JP2017117779A - Non-aqueous electrolyte secondary battery separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery separator with an excellent rate characteristic.SOLUTION: A non-aqueous electrolyte secondary battery separator is made of a porous membrane, and a value J of tensile creep compliance when the same is subjected to stress of 30 MPa for a period of t seconds satisfies one or more of the following three requirements: (i) J=4.5 to 14.0 GPawith t=300 seconds; (ii) J=9.0 to 25.0 GPawith t=1800 seconds; or (iii) J=12.0 to 32.0 GPawith t=3600 seconds.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a separator for a nonaqueous electrolyte secondary battery comprising a porous membrane, and a laminated separator for a nonaqueous electrolyte secondary battery comprising a porous layer laminated on the porous membrane.

  Non-aqueous electrolyte secondary batteries, especially lithium ion secondary batteries, are widely used as batteries for personal computers, mobile phones, personal digital assistants, etc. due to their high energy density, and recently developed as in-vehicle batteries. It has been.

  In a lithium ion secondary battery, charging / discharging progresses due to insertion / extraction of lithium ions in the crystal lattice of the electrode active material, which causes expansion and contraction of the electrode active material and the electrode including the same.

  Recent non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, are becoming smaller and thinner, and battery containers are being made thinner and softer. Therefore, there is a possibility that deformation of the battery container, that is, the battery shape may occur due to the expansion / contraction of the electrode. In order to prevent such deformation, a non-aqueous electrolyte secondary battery that uses a separator having a tensile creep amount within a certain range has been proposed (Patent Document 1).

  Further, recent non-aqueous electrolyte secondary batteries are required to be able to charge and discharge at higher speed. However, when charging / discharging at high speed, a high load stress is applied to the separator in a short time due to the expansion / contraction of the electrode accompanying charging / discharging inside the battery. The rate characteristics and the like of the battery may deteriorate due to the battery.

JP 2002-358944 A (released on December 13, 2002)

  Therefore, recently, a separator for a non-aqueous electrolyte secondary battery capable of obtaining a non-aqueous electrolyte secondary battery excellent in battery characteristics (rate characteristics) when performing high-speed discharge, corresponding to high-speed charge / discharge. Is required.

  However, the tensile creep amount specified in Patent Document 1 is a tensile creep amount corresponding to a case where a low load (10 g) is applied for a long time (2 hours), and a high load is obtained in a short time. It does not correspond to the case of applying the stress of.

  The inventors of the present invention can separate a porous film having a tensile creep compliance value within a specific range at a specific time corresponding to short-time charge / discharge when a high load stress is applied. The present inventors have found that a non-aqueous electrolyte secondary battery used as a substrate is excellent in rate characteristics and arrived at the present invention.

  The present invention may include the following non-aqueous electrolyte secondary battery separator, non-aqueous electrolyte secondary battery laminated separator, non-aqueous electrolyte secondary battery member, and non-aqueous electrolyte secondary battery.

The separator for a non-aqueous electrolyte secondary battery of the present invention is
A separator for a non-aqueous electrolyte secondary battery comprising a porous film mainly composed of a polyolefin-based resin,
The porous membrane is characterized in that the tensile creep compliance value J when a stress of 30 MPa is applied in the TD direction for t seconds satisfies one or more of the following (i) to (iii): As:
(I) When t = 300 seconds, J is 4.5 GPa ⁻¹ or more, 14.0 GPa ⁻¹ or less,
(Ii) When t = 1800 seconds, J is 9.0 GPa ⁻¹ or more and 25.0 GPa ⁻¹ or less,
(Iii) When t = 3600 seconds, J is 12.0 GPa ⁻¹ or more and 32.0 GPa ⁻¹ or less.

  It is preferable that the separator for nonaqueous electrolyte secondary batteries of the present invention satisfies all of the above (i) to (iii).

  The laminated separator for nonaqueous electrolyte secondary batteries of the present invention is characterized in that a porous layer is laminated on at least one surface of the separator for nonaqueous electrolyte secondary batteries of the present invention.

  The member for a non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a separator for a non-aqueous electrolyte secondary battery of the present invention, or a laminated separator for a non-aqueous electrolyte secondary battery of the present invention, and a negative electrode in this order. It is characterized by being arranged by.

  The nonaqueous electrolyte secondary battery of the present invention includes the separator for nonaqueous electrolyte secondary batteries of the present invention or the multilayer separator for nonaqueous electrolyte secondary batteries of the present invention.

  The separator for a non-aqueous electrolyte secondary battery of the present invention has an effect that excellent rate characteristics can be imparted to a non-aqueous electrolyte secondary battery including the separator.

It is a figure which shows the relationship between the rate characteristic (%) of the porous film manufactured in the Example and the comparative example, and the value of (void ratio / thickness).

  Hereinafter, an embodiment of the present invention will be described in detail. In the present application, “A to B” indicates “A or more and B or less”.

[Embodiment 1: Separator for non-aqueous electrolyte secondary battery, Embodiment 2: Laminated separator for non-aqueous 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 composed of a porous film mainly composed of a polyolefin-based resin, and the porous film includes: The tensile creep compliance value J when a stress of 30 MPa is applied for t seconds in the TD direction satisfies any one or more of the following (i) to (iii):
(I) When t = 300 seconds, J is 4.5 GPa ⁻¹ or more, 14.0 GPa ⁻¹ or less,
(Ii) When t = 1800 seconds, J is 9.0 GPa ⁻¹ or more and 25.0 GPa ⁻¹ or less,
(Iii) When t = 3600 seconds, J is 12.0 GPa ⁻¹ or more and 32.0 GPa ⁻¹ or less.

  The laminated separator for a nonaqueous electrolyte secondary battery according to Embodiment 2 of the present invention is porous on at least one surface of the separator for a nonaqueous electrolyte secondary battery (porous membrane) according to Embodiment 1 of the present invention. It is characterized in that the quality layers are laminated.

<Porous membrane>
The porous membrane in the present invention can be a base material for a separator for a non-aqueous electrolyte secondary battery or a laminated separator for a non-aqueous electrolyte secondary battery, which will be described later. It is possible to pass gas or liquid from one surface to the other surface. The porous film may be formed from one layer, or may be formed by laminating a plurality of layers.

“The main component is a polyolefin-based resin” means that the proportion of the polyolefin-based resin in the porous membrane is 50% by volume or more, preferably 90% by volume or more, more preferably 95% by volume of the entire porous membrane. That means that. The polyolefin resin preferably contains a high molecular weight component having a weight average molecular weight of 5 × 10 ⁵ to 15 × 10 ⁶ . In particular, when the polyolefin contains a high molecular weight component having a weight average molecular weight of 1,000,000 or more, the separator is a nonaqueous electrolyte secondary battery separator that is the porous membrane, and the laminate that includes the porous membrane. Since the intensity | strength of the laminated separator for water electrolyte secondary batteries improves, it is more preferable.

  The polyolefin-based resin that is the main component of the porous membrane is not particularly limited. For example, a monomer such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, which is a thermoplastic resin. Homopolymers (for example, polyethylene, polypropylene, polybutene) or copolymers (for example, ethylene-propylene copolymers) obtained by (co) polymerizing the above. Of these, polyethylene is more preferable because it can prevent (shut down) an excessive current from flowing at a lower temperature. Examples of the polyethylene include low density polyethylene, high density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more, and of these, weight average molecular weight. Is more preferably an ultrahigh molecular weight polyethylene having 1 million or more.

