WO2019188292A1

WO2019188292A1 - Separator for electrochemical element

Info

Publication number: WO2019188292A1
Application number: PCT/JP2019/010277
Authority: WO
Inventors: 正典森下; 境　哲男; 田中　政尚; 佐藤　芳徳
Original assignee: 日本バイリーン株式会社
Priority date: 2018-03-29
Filing date: 2019-03-13
Publication date: 2019-10-03
Also published as: JP7191536B2; JP2019175827A; CN112042006B; CN112042006A

Abstract

The present invention provides a separator for an electrochemical element such that excellent protective properties against dendrite-induced short circuits are demonstrated. The separator for an electrochemical element according to the present invention comprises a nonwoven substrate having internal gaps in which inorganic particles are adhered to nonwoven constituent fibers via polymer binders, with polyelectrolytes being in the gaps formed by the nonwoven constituent fibers, the inorganic particles, and the polymer binders. It is preferable that the amount of polyelectrolytes is 2 to 18 mass% of the entire separator for an electrochemical element; the inorganic particles are made up of silica or alumina; the nonwoven substrate is made up of a composite of nonwoven fabrics where short fibers and/or pulp fibers enter the gaps in the base nonwoven fabric; and the nonwoven constituent fibers include heat resistant fibers having a melting point or a decomposition temperature of 180°C or greater.

Description

Electrochemical element separator

The present invention relates to a separator for an electrochemical element.

In recent years, along with the reduction in size and weight of electrical equipment, there is a strong demand for a battery that is a power source for reduction in size, weight, and high energy density. Since lithium ion secondary batteries have high energy density, they are expected to satisfy such demands.

As a separator for such a lithium ion secondary battery, it was common to use a polyolefin microporous membrane. This is because the battery temperature rises markedly when an abnormal large current flows due to an external short circuit of the battery, etc., and the polyolefin microporous membrane contracts due to the heat to prevent the generation of flammable gas, battery rupture or ignition. Or it is because it is thought that it has the function (shutdown function) which melt | dissolves and obstruct | occludes a micropore and interrupts | blocks ion permeability. However, as the temperature rises, heat shrinks in the width direction of the separator to reduce the width dimension, and the electrodes that are in contact with the width direction end of the separator are exposed, which may cause a short circuit. . Alternatively, the separator may be melted due to an increase in temperature, resulting in ignition.

Therefore, it has been proposed to coat the polyolefin microporous membrane with inorganic particles to suppress thermal contraction of the polyolefin microporous membrane and prevent short circuit even when the temperature rises.

However, since the separator coated with inorganic particles is inferior in binding properties with the electrode, “the porous substrate is formed on at least one surface of the porous substrate, and the inorganic particles and the first binder are high. A porous organic-inorganic coating layer comprising a mixture of molecules, and a second binder polymer dispersed on the surface of the porous organic-inorganic coating layer, and having a large number of interspersed uncoated regions An organic coating layer, wherein the first binder polymer includes (a) a first monomer unit containing at least one amine group or amide group in the side chain, and (b) a carbon number. A separator comprising a copolymer having a second monomer unit made of (meth) acrylate having 1 to 14 alkyl groups ”(Patent Document 1) It is. This separator is considered to be able to increase the binding force with the electrode, but it cannot prevent lithium dendrite during overdischarge and cannot prevent another short circuit. .

As another electrochemical element, for example, there is a lithium ion capacitor, and it is desirable to dope lithium as a negative electrode active material from the viewpoint of sufficiently lowering the negative electrode potential. Short circuit may occur easily. Thus, even in electrochemical elements other than lithium ion secondary batteries, there is a problem that dendrites cannot be prevented and short circuits are likely to occur.

Special table 2014-505344 gazette

The present invention has been made under such circumstances, and an object of the present invention is to provide a separator for an electrochemical element that is excellent in short circuit prevention by dendrites.

The present invention provides: [1] In the internal voids of the nonwoven fabric substrate, the inorganic particles are bonded to the nonwoven fabric substrate constituting fiber by a binder polymer, and are formed by the nonwoven fabric substrate constituting fiber, the inorganic particles, and the binder polymer. It is a separator for an electrochemical element, characterized by having a polymer electrolyte polymer in the formed void.

[2] It is preferable that the amount of the polymer electrolyte polymer occupies 2 to 18 mass% of the whole separator for an electrochemical element.

[3] The inorganic particles are preferably silica and / or alumina.

Furthermore, [4] It is preferable that the nonwoven fabric base material is a composite nonwoven fabric in which short fibers and / or pulp fibers are contained in the gaps of the base nonwoven fabric.

Furthermore, [5] It is preferable that the nonwoven fabric base-constituting fibers include heat-resistant fibers having a melting point or decomposition temperature of 180 ° C. or higher.

[1] Although the detailed mechanism is unclear, even in the case of overdischarge, lithium dendrite can be prevented and charge / discharge is possible again, contrary to the conventional common sense. Excellent effect. Further, there is a limit to densification of the nonwoven fabric substrate, but in the internal voids of the nonwoven fabric substrate, the inorganic particles are bonded to the nonwoven fabric constituent fibers by the binder polymer, and the nonwoven fabric in the internal voids of the nonwoven fabric substrate The polymer electrolyte polymer has a dense structure in the gap formed by the base fiber, inorganic particles, and binder polymer. Depending on the combination of the polymer electrolyte polymer and the electrolyte, the polymer electrolyte polymer may be a battery. Since it absorbs the electrolyte during the construction and swells, it effectively closes the voids and functions as a barrier layer that prevents the diffusion of metal ions. Furthermore, since inorganic particles are included, the heat resistance is excellent, and the separator for electrochemical elements is hardly melted or shrunk, so that the safety is excellent.

[2] When the amount of the polymer electrolyte occupies 2 to 18 mass% of the entire separator for electrochemical devices, lithium dendrite can be prevented even in the case of overdischarge. It is possible to achieve a remarkably excellent effect.

[3] When the inorganic particles are silica and / or alumina, even if overdischarge occurs, lithium dendrite can be prevented and charge / discharge is possible again. Play.

[4] When the nonwoven fabric base material is a composite nonwoven fabric in which short fibers and / or pulp-like fibers are contained in the voids of the base nonwoven fabric, the nonwoven fabric base material has a uniform and dense structure, and therefore prevents short circuit due to dendrites. It is superior to the nature.

[5] If the non-woven fabric base fiber contains a heat-resistant fiber having a melting point or decomposition temperature of 180 ° C. or higher, a short circuit or ignition due to shrinkage or melting of the separator for an electrochemical element is less likely to occur. In addition, it is easy to produce an electrochemical element having a long squill life because it can be sufficiently dried and moisture can be removed when the separator for an electrochemical element is produced.

The separator for an electrochemical element of the present invention (hereinafter, sometimes simply referred to as “separator”) is excellent in retention of the electrolytic solution, and can maintain the strength of the separator. Having a nonwoven substrate.

