JP2019061972A - Separator for nonaqueous electrolyte secondary battery - Google Patents

Abstract

To provide a separator for a nonaqueous electrolyte secondary battery excellent in cycle characteristics.SOLUTION: The separator for nonaqueous electrolyte secondary battery includes a polyolefin porous film. A difference between porosity calculated from a continuous image in which void portions and porous film portions are two graded and porosity calculated from a thickness, weight basis and true density is 4 to 20%.SELECTED DRAWING: None

Description

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

  BACKGROUND OF THE INVENTION 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 and portable information terminals, or as batteries for vehicles.

  As a separator in such a non-aqueous electrolyte secondary battery, a porous film mainly composed of a polyolefin is mainly used.

  For example, in Patent Document 1, as a battery separator excellent in input / output characteristics and safety, resin occupancy and thickness calculated from a cross-sectional image obtained by a scanning electron microscope (SEM) are defined in a specific range. A battery separator comprising a porous film is disclosed.

Unexamined-Japanese-Patent No. 2016-081763 (May 16, 2016 publication)

  However, conventional battery separators as disclosed in Patent Document 1 sometimes have insufficient battery characteristics such as cycle characteristics.

The present invention includes the inventions shown in the following [1] to [5].
[1] A separator for a non-aqueous electrolyte secondary battery comprising a polyolefin porous film, which is a separator
The range of the separator surface direction is 256 pix × 256 pix, and the thickness is the separator film thickness under the conditions obtained by FIB-SEM measurement and image analysis of magnification 6500 times of the above polyolefin porous film and 1 pix of 19.2 nm And the average value of the porosity calculated from the continuous image in which the void portion and the porous film portion are formed from the separator surface toward the inner thickness direction, and the thickness of the above-mentioned polyolefin porous film And a separator for a non-aqueous electrolyte secondary battery, which has a difference of 4 to 20% from the porosity calculated from the weight basis weight and the true density.
[2] The separator for a non-aqueous electrolyte secondary battery according to [1], having a compression modulus of 1600 kPa or more.
The laminated separator for non-aqueous-electrolyte secondary batteries provided with the separator for non-aqueous-electrolyte secondary batteries as described in [3] [1] or [2], and an insulating porous layer.
[4] A positive electrode, the separator for a non-aqueous electrolyte secondary battery according to [1] or [2], or the laminated separator for a non-aqueous electrolyte secondary battery according to [3], and a negative electrode A member for a non-aqueous electrolyte secondary battery, which is disposed in order.
[5] A separator for a non-aqueous electrolyte secondary battery according to [1] or [2], or a non-aqueous electrolyte secondary battery for a laminated separator according to [3] battery.

The separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention has an effect of being excellent in rate characteristics after repeated charge and discharge.

It is a schematic diagram which shows the process of obtaining the XZ cross-sectional continuous image from the sample for measurement which is one process of the method of calculating the SEM porosity of the separator for non-aqueous electrolyte secondary batteries in one embodiment of the present invention. A schematic diagram showing a step of obtaining a continuous image for analysis from a two-graded XY surface continuous image, which is one step of a method of calculating the SEM porosity of a separator for a non-aqueous electrolyte secondary battery in one embodiment of the present invention FIG. A continuous image for analysis, which is one step of a method of calculating the SEM porosity of a separator for a non-aqueous electrolyte secondary battery in one embodiment of the present invention, is divided into a plurality of images with a size of 1 pix in the Z direction. It is a schematic diagram which shows a process.

  Although the following describes one embodiment of the present invention, 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 different embodiments can be combined as appropriate. The resulting embodiments are also included in the technical scope of the present invention. In addition, unless otherwise indicated in this specification, "A-B" showing a numerical range means "A or more, B or less".

Embodiment 1: Separator for Nonaqueous Electrolyte Secondary Battery
The separator for a non-aqueous electrolyte secondary battery according to Embodiment 1 of the present invention is a separator for a non-aqueous electrolyte secondary battery including a polyolefin porous film, and the FIB having a magnification of 6500 times of that of the above-mentioned polyolefin porous film -Obtained from SEM measurement and image analysis, and under the condition that 1 pix is 19.2 nm, the range in the separator surface direction is 256 pix x 256 pix, the thickness is for the separator film thickness, and from the separator surface toward the internal thickness direction And the average value of the porosity calculated from the continuous image in which the void portion and the porous film portion are formed into two gradations, and the porosity calculated from the thickness, weight per unit weight and true density of the above-mentioned polyolefin porous film Difference is 4 to 20%.

  The separator for a non-aqueous electrolyte secondary battery according to Embodiment 1 of the present invention contains a polyolefin porous film, and is preferably made of a polyolefin porous film. Here, a "polyolefin porous film" is a porous film which has polyolefin resin as a main component. Further, “having a polyolefin-based resin as a main component” means that the proportion of the polyolefin-based resin in the porous film is 50% by volume or more, preferably 90% by volume or more of the whole material constituting the porous film, More preferably, it means 95% by volume or more.

  The above-mentioned polyolefin porous film can be a base material for a separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention or a base material of a laminated separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention described later. . Moreover, the said polyolefin porous film has many pores connected with the inside, and it has become possible to let gas and a liquid pass from one side to the other side.

More preferably, the polyolefin resin contains a high molecular weight component having a weight average molecular weight of 3 × 10 ⁵ to 15 × 10 ⁶ . In particular, when the polyolefin resin contains a high molecular weight component having a weight average molecular weight of 1,000,000 or more, the strength of the laminated separator for a non-aqueous electrolyte secondary battery including the above polyolefin porous film and the above polyolefin porous film It is more preferable because it improves.

  The polyolefin-based resin which is the main component of the above-mentioned polyolefin porous film is not particularly limited, but for example, thermoplastic resins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like Homopolymers (e.g., polyethylene, polypropylene, polybutene) or copolymers (e.g., ethylene-propylene copolymer) in which a polymer is polymerized are mentioned. The polyolefin porous film may be a layer containing these polyolefin resins alone, or a layer containing two or more of these polyolefin resins. Among them, polyethylene is preferable because it can prevent excessive current from flowing at a lower temperature (shutdown), and in particular, polyethylene of high molecular weight mainly composed of ethylene is preferable. In addition, the polyolefin porous film does not prevent including components other than polyolefin in the range which does not impair the function of the said layer.

Examples of polyethylene include low density polyethylene, high density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), ultra high molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more, among which the weight average molecular weight is Ultrahigh molecular weight polyethylene of 1,000,000 or more is more preferable, and it is further preferable that a high molecular weight component having a weight average molecular weight of 5 × 10 ⁵ to 15 × 10 ⁶ is contained.

  The two types of calculation methods of the above-mentioned porosity are explained below. First, in the separator for a non-aqueous liquid electrolyte secondary battery according to one embodiment of the present invention, the above-mentioned polyolefin porous film is processed by FIB (focused ion beam), and it is SEM (scanning electron microscope) of magnification 6500 times. By repeating the imaging, a continuous image inside the separator is obtained. Thereafter, two gradations of the void portion and the porous film portion are performed on the obtained continuous image. Furthermore, from the continuous image in which two gradations are made, the range in the separator surface direction is 256 pix × 256 pix under the condition that 1 pix is 19.2 nm, the thickness is for the separator film thickness, and from the separator surface to the internal thickness direction Extract the continuous image formed towards. The extracted continuous image is divided into a plurality of images having a thickness of 1 pix. The porosity in each of the divided images is measured, and the average value of the porosity is calculated. Hereinafter, the average value of the porosity calculated from the said continuous image is called "SEM porosity."

