JP4780935B2 - Nonaqueous electrolyte secondary battery and method of manufacturing electrode plate thereof - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a method for manufacturing the electrode plate.

  In recent years, with the spread of portable and cordless devices such as mobile phones and notebook computers, the demand for batteries for supplying power to these devices has increased. In particular, demand for secondary batteries, particularly nonaqueous electrolyte secondary batteries, that are small and light, have high energy density, and can be repeatedly charged and discharged is increasing.

  The electrode plate of the non-aqueous electrolyte secondary battery is made by kneading an active material such as a lithium-containing composite oxide or carbon material capable of occluding and releasing lithium, a conductive material, a binder, and a binder dispersion medium. The obtained mixture paint is coated on a current collector, dried and rolled. In particular, in the production process of the electrode plate, when water is used as the dispersion medium, a method of making the paint knead and disperse easily by exerting a thickening effect by adding a thickener is employed. As this thickener, water-soluble polymer materials such as methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, sodium polyacrylate, polyacrylic acid, polyethylene glycol, polyethylene oxide and the like are used.

  However, the mixture containing the thickener is in a state in which the thickener partially covers the active material. Thus, there existed a problem that the thickener has coat | covered the active material surface, inhibits the smooth electrochemical reaction of the active material in a mixture, and has a bad influence on a battery characteristic.

In order to solve this problem, as a method for producing a positive electrode plate, a method is disclosed in which a film of a thickener partially covering the active material is decomposed and destroyed by high-temperature oxidation by heat treatment at high temperature ( Patent Document 1). Moreover, also in the manufacturing method of a negative electrode, the method of decomposing | disassembling a thickener by operation of heat processing temperature and oxygen partial pressure is disclosed (refer patent document 2, 3). These techniques optimize the form of thickener coating.
JP-A-7-105970 Japanese Patent Laid-Open No. 2001-210318 JP 2001-250536 A

  However, when the technology disclosed in Patent Documents 1 to 3 is applied for the purpose of improving battery characteristics and the electrode plate is continuously heat treated at a high temperature for a long time, a heat-resistant and durable binder is used at the heat treatment temperature. However, if heat treatment is performed for a long time at a temperature above the heat-decomposition temperature of the binder physical properties, the adhesion between the electrode plate mixture and the current collector decreases, and the output characteristics and charge / discharge cycle characteristics are reduced. Deterioration may occur. And when trying to improve the characteristics by further decomposing the thickener, the heat treatment process takes a long time and the heat treatment must be performed at a higher temperature. For this reason, deterioration of characteristics is expected. Moreover, in the technique of the said indication, since heat processing time must be performed for a long time depending on the grade which decomposes | disassembles a thickener, productivity falls.

  Therefore, in view of the above problems, the present invention efficiently removes the thickener without reducing the adhesion between the electrode plate mixture and the current collector, and the output characteristics and charge / discharge cycle characteristics are improved. It is an object to provide a method for producing an improved electrode plate.

  The present invention is a step of preparing a mixture paint containing at least an electrode active material, a binder, a thickener, and water, and a conductive material to be added if necessary, applying the mixture paint on a current collector, In the method for producing an electrode plate for a non-aqueous electrolyte secondary battery having a step of drying to form a mixture layer and a step of removing moisture in the electrode plate by heat treatment, the step of removing moisture in the electrode plate In advance, a heat treatment step is provided in a high-temperature atmosphere with water vapor introduced or higher than the boiling point of water.

The heat treatment in this high-temperature atmosphere with the introduction of water vapor decomposes and alters the thickener using a hydrolysis reaction, and lowers the temperature at which the thickener is scattered in the process of removing water in the subsequent process. The heat treatment time can be changed shorter. For this reason, it is possible to suppress a decrease in the binding force between the mixture and the current collector due to thermal deterioration of the binder, and to improve the battery characteristics by decomposing or removing the thickener. Moreover, there is an effect of improving productivity by lowering the heat treatment conditions and reducing the time.
The method for producing an electrode plate according to the present invention has an effect of improving battery characteristics even when applied to either a positive electrode plate or a negative electrode plate.

