JP7132823B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

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

Non-aqueous electrolyte secondary batteries, especially lithium-ion secondary batteries, have high energy density and are widely used in personal computers, mobile phones, personal digital assistants, etc. Recently, they are also being developed as batteries for vehicles. It is

As a non-aqueous electrolyte secondary battery, for example, a porous layer containing a plate-like inorganic filler as described in Patent Document 1 and having a porosity of 60 to 90% is formed on at least one surface of a porous substrate. A non-aqueous electrolyte secondary battery is known that includes a separator for a non-aqueous secondary battery that is laminated on the substrate.

Japanese Patent Application Laid-Open No. 2010-108753 (published on May 13, 2010)

However, the non-aqueous electrolyte secondary battery having the porous layer according to the prior art as described above has room for improvement from the viewpoint of the charge recovery capacity after the charge-discharge cycle.

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 that can exhibit excellent charge recovery capacity even after many charge-discharge cycles. It is to provide a battery.

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 that is at least 10 times, the aspect ratio of the projected image of the inorganic filler on the surface of the porous layer is in the range of 1.4 to 4.0, and the wide-angle X-ray of the porous layer Peak intensities of arbitrary diffraction planes (hkl) and (abc) orthogonal to each other measured by the diffraction method: I _(hkl) and I _(abc) satisfy the following formula (1) and are calculated by the following formula (2) The range of the maximum value of the peak intensity ratio is in the range of 1.5-300.
I _(hkl) > I _(abc) (1)
I _(hkl) / I _(abc) (2)
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, it is possible to provide a non-aqueous electrolyte secondary battery that can exhibit excellent charge recovery capacity even after many charge-discharge cycles.

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. 4 is a schematic diagram showing a projected image of an inorganic filler on the surface of the porous layer in one embodiment of the present invention.

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 that is 1650 times or more, the aspect ratio of the projected image of the inorganic filler on the surface of the porous layer is in the range of 1.4 to 4.0, and the porous layer has a wide angle X Peak intensities of arbitrary diffraction planes (hkl) and (abc) orthogonal to each other measured by the line diffraction method: I _(hkl) and I _(abc) satisfy the following formula (1) and are calculated by the following formula (2) The non-aqueous electrolyte secondary battery has a maximum peak intensity ratio range of 1.5 to 300.

I _(hkl) > I _(abc) (1)
I _(hkl) / I _(abc) (2)
Moreover, the non-aqueous electrolyte secondary battery according to one embodiment of the present invention may further include a polyolefin porous film, which will be described later.

<Positive plate>
Other configurations of the positive electrode plate in the non-aqueous electrolyte secondary battery according to one embodiment of the present invention are not particularly limited as long as the number of times of bending measured in the folding endurance test is within a specific range, as described later. . 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>
Other configurations of the negative electrode plate in the non-aqueous electrolyte secondary battery according to one embodiment of the present invention are not particularly limited as long as the number of times of bending measured in the folding endurance test is within a specific range, as described later. . 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>
The positive electrode plate and the negative electrode plate included in the non-aqueous electrolyte secondary battery according to one embodiment of the present invention are the electrodes in a folding endurance test conducted in accordance with the MIT tester method specified in JIS P 8115 (1994). The number of times of bending until the active material layer is peeled off is within a specific range. 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 electrode 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 in the course of charge-discharge cycles is suppressed as the number of times of bending is increased.

In the folding endurance test, the positive electrode plate is bent 130 times or more, 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.

Examples of methods for producing a sheet-like negative electrode plate include a method of pressure-molding a negative electrode active material on a negative electrode current collector; Examples include a method of coating the current collector and then applying pressure 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 or negative plates. 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>
The porous layer in one embodiment of the present invention is a porous layer containing an inorganic filler and a resin, and the inorganic filler on the surface of the porous layer (hereinafter sometimes referred to as "porous layer surface") The aspect ratio of the projected image of is in the range of 1.4 to 4.0, and the porous layer is measured by a wide-angle X-ray diffraction method. Peak intensity: I _(hkl) and I _(abc) satisfy the following formula (1), and the maximum value range of the peak intensity ratio calculated by the following formula (2) is in the range of 1.5-300.

I _(hkl) > I _(abc) (1)
I _(hkl) / I _(abc) (2)
In one embodiment of the present invention, the porous layer can be arranged between a polyolefin porous film and at least one of the positive electrode plate and the negative electrode plate as a member constituting a non-aqueous electrolyte secondary battery. Also, 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 of the polyolefin porous film that is in contact with the positive electrode plate.

