JP2020074276A - Manufacturing method of separator for non-aqueous electrolyte secondary battery - Google Patents

Abstract

To achieve a separator for a non-aqueous electrolyte secondary battery, in which a battery resistance increase after a charging and discharging cycle is suppressed.SOLUTION: A separator for non-aqueous electrolyte secondary battery is measured by a MIT test machine method by using a test piece having a TD of a polyolefin porous as a longitudinal direction, and the number of folding times until the length of the longitudinal direction of the test piece is changed by 2.4 cm is 1600 times or more.SELECTED DRAWING: Figure 1

Description

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

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

  As a separator in such a non-aqueous electrolyte secondary battery, for example, a porous film containing polyolefin as a main component as described in Patent Document 1 is known.

Japanese Laid-Open Patent Publication No. 11-130900 (Published May 18, 1999)

  However, in the conventional technique, the rate of increase in resistance after cycling was not sufficiently suppressed, and there was room for improvement.

  One aspect of the present invention is made in view of such problems, and an object thereof is to realize a separator for a non-aqueous electrolyte secondary battery in which an increase in battery resistance after a charge / discharge cycle is suppressed. ..

  A separator for a non-aqueous electrolyte secondary battery according to an aspect of the present invention is a separator for a non-aqueous electrolyte secondary battery including a polyolefin porous film, and is a test in which the TD of the polyolefin porous film is the longitudinal direction. The number of times of bending until the length in the longitudinal direction of the test piece changed by 2.4 cm measured by the MIT tester method specified in JIS P 8115 (1994) using the test piece was 1600 times or more.

  A separator for a non-aqueous electrolyte secondary battery according to an aspect of the present invention is a MIT tester method defined in JIS P 8115 (1994) using a test piece having the MD of the porous film as a longitudinal direction. It is preferable that the amount of change in the length of the test piece in the longitudinal direction measured after bending 5000 times per bending is 0.0004 mm / turn or more.

  A laminated separator for a non-aqueous electrolyte secondary battery according to an aspect of the present invention includes a separator for a non-aqueous electrolyte secondary battery according to an aspect of the present invention and an insulating porous layer.

  A member for a non-aqueous electrolyte secondary battery according to an aspect of the present invention, a positive electrode, a separator for a non-aqueous electrolyte secondary battery according to an aspect of the present invention, or a laminated separator for a non-aqueous electrolyte secondary battery. , And the negative electrode are arranged in this order.

  A non-aqueous electrolyte secondary battery according to an aspect of the present invention includes the separator for a non-aqueous electrolyte secondary battery according to an aspect of the present invention, or a laminated separator for a non-aqueous electrolyte secondary battery.

  According to one aspect of the present invention, it is possible to suppress an increase in battery resistance after charge / discharge cycles.

It is a schematic diagram which shows the outline of a MIT test machine. In an example, it is a mimetic diagram showing a method of performing additional stretch of the stretched film after cooling the heat-set stretched film.

  One embodiment of the present invention will be described below, but the present invention is not limited to this. The present invention is not limited to each configuration described below, various modifications are possible within the scope shown in the claims, and the technical means disclosed in different embodiments are appropriately combined. The obtained embodiments are also included in the technical scope of the present invention. Unless otherwise specified in this specification, “A to B” representing a numerical range means “A or more and B or less”.

[1. Non-aqueous electrolyte secondary battery separator]
A separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention is a separator for a non-aqueous electrolyte secondary battery including a polyolefin porous film, and the TD of the polyolefin porous film is the longitudinal direction. Using the test piece, the number of bending times until the length in the longitudinal direction of the test piece changed by 2.4 cm measured by the MIT tester method specified in JIS P 8115 (1994) is 1600 times or more. ..

  In this specification, the polyolefin porous film may be simply referred to as a porous film. Moreover, in this specification, MD (Machine Direction) of a porous film intends the conveyance direction at the time of manufacture of a porous film. The TD (Transverse Direction) of the porous film means the direction perpendicular to the MD of the porous film.

<Polyolefin porous film>
A separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention includes a polyolefin porous film, and is preferably a polyolefin porous film. The porous film has a large number of pores connected to the inside thereof, and allows gas and liquid to pass from one surface to the other surface. The porous film can be a base material for a separator for a non-aqueous electrolyte secondary battery or a laminated separator for a non-aqueous electrolyte secondary battery described later. Porous film, when the battery generates heat, by melting the non-aqueous electrolyte secondary battery separator non-porous, to give a shutdown function to the non-aqueous electrolyte secondary battery separator. obtain.

  Here, the "polyolefin porous film" is a porous film containing a polyolefin resin as a main component. In addition, the term "having a polyolefin-based resin as a main component" means that the proportion of the polyolefin-based resin in the porous film is 50% by volume or more, preferably 90% by volume or more of the entire material constituting the porous film. More preferably, it means 95% by volume or more.

