JP5170018B2 - Nonaqueous electrolyte secondary battery separator - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery separator, a method for producing the same, and a non-aqueous electrolyte secondary battery using the same.

  Non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, are widely used as batteries for personal computers, mobile phones, portable information terminals and the like because of their high energy density.

  Non-aqueous electrolyte secondary batteries represented by these lithium secondary batteries have high energy density and generated heat due to internal or external short circuits caused by accidents such as damage to the batteries or equipment using the batteries. Therefore, the non-aqueous electrolyte secondary battery is required to prevent heat generation beyond a certain level and ensure high safety. In the event of an accident, as a method of preventing a certain amount of heat generation, a separator placed between the positive electrode and the negative electrode and separated so that the positive electrode and the negative electrode are not in direct contact with each other is cut off when the heat is generated and further heat is generated. A method of providing a shutdown function to prevent is common. As a method for providing a separator with a shutdown function, a method using a porous film made of a material that melts by heat generation as a separator is used. That is, since ions pass through the porous holes before heat generation, the separator conducts electricity, but when the heat is generated, the porous melts and becomes non-porous, and the separator does not conduct electricity.

  For example, a polyolefin porous film is used as the separator. When the battery is heated, the separator made of the polyolefin porous film melts at about 80 to 180 ° C. and becomes non-porous to cut off the current (shut down) and suppress the heat generation. However, if the heat generation is intense, the polyolefin porous film has insufficient dimensional stability and may cause deformation such as shrinkage or opening of holes, and the positive and negative electrodes may be in direct contact with each other. May not be able to be suppressed.

  For this reason, a method for imparting dimensional stability at high temperature to a separator by laminating a porous film made of a heat resistant material on a polyolefin porous film has been studied. For example, a regenerated cellulose film is immersed in ethanol. A separator formed by laminating with a polyolefin porous film after being made porous has been proposed (see, for example, Patent Document 1). However, although such a separator provides a highly safe non-aqueous secondary battery, a porous film made of a heat-resistant material is provided between the positive electrode and the negative electrode in addition to the polyolefin porous film. There is a problem in that a non-aqueous secondary battery having insufficient ion conduction and insufficient load characteristics is provided.

Japanese Patent Laid-Open No. 10-3898

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery excellent in load characteristics, and to provide a separator for a non-aqueous electrolyte secondary battery excellent in dimensional stability at a high temperature, a method for producing the same, and safety including the same And providing a non-aqueous electrolyte secondary battery excellent in load characteristics.

  As a result of intensive studies on a separator for a non-aqueous electrolyte secondary battery in which a porous film made of a heat-resistant material and a polyolefin porous film are laminated, the present inventors have found that a porous film made of a heat-resistant material is water-soluble. The use of a porous polymer porous film not only provides a separator with excellent dimensional stability at high temperatures, but also surprisingly provides a non-aqueous electrolyte secondary battery with excellent load characteristics, completing the present invention. I came to let you.

  That is, the present invention provides a separator for a nonaqueous electrolyte secondary battery in which a porous film of a water-soluble polymer and a porous film of polyolefin are laminated. The present invention also provides a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte secondary battery separator. The present invention also provides the method for producing a separator for a non-aqueous electrolyte secondary battery described above, wherein a liquid containing a water-soluble polymer, fine particles and a medium is applied to a polyolefin porous film to remove the medium. Furthermore, the present invention provides a liquid containing a water-soluble polymer, fine particles and a medium on a support, then removing the medium, peeling the porous film containing the water-soluble polymer and fine particles from the support, A method for producing a separator for a non-aqueous electrolyte secondary battery as described above is provided.

  Since the separator for non-aqueous electrolyte secondary battery of the present invention is excellent in ion permeability, the non-aqueous electrolyte secondary battery using the separator for non-aqueous secondary battery of the present invention has excellent load characteristics. The separator for a non-aqueous electrolyte secondary battery of the present invention has excellent dimensional stability at high temperatures, so that the separator can be prevented from coming into direct contact with the positive electrode and the negative electrode even if the battery heats up due to an accident. The present invention is extremely useful industrially because it is a highly non-aqueous electrolyte secondary battery.

