JP2010009940A - Binder for secondary batter electrode, and electrode for secondary battery and nonaqueous electrolytic solution secondary battery using the binder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a binder for a secondary battery electrode superior in binding property, and capable of contributing to output improvement of a battery, an electrode for the secondary battery and a nonaqueous electrolytic solution secondary battery using the binder. <P>SOLUTION: The binder for the secondary battery electrode has a water soluble polymer neutralized salt, of a copolymer of methyl vinyl ether and maleic anhydride, as a main component. In the water soluble polymer neutralized salt, out of constituting metal ions, it is preferable that the content of lithium ions is 50 mol% or more and that the content of sodium ions is 3 mol% or more. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a secondary battery electrode binder, a secondary battery electrode using the binder, and a non-aqueous electrolyte secondary battery.

  With the spread of portable electronic devices such as portable personal computers and handy video cameras in recent years, non-aqueous electrolyte secondary batteries having high voltage and high energy density have been widely used as power sources. Also, from the viewpoint of environmental problems, battery cars and hybrid cars using electric power as a part of power have been put into practical use.

  Taking a lithium ion battery as an example, the secondary battery has a structure in which an electrode group produced via a separator is accommodated in a container together with an electrolyte between the positive electrode and the negative electrode. In this example, a layer formed by mutually bonding a metal oxide as an electrode active material and carbon as a conductive material with a binder is further bonded to a metal current collector such as aluminum. On the other hand, the negative electrode is obtained by further bonding a layer formed by mutually bonding crystalline carbon such as graphite as an electrode active material and carbon as a conductive material with a binder to a metal current collector such as copper. .

  By the way, in the process of creating a positive electrode layer and a negative electrode layer, conventionally, a method in which an electrode active material, a conductive material, and a binder are applied to a current collector as an organic solvent slurry has been frequently used. However, since an organic solvent has a large environmental load, recently, a method of applying an aqueous slurry that does not burden the environment to a current collector has become common. When preparing an aqueous slurry, a thickener such as carboxymethylcellulose sodium salt (CMC) is used to give the slurry an appropriate viscosity, and highly dispersed Teflon (registered trademark) is used as a binder. . The thickeners and binders used in these methods function as thickeners and binders and do not contribute to the improvement of battery performance by taking on other roles. Patent Document 1 proposes a binder for a secondary battery mainly composed of a water-soluble polymer neutralized salt of a copolymer of an α-olefin and maleic anhydride, but the α-olefin and maleic anhydride are proposed. The water-soluble polymer neutralized salt of this copolymer functions as a binder for secondary batteries, but does not contribute to the improvement of battery performance.

  Patent Document 2, Patent Document 3 and Patent Document 4 propose a non-aqueous electrolyte secondary battery (radical battery) using a radical compound such as a nitroxy radical as an electrode active material. Although the nonaqueous electrolyte secondary battery using the nitroxy radical compound has excellent characteristics in terms of output characteristics, the nitroxy radical compound is 4-methacryloyloxy-2,2,6,6- In the case of a high molecular weight polymer such as a polymer of tetramethylpiperidine-1-oxyl (PTMA), there is a problem that the affinity between the nitroxy radical compound and the binder is low and it is difficult to produce an electrode. That is, when an electrode layer was made to be thicker than a certain thickness when an electrode was made using a binder such as polyvinylidene fluoride or polytetrafluoroethylene, cracking occurred frequently when the electrode layer was dried. . Therefore, an electrode with a thick electrode layer and a large capacity could not be produced.

JP 2005-10061 A JP 2000-151084 A JP 2007-2111145 A JP 2007-213992 A

  An object of the present invention is to provide a high-performance secondary battery electrode binder that has excellent binding properties and can further contribute to an improvement in battery output, and a secondary battery electrode and a non-aqueous electrolyte solution using the binder. An object is to provide a secondary battery.

  As a result of intensive studies, the present inventors have found that a water-soluble polymer neutralized salt of a copolymer of methyl vinyl ether and maleic anhydride can be a binder for a secondary battery that meets the object of the present invention. .

That is, the present invention has been made based on the above findings, and provides a binder for a secondary battery electrode mainly composed of a water-soluble polymer neutralized salt of a copolymer of methyl vinyl ether and maleic anhydride. .
Moreover, this invention provides the electrode for secondary batteries containing the water-soluble polymer neutralization salt of the copolymer of methyl vinyl ether and maleic anhydride as a binder.
The present invention also provides a non-aqueous electrolyte secondary battery using the above electrode.

ADVANTAGE OF THE INVENTION According to this invention, the binder for high performance secondary battery electrodes which is excellent in binding property and can contribute to the output improvement of a battery can be provided. A non-aqueous electrolyte secondary battery using the binder is particularly excellent in low temperature characteristics.
The present inventors consider the reason why such an excellent effect can be obtained by using the water-soluble polymer neutralized salt of the copolymer of methyl vinyl ether and maleic anhydride proposed in the present invention as follows. ing.
The water-soluble polymer neutralized salt of a copolymer of methyl vinyl ether and maleic anhydride has a high affinity with water and can exist stably as a high-concentration aqueous solution. Moreover, the affinity with an electrode active material and a metal collector is high. For this purpose, a slurry of an electrode material containing the water-soluble polymer neutralized salt and the electrode active material is prepared in an aqueous solution system, and the slurry is applied onto a metal current collector and dried to increase the thickness. Even when the electrode layer is formed, the electrode layer is not cracked or peeled off. On the other hand, the water-soluble polymer neutralized salt of a copolymer of methyl vinyl ether and maleic anhydride contains a large amount of lithium ions as metal ions, and therefore, a non-aqueous electrolyte using the water-soluble polymer neutralized salt. In the secondary battery, the affinity between the electrode layer and the electrolytic solution can be improved. In addition, the presence of an ether group in the water-soluble polymer neutralized salt can play a role of improving the conductivity at low temperatures of alkali metal ions such as lithium ions, particularly in a non-aqueous electrolyte secondary battery. Low temperature characteristics can be improved.

The secondary battery electrode binder of the present invention, and the secondary battery electrode and non-aqueous electrolyte secondary battery using the binder will be described in detail below based on preferred embodiments.

First, the binder for secondary battery electrodes of the present invention will be described.

  The binder for a secondary battery electrode of the present invention contains a water-soluble polymer neutralized salt of a copolymer of methyl vinyl ether and maleic anhydride as a main component. In the present specification, “water-soluble” is used in the sense that it can be dispersed in water without turbidity and does not precipitate or settle even after long-term storage.

  The water-soluble polymer neutralized salt is synthesized by neutralizing a copolymer of methyl vinyl ether and maleic anhydride with an alkaline substance in water.

