JP2017084671A - Laminated separator for nonaqueous electrolyte secondary battery, component of nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated separator, for a nonaqueous electrolyte secondary battery, which includes a porous film and a porous layer containing a polyvinylidene fluoride-based resin, and has an excellent rate characteristic.SOLUTION: A laminated separator for a nonaqueous electrolyte secondary battery includes: a porous film containing a polyolefin-based resin as a main component; and a porous layer containing a polyvinylidene fluoride-biased resin, where a surface of the porous layer has a 60°-specular gloss of 3-26%.SELECTED DRAWING: None

Description

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

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

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

  As a means to ensure the safety of non-aqueous electrolyte secondary batteries, when abnormal heat generation occurs, the separator prevents the passage of ions between the positive electrode and the negative electrode to prevent further heat generation. The method of giving is common. In other words, in a non-aqueous electrolyte secondary battery, when an abnormal current flows in the separator disposed between the positive electrode and the negative electrode due to, for example, an internal short circuit between the positive electrode and the negative electrode. In addition, it is common to provide a function of blocking the current and preventing the excessive current from flowing (shut down) to suppress further heat generation. As the separator, a film-like porous film mainly composed of a polyolefin-based resin that melts at, for example, about 80 to 180 ° C. when abnormal heat generation occurs is generally used.

  In addition, a technique for laminating a porous film on at least one surface of a porous film is known in order to improve the function of a separator composed of a porous film. For example, in Patent Document 1, in order to prevent an internal short circuit of a battery, a separator, which is a microporous sheet made of a polyolefin resin, and a porous film containing an inorganic filler and a film binder are laminated. Have been described. And by defining the specular gloss of 85 ° of the porous film, a porous film that is thin, uniform, and excellent in flexibility is realized.

  Furthermore, in Patent Document 2, in a separator in which a composition containing insulating fine particles and an organic binder is applied to a microporous film made of polyethylene, a specular gloss of 60 ° is defined, thereby preventing short circuit and reliability. We are trying to improve.

Japanese Patent Laying-Open No. 2005-294216 (released on October 20, 2005) JP 2014-17264 A (published January 30, 2014)

  By the way, in recent years, for the purpose of improving the adhesion between the separator and the electrode, development of a separator in which a porous layer containing a polyvinylidene fluoride resin is laminated on at least one surface of a porous film mainly composed of polyolefin has been advanced. ing. And reduction in resistance of the non-aqueous electrolyte secondary battery has become a problem, and in a laminated separator for a non-aqueous electrolyte secondary battery including a porous film and a porous layer containing a polyvinylidene fluoride resin, Improvement of rate characteristics is desired.

  The above Patent Documents 1 and 2 are intended to improve flexibility, prevent short circuits, and improve reliability, and do not consider rate characteristics. Moreover, the porous layer described in Patent Documents 1 and 2 does not contain a polyvinylidene fluoride resin. Therefore, the techniques described in Patent Documents 1 and 2 cannot improve rate characteristics in a separator including a porous film and a porous layer containing a polyvinylidene fluoride resin.

  The present invention has been made in view of such problems, and an object thereof is a multilayer separator for a non-aqueous electrolyte secondary battery including a porous film and a porous layer containing a polyvinylidene fluoride resin. Then, it is providing the laminated separator for nonaqueous electrolyte secondary batteries which is excellent in a rate characteristic.

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

  The laminated separator for a non-aqueous electrolyte secondary battery according to the present invention is for solving the above-mentioned problem, and includes a porous film mainly composed of a polyolefin-based resin and a polyvinylidene fluoride-based resin. And a layered separator for a non-aqueous electrolyte secondary battery, wherein a mirror glossiness at 60 ° on the surface of the porous layer is 3 to 26%.

  Furthermore, in the laminated separator for a non-aqueous electrolyte secondary battery according to the present invention, the porous layer contains a filler, and the proportion of the filler in the total amount of the polyvinylidene fluoride resin and the filler is 1 It is preferable that it is -30 mass%.

  Furthermore, in the laminated separator for a nonaqueous electrolyte secondary battery according to the present invention, the puncture strength of the porous film is preferably 2N or more.

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

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

  Moreover, the member for non-aqueous electrolyte secondary batteries according to the present invention is characterized in that the positive electrode, the above-described laminated separator for non-aqueous electrolyte secondary batteries, and the negative electrode are arranged in this order.

