JP6545238B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

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

  With the recent development of electronic technology and growing interest in environmental technology, various electrochemical devices are used. In particular, there are many demands for energy saving, and expectations for things that can contribute to it are increasing. A lithium ion secondary battery, which is a typical example of a storage device and a typical example of a non-aqueous electrolyte secondary battery, has conventionally been mainly used as a charging place for portable devices, but in recent years, batteries for hybrid vehicles and electric vehicles Its use as is also expected.

  However, when a lithium ion secondary battery is used in automotive applications, conditions of temperature and charge and discharge current become severer than those used in conventional portable devices. Therefore, lithium ion secondary batteries are required to further improve cycle characteristics, storage characteristics and continuous charge characteristics so as to function well as secondary batteries even under such severe conditions.

  Heretofore, the techniques described in Patent Documents 1 and 2 have been proposed for the purpose of improving these characteristics.

JP 2007-220335 A JP 2008-243810 A

  However, among the prior art including the techniques described in Patent Documents 1 and 2, there is not yet found any one that improves all of the cycle characteristics and the continuous charge characteristics.

  Therefore, the present invention has been made in view of the above circumstances, and has excellent cycle characteristics and continuous charge characteristics even when used under conditions of severe temperature and charge / discharge current equal to or higher than those of conventional ones. An object of the present invention is to provide a non-aqueous electrolyte secondary battery separator and a non-aqueous electrolyte secondary battery.

  MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to solve the said subject, the present inventors solved the said subject, if it is a separator for non-aqueous-electrolyte secondary batteries containing polyolefin resin and a predetermined | prescribed basic phosphate. It has been found that the present invention can be accomplished.

That is, the present invention is as follows.
[1]
At least a positive electrode, a negative electrode, a non-aqueous electrolyte, an exterior body, and a separator for a non-aqueous electrolyte secondary battery,
The separator for a non-aqueous electrolyte secondary battery has a porous film containing a polyolefin resin and a basic phosphate, and the cation of the basic phosphate is an alkali metal,
The positive electrode includes a positive electrode active material,
The potential of the positive electrode active material is 4.5 V or more based on lithium,
Nonaqueous electrolyte secondary battery.
[2]
At least polypropylene as the polyolefin resin,
The nonaqueous electrolyte secondary battery as described in [1].
[3]
The alkali metal of the separator for a non-aqueous electrolyte secondary battery is Li and / or Na.
The nonaqueous electrolyte secondary battery as described in [1] or [2].
[4]
The non-aqueous electrolyte secondary battery separator further includes a porous layer containing an inorganic substance disposed on at least one surface of the porous membrane,
The porous layer comprises a basic phosphate,
The nonaqueous electrolyte secondary battery as described in any one of [1]-[3].
[5]
The basic phosphate of the separator for a non-aqueous electrolyte secondary battery is in the form of particles,
The nonaqueous electrolyte secondary battery as described in any one of [1]-[4].
[6]
When the maximum distance between any two points on the outer periphery of 1 aggregated particle is defined as the aggregated particle size, the aggregated particle size of the basic phosphate of the separator for a non-aqueous electrolyte secondary battery is 0.1 μm or more and 30 μm or less is there,
The nonaqueous electrolyte secondary battery as described in any one of [1]-[5].

  According to the present invention, a separator for a non-aqueous electrolyte secondary battery having excellent cycle characteristics and continuous charge characteristics even when used under severe temperatures or charge conditions equal to or more than those in the prior art, and a non-aqueous electrolyte secondary A battery can be provided.

  Hereinafter, modes for carrying out the present invention (hereinafter, abbreviated as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the present invention.

[For non-aqueous electrolyte secondary batteries]
The separator for a non-aqueous electrolyte secondary battery according to the present embodiment is
Containing polyolefin resin and basic phosphate,
The cation of the basic phosphate is at least one selected from the group consisting of alkali metals and alkaline earth metals.

  The embodiment is not particularly limited as long as the separator for a non-aqueous electrolyte secondary battery according to the present embodiment includes a polyolefin resin and a basic phosphate.

  In addition, the form of the non-aqueous electrolyte secondary battery separator is not particularly limited, and examples thereof include those including a porous film, a non-woven fabric, or a substrate such as papermaking. The substrate is not particularly limited, but, for example, thermoplastic resins such as cellulose, aromatic polyamide, fluorocarbon resin and polyolefin, and inorganic substances such as alumina and silica, either alone or as a mixture of two or more As, the thing included or covered is mentioned. Hereinafter, the term "thermoplastic resin" is meant to include polyolefin resin as well.

  Furthermore, the separator for a non-aqueous electrolyte secondary battery may be one in which a basic phosphate is coated on the surface of a substrate, one in which a basic phosphate is mixed with a substrate, or a basic phosphoric acid between multiple substrates. It may be one having salt.

  More specifically, the following can be mentioned as an embodiment of the separator for non-aqueous electrolyte secondary batteries.

First Embodiment
The separator for non-aqueous electrolyte secondary batteries has a porous film that can contain a polyolefin resin, and can have a basic phosphate on the surface of the porous film. More specifically, the non-aqueous electrolyte secondary battery separator has a porous film containing a polyolefin resin, and a porous layer containing an inorganic substance disposed on at least one surface of the porous film, and is porous. The layer can include basic phosphate. Thus, by having a basic phosphate on the surface of the porous membrane, the cycle characteristics tend to be excellent.

Second Embodiment
The non-aqueous electrolyte secondary battery separator can have a porous film containing a polyolefin resin and a basic phosphate. As described above, the inclusion of the basic phosphate in the porous membrane tends to be more excellent in cycle characteristics. In this case, the basic phosphate may be present on the surface of the porous membrane.

Third Embodiment
The non-aqueous electrolyte secondary battery separator is one in which two or more porous films containing a polyolefin resin are laminated, and a basic phosphate can be present between the porous films. Thus, by having a basic phosphate between porous membranes, the cycle characteristics tend to be better.

  In addition, the polyolefin resin and basic phosphate which are described below can be variously modified and applied in the said embodiment. In addition, various other specific aspects described below can be variously modified and applied in the above embodiment.

[Basic phosphate]
The cation of the basic phosphate used in the present embodiment is an alkali metal such as Li ⁺ , Na ⁺ , and K ⁺ , and an alkaline earth metal such as Be ²⁺ , Mg ²⁺ , and Ca ^2+. At least one selected from the group consisting of By containing such a cation, a stable structure can be maintained in the electrolytic solution, and thus, the continuous charge characteristic tends to be more excellent. Among these, Li salt and Na salt are preferable, and further, it is preferable that Li salt is contained. By containing the Na salt and / or the Li salt, the electrochemical stability in the non-aqueous electrolyte battery is excellent, and the cycle characteristics tend to be further improved. In addition, a phosphate containing a single metal cation is preferable because the stability of its structure tends to further improve the cycle characteristics.

