JP3955752B2 - Battery electrode manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an electrode used in a battery such as a nickel metal hydride battery.
[0002]
[Prior art]
Conventionally, as a method for producing an electrode of a nickel metal hydride battery, for a positive electrode, a paint mainly composed of nickel hydroxide powder, a binder, and a solvent is a current collector made of a metal porous body having three-dimensional communication holes. It is generally known that nickel foam metal is filled and dried, and then pressed and compressed.
[0003]
As a method for filling the porous metal body with the paint, for example, there is a method as disclosed in Japanese Patent Publication No. 7-73049.
[0004]
In addition, for the negative electrode, a paint mainly composed of a hydrogen storage alloy, a binder, and a solvent is applied and formed on both surfaces of a current collector made of rolled nickel punched metal containing nickel having a thickness of about 60 μm. What is compressed is generally known. A method of applying and drying a paint on a punching metal is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-117706.
[0005]
[Problems to be solved by the invention]
In recent years, mobile phones and notebook computers with excellent portability have been rapidly spreading due to their convenience, and the batteries used in these have become increasingly high-capacity in order to enable long-term use of the above devices. It is desired. However, in the current collector, the ratio of the current collector to the electrode plate is large, and there is a limit in increasing the amount of the active material, which hinders high capacity.
[0006]
Therefore, it is only necessary to reduce the proportion of the current collector by making the current collector a thin foil. However, if the thickness of the foil is simply reduced, the above-described method using nickel foam metal is used to collect the current collector. variations occur in the thickness of the Katsubutsu electrolyte layer formed by coating on the front and back of the body has a problem that the flatness of the electrode plate from the difference in extending in the pressing process is significantly impaired. The reason for this is thought to be that the metal foil has a low mechanical strength, so that it deforms due to the pressure of the paint discharged from the die and the coating thickness varies.
[0007]
Further described above, a method utilizing a nickel punched metal with rolled nickel, on production of deformed by heat during drying of Katsubutsu electrolyte layer, in some cases the current collector is cut into contact with the tip of the die A fatal problem occurred.
[0008]
In view of the above problems, an object of the present invention is to provide a battery electrode manufacturing method capable of improving the battery capacity by coating and forming an active material paint on a thin foil current collector with high productivity. It is.
[0013]
[Means for Solving the Problems]
The present invention provides a nickel-metal hydride battery active material which is a paint system in which a binder is used in an amount of 3% or less and a solid concentration is 50% or more by using a die on a processed current collector. In the method of producing a battery electrode by coating and forming,
The shear rate for the active material coating flowing between the inside and the tip of the die of the die and the collector as a 100 (1 / sec) or less, applying the active material coating on the current collector, the battery It is a manufacturing method of an electrode.
[0014]
2nd this invention is a manufacturing method of the battery electrode of 1st this invention whose pressure of the active material coating material between the said die tip and the said electrical power collector is 0.5 Mpa or less.
[0015]
The third aspect of the present invention is the battery electrode manufacturing method according to the first aspect of the present invention, wherein the difference between the thicknesses of the active material layers on the front surface and the back surface of the current collector is within ± 30%.
[0016]
The fourth aspect of the present invention is the battery electrode manufacturing method according to the first aspect of the present invention, wherein the difference between the thicknesses of the active material layers on the front surface and the back surface of the current collector is within ± 10%.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0019]
FIG. 1 is a schematic view according to an embodiment of a coating apparatus applicable to the battery electrode manufacturing method of the present invention and the battery electrode manufacturing method related to the present invention .
[0020]
As shown in FIG. 3, the current collector 2 has a strip-shaped curved portion 201 and 202 protruding in a convex shape on the front and back surfaces of an electrolytic nickel foil 203 having a thickness t0 (5 to 50 μm), and is arranged in one direction X Are processed with a predetermined dimension. Although the processing means of the current collector 2 is not shown, embossing such as a mold can be used. By this three-dimensional processing, the thickness of the current collector 2 becomes larger than the thickness of the foil. The thickness of the current collector 2 is t2 as will be described later.
[0021]
As shown in FIGS. 1 and 2, the step of applying to the current collector 2 is passed through substantially the center of the gap formed between the tips of the pair of left and right dies 3. An active material paint 5 (hereinafter abbreviated as “paint”) is supplied to the die 3 by a pump (not shown) so as to have a predetermined coating thickness. The paint 5 is first supplied to the inside of the manifold 301 where the pressure is made uniform in the application width direction of the die 3, flows into the slit 302, and is pushed out from the tip of the die 3 to the current collector 2 in the width direction. It is applied to both sides simultaneously and uniformly.