The present invention will be described in detail below.
The separator for a non-aqueous electrolyte secondary battery of the present invention includes a water-soluble polymer porous film (hereinafter sometimes referred to as A film) and a polyolefin porous film (hereinafter sometimes referred to as B film). Comprising. The B film melts and becomes non-porous when a battery accident occurs, and gives the separator a shutdown function. Since the water-soluble polymer has high heat resistance, the A film has heat resistance at a high temperature at which shutdown occurs, and imparts a dimensional stability function to the separator. When a non-aqueous electrolyte secondary battery is manufactured, if a separator in which an A film and a B film are laminated is used, the reason is not clear, but the B film is used and the A film is not laminated. The present inventor has found that a non-aqueous electrolyte secondary battery having a high load characteristic is provided without substantially reducing the load characteristic as compared with the case of using a separator.

The A film in the separator of the present invention will be described.
Examples of the water-soluble polymer contained in the A film of the present invention include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, polymethacrylic acid, and the like. Cellulose ether, polyvinyl alcohol, sodium alginate Preferably, cellulose ether is more preferable. Specific examples of the cellulose ether include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), carboxyethyl cellulose, methyl cellulose, ethyl cellulose, cyanethyl cellulose, oxyethyl cellulose, and the like. preferable.

  In the A film of the present invention, as a composition other than the water-soluble polymer, a dispersant, a plasticizer, fine particles, and the like can be included within a range that does not impair the object of the present invention. A nonaqueous electrolyte secondary battery may be provided, which is preferable. The fine particles are the same as those in the description of the production method of the present invention. The fine particles can be removed as necessary, for example, by immersing them in a solution in which the fine particles are soluble and the water-soluble polymer is insoluble.

  The thickness of the A film of the present invention is preferably in the range of 0.1 μm to 10 μm, and more preferably in the range of 0.5 μm to 5 μm. If it is too thick, the load characteristics of the battery may be reduced when a non-aqueous electrolyte secondary battery is manufactured. If it is too thin, the polyolefin porous membrane may be damaged when the battery generates heat due to an accident or the like. There is a risk that the separator may shrink without resisting heat shrinkage.

  In the present invention, the pore diameter of the A film is preferably 3 μm or less, more preferably 1 μm or less, as the diameter of the sphere when the hole is approximated to a sphere. When the average pore size or the pore size exceeds 3 μm, there is a possibility that a problem such as short-circuiting easily occurs when the carbon powder or the small piece as the main component of the positive electrode or the negative electrode falls off. Further, the porosity of the A film is preferably 30% to 70%, more preferably 40% to 60%.

Next, the B film in the separator of the present invention will be described.
The B film is a polyolefin porous film, and preferably contains a high molecular weight component having a weight average molecular weight of 5 × 10 ⁵ to 15 × 10 ⁶ . Examples of the polyolefin include a high molecular weight homopolymer or copolymer obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like. Among these, high molecular weight polyethylene mainly composed of ethylene is preferable.

  The porosity of the B film is preferably 30 to 80% by volume, more preferably 40 to 70% by volume. If the porosity is less than 30% by volume, the amount of electrolyte retained may be small. If it exceeds 80% by volume, non-porous formation at a high temperature that causes shutdown will be insufficient, that is, when the battery generates heat due to an accident. The current may not be cut off.

  Moreover, 5-50 micrometers is preferable and, as for the thickness of B film | membrane, More preferably, it is 5-30 micrometers. If the thickness is less than 5 μm, there is a risk that non-porous formation at a high temperature causing shutdown will be insufficient, and if it exceeds 50 μm, the thickness of the separator for a non-aqueous electrolyte secondary battery including a water-soluble polymer porous layer is increased. Since it becomes thick, there exists a possibility that the electrical capacity of a battery may become small. The pore size of the B film is preferably 3 μm or less, and more preferably 1 μm or less.