Further, the anion of the basic phosphate is a non-condensed phosphate ion such as PO ₄ ^3- , HPO ₄ ^2- and H ₂ PO ^4- , or P ₂ O ₇ ^4- or H ₂ P ₂ O ₇ ^{2 And} at least one selected from the group consisting of condensed phosphate ions such as P ₃ O ₁₀ ^5- .

The "basicity" can be determined by a conventionally known determination method. The conventionally known determination method is not particularly limited. For example, if the basic phosphate is water-soluble, a method of measuring the base dissociation constant (pKb) of the anion contained in the basic phosphate, such as basicity If the phosphate is non-water soluble or poorly water-soluble, a temperature rising desorption method of CO ₂ which is an acid gas can be mentioned. 10.83 or less is preferable, as for the base dissociation constant (pKb) of the anion contained in a basic phosphate, 7.65 or less is more preferable, and 2.00 or less is more preferable. Desorption temperature of CO ₂ in the temperature elevation withdrawal method of CO ₂ is an acid gas, preferably at least 100 ° C., more preferably at least 0.99 ° C., and even more preferably 200 ° C.. When the desorption temperature of pKb and CO ₂ is within the above range, it can be determined as basic. In addition, when the desorption temperature of pKb and CO ₂ is in the above range, the battery characteristics and safety tend to be excellent even at high temperature.

  The form of the basic phosphate is not particularly limited, and examples thereof include particulate, needle, plate and cubic. Among these, particulate form is preferable, and agglomerated particulate form in which many particles are aggregated is preferable.

  When the basic phosphate is particulate, the average particle diameter is preferably 0.1 to 100 μm, more preferably 0.5 to 30 μm, and still more preferably 1 to 10 μm. When the average particle size is 0.1 μm or more, the effect of the basic phosphate can be maintained for a long time, and excellent cycle characteristics, storage characteristics and continuous charge / discharge characteristics tend to be excellent over a long period. In addition, when the average particle size is 100 μm or less, battery characteristics such as discharge characteristics tend to be maintained favorably.

  The average particle diameter is measured by a SHIMADZU laser diffraction particle size distribution measuring apparatus (trade name: SALD-2300), and a median diameter (d50) at which large particles and small particles are equal is used as an average particle diameter.

  In addition, when the basic phosphate is in the form of aggregated particles, the aggregate particle diameter of the basic phosphate is preferably 0.1 μm to 30 μm, more preferably 0.5 μm to 10 μm, and 1 μm to 8 μm. More preferable. When the agglomerated particle diameter of the basic phosphate is in the above range, it tends to be more excellent. Here, "aggregated particle size" refers to the maximum distance between any two points on the outer periphery of one aggregated particle. The agglomerated particle size can be measured by the method described in the examples.

  In the present embodiment, when the basic phosphate is contained in the porous film, it may be contained in any form, and the thermoplastic resin and the inorganic particles forming the void portion and the porous structure of the porous film. It may be integrated. The cycle tends to be further improved by the presence of the basic phosphate in the pores of the porous membrane. When the separator has a plurality of layers, the basic phosphate may be contained in at least one layer.

  Among these, it is preferable that the basic phosphate is contained in the porous layer containing the inorganic particles. By including the basic phosphate in the porous layer containing the inorganic particles, the aggregate of the basic phosphate is surrounded by hard inorganic particles having a hardness compared to the thermoplastic resin and the like. As a result, there is no risk of the basic phosphate slipping from the separator, and it tends to be excellent in cycle characteristics under continuous conditions, continuous charging, and the like.

[Polyolefin resin]
The non-aqueous electrolyte secondary battery separator according to the present embodiment includes a polyolefin resin. Use of a polyolefin resin is excellent in properties such as shutdown performance. Here, "polyolefin resin" refers to a polyolefin resin used for ordinary extrusion, injection, inflation, blow molding and the like. Such a polyolefin resin is not particularly limited, and, for example, homopolymers and copolymers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene, and A multistage polymer etc. are mentioned. Such a polymer is not particularly limited. For example, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultrahigh molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene Random copolymers, polybutene, ethylene propylene rubber and the like can be mentioned. The polyolefin resins may be used alone or in combination of two or more. Among these, it is preferable to use a resin composed mainly of high density polyethylene. The use of high density polyethylene tends to further improve the shutdown performance due to the low melting point and to further increase the strength of the battery separator.

  Moreover, it is preferable to contain polypropylene and polyolefin resin other than polypropylene. By containing polypropylene and a polyolefin resin other than polypropylene, the heat resistance of the obtained separator tends to be further improved.

  The content of the polypropylene is preferably 1 to 35% by mass, more preferably 3 to 20% by mass, and still more preferably 4 to 10% by mass, with respect to 100% by mass of the total amount of the polyolefin resin in the porous membrane. When the content of the polypropylene is in the above range, the heat resistance tends to be excellent and the shutdown performance tends to be excellent.

  Although it does not specifically limit as polyolefin resin other than a polypropylene, For example, the homopolymer or copolymer of olefin hydrocarbons, such as ethylene, 1-butene, 4-methyl- 1-pentene, 1-hexene, 1-octene, etc. is mentioned. It can be mentioned. Such a polymer is not particularly limited, and examples thereof include polyethylene, polybutene, ethylene-propylene random copolymer and the like.

  The viscosity average molecular weight of the polyolefin resin is preferably 30,000 or more and 12,000,000 or less, more preferably 50,000 or more and 2,000,000 or less, and still more preferably 100,000 or more and 1,000,000 or less. When the viscosity average molecular weight is 30,000 or more, the melt tension at the time of melt molding is increased, the moldability is improved, and entanglement of polymers tends to result in high strength. On the other hand, when the viscosity average molecular weight is 12,000,000 or less, it becomes easy to melt and knead uniformly, and it tends to be excellent in sheet formability, particularly thickness stability. Furthermore, when the viscosity average molecular weight is 1,000,000 or less, the pores tend to be clogged when the temperature rises, and a good shutdown function tends to be obtained. For example, instead of using a polyolefin having a viscosity average molecular weight of 1,000,000 or less alone, a mixture having a viscosity average molecular weight of 1,000,000 or less containing a polyolefin having a viscosity average molecular weight of 2000000 and a polyolefin having a viscosity average molecular weight of 270000 may be used. Good. In addition, the viscosity average molecular weight of a thermoplastic resin can be measured by the method as described in an Example.

  The polyolefin resin used in the present embodiment may be a polyolefin resin composition containing any additive. Such additives are not particularly limited, but, for example, thermoplastic resins other than polyolefin resins, inorganic particles, basic phosphates, antioxidants (phenolic, phosphorus, sulfur etc.), metal soaps Examples thereof include (calcium stearate, zinc stearate and the like), UV absorbers, light stabilizers, antistatic agents, antifogging agents, color pigments and the like.