[0022]
As shown in FIG. 4, the applied thickness is t1 ≧ t2 ≧ t1 / 4, where t1 is the thickness of the electrode plate after application of the active material, and t2 is the thickness of the current collector subjected to three-dimensional processing. It is a range. This condition is a condition for sufficient current flow.
[0023]
Further, a current collector position restricting tool 4 for guiding the current collector 2 to the approximate center of the gap may be provided on the upstream side of the die 3 or on the downstream side as necessary. The position restricting tool 4 is composed of a roll and a bar.
[0024]
After the coating material 5 is applied and the active material layer 1 is formed, it is dried in a drying step (not shown) and further wound. Then, although not shown in figure, it press-compresses in a press process and becomes an electrode plate.
[0025]
The first invention relating to Oite present invention to this embodiment features, since passing a current collector 2 was subjected to three-dimensional processing between the tip of the two dies, the current collector 2 is two It runs in the center of the gap formed by the tip of the die. As a result, the variation in the coating amount between the front and back of the current collector 2 of the active material layer 1 becomes extremely small, and the flatness of the electrode plate after pressing is excellent.
[0026]
More specifically, as shown in FIG. 2, when the gap between the tips of the two dies is d and the thickness of the current collector subjected to three-dimensional processing is t2, d> t2 ≧ d / 4. By setting the range, the distance g between the tip of the convex portion of the current collector 2 and the die tip 304 becomes small. That is, d is usually 0.05 mm or more and 3 mm or less. For example, when d is 0.6 mm and t2 is 0.4 mm, the distance g between the convex portion tip of the current collector 2 and the die tip 304 shown in FIG. 2 is an extremely small value of only 0.1 mm. Therefore, it is possible to suppress the position of the current collector 2 from becoming unstable due to the viscous force of the paint 5 existing between the gaps g, and the current collector 2 can travel in the center of the gap d between the two dies. It becomes.
[0027]
Further, since the gap g can be held by the viscous force of the paint, the tip 304 of the die and the current collector 2 do not come into contact with each other, and thus the foil has a thin thickness of 5 to 50 μm and has a mechanical strength. Even a weak current collector can be stably produced without being cut during coating.
[0028]
The second aspect of the invention relating to Oite present invention to this embodiment, when the thickness of the electrode plate t1, the thickness of the current collector subjected to three-dimensional processing was t2, t1 ≧ t2 The range is ≧ t1 / 4. When the active material layer is applied thickly so as to deviate from this condition, there arises a problem that current hardly flows.
[0029]
A third aspect of the invention relating to Oite present invention to this embodiment is to use an electrolytic nickel foil. The foil as a current collector can be roughly classified into a rolled nickel foil and an electrolytic nickel foil. When an electrolytic nickel foil is used as compared with a rolled nickel foil, thermal deformation during the drying of the active material layer can be significantly suppressed. In other words, rolled nickel has stress strain due to the rolling process, and the stress strain appears as a warp due to heating.
[0030]
As a result of using the electrolytic nickel foil, the accuracy such as the flatness of the electrode plate is improved, which facilitates winding of the positive electrode, the negative electrode and the separator, and the quality and yield of the battery are remarkably improved.
[0031]
If the thickness exceeds 50 μm, it is difficult to increase the capacity. If the thickness is less than 5 μm, it cannot withstand the tension required for running the current collector in the coating process, which causes a serious problem such as cutting. Therefore, in this invention, it is set as the range of 5-50 micrometers. From the above viewpoint, the range of 10 to 30 μm is more preferable.
[0032]
The first feature of the present embodiment is that the shear rate for the active material paint flowing inside the die and between the tip of the die and the current collector is 500 (1 / sec) or less. Here, the shear rate is defined as V / g, where g is the distance between the tip of the die and the current collector and V is the moving speed of the current collector.
[0033]
FIG. 5 shows the viscosity characteristics of the paint used in this embodiment. The measurement was performed using a rheometer RF-2 manufactured by Rheometrics, and the measurement head was a cone plate type.
