Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-05-19
2002-10-08
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C205S413000, C241S016000
Reexamination Certificate
active
06461766
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention pertains to hydrogen storage powders and methods for making the same. More particularly, the present invention pertains to a method for making an electrochemical hydrogen storage powder with an engineered surface oxide to protect the powder from catching fire and to provide easier activation.
II. Description of the Related Art
Hydrogen storage materials have found use in various technologies, including battery electrode materials, fuel cells, getters, heat pumps, and the storage of hydrogen gas. Hydrogen storage materials are materials capable of absorbing and desorbing hydrogen respectively. Examples of some hydrogen storage materials include: metallic elements, such as Mg, Ti, V, Nb, Pd, and La, and some intermetallic alloys, such as TiFe, Mg
2
Ni, MgNi, misch metal based AB
5
, and Laves phase based AB
2
. It is generally practiced when making hydrogen storage materials to form the hydrogen storage material into a porous substructure to take advantage of high surface reaction area. A porous substructure is typically formed by powderizing a hydrogen storage material, forming the powderized material into a composite body with a suitable substrate material and subjecting the composite body to one or more pretreatment steps or ‘activation’. Formation of a powdered material followed by pretreatment increases surface area, active sites, and porosity among other characteristics of the hydrogen storage material.
Powderized hydrogen storage material is particularly useful in the formation of battery electrodes. Methods for making powderized hydrogen storage materials and battery electrodes therefrom are generally known and have been described in a number of patents, including for example, U.S. Pat. Nos. 4,716,088; 4,670,214; 4,765,598; 4,820,481; and 4,915,898, the disclosures of which are herein incorporated by reference. Methods for making metal hydride battery electrodes typically include applying and fixing a pulverized hydrogen storage material to a conductive substrate. A number of additives may also be added to the powder to increase cohesion to the conductive substrate and to improve battery performance. Such additives may include binders and conductive filler.
Hydrogen storage materials may be powderized by a number of methods. The particular method to be used depends upon the material's composition, hardness, tendency to form surface oxides, and desired end use. Known powderization techniques include mechanical and chemical methods of pulverization and combinations thereof, including machining, milling, shooting, granulization, atomizing, condensation, reduction, chemical precipitation, or electrodeposition. Additionally or alternatively, other conventional size reduction techniques may be used, including, abrasion, shearing, ball milling, hammer milling, shredders, fluid energy, and disk attrition. To obtain useful particle size distributions or classification, pulverization is typically followed by sieving. Other techniques which do not necessarily require pulverization involve rapid quench methods such as jet casting and gas atomization.
While certain size reduction techniques work well for some materials, there is no single technique that works for all materials. For instance some materials are soft enough to crush using only mechanical crushing methods. Some materials are best suited for a combination of mechanical and chemical pulverization methods. Other alloys are too hard for mechanical crushing and must be pulverized by chemical methods. As such, many mechanical sizing techniques are not effective for pulverizing very hard materials, particularly those having a Rockwell hardness of greater than 45.
Bulk hydrogen storage material is typically formed by melting various metals together and casting them in the form of a button or ingot. Bulk hydrogen storage material may be compositionally and structurally ordered, disordered or anywhere in between. As reported in
A Nickel Metal Hydride Battery for Electric Vehicles
, by S. R. Ovshinsky, M. A. Fetcenko and J. Ross, Science, Vol. 260, Apr. 9, 1993: “Among the elements that have become available for alloy formation in disordered electrode materials are Li, C, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Sn, La, W, and Re. The list contains elements that can increase the number of hydrogen atoms stored per metal atom (Mg, Ti, V, Zr, Nb, and La). Other elements allow the adjustment of the metal-hydrogen bond strength (V, Mn, and Zr) or provide catalytic properties to ensure sufficient charge and discharge reaction rates and gas recombination (Al, Mn, Co, Fe, and Ni); or impart desirable surface properties such as oxidation and corrosion resistance, improved porosity, and ionic conductivity (Cr, Mo and W). The wide range of physical properties that can be produced in these alloys allows the MH battery performance to be optimized.”
Order and Disorder form a spectrum and may be engineered into hydrogen storage materials to improve the above mentioned characteristics and others. The amount of structural and compositional order may be both material and process dependent. For example, more highly ordered materials may be formed by a conventional melt-and-cast. A slow cooling process allows crystal growth and substantial structural order to take place depending on the chemical formula. Highly disordered materials, on the other hand, are typically formed by melting with rapid quench, fast cooling methods. Rapid cooling provides a more highly disordered material, also dependant on the chemical constituents.
One successful method of pulverizing hydrogen storage alloy using hydrogen pulverization was developed at Ovonic Battery, Inc., the method of which is disclosed in U.S. Pat. No. 4,893,756, issued Jan. 16, 1990 to Fetcenko et al., and is entitled “Hydride Reactor Apparatus for Hydrogen Commination of Metal Hydride Hydrogen Storage Material”, the disclosure of which is herein incorporated by reference. Through continuous and ongoing research endeavors, Ovonic Battery, Inc. developed the first hydrogen storage reactor for pulverizing hard, hydrogen storage materials for use in negative electrodes for batteries. The method has paved the way for the development of new materials with improved characteristics for the formation of battery electrodes.
According to Fetcenko et al., hydrogen storage powders may be made from a bulk material, such as a metal ingot or alloy by hydride/dehydride cycling comminution. The hydride/dehydride process reduces a metal hydride or hydrogen storage material from a large ingot or bulk size to particles. To accomplish the aforementioned comminution, bulk material is placed in a stationary hydrogen reactor. The reactor is placed under vacuum and purged with argon to remove any residual air. Hydrogen is then back-filled into the reaction chamber to a pressure of at least 25 psi. The hydrogen is absorbed in the hydrogen storage material, which thereby causes volumetric expansion of the metal lattices to comminute the hydrogen storage material. Hydrogenation may take several hours and may reach elevated temperatures. Cooling is provided to maintain the reaction vessel at a temperature of less than about 100° C. After hydrogenation, the comminuted material is dehydrogenated to remove hydrogen from the hydrogen storage material. The material may then be packaged under an oxygen free atmosphere for later formation into a battery electrode.
The Fetcenko patent and its progenies teach methods of hydrogen pulverization wherein the hydrogenation step is pressure controlled. Unfortunately, a pressure-controlled reaction may result in excessive heating of the hydrogen storage material. Excessive heating is undesirable in that it may cause unpredictable changes to the compositional and structural order or disorder of the hydrogen storage material. Additionally, excessive heating results in a long cooling period and increased production time.
Exposure of hydrogen storage materials to air can produce unpredictable and va
Fetcenko Michael A.
Ovshinsky Stanford R.
Young Kwo
Ovonic Battery Company Inc.
Ruthkosky Mark
Ryan Patrick
Siskind Marvin S.
Watson Dean B.
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