  According to the present invention, since the thickener can be decomposed and denatured by hydrolysis by heat treatment in a high-temperature atmosphere with water vapor introduced or higher, the heat treatment step for removing the thickener The temperature can be lowered and the processing time can be shortened. Thereby, the heat deterioration of a binder can be suppressed and the characteristic fall by the residual of a thickener can be prevented. Furthermore, the productivity of the battery can be improved.

  The method for producing an electrode plate for a non-aqueous electrolyte secondary battery according to the present invention comprises a step of preparing a mixture paint by mixing at least an electrode active material, a binder, a water-soluble thickener, and water, the mixture paint Is applied to the current collector and dried to remove moisture, steam is introduced, heat treatment is performed in a high temperature atmosphere above the boiling point of water, and moisture in the electrode plate is removed by heat treatment. .

Here, in the process of heat-treating in a high temperature atmosphere having a boiling point of water or higher with water vapor introduced, the temperature is preferably 105 to 350 ° C, more preferably 120 to 250 ° C.
In the step of removing moisture from the electrode plate following the heat treatment, the temperature is preferably 120 to 250 ° C. in that it is excellent in the effect of scattering the thickening agent. / 5 of about 2 hours is sufficient.

The positive electrode active material, wherein _{Li x M y N 1-y} O 2 ( wherein, M and N, at least one Co, Ni, Mn, Cr, Fe, Mg, selected from the group consisting of Al, and Zn The lithium-containing composite oxide represented by 0.98 ≦ x ≦ 1.10 and 0 ≦ y ≦ 1) is preferable. The positive electrode current collector is preferably Al or an Al alloy. The binder used for the positive electrode is preferably an aqueous dispersion containing any of polytetrafluoroethylene, polyvinylidene fluoride, and tetrafluoroethylene-hexafluoropropylene copolymer.

  As the negative electrode active material, a carbon material, graphite material, alloy, or metal oxide capable of inserting and extracting lithium is used. The current collector for the negative electrode is preferably Cu, Ni, or a Cu—Ni alloy. The binder is styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, methyl methacrylate-sodium methacrylate rubber, methyl methacrylate-lithium methacrylate rubber, ammonium methacrylate-lithium methacrylate rubber, methacrylic acid. It is preferable to use any one of methyl acid-lithium methacrylate-ammonium methacrylate rubber, or a combination thereof.

  The thickener is one of water-soluble polymers such as methyl cellulose, carboxymethyl cellulose, carboxymethyl cellulose sodium salt, carboxymethyl cellulose lithium salt, polyvinyl alcohol, polyvinyl pyrrolidone, sodium polyacrylate, polyacrylic acid, polyethylene glycol, and polyethylene oxide. Alternatively, a plurality of them can be used in combination. Due to the thickening effect of the addition of the thickener, the active material, the conductive material and the binder can be easily kneaded and dispersed when preparing the mixture paint.

The nonaqueous electrolyte is composed of a nonaqueous solvent and a solute. As the solute, various lithium compounds such as LiPF ₆ and LiBF ₄ can be used. As the solvent, it is preferable to use ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or the like alone or in combination of two or more.

  The separator is not particularly limited as long as it can withstand the operating temperature range of the non-aqueous electrolyte secondary battery, but it is common to use a single or composite of microporous films of olefin resins such as polyethylene and polypropylene. And also preferred.

