Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2001-03-26
2004-03-16
Bell, Bruce F. (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S224000, C429S233000, C429S234000, C429S235000, C429S247000, C429S248000, C429S218100
Reexamination Certificate
active
06706442
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an alkaline storage battery of high capacity density exhibiting superior cycle stability.
BACKGROUND ART
With the recent development of semiconductor technology, compact and light-weight multifunctional electric appliances have been developed progressively with rapid realization of compact personal equipment of portable type represented by note-book type personal computers. Therefore, there is an increasing demand even for the alkaline storage battery that has a wide application as the power source of such equipment to have a compact and light-weight design.
Up to date, the main active material for the positive electrode of alkaline storage battery has been nickel oxide (NiOOH). Concerning the electrode substrate per se, industrialization of an electrode made of a three-dimensional foamed nickel porous material with a higher porosity (95%) into which a nickel oxide powder is filled at a high density (foamed metal type electrode) in place of a sintered type electrode using a conventional sintered substrate (Japanese Examined Patent Publication No. Sho 62-54235; U.S. Pat. No. 4,251,603; etc.) has led to drastic improvements of the energy density of such nickel positive electrode.
To the realization of high energy density nickel positive electrode, improved manufacturing method of the nickel oxide powder as the active material is an important contributory technology. Any conventional manufacturing method of the nickel oxide powder has adopted a process where an aqueous nickel salt solution is reacted with an aqueous alkaline solution such as sodium hydroxide to precipitate nickel hydroxide, which is then aged to grow crystals and subsequently ground with some mechanical grinding method. This method has drawbacks that it is not only tedious but also does not readily produce a high packing density due to irregular shapes of the powders obtained by this method. Therefore, an alternative manufacturing method was proposed that reacts an aqueous nickel salt solution with ammonia to form an ammonium complex of nickel with which an aqueous alkaline solution is further reacted to grow nickel hydroxide (Japanese Examined Patent Publication No. Hei 4-80513). This method has enabled not only cost-effective continuous production of nickel hydroxide but also high density packing because of the resembling shape of the obtained powders to a sphere.
However, the use of high density particles of a large size obtained by this method which have grown up to a size of dozens of &mgr;m as an active material produces a problem of impairment of charge/discharge efficiency due to low electronic conductivity of the active material. This problem has been coped with by an improvement to supplement electronic conductivity by adding either Co or its oxide, or Ni, etc. to the active material (Japanese Examined Patent Publication No. Sho 61-37733; Electrochemistry, Vol. 54, No. 2, p. 159 (1986); Power Sources, Vol. 12, p. 203 (1988)). Other improvements have also been attempted to incorporate an additional metallic element other than Ni, such as Cd or Co, into the active material to increase the charge/discharge efficiency (Japanese Examined Patent Publication No. Hei 3-26903; Japanese Examined Patent Publication No. Hei 3-50384; Electrochemistry, Vol. 54, No. 2, p. 164 (1986); Power Sources, Vol. 12, p. 203 (1988)). Furthermore, because of a demand for a cadmium-free battery from the aspect of environment, there are a proposal of Zn as an exemplary substitution metallic element for Cd on the one hand and a proposal of incorporation of three elements, Co, Zn and Ba, on the other hand (U.S. Pat. No. 5,366,831). Such incorporation of different metallic elements into nickel oxide and forming a solid solution in order to realize a charge/discharge characteristic of high efficiency is a long known art (Japanese Laid-Open Patent Publication No. Sho 51-122737, etc.)
Improvements in the shape, composition and additive of the electrode substrate and the active material as discussed above have drastically increased the energy density of the positive electrode and, at present, even such a positive electrode as having an energy density of about 600 mAh/cc has become commercially practical. As mentioned previously, however, there is an increasingly expanding tendency of the demand for the alkaline storage battery to have a more increased energy density for use as a power source of compact portable equipment. In order to realize more increased battery energy density, approaches from various aspects including positive electrode, negative electrode, electrolyte, separator and their structure may be contemplated. Concerning the negative electrode, by an actual use of metal hydride with high energy density (Power Sources, vol. 12, p. 393 (1988)) in place of the conventional cadmium negative electrode, a volume energy density doubling or more than that of the positive electrode has been attained. Moreover, concerning the battery structure, high energy density has been realized rapidly with the technical developments of thin separators, high density packing of active material into electrode substrate, etc., which have now almost reached their limits.
Under the circumstances, in order to realize even higher energy density, realization of a higher energy density of the positive electrode which occupies almost half the volume of a battery has been taken as playing a significant role as the most effective elementary art.
Estimated approaches for realization of improved energy density of the positive electrode may include an improvement of the active material tap density, a reduction of the amounts of any additive and a reduction of metal contents in the foamed nickel substrate. These technologies, however, are almost reaching their limits. This necessitates an attempt to modify the active material per se to improve its reactivity and reaction order. The current positive electrode active material nickel oxide is &bgr;-Ni(OH)
2
(bivalent oxide) upon production of a battery which has been considered to develop a reaction of one electron exchange (utilization=100%) with &bgr;-NiOOH (trivalent) during normal charge/discharge operation. When exposed to overcharge, however, &bgr;-NiOOH in charged state can be partially oxidized to &ggr;-NiOOH (3.5- to 3.8-valent) which is a high order oxide. Such &ggr;-NiOOH has been known to be at least a nonstoichiometric material of disordered crystal structure (J. Power Sources, Vol. 8, p. 229 (1982)). Conventionally, the &ggr;-NiOOH is electrochemically inactive and induces not only reductions of voltage and capacity but also various hazardous events such as contact failure of the active material with a conductive material or the substrate due to expansion of electrode volume resulting from a broadening interlayer space, separation of the active material from the substrate, depletion of the electrolyte due to intake of water molecules by the active material. This has led to attempts of various measures to best suppress generation of undesirable &ggr;-NiOOH.
However, in order to realize a higher energy density by using a nickel oxide-based active material, a good use of the high order oxide &ggr;-NiOOH is of much importance. For such purpose, there is a proposed material having a similar structure to that of &agr;-hydroxide wherein Ni is partially replaced with a different metal such as Mn (III), Al (III) or Fe (III) and anions and water molecules are incorporated between the layers (J. Power Sources, Vol. 35, p. 294 (1991); U.S. Pat. No. 5,569,562; Japanese Laid-Open Patent Publication No. Hei 8-225328; and others). It has been considered that this oxide readily develops charge/discharge reaction with a high order oxide having a mimicking structure to that of &ggr;-NiOOH. Another proposal of using charge/discharge between &agr;-phase and &ggr;-phase has been disclosed in the U.S. Pat. No. 5,348,822. In fact, however, this oxide is a material having wide interlayer gaps and an extremely bulky density, making it difficult to perform high density pac
Izumi Hidekatsu
Izumi Yoichi
Moriwaki Yoshio
Sakamoto Hiroyuki
Bell Bruce F.
McDermott & Will & Emery
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