JP5023645B2 - Alkaline storage battery - Google Patents

Description

  The present invention relates to an alkaline storage battery, and more particularly to an alkaline storage battery in which both productivity and characteristics of a positive electrode are enhanced.

  In recent years, alkaline storage batteries have been strongly demanded to have higher capacities with the spread of portable devices. In particular, the nickel metal hydride storage battery is a secondary battery including a positive electrode mainly composed of nickel hydroxide and a negative electrode mainly composed of a hydrogen storage alloy, and is widely used as a secondary battery having a high capacity and high reliability. The positive electrode for the alkaline storage battery is roughly classified into two types, a sintered type and a non-sintered type.

  The former sintered positive electrode is obtained by impregnating a nickel sintered substrate having a porosity of about 80% obtained by sintering a core material such as punching metal and nickel powder with a nickel salt solution such as an aqueous nickel nitrate solution. In this method, nickel hydroxide as an active material is produced in a porous nickel sintered substrate by impregnating with an alkaline aqueous solution. Since it is difficult for the positive electrode to further increase the porosity of the substrate, the amount of active material cannot be increased, and there is a limit to increasing the capacity.

  The latter non-sintered positive electrode is produced by filling a metal porous body having a three-dimensional network structure (for example, a foamed nickel substrate having a porosity of about 95%) with nickel hydroxide as an active material, and has a high capacity. Widely used as the positive electrode of the type alkaline storage battery. In this non-sintered positive electrode, spherical nickel hydroxide having a large bulk density is used from the viewpoint of increasing the capacity.

  The foamed nickel substrate is manufactured by plating the surface of a foamed three-dimensional network structure such as polyurethane with nickel and then removing the three-dimensional network structure. In general, the pore diameter of the foamed nickel substrate is set to be sufficiently larger than the particle diameter of the active material, so that the charge / discharge reaction of the active material in the vicinity of the substrate skeleton where current collection is maintained proceeds smoothly, but separated from the skeleton. The charge / discharge reaction of the active material becomes insufficient. Therefore, in the non-sintered positive electrode, in order to improve the utilization factor of the filled active material, the conductivity between the active materials is increased by using a conductive agent. As the conductive agent, a divalent cobalt oxide such as cobalt hydroxide or cobalt monoxide is used. Although these divalent cobalt oxides are not electrically conductive per se, they are electrochemically oxidized into β-cobalt oxyhydroxide having electrical conductivity in the initial charge in the battery, which functions as a conductive network. To do. Due to the presence of the conductive network, in the non-sintered positive electrode, the utilization factor of the active material filled with high density can be greatly increased, and practical battery characteristics can be exhibited.

However, when the non-sintered positive electrode absorbs the electrolyte solution by repeating charge and discharge, the active material holding force decreases because the pore diameter of the foamed nickel substrate is made larger than the particle size of the active material, and the active material from the foamed nickel substrate is reduced. The substance is easy to fall off. In order to solve this problem, a proposal has been made to provide a threaded fluororesin layer on the surface of a non-sintered positive electrode (for example, Patent Document 1).
Japanese Patent Laid-Open No. 6-20585

  However, since the fluororesin layer used in Patent Document 1 has high water repellency and reduces the remaining space in the battery, the electrolyte injectability and permeability are deteriorated. The present invention has been made based on the above problems, and an object of the present invention is to provide an alkaline storage battery having a high capacity and a high capacity retention rate by suppressing the falling off of the active material in the non-sintered positive electrode without difficulty.

  In order to solve the above-mentioned problems, the alkaline storage battery of the present invention includes a positive electrode formed by filling a porous metal body having a three-dimensional network structure with an active material, a negative electrode, a separator interposed therebetween, electrolysis It is characterized in that it is made of a liquid, a hollow is provided in the skeleton of the porous metal body, and its cross section is substantially triangular, and the thickness A of each apex portion in this cross section is made larger than the thickness B up to the hollow side.

