JP5293020B2 - Electrode mixture for non-aqueous electrolyte secondary battery, electrode and non-aqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode mixture, which provides an electrode for nonaqueous electrolyte secondary battery, capable of improving a capacity maintenance ratio in repetition of charge discharge at low temperatures, or low-temperature characteristic. <P>SOLUTION: The electrode mixture for nonaqueous electrolyte secondary battery includes an amorphous carbonaceous material, a conductive agent (the conductive agent is not the amorphous carbonaceous material), a binder and a solvent, and has a viscosity ranging between 2,000 mPa s and 10,000 mPa s. The electrode mixture further includes an aggregation inhibitor. The aggregation inhibitor is a vinyl pyrrolidone-based polymer. The binder includes an inorganic binder. The electrode is obtained by applying the electrode mixture to a current collector followed by drying. The nonaqueous electrolyte secondary battery includes the electrode as a negative electrode. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an electrode mixture for a nonaqueous electrolyte secondary battery, an electrode, and a nonaqueous electrolyte secondary battery.

  The electrode mixture for nonaqueous electrolyte secondary batteries is used for electrodes in nonaqueous electrolyte secondary batteries such as lithium secondary batteries. Lithium secondary batteries have already been used as power sources for mobile phones, notebook computers, and the like, and are also being applied to medium and large applications such as automobile applications and power storage applications.

  Conventional electrode mixtures for non-aqueous electrolyte secondary batteries are usually obtained by mixing an electrode active material, a binder and a solvent. Patent Document 1 specifically describes an electrode mixture using a non-graphitizable carbon material as an electrode active material.

International Publication No. WO 98/05083 Pamphlet (Sample 39)

  However, the non-aqueous electrolyte secondary battery obtained by using the electrode mixture described above is still in view of the capacity retention rate when the charge / discharge is repeated at a low temperature such as 0 ° C., that is, in terms of low temperature characteristics. It's not enough. An object of the present invention is to provide an electrode mixture that provides an electrode for a non-aqueous electrolyte secondary battery capable of improving the capacity retention ratio when charging and discharging are repeated at a low temperature, that is, the low temperature characteristics.

As a result of various studies in view of the above circumstances, the present inventors have reached the present invention. That is, the present invention provides the following inventions.
<1> An amorphous carbon material, a conductive agent (here, the conductive agent is not an amorphous carbon material), a binder and a solvent, and has a viscosity in the range of 2000 mPa · s to 10,000 mPa · s. An electrode mixture for a non-aqueous electrolyte secondary battery.
<2> The electrode mixture according to <1>, wherein the conductive agent includes one or more selected from the group consisting of carbon black, carbon nanotubes, and carbon nanofibers.
<3> The electrode mixture according to <1> or <2>, wherein the conductive agent has an average particle size of 3 μm or less.
<4> The electrode mixture according to any one of <1> to <3>, further including an aggregation inhibitor.
<5> The electrode mixture according to <4>, wherein the aggregation inhibitor is a vinylpyrrolidone polymer.
<6> The electrode mixture according to <4> or <5>, wherein an amorphous carbon material, a conductive agent, a binder, a solvent, and an aggregation inhibitor are mixed at the same time.
<7> The electrode mixture according to any one of <1> to <6>, further including an organic acid.
<8> The electrode mixture according to <7>, wherein the organic acid contains one or more selected from the group consisting of formic acid, oxalic acid, and citric acid.
<9> The electrode mixture according to any one of <1> to <8>, wherein the binder includes an inorganic binder.
<10> The electrode mixture according to <9>, wherein the inorganic binder contains inorganic particles.
<11> The electrode mixture according to <10>, wherein the inorganic particles have a particle size of 1 nm to 100 nm.
<12> The electrode mixture according to <10> or <11>, wherein the inorganic particles are silica particles.
<13> An electrode obtained by applying the electrode mixture according to any one of <1> to <12> to a current collector and drying.
<14> A nonaqueous electrolyte secondary battery having the electrode according to <13> as a negative electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode mixture which provides the electrode for nonaqueous electrolyte secondary batteries which can improve a capacity | capacitance maintenance factor when charging / discharging is repeated at low temperature, ie, a low temperature characteristic, can be provided.

  The electrode mixture for a non-aqueous electrolyte secondary battery of the present invention includes an amorphous carbon material, a conductive agent (here, the conductive agent is not an amorphous carbon material), a binder and a solvent, The viscosity is in the range of 2000 mPa · s to 10,000 mPa · s. In the present invention, the viscosity is measured using a rotational viscometer at a measurement temperature of 25 ° C. and a rotational speed of 10 rpm. As the rotational viscometer, a corn / plate viscometer manufactured by Brookfield can be used. The viscosity range is preferably 4000 mPa · s or more and 6000 mPa · s or less.

  In the present invention, the amorphous carbon material acts as an electrode active material. In the present invention, as the amorphous carbon material, among the carbon materials obtained by carbonizing the organic material, it is obtained by powder X-ray diffraction measurement (the measurement range of the interplanar spacing is 0.3 nm or more and 1 nm or less). In the obtained powder X-ray diffraction pattern, a carbon material that gives a broad diffraction peak (halo) in the range of 0.34 to 0.50 nm between planes may be used. Examples of the organic material include natural resources such as petroleum and coal, various synthetic resins synthesized from such resources, tar or pitch such as plant residue oil, or plant-derived organic materials such as wood, infusible organic The material etc. can be mentioned, These can be used individually or in mixture of 2 or more types.

  The amorphous carbon material in the present invention is preferably a carbon material obtained by carbonizing a synthetic resin, more preferably a thermosetting resin among the synthetic resins, and the thermosetting resin includes phenol. Examples thereof include a resin, a resorcinol resin, a furan resin, and an epoxy resin. Two or more of these thermosetting resins may be used. The thermosetting resin may contain a curing agent, an additive, and a crosslinking agent. Examples of the curing method include thermal curing, epoxy curing, and isocyanate curing in the case where a phenol resin is used. By carbonization of the thermosetting resin, an amorphous carbon material can be obtained with high yield, the environmental load is small, the manufacturing cost can be reduced, and the industrial utility value is higher.

  As the thermosetting resin, a phenol resin is preferable, and this resin is obtained by polymerizing phenol or a derivative thereof and an aldehyde compound. Phenolic resins are inexpensive among thermosetting resins and have a large industrial production amount, and a carbon material obtained by carbonizing this is preferable as an amorphous carbon material in the present invention.

  Examples of the phenol or derivatives thereof include phenol, o-cresol, m-cresol, p-cresol, catechol, resorcinol, hydroquinone, xylenol, pyrogallol, bisphenol A, bisphenol F, p-phenylphenol, p-tert- Examples thereof include butylphenol, p-tert-octylphenol, α-naphthol, β-naphthol and the like, and these can be used alone or in combination of two or more.

