JP2017069162A - Binder composition for nonaqueous electrolyte secondary battery, slurry composition for nonaqueous electrolyte secondary battery arranged by use thereof, nonaqueous electrolyte secondary battery negative electrode, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the battery characteristics of a nonaqueous electrolyte secondary battery without impairing the function as a binder, i.e. the property of binding an active material mutually and with a current collecting electrode, and the toughness as an electrode.SOLUTION: Provided are a binder composition for a nonaqueous electrolyte secondary battery and others. The binder composition for a nonaqueous electrolyte secondary battery comprises at least two kinds of neutralized salts of α-olefin-maleic copolymers obtained by copolymerization of an α-olefin and a maleic acid. The α-olefin-maleic copolymers forming the at least two kinds of copolymer neutralized salts are different in weight-average molecular weight.SELECTED DRAWING: None

Description

  The present invention relates to a binder composition for a non-aqueous electrolyte secondary battery, a slurry composition for a non-aqueous electrolyte secondary battery using the same, a negative electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

  In recent years, mobile terminals such as mobile phones, notebook computers, and pad-type information terminal devices have been widely used. Lithium ion secondary batteries are frequently used as secondary batteries used for the power sources of these portable terminals. Since portable terminals are required to have more comfortable portability, miniaturization, thinning, weight reduction, and high performance have rapidly progressed, and have come to be used in various places. This trend continues today, and batteries used in mobile terminals are further required to be smaller, thinner, lighter, and higher in performance.

A non-aqueous electrolyte battery such as a lithium ion secondary battery has a positive electrode and a negative electrode installed via a separator, and LiPF ₆ , LiBF ₄ LiTFSI (lithium (bistrifluoromethylsulfonylimide)), LiFSI (lithium (bisfluorosulfonylimide). )) And a lithium salt dissolved in an organic liquid such as ethylene carbonate in a container.

The negative electrode and the positive electrode are usually obtained by dissolving or dispersing a binder and a thickener in water and mixing an active material, a conductive aid (conductivity imparting agent) and the like with this, Hereinafter, it may be simply formed as a mixed layer by coating the current collector on the current collector and drying the water. More specifically, for example, for the negative electrode, a carbonaceous material capable of occluding and releasing lithium ions, which is an active material, and, if necessary, acetylene black, a conductive auxiliary agent, are secondary to a current collector such as copper. They are bound together by a binder for battery electrodes. On the other hand, for the positive electrode, LiCoO ₂ that is an active material and, if necessary, a conductive aid similar to that of the negative electrode are bound to a current collector such as aluminum using a secondary battery electrode binder. Is.

  Up to now, diene rubbers such as styrene-butadiene rubber and acrylics such as polyacrylic acid have been used as binders for aqueous media (for example, Patent Documents 1 and 2). Examples of the thickener include methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropoxycellulose, carboxymethylcellulose sodium salt (CMC-Na), sodium polyacrylate, etc. Among them, CMC-Na is often used. (For example, patent document 3).

  However, diene rubbers such as styrene-butadiene rubber have low adhesion to metal collectors such as copper, and there is a problem that the amount used cannot be reduced in order to increase the adhesion between the collector and the electrode material. . In addition, there is a problem that the capacity maintenance rate is low due to weakness against heat generated during charging and discharging. On the other hand, polyacrylic acid soda exhibits higher adhesion than styrene-butadiene rubber, but has a problem that the electrode is easily cracked because the electric resistance is high and the electrode becomes harder and less tough. Recently, demands for extending the usage time of mobile devices and shortening charging time have increased, and there is an urgent need to improve battery capacity (low resistance), life (cycle characteristics), and charging speed (rate characteristics). In particular, it is an obstacle.

  In the nonaqueous electrolyte battery, since the battery capacity is affected by the amount of the active material, it is effective to suppress the amount of the binder and the thickener in order to increase the active material in a limited space of the battery. Moreover, since the rate characteristics are also affected by the ease of electron movement, it is effective to suppress the amount of binder and thickener that are non-conductive and prevent electron movement. However, if the amount of the binder and the thickener is reduced, the binding property between the collector electrode and the electrode material and the active material in the electrode is lowered, and the durability (battery life) for long-term use is significantly reduced. However, the electrode becomes brittle. Thus, it has been difficult to improve battery characteristics such as battery capacity while maintaining the binding property between the collector electrode and the electrode material and maintaining the toughness as an electrode.

JP 2000-67917 A JP 2008-288214 A Japanese Patent Application Laid-Open No. 2014-13693

  The present invention has been made in view of the above-mentioned problems, and the battery characteristics in the nonaqueous electrolyte battery are obtained without impairing the function as the binder, that is, the binding property between the active materials and the collector electrode and the toughness as the electrode. The purpose is to improve.

  As a result of diligent research to solve the above problems, the present inventors have found that the above object can be achieved by using a binder composition for a nonaqueous electrolyte battery having the following constitution, and further studies are made based on this finding. The present invention was completed by overlapping.

  That is, the non-aqueous electrolyte battery binder composition according to one aspect of the present invention (hereinafter also simply referred to as a binder composition) is an α-olefin-maleic acid copolymer obtained by copolymerizing α-olefins and maleic acids. A non-aqueous electrolyte secondary battery binder composition comprising at least two neutralization salts of the above, wherein an α-olefin-maleic acid copolymer constituting the neutralization salt of the at least two or more copolymers is provided. , Which are different in weight average molecular weight.

  With such a configuration, it is considered that the battery characteristics can be improved without impairing the binding property between the active materials and the collector electrode and the toughness as the electrode.

  Further, the binder composition contains at least two neutralized salts of α-olefin-maleic acid copolymer obtained by copolymerizing α-olefins and maleic acids, and is a copolymer having the smallest weight average molecular weight. The weight average molecular weight of the α-olefin-maleic acid copolymer constituting the neutralized salt of the copolymer having the largest weight average molecular weight is the weight average molecular weight of the α-olefin-maleic acid copolymer constituting the neutralized salt It is preferable that it is the range of 0.005 or more and less than 1.0. Thereby, the above effect can be obtained more reliably.

