JP4952038B2 - Positive electrode for alkaline storage battery and alkaline storage battery - Google Patents

Description

  The present invention relates to a positive electrode for an alkaline storage battery, and more particularly to a technique for preventing a positive electrode active material from falling off.

  Batteries such as alkaline storage batteries and lithium ion secondary batteries are widely used as power sources for portable devices, electric tools, or electric vehicles. Above all, the use of nickel-metal hydride storage batteries, which have a relatively high energy density and excellent durability, is expanding mainly in power sources for electric vehicles.

  The positive electrode for alkaline storage battery is roughly classified into a sintered type and a non-sintered type. The sintered positive electrode is obtained by impregnating a porous nickel sintered substrate having a porosity of about 80% obtained by sintering nickel powder with a conductive support, which is then impregnated in a nickel salt aqueous solution such as nickel nitrate, and then an alkaline aqueous solution. The nickel hydroxide active material is deposited by immersing it in, for example. Since the pore diameter of the positive electrode conductive support is as small as about 10 μm, the holding capacity of the active material is relatively high (for example, Patent Document 1). However, on the other hand, it is difficult to increase the capacity because the filling property is low.

  The non-sintered positive electrode is obtained by filling a foamed three-dimensional porous body made of nickel metal or the like with a conductive support, and nickel hydroxide powder as an active material. Since this conductive support has a high porosity of 95% or more and a relatively large pore size of about 200 to 500 μm, the active material can be filled with high efficiency and the capacity can be increased (for example, Patent Documents). 2). However, since the pore diameter of the conductive support is larger than that of the sintered positive electrode, the holding capacity of the active material is low and it is easy to fall off, and it is difficult to obtain high current collecting performance. In order to compensate for these disadvantages, a method of preventing the loss of the active material by adding a binder such as polytetrafluoroethylene (hereinafter abbreviated as PTFE) or a conductive material such as a cobalt compound is added to enhance conductivity. Methods are generally adopted.

However, when a large amount of binder is added to prevent the active material from falling off, there is a drawback that the resistance component increases and the effect of adding the conductive material is reduced. Therefore, a method for reducing the pore diameter of the conductive support of the non-sintered positive electrode has been proposed (for example, Patent Document 3). According to this method, it is possible to simultaneously achieve the suppression of falling off of the active material and the improvement of the current collecting performance, which is ideal as the electrode performance.
Japanese Patent No. 3275594 JP-A-60-131765 Japanese Patent No. 2947284

  However, when the technique of Patent Document 3 was developed, there was a tendency that the positive electrode active material was less likely to be filled because the pore size of the conductive support was small. As described above, it is difficult to prevent the active material from dropping while easily filling the active material only by appropriately combining the conventional techniques.

  The present invention is intended to solve the above-described problems, and provides a positive electrode for an alkaline storage battery that can be easily filled with a large amount of active material and can prevent the active material from falling off.

  In order to solve the above problems, the positive electrode for an alkaline storage battery of the present invention uses a foamed three-dimensional porous body as a conductive support, and in a vertical section relative to the number per unit area of triple points in the horizontal section. The ratio of the number of triple points per unit area is set to 3.0 to 6.0.

  As a result of intensive studies, the present inventors have determined that per unit area of triple points in a vertical section relative to the number of units per unit area of triple points in a horizontal section with respect to a positive electrode using a foamed three-dimensional porous body. It was elucidated that the active material can be retained by more core material skeletons and the active material can be prevented from falling off by setting the ratio of the number (hereinafter abbreviated as “point ratio”) to 3.0 or more. Furthermore, by setting this point ratio to 6.0 or less, the number of the core material skeletons of the foamed three-dimensional porous body is appropriately reduced, each core material skeleton is made sufficiently thick, and the strength of the positive electrode is increased. It has been clarified that cracks are less likely to occur during battery construction and that active material can be prevented from falling off. The present invention utilizes the above-described knowledge and proposes a technique capable of easily filling a large amount of an active material as a positive electrode for an alkaline storage battery and preventing the active material from falling off.

