AU2002309219A1 - High-energy, rechargeable electrochemical cells - Google Patents

Description

HIGH-ENERGY, RECHARGEABLE ELECTROCHEMICAL CELLS

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to electrochemical cells utilizing a non-

aqueous gel polymer electrolyte with an intercalation cathode, and more

particularly, to electrochemical cells utilizing a non-aqueous gel polymer

electrolytic system, an intercalation cathode and a magnesium anode.

Rechargeable, high energy density electrochemical cells of various kinds

are known. Such cells usually consist of a transition metal oxide or

chalcogenide cathode-active material, an anode-active alkali metal or alkali

metal intercalation compound, and an electrolyte solution containing a

dissolved alkali-based salt in an aprotic organic or inorganic solvent, or

polymer electrolyte.

Theoretically, a rechargeable cell is capable of charging and discharging

indefinitely, however, in practice such performance is unattainable. The degradation mechanisms of the various anodes, cathodes and electrolytes are

complex and are known to those skilled in the art.

Two basic types of cathodes are appropriate for a battery system that is

rechargeable at ambient temperatures. A liquid cathode can be used, allowing

reactions to take place with facility. Liquid cathodes are also advantageous in

that thin films or crusts forming on the surface of the cathode tend to crack,

such that the cathode activity remains high over the course of the cycling. The

mobility of the cathodic material is a liability, however, in that contact with the

anode short-circuits the cell. Thus, an electrochemical cell with a liquid

cathode requires protective, insulating films on the anode.

A solid cathode must be insoluble in the electrolyte, and must be able to

absorb and desorb a charge-compensating ion in a substantially reversible and

fast manner. A prime example of a solid cathode of this variety is an

intercalation cathode. Intercalation chemistry focuses on the insertion of ions

or neutral molecules into an inorganic or organic matrix. In a typical

intercalation cathode, cations dissolved in the electrolyte solution are inserted

into the inorganic matrix structure.

A group of intercalation materials of particular importance is called

Chevrel-phase materials, also known as Chevrel compounds. Chevrel

compounds contain an invariant portion consisting of molybdenum and a

chalcogen - sulfur, selenium, tellurium, or mixtures thereof. The invariant

portion is generally of the formula Mo₆T_n, where T represents the chalcogen

and n is usually about 8. The unique crystal structure of Chevrel-phase materials allows the insertion of one or more metal ions in a reversible, partially

reversible, or irreversible manner. The stoichiometry of the intercalation

compound can be represented as M_xMo₆T_n, where M represents the intercalated

metal and x may vary from 0 (no intercalated metal) to 4 or less, depending on

the properties of the particular metal.

The intercalation of metal ions into the Chevrel compound releases

energy. Since the process is partially or fully reversible, these compounds are

particularly suitable as electrodes in electrochemical cells. For example,

lithium, the predominant intercalation ion, can be removed from the Chevrel

compound by the application of electrical energy. The energy is released as

electrical energy upon reintercalation.

The cathode-active material in the high energy density, rechargeable

electrochemical cells must be paired with a suitable anode-active material,

which is most commonly made of an active metal such as alkali metals.

However, the performance of a particular anode-cathode couple is strongly

influenced by the nature of the electrolyte system. Certain non-aqueous

electrolytes are known to perform well with a particular anode-cathode couple

and be ineffective or significantly less effective with other anode-cathode

couples, either because the electrolyte solution's components are not stable or

because the solutions components degrades during cycling active electrodes.

As a result, much of the prior art relates to the cathode-active material, the

anode-active material and the electrolyte not only as independent entities, but

also as units within an appropriate battery system. U.S. Patent No. 4,104,4δO to Klemann et al., discloses reversible

batteries with an alkali metal anode, a chalcogenide cathode, and

organometallic alkali metal salts in organic solvents as the electrolyte system.

Non- aqueous electrolyte systems containing alkali metal salts of boron or

aluminum anions based which also contain organic groups are disclosed.

Organoborate salts of alkali metals represented by the formula

Rl

M⁺ R4— B— R2

R3

are disclosed in U.S. Patent No. 4,511,642 to Higashi et al., wherein R1-R4 are

organic radicals selected from the following groups: alkyl, aryl, alkenyl,

cycloalkyl, allyl, heterocyclic, and cyano, and M* represents an alkali metal ion.

