JPH1131500A - Manufacture of negative pole plate, and non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the orientation of scale-like graphite, which has excellent intercalate characteristic of Li, in a negative electrode active material layer, and to improve the high rate characteristic by forming scale-like graphite powder into nearly spherical granular material, and coating a negative electrode collector foil with the active material paste, in which the granular material is distributed in the spherical shape condition, and drying it so as to obtain a negative pole plate. SOLUTION: Scale-like graphite powder 12 is supplied from a supplying machine 25 onto a disc 23 rotated at a constant speed, and the adhesive suspension liquid 14 is injected from an injector 26, and the scale-like graphite powder 12 is rolled on the inner wall 22 on a cylinder, and formed larger like a snowball, and discharged from a discharge port 28. After drying the discharged spherical material 15 with the hot air, the spherical material 15 is classified so as to obtain nearly spherical granular material. Continuously, polytetrafluoroethylene or the like is blended in this granular material, and it is kneaded so as to obtain the negative electrode active material paste, and this negative electrode active material paste is coated on a negative electrode collector foil of copper foil, and drying, rolling and cutting are performed so as to obtain a sheet-like negative pole plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a negative electrode plate and a non-aqueous electrolyte secondary battery such as a lithium secondary battery using the negative electrode plate manufactured by the method.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become more portable and cordless, there has been a demand for the development of secondary batteries which are small, lightweight, have a high energy density and can be repeatedly charged and discharged. Research on non-aqueous electrolyte secondary batteries as such secondary batteries, particularly lithium secondary batteries using a Li-transition metal double oxide such as LiCo _{2 as a} positive electrode active material and a carbon material or the like as a negative electrode active material , Development is being actively carried out.

However, since this type of non-aqueous electrolyte secondary battery uses a non-aqueous electrolyte, the ion mobility is lower than that of an aqueous battery, so that the electrode plate is formed into a sheet in a limited space. Many configurations have been proposed in which the electrode area is increased as much as possible. A method for manufacturing such a sheet-like electrode plate is described in, for example, Japanese Patent Application Laid-Open No. 8-111.
As disclosed in Japanese Patent Publication No. 222, a paste in which a powdery active material, a binder, and the like are dispersed in a solvent is obtained, and the paste is applied to a current collector sheet and dried.
In order to apply this paste thinly and uniformly, as a coating method, a die head coater method or a doctor method is often used. After the application, it is dried and then rolled to increase the packing density of the active material, and cut into a required size to obtain a sheet-like electrode plate (see FIG. 5). As the carbon material of the negative electrode active material, flaky graphite excellent in Li intercalation characteristics has been studied in many cases.

[0004]

However, when the flaky graphite powder is applied and dried by the paste application method as described above, due to its flat shape, as shown in FIG. At 32, the uneven plane, that is, the basal plane of the graphite crystal is oriented so as to be parallel to the surface of the negative electrode current collector 11 and distributed. As a result, the mobility of Li ions in the negative electrode active material layer 32 is reduced, so that the internal resistance is increased and the high-rate characteristics when a large discharge current flows are reduced.

In view of the above problems, the present invention provides a method for producing a negative electrode plate capable of suppressing the orientation of flaky graphite having excellent Li intercalation characteristics in a negative electrode material layer and improving high rate characteristics, and a non-aqueous electrolyte. It is intended to provide a secondary battery.

[0006]

In order to achieve the above object, the method for producing a negative electrode plate of the present invention granulates flaky graphite powder into a substantially spherical shape, and obtains a granulated body having the same shape. An active material paste dispersed in a state is applied to a negative electrode current collector foil and dried to obtain a negative electrode plate.