  In addition, a nonaqueous electrolyte secondary battery according to the present invention includes the above-described laminated separator for a nonaqueous electrolyte secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, there exists an effect which the rate characteristic of a nonaqueous electrolyte secondary battery is excellent.

  An embodiment of the present invention will be described below, but the present invention is not limited to this. The present invention is not limited to each configuration described below, and various modifications are possible within the scope shown in the claims, and various technical means disclosed in different embodiments are appropriately combined. The obtained embodiment is also included in the technical scope of the present invention. Unless otherwise specified in this specification, “A to B” indicating a numerical range means “A or more and B or less”.

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

[1-1. (Porous film)
The porous film only needs to be a porous and membrane-like substrate (polyolefin-based porous substrate) mainly composed of a polyolefin-based resin, and has a structure having pores connected to the inside thereof. It is a film in which gas and liquid can permeate from one side to the other side. That is, the porous film in the present invention is a film having pores, and is different from a nonwoven fabric in which fibers are folded.

  The porous film may be one that imparts a shutdown function to the laminated separator for a nonaqueous electrolyte secondary battery by melting and becoming nonporous when the battery generates heat. The porous film may be composed of one layer or may be formed from a plurality of layers.

  The volume-based porosity of the porous film is 0.2 to 0 so as to increase the amount of electrolyte retained and to reliably prevent the excessive current from flowing (shut down) at a lower temperature. 0.8 (20 to 80% by volume) is preferable, and 0.3 to 0.75 (30 to 75% by volume) is more preferable. In addition, the average pore diameter (average pore diameter) of the porous film can provide sufficient ion permeability when used as a separator, and prevents particles from entering the positive electrode and the negative electrode. Therefore, it is preferably 0.14 μm or less, more preferably 0.1 μm or less, and preferably 0.01 μm or more.

  As a method for controlling the average pore diameter of the porous film, for example, in the case of reducing the pore diameter, a method of homogenizing the dispersion state of the pore opening agent or phase separation agent such as an inorganic filler during the formation of the porous film, Examples thereof include a method of refining the particle size of the inorganic filler pore opening agent, a method of stretching in a state containing a phase separation agent, and a method of stretching at a low stretching ratio. In addition, as a method for controlling the porosity of the porous film, for example, when obtaining a porous film having a high porosity, a method of increasing the amount of a pore opening agent or a phase separation agent such as an inorganic filler with respect to the polyolefin resin. And a method of stretching after removing the phase separation agent, a method of stretching at a high stretching ratio, and the like.

  When the average pore diameter of the porous film decreases, it is considered that the capillary force, which is estimated to be a driving force for introducing the electrolytic solution into the pores inside the substrate, increases. Moreover, generation | occurrence | production of the dendrite (dendritic crystal) by a lithium metal can be suppressed because an average pore diameter is small.

  Moreover, when the porosity of a porous film increases, it is thought that the volume of the location in which the polyolefin which the said electrolyte solution cannot permeate | transmit in the said polyolefin base material exists decreases.

  The puncture strength of the porous film is preferably 2N or more, and more preferably 3N or more. If the piercing strength is too low, the positive and negative electrode active material particles may be used in a stacking operation of the positive and negative electrodes and the separator in the battery assembly process, a pressing operation of the winding group, or when the battery is externally pressurized. As a result, the separator may break through and the positive and negative electrodes may be short-circuited. The puncture strength of the porous film is preferably 10N or less, and more preferably 8N or less.

The proportion of the polyolefin resin component in the porous film is required to be 50% by volume or more of the whole porous film, preferably 90% by volume or more, and more preferably 95% by volume or more. The polyolefin resin component of the porous film preferably contains a high molecular weight component having a weight average molecular weight of 5 × 10 ⁵ to 15 × 10 ⁶ . In particular, the inclusion of a polyolefin component having a weight average molecular weight of 1 million or more as the polyolefin component of the porous film is preferable because the strength of the entire porous film is increased.

  Examples of the polyolefin resin include a high molecular weight homopolymer or copolymer obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like. The porous film may be a layer containing these polyolefins alone and / or a layer containing two or more of these polyolefins. In particular, high molecular weight polyethylene mainly composed of ethylene is preferable. In addition, a porous film does not prevent containing components other than polyolefin in the range which does not impair the function of the said layer.