The resin composition of the fibers constituting the nonwoven fabric substrate is not particularly limited. For example, polyolefin resins (polyethylene, polypropylene, polymethylpentene, hydrocarbons partially substituted with cyano groups or halogens such as fluorine or chlorine) Polyolefin resin having the structure described above), styrene resin, polyether resin (polyether ether ketone, polyacetal, phenol resin, melamine resin, urea resin, epoxy resin, modified polyphenylene ether, aromatic polyether ketone) Etc.), polyester resin (polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polycarbonate, polyarylate, wholly aromatic poly Steal resin, unsaturated polyester resin, etc.), polyimide resin, polyamideimide resin, polyamide resin (eg, aromatic polyamide resin, aromatic polyetheramide resin, nylon resin, etc.), a resin having a nitrile group (eg, Polyacrylonitrile), urethane resin, epoxy resin, polysulfone resin (polysulfone, polyethersulfone, etc.), fluorine resin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), cellulose, polybenzimidazole resin, acrylic resin (For example, polyacrylonitrile resin copolymerized with acrylic acid ester or methacrylic acid ester, modacrylic resin copolymerized with acrylonitrile and vinyl chloride or vinylidene chloride, etc.) Door can be. Among these, it is preferable that the fiber surface (excluding both ends of the fiber) is composed of a polyolefin-based resin, a polyester-based resin, or a polyamide-based resin. .

In addition, the nonwoven fabric base-constituting fiber may be composed of one kind of organic resin as described above, or may be composed of two or more kinds. For example, in the case of being composed of two or more types, the resin arrangement state in the cross section of the fiber can be, for example, a core-sheath type, sea-island type, side-by-side type, orange type, bimetal type, or the like. In the nonwoven fabric base material of the present invention, the fibers are in a bonded state, and the internal voids of the nonwoven fabric base material are easily retained, so that the retention of inorganic particles, the binder polymer and the polymer electrolyte polymer is excellent. The nonwoven fabric base-constituting fibers are composed of two or more kinds of organic resins, and the fiber surface preferably contains fibers composed of a low-melting-point resin. In particular, if the arrangement of the resin in the cross section of the fiber is a core-sheath type or sea-island type, the low melting point occupying the entire fiber surface (excluding both ends of the fiber) while maintaining the fiber form by the core component or island component This is preferable because the resin can be sufficiently fused.

In addition, the nonwoven fabric base material fiber is less likely to cause short circuit or ignition due to the shrinkage or melting of the separator, and can be sufficiently dried at the time of separator production to remove moisture and easily produce an electrochemical element having a long squill life. As for it, it is preferable to contain the heat resistant fiber whose melting | fusing point or decomposition temperature is 180 degreeC or more. Examples of such heat-resistant fibers include styrene fibers, polyether fibers, polyester fibers, polyimide fibers, polyamideimide fibers, polyamide fibers, epoxy fibers, polysulfone fibers, fluorine fibers, cellulose, Polybenzimidazole fiber can be mentioned, and in particular, a wholly aromatic polyamide fiber that is a polyamide-based fiber or a wholly aromatic polyester fiber that is a polyester-based fiber has excellent heat resistance and has a low moisture content and is resistant to electrolyte. In addition to excellent properties, it can be a fiber having a small fiber diameter or a pulp-like fiber having fibrils, so that the non-woven fabric substrate has a uniform and dense pore size, and is excellent in short circuit prevention due to dendrites. Therefore, it is preferable. Such heat-resistant fibers are preferably contained in an amount of 5 mass% or more of the nonwoven fabric base component fiber, more preferably 10 mass% or more, and more preferably 15 mass% or more so as to have excellent performance. More preferably, it is more preferably 20% by mass or more. “Melting point” refers to the melting temperature obtained from a differential thermal analysis curve (DTA curve) obtained by differential thermal analysis as defined in JIS K 7121-1987, and “decomposition temperature” as defined in JIS K 7120-1987. The temperature at the time when the mass of the completely dried test piece is reduced by 5% is measured.

Further, the cross-sectional shape of the nonwoven fabric substrate constituting fiber may be circular or non-circular. Examples of non-circular shapes include, for example, polygonal shapes such as substantially triangular shapes, alphabetic character shapes such as Y-shapes, symbol shapes such as irregular shapes, multileaf shapes, asterisk shapes, or a combination of these shapes. Examples include shapes.

The fiber diameter of the fibers constituting the nonwoven fabric substrate of the present invention is not particularly limited, but it is 0.1 to 0.1 so that the electrical insulation is excellent and the electrolyte retention is excellent. The thickness is preferably 20 μm, more preferably 0.5 to 16 μm, and still more preferably 0.5 to 13 μm. In addition, since it can be a nonwoven fabric base material of a dense structure, it is suitable to contain two or more types of fibers having different fiber diameters. For example, when a fiber having a fiber diameter of 0.1 to 4 μm and a fiber having a fiber diameter of 4 to 20 μm are included, the separator has a dense structure and is excellent in electrical insulation. “Fiber diameter” means the shortest length of fiber when an electron micrograph is observed on the main surface of the nonwoven fabric substrate or separator.

In addition, the fiber length of the non-woven fabric substrate constituting fiber is preferably 0.1 to 20 mm, and preferably 0.5 to 15 mm so that the fibers are uniformly dispersed and the electrolyte solution can be easily held uniformly. Is more preferably 1 to 10 mm. "Fiber length" means the length in the direction in which the fibers extend when an electron micrograph is observed on the main surface of the nonwoven fabric substrate or separator.

In addition, the nonwoven fabric base-constituting fibers may be pulp-like fibers having fibrils or fibers having no fibrils, but if they are pulp-like fibers, the pore diameter of the nonwoven fabric base material is uniform and dense. The structure is preferable because it is superior in the prevention of short circuit by dendrite.

Furthermore, the constituent fibers of the nonwoven fabric substrate may be in a state in which the fibers are bonded or in a state in which the fibers are not bonded, but when the fibers are bonded, a separator having excellent shape stability. Since it can be, it is a preferred embodiment. Such fiber-to-fiber bonding is, for example, the deformation caused by the crystal orientation caused by the fusion of the low melting point resin as described above with the fibers constituting the fiber surface and the heating and pressurization of unstretched fibers (for example, unstretched polyester fibers) It can be an adhesive action by, an intertwining of fibers and / or an adhesive by a binder.

Further, the nonwoven fabric substrate of the present invention is excellent in affinity with the electrolytic solution, and it is easy to hold the electrolytic solution uniformly, and the inorganic particles are easily adhered to the binder polymer. When the material-constituting fiber includes a hydrophobic fiber as in the case of including a polyester-based fiber, it is preferable that an affinity group is provided. For example, oxygen and / or sulfur-containing functional groups (for example, sulfonic acid groups, sulfonic acid groups, sulfofluoride groups, hydroxyl groups, carboxyl groups, or carbonyl groups) are introduced, or hydrophilic monomers are graft-polymerized. It is preferable that a surfactant is applied or a hydrophilic resin is applied.

The fibers constituting the nonwoven fabric substrate of the present invention are the resin composition, the number of resin compositions, the arrangement state of the resin in the cross section of the fiber, the fiber diameter, the fiber length, the presence or absence of fibrils, and / or the degree of affinity, etc. It may be composed of two or more types of fibers that are different from each other.

