JP5610161B2 - Non-aqueous electrolyte secondary battery active material and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to an active material used for a nonaqueous electrolyte secondary battery electrode such as a lithium ion secondary battery, a slurry composition containing the active material, a nonaqueous electrolyte secondary battery electrode, and a nonaqueous electrolyte secondary battery.

  In recent years, portable terminals such as notebook personal computers, mobile phones, and PDAs have become widespread. Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries (hereinafter sometimes simply referred to as “batteries”) are frequently used as secondary batteries used for the power sources of these portable terminals. Mobile terminals are required to have more comfortable portability, and have rapidly become smaller, thinner, lighter, and higher in performance. As a result, portable terminals are used in various places. As the usage range of mobile terminals increases, the battery as the power source is also required to be smaller, thinner, lighter, and higher in performance as with mobile terminals.

  In order to improve battery performance, improvements to electrodes, electrolytes, and other battery members have been studied. Usually, an electrode is manufactured as follows. That is, a binder and a liquid medium are mixed to obtain a binder composition, and an active material is added thereto to form an electrode slurry composition. The obtained electrode slurry composition is applied onto a current collector and dried. Thus, an active material layer is formed and manufactured.

  For example, Patent Document 1 discloses that a polymer resin solution containing an antioxidant is impregnated with an electrode in order to solve a problem related to safety of a lithium ion secondary battery, and a hindered amine-based antioxidant is disclosed. The electrode manufactured by the above method is dip-coated in a mixed solution of polymer resin such as polyvinylidene fluoride and the like, and then dried to coat the surface of the electrode with an antioxidant.

  Patent Document 2 discloses a method of coating a separator with a polymer containing an antioxidant in order to suppress the deterioration reaction of the separator during the oxidation reaction in the positive electrode.

  By the way, in a battery having a high voltage of 4.25 V or more, the electrolytic solution is exposed to a strong oxidizing environment, a peroxide intermediate is generated at the active point of the positive electrode, and gas is generated due to decomposition of the electrolytic solution and the electrolyte. There were safety issues such as bulges. Patent Document 3 discloses that an antioxidant is added to the electrolyte in order to solve this problem.

JP-A-10-106546 JP 2004-253393 A (US Patent Application Publication No. 2004/166415) JP 2006-209995 A

  However, according to the study by the present inventors, even if an antioxidant as described in Patent Documents 1 to 3 is coated on an electrode or added to an electrolyte or an electrolytic solution, it is a reaction field. It has been found that only a small amount of antioxidant can be present on the active material surface. For this reason, it has been found that sufficient effects may not be obtained for suppressing the oxidation reaction on the surface of the positive electrode.

  Particularly in an active material having a large pore area, the inside of the pores of the active material becomes an active point, so that the electrolytic solution is significantly decomposed in the pores during charge and discharge, and decomposition products such as lithium carbonate are present in the pores. Deposits inside. It was also found that this decomposition product inhibited the acceptance of lithium ions into the active material, and the acceptability particularly at low temperatures was significantly deteriorated.

  The present invention has been made in view of the above-described problems of the prior art, and improves the lithium acceptability at a low temperature in an active material having many pores, thereby improving the life characteristics of the lithium ion secondary battery. It aims at providing the active material for nonaqueous electrolyte secondary battery electrodes which suppresses deterioration of this.

  The present invention also provides a slurry composition for a non-aqueous electrolyte secondary battery electrode containing the active material, a non-aqueous electrolyte secondary battery electrode formed by applying and drying the slurry composition, and a non-aqueous electrolyte secondary battery. Also aimed.

  As a result of intensive studies to solve the above problems, the present inventors have used an active material that has been previously surface-treated with an antioxidant when preparing a slurry composition, so that the antioxidant is inside the pores of the active material. It was found that the lithium acceptability at a low temperature is improved by suppressing the decomposition of the electrolyte solution at the active point inside the pore during charging and discharging.

That is, this invention which solves the said subject contains the following matter as a summary.
(1) An active material for a nonaqueous electrolyte secondary battery electrode that is surface-treated with an antioxidant.

(2) The active material for a nonaqueous electrolyte secondary battery electrode according to (1), wherein the content of the antioxidant in the active material is 0.01 to 1% by mass.

(3) The active material for a nonaqueous electrolyte secondary battery electrode according to (1) or (2), wherein the antioxidant is an amine-based antioxidant or a phenol-based antioxidant.

(4) mercury intrusion pore volume, 0.1cm ³ /g~2.0cm ³ / g active material is one in which surface-treated with (1) to a non-aqueous electrolyte according to any one of (3) Active material for secondary battery electrode.

(5) A slurry composition for a nonaqueous electrolyte secondary battery electrode, comprising the active material for a nonaqueous electrolyte secondary battery electrode according to (1) above, a binder, and a solvent.

(6) The slurry for a nonaqueous electrolyte secondary battery electrode according to (5), wherein the binder has a glass transition temperature of 25 ° C. or lower.

(7) A nonaqueous electrolyte secondary battery electrode obtained by applying and drying the slurry composition for a lithium ion secondary battery electrode according to (5) to (6) on a current collector.

(8) A nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein at least one of the positive electrode and the negative electrode is the electrode according to (7).

  According to the present invention, by treating the active material with the antioxidant, the antioxidant is present inside the pores of the active material, the active sites inside the pores of the active material are deactivated, and the electrolytic solution is decomposed. Can be suppressed. As a result, generation of gas derived from the electrolytic solution can be suppressed, and further, a decrease in battery capacity due to decomposition of the electrolytic solution can be suppressed. As a result, cycle characteristics are improved, and generation of lithium carbonate derived from decomposition of the electrolytic solution is suppressed, so that the acceptability of lithium ions of the active material is improved.

The present invention is described below.
The active material for a non-aqueous electrolyte secondary battery electrode of the present invention is surface-treated with an antioxidant (hereinafter, the active material surface-treated with an antioxidant is referred to as “active material“ A ””). To do.) In the present invention, the surface treatment means that the surface of the active material is coated with an antioxidant. This surface also includes the pore surface of the active material.

(Active material before surface treatment)
The active material before surface treatment of the active material for a nonaqueous electrolyte secondary battery electrode used after surface treatment in the present invention (hereinafter sometimes referred to as “active material“ a ””) is used in the electrolyte. Any material can be used as long as it can reversibly insert and release lithium ions by applying a potential.

  The electrode active material (positive electrode active material) for the positive electrode of the non-aqueous electrolyte secondary battery uses an active material capable of occluding and releasing lithium ions, and is broadly classified into an inorganic compound and an organic compound.

  Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, transition metal sulfides, and lithium-containing composite metal oxides made of lithium and a transition metal. Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.

Examples of transition metal oxides include MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO ₃ , V ₂ O. ₅ , V ₆ O _{13 and the} like. Among them, MnO, V ₂ O ₅ , V ₆ O ₁₃ and TiO ₂ are preferable from the viewpoint of cycle stability and capacity.