  The above copolymer is obtained by copolymerizing methyl vinyl ether and maleic anhydride in a known polymerization method, usually in a ratio of 1: 2 to 2: 1, preferably 1: 1.5 to 1.5: 1 (molar ratio). Is obtained. Moreover, the weight average molecular weight is 1000-3 million normally, Preferably it is 20,000-2 million. When the weight average molecular weight is less than 1000, sufficient binding performance as a binder cannot be obtained. On the other hand, when the weight average molecular weight exceeds 3 million, the viscosity of the aqueous solution becomes too large and the workability of electrode application tends to be inferior.

  Examples of the alkaline substance for neutralizing the copolymer include alkali metals such as lithium, sodium, potassium, rubidium and cesium, and hydroxides such as alkaline earth metals such as beryllium, magnesium, calcium, strontium and barium. Etc. are preferably used. These alkaline substances may be used alone or in combination of two or more kinds of alkaline substances.

  In the neutralization with the alkali substance, the ratio of hydrogen and metal ion in the carboxylic acid group and carboxylate group of the resulting water-soluble polymer neutralized salt is 1:99 to 99: 1 in molar ratio, preferably 5 : 95 to 50: 50. In particular, in the metal ions constituting the water-soluble polymer neutralized salt, the lithium ion content is preferably 50 mol% or more, more preferably 60 to 90 mol%. Furthermore, it is preferable that content of sodium ion is 3 mol% or more, and 5-30 mol% is more preferable.

The binder for secondary battery electrodes of the present invention described above usually takes the form of an aqueous solution of a water-soluble polymer neutralized salt of a copolymer of methyl vinyl ether and maleic anhydride. The solid content concentration and viscosity of the aqueous solution of the water-soluble copolymer neutralized salt are not particularly limited. However, in consideration of handling properties, the solid content concentration is usually about 5 to 20% by mass, and the viscosity is usually 25 ° C. It is set to about 50-1500 mPa · s. The pH of the aqueous solution of the water-soluble polymer neutralized salt is usually about 4 to 10 at 25 ° C.
Next, the secondary battery electrode of the present invention will be described.

  The electrode for a secondary battery of the present invention contains a water-soluble polymer neutralized salt of a copolymer of methyl vinyl ether and maleic anhydride as a binder.

  In the secondary battery electrode of the present invention, the water-soluble polymer neutralized salt may be used in combination with other binders. Examples of other binders include polytetrafluoroethylene, polyvinylidene fluoride, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and styrene butadiene rubber.

  The usage-amount of these binders is about 0.1-20 mass% normally in conversion of solid content with respect to an electrode active material, Preferably it is 0.5-10 mass%. If the amount is less than 0.1% by mass, the electrode layer may be cracked or peeled. If the amount exceeds 20% by mass, the capacity density of the secondary battery electrode tends to decrease. In addition, the usage-amount of another binder is preferably 100 mass% or less in conversion of solid content with respect to the binder for secondary battery electrodes of this invention among binders.

  A thickener may be used in the secondary battery electrode of the present invention. Examples of the thickener include carboxymethylcellulose sodium salt (CMC), polyacrylate, polyvinyl alcohol, methylcellulose, hydroxypropylmethylcellulose, polyethylene oxide and the like. The amount of the thickener used is preferably 0.1 to 5% by mass with respect to the electrode active material.

  When using the secondary battery electrode of the present invention as a positive electrode, the positive electrode active material, a binder and a conductive material slurryed with an organic solvent or water are applied to a current collector and dried to form a sheet. The one that was made.

If the lithium ion battery is taken as an example of the positive electrode active material, a known positive electrode active material capable of occluding and releasing lithium as an electrode reactant can be used. Specific examples of the positive electrode active material capable of inserting and extracting lithium include metal oxides such as TiO ₂ , V ₂ O ₅ and MnO ₂ , TiS ₂ , TiS ₃ , MoS ₃ , FeS _{2, and the} like. Examples thereof include metal sulfides, metal halides such as FeF ₃ , metal intercalation compounds, and metal compounds such as metal phosphate compounds. These positive electrode active materials may be materials in which transition metals such as Li, Mg, Al, Co, Ti, Nb, and Cr are added or substituted, respectively. Among these, composite oxides containing lithium and a transition metal element are preferable, and those containing at least one of Ni, Co, Mn, Ti, and Fe are particularly preferable as the transition metal element.

Such a composite oxide containing lithium and a transition metal element is typically represented by the following general formula (1):
Li _x M ^I O ₂ (1)
[M ^I in Formula (1) represents one or more kinds of transition metal elements, and the value of x is usually 0.05 ≦ x ≦ 1.10. The compound of formula (1) generally has a layered structure.

Specific examples of the composite oxide containing lithium and a transition metal element include, for example, lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), or lithium nickel cobalt composite oxide. (Li _x Ni _1-z Co _z O ₂ (z <1)), lithium nickel cobalt manganese composite oxide (Li _x Ni _1-vw Co _v Mn _w O ₂ (v + w <1)), etc. Composite oxides containing different additive elements based on lithium nickelate structure, and composites containing different additive elements based on lithium manganese composite oxide (LiMn ₂ O ₄ ) having a spinel structure or lithium manganese composite oxide structure An oxide etc. are mentioned. Further, as a phosphate compound containing lithium and a transition metal element, for example, a lithium iron phosphate compound (LiFePO ₄ ) having an olivine structure or a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (u <1 )) Etc., and compounds containing different additive elements based on lithium iron phosphate structure.

  As the positive electrode active material capable of inserting and extracting lithium, a polymer material may be used. Examples of the polymer material include a nitroxy radical group-containing high molecular weight polymer. Examples of the nitroxy radical group-containing high molecular weight polymer include, for example, piperidyl group-containing high molecular weight polymers and copolymers described in claim 1 of JP-A-2007-2111145. The compounds described in paragraphs [0015] to [0023], piperidyl group-containing high molecular weight polymers and copolymers described in claim 5 of JP-A-2007-213992, specifically the same publication And the compounds described in paragraphs [0028] to [0036].

  The metal compounds and polymer materials described above may be used alone, or may be used by mixing a plurality of metal compounds or by mixing a plurality of polymer materials. Further, a metal compound and a polymer material can be mixed and used.

The conductive material is not particularly limited as long as it can be mixed with an appropriate amount of the positive electrode active material to impart conductivity. For example, graphite fine particles, carbon black such as acetylene black and ketjen black, needle Examples thereof include amorphous carbon fine particles such as coke, and carbon materials such as carbon nanofibers. These may be used alone or in combination of two or more. In addition to the carbon material, a metal material, a conductive polymer material, or the like may be used as long as it is a conductive material. The usage-amount of the said electrically conductive material is about 5-60 mass% normally with respect to a positive electrode active material, Preferably it is 10-50 mass%.

  As the solvent for forming a slurry, an organic solvent or water that dissolves the binder is used. Examples of the organic solvent include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, and the like. It is not limited to this. The usage-amount of the said solvent is about 25-400 mass% normally with respect to a positive electrode active material, Preferably it is 50-200 mass%.

