JP3371734B2 - Method for producing electrode for alkaline storage battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for an alkaline storage battery, and more particularly to an improved iron sintered body having three-dimensionally continuous pores. An object of the present invention is to provide an inexpensive electrode for an alkaline storage battery in which a surface is coated with nickel to form a substrate, and the substrate is filled with an active material. 2. Description of the Related Art As an electrode for an alkaline storage battery, an electrode obtained by filling an active material into a base material composed of pure nickel having three-dimensionally continuous pores as a main component is used. However, this base material is about 1/100 of the material and parts cost of the battery using it.
The more occupied, the more expensive the material. [0003] Therefore, in order to reduce the material cost of the electrode for an alkaline storage battery, as an alternative to the above-mentioned pure nickel substrate, a substrate of a three-dimensionally continuous pore-formed iron sintered body having a nickel-plated surface is used. One in which an active material is filled is proposed. [0004] This method of manufacturing a substrate of an iron sintered body is based on a method in which an iron powder slurry is applied to a synthetic resin core having three-dimensionally continuous pores, for example, a urethane foam resin core, and then heat-treated. The body is removed and the iron is sintered together, and then the sintered body is plated with nickel. [0005] However, the above-mentioned synthetic resin core having three-dimensional pores is characterized in that the pores are large on the outside and small on the inside. But thin and thick outside. For this reason, the skeleton of the iron sintered body produced by applying the iron powder slurry to this synthetic resin core, sintering and removing the synthetic resin core,
The shape follows the skeleton of the synthetic resin core, and the outside becomes thick and the inside becomes thin. In addition, since the surface of the iron powder is a sintered product of the iron powder, unevenness occurs between the iron powders. As described above, since the iron sintered body has a difference in thickness between its inner and outer skeletons and irregularities on its surface, it is necessary to perform nickel plating with a substantially equal thickness throughout the entire iron sintered body. It is necessary to repeat plating several times, and there is a problem that productivity is reduced. If the nickel plating is repeated only once instead of several times, a portion where the nickel plating is not applied to the iron sintered body occurs, and the exposed portion of the iron comes into contact with the alkaline electrolyte. In this case, there is no problem as long as the potential of the positive electrode is normally used as a battery. However, when the battery voltage decreases due to self-discharge due to storage of the battery or a leak current of a battery-using device, and the positive electrode potential shifts to −0.8 V or less, iron becomes HFeO ₂ ⁻ and elutes into the alkaline electrolyte. I do. This has an adverse effect on battery characteristics. Further, when an electrode in which the base is filled with an active material is cut into a predetermined size and used as, for example, a positive electrode plate to form an alkaline storage battery, a separator is interposed between the positive electrode plate and the negative electrode plate. When forming a group of electrodes by spirally winding them, a force such as tension or bending is applied to the positive electrode plate, causing partial breakage of the base, increasing the electrical resistance of the base, and as a result, However, there is a problem that the internal resistance of the battery increases. [0010] This is because the skeleton of the iron sintered substrate has a thick portion and a thin portion, and the thin portion has low mechanical strength and is broken when a tensile or bending force is applied to the positive electrode plate. Because there is. The present invention has been made to solve the above-mentioned problems, and an iron sintered body having three-dimensionally continuous pores is improved, and its surface is coated with nickel to form a base. An object is to provide an inexpensive electrode for an alkaline storage battery filled with an active material. The present invention is a method for manufacturing an electrode for an alkaline storage battery in which a substrate having three-dimensionally continuous pores is filled with an active material, wherein the gas is an iron powder. The manufacturing method was made of a sintered body, in which the skeleton portions forming the pores had substantially the same thickness throughout the entire thickness of the substrate, and the surface was coated with nickel. [0013] DETAILED DESCRIPTION OF THE INVENTION This onset bright is obtained by said contents, the iron sintered substrate has a skeleton portion forming the pores be approximately equal thickness throughout the thickness of the substrate ,
