JP4715125B2 - Slurry for lithium secondary battery electrode and method for producing lithium secondary battery electrode - Google Patents

Slurry for lithium secondary battery electrode and method for producing lithium secondary battery electrode Download PDF

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JP4715125B2
JP4715125B2 JP2004234407A JP2004234407A JP4715125B2 JP 4715125 B2 JP4715125 B2 JP 4715125B2 JP 2004234407 A JP2004234407 A JP 2004234407A JP 2004234407 A JP2004234407 A JP 2004234407A JP 4715125 B2 JP4715125 B2 JP 4715125B2
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slurry
water
secondary battery
lithium secondary
electrode
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JP2006054096A (en
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佐恵子 倉知
健悟 岡西
尚登 榎島
孝裕 米山
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トヨタ自動車株式会社
三菱化学株式会社
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50Manufacturing or production processes characterised by the final manufactured product
    • Y02P70/54Manufacturing of lithium-ion, lead-acid or alkaline secondary batteries

Description

  The present invention relates to an electrode slurry used for forming an electrode of a lithium secondary battery, and a method for producing a lithium secondary battery electrode using the electrode slurry.

  Conventionally, as a method for producing an electrode of a lithium secondary battery, an electrode slurry containing an electrode active material, a binder, and water (hereinafter sometimes simply referred to as “slurry”) is applied on a current collector, A method of drying is known.

  In Patent Document 1, as a negative electrode active material for a lithium secondary battery, a graphite powder coated with an amorphous material is used, and this and a water-soluble polymer binder are dispersed and dissolved in water. It is described that a negative electrode for a lithium secondary battery can be obtained by applying the resulting slurry onto a current collector substrate such as a copper foil and then drying.

In Patent Document 2, an active material that inserts and desorbs lithium ions is dispersed in a water-soluble organic solvent, and then dispersed by adding water, and further a water-insoluble binder such as a styrene-butadiene copolymer. A method for producing a battery electrode is described in which a dispersion prepared by adding and dispersing is applied to a metal foil and dried. And what contains N-methylpyrrolidone is described as one of the said water-soluble organic solvents.
Japanese Patent Laid-Open No. 2003-272627 JP 2003-142082 A

  Along with the recent increase in demand for lithium secondary batteries, the production volume thereof has been increasing rapidly, and it has been demanded to further improve the productivity in the production of the electrode as the member. Under such circumstances, efficient production is possible if the drying speed after slurry application can be increased in the production of the electrode by slurry application and drying.

  However, in the slurry described in Patent Document 1 in which an electrode active material obtained by coating graphite powder with an amorphous material and a water-soluble polymer binder are dispersed and dissolved in water, a comparative example to be described later As shown in FIG. 1, when drying is performed at a high speed after coating, the adhesive strength between the current collector substrate and the coating film after drying is low, so that high-speed drying cannot be performed. On the other hand, the dispersion described in Patent Document 2 does not contain both carboxymethylcellulose and a water-insoluble binder as a binder as in the present invention, but only contains a water-insoluble binder. However, even in this dispersion, as shown in Comparative Example 2 described later, when the coating is dried at a high speed, the adhesive strength between the current collector substrate and the dried coating film is low, Since there is a problem of film peeling, good adhesive strength cannot be obtained after high-speed drying.

  For these reasons, it has been desired to develop a technique capable of obtaining good coating strength even when drying at high speed.

  Accordingly, in the present invention, after application, high-speed drying can be performed, whereby an electrode slurry that can efficiently produce a lithium secondary battery electrode, and a lithium secondary battery electrode using the slurry. It aims at providing the method of manufacturing with high productivity.

  As a result of intensive studies to solve the above problems, the present inventors have found that an electrode active material obtained by coating graphite powder with an amorphous material, carboxymethylcellulose and a water-insoluble binder as a binder, By making a water-soluble organic compound having a boiling point of 150 ° C. or higher present in an electrode slurry containing water, high current collector substrate-coating bond strength can be obtained even at high speed drying, and electrode production The present inventors have found that good battery performance can be ensured while improving efficiency.