  Moreover, the binder aqueous solution for non-aqueous electrolyte batteries which concerns on the other situation of this invention consists of the said binder composition and water, It is characterized by the above-mentioned.

  A slurry composition for a non-aqueous electrolyte battery according to still another aspect of the present invention includes the binder composition, an active material, and a solvent.

  A nonaqueous electrolyte battery negative electrode according to still another aspect of the present invention is characterized in that a current collector is bound with a mixed layer containing at least the binder composition for a nonaqueous electrolyte battery and an active material. And

  A nonaqueous electrolyte battery according to still another aspect of the present invention includes the above nonaqueous electrolyte battery negative electrode, a positive electrode, and an electrolytic solution.

  ADVANTAGE OF THE INVENTION According to this invention, the binder composition for electrodes in the nonaqueous electrolyte battery provided with binding property and toughness can be obtained, and also the improvement of the battery characteristic of a nonaqueous electrolyte battery can be implement | achieved using it. it can.

  Hereinafter, although embodiment of this invention is described in detail, this invention is not limited to these.

  The binder composition in the nonaqueous electrolyte battery of the present embodiment is a nonaqueous electrolyte secondary containing at least two or more neutralized salts of α-olefin-maleic acid copolymers obtained by copolymerizing α-olefins and maleic acids. A binder composition for a battery, wherein the α-olefin-maleic acid copolymer constituting the neutralized salt of at least two kinds of copolymers is different in weight average molecular weight.

  Further, the binder composition contains at least two neutralized salts of α-olefin-maleic acid copolymer obtained by copolymerizing α-olefins and maleic acids, and is a copolymer having the smallest weight average molecular weight. The weight average molecular weight of the α-olefin-maleic acid copolymer constituting the neutralized salt of the copolymer having the largest weight average molecular weight is the weight average molecular weight of the α-olefin-maleic acid copolymer constituting the neutralized salt It is preferable that it is the range of 0.005 or more and less than 1.0.

  In the present embodiment, an α-olefin-maleic acid copolymer obtained by copolymerizing an α-olefin and maleic acid is composed of a unit based on the α-olefin (A) and a unit based on the maleic acid (B). The components (A) and (B) preferably satisfy (A) / (B) = 1/1 to 1/3 (molar ratio). Moreover, it is preferable that it is an alternating copolymer or linear random copolymer whose weight average molecular weights are 10,000-500,000.

In this embodiment, the unit (A) based on α-olefins is represented by the general formula —CH ₂ CR ¹ R ² — (wherein R ¹ and R ² may be the same or different from each other, hydrogen Represents an alkyl group having 1 to 10 carbon atoms, an alkenyl group, an aryl group, or an ether group. The α-olefin used in the present embodiment is a linear or branched olefin having a carbon-carbon unsaturated double bond at the α-position. In particular, olefins having 2 to 12 carbon atoms, particularly 2 to 8 carbon atoms are preferred. Representative examples that may be used include ethylene, propylene, n-butylene, isobutylene, n-pentene, isoprene, 2-methyl-1-butene, 3-methyl-1-butene, n-hexene, 2-methyl- 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 2-ethyl-1-butene, 1,3-pentadiene, 1,3-hexadiene, 2,3-dimethylbutadiene, 2,5 -Those having an ethylenic double bond such as pentadiene, 1,4-hexadiene, 2,2,4-trimethyl-1-pentene, and aromatic α-olefins such as styrene, α-methylstyrene, 4-methylstyrene And vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, and butyl vinyl ether. Among these, ethylene, isobutylene, styrene, and methyl vinyl ether are particularly preferable from the viewpoints of availability, polysynthesis, and product stability. Here, the isobutylene includes a mixture containing isobutylene as a main component, for example, a BB fraction (C4 fraction). These olefins may be used alone or in combination of two or more.

  In the present embodiment, maleic anhydride, maleic acid, maleic acid monoester (for example, methyl maleate, ethyl maleate, propyl maleate, phenyl maleate, etc.), maleic acid, as the unit (B) based on maleic acids Maleic anhydride derivatives such as diesters (eg, dimethyl maleate, diethyl maleate, dipropyl maleate, diphenyl maleate, etc.), maleic imides or N-substituted derivatives thereof (eg maleic imide, N-methylmaleimide, N N-substituted alkylmaleimide such as ethylmaleimide, N-propylmaleimide, Nn-butylmaleimide, Nt-butylmaleimide, N-cyclohexylmaleimide, N-methylphenylmaleimide, N-ethyl Phenyl male N-substituted alkylphenylmaleimide such as N-substituted alkoxyphenylmaleimide such as N-methoxyphenylmaleimide and N-ethoxyphenylmaleimide), and further halides thereof (for example, N-chlorophenyl) Maleimide), citraconic anhydride, citraconic acid, citraconic acid monoester (eg, methyl citraconic acid, ethyl citraconic acid, propyl citraconic acid, phenyl citraconic acid, etc.), citraconic acid diester (eg, dimethyl citraconic acid, diethyl citraconic acid, citraconic acid) Citraconic anhydride derivatives such as dipropyl acid, diphenyl citraconic acid, etc., citraconic acid imide or N-substituted derivatives thereof (eg citraconic acid imide, 2-methyl-N-methylmaleimide, 2-methyl-N-ethylmaleic acid) N-substituted alkylmaleimides such as 2-methyl-N-propylmaleimide, 2-methyl-Nn-butylmaleimide, 2-methyl-Nt-butylmaleimide, 2-methyl-N-cyclohexylmaleimide 2-methyl-N-substituted alkylphenylmaleimide such as methyl-N-phenylmaleimide, 2-methyl-N-methylphenylmaleimide, 2-methyl-N-ethylphenylmaleimide, or 2-methyl-N- Methoxyphenylmaleimide, 2-methyl-N-substituted alkoxyphenylmaleimide such as 2-methyl-N-ethoxyphenylmaleimide), and further halides thereof (for example, 2-methyl-N-chlorophenylmaleimide) Is preferred. Among these, use of maleic anhydride is preferable from the viewpoint of availability, polymerization rate, and ease of molecular weight adjustment. These maleic acids may be used alone or in combination.

