WO2022145029A1 - Group 14 element-containing metal hydride with a superlattice structure for use in hydrogen storage. - Google Patents

Abstract

Provided are metal hydrides for use as hydrogen storage materials that include a hydride of a group 14 element with one or more superlattice phases with a lattice constant in excess of 7 angstroms wherein C and Si are present in the metal hydride at 20 atomic percent total or greater. These materials show excellent solid hydride formation leading to improved hydrogen storage capacity for use in devices employing the materials.

Description

GROUP 14 ELEMENT-CONTAINING METAL HYDRIDE WITH A SUPERLATTICE STRUCTURE FOR USE IN HYDROGEN STORAGE.

This disclosure relates to solid hydrogen storage, more specifically to low pressure hydrogen storage materials at room temperature.

Increasing environmental concerns continues to promote the evaluation and implementation of low to zero emission energy systems. One energy solution involves the use of hydrogen as an energy source. The byproduct of energy production using hydrogen is water, which is entirely environmentally friendly. Use of clean hydrogen energy, therefore, reduces greenhouse gas emissions and coincident air pollution. One of the challenges of large scale use of hydrogen based energy is the storage and transport of large amounts of hydrogen.

There are typically two methods of hydrogen gas storage considered for use in promoting wide scale implementation as an energy source. The first is gas phase hydrogen storage whereby hydrogen gas is pressurized into a strong container. This method has the drawbacks that the hydrogen must be stored at high pressures and the energy required to pressurize the hydrogen detracts from the overall energy benefit of its use. Liquid hydrogen storage does not require the same pressure levels, but still requires large low-temperature storage containers and high costs of cooling hydrogen from gas into liquid.

An alternative method for hydrogen storage involves low pressure absorption of hydrogen onto or into hydrogen storage materials. It is know that some materials may reversibly absorb and desorb hydrogen. Many of these materials, however, require temperatures or other conditions that detract from their use at typical environmental conditions for wide scale implementation. In addition, many useful materials are not capable of storing sufficient amounts of hydrogen in a small enough volume to be economically viable. For example, the traditionally used hydrogen storage materials (AB₂) are capable of storing hydrogen at only about two weight percent hydrogen. There are some materials that are able to store more hydrogen such as the vanadium-based body-centered-cubic (BCC) materials, but these suffer from large lattice expansion upon hydrogen absorption making them impractical for use in a confined container. Even these BCC materials show a maximum hydrogen absorption of only about three weight percent.

As such, there is a need for improved materials for the reversible storage of hydrogen. This disclosure provides metal hydride materials that allow ambient temperature, low pressure, reversible hydrogen storage at high hydrogen weight percent thereby addressing the need for such materials. These and other advantages of the disclosure will be apparent from the drawings, discussion, and description that follow.

The following summary is provided to facilitate an understanding of some of the innovative features unique to the present disclosure and is not intended to be a full description. A full appreciation of the various aspects of the disclosure can be gained by taking the entire specification, claims, drawings, and abstract as a whole. The inventions as described herein are presented in the claims that follow.

The identification of materials that can reversibly absorb hydrogen in sufficient amounts and without the need for high pressures or unacceptable volume expansion is desirable. The hydrogen storage materials as provided herein are able to store hydrogen at large volumetric density and without dramatic lattice expansion allowing for solid-phase hydrogen storage in at two weight percent hydrogen or greater.

As such, provided are metal hydride materials for use as a hydrogen storage material. The hydrogen storage materials include: a hydride of a group 14 element with one or more superlattice phases, optionally two or more superlattice phases, with a lattice constant in excess of 7 angstroms, wherein C and Si are present in said metal hydride at 20 atomic percent total or greater. The metal hydride materials optionally include greater than 50 atomic percent C and Si, optionally greater than 60 atomic percent C and Si. In some aspects, the group 14 element forms hydrides that are solid at room temperature.

The metal hydride materials as provided herein optionally are capable of reversibly absorbing greater than 2 weight percent hydrogen, optionally greater than 5 weight percent hydrogen, optionally greater than or equal to 5 weight percent hydrogen, optionally greater than or equal to 10 weight percent hydrogen, optionally greater than or equal to 15 weight percent hydrogen. The hydrogen absorption optionally occurs with a lattice expansion of less than 22 linear percent upon absorption of hydrogen.

The metal hydride materials as provided herein have a microstructure. The microstructure is optionally amorphous, polycrystalline, a mixture of nanocrystalline and amorphous, or a combination of polycrystalline, nanocrystalline and amorphous. In some particular aspects, the metal hydride materials include a polycrystalline microstructure.

In the above materials or hydrogen storage systems employing such materials, the metal hydride may include in some aspects Si_xM_1-x wherein x comprises one or more non-Si group 14 elements, and wherein 0 ≦ x ≦ 1. Optionally, the metal hydride includes 1-3 different group 14 elements, optionally 2 group 14 elements, optionally 1 group 14 element. A group 14 element in a metal hydride material is optionally Si. Optionally, Si is the sole non-oxygen of non-hydrogen element in the metal hydride material. In some aspects, the metal hydride material contains no metals or metalloids other than one or more group 14 elements. Optionally, the metal hydride material includes Si and one or more non-Si group 14 elements, optionally C, Ge or combinations thereof. The non-Si group 14 elements are optionally present at 50 atomic percent or less relative to the total group 14 elements in the metal hydride material. In addition, in some aspects and metal hydride material further includes one or more non-group 14 element containing hydrogen storage materials, optionally at 50 weight percent or less.

A hydrogen storage devices are also provided that include as a hydrogen storage material the metal hydride material of any one or more of the preceding paragraphs of this section.