  Examples of the aldehyde compound include formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, polyoxymethylene, chloral, furfural, glyoxal, n-butyraldehyde, caproaldehyde, allylaldehyde, benzaldehyde, crotonaldehyde, acrolein, tetraoxy Examples include methylene, phenylacetaldehyde, o-tolualdehyde, salicylaldehyde, and the like. These can be used alone or in combination of two or more.

  Although it does not specifically limit as a phenol resin, A resol type phenol resin, a novolak type phenol resin, etc. can be used. The resol type phenol resin can be obtained by polymerizing phenol or a derivative thereof and an aldehyde compound in the presence of a basic catalyst, and the novolac type phenol resin can be obtained by using phenol or a derivative thereof and an aldehyde compound as an acidic catalyst. It can be obtained by polymerizing in the presence.

  When a self-hardening resol type phenol resin is used, an acid or a curing agent may be added to the resol type phenol resin, or a novolac type phenol resin may be added to reduce the degree of curing. Moreover, you may add combining them.

  The novolak type phenol resin is a method in which phenol or a derivative thereof and an aldehyde compound are subjected to a condensation reaction at a normal pressure of 100 ° C. for several hours using a known organic acid and / or inorganic acid as a catalyst, followed by dehydration and unreacted monomer removal. A random novolak type in which the position of the methylene group is the same as the ortho-position and the para-position, and phenol or a derivative thereof and an aldehyde compound, such as zinc acetate, lead acetate, zinc naphthenate, etc. After the addition condensation reaction with a catalyst under weak acidity, the condensation reaction proceeds directly or with further addition of an acid catalyst while dehydrating, and if necessary, the step of removing unreacted substances. Many high ortho novolaks are known.

Commercially available phenolic resins can be used, for example,
Powdered phenol resin (manufactured by Gunei Chemical Co., Ltd., trade names: Resitop, PGA-4528, PGA-2473, PGA-4704, PGA-4504, manufactured by Sumitomo Bakelite Co., Ltd., trade names: Sumilite resin PR-UFC-504, PR -EPN, PR-ACS-100, PR-ACS-150, PR-12687, PR-13355, PR-16382, PR-217, PR-310, PR-311, PR-50064, PR-50099, PR-50102 , PR-50252, PR-50395, PR-50590, PR-50590B, PR-50699, PR-50869, PR-51316, PR-51326B, PR-51350B, PR-51510, PR-51541B, PR-51794, PR -51820, PR-51939, P -53153, PR-53364, PR-53497, PR-53724, PR-53769, PR-53804, PR-54364, PR-54458A, PR-54545, PR-55170, PR-8000, PR-FTZ-1, PR -FTZ-15), flaky phenol resin (manufactured by Sumitomo Bakelite Co., Ltd., trade names: Sumilite Resin PR-12686R, PR-13349, PR-50235A, PR-51363F, PR-51494G, PR-51618G, PR-53194, PR-53195, PR-54869, PR-F-110, PR-F-143, PR-F-151F, PR-F-85G, PR-HF-3, PR-HF-6), liquid phenolic resin (Sumitomo) Bakelite Co., Ltd., trade name: Sumilite Resin PR-500 7, PR-50607B, PR-50702, PR-50781, PR-51138C, PR-51206, PR-51663, PR-51947A, PR-53123, PR-53338, PR-53365, PR-53717, PR-54135, PR-54313, PR-54562, PR-55345, PR-940, PR-9400, PR-967), novolak type liquid phenolic resin (manufactured by Sumitomo Bakelite Co., Ltd., trade names: Sumilite Resin PR-51629, PR-53093, PR-53473, PR-53522, PR-53546, PR-53800, PR-54438, PR-54540C, PR-55438), resol type liquid phenolic resin (manufactured by Gunei Chemical Co., Ltd., trade names: Resitop PL-4826, PL -2390, P L-4690, PL-3630, PL-4222, PL-4246, PL-2211, PL-3224, PL-4329, manufactured by Sumitomo Bakelite Co., Ltd., trade names: Sumilite Resin PR-50273, PR-51206, PR-51781 , PR-53056, PR-53311, PR-53416, PR-53570, PR-54387), finely divided phenol resin (trade name: Bell Pearl, R800, R700, R600, R200, R100, S830, S870) , S890, S895, S290, S190), spherical resin (manufactured by Gunei Chemical Co., Ltd., trade names: Marilyn GU-200, FM-010, FM-150, HF-008, HF-015, HF-075, HF) -300, HF-500, HF-1500), solid Fe Resin (manufactured by Gunei Chemical Co., Ltd., trade names: Resitop PS-2601, PS-2607, PS-2655, PS-2768, PS-2608, PS-4609, PSM-2222, PSK-2320, PS-6132) Etc. are exemplified.

  Moreover, examples of the infusible organic material include organic materials obtained by crosslinking the tar and pitch, and organic materials obtained by oxidizing the tar and pitch, which is a preferred embodiment.

  Examples of tar and pitch include various residual oils during the production of various petrochemical products such as ethylene. More specifically, there can be mentioned petroleum heavy oil composed of distillation residue oil, fluid catalytic cracking residue oil, hydrodesulfurized oil thereof, or mixed oil thereof. Petroleum or coal-based tar or pitch, such as coal tar produced during coal dry distillation, heavy components or pitch obtained by distilling off low-boiling components of coal tar, tar and pitch obtained by liquefaction of coal, and the like can be used. Two or more of these tars and pitches may be mixed and used. As the residual oil of the plant, a residual oil of a plant that produces an organic compound containing oxygen such as phenol is particularly preferable. By using a carbon material obtained by carbonization of tar or pitch such as plant residue oil, resources can be effectively used, and industrial utility value is higher.

  As the crosslinking agent for the crosslinking treatment, polyfunctional vinyl monomers such as divinylbenzene, trivinylbenzene, diallyl phthalate, ethylene glycol dimethacrylate, N, N-methylenebisacrylamide and the like that undergo a crosslinking reaction by radical reaction can be used. . Examples of radical initiators include α, α′-azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), lauroyl peroxide, cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, hydrogen peroxide, etc. Can be used.

As the method of oxidation treatment, an oxidizing gas such as air, O ₂ , O ₃ , NO ₂ , a mixed gas obtained by diluting these with nitrogen or the like, or an oxidizing liquid such as sulfuric acid, nitric acid or hydrogen peroxide water is used. And a method of oxidizing at a temperature of 50 to 400 ° C.

  In the carbonization of the organic material or the carbonization of the infusible organic material, the carbonization temperature is usually 800 ° C. or higher, and the carbonization atmosphere is preferably an inert gas atmosphere. Here, the infusibilization treatment can be performed by the above oxidation treatment method. Examples of the inert gas include nitrogen and argon. Carbonization may be performed under reduced pressure. For these infusibilization treatment and carbonization, for example, equipment such as a rotary kiln, roller hearth kiln, pusher kiln, multi-stage furnace, fluidized furnace, etc. may be used. The rotary kiln is general purpose.

