JPH11149918A - Manufacture of battery electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain cracks due to solvent scattering or internal stress and facilitate membrane thickness control by powdering a mixed material with fluid properties including an active substance and a bonding agent by spray dryer means, and integrally molding a produced power with a current collector by hot press means to form an electrode. SOLUTION: As spray dryer means, for example, a mixed material with fluid properties including an active substance and a bonding agent is sprayed toward hot gas such as hot air, and thereby powder is dried at a high speed by heating of the hot gas. As a typical bonding agent, a polyvinylidene fluoride having its thermal fusion properties is exemplified. The temperature in hot press is more than a melting point of the bonding agent or near the melting point. Thereby, re-arrangement due to flow of the bonding agent in the hot press is made possible, reduction of a void in a laminate membrane formed at the current collector can be ensured, make it more advantageous to reduce crack in the laminate membrane and reduction in internal stress.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a battery electrode.

[0002]

2. Description of the Related Art As a method of manufacturing a battery electrode, generally, a paste-like mixed material containing a battery active material, a binder and a solvent is formed, and this is applied to a current collector to collect a laminated film. The solvent in the laminated film is scattered by drying the laminated film formed on the current collector and laminated on the current collector, and the dried laminated film is pressed together with the current collector.

[0003] Japanese Patent Application Laid-Open No. 8-167411 discloses that
The slurry containing the nickel oxide powder is formed into a spherical composite particle powder by a spray drier, and the spherical composite particle powder, a binder and a solvent are mixed to form a paste, and the paste is collected. A method for manufacturing a nickel electrode including an operation of forming a laminated film by applying to a body is disclosed. In this method, after forming the laminated film on the current collector, drying and pressing are performed as described above.

[0004]

In the above-described method for manufacturing a battery electrode according to the prior art, the laminated film before drying applied to the current collector contains a large amount of solvent. When the solvent is contained in the laminated film as described above, the rate of volume reduction of the laminated film due to the scattering of the solvent is large. Volume reduction is typically quite high, about 40-60%.

[0005] Therefore, a large amount of holes are formed in the laminated film formed on the current collector due to scattering of the solvent. Therefore, there is a problem that a fine crack is induced in the laminated film or an internal stress due to compression at the time of pressing is apt to be induced. Further, since the volume decrease of the laminated film due to the scattering of the solvent is large as described above, the thickness of the laminated film formed on the current collector fluctuates greatly, and it is not easy to control the thickness of the electrode.

In the method described in Japanese Patent Application Laid-Open No. 8-167411, spherical composite particle powder is formed by spray dryer means, but the spherical composite particle powder is mixed with a solvent to form a paste. , To apply the paste to the current collector to form a laminated film,
The laminated film according to Japanese Patent Application Laid-Open No. 8-167411 also contains a large amount of solvent, and therefore, the above-described disadvantages due to solvent scattering are likely to occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to suppress cracks caused by scattering of a solvent,
An object of the present invention is to provide a method of manufacturing a battery electrode which is advantageous for suppressing internal stress and advantageous for controlling film thickness.

[0008]

According to a first aspect of the present invention, there is provided a method of manufacturing a battery electrode, comprising the steps of powdering a fluid mixed material containing a battery active material and a binder by a spray drier to produce a powder. And forming the electrode by integrally molding the generated powder on the current collector by hot pressing means.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Spray dryer means is a means for powdering a fluid mixed material and drying it at a high speed. In the method of the present invention, a mixed material having fluidity including a battery active material and a binder is used, and the mixed material and a heated gas are supplied to spraying means, and the mixed material is sprayed and powdered with the heated gas, A form in which the powder is dried at high speed by the heat of the heated gas can be adopted. In addition, a fluid mixed material containing a battery active material and a binder is used, and the mixed material is sprayed toward a heated gas such as hot air by a spraying means, whereby powder is dried at high speed by the heat of the heated gas. Can also be adopted.

[0010] The powder thus formed by the spray drier means is dried at a high speed and contains no or substantially no solvent. The electrode active material used in the method of the present invention may be either a positive electrode active material or a negative electrode active material. For example, a powder of a lithium-containing compound can be used as the positive electrode active material. LiCoO ₂ , Li
NiO ₂ and LiMn ₂ O ₄ can be employed. A carbonaceous material can be used as the negative electrode active material. As a typical binder used in the method of the present invention, a thermoplastic resin having a heat melting property, in particular, a fluororesin having a heat melting property can be adopted. One such binder is polyvinylidene fluoride (PVDF).