The metal hydride materials and hydrogen storage devices employing these materials are capable of achieving excellent hydrogen storage capabilities.

FIG. 1 illustrates an x-ray diffraction (XRD) pattern of a silicon sample from a charged anode in an electrochemical cell including a hydrogen storage material according to some aspects as provided herein illustrating the presence of three independent diffraction peaks indicative of three superlattice phases of the group 14 element in solid form in the hydrogen storage material; FIG. 2 illustrates an XRD pattern of an as received sample of Si powder used in a discharged anode in an electrochemical cell according to some aspects as provided herein with arrows pointing to the presence of MH and MH₂ (where M is one group 14 element) superlattice phases in solid form in the anode electrochemically active material, and the presence of polycrystalline Si in the materials; FIG. 3 illustrates a test cell as used to characterize the hydrogen storage materials as provided herein; FIG. 4 illustrates the discharge voltage profile at cycle 28 for a silicon containing hydrogen storage material as provided herein demonstrating greater than 20 weight percent hydrogen storage; and FIG. 5 illustrates the discharge voltage profile at cycle 38 for a silicon containing hydrogen storage material as provided herein demonstrating greater than 19 weight percent hydrogen storage.

Provided are metal hydrides suitable for use as hydrogen storage materials. The metal hydride materials allow for the reversible storage of large amounts of hydrogen that are at or in excess of two weight percent at ambient temperature and pressure, and in some aspects at or above 10 weight percent and often at 20 weight percent or more. Thus, the metal hydride materials as provided herein address the need for materials capable of storing large amounts of hydrogen without the drawbacks of gas or liquid phase storage methods.

The metal hydride materials as provided herein include a hydride of a group 14 element with one or more superlattice phases with a lattice constant in excess of 7 angstroms. As such, hydrogen storage devices also as provided herein for the first time employ solid hydrides of the group 14 element capable of efficiently and effectively reversibly storing protons for use in addressing energy needs.

The metal hydride materials as provided herein are one or more hydrides of the group 14 element and optionally one or more additional elements are optionally formed as an anode employing the material during charge. This hydride is formed reversibly such that during discharge the hydride becomes the elemental portion of the anode hydrogen storage material generating both a proton and an electron. The half reaction that takes place in the hydrogen storage material can be described as per the following:

where M as provided herein one or more group 14 elements.

The corresponding cathode reaction half reaction is typically:

wherein M_c is any suitable metal(s) optionally with a greater affinity for hydrogen that the metal hydride material, optionally Ni.

As used herein, an “anode” includes a hydrogen storage material that acts as an electron acceptor during charge.

As used herein, a “cathode” includes a material with greater affinity for hydrogen than the hydrogen storage material as provided herein and that acts as an electron donor during charge.

The term “charge” as used herein is the absorption of protons onto or into the metal hydride material as provided herein.

When atomic percentages (at%) are presented and not otherwise defined, the atomic percentages are presented on the basis of the amount of all elements in the described material other than hydrogen and oxygen.

A “metal” as used in the term “metal hydride” includes elements traditionally considered metals, and metalloids such as C, Si, Ge, and B.

A “superlattice” as used herein is understood as a periodic structure of layers of differing physical or chemical characteristics. Different hydrides of the same host metal(s) may have different superlattice structures with different hydrogen content.

Provided herein are metal hydride materials and hydrogen storage devices that include a cathode, an anode employing one or more of the metal hydride materials, and an electrolyte, optionally a non-aqueous electrolyte. The cells employ an anode with a hydrogen storage material that includes a metal hydride as provided herein. The metal hydrides as provided herein include a hydride of a group 14 element, optionally where the C and Si are present at 20 atomic percent total or greater. The hydride of the group 14 element is characterized by a superlattice phase with a lattice constant in excess of seven (7) angstroms. Pure Si materials are known to have a lattice constant of about 5.43 angstroms. Hydrogenation of Si, as well as other metals, results in an expansion of the crystal lattice of the material. For expansion of Si, the expansion direction may be, but need not necessarily be in the c direction. For example, the silicon hydride SiH has a lattice constant of 7.12 angstroms, which is a significant expansion relative to crystalline Si. These expanded lattice constants are indicative of the formation of Si hydrides in a material. As such, the Si hydrides as provided herein include material with a lattice constant in excess of 7 angstroms, optionally at or in excess of 7.12 angstroms, optionally at or in excess of 7.64 angstroms, optionally at or in excess of 7.95 angstroms. These borders are representative of different hydrides of Si present in the Si hydride material.

The metal hydride materials as provided herein are capable of reversibly storing hydrogen at a weight percent (relative to metal in the metal hydride material) of 2 weight percent or more at ambient temperature and pressure (defined as 25 °C and 760 mmHg). Optionally, the metal hydride materials are capable of reversibly storing hydrogen 3 weight percent or more, optionally 4 weight percent or more, optionally 5 weight percent or more, optionally 6 weight percent or more, optionally 7 weight percent or more, optionally 7 weight percent or more, optionally 8 weight percent or more, optionally 9 weight percent or more, optionally 10 weight percent or more, optionally 11 weight percent or more, optionally 12 weight percent or more, optionally 13 weight percent or more, optionally 14 weight percent or more, optionally 15 weight percent or more, optionally 16 weight percent or more, optionally 17 weight percent or more, optionally 18 weight percent or more, optionally 19 weight percent or more, optionally 20 weight percent or more.

The metal hydride materials as provided herein present a lattice constant expansion during absorption of hydrogen as is required of all such materials. The provided metal hydride materials, however, do not suffer lattice expansion to as much a degree as many previously used materials such as BCC materials that show lattice expansions of 30 percent or more and are too great to be useful in a closed container. In some aspects, the lattice expansion is observed in the c direction whereby hydrogen is inserted into Si crystal layers. With the provided hydrogen storage materials, lattice expansion is optionally less than 22 percent (linear dimensional percent) upon absorption of hydrogen.

