EP1034572A1

EP1034572A1 - Transition metal-based ceramic material and articles fabricated therefrom

Info

Publication number: EP1034572A1
Application number: EP97947314A
Authority: EP
Inventors: Levi T. Thompson; Michael R. Wixom
Original assignee: TJ Technologies Inc
Current assignee: TJ Technologies Inc
Priority date: 1997-10-30
Filing date: 1997-10-30
Publication date: 2000-09-13
Also published as: EP1034572A4; WO1999023712A1; JP2001522133A; CA2308613A1

Abstract

A non-oxide, transition metal-based ceramic material has the general formula AyM2Zx, wherein A is a group IA element, M is a transition metal and Z is selected from the group consisting of N, C, B, Si, and combinations thereof, and wherein x ≤ 2 and y ≤ 6-x. In these materials, the group IA element occupies interstitial sites in the metallic lattice, and may be readily inserted into or released therefrom. The materials may be used as catalysts and as electrodes. Also disclosed herein are methods for the fabrication of the mates.

Description

TRANSITION METAL-BASED CERAMIC MATERIAL AND ARTICLES FABRICATED THEREFROM

Field of the Invention

This invention relates generally to synthetic materials. More specifically, the

invention relates to ceramic materials, and in particular to non-oxide ceramic materials

comprised of transition metals in combination with one or more of nitrogen, carbon,

boron, and silicon, and optionally with a group IA element intercalated therein. The

invention further relates to methods for fabricating these materials, and for devices

made therefrom. Background of the Invention

The present invention relates to a novel class of non-oxide, transition metal

based ceramics which are capable of intercalating group I A elements therein. These

materials have utility as electrodes for batteries, fuel cells, capacitors, electrochromic

displays and the like. They may also be used as elements in semiconductor devices,

as catalysts, and as structural elements in a variety of specialized devices.

The materials of the present invention are described as being non-oxide

ceramics, and within the context of this disclosure the term is meant to refer to

compounds of transition metals having one or more of boron, carbon, nitrogen and

silicon occupying a number of interstitial sites in their crystalline lattice. As such,

they are distinguished from prior art oxide based ceramics. It is to be understood that

in some instances, the materials of the present invention may include some minor

proportions of oxygen therein, either as a native oxide formed on the surface thereof,

or as a minor proportion of oxygen occupying internal sites of the bulk material. Nonetheless, the properties of the materials of the present invention are attributable

to the non-oxygen components thereof, and as such, it will be understood that non-

oxide ceramics, as defined herein, may include some small portions of oxygen therein.

It is notable that the materials of the present invention can incorporate group

IA elements therein. The group IA elements occupy interstitial sites in the lattice, and

may be readily inserted and removed therefrom and such insertion and removal is

referred to herein as intercalation. It is further to be noted that as used herein, the term

group IA elements is meant to refer to hydrogen group elements of the periodic table.

The materials of the present invention are capable of intercalating large

amounts of hydrogen or lithium in relatively small volumes, therefore, they have

significant utility as electrodes for batteries, sensors and the like, and as catalysts. The

materials of the present invention are low in cost and environmentally benign.

Furthermore, they have high electrical conductivities, compared to other ceramics, and

manifest good thermal stability. It has been found that the electrochemical potential

of these materials can be controlled by varying their stoichiometry, and this feature

is significant, insofar as it permits manufacture of electrochemical cells having a

controlled discharge profile.

Previously, oxide based ceramic materials have been employed as battery

electrodes, and one particular lithium ion battery electrode utilizing oxide based

ceramics is disclosed in U.S. Patent 5,110,696. Another such oxide based battery

electrode is disclosed in U.S. Patent 5,358,801. As will be explained hereinbelow, the mechanical, chemical and electrical

properties of the materials of the present invention distinguish them from prior art

ceramics, and greatly enhance their utility as catalysts, electrodes, and the like.

Also disclosed herein are some novel methods for the fabrication of the

materials of the present invention. These and other advantages of the present

invention will be readily apparent from the drawings, discussion and description

which follow.

