JP2003132893A - Slurry composition for electrode, electrode, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slurry composition for an electrode whose swelling degree for electrolyte is low and contains a binder of good binding property as well as an electrode manufactured using the slurry composition, and to provide a lithium ion secondary battery of high battery capacity and good charge/ discharge cycle characteristics, with improved rate characteristic. SOLUTION: The slurry composition for the electrode contains a polymer (A), an active material and a liquid solvent which is capable of dissolving the polymer (A), where the polymer (A) comprises a recurring unit, with a content of 60-95 mol%, derived from acrylonitrile or methacrylonitrile, a 1-olefin of 2-4C, and a recurring unit, with a content of 5-30 mol%, derived from at least one of monomers selected from among compounds represented by the general formula (1).... (where R<1> is ...).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrode slurry composition, an electrode manufactured using the same, and a lithium ion secondary battery having the electrode.

[0002]

2. Description of the Related Art In recent years, notebook computers, mobile phones, P
The spread of mobile terminals such as DAs is remarkable. A lithium-ion secondary battery (hereinafter sometimes simply referred to as a battery) is often used for these power sources. Recently, there has been an increasing demand for extending the usage time of mobile terminals and shortening the charging time, and accordingly, there has been a strong demand for higher performance of batteries, in particular, higher capacity and improved charging speed (rate characteristics).

A lithium-ion secondary battery has a structure in which a positive electrode and a negative electrode are arranged with a separator interposed therebetween and is housed in a container together with an electrolytic solution. The electrodes (positive and negative) are
The active material and, if necessary, a conductivity-imparting agent are bound to a current collector such as aluminum or copper with a binder polymer for a secondary battery electrode (hereinafter may be simply referred to as a binder). An electrode is usually prepared by dissolving or dispersing a binder in a liquid medium, applying a slurry composition for a secondary battery electrode obtained by mixing the active material and the like to a current collector, and drying the liquid medium. It is formed by removing and binding as a mixed layer.

Battery capacity is strongly affected by the amount of active material charged. On the other hand, the rate characteristic is affected by the ease of movement of electrons, and increasing the amount of the conductivity-imparting agent such as carbon is effective for improving the rate characteristic. In order to increase the amount of the active material and the conductivity-imparting agent in the limited space of the battery, it is necessary to reduce the amount of binder. However, there is a problem that the binding property of the active material is impaired when the amount of the binder is reduced.
Further, the conventional battery has a problem that the cycle property is inferior, the battery capacity is reduced by repeated charging and discharging, and the rate property is deteriorated. It is considered that this is because the binder swells with the electrolytic solution, so that the binding property is gradually reduced and the active material is peeled from the current collector, or the binder covers the current collector and prevents the movement of electrons. . As described above, it has been difficult to achieve both high capacity and improved rate characteristics of the battery.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a slurry composition for electrodes containing a binder having a low degree of swelling with respect to an electrolytic solution and having good binding properties, and a slurry composition prepared using the slurry composition. To provide an electrode.
Another object of the present invention is to provide a lithium ion secondary battery that achieves high capacity and improved rate characteristics of the battery.

[0006]

DISCLOSURE OF THE INVENTION The present inventors have found that a binder composed of a copolymer having a specific composition having an acrylonitrile unit or a methacrylonitrile unit and a specific 1-olefin or (meth) acrylic acid ester unit is It was found that the degree of swelling in the electrolytic solution is low and the binding property is good. Furthermore, it was found that a lithium ion secondary battery produced by using an electrode slurry composition containing the polymer exhibits high battery capacity and good charge / discharge cycle characteristics and rate characteristics, and based on these findings, the present invention Has been completed.

