JP6171117B1 - Non-aqueous secondary battery separator and non-aqueous secondary battery - Google Patents

Abstract

A porous substrate and an adhesive porous layer provided on one or both surfaces of the porous substrate, wherein the proportion of hexafluoropropylene monomer units is 5.1 mass% or more and 6.9 mass% or less And a vinylidene fluoride-hexafluoropropylene binary copolymer having a weight average molecular weight of 810,000 or more and 3 million or less, wherein the vinylidene fluoride-hexafluoropropylene binary copolymer is 95% by mass of the total resin. The separator for non-aqueous secondary batteries provided with the adhesive porous layer which occupies the above.

Description

  The present invention relates to a separator for a non-aqueous secondary battery and a non-aqueous secondary battery.

  Non-aqueous secondary batteries represented by lithium ion secondary batteries are widely used as power sources for portable electronic devices such as notebook computers, mobile phones, digital cameras, and camcorders. With the miniaturization and weight reduction of portable electronic devices, the non-aqueous secondary battery exterior has been simplified and reduced in weight, and aluminum cans have been developed instead of stainless steel cans as exterior materials. Furthermore, instead of metal cans, packs made of aluminum laminate film have been developed. However, since the pack made of aluminum laminate film is soft, in a battery using the pack as an exterior material (so-called soft pack battery), due to impact from the outside or expansion and contraction of the electrode due to charge / discharge, the electrode and the separator Gaps are easily formed between them, and the cycle life may be reduced.

  In order to solve the above problems, a technique for improving the adhesion between the electrode and the separator has been proposed. As one of the techniques, a separator having an adhesive porous layer containing a polyvinylidene fluoride resin on a polyolefin microporous film is known. When this separator is hot-pressed over the electrode in a state containing an electrolytic solution, the separator adheres favorably to the electrode via the adhesive porous layer, so that the cycle life of the soft pack battery can be improved. A separator in which an adhesive porous layer containing a polyvinylidene fluoride resin is formed on a polyolefin microporous film is suitable for a soft pack battery, and various technical proposals have been made with the aim of further improving performance.

  For example, Patent Document 1 discloses an adhesive porous layer containing two types of polyvinylidene fluoride resins having different ratios of hexafluoropropylene monomer units. For example, Patent Document 2 discloses a porous layer containing a polyvinylidene fluoride resin and inorganic particles. For example, Patent Document 3 discloses a porous organic polymer film containing a polyvinylidene fluoride resin that is a terpolymer. For example, Patent Document 4 discloses an adhesive porous layer containing a polyvinylidene fluoride resin in which the ratio of hexafluoropropylene monomer units is 0.1 mol% or more and 5% mol or less. For example, Patent Document 5 discloses a porous layer containing a polyvinylidene fluoride resin having a weight average molecular weight of 1,000,000 or more.

International Publication No. 2013/058367 JP 2012-74367 A Japanese Patent No. 5171150 International Publication No. 2014/021293 International Publication No. 2016/002567

  In recent years, non-aqueous secondary batteries represented by lithium ion secondary batteries have been studied for application as batteries for electric power storage and electric vehicles because of their high energy density. When non-aqueous secondary batteries are used for power storage and electric vehicles, it is necessary to increase the area, but with the increase in the area of soft pack batteries, adhesive porous materials containing polyvinylidene fluoride resin Even in the case of a separator having a layer, adhesion between the electrode and the separator is insufficient, and the battery capacity may be reduced, the charge / discharge characteristics may be deteriorated, and the battery may be swollen. As the area of the battery increases, it is desired to improve the adhesion of the adhesive porous layer to the electrode.

  By the way, a battery including a separator having an adhesive porous layer containing a polyvinylidene fluoride resin generally manufactures a laminate of an electrode and a separator, and accommodates the laminate in an exterior material. After injecting the liquid, it is manufactured by performing a heat press treatment (referred to as “wet heat press” in this specification). As the area of the battery increases, a separator that is superior in adhesion by wet heat press is desired.

The embodiment of the present disclosure has been made under the above circumstances.
Embodiments of the present disclosure provide a separator for a non-aqueous secondary battery that is provided with an adhesive porous layer containing a polyvinylidene fluoride-based resin and has excellent adhesion to an electrode by wet heat press. Objective.
Another object of the embodiment of the present disclosure is to provide a non-aqueous secondary battery excellent in cell strength and cycle characteristics.

  Specific means for solving the problems include the following aspects.

[1] A porous base material and an adhesive porous layer provided on one or both sides of the porous base material, wherein the proportion of hexafluoropropylene monomer units is 5.1% by mass or more and 6.9%. A vinylidene fluoride-hexafluoropropylene binary copolymer having a mass% or less and a weight average molecular weight of 810,000 to 3,000,000, wherein the vinylidene fluoride-hexafluoropropylene binary copolymer is An adhesive porous layer occupying 95% by mass or more , wherein the adhesive porous layer further contains an inorganic filler, and the content of the inorganic filler in the adhesive porous layer is the adhesive porous layer A separator for a non-aqueous secondary battery that is 33% by volume or more and 80% by volume or less of the total solid content of the layer .
[2] The separator for a non-aqueous secondary battery according to [1], wherein the thickness of one surface of the adhesive porous layer is 0.5 μm or more and 5 μm or less.
[ 3 ] The non-aqueous secondary battery separator according to [ 1 ] or [2] , wherein the inorganic filler is at least one selected from a metal hydroxide and a metal oxide.
[ 4 ] The non-aqueous secondary battery separator according to any one of [ 1 ] to [3], wherein the inorganic filler is at least one of magnesium hydroxide and magnesium oxide.
[ 5 ] A positive electrode, a negative electrode, and a separator for a nonaqueous secondary battery according to any one of the above [1] to [ 4 ] disposed between the positive electrode and the negative electrode. A non-aqueous secondary battery that obtains an electromotive force by doping.

According to an embodiment of the present disclosure, a separator provided with an adhesive porous layer containing a polyvinylidene fluoride-based resin, which is excellent in adhesion with an electrode by wet heat press, is provided for a non-aqueous secondary battery. The
Moreover, according to the embodiment of the present disclosure, a non-aqueous secondary battery excellent in cell strength and cycle characteristics is provided.

  Embodiments will be described below. In addition, these description and an Example illustrate embodiment, and do not restrict | limit the range of embodiment.

  In the present specification, a numerical range indicated using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.

  In this specification, the term “process” is not limited to an independent process, and is included in this term if the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes. .

  With respect to the separator of the present disclosure, the “longitudinal direction” means the longitudinal direction of the porous substrate and the separator manufactured in a long shape, and the “width direction” means a direction orthogonal to the “longitudinal direction”. means. The “longitudinal direction” is also referred to as “MD direction”, and the “width direction” is also referred to as “TD direction”.

  In this specification, the “monomer unit” of the polyvinylidene fluoride resin means a constituent unit of the polyvinylidene fluoride resin, which is obtained by polymerizing the monomer.

<Separator for non-aqueous secondary battery>
A separator for a nonaqueous secondary battery of the present disclosure (also simply referred to as “separator”) includes a porous substrate and an adhesive porous layer provided on one or both surfaces of the porous substrate. In the separator of the present disclosure, the adhesive porous layer includes a vinylidene fluoride having a hexafluoropropylene monomer unit ratio of 5.1 mass% to 6.9 mass% and a weight average molecular weight of 810,000 to 3 million. -It contains a hexafluoropropylene binary copolymer, and the vinylidene fluoride-hexafluoropropylene binary copolymer accounts for 95% by mass or more of the total resin.