Both the "aspect ratio of the projected image of the inorganic filler on the surface of the porous layer" and the "maximum value of the peak intensity ratio calculated by formula (2)" both indicate the orientation of the inorganic filler in the porous layer. It is an index that represents FIG. 1 shows schematic diagrams of aspects of the inorganic filler in the porous layer when the orientation is high and when the orientation is low. The left diagram of FIG. 1 is a schematic diagram showing the structure of a porous layer containing an inorganic filler when the orientation of the filler is large and the anisotropy is high, and the right diagram of FIG. FIG. 4 is a schematic diagram showing the structure of the porous layer when the orientation of the filler is small and the anisotropy is low.

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 for the non-aqueous electrolyte secondary battery As the outermost layer of the laminated separator, it can be a layer in contact with the electrode.

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

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

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.

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, and the like, and fluorine-containing rubbers having a glass transition temperature of 23° C. or lower among the fluorine-containing resins can be mentioned.

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, it is easy to maintain various performances such as rate characteristics and resistance characteristics of the non-aqueous electrolyte secondary battery due to oxidation deterioration during battery operation. Therefore, fluorine-containing resins are preferred.

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. Inorganic fillers also preferably contain oxides of the aforementioned elements.

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 elements.

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 oxide of the element constituting the inorganic filler contained in the porous layer in one embodiment of the present invention is preferably 10% to 50%, and is 20% to 50%. is more preferred. In the present invention, "oxygen atom mass percentage" means the ratio of the mass of oxygen atoms in the oxide to the total mass of the oxide of the element, 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 oxide of the element is within the above-mentioned range means 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 improved. By keeping it suitable and keeping the distance between the inorganic fillers at an appropriate distance, the dispersibility of the coating liquid can be improved. ” and “the degree of orientation of the porous layer” can be controlled within an appropriately defined range.

The aspect ratio of the inorganic filler itself contained in the porous layer in one embodiment of the present invention is a state in which the inorganic filler is arranged on a plane, and an SEM image observed from vertically above the arrangement surface overlaps in the thickness direction. It is expressed as the average value of the ratio of the minor axis length to the major axis length of 100 particles without particles. In this specification, the length of the major axis is also referred to as the major axis diameter, and the length of the minor axis is also referred to as the minor axis diameter. The aspect ratio of the inorganic filler itself is preferably 1-10, more preferably 1.1-8, even more preferably 1.2-5. When the aspect ratio of the inorganic filler itself is within the above range, the orientation of the filler and the The uniformity of filler distribution on the surface of the porous layer can be controlled within a preferred range.

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.

<Aspect Ratio of Projected Image of Inorganic Filler on Porous Layer Surface>
In one embodiment of the porous layer of the present invention, the aspect ratio of the projected image of the inorganic filler on the surface of the porous layer is in the range of 1.4 to 4.0, and 1.5 to 2.3. A range is preferred. Here, using a scanning electron microscope (SEM), an SEM image, which is an electron micrograph of the surface of the porous layer, is taken from directly above the porous layer, that is, from the vertical direction. It is a value obtained by creating a projected image of the filler and calculating the ratio of the length of the major axis to the length of the minor axis of the projected image of the inorganic filler. That is, the aspect ratio indicates the shape of the inorganic filler observed when the inorganic filler on the surface of the porous layer is observed from directly above the porous layer.

FIG. 3 shows a schematic diagram of a projected image of the inorganic filler created from the SEM image of the surface of the porous layer described above.

A specific method for measuring the aspect ratio includes, for example, a method comprising the following steps (1) to (4). In addition, the "surface" of the porous layer refers to the surface of the porous layer that can be observed by SEM from directly above the porous layer.
(1) In a laminate obtained by laminating a porous layer on a substrate, SEM at an acceleration voltage of 5 kV using a field emission scanning electron microscope JSM-7600F manufactured by JEOL from directly above the porous side of the laminate. A step of performing surface observation (backscattered electron image) and obtaining an SEM image.
(2) An OHP film is placed on the SEM image obtained in step (1), and a projection image is created by spreading along the contours of the inorganic filler particles shown in the SEM image. The process of photographing with a digital still camera.
(3) The photographic data obtained in the step (2) is loaded into a computer, and the filler particles 100 are analyzed using image analysis free software IMAGEJ published by the National Institutes of Health (NIH). Calculating the aspect ratio of each piece. Here, each filler particle is approximated to an elliptical shape, the major axis diameter and the minor axis diameter are calculated, and the value obtained by dividing the major axis diameter by the minor axis diameter is defined as the aspect ratio.
(4) A step of calculating the average value of the aspect ratios of the projected images of the respective particles obtained in step (3), and using that value as the aspect ratio of the projected image of the inorganic filler on the surface of the porous layer.