According to the method for producing a negative electrode plate of the present invention, since the granules of the flaky graphite powder are substantially spherical, a large number of granules are not oriented parallel to the negative electrode current collector foil surface. . Therefore, even if the flaky graphite powder is oriented in one direction in one of the granules, the flaky graphite powder is not generally oriented parallel to the negative electrode current collector foil surface, and generally has a substantially spherical shape. Since the flaky graphite powder is oriented in various directions in the granules, the flaky graphite powder is distributed in a random direction as a whole. Therefore, the orientation of the flaky graphite excellent in the intercalation characteristics of Li in the negative electrode material layer can be suppressed, and the high rate characteristics can be improved.

The average particle size of the flaky graphite powder is 10 to 40 μm.
m, this flaky graphite powder is granulated in a substantially spherical shape to obtain a granule having an average particle size of 50 to 200 μm. The use of the flaky graphite powder makes it possible to easily obtain a substantially spherical granule having good dispersibility in the active material paste, which is preferable. When the average particle size of the flaky graphite powder is less than 10 μm, the filling rate is low, and the high rate characteristics are unfavorably reduced. When the average particle size of the flaky graphite powder exceeds 40 μm, granulation becomes difficult. Not preferred. Also,
When the average particle size of the granules is less than 50 μm, the granules do not become substantially spherical, which is not preferable. When the average particle size of the granules exceeds 200 μm, the dispersibility of the granules in the active material paste deteriorates. It is not preferable because of segregation.

Also, a positive electrode plate containing a Li-transition metal complex oxide as a main component of a positive electrode active material, a negative electrode plate containing flaky graphite powder as a main component of a negative electrode active material, and a lithium salt dissolved in an organic solvent. In a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte, when the negative electrode plate is manufactured by the method for manufacturing a negative electrode plate of the present invention, in the negative electrode material layer of flaky graphite excellent in intercalation characteristics of Li. The orientation can be suppressed, and a non-aqueous electrolyte secondary battery having good high rate characteristics can be easily obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, one embodiment of the method for manufacturing a negative electrode plate according to the present invention includes a first step of obtaining granules 16,
It comprises a second step of obtaining a negative electrode active material paste and a third step of obtaining a negative electrode plate 3.

The first step is a step of using the granulator 20 to granulate the flaky graphite powder 12 into a substantially spherical shape.

As shown in FIG. 2, a granulating apparatus 20 includes a container body 21 having a cylindrical inner wall 22 and a container body 21 having a cylindrical inner wall 22.
A disk 23 that rotates in a horizontal plane, a motor 24 that drives the disk 23, a feeder 25 that receives the scale-like graphite powder 12 and supplies it quantitatively onto the disk 23, The sprayer 26 includes a sprayer 26 that stores and supplies the suspension 14 quantitatively onto the disk 23 and a blower 27 that blows dry air from below the periphery of the disk 23.

The first step performed by the granulating apparatus 20 will be described. First, flaky graphite powder 12 having an average particle diameter of 20 μm is continuously supplied from a supply device 25 onto a disk 23 rotating at a constant speed at a constant supply speed, and at the same time, PVDF (polyvinylidene fluoride) 10 wt. % Organic solvent suspension (binder suspension) 14 is sprayed quantitatively from sprayer 26 so that flake graphite powder 12 becomes 99% by weight of PVDF and 1% by weight of PVDF. Is the disk 23
It is rotated on the top and bound by the binder suspension 14,
It is accelerated and rolls on the surface of the inner cylindrical wall 22, granulated in a snowball manner, and discharged from the outlet 28 through the opening 22 a of the inner cylindrical wall 22. Next, the discharged spherical material 15 was dried with hot air at 100 ° C., and then classified into 10 to 200 μm to obtain a substantially spherical granule 16 having an average particle diameter of 100 μm. As shown in FIG. 3, in each of the obtained granules 16, the crystal directions of a large number of flaky graphite powders 12 are random.

Next, in the second step, the granules 16
0 wt%, PTFE (polytetrafluoroethylene) 50
A 9% by weight aqueous dispersion and a 41% by weight aqueous solution of 1% by weight carboxymethyl cellulose were blended and kneaded to obtain a negative electrode active material paste. Here, since the PVDF binder in the granules 16 does not react or dissolve even when it comes into contact with the aqueous solution, the granules 16 do not fall apart during kneading of the negative electrode active material paste.

