JP2000106175A - Manufacture of electrode plate for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent undrying of a coating film and lowering of binding performance even at changing of air absolute humidity outside a drying oven, by regulating the absolute humidity of the air taken from drying oven air suction ports at constant, in the process of applying coating liquid including a positive or negative electrode active material as a primary ingredient on a collector substrate, and drying it. SOLUTION: A coating liquid is applied on an aluminum foil substrate 17 via a piping 13, a pump 14, and a manifold 16 in a nozzle 15. The coating liquid applied on the substrate 17 is dried in a drying oven 18, to form a coating film 19. The absolute humidity of the air sucked in from air suction port 20 of the drying oven 18 is regulated at 6-8 g/m3 by absolute humidity regulators 21, thereafter it is heated to 120 deg.C by heater fans 22, then it is blown on the coating liquid at the flow rate of 250 m3/min via blow nozzles 23. The air after the drying in the drying oven 18 in exhausted through air outlets 25 by exhaust fans 24. Thus, the coating film 19 is applied to the base material 17, without lowering binding performance between them, even when the absolute humidity of the air outside the drying oven 18 is varied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrode plate for a positive electrode or a negative electrode used in a secondary battery.

[0002]

2. Description of the Related Art In recent years, miniaturization and weight reduction of electronic devices and communication devices have been rapidly progressing, and there is a strong demand for miniaturization and weight reduction of secondary batteries used as power sources for driving these devices. It has become to. For these requests,
A secondary battery having a high energy density and a high voltage, such as a lithium ion secondary battery, has been proposed.

[0003] Further, with respect to the electrode plate which greatly affects the performance of the secondary battery, it is proposed to increase the area of the film in order to extend the charge / discharge cycle life and to increase the energy density. Have been. For example, JP
As described in JP-A-3-10456 and JP-A-3-285262, a conductive agent and a binder are added to a powder of a positive electrode active material such as a metal oxide, a sulfide, and a halide, and a suitable material is added thereto. Dispersed in a solvent to prepare a liquid active material coating liquid, to form a coating film to be an active material layer by applying the coating liquid to a base material to be a metal foil current collector The resulting positive electrode plate is disclosed. As a binder, a fluorine-based resin such as polyvinylidene fluoride or a silicon-acryl copolymer is used. In addition, a negative electrode plate is prepared by dissolving a binder in a suitable solvent into a negative electrode active material such as carbon to prepare a liquid active material coating liquid, and a base material serving as a metal foil current collector. Obtained by coating on

[0004] The coating film is formed by coating and drying with an apparatus shown in FIG. The coating liquid containing the active materials of the positive electrode and the negative electrode as main components passes through a pipe 1 in FIG. 4, is supplied to a manifold 4 in a nozzle 3 by a pump 2, and is coated on a base material 5 serving as a current collector. You. The coated base material is dried by passing through a drying furnace 6 to form a coating film 7.

Here, the drying furnace 6 is configured as follows. Air outside the drying furnace is taken into the drying furnace through the air inlet 8, heated to a predetermined temperature by the heater fan 9, and hot air is blown at a predetermined flow rate to the coating liquid on the substrate 5 through the blow nozzle 10. The coating liquid is dried by spraying to form a coating film 7. The air after the drying process in the drying furnace is exhausted to the outside through the air exhaust port 12 by the exhaust fan 11.

However, immediately after coating, the base material 5 serving as a current collector is used.
The binder in the coating liquid applied on top is distributed uniformly, but during the drying process, the coating liquid is applied at the drying temperature necessary for drying and the temperature in the drying furnace exceeding the drying air volume, and the air volume. When dried, the binder floats up on the coating film surface with the solvent,
The binder is unevenly distributed on the surface of the coating film after drying, and the binding property of a portion where the binder is diluted in the coating film and the binding property between the coating film and the base material are reduced. . For this reason, the coating film peels off from the base material during the formation of the coating film under pressure, and the coating film peels off, falls off, cracks, etc. during the battery assembling process and during charging and discharging. Due to the overvoltage caused by the uneven distribution of the binder inside, the discharge capacity is reduced, or due to insufficient binding force,
Repeated charging / discharging causes deterioration of discharge capacity. Therefore, it is necessary to set the optimum coating speed, drying temperature, and drying air flow according to the coating amount, and to dry the coating liquid without lowering the binding property of the coating film.

In order to solve this problem, for example, in Japanese Patent Application Laid-Open No. 63-114058, the temperature of the coating film on the outlet side of the drying furnace is measured by a non-contact thermometer, and the temperature of the coating film is reduced to a set temperature. A method is described in which the temperature in a drying furnace is controlled so as to coincide with each other, whereby the coating film is accurately and easily dried in accordance with the coating amount.