  More specifically, when carbonizing the said thermosetting resin, it is preferable that the temperature of carbonization is 1000 degreeC-3000 degreeC. Moreover, when carbonizing the organic material which made these infusible using the said tar and pitch, it is preferable that the temperature of carbonization is a temperature of 800 to 1500 degreeC. However, it is preferable to use, as tar and pitch, residual oil from a plant that produces an organic compound containing oxygen such as phenol. When carbonizing this, the temperature of carbonization is a temperature of 1000 ° C to 3000 ° C. It is preferable.

  Further, the amorphous carbon material obtained by carbonization may be pulverized as necessary. For pulverization, for example, an impact friction pulverizer, a centrifugal pulverizer, a ball mill (tube mill, compound mill, A pulverizer for fine pulverization such as a conical ball mill, a rod mill), a vibration mill, a colloid mill, a friction disk mill, or a jet mill is preferably used, and pulverization by a ball mill is generally used.

  In the present invention, the conductive agent is not an amorphous carbon material. In terms of obtaining a nonaqueous electrolyte secondary battery having excellent low-temperature characteristics, the conductive agent preferably includes one or more selected from the group consisting of carbon black, carbon nanotubes, and carbon nanofibers.

  Further, in terms of obtaining a non-aqueous electrolyte secondary battery having a high capacity and excellent low-temperature characteristics, the conductive agent is usually in a powder form, and the average particle size is preferably 3 μm or less, and more preferably 1 μm. The following is desirable. Here, the average particle diameter means the value of the particle diameter (D50) viewed from the fine particle side when 50% is accumulated in the volume-based cumulative particle size distribution of the powder. The average particle diameter is a value measured by a laser diffraction scattering method particle size distribution measuring apparatus, and the value of D50 can be used.

  In the electrode mixture of the present invention, examples of the binder include a thermoplastic resin. Specifically, polyvinylidene fluoride (hereinafter sometimes referred to as PVdF), thermoplastic polyimide, carboxymethylcellulose, polyethylene, polypropylene And so on.

  In the electrode mixture of the present invention, the binder may contain an inorganic binder. By using an inorganic binder, the decomposition reaction of the binder may be suppressed in some cases. Moreover, you may mix and use binders, such as said thermoplastic resin. The inorganic binder usually contains inorganic particles, and the particle size of the inorganic particles is preferably 1 nm or more and 100 nm or less, more preferably 1 nm or more and 50 nm or less, and even more preferably 1 nm or more and 10 nm or less. By setting it as such a particle size, the binder which is more excellent in the dispersibility and adhesive force of an electrode mixture can be obtained. Here, examples of the inorganic particles include silica particles, and the use of silica particles is preferable because a nonaqueous electrolyte secondary battery having better cycle characteristics may be obtained.

  In the present invention, as the solvent, amine solvents such as N, N-dimethylaminopropylamine and diethylenetriamine, ether solvents such as tetrahydrofuran, ketone solvents such as methyl ethyl ketone, ester solvents such as methyl acetate, dimethylacetamide, N Examples include amide solvents such as -methyl-2-pyrrolidone.

  Moreover, it is preferable that the electrode mixture of this invention further contains the aggregation inhibitor in the meaning which obtains the nonaqueous electrolyte secondary battery excellent in the low temperature characteristic with the high capacity | capacitance.

  As the aggregation inhibitor, a vinylpyrrolidone-based polymer is preferable. An example of the vinylpyrrolidone polymer is polyvinylpyrrolidone. The vinylpyrrolidone-based polymer is useful because it can be dissolved in either an organic solvent or an aqueous solvent.

  Moreover, it is preferable that the electrode mixture of this invention further contains an organic acid. When an organic acid is included, the aggregation inhibitor is preferably a vinyl pyrrolidone polymer. Examples of the organic acid include one or more selected from the group consisting of formic acid, oxalic acid, and citric acid. By further including an organic acid, the effect of containing a vinylpyrrolidone-based polymer can be further improved.

  The electrode mixture of the present invention can be obtained by mixing the above-mentioned amorphous carbon material, conductive agent, binder and solvent. When mixing these, a normal stirrer, a disperser, and a kneader can be used. Viscosity adjustment may be performed by controlling the amount of solvent used. When an aggregation inhibitor is used, it is preferable to obtain an electrode mixture by simultaneously mixing an amorphous carbon material, a conductive agent, a binder and a solvent and an aggregation inhibitor. An electrode mixture in which an amorphous carbon material, a conductive agent, a binder and a solvent, and an aggregation inhibitor are mixed at the same time can be an electrode mixture excellent in dispersibility of the conductive agent. Moreover, it is a preferred embodiment also in terms of shortening the process time.

  Using the electrode mixture of the present invention, this can be applied to a current collector and dried to obtain an electrode. An electrode obtained by applying the electrode mixture of the present invention to a current collector and drying it has a very low resistance, and the obtained nonaqueous electrolyte secondary battery is excellent in low temperature characteristics. Moreover, you may press after drying. Moreover, the thickness of an electrode is about 5-500 micrometers normally.

  Examples of the current collector include copper, nickel, and stainless steel, and copper may be used because it is difficult to form an alloy with lithium and it is easy to process into a thin film. Examples of the method of applying the electrode mixture to the current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method. Moreover, what is necessary is just to perform drying at about 20-150 degreeC. Examples of the shape of the current collector include a foil shape, a flat plate shape, a mesh shape, a net shape, a lath shape, a punching metal shape, an emboss shape, or a combination thereof (for example, a mesh flat plate). Can be mentioned. Concavities and convexities may be formed by etching on the current collector surface.

  The nonaqueous electrolyte secondary battery having an electrode obtained as described above has a negative electrode and a positive electrode. In a non-aqueous electrolyte secondary battery, the electrode of the present invention acts as a positive electrode when a lithium metal or a lithium alloy is used for the counter electrode, and a lithium metal oxide that can be doped / undoped with lithium ions is used for the counter electrode Acts as a negative electrode.

  Hereinafter, the nonaqueous electrolyte secondary battery in the present invention will be described with reference to an example in which the electrode of the present invention is used as a negative electrode. That is, after the separator, the positive electrode in which the positive electrode mixture is supported on the positive electrode current collector, and the electrode group obtained by laminating and winding the above-described electrode in a container such as a battery can, It can be produced by impregnating an electrolytic solution comprising an organic solvent containing

  Examples of the shape of the electrode group include a shape in which a cross-section when the electrode group is cut in a direction perpendicular to the winding axis is a circle, an ellipse, a rectangle, a rectangle with rounded corners, or the like. be able to. In addition, examples of the shape of the battery include a paper shape, a coin shape, a cylindrical shape, and a square shape.

As the positive electrode, a positive electrode mixture containing a positive electrode active material supported on a positive electrode current collector can be used. Specifically, as the positive electrode active material, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ and Examples thereof include LiFePO ₄ . Some of the transition metal elements in these materials may be substituted with one or more other metal elements.