  As described above, according to the present invention, it is possible to provide a positive electrode for an alkaline storage battery that can be easily filled with a large amount of active material and can prevent the active material from falling off.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  1st invention is the positive electrode for alkaline storage batteries which uses a foaming type three-dimensional porous body as an electroconductive support body, Comprising: The point ratio mentioned above was 3.0 to 6.0 times, It is characterized by the above-mentioned.

  FIG. 1 is a schematic cross-sectional view showing a positive electrode for an alkaline storage battery after pressing according to the present invention. A positive electrode is formed by filling the active material 3 into the pores 2 formed in the gaps of the skeleton 1 of the foamed three-dimensional porous body. In the present invention, the holes 2 are elongated in the direction perpendicular to the thickness of the positive electrode. The falling off of the active material 3 occurs sequentially from the surface of the positive electrode, but the structure of the present invention is a structure in which the skeleton 1 itself prevents the dropping of the active material 3 from the periphery of the surface. This effect becomes remarkable when the above-mentioned point ratio is set to 3.0 or more. Furthermore, if this point ratio is 6.0 or less, the number of the skeletons 1 of the foamed three-dimensional porous body is appropriately reduced to make each skeleton 1 sufficiently thick, and the strength of the positive electrode is increased to increase the strength of the positive electrode. By making cracks difficult to occur, the active material 3 can be prevented from falling off.

  Here, triple points will be described in detail. The foamed three-dimensional porous body made of nickel metal or the like is produced by burning the foamed urethane as a base material after metal plating is performed on the surface of the foamed urethane. The urethane foam as a base material is produced by generating bubbles with a foaming agent, but urethane remains in the gap between the bubbles when foamed, specifically, the gap formed by three bubbles, and the triangular skeleton 1 A three-dimensional porous body having Since this foamed urethane is used as a base material, the foamed three-dimensional porous body also has a triangular skeleton 1. Since a part of the triangular skeleton 1 is bonded to a plurality of other skeletons 1, the cross section of the actual foamed three-dimensional porous body is observed in a mixed form. A section of the triangular skeleton 1 appearing in this section is called a triple point. Specific triple points are shown in FIG. The number of triple points can be counted as 1 in FIG. 2A, 2 in FIGS. 2B and 2C, 4 in FIG. 2D, and 6 in FIG. 2E.

A specific method for measuring the number of triple points is as follows. First, a part of the positive electrode is cut out, immersed in a solution of a curable resin such as epoxy, and sufficiently degassed after vacuum to be cured. Next, the cured product is polished so that the cross section of the foamed three-dimensional porous body can be seen. Here, assuming that the thickness direction of the positive electrode is t, the vertical section refers to the hatched plane of FIG. 3A relative to the original positive electrode, and the horizontal section refers to the hatched line of FIG. 3B relative to the original positive electrode. It refers to a plane. The result of observing this cross section with a microscope is shown in FIG. Incidentally, FIG. 4 shows a cross section in the horizontal direction. Since the area of the observation field can be calculated from the area of the captured image and the magnification of the microscope, calculate the number of triple points per unit area from the number of triple points in the observation field and the area of the observation field. Can do.

  When the point ratio described above is less than 3.0, the pores 2 of the foamed three-dimensional porous body are not easily distorted in the thickness direction of the positive electrode, and the effect of the present invention becomes insufficient. Since the number of the skeletons 1 of the foamed three-dimensional porous body is excessive, each skeleton 1 becomes thin, the strength of the positive electrode cannot be maintained, and cracks are likely to occur when the battery is constructed. Will increase.

  In order to obtain the positive electrode of the first invention, a foamed three-dimensional porous body having a thickness larger than that of a conventional one is prepared, and after filling the active material 3, the rolling ratio (foamed three-dimensional porous material before filling) is increased. The thickness of the body / the thickness of the positive electrode after filling) may be increased and rolled. With this method, since there is a sufficient gap between the foam metal skeletons when filling, the active material 3 can be easily filled. As an example, when a positive electrode having a thickness of 600 μm is obtained, it is preferable that the thickness of the foamed three-dimensional porous body before filling is 1800 to 4200 μm and the rolling ratio is 3.0 to 6.0. Even when positive electrodes having different thicknesses are obtained, the positive electrode of the first invention can be obtained within the above-described rolling ratio range.

