JP2006310120A - Manufacturing method of paste of electrode for lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that, when electrode plate paste is defoamed under high vacuum, a solvent in the paste starts to be evaporated, coagulation takes place in the paste, and, therefore, an appearance defect ratio of electrode plates is high. <P>SOLUTION: The manufacturing method of paste for an electrode for a lithium-ion secondary battery of forming an active material layer by coating paste consisting of an active material, a binder, a conductive agent, and a solvent on a collector and drying it, comprises a process of kneading the active material, binder, conductive agent and solvent into paste, a process of putting the paste under a vacuum defoaming treatment, and further, a process of stirring the paste while adding ultrasonic waves to it. The process of the vacuum defoaming treatment is carried out at a vacuum degree of 100 torr or more. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a lithium ion secondary battery, and to a method for manufacturing a paste for an electrode plate.

  In recent years, consumer electronic devices such as AV devices, notebook computers, and portable communication devices have been rapidly becoming portable and cordless. Conventionally, nickel cadmium storage batteries and nickel have been used as power sources for driving these electronic devices. Although hydrogen storage batteries were mainly used, demands for higher energy density and smaller and lighter secondary batteries that serve as driving power sources are increasing as electronic devices become more portable and more cordless. It is getting stronger.

Under such circumstances, a carbon material capable of occluding and releasing lithium ions is used as the negative electrode active material, and a lithium-containing composite oxide exhibiting a high charge / discharge voltage, for example, lithium cobaltate (LiCoO ₂ ) is used as the positive electrode active material. Lithium secondary batteries represented by lithium ion secondary batteries using insertion and removal of lithium ions are becoming mainstream.

  This lithium secondary battery has extremely remarkable features such as being small and lightweight, capable of rapid charging, and having a high energy density. The essential positive electrode plate and negative electrode plate are used as a current collector. The electrode paste is applied and dried.

  When producing a paste for an electrode plate for a lithium ion secondary battery, if the paste is applied on the current collector in a state where air bubbles are present in the paste, the air bubbles concentrate on the surface of the electrode plate after drying.

  As a result, defects are generated on the surface of the electrode plate.

  Therefore, in order to reliably remove bubbles from the electrode plate paste, it has been proposed to knead under a high vacuum of 10 torr or less in the final process of manufacturing the electrode plate paste (see, for example, Patent Document 1). ).

In addition, in order to uniformly disperse the fluororesin in the paste used for the nickel metal hydride storage battery, dispersion using ultrasonic waves has been proposed (for example, see Patent Document 2).
Japanese Patent Laid-Open No. 11-213990 JP 2001-291509 A

  However, when the electrode plate paste is degassed under high vacuum as in Patent Document 1 described above, the solvent contained in the electrode plate paste is volatilized. In order to perform defoaming effectively, defoaming is performed while stirring or shaking. However, in order to reduce the entrapment of bubbles, it was not possible to stir or shake with low shear. The reason is that the electrode plate paste may aggregate.

  Further, Patent Document 2 described above uses ultrasonic waves in order to uniformly disperse a fluororesin used as a binder in the field of nickel metal hydride storage batteries. In this document, it has not been studied as a solution to the problem of degassing bubbles contained in the electrode plate paste and reaggregation of active materials.

  The present invention solves such a conventional problem, and it is possible to defoam bubbles without volatilizing the solvent in the electrode plate paste, and even if the electrode plate paste is stirred with low shear, an active material, etc. The present invention provides a method for producing an electrode plate paste for a lithium ion secondary battery that does not cause agglomeration.

  In order to solve the above-mentioned conventional problems, the method for producing a paste for an electrode plate for a lithium secondary battery according to the present invention comprises applying a paste comprising an active material, a binder, a conductive agent, and a solvent to a current collector and drying. A paste manufacturing method for an electrode plate for a lithium ion secondary battery that forms an active material layer, the step of kneading the active material, the binder, the conductive agent, and the solvent into a paste; The process includes a step of vacuum defoaming the paste and a step of stirring the paste while applying ultrasonic waves. The vacuum defoaming step has a degree of vacuum of 100 torr or more.

