KR20210104054A - Manufacturing method of porous layer, laminate, separator for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

An object of the present invention is to produce a porous layer having excellent film thickness precision. The method for producing a porous layer according to the present invention comprises a step of applying a coating solution containing a non-conductive solvent and particles through a coating device and a substrate to apply the coating on the surface of the substrate; from which the coating construction solution, and a step of removing the solvent of the non-conductive, and the potential difference applied to the construction equipment and the base material at the time that the coating installation fluid passing between the coating installation device and substrate 1.0 × 10 ⁵ V / more than m.

Description

Manufacturing method of porous layer, laminate, separator for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery

The present invention relates to a method for producing a porous layer, and to a laminate, a separator for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery comprising the porous layer produced by the production method.

Non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, have high energy density, so they are widely used as batteries used in personal computers, mobile phones, portable information terminals, and the like, and in recent years, development as batteries for in-vehicle use is progressing.

With the expansion of the energy density or capacity of a lithium ion secondary battery, the mechanism which has higher safety|security is calculated|required. For example, a multilayer porous film (Patent Documents 1 to 4, 6) in which a heat-resistant porous layer containing a metal oxide and a resin binder is coated on a separator that separates the electrodes, and a metal oxide and a resin on the electrode A non-aqueous electrolyte secondary battery including a laminate in which a porous layer containing a binder is coated has been proposed or put into practical use (Patent Document 5).

Moreover, in recent years, for the purpose of further energy density expansion or capacity expansion of a lithium ion secondary battery, thin film formation of members, such as a collector plate of a separator and an electrode, is progressing. For example, the conventional separator has a thickness of about several tens of mu m, as represented by Celgard (registered trademark) #2500 having a film thickness of 25 mu m. However, in recent years, thin film separators having a thickness of 10 µm or less have been used in battery applications for consumer use such as portable information terminals. Thereby, the request|requirement with respect to the thickness precision of porous bodies, such as a separator provided between electrodes, and an electrode coating layer, has also improved.

Specification of Japanese Patent No. 6309661 International Publication No. 2017/047576 pamphlet Japanese Patent Laid-Open No. 2018-063943 Japanese Patent No. 4792688 Specification Japanese Patent Laid-Open No. 2010-244818 Japanese Patent No. 6017446 Specification Japanese Patent Laid-Open No. 2008-179903 Japanese Patent No. 6249589 Specification

As a separator containing a polyolefin porous film, the separator which has a small fluctuation|variation in a film thickness and has high film-thickness precision with development of a manufacturing method is manufactured. On the other hand, in a coating-type separator, that is, a laminated separator, in which a polyolefin porous film is used as a substrate and a porous layer containing metal oxide particles is coated on the substrate, the film thickness accuracy thereof is higher than that of the polyolefin porous film as the substrate. Since it falls, the film thickness precision had room for improvement.

As a conventional technique, in the process of forming a porous layer, a low-viscosity coating liquid is coated on a base material, and the method of forming a smooth coating layer by leveling the coating liquid after coating is known. For example, Patent Documents 7 and 8 disclose a battery separator with a small variation in the film thickness of the heat-resistant layer, manufactured using the above conventional technique.

However, in the above prior art, slight wrinkles of the substrate during coating were caused, and it was difficult to control the film thickness in the order of micrometers or less. For example, the film thickness precision of the coating type separator obtained by the conventional manufacturing method has a standard dispersion, ie, a value of the standard deviation of the film thickness of 1 µm or more, and there is room for improvement.

That is, an object of the present invention is to form a laminate in which a porous layer is laminated on a substrate between the positive electrodes of a nonaqueous electrolyte secondary battery, that is, a laminate separator, to produce a laminate including a porous layer with high film thickness precision. to provide a way

As a result of repeated research in consideration of the foregoing, the present inventors have developed a porous layer with high thickness precision by using the electrorheology effect in the process of applying a coating solution on a substrate to form a porous layer. found to be able to form.

The present invention is an invention based on the above findings, and includes the inventions shown in [1] to [7] below.

[1] a step of applying a coating liquid containing a non-conductive solvent and particles to the surface of the substrate by passing between the coating apparatus and the substrate;

a step of removing the non-conductive solvent from the coating solution applied to the surface of the substrate;

The method for producing a porous layer, wherein the electric field strength between the coating device and the substrate when the coating liquid passes between the coating device and the substrate is 1.0×10 ^{5 V/m or more.}

[2] The period between after the step of applying the coating solution to the surface of the substrate and before the step of removing the non-conductive solvent,

The method for producing a porous layer according to [1], wherein the coating liquid is leveled.

[3] The method for producing a porous layer according to [1] or [2], wherein the coating solution contains a resin.

[4] The method for producing a porous layer according to [3], wherein the resin contains an aromatic polyamide.

[5] A laminate comprising a substrate and a porous layer containing particles laminated on at least one surface of the substrate,

The standard deviation of the film thickness of the said laminated body is 0.5 micrometer or less.

[6] The laminate according to [5], wherein the laminate has a film thickness of 15.0 µm or less.

[7] The laminate according to [5] or [6], wherein the porous layer contains a resin.

[8] The laminate according to [7], wherein the resin contains an aromatic polyamide.

[9] A separator for a non-aqueous electrolyte secondary battery comprising the laminate according to any one of [5] to [8].

[10] A non-aqueous electrolyte secondary battery comprising the separator for a non-aqueous electrolyte secondary battery according to [9].

According to the manufacturing method of the porous layer which concerns on one Embodiment of this invention, the porous layer excellent in film thickness precision can be manufactured.

