JP2018147656A - Nonaqueous secondary battery separator and nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a nonaqueous secondary battery separator which can achieve good adhesion with an electrode by dry heat pressing, and which is low in resistance against ion conduction.SOLUTION: A nonaqueous secondary battery separator comprises: a porous base material; and an adhesive porous layer provided on one or each face of the porous base material, and including an acrylic resin and a polyvinylidene fluoride-based resin. The adhesive porous layer has a porous structure which contains the acrylic resin and the polyvinylidene fluoride-based resin are in the state of being mixed. In the adhesive porous layer, the acrylic resin is included at 2-40 mass% to a total mass of the acrylic resin and the polyvinylidene fluoride-based resin. The acrylic resin is a copolymer including, as monomer components, a first monoacrylate-based monomer, and a second monoacrylate-based monomer having oxyalkylene structural units of which the repetition number is 2-10000.SELECTED DRAWING: None

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 an aluminum laminate film pack is soft, a battery (so-called soft pack battery) using the pack as an outer packaging material (a so-called soft pack battery) has an electrode and a separator formed by impact from the outside or expansion and contraction of the electrode accompanying charge / discharge. A gap is easily formed between the two, and the cycle life of the battery 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 such techniques, a separator having a porous layer containing a polyvinylidene fluoride resin on a porous substrate is known (for example, see Patent Document 1).

  By the way, when manufacturing a battery, the laminated body which has arrange | positioned the separator between the positive electrode and the negative electrode may perform dry heat press (The heat press process performed without impregnating electrolyte solution in a separator). If the separator and the electrode are satisfactorily bonded by dry heat pressing, the manufacturing yield of the battery can be improved. However, the conventional technique such as Patent Document 1 described above lacks the function of adhering to an electrode by dry heat pressing.

  On the other hand, Patent Document 2 discloses a method of applying a mixture of a polyvinylidene fluoride resin and an ion conductive polymer such as polyethylene glycol to a separator for the purpose of improving battery characteristics such as charge / discharge characteristics. However, even in this method, there is a problem that the structural portion contributing to ionic conductivity lowers the adhesive force, and the pores of the separator are crushed by the adhesive application to the separator, thereby increasing the internal resistance of the battery. there were.

Japanese Patent No. 4127989 Japanese Patent No. 3997573

  From such a background, there is a demand for a separator having good adhesion to an electrode by dry heat press and having low ion conduction resistance.

The embodiment of the present disclosure has been made under the above circumstances.
An embodiment of the present disclosure is a separator including an adhesive porous layer containing a polyvinylidene fluoride-based resin, has good adhesion to an electrode by dry heat press, and has a low ion conduction resistance. It aims at providing the separator for secondary batteries, and makes it a subject to solve this.

Specific means for solving the problems include the following aspects.
[1] A porous substrate, and an adhesive porous layer that is provided on one or both surfaces of the porous substrate and includes an acrylic resin and a polyvinylidene fluoride resin, and the adhesive porous layer includes: And having a porous structure in which the acrylic resin and the polyvinylidene fluoride resin are mixed, and in the adhesive porous layer, the total mass of the acrylic resin and the polyvinylidene fluoride resin On the other hand, the acrylic resin is contained in an amount of 2 to 40% by mass, and the acrylic resin has a first monoacrylate monomer as a monomer component and an oxyalkylene structure having 2 to 10,000 repetitions. A separator for a non-aqueous secondary battery, which is a copolymer containing a second monoacrylate monomer having a unit.
[2] The first monoacrylate monomer has one or more structural units selected from the group consisting of acrylic acid, acrylic acid salt, acrylic acid ester, methacrylic acid, methacrylic acid salt, and methacrylic acid ester. 1] The separator for non-aqueous secondary batteries as described in 1].
[3] The separator for a non-aqueous secondary battery according to [1] or [2], wherein the proportion of the second monoacrylate monomer in the acrylic resin is 30 to 95% by mass.
[4] The polyvinylidene fluoride resin is a copolymer containing vinylidene fluoride and hexafluoropropylene as monomer components, and the content of the hexafluoropropylene monomer component in the copolymer is 3% by mass. The separator for non-aqueous secondary batteries according to any one of [1] to [3], which is ˜20% by mass and the weight average molecular weight of the copolymer is 100,000 to 1,500,000.
[5] A positive electrode, a negative electrode, and a separator for a nonaqueous secondary battery according to any one of [1] to [4] disposed between the positive electrode and the negative electrode, and lithium doping / dedoping A non-aqueous secondary battery that obtains an electromotive force.

  According to the present disclosure, a separator having an adhesive porous layer containing a polyvinylidene fluoride-based resin, having good adhesion to an electrode by dry heat press and having a low ion conduction resistance, is a non-aqueous secondary A battery separator is provided.

  Hereinafter, embodiments of the present disclosure will be described. These descriptions and examples illustrate the embodiments and do not limit the scope of the embodiments.

  In the present disclosure, numerical ranges indicated using “to” indicate ranges including numerical values described before and after “to” as the minimum value and the maximum value, respectively.

  In the present disclosure, the term “process” is not only included in an independent process, but is included in the term if the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes.

  In the present disclosure, when referring to the amount of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, the plurality of the substances present in the composition unless otherwise specified. It means the total amount of substance.

  In the present disclosure, the “machine direction” means the long direction in the porous substrate and separator manufactured in a long shape, and the “width direction” means the direction orthogonal to the “machine direction”. . In the present disclosure, “machine direction” is also referred to as “MD direction”, and “width direction” is also referred to as “TD direction”.

  In the present specification, the “monomer component” of a copolymer means a constituent unit formed by polymerizing monomers, which is a constituent component of the copolymer.

<Separator for non-aqueous secondary battery>
The separator for non-aqueous secondary batteries (also referred to as “separator”) of the present disclosure 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 has a porous structure in which an acrylic resin and a polyvinylidene fluoride resin are mixed. In this adhesive porous layer, the acrylic resin is contained in an amount of 2 to 40% by mass with respect to the total mass of the acrylic resin and the polyvinylidene fluoride resin. The acrylic resin is a copolymer containing a first monoacrylate monomer and a second monoacrylate monomer having an oxyalkylene structural unit having a repeating number of 4 to 10,000 as monomer components. This is very important.

