JP2000100408A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery further improved in safety and high energy density. SOLUTION: (1) This battery comprises a positive electrode sheet, a separator, nonaqueous electrolyte, and a negative electrode sheet. In this case, the separator is composed of a heat-resistant porous layer and a shut down layer, and the heat-resistant porous layer is arranged on the positive electrode sheet side. (2) The heat-resistant porous layer may be composed of a heat-resistant resin having the deflection temperature under load of not less than 100 deg.C, and the limiting oxygen index of not less than 20. (3) The shut down layer is a porous layer composed of a thermoplastic resin, and it may substantially become a nonporous layer at the temperature of 80 deg.C-180 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery including a positive electrode sheet, a separator, a non-aqueous electrolyte and a negative electrode sheet.

[0002]

2. Description of the Related Art In recent years, portable information devices including personal computers, portable telephones, portable information terminals and the like have been remarkably spread. Since these devices as multimedia are desired to have multiple functions, secondary batteries used as power sources are required to be small, light, and have large capacity, that is, high energy density. I have. In this regard, conventional aqueous secondary batteries such as lead storage batteries and nickel cadmium storage batteries are not satisfactory, and lithium secondary batteries capable of realizing higher energy densities, especially lithium cobalt oxide, lithium nickel oxide, and lithium manganese spinel Research and development of lithium secondary batteries using a composite oxide of lithium as a positive electrode active material and a carbon material capable of doping / dedoping lithium ions as a negative electrode active material have been actively conducted.

[0003] Since these lithium secondary batteries have large inherent energy, higher safety is required against abnormal situations such as internal short-circuits and external short-circuits. When such an abnormality occurs, the temperature of the battery may increase, leading to thermal runaway. As a countermeasure, in a separator composed of a polyolefin-based porous layer, a thermal runaway is prevented by a structure in which the polyolefin layer becomes nonporous at about 80 ° C. to 180 ° C. and does not conduct electricity at the time of abnormal heat generation. However, when heat generation is intense, the positive electrode and the negative electrode come into direct contact due to melting and shrinkage of the polyolefin layer, which may lead to thermal runaway.

On the other hand, when a porous film made of a heat-resistant resin is used alone as a separator, melting and shrinkage can be avoided to some extent like a polyolefin, but the shutdown function does not work and external or high-speed charging / discharging is not possible. There is a high possibility that sufficient safety against the accompanying internal heating cannot be obtained.

[0005] Therefore, it has been studied to combine a heat-resistant porous body with a porous body mainly composed of polyolefin to form a separator. For example, JP-A-8-87
No. 995 proposes a laminated structure of a polyphenylene sulfide with a porous body for the purpose of preventing the polyolefin layer from being completely melted or cracked. Similarly, for the purpose of preventing large heat generation triggered by thermal melting of the separator,
Japanese Patent Application Laid-Open No. 9-161775 describes a structure in which each of a positive electrode sheet and a negative electrode sheet is covered with a polyolefin-based separator, and a heat-resistant porous film is arranged between the separators.

There are few cases where the arrangement of the heat-resistant porous layer and the shutdown layer is specified, but a few examples are known. JP-A-6-76808 proposes a separator comprising a laminate of a porous fluororesin and a porous polyolefin. In this patent, metallic lithium is used as the negative electrode material.However, since the fluororesin reacts with the metallic lithium and carbonizes, the polyolefin porous body is disposed on the metallic lithium side, and the fluororesin porous body is formed from metallic lithium. Isolation is described. In Japanese Patent Application Laid-Open No. 62-37871, when a welding piece is attached to the surface of a negative electrode can in a so-called flat battery,
It is described that a polyimide nonwoven fabric is disposed on the negative electrode side in order to prevent the polyolefin-based nonwoven fabric from being melted and divided.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-aqueous electrolyte secondary battery having a high energy density and improved safety.

