KR101810777B1 - Laminated separator for non-aqueous secondary battery, non-aqueous secondary battery member, and non-aqueous secondary battery - Google Patents

Abstract

[PROBLEMS] To provide a laminated separator for a nonaqueous electrolyte secondary battery which suppresses deterioration of cycle characteristics.
[MEANS FOR SOLVING PROBLEMS] A laminate separator for a nonaqueous electrolyte secondary battery comprises a porous film comprising a polyolefin resin and a porous layer, wherein the surface of the porous layer has a specular gloss of 60 to 60% and a volume of the porous layer And the basis weight is 0.1 to 2.5 cm 3 / m 2.

Description

TECHNICAL FIELD [0001] 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,

The present invention relates to a laminate separator for a nonaqueous electrolyte secondary battery, a member for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery.

BACKGROUND ART Non-aqueous electrolyte secondary batteries such as lithium secondary batteries are currently widely used as batteries for use in devices such as personal computers, mobile phones, portable information terminals, and the like.

These nonaqueous electrolyte secondary batteries, typified by lithium secondary batteries, have high energy density, and therefore, when an internal short circuit or an external short circuit occurs due to breakage of a battery or breakage of a device using the battery, . Therefore, it is required to secure high safety by preventing heat generation of a certain amount or more in the nonaqueous electrolyte secondary battery.

As a means for securing the safety of the nonaqueous electrolyte secondary battery, a method of shutting off the passage of ions between the positive electrode and the negative electrode by the separator when abnormal heat generation occurs is generally applied to provide a shutdown function for preventing further heat generation. That is, in the nonaqueous electrolyte secondary battery, when an abnormal current flows in the battery due to, for example, an internal short between the positive electrode and the negative electrode, the separator disposed between the positive electrode and the negative electrode interrupts the current, (Shut down), thereby imparting a function of suppressing further heat generation. As the separator, a film-like porous film containing a polyolefin-based resin as a main component, which is melted at about 80 to 180 ° C, for example, when abnormal heat generation occurs, is generally used.

In order to improve the function of the 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, Patent Document 1 discloses a lamination of a separator, which is a microporous sheet containing a polyolefin resin, and a porous film containing an inorganic filler and a film binder, in order to prevent an internal short circuit of the battery. By defining the polished surface of the porous film at a mirror polish degree of 85 DEG, a porous film having thinness, uniformity, and excellent flexibility is realized.

Patent Document 2 discloses a separator coated with a composition comprising insulating microparticles and an organic binder in a microporous film made of polyethylene to define a mirror polish degree of 60 DEG to prevent short circuiting and improve reliability .

Japanese Patent Application Laid-Open No. 2005-294216 (published on October 20, 2005) Japanese Patent Application Laid-Open No. 2014-17264 (published on January 30, 2014)

However, the above Patent Documents 1 and 2 aim at improvement of flexibility, prevention of short circuit, and improvement of reliability, and the cycle characteristics are not considered.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and an object of the present invention is to provide a laminated separator for a non-aqueous electrolyte secondary battery which suppresses deterioration of cycle characteristics.

The inventors of the present invention have found that in a laminate separator for a nonaqueous electrolyte secondary battery comprising a porous film and a porous layer, the surface gloss of 60 ° on the surface of the porous layer and the volume basis weight of the porous layer are related to the cycle characteristics of the nonaqueous electrolyte secondary battery And that the decrease in the cycle characteristics of the nonaqueous electrolyte secondary battery can be suppressed by setting the specular gloss and the volume basis weight to fall within a predetermined range. The present invention has been accomplished based on these findings.

The laminated separator for a nonaqueous electrolyte secondary battery according to the present invention is for solving the above problems and is a laminated separator for a nonaqueous electrolyte secondary battery comprising a porous film containing a polyolefin resin and a porous layer, A surface gloss of 60 ° is 3 to 26%, and a volume basis weight of the porous layer is 0.1 to 2.5 cm 3 / m 2.

In the laminated separator for a nonaqueous electrolyte secondary cell according to the present invention, it is preferable that the porous layer includes a filler.

In the laminated separator for a nonaqueous electrolyte secondary battery according to the present invention, it is preferable that the porous layer contains a filler and a resin, and the ratio of the filler in the total amount of the filler and the resin is 50 to 99 mass%.

In the laminated separator for a non-aqueous electrolyte secondary cell according to the present invention, it is preferable that the sticking strength of the porous film is 2N or more.

In the laminated separator for a non-aqueous electrolyte secondary battery according to the present invention, the average pore diameter of the porous film is preferably 0.14 탆 or less.

The nonaqueous electrolyte secondary cell according to the present invention is characterized in that the positive electrode, the laminate separator for the nonaqueous electrolyte secondary battery and the negative electrode are arranged in this order.

The nonaqueous electrolyte secondary battery according to the present invention is characterized by including the above-described laminated separator for a nonaqueous electrolyte secondary battery.

According to the present invention, the effect of suppressing the deterioration of the cycle characteristics of the nonaqueous electrolyte secondary battery is exhibited.

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 constitutions described below, but may be modified in various ways within the scope of the claims, and embodiments obtained by suitably combining the technical means disclosed in the other embodiments with the technical scope of the present invention . Unless specifically stated in the present specification, "A to B" indicating numerical ranges means "A to B".

〔One. Laminated separator for non-aqueous electrolyte secondary battery]

A laminated separator for a nonaqueous electrolyte secondary battery according to the present invention is a nonaqueous electrolyte secondary battery comprising a membrane-like porous film which is disposed between a positive electrode and a negative electrode in a nonaqueous electrolyte secondary battery and contains a polyolefin-based resin as a main component, and a porous layer .