U.S. Patent No. 4,139,681 describes cells containing electrolytically

active metal salt complexes having the formula ZMR_nX_i; wherein Z is a metal

from a group containing aluminum, the Rs are specified haloorganic radicals,

the Xs are selected from various halides, alkyls, aryls, alkaryls and aralkyls. M

is specified to be an alkali metal, with lithium being the preferred embodiment.

U.S. Patent No. 4,542,081 to Armand et al., describes solutions for the

constitution of solid electrolyte materials of electrochemical generators. The

compound is of the formula

(R-C≡C)₄ Z^~, M" in which Z is a trivalent element capable of entering into 4-coordination, such

as aluminum, and R represents groups which are non-proton donors. M is

specified to be an alkali metal.

The prior art described above, including U.S. Patent Nos. 4,104,4S^"€^

4,511,642, 4,139,681 and 4,542,081, specifies that M is an alkali metal The

use of an alkaline earth metal anode such as magnesium would appear

disadvantageous relative to the use of an alkali metal such as lithium because

alkali metal anodes are much more readily ionized than are alkaline earth metal

anodes. In addition, on recharge the cell must be capable of re-depositing the

anode metal that was dissolved during discharge, in a relatively pure state, and

without the formation of deposits on the electrodes.

However, there are numerous disadvantages to alkali batteries. Alkali

metals, and lithium in particular, are expensive. Alkali metals are highly

reactive. Alkali metals are also highly flammable, and fire due to reaction of

alkali metal with oxygen or other active material is extremely difficult to

extinguish. Lithium is poisonous and compounds thereof are known for their

severe physiological effects, even in minute quantities. As a result, the use of

alkali metals requires specialized facilities, such as dry rooms, specialized

equipment and specialized procedures.

In contradistinction, magnesium metal and aluminum metal are easy to

process. The metals are reactive, but undergo rapid passivation of the surface,

such that the metals exhibit highly stable behavior. Both magnesium and

aluminum are inexpensive relative to the alkali metals. U.S. Patent No. 4,894,302 to Hoffman et al., discloses an

electrochemical cell having an intercalation cathode, an alkaline earth anode,

and a non-aqueous liquid electrolyte containing an organic solvent and an

electrolytically active, organometallic alkaline earth metal salt represented by

the formula

Rl

Tvl +2 R4— Z— R2

R3

wherein Z is boron or aluminum; R1-R4 are radicals selected from the

following groups: alkyl, aryl, alkaryl, aralkyl, alkenyl, cycloalkyl, allyl,

heterocyclic alkyl, and cyano; and M represents an alkaline earth metal such as

magnesium. The radicals can be inertly substituted with substituents that have

no detrimental effect upon the electrolytic properties of the electrolyte

composition with respect to effectiveness in an electrochemical cell, such as

halogenated or partially halogenated derivatives of the above groups. While

exhaustive care is taken to disclose a broad range of organic radicals and

halogenated organic radicals, bonding the metallic species of the anion (Z) to

another inorganic species is not considered.

U.S. Patent No. 5,491,039 describes a solid, single-phase electrolyte

containing a solid polymeric matrix and an organometallic ion salt represented

by the formula

M_c(ZR_n) wherein Z is boron, aluminum or titanium; R_n are various subsituted or

unsυbsituted organic radicals; M is lithium, sodium, potassium, or magnesium,

c is 1 or 2, and n is an integer from 1 to 6. As in U.S. Patent No. 4,894,302, a

broad range of organic radicals including halogenated organic radicals is

disclosed, but the bonding of the metallic species of the anion (Z) to another

inorganic species is not reported. In all cases, metallic species Z is bonded to a

carbon atom. More specifically, the bonding of the metallic species of the

anion (Z) directly to a halogen is not disclosed. It must be emphasized that this

is of particular significance in light of the fact that U.S. Patent No. 5,491,039

teaches an extremely broad range of radicals that may be appropriate for

attaching to the metallic species of the anion.

