JPH10270036A - Manufacture of paste electrode and roller for manufacturing it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain wearing of a roller and increase filling density of paste, by filling or coating active-substance-containing paste on an electric collector and drying it, and by rolling the collector with a roller having specific surface roughness. SOLUTION: The maximum value of roller surface roughness (R max) is within the range of 2.5-5 μm. It is preferable that material of roller is especially high-carbon chrome bearing steel. The roller surface roughness is defined within the above range according to the following reasons. Under the lowest limit, because pressing pressure needs to be increased to increase filling density of the paste, it is difficult to restrain wearing of the roller surface. Over the upper limit, increase of paste filling density may cause the liquid absorbing factor of alkali electrolyte to decrease. When a separator is inserted between a positive electrode and a negative electrode and a electrode assembly is formed by winding them spirally, cracks may arise on the positive electrode or active substance may fall.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a paste-type electrode with an improved rolling process.

[0002]

2. Description of the Related Art Paste electrodes are used for positive electrodes and negative electrodes of alkaline secondary batteries and lithium ion secondary batteries. For example, a paste-type nickel positive electrode is prepared by adding and mixing a conductive material, a binder, and water to nickel hydroxide particles to prepare a paste, and then applying the paste to a three-dimensional structure such as a sponge-like porous metal body or metal fiber mat. , Dried, cut, and rolled. This rolling is performed by causing a pair of rollers to face each other and passing the paste-filled porous metal between the rollers. As this roller, a roller having a maximum surface roughness of about 0.3 to 0.8 μm is used.

In recent years, portable electric devices (for example,
With the spread of PHS and notebook personal computers) and higher performance, there is a demand for further improvement in capacity of alkaline secondary batteries. In order to increase the capacity, it is necessary to increase the active material filling density of the paste-type positive electrode.

However, in order to increase the packing density of the active material using the above-mentioned roller, the pressure applied to the paste-filled porous metal during rolling is increased, so that the surface of the roller is worn as the rolling process proceeds. As a result, the surface roughness (surface irregularities) becomes non-uniform. For this reason, the pressure applied at the time of rolling becomes uneven, and the thickness of the positive electrode varies. When the thickness of the positive electrode varies, the capacity of the alkaline secondary battery decreases. In addition, when a separator is interposed between the positive electrode and the negative electrode, and this is spirally wound to form an electrode group, the degree of tightness of the electrode group may be increased. Cracks may occur.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a paste-type electrode and a roller for manufacturing a paste-type electrode capable of improving the paste filling density while suppressing the abrasion of the roller. Is what you do.

[0006]

According to the present invention, there is provided a method of manufacturing a paste-type electrode, comprising the steps of: filling a current collector with a paste containing an active material; and applying the paste filled or coated with the paste to the current collector. Drying step and surface roughness (R
rolling the current collector filled or coated with the paste by a roller having a maximum value of _max ) in the range of 2.5 μm to 5 μm. The paste-type electrode manufacturing roller according to the present invention is characterized in that the maximum value of the surface roughness (R _max ) is in the range of 2.5 μm to 5 μm.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for producing a paste electrode according to the present invention will be described with reference to a paste electrode for an alkaline secondary battery as an example. <Method of Manufacturing Paste-Type Positive Electrode for Alkaline Secondary Battery> (1) A paste containing a positive electrode active material is filled or applied to a positive electrode current collector.

[0008] The paste can be prepared, for example, by kneading nickel hydroxide particles, a conductive agent and a binder in the presence of water. As the nickel hydroxide particles, for example, single nickel hydroxide particles or nickel hydroxide particles in which zinc and / or cobalt are coprecipitated with metallic nickel can be used. The latter positive electrode containing nickel hydroxide particles can further improve the charging efficiency in a high temperature state.

