JP4488779B2 - Nonaqueous electrolyte secondary battery manufacturing method and nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a method for producing a non-aqueous electrolyte secondary battery electrode, a non-aqueous electrolyte secondary battery electrode produced by the production method, and a non-aqueous electrolyte secondary battery using the same.

  In recent years, non-aqueous electrolyte secondary batteries such as lithium secondary batteries have been used as secondary batteries that are small, lightweight, and have high energy density.

  An electrode of a non-aqueous electrolyte secondary battery is generally manufactured by applying a slurry containing an active material, a binder and a solvent on a metal core to form a mixture layer. If the dispersion of the active material in the slurry is insufficient, problems arise such that the electrode surface becomes rough and the thickness becomes nonuniform when applied onto the metal core.

  In Patent Document 1, a mixing stirrer having a planetary mixer unit in which two blades (blades) having a rotation and a revolving function are paired as a stirring mechanism, and a dissolver unit revolving while rotating in the same manner as the planetary mixer unit. Etc. is used to disperse the active material in the slurry. Moreover, in patent document 2, the active material in a slurry is disperse | distributed using the kneader in which the wheel with which one or several load applied eccentrically attached with respect to the main shaft rolls on a bottom plate. Yes.

However, the slurry stirred by these methods has a problem that the dispersion of the active material is insufficient, and the dispersed particles immediately reaggregate. For this reason, in the process of apply | coating a slurry to a metal core, there existed a problem that the surface of a mixture layer became rough with the reaggregated active material. This was particularly noticeable when the electrode was formed by reducing the thickness of the mixture layer. In addition, when polyamic acid, which is a polyimide precursor, is used as a binder, reaggregation and solid-liquid separation are observed in a short time, and it is difficult to uniformly disperse, so that the adhesion to the metal core is poor. was there. There was a similar problem when a thermoplastic polyimide resin was used as a binder.
Japanese Patent Laid-Open No. 11-213990 Japanese Patent Laid-Open No. 2001-283737 JP-A-11-347388

  An object of the present invention is to prepare a slurry in which an active material is uniformly dispersed so as not to re-aggregate, and to produce an electrode for a non-aqueous electrolyte secondary battery excellent in adhesion between a mixture layer and a metal core. The present invention provides a method, an electrode manufactured by the method, and a non-aqueous electrolyte secondary battery using the electrode.

  The present invention is a method for producing an electrode for a nonaqueous electrolyte secondary battery in which a slurry containing an active material is applied to a metal core to form a mixture layer. The active material, a binder and a solvent are mixed together. A rotating blade having a step of preparing a slurry, a cylindrical stirring tank, and a cylindrical portion provided in the stirring tank and rotating around the inner surface of the stirring tank and having a plurality of holes formed therein The slurry is placed in a stirring tank of a stirrer equipped with a slurry, the slurry is pressed against the inner surface of the stirring tank by rotation of a rotating blade, and the stirring process is performed while spreading the thin film into a cylindrical shape, and the stirred slurry is applied to the metal core. And a step of forming a mixture layer.

  According to the present invention, the active material contained in the slurry can be uniformly dispersed by stirring the slurry using the agitator. For this reason, the particle size distribution of the active material in the slurry becomes sharp, and a slurry in which reaggregation does not occur even when left for a long time can be obtained. Moreover, the mixture layer formed using the slurry which carried out such a stirring process is excellent in adhesiveness with a metal core.

  In the present invention, a polyamic acid that forms a polyimide resin by dehydrating imidization can be used as the binder. Conventionally, when such a polyamic acid is used, re-aggregation in the slurry is likely to occur. Therefore, the present invention is particularly useful when a polyamic acid is used.