  Hereinafter, the vinylidene fluoride monomer unit is also referred to as “VDF unit”, the hexafluoropropylene monomer unit is also referred to as “HFP unit”, and the vinylidene fluoride-hexafluoropropylene binary copolymer is referred to as “VDF-HFP binary”. VDF-HFP binary copolymer having an HFP unit ratio of 5.1 mass% to 6.9 mass% and a weight average molecular weight of 810,000 to 3 million is also referred to as “specific VDF-”. It is also referred to as “HFP binary copolymer”.

  The separator of this indication is excellent in adhesion with an electrode by wet heat press by providing the adhesive porous layer which contains specific VDF-HFP binary copolymer in the ratio of 95 mass% or more of all resin. This mechanism is not necessarily clear, but is presumed as follows.

In the VDF-HFP binary copolymer, the greater the proportion of HFP units, the higher the mobility of the polymer chain when heated. Therefore, when hot pressing is performed, the VDF-HFP binary copolymer is more easily bonded to the electrode as the proportion of HFP units is larger, and is also bonded under lower temperature hot pressing conditions.
In addition, the VDF-HFP binary copolymer is more likely to swell in the electrolyte solution as the proportion of HFP units increases. For this reason, when wet heat pressing is performed, the VDF-HFP binary copolymer is appropriately swollen and easily adhered to the electrode when the proportion of the HFP unit is large to some extent.
Therefore, when paying attention to the behavior of the VDF-HFP binary copolymer, it is advantageous for adhesion to the electrode that the proportion of the HFP unit in the VDF-HFP binary copolymer is large to some extent.

However, when the adhesive porous layer is formed from a VDF-HFP binary copolymer having a large proportion of HFP units, the porosity tends to be high and the pore diameter tends to be large. When the porosity of the adhesive porous layer is high and the pore diameter is large, the area of the VDF-HFP binary copolymer portion that becomes the adhesion site with the electrode on the surface of the adhesive porous layer decreases, and VDF- HFP binary copolymers will be present sparsely. Therefore, as the proportion of HFP units in the VDF-HFP binary copolymer constituting the adhesive porous layer increases, the adhesion between the adhesive porous layer and the electrode tends to weaken. In addition, if the porosity of the adhesive porous layer is high and the pore diameter is large, ion migration at the electrode interface becomes non-uniform, which adversely affects the cycle characteristics and load characteristics of the battery.
Moreover, when there are too many ratios of the HFP unit of a VDF-HFP binary copolymer, it will melt | dissolve in electrolyte solution and there exists a tendency for adhesion | attachment with an electrode to become weak.
Therefore, if attention is paid to the surface morphology of the adhesive porous layer, it is advantageous that the proportion of HFP units in the VDF-HFP binary copolymer is smaller, and the VDF-HFP copolymer is not dissolved in the electrolyte. It is preferable that the ratio of HFP units in the VDF-HFP binary copolymer is not too large.

Therefore, the specific VDF-HFP binary copolymer has a HFP unit ratio of 5.1 mass% to 6.9 mass%.
The specific VDF-HFP binary copolymer has a high mobility of the polymer chain when heated because the ratio of HFP units is 5.1% by mass or more, and it is compared with the electrode when hot pressing is performed. Strong adhesion can be obtained. On the other hand, the specific VDF-HFP binary copolymer has an HPF unit ratio of 6.9% by mass or less, so that an adhesive porous layer having a porosity and a pore size that are small enough not to inhibit ion permeability. Realized and realizes a surface morphology suitable for adhesion to electrodes.
Moreover, since the specific VDF-HFP binary copolymer swells appropriately in the electrolytic solution when the ratio of HFP units is 5.1 mass% to 6.9 mass%, when wet heat pressing is performed. Since it adheres well to the electrode and does not dissolve in the electrolyte solution and does not swell excessively, adhesion to the electrode is maintained.
From the above viewpoint, the lower limit of the ratio of HFP units of the specific VDF-HFP binary copolymer is 5.1% by mass or more, and the upper limit of the ratio of HFP units of the specific VDF-HFP binary copolymer is It is 6.9 mass% or less, More preferably, it is 6.5 mass% or less, More preferably, it is 6.0 mass% or less.

In addition, the specific VDF-HFP binary copolymer has a weight average molecular weight (Mw) of 810,000 to 3 million.
When the specific VDF-HFP binary copolymer has an Mw of 810,000 or more, the adhesive porous layer can be sufficiently imparted with a mechanical property that can withstand the adhesion treatment with the electrode. For this reason, it is possible to increase the pressure of the hot press conditions to more firmly bond the separator to the electrode.
From the above viewpoint, the Mw of the specific VDF-HFP binary copolymer is 810,000 or more, more preferably 1 million or more, and further preferably 1.1 million or more.
On the other hand, the VDF-HFP binary copolymer having an Mw of over 3 million, the viscosity of the coating liquid for coating and forming the adhesive porous layer becomes too high, and the porous porous layer is formed. Difficult to do.
From the above viewpoint, the Mw of the specific VDF-HFP binary copolymer is 3 million or less, more preferably 2.5 million or less, and further preferably 2 million or less.

  In this embodiment, 95% by mass or more of the total resin contained in the adhesive porous layer is a specific VDF-HFP binary copolymer. This means that the adhesive porous layer contains substantially no other resin other than the specific VDF-HFP binary copolymer, and substantially contains only the specific VDF-HFP binary copolymer as the binder resin. It means to do. As a result, the adhesive porous layer of the present embodiment suppresses the non-uniformity of the porous structure due to uneven mixing of multiple types of resins, is excellent in the uniformity of the porous structure, and adheres to the electrode. A suitable surface morphology is achieved.

  As described above, the effect of the HFP unit ratio of the specific VDF-HFP binary copolymer, the effect of the weight average molecular weight of the specific VDF-HFP binary copolymer, and the adhesive porous layer are substantially specific VDF. Combined with the effect of containing only the -HFP binary copolymer, the separator of the present disclosure is excellent in adhesion with an electrode by hot pressing, and particularly excellent in adhesion with an electrode by wet heat pressing.

  The separator of the present disclosure is applied not only to an electrode using a solvent-based binder (specifically, a polyvinylidene fluoride-based resin) but also to an electrode using an aqueous binder (specifically, a styrene-butadiene copolymer). Excellent adhesion.

Since the separator of this indication is excellent in adhesion to an electrode, the nonaqueous secondary battery to which the separator of this indication is applied is excellent in cell strength.
Moreover, since the separator of this indication is excellent in the uniformity of the porous structure of an adhesive porous layer, and is excellent in the adhesion | attachment with respect to an electrode, the non-aqueous secondary battery to which the separator of this indication is applied is excellent in cycling characteristics.

  According to the separator of the present disclosure, formation of a gap between the electrode and the separator due to expansion and contraction of the electrode accompanying charging / discharging or external impact is suppressed. Therefore, the separator of the present disclosure is suitable for a soft pack battery having an aluminum laminate film pack as an exterior material. According to the separator of the present disclosure, a soft pack battery having high battery performance is provided.

  In one embodiment of the separator of the present disclosure, the adhesive porous layer contains the specific VDF-HFP binary copolymer in a proportion of 95% by mass or more of the total resin, so that a relatively low pressure and low temperature heat can be obtained. Even with pressing, it adheres well to the electrode. Where the hot press conditions are high pressure and high temperature, the porous structure of the adhesive porous layer is crushed. According to one embodiment of the separator of the present disclosure, the hot press conditions can be relatively gentle, The ion permeability of the separator after bonding is maintained, and the battery characteristics are excellent. Moreover, according to one embodiment of the separator of the present disclosure, the temperature at the time of performing the wet heat press can be set to a relatively low temperature, so that gas generation due to decomposition of the electrolytic solution and the electrolyte is suppressed.

  In one embodiment of the separator of the present disclosure, the adhesive porous layer contains the specific VDF-HFP binary copolymer in a proportion of 95% by mass or more of the total resin, so that the porous substrate and the adhesive porous layer The adhesion between the layers is also improved, and the peel resistance between the layers is improved.