The nonwoven fabric substrate of the present invention may have a single layer structure or a multilayer structure of two or more layers. In particular, a single-layer or double-layer composite nonwoven fabric in which short fibers and / or pulp-like fibers enter the voids of the base nonwoven fabric has a uniform and dense structure in the pore diameter of the nonwoven fabric substrate, and prevents short circuiting due to dendrites. It is suitable because it is more excellent in properties. In addition, the short fiber and / or pulp-like fiber which entered in this composite nonwoven fabric are entangled with the base nonwoven fabric constituting fiber, bonded with a binder, or entered with the short fiber or pulp-like fiber. At least one of the base nonwoven fabric constituent fibers can be fused, and the short fibers and / or the pulp-like fibers can be fixed to the base nonwoven fabric. The base non-woven fabric is not particularly limited as long as it can maintain the strength of the non-woven fabric substrate. For example, the base non-woven fabric can be a wet non-woven fabric including non-woven fabric constituting fibers as described above. Further, as described above, since the nonwoven fabric base material preferably contains heat-resistant fibers, it is preferable that the base nonwoven fabric and / or short fibers and / or pulp-like fibers contain heat-resistant fibers. It is more preferable that both the short fiber and / or the pulp-like fiber contained in the nonwoven fabric contain a heat-resistant fiber.

The basis weight of the nonwoven fabric base material of the present invention is not particularly limited, but is preferably 1 g / m ² or more, and preferably 3 g / m ² or more so that the retention of inorganic particles described later is excellent. Is more preferably 5 g / m ² or more, and further preferably 6 g / m ² or more. The upper limit of the basis weight is not particularly limited, but if the basis weight is high and the amount of fibers is large, the internal resistance tends to be high. Therefore, it is preferably 30 g / m ² or less, and 25 g / m ² or less. More preferably, it is more preferably 20 g / m ² or less. In the present invention, “weight per unit” means the basis weight obtained based on the method defined in JIS P8124 (paper and paperboard—basis weight measurement method).

The thickness of the nonwoven fabric substrate of the present invention is not particularly limited, but is preferably 50 μm or less, and preferably 40 μm or less so that an electrochemical element having a low internal resistance can be easily produced due to its thin thickness. Is more preferable, and it is still more preferable that it is 30 micrometers or less. On the other hand, if the thickness is too thin, the strength tends to decrease and the separator tends to be cracked, and the handleability tends to be inferior. Therefore, the thickness is preferably 5 μm or more, and more preferably 10 μm or more. The “thickness” in the present invention is measured at 10 points selected at random using an outer micrometer (0 to 25 mm) defined in JIS B 7502: 1994, and the arithmetic average is obtained. Value.

The separator of the present invention is safe because the inorganic particles are bonded to the nonwoven fabric constituent fibers by the binder polymer in the internal voids of the nonwoven fabric base as described above, so that it has excellent heat resistance and is difficult to melt or shrink. Excellent in properties.

The particle diameter of the inorganic particles can be present in the internal voids in the nonwoven fabric base material, and can be any one that can reduce the internal voids of the nonwoven fabric base material, and is not particularly limited, but is preferably 3 μm or less, It is more preferably 1 μm or less, and further preferably 0.8 μm or less. The lower limit value of the particle diameter of the inorganic particles is not particularly limited, but it is realistic that it is 0.01 μm or more.

The “particle size” in the present invention is particle size measurement data obtained from scatter intensity by performing continuous measurement for 3 minutes by dynamic light scattering method using FPRA1000 (measurement range: 3 nm to 5000 nm) manufactured by Otsuka Electronics Co., Ltd. The value obtained from. More specifically, the particle size measurement data obtained by performing the particle size measurement five times and arranging the particle size measurement data obtained in the order of narrowing the particle size distribution width are the third particles having the narrowest particle size distribution width. In the diameter measurement data, the particle diameter D ₅₀ (hereinafter abbreviated as D ₅₀ ) at the 50% cumulative value of particles is defined as the particle diameter. In addition, the measurement liquid used for the measurement is adjusted to a temperature of 25 ° C., and pure water at 25 ° C. is used as a blank for scattering intensity.

The particle size distribution of the inorganic particles is not particularly limited. However, if the particle size distribution of the inorganic particles is too wide, the inorganic particles are non-uniformly present, resulting in variations in the pore diameter of the separator, resulting in a decrease in electrical insulation. because of its tendency to particle size distribution of the inorganic particles (D _50/2) or more, and preferably in the (D ₅₀ × 2) within the following range. The “particle size distribution” in the present invention is determined from the particle size measurement data obtained from the measured intensity measured by the dynamic light scattering method described above.

The composition of the inorganic particles used in the present invention is not particularly limited. For example, SiO ₂ (silica), Al ₂ O ₃ (alumina), alumina-silica composite oxide, TiO ₂ , SnO ₂ , BaTiO ₂ , Oxides such as ZrO and tin-indium oxide (ITO); nitrides such as aluminum nitride and silicon nitride; poorly soluble ionic crystals such as calcium fluoride, barium fluoride and barium sulfate; covalent bonds such as silicon and diamond Examples thereof include clays such as talc and montmorillonite; substances derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite and mica, or artificial products thereof. Among these, silica and alumina are preferable because lithium dendrite can be prevented and charge / discharge can be easily performed again even when overdischarge occurs. In addition, in the nonwoven fabric base material, two or more kinds of inorganic particles having different compositions as described above may be included. For example, silica particles and alumina particles may be included. Further, inorganic particles having two or more kinds of compositions as described above, for example, silica-alumina particles may be contained.

The shape of the inorganic particles is not particularly limited, but for example, spherical (substantially spherical or true spherical), fibrous, needle-like (for example, tetrapot-like), flat plate, polyhedron, feather, A regular shape can be mentioned. In particular, a true spherical shape is suitable because it can be easily packed in the inner space of the nonwoven fabric base material and the pore diameter of the separator can be reduced.

In particular, a method for producing inorganic particles by detonating a dust cloud of a raw material capable of preparing inorganic particles as an inorganic particle in a reaction gas atmosphere such as air, oxygen, chlorine, nitrogen or the like (for example, JP-A-60). Inorganic particles obtained by the method disclosed in JP-A-255602) (hereinafter sometimes referred to as “deflagration inorganic particles”) are preferable. This is because the deflagration inorganic particles have a spherical shape, have a small water content, and do not easily deteriorate the performance of the electrochemical device.

The separator of the present invention has inorganic particles in the internal voids of the nonwoven fabric substrate, but may contain not only internal voids but also inorganic particles deposited on the fibers constituting the surface of the nonwoven fabric substrate.

The amount of the inorganic particles is not particularly limited because the total volume of the inorganic particles varies depending on the specific gravity. However, the inorganic voids are sufficiently filled in the internal voids of the nonwoven fabric substrate, and preferably the nonwoven fabric substrate. It is preferable that the inorganic particle volume ratio (Vr) defined by the following formula is 0.1 or more so that inorganic particles are deposited on the surface and the electrolyte retainability is excellent. More preferably, it is 15 or more.

Vr = Iv / Fv
In the formula, Iv means the total volume of the inorganic particles and is a value obtained from the following formula, and Fv means the total volume of the nonwoven fabric substrate constituting fibers and is a value obtained from the following formula.
Iv = It / Is
Fv = Ft / Fs
In the formula, It is the total mass of the inorganic particles, Is is the specific gravity of the inorganic particles, Ft is the total mass of the nonwoven fabric base component fibers, and Fs is the specific gravity of the nonwoven fabric base fabric fibers.