  The total addition amount of these additives can be suitably determined as needed. 50 mass parts or less are preferable with respect to 100 mass parts of polyolefin resin compositions, as for the total addition amount of an additive, 20 mass parts or less are more preferable, and 10 mass parts or less are more preferable.

  The thermoplastic resin other than the polyolefin resin is not particularly limited as long as it has electrochemical stability, resistance to the electrolytic solution, and the like. The thermoplastic resin other than the polyolefin resin is not particularly limited, and examples thereof include fluorinated polyolefin resin, polyester resin, polyamide resin, polyimide resin, polyamide imide resin, polyphenylene ether resin and the like. The content of the polyolefin resin is preferably 50% to 100%, more preferably 60% to 100%, and still more preferably 70% to 100% with respect to 100% by mass of the thermoplastic resin.

  When the polyolefin resin composition contains the inorganic particles, the thermal shrinkage of the porous film is further reduced, the permeability is further improved, and the porosity tends to be further improved. The inorganic particles are not particularly limited, but, for example, oxide-based ceramics such as alumina, silica, zirconia, magnesia, zinc oxide and iron oxide; nitride-based ceramics such as silicon nitride, titanium nitride and boron nitride; silicon carbide, Calcium carbonate, aluminum sulfate, barium sulfate, aluminum hydroxide, mica, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, silica Ceramics such as magnesium acid, kieselguhr, silica sand, glass fibers, etc. may be mentioned.

  When the polyolefin resin composition that can constitute the porous film contains a basic phosphate, the high temperature characteristics of the porous film tend to be further improved. Although it does not specifically limit as a basic phosphate, For example, the above-mentioned thing can be mentioned.

  In addition, when the polyolefin resin composition that can constitute the porous film contains an antioxidant, the performance deterioration of the porous film under severe charge and discharge conditions tends to be further reduced. The antioxidant is not particularly limited, and examples thereof include phenol-based antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants.

  Furthermore, in the case where the polyolefin resin composition that can constitute the porous film contains inorganic particles, it is preferable that the polyolefin resin composition further contain a binder component that binds the inorganic particles. The binder is not particularly limited. For example, when using the separator according to the present embodiment, it is preferably insoluble or poorly soluble in the electrolytic solution and electrochemically stable. More specifically, those usable in the porous layer described later can be mentioned.

[Physical properties of porous membrane]
The porosity of the porous film is preferably 30% to 70%, more preferably 40% to 65%, and still more preferably 45% to 60%. When the porosity is 30% or more, sufficient permeability as a battery separator is exhibited, and when used as a non-aqueous battery separator, the output characteristics tend to be more excellent. In addition, when the porosity is 70% or less, the possibility of self-discharge is low when used as a battery separator, and the reliability tends to be further improved. In addition, the porosity of a porous film can be measured by the method as described in an Example.

  The porosity can be controlled by combining the mixing ratio of the polyolefin resin and the plasticizer, the draw ratio of the extruded sheet, the draw temperature, the draw ratio, the heat setting temperature, the draw ratio at the heat setting, and the relaxation rate at the heat setting. It is.

  The thickness of the porous film is preferably 2 μm to 40 μm, more preferably 5 μm to 35 μm, and still more preferably 5 μm to 30 μm. When the film thickness is 2 μm or more, the mechanical strength of the porous film tends to be further improved. In addition, when the film thickness is 40 μm or less, the occupied volume of the battery separator in the battery is reduced, so the battery tends to have a higher capacity. In addition, the film thickness of a porous film can be measured by the method as described in an Example.

  The air permeability is preferably 10 seconds to 500 seconds, more preferably 20 seconds to 400 seconds, and still more preferably 40 seconds to 350 seconds. When the air permeability is 10 seconds or more, the self-discharge tends to be less when used as a battery separator. Further, when the air permeability is 500 seconds or less, good charge / discharge characteristics tend to be obtained. In addition, the air permeability of a porous membrane can be measured by the method as described in an Example.

  The average pore diameter of the porous membrane is preferably 0.01 to 5 μm, more preferably 0.02 to 1 μm, and still more preferably 0.035 μm to 0.060 μm. When the porous layer is formed on the surface of the porous membrane by having an average pore diameter of 0.01 μm or more, the permeability of the porous membrane is further reduced due to penetration of inorganic particles and binders into the pores and clogging of the pores. It becomes smaller and the battery output tends to be further improved. In addition, when the pore diameter is 5 μm or less, the self-discharge tends to be smaller. The average pore diameter of the porous membrane can be measured by the method described in the examples.

  The control of the pore size is the mixing ratio of the thermoplastic resin and the plasticizer, the cooling rate of the extruded porous film, the degree of rolling of the extruded porous film, the stretching temperature, the stretching ratio, the heat setting temperature, the heat setting ratio, the heat setting It is possible by combining the relaxation rate of the hour. Among these, the influence of the mixing ratio of the thermoplastic resin and the plasticizer, the stretching temperature, the stretching ratio, and the heat setting temperature on the pore diameter is large.

[Method for producing porous membrane]
Although it does not specifically limit as a method to manufacture a porous film, For example, a well-known manufacturing method is employable. The known manufacturing method is not particularly limited, and for example, a method of melt-kneading a thermoplastic resin and a plasticizer to form a sheet, optionally stretching, and then extracting the plasticizer to make it porous Thermoplastic resin is melt-kneaded and extruded at a high draw ratio (ratio of take-up speed to extrusion speed), then the crystal interface of the thermoplastic resin is exfoliated by heat treatment and stretching, and the thermoplastic resin is made porous Method of melt-kneading inorganic particles and forming them on a sheet, then peeling off the interface between the thermoplastic resin and the inorganic particles by stretching, making it porous, dissolving the thermoplastic resin and immersing in a poor solvent for the thermoplastic resin And a method of making the resin porous by removing the solvent while solidifying the thermoplastic resin.

[Porous layer]
Next, the porous layer which can contain an inorganic particle as a main component is demonstrated.

(Inorganic particles)
The inorganic particles used in the porous layer are not particularly limited, and for example, those having a melting point of 200 ° C. or higher, having high electrical insulation, and being electrochemically stable in the use range of the lithium ion secondary battery Is preferred. Such inorganic particles are not particularly limited, but, for example, oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, etc .; silicon nitride, titanium nitride, boron nitride, etc. Silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, boehmite, potassium titanate, talc, kaolinite, dicite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, Ceramics such as amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, glass fibers, etc. may be mentioned. The inorganic particles may be used alone or in combination of two or more.

