JP2001283857A - Binder composite, slurry for battery electrode, electrode, and lithium-ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder composition for manufacturing electrodes for obtaining a lithium secondary battery which has excellent charge/discharge characteristics even after high temperature storage. SOLUTION: The electrode for a lithium secondary battery is manufactured with a binder composition containing an organic liquid material, a polysaccharide soluble in the organic liquid material which is composed of D-glucose structural unit obtained by combining 1,4-bonding and 1,6-bonding, and other polymers soluble in the above organic liquid material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder composition used for manufacturing an electrode of a lithium secondary battery typified by a lithium ion secondary battery, a slurry for a battery electrode using the same, an electrode using the same, and lithium. Related to secondary batteries.

[0002]

2. Description of the Related Art In recent years, portable terminals such as notebook computers, portable telephones, and electronic organizers have rapidly become widespread, and it is required to improve portability by further reducing the size and weight. . These portable terminals use rechargeable batteries, and nickel cadmium batteries have conventionally been the mainstream. However, this battery is not suitable for miniaturization because of its low voltage, difficulty in improving the energy density, high self-discharge rate, etc.In addition, since it uses heavy metals such as nickel and cadmium, its specific gravity is heavy and its weight is also reduced. Not suitable. Accordingly, lithium ion secondary batteries using lithium as a light metal have been studied. Lithium ion secondary batteries have the advantages of high voltage, high energy density, and light weight, and have been actively studied in recent years.

[0003] By the way, these secondary batteries can theoretically be repeatedly used for charging and discharging forever, but in reality, the electric capacity due to charging and discharging eventually decreases due to internal deterioration. Such a phenomenon is a phenomenon widely observed in a nickel-hydrogen secondary battery, a lithium-ion secondary battery, a capacitor, and the like provided with an electrode manufactured using a current collector holding an active material. One of the causes is that the active material is separated from the current collector. In the case of a lithium ion secondary battery (hereinafter sometimes simply referred to as “battery”), metals such as aluminum, copper, iron, nickel, titanium, and stainless steel are usually used for a current collector used for a positive electrode and a negative electrode. ing. The electrode is manufactured by applying a slurry containing an active material, a binder and a liquid material to a current collector made of such a metal, and drying the applied material. Usually, this slurry is prepared by adding an active material to a binder composition containing a binder and a liquid material.

As a binder composition, an N-methylpyrrolidone solution of polyvinylidene fluoride has been widely used. However, due to the repetition of charge and discharge, the active material expands and contracts, so that the binding property decreases. It has been pointed out that poor conductivity results in a decrease in battery capacity, and a new binder composition has been demanded (JP-A-4-294060). Further, it has been proposed to use a water dispersion of a rubber-based polymer as a binder composition (JP-A-53-74242, etc.). When such an aqueous slurry of a rubber-based polymer is used as a binder, it has been proposed to use a cellulose-based compound in combination for the purpose of improving the charge / discharge cycle life and the battery capacity retention ratio (Japanese Patent Laid-Open No. 4-342966). .

However, such celluloses have poor electrolytic solution resistance, and a problem with current lithium ion secondary batteries that require stable charge / discharge characteristics even under high temperature conditions is that the battery capacity decreases at high temperatures. It was becoming. Also, the binder composition used for the lithium ion secondary battery is desirably a non-aqueous binder composition in view of the high reactivity of lithium with water. From such demands, non-aqueous binders exhibiting excellent battery characteristics have been demanded.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery having a particularly high discharge capacity and excellent charge / discharge cycle characteristics.

[0007]

Thus, according to the present invention, as a first invention, an organic liquid substance is combined with a 1,4-bond and a 1,4-bond.
A binder composition for a lithium secondary battery electrode, comprising a polysaccharide that is composed of D-glucose structural units bonded by a 6-bond and is soluble in the organic liquid substance, and another polymer that is soluble in the organic liquid substance Is provided.

Further, as a second invention, there is provided a slurry for an electrode of a lithium secondary battery obtained by mixing an active material with the binder composition according to the first invention; Applying the slurry of the invention to the current collector,
A dried lithium secondary battery electrode is provided; as a fourth invention, a lithium secondary battery provided with the electrode according to the third invention is provided as at least one of a positive electrode and a negative electrode.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a binder composition, a slurry, an electrode and a lithium secondary battery of the present invention will be sequentially described. (Binder composition) The binder composition for an electrode of a lithium secondary battery of the present invention comprises an organic liquid substance and a D-glucose structural unit bonded by 1,4-bond and 1,6-bond. A polysaccharide that dissolves in the liquid substance,
And other polymers soluble in the organic liquid substance. Further, a surfactant, a viscosity modifier and the like can be added as needed.

