JP2006196207A - Alkaline storage battery and manufacturing method of its electrode group - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the generation of a minute short circuit caused by whiskers or burrs of substrates of a positive electrode and a negative electrode, and enhance the reliability of a battery. <P>SOLUTION: An alkaline storage battery is comprised of a positive electrode, a negative electrode, a separator interposed between them, and an electrolyte. The separator has a nonwoven fabric as the main composition, and high fiber density portions are partially present in the separator. By this constitution, high short circuit resistance and high discharge characteristics are compatible. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an alkaline storage battery and a method for manufacturing the same, and more particularly, to an alkaline storage battery that can reduce the occurrence of minute short-circuits due to whiskers and burrs of positive and negative electrode substrates and improve battery reliability, and a method for manufacturing the same. .

In general, a separator for a sealed alkaline storage battery must be interposed between positive and negative electrodes to prevent contact between the two and to sufficiently hold an electrolytic solution so that an electromotive reaction proceeds smoothly. At the same time, it is necessary to have a property of allowing the gas to pass efficiently so that oxygen gas generated from the positive electrode at the time of overcharge is quickly absorbed by the negative electrode. As a separator satisfying such characteristics, a nonwoven fabric having a fiber diameter of 10 to 20 μm, a thickness of 0.1 to 0.2 mm, and a fiber density of 60 to 100 g / m ² is generally used. Has been used.

  However, in such a separator, since the fiber diameter is thicker than the thickness, a portion having a large hole diameter is likely to occur due to unevenness of single fiber distribution. In particular, in a nickel cadmium battery, cadmium, which is a negative electrode active material, generates dendritic crystals on the surface of the separator fiber and in the gaps between the fibers as the charge / discharge cycle progresses. It is important for extending the life of the battery not to increase the pore size more than necessary.

  Furthermore, nickel hydroxide, which is a positive electrode active material for nickel cadmium batteries or nickel metal hydride batteries, swells as the charge / discharge cycle progresses. As it swells, it penetrates the separator and causes a short circuit with the negative electrode.

In order to prevent these problems, a proposal has been made to melt and coat a portion of the separator facing the positive electrode tab (for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-40147

  However, in the separator of Patent Document 1, only a portion facing the attachment portion of the positive electrode tab can be melted and formed into a film to prevent a minute short circuit due to whisker / burr at the positive electrode edge. If it exists on the surface, the technique of Patent Document 1 cannot prevent a minute short circuit. In addition, since the separator needs to have a property of sufficiently holding an electrolyte solution to smoothly promote an electromotive reaction and simultaneously allowing gas to pass efficiently, the technique of Patent Document 1 cannot be used for the entire electrode surface. .

  The present invention has been made on the basis of the above problems, and it is an object of the present invention to reduce the occurrence of minute short-circuits due to whisker burrs on the positive and negative electrode substrates, and to improve battery reliability.

  In order to solve the above problems, a sealed alkaline storage battery of the present invention is an alkaline storage battery comprising a positive electrode, a negative electrode, a separator interposed therebetween, and an electrolytic solution, and the separator is made of a nonwoven fabric. The main component is characterized in that the separator has a portion with a high fiber density partially.

  Furthermore, in order to embody the above-described battery structure, the method for producing an alkaline storage battery electrode group of the present invention is a method for producing an electrode group from a positive electrode, a negative electrode, and a separator having a nonwoven fabric as a main component. And a step of unwinding each of the positive electrode, the negative electrode, and the separator, a step of densifying a part of the separator, and a step of forming a winding electrode group of the positive electrode, the negative electrode, and the separator.

  By providing a part with a high fiber density on the entire separator surface, it is possible to satisfactorily prevent a minute short circuit from occurring at any location on the positive electrode surface without interfering with the battery reaction. become.

  The separator for an alkaline storage battery of the present invention can reduce the occurrence of minute short-circuits due to the beard of the positive electrode substrate, and can improve battery reliability.

  Hereinafter, the best mode for carrying out the invention will be described with reference to the drawings. In addition, the figure shown here is an example, Comprising: If it has the structure represented to the claim of this invention, the same effect can be acquired.

  FIG. 1 is a schematic surface view showing an example of the alkaline storage battery separator of the present invention. A portion (hereinafter referred to as a high density portion) 2 having a high fiber density is partially provided on the entire surface of the separator 1 having a nonwoven fabric as a main component.

