JP7160636B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

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

Non-aqueous electrolyte secondary batteries such as lithium secondary batteries are currently widely used as batteries for devices such as personal computers, mobile phones, and personal digital assistants.

Devices equipped with lithium-ion batteries are equipped with various types of electrical protection circuits in chargers and battery packs, and measures are taken to ensure that the batteries operate normally and safely. When a lithium-ion battery continues to be charged, oxidation-reduction decomposition of the electrolyte solution on the surface of the positive and negative electrodes with heat generation, oxygen release due to the decomposition of the positive electrode active material, and deposition of metallic lithium on the negative electrode occur. Falling into a runaway state may cause the battery to ignite or explode in some cases.

In order to safely stop the battery before it reaches such a dangerous thermal runaway condition, most of the current lithium-ion batteries have a structure in which if the internal temperature of the battery rises for some reason, the temperature rises to about 130°C to 140°C, and the porous base material heats up. A polyolefin-based porous substrate having a shut-down function that closes open pores is used as a separator.

On the other hand, since the porous base material mainly composed of polyolefin has low heat resistance, it melts when exposed to temperatures above the temperature at which the shutdown function operates, resulting in a short circuit inside the battery and ignition of the battery. There was a risk of explosion. Therefore, in order to improve the heat resistance of the porous base material, development of a separator in which a porous layer containing a filler and a resin is laminated on at least one surface of the porous base material is being developed.

As an example of such a separator, Patent Document 1 describes a battery separator formed of a porous layer containing boehmite (plate-like particles) as fine particles.

Japanese Patent Application Laid-Open No. 2008-4438 (published on January 10, 2008)

However, the prior art as described above has room for improvement from the viewpoint of the discharge capacity recovery characteristics of the battery after charge-discharge cycles.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent discharge capacity recovery characteristics after charge-discharge cycles.

The non-aqueous electrolyte secondary battery according to aspect 1 of the present invention complies with the porous layer containing an inorganic filler and a resin, and the MIT tester method specified in JIS P 8115 (1994), with a load of 1 N and bending. A positive electrode plate that was bent 130 times or more until the electrode active material layer peeled off in a folding endurance test conducted at an angle of 45°, and a positive electrode plate that was bent 1650 times until the electrode active material layer peeled off in the folding endurance test. and a negative electrode plate of at least 10 times, and the porous layer has a value represented by the following formula (1) in the range of 0.10 to 0.42.
|1-T/M| (1)
(In formula (1), T represents the distance to the critical load in the scratch test under a constant load of 0.1 N in TD, and M represents the distance to the critical load in the scratch test under a constant load of 0.1 N in MD. , represents the distance to the critical load.)
Further, in the non-aqueous electrolyte secondary battery according to aspect 2 of the present invention, in aspect 1, the porous layer comprises polyolefin, (meth)acrylate resin, fluorine-containing resin, polyamide resin, polyester resin and It contains one or more resins selected from the group consisting of water-soluble polymers.

Further, in the non-aqueous electrolyte secondary battery according to aspect 3 of the present invention, in aspect 2, the polyamide-based resin is an aramid resin.

Further, in the non-aqueous electrolyte secondary battery according to Aspect 4 of the present invention, in any one of Aspects 1 to 3, the porous layer is laminated on one side or both sides of the polyolefin porous film.

Further, in the non-aqueous electrolyte secondary battery according to aspect 5 of the present invention, in any one of aspects 1 to 4, the positive electrode plate contains a transition metal oxide, and the negative electrode plate contains graphite.

According to one aspect of the present invention, a non-aqueous electrolyte secondary battery having excellent discharge capacity recovery characteristics after charge-discharge cycles can be realized.

It is a schematic diagram which shows the outline of an MIT testing machine. FIG. 2 is a schematic diagram showing the structure of a porous layer containing an inorganic filler when the orientation of the inorganic filler is large (left figure) and when the orientation of the inorganic filler is small (right figure). Fig. 2 shows the device and its operation in a scratch test; FIG. 4 is a diagram showing the critical load and the distance to the critical load in the graph created from the scratch test results.

An embodiment of the invention will be described below, but the invention is not limited thereto. The present invention is not limited to the configurations described below, and can be modified in various ways within the scope of the claims, by appropriately combining technical means disclosed in different embodiments. The resulting embodiment is also included in the technical scope of the present invention. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less".

A non-aqueous electrolyte secondary battery according to one embodiment of the present invention complies with a porous layer containing an inorganic filler and a resin, and the MIT tester method specified in JIS P 8115 (1994), a load of 1 N, In a folding endurance test performed at a folding angle of 45°, a positive electrode plate that was bent 130 times or more until the electrode active material layer peeled off, and a positive electrode plate that was bent the number of times until the electrode active material layer peeled off in the folding endurance test and a negative electrode plate of 1650 cycles or more, wherein the porous layer has a value represented by the following formula (1) in the range of 0.10 to 0.42.
|1-T/M| (1)
(In formula (1), T represents the distance to the critical load in the scratch test under a constant load of 0.1 N in TD (Transverse Direction), and M is 0.1 N in MD (Machine Direction). It represents the distance to the critical load in the scratch test under constant load.)
<Positive plate>
The positive electrode plate in the non-aqueous electrolyte secondary battery according to one embodiment of the present invention is not particularly limited as long as the number of times of bending measured in a folding endurance test as described later is within a specific range. For example, as the positive electrode active material layer, a sheet-like positive electrode plate in which a positive electrode mixture containing a positive electrode active material, a conductive agent, and a binder is supported on a positive electrode current collector is used. The positive electrode plate may carry the positive electrode mixture on both sides of the positive electrode current collector, or may carry the positive electrode mixture on one side of the positive electrode current collector.

Examples of the positive electrode active material include materials capable of doping and dedoping lithium ions. A transition metal oxide is preferable as the material. Specific examples of transition metal oxides include lithium composite oxides containing at least one type of transition metal such as V, Mn, Fe, Co and Ni.

Examples of the conductive agent include carbonaceous materials such as graphite (natural graphite, artificial graphite), cokes, carbon black, pyrolytic carbons, carbon fibers, and baked organic polymer compounds. Only one type of the conductive agent may be used, or two or more types may be used in combination.

Examples of the binder include polyvinylidene fluoride, vinylidene fluoride copolymers, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymers, and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers. , ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, thermoplastic polyimide, polyethylene, and thermoplastic such as polypropylene Resins, acrylics, and styrene-butadiene rubbers can be mentioned. In addition, the binder also has a function as a thickener.

Examples of the positive electrode current collector include conductors such as Al, Ni, and stainless steel. Among them, Al is more preferable because it is easy to process into a thin film and is inexpensive.

<Negative plate>
The negative electrode plate in the non-aqueous electrolyte secondary battery according to one embodiment of the present invention is not particularly limited as long as the number of times of bending measured in a folding endurance test as described later is within a specific range. For example, a sheet-like negative electrode in which a negative electrode mixture containing a negative electrode active material is supported on a negative electrode current collector is used as the negative electrode active material layer. The sheet-like negative electrode plate preferably contains the conductive agent and the binder. The negative electrode plate may carry the negative electrode mixture on both sides of the negative electrode current collector, or may carry the negative electrode mixture on one side of the negative electrode current collector.

Examples of the negative electrode active material include materials capable of doping/dedoping lithium ions, lithium metal, lithium alloys, and the like. Examples of such materials include carbonaceous materials. Examples of carbonaceous materials include graphite (natural graphite, artificial graphite), cokes, carbon black, and pyrolytic carbons. As the conductive agent and the binder, those described as the conductive agent and the binder that can be contained in the positive electrode active material layer can be used.

Examples of the negative electrode current collector include Cu, Ni, stainless steel, and the like. Cu is more preferable especially in a lithium ion secondary battery because it is difficult to form an alloy with lithium and is easy to process into a thin film.

<Number of times of bending>
In one embodiment of the present invention, the positive electrode plate and the negative electrode plate were tested for the number of times of bending until the active material layer peeled off in a folding endurance test conducted in accordance with the MIT tester method specified in JIS P 8115 (1994). is in the range of The folding endurance test is performed with a load of 1N and a bending angle of 45°. In a non-aqueous electrolyte secondary battery, expansion and contraction of the active material may occur during the process of charge-discharge cycles. The greater the number of times the electrode active material layer is bent until the electrode active material layer is peeled off, as measured by the folding endurance test, the more the adhesiveness between the components (active material, conductive agent, and binder) contained in the electrode active material layer and the electrode activity. It indicates that the adhesion between the material layer and the current collector is easily maintained. Therefore, deterioration of the non-aqueous electrolyte secondary battery during the process of charge-discharge cycles is suppressed.