From the viewpoint of improving the charge / discharge efficiency of the alkaline storage battery, the peak half-value width of the (101) plane of the nickel hydroxide particles by X-ray powder diffraction is 0.8 ゜ / 2θ.
(Cu-Kα) or more is preferable. A more preferable nickel hydroxide powder is powder X-ray diffraction method (10
1) The half width of the surface peak is 0.9 to 1.0 ° / 2θ.
(Cu-Kα).

The conductive agent can be formed of, for example, dicobalt trioxide (Co ₂ O ₃ ), cobalt metal (Co), cobalt monoxide (CoO), cobalt hydroxide {Co (OH) ₂ }, or the like. .

[0011] Examples of the binder include polytetrafluoroethylene, carboxymethylcellulose, methylcellulose, polyacrylate, and polyvinyl alcohol.

Examples of the positive electrode current collector include those having a sponge-like, fibrous, or felt-like porous structure made of, for example, a metal such as nickel or stainless steel, or a nickel-plated resin. .

(2) The current collector filled or coated with the paste is dried. (3) The current collector filled or coated with the paste is cut into a desired size. (4) The maximum value of the surface roughness (R _max ) is 2.5 μm to 5 μm
The current collector filled or coated with the paste is rolled by a roller having a range of m. The maximum value of the surface roughness (R _max ) is manufactured by Mitutoyo, and the trade name is Surf Test 301.
The surface roughness is measured by a surface roughness measuring instrument, or an equivalent measuring instrument.

The roller can be made of, for example, a stainless steel, nickel, nickel alloy plate or the like.
Among them, high carbon chromium bearing steel is preferable. The roller having the maximum surface roughness within the above range can be produced, for example, by blasting the surface of the roller formed of the above-described material.

The reason why the surface roughness of the roller is limited to the above range is as follows. When the maximum value of the surface roughness is less than 2.5 μm, it is necessary to increase the pressing pressure in order to increase the paste filling density,
It becomes difficult to suppress wear of the roller surface. On the other hand, when the maximum value of the surface roughness exceeds 5 μm, the paste filling density becomes high, which may cause a decrease in the absorption rate of the alkaline electrolyte. Further, when a separator is interposed between the positive electrode and the negative electrode and spirally wound to form an electrode group, cracks may occur in the positive electrode, or the active material may fall off. In particular, from the viewpoint of suppressing abrasion on the surface of the roller, it is preferable that the lower limit of the maximum value of the surface roughness is 3 μm. When the upper limit of the maximum value of the surface roughness is set to 4 μm, it becomes easy to manufacture an electrode having a good balance between the paste filling density and the thickness. For this reason, it is possible to avoid such a problem that the electrode group is too large to enter the container.

The manufacturing method according to the present invention allows the cutting step (3) to be performed after the rolling step (4). <Production Method of Paste-Type Negative Electrode for Alkaline Secondary Battery> (1) A paste containing a negative electrode active material is filled or applied to a negative electrode current collector.

The paste can be prepared, for example, by kneading a negative electrode active material, a conductive material and a binder in the presence of water. Examples of the negative electrode active material include cadmium compounds such as metal cadmium and cadmium hydroxide, and hydrogen. Examples of the host matrix of hydrogen include a hydrogen storage alloy.

Above all, the hydrogen storage alloy is preferable because the capacity of the secondary battery can be improved as compared with the case where the cadmium compound is used. The hydrogen storage alloy is not particularly limited, and may be any as long as it can store hydrogen electrochemically generated in an electrolytic solution and can easily release the stored hydrogen during discharge. For example, LaNi ₅ , Mm
Ni ₅ (Mm is a misch metal), LmNi ₅ (Lm is at least one selected from rare earth elements including La),
A part of Ni of these alloys is Al, Mn, Co, Ti, C
AB _x (where A is Ti and / or Z) substituted with an element such as u, Zn, Zr, Cr, B
and B is Ni, Mn, V, Co, Cr, Al, F
e, at least one element selected from Cu, Mo, La, Ce, Pr and Nd, and the atomic ratio x is 1.8 ≦ x ≦ 2.
5). In particular, the general formula _{LmNi w Co x Mn y Al z} ( atomic ratio w,
The total value of x, y, and z is 5.00 ≦ w + x + y + z ≦ 5.
The hydrogen storage alloy having the composition represented by the formula (5) is suitable because it suppresses the pulverization accompanying the progress of the charge / discharge cycle and can improve the charge / discharge cycle life.