Thus, according to the present invention, firstly, the content of repeating units derived from acrylonitrile or methacrylonitrile is 60 to 95 mol%, and 1 to 2 to 4 carbon atoms is used.
- Compound _{^{CH 2 = CR 1 -COOR 2 (}} 1) ( wherein represented by olefins and general formula (1), ^{R 1} is a hydrogen atom or a methyl group, ^{R 2} represents an alkyl group having 3 or less carbon atoms. A polymer (A) having a repeating unit content of 5 to 30 mol% derived from at least one monomer selected from (1), an active material, and a polymer (A).
There is provided a slurry composition for an electrode, which comprises a liquid medium which dissolves. This slurry composition preferably further contains a polymer (B) having a glass transition temperature of −80 to 0 ° C. and an N-methylpyrrolidone insoluble content of 50% by weight or more. Secondly, an electrode manufactured using the above slurry composition for electrodes is provided. Thirdly, a lithium ion secondary battery having the above electrode is provided.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The electrode slurry composition of the present invention comprises a repeating unit derived from acrylonitrile or methacrylonitrile, a 1-olefin having 2 to 4 carbon atoms, and a compound CH ₂ represented by the general formula (1). = CR ¹ -COOR ² (1) (In the formula, R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkyl group having 3 or less carbon atoms.) At least one monomer (hereinafter, A polymer (A) containing a repeating unit derived from a second monomer.
And an active material and a liquid medium.

The content of repeating units derived from acrylonitrile or methacrylonitrile in the polymer (A) is 60 to 95 mol%, preferably 65 to 90 mol% based on the total amount of the polymer (A). If the content of repeating units derived from acrylonitrile or methacrylonitrile is too small, the degree of swelling with respect to the electrolytic solution becomes large, resulting in poor binding durability and poor cycle characteristics. On the other hand, if the amount is too large, the binding property of the active material is poor.

The content of the repeating unit derived from the second monomer in the polymer (A) is 5 to 30 mol%, preferably 1
It is 0 to 25 mol%. When the content of the repeating unit derived from the second monomer is too small, the binding property of the active material is deteriorated, and it becomes difficult to uniformly apply the slurry composition to the current collector. On the contrary, even if it is excessively large, the binding property of the active material is rather deteriorated. Further, the degree of swelling in the electrolytic solution tends to increase.

The method for producing the polymer (A) is not particularly limited. For example, it can be obtained by copolymerizing acrylonitrile or methacrylonitrile and a second monomer by a known polymerization method such as an emulsion polymerization method, a suspension polymerization method, a dispersion polymerization method, a solution polymerization method or a bulk polymerization method. it can. As the 1-olefin having 2 to 4 carbon atoms used as the second monomer,
Examples thereof include ethylene, propylene, and 1-butene, and among them, ethylene is preferable. Examples of the compound represented by the general formula (1) include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate and isopropyl acrylate; methyl methacrylate, ethyl methacrylate, propyl methacrylate and methacrylic acid. Methacrylic acid alkyl esters such as isopropyl acid; and the like, of which methyl acrylate and methyl methacrylate are preferable.

Further, for example, a polymer obtained by using a conjugated diene such as butadiene as a part of a raw material monomer is hydrogenated to have a structure derived from the second monomer unit. Good. As the conjugated diene, 1,3-
Butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,
Examples include 3-pentadiene. These monomers capable of forming a structure derived from the second monomer unit may be used alone or in combination of two or more kinds.

The polymer (A) may contain units derived from other copolymerizable monomers as long as it is soluble in the liquid medium used in the slurry composition of the present invention.
Examples of the copolymerizable monomer include n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, hydroxypropyl acrylate, and the like. Acrylic esters such as lauryl acrylate; n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, hydroxypropyl methacrylate, lauryl methacrylate, etc. Methacrylic acid ester of

Methyl crotonate, ethyl crotonate, propyl crotonate, butyl crotonate, isobutyl crotonate, n-amyl crotonate, isoamyl crotonate, n-hexyl crotonate, 2-ethylhexyl crotonate, hydroxypropyl crotonate, etc. Crotonic acid esters; amino group-containing methacrylic acid esters such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; alkoxy group-containing methacrylic acid esters such as methoxy polyethylene glycol monomethacrylate; phosphoric acid residues and sulfonic acid residues in alkyl groups ,
Acrylic acid ester or methacrylic acid ester having a boric acid residue or the like; ethylenically unsaturated monocarboxylic acid such as acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid; maleic acid, fumaric acid, citraconic acid, mesaconic acid, glutaconic acid , Unsaturated dicarboxylic acids such as itaconic acid and acid anhydrides thereof. Two or more of these monomers may be used in combination, and the total content of these monomer units is 35 mol% or less, preferably 20 mol% or less.