Examples of the present invention will be described below.
FIG. 1 is a longitudinal sectional view showing a schematic configuration of a cylindrical lithium secondary battery manufactured in an example.
An electrode plate group 4 in which a positive electrode plate 5, a negative electrode plate 6, and a separator 7 disposed between both electrode plates are wound in a spiral shape is housed in a battery case 1 made of stainless steel. The positive electrode plate is obtained by forming a mixture containing a positive electrode active material on both surfaces of the positive electrode current collector, and the negative electrode plate is obtained by forming a mixture containing a negative electrode active material on both surfaces of the negative electrode current collector. The electrode group 4 holds an electrolytic solution. An upper insulating plate 8 and a lower insulating plate 9 are disposed above and below the electrode plate group 4, respectively. The negative electrode plate 6 is connected to the battery case 1 via the negative electrode lead 6a. The positive electrode plate 5 is connected to the sealing plate 2 provided with the positive electrode terminal via the positive electrode lead 5a. The opening of the battery case 1 is sealed with a sealing plate 2 through an insulating packing 3. Here, a cylindrical lithium secondary battery is shown, but the nonaqueous electrolyte secondary battery of the present invention is not limited to a cylindrical type.

<< Comparative Example 1 >>
[Method for producing positive electrode plate]
The lithium composite oxide LiCoO ₂ , the conductive agent acetylene black, the binder polytetrafluoroethylene resin aqueous dispersion, and the thickener carboxymethylcellulose sodium salt in a weight ratio of 100: 3: 3: Mixing was performed at a ratio of 0.5, and water was further added and kneaded to produce a mixture paint. This mixture paint was applied to both surfaces of a positive electrode current collector made of an Al foil having a thickness of 20 μm, and dried in air at 110 ° C. to vaporize and dry the water. Thereafter, heat treatment was performed at 250 ° C. for 10 hours in air having a dew point of −60 ° C., followed by rolling in a rolling process to produce a positive electrode plate having a thickness of 170 μm.

[Method for producing negative electrode plate]
The active material flaky graphite, the binder styrene-butadiene rubber aqueous dispersion, and the thickener carboxymethyl cellulose sodium salt were mixed at a weight ratio of 100: 3: 0.3 in a solid content ratio. Further, water was added and kneaded to produce a mixture paint. This mixture paint was applied to both surfaces of a negative electrode current collector made of Cu foil having a thickness of 20 μm, and dried in air at 110 ° C. to vaporize and dry water. Thereafter, heat treatment was performed at 250 ° C. for 10 hours in dry air having a dew point of −60 ° C., followed by rolling in a rolling process to produce a negative electrode plate having a thickness of 170 μm.

[Battery Manufacturing Method]
The positive electrode plate, the negative electrode plate, and the separator inserted between the two electrode plates were spirally wound to assemble the electrode plate group. The electrode plate group was housed in a case made of stainless steel SUS, and after pouring a non-aqueous electrolyte, it was sealed with a sealing plate. As the separator, a polyethylene porous film having a thickness of 20 μm was used. The porosity of the separator was 45% as measured with a mercury porosimeter (manufactured by Yuasa Ionics).
The cylindrical lithium secondary battery thus manufactured has a height of 65 mm, a diameter of 18 mm, and a design capacity of 1800 mAh. As the non-aqueous electrolyte, a solution obtained by dissolving 1 mol / l of LiPF ₆ in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 1 was used.

Example 1
[Method for producing positive electrode plate]
The same mixture paint as in Comparative Example 1 was applied to a positive electrode current collector made of an Al foil having a thickness of 20 μm, dried in air at 110 ° C. to vaporize and dry water. Thereafter, heat treatment was performed for 10 minutes in a 250 ° C. constant temperature bath (internal volume 110 L) into which saturated steam at 60 ° C. was continuously introduced at 0.5 L / min. Thereafter, heat treatment was performed at 250 ° C. for 2 hours in air having a dew point of −60 ° C., and then rolled to produce a 170 μm positive electrode plate.
A battery was fabricated in the same manner as in Comparative Example 1 except that the above positive electrode plate was used.