That is, the present invention provides a lithium secondary battery electrode slurry containing an electrode active material obtained by coating a graphite powder with an amorphous carbon material, a binder and water, and carboxymethyl cellulose as the binder. And a water-soluble organic compound having a boiling point of 150 ° C. or higher, and a non-water-soluble binder.

  In the present invention, the water-soluble organic compound having a boiling point of 150 ° C. or higher (hereinafter sometimes referred to as “high-boiling organic compound”) is preferably N-methylpyrrolidone, and the content thereof is an electrode active material. It is preferable that it is 0.1 to 40 weight% with respect to.

In addition, the present invention provides a method for producing a lithium secondary battery electrode comprising a step of applying the slurry for a lithium secondary battery electrode of the present invention on a current collector and then drying the slurry. Lithium, characterized in that drying is performed with an evaporation rate of water and a water-soluble organic compound until reaching a semi-cured dry state specified by 5500 at an average of 100 g / min or more per 1 m 2 of one surface of the current collector A method of manufacturing a secondary battery electrode.

  The details of why the adhesive strength between the current collector substrate and the dried coating film can be sufficiently obtained even after applying the slurry of the present invention to the current collector substrate and drying at high speed is not yet sufficiently clear. Is estimated as follows. That is, conventionally, in an aqueous slurry containing an electrode active material obtained by coating graphite powder with an amorphous material and a water-insoluble binder, hot air is applied to the applied slurry film, for example, during mass production coating. As the moisture evaporates from the surface of the coating film during the drying process, such as by directly spraying the liquid, the dispersion medium rises due to capillary action between the active material particles inside the coating film. It tends to rise to the surface of the coating, and the water-insoluble binder segregates on the surface of the coating after drying, so the binder concentration at the boundary between the current collector substrate and the coating tends to decrease. Therefore, it is considered that the adhesion strength of the coating film is low. On the other hand, in an electrode active material formed by coating a graphite powder with an amorphous material, a slurry for a lithium secondary battery electrode having carboxymethyl cellulose and a water-insoluble binder, and water, When high-boiling organic compounds coexist, the concentration of the high-boiling organic compound, which is a poor solvent for carboxymethylcellulose, increases in the slurry with the evaporation of moisture from the coating during drying, and carboxymethylcellulose cannot be completely dissolved. Since the above-mentioned capillary phenomenon starts to precipitate in the slurry and further, the capillary rise of the water-insoluble binder due to the capillary phenomenon can also be suppressed, In this case, a sufficient amount of binder is also present at the boundary portion between the current collector substrate and the coating film, so that the adhesive strength between the current collector substrate and the coating film can be ensured. thing Conceivable.

  Even if the slurry for lithium secondary battery electrodes of this invention performs high-speed drying after apply | coating to a collector, it can obtain high collector adhesive strength. According to the method for producing a lithium secondary battery electrode of the present invention using such an electrode slurry of the present invention, a high performance lithium secondary battery electrode can be produced with high productivity.

  Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention does not exceed the gist thereof. It is not limited to the following contents.

[Slurry for lithium secondary battery electrode]
The slurry for the lithium secondary battery electrode of the present invention comprises an electrode active material obtained by coating a graphite powder with an amorphous material, carboxymethyl cellulose and a water-insoluble binder, water, and a boiling point of 150 ° C. or higher. The water-soluble organic compound (high boiling point organic compound) which has this.

<High boiling point organic compounds>
In the present invention, examples of the high boiling point organic compound present in the slurry include amides such as N-methylpyrrolidone (boiling point 202 ° C.), dimethylformamide (boiling point 153 ° C.), dimethylacetamide (boiling point 166 ° C.), ethylene glycol (boiling point). Diols such as propylene glycol (boiling point 187 ° C.), butanediol (boiling point 193-228 ° C.), ethylene glycol monobutyl ether (boiling point 171 ° C.), derivatives thereof, gamma butyrolactone (boiling point 203 ° C.), ethylene carbonate ( And cyclic esters having a boiling point of 238 ° C., dimethyl sulfoxide (boiling point of 189 ° C.), and the like. These may be used alone or in combination of two or more.