The laminate according to one embodiment of the present invention can improve the battery performance of a non-aqueous electrolyte secondary battery including the laminate as a separator for a non-aqueous electrolyte secondary battery or a member thereof.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the aspect of the coating method in one Embodiment of this invention.

One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, various modifications are possible within the scope shown in the claims, and the technical means of the present invention are also described in the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. included in the scope. In addition, unless otherwise specified in this specification, "A to B" which shows a numerical range means "A or more and B or less."

[Embodiment 1: Manufacturing method of porous layer]

The manufacturing method of the porous layer according to Embodiment 1 of the present invention includes a step of applying a coating liquid containing a non-conductive solvent and particles to a surface of a substrate by passing a coating solution containing a non-conductive solvent and particles through a coating apparatus and a substrate; and removing the non-conductive solvent from the coating solution applied to the surface, wherein the electric field strength between the coating device and the substrate when the coating solution passes between the coating device and the substrate is 1.0×10 ⁵ V/m or more.

Further, in one embodiment of the present invention, the non-conductive solvent may be a dispersion solvent for dispersing particles to be described later, or a solvent for dissolving a resin to be described later. In addition, in one embodiment of the present invention, the coating solution may be a dispersion in which particles to be described later are dispersed, or a solution in which a resin to be described later is dissolved. Therefore, in this specification, the said coating liquid is also called "dispersion liquid" or "solution", and the said non-conductive solvent is also called "dispersion solvent" or "solvent".

<Electrorheology effect (ER effect)>

The ER effect is an effect of increasing the viscosity of the dispersion by applying an electric field to a dispersion, which is a system in which particles are dispersed in an insulating solvent, and then recovering the original fluidity by removing the applied electric field. That is, the dispersion liquid increases in viscosity by application of an electric field, and decreases in viscosity by removing the electric field (Reference Document 1: WM Winslow: J. Appl. Phys. 20, 1137 (1949), Reference Document 2: Surface Chemistry) , 22, 2-8 (2001)).

In the ER effect, the yield stress when shear is applied to the dispersion is expressed by the following formula (1).

In Formula (1), σ represents the yield stress when shear is applied to the dispersion. φ represents the volume fraction of particles in the dispersion. ε ₀ represents the permittivity of vacuum. ε _p represents the dielectric constant of the solvent in the dispersion. ε _c represents the dielectric constant of the particle. E represents the electric field strength applied to the dispersion.

Here, the large yield stress indicates that the viscosity of the dispersion is more greatly improved by the ER effect. That is, it is suggested that the viscosity of the dispersion liquid at the moment of application of the electric field to the dispersion liquid is proportional to the square of the applied electric field strength, and increases as the difference in permittivity between the solvent and the dispersion solvent increases.

Therefore, in the method for producing a porous layer according to an embodiment of the present invention, in the step of applying a coating liquid to be described later on a substrate, at the moment of coating, an electric field is applied between the coating apparatus and the substrate. Increase the viscosity of the coating solution. Thereby, the influence of slight wrinkles, etc. resulting from sagging, flapping, etc. of the said base material can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the aspect of the coating method in one Embodiment of this invention. In the conventional coating method, the gap (clearance) between the coating apparatus 1 and the base material 3 cannot be kept constant under the influence of slight wrinkles of the base material 3, etc. Therefore, the film thickness precision of the coating layer containing the coating liquid 2 which was coated falls, as a result, the film thickness precision of the porous layer obtained by removing a solvent from the said coating layer falls. In particular, when the base material is thin, slight wrinkles caused by sagging and fluttering of the base material are likely to occur, so that the precision of the film thickness of the porous layer tends to decrease. On the other hand, in the coating method according to the embodiment of the present invention, since the viscosity of the coating solution increases due to the ER effect at the moment of coating, the coating is stable and the influence of slight wrinkles on the substrate is reduced. can be alleviated As a result, the film thickness precision of the above-mentioned coating layer 2 improves, and the film thickness precision of the porous layer to be manufactured can be improved.

Further, in one embodiment of the present invention, in the period between after the step of applying the coating solution to the surface of the substrate and before the step of removing the non-conductive solvent, the coating solution is leveled. it is preferable Here, after the step of applying the coating solution to the surface of the substrate, the electric field applied to the coating solution is dissolved. Accordingly, the viscosity of the coating solution is lowered to the same extent as before the application of the electric field. As a result, it is considered that the coating liquid is leveled. By this leveling, the film thickness of the coating layer containing the coating liquid applied becomes more uniform, and the film thickness precision of the porous layer obtained can further be improved.

<Applying construction process>

The process of applying the coating liquid containing a non-conductive solvent and particle|grains to the surface of a base material by passing between a coating apparatus and a base material is also called "coating process". The method for applying the coating solution to the porous substrate is not particularly limited, and, for example, known coating methods such as a knife, blade, bar, gravure, and die can be used. Since the electric field is uniformly applied, coating by a bar, gravure or die is preferable, and among them, coating by a bar is particularly preferable from the point of easy installation.

A coating apparatus is a member which contacts a base material through a coating liquid in the said coating method, and applies the said coating liquid to the surface of the said base material. As for the said coating apparatus, the coating apparatus used by the said coating method, such as a knife, a blade, a coating bar, a die, and a gravure roll, is mentioned, for example.

In the present specification, "when passing the coating liquid through between the coating apparatus and the base material" means in the step of applying the coating liquid to the surface of the substrate, both of the coating apparatus and the substrate are coated It means the moment at which the coating liquid is actually applied onto the substrate by contact with the liquid. Therefore, in one Embodiment of this invention, an electric field is applied only to the part which overlaps the coating apparatus 1 among the coating liquid 2 in FIG. 1 at the moment of coating.