Examples of the binder include polyacrylates such as sodium polyacrylate and potassium polyacrylate, fluorine resins such as polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (C).
MC) and the like.

Examples of the conductive material include carbon black and graphite. As the current collector, for example, punched metal, expanded metal,
Examples include a two-dimensional substrate such as a perforated rigid plate and a nickel net, and a three-dimensional substrate such as a felt-like porous metal body and a sponge-like porous metal body.

(2) The current collector filled or coated with the paste is dried. (3) The current collector filled or coated with the paste is cut into a desired size. (4) The maximum value of the surface roughness (R _max ) is 2.5 μm to 5 μm
The current collector filled or coated with the paste is rolled by a roller having a range of m.

The roller can be formed from the same material as described for the positive electrode. The roller having the maximum surface roughness within the above range can be manufactured by the same method as described for the positive electrode.

The reason for limiting the surface roughness of the roller to the above range is based on the same reason as described above for the positive electrode. In particular, the lower limit of the maximum value of the surface roughness is preferably set to 3 μm for the same reason as described for the positive electrode. Further, the upper limit of the maximum value of the surface roughness is set to 4 due to the same reason as described for the positive electrode.
It is preferable to set it to μm.

The manufacturing method according to the present invention allows the cutting step (3) to be performed after the rolling step (4). Hereinafter, an example of an alkaline secondary battery incorporating a paste-type positive electrode and a paste-type negative electrode manufactured by the method according to the present invention will be described in detail with reference to FIG.

In the bottomed cylindrical container 1, a separator 3 is interposed between a paste-type positive electrode 2 manufactured by the above-described method and a paste-type negative electrode 4 manufactured by the above-described method, and is spirally formed. The electrode group 5 produced by winding is stored. The negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1. The alkaline electrolyte is contained in the container 1. A circular first sealing plate 7 having a hole 6 in the center is arranged at the upper opening of the container 1. The ring-shaped insulating gasket 8 is disposed between the peripheral edge of the sealing plate 7 and the inner surface of the upper opening of the container 1, and the sealing plate is formed on the container 1 by caulking to reduce the diameter of the upper opening inward. 7
Are hermetically fixed via the gasket 8. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 having a hat shape is attached on the sealing plate 7 so as to cover the hole 6. A rubber safety valve 11 is disposed so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10. A circular holding plate 12 made of an insulating material having a hole in the center is arranged on the positive electrode terminal 10 such that a projection of the positive electrode terminal 10 projects from the hole of the holding plate 12. The outer tube 13 covers the periphery of the holding plate 12, the side surface of the container 1, and the periphery of the bottom of the container 1.

The separator 3 and the alkaline electrolyte will be described in detail. <Separator 3> As the separator 3, for example,
Examples thereof include a nonwoven fabric made of a polyamide fiber and a nonwoven fabric made of a polyolefin fiber such as polyethylene or polypropylene provided with a hydrophilic functional group.

<Alkaline Electrolyte> Examples of the alkaline electrolyte include an aqueous solution of sodium hydroxide (NaOH), an aqueous solution of lithium hydroxide (LiOH), an aqueous solution of potassium hydroxide (KOH), and a mixed solution of NaOH and LiOH. , A mixed solution of KOH and LiOH, KOH, LiOH and N
A mixed solution of aOH or the like can be used.

Although FIG. 1 shows an example in which the present invention is applied to a cylindrical alkaline secondary battery, the present invention can be similarly applied to a rectangular alkaline secondary battery having a bottomed rectangular cylindrical container.

