JP2001216957A - Method for manufacturing electrode for secondary battery of nonaqueous electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an electrode for secondary battery of nonaqueous electrolyte, which has no such problems as shrinking or swelling of active materials for a cathode and an anode when charging or discharging, followed by increase for contact resistance between an active material and a metal collector while reducing cyclic characteristics in charging and discharging. SOLUTION: For the electrode for secondary battery of nonaqueous electrolyte, the process of manufacturing it is designed in such ways that the temperature of thermal treatment with the electrode should be higher than the melting point of binders and the treatment should be done at higher temperature than softening temperature for the metal collector of electrode, and this thermal treatment should be done before the process of rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a method for manufacturing an electrode thereof.

[0002]

2. Description of the Related Art In recent years, portable electronic devices have become more portable.
Cordless use is progressing. In the past, nickel cadmium batteries or sealed small lead-acid batteries played the role of power sources for driving these electronic devices.
As cordless technology has been established, demands for higher energy density, smaller size and lighter weight of secondary batteries serving as driving power sources have been increasing. In recent years, there has been a demand for batteries capable of high-rate charging and discharging, as represented by the rapid expansion of the market for notebook personal computers.

[0003] Under such circumstances, in a lithium secondary battery exhibiting a high charge / discharge voltage, for example, disclosed in Japanese Patent Application Laid-Open No. 63-59507, LiCoO ₂ is used as a positive electrode active material to insert lithium ions, A non-aqueous electrolyte secondary battery utilizing desorption is disclosed.

A method of manufacturing a positive electrode plate for a non-aqueous electrolyte secondary battery involves kneading a positive electrode active material, a conductive agent, and a binder in a solvent to form a paste, applying the paste to a metal current collector, and drying the paste. After that, rolling is generally performed to produce an electrode plate. In the negative electrode, it is common to knead a negative electrode active material and a binder in a solvent to form a paste, apply the paste to a metal current collector, dry the paste, and then roll it to form an electrode plate. .

[0005]

However, in the above-described conventional configuration, the adhesion between the active material mixture and the metal current collector deteriorated due to expansion and contraction of the active material when the battery was charged and discharged. For this reason, the contact resistance between the active material mixture and the metal current collector is increased, and the charge and discharge cycle characteristics are reduced.

In order to solve these problems, for example, in Japanese Patent Application Laid-Open No. 7-6752, the binding force between the active material mixture and the metal current collector is increased by subjecting electrodes to pressure molding and then performing heat treatment. Methods for strengthening are disclosed. However, when PTFE or FEP is used as the binder, in these methods, the heat treatment is performed after the pressure molding, whereby the active material mixture emerges again from the metal current collector, and the gap between the active material mixture and the metal current collector is reduced. And the adhesion deteriorated.

The present invention solves such a conventional problem, and has an excellent binding force between a metal current collector and an active material mixture applied to the metal current collector, and has a good charge-discharge cycle life characteristic. A non-aqueous electrolyte secondary battery is provided.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a method for producing an electrode in which a paste mainly composed of a material which reacts reversibly with lithium is applied to a metal current collector to form an electrode, and the electrode is heat-treated and then rolled. In the method, the temperature at which the electrode is heat-treated is higher than the melting point of the binder and higher than the temperature at which the metal current collector of the electrode softens.

With this configuration, the binder present in the electrode plate is melted at a temperature higher than the melting point, and the binder is uniformly dispersed at the interface between the active material mixture and the metal current collector. I do. Thereby, the binding force between the active material mixture and the metal current collector can be improved.