In the separator of the present invention, the inorganic particles are bonded to the nonwoven fabric base fiber with a binder polymer so that such inorganic particles do not fall off and are excellent in heat resistance and denseness. The binder polymer is not particularly limited as long as it is capable of adhering inorganic particles to fibers constituting the nonwoven fabric base material and resistant to electrolytic solution. For example, polyolefin, ethylene vinyl alcohol copolymer, ethylene -Ethylene-acrylate copolymers such as ethyl acrylate copolymer, various rubbers or derivatives thereof [styrene-butadiene rubber (SBR), fluororubber, urethane rubber, ethylene-propylene-diene rubber (EPDM), etc.], cellulose derivatives [carboxy Methyl cellulose (CMC), hydroxyethyl cellulose, hydroxypropyl cellulose, etc.], polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), polyurethane, epoxy resin, PVDF, vinyl fluoride Down - hexafluoropropylene copolymer (PVDF-HFP), mention may be made of an acrylic resin, can these alone, or two or more kinds. Among these, a binder polymer made of an acrylic resin is suitable because it is excellent not only in the adhesion of inorganic particles but also in the permeability of the electrolytic solution and the withstand voltage.

The binder polymer preferably accounts for 0.5 mass% or more of the total amount of the inorganic particles and the binder polymer, more preferably 1 mass% or more so that the inorganic particles can be sufficiently bonded. It is more preferable to occupy the above. On the other hand, when the ratio of the binder polymer is too high, the internal resistance of the separator tends to increase, and therefore it is preferably 10 mass% or less.

In addition to the inorganic particles and the binder polymer as described above, the separator of the present invention has a polymer electrolyte polymer in the void formed by the nonwoven fabric substrate constituting fiber, the inorganic particles, and the binder polymer in the internal void of the nonwoven fabric substrate. Depending on the combination of the polymer electrolyte polymer and the electrolyte, the polymer electrolyte polymer absorbs the electrolyte during battery construction and swells to effectively close the voids and diffuse metal ions. Since it functions as a barrier layer that prevents the occurrence of short circuiting, it is excellent in short circuit prevention by dendrite. Furthermore, it has been found that even when overdischarge occurs, dendrite can be prevented and charge / discharge can be performed again, which is remarkably excellent, contrary to conventional common sense.

Thus, the polyelectrolyte polymer in the separator of the present invention exists in the void formed by the nonwoven fabric substrate constituting fibers, the inorganic particles, and the binder polymer in the internal void of the nonwoven fabric substrate. When the surface has inorganic particles and a binder polymer, they may be present in the voids between the inorganic particles and the binder polymer.

The polyelectrolyte polymer is not particularly limited, and can be, for example, an ionomer resin, and includes, for example, an anion exchange group such as a quaternary ammonium group, a pyridinium group, an imidazolium group, a phosphonium group, and a sulfonium group. It can be a hydrocarbon-based resin (for example, polystyrene, polysulfone, polyethersulfone, polyetheretherketone, polyphenylene, polybenzimidazole, polyimide, polyarylene ether, polyethylene oxide, etc.). In addition, the polymer electrolyte polymer can be a fluorine-based resin, such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-6-propylene fluoride (PVDF-HFP) copolymer, polyvinylidene fluoride-trifluoride chloride. Swells by contact with non-aqueous solvent (electrolyte) such as ethylene (PVDF-CTFE) copolymer, polyvinylidene fluoride-4 ethylene fluoride-6 propylene copolymer (PVDF-TFE-HFP) copolymer, etc. And can form a gel. Further, the fluororesin may be a perfluorocarbon sulfonic acid resin comprising a main chain made of polytetrafluoroethylene and a side chain having a sulfonic acid group. More specifically, it can be a perfluorocarbon sulfonic acid resin represented by the following general formula.

[Wherein m is 5 to 13.5, n is 5 to 10000 (preferably about 1000), and z is 1 to 30]

Among these polymer electrolyte polymers, the polymer electrolyte polymer absorbs the electrolyte during battery construction and effectively swells to effectively close the voids and function as a barrier layer to prevent the diffusion of metal ions. It is preferably a fluorine-based resin that is excellent in preventing properties and that can easily be charged and discharged again and can form a gel by contact with a non-aqueous solvent (electrolytic solution). In particular, polyvinylidene fluoride-6-propylene fluoride ( PVDF-HFP) copolymer, polyvinylidene fluoride (PVDF) is preferred.

The polyelectrolyte polymer can prevent dendrite, and the polyelectrolyte polymer occupies 2 to 18 mass% of the entire separator so that charge and discharge can be easily performed even after overdischarge. It is preferable that it occupies 3 mass% or more, and more preferably occupies 3.5 mass% or more. On the other hand, if the amount of the polymer electrolyte polymer is too large, the internal resistance of the electrochemical element tends to increase. Therefore, the polymer electrolyte polymer preferably occupies 18 mass% or less of the entire separator, and 17.5 mass%. It is more preferable to occupy the following, and it is still more preferable to occupy 17 mass% or less.

As described above, the polyelectrolyte polymer of the present invention has a void formed by the nonwoven fabric base constituent fiber, the inorganic particles, and the binder polymer. Although the binder polymer and the polymer electrolyte polymer may be mixed, it is preferable that the binder polymer and the polymer electrolyte polymer are not mixed and are in a separated state. If mixed, the polymer electrolyte polymer absorbs the electrolyte and swells to weaken the action of plugging the gap, resulting in a decrease in the function as a barrier layer and a tendency to reduce short-circuit prevention due to dendrites. Because there is. For example, the polyelectrolyte polymer is preferably in a state where it is coated with a binder polymer or in a state where it is partially in contact with the binder polymer. Thus, the state in which the binder polymer and the polymer electrolyte polymer are separated can be formed, for example, by attaching the polymer electrolyte polymer after the inorganic particles are bonded to the nonwoven fabric constituting fiber with the binder polymer.

The basis weight of the separator of the present invention is not particularly limited, but is preferably 5 to 35 g / m ² , more preferably 10 to 30 g / m ² , and 15 to 25 g / m ^2. Further preferred. The thickness of the separator is not particularly limited, but is preferably 50 μm or less, more preferably 40 μm or less, and more preferably 35 μm or less so that an electrochemical element having a low internal resistance can be easily produced. Is more preferable, and it is still more preferable that it is 30 micrometers or less. On the other hand, if the thickness is too thin, the strength tends to decrease and the separator tends to be cracked, and the handleability tends to be inferior. Therefore, the thickness is preferably 5 μm or more, and more preferably 10 μm or more.

Since the separator of the present invention is excellent in prevention of short circuit by dendrite, it can be suitably used as a separator for various electrochemical elements. For example, it can be suitably used as a separator for lithium ion secondary batteries, electric double layer capacitors such as lithium ion capacitors, electrolytic capacitors such as aluminum electrolytic capacitors, solid polymer type aluminum electrolytic capacitors, and in particular, separators for lithium ion secondary batteries. It is suitable as. In addition, the form is not specifically limited, For example, it can be a coin type, a pouch type, or a cylindrical type. Moreover, the kind of electrolyte solution is not specifically limited, It can apply with respect to the electrolyte solution of a water system, an organic type, or an ionic liquid.

The separator of the present invention can be manufactured, for example, by the following method.

First, fibers are prepared in order to produce a nonwoven fabric base material that will be the skeleton of the separator. As this fiber, the fiber as described above can be used. That is, a fiber having a low moisture content and excellent electrolytic solution resistance, and a fiber surface composed of a polyolefin resin, a polyester resin, or a polyamide resin (excluding both ends of the fiber), a melting point or a decomposition temperature of 180 It is preferable to prepare a heat-resistant fiber having a temperature of 0 ° C. or higher. In particular, it is preferable to prepare a fully aromatic polyamide fiber or a fully aromatic polyester fiber.