  The positive electrode can be produced by supporting a positive electrode active material, a binder, and, if necessary, a positive electrode mixture containing a conductive agent on a positive electrode current collector.

  A carbon material can be used as the conductive agent in the positive electrode, and examples of the carbon material include graphite powder, carbon black, acetylene black, and fibrous carbon material. Since carbon black and acetylene black are fine and have a large surface area, adding a small amount to the positive electrode mixture can increase the electrical conductivity inside the electrode and improve the charge / discharge efficiency and rate characteristics. This decreases the binding property between the positive electrode mixture and the positive electrode current collector by the binder, and causes an increase in internal resistance. Usually, the ratio of the conductive agent in the positive electrode mixture is 5 parts by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the positive electrode active material. When a fibrous carbon material such as graphitized carbon fiber or carbon nanotube is used as the conductive agent, this ratio can be lowered.

  As the binder in the positive electrode, a thermoplastic resin can be used. Specifically, PVdF, polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), tetrafluoroethylene / hexafluoropropylene / fluoride. Examples thereof include fluorine resins such as vinylidene copolymers, propylene hexafluoride / vinylidene fluoride copolymers, tetrafluoroethylene / perfluorovinyl ether copolymers, and polyolefin resins such as polyethylene and polypropylene. Moreover, you may mix and use these 2 or more types. Further, by using a fluororesin and a polyolefin resin as a binder, the ratio of the fluororesin to the positive electrode mixture is 1 to 10% by weight, and the ratio of the polyolefin resin is 0.1 to 2% by weight, A positive electrode mixture excellent in binding property with the positive electrode current collector can be obtained.

  Examples of the positive electrode current collector include Al, Ni, and stainless steel, and Al is preferable because it can be easily processed into a thin film and is inexpensive. Examples of the shape of the positive electrode current collector include a foil shape, a flat plate shape, a mesh shape, a net shape, a lath shape, a punching metal shape, an embossed shape, or a combination thereof (for example, a mesh flat plate). Is mentioned. Concavities and convexities by etching treatment may be formed on the surface of the positive electrode current collector.

  As a method of supporting the positive electrode mixture on the positive electrode current collector, it is fixed by press molding or pasting with an organic solvent, coating on the electrode current collector, drying and pressing. A method is mentioned. In the case of forming a paste, a slurry composed of an electrode active material, a conductive agent, a binder, and an organic solvent is prepared. Examples of organic solvents include amines such as N, N-dimethylaminopropylamine and diethyltriamine; ethers such as ethylene oxide and tetrahydrofuran; ketones such as methyl ethyl ketone; esters such as methyl acetate; dimethylacetamide and N-methyl- Examples include aprotic polar solvents such as 2-pyrrolidone. Examples of the method of coating the electrode mixture on the electrode current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method. The thickness of the positive electrode is usually about 5 to 500 μm.

  As the separator, for example, a material having a form such as a porous membrane, a nonwoven fabric, a woven fabric made of a polyolefin resin such as polyethylene and polypropylene, a fluororesin, a nitrogen-containing aromatic polymer, and the like can be used. Moreover, it is good also as a separator using 2 or more types of the said material, and the said material may be laminated | stacked. Examples of the separator include separators described in JP 2000-30686 A, JP 10-324758 A, and the like. The thickness of the separator is preferably about 5 to 200 μm, and preferably about 5 to 40 μm, as long as the mechanical strength is maintained because the volume energy density of the battery is increased and the internal resistance is reduced. From the viewpoint of ion permeability, the separator preferably has an air permeability of 50 to 300 seconds / 100 cc, more preferably 50 to 200 seconds / 100 cc, in terms of air permeability by the Gurley method. Moreover, the porosity of a separator is 30-80 volume% normally, Preferably it is 40-70 volume%. The separator may be a laminate of separators having different porosity.

  The separator preferably has a porous film containing a thermoplastic resin. In a non-aqueous electrolyte secondary battery, normally, when an abnormal current flows in the battery due to a short circuit between the positive electrode and the negative electrode, the function of shutting down the current and preventing the excessive current from flowing (shut down) It is preferable to have. Here, the shutdown is performed by closing the fine pores of the separator when the normal use temperature is exceeded. Even if the temperature in the battery rises to a certain high temperature after the fine pores of the separator are closed, it is preferable to maintain the closed state of the fine pores of the separator without causing the separator to break down due to the temperature. Examples of such a separator include a laminated film formed by laminating a heat-resistant porous layer and a porous film. By using the film as a separator, the heat resistance of the secondary battery of the present invention can be further increased. It becomes. Here, the heat-resistant porous layer may be laminated on both surfaces of the porous film.

  Next, the laminated film formed by laminating the heat resistant porous layer and the porous film will be described more specifically.

  In the laminated film, the heat resistant porous layer is a layer having higher heat resistance than the porous film, and the heat resistant porous layer may be formed of an inorganic powder or may contain a heat resistant resin. When the heat resistant porous layer contains a heat resistant resin, the heat resistant porous layer can be formed by an easy technique such as coating. Examples of the heat resistant resin include polyamide, polyimide, polyamideimide, polycarbonate, polyacetal, polysulfone, polyphenylene sulfide, polyether ketone, aromatic polyester, polyether sulfone, and polyetherimide. Preferred heat resistant resins are polyamide, Polyimide, polyamideimide, polyethersulfone, and polyetherimide are preferable, and polyamide, polyimide, and polyamideimide are more preferable heat resistant resins. Even more preferred heat resistant resins are nitrogen-containing aromatic polymers such as aromatic polyamides (para-oriented aromatic polyamides, meta-oriented aromatic polyamides), aromatic polyimides, aromatic polyamideimides, and particularly preferred heat-resistant resins are aromatic. From the viewpoint of being a polyamide and easily usable, a particularly preferred heat resistant resin is a para-oriented aromatic polyamide (hereinafter sometimes referred to as “para-aramid”). Further, examples of the heat resistant resin include poly-4-methylpentene-1 and cyclic olefin polymers. By using these heat resistant resins, the heat resistance of the laminated film, that is, the thermal film breaking temperature of the laminated film is further increased. Among these heat-resistant resins, when using a nitrogen-containing aromatic polymer, because of the polarity in the molecule, compatibility with the electrolyte, that is, the liquid retention in the heat-resistant porous layer may be improved, The rate of impregnation of the electrolytic solution during the production of the nonaqueous electrolyte secondary battery is also high, and the charge / discharge capacity of the nonaqueous electrolyte secondary battery is further increased.

  The thermal film breaking temperature of such a laminated film depends on the type of heat-resistant resin, and is selected and used according to the use scene and purpose of use. More specifically, as the heat resistant resin, the cyclic olefin polymer is used at about 400 ° C. when the nitrogen-containing aromatic polymer is used, and at about 250 ° C. when poly-4-methylpentene-1 is used. When using, the thermal film breaking temperature can be controlled to about 300 ° C., respectively. In addition, when the heat resistant porous layer is made of an inorganic powder, the thermal film breaking temperature can be controlled to, for example, 500 ° C. or higher.