The electric field strength between the coating apparatus and the base material is expressed by the following formula (2).

E (unit: V/m) in the formula (2) is the electric field strength between the coating device and the substrate when the coating liquid in the embodiment of the present invention passes between the coating device and the substrate indicates E ₁ (unit: V) represents the potential of the coating device. E ₂ (unit: V) represents the potential on the surface of the substrate. d (unit: m) represents the distance between the coater and the base material at the time of application. This distance is also called "clearance".

^{The electric field strength between the coating device and the substrate should be 1.0×10 5} V/m or more, that is, 0.1 MV/m or more, and 0.3 MV/m or more, from the viewpoint that the viscosity of the coating liquid is suitably improved by the ER effect. It is preferable, and it is more preferable that it is 0.5 MV/m or more. In addition, it is desirable to prevent dielectric breakdown from occurring due to excessively high electric field strength between the coating apparatus and the substrate, and to prevent the interior of the substrate from being destroyed by treeing. From this viewpoint, it is preferable that it is 100 MV/m or less, and, as for the electric field intensity between the coating apparatus and the base material in one Embodiment of this invention, it is more preferable that it is 10 MV/m or less.

The method of controlling the electric field strength between the coating device and the substrate is not particularly limited, and for example, a method of charging one or both of the substrate and the coating device can be employed. As a method of charging the substrate, for example, a method of changing the electric potential with a charging gun before coating, and a method of peeling and charging the substrate by bringing the substrate into contact with a conveying roller or the like immediately before coating and then peeling, etc. can Moreover, as a method of charging a coating apparatus, the method etc. which hit the charging gun to a coating apparatus are mentioned, for example. The coating apparatus is generally made of metal and in many cases is grounded, and it is difficult to charge it. Therefore, as a method of controlling the electric field strength between the coating apparatus and the substrate, the method of charging the substrate is more preferable from the viewpoint of simplicity.

<Coating solution>

The coating solution in one embodiment of the present invention contains a non-conductive solvent and particles constituting the porous layer according to an embodiment of the present invention to be described later, and the particles are dispersed in a non-conductive solvent. .

The particle|grains in one Embodiment of this invention will not be specifically limited if it is particle|grains disperse|distributed in the nonelectroconductive solvent mentioned later. Examples of the particles include fillers containing inorganic oxides such as alumina, boehmite, silica, titania, zirconia, magnesia, aluminum hydroxide, barium titanate, and calcium carbonate; fillers containing minerals such as mica, zeolite, kaolin and talc; and fillers containing resin such as crosslinked polystyrene, phenolic resin, melamine resin, resorcinol-formalin resin (RF resin), crosslinked polymethyl methacrylate, acrylic core shell, and polyolefin beads. The said particle|grains may be used independently and may be used in combination of 2 or more types. Moreover, it is preferable that the said particle|grain is electrochemically stable and has electrical insulation. In addition, it is preferable that the particles do not elute with respect to a solvent and an electrolyte.

When an electric field is applied to a coating solution containing particles having a large relative permittivity, the viscosity thereof is further improved by the ER effect. From this, a filler containing alumina, barium titanate, etc. which are inorganic oxides with comparatively high dielectric constant of the said particle|grains is preferable, and among these, the filler containing alumina is the most preferable from a viewpoint of material cost.

It is preferable that the volume average particle diameter of the said particle|grains is 0.01 micrometer - 11 micrometers from a viewpoint of ensuring favorable adhesiveness and sliding property, and the moldability of a laminated body. As the lower limit thereof, 0.05 µm or more is more preferable, and 0.1 µm or more is still more preferable. As the upper limit, 10 micrometers or less are more preferable, 5 micrometers or less are still more preferable, and 1 micrometer or less is especially preferable.

The shape of the said particle|grains is arbitrary, and is not specifically limited. The shape of the particles may be, for example, a spherical shape; oval shape; plate; rod shape; scale; irregular shape; fibrous; Any of shapes in which single particles are thermally fused may be used, such as a peanut shape and/or a tetrapod shape. From the viewpoint of preventing the short circuit of the battery, the particles are preferably plate-shaped particles and/or non-agglomerated primary particles. In addition, from the viewpoint of ion permeation, the shape of the particles is an irregular shape in which the particles in the porous mass are hardly filled with the closest; fibrous; It is preferable to have a shape in which single particles are heat-sealed, such as a peanut shape and/or a tetrapod shape. It is particularly preferable that the shape of the particle is a shape in which single particles are heat-sealed, such as a peanut shape and/or a tetrapod shape.

The concentration of the particles is preferably 50% by volume or less, more preferably 30% by volume or less, based on the total volume of the coating solution. Moreover, 1 volume% or more is preferable and, as for the density|concentration of the said particle|grain, 3 volume% or more is more preferable. When the concentration of the particles is 50% by volume or less, there is a preferable aspect from the viewpoint of production, such as liquid feeding properties of the coating solution. In addition, if the concentration of the particles is 1% by volume or more, there is a preferable aspect from the viewpoint of economy.

The non-conductive solvent in one Embodiment of this invention will not be specifically limited if it is insulating in order to express an ER effect. The conductivity of the non-conductive solvent is usually 1 µS/cm or less. Examples of the non-conductive solvent include alcohols such as methanol, ethanol, propanol and isopropyl alcohol; ketones such as acetone, methyl ethyl ketone and diethyl ketone; ethers; amines such as N-methylpyrrolidone; hydrocarbons such as hexane, octane and benzene; Silicone oil etc. are mentioned. One type of solvent may be sufficient as the said nonelectroconductive solvent, and the mixed solvent of 2 or more types of solvent may be sufficient as it.

