CA2184377C - Improved metal hydride hydrogen storage electrodes - Google Patents
Improved metal hydride hydrogen storage electrodes Download PDFInfo
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- CA2184377C CA2184377C CA002184377A CA2184377A CA2184377C CA 2184377 C CA2184377 C CA 2184377C CA 002184377 A CA002184377 A CA 002184377A CA 2184377 A CA2184377 A CA 2184377A CA 2184377 C CA2184377 C CA 2184377C
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
- C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
- C01B3/0084—Solid storage mediums characterised by their shape, e.g. pellets, sintered shaped bodies, sheets, porous compacts, spongy metals, hollow particles, solids with cavities, layered solids
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/24—Electrodes for alkaline accumulators
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/0005—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes
- C01B3/001—Reversible uptake of hydrogen by an appropriate medium, i.e. based on physical or chemical sorption phenomena or on reversible chemical reactions, e.g. for hydrogen storage purposes ; Reversible gettering of hydrogen; Reversible uptake of hydrogen by electrodes characterised by the uptaking medium; Treatment thereof
- C01B3/0078—Composite solid storage mediums, i.e. coherent or loose mixtures of different solid constituents, chemically or structurally heterogeneous solid masses, coated solids or solids having a chemically modified surface region
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/24—Electrodes for alkaline accumulators
- H01M4/242—Hydrogen storage electrodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/383—Hydrogen absorbing alloys
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/32—Hydrogen storage
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Abstract
An improved metal hydride hydrogen storage alloy electrode (20) for use in an electrochemical cell (10). The improved electrode (20) includes a hydrogen storage alloy material (22) having a layer of a passivation material (25) disposed thereon.
Description
1. ._.
w0 95127315 218 4 3 7 7 pCT~S94~03496 ~pg~p~ METAL HYDR~E HYDft(~EN STORAGE ELECTRODES
Wchnic~l Field This present invention relates to electrochemical hydrogen storage alloys and rechargeable electrochemical cells using these alloys.
Background of the Invention Rechargeable electrochemical cells that use a nickel-hydroxide positive electrode and a metal hydride forming hydrogen storage negative electrode are well known in the art. In fact over the past several years, metal hydride cells have gained widespread market acceptance due to the fact that they incorporate highly desirable performance characteristics. Examples of these desirable characteristics include high charge acceptance, relatively long-cycle life and operation over a wide range of temperatures. Each of these performance characteristics represent improvements over the nickel cadmium and other battery systems known in the prior art.
Typically, the metal hydride hydrogen storage electrode is the negative electrode in a hydrogen storage system. The negative electrode material (M) is charged by the electrochemical absorption of hydrogen, and the electrochemical evolution of a hydroxyl ion. The reaction which takes place at the metal hydride electrode may be described according to the following formula:
charge M+H20+e- <-------------> M-H+OH-discharge The reaction that takes place at the posit'-~e electrode of a nickel metal hydride cell is also a reversible reaction. In the case of a nickel hydroxide electrode, the positive electrode reaction is as follows:
w0 95/27315 218 4 3 7 7 pCT/US94/03496 Ni(OH)2+OH- <-----------------> Ni00H+H20+e-The negative electrode of most metal hydride electrochemical cells can be characterized by one of two chemical formulas: The first is AB2, which describes TiNi type battery systems such as described in, for example, United States Patent No. 5,277,999. The second formula is AB5 which describes LaNiS type systems as described in, for example, U.S.
Patent No. 4,487,817.
Substantially all metal hydride electrochemical cells fall into one of these two categories. However, with respect to both of these types of materials, it has been found that the failure mode is usually the result of degradation of the metal hydride electrode. This degradation has been ascribed to the growth of a surface oxide film on the surface of the metal hydride electrode. The oxide film reduces the active area of the electrode, thus reducing the available area for the hydrogen reduction/oxidation reaction to occur. Since the total current has to be distributed over a smaller total area, the current density on the active surface increases.
As a consequence, the rate of formation of the irreversible oxide layer increases. The internal resistance of the electrode also increases, further hastening failure of the electrode.
Moreover, the power density of metal hydride cells is not as great as in some other types of cells, notably nickel cadmium. Accordingly, metal hydride cells have not been appropriate for several applications, such as power tools.
Prior attempts to address these problems have focused mainly on the addition of more and more modifier elements to the hydrogen storage alloy material which makes up the metal hydride electrode. For example, many current examples of metal hydride materials include ten or more components mixed in varying ratios. As with any alloy, adding new elements to the hydrogen storage material increases complexity of the formation process, and adds to the cost of the overall material.