  The para-aramid is obtained by condensation polymerization of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide, and the amide bond is in the para position of the aromatic ring or an oriented position equivalent thereto (for example, 4,4′- It consists essentially of repeating units bonded at opposite orientations, such as biphenylene, 1,5-naphthalene, 2,6-naphthalene, etc., oriented in the opposite direction coaxially or in parallel. Specifically, poly (paraphenylene terephthalamide), poly (parabenzamide), poly (4,4′-benzanilide terephthalamide), poly (paraphenylene-4,4′-biphenylenedicarboxylic acid amide), poly ( Para-aligned or para-oriented such as paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly (2-chloro-paraphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer Examples include para-aramid having a structure according to the type.

  The aromatic polyimide is preferably a wholly aromatic polyimide produced by condensation polymerization of an aromatic dianhydride and a diamine. Specific examples of the dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic Examples thereof include acid dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, and the like. Specific examples of the diamine include oxydianiline, paraphenylenediamine, benzophenonediamine, 3,3′-methylenedianiline, 3,3′-diaminobenzophenone, 3,3′-diaminodiphenylsulfone, 1,5 '-Naphthalenediamine and the like. Moreover, a polyimide soluble in a solvent can be preferably used. An example of such a polyimide is a polycondensate polyimide of 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride and an aromatic diamine.

  As the above-mentioned aromatic polyamideimide, those obtained from condensation polymerization using aromatic dicarboxylic acid and aromatic diisocyanate, those obtained from condensation polymerization using aromatic diacid anhydride and aromatic diisocyanate Is mentioned. Specific examples of the aromatic dicarboxylic acid include isophthalic acid and terephthalic acid. Specific examples of the aromatic dianhydride include trimellitic anhydride. Specific examples of the aromatic diisocyanate include 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, orthotolylane diisocyanate, m-xylene diisocyanate, and the like.

  In order to further enhance the ion permeability, the heat-resistant porous layer is preferably a thin heat-resistant porous layer having a thickness of 1 μm to 10 μm, more preferably 1 μm to 5 μm, particularly 1 μm to 4 μm. The heat-resistant porous layer has fine pores, and the size (diameter) of the pores is usually 3 μm or less, preferably 1 μm or less.

  In addition, when the heat resistant porous layer contains a heat resistant resin, it can further contain a filler. The filler may be selected from organic powder, inorganic powder, or a mixture thereof as the material thereof. The particles constituting the filler preferably have an average particle size of 0.01 μm or more and 1 μm or less.

  Examples of the organic powder include styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, and methyl acrylate, or a copolymer of two or more kinds, polytetrafluoroethylene, 4 fluorine. Examples include fluorine-containing resins such as fluorinated ethylene-6-propylene-propylene copolymer, tetrafluoroethylene-ethylene copolymer, and polyvinylidene fluoride; melamine resin; urea resin; polyolefin; and powders made of organic substances such as polymethacrylate. . The organic powder may be used alone or in combination of two or more. Among these organic powders, polytetrafluoroethylene powder is preferable from the viewpoint of chemical stability.

  Examples of the inorganic powder include powders made of inorganic substances such as metal oxides, metal nitrides, metal carbides, metal hydroxides, carbonates, sulfates, etc. Among these, they are made of inorganic substances having low conductivity. Powder is preferably used. Specific examples include powders made of alumina, silica, titanium dioxide, calcium carbonate, or the like. The inorganic powder may be used alone or in combination of two or more. Among these inorganic powders, alumina powder is preferable from the viewpoint of chemical stability. Here, it is more preferable that all of the particles constituting the filler are alumina particles, and it is even more preferable that all of the particles constituting the filler are alumina particles, and part or all of them are substantially spherical alumina particles. It is embodiment which is. Incidentally, when the heat-resistant porous layer is formed from an inorganic powder, the inorganic powder exemplified above may be used, and may be mixed with a binder as necessary.

  When the heat-resistant porous layer contains a heat-resistant resin, the filler content depends on the specific gravity of the filler material. For example, when the total weight of the heat-resistant porous layer is 100, the filler weight is usually 5 It is preferably 95 or more, preferably 20 or more and 95 or less, and more preferably 30 or more and 90 or less. These ranges are particularly suitable when all of the particles constituting the filler are alumina particles.

  Examples of the shape of the filler include a substantially spherical shape, a plate shape, a columnar shape, a needle shape, a whisker shape, and a fibrous shape, and any particle can be used. It is preferable that Examples of the substantially spherical particles include particles having a particle aspect ratio (particle major axis / particle minor axis) in the range of 1 to 1.5. The aspect ratio of the particles can be measured by an electron micrograph.

  In the laminated film, the porous film has fine pores and usually has a shutdown function. The size (diameter) of the micropores in the porous film is usually 3 μm or less, preferably 1 μm or less. The porosity of the porous film is usually 30 to 80% by volume, preferably 40 to 70% by volume. In the nonaqueous electrolyte secondary battery, when the normal use temperature is exceeded, the micropores can be blocked by the deformation and softening of the porous film by the shutdown function.

  In the laminated film, the resin constituting the porous film may be selected from those that do not dissolve in the electrolyte solution in the nonaqueous electrolyte secondary battery. Specific examples include polyolefin resins such as polyethylene and polypropylene, and thermoplastic polyurethane resins, and a mixture of two or more of these may be used. In terms of softening and shutting down at a lower temperature, the porous film preferably contains a polyolefin resin, and more preferably contains polyethylene. Specific examples of polyethylene include polyethylene such as low density polyethylene, high density polyethylene, and linear polyethylene, and also include ultrahigh molecular weight polyethylene. In the sense of further increasing the puncture strength of the porous film, the resin constituting it preferably contains at least ultra high molecular weight polyethylene. Moreover, it may be preferable to contain the wax which consists of polyolefin of a low molecular weight (weight average molecular weight 10,000 or less) in the manufacture surface of a porous film.

  Moreover, the thickness of the porous film in a laminated | multilayer film is 3-30 micrometers normally, Preferably it is 3-25 micrometers. Moreover, as thickness of a laminated film, it is 40 micrometers or less normally, Preferably, it is 20 micrometers or less. Moreover, when the thickness of the heat resistant porous layer is A (μm) and the thickness of the porous film is B (μm), the value of A / B is preferably 0.1 or more and 1 or less.

