JP2002141060A - Manufacturing method of negative electrode mixture and non-aqueous system secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a negative electrode mixture that is superior in kneading dispersion even with small quantity of conductive agent and binder, and a non-aqueous system secondary battery using the same that has excellent battery property and high capacity and is of small size and light weight. SOLUTION: This is a manufacturing method of a negative electrode mixture which is comprised of at least a wetting dispersing process in which a solvent is added in the negative electrode active material and dispersion is made, and a mixing process in which the binder solution that has in advance dispersed a binder in the solvent is added in the above wetting dispersion material and kneading dispersion is made.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a negative electrode mixture and a non-aqueous secondary battery using the same.
More specifically, the present invention relates to a method for producing a negative electrode mixture having excellent kneading and dispersing properties, and a non-aqueous secondary battery having excellent battery characteristics using the same.

[0002]

2. Description of the Related Art In recent years, the performance of portable electronic devices such as cellular phones and personal digital assistants largely depends on the performance of not only semiconductor elements and electronic circuits to be mounted but also rechargeable secondary batteries. It is desired that the capacity of the secondary battery to be mounted be increased and the weight and size be reduced at the same time. As a secondary battery that meets these demands, a nickel-metal hydride storage battery having an energy density about twice that of a nickel-cadmium storage battery has been developed, and then a lithium-ion battery exceeding this has been developed and has been in the spotlight.

[0003] A lithium ion battery has a non-aqueous electrolyte solution and an electrode plate group in which positive and negative electrodes are arranged via a separator, and each of the positive and negative electrode plates has an active material on the surface of a current collector. It has a configuration that is bound. These electrode plates are generally made of an electrode plate mixture (a positive electrode mixture, a negative electrode mixture) in which an active material (a positive electrode active material, a negative electrode active material), a conductive additive, a binder (a binder), and the like are kneaded and dispersed in a solvent. Is coated on one or both sides of the current collector and dried, and then pressed if necessary, and cut into a predetermined shape.

[0004] In the production process of the electrode plate, the composition of the electrode plate mixture and the method of kneading and dispersing have a large effect on battery performance such as discharge characteristics, charge / discharge cycle characteristics, battery blistering amount and safety of the completed battery. . For this reason, it is preferable to obtain an electrode plate having excellent electrode strength only by adding a small amount of a conductive auxiliary material or a binder that does not contribute to the charge / discharge reaction. Therefore, a method has been proposed in which a conductive additive is dispersed in a solvent, an active material and a binder are added, and the mixture is kneaded and dispersed (JP-A-11-541).
No. 13).

[0005]

However, in an electrode plate mixture obtained by dispersing a conductive additive in a solvent and then adding a powdered active material and a powder or a liquid binder, a small amount of the conductive additive,
With the binder, an electrode plate satisfying satisfactory electrode plate strength, discharge rate characteristics, discharge temperature characteristics, and charge / discharge cycle characteristics cannot be obtained, and as a result, a non-aqueous secondary battery excellent in battery characteristics cannot be obtained.

The present invention provides a method for producing an electrode plate mixture which is capable of obtaining an electrode plate having excellent electrode strength even with a small amount of a binder, and satisfying discharge rate characteristics, discharge temperature characteristics, and charge / discharge cycle characteristics. A main object of the present invention is to provide a high-capacity, small-sized and light-weight non-aqueous secondary battery excellent in battery characteristics by applying and drying the electrode plate mixture on a current collector.

[0007]

In order to achieve the above object, the method for producing a negative electrode mixture of the present invention comprises a wet dispersion step in which a solvent is added to at least a negative electrode active material for dispersion, and a binder is added to the solvent in advance. A kneading step of adding a binder solution in which is dispersed to the wet dispersion and performing kneading and dispersion.

In the wet dispersing step, 30 parts by weight to 80 parts by weight of the solvent contained in the entire negative electrode mixture to be produced is used.
It is preferable to perform kneading and dispersion by adding a part by weight of a solvent. Further, before the wet dispersing step, a dry step of mixing at least the negative electrode active material and the conductive additive in a dry manner may be provided.

Further, a non-aqueous secondary battery according to the present invention is characterized in that a negative electrode mixture obtained by the above-described manufacturing method is applied to a current collector,
A wound negative electrode plate and a dried positive electrode plate are interposed, and a wound or laminated electrode plate group is accommodated in a battery case.

[0010]

Embodiments of the present invention will be described below.

First, the negative electrode plate of the present invention contains at least a negative electrode active material and a binder, and may contain a conductive auxiliary as needed.

The negative electrode active material in the case of adding a conductive additive is not particularly limited. For example, a carbon material obtained by firing an organic polymer compound (phenol resin, polyacrylonitrile, cellulose, etc.) ,
Carbon materials, artificial graphite, natural graphite, etc. obtained by firing coke or pitch can be used alone or as a mixture of two or more.