The metal hydride materials as provided herein may be used as a hydrogen material that includes C and Si at 20 atomic percent total or greater. The hydrogen storage material is suitable to reversibly absorb hydrogen for use in a hydrogen storage device, optionally opposite a material that is used as a cathode in the device. As such, a hydrogen storage material optionally includes Si alone or in combination with one or more other metals and/or one or more non-Si group 14 elements. Group 14 elements include carbon (C), silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). In some aspects, a group 14 element excludes Pb. Optionally, a group 14 element is C, Si, Ge, or any combination thereof. In some aspects, a hydrogen storage material includes Si as the sole group 14 element. Optionally, a hydrogen storage material includes C. Optionally, a hydrogen storage material includes Ge.

In some aspects, a hydrogen storage material includes two or more group 14 elements. Optionally, a hydrogen storage material includes two group 14 elements. Optionally, a hydrogen storage material includes three group 14 elements. In some aspects, a hydrogen storage material includes Si and C. Optionally, a hydrogen storage material includes Si and Ge. Optionally, a hydrogen storage material includes C and Ge. Optionally, a hydrogen storage material includes Si, C, and Ge.

A hydrogen storage material according to some aspects includes Si and one or more non-Si group 14 elements, optionally C and/or Ge. The non-Si group 14 elements are optionally present at 50 atomic percent or less relative to all group 14 elements in the anode electrochemically active material. Optionally, the non-Si group 14 elements are optionally present at 45 atomic percent or less, optionally 40 atomic percent or less, optionally 35 atomic percent or less, optionally 30 atomic percent or less, optionally 29 atomic percent or less, optionally 28 atomic percent or less, optionally 27 atomic percent or less, optionally 26 atomic percent or less, optionally 25 atomic percent or less, optionally 24 atomic percent or less, optionally 23 atomic percent or less, optionally 22 atomic percent or less, optionally 21 atomic percent or less, optionally 20 atomic percent or less, optionally 15 atomic percent or less, optionally 10 atomic percent or less, optionally 5 atomic percent or less, optionally 4 atomic percent or less, optionally 3 atomic percent or less, optionally 2 atomic percent or less, or optionally 1 atomic percent or less.

In some aspects, a hydrogen storage material includes Si and Ge, wherein the Ge is present at 50 atomic percent or less relative to all group 14 elements in the hydrogen storage material. Optionally, the Ge is present at 45 atomic percent or less, optionally 40 atomic percent or less, optionally 35 atomic percent or less, optionally 30 atomic percent or less, optionally 29 atomic percent or less, optionally 28 atomic percent or less, optionally 27 atomic percent or less, optionally 26 atomic percent or less, optionally 25 atomic percent or less, optionally 24 atomic percent or less, optionally 23 atomic percent or less, optionally 22 atomic percent or less, optionally 21 atomic percent or less, optionally 20 atomic percent or less, optionally 15 atomic percent or less, optionally 10 atomic percent or less, optionally 5 atomic percent or less, optionally 4 atomic percent or less, optionally 3 atomic percent or less, optionally 2 atomic percent or less, or optionally 1 atomic percent or less.

In other aspects, a hydrogen storage material includes Si and C, wherein the C is present at 50 atomic percent or less relative to all group 14 elements in the a hydrogen storage material. Optionally, the C is present at 45 atomic percent or less, optionally 40 atomic percent or less, optionally 35 atomic percent or less, optionally 30 atomic percent or less, optionally 29 atomic percent or less, optionally 28 atomic percent or less, optionally 27 atomic percent or less, optionally 26 atomic percent or less, optionally 25 atomic percent or less, optionally 24 atomic percent or less, optionally 23 atomic percent or less, optionally 22 atomic percent or less, optionally 21 atomic percent or less, optionally 20 atomic percent or less, optionally 15 atomic percent or less, optionally 10 atomic percent or less, optionally 5 atomic percent or less, optionally 4 atomic percent or less, optionally 3 atomic percent or less, optionally 2 atomic percent or less, or optionally 1 atomic percent or less.

A hydrogen storage material optionally includes Si_xM_1-x wherein M comprises one or more non-Si group 14 elements, and wherein 0 ≦ x≦ 1, optionally 0 < x< 1. M is optionally C, Ge, a transition metal or other hydride forming element, or any combination thereof. Optionally, M is C. Optionally, M is Ge. Optionally, x is 0.2 or greater, optionally x is 0.25 or greater, optionally x is 0.3 or greater, optionally x is 0.35 or greater, optionally x is 0.4 or greater, optionally x is 0.45 or greater, optionally x is 0.5 or greater, optionally x is 0.55 or greater, optionally x is 0.6 or greater, optionally x is 0.65 or greater, optionally x is 0.7 or greater, optionally x is 0.71 or greater, optionally x is 0.72 or greater, optionally x is 0.73 or greater, optionally x is 0.74 or greater, optionally x is 0.75 or greater, optionally x is 0.76 or greater, optionally x is 0.77 or greater, optionally x is 0.78 or greater, optionally x is 0.79 or greater, optionally x is 0.8 or greater, optionally x is 0.85 or greater, optionally x is 9 or greater, optionally x is 0.95 or greater, optionally x is 0.96 or greater, optionally x is 0.97 or greater, optionally x is 0.98 or greater, or optionally x is 0.99 or greater.