The polysaccharide used in the present invention is a polysaccharide in which D-glucose structural units are 1,4-linked and 1,6-linked, and such polysaccharides include starch, dextrin, pullulan and the like. No. Among them, starch and pullulan are preferred. Polysaccharides can be used alone or in combination of two or more. The starch is preferably a pregelatinized starch because of its good solubility in organic liquid substances, and more preferably a modified pregelatinized starch. The modification may be any type of chemical modification, but preferably, instead of a hydrogen atom bonded to a hydroxyl group in the molecule,
Etherified starch having an organic group such as a carboxyalkyl group or a hydroxyalkyl group bonded thereto; esterified starch obtained by a dehydration condensation reaction between a hydroxyl group in a molecule and an organic acid or an inorganic acid; a hydroxyl group in a molecule and an unsaturated bond Grafted starch obtained by a graft reaction with a low molecular compound having the following; a starch-type crosslinked starch in which etherified starch or esterified starch is crosslinked; and the like.

Examples of the etherified starch include carboxyalkyl etherified starch such as carboxymethylated starch and carboxyethylated starch (having an alkyl moiety having 1 to 1 carbon atoms).
2, preferably 1 to 6, more preferably 1 to 4); hydroxyalkyl etherified starch such as hydroxymethylated starch, hydroxyethylated starch, hydroxypropylated starch (the alkyl moiety has the same carbon number as described above); carboxy Cationized starch such as a metal salt of an alkyl etherified starch or a hydroxyalkylated starch (preferably an alkali metal salt or an alkaline earth metal salt);

Examples of the esterified starch include organic carboxylic esterified starch such as acetic esterified starch and propionated esterified starch; organic sulfonic acid esterified starch such as methylsulfonic esterified starch; and trimethylphosphoric esterified starch. Organic phosphorylated esterified starch. Examples of the grafted starch include a vinyl-grafted starch grafted with a vinyl ester compound such as vinyl acetate; and an unsaturated fatty acid-grafted starch grafted with an unsaturated fatty acid such as acrylic acid or methacrylic acid.

Examples of the crosslinked starch include distarch phosphate, glycerol distarch and the like. Pullulan
It is a polysaccharide in which three units of D-glucose are 1,4-linked to form one block and a plurality of such blocks are linked by 1,6-bonds.

A particularly preferred modified starch, a hydroxyalkyl etherified starch, has a glucose structural unit in the skeleton, wherein the structural unit has a β-1,4-bond and 1,6 bonds.
A polysaccharide having a structure in which a hydroxyalkyl group is bonded instead of a hydrogen atom bonded to at least a part of a hydroxyl group in the skeleton structure to form an etherified structure. These polysaccharides can be used alone or in combination of two or more.

[0015] These polysaccharides have a solution viscosity of 10 centipoise (hereinafter referred to as "measured using a BM viscometer" at 23 ° C when a 2% by weight solution of an organic liquid substance contained in a binder composition is prepared. , CP) or more, preferably from 20 cP to 10,000 cP, more preferably from 50 cP to 5,000 cP, the viscosity can be easily adjusted and excellent battery characteristics can be exhibited.

The organic liquid substance used in the binder composition of the present invention preferably has a boiling point at ordinary pressure of 80 ° C. or higher,
More preferably, the temperature is 100 ° C. or higher. When used as a bander composition for a battery in the production of an electrode, the boiling point is preferably 300 ° C. or lower because the organic liquid substance must be removed under conditions that do not deteriorate the current collector.
When an organic liquid substance having a low boiling point is used, it is difficult to apply the liquid to the current collector, or a phenomenon in which polysaccharides and polymers move and concentrate on the electrode surface during the organic liquid substance removal step occurs.
There is a tendency for the strength of the electrode to decrease or the binding force to decrease.