  The polyolefin resin which is the main component of the porous film is not particularly limited, but examples thereof include thermoplastic resins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene and / or 1-hexene. Examples thereof include homopolymers and copolymers obtained by polymerizing monomers. That is, examples of the homopolymer include polyethylene, polypropylene and polybutene, and examples of the copolymer include ethylene-propylene copolymer. The porous film may be a layer containing these polyolefin resins alone or a layer containing two or more of these polyolefin resins. Among these, polyethylene is more preferable because it can block (shut down) an excessive current from flowing at a lower temperature, and particularly, a high-molecular-weight polyethylene mainly containing ethylene is preferable. In addition, the porous film does not prevent inclusion of components other than the polyolefin, as long as the function of the layer is not impaired.

Examples of polyethylene include low density polyethylene, high density polyethylene, linear polyethylene (ethylene-α-olefin copolymer) and ultra high molecular weight polyethylene. Among these, ultrahigh molecular weight polyethylene is more preferable, and it is further preferable that the high molecular weight component having a weight average molecular weight of 5 × 10 ⁵ to 15 × 10 ⁶ is contained. In particular, it is more preferable that the polyolefin resin contains a high molecular weight component having a weight average molecular weight of 1,000,000 or more because the strength of the porous film and the non-aqueous electrolyte secondary battery laminated separator is improved.

  The thickness of the porous film is preferably 4 to 40 μm, more preferably 5 to 20 μm. When the thickness of the porous film is 4 μm or more, internal short circuit of the battery can be sufficiently prevented, which is preferable. On the other hand, when the thickness of the porous film is 40 μm or less, it is possible to prevent the non-aqueous electrolyte secondary battery from increasing in size, which is preferable.

Fabric weight per unit area of the porous film, to be able to increase the weight energy density and volume energy density of the battery, usually, it is preferably ^{4~20g / m 2, 5~12g / m} 2 Is more preferable.

  The air permeability of the porous film is preferably 30 to 500 sec / 100 mL as a Gurley value, and more preferably 50 to 300 sec / 100 mL. As a result, the non-aqueous electrolyte secondary battery separator can obtain sufficient ion permeability.

  The porosity of the porous film is preferably 20 to 80% by volume, more preferably 30 to 75% by volume. As a result, it is possible to increase the amount of the electrolytic solution held and to reliably prevent (shut down) the flow of an excessive current at a lower temperature.

  The pore size of the pores of the porous film is preferably 0.3 μm or less, and more preferably 0.14 μm or less. As a result, sufficient ion permeability can be obtained, and entry of particles forming the electrode can be further prevented.

  The porous film has a TD strength within a specific range. This strength can be specified by the number of times of bending, which is measured by the MIT tester method defined in JIS P 8115 (1994) using a test piece having the TD of the porous film as the longitudinal direction. The number of times of bending until the length of the test piece in the longitudinal direction changes by 2.4 cm is preferably 1600 times or more, more preferably 2000 times or more, and further preferably 2500 times or more. The number of times of bending is preferably 40,000 times or less, more preferably 35,000 times or less, and further preferably 30,000 times or less.

  The number of folds reflects the ease of stretch of the porous film in TD. The fact that the number of folds is 1600 or more means that the porous film is difficult to stretch to some extent in TD. As a result, wrinkles of the separator or deformation of the internal structure are unlikely to occur, and therefore an increase in battery resistance can be suppressed.

  FIG. 1 is a schematic diagram showing an outline of an MIT tester used in the MIT tester method. The x-axis represents the horizontal direction and the y-axis represents the vertical direction. The outline of the MIT test machine method will be described below. One end of the test piece 1 in the longitudinal direction is clamped by the spring-loaded clamp 2 and the other end is clamped by the bending clamp 3 to be fixed. The spring-loaded clamp 2 is connected to the weight 4. As a result, the test piece 1 is in a state in which tension is applied in the longitudinal direction. In this state, the longitudinal direction of the test piece 1 is parallel to the vertical direction. Then, the test piece 1 is bent by rotating the bending clamp 3.

  In the measurement of the number of folds, a test piece having the TD of the porous film as the longitudinal direction is used. That is, the test piece used for measuring the number of times of bending is prepared so that the TD of the porous film is in the longitudinal direction of the test piece. In other words, in measuring the number of times of bending, the test piece is fixed so that the TD of the porous film is parallel to the vertical direction.

  Moreover, the longitudinal direction of the test piece when bent 5000 times was measured by the MIT tester method defined in JIS P 8115 (1994) using the test piece whose MD was the longitudinal direction of the porous film. It is preferable that the amount of change in the length of 1 per bending is within a specific range. Specifically, the amount of change is preferably 0.0004 mm / time or more, and more preferably 0.0005 mm / time or more. The amount of change is preferably 0.005 or less and more preferably 0.0045 or less.

  The amount of change reflects the strength of the porous film in MD. The amount of change of 0.0004 mm / time or more indicates that the porous film has some flexibility in MD. That is, the porous film has good conformability to deformation. Therefore, the positional displacement of the interface between the separator and the electrode mixture layer is unlikely to occur. Therefore, current unevenness and a gap between the electrode and the separator are unlikely to occur, and an increase in resistance at the electrode interface can be suppressed.

  In measuring the amount of change, a test piece having the MD of the porous film in the longitudinal direction is used. That is, the test piece used for measuring the amount of change is prepared so that the MD of the porous film is in the longitudinal direction of the test piece. In other words, in measuring the amount of change, the test piece is fixed so that the MD of the porous film is parallel to the vertical direction.