Accordingly, there exists a need to provide a means by which to .
reduce the formation of surface oxides on the surface of the metal hydride electrode and in the metal hydride electrochemical cells. The -means for reducing oxide formation should be relatively simple, and not necessitate the use of additional elements added to the hydrogen storage alloy. Further, a need exists for metal hydride cells having relatively high power densities and capacities.
Summary of the Invention Briefly, according to the invention, there is provided an electrode for an electrochemical hydrogen storage cell. The hydrogen storage electrode comprises a hydrogen storage alloy capable of reversibly electrochemically storing and discharging hydrogen, and a layer of a passivation material disposed atop said hydrogen storage alloy material.
In one preferred embodiment, the layer of passivation material may be hydrogen permeable, and may further prevent or reduce the formation of oxides on the surface of the hydrogen storage alloy material.
Further according to the invention, there is provided a method of passivating a electrochemical hydrogen storage alloy material so as to prevent the formation of oxides on the surface thereof. This method includes the steps of providing a hydrogen storage alloy material capable of electrochemically storing and discharging hydrogen, and disposing a layer of a hydrogen permeable passivation material atop said hydrogen storage alloy material.
Further according to the invention, there is provided electrochemical hydrogen storage cells including a negative electrode, a positive electrode, and an electrolyte. The negative electrode comprises a hydrogen storage alloy capable of reversibly electrochemically storing and discharging hydrogen and having a layer of hydrogen permeable passivation material disposed there atop.
Brief Description of the Drawing:
FIG. 1 is a schematic representation of an electrochemical cell including an improved metal hydride hydrogen storage alloy electrode in accordance with the instant invention;
FIG. 2. is a schematic side view of a metal hydride hydrogen storage alloy electrode coated with a layer of passivation material;
FIG. 3. is a chart illustrating voltage versus time for metal hydride hydrogen storage electrodes including a layer of passivation material versus unpassivated metal hydride electrodes and illustrating electrode potential during charge;
w0 95127315 218 4 3 7 7 pCT~S94~03496 ~pg~p~ METAL HYDR~E HYDft(~EN STORAGE ELECTRODES
Wchnic~l Field This present invention relates to electrochemical hydrogen storage alloys and rechargeable electrochemical cells using these alloys.
Background of the Invention Rechargeable electrochemical cells that use a nickel-hydroxide positive electrode and a metal hydride forming hydrogen storage negative electrode are well known in the art. In fact over the past several years, metal hydride cells have gained widespread market acceptance due to the fact that they incorporate highly desirable performance characteristics. Examples of these desirable characteristics include high charge acceptance, relatively long-cycle life and operation over a wide range of temperatures. Each of these performance characteristics represent improvements over the nickel cadmium and other battery systems known in the prior art.
Typically, the metal hydride hydrogen storage electrode is the negative electrode in a hydrogen storage system. The negative electrode material (M) is charged by the electrochemical absorption of hydrogen, and the electrochemical evolution of a hydroxyl ion. The reaction which takes place at the metal hydride electrode may be described according to the following formula:
charge M+H20+e- <-------------> M-H+OH-discharge The reaction that takes place at the posit'-~e electrode of a nickel metal hydride cell is also a reversible reaction. In the case of a nickel hydroxide electrode, the positive electrode reaction is as follows:
w0 95/27315 218 4 3 7 7 pCT/US94/03496 Ni(OH)2+OH- <-----------------> Ni00H+H20+e-The negative electrode of most metal hydride electrochemical cells can be characterized by one of two chemical formulas: The first is AB2, which describes TiNi type battery systems such as described in, for example, United States Patent No. 5,277,999. The second formula is AB5 which describes LaNiS type systems as described in, for example, U.S.
Patent No. 4,487,817.
Substantially all metal hydride electrochemical cells fall into one of these two categories. However, with respect to both of these types of materials, it has been found that the failure mode is usually the result of degradation of the metal hydride electrode. This degradation has been ascribed to the growth of a surface oxide film on the surface of the metal hydride electrode. The oxide film reduces the active area of the electrode, thus reducing the available area for the hydrogen reduction/oxidation reaction to occur. Since the total current has to be distributed over a smaller total area, the current density on the active surface increases.
As a consequence, the rate of formation of the irreversible oxide layer increases. The internal resistance of the electrode also increases, further hastening failure of the electrode.
Moreover, the power density of metal hydride cells is not as great as in some other types of cells, notably nickel cadmium. Accordingly, metal hydride cells have not been appropriate for several applications, such as power tools.
Prior attempts to address these problems have focused mainly on the addition of more and more modifier elements to the hydrogen storage alloy material which makes up the metal hydride electrode. For example, many current examples of metal hydride materials include ten or more components mixed in varying ratios. As with any alloy, adding new elements to the hydrogen storage material increases complexity of the formation process, and adds to the cost of the overall material.