As for the content rate of each said structural unit in the copolymer of this embodiment, it is desirable for (A) / (B) to exist in the range of 1 / 1-1 / 3 by molar ratio. This is because the advantages of hydrophilicity, water solubility, and affinity for metals and ions as a high molecular weight substance that dissolves in water can be obtained. In particular, the molar ratio of (A) / (B) is desirably 1/1 or a value close thereto, in which case the unit based on α-olefin, that is, —CH ₂ CR ¹ R ² — A copolymer having a structure in which the units shown and units based on maleic acids are alternately repeated is obtained.

  The mixing ratio of α-olefins and maleic acids for obtaining the copolymer of the present embodiment varies depending on the composition of the target copolymer, but α- 1 to 3 times the number of moles of maleic acids. Use of olefin is effective for increasing the reaction rate of maleic acids.

  The method for producing the copolymer of the present embodiment is not particularly limited, and for example, the copolymer can be obtained by radical polymerization. In this case, the polymerization catalyst used is an azo catalyst such as azobisisobutyronitrile, 1,1-azobiscyclohexane-1-carbonitrile, or an organic peroxide catalyst such as benzoyl peroxide or dicumyl peroxide. preferable. The amount of the polymerization catalyst used is required to be in the range of 0.1 to 5 mol% with respect to maleic acids, but is preferably 0.5 to 3 mol%. As a method for adding the polymerization catalyst and the monomer, they may be added all at the beginning of the polymerization, but it is desirable to add them sequentially as the polymerization proceeds.

In the method for producing a copolymer of this embodiment, the molecular weight can be appropriately adjusted mainly depending on the monomer concentration, the amount of catalyst used, and the polymerization temperature. For example, as a substance for reducing the molecular weight, a metal salt of Group I, II or III of the periodic table, a hydroxide, a halide of a Group IV metal, a general formula N≡, HN =, H ₂ N— or H It is also possible to adjust the molecular weight of the copolymer by adding an amine represented by ₄ N-, a nitrogen compound such as ammonium acetate or urea, or a mercaptan during the polymerization or during the polymerization. The polymerization temperature is preferably 40 ° C to 150 ° C, more preferably 60 ° C to 120 ° C. If the polymerization temperature is too high, the resulting copolymer tends to be in a block form, and the polymerization pressure may be significantly increased. The polymerization time is usually preferably about 1 to 24 hours, more preferably 2 to 10 hours. The amount of the polymerization solvent used is preferably adjusted so that the concentration of the obtained copolymer is 5 to 40% by weight, more preferably 10 to 30% by weight.

  As described above, the copolymer of the present embodiment usually preferably has a weight average molecular weight of 1,000 to 500,000. A more preferred weight average molecular weight is 1,700-450,000. When the weight average molecular weight of the copolymer of this embodiment is less than 1,000, the crystallinity is high and the adhesive strength between particles may be low. On the other hand, when it exceeds 500,000, the solubility in water or a solvent becomes small, and it may precipitate easily.

  The weight average molecular weight of the copolymer of this embodiment can be measured by, for example, a light scattering method or a viscosity method. When the intrinsic viscosity ([η]) in dimethylformamide is measured using a viscosity method, the copolymer of this embodiment preferably has an intrinsic viscosity in the range of 0.05 to 1.5. The copolymer of the present embodiment is usually obtained in the form of a powder having a grain size of about 16 to 60 mesh.

  In this embodiment, the neutralized salt of a copolymer is a neutralized product in which active hydrogen of carbonyl acid generated from maleic acids reacts with a basic substance to form a salt. Is preferred. In the neutralized product of α-olefin-maleic acid copolymer used in the present embodiment, a basic substance containing a monovalent metal and / or ammonia as the basic substance from the viewpoint of binding properties as a binder. Is preferably used.

  The degree of neutralization is not particularly limited, but when used as a binder, considering the reactivity with the electrolytic solution, it is usually 0.3 to 1 mol of carboxylic acid produced from maleic acids. It is preferably in the range of 1 mol, and more preferably, a neutralized one in the range of 0.4 to 1 mol is used. With such a neutralization degree, it is possible to adjust the pH of the binder composition of the present embodiment to a predetermined range, and further, there is an advantage that the acidity is low and the electrolytic solution decomposition is suppressed.

  In this embodiment, the degree of neutralization can be determined by a method such as titration with a base, an infrared spectrum, or an NMR spectrum. To measure the neutralization point simply and accurately, titration with a base can be performed. preferable. The specific titration method is not particularly limited, but it can be dissolved in water with little impurities such as ion-exchanged water, and a basic substance such as lithium hydroxide, sodium hydroxide, potassium hydroxide, It can be carried out by neutralization. The indicator for the neutralization point is not particularly limited, but an indicator such as phenolphthalein whose pH is indicated by a base can be used.

  In the present embodiment, the amount of the basic substance containing monovalent metal and / or ammonia is not particularly limited and is appropriately selected depending on the purpose of use and the like, but usually in the maleic acid copolymer. The amount is preferably 0.1 to 2 mol per mol of maleic acid unit. If it is such usage-amount, it will be possible to adjust pH of the binder composition of this embodiment to the predetermined range. In addition, the usage-amount of the basic substance containing a monovalent metal becomes like this. Preferably, it is 0.6-2.0 mol per mol of maleic acid units in a maleic acid copolymer, More preferably, it is 0.7-2. When the amount is 0 mol, a water-soluble copolymer salt with little alkali residue can be obtained.

  The reaction of the α-olefin-maleic acid copolymer with the basic substance containing monovalent metal and / or ammonia can be carried out according to a conventional method, but is carried out in the presence of water, and the α-olefin-maleic acid is obtained. A method for obtaining a neutralized copolymer as an aqueous solution is simple and preferable.

