阅读说明：本技术 非水系二次电池用隔膜、非水系二次电池及非水系二次电池的制造方法 (Separator for nonaqueous secondary battery, and method for producing nonaqueous secondary battery ) 是由 佐藤惠美 于 2018-05-16 设计创作，主要内容包括：本发明的一个实施方式提供非水系二次电池用隔膜,其具备多孔质基材和粘接性多孔质层,所述粘接性多孔质层被设置于上述多孔质基材的一面或两面、并且包含聚偏二氟乙烯系树脂,上述聚偏二氟乙烯系树脂包含共聚物A(聚偏二氟乙烯系树脂A),所述共聚物A具有偏二氟乙烯及式(1)表示的单体作为单体成分、并且熔点为130℃以上且148℃以下。R<Sup>1</Sup>～R<Sup>3</Sup>：氢原子、卤素原子、羧基或其衍生物、碳原子数为1～5的烷基；X：单键、碳原子数为1～5的亚烷基、具有取代基的碳原子数为1～5的亚烷基；Y：氢原子、碳原子数为1～5的烷基、包含至少一个羟基的碳原子数为1～5的烷基。<Image he="313" wi="700" file="DDA0002273494210000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>(One embodiment of the present invention provides a separator for a nonaqueous secondary battery, comprising a porous base material and an adhesive porous layer that is provided on one or both surfaces of the porous base material and contains a polyvinylidene fluoride resin containing a copolymer a (polyvinylidene fluoride resin a) containing vinylidene fluoride and represented by formula (1)A monomer as a monomer component and having a melting point of 130 ℃ or higher and 148 ℃ or lower. R 1 ～R 3 : a hydrogen atom, a halogen atom, a carboxyl group or a derivative thereof, and an alkyl group having 1 to 5 carbon atoms; x: a single bond, an alkylene group having 1 to 5 carbon atoms, and an alkylene group having 1 to 5 carbon atoms and having a substituent; y: a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, and an alkyl group having 1 to 5 carbon atoms including at least one hydroxyl group.)

1. A separator for a nonaqueous secondary battery, comprising:

porous base material, and

an adhesive porous layer provided on one or both surfaces of the porous base material and containing a polyvinylidene fluoride resin,

the polyvinylidene fluoride resin comprises a copolymer A having vinylidene fluoride and a monomer represented by the following formula (1) as monomer components and having a melting point of 130 ℃ to 148 ℃,

[ chemical formula 1]

In the formula (1), R¹、R²And R³Each independently represents a hydrogen atom, a halogen atom, a carboxyl group or a derivative thereof, or an alkyl group having 1 to 5 carbon atoms; x represents a single bond, an alkylene group having 1 to 5 carbon atoms, or a substituted alkylene group having 1 to 5 carbon atoms; y represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or an alkyl group having 1 to 5 carbon atoms including at least one hydroxyl group.

2. The nonaqueous secondary battery separator according to claim 1, wherein the weight average molecular weight of the copolymer A is 30 to 300 ten thousand.

3. The nonaqueous secondary battery separator according to claim 1, wherein the weight average molecular weight of the copolymer A is less than 30 ten thousand,

the polyvinylidene fluoride resin further comprises a polyvinylidene fluoride resin B having a weight average molecular weight of 30 ten thousand or more other than the copolymer A,

the intermediate value between the melting point of the copolymer A and the melting point of the polyvinylidene fluoride resin B is 155 ℃ or less.

4. The nonaqueous secondary battery separator according to any one of claims 1 to 3, wherein the adhesive porous layer further contains an inorganic filler.

5. The separator for a nonaqueous secondary battery according to any one of claims 1 to 4, wherein the copolymer A contains a monomer represented by the formula (1) in an amount of 0.5 mol% or more as a monomer component.

6. The separator for a nonaqueous secondary battery according to any one of claims 1 to 5, wherein the copolymer A further contains hexafluoropropylene as a monomer component.

7. A nonaqueous secondary battery comprising:

a positive electrode,

A negative electrode, and

the separator for a nonaqueous secondary battery according to any one of claims 1 to 6, which is disposed between the positive electrode and the negative electrode,

the nonaqueous secondary battery obtains electromotive force by doping/dedoping lithium.

8. A method for manufacturing a nonaqueous secondary battery, comprising the steps of:

a step for producing a laminate by disposing the nonaqueous secondary battery separator according to any one of claims 1 to 6 between a positive electrode and a negative electrode;

a step of housing the laminate in an external packaging material, injecting an electrolyte into the external packaging material, and then sealing the external packaging material to produce a battery element; and

and a step of bonding at least one of the positive electrode and the negative electrode to the nonaqueous secondary battery separator by hot-pressing the battery element at a temperature of 65 ℃ or higher and 75 ℃ or lower.

Technical Field

The present disclosure relates to a separator for a nonaqueous secondary battery, and a method for manufacturing a nonaqueous secondary battery.

Background

Nonaqueous secondary batteries, typified by lithium ion secondary batteries, are widely used as power sources for portable electronic devices such as notebook personal computers, cellular phones, digital cameras, and portable camcorders (camcorders). As portable electronic devices have been reduced in size and weight, the external packaging of nonaqueous secondary batteries has been simplified and reduced in weight, and aluminum housings have been developed as external packaging materials in place of stainless steel housings, and aluminum laminate film packages (packs) have been developed in place of metal housings. However, since an aluminum laminate film-made package is flexible, batteries using the package as an outer packaging material (so-called flexible packaging batteries) may have the following cases: due to external impact and expansion and contraction of the electrode accompanying charge and discharge, a gap is easily formed between the electrode and the separator, and the cycle life is reduced.

In order to solve such a situation, a technique of improving adhesion between an electrode and a separator has been proposed. As one of the techniques, a separator is known in which an adhesive porous layer containing a polyvinylidene fluoride resin (hereinafter, also referred to as PVDF resin) is formed on a porous substrate such as a polyolefin microporous membrane (for example, japanese patent No. 5837437 and japanese patent No. 5670811). This separator is stacked on an electrode in a state of containing an electrolyte solution and is hot-pressed (hereinafter, also referred to as "wet hot-pressing" as appropriate), whereby the entire separator is favorably bonded to the electrode via an adhesive porous layer, and therefore, the cycle life of the flexible package battery can be improved.

Disclosure of Invention

Problems to be solved by the invention

However, since PVDF-based resins have high crystallinity, hot pressing under severe conditions such as high temperature of 90 ℃ or higher and high pressure is required to ensure sufficient adhesion to electrodes. Specifically, for example, in the prior art such as Japanese patent No. 5837437 and Japanese patent No. 5670811, the temperature is 90 ℃ and the pressure is 20kgf/cm²(about 2MPa) under wet hot pressing.