  The film thickness of the porous film is preferably 4 μm to 40 μm, more preferably 5 μm to 30 μm, and more preferably 6 μm to 15 μm when the porous film alone becomes a separator for a nonaqueous electrolyte secondary battery. More preferably. Further, a porous membrane is used as a base material for a laminated separator for a non-aqueous electrolyte secondary battery, and a porous layer is laminated on one side or both sides of the porous membrane to obtain a laminated separator for a non-aqueous electrolyte secondary battery (laminated body). ), The thickness of the porous film may be appropriately determined in consideration of the thickness of the laminate, but is preferably 4 to 40 μm, more preferably 5 to 20 μm. preferable.

  A nonaqueous electrolyte secondary battery comprising a porous separator and a nonaqueous electrolyte secondary battery separator and a laminated separator for a nonaqueous electrolyte secondary battery, the porous membrane having a thickness of 4 μm or more In the aspect which can fully prevent the internal short circuit by damage etc. of a battery. On the other hand, when the porous membrane has a thickness of 40 μm or less, the lithium ion permeation resistance of the nonaqueous electrolyte secondary battery separator and the laminated separator for the nonaqueous electrolyte secondary battery using the porous membrane is the same. In a non-aqueous electrolyte secondary battery including the separator, it is possible to prevent deterioration of the positive electrode due to repeated charge / discharge cycles, deterioration of rate characteristics and cycle characteristics, and between the positive electrode and the negative electrode. This is preferable in terms of preventing an increase in the size of the non-aqueous electrolyte secondary battery itself accompanying an increase in distance.

The basis weight per unit area of the porous membrane takes into account the strength, film thickness, weight, and handling properties of the nonaqueous electrolyte secondary battery separator or the nonaqueous electrolyte secondary battery multilayer separator provided with the porous membrane. And may be determined as appropriate. Specifically, in order to increase the weight energy density and volume energy density of the battery including the separator for non-aqueous electrolyte secondary battery or the laminated separator for non-aqueous electrolyte secondary battery, it is preferably 4~20g / ^{m 2,} and more preferably 5~12g / ^{m 2.}

  The air permeability of the porous membrane is preferably a Gurley value of 30 to 500 sec / 100 mL, and more preferably 50 to 300 sec / 100 mL. When the porous membrane has the above air permeability, the non-aqueous electrolyte secondary battery separator or the laminated separator for non-aqueous electrolyte secondary batteries provided with the porous membrane can obtain sufficient ion permeability. it can.

  The porosity of the porous membrane is 20 to 80% by volume so as to increase the amount of electrolyte retained and to obtain a function of reliably blocking (shutdown) the flow of excessive current at a lower temperature. Is preferable, and it is more preferable that it is 30 to 75 volume%.

  Further, in order to set the “tensile creep compliance” of the porous film in the present invention within a preferable range described later, the porosity of the porous film is preferably 40 to 75% by volume, and 50 to 75 volume. % Is more preferable.

  When the porosity of the porous film is less than 20% by volume, the resistance of the porous film increases. Moreover, when the porosity of a porous membrane exceeds 80 volume%, the mechanical strength of the said porous membrane will fall. In addition, when the porosity of the porous film is 40% by volume or more, the ratio of the resin in the area to which stress is applied in the porous film decreases, and thus the porous film is easily stretched. The porosity of the porous membrane is preferably 75% by volume or less in terms of maintaining the mechanical strength of the porous membrane.

  In addition, the pore diameter of the porous membrane is such that the nonaqueous electrolyte secondary battery separator or the nonaqueous electrolyte secondary battery laminated separator provided with the porous membrane can obtain sufficient ion permeability. It is preferably 0.3 μm or less, more preferably 0.14 μm or less so that particles can be prevented from entering the positive electrode and the negative electrode.

The “tensile creep compliance” in this specification is a “tensile creep” measured according to JIS K 7115 under a condition in which a stress of 30 MPa is applied to the porous membrane in the TD direction at a temperature of 23 ° C. and a humidity of 50%. It is the reciprocal of "creep elastic modulus", and is a value obtained by dividing strain (creep amount) at a specific time (t) by the above stress with GPa ^-1 as a unit. Further, “tensile creep compliance” is an index indicating the easiness of elongation of the porous membrane with respect to the external force. That is, a porous film having a high “tensile creep compliance” means that when the stress is applied from the outside, the film expands (deforms) in response to the stress, so that the internal structure of the porous film is hardly damaged. Indicates a porous membrane.

The porous membrane in the present invention satisfies one or more of the following requirements (i) to (iii) with respect to the value of “tensile creep compliance”: J, and preferably the following ( Satisfy all requirements of i) to (iii):
(I) When t = 300 seconds, J is 4.5 GPa ⁻¹ or more, 14.0 GPa ⁻¹ or less,
(Ii) When t = 1800 seconds, J is 9.0 GPa ⁻¹ or more and 25.0 GPa ⁻¹ or less,
(Iii) When t = 3600 seconds, J is 12.0 GPa ⁻¹ or more and 32.0 GPa ⁻¹ or less.

  In a lithium ion secondary battery, a tensile stress is generated in the TD direction of the separator along with charging, and the magnitude is usually about 20 to 200 MPa, preferably 30 MPa. That is, the tensile creep compliance specified in the specification of the present application is added to the porous membrane when the target porous membrane is actually used as a separator or a separator substrate of a non-aqueous electrolyte secondary battery. This is an index indicating the easiness of elongation of the porous film when a stress comparable to the stress is applied.

Further, t = 300 seconds corresponds to a case where a nonaqueous electrolyte secondary battery including a porous film as a separator or a separator base material is charged / discharged over 300 seconds = 5 minutes. When t = 300 seconds, J is, 4.5 GPa ^-1 or more and 14.0GPa ^-1 or less, 4.5 GPa ^-1 or more, preferably 12.0GPa ^-1 or less, 5.0 GPa ^-1 As described above, it is more preferably 11.0 GPa ⁻¹ or less.

Similarly, t = 1800 seconds and 3600 seconds means that a nonaqueous electrolyte secondary battery including a porous membrane as a separator or a separator base material is charged and discharged over 1800 seconds = 30 minutes, 3600 seconds = 1 hour. Equivalent to. When t = 1800 seconds, J is, 9.0GPa ^-1 or more and 25.0GPa ^-1 or less, 9.0GPa ^-1 or more, preferably 22.0GPa ^-1 or less, 10.0 GPa ^-1 As mentioned above, it is more preferable that it is 20.0 GPa- ¹ or less. When t = 3600 seconds, J is, 12.0GPa ^-1 or more and 32.0GPa ^-1 or less, 12.0GPa ^-1 or more, preferably 28.0GPa ^-1 or less, 13.0GPa ^-1 As mentioned above, it is more preferable that it is 26.0GPa- ¹ or less.

