JP2015088314A - Method of producing paste for electrode of secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing the paste for electrode of a secondary battery which allows for reduction of the amount of bubbles, regardless of the production conditions.SOLUTION: A method of producing the paste for electrode of a secondary battery sequentially includes step (A) for reducing the dissolved oxygen in a dispersion medium, step (B) for kneading the raw material of paste for electrode containing an electrode active material and a dispersion medium, and step (C) for removing bubbles in the paste for electrode, by supplying the paste for electrode under vacuum pressure of -85 kPa or less (the vacuum pressure is a gauge pressure for making the atmospheric pressure to 0 kPa).

Description

  The present invention relates to a method for producing an electrode paste for a secondary battery.

Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries are used in applications such as hybrid vehicles (HV), plug-in hybrid vehicles (PHV), and electric vehicles (EV).
A nonaqueous electrolyte secondary battery includes a positive electrode and a negative electrode that are a pair of electrodes, a separator that insulates between them, and a nonaqueous electrolyte.

As a structure of the electrode (positive electrode or negative electrode) for the nonaqueous electrolyte secondary battery, a laminated structure including a current collector and an electrode active material layer (positive electrode active material layer or negative electrode active material layer) formed thereon is used. Are known.
The positive electrode active material layer includes, for example, a positive electrode active material such as a lithium-containing composite oxide, a conductive assistant such as carbon powder, a binder such as polyvinylidene fluoride (PVDF), and N-methyl-2-pyrrolidone (NMP). A paste containing a dispersion medium is applied onto a current collector such as an aluminum foil, dried, and pressed to form.
The negative electrode active material layer includes, for example, a negative electrode active material such as graphite, a binder such as modified styrene-butadiene copolymer latex (SBR), a thickener such as carboxymethyl cellulose Na salt (CMC), and a dispersion medium such as water. The paste containing is applied onto a current collector such as copper foil, dried, and pressed to form.

Usually, the above-mentioned electrode paste is manufactured by mixing the active material and other solid components, and then kneading the obtained mixed powder and a dispersion medium such as NMP or water.
The electrode paste after kneading usually contains bubbles. If the electrode paste containing bubbles is applied as it is onto the current collector, the active material or the like is not applied to the bubble portions, resulting in defects. Therefore, a defoaming step for removing bubbles in the electrode paste is performed after the kneading step.

  For example, Patent Document 1 discloses a lithium ion secondary having a defoaming step of defoaming a paste at a vacuum degree of 100 torr or more (a vacuum pressure of 13.3 kPa or more) and a step of stirring while adding ultrasonic waves to the paste. A battery electrode paste manufacturing method is disclosed (claim 1).

In the defoaming step, for example, after a container such as a tank (defoaming tank) containing paste is sealed, the gas in the container is extracted to obtain a desired vacuum pressure and set for a predetermined time. By doing so, bubbles in the paste rise and are removed from the paste and removed.
In Patent Document 1, in order to suppress the volatilization of the dispersion medium in the paste in the defoaming step, the degree of vacuum in the defoaming step is set to a high value of 100 torr or more (paragraph 0018).
In Examples 1 to 12 of Patent Document 1, the degree of vacuum in the defoaming process is set to 100 torr or 200 torr.
Note that the degree of vacuum described in Patent Document 1 is expressed in absolute pressure (absolute vacuum is 0 torr and atmospheric pressure is 760 torr).

JP 2006-310120 A

  By carrying out the high-vacuum defoaming step, it is possible to satisfactorily remove bubbles mixed in the paste during kneading. However, as a result of examination by the present inventors, it was found that a small amount of dissolved oxygen contained in the dispersion medium becomes new bubbles in the high-vacuum defoaming process, which may lead to poor coating during paste coating. . If the degree of vacuum in the defoaming step is lowered, the generation of new bubbles due to dissolved oxygen contained in the dispersion medium is suppressed, but there is a risk that the removal of bubbles mixed during kneading may be insufficient.