However, when wet hot pressing is performed under such severe conditions, the porous structure of the porous layer of the separator may be damaged. Therefore, there is a problem that: in some cases, the ion permeability of the separator after hot pressing is reduced, and it is difficult to obtain good load characteristics. Therefore, a separator that can be well bonded even under a hot pressing condition at a relatively low temperature of less than 90 ℃ is desired.

Accordingly, an object to be solved by one embodiment of the present invention is to provide the following separator for a nonaqueous secondary battery: compared with the conventional separator, the separator has excellent adhesion to the electrode even when wet hot pressing is performed under mild conditions, and can ensure good ion permeability even after adhesion to the electrode.

Another object of another embodiment of the present invention is to provide a nonaqueous secondary battery having excellent cell (cell) strength and battery characteristics.

Means for solving the problems

Specific means for solving the above problems include the following means.

[1] A separator for a nonaqueous secondary battery, comprising a porous base material and an adhesive porous layer which is provided on one or both surfaces of the porous base material and contains a polyvinylidene fluoride resin containing a copolymer A (hereinafter also referred to as a PVDF resin A.) containing vinylidene fluoride and a monomer represented by the following formula (1) as monomer components and having a melting point of 130 ℃ to 148 ℃.

[ chemical formula 1]

In the formula (1), R¹、R²And R³Each independently represents a hydrogen atom, a halogen atom, a carboxyl group or a derivative thereof, or an alkyl group having 1 to 5 carbon atoms. X represents a single bond, an alkylene group having 1 to 5 carbon atoms, or a substituted alkylene group having 1 to 5 carbon atoms. Y represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or an alkyl group having 1 to 5 carbon atoms including at least one hydroxyl group.

[2] The separator for a nonaqueous secondary battery according to [1], wherein the PVDF resin A has a weight average molecular weight of 30 to 300 ten thousand.

[3] The separator for a nonaqueous secondary battery according to [1], wherein the PVDF resin A has a weight average molecular weight of less than 30 ten thousand, the polyvinylidene fluoride resin further contains a polyvinylidene fluoride resin B (hereinafter, also referred to as PVDF resin B.) having a weight average molecular weight of 30 ten thousand or more other than the copolymer A (PVDF resin A), and the median value between the melting point of the PVDF resin A and the melting point of the PVDF resin B is 155 ℃ or less.

[4] The separator for a nonaqueous secondary battery according to any one of the above [1] to [3], wherein the adhesive porous layer further contains an inorganic filler.

[5] The separator for a nonaqueous secondary battery according to any one of the above [1] to [4], wherein the PVDF resin A contains 0.5 mol% or more of a monomer represented by the above formula (1) as a monomer component.

[6] The separator for a nonaqueous secondary battery according to any one of the above [1] to [5], wherein the PVDF resin A further contains hexafluoropropylene as a monomer component.

[7] A nonaqueous secondary battery comprising a positive electrode, a negative electrode, and the separator for a nonaqueous secondary battery according to any one of [1] to [6] disposed between the positive electrode and the negative electrode, wherein the nonaqueous secondary battery obtains an electromotive force by doping and dedoping of lithium.

[8] A method for manufacturing a nonaqueous secondary battery, comprising the steps of: a step of disposing the nonaqueous secondary battery separator according to any one of [1] to [6] between a positive electrode and a negative electrode to produce a laminate; a step of housing the laminate in an external packaging material, injecting an electrolyte into the external packaging material, and then sealing the external packaging material to produce a battery element; and a step of bonding at least one of the positive electrode and the negative electrode to the nonaqueous secondary battery separator by hot-pressing the battery element at a temperature of 65 ℃ to 75 ℃.

ADVANTAGEOUS EFFECTS OF INVENTION

According to one embodiment of the present invention, there can be provided the following separator for a nonaqueous secondary battery: compared with the conventional separator, the separator has excellent adhesion to the electrode even when wet hot pressing is performed under mild conditions, and can ensure good ion permeability even after adhesion to the electrode.

According to another embodiment of the present invention, a nonaqueous secondary battery having excellent cell strength and battery characteristics can be provided.

Detailed Description

Hereinafter, embodiments will be described. It should be noted that the description and examples are for illustrating the embodiments and do not limit the scope of the embodiments.

In the present specification, the numerical range represented by "to" means a range in which the numerical values recited before and after "to" are included as the minimum value and the maximum value, respectively. In the numerical ranges recited in the present disclosure in stages, the upper limit value or the lower limit value recited in a certain numerical range may be replaced with the upper limit value or the lower limit value recited in other numerical ranges recited in stages. In the numerical ranges disclosed in the present disclosure, the upper limit or the lower limit described in a certain numerical range may be replaced with the values shown in the examples.

In the present specification, the term "step" is not limited to an independent step, and is also included in the term as long as the desired purpose of the step can be achieved even when the step cannot be clearly distinguished from other steps.

In the present specification, the "monomer component" of the resin means a constituent component of the resin and is a structural unit formed when a monomer is polymerized.

< separator for nonaqueous Secondary Battery >

The separator for a nonaqueous secondary battery (also simply referred to as "separator") according to the present disclosure includes a porous base material and an adhesive porous layer provided on one surface or both surfaces of the porous base material. In the separator of the present disclosure, the adhesive porous layer contains a copolymer A (polyvinylidene fluoride resin; PVDF resin A) which has vinylidene fluoride and a monomer represented by the following formula (1) as monomer components and has a melting point of 130 ℃ to 148 ℃.

[ chemical formula 2]

In the formula (1), R¹、R²And R³Each independently represents a hydrogen atom, a halogen atom, a carboxyl group or a derivative thereof, or an alkyl group having 1 to 5 carbon atoms. X represents a single bond, an alkylene group having 1 to 5 carbon atoms, or a substituted alkylene group having 1 to 5 carbon atoms. Y represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or an alkyl group having 1 to 5 carbon atoms and containing at least one hydroxyl group.

Hereinafter, vinylidene fluoride or a monomer component thereof is also referred to as "VDF", hexafluoropropylene or a monomer component thereof is also referred to as "HFP", and the monomer represented by the formula (1) or a monomer component thereof is also referred to as "functional group-containing monomer".

The separator of the present disclosure has excellent adhesion to an electrode by wet hot pressing (hereinafter, also referred to as "wet adhesion") because it includes an adhesive porous layer containing a PVDF-based resin a having a specific melting point and a specific structure.

Generally, in the PVDF-based resin, the crystallinity is broken as the proportion of the copolymerization component such as HFP increases, and therefore, the fluidity during heating at high temperature increases, and the melting point decreases. In addition, the swelling property in the electrolytic solution is also increased. Therefore, by selecting a copolymer having a specific melting point or lower, adhesion can be easily performed under mild conditions.

