KR20170036018A - Laves phase-related bcc metal hydride alloys and activation thereof for electrochemical applications - Google Patents

Abstract

Laveth phase-related BCC metal hydride alloys have historically limited electrochemical capacities. A new example of such an alloy useful as an electrode active material is provided. Also provided is a method of activating such an alloy. Wherein the alloy has a composition represented by the following formula (I) Ti _w V _x Cr _y M _z wherein w + x + y + z = 1, 0.1 <w <0.6, 0.1 <x <0.6, 0.01 < , B, Al, Si, Sn, and one or more transition metals to achieve a discharge capacity of at least 350 mAh / g for more than one cycle.

Description

LABES PHASE-RELATED BCC METAL HYDRIDE ALLOYS AND ACTIVATION THEREOF FOR ELECTROCHEMICAL APPLICATIONS FIELD OF THE INVENTION [0001]

Cross reference of related application

This application claims priority to and claims priority from U.S. Patent Application Serial No. 14 / 340,913, filed July 25, 2014, and U.S. Patent Application Serial No. 14 / 340,959, filed July 25, 2014, The contents of which are incorporated herein by reference.

Technical field

The present invention relates to an alloy material and a method of manufacturing the same. Specifically, the present invention relates to a metal hydride alloy material capable of absorbing and desorbing hydrogen. There is provided an activated metal hydride alloy having a Lavess phase-related body-centered cubic (BCC) structure having specific electrochemical properties including a high capacity for use in electrochemical applications.

Certain metal hydride (MH) alloy materials can absorb and desorb hydrogen. Such materials can be used as electrode materials for metal hydride batteries, including fuel cells and nickel / metal hydride (Ni / MH) and metal hydride / air battery systems, and / or as hydrogen storage media. However, due to the limited weight energy density (<110 Wh kg ^-1 ), current Ni / MH batteries are losing market share in portable electronics and battery-powered electric vehicles with lighter Li-ion technology. Because of this, next-generation Ni / MH batteries are tailored to improve two primary purposes of increasing energy density and reducing costs.

When a potential is applied between the MH anode and the cathode in the MH cell, the negative electrode material M is charged by the electrochemical absorption of hydrogen to form electrochemical emissions of MH and hydroxide ions. During the discharge, the stored hydrogen is released to form water molecules and emit electrons. The reactions taking place at the anode of a Ni / MH cell are also reversible. Most Ni / MH batteries use a nickel hydroxide anode. The following charge and discharge reactions take place in nickel hydroxide anodes.

In Ni / MH batteries having nickel hydroxide anodes and hydrogen storage cathodes, the electrodes are typically separated by nonwoven, felted, nylon or polypropylene separators. The electrolyte is usually an alkaline aqueous electrolyte, for example, 20 to 45 weight percent potassium hydroxide.

One specific group of MH materials that have utility in Ni / MH battery systems is known as AB _x class materials, meaning crystalline sites filled by their member constituent elements. AB _x type materials are disclosed, for example, in U.S. Patent 5,536,591 and U.S. Patent 6,210,498. Such materials include, but are not limited to, modified LaNi ₅ type (AB ₅ ) as well as LABES-based active material (AB ₂ ). These materials reversibly form hydrides to store hydrogen. These materials utilize a generic Ti - Zr - Ni composition wherein at least Ti, Zr, and Ni are present with at least one modifier in the group of Cr, Mn, Co, V, and Al. The materials are, but are not limited to, polyhedral materials that can include one or more Laveth-like crystal structures and other non-LABES secondary phases. Currently, AB ₅ alloys have a capacity of ~ 320 mAh g ^-1 and LABES-based AB ₂ has a capacity of 440 mAh g ^-1 or less and they have high-rate dischargeability (HRD), cycle life, charge It is the most promising alloying alternative with good balance among retention, activation, self-discharge and applicable temperature ranges.

A rare-earth (RE) magnesium-based AB ₃ - or A ₂ B ₇ -type MH alloy is a promising candidate replacing AB ₅ MH alloys currently used as negative electrodes in Ni / MH batteries due to their higher capacity. It is reported that most of the RE-Mg-Ni MH alloys are La as only rare earth metals, while A ₂ B ₇ (AB ₃ ) alloys containing only Nd have recently been reported. In these materials, AB _3.5 stoichiometric ratios are considered to provide the best overall balance of storage capacity, activation, HRD, charge retention, and cycle stability. The pressure-concentration-temperature (PCT) isotherm of an Nd-only A ₂ B ₇ alloy exhibits a very sharp take-off angle on the α-phase that can maintain a relatively high voltage during low charge conditions [K. Young, et al., Alloys Compd . 2010; 506: 831]). Compared with commercial AB ₅ MH alloys, A ₂ B ₇ with Nd alone exhibited higher anodic utilization and less resistance increase during storage at 60 ° C, but also undergone a higher capacity drop during cycling (K. Young, et al., Int . J. Hydrogen Energy , 2012; 37: 9882). Another problem with known A ₂ B ₇ alloys is that they suffer inferior HRD compared to the prior AB ₅ alloy system because of the lower Ni content in the chemical composition of the alloy.

Other AB _x materials include Lavess phase-related body center cubic (BCC) materials which are families of MH alloys with a two-phase microstructure comprising a BCC phase represented by C14 and a Lavess phase as a historical example. These materials are unfortunately based on the theoretical electrochemical capacity of 938 mAh g &lt; ^-1 &gt; for Ti-V-Cr alloys having a complete BCC structure with very poor electrochemical properties. As such, a Laveth phase with a similar chemical composition is added to the BCC material. This Laveth phase-related BCC material exhibits a higher density of phase boundaries allowing a higher hydrogen storage capacity of BCC and a combination of a better hydrogen uptake rate and a relatively higher surface catalytic activity on C14. Many studies have been undertaken to optimize these materials. Young et al., Int . J. Hydrogen Energy ], http://dx.doi.org/10.1016/j.ijhydene.2014.01.134 (paper in press) describes a systematic study of these materials with a broad range of BCC / C14 ratios . These results indicate that the electrochemical discharge capacity produced by these materials does not exceed 175 mAh / g, while these materials have many desirable properties.

