Chamber for reaction of lithium and deuterium

Abstract

An electrochemical device is described which consists of two electrolyte chambers separated by a common electronically conducting cathode, such as a metal foil. On one side of the common cathode is a non-aqueous electrolyte which does not react with lithium metal and from which lithium metal may be plated. On the other side of the common cathode is an aqueous electrolyte from which isotopes of hydrogen may be electrochemically reduced on the common cathode. The cathode is impervious to either electrolyte. The anode on the non-aqueous side contains lithium metal, and on the aqueous side, the anode is an electronically conductive material which will not react with the electrolyte during the electrochemical release of oxygen. The purpose of the common cathode is to bring elemental lithium and elemental hydrogen together by diffusion within a metallic matrix, free of either electrolyte. Additionally, a non-electrochemical device is described which allows isotopes of lithium and hydrogen to interact within an alloy capable of absorbing both elements in a condensed phase.

Description

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/754,576, filed on Dec. 27, 2005. The entire teachings of the above application is incorporated herein by reference.

TECHNICAL FIELD

This invention relates to electrochemical devices, and particularly devices intended to separate elements from electrolytic solutions containing their compounds. Further, this invention relates to a novel method for bringing reactants together apart from the electrolyte from which they are obtained, in a way which can be controlled by regulating the current or pressure.

BACKGROUND OF THE INVENTION

One of the most serious problems facing society is our ever growing need for energy, and our almost complete dependence on non-renewable sources, including fossil fuels such as petroleum and coal, to fill this need. If renewable sources of energy could be used to offset some of our stationary needs, such as heating and electrical power, some of the pressure placed on fossil fuels could be relieved. However, the alternative sources of energy we do have are only capable of supplying a fraction of the energy that we use. Further, alternative sources of energy cannot address one of the most urgent needs that we have: how to replace the gasoline, oil, and natural gas we use for transportation.

The recent summary by Hagelstein et al. (see Peter L. Hagelstein, Michael C. H. McCubre, David J. Nagel, Talbot A. Chubb, and Randall J. Heckman, “New Physical Effects in Metal Deuterides”, http://www.lenr-canr.org/acrobat/Hagelsteinnewhysica .pdf; December, 2004) cites 141 references of the voluminous effort to understand the effect first reported by Fleischmann et al. in 1989 (see. Martin Fleischmann, S. Pons, and M. Hawkins, J. Electroanal. Chem., 201, 301 (1989); 263, 187 (1990) and Martin Fleischmann, S. Pons, M. W. Anderson, L. J. Li, and M. Hawkins, J. Electroanal. Chem., 287, 293 (1990)). Hagelstein et al. concluded that at least one nuclear reaction, perhaps more, was occurring when deuterium was confined in palladium or palladium alloys such as palladium/silver or palladium/gold, after introducing it electrochemically by electrolysis of heavy water, or physically by introduction of deuterium gas. The evidence was based partly on “excess heat” sometimes produced, which exceeded by several orders of magnitude the amount which could be accounted for by chemical reaction products. The reaction thought responsible was the interaction of deuterons (heavy hydrogen nuclei) with each other. “Excess heat” was not observed when deuterium was replaced with ordinary hydrogen. Helium 4 was thought to be one of the products, but the amounts of helium 4 actually found have been at such a low level that many are skeptical as to whether it actually was a product of some nuclear reaction or just part of naturally occurring helium. In fact no one has yet produced the effect at a high enough power level to dispel these doubts.

Three reactions are known to occur during the bombardment of a target containing deuterium with deuterons, according to conventional physics:
₁H²+₁H²→₂He⁴+γ(23.08 MeV); 10⁻⁵ %   1)
₁H²+₁H²→₂He³(0.82 MeV)+n(2.45 MeV); 50%   2)
₁H²+₁H²→₁H³(1.01 MeV)+₁H¹(3.02 MeV); 50%   3)

Reaction 1 is presumed to be responsible for “excess heat” when deuterium is confined in a palladium lattice. However, it occurs during bombardment as a very minor fraction of the other two, which predict the formation of neutrons, helium 3, and tritium (hydrogen 3). One would have to assume that in the condensed phase, previously unknown physical phenomena were occurring which would somehow allow Reaction 1 to predominate. Most of the energy would be in the gamma ray. At least some of it would be expected to escape or appear as secondary radiation.

