JP6919801B2 - Electrode manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing an electrode, specifically, a method for manufacturing an electrode for a secondary battery.

In recent years, secondary batteries such as lithium ion secondary batteries and nickel-metal hydride batteries have been widely used as so-called portable power sources for personal computers and mobile terminals and power sources for driving vehicles. In such a secondary battery, a sheet-shaped electrode in which an electrode mixture layer is provided on the surface of a foil-like current collector is used, and the electrode mixture layer of the electrode is an electrode active material or a binder. It contains electrode materials such as agents (binders) and conductive materials. Patent Documents 1 and 2 disclose examples of electrode active materials contained in the electrode mixture layer of such a secondary battery.

Further, as an example of a method for producing a sheet-shaped electrode, a wet granulated body made of a wet electrode material as described in Patent Document 3 is rolled to form an electrode mixture layer, and the combination thereof is performed. A method of adhering the material layer to the surface of the current collector can be mentioned. Specifically, the production method described in Patent Document 3 has a diameter of 1.0 mm to 5.0 mm in which a mixture of an electrode active material, a conductive material, polytetrafluoroethylene (binder) and water is kneaded in a wet state. It is provided with a granulation step of granulating to the size of the above and a filling step of passing the obtained granulated product (wet granulated material) together with a conductive base material (current collector) between two rotating rolls.

International Publication No. 2011/083648 Special Table 2010-522868 Japanese Unexamined Patent Publication No. 03-263757

However, in the electrode manufactured by the manufacturing method as in Patent Document 3, large irregularities may occur on both side edges in the width direction of the electrode mixture layer after molding. An electrode having such large irregularities in the electrode mixture layer may cause a decrease in battery capacity when used in a secondary battery because the electrode material is insufficient in the recesses. In particular, in recent years, the use of wet granulated bodies having a high solid content with a low solvent content has been studied in consideration of the impact on the environment and improvement of production efficiency. When the body was used, the problem that the above-mentioned electrode mixture layer had large irregularities frequently occurred.

The present invention has been made in view of this point, and its main purpose is to have large irregularities on both side edges of the electrode mixture layer, despite the fact that a wet granulated body having a high solid component is used. It is an object of the present invention to provide a manufacturing method capable of stably manufacturing an electrode having a high battery capacity by suppressing the occurrence of the above.

In order to realize the above object, the present invention provides a method for manufacturing an electrode having the following configuration.

The method for producing an electrode disclosed here is at least a granulation body manufacturing step of producing a wet granulation body by mixing a granular electrode active material and a solvent, and an electrode by rolling the wet granulation body. It is provided with a rolling step of forming a mixture layer and adhering the electrode mixture layer onto a foil-shaped current collector.
In the electrode manufacturing method disclosed here, the solid content of the wet granulated body is 70% or more, the projected particle area of the electrode active material is S, and the particle peripheral length of the electrode active material is L. Then, the circularity R of the electrode active material calculated based on the following equation: R = 4πS / L ^{2; is 0.6 or more.}

As a result of various studies conducted by the present inventor in order to solve the above-mentioned problems, the wet granulated body does not sufficiently extend and spread in the rolling process, and a sufficient electrode material (electrode) is provided on both side edges of the electrode mixture layer. It was found that the lack of supply of active material, etc.) was the cause of large irregularities on both side edges of the electrode mixture layer after molding.
Then, the present inventor further provides a means for sufficiently extending and spreading the wet granulated body even when a wet granulated body having a high solid content of 70% or more, which is particularly difficult to roll, is used. After repeated studies, the shape of the electrode active material should be made closer to a spherical shape, and the frictional force between the particles of the electrode active material contained in the wet granulated body should be reduced to facilitate the flow of the wet granulated body during rolling. I came up with.

The electrode manufacturing method disclosed here is made by conducting various experiments based on the above findings, and the circularity R calculated by the formula ^{R = 4πS / L 2 is 0.6 or more.} An electrode active material with a shape close to a sphere is used. As a result, the frictional force between the particles of the electrode active material in the rolling step can be reduced, so that the wet granulated body can be sufficiently extended and spread. As a result, even when a wet granulated body having a high solid content of 70% or more is used, it is possible to suppress the occurrence of large irregularities on both side edges of the electrode mixture layer after molding, resulting in a high battery capacity. It is possible to stably manufacture an electrode having the above.
The "circularity R" is a value obtained by dividing the peripheral length of the circle corresponding to the projected particle area by the peripheral length of the particles, where the projected area of the electrode active material is S and the peripheral length of the electrode active material is L. Sometimes it can be obtained by the above formula, and the closer this value is to 1, the closer the particle shape of the electrode active material is to a spherical shape.