Moreover, in order to shorten the drying process after applying the paste to the current collector, it is preferable that the amount of the dispersion medium in the paste is small. However, if the amount of the dispersion medium in the paste is reduced, the paste viscosity increases, so that it is difficult to satisfactorily remove bubbles mixed during kneading in the defoaming step.
Further, as the amount of paste manufactured at one time in the kneading step or the amount of paste processed at one time in the defoaming step increases, it becomes more difficult to remove bubbles mixed during kneading.

  The above-mentioned problem is not limited to non-aqueous electrolyte secondary batteries, and is the same in the manufacture of electrode pastes for all secondary batteries.

This invention is made | formed in view of the said situation, and it aims at providing the manufacturing method of the paste for electrodes of the secondary battery which can reduce the amount of bubbles irrespective of manufacturing conditions. .
Here, the production conditions include the amount of dissolved oxygen in the dispersion medium, the solid content of the paste, the amount of paste produced at one time in the kneading step, or the amount of paste processed at one time in the defoaming step.

The manufacturing method of the paste for the electrode of the secondary battery of the present invention,
A method for producing an electrode paste for a secondary battery comprising an electrode active material and a dispersion medium,
Reducing the dissolved oxygen in the dispersion medium (A);
A step (B) of kneading the raw material of the electrode paste containing the electrode active material and the dispersion medium;
A process of removing bubbles in the electrode paste by subjecting the electrode paste to a vacuum pressure of −85 kPa or less (where the vacuum pressure is a gauge pressure with an atmospheric pressure of 0 kPa) (C ) In order.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the paste for electrodes of the secondary battery which can reduce the amount of bubbles irrespective of manufacturing conditions can be provided.

It is a schematic whole view which shows the structural example of a nonaqueous electrolyte secondary battery. It is a schematic cross section of the electrode laminated body in the nonaqueous electrolyte secondary battery of FIG. It is a schematic cross section which shows the structure of the electrode in the nonaqueous electrolyte secondary battery of FIG. It is a schematic diagram which shows the schematic structural example of the manufacturing apparatus which can implement process (A)-(C).

"Secondary battery"
As an example of the secondary battery, a configuration of a non-aqueous electrolyte secondary battery will be described.
1 to 3 show configuration examples of the nonaqueous electrolyte secondary battery. 1 is a schematic overall view, FIG. 2 is a schematic cross-sectional view of an electrode laminate, and FIG. 3 is a schematic cross-sectional view of an electrode.

A non-aqueous electrolyte secondary battery 1 shown in FIG. 1 is one in which an electrode laminate 30 and a non-aqueous electrolyte (not shown) are accommodated in an exterior body (battery container) 11.
As shown in FIG. 2, the electrode laminate 30 is obtained by laminating a positive electrode 21 and a negative electrode 22 with a separator 31 insulating them.
Two external terminals (a plus terminal and a minus terminal) 12 for external connection are provided on the outer surface of the exterior body 11.
As shown in FIG. 3, the electrode 20 (positive electrode 21 or negative electrode 22) is obtained by forming an electrode active material layer 20B on a current collector 20A. The electrode active material layer 20B is provided on one side or both sides of the current collector 20A. FIG. 3 shows an example in which the electrode active material layer 20B is provided on one surface of the current collector 20A.

The positive electrode active material layer includes, for example, a positive electrode active material such as a lithium-containing composite oxide, a conductive assistant such as carbon powder, a binder such as polyvinylidene fluoride (PVDF), and N-methyl-2-pyrrolidone (NMP). A paste containing a dispersion medium is applied onto a current collector such as an aluminum foil, dried, and pressed to form.
The negative electrode active material layer includes, for example, a negative electrode active material such as graphite, a binder such as modified styrene-butadiene copolymer latex (SBR), a thickener such as carboxymethyl cellulose Na salt (CMC), and a dispersion medium such as water. The paste containing is applied onto a current collector such as copper foil, dried, and pressed to form.