In the electrode slurry composition of the present invention,
The polymer (A) can be used alone as a binder, but may be used in combination with another polymer. Above all, it is preferably used in combination with the polymer (B) having a glass transition temperature (Tg) of −80 to 0 ° C. and an N-methylpyrrolidone insoluble content of 50% by weight or more. The ratio of the amounts of polymer (A) and polymer (B) is not particularly limited, but the ratio of (amount of polymer (A)) :( amount of polymer (B)) is usually 1:
It is 10 to 10: 1, preferably 1: 5 to 5: 1, more preferably 1: 3 to 3: 1. By using the polymer (B) together, the balance between the binding property and the rate property can be further improved. Also, the flexibility of the electrode increases,
It is possible to prevent peeling of the active material.

The Tg of the polymer (B) is -80 to 0 ° C,
Preferably -60 to -5 ° C, more preferably -50 to-.
It is 10 ° C. If the Tg is too high, the flexibility of the electrode is reduced, and the active material is likely to peel from the current collector when charging and discharging are repeated. If Tg is too low, the battery capacity may decrease.

The polymer (B) is preferably one which is difficult to dissolve in the liquid medium or the electrolytic solution used in the electrode slurry composition. The insoluble content of the polymer (B) in N-methylpyrrolidone (NMP), which is a commonly used liquid medium, is 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more. If the NMP insoluble content is too small, the binding durability of the active material may decrease.

In order for the polymer (B) to exhibit the property of being hardly dissolved in a liquid medium or an electrolytic solution, it preferably has a crosslinked structure. The polymer having a crosslinked structure is, for example,
It can be obtained by using a polyfunctional ethylenically unsaturated monomer as a part of the raw material during the polymerization. The amount of the polyfunctional ethylenically unsaturated monomer used is preferably 0.3 to 5% by weight, more preferably 0.5 to 3% by weight, based on the total amount of the monomers used.

Examples of polyfunctional ethylenically unsaturated monomers are divinyl compounds such as divinylbenzene; dimethacrylic acid esters such as ethylene diglycol dimethacrylate, diethylene glycol dimethacrylate, and ethylene glycol dimethacrylate; trimethylolpropane tri. Trimethacrylates such as methacrylate; polyethylene glycol diacrylate, 1,
And diacrylic acid esters such as 3-butylene glycol diacrylate; triacrylic acid esters such as trimethylolpropane triacrylate.
When a polymer obtained by copolymerizing a conjugated diene compound such as butadiene or isoprene is used, a crosslinked polymer may be obtained by appropriately adjusting the polymerization reaction conditions such as the polymerization temperature, the polymerization conversion rate and the amount of the molecular weight modifier. it can.

The polymer (B) that can be preferably used is, for example, 2-ethylhexyl acrylate-methacrylic acid-methacrylonitrile-diethylene glycol dimethacrylate copolymer, butyl acrylate-acrylonitrile-diethylene glycol dimethacrylate copolymer. Examples thereof include acrylic rubbers such as coalesced butyl acrylate-acrylic acid-trimethylolpropane trimethacrylate copolymers, and rubbery polymers such as acrylonitrile-butadiene rubber, butadiene rubber, and methyl methacrylate-butadiene rubber. Among them, acrylic rubber and acrylonitrile-butadiene rubber are particularly preferable.

The method for producing the polymer (B) is not particularly limited. For example, each of the above-mentioned monomer components can be obtained by polymerization by a known polymerization method such as an emulsion polymerization method, a suspension polymerization method, a dispersion polymerization method or a solution polymerization method. Among them, the emulsion polymerization method is preferable because it has a good particle size and particle shape when dispersed in a liquid medium.

