JP2009032427A - Method of manufacturing electrode for lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problems: in preparation of porous film slurry, when solid content concentration is increased or treatment amount per once is increased, a load is increased and dispersion is made impossible. <P>SOLUTION: In a method of manufacturing an electrode for a lithium ion secondary battery containing at least a step of forming a porous film layer comprising an inorganic oxide fillers and a binder by adhesion on at least one of a positive electrode made of a composite lithium oxide and a negative electrode made of a lithium-retainable material, the step of forming the porous film layer by adhesion is that the inorganic oxide fillers are dispersed in paste comprising the inorganic oxide fillers, the binder and an organic solvent which is a dispersing medium by applying ultrasonic vibration and the porous film slurry for the lithium ion secondary battery is prepared. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing an electrode for a lithium ion secondary battery, and more particularly to a method for dispersing the porous membrane slurry.

In a chemical battery such as a lithium ion secondary battery, there is a separator between a positive electrode and a negative electrode that electrically insulates each electrode plate and further holds an electrolytic solution. Currently, microporous thin film sheets mainly made of polyethylene are used in lithium ion secondary batteries.
However, sheet-like separators made of these resins generally tend to shrink at low temperatures, so that when the sharply shaped protrusion such as an internal short circuit or a nail penetrates the battery, the short circuit part is caused by the short-circuit reaction heat that occurs instantaneously. It had the problem of expanding and generating much more heat of reaction and promoting abnormal overheating.

  Therefore, in order to improve safety including the above-mentioned problems, a technique for forming a porous film layer containing a resin binder and solid particles such as alumina on either the positive or negative electrode has been proposed (for example, Patent Documents). 1).

Among them, in order to provide a lithium-ion secondary battery that achieves both high safety and good discharge characteristics due to the porous membrane layer, medialess dispersion, especially high-speed rotary shear type devices and high-speed rotary type devices using centrifugal fields are used. A method for preparing a porous membrane slurry has been proposed (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 07-220759 International Publication No. 2005/124899 Pamphlet

  However, when a porous membrane slurry is prepared based on Patent Document 2, since it contains many inorganic oxide fillers, it cannot be dispersed when the solid concentration increases. Further, if it is attempted to increase the amount of processing per one time, it is necessary to increase the size of the rotor blades. Therefore, the load on the rotating shaft becomes high and cannot be dispersed, so that a large facility is required.

  This invention solves the said subject, and it aims at providing the method of producing a porous membrane slurry continuously and efficiently.

  In the method for producing an electrode for a lithium ion secondary battery of the present invention, a porous film layer composed of an inorganic oxide filler and a binder is bonded to at least one of a positive electrode and a negative electrode. Ultrasonic waves are used as the creation method.

  Also, at this time, by applying the ultrasonic wave having a frequency of 10 to 30 kHz and a vibration amplitude of 20 to 40 μm while flowing the slurry prepared by simply stirring with a disper or the like at a speed of 0.5 to 2.0 L / min. It is preferable to disperse continuously.

  As described above, according to the present invention, a porous membrane slurry can be continuously and efficiently produced.

  Preferred embodiments of the present invention are shown below.

  According to the first aspect of the present invention, there is provided a porous film comprising an inorganic oxide filler and a binder on at least one of a positive electrode made of a composite lithium oxide and a negative electrode made of a material capable of holding lithium. In the method of manufacturing an electrode for a lithium ion secondary battery including at least a step of forming an adhesive layer, the step of forming the adhesive layer includes an inorganic oxide filler, a binder, and an organic solvent serving as a dispersion medium. This is a step of applying ultrasonic vibration to the paste to disperse the inorganic oxide filler to form a porous membrane slurry for a lithium ion secondary battery to form a porous membrane layer.

  First, the porous membrane layer, which is the gist of the present invention, must be bonded to one of the positive and negative electrodes described in detail below.

  As the binder constituting the porous film, one having heat resistance and electrolytic solution resistance is used. As the binder, for example, a fluororesin can be used. As the fluororesin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or the like can be used. Moreover, a polyacrylic acid derivative, a polyacrylonitrile derivative, etc. can also be used for a binder. The polyacrylic acid derivative or polyacrylonitrile derivative preferably contains at least one selected from the group consisting of an ethyl acrylate unit, a methyl methacrylate unit, and an ethyl methacrylate unit. Polyethylene, styrene-butadiene rubber, etc. can also be used. These may be used alone or in combination of two or more. Among these, a polymer containing an acrylonitrile unit, that is, a polyacrylonitrile derivative is particularly preferable. When such a material is used as a binder, the porous film is given more flexibility, and thus the porous film is less likely to be cracked or peeled off.

  What is used as a filler in the porous membrane layer must be an inorganic oxide. Various resin fine particles are also commonly used as fillers, but they need heat resistance and must be electrochemically stable within the range of use of lithium ion secondary batteries. As a material suitable for the above, an inorganic oxide is most preferable.

