiene copolymer latex as a binder were dispersed in purified water to prepare a slurry. Prepared. This slurry was applied to one side of a 12 μm thick copper foil serving as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material coating amount of the negative electrode was set to 106 g / m ² , and the active material bulk density was set to 1.35 g / cm ³ .

c. 90 ° peel strength (gf / mm) measurement The positive electrode and the negative electrode are cut into a width of 20 mm and a length of 40 mm. On this electrode, ethylene carbonate and ethyl methyl carbonate were mixed at a ratio (volume ratio) of 1: 2, and an electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L was soaked that the electrode was immersed, and on this, The separator was stacked. This laminate was put in an aluminum zip and pressed for 2 minutes under the conditions of 100 ° C. and 10 MPa to obtain a test sample. The 90 ° peel strength of the obtained sample was measured at a tensile speed of 10 mm / min according to JIS Z 0237 using a vertical electric measurement stand MX-500N manufactured by Imada Corporation. For each of the positive electrode and the negative electrode, the peel strength of the separator was evaluated according to the following evaluation criteria.
○ (Good): Peel strength is 3 gf / mm or more Δ (Acceptable): Peel strength is 1 gf / mm or more and less than 3 gf / mm × (Bad): Peel strength is less than 1 gf / mm

(6) Adhesion test In the 90 ° peel strength (gf / mm) measurement method described above, the separator after peeling off from the electrode is more closely adhered than the adhesion area ratio of the electrode active material transferred to the separator surface. Sex was evaluated.
○ (Good): When the electrode active material adheres to 30% or more of the separator.
Δ (Acceptable): When the electrode active material adheres to 10% or more and less than 30% of the separator.
X (defect): When an electrode active material adheres to less than 10% of a separator.

(7) Tensile modulus The thermoplastic polymer coating polymer solution is coated on a glass substrate using a bar coater, dried and dried under reduced pressure to remove the solvent, and the thermoplastic polymer having a thickness of 0.03 mm A nonporous membrane was obtained. The polymer solution can be prepared by the method described in each of the thermoplastic polymer separator production examples described later.

The thermoplastic polymer nonporous film was immersed in an electrolytic solution at 100 ° C. for 2 minutes, then cooled to 25 ° C. while immersed in the electrolytic solution, and immersed in the electrolytic solution for 24 hours to swell in the electrolytic solution. Here, the ratio of the resin non-porous film to the electrolytic solution during immersion was 10 parts by mass for the non-porous film and 90 parts by mass for the electrolytic solution. The swelling membrane was cut into a width of 10 mm and a length of 80 mm to obtain a measurement sample. Incidentally, the electrolyte, 1 ethylene carbonate and ethyl methyl carbonate: the mixed solvent at 2 ratio (volume ratio) was used to LiPF ₆ things dissolved 1 mol / L.

The tensile elastic modulus of the measurement sample was measured using a vertical electric measurement stand MX-500N manufactured by Imada Corporation. The sample was 30 mm between the chucks, and the measurement was performed at a temperature of 25 ° C. and a tensile speed of 30 mm / min.
The tensile modulus (MPa) was obtained by obtaining the slope of an approximate straight line between 1 to 4% in elongation and dividing by the cross-sectional area of the sample before the test in the stress-strain curve. Here, the elongation (%) was obtained by dividing the amount of elongation by the distance between chucks and multiplying by 100.

<Example 1>
14.25 parts by mass of high density polyethylene 1 having a viscosity average molecular weight of 250,000 and a melting point of 137 ° C., 14.25 parts by mass of high density polyethylene 2 having a viscosity average molecular weight of 700,000 and a melting point of 137 ° C., a viscosity average molecular weight of 400,000, a melting point of 163 A raw material containing 1.5 parts by mass of polypropylene at 0 ° C. and 0.2 parts by mass of tetrakis- [methylene- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane as an antioxidant A formulation was prepared.

  Each formulation was charged through a twin screw extruder feeder with a caliber of 25 mm L / D = 48. Further, 68 parts by mass of liquid paraffin was injected into each extruder by side feed, adjusted so that the extrusion amount was 16 kg per hour, kneaded under conditions of 200 ° C. and 200 rpm, and then 200 ° C. from the T die. Extruded under the conditions of Immediately, the extrudate was cooled and solidified with a cast roll adjusted to 40 ° C. to form a sheet having a desired thickness. This sheet was stretched 7 × 7 times at 123 ° C. with a simultaneous biaxial stretching machine. Thereafter, the stretched sheet was immersed in methylene chloride to extract and remove liquid paraffin, and then dried, and stretched 1.4 times at 127 ° C. in the transverse direction by a tenter stretching machine. Thereafter, the stretched sheet was relaxed in the width direction and heat-treated to obtain a polyolefin microporous film. At that time, the relaxation rate was 13%.

  10 parts by mass of polyphenylsulfone having a weight average molecular weight of 550,000 and a glass transition point of 220 ° C. and 90 parts by mass of N-methylpyrrolidone were mixed and stirred at 25 ° C. for 24 hours to obtain a coating polymer solution. Table 1 shows the tensile elastic modulus in the swollen state of the nonporous film obtained by applying the coating polymer solution by the method described in (7) above.