Example 2
[Method for producing negative electrode plate]
The same mixture paint as in Comparative Example 1 was applied to a negative electrode current collector made of Cu foil having a thickness of 20 μm, dried in air at 110 ° C. to vaporize and dry water. Thereafter, heat treatment was performed for 10 minutes in a 250 ° C. constant temperature bath (internal volume 110 L) into which saturated steam at 60 ° C. was continuously introduced at 0.5 L / min. Thereafter, heat treatment was performed at 250 ° C. for 2 hours in air having a dew point of −60 ° C., and then rolled to produce a 170 μm negative electrode plate.
A battery was manufactured in the same manner as in Comparative Example 1 except that the above negative electrode plate was used.

Example 3
Using the positive electrode plate of Example 1 and the negative electrode plate of Example 2, a battery was produced in the same manner as above.

<< Comparative Example 2 >>
In the manufacturing method of the positive electrode plate and the manufacturing method of the negative electrode plate of Comparative Example 1, except that the heat treatment conditions in the air at a dew point of −60 ° C. after applying the mixture paint and drying were changed to 250 ° C. for 8 hours. Similarly, a positive electrode plate and a negative electrode plate were produced. A battery was manufactured in the same manner as in Comparative Example 1 except for the above.

<< Comparative Example 3 >>
In the manufacturing method of the positive electrode plate and the manufacturing method of the negative electrode plate of Comparative Example 1, the heat treatment conditions in the air having a dew point of −60 ° C. after applying the mixture paint and drying were changed to 250 ° C. for 4 hours. Similarly, a positive electrode plate and a negative electrode plate were produced. A battery was manufactured in the same manner as in Comparative Example 1 except for the above.

<< Comparative Example 4 >>
In the manufacturing method of the positive electrode plate of Comparative Example 1, the positive electrode plate was prepared in the same manner except that the heat treatment conditions in the air having a dew point of −60 ° C. were changed to 2 hours at 250 ° C. after the mixture paint was applied and dried. Manufactured. A battery was manufactured in the same manner as in Comparative Example 1 except that this positive electrode plate was used.

<< Comparative Example 5 >>
In the method for producing the negative electrode plate of Comparative Example 1, the negative electrode plate was prepared in the same manner except that the heat treatment conditions in the air having a dew point of −60 ° C. were changed to 2 hours at 250 ° C. after the mixture paint was applied and dried. Manufactured. A battery was manufactured in the same manner as in Comparative Example 1 except that this negative electrode plate was used.

Example 4
In the manufacturing method of the positive electrode plate of Example 1, the positive electrode plate was prepared in the same manner except that the heat treatment conditions in the air having a dew point of −60 ° C. were changed to 10 hours at 150 ° C. after the heat treatment in an atmosphere into which water vapor was introduced. Manufactured. A battery was manufactured in the same manner as in Example 1 except that this positive electrode plate was used.

Example 5
In the method for producing the negative electrode plate of Example 2, the negative electrode plate was prepared in the same manner except that the heat treatment conditions in the air with a dew point of −60 ° C. were changed to 10 hours at 150 ° C. after the heat treatment in the atmosphere into which water vapor was introduced. Manufactured. A battery was manufactured in the same manner as in Example 2 except that this negative electrode plate was used.

Example 6
A battery was manufactured in the same manner as in Example 4 except that the negative electrode plate manufactured by the negative electrode plate manufacturing method of Example 5 was used.

<< Comparative Example 6 >>
In the manufacturing method of the positive electrode plate of Comparative Example 1, the positive electrode plate was prepared in the same manner except that the heat treatment conditions in the air having a dew point of −60 ° C. were changed to 10 hours at 150 ° C. after applying the mixture paint and drying. Manufactured. A battery was manufactured in the same manner as in Comparative Example 1 except that this positive electrode plate was used.