  Polyamic acid is generally a polyimide precursor in which an aromatic diamide and an acid anhydride are subjected to a condensation polymerization reaction, and a polyimide resin is formed through imidization by heat dehydration. As such polyamic acid, the trade name “Pyer ML” (manufactured by DuPont), the trade name “TVE5051” (manufactured by Toshiba Chemical Corporation), the trade name “X-600W” (manufactured by Nitto Denko Corporation), and the trade name “U-” Varnish ”(manufactured by Ube Industries). Moreover, you may use the thermoplastic polyimide resin which the imidation reaction was complete | finished as a binder. As a polyimide varnish in which a thermoplastic polyimide resin is dissolved in an organic solvent, there is a trade name “Rika Coat” (manufactured by Shin Nippon Rika Co., Ltd.).

  In the present invention, a rubber binder and water-soluble cellulose may be used as the binder, and water may be used as the solvent. In this case, a first slurry in which an active material, water-soluble cellulose and water are mixed is prepared, and the first slurry is stirred with the stirrer, and then a rubber-based binder is added and mixed in the first slurry. It is preferable to form a mixture layer by forming the second slurry and applying the second slurry to the metal core. Since water-soluble cellulose is difficult to dissolve in water, the water-soluble cellulose can be dissolved in water in a better state than normal stirring by stirring with the above stirrer. Further, when the rubber binder is agitated with the agitator, the molecules are cut and the adhesive strength is reduced. Therefore, it is preferable to add the rubber binder after the water-soluble cellulose and water alone are previously stirred with the stirrer as described above.

  In preparing the first slurry, it is preferable to mix water-soluble cellulose and water in advance, stir the mixture with the stirrer, and then add and mix the active material to form the first slurry. Thus, water-soluble cellulose and water are previously stirred with the above stirrer, whereby water-soluble cellulose can be further dissolved in water in a good state. The active material is added to and mixed with the water-soluble cellulose and water mixture thus dissolved, and further stirred with the agitator.

  Examples of the water-soluble cellulose include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, and ethyl cellulose.

  The content of the water-soluble cellulose in the second slurry is preferably 0.5 to 3% by weight in terms of solid content. Water-soluble cellulose acts as a thickener for the slurry, and if the content is less than 0.5% by weight, the slurry does not thicken, which affects the coatability. On the other hand, if it exceeds 3% by weight, the resistance of the produced electrode plate increases, which may adversely affect the battery characteristics.

  Moreover, as content of the rubber-type binder in a 2nd slurry, 0.5 to 5 weight% is preferable. The rubber-based binder has an effect of increasing the binding between the active materials and the adhesion to the core, and if it is less than 0.5% by weight, the effect may not be sufficiently obtained. On the other hand, if it exceeds 5% by weight, the resistance of the electrode plate increases, which may adversely affect battery characteristics.

  The rubber binder is not particularly limited as long as it is a rubber polymer that can be used as a binder, and styrene butadiene rubber is preferable.

  The active material in this invention is not specifically limited, Any of a positive electrode active material and a negative electrode active material may be sufficient. Since the present invention uniformly disperses the active material so as not to reaggregate as described above, the present invention is particularly useful when a carbon material that has been conventionally an active material that easily reaggregates is used. Examples of the carbon material include graphite, amorphous carbon, and amorphous carbon.

In the present invention, the carbon material having an average particle diameter D ₅₀ measured in a powder state of 20 to 30 μm can be stirred with the agitator until the average particle diameter D ₅₀ measured in a slurry state is 18 μm or less. preferable.

  According to the present invention, an electrode having a thin mixture layer, for example, an electrode having a mixture layer having a thickness of 5 to 40 μm, can be produced in a highly reliable state with good adhesion to the metal core. . The thickness of the mixture layer of the negative electrode active material is preferably 20 to 40 μm, and the thickness of the mixture layer of the positive electrode active material is preferably 5 to 40 μm.

  As the agitator used for the agitation treatment in the present invention, for example, a high-speed agitator described in Patent Document 3 can be used. In this high-speed stirrer, the slurry is pressed against the inner surface of the stirring tank by high-speed rotation of the rotating blades to form a thin-film cylindrical shape, and a large shearing force is applied to the slurry by moving the cylindrical portion of the rotating blades in the thin-film cylindrical slurry. In addition, the aggregation of the active material in the slurry can be loosened and dispersed.