  In addition, nickel hydroxide powder can be selected as the active material 3 filled in the foamed three-dimensional porous body. The shape of the nickel hydroxide powder is preferably spherical, and the average particle size is preferably 5 to 20 μm.

  In addition to the active material 3, it is preferable to use a cobalt compound such as metallic cobalt and cobalt hydroxide as the conductive agent. These conductive agents may be added as a powder having an average particle diameter of 0.1 to 1.0 μm, and may be coated on the surface of the active material 3 so as to have a thickness of 0.02 to 1 μm. The addition of and the coating on the surface of the active material 3 may be used in combination. In addition, it is preferable that the addition amount is in the range of 3 to 15 parts by weight with respect to 100 parts by weight of the active material 3.

  Furthermore, in addition to the active material 3, a small amount of polytetrafluoroethylene (hereinafter abbreviated as PTFE), polyethylene, or the like can be used as a binder (0.05 to 2 parts by weight with respect to 100 parts by weight of the active material 3). . In particular, PTFE is arranged as fine particles on the surface of the positive electrode of the first invention, and then can generate fine fibers called fibrils by rolling or the like to cover the surface of the positive electrode, so that the active material 3 can be more strongly removed. It is preferable from the viewpoint of prevention. In addition to this binder, a water-soluble polymer such as carboxymethyl cellulose (hereinafter abbreviated as CMC) is added as a thickener for imparting an appropriate viscosity to the paste containing the active material 3 (positive electrode precursor). You can also.

According to a second invention, in the first invention, the number of triple points per unit area in a horizontal cross section is 1000 to 3038 / cm ² , and the above-mentioned point ratio is 3.5 to 5.5. It is characterized by that. In order to maximize the effects of the first invention, the number of triple points per unit area in the cross section in the horizontal direction is preferably within the scope of the second invention. When this number is less than 1000 / cm ² , the pore diameter of the foamed three-dimensional porous body cannot be made sufficiently small, and the holding power of the active material 3 is slightly reduced. When it exceeds 3038 / cm ² , each skeleton 1 is slightly As the thickness becomes thinner, the strength of the positive electrode slightly decreases, and cracks are likely to occur at the time of battery construction, and the active material 3 is slightly dropped. Further, when the point ratio is less than 3.5, the pores 2 of the foamed three-dimensional porous body are not sufficiently distorted in the thickness direction of the positive electrode, and the effect of the present invention is slightly reduced. Since the number of the skeletons 1 of the foamed three-dimensional porous body is excessive, each skeleton 1 is slightly thinned, and the strength of the positive electrode cannot be maintained sufficiently, and cracks are easily generated at the time of battery construction. This is not preferable because the dropout slightly increases.

  3rd invention is related with the alkaline storage battery which uses as a main component the electrolyte solution which consists of the positive electrode for alkaline storage batteries of 1st, 2nd invention, a negative electrode, a separator, and alkaline aqueous solution.

  When a nickel cadmium storage battery is configured using the positive electrodes of the first and second inventions, cadmium can be used as the active material for the negative electrode. Moreover, when comprising a nickel metal hydride storage battery using the positive electrode of 1st-2nd invention, a hydrogen storage alloy can be used as an active material for a negative electrode. When a hydrogen storage alloy is used as the negative electrode active material, a conductive agent such as carbon black, a binder such as styrene-butadiene copolymer (hereinafter abbreviated as SBR), and a thickener such as carboxymethyl cellulose (hereinafter abbreviated as CMC). Can be added as appropriate. In addition to the above-described foamed three-dimensional porous material, a two-dimensional porous material such as punching metal can be used as the conductive support for the negative electrode of the nickel metal hydride storage battery.

  Examples of the present invention will be described in detail below.