Regarding safety, it is important that safety is ensured not only for the above-described internal short-circuit and external short-circuit, but also for a severe test involving forced local heat generation. In particular, it is known that the charged positive electrode active material decomposes while releasing oxygen due to heat generation, and further generates heat, for a short circuit involving local heat generation such as a nail penetration or crush test. Have been. Under these circumstances, if a separator made of polyethylene or polypropylene, which is conventionally used, is present near the positive electrode at the short circuit, it is oxidized by oxygen released from the positive electrode active material and generates significant heat. It is suggested that it may lead to

In a non-aqueous electrolyte secondary battery having a high energy density, a high electrical capacity is also a technical issue, but more importantly, ensuring safety even in the above-described severe test is a more important issue. It has become.

[0010]

[Means for Solving the Problems] In view of such circumstances,
As a result of intensive studies, the present inventors have found that by using a separator composed of a heat-resistant porous layer and a shutdown layer, the safety is significantly improved by disposing the heat-resistant porous layer on the positive electrode sheet side. The invention has been completed.

More specifically, in the case of a short circuit involving local heat generation, such as a nail penetration or crush test, the charged positive electrode active material is decomposed while releasing oxygen due to heat generation, It is known that heat is further generated. The present inventors have found that, in such a situation, when a separator made of polyethylene or polypropylene conventionally used is present near the positive electrode at the short-circuit portion, the separator is oxidized by oxygen released from the positive electrode active material and generates significant heat. Therefore, it is thought that thermal runaway may occur, and when the heat-resistant porous layer is disposed on the positive electrode side, a remarkable effect on safety is found.

That is, the present invention provides (1) a non-aqueous electrolyte secondary battery including a positive electrode sheet, a separator, a non-aqueous electrolyte and a negative electrode sheet, wherein the separator comprises a heat-resistant porous layer and a shutdown layer; The present invention relates to a non-aqueous electrolyte secondary battery having a porous layer disposed on the positive electrode sheet side. The present invention also provides (2) the non-aqueous electrolyte secondary battery according to (1), wherein the heat-resistant porous layer is made of a heat-resistant resin having a deflection temperature under load of 100 ° C. or more and a limiting oxygen index of 20 or more. It is related to. Further, the present invention provides (3)
The nonaqueous electrolyte secondary battery according to (1), wherein the shutdown layer is a porous layer made of a thermoplastic resin and becomes a substantially nonporous layer at a temperature of 80 ° C to 180 ° C. .

[0013]

Next, the present invention will be described in detail.
As the positive electrode sheet in the present invention, a sheet in which a mixture containing a positive electrode active material, a conductive material, and a binder is carried on a current collector is used. Specifically, a material containing a material capable of doping and undoping lithium ions, a carbonaceous material as a conductive material, and a thermoplastic resin as a binder can be used as the positive electrode active material. Materials that can be doped / undoped with lithium ions include V, Mn, Fe, C
Examples of the lithium composite oxide include at least one transition metal such as o and Ni. Among them, preferably, in terms of high average discharge potential, lithium nickelate, a layered lithium composite oxide based on α-NaFeO ₂ type structure such as lithium cobaltate as a base, and a spinel type structure such as lithium manganese spinel as a base. And a lithium composite oxide.

The lithium composite oxide may contain various additional elements, and in particular, Ti, V, Cr, Mn, Fe, C
o, the sum of the number of moles of at least one metal selected from the group consisting of Cu, Ag, Mg, Al, Ga, In, and Sn and the number of moles of Ni in lithium nickelate,
It is preferable to use a composite lithium nickelate containing the metal such that the content of the at least one metal is 0.1 to 20 mol%, since the cyclability in high capacity use is improved.

As the thermoplastic resin as the binder,
Polyvinylidene fluoride, vinylidene fluoride copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, ethylene-tetrafluoroethylene copolymer Examples include a polymer, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene.

Examples of the carbonaceous material as the conductive agent include natural graphite, artificial graphite, cokes, and carbon black. As the conductive material, each may be used alone, or for example, a composite conductive material system in which artificial graphite and carbon black are used in combination may be selected.