  Examples of basic substances containing monovalent metals that can be used in the present embodiment include hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; alkali metals such as sodium carbonate and potassium carbonate. Carbonates of alkali metals such as sodium acetate and potassium acetate; phosphates of alkali metals such as trisodium phosphate, and the like. Among these, ammonia, lithium hydroxide, sodium hydroxide, and potassium hydroxide are preferable. In particular, it is preferable to use ammonia or lithium hydroxide as a binder for a lithium ion secondary battery. The basic substance containing monovalent metal and / or ammonia may be used alone or in combination of two or more. Moreover, if it is in the range which does not have a bad influence on battery performance, the basic substance containing alkali metal hydroxides, such as sodium hydroxide, is used together, and the neutralized product of alpha-olefin-maleic acid copolymer May be prepared.

  Next, in this embodiment, the ring-opening rate of the copolymer represents the hydrolysis rate of the maleic anhydride sites that polymerize with α-olefins when maleic anhydride is used as the maleic acid. In the copolymer of the present embodiment, a preferable ring opening rate is 60 to 100%, more preferably 70% to 100%, and still more preferably 80 to 100%. If the ring-opening rate is too low, the structural freedom of the copolymer becomes small and the stretchability becomes poor, so that the force for adhering the electrode material particles to be bonded may be small, which is not preferable. Furthermore, there is a possibility that problems such as low affinity for water and poor solubility may occur. The ring-opening rate can be determined, for example, by measuring the hydrogen at the α-position of maleic acid opened by 1H-NMR with reference to the hydrogen at the α-position of maleic anhydride. The ratio of the carbonyl group derived from the carbonyl group and the ring-opened maleic anhydride can also be determined by IR measurement.

  In this embodiment, when the maleic acid is maleic anhydride, the neutralized salt of the copolymer means that the active hydrogen of the carbonyl acid generated by the ring opening of maleic anhydride is a basic substance as described above. It forms a salt by forming a salt. The degree of neutralization in this case is not particularly limited. However, when used as a binder, in consideration of reactivity with the electrolytic solution, usually with respect to 1 mol of carbonyl acid generated by ring opening, A range of 0.5 to 1 mol is preferable, and a neutralized range of 0.6 to 1 mol is more preferable. Such a neutralization degree has the advantage of low acidity and suppression of electrolyte decomposition. The degree of neutralization of the copolymer when maleic anhydride is used can be measured by the same method as described above.

  The binder composition of the present embodiment includes at least two or more neutralized salts of α-olefin-maleic acid copolymer obtained by copolymerizing α-olefins and maleic acids as described above, and the at least two or more of them. The α-olefin-maleic acid copolymer constituting the neutralized salt of the copolymer is different in weight average molecular weight.

  With such a configuration, it is considered that the battery characteristics can be improved without impairing the binding property between the active materials and the collector electrode and the toughness as the electrode.

  Further, the binder composition contains at least two neutralized salts of α-olefin-maleic acid copolymer obtained by copolymerizing α-olefins and maleic acids, and is a copolymer having the smallest weight average molecular weight. The weight average molecular weight of the α-olefin-maleic acid copolymer constituting the neutralized salt of the copolymer having the largest weight average molecular weight is the weight average molecular weight of the α-olefin-maleic acid copolymer constituting the neutralized salt It is preferable that it is the range of 0.005 or more and less than 1.0. Thereby, the above effect can be obtained more reliably.

  In this embodiment, an α-olefin-maleic acid copolymer obtained by copolymerizing α-olefins and maleic acids having different weight average molecular weights constitutes the copolymer if the weight average molecular weights are different. The unit (A) based on the class and the unit (B) based on the maleic acid may be the same or different. Moreover, you may use what differs in a kind as a salt at the time of forming a neutralized material.

  In this embodiment, when at least two kinds of neutralized salts of α-olefin-maleic acid copolymer obtained by copolymerization of α-olefins and maleic acids are included, the amount of each added is not particularly limited, The α-olefins and maleic acid copolymers having different weight average molecular weights to be added are further added to 100 parts by weight of the main α-olefins and maleic acid copolymers (most amount) (solid content). It is preferable to add in the range of 1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight. Too much addition amount is not preferable because it decreases the adhesion to the collector electrode, and too little addition amount is not preferable because toughness cannot be imparted.

  In this embodiment, when three or more neutralized salts of α-olefin-maleic acid copolymer obtained by copolymerization of α-olefins and maleic acids are contained, neutralization of the copolymer having the smallest weight average molecular weight is performed. The weight average molecular weight of the α-olefin-maleic acid copolymer constituting the salt is 0 of the weight average molecular weight of the α-olefin-maleic acid copolymer constituting the neutralized salt of the copolymer having the largest weight average molecular weight. As long as it is in the range of 0.005 or more and less than 1.0, there is no problem even if a copolymer having another weight average molecular weight is contained in a range that does not affect the effects of the present invention.

  The binder composition of the present embodiment is usually used as a binder aqueous solution for a non-aqueous electrolyte battery comprising the above-described binder composition and water.

  In addition, the nonaqueous electrolyte battery binder composition of the present embodiment is usually a nonaqueous electrolyte battery slurry composition (hereinafter simply referred to as slurry), which further contains an active material and water in addition to the above-described binder composition. It is preferably used as a composition).

  Further, in the present embodiment, the nonaqueous electrolyte battery negative electrode is formed by binding a current collector to a mixed layer containing at least the binder composition for a nonaqueous electrolyte battery of the present embodiment and a negative electrode active material. . This negative electrode can be formed by applying the slurry composition for a non-aqueous electrolyte battery negative electrode to a current collector and then removing the solvent by a method such as drying. If necessary, a thickener, a conductive aid and the like can be added to the mixed layer.