However, when the conductive additive is not added, at least spherical graphite such as mesophase carbon microbeads (MCMB) and massive graphite such as artificial massive graphite are used from the viewpoint of kneading properties of the mixture and battery characteristics. It is preferable to mix two types selected from fibrous graphite such as mesophase carbon fiber.

As the negative electrode binder, modified acrylic rubber,
For example, a copolymer of 2-ethylhexyl acrylate and acrylic acid and acrylonitrile, a fluororesin, for example, polyvinylidene fluoride, polyvinylidene fluoride and hexafluoropropylene alone, or a mixture or copolymer of two or more thereof may be used as an organic solvent. Can be used, or a dispersion can be used.

[0015] As the conductive additive, vapor-grown carbon fiber or the like can be used.

The weight ratio of the binder to 100 parts by weight of the negative electrode active material is preferably in the range of 1 part by weight to 4 parts by weight. When the amount is 1 part by weight or less, the binding force between the electrode plate material and the current collector is insufficient, and problems such as falling off of the electrode plate material occur. Is abundant in the electrode plate,
It is not preferable because the battery capacity is reduced.

The weight ratio of the conductive additive that can be added as needed to 100 parts by weight of the negative electrode active material is preferably in the range of 2 to 8 parts by weight, and more preferably in the range of 2 parts by weight or less. When the amount is 8 parts by weight or more, only the same effect as 8 parts by weight can be obtained.

Although the solvent is not particularly limited, N-methyl-2-pyrrolidone, cyclohexanone, N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide, dimethylsulfoxide, hexamethylsulfamide, tetramethylurea , Acetone, methyl ethyl ketone or the like can be used alone or as a mixture of two or more kinds. In the wet dispersion step, the solvent is added by 30 to 80 parts by weight of the solvent amount contained in the negative electrode mixture, and wet dispersion is performed. Is preferred, and the range of 40 to 65 parts by weight is optimal. 30
If the amount is less than 10 parts by weight, the solvent cannot uniformly disperse on the surface of the negative electrode active material and cannot be dispersed.

If necessary, a thickener can be added to the positive electrode mixture and / or the negative electrode mixture, and polyvinyl alcohol, carboxymethyl cellulose, ethylene-vinyl alcohol copolymer and the like are preferable.

The positive electrode plate contains, but is not particularly limited to, at least a positive electrode active material, a conductive additive, and a binder.

The positive electrode active material is not particularly limited. For example, oxides such as manganese dioxide, vanadium pentoxide and molybdenum oxide, or lithium such as lithium cobaltate, lithium nickelate and lithium manganate are used. A composite oxide with a transition metal, a sulfide such as titanium sulfide, molybdenum sulfide, or iron sulfide, or a composite sulfide of lithium and a transition metal can be used.

The conductive auxiliary material is not particularly limited, and for example, carbon black such as acetylene black, graphite, etc. can be used alone or as a mixture of two or more types.

Further, the kneading and dispersing method of the present invention
There is no particular limitation, and for example, a planetary mixer, a homomixer, a pin mixer, a kneader, a homogenizer and the like can be used. These can be used alone or in combination.

Further, various dispersants, surfactants, stabilizers, and the like can be added to the above-mentioned electrode plate mixture as needed.

The method for applying the electrode plate mixture to the current collector in the present invention is not particularly limited, and examples thereof include a slit die coater, a reverse roll coater, a lip coater, a blade coater, a knife coater, a gravure coater, and the like. A dip coater or the like can be used.

After application and drying of the electrode plate mixture, if necessary, a treatment such as a heat treatment or a press may be performed.

Further, the electrolytic solution in the present invention is prepared by dissolving the electrolyte in a non-aqueous solvent. As the non-aqueous solvent, for example, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-dichloroethane, 1,3-dimethoxypropane, 4- Methyl-2-pentanone, 1,4-dioxane, acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, sulfolane, 3-methyl-sulfolane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylformamide, dimethylsulfoxide, dimethylformamide, Trimethyl phosphate, triethyl phosphate and the like can be used. These non-aqueous solvents can be used alone or as a mixed solvent of two or more kinds.

The electrolyte contained in the non-aqueous electrolyte of the present invention includes, for example, lithium perchlorate, lithium hexafluorophosphate, lithium borofluoride, lithium arsenide hexafluoride, lithium trifluorometasulfonic acid, A lithium salt such as lithium bistrifluoromethylsulfonylimide can be used.

[0029]

The present invention will be described below in more detail with reference to examples and comparative examples.