  A particularly preferred high boiling point organic compound for the present invention includes N-methylpyrrolidone, which is generally widely used in the production of lithium secondary battery electrodes.

  The amount of the high-boiling organic compound added is usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more, and usually 40% by weight, based on the electrode active material in the slurry. Hereinafter, it is preferably 30% by weight or less, more preferably 20% by weight or less. If the amount of the high-boiling organic compound added is too small, the effect of improving the adhesive strength between the current collector substrate and the coating film may be insufficient, and if it is too large, the drying process may be overloaded. .

<Electrode active material>
In the present invention, the material used as the electrode active material is a graphite powder coated with an amorphous material.

(Amorphous material)
As the amorphous material, it is preferable to use a carbonaceous powder whose crystal plane (002) has an interplanar spacing d 002 of 0.349 nm or more and a crystallite thickness Lc in the C-axis direction of less than 10 nm. It is more preferable that the interplanar spacing d 002 of the crystal plane (002) is 0.349 nm or more and 0.355 nm or less, and the crystallite thickness Lc in the C-axis direction is 7 nm or less. More preferably, it is 1.5 to 10 nm, more preferably 1.5 to 5 nm.

(Physical properties of graphite powder)
The preferred particle size and specific surface area of the graphite powder as the base material are as follows.
That is, the average particle diameter (D 50 ) measured by a laser diffraction particle size distribution meter is usually 20 μm or less, preferably 15 μm or less, more preferably 13 μm or less, particularly preferably 8 to 13 μm, and the BET specific surface area is 15 m 2. / G or less, preferably 13 m 2 / g or less, most preferably 12 m 2 / g or less, preferably 2 m 2 / g or more, more preferably 3 m 2 / g or more, and most preferably 8 m 2 / g or more.

(Production method of graphite powder)
Although the graphite material applied to the active material of the present invention is not particularly limited, for example, natural graphite is used, or carbonization or graphite by changing firing conditions appropriately from the carbon precursor described below. Can be obtained.

  In this case, as the carbon precursor for proceeding carbonization in the liquid phase, coal tar pitch from soft pitch to hard pitch, or heavy coal based oil such as dry distillation liquefied oil, normal pressure residual oil, reduced pressure residual oil DC Heavy petroleum oil, crude oil, naphtha cracked petroleum heavy oil such as ethylene tar, and aromatic hydrocarbons such as acenaphthylene, decacyclene, anthracene, phenanthrene, N-ring compounds such as phenazine and acridine, S-ring compounds such as thiophene and bithiophene, polyphenylenes such as biphenyl and terphenyl, polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insolubilized products of these, organic polymers such as nitrogen-containing polyacrylonitrile and polypyrrole, Sulfur-containing polythiophene, organic polymers such as polystyrene, cellulose Natural polymers such as polysaccharides represented by lignin, mannan, polygalacturonic acid, chitosan, saccharose, thermoplastic resins such as polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, imide resin, etc. One or more carbonizable organic compounds selected from thermosetting resins, mixtures of the above and low molecular organic solvents such as benzene, toluene, xylene, quinoline, and n-hexane are used.

(Production method of electrode active material)
The electrode active material used in the present invention is usually amorphous on the surface of the graphite particles by heating a mixture of such graphite powder and a carbon precursor, passing through an intermediate material, then carbonizing and pulverizing. Graphite carbonaceous composite powder coated with carbonaceous material (amorphous carbon-coated graphite composite material), the proportion of amorphous carbonaceous material in such amorphous carbon-coated graphite composite material is Usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more, particularly preferably 2% by weight or more, usually 50% by weight or less, preferably 25% by weight or less, more preferably It may be adjusted to 15% by weight or less, particularly preferably 10% by weight or less.

More specifically, the production process for obtaining such an amorphous carbon-coated graphite composite material is usually divided into the following four processes.
First step: Graphite particles, a carbon precursor, and, if necessary, a solvent are mixed using various commercially available mixers and kneaders to obtain a mixture.
Second step: If necessary, the mixture is heated with stirring to obtain an intermediate substance from which the solvent has been removed.
Third step: The mixture or intermediate substance is heated to 700 ° C. or higher and 2800 ° C. or lower in an inert gas atmosphere such as nitrogen gas, carbon dioxide gas, or argon gas to obtain a carbonized substance.
Fourth step: The carbonized material is subjected to powder processing such as pulverization, pulverization, and classification as required.