As such, there is a need for improved hydrogen storage materials. As described herein below, the present invention addresses this need by first providing an activated Laveth phase-related BCC metal hydride alloy exhibiting greatly improved electrochemical properties. These and other advantages of the present invention will be apparent from the following drawings, discussion, and description.

The following summary of the invention is provided to facilitate an understanding of some innovative features of the invention and is not intended to be exhaustive of the description. A full understanding of the various aspects of the present invention may be obtained by taking the entire specification, claims, drawings, and summary in its entirety.

The alloying materials described have a significantly improved cycle life in high capacity as well as improved capacity compared to prior alloys of similar composition. While some predecessors are capable of high doses, these doses sharply decrease in 1-5 cycles. Improvements in cycle life in Laveth phase-related BCC metal hydrides have historically reduced capacity. The Lavess phase-related BCC metal hydride alloys as provided herein address the reduced capacity problem and customize the ratio of Ti to Cr in the system to demonstrate significantly improved capacity over many cycles.

The metal hydride alloy has a capacity of greater than 350 mAh / g at cycle 10 and is provided with a Laveth phase-related BCC metal hydride comprising the composition of formula (I).

&Lt; Formula (I) >

Ti _w V _x Cr _y M _z

Wherein w + x + y + z = 1, 0.1? W? 0.6, 0.1? X? 0.6, 0.01? Y? 0.6 and M is selected from the group consisting of B, Al, Si, Sn and transition metal. Some aspects have a capacity of 400 mAh / g or more, optionally 420 mAh / g or more in cycle 10. The alloy optionally contains less than 24% C14 phase. In some aspects, the alloy is primarily a combination of a BCC phase and a Laveth phase, wherein the BCC phase has an abundance ratio of greater than 5% and less than 95%, and wherein the Laveth phase has an abundance ratio of greater than 5% and less than 95%. Optionally, the alloy comprises a BCC phase crystallite size of less than 400 angstroms, and optionally less than 200 angstroms. In some aspects, the B / A ratio is from 1.20 to 1.31, optionally from 1.20 to 1.30. Optionally, the ratio x / y is from 1 to 3. Certain aspects of any of the foregoing include compositions of formula (II).

&Lt; Formula (II) >

Ti _{13.6 + x} Zr _2.1 V ₄₄ Cr _{13.2- x} M _27.1

Where x is a value greater than 0 and less than or equal to 12, and M is a combination of Mn, Fe, Co, Ni, and Al. The alloys of formula (II) optionally have x of 2, 4, 6, 8, 10 or 12. Some of the foregoing aspects include the composition of Formula III.

&Lt; Formula (III) >

Ti _{0 .4 + x / 6} Zr _{0 .6-x / 6} Mn _{0 . 44} Ni _{1 . 0} Al _{0 . 02 Co 0 .09 (VCr 0.} 3 Fe 0. 063) x

Where x is 0.7 to 2.8.

The provided alloys and their equivalents represent superior materials for use in the anode of a battery or battery system.

Also provided is a method useful for generating an increased stable capacity over the prior art. As such, placing the Laveth phase-associated BCC metal hydride alloy in an atmosphere containing hydrogen at hydrogen pressure; And cooling the alloy during the laying so as to produce an activated metal hydride alloy having a level of capacity that is not achieved by the prior activation method of greater than 200 mAh / g. &Lt; RTI ID = 0.0 &gt; A method of activating the relevant BCC metal hydride alloy is provided.

&Lt; Formula (I) >

Ti _w V _x Cr _y M _z

Wherein w + x + y + z = 1, 0.1? W? 0.6, 0.1? X? 0.6, 0.01? Y? 0.6 and M is selected from the group consisting of B, Al, Si, Sn and transition metal. In some aspects, the cooling step is at a maximum activation temperature of 300 degrees Celsius or less. The atmosphere is optionally at a hydrogenation pressure of at least 1.4 megapascals, optionally at least 6 megapascals. The present method produces an activated metal hydride alloy having an arbitrarily greater than 300 mAh / g, optionally greater than 350 mAh / g, optionally greater than 400 mAh / g and optionally greater than 450 mAh / g. In some aspects, the activated metal hydride alloy has a C14 phase of less than 24%. In some aspects, the activated metal hydride alloy is primarily a combination of a BCC phase and a Laveth phase, the BCC phase has an abundance ratio of greater than 5% and less than 95%, and the Laveth phase has an abundance ratio of greater than 5% and less than 95%. Optionally, the activated metal hydride alloy comprises a BCC phase crystallite size of less than 400 angstroms. In any of the foregoing or combinations thereof, the Laveth phase-related BCC metal hydride alloy is optionally of formula (II).

&Lt; Formula (II) >

Ti _{0.4 + x / 6} Zr _{0.6-x / 6} Mn _0.44 Ni _1.0 Al _0.02 Co _0.09 (VCr _0.3 Fe _0.063 ) _x

Where x is 0.7 to 2.8. In any of the foregoing, or in any combination thereof, the Laveth phase-related BCC metal hydride alloy is optionally of formula (III).

&Lt; Formula (III) >

Ti _{0.4 + x / 6} Zr _{0.6-x / 6} Mn _0.44 Ni _1.0 Al _0.02 Co _0.09 (VCr _0.3 Fe _0.063 ) _x

Where x is 0.7 to 2.8.