In one embodiment of the separator of the present disclosure, the adhesive porous layer contains the specific VDF-HFP binary copolymer in a proportion of 95% by mass or more of the total resin, so that the porous substrate and the adhesive porous layer Excellent ion transfer at the interface between layers.
Conventionally, a separator formed by applying an adhesive porous layer to a porous substrate is likely to clog the interface between the two, and the ion migration at the interface deteriorates, realizing good battery characteristics. There were things that were difficult.
On the other hand, the adhesive porous layer according to an embodiment of the present disclosure has a fine porous structure, and therefore has an even distribution of pores and a large number of pores. Therefore, the probability that the hole of the porous substrate and the hole of the adhesive porous layer can be connected is increased, and the deterioration of the battery performance due to clogging can be suppressed.

  One embodiment of the separator of the present disclosure has good adhesion to the electrode even by a heat press treatment (referred to as “dry heat press” in this specification) performed without impregnating the electrolytic solution. Prior to the wet heat press, if the laminate is dry heat pressed to adhere the electrode and the separator, deformation of the laminate can be suppressed.

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

[Porous substrate]
In the present disclosure, the porous substrate means a substrate having pores or voids therein. Examples of such a substrate include a microporous membrane; a porous sheet made of a fibrous material such as a nonwoven fabric and paper; a composite porous material in which one or more other porous layers are laminated on a microporous membrane or a porous sheet. Sheet; and the like. A microporous membrane means a membrane that has a large number of micropores inside and has a structure in which these micropores are connected, allowing gas or liquid to pass from one surface to the other. To do.

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

  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 a function of preventing thermal runaway of the battery by blocking the movement of ions by dissolving the material and closing the pores of the porous base material when the battery temperature increases. As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200 ° C. is preferable. Examples of the thermoplastic resin include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; among these, polyolefins are preferable.

  As the porous substrate, a microporous membrane containing polyolefin (referred to as “polyolefin microporous membrane”) is preferable. Examples of the polyolefin microporous membrane include polyolefin microporous membranes that are applied to conventional separators for non-aqueous secondary batteries, and it is possible to select those having sufficient mechanical properties and ion permeability. preferable.

  The polyolefin microporous membrane preferably contains polyethylene from the viewpoint of exhibiting a shutdown function, and the polyethylene content is preferably 95% by mass or more of the total mass of the polyolefin microporous membrane.

  The polyolefin microporous membrane is preferably a polyolefin microporous membrane containing polyethylene and polypropylene from the viewpoint of imparting heat resistance that does not easily break when exposed to high temperatures. Examples of such a polyolefin microporous membrane include a microporous membrane in which polyethylene and polypropylene are mixed in one layer. The microporous membrane preferably contains 95% by mass or more of polyethylene and 5% by mass or less of polypropylene from the viewpoint of achieving both a shutdown function and heat resistance. Further, from the viewpoint of achieving both shutdown function and heat resistance, the polyolefin microporous membrane has a laminated structure of two or more layers, at least one layer contains polyethylene, and at least one layer contains polypropylene, preferable.

  The polyolefin contained in the polyolefin microporous membrane is preferably a polyolefin having a weight average molecular weight (Mw) of 100,000 to 5,000,000. When the Mw of the polyolefin is 100,000 or more, sufficient mechanical properties can be secured. On the other hand, when the Mw of the polyolefin is 5 million or less, the shutdown characteristics are good and the film is easy to mold.

  The polyolefin microporous membrane can be produced, for example, by the following method. That is, it is a method in which a melted polyolefin resin is extruded from a T-die to form a sheet, which is crystallized and then stretched, and further heat-treated to form a microporous film. Alternatively, by extruding a polyolefin resin melted with a plasticizer such as liquid paraffin from a T-die, cooling it into a sheet, stretching, and then extracting the plasticizer and heat treating it into a microporous membrane. is there.

  Examples of porous sheets made of fibrous materials include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; heat resistant resins such as aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide; Nonwoven fabric, paper, etc. made of the fibrous material of Here, the heat resistant resin means a polymer having a melting point of 200 ° C. or higher, or a polymer having no melting point and a decomposition temperature of 200 ° C. or higher.

  Examples of the composite porous sheet include a microporous film or a sheet in which a functional layer is laminated on a porous sheet. Such a composite porous sheet is preferable from the viewpoint of further function addition by the functional layer. As the functional layer, from the viewpoint of imparting heat resistance, a porous layer containing a heat resistant resin or a porous layer containing a heat resistant resin and an inorganic filler is preferable. 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. As a method of providing a functional layer on a microporous membrane or a porous sheet, a method of applying a functional layer to a microporous membrane or a porous sheet, a method of bonding a microporous membrane or a porous sheet and a functional layer with an adhesive And a method of thermocompression bonding a microporous membrane or a porous sheet and a functional layer.

  The porous substrate may be subjected to various surface treatments within the range that does not impair the properties of the porous substrate for the purpose of improving the wettability with the coating liquid for forming the adhesive porous layer. Good. Examples of the surface treatment include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

[Characteristics of porous substrate]
From the viewpoint of obtaining good mechanical properties and internal resistance, the thickness of the porous substrate is preferably 3 μm to 25 μm, more preferably 5 μm to 25 μm, and even more preferably 5 μm to 20 μm.

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

  The Gurley value (JIS P8117: 2009) of the porous substrate is preferably 50 seconds / 100 cc to 800 seconds / 100 cc from the viewpoint of preventing short circuit of the battery and obtaining sufficient ion permeability, and 50 seconds / 100 cc to 400 seconds / 100 cc is more preferable.

  The puncture strength of the porous substrate is preferably 200 g or more and more preferably 250 g or more from the viewpoint of improving the production yield. The puncture strength of the porous substrate is measured by performing a puncture test using a KES-G5 handy compression tester manufactured by Kato Tech Co., Ltd. under the conditions of a radius of curvature of the needle tip of 0.5 mm and a puncture speed of 2 mm / sec. Refers to load (g).

  The average pore diameter of the porous substrate is preferably 20 nm to 100 nm. When the average pore diameter of the porous substrate is 20 nm or more, ions easily move and good battery performance is easily obtained. From this viewpoint, the average pore diameter of the porous substrate is more preferably 30 nm or more, and further preferably 40 nm or more. On the other hand, when the average pore diameter of the porous substrate is 100 nm 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 90 nm or less, and further preferably 80 nm or less. The average pore diameter of the porous substrate is a value measured using a palm porometer, and can be measured using, for example, a palm porometer (PFP CFP-1500-A) based on ASTM E1294-89. .

[Adhesive porous layer]
In the present disclosure, the adhesive porous layer is a porous layer that is provided on one side or both sides of a porous substrate and contains a specific VDF-HFP binary copolymer.

  The adhesive porous layer has a structure in which a large number of micropores are connected to each other and these micropores are connected to each other, and gas or liquid can pass from one surface to the other surface.

  The adhesive porous layer is a layer that is provided on one or both sides of the porous substrate as the outermost layer of the separator and can adhere to the electrode when the separator and the electrode are stacked and hot pressed.

  The adhesive porous layer is preferably present on both sides rather than only on one side of the porous substrate from the viewpoint of excellent cell strength and battery cycle characteristics (capacity retention rate). This is because when the adhesive porous layer is on both sides of the porous substrate, both sides of the separator are well adhered to both electrodes via the adhesive porous layer.

  The adhesive porous layer contains at least a specific VDF-HFP binary copolymer. The adhesive porous layer may further contain other resins or fillers other than the specific VDF-HFP binary copolymer.

[Specific VDF-HFP binary copolymer]
In the present disclosure, the specific VDF-HFP binary copolymer is a binary copolymer having only VDF units and HFP units. From the viewpoint that VDF-HFP binary copolymer can be firmly bonded to an electrode at an appropriate bonding temperature as compared with a multi-component copolymer having VDF units, HFP units and other monomer units. preferable.