  Therefore, when the value of J is smaller than the above range, in a non-aqueous electrolyte secondary battery including a porous membrane as a separator or a separator substrate, the electrode expands / contracts (changes in volume) with charge / discharge of the corresponding time. ) Cannot follow the separator, and the separator is partially damaged, so that the rate characteristics of the non-aqueous electrolyte secondary battery may be deteriorated. On the other hand, when the value of J is larger than the above range, in the non-aqueous electrolyte secondary battery including the porous membrane as a separator or separator base material, the elongation of the porous membrane increases due to the volume change of the electrode, The porous membrane itself becomes too thin, and the mechanical strength of the separator is lowered. That is, the non-aqueous electrolyte secondary battery including a porous film satisfying the above requirement (i) as a separator or a separator base material is excellent in rate characteristics particularly when charged and discharged in 5 minutes, and the above (ii) The non-aqueous electrolyte secondary battery including a porous membrane that satisfies the above requirements as a separator or a separator base material is excellent in rate characteristics particularly when charged and discharged in 30 minutes, and is porous that satisfies the above requirement (iii) A non-aqueous electrolyte secondary battery including a membrane as a separator or a separator substrate is particularly excellent in rate characteristics when charging / discharging in one hour.

  That is, since the separator for a nonaqueous electrolyte secondary battery of the present invention is composed of a porous film having a tensile creep compliance in a specific range, the separator containing the porous film as a separator for a nonaqueous electrolyte secondary battery is used. The porous membrane can appropriately follow the volume change of the electrode during charge / discharge of the water electrolyte secondary battery, and as a result, the non-aqueous electrolyte secondary battery is considered to have excellent rate characteristics. It is done.

In addition, since the tensile creep compliance J (t) generally increases with time, in a porous film satisfying all the three requirements (i) to (iii), usually, t = 300 to 3600 seconds. In this range, the lower limit value of J (t) is between 4.5 GPa ^{−1 to} 12.0 GPa ⁻¹ , and the upper limit value of J (t) is 14.0 GPa ^{−1 to} 32.0 GPa ⁻¹ . Between. Therefore, a non-aqueous electrolyte secondary battery including a porous membrane that satisfies all the above three requirements as a separator or a separator substrate usually has a rate characteristic when charging / discharging in a short time of 5 minutes to 1 hour. The decrease is suppressed, and the rate characteristics are excellent.

  As a method for controlling the tensile creep compliance, (a) a method for adjusting the molecular weight, aspect, etc. of the polyolefin resin that is a raw material of the porous membrane in the porous membrane production method described later, and (b) porous Examples thereof include a method of adjusting the porosity of the film to the above range.

  Moreover, you may provide well-known porous layers, such as an adhesion layer, a heat-resistant layer, and a protective layer, on a porous membrane. In this specification, a separator provided with a separator for a non-aqueous electrolyte secondary battery and a porous layer is referred to as a laminated separator for a non-aqueous electrolyte secondary battery (hereinafter sometimes referred to as a laminated separator). When forming the porous layer on the porous membrane, that is, when producing a laminated separator for a non-aqueous electrolyte secondary battery, before forming the porous layer, that is, applying a coating liquid described later. It is more preferable to perform a hydrophilic treatment before the work. By applying a hydrophilic treatment to the porous film, the coating property of the coating liquid is further improved, and therefore a more uniform porous layer can be formed. This hydrophilization treatment is effective when the proportion of water in the solvent (dispersion medium) contained in the coating liquid is high. Specific examples of the hydrophilic treatment include known treatments such as chemical treatment with acid or alkali, corona treatment, plasma treatment and the like. Among the above hydrophilization treatments, the porous membrane can be hydrophilized in a relatively short time, and the hydrophilization is limited only to the vicinity of the surface of the porous membrane, so that the inside of the porous membrane does not change, Corona treatment is more preferred.

[Method for producing porous membrane]
The method for producing the porous membrane is not particularly limited. For example, a method of adding a pore-forming agent to a resin such as polyolefin to form a film (film-like) and then removing the pore-forming agent with an appropriate solvent. Can be mentioned.

Specifically, for example, when manufacturing a porous membrane using a polyolefin resin containing ultrahigh molecular weight polyethylene and a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, from the viewpoint of manufacturing cost, It is preferable to produce the porous membrane by the method shown. (1) A step of obtaining a polyolefin resin composition by kneading 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 a pore-forming agent. ,
(2) forming a rolled sheet by rolling the polyolefin resin composition;
Then
(3) A step of removing the hole forming agent from the rolled sheet obtained in step (2),
(4) A step of stretching the sheet from which the hole forming agent has been removed in step (3),
(5) A step of heat-fixing the sheet stretched in step (4) at a heat setting temperature of 100 ° C. or higher and 150 ° C. or lower to obtain a porous film.
Or
(3 ′) a step of stretching the rolled sheet obtained in step (2),
(4 ′) a step of removing the hole forming agent from the sheet stretched in the step (3 ′),
(5 ′) A step of heat-fixing the sheet obtained in step (4 ′) at a heat setting temperature of 100 ° C. or higher and 150 ° C. or lower to obtain a porous film.

  Examples of the pore forming agent include inorganic fillers and plasticizers.

  The inorganic filler is not particularly limited, and examples thereof include an aqueous solvent containing an acid, an aqueous solvent containing an alkali, and an inorganic filler that can be dissolved in an aqueous solvent mainly composed of water. Examples of inorganic fillers that can be dissolved in an aqueous solvent containing an acid include calcium carbonate, magnesium carbonate, barium carbonate, zinc oxide, calcium oxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and calcium sulfate. Calcium carbonate is preferred because it is inexpensive and easily obtains a fine powder. Examples of the inorganic filler that can be dissolved in an aqueous solvent containing an alkali include silicic acid and zinc oxide. Silicic acid is preferred because it is easy to obtain an inexpensive and fine powder. Examples of the inorganic filler that can be dissolved in an aqueous solvent mainly composed of water include calcium chloride, sodium chloride, and magnesium sulfate.

  The plasticizer is not particularly limited, and examples thereof include low molecular weight hydrocarbons such as liquid paraffin.

  The weight average molecular weight of the whole polymer constituting the resin used for producing the porous membrane is preferably 1,000,000 or less, more preferably 800,000 or less in the resin composition obtained in the step (1). . The weight average molecular weight is preferably 1,000,000 or less because the entanglement between the polymers is reduced in the porous membrane, so that the porous membrane is easily stretched (easy to creep). The resin polymer constituting the porous membrane may be a linear type or a branched type, but is preferably a linear type in terms of reducing entanglement between the polymers.

  Further, the melt flow rate (MFR) of the resin composition obtained in the step (1) is preferably 20 g / 10 min or more, more preferably 30 g / 10 min or more, and further preferably 32 g / 10 min or more. It is. The melt flow rate is preferably 50 g / 10 min or less.

The melt flow rate is measured by the following method.
Measurement standard: JIS K 7120-1
Measurement condition:
・ Orifice: 3mm diameter x 10mm length
・ Measurement temperature: 240 ℃
-Load: 21.6 kg.

  Furthermore, examples of the method for adjusting the porosity of the obtained porous membrane include a method for adjusting the amount of the pore-forming agent used. The amount of the pore-forming agent used is preferably 100 to 300 parts by weight and more preferably 100 to 200 parts by weight with respect to 100 parts by weight of the resin contained in the porous membrane.

  In addition, the heat setting temperature in the step (5) is preferably 100 ° C. or higher and 140 ° C. or lower, more preferably 105 ° C. or higher and 120 ° C. or higher. If the heat setting temperature exceeds 140 ° C, the pores of the porous membrane may be crushed and blocked.

[Porous layer]
The porous layer according to the present invention may contain fine particles and is usually a resin layer containing a resin. The porous layer according to the present invention is preferably a heat-resistant layer or an adhesive layer laminated on one side or both sides of the porous membrane. The resin constituting the porous layer is preferably insoluble in the battery electrolyte and electrochemically stable in the battery usage range. When a porous layer is laminated on one side of the porous membrane, the porous layer is preferably laminated on the surface of the porous membrane facing the positive electrode when a non-aqueous electrolyte secondary battery is used. More preferably, it is laminated on the surface in contact with the positive electrode.