[1-1. Porous film]

The porous film may be a base material (polyolefin-based porous substrate) which is porous and mainly composed of a polyolefin-based resin, and has a structure having pores connected to the inside thereof so that gas or liquid can permeate from one side to the other side Film. That is, the porous film in the present invention is a film having pores, which is different from a nonwoven fabric in which fibers are superimposed on each other.

The porous film may be one in which the separator for a nonaqueous electrolyte secondary battery is given a shutdown function by making the separator for a nonaqueous electrolyte secondary battery non-porous (non-porous) when the battery is heated. The porous film may include one layer, or may include a plurality of layers.

The porosity based on the volume of the porous film is preferably in the range of 0.2 to 0.8 (20 to 80% by volume) so as to obtain a function of increasing the amount of the electrolyte retained and reliably shutting down the flow of the excessive current at a lower temperature , More preferably from 0.3 to 0.75 (30 to 75% by volume). The mean diameter (average pore diameter) of the pores of the porous film is preferably 0.14 占 퐉 or less so that sufficient ion permeability can be obtained when used as a separator and particles can be prevented from being drawn into the positive electrode and the negative electrode More preferably 0.1 탆 or less, and more preferably 0.01 탆 or more.

As a method for controlling the average pore diameter of the porous film, for example, in the case of decreasing the pore diameter, a method of uniformizing the dispersing state of the pitching agent such as an inorganic filler or the phase separator at the time of forming the porous film, A method of making a particle diameter of fine particles fine, a method of stretching in the state including a phase separator, and a method of stretching at a low stretching magnification. As a method for 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 phase separation agent or phase separation agent such as an inorganic filler for a polyolefin resin, A method of stretching at a later stage, and a method of stretching at a higher stretching magnification.

If the average pore diameter of the porous film is decreased, it is considered that the capillary force assumed to be the driving force for introducing the electrolyte into the pores inside the substrate is increased. Further, since the average pore diameter is small, generation of dendrites (dendritic crystals) by lithium metal can be suppressed.

Further, when the porosity of the porous film is increased, it is considered that the volume of the portion in which the polyolefin that can not infiltrate the electrolyte solution exists in the polyolefin substrate decreases.

The sticking strength of the porous film is preferably 2N or more, more preferably 3N or more. If the sticking strength is too small, the separator may be broken by the positive electrode active material particles in the case where the positive pole of the battery assembling process and the coiling operation of the separator, the pressing operation of the winding group, There is a fear that the government poles may be short-circuited. The sticking strength of the porous film is preferably 10 N or less, more preferably 8 N or less.

The proportion of the polyolefin resin component in the porous film is preferably 50 vol.% Or more, more preferably 90 vol.% Or more, and more preferably 95 vol.% Or more. The polyolefin resin component of the porous film preferably contains a high molecular weight component having a weight average molecular weight of 5 10 ⁵ to 15 10 ⁶ . Particularly, the polyolefin component having a weight average molecular weight of at least 1,000,000 as the polyolefin component of the porous film is preferable because the strength of the whole of the porous film (that is, the separator for the nonaqueous electrolyte secondary battery) is increased.

Examples of the polyolefin-based resin include homopolymers or copolymers of high molecular weight obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene or the like. The porous film may be a layer containing these polyolefins alone and / or a layer containing two or more of these polyolefins. Particularly, a high molecular weight polyethylene mainly composed of ethylene is preferred. Further, the porous film does not interfere with the inclusion of components other than the polyolefin within a range that does not impair the function of the layer.

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

 The thickness of the porous film is suitably determined in consideration of the number of stacked layers of the laminate separator for a nonaqueous electrolyte secondary battery. Particularly, since the porous layer is formed on one surface (or both surfaces) of the porous film, it is preferably 4 to 40 탆, more preferably 7 to 30 탆. The basis weight of the porous film is preferably 4 to 20 g, more preferably 5 to 20 g, in terms of strength, film thickness, handleability and weight, and further in that the weight energy density or the volume energy density of the battery when used as a separator of the non- / M < 2 >, and preferably 5 to 12 g / m < 2 >.

A known method can be used for the production of such a porous film, and is not particularly limited. For example, as described in Japanese Patent Application Laid-Open No. 7-29563, there is a method of adding a hole-forming agent to a thermoplastic resin and forming the film, followed by removing the hole-forming agent 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, from the viewpoint of production cost, .

(1) 100 parts by weight of ultrahigh 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 to obtain a polyolefin resin composition

(2) a step of molding a sheet using the polyolefin resin composition

(3) a step of removing the inorganic filler from the sheet obtained in the step (2)

(4) A step of stretching the sheet obtained in the step (3) to obtain a porous film.

[1-2. Porous layer]

The porous layer according to the present invention has a plurality of pores therein and has a structure in which the pores are connected to each other, so that the porous layer can be a layer in which gas or liquid can pass from one surface to the other surface. In the present embodiment, the porous layer is provided as an outermost layer of the separator on one surface or both surfaces of the porous film, and becomes a layer which can be bonded to the electrode.

As a result of intensive studies, the inventors of the present invention have found that, by setting the surface gloss of 60 degrees on the surface of the porous layer to 3 to 26%, the cycle of the nonaqueous electrolyte secondary battery comprising the laminate separator for the nonaqueous electrolyte secondary battery containing the porous layer It is possible to suppress deterioration of the characteristics. Here, the specular gloss of 60 DEG shows the glossiness when the incident angle and the light receiving angle are 60 DEG, and is measured by a measuring method specified in JIS Z8741. The mirror surface gloss of the porous layer is a parameter related to the denseness and uniformity of the porous layer.