Figure 1a shows the alloy phase distribution as observed in the SEM image of the hydrogen storage alloy P8.
Figure 1B shows the alloy phase distribution as observed in the SEM image of hydrogen storage alloy P9.
1C shows the alloy phase distribution as observed in the SEM image of hydrogen storage alloy P10.
Figure 1d shows the alloy phase distribution as observed in the SEM image of hydrogen storage alloy P11.
Figure 1e shows the alloy phase distribution as observed in the SEM image of the hydrogen storage alloy P12.
1F shows the alloy phase distribution as observed in the SEM image of the hydrogen storage alloy P13.
Figure 1G shows the alloy phase distribution as observed in the SEM image of hydrogen storage alloy P14.
Figure 2a shows the principal element and metal ratio on C14 as a function of Ti-content in the alloy design.
Figure 2b shows the principal component and metal ratio on the BCC as a function of the Ti content in the alloy design.
Figure 3a shows the microstructure of a hydrogen storage alloy which is activated to provide improved electrochemical properties and exhibits two main phases, C14 and BCC;
Figure 3b shows the FWHM of the BCC (110) peak from the hydrogen storage alloy and the control, which is activated to provide improved electrochemical properties and to illustrate the reduced crystallite size of the activated alloy by an exemplary method as described herein;
Figure 4 is a larger atom A- 4 f - to occupy a smaller B- atoms seat 2 a - position (A2B layer a) and 6 h - position (B3 layer a) occupied by the other hand along the axis c A2B stacked alternately and the layer B3 Lt; RTI ID = 0.0 &gt; C14 &lt; / RTI &gt;
Figure 5 shows the FWHM of the BCC (110) peak from the hydrogen storage alloy and the control, which is activated to provide improved electrochemical properties and to illustrate the reduced crystallite size of the activated alloy by an exemplary method as described herein;
Figure 6 depicts the gaseous hydrogen storage characteristics of various alloy materials formed by the exemplary method as described herein;
Figure 7a shows the vapor phase hydrogen storage characteristics of various alloying materials;
Figure 7b shows the vapor phase hydrogen storage characteristics of various alloying materials;
8A shows the half cell discharge capacity measured at 4 mA / g for the first 13 cycles;
Figure 8b shows the high-efficiency discharge (HRD) in the first 13 cycles;
Figure 9 shows the hydrogen storage capacity converted from the gaseous hydrogen storage electrochemically measured as a function of the number of alloys;
Figure 10 shows the diffusion coefficient and the C14-phase crystallite size as a function of the number of alloys indicating the tendency of hydrogen to diffuse more readily in alloys with smaller C14-phase crystallites.

The following description of a particular aspect (s) is by no means intended to limit the scope of the present invention, its application, or uses, which are merely exemplary and, of course, may vary. The present invention is described herein in the context of non-limiting definitions and terms incorporated herein. These definitions and terms are not intended to function either as a limitation of the scope or practice of the invention, but are for explanation and technical purposes only. While the method or composition is described in the order of the individual steps or using specific materials, the steps or materials may be interchanged such that the description of the invention may include multiple portions or steps arranged in many ways as readily understood by those skilled in the art It is understood that this is possible.

When an element is referred to as being "on " another element, it will be understood that it may be directly on the other element or there may be an intervening element therebetween. In contrast, if an element is referred to as being "directly on" another element, there is no intervening element.

Although the terms "first," "second," "third," etc. may be used herein to describe various elements, components, regions, layers, and / or sections, , And / or sections are not to be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, a "first element," "component," "region," "layer," or "section" discussed below may be replaced with another element, component, region, layer or section without departing from the teachings herein. , &Lt; / RTI &gt; or a section.

The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms, unless the context clearly dictates otherwise. Quot; or "means" and / or ". As used herein, the terms "and / or" include any and all combinations of one or more of the listed listed items. The terms "comprising" and / or "comprising" or "comprising" and / or "comprising" when used herein are to be interpreted as referring to the stated features, Or " an ") element, but it will be understood that they do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and / The term "or a combination thereof" means a combination comprising at least one of the foregoing elements.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It should be understood that commonly used terms as defined in the preamble should be construed as having a meaning consistent with its meaning in the context of the relevant technical field and the present disclosure and should not be construed as being idealized or overly formal, It will be understood further.

Hydrogen storage alloys with Laveth-phase-related BCC structures have been studied for some time to see how they promote the synergistic effect between the C14 and BCC phases of the system. Previous studies that replace A- and B-site elements have been performed on a number of mixed phase alloys found to increase or decrease the C14 phase abundance ratio in part. The refinement of the composition continued in a manner that improved both the meteorological and electrochemical hydrogen storage properties of these alloys. While these efforts have achieved some success and often mixed conclusions, achieving capacities of greater than 200 mAh / g remains unchallenged. The alloys provided herein exhibit a simple and elegant solution to this problem by representing hydrogen storage alloys of materials of the Laveth-phase related BCC structure exhibiting good electrochemical properties.

There is provided a hydrogen storage alloy having a Laveth phase-related BCC structure exhibiting excellent electrochemical properties that are unexpectedly superior to those of similar compositions. There is provided a Laveth-phase related BCC metal hydride alloy of the composition of formula (I).

&Lt; Formula (I) >

Ti _w V _x Cr _y M _z

Wherein w + x + y + z = 1, 0.1? W? 0.6, 0.1? X? 0.6, 0.01? Y? 0.6 and M is selected from the group consisting of B, Al, Si, Sn and one or more transition metals do. The alloy is activated by a specific method to promote the formation of an increased BCC phase in the resulting material and to limit the AB ₂ phase. What is obtained is an activated metal hydride alloy having improved electrochemical properties comprising a capacity of 200 mAh / g or more, optionally 350 mAh / g or more in cycle 10. [

Optionally a Laveth-phase related BCC metal hydride alloy of the formula II.