The aspect ratio of the projected image of the inorganic filler on the surface of the porous layer is an index showing the uniformity of distribution of the inorganic filler on the surface of the porous layer, particularly on the surface. The fact that the aspect ratio is close to 1 means that the shape and distribution of the constituent materials on the surface of the porous layer are uniform, and they are likely to be densely packed. On the other hand, when the aspect ratio is large, the arrangement of constituent components in the surface structure of the porous layer becomes non-uniform, and as a result, the uniformity of the shape and distribution of the openings on the surface of the porous layer deteriorates.

If the aspect ratio is greater than 4.0, the uniformity of the shape and distribution of the porous layer, particularly the openings on the surface thereof, is excessively reduced. In the battery, there are places where the ability of the porous layer to accept the electrolyte is lowered during battery operation. As a result, it is considered that the rate characteristics of the non-aqueous electrolyte secondary battery are degraded. On the other hand, when the aspect ratio is less than 1.4, the porous layer, particularly the distribution of the inorganic filler on the surface thereof, becomes an excessively uniform structure, resulting in a surface opening area of the porous layer. As a result, in a non-aqueous electrolyte secondary battery incorporating the porous layer, the ability of the porous layer to accept the electrolyte during operation of the battery is reduced. As a result, it is considered that the battery rate characteristics of the non-aqueous electrolyte secondary battery are degraded.

<Orientation degree of porous layer>
The porous layer in one embodiment of the present invention has peak intensities of arbitrary diffraction planes (hkl) and (abc) orthogonal to each other in the porous layer measured by wide-angle X-ray diffraction: I _(hkl) and I _(abc) satisfies the following formula (1), and the range of the maximum value of the peak intensity ratio calculated by the following formula (2) is in the range of 1.5 to 300, and in the range of 1.5 to 250 is more preferable.

I _(hkl) > I _(abc) (1),
I _(hkl) / I _(abc) (2)
Hereinafter, in this specification, the maximum value of the peak intensity ratio calculated by the formula (2) is also referred to as "orientation degree of the porous layer".

The method for measuring the peak intensities I _(hkl) and I _(abc) and the peak intensity ratio I _(hkl) / I _(abc) is not particularly limited, but for example, the following (1) to (3) A method consisting of the steps shown can be mentioned.
(1) A step of cutting a laminate (laminated porous film) obtained by laminating a porous layer on a substrate into a 2 cm square to prepare a sample for measurement.
(2) The measurement sample obtained in step (1) is mounted on an Al holder with the porous layer side of the sample as the measurement surface, and an X-ray profile is obtained by a wide-angle X-ray diffraction method (2θ-θ scanning method). the step of measuring The apparatus and measurement conditions for measuring the X-ray profile are not particularly limited. A method of measuring with an output of 50 KV-200 mA and a scan speed of 2°/min can be used.
(3) Based on the X-ray profile obtained in step (2), the peak intensity I _(hkl) of arbitrary diffraction planes (hkl) and (abc) orthogonal to each other in the wide-angle X-ray diffraction measurement of the porous layer When I _(abc) satisfies the above formula (1), the peak intensity ratio calculated by the above formula (2) is calculated, and the maximum value of the peak intensity ratio, that is, the degree of orientation of the porous layer is calculated. process.

In calculating the degree of orientation of the porous layer, it is important to determine both the horizontal direction and the normal direction with respect to the substrate surface by using mutually orthogonal diffraction planes. be.

The maximum value of the peak intensity ratio represented by the formula (2) is an index indicating the degree of orientation inside the porous layer. A small peak intensity ratio represented by the above formula (2) indicates that the degree of orientation in the internal structure of the porous layer is low, and a large peak intensity ratio represented by the above formula (2) indicates that the porous This indicates a high degree of orientation in the internal structure of the layer.

When the maximum value of the peak intensity ratio represented by the formula (2) is greater than 300, the anisotropy of the internal structure of the porous layer becomes excessively high, and the ion permeation channel length inside the porous layer becomes become longer. 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 battery rate characteristics of the non-aqueous electrolyte secondary battery are considered to deteriorate.