  Among these, aluminum compounds such as alumina and boehmite; or aluminum silicate compounds having no ion exchange ability such as kaolinite, dickite, nacrite, halloysite and pyrophyllite are preferable. The use of such inorganic particles tends to further improve the electrochemical stability and the heat shrinkage suppressing property of the separator.

  Among the above, the aluminum compound is not particularly limited but, for example, boehmite is more preferable. Further, among the above, the aluminum silicate compound having no ion exchange ability is not particularly limited, but, for example, kaolin mainly composed of kaolin mineral is more preferable because it is inexpensive and easy to obtain. Kaolin includes wet kaolin and calcined kaolin obtained by subjecting the kaolin to calcination, however, in addition to the fact that water of crystallization is released during calcination, calcined kaolin removes impurities, so that in terms of electrochemical stability. More preferable.

  The shape of the inorganic particles is not particularly limited, and examples thereof include plate, scale, needle, column, sphere, polyhedron, and lump. The inorganic particles having the above shape may be used singly or in combination of two or more. From the viewpoint of improving the permeability, a polyhedron having a plurality of faces is preferable.

  When the porous layer contains inorganic particles, it is preferable that the porous layer contains a binder component for binding between the inorganic particles. The binder is not particularly limited. For example, when using the battery separator of the present embodiment, it is preferably insoluble or poorly soluble in the electrolytic solution and electrochemically stable. Such a binder is not particularly limited. For example, polyolefins such as polyethylene and polypropylene; fluorocarbon resins such as vinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer Fluorine-containing rubbers such as ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, Methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate, etc. Cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, etc. Melting point and / or glass transition temperature of polyphenylene ether, polysulfone, polyether sulfone, polyphenyl sulfone, polyphenylene sulfide, polyether imide, polyamide imide, polyester etc. The resin etc. of 180 degreeC or more are mentioned.

[Method of forming porous layer]
The method for forming the porous layer is not particularly limited. For example, a coating solution containing inorganic particles, and if necessary, a basic phosphate and a binder, is applied to at least one surface of a porous film that may contain a polyolefin resin. And a method of forming a porous layer.

  The solvent for the coating solution is not particularly limited, but preferred are, for example, those capable of uniformly and stably dissolving or dispersing inorganic particles, if necessary, a basic phosphate, and a binder. Such solvent is not particularly limited, and examples thereof include N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, ethanol, toluene, thermal xylene, methylene chloride, hexane and the like. .

  The method of dispersing the inorganic particles and the like in the solvent of the coating solution is not particularly limited as long as it can realize the dispersion property of the coating solution necessary for the coating process. Such methods are not particularly limited, but, for example, ball mill, bead mill, planetary ball mill, vibration ball mill, sand mill, colloid mill, attritor, roll mill, high speed impeller dispersion, disperser, homogenizer, high speed impact mill, ultrasonic dispersion, It can carry out using mechanical stirring etc. by a stirring blade etc.

  The method for applying the coating solution to the porous film is not particularly limited as long as the required layer thickness and application area can be realized. Such a method is not particularly limited. For example, a gravure coater method, a small diameter gravure coater method, a reverse roll coater method, a transfer roll coater method, a kiss coater method, a dip coater method, a knife coater method, an air doctor coater method, a blade A coater method, a rod coater method, a squeeze coater method, a cast coater method, a die coater method, a screen printing method, a spray coating method and the like can be mentioned.

  Furthermore, prior to coating, the surface of the porous membrane is subjected to surface treatment to facilitate coating of the coating solution, and the adhesiveness between the porous layer and the porous membrane after coating tends to be improved. The surface treatment method is not particularly limited as long as the porous structure of the porous film is not significantly impaired, and examples thereof include corona discharge treatment, mechanical surface roughening, solvent treatment, acid treatment, and ultraviolet oxidation. Law etc. are mentioned.

  The method for removing the solvent from the coating film after coating is not particularly limited as long as the porous film is not adversely affected. Such a method is not particularly limited, and examples thereof include a method of drying at a temperature below the melting point while fixing the porous film, a method of drying under reduced pressure at a low temperature, and the like.

  The thickness of the porous layer containing inorganic particles as a main component is preferably 1 μm to 50 μm, more preferably 1.5 μm to 20 μm, still more preferably 2 μm to 10 μm, and still more preferably 2 μm to 7 μm. When the layer thickness is 1 μm or more, the heat resistance and the insulation property tend to be excellent. Further, when the layer thickness is 50 μm or less, the battery tends to be more excellent in capacity and permeability.

The layer density of the porous layer is preferably 0.5 g / cm ³ or more and 2.0 g / cm ³ or less, more preferably 0.7 g / cm ³ or more and 1.8 g / cm ³ or less, and 0.9 g / cm ³ or more 1.7 g / cm ³ or less is more preferable. When the layer density is 0.5 g / cm ³ or more, thermal contraction tends to be further suppressed. In addition, when the layer density of the porous layer is 2.0 g / cm ³ or less, the cycle characteristics tend to be further improved. In addition, the layer density of a porous layer can be measured by the method as described in an Example.

Non-aqueous electrolyte secondary battery
Next, the case where the porous film of the present embodiment is used as a separator for a non-aqueous electrolyte secondary battery will be described. The non-aqueous electrolyte secondary battery according to the present embodiment includes at least a positive electrode, a negative electrode, a non-aqueous electrolyte, an outer package, and the above-described separator for a non-aqueous electrolyte secondary battery.

(Positive electrode)
The positive electrode preferably includes a positive electrode active material, a conductive material, a binder, and a current collector.

As a positive electrode active material that can be contained in the positive electrode, known materials capable of electrochemically absorbing and desorbing lithium ions can be used. Among them, as the positive electrode active material, a material containing lithium is preferable. As a positive electrode active material, for example, formula (1):
Li _x Mn _2-y M _y O _z (1)
(Wherein, M represents at least one element selected from the group consisting of transition metal elements, and 0 <x ≦ 1.3, 0.2 <y <0.8, 3.5 <z <4. 5))
An oxide represented by the formula (2):
Li _x M _y O _z (2)
(Wherein, M represents at least one element selected from the group consisting of transition metal elements, and 0 <x ≦ 1.3, 0.8 <y <1.2, 1.8 <z <2.2 Is)
Layered oxide represented by the formula (3):
LiMn ₂ -xMa _x O ₄ (3)
(In the formula, Ma represents at least one element selected from the group consisting of transition metal elements, and 0.2 ≦ x ≦ 0.7.)
Spinel type oxide represented by, Formula (4):
Li ₂ McO ₃ (4)
(Wherein, M c represents at least one element selected from the group consisting of transition metal elements), and an oxide represented by the formula (5):
LiMdO ₂ (5)
(Wherein, Md represents at least one element selected from the group consisting of transition metal elements). A complex oxide with an oxide represented by the formula (6):
zLi ₂ McO _{3- (1-z)} LiMdO ₂ (6)
(Wherein, Mc and Md are the same as those in the above formulas (4) and (5), respectively, and 0.1 ≦ z ≦ 0.9)
Li-rich layered oxide cathode active material represented by the formula (7):
LiMb _1-y Fe _y PO ₄ (7)
(Wherein, Mb represents at least one element selected from the group consisting of Mn and Co, and 0 ≦ y ≦ 1.0).
An olivine type positive electrode active material represented by the formula (8):
Li ₂ MePO ₄ F (8)
(Wherein, Me represents at least one element selected from the group consisting of transition metal elements). These positive electrode active materials may be used alone or in combination of two or more.

