JP6762089B2 - Laminated separator for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery member and non-aqueous electrolyte secondary battery - Google Patents

Description

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

These non-aqueous electrolyte secondary batteries represented by lithium secondary batteries have a high energy density, and therefore, when an internal short circuit or an external short circuit occurs due to damage to the battery or damage to the equipment using the battery. , A large current may flow and generate heat. Therefore, the non-aqueous electrolyte secondary battery is required to ensure high safety by preventing heat generation of a certain amount or more.

As a means of ensuring the safety of the non-aqueous electrolyte secondary battery, a shutdown function is provided to prevent further heat generation by blocking the passage of ions between the positive electrode and the negative electrode with a separator when abnormal heat generation occurs. The method of giving is common. That is, in a non-aqueous electrolyte secondary battery, when an abnormal current flows through the separator arranged between the positive electrode and the negative electrode due to, for example, an internal short circuit between the positive electrode and the negative electrode. In addition, a method of interrupting the current to prevent (shut down) the flow of an excessive current and impart a function of suppressing further heat generation is common. As the separator, a film-like porous film containing a polyolefin resin as a main component, which melts at, for example, about 80 to 180 ° C. when abnormal heat generation occurs, is generally used.

Further, in order to improve the function of a separator composed of a porous film, a technique of laminating a porous film on at least one surface of the porous film is known. For example, in Patent Document 1, in order to prevent an internal short circuit of a battery, a separator which is a microporous sheet made of a polyolefin resin and a porous film containing an inorganic filler and a film binder may be laminated. Are listed. By defining the mirror glossiness of 85 ° of the porous film, a thin, uniform, and highly flexible porous film is realized.

Further, Patent Document 2 defines a mirror gloss of 60 ° in a separator obtained by applying a composition containing insulating fine particles and an organic binder to a microporous film made of polyethylene to prevent short circuits and provide reliability. We are trying to improve.

Japanese Unexamined Patent Publication No. 2005-294216 (published on October 20, 2005) Japanese Unexamined Patent Publication No. 2014-17264 (published on January 30, 2014)

By the way, in recent years, for the purpose of improving the adhesiveness between the separator and the electrode, the development of a separator in which a porous layer containing a polyvinylidene fluoride resin is laminated on at least one surface of a porous film containing polyolefin as a main component has been promoted. ing. Further, lowering the resistance of the non-aqueous electrolyte secondary battery has become an issue, and even in a laminated separator for a non-aqueous electrolyte secondary battery provided with a porous film and a porous layer containing a polyvinylidene fluoride resin. Improvement of rate characteristics is desired.

The above-mentioned Patent Documents 1 and 2 aim at improving flexibility, preventing short circuits, and improving reliability, and do not consider rate characteristics. Further, the porous layers described in Patent Documents 1 and 2 do not contain a polyvinylidene fluoride-based resin. Therefore, the techniques described in Patent Documents 1 and 2 cannot improve the rate characteristics of the separator provided with the porous film and the porous layer containing the polyvinylidene fluoride-based resin.

The present invention has been made in view of such problems, and an object of the present invention is a laminated separator for a non-aqueous electrolyte secondary battery including a porous film and a porous layer containing a polyvinylidene fluoride-based resin. Therefore, it is an object of the present invention to provide a laminated separator for a non-aqueous electrolyte secondary battery having excellent rate characteristics.

The present inventor has determined that the mirror surface gloss of 60 ° in the porous layer of the laminated separator for a non-aqueous electrolyte secondary battery is the rate of the non-aqueous electrolyte secondary battery using the laminated separator for a non-aqueous electrolyte secondary battery. Focusing for the first time on the relationship with the characteristics, it was found that the rate characteristics of the non-aqueous electrolyte secondary battery can be improved by keeping the mirror surface gloss within a predetermined range, and the present invention has been completed. It was.

The laminated separator for a non-aqueous electrolyte secondary battery according to the present invention is for solving the above-mentioned problems, and is a porous film containing a polyolefin resin as a main component and a porous film containing a polyvinylidene fluoride resin. It is a laminated separator for a non-aqueous electrolyte secondary battery containing a layer, and is characterized in that a mirror surface gloss of 60 ° on the surface of the porous layer is 3 to 26%.

Further, in the laminated separator for a non-aqueous electrolytic solution secondary battery according to the present invention, the porous layer contains a filler, and the ratio of the polyvinylidene fluoride resin and the filler to the total mass of the filler is 1. It is preferably ~ 30% by mass.

Further, in the laminated separator for a non-aqueous electrolytic solution secondary battery according to the present invention, the piercing strength of the porous film is preferably 2N or more.

Further, in the laminated separator for a non-aqueous electrolytic solution secondary battery according to the present invention, the average pore size of the porous film is preferably 0.14 μm or less.

Further, in the laminated separator for a non-aqueous electrolyte secondary battery according to the present invention, the polyvinylidene fluoride-based resin is selected from the group consisting of hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, and vinyl fluoride. It is preferably a copolymer of at least one kind of monomer and vinylidene fluoride, a homopolymer of vinylidene fluoride, or a mixture of these polymers.

Further, the member for a non-aqueous electrolytic solution secondary battery according to the present invention is characterized in that a positive electrode, the above-mentioned laminated separator for a non-aqueous electrolytic solution secondary battery, and a negative electrode are arranged in this order.

Further, the non-aqueous electrolyte secondary battery according to the present invention is characterized by including the above-mentioned laminated separator for a non-aqueous electrolyte secondary battery.

According to the present invention, the rate characteristic of the non-aqueous electrolyte secondary battery is excellent.