<Method for producing porous film>
The method for producing the porous film is not particularly limited, and examples thereof include a method of adding a pore-forming agent to a resin such as polyolefin to form a film, and then removing the pore-forming agent with an appropriate solvent.

Specifically, for example, a method of producing a porous film using a polyolefin resin containing ultrahigh molecular weight polyethylene can be mentioned. In this case, it is preferable to manufacture the porous film by the following method from the viewpoint of manufacturing cost.
(1) A step of kneading 100 parts by weight of ultrahigh molecular weight polyethylene and 100 to 500 parts by weight of a pore forming agent such as calcium carbonate or a plasticizer to obtain a polyolefin resin composition,
(2) a step of extruding the polyolefin resin composition from an extruder and molding it into a sheet while cooling, to obtain a sheet-shaped polyolefin resin composition,
(3) a step of removing the pore forming agent from the sheet obtained in the step (2),
(4) a step of stretching the sheet from which the pore forming agent has been removed in the step (3),
(5) A step of heat-setting the sheet stretched in the step (4) at a heat-setting temperature of 100 ° C. or higher and 150 ° C. or lower to obtain a porous film.
Alternatively,
(3 ′) a step of stretching the sheet obtained in the step (2),
(4 ') a step of removing the pore forming agent from the sheet stretched in the step (3'),
(5 ′) A step of heat-setting the sheet obtained in the step (4 ′) at a heat-setting temperature of 100 ° C. or higher and 150 ° C. or lower to obtain a porous film.

  Here, with respect to the obtained porous film, it is preferable to perform the operations of stretching and heat setting again (hereinafter, the above-mentioned re-stretching is referred to as additional stretching, and the above-mentioned re- heat-setting is performed. May be called additional heat fixation). Specifically, after the step (5) or (5 '), the film cooled to room temperature is heated and stretched again, and then heat-fixed. By performing such stretching, the crystallinity and crystal orientation of the porous film can be enhanced, and as a result, the resistance of the porous film to deformation in the stretching direction tends to be enhanced. Further, by subsequently heat fixing, the stress generated inside the porous film is relieved, and the effect of the stretching can be maintained. The direction of additional stretching is preferably in the TD direction, which tends to have relatively poor strength due to the manufacturing method of the porous film.

  The holding time in the additional heat setting is preferably 15 seconds to 600 seconds, more preferably 30 seconds to 300 seconds, and further preferably 45 seconds to 180 seconds. If the holding time is shorter than the above range, the internal stress generated by the additional stretching is not relaxed, and the curl and other adverse effects on the operability of the film are likely to occur. If the holding time is long, the crystallinity and the degree of crystal orientation improved by the additional stretching may be disturbed, and the strength improving effect may not be obtained.

  In addition, in the above step (1), a petroleum resin may be added as an additive to tend to obtain a porous film having excellent adaptability to deformation. For example, a polyolefin resin composition may be obtained by mixing ultra-high molecular weight polyethylene and petroleum resin, adding a plasticizer such as liquid paraffin thereto, and kneading the mixture. It is considered that the petroleum resin has a tendency to thicken the resin portion inside the porous film or to easily cause crystallization by stretching, unlike a general plasticizer in a phase separation state with a polyolefin resin. ..

  As the petroleum resin, for example, an aliphatic hydrocarbon resin polymerized from C5 petroleum fraction such as isoprene, pentene and pentadiene as a main raw material, and a C9 petroleum fraction such as indene, vinyltoluene and methylstyrene as a main raw material are polymerized. And aromatic hydrocarbon resins, copolymer resins thereof, alicyclic saturated hydrocarbon resins obtained by hydrogenating the above resins, and mixtures thereof. When the plasticizer is an aliphatic hydrocarbon compound, the petroleum resin is preferably an alicyclic saturated hydrocarbon resin.

[2. Non-aqueous electrolyte secondary battery laminated separator]
In another embodiment of the present invention, a laminated separator for a non-aqueous electrolyte secondary battery including the above-mentioned separator for a non-aqueous electrolyte secondary battery and an insulating porous layer may be used as the separator. Since the porous film is as described above, the insulating porous layer will be described here. In the following, the insulating porous layer will also be simply referred to as “porous layer”.

<Insulating porous layer>
The porous layer is usually a resin layer containing a resin, and is preferably a heat resistant layer or an adhesive layer. The resin that constitutes the porous layer preferably has the function required for the porous layer, is insoluble in the electrolytic solution of the battery, and is electrochemically stable in the range of use of the battery.

  The porous layer is laminated on one side or both sides of the separator for a non-aqueous electrolyte secondary battery, if necessary. When the porous layer is laminated on one surface of the porous film, the porous layer is preferably laminated on the surface of the porous film facing the positive electrode in the non-aqueous electrolyte secondary battery. More preferably, it is laminated on the surface in contact with the positive electrode.

  Examples of the resin forming the porous layer include polyolefin; (meth) acrylate resin; fluorine-containing resin; polyamide resin; polyimide resin; polyester resin; rubbers; melting point or glass transition temperature of 180 ° C. or higher. Resin; water-soluble polymers and the like can be mentioned.