  In the alkaline storage battery according to the present invention, when the separator 1 is partially provided with the high-density portion 2, a minute short circuit can be satisfactorily prevented regardless of the location of the beard at any location on the positive electrode surface without interfering with the battery reaction. It has been found that it will be possible.

  Here, the porosity in the high density portion 2 is preferably 10% or more and 30% or less, from the viewpoint of preventing the penetration of the beard of the positive electrode substrate. When the porosity is less than 10%, it is not preferable because good charge / discharge characteristics cannot be obtained for an alkaline storage battery, and when the porosity is more than 30%, it is not preferable in that the effect of preventing the penetration of the positive electrode substrate becomes small. . The porosity C in the high-density portion 2 can be changed depending on the applied pressure and temperature applied to this portion. The theoretical thickness when the porosity is zero determined from the specific gravity of the separator 1 is A, and the high-density portion 2 When the thickness of B is B, it can be calculated by the following (Formula 1).

C = (B−A) / B × 100 (Equation 1)
Moreover, the high density part 2 is preferable at the point which prevents the penetration of the beard of a positive electrode board | substrate as it is 5% or more and 20% or less by area ratio with respect to the separator 1 whole. When the area ratio is larger than 20%, the nonwoven fabric 1 is preferable because it may hinder the original role of holding the electrolyte sufficiently to smoothly promote the electromotive reaction and at the same time efficiently passing the gas. Absent. On the contrary, when the area ratio is less than 20%, it is not preferable in that the effect of preventing the penetration of the positive electrode substrate becomes low. Therefore, it is preferable to set the area ratio within the above range in order to achieve both the maintenance of the charge / discharge characteristics of the alkaline storage battery by ensuring the ionic conductivity and the prevention of a short circuit between the positive and negative electrodes.

  The shape of the high density portion 2 can be not only a spot shape as shown in FIG. 1 but also a lattice shape as shown in FIG. 2 or a streak shape as shown in FIG. It is preferable that these shapes are applied to the entire surface of the separator 1 in a uniform shape from the viewpoint of providing a battery having no variation in discharge characteristics.

Here, a nickel-metal hydride battery using the separator of the present invention is taken as an example, and the manufacturing method thereof will be specifically described. First, a positive electrode (nickel electrode) is prepared by, for example, mixing a powder of a divalent cobalt compound such as CoO or Co (OH) ₂ with a powder of nickel hydroxide (Ni (OH) ₂ ) which is a positive electrode active material. After adding a thickener aqueous solution prepared by dissolving carboxymethylcellulose (hereinafter abbreviated as CMC) or methylcellulose to the mixed powder and kneading the whole, a viscous mixture paste is prepared. It is manufactured by filling and applying to a conductive substrate having a three-dimensional network structure such as a nickel sheet or nickel felt, followed by drying and rolling. Here, the conductive substrate, the predetermined position is crushed in the thickness direction, a recessed portion is formed in advance, a metal piece such as a nickel piece is spot welded to the recessed portion as a positive electrode current collector, A positive electrode is obtained. For the negative electrode (hydrogen storage alloy electrode), a conductive material powder such as a hydrogen storage alloy powder and a binder powder such as polyvinylidene fluoride are provided on a porous conductive plate such as a punched nickel plate or nickel net, for example. It is manufactured by applying a mixture slurry mixed at a ratio, followed by drying and rolling. The separator is cut larger than the dimensions of the positive electrode and the negative electrode, wound in a state of being interposed therebetween, and wound so that the negative electrode is located on the outermost periphery. The electrode group formed as described above is inserted into the outer can through the opening of the outer can. After an alkaline electrolyte mainly composed of KOH or the like is injected into the outer can, the positive electrode current collector and the sealing body are welded, and the sealing body becomes a positive electrode terminal. On the other hand, in the negative electrode, the negative electrode located on the outermost periphery of the electrode group comes into contact with the outer can serving as the negative electrode terminal, whereby the negative electrode and the negative electrode terminal are electrically connected. Finally, the sealing body is fitted and attached to the opening of the outer can via an insulating plate, and the outer can and the sealing body are sealed and welded to produce a sealed nickel-metal hydride battery.

  Next, the best manufacturing method of the electrode group for alkaline storage batteries of this invention is demonstrated using figures. The present invention relates to a method for producing an electrode group from a positive electrode, a negative electrode, and a separator having a nonwoven fabric as a main component, the step of unwinding the positive electrode, the negative electrode, and the separator, respectively, It is the manufacturing method of the electrode group for alkaline storage batteries which has the process of densifying a part and the process of winding up the said positive electrode, the said negative electrode, and the said separator, and comprising an electrode group. Above all, the gist of the present invention is in the process of densifying part of the separator.