It is appreciated that a hydrogen storage material may include one or more other non-group 14 elements. Illustrative examples of non-group 14 elements include, but are not limited to lithium, boron, sodium, magnesium, and aluminum. Optionally, when a non-group 14 element(s) is present, the element is at 50 atomic percent or less, optionally 20 at% or less, optionally 10 at% or less, optionally 5 at% or less, optionally 4 at% or less, optionally 3 at% or less, optionally 2 at% or less, optionally 1 at% or less.

A hydrogen storage material optionally includes one or more non-group 14 element containing hydrogen storage materials. If a non-group 14 element containing hydrogen storage material is present in an anode electrochemically active material, the non-group 14 element containing hydrogen storage material is optionally present at 50 weight percent or less. Optionally the non-group 14 element containing hydrogen storage material is present at 40 weight percent or less, optionally 30 weight percent or less, optionally 20 weight percent or less, optionally 10 weight percent or less, optionally 5 weight percent or less, optionally 3 weight percent or less, optionally 20 weight percent or less, optionally 1 weight percent or less, optionally 0.1 weight percent or less, optionally 0.01 weight percent or less.

Illustrative examples of a non-group 14 element containing hydrogen storage materials that may be included in a hydrogen storage material as provided herein include any material known in the art as capable of electrochemically and reversibly storing hydrogen. Illustrative examples of such materials are the AB_x class of hydrogen storage materials where A is a hydride forming element, B is a non-hydride forming element and x is from 1-5. Illustrative examples include the AB, AB₂, AB₃, A₂B₇, A₅B₁₉ and AB₅ type materials as they are known in the art. A hydride forming metal component (A) optionally includes but is not limited to titanium, zirconium, vanadium, hafnium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, yttrium, or combinations thereof or other metal(s) such as a mischmetal. A B (non-hydride forming) component optionally includes a metal selected from the group of aluminum, chromium, manganese, iron, nickel, cobalt, copper, and tin, or combinations thereof. In some aspects, AB_x type materials that may be further included in an anode electrochemically active material are disclosed, for example, in U.S. Patent 5,536,591 and U.S. Patent 6,210,498. Optionally, non-group 14 element containing hydrogen storage materials are as described in Young, et al., International Journal of Hydrogen Energy, 2014; 39(36):21489-21499 or Young, et al., Int. J. Hydrogen Energy, 2012; 37:9882. Optionally, non-group 14 element containing hydrogen storage materials are as described in U.S. Patent Application Publication No: 2016/0118654. In some aspects, a non-group 14 containing hydrogen storage material includes hydroxides, oxides, or oxyhydroxides of Ni, Co, Al, Mn, or combinations thereof, optionally as described in U.S. Patent No. 9,502,715. Optionally, a non-group 14 containing hydrogen storage material includes a transition metal such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Au, Cd, or combinations thereof, optionally as disclosed in U.S. Patent No: 9,859,531.

The group 14 element component of the hydrogen storage material as provided herein is characterized by a microstructure. The microstructure of the group 14 element in a hydrogen storage material is optionally polycrystalline, a mixture of nanocrystalline and amorphous, amorphous, or a combination of polycrystalline, nanocrystalline and amorphous. Optionally, a microstructure is not solely amorphous.

Optionally, a microstructure of the group 14 element material in the hydrogen storage material is or includes polycrystalline. Polycrystalline silicon is formed of multiple small silicon crystals or crystallites. The multiple crystallites are typically randomly arranged. Illustratively, polycrystalline Si may be obtained from any recognized commercial supplier, illustratively Wacker Chemi or Hemlock Semiconductor, among others.

Optionally, a microstructure of the Si in the hydrogen storage material is a combination of nanocrystalline and amorphous. Nanocrystalline silicon is a form of silicon with a paracrystalline structure that typically includes an amorphous phase, but the nanocrystalline silicon differs from amorphous Si in that the nanocrystalline silicon also includes grains of crystalline silicon within the amorphous phase. Typical sources of nanocrystalline silicon include Strem (USA) and Cenate (Norway).

In some aspects, a microstructure of the Si in hydrogen storage material is a combination of polycrystalline, nanocrystalline and amorphous. When polycrystalline Si is present in a mixture of other microstructure silicon(s), the percentage (mass) of polycrystalline phase is 20 percent or less. Optionally, the percentage of polycrystalline Si is 15 percent or less, optionally 10 percent or less, optionally 5 percent or less.

The hydrogen storage material is optionally presented in a powder form, meaning that the hydrogen storage material is a solid at 25 degrees Celsius (°C) and free of any substrate. Despite prior belief to the contrary, it was found that solid group 14 elements may be used to form hydrides in the solid state and be useful for hydrogen storage or battery applications. The powder is held together by a binder that associates the powder particles in a layer that is coated on a current collector in the formation of an anode.

A hydrogen storage device with an anode including a hydrogen storage material as provided herein also includes a cathode that includes a cathode electrochemically active material. A cathode electrochemically active material has the capability to absorb and desorb a proton in the cycling of a hydrogen storage device so that the cathode active material functions in pair with the hydrogen storage material as provided herein to charge the hydrogen storage material. Illustrative materials suitable for use in a cathode electrochemically active material include metal hydroxides. Illustrative examples of metal hydroxides that may be used in a cathode electrochemically active material include those described in U.S. Patent Nos: 5,348,822; 5,637,423; 5,366,831; 5,451,475; 5,455,125; 5,466,543; 5,498,403; 5,489,314; 5,506,070; 5,571,636; 6,177,213; and 6,228,535.

In some aspects, a cathode electrochemically active material includes a hydroxide of Ni alone or in combination with one or more additional metals. Optionally, an electrochemically active material includes Ni and 1, 2, 3, 4, 5, 6, 7, 8, 9, or more additional metals. Optionally, a cathode electrochemically active material include Ni as the sole metal.