  The dimension retention rate of the B film at a high temperature at which shutdown occurs is 70% or more, preferably 75% or more, and more preferably 80% or more. If the dimensional retention is less than 70%, the separator may be deformed at a high temperature at which shutdown occurs and the shutdown function may be insufficient. Note that the high temperature at which shutdown occurs is a temperature of 80 to 180 ° C., and usually about 130 to 150 ° C.

  In the separator of the present invention composed of the A film and the B film described above, the A film and the B film are laminated to constitute the separator. Other than the A film and the B film, for example, a porous film such as an adhesive film and a protective film may be included in the separator of the present invention as long as the object of the present invention is not impaired. When a non-aqueous secondary battery is produced using the separator of the present invention, high load characteristics can be obtained, but the air permeability of the separator is preferably 50 to 2000 seconds / 100 cc, and more preferably 50 to 1000 seconds / 100 cc. When the air permeability is 2000 seconds / 100 cc or more, the load characteristics may be lowered.

Next, the manufacturing method of the separator of this invention is demonstrated.
The separator for a non-aqueous electrolyte secondary battery of the present invention is obtained by applying a liquid containing a water-soluble polymer, fine particles, and a medium onto a suitable support, removing the medium by drying or the like, and using the obtained membrane as a support. It is also possible to produce a porous film containing a water-soluble polymer and fine particles by peeling it off from the film, and press-bonding with a polyolefin porous film. It can be manufactured by molding into a porous film of polyolefin and press-bonding it with a porous film of polyolefin, or by applying a liquid containing a water-soluble polymer, fine particles and medium to the porous film of polyolefin and removing the medium by drying or the like. it can. In addition, about the polyolefin porous membrane, the commercial item which has the characteristic of the said description can be used. Alternatively, a porous polyolefin raw film containing calcium carbonate as an inorganic filler is immersed in an equal amount of a mixed solution of hydrochloric acid and methanol, and manufactured by a known manufacturing method such as a manufacturing method by dissolving and removing calcium carbonate Can be used.

  As fine particles in the production method of the present invention, inorganic or organic fine particles generally called fillers are used. As fine particles, styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, methyl acrylate, or a copolymer of two or more kinds; polytetrafluoroethylene, tetrafluoroethylene-6 fluorine Fluorine resin such as propylene fluoride copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride; melamine resin; urea resin; polyethylene; polypropylene; fine particles made of organic matter such as polymethacrylate. Also, calcium carbonate, talc, clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium oxide, magnesium oxide, titanium oxide , Fine particles composed of inorganic substances such as alumina, mica, zeolite, glass and the like. Two or more kinds of fine particles or the same kind of fine particles having different particle size distributions may be mixed and used. Among these, alumina is preferable as the fine particles. The average particle size of the fine particles is preferably 3 μm or less, and more preferably 1 μm or less. In addition, an average particle diameter is an average of the primary particle diameter calculated | required by SEM observation.

  In the production method of the present invention, when a liquid containing a water-soluble polymer, fine particles and a medium (hereinafter sometimes referred to as “coating liquid”) is applied to a support or a B film and the medium is removed by drying or the like, the reason is Although it is not clear, the film containing the water-soluble polymer and the fine particles becomes a porous film. It seems that when the applied coating solution dries, a gap is formed around the fine particles to form a porous film. If the liquid containing the water-soluble polymer does not contain fine particles, it does not become a porous film.