As described above, the skeleton portion of the base does not have a thin skeleton portion having low strength, and even if the electrode plate group is formed using the skeleton portion, the base does not break. Therefore, an increase in electric resistance due to the breakage of the base can be suppressed. In addition, since the skeleton portion of the iron sintered substrate has a substantially equal thickness throughout the entire substrate, the skeleton forming the pores can be nickel-coated with a substantially equal thickness throughout the entire substrate, and an alkaline electrolyte can be formed. Contact can be prevented. According to the first aspect of the present invention, there is provided a method of manufacturing an electrode in which a substrate having three-dimensionally continuous pores is filled with an active material, wherein the substrate is made of a synthetic resin having three-dimensionally continuous pores. The core powder is coated with a slurry of iron powder, dried, then immersed in an alcohol solution of iron alkoxide, dried to make the outer dimensions of the iron skeleton applied to the synthetic resin core substantially equal, and the surface thereof is smoothed. After that, the heat treatment was performed to remove the synthetic resin core, sinter the iron, and then coat the sintered body with nickel, and then fill the active material with a method for producing an electrode for an alkaline storage battery. Things. In this case, a slurry of iron powder is applied to the synthetic resin core, dried, and the iron skeleton applied to the synthetic resin core has a thick outer portion and a thinner inner portion. By drying by dipping in, the iron skeleton adheres particularly to the thin skeleton inside, and the outer diameter of the iron skeleton can be made substantially equal. Further, since the iron skeleton applied to the synthetic resin core is formed of iron powder, the surface thereof has irregularities. However, the surface can be smoothed by immersing in an iron alkoxide solution and drying. Then, the synthetic resin core provided with the iron skeleton is subjected to a heat treatment to remove the synthetic resin core and sinter each other to form an iron sintered body. The skeleton of the iron sintered body remains in a shape before the removal of the synthetic resin core, which has substantially the same thickness throughout the thickness of the sintered body, and has a smooth surface. Therefore, a substrate in which the surface of the iron sintered body is uniformly coated with nickel can be formed, and if this is filled with an active material, an inexpensive electrode for an alkaline storage battery can be easily formed. Next, specific examples of the present invention will be described. First, the production of an iron sintered body is described in the following first to fourth.
Will be described. First, three-dimensionally continuous about 500 μm
The polyurethane resin core 1 having the pores described above is charged into a mixed slurry 2 of fine powder of Fe ₂ O ₃ and a phenol resin, and the iron powder slurry 2 is applied to the surface of the polyurethane resin 1, and 9
Dried at 0 ° C. Second, the process of dipping a polyurethane resin 1 coated with an iron powder slurry 2 in an iron alkoxide 3 solution and drying it at 90 ° C. was repeated twice. At this time, the first portion where the iron alkoxide was attached was 3a, and the second portion was 3b. FIG. 1 is a schematic cross-sectional view showing the state of an iron skeleton obtained by attaching an iron powder slurry 2 and an iron alkoxide 3 to the polyurethane resin 1. As shown in FIG. 1, by attaching iron alkoxide 3 to the skeleton of polyurethane resin core 1 coated with iron powder slurry 2, iron alkoxides 3a and 3b adhere to thin portion 1a and thick portion 1b And the surface can be made smooth. At this time, the iron alkoxide 3 solution is made of Fe
(NO _{3) 3} · 9H ₂ and O, 2-methoxyethanol (C
H ₃ OCH ₂ CH ₂ OH) and 2,4-pentadione (CH ₃
COCH ₂ COCH ₃ ) in a molar ratio of 2:20
At a constant temperature of 30 ° C. for 2 hours. Third, the polyurethane resin 1 having the second iron skeleton formed on the surface is heat-treated at 1400 ° C. for 30 minutes to remove the polyurethane resin core 1, and the iron powder 2 and the iron alkoxide 3 are sintered. Thus, an iron sintered body 4 is formed.