[0008]

However, in the above-mentioned method for drying a coating film, even if the optimum coating speed, drying temperature and drying air flow are set for the coating amount, the absolute humidity of the air outside the dryer can be reduced. Therefore, there is a problem that the coating film is in an undried state, and the binding property of the coating film is reduced even though the moisture content of the coating film is a predetermined amount or less.

This phenomenon is described in Japanese Patent Application Laid-Open No. 63-114.
No. 058, the temperature of the coating film on the outlet side of the drying furnace is measured by a non-contact thermometer, and the temperature in the drying furnace is controlled so that the temperature of the coating film matches the set temperature. This cannot be solved by a method for accurately and easily drying the coating film according to the coating amount.

Accordingly, the present invention prevents the undried state of the coating film and the decrease in the binding property of the coating film even when the absolute humidity of the air outside the dryer changes, and allows the coating to be performed in a stable dry state. It is an object of the present invention to provide a method of manufacturing an electrode plate for a secondary battery in which the discharge capacity is reduced and the discharge capacity is less deteriorated due to repeated charging and discharging.

[0011]

According to the present invention, in order to achieve the above object, a coating liquid containing a positive electrode or a negative electrode active material as a main component is applied to a substrate serving as a current collector and dried. In the step of applying the electrode plate for the next battery, an absolute humidity controller was attached to the air suction port of the drying oven, and the absolute humidity of the air sucked from the air suction port was adjusted to be constant.

By this means, even if the absolute humidity of the air outside the dryer changes, it is possible to prevent the undried state of the coating film and the decrease in the binding property of the coating film, and to apply the coating in a stable dry state. Can be realized.

It is preferable that the absolute humidity of the air sucked from the air suction port is adjusted to 4 g / m ³ or more and 10 g / m ³ or less so that the wet state of the coating film is not caused and the coating film is not dried. It has been found that it is more preferable to improve the binding property.

By the above means, it is possible to prevent a decrease in the binding property of the coating film due to a change in the absolute humidity of the air outside the dryer. Peeling, peeling, falling off, cracks, and the like of the coating film occurring during the battery assembling process and during charging and discharging can be reduced. In addition, the overvoltage due to the uneven distribution of the binder in the coating film reduces the decrease in the discharge capacity, suppresses the deterioration of the discharge capacity due to repeated charging and discharging due to insufficient binding force, and improves the quality of the battery. be able to.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described in comparison with a conventional technique.

Embodiment 1 The present invention was applied to a positive electrode plate to produce a positive electrode plate.

That is, 100 parts by weight of lithium cobalt oxide (LiCoO ₂ ) powder as a positive electrode active material, 3.0 parts by weight of acetylene black as a conductive agent, and carboxymethyl cellulose as a thickener as a coating liquid for coating on a substrate. An aqueous solution in which 1 part by weight was dissolved in 100 parts by weight of water was used.
3 parts by weight, polytetrafluoroethylene 6 as a binder
An aqueous solution of 0 parts by weight dissolved in 100 parts by weight of water is 11.5 parts by weight.
Parts by weight were blended and mixed and dispersed.

The electrode plate was manufactured by the apparatus shown in FIG. The coating liquid passes through a pipe 13 in FIG. 1 and is supplied to a manifold 16 in a nozzle 15 by a pump 14. The coating liquid is applied onto a base material 17 using a 20 μm-thick aluminum foil as a base material serving as a current collector. Wearing speed 15m / min
The width of the coating film is 500 mm, and the thickness after drying is 180 μm.
m. The coating liquid on the coated substrate is
Drying by a drying furnace 18 according to the drying method of the present invention,
The coating film 19 was produced.

Here, the air inlet 20 of the drying furnace 18 is used.
The air taken in from the absolute humidity controller 21 has an absolute humidity of not less than 6 g / m ^{3 and not} more than 8 g / m ^3.
And then adjusted by the heater fan 22 to 120
° C, and 250 m ³
/ Min was blown onto the coating liquid. The air after the drying process in the drying furnace is exhausted to the outside through the air exhaust port 25 by the exhaust fan 24. The absolute humidity of the air outside the drying oven is 2 g from 2 g / m ³ to 24 g / m ³
/ M ^{3 at a} time to produce a positive electrode plate. The coating was performed on both surfaces of the substrate in the same manner.

Comparative Example 1 A positive electrode plate was manufactured by applying a conventional technique to a positive electrode plate.