An 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 configurations described below, and various modifications can be made within the scope of the claims, and the technical means disclosed in the different embodiments may be appropriately combined. The obtained embodiments are also included in the technical scope of the present invention. Unless otherwise specified in the present specification, "A to B" representing a numerical range means "A or more and B or less".

[1. Laminated separator for non-aqueous electrolyte secondary battery]
The laminated separator for a non-aqueous electrolyte secondary battery according to the present invention is a film-like porous film mainly composed of a polyolefin resin, which is arranged between a positive electrode and a negative electrode in a non-aqueous electrolyte secondary battery. It includes a porous layer containing a polyvinylidene fluoride-based resin (PVDF-based resin) laminated on at least one surface of the porous film.

[1-1. Porous film]
The porous film may be a porous and film-like base material (polyolefin-based porous base material) containing a polyolefin-based resin as a main component, and has a structure having pores connected to the inside thereof. It is a film that allows gas and liquid to permeate from one surface to the other. That is, the porous film in the present invention is a film having pores, which is different from a non-woven fabric in which fibers are folded.

The porous film may melt when the battery generates heat to make it non-porous, thereby imparting a shutdown function to the laminated separator for the non-aqueous electrolyte secondary battery. The porous film may be composed of one layer or may be formed of a plurality of layers.

The volume-based porosity of the porous film is 0.2 to 0 so that the retention amount of the electrolytic solution can be increased and the function of reliably blocking (shutting down) the flow of an excessive current at a lower temperature can be obtained. It is preferably .8 (20 to 80% by volume), more preferably 0.3 to 0.75 (30 to 75% by volume). Further, the average diameter of the pores (average pore diameter) of the porous film can obtain sufficient ion permeability when used as a separator and prevents particles from entering the positive electrode and the negative electrode. It is preferably 0.14 μm or less, more preferably 0.1 μm or less, and more preferably 0.01 μm or more so that it can be used.

As a method of controlling the average pore size of the porous film, for example, when the pore size is reduced, a method of making the dispersed state of a pore-opening agent such as an inorganic filler or a phase separation agent uniform during film formation of the porous film, Examples thereof include a method of reducing the particle size of the inorganic filler pore-forming agent, a method of stretching with a phase-separating agent contained, and a method of stretching at a low stretching ratio. Further, as a method of controlling the porosity of the porous film, for example, in the case of obtaining a porous film having a high porosity, a method of increasing the amount of a pore-forming agent such as an inorganic filler or a phase separation agent with respect to a polyolefin resin. , A method of stretching after removing the phase separating agent, a method of stretching at a high stretching ratio, and the like.

It is considered that when the average pore diameter of the porous film decreases, the capillary force estimated to be the driving force for introducing the electrolytic solution into the pores inside the base material increases. Moreover, since the average pore diameter is small, the formation of dendrites (dendritic crystals) due to lithium metal can be suppressed.

Further, it is considered that when the porosity of the porous film increases, the volume of the portion of the polyolefin base material where the polyolefin cannot penetrate is reduced.

The piercing strength of the porous film is preferably 2N or more, more preferably 3N or more. If the piercing strength is too small, the positive and negative electrode active material particles will be used when the positive and negative electrodes and the separator are laminated and wound in the battery assembly process, when the winding group is pressed, or when pressure is applied to the battery from the outside. May break through the separator and short-circuit the positive and negative electrodes. The piercing strength of the porous film is preferably 10 N or less, more preferably 8 N or less.

The proportion of the polyolefin-based resin component in the porous film is essential to be 50% by volume or more of the entire porous film, preferably 90% by volume or more, and more preferably 95% by volume or more. The polyolefin resin component of the porous film, it is preferable that the weight average molecular weight are included high molecular weight component of ^{5 × 10 5 ~15 × 10 6} . In particular, it is preferable that the polyolefin component of the porous film contains a polyolefin component having a weight average molecular weight of 1 million or more because the strength of the entire porous film is increased.

Examples of the polyolefin-based resin include high-molecular-weight homopolymers or copolymers obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like. The porous film can be a layer containing these polyolefins alone and / or a layer containing two or more of these polyolefins. In particular, high molecular weight polyethylene mainly composed of ethylene is preferable. The porous film does not prevent the mixture of components other than polyolefin as long as the function of the layer is not impaired.

The air permeability of the porous film is usually in the range of 30 to 500 seconds / 100 cc in terms of Gale value, preferably in the range of 50 to 300 seconds / 100 cc. When the porous film has the air permeability in the above range, sufficient ion permeability can be obtained when used as a separator.

The film thickness of the porous film is appropriately determined in consideration of the number of laminated separators for a non-aqueous electrolytic solution secondary battery. In particular, since a porous layer is formed on one side (or both sides) of the porous film, 4 to 40 μm is preferable, and 7 to 30 μm is more preferable. In addition, the texture of the porous film is such that the strength, film thickness, handleability and weight, and the weight energy density and volume energy density of the battery when used as a separator for a non-aqueous electrolyte secondary battery can be increased. in, usually from ^{4~20g / m 2, 5~12g / m} 2 is preferred.

A known method can be used as a method for producing such a porous film, and the method is not particularly limited. For example, as described in JP-A-7-29563, there is a method in which a pore-forming agent is added to a thermoplastic resin to form a film, and then the pore-forming agent is removed with an appropriate solvent.