  On the other hand, in the separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention, the porosity is calculated from the thickness, weight per unit weight and true density of the above-mentioned polyolefin porous film. Hereinafter, the porosity calculated from the thickness, weight per unit weight and true density of the polyolefin porous film is referred to as "true porosity".

  In the separator for non-aqueous electrolyte secondary batteries according to one embodiment of the present invention, the difference between “SEM porosity” and “true porosity” is 4 to 20%. In the present specification, the difference between the “SEM porosity” and the “true porosity” is referred to as “a difference between the porosity measurement methods”.

  Here, in the measurement of “SEM porosity”, an ultra-thin resin portion of nanometer order is not observed in SEM, so the ultra-fine resin portion is measured as a void.

  On the other hand, the “true porosity” is calculated from the weight per unit weight, film thickness and true density of the above-mentioned polyolefin porous film, so the ultra-fine resin portion is not measured as a void, but is measured as a portion where resin exists. Be done.

  Therefore, the “difference in porosity measurement method” in the present invention indicates the amount (volume ratio) of the ultrafine resin portion in the entire polyolefin porous film.

In the case where the above-mentioned "difference in porosity measurement method" is small, the amount of the ultrafine resin portion is small, and the number of fine voids (voids) having a complex structure partitioned by the ultrafine resin portion is small. It means that the number is large.

  On the other hand, when the above-mentioned "difference in porosity measurement method" is large, the amount of the ultrafine resin portion is large, the number of fine voids having a complex structure partitioned by the ultrafine resin portion is large, and the number of large voids is It means less.

  In the separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention, the fact that the “difference in porosity measurement method” is 4% or more is an ultra-thin film that contributes to the strength of the separator in the above-mentioned polyolefin porous film. Since a certain amount of the resin portion is contained and the number of large voids is reduced, the strength of the non-aqueous electrolyte secondary battery separator is enhanced. Therefore, the mechanical stress applied to the non-aqueous electrolyte secondary battery separator during charge and discharge collapses the void structure inside the non-aqueous electrolyte secondary battery separator, and the battery performance is dominated by the ion permeability and electrolysis of the separator. It is possible to prevent the liquid retention from deteriorating. Therefore, it is possible to suppress a decrease in battery characteristics (rate characteristics) after repeated charge and discharge. From the above viewpoint, the “difference in porosity measurement method” is preferably 4.5% or more.

  On the other hand, in the separator for a non-aqueous liquid electrolyte secondary battery according to one embodiment of the present invention, the "fineness difference between the porosity measurement methods" is 20% or less, in the above-mentioned polyolefin porous film Not too many, indicating that there are not too many fine voids. Therefore, during charging and discharging, the by-products derived from the non-aqueous electrolyte clog the voids of the separator for the non-aqueous electrolyte secondary battery, particularly the voids at the interface with the electrodes, with the by-products. Can be prevented, and deterioration of rate characteristics (cycle characteristics) when the charge and discharge cycle is repeated can be reduced. From the above viewpoint, the “difference in porosity measurement methods” is preferably 19.0% or less.

  The more specific calculation method of "SEM porosity" in the separator for non-aqueous electrolyte secondary batteries which concerns on one Embodiment of this invention is demonstrated below (refer FIGS. 1-3).

  First, a polyolefin porous film is impregnated with an embedding resin (such as an epoxy resin), the voids of the polyolefin porous film are filled and cured, and the sample is treated with osmium tetraoxide to prepare a measurement sample.

  As shown in FIG. 1, the thickness direction of the measurement sample is the Z direction, and an arbitrary direction parallel to the surface of the measurement sample orthogonal to the thickness is the X direction, and a direction orthogonal to X and Z is the Y direction I assume. By performing FIB processing using FIB-SEM (manufactured by FEI; HELIOS 600), a cross section (hereinafter referred to as an XZ cross section) including an arbitrary side X and a thickness Z of the surface of the measurement sample is produced. The cross section is subjected to SEM observation (reflected electron image) at an acceleration voltage of 2.1 kV and a magnification of 6500 times to obtain a SEM image.

  After the SEM observation, FIB processing is performed with a thickness of 19.2 nm in the Y direction orthogonal to the XZ cross section to newly prepare an XZ cross section. The cross section is subjected to SEM observation (reflected electron image) under the above conditions to obtain a SEM image. Subsequently, the XZ cross-sectional continuous image of the measurement sample is acquired by repeating the FIB processing and the acquisition of the SEM image of the cross section at intervals of 19.2 nm in thickness.

  That is, as shown in FIG. 1, the XZ cross section of the measurement sample is repeatedly produced by FIB processing at intervals of 19.2 nm along the Y axis by SEM, and each cross section produced is observed by SEM. A continuous XZ cross-sectional image (XZ cross-sectional continuous image) of the measurement sample is obtained.

Subsequently, position correction is performed on the XZ cross-sectional continuous image using an image analysis software (manufactured by Visualization Sciences Group; Avizo Ver. 6.0), and the XZ cross-sectional continuous image after correction is taken along the X, Y, Z axes. Obtained at a scale of 19.2 nm / pix.

  Using the quantitative analysis software (manufactured by Rattock System Engineering; TRI / 3D-BON-FCS), the above-mentioned position-corrected XZ cross-sectional continuous image is binarized so that the resin portion and the void portion can be distinguished. . Thereby, the portion (hereinafter, referred to as a resin portion) made of the resin constituting the above-mentioned polyolefin porous film of the above-mentioned measurement sample and the embedding resin portion are identified. That is, the porous film portion (resin portion) and the void portion in the polyolefin porous film are identified.

  Next, the XZ plane of the XZ cross-sectional continuous image obtained by two-gradation into the resin portion and the embedding resin portion is rotated to the XY plane in SectionView in EditViewer mode on TRI / 3D-BON-FCS. Thereby, the plane direction of the measurement sample in which the XZ cross-sectional continuous image is binarized in the thickness direction from the surface to the inside of the measurement sample on the scale of X, Y, Z axes 19.2 nm / pix It is converted into a continuous image (hereinafter referred to as an XY plane continuous image).

  Thereafter, from an arbitrary part of the XY plane continuous image, the number of pixels is 256 pix in the X direction, 256 pix in the Y direction, and the range for thickness in the Z direction is trimmed to extract a continuous image for analysis.

  That is, as shown in FIG. 2, a continuous image for analysis is extracted by trimming an analysis portion from the XZ cross-sectional continuous image which has been two-graded.

  Thereafter, as shown in FIG. 3, the analysis continuous image is divided into a plurality of images whose size in the Z direction is 1 pix. For each of the above divided images, the ratio of void to the analysis area (porosity) is measured using a 2D label density function. The average value of the porosity of each of the measured images (porosity of the measurement sample) is calculated. As a result, let the porosity of the sample for measurement calculated be "SEM porosity" of the said polyolefin porous film.