Since the separator of this indication is excellent in adhesion with an electrode by dry heat press, it becomes difficult to shift with an electrode in the manufacturing process of a battery, and can improve the manufacture yield of a battery.
Moreover, the separator of this indication is excellent in adhesion | attachment with the electrode by dry heat press, and can improve the cycling characteristics (capacity maintenance factor) of a battery because of low ion conduction resistance.
The reason for this is not clear, but it is presumed that the polarities derived from the acrylic groups of the first and second monoacrylate monomers constituting the acrylic resin greatly affect the adhesion. On the other hand, the second monoacrylate monomer has an oxyalkylene repeating structural unit exhibiting excellent ionic conductivity in its molecular structure. With these combinations, it is presumed that the adhesiveness with the electrode by dry heat press can be improved, a lower ion conduction resistance is realized, and the cycle characteristics of the battery are improved.
In addition, such an acrylic resin has a high affinity with the polyvinylidene fluoride-based resin, and both resins can be uniformly dissolved in a solvent, so that a uniform adhesive porous layer can be easily formed. In the adhesive porous layer, acrylic resin and polyvinylidene fluoride resin are included in a specific composition ratio, and both resins are uniformly dispersed at the molecular level, so that the adhesion between the separator and the electrode is uniform. This is considered to contribute to the improvement of the cycle characteristics of the battery.

  Hereinafter, the details of the porous substrate and the adhesive porous layer included in the separator of the present disclosure will be described.

[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 film; 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 the microporous film or the porous sheet. Quality sheet; and the like. The porous substrate is preferably a microporous membrane from the viewpoint of thinning the separator and strength. 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 material for the porous substrate is preferably an electrically insulating material, and may be either an organic material or an inorganic material.

  The porous substrate preferably contains a thermoplastic resin in order to provide a shutdown function to the porous substrate. The shutdown function refers to a function of preventing the thermal runaway of the battery by blocking the movement of ions by dissolving the constituent materials and closing the pores of the porous base material when the battery temperature rises. 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 a polyolefin microporous membrane applied to conventional battery separators, and it is preferable to select one having sufficient mechanical properties and ion permeability.

  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 mass of the entire 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. From the viewpoint of achieving both a shutdown function and heat resistance, a polyolefin microporous membrane having a laminated structure of two or more layers, at least one layer containing polyethylene and at least one layer containing polypropylene is also 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 imparted to the microporous membrane. On the other hand, when the Mw of the polyolefin is 5 million or less, the shutdown characteristics of the microporous film are good and the microporous film can be easily molded.

  As a method for producing a polyolefin microporous membrane, a melted polyolefin resin is extruded from a T-die to form a sheet, which is crystallized and then stretched, and then heat-treated to form a microporous membrane: liquid paraffin, etc. Examples include a method in which a polyolefin resin melted together with a plasticizer is extruded from a T-die, cooled, formed into a sheet, and stretched, and then the plasticizer is extracted and heat-treated to form a microporous film.

  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; cellulose And a porous sheet made of a fibrous material such as non-woven fabric and paper. The heat resistant resin refers to a resin having a melting point of 200 ° C. or higher, or a resin having no melting point and a decomposition temperature of 200 ° C. or higher.

  Examples of the composite porous sheet include a sheet in which a functional layer is laminated on a porous sheet made of a microporous film or a fibrous material. Such a composite porous sheet is preferable from the viewpoint of further function addition by the functional layer. Examples of the functional layer include a porous layer made of a heat resistant resin and a porous layer made of a heat resistant resin and an inorganic filler from the viewpoint of imparting heat resistance. Examples of the heat resistant resin include one or more heat resistant resins selected from aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone and polyetherimide. Examples of the inorganic filler include metal oxides such as alumina; metal hydroxides such as magnesium hydroxide. As a composite method, a method of applying a functional layer to a microporous membrane or a porous sheet, a method of bonding the microporous membrane or porous sheet and the functional layer with an adhesive, a microporous membrane or a porous sheet, Examples include a method of thermocompression bonding with the functional layer.

  The surface of 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 porous layer. Good. Examples of the surface treatment include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

[Characteristics of porous substrate]
In the present disclosure, the thickness of the porous substrate is preferably 5 μm to 25 μm from the viewpoint of obtaining good mechanical properties and internal resistance.

  The Gurley value (JIS P8117: 2009) of the porous substrate is preferably 50 seconds / 100 cc to 300 seconds / 100 cc from the viewpoint of suppressing short circuit of the battery and obtaining sufficient ion permeability.

The porosity of the porous substrate is preferably 20% to 60% from the viewpoint of obtaining appropriate film resistance and a shutdown function. The porosity of the porous substrate is determined according to the following calculation method. That is, 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

  The puncture strength of the porous base material is preferably 300 g or more from the viewpoint of improving the production yield of the separator and the production yield of the battery. The puncture strength of the porous substrate is measured by performing a puncture test using a Kato Tech KES-G5 handy compression tester under the conditions of a radius of curvature of the needle tip of 0.5 mm and a puncture speed of 2 mm / sec. (G).

[Adhesive porous layer]
In the present disclosure, the adhesive porous layer is a layer that is provided on one or both sides of a porous substrate as the outermost layer of the separator and adheres to the electrode when the separator and the electrode are stacked and pressed or hot pressed.

  In the present disclosure, the adhesive porous layer has a large number of micropores inside and has a structure in which these micropores are connected, and gas or liquid can pass from one surface to the other. ing. Further, the adhesive porous layer has a porous structure in which an acrylic resin and a polyvinylidene fluoride resin are mixed. Such a porous structure forms a fibril-like body in a state where an acrylic resin and a polyvinylidene fluoride-based resin are compatibilized or uniformly mixed at a molecular level, and such a large number of fibril-like bodies are integrally formed. They are connected to form a three-dimensional network structure. Such a porous structure can be confirmed with, for example, a scanning electron microscope (SEM).

  The adhesive porous layer is preferably present on both surfaces rather than only on one surface of the porous substrate from the viewpoint of excellent battery cycle characteristics. 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. In the present disclosure, the adhesive porous layer may further contain a resin other than the acrylic resin and the polyvinylidene fluoride resin, an inorganic filler, an organic filler, and the like as long as the effects of the present invention are not impaired.