Fleischmann and Pons (see for example Eugene Mallove, “Fire from Ice”, Infinite Energy Press, softbound (1999). page 43. Originally published by John Wiley & Sons, Hoboken, N.J. (1991)) claimed that their cells were producing 25 watts per cubic centimeter of heat beyond what could be accounted for by chemical and electrochemical reactions. If the heat had come from a deuteron-deuteron reaction with the known branching ratio shown above, radiation from neutrons would have been fatal. R. Petrasso (see in Mallove, page 190) observed that no gamma ray accompanied the formation of “excess heat”.

These observations would then suggest that none of reactions 1, 2, or 3, were responsible for the “excess heat”. In many of the electrochemical experiments, lithium deuteroxide was present in the heavy water. Palladium and palladium alloys have been used successfully as the cathode to produce “excess heat”. Palladium not only absorbs over 600 times its volume in hydrogen gas, palladium is the only metal in its subgroup (nickel, palladium, and platinum) which is also capable of forming solid solutions with low concentrations of lithium near ambient temperature. Appleby (Mallove, page 220) indicated that lithium deuteroxide was needed in order to produce “excess heat”. There is therefore evidence that both deuterium and lithium are essential reactants during the production of “excess heat” in at least some electrochemical experiments. The element lithium occurs in nature as two stable isotopes, lithium 6 (7.39%) and the remainder, lithium 7. Lithium metal enriched in lithium 6 may be obtained commercially. Two nuclear reactions between hydrogen (or deuterium) and the two stable isotopes of lithium known to occur during the bombardment of lithium metal targets with either ordinary hydrogen or deuterium are as follows (see, for example, http://www.physics.isu.edu/sigmabase/data/li6.html and /li7.html):
₁H¹+₃Li⁷→2 ₂He⁴ (17.25 MeV)   4)
₁H²+₃Li⁶→2 ₂He⁴ (25 MeV)   5)

Neither of these reactions would produce gamma rays, neutrons, ₁H³ (tritium), or ₂He³ nuclei, but only ordinary helium, ₂He⁴. The cross section for reaction 5 is larger than that for reaction 4, (last reference above) which may account for why “excess heat” has not been observed in ordinary water.

Since metallic lithium reacts with water, an explanation is needed as to how lithium might have found its way from an aqueous electrolyte into palladium to take part in the proposed reactions shown above. When exposed to a solvent or an electrolyte, metallic lithium reacts superficially to form a thin salt film on its surface. This film has been called a “solid electrolyte interphase” (SEI) (see for example E. Peled, “The Electrochemical Behavior of Alkali and Alkaline Earth Metals in Nonaqueous Battery Systems—The Solid Electrolyte Interphase Model”, J. Electrochem. Soc. 126, 2047-2051 (1979)). If the SEI is soluble, such as in water, the lithium takes part in a violent reaction. If it is not, such as in many organic solvents including propylene carbonate, the film acts as a solid electrolyte, through which only lithium ions may pass. In the past, hundreds of hours of electrolysis were needed before “excess heat” was apparent (Hagelstein et al., page 2). During this time, the possibility exists that a slightly soluble film of lithium carbonate formed on the palladium cathode, through which lithium was plated. The electrolyte had originally contained lithium deuteroxide, which would eventually have formed slightly soluble lithium carbonate by reaction with carbon dioxide from the atmosphere.

SUMMARY OF THE INVENTION

The purpose of this invention is principally to provide a better means for facilitating interactions occurring in systems which contain the materials discussed above. The objective is to bring both deuterium and lithium into a metallic matrix at the same time.

In one embodiment, the stated purpose is accomplished through electrochemical means, for example by reducing hydrogen (deuterium) from an aqueous electrolyte into the metallic matrix such as palladium. Yet an aqueous electrolyte seems hardly the only appropriate one to choose to admit lithium into the metallic matrix, since as already stated, metallic lithium reacts with water.