The non-conductive solvent is preferably one or more solvents selected from the group consisting of alcohols, ketones and amines from the viewpoint that the non-conductive solvent is easily removed by evaporation or washing in the process after coating. do. Among them, from the viewpoint of price, the non-conductive solvent is more preferably at least one solvent selected from the group consisting of ethanol, isopropyl alcohol, acetone, methyl ethyl ketone and N-methyl pyrrolidone.

The coating solution may include a resin. The resin is not particularly limited as long as it can favorably bind the particles and the porous layer to the substrate, is electrochemically stable, and does not elute with respect to the electrolytic solution. As a specific example of the said resin, For example, polyolefin; (meth)acrylate-based resin; fluorine-containing resin; polyamide-based resin; polyimide-based resin; polyester-based resin; rubber; a resin having a melting point or glass transition temperature of 180°C or higher; water-soluble polymers; Polycarbonate, polyacetal, polyether ether ketone, etc. are mentioned.

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

As polyolefin, polyethylene, polypropylene, polybutene, an ethylene-propylene copolymer, etc. are preferable.

As the polyamide-based resin, aramid resins such as aromatic polyamide and wholly aromatic polyamide are preferable.

In addition, as said aramid resin, specifically, for example, poly (paraphenylene terephthalamide), poly (metaphenylene isophthalamide), poly (parabenzamide), poly (metabenzamide), poly (4) ,4'-benzanilide terephthalamide), 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, etc. are mentioned. Among these, poly(paraphenylene terephthalamide) is more preferable.

As polyester-type resin, aromatic polyesters, such as polyarylate, and liquid crystal polyester are preferable.

As rubbers, a styrene-butadiene copolymer and its hydride, a methacrylic acid ester copolymer, an acrylonitrile-acrylic acid ester copolymer, a styrene-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl acetate, etc. are mentioned.

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

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

Examples of the fluorine-containing resin include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro Alkyl vinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trichloroethylene copolymer, vinylidene fluoride-vinyl fluoride copolymer, vinylidene fluoride -hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, etc., and among the said fluorine-containing resin, the fluorine-containing rubber whose glass transition temperature is 23 degrees C or less is mentioned.

One type of resin may be sufficient as the said resin, and two or more types of resin may be used together.

The resin is preferably at least one resin selected from the group consisting of polyamide, polyester, acrylic, polyvinylidene fluoride (PVDF), ethylene acrylate copolymer, styrene-butadiene rubber (SB) and polyvinyl alcohol (PVA). It is more preferable that it is a resin containing an aromatic polyamide, and it is still more preferable that it is a resin containing an aromatic polyamide as a main component. Here, "the aromatic polyamide is included as a main component" means that the content of the aromatic polyamide in the entire resin is 50 vol% or more, preferably 90 vol% or more, and more preferably 95 vol% or more.

The preparation method of the coating liquid will not be specifically limited, if the said particle|grains can be disperse|distributed uniformly in the said nonelectroconductive solvent to the extent which can control the film thickness of the porous layer obtained. As a method for preparing a coating solution, generally, a method in which the particles are dispersed in the non-conductive solvent and optionally the resin is dissolved is exemplified. As a method for dispersing the particles in the non-conductive solvent, for example, high-pressure dispersion, opposed-impact dispersion, ball mill, bead mill, paint shaker, high-speed impeller dispersion, ultrasonic dispersion, homogenizer, and a machine using a stirring blade A stirring method etc. are mentioned.

The viscosity before application of the coating solution is preferably 100 Pa·Sec or less, more preferably 10 Pa·Sec or less, from the viewpoint of appropriately generating the leveling. In addition, from the viewpoint of improving the viscosity at the time of coating by the ER effect to a suitable range, it is preferably 0.001 Pa·Sec or more, and more preferably 0.01 Pa·Sec or more.

<Reference>

As for the base material in one Embodiment of this invention, the porous base material and electrode plate mentioned later are mentioned, for example, It is preferable that it is a porous base material. Examples of the porous substrate include a resin porous membrane, a nonwoven fabric, a woven fabric, and a paper sheet. Moreover, a positive electrode or a negative electrode is mentioned as said electrode plate.

The thickness of the substrate is preferably 12 µm or less, more preferably 11 µm or less, and still more preferably 10 µm or less. Moreover, it is preferable that it is 4 micrometers or more, and, as for the film thickness of the said base material, it is more preferable that it is 5 micrometers or more.

<Porous substrate>

The porous substrate preferably contains, as a main component, a resin component such as polyolefin, polyamide, polyester, polyphenylene sulfide or polysulfone. Here, "contained as a main component" indicates that the content of the entire porous substrate is 50 vol% or more, preferably 90 vol% or more, and more preferably 95 vol% or more.

The porous substrate has a large number of pores connected therein, so that gas and liquid can pass from one surface to the other. The porous substrate may be a separator for a non-aqueous electrolyte secondary battery alone. Moreover, it can serve as a description of the laminated body which concerns on one Embodiment of this invention mentioned later.

The porous substrate may be a resin-made porous membrane containing polyolefin as a main component. Hereinafter, the said porous film is called a "polyolefin porous film."

It is more preferable that the polyolefin 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 million or more, it is more preferable because the strength of the separator for nonaqueous electrolyte secondary batteries is improved.