(Example 1) First, as a positive electrode material, 100 parts by weight of lithium cobalt oxide as a positive electrode active material, 3 parts by weight of acetylene black as a conductive aid, and an NMP solution of polyvinylidene fluoride as a binder (solid content) 12%) to 3
3 parts by weight, N-methyl-2-pyrrolidone (N
MP) was kneaded and dispersed at a mixing ratio of 13 parts by weight using a homomixer to prepare a positive electrode mixture.

Next, as the negative electrode material, 100 parts by weight of artificial massive graphite as a negative electrode active material, 67 parts by weight of an NMP solution of polyvinylidene fluoride (solid content: 6%) as a binder, and N-methyl-2 as a solvent were used. -Pyrrolidone (NMP) was prepared so as to have a mixing ratio of 55 parts by weight, and kneaded and dispersed using a planetary mixer according to the method shown in FIG. 1 to produce a negative electrode mixture.

(Example 2) First, the positive electrode material was used in Example 1.
It was produced in the same manner as described above.

Next, as the negative electrode material, 100 parts by weight of spheroidal graphite was used as the negative electrode active material, 4 parts by weight of vapor grown carbon fiber was used as the conductive additive, and 2-ethylhexyl acrylate and acrylic acid were used as the binder. 50 parts by weight of an acrylonitrile copolymer (solid content 8%), 55 parts by weight of N-methyl-2-pyrrolidone (NMP) as a solvent, and ethylene-vinyl alcohol copolymer (solids 10%) as a thickener
%) Was prepared so as to have a mixing ratio of 20 parts by weight.
The negative electrode mixture was produced by kneading and dispersing according to the method shown in (1).

(Example 3) First, the positive electrode material was prepared in the same manner as in Example 1.
It was produced in the same manner as described above.

Next, as the negative electrode material, 50 parts by weight of artificial bulk graphite as the negative electrode active material A, 50 parts by weight of multi-phase graphite as the negative electrode active material B, and an NMP solution of polyvinylidene fluoride (solid content of 4 parts) as a binder were used. .7%) to 86 parts by weight,
N-methyl-2-pyrrolidone (NMP) as a solvent
The mixture was prepared so as to have a mixing ratio of 6 parts by weight, and kneaded and dispersed according to the method shown in FIG. 3 to produce a negative electrode mixture.

(Example 4) First, the positive electrode material was prepared as in Example 1.
It was produced in the same manner as described above.

Next, as the negative electrode material, 70 parts by weight of artificial massive graphite as the negative electrode active material A, 30 parts by weight of mesophase carbon fiber as the negative electrode active material B, and an NMP solution of polyvinylidene fluoride (solid content 15%) as the binder were used. %) Is 27 parts by weight,
As a solvent, the weight ratio of acetone to cyclohexane is 3: 1.
Was prepared so as to have a mixing ratio of 95 parts by weight, and kneaded and dispersed according to the method shown in FIG. 3 to produce a negative electrode mixture.

(Comparative Example 1) First, a positive electrode material was prepared in Example 1.
It was produced in the same manner as described above.

Next, the negative electrode material was prepared so as to have the same mixing ratio as in Example 1, and kneaded and dispersed according to the method shown in FIG. 4 to produce a negative electrode mixture.

(Comparative Example 2) First, a positive electrode material was prepared in Example 1.
It was produced in the same manner as described above.

Next, the negative electrode material was prepared to have the same compounding ratio as in Example 2, and kneaded and dispersed according to the method shown in FIG. 6 to prepare a negative electrode mixture.

(Comparative Example 3) First, a positive electrode material was prepared in Example 1.
It was produced in the same manner as described above.

Next, a negative electrode material was prepared so as to have the same mixing ratio as in Example 3, and kneaded and dispersed according to the method shown in FIG. 5 to prepare a negative electrode mixture.

(Comparative Example 4) First, a positive electrode material was prepared in Example 1.
It was produced in the same manner as described above.

Next, the negative electrode material was prepared to have the same compounding ratio as in Example 4, and kneaded and dispersed according to the method shown in FIG. 5 to prepare a negative electrode mixture.

The positive electrode material mixture prepared in each of the examples and comparative examples was coated on both sides of a 15 μm-thick aluminum foil using a slit die coater, dried and roll-pressed to a predetermined size. By slitting, a positive electrode plate was produced.

Similarly, the negative electrode mixture prepared in each of the examples and comparative examples was coated on a copper foil having a thickness of 10 μm using a slit die coater on both sides, dried and roll-pressed. A negative electrode plate was produced by slitting to dimensions.

Next, a polyethylene separator having a thickness of 20 μm was arranged between the obtained positive electrode plate and negative electrode plate and wound to form an elliptical electrode plate group.