This invention seeks to eliminate this problem by providing a double-chambered electrochemical cell in which each chamber contains a different liquid electrolyte, one aqueous and the other non-aqueous. The chambers are separated by an electronically conductive membrane such as palladium foil, impervious to each of the liquid electrolytes but capable of absorbing both elemental lithium and elemental hydrogen (deuterium). The non-aqueous electrolyte is heat resistant and one from which lithium can be plated. When the membrane is made cathodic with respect to a lithium anode situated in the non-aqueous electrolyte, lithium is electrochemically plated on the membrane from the non-aqueous side. The metal will begin to diffuse into the membrane. When the membrane is made cathodic with respect to an appropriate anode situated in the aqueous electrolyte, hydrogen (deuterium) is electrochemically reduced from the aqueous side. The hydrogen will also begin to diffuse into the membrane. The elements will then meet within the membrane, each free of its respective electrolyte.

In other embodiments, lithium and deuterium can be brought together within a metallic matrix by selecting a solid solution or compound of lithium with metals which are also capable of absorbing hydrogen (deuterium), for example, magnesium to which nickel has been added. The alloy can be placed within a container from which ambient atmosphere is withdrawn, said container then being charged with hydrogen (deuterium) at a measured rate.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 is a representation of an electrochemical cell constructed according to this invention. Shown in this cross section are the two cylindrical electrolyte chambers, the membrane, for example palladium foil, the Viton™ O ring seals as a means for containing the electrolytes within the cell, the lithium anode on the non-aqueous electrolyte side, the inert anode on the aqueous side, the thermocouple for measuring temperature, and the exhaust ports as a means to allow the hydrogen (deuterium) and oxygen generated during electrolysis to escape from the system without mixing with each other, and to allow the equalization of pressure on the non-aqueous side. Not shown are the clamp needed to hold the two chambers against the O ring seals and the palladium foil, and the two constant current DC power supplies needed to run current through each of the electrolyte chambers.

FIG. 2 shows a hollow tube of resilient metal or alloy such as stainless steel, in which is placed an alloy, as a powder or a sintered powder, capable of absorbing both lithium and hydrogen (deuterium). One example is an alloy consisting of magnesium, lithium (preferably lithium 6) and nickel. The tube includes an opening to permit charging the tube with the alloy, and a valve through which air may be evacuated and hydrogen (deuterium) may be admitted.

DETAILED DESCRIPTION OF THE INVENTION

A description of preferred embodiments of the invention follows.

FIG. 1 is a cross section of an electrochemical cell according to one embodiment of this invention. The body is constructed from cylindrical borosilicate glass tubes, such as Pyrex™. Element number 1 is a flat membrane, for example palladium foil, in which the hydrogen (deuterium) and the lithium are to be brought together. It is the common cathode, or the negative electrode where electrochemical reduction occurs. This electrode is connected to the negative terminal of each of the two direct current power supplies. The power supplies regulate the current through each half of the cell.

Element number 2 shows the position of the O ring seals which fit within flanges, 3, on each half of the cell. Not shown is the clamp needed to compress the flanges against the O rings and the common cathode, 1.

During electrolysis in the aqueous (left) side, some, but not all of the hydrogen (deuterium) will be absorbed by the palladium, 1. That which is released will find its way to the vertical tube (arm) in which the thermocouple, 4, is positioned to measure temperature. The thermocouple is situated in a glass sleeve (not shown) to protect it from the aqueous electrolyte, 7. The thermocouple housing includes means such as matching ground glass joints to protect the electrolyte from the environment, and a port to which is attached a sealed flexible tube which leads the hydrogen (deuterium) released by electrolysis safely away from the cell. The escaping hydrogen (deuterium) keeps the aqueous electrolyte stirred. For clarity, the sleeve, housing, and flexible tube are not shown.

Number 5 represents the electrolyte levels in each of the four arms in the cell. Since the common cathode, 1, is impervious to both electrolytes, the level in each half of the cell will not necessarily be the same. The level will be the same in each of the two arms on either side. It is only important that the two anodes, 6 and 9, be immersed in their respective electrolytes. For this reason, water (heavy water) has to be added to the aqueous side from time to time.