  The coating polymer solution is applied onto the polyolefin microporous membrane using a bar coater, and the polymer is coagulated by being immersed in a coagulation liquid in which 95 parts by mass of water and 5 parts by mass of N-methylpyrrolidone are mixed, The solvent was extracted. The solidified body was dried at 60 ° C. to remove water. Further, the other side of the dried solidified body is coated, solidified and dried in the same manner, and then dried under reduced pressure at 60 ° C. and −0.1 MPa, thereby separating the separator for an electricity storage device. Got. The physical properties and evaluation results of the obtained separator are shown in Table 1.

  About the surface of the obtained separator, SEM measurement was performed by the acceleration voltage of 0.5 kV using Hitachi High-Technologies Corporation make and field emission type scanning electron microscope SU-8220. The obtained SEM observation image is shown in FIG. It is confirmed that a microporous membrane layer of polyphenylsulfone is formed on the separator surface.

<Comparative Example 1>
5 parts by mass of polyvinylidene fluoride having a weight average molecular weight of 1,000,000 and a glass transition point of -34 ° C. and 95 parts by mass of N-methylpyrrolidone were mixed and stirred at 25 ° C. for 24 hours to obtain a coating polymer solution. Table 1 shows the tensile elastic modulus in the swollen state of the nonporous film obtained by coating the coating polymer solution. On the polyolefin microporous membrane obtained by the method described in Example 1, the coating polymer solution obtained in Comparative Example 1 was applied using a bar coater, and 95 parts by mass of water and 5 parts by mass of N-methylpyrrolidone. The polymer was coagulated by immersing it in a coagulation liquid mixed with, and the solvent was extracted. The solidified body was dried at 60 ° C. to remove water. Further, the other side of the dried solidified body is coated, solidified and dried in the same manner, and then dried under reduced pressure at 60 ° C. and −0.1 MPa, thereby separating the separator for an electricity storage device. Got. The physical properties and evaluation results of the obtained separator are shown in Table 1.

<Comparative example 2>
10 parts by mass of polysulfone having a weight average molecular weight of 700,000 and a glass transition point of 186 ° C. and 90 parts by mass of N-methylpyrrolidone were mixed and stirred at 25 ° C. for 24 hours to obtain a coating polymer solution. Table 1 shows the tensile elastic modulus in the swollen state of the nonporous film obtained by coating the coating polymer solution.

  On the polyolefin microporous membrane obtained by the method described in Example 1, the coating polymer solution obtained in Comparative Example 2 was applied using a bar coater, and 95 parts by mass of water and 5 parts by mass of N-methylpyrrolidone. The polymer was coagulated by immersing it in a coagulation liquid mixed with, and the solvent was extracted. The solidified body was dried at 60 ° C. to remove water. Further, the other side of the dried solidified body is coated, solidified and dried in the same manner, and then dried under reduced pressure at 60 ° C. and −0.1 MPa, thereby separating the separator for an electricity storage device. Got. The physical properties and evaluation results of the obtained separator are shown in Table 1.

<Comparative Example 3>
10 parts by mass of polyacrylonitrile having a weight average molecular weight of 150,000 and a glass transition point of 94 ° C. and 90 parts by mass of N-methylpyrrolidone were mixed and stirred at 25 ° C. for 24 hours to obtain a coating polymer solution. Table 1 shows the tensile elastic modulus in the swollen state of the nonporous film obtained by coating the coating polymer solution.

  On the polyolefin microporous membrane obtained by the method described in Example 1, the coating polymer solution obtained in Comparative Example 3 was applied using a bar coater, and 95 parts by mass of water and 5 parts by mass of N-methylpyrrolidone. The polymer was coagulated by immersing it in a coagulation liquid mixed with, and the solvent was extracted. The solidified body was dried at 60 ° C. to remove water. Further, after coating, coagulating, and drying the coating solution on the other side of the solidified body after drying in the same manner, the separator for an electricity storage device was obtained by drying under reduced pressure at 60 ° C. and −0.1 MPa. Obtained. The physical properties and evaluation results of the obtained separator are shown in Table 1.

Claims (7)

  A separator for an electricity storage device, wherein at least a part of at least one surface of a polyolefin microporous membrane is coated with a thermoplastic polymer having a sulfonyl group and a tensile elastic modulus at 25 ° C. in a swollen state of 300 MPa to 3000 MPa. .   The power storage device separator according to claim 1, wherein the polymer is polyphenylsulfone.   The electricity storage device separator according to claim 1, wherein the polymer is formed in a microporous film shape or a dot shape. Coating basis weight of the resin layer containing the polymer is 0.05 g / ^{m 2} or more 5.0 g / ^{m 2} or less, a separator for an electricity storage device according to any one of claims 1-3.   The electrical storage device separator according to claim 4, wherein a total thickness of the polyolefin microporous membrane and the resin layer is 5 µm or more and 25 µm or less.   The electrical storage device separator according to claim 1, wherein the air permeability is 40 seconds / 100 cc or more and 1000 seconds / 100 cc or less.   The lithium ion battery containing the separator for electrical storage devices of any one of Claims 1-6.