It is sectional drawing which shows typically the stirring granulation machine used in the mixing step in the manufacturing method of the electrode which concerns on one Embodiment of this invention. It is a side view explaining the rolling process in the manufacturing method of the electrode which concerns on one Embodiment of this invention. It is an enlarged view which shows typically the state between the rollers of the rolling process shown in FIG. It is an SEM photograph of the negative electrode active material of Test Example 1 and Test Example 4. It is an optical micrograph at the side edge portion of the negative electrode mixture layer of Test Example 1 and Test Example 4. It is a graph which shows the measurement result of the size of the unevenness in the side edge portion of the negative electrode mixture layer of Test Example 1 to Test Example 4.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the embodiment described below, a method for manufacturing a negative electrode of a lithium ion secondary battery is given as a preferable example to which the method for manufacturing an electrode disclosed here is applied. Such an embodiment is the embodiment of the present invention. It is not intended to limit the scope.

In the electrode manufacturing method according to the present embodiment, a negative electrode for a lithium ion secondary battery in which an electrode mixture layer is provided on the surface of a current collector is manufactured by carrying out a granulated body manufacturing step and a rolling step. do. Hereinafter, each step will be specifically described.

1. 1. Granulation body production step In the granulation body production step, at least a wet granulation body is produced by mixing a granular electrode active material and a solvent. Here, first, the materials that can be used in the granulation body manufacturing step will be described, and then the procedure of the granulation body manufacturing step will be described.

(1) Material of wet granulated body (a) Electrode active material In the manufacturing method according to the present embodiment for manufacturing a negative electrode of a lithium ion secondary battery, the negative electrode is used as an electrode active material to charge and discharge the lithium ion secondary battery. Materials involved in are used. The electrode active material (negative electrode active material) of the negative electrode has, for example, graphite (graphite), non-graphitized carbon (hard carbon), easily graphitized carbon (soft carbon), carbon nanotubes, or a structure in which these are combined. Examples include carbon materials such as graphite.
Then, in the manufacturing method according to the present embodiment, an electrode active material having a circularity R of 0.6 or more is used. The circularity R is a value that serves as an index that the particle shape of the electrode active material approaches a sphere as it approaches 1. As will be described in detail later, the use of an electrode active material having a circularity R of 0.6 or more and a particle shape close to a sphere causes large irregularities on both side edges of the electrode mixture layer formed in the rolling process. Can be suppressed.

The circularity R of the electrode active material described above is obtained by obtaining a particle projection area S in which the area of the electrode active material is directly measured based on an SEM photograph or the like and a particle peripheral length L of the electrode active material, and the particle projection area S is used. It is calculated by defining a circle having the same area (a circle corresponding to the projected particle area) and then dividing the peripheral length of the circle corresponding to the projected particle area by the peripheral length L of the electrode active material. More specifically, the circularity R of the electrode active material is calculated based on the following formula (1).
R = 4πS / L ² (1)

(B) Solvent As the solvent, a general solvent used for producing a wet granulated product can be used. Specific examples of such a solvent include water, N-methyl-2-pyrrolidone (NMP) and the like. In the production method according to the present embodiment, the amount of the solvent used is adjusted so that a wet granulated body having a solid content of 70% or more is produced in consideration of the amounts of the electrode active material and the additives described below. .. By using such a wet granulated body having a high solid content, it is possible to reduce the burden on the environment and improve the production efficiency in the manufacturing process.

(C) Other Additives In addition, additives contained in the negative electrode mixture layer of a general lithium ion secondary battery may be appropriately added to the wet granulated body produced in this step, if necessary. can. Examples of such additives include carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyethylene (PE), and polyacrylic. Binders such as acid (PAA) can be mentioned.