Brief Description of the Invention

There is disclosed herein a transition metal based ceramic material having the

general formula A_yM₂Z_x, wherein A is a group IA element, M is a transition metal,

and Z is a member selected from the group consisting of: N, C, B, Si, and

combinations thereof; and wherein x ≤ 2 and y < 6-x.

In particular embodiments, the material has a cubic, tetragonal or hexagonal

lattice structure, and in some instances, A and Z occupy interstitial sites in said lattice.

In some embodiments the group IA element is lithium, and in other

embodiments the transition metal is selected from groups IIIB-VIIB of the periodic

table. In some specific embodiments, the transition metal is selected from groups

IVB-VIB of the periodic table.

There is also disclosed herein electrochemical electrodes and catalytic bodies

fabricated from the group IA containing transition metal based ceramic. Also

disclosed herein are electrodes fabricated from a powder comprised of a compound

of a transition metal and members selected from the group consisting of N, C, B, Si, and combinations thereof, in which the surface area of the powder is in excess of 5 m²/g.

Also disclosed herein are methods for manufacturing the materials of the

present invention. In some instances, materials are fabricated by electrochemically

adding a group IA element into a transition metal containing intermediate. In other

instances, materials are fabricated by chemically reacting an intermediate with a

reagent.

Brief Description of the Drawings

Figure 1 illustrates the charging and discharging behavior of an

electrochemical cell having an electrode fabricated from a material of the present

invention;

Figure 2 illustrates the coulombic efficiency of the cell of Figure 1; and

Figure 3 illustrates the discharge capacity of an electrode incorporating a

material of the present invention.

Detailed Description of the Invention

The present invention is directed to non-oxide, transition metal based ceramic

materials as well as to methods for manufacturing such materials and devices made

from the materials. The materials of the present invention are comprised of a

transition metal together with one or more of: N, C, B and Si. The materials of the

present invention readily intercalate group IA elements, as for example during the

charging and discharging of a battery electrode. Therefore, in accord with the present

invention, the materials can also include a group IA element therein; although, in

some instances, as for example when a battery electrode is being fabricated or

operated, the material may not include a group IA element therein. Most preferably, the general formula for the materials of the present invention

can be represented as A_yM₂Z_x, wherein A is a group IA element, M is a transition

metal, and Z is N, C, B, and Si, and in which x < 2 and y < 6-x.

Most typically the group IA element comprises hydrogen, lithium, sodium or

potassium; and in some particularly preferred embodiments, the group IA element is

lithium. In some other instances, the group IA element will preferably be hydrogen,

particularly when the resultant material is being utilized for electrochemical

applications as for metal hydride batteries. The transition metal component of the

material may comprise a single transition metal as well as a mixture of transition

metals. Among some of the more preferred transition metals are the early transition

metals, that is to say metals from groups IIIB-VIIB. It has been found that metals

from groups IVB-VIB have some particular utility in the practice of the present

invention.

The transition metals typically manifest a cubic, tetragonal or hexagonal

crystalline structure, and in the materials of the present invention, the crystalline

lattice of the transition metal is preserved, and the remaining elements thereof are

disposed interstitially in the lattice. While the interstitial elements may create some

lattice distortion, it has been shown by x-ray diffraction that the general lattice

structure is preserved. Typically, the group IA element occupies tetrahedral and/or

octahedral interstitial sites while the hydrogen, carbon, boron and/or silicon occupies

octahedral sites.

A variety of techniques may be employed to fabricate the materials of the

present invention. In one particular group of processes, the materials may be fabricated by using an electrochemical potential to insert the group IA element into

the remaining elements of the material. For example, an electrochemical cell may be

configured to include an electrode fabricated from a transition metal compound such

as Mo₂N as a cathode of the cell, and a body of lithium metal as the anode. Charging

of the cell will occur by insertion of lithium into the lattice of the Mo₂N; and similar

results may be obtained utilizing other elements.