  FIG. 4A is a schematic side view showing an example of a process for densifying a part of the separator of the present invention only on one side. The high density part 2 is provided by allowing the separator 1 which has a nonwoven fabric as a main component to pass between the embossing roller 3 and the flat roller 4 which processed the unevenness | corrugation on one side. The uneven shape of the embossing roller 3 can be changed in accordance with the desired shape and area ratio of the high-density portion 2. For example, FIG. 4B shows a spot shape as shown in FIG. 1, FIG. 4C shows a grid shape like FIG. 2, and FIG. 4B shows a horizontal line shape like FIG. D) When the vertical streak is desired, the uneven pattern can be changed as shown in FIG.

  FIG. 4 (F) is a schematic side view showing an example of a process of densifying part of the separator of the present invention on both sides. The embossing roller 3 is used on both sides and the protrusions are overlapped to separate the separators. The high density portion 2 is provided by passing 1. For example, the concave / convex pattern can be changed as shown in FIG. 4G when the high density portion 2 is desired to have a horizontal streak shape as shown in FIG. 3 and as shown in FIG.

Moreover, the preferable form of the process which densifies a part of separator of this invention is demonstrated using FIG. FIG. 5 (A) is a schematic side view. As shown in FIG. 4, the embossing roller 3 is used on both sides, and the high density portion 2 is provided by passing the separator 1 so that the protruding portions do not overlap. According to this method, since the high density part 2 exists on both surfaces of the separator 1 and the high density part 2 does not overlap on both surfaces, both short-circuit resistance and battery characteristics can be achieved at a high level. 5 (B) and 5 (C) are examples of schematic perspective views, and the high-density portion 2 having a desired shape can be provided by changing the concavo-convex pattern of the embossing roller 3 as in FIGS. it can.

  In addition, nylon, a polypropylene, etc. can be selected as a fiber material of the nonwoven fabric used for the separator of this invention.

  The secondary battery that can use the separator of the present invention may be a secondary battery that uses the above-mentioned nonwoven fabric separator in addition to an alkaline storage battery such as a nickel metal hydride battery or a nickel cadmium battery. Among them, the use of a nickel-hydrogen battery having a nickel electrode as a positive electrode and a high weight energy density is most consistent with the gist of the present invention.

  Below, it demonstrates in detail using the Example and comparative example of this invention. In addition, although the example shows the case of a nickel metal hydride storage battery as a representative example, the present invention is not limited to this, and can be expanded to other alkaline storage batteries including a nickel positive electrode, specifically, nickel cadmium storage batteries. Needless to say.

Example 1
The positive electrode was obtained by filling and rolling nickel hydroxide, which is an active material, and cobalt hydroxide and cobalt monoxide powder, which are conductive agents, into a foamed nickel three-dimensional porous body, and cutting the powder into predetermined dimensions. On the other hand, the negative electrode is formed by perforating a paste composed of hydrogen storage alloy powder as an active material, ketjen black as a conductive agent, styrene-butadiene rubber copolymer as a binder, and CMC as a thickener. The obtained iron plate was applied to a punching metal, which is a two-dimensional porous body obtained by performing nickel plating, dried, then rolled, and cut into predetermined dimensions. These positive and negative electrodes were wound through a separator 1 having a polypropylene non-woven fabric as a main constituent element to constitute an electrode group. This electrode group was inserted into a cylindrical bottomed can, and an electrolytic solution made of an aqueous potassium hydroxide solution was injected therein to produce 10,000 nickel hydride storage batteries having a nominal capacity of 3 Ah.

At this time, the group constituting machine constituting the electrode group has a step of unwinding the positive electrode, the negative electrode, and the separator 1 before the high-density treatment as a first step, and a step of densifying part of the separator 1. The step of forming the electrode group by winding up the positive electrode, the negative electrode, and the separator 1 as the second step is the third step. In the second step, as shown in FIG. 4 (F), the concavo-convex portion in contact with the separator 1 of the embossing roller 3 is compressed at a pressure of 7 kgf / cm ² for 0.4 seconds while being heated to 90 ° C. The densification process was performed. At this time, the opposite side of the embossing roller 3 is a flat roller 4. After a certain distance from the densification processing section, the embossing roller 3 and the flat roller 4 were disposed in opposite directions, and the other surface of the separator 1 was subjected to the same processing.