  Among these steps, the second step and the fourth step may be omitted depending on circumstances, and the fourth step may be performed before the third step.

  In addition, the heat history temperature condition is important as the heat treatment condition in the third step. The lower limit temperature is usually 700 ° C. or higher, preferably 900 ° C. or higher, although it varies slightly depending on the type of carbon precursor and its thermal history. On the other hand, the upper limit temperature can be raised to a temperature that basically does not have a structural order exceeding the crystal structure of the graphite particle nucleus. Therefore, the upper limit temperature of the heat treatment is usually 2800 ° C. or lower, preferably 2000 ° C. or lower, more preferably 1500 ° C. or lower. Under such heat treatment conditions, the heating rate, cooling rate, heat treatment time, etc. can be arbitrarily set according to the purpose. Further, after heat treatment in a relatively low temperature region, the temperature can be raised to a predetermined temperature. In addition, the reactor used for this process may be a batch type or a continuous type, and may be one or more.

The amorphous carbon-coated graphite composite material thus obtained has a peak intensity ratio R value obtained by Raman spectrum analysis, a half-value width of a peak in the vicinity of 1580 cm −1 , and a diffraction pattern obtained by X-ray wide angle diffraction. The 002 and Lc values do not exceed the crystallinity of the graphite material, that is, the R value is equal to or greater than that of the graphite, the half width is equal to or greater than that of the graphite, and the d 002 value is equal to that of the graphite. Above, it is preferable that Lc is below that value of graphite.

  The R value of a specific amorphous carbon-coated graphite composite material as an electrode active material used in the present invention is usually 0.01 or more, preferably 0.05 or more, more preferably 0.2 or more, and still more preferably 0.3 or more, usually 1.0 or less, preferably 0.8 or less, more preferably 0.7 or less, still more preferably 0.5 or less, and more than the value of graphite as a base material. There are some.

(Physical properties of electrode active material)
-Average particle diameter The minimum of the average particle diameter of an electrode active material is 5 micrometers or more normally, Preferably it is 8 micrometers or more, and an upper limit is 20 micrometers or less normally, Preferably it is 15 micrometers or less. When this upper limit is exceeded, coating film defects due to coarse particles and aggregated particles are likely to occur, and when the lower limit is exceeded, it may be difficult to disperse during slurry preparation.
-Specific surface area The upper limit of the specific surface area of an electrode active material is 10 m < 2 > / g or less normally, Preferably it is 5 m < 2 > / g or less. If this upper limit is exceeded, it may be difficult to disperse during slurry preparation. The lower limit of the electrode active material is 1 m 2 / g or more from the viewpoint of battery characteristics.

(Content of electrode active material)
The content of the electrode active material in the slurry is usually 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more, and 99% by weight or less based on the solid content excluding the solvent. To do. If the content of the electrode active material in the slurry is too small, battery characteristics such as capacity tend to be insufficient, and if too large, the strength of the coating film may be deteriorated.

<Carboxymethylcellulose>
As carboxymethylcellulose, commercially available sodium carboxymethylcellulose can be widely used. As the molecular weight, the average molecular weight has a lower limit of usually 20,000 or more, preferably 50,000 or more, and an upper limit of usually 700,000 or less. Preferably it is 500,000 or less. When the molecular weight of carboxymethyl cellulose is out of the above range, a slurry having appropriate fluidity may not be obtained.

  Further, the content of carboxymethyl cellulose in the slurry is usually 0.1% by weight or more and 10% by weight or less based on the solid content excluding the solvent. When the content of carboxymethyl cellulose is too small, the adhesive strength between the current collector substrate and the coating film is insufficient. On the other hand, when the content is too large, the battery capacity and conductivity may be lowered.

<Water-insoluble binder>
The “water-insoluble” of the water-insoluble binder used in the present invention means that the solubility in water at 25 ° C. is 100 mg / l or less.