Accordingly, there exists a need to provide a means by which to .
reduce the formation of surface oxides on the surface of the metal hydride electrode and in the metal hydride electrochemical cells. The -means for reducing oxide formation should be relatively simple, and not necessitate the use of additional elements added to the hydrogen storage alloy. Further, a need exists for metal hydride cells having relatively high power densities and capacities.
Summary of the Invention Briefly, according to the invention, there is provided an electrode for an electrochemical hydrogen storage cell. The hydrogen storage electrode comprises a hydrogen storage alloy capable of reversibly electrochemically storing and discharging hydrogen, and a layer of a passivation material disposed atop said hydrogen storage alloy material.
In one preferred embodiment, the layer of passivation material may be hydrogen permeable, and may further prevent or reduce the formation of oxides on the surface of the hydrogen storage alloy material.
Further according to the invention, there is provided a method of passivating a electrochemical hydrogen storage alloy material so as to prevent the formation of oxides on the surface thereof. This method includes the steps of providing a hydrogen storage alloy material capable of electrochemically storing and discharging hydrogen, and disposing a layer of a hydrogen permeable passivation material atop said hydrogen storage alloy material.
Further according to the invention, there is provided electrochemical hydrogen storage cells including a negative electrode, a positive electrode, and an electrolyte. The negative electrode comprises a hydrogen storage alloy capable of reversibly electrochemically storing and discharging hydrogen and having a layer of hydrogen permeable passivation material disposed there atop.
Brief Description of the Drawing:
FIG. 1 is a schematic representation of an electrochemical cell including an improved metal hydride hydrogen storage alloy electrode in accordance with the instant invention;
FIG. 2. is a schematic side view of a metal hydride hydrogen storage alloy electrode coated with a layer of passivation material;
FIG. 3. is a chart illustrating voltage versus time for metal hydride hydrogen storage electrodes including a layer of passivation material versus unpassivated metal hydride electrodes and illustrating electrode potential during charge;
FIG. 4. is a chart illustrating voltage versus time for passivated and unpassivated metal hydride hydrogen storage electrodes showing electrode potential during charge/discharge; and FIG. 5 is a chart illustrating capacity versus cycle life with of ' electrodes in accordance with the instant invention versus unpassivated electrodes.
Detailed Description of the Preferred Embodiment While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward.
Referring now to FIG. 1, there is illustrated therein a schematic representation of an electrochemical cell including a metal hydride hydrogen storage alloy electrode coated with a layer of a passivation material in accordance with the instant invention. The electrochemical cell 10 includes a negative electrode 20 and a positive electrode 30. Both electrodes are immersed in an electrolyte 40 and separated from one another by an appropriate separator 50.
The negative electrode 20 of the electrochemical cell 10 is a metal hydride hydrogen storage alloy electrode. Accordingly, the material may be either the AB2 or AB5 type metal hydride hydrogen storage alloy material. The metal hydride hydrogen storage alloy materials may be characterized by the following formula: (Ti2_XZrXV4_yNiy) 1_z Mz wherein M is a modifier element selected from the groups of materials, including chromium, cobalt, manganese, aluminum, iron, iridium, molybdenum and combinations thereof and where x, y, and z indicate the relative proportion of each of the materials in the alloy. Disposed atop the metal hydride hydrogen storage alloy material is a layer of hydrogen permeable passivation material (as illustrated in more detail in FIG. 2 hereof). ' The positive electrode 30 may be fabricated of any of the number of known materials in the electrochemical arts. In one preferred embodiment, a positive electrode may be a nickel hydroxide positive electrode.
The negative and positive electrodes 20 and 30 respectively, are immersed in electrolyte 40. The electrolyte may be an electrolyte known in the art, such as, for example, 31% KOH. Disposed between the negative and positive electrodes is a separator 50 fabricated of, for 5 example, a polymeric material, such as one or more layers of, or a combination of non-woven or microporous polypropylene (Celgard*) Referring now to FIG. 2, there is illustrated therein a cross sectional side view of the negative electrode 20 of FIG. 1. The negative electrode 20 includes a body of a metal hydride hydrogen storage alloy 22, and a layer of a hydrogen permeable passivation material 25 disposed atop the metal hydride hydrogen storage alloy material 22. As used herein, a passivation material refers to a material which is a relatively hydrogen-permeable material, and which discourages, reduces, or prevents the formation of oxides, such as oxides of lanthanum and/or nickel, on the surface of the metal hydride hydrogen storage alloy material. The layer of passivation material serves several beneficial purposes. For example, by preventing or reducing the formation of oxides on the surface of the hydrogen storage alloy material, there is no decrease in the active area of the electrode. In other words, the available area for the hydrogen oxidation/reduction reaction remains unreduced.