On the other hand, when the maximum value of the peak intensity ratio represented by the formula (2) is less than 1.5, compared to the case of using a porous layer having a peak intensity ratio of 1.5 or more, the above In a non-aqueous electrolyte secondary battery incorporating a porous layer, since ions supplied from the electrode are allowed to permeate at high speed, the supply of ions from the electrode becomes rate-determining (that is, ions are depleted on the electrode surface), and the battery operates. The limit current, which is the current value condition, becomes smaller. As a result, it is considered that the battery rate characteristics of the non-aqueous electrolyte secondary battery are degraded.

<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 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, positive electrodes, negative electrodes, 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.

In addition, as a method for controlling the orientation of the porous layer in one embodiment of the present invention, that is, the "aspect ratio of the projected image of the inorganic filler on the surface of the porous layer" and the "degree of orientation of the porous layer", the following are described. As shown, the solid content concentration of the coating liquid containing the inorganic filler and the resin used for producing the porous layer, and the coating shear rate when the coating liquid is applied onto the substrate are adjustment can be mentioned.

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. When the solid content concentration is in the above range, the viscosity of the coating liquid is appropriately maintained, and as a result, the "aspect ratio of the projected image of the inorganic filler on the surface of the porous layer" and the "degree of orientation of the porous layer ” can be controlled within the preferred range described above.

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.

<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 and the negative electrode. is preferable, and 0.14 μm or less is more preferable.

<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. A polyolefin porous film can be produced by removing the pore-forming agent from the sheet-shaped polyolefin resin composition with an appropriate solvent and then 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-described "method for producing a porous layer", the polyolefin is used as the base material to which the coating liquid is applied. A method using a 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 the non-aqueous secondary battery according to one embodiment of the present invention, a conventionally known manufacturing method can be adopted. For example, a non-aqueous electrolyte secondary battery member is formed by arranging a positive electrode plate, a polyolefin porous film and a negative electrode plate in this order. Here, the porous layer may exist between the polyolefin porous film and at least one of the positive electrode plate and the negative electrode plate. Next, the non-aqueous electrolyte secondary battery member is placed in a container that serves as a housing for the non-aqueous electrolyte secondary battery. After filling the inside of the container with the non-aqueous electrolyte, the container is sealed while reducing the pressure. Thereby, a non-aqueous electrolyte secondary battery according to one embodiment of the present invention can be manufactured.

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]
The physical properties of the porous layers and polyolefin porous films produced in Examples and Comparative Examples, and the charge recovery capacity after 100 cycles of charging and discharging of non-aqueous electrolyte secondary batteries were measured using the following methods. It was measured.

(1) Film thickness (unit: μm)
The polyolefin porous film and the film thickness of the porous layer were measured using a high-precision digital length measuring machine (VL-50) manufactured by Mitutoyo Corporation. The thickness of the porous layer was obtained by subtracting the thickness of the portion where the porous layer was not formed from the thickness of the portion where the porous layer was formed in each laminate.

(2) Measurement of the aspect ratio of the projected image of the inorganic filler on the surface of the porous layer Using a field-emission scanning electron microscope JSM-7600F manufactured by Manufacture Co., Ltd., SEM surface observation (backscattered electron image) was performed at an acceleration voltage of 5 kV to obtain an electron micrograph (SEM image).

An OHP film was placed on the obtained SEM image, and a projection image was created by spreading along the contours of the particles of the inorganic filler, and the projection image was photographed with a digital still camera. The data of the obtained photograph was loaded into a computer, and the aspect ratio of each of 100 particles was calculated using the image analysis free software IMAGEJ published by the National Institutes of Health (NIH). The average was taken as the aspect ratio of the projected image of the inorganic filler on the surface of the porous layer in the porous layer (hereinafter also referred to as "surface filler aspect ratio"). Here, each inorganic filler particle was approximated to an elliptical shape, the major axis diameter and the minor axis diameter were calculated, and the value obtained by dividing the major axis diameter by the minor axis diameter was defined as the aspect ratio per inorganic filler particle.

(3) Measurement of Maximum Value of Peak Intensity Ratio A 2 cm-square piece was cut from the laminate comprising the polyolefin porous film and the porous layer produced in Examples and Comparative Examples to obtain a sample for measurement. The obtained measurement sample was attached to an Al holder using the porous layer of the sample as a measurement surface, and the X-ray profile was measured by a wide-angle X-ray diffraction method (2θ-θ scanning method). RU-200R (rotating anticathode type) manufactured by Rigaku Denki Co., Ltd. was used as the apparatus, CuKα rays were used as the X-ray source, the output was 50 KV-200 mA, and the scan rate was 2°/min.