For the above-mentioned reasons, preferred specific examples of the organic liquid substance include aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene; aliphatic hydrocarbons such as heptane, octane, nonane and decane; cyclohexane; Cycloaliphatic hydrocarbons such as methylcyclohexane and ethylcyclohexane; methyl ethyl ketone;
Ketones such as methyl isobutyl ketone, cyclopentanone, cyclohexanone and cycloheptanone; linear and cyclic amides such as dimethylformamide and N-methylpyrrolidone; alcohols such as butyl alcohol, amyl alcohol and hexyl alcohol; methyl lactate , Ethyl lactate, butyl lactate, butyl acetate, esters such as methyl benzoate, etc .; When used as a battery binder composition, from the balance of solubility of polysaccharides and polymers, ease of handling, safety, ease of synthesis, etc., chain and cyclic amides, ketones, esters and Among the aromatic hydrocarbons, especially, the boiling point is 100 to 25.
Those at 0 ° C. are preferred.

(Polymer) The binder composition contains, in addition to the above-mentioned polysaccharides, other polymers soluble in the above-mentioned organic liquid substance (hereinafter sometimes simply referred to as “other polymers” or “polymers”). . Preferred polymers include diene-based polymers, olefin-based polymers, styrene-based polymers, acrylic and methacryl-based polymers, polyamide-based and polyimide-based polymers, ester-based polymers, fluorine-based polymers, cellulose-based compounds, and the like.

More specifically, poly-1,3-butadiene, polyisoprene, isoprene-isobutylene copolymer, natural rubber, styrene-1,3-butadiene copolymer, styrene-isoprene copolymer, 1,3-butadiene-isoprene-acrylonitrile Copolymer, styrene-1,3-butadiene-isoprene copolymer,
1,3-butadiene-acrylonitrile copolymer, styrene-acrylonitrile-1,3-butadiene-methyl methacrylate copolymer, styrene-acrylonitrile-1,3-butadiene-itaconic acid copolymer, styrene-acrylonitrile-1,3-butadiene-methacrylic acid Methyl-fumaric acid copolymer, styrene-1,3
-Butadiene-itaconic acid-methyl methacrylate-acrylonitrile copolymer, acrylonitrile-1,3-
Butadiene-methacrylic acid-methyl methacrylate copolymer, 1,3-butadiene-styrene-methyl methacrylate copolymer, styrene-1,3-butadiene-itaconic acid-methyl methacrylate-acrylonitrile copolymer, styrene-acrylonitrile-1,3-butadiene -Diene-based polymers such as methyl methacrylate-fumaric acid copolymer;

Ethylene-propylene copolymer, ethylene-propylene-diene copolymer, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene ionomer, polyvinyl alcohol,
Olefin polymers such as ethylene-vinyl alcohol copolymer, chlorinated polyethylene, and chlorosulfonated polyethylene; styrene-ethylene-butadiene copolymer, styrene-butadiene-propylene copolymer, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymer , Styrene-
Styrene polymers such as n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymer; polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer, 2-ethylhexyl acrylate-acrylic acid (Meth) acrylic polymers such as methyl-acrylic acid-methoxypolyethylene glycol monomethacrylate, polyacrylic acid, polymethacrylic acid, polyacrylamide, poly-N-isopropylacrylamide, poly-N, N-dimethylacrylamide;

Polyamide and polyimide polymers such as polyamide 6, polyamide 66, polyamide 11, polyamide 12, aromatic polyamide and polyimide; ester condensed polymers such as polyethylene terephthalate and polybutylene terephthalate; polyvinylidene fluoride, polytetrafluoro Ethylene, polyhexafluoropropylene, vinylidene fluoride-hexafluoropropylene (VDF-HFP) copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene (VDF-HFP-TFE) copolymer, vinylidene fluoride-pentafluoropropylene (VDF) -PFP) copolymer, vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene (VDF- FP-TFE) copolymer, vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene (VDF-PFMVE-TF
E) Copolymers and fluorine-based polymers such as vinylidene fluoride-chlorotrifluoroethylene (VDF-CTFE) copolymer. Further, polyvinylpyrrolidone, polyethyleneimine, polyoxyethylene, poly (2-methoxyethoxyethylene), poly (3
-Morphinyl ethylene), polyvinyl sulfonic acid and the like.

Further, polystyrene-polybutadiene block copolymer, styrene-butadiene-styrene.
Block copolymer, styrene-ethylene-butylene-
Block polymers such as styrene block copolymers, styrene-isoprene block copolymers, styrene-ethylene-propylene-styrene block copolymers are also used.