The present invention relates to a method for producing an electrode paste for a secondary battery.
The present invention is applicable to both positive electrode pastes and negative electrode pastes.
In the method for producing an electrode paste of the present invention, a powder containing an active material and a dispersion medium such as NMP or water are kneaded.

(Process (A))
In the present invention, before the paste kneading, the step (A) (dissolved oxygen reduction step) of reducing the dissolved oxygen in the dispersion medium is carried out in advance.
The dissolved oxygen reduction step can be performed by, for example, supplying the dispersion medium under a vacuum pressure of −85 kPa or less, as in the defoaming step described later.
In the dissolved oxygen reduction step, for example, after a container such as a tank containing a dispersion medium is sealed, the gas in the container is extracted to obtain a desired vacuum pressure, and is set for a predetermined time. By doing so, the dissolved oxygen in the dispersion medium floats as a gas and escapes out of the dispersion medium and is removed.
The vacuum pressure in the dissolved oxygen reduction step is particularly preferably −95 kPa or less.
The vacuum holding time in the dissolved oxygen reduction step is not particularly limited and is preferably 10 minutes or more, particularly preferably 30 minutes or more.

(Process (B))
A step (B) (kneading step) of kneading the raw material of the electrode paste including the electrode active material and the dispersion medium using the dispersion medium in which dissolved oxygen is reduced is performed.
The kneading of the raw material for the electrode paste can be carried out by a known method.

(Process (C))
Finally, the electrode paste obtained after paste kneading is subjected to a vacuum pressure of −85 kPa or less (where the vacuum pressure is a gauge pressure at which atmospheric pressure is 0 kPa), and the electrode paste in the electrode paste Step (C) for removing bubbles (defoaming step) is performed.
In the defoaming step, for example, after a container such as a tank (defoaming tank) containing paste is sealed, the gas in the container is extracted to obtain a desired vacuum pressure and set for a predetermined time. By doing so, bubbles in the paste rise and are removed from the paste and removed.
The vacuum pressure in the defoaming step is particularly preferably −95 kPa or less.
The vacuum holding time in the defoaming step is not particularly limited and is preferably 10 minutes or more, particularly preferably 30 minutes or more.

In the production method of the present invention, the defoaming step is performed under a high vacuum of −85 kPa or less. This allows kneading even under conditions where the amount of the dispersion medium in the paste is less than in the past, the amount of paste manufactured at one time in the kneading process, or the amount of paste processed at one time in the defoaming process. It is possible to satisfactorily remove air bubbles mixed in sometimes.
If the vacuum pressure in the defoaming step exceeds -85 kPa, depending on the production conditions, there is a risk that removal of bubbles mixed in the paste during kneading may be insufficient.
By setting the vacuum pressure in the defoaming step to −85 kPa or less, it is possible to satisfactorily remove bubbles mixed in the paste during kneading regardless of manufacturing conditions.

As described in the section of “Problems to be Solved by the Invention”, the present inventor has examined the conventional manufacturing method, particularly in a high vacuum defoaming step, due to a small amount of dissolved oxygen contained in the dispersion medium. It has been found that new bubbles may be generated.
In the production method of the present invention, since the dissolved oxygen in the dispersion medium is reduced in advance before kneading, even if the pressure in the defoaming step is set to a higher vacuum than in the past, it is caused by the dissolved oxygen contained in the dispersion medium. The generation of new bubbles is suppressed.

  Combined with the above effects, according to the manufacturing method of the present invention, an electrode paste with a reduced amount of bubbles can be manufactured regardless of manufacturing conditions. By applying coating on the current collector using this electrode paste, it is possible to suppress poor coating due to bubbles.

In the production method of the present invention, an electrode paste with a reduced amount of bubbles can be produced even if the amount of the dispersion medium in the paste is smaller than before, so that drying after applying the paste to the current collector is possible. The process can be shortened.
For example, the solid content of the conventional electrode paste is usually about 40 to 55% by mass, but may be 60% by mass or more.