The transition metal _sulfide, TiS _2, TiS _3, amorphous _MoS 2, FeS, and the like.

  The structure of the lithium-containing composite metal oxide is not particularly limited, and examples thereof include a layered structure, a spinel structure, and an olivine structure.

As the lithium-containing composite metal oxide having a layered structure, lithium-containing composite oxide mainly composed of lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), and Co—Ni—Mn composite oxide. Products, lithium-containing composite oxides having a Ni-Mn-Al composite oxide as a main structure, lithium-containing composite oxides having a Ni-Co-Al composite oxide as a main structure, and the like.

Examples of lithium-containing composite metal oxides having a spinel structure include lithium manganate (LiMn ₂ O ₄ ) and Li [Mn _3/2 M _1/2 ] O _{4 in} which a part of Mn is substituted with another transition metal (here M may be Cr, Fe, Co, Ni, Cu or the like.

Li _X MPO ₄ (wherein, M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Li _X MPO ₄ as the lithium-containing composite metal oxide having an olivine structure) An olivine-type lithium phosphate compound represented by at least one selected from Si, B and Mo, 0 ≦ X ≦ 2) may be mentioned. Among them, LiFePO ₄ and LiCoPO ₄ are often used after being atomized due to their low conductivity. Therefore, the effect of improving the cycle characteristics due to the surface treatment of the anti-aging agent is high because they have many pores.

  As the organic compound, for example, a conductive polymer such as polyacetylene or poly-p-phenylene can be used.

  An iron-based oxide having poor electrical conductivity may be used as an electrode active material covered with a carbon material by allowing a carbon source material to be present during reduction firing. These compounds may be partially element-substituted. The positive electrode active material for a lithium ion secondary battery may be a mixture of the above inorganic compound and organic compound.

  As the electrode active material (negative electrode active material) for the negative electrode of the nonaqueous electrolyte secondary battery, an active material capable of occluding and releasing lithium ions is used, and is mainly classified into a carbon-based active material and a non-carbon-based active material. .

  Examples of the carbon-based active material include carbonaceous materials and graphite materials. The carbonaceous material generally indicates a carbon material having a low graphitization degree (low crystallinity) obtained by heat-treating (carbonizing) a carbon precursor at 2000 ° C. or lower. A graphitic material having high crystallinity close to that of graphite obtained by heat-treating at a temperature of 0 ° C. or higher is shown.

  Examples of the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitizable carbon having a structure close to an amorphous structure typified by glassy carbon. Examples of graphitizable carbon include carbon materials made from tar pitch obtained from petroleum and coal, such as coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, pyrolytic vapor-grown carbon fibers, etc. Is mentioned. MCMB is a carbon fine particle obtained by separating and extracting mesophase spherules produced in the process of heating pitches at around 400 ° C., and mesophase pitch-based carbon fiber is a mesophase pitch obtained by growing and coalescing the mesophase spherules. Is a carbon fiber made from a raw material.

  Examples of the non-graphitizable carbon include phenol resin fired bodies, polyacrylonitrile-based carbon fibers, pseudo-isotropic carbon, and furfuryl alcohol resin fired bodies (PFA).

  Examples of the graphite material include natural graphite and artificial graphite. Artificial graphite mainly includes artificial graphite heat-treated at 2800 ° C. or higher, graphitized MCMB heat-treated at 2000 ° C. or higher, graphitized mesophase pitch-based carbon fiber heat-treated at 2000 ° C. or higher. Used as an active material.

  As the non-carbon-based active material, lithium metal can be used, and simple metals and alloys thereof forming an alloy with lithium, oxides and sulfides thereof, and the like are used.

  Examples of single metals and alloys forming lithium alloys include compounds containing metals such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, and Zn. Is mentioned. Among these, silicon (Si), tin (Sn) or lead (Pb) simple metals, alloys containing these atoms, or compounds of these metals are used.

  Examples of oxides and sulfides include oxides, carbides, nitrides, silicides, sulfides, and phosphides. Among these, lithium-containing metal composite oxide materials containing a metal element selected from the group consisting of oxides such as tin oxide, manganese oxide, titanium oxide, niobium oxide, vanadium oxide, Si, Sn, Pb and Ti atoms are used. ing.

As the lithium-containing metal composite oxide, a lithium titanium composite oxide represented by Li _x Ti _y M _z O ₄ (0.7 ≦ x ≦ 1.5, 1.5 ≦ y ≦ 2.3, 0 ≦ z ≦ 1.6, M includes Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb), among which Li _4/3 Ti _5/3 O ₄ , Li ₁ Ti ₂ O ₄ and Li _4/5 Ti _11/5 O ₄ are used.

  Among these active materials, the effect of surface treatment on the antioxidant of the present invention in an electrode active material for lithium ion secondary batteries, which is prone to reaction by the electrolytic solution on the active material surface, particularly in the pores, and whose cycle characteristics are severely deteriorated Is big. Of these, the active material “a” is most preferably a negative electrode active material for a nonaqueous electrolyte secondary battery because it has a large effect on the surface of the negative electrode active material for a nonaqueous electrolyte secondary battery.

The active material "a" used in the present invention, mercury intrusion pore volume in the voltage step-up from the pressure 4kPa to 400MPa ^is, preferably has in the range of 0.1cm ³ /g~2.0cm 3 / g , it is more preferable in a range of 0.4cm ³ /g~1.5cm ³ / g. The pre-treatment active material “a” whose mercury intrusion pore volume is in the above range usually has pores having a diameter of 0.01 to 10 μm inside the active material. By using the active material “a” having a mercury intrusion pore volume within the above range, when the active material “a” is surface-treated with an antioxidant, the antioxidant easily enters the pores. Thus, the active sites inside the pores of the active material are deactivated, and the low-temperature lithium acceptability is greatly improved. Furthermore, it is possible to reduce the amount of binder when preparing a slurry composition to be described later, to suppress a decrease in the capacity of the battery, and to easily prepare the slurry composition to have an appropriate viscosity for application. become. The pore volume can be determined by measuring pore size distribution by mercury porosimetry.

  In the present invention, the particle shape of the active material “a” used may be a lump shape, polyhedron shape, spherical shape, elliptical spherical shape, plate shape, needle shape, columnar shape, etc., as used conventionally. Since there are many pores and the effect of improving lithium acceptability by surface treatment using an antioxidant is large, it is preferable that the particles are agglomerated or formed by agglomerating primary particles to form secondary particles.

The specific surface area of the active material "a" used in the present invention is preferably one in the range of 0.1 to 20 m ² / g, it is more preferable in the range of 0.5 to 10 m ² / g. By using a material having a specific surface area of the active material “a” within the above range, the effect of adding an antioxidant can be greatly seen. Furthermore, the amount of binder at the time of preparation of the slurry composition described later can be reduced, the decrease in battery capacity can be suppressed, and the slurry composition described later can be easily prepared to have an appropriate viscosity for application. become.