  Specific examples of the resin include polyolefins such as polyethylene, polypropylene, polybutene, and ethylene-propylene copolymers; fluorine-containing resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene; vinylidene fluoride-hexa Fluorinated rubber such as fluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; aromatic polyamide; wholly aromatic polyamide (aramid resin); styrene-butadiene copolymer and its hydride, methacrylic acid Ester copolymers, acrylonitrile-acrylic acid ester copolymers, styrene-acrylic acid ester copolymers, rubbers such as ethylene propylene rubber and polyvinyl acetate; polyphenylene ether, polysulfone, polyether sulfone Polyphenylene sulfide, polyether imide, polyamide imide, polyether amide, polyester and other resins having a melting point or glass transition temperature of 180 ° C. or higher; polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, polymethacryl Examples thereof include water-soluble polymers such as acids.

  Specific examples of the aromatic polyamide include poly (paraphenylene terephthalamide), poly (metaphenylene isophthalamide), poly (parabenzamide), poly (metabenzamide), and poly (4,4 ′). -Benzanilide terephthalamide), poly (paraphenylene-4,4'-biphenylenedicarboxylic acid amide), poly (metaphenylene-4,4'-biphenylenedicarboxylic acid amide), poly (paraphenylene-2,6-naphthalenedicarboxylic acid) Acid amide), poly (metaphenylene-2,6-naphthalenedicarboxylic acid amide), poly (2-chloroparaphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer, metaphenylene Terephthalamide / 2 6-dichloro-para-phenylene terephthalamide copolymer and the like. Of these, poly (paraphenylene terephthalamide) is more preferable.

  Of the above resins, polyolefins, fluorine-containing resins, aromatic polyamides, and water-soluble polymers are more preferable. In particular, when the porous layer is arranged facing the positive electrode, various performances such as rate characteristics and resistance characteristics (liquid resistance) of the non-aqueous electrolyte secondary battery are maintained due to acid degradation during battery operation. Fluorine-containing resins or fluorine-containing rubbers are more preferable because they are easy to handle. Polyvinylidene fluoride resins (vinylidene fluoride homopolymers (ie, polyvinylidene fluoride), vinylidene fluoride and hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, A copolymer with trichlorethylene and vinyl fluoride) is particularly preferred. Since water-soluble polymer can use water as a solvent when forming a porous layer, it is more preferable from the viewpoint of process and environmental load, cellulose ether and sodium alginate are more preferable, and cellulose ether is particularly preferable.

  Specific examples of the cellulose ether include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), carboxyethyl cellulose, methyl cellulose, ethyl cellulose, cyanethyl cellulose, oxyethyl cellulose, etc. CMC and HEC which are excellent in chemical stability are more preferable, and CMC is particularly preferable.

  The fine particles in the present specification are organic fine particles or inorganic fine particles generally called a filler. Therefore, the resin has a function as a binder resin that binds the fine particles to each other and the fine particles and the porous film. The fine particles are preferably insulating fine particles.

  Specific examples of the organic fine particles contained in the porous layer in the present invention include monomers such as styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, and methyl acrylate. Homopolymer or two or more types of copolymers; fluorinated resins such as polytetrafluoroethylene, tetrafluoroethylene-6-fluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride; melamine Resin; urea resin; polyethylene; polypropylene; polyacrylic acid, polymethacrylic acid; These organic fine particles are insulating fine particles.

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

  Among the above fillers, fillers made of inorganic materials are suitable, fillers made of inorganic oxides such as silica, calcium oxide, magnesium oxide, titanium oxide, alumina, mica, zeolite, aluminum hydroxide, boehmite are more preferable, silica, More preferred is at least one filler selected from the group consisting of magnesium oxide, titanium oxide, aluminum hydroxide, boehmite and alumina, and alumina is particularly preferred. Alumina has many crystal forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and any of them can be suitably used. Among these, α-alumina is most preferable because of its particularly high thermal stability and chemical stability.

  The shape of the filler varies depending on the manufacturing method of the organic or inorganic material that is the raw material, the dispersion condition of the filler when producing the coating liquid for forming the porous layer, and the like, spherical, oval, short, The shape may be any shape such as a shape or an indefinite shape having no specific shape.

  When the porous layer contains a filler, the filler content is preferably 1 to 99% by volume, more preferably 5 to 95% by volume of the porous layer. By setting the filler content in the above range, voids formed by contact between fillers are less likely to be clogged with a resin and the like, and sufficient ion permeability can be obtained, and per unit area. The basis weight can be set to an appropriate value.

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

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

  The film thickness of the porous layer according to the present invention may be appropriately determined in consideration of the film thickness of the laminate that is a laminated separator for a non-aqueous electrolyte secondary battery. In the case of forming a laminate by laminating a porous layer on one side or both sides of a membrane, it is preferably 0.5 to 15 μm (per one side), more preferably 2 to 10 μm (per one side). preferable.

  When the thickness of the porous layer is less than 1 μm, an internal short circuit due to battery breakage or the like cannot be sufficiently prevented when the laminate is used as a laminate separator for a nonaqueous electrolyte secondary battery. In addition, the amount of electrolytic solution retained in the porous layer decreases. On the other hand, if the total thickness of the porous layer exceeds 30 μm, when the laminate is used as a laminated separator for a non-aqueous electrolyte secondary battery, the lithium ion permeation resistance increases across the separator. When the cycle is repeated, the positive electrode deteriorates, and the rate characteristics and cycle characteristics deteriorate. In addition, since the distance between the positive electrode and the negative electrode is increased, the nonaqueous electrolyte secondary battery is increased in size.

  In the following explanation regarding the physical properties of the porous layer, when the porous layer is laminated on both sides of the porous membrane, the surface of the porous membrane facing the positive electrode when a non-aqueous electrolyte secondary battery is formed is used. It refers to at least the physical properties of the laminated porous layer.

The basis weight per unit area (per side) of the porous layer may be appropriately determined in consideration of the strength, film thickness, weight, and handling properties of the laminate, but the laminate is used for a non-aqueous electrolyte secondary battery. It is usually preferably 1 to 20 g / m ² and preferably ² to 10 g / m ² so that the weight energy density and volume energy density of the battery when used as a laminated separator can be increased. More preferred. When the basis weight of the porous layer exceeds the above range, the non-aqueous electrolyte secondary battery becomes heavy when the laminate is used as a laminated separator for non-aqueous electrolyte secondary batteries.

  The porosity of the porous layer is preferably 20 to 90% by volume, and more preferably 30 to 80% by volume so that sufficient ion permeability can be obtained. The pore diameter of the porous layer is 3 μm so that the porous layer and the laminated separator for a non-aqueous electrolyte secondary battery including the porous layer can obtain sufficient ion permeability. Is preferably 1 μm or less, more preferably 0.5 μm or less.

[Laminate]
The laminated body which is a laminated separator for non-aqueous electrolyte secondary batteries of the present invention has a configuration in which the above porous layer is laminated on one side or both sides of the above porous membrane.