Among these rubbers, diene-based polymers such as homopolymers of conjugated diene-based monomers, copolymers of conjugated diene-based monomers and (meth) acrylate-based monomers, and copolymers of monomers copolymerizable therewith are particularly preferred. And homopolymers of (meth) acrylate monomers and fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene.

The method for preparing a binder composition by dissolving a polysaccharide and a polymer in an organic liquid substance is not particularly limited. The polysaccharide and the polymer may be simultaneously added to and dissolved in the organic liquid substance, or the other may be added to and dissolved in one of the organic liquid substance solutions of the polysaccharide and the polymer. Further, an organic liquid substance solution of a polysaccharide and an organic liquid substance solution of a polymer may be mixed. In this case, the organic liquid substances of both solutions may be the same or different. The binder composition of the present invention does not have to be in a solution state in which the constituent components are integrated before preparing the battery electrode slurry. That is, the organic liquid material solution of the polysaccharide and the organic liquid material solution of the polymer are separately prepared in advance, and when preparing the slurry for the battery electrode, both the solution and additives such as the active material and the conductive material are mixed. You may mix.

The weight ratio of the polysaccharide to the other polymer is from 1: 0.01 to 1: 100, preferably from 1: 0.05 to 1:70, more preferably from 1: 0.1 to 1: 100.
1:30. If the use ratio of the polysaccharide is too small, the surface of the coating film obtained by applying the slurry to the current collector or the electrode surface after the slurry is dried lacks smoothness, and the active material generally tends to peel off from the current collector. Further, the lithium secondary battery provided with this electrode cannot obtain the effect of improving the high-temperature charge / discharge cycle. Conversely, when the use ratio of the polysaccharide is large, the continuity of binding of the active material to the current collector is reduced, and the deterioration over time of the charge / discharge cycle characteristics of the battery is also increased.

The total concentration of the polysaccharide and the polymer in the binder composition of the present invention is usually 0.1 to 80% by weight, preferably 0.5 to 70% by weight, more preferably 1 to 60% by weight. . If the ratio is out of this range, the time required for the drying step becomes too long, or the coating property is reduced.

(Battery Electrode Slurry) The battery electrode slurry of the present invention contains the aforementioned binder composition and an active material. The slurry may be any as long as the active material is uniformly dispersed in the binder composition, and its preparation method is not particularly limited. Examples of the negative electrode active material include amorphous carbon, hard carbon, graphite, natural graphite, mesomorphic carbon microbeads (MCMB), carbonaceous materials such as pitch-based carbon fibers, conductive polymers such as polyacene, composite metal oxides, and others. And the like.

As the positive electrode active material, transition metal oxides such as Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MO ₃ , V ₂ O ₅ , V ₆ O ₁₃ , and LiCoO ₂ , LiNiO ₂ , LiMnO
₂ , LiMn ₂ O ₄ , and the like, and lithium-containing composite metal oxides and mixtures thereof. Further, organic compounds such as conductive polymers such as polyacetylene and poly-p-phenylene can be used.

Although the amount of the active material in the battery electrode slurry is not particularly limited, it is generally 1 to 1,000 times, preferably 5 to 1, times the weight of the sum of the weight of the polysaccharide and the polymer.
It is blended so as to be 000 times, more preferably 10 to 1,000 times, particularly preferably 12 to 500 times. If the amount of the active material is too small, the active material layer formed on the current collector has many inactive portions, and the function as an electrode may be insufficient. On the other hand, if the amount of the active material is too large, the active material is not sufficiently bound to the current collector and tends to fall off. Note that an organic liquid substance may be added to the slurry so that the slurry can be used at a concentration that can be easily applied to the current collector. In the slurry of the present invention,
If necessary, additives such as a surfactant and a viscosity modifier can be added.

(Electrode) In the electrode of the present invention, the above-mentioned slurry for a battery electrode is applied to a current collector, and the applied material is dried to remove an organic liquid substance and bind an active material to the surface of the current collector. It was made. The current collector is not particularly limited as long as the current collector is made of a conductive material. Usually, a current collector made of a metal such as iron, copper, or aluminum is used. The shape is not particularly limited, but usually a sheet having a thickness of about 0.01 to 0.5 mm is used.