Optionally, a cathode electrochemically active material includes one or more metals selected from the group of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, a hydride thereof, an oxide thereof, a hydroxide thereof, an oxyhydroxide thereof, or any combination of the foregoing. Optionally, a cathode electrochemically active material includes one or more of Ni, Co, Mn, Zn, Al, Zr, Mo, Mn, a rare earth, or combinations thereof. In some aspects, a cathode electrochemically active material includes Ni, Co, Al, or combinations thereof.

A cathode electrochemically active material may include Ni. Ni is optionally present at an atomic percentage relative to the total metals in the cathode electrochemically active material of 10 atomic percent (at%) or greater. Optionally, Ni is present at 15 at% or greater, optionally 20 at% or greater, optionally 25 at% or greater, optionally 30 at% or greater, optionally 35 at% or greater, optionally 40 at% or greater, optionally 45 at% or greater, optionally 50 at% or greater, optionally 55 at% or greater, optionally 60 at% or greater, optionally 65 at% or greater, optionally 70 at% or greater, optionally 75 at% or greater, optionally 80 at% or greater, optionally 85 at% or greater, optionally 90 at% or greater, optionally 91 at% or greater, optionally 92 at% or greater, optionally 93 at% or greater, optionally 94 at% or greater, optionally 95 at% or greater, optionally 96 at% or greater, optionally 97 at% or greater, optionally 98 at% or greater, optionally 99 at% or greater. Optionally the sole metal in the cathode electrochemically active material is Ni.

An anode electrochemically active material, a cathode electrochemically active material, or both are optionally in a powder or particulate form. The particles may be held together by a binder to form a layer on a current collector in the formation of the anode or cathode. A binder suitable for use in forming an anode, a cathode or both is optionally any binder known in the art suitable for such purposes and for the conduction of a proton.

Illustratively, a binder for use in the formation of an anode including a hydrogen storage material as provided herein or a cathode electrochemically active material includes but is not limited to polymeric binder materials. Optionally a binder material is an elastomeric material, optionally styrene-butadiene (SB), styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS) and styrene-ethylene-butadiene-styrene block copolymer (SEBS). Illustrative specific examples of a binder include, but are not limited to polytetrfluoroethylene (PTFE), polyvinyl alcohol (PVA), teflonized acetylene black (TAB-2), styrene-butadiene binder materials, or/and carboxymethyl cellulose (CMC). Illustrative examples may be found in U.S. Patent No: 10,522,827. The ratio of hydrogen storage or cathode electrochemically active material to binder is optionally from 4:1 to 1:4. Optionally, the ratio of hydrogen storage or cathode electrochemically active material to binder is 1:3 to 1:2.

A cathode, anode or both may further include one or more additives intermixed with the hydrogen storage or cathode electrochemically active materials. An additive is optionally a conductive material. A conductive material is optimally a conductive carbon. Illustrative examples of a conductive carbon include graphite. Other examples are materials that contain graphitic carbons, such as graphitized cokes. Still other examples of possible carbon materials include non-graphitic carbons that may be amorphous, non-crystalline, and disordered, such as petroleum cokes and carbon black. A conductive material is optionally present in a hydrogen storage or a cathode electrochemically active material at a weight percent (wt%) of 0.1 wt% to 20 wt%, or any value or range therebetween.

An anode or a cathode may be formed by any method known in the art. For example, a hydrogen storage material or a cathode electrochemically active material may be combined with a binder, and optionally conductive material, in an appropriate solvent to form a slurry. The slurry may be coated onto a current collector and dried to evaporate some or all of the solvent to thereby form an electrochemically active layer on the surface of the current collector.

A current collector may be in the form of a mesh, foil, or other suitable form. Optionally, a current collector may be formed of aluminum, such as an aluminum alloy, nickel or nickel alloy, steel such as stainless steel, copper or copper alloys, or other such material. A current collector is optionally in the form of a sheet, and may be in the form of a foil, solid substrate, porous substrate, grid, foam or foam coated with one or more metals, or other form known in the art. In some aspects a current collector is in the form of a foil. Optionally, a grid may include expanded metal grids and perforated foil grids. A current collector is optionally formed of any suitable electronically conductive and optionally impermeable or substantially impermeable material, including, but not limited to copper, stainless steel, titanium, or carbon papers/films, a non-perforated metal foil, aluminum foil, cladding material including nickel and aluminum, cladding material including copper and aluminum, nickel plated steel, nickel plated copper, nickel plated aluminum, gold, silver, any other suitable electronically conductive and impermeable material or any suitable combination thereof. Optionally, a current collector may be formed of one or more suitable metals or combination of metals (e.g., alloys, solid solutions, plated metals). Optionally, a current collector for an anode includes or is exclusively steel such as stainless steel.

The current collector or substrates may include one or more tabs to allow the transfer of electrons from the current collector to a region exterior of the cell and to connect the current collector(s) to a circuit so that the electrons produced during discharge of the cell may be used to power one or more devices. A tab may be formed of any suitable conductive material (e.g. Ni, Al, or other metal) and may be welded onto the current collector. Optionally, each electrode has a single tab.

A hydrogen storage device may include a separator interposed between an anode and a cathode. A separator may be permeable to a proton so as to not appreciably or unacceptably restrict ion transfer between the anode and the cathode. Illustrative examples of a separator include but are not limited to materials such as nylons, polyesters, polyvinyl chloride, glass fibers, cotton, among others. Illustratively, a separator may be polyethylene or polypropylene.