  The thickness of the laminate in 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 in the present invention is preferably 30 to 1000 sec / 100 mL as a Gurley value, and more preferably 50 to 800 sec / 100 mL. When the laminate has the above air permeability, sufficient ion permeability can be obtained when the laminate is used as a laminate separator for a non-aqueous electrolyte secondary battery. When the air permeability exceeds the above range, it means that the laminated structure is rough because the porosity of the laminated body is high, and as a result, the strength of the laminated body is reduced, and the shape at a high temperature is particularly high. Stability may be insufficient. On the other hand, if the air permeability is less than the above range, sufficient ion permeability cannot be obtained when used as a laminated separator for a non-aqueous electrolyte secondary battery, and the non-aqueous electrolyte secondary battery Battery characteristics may be degraded.

  In addition to the porous film and the porous layer, the laminate in the present invention can be replaced with a known porous film such as a heat-resistant layer, an adhesive layer, a protective layer, or the like, if necessary, without impairing the object of the present invention. May be included.

  The laminate in the present invention includes a porous film having a tensile creep compliance in a specific range as a base material. Therefore, the laminate can appropriately follow the volume change of the electrode during charge / discharge of the non-aqueous electrolyte secondary battery including the laminate as a laminated separator for a non-aqueous electrolyte secondary battery, and as a result The non-aqueous electrolyte secondary battery has excellent rate characteristics.

[Method for producing porous layer and laminate]
As a manufacturing method of the porous layer and laminated body in this invention, the method of depositing a porous layer by apply | coating the coating liquid mentioned later to the surface of the said porous membrane, and drying is mentioned, for example.

  The coating liquid used in the method for producing a porous layer in the present invention usually dissolves the resin contained in the porous layer in the present invention in a solvent and disperses the fine particles contained in the porous layer in the present invention. Can be prepared.

  The solvent (dispersion medium) is not particularly limited as long as it does not adversely affect the porous membrane, can dissolve the resin uniformly and stably, and can uniformly and stably disperse the fine particles. 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, N, N-dimethylformamide and the like. The solvent (dispersion medium) may be used alone or in combination of two or more.

  The coating liquid may be formed by any method as long as the conditions such as the resin solid content (resin concentration) and the amount of fine particles necessary for obtaining a desired porous layer can be satisfied. Specific examples of the method for forming the coating liquid include a mechanical stirring method, an ultrasonic dispersion method, a high-pressure dispersion method, and a media dispersion method. Further, for example, fine particles may be dispersed in a solvent (dispersion medium) by using a conventionally known disperser such as a three-one motor, a homogenizer, a media type disperser, or a pressure disperser. Furthermore, a solution obtained by dissolving or swelling a resin or an emulsion of a resin is supplied into a wet pulverization apparatus at the time of wet pulverization to obtain fine particles having a desired average particle size, and is applied simultaneously with the wet pulverization of the fine particles A liquid can also be prepared. That is, the wet pulverization of the fine particles and the preparation of the coating liquid may be performed simultaneously in one step. In addition, the coating liquid may contain additives such as a dispersant, a plasticizer, a surfactant, and a pH adjuster as components other than the resin and fine particles 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 this invention.

  The method for applying the coating liquid to the porous film, that is, the method for forming the porous layer on the surface of the porous film that has been subjected to hydrophilic treatment as necessary is not particularly limited. In the case of laminating a porous layer on both sides of the porous membrane, a sequential laminating method in which a porous layer is formed on one surface of the porous membrane and then a porous layer is formed on the other surface, or a porous membrane A simultaneous lamination method in which a porous layer is simultaneously formed on both surfaces of the substrate can be performed. As a method for forming a porous layer, that is, a method for producing a laminate, for example, a method in which a coating liquid is directly applied to the surface of a porous film and then a solvent (dispersion medium) is removed; A method in which a porous layer is formed by removing the solvent (dispersion medium) after applying to the body, and then pressing the porous layer and the porous membrane and then peeling the support; A method of removing the solvent (dispersion medium) after peeling the support, and then immersing the porous membrane in the coating solution and performing dip coating And a method of removing the solvent (dispersion medium). The thickness of the porous layer is the thickness of the coating film in the wet state (wet) after coating, the weight ratio between the resin and fine particles, and the solid content concentration of the coating liquid (the sum of the resin concentration and fine particle concentration) It can be controlled by adjusting etc. In addition, as a support body, a resin film, a metal belt, a drum, etc. can be used, for example.

  The method for applying the coating liquid to the porous membrane or the support is not particularly limited as long as it is a method capable of realizing the necessary weight per unit area and coating area. As a coating method of the coating liquid, conventionally known methods can be employed. Specifically, for example, a gravure coater method, a small diameter gravure coater method, a reverse roll coater method, a transfer roll coater method, a kiss coater method, a dip coater method, Examples include a coater method, a knife coater method, an air doctor blade coater 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, and a spray coating method.

  As a method for removing the solvent (dispersion medium), a drying method is generally used. Examples of the drying method include natural drying, air drying, heat drying, and drying under reduced pressure. Any method may be used as long as the solvent (dispersion medium) can be sufficiently removed. Further, the solvent (dispersion medium) contained in the coating liquid may be replaced with another solvent before drying. As a method for removing the solvent (dispersion medium) after replacing it with another solvent, for example, it is possible to dissolve in the solvent (dispersion medium) contained in the coating liquid and not dissolve the resin contained in the coating liquid. A porous film or support on which a coating liquid is applied and a coating film is formed by immersing the solvent X in the solvent X to form a coating film on the porous film or the support. A method of evaporating the solvent X after replacing the solvent (dispersion medium) therein with the solvent X can be mentioned. This method can efficiently remove the solvent (dispersion medium) from the coating solution. When heating is performed when the solvent (dispersion medium) or the solvent X is removed from the coating film of the coating liquid formed on the porous film or the support, the pores of the porous film contract and become transparent. In order to avoid a decrease in the air temperature, it is desirable to carry out at a temperature at which the air permeability of the porous membrane does not decrease, specifically 10 to 120 ° C., more preferably 20 to 80 ° C.

  A normal drying apparatus can be used for the drying.

[Embodiment 3: Nonaqueous electrolyte secondary battery member, Embodiment 4: Nonaqueous electrolyte secondary battery]
A member for a non-aqueous electrolyte secondary battery according to Embodiment 3 of the present invention is a positive electrode, a separator for a non-aqueous electrolyte secondary battery according to Embodiment 1 of the present invention, or a non-aqueous liquid according to Embodiment 2 of the present invention. The laminated separator for electrolyte secondary batteries and the negative electrode are arranged in this order. In addition, the nonaqueous electrolyte secondary battery according to Embodiment 4 of the present invention is a nonaqueous electrolyte secondary battery separator according to Embodiment 1 of the present invention, or the nonaqueous electrolyte solution according to Embodiment 2 of the present invention. It includes a laminated separator for a secondary battery, and preferably includes a nonaqueous electrolyte secondary battery member according to Embodiment 3 of the present invention. In addition, the non-aqueous electrolyte secondary battery according to Embodiment 4 of the present invention additionally includes a non-aqueous electrolyte.

[Non-aqueous electrolyte]
The non-aqueous electrolyte in the present invention is a non-aqueous electrolyte generally used for a non-aqueous electrolyte secondary battery and is not particularly limited. For example, a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent is used. Can be used. Examples of the lithium salt include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , lower aliphatic carboxylic acid lithium salt, LiAlCl _{4 and the} like. The lithium salt may be used alone or in combination of two or more. Among the lithium salts, at least one selected from the group consisting of LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiC (CF ₃ SO ₂ ) _3. More preferred are fluorine-containing lithium salts.