&Lt; Formula (II) >

Ti _{13.6 + x} Zr _2.1 V ₄₄ Cr _{13.2- x} M _27.1

Where x is a value greater than 0 and less than or equal to 12, and M is a combination of Mn, Fe, Co, Ni, and Al. Optionally x is any value greater than 0 and less than or equal to 12, including 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, In some aspects, x is 2, 4, 6, 8, 10, or 12. Optionally, x is 2 or 4.

Optionally, the Laveth-phase related BCC metal hydride alloy is of the composition of formula (III).

&Lt; Formula (III) >

Ti _{0.4 + x / 6} Zr _{0.6-x / 6} Mn _0.44 Ni _1.0 Al _0.02 Co _0.09 (VCr _0.3 Fe _0.063 ) _x

Where x is 0.7 to 2.8.

In some aspects, the Laveth-phase related BCC metal hydride alloys have a specific surface area of greater than 200 mAh / g, optionally 220 mAh / g, 240 mAh / g, 260 mAh / g, 280 mAh / g, 300 mAh / g, 340 mAh / g, 350 mAh / g, 360 mAh / g, 370 mAh / g, 380 mAh / g, 390 mAh / g, 400 mAh / mAh / g, 420 mAh / g, 430 mAh / g, 440 mAh / g, and 450 mAh / g. Optionally, the metal hydride alloy comprises a capacity of 200 to 450 mAh / g. Optionally, the activated metal hydride alloy comprises a capacity of 200 to 450 mAh / g. Optionally, the metal hydride alloy comprises a capacity of 300 to 450 mAh / g. Optionally, the activated metal hydride alloy comprises a capacity of 300 to 380 mAh / g. Optionally, the metal hydride alloy comprises a capacity of 350 to 450 mAh / g. Optionally, the metal hydride alloy comprises a capacity of 400 to 450 mAh / g. Optionally, the metal hydride alloy comprises a capacity of 400 to 420 mAh / g. In some aspects, any of the above-described capacities may optionally comprise more than one cycle, optionally 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 19, 20, or more cycles. Optionally, the metal hydride alloy has a capacity of at least 350 mAh / g at cycle 10, optionally at least 400 mAh / g at cycle 10, and optionally at least 420 mAh / g at cycle 10.

In addition to the composition of the material, the lack of oxidation compared to its physical structure and similar chemical composition of the preceding alloy materials promotes the excellent electrochemical properties of the metal hydride alloys. The metal hydride alloy is optionally formed mainly of BCC phase and Laveth phase structure. Without being limited to one particular theory, it is believed that the dominance of the BCC phase and Laveth phase structure increases the synergistic effect caused by the presence of the two phases. As such, the metal hydride alloys optionally produced by the process disclosed herein optionally have a BCC phase of greater than 5% and an abundance ratio of less than 95%, a Laveth phase of greater than 5% and less than 95% A BCC phase and a Laveth phase combination that are greater than 50% of the material structure. Optionally, the BCC phase may comprise 10% to 95%, 20% to 95%, 30% to 95%, 40% to 95%, 50% to 95%, 60% to 95%, 70% to 95% To 95%, and in any such case the LABES phase is optionally greater than 5%. Optionally, the Laveth phase may comprise 10% to 95%, 20% to 95%, 30% to 95%, 40% to 95%, 50% to 95%, 60% to 95%, 70% to 95% % To 95%, and in any such case the BCC phase is optionally greater than 5%. In some aspects, the composition comprises less than 30%, optionally less than 25%, optionally less than 24%, optionally less than 20%, optionally less than 15%, optionally less than 14%, optionally less than 13% % C14 Lavess phase.

The hydrogen storage alloy is provided with a crystallite size on the BCC that is small enough to allow a large intergranular region to promote electrochemical properties and a higher synergistic linkage between the storage and catalyst phases. The alloys provided may have a thickness of 400 Å or less, optionally 390 Å or less, optionally 380 Å or less, optionally 370 Å or less, optionally 360 Å or less, optionally 350 Å or less, optionally 340 Å or less, optionally 330 Å or less, Optionally up to 320 Å, optionally up to 310 Å, optionally up to 300 Å, optionally up to 290 Å, optionally up to 280 Å, optionally up to 270 Å, optionally up to 260 Å, optionally up to 250 Å, optionally Optionally less than 240 A, optionally less than 230 A, optionally less than 220 A, optionally less than 210 A, optionally less than 200 A, optionally less than 19 A, optionally less than 180 A, optionally less than 170 A, Or less, optionally less than 150 A, optionally less than 140 A, optionally less than 130 A, optionally less than 120 A. Optionally, the crystallite size on the BCC is 200 A to 300 A. Optionally, the crystallite size on the BCC is from 120 A to 300 A. Optionally, the crystallite size on the BCC is 120 A to 200 A. Optionally, the crystallite size on the BCC is from 120 A to 160 A. Optionally, the crystallite size on the BCC is from 140 A to 160 A.

The physical, structural, and electrochemical properties of the hydrogen storage alloy are promoted by preventing too much Laves phase from forming in the material, increasing the amount of BCC phase structure in the material, or by a combination thereof. As such, a method of activation (hydration) of a Laveth phase-associated BCC metal hydride alloy of formula I, formula II, or formula III is provided. The method comprises the steps of placing a Laveth-phase-related BCC metal hydride alloy in an atmosphere containing hydrogen at hydrogenation pressure, and producing an activated metal hydride alloy having a desired capacity, preferably 200 mAh / g or more, , And cooling the alloy at the same time. The step of placing the Laveth phase-associated BCC metal hydride alloy in hydrogen at increased pressure will increase the temperature of the material due to the exothermic nature of the hydride formation reaction. It has been found that allowing the temperature of the alloy to increase in an uncontrolled manner is detrimental to the resulting electrochemical properties of the activated alloy. As such, in some aspects, the alloy is hydrogenated by a method comprising an active cooling step. Without being limited to one particular theory, controlling the temperature of the material during hydration promotes excess AB _two- phase structure from being formed in the alloy during activation. Temperature control is accomplished, for example, by cooling the reaction vessel with a water jacketed system or bath, or by other methods known in the art. Optionally, the reaction temperature of the alloy does not exceed 300 ° C.