  In the slurry composition for a non-aqueous electrolyte battery, the amount of the neutralized salt of the α-olefin-maleic acid copolymer used relative to 100 parts by weight of the active material is usually preferably 0.1 to 4 parts by weight. More preferably, it is 0.3-3 weight part, More preferably, it is 0.5-2 weight part. If the amount of copolymer is too small, the viscosity of the slurry for nonaqueous electrolyte batteries may be too low and the thickness of the mixed layer may be reduced. Conversely, if the amount of copolymer is too large, the discharge capacity may decrease. There is sex.

  On the other hand, the amount of the solvent in the slurry composition is usually preferably 40 to 150 parts by weight, more preferably 70 to 130 parts by weight with respect to 100 parts by weight of the active material.

  As the solvent in the negative electrode slurry composition of the present embodiment, in addition to the above water, for example, alcohols such as methanol, ethanol, propanol and 2-propanol, cyclic ethers such as tetrahydrofuran and 1,4-dioxane, N, Amides such as N-dimethylformamide and N, N-dimethylacetamide, cyclic amides such as N-methylpyrrolidone and N-ethylpyrrolidone, and sulfoxides such as dimethylsulfoxide can also be used. In these, use of water is preferable from a viewpoint of safety.

  Further, in addition to water as the solvent in the slurry composition of the present embodiment, the following organic solvent may be used in combination within a range of preferably 20% by weight or less of the entire solvent. As such an organic solvent, those having a boiling point of 100 ° C. or more and 300 ° C. or less at normal pressure are preferable, for example, hydrocarbons such as n-dodecane; alcohols such as 2-ethyl-1-hexanol and 1-nonanol. Esters such as γ-butyrolactone and methyl lactate; amides such as N-methylpyrrolidone, N, N-dimethylacetamide and dimethylformamide; organic dispersion media such as sulfoxides and sulfones such as dimethyl sulfoxide and sulfolane.

When the slurry composition of the present embodiment is used for a negative electrode, examples of the negative electrode active material (sometimes abbreviated as active material) added to the negative electrode slurry composition include amorphous carbon, graphite, natural graphite, Carbonaceous materials such as mesocarbon microbeads (MCMB) and pitch-based carbon fibers; conductive polymers such as polyacene; composite metal oxides represented by SiOx, SnOx, LiTiOx, other metal oxides, lithium metal, lithium Examples include lithium-based metals such as alloys; metal compounds such as TiS ₂ and LiTiS ₂ .

  In the present embodiment, a third component can be further added to the slurry composition as necessary. The thickener that can be added is not particularly limited, and various alcohols, in particular, polyvinyl alcohol and modified products thereof, polysaccharides such as celluloses and starches, and polyethers such as polyethylene glycol and polypropylene glycol. Can be used.

  The amount of the thickener used in the slurry composition as needed is preferably about 0.1 to 4 parts by weight, more preferably 0.3 to 3 parts by weight with respect to 100 parts of the negative electrode active material. More preferably, it is 0.5 to 2 parts by weight. If the amount of the thickener is excessively small, the viscosity of the slurry may be too low and the thickness of the mixed layer may be reduced. Conversely, if the amount of the thickener is excessively large, the discharge capacity may be decreased.

  Moreover, as a conductive support agent mix | blended with a slurry composition as needed, metal powder, a conductive polymer, acetylene black etc. are mentioned, for example. The amount of the conductive aid used is usually preferably 0.5 to 10 parts by weight, more preferably 1 to 7 parts by weight with respect to 100 parts by weight of the active material.

  The current collector used for the nonaqueous electrolyte battery negative electrode of the present embodiment is not particularly limited as long as it is made of a conductive material. For example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold Metal materials such as platinum can be used. One of these may be used alone, or two or more of these may be used in combination at any ratio.

  In particular, when copper is used as the negative electrode, the effect of the slurry for a nonaqueous electrolyte battery negative electrode of the present invention is most apparent. The shape of the current collector is not particularly limited, but usually a sheet shape having a thickness of about 0.001 to 0.5 mm is preferable.

  The method for applying the slurry to the current collector is not particularly limited. Examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a dipping method, and a brush coating method. The amount to be applied is not particularly limited, but the thickness of the mixed layer containing the active material, conductive additive, binder and thickener formed after removing the solvent or dispersion medium by a method such as drying is preferably 0.005 to 0.005. An amount of 5 mm, more preferably 0.01 to 2 mm is common.

  The method for drying a solvent such as water contained in the slurry composition is not particularly limited, and examples thereof include aeration drying with hot air, hot air, and low-humidity air; vacuum drying; drying with infrared rays, far infrared rays, electron beams, and the like. . The drying conditions may be adjusted so that the solvent can be removed as soon as possible while the active material layer is cracked due to stress concentration or the active material layer is in a speed range that does not peel from the current collector. Furthermore, in order to increase the density of the active material of the electrode, it is effective to press the current collector after drying. Examples of the pressing method include a die press and a roll press.

  Furthermore, the present invention also includes a nonaqueous electrolyte battery having the negative electrode. The nonaqueous electrolyte battery usually includes the negative electrode, the positive electrode, and an electrolytic solution.

In this embodiment, the positive electrode normally used for nonaqueous electrolyte batteries, such as a lithium ion secondary battery, is especially used for a positive electrode without a restriction | limiting. For example, as the positive electrode active material, TiS ₂ , TiS ₃ , amorphous MoS ₃ , Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O Transition metal oxides such as ₁₃ and lithium-containing composite metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiMn ₂ O ₄ are used. Further, the positive electrode active material is made of a conductive additive similar to that of the negative electrode, and a binder such as SBR, NBR, acrylic rubber, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinylidene fluoride, and the boiling point at 100 ° C. in water or the above normal pressure. The positive electrode slurry prepared by mixing in a solvent of 300 ° C. or lower can be applied to a positive electrode current collector such as aluminum and the solvent can be dried to obtain a positive electrode.