The coating liquid was prepared in the same manner as in the first embodiment. The electrode plate was produced by the device shown in FIG. The coating liquid passes through the pipe 1 shown in FIG. 4 and is provided to the manifold 4 in the nozzle 3 by the pump 2, and on a substrate 5 using a 20 μm-thick aluminum foil as a substrate serving as a current collector, Coating was performed so that the coating speed was 15 m / min, the width of the coating film was 500 mm, and the thickness after drying was 180 μm. The coating liquid on the coated substrate was dried in a drying furnace 6 according to a conventional drying method, and a coating film 7 was produced.

Here, from the air inlet 8 of the drying furnace 6
Inhaled air, without adjusting its absolute humidity,
1 through the blow nozzle 10 by the heater fan 9
Heat up to 20 ° C, 250m^Three/ Min air flow
Sprayed on the liquid. In addition, the air after drying treatment in the drying furnace
Passes through the air outlet 12 by the exhaust fan 11
It is exhausted outside. The absolute humidity of the air outside the drying oven is 2
g / m^Three To 24g / m ^Three Up to 2g / m^Three Changed by
A positive electrode plate was produced. In addition, the same coating on both sides of the substrate
Made by the way.

(Evaluation of Binding Property) The binding properties of the positive electrode plates obtained in Embodiment 1 and Comparative Example 1 were measured with a peel strength tester. The result is shown in FIG. In FIG. 2, the horizontal axis indicates the absolute humidity of the air outside the drying furnace, and the vertical axis indicates the peel strength indicating the binding property.

Regarding the binding property of the positive electrode plate of the first embodiment, even if the absolute humidity of the air outside the drying furnace changes greatly, the peel strength is almost constant.

On the other hand, the peel strength of the positive electrode plate of Comparative Example 1 greatly depends on the absolute humidity of the air outside the drying furnace.
At an absolute humidity of less than 4 g / m ³ or more than 10 g / m ³ , the peel strength is greatly reduced. In addition, 12g /
If it exceeds m ³ , the electrode plate will be in an undried state.

As described above, according to the method for manufacturing an electrode plate of the present invention, even if the absolute humidity of the air outside the drying furnace changes, the binding property of the coating film and the binding property between the coating film and the substrate are improved. Coating can be performed without lowering.

In the first embodiment, the humidity was adjusted by the humidity controller so that the absolute humidity of the air outside the drying furnace was 6 g / m ³ or more and 8 g / m ³ or less. The evaluation result shows that the absolute humidity of the air outside the drying furnace was 4 g / m.
³ to 10 g / m ³ is desirable, and the adjustment range of the absolute humidity of the air outside the drying furnace by the absolute humidity controller of the first embodiment is 4 g / m 3 at the same time.
^This indicates that ^{3 to} 10 g / m ³ is desirable.

Embodiment 2 The present invention was applied to a negative electrode plate to prepare a negative electrode plate.

As a coating liquid to be coated on the substrate, 100 parts by weight of spherical graphite powder as a negative electrode active material, and 107.2 parts by weight of an aqueous solution obtained by dissolving 1 part by weight of carboxymethylcellulose in 100 parts by weight of water as a thickener. Then, 7.3 parts by weight of an aqueous solution obtained by dissolving 3.5 parts by weight of styrene butadiene rubber as a binder in 100 parts by weight of water was blended, mixed, and dispersed to prepare a mixture.

The electrode plate was manufactured by the apparatus shown in FIG. The coating liquid passes through a pipe 13 in FIG. 1 and is supplied to a manifold 16 in a nozzle 15 by a pump 14. The coating liquid is coated on a base material 17 using a copper foil having a thickness of 14 μm as a base material serving as a current collector. Coating was performed so that the coating speed was 15 m / min, the width of the coating film was 500 mm, and the thickness after drying was 120 μm. The coating liquid on the coated substrate is dried in a drying furnace 18 according to the drying method of the present invention, and a coating film 19 is formed.
Was prepared.

Here, the air inlet 20 of the drying furnace 18
The air taken in from the absolute humidity controller 21 has an absolute humidity of not less than 6 g / m ^{3 and not} more than 8 g / m ^3.
After that, the temperature was raised to 100 ° C. by the heater fan 22 through the blow nozzle 23, and 50 m ³ /
The coating liquid was sprayed at a flow rate of min. The air after the drying process in the drying furnace is exhausted to the outside through the air exhaust port 25 by the exhaust fan 24. The absolute humidity of the air outside the drying furnace is 2 g / m ³ from 24 g / m ³ to 24 g / m ^3.
The negative electrode plate was manufactured by changing m ^{3 in} steps. The coating was performed on both surfaces of the substrate in the same manner.