  The specific VDF-HFP binary copolymer has a HFP unit ratio of 5.1 mass% to 6.9 mass%. The proportion of HFP units significantly affects the bonding temperature, and if it is less than 5.1% by mass, hot pressing at a high temperature is required, and the hot pressing process may adversely affect the performance of the battery. When the ratio of the HFP unit exceeds 6.9% by mass, the VDF-HFP binary copolymer may not be able to maintain sufficient adhesion with the electrode within the normally assumed battery operating temperature range, which is not preferable. The proportion of HFP units in the specific VDF-HFP binary copolymer is more preferably 6.5% by mass or less, and still more preferably 6.0% by mass or less.

  The specific VDF-HFP binary copolymer has a weight average molecular weight (Mw) of 810,000-3 million. When the Mw of the VDF-HFP binary copolymer is smaller than 810,000, sufficient adhesive strength is not exhibited and good battery performance may not be obtained. When the Mw of the VDF-HFP binary copolymer exceeds 3 million, the moldability of the adhesive porous layer is unfavorable. Moreover, it is difficult to obtain a polymer having a weight average molecular weight exceeding 3 million. The Mw of the specific VDF-HFP binary copolymer is more preferably 1 million or more, further preferably 1.1 million or more, more preferably 2.5 million or less, and further preferably 2 million or less.

  Examples of the method for producing the specific VDF-HFP binary copolymer include emulsion polymerization and suspension polymerization. It is also possible to select a commercially available VDF-HFP binary copolymer that satisfies the ratio of HFP units and the weight average molecular weight.

  The content of the specific VDF-HFP binary copolymer contained in the adhesive porous layer is 95% by mass or more of the total amount of all resins contained in the adhesive porous layer, more preferably 97% by mass or more, More preferably, it is 98 mass% or more, More preferably, it is 99 mass% or more, Most preferably, it is 100 mass%.

[Other resins]
In the present disclosure, the adhesive porous layer may contain a polyvinylidene fluoride resin other than the specific VDF-HFP binary copolymer, or may contain a resin other than the polyvinylidene fluoride resin. Good. However, the resin other than the specific VDF-HFP binary copolymer contained in the adhesive porous layer is 5% by mass or less of the total amount of all resins contained in the adhesive porous layer.

  Examples of the polyvinylidene fluoride resin other than the specific VDF-HFP binary copolymer include, for example, a VDF-HFP binary copolymer in which the proportion of HFP units is different from that of the specific VDF-HFP binary copolymer; Homopolymer (ie, polyvinylidene fluoride); a copolymer of vinylidene fluoride and at least one selected from fluorine-containing monomers such as tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, and vinyl fluoride A copolymer of vinylidene fluoride, hexafluoropropylene, and at least one selected from fluorine-containing monomers such as tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, and vinyl fluoride.

  Other resins than the polyvinylidene fluoride resin include fluorine rubber, acrylic resin, styrene-butadiene copolymer, homopolymer or copolymer of vinyl nitrile compound (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose , Hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyether (polyethylene oxide, polypropylene oxide, etc.) and the like.

[Filler]
In the present disclosure, the adhesive porous layer may contain a filler made of an inorganic material or an organic material for the purpose of improving the slipperiness and heat resistance of the separator. In that case, it is preferable to make it content and particle size which do not interfere with the effect of this indication.

  The average primary particle diameter of the filler is preferably from 0.01 μm to 5 μm, the lower limit is more preferably 0.1 μm or more, the upper limit is more preferably 1.5 μm or less, and even 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 10% cumulative particle diameter (μm) in the volume-based particle size distribution calculated from the small particle side, and d90 represents a 90% cumulative particle in the volume-based particle size distribution calculated from the small particle side. Represents the diameter (μm). The particle size distribution is measured using, for example, a laser diffraction particle size distribution measuring apparatus (for example, Mastersizer 2000 manufactured by Sysmex Corporation), using water as a dispersion medium, and a small amount of a nonionic surfactant Triton X-100 as a dispersant. Done with.

[Inorganic filler]
The adhesive porous layer preferably contains an inorganic filler from the viewpoint of further improving the heat resistance of the separator, the cell strength, and ensuring the safety of the battery.

  The inorganic filler in the present disclosure is preferably an inorganic filler that is stable with respect to the electrolytic solution and electrochemically stable. Specifically, for example, metal hydroxide such as magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, boron hydroxide; magnesium oxide, alumina, titania Metal oxides such as silica, zirconia 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; And clay minerals such as calcium silicate and talc. These inorganic fillers may be used alone or in combination of two or more. The inorganic filler may be surface-modified with a silane coupling agent or the like.

  The inorganic filler in the present disclosure is preferably at least one of a metal hydroxide and a metal oxide from the viewpoint of ensuring stability in the battery and ensuring the safety of the battery. The inorganic filler in the present disclosure is preferably an inorganic compound containing magnesium (for example, magnesium hydroxide, magnesium oxide, magnesium carbonate, magnesium sulfate, magnesium fluoride, etc.) from the viewpoint of suppressing gas generation in the battery. Magnesium hydroxide or magnesium oxide is more preferred. The gas generated by the decomposition of the electrolyte or electrolyte contains hydrogen fluoride as the main component. Inorganic compounds containing magnesium easily form a film on the particle surface by reaction with hydrogen fluoride. It is presumed that the reaction with hydrogen fluoride is limited, and the generation reaction of gas that easily occurs in a chain is suppressed.

  The particle shape of the inorganic filler is not limited, and may be a shape close to a sphere or a plate shape, but from the viewpoint of suppressing short circuit of the battery, it should be a plate-like particle or a non-aggregated primary particle. Is preferred.

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

[Organic filler]
Examples of the organic filler in the present disclosure include cross-linked acrylic resins such as cross-linked polymethyl methacrylate, cross-linked polystyrene, and the like, and cross-linked polymethyl methacrylate is preferable.

[Other additives]
The adhesive porous layer in the present disclosure may contain additives such as a dispersant such as a surfactant, a wetting agent, an antifoaming agent, and a pH adjusting agent. The dispersant is added to the coating solution for forming the adhesive porous layer for the purpose of improving dispersibility, coating property, and storage stability. Wetting agents, antifoaming agents, and pH adjusters are used in coating liquids for forming an adhesive porous layer, for example, for the purpose of improving familiarity with porous substrates, and for entraining air in the coating liquid. It is added for the purpose of suppressing or adjusting the pH.

[Characteristics of adhesive porous layer]
The thickness of the adhesive porous layer is preferably 0.5 μm to 5 μm on one side of the porous substrate. When the thickness is 0.5 μm or more, the adhesion to the electrode is 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 further preferably 4 μm or less.

  When the adhesive porous layer is provided on both sides of the porous substrate, the difference between the coating amount on one side and the coating amount on the other side is 20% by mass or less of the total coating amount on both sides. Is preferred. When the content is 20% by mass or less, the separator is difficult to curl, the handling property is 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, it is possible to secure mechanical properties that can withstand the pressing process for bonding to the electrode, and the surface opening ratio does not become too high, which is suitable for securing the adhesive force. On the other hand, a porosity of 30% or more is preferable from the viewpoint of improving ion permeability.

  The average pore size of the adhesive porous layer is preferably 10 nm to 300 nm, and more preferably 20 nm to 200 nm. When the average pore size is 10 nm or more (preferably 20 nm or more), when the adhesive porous layer is impregnated with the electrolyte, the pores are not easily blocked even if the resin contained in the adhesive porous layer swells. On the other hand, when the average pore diameter is 300 nm or less (preferably 200 nm or less), non-uniformity of the opening is suppressed on the surface of the adhesive porous layer, and the adhesion points are evenly distributed, and the adhesion to the electrode is excellent. Further, when the average pore diameter is 300 nm or less (preferably 200 nm or less), the uniformity of ion migration is high, and the cycle characteristics and load characteristics of the battery are excellent.