Reaction may also be carried out in the absence of any externally applied

electrical field by chemical reaction of the various materials. In one group of chemical

reactions, an intermediate reactant which comprises a compound of the group IA

element and the transition metal is reacted with another reagent to produce the final

compound. For example, LiMoO₄ or LiVO₃ may be reacted with ammonia at an

elevated temperature so as to displace oxygen and incorporate nitrogen therein. In

another group of chemical reactions, a further displacement reaction may be carried

out wherein nitrogen is replaced by carbon in a high temperature carburizing reaction

by utilizing a carbon containing gas such as CH₄. Similarly, SiH₄, B₂H₆, and the like

may be reacted with a variety of materials to produce the compositions of the present

invention.

In another group of chemical reactions, an intermediate compound which

includes a transition metal is reacted with a reagent which contains a group IA element

and N, C, B, Si. For example, a transition metal halide may be reacted with a nitride

of a group IA element to produce the compounds of the present invention.

The materials of the present invention are not restricted to any particular

method of fabrication. Other reactions will be apparent to those of skill in the art, in view of the teaching presented herein. For example, organometallic compounds may

be employed to insert lithium or other group IA elements into a material. Treatment

with activated hydrogen, as for example in a hydrogen plasma, or treatment with high

pressure hydrogen, may be employed to insert hydrogen into the matrix.

The unique configurations and compositions of the materials of the present

invention provide physical and electronic properties which make them useful in a

variety of applications. For example, the materials of the present invention have

significant utility as electrodes of the type utilized in batteries, capacitors and the like,

and have been found to have particular advantage as electrochemical electrodes for

lithium ion and lithium polymer batteries. The materials of the present invention also

have utility as electrodes for other processes such as the electrosynthesis of chemical

products. These materials may be also employed as catalysts, either in the presence

of an applied electrical field, or as strictly chemical catalysts. The unique electronic

properties of these materials also present a number of opportunities for their use as

components of semiconductor devices.

Examples

The principles of the present invention will be illustrated by the following

examples, it being understood that the invention is not limited thereto.

Example 1

A lithium molybdenum nitride material was prepared by a solid state,

temperature programmed reaction in which Li₂MoO₄ was reacted with NH₃.

Approximately 1 gram of Li₂MoO₄ was placed in an alumina boat inside a quartz

reactor tube. Ammonia gas was flowed over the material at a flow rate of approximately lOOcc/min, and the temperature of the material was increased at a

heating rate of 350°C/hr to 400°C, and then at a heating rate of 60°C/hr to a final

reaction temperature of approximately 700 °C. The reactants were then held at this

temperature for approximately 60 minutes and then allowed to cool to room

temperature while maintaining the flow of ammonia. The cooled material was then

exposed to an atmosphere comprising approximately 1% oxygen in helium for

approximately 15 minutes in order to inhibit bulk oxidation of the material. The

resultant material is a compound characterized as Li₂MoN_x. The product was

analyzed by x-ray diffraction, and since scattering by lithium and nitrogen is

insignificant compared to that of the transition metals, the diffraction pattern was

dominated by the lattice structure of the molybdenum atoms. The lattice parameters

were similar to those listed in the reference literature tables for cubic molybdenum

nitride and carbide, but did not match exactly. The differences in parameters were

statistically significant, and could not be attributed to physical effects including those

due to crystalline size and micro strain. The results are consistent with the materials

being interstitial compounds having lithium and nitrogen at the interstitial sites of a

cubic metal lattice. The lattice structure is face centered cubic or Bl like that of NaCl.

The thus produced lithium molybdenum nitride material was also evaluated

coulometrically. The material was incorporated into an electrode which was

assembled into a cell with a lithium metal counter electrode. The cell was charged at

constant current which resulted in a transfer of lithium from the lithium molybdenum

nitride cathode to the lithium metal anode. The amount of lithium transferred was calculated by integrating the current to determine the total amount of charge

transfeπed, assuming Z=l for lithium ions.