  Among the above resins, polyolefin, acrylate resin, fluorine-containing resin, polyamide resin, polyester resin and water-soluble polymer are preferable. As the polyamide resin, wholly aromatic polyamide (aramid resin) is preferable. As the polyester resin, polyarylate and liquid crystal polyester are preferable.

  The porous layer may include fine particles. The fine particles in the present specification are organic fine particles or inorganic fine particles generally called filler. Therefore, when the porous layer contains fine particles, the above-mentioned resin contained in the porous layer has a function as a binder resin for binding the fine particles to each other and the fine particles to the porous film. The fine particles are preferably insulating fine particles.

  Examples of the organic fine particles contained in the porous layer include fine particles made of a resin.

  As the inorganic fine particles contained in the porous layer, specifically, for example, calcium carbonate, talc, clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, Examples of the filler include inorganic substances such as aluminum hydroxide, boehmite, magnesium hydroxide, calcium oxide, magnesium oxide, titanium oxide, titanium nitride, alumina (aluminum oxide), aluminum nitride, mica, zeolite and glass. These inorganic fine particles are insulating fine particles. The fine particles may be used alone or in combination of two or more.

  Of the above fine particles, fine particles made of an inorganic material are preferable, and fine particles made of an inorganic oxide such as silica, calcium oxide, magnesium oxide, titanium oxide, alumina, mica, zeolite, aluminum hydroxide, or boehmite are more preferable, and silica. Further, at least one kind of fine particles selected from the group consisting of magnesium oxide, titanium oxide, aluminum hydroxide, boehmite and alumina is more preferable, and alumina is particularly preferable.

  The content of the fine particles in the porous layer is preferably 1 to 99% by volume of the porous layer, and more preferably 5 to 95% by volume. By setting the content of the fine particles within the above range, the voids formed by the contact between the fine particles are less likely to be blocked by the resin or the like. Therefore, sufficient ion permeability can be obtained, and the weight per unit area can be set to an appropriate value.

  As the fine particles, particles or two or more kinds having different specific surface areas may be used in combination.

  The thickness of the porous layer is preferably 0.5 to 15 μm, and more preferably 2 to 10 μm, per one side of the laminated separator for non-aqueous electrolyte secondary batteries.

  If the thickness of the porous layer is less than 1 μm, it may not be possible to sufficiently prevent an internal short circuit due to damage to the battery or the like. In addition, the amount of the electrolytic solution retained in the porous layer may decrease. On the other hand, when the total thickness of the porous layer exceeds 30 μm on both sides, rate characteristics or cycle characteristics may deteriorate.

Weight per unit area of the porous layer having a basis weight (per one side) is preferably from 1 to 20 g / ^{m 2,} and more preferably 4~10g / ^{m 2.}

The volume of the porous layer constituents contained per square meter porous layer (per one side) is preferably 0.5～20Cm ^3, more preferably 1 to 10 cm ^3,. 2 to More preferably, it is 7 cm ³ .

  The porosity of the porous layer is preferably 20 to 90% by volume, and more preferably 30 to 80% by volume so that sufficient ion permeability can be obtained. The pore size of the pores of the porous layer is preferably 3 μm or less, and preferably 1 μm or less so that the laminated separator for a non-aqueous electrolyte secondary battery can obtain sufficient ion permeability. Is more preferable.

  The thickness of the laminated separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention is preferably 5.5 μm to 45 μm, and more preferably 6 μm to 25 μm.

  The air permeability of the laminated separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention is preferably 30 to 1000 sec / 100 mL in Gurley value, and more preferably 50 to 800 sec / 100 mL.

<Method for producing porous layer>
Examples of the method for producing the porous layer include a method in which the coating liquid described below is applied to the surface of the above-mentioned porous film and dried to precipitate the porous layer.

  The coating liquid used in the method for producing the porous layer can be usually prepared by dissolving the resin in a solvent and dispersing the fine particles. Here, the solvent that dissolves the resin also serves as a dispersion medium that disperses the fine particles. Further, the resin may be made into an emulsion with a solvent.

  The solvent is not particularly limited as long as it does not adversely affect the porous film, can dissolve the resin uniformly and stably, and can disperse the fine particles uniformly and stably. Specific examples of the solvent include water and organic solvents. The solvent may be used alone or in combination of two or more.

  The coating liquid may be formed by any method as long as the conditions such as the resin solid content (resin concentration) or the amount of fine particles necessary for obtaining the desired porous layer can be satisfied. Specific examples of the method for forming the coating liquid include a mechanical stirring method, an ultrasonic dispersion method, a high pressure dispersion method, and a media dispersion method. Further, the coating liquid may contain additives such as a dispersant, a plasticizer, a surfactant and a pH adjuster as a component other than the resin and the fine particles as long as the object of the present invention is not impaired. ..

  The method for applying the coating liquid to the porous film, that is, the method for forming the porous layer on the surface of the polyolefin porous film is not particularly limited. If necessary, a porous layer may be formed on the surface of the porous film that has been subjected to a hydrophilic treatment.