Based on the obtained X-ray profile, the peak intensities I _(hkl) and I _(abc) of arbitrary orthogonal diffraction planes (hkl) and (abc) in the wide-angle X-ray diffraction measurement of the porous layer are expressed by the following formula (1 ), the peak intensity ratio calculated by I _(hkl) /I _(abc) was calculated, and the maximum value of the peak intensity ratio was calculated.
I _(hkl) >I _(abc) (1).

(4) Folding endurance test A test piece having a length of 105 mm and a width of 15 mm was cut out from each of the positive electrode plates or negative electrode plates obtained in 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 bending here means the number of times of reciprocating bending displayed on the counter of the MIT type folding endurance tester.

(5) Charge recovery capacity after 100 cycles of charge and discharge (5-1) Initial charge and discharge CC-CV charging with voltage range: 2.7 to 4.1 V, charging current value: 0.2 C (final current condition 0.02 C) for a new non-aqueous electrolyte secondary battery that has not undergone a discharge cycle, Discharge current value: 4 cycles of initial charge/discharge were performed at 25°C, with CC discharge at 0.2C as one cycle. Here, 1C is the current value for discharging the rated capacity based on the discharge capacity of 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.

(5-2) Cycle test The non-aqueous electrolyte secondary battery after the initial charge and discharge is CC-CV charged with a voltage range of 2.7 to 4.2 V and a charging current value of 1 C (final current condition 0.02 C). , discharge current value: 100 cycles of charge and discharge were performed at 55°C, with CC discharge at 10C being one cycle.

(5-3) Charge Recovery Capacity Test after 100 Cycles of Charge and Discharge Voltage range: 2.7 V to 4.2 V, charge current value: Three cycles of CC-CV charging (final current condition: 0.02C) and discharge current value: 0.2C CC discharging were performed at 55°C. The charge capacity at the third cycle was defined as the charge recovery capacity after 100 cycles of charge and discharge.

The charge recovery capacity test is a test method for more accurately confirming the charge capacity after discharging at a low rate (0.2 C) after the charge-discharge cycle to empty the capacity inside the battery. It is possible to check the degree of deterioration of the charging performance, particularly the deterioration of the charging performance of the electrode.

[Example 1]
[Production of porous substrate (A layer)]
A porous substrate, which is a polyolefin porous film, 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 film thickness of 16 μm.

[Production of porous layer (B layer)]
(Manufacture of coating liquid)
As the inorganic filler, hexagonal tabular zinc oxide (trade name: XZ-100F, manufactured by Sakai Chemical Industry Co., Ltd.) having an oxygen atomic mass percentage of 20% was used. Let the said inorganic filler be the inorganic filler 1. As shown in FIG. In this specification, the volume-based particle size distribution of the inorganic 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 reaches 50%, 10%, and 90% are referred to as D50, D10, and D90, respectively. D10, D50 and D90 of inorganic filler 1 were 0.2 μm, 0.4 μm and 2.1 μm, respectively.

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

In this specification, the specific surface area of the inorganic filler was calculated by the BET method after measuring the adsorption-desorption isotherm with nitrogen using the constant volume method. The BET specific surface area per unit area of the inorganic filler 1 was 7.3 m ² /g.

Inorganic filler 1, a vinylidene fluoride-hexafluoropropylene copolymer and a 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 the inorganic filler 1 (90 parts by weight), and the solid content of the inorganic filler 1 and the vinylidene fluoride-hexafluoropropylene copolymer is A mixed solution was prepared by mixing solvents so that the concentration in the mixed solution was 37% by weight. The resulting mixed solution was stirred and mixed with a thin-film rotating high-speed mixer (Filmiku (registered trademark) manufactured by Primix Co., Ltd.) to obtain a uniform coating solution. The coating liquid is referred to as coating liquid 1.

(Manufacturing of multi-layer and laminated porous film)
The coating liquid 1 was applied to one side of the A layer at a coating shear rate of 3.9 (1/s) by a doctor blade method to form a coating film on one side of the A layer. Thereafter, 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)
As a positive electrode mixture, 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 an aluminum foil as a positive electrode current collector. Thus, a positive electrode plate was obtained. A confining pressure (0.7 MPa) was applied to the 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 the portion where the positive electrode active material layer is not laminated remains at the outer periphery with a width of 13 mm. , a positive electrode plate 1 was obtained. The thickness of the positive electrode active material layer of the positive electrode plate 1 was 38 μm.