In the folding endurance test, the positive electrode plate is bent 130 times or more, preferably 150 times or more, until the electrode active material layer is peeled off. In the folding endurance test, the number of times of bending the negative electrode plate until the electrode active material layer peels off is 1650 times or more, preferably 1800 times or more, and more preferably 2000 times or more.

FIG. 1 is a schematic diagram showing an outline of an MIT testing machine used in the MIT testing machine method. The x-axis represents the horizontal direction and the y-axis represents the vertical direction. An overview of the MIT tester method is provided below. One longitudinal end of the specimen is clamped with a spring-loaded clamp and the other end is clamped with a folding clamp. A spring-loaded clamp is connected to the weight. In the folding endurance test, the load applied by this weight is 1N. As a result, the test piece is placed under tension in the longitudinal direction. In this state, the longitudinal direction of the test piece is parallel to the vertical direction. The specimen is then bent by rotating the bending clamp. In the folding endurance test, the folding angle at this time was 45°. That is, the test piece is bent left and right at 45°. Also, the speed at which the test piece is bent is 175 reciprocations/minute.

<Method for producing positive electrode plate and negative electrode plate>
Examples of the method for producing a sheet-like positive electrode plate include a method of pressure-molding a positive electrode active material, a conductive agent and a binder on a positive electrode current collector; Examples include a method in which a binder is made into a paste, then the paste is applied to a positive electrode current collector, and then pressed in a wet state or after drying to adhere to the positive electrode current collector.

Similarly, as a method for producing a sheet-like negative electrode plate, for example, a method of pressure-molding a negative electrode active material on a negative electrode current collector; Examples include a method in which the paste is applied to the negative electrode current collector and then pressed in a wet state or after drying to adhere to the negative electrode current collector. The paste preferably contains the conductive agent and the binder.

Here, the number of times of bending can be controlled by adjusting the time, pressure, or method of applying pressure. The time for pressurization is preferably 1 to 3600 seconds, more preferably 1 to 300 seconds. Pressurization may be performed by constraining the positive plate or the negative plate. Constraint pressure is also referred to herein as confinement pressure. The confining pressure is preferably 0.01-10 MPa, more preferably 0.01-5 MPa. Alternatively, pressure may be applied in a state in which the positive electrode plate or the negative electrode plate is moistened with an organic solvent. This can improve the adhesion between the components contained in the electrode active material layer and the adhesion between the electrode active material layer and the current collector. Examples of organic solvents include carbonates, ethers, esters, nitriles, amides, carbamates, sulfur-containing compounds, and fluorine-containing organic solvents obtained by introducing a fluorine group into these organic solvents. .

<Porous layer>
In one embodiment of the present invention, the porous layer can be arranged between the polyolefin porous film and at least one of the positive electrode plate and the negative electrode plate as a member constituting the non-aqueous electrolyte secondary battery. The porous layer may be formed on one side or both sides of the polyolefin porous film. Alternatively, the porous layer may be formed on the active material layer of at least one of the positive electrode plate and the negative electrode plate. Alternatively, the porous layer may be arranged between and in contact with the polyolefin porous film and at least one of the positive electrode plate and the negative electrode plate. The porous layer disposed between the polyolefin porous film and at least one of the positive electrode plate and the negative electrode plate may be one layer or two layers or more. The porous layer is preferably an insulating porous layer containing a resin.

When the porous layer is laminated on one side of the polyolefin porous film, the porous layer is preferably laminated on the surface of the polyolefin porous film facing the positive electrode plate. More preferably, the porous layer is laminated on the surface in contact with the positive electrode plate.

A porous layer in one embodiment of the present invention contains an inorganic filler and a resin. The porous layer has a large number of pores inside and has a structure in which these pores are connected, and is a layer that allows gas or liquid to pass from one surface to the other surface. Further, when the porous layer in one embodiment of the present invention is used as a member constituting a laminated separator for a non-aqueous electrolyte secondary battery described later, the porous layer is the outermost layer of the laminated separator, an electrode can be a layer in contact with

The resin contained in the porous layer in one embodiment of the present invention is preferably insoluble in the electrolyte of the battery and electrochemically stable within the range of use of the battery. Specific examples of the resin include polyolefins; (meth)acrylate resins; fluorine-containing resins; polyamide resins; polyimide resins; polyester resins; rubbers; resin; water-soluble polymer; polycarbonate, polyacetal, polyetheretherketone, and the like.

Among the above resins, polyolefins, (meth)acrylate resins, fluorine-containing resins, polyamide resins, polyester resins and water-soluble polymers are preferred.

Preferred polyolefins include polyethylene, polypropylene, polybutene, and ethylene-propylene copolymers.

Examples of fluorine-containing resins include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. coalescence, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trichlorethylene copolymer, vinylidene fluoride-vinyl fluoride copolymer, vinylidene fluoride-hexafluoro Propylene-tetrafluoroethylene copolymers, ethylene-tetrafluoroethylene copolymers, etc., and among the fluorine-containing resins, fluorine-containing rubbers having a glass transition temperature of 23° C. or lower can be mentioned.

As polyamide-based resins, aramid resins such as aromatic polyamides and wholly aromatic polyamides are preferred.

Specific examples of aramid resins include poly(paraphenylene terephthalamide), poly(metaphenylene isophthalamide), poly(parabenzamide), poly(methabenzamide), poly(4,4'-benzanilide terephthalate amide), poly(paraphenylene-4,4′-biphenylenedicarboxylic acid amide), poly(metaphenylene-4,4′-biphenylenedicarboxylic acid amide), poly(paraphenylene-2,6-naphthalenedicarboxylic acid amide), Poly(metaphenylene-2,6-naphthalenedicarboxylic acid amide), poly(2-chloroparaphenylene terephthalamide), paraphenylene terephthalamide/2,6-dichloroparaphenylene terephthalamide copolymer, metaphenylene terephthalamide/2 , 6-dichloroparaphenylene terephthalamide copolymer. Among these, poly(paraphenylene terephthalamide) is more preferable.

Aromatic polyesters such as polyarylates and liquid crystalline polyesters are preferable as the polyester-based resin.

Rubbers include styrene-butadiene copolymer and its hydride, methacrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl acetate, etc. can be mentioned.

Examples of resins having a melting point or glass transition temperature of 180° C. or higher include polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, and polyetheramide.

Examples of water-soluble polymers include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, and polymethacrylic acid.

The resin contained in the porous layer in one embodiment of the present invention may be of one type or a mixture of two or more types of resin.

Among the above resins, when the porous layer is arranged facing the positive electrode plate, various performances such as rate characteristics and resistance characteristics of the non-aqueous electrolyte secondary battery are maintained due to oxidation deterioration during battery operation. Fluorine-containing resins are preferred because they are easy to use.

The porous layer in one embodiment of the invention contains an inorganic filler. The lower limit of the content is preferably 50% by weight or more, and 70% by weight or more, based on the total weight of the filler and the resin constituting the porous layer in one embodiment of the present invention. is more preferable, and 90% by weight or more is even more preferable. On the other hand, the upper limit of the inorganic filler content in the porous layer in one embodiment of the present invention is preferably 99% by weight or less, more preferably 98% by weight or less. The content of the filler is preferably 50% by weight or more from the viewpoint of heat resistance, and the content of the filler is preferably 99% by weight or less from the viewpoint of adhesion between fillers. Containing the inorganic filler can improve the lubricity and heat resistance of the separator including the porous layer. The inorganic filler is not particularly limited as long as it is stable in a non-aqueous electrolyte and electrochemically stable. From the viewpoint of ensuring battery safety, a filler having a heat resistance temperature of 150° C. or higher is preferable.

Although the inorganic filler is not particularly limited, it is usually an insulating filler. The inorganic filler is preferably an inorganic substance containing at least one element selected from the group consisting of an aluminum element, a zinc element, a calcium element, a zirconium element, a silicon element, a magnesium element, a barium element, and a boron element. is an inorganic substance containing aluminum element. Also, the inorganic filler preferably contains an oxide of the metal element.

Specifically, inorganic fillers include titanium oxide, alumina (Al ₂ O ₃ ), zinc oxide (ZnO), calcium oxide (CaO), zirconia oxide (ZrO ₂ ), silica, magnesia, barium oxide, boron oxide, Examples include mica, wollastonite, attapulgite, and boehmite (alumina monohydrate). As the inorganic filler, one type of filler may be used alone, or two or more types of filler may be used in combination.

The inorganic filler in the porous layer in one embodiment of the present invention preferably contains alumina and plate-like filler. Examples of the plate-like filler include one or more fillers selected from the group consisting of zinc oxide (ZnO), mica, and boehmite among the oxides of the metal elements listed above.