  The binder in the present invention is not limited to the above-mentioned polyamic acid and polyimide resin or rubber-based binder and water-soluble cellulose, but includes fluororesin such as polytetrafluoroethylene and polyvinylidene fluoride and other binders. It may be used. Moreover, you may add a electrically conductive agent to the slurry in this invention as needed.

  The metal core in the present invention is not limited as long as it is used as the metal core of the electrode of the nonaqueous electrolyte secondary battery. For the negative electrode, for example, a copper foil can be used, and for the positive electrode, for example, an aluminum foil. Can be used.

  The electrode for nonaqueous electrolyte secondary batteries of the present invention is an electrode produced by the method of the present invention. Moreover, the non-aqueous electrolyte secondary battery of the present invention is a non-aqueous electrolyte secondary battery using the electrode of the present invention. In the non-aqueous electrolyte secondary battery of the present invention, the electrode of the present invention may be used as a positive electrode or a negative electrode.

  As the positive electrode active material, for example, a lithium-containing transition metal composite oxide such as lithium cobaltate, lithium nickelate, or lithium manganate can be used. Moreover, a electrically conductive agent can be added to a slurry as needed.

  As the negative electrode active material, carbon materials such as graphite, amorphous carbon, and amorphous carbon, and metals that can be alloyed with lithium such as Si and Sn can be used.

  The non-aqueous electrolyte in the present invention can be used as long as it can be used for a non-aqueous electrolyte secondary battery. Examples of the solvent include cyclic carbonates such as ethylene carbonate and propylene carbonate, dimethyl carbonate, and diethyl carbonate. And non-cyclic carbonates such as ethyl methyl carbonate.

As the solute, any solute that can be used for a non-aqueous electrolyte secondary battery can be used. For example, LiBF ₄ , LiPF _6, or the like is used.

  Moreover, the gel electrolyte which made the organic solid electrolyte contain the said non-aqueous electrolyte can also be used.

  According to this invention, it can be set as the slurry which disperse | distributed the active material uniformly so that it may not re-aggregate. Moreover, by applying this slurry to form a mixture layer, a highly reliable electrode for a non-aqueous electrolyte secondary battery excellent in adhesion between the mixture layer and the metal core can be obtained. Therefore, it can be set as the nonaqueous electrolyte secondary battery excellent in battery characteristics, such as cycling characteristics and storage characteristics.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples, and can be appropriately modified and implemented without changing the gist thereof. It is.

[Preparation of slurry]
Example 1
FIG. 1 is a cross-sectional view showing a high-speed stirrer used for stirring the slurry. Specifically, the trade name “TK Fillmix” (manufactured by Tokushu Kika Kogyo Co., Ltd.) was used.

  As shown in FIG. 1, the stirrer is provided with a stirring tank 1 having a cylindrical inner surface, and an outer tank 2 is provided around the stirring tank 1. A cooling water chamber 3 is formed between the stirring tank 1 and the outer tank 2. Cooling water is supplied to the cooling water chamber 3 from the inflow pipe 4, absorbs frictional heat generated by stirring, and is discharged from an outflow pipe (not shown). Supply pipes 5 and 6 having valves 5 a and 6 a are connected to the bottom of the stirring tank 1. The supply pipes 5 and 6 can be used for supplying raw materials, but can also be used for discharging products in the case of batch production.

  A weir plate 7 is placed on the top of the stirring tank 1, and an upper container 8 is mounted thereon. An outflow pipe 9 is connected to the upper container 8. The upper container 8 has a lid 8a and a cooling water chamber 8b, and is used when products are continuously produced. In this case, the dam plate 7 is replaced with one having an inner diameter larger than that shown in the figure, and the raw material is continuously supplied from the supply pipes 5 and 6 so that the liquid after stirring continuously flows over the dam plate 7. To be treated. The cooling water chamber 8b is connected to the water channel in parallel with the cooling water chamber 3.

