JP2005353434A - Alkaline battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alkaline battery capable of keeping an excellent heavy load discharge characteristic even after high-temperature storage. <P>SOLUTION: This alkaline battery is provided with: a metallic positive electrode case with a nickel-cobalt alloy layer formed on its inside surface; a positive electrode mix stored in the positive electrode case and contacting the nickel-cobalt alloy layer; and a zinc negative electrode disposed by facing the positive electrode mix through a separator; and the positive electrode mix contains at least nickel oxyhydroxide as an active material. Oxidation by the nickel oxyhydroxide of the positive electrode case can surely be prevented by the nickel-cobalt alloy layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement of an alkaline battery, in particular, an alkaline battery in which a positive electrode mixture mainly composed of nickel oxyhydroxide is housed in a metal positive electrode case.

  The alkaline manganese battery has a structure in which a cylindrical positive electrode mixture is disposed in close contact with the positive electrode case in a positive electrode case also serving as a positive electrode terminal, and a gelled negative electrode is disposed in the center thereof via a separator. Recently, devices using these batteries have increased loads, and the batteries used are required to have excellent performance for heavy load discharge. Therefore, it has been studied to produce a battery having excellent heavy load discharge performance by mixing nickel oxyhydroxide with the positive electrode mixture.

  However, nickel oxyhydroxide has lower storage stability than manganese dioxide. In particular, when stored at a high temperature, nickel oxyhydroxide has a large self-discharge. Therefore, after storing a battery containing nickel oxyhydroxide, the heavy load discharge performance is lower than that of a conventional battery. In addition, when the positive electrode case and the positive electrode mixture are in direct contact with each other, a thin oxide film is formed on the surface of the positive electrode case due to oxidation by manganese dioxide, nickel oxyhydroxide, etc. during storage of the battery. The state of electrical contact with the mixture deteriorates, and the storage performance of the battery decreases.

  In particular, since nickel oxyhydroxide has a higher potential and higher reducing action than manganese dioxide, the battery containing nickel oxyhydroxide has a higher rate of oxidation on the surface of the positive electrode case than the battery not containing nickel oxyhydroxide. Becomes larger.

For this reason, Japanese Patent Laid-Open No. 2000-48827 discloses a case in which a conductive film of graphite is formed between the positive electrode case and the positive electrode mixture, and this film suppresses the formation of an oxide film on the inner wall surface of the positive electrode case. And a technique for suppressing an increase in resistance between the positive electrode mixture and the positive electrode mixture.
JP 2000-48827 A

  However, since nickel oxyhydroxide has an extremely high oxidizing power, the formation of an oxide film could not be suppressed only by forming a conductive film between the positive electrode case and the positive electrode mixture. Further, the conductive coating was difficult to form uniformly on the entire inner wall of the case, and unevenness was likely to occur.

  In a battery containing nickel oxyhydroxide, there is a problem that the heavy load discharge characteristics after storage, particularly after high temperature storage, decrease due to an increase in resistance between the positive electrode case and the positive electrode mixture and a decrease in the amount of positive electrode active material that can be discharged. there were.

  The present invention solves such problems, and aims to stably improve the high-load discharge characteristics after high-temperature storage of an alkaline battery containing a highly oxidizing nickel oxyhydroxide in a positive electrode mixture. To do.

  The alkaline battery of the present invention includes a metal positive electrode case having a nickel-cobalt alloy layer formed on the inner surface, a positive electrode mixture housed in the positive electrode case and in contact with the nickel-cobalt alloy layer, and a positive electrode mixture. It has a negative electrode arranged opposite to each other with a separator, and the positive electrode mixture contains at least nickel oxyhydroxide as an active material. In particular, the positive electrode mixture preferably contains manganese dioxide and nickel oxyhydroxide as active materials, and is preferably in the range of manganese dioxide: nickel oxyhydroxide = 20: 80 to 90:10 by weight ratio. Furthermore, it is preferable to form a conductive film between the nickel-cobalt alloy layer and the positive electrode mixture.

  As described above, according to the present invention, it is possible to provide an alkaline battery having excellent heavy load discharge characteristics even after high-temperature storage.

  In the present invention, in order to improve the heavy load discharge characteristics of a battery, the positive electrode mixture contains nickel oxyhydroxide, and a nickel-cobalt alloy layer is formed inside the positive electrode case.

  Considering the self-discharge of nickel oxyhydroxide, in order to maintain the heavy load discharge performance of the battery after high temperature storage, it is conceivable to increase the proportion of nickel oxyhydroxide in the positive electrode mixture. Since nickel oxyhydroxide has a strong oxidizing power, a thin oxide film was formed on the surface of the positive electrode case. In order to prevent this film formation, it is conceivable to form a conductive film such as graphite or a nickel metal film on the inner wall surface of the positive electrode case.