However, when the adhesive porous layer is formed of a PVDF-based resin having a low melting point and low crystallinity, the porosity tends to increase, and the pore diameter tends to increase. When the porosity of the adhesive porous layer is high and the pore diameter is also large, the area of the PVDF resin portion that becomes the bonding portion with the electrode on the surface of the adhesive porous layer decreases, and the PVDF resin is present sparsely. Therefore, the adhesion between the adhesive porous layer and the electrode tends to be weak. Further, when the porosity of the adhesive porous layer is high and the pore diameter is also large, the ion transfer at the electrode interface becomes uneven, which adversely affects the cycle characteristics and load characteristics of the battery.

In addition, when the crystallinity of the PVDF resin is too low, that is, when the melting point is not more than a specific melting point, the following tendency is present: the swelling property in the electrolyte is too high to block pores, thereby inhibiting ion transfer, and thus reducing cycle characteristics and/or load characteristics.

Therefore, in order to achieve both the development of wet adhesion under mild conditions and the battery characteristics, it is of course important to use a PVDF-based resin having a melting point within a specific range, but it is also important to appropriately control the porous structure and the swelling property in the electrolyte solution, thereby improving the affinity with the electrode material. Accordingly, the present disclosure solves all of these problems by including a copolymer a (PVDF-based resin a) having vinylidene fluoride and a monomer represented by the above formula (1) as monomer components and having a melting point of 130 ℃ or higher and 148 ℃ or lower in an adhesive porous layer. The separator of the present disclosure has excellent adhesion to an electrode even when wet hot pressing is performed under mild conditions, and exhibits good ion permeability even after hot pressing. The separator of the present disclosure has excellent wet adhesion to an electrode using a solvent-based binder (e.g., PVDF-based resin) and also excellent wet adhesion to an electrode using an aqueous binder (e.g., styrene-butadiene copolymer).

Since the separator of the present disclosure has excellent adhesion to the electrode, the strength of the unit cell of the nonaqueous secondary battery to which the separator of the present disclosure is applied is excellent. In addition, since the separator of the present disclosure is well bonded to the electrode even when wet hot pressing is performed under relatively mild conditions, a good porous structure can be maintained after hot pressing, and as a result, the nonaqueous secondary battery to which the separator of the present disclosure is applied is excellent in electrode characteristics such as cycle characteristics and load characteristics. Further, since the temperature at the time of wet hot pressing can be set to a relatively low temperature, the generation of gas due to decomposition of the electrolyte solution and the electrolyte can be suppressed, and the problem of gas expansion of the battery is unlikely to occur.

In addition, according to the separator of the present disclosure, it is possible to suppress formation of a gap between the electrode and the separator due to expansion and contraction of the electrode accompanying charge and discharge and an impact from the outside. Therefore, the separator of the present disclosure is suitable for a flexible packaging battery having an aluminum laminated film-made package as an outer packaging material. According to the separator of the present disclosure, a flexible package battery having high battery performance can be provided.

Hereinafter, the material, composition, physical properties, and the like of the separator of the present disclosure will be described in detail.

[ porous base Material ]

The porous substrate in the present disclosure refers to a substrate having pores or voids therein.

Examples of such a base material include: a microporous membrane; porous sheets made of fibrous materials such as nonwoven fabrics and paper; a composite porous sheet obtained by laminating 1 or more other porous layers on a microporous membrane or a porous sheet; and so on.

The microporous membrane refers to the following membranes: a structure having a large number of fine holes inside and connecting these fine holes, gas or liquid can pass through from one side surface to the other side surface.

The porous base material contains an organic material and/or an inorganic material having electrical insulation properties.

The porous substrate preferably contains a thermoplastic resin from the viewpoint of imparting a shutdown function to the porous substrate.

The shutdown function refers to the following functions: when the temperature of the battery rises, the material melts to block the pores of the porous base material, thereby blocking the movement of ions and preventing thermal runaway of the battery.

As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200 ℃ is preferable. Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; and the like, among which polyolefins are preferred.

The porous substrate is preferably a microporous membrane containing polyolefin (referred to as "polyolefin microporous membrane"). The polyolefin microporous membrane is, for example, a polyolefin microporous membrane used for a conventional separator for a nonaqueous secondary battery, and it is preferable to select a polyolefin microporous membrane having good mechanical properties and ion permeability from among these.

From the viewpoint of exhibiting the shutdown function, the polyolefin microporous membrane preferably contains polyethylene.

From the viewpoint of imparting heat resistance to such an extent that the film is not easily broken when exposed to high temperatures, a polyolefin microporous film containing polyethylene and polypropylene is preferred. Examples of such a polyolefin microporous membrane include a microporous membrane in which polyethylene and polypropylene are mixed in 1 layer.

In addition, from the viewpoint of achieving both shutdown function and heat resistance, the following polyolefin microporous membrane is also preferable: the polyolefin microporous membrane has a laminated structure of 2 or more layers, at least 1 layer containing polyethylene and at least 1 layer containing polypropylene.

The polyolefin contained in the polyolefin microporous membrane is preferably a polyolefin having a weight average molecular weight (Mw) of 10 to 500 ten thousand. When the Mw of the polyolefin is 10 ten thousand or more, sufficient mechanical properties can be secured. On the other hand, when the Mw of the polyolefin is 500 ten thousand or less, the shutdown properties are good, and the film can be easily molded.

The polyolefin microporous membrane can be produced, for example, by the following method. Namely, the following method: the molten polyolefin is extruded from a T-die to form a sheet, which is subjected to crystallization treatment, then stretched, and further subjected to heat treatment to form a microporous film. Alternatively, the following method is used: a polyolefin melted together with a plasticizer such as liquid paraffin is extruded from a T-die, cooled to prepare a sheet, stretched, and then the plasticizer is extracted and heat-treated to prepare a microporous membrane.

Examples of the porous sheet made of a fibrous material include a porous sheet made of a polyester such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; nonwoven fabrics and papers made of fibrous materials such as heat-resistant resins including aromatic polyamides, polyimides, polyether sulfones, polysulfones, polyether ketones, and polyether imides.

The heat-resistant resin herein refers to a polymer having a melting point of 200 ℃ or higher, or a polymer having a decomposition temperature of 200 ℃ or higher, which does not have a melting point.

The composite porous sheet may be a sheet obtained by laminating a functional layer on a microporous film or a porous sheet. Such a composite porous sheet is preferable in terms of the availability of the functional layer and the addition of further functions.

The functional layer is preferably a porous layer containing a heat-resistant resin or a porous layer containing a heat-resistant resin and an inorganic filler, from the viewpoint of imparting heat resistance.

Examples of the heat-resistant resin include aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. Examples of the inorganic filler include metal oxides such as alumina and metal hydroxides such as magnesium hydroxide.

Examples of the method for providing a functional layer on a microporous membrane or a porous sheet include: a method of coating a functional layer on a microporous membrane or a porous sheet; a method of bonding a microporous film or a porous sheet to a functional layer with an adhesive; a method of thermocompression bonding a microporous membrane or a porous sheet to a functional layer; and so on.