  The particle diameter of the active material “a” used in the present invention is usually 1 to 50 μm, preferably 2 to 30 μm. When the particle diameter of the active material “a” is in the above range, the amount of the binder when preparing a slurry composition to be described later can be reduced, the decrease in battery capacity can be suppressed, It becomes easy to adjust the viscosity to be appropriate for application.

  In the present invention, as the active material “a”, a material obtained by attaching a conductivity imparting material to the surface by a mechanical modification method can also be used.

(Antioxidant)
Examples of the antioxidant used in the present invention include amine-based antioxidants, phenol-based antioxidants, quinone-based antioxidants, organic phosphorus-based antioxidants, sulfur-based antioxidants, and phenothiazine-based antioxidants. .

  Examples of the amine-based antioxidant include bis (4-t-butylphenyl) amine, poly (2,2,4-trimethyl-1,2-dihydroquinoline), 6-ethoxy-1,2-dihydro- 2,2,4-trimethylquinoline, reaction product of diphenylamine and acetone, 1- (N-phenylamino) -naphthalene, diphenylamine derivative, dialkyldiphenylamines, N, N′-diphenyl-p-phenylenediamine, mixed diallyl- Examples thereof include p-phenylenediamine, N-phenyl-N′-isopropyl-p-phenylenediamine, and N, N′-di-2-naphthyl-p-phenylenediamine compound.

  Examples of the phenolic antioxidant include 3,5-di-t-butyl-4-hydroxytoluene, dibutylhydroxytoluene, 2,2′-methylenebis (6-t-butyl-4-methylphenol), 4,4. '-Butylidenebis (3-t-butyl-3-methylphenol), 4,4'-thiobis (6-t-butyl-3-methylphenol), α-tocophenol, 2,2,4-trimethyl-6- Examples thereof include hydroxy-7-t-butylchroman and polymer type phenol having a relatively high molecular weight.

  Examples of the quinone antioxidant include 2,5-di-t-butylhydroquinone, 2,5-di-t-octylhydroquinone, 2,6-di-n-dodecylhydroquinone, 2-n-dodecyl-5 Examples include hydroquinone compounds such as chlorohydroquinone and 2-t-octyl-5-methylhydroquinone.

  Examples of the phosphorus antioxidant include triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, and 4,4′-butylidene-bis (3-methyl-6-tert-butylphenylditridecyl) phos. Phyto, cyclic neopentanetetrayl bis (octadecyl phosphite), tris (nonylphenyl phosphite), tris (mono (or di) nonylphenyl) phosphite, diisodecyl pentaerythritol diphosphite, 9,10-dihydro-9 -Oxa-10-phosphaphenanthrene-10-oxide, 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10- Oxide, 10-decyloxy- , 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, tris (2,4-di-t-butylphenyl) phosphite, cyclic neopentanetetraylbis (2,4-di-t -Butylphenyl) phosphite, cyclic neopentanetetraylbis (2,6-di-t-butyl-4-methylphenyl) phosphite, 2,2-methylenebis (4,6-di-t-butylphenyl) Examples include octyl phosphite.

Examples of the sulfur-based antioxidant include dilauryl-3,3′-thiodipropionate and distearyl-3,3′-tridipropionate.
Examples of the phenothiazine antioxidant include phenothiazine, 10-methylphenothiazine, 2-methylphenothiazine, and 2-trifluoromethylphenothiazine.

  Among these antioxidants, the effect of improving the cycle characteristics of the battery is great, and the reaction with the electrolyte solvent, lithium salt, surface active group of the electrode active material, etc. hardly occurs in the battery, so that the surface treatment significantly increases. An amine antioxidant, a phenolic antioxidant, a hydroquinone antioxidant, or an organic phosphorus antioxidant is preferred from the viewpoint of improving low-temperature lithium acceptability. In addition, the solubility in the electrolyte is low, and it exists on the surface of the electrode active material and in the pores even inside the battery. By deactivating the active material surface, both the life characteristics and the low-temperature lithium acceptability are greatly improved. Therefore, an amine-based antioxidant or a phenol-based antioxidant is more preferable. Among them, in particular, the solubility in the electrolytic solution is very low, and the diphenylamine derivative is particularly preferable because it is adsorbed and stabilized on the active material surface and easily exists inside the electrode, and is difficult to dissolve in the electrolytic solution. Most preferred are electrophenyl groups, for example, diphenylamine derivatives having an imide skeleton in the side chain. Moreover, these antioxidants may be used alone or in combination of two or more.

(Surface treatment method of active material)
In the present invention, an active material “A” surface-treated with an antioxidant is used.
As a surface treatment method of the active material “a” with an antioxidant, a gas phase treatment method in which an antioxidant in a gaseous state is brought into contact with the surface of the active material “a”; an antioxidant dissolved or dispersed in a solvent is used. Various liquid phase treatment methods for bringing the surface of the active material “a” into contact; solid phase treatment methods in which a solid, preferably powdered, antioxidant is brought into contact with the active material “a” for surface treatment The method is mentioned.

  Examples of the gas phase treatment method include a method of forming an antioxidant layer on the active material surface by applying a CVD method or the like.

  Examples of the liquid phase treatment method include a wet method in which an antioxidant and an active material are dissolved or dispersed in a solvent to form an antioxidant layer on the surface of the active material, as well as a spray drying method and a vacuum deposition method. .

 Examples of the solid phase treatment method include a mechanochemical method in which an active material and an antioxidant coexist in a disperser, and a mechanical force is applied thereto to attach the antioxidant to the active material surface.

  Among these methods, it is the simplest method, and an antioxidant can be present inside the pores of the active material, and the lithium accepts lithium at a low temperature by deactivating the active sites inside the pores. From the viewpoint of improving the properties, a liquid phase treatment method is preferable, and among them, a wet method in which an antioxidant and an active material are dissolved or dispersed in a solvent to form an antioxidant layer on the surface of the active material is more preferable.

  As the liquid phase treatment method, 1) a method in which an antioxidant and an active material “a” are added and dispersed in a solvent, and the resulting dispersion is dried; 2) an antioxidant is added in the solvent. The active material “a” is added to the resulting dispersion, mixed and dried; 3) The active material “a” is added and dispersed in the solvent, and the resulting dispersion is oxidized. A method of adding an inhibitor and mixing and drying; 4) a method of mixing the antioxidant, the active material “a” and a solvent in a lump and performing spray drying.

  The method for dispersing the antioxidant and the active material “a” is not particularly limited, and a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, and a planetary kneader can be used.