  Among these, from the viewpoint of cost, the positive electrode preferably contains a lithium transition metal oxide containing manganese. Such an oxide is not particularly limited, and examples thereof include compounds represented by formulas (1), (3) and (7).

  Furthermore, the potential of the positive electrode active material is preferably 4.5 V or more based on lithium. When the potential of the positive electrode active material is 4.5 V or more based on lithium, the electrolyte is easily decomposed, and the accompanying hydrofluoric acid can be removed by the basic phosphate, which is more effective.

  As the conductive material that can be contained in the positive electrode, known materials capable of conducting electrons can be used. Such a conductive material is not particularly limited, but preferred examples thereof include activated carbon, various cokes, non-graphite carbonaceous materials such as carbon black and acetylene black, and graphite. These may be used alone or in combination of two or more.

  As a binder that can be contained in the positive electrode, a known material that can bind at least two of a positive electrode active material, a conductive material that can be contained in the positive electrode, and a current collector that can be contained in the positive electrode can be used. Such a binder is not particularly limited, but, for example, polyvinylidene fluoride and fluororubber are preferable. The binder may be used alone or in combination of two or more.

  Although it does not specifically limit as a collector which may be contained in a positive electrode, For example, metal foils, such as aluminum, titanium, stainless steel, an expanded metal, a punch metal, a foam metal, carbon cloth, and carbon paper are mentioned. These may be used alone or in combination of two or more.

(Negative electrode)
The negative electrode used in the present embodiment preferably includes a negative electrode active material, a binder, and a current collector.

  As a negative electrode active material that can be contained in the negative electrode, known materials capable of electrochemically absorbing and desorbing lithium ions can be used. Such a negative electrode active material is not particularly limited, but preferred are, for example, carbon materials such as graphite powder, mesophase carbon fibers and mesophase microspheres, as well as metals, alloys, oxides and nitrides. These may be used alone or in combination of two or more.

  As a binder that can be contained in the negative electrode, a known material that can bind at least two of a negative electrode active material, a conductive material that can be contained in the negative electrode, and a current collector that can be contained in the negative electrode can be used. Such a binder is not particularly limited, but, for example, carboxymethylcellulose, a crosslinked rubber latex of styrene-butadiene, an acrylic latex and polyvinylidene fluoride are preferable. These may be used alone or in combination of two or more.

  Although it does not specifically limit as a collector which may be contained in a negative electrode, For example, metal foils, such as copper, nickel, and stainless steel, an expanded metal, a punch metal, a foam metal, carbon cloth, and carbon paper are mentioned. These may be used alone or in combination of two or more.

(Non-aqueous electrolyte)
The electrolyte (salt) contained in the non-aqueous electrolyte used in the present embodiment is not particularly limited, and conventionally known ones can be used. Such electrolytes are not particularly limited, and examples thereof include LiPF ₆ (lithium hexafluorophosphate), LiClO ₄ , LiBF ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ CkF _{2k + 1} [k is 1 to 4] Integer of 8], LiN (SO ₂ C _k F _{2 k + 1} ) ₂ [k is an integer of 1 to 8], LiPF _n (CkF _{2k + 1} ) _6-n [n is an integer of 1 to 5 and k is 1 And LiPF ₄ (C ₂ O ₄ ) and LiPF ₂ (C ₂ O ₄ ) ₂ . Among these, LiPF ₆ is preferable. The use of LiPF ₆ tends to be more excellent in battery characteristics and safety even at high temperatures. These electrolytes may be used alone or in combination of two or more.

  The non-aqueous solvent used for the non-aqueous electrolyte in the present embodiment is not particularly limited, and conventionally known ones can be used. Such non-aqueous solvent is not particularly limited, but for example, an aprotic polar solvent is preferable. The aprotic polar solvent is not particularly limited. For example, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate Cyclic carbonates such as trifluoromethyl ethylene carbonate, fluoroethylene carbonate and 4,5-difluoroethylene carbonate; lactones such as γ-peptirolactone and γ-valerolactone; cyclic sulfones such as sulfolane; cyclic ethers such as tetrahydrofuran and dioxane; ethyl methyl carbonate , Dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl Linear carbonates such as carbonate, dibutyl carbonate, ethyl propyl carbonate and methyl trifluoroethyl carbonate; nitriles such as acetonitrile; linear ethers such as dimethyl ether; linear carboxylic esters such as methyl propionate; linear ethers such as dimethoxyethane A carbonate compound is mentioned. These may be used alone or in combination of two or more.

  The non-aqueous electrolyte of this embodiment may be a liquid electrolyte or a solid electrolyte.

  The air permeability of the separator according to the present embodiment is preferably 10 seconds / 100 cc to 500 seconds / 100 cc, more preferably 20 seconds / 100 cc to 450 seconds / 100 cc, and 30 seconds / 100 cc to 400 seconds / 100 cc. More preferable. When the air permeability is 10 seconds / 100 cc or more, the self-discharge when used as a battery separator tends to be reduced. In addition, when the air permeability is 500 seconds / 100 cc or less, good charge / discharge characteristics can be obtained, and the battery capacity retention ratio tends to be more excellent. The air permeability of the battery separator can be measured by the method described in the examples.

The total thickness of the separator is preferably 2 μm or more and 200 μm or less, more preferably 5 μm or more and 100 μm or less, and still more preferably 7 μm or more and 30 μm or less.
When the film thickness is 2 μm or more, the mechanical strength is sufficient, and when the film thickness is 200 μm or less, the occupied volume of the separator is reduced, which is advantageous in increasing the capacity of the battery.

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

  The non-aqueous electrolyte secondary battery of the present embodiment may have the same configuration as that of the conventionally known one, except for having the above-described configuration. Examples of the non-aqueous electrolyte secondary battery of the present embodiment include a lithium ion secondary battery and a lithium ion capacitor. In addition, the manufacturing method of the non-aqueous electrolyte secondary battery of the present embodiment may be the same as the conventional manufacturing method of the non-aqueous electrolyte secondary battery except that the basic phosphate is contained as described above. it can.

  The non-aqueous electrolyte secondary battery of the present embodiment has all of the cycle characteristics, the storage characteristics and the continuous charge characteristics even when used under conditions of severe temperature or charge current equivalent to or more than conventional ones such as automotive applications. It will be excellent.