[0034]
In FIG. 5, the horizontal axis represents measurement time (sec), and the vertical axis represents viscosity (Pa · s). While changing the shear rate to 1 (1 / sec), 10 (1 / sec), 100 (1 / sec), and 1000 (1 / sec) every 30 seconds, changes in viscosity were observed. FIG. 5 shows the result of two measurements.
[0035]
As is clear from FIG. 5, at a shear rate of 1000 (1 / sec), it was found that the values varied with each measurement, and the viscosity showed a very unstable value.
[0036]
According to the study by the present inventors, this phenomenon is based on a powder having a relatively high specific gravity such as nickel hydroxide or a hydrogen storage alloy as a main component, and a binder amount such as CMC or SBR is an extremely small amount of 3% or less. Furthermore, the present inventors have found that this is a phenomenon observed in a paint system having a solid content concentration of 50% or more, that is, a paint system for a nickel metal hydride battery.
[0037]
In the conventional method for producing an electrode plate in which a foam metal is filled with paint, the pore diameter of the foam metal is in the range of 50 to 200 μm, so the shear rate is 1000 (1 / s) at the maximum, and the above-described viscosity is unstable. Become an area. Portions with high viscosity cause clogging and only incomplete filling is possible. As a result, the filling of the paint in the foam metal becomes uneven, which is a fatal problem in terms of battery characteristics such as battery capacity variation and cycle life variation. In the present invention, when the shear rate is 500 (1 / sec) or less, such a viscosity does not become unstable, so that a uniform active material layer can be formed on the current collector.
[0038]
The second feature of the present embodiment is that the gap pressure is desirably appropriate. According to the study by the present inventors, it has been found that the pressure in the gap and the viscosity instability phenomenon are closely related. If the gap pressure is within 0.5 MPa, more preferably within 0.3 MPa, the viscosity instability phenomenon does not occur. This phenomenon is presumably due to the separation of powder and solvent at high pressure.
[0039]
For reference, regarding the viscosity of the active material paint for nickel metal hydride battery, the viscosity η1 when the shear rate is 1 (1 / sec) is in the range of 1 to 100 (Pa · s), and the shear rate is 100 (1 / sec). ) Is in the range of 1 (Pa · s) or less. When the viscosity η1 is smaller than 1 (Pa · s), the coating film immediately after coating flows until it dries, resulting in uneven thickness. On the other hand, if it is larger than 100 (Pa · s), the flow becomes worse and the viscosity instability phenomenon at the shear rate of 1000 (1 / s) becomes remarkable. When the viscosity η2 at a shear rate of 100 (1 / sec) is greater than 1 (Pa · s), the pressure of the paint in the gap between the current collector and the die tip when the paint is applied with a die is 0. It becomes higher than .5 MPa and cannot be applied.
[0040]
From the above characteristics, it is possible to obtain a highly accurate electrode plate in which the difference in thickness between the front and back active material layers of the current collector is within ± 30% to ± 10%. With such a thickness difference, the difference in contraction of the coating film on the front and back of the current collector is reduced in the drying process, and thus a flat electrode plate can be produced. Furthermore, the flatness of the electrode plate in the pressure compression process could be improved.
[0041]
In the conventional manufacturing method, the flatness is within ± 3 mm, but according to the present invention, it can be improved to within ± 1 mm, and the battery capacity and cycle characteristics can be improved. Moreover, by setting it as the above-mentioned thickness difference, the curvature degree of an electrode plate can suppress a curvature radius within 1000 mm. Thereby, it becomes easy to wind an electrode plate and the quality of a battery can be improved.
[0042]
【Example】
A specific example of this embodiment will be described. A current collector made of an electrolytic nickel foil with a thickness of 25 μm and a width of 500 mm processed as shown in FIG. 3 is used as a current collector, with two dies having a predetermined slit gap facing each other. A material layer was applied and formed. Further, in the comparative example, a nickel foil having a thickness of 25 μm, which was not processed, was used as a current collector, and both sides were simultaneously coated with a die.
[0043]
The negative electrode paint is obtained by kneading hydrogen storage alloy, SBR, CMC and water. The viscosity η1 at a shear rate of 1 (1 / sec) is 50 (Pa · s) by setting the kneading conditions and the amount of CMC and water. ), The viscosity η2 at a shear rate of 100 (1 / sec) was 0.5 (Pa · s). As a comparative example, as a paint outside the viscosity range of the present invention, the viscosity η1 at a shear rate of 1 (1 / sec) is 0.5 (Pa · s), and the viscosity η2 at a shear rate of 100 (1 / sec) is 0.5 (Pa · s).