As described above in detail, according to the method of manufacturing a paste electrode according to the present invention, the paste is filled or applied with a roller having a maximum surface roughness (R _max ) in the range of 2.5 μm to 5 μm. By rolling the collected current collector, the paste filling density of the electrode can be appropriately increased at a low press pressure. As a result, the abrasion of the surface of the roller can be suppressed, so that the target packing density and thickness can be maintained for a long period of time in the rolling process. In addition, the electrode can ensure a high electrolyte absorption rate and excellent flexibility. Therefore, by manufacturing the paste type electrode of the alkaline secondary battery by the method according to the present invention, it is possible to produce a high capacity alkaline secondary battery with high mass productivity.

By setting the maximum value of the surface roughness (R _max ) of the roller to 3 to 4 μm, it is possible to increase the packing density while maintaining the size and thickness of the paste type electrode at desired values. it can. In addition, since the pressing pressure required for achieving the above packing density can be significantly reduced, it is possible to suppress surface wear due to rolling. As a result, a paste-type electrode having the desired thickness, size, and packing density and having excellent characteristics can be continuously manufactured over a long period of time. Can be manufactured with high mass productivity.

[0031]

Embodiments of the present invention will be described below in detail with reference to the drawings. (Example 1) For 90 parts by weight of nickel hydroxide powder,
5.5 parts by weight of cobalt monoxide powder were added as a conductive agent, and a binder (0.2 parts by weight of sodium polyacrylate powder and 1.5 parts by weight of polytetrafluoroethylene dispersion in terms of solid content) was added. And kneaded with 28 parts by weight of water to prepare a paste. The paste is filled into a strip-shaped porous nickel-plated metal having a porosity of 93% and an average pore diameter of 20 μm, dried, and cut into a predetermined size to obtain an unrolled paste-type nickel positive electrode having a thickness of 1.4 mm. Was.

As shown in FIG. 2, the maximum value of the surface roughness is 3
μm (manufactured by Mitutoyo, trade name is measured by a surface roughness measuring device of Surf Test 301), high carbon chromium bearing steel (JIS SUJ, chemical components; C and Cr are main components, and impurities such as Si, Mn, P , And S) (rollers 21a and 21b).
1a and 21b were arranged up and down. The roller 21a is
It rotates, for example, counterclockwise around the rotation shaft 22a. On the other hand, the roller 21b rotates in a direction opposite to the roller 21a about a rotation shaft 22b. The unrolled positive electrode 22 described above was inserted from the left side between the rotating rollers 21a and 21b and passed therethrough, and both surfaces of the positive electrode 22 were pressed at a pressure of 20 ton. This operation was repeated once again to produce a paste-type nickel positive electrode. When the first rolling was completed and when the second rolling was completed, the elongation percentage (the length of the positive electrode after rolling with respect to the length of the positive electrode before rolling) and the thickness of the positive electrode were measured. It is shown in Table 1.

Example 2 An unrolled paste-type nickel positive electrode was produced in the same manner as in Example 1. Two rollers having a maximum surface roughness of 3.5 μm were prepared and arranged as shown in FIG. The unrolled positive electrode described above was passed between these rollers, and both surfaces of the positive electrode were pressed at the same pressure as in Example 1. This operation was repeated once again to produce a paste-type nickel positive electrode. When the first rolling and the second rolling were completed, the elongation and the thickness of the positive electrode were measured, and the results are shown in Table 1 below.

Example 3 An unrolled paste-type nickel positive electrode was produced in the same manner as in Example 1. Two rollers having a maximum surface roughness of 4 μm were prepared and arranged as shown in FIG. The unrolled positive electrode described above was passed between these rollers, and both surfaces of the positive electrode were pressed at the same pressure as in Example 1. This operation was repeated once again to produce a paste-type nickel positive electrode. When the first rolling and the second rolling were completed, the elongation and the thickness of the positive electrode were measured, and the results are shown in Table 1 below.