Example 2

In this example, a lithium vanadium nitride material was prepared by a solid

state, temperature programmed reaction between LiVO₃ and ammonia, in a procedure

generally similar to that described hereinabove. Specifically, one gram of LiVO₃ was

placed in an alumina boat inside a quartz reactor tube, and ammonia flowed thereover

at a rate of lOOcc/min. The temperature was increased linearly from room temperature

to a final reaction temperature of approximately 600 °C, at a rate of approximately

300°C at a rate of 250°C/hr and then 60°C/hr. The reactants were held at the final

temperature for approximately 60 minutes, and then cooled to room temperature under

a flow of ammonia, and subsequently exposed to a mixture containing 1% oxygen in

helium for approximately 15 minutes in order to inhibit bulk oxidation of the material.

The product was analyzed by x-ray diffraction, and the results are consistent with the

material being an interstitial compound of lithium and nitrogen in the interstitial sites

of a cubic metal lattice. The structure of the resultant material is face centered cubic

or Bl like that of NaCl. The thus produced product was also evaluated

coulometrically, as in the foregoing example, and it was noted that when it was made

the cathode of an electrochemical cell, lithium was transferred from the cathode to an

anode, when the cell was charged at constant current.

Example 3

In this example, lithium vanadium nitride materials are prepared from a gelled

precursor. The gelled precursor is prepared by hydrolysis of a mixture of lithium and vanadium alkoxides by water, in an alcoholic solvent with an acid or base catalyst.

Common alkoxides of the metals, such as ethoxides, methoxides and isopropoxydes

may be employed, and the lithium vanadium ratio controlled by adjusting the relative

amounts of the precursors. Hydrolysis is effected by water in the alcohol solvent, and

the ratio of water to alkoxides should be near stoichiometric to cause complete

hydrolysis of the alkoxide mixture. Hydrolysis produces a gelled microstructure. The

solvent may be extracted from the gel, at ambient pressure to produce a high surface

area xerogel material. Alternatively, supercritical extraction may be employed to

produce an aerogel material. The resultant gels are calcined at approximately 400-

500 °C for 3 hours to produce a lithium vanadium oxide structure, which is

subsequently reacted as in the foregoing experiment to produce a high surface area

lithium vanadium nitride material.

It is to be noted that many of the oxide or nitride materials prepared according

to these examples may be converted to a corresponding carbide material by a high

temperature carburization process carried out at elevated temperature, and under an

atmosphere of a carbon containing material such as CH₄.

Example 4

In this example, an electrochemical reaction was employed to convert a

molybdenum nitride film into a lithium molybdenum nitride material. In a first stage

of the preparation, a molybdenum oxide film was prepared on a titanium foil substrate.

In order to prepare the oxide, an aqueous solution of ammonium paramolybdate was

dissolved in distilled water and acidified with 10% nitric acid. The resultant solution

was sprayed onto a heated titanium foil, using an ultrasonic nebulizer. The coating was converted to MoO₃ by calcination in stagnant air for 30 minutes at a temperature

of approximately 450°C. The oxide film was then converted to a nitride, by treatment

with ammonia at an elevated temperature. The molybdenum oxide was quickly heated

to approximately 350°C in a quartz tube furnace under a flow of approximately

lOOcc/m of ammonia. The temperature was then increased to approximately 450°C

at a rate of 40°C/min, and subsequently to 700 °C at a rate of 200°C/min, and held

constant thereat for approximately one hour. The material was then cooled to room

temperature under ammonia flow, and passivated in a flowing mixture of 1% oxygen

in helium for one hour so as to produce a molybdenum nitride film.

The molybdenum nitride film was then assembled as the cathode of an

electrochemical cell which included a lithium anode. Under constant current

conditions a potential was applied between the anode and cathode, and lithium ions

generated at the anode were transported to and inserted into the cathode to form

lithium molybdenum nitride. As noted above, carbide materials may be prepared from

the nitride by appropriate carburization steps, either before or after formation of the

lithium compound. In one carburization process, the nitride is heated in methane, at

a linear rate, from room temperature to 425 °C over one hour, and then raised to a

temperature of 650°C, at a linear rate, over 6.5 hours and held at 650°C for one hour.

Alternatively, the oxide may be directly reacted with methane or methane and

hydrogen.