In order to improve the wettability of the coating liquid for forming the adhesive porous layer, the porous substrate may be subjected to various surface treatments within a range that does not impair the properties of the porous substrate.

Examples of the surface treatment include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

Characteristics of the porous substrate

The thickness of the porous substrate is preferably 3 to 25 μm, more preferably 5 to 25 μm, and still more preferably 5 to 20 μm, from the viewpoint of obtaining good mechanical properties and internal resistance.

The porosity of the porous substrate is preferably 20% to 60% from the viewpoint of obtaining an appropriate membrane resistance and shutdown function.

From the viewpoint of preventing a short circuit of a battery and obtaining good ion permeability, the Gurley value (JIS P8117: 2009) of the porous substrate is preferably 50 seconds/100 ml to 800 seconds/100 ml, and more preferably 50 seconds/100 ml to 400 seconds/100 ml.

The puncture strength of the porous substrate is preferably 180gf or more, and more preferably 200gf or more, from the viewpoint of improving the production yield. The puncture strength of the porous substrate is: maximum puncture strength (gf) measured by performing a puncture test under the conditions that the radius of curvature of the needle tip was 0.5mm and the puncture speed was 2mm/sec using a hand-held compression tester KES-G5 manufactured by Kato Tech.

The average pore diameter of the porous substrate is preferably 15nm to 100 nm. When the average pore diameter of the porous substrate is 15nm or more, ions are easily moved, and thus, good battery performance can be easily obtained. From this viewpoint, the average pore diameter of the porous substrate is more preferably 25nm or more, and still more preferably 30nm or more. On the other hand, when the average pore diameter of the porous substrate is 100nm or less, the peel strength between the porous substrate and the adhesive porous layer can be improved, and a good shutdown function can be exhibited. From this viewpoint, the average pore diameter of the porous substrate is more preferably 90nm or less, and still more preferably 80nm or less.

The average pore diameter of the porous substrate is a value measured by a method according to ASTM E1294-89 using a Perm-Porometer (Pemm pore gauge), and is measured, for example, by Perm-Porometer CFP-1500-A manufactured by PMI Corp.

[ adhesive porous layer ]

The adhesive porous layer in the present disclosure is a porous layer that is provided on one or both surfaces of a porous substrate and contains a polyvinylidene fluoride resin.

The adhesive porous layer has a structure in which a large number of micropores are formed inside and the micropores are connected, and gas or liquid can pass through the surface facing the other surface. The adhesive porous layer is a layer that is provided on one surface or both surfaces of the porous base material as an outermost layer of the separator and can be adhered to the electrode when the separator and the electrode are stacked and hot-pressed. From the viewpoint of excellent cell strength and battery cycle characteristics (capacity retention rate), it is preferable that the adhesive porous layer be present on both sides of the porous substrate, as compared with the case where the adhesive porous layer is present on only one side of the porous substrate. This is because, when the adhesive porous layer is present on both surfaces of the porous substrate, both surfaces of the separator are favorably adhered to both electrodes via the adhesive porous layer.

The adhesive porous layer contains at least a PVDF resin A. The adhesive porous layer may contain a resin other than the PVDF resin, a filler, and the like.

In the present disclosure, the PVDF resin a may be contained in at least one surface of the separator, and for example, one surface may be an adhesive porous layer containing the PVDF resin a, and the other surface may be an adhesive porous layer containing another PVDF resin such as a PVDF homopolymer or a VDF-HFP binary copolymer, or another resin such as an acrylic resin. In this way, when separators having different adhesive porous layers disposed on both surfaces are applied to a battery including a negative electrode using a styrene-butadiene rubber binder, in particular, it is preferable that an adhesive porous layer containing PVDF resin a be disposed on the negative electrode side.

(PVDF resin A)

The PVDF resin a in the present disclosure is a copolymer having VDF and a monomer represented by the following formula (1) as monomer components and having a melting point of 130 ℃ to 148 ℃.

[ chemical formula 3]

In the formula (1), R¹、R²And R³Each independently represents a hydrogen atom, a halogen atom, a carboxyl group or a derivative thereof, or an alkyl group having 1 to 5 carbon atoms. X represents a single bond, an alkylene group having 1 to 5 carbon atoms, or a substituted alkylene group having 1 to 5 carbon atoms. Y represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or an alkyl group having 1 to 5 carbon atoms including at least one hydroxyl group.

The melting point of the PVDF resin a significantly affects the bonding temperature, and when the melting point is higher than 148 ℃, hot pressing is required at high temperature, and the hot pressing process may adversely affect the performance of the battery. From such a viewpoint, the melting point of the PVDF resin a is preferably 145 ℃ or lower, more preferably 143 ℃ or lower, and still more preferably 140 ℃ or lower. If the melting point of the PVDF-based resin is less than 130 ℃, the swelling property in the electrolyte solution is increased, and therefore, the battery performance may be adversely affected, which is not preferable. From such a viewpoint, the melting point of the PVDF resin a is preferably 132 ℃ or higher, and more preferably 135 ℃ or higher.

As R¹、R²And R³Examples of the halogen atom in (2) include a fluorine atom, a chlorine atom, an iodine atom and the like.

As R¹、R²And R³The alkyl group having 1 to 5 carbon atoms in (A) includes, for example, methyl, ethyl, propyl, isopropyl, butyl and the like, and an alkyl group having 1 to 4 carbon atoms is preferable.

Examples of the alkylene group having 1 to 5 carbon atoms in X include a methylene group, an ethylene group, and a propylene group.

Examples of the "alkylene group having 1 to 5 carbon atoms and having a substituent" in X include 2-methylethyl group and 2-ethylpropyl group.

Examples of the alkyl group having 1 to 5 carbon atoms in Y include methyl, ethyl, propyl, isopropyl, butyl and the like, and an alkyl group having 1 to 4 carbon atoms is preferable.

Examples of the "alkyl group having 1 to 5 carbon atoms and including at least one hydroxyl group" in Y include a 2-hydroxyethyl group, a 2-hydroxypropyl group and the like, and an alkyl group having 1 to 3 carbon atoms and including at least one hydroxyl group is preferable.

Among the above, the following is more preferable: r¹、R²And R³The hydrogen atom or the alkyl group having 1 to 4 carbon atoms, X is a single bond, and Y is the alkyl group having 1 to 4 carbon atoms or the alkyl group having 1 to 3 carbon atoms including at least one hydroxyl group.

Examples of the formula (1) include, but are not limited to, acrylic monomers, unsaturated dibasic acids, and monoester monomers of unsaturated dibasic acids.

Examples of the acrylic monomer include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, acrylic acid, methacrylic acid, crotonic acid, pentenoic acid, and hexenoic acid.

Examples of the unsaturated dibasic acid include unsaturated dicarboxylic acids, and more specifically, maleic acid (anhydride), citraconic acid, itaconic acid, and the like.