(Polyvinylidene fluoride resin)
In the present disclosure, as the polyvinylidene fluoride-based resin contained in the adhesive porous layer, a homopolymer of vinylidene fluoride (that is, polyvinylidene fluoride); a copolymer of vinylidene fluoride and other copolymerizable monomers (Polyvinylidene fluoride copolymer); and a mixture thereof. Examples of the monomer copolymerizable with vinylidene fluoride include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, trichloroethylene, and the like. One type or two or more types should be used. Can do. Among these, a VDF-HFP copolymer is preferable from the viewpoint of adhesion to electrodes. Here, “VDF” refers to a vinylidene fluoride monomer component, “HFP” refers to a hexafluoropropylene monomer component, and “VDF-HFP copolymer” refers to a VDF monomer component and This means a polyvinylidene fluoride resin having an HFP monomer component. By copolymerizing hexafluoropropylene with vinylidene fluoride, it is possible to control the crystallinity, heat resistance, resistance to electrolyte solution, and the like of the polyvinylidene fluoride resin to an appropriate range.

  In the separator of the present disclosure, the content of the HFP monomer component is 3% by mass to 20% by mass of the total monomer component, and the weight average molecular weight (Mw) is 100,000 to 1,500,000 for the following reasons. It is preferable that the specific VDF-HFP copolymer as described above is included in the adhesive porous layer. Moreover, such a VDF-HFP copolymer is preferable also in the point with high affinity with the said acrylic resin.

When the content of the HFP monomer component in the VDF-HFP copolymer is 3% by mass or more, the polymer chain has high mobility when dry heat pressing is performed, and the polymer chain enters the unevenness of the electrode surface and anchors. The effect is exhibited and the adhesion of the adhesive porous layer to the electrode can be improved. In this respect, the HFP monomer component content of the VDF-HFP copolymer is preferably 3% by mass or more, more preferably 5% by mass or more, and still more preferably 6% by mass or more.
When the content of the HFP monomer component in the VDF-HFP copolymer is 20% by mass or less, it is difficult to dissolve in the electrolytic solution and does not swell excessively. Therefore, the electrode and the adhesive porous layer are formed inside the battery. Adhesion can be maintained. From this viewpoint, the HFP monomer component content of the VDF-HFP copolymer is preferably 20% by mass or less, more preferably 18% by mass or less, and still more preferably 15% by mass or less.

When the Mw of the VDF-HFP copolymer is 100,000 or more, the adhesive porous layer can secure mechanical properties that can withstand the adhesion treatment with the electrode, and the adhesion with the electrode can be improved. Further, if the Mw of the VDF-HFP copolymer is 100,000 or more, it is difficult to dissolve in the electrolytic solution, and thus the adhesion between the electrode and the adhesive porous layer is easily maintained inside the battery. From these viewpoints, the Mw of the VDF-HFP copolymer is preferably 100,000 or more, more preferably 200,000 or more, further preferably 300,000 or more, and further preferably 500,000 or more.
If the Mw of the VDF-HFP copolymer is 1.5 million or less, the viscosity of the coating liquid used for coating molding of the adhesive porous layer does not become too high, and the moldability and crystal formation are good, and the adhesive porous The uniformity of the surface properties of the layer is high, and as a result, the adhesion of the adhesive porous layer to the electrode is good. Moreover, when the Mw of the VDF-HFP copolymer is 1.5 million or less, the mobility of the polymer chain is high when dry heat pressing is performed, the polymer chain enters the irregularities on the electrode surface, and an anchor effect is expressed. The adhesion of the adhesive porous layer to the electrode can be improved. From these viewpoints, the Mw of the VDF-HFP copolymer is preferably 1.5 million or less, more preferably 1.2 million or less, and still more preferably 1 million or less.

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

(Acrylic resin)
In the separator of the present disclosure, the adhesive porous layer includes an acrylic resin in addition to the polyvinylidene fluoride resin. The acrylic resin is a copolymer containing, as a monomer component, a first monoacrylate monomer and a second monoacrylate monomer having an oxyalkylene structural unit having a repeating number of 4 to 10,000. is important.

  As the first monoacrylic monomer constituting the acrylic resin, one or more structural units selected from the group consisting of acrylic acid, acrylic acid salt, acrylic acid ester, methacrylic acid, methacrylate, and methacrylic acid ester are used. It is preferable to have. For example, examples of the acrylate include sodium acrylate, potassium acrylate, magnesium acrylate, and zinc acrylate. Examples of acrylic esters include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, methoxypolyethylene glycol acrylate, and isobornyl allylate. , Dicyclopentanyl acrylate, cyclohexyl acrylate, 4-hydroxybutyl acrylate and the like. Examples of the methacrylate include sodium methacrylate, potassium methacrylate, magnesium methacrylate, and zinc methacrylate. Methacrylic acid esters include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, hydroxy methacrylate Examples include propyl, diethylaminoethyl methacrylate, methoxypolyethylene glycol methacrylate, isobornyl methacrylate, dicyclopentanyl methacrylate, cyclohexyl methacrylate, and 4-hydroxybutyl methacrylate.

  Among these, the first monoacrylic monomer includes methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, acrylic acid 2 -Hydroxyethyl and 2-hydroxyethyl methacrylate are preferred. In particular, methyl methacrylate, which is excellent in compatibility with the polyvinylidene fluoride resin, has the effect of lowering the glass transition temperature of the adhesive porous layer, and is most preferred.

  The second monoacrylic monomer constituting the acrylic resin is not limited as long as it is a monoacrylic monomer having an oxyalkylene structural unit having a repeating number of 2 to 10,000. For example, ethoxydiethylene glycol monoacrylate, methoxytriethylene glycol Monoacrylate, 2-ethylhexyl diglycol monoacrylate, methoxypolyethylene glycol monoacrylate (ethylene glycol repeat number (n) is 4 to 10,000), methoxydipropylene glycol monoacrylate, phenoxydiethylene glycol monoacrylate, phenoxypolyethylene glycol monoacrylate (n = 3 to 10000), ethoxydiethylene glycol monomethacrylate, methoxytriethylene glycol Methacrylate, 2-ethylhexyl diglycol monomethacrylate, methoxypolyethylene glycol monomethacrylate (ethylene glycol repeat number (n) is 4 to 10,000), methoxydipropylene glycol monomethacrylate, phenoxydiethylene glycol monomethacrylate, phenoxypolyethyleneglycol monomethacrylate (n = 3 to 10,000).