The volume average particle size of the inorganic filler is preferably in the range of 0.01 μm to 10 μm from the viewpoint of ensuring good adhesiveness and lubricity and moldability of the laminate. The lower limit thereof is more preferably 0.05 μm or more, more preferably 0.1 μm or more. The upper limit thereof is more preferably 5 μm or less, more preferably 1 μm or less.

The shape of the inorganic filler is arbitrary and not particularly limited. The shape of the inorganic filler can be particulate, for example, spherical, elliptical, plate-like, rod-like, amorphous, fibrous, spherical or columnar single particles such as peanut-like and/or tetrapod-like. is heat-sealed; From the viewpoint of battery short circuit prevention, the inorganic filler is preferably plate-like particles and/or non-agglomerated primary particles, and from the viewpoint of ion permeation, the particles in the porous irregular shapes such as dendritic, coral-like, or tuft-like, having knobs, dents, constrictions, protuberances, or tufts; fibrous; peanut-like and/or tetra A pot-like shape in which single particles are thermally fused is preferred, and a shape in which spherical or columnar single particles are thermally fused, such as a peanut shape and/or a tetrapod shape, is particularly preferred.

The filler can improve slipperiness by forming fine irregularities on the surface of the porous layer. As a result, the irregularities formed on the surface of the porous layer become finer, and the adhesiveness between the porous layer and the electrode becomes better.

The oxygen atomic mass percentage of the metal oxide constituting the inorganic filler contained in the porous layer in one embodiment of the present invention is preferably 10% to 50%, more preferably 20% to 50%. preferable. In the present invention, the "oxygen atom mass percentage" means the ratio of the mass of oxygen atoms in the metal oxide to the total mass of the metal oxide, expressed as a percentage. For example, in the case of zinc oxide, since the atomic weight of zinc is 65.4 and the atomic weight of oxygen is 16.0, the molecular weight of zinc oxide (ZnO) is 65.4 + 16.0 = 81.4. The atomic mass percentage is 16.0/81.4×100=20(%).

The fact that the oxygen atomic mass percentage of the metal oxide is within the above-mentioned range ensures that the affinity between the inorganic filler and the solvent or dispersion medium in the coating liquid used in the method for producing the porous layer described later is suitable. By maintaining an appropriate distance between the inorganic fillers, the dispersibility of the coating liquid can be improved, and as a result, the above formula (1) can be controlled within an appropriate specified range. preferable in terms of

The porous layer in one embodiment of the present invention may contain components other than the inorganic filler and resin described above. Examples of the other components include surfactants, waxes, and binder resins. Also, the content of the other components is preferably 0% by weight to 50% by weight with respect to the weight of the entire porous layer.

In one embodiment of the present invention, the average film thickness of the porous layer is preferably in the range of 0.5 μm to 10 μm per one porous layer from the viewpoint of ensuring adhesion to the electrode and high energy density. More preferably, it is in the range of 1 μm to 5 μm.

The basis weight per unit area of the porous layer can be appropriately determined in consideration of the strength, film thickness, weight and handleability of the porous layer. The basis weight per unit area of the porous layer is preferably 0.5 to 20 g/m ² and more preferably 0.5 to 10 g/m ² per one porous layer.

By setting the basis weight per unit area of the porous layer within these numerical ranges, the weight energy density and volume energy density of the non-aqueous electrolyte secondary battery can be increased. If the basis weight of the porous layer exceeds the above range, the non-aqueous electrolyte secondary battery tends to be heavy.

The porosity of the porous layer is preferably 20 to 90% by volume, more preferably 30 to 80% by volume, so as to obtain sufficient ion permeability. Moreover, the pore size of the pores of the porous layer is preferably 1.0 μm or less, more preferably 0.5 μm or less. By setting the pore diameters of the pores to these sizes, the non-aqueous electrolyte secondary battery can obtain sufficient ion permeability.

<T/M ratio of porous layer surface>
The porous layer in one embodiment of the present invention preferably has a value represented by the following formula (1) in the range of 0.10 to 0.42, and in the range of 0.10 to 0.30 It is more preferable to have

|1-T/M| (1)
(In formula (1), T represents the distance to the critical load in the scratch test under a constant load of 0.1 N in TD, and M represents the distance to the critical load in the scratch test under a constant load of 0.1 N in MD. , represents the distance to the critical load.)
The ratio of the distance (T) to the critical load in TD and the distance (M) to the critical load in MD (hereinafter also simply referred to as “formula (1)”) measured by the scratch test described above is It is an index representing the orientation of the inorganic filler in the solid layer. FIG. 2 shows schematic diagrams of the inorganic filler in the porous layer when the orientation is high (anisotropic) and when the orientation is low (isotropic). The left diagram of FIG. 2 is a schematic diagram showing the structure of the porous layer containing the inorganic filler when the orientation of the inorganic filler is large and exhibits anisotropy, and the right diagram of FIG. FIG. 3 is a schematic diagram showing the structure of the porous layer when the orientation of the inorganic filler is small and exhibits isotropy.

The value represented by the above formula (1) is a value indicating the anisotropy of the distance to the critical load in the scratch test, and the closer the value is to zero, the more isotropic the distance to the critical load. indicates that there is

The "scratch test" in the present invention is, as shown in FIG. This is a test for measuring the generated stress at a certain indenter movement distance when the porous membrane is moved in the horizontal direction, and is specifically carried out by the following method:
(1) After cutting the laminated porous film laminated with the porous layer to be measured to 20 mm × 60 mm, the cut laminated porous film was pasted on a 30 mm × 70 mm glass slide with aqueous glue. A test sample is prepared by drying overnight at a temperature of 25°C. During the lamination, air bubbles should be prevented from entering between the laminated porous film and the glass preparation.
(2) The test sample prepared in step (1) is placed in a microscratch test device, and a diamond indenter in the test device is placed on the test sample to apply a vertical load of 0.1N. While being applied, the table in the test device is moved toward the TD of the laminated porous film at a speed of 5 mm / min for a distance of 10 mm, and the diamond indenter and the test are moved in the meantime. Measure the stress (frictional force) generated between the sample and the sample.
(3) Create a curve graph showing the relationship between the stress displacement measured in step (2) and the movement distance of the table, and from the curve graph, as shown in FIG. 4, the critical load at TD Calculate the value and the distance to the critical load.
(4) Change the moving direction of the table to MD, repeat the above steps (1) to (3), and calculate the critical load value and the distance to reach the critical load in MD.

In the above scratch test, measurement conditions other than those described above are the same as those of the method described in JIS R 3255.

The distance to the critical load value calculated in the scratch test is (a) an index of plastic deformation easiness of the surface layer of the laminated porous film, and (b) an index of shear stress transferability to the surface opposite to the measurement surface. becomes. The long distance to the critical load value means that (a') the surface layer is difficult to plastically deform and (b') the shear stress is transmitted to the surface opposite to the measurement surface in the laminated porous film to be measured. is low (stress is difficult to transmit).

Note that the distances to the critical load in the TD and MD directions are considered to be strongly influenced by the following structural factors of the laminated porous film.
(i) Oriented state of resin to MD in laminated porous film (ii) Oriented state of resin to TD in laminated porous film (iii) Resin oriented in MD direction and TD direction in thickness direction of laminated porous film contact state When the above formula (1) is larger than 0.42, the anisotropy of the internal structure of the porous layer becomes excessively high, the length of the ion permeation channel inside the porous layer becomes long, and the As a result, in the non-aqueous electrolyte secondary battery incorporating the porous layer, the ion permeation resistance of the porous layer increases, and the resistance of the separator in the non-aqueous electrolyte secondary battery increases. On the other hand, when the above formula (1) is less than 0.10, the structure of the porous layer is considered to have excessively high isotropy. When the structure of the porous layer has excessively high isotropy, in a non-aqueous electrolyte secondary battery incorporating the porous layer, the ability of the porous layer to accept the electrolyte during battery operation tends to be excessively high. There is As a result, the electrolyte supply capability of the separator base material and the electrodes, which are in contact with the porous layer and supply the electrolyte to the porous layer, determines the rate of electrolyte flow in the entire non-aqueous electrolyte secondary battery. As a result, the resistance of the separator in the non-aqueous electrolyte secondary battery increases.

<Center particle size (D50)>
In one embodiment of the present invention, the porous layer preferably has a median particle size (D50) of the inorganic filler in the range of 0.1 μm to 11 μm, more preferably in the range of 0.1 μm to 10 μm. It is more preferably in the range of 0.1 μm to 5 μm, particularly preferably 0.5 μm.