Examples of the monoester of the unsaturated dibasic acid include monomethyl maleate, monoethyl maleate, monomethyl citraconate, monoethyl citraconate, monomethyl itaconate, monoethyl itaconate, and the like, and monomethyl maleate and monomethyl citraconate are particularly preferable.

When X is an alkylene group having a substituent, a substituent containing a hetero atom may be contained. Examples of the monomer containing oxygen as a hetero atom include carboxyethyl acrylate, acryloyloxyethyl succinate, methacryloyloxyethyl succinate, and the like.

The content ratio of the monomer represented by formula (1) in the PVDF-based resin a is preferably 0.1 mol% or more. Thus, the resin a has an acid group or an ester group in the molecule, the affinity with the electrode material is further improved, and the PVDF-based resin a forming the adhesive porous layer interacts with the electrode active material. As a result, the adhesiveness between the adhesive porous layer and the electrode (adhesiveness by wet hot pressing or dry hot pressing) is improved, and the pressing conditions required particularly in the case of wet hot pressing are widened.

The content ratio of the monomer represented by formula (1) in the PVDF-based resin a is more preferably 0.1 mol% or more, still more preferably 0.2 mol% or more, and particularly preferably 0.5 mol% or more. The upper limit of the content ratio of the monomer represented by formula (1) in the resin a is preferably 3.0 mol% or less.

The PVDF-based resin a may be a copolymer containing, as a monomer component, other monomers in addition to vinylidene fluoride and the monomer represented by the formula (1). Examples of the other monomer include Hexafluoropropylene (HFP), tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and a combination of one or more of these monomers. Among them, the PVDF-based resin a is preferably a copolymer containing, as monomer components, vinylidene fluoride, Hexafluoropropylene (HFP), and a monomer represented by the above formula (1). When the PVDF-based resin a is a copolymer containing VDF, HFP, and the monomer represented by the above formula (1) as monomer components, it is preferable to contain the monomer represented by the formula (1) in an amount of 0.5 mol% or more and 5 mol% or less as monomer components in order to improve the effect of the present disclosure. Similarly, when the PVDF-based resin a is a copolymer containing VDF, HFP, and a monomer represented by formula (1) as monomer components, HFP is preferably contained in an amount of more than 3.5 mol% and 7 mol% or less, and more preferably 4 mol% or more and 6.5 mol% or less.

In the present disclosure, the weight average molecular weight (Mw) of the PVDF-based resin a is preferably 30 to 300 ten thousand.

By setting the Mw of the PVDF-based resin a to 30 ten thousand or more, it is possible to effectively impart mechanical properties to the adhesive porous layer that can withstand the adhesion treatment with the electrode. From such a viewpoint, the Mw of the PVDF resin a is more preferably 50 ten thousand or more, and still more preferably 100 ten thousand or more.

On the other hand, if the Mw of the PVDF-based resin a is 300 ten thousand or less, the viscosity of the coating liquid for coating and molding the adhesive porous layer does not become too high, and the PVDF-based resin a is suitable for use in the field of molding an adhesive porous layer having a uniform porous structure. In addition, even when wet hot pressing is performed under mild conditions, fluidity is easily maintained well, and wet adhesiveness is easily obtained. From such a viewpoint, the Mw of the PVDF-based resin a is more preferably 250 ten thousand or less, and still more preferably 230 ten thousand or less.

On the other hand, in the present disclosure, when a material having a weight average molecular weight of less than 30 ten thousand is used as the PVDF-based resin a, it is preferable that the polyvinylidene fluoride-based resin constituting the adhesive porous layer further contains a polyvinylidene fluoride-based resin (PVDF-based resin B) having a weight average molecular weight of 30 ten thousand or more, and the melting point intermediate value between the PVDF-based resin a and the PVDF-based resin B is 155 ℃.

If the Mw of the PVDF-based resin B is 30 ten thousand or more, good mechanical strength can be imparted when wet hot pressing is performed on the electrode. In particular, even if the Mw of the PVDF-based resin a is less than 30 ten thousand, it is preferable to increase the Mw of the PVDF-based resin B because it can provide mechanical properties that can withstand the bonding treatment with the electrode. Further, when the PVDF resin B is selected so that the median of the melting points of the PVDF resin a and the PVDF resin B becomes 155 ℃ or less, the favorable swelling degree in the electrolyte is maintained, and therefore, the wet adhesion of the PVDF resin a is not inhibited even under mild wet hot pressing conditions.

The Mw of the PVDF-based resin B is more preferably 50 ten thousand or more, and still more preferably 80 ten thousand or more. The Mw of the PVDF-based resin B is more preferably 300 ten thousand or less, and still more preferably 250 ten thousand or less.

The weight average molecular weights (Mw) of the PVDF-based resin a and the PVDF-based resin B were measured by Gel Permeation Chromatography (GPC).

Specifically, the measurement was carried out using a GPC apparatus "GPC-900" manufactured by Nippon spectral Co., Ltd., two TSKgel SUPER AWM-H manufactured by Tosoh Co., Ltd., as columns, and dimethylformamide as a solvent. The measurement conditions were temperature 40 ℃ and flow rate 0.6 mL/min, and the molecular weight in terms of polystyrene was determined.

Examples of the method for producing the PVDF resin include emulsion polymerization and suspension polymerization. Further, a commercially available PVDF-based resin having a specific melting point and containing a specific copolymerized unit may be selected.

The content of the PVDF-based resin a in the adhesive porous layer is preferably 10 mass% or more, more preferably 25 mass% or more, and still more preferably 50 mass% or more of the total amount of all the resins in the adhesive porous layer.

(other resins)

The adhesive porous layer in the present disclosure may contain a polyvinylidene fluoride resin other than the PVDF resin a, which can be mixed with the PVDF resin a, or may contain a resin other than the polyvinylidene fluoride resin.

Examples of other polyvinylidene fluoride resins that can be mixed with the PVDF resin a include: a VDF-HFP binary copolymer not containing a monomer represented by the formula (1) as a monomer component; homopolymers of vinylidene fluoride (i.e., polyvinylidene fluoride); a copolymer of vinylidene fluoride and at least one member selected from among fluorine-containing monomers (e.g., tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, etc.); a copolymer of vinylidene fluoride and hexafluoropropylene and at least one member selected from among fluorine-containing monomers (e.g., tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, etc.). The PVDF-based resin B is also included in the "other polyvinylidene fluoride-based resin".

Examples of the resin other than the polyvinylidene fluoride resin include fluorine-based rubbers, acrylic resins, styrene-butadiene copolymers, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol polymers, polyvinyl butyral, polyvinyl pyrrolidone, polyethers (polyethylene oxide, polypropylene oxide, etc.), and the like.