Comparative Example 2 A conventional technique was applied to a negative electrode plate to produce a negative electrode plate.

The coating liquid to be applied to the substrate was prepared in the same manner as the coating liquid in the second embodiment. The electrode plate was produced by the device shown in FIG. The coating liquid passes through the pipe 1 in FIG. 4, is supplied to the manifold 4 in the nozzle 3 by the pump 2, and is coated on the base material 5 using a 14 μm-thick copper foil as a base material serving as a current collector. At a wearing speed of 15 m / min,
The coating was performed so that the width of the coating film was 500 mm and the thickness after drying was 120 μm. The coating liquid on the coated base material was dried in a drying furnace 6 according to a conventional drying method to form a coating film 7.

Here, the air taken in from the air inlet 8 of the drying furnace 6 is heated up to 100 ° C. by the heater fan 9 without adjusting the absolute humidity, and is heated for 50 m.
^The coating liquid was sprayed at a flow rate of ³ / min. The air after the drying process in the drying furnace is exhausted to the outside through the air exhaust port 12 by the exhaust fan 11. The absolute humidity of the air outside the drying oven ranges from 2 g / m ³ to 24 g / m ³
The negative electrode plate was manufactured by changing the ratio by g / m ³ . The coating was performed on both surfaces of the substrate in the same manner.

(Evaluation of Binding Property) The binding properties of the negative electrode plates obtained in Embodiment 2 and Comparative Example 2 were measured with a peel strength tester. The result is shown in FIG. The horizontal axis indicates the absolute humidity of the air outside the drying furnace, and the vertical axis indicates the peel strength indicating the binding property.

Regarding the binding property of the negative electrode plate of the second embodiment, the peel strength is almost constant even if the absolute humidity of the air outside the drying furnace changes greatly.

On the other hand, in the negative electrode plate of Comparative Example 2, the peel strength greatly depends on the absolute humidity of the air outside the drying furnace.
At an absolute humidity of less than 4 g / m ³ or more than 10 g / m ³ , the peel strength is greatly reduced. In addition, 12 g / m
^If it exceeds ³ , the electrode plate will be in an undried state.

As described above, according to the method for manufacturing an electrode plate of the present invention, even when the absolute humidity of the air outside the drying furnace changes, the binding property of the coating film and the binding property between the coating film and the base material can be improved. Coating can be performed without lowering.

In the second embodiment, the space outside the drying furnace is empty.
Absolute humidity of 6g / m^Three Above, 8 g / m^Three Becomes
Was adjusted by the humidity controller as described above,
The evaluation results show that the absolute humidity of the air outside the drying oven is 4 g / m.
^Three More than 10g / m^Three Indicate that the following is desirable
This is the same as the absolute humidity controller 21 of the second embodiment.
Adjustment range of the absolute humidity of the air outside the drying oven by 4g
/ M^Three More than 10g / m ^Three Show that the following is desirable
Will be.

(Embodiment 3) A battery having a size of 17 mm in diameter and 50 mm in height was manufactured using the positive electrode plate manufactured in Embodiment 1 and the negative electrode plate manufactured in Embodiment 2.

The positive electrode plate manufactured in the first embodiment was molded under pressure until the entire thickness became 180 μm, and the electrode portion was cut into a size having a width of 38 mm and a length of 345 mm. In order to remove moisture in the film, a drying treatment was performed in an air atmosphere at 250 ° C. for 10.5 hours. The negative electrode plate manufactured in Embodiment 2 has a total thickness of 195 μm.
m, and the electrode portion is cut into a size having a width of 40 mm and a length of 395 mm. In order to remove moisture in the coating film, the electrode portion is heated at 110 ° C. for 7.5 hours in an air atmosphere. A drying process was performed.

Using the thus-processed positive electrode plate of the first embodiment and the negative electrode plate of the second embodiment, a separator made of a porous polypropylene film wider than the positive electrode and the negative electrode plate is used to insulate both. Then, the electrode was wound in a spiral to form an electrode plate group. Next, this electrode plate group
Insert into a cylindrical stainless steel container with a bottom, which also serves as the negative electrode terminal. Ethylene carbonate 30% by volume and diethyl carbonate 50% by volume
A solution of lithium hexafluorophosphate dissolved at a concentration of 1 mol / liter in a mixture of 20% by volume of methylpropionate and methylpropionate was poured as an electrolyte, and the diameter was 17 mm and the height was 50 mm.
And a battery with a rated capacity of 720 Ah was manufactured.