When the specular gloss is less than 3%, the uniformity of the porous layer is low and the ion permeability is uneven. As a result, the progress of deterioration by repetition of charging and discharging is fast, and the cycle characteristics are deteriorated. Therefore, by setting the mirror surface gloss to 3% or more, it is possible to suppress the deterioration of the cycle characteristics due to the nonuniformity of the porous layer.

On the other hand, when the specular glossiness exceeds 26%, the density of the porous layer becomes excessively high, and the internal resistance of the battery is increased due to clogging of pores caused by insoluble byproducts or bubbles generated by charging and discharging. Further, at the interface between the porous layer and the electrode, the place where the electrolytic solution is held is small, and the electrolytic solution is easily partially depleted by repeating charge and discharge. As a result, the ion permeability is lowered and the cycle characteristics are lowered. Therefore, by setting the mirror surface gloss to 26% or less, it is possible to suppress the clogging of the pores caused by insoluble by-products and the deterioration of the cycle characteristics due to the depletion of the electrolyte at the interface between the porous layer and the electrode.

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

The volume basis weight of the porous layer is 0.1 to 2.5 cm 3 / m 2. In the porous layer having a volume basis weight in this range, the effect of suppressing the deterioration of the cycle characteristics can be realized by making the specular glossiness at 60 占 3 to 26%. When the volume basis weight of the porous layer is less than 0.1 cm 3 / m 2, clogging of the pores due to the insoluble byproducts and an electrolyte retention function at the interface between the porous layer and the electrode are insufficient, and the cycle characteristics are lowered. When the volume basis weight of the porous layer is more than 2.5 cm 3 / m 2, the ion permeability of the porous layer is lowered and the cell characteristics from the beginning are lowered.

Specific examples of the resin constituting the porous layer include polyolefins such as polyethylene, polypropylene, polybutene and ethylene-propylene copolymer; Fluorine-containing resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene; Fluorine-containing rubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; Aromatic polyamides; Wholly aromatic polyamide (aramid resin); Styrene-butadiene copolymers and hydrides thereof, methacrylic acid ester copolymers, acrylonitrile-acrylic acid ester copolymers, styrene-acrylic acid ester copolymers, ethylene propylene rubbers and polyvinyl acetate; A resin having a melting point or a glass transition temperature of 180 DEG C or higher such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyetheramide and polyester; And water-soluble polymers such as polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, and polymethacrylic acid.

Specific examples of the aromatic polyamide include poly (paraphenylene terephthalamide), poly (metaphenylene isophthalamide), poly (parabenzamide), poly (methabenzamide), poly (4,4'-benzanilide terephthalamide), poly (paraphenylene-4,4'-biphenylene dicarboxylic acid amide), poly (metaphenylene-4,4'-biphenylene dicarboxyl Naphthalene dicarboxylic acid amide), poly (paraphenylene-2,6-naphthalene dicarboxylic acid amide), poly (metaphenylene-2,6-naphthalene dicarboxylic acid amide), poly (2-chloropara- phenene terephthalamide ), Paraphenylene terephthalamide / 2,6-dichloro-paraphenylene terephthalamide copolymer, and metaphenylene terephthalamide / 2,6-dichloropara phenylene terephthalamide copolymer. Of these, poly (paraphenylene terephthalamide) is more preferable.

Of the above resins, fluorine-containing resins and aromatic polyamides are more preferable, and among the fluorine-containing resins, polyfluorinated polymers such as polyvinylidene fluoride (PVDF), copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) A vinylidene resin is more preferable, and PVDF is more preferable.

The porous layer may include a filler. Examples of the filler that can be included in the porous layer include a filler containing an organic substance and a filler containing an inorganic substance. Specific examples of the filler containing an organic substance include styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, methyl acrylate and the like A homopolymer or two or more kinds of copolymers of monomers; Fluorine-containing resins such as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer and polyvinylidene fluoride; Melamine resin; Urea resin; Polyethylene; Polypropylene; Polyacrylic acid, polymethacrylic acid; And the like. Specific examples of the inorganic filler include calcium carbonate, talc, clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, A filler containing an inorganic substance such as magnesium, calcium oxide, magnesium oxide, titanium oxide, titanium nitride, alumina (aluminum oxide), aluminum nitride, mica, zeolite and glass can be mentioned. The filler may be used alone or in combination of two or more.

Of these fillers, fillers containing an inorganic substance, which are generally referred to as fillers, are suitable and fillers containing inorganic oxides such as silica, calcium oxide, magnesium oxide, titanium oxide, alumina, mica and zeolite are more preferred, , Magnesium oxide, titanium oxide and alumina is more preferable, and alumina is particularly preferable. Alumina has many crystalline forms such as? -Alumina,? -Alumina,? -Alumina,? -Alumina, and the like, but all of them can be suitably used. Of these,? -Alumina is most preferable because of its particularly high thermal stability and chemical stability.

The fillers may be used singly or in combination of two or more kinds.

The volume average particle diameter of the filler is preferably 0.01 탆 to 10 탆 from the viewpoints of good adhesion, ensuring slipperiness and moldability of the separator. The lower limit value is more preferably 0.1 m or more, and the upper limit value is more preferably 5 m or less.

The particle shape of the filler is optional and may be any of spherical, elliptical, plate, rod, and irregular shapes. From the viewpoint of preventing short-circuiting of the battery, it is preferable that the particles are plate-like particles or primary particles that are not agglomerated.