As said polyolefin which is a thermoplastic resin, the homopolymer or copolymer formed by superposing|polymerizing monomers, such as ethylene, propylene, 1-butene, 4-methyl-1- pentene, and 1-hexene, is specifically mentioned, for example. As said homopolymer, polyethylene, polypropylene, and polybutene are mentioned, for example. Moreover, as said copolymer, an ethylene-propylene copolymer is mentioned, for example.

Among these, since it can prevent the flow of an excessive current at a lower temperature, polyethylene is more preferable. In addition, preventing this excessive current from flowing 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 million or more is more preferable.

The weight per unit area of the porous substrate may be appropriately determined in consideration of strength, film thickness, weight, and handling properties. However, in order to increase the weight energy density and volume energy density of the nonaqueous electrolyte secondary battery, the weight per unit area is preferably 4 to 20 g/m 2 , more preferably 4 to 12 g/m 2 , and 5 to 10 g/m 2 . It is more preferable that it is m2.

The air permeability of the porous substrate is preferably 30 to 500 sec/100 mL in Gurley value, and more preferably 50 to 300 sec/100 mL. When the said porous substrate has an air permeability within the above-mentioned range, sufficient ion permeability can be acquired.

The porosity of the porous substrate is preferably 20 to 80% by volume, preferably 30 to 75% by volume, so as to obtain a function of reliably preventing excessive current from flowing at a lower temperature while increasing the amount of electrolyte retained. more preferably. In addition, the pore diameter of the pores of the porous substrate is preferably 0.3 µm or less, more preferably 0.14 µm or less, so that sufficient ion permeability can be obtained and the penetration of particles into the positive electrode and the negative electrode can be prevented.

<Manufacturing method of polyolefin porous film>

The manufacturing method of the said polyolefin porous film is not specifically limited. For example, a sheet-like polyolefin resin composition is produced by extruding a polyolefin-based resin, after kneading a pore-forming agent such as an inorganic filler and a plasticizer and optionally an antioxidant. A polyolefin porous film can be manufactured by removing the said pore former from the said sheet-like polyolefin resin composition with a suitable solvent, and then extending|stretching the polyolefin resin composition from which the said pore former was removed.

It does not specifically limit as said inorganic filler, An inorganic filler, specifically calcium carbonate, etc. are mentioned. It does not specifically limit as said plasticizer, Low molecular weight hydrocarbons, such as liquid paraffin, are mentioned.

Specifically, a method including a process as shown below is mentioned.

(A) a step of kneading ultra-high molecular weight polyethylene, low molecular weight polyethylene having a weight average molecular weight of 10,000 or less, a pore former 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 and cooling it stepwise while pulling it with a winding roller having a different speed ratio to form a sheet;

(C) removing the pore-forming agent from the inside of the obtained sheet with a suitable solvent;

(D) A step of stretching the sheet from which the hole former has been removed at an appropriate draw ratio.

Here, the order of (C) and (D) may be reversed. That is, after the sheet obtained in step (B) is stretched at an appropriate draw ratio, the pore former may be removed from the stretched sheet with an appropriate solvent.

<Positive pole>

The positive electrode is not particularly limited as long as it is generally used as a positive electrode of a nonaqueous electrolyte secondary battery. For example, as a positive electrode, the positive electrode sheet provided with the structure in which the active material layer containing a positive electrode active material and a binder was shape|molded on the positive electrode collector can be used. In addition, the active material layer may further contain a conductive agent.

Examples of the positive electrode active material include materials capable of doping/undoping metal ions such as lithium ions or sodium ions. Specific examples of the material include lithium composite oxide containing at least one transition metal such as V, Mn, Fe, Co, and Ni.

As said electrically conductive agent, carbonaceous materials, such as natural graphite, artificial graphite, coke, carbon black, pyrolytic carbon, carbon fiber, and organic high molecular compound sintered body, etc. are mentioned, for example. One type of the said electrically conductive agent may be used and may be used combining two or more types.

Examples of the binder include fluorine-based resins such as polyvinylidene fluoride (PVDF), acrylic resins, and styrene-butadiene rubber. Moreover, the binder also has a function as a thickener.

As said positive electrode current collector, conductors, such as Al, Ni, and stainless steel, are mentioned, for example. Among them, Al is more preferable because it is easy to process into a thin film and is inexpensive.

As a manufacturing method of a positive electrode sheet, For example, a method of press-molding a positive electrode active material, a electrically conductive agent, and a binder on a positive electrode electrical power collector; A method in which the positive electrode active material, the conductive agent and the binder are made into a paste using an appropriate organic solvent, the paste is applied to the positive electrode current collector, dried and then pressurized to adhere to the positive electrode current collector, and the like.

<Negative Electrode>

The negative electrode is not particularly limited as long as it is generally used as a negative electrode of a nonaqueous electrolyte secondary battery. For example, as a negative electrode, the negative electrode sheet provided with the structure in which the active material layer containing a negative electrode active material and a binder was shape|molded on the negative electrode collector can be used. In addition, the active material layer may further contain a conductive agent.

Examples of the negative electrode active material include a material capable of doping/undoping lithium ions, a lithium metal, or a lithium alloy. Specific examples of the material include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers and organic high molecular compound fired bodies; chalcogen compounds such as oxides and sulfides that perform doping and dedoping of lithium ions at a potential lower than that of the positive electrode; metals alloyed with alkali metals such as aluminum (Al), lead (Pb), tin (Sn), bismuth (Bi) and silicon (Si); Cubic intermetallic compounds capable of intercalating alkali metals between lattices (eg, AlSb, Mg ₂ Si and NiSi _{2 ,} etc.); A lithium nitrogen compound (Li _3-x M _x N (M: transition metal)) or the like may be used.