The hot pressing means is a means for simultaneously applying pressure and heat. The pressure and temperature in the hot press according to the method of the present invention can be selected according to the type of the binder and the like. When the binder has a melting point, the temperature in the hot press can be set to the melting point of the binder or higher or around the melting point. In this case, since rearrangement due to the flow of the binder can be expected in the hot press, it is possible to reduce vacancies in the laminated film formed on the current collector, and to mysteriously reduce cracks and reduce internal stress in the laminated film. It is more advantageous for reduction.

When the binder is polyvinylidene fluoride, the temperature in the hot pressing means is 175
The temperature is preferably about -220C, particularly preferably about 180-200C.

[0013]

Embodiments will be described below with reference to the drawings. This embodiment is a case where the present invention is applied to an electrode used for a lithium ion battery. In this example, LiCoO ₂ having an average particle size of 10 μm was used as the positive electrode active material. Carbon having an average particle size of 2 μm was used as the conductive material. As a binder, polyvinylidene fluoride (PVDF), which is a thermoplastic resin having a melting point of 183 ° C., was used.

Then, polyvinylidene fluoride in a molten state was mixed with the mixture adjusted to have a weight ratio of LiCoO ₂ : carbon = 9: 1 to form a mixed material having fluidity. Then, as can be understood from FIG.
Current collector 1 (aluminum foil, average thickness 2
A mixed material and a heated gas (specifically, argon at about 250 to 300 ° C.) were supplied to the spray gun 2 by using a spray gun 2 (functioning as a spray drier means) disposed above (0 μm). As the supply flow rate, the mixed material is 20
-30 g / min, and the heated gas has a nozzle diameter of 1.0
～1.3Mm, pressure 3.0~4.0kgf / cm ² = about 29
It was 4-392 kPa. However, it is not limited to this.

According to the above operation, powder was sprayed from the spray gun 2, the powder was laminated on the current collector 1, and a laminated film 3 was formed on the current collector 1. In this case, the spray gun 2 can be moved appropriately. The target thickness of the laminated film 3 before hot pressing is 8
It is about 0 to 90 μm. In this example, the powder obtained by the spray dryer method was a composite particle having an average particle size of about 30 μm. As a result of the weight measurement, polyvinylidene fluoride was 5% based on the total weight of the solid content (or the applied material).
% By weight.

With the laminated film 3 formed of the powder produced by the spray drier method as described above, laminated on the current collector 1, the laminated film 3 and the current collector 1 are hot-pressed.
Were integrally formed to form electrodes according to Examples 1 to 3. In this case, the laminated film 3 was prepared using a surrounding jig 6 surrounding the laminated film 3. That is, as can be understood from FIG. 2, the upper mold 42 having the heater 41 and the heater 43
The upper mold 42 is lowered using the mold apparatus 4 having a lower mold 44 having a function as a hot press means, and the laminated film 3 on the current collector 1 is pressed by the mold surface 42 a of the upper mold 42. The thickness of the laminated film 3 was made uniform by heating, and the heaters 41 and 43 heated the laminated film 3.

The condition of the hot press according to this embodiment is 20
0 ° C, 5 minutes, but not limited to this
No. In the electrodes according to Examples 1 to 3,
Pressure, average film thickness of the laminated film 3 after hot pressing, hot pressing
The film density of the laminated film 3 after the heat treatment was as shown in Table 1.
That is, in Example 1, the pressing pressure was 100 kg.
f / cm^Two(≒ 980 × 10^FourPa = 9.8 MPa)
In Example 2, 130 kgf / cm^Two(≒ 1274 ×
10^FourPa = 12.74 MPa), and in Example 3, 1
60kgf / cm ^Two(≒ 1568 × 10^FourPa = 15.6
8 MPa).

[0018]

[Table 1] As can be understood from the above description, in the present embodiment in which the laminated film 3 is formed from the powder generated by the spray dryer method, the solvent is not applied to the laminated film 3 formed on the current collector 1 before hot pressing. Not included.