  Since the metal porous body having the cross-sectional structure as described above efficiently encloses the active material in the pores, it is possible to avoid the loss of the active material from the non-sintered positive electrode and to increase the capacity retention rate. It becomes like this.

  By providing protrusions on the skeleton plane of the porous metal body, the contact area between the porous metal body and the active material is increased, so that the contact property is improved, and the high rate discharge characteristics and the capacity retention rate can be further increased.

  By utilizing the configuration of the present invention, it is possible to solve the problem of the non-sintered positive electrode, in which the active material has been noticeably dropped even though the capacity is high, and thus it is possible to provide an alkaline storage battery having a high capacity and a high capacity retention rate. .

  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.

  1st invention consists of the positive electrode formed by filling the metal porous body which has a three-dimensional network structure with an active material, the negative electrode, the separator interposed between these, and electrolyte solution, The frame | skeleton of a metal porous body The present invention relates to an alkaline storage battery, characterized in that a hollow is provided in the cross section, the cross section thereof is substantially triangular, and the thickness A of each apex portion in the cross section is larger than the thickness B of the side portion up to the hollow.

  FIG. 1 is a schematic view showing a skeleton cross section of a metal porous body of the alkaline storage battery of the present invention. The metal porous body 1 has a substantially triangular cross section and a hollow 4 provided inside thereof. The thickness A of the vertex 2 in this cross section is larger than the thickness B of the side 3 up to the hollow 4. Since the metal porous body 1 having such a cross-sectional structure efficiently encloses the active material in the pores, it is possible to prevent the active material from falling off from the non-sintered positive electrode and to increase the capacity retention rate. It becomes like this.

The metal porous body 1 having a cross-sectional structure as shown in FIG. 1 is obtained by plating a polyurethane having a fiber system of 5 to 100 μm so that a current concentration phenomenon at the edge portion occurs at a current density of 5 A / dm ² or more. It is possible to obtain. The metal to be plated can be copper, zinc or the like in addition to nickel.

  The second invention is characterized in that, in the first invention, the ratio A / B between the thickness A of the apex portion 2 and the thickness B of the side portion 3 up to the hollow 4 is 1.5 to 3.0. . When this ratio is less than 1.5 times, the effective enclosure of the active material, which is the effect of the present invention, becomes insufficient, and the capacity reduction due to the falling off of the active material becomes somewhat remarkable. Moreover, when this ratio is larger than 3.0 times, it becomes difficult to fill the pores of the metal porous body 1 with the active material, and a desired capacity cannot be obtained. This ratio can be adjusted by changing the above-described plating conditions (specifically, the plating speed).

A third invention is characterized in that, in the first invention, a protrusion is provided on the skeleton plane of the metal porous body 1. FIG. 2 is a view showing the surface of the metal porous body 1 in the alkaline storage battery of the present invention, and C surrounded by a circle corresponds to the skeleton cross section of the metal porous body 1 shown in FIG. 1 (however, there is no hollow 4 per terminal portion). . By providing the protrusions 5 on the surface of the metal porous body 1, in addition to the effect of the first invention, the contact area between the metal porous body 1 and the active material is increased and the contact property is improved. The characteristics and capacity maintenance rate can be further increased. In the metal porous body 1 shown in the third invention, for example, after applying carbon to polyurethane having a fiber system of 5 to 100 μm, plating is performed so that a current concentration phenomenon at the edge occurs at a current density of 5 A / dm ² or more. It can be obtained by doing. Note that, as shown in FIG. 2, the portion recognized as the protrusion 5 by the electron micrograph has a thickness of 1.2 times or more of the thickness of the normal skeleton plane in the cross section of the metal porous body 1.