  Hereinafter, the present invention will be more specifically described using examples and comparative examples. The present invention is not limited at all by the following examples.

(1) Viscosity average molecular weight of polyolefin (hereinafter, also referred to as "Mv")
The intrinsic viscosity [D] (dl / g) at 135 ° C. in decalin solvent was determined based on ASTM-D4020.
In addition, about polyethylene (henceforth "PE"), it computed by following Formula.
[Η] = 6.77 × 10 ^-4 Mv ^0.67
Moreover, about polypropylene (henceforth "PP"), Mv was computed by following Formula.
[Η] = 1.10 × 10 ^-4 Mv ^0.80

(2) Film thickness of porous membrane and separator, layer thickness of porous layer, layer density of porous layer A sample of MD10 mm × TD10 mm is cut out from the porous membrane and the separator, and 9 places (3 points × 3 points) in a grid shape The film thickness was selected and measured using a dial gauge (PEACOCK No. 25 (registered trademark) manufactured by Ozaki Mfg. Co., Ltd.), and the average value of the measured values at nine locations was taken as the film thickness (μm) of the porous film and the separator. Further, the difference between the film thickness of the separator and the porous film measured as described above was taken as the layer thickness (μm) of the porous layer.

A porous membrane and a separator (a porous layer was formed on the porous membrane) were cut into 10 cm × 10 cm squares, and their weight (g) and film thickness (μm) were measured. The difference between the weight of the separator and the porous film was taken as the weight (g) of the porous layer, and the difference between the film thickness was taken as the layer thickness (μm) of the porous layer. The layer density of the porous layer was determined by the following equation based on the weight (g) of the obtained porous layer and the layer thickness (μm) of the porous layer.
Layer density of porous layer (g / cm ³ ) = weight of porous layer (g) / layer thickness of porous layer (μm) × 100

(3) Porosity of Porous Membrane A 10 cm × 10 cm square sample is cut out of the porous membrane, its volume (cm ³ ) and mass (g) are determined, and the density of the porous membrane is set to 0.95 (g / cm ³ ). Calculated using the equation.
Porosity (%) = (1-mass / volume / 0.95) x 100

(4) Air permeability of porous film and separator Using a Gurley-type air permeability meter (manufactured by Toyo Seiki G-B2 (trade mark), inner cylinder weight: 567 g) according to JIS P-8117, the area (diameter 28) of 645 mm ² The time (seconds) in which 100 cc of air passes through the porous membrane of 6 mm and the separator) was measured, and this was taken as the air permeability (second / 100 cc) of the porous membrane and the separator.

(5) Average particle size of inorganic particles (Dp 50)
In the case of measuring the average particle size when the inorganic particles are not crushed, the inorganic particles are added to distilled water, a small amount of an aqueous solution of sodium hexametaphosphate is added, and then dispersed for 1 minute with an ultrasonic homogenizer. The particle size distribution was measured using (Microtrac MT3300EX manufactured by Nikkiso Co., Ltd.), and the particle size at which the volume cumulative frequency became 50% was defined as the average particle size (μm).

  Moreover, as a measurement of the average particle diameter in the case of grind | pulverizing inorganic particle, when particle diameter control of inorganic particle is carried out by bead mill etc., the prepared dispersion liquid is a laser type particle size distribution measuring apparatus (Nikkiso Co., Ltd. Microtrac MT3300EX The particle size distribution was measured by using the above-mentioned formula), and the particle size at which the volume cumulative frequency became 50% was defined as the average particle size (μm).

(6) Aggregated Particle Size of Basic Phosphate The cross-sectional scanning electron microscope (SEM) image of the multilayer porous film is observed, and the maximum distances of the particulate aggregates of the basic phosphate arbitrarily selected at 10 points The average particle size was taken as the aggregated particle size. The "maximum distance" is the maximum distance between any two points on the periphery of one aggregated particle. The measurement was carried out at 0.1 μm or less, and the average value was expressed in μm.

(7) Average Pore Diameter of Porous Membrane It is known that the fluid inside the capillary follows the Knudsen flow when the mean free path of the fluid is larger than the pore diameter of the capillary and the Poiseuille flow when it is smaller. Therefore, it was assumed that the flow of air in the measurement of air permeability of the porous membrane follows the flow of Knudsen, and the flow of water in the measurement of water permeability of the porous membrane follows the flow of Poiseuille.

In this case, the average pore diameter d (μm) of the porous membrane and the tortuosity factor τ _a (non-dimensional) are the air permeation rate constant R _gas (m ³ / (m ² · sec · Pa)), the water permeation rate constant R _liq (m ³ / (m ² · sec · Pa)), molecular velocity of air ((m / sec), viscosity of water η (Pa · sec), standard pressure P _s (= 101325 Pa), porosity ε ( %) And film thickness L (μm) using the following equation.
d = 2ν × (R _liq / R _gas ) × (16/3/3 Ps) × 10 ⁶
τ _a = (d × (ε / 100) × ν / (3L × P _s × R _gas )) ^1/2

Here, R _gas was determined from the air permeability (sec) using the following equation.
R _gas = 0.0001 / (air permeability × (6.424 × 10 ⁻⁴ ) × (0.01276 × 101325))

Moreover, R _liq was calculated | required using the following formula from water permeability (cm _< ³ > / (cm < ² > * sec * Pa)).
R _liq = permeability / 100

The water permeability was determined as follows. A porous membrane previously dipped in alcohol was set in a stainless steel liquid-permeable cell with a diameter of 41 mm, and after washing the alcohol of the membrane with water, water was allowed to permeate at a differential pressure of about 50000 Pa, and 120 seconds elapsed. From the water permeation amount (cm ³ ) at that time, the unit time, the unit pressure, and the water permeation amount per unit area were calculated, and this was taken as the water permeability.

Also, ν is the gas constant R (= 8.314), absolute temperature T (K), pi, and the average molecular weight M of air (= 2. 896 × 10 ^-2 kg / mol) I asked.
== ((8R × T) / (π × M)) ^1/2
Further, the number of holes B (number / μm ² ) was determined by the following equation.
B = 4 × (ε / 100) / (π × d ² × τ _a )

Example 1
[I] Preparation of porous film 1 wt% of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant to 99 wt% of polypropylene having a homopolymer of Mv 200,000 The polyolefin resin composition was obtained by adding and dry blending using a tumbler blender. The resulting polyolefin resin composition was replaced with nitrogen and then fed to a twin-screw extruder by a feeder under a nitrogen atmosphere. Also, liquid paraffin (kinetic viscosity 7.59 × 10 ⁻⁵ m ² / s at 37.78 ° C.) was injected into the extruder cylinder by a plunger pump.