  The method for forming the porous layer is, for example, a method in which the coating liquid is directly applied to the surface of the porous film and then the solvent (dispersion medium) is removed; the coating liquid is applied to an appropriate support and the solvent ( (Dispersion medium) is removed to form a porous layer, the porous layer and the porous film are pressure-bonded, and then the support is peeled off; the coating liquid is applied to an appropriate support, and then the coated surface A method in which a porous film is pressure-bonded to the above, then the support is peeled off, and then the solvent (dispersion medium) is removed, and the like.

  As a method of applying the coating liquid, a conventionally known method can be adopted, and examples thereof include a gravure coater method, a dip coater method, a bar coater method and a die coater method.

  The solvent is usually removed by drying. Further, the solvent contained in the coating liquid may be replaced with another solvent before drying.

[3. Non-aqueous electrolyte secondary battery member]
Non-aqueous electrolyte secondary battery member according to an embodiment of the present invention, the positive electrode, the above-mentioned non-aqueous electrolyte secondary battery separator or non-aqueous electrolyte secondary battery laminated separator, and the negative electrode is this. It is a member for a non-aqueous electrolyte secondary battery that is arranged in order.

<Positive electrode>
The positive electrode is not particularly limited as long as it is generally used as a positive electrode of a non-aqueous electrolyte secondary battery. For example, an active material layer containing a positive electrode active material and a binder resin is formed on a current collector. A positive electrode sheet having a structure can be used. The active material layer may further contain a conductive agent and / or a binder.

  Examples of the positive electrode active material include materials that can be doped with lithium ions and dedoped. Specific examples of the material include a lithium composite oxide containing at least one transition metal such as V, Mn, Fe, Co, and Ni.

  Examples of the conductive agent include natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and carbonaceous materials such as organic polymer compound fired bodies. The conductive material may be used alone or in combination of two or more.

  Examples of the binder include fluororesin such as polyvinylidene fluoride, acrylic resin, and styrene-butadiene rubber. 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 easily processed into a thin film and is inexpensive.

  The sheet-shaped positive electrode may be produced, for example, by pressure-molding a positive electrode active material, a conductive material and a binder on a positive electrode current collector; using a suitable organic solvent, the positive electrode active material, the conductive material and the binder. Examples include a method of forming the paste into a paste, coating the paste on the positive electrode current collector, drying it, and then applying pressure to fix it to the positive electrode current collector.

<Negative electrode>
The negative electrode is not particularly limited as long as it is generally used as a negative electrode of a non-aqueous electrolyte secondary battery. For example, an active material layer containing a negative electrode active material and a binder resin is formed on a current collector. A negative electrode sheet having a structure can be used. The active material layer may further contain a conductive additive.

  Examples of the negative electrode active material include materials that can be doped / dedoped with lithium ions, lithium metal, lithium alloys, and the like. Examples of the material include carbonaceous materials. Examples of the carbonaceous material include natural graphite, artificial graphite, cokes, carbon black and pyrolytic carbons.

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

  As a method for producing a sheet-shaped negative electrode, for example, a method in which the negative electrode active material is pressure-molded on a negative electrode current collector; the negative electrode active material is made into a paste using an appropriate organic solvent, and the paste is then collected. Examples thereof include a method in which the negative electrode current collector is adhered to the negative electrode current collector by applying it to the current collector, drying it and then applying pressure.

  The paste preferably contains the conductive additive and the binder.

  As a method for manufacturing a member for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, for example, the positive electrode, the separator for a non-aqueous electrolyte secondary battery or a laminate for a non-aqueous electrolyte secondary battery described above. A method of arranging the separator and the negative electrode in this order may be mentioned. The method for manufacturing the non-aqueous electrolyte secondary battery member is not particularly limited, and a conventionally known manufacturing method can be adopted.

[4. Non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery according to an embodiment of the present invention includes the separator for a non-aqueous electrolyte secondary battery or the laminated separator for a non-aqueous electrolyte secondary battery described above.

  The manufacturing method of the non-aqueous electrolyte secondary battery is not particularly limited, and a conventionally known manufacturing method can be adopted. For example, after forming the non-aqueous electrolyte secondary battery member by the above-described method, the non-aqueous electrolyte secondary battery member is placed in a container that serves as a casing of the non-aqueous electrolyte secondary battery. Next, after filling the inside of the container with the non-aqueous electrolyte, the container is sealed while being decompressed, whereby the non-aqueous electrolyte secondary battery according to an embodiment of the present invention can be manufactured.

<Non-aqueous electrolyte>
The non-aqueous electrolytic solution is not particularly limited as long as it is a non-aqueous electrolytic solution generally used in a non-aqueous electrolytic solution secondary battery, and for example, a non-aqueous electrolytic solution obtained by dissolving a lithium salt in an organic solvent is used. You can Examples of the lithium salt 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 salt, LiAlCl _{4 and the} like. The lithium salt may be used alone or in combination of two or more kinds.

  Examples of the organic solvent that constitutes the non-aqueous electrolyte include carbonates, ethers, esters, nitriles, amides, carbamates and sulfur-containing compounds, and fluorine-containing compounds introduced into these organic solvents. Fluorine organic solvents and the like can be mentioned. The organic solvent may be used alone or in combination of two or more.

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

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

[Measurement]
In the following examples and comparative examples, the number of bendings and the amount of change by the MIT tester method, and the 1 kHz resistance increase rate were measured by the following methods.