When the filler is a plate-like particle or a primary particle which does not coagulate, the filler may be formed on the surface of the porous layer by the irregularities formed on the surface of the porous layer by the filler And the adhesion to the electrode is better.

In the porous layer, the proportion of the filler in the total amount of the resin and the filler is 5 mass% to 99 mass%, more preferably 10 mass% to 99 mass%, still more preferably 25 mass% to 99 mass% The preferable proportion of the filler is 50% by mass to 99% by mass. When the ratio of the filler is less than 5% by mass, the proportion of the filler in the porous layer is low, and the filler is unevenly distributed at the time of coating, and as a result, the uniformity of the porous layer is deteriorated in some cases. It becomes difficult to express the function. On the other hand, when the proportion of the filler is more than 99% by mass, the proportion of the resin in the porous layer is lowered, so that the bondability between the fillers is lowered, and problems such as dropping of the filler at the time of handling occur.

The average film thickness of the porous layer is preferably 0.5 占 퐉 to 10 占 퐉 and more preferably 1 占 퐉 to 5 占 퐉 on one side of the porous film from the viewpoint of adhesion with the electrode and securing a high energy density.

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

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

〔2. Method for producing laminated separator for non-aqueous electrolyte secondary battery]

The laminated separator for a nonaqueous electrolyte secondary battery according to the present invention is not particularly limited as long as a laminated separator for the nonaqueous electrolyte secondary battery can be obtained, and can be produced by various methods. For example, by forming a porous layer containing a resin by using any one of the following methods (1) to (3).

(1) A coating liquid in which the resin forming the porous layer is dissolved is coated on the surface of the porous film, and then the film is dipped in a precipitation solvent which is a poor solvent for the resin to form a porous layer composed of the resin Precipitation.

(2) a coating solution obtained by dissolving the resin forming the porous layer is coated on the surface of the porous film, and then the liquid of the coating liquid is made acidic by using a low boiling point positive property, .

(3) A method for coating a surface of a porous film obtained by dissolving a resin forming the porous layer on a surface of the porous film, followed by evaporating the solvent in the coating liquid to precipitate a porous layer composed of the resin.

In the case of the above methods (1) and (2), a step of further drying the obtained laminate after the porous layer has been precipitated may be included.

The solvent (dispersion medium) for dissolving the resin is not particularly limited as long as it can uniformly and stably dissolve the resin without adversely affecting the porous film and uniformly and stably disperse the filler. Specific examples of the solvent (dispersion medium) include water; Lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol and t-butyl alcohol; Acetone, toluene, xylene, hexane, N-methylpyrrolidone, N, N-dimethylacetamide and N, N-dimethylformamide. The solvent (dispersion medium) may be used alone or in combination of two or more. In the above method, when the resin constituting the porous layer is a polyvinylidene fluoride (PVDF) resin, an amide-based solvent such as N-methylpyrrolidone may be used as the solvent for dissolving the PVDF- And it is more preferable to use N-methylpyrrolidone.

As the precipitation solvent, for example, another solvent which dissolves in a solvent (dispersion medium) contained in the coating solution and does not dissolve the resin contained in the coating solution (hereinafter referred to as solvent X) may be used. The porous film on which the coating liquid is applied to form a coating film is immersed in the solvent X and the solvent (dispersion medium) on the porous film or the coating film on the support is replaced with the solvent X and then the solvent X is evaporated, ) Can be efficiently removed. Specific examples of the precipitation solvent include water; Lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol and t-butyl alcohol; Acetone, and the like. The precipitation solvent may be used alone or in combination of two or more. In the above method (1), for example, when the resin constituting the porous layer is a PVDF-based resin, isopropyl alcohol or t-butyl alcohol is preferable as a solvent for precipitating the porous layer.

In the above method (2), examples of the low boiling point positive amines include hydrochloric acid, acetic acid and the like.

In the method (3), conventionally known drying methods are employed for evaporating the solvent. Among them, the far-infrared heating or freeze-drying has an advantage that the pore shape of the porous layer is hardly collapsed at the time of precipitation as compared with other drying methods (air drying, etc.).

The laminated separator for a nonaqueous electrolyte secondary battery in the present invention can be produced by forming a porous layer containing a resin on the surface of a porous film as a base material by the method shown in the following (4).

(4) A method for forming a porous layer by coating a substrate with a coating liquid dispersed in a dispersion medium such as water of the resin fine particles forming the porous layer, and drying and removing the dispersion medium.

In the method (4), the dispersion medium is preferably water, and a dispersion medium such as water can be diluted and substituted by immersing the laminated film before drying in a lower alcohol. As the lower alcohol in this case, isopropyl alcohol Or t-butyl alcohol is preferable.

When a filler is contained in the porous layer, a porous layer containing a filler can be formed by using a dispersion in which a filler is further dispersed in a coating liquid in which the resin forming the porous layer is dissolved.

The method of applying the coating liquid to the porous film, that is, the method of forming the porous layer on the surface of the porous film subjected to the hydrophilization treatment if necessary, is not particularly limited. In the case of laminating the porous layer on both surfaces of the porous film, there can be used a laminating method in which a porous layer is formed on one surface of a porous film and then a porous layer is formed on the other surface, Can be simultaneously formed.