The hydrogen storage devices as provided herein may include a non-aqueous proton conducting electrolyte. The electrolyte is disposed between the hydrogen storage material and the cathode electrochemically active material and allows the flow or other transfer of protons between the anode and the cathode. A non-aqueous electrolyte optionally includes less than 10 wt% water, optionally less than 5 wt% water, optionally less than 1 wt% water. In some aspects, a nonaqueous electrolyte includes less than 100 ppm water, less than 50 ppm water, optionally less than 10 ppm water.

The nonaqueous electrolyte optionally includes one or more aprotic compounds alone or in combination with one or more proton sources such as an organic acid. An aprotic compound is any compound suitable for use in an electrolyte and that is not otherwise detrimentally reactive with any other component of an electrochemical cell. Illustrative examples of an aprotic acid include ammonium or phosphonium compounds, optionally where the ammonium or phosphonium includes one or more linear, branched or cyclic substituted or non-substituted alkyl groups connected to a nitrogen or phosphorous.

A nonaqueous electrolyte optionally includes an ammonium or phosphonium compound with 1, 2, or more linear, branched or cyclic substituted or non-substituted alkyl groups bound to a positively charged nitrogen or phosphorus atom. Optionally, the compounds include one such alkyl, optionally two such alkyls that may be the same or different. Optionally, the ammonium or phosphonium compound alkyl is or includes 1-6 carbon atoms, optionally 1-4 carbon atoms and may be branched, linear or cyclic. In some aspects, the nitrogen or phosphorous is a member of a 5 or 6 membered ring structure that may have one or more pendant groups extending from the central ring. Optionally, ammonium ion is an imidazolium ion. Optionally, a phosphonium ion is a pyrrolidinium ion.

In some aspects, an ammonium or phosphonium includes 1 or 2 linear or cyclic, substituted or unsubstituted alkyls of 1-6 carbon atoms. Optionally, the alkyl includes 2, 3, 4, 5, or 6 carbons. In some aspects, the aprotic compound includes 1 or 2 alkyls of 1-6 carbons. A substitution in an alkyl is optionally a nitrogen, oxygen, sulfur, or other such element. Optionally, an ammonium or phosphonium includes a ring structure with 5-6 members where the ring is substituted with an N, an O, or P.

Illustrative examples of an aprotic compound for use as an electrolyte include, but are not limited to 1-butyl-3-methylimidazolium (BMIM), 1-ethyl-3-methylimidazolium (EMIM), 1,3-dimethylimdiazolium, 1-ethyl-3-methylimidazolium, 1,2,3-trimethylimidazolium, tris-(hydroxyethyl)methylammonium, 1,2,4-trimethylpyrazolium, or combinations thereof.

The aprotic compound optionally includes one or more anions in conjunction with the aprotic compound. Illustrative examples of an anion include but are not limited to methides, nitrate, carboxylates, imides, halides, borates, phosphates, phosphinates, phosphonates, sulfonates, sulfates, carbonates and aluminates. Further illustrative examples may be found in U.S. Patent Nos: 6,254,797 and 9,006,457. In specific exemplary aspects, an anion includes carboxylates such as an acetate, phosphates such as a hydrogen, alkyl, or fluorophospate, phophinates such as alkyl phosphinates, among others. Illustrative examples of such aprotic compounds include but are not limited to acetates, sulfonates, or borates of 1-butyl-3-methylimidazolium (BMIM), 1-ethyl-3-methylimidazolium (EMIM), 1,3-dimethylimdiazolium, 1-ethyl-3-methylimidazolium, 1,2,3-trimethylimidazolium, tris-(hydroxyethyl)methylammonium, 1,2,4-trimethylpyrazolium, or combinations thereof. Specific examples include diethylmethylammonium trifluoromethanesulfonate (DEMA TfO), 1-ethyl-3-methylimidazolium acetate (EMIM Ac) or 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM TFSI).

In addition to the aprotic compound, an electrolyte is optionally further supplemented with an organic acid that serves as a proton donor. The presence of the organic acid improves the overall proton conductivity of the electrolyte and thereby improves the function of the hydrogen storage device employing the electrolyte. Optionally, an organic acid is a carboxylate. Illustrative examples of a carboxylate include those with 0-10 or more carbons attached to a terminal carboxylic acid. Specific illustrative examples include an acetic acid such as acetic acid or haloacetic acid (e.g. with 1-3 fluorine or chlorine atoms). Optionally an organic acid is acetic acid.

The organic acid is optionally present in the electrolyte at 1-5 moles/kg (m). Optionally, the organic acid is present at 3-4 m. Optionally, the organic acid is present at a molar concentration that is 3-3.5 m.

A nonaqueous electrolyte as used in any of the aspects as provided above or otherwise herein optionally includes one or more additives suitable to produce a maximum capacity of a proton conducting electrochemical cell housing the electrolyte to a discharge capacity of greater than 1000 mAh/g per weight of anode electrochemically active material. It was found that the addition of one or more suitable additives, such as a suitable salt, dramatically improves the formation of a hydrogen storage device as provided herein, and thereby improves the discharge capacity achievable by the cell. In the otherwise identical cell, it was found that the addition of one or more such additives could boost the hydrogen storage capacity, often by as much as 3-7 fold. Without being limited to one particular theory, it is believed that during formation, the availability of free hydrogen within the electrolyte varies to such an extent that cell formation is inhibited. The addition of a suitable salt stabilizes the free hydrogen concentration to thereby boost the resulting capacity achievable by the hydrogen storage device.

A salt additive suitable to produce a hydrogen storage capacity of a hydrogen storage device housing the electrolyte to a hydrogen weight percent of greater than two weight percent,m optionally 10 weight percent, optionally 20 weight percent, or any other weight percent as provided herein, optionally includes those with a pKa in water of 1-14, optionally 3-13, optionally 7-13, optionally 3-8.