Although the method for measuring the median particle size of the inorganic filler is not particularly limited, it is measured, for example, by the method described in Examples.

When the median particle size of the inorganic filler is larger than 11 μm, the film thickness of the heat-resistant layer is increased and unevenness occurs, and the ion permeation of the porous layer also becomes uneven. There is a tendency for the resistance of the separator in the incorporated non-aqueous electrolyte secondary battery to increase. On the other hand, when the median particle diameter of the inorganic filler is less than 0.1 μm, the viscosity of the paint becomes high, the dilatancy is exhibited, the coating performance becomes poor, and uneven coating on the porous layer may occur. be. In addition, since the central particle size of the inorganic filler is small, the amount of binder required for binding the inorganic filler increases. As a result, in the non-aqueous electrolyte secondary battery incorporating the porous layer, the ion permeation resistance of the porous layer increases, and the resistance of the separator in the non-aqueous electrolyte secondary battery increases.

<BET specific surface area>
The porous layer in one embodiment of the present invention preferably has a BET specific surface area per unit area of the inorganic filler of 100 m ² /g or less, more preferably 50 m ² /g or less, and more preferably 10 m ² /g. It may be below.

Although the method for measuring the BET specific surface area per unit area of the inorganic filler is not particularly limited, for example, a method comprising the following steps (1) to (3) can be mentioned.
(1) A step of pre-treating the filler by vacuum drying at 80° C. for 8 hours.
(2) A step of measuring an adsorption-desorption isotherm with nitrogen by a constant volume method.
(3) A step of calculating the specific surface area of the filler by the BET method.

In the measurement of the specific surface area of the filler, the pretreatment device and the measurement device are not particularly limited. BELSORP-mini (manufactured by Microtrack Bell Co., Ltd.) can be used.

Moreover, the measurement conditions for measuring the specific surface area of the filler are not particularly limited, and can be appropriately set by those skilled in the art.

When the BET specific surface area per unit area of the inorganic filler is greater than 100 m ² /g, the increase in the BET specific surface area increases the filler oil supply, and accordingly, the paint properties of the porous layer deteriorate, resulting in poor coatability. As a result, the resistance of the separator in the non-aqueous electrolyte secondary battery incorporating the porous layer tends to increase.

<Method for producing porous layer>
The method for producing the porous layer in one embodiment of the present invention is not particularly limited. A method of forming a porous layer containing the inorganic filler and the resin can be mentioned. In the case of steps (2) and (3) shown below, the resin can be produced by further drying after precipitating the resin to remove the solvent. The coating liquid in steps (1) to (3) may be in a state in which the inorganic filler is dispersed and the resin is dissolved. The solvent can be said to be a solvent for dissolving the resin and also a dispersion medium for dispersing the resin or the inorganic filler.
(1) A step of forming a porous layer by applying a coating liquid containing the inorganic filler and the resin onto a substrate and removing the solvent in the coating liquid by drying.
(2) After coating the surface of the base material with a coating liquid containing the inorganic filler and the resin, the base material is immersed in a deposition solvent that is a poor solvent for the resin. A step of depositing a resin to form a porous layer.
(3) After coating the coating liquid containing the inorganic filler and the resin on the surface of the substrate, using a low boiling point organic acid to acidify the coating liquid, thereby A step of depositing a resin to form a porous layer.

As the substrate, in addition to the polyolefin porous film described later, other films, a positive electrode plate, a negative electrode plate, and the like can be used.

The solvent is preferably a solvent that does not adversely affect the substrate, uniformly and stably dissolves the resin, and uniformly and stably disperses the inorganic filler. Examples of the solvent include N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, acetone and water.

As the precipitation solvent, for example, isopropyl alcohol or t-butyl alcohol is preferably used.

In the step (3), for example, p-toluenesulfonic acid, acetic acid, etc. can be used as the low-boiling organic acid.

The coating amount (that is, basis weight) of the porous layer is usually 0.5 to 20 g/solids per one layer of the porous layer, from the viewpoint of adhesion to the electrode or electrode sheet and ion permeability. It is preferably m ² , more preferably 0.5 to 10 g/m ² , even more preferably in the range of 0.5 g/m ² to 1.5 g/m ² . That is, it is preferable to adjust the amount of the coating liquid to be applied onto the substrate so that the coating amount (basis weight) of the obtained porous layer is within the above range.

As a method for controlling the orientation of the porous layer in one embodiment of the present invention, that is, the above formula (1), a coating containing an inorganic filler and a resin used for manufacturing the porous layer is used as shown below. Examples include adjusting the solid content concentration of the working liquid and the coating shear rate when the coating liquid is applied onto the base material.

A suitable solid content concentration of the coating liquid may vary depending on the type of filler and the like, but generally it is preferably more than 20% by weight and 40% by weight or less. It is preferable that the solid content concentration is within the above range in that the viscosity of the coating liquid can be appropriately maintained and, as a result, the above formula (1) can be controlled within an appropriately specified range.

The coating shear rate at which the coating liquid is applied onto the substrate may vary depending on the type of filler, but is generally preferably 2 (1/s) or more, and 4 (1/s). s) to 50 (1/s) is more preferable.

Here, for example, the inorganic filler may have a peanut-shaped and/or tetrapod-shaped spherical or columnar single particle thermally fused together, a spherical shape, an elliptical shape, a plate shape, a rod shape, or an irregular shape. When the inorganic filler having the shape of is used, increasing the coating shear rate tends to increase the anisotropy because a high shearing force is applied to the inorganic filler. On the other hand, when the coating shear rate is reduced, the inorganic filler tends to be oriented isotropically because the shear force is not applied to the inorganic filler.

On the other hand, when the inorganic filler is a long fiber diameter inorganic filler such as wollastonite having a long fiber diameter, if the coating shear rate is increased, the long fibers will entangle with each other or the blade of the doctor blade will become long. Since the fibers are caught, the orientation tends to be random and the anisotropy tends to be low. On the other hand, when the coating shear rate is decreased, the long fibers are not caught by each other and by the edge of the doctor blade, so that they are easily oriented and the anisotropy tends to be high.

<Separator for non-aqueous electrolyte secondary battery>
A separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes a polyolefin porous film. In this specification, the polyolefin porous film may be referred to as "porous film". The porous film alone can serve as a separator for a non-aqueous electrolyte secondary battery. It can also be used as a base material of a laminated separator for a non-aqueous electrolyte secondary battery on which a porous layer is laminated, which will be described later. The porous film has a polyolefin resin as a main component and has a large number of interconnected pores therein, allowing gas and liquid to pass from one surface to the other surface.

A porous layer may be laminated on at least one surface of the separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. In this case, a laminate obtained by laminating the porous layer on at least one surface of the separator for a non-aqueous electrolyte secondary battery is referred to herein as a "laminated separator for a non-aqueous electrolyte secondary battery or "laminated separator". Moreover, the separator for non-aqueous electrolyte secondary batteries according to one embodiment of the present invention may further include other layers such as an adhesive layer, a heat-resistant layer, and a protective layer in addition to the polyolefin porous film.

<Polyolefin porous film>
A non-aqueous electrolyte secondary battery in one embodiment of the present invention may include a polyolefin porous film. Hereinafter, the polyolefin porous film may be simply referred to as "porous film". The porous film has a polyolefin resin as a main component and has a large number of interconnected pores therein, allowing gas and liquid to pass from one surface to the other surface. The porous film alone can serve as a separator for a non-aqueous electrolyte secondary battery. It can also be used as a base material of a laminated separator for a non-aqueous electrolyte secondary battery in which the above porous layer is laminated.

A laminate obtained by laminating the porous layer on at least one surface of the polyolefin porous film is also referred to herein as a "laminated separator for a non-aqueous electrolyte secondary battery" or a "laminated separator". . Moreover, the separator for non-aqueous electrolyte secondary batteries in one embodiment of the present invention may further include other layers such as an adhesive layer, a heat-resistant layer, and a protective layer in addition to the polyolefin porous film.

The proportion of polyolefin in the porous film is 50% by volume or more, more preferably 90% by volume or more, and even more preferably 95% by volume or more, of the entire porous film. Further, the polyolefin more preferably contains a high molecular weight component having a weight average molecular weight of 5×10 ⁵ to 15×10 ⁶ . In particular, when the polyolefin contains a high molecular weight component having a weight average molecular weight of 1,000,000 or more, the strength of the separator for non-aqueous electrolyte secondary batteries is improved, which is more preferable.

Specific examples of the polyolefin, which is a thermoplastic resin, include homopolymers obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene and 1-hexene. Or a copolymer is mentioned. Examples of the homopolymer include polyethylene, polypropylene, and polybutene. Further, examples of the copolymer include an ethylene-propylene copolymer.