  The rotating shaft 10 passes through the lid 8a in an airtight manner and is installed concentrically with the stirring tank 1. The rotating shaft 10 is driven to rotate at a high speed by a motor provided at the top. A rotating blade 11 is attached to the lower end of the rotating shaft 10.

  The rotary blade 11 has a cylindrical portion 12, and the cylindrical portion 12 is attached to the rotary shaft 10 by a boss 14 via an arm 13. A large number of holes 12 a are formed in the cylindrical portion 12. An appropriate number of communication holes 13 a are formed in the arm 13.

  FIG. 1 shows a state in which the slurry L is put. The slurry L is pressed in the circumferential direction by high-speed rotation of the rotary blade 11 and rotates while being in close contact with the inner surface of the agitation tank 1 in a thin film cylindrical shape by centrifugal force generated by the rotation. The slurry L is subjected to a stirring action due to a deviation due to a speed difference between the surface and the inner surface of the stirring tank 1, and the active material contained in the slurry L is atomized and dispersed. The slurry L that has flowed into the hole 12a receives a strong rotational force due to the rotation of the hole, flows into the gap S from the hole 12a, increases the pressure, and disturbs the flow of the slurry L in the gap S. Assist the stirring action.

  The slurry was prepared by mixing graphite powder and a binder with a solvent. As the binder, a polyamic acid solution (18 wt% solution) (trade name “U-Vanice”, manufactured by Ube Industries, Ltd.) obtained by dissolving polyamic acid in N-methyl-2-pyrrolidone (NMP) was used. Graphite and polyamic acid were added to NMP in a weight ratio of 97: 3 to prepare a slurry. The mixing ratio was such that the total of graphite and polyamic acid was 85 g and NMP was 203 g.

As the graphite powder, graphite powder having an average particle diameter D ₅₀ of 21 μm was used. In addition, this particle diameter measured the powdery graphite powder using the laser diffraction type particle size distribution measuring apparatus (SALD-2000J, Shimadzu Corporation make). This slurry was placed in the processing tank 1 of the high-speed stirrer shown in FIG. 1, and the peripheral speed of the rotary blade 11 was set to 50 m / second, and the stirring process was performed for 60 seconds. The stirring tank 1 has an inner diameter D of 80 mm and a depth of 75 mm. The outer diameter d of the rotary blade 11 is 76 mm. The amount of the slurry L added to the stirring vessel 1 was 288 g, and the thickness t of the slurry that became a thin-film cylinder during the stirring treatment was 17 mm.

(Comparative Example 1)
The slurry of Comparative Example 1 was stirred using the stirrer shown in FIG. In the stirrer shown in FIG. 2, a vertical stirring blade 24 is provided in the stirring tank 21, and two homodispers 22 and 23 are provided inside the vertical stirring blade 24. The vertical stirring blade 24 is rotated by a motor 27, and the homodispers 22 and 23 are rotated by motors 25 and 26, respectively. A discharge valve 28 is provided at the bottom of the stirring tank 21 to discharge the stirred slurry. A cooling water chamber is formed between the stirring tank 21 and the outer tank 29. The cooling water enters from the cooling water inlet 30 and is discharged from the cooling water outlet 31.

  A slurry was prepared using the same graphite powder as in Example 1 and the same binder as in Example 1. The graphite powder and the polyamic acid were mixed at a weight ratio of 97: 3, and these were added to NMP to prepare a slurry. The total amount of graphite and polyamic acid was 3093 g, and NMP was 3900 g.

  This slurry was put in the stirrer shown in FIG. 2, and the stirring speed of the homodispers 22 and 23 was rotated at 2400 rpm and the vertical stirring blade 24 was rotated at a speed of 36 rpm, respectively, and stirred for 2 hours to prepare a slurry.

[Production of electrodes]
The slurry of Example 1 and Comparative Example 1 was applied to both sides of the copper foil by the doctor blade method and dried at 150 ° C., and a mixture layer was formed on the metal core to produce an electrode. Thereafter, the mixture layer was compressed until the thickness of the mixture layer became 38 μm. Next, for dehydration and imidization of the polyamic acid, heat treatment was performed at 350 ° C. for 2 hours to obtain an electrode. The amount of slurry applied on the metal core was about 50 mg / 10 cm ² .