[0010] In addition, by performing the rolling step after the electrode is subjected to a heat treatment at a temperature higher than the temperature at which the metal current collector softens, the active material mixture can easily physically penetrate into the softened metal current collector, and the active material is further increased. The binding force between the material mixture and the metal current collector can be improved. Therefore, by configuring the nonaqueous electrolyte secondary battery as described above, it is possible to improve the binding force between the metal current collector and the active material mixture applied to the metal current collector.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a longitudinal sectional view of a cylindrical battery used in this embodiment. In FIG. 1, reference numeral 1 denotes a battery case processed from a stainless steel sheet having resistance to organic electrolyte, 2 denotes a sealing plate provided with a safety valve, and 3 denotes an insulating packing. Reference numeral 4 denotes an electrode plate group, in which a positive electrode plate 5 and a negative electrode plate 6 are spirally wound a plurality of times via a separator 7. A positive electrode lead 5 a is drawn out of the positive electrode plate 5 and connected to the sealing plate 2, and a negative electrode lead 6 a is drawn out of the negative electrode plate 6 and connected to the bottom of the battery case 1. Numeral 8 denotes an insulating ring provided above and below the electrode plate group 4 respectively. Hereinafter, the positive electrode plate 5, the negative electrode plate 6, the electrolyte and the like will be described in detail.

The positive electrode plate 5 is made of LiCoO ₂ which is a positive electrode active material.
100 parts by weight of powder, 5 parts by weight of acetylene black,
10 parts by weight of PTFE of a fluororesin was mixed, and this was turbid in an aqueous solution of carboxymethylcellulose to form a paste. This paste was applied to both sides of an aluminum foil, dried and then heat-treated at 350 ° C. for 15 minutes. This was rolled to 0.17 mm by a roll press and cut out to a width of 35 mm and a length of 250 mm. Here, the softening temperature of the aluminum foil is about 100 ° C.

The negative electrode plate 6 was prepared by mixing 100 parts by weight of carbon powder obtained by heat-treating coke with 10 parts by weight of a styrene-based binder, and suspending the mixture in an aqueous solution of carboxymethyl cellulose to form a paste. . Then, this paste is applied to the surface of a copper foil having a thickness of 0.015 mm, dried at 110 ° C., and then rolled to a thickness of 0.2 mm, and has a width of 37 mm and a length of 280.
It cut out to the size of mm.

The leads 5a and 6a are respectively connected to the positive electrode plate and the negative electrode plate.
a, and spirally wound through a separator,
It was inserted into a battery case having a diameter of 13.8 mm and a height of 50 mm.

In the electrolyte, 1 mol of lithium hexafluorophosphate was mixed with an equal volume mixed solvent of ethylene carbonate and diethyl carbonate.
After dissolving a predetermined amount in a battery case, the battery was sealed in the opening of the case to obtain a battery.

Comparative Example 1 A battery was prepared in the same manner as in Example 1, except that the heat treatment was performed at 150 ° C., which is lower than the melting point of PTFE, for 15 minutes.

Comparative Example 2 A battery was prepared in the same manner as in Example 1, except that the heat treatment step was performed after the rolling step.

Example 2 LiCoO as a positive electrode active material
To 100 parts by weight of ₂ powder, acetylene black 5 parts by weight, were mixed FEP10 parts of fluorine resin, which was a paste by turbidity in an aqueous solution of carboxymethyl cellulose. This paste was applied to both sides of an aluminum foil, dried and then heat-treated at 300 ° C. for 15 minutes. This was rolled to 0.17 mm by a roll press,
It was cut out to a width of 35 mm and a length of 250 mm. Using this electrode, a battery similar to that of Example 1 was produced.

Comparative Example 3 A battery was prepared in the same manner as in Example 2 except that the heat treatment was performed at 150 ° C., which is lower than the melting point of FEP, for 15 minutes.

Comparative Example 4 A battery was prepared in the same manner as in Example 2, except that the heat treatment step was performed after the rolling step.

Example 3 A positive electrode plate was prepared by mixing 100 parts by weight of LiCoO ₂ powder, 5 parts by weight of acetylene black and 10 parts by weight of a styrene-based binder, and making the mixture turbid in an aqueous solution of carboxymethylcellulose. I made it. Apply this paste on both sides of aluminum foil, 11
After drying at 0 ° C., it was rolled to 0.17 mm by a roll press and cut out to a width of 35 mm and a length of 250 mm.