  In the production method of the present invention, even if the amount of paste produced at one time in the kneading step or the amount of paste processed at one time in the defoaming step is larger than conventional, the air bubbles mixed during kneading can be removed well. Therefore, the efficiency of the kneading process or the defoaming process can be improved.

In FIG. 4, the example of schematic structure of the manufacturing apparatus which can implement process (A)-(C) is shown.
Here, an example of an apparatus for producing a negative electrode paste is shown.
The manufacturing apparatus 100 shown in the figure is
A first raw material tank 110 for storing a negative electrode active material such as graphite;
A second raw material tank 120 for storing a dispersion medium such as water;
A third raw material tank 130 for storing a binder such as modified styrene-butadiene copolymer latex (SBR);
And a fourth raw material tank 140 for storing a thickener such as carboxymethyl cellulose Na salt (CMC).
Among these raw material tanks, the second raw material tank 120 can be sealed, and the vacuum device Vac. It is connected to the.
The manufacturing apparatus 100 also includes a kneading apparatus 150 for kneading the raw materials supplied from the first to fourth raw material tanks, and a defoaming tank 160 for defoaming the electrode paste Pa manufactured by the kneading apparatus 150. I have.
The defoaming tank 160 can be sealed, and a vacuum device Vac. It is connected to the.
The electrode paste Pa after defoaming by the defoaming tank 160 is applied to the current collector.

Examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery.
Hereinafter, main components will be described by taking a lithium ion secondary battery as an example.

(Positive electrode)
The positive electrode can be manufactured by applying a positive electrode active material to a positive electrode current collector such as an aluminum foil by a known method.
Known no particular limitation on the positive electrode active material, for _{example, LiCoO 2, LiMnO 2, LiMn} 2 O 4, LiNiO 2, LiNi x Co (1-x) O 2, and _{LiNi x Co y Mn (1-} x-y _And lithium-containing composite oxides such as O ₂ (where 0 <x <1, 0 <y <1).
The method for producing the positive electrode is as described above.

(Negative electrode)
The negative electrode active material is not particularly limited, and a material having a lithium storage capacity of 2.0 V or less on the basis of Li / Li + is preferably used. As the negative electrode active material, carbon such as graphite, metallic lithium, lithium alloy, transition metal oxide / transition metal nitride / transition metal sulfide capable of doping / dedoping lithium ions, and these A combination etc. are mentioned.
The method for producing the negative electrode is as described above.

(Nonaqueous electrolyte)
As the non-aqueous electrolyte, known ones can be used, and liquid, gel-like or solid non-aqueous electrolytes can be used.
For example, a lithium-containing electrolyte is dissolved in a mixed solvent of a high dielectric constant carbonate solvent such as propylene carbonate or ethylene carbonate and a low viscosity carbonate solvent such as diethyl carbonate, methyl ethyl carbonate, or dimethyl carbonate. A water electrolyte is preferably used.

As the mixed solvent, for example, a mixed solvent such as ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) and ethylene carbonate (EC) / diethyl carbonate (DEC) is preferably used.
Examples of the lithium-containing electrolyte include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _{(2k + 1)} (k = 1 to 8), LiPF _n {C _k F _{(2k + 1) )} (6-n) (} n = 1~5 integer, k = 1 to 8 integer) lithium salts such as, and combinations thereof.

(Separator)
The separator may be a film that electrically insulates the positive electrode and the negative electrode and is permeable to lithium ions, and a porous polymer film is preferably used.
As the separator, for example, a porous film made of polyolefin such as a porous film made of PP (polypropylene), a porous film made of PE (polyethylene), or a laminated porous film of PP (polypropylene) -PE (polyethylene) is preferably used. It is done.

(Exterior body (battery container))
A well-known thing can be used as an exterior body.
As a type of the secondary battery, there are a cylindrical type, a coin type, a square type, a film type (laminate type), and the like, and an exterior body can be selected according to a desired type.

  In addition, this invention is applicable not only to a nonaqueous electrolyte secondary battery but the manufacture of the paste for electrodes of the secondary battery at large.