[0044]
The positive electrode paint is a mixture of nickel hydroxide, conductive agent, fluororesin, CMC and water. The viscosity η1 at a shear rate of 1 (1 / sec) is determined by setting the kneading conditions and the amount of CMC and water. The viscosity η2 at 30 (Pa · s) and a shear rate of 100 (1 / sec) was 0.7 (Pa · s). As a comparative example, as a coating material outside the viscosity range of the present invention, the viscosity η1 at a shear rate of 1 (1 / sec) was 0.8 (Pa · s), and the viscosity η2 was 0.7 (Pa · s). I also created one.
[0045]
The electrode plate thus obtained was compressed under a predetermined pressure and cut into a predetermined width to produce a nickel metal hydride battery. The following evaluation was performed on the obtained battery to confirm the effect of the present invention.
[0046]
(1) Uniformity of coating The sagging of the coating film was confirmed by a difference in thickness between the front and back surfaces of the current collector using a micrometer and visual observation after coating. In the above examples where the viscosity of the paint is within the range of the present invention, the thickness difference was in the range of ± 18%, and in the comparative example, it was in the range of ± 56%.
[0047]
(2) Paint sag after application In addition, the sag of the coating film was satisfactory in this example, but in the comparative example, sag occurred and the flatness of the coating film was significantly impaired.
[0048]
(3) Flatness of electrode plate As a result of pressing the electrode plate obtained in this example, the flatness was in the range of ± 0.5 mm, but the flatness of the electrode plate obtained in the comparative example was ± 3. There was also 0.5 mm. Therefore, the winding at the time of insertion into the battery case has a problem yield of 98% in the present embodiment, but it is extremely difficult in the comparative example and the yield is as bad as 50%.
[0049]
(4) The battery characteristic cycle life is shown in FIG. 6, and the discharge capacity ratio is shown in FIG. In this example, the cycle life was increased by about 20% compared to the comparative example. Further, the discharge capacity ratio of the battery of this example was increased by about 20% compared to the comparative example.
[0050]
In addition, the above effect is not restricted to the said Example, The equivalent effect was acquired if it was the range of this invention described in the claim. As described above, according to the present embodiment, a paint can be uniformly applied with high productivity to a current collector made of electrolytic nickel foil, and the flatness of the electrode plate can be improved, the discharge capacity can be improved, the variation can be suppressed, and the cycle characteristics can be improved. I can plan.
[0051]
【The invention's effect】
As is apparent from the above description, according to the present invention, the paint can be uniformly applied to the current collector with high productivity, and the flatness of the electrode plate, the discharge capacity, the cycle characteristics, etc. can be improved. The effect is great.
[Brief description of the drawings]
FIG. 1 is a configuration diagram according to an embodiment of a coating apparatus to which the present invention can be applied. FIG. 2 is a configuration diagram according to an embodiment of a coating apparatus to which the present invention can be applied. FIG. 4 is a cross-sectional view of an electrode plate according to an embodiment of the present invention. FIG. 5 is a diagram showing viscosity characteristics of a coating material according to an embodiment of the present invention. The figure which shows the cycle life characteristic of the battery in FIG. 7 is a figure which shows the discharge capacity characteristic of the battery in the embodiment of the present invention.
DESCRIPTION OF SYMBOLS 1 Active material layer 2 Current collector 3 Die 4 Position control tool 5 Paint 6 Liquid pool

Claims (4)

A battery electrode is formed by applying and forming a nickel hydride battery active material, which is a paint system having a solid content concentration of 50% or more, to a processed current collector using a die and having a binder amount of 3% or less. In the method of manufacturing
The shear rate for the active material coating flowing between the inside and the tip of the die of the die and the collector as a 100 (1 / sec) or less, applying the active material coating on the current collector, the battery Electrode manufacturing method.   The method for producing a battery electrode according to claim 1, wherein the pressure of the active material paint between the die tip and the current collector is 0.5 MPa or less.   The battery electrode manufacturing method according to claim 1, wherein a difference between the thicknesses of the active material layers on the front surface and the back surface of the current collector is within ± 30%.   The battery electrode manufacturing method according to claim 1, wherein a difference between the thicknesses of the active material layers on the front surface and the back surface of the current collector is within ± 10%.

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