  Among these, styrene, paramethoxystyrene, and paramethyl-α-methylstyrene are preferable as the second monoacrylic monomer, and styrene is particularly preferable because it has a strong effect of inhibiting dissolution and swelling.

  In the separator of the present disclosure, the proportion of the second monoacrylate monomer in the acrylic resin is preferably in the range of 30 to 95% by mass, more preferably 35 to 80% by mass, from the viewpoint of further improving the effect of the present invention. %, More preferably 40 to 70% by mass. It is preferable that the proportion of the second monoacrylate monomer is 95% by mass or less because strong adhesive force with the electrode can be obtained. On the other hand, when the proportion of the second monoacrylate monomer is 30% by mass or more, the acrylic resin is difficult to dissolve in the electrolytic solution, which is preferable.

The glass transition temperature of the acrylic resin used in the separator of the present disclosure is preferably in the range of −40 ° C. to 120 ° C. Generally, the lower the glass transition temperature of the acrylic resin, the higher the fluidity of the adhesive porous layer during dry heat pressing. Adhesion of the adhesive porous layer to improve. On the other hand, even when an acrylic resin having a high glass transition is compatible with a vinylidene fluoride resin, for example, when completely compatible or partially compatible, the glass transition temperature of the adhesive porous layer is substantially lowered. Therefore, a high adhesive force may be expressed. A glass transition temperature of −40 ° C. or higher is preferred in that the adhesive porous layer located on the separator surface is less likely to cause blocking. If glass transition temperature is 120 degrees C or less, it is preferable at the point which becomes easy to improve the adhesion effect by dry heat press.
The acrylic resin used in the separator of the present disclosure is that the starting material is a first monoacrylate monomer and a second monoacrylate monomer having an oxyalkylene structural unit having a repeating number of 2 to 10,000. It becomes a linear polymer. Such a linear polymer has a characteristic that it is excellent in fluidity as compared with, for example, a resin having a crosslinked structure. Therefore, when the electrode and the separator are bonded by dry heat pressing, a polymer chain enters the irregularities on the electrode surface to develop an anchor effect, and the adhesion of the adhesive porous layer to the electrode can be improved. Further, since the acrylic resin used in the present invention is linear, it is easy to form a uniform adhesive porous layer in a state where it is compatibilized or uniformly mixed with the polyvinylidene fluoride resin at the molecular level. . In the adhesive porous layer, acrylic resin and polyvinylidene fluoride resin are included in a specific composition ratio, and both resins are uniformly dispersed at the molecular level, so that the adhesion between the separator and the electrode is uniform. This is considered to contribute to the improvement of the cycle characteristics of the battery.

  The Mw of the acrylic resin used in the separator of the present disclosure is preferably 10,000 to 500,000. It is preferable that Mw of the acrylic resin is 10,000 or more from the viewpoint of improving the adhesive strength with the electrode by dry heat pressing. On the other hand, when the Mw of the acrylic resin is 500,000 or less, it is preferable in that the fluidity of the adhesive porous layer is improved during dry heat pressing. The more preferable range of Mw of the acrylic resin is 30,000 to 300,000, and the most preferable range is 50,000 to 200,000.

  The content of the acrylic resin in the adhesive porous layer is the adhesive porous layer from the viewpoint of increasing the peel strength between the porous substrate and the adhesive porous layer in order to achieve the effects of the present invention. Is preferably 2% by mass or more, more preferably 7% by mass or more, still more preferably 10% by mass or more, and still more preferably 15% by mass or more. On the other hand, from the viewpoint of suppressing cohesive failure of the adhesive porous layer, the content of the acrylic resin in the adhesive porous layer is preferably 40% by mass or less of the total amount of all resins contained in the adhesive porous layer, 38 mass% or less is more preferable, 35 mass% or less is still more preferable, and 30 mass% or less is still more preferable.

(Other resins)
In the present disclosure, the adhesive porous layer may contain a resin other than the vinylidene fluoride resin and the acrylic resin.

  Other resins include fluorine rubber, styrene-butadiene copolymer, homopolymer or copolymer of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, Examples include polyvinyl pyrrolidone and polyether (polyethylene oxide, polypropylene oxide, etc.).

(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 filler is preferably an inorganic filler from the viewpoint of improving cell strength and ensuring battery safety.

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

  As the inorganic filler, an inorganic filler that is stable with respect to the electrolytic solution and electrochemically stable is preferable. Specifically, for example, metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, boron hydroxide; alumina, titania, magnesia, Metal oxides such as silica, zirconia, and barium titanate; carbonates such as calcium carbonate and magnesium carbonate; sulfates such as barium sulfate and calcium sulfate; 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 is preferably at least one of a metal hydroxide and a metal oxide from the viewpoint of ensuring the stability in the battery and the safety of the battery, and from the viewpoint of imparting flame retardancy and neutralizing effect, metal hydroxide Products are preferred, and magnesium hydroxide is more preferred.

  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.

  When an inorganic filler is contained in the adhesive porous layer, the content of the inorganic filler in the adhesive porous layer is 5% by mass to 80% of the total amount of all resins and inorganic fillers contained in the adhesive porous layer. Mass% is preferred. When the content of the inorganic filler is 5% by mass or more, thermal contraction of the separator is suppressed when heat is applied, which is preferable from the viewpoint of dimensional stability. From this viewpoint, the content of the inorganic filler is more preferably 10% by mass or more, and further preferably 20% by mass or more. On the other hand, when the content of the inorganic filler is 80% by mass or less, it is preferable from the viewpoint of ensuring adhesion of the adhesive porous layer to the electrode. From this viewpoint, the content of the inorganic filler is more preferably 78% by mass or less, and further preferably 75% by mass or less.