As a polymer other than the polymer (B), a polymer having a styrene unit such as an ethyl acrylate-styrene-diethylene glycol dimethacrylate copolymer or a 2-ethylhexyl acrylate-methacrylic acid-styrene copolymer; polyvinylidene fluoride Or a fluorine-containing polymer such as polytetrafluoroethylene; and the like may be used in combination with the polymer (A).

Active material used in the slurry composition of the present invention
The quality is appropriately selected depending on the type of battery or capacitor.
When used in a lithium-ion secondary battery, the active material is usually
If it is used in the lithium ion secondary battery of
Either can be used. As a positive electrode active material
For example, LiCoO_Two, LiNiO_Two, LiMn
O_Two, LiMn _TwoO_FourLithium-containing composite metal oxidation such as
Thing; TiS_Two, TiS_Three, Amorphous MoS _ThreeTransition money such as
Genus sulfide; Cu_TwoV_TwoO_Three, Amorphous V_TwoOP_TwoO₅,
MoO_Three, V_TwoO₅, V₆O_ThirteenTransition metal oxidation such as
Thing; is illustrated. Furthermore, polyacetylene, poly-p
-A conductive polymer such as phenylene can also be used.
It

Examples of the negative electrode active material include amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), carbonaceous materials such as pitch-based carbon fibers, and conductive polymers such as polyacene. . The shape and size of the active material are not particularly limited, and those having a conductivity-imparting agent attached to the surface by a mechanical modification method can also be used.

When used in an electrochemical capacitor, any active material may be used as long as it is used in a usual electrochemical capacitor. Examples of the active material for the positive electrode and the negative electrode include activated carbon.

The amount of the active material is not particularly limited, but it is preferably 20 to 1000 by weight based on the total amount of polymer.
Times, more preferably 30 to 500 times, particularly preferably 4 times.
It is blended so as to be 0 to 200 times. When the amount of the active material is excessively small, the active material layer formed on the current collector has many inactive portions, and the function as the electrode may be insufficient. Further, when the amount of the active material is excessively large, the active material is not sufficiently fixed to the current collector and is likely to fall off.

The liquid medium used for the electrode slurry composition of the present invention is not particularly limited as long as it dissolves the polymer (A), but when the polymer (B) is used in combination,
It is preferable that the polymer (B) is not dissolved. Specific examples thereof include amides such as N-methylpyrrolidone, N, N-dimethylacetamide, and dimethylformamide. Among them, N-methylpyrrolidone is particularly preferable because it has good coatability on the current collector and dispersibility of the polymer (B).

When the slurry composition of the present invention is used for the positive electrode of a lithium ion secondary battery, it is preferable to add a conductivity imparting agent. Examples of the conductivity imparting agent include acetylene black, Ketjen black, graphite, conductive polymers, and metal powders. The amount of the conductivity imparting agent used is usually 1 to 10 parts by weight, preferably 2 to 7 parts by weight, per 100 parts by weight of the positive electrode active material.

If necessary, a viscosity modifier, a fluidizing agent, etc. may be added to the above slurry composition.

The electrode slurry composition of the present invention is produced by mixing the above components. The mixing method and mixing order are not particularly limited. For example, it can be produced by adding the polymer (A), the active material and the conductivity-imparting agent to a dispersion liquid in which the polymer (B) is dispersed in a liquid medium, and mixing them with a mixer. As the mixer, a ball mill, a sand mill, a pigment disperser, a grinder, an ultrasonic disperser, a homogenizer, a planetary mixer, or the like can be used.

The electrode of the present invention is manufactured using the above slurry composition. As an electrode manufacturing method, for example, the above slurry composition is applied to a current collector such as a metal foil and dried to form the electrode. The active material is dispersed and fixed to the electrodes in a matrix formed on the surface of the current collector.

The current collector is not particularly limited as long as it is made of a conductive material, but usually metal such as iron, copper, aluminum, nickel and stainless is used. The shape is not particularly limited, but the thickness is 0.001 to 0.001.
A 0.5 mm sheet is preferable.