Number 6 represents the anode on the aqueous side, preferably a piece of metal foil. The anode may be nickel if the electrolyte is caustic, or a noble metal such as platinum if the electrolyte is not caustic. It is placed high enough in its arm such that the oxygen released by electrolysis cannot escape back into the cell. It is attached to an electrical feedthrough such as a platinum wire which is hermetically sealed in a Pyrex ground glass joint. The joint fits into a corresponding joint on the cell. The electrical feedthough leads to the positive terminal of one of the direct current power supplies. The joint containing the platinum wire also has a port for a sealed flexible tube similar to the one in the arm with the thermocouple, 4. This flexible tube prevents the atmosphere from entering the cell and leads the oxygen released by electrolysis safely away from the apparatus. For clarity, the seals and the tube are not shown.

Number 7 represents the aqueous electrolyte containing of course either water or heavy water. The electrolyte should be as conductive as possible to minimize the energy needed to carry out electrolysis. For this reason, the most preferred electrolyte solutes are strong acids or bases, such as sulfuric acid, methanesulfonic acid, trifluoromethanesulfonic acid, trifluoroacetic acid, trichloroacetic acid, toluenesulfonic acid or mixtures thereof, and lithium, sodium, potassium, rubidium, or cesium hydroxide (deuteroxide) or mixtures thereof. Preferred are alkali or alkaline earth sulfates or carbonates such as lithium, sodium, potassium, or magnesium sulfate, or sodium or potassium carbonate. Less preferred are hyrdohalic acids such as hydrochloric acid, halide salts such as alkali chlorides, bromides, or iodides, or acids or salts of toxic or reactive species such as nitrates, chlorates, perchlorates, iodates, periodates, bromates, or oxalates.

Number 8 represents the nonaqueous electrolyte. Many nonaqueous electrolytes have been identified which are stable at ambient temperature in the presence lithium and are, for example, useful in lithium batteries. Electrolytes for the purpose of this invention must be thermally stable at temperatures from ambient up to at least 100 degrees centigrade (the boiling point of water), preferably have relatively low vapor pressure over this range, and most important, not react with lithium at an appreciable rate at least up to and preferably beyond this temperature. The most preferred electrolyte solvents are glycol ethers such as diethylene glycol dimethyl or diethyl ether, triethylene glycol dimethyl or diethyl ether, or tetraethylene glycol dimethyl or diethyl ether, the methyl and ethyl ethers of 1,3-propane diol and propylene glycol, or mixtures thereof. Less preferred are cyclic carbonate esters such as ethylene or propylene carbonate, dimethyl sulfoxide, ethylene and propylene sulfite, sulfolane, succinic anhydride, or mixtures thereof The most preferred lithium electrolyte salts are bis(oxalato)borate, malonato-oxalatoborate, bis-(malonato)borate, and tris-(oxalato)phosphate. Less preferred lithium salts include tetrafluoroborate, hexafluorophosphate, trifluoromethanesulfonate, trifluoroacetate, bis-(trifluoromethanesulfonyl)imide and bis-(perfluoroethanesulfonyl) imide.

Number 9 represents the anode for the nonaqueous electrolyte, which contains metallic lithium, preferably lithium 6. It may for example consist of metallic lithium pressed on a nickel screen, which is in turn connected to a platinum wire which is hermetically sealed within a borosilicate ground glass joint. Said platinum wire leads to the positive terminal of the second direct current power supply. Said joint in turn fits on a mating joint which seals the compartment and protects it from the environment. No gas is expected to form in the arm containing the lithium anode, 9, but as the temperature rises, the vapor pressure of the solvent may lower the electrolyte level. In addition, hydrogen may diffuse through the palladium cathode, 1, and have to be expelled through the port at 10. Therefore, each arm on the nonaqueous side will have a port and sealed flexible tubing similar to the ones on the aqueous side. The cell is submerged in a circulated heat transfer fluid.

Other Preferred Embodiments

Elaboration of the basic design of the cell is within the scope of this invention. For example, the cell could include means such as a catalyst to recombine the hydrogen (deuterium) and oxygen released by electrolysis, so that the addition of water (heavy water) would not be necessary during operation. The cell would be expected to accumulate oxygen, particularly shortly after startup, which might have to be vented, or the vapor volume preloaded with hydrogen (deuterium).