Moreover, the more specific calculation method of the "true porosity" in the separator for non-aqueous electrolyte secondary batteries which concerns on one Embodiment of this invention is demonstrated below. Using the “true porosity” as the film thickness [μm], weight per unit weight [g / m ² ] and true density [g / m ³ ] of the separator for non-aqueous electrolyte secondary batteries, the following formula (1 Calculated based on

(True porosity) = [1- (weight basis weight) / {(film thickness) × 10 ⁻⁶ × 1 [m ² ] × (true density)}] × 100 (1)
Here, the methods for measuring the film thickness, weight per unit weight and true density of the above-mentioned polyolefin porous film are not limited, and methods which can be generally used in the field of the present invention can be used.

  The difference between the “SEM porosity” measured by the above-mentioned method and the “true porosity” is calculated, and the value is taken as the “porosity measurement method difference”.

  In the separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention, the compressive elastic modulus is preferably 1600 kPa or more, from the viewpoint of suppressing a decrease in rate characteristics after repeated charge and discharge. It is more preferable that it is more than. Moreover, 10000 kPa or less is preferable, 5000 kPa or less is more preferable, and 2500 kPa or less may be sufficient.

  Although the film thickness of the said polyolefin porous film is not specifically limited, It is preferable that it is 4-40 micrometers, and it is more preferable that it is 5-20 micrometers.

If the film thickness of the said polyolefin porous film is 4 micrometers or more, it is preferable from a viewpoint that internal short circuit of a battery can fully be prevented.

  On the other hand, if the film thickness of the said polyolefin porous film is 40 micrometers or less, it is preferable from a viewpoint that the enlargement of a non-aqueous-electrolyte secondary battery can be prevented.

The weight per unit area of the above-mentioned polyolefin porous film is usually preferably 4 to 20 g / m ² so that the weight energy density and volume energy density of the battery can be increased, and 5 to 12 g It is more preferable that it is / m ² .

  The air permeability of the above-mentioned polyolefin porous film is preferably 30 to 500 sec / 100 mL, more preferably 50 to 300 sec / 100 mL in terms of Gurley value, from the viewpoint of showing sufficient ion permeability.

  The porosity of the above-mentioned polyolefin porous film is 20% by volume to 80% so that the function to prevent excessive current flow (shutdown) reliably at a lower temperature can be obtained while increasing the holding amount of the electrolytic solution. % Is preferable, and 30 to 75% by volume is more preferable.

  The pore diameter of the pores of the above-mentioned polyolefin porous film is preferably 0.3 μm or less from the viewpoint of sufficient ion permeability and preventing entry of particles constituting the electrode, and is 0.14 μm or less It is more preferable that

  The separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention may include a porous layer, as necessary, in addition to the above-mentioned polyolefin porous film. Examples of the porous layer include an insulating porous layer constituting a non-aqueous electrolyte laminated separator described later, and other porous layers include known porous layers such as a heat-resistant layer, an adhesive layer, and a protective layer. Be

[Method for producing polyolefin porous film]
The method for producing the polyolefin porous film is not particularly limited. For example, a polyolefin resin composition is obtained by melt-kneading a polyolefin resin and an additive, and extruding the resulting polyolefin resin composition. The method includes stretching, washing and drying.

Specifically, the following methods can be mentioned.
(A) adding a polyolefin resin and an additive to a kneader and melt-kneading it to obtain a polyolefin resin composition,
(B) A step of obtaining a sheet-like polyolefin resin composition by extruding the molten polyolefin resin composition obtained in the above step A from a T-die of an extruder and forming into a sheet while cooling.
(C) a step of stretching the sheet-like polyolefin resin composition obtained in the step B,
(D) a step of washing the polyolefin resin composition stretched in the step C using a washing solution,
(E) A step of obtaining a polyolefin porous film by drying and / or heat-setting the polyolefin resin composition washed in the step D.

  The amount of the polyolefin resin used in step (A) is preferably 6% by weight to 45% by weight, and 9% by weight to 36% by weight, based on 100% by weight of the polyolefin resin composition to be obtained. It is more preferable that

  Examples of the additive in step (A) include phthalate esters such as dioctyl phthalate, unsaturated higher alcohols such as oleyl alcohol, saturated higher alcohols such as stearyl alcohol, and low molecular weight polyolefin resins such as paraffin wax, Petroleum resin, liquid paraffin and the like can be mentioned. Aliphatic hydrocarbon resins obtained by polymerizing C5 petroleum fractions such as isoprene, pentene and pentadiene as main materials as the above-mentioned petroleum resins; C9 petroleum fractions such as indene, vinyl toluene and methylstyrene as main materials Aromatic hydrocarbon resins; copolymer resins thereof; alicyclic saturated hydrocarbon resins obtained by hydrogenating the above-mentioned resins; and mixtures thereof. As a petroleum resin, an alicyclic saturated hydrocarbon resin is preferable.

  Among them, pore forming agents such as liquid paraffin are preferably used as the additive.

  Furthermore, particularly, by using a petroleum resin as an additive, the amount of the ultrafine resin portion inside the obtained polyolefin porous film tends to be able to be in a suitable range. As a result, it is possible to control the difference in the method of measuring the porosity of the non-aqueous electrolyte secondary battery separator including the above-mentioned polyolefin porous film within a suitable range.

  For the cooling in the step (B), a method of contacting with a refrigerant such as cold air, cooling water, a method of contacting with a cooling roll, or the like can be used, and preferably a method of contacting with a cooling roll. By the cooling, the micro phase of the polyolefin resin is immobilized. When the cooling rate in the above cooling is reduced, the microphase structure becomes rough, and when the cooling rate is increased, the microphase structure tends to be dense. That is, as the cooling rate is increased, the amount of the ultrafine resin portion contained in the polyolefin porous film to be obtained later tends to be increased. 0 degreeC or more and 60 degrees C or less are preferable, and, as for the temperature of the cooling roll which may be used for the said cooling, 20 degrees C or more and 60 degrees C or less are more preferable. The peripheral speed of the cooling roll is preferably 0.1 m / min or more and 30 m / min or less, more preferably 0.5 m / min or more and 10 m / min or less. By cooling under the conditions of the above-mentioned range, the crystallinity degree of the obtained polyolefin resin does not increase, and a sheet-like polyolefin resin composition suitable for stretching tends to be obtained.

  In the step (C), the stretching of the sheet-like polyolefin resin composition can be performed using a commercially available stretching device. The temperature of the sheet-like polyolefin resin composition at the time of stretching is not more than the crystalline melting point of the polyolefin resin, preferably 80 ° C. or more and 125 ° C. or less, and more preferably 100 ° C. or more and 120 ° C. or less.

  The stretching may be performed only in the MD direction, may be performed only in the TD direction, or may be performed in both the MD direction and the TD direction. As a method of stretching in both MD and TD directions, sequential biaxial stretching in which the film is stretched in the MD direction and then in the TD direction, and simultaneously biaxial stretching in which the MD and TD directions are simultaneously stretched Can be mentioned.

In the present specification, the MD (Machine Direction) of the polyolefin porous film
The term ")" means the transport direction at the time of production of the polyolefin porous film. Moreover, TD (Transverse Direction) of a polyolefin porous film means the direction perpendicular | vertical to MD of a polyolefin porous film.

  For stretching, a method may be used in which the end of the sheet is gripped and stretched by a chuck, or may be stretched by changing the rotational speed of a roll for conveying the sheet, or a sheet may be used with a pair of rolls. You may use the method of rolling.