Example 4A

In this example a vanadium carbide material was prepared and lithium inserted

thereinto via an electrochemical reaction. In a first stage of the preparation, a vanadium oxide film was prepared on a titanium foil by spraying an aqueous solution

of NH₄VO₃ onto a heated titanium foil, and calcining the salt in stagnant air for one

hour at 420°C to produce a V₂O₅ film. The oxide film was converted to the carbide

by treatment with methane at elevated temperature. Methane was flowed over the

sample at lOOcc/min, and the sample first heated, at a linear rate, from room

temperature to 300 °C over 30 minutes. The temperature was then linearly increased

to 921 °C over 207 minutes, and held thereat for 15 minutes. (In an alternative run,

the second heating was from 300°C to 870°C over 9.5 hours, with a 15 minute soak

at 870 °C.) After carburization was complete, the samples were cooled to room

temperature under methane and passivated for one hour in a 1 % mixture of oxygen in

helium.

Example 5

In this example, the compounds of the present invention are formed by

chemical reaction between Li₃N and transition metal halide compounds. For example,

compounds may be prepared by reacting transition metal halide with Li₃N in benzene,

in a high pressure vessel, under an argon atmosphere, at a temperature of

approximately 200°C to 400°C for 6 to 12 hours. Reactions under conditions of this

type produce a precipitate which may be collected and washed with dry ethanol to

remove any resultant lithium halide salts. The final product is dried under vacuum for

approximately 2 hours at 100° C to remove residual solvent. The final composition

of the product will depend upon the amount of lithium reagent in the starting mixture,

since the lithium will apportion between the products and reactants according to the

concentrations and thermodynamic stability of the compounds. In another variation of the foregoing, organolithium compounds such as n-butyl lithium may be added to

the initial reactants. During and subsequent to the thermal synthesis of the metal

nitride, lithium is transferred from the organolithium and inserted so as to form the

lithium metal nitride compound. This synthetic approach is attractive since it

generally requires somewhat lower processing temperatures than temperature

programmed nitridation reactions as described above.

Example 6

Sodium based transition metal ceramics may also be prepared in accord with

the foregoing procedures, as will be readily apparent to one of skill in the art. These

materials may be used as prepared, or sodium ions may be exchanged with lithium

ions to form a lithium based material. Such ion exchange reactions may be carried out

in excess of molten lithium nitrate for approximately 6 hours at a temperature of

250°C to 300°C. Ideally, the procedure is repeated several times to ensure complete

ion exchange. By first building the host lattice with sodium ions and subsequently

exchanging them for smaller lithium ions, higher ionic diffusivity will result.

Example 7

In another experimental series, metal nitride or metal carbide precursor

compounds are prepared in accord with the procedure of Example 4, and converted

to the corresponding lithium containing materials by a chemical process. In this

procedure, the metal nitrides or metal carbides are stirred for several days under argon

in a solvent containing an organolithium compound, as for example in a hexane

solution of n-butyl lithium. The resultant products are recovered and washed in

hexane and dried in vacuum. They may be annealed to improve crystallinity. Example 8

In this example, lithium molybdenum nitride was fabricated into a cathode of

a battery. The material was prepared from high surface area (greater than 5 m²/gr)

lithium molybdenum nitride powder prepared in accord with the general procedure

detailed with regard to Example 4. The powder was mixed with about 10% by weight

of a Teflon binder to form an aqueous suspension, and the electrode/binder mixture

blended for 2 minutes with isopropanol added as needed to maintain liquid

consistency. The electrode/binder mixture was separated from the liquid by filtration,

and kneaded and rolled into progressively thinner cakes so as to form a layer of

approximately 0.010-0.015 inch thickness. Nickel mesh was pressed into the layer

and the mesh/electrode/binder mixture consolidated by uniaxial pressing at

approximately 10,000 psi. The resulting electrode was dried for approximately 6

hours at 120°C to remove isopropanol and water. The still warm electrode was

transferred into a dry box and used to assemble a test cell. The anode of the test cell

was lithium foil and the electrolyte was IM LiPF₆ in 1:1 propylene carbonate/

ethylene carbonate. A porous polypropylene paper was used to separate the electrode

from the lithium foil, and constant current charging and discharging experiments were

performed.