The average pore diameter (nm) of the adhesive porous layer is calculated according to the following formula, assuming that all pores are cylindrical.
d = 4V / S
In the formula, d is an average pore diameter (diameter) of the adhesive porous layer, V is a pore volume per 1 m ² of the adhesive porous layer, and S is a pore surface area per 1 m ² of the adhesive porous layer.
The pore volume V per 1 m ² of the adhesive porous layer is calculated from the porosity of the adhesive porous layer.
The pore surface area S per 1 m ^{2 of the} adhesive porous layer is determined by the following method.
First, a specific surface area of the porous substrate (m 2 ^{/ g)} and specific surface area of the separator (m 2 ^{/ g),} by applying the BET equation to the nitrogen gas adsorption method, is calculated from the nitrogen gas adsorption. The specific surface area (m ² / g) is multiplied by the basis weight (g / m ² ) to calculate the pore surface area per 1 m ² . Then, the pore surface area per 1 m ^{2 of the} porous substrate is subtracted from the pore surface area per 1 m ² of the separator to calculate the pore surface area S per 1 m ² of the adhesive porous layer.

[Characteristics of non-aqueous secondary battery separator]
The thickness of the separator of the present disclosure is preferably 5 μm to 35 μm, more preferably 5 μm to 30 μm, still more preferably 10 μm to 25 μm, and even more preferably 10 μm to 20 μm, from the viewpoints of mechanical strength, battery energy density, and output characteristics. .

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

  The Gurley value (JIS P8117: 2009) of the separator of the present disclosure is preferably 50 seconds / 100 cc to 800 seconds / 100 cc, and preferably 50 seconds / 100 cc to 400 seconds / 100 cc, from the viewpoint of a good balance between mechanical strength and membrane resistance. More preferred.

  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 (the state in which the adhesive porous layer is formed on the porous substrate) (hereinafter referred to as “Gurley”). The value difference ”is preferably 300 seconds / 100 cc or less, more preferably 150 seconds / 100 cc or less, and still more preferably 100 seconds / 100 cc or less. When the Gurley value difference is 300 seconds / 100 cc or less, the adhesive porous layer does not become too dense, the ion permeability is kept good, and excellent battery characteristics are obtained. On the other hand, the Gurley value difference is preferably 0 second / 100 cc or more, and preferably 10 seconds / 100 cc or more from the viewpoint of increasing the adhesive force between the adhesive porous layer and the porous substrate.

The film resistance of the separator of the present disclosure, in view of the load characteristics of the ^{battery, 1ohm · cm 2 ~10ohm · cm} 2 is preferred. Here, the membrane resistance is a resistance value when the separator is impregnated with an electrolytic solution, and is measured by an alternating current method. The value of the membrane resistance varies depending on the type and temperature of the electrolytic solution. The above value is a mixed solvent of 1 mol / L LiBF ₄ -propylene carbonate: ethylene carbonate (mass ratio 1: 1) as the electrolytic solution, and the temperature is 20 ° C. It is the value measured by.

  The puncture strength of the separator of the present disclosure is preferably 200 g to 1000 g, and more preferably 250 g to 600 g. The method for measuring the puncture strength of the separator is the same as the method for measuring the puncture strength of the porous substrate.

  The thermal shrinkage rate at 120 ° C. of the separator of the present disclosure is preferably 10% or less in both the MD direction and the TD direction from the viewpoint of the balance between shape stability and shutdown characteristics.

  The curvature of the separator of the present disclosure is preferably 1.5 to 2.5 from the viewpoint of ion permeability.

  The moisture content (mass basis) contained in the separator of the present disclosure is preferably 1000 ppm or less. The smaller the moisture content of the separator, the more the reaction between the electrolytic solution and water can be suppressed when the battery is configured, the gas generation in the battery can be suppressed, and the cycle characteristics of the battery are improved. From this viewpoint, the amount of water contained in the separator of the present disclosure is more preferably 800 ppm or less, and further preferably 500 ppm or less.

[Method for producing separator for non-aqueous secondary battery]
The separator of the present disclosure is formed by, for example, coating a coating liquid containing a polyvinylidene fluoride resin on a porous substrate to form a coating layer, and then solidifying the polyvinylidene fluoride resin contained in the coating layer By making it, it manufactures with the method of forming an adhesive porous layer on a porous base material. Specifically, the adhesive porous layer can be formed, for example, by the following wet coating method.

  The wet coating method includes (i) a coating liquid preparation step in which a polyvinylidene fluoride resin is dissolved or dispersed in a solvent to prepare a coating liquid, and (ii) the coating liquid is applied onto a porous substrate. A coating step for forming a coating layer; (iii) bringing the coating layer into contact with a coagulation liquid, solidifying the polyvinylidene fluoride resin while inducing phase separation, and then adhering the porous layer on the porous substrate (Iv) a water washing step for washing the composite membrane with water, and (v) a drying step for removing water from the composite membrane. Details of the wet coating method suitable for the separator of the present disclosure are as follows.

  As a solvent for dissolving or dispersing the polyvinylidene fluoride resin used for the preparation of the coating liquid (hereinafter also referred to as “good solvent”), N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), Polar amide solvents such as dimethylformamide and dimethylformamide are 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 in a good solvent. Examples of the phase separation agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol (TPG). The phase separation agent is preferably mixed with a good solvent as long as a viscosity suitable for coating can be secured.

  The solvent used for preparing the coating liquid is a mixture containing 60% by mass or more of a good solvent and 5% by mass to 40% by mass of a phase separation agent from the viewpoint of forming an adhesive porous layer having a good porous structure. A solvent is preferred.

Conventionally, as a coating liquid for forming an adhesive porous layer, a coating liquid in which a polyvinylidene fluoride resin is dissolved in a mixed solvent of a good solvent such as DMAc and NMP and a poor solvent such as water and TPG is used. It is done.
However, the coating solution containing a poor solvent is easily gelled depending on the environmental conditions after the preparation, and when gelled, an adhesive porous layer having a fine porous structure cannot be formed, There is a possibility that streaks occur on the surface of the adhesive porous layer. Since the porous structure and the surface morphology of the adhesive porous layer affect the adhesion to the electrode and the battery characteristics, the coating solution is required to have storage stability.
In this embodiment, the binder resin contained in the coating liquid for forming the adhesive porous layer is substantially only the specific VDF-HFP binary copolymer. As a result, the detailed mechanism is unknown, but the storage stability of the coating liquid is high and gelation is difficult. Therefore, even when a coating solution that is not immediately after preparation is used, a fine porous structure develops, an adhesive porous layer having a good surface morphology is formed, and the cycle characteristics and load characteristics of the battery are excellent.

  The concentration of the polyvinylidene fluoride resin in the coating liquid is preferably 3% by mass to 10% by mass with respect to the total mass of the coating liquid from the viewpoint of forming an adhesive porous layer having a good porous structure.

  When the filler or other component is contained in the adhesive porous layer, the filler or other component may be dissolved or dispersed in the coating liquid.

  The coating liquid may contain a dispersing agent such as a surfactant, a wetting agent, an antifoaming agent, a pH adjusting agent and the like. These additives may remain in the adhesive porous layer as long as they are electrochemically stable in the use range of the non-aqueous secondary battery and do not inhibit the reaction in the battery.

  The coagulating liquid is generally composed of a good solvent and a phase separation agent used for preparing the coating liquid and water. It is preferable in production that the mixing ratio of the good solvent and the phase separation agent is matched to the mixing ratio of the mixed solvent used for preparing the coating liquid. The content of water in the coagulation liquid is preferably 40% by mass to 90% by mass from the viewpoint of formation of a porous structure and productivity.