[Measurement of particle size distribution of slurry]
The particle size distribution of the active material in the slurry of Example 1 and Comparative Example 1 was measured, and the results are shown in Table 1. All were measured in a slurry state and measured using a laser diffraction particle size distribution measuring apparatus similar to the above. D ₁₀ represent respectively the particle diameters is the particle diameter at the cumulative value 10%, D ₅₀ is the particle diameter at 50% cumulative value, D ₉₀ is the particle diameter at the cumulative value of 90%.

As is clear from the results shown in Table 1, it can be seen that the slurry of Example 1 stirred according to the present invention has a D ₅₀ of 18 μm or less and a sharp particle size distribution.

[Change in slurry viscosity over time]
The changes over time in the viscosities of the slurries of Example 1 and Comparative Example 1 were measured and are shown in FIG. As the viscometer, “IVC-5L” manufactured by Malcolm Co., Ltd. was used, and the viscosity of the slurry was read at regular intervals while continuously rotating the rotor at 40 rpm to obtain the slurry viscosity.

  As shown in FIG. 3, the viscosity of the slurry of Comparative Example 1 gradually increases, whereas the viscosity of the slurry of the Example does not change with time.

[Evaluation of adhesion]
About the electrode produced as mentioned above, the adhesiveness of a mixture layer and a metal core was evaluated. A double-sided tape was affixed to the bottom surface of a cylinder having a diameter of 20 mm and a height of 12 mm, and one adhesive surface of this double-sided tape was affixed to the surface of the electrode, and the cylinder was pulled up at a speed of 27 mm / min. The load peak (g) at the time was measured as the peel strength. The measurement results are shown in Table 2.

  As is apparent from the results shown in Table 2, the electrode of Example 1 according to the present invention exhibits a peel strength that is 5 times higher than that of the electrode of Comparative Example 1, and the adhesion between the mixture layer and the metal core body It can be seen that the properties are good.

(Examples 2 and 3)
1 g of carboxymethylcellulose (CMC) as a binder and 100 g of water are put into the stirring tank 1 of the high-speed stirrer used in Example 1, and stirred for 60 seconds at a peripheral speed of the rotary blade of 50 m / sec. An aqueous solution was prepared. Next, 139.7 g of graphite (average particle size 21 μm) and 10 g of water were put into a stirring tank, and a stirring process was performed for 60 seconds at a peripheral speed of the rotary blade of 30 m / sec. Thereafter, this was transferred to another container, 4.46 g of a dispersion of styrene butadiene rubber (SBR) (solid content 48 wt%) was added, and the mixture was stirred at a rotational speed of 500 rpm using a propeller type three blade agitator. The mixture was stirred for minutes to prepare negative electrode slurry A.

  Further, negative electrode slurry B was prepared in the same manner as described above, except that, when graphite was added to the CMC aqueous solution and stirring was performed, the peripheral speed was changed from 30 m / sec to 50 m / sec.

  In both of the negative electrode slurries A and B, the weight ratio of the solid content of graphite: SBR: CMC was 97.8: 1.5: 0.7.

  In addition, the internal diameter D of a stirring tank is 80 mm, the depth is 75 mm, and the outer diameter of a rotary blade is 76 mm. The total amount of slurry added to the stirring tank was 255.16 g, and the thickness of the slurry that became a thin-film cylinder during the stirring treatment was about 17 mm.

(Comparative Example 2)
A negative electrode slurry was prepared using the stirrer shown in FIG. 2 used in Comparative Example 1.