  By using the paste manufacturing of the electrode plate for a lithium secondary battery of the present invention, bubbles can be degassed without volatilizing the solvent in the electrode plate paste, and the ultrasonic wave is applied to the electrode plate paste while reducing the bubbles. Even if stirring is performed by shearing, the active material and the like are not aggregated, so that defects on the surface of the electrode plate due to bubbles and streaks and protrusions on the surface of the electrode plate due to aggregation can be suppressed. By doing so, an electrode plate for a lithium ion secondary battery with few appearance defects can be obtained.

  According to the present invention, bubbles can be degassed without volatilizing the solvent in the electrode plate paste, and even if the electrode plate paste is stirred with low shear, the active material and the like are not aggregated. It is possible to suppress streaks and protrusions on the surface of the electrode plate due to defects or aggregation on the surface of the electrode plate. As a result, an electrode plate for a lithium ion secondary battery with few appearance defects can be obtained.

The method for producing a paste for an electrode plate for a lithium ion secondary battery according to the present invention comprises applying a paste comprising an active material, a binder, a conductive agent, and a solvent to a current collector and drying to form an active material layer. A method for producing a paste for an electrode plate for a secondary battery, the step of kneading the active material, the binder, the conductive agent, and the solvent into a paste, and the step of subjecting the paste to a vacuum defoaming process. ,
Furthermore, it comprises a step of stirring while applying ultrasonic waves to the paste, and the step of performing the vacuum defoaming treatment has a degree of vacuum of 100 torr or more.

  In the defoaming process, air bubbles contained in the electrode plate paste are degassed, so that when the electrode plate paste is applied on the current collector and dried to form an active material layer, defects on the electrode plate surface are suppressed. Therefore, an electrode plate with few appearance defects can be obtained.

  By adding ultrasonic waves to the electrode plate paste, aggregation of the active material or the like can be suppressed even if stirring is performed with low shear. Agitation of the electrode plate paste with high shear can suppress aggregation of the active material and the like, but bubbles are embraced in the electrode plate paste during stirring, and efficient defoaming cannot be performed.

  When the electrode plate paste is degassed at a degree of vacuum less than 100 torr, the solvent contained in the electrode plate is volatilized, and the viscosity and solid content of the electrode plate paste change. Therefore, the degree of vacuum needs to be 100 torr or more.

  In the paste manufacturing method for an electrode plate for a lithium ion secondary battery according to a preferred embodiment of the present invention, the ultrasonic wave preferably has a frequency of 5 to 40 kHz and an amplitude of 10 to 100 μm.

  When the frequency is smaller than 5 kHz or the amplitude is smaller than 10 μm, the ability to disperse the electrode plate paste is insufficient, and when the frequency is larger than 40 kHz or larger than the amplitude of 100 μm, the ultrasonic equipment becomes large and is practically used. Have difficulty. Therefore, it is preferable that the ultrasonic wave has a frequency of 5 to 40 kHz and an amplitude of 10 to 100 μm.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic sectional view of the electrode plate.

  For the positive electrode plate, a positive electrode plate having the positive electrode active material layer 1 is produced by applying a paste containing a positive electrode active material and a binder to the positive electrode current collector 2, drying, and pressing.

  Next, the negative electrode plate is prepared by applying a paste containing a negative electrode active material and a binder to the negative electrode current collector 4, drying, and pressing to produce a negative electrode plate having the negative electrode active material layer 3.

  As the positive electrode current collector 2, a foil made of aluminum (hereinafter abbreviated as Al), a foil subjected to lath processing, or a foil subjected to etching processing can be used. The thickness of the positive electrode current collector is preferably 10 to 60 μm.

As the positive electrode active material, a lithium-containing transition metal compound that can accept lithium ions as a guest can be used. For example, at least one metal selected from cobalt, manganese, nickel, chromium, iron and vanadium and a composite metal oxide of lithium, LiCoO ₂ , LiMoO ₂ , LiNiO ₂ , LiCo _x Ni _(1-x) O ₂ (0 <X <1) LiCrO ₂ , αLiFeO ₂ , LiVO _{2 and the} like are preferable.

  The binder is not particularly limited as long as it can be kneaded and dispersed in a solvent. For example, a fluorine-based binder, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber (hereinafter abbreviated as SBR). ), An acrylic polymer, a vinyl polymer or the like can be used alone or as a mixture or copolymer of two or more. Examples of the fluorine-based binder include a polyvinylidene fluoride (hereinafter abbreviated as PVDF), a copolymer P (VDF-) of vinylidene fluoride (hereinafter abbreviated as VDF) and hexafluoropropylene (hereinafter abbreviated as HFP). A dispersion of HFP) or polytetrafluoroethylene (hereinafter abbreviated as PTFE) resin is preferable.