Illustrative examples of a salt additive suitable to produce a hydrogen storage capacity of a hydrogen storage device housing the electrolyte to two weight percent hydrogen or greater optionally includes salts of potassium or sodium. Suitable salts include phosphates, carbonates, or sulfates of potassium or sodium. Specific illustrative examples of potassium salts include, but are not limited to potassium phosphate such as mono- or dipotassium phosphate, potassium carbonate, potassium sulfate, among others. Illustrative examples of sodium salts include, but are not limited to sodium mono-, di-, tetra-phosphate, sodium bicarbonate, and sodium hydrogen sulfate.

The salt additive suitable to produce a maximum hydrogen storage capacity of a hydrogen storage device housing the electrolyte to a hydrogen storage capacity of 2 weight percent or greater may be present in an electrolyte at 0.01 to 1 m, optionally 0.01 to 0.2 m, optionally 0.5 to 1 m.

The anode, cathode, separator, and nonaqueous electrolyte may be housed in a cell case (e.g. housing). The housing may be in the form of a metal or polymeric can, or can be a laminate film, such as a heat-sealable aluminum foil, such as an aluminum coated polypropylene film.

The hydrogen storage material is optionally in contact, either gaseous, via a proton conducting electrolyte, or other with a hydrogen source. In some aspects, a hydrogen source is a cathode electrochemically active material as provided herein. In some aspects, a hydrogen source is a hydrogen storage alloy or other material that differs from the metal hydride material as provided herein, or is a gas phase hydrogen source. The hydrogen source is optionally connected to the metal hydride material as provided herein via a valve that may regulate the rate or other transfer parameter from the hydrogen source to the metal hydride material. A hydrogen source is optionally purified hydrogen or otherwise enriched hydrogen relative to air. In other aspects, a hydrogen storage device as provided herein may function substantially as described in U.S. Patent Nos: 7,320,726; 7,651,554; and 9,343,735.

EXPERIMENTAL

Example 1
A series of silicon containing compositions were obtained from commercial sources. Polycrystalline silicon was obtained from Alfa Aesar (US), Fijifilm (Japan), Hongwu (China), Silican (Taiwan) and Paraclete (US). Amorphous/nanocrystalline silicon was obtained from Cenate (Norway) and Strem (US). To confirm the microstructure of the polycrystalline silicon, each sample was subjected to analysis by x-ray diffraction (XRD) utilizing a Philips X’Pert Pro x-ray diffractometer with Cu-K_α as radiation source.

Anodes were constructed from each of the sample silicon containing materials. The Silicon materials were in powder form and combined with a TAB-2 binder in the dry form at a weight ratio of 1:3. The materials were pressed into a Ni mesh substrate as a current collector. Ni(OH)₂ cathodes as a hydrogen source were made by standard methods using commercially sourced and sintered Ni(OH)₂. To test the metal hydride materials were tested by forming an electrochemical cell within an all-teflon Swagelock tee. The cell used for electrochemical analyses is illustrated in FIG. 3 and includes a central gland 1 capped with ferrules 2 at both ends secured by collars 3. The sample 4 is sandwiched between two current collector rods 5 made from Ni-plated steel (NS) or stainless steel (SS). The top channel is covered with a parafilm 6 as a pressure vent device. The sample is a sandwich of an anode including the hydrogen storage material, cathode, and separated by a standard separator. The cell is flooded with an electrolyte including EMIM/AC with 3.33 m acetic acid that included one or more salt additives.

The sample silicon hydride materials were charged charge rate of 700 mA/g for 20 hours, and the charged material subjected to analyses by XRD as per the raw group 14 element materials. FIG. 1 illustrates the presence of several hydrides of group 14 element in the materials. In addition to peaks indicative of polycrystalline M, MH (▲) with a superlattice hydride size of 7.12 Å, MH₂ with a superlattice hydride size of 7.64 Å (●) and MH₃ with a superlattice hydride size of 7.95 Å (↓) are all observed in the charged material indicating the presence of solid hydrides of M all with a lattice constant in excess of 7 Å in the anode electrochemically active material, where M is a group 14 element.

The anodes including the silicon hydride materials were discharged at a discharge rate of 70 mA/g to a discharge cut-off of 0 V and the discharged electrode material also analyzed by XRD. As revealed in FIG. 2, the discharged anode electrochemically active material includes MH and MH₂ superlattice phases as well as peaks representative of polycrystalline Si as expected. The polysilicon peaks are compared to the raw polysilicon material with peaks at the same locations.

Cells with the polycrystalline Si formed as per above were cycled with a charge rate of 700 mA/g, charge time: 20 hours and a discharge rate of 70 mA/g to a discharge cut-off of 1.0 V, 0.5 V or 0 V. The discharge profiles following cell formation for polycrystalline silicon at cycle 28 (FIG. 4) and cycle 38 (FIG. 5) demonstrate high capacity in excess of 5000 mA/g (of Si) for all samples tested.

The discharge capacity as derived from the test cell can be readily converted into weight hydrogen storage percentages by dividing the discharge capacity to 0 V in mAh/g by 268. The results at several cycles are illustrated in Table 1.

In all instances, a weight percent hydrogen storage for this material in excess of 15.4 weight percent was achieved. Following full cell formation, hydrogen storage capacity exceeded 20 weight percent.

Example 2
Polycrystalline silicon materials that also include one or more non-Si group 14 elements were obtained from commercial sources. An alloy of Si and Ge was obtained from Ge Solartech (US). The SiGe alloy was subjected to analyses using a Varian Liberty 100 inductively coupled plasma optical emission spectrometer (ICP-OES) in accord with principles known in the art. Microstructure of the alloys was studied utilizing a Philips X’Pert Pro x-ray diffractometer and a JEOL-JSM6320F scanning electron microscope with energy dispersive spectroscopy (EDS) capability. The alloy tested consisted of Si_0.78Ge_0.22.

