JP2012094288A - Separator for electrochemical element and electrochemical element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for electrochemical elements excellent in permeability of electrolyte, high in puncture strength before and after permeation of the electrolyte and excellent in dendrite resistance and pressure resistance, and to provide an electrochemical element which is low in internal resistance, hardly causes short circuit and is excellent in high-rate characteristics even under high pressure.SOLUTION: A separator for electrochemical elements includes wet-type nonwoven fabric obtained by wet paper-making using slurry containing an aggregate of acrylic polymer particles and fibrillated fibers.

Description

  The present invention relates to a separator for an electrochemical element and an electrochemical element using the same.

  Conventionally, a microporous film made of a polyolefin resin has been used as a separator for a lithium secondary battery. Recently, as a separator for a lithium secondary battery, a separator made of a woven or non-woven porous sheet and insulating fine particles (see, for example, Patent Document 1), a resin porous membrane and / or A separator for electronic parts in which fine particles are dispersed on the surface (see, for example, Patent Document 2), plate-like inorganic fine particles having an average thickness of 0.1 μm or less, and spherical organic fine particles having an average particle size smaller than the inorganic fine particles, A battery separator having a binder resin (see, for example, Patent Document 3), fine particles (swellable fine particles) that can swell by absorbing a non-aqueous electrolyte and whose degree of swelling increases with an increase in temperature. A lithium secondary battery (see, for example, Patent Document 4), a secondary battery including a separator made of a porous membrane and resin fine particles (for example, see Patent Document 5), regeneration Non-aqueous battery using paper containing beaten raw material cellulose as a separator (e.g., see Patent Document 6) have been disclosed.

  The separator of patent document 1 is produced by the method of apply | coating the slurry which has insulating fine particles to the porous sheet formed by laminating | stacking two or more layers. However, since the porous sheet is a woven fabric or a non-woven fabric, it is difficult to have the strength to withstand the coating operation, and the two-layer porous sheet is displaced, wrinkled, broken, and the slurry penetrates the porous sheet. Problems such as poor coating workability, problems that the porous sheet tends to stretch in the flow direction during drying, and wrinkles, the binder resin fills part or all of the voids of the porous sheet, and electrolyte permeability and If the amount of the binder is reduced so that the binder component does not fill the voids in the porous sheet, the pinholes in the porous sheet may remain or the strength may be insufficient. There was a problem that it was very difficult to balance the amount of binder.

  The separator of Patent Document 2 forms a film by applying a resin solution prepared by adding a poor solvent and fine particles to a resin solution in which a vinylidene fluoride homopolymer is dissolved, for example, on a substrate such as a resin film or a glass plate And after drying, it is produced by a method of peeling from the substrate. In this method, since it takes a long time to remove the solvent, the production efficiency is poor, the separator obtained by peeling from the base material is brittle, the puncture strength, tear strength, tensile strength, etc. are weak, and it is damaged during handling. There are cases where it is difficult to remove the separator from the base material because the resin and the base material adhere to each other.

  The separator of Patent Document 3 includes: 1) a plate-like inorganic fine particle having an average thickness of 0.1 μm or less on a sheet-like material such as a woven fabric or a nonwoven fabric; an organic fine particle having an average particle size smaller than the inorganic fine particle; and a binder resin. 2) A method of applying or impregnating a slurry containing 2) A method of applying the slurry onto a substrate such as a film or a metal foil, and peeling it from the substrate after drying. 3) Applying the slurry onto an electrode and drying. In this way, the separator is directly formed on the electrode. However, in the method 1), the inorganic fine particles and the organic fine particles are too small to close the large through-holes of several μm or more in the sheet-like material, and a pinhole is formed. If the amount of the binder is reduced to prevent the binder component from filling the gaps in the sheet-like material, a problem that deteriorates the permeability or retention of the electrolyte solution due to filling part or all of the gaps. Pinholes may remain or strength may be insufficient, and it is very difficult to balance the amount of binder. The separator produced by the method 2) is brittle and has a weak puncture strength, tear strength, tensile strength, and the like, and has a problem of being easily damaged during handling. In some cases, the binder resin adheres to the substrate, and only the separator cannot be peeled from the substrate. The separator produced by the method 3) has a problem that cracks and peeling occur during the winding operation and the cutting operation.

  In the lithium secondary battery of Patent Document 4, when the swellable fine particles are contained in the separator, the separator is 1) a method of applying or impregnating a slurry containing the swellable fine particles to a sheet-like material such as a woven fabric or a non-woven fabric. A method in which a fibrous material is included in a slurry containing swellable fine particles as required, and this is applied onto a substrate such as a film or a metal foil, dried, and then peeled off from the substrate. 3) It is produced by any method of blending a fibrous material and producing a porous film by a conventionally known method. In the method 1), there is a problem that the woven fabric and the non-woven fabric are not easily strong enough to withstand the coating operation, and wrinkles and breaks, and the slurry penetrates the sheet-like material and the coating workability is poor. In addition, in order to support the swellable fine particles on the sheet-like material later as in the method 1), a binder component is substantially required, and the binder component covers the swellable fine particles. The problem that the effect is not manifested, the binder component fills part or all of the gap of the sheet-like material, the problem of worsening the permeability and retention of the electrolyte, the binder component does not fill the gap of the sheet-like material Thus, if the amount of the binder is reduced, pinholes in the sheet-like material may remain or the strength may be insufficient, and it is very difficult to balance the amount of the binder. The separator produced by the method 2) is fragile and has poor puncture strength, tear strength, tensile strength, and the like, and is easily damaged during handling. The binder component and the base material adhere to each other, so that only the separator cannot be peeled off from the base material. There was a case. About the method of 3), since the specific example is not described, it is unknown, but it is estimated that it is based on the melt extrusion method or the phase separation method. The melt extrusion method has a problem of poor heat resistance in the case of polyethylene or polypropylene. In the case of the phase separation method, there is a problem that it is difficult to produce a separator having high uniformity continuously.

  The secondary battery of Patent Document 5 prepares a paste in which resin particles B not dissolved in a solution are dispersed in a solution in which a porous resin A is dissolved, and this is applied to the electrode surface, and a separator is formed directly on the electrode. Formed. The solvent that dissolves the porous resin A is substantially an organic solvent. This separator has no problem of poor battery characteristics because it does not have pores and the electrolyte does not penetrate.

  In the non-aqueous battery of Patent Document 6, paper is used as a separator. When the paper is infiltrated with the electrolytic solution, the entanglement between the cellulose fibers is loosened, the puncture strength is lowered, and the pressure resistance is lowered. For this reason, when an electrode and a separator are brought into close contact with each other with a strong pressure when manufacturing a laminated or laminated battery, there is a problem that an electrode burr or an electrode active material penetrates the separator and is short-circuited.

  When the separator has poor electrolyte solution permeability, the electrochemical elements equipped with these separators have a high internal resistance, and there is a problem that the battery characteristics when charged / discharged with a large current, that is, the high rate characteristics are extremely poor.