Next, an example of manufacturing a laminated film will be described.
First, the manufacturing method of a porous film is demonstrated. The production of the porous film is not particularly limited. For example, as described in JP-A-7-29563, a plasticizer is added to a thermoplastic resin to form a film, and then the plasticizer is mixed with an appropriate solvent. As described in JP-A-7-304110, a film made of a thermoplastic resin produced by a known method is used, and a structurally weak amorphous portion of the film is selectively stretched. And a method of forming micropores. For example, when the porous film is formed from a polyolefin resin containing ultrahigh molecular weight polyethylene and a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, it is produced by the following method from the viewpoint of production cost. It is preferable. That is,
(1) Step of obtaining a polyolefin resin composition by kneading 100 parts by weight of ultrahigh molecular weight polyethylene, 5 to 200 parts by weight of a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, and 100 to 400 parts by weight of an inorganic filler ( 2) Step of forming a sheet using the polyolefin resin composition (3) Step of removing inorganic filler from the sheet obtained in step (2) (4) Stretching of the sheet obtained in step (3) Or a method comprising a step of obtaining a porous film, or (1) 100 parts by weight of ultrahigh molecular weight polyethylene, 5 to 200 parts by weight of a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, and 100 to 400 parts by weight of an inorganic filler And a step of obtaining a polyolefin resin composition by kneading (2) a step of molding a sheet using the polyolefin resin composition (3) obtained in step (2) From in stretched sheet obtained in the step of stretching the sheet (4) Step (3), the method comprising the step of removing the inorganic filler to obtain a porous film.

  From the viewpoint of the strength and ion permeability of the porous film, the inorganic filler used preferably has an average particle diameter (diameter) of 0.5 μm or less, more preferably 0.2 μm or less. Here, the value measured from an electron micrograph is used for the average particle diameter. Specifically, 50 particles are arbitrarily extracted from the inorganic filler particles photographed in the photograph, each particle diameter is measured, and the average value is used.

  Inorganic fillers include calcium carbonate, magnesium carbonate, barium carbonate, zinc oxide, calcium oxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, calcium sulfate, silicic acid, zinc oxide, calcium chloride, sodium chloride, magnesium sulfate, etc. Is mentioned. These inorganic fillers can be removed from the sheet or film with an acid or alkaline solution. Calcium carbonate is preferably used from the viewpoints of particle size controllability and selective solubility in acid.

  The method for producing the polyolefin resin composition is not particularly limited, but a mixing device, such as a roll, a Banbury mixer, a single screw extruder, a twin screw extruder, or the like, is used to mix materials constituting the polyolefin resin composition such as polyolefin resin and inorganic filler. And mixed to obtain a polyolefin resin composition. When mixing the materials, additives such as fatty acid esters, stabilizers, antioxidants, ultraviolet absorbers and flame retardants may be added as necessary.

  The manufacturing method of the sheet | seat which consists of the said polyolefin resin composition is not specifically limited, It can manufacture by sheet | seat shaping | molding methods, such as an inflation process, a calendar process, T-die extrusion process, and a Skyf method. Since a sheet with higher film thickness accuracy can be obtained, it is preferable to produce the sheet by the following method.

  A preferred method for producing a sheet comprising a polyolefin resin composition is a method of rolling a polyolefin resin composition using a pair of rotational molding tools adjusted to a surface temperature higher than the melting point of the polyolefin resin contained in the polyolefin resin composition. It is a method to do. The surface temperature of the rotary forming tool is preferably (melting point + 5) ° C. or higher. The upper limit of the surface temperature is preferably (melting point + 30) ° C. or less, and more preferably (melting point + 20) ° C. or less. Examples of the pair of rotary forming tools include a roll and a belt. The peripheral speeds of the two rotary forming tools do not necessarily have to be exactly the same peripheral speed, and the difference between them may be about ± 5% or less. By producing a porous film using a sheet obtained by such a method, a porous film excellent in strength, ion permeation, air permeability and the like can be obtained. Moreover, you may use what laminated | stacked the sheet | seat of the single layer obtained by the above methods for manufacture of a porous film.

  When the polyolefin resin composition is roll-formed with a pair of rotary molding tools, the polyolefin resin composition discharged in a strand form from an extruder may be directly introduced between the pair of rotary molding tools, and once pelletized polyolefin A resin composition may be used.

  When stretching a sheet made of a polyolefin resin composition or a sheet from which the inorganic filler has been removed, a tenter, a roll, an autograph or the like can be used. From the air permeable side, the draw ratio is preferably 2 to 12 times, more preferably 4 to 10 times. The stretching temperature is usually carried out at a temperature not lower than the softening point of the polyolefin resin and not higher than the melting point, preferably 80 to 115 ° C. If the stretching temperature is too low, film breakage tends to occur during stretching, and if it is too high, the air permeability and ion permeability of the resulting porous film may be lowered. Moreover, it is preferable to heat set after extending | stretching. The heat set temperature is preferably a temperature below the melting point of the polyolefin resin.

  In the present invention, a porous film containing a thermoplastic resin obtained by the method as described above and a heat-resistant porous layer are laminated to obtain a laminated film. The heat resistant porous layer may be provided on one side of the porous film or may be provided on both sides.

As a method of laminating a porous film and a heat-resistant porous layer, a method of separately producing a heat-resistant porous layer and a porous film and laminating each of them, and containing a heat-resistant resin and a filler on at least one surface of the porous film Examples of the method include forming a heat-resistant porous layer by applying a coating liquid to be applied. In the present invention, when the heat-resistant porous layer is relatively thin, the latter method is preferable from the viewpoint of productivity. Specific examples of a method for forming a heat resistant resin layer by applying a coating solution containing a heat resistant resin and a filler to at least one surface of the porous film include the following steps.
(A) A slurry-like coating liquid is prepared by dispersing 1 to 1500 parts by weight of a filler in 100 parts by weight of a heat resistant resin in a polar organic solvent solution containing 100 parts by weight of a heat resistant resin.
(B) The coating solution is applied to at least one surface of the porous film to form a coating film.
(C) The heat resistant resin is deposited from the coating film by means of humidification, solvent removal, or immersion in a solvent that does not dissolve the heat resistant resin, and then dried as necessary.
The coating liquid is preferably applied continuously by a coating apparatus described in JP-A-2001-316006 and a method described in JP-A-2001-23602.

  When the heat resistant resin is para-aramid in the polar organic solvent solution, a polar amide solvent or a polar urea solvent can be used as the polar organic solvent. Specifically, N, N— Examples include, but are not limited to, dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), and tetramethylurea.

  When para-aramid is used as the heat-resistant resin, it is preferable to add an alkali metal or alkaline earth metal chloride during para-aramid polymerization for the purpose of improving the solubility of para-aramid in a solvent. Specific examples include lithium chloride or calcium chloride, but are not limited thereto. The amount of the chloride added to the polymerization system is preferably in the range of 0.5 to 6.0 mol, more preferably in the range of 1.0 to 4.0 mol, per 1.0 mol of the amide group produced by condensation polymerization. . If the chloride is less than 0.5 mol, the solubility of the resulting para-aramid may be insufficient, and if it exceeds 6.0 mol, the solubility of the chloride in the solvent may be substantially exceeded, which may be undesirable. . In general, if the alkali metal or alkaline earth metal chloride is less than 2% by weight, the solubility of para-aramid may be insufficient. If it exceeds 10% by weight, the alkali metal or alkaline earth metal chloride may be insufficient. May not dissolve in polar organic solvents such as polar amide solvents or polar urea solvents.