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

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

  The manufacturing method of such a porous film can use a well-known method, and is not specifically limited. For example, as described in JP-A-7-29563, there is a method in which a hole forming agent is added to a thermoplastic resin to form a film, and then the hole forming agent is removed with an appropriate solvent.

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

  Moreover, about a porous film, you may use the commercial item which has the characteristic mentioned above.

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

  As a result of intensive studies, the inventors have determined that the 60 ° specular gloss on the surface of the porous layer is 3 to 26%, whereby the multilayer separator for a non-aqueous electrolyte secondary battery including the porous layer is provided. It has been found that the rate characteristics of a non-aqueous electrolyte secondary battery comprising can be improved. Here, the specular glossiness of 60 ° indicates the glossiness when the incident angle and the light receiving angle are 60 °, and is measured by a measuring method defined in JIS Z8741. The specular glossiness of the porous layer is a parameter related to the denseness and uniformity of the porous layer.

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

  On the other hand, when the specular gloss exceeds 26%, the denseness of the porous layer becomes too high, and the ion permeability of the separator decreases due to clogging of pores due to insoluble by-products and bubbles generated by charging and discharging. There is. In addition, since the amount of electrolyte at the interface between the porous layer and the electrode is reduced, the amount of electrolyte at the interface between the porous layer and the electrode is reduced. , Li ions are easily depleted at the interface, and as a result, the rate characteristics may be deteriorated. Therefore, by setting the specular gloss to 26% or less, it is possible to suppress a decrease in ion permeability of the separator and a decrease in rate characteristics due to depletion of the electrolyte solution at the interface between the porous layer and the electrode, and an excellent rate. Characteristics can be obtained.

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

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

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

  The polyvinylidene fluoride resin preferably contains 85 mol% or more of vinylidene fluoride as a structural unit. More preferably, it is 90 mol% or more, more preferably 95 mol% or more, still more preferably 98 mol% or more. When 85 mol% or more of vinylidene fluoride is contained, it is easy to ensure mechanical strength and heat resistance that can withstand pressurization and heating during battery production.

In addition, an embodiment in which the porous layer contains two types of polyvinylidene fluoride resins (the following first resin and second resin) having different hexafluoropropylene contents is also preferable.
First resin: a vinylidene fluoride / hexafluoropropylene copolymer or a vinylidene fluoride homopolymer (hexafluoropropylene content) having a hexafluoropropylene content of more than 0 mol% and not more than 1.5 mol% Is 0 mol%)
Second resin: vinylidene fluoride / hexafluoropropylene copolymer having a hexafluoropropylene content of more than 1.5 mol% The porous layer containing the two types of polyvinylidene fluoride resins is any of Compared with a porous layer not containing one, the adhesion with the electrode is improved. In addition, the porous layer containing the two types of polyvinylidene fluoride resins has improved adhesion to the porous film and improved peel strength between these layers compared to a porous layer that does not contain any one of them. To do. The mixing ratio (mass ratio, first resin: second resin) of the first resin and the second resin is preferably 15:85 to 85:15.

  The polyvinylidene fluoride resin preferably has a weight average molecular weight of 300,000 to 3,000,000. When the weight average molecular weight is 300,000 or more, mechanical properties that the porous layer can withstand the adhesion treatment with the electrode can be secured, and sufficient adhesion can be obtained. On the other hand, when the weight average molecular weight is 3 million or less, the viscosity of the coating liquid at the time of coating molding does not become too high, and the moldability is excellent. The weight average molecular weight is more preferably in the range of 300,000 to 2,000,000, still more preferably in the range of 500,000 to 1,500,000.

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

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

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

  Examples of the organic filler include cross-linked polyacrylic acid, cross-linked polyacrylic ester, cross-linked polymethacrylic acid, cross-linked polymethacrylic acid ester, cross-linked polymethyl methacrylate, cross-linked polysilicon, cross-linked polystyrene, cross-linked polydivinylbenzene, and styrene-divinyl. Crosslinked polymer fine particles such as benzene copolymer cross-linked product, polyimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensate; Heat-resistant polymer fine particles such as polysulfone, polyacrylonitrile, polyaramid, polyacetal, thermoplastic polyimide It is done.

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

  Examples of the inorganic filler include metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, nickel hydroxide, and boron hydroxide; metal oxides such as alumina and zirconia; Examples thereof include carbonates such as calcium carbonate and magnesium carbonate; sulfates such as barium sulfate and calcium sulfate; clay minerals such as calcium silicate and talc; From the viewpoint of imparting flame retardancy and charge removal effect, metal hydroxides are preferred.

