Alloys or metallic compositions – Containing over 50 per cent metal but no base metal
Reexamination Certificate
2003-04-01
2004-12-14
Mai, Ngoclan T. (Department: 1742)
Alloys or metallic compositions
Containing over 50 per cent metal but no base metal
C420S900000, C429S218100, C429S220000, C429S221000, C429S223000, C429S226000
Reexamination Certificate
active
06830725
ABSTRACT:
FIELD OF THE INVENTION
The instant invention pertains to hydrogen storage alloys as well as to electrochemical cells, batteries and fuel cells using these alloys. More particularly, the instant invention relates to hydrogen storage alloys having microstructures that are highly permeable and/or that include high concentrations of catalytically active metal or metal alloy particles. Most particularly, the instant invention relates to hydrogen storage alloys suitable for use as negative electrode materials in metal hydride batteries that exhibit high powers and high discharge rates at low operating temperatures.
BACKGROUND OF THE INVENTION
Consumer and industrial applications continue to drive demand for new and efficient batteries for use as energy sources. Important goals include obtaining ever more power from increasingly smaller battery packages in an environmentally respectful fashion. Envisioned applications for batteries include everything from mobile electronics to electric vehicles. Portability, rechargeability over a large number of cycles, low cost, high power, lightweight and consistent performance over widely varying loads are among the key attributes required for batteries. The specific combination of battery performance requirements varies widely with the intended application and the battery components and materials are typically optimized accordingly. An important developing application area for rechargeable batteries is electric vehicles (EV) and hybrid electric vehicles (HEV). In these applications, the battery must have the ability to provide high currents in short time periods in order to achieve effective acceleration. High discharge rates are therefore necessary. High battery power over extended time periods are also needed so that vehicles of reasonable size and weight can be maintained in motion for reasonable time intervals without recharging. Rapid recharging over many cycles should also be possible using readily available electrical power sources. The preferred cycle life profile also requires a high number of charge/discharge cycles at a low, rather than high, depth of discharge. Progress has been made in the development of batteries for HEV applications and two HEV automobiles have recently been made available to the U.S. public. Nonetheless, the batteries used in these automobiles represent compromises and trade-offs in relevant performance parameters and new developments are needed to further the capabilities of HEV and EV products.
One aspect of rechargeable batteries for HEV, EV, 42 V SLI and other applications that has received relatively little attention is low temperature operation. For HEV and EV products it is desirable to have batteries that perform well in winter climates. Similarly, achievement of portable and stationary power sources based on rechargeable batteries that are capable of functioning outdoors in cold climates or in indoor cold environments is also desirable. A basic limitation of virtually every battery technology is a diminution of power and performance at low temperature. The deleterious effects of temperature are especially pronounced below freezing.
Nickel metal hydride batteries have emerged as the leading class of rechargeable batteries and are replacing earlier generation nickel-cadmium batteries in many applications. Current HEV and EV products, for example, utilize nickel metal hydride batteries and expanded performance of HEV and EV products in the future are expected to depend largely on the capabilities of nickel metal hydride batteries. Like other rechargeable batteries, nickel metal hydride batteries suffer significant degradation in power and performance upon a lowering of temperature.
Improvements in the low temperature performance require consideration of the underlying components and principles of operation of nickel metal hydride batteries.
Nickel metal hydride batteries typically include a nickel hydroxide positive electrode, a negative electrode that incorporates a metal containing hydrogen storage alloy, a separator and an aqueous alkaline electrolyte. The positive and negative electrodes are housed in adjoining battery compartments that are typically separated by a non-woven, felled, nylon or polypropylene separator. Several batteries may also be combined in series to form larger battery packs capable of providing higher powers, voltages or discharge rates.
The charging and discharging reactions of nickel metal hydride batteries have been discussed in the art and may be summarized as shown below:
Charging:
positive electrode: Ni(OH)
2
+OH→NiOOH+H
2
O+e
−
negative electrode: M+H
2
O+e
−
→MH+OH
−
Discharging
positive electrode: NiOOH+H
2
O+e
−
→Ni(OH)
2
+OH
−
negative electrode: MH+OH W M+H
2
O+e
−
Much work has been completed over the past decade to improve the performance of nickel metal hydride batteries. Optimization of the batteries ultimately depends on controlling the rate, extent and efficiency of the charging and discharging reactions. Factors relevant to battery performance include the physical state, chemical composition, catalytic activity and other properties of the positive and negative electrode materials, the composition and concentration of the electrolyte, the separator, the operating conditions, and external environmental factors. Various factors related to the performance of the positive nickel hydroxide electrode have been considered, for example, in U.S. Pat. Nos. 5,348,822; 5,637,423; 5,905,003; 5,948,564; and 6,228,535 by the instant assignee, the disclosures of which are hereby incorporated by reference. Work on suitable negative electrode materials has focused on intermetallic compounds as hydrogen storage alloys since the late 1950's when it was determined that the compound TiNi reversibly absorbed and desorbed hydrogen. Subsequent work has shown that intermetallic compounds having the general formulas AB, AB
2
, A
2
B and AB
5
, where A is a hydride forming element and B is a weak or non-hydride forming element, are able to reversibly absorb and desorb hydrogen. Consequently, most of the effort in developing negative electrodes has focused on hydrogen storage alloys having the AB, AB
2
, AB
5
or A
2
B formula types.
Desirable properties of hydrogen storage alloys include: good hydrogen storage capabilities to achieve a high energy density and high battery capacity; thermodynamic properties suitable for the reversible absorption and desorption of hydrogen; low hydrogen equilibrium pressure; high electrochemical activity; fast discharge kinetics for high rate performance; high oxidation resistance; weak tendency to self-discharge; and reproducible performance over many cycles. The chemical composition, physical state, electrode structure and battery configurations of hydrogen storage alloys as negative electrode materials in nickel metal hydride have been investigated and reported in the prior art. Some of this work is described in U.S. Pat. Nos. 4,716,088; 5,277,999; 5,536,591; 5,616,432; and 6,270,719 to the instant assignee, the disclosures of which are hereby incorporated by reference.
Efforts to date indicate that intermetallic compounds are capable of effectively functioning as negative electrode materials in rechargeable batteries, but that important properties are difficult to optimize simultaneously. Hydrogen storage alloys of the AB
5
type, for example, generally have high initial activation, good charge stability and relatively long charge-discharge cycle life, but at the same time have low discharge capacity. Furthermore, attempts to increase the cycle life generally lead to reductions in the initial activation. Hydrogen storage alloys of the AB
2
type, on the other hand, typically possess high discharge capacity, but low initial activation and relatively short cycle life. Efforts to improve upon the initial activation generally come at the expense of cycle life. Other important properties include discharge rate, discharge current, and constancy of o
Fetcenko Michael A.
Koch John
Mays William
Ouchi Taihei
Ovshinsky Stanford R.
Bray Kevin L.
Siskind Marvin S.
Texaco Ovonic Battery Systems, LLC
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