  Examples and comparative examples according to the present invention will be described.

(Examples 1 to 3, Comparative Example 1)
In Examples 1 to 3 and Comparative Example 1, a negative electrode paste was produced.
Materials include graphite as negative electrode active material, carboxymethylcellulose Na salt (CMC) as thickener, modified styrene-butadiene copolymer latex (SBR) as binder solution, and ion-exchanged water as dispersion medium. Prepared.
The material mixing ratio of the solid content was graphite / CMC / SBR = 98.6 / 0.7 / 0.7 (solid content mass ratio).
The solid content of the paste was 61% by mass.

In Examples 1 to 3, the step (A) of reducing dissolved oxygen in the dispersion medium, the step (B) of kneading the raw material for the electrode paste containing the electrode active material and the dispersion medium, and the electrode paste- The step (C) of removing bubbles in the electrode paste was sequentially performed under a vacuum pressure of 85 kPa or less.
In the step (A), before the paste kneading, after the tank containing the ion exchange water as the dispersion medium is sealed, the gas in the tank is evacuated to a vacuum pressure and left for a predetermined time, so that dissolved oxygen in the ion exchange water is placed. Reduced.
In the step (B), the electrode paste raw material was kneaded by the known method using the above ion-exchanged water to obtain an electrode paste.
In the step (C), after the tank containing the obtained paste was sealed, the gas in the tank was removed to a vacuum pressure and left for a predetermined time to remove bubbles in the paste.
In Comparative Example 1, the step (A) of reducing the dissolved oxygen in the dispersion medium is not carried out, the step (B) of kneading the electrode paste material containing the electrode active material and the dispersion medium, and the electrode paste The step (C) of removing bubbles in the electrode paste was performed in sequence under a vacuum pressure of −85 kPa or less.
The main production conditions in each example are as shown in Table 1. Manufacturing conditions other than those listed in Table 1 were common conditions.

In each example, the obtained electrode paste was applied onto a copper foil as a current collector, dried, and pressed to produce a negative electrode continuously. The conditions for coating, drying, and pressing were common conditions.
The negative electrode obtained in each example was visually observed, and the number of pinholes per 4000 m was measured.
The evaluation results in each example are shown in Table 1.

  In Examples 1 to 3 in which the step (A) for reducing dissolved oxygen in the dispersion medium was performed, it was possible to reduce coating defects. In particular, in Step (A), in Example 3 in which a high vacuum of −95 Pa or less was set and the vacuum holding time was 30 minutes, no coating failure was observed at all.

  The method for producing an electrode paste for a secondary battery according to the present invention includes a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery mounted in a hybrid vehicle (HV), a plug-in hybrid vehicle (PHV), or an electric vehicle (EV). It can be preferably applied to batteries and the like.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 11 Exterior body 20 Electrode 20A Current collector 20B Electrode active material layer 21 Positive electrode 22 Negative electrode 30 Electrode laminated body 31 Separator 100 Manufacturing apparatus 110-140 Raw material tank 150 Kneading apparatus 160 Defoaming tank Pa Electrode paste Vac. Vacuum equipment

Claims (3)

A method for producing an electrode paste for a secondary battery comprising an electrode active material and a dispersion medium,
Reducing the dissolved oxygen in the dispersion medium (A);
A step (B) of kneading the raw material of the electrode paste containing the electrode active material and the dispersion medium;
A process of removing bubbles in the electrode paste by subjecting the electrode paste to a vacuum pressure of −85 kPa or less (where the vacuum pressure is a gauge pressure with an atmospheric pressure of 0 kPa) (C And a paste for an electrode of a secondary battery.   The manufacturing method of the paste for electrodes of the secondary battery of Claim 1 which implements a process (A) by using the said dispersion medium under the vacuum pressure of -85 kPa or less.   The method for producing a paste for an electrode of a secondary battery according to claim 1 or 2, wherein the vacuum pressure in the step (C) is -95 kPa or less.

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