The test results showed that the resultant cell manifested reproducible and

reversible energy storage, and the shape of the charge and discharge curves suggest

that lithium ions are inserted into the high surface area electrode material.

Specifically, the voltage change with time (under constant current) was nonlinear.

The relationship between voltage and time is typically linear for charged storage via double layer formation. Ion insertion was also inferred from the measured

capacitances. Results at larger charging currents were also consistent with the energy

storage process being based on mechanisms other than electrochemical double layer

charging. The charge storage capacity for the electrode material was 119 mAh/g. The

theoretical capacity corresponding to inserting one half equivalent of lithium per

molybdenum atom is 126 mAh/g. This capacity is consistent with the reversible

lithium ion occupation of one half of the octahedral lattice sites, while the other half

of the octahedral sites are permanently occupied by nitrogen.

Example 9

In this example, an electrochemical cell was prepared utilizing a high surface

area of vanadium nitride material as an electrode. The vanadium nitride material was

prepared in accord with the general procedure set forth in Example 4A, and had a

surface area of approximately 28 m²/gr. Electrodes and test cells were fabricated

according to the methods of Example 8. Figure 1 illustrates the behavior of the

vanadium nitride electrode on cycling between 0.5 and 4.2 volts utilizing charging and

discharging currents. The test results show reproducible and reversible energy storage

consistent with the insertion of lithium ions into the electrode material. Ion insertion

was also inferred from the measured specific capacitances of the electrode. Typical

double layer capacitances are in the range of 1-100 microfarad per cm² (usually at the

lower end for aprotic electrolytes). Equivalent capacitances in excess of 390

microfarad per cm² were observed at the lower charging currents for the present

electrodes. Results at the higher charging currents are also consistent with the energy storage process being based on mechanisms other than electrochemical double layer

charging.

The electrode area and vanadium nitride loading were 0.6 cm² and 26 mg

respectively corresponding to current densities of 0.5-8.0 mA/cm² and 12-183 mA/gr.

The coulombic efficiency for the charge/discharge was high and reproducible over

extended cycling as shown in Figure 2. The capacity was greater than 1 mA/hr for a

current density of 0.5 mA/cm² yielding an energy density of greater than 90 Wh/kg.

Corresponding average power density was 27 W/kg. Table 1 summarizes the results

for this experiment. Additional experiments demonstrate that the subject electrode is

stable up to 4.2 volts. Charge storage capacities of up to 150 mAh/g were observed

for this material, and the theoretical capacity for this material (corresponding to

insertion of one half equivalent of lithium per vanadium atom) is 218 mAh/g.

Table 1

Charging/Discharging Energy Density Average Power

Current ( mA) (Whlkz) Densitv (W/kg

0.3 94.9 27.1

0.6 74.6 54.2

1.25 56.5 113.0

2.4 36.2 217.0

4.75 7.2 429.3

Example 10

In this experiment, a test cell was assembled utilizing high surface area

(greater than 5 m²/gr) vanadium carbide powders as starting material for electrodes.

The vanadium carbide was prepared in a procedure generally similar to that set forth in Example 4, and electrodes of test cells fabricated according to the methods of

Example 8.

This experimental series showed that the electrode provided for reproducible

and reversible energy storage consistent with insertion of lithium ions thereinto.

Figure 3 illustrates the behavior of the electrode on cycling between 1.0 and 3.7 volts

using charging/discharging rates of approximately C/3. Ion insertion is also inferred

from the measured specific capacitance of the electrode, which was in excess of 300

microfarad/cm² at low charging currents. Capacitances at higher currents were also

consistent with an energy storage process which is not based on double layer charging.

The capacity was in excess of 200mAh/g, with the theoretical maximum being 222

mAh/g (assuming occupancy of one-half of the octahedral sites by lithium, with the

other half of the sites being occupied by carbon).

The foregoing examples are illustrative of particular aspects of the present

invention, but are not meant to be limitations upon the practice thereof. Yet another

embodiments of the present invention may be readily implemented. For example, the

materials of the present invention, particularly when fabricated in high surface area

morphologies, can be used as electrodes for electrochemical, double layer capacitors.