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

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

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

  The filler can improve slipperiness by forming fine irregularities on the surface of the porous layer. However, when the filler is a plate-like particle or non-aggregated primary particle, the filler is porous. The unevenness formed on the surface of the porous layer becomes finer, and the adhesion with the electrode is better.

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

  In the porous layer, the proportion of the filler in the total amount of the polyvinylidene fluoride resin and the filler is preferably 1% by mass to 30% by mass, and more preferably 3% by mass to 28% by mass. When the content of the filler is 1% by mass or more, the effect of improving the slipperiness of the separator by forming fine irregularities on the surface of the porous layer is easily exhibited. In this respect, the filler content is more preferably 3% by mass or more. On the other hand, when the filler content is 30% by mass or less, the mechanical strength of the porous layer is maintained. For example, when an electrode body is produced by rolling the electrode and the separator, the separator is cracked. Hard to occur. In this respect, the filler content is more preferably 20% by mass or less, and still more preferably 10% by mass or less.

  In the porous layer, when slitting the separator, the ratio of the filler to the total amount of the polyvinylidene fluoride resin and the filler in terms of suppressing the occurrence of slitting and bending at the slit end face, and mixing of slit waste, The content is preferably 1% by mass or more, and more preferably 3% by mass or more.

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

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

The basis weight per unit area of the porous layer may be appropriately determined in consideration of the strength, film thickness, weight, and handling properties of the non-aqueous electrolyte secondary battery laminated separator, but non-aqueous electrolysis including the separator to be able to increase the weight energy density and volume energy density of the liquid secondary battery, usually, is preferably 0.1-5 g / ^{m 2,} and more to be 0.5 to 3 g / ^{m 2} preferable.

The volume basis weight of the porous layer is preferably 0.1 to 2.5 cm ³ / m ² . In the porous layer having a volume basis weight in the above range, a more excellent rate characteristic can be realized by setting the 60 ° specular glossiness to 3 to 26%. When the volume basis weight of the porous layer is less than 0.1 cm ³ / m ^2, clogging of pores due to insoluble by-products and the retention function of the electrolyte solution at the interface between the porous layer and the electrode are not sufficient, and rate characteristics May decrease. Moreover, when the volume basis weight of a porous layer exceeds 2.5 cm < ³ > / m < ² >, the ion permeability in a porous layer falls and a battery characteristic becomes low from the initial stage.

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

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

  The porous layer containing the polyvinylidene fluoride resin can be formed, for example, by the following wet coating method, and a porous layer having a three-dimensional network structure can be obtained by such a method. First, a polyvinylidene fluoride resin may be dissolved in a solvent, and a filler may be dispersed therein to prepare a coating solution. This coating solution is applied to a porous film, and then immersed in an appropriate coagulation solution to solidify the polyvinylidene fluoride resin while inducing phase separation. Through this step, a layer having a porous structure (preferably a three-dimensional network structure) containing a polyvinylidene fluoride resin is formed on the porous film. Thereafter, washing and drying are performed to remove the coagulating liquid from the porous structure layer.

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

  As a solvent for dissolving the polyvinylidene fluoride resin used for preparing the coating liquid (hereinafter also referred to as “good solvent”), N-methyl-2-pyrrolidone (NMP), dimethylacetamide, dimethylformamide, dimethylformamide A polar amide solvent such as is preferably used.

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

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

  A conventional coating method such as a Meyer bar, a die coater, a reverse roll coater, or a gravure coater can be applied to the coating liquid applied to the porous film.

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

  A known method can be employed for drying the deposited coating film.

  As a method for adjusting the glossiness of the deposited coating layer, chemical treatment with acid, alkali, organic solvent, etc., physical treatment for scraping the surface of the coating layer with sandpaper, corona treatment, plasma treatment, etc. A well-known processing method is mentioned. Among them, chemical treatment is preferable, and organic solvents used for chemical treatment include ketones such as acetone; amides such as N-methyl-2-pyrrolidone (NMP), dimethylacetamide, dimethylformamide, and dimethylformamide; ethylene carbonate, propylene carbonate Cyclic carbonates such as fluoroethylene carbonate and difluoroethylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, and fluorine-substituted products thereof; cyclic esters such as γ-butyrolactone and γ-valerolactone Is mentioned. Of these, treatment with diethyl carbonate is preferred.