  When surface-treating the active material “a” by the liquid phase treatment method, the solid content concentration in the dispersion is preferably 40 to 80% by mass, and more preferably 50 to 70% by mass. When the solid content concentration in the dispersion is within the above range, the active material is well dispersed, so that the surface of the active material can be uniformly coated with the antioxidant. Further, the concentration of the antioxidant in the dispersion is preferably 0.1 to 10% by mass, preferably 0.5 to 5% by mass in terms of solid content with respect to the solvent. It is more preferable that it is 2 mass%. When the concentration of the antioxidant is within the above range, the antioxidant is uniformly dissolved in the solvent, so that the active material surface can be uniformly coated.

  The drying temperature and the drying time are preferably a temperature and a time at which the solvent can be completely removed, the structure of the active material is not changed, and the antioxidant is not decomposed. Although it depends on the type of solvent used, the drying temperature is preferably less than the decomposition temperature of the antioxidant, preferably 50 to 300 ° C, more preferably 100 to 250 ° C. The drying time is preferably 1 to 48 hours, more preferably 5 to 24 hours. Drying may be performed under normal pressure or under reduced pressure.

  The solvent is not particularly limited as long as the antioxidant can be dissolved. As the solvent, either water or an organic solvent can be used. Examples of organic solvents include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; acetone, ethyl methyl ketone, disopropyl ketone, cyclohexanone, methylcyclohexane, and ethylcyclohexane. Ketones; chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; esters such as ethyl acetate, butyl acetate, γ-butyrolactone and ε-caprolactone; acylonitriles such as acetonitrile and propionitrile; tetrahydrofuran; Ethers such as ethylene glycol diethyl ether: alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; Amides such as loridone and N, N-dimethylformamide are exemplified. These solvents may be used alone, or two or more of these may be mixed and used as a mixed solvent. Among these, a solvent having excellent solubility of the antioxidant used in the present invention and having a low boiling point and high volatility is preferable because it can be removed in a short time and at a low temperature. Acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, or N-methylpyrrolidone, or a mixed solvent thereof is preferable, and particularly N- is preferred because it easily wets the active material and the antioxidant easily penetrates the active material. Methyl pyrrolidone is preferred.

  The content of the antioxidant in the surface-treated active material “A” is preferably 0.01 to 1.0% by mass, more preferably 0.01 to 0.5% by mass, and particularly preferably 0. 0.01 to 0.2% by mass. When the content of the antioxidant in the active material “A” is within the above range, the antioxidant is not released into the electrolyte inside the battery, and the antioxidant is also added inside the pores of the active material. The lithium acceptability at a low temperature can be greatly improved by deactivating the active sites inside the pores.

  The content of the antioxidant in the active material “A” of the present invention can be measured by GC-MS in which a gas chromatograph and a mass spectrometer are directly connected. The active material “A” is separated into the antioxidant and the active material “a”, and the content of the antioxidant in the active material is determined by analyzing the mass of each from the GC-MS and calculating the ratio. It can be measured.

  In the measurement, first, a predetermined amount of the active material “A” surface-treated with an antioxidant and a solvent capable of dissolving the antioxidant, for example, N-methylpyrrolidone, are mixed to obtain a mixed solution. Next, this is filtered and separated into an active material “a” and a solution containing an antioxidant. Then, the amount of the antioxidant in the solution containing the antioxidant is detected by GC-MS. For the detection, an N-methylpyrrolidone solution in which an antioxidant is dissolved at several concentrations is prepared, and a calibration curve is prepared using this solution. The content of the antioxidant in the surface-treated active material “A” is calculated from the detected weight ratio of the antioxidant in the solution and the active material “a” separated by filtration.

(Slurry composition for non-aqueous electrolyte secondary battery electrode)
The slurry composition for a non-aqueous electrolyte secondary battery electrode of the present invention contains an active material “A” for a non-aqueous electrolyte secondary battery electrode that has been surface-treated with an antioxidant in advance, a binder, and a solvent.

(binder)
The binder is a solution or dispersion in which binder (polymer) particles having binding properties are dissolved or dispersed in water or an organic solvent (hereinafter, these may be collectively referred to as “binder dispersion”). ). The binder dispersion may be non-aqueous or aqueous. When the binder dispersion is aqueous, it is usually a polymer particle dispersion using water as a dispersion medium. For example, a diene polymer particle dispersion, an acrylic polymer particle dispersion, or a fluorine polymer particle described later. Examples thereof include a dispersion and a silicon-based polymer particle dispersion. Among these, a diene polymer particle dispersion or an acrylic polymer particle dispersion is preferable because it has excellent binding properties to the active material and the strength and flexibility of the obtained electrode. Because of its high binding properties with the active material, it is difficult for the electrode to peel off. As a result, the antioxidant on the surface of the active material does not desorb from the surface even during long-term cycles, and the presence of the antioxidant on the surface deactivates the active sites on the surface of the active material, thereby accepting lithium. The effect of improving is sustained. As a result, high cycle characteristics can be exhibited.

  When the binder dispersion is non-aqueous (using an organic solvent as a dispersion medium), usually polyethylene, polypropylene, polyisobutylene, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyacetic acid Vinyl-polyvinyl alcohol, vinyl, isobutyl ether, polyacrylonitrile, polymethacrylonitrile, polymethyl methacrylate, polymethyl acrylate, polyethyl methacrylate, polyallyl acetate, polystyrene and other vinyl polymers; polybutadiene, polyisoprene, and other diene polymers Polymer: Polyoxymethylene, polyoxyethylene, polycyclic thioether, polydimethylsiloxane, and other ether-based polymers containing a hetero atom in the main chain; polylactone, polycyclic anhydride, polyethylene N-terephthalate, polycarbonate, and other condensed ester polymers; Nylon 6, nylon 66, poly-m-phenylene isophthalamide, poly-p-phenylene terephthalamide, polypyromellitimide, and other condensed amide polymers -What was melt | dissolved in methylpyrrolidone (NMP) is mentioned.

  The diene polymer particle dispersion is an aqueous dispersion of a polymer containing monomer units formed by polymerizing a conjugated diene such as butadiene or isoprene. The proportion of monomer units obtained by polymerizing conjugated diene in the diene polymer is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more. Examples of the polymer include homopolymers of conjugated dienes such as polybutadiene and polyisoprene; and copolymers of monomers that are copolymerizable with conjugated dienes. Examples of the copolymerizable monomer include α, β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid and methacrylic acid; styrene, chlorostyrene, vinyltoluene, and t-butyl. Styrene monomers such as styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, divinylbenzene; olefins such as ethylene, propylene; butadiene, isoprene, etc. Diene monomers; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate; methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, etc. Vinylue Ethers; vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; and heterocyclic ring-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole.