The method for applying the battery electrode slurry to the current collector is not particularly limited. For example, it is applied by a blade method, a dipping method, a reverse roll method, a direct roll method, a knife method, or the like. Although the amount to be applied is not particularly limited,
The thickness of the active material layer formed after removing the organic liquid material is about 0.01 to 5 mm, preferably about 0.05 to 1 mm. The method of removing the organic liquid material is not particularly limited, but usually, stress concentration occurs, the active material layer is cracked, and the active material layer is separated from the current collector within a speed range where the organic material is removed as quickly as possible. The degree of pressure reduction and the degree of heating are adjusted so that the liquid substance is volatilized and removed.

(Lithium Secondary Battery) The lithium secondary battery of the present invention uses the above-mentioned electrode for at least one of a positive electrode and a negative electrode. As a lithium secondary battery,
Examples include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

The electrolyte for the lithium secondary battery is not particularly limited, and may be used in liquid or gel form. Depending on the types of the negative electrode active material and the positive electrode active material, a material exhibiting a function as a battery may be appropriately selected. For example, as the electrolyte,
LiClO ₄ , LiBF ₄ , CF ₃ SO ₃ Li, LiI, L
Examples of such electrolytes include iAlCl ₄ and LiPF _{6 which} are commonly used in lithium secondary batteries. Examples of the solvent for the electrolyte include ethers, ketones, lactones, nitriles,
Examples include amines, amides, sulfur compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds, phosphate compounds, and sulfolane compounds. Generally, carbonates such as ethylene carbonate and diethyl carbonate are preferred.

[0034]

Hereinafter, the present invention will be described with reference to examples.
The present invention is not limited by these examples. In the examples and comparative examples, the characteristics of the electrodes and the battery were evaluated by the following methods. (1) Bending resistance: The electrode was cut into a width of 3 cm and a length of 9 cm, and the center (4.5 cm) in the length direction was 1 m in diameter.
The state of the coating film in the bent portion when the stainless steel rod was bent at 180 ° with a stainless steel rod as a support was tested for ten electrode pieces. A case where no crack or peeling occurred in all 10 sheets is evaluated as ○, and a case where cracks or peeling occurred in one or more sheets in one or more places is evaluated as x.

(2) Peel strength: When the electrode is cut into a rectangle similar to the above (1), a tape (cellophane tape: Nichiban, specified in JIS Z1522) is affixed to the electrode, the electrode is fixed, and the tape is peeled off at once. Strength (g / c
m) is measured 10 times each, and the average value is determined. (3) High temperature initial discharge capacity: This is the discharge capacity at the third cycle measured at the time of high temperature charge / discharge cycle characteristics described later.

(4) High-temperature charge / discharge cycle characteristics: In a negative electrode test (Examples 1 to 3 and Comparative Examples 1 to 3) in a 60 ° C. atmosphere using a coin-type battery manufactured by the following method, In the positive electrode test (Examples 4 to 6 and Comparative Examples 4 to 6) from 0 V to 1.2 V as lithium, the negative electrode was changed from 3 V to 4.2 V as metallic lithium in three cycles by a 0.1 C constant current method. The discharge capacity at the eye (unit = mAh / g (per active material)) and the discharge capacity at the 50th cycle (unit = mAh / g (per active material)) are measured. The high-temperature charge / discharge cycle characteristics are values in which the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the third cycle is expressed in percentage. The larger the value is, the smaller the capacity decrease is, and the better the high temperature charge / discharge characteristics are.

A coin-type battery used for measuring the discharge capacity is manufactured as follows. That is, the positive electrode slurry is uniformly applied to an aluminum foil (thickness 20 μm) and the negative electrode slurry is evenly applied to a copper foil (thickness 18 μm) by a doctor blade method, dried at 120 ° C. for 15 minutes by a drier, and further dried under vacuum. after 2 hours drying under reduced pressure at 5 mmHg, 120 ° C. at the machine, the active material density by roll press biaxial compression such that the positive electrode 3.2 g / cm ^3, the anode 1.3 g / cm ^3. This electrode was cut out into a circle having a diameter of 15 mm, the active materials were opposed to each other with a separator made of a circular polypropylene porous membrane having a diameter of 18 mm and a thickness of 25 μm interposed therebetween, and the aluminum foil or metallic lithium of the positive electrode came into contact with the bottom of the outer container. Stainless steel coin-type outer container (diameter: 20 mm, height: 1.8), in which expanded metal is placed on copper foil or lithium metal of the negative electrode, and polypropylene packing is installed.
mm, stainless steel thickness 0.25 mm).
The electrolyte was injected into this container so that no air was left, and the thickness of the electrolyte was reduced to 0.
A 2 mm stainless steel cap is attached and fixed, the battery can is sealed, and a coin-type battery having a diameter of 20 mm and a thickness of about 2 mm is manufactured. The electrolytic solution was 1 mol / liter of LiPF ₆ propylene carbonate / ethylene carbonate / diethyl carbonate / dimethyl carbonate / methyl ethyl carbonate = 20/20/20/20/2.
A 0 (volume ratio at 20 ° C.) solution is used.