In the step (C), conditions for sequential biaxial stretching are described in detail. The stretching ratio in stretching the sheet-like polyolefin resin composition in the MD direction is preferably 3.0 times or more and 7.0 times or less, more preferably 4.5 times or more, 6.5 Less than twice. Furthermore, the strain rate in the MD direction is preferably 750% / min or more and 1500% / min or less, and more preferably 800% / min or more and 1500% / min or less.

  In the step (C), the draw ratio at the time of further drawing the polyolefin resin composition drawn in the MD direction in the TD direction is preferably 3.0 times or more and 7.0 times or less, more preferably 4 .5 or more and 6.5 or less. In the stretching, the strain rate in the TD direction is preferably 550% / min or more and 3000% / min or less, more preferably 600% / min or more and 2000% / min or less.

  When stretching is performed at a temperature equal to or lower than the crystalline melting point of the polyolefin resin, the resin in the noncrystalline portion is cut or a molecular chain of the resin is stretched to form a void. When the strain rate at the time of stretching is reduced, large voids are generated sparsely, the resin portion tends to be thick, and the amount of the ultrafine resin portion tends to be small. On the other hand, when the drawing strain rate is increased, fine voids and extra-thin resin portions tend to be increased.

  The magnitude of the difference between the strain rate in the MD direction and the strain rate in the TD direction in the stretching is preferably 1250% / min or less, more preferably 1000% / min or less. When the magnitude of the difference between the strain rate in the MD direction and the strain rate in the TD direction is larger than the above range, the orientation of the resin in the fast speed direction is further promoted, the resin portion becomes thicker, and the ultrafine resin portion There is a tendency for the amount of

  The washing liquid used in the step (D) is not particularly limited as long as it is a solvent capable of removing an additive such as a pore forming agent, and examples thereof include heptane, dichloromethane and the like.

[Second Embodiment: Laminated Separator for Nonaqueous Electrolyte Secondary Battery]
A laminated separator for a non-aqueous electrolyte secondary battery according to Embodiment 2 of the present invention includes the separator for a non-aqueous electrolyte secondary battery according to Embodiment 1 of the present invention and an insulating porous layer. Therefore, a multilayer separator for a non-aqueous electrolyte secondary battery according to Embodiment 2 of the present invention is a polyolefin porous film constituting the separator for a non-aqueous electrolyte secondary battery according to Embodiment 1 of the present invention described above. including.

[Insulating porous layer]
The insulating porous layer constituting the laminated separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention is usually a resin layer containing a resin, preferably a heat-resistant layer or an adhesive layer. . The resin constituting the insulating porous layer (hereinafter simply referred to as "porous layer") is insoluble in the non-aqueous electrolyte solution of the battery, and is electrochemically stable in the range of use of the battery Is preferred.

  The porous layer is laminated on one side or both sides of the non-aqueous electrolyte secondary battery separator, as necessary. When the porous layer is laminated on one side of the polyolefin porous film, the porous layer is preferably formed on the surface of the polyolefin porous film facing the positive electrode when the non-aqueous electrolyte secondary battery is used. It is laminated, more preferably, laminated on the surface in contact with the positive electrode.

  The resin constituting the porous layer is, for example, polyolefin; (meth) acrylate resin; fluorine-containing resin; polyamide resin; polyester resin; polyimide resin; rubbers; melting point or glass transition temperature is 180 ° C. or more Resin; water-soluble polymer etc. may be mentioned.

  Further, among the above-mentioned resins, polyolefins, acrylate resins, fluorine-containing resins, polyamide resins, polyester resins, and water-soluble polymers are preferable. As a polyamide resin, a wholly aromatic polyamide (aramid resin) is preferable. As polyester resin, polyarylate and liquid crystal polyester are preferable.

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

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

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

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

  The content of the fine particles in the porous layer is preferably 1 to 99% by volume of the porous layer, and more preferably 5 to 95% by volume. By making content of microparticles | fine-particles into the said range, it is less likely that the space | gap formed by contact of microparticles | fine-particles will be obstruct | occluded by resin etc. Thus, sufficient ion permeability can be obtained, and the basis weight per unit area can be set to an appropriate value.

  The fine particles may be used in combination of two or more kinds of particles or different specific surface areas.

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

  If the thickness of the porous layer is less than 1 μm, internal short circuit due to breakage of the battery may not be sufficiently prevented. In addition, the amount of electrolyte held in the porous layer may be reduced. On the other hand, if the thickness of the porous layer exceeds 30 μm in total on both sides, rate characteristics or cycle characteristics may be degraded.

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

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

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

[Laminate]
A laminate that is a laminated separator for a non-aqueous electrolyte secondary battery according to Embodiment 2 of the present invention comprises a separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention and an insulating porous layer, Preferably, the above-mentioned insulating porous layer is laminated on one side or both sides of the separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention.

  The film thickness of the laminate according to one embodiment of the present invention is preferably 5.5 μm to 45 μm, and more preferably 6 μm to 25 μm.

The air permeability of the laminate according to an embodiment of the present invention is 30 to 1000 sec / 100 in Gurley value.
It is preferably mL, and more preferably 50 to 800 sec / 100 mL.

  In addition to the polyolefin porous film and the insulating porous layer, the laminate according to one embodiment of the present invention may be any known porous film such as a heat-resistant layer, an adhesive layer, a protective layer, etc. The quality layer may be included in the range which does not impair the object of the present invention.

  The laminate according to an embodiment of the present invention includes, as a base material, a separator for a non-aqueous electrolyte secondary battery, in which the difference in porosity measurement method per unit film thickness is in a specific range. Therefore, it is possible to suppress the deterioration of the rate characteristics after repeating the charge and discharge cycle of the non-aqueous electrolyte secondary battery including the laminate as the laminated separator for the non-aqueous electrolyte secondary battery, and to improve the cycle characteristics. it can.

[Method of manufacturing porous layer, laminate]
Examples of the method for producing the insulating porous layer according to the embodiment of the present invention and the laminate according to the embodiment of the present invention include, for example, a non-aqueous electrolyte solution 2 according to the embodiment of the present invention. The method may be applied to the surface of the polyolefin porous film provided in the secondary battery separator, and then dried to precipitate the insulating porous layer.

  In addition, before apply | coating the said coating liquid to the surface of the polyolefin porous film with which the separator for non-aqueous-electrolyte secondary batteries which concerns on one Embodiment of this invention is equipped, the coating liquid of the said polyolefin porous film is apply | coated. The surface can be subjected to a hydrophilization treatment as required.

  The coating liquid used in the method for producing a porous layer according to an embodiment of the present invention and the method for producing a laminate according to an embodiment of the present invention generally comprises a resin capable of being contained in the above-mentioned porous layer as a solvent. In addition, it can be prepared by dispersing fine particles that can be contained in the above-mentioned porous layer while being dissolved in Here, the solvent for dissolving the resin also serves as a dispersion medium for dispersing the fine particles. Alternatively, the resin may be made into an emulsion by a solvent.

  The solvent (dispersion medium) is not particularly limited as long as the resin can be uniformly and stably dissolved and the fine particles can be uniformly and stably dispersed without adversely affecting the polyolefin porous film. Specifically as said solvent (dispersion medium), water and an organic solvent are mentioned, for example. Only one type of solvent may be used, or two or more types may be used in combination.