Among these, polyethylene is more preferable because it can prevent the flow of excessive current at a lower temperature. It should be noted that blocking the flow of this excessive current is also called shutdown. Examples of the polyethylene include low-density polyethylene, high-density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), and ultra-high molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more. Among them, ultra-high molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more is more preferable.

The thickness of the porous film is preferably 4 to 40 μm, more preferably 5 to 30 μm, even more preferably 6 to 15 μm.

The basis weight per unit area of the porous film can be appropriately determined in consideration of strength, film thickness, weight and handleability. However, the basis weight is preferably 4 to 20 g/m ² and more preferably 4 to 12 g/m ² so that the weight energy density and volume energy density of the non-aqueous electrolyte secondary battery can be increased. more preferably 5 to 10 g/m ² .

The air permeability of the porous film is preferably 30 to 500 sec/100 mL, more preferably 50 to 300 sec/100 mL in Gurley value. Sufficient ion permeability can be obtained by the porous film having the air permeability. The air permeability of the laminated separator for a non-aqueous electrolyte secondary battery in which the above porous layer is laminated on a porous film is preferably 30 to 1000 sec/100 mL, more preferably 50 to 800 sec/100 mL in Gurley value. is more preferable. The laminated separator for a non-aqueous electrolyte secondary battery can obtain sufficient ion permeability in a non-aqueous electrolyte secondary battery by having the above air permeability.

The porosity of the porous film is preferably 20 to 80% by volume so as to increase the retention amount of the electrolytic solution and to obtain the function of reliably preventing the flow of excessive current at a lower temperature. It is more preferably 30 to 75% by volume. In addition, the pore diameter of the pores of the porous film is 0.3 μm or less so that sufficient ion permeability can be obtained and particles can be prevented from entering the positive electrode plate and the negative electrode plate. It is preferably 0.14 μm or less, more preferably 0.14 μm or less.

<Method for producing polyolefin porous film>
The method for producing the polyolefin porous film is not particularly limited. For example, a sheet-like polyolefin resin composition is produced by kneading a polyolefin resin, a pore-forming agent such as an inorganic filler and a plasticizer, and optionally an antioxidant or the like and then extruding the mixture. After removing the pore-forming agent from the sheet-shaped polyolefin resin composition with an appropriate solvent, the polyolefin porous film can be produced by stretching the polyolefin resin composition from which the pore-forming agent has been removed. can.

The inorganic filler is not particularly limited, and includes inorganic fillers, specifically calcium carbonate and the like. The plasticizer is not particularly limited, and examples thereof include low-molecular-weight hydrocarbons such as liquid paraffin.

Specifically, a method including the steps shown below can be mentioned.
(A) a step of kneading an ultra-high molecular weight polyethylene, a low molecular weight polyethylene having a weight average molecular weight of 10,000 or less, a pore forming agent such as calcium carbonate or a plasticizer, and an antioxidant to obtain a polyolefin resin composition;
(B) A step of rolling the obtained polyolefin resin composition with a pair of rolling rollers, cooling it step by step while pulling it with winding rollers with different speed ratios, and forming a sheet;
(C) removing the pore-forming agent from the obtained sheet with a suitable solvent;
(D) A step of stretching the sheet from which the pore-forming agent has been removed at an appropriate stretching ratio.

<Method for manufacturing laminated separator for non-aqueous electrolyte secondary battery>
As a method for producing a laminated separator for a non-aqueous electrolyte secondary battery in one embodiment of the present invention, for example, in the above-mentioned "method for producing a porous layer", the above-mentioned base material for applying the coating liquid is used. A method using a polyolefin porous film can be mentioned.

<Non-aqueous electrolyte>
The non-aqueous electrolyte that can be contained in the non-aqueous electrolyte secondary battery according to one embodiment of the present invention is not particularly limited as long as it is a non-aqueous electrolyte generally used in non-aqueous electrolyte secondary batteries. As the non-aqueous electrolyte, for example, a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent can be used. Examples of lithium salts include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , lower aliphatic carboxylic acid lithium salts and _LiAlCl4 . Only one type of the lithium salt may be used, or two or more types may be used in combination.

Organic solvents constituting the non-aqueous electrolyte include, for example, carbonates, ethers, esters, nitriles, amides, carbamates, sulfur-containing compounds, and fluorine groups introduced into these organic solvents. Fluorinated organic solvents and the like are included. Only one type of the organic solvent may be used, or two or more types may be used in combination.

<Method for manufacturing non-aqueous electrolyte secondary battery>
As a method for manufacturing a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, for example, the positive electrode plate, the porous layer, the separator for the non-aqueous electrolyte secondary battery, and the negative electrode plate are arranged in this order. After forming the non-aqueous electrolyte secondary battery member by using A method of sealing while reducing the pressure after filling with the electrolytic solution can be mentioned.

As described above, the non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes a non-aqueous electrolyte secondary battery separator including a polyolefin porous film, a porous layer, a positive electrode plate, and a negative electrode plate. and have. In particular, the nonaqueous electrolyte secondary battery according to one embodiment of the present invention satisfies the following requirements (i) to (iii).
(i) The porous layer has a value represented by the following formula (1) in the range of 0.10 to 0.42.
|1-T/M| (1)
(In formula (1), T represents the distance to the critical load in the scratch test under a constant load of 0.1 N in TD, and M represents the distance to the critical load in the scratch test under a constant load of 0.1 N in MD. , represents the distance to the critical load.)
(ii) The positive electrode plate is bent 130 times or more until the electrode active material layer is peeled off.
(iii) The negative electrode plate is bent 1650 times or more until the electrode active material layer is peeled off.

According to the requirement (i), in the non-aqueous electrolyte secondary battery according to one embodiment of the present invention, the porous layer has a uniform and dense structure, so that lithium ions are uniformly distributed in the porous layer. retained. Then, the requirements of (ii) and (iii) make it easier for the entire electrode to follow the expansion and contraction of the active material isotropically. Therefore, the adhesion between the components contained inside the electrode active material layer and the adhesion between the electrode active material layer and the current collector are easily maintained.

Therefore, in the non-aqueous electrolyte secondary battery that satisfies the above requirements (i) to (iii), (a) the lithium ion distribution is uniform in the porous layer, so the lithium ion permeability is good. and (b) deterioration of the non-aqueous electrolyte secondary battery in the process of charge-discharge cycles is suppressed because the above-described adhesion is easily maintained. Therefore, it is considered that the discharge capacity recovery characteristics of the battery are improved even after charge-discharge cycles (for example, after 100 cycles).

The present invention is not limited to the above-described embodiments, but can be modified in various ways within the scope of the claims, and can be obtained by appropriately combining technical means disclosed in different embodiments. is also included in the technical scope of the present invention.

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Measuring method]
Each measurement in Examples and Comparative Examples was performed by the following methods.

(1. Folding endurance test)
A test piece having a length of 105 mm and a width of 15 mm was cut out from the positive electrode plate or the negative electrode plate obtained in the following examples and comparative examples. Using this test piece, a folding endurance test was carried out according to the MIT tester method.

The folding endurance test uses an MIT type folding endurance tester (manufactured by Yasuda Seiki), according to the MIT tester method specified in JIS P 8115 (1994), load: 1 N, bending part R: 0.38 mm, bending speed It was carried out by fixing one end of the test piece and bending it to the left and right at an angle of 45 degrees at 175 reciprocations/minute.

Thereby, the number of times of bending until the electrode active material layer was peeled off from the positive electrode plate or the negative electrode plate was measured. The number of times of folding here means the number of times of reciprocating folding displayed on the counter of the MIT type folding endurance tester.

(2. Scratch test)
The critical load value and the T/M ratio of the distance to the critical load were measured by the scratch test shown below. Measurement conditions other than those described below were the same as those of JIS R 3255. A microscratch tester (manufactured by CSEM Instruments) was used as a measuring device.
(1) After cutting the laminated porous film laminated with the porous layer produced in Examples and Comparative Examples to 20 mm × 60 mm, the cut laminated porous film is placed on a glass slide of 30 mm × 70 mm. , Arabic Yamato water-based liquid paste (manufactured by Yamato Co., Ltd.) diluted 5 times with water is applied to the entire surface in a small amount of about 1.5 g / ^m2 of basis weight, and it is laminated to the separator and dried overnight at 25 ° C. A test sample was prepared by It should be noted that during the lamination, air bubbles were prevented from entering between the laminated porous film and the glass preparation.
(2) The test sample prepared in step (1) was placed in a microscratch tester (manufactured by CSEM Instruments). A diamond indenter (vertical angle of 120°, tip radius of 0.2 mm) in the test device is applied to the test sample while a vertical load of 0.1 N is applied. The table in the apparatus is moved toward the TD of the laminated porous film at a speed of 5 mm/min for a distance of 10 mm, during which the stress generated between the diamond indenter and the test sample ( friction force) was measured.
(3) Create a curve graph showing the relationship between the stress displacement measured in step (2) and the movement distance of the table, and from the curve graph, reach the critical load value and critical load in TD Calculated the distance to
(4) Changing the moving direction of the table to MD, the above steps (1) to (3) were repeated to calculate the critical load value and the distance to reach the critical load in MD.