The thickness of the porous layer can be controlled by controlling the thickness of the coating film in the wet state (wet) after coating, the weight ratio of resin and filler, the solid content concentration of the coating liquid (sum of the resin concentration and filler concentration)

The method of applying the coating liquid to the porous film is not particularly limited as long as it is a method capable of realizing a necessary basis weight or a coating area. As a coating method of the coating solution, conventionally known methods can be employed. Specifically, gravure coating method, small-diameter gravure coating method, reverse roll coating method, transfer roll coating method, kiss coating method, A blade coater method, a rod coater method, a squeeze coater method, a cast coater method, a bar coater method, a die coater method, a screen printing method, a spray coating method and the like.

A conventional drying apparatus may be used for the drying. The drying temperature is preferably set at a temperature at which the permeability of the porous film is not lowered, specifically 10 to 120 ° C, more preferably 20 to 80 ° C, in order to prevent the pores of the porous film from shrinking and lowering the permeability desirable.

The specular surface gloss of 60 deg. On the surface of the porous layer can be adjusted by subjecting the porous surface to a known treatment such as surface treatment with sandpaper, acid treatment, alkali treatment, chemical treatment with organic solvent, corona treatment and plasma treatment have. By appropriately adopting the treatment, a porous layer having a mirror polish degree of 60 to 60% can be produced. Among them, a chemical treatment with an organic solvent or the like is preferable. Examples of the organic solvent include ketones such as acetone; Amides such as N-methyl-2-pyrrolidone (NMP), dimethylacetamide, dimethylformamide and dimethylformamide; Cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; Chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and its fluorine substituents; cyclic esters such as? -butyrolactone,? -valerolactone, and the like, and diethyl carbonate is preferable. When the chemical treatment is carried out with an organic solvent such as diethyl carbonate, the surface gloss of the porous layer tends to increase at 60 °.

〔2. Non-aqueous electrolyte secondary battery]

The nonaqueous electrolyte secondary battery according to the present invention is a nonaqueous secondary battery that obtains an electromotive force by doping and undoping lithium, and is a laminated body in which a positive electrode sheet, a laminated separator for a nonaqueous electrolyte secondary battery described above, and a negative electrode sheet A member for a secondary battery), and the other configuration is not particularly limited. The nonaqueous electrolyte secondary battery has a structure in which a negative electrode sheet and a positive electrode sheet are sealed in a casing in which a battery element impregnated with an electrolyte is sealed in a casing in which the structure is opposed via the laminate separator for the nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery is particularly suitable for a lithium ion secondary battery. Doping refers to the phenomenon that lithium ions enter the active material of an electrode such as a positive electrode, which means that the electrode is inserted, held, adsorbed, or inserted.

The positive electrode sheet may have a structure in which an active material layer including a positive electrode active material and a binder resin is molded on a current collector. The active material layer may further include a conductive auxiliary agent.

As the positive electrode active material, for example, there may be mentioned lithium-containing transition metal oxide, specifically, _{LiCoO 2, LiNiO 2, LiMn 1} /2 Ni 1/2 O 2, LiCo 1/3 Mn 1/3 Ni 1/3 O _2, LiMn there may be mentioned _{2 O 4, LiFePO 4, LiCo} 1/2 Ni 1/2 O 2, LiAl 1/4 Ni 3/4 O 2 or the like.

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

As the collector, for example, an aluminum foil, a titanium foil and a stainless foil having a thickness of 5 mu m to 20 mu m can be cited.

The negative electrode sheet may have a structure in which the active material layer including the negative electrode active material and the binder resin is molded on the current collector. The active material layer may further include a conductive auxiliary agent. Examples of the negative electrode active material include a material capable of electrochemically occluding lithium, and specifically, for example, a carbon material; An alloy of lithium, such as silicon, tin, aluminum and the like; And the like.

Examples of the binder resin include polyvinylidene fluoride resin and styrene-butadiene rubber. The separator of the present invention can secure sufficient adhesion 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 and stainless foil having a thickness of 5 占 퐉 to 20 占 퐉. Further, in place of the negative electrode, a metal lithium foil can 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 and LiClO ₄ .

As the non-aqueous solvent, all solvents commonly used in non-aqueous electrolyte secondary batteries are included. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; Chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and its fluorine substituents; cyclic esters such as? -butyrolactone and? -valerolactone; These may be used alone or in combination.

As the electrolytic solution, a lithium salt is added to a solvent in which a cyclic carbonate and a chain carbonate are mixed in a mass ratio (cyclic carbonate / chain carbonate) of 20/80 to 40/60 (more preferably 30/70) 0.5M to 1.5M is preferable.

Examples of the exterior material include metal cans and aluminum laminated film packs. The shape of the battery is square, cylindrical, and coin-shaped.

The non-aqueous electrolyte secondary battery can be obtained by, for example, impregnating a laminate in which the above-described laminate separator for a nonaqueous electrolyte secondary battery is disposed between a positive electrode sheet and a negative electrode sheet, impregnating the battery with an electrolytic solution and housing the battery in a casing (for example, And pressing the laminate from above the casing. At this time, in order to improve the adhesiveness of the electrode and the laminated separator for a non-aqueous electrolyte secondary battery, it is preferable to press (heat press) while heating.

A method of arranging the separator between the positive electrode sheet and the negative electrode sheet may be a method in which the positive electrode sheet, the separator, and the negative electrode sheet are laminated in order of at least one layer (so-called stacking method) in this order, and the positive electrode sheet, the separator, They may be overlapped and wound in the longitudinal direction.

[Example]

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto.

≪ Measurement of surface glossiness >

Five samples of KB paper (product number: KB-39N, manufactured by Kokuyo Co., Ltd.) were superimposed on the surface of the sample using a gloss meter (PG-IIM type, manufactured by Nippon Denshoku Kogyo K.K.) A nonaqueous electrolyte secondary battery laminated separator was mounted, and the incident angle and the receiving angle of the laminated separator for the nonaqueous electrolyte secondary battery were measured at 60 °.