  Examples of the material used as the water-insoluble binder in the present invention include water-insoluble materials among various polymer materials generally used as an electrode binder. Specifically, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose Etc. These may be used alone or in combination of two or more.

  The content of the water-insoluble binder in the slurry is usually 0.1% by weight or more and 10% by weight or less based on the solid content excluding the solvent. If the content of the water-insoluble binder in the slurry is too small, the active material cannot be retained sufficiently and the adhesion strength of the electrode to the current collector is insufficient. On the other hand, if the content is too large, the battery capacity and conductivity are reduced. Sometimes.

<Other solids>
In the slurry of this invention, solid content components other than an active material and carboxymethylcellulose, a water-insoluble binder, and a high boiling point organic compound can be contained as needed. For example, a conductive agent can be included to improve the electronic conductivity of the electrode. Examples of the conductive agent include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke. The proportion of the conductive agent in the solid content of the slurry is usually 50% by weight or less, preferably 30% by weight or less, and more preferably 15% by weight or less. If the content of the conductive agent in the slurry is too large, the battery capacity may be reduced.

<Slurry solvent>
In the present invention, water is used as the solvent for the slurry.

  The slurry of the present invention uses water as a solvent, and the solid content in the slurry is usually 1% by weight or more, preferably 5% by weight or more, more preferably 10% by weight or more, and most preferably 20% by weight or more. In addition, the amount is usually 99% by weight or less, preferably 95% by weight or less, more preferably 90% by weight or less, and most preferably 80% by weight or less. If the solid content is too large, the viscosity of the slurry increases and it becomes difficult to apply, and if it is too small, the drying load tends to increase. In addition, solid content refers to the non-volatile component also containing carboxymethylcellulose.

<Slurry viscosity>
The slurry of the present invention has a viscosity (viscosity according to a measurement method in Examples described later) of usually 50 mPa · s or more, preferably 100 mPa · s or more, and usually 100,000 mPa · s or less, preferably 50,000, by the above-described blending. It is preferably mPa · s or less. When the viscosity of the slurry is too high, it becomes difficult to apply, and when the slurry is too low, the solid content concentration is low and the drying load is increased.

<Method for producing slurry>
There is no restriction | limiting in particular as a manufacturing method of the slurry of this invention, It prepares by mixing an electrode active material, a carboxymethylcellulose, a water-insoluble binder, water, a high boiling point organic compound, and another combination component by arbitrary prescriptions. For example, the following method is suitable.

  That is, first, (i) after mixing the electrode active material and other concomitant components and carboxymethyl cellulose in a powder state, (ii) sequentially adding and mixing water, and (iii) water-insoluble binding Add and mix the agent. The high boiling point organic compound can be added at any time after the completion of the step (i) depending on the amount of use.

[Method for producing lithium secondary battery electrode]
The method for producing a lithium secondary battery electrode of the present invention is a method for producing an electrode by applying the slurry for a lithium secondary battery electrode of the present invention on a current collector and drying it under predetermined drying conditions. .

  As a method for applying the electrode slurry to the current collector, various methods such as roll coating, comma coating, doctor coating, doctor reverse coating, and die coating can be employed.

  The thickness of the coating film is usually 1 μm or more, preferably about 10 μm or more, and usually about 1000 μm or less, preferably about 200 μm or less, as the film thickness after drying. If the coating film is too thick, the conductivity tends to decrease, and if it is too thin, the capacity tends to decrease.

  There is no restriction | limiting in particular in the material of an electrical power collector, Various metals can be used according to the kind of applied battery. For example, as the material of the current collector, copper, nickel, stainless steel, nickel-plated steel or the like is used, and copper is preferable. The thickness of the current collector is usually about 1 μm or more, preferably about 5 μm or more, and is usually about 500 μm or less, preferably about 200 μm or less. If the current collector is too thick, the capacity of the battery as a whole decreases, and if it is too thin, the mechanical strength may be insufficient.

  Various methods such as warm air drying, far-infrared drying, induction heating drying and the like can be adopted as the method for drying the coating film. At that time, the drying temperature is usually 10 ° C. or more, preferably about 50 ° C. or more, and usually about 500 ° C. or less, preferably about 250 ° C. or less at the maximum temperature in the coating film.