Moreover, it is more preferable that the content rate which occupies for a porous membrane layer is 50 to 99 weight part. When the amount of the binder is less than 50 parts by weight, it becomes difficult to control the pore structure formed by the gaps between the alumina, and when the amount of the binder is more than 99 parts by weight, the adhesion of the porous membrane layer is lowered. This is because loss of function is caused by dropout. This inorganic oxide may be used as a mixture of a plurality of types or in multiple layers. The filler shape is not limited to a spherical shape, and is not particularly limited as long as the bulk density is 0.01 to 0.8 g / cm ³ . For example, it is one of preferred embodiments to obtain a porous film layer having a high porosity by using a secondary particle shape in which primary particles are aggregated, a multiparticle shape, a resin shape, a cage shape, a cluster shape, or a whisker shape. is there.

  Although the thickness of this porous membrane layer is not specifically limited, 0.5-20 micrometers is preferable from the point which ensures high capacity | capacitance, exhibiting the effect of a porous membrane layer.

For the positive electrode, lithium cobaltate as an active material (LiCoO ₂₎ or a modified product thereof (aluminum (Al), magnesium (Mg), such as those obtained by eutectic), lithium nickel oxide (LiNiO ₂₎ or modifications thereof (an Composite oxides such as lithium manganate (LiMnO ₂ ) and modified products thereof.

  As the first binder, polytetrafluoroethylene (PTFE) and modified acrylonitrile rubber particle binder (such as BM-500B manufactured by Nippon Zeon Co., Ltd.), carboxymethyl cellulose having a thickening effect (hereinafter abbreviated as CMC), It may be combined with polyethylene oxide (PEO) and soluble modified acrylonitrile rubber (such as BM-720H manufactured by Nippon Zeon Co., Ltd.). Moreover, you may use the polyvinylidene fluoride (PVDF) which has both the characteristics of a binding property and a viscosity increase, and its modified body individually or in combination. As the conductive agent, acetylene black, ketjen black, and various graphites may be used alone or in combination.

  For the negative electrode, various natural graphite, artificial graphite, silicon-based composite materials such as silicide, and various alloy composition materials can be used as the active material. As the first binder, various binders such as PVDF and modified products thereof can be used. However, from the viewpoint of improving lithium ion acceptability as described above, it is more preferable to use a styrene-butadiene rubber (SBR) resin or a modified product thereof in combination with a cellulose resin such as CMC, or to add a small amount. .

  According to a second aspect of the present invention, in the method for manufacturing an electrode for a lithium ion secondary battery according to the first aspect, the ultrasonic vibration has a frequency of 10 to 30 kHz and an amplitude of 20 to 40 μm. is there.

  According to a third aspect of the present invention, in the method for manufacturing an electrode for a lithium ion secondary battery according to the first aspect, the adjustment of ultrasonic vibration is performed by changing the number of ultrasonic transmitters. Is.

  Hereinafter, it demonstrates in detail using an Example.

Example 1
Alumina 950g of bulk density 0.01 g / cm ^3, Nippon Zeon Co., Ltd. of polyacrylonitrile modified rubber binder BM-720H (solids 8 parts by weight) 625 g and the appropriate amount of NMP to a solid concentration of 40% At the same time, the mixture was stirred with a homodisper to prepare a primary slurry. While flowing this slurry at a speed of 1.0 L / min, a secondary slurry was prepared by applying ultrasonic waves having a frequency of 20 kHz and a vibration amplitude of 30 μm. Similarly, up to 10 passes, slurry samples were taken in 1, 2, 3, 4, 6, 8, and 10 passes. Since the primary paste produced by the homodisper was continuously dispersed by flowing it, there was no influence of the charged amount, so a small amount of slurry was used.

(Example 2)
While flowing the primary slurry at a speed of 1.0 L / min, a secondary slurry was prepared by applying ultrasonic waves having a frequency of 20 kHz and a vibration amplitude of 20 μm. Thereafter, a slurry sample was collected in the same manner as described above.

(Example 3)
While flowing the primary slurry at a speed of 1.0 L / min, a secondary slurry was prepared by applying ultrasonic waves having a frequency of 20 kHz and a vibration amplitude of 40 μm. Thereafter, a slurry sample was collected in the same manner as described above.

Example 4
950 g of alumina having a bulk density of 0.01 g / cm ³ is mixed with 625 g of polyacrylonitrile-modified rubber binder BM-720H (solid content 8 parts by weight) manufactured by Nippon Zeon Co., Ltd. and an appropriate amount of NMP so that the solid content concentration is 50%. At the same time, the mixture was stirred with a homodisper to prepare a primary slurry. This slurry was treated in the same manner as in Example 1 to produce a slurry.

(Comparative Example 1)
Appropriate amount of 19 kg of alumina having a bulk density of 0.01 g / cm ^{3 so that} the polyacrylonitrile modified rubber binder BM-720H (solid content 8 parts by weight) 12.5 kg and solid content concentration of 40% by Nippon Zeon Co., Ltd. The slurry was collected by stirring at 8,400 rpm for 15, 30, 45, 60, and 75 minutes using a high-speed rotating stage type device (blade diameter φ70) together with NMP.