Upon polarizing such an electrode, in an electrolytic medium, capacities in the range

of 1-50 microfarad per cm² of surface area are obtained. The presence of lithium or

other group IA elements will further improve the open circuit potential and stability

of the capacitors.

Electrodes based on titanium or solid solutions including titanium in

substantial atomic fractions are very attractive due to their low cost and low mass density. For example, the theoretical gravimetric charge storage densities of lithium

titanium carbide is greater than 230 mAh/g, which is substantially higher than

presently favored cobalt, nickel or manganese oxide electrode materials. In accord

with the present invention, group IV carbide or nitride materials may be employed to

form interstitial lithium containing compounds. In order to optimize the crystal

structure of the group IV element containing materials, dopants or crystal structure

stabilizing materials may further be included in the material. For example, the

inclusion of vanadium and/or molybdenum in the host lattice material will facilitate

the formation of crystalline lattices which form interstitial compounds with group I A

elements, since phase diagrams indicate that these two metals form a continuous series

of solid solutions with group IV metals. Hence, in accord with the present invention,

the gravimetric charge of storage density of electrochemical devices may be enhanced

by combining metals to form a solid solution, interstitial lithium metal compound.

The addition of yet other elements can lead to improved microstructural properties

through the creation of larger pores and higher concentrations of defects, both of

which may enhance the ionic diffusivity in these materials. Adding other metal atoms

as dopants offers additional promise of enhancing the energy density by increasing the

free energy associated with the insertion reaction.

While the foregoing examples primarily describe the use of the materials of

the present invention as cathodes of electrochemical cells, in some instances, the

materials of the present invention may also have utility as anodes of electrochemical

cells. For example, it has been found that host materials in which lithium occupies

energy levels closer to that of elemental lithium are best suited for anode materials, and the materials of the present invention intercalate lithium in low energy states. In

yet other instances, the materials of the present invention are useful as additives to

enhance the conductivity of lithium ion battery electrodes. Commercial electrodes are

fabricated from lithiated metal oxides based on nickel, cobalt or manganese. Because

the intrinsic conductivity of these materials is low, the electrodes utilized in

commercial batteries generally require the addition of carbon or other additives to

enhance their electrical conductivity. Such materials are typically present in volume

fractions of 10% or more. Such conductivity enhancing additives do not participate

in energy storage and thus represent parasitic mass. The nitride and carbide materials

of the present invention have higher conductivity than carbon and furthermore can

participate in energy storage. Therefore, these materials may be incorporated into

conventional lithium batteries as conductivity enhancers.

As noted above, the electrochemical potential of the materials of the present

invention can be controlled by varying their stoichiometry. This is important, since

in many prior art cathode materials, lithium insertion occurs at a relatively constant

potential, hence such cells give no indication of impending depletion of charge or

overcharging. Hence, such prior art cells can often produce unexpected power losses,

or may be inadvertently overcharged, or over discharged, since the state of their

charge cannot be readily measured.

The materials of the present invention can be made to manifest an

electrochemical potential which varies with the state of charge, hence such materials

may be incorporated into a storage battery, either as an electrode, or as an electrode

additive, and when this is done, the resultant cell will provide a charge/discharge potential profile which is indicative of the state of its charge. Therefore, such cells

can be made to effectively signal their state of charge so as to allow for control of

charging and discharging.

While the foregoing examples have primarily been directed to the insertion

of sodium and lithium into the materials of the present invention, protons may be

similarly inserted into these materials, as for example by using methods corresponding

to those set forth in Example 6. Such hydrogen containing materials have widespread

use as metal hydride battery electrodes, hydrogen storage materials and hydrogenation

catalysts.

It will be appreciated from the foregoing, that the present invention provides

for the synthesis of a wide variety of unique materials having electrical, chemical and

electrochemical properties which may be readily controlled and tailored. The

materials of the present invention are based upon a crystalline lattice structure

determined by one or more host transition metals. The materials of the present

invention can readily accommodate, and release, hydrogen, lithium, sodium,

potassium and other group I elements. Hence, the materials of the present invention

can be custom tailored for particular applications. The foregoing examples have

described some particular embodiments and applications of the materials of the

present invention. In view of the teaching presented herein, one of skill in the art will

readily appreciate that other modifications, variations and embodiments may be

implemented in accord with the present invention. Therefore, the foregoing is

illustrative of the present invention, but is not to be a limitation upon the practice thereof. It is the following claims, including all equivalents, which define the scope

of the invention.