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

  The separator of the present invention can also be produced by a method in which a porous layer is produced as an independent sheet, and this porous layer is superimposed on a porous film and combined by thermocompression bonding or an adhesive. As a method for producing a porous layer as an independent sheet, a coating liquid containing a polyvinylidene fluoride resin and a filler is applied onto a release sheet, and the porous layer is formed by applying the above-described production method. The method of peeling a porous layer from a peeling sheet is mentioned.

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

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

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

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

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

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

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

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

  Examples of the current collector include copper foil, nickel foil, and stainless steel foil having a thickness of 5 to 20 μm. Moreover, it may replace with the said negative electrode and may use metal lithium foil as a negative electrode.

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

  Nonaqueous solvents include all solvents generally used in nonaqueous electrolyte secondary batteries. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted products thereof; γ-butyrolactone, γ-valerolactone, etc. These may be used alone or in admixture.

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

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

  A non-aqueous electrolyte secondary battery is obtained by, for example, impregnating an electrolyte with a laminate in which the above-described laminated separator for a non-aqueous electrolyte secondary battery is disposed between a positive electrode sheet and a negative electrode sheet. The laminate can be manufactured by pressing the laminate from above the exterior material. At this time, in order to improve the adhesiveness between the electrode and the laminated separator for a non-aqueous electrolyte secondary battery, the press is preferably a press while heating (hot press).

  The method of disposing the separator between the positive electrode sheet and the negative electrode sheet may be a method of stacking at least one layer of the positive electrode sheet, the separator, and the negative electrode in this order (so-called stack method). The positive electrode sheet, the separator, the negative electrode sheet, and the separator It is also possible to use a method in which these are stacked in this order and rolled in the length direction.

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

<Measurement of specular gloss>
The specular gloss is measured by using a gloss meter (PG-IIM type, manufactured by Nippon Denshoku Industries Co., Ltd.), with 5 sheets of KB paper (manufactured by KOKUYO Co., Ltd., product number: KB-39N) stacked on top of each other. The laminated separator for electrolyte secondary batteries was mounted, and the incident angle and the light receiving angle on the surface of the porous layer in the laminated separator for nonaqueous electrolyte secondary batteries were measured at 60 °.

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

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

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

<Preparation of separator>
The laminated separator for nonaqueous electrolyte secondary batteries which concerns on Examples 1-6 and Comparative Examples 1 and 2 was produced as follows.

Example 1
A PVDF resin (manufactured by Arkema; trade name “KYNAR2801”) was stirred and dissolved in N-methyl-2-pyrrolidone at 65 ° C. for 30 minutes so that the solid content was 7% by mass. The obtained solution was used as a coating liquid, and the volume basis weight of the PVDF resin in the coating liquid was measured on a polyethylene porous film (thickness 12 μm, porosity 44%, average pore diameter 0.035 μm) by the doctor blade method. It apply | coated so that it might become 0.56 cm < ³ > / m < ² >. The laminate (1-i), which is the obtained coated product, is immersed in 2-propanol while the coating film is in an NMP wet state, and is allowed to stand at 25 ° C. for 5 minutes to obtain a laminated porous film (1- ii) was obtained. The obtained laminated porous film (1-iii) was dipped in another 2-propanol in a dipping solvent wet state and allowed to stand at 25 ° C. for 5 minutes to obtain a laminated porous film (1-iii). . The obtained laminated porous film (1-iii) was dried at 65 ° C. for 5 minutes to obtain a laminated porous film (1-iv). The obtained laminated porous film (1-iv) was immersed in diethyl carbonate at 70 ° C. for 1 minute. The film was taken out from diethyl carbonate and dried at room temperature to obtain a non-aqueous electrolyte secondary battery laminated separator of Example 1. Table 1 shows the rate characteristics of the laminated separator for a nonaqueous electrolyte secondary battery of Example 1.

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

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

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

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

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

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

(Comparative Example 2)
A PVDF resin (manufactured by Arkema; trade name “KYNAR2801”) was stirred and dissolved in N-methyl-2-pyrrolidone at 65 ° C. for 30 minutes so that the solid content was 7% by mass. The obtained solution was used as a coating liquid, and the volume basis weight of the PVDF resin in the coating liquid was measured on a polyethylene porous film (thickness 12 μm, porosity 44%, average pore diameter 0.035 μm) by the doctor blade method. It apply | coated so that it might become 0.56 cm < ³ > / m < ² >. The laminate (8-i), which was the obtained coated product, was dried at 85 ° C. for 5 minutes to obtain a multilayer separator for a nonaqueous electrolyte secondary battery in Comparative Example 2. Table 1 shows the rate characteristics of the non-aqueous electrolyte secondary battery laminated separator of Comparative Example 2.