The method of applying the slurry composition to the current collector is not particularly limited. For example, it is applied by a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating or the like. The amount to be applied is not particularly limited, but the thickness of the mixed layer containing the active material formed after drying is usually 0.0
It is adjusted to be 05 to 5 mm, preferably 0.01 to 2 mm.

The drying method is not particularly limited, and for example, warm air,
Examples of the method include drying with hot air or low humidity air, vacuum drying, and drying with irradiation with (far) infrared rays or electron beams. The drying conditions are
Adjustment is made so that the liquid medium can be removed as soon as possible within a speed range where stress concentration causes cracks in the active material layer and the active material layer does not separate from the current collector. Furthermore, the electrode may be stabilized by pressing the current collector after drying. Examples of the pressing method include a die pressing method and a roll pressing method.

The lithium ion secondary battery of the present invention has the above electrode. The above electrode may be used for either one of the positive electrode and the negative electrode, or may be used for both, but it is particularly preferably used for the positive electrode. The lithium ion secondary battery includes an electrode and an electrolytic solution described later, and is manufactured according to a conventional method using components such as a separator as necessary.
As a specific example of the manufacturing method, first, a positive electrode and a negative electrode are stacked with a separator interposed therebetween, and the positive electrode and the negative electrode are wound according to the shape of the battery, folded, or the like, placed in a battery container, and an electrolytic solution is injected to use a sealing plate. Seal. Further, if necessary, an expanded metal, a fuse, an overcurrent preventing element such as a PTC element, a lead plate, etc. may be inserted to prevent a pressure increase in the battery and an overcharge / discharge. The shape of the battery may be any of coin type, button type, sheet type, cylindrical type, prismatic type, flat type and the like.

The electrolyte solution is used for lithium ion secondary batteries.
There is no particular limitation as long as it is a commonly used one, and the negative electrode active material
Functions as a battery depending on the quality and type of positive electrode active material
Just choose what you want to do. For example, dissolve the electrolyte in a solvent
Dissolved liquid electrolyte or poly swellable by solvent
Use a gel-type electrolytic solution with mer added as a gelling agent
be able to. As the electrolyte, for example, known lithium
You can use any of these salts, LiClO _Four, LiBF_Four,
LiPF₆, LiCF_ThreeSO_Three, LiCF_ThreeCO_Two, L
iAsF₆, LiSbF₆, LiB₁₀Cl₁₀, Li
AlCl_Four, LiCl, LiBr, LiB (C_TwoH₅)
_Four, CF_ThreeSO_ThreeLi, CH_ThreeSO_ThreeLi, LiCF_Three
SO_Three, LiC_FourF₉SO_Three, Li (CF_ThreeSO_Two)_Two
N, lower fatty acid carboxylate lithium, etc. may be mentioned.

The solvent for dissolving the electrolyte is not particularly limited as long as it is usually used, and carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate and methyl ethyl carbonate; γ- Lactones such as butyl lactone; ethers such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran;
Sulfoxides such as dimethyl sulfoxide; 1,3-
Oxolanes such as dioxolane, 4-methyl-1,3-dioxolane; nitrogen-containing compounds such as acetonitrile and nitromethane; methyl formate, methyl acetate, ethyl acetate,
Organic acid esters such as butyl acetate, methyl propionate and ethyl propionate; inorganic acid esters such as phosphoric acid triesters; diglymes; triglymes; sulfolanes; oxazolidinones such as 3-methyl-2-oxazolidinone; 1 , 3-Propane sultone, 1,4
-Sultones such as butane sultone, naphthal sultone;
Etc. can be used, and carbonates are preferable. These solvents may be used alone or as a mixed solvent of two or more kinds. When using a gel electrolyte, a gelling agent such as a nitrile polymer, an acrylic polymer, a fluorine polymer, an alkylene oxide polymer can be added.