In addition, when the surface of the laminate separator for a non-aqueous electrolyte secondary battery has deposits such as resin and inorganic matters, the separator may be added to an organic solvent such as diethyl carbonate (DEC) and / or water It is possible to carry out pretreatment such as immersion, washing and removing the adherend, and drying the solvent or water.

<Measurement of sting intensity>

The maximum stress (N) when the porous film was stuck with a washer of 12 mm and the pin was stuck at 200 mm / min was measured using a handy compression tester (Kato-G5, model no .; KES-G5) Was determined as the sticking strength of the film. A fin having a pin diameter of 1 mm and a tip of 0.5 R was used.

&Lt; Measurement of volume basis weight of porous layer &

By measuring the basis weight (the weight per square meter) of the porous layer in the dry state and dividing the basis weight by the specific gravity of the porous layer at 25 DEG C, the volume basis weight (volume per square meter) of the porous layer in the dry state Respectively.

<Fabrication of Separator>

A laminated separator for a nonaqueous electrolyte secondary battery according to Examples 1 to 4 and Comparative Examples 1 to 4 was produced as follows.

(Example 1)

As the binder resin, carboxymethylcellulose sodium (CMC) (CMC1110, manufactured by Dainippon Ink and Chemicals, Inc.) was used. As a filler, fluoroapatite (manufactured by Wako Pure Chemical Industries, Ltd.; apatite FAP, hexagonal) was used. The fluoroapatite, CMC and a solvent (a mixed solvent of water and isopropyl alcohol) were mixed in the following proportions. That is, 3 parts by weight of CMC was mixed with 100 parts by weight of the fluoroapatite, and the solid content concentration (fluorophatite + CMC) in the obtained mixed solution was adjusted to 27.7% by weight and the solvent composition was 95% And 5% by weight of isopropyl alcohol. Thus, a dispersion liquid was obtained. Then, the resultant dispersion was subjected to high-pressure dispersion (high-pressure dispersion condition; 100 MPa x 3 passes) using a high-pressure dispersing device (Starchust Co., Ltd., Gunma Machine Co., Ltd.) to obtain a coating solution. The resultant coating liquid was coated on a porous polyethylene membrane (thickness 16.5 占 퐉, porosity 51%, average pore diameter 0.096 占 퐉) by the gravure method and dried to obtain a laminated porous film (1-i). The resultant laminated porous film (1-i) was dipped in diethyl carbonate at 70 DEG C for 5 minutes. This film was taken out from diethyl carbonate and dried at room temperature to obtain a laminated separator for a nonaqueous electrolyte secondary battery of Example 1. Table 1 shows the cell characteristics retention after 100 cycles of the laminated separator for a nonaqueous electrolyte secondary battery of Example 1. [

(Example 2)

A laminated separator for a nonaqueous electrolyte secondary battery of Example 2 was obtained in the same manner as in Example 1 except that fluorine-containing mica (manufactured by Wako Pure Chemical Industries, Ltd.; synthetic mica, non-swelling) was used as a filler. Table 1 shows the cell characteristics retention after 100 cycles of the laminated separator for a nonaqueous electrolyte secondary battery of Example 2. [

(Example 3)

PVDF resin (product name: "KYNAR2801") was stirred and dissolved in N-methyl-2-pyrrolidone at 65 ° C for 30 minutes so as to have a solid content of 10% by mass. The obtained solution was used as a binder solution. As the filler, alumina fine particles (Sumitomo Chemical Co., Ltd., trade name &quot; AKP3000 &quot;) were used. The alumina fine particles, the binder solution and the solvent (N-methyl-2-pyrrolidone) were mixed in the following proportions. That is, the binder solution was mixed so that 90 parts by weight of the PVDF resin was added to 10 parts by weight of the alumina fine particles, and a solvent was added thereto so that the solid content concentration (alumina fine particles + PVDF type resin) The dispersion was obtained by mixing. Then, the obtained dispersion was stirred and mixed twice under a condition of 2000 rpm and 30 seconds at room temperature with a rotary mixer (trade name: "Awatolian Taro" manufactured by Kabushiki Kaisha). The resulting mixed solution was applied as a coating solution onto a porous polyethylene membrane (thickness: 12 μm, porosity: 44%, average pore diameter: 0.035 μm) by the doctor blade method. The resultant laminate (2-i) was immersed in 2-propanol as the coating film was in an NMP wet state and allowed to stand at 25 占 폚 for 5 minutes to obtain a laminated porous film (2-ii). The resultant laminated porous film (2-ii) was immersed again in another 2-propanol under immersion solvent wet condition, and left at 25 캜 for 5 minutes to obtain a laminated porous film (2-iii). The resultant laminated porous film (2-iii) was dried at 65 캜 for 5 minutes to obtain a laminated porous film (2-iv). The resultant laminated porous film (2-iv) was dipped in diethyl carbonate at 70 DEG C for 1 minute. This film was taken out from diethyl carbonate and dried at room temperature to obtain a laminated separator for a nonaqueous electrolyte secondary battery of Example 3. Table 1 shows the cell property retention after 100 cycles of the laminated separator for a nonaqueous electrolyte secondary battery of Example 3. [

(Example 4)

A laminated separator for a non-aqueous electrolyte secondary battery of Example 4 was obtained in the same manner as in Example 3, except that the substrate was immersed in diethyl carbonate at 70 캜 for 15 minutes. Table 1 shows the cell characteristics retention after 100 cycles of the laminated separator for a nonaqueous electrolyte secondary battery of Example 4. [