  The coating liquid may be formed by any method as long as it can satisfy the conditions such as resin solid content (resin concentration) and the amount of fine particles necessary to obtain a desired porous layer. Specific examples of the method for forming the coating liquid include a mechanical stirring method, an ultrasonic dispersion method, a high pressure dispersion method, and a media dispersion method. In addition, the coating liquid may contain, as components other than the resin and the fine particles, additives such as a dispersant, a plasticizer, a surfactant, and a pH adjuster as long as the object of the present invention is not impaired. . In addition, the addition amount of an additive should just be a range which does not impair the objective of the present invention.

  The method of applying the coating liquid to the polyolefin porous film, that is, the method of forming the porous layer on the surface of the polyolefin porous film is not particularly limited. As a method of forming a porous layer, for example, a method of directly applying a coating liquid to the surface of a polyolefin porous film and then removing a solvent (dispersion medium); a coating liquid is applied to a suitable support, a solvent (Dispersion medium) is removed to form a porous layer, and then the porous layer and the polyolefin porous film are pressure-bonded and then the support is peeled off; after the coating liquid is applied to a suitable support, The method of pressure-bonding a polyolefin porous film to a coated surface and then removing the support and then removing the solvent (dispersion medium) may, for example, be mentioned.

  As a coating method of a coating liquid, the conventionally well-known method can be employ | adopted and a gravure coater method, a dip coater method, the bar coater method, the die-coater method etc. are specifically mentioned, for example.

  The solvent (dispersion medium) is generally removed by drying. Moreover, after replacing the solvent (dispersion medium) contained in a coating liquid with another solvent, you may dry.

Embodiment 3: Member for Nonaqueous Electrolyte Secondary Battery, Embodiment 4: Nonaqueous Electrolyte Secondary Battery
The member for a non-aqueous electrolyte secondary battery according to Embodiment 3 of the present invention is a positive electrode, the separator for a non-aqueous electrolyte secondary battery according to Embodiment 1 of the present invention, or the non-aqueous electrolyte secondary battery according to Embodiment 2 of the present invention. A laminated separator for a water electrolyte secondary battery and a negative electrode are disposed in this order.

  The nonaqueous electrolyte secondary battery according to Embodiment 4 of the present invention is a separator for nonaqueous electrolyte secondary batteries according to Embodiment 1 of the present invention, or nonaqueous electrolyte 2 according to Embodiment 2 of the present invention. Includes laminated separators for secondary batteries.

  The non-aqueous electrolyte secondary battery according to an embodiment of the present invention is, for example, a non-aqueous secondary battery that obtains an electromotive force by doping and dedoping of lithium, and is related to a positive electrode and an embodiment of the present invention A non-aqueous electrolyte secondary battery member can be provided, in which the non-aqueous electrolyte secondary battery separator and the negative electrode are stacked in this order. The non-aqueous electrolyte secondary battery according to one embodiment of the present invention is, for example, a non-aqueous secondary battery that obtains an electromotive force by doping and de-doping of lithium, and it comprises a positive electrode, a porous layer, A non-aqueous electrolyte secondary battery member in which a separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention and a negative electrode are stacked in this order, that is, a positive electrode, according to an embodiment of the present invention It may be a lithium ion secondary battery provided with a non-aqueous electrolyte secondary battery member in which a laminate separator for non-aqueous electrolyte secondary battery and a negative electrode are stacked in this order. The components of the non-aqueous electrolyte secondary battery other than the non-aqueous electrolyte secondary battery separator are not limited to the components described below.

In a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, in general, the negative electrode and the positive electrode are the separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention or an embodiment of the present invention The battery element in which the electrolytic solution is impregnated in the structure facing each other through the laminated separator for the non-aqueous electrolyte secondary battery is sealed in the exterior material. The non-aqueous electrolyte secondary battery is preferably a non-aqueous electrolyte secondary battery, in particular a lithium ion secondary battery. In addition, dope means occlusion, support, adsorption, or insertion, and means the phenomenon in which a lithium ion enters into the active material of electrodes, such as a positive electrode.

  The nonaqueous electrolyte secondary battery member according to an embodiment of the present invention is a separator for nonaqueous electrolyte secondary batteries according to an embodiment of the present invention, or the nonaqueous electrolyte secondary battery according to an embodiment of the present invention Since the laminated separator for a separator is provided, when it is incorporated in a non-aqueous electrolyte secondary battery, it is possible to suppress a decrease in rate characteristics after charge and discharge cycles of the non-aqueous electrolyte secondary battery. A non-aqueous electrolyte secondary battery according to an embodiment of the present invention includes a separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, in which the difference in porosity measurement is adjusted to a specific range. Thus, the cycle characteristics are excellent.

<Positive electrode>
The positive electrode in the non-aqueous electrolyte secondary battery member and the non-aqueous electrolyte secondary battery according to one embodiment of the present invention is particularly limited as long as it is generally used as a positive electrode of a non-aqueous electrolyte secondary battery For example, a positive electrode sheet having a structure in which an active material layer containing a positive electrode active material and a binder resin is formed on a current collector can be used. The active material layer may further contain a conductive agent.

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

  Examples of the conductive material include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and a sintered body of an organic polymer compound. Only one type of conductive material may be used, or two or more types may be used in combination.

  Examples of the binder include fluorine resins such as polyvinylidene fluoride, acrylic resins, and styrene butadiene rubber. The binder also has a function as a thickener.

  Examples of the positive electrode current collector include conductors such as Al, Ni and stainless steel. Among them, Al is more preferable because it is easily processed into a thin film and inexpensive.

  As a method for producing a sheet-like positive electrode, for example, a method of press-molding a positive electrode active material, a conductive material and a binder on a positive electrode current collector; a positive electrode active material, a conductive material and a binder using a suitable organic solvent After the adhesive is formed into a paste, the paste is applied to the positive electrode current collector, dried and then pressurized to be fixed to the positive electrode current collector, and the like.

<Negative electrode>
The negative electrode in the non-aqueous electrolyte secondary battery member and the non-aqueous electrolyte secondary battery according to one embodiment of the present invention is particularly limited as long as it is generally used as a negative electrode of a non-aqueous electrolyte secondary battery However, for example, a negative electrode sheet having a structure in which an active material layer containing a negative electrode active material and a binder resin is formed on a current collector can be used. The active material layer may further contain a conductive aid.

  As said negative electrode active material, the material which can dope and de-dope lithium ion, lithium metal, lithium alloy, etc. are mentioned, for example. As the said material, carbonaceous material etc. are mentioned, for example. Examples of carbonaceous materials include natural graphite, artificial graphite, cokes, carbon black, and pyrolytic carbons.

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

  As a method for producing a sheet-like negative electrode, for example, a method of press-molding a negative electrode active material on a negative electrode current collector; a paste-like negative electrode active material using an appropriate organic solvent, and collecting the paste A method of applying to a current collector, drying and pressing to fix the current collector to a negative electrode current collector; The paste preferably contains the above-mentioned conductive aid and the above-mentioned binder.

<Non-aqueous electrolyte>
The non-aqueous electrolyte in the non-aqueous electrolyte secondary battery according to one embodiment of the present invention is not particularly limited as long as it is a non-aqueous electrolyte generally used for non-aqueous electrolyte secondary batteries, for example, lithium salt A non-aqueous electrolyte prepared by dissolving Examples of lithium salts include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , Li ₂ B ₁₀ Cl _{2 10} , lower aliphatic carboxylic acid lithium salts, LiAlCl _{4 and the} like. Only one type of lithium salt may be used, or two or more types may be used in combination.