[0038]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited thereto. The parts and% in the examples are based on weight unless otherwise specified. The tests and evaluations in Examples and Comparative Examples were carried out by the following methods. (1) Electrolytic solution solvent swelling degree The swelling degree of the polymer in the electrolytic solution solvent is 0.
Cast film 4 cm obtained by casting a liquid obtained by dissolving 2 g in 10 ml of N-methylpyrrolidone (NMP) on a sheet made of polytetrafluoroethylene and drying the sheet.
^After the weight of ² was measured, it was mixed with 5 kinds of solvents of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate in a volume ratio of 1: 1: 1: 1: 1 at a temperature of 60 ° C. Immerse at 72 hours, and pull up and wipe with towel paper to measure the weight immediately (weight after immersion) /
The value of (weight before immersion) was defined as the electrolytic solution solvent swelling degree.

(2) NMP insoluble content The NMP insoluble content of the polymer is 0.2 g of the polymer.
After soaking in 20 ml of P at room temperature for 24 hours,
The weight obtained by filtering with a mesh sieve and drying the components on the sieve is shown as a percentage with respect to the original polymer weight. (3) Glass transition temperature (Tg) The Tg of a polymer was measured with a differential scanning calorimeter (DSC) at a temperature of 10 ° C./min.

(4) Manufacture of Peel Strength Positive Electrode The positive electrode slurry was uniformly applied to an aluminum foil (thickness 20 μm) by a doctor blade method, and 120 ° C., 4
It was dried in a dryer for 5 minutes. 0.6 in a vacuum dryer
After drying under reduced pressure at 120 ° C. and kPa for 2 hours, the positive electrode was obtained by compressing with a biaxial roll press so that the electrode density was 3.3 g / cm ³ . Production of Negative Electrode The negative electrode slurry was uniformly applied to a copper foil (thickness 18 μm) by the doctor blade method, and dried under the same conditions as the positive electrode. The electrode density is 1.4 g /
A negative electrode was obtained by compressing to have a size of cm ³ . Peel strength measurement Electrode (positive electrode or negative electrode) is cut into a rectangle with a width of 3 cm and a length of 9 cm, and a tape (cellophane tape: manufactured by Nichiban Co., JIS Z 1522) is attached to the electrode surface, and the electrode is fixed, and the tape is fixed. The strength (N / cm) when peeled in the 180 ° direction at a speed of 50 mm / min was measured 10 times, and the average value thereof was obtained. The larger this value, the higher the binding strength,
It shows that the active material is not easily peeled off from the current collector.

(5) Production of battery capacity coin type battery (for positive electrode evaluation) In the positive electrode evaluation, metallic lithium was used as the negative electrode.
A positive electrode manufactured in the same manner as in (4) was cut out into a circle having a diameter of 15 mm, and a separator made of a circular polypropylene porous membrane having a diameter of 18 mm and a thickness of 25 μm was interposed,
It was arranged so that the metallic lithium of the negative electrode was in contact. A coin-type outer container made of stainless steel (diameter: 20 mm, height: 1. mm), in which expanded metal was placed on metallic lithium on the side opposite to the separator, and polypropylene packing was installed.
8 mm, stainless steel thickness 0.25 mm). The electrolyte was poured into this container so that no air remained, and a 0.2 mm-thick stainless steel cap was put on the outer container via a polypropylene packing to fix it, and the battery can was sealed to a diameter of A coin type battery (for positive electrode evaluation) having a thickness of 20 mm and a thickness of about 2 mm was manufactured. Electrolyte solution is ethylene carbonate / methyl ethyl carbonate = 1/2
(Volume ratio at 20 ° C.) A solution in which LiPF ₆ was dissolved in the mixed solution at a concentration of 1 mol / liter was used.