Claims

1. A transition metal based ceramic material having the general formula:

A_yM₂Z_x, wherein A is a group IA element, M is a transition metal, and Z is a member

selected from the group consisting of: N, C, B, Si, and combinations thereof; wherein

x < 2 and y < 6-x.

2. A material as in claim 1, further characterized in that said material has

a cubic, tetragonal or hexagonal lattice structure.

3. A material as in claim 1, wherein said transition metal has a cubic,

tetragonal or hexagonal crystalline lattice and wherein A and Z occupy interstitial sites

in said lattice.

4. A material as in claim 1 , wherein A is lithium.

5. A material as in claim 1 , wherein M is a transition metal selected from

groups IIIB-VIIB of the periodic table.

6. A material as in claim 1 , wherein M is a transition metal selected from

groups IVB-VIB of the periodic table.

7. A material as in claim 1 , wherein M comprises a plurality of transition

metals.

8. An electrochemical electrode comprised of a transition metal based

ceramic material having the general formula A_yM₂Z_x wherein A is a group IA

element, M is a transition metal and Z is a member selected from the group consisting

of: N, C, B, Si, and combinations thereof, wherein X < 2 and Y < 6-x.

9. A catalytic body comprised of a transition metal based ceramic material

having the general formula A_yM₂Z_x wherein A is a group IA element, M is a transition

metal and Z is a member selected from the group consisting of: N, C, B, Si, and

combinations thereof, wherein X < 2 and Y < 6-x.

10. An electrode for a battery comprising a powder having a surface area

in excess of 5 m²/g, said powder comprising a compound of a transition metal and a

member selected from the group consisting of: N, C, B, Si, and combinations thereof.

11. A method for making a material of the general formula A_yM₂Z_x,

wherein A is a group IA element, M is a transition metal and Z is a member selected

from the group consisting of: N, C, B, Si, and combinations thereof, wherein X < 2

and Y < 6-x, said method including the steps of:

providing an intermediate of the general formula M₂Z_x; and

electrochemically adding a group IA element thereto.

12. A method as in claim 11 , wherein said step of electrochemically adding

said group I A element comprises:

making said M₂Z_X the cathode of an electrochemical cell;

making said IA element a component of the anode of said electrochemical cell;

and

passing current through said electrochemical cell, whereby said group IA

element is inserted in said M₂Z_x intermediate so as to provide a material of the

formula A_yM₂Z_x.

13. A method of making a material of the general formula A_yM₂Z_x,

from the group consisting of N, C, B, Si, and combinations thereof; wherein x < 2 and

y < 6-x, said method including the steps of:

providing an intermediate reactant which comprises a compound of said group

IA element, A, said transition element, M, and another element, B, which is different

from A and M; and

chemically reacting said intermediate with a reagent containing an element Z

as set forth above, so as to convert said intermediate to said material having the

general formula A_yM₂Z_x.

14. A method as in claim 13, wherein B is oxygen, and said reagent is

ammonia.

15. A method as in claim 13 , wherein B is oxygen or nitrogen and wherein

said reagent is a hydrocarbon.

16. A method of fabricating a transition metal based ceramic material

having the general formula A_yM₂Z_x, wherein A is a group IA element, M is a

transition metal, and Z is a member selected from the group consisting of: N, C, B, Si,

and combinations thereof; wherein X < 2 and Y < 6-x, said method including the steps

of:

providing an intermediate compound which includes said transition metal

therein; and

reacting said intermediate compound with a reagent which contains said group

IA element and said member Z so as to convert said intermediate compound to said

material having the general formula A_yM₂Z_x.

17. A method as in claim 16, wherein said intermediate is a transition metal

halide.

18. A method as in claim 17, wherein said reagent is a nitride of a group

IA element.