  The acrylic polymer particle dispersion is an aqueous dispersion of a polymer containing monomer units obtained by polymerizing an acrylic ester and / or a methacrylic ester. The proportion of monomer units obtained by polymerizing acrylic acid ester and / or methacrylic acid ester is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more. Examples of the polymer include homopolymers of acrylic acid esters and / or methacrylic acid esters, and copolymers with monomers copolymerizable therewith. Examples of the copolymerizable monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; two or more carbons such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate. -Carboxylic acid ester having a carbon double bond; styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, vinyl benzoate methyl, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, Styrene monomers such as divinylbenzene; Amide monomers such as acrylamide, N-methylol aquaylamide, and acrylamide-2-methylpropanesulfonic acid; α, β- such as acrylonitrile and methacrylonitrile Saturated nitrile compounds; olefins such as ethylene and propylene; diene monomers such as butadiene and isoprene; monomers containing halogen atoms such as vinyl chloride and vinylidene chloride; vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate Vinyl esters such as methyl vinyl ether, ethyl vinyl ether, and butyl vinyl ether; vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; N-vinyl pyrrolidone, Heterocycle-containing vinyl compounds such as vinylpyridine and vinylimidazole can be mentioned.

  As the binder for the positive electrode, it is excellent in oxidation resistance during charging, the binder itself is not decomposed and the cycle characteristics are not deteriorated, the binder is appropriately swollen in the electrolyte, and Li ions are conducted. An acrylic polymer particle dispersion, which is a dispersion of a saturated polymer that does not have an unsaturated bond in the polymer main chain, is most preferable in that it is easy to obtain and has excellent Li acceptance characteristics.

  The binder dispersion may be an aqueous binder using water as a dispersion medium, or may be a non-aqueous binder using an organic solvent as a dispersion medium. However, when a non-aqueous binder is used, the active material is surface-treated. Since the antioxidant is dissolved and the effects of the present invention may not be obtained, an aqueous binder is preferably used.

  The aqueous binder can be produced, for example, by emulsion polymerization of the monomer in water. The non-aqueous binder can be produced by replacing the aqueous binder with an organic solvent. The average particle size of the binder particles in the binder dispersion is preferably 50 nm to 500 nm, and more preferably 70 nm to 400 nm. When the average particle size is within this range, the strength and flexibility of the obtained electrode are good.

  In the present invention, the glass transition temperature of the binder is preferably 25 ° C. or less, more preferably −100 ° C. to + 25 ° C., still more preferably −80 ° C. to + 10 ° C., and most preferably −80 ° C. to 0 ° C. is there. When the glass transition temperature of the binder is within the above range, characteristics such as flexibility, binding and winding properties of the electrode, and adhesion between the active material layer and the current collector layer are highly balanced and suitable. Moreover, since the state in which the active material surface is coated with the binder can be maintained, peeling of the antioxidant and the binder from the active material in the electrode plate pressing step can be suppressed.

  In the slurry composition for an electrode of the present invention, the total content of the surface-treated active material “A” and the binder is preferably 10 to 90 parts by mass, more preferably 30 with respect to 100 parts by mass of the slurry. ~ 80 parts by mass. Further, the binder content (solid content equivalent) relative to the surface-treated active material “A” is preferably 0.1 to 5 parts by mass, more preferably 100 parts by mass of the active material “A”. Is 0.5-2 parts by mass. If the total content of the active material “A” subjected to the surface treatment in the electrode slurry composition and the binder content and the binder content are within the above ranges, the viscosity of the resulting slurry composition is optimized, and the coating is smoothly performed. In addition, sufficient adhesion strength can be obtained without increasing the resistance of the obtained electrode plate. As a result, peeling of the antioxidant and binder from the active material in the electrode plate pressing step can be suppressed.

(solvent)
The solvent used for the electrode slurry is not particularly limited as long as it can uniformly disperse the above-described solid content (active material “A” for non-aqueous electrolyte secondary battery electrode surface-treated with an antioxidant, binder). Although not used, a solvent that does not dissolve the antioxidant is preferably used.

  As the solvent used for the electrode slurry, either water or an organic solvent can be used. Examples of organic solvents include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; acetone, ethyl methyl ketone, disopropyl ketone, cyclohexanone, methylcyclohexane, and ethylcyclohexane. Ketones; chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; esters such as ethyl acetate, butyl acetate, γ-butyrolactone and ε-caprolactone; acylonitriles such as acetonitrile and propionitrile; tetrahydrofuran; Ethers such as ethylene glycol diethyl ether: alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; Amides such as loridone and N, N-dimethylformamide are exemplified.

  These solvents may be used alone, or two or more of these may be mixed and used as a mixed solvent. Among these, a solvent having a low boiling point and high volatility is preferable because it can be removed at a low temperature in a short time. Specifically, acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, water, N-methylpyrrolidone, or a mixed solvent thereof is preferable. Furthermore, water is particularly preferable from the viewpoint of maintaining the amount of antioxidant in the active material without dissolving the antioxidant used for the surface treatment of the active material.

(Thickener)
The slurry composition for electrodes of the present invention may further contain a thickener. Examples of thickeners include cellulosic polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof; ) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified Examples include polyacrylic acid, oxidized starch, phosphoric acid starch, casein, various modified starches, and preferably ammonium salts and alkali metal salts of carboxymethyl cellulose. Used. This is because the above thickener tends to uniformly cover the surface of the active material at the time of slurry preparation, and thus has an effect of preventing the removal of the antioxidant on the surface of the active material.

  The blending amount of the thickener is preferably 0.5 to 2.0 parts by mass with respect to 100 parts by mass of the active material “A” surface-treated with the antioxidant. When the blending amount of the thickener is within this range, the coating property and the adhesion with the current collector are good. In the present invention, “(modified) poly” means “unmodified poly” or “modified poly”, and “(meth) acryl” means “acryl” or “methacryl”.

(Conductive material)
In the slurry composition for electrodes of the present invention, a conductive material may be contained. As the conductive material, conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube can be used. By using the conductive material, the electrical contact between the active materials can be improved, and the discharge rate characteristics can be improved when used for a lithium ion secondary battery. The amount of the conductive material is usually 0 to 20 parts by mass, preferably 1 to 10 parts by mass with respect to 100 parts by mass of the active material “A” surface-treated with the antioxidant.

  In addition to the above-mentioned components, the electrode slurry composition of the present invention further contains other components such as a reinforcing material, a dispersing agent, a leveling agent, and an electrolyte additive having a function of inhibiting electrolyte decomposition. It may be included in a secondary battery electrode described later. These are not particularly limited as long as they do not affect the battery reaction.

  As the reinforcing material, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. By using a reinforcing material, a tough and flexible electrode can be obtained, and excellent long-term cycle characteristics can be exhibited. The usage-amount of the electroconductivity imparting material and the reinforcing agent in the slurry composition for electrodes is usually 0.01 to 20 parts by mass, preferably 1 to 100 parts by mass with respect to 100 parts by mass of the active material “A” surface-treated with the antioxidant. 10 parts by mass. By being included in the range, high capacity and high load characteristics can be exhibited.