  As a coating solution in the production method of the present invention, for example, a water-soluble polymer is dissolved or swollen in a medium (a solution in which a water-soluble polymer swells may be used if there is no problem in coating), and the water-soluble polymer 100 weight. A liquid containing 1 to 2000 parts by weight, preferably 50 to 1000 parts by weight, and more preferably 100 to 800 parts by weight of fine particles with respect to parts. If the amount of the fine particles is too small, the air permeability of the separator obtained is lowered, the ion permeation is lowered, and the load characteristics of the battery may be lowered. If the amount of fine particles is too large, the dimensional stability of the resulting separator may be reduced. In addition, a surfactant, a pH adjuster, an inorganic salt, and the like can be added to this liquid as long as the object of the present invention is not impaired. The water-soluble polymer may be used by appropriately selecting the molecular weight or the like so that the viscosity is suitable for coating. Similarly, the concentration of the water-soluble polymer in the liquid may be adjusted so as to have a viscosity suitable for coating.

  The method of applying the coating solution to the support or the B film can be carried out by a method commonly used industrially, such as coating by a coater (also referred to as a doctor blade) or coating by brush coating. The thickness of the A film can be controlled by adjusting the thickness of the coating film, the concentration of the water-soluble polymer in the coating solution, and the ratio of the fine particles to the water-soluble polymer. As the support, a resin film, a metal belt, a drum, or the like can be used.

  The medium is generally removed by drying. A solvent that dissolves in the medium and does not dissolve the water-soluble polymer used is prepared, and after coating, the film before drying is immersed in the solvent to replace the medium with the solvent to precipitate the water-soluble polymer. The medium can also be removed and the solvent can be removed by drying. When the coating solution is applied on the B film, the drying temperature of the medium or solvent is preferably a temperature that does not decrease the air permeability of the B film.

  When the coating solution is applied onto the support, the A film obtained after removing the medium is peeled off from the support and laminated with the A film. Examples of the laminating method include a method of thermocompression bonding using a heating roll and a method of using a porous film adhesive film.

Next, the nonaqueous electrolyte secondary battery of the present invention will be described.
The battery of the present invention includes the separator for a non-aqueous electrolyte secondary battery of the present invention. Below, the case where the battery of the present invention is a non-aqueous electrolyte secondary battery such as a lithium battery will be described as an example, but the components other than the separator for the non-aqueous electrolyte secondary battery will be described. However, the present invention is not limited thereto. Absent.

As the nonaqueous electrolytic solution, for example, a nonaqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent can be used. Examples of lithium salts include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , One or a mixture of two or more of lower aliphatic carboxylic acid lithium salts, LiAlCl _{4 and the} like can be mentioned. The lithium salt is selected from the group consisting of LiPF ₆ containing fluorine, LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiC (CF ₃ SO ₂ ) ₃ among these. It is preferable to use those containing at least one selected from the above.

  Examples of the non-aqueous electrolyte include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, 1,2-di (methoxycarbonyloxy) Carbonates such as ethane; ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran Esters such as methyl formate, methyl acetate and Y-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N, N-dimethylformamide and N, N-dimethylacetamide Carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propane sultone, or those obtained by introducing a fluorine group into the above-mentioned substances can be used. Two or more of these are mixed and used.

  Among these, those containing carbonates are preferred, and cyclic carbonates and acyclic carbonates, or mixtures of cyclic carbonates and ethers are more preferred. As a mixture of cyclic carbonate and acyclic carbonate, ethylene carbonate and dimethyl have a wide operating temperature range and are hardly decomposable even when a graphite material such as natural graphite or artificial graphite is used as the negative electrode active material. A mixture comprising carbonate and ethyl methyl carbonate is preferred.

As the positive electrode sheet, a sheet in which a mixture containing a positive electrode active material, a conductive material, and a binder is supported on a current collector is usually used. Specifically, as the positive electrode active material, a material containing a material that can be doped / undoped with lithium ions, a carbonaceous material as a conductive material, and a thermoplastic resin as a binder can be used. Examples of the material that can be doped / undoped with lithium ions include lithium composite oxides containing at least one transition metal such as V, Mn, Fe, Co, and Ni. Among these, lithium composite oxides having an α-NaFeO ₂ type structure such as lithium nickelate and lithium cobaltate, and lithium composite oxides having a spinel type structure such as lithium manganese spinel are preferable in that the average discharge potential is high. Can be mentioned.