  As the positive electrode current collector, aluminum, stainless steel, nickel-plated steel or the like is usually used.

  When the secondary battery electrode of the present invention is used as a negative electrode, the negative electrode is usually coated with a negative electrode active material and a binder, and if necessary, a conductive material slurried with an organic solvent or water on a current collector. And then dried to form a sheet.

  Examples of the negative electrode active material include lithium, lithium alloys, inorganic compounds such as tin / silicon compounds, titanium oxides, carbonaceous materials, and conductive polymers. In particular, a carbonaceous material that can occlude and release highly safe lithium ions is preferable. Although this carbonaceous material is not particularly limited, natural carbon, artificial graphite, fullerene, graphite fiber chop, carbon nanotube, graphite whisker, highly oriented pyrolytic graphite, crystalline carbon such as quiche graphite, petroleum coke, coal -Based coke, petroleum-based pitch carbide, coal-based pitch carbide, phenolic resin / crystalline cellulose resin carbide, etc., and partially carbonized carbon materials, furnace black, acetylene black, pitch-based carbon fiber, PAN-based carbon Examples thereof include fibers.

Examples of the conductive material and the solvent to be slurried include the same materials as those for the positive electrode. Moreover, copper, nickel, stainless steel, nickel-plated steel, aluminum, etc. are normally used for the negative electrode current collector. The usage-amount of the said electrically conductive material is about 0-10 mass% normally with respect to a negative electrode active material, Preferably it is 0-5 mass%. Moreover, the usage-amount of the said solvent is about 50-200 mass% normally with respect to a negative electrode active material, Preferably it is 60-150 mass%.

Next, the nonaqueous electrolyte secondary battery of the present invention will be described.

  The nonaqueous electrolyte secondary battery of the present invention is configured in the same manner as a conventional nonaqueous electrolyte secondary battery except that the secondary battery electrode of the present invention is used as the positive electrode and / or the negative electrode.

  As the non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery of the present invention, organic solvents usually used in non-aqueous electrolytes can be used alone or in combination of two or more. Specifically, it contains at least one selected from the group consisting of cyclic carbonate compounds, cyclic ester compounds, sulfone or sulfoxide compounds, amide compounds, chain carbonate compounds, chain or cyclic ether compounds, and chain ester compounds. It is preferable. In particular, it is preferable to contain at least one cyclic carbonate compound and a chain carbonate compound, and by using this combination, not only the cycle characteristics are excellent, but also the viscosity of the electrolyte, the electric capacity / output of the obtained battery, etc. A non-aqueous electrolyte with a good balance can be provided.

  More specifically, the organic solvents are listed below. However, the organic solvent used in the present invention is not limited by the following examples.

  Since the cyclic carbonate compound, the cyclic ester compound, the sulfone or sulfoxide compound, and the amide compound have a high relative dielectric constant, they serve to increase the dielectric constant of the electrolytic solution. Specifically, examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, and isobutylene carbonate. Examples of the cyclic ester compound include γ-butyrolactone and γ-valerolactone. Examples of the sulfone or sulfoxide compound include sulfolane, sulfolene, tetramethylsulfolane, diphenyl sulfone, dimethyl sulfone, dimethyl sulfoxide, propane sultone, butylene sultone, and among these, sulfolanes are preferable. Examples of the amide compound include N-methylpyrrolidone, dimethylformamide, dimethylacetamide and the like.

  The chain carbonate compound, the chain or cyclic ether compound, and the chain ester compound can lower the viscosity of the non-aqueous electrolyte. Therefore, battery characteristics such as power density can be improved, such as the mobility of electrolyte ions can be increased. Moreover, since it is low-viscosity, the performance of the non-aqueous electrolyte at low temperatures can be increased. Specifically, as the chain carbonate compound, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl Examples thereof include carbonate and t-butyl-i-propyl carbonate. Examples of the linear or cyclic ether compounds include dimethoxyethane (DME), ethoxymethoxyethane, diethoxyethane, tetrahydrofuran, dioxolane, dioxane, 1,2-bis (methoxycarbonyloxy) ethane, 1,2-bis (ethoxycarbonyloxy). ) Ethane, 1,2-bis (ethoxycarbonyloxy) propane, ethylene glycol bis (trifluoroethyl) ether, i-propylene glycol (trifluoroethyl) ether, ethylene glycol bis (trifluoromethyl) ether, diethylene glycol bis (tri Fluoroethyl) ether and the like. Among these, dioxolanes are preferable. Examples of the chain ester compound include a carboxylic acid ester compound represented by the following general formula (1).

  In the general formula (1), n represents an integer of 1 to 4, and R represents an alkyl group having 1 to 4 carbon atoms (methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl). . Specific examples include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, sec-butyl acetate, butyl acetate, methyl propionate, and ethyl propionate. The carboxylic acid ester compound represented by the general formula (1) has a low freezing point, and when further added to an organic solvent, particularly an organic solvent containing at least one cyclic carbonate compound and at least one chain carbonate compound, even at a low temperature. It is preferable because battery characteristics can be improved. The addition amount of the carboxylic acid ester compound represented by the general formula (1) is preferably 1 to 50% by volume in the organic solvent.

  In addition, acetonitrile, propionitrile, nitromethane, and derivatives thereof can also be used.

  In order to impart flame retardancy, halogen-based, phosphorus-based, and other flame retardants can be appropriately added to the non-aqueous electrolyte. Examples of the phosphorus flame retardant include phosphate esters such as trimethyl phosphate and triethyl phosphate.

  5-100 mass% is preferable with respect to the organic solvent which comprises the said non-aqueous electrolyte, and, as for the addition amount of the said flame retardant, 10-50 mass% is especially preferable. If it is less than 5% by mass, sufficient flame retarding effect cannot be obtained.

As the electrolyte salt used in the non-aqueous electrolyte, a conventionally known electrolyte salt is used. For example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF _{3 SO 2) 3, LiB (} CF 3 CO 2) 4, LiSbF 6, LiSiF 5, LiAlF 4, LiSCN, LiClO 4, LiCl, LiF, LiBr, LiI, LiAlF 4, LiAlCl 4, NaClO 4, NaBF 4, NaI And derivatives thereof. Among these, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiB ( CF ₃ CO _{2) 4,} and LiCF ₃ derivatives of _{SO 3, LiN (CF 3 SO} 2) 2 derivative, and LiC (CF ₃ SO _{2) 3} To use at least one member selected from the group consisting of derivatives, because of excellent electrical characteristics preferred.

  The electrolyte salt can be dissolved in the organic solvent so that the concentration in the non-aqueous electrolyte is 0.1 to 3.0 mol / liter, particularly 0.5 to 2.0 mol / liter. preferable. If the concentration of the electrolyte salt is less than 0.1 mol / liter, a sufficient current density may not be obtained. If the concentration is more than 3.0 mol / liter, the stability of the nonaqueous electrolyte may be impaired. .