  Examples of the organic filler include cross-linked acrylic resins such as cross-linked polymethyl methacrylate, cross-linked polystyrene, and cross-linked urethane resin. Cross-linked polymethyl methacrylate is preferable.

(Other ingredients)
In the present disclosure, the adhesive porous layer 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 a coating solution used for coating and forming the adhesive porous layer for the purpose of improving dispersibility, coating properties, and storage stability. Wetting agents, antifoaming agents, and pH adjusters are used in coating liquids used for coating and forming porous adhesive layers, for example, to improve compatibility with porous substrates. It is added for the purpose of suppressing the entrainment or for the purpose of pH adjustment.

[Characteristics of adhesive porous layer]
In the present disclosure, the thickness of the adhesive porous layer is preferably 0.5 μm or more, more preferably 1.0 μm or more, and the energy density of the battery on one side of the porous substrate from the viewpoint of adhesion to the electrode. In view of the above, 8.0 μm or less is preferable and 6.0 μm or less is more preferable.

  When the adhesive porous layer is provided on both surfaces of the porous substrate, the difference between the thickness of the adhesive porous layer on one surface and the thickness of the adhesive porous layer on the other surface is the sum of both surfaces The thickness is preferably 20% or less of the thickness, and the lower the thickness, the better.

The weight of the adhesive porous layer is preferably 0.5 g / m ² or more, more preferably 0.75 g / m ² or more, from the viewpoint of adhesion to the electrode on one side of the porous substrate, and ion permeability. In view of the above, 5.0 g / m ² or less is preferable, and 4.0 g / m ² or less is more preferable.

  The porosity of the adhesive porous layer is preferably 30% or more from the viewpoint of ion permeability, more preferably 40% or more, and preferably 80% or less, more preferably 60% or less from the viewpoint of mechanical strength. preferable. The method for obtaining the porosity of the adhesive porous layer in the present disclosure is the same as the method for obtaining the porosity of the porous substrate.

The average pore diameter of the adhesive porous layer is preferably 10 nm or more from the viewpoint of ion permeability, and 200 nm or less is preferable from the viewpoint of adhesion to the electrode. The average pore diameter of the adhesive porous layer in the present disclosure is calculated by the following equation assuming that all the 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.

  The peel strength between the porous substrate and the adhesive porous layer is preferably 0.20 N / 10 mm or more. When the peel strength is 0.20 N / 10 mm or more, the separator is easily handled in the battery manufacturing process. From this viewpoint, the peel strength is more preferably 0.30 N / 10 mm or more, and the higher the better. The upper limit of the peel strength is not limited, but is usually 2.0 N / 10 mm or less.

[Separator characteristics]
The thickness of the separator of the present disclosure is preferably 5 μm or more from the viewpoint of mechanical strength, and is preferably 35 μm or less from the viewpoint of the energy density of the battery.

  The puncture strength of the separator of the present disclosure is preferably 250 g to 1000 g, and more preferably 300 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 porosity of the separator of the present disclosure is preferably 30% to 65%, more preferably 35% to 60%, from the viewpoints of adhesion to electrodes, handling properties, ion permeability, and mechanical strength.

  The Gurley value (JIS P8117: 2009) of the separator of the present disclosure is preferably 100 seconds / 100 cc to 300 seconds / 100 cc from the viewpoint of mechanical strength and battery load characteristics.

[Manufacturing method of separator]
The separator of the present disclosure can be manufactured by, for example, a wet coating method having the following steps (i) to (iii).

(I) A step of coating a porous substrate with a coating liquid containing a vinylidene fluoride resin and an acrylic resin to form a coating layer.
(Ii) The porous base material on which the coating layer is formed is immersed in a coagulation liquid, and the polyvinylidene fluoride resin and the acrylic resin are solidified while inducing phase separation in the coating layer. A step of forming a composite layer to obtain a composite film.
(Iii) A step of washing and drying the composite membrane.

  The coating liquid is prepared by dissolving or dispersing a polyvinylidene fluoride resin and an acrylic resin in a solvent. When the filler is contained in the adhesive porous layer, the filler is dispersed in the coating liquid.

  The solvent used for preparing the coating solution includes a solvent that dissolves the polyvinylidene fluoride resin (hereinafter, also referred to as “good solvent”). Examples of the good solvent include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylformamide.

  The solvent used for preparing the coating liquid preferably contains a phase separation agent that induces phase separation from the viewpoint of forming a porous layer having a good porous structure. Therefore, the solvent used for preparing the coating liquid is preferably a mixed solvent of a good solvent and a phase separation agent. The phase separation agent is preferably mixed with a good solvent in an amount within a range that can ensure a viscosity suitable for coating. Examples of the phase separation agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

  The solvent used for the preparation of the coating liquid is a mixed solvent of a good solvent and a phase separation agent from the viewpoint of forming a good porous structure, including 60% by mass or more of the good solvent, and 40% of the phase separation agent. % Is preferable.

  The resin concentration of the coating liquid is preferably 1% by mass to 20% by mass from the viewpoint of forming a good porous structure.

  Examples of means for applying the coating liquid to the porous substrate include a Mayer bar, a die coater, a reverse roll coater, and a gravure coater. When forming a porous layer on both surfaces of a porous base material, it is preferable from a viewpoint of productivity to apply a coating liquid to a base material simultaneously on both surfaces.

  The coagulation liquid may be water alone, but generally contains 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. The temperature of the coagulation liquid is, for example, 20 ° C to 50 ° C.

  The separator of the present disclosure can also be manufactured by a dry coating method. The dry coating method is a method in which a coating liquid containing a resin is applied to a porous substrate to form a coating layer, and then the coating layer is dried to solidify the coating layer. This is a method of forming a porous layer. However, since the porous layer tends to be denser in the dry coating method than in the wet coating method, the wet coating method is preferable from the viewpoint of obtaining a good porous structure.

  The separator of the present disclosure can also be manufactured by a method in which a porous layer is produced as an independent sheet, and this porous layer is stacked on a porous substrate and laminated by thermocompression bonding or an adhesive. Examples of a method for producing the porous layer as an independent sheet include a method in which the wet coating method or the dry coating method described above is applied to form a porous layer on the release sheet, and the release sheet is peeled off from the porous layer. It is done.