  The lithium composite oxide may contain various metal elements, particularly at least selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Ag, Mg, Al, Ga, In, and Sn. The metal element is included so that the at least one metal element is 0.1 to 20 mol% with respect to the sum of the number of moles of one metal element and the number of moles of Ni in lithium nickelate. It is preferable to use composite lithium nickelate because the cycle performance in use at a high capacity is improved.

  As the binder, polyvinylidene fluoride, vinylidene fluoride copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, Examples include ethylene-tetrafluoroethylene copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, thermoplastic resins such as thermoplastic polyimide, polyethylene, and polypropylene.

  Examples of the conductive agent include carbonaceous materials such as natural graphite, artificial graphite, cokes, and carbon black. As the conductive material, each may be used alone, for example, artificial graphite and carbon black may be mixed and used.

  As the negative electrode sheet, for example, a material capable of doping and dedoping lithium ions, lithium metal, or a lithium alloy can be used. Materials that can be doped / undoped with lithium ions include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired organic polymer compounds, and lower potential than the positive electrode. And chalcogen compounds such as oxides and sulfides for doping and dedoping lithium ions. As a carbonaceous material, a carbonaceous material mainly composed of graphite materials such as natural graphite and artificial graphite, because it has a high potential flatness and a low average discharge potential, so that a large energy density can be obtained when combined with a positive electrode. Is preferred.

  As the negative electrode current collector, Cu, Ni, stainless steel, or the like can be used. In particular, in a lithium secondary battery, Cu is preferable because it is difficult to form an alloy with lithium and it can be easily processed into a thin film. As a method of supporting the mixture containing the negative electrode active material on the negative electrode current collector, a method of pressure molding, or a method of pasting into a paste using a solvent or the like and applying pressure to the current collector by pressing after drying Is mentioned.

  The shape of the battery of the present invention is not particularly limited, and may be any of a paper type, a coin type, a cylindrical type, a rectangular shape, and the like.

  When a non-aqueous electrolyte secondary battery is manufactured using the non-aqueous electrolyte secondary battery separator of the present invention, the separator has a high load characteristic, and even if the battery generates heat severely due to an accident, the separator exhibits a shutdown function. Thus, contact between the positive electrode and the negative electrode due to shrinkage of the separator is avoided, and a highly safe non-aqueous electrolyte secondary battery is obtained.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.
In Examples and Reference Examples, the physical properties and the like of porous films were measured by the following methods.
(1) Air permeability: compliant with JIS P8117.
(2) Average pore diameter: Conforms to ASTM F316-86.
(3) Film thickness: compliant with JIS K7130.
(4) Porosity The film was cut into a 10 cm long square, and the weight: W (g) and the thickness: D (cm) were measured. The weight of the material in the sample was divided by calculation, the weight of each material: Wi (g) was divided by the true specific gravity, the volume of each material was calculated, and the porosity (volume%) was obtained from the following formula. .
Porosity (%) = 100-[{(W1 / true specific gravity 1) + (W2 / true specific gravity 2) + .. + (Wn / true specific gravity n)} / (100 × D)] × 100
The basis weight of the film was obtained from the following equation by cutting the film into a 10 cm square and measuring its weight.
Film weight (g / m ² ) = weight of sample cut out of 10 cm square square (g) /0.01 (m ² )
The basis weight of each material was calculated from the amount and ratio used for film formation.

(5) Dimension retention The film is cut into a 15 cm square, a 10 cm square square ruled line is written in the center, and sandwiched between two 0.5 mm thick aluminum plates coated with a release agent. In a heated oven. The temperature of the oven was raised to 150 ° C. at a rate of 1 ° C./minute and held for 10 minutes, then taken out, the square dimensions were measured, and the dimension retention rate was calculated. The calculation method of the dimensional retention rate is as follows.
Ruled line length before heating in MD direction: L1
Ruled line length before heating in TD direction: W1
Ruled line length in MD direction after heating: L2
Ruled line length in TD direction after heating: W2
Dimension retention (%) = ((L2 × W2) / (L1 × W1)) × 100