Further, since there is no decrease in the total area of the electrode (since no oxides are formed)over which current is distributed, the current density at the surface is not increased. As a result, cycle life of the metal hydride hydrogen storage alloy material may be considerably lengthened.
It has also been found that the layer of passivation material contributes to increased power density for the hydrogen storage alloy material. This is due to the fact that hydrogen will react with, for example, a palladium passivation material much more quickly than the metal hydride material.
The electrochemical hydrogen storage alloy material may be passivated so as to prevent the formation of oxides on the surface thereof by providing a hydrogen storage alloy material capable of reversibly electrochemically storing and discharging hydrogen, and disposing a layer of hydrogen permeable passivation material atop the hydrogen storage alloy material. Preferred materials for use as the passivation material include palladium, cobalt, nickel, copper, gold, silver, * trade-mark platinum, iridium, vanadium, niobium, titanium, palladium alloys, cobalt alloys, nickel alloys, copper alloys, gold alloys, silver alloys, platinum alloys, iridium alloys, vanadium alloys, niobium alloys, titanium alloys, and combinations thereof. Further, the passivation material may be selected so that the reversible potential of the material is not within the potential range of the positive and negative electrodes.
This will reduce the possibility of oxidation of the passivation material.
Accordingly, the passivation material may, in a preferred embodiment, be palladium.
The passivation material may be disposed atop the layer of metal hydride hydrogen storage alloy material in any one of the number of known techniques. For example, the passivation material may be deposited atop the hydrogen storage alloy by a vacuum deposition method. Alternatively, the hydrogen storage alloy may be coated by the passivation material in an electrodeposition process. In yet another embodiment, the passivation material is mechanically sheared/mixed, i.e., mechanically alloyed with said hydrogen storage alloy material so as to coat it. An example of this process may be, for example, ball milling. The passivation material is typically deposited atop the hydrogen storage alloy material to a thickness of between 0.01 and 5.O~t, and preferably approximately 0.5~t.
By providing a layer of passivation material on the surface of the hydrogen storage alloy material, several improvements in the performance of the alloy are observed. First, the passivation material reduces the rate of growth of the irreversible oxide layers on the surface of the metal hydride electrodes. This occurs since the passivation layer acts essentially as a barrier between the metal hydride electrode and the electrolyte. Thus, the majority of the hydrogen oxidation/reduction occurs on the surface of the passivation material, rather than on the surface of the metal hydride electrode. Thus, the cycle life of the electrode is extended. Further, the passivation material, such as palladium, is typically a good catalyst for the hydrogen oxidation/reduction reaction. Thus, the passivation layer provides reaction sites with less kinetic overpotential for hydrogen reactions. .
Accordingly, the electrode has less voltage loss, producing higher working voltages and requiring lower charging voltage during recharging cycles.
. 2184371 Finally, a passivation material such as palladium is hydrogen permeable. The hydrogen storing characteristics of the metal hydride electrode is therefor not hindered in any way. During the charging of the cell, hydrogen atoms diffuse through the palladium layer, entering the body of metal hydride alloy and are stored therein. Thus, the capacity of the cell will not be reduced.
EXAMPLES
An improved metal hydride hydrogen storage alloy material including a layer of passivation material thereon was fabricated in accordance with the instant invention. More particularly, metal hydride hydrogen storage alloy material having the composition:
Lap,52Nd0,44Ce0.04Ni~.1~0.33~0.14Co0.1Fe0.41 and known as International Battery Association Common Sample No. 3 was mixed with a palladium powder. Combination of the materials was via mechanical shearing/mixing. The mixing not only produced a homogenous mixture of the two powders but by the shear force of the two phases, the softer palladium was pressed against the harder, more brittle metal hydride hydrogen storage alloy particles. As a result, the palladium powder deformed and coated the metal hydride hydrogen storage alloy particles. An example of mechanical shear/mixing is ball milling. Experiments were carried out by grinding a 10% palladium powder with the metal hydride hydrogen storage alloy powder in an agate mortar prior to being fabricated onto teflon*-bonded electrodes. The thickness of the palladium layer was about 0.5~.. The bonded, fixed electrodes were then tested against the conventional metal hydride hydrogen storage alloy electrodes described above, lacking the palladium passivating layer. The results are illustrated in FIGS. 3-5.