<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 for the non-aqueous secondary battery 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 nonaqueous secondary battery of the present disclosure is suitable for a nonaqueous electrolyte secondary battery, particularly a lithium ion secondary battery.

The non-aqueous secondary battery of the present disclosure has a high production yield because the separator of the present disclosure is excellent in adhesion to an electrode by dry heat press.
The non-aqueous secondary battery of the present disclosure has the battery cycle characteristics (capacity maintenance) because the separator of the present disclosure is firmly bonded to the electrode by dry heat press and realizes low ion conduction resistance by the ion conductive polymer. Rate).

  Hereinafter, 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.

As an embodiment of the positive electrode, there is a structure in which an active material layer including a positive electrode active material and a binder resin is disposed 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 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 aluminum foil, titanium foil, and stainless steel foil having a thickness of 5 μm to 20 μm.

In the non-aqueous secondary battery of the present disclosure, the polyvinylidene fluoride resin contained in the adhesive porous layer of the separator of the present disclosure has excellent oxidation resistance, so the adhesive porous layer is used as the positive electrode of the non-aqueous secondary battery. LiMn _1/2 Ni _1/2 O ₂ , LiCo _1/3 Mn _1/3 Ni _1/3 O _{2 and the} like that can be operated at a high voltage of 4.2 V or more as a positive electrode active material Easy to apply.

  As an embodiment example of the negative electrode, there is a structure in which an active material layer including a negative electrode active material and a binder resin is disposed 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; wood alloys. Examples of the binder resin include a polyvinylidene fluoride resin and a styrene-butadiene copolymer. Examples of the conductive assistant include carbon materials such as acetylene black, ketjen black, graphite powder, and ultrafine carbon fibers. 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.

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, ethylmethyl carbonate, and fluorine-substituted products thereof; and cyclic esters such as γ-butyrolactone and γ-valerolactone; these may be used alone or in combination. 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. A solution is 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.

  As a manufacturing method of the non-aqueous secondary battery of the present disclosure, the separator is subjected to a hot press treatment (referred to as “dry heat press” in the present disclosure) without impregnating the electrolytic solution, and then adhered to the electrode, and then the separator is applied. A production method including impregnating with an electrolytic solution may be mentioned. The manufacturing method includes, for example, a stacking process for manufacturing a laminate in which the separator of the present disclosure is disposed between a positive electrode and a negative electrode, and a dry bonding process in which a dry heat press is performed on the stack to bond the electrode and the separator. And a post-process for sealing the exterior material by injecting an electrolyte into the laminate housed in the exterior material.

  In the laminating step, the method of disposing the separator between the positive electrode and the negative electrode may be a method of laminating at least one layer of the positive electrode, the separator, and the negative electrode in this order (so-called stack method). A method of overlapping in order and rolling in the length direction may be used.

  The dry bonding step may be performed before the laminate is accommodated in an exterior material (for example, an aluminum laminate film pack), or may be performed after the laminate is accommodated in the exterior material. That is, the laminate in which the electrode and the separator are bonded by dry heat pressing may be accommodated in the exterior material, and after the laminate is accommodated in the exterior material, dry heat press is performed from above the exterior material to remove the electrode and separator. It may be adhered.

The press temperature in the dry bonding step is preferably 70 ° C to 120 ° C, more preferably 75 ° C to 110 ° C, and still more preferably 80 ° C to 100 ° C. Within this temperature range, the adhesion between the electrode and the separator is good, and since the separator can expand appropriately in the width direction, short-circuiting of the battery is unlikely to occur.
The press pressure in the dry bonding step is preferably 0.5 kg to 40 kg as a load per 1 cm ^{2 of} electrode. The pressing time is preferably adjusted according to the pressing temperature and pressing pressure, and is adjusted, for example, in the range of 0.1 minute to 60 minutes.

  In the manufacturing method described above, the laminate may be temporarily bonded by subjecting the laminate to room temperature press (pressurization at room temperature) before dry heat pressing.

  In a post process, after performing dry heat press, electrolyte solution is inject | poured into the exterior material which accommodates the laminated body, and an exterior material is sealed. After injecting the electrolytic solution, the laminate may be further heat-pressed from above the exterior material, but a good adhesion state can be maintained without heat-pressing. Before sealing, the inside of the exterior body is preferably in a vacuum state. Examples of a method for sealing the exterior material include a method in which the opening of the exterior material is bonded with an adhesive, and a method in which the opening of the exterior material is heated and pressed to be thermocompression bonded.

  The separator and non-aqueous secondary battery of the present disclosure will be described more specifically with reference to examples. The materials, amounts used, ratios, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present disclosure. Therefore, the range of the separator and the nonaqueous secondary battery of the present disclosure should not be limitedly interpreted by the specific examples shown below.

<Measurement method, evaluation method>
The measurement methods and evaluation methods applied in Examples and Comparative Examples are as follows.

[Composition of polyvinylidene fluoride resin]
20 mg of a polyvinylidene fluoride resin was dissolved in 0.6 ml of heavy dimethyl sulfoxide at 100 ° C., a ¹⁹ F-NMR spectrum was measured at 100 ° C., and the composition of the polyvinylidene fluoride resin was determined from the NMR spectrum.

[Weight average molecular weight of resin]
The weight average molecular weight (Mw) of the resin was determined by using a gel permeation chromatography analyzer (JASCO Corp. GPC-900), using two Tosoh TSKgel SUPER AWM-H in the column and N, N-dimethylformamide in the solvent. It was used and measured as a molecular weight in terms of polystyrene under the conditions of a temperature of 40 ° C. and a flow rate of 10 ml / min.

[Glass transition temperature of resin]
The glass transition temperature of the resin was determined from a differential scanning calorimetry curve (DSC curve) obtained by performing differential scanning calorimetry (DSC). The glass transition temperature is a temperature at a point where a straight line obtained by extending the base line on the low temperature side to the high temperature side and a tangent line of the curve of the step-like change portion and the maximum gradient.