Specifically, for example, when the porous film is formed of a polyolefin resin containing ultra-high molecular weight polyethylene and a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, it is as shown below from the viewpoint of manufacturing cost. It is preferable to produce by the above method.
(1) A polyolefin resin composition by kneading 100 parts by weight of ultra-high molecular weight polyethylene, 5 to 200 parts by weight of a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, and 100 to 400 parts by weight of an inorganic filler such as calcium carbonate. (2) A step of molding a sheet using a polyolefin resin composition (3) A step of removing an inorganic filler from the sheet obtained in the step (2) (4) Obtained in the step (3). In addition to the step of stretching the sheet to obtain the A layer, the methods described in the above-mentioned patent documents may be used.

Further, as the porous film, a commercially available product having the above-mentioned characteristics may be used.

[1-2. Porous layer]
The porous layer according to the present invention contains a polyvinylidene fluoride-based resin (PVDF-based resin). The porous layer has a large number of pores inside and has a structure in which these pores are connected, and may be a layer in which a gas or liquid can pass from one surface to the other. .. Further, in the present embodiment, the porous layer is provided on one side or both sides of the porous film as the outermost layer of the separator, and is a layer that can be adhered to the electrode.

As a result of diligent studies, the present inventors set the mirror surface gloss of 60 ° on the surface of the porous layer to 3 to 26%, thereby setting the laminated separator for a non-aqueous electrolyte secondary battery containing the porous layer. It was found that the rate characteristics of the non-aqueous electrolyte secondary battery provided with the above can be increased. Here, the mirror surface glossiness of 60 ° indicates the glossiness when the incident angle and the light receiving angle are 60 °, and is measured by the measuring method specified in JIS Z8741. The mirror glossiness of the porous layer is a parameter related to the density and uniformity of the porous layer.

When the mirror glossiness is less than 3%, the uniformity of the porous layer is low and the ion permeability becomes uneven. The portion with low ion permeability becomes rate-determining and reduces the efficient ion transport of the entire porous layer, resulting in low rate characteristics. Therefore, by setting the mirror glossiness to 3% or more, it is possible to suppress a decrease in the rate characteristic due to the non-uniformity of the porous layer and obtain an excellent rate characteristic.

On the other hand, when the mirror glossiness exceeds 26%, the density of the porous layer becomes too high, and the ion permeability of the separator decreases due to clogging of pores by insoluble by-products and bubbles generated by charging and discharging. There is. In addition, since the number of places where the electrolytic solution is held at the interface between the porous layer and the electrode is reduced, the amount of the electrolytic solution at the interface between the porous layer and the electrode is reduced, so that the battery is operated under a large current condition. , Li ion depletion at the interface is likely to occur, and as a result, the rate characteristics may be deteriorated. Therefore, by setting the mirror glossiness to 26% or less, it is possible to suppress a decrease in ion permeability of the separator and a decrease in rate characteristics due to depletion of the electrolytic solution at the interface between the porous layer and the electrode, resulting in an excellent rate. The characteristics can be obtained.

The lower limit of the 60 ° mirror gloss on the surface of the porous layer is preferably 4% or more, more preferably 5% or more. That is, the mirror glossiness is preferably 4% or more and 26% or less, and more preferably 5% or more and 26% or less. The upper limit of the mirror glossiness is preferably 22% or less, more preferably 18% or less.

The resin constituting the porous layer contains a polyvinylidene fluoride-based resin, and is preferably made of a resin having a structure in which skeletons having a diameter of 1 μm or less are connected in a three-dimensional network.

Examples of the polyvinylidene fluoride-based resin include a homopolymer of vinylidene fluoride (that is, polyvinylidene fluoride), a copolymer of vinylidene fluoride and another copolymerizable monomer (polyvinylidene fluoride copolymer), and the like. Be done. The polyvinylidene fluoride-based resin contained in the porous layer is preferably a homopolymer of vinylidene fluoride, a vinylidene fluoride copolymer, or a mixture of these polymers. Examples of the monomer copolymerizable with vinylidene fluoride include hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichlorethylene, and vinyl fluoride. That is, the polyvinylidene fluoride copolymer preferably contains at least one monomer selected from the group consisting of hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, and vinyl fluoride, and vinylidene fluoride. It is a coalescence. The polyvinylidene fluoride-based resin can be synthesized by emulsion polymerization or suspension polymerization.

The polyvinylidene fluoride-based resin preferably contains 85 mol% or more of vinylidene fluoride as a constituent unit thereof. It is more preferably 90 mol% or more, further preferably 95 mol% or more, still more preferably 98 mol% or more. When vinylidene fluoride is contained in an amount of 85 mol% or more, it is easy to secure mechanical strength and heat resistance that can withstand pressurization and heating during battery manufacturing.

Further, it is also preferable that the porous layer contains two kinds of polyvinylidene fluoride-based resins (the following first resin and second resin) having different hexafluoropropylene contents.
First resin: a vinylidene fluoride / hexafluoropropylene copolymer having a hexafluoropropylene content of more than 0 mol% and 1.5 mol% or less, or a vinylidene fluoride homopolymer (content of hexafluoropropylene). Is 0 mol%)
-Second resin: Vinylidene fluoride / hexafluoropropylene copolymer having a hexafluoropropylene content of more than 1.5 mol% Whichever is the porous layer containing the two types of polyvinylidene fluoride-based resins? Adhesion to the electrode is improved as compared with the porous layer containing no one. Further, the porous layer containing the two types of polyvinylidene fluoride-based resin has improved adhesiveness to the porous film and improved peeling force between these layers as compared with the porous layer containing no one of them. To do. The mixing ratio (mass ratio, first resin: second resin) of the first resin and the second resin is preferably 15:85 to 85:15.