  Examples of the organic solvent constituting the non-aqueous electrolytic solution include carbonates, ethers, esters, nitriles, amides, carbamates, sulfur-containing compounds, and fluorine-containing compounds introduced into these organic solvents. A fluorine organic solvent etc. are mentioned. The organic solvents may be used alone or in combination of two or more.

<A member for a non-aqueous electrolyte secondary battery and a method of manufacturing a non-aqueous electrolyte secondary battery>
As a method of manufacturing a member for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, for example, the above-mentioned positive electrode, a separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention The method of arrange | positioning the laminated separator for non-aqueous electrolyte secondary batteries which concerns on embodiment, and a negative electrode in this order is mentioned.

  In addition, as a method of manufacturing a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, for example, after a member for a non-aqueous electrolyte secondary battery is formed by the above method, a non-aqueous electrolyte secondary battery is produced The member for the non-aqueous electrolyte secondary battery is placed in a container that is the case of the above, and then the inside of the container is filled with the non-aqueous electrolyte, and then the container is decompressed and sealed. The non-aqueous electrolyte secondary battery can be manufactured.

  Hereinafter, the present invention will be described in more detail by way of examples and comparative examples, but the present invention is not limited to these examples.

[Measuring method]
<Measurement method of SEM porosity>
The SEM porosity of the non-aqueous electrolyte secondary battery separator (polyolefin porous film) manufactured in the example and the comparative example was calculated using the method described below.

  First, a polyolefin porous film was impregnated with an embedding resin (such as an epoxy resin), and the voids of the polyolefin porous film were filled and cured. After curing, the sample was treated with osmium tetraoxide to prepare a measurement sample, and Pt—Pd was vapor-deposited on the surface of the measurement sample.

When the thickness direction of the sample for measurement is Z direction, an arbitrary direction parallel to the plane of the sample for measurement orthogonal to the thickness is X direction, and further, the direction orthogonal to X and Z is Y direction. S
By performing FIB processing using EM (FEI; HELIOS 600), a cross section (hereinafter referred to as XZ cross section) made of an arbitrary side X and thickness Z of the surface of the sample for measurement is produced, and the cross section is accelerated voltage; An SEM image (reflected electron image) was observed at 1 kV and a magnification of 6500 × to obtain a SEM image.

  After the SEM observation, FIB processing is performed in a thickness of 19.2 nm in the Y direction orthogonal to the XZ cross section to newly prepare an XZ cross section, and the cross section is subjected to SEM observation (reflected electron image) under the above conditions to obtain a SEM image obtain. Thereafter, in the same manner, an XZ cross-sectional continuous image of the measurement sample was acquired by repeating FIB processing and acquisition of an SEM image of the cross section at intervals of 19.2 nm in thickness.

  Subsequently, position correction was performed on the XZ cross-sectional continuous image using an image analysis software (manufactured by Visualization Sciences Group; Avizo Ver. 6.0) to obtain a corrected XZ cross-sectional continuous image. The scale was X, Y, Z axis 19.2 nm / pix.

  Using the quantitative analysis software (manufactured by Rattock System Engineering; TRI / 3D-BON-FCS), the above-mentioned position-corrected XZ cross-sectional continuous image is subjected to two gradations so that the resin portion and the void portion can be distinguished. The

  Specifically, in two-gradation, first, an XZ cross-sectional continuous image is opened on TRI / 3D-BON-FCS, a median filter is applied to remove noise, and then two-gradation is performed using Auto-LW. Did.

  Next, the XZ plane of the above XZ cross-sectional continuous image, which is bi-tonalized in the resin portion and the void portion, is converted to the XY plane in SectionView in EditViewer mode on TRI / 3D-BON-FCS, and the surface of the sample for measurement It converted into the surface direction continuous image (it calls an XY surface continuous image hereafter) of the sample of the said measurement sample which carried out the two gradations of the thickness direction which goes to the opposite direction. The scale of the XY plane continuous image after conversion was also X, Y, Z axes 19.2 nm / pix.

  Thereafter, from an arbitrary part of the XY plane continuous image, the range of the number of pixels is 256 pix in the X direction, 256 pix in the Y direction, and pix in the Z direction, and the continuous image for analysis is extracted.

  The continuous image for analysis was divided into a plurality of images with a size of 1 pix in the Z direction. For each of the above images, the percentage of void to analysis area (porosity) was measured using a 2D label density function. The average value of the porosity of each of the measured images (porosity of the measurement sample) was calculated. As a result, the porosity of the sample for measurement calculated was made into the "SEM porosity" of the said polyolefin porous film.

<Method of measuring true porosity>
The true porosity of the non-aqueous electrolyte secondary battery separator (porous film) manufactured in the example and the comparative example was calculated using the following steps (a) to (d).

(A) Measurement of Film Thickness The film thickness of the porous film was measured using a high precision digital length measuring machine (VL-50) manufactured by Mitutoyo Corporation.

(B) Measurement of weight basis weight From the porous film, a square having a side length of 8 cm was cut out as a sample, and the weight W (g) of the sample was measured. And the fabric weight of a porous film was computed according to the following formula (2).

Weight basis weight (g / m ² ) = W / (0.08 × 0.08) (2)
(C) Measurement of true density The porous film is cut into 4 mm square to 6 mm square and vacuum dried at 30 ° C. or less for 17 hours, and then helium gas is measured using a dry automatic densitometer (AccuPye II 1340 manufactured by Micromeritex Co., Ltd.) The true density of the porous film was measured by the substitution method.

(D) Calculation of true porosity The film thickness [μm], weight per unit area [g / m ² ] and true density [g / m] of the porous film calculated and measured in the above steps (a) to (c) ³ ] Based on the following formula (1), the true porosity [%] of the said porous film was computed.

(True porosity) = [1- (weight basis weight) / {(film thickness) × 10 ⁻⁶ × 1 [m ² ] × (true density)}] × 100 (1)
<Method of calculating difference in void ratio measurement>
The difference between the SEM porosity calculated by the above-mentioned method and the true porosity is calculated, and the porosity of the non-aqueous electrolyte secondary battery separator (polyolefin porous film) manufactured in the examples and comparative examples It was taken as the difference between rate measurement.

<Method of measuring air permeability>
The air permeability [sec / 100 mL] of the polyolefin porous film produced in Examples and Comparative Examples was measured in accordance with JIS P8117.

<Method of measuring compressive modulus>
The compressive elastic modulus in the thickness direction of the non-aqueous electrolyte secondary battery separator (polyolefin porous film) produced in Examples and Comparative Examples was measured by the following method.

By using TMA / SS7100 (manufactured by SII Nano Technology Inc.), temperature 25 ° C., start load 5 mN, compression speed 150.17 mN / min, probe area 0.785 mm ² (probe tip diameter 1.0 mmφ) Measure the magnitude of strain when stress is applied in the thickness direction to the separator for a non-aqueous electrolyte secondary battery, and plot the magnitude of strain against stress, and the strain is between 0 and 10%. A stress-strain line was created. The compressive elastic modulus in the thickness direction was calculated from the slope of the stress-strain line. In the measurement of the above-described compressive elastic modulus, the position at a start load of 5 mN was set to 0% strain.