Referring now to FIG. 3, there is illustrated therein the potential of a palladium coated metal hydride electrode versus the potential of a conventional nickel metal hydride electrode during constant current charging at two different current levels. Specifically, lines 60 and 62 illustrate results for an electrode with and without a passivation material, respectively. Testing for both electrodes was conducted at 50 mA. Similarly, lines 64 and 66 illustrate results for passivated and unpassivated electrodes respectively, at 115 mA. From the curves illustrated on FIG. 3, it is apparent that the electrode including the * trade-mark -., P~- w0 95127315 2 7 8 4 3 7 7 p~/pg94/03496 palladium coating not only exhibited less overpotential, (at least 100 m/V
improvement over conventional metal hydride electrodes) but also required less voltage at the initial moment of the charging process.
Referring now to FIG. 4, there is illustrated therein a comparison of the charge acceptance of a conventional nickel metal hydride electrode versus that of a palladium coated metal hydride electrode. Both electrodes were charged at C rate for 30 minutes and then discharged at C/2 to measure the discharge capacity. Lines 70 and 72 illustrate results, respectively, for electrodes with and without a layer of passivation material, for tests conducted at 115 mA. Similarly, lines 74 and 76 illustrate results, respectively, for passivated and unpassivated electrodes for tests run at a C/2 rate of 58 mA. The palladium coated electrode demonstrated approximately 35% coulombic efficiency whereas the conventional electrode demonstrated that only approximately 3% of the charge was accepted. Accordingly, it may be appreciated that the palladium coated electrode is considerably more efficient than conventional metal hydride electrodes.
FIG. 5 illustrates life cycle testing for both passivated and unpassivated metal hydride hydrogen storage electrodes. Specifically, lines 80 and 82 illustrate voltage at end of discharge for passivated and unpassivated electrodes respectively. Similarly, lines 84 and 86 illustrate, respectively, capacity for passivated and unpassivated electrodes. As may be appreciated from FIG. 5, the voltage and capacity performance characteristics of both electrodes was substantially the same, except for cycle life, which was considerably longer for the passivated electrode.
While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.
Detailed Description of the Preferred Embodiment While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward.
Referring now to FIG. 1, there is illustrated therein a schematic representation of an electrochemical cell including a metal hydride hydrogen storage alloy electrode coated with a layer of a passivation material in accordance with the instant invention. The electrochemical cell 10 includes a negative electrode 20 and a positive electrode 30. Both electrodes are immersed in an electrolyte 40 and separated from one another by an appropriate separator 50.
The negative electrode 20 of the electrochemical cell 10 is a metal hydride hydrogen storage alloy electrode. Accordingly, the material may be either the AB2 or AB5 type metal hydride hydrogen storage alloy material. The metal hydride hydrogen storage alloy materials may be characterized by the following formula: (Ti2_XZrXV4_yNiy) 1_z Mz wherein M is a modifier element selected from the groups of materials, including chromium, cobalt, manganese, aluminum, iron, iridium, molybdenum and combinations thereof and where x, y, and z indicate the relative proportion of each of the materials in the alloy. Disposed atop the metal hydride hydrogen storage alloy material is a layer of hydrogen permeable passivation material (as illustrated in more detail in FIG. 2 hereof). ' The positive electrode 30 may be fabricated of any of the number of known materials in the electrochemical arts. In one preferred embodiment, a positive electrode may be a nickel hydroxide positive electrode.
The negative and positive electrodes 20 and 30 respectively, are immersed in electrolyte 40. The electrolyte may be an electrolyte known in the art, such as, for example, 31% KOH. Disposed between the negative and positive electrodes is a separator 50 fabricated of, for 5 example, a polymeric material, such as one or more layers of, or a combination of non-woven or microporous polypropylene (Celgard*) Referring now to FIG. 2, there is illustrated therein a cross sectional side view of the negative electrode 20 of FIG. 1. The negative electrode 20 includes a body of a metal hydride hydrogen storage alloy 22, and a layer of a hydrogen permeable passivation material 25 disposed atop the metal hydride hydrogen storage alloy material 22. As used herein, a passivation material refers to a material which is a relatively hydrogen-permeable material, and which discourages, reduces, or prevents the formation of oxides, such as oxides of lanthanum and/or nickel, on the surface of the metal hydride hydrogen storage alloy material. The layer of passivation material serves several beneficial purposes. For example, by preventing or reducing the formation of oxides on the surface of the hydrogen storage alloy material, there is no decrease in the active area of the electrode. In other words, the available area for the hydrogen oxidation/reduction reaction remains unreduced.
Further, since there is no decrease in the total area of the electrode (since no oxides are formed)over which current is distributed, the current density at the surface is not increased. As a result, cycle life of the metal hydride hydrogen storage alloy material may be considerably lengthened.
It has also been found that the layer of passivation material contributes to increased power density for the hydrogen storage alloy material. This is due to the fact that hydrogen will react with, for example, a palladium passivation material much more quickly than the metal hydride material.