JP 2008-4442 A JP 2004-281208 A JP 2009-64566 A JP 2008-4441 A JP 2004-241135 A Japanese Patent No. 3661104

  The problem of the present invention is that the electrolyte solution has good permeability, strong puncture strength before and after electrolyte solution penetration, excellent dendrite resistance and pressure resistance, and has a low internal resistance and is not easily short-circuited. An object of the present invention is to provide an electrochemical device having excellent high rate characteristics even under high pressure.

  As a result of diligent research to solve the above-mentioned problems, the present inventors have made a separator for an electrochemical device comprising a wet nonwoven fabric obtained by wet papermaking a slurry containing an aggregate of acrylic polymer particles and fibrillated fibers. (Hereinafter, sometimes referred to as “separator”) and an electrochemical device using the same.

  The separator for an electrochemical element of the present invention is made of a wet nonwoven fabric obtained by wet papermaking a slurry containing an aggregate of acrylic polymer particles and fibrillated fibers, and therefore a resin or binder that easily forms a film such as latex. Is not required, and the gap between the acrylic polymer particles, the gap between the acrylic polymer particles and the fibers, and the gap between the fibers are not blocked by a resin or binder, and the electrolyte has excellent permeability and internal resistance. Low electrochemical device. In addition, since the piercing strength before and after electrolyte penetration is strong and excellent in pressure resistance, an electrochemical element that prevents electrode burr and electrode active material from penetrating, short-circuiting, and excellent in high-rate characteristics even under high pressure can get. By laminating the acrylic polymer particles in multiple layers, even if dendrite is generated on the electrode surface, the dendrite hardly penetrates the separator and is excellent in dendrite resistance.

An example of the surface electron micrograph (1000 magnification) in the separator produced in Example 6 of this invention is shown. An example of the electron micrograph (1000 magnification) of the cross section in the separator produced in Example 6 of this invention is shown.

  In the present invention, the acrylic polymer is a homopolymer or copolymer of an acrylic monomer. Examples of acrylic monomers include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, Pentyl (meth) acrylate, hexyl (meth) acrylate, (meth) 2-ethylhexyl acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate , Alkyl methacrylates such as dodecyl (meth) acrylate, phenyl (meth) acrylate, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, propoxyethyl (meth) acrylate, (meth) acrylic acid Butoxyethyl, ethoxypropyl (meth) acrylate (Meth) acrylic acid alkoxyesters such as, dialkylaminoalkyl (meth) acrylates such as diethylaminoethyl (meth) acrylate, and (poly) alkylene glycol di (meth) acrylic acid esters include di (meth) acrylic Of ethylene glycol acid, diethyl glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, di (meth) acrylic acid ester of polyethylene glycol, di (meth) acrylic acid ester of dipropylene glycol, tripropylene glycol Di (meth) acrylic acid esters and polyvalent (meth) acrylic acid esters include (meth) acrylic acid esters of alicyclic alcohols such as trimethylolpropane tri (meth) acrylic acid and cyclohexyl (meth) acrylic acid. These may be either a copolymer with a homopolymer thereof.

  Other monomers that can be copolymerized with the above acrylic monomers include, for example, vinyl pyridine, vinyl pyrrolidone, vinyl carbazole, vinyl acetate, vinyl propionate, vinyl laurate, vinyl stearate, vinyl benzoate, acrylonitrile, vinyl. Vinyl groups such as toluene, α-methylstyrene, butadiene, isoprene, chloroprene, vinyl chloride, vinyl bromide, vinylidene chloride, vinylidene bromide, vinylidenes, vinyl ethers, vinyltrimethoxysilane, vinyltriethoxysilane, divinylbenzene, etc. Monomer having, styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, diethyl styrene, triethyl styrene, propyl styrene, butyl styrene, hexyl styrene Alkyl styrene such as ethylene, heptyl styrene, octyl styrene, fluorostyrene, chlorostyrene, bromostyrene, dibromostyrene, iodostyrene, halogenated styrene such as chloromethylstyrene, (meth) acrylic acid, α-ethyl (meth) acrylic acid , Crotonic acid, α-methylcrotonic acid, α-ethylcrotonic acid, isocrotonic acid, tiglic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid and hydromuconic acid.

  The acrylic polymer used in the present invention is preferably a crosslinked structure since it is excellent in resistance to electrolytic solution and heat resistance. Examples of the crosslinking agent include ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and tri (meth). Pentaerythritol acrylate, 1,1,1-trishydroxymethylethanediacrylic acid, 1,1,1-trishydroxymethylethanetriacrylic acid, 1,1,1-trishydroxymethylpropanetriacrylic acid, vinylbenzene Can be mentioned.

  Acrylic polymer particles can be produced by methods such as emulsion polymerization, soap-free emulsion polymerization, and dispersion polymerization. The acrylic polymer particles are preferably spherical or substantially spherical. Examples of the particle diameter include a general-purpose type having a particle size distribution and a monodispersed type in which the particle diameters are substantially uniform, but a monodispersed type is preferable because a highly uniform separator can be obtained. The general-purpose particle size can be confirmed by measuring with a laser diffraction particle size distribution measuring device, and the monodisperse particle size can be confirmed with a laser diffraction particle size distribution measuring device or electron microscope observation. When the general-purpose type is measured with a laser diffraction particle size distribution analyzer, the particle diameter when the mass ratio is 50%, that is, D50 is preferably 0.1 to 10 μm, more preferably 1 to 8 μm. If D50 is less than 0.1 μm, the effect of adding acrylic polymer particles may not be obtained because it is too small. If it is greater than 10 μm, it may be difficult to reduce the thickness of the separator. The average particle size of the monodispersed type is preferably from 0.1 to 10 μm, more preferably from 1 to 8 μm, still more preferably from 3 to 6 μm. If the average particle size of the monodisperse type is less than 0.1 μm, the effect of adding acrylic polymer particles may not be obtained because it is too small. If it is greater than 10 μm, the volume of the acrylic polymer in the separator increases. In some cases, the electrical resistance of the separator is increased, and it is difficult to reduce the thickness of the separator.

  5-80 mass% is preferable, as for the content rate of the acrylic polymer particle in the separator of this invention, 6-70 mass% is more preferable, and 10-60 mass% is further more preferable. If the amount is less than 5% by mass, the effect of adding acrylic polymer particles may be difficult to obtain. If the amount is more than 80% by mass, the separator may have insufficient tensile strength or puncture strength, or the thickness of the separator may be reduced. It may be difficult.

  The separator of the present invention is produced by wet papermaking a slurry containing an aggregate of acrylic polymer particles and fibrillated fibers. In order to form an aggregate of acrylic polymer particles and fibrillated fibers, a slurry in which acrylic polymer particles and fibrillated fibers are separately dispersed in a medium is prepared, and both slurries are mixed and stirred. . The medium is preferably water, but an organic solvent such as alcohols may be mixed. In order to confirm whether or not the particles are aggregated, it is only necessary to visually confirm whether or not aggregates are formed and whether or not the slurry is cloudy. When the slurry is cloudy, it means that there are many acrylic polymer particles that are not aggregated. When it is difficult to aggregate only by mixing the acrylic polymer particles and the fibrillated fiber, a flocculant is added. After forming the aggregate, if necessary, non-fibrillated fibers and additives are mixed and diluted to a predetermined solid content concentration to prepare a raw slurry. The raw material slurry is subjected to wet paper making with a paper machine to obtain the separator of the present invention.