  In addition, various additives can be appropriately added to the non-aqueous electrolyte for the purpose of reducing the irreversible capacity at the negative electrode and suppressing the decomposition reaction of the electrolytic solution at the negative electrode. They are mainly added to form a coating (SEI) on the negative electrode surface, and unsaturated carbonates such as vinylene carbonate, vinyl ethylene carbonate, diallyl carbonate, allyl ethyl carbonate, allyl methyl carbonate, dipropargyl carbonate, etc. Esters, sulfur compounds such as propane sultone, butane sultone, sulfolene, unsaturated esters such as dimethyl maleate, diethyl maleate, dimethyl fumarate, diethyl fumarate, dimethyl acetylenedicarboxylate, diethyl acetylenedicarboxylate, fluoroethylene carbonate, Halogenated carbonates such as chloroethylene carbonate, 4-trifluoromethyl-ethylene carbonate, tetravinylsilane, methyltrivinylsilane, dimethyldivinyli Silane, diethyldivinylsilane, trimethylvinylsilane, tetraallylsilane, triallylmethylsilane, diallyldimethylsilane, diallyldiethylsilane, allyltrimethylsilane and other unsaturated silane compounds, hexamethyldisilane, 1,2-divinyltetramethyldisilane and other disilanes And the like.

  In addition, various additives can be appropriately added to the non-aqueous electrolyte for the purpose of suppressing the decomposition reaction of the electrolyte at the positive electrode. They mainly change the surface of the positive electrode to form a protective layer. 1,2-bis (fluorodimethylsilyl) ethane, 1,4-bis (fluorodimethylsilyl) -2-methylbutane, 1,6 -Bis (fluorodimethylsilyl) hexane, 1,4-bis (fluorodimethylsilyl) cyclohexane, fluoro-3-methoxypropyldimethylsilane, fluoro-3-ethoxypropyldimethylsilane, fluoro-3-propoxypropyldimethylsilane, fluorodimethyl Non-aromatic fluorosilane compounds such as vinylsilane, allylfluorodimethylsilane, crotylfluorodimethylsilane, 3-butenylfluorodimethylsilane, 1,1,3,3-tetramethyl-1,3-divinylsiloxane, 1,3-dimethyl-1,3-dipropy 1,3 unsaturated siloxane compounds of the divinyl siloxanes, and the like.

In the non-aqueous electrolyte secondary battery of the present invention, a separator is used between the positive electrode and the negative electrode. As the separator, a commonly used polymer microporous film can be used without any particular limitation. Examples of the film include polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyethylene oxide and polypropylene oxide. Films composed of ethers, various celluloses such as carboxymethylcellulose and hydroxypropylcellulose, polymer compounds mainly composed of poly (meth) acrylic acid and various esters thereof, derivatives thereof, copolymers and mixtures thereof. Etc. These films may be used alone, or may be used as a multilayer film by superimposing these films. Furthermore, various additives may be used for these films, and the type and content thereof are not particularly limited. Among these films, a film made of polyethylene, polypropylene, polyvinylidene fluoride, or polysulfone is preferably used for the nonaqueous electrolyte secondary battery of the present invention.
These films are microporous so that the electrolyte can penetrate and ions can easily pass therethrough. The microporosity method includes a phase separation method in which a polymer compound and a solvent solution are formed into a film while microphase separation is performed, and the solvent is extracted and removed to make it porous. The film is extruded and then heat-treated, the crystals are aligned in one direction, and a gap is formed between the crystals by stretching to make it porous, and so on.

  In the non-aqueous electrolyte secondary battery of the present invention, the electrode material, the non-aqueous electrolyte, and the separator have a phenol-based antioxidant, a phosphorus-based antioxidant, and a thioether-based antioxidant for the purpose of improving safety. A hindered amine compound or the like may be added.

  Examples of the phenol-based antioxidant include 1,6-hexamethylene bis [(3-tert-butyl-5-methyl-4-hydroxyphenyl) propionic acid amide], 4,4′-thiobis (6-tert. Tributyl-m-cresol), 4,4′-butylidenebis (6-tert-butyl-m-cresol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane 1,3,5-tris (2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate, 1,3,5-tris (3,5-ditert-butyl-4-hydroxybenzyl) ) Isocyanurate, 1,3,5-tris (3,5-ditert-butyl-4-hydroxybenzyl) -2,4,6-trimethylbenzene, tetrakis [3- (3,5-ditert-butyl- 4- Droxyphenyl) methyl propionate] methane, thiodiethylene glycol bis [(3,5-ditert-butyl-4-hydroxyphenyl) propionate], 1,6-hexamethylenebis [(3,5-ditert-butyl- 4-hydroxyphenyl) propionate], bis [3,3-bis (4-hydroxy-3-tert-butylphenyl) butyric acid] glycol ester, bis [2-tert-butyl-4-methyl-6- (2 -Hydroxy-3-tert-butyl-5-methylbenzyl) phenyl] terephthalate, 1,3,5-tris [(3,5-ditert-butyl-4-hydroxyphenyl) propionyloxyethyl] isocyanurate, 3, 9-bis [1,1-dimethyl-2-{(3-tert-butyl-4-hydroxy-5-methylphenyl) propiyl Nyloxy} ethyl] -2,4,8,10-tetraoxaspiro [5,5] undecane, triethylene glycol bis [(3-tert-butyl-4-hydroxy-5-methylphenyl) propionate] and the like. When adding to an electrode material, it is preferable to use 0.01-10 mass parts with respect to 100 mass parts of electrode materials, especially 0.05-5 mass parts.

Examples of the phosphorus antioxidant include trisnonylphenyl phosphite, tris [2-tert-butyl-4- (3-tert-butyl-4-hydroxy-5-methylphenylthio) -5-methylphenyl]. Phosphite, tridecyl phosphite, octyl diphenyl phosphite, di (decyl) monophenyl phosphite, di (tridecyl) pentaerythritol diphosphite, di (nonylphenyl) pentaerythritol diphosphite, bis (2,4-di Tert-butylphenyl) pentaerythritol diphosphite, bis (2,6-ditert-butyl-4-methylphenyl) pentaerythritol diphosphite, bis (2,4,6-tritert-butylphenyl) pentaerythritol diphosphite Phosphite, bis (2,4-dicumylphenyl) pen Erythritol diphosphite, tetra (tridecyl) isopropylidene diphenol diphosphite, tetra (tridecyl) -4,4′-n-butylidenebis (2-tert-butyl-5-methylphenol) diphosphite, hexa (tridecyl) -1 , 1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane triphosphite, tetrakis (2,4-ditert-butylphenyl) biphenylene diphosphonite, 9,10-dihydro-9 -Oxa-10-phosphaphenanthrene-10-oxide, 2,2'-methylenebis (4,6-tert-butylphenyl) -2-ethylhexyl phosphite, 2,2'-methylenebis (4,6- Tributylphenyl) -octadecyl phosphite, 2,2′-ethylidenebis (4,6- Tert-butylphenyl) fluorophosphite, tris (2-[(2,4,8,10-tetrakis tert-butyldibenzo [d, f] [1,3,2] dioxaphosphin-6-yl) Oxy] ethyl) amine, phosphite of 2-ethyl-2-butylpropylene glycol and 2,4,6-tritert-butylphenol, and the like.