In the nonaqueous electrolyte battery of this embodiment, an electrolytic solution in which an electrolyte is dissolved in a solvent can be used. The electrolyte solution may be liquid or gel as long as it is used for a non-aqueous electrolyte battery such as a normal lithium ion secondary battery, and functions as a battery depending on the type of the negative electrode active material and the positive electrode active material. What is necessary is just to select suitably. Specific electrolytes, for example, also known lithium salt is any conventionally _{available, LiClO 4, LiBF 6, LiPF} 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10 _{, LiAlC l4, LiCl, LiBr,} LiB (C 2 H 5) 4, CF 3 SO 3 Li, CH 3 SO 3 Li, LiCF 3 SO 3, LiC 4 F 9 SO 3, Li (CF 3 SO 2) 2 N And lower aliphatic lithium carboxylates.

A solvent (electrolyte solvent) for dissolving such an electrolyte is not particularly limited. Specific examples include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, and diethyl carbonate; lactones such as γ-butyllactone; trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, and 2-ethoxyethane. Ethers such as tetrahydrofuran, 2-methyltetrahydrofuran; sulfoxides such as dimethyl sulfoxide; oxolanes such as 1,3-dioxolane, 4-methyl-1,3-dioxolane; nitrogen-containing compounds such as acetonitrile and nitromethane; formic acid Organic acid esters such as methyl, methyl acetate, ethyl acetate, butyl acetate, methyl propionate and ethyl propionate; inorganic acid esters such as triethyl phosphate, dimethyl carbonate and diethyl carbonate Terigres; diglymes; triglymes; sulfolanes; oxazolidinones such as 3-methyl-2-oxazolidinone; sultones such as 1,3-propane sultone, 1,4-butane sultone, naphtha sultone, and the like. Alternatively, two or more kinds can be mixed and used. When a gel electrolyte is used, a nitrile polymer, an acrylic polymer, a fluorine polymer, an alkylene oxide polymer, or the like can be added as a gelling agent.

  Although there is no limitation in particular as a method of manufacturing the nonaqueous electrolyte battery of this embodiment, For example, the following manufacturing method is illustrated. That is, the negative electrode and the positive electrode are overlapped with each other via a separator such as a polypropylene porous membrane, wound or folded according to the shape of the battery, put into a battery container, injected with an electrolyte, and sealed. The shape of the battery may be any known coin type, button type, sheet type, cylindrical type, square type, flat type, and the like.

  The nonaqueous electrolyte battery of this embodiment is a battery that achieves both improved adhesion and improved battery characteristics, and is useful for various applications. For example, the battery is very useful as a battery used in a portable terminal that is required to be small, thin, light, and have high performance.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

Example 1
<Binder composition for negative electrode>
A 10 w% aqueous solution of a water-soluble lithium-modified isobutene-maleic anhydride copolymer resin (weight average molecular weight 325,000, neutralization degree 0.5, ring opening rate 96%) was prepared as a binder composition for a negative electrode. Further, a 10 w% aqueous solution of water-soluble lithium-modified isobutene-maleic anhydride copolymer resin (weight average molecular weight 6,000, neutralization degree 1.0, ring opening rate 96%) having different molecular weight and neutralization degree was prepared. These 10 w% solutions were mixed so that the weight ratio of high molecular weight body: low molecular weight body = 100: 1.01.

<Preparation of slurry for negative electrode>
The slurry for the electrode is 6.452 parts by weight of a 10% by weight aqueous solution of the binder composition for the negative electrode as a solid content with respect to 100 parts by weight of natural graphite (DMGS, manufactured by BYD) as the negative electrode active material, and a conductive auxiliary agent (conductive As an imparting agent, Super-P (manufactured by Timcal Co., Ltd.) as a solid was added in an amount of 1.075 parts by weight, and kneaded using a planetary stirrer (ARE-250, manufactured by Sinky). In order to adjust the viscosity of the slurry, an electrode coating slurry was prepared by adding water at the time of kneading and kneading again. The composition ratio of the active material and the binder in the slurry is, as a solid content, graphite powder: conducting aid: binder composition = 100: 1.075: 6.452.

<Preparation of negative electrode for battery>
The obtained slurry was coated on a current collector copper foil (C1100H, manufactured by UACJ) using a bar coater (T101, manufactured by Matsuo Sangyo), and then heated at 80 ° C. for 30 minutes with a hot air dryer (manufactured by Yamato Scientific) After primary drying, rolling was performed using a roll press (made by Hosen). Then, after punching out as a battery electrode (φ14 mm), a coin battery electrode was produced by secondary drying under reduced pressure conditions at 120 ° C. for 3 hours.

<Electrode toughness test>
Evaluation of electrode toughness is based on JIS K5600-5-1 (General coating test method-Part 5: Mechanical properties of coating film-Section 1: Bending resistance (cylindrical mandrel method)) of type 1 test equipment. Used. The electrode cracks were confirmed visually, and the results of the minimum mandrel diameter at which no cracks occurred are shown in Table 1 below. In addition, toughness is so high that a mandrel diameter is small, and it is preferable to use it as an electrode as it is 5 mm or less.

<Measurement of peel strength of electrode>
The strength when the electrode was peeled off from the copper foil as the collecting electrode was measured. The peel strength was measured at 180 ° peel strength using a 50N load cell (manufactured by Imada Co., Ltd.). The slurry-coated surface of the battery-coated electrode obtained above and a stainless steel plate were bonded together using a double-sided tape (double-faced tape made by Nichiban), and the 180 ° peel strength (peel width 10 mm, peel rate 100 mm / min) was measured. did. The results are shown in Table 1 below.

<Production of battery>
The battery coating electrode obtained above was transferred to a glove box (Miwa Seisakusho) under an argon gas atmosphere. A metal lithium foil (thickness 0.2 mm, φ16 mm) was used for the positive electrode. In addition, a polypropylene system (Celgard # 2400, manufactured by Polypore) is used as a separator, and the electrolyte is ethylene carbonate (EC) of lithium hexafluorophosphate (LiPF ₆ ) and vinylene carbonate (EMC) to vinylene carbonate (EMC). VC) was added using a mixed solvent system (1M-LiPF ₆ , EC / EMC = 3/7 vol%, VC 2 wt%) to prepare a coin battery (2032 type).