The electrochemical hydrogen storage alloy material may be passivated so as to prevent the formation of oxides on the surface thereof by providing a hydrogen storage alloy material capable of reversibly electrochemically storing and discharging hydrogen, and disposing a layer of hydrogen permeable passivation material atop the hydrogen storage alloy material. Preferred materials for use as the passivation material include palladium, cobalt, nickel, copper, gold, silver, * trade-mark platinum, iridium, vanadium, niobium, titanium, palladium alloys, cobalt alloys, nickel alloys, copper alloys, gold alloys, silver alloys, platinum alloys, iridium alloys, vanadium alloys, niobium alloys, titanium alloys, and combinations thereof. Further, the passivation material may be selected so that the reversible potential of the material is not within the potential range of the positive and negative electrodes.
This will reduce the possibility of oxidation of the passivation material.
Accordingly, the passivation material may, in a preferred embodiment, be palladium.
The passivation material may be disposed atop the layer of metal hydride hydrogen storage alloy material in any one of the number of known techniques. For example, the passivation material may be deposited atop the hydrogen storage alloy by a vacuum deposition method. Alternatively, the hydrogen storage alloy may be coated by the passivation material in an electrodeposition process. In yet another embodiment, the passivation material is mechanically sheared/mixed, i.e., mechanically alloyed with said hydrogen storage alloy material so as to coat it. An example of this process may be, for example, ball milling. The passivation material is typically deposited atop the hydrogen storage alloy material to a thickness of between 0.01 and 5.O~t, and preferably approximately 0.5~t.
By providing a layer of passivation material on the surface of the hydrogen storage alloy material, several improvements in the performance of the alloy are observed. First, the passivation material reduces the rate of growth of the irreversible oxide layers on the surface of the metal hydride electrodes. This occurs since the passivation layer acts essentially as a barrier between the metal hydride electrode and the electrolyte. Thus, the majority of the hydrogen oxidation/reduction occurs on the surface of the passivation material, rather than on the surface of the metal hydride electrode. Thus, the cycle life of the electrode is extended. Further, the passivation material, such as palladium, is typically a good catalyst for the hydrogen oxidation/reduction reaction. Thus, the passivation layer provides reaction sites with less kinetic overpotential for hydrogen reactions. .
Accordingly, the electrode has less voltage loss, producing higher working voltages and requiring lower charging voltage during recharging cycles.
. 2184371 Finally, a passivation material such as palladium is hydrogen permeable. The hydrogen storing characteristics of the metal hydride electrode is therefor not hindered in any way. During the charging of the cell, hydrogen atoms diffuse through the palladium layer, entering the body of metal hydride alloy and are stored therein. Thus, the capacity of the cell will not be reduced.
EXAMPLES
An improved metal hydride hydrogen storage alloy material including a layer of passivation material thereon was fabricated in accordance with the instant invention. More particularly, metal hydride hydrogen storage alloy material having the composition:
Lap,52Nd0,44Ce0.04Ni~.1~0.33~0.14Co0.1Fe0.41 and known as International Battery Association Common Sample No. 3 was mixed with a palladium powder. Combination of the materials was via mechanical shearing/mixing. The mixing not only produced a homogenous mixture of the two powders but by the shear force of the two phases, the softer palladium was pressed against the harder, more brittle metal hydride hydrogen storage alloy particles. As a result, the palladium powder deformed and coated the metal hydride hydrogen storage alloy particles. An example of mechanical shear/mixing is ball milling. Experiments were carried out by grinding a 10% palladium powder with the metal hydride hydrogen storage alloy powder in an agate mortar prior to being fabricated onto teflon*-bonded electrodes. The thickness of the palladium layer was about 0.5~.. The bonded, fixed electrodes were then tested against the conventional metal hydride hydrogen storage alloy electrodes described above, lacking the palladium passivating layer. The results are illustrated in FIGS. 3-5.
Referring now to FIG. 3, there is illustrated therein the potential of a palladium coated metal hydride electrode versus the potential of a conventional nickel metal hydride electrode during constant current charging at two different current levels. Specifically, lines 60 and 62 illustrate results for an electrode with and without a passivation material, respectively. Testing for both electrodes was conducted at 50 mA. Similarly, lines 64 and 66 illustrate results for passivated and unpassivated electrodes respectively, at 115 mA. From the curves illustrated on FIG. 3, it is apparent that the electrode including the * trade-mark -., P~- w0 95127315 2 7 8 4 3 7 7 p~/pg94/03496 palladium coating not only exhibited less overpotential, (at least 100 m/V
improvement over conventional metal hydride electrodes) but also required less voltage at the initial moment of the charging process.