  Examples of the thioether-based antioxidant include dialkylthiodipropionates such as dilauryl thiodipropionate, dimyristyl thiodipropionate, and distearyl thiodipropionate, and pentaerythritol tetra (β-alkylmercaptopropionate esters). Is mentioned.

  Examples of the hindered amine compound include 2,2,6,6-tetramethyl-4-piperidyl stearate, 1,2,2,6,6-pentamethyl-4-piperidyl stearate, 2,2,6,6. -Tetramethyl-4-piperidylbenzoate, bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, tetrakis (2,2,6,6-tetramethyl-4-piperidyl) -1,2, 3,4-butanetetracarboxylate, tetrakis (1,2,2,6,6-pentamethyl-4-piperidyl) -1,2,3,4-butanetetracarboxylate, bis (2,2,6,6) -Tetramethyl-4-piperidyl) -di (tridecyl) -1,2,3,4-butanetetracarboxylate, bis (1,2,2,6,6-pentamethyl-4-pi Lysyl) .di (tridecyl) -1,2,3,4-butanetetracarboxylate, bis (1,2,2,4,4-pentamethyl-4-piperidyl) -2-butyl-2- (3,5 -Di-tert-butyl-4-hydroxybenzyl) malonate, 1- (2-hydroxyethyl) -2,2,6,6-tetramethyl-4-piperidinol / diethyl succinate polycondensate, 1,6- Bis (2,2,6,6-tetramethyl-4-piperidylamino) hexane / 2,4-dichloro-6-morpholino-s-triazine polycondensate, 1,6-bis (2,2,6,6 -Tetramethyl-4-piperidylamino) hexane / 2,4-dichloro-6-tert-octylamino-s-triazine polycondensate, 1,5,8,12-tetrakis [2,4-bis (N-butyl) -N- (2,2,6, -Tetramethyl-4-piperidyl) amino) -s-triazin-6-yl] -1,5,8,12-tetraazadodecane, 1,5,8,12-tetrakis [2,4-bis (N- Butyl-N- (1,2,2,6,6-pentamethyl-4-piperidyl) amino) -s-triazin-6-yl] -1,5,8-12-tetraazadodecane, 1,6,11 -Tris [2,4-bis (N-butyl-N- (2,2,6,6-tetramethyl-4-piperidyl) amino) -s-triazin-6-yl] aminoundecane, 1,6,11 Hindered amine compounds such as tris [2,4-bis (N-butyl-N- (1,2,2,6,6-pentamethyl-4-piperidyl) amino) -s-triazin-6-yl] aminoundecane Can be mentioned.

  The shape of the non-aqueous electrolyte secondary battery of the present invention having the above configuration is not particularly limited, and can be various shapes such as a coin shape, a cylindrical shape, and a square shape. FIG. 1 shows an example of a coin-type battery of the nonaqueous electrolyte secondary battery of the present invention, and FIGS. 2 and 3 show examples of a cylindrical battery, respectively.

  In the coin-type nonaqueous electrolyte secondary battery 10 shown in FIG. 1, 1 is a positive electrode, 1a is a positive electrode current collector, 2 is a negative electrode made of a carbonaceous material capable of inserting and extracting lithium ions released from the positive electrode, 2a Is a negative electrode current collector, 3 is a non-aqueous electrolyte, 4 is a positive electrode case made of stainless steel, 5 is a negative electrode case made of stainless steel, 6 is a gasket made of polypropylene, and 7 is a separator made of polyethylene.

  2 and 3, 11 is a negative electrode, 12 is a negative electrode assembly, 13 is a positive electrode assembly, 13 is a positive electrode, 14 is a positive electrode current collector, 15 is a nonaqueous electrolyte solution, 16 Is a separator, 17 is a positive electrode terminal, 18 is a negative electrode terminal, 19 is a negative electrode plate, 20 is a negative electrode lead, 21 is a positive electrode plate, 22 is a positive electrode lead, 23 is a case, 24 is an insulating plate, 25 is a gasket, 26 is a safety valve, Reference numeral 27 denotes a PTC element.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples.

  In the following examples and comparative examples, lithium ion batteries (Examples 1 to 4 and Comparative Examples 1 to 5) and radical batteries (Examples 5 to 8 and Comparative Examples 6 to 10) are produced according to the following production procedure. It was.

Example 1
<Production procedure>
1. Preparation of aqueous solution of water-soluble polymer neutralized salt (VEMALi) of copolymer of methyl vinyl ether and maleic anhydride)
Using a magnetic stirrer in a beaker, 80.0 g of a methyl vinyl ether / maleic anhydride copolymer (VEMA) having a weight average molecular weight of 1,080,000, 38.7 g of lithium hydroxide monohydrate, and 562 g of ion-exchanged water. Stir. When a uniform aqueous solution was obtained, the solution was filtered through a glass filter to obtain an aqueous solution of a water-soluble polymer neutralized salt (VEMALi) of a copolymer of methyl vinyl ether and maleic anhydride. The ratio (molar ratio) of hydrogen and metal ion in the carboxylic acid group and carboxylate group of the obtained water-soluble polymer neutralized salt (VEMALi) was H / Li / Na = 1/9/0. Moreover, the obtained aqueous solution had a solid content concentration of 15% by mass, a pH of 8.1, and a viscosity of 466 mPa · s.

2. Production of positive electrode 85 parts by mass of LiNi _0.8 Co _0.17 Al _0.03 O ₂ as a positive electrode active material, 12 parts by mass of acetylene black as a conductive material, and 1 part by mass of carboxymethylcellulose sodium salt (CMC) as a thickener, 70 parts by mass of water Further, 14 parts by mass of a 15% by mass aqueous solution of a water-soluble polymer neutralized salt (VEMALi) of the above copolymer of methyl vinyl ether and maleic anhydride was added as a binder and dispersed to obtain a slurry. This slurry was applied to both sides of a positive electrode current collector made of aluminum, dried and press-molded to obtain a positive electrode plate. Then, this positive electrode plate was cut into a predetermined size, and a sheet-like positive electrode was produced by scraping off the electrode composite material at the portion to be a lead tab weld for extracting current.