<Evaluation method: charge / discharge characteristic test>
The produced coin battery was subjected to a charge / discharge test using a commercially available charge / discharge tester (TOSCAT3100, manufactured by Toyo System). The coin battery is placed in a constant temperature bath at 25 ° C., and charging is performed with a constant current of 0.1 C (about 0.5 mA / cm ² ) with respect to the amount of active material until the voltage reaches 0 V with respect to the lithium potential. On the other hand, constant voltage charging of 0 V was carried out until a current of 0.02 mA. The capacity at this time was defined as a charging capacity (mAh / g). Next, a constant current discharge of 0.1 C (about 0.5 mA / cm ² ) was performed up to 1.5 V with respect to the lithium potential, and the capacity at this time was defined as a discharge capacity (mAh / g). The difference between the initial discharge capacity and the charge capacity was taken as the irreversible capacity, and the percentage of the discharge capacity / charge capacity was taken as the charge / discharge efficiency. As the direct current resistance of the coin battery, a resistance value after being charged once (fully charged state) was adopted. The results are shown in Table 1 below.

(Example 2)
The resin used in Example 1 was mixed so that the weight ratio of high molecular weight body: low molecular weight body = 100: 4.16. A slurry for a nonaqueous electrolyte battery was produced in the same manner as in Example 1 above. Further, a coated negative electrode was prepared by the same method as in Example 1 to obtain a coin battery, and a charge / discharge characteristic test was performed. Moreover, the toughness test and peel strength measurement were performed using the coated electrode. The results are shown in Table 1 below.

(Example 3)
The resin used in Example 1 was mixed so that the weight ratio of high molecular weight body: low molecular weight body = 100: 8.69. A slurry for a nonaqueous electrolyte battery was produced in the same manner as in Example 1 above. Further, a coated negative electrode was prepared by the same method as in Example 1 to obtain a coin battery, and a charge / discharge characteristic test was performed. Moreover, the toughness test and peel strength measurement were performed using the coated electrode. The results are shown in Table 1 below.

Example 4
A 10 w% aqueous solution of a water-soluble lithium-modified isobutene-maleic anhydride copolymer resin (weight average molecular weight 325,000, neutralization degree 0.5, ring opening rate 96%) was prepared as a binder composition for a negative electrode. Further, a 10 w% aqueous solution of water-soluble lithium-modified isobutene-maleic anhydride copolymer resin (weight average molecular weight 170,000, neutralization degree 1.0, ring opening rate 96%) having different molecular weight and neutralization degree was prepared. These 10 w% solutions were mixed so that the weight ratio of high molecular weight body: low molecular weight body = 100: 4.16.

  A slurry for a nonaqueous electrolyte battery was produced in the same manner as in Example 1 above. Further, a coated negative electrode was prepared by the same method as in Example 1 to obtain a coin battery, and a charge / discharge characteristic test was performed. Moreover, the toughness test and peel strength measurement were performed using the coated electrode. The results are shown in Table 1 below.

(Example 5)
A 10 w% aqueous solution of a water-soluble lithium-modified isobutene-maleic anhydride copolymer resin (weight average molecular weight 325,000, neutralization degree 0.5, ring opening rate 96%) was prepared as a binder composition for a negative electrode. Further, a 10 w% aqueous solution of a water-soluble lithium-modified methyl vinyl ether-maleic anhydride copolymer resin (weight average molecular weight 63,000, neutralization degree 1.0, ring opening rate 96%) was prepared. These 10 w% solutions were mixed so that the weight ratio of high molecular weight body: low molecular weight body = 100: 4.16. A slurry for a nonaqueous electrolyte battery was produced in the same manner as in Example 1 above. Further, a coated negative electrode was prepared by the same method as in Example 1 to obtain a coin battery, and a charge / discharge characteristic test was performed. Moreover, the toughness test and peel strength measurement were performed using the coated electrode. The results are shown in Table 1 below.

(Example 6)
A 10 w% aqueous solution of a water-soluble lithium-modified isobutene-maleic anhydride copolymer resin (weight average molecular weight 325,000, neutralization degree 0.5, ring opening rate 96%) was prepared as a binder composition for a negative electrode. Further, a 10 w% aqueous solution of a water-soluble lithium-modified ethylene-maleic anhydride copolymer resin (weight average molecular weight 100,000, neutralization degree 1.0, ring opening rate 96%) was prepared. These 10 w% solutions were mixed so that the weight ratio of high molecular weight body: low molecular weight body = 100: 4.16. A slurry for a nonaqueous electrolyte battery was produced in the same manner as in Example 1 above. Further, a coated negative electrode was prepared by the same method as in Example 1 to obtain a coin battery, and a charge / discharge characteristic test was performed. Moreover, the toughness test and peel strength measurement were performed using the coated electrode. The results are shown in Table 1 below.

(Example 7)
A 10 w% aqueous solution of a water-soluble lithium-modified isobutene-maleic anhydride copolymer resin (weight average molecular weight 325,000, neutralization degree 0.5, ring opening rate 96%) was prepared as a binder composition for a negative electrode. Further, a 10 w% aqueous solution of a water-soluble lithium-modified styrene-maleic anhydride copolymer resin (weight average molecular weight 1,700, neutralization degree 1.0, ring opening rate 96%) was prepared. These 10 w% solutions were mixed so that the weight ratio of high molecular weight body: low molecular weight body = 100: 4.16. A slurry for a nonaqueous electrolyte battery was produced in the same manner as in Example 1 above. Further, a coated negative electrode was prepared by the same method as in Example 1 to obtain a coin battery, and a charge / discharge characteristic test was performed. Moreover, the toughness test and peel strength measurement were performed using the coated electrode. The results are shown in Table 1 below.