It should be noted that two or more types of organic resins are used so that the fibers are bonded to each other and the internal voids of the nonwoven fabric base material are easily retained, so that the retention of the inorganic particles, the binder polymer, and the polymer electrolyte polymer is excellent. The fiber surface is composed of a low melting point resin (for example, a core-sheath type or sea-island type composite fiber in which the resin is arranged in the cross section of the fiber), or an unstretched fiber (for example, unstretched fiber). It is preferable to prepare a fiber that exhibits an adhesive action by deformation accompanying crystal orientation by heating and pressing, such as a stretched polyester fiber).

Further, the cross-sectional shape of the fiber may be circular or non-circular.

Further, the fiber diameter of the fiber is preferably 0.1 to 20 μm, preferably 0.5 to 16 μm so that the electrical insulation property is excellent and the electrolytic solution retainability is excellent. Is more preferably 0.5 to 13 μm. The fiber length of the fiber is preferably 0.1 to 20 mm, more preferably 0.5 to 15 mm, and still more preferably 1 to 10 mm. Furthermore, it may be a pulp-like fiber having fibrils or may be a fiber not having fibrils, but a pulp-like fiber is preferable because a nonwoven fabric substrate having a uniform and dense pore diameter can be produced. It is.

Next, a fiber web is formed using one kind or two or more kinds of such fibers. Examples of the method for forming the fiber web include direct methods such as a dry method, a wet method, and a melt blow method. However, a wet method is used so that the fibers can be uniformly dispersed and the electrolyte can be held uniformly. It is preferable to form a fiber web. Examples of the preferable wet method include a horizontal long net method, an inclined wire type short net method, a circular net method, and a long net / circular net combination method. In addition, it is suitable for the fiber web to have two or more layers because it can have a dense structure and is more excellent in short circuit prevention.

Also, a composite fiber web may be formed by laminating or combining a fiber web and a base nonwoven fabric. For example, after preparing a base nonwoven fabric, the formed fiber web is laminated on one main surface of the base nonwoven fabric, or short fibers and / or pulp-like fibers are included on one main surface of the base nonwoven fabric. By drawing up the dispersion, a composite fiber web in which short fibers and / or pulp-like fibers are contained in the voids of the base nonwoven fabric may be formed. In addition, when forming a composite fiber web, it is preferable that at least one of the base nonwoven fabric and the fiber web or the dispersion contains heat-resistant fibers, and more preferably both include heat-resistant fibers.

Next, the nonwoven fabric substrate can be formed by bonding the fiber web constituent fibers together. The bonding between the fibers can be performed, for example, by fusing the fibers, an adhesion action due to deformation accompanying the crystal orientation of the unstretched fibers, entanglement between the fibers, and / or adhesion of the binder polymer. When fusing fibers together, they may be performed under no pressure, may be performed under pressure, or may be pressurized after being melted under no pressure. As an apparatus capable of performing such fusion, there are, for example, a thermal calendar, a hot air through heat treatment device, a cylinder contact heat treatment device, and the like. Moreover, when making it adhere | attach by the deformation | transformation accompanying the crystal orientation of an unstretched fiber, it can implement by heating and pressurizing a fiber web, for example, can be implemented by using a heat calendar. Further, when the fibers are entangled with each other, for example, a fluid flow such as a water flow or a needle can be applied to the fiber web. Furthermore, when bonding fibers with a binder polymer, it can be carried out by imparting a binder polymer to the fiber web and exerting an adhesive action of the binder polymer. The binder polymer can be the same binder polymer as the binder polymer that can participate in the bonding of the inorganic particles to the non-woven fabric substrate constituting fiber. The binder polymer can be in the form of an emulsion, suspension, dispersion, or solution, and can be impregnated, applied, or sprayed onto the fiber web, and then dried and bonded.

When the affinity of the nonwoven fabric substrate thus formed with the binder polymer or inorganic particles is insufficient, it is preferable to impart or improve the affinity of the nonwoven fabric substrate. Examples of methods for imparting or improving this affinity include sulfonation treatment (particularly sulfonation treatment with anhydrous sulfuric acid gas), fluorine gas treatment, graft polymerization treatment, discharge treatment (particularly plasma treatment), surfactant treatment, Or hydrophilic resin provision processing etc. can be mentioned.

On the other hand, the inorganic particle provided with respect to a nonwoven fabric base material is prepared. As described above, the inorganic particles preferably have a particle size of 0.01 to 3 μm, more preferably 0.01 to 1 μm, and still more preferably 0.01 to 0.5 μm. The particle size distribution of the inorganic particles _(D 50/2) or more, and preferably in the _{(D 50} × 2) within the following range. The composition of the inorganic particles is preferably silica and / or alumina. Furthermore, the shape of the inorganic particles is preferably a true sphere. In particular, deflagration inorganic particles are preferable.

Furthermore, a binder polymer for bonding the inorganic particles to the nonwoven fabric base fiber is prepared. This binder polymer can be the above-mentioned binder polymer, and a binder polymer made of an acrylic resin that is excellent not only in the adhesion of inorganic particles but also in the permeability and withstand voltage of the electrolyte is suitable. . The binder polymer can be in the form of an emulsion, suspension, dispersion, or solution.

Next, after applying a binder solution in which inorganic particles and a binder polymer are mixed to the nonwoven fabric substrate, drying is performed, and in the internal space of the nonwoven fabric substrate, the precursor separator in which the inorganic particles are bonded to the nonwoven fabric substrate constituting fibers by the binder polymer Can be prepared. The volume ratio (Vr) of the inorganic particles in the precursor separator is 0.1 or more, more preferably 0.15 or more, and the binder polymer is 0.5 to 10 mass% (total amount of the inorganic particles and the binder polymer). The binder solution is preferably applied so as to occupy 1 to 10 mass%, more preferably 2 to 10 mass%.

In addition, the application of the binder solution to the nonwoven fabric base material is not particularly limited as long as the inorganic particles can be applied to the internal voids of the nonwoven fabric base material. For example, the nonwoven fabric base material is immersed in the binder solution. The method can be carried out by a method in which a binder solution is applied to or spread on a nonwoven fabric substrate.

The above is a method for producing a precursor separator in which a binder solution is applied after forming a nonwoven fabric substrate. However, when a nonwoven fabric substrate is produced by adhering a fiber web with a binder polymer, the fiber web is inorganic. A binder solution containing particles and a binder polymer is applied, and the fibers are bonded to each other with a binder polymer. At the same time, inorganic particles are bonded to the fibers with a binder polymer, and a precursor separator can be produced simultaneously with the formation of the nonwoven fabric substrate.

Furthermore, a polymer electrolyte polymer to be applied to the precursor separator is prepared. As described above, the polymer electrolyte polymer is preferably a fluororesin that can form a gel by contact with a non-aqueous solvent (electrolyte), and in particular, a polyvinylidene fluoride-6-propylene fluoride (PVDF-HFP) copolymer. Polyvinylidene fluoride (PVDF) is preferred. The polyelectrolyte polymer can be in the form of an emulsion, suspension, dispersion, or solution.