3. Production of Negative Electrode 98 parts by mass of graphitic carbon powder as a negative electrode active material and 1 part by mass of carboxymethylcellulose sodium salt (CMC) as a thickener are dispersed in 94 parts by mass of water, and the above methyl vinyl ether and maleic anhydride as binders. 7 parts by mass of a 15% by mass aqueous solution of a water-soluble polymer neutralized salt (VEMALi) of the copolymer was added and dispersed to prepare a slurry. This slurry was applied to both sides of a copper negative electrode current collector, dried and press-molded to obtain a negative electrode plate. Then, this negative electrode plate was cut into a predetermined size, and a sheet-like negative electrode was produced by scraping off the electrode composite material at a portion to be a lead tab weld for extracting current.

4). Preparation of non-aqueous electrolyte LiPF ₆ was dissolved at a concentration of 1.0 mol / liter in a mixed solvent consisting of 25% by volume of ethylene carbonate, 5% by volume of diethyl carbonate, 40% by volume of ethyl methyl carbonate, and 30% by volume of dimethyl carbonate. Then, 0.40 part by weight of 1,2-bis (fluorodimethylsilyl) ethane, 0.40 part by weight of vinylene carbonate and 0.05 part by weight of dimethyldivinylsilane were added as additives to obtain a non-aqueous electrolyte.

5). Assembly of Cylindrical Lithium Ion Battery The obtained sheet-like positive electrode and sheet-like negative electrode were wound through a polyethylene microporous film having a thickness of 25 μm to form a wound electrode body. The obtained wound electrode body was inserted into the case and held in the case. At this time, the current collecting lead having one end welded to the lead tab weld portion of the sheet-like positive electrode or the sheet-like negative electrode was joined to the positive electrode terminal or the negative electrode terminal of the case, respectively. Thereafter, a non-aqueous electrolyte was poured into the case holding the wound electrode body, and the case was sealed and sealed to produce a cylindrical lithium ion battery having a diameter of 18 mm and an axial length of 65 mm.

Example 2
In the synthesis of a water-soluble polymer neutralized salt (VEMALi) of a copolymer of methyl vinyl ether and maleic anhydride, the ratio of hydrogen to metal ion in the carboxylic acid group and carboxylic acid group was determined as H / Li / Na = 2/8 /. A cylindrical lithium ion battery was produced in the same manner as in Example 1 except that the amount was adjusted to 0.

Example 3
In the synthesis of a water-soluble polymer neutralized salt (VEMALi) of a copolymer of methyl vinyl ether and maleic anhydride, the ratio of hydrogen to metal ion in the carboxylic acid group and carboxylate group was determined as H / Li / Na = 4/6 / A cylindrical lithium ion battery was produced in the same manner as in Example 1 except that the amount was adjusted to 0.

Example 4
In the synthesis of a water-soluble polymer neutralized salt (VEMALi) of a copolymer of methyl vinyl ether and maleic anhydride, the ratio of hydrogen to metal ion in the carboxylic acid group and carboxylic acid group was determined as H / Li / Na = 1/8 / A cylindrical lithium ion battery was produced in the same manner as in Example 1 except that the amount was adjusted to 1.

Comparative Example 1
Example 1 except that an aqueous dispersion of Teflon (PTFE) was used in place of the water-soluble polymer neutralized salt (VEMALi) of a copolymer of methyl vinyl ether and maleic anhydride in the production of the positive electrode. In the same manner, a cylindrical lithium ion battery was produced.

Comparative Example 2
In the production of the positive electrode, the same procedure as in Example 1 was performed except that an aqueous solution of polyacrylic acid (PAA) was used instead of the water-soluble polymer neutralized salt (VEMALi) of a copolymer of methyl vinyl ether and maleic anhydride. A cylindrical lithium ion battery was produced.

Comparative Example 3
In the production of the positive electrode, the same procedure as in Example 1 was performed except that an aqueous solution of lithium polyacrylate (PAALi) was used instead of the water-soluble polymer neutralized salt (VEMALi) of a copolymer of methyl vinyl ether and maleic anhydride. Thus, a cylindrical lithium ion battery was produced.

Comparative Example 4
In the production of the positive electrode, the same procedure as in Example 1 was performed except that an aqueous solution of sodium polyacrylate (PAANA) was used instead of the water-soluble polymer neutralized salt (VEMALi) of a copolymer of methyl vinyl ether and maleic anhydride. Thus, a cylindrical lithium ion battery was produced.

Comparative Example 5
In the production of the positive electrode, instead of the water-soluble polymer neutralized salt (VEMALi) of the copolymer of methyl vinyl ether and maleic anhydride, the water-soluble polymer neutralized salt (ISOBAMLi) of the copolymer of isobutylene and maleic anhydride is used. A cylindrical lithium ion battery was produced in the same manner as in Example 1 except that the aqueous solution was used.

  The cylindrical lithium ion batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 5 were subjected to an initial characteristic test and a cycle characteristic test. In the initial characteristic test, the discharge capacity ratio (%) and the low temperature discharge capacity ratio (%) were measured. In the cycle characteristic test, the discharge capacity retention rate (%) and the low temperature discharge capacity rate (%) after the cycle test were measured. In addition, each measuring method is as follows.

<Initial characteristic test>
1. Method of measuring discharge capacity ratio First, constant current and constant voltage charge to 4.1 V was performed at a charging current of 0.25 mA / cm ² (current value equivalent to 1/4 C), and a discharge current of 0.33 mA / cm ² (equivalent to 1/3 C). The constant current discharge was performed up to 3.0V. Then, constant current constant voltage to 4.1V at a charging current 1.1 mA / cm ² (current value of 1C equivalent) charged, up to 3.0V discharge current 1.1 mA / cm ² (current value of 1C equivalent) The operation of discharging with constant current was performed 4 times. Thereafter, 3.0 V at a charging current 1.1 mA / cm ² at (1C equivalent current value) to 4.1V charging constant current constant voltage, discharge current 0.33mA / cm ² (1 / 3C equivalent current value) The discharge capacity at this time was defined as the initial discharge capacity. From this initial discharge capacity, the discharge capacity ratio (%) was determined according to the following formula. The measurement was performed in an atmosphere at 20 ° C.
Discharge capacity ratio (%) = [(initial discharge capacity) / (initial discharge capacity in Example 1)] × 100

2. Measurement method of low temperature discharge capacity ratio The discharge capacity at -30 ° C was measured in the same manner as the measurement method of the discharge capacity ratio except that the measurement temperature was set to -30 ° C. From this discharge capacity at −30 ° C., the low-temperature discharge capacity ratio (%) was determined according to the following formula.
Low temperature discharge capacity ratio (%) = [(discharge capacity at −30 ° C.) / (Discharge capacity at −30 ° C. in Example 1)] × 100