  The feeder and the pump were adjusted so that the amount ratio of liquid paraffin occupied in the entire mixture extruded by melt-kneading was 66 wt% (the resin composition concentration was 34%). Melt-kneading conditions were a set temperature of 200 ° C., a screw rotation speed of 100 rpm, and a discharge amount of 12 kg / h.

  Subsequently, the melt-kneaded product was extruded and cast on a cooling roll controlled to a surface temperature of 25 ° C. through a T-die to obtain a gel sheet with a thickness of 2000 μm.

  Next, it was introduced into a simultaneous biaxial tenter stretching machine and biaxial stretching was performed. The set stretching conditions were an MD magnification of 5.0 times, a TD magnification of 4.5 times, and a set temperature of 130 ° C.

  Next, it was introduced into a methyl ethyl ketone tank and thoroughly immersed in methyl ethyl ketone to extract and remove liquid paraffin, and then the methyl ethyl ketone was dried and removed.

  Next, it was introduced to a TD tenter and subjected to stretching and thermal relaxation. The stretching temperature is 130 ° C., thermal relaxation temperature is 133 ° C., TD maximum magnification is 1.85 times, relaxation rate is 0.9, film thickness 25 μm, porosity 50%, air permeability 180 seconds, average pore diameter 0. A porous membrane of 1 μm was obtained.

[II] Preparation of Separator Between two obtained porous films made of polypropylene (film thickness 25 μm, porosity 50%, average pore diameter 0.1 μm), an amount of 100% by mass with respect to the mass of the positive electrode active material Then, Li ₃ PO ₄ , which is solid particles with an average particle diameter of 30 μm, was spread to obtain a separator of Example 1.

Example 2
Between two porous films made of polypropylene (film thickness 25 μm, porosity 50%, average pore diameter 0.1 μm) obtained in Example 1, an amount of 50 mass% based on the mass of the positive electrode active material Li ₃ PO ₄ which is solid particles with a particle size of 30 μm was spread to obtain a separator of Example 2.

Comparative Example 1
Two separators made of polypropylene porous film (film thickness 25 μm, porosity 50%, average pore diameter 0.1 μm) obtained in Example 1 were directly superposed to obtain a separator of Comparative Example 1.

[Example 3]
[I] Preparation of porous film A dry blend of 47.5 parts by mass of Mv 700000 homopolymer, 47.5 parts by mass of Mv 250,000 homopolymer, and 5 parts by mass of Mv 400000 homopolymer polypropylene using a tumbler blender did. 1 wt% of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] is added as an antioxidant to 99 wt% of pure polymer, and dry blending is performed again using a tumbler blender By doing this, a polyolefin resin composition was obtained. The resulting polyolefin resin composition was replaced with nitrogen and then fed to a twin-screw extruder by a feeder under a nitrogen atmosphere. Also, liquid paraffin (kinetic viscosity 7.59 × 10 ⁻⁵ m ² / s at 37.78 ° C.) was injected into the extruder cylinder by a plunger pump.

  The feeder and the pump were adjusted so that the amount ratio of liquid paraffin occupied in the entire mixture extruded by melt-kneading was 66 wt% (the resin composition concentration was 34%). Melt-kneading conditions were a set temperature of 200 ° C., and a screw rotation speed of 100 rpm and a discharge amount of 12 kg / h.

  Subsequently, the melt-kneaded product was extruded and cast on a cooling roll controlled to have a surface temperature of 25 ° C. through a T-die to obtain a gel sheet having a thickness of 1600 μm.

  Next, it was introduced into a simultaneous biaxial tenter stretching machine and biaxial stretching was performed. The set stretching conditions were an MD magnification of 7.0 times, a TD magnification of 6.1 times, and a set temperature of 123 ° C.

  Next, it was introduced into a methyl ethyl ketone tank and thoroughly immersed in methyl ethyl ketone to extract and remove liquid paraffin, and then the methyl ethyl ketone was dried and removed.

  Next, it was introduced to a TD tenter and subjected to stretching and thermal relaxation. The stretching temperature is 125 ° C., thermal relaxation temperature is 133 ° C., TD maximum magnification is 1.65 times, relaxation rate is 0.9, film thickness 16 μm, porosity 40%, air permeability 230 seconds, average pore size 0. A porous membrane of 06 μm was obtained.

[II] Preparation of Separator 56.0 parts by mass of aluminum silicate (Al ₂ O ₃ .2SiO ₂ ) and 45.8 parts by mass of trilithium phosphate (Li ₃ PO ₄ ) in 100 parts by mass of ion exchanged water After mixing 0.28 parts by mass of an aqueous solution of ammonium carboxylate (SN Disperse 5468 manufactured by SAN NOPCO), bead milling was performed to adjust the average particle diameter (Dp50) of aluminum silicate to 1.9 μm, thereby obtaining a dispersion. Furthermore, 4.4 parts by mass of acrylic latex suspension (solid content concentration 40%, average particle diameter 150 nm) as a binder was mixed with 100 parts by mass of the obtained dispersion to prepare a dispersion. Next, the dispersion was applied to the surface of the porous film using a microgravure coater. It was dried at 60 ° C. to remove water, to form a porous layer with a thickness of 5 μm on the porous film, to obtain a separator containing trilithium phosphate in the inorganic layer. In the cross-sectional SEM image of the separator, an aggregate of Li ₃ PO _{4 with} a diameter of 3 μm was confirmed in the void portion. The separator had a film thickness of 21 μm, an air permeability of 248 seconds, and the layer density of the inorganic layer was 1.15 g / cm ³ .

Comparative Example 2
A separator was obtained in the same manner as Example 2, except that the dispersion was changed to the following.
After mixing 56.0 parts by mass of aluminum silicate (Al ₂ O ₃ .2SiO ₂ ) and 0.28 parts by mass of ammonium polycarboxylate aqueous solution (SN Disperse 5468 manufactured by SAN NOPCO) in 100 parts by mass of ion exchange water, Bead milling was performed, and the average particle size (Dp50) of aluminum silicate was adjusted to 1.9 μm to obtain a dispersion. Furthermore, 4.4 parts by mass of acrylic latex suspension (solid content concentration 40%, average particle diameter 150 nm) as a binder was mixed with 100 parts by mass of the obtained dispersion to prepare a dispersion. After the dispersion was applied and dried, a separator with a film thickness of 21 μm and an air permeability of 244 seconds was obtained.

Comparative Example 3
A separator was obtained in the same manner as in Example 3, except that zinc phosphate was used instead of trilithium phosphate used in Example 3. The separator had a film thickness of 21 μm, an air permeability of 254 seconds, and the layer density of the inorganic layer was 1.2 g / cm ³ .