  Examples of the dispersant include an anionic compound, a cationic compound, a nonionic compound, and a polymer compound. A dispersing agent is selected according to the electrode active material and electrically conductive agent to be used. It is preferable that the content rate of the dispersing agent in the slurry composition for electrodes is 0.01-10 mass parts with respect to 100 mass parts of active material "A" surface-treated with antioxidant. When the amount of the dispersant is in the above range, the slurry has excellent stability, a smooth electrode can be obtained, and a high battery capacity can be exhibited.

  Examples of the leveling agent include surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants. By mixing the surfactant, it is possible to prevent the repelling that occurs during coating or to improve the smoothness of the electrode. The content ratio of the leveling agent in the electrode slurry composition is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the active material “A” surface-treated with the antioxidant. When the leveling agent is within the above range, the productivity, smoothness, and battery characteristics during electrode production are excellent.

  As the electrolytic solution additive, vinylene carbonate used in the slurry composition for electrodes and in the electrolytic solution can be used. The content ratio of the electrolytic solution additive in the electrode slurry composition is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the active material “A” surface-treated with the antioxidant. When the electrolytic solution additive is in the above range, the cycle characteristics and the high temperature characteristics are excellent. Other examples include nanoparticles such as fumed silica and fumed alumina. By mixing the nanoparticles, the thixotropy of the electrode forming slurry can be controlled, and the leveling property of the resulting electrode can be improved. The content ratio of the nano fine particles in the electrode slurry composition is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the active material “A” surface-treated with the antioxidant. When the nanoparticles are in the above range, the slurry stability and productivity are excellent, and high battery characteristics are exhibited.

(Method for producing slurry composition for nonaqueous electrolyte secondary battery electrode)
The slurry composition for a non-aqueous electrolyte secondary battery electrode is prepared by mixing the binder, the active material “A” surface-treated with an antioxidant, a solvent, a thickener used as necessary, a conductive material, and the like. can get.

  The mixing method is not particularly limited, and examples thereof include a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type. Further, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, and a planetary kneader can be used.

(electrode)
The electrode for a non-aqueous electrolyte secondary battery of the present invention is formed by binding an active material layer formed by applying and drying the electrode slurry composition of the present invention on a current collector.

  Although the manufacturing method of the electrode of this invention is not specifically limited, For example, the method of apply | coating and drying the said slurry composition for electrodes on at least one surface of an electrical power collector, Preferably both surfaces and forming an active material layer is mentioned.

  The method for applying the electrode slurry composition onto the current collector is not particularly limited. Examples of the method include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

  Examples of the drying method include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying time is usually 5 to 30 minutes, and the drying temperature is usually 40 to 180 ° C.

  When manufacturing the electrode of the present invention, after applying and drying the slurry composition for an electrode on a current collector, a step of lowering the porosity of the active material layer by pressure treatment using a die press or a roll press, etc. It is preferable to have. The preferable range of the porosity is 5% to 15%, more preferably 7% to 13%. If the porosity is too high, charging efficiency and discharging efficiency are deteriorated. When the porosity is too low, there arises a problem that the volume capacity of the battery is lowered, or the active material layer is easily peeled off from the current collector, and the battery is liable to be defective.

  Further, when a curable polymer is used as the binder, it is preferably cured.

  In the present invention, the thickness of the active material layer of the electrode for a nonaqueous electrolyte secondary battery is usually 5 to 300 μm, preferably 30 to 250 μm, for both the positive electrode and the negative electrode. When the electrode thickness is in the above range, both load characteristics and cycle characteristics are high.

(Current collector)
The current collector used in the present invention is not particularly limited as long as it is an electrically conductive and electrochemically durable material. However, a metal material is preferable because it has heat resistance. For example, iron, copper, aluminum Nickel, stainless steel, titanium, tantalum, gold, platinum and the like. Among these, aluminum is particularly preferable for the positive electrode of the lithium ion secondary battery, and copper is particularly preferable for the negative electrode. The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 to 0.5 mm is preferable. In order to increase the adhesive strength with the active material layer, the current collector is preferably used after roughening in advance. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, an abrasive cloth paper with a fixed abrasive particle, a grindstone, an emery buff, a wire brush provided with a steel wire or the like is used. Further, an intermediate layer may be formed on the current collector surface in order to increase the adhesive strength and conductivity of the mixture.

(Non-aqueous electrolyte secondary battery)
The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolytic solution, and at least one of the positive electrode and the negative electrode is the non-aqueous electrolyte secondary battery electrode.

(Electrolyte)
The electrolytic solution used in the present invention is not particularly limited. For example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent can be used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and other lithium salts. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used. These can be used alone or in admixture of two or more. The amount of the supporting electrolyte is usually 1% by mass or more, preferably 5% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less, with respect to the electrolytic solution. If the amount of the supporting electrolyte is too small or too large, the ionic conductivity is lowered, and the charging characteristics and discharging characteristics of the battery are degraded.

  The solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. Usually, dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene. Alkyl carbonates such as carbonate (BC) and methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfolane and dimethyl sulfoxide Sulfur-containing compounds are used. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable because high ion conductivity is easily obtained and the use temperature range is wide. These can be used alone or in admixture of two or more.

  Moreover, it is also possible to use the electrolyte solution by containing an additive. As the additive, carbonate compounds such as vinylene carbonate (VC) are preferable.

Examples of the electrolytic solution other than the above include a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolytic solution, and an inorganic solid electrolyte such as lithium sulfide, LiI, and Li ₃ N.

(separator)
The separator is a porous substrate having pores, and usable separators include (a) a porous separator having pores, and (b) a porous material having a polymer coating layer formed on one or both sides. There is a separator or (c) a porous separator on which a porous resin coat layer containing an inorganic ceramic powder is formed. Non-limiting examples of these include polypropylene, polyethylene, polyolefin, or aramid porous Polymer film for solid polymer electrolyte or gel polymer electrolyte such as conductive separator, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride hexafluoropropylene copolymer, and gelled polymer coating layer Coated separator or inorganic filler And the like porous membrane layer made of an inorganic filler dispersant is coated separator.

(Battery manufacturing method)
The method for producing the nonaqueous electrolyte secondary battery of the present invention is not particularly limited. For example, the negative electrode and the positive electrode are overlapped via a separator, and this is wound or folded according to the shape of the battery and placed in the battery container, and the electrolytic solution is injected into the battery container and sealed. Further, if necessary, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate and the like can be inserted to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a laminated cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, and the like.

(Example)
Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, unless otherwise indicated, the part and% in a present Example are a mass reference | standard. In the examples and comparative examples, various physical properties were evaluated as follows.

(Measurement of mercury intrusion pore volume of active material before surface treatment)
The pore volume of the active material “a” before the surface treatment was measured using a mercury porosimeter (Autopore IV9510 manufactured by Micromeritics). Inject 0.2 g of active material “a” before surface treatment into a powder cell, perform pretreatment by degassing for 10 minutes at room temperature under vacuum, introduce mercury under reduced pressure and change pressure The amount of mercury intrusion was measured. The mercury intrusion pore volume of the active material “a” before the surface treatment was calculated from the obtained mercury intrusion curve.