(negative plate)
As a negative electrode mixture, 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 the negative electrode current collector. A negative electrode plate was obtained by laminating on one side of the copper foil. Confining pressure (0.7 MPa) was applied to the 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 the portion where the negative electrode active material layer is not laminated remains at the outer periphery with a width of 13 mm. , a negative electrode plate 1 was obtained. The thickness of the negative electrode active material layer of the negative electrode plate 1 was 38 μm.

(Assembly 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 shown below.

First, the positive electrode plate 1, the laminate 1, and the negative electrode plate 1 were laminated (arranged) in this order in a laminate pouch to obtain a non-aqueous electrolyte secondary battery member 1. At this time, the positive electrode plate 1 and the negative electrode were arranged so that the entire main surface of the positive electrode active material layer of the positive electrode plate 1 was included in the range of the main surface of the negative electrode active material layer of the negative electrode plate 1, that is, overlapped with the main surface. Plate 1 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 was prepared by dissolving LiPF ₆ in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate at a volume ratio of 3:5:2 so as to have a concentration of 1 mol/L. . 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 were measured. Table 1 shows the results.

[Example 2]
[Preparation of porous layer and laminated porous film]
As the inorganic filler, 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. The mixture was prepared by mixing 50 parts by weight of spherical alumina and 50 parts by weight of synthetic mica in a mortar. Let the said mixture be the inorganic filler 2. The oxygen atomic mass percentage of inorganic filler 2 was 45%. In addition, D10, D50, and D90 of the inorganic filler 2 are each 0.5
μm, 4.2 μm and 11.5 μm. 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 the inorganic filler 2 (90 parts by weight), and the solid content of the inorganic filler 2 and the vinylidene fluoride-hexafluoropropylene copolymer is A mixed solution was prepared by mixing solvents so that the concentration of was 30% by weight in the mixed solution. The resulting mixed solution was stirred and mixed with the thin-film rotating high-speed mixer to obtain a uniform coating solution. Let this coating liquid be coating liquid 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 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. The wollastonite is used as the inorganic filler 3 . D10, D50 and D90 of inorganic filler 3 were 2.4 μm, 10.6 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 the inorganic filler 3 (90 parts by weight), and the solid content of the inorganic filler 3 and the vinylidene fluoride-hexafluoropropylene copolymer is A mixed solution was prepared by mixing solvents so that the concentration of was 40% by weight in the mixed solution. The resulting mixed solution was stirred and mixed with the thin-film rotating high-speed mixer to obtain a uniform coating solution. Let this coating liquid be 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 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 alpha alumina and 1 part by weight of hexagonal platelet zinc oxide in a mortar. Let the said mixture be the inorganic filler 4. As shown in FIG. The oxygen atomic mass percentage of inorganic filler 4 was 47%. D10, D50 and D90 of inorganic filler 4 were 0.4 μm, 0.8 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 the inorganic filler 4 (90 parts by weight), and the solid content of the inorganic filler 4 and the vinylidene fluoride-hexafluoropropylene copolymer is A mixed solution was prepared by mixing solvents so that the concentration of was 40% by weight in the mixed solution. The resulting mixed solution was stirred and mixed with the thin-film rotating high-speed mixer to obtain a uniform coating solution. This coating liquid is referred to as coating liquid 4 .

The inorganic filler used to prepare the porous layer (B layer) was changed to the inorganic filler 4, the coating liquid was changed to the 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.

[Preparation of non-aqueous electrolyte secondary battery]
(Positive plate)
As a positive electrode mixture, 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 an aluminum foil as a positive electrode current collector. Thus, a positive electrode plate was obtained. While the positive electrode plate was wetted with diethyl carbonate, a confining pressure (0.7 MPa) was applied to the 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 the portion where the positive electrode active material layer is not laminated remains at the outer periphery with a width of 13 mm. , a positive electrode plate 2 was obtained. The thickness of the positive electrode active material layer of the positive electrode plate 2 was 37 μm.

(Assembly 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 were measured. Table 1 shows the results.