Then, after applying the polymer electrolyte polymer solution to the precursor separator, the polymer electrolyte is dried, and the polymer electrolyte is formed in the voids formed by the nonwoven fabric substrate constituent fibers, the inorganic particles, and the binder polymer in the voids of the nonwoven fabric substrate. A separator having a polymer can be prepared. The amount of the polymer electrolyte polymer in this separator is preferably 2 to 18 mass% of the whole separator, more preferably 3 to 17.5 mass%, further preferably 3.5 to 17 mass%, still more preferably 3.5 to 17 mass%. Apply polyelectrolyte polymer solution to occupy.

The application of the polymer electrolyte polymer solution to the precursor separator is not particularly limited as long as the polymer electrolyte polymer can be applied to the internal voids of the precursor separator. For example, the precursor separator is attached to the polymer electrolyte. It can be carried out by a method of immersing in a polymer solution or a method of applying or dispersing a polymer electrolyte polymer solution to a precursor separator. In particular, according to the method of applying the polyelectrolyte polymer solution to the precursor separator, a dense structure in which the polyelectrolyte polymer exists in the voids formed by the non-woven fabric substrate constituent fibers, the inorganic particles, and the binder polymer, The molecular electrolyte polymer is preferred because it easily absorbs the electrolyte during battery construction and swells to form a barrier layer.

In addition, when the water content in the separator is large, the charge / discharge characteristics of the electrochemical element tend to be deteriorated. Therefore, it is preferable to dry the water so that the water content is small. For example, drying at a temperature of 120 ° C. or higher is preferable, drying at a temperature of 130 ° C. or higher is more preferable, and drying at a temperature of 140 ° C. or higher is particularly preferable. On the other hand, the upper limit of the drying temperature varies depending on the heat resistance of the separator and is not particularly limited. However, from the viewpoint of removing moisture, it is sufficient up to 180 ° C. May be.

According to the above method, the binder solution is applied to the nonwoven fabric substrate and dried to prepare a precursor separator, and then the polymer electrolyte polymer solution is applied to the precursor separator and dried. A separator in which the polymer electrolyte polymer and the binder polymer are separated from each other in the voids formed by the nonwoven fabric base-constituting fibers, the inorganic particles, and the binder polymer can be produced.

Examples of the present invention will be described below, but the present invention is not limited to the following examples.

(Preparation of base material)
(1) Preparation of nonwoven fabric substrate A;
Polyethylene terephthalate short fibers (fineness: 0.2 dtex, fiber diameter: 4.3 μm, fiber length: 3 mm, melting point: 260 ° C., cross-sectional shape: circular) are derived from unstretched polyethylene terephthalate short fibers (melting point: 260 ° C.) A wet nonwoven fabric (weight per unit: 9 g / m ² , thickness: 10 μm, porosity: 56%) bonded and fixed with a resin was prepared as a base nonwoven fabric.

Next, polyethylene terephthalate unstretched short fibers (fineness: 0.2 dtex, fiber diameter: 4.3 μm, fiber length: 3 mm, melting point: 260 ° C., cross-sectional shape: circular) and pulp-like wholly aromatic polyamide fibers (freeness) : 50 ml CSF, decomposition temperature: about 500 ° C.) in a mass ratio of 20:80 was prepared.

Then, after drawing up the dispersion on one main surface of the base non-woven fabric, water as a dispersion medium is suctioned and removed from the base non-woven fabric side, and polyethylene terephthalate uncoated on one main surface of the base non-woven fabric. A composite fiber having a fiber accumulation layer in which stretched short fibers and pulp-like wholly aromatic polyamide fibers are mixed, and part of the fibers constituting the fiber accumulation layer enter the voids of the base nonwoven fabric and entangle with the base nonwoven fabric constituting fibers. A web was formed.

Subsequently, while the composite fiber web is supported on the conveyor, the composite fiber web is dried by heat treatment in an atmosphere at a temperature of 145 ° C., and then heated and pressurized through a heat roll adjusted to a surface temperature of 180 ° C. By using the drawn short fiber, the polyethylene terephthalate undrawn short fiber itself and the pulp-like wholly aromatic polyamide fiber are bonded to the base non-woven fabric to form a two-layer composite non-woven fabric (= nonwoven fabric substrate A, basis weight: 12 g / m ² , thickness : 17 μm, heat-resistant fiber ratio: 20 mass%).

(2) Preparation of nonwoven fabric substrate B;
Polyethylene terephthalate unstretched short fiber (fineness: 0.2 dtex, fiber diameter: 4.3 μm, fiber length: 3 mm, melting point: 260 ° C., cross-sectional shape: circular) and pulp-like wholly aromatic polyamide fiber (freeness: 80 ml CSF) , Decomposition temperature: about 500 ° C.) in a mass ratio of 30:70 was prepared.

And after making up the said dispersion liquid, the water which is a dispersion medium is suctioned and removed, and after forming a fiber web, it heat-processes in the atmosphere of a temperature of 145 degreeC, supporting a fiber web with a conveyor. After drying the fiber web, it is heated and pressurized through a heat roll whose surface temperature is adjusted to 180 ° C., and the non-stretched short fibers of polyethylene terephthalate are used to bond the pulp-like wholly aromatic polyamide fibers together to form a single-layer nonwoven fabric ( = Nonwoven fabric base material B, basis weight: 12 g / m ² , thickness: 17 μm, heat-resistant fiber ratio: 70 mass%)).

(3) Preparation of nonwoven fabric substrate C;
Fused fiber (average fiber diameter: 0.8 dtex, fiber diameter: 10.5 μm, fiber length: 5 mm) whose core component is made of polypropylene (melting point: 168 ° C.) and whose sheath component is made of high-density polyethylene (melting point: 135 ° C.) , The cross-sectional shape: circular) only, and a wet fiber web was formed by an inclined wire type short net wet method.

Next, the wet fiber web is supported by a conveyor, and sucked from below the conveyor to convey the wet fiber web in close contact with the conveyor. By heat-treating, only the sheath component of the fused fiber was fused to produce a fused nonwoven fabric (= base nonwoven fabric, basis weight: 10 g / m ² ).

On the other hand, after preparing polypropylene fine fibers (fineness: 0.02 dtex, fiber diameter: 1.7 μm, fiber length: 2 mm, melting point: 168 ° C., cross-sectional shape: circular), a dispersion in which polypropylene fine fibers are dispersed is prepared. did.

And after drawing up the said dispersion liquid on one main surface of a base nonwoven fabric, the water which is a dispersion medium is suctioned and removed from the base nonwoven fabric side, and a polypropylene microfiber is formed on one main surface of a base nonwoven fabric. While having a deposited layer, a part of the polypropylene ultrafine fibers entered the voids of the base nonwoven fabric to form a composite fiber web integrated with the base nonwoven fabric constituting fibers.

Subsequently, while the composite fiber web is supported on the conveyor, the composite fiber web is dried by heat treatment in an atmosphere at a temperature of 138 ° C., and at the same time, the fusion fibers constituting the base nonwoven fabric are re-fused, and the polypropylene ultrafine fiber is used as the base. A composite nonwoven fabric having a two-layer structure (= nonwoven fabric substrate C, basis weight: 13 g / m ² , thickness: 25 μm) was prepared by fusing to a nonwoven fabric.