  In general, the electrode obtained by applying and drying the electrode slurry is preferably consolidated by a roller press or the like in order to increase the packing density of the active material.

  The obtained electrode can usually be used as an electrode of a lithium secondary battery, particularly as a negative electrode.

As described above, the slurry for the lithium secondary battery electrode of the present invention is difficult to reduce the adhesive strength between the current collector substrate and the dried coating film even after high-speed drying after coating. Even if high-speed drying is performed, good current collector substrate-coating bond strength can be maintained. Thus, in the method for producing a lithium secondary battery electrode of the present invention using such an electrode slurry of the present invention, the electrode slurry of the present invention is applied on a current collector and then dried as JIS K. Adequate adhesive strength even under high-speed drying conditions where the evaporation rate of water and water-soluble organic compounds until reaching the semi-cured dry state specified by 5500 is 100 g / min or more per 1 m 2 on one side of the current collector. This is industrially advantageous in that it can be obtained.

  Below, the drying conditions (evaporation rate) in this invention are demonstrated.

<Drying conditions (evaporation rate)>
According to JIS K 5500, “semi-curing drying” is one of the dry states of the paint. “Dry to touch the surface of the paint-coated surface by rubbing it with your fingertips (dry to touch). ) ”, And in the present invention,“ semi-cured and dried ”is determined according to the criteria. Then, the evaporation rate is calculated by dividing the total amount of water and water-soluble organic compound on the coated surface by the time until semi-curing drying from the total amount of water and water-soluble organic compound in the coating solution and the coating amount. In the present invention, this value is evaluated as an average per 1 m 2 on one side. Hereinafter, this evaporation rate may be referred to as “semi-cured dry evaporation rate”.

  This semi-cured drying evaporation rate was less than 100 g / min in the prior art, but according to the present invention, even if ultra-high speed drying of 100 g / min or more, especially 200 g / min or more is performed, the adhesive strength is reduced. Thus, a good electrode can be produced with high productivity.

  The drying conditions according to the present invention are not particularly limited as long as the semi-cured drying evaporation rate can be achieved. For example, in the case of warm air drying, the temperature, the wind speed, and the air volume are preferably set as follows. The

(temperature)
The lower limit of the temperature of the warm air is usually 30 ° C or higher, preferably 50 ° C or higher, and the upper limit is usually 300 ° C or lower, preferably 250 ° C or lower. When the temperature exceeds this upper limit, the current collector and the binder component are deteriorated, and the mechanical strength of the electrode plate is easily impaired. When the temperature is lower than the lower limit, the drying time tends to be longer.

(wind speed)
The lower limit of the warm air velocity is usually 0.5 m / s or more, preferably 1 m / s or more, and the upper limit is usually 50 m / s or less, preferably 30 m / s or less. When the wind speed exceeds this upper limit, the applied slurry thin film tends to scatter due to the force of the wind, and when the wind speed falls below the lower limit, the drying time tends to be longer.

(Air flow)
The air volume of the warm air is, as the air volume per 1 m 2 of coating on one side of the current collector, the lower limit is usually 0.1 m 3 / min or more, preferably 0.5 m 3 / min or more, and the upper limit is usually 100 m 3 / min. Hereinafter, it is preferably 50 m 3 / min or less. If the air volume exceeds this upper limit, the load on the drying process becomes excessive, while if it falls below the lower limit, the drying time tends to be longer.

(Semi-cured drying evaporation rate)
In the present invention, the semi-cured drying evaporation rate is 100 g / min or more, and as described above, it can sufficiently withstand high-speed drying of 200 g / min or more. Since the load is excessive, the upper limit of the semi-cured dry evaporation rate is usually preferably 500 g / min or less.

  EXAMPLES The present invention will be described in more detail with reference to examples and comparative examples below, but the present invention is not limited to the following examples unless it exceeds the gist.