(Positive electrode A1)
A foamed three-dimensional porous body was produced by the following method. First, a foamed urethane substrate having a thickness of 1.2 mm was immersed in a coating material in which carbon was dispersed in an acrylic ester resin aqueous solution, the amount of immersion was adjusted with a pair of rolls, dried, and subjected to a conductive treatment. The amount of carbon deposited was 50 g / m ² . Next, the amount of energization was adjusted so that the nickel plating amount was 550 g / m ² in a nickel bath, and electrolytic nickel plating was performed. After the plating, the foamed urethane substrate was removed by baking at 600 ° C., and further nickel reduction treatment was performed in a hydrogen stream at 900 ° C. to obtain a foam type three-dimensional porous body having a thickness of 1.2 mm. The number of triple points per unit area of this foamed three-dimensional porous body is 1500 / cm ² for both the horizontal cross section and the vertical cross section, and the weight per unit area (weight per unit area) is 552 g / m ² . there were.

  On the other hand, a sodium hydroxide aqueous solution is dropped while maintaining a constant pH while dropping and stirring an aqueous solution containing a predetermined amount of cobalt sulfate and zinc sulfate in a main component nickel sulfate and an aqueous ammonium sulfate solution at a constant rate. As a result, precipitates were formed, washed with water and dried to obtain spherical nickel hydroxide powder as a positive electrode active material.

  Also, while dripping and stirring a cobalt sulfate aqueous solution and an ammonium sulfate aqueous solution at a constant rate, while maintaining the pH constant, a sodium hydroxide aqueous solution is dropped to form a precipitate, which is washed with water and dried to be a conductive agent. A cobalt hydroxide powder was obtained.

To 100 parts by weight of nickel hydroxide, added to water together with a dispersion containing 10 parts by weight of cobalt hydroxide and 0.5 parts by weight of PTFE, and after adding an appropriate amount of 1% by weight CMC solution, mixing and dispersing the paste Was made.
The above-described foamed three-dimensional porous material is filled with a paste so that the active material filling amount is 0.14 g / cm ² , dried, and then rolled with a roller press to a thickness of 0.6 mm. As a result, the number of triple points per unit area in the horizontal section is 1846 / cm ² , the number of triple points per unit area in the vertical section is 3692 / cm ² , and the point ratio is 2.0. A positive electrode precursor was obtained. This precursor was cut to a predetermined size to provide a lead portion, and a positive electrode A1 was produced.

(Positive electrodes A2 to A5)
The thickness of the positive electrode A1 is 1.5 mm (A2), 2.4 mm (A3), 3.6 mm (A4) and 4.8 mm (A5), and the thickness is 1.8 mm (A2). A foam type three-dimensional porous body of 2.4 mm (A3), 3.6 mm (A4), and 4.8 mm (A5) is formed, and the thickness is 0.6 mm while the active material filling amount is the same as that of the positive electrode A1. By rolling in this manner, the number of triple points per unit area in the horizontal cross section is 1846 / cm ² (A2 to A5), and the number of triple points per unit area in the vertical cross section is 5538 / cm ^2. (A2), 7384 / cm ² (A3), 11076 / cm ² (A4) and 14768 / cm ² (A2), the point ratio is 3.0 (A2), 4.0 (A3), 6.0 (A4) ) And 8.0 to obtain a positive electrode of the precursor is (A5). Other than this, what was produced similarly to positive electrode A1 is set as positive electrode A2-A5.

  The produced positive electrode A1 to positive electrode A5, a negative electrode mainly composed of a hydrogen storage alloy, and a separator made of a nonwoven fabric made of polypropylene subjected to hydrophilic treatment are wound with the separator disposed so as to insulate the positive electrode plate and the negative electrode. Several groups were made. Several of the electrode groups were disassembled and the amount of dropout was evaluated as follows.

(Active material loss)
In order to investigate the amount of the active material falling from the positive electrode, the electrode group produced by winding was disassembled and the positive electrode was taken out. The taken out positive electrode was put in a beaker together with water, and was irradiated with ultrasonic waves for 10 minutes by an ultrasonic cleaner. Thereafter, the electrode plate was taken out and dried, and the amount of decrease from the weight before preparation of the electrode group was determined, and the amount of active material falling off was examined on the basis of the amount of weight decrease of A1 as a comparative example. The results are shown in (Table 1).