<Measurement of strength by MIT tester method>
The porous film was cut out so that MD or TD was in the longitudinal direction to prepare a test piece having a length of 105 mm and a width of 15 mm. That is, a test piece having a porous film having an MD length of 105 mm and a TD length of 15 mm and a test piece having a porous film having a TD length of 105 mm and an MD length of 15 mm were prepared. .. The MIT test machine method was performed using this test piece.

  The MIT tester method uses a MIT folding endurance tester (manufactured by Yasuda Seiki), and according to JIS P 8115 (1994), load: 6N, bending part R: 0.38 mm, bending speed 175 reciprocations / min, and test One end of the piece was fixed and bent to the left and right at an angle of 135 degrees.

  Thereby, the number of times of bending until the length in the longitudinal direction of the test piece having the TD of the porous film as the longitudinal direction was deformed by 2.4 cm was measured. The number of times of bending here is the number of times of reciprocal bending displayed on the counter of the MIT folding endurance tester. Regarding the amount of change (mm / time) in the longitudinal direction of the test piece with the MD of the porous film as the longitudinal direction, the test piece when the number of folds reached 5000 It was calculated from the change amount (mm) of the length in the longitudinal direction.

<1 kHz resistance increase rate>
(1) Initial Charge / Discharge Test Using a separator for a non-aqueous electrolyte secondary battery manufactured in Examples and Comparative Examples, a new non-aqueous electrolyte secondary battery that has not been subjected to a charge / discharge cycle is subjected to an initial test. It was charged and discharged. Specifically, at 25 ° C, voltage range: 4.1 to 2.7V, current value: 0.2C (1C is the current value for discharging the rated capacity according to the discharge capacity of 1 hour rate, The same) was set as one cycle and four cycles of initial charge and discharge were performed.

(2) Initial 1 kHz AC resistance measurement After the above initial charge / discharge test, a voltage was applied to the non-aqueous electrolyte secondary battery at room temperature of 25 ° C. by an LCR meter (trade name: Chemical Impedance Meter, model 3532-80) manufactured by Hioki Electric Co., Ltd. An amplitude of 10 mV was applied and a Nyquist plot was calculated. As the resistance value after the initial charge / discharge test, the resistance value of the real part at the measurement frequency of 1 kHz was read. Hereinafter, the resistance value is referred to as “initial 1 kHz resistance value”.

(3) Cycle test Subsequently, at 55 ° C, 100 cycles of charging / discharging were performed, with charging / discharging performed at a constant current of charging current value: 1 C and discharging current value: 10 C as one cycle.

(4) 1 kHz AC resistance measurement after cycle test In the same manner as (2), the resistance value of the real part at the measurement frequency of 1 kHz after 100 cycles was read. Hereinafter, the resistance value is referred to as a “1 kHz resistance value after the cycle test”.

(5) 1 kHz resistance increase rate after 100 cycles of charge / discharge (1 kHz resistance value after cycle test / initial 1 kHz resistance value) × 100 was calculated as a 1 kHz resistance increase rate (%) after 100 cycles of charge / discharge.

[Manufacture of separator for non-aqueous electrolyte secondary battery]
<Comparative Example 1>
A commercially available polyethylene porous film (1) (thickness: 16.2 μm, basis weight: 10.0 g / m ² ) was used as a separator (5) for a non-aqueous electrolyte secondary battery.

<Comparative example 2>
68 wt% of ultra-high molecular weight polyethylene powder (GUR2024, manufactured by Ticona) and 32 wt% of polyethylene wax having a weight average molecular weight of 1000 (FNP-0115, manufactured by Nippon Seiro Co., Ltd.) were prepared. 0.4 parts by weight of an antioxidant (Irg1010, manufactured by Ciba Specialty Chemicals Co., Ltd.), (P168, manufactured by Ciba Specialty Chemicals Co., Ltd.) as a total of 100 parts by weight of the ultra high molecular weight polyethylene and polyethylene wax. 1 part by weight and 1.3 parts by weight of sodium stearate were added. Further, calcium carbonate (manufactured by Maruo Calcium Co., Ltd.) having an average particle diameter of 0.1 μm was added so as to be 38% by volume based on the total volume of the obtained mixture. These powders were mixed as powders with a Henschel mixer, and then melt-kneaded with a biaxial kneader to obtain a polyolefin resin composition.

  The polyolefin resin composition was rolled with a pair of rolls having a surface temperature of 150 ° C to prepare a sheet. Calcium carbonate was removed by immersing this sheet in an aqueous hydrochloric acid solution (hydrochloric acid 4 mol / L, nonionic surfactant 0.5% by weight). Then, the film was stretched 6.2 times at 105 ° C. to obtain a film having a thickness of 10.9 μm. Further, the polyethylene porous film (2) obtained by heat setting treatment at 126 ° C. was used as a separator (6) for a non-aqueous electrolyte secondary battery.

<Comparative example 3>
20% by weight of ultra-high molecular weight polyethylene powder (Hi-Zex Million 145M, manufactured by Mitsui Chemicals, Inc.) was prepared. This powder was melt-kneaded by adding it to a biaxial kneader from a quantitative feeder. At this time, 80% by weight of liquid paraffin was added to the twin-screw kneader with a pump while pressurizing, and melted and kneaded together. Then, a polyolefin resin composition was produced by extruding from a T die through a gear pump.