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

As a manufacturing method of a negative electrode sheet, For example, a method of press-molding a negative electrode active material on a negative electrode collector; A method in which the negative electrode active material is made into a paste using an appropriate organic solvent, the paste is applied to the negative electrode current collector, dried and then pressurized to adhere to the negative electrode current collector, and the like. The paste preferably includes the conductive agent and the binder.

<Porous layer>

After the coating solution is applied onto the substrate, a porous layer can be obtained by removing the non-conductive solvent from the coating solution. The porous layer manufactured by the manufacturing method of the porous layer which concerns on one Embodiment of this invention is excellent in film thickness precision by the effect of ER effect and arbitrary leveling mentioned above.

The thickness of the porous layer is preferably 5 µm or less per layer, more preferably 4 µm or less per layer, from the viewpoint of preventing deterioration of battery characteristics. In addition, the film thickness of the porous layer is preferably 0.5 µm or more per layer, and 1 µm or more per layer from the viewpoint of sufficiently preventing internal short circuit due to battery damage or the like, and also preventing a decrease in the amount of electrolyte retained. more preferably.

It is preferable that it is an adhesive porous layer or a heat-resistant porous layer, and, as for the said porous layer, it is more preferable that it is a heat-resistant porous layer.

The weight per unit area of the porous layer can be appropriately determined in consideration of the strength, film thickness, weight, and handling properties of the porous layer. It is preferable that it is 0.5-10 g/m<2>, and, as for the weight per unit area of a porous layer, it is more preferable that it is 0.5-5 g/m<2> per porous layer.

By making the weight per unit area of a porous layer into these numerical ranges, the weight energy density and volume energy density of a nonaqueous electrolyte secondary battery can be made high. When the weight per unit area of a porous layer exceeds the said range, there exists a tendency for a nonaqueous electrolyte secondary battery to become heavy.

The porous layer preferably has a sufficiently porous structure from the viewpoint of ion permeability. Specifically, the porous layer preferably has a porosity in the range of 30% to 60%. Further, the porous layer preferably has an average pore diameter in the range of 20 nm to 100 nm.

[Embodiment 2: Laminate, Embodiment 3: Separator for non-aqueous electrolyte secondary battery]

A laminate according to Embodiment 2 of the present invention is a laminate comprising a substrate and a porous layer containing particles laminated on at least one surface of the substrate, wherein the standard deviation of the film thickness of the laminate is 0.5 μm or less.

The separator for nonaqueous electrolyte rechargeable batteries according to Embodiment 3 of the present invention includes the laminate according to Embodiment 2 of the present invention, wherein the substrate is a porous substrate. That is, the laminated body contained in the separator for nonaqueous electrolyte rechargeable batteries which concerns on one Embodiment of this invention does not contain an electrode plate.

The laminate according to Embodiment 2 of the present invention and the separator for a non-aqueous electrolyte secondary battery according to Embodiment 3 of the present invention are the porous layer manufacturing method according to Embodiment 1 of the present invention, to be manufactured by forming a porous layer on a substrate can

Each member in Embodiment 1 of this invention is applicable to each member which comprises the laminated body which concerns on one Embodiment of this invention, and the separator for nonaqueous electrolyte rechargeable batteries.

The standard deviation of the film thickness of the laminate according to the embodiment of the present invention is 0.5 µm or less, preferably 0.45 µm or less, and more preferably 0.43 µm or less. Moreover, the standard deviation of the film thickness of the laminated body which concerns on one Embodiment of this invention may be 0.1 micrometer or more.

In the laminate according to the embodiment of the present invention, the standard deviation of the film thickness is within the above range, and when the laminate is incorporated in a non-aqueous electrolyte secondary battery as a separator for a non-aqueous electrolyte secondary battery or a member thereof, the non-aqueous electrolyte secondary Improve the uniformity of the distance between the electrodes of the cell. Thereby, the battery performance of the said non-aqueous electrolyte secondary battery can be improved by preventing the flow of ions from concentrating on the area with a narrow distance between electrodes. Similarly, when the separator for nonaqueous electrolyte secondary batteries according to one embodiment of the present invention is incorporated in a nonaqueous electrolyte secondary battery, the battery performance of the nonaqueous electrolyte secondary battery can be improved.

The film thickness of the laminate according to one embodiment of the present invention is 15.0 µm or less from the viewpoint of preventing a decrease in battery characteristics when the laminate is embedded in a non-aqueous electrolyte secondary battery as a separator for a non-aqueous electrolyte secondary battery or a member thereof. It is preferable, and it is more preferable that it is 10.0 micrometers or less. Moreover, it is preferable that it is 5.5 micrometers or more, and, as for the film thickness of a nonaqueous electrolyte secondary battery, it is preferable that it is 5.5 micrometers or more, and it is more preferable that it is 6.0 micrometers or more from a viewpoint of fully preventing the internal short circuit by the damage|damage of the said nonaqueous electrolyte rechargeable battery.

It is preferable that it is 30-1000 sec/100mL in Gurley value, and, as for the air permeability of the laminated body which concerns on one Embodiment of this invention, it is more preferable that it is 50-800 sec/100mL. When the laminate according to the embodiment of the present invention has an air permeability within the range described above, sufficient ion permeability can be obtained in a nonaqueous electrolyte secondary battery.

The laminate according to one embodiment of the present invention may further include other layers, such as an adhesive layer, a heat-resistant layer, and a protective layer, as members other than the said base material and the said porous layer.