<Method of measuring temperature compatible with liquid paraffin of alicyclic saturated hydrocarbon resin>
Both 1 g of the alicyclic saturated hydrocarbon resin and liquid paraffin were weighed into a sample tube. The sample tube was heated on a hot plate, and the temperature of the compatible material inside the sample tube when the alicyclic saturated hydrocarbon resin and the liquid paraffin were uniformly compatible was measured. The measured temperature was taken as the temperature compatible with the liquid paraffin of the alicyclic saturated hydrocarbon resin.

<Method of measuring rate characteristics after 100 cycles>
The rate characteristics after 100 cycles of the non-aqueous electrolyte secondary batteries manufactured in Examples and Comparative Examples were measured by the methods described below.

  With respect to a new non-aqueous electrolyte secondary battery not subjected to charge and discharge cycles manufactured in Examples and Comparative Examples, a voltage range at 25 ° C .: 4.1 to 2.7 V, a current value: 0.2 C Initial cycle charge / discharge of 4 cycles was performed with 1 cycle (a current value for discharging a rated capacity by a 1 hour rate discharge capacity in 1 hour is 1 C, the same applies hereinafter).

  For a non-aqueous electrolyte secondary battery that has been initially charged and discharged, the charge current value at 55 ° C .; 1 C, the discharge current value 0.2 C, 1 C, 5 C, 10 C, 20 C, 0.2 C in order of constant current Three cycles of charge and discharge were performed to measure the initial rate characteristics.

  With respect to the non-aqueous electrolyte secondary battery after measuring the initial rate characteristics, the voltage range of 55 ° C .: 4.2 to 2.7 V, the charge current value: 1 C, the discharge current value; 10 C constant current of 1 cycle As 100 cycles of charge and discharge were performed. For a non-aqueous electrolyte secondary battery that has been charged and discharged for 100 cycles, the charge current value at 55 ° C .; 1 C, and the discharge current value is determined in order of 0.2 C, 1 C, 5 C, 10 C, 20 C, 0.2 C Charging and discharging were carried out for 3 cycles each with current.

  Then, after 100 cycles, the ratio (20 C discharge capacity / 0.2 C discharge capacity) of the discharge capacity at the third cycle in each of the first charge and discharge with a discharge current value of 0.2 C and the charge and discharge with 20 C. Calculated as rate characteristics.

Example 1
[Production of Separator for Nonaqueous Electrolyte Secondary Battery]
Prepare 18 wt% of ultra high molecular weight polyethylene powder (Hisex Million 145M, Mitsui Chemicals Co., Ltd.) and 2 wt% of alicyclic saturated hydrocarbon resin (softening point 115 ° C) compatible with liquid paraffin at 155 ° C. These powders were crushed and mixed in a blender until the particle size of the powders became the same, and then the mixed powder was added from a metering feeder to a twin-screw kneader, and melt-kneaded. At this time, 80% by weight of the liquid paraffin was added to the twin-screw kneader with a pump while being pressurized, and melt-kneaded together.

  Then, the polyolefin resin composition was produced by pushing out from a T-die through a gear pump. The said polyolefin resin composition was cooled with a 40 degreeC cooling roll, and the winding body of the sheet-like polyolefin resin composition was obtained. The peripheral speed of the cooling roll at this time was 1.3 m / min.

  The obtained sheet-like polyolefin resin composition was stretched at 117 ° C. in the MD direction at a draw ratio of 6.4 times. The strain rate at this time was 1000% / min. Subsequently, the film was drawn at a draw ratio of 6.0 in the TD direction at 115 ° C. The strain rate at this time was 700% / min.

  The drawn sheet-like polyolefin resin composition is immersed in heptane to remove the additive, and then left to stand in a ventilated oven at 120 ° C. for 1 minute for drying, and the film thickness is 19.7 μm, the air permeability is A porous film of 115 sec / 100 mL was obtained. The porous film is referred to as a polyolefin porous film 1.

[Manufacture of non-aqueous electrolyte secondary battery]
The positive electrode and the negative electrode were manufactured by the method described below.

(Production of positive electrode)
A commercially available positive electrode manufactured by applying LiNi _0.5 Mn _0.3 Co _0.2 O ₂ / conductive material / PVDF (weight ratio 92/5/3) to an aluminum foil was used. In the commercially available positive electrode, the size of the portion where the positive electrode active material layer is formed is 45 mm × 30 mm, and the aluminum foil is made so that a portion where the positive electrode active material layer is not formed with a width of 13 mm remains on the outer periphery. It cut out and set it as the positive electrode. The thickness of the positive electrode active material layer was 58 μm, the density was 2.50 g / cm ³ , and the positive electrode capacity was 174 mAh / g.

(Fabrication of negative electrode)
A commercially available negative electrode manufactured by applying a graphite / styrene-1,3-butadiene copolymer / sodium carboxymethylcellulose (weight ratio 98/1/1) to a copper foil was used. The commercially available negative electrode is a copper foil so that the size of the portion where the negative electrode active material layer is formed is 50 mm × 35 mm, and the portion where the negative electrode active material layer is not formed remains at a width of 13 mm. It cut out and set it as the negative electrode. The thickness of the negative electrode active material layer was 49 μm, the density was 1.40 g / cm ³ , and the negative electrode capacity was 372 mAh / g.

(Assembly of non-aqueous electrolyte secondary battery)
Using the positive electrode, the negative electrode, and the polyolefin porous film 1, a non-aqueous electrolyte secondary battery was manufactured by the method described below.

  A member for a non-aqueous electrolyte secondary battery was obtained by laminating (arranging) the above-described positive electrode, the polyolefin porous film 1 as a separator for a non-aqueous electrolyte secondary battery, and a negative electrode in this order in a laminate pouch. . At this time, the positive electrode and the negative electrode were disposed such that the whole of the main surface in the positive electrode active material layer of the positive electrode was included in the range of the main surface in the negative electrode active material layer of the negative electrode (overlapping the main surface).

Subsequently, the member for a non-aqueous electrolyte secondary battery was placed in a bag in which an aluminum layer and a heat seal layer were laminated, and further, 0.25 mL of the non-aqueous electrolyte was placed in the bag. The above non-aqueous electrolyte is a 25 ° C. non-aqueous electrolyte in which 1.0 mol / l of LiPF ₆ is dissolved in a mixed solvent of ethyl methyl carbonate, diethyl carbonate and ethylene carbonate in a volume ratio of 50:20:30. Was used. And the non-aqueous secondary battery was produced by heat-sealing the said bag, pressure-reducing the inside of a bag. The design capacity of the non-aqueous secondary battery was 20.5 mAh. The non-aqueous electrolyte secondary battery is referred to as a non-aqueous electrolyte secondary battery 1.

Example 2
[Production of porous film]
Prepare 18 wt% of ultra high molecular weight polyethylene powder (Hisex Million 145M, Mitsui Chemicals Co., Ltd.) and 2 wt% of alicyclic saturated hydrocarbon resin (softening point 90 ° C) compatible with liquid paraffin at 130 ° C. These powders were crushed and mixed in a blender until the particle size of the powders became the same, and then the mixed powder was added from a metering feeder to a twin-screw kneader, and melt-kneaded. At this time, 80% by weight of the liquid paraffin was added to the twin-screw kneader with a pump while being pressurized, and melt-kneaded together.