  In a stirring vessel, 1431 g of a 1% by weight aqueous solution of carboxymethylcellulose (CMC) was prepared, and 2000 g of the same graphite used in Examples 2 and 3 was added thereto, and the homodisper speed was 2400 rpm, vertical stirring. Each blade was rotated at a speed of 36 rpm and stirred for 2 hours. Thereafter, 64 g of a dispersion of styrene-butadiene rubber (SBR) (solid content 48 wt%) was added, and a vertical stirring blade was stirred at a speed of 36 rpm for 30 minutes to prepare a slurry.

[Production of electrodes]
The slurry A and B of the said Example and the slurry of the comparative example were apply | coated to both surfaces of copper foil with the doctor blade method, respectively, and it dried at 150 degreeC, and formed the mixture layer on the metal core. Then, it rolled until the thickness of the mixture layer became 30 micrometers. The amount of slurry applied on the metal core is about 30 mg / 10 cm ² .

  The electrode coated with the negative electrode slurry A was designated as Example 2, the electrode coated with the negative electrode slurry B was designated as Example 3, and the electrode coated with the slurry of Comparative Example 2 was designated as Comparative Example 2.

[Evaluation of adhesion]
In the same manner as in Example 1, the adhesion between the mixture layer and the metal core was evaluated for the produced electrodes. Table 3 shows the measurement results.

  As is clear from the results shown in Table 3, the electrodes of Examples 2 and 3 according to the present invention show higher peel strength than the electrode of Comparative Example 2, and the gap between the mixture layer and the metal core is higher. It can be seen that the adhesion is good.

Sectional drawing which shows the high-speed stirrer used in the Example according to this invention. Sectional drawing which shows the stirrer used in the comparative example. The figure which shows the time-dependent change of the viscosity of the slurry of Example 1 and Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Stirring tank 3, 8b ... Cooling water chamber 5, 6 ... Supply pipe 7 ... Dam plate 10 ... Rotating shaft 11 ... Rotating blade 12 ... Cylindrical part 12a ... Hole L ... Slurry S ... Gap t ... Film thickness

Claims (8)

A method for producing an electrode for a non-aqueous electrolyte secondary battery in which a slurry containing an active material is applied to a metal core to form a mixture layer,
A step of preparing a slurry by mixing an active material, a binder and a solvent;
In a stirring tank of a stirrer provided with a cylindrical stirring tank and a rotating blade having a cylindrical portion formed with a plurality of holes, which is provided in the stirring tank and moves in the vicinity of the inner surface of the stirring tank. Adding the slurry, stirring the slurry while pressing the slurry against the inner surface of the stirring tank by rotation of the rotary blade,
A method for producing an electrode for a non-aqueous electrolyte secondary battery, comprising: applying the stirred slurry to a metal core to form a mixture layer.   The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the binder is a polyamic acid that forms a polyimide resin by dehydration imidization.   The binder is a rubber binder and water-soluble cellulose, the solvent is water, and a first slurry is prepared by mixing an active material, water-soluble cellulose and water, and the first slurry is stirred. After mixing with a machine, a rubber-based binder is added to and mixed with the first slurry to form a second slurry, and the second slurry is applied to a metal core to form a mixture layer. The manufacturing method of the electrode for nonaqueous electrolyte secondary batteries of Claim 1.   The non-aqueous electrolyte according to claim 3, wherein water-soluble cellulose and water are mixed in advance, and after stirring with the stirrer, an active material is added and mixed to form the first slurry. A method for producing an electrode for a secondary battery.   The said active material is a carbon material, The manufacturing method of the electrode for nonaqueous electrolyte secondary batteries of any one of Claims 1-4 characterized by the above-mentioned. Claim average particle diameter D ₅₀ as measured by powder state carbon material is 20 to 30 [mu] m, an average particle diameter D ₅₀ as measured in a slurry state and performing the stirring process until the 18μm or less 5 The manufacturing method of the electrode for nonaqueous electrolyte secondary batteries as described in any one of.   An electrode for a non-aqueous electrolyte secondary battery manufactured by the method according to claim 1. A nonaqueous electrolyte secondary battery comprising a negative electrode comprising the electrode according to claim 7, a positive electrode, and a nonaqueous electrolyte.

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