  Here, the porosity of the high-density part 2 in the separator 1 was 20%, and the area ratio of the high-density part 2 to the whole separator was 10%. Further, the high density portion 2 exists on both the front and back sides of the separator, but exists in a portion where the both surfaces do not overlap, and the shape thereof is not a specific part of the separator, but a spot shape uniformly extending over the entire surface. This is the alkaline storage battery of Example 1.

(Examples 2 to 5)
An alkaline storage battery similar to that of Example 1 was configured except that the porosity of the high density portion 2 in the separator 1 was set to 5, 10, 30, and 35% with respect to the alkaline storage battery of Example 1. Let this be the alkaline storage battery of Examples 2-5.

(Examples 6 to 9)
The alkaline storage battery similar to Example 1 was comprised except having set the area ratio of the high-density part 2 in the separator 1 to 3, 5, 20, 25% with respect to the alkaline storage battery of Example 1. Let this be the alkaline storage battery of Examples 6-9.

(Example 10)
An alkaline storage battery similar to that of Example 1 was configured except that the high-density portion 2 overlapped on both the front and back surfaces of the separator 1 with respect to the alkaline storage battery of Example 1. This is the alkaline storage battery of Example 10.

(Example 11)
An alkaline storage battery similar to that of Example 1 was configured except that the high-density portion 2 in the separator 1 was unevenly provided with respect to the alkaline storage battery of Example 1. This is the alkaline storage battery of Example 11.

(Example 12)
With respect to the alkaline storage battery of Example 1, an alkaline storage battery similar to that of Example 1 was configured, except that the shape of the high-density portion 2 in the separator 1 was changed to a lattice by the combination of rollers shown in FIG. . This is the alkaline storage battery of Example 12.

(Example 13)
For the alkaline storage battery of Example 1, the same alkaline storage battery as that of Example 1 is configured except that the shape of the high-density portion 2 in the separator 1 is a horizontal stripe by the combination of rollers shown in FIG. did. This is the alkaline storage battery of Example 12.

(Comparative Example 1)
An alkaline storage battery similar to that of Example 1 was configured except that the separator 1 was not provided with the high density portion 2 with respect to the alkaline storage battery of Example 1. This is the alkaline storage battery of Comparative Example 1.

(Comparative Example 2)
The alkaline storage battery of Example 1 was configured in the same manner as in Example 1 except that the entire surface of the separator 1 was pressurized to form the high density portion 2 and the porosity was 45%. This is the alkaline storage battery of Comparative Example 2.

  The following evaluation was performed on these alkaline storage batteries.

(Internal short circuit evaluation)
An applied voltage of 100 V was applied between the positive and negative terminals after the group configuration of the batteries and immediately before the electrolyte injection. Here, batteries showing a resistance value of 0.002 MΩ or less were excluded as internal short-circuit batteries. The number of internal short-circuit defects is counted, the ratio to 10,000 assembled batteries is obtained, and the result is shown in Table 1 as the battery short-circuit occurrence rate.

(High rate discharge capacity ratio)
In the non-defective battery that was free from the internal short circuit failure, after charging to 1.5 V at 3 A in a 20 ° C. environment, the battery was discharged to 0.8 V at 0.6 A and 10 A. Here, the 10A discharge capacity is divided by the 0.6A discharge capacity, and the obtained ratio is shown in Table 1 as the capacity ratio.

From Table 1, the comparative example 1 in which the separator 1 does not have the high density part 2 has a good capacity ratio of 92%, but the short-circuit occurrence rate is as high as 1.10%, and the short-circuit prevention effect is low. It can be said. On the contrary, Comparative Example 2 having a high fiber density uniformly over the entire surface has a good short-circuit occurrence rate of 0.02%, but has a low capacity ratio of 66% and low ionic conductivity. In contrast to these comparative examples, it can be seen that Examples 1 to 14 of the present invention have a good balance of short-circuit occurrence rate and capacity ratio.

  In Example 2 in which the porosity of the high-density portion 2 in the separator 1 is less than 10%, the capacity ratio is slightly decreased, and in Example 5 in which the porosity exceeds 30%, the short-circuit occurrence rate is slightly increased. Therefore, the porosity of the high density portion 2 in the separator 1 is desirably 10 to 30%.