The separator for nonaqueous electrolyte secondary batteries according to an embodiment of the present invention includes a laminate in which the porous layer is laminated on the surface of the porous substrate, and is also referred to as a so-called "laminated separator for nonaqueous electrolyte secondary batteries" or "laminated separator". It is the separator for nonaqueous electrolyte secondary batteries called.

[Embodiment 4: Non-aqueous electrolyte secondary battery]

The nonaqueous electrolyte secondary battery according to the fourth embodiment of the present invention includes the separator for the nonaqueous electrolyte secondary battery according to the third embodiment of the present invention.

For each member constituting the nonaqueous electrolyte secondary battery according to the embodiment of the present invention, the respective members in the first to third embodiments of the present invention can be applied.

<Non-aqueous electrolyte>

The non-aqueous electrolyte in the non-aqueous electrolyte secondary battery according to the embodiment of the present invention is a non-aqueous electrolyte generally used in a non-aqueous electrolyte secondary battery, and is not particularly limited, but for example, a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent can be used 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 , a lower aliphatic carboxylate lithium salt, LiAlCl ₄ and the like. As for the said lithium salt, only 1 type may be used and it may use it in combination of 2 or more types. Among the lithium salts, at least one fluorine selected from the group _{consisting of LiPF 6} , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ and LiC(CF ₃ SO ₂ ) _{3 .} Contained lithium salt is more preferable.

Specific examples of the organic solvent constituting the non-aqueous electrolyte in the present invention include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, and 4-tri carbonates such as fluoromethyl-1,3-dioxolan-2-one and 1,2-di(methoxycarbonyloxy)ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethyl ether, 2,2,3,3-tetrafluoropropyldifluoromethyl ether, tetrahydrofuran and 2-methyltetrahydro ethers such as furan; esters such as methyl formate, methyl acetate, and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone; And the fluorine-containing organic solvent etc. which fluorine group is introduce|transduced into the said organic solvent are mentioned. As for the said organic solvent, only 1 type may be used and it may use it in combination of 2 or more types. Among the organic solvents, carbonates are more preferable, and a mixed solvent of a cyclic carbonate and an acyclic carbonate or a mixed solvent of a cyclic carbonate and an ether is still more preferable. As a mixed solvent of a cyclic carbonate and a non-cyclic carbonate, the operating temperature range is wide, and even when graphite materials such as natural graphite and artificial graphite are used as the negative electrode active material, it exhibits resistance to decomposition. A mixed solvent containing nitrate, dimethyl carbonate and ethylmethyl carbonate is more preferable.

<Method for manufacturing non-aqueous electrolyte secondary battery>

As a manufacturing method for nonaqueous electrolyte secondary batteries which concerns on one Embodiment of this invention, a conventionally well-known method is applicable. For example, after the positive electrode, the separator for a non-aqueous electrolyte secondary battery according to the embodiment of the present invention, and the negative electrode are arranged in this order to form a member for a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte is placed in a container serving as a housing of the non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery according to one embodiment of the present invention can be manufactured by putting the member for secondary batteries, then filling the container with the non-aqueous electrolyte, and sealing the container while reducing the pressure.

The shape of the non-aqueous electrolyte secondary battery is not particularly limited, and may have any shape such as a thin plate (paper) type, a disk shape, a cylindrical shape, and a prismatic shape such as a rectangular parallelepiped. In addition, the manufacturing method of the member for nonaqueous electrolyte solution secondary batteries and a nonaqueous electrolyte solution secondary battery is not specifically limited, A conventionally well-known manufacturing method is employable.

This invention is not limited to each embodiment mentioned above, Various changes are possible in the range shown in the claim, The embodiment obtained by combining the technical means disclosed in each different embodiment suitably is also included in the technical scope of this invention. . Moreover, new technical features can be formed by combining the technical means disclosed in each embodiment, respectively.

Example

Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.

[measurement]

<Average film thickness and standard deviation (unit: μm)>

The film thickness was measured using a film thickness measuring instrument VL-50A manufactured by Mitsutoyo. The film thickness was measured in 15 arbitrary points|pieces of each laminated body manufactured by Examples 1-4 and Comparative Examples 1-2, the average value was computed, and it was set as the average film thickness. In addition, the standard deviation of the film thickness was computed based on the measured value of the film thickness in said 15 points|pieces. Subsequently, the value of "standard deviation of film thickness/average film thickness" was calculated.

<Electric field strength (unit: MV/m)>

Using a non-contact electrometer Hakko FG-450 manufactured by Hakko, the potential (unit: V) of the coating bar as the coating apparatus in Examples 1 to 4 and Comparative Examples 1 and 2 was measured. From the obtained measured values, the potential difference between the coating apparatus and the base material was calculated. Then, the electric field strength was calculated by dividing the calculated potential difference by the value of the clearance (unit: μm).

[Abbreviation of compound]

The abbreviations of the compounds used in Examples and Comparative Examples are shown below.

NMP: N-methylpyrrolidone

PPD: paraphenylenediamine

TPC: terephthalic acid dichloride

PE: Polyethylene

[Example 1]

<Preparation of coating solution>

Para-aramid was synthesized using a 5 L separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port. Specifically, after sufficiently drying the separable flask, 4200 g of NMP was added thereto, 272.65 g of calcium chloride dried at 200°C for 2 hours was added, and the temperature was raised to 100°C. After the calcium chloride was completely dissolved, the temperature in the flask was returned to room temperature, and then 132.91 g of PPD was added. The PPD was completely dissolved to obtain a first solution. While maintaining the temperature of the obtained first solution at 20±2° C., 243.32 g of TPC was divided into 10 portions to the first solution and added at intervals of about 5 minutes to obtain a second solution. After that, while maintaining the temperature of the obtained second solution at 20 ± 2 ° C., the second solution was aged for 1 hour, and then stirred for 30 minutes under reduced pressure to remove air bubbles to obtain a para-aramid/NMP solution. With respect to 100 parts by weight of para-aramid in the obtained para-aramid/NMP solution, an alumina powder having an average particle diameter of 0.02 µm (EVONIK product: Alumina C) and an alumina powder having an average particle diameter of 0.3 µm (Sumitomo Chemical Co., Ltd. product: high purity alumina AA) -03) was added in 100 parts by weight each. Subsequently, the solution was diluted with NMP so that the solid content concentration was 6%. Thereafter, the coating solution 1 was obtained by stirring using a homogenizer and further processing 50 MPa×2 times with a pressure disperser.