The heat-resistant porous layer in the present invention is manufactured from a heat-resistant resin. The size of the voids in the heat-resistant porous layer or, when the voids can be approximated to a sphere, the diameter of the sphere (hereinafter sometimes referred to as the pore diameter) is preferably 3 μm or less, more preferably 1 μm or less. When the average size or pore size of the voids exceeds 3 μm, when carbon powder or a small piece of the main component of the positive electrode or the negative electrode falls off,
Problems such as easy short-circuiting may occur. The porosity of the heat-resistant porous layer is preferably 30 to 80% by volume, more preferably 40 to 70% by volume. The porosity is 3
If the volume is less than 0% by volume, the holding amount of the electrolyte is small, and
If it exceeds, the strength of the heat resistant porous layer becomes insufficient. The thickness of the heat-resistant porous layer is preferably 3 to 30 μm, more preferably 5 to 20 μm. When the thickness is less than 3 μm, the effect on safety as a heat-resistant porous layer is insufficient, and when the thickness exceeds 30 μm, the thickness of the separator for a non-aqueous electrolyte battery including a shutdown layer is too large to increase the electric capacity. Difficult to achieve.

The heat-resistant resin for forming the heat-resistant porous layer is 18.6 kg / cm ² according to JIS K 7207.
At least one heat-resistant resin selected from resins having a deflection temperature under load of 100 ° C. or higher in the measurement under load is used. In order to be safer even at a high temperature due to severe use, the heat-resistant resin in the present invention is preferably at least one heat-resistant resin selected from resins having a deflection temperature under load of 200 ° C. or higher. The deflection temperature under load is 10
Examples of the resin at 0 ° C. or higher include polyimide, polyamideimide, aramid, polycarbonate, polyacetal, polysulfone, polyphenylsulfide, polyetheretherketone, aromatic polyester, polyethersulfone, and polyetherimide. Examples of the resin having a deflection temperature under load of 200 ° C. or higher include polyimide, polyamideimide, aramid, polyethersulfone, and polyetherimide. Further, it is particularly preferable that the heat-resistant resin is selected from the group consisting of polyimide, polyamideimide and aramid.

Further, the heat-resistant resin in the present invention includes:
The limiting oxygen index is preferably 20 or more. The limiting oxygen index is the minimum oxygen concentration at which a specimen placed in a glass tube can keep burning. A feature of the present invention is that the shutdown layer made of polyolefin or the like is isolated from the positive electrode sheet by the heat-resistant porous layer.
Therefore, the heat-resistant porous layer is preferably flame-retardant in consideration of oxygen generated from the positive electrode material at high temperature, in addition to heat resistance. Specific examples of such a resin include the above-described heat-resistant resin.

The shutdown layer in the present invention is a porous layer made of a thermoplastic resin, and has the same void size, porosity and thickness as those of the heat-resistant porous layer. Specifically, the size of the void, or when the void can be approximated to a sphere, the diameter of the sphere (hereinafter, sometimes referred to as the pore diameter) is preferably 3 μm or less, more preferably 1 μm or less. The average size or pore size of the voids is 3
When the thickness exceeds μm, there is a possibility that a problem such as a short circuit is likely to occur when carbon powder or a small piece thereof, which is a main component of the positive electrode or the negative electrode, falls off. The porosity of the heat-resistant porous layer is
30-80 volume% is preferable, More preferably, 40-80 volume%.
70% by volume. If the porosity is less than 30% by volume, the retained amount of the electrolytic solution is small, and if it exceeds 80%, the strength of the heat-resistant porous layer becomes insufficient and the shutdown function decreases. The thickness of the heat-resistant porous layer is preferably 3 to 30 μm, more preferably 5 to 20 μm. The thickness is 3
If it is less than μm, the shutdown function is insufficient and
If it exceeds 0 μm, the thickness of the separator for a non-aqueous electrolyte battery including the heat-resistant porous layer is too large, and it is difficult to achieve a high electric capacity. However, as for the size of the void, if one of the heat-resistant porous layer and the shutdown layer satisfies the above condition, the other may be larger than 3 μm.