<Cycle characteristic test>
1. Method for measuring discharge capacity maintenance rate Place a lithium ion battery in a thermostatic chamber at an atmospheric temperature of 60 ° C., and charge current 2.2 mA / cm ² (current value equivalent to ² C, 1 C is the current value at which the battery capacity is discharged in one hour. ) And a constant current charge up to 4.1 V and a constant current discharge up to 3 V at a discharge current of 2.2 mA / cm ² (current value corresponding to ² C) was repeated 500 times. Thereafter, the ambient temperature is returned to 20 ° C., and constant current and constant voltage charging is performed up to 4.1 V with a charging current of 1.1 mA / cm ² (current value corresponding to 1 C), and a discharge current of 0.33 mA / cm ² (1/3 C). The current was discharged at a constant current to 3.0 V, and the discharge capacity at this time was defined as the discharge capacity after the cycle. From the discharge capacity after this cycle and the initial discharge capacity, the discharge capacity retention rate (%) was determined according to the following formula.
Discharge capacity retention rate (%) = [(discharge capacity after cycle) / (initial discharge capacity)] × 100

2. Method for measuring low-temperature discharge capacity ratio In the above-described method for measuring discharge capacity retention ratio, the lithium ion battery after repeating the cycle 500 times was treated in the same manner as the method for measuring low-temperature discharge capacity ratio at −30 ° C. after the cycle. The discharge capacity was measured. From the discharge capacity at −30 ° C. after this cycle, the low-temperature discharge capacity ratio (%) after the cycle was determined according to the following formula.
Low temperature discharge capacity ratio (%) = [(discharge capacity at −30 ° C. after cycle) / (initial discharge capacity at −30 ° C. in Example 1)] × 100

Example 5
<Production procedure>
1. Preparation of Positive Electrode As a positive electrode active material, 97: 3 of 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TMA), which is a nitroxy radical group-containing high molecular weight polymer, and dodecyl dimethacrylate. A composition (PTMA / C) in which ketjen black was compounded at a mass ratio of 2: 1 to a copolymer (PTMA) of a mass ratio of 25 parts by mass of this nitroxy radical group-containing high molecular weight polymer carbon composite composition (PTMA / C) and a water-soluble polymer neutralized salt of a copolymer of methyl vinyl ether and maleic anhydride of Example 1 as a binder ( VEMALi) 8.3 parts by mass aqueous solution, carboxymethylcellulose sodium salt (CMC) 2% by mass aqueous solution 63 parts by mass, and 3.7 parts by mass water were mixed with a mixer to form a slurry. . This slurry was applied to one surface of an aluminum positive electrode current collector so that the thickness of the dried electrode material was 100 microns, dried, and then molded into a disk shape to obtain a positive electrode plate.

2. Production of Negative Electrode As a negative electrode active material, 85 parts by mass of Li ₄ Ti ₅ O _{12, 12} parts by mass of acetylene black as a conductive material, and 1 part by mass of carboxymethyl cellulose sodium salt (CMC) were dispersed in 70 parts by mass of water, Furthermore, 14 parts by mass of a 15% by mass aqueous solution of a water-soluble polymer neutralized salt of the copolymer of methyl vinyl ether and maleic anhydride of Example 1 was added and dispersed as a binder to prepare a slurry. This slurry was applied to both sides of a copper negative electrode current collector, dried and then formed into a disk shape to obtain a negative electrode plate.

3. Preparation of electrolyte solution LiPF ₆ was dissolved at a concentration of 1.2 mol / liter in a mixed solvent composed of 25% by volume of ethylene carbonate, 5% by volume of diethyl carbonate, 40% by volume of ethyl methyl carbonate, and 30% by volume of dimethyl carbonate. A non-aqueous electrolyte was used.

4). Assembly of coin-type radical battery The above positive electrode plate and negative electrode plate are overlapped with a microporous film made of polyethylene having a thickness of 25 μm sandwiched therebetween, set in a coin cell, and a predetermined amount of non-aqueous electrolyte is applied. After dropping, the coin type radical battery was produced by sealing with a caulking machine.

Example 6
In the synthesis of the water-soluble polymer neutralized salt (VEMALi) of the copolymer of methyl vinyl ether and maleic anhydride in Example 1, the ratio of hydrogen to metal ion in the carboxylic acid group and the carboxylate group was determined as H / Li / Na = A coin-type radical battery was prepared in the same manner as in Example 5 except that the water-soluble polymer neutralized salt (VEMALi) prepared by adjusting to 2/8/0 was used as a binder.

Example 7
In the synthesis of the water-soluble polymer neutralized salt (VEMALi) of the copolymer of methyl vinyl ether and maleic anhydride in Example 1, the ratio of hydrogen to metal ion in the carboxylic acid group and the carboxylate group was determined as H / Li / Na = A coin-type radical battery was produced in the same manner as in Example 5 except that a water-soluble polymer neutralized salt (VEMALi) prepared by adjusting to 4/6/0 was used as a binder.

Example 8
In the synthesis of the water-soluble polymer neutralized salt (VEMALi) of the copolymer of methyl vinyl ether and maleic anhydride in Example 1, the ratio of hydrogen to metal ion in the carboxylic acid group and the carboxylate group was determined as H / Li / Na = A coin-type radical battery was prepared in the same manner as in Example 5 except that a water-soluble polymer neutralized salt (VEMALi) prepared by adjusting to 1/8/1 was used as a binder.

Comparative Example 6
In preparation of the positive electrode of Example 5, when an aqueous dispersion of Teflon (registered trademark) (PTFE) was used instead of the water-soluble polymer neutralized salt (VEMALi) of a copolymer of methyl vinyl ether and maleic anhydride, Since the electrode layer cracked during drying, the battery could not be produced.

Comparative Example 7
Except for using an aqueous solution of polyacrylic acid (PAA) in place of the water-soluble polymer neutralized salt (VEMALi) of a copolymer of methyl vinyl ether and maleic anhydride in the production of the positive electrode, the same procedure as in Example 5 was performed. A coin-type radical battery was produced.

Comparative Example 8
Except for using an aqueous solution of lithium polyacrylate (PAALi) in place of the water-soluble polymer neutralized salt (VEMALi) of a copolymer of methyl vinyl ether and maleic anhydride in the production of the positive electrode, all the same as in Example 5. Thus, a coin-type radical battery was produced.

Comparative Example 9
In the production of the positive electrode, the same procedure as in Example 5 was conducted except that an aqueous solution of sodium polyacrylate (PAANA) was used instead of the water-soluble polymer neutralized salt (VEMALi) of a copolymer of methyl vinyl ether and maleic anhydride. Thus, a coin-type radical battery was produced.

Comparative Example 10
In the production of the positive electrode, instead of the water-soluble polymer neutralized salt (VEMALi) of the copolymer of methyl vinyl ether and maleic anhydride, the water-soluble polymer neutralized salt (ISOBAMLi) of the copolymer of isobutylene and maleic anhydride is used. A coin-type radical battery was produced in the same manner as in Example 5 except that an aqueous solution was used.