  A conventional coating method using a Meyer bar, a die coater, a reverse roll coater, a gravure coater, or the like may be applied to the coating liquid on the porous substrate. In the case where the adhesive porous layer is formed on both surfaces of the porous substrate, it is preferable from the viewpoint of productivity to apply the coating liquid to both surfaces simultaneously on both surfaces.

  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 in which a coating liquid containing a polyvinylidene fluoride resin and a solvent is applied to a porous substrate, and this coating layer is dried to volatilize and remove the solvent. How to get. However, since the dry coating method tends to be denser than the wet coating method, the wet coating method is preferred in that a good porous structure can be obtained.

  The separator of the present disclosure can also be manufactured by a method in which an adhesive porous layer is produced as an independent sheet, and this adhesive porous layer is stacked on a porous substrate and combined by thermocompression bonding or an adhesive. Examples of the method for producing the adhesive porous layer as an independent sheet include a method of forming the adhesive porous layer on the release sheet by applying the wet coating method or the dry coating method described above.

<Non-aqueous secondary battery>
The non-aqueous secondary battery of the present disclosure is a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium, and includes a positive electrode, a negative electrode, and a separator of the present disclosure. Doping means occlusion, loading, adsorption, or insertion, and means a phenomenon in which lithium ions enter an active material of an electrode such as a positive electrode.

  The non-aqueous 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 face each other via a separator is enclosed in an exterior material together with an electrolytic solution. The non-aqueous secondary battery of the present disclosure is particularly suitable for a lithium ion secondary battery. The non-aqueous secondary battery of the present disclosure can be efficiently manufactured by using the separator of the present disclosure that is excellent in adhesion to electrodes.

The non-aqueous secondary battery of the present disclosure is excellent in cell strength by including the separator of the present disclosure that is excellent in adhesion to an electrode.
Moreover, the non-aqueous secondary battery of this indication is excellent in cycling characteristics by providing the separator of this indication which is excellent in the uniformity of the porous structure of an adhesive porous layer, and excellent in adhesion | attachment with an electrode.

  Hereinafter, exemplary embodiments of the positive electrode, the negative electrode, the electrolytic solution, and the exterior material included in the nonaqueous secondary battery of 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 additive. Examples of the positive electrode active material include lithium-containing transition metal oxides. Specifically, LiCoO ₂ , LiNiO ₂ , LiMn _1/2 Ni _1/2 O ₂ , LiCo _1/3 Mn _1/3 Ni _{1 / 3 O 2, LiMn 2 O 4} , LiFePO 4, LiCo 1/2 Ni 1/2 O 2, LiAl 1/4 Ni 3/4 O 2 and 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 aluminum foil, titanium foil, and stainless steel foil having a thickness of 5 μm to 20 μm.

According to one embodiment of the separator of the present disclosure, since the adhesive porous layer is excellent in oxidation resistance, by disposing the adhesive porous layer on the positive electrode side of the non-aqueous secondary battery, as the positive electrode active material, It is easy to apply LiMn _1/2 Ni _1/2 O ₂ , LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ or the like that can operate at a high voltage of 4.2 V or higher.

  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 additive. Examples of the negative electrode active material include materials that can occlude lithium electrochemically, and specific examples include carbon materials; alloys of silicon, tin, aluminum, and the like with lithium. 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 copper foil, nickel foil, and stainless steel foil having a thickness of 5 to 20 μm. Moreover, it may replace with said negative electrode and may use metal lithium foil as a negative electrode.

  By applying the separator of the present disclosure, the non-aqueous secondary battery of the present disclosure can be applied not only to a negative electrode using a solvent-based binder (specifically, polyvinylidene fluoride resin) but also to an aqueous binder (specifically Is excellent in adhesion to a negative electrode using a styrene-butadiene copolymer.

  From the viewpoint of adhesion to the separator, the electrode preferably contains a large amount of binder resin in the active material layer. On the other hand, from the viewpoint of increasing the energy density of the battery, it is preferable that the active material layer contains a large amount of active material, and the amount of the binder resin is relatively small. Since the separator of this indication is excellent in adhesion with an electrode, it becomes possible to increase the amount of active materials by reducing the amount of binder resin of an active material layer, and can raise the energy density of a battery.

The electrolytic solution is a solution in which a lithium salt is dissolved in a non-aqueous solvent. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO _{4, and the} like. Examples of the non-aqueous 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-substituted products thereof; γ -Cyclic esters such as butyrolactone and γ-valerolactone; these may be used alone or in admixture. As an electrolytic solution, cyclic carbonate and chain carbonate were mixed at a mass ratio (cyclic carbonate: chain carbonate) of 20:80 to 40:60, and lithium salt was dissolved in 0.5 mol / L to 1.5 mol / L. Those are preferred.

  Examples of the exterior material include metal cans and aluminum laminate film packs. The battery has a square shape, a cylindrical shape, a coin shape, and the like, but the separator of the present disclosure is suitable for any shape.

  The non-aqueous secondary battery of the present disclosure is manufactured by manufacturing a laminated body in which the separator of the present disclosure is disposed between a positive electrode and a negative electrode, and using the laminated body, for example, according to any of 1) and 2) below Can be manufactured.

  1) The laminate is housed in an exterior material (for example, an aluminum laminate film pack; the same applies hereinafter), an electrolyte is injected therein, and the laminate is hot-pressed (wet heat press) from above the exterior material. And sealing of the exterior material.

  2) After heat-pressing (dry heat-pressing) the laminate and bonding the electrode and the separator, the laminate is accommodated in an exterior material, an electrolyte solution is injected therein, and the laminate is further hot-pressed (wet) from above the exterior material. Heat press) to bond the electrode and the separator and seal the exterior material.

  According to the production method of 1) above, the laminate is hot pressed in a state where the specific VDF-HFP binary copolymer contained in the adhesive porous layer of the separator is swollen in the electrolyte solution, and the electrode and the separator adhere well. Thus, a non-aqueous secondary battery excellent in cell strength and battery characteristics can be obtained.

According to the manufacturing method of 2), since the electrode and the separator are bonded prior to housing the laminate in the exterior material, deformation of the laminate that occurs during transportation for housing in the exterior material is suppressed. .
Moreover, according to the manufacturing method of said 2), since a laminated body is further hot-pressed in the state which the specific VDF-HFP binary copolymer contained in the adhesive porous layer of a separator swelled in electrolyte solution, an electrode And the separator becomes stronger.
In addition, the wet heat press in the production method 2) may be performed under such a mild condition that the adhesion between the electrode and the separator, which has been somewhat attenuated by impregnation with the electrolytic solution, is recovered, that is, the temperature of the wet heat press is relatively low. Since it can set, the gas generation resulting from decomposition | disassembly of the electrolyte solution and electrolyte in a battery at the time of battery manufacture is suppressed.

  As conditions for the hot press in the production methods 1) and 2) above, in the wet heat press, the press pressure is preferably 0.5 MPa to 2 MPa, and the temperature is preferably 70 ° C to 110 ° C. In the dry heat press, the press pressure is preferably 0.5 MPa to 5 MPa, and the temperature is preferably 20 ° C to 100 ° C.

  The separator of the present disclosure can be bonded by overlapping with the electrode. Therefore, although pressing is not an essential step in battery production, it is preferable to perform pressing from the viewpoint of strengthening the adhesion between the electrode and the separator. Further, from the viewpoint of strengthening the adhesion between the electrode and the separator, the press is preferably a press while heating (hot press).

  When manufacturing the laminate, the method of arranging the separator between the positive electrode and the negative electrode may be a method of stacking at least one layer of the positive electrode, the separator, and the negative electrode in this order (so-called stack method). The separators may be stacked in this order and rolled in the length direction.