Example 1 A pre-gelatinized hydroxypropyl etherified starch was dissolved in N-methylpyrrolidone (hereinafter sometimes referred to as NMP) to obtain a solution having a solid content of 3% by weight. 2% by weight N of the pregelatinized hydroxypropyl etherified starch used here
The solution viscosity of the MP solution at 23 ° C. was measured with a BM type viscometer “RB-80L” (manufactured by Toki Sangyo Co., Ltd.) using rotor No. 2 was measured at 60 rpm, and 65c
P. A styrene-butadiene / radial block copolymer to be mixed into the binder composition together with the starch was produced as follows. After sufficiently replacing the stainless steel autoclave polymerization reactor equipped with a jacket and a stirrer with nitrogen, 6,000 parts by weight of cyclohexane, 450 parts by weight of styrene, 150 parts by weight of 1,3-butadiene, 0.14 parts by volume of tetramethylethylenediamine Was charged, and the contents were brought to 70 ° C. by passing warm water through a jacket. Next, 1.345 parts by weight of n-butyllithium was added to initiate polymerization. After the completion of the polymerization, 850 parts by weight of 1,3-butadiene was further added to continue the polymerization, and after the polymerization was almost completed, 0.52 parts by volume of silicon tetrachloride was added as a coupling agent, and the reaction was carried out for 30 minutes. Was. After the reaction, 1.5 parts by volume of methanol was added and stirred for 10 minutes,
The contents were taken out of the reactor, and after adding an antioxidant, the resulting block copolymer was separated by steam stripping and dried under reduced pressure. Thus, a radial block copolymer was obtained. The styrene-butadiene / radial block copolymer obtained as described above was dissolved in NMP, and NM having a polymer content of 13% by weight was dissolved.
A P solution was obtained.

A 3% by weight NMP solution of the pre-gelatinized hydroxypropyl etherified starch (1 part as solid content of polysaccharide) and a 13% by weight NMP solution of styrene / butadiene / radial block copolymer (2% as polymer solid content) Parts by weight) and 97 parts of MCMB (manufactured by Osaka Gas Chemical Company) were further added with NMP and stirred to prepare a slurry having a solid concentration of 51% by weight. Using the slurry obtained here, an electrode was obtained by the method described in the above-described method for manufacturing a coin-type battery. A lithium secondary electrode was manufactured using the obtained electrode as a negative electrode and lithium metal as a positive electrode. When the characteristics of the electrode and the lithium secondary battery were evaluated, the results are shown in Table 1.

Example 2 Pullulan was dissolved in N-methylpyrrolidone to obtain a solution having a solid content of 3% by weight. The solution viscosity at 23 ° C. of the 2 wt% NMP solution of pullulan used here was measured in Example 1.
It was 60 cP when measured by the same method as in the above. As the polymer, commercially available polyvinylidene fluoride (PVDF; KF # 110 manufactured by Kureha Chemical Industry Co., Ltd.)
0) was dissolved in NMP, and the polymer content was 11% by weight.
NMP solution was obtained. 3% by weight NM of pullulan obtained earlier
P solution (1 part by weight as polysaccharide solids), PVDF 1
NMP was further added to a 1% by weight NMP solution (3 parts by weight as a polymer solid content) and 96 parts by weight of MCMB (manufactured by Osaka Gas Chemical Co., Ltd.), followed by stirring to obtain a solid content of 51% by weight.
Was prepared. Using the slurry thus obtained, a negative electrode was obtained in the same manner as in Example 1, and a lithium secondary battery was manufactured. Table 1 shows the results of evaluating the characteristics of the lithium secondary battery.