(2) Preparation of Wet Granulation In the granulation production step in the present embodiment, a wet granulation is produced by mixing the above-mentioned materials using a stirring granulator 10 as shown in FIG. do. The stirring granulator 10 includes a cylindrical mixing container 12, a mixing blade 14 housed inside the mixing container 12, and a motor 18 connected to the mixing blade 14 via a support shaft 16. There is.
In the granulation body manufacturing step, it is preferable to mix the materials (solids) excluding the solvent from the above-mentioned materials in advance, and then add the solvent to the mixture and further mix the mixture. This makes it possible to prepare a wet granulated body in which the solid matter is suitably mixed. Specifically, the electrode active material and the additive are put into the mixing container 12 of the stirring granulator 10 described above, and the motor 18 is driven to rotate the mixing blade 14 to prepare a solid mixture. .. Then, a small amount of solvent measured so that the solid content becomes 70% or more is added into the mixing container 12, and the mixing blade 14 is further rotated. As a result, each material in the mixing container 12 and the solvent are mixed to produce a wet granulated body (wet granulated body).

2. Rolling process FIG. 2 is a side view for explaining a rolling process in the electrode manufacturing method according to the present embodiment, and FIG. 3 is an enlarged view schematically showing a state between rollers in the rolling process shown in FIG. ..
As shown in FIG. 2, in the rolling process in the present embodiment, a rolling apparatus 20 provided with three rollers 21 to 23 is used, and the wet granulated body P is rolled by the rolling apparatus 20. The electrode E1 is manufactured by molding the electrode mixture layer P1 and adhering the electrode mixture layer P1 to the surface of the foil-shaped current collector E. For the current collector E in FIG. 2, a foil-like member mainly composed of a metal having excellent conductivity, for example, a copper foil or the like is used.

Hereinafter, the rolling process in the present embodiment will be specifically described.
In such a rolling step, first, the wet granulated body P produced in the granulated body manufacturing step is supplied between the first roller 21 and the second roller 22.
When the first roller 21 and the second roller 22 are rotated in this state, the wet granulated body P is rolled to form the electrode mixture layer P1. Then, the molded electrode mixture layer P1 is attached to the surface of the second roller 22, and the electrode E1 is pressed against the current collector E between the second roller 22 and the third roller 23. Manufactured.

At this time, as shown in FIG. 3, the wet granulated body P is extended and expanded by applying a shearing force by the first roller 21 and the second roller 22, but the wet granulated body P is sufficiently present. If it is not stretched and expanded, sufficient electrode material will not be supplied to both side edges of the electrode mixture layer P1 (see FIG. 2) after molding, and large irregularities will occur.
In contrast, in the manufacturing method according to the present embodiment uses an electrode active material P _A nearly spherical as roundness R is 0.6 or more, each of the electrode active during rolling of the wet granulated product P it can be easily in flowing wet granules P to reduce the frictional force applied to the material P _a. As a result, although the wet granulated body P having a high solid content (solid content of 70% or more) that is difficult to be rolled is used, the wet granulated body P can be easily extended and expanded to obtain the electrode mixture layer P1. Since a sufficient electrode material can be supplied to both side edges, it is possible to appropriately suppress the occurrence of large irregularities on both side edges and stably manufacture an electrode having a high battery capacity.

Further, the electrode manufacturing method according to the present embodiment targets the negative electrode of the lithium ion secondary battery, and the negative electrode of the lithium ion secondary battery has large irregularities on both side edges of the electrode mixture layer after molding. Therefore, the effect of the electrode manufacturing method disclosed here can be more remarkably exhibited.

As described above, the electrode manufacturing method disclosed here is not limited to the manufacturing of the negative electrode of the lithium ion secondary battery, and can be applied to the manufacturing of various electrodes. For example, when a positive electrode of a lithium ion secondary battery is manufactured by using the manufacturing method disclosed here, a lithium transition metal composite oxide such _{as lithium nickel cobalt manganese composite oxide (LiNiComnO 2) is used as an electrode active material.} Is used, and a binder, a conductive material, etc. are used as other additives. Further, the electrode manufacturing method disclosed here can also be applied to the manufacturing of electrodes of a secondary battery (for example, a nickel hydrogen battery) other than a lithium ion secondary battery.

[Test example]
Hereinafter, test examples relating to the present invention will be described, but such description is not intended to limit the present invention.

1. 1. Each Test Example (1) Test Example 1
In Test Example 1, the negative electrode active material (natural graphite) having a circularity R of 0.3 calculated by the above formula (1) and the binder (CMC) are weighed so as to have a weight ratio of 99: 1. Then, a solvent (water) was added to these solids and mixed to prepare a wet granulated body having a solids ratio of 70%. Specifically, first, using the stirring granulator 10 (capacity 1 L) shown in FIG. 1, the rotation speed of the motor 18 was set to 4500 rpm, and the negative electrode active material and the binder were mixed for 20 seconds. Then, a solvent was added to the mixture of the negative electrode active material and the binder, and a granulation treatment was performed in which the mixture was mixed at a rotation speed of 800 rpm for 20 seconds to prepare a wet granulated body.