  The polyolefin resin composition was cooled with a cooling roll, and then simultaneously stretched 6 times in the MD and TD directions at 118 ° C. Liquid paraffin was removed by immersing the stretched sheet-shaped polyolefin resin composition in heptane. After drying at room temperature, heat setting was performed in an oven at 120 ° C. for 1 minute to obtain a polyethylene porous film (3) having a thickness of 14.2 μm. The obtained polyethylene porous film (3) was used as a separator (7) for a non-aqueous electrolyte secondary battery.

<Example 1>
The polyethylene porous film (2) obtained in Comparative Example 2 was cut into a size of MD: 10.8 cm × TD: 13 cm. The porous film was fixed to a SUS jig having a 15 cm × 15 cm frame as shown in FIG. 2 so as to allow additional stretching in the TD direction. With a small tabletop tester (EZ-L) manufactured by Shimadzu Co., which has a thermostat, the temperature inside the thermostat was 85 ° C., the stretching speed was 5 mm / min, and the original length of the porous film was 1. Additional stretching was performed so as to be 02 times. The polyethylene porous film (4) was obtained by heat setting as it was for 1 minute in a constant temperature bath. The obtained polyethylene porous film (4) was used as a separator (1) for a non-aqueous electrolyte secondary battery.

<Example 2>
Ultra-high molecular weight polyethylene powder (Hi-Zex Million 145M, manufactured by Mitsui Chemicals, Inc.) 18% by weight and petroleum resin (indene, vinyltoluene and methylstyrene as a main raw material and polymerized from an alicyclic saturated hydrocarbon resin with a softening point of 115 ° C) 2% by weight was prepared. These powders were crushed and mixed with a blender until the powders had the same particle size. Then, the obtained mixed powder was melt-kneaded by adding it to a biaxial kneader from a quantitative feeder. At this time, 80% by weight of liquid paraffin was added to the twin-screw kneader with a pump while pressurizing, and melted and kneaded together. Then, a polyolefin resin composition was produced by extruding from a T die through a gear pump.

  The polyolefin resin composition was cooled with a cooling roll, and then stretched at 117 ° C. in the MD direction by 6.43 times. Subsequently, the film was stretched 6 times in the TD direction at 117 ° C.

  Liquid paraffin was removed by immersing the stretched sheet-shaped polyolefin resin composition in heptane. The polyolefin resin composition was dried at room temperature and then heat set in an oven at 120 ° C. for 1 minute to obtain a polyethylene porous film (5) having a thickness of 19.7 μm. The obtained polyethylene porous film (5) was used as a separator (2) for a non-aqueous electrolyte secondary battery.

<Example 3>
The same commercially available polyethylene porous film (1) as in Comparative Example 1 (thickness 16.2 μm, basis weight 10.0 g / m ² ) was cut into a size of MD: 10.8 cm × TD: 13 cm. The separator was fixed to a SUS jig having a 15 cm × 15 cm frame as shown in FIG. 2 so that it could be additionally stretched in the TD direction. A small tabletop tester (EZ-L) manufactured by Shimadzu Co., which has a thermostatic chamber installed, has an internal temperature of 85 ° C and a stretching speed of 5 mm / min, and is 1.15 times the original length of the separator. Was additionally stretched. The polyethylene porous film (6) was obtained by heat setting as it was for 1 minute in a constant temperature bath. The obtained polyethylene porous film (6) was used as a separator (3) for a non-aqueous electrolyte secondary battery.

<Example 4>
The same commercially available polyethylene porous film (1) as in Comparative Example 1 (thickness 16.2 μm, basis weight 10.0 g / m ² ) was cut into a size of MD: 10.8 cm × TD: 13 cm. The separator was fixed to a SUS jig having a 15 cm × 15 cm frame as shown in FIG. 2 so that additional stretching in the TD direction was possible. With a small tabletop tester (EZ-L) manufactured by Shimadzu Co., which has a thermostat, the temperature inside the thermostat is 85 ° C., the stretching speed is 5 mm / min, and the separator is 1.3 times the original length. Was additionally stretched. The polyethylene porous film (7) was obtained by heat setting as it was for 1 minute in a constant temperature bath. The obtained film was used as a separator (4) for a non-aqueous electrolyte secondary electrolyte battery.

[Preparation of non-aqueous electrolyte secondary battery]
Next, a nonaqueous electrolyte secondary battery was produced as follows using each of the separators for nonaqueous electrolyte secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 3 produced as described above.

<Positive electrode>
A commercially available positive electrode manufactured by applying LiNi _0.5 Mn _0.3 Co _0.2 O ₂ / conductive material / PVDF (weight ratio 92/5/3) to an aluminum foil was used. The positive electrode was cut with an aluminum foil so that the size of the part where the positive electrode active material layer was formed was 45 mm × 30 mm and the part where the positive electrode active material layer was not formed had a width of 13 mm on the outer periphery. Using. The thickness of the positive electrode active material layer was 58 μm, the density was 2.50 g / cm ³ , and the positive electrode capacity was 174 mAh / g.