  Specific examples of the organic solvent constituting the non-aqueous electrolyte in the present invention include, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolane- Carbonates such as 2-one and 1,2-di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoro Ethers such as propyldifluoromethyl ether, tetrahydrofuran and 2-methyltetrahydrofuran; esters such as methyl formate, methyl acetate and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, Amides such as dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone; and a fluorine group introduced into the organic solvent. And the like. Only one kind of the organic solvent may be used, or two or more kinds may be used in combination. Among the organic solvents, carbonates are more preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate, or a mixed solvent of cyclic carbonate and ethers is more preferable. As a mixed solvent of cyclic carbonate and non-cyclic carbonate, ethylene carbonate has a wide operating temperature range and is difficult to decompose even when a graphite material such as natural graphite or artificial graphite is used as the negative electrode active material. More preferred is a mixed solvent containing dimethyl carbonate and ethyl methyl carbonate.

[Positive electrode]
As the positive electrode, a sheet-like positive electrode in which a positive electrode mixture containing a positive electrode active material, a conductive material, and a binder is usually supported on a positive electrode current collector is used.

Examples of the positive electrode active material include materials that can be doped / undoped with lithium ions. Specific examples of the material include lithium composite oxides containing at least one transition metal such as V, Mn, Fe, Co, and Ni. Among the lithium composite oxides, since the average discharge potential is high, lithium composite oxides having an α-NaFeO ₂ type structure such as lithium nickelate and lithium cobaltate, and lithium composites having a spinel type structure such as lithium manganese spinel Oxides are more preferred. The lithium composite oxide may contain various metal elements, and composite lithium nickelate is more preferable.

  Furthermore, the number of moles of at least one metal element selected from the group consisting of Ti, Zr, Ce, Y, V, Cr, Mn, Fe, Co, Cu, Ag, Mg, Al, Ga, In, and Sn When using the composite lithium nickelate containing the metal element so that the ratio of the at least one metal element is 0.1 to 20 mol% with respect to the sum of the number of moles of Ni in the lithium nickelate, It is even more preferable since it is excellent in cycle characteristics in use at a high capacity. Among them, an active material containing Al or Mn and having a Ni ratio of 85% or more, more preferably 90% or more is used in a high capacity of a non-aqueous electrolyte secondary battery including a positive electrode containing the active material. Since it is excellent in cycling characteristics, it is especially preferable.

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

  Examples of the binder include polyvinylidene fluoride, vinylidene fluoride copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. , Ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, thermoplastic resins such as thermoplastic polyimide, polyethylene, and polypropylene, acrylic resin, and styrene-butadiene rubber Can be mentioned. The binder also has a function as a thickener.

  As a method for obtaining the positive electrode mixture, for example, a method of obtaining a positive electrode mixture by pressurizing 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 using an appropriate organic solvent And a method of obtaining a positive electrode mixture by pasting a material and a binder.

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

  As a method for producing a sheet-like positive electrode, that is, a method of loading a positive electrode mixture on a positive electrode current collector, for example, a positive electrode active material, a conductive material, and a binder as a positive electrode mixture are added on the positive electrode current collector. Method of pressure molding: After a positive electrode active material, a conductive material and a binder are pasted using an appropriate organic solvent to obtain a positive electrode mixture, the positive electrode mixture is applied to the positive electrode current collector and dried. And a method of pressurizing the obtained sheet-like positive electrode mixture and fixing it to the positive electrode current collector.

[Negative electrode]
As the negative electrode, a sheet-like negative electrode in which a negative electrode mixture containing a negative electrode active material is usually supported on a negative electrode current collector is used. The sheet-like negative electrode preferably contains the conductive material and the binder.

Examples of the negative electrode active material include materials that can be doped / undoped with lithium ions, lithium metal, and lithium alloys. Specific examples of the material include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired organic polymer compounds; Lithium ion doping and dedoping oxides, chalcogen compounds such as sulfides; aluminum (Al), lead (Pb), tin (Sn), bismuth (Bi), silicon (Si), etc. alloyed with alkali metals And cubic intermetallic compounds (AlSb, Mg ₂ Si, NiSi ₂ ), lithium nitrogen compounds (Li ₃ -xM _x N (M: transition metal)), and the like, which can insert an alkali metal between the lattices. It is done. Among the negative electrode active materials, the potential flatness is high, and since the average discharge potential is low, a large energy density can be obtained when combined with the positive electrode. Therefore, the main component is a graphite material such as natural graphite or artificial graphite. A carbonaceous material is more preferable. Moreover, the mixture of graphite and silicon may be sufficient, The negative electrode active material whose ratio of Si with respect to the carbon (C) which comprises the graphite is 5% or more is preferable, and the negative electrode active material which is 10% or more is more preferable.

  As a method for obtaining the negative electrode mixture, for example, a method in which the negative electrode active material is pressurized on the negative electrode current collector to obtain the negative electrode mixture; the negative electrode active material is pasted into a paste using an appropriate organic solvent. And the like.

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

  As a method for producing a sheet-like negative electrode, that is, a method of supporting the negative electrode mixture on the negative electrode current collector, for example, a method in which a negative electrode active material to be the negative electrode mixture is pressure-molded on the negative electrode current collector; After the negative electrode active material is made into a paste using an organic solvent to obtain a negative electrode mixture, the negative electrode mixture is applied to the negative electrode current collector and dried to press the sheet-like negative electrode mixture. And a method of fixing to the negative electrode current collector. The paste preferably contains the conductive material and the binder.

  As a manufacturing method of the member for nonaqueous electrolyte secondary batteries of the present invention, for example, a method of arranging the above-mentioned positive electrode, the above-mentioned porous membrane, or the above-mentioned layered product, and a negative electrode in this order is mentioned. Moreover, as a manufacturing method of the nonaqueous electrolyte secondary battery of this invention, after forming the member for nonaqueous electrolyte secondary batteries by the said method, it becomes a housing | casing of a nonaqueous electrolyte secondary battery, for example. The non-aqueous electrolyte secondary battery according to the present invention is sealed by putting the non-aqueous electrolyte secondary battery member into a container, and then filling the container with the non-aqueous electrolyte and then sealing the container while reducing the pressure. Can be manufactured. The shape of the non-aqueous electrolyte secondary battery is not particularly limited, and may be any shape such as a thin plate (paper) type, a disc type, a cylindrical type, and a rectangular column type such as a rectangular parallelepiped. In addition, the manufacturing method of the member for nonaqueous electrolyte secondary batteries and a nonaqueous electrolyte secondary battery is not specifically limited, A conventionally well-known manufacturing method is employable.

  The member for a non-aqueous electrolyte secondary battery of the present invention and the non-aqueous electrolyte secondary battery of the present invention include a porous membrane having a specific range of tensile creep compliance at a specific time as a separator or a separator substrate. . Therefore, the non-aqueous electrolyte secondary battery provided with the non-aqueous electrolyte secondary battery member of the present invention and the non-aqueous electrolyte secondary battery of the present invention suppress the deterioration of rate characteristics when performing high-speed charge / discharge. And excellent rate characteristics.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

  Hereinafter, although an example and a comparative example explain the present invention still in detail, the present invention is not limited to these examples.

[Measurement]
In the following examples and comparative examples, the melt flow rate (MFR) of the polyolefin resin composition, and the thickness, porosity and tensile creep compliance (J (t)) in the separator for nonaqueous electrolyte secondary batteries, In addition, the rate characteristic (20C / 0.2C) of the nonaqueous electrolyte secondary battery was measured.