(3. Film thickness (unit: μm))
The thicknesses of the porous layer, the porous film, the positive electrode active material layer, and the negative electrode active material layer were measured using a high-precision digital length measuring machine (VL-50) manufactured by Mitutoyo Corporation. The thickness of the positive electrode active material layer is calculated by subtracting the thickness of the aluminum foil that is a current collector from the thickness of the positive electrode plate, and the thickness of the negative electrode active material layer is the thickness of the negative electrode plate. It was calculated by subtracting the thickness of the copper foil, which is a current collector, from The thickness of the porous layer was calculated by subtracting the thickness of the uncoated portion from the thickness of each coated portion.

(4. Particle size distribution)
The volume-based particle size distribution of the filler was calculated by measuring D10, D50, and D90 using a laser diffraction particle size distribution meter SALD2200 manufactured by Shimadzu Corporation. Here, the particle diameter at which the volume-based integrated distribution is 50%, 10%, and 90% are referred to as D50, D10, and D90, respectively. D50 is also referred to as median particle size.

(5. Specific surface area)
The specific surface area of the filler was measured using BELSORP-mini (manufactured by Microtrack Bell Co., Ltd.). The filler was subjected to vacuum drying at a pretreatment temperature of 80.degree. Various conditions in the constant volume method are as follows: Adsorption temperature; 77 K, ^Adsorbate ; nitrogen, Saturated vapor pressure; Waiting time after reaching a state where the pressure change at the time of attachment/detachment is equal to or less than a predetermined value); 500 sec. The pore volume was calculated by the MP method and the BJH method, and BELPREP-vacII (manufactured by Microtrack Bell Co., Ltd.) was used as the pretreatment device.

(Measurement of discharge recovery capacity after 6.100 cycles of charging and discharging)
<1. Initial charge/discharge>
CC of voltage range: 2.7 to 4.1 V, charging current value: 0.2 C for new non-aqueous electrolyte secondary batteries that have not undergone charge-discharge cycles, manufactured in Examples and Comparative Examples Four cycles of initial charging and discharging were carried out at 25° C., with −CV charging (final current condition of 0.02 C) and CC discharging at a discharge current value of 0.2 C being one cycle. Here, 1C is the current value for discharging the rated capacity based on the discharge capacity at the 1 hour rate in 1 hour. Further, CC-CV charging is a charging method in which charging is performed with a set constant current, and after reaching a predetermined voltage, the voltage is maintained while reducing the current. Furthermore, CC discharge is a method of discharging to a predetermined voltage with a set constant current. These terms have the same meaning in this specification.

<2. Cycle test>
The non-aqueous electrolyte secondary battery after the initial charge and discharge is charged with a voltage range of 2.7 to 4.2 V, a charge current value of 1C (final current condition of 0.02C), and a discharge current value of 10C. 100 cycles of charging and discharging were performed at 55° C. with CC discharging as one cycle.

<3. Discharge recovery capacity test after 100 cycles of charging and discharging>
Voltage range: 2.7 V to 4.2 V, charging current value: 1 C CC-CV charge (final current condition 0.02 C) and discharge for a non-aqueous electrolyte secondary battery that has been charged and discharged for 100 cycles Current value: 3 cycles of charge/discharge were performed at 55°C, with CC discharge at 0.2C as one cycle. The discharge capacity at the third cycle was defined as the discharge recovery capacity (shown as "discharge recovery capacity after 100 cycles" in Table 1 described later).

The above-mentioned discharge recovery capacity test is a test method for more accurately confirming the discharge capacity by discharging at a low rate (0.2 C) after 100 charge-discharge cycles. In particular, it is possible to check the degree of deterioration of the discharge performance of the electrode.

[Example 1]
[Preparation of porous layer and laminated porous film]
(Porous substrate (A layer))
A porous substrate was produced using polyethylene, which is a polyolefin.

That is, 70 parts by weight of ultra-high molecular weight polyethylene powder (340M, manufactured by Mitsui Chemicals, Inc.) and 30 parts by weight of polyethylene wax having a weight average molecular weight of 1000 (FNP-0115, manufactured by Nippon Seiro Co., Ltd.) are mixed to obtain a mixed polyethylene. got To 100 parts by weight of the resulting mixed polyethylene, 0.4 parts by weight of an antioxidant (Irg1010, manufactured by Chiba Specialty Chemicals Co., Ltd.) and 0.4 parts by weight of an antioxidant (P168, manufactured by Chiba Specialty Chemicals Co., Ltd.) were added. 1 part by weight and 1.3 parts by weight of sodium stearate are added, and further calcium carbonate with an average particle size of 0.1 μm (manufactured by Maruo Calcium Co., Ltd.) is added so that the ratio of the total volume is 38% by volume. rice field. This composition as powder was mixed with a Henschel mixer and then melt-kneaded with a twin-screw kneader to obtain a polyethylene resin composition. Next, a sheet was produced by rolling this polyethylene resin composition with a pair of rolls whose surface temperature was set to 150°C. This sheet was immersed in a hydrochloric acid aqueous solution (containing 4 mol/L of hydrochloric acid and 0.5% by weight of a nonionic surfactant) to dissolve and remove calcium carbonate. Subsequently, the sheet was stretched 6 times at 105° C. to produce a polyethylene porous substrate (A layer). The porous substrate had a porosity of 53%, a basis weight of 7 g/m ² and a thickness of 16 μm.

(Porous layer (B layer))
(Manufacture of coating liquid)
As the inorganic filler, hexagonal plate-shaped zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., trade name: XZ-100F) having an oxygen atomic mass percentage of 20% was used (inorganic filler 1). D50, D10 and D90 of inorganic filler 1 were 0.4 μm, 0.2 μm and 2.1 μm, respectively. Also, the BET specific surface area per unit area of the inorganic filler 1 was 7.3 m ² /g.

A vinylidene fluoride-hexafluoropropylene copolymer (manufactured by Arkema Co., Ltd.: trade name “KYNAR2801”) was used as the binder resin.

The inorganic filler, vinylidene fluoride-hexafluoropropylene copolymer and solvent (N-methyl-2-pyrrolidinone manufactured by Kanto Kagaku Co., Ltd.) were mixed in the following proportions. That is, 10 parts by weight of the vinylidene fluoride-hexafluoropropylene copolymer is mixed with 90 parts by weight of the inorganic filler, and the solid content (inorganic filler and vinylidene fluoride-hexafluoropropylene copolymer) in the resulting mixed liquid is The solvents were mixed so that the concentration was 37% by weight. The resulting mixed solution was stirred and mixed by a thin-film rotating high-speed mixer (Filmiku (registered trademark) manufactured by Primix Co., Ltd.) to obtain a uniform coating solution (Coating solution 1).
(Manufacturing of porous layer and laminated porous film)
The resulting coating solution was applied to one side of the A layer by a doctor blade method at a coating shear rate of 3.9 (1/s) to form a coating film on one side of the A layer. After that, the coating film was dried at 65° C. for 20 minutes to form a B layer on one side of the A layer. As a result, a laminate 1 (laminated separator) in which the B layer was laminated on one side of the A layer was obtained. The B layer had a basis weight of 7 g/m ² and a thickness of 4 μm.

[Preparation of non-aqueous electrolyte secondary battery]
(Positive plate)
A positive electrode in which a positive electrode mixture of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ /conductive agent/PVDF (weight ratio: 92/5/3) is laminated on one side of a positive current collector (aluminum foil) got a board Constraint pressure (0.7 MPa) was applied to this positive electrode plate at room temperature for 30 seconds.

The positive electrode plate is cut so that the size of the portion where the positive electrode active material layer is laminated is 45 mm × 30 mm, and a portion with a width of 13 mm where the positive electrode active material layer is not laminated remains on the outer periphery, A positive electrode plate 1 was obtained. The thickness of the positive electrode active material layer was 38 μm.