(6) Evaluation as a separator for non-aqueous electrolyte batteries Paste prepared by mixing lithium cobaltate powder, graphite powder, acetylene black and polyvinylidene fluoride in a weight ratio of 87: 9: 1: 3 (solvent: N-methylpyrrolidone (NMP) ) Was applied to an aluminum foil having a thickness of 20 μm, dried and pressed to produce a sheet having a thickness of 85 μm, which was used as a positive electrode. Lithium metal was used as the negative electrode. As the electrolytic solution, a solution obtained by dissolving lithium hexafluorophosphate (concentration 1 mol / L) in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was used. As the separator, a separator for a nonaqueous electrolyte battery described in Examples of the present invention was used.

The battery has a flat-plate structure with a positive electrode area of 3.0 cm ² , and after stacking the negative electrode sheet, the separator, and the positive electrode sheet in this order in a glove box in which the above-prepared one is an argon atmosphere, the separator is sufficiently filled with an electrolyte. Was impregnated. The produced flat battery is charged to 4.2 V at a charging current of 1.5 mA, and the discharge capacity (discharge current of 1.5 mA) is measured when discharged to 3.0 V at a discharge current of 1.5 mA to obtain a discharge capacity DA. . When the battery is charged under the above conditions and the discharge capacity (discharge current 30.0 mA) is measured, this is defined as the discharge capacity DB. It calculated | required by the following Formula as the load characteristic of a battery.
Load characteristics (%) = (DB / DA) × 100

Example 1
1-1. Preparation of slurry solution for coating 591 g of ion-exchanged water was placed in a 1000 ml separable flask, and 9 g of CMC (Daiichi Kogyo Seiyaku, product number 3H) was gradually added with stirring, followed by stirring for 120 minutes. Subsequently, 45 g of alumina fine particles (manufactured by Nippon Aerosil Co., Ltd., alumina C (trade name), particle size 0.013 μm) were mixed and stirred for 240 minutes. The fine alumina particles were sufficiently dispersed and defoamed under reduced pressure to obtain a slurry solution for coating.

1-2. Production of Separator for Nonaqueous Electrolyte Secondary Battery Battery A PET (polyethylene terephthalate) film having a thickness of 100 μm is wound on a drum having a diameter of 550 mm, and a porous film (porous polyethylene film: basis weight 15 g / m ² ) is formed on the PET film. , 25 μm thick). A slurry solution was applied on the porous film. After coating the entire porous film with a coating speed of 870 mm / min and a clearance of 0.1 mm, both ends of the porous film are fixed to the drum, dried with hot air of 50 ° C. for 60 minutes to remove the medium (water) The composite porous film was removed.

1-3. Composite porous film properties above composite porous film had a thickness of 28 .mu.m, basis weight 18 g / m ² (porous polyethylene film ^{15g / m 2, CMC0.5g / m} 2, alumina 2.5 g / m ^2), the gap The rate was 53%. When the film was observed with a scanning electron microscope, it was a porous layer in which CMC resin and alumina fine particles having a particle size of about 0.013 μm were uniformly dispersed. The air permeability of this film was 500 seconds / 100 cc, and the dimensional retention was 86%.

1-4. Evaluation as separator for non-aqueous electrolyte battery The discharge capacity was 160 mAH / g (discharge current 1.5 mA), and it operated normally without cycle deterioration. The load characteristic was 41%. From the above results, it was found that this separator has performance as a separator for nonaqueous electrolyte batteries.

1-5. Safety test in cylindrical battery (1) Preparation of positive electrode sheet electrode Concentration of polytetrafluoroethylene in such an amount that 1 part by weight of carboxymethylcellulose is dissolved in water and 4.5 parts by weight of polytetrafluoroethylene is dissolved therein. A 60 wt% aqueous dispersion, 2.5 parts by weight of acetylene black, and 92 parts by weight of lithium cobaltate powder as a positive electrode active material were added and dispersed and kneaded to obtain a positive electrode mixture paste. The paste was applied to predetermined portions on both sides of a 20 μm thick Al foil as a current collector, dried and roll pressed to obtain a positive electrode sheet electrode.