Rather than operating at atmospheric pressure, the cell could be sealed so that it could operate under pressure at higher temperature. To contain molten lithium when the temperature rises above its melting point, the nickel screen in the anode, 9, may consist instead of sponge metal of a 1 to 1 alloy of nickel and aluminum. Lithium does not alloy with nickel, but it will alloy with aluminum and will therefore wet and be absorbed within the metal sponge.

Instead of using a cathode in the shape of a flat piece of metal, the cathode could be a long hollow cylindrical container filled with non-aqueous electrolyte and concentric with an inner lithium anode and an outer container filled with aqueous electrolyte. The whole assembly could be placed with similar cells in a heat transfer fluid.

FIG. 2 shows an alternative embodiment for carrying out the purpose of this invention by other than electrochemical means. Object “1” represents a hollow cylindrical tube or container made of a metal or alloy such as stainless steel, capable of withstanding heat and corrosion. A top or cover 2, made of the same material as container 1, fits the open end of the container 1, and can be tightly sealed to the tube, either by a tapered thread, an O ring seal, or both (3). A reaction medium 4, is preferably a sintered powder prepared from an alloy capable of absorbing both hydrogen (deuterium) and lithium. Lithium and magnesium form solid solutions over the entire range of composition. Alloys of magnesium and nickel, (1 to 55% nickel) are capable of absorbing up to 7% hydrogen (deuterium) by weight (See R. L. Holtz and M. A. Imam, J. Mater. Sci. 32, 2267 (1997); 34, 2655 (1999)). Calcium-nickel alloys also absorb hydrogen (Sandrock, U.S. Pat. No. 4,161,401), and calcium forms uniform solid phases with lithium. Alloys of magnesium, nickel, and titanium are also known to absorb hydrogen (See Lomness, J. K., Hampton, M. D., Giannuzzi, L. A., “Hydrogen Storage in Titanium-Magnesium-Nickel Mixtures”, Defect Properties and Related Phenomena in Intermetallic Alloys, Boston, Mass., Materials Research Society Symposium, Proceedings v. 753 (2003) p. 541-546.)

It can also be advantageous to have the alloy in a form such as nanoparticles, or ball-milled according to the cited references, to maximize the amount of hydrogen (deuterium) which can be absorbed.

The alloy is preferably placed within the tube under inert atmosphere, such as argon in a glove box, since these alloys are air sensitive. A valve 5, such as a needle valve, and connecting tube 6, provide passages through which the ambient atmosphere is exhausted, and through which the hydrogen (deuterium) may be admitted at a measured rate.

The entire apparatus of FIG. 2 (except for the valve 5) may be positioned in a heat transfer fluid such as water.

The examples given here are not meant to limit the scope of this invention. Those skilled in the art will recognize alternative designs which will allow the interaction of reagents by introducing them to each other within a solid matrix by diffusion from opposing directions, and otherwise accomplishing the goals described above.

While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims

1. An apparatus for introducing deuterium and lithium into a metallic matrix comprising:

a double-chambered electrochemical cell in which each chamber contains a different liquid electrolyte, one aqueous (solvent plus conductive solute) and the other non-aqueous (solvent plus conductive solute), the non-aqueous electrolyte being heat resistant and one from which lithium can be plated;

an electronically conductive membrane arranged so as to separate the chambers, the membrane impervious to each of the liquid electrolytes but capable of absorbing both elemental lithium and elemental hydrogen (deuterium), and serving as the cathode for both chambers;

a lithium anode situated in the non-aqueous electrolyte serving as the counter electrode for that chamber, a current thereby causing lithium to be electrochemically plated on the membrane from the non-aqueous side, and allowing the metal to begin diffusing into the membrane; and

a second anode on the aqueous side to serve as a counter electrode for applying a cathodic current to the membrane, thereby electrochemically reducing hydrogen (deuterium) from the aqueous side, and also causing hydrogen to diffuse into the membrane, and thus causing the deuterium and lithium elements to meet within the membrane, each free of their respective electrolyte.

2. An apparatus as in claim 1 wherein the electrically conductive membrane is palladium foil, or a foil prepared from an alloy of palladium with silver.

3. An apparatus as in claim 1 wherein the solvent in the aqueous side is light water (H2O), heavy water (D2O), or a mixture.