<Synthesis of positive electrode active material>
Synthesis of LiNi _0.5 Mn _1.5 O ₄ Nickel sulfate and manganese sulfate in a ratio of 1: 3 as a molar ratio of transition metal elements are dissolved in water so that the total metal ion concentration becomes 2 mol / L. A manganese mixed aqueous solution was prepared. Next, this nickel-manganese mixed aqueous solution was dropped in 3000 mL of a 2 mol / L sodium carbonate aqueous solution heated to 70 ° C. for 120 minutes at an addition rate of 12.5 mL / min. In addition, at the time of dripping, while stirring, air was bubbled into the aqueous solution while bubbling air at a flow rate of 200 mL / min. Thereby, a precipitated substance was generated, and the obtained precipitated substance was sufficiently washed with distilled water and dried to obtain a nickel manganese compound. The obtained nickel manganese compound and lithium carbonate having a particle diameter of 2 μm are weighed so that the molar ratio of lithium: nickel: manganese is 1: 0.5: 1.5, dry-mixed for 1 hour, and then obtained. The mixture was fired at 1000 ° C. for 5 hours in an oxygen atmosphere to obtain a positive electrode active material represented by LiNi _0.5 Mn _1.5 O ₄ .

<Fabrication of positive electrode>
The positive electrode active material obtained as described above, a powder of graphite (made by TIMCAL, KS-6) as a conductive additive, a powder of acetylene black (made by Denki Kagaku Kogyo, HS- 100), It mixed with the vinylidene fluoride solution (Kureha company make, L # 7208) by mass ratio of 80: 5: 5: 10 in solid content ratio. To the obtained mixture, N-methyl-2-pyrrolidone was added as a dispersion solvent so as to have a solid content of 35% by mass, and they were further mixed to prepare a slurry-like solution. The slurry-like solution was applied to one side of a 20 μm thick aluminum foil, the solvent was removed by drying, and then rolled by a roll press. The rolled product was punched into a disk shape having a diameter of 16 mm to obtain a positive electrode.

<Fabrication of negative electrode>
Graphite powder (OMAC Gas Chemical Co., Ltd., OMAC1.2H / SS) and graphite powder (TIMCAL Co., SFG6) as negative electrode active materials, and styrene butadiene rubber (Nippon Zeon Co., product name BM-400B, SBR) as a binder And carboxymethylcellulose aqueous solution (manufactured by Daicel Finechem, product name Daicel 2200) at a solid content weight ratio of 90: 10: 1.5: 1.8. The resulting mixture was added to water as a dispersion solvent so that the solid content concentration was 45% by mass, to prepare a slurry-like solution. The slurry-like solution was applied to one side of a copper foil having a thickness of 18 μm, the solvent was removed by drying, and rolling was performed with a roll press. The rolled product was punched into a disk shape having a diameter of 16 mm to obtain a negative electrode.

<Preparation of Nonaqueous Electrolyte>
LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 1: 2 so as to be 1 mol / L to obtain an electrolyte solution which is a non-aqueous electrolyte .

<Fabrication of battery>
Fabrication of the cell was performed in an argon box. A laminated body in which the positive electrode and the negative electrode produced as described above were stacked on both sides of a separator made of multilayer porous films produced in Examples and Comparative Examples was inserted into a stainless steel disk-shaped battery case. Then, 0.5 mL of the above-mentioned electrolytic solution was injected therein, and the laminate was immersed in the electrolytic solution, and then the battery case was sealed to prepare a non-aqueous electrolytic solution secondary battery.

<Battery evaluation>
-Initial charge and discharge The obtained non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as "battery") is housed in a thermostatic chamber (thermostatic chamber PLM-73S manufactured by Two Leaf Science Co., Ltd., set at 25 ° C) and charged. The discharge device was connected to a charge / discharge device ACD-01 manufactured by Aska Electronics Co., Ltd. Then, the battery was charged with a constant current of 0.05 C, and after reaching 4.8 V, it was charged for 2 hours with a constant voltage of 4.8 V and discharged to 3.0 V with a constant current of 0.3 C. Here, 1 C is a current value at which the battery is discharged in one hour.

・ Continuous charge characteristic test The battery after the above initial charge and discharge is accommodated in a constant temperature bath (constant temperature bath PLM-73S manufactured by Futaba Scientific Co., Ltd.) set at 55 ° C. Connected to device ACD-01). Next, the battery was charged with a constant current of 0.5 C, and after reaching 4.8 V, it was charged for 6 hours with a constant voltage of 4.8 V, and the current value at 6 hours was confirmed as a leak current value. Thereafter, the battery was discharged to 3.0 V at a constant current of 0.5C.

Cycle Test The battery after the above continuous charge characteristic test is housed in a thermostatic chamber (constant temperature tank PLM-73S manufactured by Futaba Scientific Co., Ltd.) set at 55 ° C. It connected to ACD-01). The cell was then charged to 4.8 V with a constant current of 0.5 C and discharged to 3.0 V with a constant current of 0.5 C. This series of charging and discharging was regarded as one cycle, and 28 cycles were further charged and discharged. Subsequently, the battery was charged with a constant current of 0.1 C, reached 4.8 V, charged with a constant voltage of 4.8 V for 1 hour, and discharged to 3.0 V with a constant current of 0.1 C ( 30th cycle). The discharge capacity of the first cycle and the 30th cycle was confirmed.

  When the porous film containing the basic phosphate is used as a separator, the leakage current value is small during continuous charge and discharge, and the high temperature, high voltage and severe conditions are further compared. Good characteristics were also shown in the cycle test.

  The present invention has industrial applicability as a battery separator having excellent cycle characteristics and continuous charge characteristics.

Claims (6)

At least a positive electrode, a negative electrode, a non-aqueous electrolyte, an exterior body, and a separator for a non-aqueous electrolyte secondary battery,
The nonaqueous electrolyte secondary battery separator comprises a polyolefin resin has a basic phosphate, a porous film containing a cation of the basic phosphate, Ri alkali metal der,
The positive electrode includes a positive electrode active material,
The potential of the positive electrode active material is 4.5 V or more based on lithium,
Nonaqueous electrolyte secondary battery.   At least polypropylene as the polyolefin resin,
  The non-aqueous electrolyte secondary battery according to claim 1. The alkali metal of the separator for a non-aqueous electrolyte secondary battery is Li and / or Na.
The non-aqueous electrolyte secondary battery according to claim 1 or 2 . The non-aqueous electrolyte secondary battery separator further includes a porous layer containing an inorganic substance disposed on at least one surface of the porous membrane,
The porous layer comprises a basic phosphate,
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3 . The basic phosphate of the separator for a non-aqueous electrolyte secondary battery is in the form of particles,
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4 . When the maximum distance between any two points on the outer periphery of 1 aggregated particle is defined as the aggregated particle size, the aggregated particle size of the basic phosphate of the separator for a non-aqueous electrolyte secondary battery is 0.1 μm or more and 30 μm or less is there,
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5 .