[ Filler ]

The adhesive porous layer in the present disclosure may contain a filler made of an inorganic material or an organic material. By including the filler in the adhesive porous layer, the heat resistance and the electrolyte affinity of the separator can be improved. In this case, it is preferable to make the content and the particle size to such an extent that the effects in the present disclosure are not hindered.

The average primary particle diameter of the filler is preferably 0.01 to 5 μm, and the lower limit is more preferably 0.1 μm or more, and the upper limit is more preferably 1.5 μm or less, and still more preferably 1 μm or less.

The particle size distribution of the filler is preferably 0.1 μm < d90-d10<3 μm. Here, d10 represents a cumulative 10% particle diameter (μm) in the volume-based particle size distribution from the small particle side, and d90 represents a cumulative 90% particle diameter (μm) in the volume-based particle size distribution from the small particle side.

The particle size distribution was determined by: a laser diffraction type particle size distribution measuring apparatus (e.g., Mastersizer 2000 manufactured by Sysmex Corporation) was used, water was used as a dispersion medium, and a nonionic surfactant Triton X-100 was used as a dispersant.

The shape of the filler is not limited, and may be a shape close to a sphere, a plate shape, or a fiber shape. From the viewpoint of suppressing a short circuit of the battery, the filler is preferably a plate-like particle, and is preferably a primary particle that does not aggregate.

The content of the filler contained in the adhesive porous layer is preferably 40 to 85 vol% of the total solid content of the adhesive porous layer. When the content of the filler is 40% by volume or more, further improvement in heat resistance of the separator, strength of the unit cell, and securing of battery safety can be expected. On the other hand, when the content of the filler is 85 vol% or less, the moldability and form of the adhesive porous layer can be maintained, which contributes to the improvement of the cell strength. The content of the filler is more preferably 45 vol% or more, still more preferably 50 vol% or more, still more preferably 80 vol% or less, and still more preferably 75 vol% or less of the total solid content of the adhesive porous layer.

The inorganic filler is preferably an inorganic filler that is stable against an electrolytic solution and electrochemically stable. Specific examples of the inorganic filler include metal hydroxides such as magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide; metal oxides such as magnesium oxide, aluminum oxide, boehmite (aluminum oxide monohydrate), titanium oxide, silica, zirconium oxide, and barium titanate; carbonates such as magnesium carbonate and calcium carbonate; sulfates such as magnesium sulfate, calcium sulfate, and barium sulfate; metal fluorides such as magnesium fluoride and calcium fluoride; clay minerals such as calcium silicate and talc; and so on. These inorganic fillers may be used alone in an amount of 1 kind, or may be used in combination with 2 or more kinds. The inorganic filler may be an inorganic filler whose surface is modified with a silane coupling agent or the like.

Examples of the organic filler include crosslinked acrylic resins such as crosslinked polymethyl methacrylate and crosslinked polystyrene, and crosslinked polymethyl methacrylate is preferable.

(other additives)

The adhesive porous layer in the present disclosure may contain a dispersant such as a surfactant, a wetting agent, an antifoaming agent, a pH adjuster, and other additives.

When the dispersant is contained, the dispersibility, coatability and storage stability of the coating liquid for forming the adhesive porous layer can be improved.

When the wetting agent, the defoaming agent, or the pH adjuster is contained, for example, affinity with the porous base material can be easily provided to the coating liquid for forming the adhesive porous layer, air absorption into the coating liquid can be suppressed, or pH adjustment can be performed.

Characteristics of the adhesive porous layer-

The thickness of the adhesive porous layer is preferably 0.5 to 5 μm on one surface of the porous substrate. When the thickness is 0.5 μm or more, the adhesion to the electrode is more excellent, and as a result, the cell strength of the battery is more excellent. From this viewpoint, the thickness is more preferably 1 μm or more. On the other hand, when the thickness is 5 μm or less, the cycle characteristics and load characteristics of the battery are more excellent. From this viewpoint, the thickness is more preferably 4.5 μm or less, and still more preferably 4 μm or less.

When the adhesive porous layer is provided on both surfaces of the porous substrate, the difference between the amount of coating on one surface and the amount of coating on the other surface is preferably 20 mass% or less of the total amount of coating on both surfaces. When the content is 20% by mass or less, the separator is less likely to curl, the handling properties are good, and the cycle characteristics of the battery are good.

The porosity of the adhesive porous layer is preferably 30% to 80%. When the porosity is 80% or less, mechanical properties that can withstand the pressurization step for bonding to the electrode can be ensured, and the surface opening ratio is not excessively high, which is suitable for ensuring the adhesive strength. On the other hand, a porosity of 30% or more is preferable from the viewpoint of good ion permeability.

The average pore diameter of the adhesive porous layer is preferably 10nm to 300nm, and more preferably 20nm to 200 nm. When the average pore diameter is 10nm or more (preferably 20nm or more), pores are less likely to be closed even if the resin contained in the adhesive porous layer swells when the adhesive porous layer is impregnated with the electrolyte solution. On the other hand, if the average pore diameter is 300nm or less (preferably 200nm or less), unevenness of the pores can be suppressed on the surface of the adhesive porous layer, and adhesive spots are uniformly distributed, and the adhesiveness to the electrode is further excellent. When the average pore diameter is 300nm or less (preferably 200nm or less), uniformity of ion transfer is high, and cycle characteristics and load characteristics of the battery are more excellent.

The average pore diameter (nm) of the adhesive porous layer was calculated by the following equation, assuming that all pores were cylindrical.

d＝4V/S

Wherein d represents the average pore diameter of the adhesive porous layer, and V represents the average pore diameter per 1m²The pore volume of the adhesive porous layer, S represents 1m per unit²Pore surface area of the adhesive porous layer.

Every 1m²The pore volume V of the adhesive porous layer was calculated from the porosity of the adhesive porous layer.

Every 1m²The pore surface area S of the adhesive porous layer was determined by the following method.

First, the BET formula is applied by nitrogen adsorption method to prepare a catalystThe specific surface area (m) of the porous substrate was calculated from the amount of nitrogen adsorbed²Specific surface area of the separator (m)²In terms of/g). Their specific surface area (m)²Multiplied by the respective weights per unit area (g/m)²) Calculating each 1m²Pore surface area of (a). Then, from every 1m²Pore surface area of the separator minus 1m per²The pore surface area of the porous substrate was calculated for each 1m²The pore surface area S of the adhesive porous layer.

Characteristics of separator for nonaqueous secondary battery

The thickness of the separator of the present disclosure is preferably 5 μm to 35 μm, more preferably 5 μm to 30 μm, even more preferably 5 μm to 25 μm, and even more preferably 5 μm to 20 μm, from the viewpoint of balance among mechanical strength, energy density of the battery, and output characteristics.

The porosity of the separator of the present disclosure is preferably 30% to 60% from the viewpoints of mechanical strength, adhesiveness to an electrode, and ion permeability.