In some aspects, the temperature of the alloy is maintained during the hydrogenation from room temperature to optional 300 ° C, optionally 295 ° C, optionally 290 ° C, optionally 285 ° C, optionally 280 ° C, optionally 275 ° C, optionally 270 ° C, optionally 260 Optionally 200 ° C, optionally 250 ° C, optionally 240 ° C, optionally 230 ° C, optionally 220 ° C, optionally 210 ° C, optionally 200 ° C, optionally 190 ° C, optionally 180 ° C, optionally 170 ° C, optionally 160 Optionally at 150 ° C, optionally at 140 ° C, optionally at 130 ° C, optionally at 120 ° C, optionally at 110 ° C, optionally at 100 ° C, optionally at 90 ° C, optionally at 80 ° C, optionally at 70 ° C, Lt; 0 &gt; C, optionally 50 &lt; 0 &gt; C, optionally 40 &lt; 0 &gt; C, In some aspects, the alloy is maintained at room temperature to 300 &lt; 0 &gt; C during hydrogenation, or any value or range therebetween.

Increasing the hydrogen pressure has also been found to be useful in promoting the formation of increased amounts of BCC on the resulting activated hydrogen storage alloy. As such, the hydrogenation of some aspects of the Laveth-phase-related BCC metal hydride alloys requires hydrogenation of at least 1.4 MPa, optionally at least 1.5 MPa, optionally at least 1.8 MPa, optionally at least 2 MPa, optionally at least 3 MPa, At a hydrogenation pressure of at least 4 MPa, optionally at least 5 MPa, optionally at least 6 MPa.

In some aspects, the Laveth phase-related BCC metal hydride alloys are hydrogenated using both a hydrogenation pressure of greater than 1.4 MPa and temperature control below 300 占 폚. As such, the alloy is heated to 300 ° C, optionally 295 ° C, optionally 290 ° C, optionally 285 ° C, optionally 280 ° C, optionally 275 ° C, optionally 270 ° C, optionally 260 ° C, optionally 250 ° C, Optionally 160 ° C, optionally 150 ° C, optional 240 ° C, optionally 230 ° C, optionally 220 ° C, optionally 210 ° C, optionally 200 ° C, optionally 190 ° C, optionally 180 ° C, Optionally at 120 캜, optionally at 110 캜, optionally at 100 캜, optionally at 90 캜, optionally at 80 캜, optionally at 70 캜, optionally at 60 캜, optionally at 50 캜, optionally at 140 캜, optionally at 130 캜, The alloy is optionally activated with a hydrogenation pressure of 1.4 MPa to 6 MPa or higher. In any of the above temperature ranges the hydrogenation pressure may optionally be between 6 MPa and optionally 1.4 MPa, optionally 1.5 MPa, optionally 1.6 MPa, optionally 1.7 MPa, optionally 1.8 MPa, optionally 1.9 MPa, optionally 2 MPa, Optionally 2.1 MPa, optionally 2.2 MPa, optionally 2.3 MPa, optionally 2.4 MPa, optionally 2.5 MPa, optionally 2.6 MPa, optionally 2.7 MPa, optionally 2.8 MPa, optionally 2.9 MPa, optionally 3 MPa, Optionally 3.1 MPa, optionally 3.2 MPa, optionally 3.3 MPa, optionally 3.4 MPa, optionally 3.5 MPa, optionally 3.6 MPa, optionally 3.7 MPa, optionally 3.8 MPa, optionally 3.9 MPa, optionally 4 MPa, Optionally 4.1 MPa, optionally 4.2 MPa, optionally 4.3 MPa, optionally 4.4 MPa, optionally 4.5 MPa, optionally 4.6 MPa, optionally 4.7 MPa, optionally 4.8 MPa, optionally 4.9 MPa, 5 MPa, an optionally 5.1 MPa, 5.2 MPa, optionally, optionally 5.3 MPa, 5.4 MPa, optionally, optionally 5.5 MPa, 5.6 MPa, optionally, optionally 5.7 MPa, 5.8 MPa, optionally, optionally 5.9 MPa. In some aspects, the hydrogenation pressure is at least 6 MPa.

The resulting activated hydrogen storage alloy produced by the provided method possesses a capacity of almost twice and often more than twice the capacity of formally similar materials prepared in the conventional manner.

The various aspects of the invention are illustrated by the following non-limiting examples. The embodiments are for illustrative purposes and are not limitations on any implementation of the invention. It will be understood that variations and modifications may be made without departing from the spirit and scope of the invention.

Experiment

Metal hydride alloys of the series of formula I or II were prepared and hydrated according to various conditions in connection with a series of experiments that illustrate the principles of the present invention. The raw materials were melted under continuous argon flow conditions using a non-consumable tungsten electrode and a water cooled copper tray. Prior to formation, a piece of sacrificial titanium was placed in several melt-cooling cycles to reduce the residual oxygen concentration in the system. The research ingots are then placed in some re-melting cycles while being turned to ensure uniformity in chemical composition.

The chemical composition of an alloy sample prepared using a Varian Liberty 100 Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) was measured according to principles known in the art. The ICP results from ingots prior to activation in atomic percent increments are shown in FIG.

<Table 1: Design compositions and ICP results>

The as-cast composition has good agreement with the composition as designed. The alloys of the previous series showed unevenness in the Cr content, which was improved by increasing power during arc melting. The measured B / A ratio of the alloys of this series (P8-P14) varied from 2.61 to 5.36, the range of which is described in Young et al., Int . J. Hydrogen Energy , http://dx.doi.org/10.1016/j.ijhydene.2014.01.134] (paper in the press).