(Content of antioxidant in the surface-treated active material “A”)
The surface-treated active material “A” and N-methylpyrrolidone are mixed to obtain a mixed solution having a solid content concentration of 10%. Next, this is filtered and separated into an active material “a” and a solution containing an antioxidant. Then, the amount of the antioxidant in the solution containing the antioxidant is detected by GC-MS. The amount of antioxidant in the surface-treated active material “A” was calculated from the weight ratio of the detected amount of antioxidant in the solution and the active material “a” separated by filtration. In the detection, a solution in which an antioxidant was dissolved at several concentrations was prepared, and a calibration curve was prepared using these solutions.

(Peel strength)
Each electrode is cut into a rectangular shape having a width of 1 cm and a length of 10 cm to form a test piece, which is fixed with the electrode active material layer surface facing up. After applying the cellophane tape to the surface of the electrode active material layer of the test piece, the stress was measured when the cellophane tape was peeled off from one end of the test piece in the 180 ° direction at a speed of 50 mm / min. The measurement was performed 10 times, the average value was obtained, and this was used as the peel strength. It shows that the adhesiveness of an electrode plate is so favorable that peel strength is large.
A: 6 N / m or more B: 5 N / m or more to less than 6 N / m C: 4 N / m or more to less than 5 N / m D: 3 N / m or more to less than 4 N / m E: 2 N / m or more to less than 3 N / m F: Less than 2 N / m

(Charge / discharge characteristics)
(1) Lithium-accepting characteristics Using the obtained laminated cell type battery, the charge / discharge rate was set to 0.1 C at 25 ° C., respectively, and the battery was charged at a constant current until it reached 4.2 V by the constant current constant voltage charging method. Charge at a constant voltage. Charging / discharging to 3V after charging was repeated twice, and then constant current / constant voltage charging was performed at 0.1 C in a thermostat set to 0 ° C. The battery capacity obtained at the time of constant current in this constant current and constant voltage charge was used as an index of lithium acceptability, and the determination was made according to the following criteria. The larger this value, the better the battery.
A: 220 mAh / g or more B: 200 mAh / g or more and less than 220 mAh / g C: 180 mAh / g or more and less than 200 mAh / g D: 160 mAh / g or more and less than 180 mAh / g E: 140 mAh / g or more and less than 160 mAh / g E: 140 mAh / less than g

(2) Charging / discharging cycle characteristics Using the obtained laminate cell type battery, charging at a constant current until reaching 4.2V by a method of constant current constant voltage charging at 25C at 25C, respectively, and then constant voltage And a charge / discharge cycle in which the battery was discharged to 3.0 V with a constant current of 0.5 C. The charge / discharge cycle was performed up to 50 cycles, and the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity was defined as the capacity maintenance rate, and the following criteria were used. It shows that the capacity | capacitance reduction by repeated charging / discharging is so small that this value is large.
A: 60% or more B: 55% or more and less than 60% C: 50% or more and less than 55% D: 45% or more and less than 50% E: 40% or more and less than 45% E: Less than 40%

(Gas generation during charging / discharging)
In the same manner as in the above method, using the obtained laminated cell type battery, charging and discharging were repeated at 0.1 C, and then the cell charged at 0.1 C was again placed in a thermostatic bath at 80 ° C. and allowed to stand for 30 hours. . Measure the cell thickness (a) after standing for 30 hours in a thermostat and the thickness (b) of the cell before entering the thermostat, and {(a)-(b)} / (a) × 100 (%) Is determined by the following criteria. The expansion rate of the cell is an indicator of the amount of gas generation, and the smaller the expansion rate of the cell, the smaller the amount of gas generation.
A: Less than 10% B: 10% or more and less than 20% C: 20% or more and less than 30% D: 30% or more and less than 40% E: 40% or more

Example 1
(Surface treatment with active material antioxidant)
A mixed solution was prepared by dissolving 0.02 part of an antioxidant of a diphenylamine derivative represented by the following chemical formula 1 in 50 parts of N-methylpyrrolidone. Into a container, 100 parts of artificial graphite having a mercury intrusion pore volume of 0.95 cm ³ / g and a specific surface area of 3.8 m ² / g as an active material “a” before treatment is added, and then the mixed solution is added. The mixture was stirred for 1 hour with a planetary mixer, and the resulting mixture was vacuum-dried at 100 ° C. for 24 hours to subject the artificial graphite to a surface treatment.

(Manufacture of negative electrode)
A 1% aqueous solution was prepared using carboxymethylcellulose (“Daicel 2200” manufactured by Daicel Chemical Industries, Ltd.) having a 1% aqueous solution viscosity of 2000 mPa · s.

  Into a planetary mixer with a disper, 100 parts of artificial graphite surface-treated with an antioxidant was added, and 100 parts of the aqueous solution was added thereto, and the solid content concentration was adjusted to 53.5% with ion-exchanged water. For 60 minutes. Next, after adjusting to 44% of solid content concentration with ion-exchange water, it mixed for 15 minutes at 25 degreeC.

  Next, 2.5 parts of a dispersion of styrene-butadiene polymer particles having a solid content concentration of 40% and a glass transition temperature of −15 ° C. was added and further mixed for 10 minutes. This was defoamed under reduced pressure to obtain a slurry composition for electrodes with good fluidity.

  The electrode slurry composition was applied on a copper foil having a thickness of 20 μm with a comma coater so that the film thickness after drying was about 200 μm, and the speed was 0.5 m / min at 60 ° C. for 2 minutes. The electrode raw material was obtained by drying and heat treatment at 120 ° C. for 2 minutes. This electrode fabric was rolled with a roll press to obtain a negative electrode having an active material layer thickness of 80 μm.

(Manufacture of positive electrode)
Polyvinylidene fluoride was added as a binder to 100 parts of LiMn ₂ O ₄ having a spinel structure as a positive electrode active material so that the solid content equivalent amount was 2 parts, and further 2 parts of acetylene black and 20 parts of N-methylpyrrolidone were added. In addition, the slurry for positive electrodes was obtained by mixing with a planetary mixer. This positive electrode slurry was applied to an aluminum foil having a thickness of 18 μm, dried at 150 ° C. for 3 hours, and then roll-pressed to obtain a positive electrode having an active material layer thickness of 100 μm.

(Manufacture of lithium ion secondary batteries)
A battery container was prepared using a laminate film in which both surfaces of an aluminum sheet were coated with a resin made of polypropylene. Next, using the positive electrode and the negative electrode, the active material layer was removed from each end, and the Ni tab was welded to the removed portion and the Cu tab was welded to the negative electrode. The obtained positive electrode and negative electrode were wound with a separator made of a polyethylene microporous membrane so that the active material layer surfaces of both electrodes were opposed, and wound and stored in the battery container. Subsequently, an electrolytic solution in which LiPF ₆ was dissolved to a concentration of 1 mol / liter was injected into a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 2 at 25 ° C. Next, the laminate film was sealed to produce a laminate cell type lithium ion secondary battery. Table 1 shows the evaluation results of the performance of this battery.