As Comparative Example 1, an electrode was formed from a slurry containing a solvent according to a conventional method. That is, the weight ratio was LiCoO2: carbon: polyvinylidene fluoride = 9: 1: 0.53. In this case, when the solid content is 100%, the ratio of polyvinylidene fluoride is 5% by weight. In Comparative Example 1, N-methylpyrrolidone (NMP) was used as a solvent, and the binder was adjusted so that the ratio of (PVDF / NMP) was 8% by weight. Thereby, battery active material, binder, solvent (NM
A slurry containing P) was produced.

In Comparative Example 1, the obtained slurry was applied to a current collector (aluminum foil, average thickness: 20 μm) using a coater as a paste application device to form a laminated film, and dried (at 80 ° C.). After temporary drying for 10 minutes and main drying at 200 ° C. for 1 hour), press (press pressure: 130 kgf / c)
m ² , time: 1 minute). The above-mentioned temporary drying has a main purpose of scattering the solvent in the laminated film. The main purpose of this drying is to melt polyvinylidene fluoride as a binder in the laminated film.

As can be understood from the above description, in Comparative Example 1, the laminated film before drying formed on the current collector contains a large amount of the solvent (NMP). As shown in Table 1, the electrode according to Comparative Example 1 had an average film thickness of 66 μm and a film density of 2.94 gf / cm ³ after pressing.
As can be understood from Table 1, when Comparative Example 1 and Example 2 are compared, Comparative Example 1 and Example 2 show that the press
Although the average film thicknesses are almost the same, the film density of the laminated film 3 is higher in Example 2 than in Comparative Example 1. The reason is presumed that in Comparative Example 1, since the solvent was contained in the laminated film before drying laminated on the current collector, the solvent was scattered due to drying, and the film density was lowered. You.

(Comparative Example 2) The inventor hot-pressed the electrode obtained in Comparative Example 1 on a trial basis. The hot pressing conditions were 200 ° C. for 1 minute, 5 minutes, and 10 minutes. Then, the detachment of the laminated film from the current collector was remarkable. This is presumed to be due to the effect of pores interposed at the time of solvent scattering and cracks generated at the time of pressing.

For this reason, in Comparative Example 2, the electrode obtained in Comparative Example 1 was subjected to a heat treatment at 200 ° C. for 30 minutes in order to alleviate the internal stress of the laminated film instead of hot pressing. In the electrode according to Comparative Example 2 that has been subjected to the heat treatment but not subjected to hot pressing, the average film thickness is about 5 to 10 μm thicker than when the electrode obtained in Comparative Example 1 is hot pressed. As a result, a decrease in the packing density of the active material was observed.

(Battery Cell Test 1) A battery cell (hereinafter, simply referred to as a cell) 1 was formed by assembling the electrodes prepared in Example 2 described above. Further, a cell 2 was formed by assembling the electrodes prepared in Comparative Example 1. The cell 3 was formed by assembling the electrodes prepared in Comparative Example 2. And cell 1
-Battery performance of cell 3 was investigated. That is, the investigation items are the initial capacity (１ ／ C: capacity when two cycles of charge and discharge are executed) and cycle characteristics (１ ／ C: change in capacity when charge and discharge are repeated up to 30 cycles). Table 2 shows the results of the initial capacity, and FIG. 3 shows the results of the cycle characteristics.

[0025]

[Table 2] In such a battery cell test 1, metallic lithium was used for the counter electrode, LiClO ₄ as an electrolyte dissolved in a solvent (concentration: 1 mol / l) was used as an electrolytic solution, and ethylene carbonate (ethylene carbonate) was used as a solvent. A mixture of EC) and diethyl carbonate (DEC) at a volume ratio of 8: 2 was used. A polyethylene (PE) film was used as the separator.

As a result of the test, as shown in FIG. 3, the initial capacity was almost the same in all of the cells 1 to 3 and good, but the cycle characteristics were as follows: cell 1 (（), cell 3 (□),
Cell 2 (marked with △) became worse in order. That is, the results became worse in the order of Example 2, Comparative Example 2, and Comparative Example 1. The reason for this is that, in Comparative Examples 1 and 2, since the solvent is contained in the laminated film before drying, the solvent is scattered with drying, and internal stress in the laminated film and cracks in the laminated film 3 are induced. It is considered that due to such internal stress and existence of cracks, repetition of charge / discharge induced exfoliation and dropping of the active material, and the cycle characteristics were degraded.