  Further, in Example 6 in which the area ratio of the high-density portion 2 in the separator 1 is less than 5%, the short-circuit occurrence rate slightly increases, and in Example 9 in which the area ratio exceeds 20%, the capacity ratio slightly decreases. Therefore, the area ratio of the high density portion 2 in the separator 1 is desirably 5 to 20%.

  As is clear from Example 10, even when the high-density part 2 is overlapped on the front and back, the short-circuit resistance and the discharge characteristics are good as in Example 1. Moreover, when the high density part 2 is unevenly distributed like Example 11, the effect is not enough in both a short circuit generation rate and a capacity | capacitance ratio. Therefore, it is desirable that the high density portion 2 has a shape that extends uniformly over the entire surface, not a specific portion of the separator 1. However, the effect remains the same regardless of whether the shape is a spot shape (Example 1), a lattice shape (Example 12), or a horizontal streak shape (Example 13).

  In Example 1, the separator 1 was provided with the high-density part 2 separately on the front and back sides, but the same effect was obtained when the high-density part 2 was provided simultaneously on the front and back by the combination of rollers shown in FIG. Needless to say.

The present invention is suitable for a secondary battery using a nonwoven fabric made of fibers such as nylon and polypropylene as a separator, and there is a beard of the positive electrode substrate at any location of the positive electrode without interfering with the battery reaction. Since it becomes possible to prevent micro short-circuits well,
Industrial applicability is considered high.

Schematic diagram of a separator used in the alkaline storage battery of the present invention, in which a high density portion is provided in a spot shape. Schematic diagram of a separator used in the alkaline storage battery of the present invention, in which high-density portions are provided in a lattice shape Schematic diagram of a separator used for the alkaline storage battery of the present invention, in which high-density portions are provided in a streak pattern (A) Schematic side view of the step of densifying one side of the separator used in the alkaline storage battery of the present invention, (B) Schematic perspective view of the step of densifying the separator when the high-density portion is single-sided and spot-shaped, (C) Schematic perspective view of separator densification process when the high-density part is single-sided and lattice-shaped, (D) Schematic perspective view of separator densification process when the high-density part is single-sided and horizontal stripe-shaped. , (E) Schematic perspective view of separator densification process when the high-density portion is single-sided and vertical stripes, (F) Densification of both sides of the separator used in the alkaline storage battery of the present invention simultaneously and at the same location Schematic side view of processing step, (G) Schematic perspective view of separator densification process when the high-density portion has the same location on both sides and horizontal stripes, (H) The high-density portion has the same location on both sides and vertical stripes Densification process of separator in case of Schematic perspective view (A) Schematic side view of the process of densifying both sides of the separator used in the alkaline storage battery of the present invention simultaneously and at different locations, (B) High density of the separator in the case where the high-density portion is different in both sides and spot-like Schematic perspective view of the forming step, (C) Schematic perspective view of the separator densifying step in the case where the high-density portion is different in both sides and has vertical streaks

Explanation of symbols

1 Separator 2 High-density part 3 Embossed roller 4 Flat roller

Claims (7)

An alkaline storage battery comprising a positive electrode, a negative electrode, a separator interposed therebetween, and an electrolyte solution,
The separator is an alkaline storage battery characterized in that a non-woven fabric is a main constituent, and a portion having a high fiber density is partially present. The alkaline storage battery according to claim 1, wherein a porosity of the separator at a high fiber density is 10% or more and 30% or less. 2. The alkaline storage battery according to claim 1, wherein the portion having a high fiber density of the separator is 5% or more and 20% or less in an area ratio with respect to the whole separator. The alkaline storage battery according to claim 1, wherein the separator has a high fiber density in a spot shape, a lattice shape, or a line shape. 2. The alkaline storage battery according to claim 1, wherein the separator has a high fiber density on both the front and back surfaces of the separator, and the front and back surfaces have a high fiber density and do not overlap. A method for producing an electrode group from a positive electrode, a negative electrode, and a separator having a nonwoven fabric as a main component,
A step of unwinding each of the positive electrode, the negative electrode, and the separator, a step of densifying a part of the separator, and a step of forming a winding electrode group of the positive electrode, the negative electrode, and the separator. The manufacturing method of the electrode group for alkaline storage batteries. The method for producing an electrode group for an alkaline storage battery according to claim 7, wherein portions having a high fiber density of the separator are present on both sides of the separator, and portions having a high fiber density do not overlap on both sides.