[Film thickness of porous substrate and separator]
The film thickness (μm) of the porous substrate and the separator was determined by measuring 20 points with a contact-type thickness meter (LITEMATIC, Mitutoyo Corp.) and averaging them. The measurement terminal was a cylindrical terminal having a diameter of 5 mm, and was adjusted so that a load of 7 g was applied during the measurement.

[Layer thickness of adhesive porous layer]
The layer thickness (μm) of the adhesive porous layer was obtained by subtracting the film thickness of the porous substrate from the film thickness of the separator to obtain the total layer thickness of both surfaces, and this half was defined as the layer thickness of one surface.

[Gurley value]
The Gurley value (second / 100 cc) of the porous substrate and the separator was measured using a Gurley type densometer (Toyo Seiki G-B2C) according to JIS P8117: 2009.

[Porosity]
The porosity (%) of the porous substrate and the adhesive porous layer was determined according to the following formula.
ε = {1-Ws / (ds · t)} × 100
In the formula, ε is a porosity (%), Ws is a basis weight (g / m ² ), ds is a true density (g / cm ³ ), and t is a thickness (μm).

[Peel strength between porous substrate and adhesive porous layer]
Adhesive tape was applied to one surface of the separator (when the adhesive was applied, the length direction of the adhesive tape was matched with the MD direction of the separator), and the separator was cut out in the TD direction 1.2 cm and MD direction 7 cm together with the adhesive tape. It was. The adhesive tape was peeled off together with the adhesive porous layer directly below, and the two separated ends were held by Tensilon (RTC-1210A manufactured by Orientec Co., Ltd.), and a T-shaped peel test was performed. The pressure-sensitive adhesive tape is used as a support for peeling the adhesive porous layer from the porous substrate. The tensile speed of the T-peeling test was 20 mm / min, and the load (N) when the adhesive porous layer was peeled from the porous substrate was measured. After the start of measurement, loads from 10 mm to 40 mm were sampled at intervals of 0.4 mm, the average was calculated, converted to a load per 10 mm width (N / 10 mm), and the measured values of three test pieces were averaged, The peel strength (N / 10 mm) was used.

[Adhesive strength with positive electrode: Dry heat press]
89.5 g of lithium cobaltate powder as a positive electrode active material, 4.5 g of acetylene black as a conductive auxiliary agent, and 6 g of polyvinylidene fluoride as a binder are mixed with N-methyl so that the concentration of polyvinylidene fluoride is 6% by mass. -It melt | dissolved in the pyrrolidone and stirred with the double arm type mixer, and produced the slurry for positive electrodes. This positive electrode slurry was applied to one side of an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a positive electrode active material layer.

  The positive electrode obtained above was cut into a width of 1.5 cm and a length of 7 cm, and a separator was cut into a TD direction of 1.8 cm and an MD direction of 7.5 cm. The positive electrode and the separator were stacked and hot pressed under the conditions of a temperature of 80 ° C., a pressure of 5.0 MPa, and a time of 3 minutes to bond the positive electrode and the separator, and this was used as a test piece. At one end in the length direction of the test piece (that is, MD direction of the separator), the separator is slightly peeled off from the positive electrode, and the two separated ends are held by Tensilon (RTC-1210A manufactured by Orientec Co., Ltd.), and a T-shaped peel test is performed. went. The tensile speed of the T-peel test is 20 mm / min, the load (N) when the separator peels from the positive electrode is measured, and the load from 10 mm to 40 mm is sampled at intervals of 0.4 mm after the measurement is started, and the average is calculated. Further, the measured values of the three test pieces were averaged to obtain the adhesive strength (N) of the separator.

[Adhesive strength with negative electrode]
300 g of artificial graphite as negative electrode active material, 7.5 g of water-soluble dispersion containing 40% by mass of modified styrene-butadiene copolymer as binder, 3 g of carboxymethyl cellulose as thickener, and appropriate amount of water The mixture was stirred with a type mixer to prepare a negative electrode slurry. This negative electrode slurry was applied to one side of a 10 μm thick copper foil, dried and pressed to obtain a negative electrode having a negative electrode active material layer.

  Using the negative electrode obtained above, a T-peel test was conducted in the same manner as in [Adhesive strength with positive electrode: dry heat press] to determine the adhesive strength (N) of the separator.

[Cycle characteristics (capacity maintenance ratio)]
A lead tab was welded to the positive electrode and the negative electrode, and the positive electrode, the separator, and the negative electrode were laminated in this order. This laminate is inserted into a pack made of aluminum laminate film, and the inside of the pack is vacuum-sealed using a vacuum sealer, and the whole pack is heat-pressed using a hot press machine in the stacking direction of the laminate. Thus, the electrode and the separator were bonded. The conditions for hot pressing were a temperature of 90 ° C., a load of 20 kg per 1 cm ^{2 of} electrode, and a pressing time of 2 minutes. Next, an electrolytic solution (1 mol / L LiPF ₆ -ethylene carbonate: ethyl methyl carbonate [mass ratio 3: 7]) was injected into the pack, and the laminate was impregnated with the electrolytic solution. Was sealed under vacuum to obtain a battery.

  Under an environment of a temperature of 40 ° C., the battery was charged and discharged for 500 cycles. The charging was a constant current and constant voltage charging of 1C and 4.2V, and the discharging was a constant current discharging of 1C and 2.75V cut-off. The discharge capacity at the 500th cycle was divided by the initial capacity, the average of 10 batteries was calculated, and the obtained value (%) was taken as the capacity retention rate.

[Load characteristics]
A battery was produced in the same manner as the battery production in [Cycle characteristics (capacity maintenance ratio)]. The battery was charged and discharged in an environment of a temperature of 15 ° C., the discharge capacity when discharged at 0.2 C and the discharge capacity when discharged at 2 C were measured, the latter was divided by the former, and 10 batteries were The average was calculated, and the obtained value (%) was taken as the load characteristic. The charging conditions were 0.2 C, 4.2 V constant current constant voltage charging for 8 hours, and the discharging conditions were 2.75 V cut-off constant current discharging.