  On the other hand, after the remaining electrode group was inserted into the battery case, an alkaline electrolyte having a total concentration of 8 mol / l of solute potassium hydroxide, sodium hydroxide and lithium hydroxide was injected and sealed, A battery (commonly called AAA size) having a diameter of 10.5 mm, a length of 44.5 mm, and a nominal capacity of 600 mAh was produced. The batteries were charged at 60 mA for 15 hours under the conditions of an atmospheric temperature of 20 ° C., then discharged twice at 600 mA for 40 minutes, stored at 45 ° C. for 3 days, and the negative electrode was activated. Thereafter, each battery was discharged to 1.0 V at 600 mA and then charged at 60 mA for 15 hours. Each of these batteries was allowed to stand for 60 minutes, and then discharged to 1.0 V at 120 mA to determine the capacity. Charging / discharging was performed under an atmosphere temperature of 20 ° C. The theoretical capacity of the positive electrode is a capacity when nickel hydroxide is charged and discharged by a one-electron reaction, and was calculated by multiplying the weight of nickel hydroxide in the positive electrode active material by 289 mAh / g. The positive electrode utilization rate was calculated by dividing the discharge capacity by the positive electrode theoretical capacity. The results are shown in (Table 2).

As can be seen from (Table 2), the batteries using the positive electrodes A1 to A5 all show high utilization rates, but as can be seen from (Table 1), the positive electrode A1 having a point ratio of less than 3.0 and the point ratio are Both positive electrode A5 exceeding 6.0 had a significant amount of active material falling off. The reason for this is that A1 with a point ratio of less than 3.0 cannot sufficiently retain the active material because the distortion of pores in the electrode plate is small, and conversely, each skeleton with A5 having a point ratio of more than 6.0. Therefore, it is presumed that the fracture of the skeleton and the crack of the electrode plate are liable to occur at the time of construction, and the amount of the active material can be prevented from dropping. As described above, when the point ratio is 3.0 to 6.0, an excellent alkaline storage battery in which the amount of falling off of the active material is suppressed can be obtained.

  A foamed nickel substrate was produced in the same manner as in Example 1 except that the type and thickness of urethane used for producing the foamed three-dimensional porous material were changed. Specifically, it is as follows.

First, the number of triple points per area in the horizontal cross-section is 808 / cm ² of urethane foam, and the thickness of five types of 1.8 mm, 2.1 mm, 2.4 mm, 3.3 mm, and 3.6 mm. The foamed urethane substrate was cut out, and five types of foamed nickel substrates of 1.8 mm, 2.1 mm, 2.4 mm, 3.3 mm, and 3.6 mm were produced in the same manner as the positive electrode A. Next, the number of triple points per unit area in the horizontal cross-section is 808 / cm ² by rolling the active material so that the thickness is 0.6 mm while maintaining the same filling amount as the positive electrode A1. The number of triple points per unit area in the cross section in the vertical direction is 2423 / cm ² , 2827 / cm ² , 3231 / cm ² , 4442 / cm ² and 4846 / cm ² , the point ratio is 3.0, 3.5, Positive electrode precursors of 4.0, 5.5, and 6.0 were obtained. Other than this, it was fabricated in the same manner as the positive electrode A1.

Similarly, five types of thicknesses of 1.8 mm, 2.1 mm, 2.4 mm, 3.3 mm, and 3.6 mm are similarly applied to urethane foam whose number per unit area of triple points in the horizontal cross section is 1000 / cm ^2. Each of the foamed urethane substrates was cut out, and similarly to the positive electrode A, five types of foamed nickel substrates of 1.8 mm, 2.1 mm, 2.4 mm, 3.3 mm, and 3.6 mm were produced. Next, the number of triple points per unit area in the horizontal cross section is 1000 / cm ² by performing rolling so that the thickness is 0.6 mm while maintaining the filling amount of the active material in the same manner as the positive electrode A1. The number of triple points per unit area in the cross section in the vertical direction is 3000 / cm ² , 3500 / cm ² , 4000 / cm ² , 5500 / cm ² and 6000 / cm ² , and the point ratio is 3.0, 3.5, Positive electrode precursors of 4.0, 5.5, and 6.0 were obtained. Other than this, it was fabricated in the same manner as the positive electrode A1.