The SiGe alloy was formed into an anode and tested against a sintered Ni(OH)₂ as in Example 1 using the same apparatus design and using an EMIM/Ac electrolyte supplemented with 3.33 m acetic acid and 0.1 m K₂HSO₄. The hydrogen storage device was charged at 700 mAh/g for 20 hours followed by discharge at 70 mAh/g to a cut-off of 0 V. The cell was capable of reaching a hydrogen absorption weight percentage of 4.4 weight percent. These studies demonstrate that an alloy of Si with a non-Si group 14 element can readily function as a hydride forming material for use in a hydrogen storage device and do so with excellent hydrogen storage capacity.

The foregoing description of particular aspect(s) is merely exemplary in nature and is in no way intended to limit the scope of the invention as claimed below, its application, or uses, which may, of course, vary. The disclosure is provided with relation to the non-limiting definitions and terminology included herein. These definitions and terminology are not designed to function as a limitation on the scope or practice of the invention but are presented for illustrative and descriptive purposes only. While the processes or compositions are described as an order of individual steps or using specific materials, it is appreciated that steps or materials may be interchangeable such that the description of the invention may include multiple parts or steps arranged in many ways as is readily appreciated by one of skill in the art.

It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be present therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

It will be understood that, although the terms “first,” “second,” “third” etc. may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not 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 could be termed a second (or other) element, component, region, layer, or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particular embodiments 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, including “at least one,” unless the content clearly indicates otherwise. “Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. The term “or a combination thereof” means a combination including 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 will be further understood that terms such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Patents, publications, and applications mentioned in the specification are indicative of the levels of those skilled in the art to which the invention pertains. These patents, publications, and applications are incorporated herein by reference to the same extent as if each individual patent, publication, or application was specifically and individually incorporated herein by reference.

In view of the foregoing, it is to be understood that other modifications and variations of the present invention may be implemented. The foregoing drawings, discussion, and description are illustrative of some specific embodiments of the invention but are not meant to be limitations upon the practice thereof. It is the following claims, including all equivalents, which define the scope of the invention.

Claims (23)

1. A metal hydride material for use as a hydrogen storage material comprising:
   a hydride of a group 14 element with one or more superlattice phases with a lattice constant in excess of 7 angstroms; and
   wherein C and Si are present in said metal hydride at 20 atomic percent total or greater.
2. The material of claim 1 wherein said hydride of the group 14 element is capable of reversibly absorbing greater than 2 weight percent hydrogen.
3. The material of claim 1 wherein said hydride of the group 14 element is capable of reversibly absorbing greater than 5 weight percent hydrogen, optionally greater than or equal to 5 weight percent hydrogen, optionally greater than or equal to 10 weight percent hydrogen, optionally greater than or equal to 15 weight percent hydrogen.
4. The material of claim 1 with a lattice expansion of less than 22 linear percent upon absorption of hydrogen.
5. The material of any one of claims 1-4 wherein said metal hydride material has a microstructure that is amorphous, polycrystalline, a mixture of nanocrystalline and amorphous, or a combination of polycrystalline, nanocrystalline and amorphous.
6. The material of claim 5 comprising a polycrystalline microstructure.
7. The material of any one of claims 1-4 comprising two or more superlattice phases.
8. The material of any one of claims 1-4 wherein said metal hydride material comprises Si_xM_1-x wherein x comprises one or more non-Si group 14 elements, and wherein 0 ≦ x ≦ 1.
9. The material of any one of claims 1-4 wherein the metal hydride material comprises two or more group 14 elements.
10. The material of any one of claims 1-4 wherein the metal hydride material consists of Si as the sole non-oxygen of non-hydrogen element.
11. The material of any one of claims 1-4 wherein the metal hydride material comprises Si and one or more non-Si group 14 elements.
12. The material of claim 11 wherein the one or more non-Si group 14 elements is Ge, C, or a combination thereof.
13. The material of claim 1 wherein said metal hydride material is equal to or greater than 50 atomic percent Si relative to all non-oxygen or hydrogen elements in the metal hydride material, optionally equal to or greater than 60 atomic percent Si.
14. A hydrogen storage device capable of reversibly storing hydrogen comprising:
    the metal hydride of any one of claims 1-4.
15. The device of claim 14 wherein said metal hydride comprises two or more superlattice phases.
16. The device of claim 14 wherein said metal hydride material has a microstructure that is polycrystalline, a mixture of amorphous, nanocrystalline and amorphous, or a combination of polycrystalline, nanocrystalline and amorphous.
17. The device of claim 16 wherein the material comprises a polycrystalline microstructure.
18. The device of any one of claims 14-17 wherein said metal hydride material comprises Si_xM_1-x wherein x comprises one or more non-Si group 14 elements, and wherein 0 ≦ x ≦ 1.
19. The device of any one of claims 14-17 wherein the metal hydride material comprises two or more group 14 elements.
20. The device of any one of claims 14-17 wherein the metal hydride material consists of Si as the sole non-hydrogen or oxygen element in said metal hydride material.
21. The device of any one of claims 14-17 wherein the metal hydride material comprises Si and one or more non-Si group 14 elements.
22. The device of claim 21 wherein the one or more non-Si group 14 elements is Ge, C, or a combination thereof.
23. The device of any one of claims 14-17 wherein the metal hydride comprises one or more non-Si group 14 elements, wherein an amount of non-Si group 14 elements is 50 atomic percent or less relative to the total group 14 elements in the metal hydride material, optionally wherein the amount of non-Si group 14 elements is less than 40 atomic percent.

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