<Production of non-aqueous electrolyte secondary battery>
Next, a non-aqueous electrolyte secondary battery was manufactured according to the following using each of the laminated separators for non-aqueous electrolyte secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 2 manufactured as described above.

(Positive electrode)
A commercially available positive electrode manufactured by applying LiNi _0.5 Mn _0.3 Co _0.2 O ₂ / conductive material / PVDF (weight ratio 92/5/3) to 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 .

(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 thickness of the negative electrode active material layer was 49 μm, and the density was 1.40 g / cm ³ .

(assembly)
By laminating (arranging) the positive electrode, the non-aqueous electrolyte secondary battery laminate separator, and the negative electrode in this order in a laminate pouch, a non-aqueous electrolyte secondary battery member 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 was put in a bag in which an aluminum layer and a heat seal layer were laminated, and 0.25 mL of the non-aqueous electrolyte was put in this bag. The non-aqueous electrolyte was prepared by dissolving LiPF ₆ having a concentration of ethylene carbonate and diethyl carbonate of 1.0 mol / liter in a mixed solvent having a volume ratio of ethyl methyl carbonate, diethyl carbonate and ethylene carbonate of 50:20:30. The electrolyte solution was used. And the non-aqueous-electrolyte secondary battery was produced by heat-sealing the said bag, decompressing the inside of a bag.

<Rate test>
For a new non-aqueous electrolyte secondary battery that has not undergone a charge / discharge cycle, voltage range at 25 ° C .; 4.1 to 2.7 V, current value; 0.2 C (rated capacity by discharge capacity at 1 hour rate) 4 cycles of initial charge / discharge were carried out, assuming that the current value discharged in 1 hour was 1 C, and so on).

Subsequently, at 55 ° C., the following formula: Rate characteristics (%) = (20 C discharge capacity / 0.2 C discharge capacity) × 100
According to the calculation, the rate characteristics were calculated.

  As shown in Table 1, in the nonaqueous electrolyte secondary battery using the laminated separator for a nonaqueous electrolyte secondary battery according to Comparative Example 2 in which the specular gloss exceeds 26%, the rate characteristic is remarkable at 43%. Was confirmed to be low. This is because when the specular gloss exceeds 26%, the denseness of the porous layer becomes too high, and the ion permeability is increased due to an increase in the internal resistance of the battery and a decrease in the electrolyte retention function at the interface between the separator and the electrode. This is thought to be due to the decrease in

  Further, it was confirmed that the rate characteristic was low as 65% even in the non-aqueous electrolyte secondary battery using the non-aqueous electrolyte secondary battery laminated separator according to Comparative Example 1 having a specular gloss of less than 3%. . This is presumably because when the specular gloss was less than 3%, the uniformity of the porous layer was low and the ion permeability was uneven.

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

Claims (7)

A non-aqueous electrolyte secondary battery laminated separator comprising a porous film mainly comprising a polyolefin-based resin, and a porous layer containing a polyvinylidene fluoride-based resin,
A laminated separator for a non-aqueous electrolyte secondary battery, wherein the surface glossiness at 60 ° on the surface of the porous layer is 3 to 26%. The porous layer contains a filler;
The laminated separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein a ratio of the filler to a total amount of the polyvinylidene fluoride resin and the filler is 1 to 30% by mass.   The laminated separator for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the puncture strength of the porous film is 2N or more.   The laminated separator for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein an average pore diameter of the porous film is 0.14 µm or less.   The polyvinylidene fluoride-based resin is a copolymer of at least one monomer selected from the group consisting of hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, and vinyl fluoride, and vinylidene fluoride. The multilayer separator for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the laminate is a homopolymer of vinylidene chloride or a mixture of these polymers.   A member for a nonaqueous electrolyte secondary battery in which the positive electrode, the laminated separator for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, and the negative electrode are arranged in this order.   A nonaqueous electrolyte secondary battery comprising the multilayer separator for a nonaqueous electrolyte secondary battery according to claim 1.