(Comparative Example 1)

PVDF resin (product name: "KYNAR2801") was stirred and dissolved in N-methyl-2-pyrrolidone at 65 ° C for 30 minutes so as to have a solid content of 7% by mass. The obtained solution was applied as a coating solution onto the porous membrane of polyethylene (thickness 12 占 퐉, porosity 44%, average pore diameter 0.035 占 퐉) by the doctor blade method. The resultant laminate (3-i) was immersed in 2-propanol as the coating film was in an NMP wet state and allowed to stand at 25 占 폚 for 5 minutes to obtain a laminated porous film (3-ii). The resultant laminated porous film (3-ii) was immersed again in another 2-propanol under immersion solvent wet condition and allowed to stand at 25 占 폚 for 5 minutes to obtain a laminated porous film (3-iii). The resultant laminated porous film (3-iii) was dried at 65 캜 for 5 minutes to obtain a laminated porous film (3-iv). The resultant laminated porous film (3-iv) was folded to obtain a laminated separator for a non-aqueous electrolyte secondary battery of Comparative Example 1. [ Table 1 shows the cell characteristics retention after 100 cycles of the laminated separator for a nonaqueous electrolyte secondary battery of Comparative Example 1. [

(Comparative Example 2)

PVDF resin (product name: "KYNAR2801") was stirred and dissolved in N-methyl-2-pyrrolidone at 65 ° C for 30 minutes so as to have a solid content of 7% by mass. The obtained solution was applied as a coating solution onto the porous membrane of polyethylene (thickness 12 占 퐉, porosity 44%, average pore diameter 0.035 占 퐉) by the doctor blade method. The resultant laminate (4-i) was dried at 85 캜 for 5 minutes to obtain a laminated separator for a non-aqueous electrolyte secondary battery of Comparative Example 2. Table 1 shows the cell characteristics retention after 100 cycles of the laminated separator for a nonaqueous electrolyte secondary battery of Comparative Example 2. [

(Comparative Example 3)

PVDF resin (product name: "KYNAR2801") was stirred and dissolved in N-methyl-2-pyrrolidone at 65 ° C for 30 minutes so that the solid content became 0.3% by mass. The obtained solution was applied as a coating solution onto the porous membrane of polyethylene (thickness 12 占 퐉, porosity 44%, average pore diameter 0.035 占 퐉) by the doctor blade method. The resultant laminate (5-i) was immersed in 2-propanol in the wet state of NMP and allowed to stand at 25 占 폚 for 5 minutes to obtain a laminated porous film (5-ii). The obtained laminated porous film (5-ii) was immersed again in the other 2-propanol under immersion solvent wet condition, and left at 25 캜 for 5 minutes to obtain a laminated porous film (5-iii). The resultant laminated porous film (5-iii) was dried at 65 캜 for 5 minutes to obtain a laminated separator for a nonaqueous electrolyte secondary battery of Comparative Example 3. Table 1 shows the cell characteristics retention after 100 cycles of the laminated separator for a nonaqueous electrolyte secondary battery of Comparative Example 3. [

(Comparative Example 4)

As the binder resin, carboxymethylcellulose sodium (CMC) (CMC1110, manufactured by Dainippon Ink and Chemicals, Inc.) was used. As the filler, hydroxyapatite (manufactured by Wako Pure Chemical Industries, Ltd.; apatite HAP, monodisperse) was used. The hydroxyapatite, CMC and a solvent (a mixed solvent of water and isopropyl alcohol) were mixed in the following proportions. That is, 3 parts by weight of CMC was mixed with 100 parts by weight of the fluoroapatite, and the solid content concentration (hydroxyapatite + CMC) in the resulting mixed solution was adjusted to 27.7% by weight and the solvent composition was 95% And 5% by weight of isopropyl alcohol. Thus, a dispersion liquid was obtained. Then, the resultant dispersion was subjected to high-pressure dispersion (high-pressure dispersion condition; 100 MPa x 3 passes) using a high-pressure dispersing device (Starchust Co., Ltd., Gunma Machine Co., Ltd.) to obtain a coating solution. The obtained coating liquid was applied onto a porous polyethylene membrane (thickness 16.5 占 퐉, porosity of 51%, average pore diameter 0.096 占 퐉) so as to have a volume basis weight of the resulting porous layer of 7.52 cm3 / m2 by the gravure method, Thereby obtaining a laminated separator for a non-aqueous electrolyte secondary battery. Table 1 shows the cell characteristics retention after 100 cycles of the laminated separator for a nonaqueous electrolyte secondary battery of Comparative Example 4. [

<Production of non-aqueous electrolyte secondary battery>

Next, each of the laminated separators for non-aqueous electrolyte secondary cells of Examples 1 to 4 and Comparative Examples 1 to 4 prepared as described above was used to prepare a non-aqueous electrolyte secondary battery as follows.

(Positive electrode)

LiNi _{0 . 5} Mn _{0 . 3} Co _{0 .} The ₂ O ₂ / conductive agent / PVDF (weight ratio 92/5/3) by coating the aluminum foil was used as the positive electrode of the produced commercially. The aluminum foil was cut out of the positive electrode so that the size of the portion where the positive electrode active material layer was formed was 40 mm x 35 mm and the portion without the positive electrode active material layer was 13 mm wide on the outer periphery. 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 prepared by coating graphite / styrene-1,3-butadiene copolymer / sodium carboxymethylcellulose (weight ratio 98/1/1) to copper foil was used. The negative electrode was cut out of the copper foil so that the size of the portion where the negative electrode active material layer was formed was 50 mm x 40 mm and the portion where the negative electrode active material layer was not formed on the outer periphery was 13 mm. The thickness of the negative electrode active material layer was 49 μm and the density was 1.40 g / cm 3.

