Alloys or metallic compositions – Containing over 50 per cent metal but no base metal – Chromium containing
Reexamination Certificate
1999-04-12
2001-08-07
Sheehan, John (Department: 1742)
Alloys or metallic compositions
Containing over 50 per cent metal but no base metal
Chromium containing
C420S420000, C420S421000, C420S422000, C420S424000, C420S449000, C420S900000, C148S421000, C148S428000, C148S442000
Reexamination Certificate
active
06270719
ABSTRACT:
FIELD OF THE INVENTION
The instant invention involves electrochemical hydrogen storage alloys and more specifically to modified VTiZrNiCrMn alloys. Most specifically, the instant invention comprises a modified VTiZrNiCrMn-based alloy which has at least one of 1) an increased charge/discharge rate capability over that of the base VTiZrNiCrMn electrochemical hydrogen storage alloy, 2) a formation cycling requirement which is reduced to one tenth that of the base VTiZrNiCrMn electrochemical hydrogen storage alloy, or 3) an oxide surface layer having a higher electrochemical hydrogen storage catalytic activity than the base Ti—V—Zr—Ni—Mn—Cr electrochemical hydrogen storage alloy.
BACKGROUND OF THE INVENTION
In rechargeable alkaline cells, weight and portability are important considerations. It is also advantageous for rechargeable alkaline cells to have long operating lives without the necessity of periodic maintenance. Rechargeable alkaline cells are used in numerous consumer devices such as portable computers, video cameras, and cellular phones. They are often configured into a sealed power pack that is designed as an integral part of a specific device. Rechargeable alkaline cells can also be configured as larger cells that can be used, for example, in industrial, aerospace, and electric vehicle applications.
The materials proposed in the prior art for use as hydrogen storage negative electrode materials for secondary batteries are materials that have essentially simple crystalline structures. In simple crystalline materials, limited numbers of catalytic site are available resulting from accidently occurring, surface irregularities which interrupt the periodicity of the crystalline lattice. A few examples of such surface irregularities are dislocation sites, crystal steps, surface impurities and foreign absorbates. For more than three decades, virtually every battery manufacturer in the world pursued such crystalline electrode materials for electrochemical applications, but none produced a commercially viable nickel metal hydride battery until after the publication of U.S. Pat. No. 4,623,597 (the '597 patent) to Ovshinsky, et al, which disclosed fundamentally new principles of electrode material design.
As taught in the '597 patent (the contents of which are incorporated by reference), a major shortcoming of basing negative electrode materials on simple ordered crystalline structures is that irregularities which result in the aforementioned catalytically active sites occur relatively infrequently. This results in a relatively low density of catalytic and/or storage sites and consequently poor stability. Of equal importance is that the type of catalytically active sites available are of an accidental nature, relatively few in number and are not designed into the material as are those of the present invention. Thus, the efficiency of the material in storing hydrogen and its subsequent release is substantially less than that which would be possible if a greater number and variety of sites were available,
Ovshinsky, et al, fundamental principles overcome the limitations of the prior art by improving the characteristics of the negative electrode through the use of disordered materials to greatly increase the reversible hydrogen storage characteristics required for efficient and economical battery applications. By applying the principles of disorder, it has become possible to obtain a high energy storage, efficiently reversible, and high electrically efficient battery in which the negative electrode material resists structural change and poisoning, with improved resistance to the alkaline environment, good self-discharge characteristics and long cycle life and deep discharge capabilities. The resulting disordered negative electrode materials are formed from lightweight, low cost elements by techniques that assure formation of primarily non-equilibrium metastable phases resulting in high energy and power densities at low cost. These non-equilibrium, metastable phases assure the formation of localized states where a special degree of disorder, if properly fabricated, can come from the structural and compositional disorder of the material.
The materials described generally in the '597 patent have a greatly increased density of catalytically active sites providing for the fast and stable storage and release of hydrogen. This significantly improved the electrochemical charging/discharging efficiencies and also showed an increase in hydrogen storage capacity. Generally, this was accomplished by the bulk storage of hydrogen atoms at bonding strengths within the range of reversible electromotive force suitable for use in secondary battery applications. More specifically, such negative electrode materials were fabricated by manipulating the local chemical order and hence the local structural order by the incorporation of selected modifier elements into the host matrix to create the desired disorder, type of local order and metal hydrogen bond strengths. The resulting multicomponent disordered material had a structure that was amorphous, microcrystalline, multiphase polycrystalline (but lacking long range compositional order), or a mixture of any combination of these structures.
The host matrix of the materials described in the '597 patent were formed from elements capable of storing hydrogen an thus are considered hydride formers. This host matrix was modified by incorporating selected modifier elements which could also be hydride formers. These modifiers enhanced the disorder of the final material, thus creating a much greater number and spectrum of catalytically active sites with an increase in the number of hydrogen storage sites. Multiorbital modifiers (such as transition elements) provided the greatly increased number of sites due to various bonding configurations available. Because of more efficient storage and release of hydrogen and because of the higher density of the catalytic sites, the hydrogen more readily found a storage site. Unfortunately, there remained, until U.S. Pat. No. 5,840,440 ('440), an insufficient density of new hydrogen storage sites formed due to disorder to significantly increase the hydrogen storage capacity of the material.
The '597 patent describes the use of, inter alia, rapid quench to form disordered materials having unusual electronic configurations, which results from varying the three-dimensional interactions of constituent atoms and their various orbitals. Thus, it was taught that the compositional, positional and translational relationships of the constituent atoms were not limited by crystalline symmetry in their freedom to interact. Selected elements could be utilized to further control the disorder of the material by their interaction with orbitals so as to create the desired local internal chemical environments. These various and at least partially unusual configurations generate a large number of catalytically active sites and hydrogen storage sites not only on the surface but throughout the bulk of the material. The internal topology generated by these various configurations allowed for selective diffusion of hydrogen atoms.
In general, disorder in the modified material can be of an atomic nature in the form of compositional or configurational disorder provided throughout the bulk of the material or in numerous regions or phases of the material. Disorder can also be introduced into the host matrix by creating microscopic phases within the material which mimic the compositional or configurational disorder at the atomic level by virtue of the relationship of one phase to another. For example, disordered materials can be created by introducing microscopic regions or phases of a different kind or kinds of crystalline phases, or by introducing regions of an amorphous phase or phases, or by introducing regions of an amorphous phase or phases in addition to regions of a crystalline phase or phases. The types of disordered structures that provide local structural chemical environments for improved hydrogen storage characteri
Fetcenko Michael A.
Koch John
Mays William
Ovshinsky Stanford R.
Reichman Benjamin
Ovonic Battery Company Inc.
Schumaker David W.
Sheehan John
Siskind Marvin S.
Watson Dean B.
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