The negative electrode plate was prepared by mixing 100 parts by weight of carbon powder obtained by heat-treating coke with 10 parts by weight of PTFE, a fluororesin, and suspending the mixture in an aqueous solution of carboxymethyl cellulose to form a paste. This paste is applied to the surface of a copper foil having a thickness of 0.015 mm, dried, and dried.
Heat treatment was performed at 50 ° C. for 15 minutes. Thick this with a thickness of 0.
It was rolled to 2 mm and cut into a size of 37 mm in width and 280 mm in length.

Comparative Example 5 A battery was prepared in the same manner as in Example 3 except that the heat treatment was performed at 150 ° C., which is lower than the melting point of PTFE, for 15 minutes.

Comparative Example 6 A battery was prepared in the same manner as in Example 3, except that the heat treatment step was performed after the rolling step.

Example 4 10 parts by weight of a fluororesin FEP was mixed with 100 parts by weight of carbon powder obtained by heat treatment of coke, and this was suspended in an aqueous solution of carboxymethyl cellulose to form a paste. This paste is applied to the surface of a copper foil having a thickness of 0.015 mm, dried, and dried.
Heat treatment was performed at 00 ° C. for 15 minutes. Thick this with a thickness of 0.
It was rolled to 2 mm and cut into a size of 37 mm in width and 280 mm in length. Using this electrode, a battery similar to that of Example 3 was produced.

Comparative Example 7 A battery was prepared in the same manner as in Example 4, except that the heat treatment was performed at 150 ° C., which is lower than the melting point of FEP, for 15 minutes.

Comparative Example 8 A battery was prepared in the same manner as in Example 4, except that the heat treatment step was performed after the rolling step.

Each of the batteries constructed as described above was subjected to the following tape peeling test and charge / discharge cycle life test.

In the tape peeling test, the electrode plate was cut into an appropriate size, scratched at intervals of 5 mm in a horizontal direction and a vertical direction with a cutter knife, and then peeled off with a cellophane tape. Was measured to evaluate the binding force between the active material mixture and the current collector.

In the charge / discharge cycle test, charging was performed at an ambient temperature of 20.
Charge / discharge cycle at 100 ° C., constant current / constant voltage charge with charge voltage of 4.2 V, limited current of 500 mA, charge time of 2 hours, discharge at 20 ° C. with discharge current of 1000 mA, discharge end voltage of 3.0 V, and charge / discharge cycle of 100 The first charge / discharge capacity was compared with the 100th charge / discharge capacity, and the discharge capacity retention ratio was calculated based on the ratio of the 100th capacity to the first charge.

Table 1 shows the results of these evaluations.

[0033]

[Table 1]

In Table 1, PTF was used as a binder for the positive electrode.
In Example 1 using E, more active material mixture remained on the aluminum current collector in the tape peeling test than in Comparative Examples 1 and 2. This indicates that the electrode plate obtained by the method for producing an electrode plate for a non-aqueous electrolyte secondary battery of the present invention has a strong binding force between the metal current collector and the active material mixture. Further, in Example 1, no significant change was observed in the impedance of the battery (resistance measured at 1 kHz alternating current) even after the charge / discharge cycle was performed. On the other hand, in Comparative Examples 1 and 2, the impedance after the charge / discharge cycle was significantly increased.

When FEP was used as the binder for the positive electrode, almost the same results were obtained. In Example 2, the active material mixture remaining on the aluminum current collector in the tape peeling test was Comparative Example 3,
More than in Comparative Example 4. In Example 2, the impedance of the battery did not increase even after the charge / discharge cycle. On the other hand, in Comparative Examples 3 and 4, the impedance after the charge / discharge cycle was significantly increased.

In Table 1, PTF was used as a binder for the negative electrode.
In Example 3 using E, more active material mixture remained on the copper foil in the tape peeling test than in Comparative Examples 5 and 6. This indicates that the electrode plate obtained by the method for producing an electrode plate for a non-aqueous electrolyte secondary battery of the present invention has a strong binding force between the metal current collector and the active material mixture. In Example 3, no significant change was observed in the impedance of the battery even after performing the charge / discharge cycle. On the other hand, in Comparative Examples 5 and 6, the impedance after the charge / discharge cycle was significantly increased.