  However, even when a nickel metal film was formed on the case surface in a battery containing nickel oxyhydroxide as the positive electrode, manganese dioxide was used as the positive electrode mixture without nickel oxyhydroxide when stored at 60 ° C. for one month. Compared with a battery, the heavy load discharge characteristics are degraded.

  Therefore, in order to use nickel oxyhydroxide at a suitable ratio for the positive electrode and maintain the heavy load discharge characteristics of the battery, an oxide film formed on the surface of the positive electrode case by the oxidizing action of nickel oxyhydroxide during storage of the battery It is necessary to increase the electrical conductivity of the film or to suppress the formation of an oxide film.

  In the present invention, a nickel-cobalt alloy layer is formed on the inner side of the positive electrode case in order to enhance the conductivity of the oxide film formed on the surface of the positive electrode case. Therefore, by taking the above-described configuration, the storage characteristics of the battery can be improved, and the heavy load discharge performance after high-temperature storage can be improved.

  The mixing ratio of manganese dioxide and nickel oxyhydroxide in the positive electrode mixture is excellent in discharge characteristics after initial storage and high temperature storage when manganese dioxide is 20 to 90 wt% and nickel oxyhydroxide is 80 to 10 wt%. It is. In particular, it is effective to regulate manganese dioxide to 50 to 90 wt% and nickel oxyhydroxide to 50 to 10 wt%.

  Furthermore, when a conductive film is formed on the nickel-cobalt alloy layer, it is possible to suppress the formation of an oxide film on the inner wall surface of the positive electrode case due to oxidizing nickel oxyhydroxide. An effect of suppressing an increase in resistance between agents can also be expected.

  FIG. 1 is a front view, partly in section, of an alkaline battery in one embodiment of the present invention. This battery is manufactured as follows. 1 represents a positive electrode case made of steel. As shown in FIG. 2, a nickel layer by electroplating is formed on the inner surface of the positive electrode case 1. Inside the positive electrode case 1, a plurality of short cylindrical positive electrode mixture moldings using manganese dioxide as an active material are inserted, and are brought into close contact with the inner surface of the case 1 by being re-pressurized in the case. After inserting the separator 4 and the insulating cap 5 inside the positive electrode mixture 3 thus filled in the case, the gelled zinc negative electrode 6 is injected inside the separator. The gelled negative electrode 6 comprises a gelling agent such as sodium polyacrylate, an alkaline electrolyte, and a zinc alloy powder containing bismuth 250 ppm, indium 250 ppm, and aluminum 35 ppm as negative electrode active materials. Next, the resin sealing plate 7, the bottom plate 8 also serving as the negative electrode terminal, and the negative electrode current collector 10 integrated with the insulating washer 9 are inserted into the gelled negative electrode 6, and the opening end of the positive electrode case 1 is connected to the sealing plate 7. The opening of the positive electrode case 1 is brought into close contact with the peripheral edge of the bottom plate 8 via the end. Next, the outer label 11 is coated on the outer surface of the positive electrode case 1. An alkaline battery is thus completed.

  << Conventional Example >> Manganese dioxide and graphite powder are blended in a weight ratio shown in Table 1, and after mixing 1 part by weight of an electrolytic solution with respect to 100 parts by weight of the active material, granulation and pressure molding are performed. A positive electrode mixture was prepared. As the electrolytic solution, a 41 wt% aqueous solution of potassium hydroxide was used.

  A nickel layer 2 was formed inside the positive electrode case 1 by electroplating. The thickness of the nickel layer was 2 μm. And the AA size alkaline battery 1 shown in FIG. 1 was produced using the positive electrode mixture and the positive electrode case produced as described above.

  Comparative Example 1 Alkaline batteries 2 to 9 were prepared in the same manner as in the conventional example except that manganese dioxide, nickel oxyhydroxide, and graphite powder were blended in the weight ratio shown in Table 1.

  Comparative Example 2 An alkaline battery 10 was produced in the same manner as in the conventional example except that a nickel-cobalt alloy plating layer was formed inside the positive electrode case 1 instead of the nickel layer 2.

  << Example 1 >> Manganese dioxide, nickel oxyhydroxide, and graphite powder are blended in a weight ratio shown in Table 1, and a nickel-cobalt alloy plating layer is formed inside the positive electrode case 1 in place of the nickel layer 2 Produced alkaline batteries 11 to 18 in the same manner as in the prior art.