Manufacture of coin type battery (for negative electrode evaluation) In negative electrode evaluation, metallic lithium was used as the positive electrode.
The negative electrode manufactured in the same manner as in (4) was cut out into a circle with a diameter of 15 mm, and was placed so that the lithium metal of the positive electrode was in contact with it with a separator interposed. Expanded metal was put on metallic lithium on the side opposite to the separator and housed in a coin type outer container, and a coin type battery (for negative electrode evaluation) was manufactured in the same manner as the battery for positive electrode evaluation in the subsequent steps. The separator and the coin type outer container were also of the same type as those used for positive electrode evaluation. Measurement of Battery Capacity Using the coin-type battery manufactured by the above method, the positive electrode was evaluated at 3 V to 4.2 V, and the negative electrode was evaluated at 0 V to 1.2 V at a predetermined temperature of 0.1 C. The battery capacity was obtained as the discharge capacity at the third cycle (initial discharge capacity) measured by the current method. Unit is mAh / g
(Per active material).

(6) Charging / discharging cycle characteristics Similarly to the measurement of the initial discharging capacity, the third cycle and the fifth cycle
The discharge capacity at the 0th cycle was measured, and the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the 3rd cycle was calculated as a percentage. The larger this value is, the smaller the capacity decrease is. (7) The charge and discharge rate characteristic measurement conditions were the same as the initial discharge capacity except that the constant current amount was changed to 1 C, and the discharge capacity at the third cycle at each constant current amount was measured. 0.1C in the 3rd cycle
The ratio of the discharge capacity at 1C to the discharge capacity at was calculated as a percentage. The larger this value is, the faster the charge / discharge is possible.

Example 1 Ethylene-acrylonitrile copolymer produced by solution polymerization (ethylene unit: 22 mol%, acrylonitrile unit: 7)
8 mol%) in a solution of 1.5 parts in NMP, 100 parts of lithium cobalt oxide as an active material, and acetylene black (HS-100) manufactured by Denki Kagaku as a conductivity-imparting agent.
Parts are mixed, and further NMP is performed so that the solid content becomes 77%.
Was added and stirred and mixed with a planetary mixer to obtain a uniform positive electrode slurry. A positive electrode was produced using this slurry. Table 1 shows the results of measuring the polymer composition, the degree of solvent swelling in the electrolytic solution, the peel strength, the battery capacity measured at 25 ° C., the charge / discharge cycle characteristics, and the charge / discharge rate characteristics.

Examples 2 to 8 and Comparative Examples 1 to 3 Various characteristics were measured in the same manner as in Example 1 except that the polymer having the composition and production method shown in Table 1 was used. The results are shown in Table 1.

Example 9 5 parts of an acrylonitrile-methyl acrylate-methyl methacrylate copolymer produced by suspension polymerization (80 mol% of acrylonitrile unit, 14 mol% of methyl acrylate unit, 6 mol% of methyl methacrylate unit) To a solution dissolved in NMP, 95 parts of MCMB as an active material is mixed, NMP is further added so that the solid content becomes 68%, and the mixture is stirred.
By mixing, a uniform slurry for negative electrode was obtained. A negative electrode was produced using this slurry. Table 1 shows the results of measuring various characteristics as in Example 1.

[0047]

[Table 1]

The electrode produced by using the slurry of the present invention containing a polymer having a low degree of swelling in an electrolytic solution solvent and excellent in binding property had a large peel strength and exhibited a high binding performance. In addition, the lithium ion secondary battery having this electrode had a high battery capacity, good cycle characteristics, and excellent rate characteristics (Example 1).
~ 9). On the other hand, the polymer of acrylonitrile alone was excellent in the solvent swellability of the electrolytic solution, but inferior in the binding property (Comparative Example 1). Further, those having a small acrylonitrile component, or those having a too large proportion of monomer units to be combined have poor swelling properties in an electrolytic solution solvent and poor binding properties (Comparative Examples 2 to 2).
3). Then, the lithium ion secondary battery having electrodes using these was inferior to the product of the present invention in all of the battery capacity, cycle characteristics and rate characteristics.