  Examples of fibrillated fibers include fibers formed by fibrillating natural fibers, regenerated fibers, synthetic fibers, and the like. Examples of natural fibers include cellulose fibers derived from wood, cellulose fibers derived from non-wood such as hemp, cotton, and sugarcane, biocellulose fibers, wool, and silk. Examples of regenerated fibers include solvent-spun cellulose fibers and cupra fibers. Synthetic fibers include polypropylene, polyethylene, polymethylpentene, polyester, polyester derivatives, acrylic polymers, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl chloride, polyvinylidene chloride, polyvinyl ether, polyvinyl ketone, poly Ether, polyvinyl alcohol, aliphatic polyamide, aromatic polyamide, wholly aromatic polyamide, wholly aromatic polyester, polyamideimide, polyimide, polyetheretherketone, polyphenylene sulfide, polybenzimidazole, poly-p-phenylenebenzobisthiazole, poly Examples thereof include fibers made of a resin such as -p-phenylenebenzobisoxazole and polytetrafluoroethylene. Among these, fibrillated fibers made of wholly aromatic polyamide or wholly aromatic polyester are preferable because of their excellent aggregation ability. The degree of fibrillation is preferably 0 to 600 ml, more preferably 0 to 500 ml, and even more preferably 0 to 400 ml, according to JIS P8121. If the Canadian standard freeness is larger than 600 ml, the ratio of the thick fiber diameter increases, so that the aggregation with the acrylic polymer particles becomes non-uniform, and the separator may have unevenness or thickness unevenness.

  When the degree of fibrillation exceeds a certain level, the fiber length becomes too short, and the fibrillated fiber passes through the hole in the sieve plate used for the measurement of Canadian standard freeness. Accurate freeness cannot be measured. In that case, the modified freeness is adopted in the present invention. The modified freeness in the present invention was measured in accordance with JIS P811, except that an 80 mesh wire net having a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as a sieve plate, and the sample concentration was 0.1%. Freeness. The modified freeness of the fibrillated fiber used in the present invention is preferably 0 to 400 ml, more preferably 0 to 300 ml. When it exceeds 400 ml, the ratio of the thick fiber diameter increases, so that the aggregation with the acrylic polymer particles becomes non-uniform, and there are cases where separators and thickness spots of the separator occur.

  Therefore, the fibrillated fiber in the present invention is preferably used if the Canadian standard freeness is in the range of 0 to 600 ml or the modified freeness is in the range of 0 to 400 ml. In general, the modified freeness value is larger than the Canadian standard freeness value. For example, in the fibrillated fibers shown in Table 1, F6, F8, and F11 indicate values that are greater in Canadian standard freeness than in modified freeness. This means that the fiber length of the fibrillated fiber is short and slips through the sieve plate of Canadian standard freeness, so that it does not show accurate Canadian standard freeness.

In the present invention, only one type of fibrillated fiber may be used, or two or more types of different materials or different freeness may be used in combination. When two or more types are used in combination, fibrillated fibers having a Canadian freeness or modified freeness that is not a preferable value may be used as long as they do not cause formation unevenness or thickness unevenness of the wet nonwoven fabric.

  5-85 mass% is preferable, as for the content rate of the fibrillated fiber in the separator of this invention, 10-70 mass% is more preferable, and 25-70 mass% is further more preferable. When the amount is less than 5% by mass, the ability to form aggregates with the acrylic polymer particles may be insufficient, and when the amount exceeds 85% by mass, the puncture strength may be insufficient.

  The total content of the acrylic polymer particles and the fibrillated fibers in the separator of the present invention is preferably 50 to 100% by mass, more preferably 60 to 95% by mass, and further preferably 70 to 90% by mass. If it is less than 50% by mass, pinholes may occur.

  As the flocculant, organic flocculants such as polyamine, polyacrylamide, sodium alginate, dicyanamide, inorganic systems such as sulfate band, ferric sulfate, polyferric sulfate, calcium sulfate, ferric chloride, polyaluminum chloride, etc. A flocculant is mentioned. The organic flocculant alone or the inorganic flocculant alone may be used, or the organic and inorganic flocculants may be used in combination. The organic flocculant may contain a salt such as sodium salt or potassium salt. In order to increase the acting force of the flocculant, the pH of the slurry may be adjusted. pH adjusters include sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, carbon dioxide, ammonia, citric acid, gluconic acid, succinic acid, lactic acid, fumaric acid Etc. The addition amount of the flocculant is preferably 0.01 to 10% by mass and more preferably 0.1 to 10% by mass with respect to the solid content of the slurry in terms of solid content. If the addition amount of the flocculant is less than 0.01% by mass, aggregation of the raw material slurry may be insufficient, and if it is more than 10% by mass, the drainage of the raw material slurry may deteriorate and papermaking may be difficult. is there.

  The slurry may contain a thickener. Thickeners include alginic acid, sodium alginate, albumin, casein, starch, polysaccharides, agar, sodium carboxymethylcellulose, carboxymethylcellulose calcium, polyacrylic acid, sodium polyacrylate, acrylic acid / alkyl acrylate copolymer, acrylamide / Acrylic acid copolymer, carboxyvinyl polymer, dimethyl distearyl ammonium hectorite, vinyl compound, vinylidene compound, polyester compound, polyether compound, polyglycol compound and the like. As addition amount of a thickener, 0.1-10 mass% is preferable with respect to the total solid of raw material slurry in conversion to solid content, and 0.3-5 mass% is more preferable. When the addition amount of the thickener is less than 0.1% by mass, the bonds between the aggregates may be weak, and when the amount exceeds 10% by mass, the aggregates become too large and the formation of the separator becomes uneven. There is.

  The slurry may contain a paper strength enhancer. Examples of the paper strength enhancer include anionic polyacrylamide, cationic polyacrylamide, amphoteric polyacrylamide, and epoxy-modified polyamide. The paper strength enhancer is preferably 1 to 10% by mass based on the solid content of the slurry. If it is less than 1% by mass, the effect of adding the paper strength enhancer may not appear, and even if it is added more than 10% by mass, the strength of the wet nonwoven fabric may be saturated.

  The slurry may contain non-fibrillated fibers. Non-fibrillated fibers include fibers and inorganic fibers that are not fibrillated in the fiber group exemplified for fibrillated fibers. When non-fibrillated fibers are included in the slurry, only non-fibrillated fibers or non-fibrillated fibers and additives are dispersed in advance, and aggregates of acrylic polymer particles and fibrillated fibers are contained. Add to the slurry and stir. Mixing non-fibrillated fibers and acrylic polymer particles or fibrillated fibers before forming aggregates of acrylic polymer particles and fibrillated fibers will form aggregates incorporating non-fibrillated fibers. Since the aggregate grows greatly, a wet nonwoven fabric having a uniform texture cannot be obtained.