Similarly, five types of thicknesses of 1.8 mm, 2.1 mm, 2.4 mm, 3.3 mm, and 3.6 mm are similarly applied to urethane foam having a number of triple points per unit area of 1846 / cm ² in the horizontal cross section. Each of the foamed urethane substrates was cut out, and similarly to the positive electrode A, five types of foamed nickel substrates of 1.8 mm, 2.1 mm, 2.4 mm, 3.3 mm, and 3.6 mm were produced. Next, the number of triple points per unit area in the horizontal cross section is 1846 / cm ² , respectively, by rolling the active material so that the thickness is 0.6 mm while maintaining the same filling amount as the positive electrode A1. The number of triple points per unit area in the cross section in the vertical direction is 5538 / cm ² , 6462 / cm ² , 7385 / cm ² , 10154 / cm ² and 11077 / cm ² , the point ratio is 3.0, 3.5, Positive electrode precursors of 4.0, 5.5, and 6.0 were obtained. Other than this, it was fabricated in the same manner as the positive electrode A1.

Similarly, five types of thicknesses of 1.8 mm, 2.1 mm, 2.4 mm, 3.3 mm, and 3.6 mm are similarly applied to urethane foam in which the number of triple points per unit area in the horizontal cross section is 3038 / cm ^2. Each of the foamed urethane substrates was cut out, and similarly to the positive electrode A, five types of foamed nickel substrates of 1.8 mm, 2.1 mm, 2.4 mm, 3.3 mm, and 3.6 mm were produced. Next, the number of triple points per unit area in the horizontal cross section is 3038 / cm ² by rolling the active material so that the thickness is 0.6 mm while maintaining the same filling amount as the positive electrode A1. The number of triple points per unit area in the vertical cross section is 9115 / cm ² , 10635 / cm ² , 12154 / cm ² , 16712 / cm ² and 18231 / cm ² , the point ratio is 3.0, 3.5, Positive electrode precursors of 4.0, 5.5, and 6.0 were obtained. Other than this, it was fabricated in the same manner as the positive electrode A1.

Similarly, five types of thicknesses of 1.8 mm, 2.1 mm, 2.4 mm, 3.3 mm and 3.6 mm are similarly applied to urethane foam whose number per unit area of triple points in the horizontal cross section is 4962 / cm ^2. Each of the foamed urethane substrates was cut out, and similarly to the positive electrode A, five types of foamed nickel substrates of 1.8 mm, 2.1 mm, 2.4 mm, 3.3 mm, and 3.6 mm were produced. Next, the number of triple points per unit area in the horizontal cross section is 4962 / cm ² and vertical by rolling so that the thickness of the active material is the same as that of the positive electrode A1 and the thickness is 0.6 mm. The number of triple points per unit area in the cross section in the direction is 14885 / cm ² , 17365 / cm ² , 19846 / cm ² , 27288 / cm ² and 29769 / cm ² , and the point ratio is 3.0, 3.5, 4 Positive electrode precursors of 0.0, 5.5, and 6.0 were obtained. Other than this, it was fabricated in the same manner as the positive electrode A1.

  A total of 25 types of positive electrode plates were produced by the above method.

  In the same manner as in Example 1, the prepared positive electrode plate was made of a negative electrode mainly composed of a hydrogen storage alloy, a separator made of a polypropylene nonwoven fabric subjected to a hydrophilic treatment, and the separator was disposed so as to insulate the positive electrode plate and the negative electrode. A plurality of electrode groups were produced by winding. Several of the electrode groups were disassembled and the amount of dropout was evaluated as follows.

(Active material loss)
In the same manner as in Example 1, in order to examine the amount of the active material dropped from the positive electrode, the electrode group produced by winding was disassembled and the positive electrode was taken out. The taken out positive electrode was put in a beaker together with water, and was irradiated with ultrasonic waves for 10 minutes by an ultrasonic cleaner. Thereafter, the electrode plate was taken out and dried, and the amount of decrease from the weight before preparation of the electrode group was determined. The results are shown in (Table 3).