(Comparative Example 3) Using the positive electrode plate manufactured in Comparative Example 1 and the negative electrode plate manufactured in Comparative Example 2, a diameter of 17
A battery having a size of 50 mm and a height of 50 mm was prepared. The manufacturing method was the same as in Embodiment 3.

The positive electrode plate manufactured in Comparative Example 1
Press molding until the total thickness becomes 180 μm, cut the electrode part width 38mm, length 345mm,
A drying treatment was performed for 10.5 hours in an air atmosphere at 250 ° C. to remove moisture in the coating film. The negative electrode plate manufactured in Comparative Example 2 was molded under pressure until the entire thickness became 195 μm, and the width of the electrode portion was 40 mm and the length was 395.
The coating film was cut into a size of mm, and dried in an air atmosphere at 110 ° C. for 7.5 hours to remove moisture in the coating film.

(Results of Battery Performance Evaluation) A charge / discharge measuring device was used for measuring battery characteristics. Under a temperature condition of 25 ° C., charging was performed at a constant current of 500 mA, and when the voltage reached 4.1 V, switching to 4.1 V constant voltage charging was performed, and charging was performed for a total of 2 hours. Discharge was performed at a temperature of
The discharge was terminated when the discharge potential reached 3.0 V, and the next charge was started. Thus, 50 under the same conditions
The charge / discharge was repeated 0 times, and the discharge characteristics were measured. Table 1 shows the results.

[0046]

[Table 1]

The respective discharge capacities are shown as ratios with the first discharge capacity value of the third embodiment as 100.

As is clear from Table 1, the battery prepared in Embodiment 3 has a higher initial discharge capacity, and also has a higher discharge capacity when repeatedly charged and discharged. Also, the variation in the discharge capacity is suppressed low.

As described above, in the battery manufactured by the method for manufacturing an electrode plate of the present invention, peeling, falling off, cracks, and the like of the coating film that occur during charging and discharging are reduced, and the binder is unevenly distributed in the coating film. , The discharge capacity is prevented from being reduced due to the overvoltage, and the deterioration of the discharge capacity due to the repetition of charge and discharge due to insufficient binding force can be suppressed, and the quality of the battery can be improved.

[0050]

As is apparent from the above description, according to the method for manufacturing an electrode plate for a secondary battery of the present invention, even if the absolute humidity of the air outside the drying furnace changes, the binding property of the coating film can be improved. Because it is possible to stably produce a coating film without lowering the binding property between the coating film and the base material, the coating film peels off from the base material during the pressure forming of the coating film, It is possible to reduce peeling, falling off, cracks, and the like of the coating film that occur during the battery assembling process and during charging and discharging. Further, it is possible to reduce the discharge capacity from being reduced due to overvoltage due to uneven distribution of the binder in the coating film,
It is possible to suppress the deterioration of the discharge capacity and the variation in the discharge capacity due to the repetition of charge and discharge due to the insufficient binding force, and to improve the quality of the battery.

[Brief description of the drawings]

FIG. 1 is a schematic view of a method for manufacturing an electrode plate for a secondary battery according to the present invention.

FIG. 2 is a diagram showing binding evaluation results of Embodiment 1 and Comparative Example 1 in the present invention.

FIG. 3 is a diagram showing binding evaluation results of Embodiment 2 and Comparative Example 2 in the present invention.

FIG. 4 is a schematic view of a conventional method for manufacturing an electrode plate for a secondary battery.

[Explanation of symbols]

 1,13 Piping 2,14 Pump 3,15 Nozzle 4,16 Manifold 5,17 Base 6,18 Drying Furnace 7,19 Coating Film 8,20 Air Inlet 9,22 Heater Fan 10,23 Blow Nozzle 11, 24 Exhaust fan 12, 25 Air outlet 21 Absolute humidity controller

Claims (2)

[Claims] In a coating step of a secondary battery electrode plate, a coating liquid containing a binder or a positive electrode as a main component and a binder is applied to a base material serving as a current collector and dried. A method for manufacturing an electrode plate for a secondary battery, comprising: attaching an absolute humidity adjusting device to an air inlet of a drying furnace to adjust the absolute humidity of air sucked from the air inlet to a constant value. 2. A step of applying an electrode plate for a secondary battery, comprising applying a coating liquid containing a binder as a main component containing a positive electrode or a negative electrode active material to a base material serving as a current collector and drying the coating liquid. Attach an absolute humidity controller to the air inlet of the drying oven, and adjust the absolute humidity of the air sucked from the air inlet to 4 g / m ³ or more.
A method for producing an electrode plate for a secondary battery, wherein the method is adjusted to 0 g / m ³ or less.