  Examples of the inorganic fibers include silica / alumina fibers, alumina fibers, glass fibers, micro glass fibers, zirconia fibers, silicon nitride fibers, silicon carbide fibers, and the like. In the present invention, the non-fibrillated fiber increases the tensile strength and puncture strength of the separator and increases the folding resistance and winding property of the separator. Among non-fibrillated fibers, an acrylic polymer-based fiber is preferable because of its excellent resistance to electrolytic solution and excellent compatibility with the electrolytic solution.

  The fiber length of the non-fibrillated fiber is preferably 0.1 to 10 mm, and more preferably 0.3 to 6 mm. If the fiber length is less than 0.1 mm, it may fall off from the separator, and if it is longer than 10 mm, the fibers may rely on each other to cause formation unevenness or thickness unevenness. The fineness of the non-fibrillated fiber is preferably 0.0001 to 1.1 dtex, more preferably 0.001 to 0.7 dtex. When the fineness of the non-fibrillated fiber exceeds 1.1 dtex, the number of fibers in the thickness direction is reduced, and thus there may be a case where a large through hole or thickness unevenness is generated in the separator or it is difficult to reduce the thickness. When the fineness of the non-fibrillated fiber is less than 0.0001 dtex, stable production of the fiber becomes difficult. The non-fibrillated fiber may be a fiber (single fiber) made of a single resin or a composite fiber made of two or more kinds of resins. Moreover, the non-fibrillated fiber contained in the separator for electrochemical devices of the present invention may be used alone or in combination of two or more. Examples of the composite fiber include a core-sheath type, an eccentric type, a side-by-side type, a sea-island type, an orange type, and a multiple bimetal type.

  The separator of the present invention may be a single layer or a multilayer. Multi-layer means that two or more layers having the same constituent material, blending ratio, basis weight, etc. are laminated, and two or more layers having different conditions such as constituent material, blending ratio, basis weight, etc. are laminated. Refers to things. The latter is, for example, a layer in which two or more layers containing acrylic polymer particles are alternately laminated, and a layer containing acrylic polymer particles on the front and back surfaces of a layer not containing acrylic polymer particles. Are laminated to form three layers, and layers that do not contain acrylic polymer particles are laminated on the front and back surfaces of the layer containing acrylic polymer particles. In the present invention, a multilayer structure is preferable because it is easy to intensively support acrylic polymer particles even at a low blending ratio. To make a multi-layer separator, a combination paper machine consisting of a circular paper machine, a long paper machine, a short paper machine, a slanted paper machine, or a slanted short paper machine and the same or different paper machines. To make multilayer paper. In addition, a multi-layered paper may be used in which slurries are supplied to the net of a slanted paper machine or a slanted short paper machine. In the present invention, after wet papermaking, calendering, thermal calendering, heat treatment and the like may be performed as necessary.

  FIG. 1 is an example of an electron micrograph of the separator surface produced in the example of the present invention. It can be confirmed that aggregates of spherical acrylic polymer particles and fibrillated fibers are formed. FIG. 2 is an example of an electron micrograph of the cross section of the separator produced in the example of the present invention. Both FIG. 1 and FIG. 2 show that the acrylic polymer particles are in close contact with each other in the depth direction.

  10-60 micrometers is preferable, as for the thickness of the separator of this invention, 15-50 micrometers is more preferable, and 20-40 micrometers is more preferable. When the thickness exceeds 60 μm, the electrical resistance of the separator may be increased. When the thickness is less than 10 μm, the strength of the separator becomes too weak and may be damaged when the separator is handled.

The density of the separator of the present invention is preferably 0.250~0.800g / cm ^3, more preferably 0.400~0.750g / cm ^3, more preferably 0.500~0.750g / cm ^3. When the density is less than 0.250 g / cm ³ , the coating liquid may be exposed, and when it exceeds 0.800 g / cm ³ , the electrical resistance of the separator may be increased.

The electrochemical element in the present invention is a lithium battery, lithium secondary battery, polyacene battery, organic radical battery, electric double layer capacitor, lithium ion capacitor, hybrid capacitor, redox capacitor, aluminum electrolytic capacitor, conductive polymer aluminum electrolytic capacitor It means an electrochemical element having a power storage function and a rectifying function. The lithium secondary battery means a lithium ion battery or a lithium ion polymer battery. Examples of the negative electrode active material of the lithium secondary battery include carbon materials such as graphite and coke, metallic lithium, aluminum, silica, tin, nickel, and an alloy of lithium and lithium, SiO, SnO, Fe Metal oxides such as ₂ O ₃ , WO ₂ , Nb ₂ O ₅ , Li _4/3 Ti _5/3 O ₄ , and nitrides such as Li _0.4 CoN are used. As the positive electrode active material, lithium cobaltate, lithium manganate, lithium nickelate, lithium titanate, lithium nickel manganese oxide, or lithium iron phosphate is used. Further, the lithium iron phosphate may be a composite with one or more metals selected from manganese, chromium, cobalt, copper, nickel, vanadium, molybdenum, titanium, zinc, aluminum, gallium, magnesium, boron, and niobium.

  As an electrolytic solution for a lithium secondary battery, a solution obtained by dissolving a lithium salt in an organic solvent such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, dimethoxymethane, or a mixed solvent thereof is used. Examples of the lithium salt include lithium hexafluorophosphate and lithium tetrafluoroborate. As solid electrolyte, what melt | dissolved lithium salt in gel-like polymers, such as polyethyleneglycol, its derivative (s), polymethacrylic acid derivative, polysiloxane, its derivative (s), polyvinylidene fluoride, is used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a present Example.

Example 1
R1, F6, F11, and S3 were weighed so that the mixing ratio of the slurry 1 shown in Table 1 was obtained. A slurry in which F6 and F11 are dispersed together in water and a slurry in which R1 is dispersed in water are prepared separately and mixed while stirring. Further, polyacrylamide flocculant (manufactured by Ciba Specialty Chemicals, product) Name: Hydrocol (registered trademark) HC-880) with respect to the total mass of R1, F6, and F11, 1% by mass in solid content is added, and agglomerates of acrylic polymer particles and fibrillated fibers are stirred. Formed. Next, a slurry in which S3 is dispersed in water is mixed, and an amphoteric polyacrylamide-based paper strength enhancer (manufactured by Arakawa Chemical Industries, trade name: Polystron (registered trademark) 1250) is added to R1, F6, F11, and S3. Based on the mass, 5% by mass as a solid content was added and stirred for 3 minutes to obtain a slurry 1. Slurry 1 was fed to a circular paper machine, wet-made, and then calendered to adjust the thickness to produce the separator of Example 1.

Example 2
S4 is used instead of S3, and slurry 2 is prepared in the same manner as slurry 1 according to the mixing ratio of slurry 2 shown in Table 1, and after wet papermaking using a circular net paper machine, the thickness is adjusted by calendaring. The separator of Example 2 was produced.