  The separator and non-aqueous secondary battery of the present disclosure will be described more specifically with reference to examples. However, the separator and the non-aqueous secondary battery of the present disclosure are not limited to the following examples.

Measurement methods and evaluation methods applied to Examples , Reference Examples and Comparative Examples are as follows.

[Percentage of HFP units in the polyvinylidene fluoride resin]
The proportion of HFP units in the polyvinylidene fluoride resin was determined from the NMR spectrum. Specifically, 20 mg of polyvinylidene fluoride resin was dissolved in 0.6 mL of heavy dimethyl sulfoxide at 100 ° C., and a ¹⁹ F-NMR spectrum was measured at 100 ° C.

[Weight average molecular weight of polyvinylidene fluoride resin]
The weight average molecular weight (Mw) of the polyvinylidene fluoride resin was measured by gel permeation chromatography (GPC). For molecular weight measurement by GPC, a GPC apparatus “GPC-900” manufactured by JASCO Corporation is used, TSKgel SUPER AWM-H manufactured by Tosoh Corporation is used for the column, dimethylformamide is used for the solvent, the temperature is 40 ° C., and the flow rate is 10 mL. The molecular weight in terms of polystyrene was obtained under the conditions of / min.

[Amount of adhesive porous layer applied]
The separator was cut into 10 cm × 10 cm, the mass was measured, and this mass was divided by the area to determine the basis weight of the separator. Moreover, the porous base material used for preparation of a separator was cut out to 10 cm x 10 cm, the mass was measured, and this mass was divided | segmented by the area, and the fabric weight of the porous base material was calculated | required. And the total coating amount of both surfaces of the adhesive porous layer was calculated | required by subtracting the fabric weight of a porous base material from the fabric weight of a separator.

[Film thickness]
The film thickness of the porous substrate and the separator was measured using a contact-type thickness meter (LITEMATIC manufactured by Mitutoyo Corporation). The measurement terminal is a cylinder with a diameter of 5 mm, and is adjusted so that a load of 7 g is applied during the measurement. Any 20 points within 10 cm × 10 cm are measured, and the average value is calculated. did.

  The thickness of the adhesive porous layer was determined by subtracting the thickness of the porous substrate from the thickness of the separator.

[Porosity]
The porosity of the porous substrate and the separator was determined according to the following calculation method.
The constituent materials are a, b, c,..., N, the mass of each constituent material is Wa, Wb, Wc,..., Wn (g / cm ² ), and the true density of each constituent material is da, db, dc,..., dn (g / cm ³ ), and when the film thickness is t (cm), the porosity ε (%) is obtained from the following equation.
ε = {1− (Wa / da + Wb / db + Wc / dc +... + Wn / dn) / t} × 100

[Gurley value]
The Gurley value of the porous substrate and the separator was measured with a Gurley type densometer (G-B2C manufactured by Toyo Seiki Co., Ltd.) according to JIS P8117: 2009.

[Heat-resistant]
Place the separator on a horizontal base, heat the soldering iron with a tip diameter of 2 mm, and bring the tip of the soldering iron into contact with the separator surface for 60 seconds in a state where the tip temperature is 260 ° C. ² ) was measured. The higher the heat resistance of the separator, the smaller the area of the holes generated in the separator.

[Wet adhesive strength with electrode]
91 g of lithium cobaltate powder as a positive electrode active material, 3 g of acetylene black as a conductive additive, and 3 g of polyvinylidene fluoride as a binder are dissolved in N-methyl-pyrrolidone so that the concentration of polyvinylidene fluoride is 5% by mass. Then, the mixture was stirred with a double arm mixer to prepare a positive electrode slurry. This positive electrode slurry was applied to one side of an aluminum foil with a thickness of 20 μm, dried and pressed to obtain a positive electrode (single side coating) having a positive electrode active material layer as an electrode for evaluating the wet adhesion between the separator and the electrode. .

The electrode and aluminum foil (thickness 20 μm) obtained above were cut to a width of 1.5 cm and a length of 7 cm, respectively , and each separator obtained in the following examples , reference examples and comparative examples was 1.8 cm in width and length. Cut to 7.5 cm. An electrode-separator-aluminum foil is laminated in order to produce a laminate, and an electrolytic solution (1 mol / L LiBF ₄ -ethylene carbonate: propylene carbonate [mass ratio 1: 1]) is soaked in the laminate to obtain aluminum. It accommodated in the pack made from a laminate film, and sealed under reduced pressure using the vacuum sealer. Next, the laminated body was hot-pressed together with the pack using a hot press machine, and the electrode and the separator were bonded. The conditions for hot pressing were a pressure of 1 MPa, a temperature of 90 ° C., and a pressing time of 2 minutes. Thereafter, the pack was opened, the laminate was taken out, and the one obtained by removing the aluminum foil from the laminate was used as a measurement sample.

  The uncoated surface of the electrode of the measurement sample was fixed to the metal plate with double-sided tape, and the metal plate was fixed to the lower chuck of Tensilon (STB-1225S manufactured by A & D). At this time, the metal plate was fixed to Tensilon so that the length direction of the measurement sample was the gravity direction. The separator was peeled from the electrode by about 2 cm from the lower end, and the end was fixed to the upper chuck so that the tensile angle (angle of the separator with respect to the measurement sample) was 180 °. The separator was pulled at a pulling speed of 20 mm / min, and the load when the separator was peeled off from the electrode was measured. Loads from 10 mm to 40 mm at the start of measurement were sampled at intervals of 0.4 mm. This measurement was performed three times, the average was calculated, and the wet adhesion force with the electrode (N / 15 mm, adhesion force between the electrode and the separator by wet heat press) was used.

[Gas generation amount]
The separator was cut out to a size of 600 cm ² and placed in an aluminum laminate film pack, the electrolyte was poured into the pack, the separator was impregnated with the electrolyte, and the pack was sealed to obtain a test cell. As the electrolytic solution, 1 mol / L LiPF ₆ -ethylene carbonate: ethyl methyl carbonate (mass ratio 3: 7) was used. The test cell was placed in an environment at a temperature of 85 ° C. for 3 days, and the volume of the test cell before and after the heat treatment was measured. The gas generation amount V (= V2-V1, unit: ml) was determined by subtracting the volume V1 of the test cell before the heat treatment from the volume V2 of the test cell after the heat treatment.

[Cell strength]
91 g of lithium cobaltate powder as a positive electrode active material, 3 g of acetylene black as a conductive additive, and 3 g of polyvinylidene fluoride as a binder are dissolved in N-methyl-pyrrolidone so that the concentration of polyvinylidene fluoride is 5% by mass. Then, the mixture was stirred with a double arm mixer to prepare a positive electrode slurry. This positive electrode slurry was applied to an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a positive electrode active material layer.

  Manufactured graphite 300 g as a negative electrode active material, 7.5 g of a water-soluble dispersion containing 40% by mass of a modified styrene-butadiene copolymer as a binder, 3 g of carboxymethyl cellulose as a thickener, and an appropriate amount of water The mixture was stirred and mixed with an arm mixer to prepare a negative electrode slurry. This negative electrode slurry was applied to a 10 μm thick copper foil as a negative electrode current collector, dried and pressed to obtain a negative electrode having a negative electrode active material layer.

The positive electrode and the negative electrode were wound through the separators obtained in the following examples , reference examples, and comparative examples, and lead tabs were welded to obtain battery elements. The battery element was housed in an aluminum laminate film pack and impregnated with an electrolytic solution, followed by heat press (wet heat press) at a pressure of 1 MPa, a temperature of 90 ° C., and a time of 2 minutes to seal the exterior. A test secondary battery (length 65 mm, width 35 mm, thickness 2.5 mm, capacity 700 mAh) was obtained. As the electrolytic solution, 1 mol / L LiPF ₆ -ethylene carbonate: diethyl carbonate (mass ratio 3: 7) was used.