Here, a nickel-metal hydride storage battery using the porous metal body 1 of the present invention is taken as an example, and a method for producing an alkaline storage battery will be specifically described. First, in the positive electrode, a powder of a divalent cobalt compound such as CoO or Co (OH) ₂ is mixed with a powder of nickel hydroxide (Ni (OH) ₂ ) as an active material, and carboxymethyl cellulose (hereinafter referred to as “mixed powder”). , Abbreviated as CMC) and an aqueous solution of a thickener prepared by dissolving methylcellulose and the like, kneading the whole to prepare a viscous mixture paste, and then mixing the mixture paste with a sponge-like nickel sheet or nickel felt The metal porous body 1 having a three-dimensional network structure as described above is filled and applied, followed by drying and rolling in order. The metal porous body 1 has a recessed portion crushed in the thickness direction at a predetermined position in advance. A metal piece such as a nickel piece is spot-welded as a positive electrode current collector to the recessed portion, can get.

  The negative electrode is a porous conductive plate such as punching metal (perforated steel plate plated with nickel) or nickel net, a hydrogen storage alloy powder that is an active material, and a conductive material powder, a binder and a thickener. It is manufactured by applying a mixture slurry mixed at a ratio, followed by drying and rolling.

  As the separator, a non-woven fabric made of polyolefin such as polypropylene is subjected to a surface treatment such as sulfonation. The separator is cut larger than the dimensions of the positive electrode and the negative electrode, wound with the separator 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.

  Examples of the alkaline storage battery that can use the porous metal body 1 of the present invention include a nickel cadmium storage battery, a nickel iron storage battery, and a nickel zinc storage battery in addition to the nickel hydride storage battery described above. Among them, the nickel-metal hydride storage battery most closely matches the gist of the present invention because of its high energy density.

  Below, the Example and comparative example of this invention are described in detail using a nickel metal hydride storage battery.

Example 1
Nickel is deposited in a vacuum on a foamed urethane substrate having about 50 holes per inch, fiber diameter of 40 μm, average pore diameter of 300 μm, porosity of 96%, and thickness of 1.8 mm. 10 g / m ² of nickel The metal was coated. This was then subjected to electrolytic nickel plating in a watt bath at a current density of 10 A / dm ² to form a plating layer. The amount of plating deposition was 400 g / m ² . Thereafter, the foamed urethane substrate as a base was baked and removed at 600 ° C., and further nickel reduction treatment was performed in a hydrogen stream at 900 ° C. The obtained metal porous body 1 was roll-pressed so as to have a uniform thickness of 1.3 mm. The thickness A of the apex portion 2 of the obtained metal porous body 1 was 30 μm, the thickness B up to the hollow 4 of the side portion 3 was 15 μm, and the ratio A / B was 2.0.

  The metal porous body 1 was filled with nickel hydroxide as an active material, cobalt hydroxide and cobalt monoxide powder as conductive agents, and then rolled and cut into predetermined dimensions to obtain a positive electrode. 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. After coating and drying on a two-dimensional porous body (punching metal) in which nickel was plated on a steel plate, the steel sheet was rolled and cut into predetermined dimensions. These positive and negative electrodes were wound through a separator 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 composed of an aqueous potassium hydroxide solution was injected therein to produce a nickel hydride storage battery having a nominal capacity of 3 Ah. This is Example 1.

(Examples 2 to 5)
For the alkaline storage battery of Example 1, the current density of the nickel plating of the metal porous body 1 is 5 A / dm ² (Example 2), 7 A / dm ² (Example 3), 15 A / dm ² (Example 4), By setting 18 A / dm ² (Example 5), the thickness A of the apex 2 is 23.5 μm (Example 2), 27 μm (Example 3), 33.8 μm (Example 4), and 35 μm (Example). 5), and the thickness B of the side 3 up to the hollow 4 is 21.5 μm (Example 2), 18 μm (Example 3), 11.2 μm (Example 4), 10 μm (Example 5), and the ratio A / B was the same alkali as in Example 1 except that 1.1 (Example 2), 1.5 (Example 3), 3.0 (Example 4), and 3.5 (Example 5). A storage battery was constructed. Let this be Examples 2-5.