(Battery Cell Test 2) The electrodes prepared in Examples 1 to 3 were incorporated into cells, and cells A, B, and C were obtained. And it evaluated on the same conditions as the case of the above-mentioned battery cell test 1. Table 3 shows the results of the initial capacity, and FIG. 4 shows the results of the cycle characteristics. Table 3,
As can be understood from FIG.
Both the initial capacities were good, and the capacity did not decrease much even after 30 cycles of charging and discharging. That is, in Examples 1 to 3, the cycle characteristics were good even after repeated charging and discharging.

The reason is that since no solvent is contained in the laminated film 3, the internal stress and cracks caused by the scattering of the solvent are suppressed, so that even if charging and discharging are repeated,
It is presumed that peeling and falling off of the active material are suppressed and the cycle characteristics are improved. Further, it is presumed that the packing density was increased due to the re-melting and rearrangement of polyvinylidene fluoride by hot pressing.

[0029]

[Table 3] In the test results described above, as can be understood from FIG. 4, the cell B using the electrode of Example 2 showed excellent performance. Further, in the cell C using the electrode of Example 3 and the cell A using the electrode of Example 1, although the performance was slightly lower than that of the cell B in the cycle characteristics, it was generally good.

(Other Examples) In the above-described example, when the spray dryer method is performed, the mixed material having fluidity and the heated gas are supplied to the spray gun 2. However, the present invention is not limited to this. It is also possible to use a drying chamber in which the mixed material is pulverized by the pulverizing means and supply the mixed material to the drying chamber. In this case, the powder comes into contact with hot air and is instantaneously dried by the hot air. In addition to the spray gun 2, a method in which a rotating disk or a rotating nozzle that rotates at a high speed and functions as a powdering means may be disposed in a drying chamber to which hot air is supplied.

In the example shown in FIG. 5, when the laminated film 3 laminated on the current collector 1 is hot-pressed by the mold device 4, the thin plate 8
And the upper film 42 and the laminated film 3 substantially containing no solvent.
The plate body 8 is interposed between the mold body 42a and the mold surface 42a. This is advantageous for making the film density of the laminated film 3 laminated on the current collector 1 uniform. Further, the non-adhesive layer 8
Since h is formed, it is advantageous in separating the laminated film 3 and the upper die 42 after hot pressing.

In the above example, the present invention is applied to the manufacture of an electrode of a lithium ion battery, but may be applied to the manufacture of an electrode of another battery.

[0033]

According to the method of the present invention, an operation of pulverizing a fluid mixed material containing a battery active material and a binder by a spray drier means to produce a powder, and applying the produced powder to a current collector And forming an electrode by integral molding by hot pressing means.

According to the method of the present invention, the powder produced by the spray dryer means, that is, the laminated film formed of the powder on the current collector contains no or substantially no solvent. Therefore, unlike the related art, the generation of cracks and the generation of internal stress due to the drying of the solvent can be suppressed. Therefore, it is advantageous for suppressing peeling and falling off of the active material. Therefore, it is advantageous for uniform distribution of the active material in the electrode, and is also advantageous for improving the performance of the battery electrode.

Further, the thickness variation of the laminated film formed on the current collector can be suppressed, which is advantageous for controlling the thickness of the electrode. Further, according to the method of the present invention, since the scattering of the solvent due to the drying can be prevented, it is advantageous for simplifying or eliminating the exhaust equipment for discharging the solvent.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a state in which powder generated by a spray drier is laminated on a current collector.

FIG. 2 is a configuration diagram schematically showing a state in which a laminated film formed by laminating on a current collector is heated under pressure by hot pressing.

FIG. 3 is a graph showing charge / discharge characteristics.

FIG. 4 is a graph showing charge / discharge characteristics.

FIG. 5 is a configuration diagram schematically showing a state in which a laminated film laminated on a current collector is heated under pressure by a hot press according to another example.

[Explanation of symbols]

In the figure, 1 is a current collector, 2 is a spray gun, 3 is a laminated film, and 4 is a mold device.

Claims (1)

[Claims] An operation for pulverizing a fluid mixed material containing a battery active material and a binder by a spray drier means to produce a powder; and forming the produced powder integrally with a current collector by a hot press means. And a step of forming an electrode by performing the method.