  As the conductive agent, acetylene black (hereinafter abbreviated as AB), graphite, carbon fiber or the like is used alone, or a mixture of two or more kinds is preferable.

  As the thickener, ethylene-vinyl alcohol copolymer, carboxyl methyl cellulose, methyl cellulose and the like are preferable, and as the plasticizer, diisobutyl phthalate, diethyl phthalate, di-n-butyl phthalate, dipropyl phthalate, dihexyl phthalate and the like The phthalate ester is preferred.

As the solvent, a solvent that can dissolve the binder is suitable.
In the case of an organic binder, N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide, dimethylsulfoxide, hexamethylsulfoxide, hexamethylsulfuramide, An organic solvent such as tetramethylurea, acetone, and methyl ethyl ketone (hereinafter abbreviated as MEK) alone or a mixed solvent obtained by mixing them is preferable.
In the case of an aqueous binder, water or warm water is preferred.

  Further, when kneading or dispersing the paste for the electrode plate, various dispersants, surfactants, stabilizers and the like can be added as necessary.

  As the negative electrode current collector, a copper foil, a lathed foil, or an etched foil can be used. The thickness of the negative electrode current collector is preferably 10 to 50 μm.

Examples of the negative electrode active material include graphite, activated carbon, or a baked carbonized phenol resin or pitch.
In particular, from the viewpoint of the safety and cycle life characteristics of a lithium ion secondary battery, a carbon material having a graphite-type crystal structure with a lattice plane (002) spacing (d ₀₀₂ ) of 3.350 to 3.400 mm is used. preferable.

  As the binder, the conductive agent, the thickener, and the plasticizer that can be added as necessary, the same as the positive electrode can be used.

  The present invention will be described in detail using examples and comparative examples, but these do not limit the present invention.

(Example 1)
Spherical graphite as a negative electrode active material, vapor grown carbon fiber as a conductive agent, P (VDF-HFP) as a binder, and phthalate-n-dibutyl (hereinafter abbreviated as DBP) as a plasticizer mixed in acetone as a solvent. A smelted and dispersed negative electrode paste was prepared.

  In the final stage of the kneading and dispersion, a vacuum of 100 torr was applied while stirring at 500 rpm for 10 minutes for defoaming, and ultrasonic waves with an amplitude of 30 μm and a frequency of 20 kHz were added. This paste was applied as a current collector to both sides of a copper foil having a thickness of 10 μm, dried, and then pressed to prepare a negative electrode plate having the negative electrode active material layer 3.

(Example 2)
A negative electrode plate similar to that of Example 1 was produced except that a vacuum of 200 torr was applied while stirring at 200 rpm for 10 minutes for defoaming, and ultrasonic waves having an amplitude of 30 μm and a frequency of 20 kHz were added.

(Comparative Example 1)
For defoaming, a vacuum of 10 torr was applied while stirring at 1500 rpm for 10 minutes, but a negative electrode plate similar to that of Example 1 was prepared except that no ultrasonic wave was applied.

(Comparative Example 2)
In order to remove bubbles, a vacuum of 100 torr was obtained while stirring at 200 rpm for 10 minutes, but a negative electrode plate similar to that of Example 1 was produced except that no ultrasonic wave was added.

(Examples 3 to 7)
A negative electrode plate similar to that of Example 1 was prepared except that a vacuum of 100 torr was applied while stirring at 200 rpm for 10 minutes for defoaming, and ultrasonic waves having a frequency and an amplitude of 50 μm shown in Table 2 were added.

(Examples 8 to 12)
A negative electrode plate similar to that of Example 1 was prepared except that a vacuum of 100 torr was applied while stirring at 200 rpm for 10 minutes for defoaming, and ultrasonic waves having an amplitude and a frequency of 30 kHz shown in Table 3 were added.

  About the negative electrode plate produced in Examples 1-12 and Comparative Examples 1 and 2, it confirmed about the volatilization of a solvent, the external appearance of an electrode plate, and the presence or absence of granulation of an electrode plate paste.

  Each evaluation method is shown below.

  The method for evaluating the volatilization of the solvent was confirmed visually, and in an apparatus for kneading the electrode plate paste, it was confirmed whether or not the solvent was attached to the upper part of the upper end of the kneading pot.