  The coin-type radical batteries obtained in Examples 5 to 8 and Comparative Examples 7 to 10 were subjected to an initial characteristic test and a cycle characteristic test. In the initial characteristic test, the discharge capacity expression rate (%) and output (%) were measured. In the cycle characteristic test, the discharge capacity retention rate (%) and the output (%) after the cycle test were measured. In addition, each measuring method is as follows.

<Initial characteristic test>
1. Method for measuring discharge capacity expression rate First, constant current and constant voltage charging to 2.5 V was performed at a charging current of 0.25 mA / cm ² (current value equivalent to ¼ C), and a discharging current of 0.33 mA / cm ² (1/3 C). A constant current discharge was performed up to 1.0 V at a corresponding current value). Next was charged a constant current constant voltage to 2.5V at a charging current 1.1 mA / cm ² (current value of 1C equivalent), up to 1.0V discharge current 1.1 mA / cm ² (current value of 1C equivalent) The operation of discharging with constant current was performed 4 times. Thereafter, 1.0 V at a charging current 1.1 mA / cm ² at (1C equivalent current value) to 2.5V charging constant current constant voltage, discharge current 0.33mA / cm ² (1 / 3C equivalent current value) The discharge capacity at this time was defined as the initial discharge capacity. The measurement was performed in an atmosphere at 20 ° C. Calculate the theoretical capacity per positive electrode active material (nitroxy radical group-containing high molecular weight polymer) used, and calculate the discharge capacity expression rate (%) from the numerical value and the measured initial discharge capacity according to the following formula. did.
Discharge capacity expression rate (%) = [(initial discharge capacity) / (theoretical capacity)] × 100

2. Measurement method charging current 1.1 mA / cm ² at (1C current value corresponding) to 2.5V charging constant current constant voltage output, the constant discharge current 22mA / cm ² (current value of 20C or equivalent) to 1.0V The current was discharged, and the discharge capacity at this time was used as the output value. From this output value and the theoretical capacity calculated by the method for measuring the discharge capacity expression rate, the output (%) was calculated according to the following formula. The measurement was performed in an atmosphere at 20 ° C.
Output (%) = [(Output value) / (Theoretical capacity)] × 100

<Cycle characteristic test method>
1. Method of measuring discharge capacity maintenance rate Place the radical battery in a thermostatic chamber with an ambient temperature of 35 ° C., and charge current 2.2 mA / cm ² (current value equivalent to ² C, 1 C is the current value that discharges the battery capacity in 1 hour) The cycle of charging at a constant current up to 2.5 V and discharging at a constant current of up to 1.0 V at a discharge current of 2.2 mA / cm ² (current value corresponding to 2C) was repeated 500 times. Thereafter, the ambient temperature is returned to 20 ° C., and the battery is charged with a constant current and a constant voltage up to 2.5 V with a charging current of 1.1 mA / cm ² (current value equivalent to 1 C), and a discharge current of 0.33 mA / cm ² (1/3 C A constant current was discharged to 1.0 V at a corresponding current value), and the discharge capacity at this time was defined as the discharge capacity after the cycle. From the discharge capacity after this cycle and the initial discharge capacity, the discharge capacity retention rate (%) was determined according to the following formula.
Discharge capacity retention rate (%) = [(discharge capacity after cycle) / (initial discharge capacity)] × 100

2. Output measurement method In the measurement method of the discharge capacity maintenance rate, the output value after the cycle was measured in the same manner as the output measurement method of the coin-type radical battery after the cycle was repeated 500 times. From the output value after this cycle and the theoretical capacity calculated by the method for measuring the discharge capacity expression rate, the output (%) after the cycle was determined according to the following formula.
Output (%) = [(Output value) / (Theoretical capacity)] × 100

  As is apparent from the results of Tables 1 and 2, the non-aqueous electrolyte secondary battery of the present invention using a water-soluble polymer neutralized salt of a copolymer of methyl vinyl ether and maleic anhydride as a binder has initial characteristics. In addition, in the cycle characteristics, it was confirmed that the discharge capacity retention rate was excellent, and in particular, the low temperature characteristics were excellent. On the other hand, in the non-aqueous electrolyte secondary battery using a binder different from the present invention, the low-temperature characteristics and the discharge capacity retention rate in the initial characteristics and cycle characteristics are non-aqueous electrolyte secondary batteries using the binder of the present invention. It was inferior to.

FIG. 1 is a longitudinal sectional view schematically showing an example of the structure of a coin-type battery of the nonaqueous electrolyte secondary battery of the present invention. FIG. 2 is a schematic diagram showing a basic configuration of a cylindrical battery of the nonaqueous electrolyte secondary battery of the present invention. FIG. 3 is a perspective view showing the internal structure of the cylindrical battery of the nonaqueous electrolyte secondary battery of the present invention as a cross section.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Positive electrode collector 2 Negative electrode 2a Negative electrode collector 3 Electrolyte 4 Positive electrode case 5 Negative electrode case 6 Gasket 7 Separator 10 Coin type nonaqueous electrolyte secondary battery 10 'Cylindrical type nonaqueous electrolyte secondary battery 11 Negative electrode 12 Negative electrode assembly 13 Positive electrode 14 Positive electrode assembly 15 Electrolyte 16 Separator 17 Positive electrode terminal 18 Negative electrode terminal 19 Negative electrode plate 20 Negative electrode lead 21 Positive electrode 22 Positive electrode lead 23 Case 24 Insulating plate 25 Gasket 26 Safety valve 27 PTC element

Claims (10)

  A binder for a secondary battery electrode comprising a water-soluble polymer neutralized salt of a copolymer of methyl vinyl ether and maleic anhydride as a main component.   The binder for secondary battery electrodes according to claim 1, wherein the metal ions constituting the neutralized salt have a lithium ion content of 50 mol% or more.   The binder for secondary battery electrodes according to claim 1, wherein the metal ions constituting the neutralized salt have a lithium ion content of 50 mol% or more and a sodium ion content of 3 mol% or more.   An electrode for a secondary battery comprising a water-soluble polymer neutralized salt of a copolymer of methyl vinyl ether and maleic anhydride as a binder.   The electrode for secondary batteries of Claim 4 which contains a nitroxy radical group containing high molecular weight polymer as an electrode active material.   The electrode for secondary batteries of Claim 4 which contains the metal oxide containing at least one of Ni, Co, Mn, Ti, and Fe as an electrode active material.   The electrode for secondary batteries which contains crystalline carbon as an electrode active material.   The secondary battery electrode according to any one of claims 4 to 7, wherein a metal ion constituting the neutralized salt has a lithium ion content of 50 mol% or more.   The secondary battery electrode according to any one of claims 4 to 7, wherein the metal ions constituting the neutralized salt have a lithium ion content of 50 mol% or more and a sodium ion of 3 mol% or more. .   A non-aqueous electrolyte secondary battery using the electrode according to claim 4.

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