<Example 1>
98 parts by weight of graphite powder coated with an amorphous carbon material having an average particle size of 12 μm and a specific surface area of 3.9 m 2 / g, and 1 part by weight of carboxymethyl cellulose having an average molecular weight of about 250,000 to 300,000 and powder This was kneaded for 30 minutes while sequentially adding water in a twin-screw kneader, and then 1 part by weight of styrene / butadiene rubber aqueous dispersion was added in terms of solid content and mixed for 10 minutes. At this time, 107 parts by weight of water was added. Finally, 10 parts by weight of N-methylpyrrolidone, that is, 10.2% by weight based on the graphite powder was added and mixed for 10 minutes to obtain a slurry. The viscosity of this slurry is shown in Table 1. The viscosity of the slurry was measured using an E-type viscometer at 25 ° C. and 10 s −1 .

Next, 5.0 ± 0.3 mg of the electrode active material per 1 cm 2 is deposited on the copper foil (thickness: 15 μm) as the current collector (the amount of water and water-soluble organic compound adhered accordingly). 5.9 ± 0.4 mg, 59 ± 4 g / m 2 ), coated on one side, using warm air of 200 ° C., wind speed 6 m / s, air volume 27 m 3 / min per 1 m 2 of coated surface Dried under conditions.

At this time, it took 10 seconds to reach the semi-cured dry state of JIS K 5500, but actually it was dried for 15 seconds. Accordingly, the semi-cured dry evaporation rate was 354 ± 24 g / min (= (59 ± 4) ÷ 10 × 60) per 1 m 2 on one side.

Finally, the electrode density was adjusted to 1.30 ± 0.05 g / cm 3 with a roll press to obtain an electrode film.

  Using a continuous load type scratch strength tester “Tribogear HEIDON-18” manufactured by Shinto Kagaku Co., Ltd., the coating film is scratched with a conical needle whose tip is processed at 0.3 mmR, and the copper foil is exposed. The load to be measured was measured, and the results are shown in Table 1.

<Comparative Example 1>
A slurry having the viscosity shown in Table 1 was prepared in the same manner as in Example 1 except that water was used instead of N-methylpyrrolidone, and an electrode film was produced in the same manner as in Example 1 using this slurry. The scratch test was conducted and the results are shown in Table 1.

<Comparative Example 2>
Without using carboxymethylcellulose, a slurry having the viscosity shown in Table 1 was prepared in the same manner as in Example 1 except that the addition amount of the aqueous dispersion of styrene / butadiene rubber was increased to 2 parts by weight in terms of solid content. Using this slurry, production of an electrode film and a scratch test were carried out in the same manner as in Example 1, and the results are shown in Table 1.

  As shown in Table 1, high speed drying is performed by adding N-methylpyrrolidone, which is a high boiling point organic compound, to a slurry composed of an electrode active material, carboxymethyl cellulose, a water-insoluble binder, and water. However, an excellent electrode capable of maintaining good electrode film adhesion strength can be obtained.

  The application of the lithium secondary battery to which the present invention is applied is not particularly limited, and can be used for various known applications. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. Electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, game machines, watches, strobes, cameras, automobile power sources, and the like.

Claims (4)

  1. In a lithium secondary battery electrode slurry containing an electrode active material obtained by coating a graphite powder with an amorphous carbon material, a binder and water, carboxymethyl cellulose and a water-insoluble binder as the binder The slurry for lithium secondary battery electrodes characterized by including the water-soluble organic compound which contains an agent and has a boiling point of 150 degreeC or more.
  2.   2. The slurry for a lithium secondary battery electrode according to claim 1, wherein the water-soluble organic compound having a boiling point of 150 ° C. or higher is N-methylpyrrolidone.
  3.   3. The lithium secondary battery electrode according to claim 1, wherein the content of the water-soluble organic compound having a boiling point of 150 ° C. or higher is 0.1 to 40% by weight with respect to the electrode active material. Slurry.
  4. In the manufacturing method of the lithium secondary battery electrode which has the process of apply | coating the slurry for lithium secondary battery electrodes of any one of Claim 1 thru | or 3 on a collector, and drying, JIS JIS is used as this drying condition. The water and water-soluble organic compound are evaporated at an average rate of 100 g / min or more per 1 m 2 on one side of the current collector until reaching the semi-cured dry state defined by K 5500. A method for producing a lithium secondary battery electrode.
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