(negative plate)
A negative electrode mixture of natural graphite/styrene-1,3-butadiene copolymer/sodium carboxymethylcellulose (weight ratio 98/1/1) having an average particle size (D50) based on volume of 15 μm was used as a negative electrode current collector ( A negative electrode plate laminated on one side of the copper foil) was obtained. Confining pressure (0.7 MPa) was applied to this negative electrode plate at room temperature for 30 seconds.

The negative electrode plate is cut so that the size of the portion where the negative electrode active material layer is laminated is 50 mm × 35 mm, and a portion with a width of 13 mm where the negative electrode active material layer is not laminated remains on the outer periphery, A negative electrode plate 1 was obtained. The thickness of the negative electrode active material layer was 38 μm.

(Preparation of non-aqueous electrolyte secondary battery)
Using the positive electrode plate 1, the negative electrode plate 1, and the laminate 1, a non-aqueous electrolyte secondary battery was manufactured by the method described below.

By stacking (arranging) the positive electrode plate 1, the laminate 1 and the negative electrode plate 1 in this order in a laminate pouch, a non-aqueous electrolyte secondary battery member 1 was obtained. At this time, the positive electrode plate 1 and the negative electrode plate 1 are arranged such that the entire main surface of the positive electrode active material layer of the positive electrode plate 1 is included in the range of the main surface of the negative electrode active material layer of the negative electrode plate 1 (overlaps the main surface). was placed. In addition, the surface of the laminate 1 on the porous layer side was made to face the positive electrode active material layer of the positive electrode plate 1 .

Subsequently, the non-aqueous electrolyte secondary battery member 1 is placed in a prefabricated bag in which an aluminum layer and a heat seal layer are laminated, and 0.23 mL of the non-aqueous electrolyte is added to the bag. rice field. The non-aqueous electrolyte is dissolved in a mixed solvent of ethylene carbonate, ethylmethyl carbonate, and diethyl carbonate at a volume ratio of 3:5:2 so that the concentration of LiPF ₆ is 1 mol/L. was prepared by Then, the non-aqueous electrolyte secondary battery 1 was produced by heat-sealing the bag while decompressing the inside of the bag.

After that, the battery characteristics of the non-aqueous electrolyte secondary battery 1 obtained by the method described above were measured. Table 1 shows the results.

[Example 2]
[Preparation of porous layer and laminated porous film]
A mixture of spherical alumina (manufactured by Sumitomo Chemical Co., Ltd., trade name AA03) and synthetic mica (manufactured by Wako Pure Chemical Industries, Ltd., trade name: non-swelling synthetic mica) was used as the inorganic filler. The mixture was prepared by mixing 50 parts by weight of spherical alumina and 50 parts by weight of synthetic mica in a mortar (inorganic filler 2). The oxygen atomic mass percentage of inorganic filler 2 was 45%. D50, D10 and D90 of inorganic filler 2 were 4.2 μm, 0.5 μm and 11.5 μm, respectively. Furthermore, the BET specific surface area per unit area of inorganic filler 2 was 4.5 m ² /g.

A coating liquid was prepared as follows. That is, 10 parts by weight of the vinylidene fluoride-hexafluoropropylene copolymer is mixed with 90 parts by weight of the inorganic filler, and the solid content in the resulting mixture (inorganic filler + vinylidene fluoride-hexafluoropropylene copolymer) The solvent was mixed so that the concentration of was 30% by weight. The resulting mixed solution was stirred and mixed with a thin-film rotating high-speed mixer to obtain a uniform coating solution (coating solution 2).

The inorganic filler used to prepare the porous layer (B layer) was changed to the inorganic filler 2, the coating liquid was changed to the coating liquid 2, and the coating shear rate was 7.9 (1 / s). A laminate 2 was obtained in the same manner as in Example 1, except for the change.

[Preparation of non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery 2 was obtained in the same manner as in Example 1, except that the laminate 2 was used instead of the laminate 1 .

After that, the battery characteristics of the non-aqueous electrolyte secondary battery 2 obtained by the method described above were measured. Table 1 shows the results.

[Example 3]
[Preparation of porous layer and laminated porous film]
Wollastonite (manufactured by Hayashi Kasei Co., Ltd., trade name: Wollastonite VM-8N) having an oxygen atomic mass percentage of 42% was used as the inorganic filler (inorganic filler 3). D50, D10 and D90 of inorganic filler 3 were 10.6 μm, 2.4 μm and 25.3 μm, respectively. Also, the BET specific surface area per unit area of the inorganic filler 3 was 1.3 m ² /g.

A coating liquid was prepared as follows. That is, 10 parts by weight of the vinylidene fluoride-hexafluoropropylene copolymer is mixed with 90 parts by weight of the inorganic filler, and the solid content in the resulting mixture (inorganic filler + vinylidene fluoride-hexafluoropropylene copolymer) The solvent was mixed so that the concentration of was 40% by weight. The resulting mixed liquid was stirred and mixed with a thin-film rotating high-speed mixer to obtain a uniform coating liquid (coating liquid 3).

The inorganic filler used to prepare the porous layer (B layer) was changed to the inorganic filler 3, the coating liquid was changed to the coating liquid 3, and the coating shear rate was 7.9 (1 / s). A laminate 3 was obtained in the same manner as in Example 1, except for the change.

[Preparation of non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery 3 was obtained in the same manner as in Example 1, except that the laminate 3 was used instead of the laminate 1 .

After that, the battery characteristics of the non-aqueous electrolyte secondary battery 3 obtained by the method described above were measured. Table 1 shows the results.

[Example 4]
[Preparation of porous layer and laminated porous film]
As the inorganic filler, a mixture of α-alumina (manufactured by Sumitomo Chemical Co., Ltd., trade name: AKP3000) and hexagonal plate-like zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., trade name: XZ-1000F) was used. The mixture was prepared by mixing 99 parts by weight of α-alumina and 1 part by weight of hexagonal plate-like zinc oxide in a mortar (inorganic filler 4). The oxygen atomic mass percentage of inorganic filler 4 was 47%. D50, D10 and D90 of inorganic filler 4 were 0.8 μm, 0.4 μm and 2.2 μm, respectively. Furthermore, the BET specific surface area per unit area of the inorganic filler 4 was 4.5 m ² /g.

A coating liquid was prepared as follows. That is, 10 parts by weight of the vinylidene fluoride-hexafluoropropylene copolymer is mixed with 90 parts by weight of the inorganic filler, and the solid content in the resulting mixture (inorganic filler + vinylidene fluoride-hexafluoropropylene copolymer) The solvent was mixed so that the concentration of was 40% by weight. The resulting mixed solution was stirred and mixed with a thin-film rotating high-speed mixer to obtain a uniform coating solution (coating solution 4).

The inorganic filler used to prepare the porous layer (B layer) was changed to the above inorganic filler 4, the coating liquid was changed to the above coating liquid 4, and the coating shear rate was 39.4 (1 / s). A laminate 4 was obtained in the same manner as in Example 1, except for the change.

(Positive plate)
A positive electrode in which a positive electrode mixture of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ /conductive agent/PVDF (weight ratio: 92/5/3) is laminated on one side of a positive current collector (aluminum foil) got a board A confining pressure (0.7 MPa) was applied at room temperature for 30 seconds while the positive electrode plate was wetted with diethyl carbonate.

The positive electrode plate is cut so that the size of the portion where the positive electrode active material layer is laminated is 45 mm × 30 mm, and a portion with a width of 13 mm where the positive electrode active material layer is not laminated remains on the outer periphery, A positive electrode plate 2 was obtained. The thickness of the positive electrode active material layer was 37 μm.

[Preparation of non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery 4 was obtained in the same manner as in Example 1, except that the laminate 4 was used instead of the laminate 1 and the positive electrode plate 2 was used as the positive electrode plate.

After that, the battery characteristics of the non-aqueous electrolyte secondary battery 4 obtained by the method described above were measured. Table 1 shows the results.

[Example 5]
(Positive plate)
A positive electrode plate was obtained in which a positive electrode mixture (LiCoO ₂ /conductive agent/PVDF (weight ratio: 100/5/3)) was laminated on one side of a positive electrode current collector (aluminum foil). A confining pressure (0.7 MPa) was applied at room temperature for 30 seconds while the positive electrode plate was wetted with diethyl carbonate.

The positive electrode plate is cut so that the size of the portion where the positive electrode active material layer is laminated is 45 mm × 30 mm, and a portion with a width of 13 mm where the positive electrode active material layer is not laminated remains on the outer periphery. Plate 3 was obtained. The thickness of the positive electrode active material layer was 38 μm.

[Preparation of non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery 5 was obtained in the same manner as in Example 1, except that the laminate 4 was used instead of the laminate 1 and the positive electrode plate 3 was used as the positive electrode plate.