Example 3
R1, F1, F9, F11, and S4 were weighed so that the mixing ratio of the slurry 3 shown in Table 1 was obtained. A slurry in which F1, F9, and F11 are dispersed together in water and a slurry in which R1 is dispersed in water are prepared separately, and both are mixed while stirring to coagulate the acrylic polymer particles and the fibrillated fibers. Aggregates were formed. Next, a slurry in which S4 is dispersed in water is mixed, and the paper strength enhancer used in Example 1 is 5% by mass in solid content with respect to the total mass of R1, F1, F9, F11, and S4. Added and stirred for 3 minutes to give slurry 3. Slurry 3 was fed to a circular paper machine, wet-made, and then calendered to adjust the thickness to produce the separator of Example 3.

Example 4
R2, F2, S1, and S2 were weighed so that the mixing ratio of the slurry 4 shown in Table 1 was obtained. A slurry in which F2 was dispersed in water and a slurry in which R2 was dispersed in water were prepared separately, and both were mixed while stirring to form an aggregate of acrylic polymer particles and fibrillated fibers. Next, a slurry in which S1 and S2 are dispersed in water is mixed, and the paper strength enhancer used in Example 1 is added at 5% by mass in solid content with respect to the total mass of R2, F2, S1, and S2. The mixture was stirred for 3 minutes to obtain slurry 4. Slurry 4 was fed to a circular paper machine, wet-made, and then calendered to adjust the thickness to produce the separator of Example 4.

Example 5
R2, F7, and S4 were weighed so that the mixing ratio of the slurry 5 shown in Table 1 was obtained. A slurry in which F7 is dispersed in water and a slurry in which R2 is dispersed in water are prepared separately, and both are mixed while stirring. The flocculant used in Example 1 is added to the total mass of R2 and F7. Then, 1% by mass in solid content was added and stirred to form an aggregate of acrylic polymer particles and fibrillated fibers. Next, a slurry in which S4 is dispersed in water is mixed, and the paper strength enhancer used in Example 1 is further added in an amount of 5% by mass with respect to the total mass of R2, F7, and S4. A slurry 5 was obtained by stirring for 5 minutes. Slurry 5 was fed to a circular paper machine, wet-made, and then calendered to adjust the thickness to produce the separator of Example 5.

Example 6
R2, F10, and F11 were weighed so that the mixing ratio of the slurry 6 shown in Table 1 was obtained. A slurry in which F10 and F11 are dispersed together in water and a slurry in which R2 is dispersed in water are prepared separately, and both are mixed while stirring. Further, the flocculant used in Example 1 is R2, F10. , 1% by mass in terms of solid content was added to the total mass of F11 and stirred to form aggregates of acrylic polymer particles and fibrillated fibers. Subsequently, the paper strength enhancer used in Example 1 was added in an amount of 5 mass% as a solid content with respect to the total mass of R2, F10, and F11, and stirred for 3 minutes to obtain slurry 6. The slurry 6 was fed to a circular paper machine and wet-made, and then calendered to adjust the thickness to produce the separator of Example 6.

Example 7
R2, F3, F8, and S2 were weighed so that the mixing ratio of the slurry 7 shown in Table 1 was obtained. A slurry in which F3 and F8 are dispersed together in water and a slurry in which R2 is dispersed in water are prepared separately, and both are mixed while stirring to form an aggregate of acrylic polymer particles and fibrillated fibers. Formed. Next, a slurry in which S2 is dispersed in water is mixed, and further, the paper strength enhancer used in Example 1 is added in a solid content of 5% by mass with respect to the total mass of R2, F3, F8, and S2. A slurry 7 was obtained by stirring for 3 minutes. Slurry 7 was fed to a circular paper machine, wet-made, and then calendered to adjust the thickness to produce the separator of Example 7.

Example 8
Except that S4 was used instead of S2, slurry 8 was prepared in the same manner as slurry 7 in accordance with the blending ratio of slurry 8 shown in Table 1, and fed to a circular paper machine for wet paper making, followed by calendar treatment. Then, the thickness was adjusted, and the separator of Example 8 was produced.

Example 9
R2, F5, F10, and S4 were weighed so that the blending ratio of the slurry 9 shown in Table 1 was obtained. A slurry in which F5 and F10 are dispersed together in water and a slurry in which R2 is dispersed in water are prepared separately, and both are mixed while stirring to form an aggregate of acrylic polymer particles and fibrillated fibers. Formed. Next, a slurry in which S4 is dispersed in water is mixed, and further, the paper strength enhancer used in Example 1 is added in a solid content of 5% by mass with respect to the total mass of R2, F5, F10, and S4. A slurry 9 was obtained by stirring for 3 minutes. Slurry 9 was fed to a circular paper machine, wet-made, and then calendered to adjust the thickness to produce the separator of Example 9.

Example 10
R3, F4, F9, F11, and S2 were weighed so that the mixing ratio of the slurry 10 shown in Table 1 was obtained. A slurry in which F4, F9, and F11 are dispersed together in water and a slurry in which R3 is dispersed in water are prepared separately and mixed while stirring to coagulate acrylic polymer particles and fibrillated fibers. Aggregates were formed. Next, a slurry in which S2 is dispersed in water is mixed, and further, the paper strength enhancer used in Example 1 is added in a solid content of 5% by mass with respect to the total mass of R3, F4, F9, F11, and S2. Then, the mixture was stirred for 3 minutes to obtain slurry 10. The slurry 10 was fed to a circular paper machine, wet-made, and then calendered to adjust the thickness to produce the separator of Example 10.

Example 11
R4, F1, F11, and S1 were weighed so that the mixing ratio of the slurry 11 shown in Table 1 was obtained. A slurry in which F1 and F11 are dispersed together in water and a slurry in which R4 is dispersed in water are prepared separately, and both are mixed while stirring to form an aggregate of acrylic polymer particles and fibrillated fibers. Formed. Next, a slurry in which S1 is dispersed in water is mixed, and the paper strength enhancer used in Example 1 is further added in an amount of 5% by mass with respect to the total mass of R4, F1, F11, and S1. A slurry 11 was obtained by stirring for 3 minutes. Slurry 11 was fed to a circular paper machine, wet-made, and then calendered to adjust the thickness to produce the separator of Example 11.

Example 12
R4, F3, F10, and S2 were weighed so that the mixing ratio of the slurry 12 shown in Table 1 was obtained. A slurry in which F3 and F10 are dispersed together in water and a slurry in which R4 is dispersed in water are prepared separately, and both are mixed while stirring to form an aggregate of acrylic polymer particles and fibrillated fibers. Formed. Next, a slurry in which S2 is dispersed in water is mixed, and further, the paper strength enhancer used in Example 1 is added in a solid content of 5% by mass with respect to the total mass of R4, F3, F10, and S2. A slurry 12 was obtained by stirring for 3 minutes. Slurry 12 was fed to a circular paper machine, wet-made, and then calendered to adjust the thickness to produce the separator of Example 12.