Phase distribution and composition

JEOL-JSM6320F scanning electron microscope with energy dispersive spectroscopy (EDS) capability was used to investigate the distribution and composition of alloy phases. Samples were mounted, polished on epoxy blocks, rinsed and dried before entering the SEM chamber. Backscattering electron images are shown in Figures la-g. Several areas were selected for study by EDS, each of which is numbered in Figures 1a-g. The results of the EDS measurements are shown in FIG. 2, which illustrate the compositions of composition P8-P14 in Figures 1a-1g, respectively.

< Table 2: Summary of EDS results>

All compositions are expressed as atomic percentages. The compositions on C14 and BCC are in italic and bold, respectively.

As the Ti content in the alloy increases, both the grain size on BCC and C14 decrease and then increase. Unreacted metal Zr is found in the first few alloys (Fig. 1a spot 5). In addition, an increase in the Ti-content produced an increase in the C14 phase abundance ratio, so less pure Zr can be found in the final sample. The TiNi phase begins to appear in alloys P13 and P14, which are the alloys with the highest Ti content in the study, as shown in Figures 1f-3 and 1g-3.

In Figure 2a, the Zr-, Ti-, V-, Ni- content and B / A ratio on C14 were plotted. As the overall Ti-content in the alloy increases, the Ti-content on C14 linearly increases while the Zr-content decreases; Ni-content decreased and stabilized; V-content was maintained at the level; The B / A ratio decreased uniformly from 2.1 to 1.5.

Hydriding

The alloy of P8-P14 was placed under various activation conditions by varying the maximum temperature of the alloy during activation through the cooling system, changing the hydrogen pressure, or both. The four activation methods are shown in Table 3.

< Table 3: Exemplary activation conditions>

The active alloys of the control group using the conventional activation method and those prepared according to the methods of Examples 1-3 were analyzed for the hydrogen storage properties and the electrochemical properties as well as the structural arrangement.

XRD  analysis

The microstructure of the alloy was studied using a Philips X'Pert Pro x-ray diffractometer. The XRD patterns of all seven alloys P8-P14 are shown in Fig. 3A (a-g, respectively). It is clear that both C14 and BCC diffraction peaks are observed. Increasing V in the alloy corresponds to a decrease in the BCC peak in intensity and a shift to a lower angle, and an increase in the C14 peak in intensity and a shift in the same direction as the BCC peak.

The XRD pattern of hydrogenated P8 under various conditions (control and Example 1-3) is shown in Figure 3b. Two sets of diffraction peaks of C14 and BCC are observed, indicating the importance of this structure in the overall system.

Crystalline sizes of each phase were obtained from all alloy samples from the full pattern fitting of XRD data using the Rietveld method and Jade 9 software. The two-phase lattice constants calculated from the XRD pattern are listed in Table 4 and plotted in FIG.

< Table 4: >

As the amount of Ti is increased, it showed the lattice constant a for both the lattice constants a and c and the increase of the BCC phase C14. On C14, the c / a ratio increased, stabilized, and decreased with increasing Ti content. Anisotropic growth of the C14 unit cell takes place from the partial substitution of the relatively larger spot Ti A- B- place Cr (metallic radius of the metal alloy of the AB ₂ 1.423 Å) to (the radius of 1.614 Å). The lattice constant a on the BCC increased from 2.9683 to 3.0165 Å as the V - content in the alloy increased.

Table 4 also shows the crystallite size of each phase in the P8-P14 alloy. As the Ti-content in the alloy increased, the abundance ratio on C14 increased from 11.0 to 56.4 wt% and slightly decreased to 52.5 wt% in alloy P14. The BCC phase showed the opposite trend from P8 to P14, falling from 89.0% to 47.5%. At the same time, the C14 crystallite size initially increased and decreased while the BCC crystallite size decreased uniformly.

Figure 4 shows the FWHM of BCC peak 110 for sample P8, which varies between the control and the samples hydrogenated by the methods of Examples 1-3. The calculated crystallite size on the BCC is shown in Fig.

TABLE 5 Crystallite Size on BCC (110)

Each exemplary hydrogenation material showed a crystallite size on the BCC of less than 300 ANGSTROM.

The lattice constants a and c from each hydrogenated P8 sample are listed in Table 6.

<Table 6>

Weather feature

The gas-phase hydrogen storage properties of the control and of Examples 1-3 were measured using a Suzuki-Shokan multi-channel pressure-concentration-temperature (PCT) system. The PCT isotherms were then measured at 30 캜 and 60 캜. The resulting absorption and desorption isotherms for the hydrogenated alloy P8 according to the control and according to Example 1 are shown in Fig. Depending on the control, the hydrogenated P8 alloy exhibits significant hysteresis and does not exceed 1.1% by weight of hydrogen after activation. The same material activated by the method of using the same hydrogen gas pressure but controlling the maximum temperature of the alloy during activation to not exceed 300 캜 shows the completion of the second plateau and a hydrogen weight percentage of more than 1.5%.

PCT isotherm hysteresis is defined as P _a and P _d is the absorption and desorption equilibrium pressure at each midpoint of the desorption _{isotherm, ln (P a / P d} ). Hysteresis can be used to predict the grinding speed of the alloy during cycling. Alloys with larger hysteresis have a higher grinding rate during the hydriding / dehydriding cycle. From hysteresis, a large increase in cycle stability is expected by activation according to the method of Examples 1-3. Specifically, by cooling the ingot during activation so that the maximum temperature does not exceed 300 DEG C, the hysteresis decreases significantly.