<Preparation of separator>
[Example 1]
In a mixed solvent of dimethylacetamide and tripropylene glycol (dimethylacetamide: tripropylene glycol = 80: 20 [mass ratio]), a polyvinylidene fluoride resin (VDF-HFP copolymer, HFP unit content 12.4% by mass, Weight average molecular weight 860,000), acrylic resin (methyl methacrylate-polymethoxydiethylene glycol methacrylate (n = 4)), polymerization ratio [mass ratio] 45:55, weight average molecular weight 115,000, glass transition temperature 55 ° C. And a coating liquid for forming an adhesive porous material was prepared. The mass ratio of the polyvinylidene fluoride resin and acrylic resin contained in the coating liquid was 80:20, and the resin concentration of the coating liquid was 5.0 mass%.

  The coating solution is applied to both sides of a polyethylene microporous membrane (film thickness 9.0 μm, Gurley value 150 sec / 100 cc, porosity 43%), which is a porous substrate (in this case, the amount of coating on the front and back sides) ) And solidified by dipping in a coagulating liquid (water: dimethylacetamide: tripropylene glycol = 62.5: 30: 7.5 [mass ratio], liquid temperature 35 ° C.). . 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.

[Example 2]
Implementation was carried out except that the acrylic resin was changed to methyl methacrylate-polymethoxydiethylene glycol methacrylate (n = 9) (polymerization ratio [mass ratio] 45:55, weight average molecular weight 125,000, glass transition temperature 55 ° C.). A separator was prepared in the same manner as in Example 1.

[Example 3]
Except for further dispersing magnesium hydroxide particles (volume average particle size of primary particles 0.8 μm, BET specific surface area 6.8 m ² / g) in the coating solution so as to have the contents shown in Table 1, A separator was produced in the same manner as in Example 1.

[Example 4]
Except for further dispersing magnesium hydroxide particles (volume average particle size of primary particles 0.8 μm, BET specific surface area 6.8 m ² / g) in the coating solution so as to have the contents shown in Table 1, A separator was produced in the same manner as in Example 2.

[Comparative Example 1]
A separator was produced in the same manner as in Example 1 except that the coating liquid did not contain an acrylic resin.

[Comparative Example 2]
A separator was prepared in the same manner as in Example 3 except that the coating liquid did not contain an acrylic resin and the contents of the polyvinylidene fluoride resin and magnesium hydroxide particles were changed as shown in Table 1.

[Comparative Example 3]
Using poly (ethylene glycol) methacrylate (Aldrich) having an average molecular weight of 360, solid poly [poly (ethylene glycol) methacrylate] was obtained. The above-mentioned solid poly [poly (ethylene glycol) methacrylate] is mixed at a composition ratio of 3.0 parts by weight, 2.0 part by weight of polyvinylidene fluoride (Aldrich) having an average molecular weight (Mw) of 534,000, and 95 parts by weight of NMP. A viscous adhesive was prepared by sufficiently stirring to obtain a homogeneous solution.
A polyethylene microporous film (film thickness: 9.0 μm, Gurley value: 150 sec / 100 cc, porosity: 43%) as a porous substrate was applied to both surfaces. After that, before the adhesive was dried, the positive electrode and the negative electrode were brought into close contact with each other with the separator interposed therebetween, and were bonded together to produce a battery laminate in which the positive electrode, the separator, and the negative electrode were joined. The laminated battery laminate was placed in a 60 ° C. hot air dryer for 2 hours to evaporate NMP. After NMP has completely evaporated, the battery stack is placed in the pack, an electrolyte (1 mol / L LiPF ₆ -ethylene carbonate: ethyl methyl carbonate [mass ratio 3: 7]) is injected, and the electrolyte is poured into the stack. After soaking, the inside of the pack was evacuated using a vacuum sealer and sealed to obtain a battery.
The adhesive strength between the electrode and the separator was determined by applying an adhesive on one side of the separator and then evaporating NMP in a hot air dryer at 60 ° C. for 2 hours. Cut into 5 cm. Next, the electrode cut into a width of 1.5 cm and a length of 7 cm and the cut-out separator are overlapped, and hot pressed under conditions of a temperature of 80 ° C., a pressure of 5.0 MPa, and a time of 3 minutes to bond the electrode and the separator. This was used as a test piece.
[Comparative Example 4]
An adhesive was prepared using 3.0 parts by weight of polyethylene glycol (Aldrich) having an average molecular weight (Mw) of 10,000 and 2.0 parts by weight of polyvinylidene fluoride (Aldrich) having an average molecular weight (Mw) of 534,000. A battery was fabricated in the same manner as in Comparative Example 3 except for the above.

  Table 1 shows the physical properties and evaluation results of the separators of Examples 1 to 4 and Comparative Examples 1 to 4.

Claims (5)

A porous substrate;
An adhesive porous layer provided on one or both sides of the porous base material and comprising an acrylic resin and a polyvinylidene fluoride resin;
The adhesive porous layer has a porous structure included in a state where the acrylic resin and polyvinylidene fluoride resin are mixed,
In the adhesive porous layer, the acrylic resin is contained in an amount of 2 to 40% by mass with respect to the total mass of the acrylic resin and the polyvinylidene fluoride resin.
The acrylic resin is a copolymer containing, as a monomer component, a first monoacrylate monomer and a second monoacrylate monomer having an oxyalkylene structural unit having a repeating number of 2 to 10,000. Separator for non-aqueous secondary battery.   The first monoacrylate monomer has at least one structural unit selected from the group consisting of acrylic acid, acrylic acid salt, acrylic acid ester, methacrylic acid, methacrylic acid salt, and methacrylic acid ester. The separator for non-aqueous secondary batteries as described.   The separator for non-aqueous secondary batteries according to claim 1 or 2, wherein a proportion of the second monoacrylate monomer in the acrylic resin is 30 to 95 mass%.   The polyvinylidene fluoride resin is a copolymer containing vinylidene fluoride and hexafluoropropylene as monomer components, and the content of the hexafluoropropylene monomer component in the copolymer is 3% by mass to 20% by mass. The separator for nonaqueous secondary batteries according to any one of claims 1 to 3, wherein the copolymer has a weight average molecular weight of 100,000 to 1,500,000. A positive electrode, a negative electrode, and a separator for a non-aqueous secondary battery according to any one of claims 1 to 4 disposed between the positive electrode and the negative electrode, and an electromotive force by doping and dedoping of lithium Get non-aqueous secondary battery.