Example 13
R4, F4, F6, S1, S2, and S5 were weighed so that the mixing ratio of the slurry 13 shown in Table 1 was obtained. A slurry in which F4 and F6 are dispersed together in water and a slurry in which R4 is dispersed in water are prepared separately, and both are mixed while stirring to form an aggregate of acrylic polymer particles and fibrillated fibers. Formed. Next, a slurry in which S1, S2, and S5 are dispersed together in water is mixed, and the paper strength enhancer used in Example 1 is added to the total mass of R4, F5, F6, S1, S2, and S5. Then, 5% by mass as a solid content was added and stirred for 3 minutes to obtain slurry 13. The slurry 13 was fed to a circular paper machine, wet-made, and then calendered to adjust the thickness to produce the separator of Example 13.

Example 14
R2, F1, F7, and S1 were weighed so that the mixing ratio of the slurry 14 shown in Table 1 was obtained. A slurry in which F1 and F7 are dispersed together in water and a slurry in which R2 is dispersed in water are prepared separately, and both are mixed while stirring to form an aggregate of acrylic polymer particles and fibrillated fibers. Formed. Next, the slurry in which S1 is dispersed in water is mixed, and further, the paper strength enhancer used in Example 1 is added in a solid content of 5% by mass with respect to the total mass of R2, F1, F7, and S1. The mixture was stirred for 3 minutes to obtain slurry 14.

F7, F11, and S4 were weighed so that the mixing ratio of the slurry 17 shown in Table 1 was obtained. After dispersing F11 in water, S4 is added and stirred, and F7 is further added and stirred. Further, the paper strength enhancer used in Example 1 is added to the total mass of F7, F11, and S4. Then, 5% by mass in solid content was added, and stirred for 3 minutes to obtain slurry 17. Slurry 14 is fed to a circular paper machine and wet paper is made to a basis weight of 5 g / m ^2. At the same time, slurry 17 is fed to a slanted paper machine and wet paper is made to a basis weight of 15 g / m ² and is combined. After preparing the wet nonwoven fabrics having different two-layer structures, the thickness was adjusted by calendering to prepare the separator of Example 14.

Example 15
R2, F2, F7, F11, and S4 were weighed so that the mixing ratio of the slurry 15 shown in Table 1 was obtained. A slurry in which F2, F7, and F11 are dispersed together in water and a slurry in which R2 is dispersed in water are prepared separately, and both are mixed while stirring to coagulate the acrylic polymer particles and the fibrillated fibers. Aggregates were formed. Next, a slurry in which S4 is dispersed in water is mixed, and the paper strength enhancer used in Example 1 is further 5% by mass in solid content with respect to the total mass of R2, F2, F7, F11, and S4. Added and stirred for 3 minutes to give slurry 15. Slurry 15 is fed to a circular paper machine and wet-made to a basis weight of 6 g / m ^2. Simultaneously, slurry 17 prepared in the same manner as in Example 14 is fed to an inclined paper machine, and a basis weight of 14 g / m ^{2 is obtained.} The paper was wet-made and bonded together to prepare wet nonwoven fabrics having different two-layer structures, and then calendered to adjust the thickness, thereby preparing the separator of Example 15.

Example 16
R2, F2, F7, F11, and S4 were weighed so that the mixing ratio of the slurry 16 shown in Table 1 was obtained. A slurry in which F2, F7, and F11 are dispersed together in water and a slurry in which R2 is dispersed in water are prepared separately, and both are mixed while stirring to coagulate the acrylic polymer particles and the fibrillated fibers. Aggregates were formed. Next, a slurry in which S4 is dispersed in water is mixed, and the paper strength enhancer used in Example 1 is further 5% by mass in solid content with respect to the total mass of R2, F2, F7, F11, and S4. Added and stirred for 3 minutes to make slurry 16. Slurry 15 is fed to a circular paper machine and wet-made to a basis weight of 5 g / m ^2. At the same time, slurry 17 prepared in the same manner as in Example 14 is fed to an inclined paper machine, and the basis weight is 15 g / m ^2. The paper was wet-sheeted and bonded together to prepare wet nonwoven fabrics having different two-layer structures, and then calendered to adjust the thickness to prepare the separator of Example 16.

(Comparative Example 1)
F2 and S3 were weighed so that the mixing ratio of the slurry 18 shown in Table 1 was obtained. After F2 was dispersed in water, S3 was added and stirred to prepare slurry 18. The slurry 18 was fed to a slanted short paper machine and wet-made, and then heat calendering was performed at 220 ° C. to adjust the thickness, whereby the separator of Comparative Example 1 was produced.

(Comparative Example 2)
R2 and S2 were weighed so that the mixing ratio of the slurry 19 shown in Table 1 was obtained. A slurry in which R2 is dispersed in water and a slurry in which S2 is dispersed in water are prepared separately, and both are mixed with stirring. Further, the polyacrylamide-based flocculant used in Example 1 is mixed with R2 and S2. Based on the total mass, 1% by mass of solid content was added and stirred to obtain slurry 19. Slurry 19 was sent to a circular paper machine and wet papermaking, but there was almost no adhesion between the fibers after drying, and the fibers were picked up by felt, and the wet nonwoven fabric was cut stably. It could not be produced.

(Comparative Example 3)
A slurry 17 was prepared in the same manner as in Example 14 except that no paper strength enhancer was added. The slurry 17 was fed to a circular paper machine, wet-made, and then calendered to adjust the thickness. Comparative Example 3 A separator was prepared.

(Comparative Example 4)
Polyvinylidene fluoride (mass average molecular weight 300,000) was dissolved in N-methyl-2-pyrrolidone so that the solid content concentration was 5% by mass, and then 5% by mass of dibutyl phthalate was added to the polyvinylidene fluoride. After dissolution, 5% by mass of the acrylic polymer particles used in Example 9 was added to the polyvinylidene fluoride and stirred until uniformly dispersed. This solution was applied to a 20 μm thick polyester nonwoven fabric and dried at 90 ° C. to produce a separator of Comparative Example 4.

(Comparative Example 5)
Poly (vinylidene fluoride-hexafluoropropylene) copolymer (manufactured by Aldrich Chemical Company, Inc., mass average molecular weight 400,000) was dissolved in N-methyl-2-pyrrolidone so that the solid content concentration was 5% by mass. Thereafter, acrylic polymer particles (cross-linked polymethyl methacrylate) having a D50 of 0.2 μm were added and stirred until uniformly dispersed. This solution was applied to a 20 μm thick polyester nonwoven fabric and dried at 90 ° C. to produce a separator of Comparative Example 5.

(Comparative Example 6)
A uniform slurry was prepared by stirring 1000 g of spherical general-purpose acrylic polymer particles having an average particle diameter of 1 μm, 800 g of water, 200 g of isopropyl alcohol, and 375 g of polyvinyl butyral as a binder with a three-one motor for 1 hour. This slurry was applied to a polypropylene nonwoven fabric having a thickness of 15 μm and dried at 90 ° C. to produce a separator of Comparative Example 6.