Referring now to FIG. 4, there is illustrated therein a comparison of the charge acceptance of a conventional nickel metal hydride electrode versus that of a palladium coated metal hydride electrode. Both electrodes were charged at C rate for 30 minutes and then discharged at C/2 to measure the discharge capacity. Lines 70 and 72 illustrate results, respectively, for electrodes with and without a layer of passivation material, for tests conducted at 115 mA. Similarly, lines 74 and 76 illustrate results, respectively, for passivated and unpassivated electrodes for tests run at a C/2 rate of 58 mA. The palladium coated electrode demonstrated approximately 35% coulombic efficiency whereas the conventional electrode demonstrated that only approximately 3% of the charge was accepted. Accordingly, it may be appreciated that the palladium coated electrode is considerably more efficient than conventional metal hydride electrodes.
FIG. 5 illustrates life cycle testing for both passivated and unpassivated metal hydride hydrogen storage electrodes. Specifically, lines 80 and 82 illustrate voltage at end of discharge for passivated and unpassivated electrodes respectively. Similarly, lines 84 and 86 illustrate, respectively, capacity for passivated and unpassivated electrodes. As may be appreciated from FIG. 5, the voltage and capacity performance characteristics of both electrodes was substantially the same, except for cycle life, which was considerably longer for the passivated electrode.
While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.
Claims (14)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrode for an electrochemical hydrogen storage cell, said electrode comprising a plurality of hydrogen storage alloy material powder particles capable of electronically storing and discharging hydrogen, each said powder particle being coated with a layer of palladium or a palladium alloy passivation material.
2. An electrode as in claim 1, wherein said layer of passivation material prevents the formation of oxides on the surface of said hydrogen storage alloy material.
3. An electrode as in claim 1, wherein said passivation material is hydrogen permeable.
4. An electrode as in claim 1, wherein said hydrogen storage alloy material is an AB5 -type hydrogen storage alloy material.
5. An electrode as in claim 1, wherein said hydrogen storage alloy material is an AB2 -type hydrogen storage alloy material.
6. A method of fabricating an electrochemical hydrogen storage alloy electrode, said method comprising the steps of:
providing hydrogen storage alloy powder particles capable of reversibly, electrochemically storing and discharging hydrogen;
coating said hydrogen storage alloy powder particles with a layer of palladium or a palladium alloy, passivation material; and bonding said passivation material coated hydrogen storage alloy into an electrode.
providing hydrogen storage alloy powder particles capable of reversibly, electrochemically storing and discharging hydrogen;
coating said hydrogen storage alloy powder particles with a layer of palladium or a palladium alloy, passivation material; and bonding said passivation material coated hydrogen storage alloy into an electrode.
7. A method as in claim 6, wherein said step of coating includes vacuum depositing said layer of passivation material atop said hydrogen storage alloy.
8. A method as in claim 6, wherein said step of coating includes disposing said layer of passivation material by mechanically shearing/mixing said passivation material and said hydrogen storage alloy material.
9. A method as in claim 6, wherein said step of coating includes the electrodepositing said layer of passivation material atop said hydrogen storage alloy.
10. A method as in claim 6, wherein said step of coating includes disposing said passivation material to a thickness of between 0.1 µ and 2.0 µ.
11. An electrochemical hydrogen storage cell, comprising:
a negative electrode including a plurality of hydrogen storage alloy particles powder capable of reversibly electrochemically storing and discharging hydrogen, each said particle being coated with palladium or a palladium alloy, passivation material;
a positive electrode; and an electrolyte.
a negative electrode including a plurality of hydrogen storage alloy particles powder capable of reversibly electrochemically storing and discharging hydrogen, each said particle being coated with palladium or a palladium alloy, passivation material;
a positive electrode; and an electrolyte.
12. A cell as in claim 11, wherein said passivation material prevents the formation of oxides on the surface of said hydrogen storage alloy material.