(Example 2)
In the surface treatment of the active material, the same operation as in Example 1 was performed except that 0.1 part of a diphenylamine derivative antioxidant was dissolved in 50 parts of N-methylpyrrolidone as a mixed solution. Then, a negative electrode and a laminate cell type lithium ion secondary battery were prepared, and the performance of the battery was evaluated. The results are shown in Table 1.

(Example 3)
In the surface treatment of the active material, the same operation as in Example 1 was performed except that 1.0 part of a diphenylamine derivative antioxidant was dissolved in 50 parts of N-methylpyrrolidone as a mixed solution. Then, a negative electrode and a laminate cell type lithium ion secondary battery were prepared, and the performance of the battery was evaluated. The results are shown in Table 1.

Example 4
In the surface treatment of the active material, the same operation as in Example 1 was performed except that 100 parts of artificial graphite having a mercury intrusion pore volume of 0.3 cm ³ / g was used as the active material “a” before the treatment. Then, a negative electrode and a laminate cell type lithium ion secondary battery were prepared, and the performance of the battery was evaluated. The results are shown in Table 1.

(Example 5)
In the surface treatment of the active material, 0.02 part of a diphenylamine derivative antioxidant (NOCRAK DP manufactured by Ouchi Shinsei Chemical Co., Ltd.) represented by the following chemical formula 2 is dissolved in 50 parts of N-methylpyrrolidone as a mixed solution A negative electrode and a laminate cell type lithium ion secondary battery were produced by performing the same operation as in Example 1 except that the battery was evaluated, and the performance of this battery was evaluated. The results are shown in Table 1.

(Example 6)
In the surface treatment of the active material, the same operation as in Example 1 was carried out except that 0.02 part of the phenolic antioxidant represented by the following chemical formula 3 was used as the mixed solution, and the negative electrode and laminate cell type A lithium ion secondary battery was manufactured and the performance of this battery was evaluated. The results are shown in Table 1.

(Example 7)
In the preparation of the slurry composition, instead of the dispersion of styrene-butadiene polymer particles having a solid content concentration of 40% and a glass transition temperature of −15 ° C., the solid content concentration is 40% and the glass transition temperature is 17 Except for using 2.5 parts of a styrene-butadiene polymer particle dispersion at ℃, the same operation as in Example 1 was performed to produce a negative electrode and a laminate cell type lithium ion secondary battery. The battery performance was evaluated. The results are shown in Table 1.

(Comparative Example 1)
The same operation as in Example 1 was performed except that 100 parts of artificial graphite having a mercury intrusion pore volume of 0.95 cm ³ / g was used as the active material “a” without performing surface treatment with an antioxidant. Then, a negative electrode and a laminate cell type lithium ion secondary battery were prepared, and the performance of the battery was evaluated. The results are shown in Table 1.

(Comparative Example 2)
Into a planetary mixer with a disper, 100 parts of artificial graphite and 0.02 part of an antioxidant of a diphenylamine derivative represented by the chemical formula 1 are added, and 100 parts of a carboxymethylcellulose aqueous solution is added thereto, and the solid content concentration is 53.5 with ion-exchanged water. % And then mixed at 25 ° C. for 60 minutes. Next, after adjusting to 44% of solid content concentration with ion-exchange water, it mixed for 15 minutes at 25 degreeC, and the slurry composition for negative electrodes was prepared. Except that the slurry composition was used as the negative electrode slurry composition, the same operation as in Example 1 was performed to produce a negative electrode and a laminate cell type lithium ion secondary battery. Evaluation was performed. The surface of the electrode plate obtained at this time was spotted. The results are shown in Table 1.

(Comparative Example 3)
The negative electrode obtained in Comparative Example 1 was dissolved in 50 parts of N-methylpyrrolidone in which 0.02 part of the antioxidant of the diphenylamine derivative represented by Chemical Formula 1 was dissolved in 100 parts of the active material amount in the electrode. The laminate cell type lithium ion secondary battery was manufactured by performing the same operation as in Example 1 except that the electrode plate obtained by immersing in 1 hour and then drying was used as the negative electrode. The performance of this battery was evaluated. The results are shown in Table 1.

From the results in Table 1, the following can be understood.
According to the present invention, as shown in Examples 1 to 7, by using an active material that has been surface-treated with an antioxidant in advance, it is excellent in peel strength, lithium acceptance characteristics, and gas generation during charging and discharging. A lithium ion secondary battery can be obtained. Further, among the examples, the content of the amine-based antioxidant is 0.01 to 0.2% by mass, and the mercury intrusion pore volume of the active material “a” used for the surface treatment is 0.4 cm ^3. Example 1 and Example 2 in which a binder having a glass transition temperature of 0 ° C. or lower is used in combination with peel strength, charge / discharge characteristics, and charge / discharge gas, in the range of / g to 1.5 cm ³ / g. Excellent in all of the amount generated.

  On the other hand, an active material that has not been surface-treated with an antioxidant in advance (Comparative Example 1), an active material that is not subjected to a surface treatment, and an antioxidant is prepared when preparing a slurry composition for an electrode. What was added (Comparative Example 2), and the surface treatment of the active material was not performed, and the electrode was impregnated with a polymer solution containing an antioxidant (Comparative Example 3) was peel strength, lithium receiving characteristics, charging / discharging At least one of the gas generation amounts is significantly inferior.

Claims (7)

Ri Na been surface-treated graphite material with an antioxidant,
The content of the antioxidant in the graphite material is 0.01 to 1% by mass,
Mercury intrusion pore ^volume, 0.1cm ^{3 /g~2.0cm} 3 / g non-aqueous electrolyte secondary battery electrode active material, including those of the graphite material was treated surface is. The active material for a nonaqueous electrolyte secondary battery electrode according to claim 1, wherein the graphite material is artificial graphite.   The active material for a nonaqueous electrolyte secondary battery electrode according to claim 1, wherein the antioxidant is an amine-based antioxidant or a phenol-based antioxidant.   The slurry composition for nonaqueous electrolyte secondary battery electrodes containing the active material for nonaqueous electrolyte secondary battery electrodes of Claim 1, a binder, and a solvent. The slurry composition for a nonaqueous electrolyte secondary battery electrode according to claim 4 , wherein the binder has a glass transition temperature of 25 ° C. or lower. A nonaqueous electrolyte secondary battery electrode obtained by applying and drying the slurry composition for a nonaqueous electrolyte secondary battery electrode according to claim 4 or 5 on a current collector. Comprising a positive electrode, a negative electrode, a separator and an electrolyte,
At least one of the positive electrode and the negative electrode is the electrode according to claim 6 ,
Non-aqueous electrolyte secondary battery.