The alloys of P8-P14 are similarly hydrogenated for the PCT study. All samples are activated with one thermal cycle in the presence of hydrogen at a maximum pressure (5.0 MPa). The resulting measurement did not significantly change the PCT characteristics. The resulting absorption and desorption isotherms measured at 30 and 60 [deg.] C are shown in Figures 7a and b. As shown in Figure 7a, as a comparative material, sample P8 * was activated and measured at a maximum hydrogen pressure fixed at 1.1 MPa, while all other samples were measured up to 5 MPa. The information obtained from the PCT study is summarized in Table 7.

< Table 7 > Summary of meteorological and thermodynamic properties>

The desorption pressure, hysteresis, and thermodynamic properties were calculated at 1.3 wt% for P8-P10 and at 1.5 wt% for P11-P14.

The equilibrium pressures of the desorption curves at 1.3 and 1.5 wt% hydrogen storage were used as Plateau pressures for alloys P8-P10 and alloys P11-P14, respectively; They showed a tendency to decrease with increasing Ti content. Lower equilibrium pressures arise from the extended unit cells in both BCC and C14 phases. PCT isotherm hysteresis is defined as P _a and P _d is the absorption and desorption equilibrium pressure of hydrogen storage density in the respective _{reference, ln (P a / P d} ). In general, hysteresis decreases as the Ti content increases, which is expected to increase cycle stability by reducing crushing during cycling. As the Ti-content increases, the maximum capacity increases due to the larger unit cell size and its ability to accommodate more hydrogen; The reversible hydrogen storage capacity decreases due to the increase in the metal-hydrogen bond strength (judged from the lower equilibrium pressure). The desorption equilibrium pressures at 30, 60, and 90 &lt; 0 &gt;

ΔG =ΔH - TΔS = RTln P (2)

Is used to evaluate the change in enthalpy (? H ) and entropy (? S ) by R, where R is the ideal gas constant and T is the absolute temperature. The results of these calculations are listed in Table 7. Values are primarily useful for comparison between these alloys. As the Ti content in the alloy increases, both -Δ H and -Δ S decrease initially and then increase. Δ H values are not correlated with the plateau pressure, which is observed in rare cases that different one days lead alloy. Δ S is an indication of how far the MH system is from a perfect, ordered state (disordered). The theoretical value of Δ S is the entropy of hydrogen gas, close to -135 J mol ^{- 1} K ^-1 . It is an alloy having a more equal and C14 abundance BCC (P13 and P14) does not have the highest value of Δ S is interesting. Instead, the alloy P10 and P11 having a high density of BCC / C14 grain boundaries to have a highest Δ S.

Electrochemical characterization

The discharge capacities of the respective alloys were measured in a flooded-cell arrangement for the partially pre-charged Ni (OH) ₂ anode. For half-cell electrochemical studies, each ingot was first crushed and then passed through a 200-mesh sieve. The powder sieved on a nickel metal substrate expanded with a 10-tone press was then compressed to form a test electrode (about 1 cm ² area and 0.2 mm thickness) without using any binder. This allowed an improved measurement of the activation behavior. The discharge capacity of a small electrode obtained from a partially pre-filled Ni (OH) ₂ pasted electrode as an anode and a 6M KOH solution as an electrolyte was measured. Each sample electrode is charged at a constant current density of 50 mA / g for 10 h followed by two pulls at 12 and 4 mA / g after discharge at a current density of 50 mA / g. A full capacity (4 mA / g) from the first 13 cycles was plotted in Figure 8a to study the activation and cycling behavior of these alloys. Activation of the alloy is facilitated by a reduction in the BCC abundance ratio and Cr-content due to the corrosion resistance of the BCC phase and the corrosion resistance of Cr to KOH compared to the C14 phase. Reduced corrosion resistance aids activation but also reduces cycle stability.

The capacities from the 50 and 4 mA g ^-1 discharge rates measured at 4 ^th and 2 ^nd cycles, respectively, are listed in Table 8.

< Table 8: Summary of electrochemical properties>

All of the capacity increased with increasing overall Ti content and then decreased. The highest capacity, 463 mAh / g, was measured as alloy P12. When the gas phase capacity is converted to the theoretical electrochemical capacity and plotted against the number of alloys together with the measured electrochemical storage capacity, the 4 mA / g (low velocity) curve moves along the maximum gas phase capacity and reaches 50 mA / g High velocity) curve moves along the reversible vapor capacity (Figure 9). In these plots, the vapor capacity is

1 wt% H ₂ = 268 mAh g ^{- 1} (3)

To an electrochemical capacity.

The electrochemical capacity of this series of alloys is between the boundaries set by similar maximum and reversible vapor capacities to other MH systems after the sample is put into full activation by the 5 MPa hydrogenation process.

Lt; RTI ID = 0.0 &gt; 50 mA / g &lt; / RTI &gt; versus the discharge capacity measured at 4 mA / g, Half cell HRD values for each alloy were measured in a stabilized 4 ^th cycle and are listed in Table 8. With the exception of P10, the HRD of all alloys is stabilized within 4 cycles. As the Ti content in the alloy increases, the HRD rapidly decreases. The increase in catalytic C14 phase abundance does not contribute to HRD performance. Comparing the HRD of P8 * and P8, the inventors found that the electrochemical HRD of P8 * is higher, despite the lower hydrogen pressure used during activation and its lower reversibility in the gas phase (FIG. 7A). The inventors can attribute this observation to the different phases in the alloy. The two pressure plateways observed in the PCT curve can be related to two different phases. The first phase (0.3 to 1.0 wt.% In FIG. 7A) having a lower Plateau pressure has a better velocity capability than the second phase (1.0 to 1.6 wt.% In FIG. 7A). The C14 phase is believed to be more catalytic than the BCC phase. Thus, the inventors confer the BCC phase on the phase with C14 phase and the phase with higher Platow pressure on the phase with lower platow pressure. The increasing range of the first plateau is consistent with the increase in the C14 phase abundance ratio and the decreasing range of the second plateau is consistent with the decrease in the BCC onset ratio induced by XRD analysis (Table 4).