  The test secondary battery obtained above was subjected to a three-point bending test in accordance with ISO178 to determine the cell strength (N).

[Cycle characteristics]
A test secondary battery was prepared by the same manufacturing method as described above. Under an environment of 25 ° C., 4.2 V constant current / constant voltage charging at 1C was performed for 2 hours, and 300 cycles of charge / discharge cycles were performed under the condition of 3V cutoff constant current discharging at 1C. Based on the discharge capacity obtained in the first cycle, the ratio of the discharge capacity obtained after 300 cycles was obtained as a percentage, and this was used as an index of cycle characteristics.

[ Reference Example 1]
A VDF-HFP binary copolymer (HFP unit ratio 5.1 mass%, weight average molecular weight 1.13 million) was mixed with dimethylacetamide and tripropylene glycol mixed solvent (dimethylacetamide so that the resin concentration would be 5 mass%. : Tripropylene glycol = 80: 20 [mass ratio]) to prepare a coating liquid for forming an adhesive porous material. An equal amount of this coating solution was applied to both sides of a polyethylene microporous membrane (film thickness 9 μm, porosity 38%, Gurley value 160 seconds / 100 cc), and a coagulation solution (water: dimethylacetamide: tripropylene glycol = 62: 30: 8 [mass ratio], temperature 40 ° C.) and solidified. Next, this was washed with water and dried to obtain a separator in which an adhesive porous layer was formed on both sides of a polyethylene microporous membrane.

[ Reference Examples 2 to 5]
Adhesive porous layers were formed on both sides of the polyethylene microporous membrane in the same manner as in Reference Example 1 except that the VDF-HFP binary copolymer was changed to another VDF-HFP binary copolymer shown in Table 1. The formed separator was produced.

[ Reference Example 6]
The VDF-HFP binary copolymer is mixed with the first VDF-HFP binary copolymer (5.4% by mass of HFP units, 1.13 million weight average molecular weight) and the second VDF-HFP binary copolymer. Adhesiveness to both sides of the polyethylene microporous membrane in the same manner as in Reference Example 1 except that the mixture (mass ratio 99: 1) with a blend (HFP unit ratio 2.5 mass%, weight average molecular weight 1,500,000) was changed. A separator in which a porous layer was formed was produced.

[Comparative Example 1]
On both sides of the polyethylene microporous membrane in the same manner as in Reference Example 6 except that the mixing ratio of the first VDF-HFP binary copolymer and the second VDF-HFP binary copolymer was changed to 90:10. A separator in which an adhesive porous layer was formed was produced.

[Comparative Examples 2 to 4]
Adhesive porous layers were formed on both sides of the polyethylene microporous membrane in the same manner as in Reference Example 1 except that the VDF-HFP binary copolymer was changed to another VDF-HFP binary copolymer shown in Table 1. The formed separator was produced.

[Comparative Example 5]
The VDF-HFP binary copolymer was changed to another VDF-HFP binary copolymer (HFP unit ratio 5.4 mass%, weight average molecular weight 3.1 million), and polyethylene microporous as in Reference Example 1. An attempt was made to form an adhesive porous layer on both sides of the membrane, but the viscosity of the coating solution was too high to form the adhesive porous layer.

[Comparative Example 6]
VDF-HFP binary copolymer was converted to vinylidene fluoride-hexafluoropropylene-chlorotrifluoroethylene terpolymer (HFP unit ratio 5.2 mass%, CTFE unit ratio 3.8 mass%, weight average). A separator having an adhesive porous layer formed on both sides of a polyethylene microporous membrane was prepared in the same manner as in Reference Example 1 except that the molecular weight was changed to 600,000.

[Examples 7 to 12, Reference Example 13]
In the coating solution in which the resin is dissolved, magnesium hydroxide (Kisuma 5P manufactured by Kyowa Chemical Industry Co., Ltd., average primary particle size 0.8 μm, BET specific surface area 6.8 m ² / g) as an inorganic filler is shown in Table 1. Volume ratio to the total solid content), and stirring until uniform to produce a coating liquid, the same as in Reference Example 5 except that the coating amount of the coating liquid was changed as shown in Table 1 Thus, a separator having an adhesive porous layer formed on both sides of a polyethylene microporous membrane was produced.

[ Reference Example 14]
A separator having an adhesive porous layer formed on both sides of a polyethylene microporous membrane was produced in the same manner as in Reference Example 5 except that the coating amount of the coating solution was changed as shown in Table 1.

[Example 15]
Two types of inorganic filler (magnesium hydroxide: alumina = 95: 5 [magnesium hydroxide: alumina = 95: 5] manufactured by Kyoma 5P manufactured by Kyowa Chemical Industry Co., Ltd.) and alumina (AL-160SG-3 manufactured by Showa Denko KK, average primary particle size 0.5 μm). A separator having an adhesive porous layer formed on both sides of a polyethylene microporous membrane was prepared in the same manner as in Example 11 except that the volume ratio]) was changed.

[Example 16]
Adhesive porous layers were formed on both sides of the polyethylene microporous membrane in the same manner as in Example 11 except that the inorganic filler was changed to magnesium oxide (PUREMAG FNM-G manufactured by Tateho Chemical Industry Co., Ltd., average primary particle size 0.5 μm). The formed separator was produced.

[Example 17]
An adhesive porous layer is formed on both sides of the polyethylene microporous membrane in the same manner as in Example 11 except that the inorganic filler is changed to alumina (AL-160SG-3, Showa Denko Co., Ltd., average primary particle size 0.5 μm). A separator was prepared.

[Example 18]
An adhesive porous layer was formed on both sides of the polyethylene microporous membrane in the same manner as in Example 11 except that the VDF-HFP binary copolymer was changed to another VDF-HFP binary copolymer shown in Table 1. The formed separator was produced.

Table 1 shows the physical properties and evaluation results of the separators of Reference Examples 1 to 6, Examples 7 to 12, Reference Examples 13 to 14, Examples 15 to 18, and Comparative Examples 1 to 6.

  The disclosure of Japanese Patent Application No. 2015-221570 filed on November 11, 2015 is incorporated herein by reference in its entirety. The disclosure of Japanese Patent Application No. 2015-221600 filed on November 11, 2015 is incorporated herein by reference in its entirety.

  All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference, Incorporated herein by reference.

Claims (5)

A porous substrate;
An adhesive porous layer provided on one or both sides of the porous substrate, wherein the proportion of hexafluoropropylene monomer units is 5.1 mass% or more and 6.9 mass% or less and the weight average molecular weight is An adhesive porous material containing 810,000 to 3 million vinylidene fluoride-hexafluoropropylene binary copolymer, and the vinylidene fluoride-hexafluoropropylene binary copolymer accounts for 95% by mass or more of the total resin Quality layer,
Equipped with a,
The adhesive porous layer further contains an inorganic filler, and the content of the inorganic filler in the adhesive porous layer is 33% by volume or more and 80% by volume or less of the total solid content of the adhesive porous layer. , Separator for non-aqueous secondary battery.   The separator for a non-aqueous secondary battery according to claim 1, wherein the thickness of one surface of the adhesive porous layer is 0.5 µm or more and 5 µm or less. The separator for non-aqueous secondary batteries according to claim 1 or 2 , wherein the inorganic filler is at least one selected from metal hydroxides and metal oxides. The separator for nonaqueous secondary batteries according to any one of claims 1 to 3, wherein the inorganic filler is at least one of magnesium hydroxide and magnesium oxide. A positive electrode, a negative electrode, and a separator for a nonaqueous secondary battery according to any one of claims 1 to 4 disposed between the positive electrode and the negative electrode, and by lithium doping / dedoping Non-aqueous secondary battery for obtaining electromotive force.