Both U.S. Patent No. 5,491,039 and U.S. Patent No. 4,894,302 disclose

electrochemical cells having an alkaline earth anode such as magnesium. For

commercial application, however, such magnesium batteries must be essentially

rechargeable and must have a reasonable shelf life. Sustaining a voltage of 1.5

volts is problematic or impossible with the usual intercalation cathodes and

electrolytes according to prior art. Magnesium batteries operating at 1.5 volts

are particularly prone to electrolyte decomposition and to

encrustation/passivation of both electrode surfaces.

In our co-pending parent application, Serial No. 09/419,940, a new type

of electrolyte for electrochemical cell was disclosed. The general formula of the

electrolyte is M'^+m (ZR_nX_q-n)_m in which: M' is selected from the group

consisting of magnesium, calcium, and aluminum; Z is selected from the group consisting of aluminum, boron, phosphorus, antimony and arsenic; R represents

radicals selected from the following groups: alkyl, alkenyl, aryl, phenyl, benzyl,

and a ido; X is a halogen (I, Br, Cl, F); m = 1-3; and n = 0-5 and q = 6 in the

case of Z = phosphorus, antimony and arsenic, and n = 0-3 and q = 4 in the

case of Z = aluminum and boron. The above-mentioned co-pending application

disclosed the compatibility of this electrolyte type with Mg and a magnesium-

Chevrel intercalation cathode of the form

Cu_xMg_yMo₆S₈

to provide the basis for the production of a viable, rechargeable magnesium

battery with a nominal voltage exceeding 1.5 volts.

Special interest is currently being focused on the use of solid polymeric

electrolytes in advanced battery systems. The substitute of liquid electrolyte

with solid gel polymeric electrolyte provides advantages in terms of safety,

design flexibility and simplicity of production equipment and process operation.

Gels based on Li, Na and K ions are well known in academic literature

and some of them have seen some extent of commercial implementation. By

sharp contrast, very little work has been performed on gels based on Mg, Ca

and Al ions. The relative paucity of work on Mg, Ca and Al gels may be

attributed to several physical properties. The lattice energy of salts of Mg, Ca

and Al is usually very high relative to those of salts of the alkali metals. Hence,

it is extremely difficult to identify a polymer matrix that is polar enough to

effectively cause ionic dissociation of these salts. It must be emphasized that

the solubility of most of these salts is very low, even in water and in other high dielectric mediums, such that the possibility of finding a polymeric medium that

can dissolve them with reasonable ionic dissociation appears remote. In

addition, the ions of Mg, Ca, and Al are small and multivalent, such that the

ions are characterized by extremely high charge densities, which tend to

severely restrict ion mobility in solution. The transference number of such ions

is expected to be less than 0.5 and the electrical conductivity of the solutions of

such ions appear to be insufficient for the inventive electrolyte systems.

It must be further emphasized that the liquid electrolyte taught by our

above-referenced co-pending parent application is based on a delicate

equilibrium state in the solution. The electrochemical reactivity of the

electrolyte is strongly dependent on the solvent structure and polarity. For

example, the most extensively tested ethereal solvent in the above-referenced

liquid electrolyte systems is tetrahydrofuran (THF). The use of very similar

ether such as 2Me-THF, which differs from THF only by the addition of a

single methyl group, was investigated. This seemingly minor difference has

only a small effect on the polarity of the solvent, but in the inventive electrolyte

system, such a difference was enough to cause a segregation of the complex salt

and a loss in electrochemical reactivity. This example manifestly demonstrates

that which is l nown on purely theoretical grounds, namely, that the solvent

medium critically influences the structure and reactivity of the electrolyte

complex salt.

Therefore, it would be surprising to find a polymer matrix in which the

inventive electrolyte system will be soluble and compatible in such way that the complex will not segregate or react with the polymer matrix and the

electrochemical reactivity will maintain.

Prior to the liquid electrolyte system taught by our above-referenced co-

pending parent application, the only known type of electrolyte system in which

magnesium could be electrochemically deposited and dissolved reversibly was

a Grignard reagent in an ethereal solution. For example, Liebenow

(Electrochimica Acta, Vol 43, Nos. 10-1 1 , pp. 1253-1256, 1998) prepared a gel

polymer based on ethyl magnesium bromide in tetrahydrofuran solution with

polyethylene oxide as the polymeric matrix and demonstrated the ability of the

system to reduce and oxidize magnesium. However, while gel polymers based

on Grignard reagents may be of scientific interest, they cannot be applied to

commercial battery technologies. The extremely poor anodic stability of gel

polymers based on Grignard reagents precludes their use in such solid gel

electrolytes. Moreover, the Grignard reagents are extremely flammable,

corrosive and dangerous reduction materials.