When FEP was used as the binder for the negative electrode, almost the same results were obtained. In Example 4, the active material mixture remaining on the copper foil in the tape peeling test was larger than in Comparative Examples 7 and 8. In Example 4, the impedance of the battery did not increase even after the charge / discharge cycle. On the other hand, in Comparative Examples 7 and 8, the impedance after the charge / discharge cycle was significantly increased.

From the above results, in the method of manufacturing an electrode for a non-aqueous electrolyte secondary battery, the temperature at which the electrode is heat-treated is higher than the melting point of the binder, and the metal current collector of the electrode is softened. It can be seen that by performing the heat treatment at a temperature higher than the temperature and performing this heat treatment step before the rolling step, the binding force between the metal current collector and the active material mixture can be increased.

In this example, the metal current collector was evaluated using an aluminum foil and a copper foil. The same effect was obtained when a stainless steel foil was used.

Further, although LiCoO ₂ was used as a positive electrode material which reversibly reacts with lithium in this embodiment, the same applies to the case where a lithium-containing composite oxide such as LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ is used. The effect was obtained.

Further, in each of the above embodiments, coke was used as the negative electrode material which reversibly reacts with lithium. However, similar effects were obtained by using a carbon material such as graphite or amorphous. .

Further, in each of the above examples, evaluation was made using a cylindrical battery. Similar effects were obtained even when the battery shape was different, such as a prismatic shape.

Further, in each of the above embodiments, lithium hexafluorophosphate was used as the electrolyte, but other lithium salts, such as lithium perchlorate, lithium tetrafluoroborate, and the like, provided the same effect. .

Furthermore, in each of the above embodiments, the salt concentration of the electrolyte was 1 mol / l, but the salt concentration was 0.5 to 2.0.
The same effect was obtained even when using 0 mol / l.

Furthermore, in each of the above embodiments, a mixed solvent of ethylene carbonate and diethyl carbonate was used as the electrolytic solution. However, other non-aqueous solvents such as cyclic esters such as propylene carbonate, cyclic ethers such as tetrahydrofuran, dimethoxyethane, etc. The same effect was obtained by using a non-aqueous solvent such as a chain ether such as a chain ether or a chain ester such as methyl propionate, or a mixed solvent of these multicomponent systems.

[0046]

As described above, the present invention relates to an electrode for a non-aqueous electrolyte secondary battery, wherein the temperature at which the electrode is heat-treated is higher than the melting point of the binder and the metal current collector of the electrode is By performing heat treatment at a temperature higher than the softening temperature and performing this heat treatment process before the rolling process, the binding force between the metal current collector and the active material mixture can be strengthened, and excellent charge / discharge cycle characteristics Can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram showing a configuration of a cylindrical battery according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulating packing 4 Electrode plate group 5 Positive plate 5a Positive lead 6 Negative plate 6a Negative lead 7 Separator 8 Insulation ring

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Tatsuya Hashimoto 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Toyoji Sugimoto 1006 Kazuma Kadoma, Kazuma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. 5H029 AJ05 AK03 AK08 AL08 AM02 CJ02 CJ03 DJ08 EJ12

Claims (5)

[Claims] 1. A method of manufacturing an electrode in which a material that reversibly reacts with lithium is used as a main constituent material, a paste containing a binder is applied to a metal current collector to form an electrode, and the electrode is heat-treated and then rolled. A method for producing an electrode for a non-aqueous electrolyte secondary battery, wherein the heat treatment temperature of the electrode is higher than the melting point of the binder and higher than the temperature at which the metal current collector softens. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the binder is at least one selected from polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Method of manufacturing electrodes. 3. The method according to claim 1, wherein the metal current collector is any one of an aluminum foil, a copper foil, and a stainless steel foil. 4. The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the material reversibly reacting with lithium is a lithium-containing composite oxide. 5. The lithium composite oxide is LiCoO._Two, L
iNiO_Two, LiMnO _Two, LiMn_TwoO_FourAny of
A method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 4.
Law.