  For each of the above batteries, after being stored for the first time at 60 ° C. for one month, continuous discharge was performed at a constant current of 1000 mA at room temperature, and the duration until the voltage reached a final voltage of 0.9 V was measured. Table 1 shows the average value of 10 batteries. In addition, the initial duration of the battery 1 which did not contain nickel oxyhydroxide and formed a nickel plating layer inside the positive electrode case was shown as 100.

  As is apparent from Table 1, the batteries 2 to 9 of Comparative Example 1 and the batteries 11 to 18 of the present invention, which are batteries using a positive electrode mixture in which manganese dioxide and nickel oxyhydroxide are mixed, are the first 1000 mA continuous discharge. The performance was improved over the battery 1 of the conventional example and the battery 10 of the comparative example 2 in which nickel oxyhydroxide was not mixed. However, even when nickel oxyhydroxide was mixed, the batteries 2 to 9 of Comparative Example 1 in which the nickel-cobalt plating layer was not formed inside the positive electrode case had deteriorated performance after being stored at 60 ° C. for one month. The discharge performance was significantly lower than that of the conventional battery 1 in which nickel oxyhydroxide was not added.

  In contrast, the batteries 11 to 18 of the present invention in which the nickel-cobalt alloy layer is formed on the positive electrode case can increase the conductivity of the oxide film formed on the surface of the positive electrode case by the oxidizing action of nickel oxyhydroxide. The heavy load discharge performance after high temperature storage was good. In particular, when the proportion of nickel oxyhydroxide in the positive electrode active material was 20 to 80 wt%, a battery having excellent discharge characteristics was obtained.

  In addition, in the case of a battery containing nickel oxyhydroxide, a uniform alloy layer is formed on the inner wall of the case by removing impurities on the inner surface of the positive electrode case by electrolytic polishing in the pretreatment for forming the nickel-cobalt alloy layer by electroplating. It is possible to improve the characteristics after storage at high temperature and reduce variations.

  Furthermore, by using artificial graphite or expanded graphite with few impurities by artificial treatment as graphite powder used in the positive electrode mixture, self-discharge of the positive electrode active material nickel oxyhydroxide can be suppressed, and after high temperature storage It is possible to further improve the characteristics.

  << Example 2 >> An alkaline battery similar to the battery 1 was prepared except that a conductive coating material mainly composed of conductive carbon was applied to the inside of the metal coating on the inner surface of the positive electrode case and dried to form a conductive coating. This was designated as battery 19. Further, a battery similar to the battery 19 was prepared, except that the mixing ratio in the positive electrode mixture of manganese dioxide and nickel oxyhydroxide and the type of the metal coating on the inner wall of the positive electrode case were as shown in Table 2, and these were prepared as the battery 20 It was set to ~ 22. For these batteries, the duration was measured under the same conditions as above, and the results are shown in Table 2.

  From Table 2, the initial discharge characteristics are improved regardless of the content of nickel oxyhydroxide by applying a carbon conductive film inside the metal film on the inner wall of the positive electrode case. However, regarding the discharge characteristics after storage at high temperature, the conductive film of carbon can suppress the formation of an oxide film on the inner wall surface of the positive electrode case, so the battery containing nickel oxyhydroxide showed better discharge characteristics. . In addition, the synergistic effect of the combination of the nickel-cobalt alloy layer and the conductive film is more remarkable in the battery containing nickel oxyhydroxide.

  Since the present invention is an alkaline battery containing nickel oxyhydroxide as a positive electrode active material and has excellent high load discharge characteristics, it can be applied to power supplies for electronic devices and portable devices.

1 is a partial longitudinal sectional view of an alkaline battery in an embodiment of the present invention. Enlarged view of the main part of the battery

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode case 2 Nickel layer 3 Positive electrode mixture 4 Separator 5 Insulation cap 6 Gel-like negative electrode 7 Resin sealing body 8 Bottom plate 9 Insulation washer 10 Negative electrode current collector 11 Exterior label

Claims (3)

A metal positive electrode case having a nickel-cobalt alloy layer formed on the inner surface, a positive electrode mixture accommodated in the positive electrode case and in contact with the nickel-cobalt alloy layer, and a positive electrode mixture opposed to the positive electrode mixture via a separator. An alkaline battery in which the positive electrode mixture contains at least nickel oxyhydroxide as an active material. 2. The alkaline battery according to claim 1, wherein the active material of the positive electrode mixture is a mixture of manganese dioxide and nickel oxyhydroxide and has a weight ratio of manganese dioxide: nickel oxyhydroxide = 20: 80 to 90:10. The alkaline battery according to claim 1, wherein a conductive coating is formed on the nickel-cobalt alloy layer on the inner surface of the positive electrode case.

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