(A) Thickness (unit: μm)
In accordance with JIS standard (K 7130-1992), the thickness of the porous membrane, which is a separator for a non-aqueous electrolyte secondary battery manufactured in Examples and Comparative Examples, is a high precision digital length measuring machine manufactured by Mitutoyo Corporation. And measured.

(B) Porosity (unit: volume%)
The porosity of the porous membrane, which is a separator for non-aqueous electrolyte secondary batteries manufactured in Examples and Comparative Examples, was measured by the following method.
(I) The produced porous membrane was cut into a 10 cm long square, and the weight of the cut piece: W (g) was measured.
(Ii) The thickness of the porous film measured in (a) was changed to “cm”, and E (cm) was obtained.
(Iii) The small piece after measuring the weight in (i) was pulverized into a fine powder. After the powder was filled in a container and compressed, its volume: V (cm ³ ) was measured. According to the following formula (1), from the volume of the fine powder: V (cm ³ ) and the weight: W (g), the true density of the resin composition constituting the porous film: ρ (g / cm ³ ) Was calculated.
True density ρ (g / cm ³ ) = W (g) / V (cm ³ ) (1)
(Iv) According to the following formula (2), measured and calculated by (i) to (iii), weight: W (g), thickness: E (cm), and true density: ρ (g / cm ³ ) From this, the porosity (volume%) was calculated.
Porosity (volume%) = [1-{(W / ρ)} / (10 × 10 × E)] × 100 (2)
(C) Tensile creep compliance (J (t)) (unit: GPa ⁻¹ )
Measures “tensile creep modulus” at a specific time (t) based on JIS K 7115 under the condition of applying a stress of 30 MPa in the TD direction to the porous membrane at a temperature of 23 ° C. and a humidity of 50%. The tensile creep compliance J (t) was calculated by taking the reciprocal thereof. In addition, regarding the time t, the value of tensile creep compliance: J was measured every second in the range of 1 second to 3600 seconds.

(D) Melt flow rate (MFR) (unit: g / 10 minutes)
Under the following measurement conditions, the melt flow rate (MFR) of the polyolefin resin composition in Examples and Comparative Examples was measured based on JIS K 7120-1.
Measurement condition:
・ Orifice: 3mm diameter x 10mm length
・ Measurement temperature: 240 ℃
-Load: 21.6 kg.

(E) Rate characteristics (%)
With respect to a new non-aqueous electrolyte secondary battery that has not undergone the charge / discharge cycle manufactured in Examples and Comparative Examples, voltage range at 25 ° C .; 4.1 to 2.7 V, current value; 0.2C 4 cycles of initial charge / discharge were performed with 1 cycle as the current value for discharging the rated capacity with a 1 hour rate discharge capacity in 1 hour to 1C (the same applies hereinafter).

  After the initial charge / discharge, the non-aqueous electrolyte secondary battery is charged / discharged for 3 cycles using a constant current of 55 ° C., charge current value; 1 C, discharge current value of 0.2 C, Using a constant current of 20 C, charge / discharge of 3 cycles was performed, and the discharge capacity in each case was measured.

The discharge capacity at the third cycle at discharge current values of 0.2 C and 20 C, respectively, was taken as the measured value of the discharge capacity. Subsequently, rate characteristics were obtained according to the following equation (3) using the obtained discharge capacity at 0.2C and the measured value of the discharge capacity at 20C.
Rate characteristics (%) = (20C discharge capacity / 0.2C discharge capacity) × 100 (3)
[Example 1]
<Manufacture of separator for non-aqueous electrolyte secondary battery>
Both were mixed so that ultra high molecular weight polyethylene powder (GUR4032, manufactured by Ticona) was 70% by weight and polyethylene wax having a weight average molecular weight of 1000 (FNP-0115, manufactured by Nippon Seiki Co., Ltd.) was 30% by weight. The total amount of the ultra high molecular weight polyethylene and the polyethylene wax is 100 parts by weight, and the antioxidant (Irg1010, manufactured by Ciba Specialty Chemicals) 0.4% by weight, the antioxidant (P168, manufactured by Ciba Specialty Chemicals) 0.1% by weight and 1.3% by weight of sodium stearate are added, and calcium carbonate (manufactured by Maruo Calcium Co., Ltd.) having an average pore diameter of 0.1 μm is added so that the total volume is 36% by volume. The mixture 1 was obtained by mixing with a Henschel mixer. Thereafter, the mixture 1 was melt-kneaded with a biaxial kneader to obtain a polyolefin resin composition 1. The melt flow rate (MFR) of the polyolefin resin composition 1 was 35 g / 10 min. The polyolefin resin composition 1 was rolled with a pair of rolls having a surface temperature of 150 ° C. to prepare a rolled sheet 1. Thereafter, the rolled sheet 1 is immersed in an aqueous hydrochloric acid solution (hydrochloric acid 4 mol / L, nonionic surfactant 0.5% by weight) to remove calcium carbonate from the rolled sheet 1 and subsequently at 105 ° C. The film was stretched 2 times and heat-fixed at 120 ° C. to obtain a porous membrane 1. The porous membrane 1 was used as a separator 1 for a nonaqueous electrolyte secondary battery.

<Production of non-aqueous electrolyte secondary battery>
(Preparation 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. Cut the aluminum foil so that the size of the positive electrode active material layer formed on the positive electrode is 40 mm × 35 mm and the outer periphery of the positive electrode active material layer is 13 mm wide and no positive electrode active material layer is formed. A positive electrode was obtained. The positive electrode active material layer had a thickness of 58 μm and a density of 2.50 g / cm ³ .

(Preparation of negative electrode)
A commercially available negative electrode produced by applying graphite / styrene-1,3-butadiene copolymer / sodium carboxymethylcellulose (weight ratio 98/1/1) to a copper foil was used. Cut off the copper foil from the negative electrode so that the size of the portion where the negative electrode active material layer was formed was 50 mm × 40 mm and the outer periphery had a portion with a width of 13 mm and no negative electrode active material layer formed. A negative electrode was obtained. The negative electrode active material layer had a thickness of 49 μm and a density of 1.40 g / cm ³ .

(Manufacture of non-aqueous electrolyte secondary batteries)
By laminating (arranging) the positive electrode, the porous membrane 1 (electrolyte secondary battery separator 1), and the negative electrode in this order in a laminate pouch, a nonaqueous electrolyte secondary battery member 1 was obtained. At this time, the positive electrode and the negative electrode were disposed so that the entire main surface of the positive electrode active material layer of the positive electrode was included in the range of the main surface of the negative electrode active material layer of the negative electrode (overlaid on the main surface).

Subsequently, the non-aqueous electrolyte secondary battery member 1 is put in a bag prepared in advance by laminating an aluminum layer and a heat seal layer, and 0.25 mL of the non-aqueous electrolyte is put in this bag. It was. The non-aqueous electrolyte was prepared by dissolving LiPF ₆ at 1 mol / L in a mixed solvent obtained by mixing ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate at a ratio of 3: 5: 2 (volume ratio). . And the non-aqueous-electrolyte secondary battery 1 was produced by heat-sealing the said bag, decompressing the inside of a bag.

[Example 2]
A porous membrane 2 was obtained in the same manner as in Example 1 except that the heat setting temperature was 115 ° C. The porous membrane 2 was used as a separator 2 for a nonaqueous electrolyte secondary battery.