  The evaluation method of the appearance of the electrode plate was confirmed visually.

  The defect rate was calculated by dividing the number of appearance defects of the electrode plate by the total production number.

  The evaluation method of granulation of the electrode plate paste is as follows.

  Using a particle gauge device, which is a device for measuring the size of grains in the electrode plate paste, the electrode plate paste was dropped onto a predetermined place of the particle gauge device, and the dropped electrode plate paste was drawn with a flat metal spatula. . At that time, the scale of the grain gauge device where the streak was observed was read, and the grain size was measured. A case where grains of 30 μm or more were confirmed using this grain gauge device was regarded as defective.

Tables 1 to 3 show the evaluation results for the presence or absence of volatilization of the solvent, the appearance defect rate of the electrode plate, and the presence or absence of granulation of the electrode plate paste by the method as described above.

From the results in Table 1, Examples 1 and 2 to which ultrasonic waves were added had a lower appearance defect rate of the electrode plate than Comparative Example 2 to which no ultrasonic waves were added.

  In Comparative Example 1 in which ultrasonic waves were not added, the degree of vacuum at the time of defoaming was 10 torr, and stirring was performed with high shear, the solvent in the electrode paste was volatilized.

  Moreover, since stirring was performed with high shear (the number of revolutions during defoaming was 1500 rpm), the defoaming could not be sufficiently achieved with a stirring time of 10 minutes, resulting in a high appearance defect rate of the electrode plate.

  From this, it can be said that by adding ultrasonic waves, even when the degree of vacuum at the time of defoaming is 100 torr, the volatilization of the solvent is suppressed, and defoaming can be efficiently performed in a short time.

  From the results shown in Table 2, Example 3 with an ultrasonic frequency of 3 kHz could not suppress granulation of the electrode plate paste, and the appearance defect rate of the electrode plate increased.

  In Example 7 with an ultrasonic frequency of 50 kHz, granulation of the electrode plate paste could be suppressed, and the appearance defect rate of the electrode plate was as low as 0.01%.

  However, if the ultrasonic frequency exceeds 40 kHz, the ultrasonic equipment becomes too large, which is not suitable from the viewpoint of productivity.

  From this, it can be said that the frequency of the ultrasonic wave is preferably 5 to 40 kHz.

  From the results in Table 3, Example 8 having an ultrasonic amplitude of 5 μm could not suppress granulation of the electrode plate paste, and the appearance defect rate of the electrode plate was high.

  In Example 12 having an ultrasonic amplitude of 200 μm, granulation of the electrode plate paste could be suppressed, and the appearance defect rate of the electrode plate was as low as 0.01%.

  However, when the frequency exceeds 40 kHz, the ultrasonic equipment becomes too large, which is unsuitable from the viewpoint of productivity.

  From this, it can be said that the ultrasonic amplitude is preferably 10 to 100 μm.

  Therefore, from the results in Tables 2 and 3, it can be said that the ultrasonic wave preferably has a frequency of 5 to 40 kHz and an amplitude of 10 to 100 μm.

As described above, according to the method for producing a paste of the present invention, it is possible to provide a method for producing an electrode plate that can perform sufficient defoaming without increasing the degree of vacuum and the number of rotations, and has less appearance defect of the electrode plate. it can.

  The paste production method according to the present invention enables efficient defoaming and is useful in the field of producing lithium ion secondary battery plates.

Schematic sectional view of an electrode plate according to the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode collector 2 Positive electrode active material 3 Negative electrode collector 4 Negative electrode active material layer 5 Separator

Claims (2)

A paste manufacturing method for an electrode plate for a lithium ion secondary battery, wherein a paste comprising an active material, a binder, a conductive agent, and a solvent is applied to a current collector and dried to form an active material layer,
Kneading the active material, the binder, the conductive agent, and the solvent into a paste;
Vacuum defoaming the paste; and
Furthermore, it comprises a step of stirring while adding ultrasonic waves to the paste,
The vacuum defoaming process includes:
A method for producing a paste for an electrode plate for a lithium ion secondary battery having a degree of vacuum of 100 torr or more. The method for producing a paste for an electrode plate for a lithium ion secondary battery according to claim 1, wherein the ultrasonic wave has a frequency of 5 to 40 kHz and an amplitude of 10 to 100 μm.