The iron sintered body 4 has substantially the same outer diameter and has a smooth surface. Fourth, a nickel base 5 was applied to the iron sintered body 4 at a current density of 10 A / dm ² using a nickel sulfate bath to prepare a base 6. FIG. 2 shows a schematic sectional view of the skeleton portion of the base 6. The number of times of this nickel plating was one. Using this substrate 6, a positive electrode plate 7 for an alkaline storage battery of the present invention is produced. An active material mainly composed of nickel hydroxide is mixed with water to prepare a paste-like active material, which is filled in a substrate 6, dried, pressed, cut into a predetermined size, and cut into a predetermined size. One end was spot-welded to produce a positive electrode plate 7 for an alkaline storage battery of the present invention. For comparison, a conventional substrate 8 was also prepared. In this method, a polyurethane resin core 1 having three-dimensionally continuous pores of about 500 μm is put into a mixed slurry 2 of fine powder of Fe ₂ O ₃ and a phenol resin, and an iron powder slurry 2 is applied to the surface of the polyurethane resin 1. Then, a heat treatment was performed at 1400 ° C. for 30 minutes to remove the polyurethane resin core 1 and sinter the iron with each other to produce an iron sintered body 9. This iron sintered body 9 was nickel-plated 10 in the same manner as described above to produce a conventional substrate 8. FIG. 3 is a schematic sectional view of the skeleton.
Shown in The base material 8 was filled with the paste-like active material prepared above, dried, press-molded, cut into a predetermined size, and spot-welded lead pieces to obtain a conventional positive electrode plate 11. Using the positive electrode plate 7 of the present invention produced as described above, a nickel-cadmium storage battery A was constructed. Negative electrode plate 12, an active material paste mainly composed of oxide mosquitoes Dominion um was coated on punching metal core material made of iron plated with nickel, was dried, immersed in an alkaline solution, washed with water, dried, cut into a predetermined size It was produced. The positive electrode plate 7 and the negative electrode plate 12 are spirally wound between the two with a polypropylene separator 13 interposed therebetween to form an electrode plate group, which is inserted into an iron battery case 14 and injected with an alkaline electrolyte. after, sealed with a sealing plate 15 also serving as a positive electrode terminal, nominal capacity 1 5 00mAh of 4 / 5A size cylindrical nickel -
The cadmium storage battery A is constituted, and its explanatory view is shown in FIG. A battery having the same configuration using the positive electrode plate 11 instead of the positive electrode plate 7 was referred to as a battery B. Next, Table 1 shows the results of measuring the initial substrate resistance of the base 6 according to the embodiment of the present invention and the conventional base 8 before forming the electrode plate group. [Table 1] As a method of measuring the resistance of the substrate, the substrate is cut into a size of 1 × 10 cm, the voltage at both ends of the substrate when a current of 1 A flows from the end of the substrate, and the electric resistance at this time is measured. The calculated value was used as the initial substrate resistance.
Further, after forming a spiral electrode group consisting of a positive electrode plate, a negative electrode plate, and a separator, the positive electrode plate is taken out, the positive electrode plate is dissolved with an acetic acid solution, and the substrate resistance is removed from the remaining substrate in the same manner as described above. Is measured as the substrate resistance after forming the electrode plate group, and is also shown in Table 1. As shown in Table 1, the substrate 6 according to the embodiment of the present invention has a lower initial substrate resistance than the conventional substrate 8, and also has a lower increase in the substrate resistance after forming the electrode plate group. I have. As shown in FIG. 3, the skeleton portion of the conventional iron sintered body 9 has a thick portion 9a and a thin portion 9b to conform to the surface shape of the polyurethane resin core before being removed by sintering. . The portion 9a where the base resistance of the thin portion 9b is large
As a result, the resistance of the conventional substrate 8 is higher by 50 mΩ than the resistance of the substrate 6 in the present invention. Further, when the electrode group is formed, the thin portion 9b of the base 8 as shown in FIG. 3 may be broken. Therefore, as shown in (Table 1), the conventional base 8 has the substrate resistance after forming the electrode group. Is three times that of the early days. On the other hand, as shown in FIG. 1, the base 6 of the present invention is formed by applying an iron powder slurry to a polyurethane resin core and then further adhering iron alkoxide to make the thin portion of the skeleton particularly thick. Then, the skeleton is formed to have a thickness substantially equal to the thick portion, and the sintering process is performed to remove the polyurethane resin. Therefore, as shown in FIG. In addition, since the surface of the iron powder is formed smoothly