The polyvinylidene fluoride-based resin preferably has a weight average molecular weight of 300,000 to 3,000,000. When the weight average molecular weight is 300,000 or more, the mechanical properties of the porous layer that can withstand the bonding treatment with the electrode can be ensured, and sufficient adhesiveness can be obtained. On the other hand, when the weight average molecular weight is 3 million or less, the viscosity of the coating liquid at the time of coating molding does not become too high and the moldability is excellent. The weight average molecular weight is more preferably in the range of 300,000 to 2 million, and even more preferably in the range of 500,000 to 1.5 million.

The fibril diameter of the polyvinylidene fluoride-based resin is preferably 10 nm to 1000 nm from the viewpoint of rate characteristics.

The porous layer may contain a resin other than the polyvinylidene fluoride-based resin. Examples of other resins include styrene-butadiene copolymers; homopolymers or copolymers of vinylnitriles such as acrylonitrile and methacrylonitrile; polyethers such as polyethylene oxide and polypropylene oxide; and the like.

Further, the porous layer may contain a filler composed of an inorganic substance or an organic substance. By containing the filler, the slipperiness and heat resistance of the separator can be improved. The filler may be either an organic filler or an inorganic filler that is stable in a non-aqueous electrolytic solution and is electrochemically stable. From the viewpoint of ensuring the safety of the battery, a filler having a heat resistant temperature of 150 ° C. or higher is preferable.

Examples of the organic filler include crosslinked polyacrylic acid, crosslinked polyacrylic acid ester, crosslinked polymethacrylic acid, crosslinked polymethacrylic acid ester, crosslinked polymethylmethacrylate, crosslinked polysilicone, crosslinked polystyrene, crosslinked polydivinylbenzene, and styrene-divinyl. Crosslinked polymer fine particles such as benzene copolymer crosslinked products, polyimides, melamine resins, phenol resins, benzoguanamine-formaldehyde condensates; heat resistant polymer fine particles such as polysulfone, polyacrylonitrile, polyaramid, polyacetal, thermoplastic polyimide; Be done.

The resin (polymer) constituting the organic filler is a mixture, modified product, derivative, or copolymer (random copolymer, alternate copolymer, block copolymer, graft copolymer) of the molecular species exemplified above. , It may be a crosslinked product.

Examples of the inorganic filler include metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, nickel hydroxide and boron hydroxide; and metal oxides such as alumina and zirconia; Carbon carbonates such as calcium carbonate and magnesium carbonate; sulfates such as barium sulfate and calcium sulfate; clay minerals such as calcium silicate and talc; and the like can be mentioned. From the viewpoint of imparting flame retardancy and eliminating static electricity, metal hydroxide is preferable.

Various fillers may be used alone or in combination of two or more.

The volume average particle size of the filler is preferably 0.01 μm to 10 μm from the viewpoint of ensuring good adhesiveness and slipperiness and moldability of the separator. The lower limit value is more preferably 0.1 μm or more, and the upper limit value is more preferably 5 μm or less.

The particle shape of the filler is arbitrary, and may be spherical, elliptical, plate-shaped, rod-shaped, or amorphous. From the viewpoint of preventing a short circuit of the battery, plate-shaped particles or non-aggregated primary particles are preferable.

The filler can improve slipperiness by forming fine irregularities on the surface of the porous layer, but when the filler is plate-like particles or primary particles that are not aggregated, the filler is porous. The unevenness formed on the surface of the quality layer becomes finer, and the adhesiveness with the electrode is better.

The ratio of the polyvinylidene fluoride-based resin to the total amount of the resin components other than the filler contained in the porous layer is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% or more. is there.

In the porous layer, the ratio of the filler to the total amount of the polyvinylidene fluoride-based resin and the filler is preferably 1% by mass to 30% by mass, and more preferably 3% by mass to 28% by mass. When the content ratio of the filler is 1% by mass or more, the effect of forming fine irregularities on the surface of the porous layer and improving the slipperiness of the separator is likely to be exhibited. From this viewpoint, the content ratio of the filler is more preferably 3% by mass or more. On the other hand, when the content ratio of the filler is 30% by mass or less, the mechanical strength of the porous layer is maintained, and for example, when the electrode and the separator are overlapped and wound to prepare an electrode body, the separator is cracked or the like. It is hard to occur. From this viewpoint, the content ratio of the filler is more preferably 20% by mass or less, further preferably 10% by mass or less.

In the porous layer, the ratio of the polyvinylidene fluoride resin and the filler to the total mass of the polyvinylidene fluoride-based resin and the filler is determined from the viewpoint of suppressing fluffing and bending on the slit end face and mixing of slit dust when the separator is slit. It is preferably 1% by mass or more, and more preferably 3% by mass or more.

The average thickness of the porous layer is preferably 0.5 μm to 10 μm, and more preferably 1 μm to 5 μm on one side of the porous film from the viewpoint of ensuring adhesion to the electrode and high energy density. ..

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

The texture per unit area of the porous layer may be appropriately determined in consideration of the strength, film thickness, weight, and handleability of the laminated separator for a non-aqueous electrolytic solution secondary battery, but the non-aqueous electrolytic solution containing the separator is included. to be able to increase the weight energy density and volume energy density of the liquid secondary battery, usually, is preferably 0.1-5 g / ^{m 2,} and more to be 0.5 to 3 g / ^{m 2} preferable.

The volume weight of the porous layer is preferably 0.1 to 2.5 cm ³ / m ² . In the porous layer having a volume basis weight in the above range, more excellent rate characteristics can be realized by setting the mirror glossiness at 60 ° to 3 to 26%. When the volume of the porous layer is less than 0.1 cm ³ / m ² , the pores are clogged by insoluble by-products and the holding function of the electrolytic solution at the interface between the porous layer and the electrode is not sufficient, and the rate characteristics. May decrease. Further, when the volume basis weight of the porous layer exceeds 2.5 cm ³ / m ² , the ion permeability in the porous layer is lowered, and the battery characteristics are lowered from the initial stage.