(Comparative Example 7)
1000 g of spherical general-purpose acrylic polymer particles having an average particle diameter of 4 μm, 6000 g of water, 30 g of carboxymethyl cellulose, 100 g of styrene-butadiene latex (manufactured by Nippon Zeon, trade name Nipol (registered trademark) LX421) as a binder, The mixture was stirred at 2800 rpm for 3 hours to prepare a uniform slurry. This slurry was applied to a polypropylene nonwoven fabric having a thickness of 15 μm and dried at 90 ° C. to produce a separator of Comparative Example 7.

(Comparative Example 8)
3% by mass of the styrene-butadiene latex used in Comparative Example 7 was added to 100% by mass of the acrylic polymer particles (R4), and stirred until uniformly dispersed. This solution was applied to a polyester nonwoven fabric having a thickness of 15 μm and dried at 90 ° C. to prepare a separator of Comparative Example 8.

(Comparative Example 9)
F9 was dispersed in water, and the paper strength enhancer used in Example 1 was added in an amount of 5% by mass with respect to the mass of F9, and stirred for 3 minutes to prepare slurry 20. Slurry 20 was fed to an inclined paper machine and wet papermaking was performed, then the thickness was adjusted by calendaring to produce a separator of Comparative Example 9 made of 100% cellulose.

(Comparative Example 10)
The solution prepared in Comparative Example 4 was cast on a polypropylene film, a porous film of polyvinylidene fluoride was formed by a dry method, and this was peeled from the polypropylene film to produce a separator of Comparative Example 10.

[Evaluation]
The following evaluation was performed about the lithium secondary battery produced using the separator of an Example and a comparative example, and this separator, and the result was shown in Table 2 and Table 3.

<Thickness>
The thickness was measured according to JIS C2111, and the average value is shown in Table 2.

<Density>
The density was measured according to JIS C2111 and is shown in Table 2.

<Puncture strength>
The separator was trimmed to 50 mm width × 200 mm length. A separator is mounted on a 40 mmφ fixed frame installed on a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and a metal needle (produced by Orientec Co., Ltd.) with a diameter of 1.0 mm is mounted. Table 2 shows the maximum load (N) measured at a predetermined speed of 50 mm / min at right angles to the separator surface at five or more arbitrary points, and the average value was defined as the puncture strength.

<Puncture strength maintenance rate>
The puncture strength after the separator was immersed in the electrolytic solution for 10 minutes was measured, and the ratio to the puncture strength before being immersed in the electrolytic solution was defined as the puncture strength maintenance rate. That is, when the puncture strength before being immersed in the electrolytic solution is T1, and the puncture strength after being immersed in the electrolytic solution for 10 minutes is T2, the value obtained by dividing T2 by T1 and multiplying by 100 is 100%. And shown in Table 2. After immersing the separator sample used for <Puncture Strength> in the electrolyte for 10 minutes, the separator is removed from the electrolyte, and the excess electrolyte on the separator surface is wiped off with Kim Towel (registered trademark), and <Puncture Strength> is measured. The puncture strength was measured in the same manner as the method. As the electrolytic solution, a mixed solution in which 1 mol / l of LiPF ₆ was dissolved was used. The mixed solution is ethylene carbonate and diethyl carbonate in a mass ratio of 3: 7.

<Penetration>
The separator was closely fixed to the slide glass, and one drop of the electrolyte solution was dropped from the position of 10 mm height on the separator surface in a state where the separator was tilted together. Table 2 shows the tilt angle at which the dropped electrolyte solution started to flow down the separator surface and used as an index of permeability. That is, the larger the inclination angle, the better the permeability of the electrolyte solution to the separator. The electrolytic solution is the same as that described in the evaluation of <Puncture strength maintenance ratio>.

<Particle state>
The surface or cross section of the separator was observed with an electron microscope (1000 magnifications), and the state of the acrylic polymer particles was confirmed. When there is a region where acrylic polymer particles are in close contact with two or more layers in the depth direction, "multilayer", when there is no region close to the multilayer and sparsely exists, "sparse", when not present Table 2 shows “None”, and “Built-in” when coated with a binder or resin.

<Food fall>
The surface of the separator was rubbed with a finger, and it was confirmed whether or not the acrylic polymer particles were powdered off. Table 2 shows “Yes” when powdered and “No” when not.

<Pinhole>
The separator was cut into 300 mm × 300 mm, transmitted light was applied from the back side of the separator, and the presence or absence of pinholes was visually confirmed. Table 2 shows the case where a pinhole is present as “Yes” and the case where no pinhole is present as “None”.

<Dendrite resistance>
A metal lithium foil was placed on one side of the separator and a positive electrode was placed on the opposite side of the separator and laminated, and an electrolyte was injected to prepare 100 laminate cells. The battery was charged at a constant current of up to 3.6 V at 0.5 mA / cm ² and further overcharged by applying 3.6 V for 24 hours. The case where an abnormal current flowed during this overcharge was regarded as an internal short circuit, the overcharge was stopped, the laminate cell was opened, and the generation state of lithium dendrite was confirmed. Table 3 shows the dendrite resistance as a percentage of cells that generated lithium dendrite due to overcharge and penetrated the substrate. It means that it is excellent in dendrite resistance, so that this ratio is small. For the positive electrode, a slurry in which a lithium cobaltate as an active material, acetylene black as a conductive additive, and polyvinylidene fluoride as a binder are mixed at a mass ratio of 90: 5: 5 is applied to both surfaces of an aluminum current collector. Using. The electrolytic solution is the same as that described in the evaluation of <Puncture strength maintenance ratio>. About the separators 14-16 obtained in Examples 14-16, the layer containing acrylic polymer particles was arrange | positioned so that a positive electrode might be contact | connected.

<Short rate>
The negative electrode and the positive electrode were cut to a width of 50 mm and a length of 70 mm. The separator was cut into 60 mm width × 90 mm length. The separator was allowed to infiltrate the electrolyte, and the excess liquid on the surface was wiped off with Kim Towel (registered trademark), and then laminated with one sheet sandwiched between the negative electrode and the positive electrode to produce a laminate cell. The laminate cell was sandwiched between 5 mm thick resin plates and fixed at a pressure of 0.1 kg / cm ² . The presence or absence of conduction was examined without charging the laminate cell, the percentage of conduction in 100 pieces was calculated, and the short ratio due to pinholes existing in the separator was shown in Table 3. For the negative electrode, a slurry in which natural graphite as an active material (average particle size 8 μm) and polyvinylidene fluoride as a binder (mass average molecular weight 300,000) are mixed at a mass ratio of 97: 3 is provided on both sides of a copper current collector. The coated one was used. The positive electrode is the same as that described in the evaluation of <dendritic resistance>. The electrolytic solution is the same as that described in the evaluation of <Puncture strength maintenance ratio>. About the separators 14-16 obtained in Examples 14-16, the layer containing acrylic polymer particles was arrange | positioned so that a positive electrode might be contact | connected.