(Example 6)
For the alkaline storage battery of Example 1, similar to Example 1 except that conductive carbon powder having an average particle size of 3 μm was applied to the same urethane foam substrate as in Example 1 and then nickel was evaporated in vacuum. An alkaline storage battery was constructed. This is Example 6.

(Comparative Example 1)
By setting the current density of nickel plating of the metal porous body 1 to 4 A / dm ² with respect to the alkaline storage battery of Example 1, the thickness A of the apex portion 2 and the thickness B of the side portion 3 up to the hollow 4 is 22.5 μm. An alkaline storage battery similar to that of Example 1 was configured except that the ratio A / B was 1.0. This is a comparative example.

  The following evaluation was performed on these alkaline storage batteries.

(Cycle life evaluation)
After charging to 1.5V at 3A in a 20 ° C. environment, charging / discharging to discharge to 0.9V at 3A was repeated. The discharge capacity after 5 cycles, 100 cycles and 300 cycles is shown in Table 1.

(High rate discharge evaluation)
After charging to 1.5V at 3A in a 20 ° C. environment, it was discharged to 0.9V at 10A. The discharge capacity at that time is shown in (Table 1).

（表１）より、Ａ／Ｂ比が１．０である比較例は、３００サイクルでの容量維持率が極端に低下している。この理由として、隣り合う骨格の頂点部２どうしで活物質を囲い込むという本発明の効果が発揮できなかったため、活物質の脱落による容量低下が顕著になったと考えられる。

From Table 1, the capacity retention rate at 300 cycles is extremely lowered in the comparative example having an A / B ratio of 1.0. The reason for this is that the effect of the present invention of enclosing the active material between the apex portions 2 of adjacent skeletons could not be exhibited, so that the capacity reduction due to the loss of the active material was conspicuous.

  In contrast to these comparative examples, Examples 1 to 5 of the present invention showed good cycle characteristics. However, in Example 2 in which the ratio A / B was less than 1.5 times, the efficient enclosing of the active material, which is the effect of the present invention, was insufficient, and the capacity reduction due to the falling off of the active material became somewhat remarkable. Further, in Example 5 in which the ratio A / B was larger than 3.0 times, it was difficult to fill the active material into the pores of the metal porous body 1, and the capacity at the fifth cycle was slightly reduced. From this result, it is understood that the preferable range of the ratio A / B is 1.5 to 3.0.

  In addition, Example 6 of the present invention showed better high rate discharge characteristics than Example 1. This is because the contact area between the metal porous body 1 and the active material is increased and the contact property is improved. Moreover, since the capacity retention rate is higher than in the other examples, it is presumed that the falling off of the active material could be more firmly suppressed.

  The present invention is suitable for an alkaline storage battery using a porous metal body having a three-dimensional network structure, and can reduce the active material dropout failure on the entire surface of the positive electrode without interfering with the battery reaction, thereby suppressing a decrease in the positive electrode capacity. Because it becomes possible, the industrial applicability is considered high.

Schematic which shows the frame | skeleton cross section of the metal porous body of the alkaline storage battery of this invention The figure which shows the surface of the metal porous body in the alkaline storage battery of 3rd invention

Explanation of symbols

1 Metal porous body 2 Vertex 3 Side 4 Hollow 5 Protrusion

Claims (1)

An alkaline storage battery comprising a positive electrode formed by filling a metal porous body having a three-dimensional network structure with an active material, a negative electrode, a separator interposed therebetween, and an electrolytic solution,
The metal porous body is provided with protrusions on the skeleton plane of the metal porous body by forming a metal layer on the urethane foam and carbon powder after applying the carbon powder to the urethane foam,
A hollow is provided in the skeleton of the porous metal body, and the cross section thereof is substantially triangular, and the ratio A / B between the thickness A of each apex and the thickness B of the side in the cross section is 1.5-3. An alkaline storage battery characterized by being zero .

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