Example 3 As a polymer, acrylonitrile-butadiene rubber (NBR; Nipol 104 manufactured by Zeon Corporation) was used.
2) was dissolved in NMP to obtain an NMP solution having a polymer content of 8% by weight. A negative electrode was obtained in the same manner as in Example 1 except that the above NBR was used instead of the styrene-butadiene / radial block copolymer used in Example 1, and a lithium secondary battery was manufactured. When the characteristics of the electrode and the lithium secondary battery were evaluated, the results are shown in Table 1.

Comparative Example 1 A negative electrode was obtained in the same manner as in Example 2 except that hydroxyethyl cellulose was used in place of the polysaccharide used in Example 2, and a lithium secondary battery was manufactured. When the characteristics of the electrode and the lithium secondary battery were evaluated, the results are shown in Table 1.

[0043]

[Table 1]

Example 4 The polysaccharide NMP solution obtained in Example 1 (0.5 parts as solids), the NMP solution of the block copolymer obtained in Example 1 (1.2 parts as solids), M as a substance
In place of CMB, 92 parts of lithium cobaltate and 6.3 parts of carbon black as a conductive agent were mixed, and NMP was further added so that the solid content became 71% by weight, and a uniform slurry was obtained with a stirrer. Was. An electrode was formed using the obtained slurry by the method described above. A lithium secondary battery was manufactured using the obtained electrode as a positive electrode and lithium metal as a negative electrode. When the characteristics of the electrode and the lithium secondary battery were evaluated, the results are shown in Table 2.

Example 5 A positive electrode was obtained in the same manner as in Example 4 except that the NMP solution of the polysaccharide and the polymer used in Example 2 was used, and a lithium secondary battery was manufactured. When the characteristics of the electrode and the lithium secondary battery were evaluated, the results are shown in Table 2.

Example 6 A positive electrode was obtained in the same manner as in Example 4 except that the NMP solution of the polysaccharide and the polymer used in Example 3 was used, and a lithium secondary battery was manufactured. When the characteristics of the electrode and the lithium secondary battery were evaluated, the results are shown in Table 2.

Comparative Example 2 A positive electrode was obtained in the same manner as in Example 5 except that hydroxyethyl cellulose was used instead of the polysaccharide used in Example 5, and a lithium secondary battery was manufactured. When the characteristics of the electrode and the lithium secondary battery were evaluated, the results are shown in Table 2.

[0048]

[Table 2]

From the above results, it can be seen that the organic liquid substance and 1,4
It was produced using a binder composition comprising a polysaccharide soluble in the organic liquid substance and a polymer soluble in the organic substance, comprising a D-glucose structural unit bonded by a-bond and a 1,6- bond. It was confirmed that the lithium secondary battery including the electrode maintained the charge / discharge cycle capacity even after storage at a high temperature. Comparative examples using celluloses as polysaccharides are inferior in bending resistance and peel strength. Such electrodes increase the incidence of defective batteries on the production line and hinder improvement in production efficiency.

[0050]

According to the present invention, a polysaccharide composed of D-glucose structural units linked by 1,4-bonds and 1,6-bonds and soluble in an organic liquid substance, and a polymer soluble in the organic liquid substance are contained. A lithium secondary battery including an electrode manufactured using the binder composition of the present invention is particularly excellent in maintaining a high charge / discharge cycle capacity even after storage at a high temperature.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hirohisa Yamamoto 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Japan Zeon Co., Ltd. F-term (reference) 5H029 AJ03 AJ05 AK02 AK03 AL06 AL07 AM03 AM04 AM05 AM07 CJ02 CJ08 CJ22 DJ08 EJ12 HJ02 5H050 AA07 AA08 BA17 CA07 CA08 CB07 DA09 EA21 GA02 GA10 GA22 HA02

Claims (6)

[Claims] 1. An organic liquid substance comprising 1,4-bond and 1,1,
A lithium secondary battery comprising a polysaccharide composed of D-glucose structural units bonded by a 6-bond and soluble in the organic liquid substance, and another polymer soluble in the organic liquid substance. An electrode binder composition. 2. The binder composition according to claim 1, wherein the polysaccharide is a modified starch and / or pullulan. 3. The binder composition according to claim 1, wherein the polysaccharide is hydroxypropyl etherified starch and / or pullulan. 4. A slurry for an electrode of a lithium secondary battery, comprising the binder composition according to claim 1 and an active material. 5. An electrode for a lithium secondary battery, wherein the slurry according to claim 4 is applied to a current collector and dried. 6. A lithium secondary battery comprising the electrode according to claim 5 as at least one of a positive electrode and a negative electrode.