The coefficient of kinetic friction of the porous layer is preferably 0.1 to 0.6, more preferably 0.1 to 0.4, and even more preferably 0.1 to 0.3. The coefficient of kinetic friction is a value measured by a method according to JIS K7125. Specifically, the coefficient of kinetic friction in the present invention is a value measured using a surface property tester manufactured by Haydon.

[2. Manufacturing method of laminated separator for non-aqueous electrolyte secondary battery]
As a method for producing a laminated separator for a non-aqueous electrolyte secondary battery according to the present invention, for example, a coating liquid containing a polyvinylidene fluoride-based resin is applied onto a porous film to form a coating layer. Next, by solidifying the polyvinylidene fluoride-based resin of the coating layer, it can be produced by a method of integrally forming the porous layer on the porous film.

The porous layer containing the polyvinylidene fluoride-based resin can be formed by, for example, the following wet coating method, and by forming by such a method, a porous layer having a three-dimensional network structure can be obtained. First, a polyvinylidene fluoride-based resin may be dissolved in a solvent, and a filler may be dispersed therein to prepare a coating liquid. By applying this coating liquid to a porous film and then immersing it in an appropriate coagulating liquid, the polyvinylidene fluoride-based resin is solidified while inducing phase separation. Through this step, a layer of a porous structure (preferably a three-dimensional network structure) containing a polyvinylidene fluoride-based resin is formed on the porous film. Then, washing with water and drying are performed to remove the coagulating liquid from the layer having a porous structure.

Specifically, the following methods can be mentioned.
(A) Prepare a solution (coating solution) in which a polyvinylidene fluoride-based resin is dissolved in a solvent.
(B) The coating liquid is applied to a porous film to form a coating film.
(C) The polyvinylidene fluoride-based resin is precipitated from the coating film by means such as immersing the coating film in a solvent (precipitate) that does not dissolve the polyvinylidene fluoride-based resin.
(D) If necessary, the coating film in which the wet polyvinylidene fluoride-based resin is precipitated is further immersed in a solvent that does not dissolve the polyvinylidene fluoride-based resin and washed.
(E) The coating film on which the wet polyvinylidene fluoride-based resin is precipitated is dried.
(F) The glossiness of the deposited coating layer is adjusted.

N-methyl-2-pyrrolidone (NMP), dimethylacetamide, dimethylformamide, dimethylformamide are used as a solvent for dissolving polyvinylidene fluoride-based resin (hereinafter, also referred to as "good solvent") used for preparing the coating liquid. Etc., a polar amide solvent is preferably used.

From the viewpoint of forming a good porous structure, it is preferable to mix a phase separation agent that induces phase separation with a good solvent. Examples of the phase separation agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol and the like. The phase separation agent is preferably added within a range in which an appropriate viscosity can be ensured for coating.

As the solvent used in the coating liquid, a mixed solvent containing 60% by mass or more of a good solvent and 5% by mass to 40% by mass of a phase separating agent is preferable from the viewpoint of forming a good porous structure. From the viewpoint of forming a good porous structure, the coating liquid preferably contains a polyvinylidene fluoride-based resin at a concentration of 3% by mass to 10% by mass.

Conventional coating methods such as Meyer bar, die coater, reverse roll coater, and gravure coater can be applied to the coating of the coating liquid on the porous film.

The precipitate liquid is generally composed of a good solvent used for preparing the coating liquid, a phase separation agent, and water. It is preferable in terms of production that the mixing ratio of the good solvent and the phase separating agent is adjusted to the mixing ratio of the mixed solvent used for dissolving the polyvinylidene fluoride resin. The concentration of water is preferably 40% by mass to 90% by mass from the viewpoint of forming a porous structure and productivity.

A known method can be adopted for drying the precipitated coating film.

Methods for adjusting the glossiness of the precipitated coating layer include chemical treatment with an acid, alkali, organic solvent, etc., physical treatment for scraping the surface of the coating layer with sandpaper, corona treatment, plasma treatment, and the like. Known processing methods can be mentioned. Among them, chemical treatment is preferable, and examples of the organic solvent used for chemical treatment include ketones such as acetone; amides such as N-methyl-2-pyrrolidone (NMP), dimethylacetamide, dimethylformamide, and dimethylformamide; ethylene carbonate, propylene carbonate. , Fluoroethylene carbonate, cyclic carbonate such as difluoroethylene carbonate; chain carbonate such as dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, and its fluorine-substituted product; cyclic ester such as γ-butyrolactone and γ-valerolactone, etc. Can be mentioned. Of these, treatment with diethyl carbonate is preferable.

The precipitated coating layer may be dried after the glossiness is adjusted.

Further, the separator of the present invention can also be produced by a method in which the porous layer is prepared as an independent sheet, the porous layer is laminated on the porous film, and the porous layer is composited by thermocompression bonding or an adhesive. As a method for producing the porous layer as an independent sheet, a coating liquid containing a polyvinylidene fluoride resin and a filler is applied onto the release sheet, and the above-mentioned production method is applied to form the porous layer. Examples thereof include a method of peeling the porous layer from the release sheet.