<< Comparative Example 7 >>
In the manufacturing method of the negative electrode plate of Comparative Example 1, the negative electrode plate was similarly applied except that the heat treatment conditions in the air having a dew point of −60 ° C. were changed to 10 hours at 150 ° C. after the mixture paint was applied and dried. Manufactured. A battery was manufactured in the same manner as in Comparative Example 1 except that this negative electrode plate was used.

<< Comparative Example 8 >>
The mixture paint of Comparative Example 1 was applied to a positive electrode current collector made of an Al foil having a thickness of 20 μm and dried in air at 110 ° C. to completely vaporize and dry the water. Thereafter, heat treatment was performed for 10 minutes in a 95 ° C. thermostat (internal volume 110 L) in an air atmosphere into which saturated steam at 60 ° C. was introduced at 0.5 L / min. Thereafter, heat treatment was performed at 250 ° C. for 2 hours in air having a dew point of −60 ° C., and then rolled to produce a 170 μm positive electrode plate.
A battery was manufactured in the same manner as in Comparative Example 1 except that this positive electrode plate was used.

<< Comparative Example 9 >>
The mixture paint of Comparative Example 1 was applied to a negative electrode current collector made of Cu foil having a thickness of 20 μm, and dried in air at 110 ° C. to completely vaporize and dry the water. Then, heat treatment is performed for 10 minutes in a 95 ° C. constant temperature bath (internal volume 110 L) of air atmosphere introduced with saturated water vapor at 60 ° C. at 0.5 L / min, and then at 250 ° C. in air with a dew point of −60 ° C. Heat treatment was performed for 2 hours, and then rolled to produce a 170 μm negative electrode plate.
A battery was manufactured in the same manner as in Comparative Example 1 except that this negative electrode plate was used.

The batteries of the above examples and comparative examples were evaluated as follows.
[Battery evaluation method]
(i) Low-temperature discharge test In an environment at 25 ° C, the battery was charged at a constant voltage of 4.2V (however, the maximum current was 1A). It was measured.
(ii) Cycle life test In a 25 ° C environment, the battery was charged at a constant current to 4.2V at 1A, then charged at a constant voltage of 4.2V for 30 minutes (the maximum current was 1A), and then terminated at a constant current of 1A. A life test was performed by repeating the cycle of discharging to a voltage of 3.0 V 300 times. Then, by comparing the first cycle discharge capacity C ₁ and 300th cycle discharge capacity C _300, it was calculated and the capacity retention ratio by the following formula (1).
Capacity maintenance rate (%) = C ₃₀₀ / C ₁ × 100 (1)

  These evaluation results are shown in Table 1.

  When the battery of Example 1 and the battery of Comparative Example 1 which were subjected to heat treatment at 250 ° C. for 10 minutes in an atmosphere into which water vapor was introduced in the positive electrode manufacturing process were compared, the discharge capacity at 0 ° C. was almost the same. Therefore, it can be seen that the heat treatment conditions in dry air can be reduced from 10 hours at 250 ° C. to 1 hour at 250 ° C. by performing heat treatment at 250 ° C. for 10 minutes in a steam atmosphere. Further, the capacity maintenance rate after 300 cycles is improved to 85% in Example 1 compared to 55% in Comparative Example 1.

  From the results of Comparative Examples 1 to 3, in order to secure a discharge capacity of 0 ° C., heat treatment in dry air must be performed at 250 ° C. for 10 hours. According to Example 3, the heat treatment time in dry air is from 10 hours, compared with Comparative Example 1 in which heat treatment in a water vapor atmosphere is not performed by performing heat treatment at 250 ° C. for 10 minutes in a water vapor atmosphere on the positive and negative electrode plates. It can be seen that the discharge characteristic of 0 ° C. can be secured even if the time is shortened to 2 hours. By introducing water vapor into the thermostat for heat treatment at 250 ° C., the thickener is hydrolyzed to reduce the molecular weight and lower the vaporization temperature. For this reason, even if the heat treatment time is shortened to 1/5, it is considered that the thickener was decomposed and scattered, and the discharge characteristics at 0 ° C. could be maintained. Moreover, the effect which productivity improves by the manufacturing method of the electrode plate of this invention was also able to be verified.