<Negative electrode>
A commercially available negative electrode manufactured by applying graphite / styrene-1,3-butadiene copolymer / sodium carboxymethyl cellulose (weight ratio 98/1/1) to a copper foil was used. A copper foil was cut off from the negative electrode so that the size of the part where the negative electrode active material layer was formed was 50 mm × 35 mm, and the part where the width was 13 mm and the negative electrode active material layer was not formed remained on the outer periphery. Using. The negative electrode active material layer had a thickness of 49 μm, a density of 1.40 g / cm ³ , and a negative electrode capacity of 372 mAh / g.

<Assembly>
A member for a non-aqueous electrolyte secondary battery by stacking (arranging) a positive electrode, a separator for a non-aqueous electrolyte secondary battery with a porous layer facing the positive electrode side, and a negative electrode in this order in a laminate pouch. Got At this time, the positive electrode and the negative electrode were arranged such that the entire main surface of the positive electrode active material layer of the positive electrode was included in (covered with) the main surface of the negative electrode active material layer of the negative electrode.

Then, the non-aqueous electrolyte secondary battery member was placed in a bag in which an aluminum layer and a heat seal layer were laminated, and 0.25 mL of the non-aqueous electrolyte solution was placed in this bag. The non-aqueous electrolyte is a 25 ° C. electrolyte prepared by dissolving LiPF ₆ at a concentration of 1.0 mol / liter in a mixed solvent having a volume ratio of ethyl methyl carbonate, diethyl carbonate and ethylene carbonate of 50:20:30. Was used. Then, the inside of the bag was depressurized and the bag was heat-sealed to manufacture a non-aqueous electrolyte secondary battery. The design capacity of the non-aqueous electrolyte secondary battery was 20.5 mAh.

〔Measurement result〕
The measurement results are shown in Table 1.

  In the MIT tester method using the test piece having the TD of the porous film as the longitudinal direction, the number of foldings is less than 1600 times until the length of the test piece in the longitudinal direction changes by 2.4 cm. No. 3 had a 1 kHz resistance increase rate of 400% or more after 100 cycles of charge and discharge.

  In addition, in the MIT tester method using a test piece having the MD of the porous film in the longitudinal direction, the amount of change in the length of the test piece in the longitudinal direction when bent 5000 times was 0.1. Comparative Example 2 having less than 0004 mm / times has an increase rate of 1 kHz resistance of 100% or more after 100 cycles of charging / discharging, and is not excellent in the rate of increase of 1 kHz resistance after 100 cycles of charging / discharging as compared with Comparative Examples 1 and 3. It was a result.

  On the other hand, in the MIT tester method using a test piece having the TD of the porous film as the longitudinal direction, an example in which the number of folds is 1600 times or more until the length of the test piece in the longitudinal direction changes by 2.4 cm In Nos. 1 to 4, the 1 kHz resistance increase rate after 100 cycles of charging and discharging was less than 350%. As described above, it was confirmed that Examples 1 to 4 could suppress the 1 kHz resistance increase rate after 100 cycles of charging and discharging. In addition, in Examples 1 to 4, in the MIT test machine method using the test piece having the MD of the porous film as the longitudinal direction, the length of the test piece in the longitudinal direction when bent 5000 times was bent once. The amount of change per unit was 0.0004 mm / time or more.

  The separator for a non-aqueous electrolyte secondary battery and the laminated separator for a non-aqueous electrolyte secondary battery of the present invention can be suitably used for manufacturing a non-aqueous electrolyte secondary battery in which the rate of increase in battery resistance is suppressed. ..

1 Test piece 2 Spring load clamp 3 Bending clamp 4 Weight

Claims (5)

A method for producing a separator for a non-aqueous electrolyte secondary battery containing a polyolefin porous film,
(A) a step of stretching a sheet containing a polyolefin resin,
(B) heat-setting the sheet stretched in step (a) at a heat-setting temperature of 100 ° C. or higher and 150 ° C. or lower to obtain a polyolefin porous film, and
(C) After the step (b), the polyolefin porous film is heated and stretched again, and then heat-fixed,
Including,
Using the test piece having the TD of the separator for a non-aqueous electrolyte secondary battery in the longitudinal direction, the length in the longitudinal direction of the test piece measured by the MIT tester method defined in JIS P 8115 (1994). The method for producing a separator for a non-aqueous electrolyte secondary battery, wherein the number of foldings is 1600 times or more before the change of 2.4 cm.   Using the test piece having the MD of the separator for the non-aqueous electrolyte secondary battery in the longitudinal direction, the test in the case of bending 5000 times measured by the MIT tester method defined in JIS P 8115 (1994) The method for producing a separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the amount of change in the length of the piece in the longitudinal direction per bending is 0.0004 mm / turn or more.   The method for manufacturing a separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the stretching direction in the step (c) is the TD direction.   The process of apply | coating the coating liquid containing resin to the separator for nonaqueous electrolyte secondary batteries obtained by the manufacturing method of the separator for nonaqueous electrolyte secondary batteries of any one of Claims 1-3. A method for producing a laminated separator for a non-aqueous electrolyte secondary battery, comprising:   The method for producing a laminated separator for a non-aqueous electrolyte secondary battery according to claim 4, wherein the resin contains a polyamide resin.

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