  Further, when the heat resistant resin is an aromatic polyimide, the polar organic solvent for dissolving the aromatic polyimide includes those exemplified as the solvent for dissolving the aramid, dimethyl sulfoxide, cresol, o-chlorophenol, etc. Can be suitably used.

  As a method for obtaining a slurry-like coating liquid by dispersing a filler, a pressure disperser (gorin homogenizer, nanomizer) or the like may be used as the apparatus.

  Examples of the method of applying the slurry-like coating liquid include a coating method such as a knife, blade, bar, gravure, die, etc., and coating of a bar, knife, etc. is simple, but industrially, Die coating having a structure in which the solution does not come into contact with outside air is preferable. Moreover, coating may be performed twice or more. In this case, it is usual to carry out after depositing the heat-resistant resin in the step (c).

  In the case where the heat resistant porous layer and the porous film are separately manufactured and laminated, it is preferable to fix them by a method using an adhesive, a method using heat fusion, or the like.

In the secondary battery, the electrolytic solution is usually composed of an organic solvent containing an electrolyte. Examples of the electrolyte include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (COCF ₃ ), Li (C ₄ F ₉ SO ₃ ), LiC (SO ₂ CF ₃ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , LiBOB (where BOB is bis (oxalato) borate). ), Lithium salts such as lower aliphatic carboxylic acid lithium salts and LiAlCl _4, and a mixture of two or more of these may be used. The lithium salt is usually selected from the group consisting of LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ and LiC (SO ₂ CF ₃ ) ₃ containing fluorine among these. Those containing at least one selected are used.

Examples of the organic solvent in the electrolytic solution include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di (methoxy). Carbonates such as carbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran Ethers such as methyl formate, methyl acetate, and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetoa Amides such as carbon; Carbamates such as 3-methyl-2-oxazolidone; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, 1,3-propane sultone, or those obtained by further introducing a fluorine substituent into the above organic solvent Usually, two or more of these are mixed and used. Among these, a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate or cyclic carbonate and ether is more preferable. As the mixed solvent of the cyclic carbonate and the non-cyclic carbonate, a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable in that it has a wide operating temperature range, excellent load characteristics, and hardly decomposes. Further, in view of particularly excellent safety improving effect is obtained, it is preferable to use an electrolytic solution containing an organic solvent having a lithium salt and a fluorine substituent containing fluorine such as LiPF _6. A mixed solvent containing ethers having fluorine substituents such as pentafluoropropyl methyl ether and 2,2,3,3-tetrafluoropropyl difluoromethyl ether and dimethyl carbonate has excellent high-current discharge characteristics, preferable.

Moreover, you may use a solid electrolyte instead of electrolyte solution. As the solid electrolyte, for example, an organic polymer electrolyte such as a polyethylene oxide polymer compound, a polymer compound containing at least one of a polyorganosiloxane chain or a polyoxyalkylene chain can be used. Moreover, what is called a gel type which hold | maintained the nonaqueous electrolyte solution in the high molecular compound can also be used. The _{Li 2 S-SiS 2, Li} 2 S-GeS 2, Li 2 S-P 2 S 5, Li 2 S-B 2 S 3, Li 2 S-SiS 2 -Li 3 PO 4, Li 2 S-SiS _An inorganic solid electrolyte containing a sulfide such as _2- Li ₂ SO ₄ may be used. Using these solid electrolytes, safety may be further improved. In addition, when a solid electrolyte is used in a nonaqueous electrolyte secondary battery, the solid electrolyte may serve as a separator, and in that case, the separator may not be required.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Test Example 1 (electrode mixture)
[Amorphous carbon material] SCL15 (manufactured by SEC Carbon Co.) was used as an amorphous carbon material.
[Conductive Agent] Using acetylene black as a conductive agent, this was mechanically pulverized with a ball mill to obtain acetylene black (pulverized product) having an average particle diameter (D50) of 3 μm or less.

[Electrode mixture 1]
Amorphous carbon material, acetylene black, polyvinylidene fluoride and N-methyl-2-pyrrolidone (NMP) were weighed so as to have the composition ratio shown in Table 1, and kneaded with a kneader for 0.5 hour. Further, N-methyl-2-pyrrolidone (NMP) was added to adjust the viscosity to 5000 mPa · s to obtain an electrode mixture 1. As acetylene black, the one before pulverization (unground product) was used.

[Electrode mixture 2]
An electrode mixture 2 having a viscosity of 5000 mPa · s was prepared in the same manner as the electrode mixture 1 except that acetylene black (ground product) was used instead of acetylene black (unground product) (see Table 2). Obtained.

[Electrode mixture 3]
Furthermore, an electrode mixture 3 having a viscosity of 5000 mPa · s was obtained in the same manner as in the production of the electrode mixture 2 except that polyvinylpyrrolidone was used (see Table 3).

[Electrode mixture 4]
Further, an electrode mixture 4 having a viscosity of 5000 mPa · s was obtained in the same manner as in the production of the electrode mixture 3 except that oxalic acid was used (see Table 4).

[Electrode mixture 5]
For comparison, amorphous carbon material, polyvinylidene fluoride and N-methyl-2-pyrrolidone (NMP) were weighed so as to have the composition ratio shown in Table 5, and these were mixed for 0.5 hour by a kneader. After kneading, N-methyl-2-pyrrolidone (NMP) was further added to adjust the viscosity to 5000 mPa · s to obtain an electrode mixture 5.

[Measurement of aging stability of electrode mixture]
The stability of the electrode mixtures 3, 4 and 5 was measured as follows. That is, the electrode mixture was put in a 100 ml graduated cylinder with a stopper to a 50 ml scale, capped, stored at 25 ° C., and the state after 7 days was observed. As a result, the electrode mixture 5 was separated into two layers, but no separation was observed in the electrode mixtures 3 and 4. From this, it was found that the stability of the electrode mixture to which polyvinylpyrrolidone was added was very high over time.

Test Example 2 [Production of electrode]
Using each of electrode mixture 1, 2, 3 and 4 after 2 hours of kneading, it was applied onto a current collector made of Cu foil having a thickness of 10 μm by the doctor blade method, dried at 60 ° C. for 2 hours, After vacuum drying at 150 ° C. for 10 hours to volatilize N-methyl-2-pyrrolidone, each of electrodes 1, 2, 3, and 4 was produced by rolling. The electrode coating amount after drying was 8.0 mg / cm ² in all cases. Similarly, using the electrode mixture 5, the electrode 5 was produced so that the electrode coating amount after drying was 7.6 mg / cm ² .