<Formation of porous layer>

A bar coater made by TECHNO SUPPLY was used for coating, and a Baker-type applicator was used for the coating bar. The clearance of the coating bar was set to 75 mu m. A commercially available polyethylene base material (film thickness of 10.8 µm) was affixed to a glass plate, and the electric potential was adjusted to 0 V using an ionizer. Thereafter, an electric field was generated between the bar and the polyethylene substrate by charging the polyethylene substrate using a charging gun. At this time, the potential difference between the bar and the substrate was 160 V, and the electric field strength was 2.13 MV/m.

The coating solution 1 was supplied to the bar coater, and the coating solution 1 was applied on the polyethylene substrate at a speed of 70 cm/min. Thereafter, the solvent was removed while depositing the porous layer by immediately washing with distilled water. Subsequently, the coated film was obtained by drying the polyethylene base material on which the porous layer was laminated|stacked in 80 degreeC oven. The obtained coating film was made into the laminated body 1.

[Example 2]

A coated film was obtained in the same manner as in Example 1, except that the electric field strength was controlled to 8.27 MV/m by setting the potential difference between the coating bar and the substrate to 420 V and the clearance of the coating bar to 51 μm. The obtained coating film was made into the laminated body 2.

[Example 3]

The coated film was performed in the same manner as in Example 1, except that the polyethylene substrate was charged, the electric field strength was controlled to 0.31 MV/m by setting the potential difference between the coating bar and the substrate to 20 V and the clearance of the coating bar to 65 μm. got The obtained coating film was made into the laminated body 3.

[Example 4]

A coated film was obtained in the same manner as in Example 2 except that boehmite (BG-601 manufactured by Estone) was used instead of alumina AA03. The obtained coating film was made into the laminated body 4.

[Comparative Example 1]

A coated film was obtained in the same manner as in Example 2, except that an electric field was not generated using a charging gun. The obtained coating film was made into the laminated body 5.

[Comparative Example 2]

A coated film was obtained in the same manner as in Example 4, except that an electric field was not generated using a charging gun. The obtained coating film was made into the laminated body 6.

[result]

In Examples 1 to 4 and Comparative Examples 1 to 2, "particles", "resin" and "dispersion solvent" in the coating solutions, and "constituting substances of the base material" are shown in Table 1 below. In addition, "potential difference", "clearance" and "electric field strength" in Examples 1 to 4 and Comparative Examples 1 to 2, and "average film thickness", "standard deviation of film thickness" and "film thickness" of the obtained laminate The values of "standard deviation of thickness/average film thickness" are shown in Table 2.

As shown in Table 1, the laminates 1 to 4 obtained in Examples 1 to 4 had the same average film thickness as compared to the laminates 5 and 6 obtained in Comparative Examples 1 and 2, while the standard deviation of the film thickness was small. .

Therefore, it was found that the film thickness accuracy of the resulting laminate was improved by applying an electric field of 0.1 MV/m or more to the coating solution at the moment of coating the coating solution on the substrate.

The porous layer manufactured by the manufacturing method of the porous layer which concerns on one Embodiment of this invention, the laminated body containing this porous layer, and the laminated body which concerns on one Embodiment of this invention are excellent in film thickness precision. Accordingly, the laminate can be suitably used as a member of a non-aqueous electrolyte secondary battery having excellent battery performance.

Therefore, the present invention can be suitably used in various industries dealing with nonaqueous electrolyte secondary batteries.

1: Coating Apparatus
2: coating solution
3: description

Claims (10)

a step of applying a coating liquid containing a non-conductive solvent and particles to the surface of the substrate by passing it between the coating apparatus and the substrate;
a step of removing the non-conductive solvent from the coating solution applied to the surface of the substrate;
The method for producing a porous layer, wherein the electric field strength between the coating device and the substrate when the coating liquid passes between the coating device and the substrate is 1.0×10 ^{5 V/m or more.} The production of the porous layer according to claim 1, wherein the coating solution is leveled between the step of applying the coating solution to the surface of the substrate and before the step of removing the non-conductive solvent. Way. The method for producing a porous layer according to claim 1 or 2, wherein the coating solution contains a resin. The method for producing a porous layer according to claim 3, wherein the resin contains an aromatic polyamide. A laminate comprising a substrate and a porous layer including particles laminated on at least one surface of the substrate,
The standard deviation of the film thickness of the said laminated body is 0.5 micrometer or less. The laminate according to claim 5, wherein the laminate has a film thickness of 15.0 µm or less. The laminate according to claim 5 or 6, wherein the porous layer contains a resin. The laminate according to claim 7, wherein the resin comprises an aromatic polyamide. The separator for nonaqueous electrolyte secondary batteries containing the laminated body in any one of Claims 5-8. A non-aqueous electrolyte secondary battery comprising the separator for a non-aqueous electrolyte secondary battery according to claim 9.

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