Example 10 Ethylene-acrylonitrile copolymer produced by solution polymerization (18 mol% ethylene units, 8 acrylonitrile units)
(2 mol%) 0.8 parts dissolved in NMP and 1.5 parts ethyl acrylate-styrene-diethylene glycol dimethacrylate copolymer produced by emulsion polymerization NMP
The dispersion liquid dispersed in was mixed. To this mixed liquid, 100 parts of lithium cobalt oxide as an active material and 5 parts of acetylene black (HS-100 manufactured by Denki Kagaku Co., Ltd.) as a conductivity imparting agent were added, and NMP was further added so that the solid content became 75%, The mixture was stirred and mixed using a planetary mixer to obtain a uniform positive electrode slurry. A positive electrode was produced using this slurry. Table 2 shows the composition of the copolymer, the degree of electrolytic solution swelling, the peel strength, the battery capacity measured at 30 ° C, the high temperature charge / discharge cycle characteristics and the high temperature charge / discharge rate characteristics measured at 60 ° C.

Examples 11 to 18 and Comparative Examples 4 and 5, except that polymers having the compositions shown in Table 2 were used,
Various characteristics were measured in the same manner as in Example 10. The results are shown in Table 2.

[0051]

[Table 2]

As shown in Table 2, even when the slurry composition of the present invention contains a polymer other than the polymer (A), the electrode produced using the slurry has a large peel strength and a high binding performance. Indicated. In addition, the lithium ion secondary battery having this electrode has a high battery capacity and exhibits excellent high temperature charge / discharge cycle characteristics and rate characteristics. In particular, when the polymer (B) having a glass transition temperature (Tg) of −80 to 0 ° C. and an N-methylpyrrolidone insoluble content of 50% by weight or more was contained, better battery characteristics were exhibited (Examples 10 to 10). 18). On the other hand, when a polymer of acrylonitrile alone is used instead of the polymer (A) and when a polymer having a small acrylonitrile component and an excessively large proportion of monomer units to be combined is used, the binding property is poor (Comparative Example 4, 5). Then, the lithium ion secondary battery having electrodes using these was inferior to the product of the present invention in all of the battery capacity, cycle characteristics and rate characteristics.

[0053]

EFFECT OF THE INVENTION When the electrode slurry composition of the present invention is used, an electrode having a low swelling property in an electrolytic solution and an excellent binding property of an active material can be obtained. It can be suitably used for production. In particular, it is excellent as a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery including this electrode has a high charge / discharge capacity, good cycle characteristics, and excellent rate characteristics.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masahiro Yamakawa             1-2-1, Yokou, Kawasaki-ku, Kawasaki-shi, Kanagawa               Zeon Corporation, General Development Center F term (reference) 4J002 AC032 AC072 BG042 BG101                       BM003 CE003 DA016 DA026                       DE056 DE096 DG026 EP017                       EU027 GQ00                 5H029 AJ03 AJ05 AJ06 AK03 AK05                       AK16 AL06 AL07 AL08 AL12                       AL16 AM02 AM03 AM04 AM05                       AM07 BJ02 BJ03 BJ04 DJ08                       EJ12 HJ01 HJ02 HJ14                 5H050 AA07 AA08 AA12 BA17 CA02                       CA08 CA09 CA11 CA20 CB07                       CB08 CB09 CB20 DA11 EA23                       FA02 HA01 HA02 HA10 HA11                       HA14

Claims (4)

[Claims] 1. A repeating unit content derived from acrylonitrile or methacrylonitrile is 60 to 95 mol%, a 1-olefin having 2 to 4 carbon atoms and a general formula (1).
A compound represented by the formula CH ₂ ═CR ¹ —COOR ² (1) (in the formula, R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkyl group having 3 or less carbon atoms). Polymer (A) having a repeating unit content of 5 to 30 mol% derived from a monomer, an active material, and polymer (A)
A slurry composition for an electrode, which comprises a liquid medium that dissolves. 2. The glass transition temperature is −80 to 0 ° C.,
The slurry composition for an electrode according to claim 1, further comprising a polymer (B) having an N-methylpyrrolidone insoluble content of 50% by weight or more. 3. An electrode manufactured using the slurry composition for an electrode according to claim 1. 4. A lithium ion secondary battery having the electrode according to claim 3.