After that, the battery characteristics of the non-aqueous electrolyte secondary battery 5 obtained by the method described above were measured. Table 1 shows the results.

[Example 6]
(negative plate)
A negative electrode plate was obtained in which a negative electrode mixture of natural graphite/styrene-1,3-butadiene copolymer/sodium carboxymethylcellulose (weight ratio 98/1/1) was laminated on one side of a negative electrode current collector (copper foil). rice field. A confining pressure (0.7 MPa) was applied at room temperature for 30 seconds while the negative electrode plate was wetted with diethyl carbonate.

The negative electrode plate is cut so that the size of the portion where the negative electrode active material layer is laminated is 50 mm × 35 mm, and a portion with a width of 13 mm where the negative electrode active material layer is not laminated remains on the outer periphery, A negative electrode plate 2 was obtained. The thickness of the negative electrode active material layer was 37 μm.

[Preparation of non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery 6 was obtained in the same manner as in Example 1, except that the laminate 4 was used instead of the laminate 1, and the negative electrode plate 2 was used as the negative electrode plate.

After that, the battery characteristics of the non-aqueous electrolyte secondary battery 6 obtained by the method described above were measured. Table 1 shows the results.

[Example 7]
(negative plate)
A negative electrode plate was obtained in which a negative electrode mixture of artificial spherulite graphite/conductive agent/PVDF (weight ratio 85/15/7.5) was laminated on one side of a negative electrode current collector (copper foil). While this negative electrode plate was wetted with diethyl carbonate, a confining pressure (0.7 MPa) was applied at room temperature for 30 seconds.

The negative electrode plate is cut so that the size of the portion where the negative electrode active material layer is laminated is 50 mm × 35 mm, and a portion with a width of 13 mm where the negative electrode active material layer is not laminated remains on the outer periphery, A negative electrode plate 3 was obtained. The thickness of the negative electrode active material layer was 36 μm.

[Preparation of non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery 7 was obtained in the same manner as in Example 1, except that the laminate 4 was used instead of the laminate 1, and the negative electrode plate 3 was used as the negative electrode plate.

After that, the battery characteristics of the non-aqueous electrolyte secondary battery 7 obtained by the method described above were measured. Table 1 shows the results.

[Comparative Example 1]
[Preparation of porous layer and laminated porous film]
As an inorganic filler, borax (manufactured by Wako Pure Chemical Industries, Ltd.) having an oxygen atomic mass percentage of 71% was used (inorganic filler 5). D50, D10 and D90 of inorganic filler 5 were 27 μm, 6.3 μm and 111 μm, respectively. Also, the BET specific surface area per unit area of the inorganic filler 5 was 2.5 m ² /g.

A coating liquid was prepared as follows. That is, 10 parts by weight of the vinylidene fluoride-hexafluoropropylene copolymer is mixed with 90 parts by weight of the inorganic filler, and the solid content in the resulting mixture (inorganic filler + vinylidene fluoride-hexafluoropropylene copolymer) The solvent was mixed so that the concentration of was 40% by weight. The resulting mixed liquid was stirred and mixed by a thin-film rotating high-speed mixer to obtain a uniform coating liquid (coating liquid 5).

The inorganic filler used to prepare the porous layer (B layer) was changed to the above inorganic filler 5, the coating liquid was changed to the above coating liquid 5, and the coating shear rate was 7.9 (1 / s). A laminate 5 was obtained in the same manner as in Example 1, except for the change.

[Preparation of non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery 8 was obtained in the same manner as in Example 1 except that the laminate 5 was used instead of the laminate 1 .

After that, the battery characteristics of the non-aqueous electrolyte secondary battery 8 obtained by the method described above were measured. Table 1 shows the results.

[Comparative Example 2]
(Positive plate)
A positive electrode in which a positive electrode mixture of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ /conductive agent/PVDF (weight ratio: 92/5/3) is laminated on one side of a positive current collector (aluminum foil) got a board

The positive electrode plate is cut so that the size of the portion where the positive electrode active material layer is laminated is 45 mm × 30 mm, and a portion with a width of 13 mm where the positive electrode active material layer is not laminated remains on the outer periphery, A positive electrode plate 4 was used. The thickness of the positive electrode active material layer was 38 μm.

[Preparation of non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery 9 was obtained in the same manner as in Example 1, except that the laminate 4 was used instead of the laminate 1 and the positive electrode plate 4 was used as the positive electrode plate.

After that, the battery characteristics of the non-aqueous electrolyte secondary battery 9 obtained by the method described above were measured. Table 1 shows the results.

[Comparative Example 3]
(negative plate)
A negative electrode plate was obtained in which a negative electrode mixture of natural graphite/styrene-1,3-butadiene copolymer/sodium carboxymethylcellulose (weight ratio 98/1/1) was laminated on one side of a negative electrode current collector (copper foil). rice field.

The negative electrode plate is cut so that the size of the portion where the negative electrode active material layer is laminated is 50 mm × 35 mm, and a portion with a width of 13 mm where the negative electrode active material layer is not laminated remains on the outer periphery, A negative electrode plate 4 was obtained. The thickness of the negative electrode active material layer was 38 μm.

[Preparation of non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery 10 was obtained in the same manner as in Example 1, except that the laminate 4 was used instead of the laminate 1 and the negative electrode plate 4 was used as the negative electrode plate.

After that, the battery characteristics of the non-aqueous electrolyte secondary battery 10 obtained by the method described above were measured. Table 1 shows the results.

In Table 1, two types of compounds and numerical values are described in the "inorganic filler" column of Examples 2 and 4-7 and Comparative Examples 2-3. The numbers represent parts by weight of the compound. For example, Example 2 describes “Al ₂ O ₃ /mica 50/50”, which means that 50 parts by weight of Al ₂ O ₃ and 50 parts by weight of mica were used.

[Conclusion]
As shown in Table 1, the non-aqueous electrolyte secondary batteries of Examples 1-7 are superior to the non-aqueous electrolyte secondary batteries of Comparative Examples 1-3 in discharge capacity recovery characteristics after charge-discharge cycles. It turns out that In the non-aqueous electrolyte secondary batteries of Examples 1 to 7, the number of times of bending until the electrode active material layer of the positive electrode plate peeled off was 130 times or more, and the number of times of bending until the electrode active material layer of the negative electrode plate peeled off was 1650 times. times or more, and the value represented by |1-T/M| of the porous layer is in the range of 0.10 to 0.42. On the other hand, in Comparative Example 1, |1−T/M| exceeds 0.42. In Comparative Example 2, the number of times of bending until the electrode active material layer of the positive electrode plate was peeled off was less than 130 times. In Comparative Example 3, the number of times of bending until the electrode active material layer of the negative electrode plate peeled off was less than 1650 times.

The non-aqueous electrolyte secondary battery according to one embodiment of the present invention has excellent discharge capacity recovery characteristics after charge-discharge cycles, and is therefore suitable for batteries used in personal computers, mobile phones, personal digital assistants, etc., and batteries for vehicles. can be used for

REFERENCE SIGNS LIST 1 diamond indenter 2 substrate 3 porous film mainly composed of polyolefin

Claims (5)

a porous layer containing an inorganic filler and a resin;
In a folding endurance test conducted at a load of 1 N and a bending angle of 45° in accordance with the MIT tester method specified in JIS P 8115 (1994), the number of times of bending until the electrode active material layer peels off is 130 times or more. a positive electrode plate;
a negative electrode plate that is bent 1650 times or more until the electrode active material layer is peeled off in the folding endurance test;
the porous layer is positioned between the positive electrode plate and the negative electrode plate to form a separator;
The non-aqueous electrolyte secondary battery, wherein the porous layer has a value represented by the following formula (1) in the range of 0.10 to 0.42.
|1-T/M| (1)
(In formula (1), T represents the distance to the critical load in the scratch test under a constant load of 0.1 N in TD, and M represents the distance to the critical load in the scratch test under a constant load of 0.1 N in MD. , represents the distance to the critical load.) 2. The porous layer according to claim 1, wherein the porous layer contains one or more resins selected from the group consisting of polyolefins, (meth)acrylate resins, fluorine-containing resins, polyamide resins, polyester resins and water-soluble polymers. Non-aqueous electrolyte secondary battery. 3. The nonaqueous electrolyte secondary battery in accordance with claim 2, wherein said polyamide resin is an aramid resin. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein said porous layer is laminated on one side or both sides of a polyolefin porous film. 5. The non-aqueous electrolyte secondary battery in accordance with claim 1, wherein said positive electrode plate contains a transition metal oxide, and said negative electrode plate contains graphite.

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