The thermoplastic resin forming the shutdown layer is preferably a thermoplastic resin which softens at 80 to 180 ° C., closes the porous voids, and does not dissolve in the electrolytic solution. Specific examples include polyolefin and thermoplastic polyurethane. Further, specific examples include at least one thermoplastic resin selected from polyethylene, such as low-density polyethylene, high-density polyethylene, and ultrahigh-molecular-weight polyethylene, and polypropylene.

In the present invention, any of the heat-resistant resin for the heat-resistant porous layer and the thermoplastic resin for the shutdown can contain inorganic fine powder.

As the non-aqueous electrolyte solution used in the lithium secondary battery of the present invention, for example, a non-aqueous electrolyte solution obtained by dissolving a lithium salt in an organic solvent can be used. Lithium salts include LiClO ₄ , LiPF ₆ , LiAsF ₆ ,
LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (S
O ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , Li ₂ B ₁₀ Cl
₁₀ , lower aliphatic carboxylic acid lithium salt, LiAlCl ₄
One or a mixture of two or more of these.
LiP containing fluorine among these as a lithium salt
F ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF
₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and LiC (CF ₃
It is preferable to use a material containing at least one selected from the group consisting of SO ₂ ) ₃ .

Examples of the organic solvent used in the nonaqueous electrolyte of the present invention include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, Carbonates such as 1,2-di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethyl ether,
Ethers such as 2,3,3-tetrafluoropropyldifluoromethyl ether, tetrahydrofuran and 2-methyltetrahydrofuran; methyl formate, methyl acetate,
Esters such as γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N, N-dimethylformamide and N, N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfolane, dimethylsulfoxide , 1,
A sulfur-containing compound such as 3-propane sultone or a compound obtained by introducing a fluorine substituent into the above-mentioned organic solvent can be used. Usually, a mixture of two or more of these compounds is used.

Among these, a mixed solvent containing a carbonate is preferable, and a mixed solvent of a cyclic carbonate and an acyclic carbonate or a mixed solvent of a cyclic carbonate and an ether is more preferable. The mixed solvent of cyclic carbonate and acyclic carbonate has a wide operating temperature range, excellent load characteristics, and is hardly decomposable even when a graphite material such as natural graphite or artificial graphite is used as a negative electrode active material. And a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferred.

As the negative electrode sheet in the present invention, for example, a material capable of doping / de-doping lithium ions, lithium metal or lithium alloy can be used. Materials that can be doped or 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 a lower potential than the positive electrode. And chalcogen compounds such as oxides and sulfides for doping / dedoping lithium ions. As a carbonaceous material, a carbonaceous material mainly composed of a graphite material such as natural graphite and artificial graphite, in that a high energy density can be obtained when combined with a positive electrode because the potential flatness is high and the average discharge potential is low. Is preferred.

When the liquid electrolyte does not contain ethylene carbonate when used in combination with a liquid electrolyte, it is preferable to use a polyethylene carbonate-containing negative electrode because cycle characteristics and large current discharge characteristics are improved. The shape of the carbonaceous material may be any of, for example, a flaky shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, or an aggregate of fine powder. In addition, a thermoplastic resin as a binder can be added. Examples of the thermoplastic resin include polyvinylidene fluoride, a copolymer of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene-terafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene. Examples of chalcogen compounds such as oxides and sulfides used as the negative electrode include crystalline or non-crystalline compounds mainly composed of groups 13, 14, and 15 of the periodic table, such as amorphous compounds mainly composed of tin oxide. And crystalline oxides. Also for these, a carbonaceous material as a conductive material and a thermoplastic resin as a binder can be added as necessary.

As the negative electrode current collector used in the non-aqueous electrolyte secondary battery of the present invention, Cu, Ni, stainless steel or the like can be used. Particularly in a lithium secondary battery, it is difficult to form an alloy with lithium, and Cu is preferred because 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 using a solvent or the like, applying a paste on the current collector, drying and pressing, or the like, is used. Is mentioned.