[Measurement of adhesion strength]
The adhesion strength of the electrodes 3, 4 and 5 was measured as follows. That is, a tape having a width of 20 mm and a length of 50 mm was attached to the electrode, and the strength (peel strength) at the time of peeling was measured. Table 6 shows the peel strength of the electrodes 3 and 4 when the peel strength of the negative electrode 5 is 100.

  It was found that the peel strength of the electrode 3 using the electrode mixture to which polyvinyl pyrrolidone was added was high. Further, it has been found that the peel strength can be particularly increased in the electrode 4 using the electrode mixture to which oxalic acid is added. This means that the dispersion of the conductive agent in the electrode is very good by adding polyvinylpyrrolidone, and the effect of containing the vinylpyrrolidone-based polymer can be further improved by adding oxalic acid.

Test Example 3 [Battery evaluation]
Using the above-described electrodes 1, 2, 3, 4 and 5 as the negative electrode, non-aqueous electrolyte secondary batteries 1, 2, 3, 4 and 5 were produced as follows.

[Production of positive electrode]
90 parts by weight of a positive electrode active material made of LiMn ₂ O ₄ having an average particle size (D50) of 10 μm, ₄ parts by weight of a binder made of polyvinylidene fluoride, and 6 parts by weight of a conductive agent made of acetylene black were mixed. -70 parts by weight of methyl-2-pyrrolidone was mixed to prepare a positive electrode mixture. This positive electrode mixture was applied onto a current collector made of an aluminum foil having a thickness of 15 μm by a doctor blade method, dried at 60 ° C. for 2 hours, and further vacuum dried at 150 ° C. for 10 hours to obtain N-methyl- The 2-pyrrolidone was volatilized and then rolled. The electrode coating amount after drying was 20.2 mg / cm ² . Thus, the positive electrode 1 in which the mixture containing the positive electrode active material was laminated on the current collector was produced.

[Preparation of electrolyte]
LiPF ₆ is added at 1 mol / liter to a mixed solvent obtained by mixing ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) at EC: DMC: EMC = 30: 35: 35 (volume ratio). The dissolved electrolyte was adjusted so that

[Production of non-aqueous electrolyte secondary battery]
The positive electrode is cut into a disk shape with a diameter of 14 mm, and each of the electrodes 1, 2, 3, 4 and 5 is cut into a disk shape with a diameter of 16 mm, and a polyethylene porous separator is interposed between the positive electrode and the negative electrode. The coin-type non-aqueous electrolyte secondary batteries 1, 2, 3, and the like having a diameter of 20 mm and a thickness of 3.2 mm are disposed and stored in a battery case, poured with the above electrolyte, and sealed. 4 and 5 were made.

[Charge / discharge evaluation 1]
The coin-type nonaqueous electrolyte secondary batteries 1, 2, 3, 4 and 5 were allowed to stand at room temperature for 10 hours, so that the electrode was sufficiently impregnated with the electrolytic solution. Next, after performing constant current constant voltage charging for 8 hours at 0.2 C and constant voltage charging at 4.2 C and then constant voltage charging at 4.2 V, constant current discharging to 3.0 V at 0.2 C Initial charging / discharging was performed by discharging.

  After the initial charge / discharge, the battery was fully charged at room temperature. The following tests were evaluated at 0 ° C. for these nonaqueous electrolyte secondary batteries. Table 7 shows capacity retention rates when discharging at 1C and charging at 1C were repeated 10 times.

  From Table 7, it was found that the non-aqueous electrolyte secondary battery using the electrodes 1, 2, 3 and 4 as the negative electrode had a very good capacity retention rate as compared with the case where the electrode 5 was used. This result means that the addition of the conductive agent to the electrode contributes to the improvement of the low temperature characteristics of the amorphous carbon material.

Test Example 4: Inorganic Binder Snow Latex ST-XS (Nissan Chemical Industry Co., Ltd., particle shape: spherical, average particle size of 4 to 6 nm, solid content concentration of 20 which is a colloidal silica of an inorganic binder from polyvinylidene fluoride as a binder. The electrode mixture 6 was obtained in the same manner as the electrode mixture 4 except that the solvent was changed from n-methylpyrrolidone to water (Table 8).

  The inorganic binder was changed to Snow Latex PS-S (manufactured by Nissan Chemical Industries, Ltd., particle shape: chain particles bonded with spherical silica, average particle size of 10 to 50 nm, solid content concentration of 20% by weight) (Table 9). Except for the above, electrode mixture 7 was obtained in the same manner as electrode mixture 6.

[Production of electrodes]
Each of the electrode mixtures 6 and 7 after 2 hours of kneading was coated on a current collector made of Cu foil having a thickness of 10 μm by the doctor blade method, dried at 60 ° C. for 2 hours, and further vacuumed at 150 ° C. for 10 hours. After drying and volatilizing water, each of the electrodes 6 and 7 was obtained by rolling. The electrode coating amount after drying was 8.0 mg / cm ² , respectively.

[Production of non-aqueous electrolyte secondary battery]
Similarly to the non-aqueous electrolyte secondary battery 1, non-aqueous electrolyte secondary batteries 6 and 7 using the electrodes 6 and 7 as negative electrodes were produced.

[Charge / discharge evaluation]
Table 10 shows the results when the nonaqueous electrolyte secondary batteries 6 and 7 were evaluated in the same manner as the charge / discharge evaluation 1.

Claims (11)

Amorphous carbon material, a conductive agent (here, the conductive agent, the amorphous carbon material no.), A binder, a solvent, wherein the vinylpyrrolidone-based polymer as the organic acid and aggregation inhibitor, a viscosity of 2000 mPa · s or more The electrode mixture for nonaqueous electrolyte secondary batteries characterized by being in a range of 10,000 mPa · s or less.   The electrode mixture according to claim 1, wherein the conductive agent contains one or more selected from the group consisting of carbon black, carbon nanotubes, and carbon nanofibers.   The electrode mixture according to claim 1 or 2, wherein the conductive agent has an average particle size of 3 µm or less. The electrode mixture according to any one of claims 1 to 3, wherein the amorphous carbon material, the conductive agent, the binder and the solvent, and the aggregation inhibitor are mixed at the same time. The electrode mixture according to any one of claims 1 to 4, wherein the organic acid contains one or more selected from the group consisting of formic acid, oxalic acid and citric acid. The electrode mixture according to any one of claims 1 to 5 , wherein the binder contains an inorganic binder. The electrode mixture according to claim 6, wherein the inorganic binder contains inorganic particles. The electrode mixture according to claim 7 , wherein the particle size of the inorganic particles is 1 nm or more and 100 nm or less. The electrode mixture according to claim 7 or 8 , wherein the inorganic particles are silica particles. The electrode mixture according to any one of claims 1 to 9 applied to the current collector and dried to obtain electrodes. A nonaqueous electrolyte secondary battery comprising the electrode according to claim 10 as a negative electrode.