Comparative Example 1 An unrolled paste-type nickel positive electrode was produced in the same manner as in Example 1. Two rollers having a maximum surface roughness of 0.8 μm were prepared and arranged as shown in FIG. The unrolled positive electrode described above was passed between these rollers, and both surfaces of the positive electrode were pressed at the same pressure as in Example 1. This operation was repeated once again to produce a paste-type nickel positive electrode. When the first rolling and the second rolling were completed, the elongation and the thickness of the positive electrode were measured, and the results are shown in Table 1 below.

Reference Example 1 An unrolled paste-type nickel positive electrode was produced in the same manner as in Example 1. Two rollers having a maximum surface roughness of 2 μm were prepared and arranged as shown in FIG. The unrolled positive electrode described above was passed between these rollers, and both surfaces of the positive electrode were pressed at the same pressure as in Example 1. This operation was repeated once again to produce a paste-type nickel positive electrode. When the first rolling and the second rolling were completed, the elongation and the thickness of the positive electrode were measured, and the results are shown in Table 1 below.

[0037]

[Table 1]

As is clear from Table 1, the elongation and the thickness of the paste type electrodes obtained by the methods of Examples 1 to 3 are compared with those of Comparative Example 1 and Reference Example 1, and the first and second times. In both cases, although the thickness is not much different between the two, it can be seen that the elongation is lower in Examples 1 to 3. In other words, when the pressing pressure during rolling is constant, Examples 1 to
No. 3 can increase the paste filling density as compared with Comparative Example 1 and Reference Example 1. Therefore, from Table 1, the electrodes of Examples 1 to 3 obtained by a method of rolling with a roller having a maximum surface roughness in the range of 2.5 μm to 5 μm show Comparative Example 1 in which the maximum surface roughness is 2 μm or less. It is clear that the packing density can be increased with a lower press pressure than in Reference Example 1.

Example 4 A paste was prepared in the same manner as in Example 1. The paste was filled in a strip-shaped nickel-plated metal porous body having the same porosity and average pore diameter as in Example 1 and having a thickness of 8 μm, and then dried to produce an unrolled paste-type nickel positive electrode. Two rollers having a maximum surface roughness of 3 μm were prepared and arranged as shown in FIG. The unrolled positive electrode described above was continuously passed between these rollers, and both surfaces of the positive electrode were pressed at the same pressure as in Example 1 and cut into a desired size to produce a paste-type positive electrode. The elongation and thickness of the obtained positive electrode were measured every 500 sheets, and the elongation is shown in FIG. 3 and the thickness is shown in FIG.

Example 5 A paste was prepared in the same manner as in Example 1. The paste was filled in a strip-shaped nickel-plated metal porous body having the same porosity and average pore diameter as in Example 1 and the same length as in Example 4, and then dried to produce an unrolled paste-type nickel positive electrode. Two rollers having a maximum surface roughness of 3.5 μm were prepared and arranged as shown in FIG. The unrolled positive electrode described above was continuously passed between these rollers, and both surfaces of the positive electrode were pressed at the same pressure as in Example 1 and cut into a desired size to produce a paste-type positive electrode. About the obtained positive electrode,
The elongation and thickness were measured every 500 sheets, and the elongation was measured as shown in FIG.
FIG. 4 shows the thickness.

Example 6 A paste was prepared in the same manner as in Example 1. The paste was filled in a strip-shaped nickel-plated metal porous body having the same porosity and average pore diameter as in Example 1 and the same length as in Example 4, and then dried to produce an unrolled paste-type nickel positive electrode. Maximum surface roughness of 4
Two μm rollers were prepared and arranged as shown in FIG. The unrolled positive electrode described above was continuously passed between these rollers, and both surfaces of the positive electrode were pressed at the same pressure as in Example 1 and cut into a desired size to produce a paste-type positive electrode. For the obtained positive electrode, 500
The elongation and thickness were measured for each sheet, and the elongation is shown in FIG. 3 and the thickness is shown in FIG.