with the iron alkoxide, the nickel plating 5 can be made smooth. Therefore, the initial resistance of the substrate 6 in the present invention is lower by 50 mΩ than that of the conventional substrate 8. Further, since the base 6 in the present invention does not have a thin skeleton portion and forms a skeleton of the same thickness, the skeleton portion of the iron sintered base 6 is not broken even when an electrode plate group is formed. The resistance of the base 6 after the construction of the electrode plate group is 60 mΩ, which is only 10 mΩ higher than the initial resistance, and hardly increases. Next, the internal resistances of the battery A using the positive electrode plate 7 according to the embodiment of the present invention and the battery B using the conventional positive electrode plate 9 were measured, and the results are shown in Table 1. Show. As shown in (Table 1), the internal resistance of the battery A is lower than that of the battery B. This is because the resistance of each of the bases after the above-described construction of the electrode group is linked to the respective configured batteries. Further, the capacity recoverability of the batteries A and B after overdischarge was examined as follows. First, the batteries A and B, whose initial discharge capacities were measured, were each left in an atmosphere of a temperature of 65 ° C. for 3 months while being discharged by connecting a resistance equivalent to 10 kΩ. The battery was charged at a temperature of 20 ° C. and a charging current of 1 C for 1.5 hours, and then discharged to a voltage of 1.0 V at a discharging current of 1 C. The discharge capacity was measured and the capacity recovery was examined. as a result,
Battery A had a capacity recovery of 97%, whereas battery B
Recovered only 85%. Since the battery B uses the conventional positive electrode plate 11, a part of the skeleton of the base 8 is broken when the electrode plate group is formed. In addition to this, there is unevenness during the sintering of iron powder, so there is unevenness in only one nickel plating, especially iron is exposed at the broken part, which dissolves in alkaline electrolyte and adversely affects battery characteristics 85 capacity recovery
The percentage is worse. Since the battery A uses the positive electrode plate 7 of the present invention, the base 6 of the battery A does not break in the frame when the electrode group is formed, and the surface of the iron sintered body 4 is smooth. The substrate 6 formed by using the iron sintered body 4 can be nickel-plated without pinholes or the like only by one-time nickel plating. For this reason, the battery A hardly eluted iron even when overdischarged, and its capacity recovery was 97%, which was superior to the conventional battery. As described above, according to the present invention, in the electrode substrate, the skeleton portion forming the pores has substantially the same thickness throughout the entire thickness of the substrate, and the surface is coated with nickel. As a result, the base has a lower electric resistance than before and has a higher strength than before. For this reason, by forming, for example, a positive electrode plate as an electrode for an alkaline storage battery using the base,
Even if the electrode plate group is constituted by the negative electrode plate and the separator, the base is not broken and the increase in the electric resistance can be suppressed.
In addition, since this base is constituted by using a base made of an iron sintered body whose surface is coated with nickel instead of nickel, an inexpensive electrode for an alkaline storage battery can be provided. Even when an alkaline storage battery is formed using this electrode, a battery having excellent capacity recovery after overdischarge can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view showing an iron skeleton applied to a synthetic resin in the present invention. FIG. 2 is a schematic cross-sectional view showing a skeleton of the base. FIG. 3 is a schematic view showing a conventional base. 4 is a cross-sectional view of a nickel-cadmium storage battery according to an embodiment of the present invention. [Description of References] 1 Synthetic resin core 2 Iron powder slurry 3 Iron alkoxide 4 Iron sintered body 5 Nickel plating 6 Base 7 Positive electrode plate 12 Negative electrode plate 13 Separator 14 Battery case 15 Sealing plate

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-45366 (JP, A) JP-A-56-26366 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/26 H01M 4/66 H01M 4/80

Claims (1)

(57) [Claim 1] A method for producing an electrode in which a substrate having three-dimensionally continuous pores is filled with an active material, wherein the substrate has three-dimensionally continuous pores. After applying a slurry of iron powder to the synthetic resin core having, after drying, immersing in an alcohol solution of iron alkoxide, drying to make the outer dimensions of the iron skeleton applied to the synthetic resin core substantially equal, and After the surface is made smooth, the synthetic resin core is removed by heat treatment, and the iron is sintered together. Then, after the surface of the sintered body is coated with nickel, an active material is filled to produce an electrode for an alkaline storage battery. Method.