(4) Preparation of microporous membrane substrate D;
A commercially available polypropylene microporous membrane (registered trademark: Celgard, product number: 2400, basis weight: 15 g / m ² , thickness: 25 μm) was prepared as the microporous membrane substrate D.

(Preparation of binder solution)
(1) Preparation of binder solution a;
As inorganic particles, a deflagration silica particle dispersion [shape: true sphere, particle size: 450 nm, particle size distribution: 225 to 900 nm, 2-propanol aqueous solution (10 wt%), solid content concentration: 45 mass%] was prepared. Moreover, acrylic resin dispersion (solid content concentration: 45%) was prepared as a binder polymer.

Next, a binder solution a (acrylic resin was 3 mass% of the total amount of deflagration silica particles and acrylic resin) was prepared with the following composition.

(A) Acrylic resin dispersion: 1.5 mass%
(I) Deflagration silica particle dispersion: 48.5 mass%
(U) Water: 50 mass%

(2) Preparation of binder solution b;
As inorganic particles, an alumina particle dispersion [shape: crushed, particle size: 790 nm, particle size distribution: 395 to 1580 nm, 2-propanol aqueous solution (10 wt%), solid content concentration: 45 mass%] was prepared. Moreover, acrylic resin dispersion (solid content concentration: 45%) was prepared as a binder polymer.

Next, a binder solution b (acrylic resin was 3 mass% of the total amount of alumina particles and acrylic resin) was prepared with the following composition.

(A) Acrylic resin dispersion: 1.5 mass%
(A) Alumina particle dispersion: 48.5 mass%
(U) Water: 50 mass%

(3) Preparation of binder solution c;
As inorganic particles, a deflagration silica particle dispersion [shape: true sphere, particle size: 450 nm, particle size distribution: 225 to 900 nm, 2-propanol aqueous solution (10 wt%), solid content concentration: 45 mass%] was prepared. Moreover, acrylic resin dispersion (solid content concentration: 45%) was prepared as a binder polymer. Furthermore, as the polymer electrolyte polymer, polyvinylidene fluoride-6-propylene fluoride (PVDF-HFP) particles [average particle size: 1 μm] were prepared.

Next, a binder solution c (acrylic resin was 3 mass% of the total amount of deflagration silica particles and acrylic resin) was prepared with the following composition.

(A) Acrylic resin dispersion: 1.5 mass%
(I) Deflagration silica particle dispersion: 48.5 mass%
(U) Water: 49.6 mass%
(D) PVDF-HFP particles: 0.4 mass%

(Preparation of polymer electrolyte polymer solution)
(1) Preparation of polyelectrolyte polymer solution i;
Polyvinylidene fluoride-6-propylene fluoride (PVDF-HFP) was prepared as the polymer electrolyte polymer. Next, PVDF-HFP was dissolved in N-methylpyrrolidone (NMP) to prepare a polymer electrolyte polymer solution i (solid content concentration: 3 mass%).

(2) Preparation of polyelectrolyte polymer solution ii;
Polyvinylidene fluoride (PVDF) was prepared as a polymer electrolyte polymer. Next, PVDF was dissolved in N-methylpyrrolidone (NMP) to prepare a polymer electrolyte polymer solution ii (solid content concentration: 3 mass%).

(Examples 1 to 6)
The binder solution a (containing deflagration silica particles) was applied to the fiber deposition layer surface of the nonwoven fabric substrate A using a gravure roll coating machine, and then dried with a dryer to obtain a precursor separator (weight per unit: 17.5 g / m ² , Thickness: 27 μm, inorganic particle volume ratio: 0.28) was prepared. In this precursor separator, deflagration silica particles are adhered to the constituent fibers of the nonwoven fabric substrate A by an acrylic resin binder in the internal space of the nonwoven fabric substrate A, and the fiber deposition layer surface of the nonwoven fabric substrate A The deflagration silica particles were adhered to the fibers constituting the material by an acrylic resin binder.

Next, the polymer electrolyte polymer solution i is applied to the application surface of the binder solution a of the nonwoven fabric substrate A using a gravure roll coating machine, followed by drying with a drier, the basis weight and thickness shown in Table 1 A separator according to the present invention having was prepared. The PVDF-HFP amount (solid content) was adjusted to 0.2 g / m ² (Example 1), 0.4 g / m ² (Example 2), 0.7 g / m ² by adjusting the coating amount. (Example 3) 1.7 g / m ² (Example 4), 3.4 g / m ² (Example 5), and 4.0 g / m ² (Example 6). These separators have PVDF-HFP in the voids formed by the constituent fibers of the nonwoven fabric substrate A, the deflagration silica particles, and the acrylic resin binder in the internal voids of the nonwoven fabric substrate A, and PVDF-HFP is an acrylic resin. The binder was coated and separated from the acrylic resin binder.

(Example 7)
A separator having the basis weight and thickness shown in Table 2 was prepared in the same manner as in Example 3 except that the nonwoven fabric substrate A was used instead of the nonwoven fabric substrate A. This separator has PVDF-HFP in the void formed by the constituent fibers of the nonwoven fabric base material B, the deflagration silica particles, and the acrylic resin binder in the internal space of the nonwoven fabric base material B. PVDF-HFP is an acrylic resin. The binder was coated and separated from the acrylic resin binder.

(Example 8)
A separator having the basis weight and thickness shown in Table 2 was prepared in the same manner as in Example 3 except that the binder solution b (containing alumina particles) was used instead of the binder solution a (containing deflagration silica particles). This separator has PVDF-HFP in the voids formed by the constituent fibers of the nonwoven fabric substrate A, the alumina particles, and the acrylic resin binder in the internal voids of the nonwoven fabric substrate A. PVDF-HFP is an acrylic resin binder. And was separated from the acrylic resin binder.

Example 9
A separator having the basis weight and thickness shown in Table 2 was obtained in the same manner as in Example 2 except that the polymer electrolyte polymer solution ii (PVDF) was used instead of the polymer electrolyte polymer solution i (PVDF-HFP). Prepared. This separator has PVDF in the void formed by the constituent fibers of the nonwoven fabric substrate A, the silica particles, and the acrylic resin binder in the internal void of the nonwoven fabric substrate A, and the PVDF covers the acrylic resin binder, It was in a state separated from the acrylic resin binder.

(Comparative Example 1)
A separator having the basis weight and thickness shown in Table 3 was prepared in the same manner as in Example 3 except that the polymer electrolyte polymer solution i was not applied to the precursor separator. That is, the precursor separator was a separator.

(Comparative Example 2)
A separator having the basis weight and thickness shown in Table 3 was prepared in the same manner as in Example 3 except that the microporous membrane substrate D was used instead of the nonwoven fabric substrate A. In addition, when the silica particles are filled in the micropores of the microporous membrane substrate D, the movement of ions is inhibited. Therefore, when preparing this separator, the silica particles are placed in the micropores of the microporous membrane substrate D. A layer of silica particles and an acrylic resin binder was formed on the surface of the microporous membrane substrate D so as not to be filled. Therefore, this separator has PVDF-HFP in the space between the silica particles and the acrylic resin binder, and the PVDF-HFP is covered with the acrylic resin binder and separated from the acrylic resin binder.

(Comparative Example 3)
A separator having the basis weight and thickness shown in Table 3 was prepared in the same manner as in Comparative Example 2 except that the polymer electrolyte polymer solution i was not applied to the precursor separator. That is, the precursor separator was a separator.