(Slurry preparation method before improvement)
(Comparative Example 2)
The material in Comparative Example 1 was stirred at 6,400 rpm for 15, 30, 45, 60, and 75 minutes using a high-speed rotary shear type apparatus (blade diameter φ70), and each slurry was collected. At 9000 rpm, the motor load was exceeded and stirring was not possible (Comparative Example 3).
An appropriate amount of 19 kg of alumina having a bulk density of 0.01 g / cm ³ is 12.5 kg of polyacrylonitrile modified rubber binder BM-720H (8 parts by weight of solids) manufactured by Nippon Zeon Co., Ltd. and the solids concentration is 50%. Along with NMP, an attempt was made to stir at 8400 rpm using a high-speed rotating stage device (blade diameter φ70), but the load was exceeded, so stirring was performed at 6400 rpm for 90 minutes.

(Comparative Example 4)
In order to increase the processing capacity, the blade diameter of the high-speed rotating stage type apparatus was changed to φ95, and a paste was prepared in the same manner as in Comparative Example 2. However, the rotational speed was adjusted to the peripheral speed of the blades of Comparative Example 2 and exceeded the motor load at 6200 rpm, so stirring was performed at 5700 pm which satisfied the load.

(Comparative Example 5)
While flowing the primary slurry prepared in Example 1 at a speed of 1.0 L / min, a secondary slurry was prepared by applying ultrasonic waves having a frequency of 5 Hz and an amplitude of 10 μm. Thereafter, a slurry sample was collected in the same manner as described above.

(Comparative Example 6)
While flowing the primary slurry prepared in Example 1 at a speed of 1.0 L / min, a secondary slurry was prepared by applying ultrasonic waves having a frequency of 40 Hz and an amplitude of 50 μm. However, after the third pass, the dispersion progressed rapidly, so the resonance point shifted and no transmission occurred.

<Evaluation method and results>
These slurries were evaluated by the methods shown below. The results are shown in Tables 1 and 2. The completed slurry was applied onto a metal foil with a doctor blade, and then the coating film was dried at 120 ° C. for 1 hour to obtain a porous film test piece.

Next, the true volume V1 including no void and the apparent volume V2 including the void are measured for the test piece of the porous film, and the porosity P is expressed by the following formula:
P (%) = {(V2−V1) / V2} × 100
Calculated from

  This time, a product with a porosity of 46 to 48% was judged as a good product.

  As can be seen from Table 1, Example 1 has four or more passes, and even in Examples 2 and 3 in which the amplitude was changed, the number of passes reached could be obtained, but a paste having a non-defective porosity could be obtained. Further, in Example 4 in which the solid content concentration was changed, the number of passes was increased as compared with Example 1, but a paste that was a non-defective product could be produced.

  As is clear from Table 2, a high-quality rotary shear type apparatus could not produce a good-quality porosity paste when the rotational speed was lowered. In addition, when the solid content increases as in Comparative Example 3 and the blade diameter increases as in Comparative Example 4, the current motor cannot apply the required number of rotations to the paste, and the porosity paste is a good product. Could not create.

Since the embodiment has no influence on the processing amount as described in the first embodiment, it can be prepared by continuously flowing a separately prepared primary slurry. Can be created. (60 liters of slurry can be made in 60 minutes.)
Even in Comparative Example 1, it is possible to produce a good slurry if it takes 60 minutes or more, but the paste that can be produced in 60 minutes is 30 liters. Even if it is attempted to obtain the same productivity as that of the example, the rotational speed cannot be increased as in the comparative example 2, so that the example is preferable from the viewpoint of productivity.

As is apparent from Table 3, when the frequency and amplitude are lowered, the dispersion becomes gradual.
I couldn't make a good paste even in the pass. Further, when the frequency and amplitude were increased, the dispersion was excessive and the product was out of the good product range.

  The lithium ion secondary battery of the present invention is useful as a portable power source having excellent safety.

Claims (3)

At least one of a positive electrode made of a composite lithium oxide and a negative electrode made of a material capable of holding lithium is bonded to a porous membrane layer made of an inorganic oxide filler and a binder. In the method for producing the secondary battery electrode,
The step of bonding and forming the porous membrane layer includes a step of dispersing the inorganic oxide filler by applying ultrasonic vibration to a paste made of an inorganic oxide filler and a binder and an organic solvent that serves as a dispersion medium. A method for producing an electrode for a lithium ion secondary battery, which is a step of forming a porous membrane slurry for forming a porous membrane layer.   The method of manufacturing an electrode for a lithium ion secondary battery according to claim 1, wherein the ultrasonic vibration has a frequency of 10 to 30 kHz and an amplitude of 20 to 40 µm. 2. The method for producing an electrode for a lithium ion secondary battery according to claim 1, wherein the physical properties of the slurry produced using the ultrasonic vibration are controlled by changing the number of ultrasonic transmitters.