[Example 5]
[Preparation of non-aqueous electrolyte secondary battery]
(Positive plate)
A positive electrode plate was obtained by laminating LiCoO ₂ /conductive agent/PVDF (weight ratio: 100/5/3) as a positive electrode mixture on one side of an aluminum foil as a positive electrode current collector. While the positive electrode plate was wetted with diethyl carbonate, a confining pressure (0.7 MPa) was applied to the 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 the portion where the positive electrode active material layer is not laminated remains at the outer periphery with a width of 13 mm. , a positive electrode plate 3 was obtained. The thickness of the positive electrode active material layer was 38 μm.

(Assembly 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 were measured. Table 1 shows the results.

[Example 6]
[Preparation of non-aqueous electrolyte secondary battery]
(negative plate)
As a negative electrode mixture, natural graphite/styrene-1,3-butadiene copolymer/sodium carboxymethylcellulose (weight ratio: 98/1/1) was laminated on one side of a copper foil as a negative electrode current collector. got a board While the negative electrode plate was wetted with diethyl carbonate, a confining pressure (0.7 MPa) was applied to the 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 the portion where the negative electrode active material layer is not laminated remains at the outer periphery with a width of 13 mm. , a negative electrode plate 2 was obtained. The thickness of the negative electrode active material layer of the negative electrode plate 2 was 37 μm.

(Assembly 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 were measured. Table 1 shows the results.

[Example 7]
[Preparation of non-aqueous electrolyte secondary battery]
(negative plate)
A negative electrode plate was obtained by laminating artificial spherulitic graphite/conductive agent/PVDF (weight ratio 85/15/7.5) as a negative electrode mixture on one side of a copper foil as a negative electrode current collector. While the negative electrode plate was wetted with diethyl carbonate, a confining pressure (0.7 MPa) was applied to the 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 the portion where the negative electrode active material layer is not laminated remains at the outer periphery with a width of 13 mm. , a negative electrode plate 3 was obtained. The thickness of the negative electrode active material layer of the negative electrode plate 3 was 36 μm.

(Assembly 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 were measured. Table 1 shows the results.

[Comparative Example 1]
[Preparation of porous layer and laminated porous film]
Attapulgite (manufactured by Hayashi Kasei Co., Ltd., trade name: ATTAGEL #50) having an oxygen atomic mass percentage of 48% was used as the inorganic filler. Let the attapulgite be the inorganic filler 5 . D10, D50 and D90 of inorganic filler 5 were 0.4 μm, 2.0 μm and 3.3 μm, respectively. In addition, the BET specific surface area per unit area of the inorganic filler 5 was 235.0 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 the inorganic filler 5 (90 parts by weight), and the solid content of the inorganic filler 5 and the vinylidene fluoride-hexafluoropropylene copolymer is A mixed solution was prepared by mixing solvents so that the concentration in the mixed solution was 17% by weight. The resulting mixed solution was stirred and mixed with the thin-film rotating high-speed mixer to obtain a uniform coating solution. This coating liquid is referred to as coating liquid 5 .

The inorganic filler used to prepare the porous layer (B layer) was changed to the inorganic filler 5, the coating liquid was changed to the coating liquid 5, and the coating shear rate was 1.3 (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 were measured. Table 1 shows the results.

[Comparative Example 2]
[Preparation of porous layer and laminated porous film]
As the inorganic filler, mica (manufactured by Wako Pure Chemical Industries, trade name: non-swelling mica) having an oxygen atomic mass percentage of 44% was used. Let the mica be the inorganic filler 6 . D10, D50 and D90 of inorganic filler 6 were 0.5 μm, 5.5 μm and 12.1 μm, respectively. Also, the BET specific surface area per unit area of the inorganic filler 5 was 3.2 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 the inorganic filler 6 (90 parts by weight), and the solid content of the inorganic filler 6 and the vinylidene fluoride-hexafluoropropylene copolymer is A mixed solution was prepared by mixing solvents so that the concentration in the mixed solution was 20% by weight. The resulting mixed solution was stirred and mixed with the thin-film rotating high-speed mixer to obtain a uniform coating solution. This coating liquid is referred to as coating liquid 6 .

The inorganic filler used to prepare the porous layer (B layer) was changed to the inorganic filler 6, the coating liquid was changed to the coating liquid 6, and the coating shear rate was set to 0.4 (1 / s). A laminate 6 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 9 was obtained in the same manner as in Example 1, except that the laminate 6 was used instead of the laminate 1 . After that, the battery characteristics of the non-aqueous electrolyte secondary battery 9 were measured. Table 1 shows the results.

[Comparative Example 3]
[Preparation of non-aqueous electrolyte secondary battery]
(Positive plate)
As a positive electrode mixture, 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 an aluminum foil as a positive electrode current collector. Thus, a positive electrode plate was obtained.