<Pressure resistance>
Laminate cells that were not short-circuited in the evaluation of <Short rate> were collected, and the pressure was increased to 2 kg / cm ² and re-fixed. Table 3 shows the presence / absence of conduction without charging the laminate cell, calculates the ratio of conduction with respect to the number of collected cells, and serves as an index of pressure resistance. It means that it is excellent in pressure resistance, so that a numerical value is small.

<Internal resistance>
Using a laminate cell that was not short-circuited in the evaluation of <short ratio>, the internal resistance was measured at an alternating current of 1 kHz, and the average value is shown in Table 3.

<High rate characteristics>
Using a laminate cell that was not short-circuited in the evaluation of <pressure resistance>, it was charged to 4.2 V at 25 ° C. and 1 A, further charged at 4.2 V for 3 hours at constant voltage, and then to 3.0 V at 200 mA. The discharge capacity at the time of discharge was measured and used as the initial capacity. Discharge to 3.0V at 25 ° C and 200mA, then charge to 4.2V at 1A, charge at 4.2V for 3 hours, and then discharge to 3.0V at 60 ° C and 3A. The capacity was measured, the ratio with respect to the initial capacity was calculated, and the average value was defined as the high rate characteristic, which is shown in Table 3.

  Since the separators for electrochemical elements of Examples 1 to 16 are made of a wet nonwoven fabric obtained by wet papermaking a slurry containing an aggregate of acrylic polymer particles and fibrillated fibers, the electrolyte has excellent permeability. The puncture strength before and after the electrolyte penetration was strong, and the pressure resistance was excellent. Further, the acrylic polymer particles did not fall off and no pinholes were obtained. Furthermore, since there is a region where the acrylic polymer particles are in close contact with the multilayer, the dendrite resistance was excellent. The lithium ion batteries comprising the separators for electrochemical elements of Examples 1 to 16 had low internal resistance, a low short-circuit rate, and excellent high rate characteristics under high pressure. The separators for electrochemical elements of Examples 3 to 4 and 7 to 16 have excellent flocculation ability because they contain fibrillated para-type wholly aromatic polyamide fibers or fibrillated wholly aromatic polyester fibers, and no coagulant is used. In addition, aggregates with acrylic polymer particles could be formed.

  On the other hand, although the separator for an electrochemical element of Comparative Example 1 did not have pinholes, it did not contain acrylic polymer particles, so the permeability of the electrolytic solution was slightly poor, the puncture strength after penetration of the electrolytic solution was weak, The dendrite and pressure resistance were poor. The lithium ion battery provided with the separator had a low short-circuit rate, but had a slightly high internal resistance and poor high rate characteristics under high pressure.

  In Comparative Example 2, since there was almost no adhesion between fibers after drying during wet papermaking, fibers could be taken by felt, cut, etc., so that a wet nonwoven fabric could not be stably produced. I couldn't.

  The separator for an electrochemical element of Comparative Example 3 did not have pinholes, but did not contain acrylic polymer particles. Therefore, the permeability of the electrolytic solution was slightly poor, the puncture strength after the penetration of the electrolytic solution was weak, and dendrite resistance And pressure resistance was bad. The lithium ion battery provided with the separator had a low short-circuit rate, but had a slightly high internal resistance and poor high rate characteristics under high pressure.

  The separator for the electrochemical element of Comparative Example 4 did not contain fibrillated fibers, and the amount of the acrylic polymer particles was too small, so that the acrylic polymer particles adhered sparsely, and the pinhole of the base material Many of these remained, the puncture strength after penetration of the electrolyte was weak, and the dendrite resistance and pressure resistance were extremely poor. For this reason, the lithium ion battery equipped with the separator had a low internal resistance but a very high short-circuit rate.

  The separator for an electrochemical element of Comparative Example 5 contains acrylic polymer particles, has no pinholes, does not decrease the puncture strength after permeation of the electrolyte, and has excellent dendrite resistance. The particles were buried in a poly (vinylidene fluoride-hexafluoropropylene) copolymer, the permeability of the electrolytic solution was poor, the puncture strength before penetration of the electrolytic solution was originally weak, and the pressure resistance was poor. For this reason, the lithium ion battery equipped with the separator has a low short-circuit rate, but has an extremely high internal resistance and a high rate characteristic under a high pressure.

  The separator for an electrochemical element of Comparative Example 6 contained acrylic polymer particles, had no pinholes, did not decrease the puncture strength after permeation of the electrolyte, and had excellent dendrite resistance, but the acrylic polymer The particles were buried in the binder, the permeability of the electrolyte solution was poor, the puncture strength before the electrolyte solution penetration was weak in the first place, and the pressure resistance was inferior. Therefore, the lithium ion battery provided with the separator has a low short-circuit rate, but has a high internal resistance and a high rate characteristic under a high pressure.

  The separator for an electrochemical element of Comparative Example 7 does not contain fibrillated fibers, the binder amount is insufficient with respect to the amount of the acrylic polymer particles, the acrylic polymer particles are powdered off, Pinholes remained and the dendrite resistance was poor. Moreover, the puncture strength after electrolyte solution penetration was weak, and the pressure resistance was inferior. The lithium ion battery equipped with the separator had low internal resistance, but had a high short-circuit rate and poor high rate characteristics under high pressure.

  The separator for an electrochemical element of Comparative Example 8 contains acrylic polymer particles, and the puncture strength after electrolyte penetration did not decrease due to the effect of the binder, and the dendrite resistance was good, but the acrylic polymer particles Embedded in the binder, the permeability of the electrolytic solution was poor, the puncture strength before the penetration of the electrolytic solution was originally weak, and the pressure resistance was inferior. Moreover, since the coating with the binder was incomplete, pinholes in the base material remained. Therefore, the lithium ion battery provided with the separator has a slightly short circuit rate, a high internal resistance, and a high rate characteristic under a high pressure.

  The separator for an electrochemical element of Comparative Example 9 is composed of 100% cellulose having a modified freeness of 107 ml, so it is dense and has no pinholes, but has a low piercing strength after electrolyte penetration, dendrite resistance and resistance. The pressure property was inferior. Therefore, the lithium ion battery provided with the separator has a low short-circuit rate and a low internal resistance, but has a high rate characteristic under a high pressure.

  The separator for an electrochemical element of Comparative Example 10 contains acrylic polymer particles, the puncture strength after penetration of the electrolyte solution does not decrease, there is no pinhole, and the dendrite resistance is excellent, but the electrolyte solution permeability However, the puncture strength before the electrolyte penetration was extremely weak in the first place, it was brittle, and the pressure resistance was extremely poor. Therefore, the lithium ion battery provided with the separator has a high short-circuit rate and high internal resistance.

Claims (3)

  The separator for electrochemical elements which consists of a wet nonwoven fabric obtained by wet papermaking the slurry containing the aggregate of acrylic polymer particle | grains and fibrillated fiber.   The separator for an electrochemical element according to claim 1, wherein a part of the fibrillated fiber is a fibrillated para-type wholly aromatic polyamide fiber or a fibrillated wholly aromatic polyester fiber.   The electrochemical element which comprises the separator for electrochemical elements of Claim 1 or 2.