  A nonaqueous electrolyte secondary battery 2 was produced in the same manner as in Example 1 except that the porous membrane 2 was used instead of the porous membrane 1.

[Comparative Example 1]
Both were mixed so that the amount of ultra high molecular weight polyethylene powder (GUR2024, manufactured by Ticona) was 68% by weight, and the weight average molecular weight 1000 polyethylene wax (FNP-0115, manufactured by Nippon Seiki Co., Ltd.) was 32% by weight. The total amount of the ultra high molecular weight polyethylene and the polyethylene wax is 100 parts by weight, and the antioxidant (Irg1010, manufactured by Ciba Specialty Chemicals) 0.4% by weight, the antioxidant (P168, manufactured by Ciba Specialty Chemicals) 0.1% by weight and 1.3% by weight of sodium stearate are added, and calcium carbonate (manufactured by Maruo Calcium Co., Ltd.) having an average pore size of 0.1 μm is added so that the total volume is 38% by volume. The mixture was mixed with a Henschel mixer to obtain a mixture 3. Thereafter, the mixture 3 was melt-kneaded with a biaxial kneader to obtain a polyolefin resin composition 3. The melt flow rate (MFR) of the polyolefin resin composition 3 was 15 g / 10 min. The polyolefin resin composition 3 was rolled with a pair of rolls having a surface temperature of 150 ° C. to prepare a rolled sheet 3. Thereafter, the rolled sheet 3 is immersed in an aqueous hydrochloric acid solution (hydrochloric acid 4 mol / L, nonionic surfactant 0.5% by weight) to remove calcium carbonate from the rolled sheet 1 and subsequently at 100 ° C. The film was stretched twice and heat-fixed at 126 ° C. to obtain a porous membrane 3. The porous membrane 3 was used as a separator 3 for a nonaqueous electrolyte secondary battery.

  A nonaqueous electrolyte secondary battery 3 was produced in the same manner as in Example 1 except that the porous membrane 3 was used instead of the porous membrane 1.

[Comparative Example 2]
Ultra-high molecular weight polyethylene powder (GUR4032, manufactured by Ticona) was 71.5% by weight and polyethylene wax (FNP-0115, manufactured by Nippon Seiki Co., Ltd.) having a weight average molecular weight of 1000 was 28.5% by weight. After mixing, the total amount of the ultrahigh molecular weight polyethylene and polyethylene wax is 100 parts by weight, and the antioxidant (Irg1010, manufactured by Ciba Specialty Chemicals) is 0.4% by weight, the antioxidant (P168, Ciba Specialty) Chemicals Co., Ltd.) 0.1% by weight, sodium stearate 1.3% by weight, and calcium carbonate (Maruo Calcium Co., Ltd.) with an average pore size of 0.1 μm was added so that the total volume was 37% by volume. These were mixed with a Henschel mixer in the form of powder to obtain a mixture 4. Thereafter, the mixture 4 was melt-kneaded with a biaxial kneader to obtain a polyolefin resin composition 4. The melt flow rate (MFR) of the polyolefin resin composition 4 was 30 g / 10 min. The polyolefin resin composition 4 was rolled with a pair of rolls having a surface temperature of 150 ° C. to prepare a rolled sheet 4. Further thereafter, the rolled sheet 4 is immersed in a hydrochloric acid aqueous solution (hydrochloric acid 4 mol / L, nonionic surfactant 0.5 wt%) to remove calcium carbonate from the rolled sheet 4, and subsequently at 100 ° C. The film was stretched 0 times and heat-fixed at 123 ° C. to obtain a porous membrane 4. The porous membrane 4 was used as a separator 4 for a nonaqueous electrolyte secondary battery.

  A nonaqueous electrolyte secondary battery 4 was produced in the same manner as in Example 1 except that the porous membrane 4 was used instead of the porous membrane 1.

[Measurement result]
The “thickness”, “porosity”, and “tensile creep compliance” of the separators 1 to 4 for the nonaqueous electrolyte secondary batteries obtained in Examples 1 and 2 and Comparative Examples 1 and 2 are the same as those described above. Measured. Table 1 shows the values of tensile creep compliance when t = 300 seconds, 1800 seconds, and 3600 seconds.

  Further, the “rate characteristics” of the non-aqueous electrolyte secondary batteries 1 to 4 obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were measured by the method described above. Table 2 shows the measurement results of the “thickness”, “porosity”, and “rate characteristic”. Further, FIG. 1 shows the relationship between the “rate characteristics” and “void ratio / thickness”.

[Conclusion]
From the description in Table 1, the separator for the nonaqueous electrolyte secondary battery produced in Examples 1 and 2 had the same time t than the separator for the nonaqueous electrolyte secondary battery produced in Comparative Examples 1 and 2. It has been found that the tensile creep compliance (J) in the above increases and satisfies one or more of the following requirements (i) to (iii).
(I) When t = 300 seconds, J is 4.5 to 14.0 GPa ⁻¹ ,
(Ii) When t = 1800 seconds, J is 9.0 G to 25.0 GPa ⁻¹ ,
(Iii) When t = 3600 seconds, J is 12.0 to 32.0 GPa ⁻¹ .

  Further, it is generally known that the rate characteristics of the non-aqueous electrolyte secondary battery depend on the value of the porosity / thickness of the separator. From the description of Table 2 and FIG. 1, when Example 1 and Comparative Example 1 and Example 2 and Comparative Example 2 are compared, the values of the porosity / thickness of the separators are almost the same. It was found that the non-aqueous electrolyte secondary battery produced in 1 had higher rate characteristics.

  From the above-mentioned matters, it is shown that the non-aqueous electrolyte secondary battery using the separator for non-aqueous electrolyte secondary batteries that satisfies one or more of the requirements (i) to (iii) is excellent in rate characteristics. It was.

  The separator for a non-aqueous electrolyte secondary battery and the laminated separator for a non-aqueous electrolyte secondary battery of the present invention can be suitably used for the production of a non-aqueous electrolyte secondary battery having excellent rate characteristics.

Claims (5)

A separator for a non-aqueous electrolyte secondary battery comprising a porous film mainly composed of a polyolefin-based resin,
The porous membrane has a tensile creep compliance value J when a stress of 30 MPa is applied in the TD direction for t seconds, satisfying any one or more of the following (i) to (iii): Electrolyte secondary battery separator:
(I) When t = 300 seconds, J is 4.5 GPa ⁻¹ or more, 14.0 GPa ⁻¹ or less,
(Ii) When t = 1800 seconds, J is 9.0 GPa ⁻¹ or more and 25.0 GPa ⁻¹ or less,
(Iii) When t = 3600 seconds, J is 12.0 GPa ⁻¹ or more and 32.0 GPa ⁻¹ or less.   The separator for nonaqueous electrolyte secondary batteries according to claim 1, wherein all of the above (i) to (iii) are satisfied.   A laminated separator for a nonaqueous electrolyte secondary battery, wherein a porous layer is laminated on at least one surface of the separator for a nonaqueous electrolyte secondary battery according to claim 1 or 2.   The positive electrode, the separator for a non-aqueous electrolyte secondary battery according to claim 1 or 2, or the laminated separator for a non-aqueous electrolyte secondary battery according to claim 3 and the negative electrode are arranged in this order. A member for a non-aqueous electrolyte secondary battery.   A non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte secondary battery separator according to claim 1 or the non-aqueous electrolyte secondary battery laminated separator according to claim 3. battery.