The bulk diffusion coefficient ( D ) and surface exchange current ( I _o ) were electrochemically measured to study the reason for HRD reduction with increased Ti content. Details of all measurements were previously reported in F. Li, K. Young, T. Ouchi, MA Fetcenko, J. Alloys Compd. 471 (2009) 371-7], and the values are listed in Table 8. The D value and C14 crystallite size were plotted against the number of alloys in Fig. D values tend to increase with increasing Ti content while C 14 crystallite sizes tend to decrease. This general trend suggests that the smaller crystallite size of catalytic C14 allows for the formation of more intergranular regions that facilitate proton transfer and increase the D value.

The patents, publications, and applications mentioned in this specification are indicative of the level of ordinary skill in the art to which this invention pertains. Such patents, publications, and applications are incorporated herein by reference as if each individual patent, publication, or application was specifically and individually incorporated by reference herein.

In view of the foregoing, it will be understood that other modifications and variations of the present invention may be practiced. The foregoing drawings, discussion, and description are intended to illustrate some specific aspects of the invention, but are not meant to be limiting. It is the following claims, including all equivalents, that define the scope of the invention.

Claims (24)

Having a capacity of more than 200 milliampere hours per gram in cycle 10,
A Laveth phase-related BCC metal hydride alloy comprising the composition of formula (I).
&Lt; Formula (I) >
Ti _w V _x Cr _y M _z
Wherein w + x + y + z = 1, 0.1? W? 0.6, 0.1? X? 0.6, 0.01? Y? 0.6, and M is selected from the group consisting of B, Al, Si, Sn and a transition metal ) 2. The alloy of claim 1, wherein the alloy has a capacity of at least 350 milliamperes per gram. The alloy of claim 1, wherein the alloy has a capacity of at least 400 milliampere hours per gram. The alloy of claim 1, wherein the alloy has a capacity of at least 420 milliamperes per gram. 5. The alloy according to any one of claims 1 to 4, comprising less than 24% C14 phase. 5. The method of any one of the preceding claims wherein the metal hydride alloy is primarily a combination of a BCC phase and a Laveth phase wherein the BCC phase has an abundance ratio of greater than 5% and less than 95% % And an abundance ratio of less than 95%. 5. The alloy according to any one of claims 1 to 4, comprising a BCC phase crystallite size of less than 400 angstroms. 5. The alloy according to any one of claims 1 to 4, comprising a BCC phase crystallite size of less than 200 angstroms. 5. The alloy according to any one of claims 1 to 4, comprising a B / A ratio of 1.20 to 1.31. The alloy according to any one of claims 1 to 4, wherein x / y is from 1 to 3. 5. Alloy according to any one of claims 1 to 4, comprising a composition of formula (II).
&Lt; Formula (II) >
Ti _{13.6 + x} Zr _2.1 V ₄₄ Cr _{13.2- x} M _27.1
(Where x is a value of more than 0 and not more than 12, and M is a combination of Mn, Fe, Co, Ni, and Al) 11. An alloy according to claim 10, wherein x is 2, 4, 6, 8, 10 or 12. 11. The alloy according to claim 10, wherein x is 2 or 4. 5. Alloy according to any one of claims 1 to 4, comprising a composition of formula (III).
&Lt; Formula (III) >
Ti _{0.4 + x / 6} Zr _{0.6-x / 6} Mn _0.44 Ni _1.0 Al _0.02 Co _0.09 (VCr _0.3 Fe _0.063 ) _x
(Where x is 0.7 to 2.8) (i) placing the Laveth phase-related BCC metal hydride alloy in an atmosphere containing hydrogen at hydrogen pressure; And
(ii) cooling said alloy during said laying to produce an activated metal hydride alloy having a capacity greater than 200 milliampere hours per gram
Wherein the Lattice phase-associated BCC metal hydride alloy of formula (I)
&Lt; Formula (I) >
Ti _w V _x Cr _y M _z
Wherein w + x + y + z = 1, 0.1? W? 0.6, 0.1? X? 0.6, 0.01? Y? 0.6, and M is selected from the group consisting of B, Al, Si, Sn and a transition metal ) 16. The method of claim 15, wherein the cooling step is at a maximum activation temperature of 300 degrees Celsius or less. 16. The process of claim 15, wherein the hydrogenation pressure is at least 1.4 megapascals. 16. The process of claim 15, wherein the hydrogenation pressure is at least 6 megapascals. 19. The method of any one of claims 15 to 18, wherein the activated metal hydride alloy has a capacity of 300 milliampere hours per gram or more. 19. The method of any one of claims 15 to 18, wherein the activated metal hydride alloy has a capacity of at least 350 milliampere hours per gram. 19. The method according to any one of claims 15 to 18, wherein the activated metal hydride alloy has a C14 phase of less than 24%. 19. The method of any one of claims 15-18, wherein the activated metal hydride alloy is primarily a combination of a BCC phase and a Laveth phase, the BCC phase has an abundance ratio of greater than 5% and less than 95% Wherein the phase has an abundance ratio of greater than 5% and less than 95%. 19. The method of any one of claims 15 to 18, wherein the activated metal hydride alloy comprises a BCC phase crystallite size of less than 400 Angstroms. 19. A process according to any one of claims 15 to 18, wherein the Laveth phase-related BCC metal hydride alloy is of formula III.
&Lt; Formula (III) >
Ti _{0.4 + x / 6} Zr _{0.6-x / 6} Mn _0.44 Ni _1.0 Al _0.02 Co _0.09 (VCr _0.3 Fe _0.063 ) _x
(Where x is 0.7 to 2.8)

Images