Next, the wet granulated body P is rolled using the first roller 21 and the second roller 22 of the rolling apparatus 20 shown in FIG. 2, the negative electrode mixture layer P1 is formed, and then the second roller. An electrode E1 (negative electrode of a lithium ion secondary battery) for a negative electrode was produced by pressing the electrode mixture layer P1 against the surface of the current collector E using 22 and a third roller 23. The manufacturing speed (rotational speed of each roller) in this step was set to 30 m / min, and the electrode E1 for 500 m was manufactured.

(2) Test Example 2 to Test Example 4
In Test Examples 2 to 4, a negative electrode of a lithium ion secondary battery was prepared under the same conditions as in Test Example 1 except that the circularity R of the negative electrode active material was different in each Test Example. Specifically, in Test Example 2, the circularity R of the negative electrode active material is set to 0.6, in Test Example 3, the circularity R of the negative electrode active material is set to 0.77, and in Test Example 4, the negative electrode active material is set to 0.77. The circularity R of was set to 0.83.

2. Evaluation Test (1) Observation of Electrode Active Material The SEM photographs of the wet granulated bodies used in Test Example 1 and Test Example 4 were taken, and the shape of the electrode active material contained in the wet granulated body was observed. The photograph taken is shown in FIG. In addition, (a) in FIG. 4 is an SEM photograph of the negative electrode active material (circularity R: 0.3) of Test Example 1, and (b) is the negative electrode active material (circularity R: 0.) of Test Example 4. It is an SEM photograph of 83).
As shown in FIG. 4, when the shapes of the negative electrode active materials of Test Example 1 and Test Example 4 were compared, the negative electrode active material having a shape closer to a sphere was observed in Test Example 4. From this, it was confirmed that the larger the circularity R calculated by the above formula (1), the closer the shape of the electrode active material to that of a sphere.

(2) Measurement of unevenness on both side edges In this evaluation, the size of the unevenness generated on the side edge of the electrode mixture layer of the electrodes produced in each test example was measured. Specifically, as shown in FIG. 5, an optical micrograph of the side edge portion of the electrode mixture layer is taken, 10 measurement points are randomly set from the photographed photograph, and the convex portion at each measurement point is set. The distance from the apex a to the bottom b of the recess was measured as the size c of the unevenness. In addition, (a) in FIG. 5 is an optical micrograph of Test Example 1, and (b) is an optical micrograph of Test Example 4.
Then, in this evaluation, the average value of the unevenness size c at each of the 10 measurement points was calculated. The calculation results are shown in Table 1 and FIG.

As shown in Table 1 and FIG. 6, in Test Examples 2 to 4, it was obtained that the size c of the unevenness at the side edge of the electrode mixture layer was significantly smaller than that of Test Example 1. .. From this, when an electrode active material having a circularity R of 0.6 or more and having a shape close to a sphere is used, even when a wet granulated body having a high solid content of 70% is used, the electrode combination It was found that the formation of large irregularities on both side edges of the material layer can be suitably suppressed.

Although the present invention has been described in detail above, the above-described embodiment is merely an example, and the invention disclosed here includes various modifications and modifications of the above-mentioned specific examples.

10 Stirring granulator 12 Mixing container 14 Mixing blade 16 Support shaft 18 Motor 20 Rolling device 21 1st roller 22 2nd roller 23 3rd roller a Convex top b Concave bottom c Concavity size P Wet granulation P1 electrode mixture layer _{P A} electrode active material E collector E1 electrode

Claims (1)

At least, a granulation body preparation step of producing a wet granulation body by mixing a granular electrode active material and a solvent, and
A method for manufacturing an electrode, comprising a rolling step of forming an electrode mixture layer by rolling the wet granulated body and adhering the electrode mixture layer onto a foil-shaped current collector.
The solid content of the wet granulated body is 70% or more, and
When the projected particle area of the electrode active material is S and the particle peripheral length of the electrode active material is L, the circularity R of the electrode active material calculated based on ^{the following equation: R = 4πS / L 2 ;.} A method for manufacturing an electrode, which has an average value of 0.77 or more and 0.83 or less.

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