Then, in a third step, the negative electrode active material paste is applied to a negative electrode current collector foil 11 made of a copper foil having a thickness of 50 μm by a doctor method to a thickness of about 180 μm and dried.
The sheet was rolled to a thickness of 0.2 mm and cut to obtain a sheet-shaped negative electrode plate 3.

The negative electrode plate 3 thus obtained is shown in FIG.
As shown in the figure, in the negative electrode active material layer 13, while the flaky graphite powder 12 maintains the cluster state of the granules 16, the crystal direction of each flaky graphite powder 12 is in a random direction as a whole. Facing and distributed. In the negative electrode plate 3, the packing density of the negative electrode active material is increased by crushing the voids in the negative electrode active material layer 13 exclusively by rolling. However, PVDF has higher mechanical strength and flexibility than PTFE, so that it is formed. The granules 16 are hardly crushed, and therefore the flaky graphite powder 12 is not oriented by this rolling.

Further, as shown in FIG. 5, the negative electrode plate 31 according to the conventional method is obtained by adding flaky graphite powder having an average particle size of 20 μm to 5
0 wt%, PTFE 50 wt% aqueous dispersion 9 wt%, carboxymethylcellulose 1 wt% aqueous solution 41 wt%, respectively, are blended and kneaded to obtain a negative electrode active material paste.
Approximately 180μm thick by doctor method on 50μm thick copper foil
After applying and drying, it was rolled to a thickness of 0.2 mm and cut. In the negative electrode plate 31 thus obtained, the flaky graphite powder 12 is oriented in parallel with the negative electrode current collector foil 11 in the negative electrode active material layer 32 as shown in FIG.

One embodiment of the non-aqueous electrolyte secondary battery of the present invention is a cylindrical lithium secondary battery as shown in FIG. 4, in which the negative electrode plate 3 obtained by the method of manufacturing a negative electrode plate of the present invention is used. It is composed of the used electrode plate group, the electrolytic solution, and the battery case accommodating them.

The electrode group includes a sheet-shaped positive electrode plate 1, the sheet-shaped negative electrode plate 3, a sheet-shaped separator 5 for insulating between the positive electrode plate 1 and the negative electrode plate 3, a positive electrode lead 2, and a negative electrode lead. 4, an upper insulating plate 6 and a lower insulating plate 7. The positive electrode plate 1 is formed by coating a positive electrode active material layer on both surfaces of an aluminum foil, the negative electrode plate 3 is formed by coating a negative electrode active material layer on both surfaces of a copper foil, and the separator 5 is formed of a porous polypropylene film. These are stacked and spirally wound, and are tightly housed in a cylindrical battery case.

A method for manufacturing the positive electrode plate 1 will be described. First, L
50 wt% of iCoO ₂ powder, 1.5 wt% of acetylene black, 7 wt% of 50 wt% aqueous dispersion of PTFE, and 41.5 wt% of 1 wt% aqueous solution of carboxymethyl cellulose were mixed and kneaded to obtain a positive electrode active material paste. Next, this positive electrode active material paste was applied to a 30 μm-thick aluminum foil by a doctor method with a thickness of about 180 μm and dried, and then the thickness was 0.18 mm.
, And cut to obtain a positive electrode plate.

The electrolytic solution contains 30 vol% of ethylene carbonate.
50 vol% of diethyl carbonate and methyl propionate 20
1 mol / lite of LiPF _{6 in} a mixed solution with vol%
It consists of a substance dissolved at a concentration of r. This electrolytic solution is accommodated in a battery case, and is filled in continuous voids in the positive electrode active material layer and the negative electrode active material layer 13. In the battery reaction, the positive electrode plate passes through the micropores of the porous separator 5. 1 and transports Li ions between negative electrode plate 3.