The Gurley value (JIS P8117: 2009) of the separator of the present disclosure is preferably 50 seconds/100 ml to 800 seconds/100 ml, and more preferably 50 seconds/100 ml to 450 seconds/100 ml, from the viewpoint of good balance between mechanical strength and film resistance.

In the separator of the present disclosure, from the viewpoint of ion permeability, a value obtained by subtracting the Gurley value of the porous substrate from the Gurley value of the separator (a state in which the adhesive porous layer is formed on the porous substrate) (hereinafter, referred to as "difference between Gurley values") is preferably 300 seconds/100 ml or less, more preferably 150 seconds/100 ml or less, and still more preferably 100 seconds/100 ml or less. By setting the difference in Gurley value to 300 seconds/100 ml or less, the adhesive porous layer does not become too dense, and the ion permeability is maintained well, whereby excellent battery characteristics can be obtained. On the other hand, the difference in Gurley value is preferably 0 seconds/100 ml or more, and from the viewpoint of improving the adhesion between the adhesive porous layer and the porous substrate, it is preferably 10 seconds/100 ml or more.

The membrane resistance of the separator of the present disclosure is preferably 1ohm cm from the viewpoint of the load characteristics of the battery²～10ohm·cm². Here, the film resistance is a resistance value when the separator is impregnated with the electrolyte, and is measured by an alternating current method. The value of the membrane resistance varies depending on the type of electrolyte and the temperature, and is measured as follows: using 1mol/L LiBF₄-propylene carbonate: a mixed solvent of ethylene carbonate (mass ratio: 1) was used as an electrolyte, and the measurement was performed at a temperature of 20 ℃.

The separator of the present disclosure preferably has a puncture strength of 180g to 1000g, more preferably 200g to 600 g. The puncture strength of the separator is measured by the same method as the puncture strength of the porous substrate.

The thermal shrinkage rate at 120 ℃ of the separator of the present disclosure is preferably 12% or less in both the MD (Machine Direction) Direction and the TD (transverse Direction) Direction from the viewpoint of balance between shape stability and shutdown characteristics.

The tortuosity (tortuosity) of the separator of the present disclosure is preferably 1.2 to 2.8 from the viewpoint of ion permeability.

The amount of water contained in the separator of the present disclosure (on a mass basis) is preferably 1000ppm or less. The smaller the moisture content of the separator, the more the reaction between the electrolyte and water can be suppressed when the battery is constructed, and the gas generation in the battery can be suppressed, thereby improving the cycle characteristics of the battery. From this viewpoint, the moisture content contained in the separator of the present disclosure is more preferably 800ppm or less, and still more preferably 500ppm or less.

Method for manufacturing separator for nonaqueous secondary battery

The separator of the present disclosure can be manufactured, for example, by the following method: the adhesive porous layer is formed on the porous substrate by applying a coating liquid containing a PVDF resin onto the porous substrate to form a coating layer, and then curing the PVDF resin contained in the coating layer. Specifically, the adhesive porous layer can be formed by, for example, the following wet coating method.

The wet coating method is a film forming method in which the following steps are sequentially performed: (i) a coating liquid preparation step of dissolving or dispersing a PVDF resin in a solvent to prepare a coating liquid; (ii) a coating step of applying a coating liquid to a porous base material to form a coating layer; (iii) a solidification step of bringing the coating layer into contact with a solidification solution to induce phase separation and simultaneously cure the PVDF-based resin to obtain a composite having an adhesive porous layer on the porous substrate; (iv) a water washing step of washing the composite; and (v) a drying step of removing water from the composite.

Details of a wet coating method suitable for the separator of the present disclosure are as follows.

As a solvent for dissolving or dispersing the PVDF resin (hereinafter, also referred to as a "good solvent") used for preparing the coating liquid, a polar amide solvent such as N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide, or dimethylformamide can be preferably used.

From the viewpoint of forming an adhesive porous layer having a good porous structure, it is preferable to mix a phase separation agent that induces phase separation with a good solvent. Examples of the phase separating agent include water, methanol, ethanol, propanol, butanol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol (TPG), and the like. Preferably, the phase separating agent is mixed with the good solvent within a range that can secure a viscosity suitable for coating.

As a solvent used for preparing the coating liquid, a mixed solvent containing 60 mass% or more of a good solvent and 5 to 40 mass% of a phase separating agent is preferable from the viewpoint of forming an adhesive porous layer having a good porous structure.

From the viewpoint of forming an adhesive porous layer having a good porous structure, the concentration of the PVDF resin of the coating liquid is preferably 3% by mass to 10% by mass of the total mass of the coating liquid.

When the adhesive porous layer contains the filler and/or other components, the filler and/or other components may be dissolved or dispersed in the coating liquid.

The coating liquid may contain a dispersant such as a surfactant, a wetting agent, an antifoaming agent, a pH adjuster, and the like. These additives may remain in the adhesive porous layer if they are electrochemically stable and do not inhibit the reaction in the battery within the range of use of the nonaqueous secondary battery.

The coagulating liquid is generally composed of a good solvent and a phase-separating agent used for preparing the coating liquid, and water. From the production aspect, it is preferable that the mixing ratio of the good solvent to the phase separating agent is the same as the mixing ratio of the mixed solvent used for preparing the coating liquid. From the viewpoint of formation of a porous structure and productivity, the water content of the solidification solution is preferably 40 to 90 mass%.

The coating liquid can be applied to the porous substrate by a conventional coating method using a meyer bar, a die coater, a reverse roll coater, a gravure coater, or the like. When the adhesive porous layer is formed on both surfaces of the porous substrate, it is preferable to apply the coating liquid to both surfaces of the substrate at the same time from the viewpoint of productivity.

The adhesive porous layer can be produced by a dry coating method, in addition to the wet coating method described above.

The dry coating method is a method comprising: the coating liquid containing the PVDF-based resin and the solvent is applied to the porous substrate, the coating layer is dried, and the solvent is evaporated and removed, thereby obtaining the adhesive porous layer. However, the dry coating method is more likely to make the coating layer denser than the wet coating method, and therefore, the wet coating method is preferable in terms of obtaining a good porous structure.

The separator of the present disclosure may also be manufactured by the following method: an adhesive porous layer is produced as a separate sheet, and the adhesive porous layer and the porous base material are stacked and then combined by thermocompression bonding and/or an adhesive. As a method for producing the adhesive porous layer as a separate sheet, there is a method for forming the adhesive porous layer on a release sheet by applying the above-mentioned wet coating method or dry coating method.

< nonaqueous Secondary Battery

The nonaqueous secondary battery of the present disclosure is a nonaqueous secondary battery that obtains electromotive force by doping and dedoping lithium, and includes a positive electrode, a negative electrode, and the separator of the present disclosure. Doping means absorption, support, adsorption, or intercalation, and means a phenomenon in which lithium ions enter an active material of an electrode such as a positive electrode.