(2) Production of negative electrode sheet electrode 2 parts by weight of carboxymethyl cellulose was dissolved in water, and 98 parts by weight of natural graphite was added thereto and dispersed and kneaded to obtain a negative electrode mixture paste. The paste was applied to predetermined portions on both sides of a 10 μm-thick Cu foil as a current collector, dried and roll-pressed to obtain a negative electrode sheet electrode.
The positive electrode sheet electrode and the negative electrode sheet electrode manufactured as described above are laminated in the order of the negative electrode, the separator, the positive electrode, and the separator through the separator, and the laminate is wound from one end to form a spiral electrode element. It was.
The above electrode element is inserted into a battery can, and LiPF ₆ is dissolved in a mixed solution of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 16:10:74 as a non-aqueous electrolyte solution so as to be 1 mol / liter. And a battery lid that also serves as a positive electrode terminal was caulked through a gasket to obtain a 18650 size cylindrical battery.

(3) Safety Evaluation of Cylindrical Battery The cylindrical battery thus obtained was subjected to a nail penetration test in an overcharged state of 4.3 V as a safety test. As a result, the battery used for the test showed only a gradual temperature rise despite the severe state of overcharging.

Comparative Example 1
A coating polymer solution was prepared in the same manner as in Example 1 except that alumina fine particles were not added, and a separator was prepared in the same manner as in Example 1.

The separator had a thickness of 28 μm, a basis weight of 18 g / m ² (a porous polyethylene film was 15 g / m ² , and CMC was 3 g / m ² ), and a porosity was 50%. When the film was observed with a scanning electron microscope, no pores were observed on the CMC surface at a magnification of 10,000 times. The air permeability of this film was 10,000 ≦ sec / 100 cc, the average pore size was not measurable, and the dimensional retention was 86%, which did not form a water-soluble polymer porous layer. The battery performance was not measurable due to poor impregnation of the electrolyte.

Comparative Example 2
A battery was fabricated in the same manner as in Example 1 using the same porous polyethylene film (no CMC layer) as in Example 1 as the separator. This porous polyethylene film had a thickness of 25 μm, a basis weight of 15 g / m ² , and a porosity of 50%. When the film was observed with a scanning electron microscope, fibrillated pores were observed. The air permeability of this film was 150 seconds / 100 cc, the average pore diameter was 0.05 μm, and the dimensional retention was 30%.

  The discharge capacity was 160 mAH / g (discharge current 1.5 mA), and it operated normally without cycle deterioration. The load characteristic was 41%.

2-2, Safety Test with Cylindrical Battery Using this nonaqueous electrolyte secondary battery separator, a cylindrical battery was produced in the same manner as in Example 1, and a nail penetration test was conducted in the same manner as in Example 1. . As a result, in the nail penetration test in the overcharged state, the battery used for the test showed a significant temperature increase after the nail penetration.

Claims (8)

  A separator for a nonaqueous electrolyte secondary battery, wherein a porous film of a water-soluble polymer and a porous film of polyolefin are laminated.   The separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the porous film of the water-soluble polymer is a porous film containing fine particles.   The separator for a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the water-soluble polymer is at least one selected from the group consisting of cellulose ether, polyvinyl alcohol, and sodium alginate.   The separator for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the water-soluble polymer is carboxymethyl cellulose.   The non-aqueous electrolyte secondary battery separator according to any one of claims 1 to 4, wherein the polyolefin is polyethylene.   The separator for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the air permeability is 50 to 2000 seconds / 100 cc.   The nonaqueous electrolyte secondary battery separator according to any one of claims 1 to 6, having a dimensional retention of 70% or more.   A non-aqueous electrolyte secondary battery using the non-aqueous electrolyte secondary battery separator according to claim 1.