In the separator of the present invention, various methods are available for laminating the heat-resistant porous layer and the shutdown layer. Although the two layers may not be joined and may be simply overlapped, it is preferable to stack and fix them from the viewpoint of handleability. Examples of the fixing method include a method using an adhesive and a method using heat fusion, but the present invention is not limited to these.

Further, as a preferred lamination method, a porous film for forming either a heat-resistant porous layer or a shutdown layer is used as a substrate, and the other is coated in a solution state to form a solution layer, and then a desolvation treatment is performed. This is a manufacturing method in which a laminated film is formed.

Specific examples are shown below, but the present invention is not limited to these. That is, the following (a)
To (e). (A) A solution comprising a heat-resistant resin and an organic solvent is prepared. When the inorganic fine powder is used, a slurry solution is prepared by dispersing 1 to 200 parts by weight of the inorganic fine powder with respect to 100 parts by weight of the heat-resistant resin. (B) applying the solution or slurry solution to a polyolefin-based porous film to form a coating film. (C) depositing the heat-resistant resin on the coating film. (D) removing the organic solvent from the coating film; (E) drying the coated film;

Further, the case of using para-oriented aromatic polyamide (hereinafter sometimes referred to as para-aramid) and polyimide will be specifically described. When para-aramid is used, for example, in a polar organic solvent in which 2 to 10% by weight of an alkali metal or alkaline earth metal chloride is dissolved, 1.00 mol of para-oriented aromatic diamine and para-oriented aromatic dicarboxylic acid are used. Acid dihalide 0.94-0.
A para-aramid having a concentration of 1 to 10% and an intrinsic viscosity of 1.0 to 2.8 dl / g, and an organic solvent, are added by adding 99 moles and performing condensation polymerization at a temperature of -20 ° C to 50 ° C. A solution consisting of Using this solution, the separator of the present invention in which a para-aramid porous layer is laminated on a polyolefin-based porous film by the above-mentioned production method can be produced. In the case of para-aramid, to remove the solvent and the chloride, it can be washed with the same solvent as a coagulating liquid such as water or methanol, but a part or all of the solvent was evaporated and a polymer was precipitated at the same time. Thereafter, the chloride may be removed by a method such as washing with water.

Examples of the solution comprising a polyimide and an organic solvent include 3,3 ', 4,4'-diphenylsulfonetetracarboxylic dianhydride and 4,4'-bis (p-aminophenoxy) diphenylsulfone. An example of the N-methyl-2-pyrrolidone solution of imidized polyimide obtained by a polycondensation reaction with an aromatic diamine is shown. In the solution, the inorganic fine powder is preferably 1 to 200 parts by weight, more preferably 5 to 10 parts by weight based on 100 parts by weight of the polyimide.
0 parts by weight are sufficiently dispersed to prepare a slurry solution.
If the amount of the inorganic fine powder is less than 1 part by weight, the ion permeability and battery characteristics are insufficiently improved.
The separator is not preferred because it becomes brittle and difficult to handle. Next, the slurry solution is applied to the polyolefin-based porous film to form a solution layer. Examples of the coating method include a coating method using a knife, a blade, a bar, a gravure, a die, or the like. The obtained coating film is preferably precipitated in an atmosphere controlled at a temperature of 20 ° C. or higher and a constant humidity, and then immersed in a coagulation liquid to obtain a wet coating film. Next, the resultant is washed with water, the solvent is removed, and then dried to produce a separator in which a polyimide porous layer is laminated on a polyolefin-based porous film.

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

[0035]

The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the invention thereto. (1) Intrinsic Viscosity In the present invention, the intrinsic viscosity is defined by the following measuring method. For a solution in which 0.5 g of the para-aramid polymer was dissolved in 100 ml of 96-98% sulfuric acid and for a 96-98% sulfuric acid, the flow time was measured at 30 ° C. using a capillary viscometer. Was used to determine the intrinsic viscosity. Intrinsic viscosity = ln (T / T ₀ ) / C [unit: dl / g] where T and T ₀ are the flow times of the para-aramid sulfate solution and sulfuric acid, respectively, and C is the concentration of para-aramid in the para-aramid sulfate solution ( dl / g).