The air permeability of the laminated separator for a non-aqueous electrolytic solution secondary battery of the present invention is preferably 30 to 800 sec / 100 mL, more preferably 50 to 500 sec / 100 mL in terms of Gale value. When the laminated separator for a non-aqueous electrolyte secondary battery has the above-mentioned air permeability, sufficient ion permeability can be obtained. When the air permeability exceeds the above range, it means that the laminated structure is rough due to the high porosity of the laminated separator for the non-aqueous electrolyte secondary battery, and as a result, the non-aqueous electrolyte secondary is secondary. The strength of the laminated separator for batteries may decrease, resulting in insufficient shape stability, especially at high temperatures. On the other hand, when the air permeability is less than the above range, sufficient ion permeability cannot be obtained when used as a separator, which may deteriorate the battery characteristics of the non-aqueous electrolyte secondary battery.

[3. Non-aqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous secondary battery that obtains an electromotive force by doping and dedoping lithium, and is a positive electrode sheet and a laminated separator for the non-aqueous electrolyte secondary battery described above. And the negative electrode sheet may be provided with a laminate (member for a non-aqueous electrolytic solution secondary battery) laminated in this order, and other configurations are not particularly limited. In the non-aqueous electrolyte secondary battery, a battery element in which the negative electrode sheet and the positive electrode sheet are impregnated with the electrolytic solution in a structure facing each other via the above-mentioned laminated separator for the non-aqueous electrolyte secondary battery is contained in the exterior material. It has an enclosed structure. The non-aqueous electrolyte secondary battery is particularly suitable for a lithium ion secondary battery. The dope means occlusion, support, adsorption, or insertion, and means a phenomenon in which lithium ions enter the active material of an electrode such as a positive electrode.

The positive electrode sheet may have a structure in which an active material layer containing a positive electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive additive.

Examples of the positive electrode active material include lithium-containing transition metal oxides, and specifically, LiCoO ₂ , LiNiO ₂ , LiMn _1/2 Ni _1/2 O ₂ , LiCo _1/3 Mn _1/3 Ni _{1 /.} Examples thereof include ₃ O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCo _1/2 Ni _1/2 O ₂ , LiAl _1/4 Ni _3/4 O ₂ .

Examples of the binder resin include polyvinylidene fluoride-based resins.
Examples of the conductive auxiliary agent include carbon materials such as acetylene black, ketjen black, and graphite powder.

Examples of the current collector include aluminum foil, titanium foil, stainless steel foil and the like having a thickness of 5 μm to 20 μm.

The negative electrode sheet may have a structure in which an active material layer containing a negative electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive additive. Examples of the negative electrode active material include materials capable of electrochemically occluding lithium, and specific examples thereof include carbon materials; alloys of silicon, tin, aluminum and the like with lithium; and the like.

Examples of the binder resin include polyvinylidene fluoride-based resin and styrene-butadiene rubber. The separator of the present invention can secure sufficient adhesiveness to the negative electrode even when styrene-butadiene rubber is used as the negative electrode binder.
Examples of the conductive auxiliary agent include carbon materials such as acetylene black, ketjen black, and graphite powder.

Examples of the current collector include copper foil, nickel foil, stainless steel foil and the like having a thickness of 5 μm to 20 μm. Further, instead of the above-mentioned negative electrode, a metallic lithium foil may be used as the negative electrode.

The electrolytic solution is a solution in which a lithium salt is dissolved in a non-aqueous solvent. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO _{4, and the} like.

The non-aqueous solvent includes all solvents generally used in non-aqueous electrolyte secondary batteries. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, and fluorine-substituted products thereof; γ-butyrolactone, γ-valerolactone, etc. Cyclic esters; etc., which may be used alone or in admixture.

As the electrolytic solution, 0.5 M of lithium salt was added to a solvent obtained by mixing cyclic carbonate and chain carbonate in a mass ratio (cyclic carbonate / chain carbonate) of 20/80 to 40/60 (more preferably 30/70). Those dissolved in ~ 1.5M are suitable.

Examples of the exterior material include metal cans and aluminum laminated film packs. The shape of the battery includes a square type, a cylindrical type, a coin type, and the like.

In a non-aqueous electrolyte secondary battery, for example, an exterior material (for example, aluminum) is obtained by impregnating a laminate in which the above-mentioned laminated separator for a non-aqueous electrolyte secondary battery is arranged between a positive electrode sheet and a negative electrode sheet with an electrolytic solution. It can be produced by housing it in a laminated film pack) and pressing the laminate over the exterior material. At this time, in order to improve the adhesiveness between the electrode and the laminated separator for the non-aqueous electrolyte secondary battery, it is preferable that the press is a press while heating (hot press).

The method of arranging the separator between the positive electrode sheet and the negative electrode sheet may be a method of laminating at least one layer of the positive electrode sheet, the separator, and the negative electrode in this order (so-called stack method), and the positive electrode sheet, the separator, the negative electrode sheet, and the separator may be used. May be stacked in this order and wound in the length direction.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

<Measurement of mirror gloss>
The mirror glossiness is measured by stacking 5 sheets of KB paper (manufactured by KOKUYO Co., Ltd., product number; KB-39N) using a gloss meter (PG-IIM type manufactured by Nippon Denshoku Industries Co., Ltd.) and measuring the top of them. A laminated separator for an electrolytic solution secondary battery was placed, and the incident angle and the light receiving angle on the surface of the porous layer in the laminated separator for a non-aqueous electrolytic solution secondary battery were measured as 60 °.

If necessary, such as when there are deposits such as resin powder or inorganic substances on the surface of the laminated separator for non-aqueous electrolyte secondary batteries, the separator should be an organic solvent such as diethyl carbonate (DEC) and / or before the mirror gloss measurement. Alternatively, after immersing in water to wash and remove the deposits and the like, pretreatment such as drying the solvent or water may be performed.