On the other hand, after the remaining electrode group was inserted into the battery case, an alkaline electrolyte having a total concentration of 8 mol / l of solute potassium hydroxide, sodium hydroxide and lithium hydroxide was injected and sealed, A battery (commonly called AAA size) having a diameter of 10.5 mm, a length of 44.5 mm, and a nominal capacity of 600 mAh was produced. The batteries were charged at 60 mA for 15 hours under the conditions of an atmospheric temperature of 20 ° C., then discharged twice at 600 mA for 40 minutes, stored at 45 ° C. for 3 days, and the negative electrode was activated. Thereafter, each battery was discharged to 1.0 V at 600 mA and then charged at 60 mA for 15 hours. After leaving these batteries for 60 minutes, 120m
A was discharged to 1.0 V at A, and the capacity was determined. Charging / discharging was performed under an atmosphere temperature of 20 ° C. The theoretical capacity of the positive electrode is a capacity when nickel hydroxide is charged and discharged by a one-electron reaction, and was calculated by multiplying the weight of nickel hydroxide in the positive electrode active material by 289 mAh / g. The positive electrode utilization rate was calculated by dividing the discharge capacity by the positive electrode theoretical capacity. The results are shown in (Table 4).

As can be seen from (Table 4), the batteries using the positive electrodes A1 to A5 all show high utilization rates. As can be seen from (Table 3), when the point ratio is 3.5 or more and 5.5 or less and the number of triple points per area in the horizontal direction is 1000 to 3000 / m ² , the positive electrode active The amount of material dropout can be suppressed. The reason is considered as follows.

When the triple point in the horizontal cross section is 1000 pieces / cm ² or more, the pore diameter of the foamed three-dimensional porous material is sufficiently small, and it is estimated that a particularly excellent active material drop-off suppressing effect was obtained. Further, when it is 3038 / cm ² or less, it is presumed that each skeleton becomes thick and the strength of the positive electrode is sufficiently maintained, and cracks are not particularly easily generated in the group structure.

  When the point ratio is 3.5 or more, the pores of the foamed three-dimensional porous body are sufficiently distorted in the thickness direction of the positive electrode. When the point ratio is 5.5 or less, it is presumed that the number of each skeleton is reduced to be sufficiently thick, the strength of the positive electrode is sufficiently maintained, and cracks are not particularly easily generated in the group configuration.

As described above, when the point ratio is 3.5 to 5.5 and the number of triple points per area in the horizontal direction is 1000 to 3000 / m ² , the dropout amount of the active material is particularly suppressed. It can be an excellent alkaline storage battery.

  According to the present invention, since a large amount of an active material can be easily filled and the active material can be prevented from falling off, the present invention is highly applicable to a high capacity type alkaline storage battery, and the effect thereof is extremely large.

Schematic sectional view showing a positive electrode for an alkaline storage battery after pressing according to the present invention. (A) (B) (C) (D) (E) Schematic sectional view showing a specific triple point (A) Schematic diagram showing the vertical cross section of the positive electrode, (B) Schematic diagram showing the horizontal cross section of the positive electrode The figure which shows the result of having observed the cross section of the positive electrode of this invention with a microscope

Explanation of symbols

1 skeleton 2 pore 3 active material

Claims (3)

A positive electrode for an alkaline storage battery using a three-dimensional foamed porous body having a triple point as a conductive support,
The ratio of the number per unit area of the triple points in the vertical cross section to the number per unit area of the triple points in the horizontal cross section is 3.0 to 6.0, and the alkaline storage battery Positive electrode. The number per unit area of the triple points in the horizontal cross section is 1000-3038 / cm ² ,
The ratio of the number per unit area of the triple points in the vertical cross section to the number per unit area of the triple points in the horizontal cross section is set to 3.5 to 5.5. The positive electrode for alkaline storage batteries according to 1. A positive electrode for an alkaline storage battery according to claim 1 or 2, a negative electrode, separator and alkaline storage batteries which is mainly a component of the electrolyte solution composed of an aqueous alkaline solution.