  Comparing the results of Example 2 and Comparative Example 5, when the heat treatment at 250 ° C. into which water vapor was introduced in the negative electrode plate manufacturing process was performed for 10 minutes, the discharge characteristics at 0 ° C. were maintained as in the case of the positive electrode plate. It was also confirmed that the cycle life could be improved. Further, from the results of Example 3, when the heat treatment in which water vapor is introduced is performed on both the positive electrode plate and the negative electrode plate, the cycle life can be further improved as compared with the case where either the positive electrode plate or the negative electrode plate is used. From these results, it was possible to change only the thickener to a physical property that can be easily vaporized and removed by hydrolysis, so that the thickener can be decomposed by a short heat treatment. For this reason, it is considered that the deterioration of the binder was suppressed and the cycle life could be improved.

  Next, comparing Comparative Example 1 with Example 4 in which a heat treatment at 250 ° C. with water vapor introduced in the positive electrode plate production process was performed for 10 minutes, the heat treatment in dry air was performed at 250 ° C. for 10 hours to 150 ° C. for 10 hours. It was confirmed that the discharge characteristics of 0 ° C. can be maintained even when the temperature is lowered to 100 ° C. Furthermore, it was also confirmed that the characteristics could be improved from 55% capacity retention rate after 300 cycles of Comparative Example 1 to 81% in Example 4. As a result of comparing the characteristics of Example 4 and Comparative Example 6, and Example 5 and Comparative Example 7, when such a treatment is not performed by performing heat treatment in one steam plate for 10 minutes. It is understood that heat treatment at 250 ° C. for 10 hours is required in dry air, but the heat treatment temperature can be lowered from 250 ° C. to 150 ° C., and the cycle life can be improved.

  In Comparative Examples 8 and 9, the heat treatment temperature in the water vapor atmosphere of the positive electrode plate or the negative electrode plate was 95 ° C., and the boiling point of water at 1 atm was lower than 100 ° C. It was confirmed that there was no effect of improving the characteristics. Compared with Comparative Example 1, the battery characteristics of Comparative Examples 8 and 9 are greatly deteriorated. This is presumably because water vapor did not act on the hydrolysis of the thickener, water was adsorbed on the binder and thickener, and the adsorbed water acted on the deterioration of the discharge characteristics.

  The nonaqueous electrolyte secondary battery according to the present invention is excellent in life characteristics and high output discharge characteristics, and is useful as a power source for various portable electric devices.

1 is a schematic vertical sectional view of a battery according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode plate group 5 Positive electrode plate 5a Positive electrode lead 6 Negative electrode plate 6a Negative electrode lead 7 Separator 8 Upper insulating plate 9 Lower insulating plate

Claims (4)

A step of preparing a mixture paint containing at least an electrode active material, a binder, a water-soluble thickener, and water; a step of applying the mixture paint on a current collector and drying to form a mixture layer; , Having a step of heat treatment in a high temperature atmosphere having a boiling point of water or higher, in which water vapor is introduced, and a step of removing moisture by the heat treatment ,
Non- aqueous electrolyte secondary battery electrode , wherein the thickener comprises at least one selected from the group consisting of methylcellulose, carboxymethylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, sodium polyacrylate, polyacrylic acid, polyethylene glycol, and polyethylene oxide. A manufacturing method of a board.   The method for producing an electrode plate for a non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode active material is a lithium-containing composite oxide, and the mixture paint further contains a conductive material.   The method for producing an electrode plate for a non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode active material is a carbon material capable of inserting and extracting lithium. Non-aqueous electrolyte secondary battery comprising an electrode plate manufactured by the manufacturing method according to any one of claims 1-3.

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