The nonaqueous secondary battery of the present disclosure has a structure in which, for example, a battery element in which a negative electrode and a positive electrode are opposed to each other with a separator interposed therebetween is sealed in an outer casing together with an electrolyte. The nonaqueous secondary battery of the present disclosure is particularly preferably used for a lithium ion secondary battery. The nonaqueous secondary battery of the present disclosure can be efficiently manufactured by using the separator of the present disclosure having excellent adhesion to the electrode. The nonaqueous secondary battery of the present disclosure has excellent cell strength by including the separator of the present disclosure having excellent adhesion to the electrode.

Hereinafter, embodiments of the positive electrode, the negative electrode, the electrolytic solution, and the outer casing of the nonaqueous secondary battery according to the present disclosure will be described.

The positive electrode may have a structure in which an active material layer containing a positive electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive aid. Examples of the positive electrode active material include lithium-containing transition metal oxides, and specific examples thereof include LiCoO₂、LiNiO₂、LiMn_1/2Ni_1/2O₂、LiCo_1/3Mn_1/3Ni_1/3O₂、LiMn₂O₄、LiFePO₄、LiCo_1/2Ni_1/2O₂、LiAl_1/4Ni_3/4O₂And the like. Examples of the binder resin include polyvinylidene fluoride resin. Examples of the conductive aid include carbon materials such as acetylene black, ketjen black, and graphite powder. Examples of the current collector include an aluminum foil, a titanium foil, and a stainless steel foil having a thickness of 5 to 20 μm.

According to one embodiment of the separator of the present disclosure, since the adhesive porous layer has excellent oxidation resistance, LiMn that can operate at a high voltage of 4.2V or more can be easily applied by disposing the adhesive porous layer on the positive electrode side of the nonaqueous secondary battery_1/2Ni_1/2O₂、LiCo_1/3Mn_1/3Ni_1/3O₂And the like as the positive electrode active material.

The negative electrode may have a structure in which an active material layer containing a negative electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive aid. Examples of the negative electrode active material include materials capable of electrochemically occluding lithium, and specific examples thereof include carbon materials; alloys of silicon, tin, aluminum, etc. with lithium; and so on. Examples of the binder resin include a polyvinylidene fluoride resin and a styrene-butadiene copolymer. Examples of the conductive aid include carbon materials such as acetylene black, ketjen black, and graphite powder. Examples of the current collector include a copper foil, a nickel foil, and a stainless steel foil having a thickness of 5 to 20 μm. In addition, a metal lithium foil may be used as the negative electrode instead of the above negative electrode.

In the electrode, it is preferable that the active material layer contain a large amount of a binder resin from the viewpoint of adhesiveness to the separator. On the other hand, from the viewpoint of improving the energy density of the battery, it is preferable that a large amount of the active material is contained in the active material layer, and the amount of the binder resin is relatively small. The separator of the present disclosure has excellent adhesion to the electrode, and therefore, the amount of the binder resin in the active material layer can be reduced to increase the amount of the active material, thereby improving the energy density of the battery. By applying the separator of the present disclosure, adhesion to a negative electrode using a solvent-based binder (specifically, a polyvinylidene fluoride-based resin) is excellent, and adhesion to a negative electrode using an aqueous binder (specifically, a styrene-butadiene copolymer) is also excellent.

The electrolyte is a solution obtained by dissolving a lithium salt in a nonaqueous solvent.

The lithium salt includes, for example, LiPF₆、LiBF₄、LiClO₄And the like.

Examples of the nonaqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine substitutes thereof; cyclic esters such as γ -butyrolactone and γ -valerolactone; and the like, and they may be used alone or in combination.

As an electrolytic solution, a cyclic carbonate and a chain carbonate are mixed in a ratio of 20: 80-40: an electrolyte solution obtained by mixing and dissolving 0.5 to 1.5mol/L of a lithium salt at a mass ratio of 60 (cyclic carbonate: chain carbonate) is preferable.

Examples of the outer package material include a metal case and an aluminum laminated film package. The shape of the battery is square, cylindrical, button, etc., and the separator of the present disclosure is applicable to any shape.

< method for producing nonaqueous secondary battery >

The method for manufacturing a nonaqueous secondary battery according to the present disclosure sequentially performs the following steps.

And (i) disposing the nonaqueous secondary battery separator of the present disclosure between a positive electrode and a negative electrode to produce a laminate.

And (ii) a step of housing the laminate in an outer packaging material, injecting an electrolyte solution into the outer packaging material, and then sealing the outer packaging material to produce a battery element.

And (iii) performing a hot press treatment on the battery element at a temperature of 65 ℃ to 75 ℃ to bond at least one of the positive electrode and the negative electrode to the nonaqueous secondary battery separator.

In the step (i), the separator may be disposed between the positive electrode and the negative electrode in a manner of stacking at least the positive electrode, the separator, and the negative electrode one on another in this order (so-called stack (stack) manner), or may be wound in a longitudinal direction in a manner of stacking the positive electrode, the separator, the negative electrode, and the separator in this order.

In the step (ii), the laminate may be housed in the outer package and then hot-pressed (dry hot-pressed) before the electrolyte is injected. In this case, since the electrode and the separator are bonded before the laminate is housed in the outer package, deformation of the laminate during transportation for housing in the outer package can be suppressed. In addition, since the laminate is further wet-hot-pressed in the step (iii) in a state where the PVDF resin contained in the adhesive porous layer of the separator swells in the electrolyte solution, the adhesion between the electrode and the separator can be further strengthened. In this case, the wet hot pressing may be performed under mild conditions (to the extent that the adhesion between the electrode and the separator, which is slightly weakened by the impregnation with the electrolyte solution, is recovered), that is, the temperature of the wet hot pressing may be set to a relatively low temperature, and therefore, the generation of gas due to the decomposition of the electrolyte solution and the electrolyte in the battery during the production of the battery may be suppressed. The dry hot pressing conditions are preferably 0.2MPa to 5MPa in pressure and 20 ℃ to 100 ℃. Of course, in the step (ii), the battery element may be manufactured by housing the laminate in the external packaging material and injecting the electrolyte solution into the external packaging material, and then sealing the external packaging material, without performing the dry hot pressing.

In the step (iii), the battery element produced in the step (ii) is subjected to wet hot pressing. Thus, the laminate is hot-pressed in a state where the PVDF resin contained in the adhesive porous layer of the separator swells in the electrolyte solution, and the electrode and the separator are well adhered to each other, whereby a nonaqueous secondary battery having excellent cell strength and battery characteristics can be obtained.

In the step (iii), the wet hot pressing is preferably performed under a pressing pressure of 0.2MPa to 2MPa and at a temperature of 60 ℃ or higher and less than 90 ℃. In particular, in the separator of the present disclosure, wet adhesion is exhibited even under mild conditions, and therefore a temperature of 65 ℃ or higher and 75 ℃ or lower is more preferable.