(Reference Example 1)
A separator having the basis weight and thickness shown in Table 3 was prepared in the same manner as in Example 3 except that the nonwoven fabric substrate A was used instead of the nonwoven fabric substrate A. This separator has PVDF-HFP in the void formed by the constituent fibers of the nonwoven fabric substrate C, the deflagration silica particles, and the acrylic resin binder in the internal void of the nonwoven fabric substrate C. The PVDF-HFP is an acrylic resin. The binder was coated and separated from the acrylic resin binder.

(Reference Example 2)
A separator having the basis weight and thickness shown in Table 3 was obtained in the same manner as in Example 2 except that the binder solution c was used instead of the binder solution a, and the polymer electrolyte polymer solution i was not applied. Prepared. This separator was in a state in which silica particles and PVDF-HFP particles were adhered to the constituent fibers of the nonwoven fabric substrate A by an acrylic resin binder on the constituent fibers of the nonwoven fabric substrate A in the internal voids of the nonwoven fabric substrate A. Thus, the acrylic resin binder and the PVDF-HFP particles were in a mixed state.

(Production of lithium ion secondary battery)
(1) Production of positive electrode;
Lithium nickel cobaltate [Li (NiCoAl) O ₂ ] (= NCA) and acetylene black (= AB) were prepared. Polyvinylidene fluoride (= PVDF) was prepared, and PVDF was dissolved in N-methylpyrrolidone (= NMP) to prepare a PVDF solution (solid content concentration: 13 mass%).

Next, NCA, AB, and PVDF were mixed to prepare a positive electrode material paste such that NCA: AB: PVDF = 93: 4: 3 at a solid mass ratio of NCA, AB, and PVDF.

Subsequently, this positive electrode material paste was applied onto an aluminum foil having a thickness of 20 μm, dried and then pressed to produce a positive electrode (capacity: 2.43 mAh / cm ² ). Subsequently, the terminal was connected to the aluminum foil part of the electrode with an ultrasonic welding machine.

(2) Production of negative electrode;
Natural graphite powder, hard carbon (= HC), and an acrylic binder (solid content concentration: 13 mass%) were prepared.

Next, natural graphite powder, natural graphite powder, so that (natural graphite powder): HC: (acrylic binder) = 87.3: 9.7: 3 by solid content mass ratio of natural graphite powder, HC and acrylic binder, A negative electrode material paste was prepared by mixing HC and an acrylic binder.

Subsequently, this negative electrode material paste was applied onto a copper foil having a thickness of 15 μm, dried, and pressed to prepare a negative electrode (capacitance: 2.51 mAh / cm ² ). Next, a terminal was connected to the copper foil portion of the produced negative electrode by an ultrasonic welding machine.

(3) Preparation of non-aqueous electrolyte solution;
LiPF ₆ was dissolved to a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed so that the volume ratio was (50:50) to prepare a non-aqueous electrolyte solution.

(4) Production of lithium ion secondary battery;
After laminating each separator between the positive electrode paste applied surface of the positive electrode and the negative electrode paste applied surface of the negative electrode, the laminate was dried at a temperature of 150 ° C. for 12 hours, did.

Thereafter, the electrode laminate was inserted into an aluminum laminate bag coated with a polyester resin, and after pouring the non-aqueous electrolyte, the laminate type lithium ion secondary battery was produced by vacuum lamination. .

(Battery performance test)
(1) Confirm initial capacity;
Each lithium ion secondary battery was activated by charging at a constant current / constant voltage of 0.2 C from 2.0 V to 4.2 V, and the initial battery capacity was confirmed. These results are shown in Tables 1 to 3.

(2) Confirmation of battery capacity after overdischarge;
Charging / discharging with a cycle of (constant current / constant voltage charging of 0.2C from 2.0V to 4.2V)-(constant current discharging from 0.06C to 0V)-(left for 1 hour at circuit voltage) After 10 cycles, 0.2 C constant current / constant voltage charge was performed from 2.0 V to 4.2 V, and the battery capacity after 0 V discharge, that is, after overdischarge was confirmed. These results are shown in Tables 1 to 3.

(Discussion)
From Tables 1 to 3, the following was found.
(A) From the comparison between Example 3 and Comparative Example 1, it was found that the battery capacity after overdischarge was maintained by including the polymer electrolyte polymer. That is, it was found that the short circuit prevention property by dendrite is excellent.
(B) From the comparison between Examples 2 and 3 and Comparative Example 2, an electrochemical device having a large initial battery capacity and a large battery capacity after overdischarge is produced by the base material carrying inorganic particles or the like having a nonwoven fabric structure. I understood that I could do it.
(C) From the comparison between Examples 2 and 3 and Reference Example 1, it is preferable to dry at a temperature of 120 ° C. or higher in order to remove moisture, but if the heat resistance of the nonwoven fabric substrate is insufficient, the initial Since both the battery capacity and the battery capacity after overdischarge tend to be small, it has been found that the nonwoven fabric substrate preferably contains heat-resistant fibers.
(D) From the results of Examples 1 to 6, it was found that the amount of the polymer electrolyte polymer is preferably 2 to 18 mass% of the whole separator.
(E) From the results of Examples 3 and 7, the nonwoven fabric base material has a single-layer structure or a two-layer structure, and both the initial battery capacity and the battery capacity after overdischarge are large. It was found that the structure of the nonwoven fabric substrate does not affect the short circuit prevention.
(F) From the results of Example 3 and Example 8, even if the inorganic particles are silica or alumina, both the initial battery capacity and the battery capacity after overdischarge are large, so that the short-circuit prevention property by dendrites is inorganic. It was found that the composition of the particles had no effect.
(G) From the results of Example 2 and Example 9, since the battery capacity after overdischarge was maintained, it was excellent in short circuit prevention by dendrite regardless of the type of polymer electrolyte polymer. I understood.
(H) From the results of Example 2 and Reference Example 2, it was found that the polymer electrolyte polymer is not mixed with the binder polymer, and is preferably coated with the binder polymer and separated from the binder polymer.

Since the separator of the present invention has excellent short circuit prevention and heat resistance due to dendrites, it is a lithium ion secondary battery, an electric double layer capacitor such as a lithium ion capacitor, an electrolytic capacitor such as an aluminum electrolytic capacitor, a solid polymer type aluminum electrolysis It can be suitably used as a separator for capacitors and the like, and can be particularly suitably used as a separator for lithium ion secondary batteries.

Claims

In the internal space of the nonwoven fabric substrate,
The inorganic particles are bonded to the non-woven fabric base fiber with a binder polymer, and a polymer electrolyte polymer is provided in a void formed by the non-woven fabric base material fiber, the inorganic particles, and the binder polymer. A separator for electrochemical devices.
2. The separator for an electrochemical element according to claim 1, wherein the amount of the polymer electrolyte polymer occupies 2 to 18 mass% of the whole separator for an electrochemical element.
The separator for an electrochemical element according to claim 1 or 2, wherein the inorganic particles are silica and / or alumina.
The separator for an electrochemical element according to any one of claims 1 to 3, wherein the nonwoven fabric base material is a composite nonwoven fabric in which short fibers and / or pulp fibers are contained in the gaps of the base nonwoven fabric.
The separator for an electrochemical element according to any one of claims 1 to 4, wherein the nonwoven fabric constituting fiber includes a heat-resistant fiber having a melting point or decomposition temperature of 180 ° C or higher.