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 the portion where the positive electrode active material layer is not laminated remains at the outer periphery with a width of 13 mm. , and the positive electrode plate 4 . The thickness of the positive electrode active material layer of the positive electrode plate 4 was 38 μm.

(Assembly of non-aqueous electrolyte secondary battery)
A non-aqueous electrolyte secondary battery 10 was produced 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 10 were measured. Table 1 shows the results.

[Comparative Example 4]
[Preparation of non-aqueous electrolyte secondary battery]
(negative plate)
As a negative electrode mixture, natural graphite/styrene-1,3-butadiene copolymer/sodium carboxymethylcellulose (weight ratio: 98/1/1) was laminated on one side of a copper foil as a negative electrode current collector. got a board

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 the portion where the negative electrode active material layer is not laminated remains at the outer periphery with a width of 13 mm. , was used as the negative electrode plate 4 . The thickness of the negative electrode active material layer of the negative electrode plate 4 was 38 μm.

(Assembly of non-aqueous electrolyte secondary battery)
Non-aqueous electrolysis was performed in the same manner as in Example 1, except that the laminate 4 was used instead of the laminate 1, the positive electrode plate 4 was used as the positive electrode plate, and the negative electrode plate 4 was used as the negative electrode plate. A liquid secondary battery 11 was produced. After that, the battery characteristics of the non-aqueous electrolyte secondary battery 11 were measured. Table 1 shows the results.

In Table 1, "filler" is the type of inorganic filler, "aspect ratio" is the surface filler aspect ratio described above, and "maximum peak intensity ratio" is the peak intensity ratio calculated by the above formula (2). "The number of times of bending until the electrode active material layer peels off" is the number of times of bending until the electrode active material layer peels off from the positive electrode plate or the negative electrode plate subjected to the folding endurance test. "Recovery capacity" indicates the charge recovery capacity of the non-aqueous electrolyte secondary battery subjected to the "charge recovery capacity test after 100 cycles of charging and discharging".

In addition, two types of compounds and numerical values are described in the "Filler" column of Examples 2 and 4 to 7 and Comparative Examples 3 and 4. 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.

As shown in Table 1, the nonaqueous electrolyte secondary batteries of Examples 1 to 7 have higher charge recovery capacities after 100 cycles of charging and discharging than the nonaqueous electrolyte secondary batteries of Comparative Examples 1 to 4. was very good. (ii) any mutually orthogonal diffraction planes (hkl) measured by wide-angle X-ray diffraction, (abc) a requirement for peak intensity, and (iii) A non-aqueous electrolyte secondary battery according to an embodiment of the present invention, which satisfies the requirements for the number of times the positive electrode plate and the negative electrode plate are bent until the electrode active material layer peels off in the folding endurance test, was subjected to a large number of 100 cycles. It was found that excellent charge recovery capacity was exhibited even after charge-discharge cycles.

By satisfying the above requirements (i) and (ii), the porous layer has a uniform and dense structure. distribution becomes uniform. Further, by satisfying the requirement (iii), even when the electrode active material expands and contracts during the process of charge-discharge cycles, the active material, the conductive agent, and the binder, which are components contained inside the electrode active material layer, are and the adhesion between the electrode active material layer and the current collector are maintained satisfactorily, and deterioration of the electrode is suppressed. As a result, the non-aqueous electrolyte secondary battery according to one embodiment of the present invention, which satisfies all of the requirements (i) to (iii), has good charge recovery capacity even after 100 cycles. can be maintained.

Since the non-aqueous electrolyte secondary battery according to one embodiment of the present invention can exhibit excellent charge recovery capacity even after many charge-discharge cycles, it is used in personal computers, mobile phones, and portable information devices. It can be suitably used as a battery for terminals and the like, as well as a vehicle battery.

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 aspect ratio of the projected image of the inorganic filler on the surface of the porous layer is in the range of 1.4 to 4.0,
Peak intensities of arbitrary mutually orthogonal diffraction planes (hkl) and (abc) of the porous layer measured by wide-angle X-ray diffraction: I _(hkl) and I _(abc) satisfy the following formula (1): ,
A non-aqueous electrolyte secondary battery, wherein the range of the maximum value of the peak intensity ratio calculated by the following formula (2) is in the range of 1.5 to 300.
I _(hkl) > I _(abc) (1)
I _(hkl) / I _(abc) (2) 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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