<Measurement of piercing strength>
Using a handy compression tester (manufactured by Kato Tech Co., Ltd., model number; KES-G5), the porous film was fixed with a washer of 12 mmΦ, and the maximum stress (N) when the pin was pierced at 200 mm / min was obtained from the film. The piercing strength was set. The pin used had a pin diameter of 1 mmΦ and a tip of 0.5R.

<Measurement of volume basis weight of porous layer>
By measuring the basis weight (weight per square meter) of the porous layer in the dry state and dividing the basis weight by the specific gravity of the PVDF-based resin at 25 ° C., the resin component of the porous layer in the dry state can be obtained. The volume basis weight (resin volume per square meter) was calculated.

<Making a separator>
As described below, laminated separators for non-aqueous electrolyte secondary batteries according to Examples 1 to 6 and Comparative Examples 1 and 2 were produced.

(Example 1)
A PVDF resin (manufactured by Arkema; trade name “KYNAR2801”) was dissolved in N-methyl-2-pyrrolidone at 65 ° C. for 30 minutes so that the solid content was 7% by mass. Using the obtained solution as a coating solution, the volume of PVDF resin in the coating solution was determined by the doctor blade method on a polyethylene porous film (thickness 12 μm, porosity 44%, average pore size 0.035 μm). It was applied so as to be 0.56 cm ³ / m ² . The obtained laminated body (1-i) was immersed in 2-propanol with the coating film in an NMP wet state, and allowed to stand at 25 ° C. for 5 minutes to allow the laminated porous film (1-i). ii) was obtained. The obtained laminated porous film (1-ii) was immersed in another 2-propanol in a wet state with a dipping solvent and allowed to stand at 25 ° C. for 5 minutes to obtain a laminated porous film (1-iii). .. The obtained laminated porous film (1-iii) was dried at 65 ° C. for 5 minutes to obtain a laminated porous film (1-iv). The obtained laminated porous film (1-iv) was immersed in diethyl carbonate at 70 ° C. for 1 minute. The film was taken out of diethyl carbonate and dried at room temperature to obtain a laminated separator for a non-aqueous electrolyte secondary battery of Example 1. Table 1 shows the rate characteristics of the laminated separator for a non-aqueous electrolyte secondary battery of Example 1.

(Example 2)
The laminated porous film (1-iv) obtained in Example 1 was immersed in diethyl carbonate at 70 ° C. for 5 minutes, and the film was taken out of diethyl carbonate and dried at room temperature. A laminated separator for a non-aqueous electrolyte secondary battery was obtained. Table 1 shows the rate characteristics of the laminated separator for a non-aqueous electrolyte secondary battery of Example 2.

(Example 3)
The laminated porous film (1-iv) obtained in Example 1 was immersed in diethyl carbonate at 70 ° C. for 15 minutes, and the film was taken out of diethyl carbonate and dried at room temperature. A laminated separator for a non-aqueous electrolyte secondary battery was obtained. Table 1 shows the rate characteristics of the laminated separator for a non-aqueous electrolyte secondary battery of Example 3.

(Example 4)
The laminated porous film (1-iv) obtained in Example 1 was immersed in diethyl carbonate at 70 ° C. for 30 minutes, and the film was taken out of diethyl carbonate and dried at room temperature. Example 4 A laminated separator for a non-aqueous electrolyte secondary battery was obtained. Table 1 shows the rate characteristics of the laminated separator for a non-aqueous electrolyte secondary battery of Example 4.

(Example 5)
A laminated separator for a non-aqueous electrolyte secondary battery of Example 5 was obtained in the same manner as in Example 3 except that the coating liquid was applied so that the volume basis weight was 1.58 cm ³ / m ² . Table 1 shows the rate characteristics of the laminated separator for a non-aqueous electrolyte secondary battery of Example 5.

(Example 6)
A laminated separator for a non-aqueous electrolyte secondary battery of Example 6 was obtained in the same manner as in Example 3 except that the coating liquid was applied so that the volume basis weight was 0.11 cm ³ / m ² . Table 1 shows the rate characteristics of the laminated separator for a non-aqueous electrolyte secondary battery of Example 6.

(Comparative Example 1)
A laminated separator for a non-aqueous electrolyte secondary battery of Comparative Example 1 was obtained by the same method as in Example 1 except that it was not immersed in diethyl carbonate. Table 1 shows the rate characteristics of the laminated separator for a non-aqueous electrolyte secondary battery of Comparative Example 1.

(Comparative Example 2)
A PVDF resin (manufactured by Arkema; trade name “KYNAR2801”) was dissolved in N-methyl-2-pyrrolidone at 65 ° C. for 30 minutes so that the solid content was 7% by mass. Using the obtained solution as a coating solution, the volume of PVDF resin in the coating solution was determined by the doctor blade method on a polyethylene porous film (thickness 12 μm, porosity 44%, average pore size 0.035 μm). It was applied so as to be 0.56 cm ³ / m ² . The obtained laminate (8-i), which was a coating material, was dried at 85 ° C. for 5 minutes to obtain a laminate separator for a non-aqueous electrolyte secondary battery of Comparative Example 2. Table 1 shows the rate characteristics of the laminated separator for a non-aqueous electrolyte secondary battery of Comparative Example 2.

<Manufacturing of non-aqueous electrolyte secondary battery>
Next, a non-aqueous electrolyte secondary battery was prepared according to the following using each of the laminated separators for non-aqueous electrolyte secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 2 prepared 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 the aluminum foil was used. The aluminum foil is cut off from the positive electrode so that the size of the portion where the positive electrode active material layer is formed is 40 mm × 35 mm, and the portion having a width of 13 mm and the positive electrode active material layer is not formed remains on the outer periphery thereof. It was used as the positive electrode. The thickness of the positive electrode active material layer was 58 μm, and the density was 2.50 g / cm ³ .