(2) Measurement of Thickness of Coated Film and the Like The thickness of the obtained coated film and the like is measured in accordance with JIS K7130-
1992.

(3) Porosity The coating film or the like was cut into a square having a side length of 10 cm, and the weight (Wg) and thickness (Dcm) were measured. The weight of the material in the sample was divided by calculation, the weight (Wi) of each material was divided by the true specific gravity, and the porosity (vol%) was determined from the following equation, assuming the volume of each material. Porosity (%) = 100 − ｛(W1 / true specific gravity 1) + (W2
/ True specific gravity 2) + ·· + (Wn / True specific gravity n) （/ (100
× D)

(Equation 1)

(4) The basis weight of the coating film and the like is as follows.
A square of 0 cm square was cut out, and its weight was measured and determined by the following equation. Weight of coating film (g / m ² ) = weight of sample (g)
/0.01 (m ² ) The basis weight of each material was calculated from the amount and ratio used for film formation.

Example 1 (1) Preparation of positive electrode sheet electrode 3 parts by weight of polyvinylidene fluoride (hereinafter sometimes referred to as PVDF) were dispersed in NMP, and 9 parts by weight of artificial graphite powder as a conductive material and acetylene black 1 part by weight and 87 parts by weight of lithium nickel oxide powder as a positive electrode active material were dispersed and kneaded to prepare 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.

(2) Preparation of heat-resistant porous film 2.1) Synthesis of para-aramid solution 5 having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port
Using a liter (l) separable flask, poly (paraphenylene terephthalamide) (hereinafter referred to as PPTA)
Abbreviation). Dry the flask thoroughly,
Methyl-2-pyrrolidone (hereinafter abbreviated as NMP) 420
After adding 0 g, 272.65 g of calcium chloride dried at 200 ° C for 2 hours was added, and the temperature was raised to 100 ° C. After the calcium chloride was completely dissolved, the temperature was returned to room temperature, and 132.91 g of paraphenylenediamine (hereinafter abbreviated as PPD) was obtained.
And completely dissolved. While maintaining this solution at 20 ± 2 ° C., 243.32 g of terephthalic acid dichloride (hereinafter, abbreviated as TPC) was added in about 10 minutes in 10 divided portions. Thereafter, the solution was aged for 1 hour while maintaining the solution at 20 ± 2 ° C., and stirred for 30 minutes under reduced pressure to remove bubbles. The obtained polymerization liquid showed optical anisotropy. A part was sampled, reprecipitated with water, taken out as a polymer, and the obtained PPT
When the intrinsic viscosity of A was measured, it was 1.97 dl / g. Next, 100 g of the polymerization solution was weighed into a 500 ml separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a liquid addition port, and an NMP solution in which 5.8% by weight of calcium chloride was dissolved was added. It was added slowly. Finally, a PPTA solution having a PPTA concentration of 2.8% by weight was prepared and used as solution A.

2.2) Preparation of Heat-Resistant Porous Film Using a bar coater (thickness: mm) manufactured by Tester Sangyo Co., Ltd., a film of the liquid A was prepared on a polyester film.
When put in an aluminum pad with a lid and kept in a heating oven at 60 ° C. for about 20 minutes, PPTA was precipitated and a cloudy film was obtained. The film was immersed in ion-exchanged water. After 5 minutes, the film was peeled from the glass plate. After sufficient washing with flowing ion-exchanged water, a wet film was taken out of the water and free water was wiped off. This film was sandwiched between felts made of aramid and further sandwiched between glass cloths. An aluminum plate was placed with the film-like material sandwiched between filter paper and glass cloth, a nylon film was placed on the aluminum plate, the nylon film and the aluminum plate were sealed with gum, and a conduit for decompression was provided. Put the whole in a heat oven at 120 ° C
The film was dried under reduced pressure. The para-aramid porous film (hereinafter sometimes referred to as film A) obtained by drying had a thickness of 11.4 μm and a porosity of 45%. Further, when observed with a scanning electron microscope, the film A had a large number of voids composed of about 0.1 μm fibrils, and the maximum diameter of the voids was about 1 μm or less.