4. An apparatus as in claim 1 wherein the lithium anode comprises metallic lithium, either essentially of isotope mass 6, or mass 7, or a mixture thereof, pressed onto a nickel screen.

5. An apparatus as in claim 1 wherein the second anode is formed from one of nickel or platinum.

6. An apparatus as in claim 1 wherein the conductive solute in the aqueous electrolyte is selected from sulfuric acid, methanesulfonic acid, trifluoromethanesulfonic acid, trifluoroacetic acid, trichloroacetic acid, toluenesulfonic acid or mixtures thereof, and lithium, sodium, potassium, rubidium, cesium hydroxide (deuteroxide) or mixtures thereof.

7. An apparatus as in claim 1 wherein the conductive solute in the aqueous electrolyte is selected from alkali, alkaline earth sulfates, carbonates such as Is lithium, sodium, potassium, or magnesium sulfate, sodium, or potassium carbonate.

8. An apparatus as in claim 1 wherein the conductive solute in the aqueous electrolyte is selected from hyrdohalic acids such as hydrochloric acid, halide salts such as alkali chlorides, bromides, or iodides, or acids or salts of toxic or reactive species thereof such as nitrates, chlorates, perchlorates, iodates, periodates, bromates, or oxalates.

9. An apparatus as in claim 1 wherein the non-aqueous electrolyte is thermally stable at temperatures from ambient up to at least 100 degrees centigrade (the boiling point of water), preferably have relatively low vapor pressure over this range, and most important, not react with lithium at an appreciable rate at least up to and preferably beyond this temperature.

10. An apparatus as in claim 1 wherein the non-aqueous solvent is selected from a glycol ether such as diethylene glycol dimethyl or diethyl ether, triethylene glycol dimethyl or diethyl ether, or tetraethylene glycol dimethyl or diethyl ether, the methyl and ethyl ethers of 1,3-propane diol and propylene glycol, or mixtures thereof, and the conductive solute includes a salt of lithium 6, lithium 7, or a mixture, the anion being selected from bis-(oxalato)borate, malonato-oxalatoborate, bis-(malonato)borate, tris-(oxalato)phosphate, tetrafluoroborate, hexafluorophosphate, bis-(trifluoromethanesulfonyl) imide, trifluoroacetate, perfluoroethanetrifluoromethanesulfonylimide, bis-(perfluoroethanesulfonyl) imide, trifluoromethane sulfonate, tetrachloroaluminate, trifluoromethanetrifluoroacetylsulfonyl amide, and closo-carborates and closo-borates such as B11X11CX−, B12X122−, or B10X102−,where X is hydrogen, a halogen such as F, Cl, Br, or I, or a mixture.

11. An apparatus as in claim 1 wherein the non-aqueous solvent is a cyclic 15 carbonate ester such as ethylene or propylene carbonate, dimethyl sulfoxide, ethylene and propylene sulfite, sulfolane, succinic anhydride, or mixtures thereof.

12. An apparatus as in claim 1 additionally comprising:

a catalyst arranged to recombine the hydrogen (deuterium) and oxygen released by the electrolysis.

13. An apparatus as in claim 11 additionally comprising a vent for venting hydrogen (deuterium).

14. An apparatus as in claim 1 additionally comprising: a seal for the cell to enable operation under temperature and pressure above ambient.

15. A hollow chamber of corrosion-resistant material containing a metallic alloy therein, the alloy capable of absorbing both lithium and hydrogen (deuterium) in a single phase.

16. A chamber as in claim 14 having cylindrical tube shape.

17. A chamber as in claim 15 which can be disassembled to charge the alloy.

18. A chamber as in claim 14 additionally comprising:

a gas-tight cover, which is additionally fitted with a leak-tight valve capable of allowing gasses in the chamber to be evacuated and through which hydrogen (deuterium) may then also be admitted.

19. A chamber as in claim 14 in which the metallic alloy is prepared from lithium and magnesium with 1 to 55% nickel by weight; calcium, lithium, and nickel; or magnesium, lithium, titanium, and nickel.

20. A chamber as in claim 14 in which the metallic alloy is prepared from nanoparticles.

21. A chamber as in claim 16 where the metallic alloy includes lithium 6, lithium 7, or a mixture of the two isotopes.