(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. The copper foil is cut off from the negative electrode so that the size of the portion where the negative electrode active material layer is formed is 50 mm × 40 mm and the portion having a width of 13 mm and the negative electrode active material layer is not formed remains on the outer periphery thereof. It was used as the negative electrode. The thickness of the negative electrode active material layer was 49 μm, and the density was 1.40 g / cm ³ .

(assembly)
By laminating (arranging) the positive electrode, the laminated separator for the non-aqueous electrolyte secondary battery, and the negative electrode in this order in the laminate pouch, a member for the non-aqueous electrolyte secondary battery was obtained. At this time, the positive electrode and the negative electrode were arranged so that the entire main surface of the positive electrode active material layer of the positive electrode was included in the range of the main surface of the negative electrode active material layer of the negative electrode (overlapping the main surface).

Subsequently, the member for the non-aqueous electrolyte secondary battery 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 further placed in this bag. The non-aqueous electrolyte solution was prepared by dissolving LiPF ₆ having an ethylene carbonate and diethyl carbonate concentration of 1.0 mol / liter in a mixed solvent having a volume ratio of ethyl methyl carbonate, diethyl carbonate and ethylene carbonate at 50:20:30. The electrolytic solution of was used. Then, the non-aqueous electrolyte secondary battery was produced by heat-sealing the bag while reducing the pressure inside the bag.

<Rate test>
For a new non-aqueous electrolyte secondary battery that has not undergone a charge / discharge cycle, a voltage range of 4.1 to 2.7 V and a current value of 0.2 C (rated capacity based on an hourly discharge capacity) at 25 ° C. The initial charge / discharge of 4 cycles was performed with the current value of discharging in 1 hour being 1C, and the same applies hereinafter) as 1 cycle.

Subsequently, at 55 ° C., the following formula rate characteristic (%) = (20C discharge capacity / 0.2C discharge capacity) × 100
The rate characteristics were calculated according to the above.

As shown in Table 1, in the non-aqueous electrolyte secondary battery using the laminated separator for the non-aqueous electrolyte secondary battery according to Comparative Example 2 in which the mirror glossiness exceeds 26%, the rate characteristic is remarkable at 43%. It was confirmed that it was low. This is because when the mirror gloss exceeds 26%, the density of the porous layer becomes too high, the internal resistance of the battery increases, and the retention function of the electrolytic solution at the interface between the separator and the electrode decreases, resulting in ion permeability. It is considered that this is because

Further, it was confirmed that the rate characteristic was as low as 65% even in the non-aqueous electrolyte secondary battery using the laminated separator for the non-aqueous electrolyte secondary battery according to Comparative Example 1 in which the mirror glossiness was less than 3%. .. It is considered that this is because when the mirror glossiness is less than 3%, the uniformity of the porous layer is low and the ion permeability is uneven.

On the other hand, in the non-aqueous electrolyte secondary battery using the laminated separator for the non-aqueous electrolyte secondary battery according to Examples 1 to 6 having a mirror glossiness of 3 to 26%, the rate characteristic is 70% or more. , It was confirmed that the battery characteristics are excellent.

Claims (9)

A porous film containing as a main component a polyolefin resin, a porous layer (where a filler containing no) and a non-aqueous electrolyte laminated separator for a secondary battery comprising a containing polyvinylidene fluoride resin,
The 60 ° mirror gloss on the surface of the porous layer is 3 to 26%.
The volumetric basis weight of the porous layer is 0.1 to 2.5 cm ³ / m ² .
The average film thickness of the porous layer is 0.5 μm to 10 μm on one side of the porous film.
The porous layer, Ri outermost der of the stacked separator for a nonaqueous electrolyte secondary battery,
The average pore size of the porous film is 0.01 μm or more and 0.14 μm or less.
The film thickness of the porous film is 4 to 40 μm.
A laminated separator for a non-aqueous electrolyte secondary battery, wherein the porosity of the porous film based on the volume is 20 to 80% by volume . The laminated separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the porous layer has a porosity of 30% to 60%. The laminated separator for a non-aqueous electrolyte secondary battery according to claim 1 or 2 , wherein the ratio of the polyvinylidene fluoride-based resin to the total amount of the resin component contained in the porous layer is 80% by mass or more. The laminated separator for a non-aqueous electrolytic solution secondary battery according to any one of claims 1 to 3 , wherein the porous layer is laminated on at least one surface of the porous film. The laminated separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4 , wherein the porous film has a piercing strength of 2N or more. The polyvinylidene fluoride-based resin is a copolymer of vinylidene fluoride with at least one monomer selected from the group consisting of hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, and vinyl fluoride. The laminated separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5 , which is a homopolymer of vinylidene fluoride or a mixture of these polymers. A member for a non-aqueous electrolyte secondary battery in which a positive electrode, a laminated separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6 , and a negative electrode are arranged in this order. A non-aqueous electrolyte secondary battery comprising the laminated separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6 . The method for manufacturing a laminated separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6 .
A step of applying a coating liquid in which the polyvinylidene fluoride-based resin is dissolved to the porous film to form a coating film.
A step of precipitating the polyvinylidene fluoride-based resin from the coating film, and
The step of adjusting the glossiness of the coating layer on which the polyvinylidene fluoride-based resin is precipitated is included.
A method for producing a laminated separator for a non-aqueous electrolyte secondary battery, wherein the glossiness is adjusted by a chemical treatment, a physical treatment for scraping the surface of a coating layer, a corona treatment, or a plasma treatment.