(3) Preparation of negative electrode sheet electrode Polyethylene carbonate 2 having a number average molecular weight of 50,000
After dissolving 8 parts by weight of PVDF as a binder and 8 parts by weight of NDF with NMP, 90 parts by weight of graphitized carbon fibers as an active material of the negative electrode sheet electrode were 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.

(4) Production of Cylindrical Battery The positive electrode sheet and the negative electrode sheet produced as described above were used for film A and a porous polypropylene film (thickness 25 μm).
m), a positive electrode, a film A /
A porous polypropylene film and a negative electrode were laminated in this order, and the laminate was wound from one end to form a spiral electrode element.

The above-mentioned electrode element was inserted into a battery can, and dimethyl carbonate and 2,2,3,3 were used as a nonaqueous electrolyte solution.
-Impregnating a 50:50 mixed solution with tetrafluoropropyldifluoromethyl ether in which LiPF ₆ is dissolved at a concentration of 1 mol / liter and impregnating a battery lid serving as a positive electrode terminal equipped with a safety valve through a gasket. 18
A 650 cylindrical battery was obtained.

A crush test was performed on the two cylindrical batteries thus obtained in a fully charged state of 4.2 V. As a method of the crush test, the center part of the side circumference of the battery was 30 mm in diameter.
Of the battery was compressed to a quarter diameter of the battery with an iron round bar. As a result, despite the severe condition of overcharging, the battery subjected to the test did not show a significant increase in internal pressure, did not burst, and did not ignite.

Comparative Example 1 An 18650 size cylindrical battery was obtained in the same manner as in Example 1 except that a polyolefin-based porous film was provided on the positive electrode sheet side and a heat-resistant porous layer was provided on the negative electrode sheet side. About the cylindrical battery obtained in this way, Example 1
A crush test was performed in the same manner as in the above. As a result, a marked increase in internal pressure was observed after the crush.

The non-aqueous electrolyte secondary battery of the present invention has a high energy density and further improved safety against a local short circuit such as a nail puncture / crush test.
Its industrial value is extremely large.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuo Shinohara 6 Kitahara, Tsukuba, Ibaraki Prefecture F-term (reference) 5H014 AA06 CC01 HH00 HH08 5H021 AA06 CC00 CC04 EE08 HH06 5H029 AJ03 AJ12 AK03 AM03 AM04 AM05 AM07 BJ02 DJ04 EJ12 HJ14

Claims (7)

[Claims] 1. A non-aqueous electrolyte secondary battery including a positive electrode sheet, a separator, a non-aqueous electrolyte and a negative electrode sheet, wherein the separator comprises a heat-resistant porous layer and a shutdown layer, and the heat-resistant porous layer is formed of the positive electrode sheet. A non-aqueous electrolyte secondary battery, which is disposed on the side. 2. The heat-resistant porous layer has a deflection temperature under load of 100.
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is made of a heat-resistant resin having a critical oxygen index of 20 ° C. or higher. 3. The heat-resistant porous layer has a deflection temperature under load of 200.
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is made of a heat-resistant resin having a critical oxygen index of 20 ° C. or higher. 4. The non-aqueous solution according to claim 1, wherein the shutdown layer is a porous layer made of a thermoplastic resin, and becomes a substantially non-porous layer at a temperature of 80 ° C. to 180 ° C. Electrolyte secondary battery. 5. The method according to claim 1, wherein the heat-resistant resin is polyimide, polyamideimide, aramid, polycarbonate, polyacetal, polysulfone, polyphenylsulfide, polyetheretherketone, aromatic polyester, polyethersulfone or polyetherimide. The non-aqueous electrolyte secondary battery according to claim 2. 6. The non-aqueous electrolyte secondary battery according to claim 3, wherein the heat-resistant resin is polyimide, polyamideimide, aramid, polyethersulfone or polyetherimide. 7. The non-aqueous electrolyte secondary battery according to claim 3, wherein the heat-resistant resin is polyimide, polyamide imide or aramid.