  Then, the polyolefin resin composition was produced by pushing out from a T-die through a gear pump. The said polyolefin resin composition was cooled with a 40 degreeC cooling roll, and the winding body of the sheet-like polyolefin resin composition was obtained. The peripheral speed of the cooling roll at this time was 1.3 m / min.

  The obtained sheet-like polyolefin resin composition was stretched at 117 ° C. in the MD direction at a draw ratio of 6.4 times. The strain rate at this time was 1000% / min. Subsequently, the film was drawn at a draw ratio of 6.0 in the TD direction at 115 ° C. The strain rate at this time was 700% / min.

  The drawn sheet-like polyolefin resin composition is immersed in heptane to remove the additive, and then left to stand in a ventilated oven at 135 ° C. for 12 minutes for drying, and the film thickness is 10.0 μm, and the air permeability is A porous film of 137 sec / 100 mL was obtained. The porous film is referred to as a polyolefin porous film 2.

[Manufacture of non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery was manufactured in the same manner as Example 1, except that the polyolefin porous film 2 was used instead of the polyolefin porous film 1. The manufactured non-aqueous electrolyte secondary battery is referred to as a non-aqueous electrolyte secondary battery 2.

Comparative Example 1
[Production of porous film]
68% by weight of ultra high molecular weight polyethylene powder (GUR 2024, manufactured by Ticona), 32% by weight of polyethylene wax (FNP-0115, manufactured by Nippon Seikei Co., Ltd.) with a weight average molecular weight of 1000, the total of this ultrahigh molecular weight polyethylene and polyethylene wax As 100 parts by weight, antioxidant (Irg1010, manufactured by Ciba Specialty Chemicals) 0.4% by weight, (P168 manufactured by Ciba Specialty Chemicals) 0.1% by weight, sodium stearate 1.3% by weight Further, calcium carbonate (manufactured by Maruo Calcium Co., Ltd.) having an average particle diameter of 0.1 μm is added so as to be 38% by volume with respect to the total volume, and these are mixed as they are in powder with a Henschel mixer, It melt-kneaded using this, and was set as the polyolefin resin composition. While cooling the above-mentioned polyolefin resin composition with a roll, it was drawn at a drawing strain rate of 150% / min to form a sheet. Calcium carbonate is removed by immersing this sheet in a hydrochloric acid aqueous solution (hydrochloric acid 4 mol / L, non-ionic surfactant 0.5% by weight), 6.2 at a rate of strain rate of 1250% / min at 105 ° C. It extended | stretched by the draw ratio of double, and obtained the film thickness 10.4 micrometers and the porous film of air permeability 209 sec / 100 mL. The porous film is referred to as a polyolefin porous film 3.

[Manufacture of non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery was manufactured in the same manner as Example 1, except that the polyolefin porous film 3 was used instead of the polyolefin porous film 1. The manufactured non-aqueous electrolyte secondary battery is referred to as a non-aqueous electrolyte secondary battery 3.

Comparative Example 2
[Production of porous film]
Prepare 18 wt% of ultra high molecular weight polyethylene powder (Hisex Million 145M, Mitsui Chemicals Co., Ltd.) and 2 wt% of alicyclic saturated hydrocarbon resin (softening point 125 ° C) compatible with liquid paraffin at 164 ° C, These powders were crushed and mixed in a blender until the particle size of the powders became the same, and then the mixed powder was added from a metering feeder to a twin-screw kneader, and melt-kneaded. At this time, 80% by weight of the liquid paraffin was added to the twin-screw kneader with a pump while being pressurized, and melt-kneaded together.

  Then, the polyolefin resin composition was produced by pushing out from a T-die through a gear pump. The said polyolefin resin composition was cooled with a 40 degreeC cooling roll, and the winding body of the sheet-like polyolefin resin composition was obtained. The peripheral speed of the cooling roll at this time was 1.3 m / min.

  The obtained sheet-like polyolefin resin composition was stretched at 117 ° C. in the MD direction at a draw ratio of 6.4 times. The strain rate at this time was 700% / min. Subsequently, the film was drawn at a draw ratio of 6.0 in the TD direction at 115 ° C. The strain rate at this time was 500% / min.

  The drawn sheet-like polyolefin resin composition is immersed in heptane to remove the additive, and then left standing in a ventilated oven at 120 ° C. for 1 minute for drying, and the film thickness is 19.1 μm, the air permeability is A porous film of 112 sec / 100 mL was obtained. The porous film is referred to as a polyolefin porous film 4.

[Manufacture of non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery was manufactured in the same manner as Example 1, except that the polyolefin porous film 4 was used instead of the polyolefin porous film 1. The manufactured non-aqueous electrolyte secondary battery is referred to as a non-aqueous electrolyte secondary battery 4.

[Conclusion]
"SEM porosity", "true porosity", "difference between porosity measurement methods", and "compressive elastic modulus" of the polyolefin porous films 1 to 4 produced in Examples 1 and 2 and Comparative Examples 1 and 2 Table 1 below shows the value of “1” and the value of rate characteristics after 100 cycles of the non-aqueous electrolyte secondary batteries 1 to 4 manufactured in Examples 1 and 2 and Comparative Examples 1 and 2.

[Conclusion]
From the description of Table 1, a nonaqueous electrolyte secondary battery separator (polyolefin porous film) manufactured in Examples 1 and 2 having a difference of 4 to 20% in porosity measurement method is incorporated. A non-aqueous electrolyte secondary battery incorporating the separator for a non-aqueous electrolyte secondary battery manufactured in Comparative Examples 1 and 2 in which the difference between the porosity measurement methods is out of the above range is an electrolyte secondary battery. It was found that the rate characteristic after repeating 100 cycles of charging and discharging was higher than that, and the cycle characteristic was more excellent.

  The separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention is excellent in cycle characteristics. Therefore, the separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention is useful as a member of a non-aqueous electrolyte secondary battery.

Claims (5)

A separator for a non-aqueous electrolyte secondary battery comprising a polyolefin porous film, comprising:
The range of the separator surface direction is 256 pix × 256 pix, and the thickness is the separator film thickness under the conditions obtained by FIB-SEM measurement and image analysis of magnification 6500 times of the above polyolefin porous film and 1 pix of 19.2 nm And the average value of the porosity calculated from the continuous image in which the void portion and the porous film portion are formed from the separator surface toward the inner thickness direction, and the thickness of the above-mentioned polyolefin porous film And a separator for a non-aqueous electrolyte secondary battery, which has a difference of 4 to 20% from the porosity calculated from the weight basis weight and the true density.   The separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the compression elastic modulus is 1600 kPa or more.   A laminated separator for a non-aqueous electrolyte secondary battery, comprising the separator for a non-aqueous electrolyte secondary battery according to claim 1 and an insulating porous layer.   A positive electrode, a separator for a non-aqueous electrolyte secondary battery according to claim 1 or 2, or a laminated separator for a non-aqueous electrolyte secondary battery according to claim 3, and a negative electrode are disposed in this order A member for a non-aqueous electrolyte secondary battery.   A nonaqueous electrolyte secondary battery comprising the separator for a nonaqueous electrolyte secondary battery according to claim 1 or 2, or the laminated separator for a nonaqueous electrolyte secondary battery according to claim 3.

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