13. A cell as in claim 11, wherein said hydrogen storage alloy material is an -type hydrogen storage alloy material.
14. An electrode as in claim 11, wherein said hydrogen storage alloy material is an AB2 -type hydrogen storage alloy material.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/US1994/003496 WO1995027315A1 (en) | 1994-03-31 | 1994-03-31 | Improved metal hydride hydrogen storage electrodes |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2184377A1 CA2184377A1 (en) | 1995-10-12 |
| CA2184377C true CA2184377C (en) | 2000-12-12 |
Family
ID=22242404
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002184377A Expired - Fee Related CA2184377C (en) | 1994-03-31 | 1994-03-31 | Improved metal hydride hydrogen storage electrodes |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0753208A1 (en) |
| JP (1) | JP3462878B2 (en) |
| KR (1) | KR970702589A (en) |
| AU (1) | AU6766794A (en) |
| CA (1) | CA2184377C (en) |
| WO (1) | WO1995027315A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0945907B1 (en) * | 1996-06-26 | 2006-07-26 | SANYO ELECTRIC Co., Ltd. | Process for producing a hydrogen storing alloy electrode |
| US5932372A (en) * | 1997-01-02 | 1999-08-03 | Lightyear Technologies Inc. | Composite materials, processes for manufacturing the composites, composite electrode, hydrogen occluding composite, and electrochemical cell utilizing the composite |
| US5865874A (en) * | 1997-06-27 | 1999-02-02 | Duracell Inc. | Hydrogen storage alloy |
| US6461766B1 (en) * | 1998-08-27 | 2002-10-08 | Ovonic Battery Company, Inc. | Hydrogen storage powder and process for preparing the same |
| KR100345036B1 (en) * | 1999-11-19 | 2002-07-24 | 한국과학기술원 | A surface-modification methode of metal hydride in Ni/MH secondary battery using flake-type Ni |
| GB0614444D0 (en) * | 2006-07-20 | 2006-08-30 | Univ Bath | Hydrogen storage |
| US8883371B2 (en) * | 2007-10-16 | 2014-11-11 | Motorola Mobility Llc | Hydrogen storage materials and hydrogen fuel cells |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4489049A (en) * | 1982-06-09 | 1984-12-18 | The United States Of America As Represented By The Secretary Of The Navy | Solid state hydrogen pumping and storage material |
| DE3313701A1 (en) * | 1983-04-15 | 1984-10-31 | Kernforschungsanlage Jülich GmbH, 5170 Jülich | LAYERING MATERIAL FOR THE STORAGE OF HYDROGEN |
| NL8303630A (en) * | 1983-10-21 | 1985-05-17 | Philips Nv | ELECTROCHEMICAL CELL WITH STABLE HYDRIDE-FORMING MATERIALS. |
| JPH0821378B2 (en) * | 1984-06-22 | 1996-03-04 | 松下電器産業株式会社 | Nickel-hydrogen storage battery |
| JPH067488B2 (en) * | 1985-12-27 | 1994-01-26 | 田中貴金属工業株式会社 | Gas diffusion electrode |
| JPH0763006B2 (en) * | 1987-04-23 | 1995-07-05 | 松下電器産業株式会社 | Method for manufacturing hydrogen storage electrode |
| JPH01129960A (en) * | 1987-11-16 | 1989-05-23 | Sanyo Electric Co Ltd | Manufacture of thin film of hydrogen storage alloy |
| US5104753A (en) * | 1989-09-11 | 1992-04-14 | Kabushiki Kaisha Toyoda Jidoshokki Seisakusho | Hydrogen storage electrode and process for producing the same |
| JP2982199B2 (en) * | 1990-02-21 | 1999-11-22 | 松下電器産業株式会社 | Hydrogen storage alloy electrode, method for producing the same, and sealed alkaline storage battery using the electrode |
| US5277999A (en) * | 1991-08-14 | 1994-01-11 | Ovonic Battery Company, Inc. | Electrochemical hydrogen storage alloys and batteries fabricated these alloys having significantly improved performance characteristics |
| US5238756A (en) * | 1990-04-26 | 1993-08-24 | Ovonic Battery Company | Electrode alloy having decreased hydrogen overpressure and/or low self-discharge |
| JPH04206348A (en) * | 1990-11-30 | 1992-07-28 | Hitachi Chem Co Ltd | Sealed secondary battery |
| JP3010950B2 (en) * | 1993-01-18 | 2000-02-21 | 松下電器産業株式会社 | Alkaline storage battery and method for manufacturing the same |
-
1994
- 1994-03-31 CA CA002184377A patent/CA2184377C/en not_active Expired - Fee Related
- 1994-03-31 EP EP94915773A patent/EP0753208A1/en not_active Withdrawn
- 1994-03-31 WO PCT/US1994/003496 patent/WO1995027315A1/en not_active Application Discontinuation
- 1994-03-31 JP JP51409095A patent/JP3462878B2/en not_active Expired - Lifetime
- 1994-03-31 AU AU67667/94A patent/AU6766794A/en not_active Abandoned
- 1994-03-31 KR KR1019960705378A patent/KR970702589A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0753208A1 (en) | 1997-01-15 |
| JP3462878B2 (en) | 2003-11-05 |
| AU6766794A (en) | 1995-10-23 |
| KR970702589A (en) | 1997-05-13 |
| WO1995027315A1 (en) | 1995-10-12 |
| CA2184377A1 (en) | 1995-10-12 |
| JPH09510569A (en) | 1997-10-21 |
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