(Example 8)
A 10 w% aqueous solution of a water-soluble lithium-modified methyl vinyl ether-maleic anhydride copolymer resin (weight average molecular weight 63,000, neutralization degree 0.5, ring opening rate 96%) was prepared as a binder composition for a negative electrode. Further, a 10 w% aqueous solution of a water-soluble lithium-modified isobutene-maleic anhydride copolymer resin (weight average molecular weight 6,000, neutralization degree 1.0, ring opening rate 96%) was prepared. These 10 w% solutions were mixed so that the weight ratio of high molecular weight body: low molecular weight body = 100: 4.16. A slurry for a nonaqueous electrolyte battery was produced in the same manner as in Example 1 above. Further, a coated negative electrode was prepared by the same method as in Example 1 to obtain a coin battery, and a charge / discharge characteristic test was performed. Moreover, the toughness test and peel strength measurement were performed using the coated electrode. The results are shown in Table 1 below.

Example 9
A 10 w% aqueous solution of water-soluble lithium-modified ethylene-maleic anhydride copolymer (weight average molecular weight 100,000, neutralization degree 0.5, ring opening rate 96%) was prepared as a binder composition for a negative electrode. Further, a 10 w% aqueous solution of a water-soluble lithium-modified isobutene-maleic anhydride copolymer resin (weight average molecular weight 6,000, neutralization degree 1.0, ring opening rate 96%) was prepared. These 10 w% solutions were mixed so that the weight ratio of high molecular weight body: low molecular weight body = 100: 4.16. A slurry for a nonaqueous electrolyte battery was produced in the same manner as in Example 1 above. Further, a coated negative electrode was prepared by the same method as in Example 1 to obtain a coin battery, and a charge / discharge characteristic test was performed. Moreover, the toughness test and peel strength measurement were performed using the coated electrode. The results are shown in Table 1 below.

(Comparative Example 1)
A 10 w% aqueous solution of a water-soluble lithium-modified isobutene-maleic anhydride copolymer resin (weight average molecular weight 325,000, neutralization degree 0.5, ring opening rate 96%) was prepared as a binder composition for a negative electrode. A slurry for a nonaqueous electrolyte battery was produced in the same manner as in Example 1 above. Further, a coated negative electrode was prepared by the same method as in Example 1 to obtain a coin battery, and a charge / discharge characteristic test was performed. Moreover, the toughness test and peel strength measurement were performed using the coated electrode. The results are shown in Table 1 below.

(Comparative Example 2)
A 10 w% aqueous solution of a water-soluble lithium-modified methyl vinyl ether-maleic anhydride copolymer resin (weight average molecular weight 63,000, neutralization degree 0.5, ring opening rate 96%) was prepared as a binder composition for a negative electrode. A slurry for a nonaqueous electrolyte battery was produced in the same manner as in Example 1 above. Further, a coated negative electrode was prepared by the same method as in Example 1 to obtain a coin battery, and a charge / discharge characteristic test was performed. Moreover, the toughness test and peel strength measurement were performed using the coated electrode. The results are shown in Table 1 below.

(Comparative Example 3)
A 10 w% aqueous solution of a water-soluble lithium-modified ethylene-maleic anhydride copolymer resin (weight average molecular weight 100,000, neutralization degree 0.5, ring-opening ratio 96%) was prepared as a negative electrode binder composition. A slurry for a nonaqueous electrolyte battery was produced in the same manner as in Example 1 above. Further, a coated negative electrode was prepared by the same method as in Example 1 to obtain a coin battery, and a charge / discharge characteristic test was performed. Moreover, the toughness test and peel strength measurement were performed using the coated electrode. The results are shown in Table 1 below.

(Discussion)
In Examples 1 to 10 in which polyethers are contained in the negative electrode binder composition, the molecular weight distribution of the binder composition is obtained by mixing neutralized salts of α-olefin-maleic acid copolymers having different molecular weights. By spreading, the solubility of the polymer has been widened, so there are relatively many high-molecular weight polymers with low solubility that are excellent in adhesion when dried, and the peel strength of the electrode Increased flexibility. Furthermore, even when a low molecular weight copolymer was added, the direct current resistance equivalent to that of Comparative Examples 1 to 3 was exhibited, indicating that the resistance did not increase.

  In contrast, Comparative Examples 1 to 3 using a neutralized salt of one kind of α-olefin-maleic acid copolymer resulted in poor toughness and adhesiveness.

Claims (6)

A binder composition for a non-aqueous electrolyte secondary battery comprising at least two or more neutralized salts of an α-olefin-maleic acid copolymer obtained by copolymerizing α-olefins and maleic acids,
The binder composition for a non-aqueous electrolyte secondary battery, wherein the α-olefin-maleic acid copolymer constituting the neutralized salt of at least two kinds of copolymers is different in weight average molecular weight. .   α-olefin comprising at least two kinds of neutralized salts of α-olefin-maleic acid copolymer obtained by copolymerization of α-olefins and maleic acids, and constituting a neutralized salt of the copolymer having the smallest weight average molecular weight The weight average molecular weight of the olefin-maleic acid copolymer is 0.005 or more of the weight average molecular weight of the α-olefin-maleic acid copolymer constituting the neutralized salt of the copolymer having the largest weight average molecular weight. The binder composition for a nonaqueous electrolyte secondary battery according to claim 1, wherein the binder composition is in a range of less than   A binder aqueous solution for a non-aqueous electrolyte secondary battery, comprising the binder composition for a non-aqueous electrolyte secondary battery according to claim 1 or 2 and water.   A slurry composition for a nonaqueous electrolyte secondary battery negative electrode, comprising the binder composition for a nonaqueous electrolyte secondary battery according to claim 1 or 2, an active material, and water.   A nonaqueous electrolyte secondary battery negative electrode comprising a current collector bound with the binder composition for a nonaqueous electrolyte secondary battery according to claim 1 and a mixed layer containing at least a negative electrode active material.   A nonaqueous electrolyte secondary battery comprising the nonaqueous electrolyte secondary battery negative electrode according to claim 5, a positive electrode, and an electrolytic solution.