(Assembly)

In the laminate pouch, the positive electrode, the laminate separator for the nonaqueous electrolyte secondary battery and the negative electrode were laminated in this order to obtain a member for a nonaqueous electrolyte secondary battery. At this time, the positive electrode and the negative electrode were disposed so that all of the main surface of the positive electrode active material layer of the positive electrode 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 nonaqueous electrolyte secondary battery was placed in a bag formed by laminating an aluminum layer and a heat seal layer, and 0.25 mL of a nonaqueous electrolyte solution was placed in the bag. The nonaqueous electrolyte solution was prepared by mixing ethylene carbonate, diethyl carbonate 1.0 mol / liter LiPF ₆ in a mixed solvent of ethylmethyl carbonate, diethyl carbonate and ethylene carbonate in a volume ratio of 50:20:30 Was used as the electrolytic solution. Then, while the inside of the bag was decompressed, the bag was heat sealed to produce a nonaqueous electrolyte secondary battery.

<Cycle Test>

For a new non-aqueous electrolyte secondary battery that did not undergo a charge-discharge cycle, the voltage range at 25 占 폚; 4.1 to 2.7 V, current value; 0.2C (a current value for discharging the rated capacity by the discharge capacity of 1 hour rate in 1 hour is 1C, the same applies to the following description), and the initial charge / discharge of 4 cycles was performed.

Subsequently, at 55 캜,

Initial battery characteristic retention rate (%) = (20 C discharge capacity / 0.2 C discharge capacity) x 100

, The initial battery characteristic retention ratio was calculated.

Subsequently, at 55 占 폚, the charging current value; 1C, discharge current value; Charging and discharging with a constant current of 1 C was performed in one cycle, and charging and discharging were performed in 100 cycles. Then,

Battery characteristics retention rate (%) = (20C discharge capacity at 100th cycle / 0.2C discharge capacity at 100th cycle) x 100

, The battery characteristics retention ratio after 100 cycles was calculated. Table 1 shows the results.

As shown in Table 1, in the nonaqueous electrolyte secondary battery using the laminate separator for a nonaqueous electrolyte secondary battery according to Comparative Example 2 having a specular gloss of more than 26%, the initial battery characteristic retention was 43%, and the cell characteristics after 100 cycles It was confirmed that the retention ratio was remarkably low at 27%. This is because if the mirror polish degree exceeds 26%, the density of the porous layer becomes excessively high, and clogging of pores due to insoluble byproducts or bubbles generated by charging and discharging and electrolyte retention at the interface between the separator and the electrode , The ion permeability is lowered.

Also in the nonaqueous electrolyte secondary battery using the laminate separator for a nonaqueous electrolyte secondary battery according to Comparative Example 1 having a specular gloss of less than 3%, the retention rate of the initial cell characteristics was 65% and the cell retention ratio after 100 cycles was as low as 32% . This is because, if the mirror surface gloss is less than 3%, the uniformity of the porous layer is low and the ion permeability is uneven.

In the nonaqueous electrolyte secondary battery using the laminate separator for a nonaqueous electrolyte secondary battery according to Comparative Example 3, in which the porous layer had a volume basis of less than 0.1 cm 3 / m 2, the initial cell specific retentivity was as high as 80% %. This is because the volume of the porous layer is too small and the effect of suppressing the degradation of cycle characteristics by the porous layer is small.

In the nonaqueous electrolyte secondary battery using the laminate separator for a nonaqueous electrolyte secondary battery according to Comparative Example 4 in which the volume basis weight of the porous layer exceeded 2.5 cm 3 / m 2, the initial cell specific retentivity was as low as 63% It was confirmed that the retention ratio was remarkably low at 15%. This is because the volume of the porous layer is excessively large and the ion permeability of the porous layer is deteriorated.

On the other hand, in the non-aqueous electrolyte secondary battery using the laminate separator for non-aqueous electrolyte secondary cells according to Examples 1 to 4, wherein the surface of the porous layer has a specular gloss of 3 to 26% and a volume basis of the porous layer is 0.1 to 2.5 cm 3 / , It was confirmed that the retention of the initial cell characteristics was 70% or more and the cell characteristic retention after 100 cycles was 39% or more, and the deterioration of the cycle characteristics could be suppressed.

Claims (7)

A laminated separator for a nonaqueous electrolyte secondary battery comprising a porous film comprising a polyolefin resin and a porous layer provided on one side or both sides of the porous film,
The surface gloss of the surface of the porous layer is 3 to 26%
The porous layer has a volume basis of 0.1 to 2.5 cm 3 /
The average pore diameter of the porous film is 0.14 탆 or less,
Wherein the porous layer is formed from a coating liquid in which a polyvinylidene fluoride (PVDF) resin is dissolved. The laminate separator for a nonaqueous electrolyte secondary battery according to claim 1, wherein the porous layer comprises a filler. The method according to claim 1, wherein the porous layer comprises a filler and a resin,
Wherein the ratio of the filler in the total amount of the filler and the resin is 5 to 99 mass%. The laminated separator for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the stiffness of the porous film is 2N or more. A positive electrode, a laminate separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, and a negative electrode arranged in this order. A nonaqueous electrolyte secondary battery comprising the laminated separator for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3. delete