The battery case includes a case body 8 obtained by deep drawing an organic electrolytic solution-resistant stainless steel plate and a sealing plate 1.
And an insulating gasket 9 for insulating and gas-sealing between the sealing plate 10 and the case body 8.

The battery of the present invention having the above-described configuration was obtained, and the evaluation results of the high-rate characteristics thereof are shown in Table 1 together with those of the battery according to the conventional method. The battery according to the conventional method was constituted by using the negative electrode plate 31 according to the conventional method, the same positive electrode plate 1 as the battery according to the present invention, and the electrolytic solution.

The high rate characteristic is that after charging, a constant current of 180
The ratio P / Q of the battery capacity P discharged until the discharge voltage reaches 3.0 V after discharging at 0 mA and the battery capacity Q discharged until the discharge voltage reaches 3.0 V after discharging at a constant current of 900 mA. Was evaluated. As shown in Table 1, it can be seen that the battery of the present invention has remarkably excellent high-rate characteristics as compared with the battery according to the conventional method (Comparative Example).

[0026]

[Table 1]

In the above embodiment, a 10 wt% PVDF organic solvent suspension of PVDF was used as the binder suspension 14 for obtaining the granules 16. However, the present invention is not limited to this, and the negative electrode active It is sufficient that the shape of the granulated body 16 is sufficiently maintained during kneading and application of the material paste, and examples thereof include a butadiene rubber-based binder, a styrene-butadiene rubber-based binder, a fluororesin-based binder, and a petroleum-based pitch. May be used, and it is not always necessary that the strength of the binder of the active material paste is higher than that of the active material paste, and an aqueous solution-based binder may be used.

[0028]

According to the method for producing a negative electrode plate of the present invention, since the granules of the flaky graphite powder are substantially spherical, a large number of granules are oriented parallel to the negative electrode current collector foil surface. There is no. Therefore, even if the flaky graphite powder is oriented in one direction in one of the granules, the flaky graphite powder is not generally oriented parallel to the negative electrode current collector foil surface, and generally has a substantially spherical shape. Since each flaky graphite powder is oriented in various directions in the granules,
As a whole, the flaky graphite powder is distributed in a random direction. Therefore, the orientation of the flaky graphite excellent in the intercalation characteristics of Li in the negative electrode material layer can be suppressed, and the high rate characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a flowchart showing one embodiment of a method for manufacturing a negative electrode plate of the present invention.

FIG. 2 is a schematic view showing a granulating apparatus used for manufacturing a negative electrode plate of the present invention.

FIG. 3 is a schematic cross-sectional view showing an enlarged part of a negative electrode plate obtained by the method for producing a negative electrode plate of the present invention.

FIG. 4 is a partial cross-sectional view showing one embodiment of the nonaqueous electrolyte secondary battery of the present invention.

FIG. 5 is a flowchart showing an example of a conventional method for manufacturing a negative electrode plate.

FIG. 6 is an enlarged schematic cross-sectional view showing a part of a conventional negative electrode plate.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 positive electrode plate 3 negative electrode plate 11 negative electrode current collector foil 12 flaky graphite powder 16 granulated body

Claims (3)

[Claims] 1. A scale-like graphite powder is granulated into a substantially spherical shape, and an active material paste in which the obtained granules are dispersed while maintaining the shape is applied to a negative electrode current collector foil and dried. A method for producing a negative electrode plate, comprising obtaining a negative electrode plate. 2. The scaly graphite powder has an average particle size of 10 to 40.
The method for producing a negative electrode plate according to claim 1, wherein the flake graphite powder is granulated into a substantially spherical shape to obtain a granule having an average particle size of 50 to 200 m. 3. A positive electrode plate containing a Li-transition metal complex oxide as a main component of a positive electrode active material, a negative electrode plate containing flaky graphite powder as a main component of a negative electrode active material, and a lithium salt dissolved in an organic solvent. In a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte,
A non-aqueous electrolyte secondary battery, wherein the negative electrode plate is manufactured by the method for manufacturing a negative electrode plate according to claim 1.