Further, the above-mentioned electrode plate group was set to a thickness of 5 mm and a width of 3 mm.
After the battery was inserted into an aluminum square battery can having a height of 0 mm and a height of 48 mm, the battery capacity was reduced to 70% by injecting an electrolyte.
A 0 mAh lithium ion battery was produced.

(Measurement of Bonding Strength) Using the negative electrode plate prepared as described above, the bonding strength between the copper foil as the current collector and the negative electrode mixture portion was peeled by 90 degrees in accordance with JIS K 6854. Was measured by

The size of the test piece was 12.65 ± width.
0.5 mm and the length of the bonded portion was 60 mm to 80 mm. Table 1 shows the measurement results.

[0052]

[Table 1]

As is clear from Table 1, each of the examples is excellent in kneading and dispersibility even with a small amount of the binder, and thus has a binding strength 1.5 times or more as compared with each of the comparative examples. Was.

The distribution of the binder in the negative electrode plate produced as described above was analyzed from the SEM photograph. Table 1 shows the results.
Shown in As is clear from Table 1, in each comparative example, 15 μm was used.
Although a lump of the binder was found to be more than m, no lump was found in each example, and it was found that the dispersibility of the binder was excellent.

(Discharge Rate Characteristics) A battery prepared as described above was heated at 20 ° C. and 4.2 V-CC / CV (max1 CmA).
(700 mA), 0.05 CmA (35 mA) cut)
Charge under the condition of 0.2 CmA (140 mA), 1 Cm
Table 1 also shows the results of discharge rate characteristics when discharging was performed at a constant current of A (700 mA) and 2 CmA (1400 mA) to a discharge end voltage of 3.0 V. As is clear from Table 1, it was found that each of the examples had better discharge rate characteristics than the comparative examples.

(Discharge Temperature Characteristics) The battery prepared as described above was heated at 20 ° C., 4.2 V-CC / CV (max 1 CmA,
0.05 CmAcut), -10 ° C, 0
℃, 10 ℃, 20 ℃, 45 ℃ each temperature conditions, 1Cm
Table 1 also shows the results of the discharge temperature characteristics when the battery was discharged to a discharge end voltage of 3.0 V at a constant current of A.
As is clear from Table 1, it was found that each of the examples had better discharge temperature characteristics than the comparative examples.

(Charge / Discharge Cycle Characteristics) The battery prepared as described above was charged at 20 ° C., 4.2 V-CC / CV (max1C
mA, 0.05 CmAcut), and charged for 20
Table 1 also shows the results of the charge-discharge cycle characteristics of discharging at a constant current of 1 CmA to a discharge cutoff voltage of 3.0 V at 1 ° C. As is clear from Table 1, it was found that each of the examples had better charge / discharge cycle characteristics than the comparative examples.

[0058]

As described above, the method for producing a negative electrode mixture and the nonaqueous secondary battery using the same according to the present invention provide a negative electrode mixture excellent in kneading and dispersing even with a small amount of a conductive auxiliary material and a binder. Since it is a manufacturing method, it is possible to obtain an electrode plate having excellent electrode plate strength, and it is extremely useful for obtaining a high-capacity, small-sized and lightweight non-aqueous secondary battery having excellent battery characteristics.

[Brief description of the drawings]

FIG. 1 is a kneading process diagram according to the present invention.

FIG. 2 is another kneading process diagram according to the present invention.

FIG. 3 is another kneading process diagram according to the present invention.

FIG. 4 is a kneading process diagram according to a conventional example.

FIG. 5 is another kneading process diagram according to a conventional example.

FIG. 6 is another kneading process diagram according to a conventional example.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuyuki Shimizu 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F-term (reference) 5H050 AA08 AA19 BA17 CA08 CA09 DA03 DA10 DA11 EA10 EA24 EA28 GA02 GA10 GA22 HA01

Claims (4)

[Claims] 1. A wet dispersion step of adding and dispersing a solvent to at least a negative electrode active material, and kneading and dispersing a binder solution in which a binder is previously dispersed in a solvent to the wet dispersion. A method for producing a negative electrode mixture for a non-aqueous secondary battery, comprising the steps of: 2. The method for producing a negative electrode mixture for a non-aqueous secondary battery according to claim 1, further comprising a dry step of mixing at least a negative electrode active material and a conductive additive in a dry manner before the wet dispersion step. 3. The non-aqueous secondary battery according to claim 1, wherein in the wet dispersion step, 30 to 80 parts by weight of a solvent is added to the total amount of the solvent contained in the negative electrode mixture to perform wet dispersion. Of producing negative electrode mixture for automotive use. 4. An electrode plate wherein a negative electrode plate and a positive electrode plate obtained by applying and drying a negative electrode mixture according to any one of claims 1 to 3 on a current collector are wound or laminated via a separator. A non-aqueous secondary battery in which a group is stored in a battery case.