Comparative Example 2 A paste was prepared in the same manner as in Example 1. The paste was filled in a strip-shaped nickel-plated metal porous body having the same porosity and average pore diameter as in Example 1 and the same length as in Example 4, and then dried to produce an unrolled paste-type nickel positive electrode. Two rollers having a maximum surface roughness of 0.8 μm were prepared and arranged as shown in FIG. The unrolled positive electrode described above was continuously passed between these rollers, and both surfaces of the positive electrode were pressed at the same pressure as in Example 1 and cut into a desired size to produce a paste-type positive electrode. About the obtained positive electrode,
The elongation and thickness were measured every 500 sheets, and the elongation was measured as shown in FIG.
FIG. 4 shows the thickness.

Reference Example 2 A paste was prepared in the same manner as in Example 1. The paste was filled in a strip-shaped nickel-plated metal porous body having the same porosity and average pore diameter as in Example 1 and the same length as in Example 4, and then dried to produce an unrolled paste-type nickel positive electrode. Maximum surface roughness is 2
Two μm rollers were prepared and arranged as shown in FIG. The unrolled positive electrode described above was continuously passed between these rollers, and both surfaces of the positive electrode were pressed at the same pressure as in Example 1 and cut into a desired size to produce a paste-type positive electrode. For the obtained positive electrode, 500
The elongation and thickness were measured for each sheet, and the elongation is shown in FIG. 3 and the thickness is shown in FIG.

As is clear from FIGS. 3 and 4, the electrodes of Examples 4 to 6 obtained by the method of rolling with a roller having a maximum surface roughness in the range of 2.5 μm to 5 μm were used for a long period of time. It can be seen that the elongation and the thickness can be made substantially constant, and the paste filling density can be maintained at a desired value. On the other hand, in the electrodes of Comparative Example 2 and Reference Example 2 having a maximum surface roughness of 2 μm or less, the elongation rate and the thickness fluctuate as the service life of the roller becomes longer, and the paste filling density fluctuates. Recognize.

[0045]

As described above in detail, according to the present invention, it is possible to increase the paste filling density while maintaining the absorption rate and flexibility of the alkaline electrolyte, and it is possible to extend the rolling process for a long time. Thus, it is possible to provide a paste-type electrode manufacturing method and a paste-type electrode manufacturing roller capable of maintaining the packing density.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an example of an alkaline secondary battery into which a paste electrode manufactured by the method according to the present invention is incorporated.

FIG. 2 is a cross-sectional view for explaining a rolling step in Examples 1 to 6 according to the present invention.

FIG. 3 is a characteristic diagram showing a change over time of an electrode elongation ratio by press molding in the manufacturing methods of Examples 4 to 6, the manufacturing method of Comparative Example 2, and the manufacturing method of Reference Example 2 according to the present invention.

FIG. 4 is a characteristic diagram showing time-dependent changes in electrode thickness due to press forming in the manufacturing methods of Examples 4 to 6, the manufacturing method of Comparative Example 2, and the manufacturing method of Reference Example 2 according to the present invention.

[Explanation of symbols]

21a: roller, 21b: roller, 22a: rotating shaft, 2
2b: rotating shaft, 23: unrolled paste-type positive electrode.

Claims (2)

[Claims] 1. A step of filling or applying a paste containing an active material to a current collector; a step of drying the current collector filled or applied with the paste; and a step of maximizing the surface roughness (R _max ) of 2. Rolling the current collector filled or coated with the paste by a roller having a diameter in a range of 0.5 μm to 5 μm. 2. The maximum value of the surface roughness (R _max ) is 2.5 μm.
A roller for producing a paste-type electrode, which is in the range of m to 5 μm.