Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
1995-06-07
2003-07-01
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
Reexamination Certificate
active
06586139
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an alkaline battery which uses mercuryless zinc powder as a negative electrode active material, and uses silver oxide, manganese dioxide, oxygen or the like as a positive electrode active material, and a clock or watch which uses the alkaline battery.
Conventional alkaline batteries suffer from the drawbacks in that zinc powder used in the alkaline battery is corroded and dissolved by an alkaline electrolyte solution, and in that the generation of hydrogen gas and the self-discharge in battery performance accompanying therewith are large. In addition, a battery is formed by a collector such as copper or the like which contacts with zinc, and hydrogen gas has been also generated therefrom. In the prior art, as a countermeasure to prevent the above, zinc is mercurated with mercury having a high hydrogen overvoltage, or zinc oxide is added to an electrolyte solution up to approximate saturation.
However, environmental pollution due to mercury from used dry batteries has become a problem in recent years, and various studies for reducing mercury have been performed. Among processes undertaken during the studies are the formation zinc alloys, plating of a collector, and addition of an organic or inorganic inhibitor to an electrolyte solution.
The formation of zinc alloys has been performed for a fairly long time, and metals such as bismuth, indium, lead and the like have been investigated. Many patent applications pertaining to this process have been also filed, for example, Japanese Patent Publication No. 25-27822 (1950), Japanese Patent Publication No. 33-3204 (1958), Japanese Patent Publication No. 63-3942 (1988), and Japanese Patent Application Laid-Open No. 1-10861 (1989).
As the inorganic inhibitor, indium oxide and indium hydroxide as the indium compound have been frequently studied, and many patent applications have been also filed, including for example, Japanese Patent Publication No. 51-36450 (1976), Japanese Patent Application Laid-Open No. 49-93831 (1974), Japanese Patent Application Laid-Open No. 49-112125 (1974), Japanese Patent Application Laid-Open No. 59-186255, Japanese Patent Application Laid-Open No. 59-186256 (1984), and Japanese Patent Application Laid-open No. 4-26061 (1992). The use of a compound of alkaline earth metal as the inorganic inhibitor is addressed in Japanese Patent Application Laid-Open No. 49-8727 (1974), Japanese Patent Application Laid-Open No. 49-93831 (1974), and Japanese Patent Application Laid-Open No. 49-121926 (1974). The use of organic inhibitors is addressed in Japanese Patent Application Laid-Open No. 2-86064 (1990), and Japanese Patent Application Laid-Open No. 3-29270 (1991).
On the other hand, with respect to the process of plating a collector, the surface has been coated with indium or tin having a high hydrogen overvoltage by means of a method of plating or the like, and the formation of a battery due to the contact with zinc is prevented so as to suppress the generation of hydrogen. Such process is addressed in Japanese Patent Application Laid-Open No. 52-74834 (1977), Japanese Patent Application Laid-Open No. 52-98929, Japanese Patent Application Laid-Open No. 60-221958 (1985), and Japanese Patent Publication No. 52-42211 (1977).
In the prior art, investigation has been made as to each individual technique as described above, however, because the strong anticorrosion agent mercury has been used, optimization by combination of the characteristics of each technique has not been frequently performed.
Mercury, which is added in order to prevent corrosion and dissolution of zinc, is not only expensive from a viewpoint of cost, but is also associated with the problem of environmental pollution. In addition, the addition of zinc oxide also includes such a task that the viscosity of the electrolyte is raised, and the conductivity is lowered.
Indium oxide and indium hydroxide as the inorganic inhibitor also includes many problems.
Indium oxide is extremely difficult to dissolve in the electrolyte solution which is a caustic alkali, and hydrogen gas is consequently generated due to the contact of indium oxide with zinc powder or the collector. This is considered to be due to the fact that the solubility of indium oxide is poor, it is impossible to supply indium ion of a degree to sufficiently coat the zinc surface and the collector surface, and indium oxide becomes conductive due to inevitable impurities during production contacts with zinc and the collector, resulting in formation of a local battery.
It is said that as compared with indium oxide, indium hydroxide to some extent dissolves in an electrolyte solution of caustic alkali, and its solubility relates to the size and crystallinity of particles. However, as compared with indium compounds such as indium sulfate, indium sulfamate, indium chloride and the like, it is extremely difficult to dissolve. Thus, the same problems are associated as with of indium oxide. In addition, indium as an amphoteric compound generates polyion together with hydroxide ion (those similar to the description in Inorganic Chemistry Series 7, Coordinate Stereochemistry, written by Yoichi NIIMURA, published by Baihukan Co. Ltd., 65-66), and increases the viscosity of the electrolyte solution, so that it lowers the conductivity of the electrolyte solution and deteriorates battery performance.
Considerable advantageous effects are appreciated in the use of the indium compound as the inhibitor which is easier to dissolve in the electrolyte solution as compared with the case in which the conventional scarcely soluble inhibitor is used. However, in order to further utilize the characteristic of the indium compound, it is necessary to also solve problems as follows.
The electrode potential of zinc is lower than the deposition potential of indium, so that when indium ion is present in the electrolyte, indium is deposited as metal on zinc and the collector contacting with zinc. However, hydrogen generation is accompanied as a competitive reaction in accordance with the deposition reaction of indium, and this has been the cause of deficiencies such as liquid leakage and expansion of the alkaline battery. In addition, there has been such a problem that indium ion which is not deposited precipitates as hydroxide and decreases the conductivity of the electrolyte solution.
Other than the indium compound, compounds of metals having a relatively high hydrogen overvoltage such as tin and lead are used as the inhibitor, however, there have been problems as follows.
Metal ion, which is supplied from the metal compounds of these metals to the electrolyte solution, is reduced on the surface of zinc and the collector, and deposited as metal. However, when the surface is coated with one species of metal, crystal grains become coarse, it is impossible to homogeneously coat the surface, and the effect is reduced. It is difficult to suppress the hydrogen generation and improve the discharge characteristic by means of a single metal. In addition, the compounds of indium and the like are expensive, so that the use of only one species becomes expensive from a viewpoint of cost.
With respect to the corrosion and dissolution of zinc, there is considered a case in which zinc itself is corroded by water and the hydroxyl group in the alkaline solution, and a case in which a local battery is formed by the contact with metals such as copper, brass and the like of the collector which are nobler than zinc resulting in dissolution. Thus, attempts have been frequently made to add a metal having a high hydrogen overvoltage to zinc to form an alloy so as to suppress corrosion and dissolution. It is known that the effect thereof is remarkably expressed especially when indium is added. When zinc is used in which indium is added in a relatively high concentration by, for example, not less than 400 ppm, a part of indium and zinc is once dissolved by the contact with copper and the like of the collector. It is considered that the corrosion and dissolution of zinc are suppressed by a mechanis
Sakai Tsugio
Sakamoto Hideo
Watanabe Shunji
Adams & Wilks
Brouillette Gabrielle
Seiko Instruments Inc.
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