Thus, there is a widely recognized need for, and it would be highly

advantageous to have, a solid polymeric non-aqueous electrolyte that allows the

production of an all solid, practical, rechargeable battery which would be more

safe, clean, efficient and economical than rechargeable batteries known

heretofore. It would be of further advantage if such an electrolyte would be

based on magnesium, calcium, or aluminum, which are inexpensive and

abundant raw materials. SUMMARY OF THE INVENTION

The present invention is a new type of solid gel electrolyte for use in

electrochemical cells. The properties of the solid gel electrolyte include high

conductivity and an electrochemical window that can exceed 2.2V vs.

Mg/Mg⁺². The use of the electrolyte in an appropriate cell promotes the

substantially reversible deposition of the metal and a reversible intercalation

process at the cathode material.

According to the teachings of the present invention there is provided a

solid, gel type non-aqueous electrolyte for use in an electrochemical cell, the

electrolyte including: (a) at least one polymer compound; (b) at least one

organic solvent, and (c) at least one electrolytically active salt represented by

the formula:

M'(ZR_nX_q-n)_m

in which: M' is selected from the group consisting of magnesium, calcium, and

aluminum; Z is selected from the group consisting of aluminum, boron,

phosphorus, antimony and arsenic; R represents radicals selected from the

folloλving groups: alkyl, alkenyl, aryl, phenyl, benzyl, and amido; X is a

halogen (I, Br, Cl, F); m = 2-3; n = 0-5 and q = 6 for Z = phosphorus,

antimony, and arsenic, and n = 0-3 and q = 4 for Z = aluminum and boron,

wherein the polymer compound, organic solvent, and electrolytically active salt

interact to form a non-aqueous electrolyte having a solid, gel type structure. According to another aspect of the present invention, the solid, gel type

non-aqueous electrolyte is incorporated into an electrochemical cell further

including a metal anode and an intercalation cathode.

According to yet another aspect of the present invention, there is

provided a non-aqueous electrolyte for use in an electrochemical cell, the

electrolyte including: (a) at least one organic solvent, and (b) at least one

electrolytically active salt represented by the formula:

M'(ZR_nX_q-n)_m in which: M' is selected from the group consisting of magnesium, calcium, and

aluminum; Z is selected from the group consisting of aluminum, boron,

phosphorus, antimony and arsenic; R represents radicals selected from the

following groups: alkyl, alkenyl, aryl, phenyl, benzyl, and amido; X is a

halogen (I, Br, Cl, F); = 2-3; n = 0-5 and q = 6 for Z = phosphorus,

antimony, and arsenic, and n = 0-3 and q = 4 for Z = aluminum and boron.

According to yet another aspect of the present invention, the non-

aqueous electrolyte is incorporated into an electrochemical cell further

including a metal anode and an intercalation cathode.

According to further features in preferred embodiments of the invention

described below, Z is aluminum.

According to further features in preferred embodiments of the invention

described below, M' is magnesium. According to further features in preferred embodiments of the invention

described below, M' is calcium.

According to further features in preferred embodiments of the invention

described below, the electrolytically active salt is Mg[butylAlCl₃]₂.

According to further features in preferred embodiments of the invention

described below, the electrolytically active salt is Mg[butylethylAlCl₂]₂-

According to further features in preferred embodiments of the invention

described below, M' is selected from the group consisting of magnesium and

calcium, Z is aluminum, R represents at least one type of alkyl radical, and m is

2.

According to further features in preferred embodiments of the invention

described below, the organic solvent contains tetraglyme.

According to further features in preferred embodiments of the invention

described below, the organic solvent contains tetrahydrofuran.

According to further features in preferred embodiments of the invention

described beloλv, the polymer compound serves as a matrix.

According to further features in preferred embodiments of the invention

described below, the polymer compound is selected from the group consisting

ofPVdF. PEO, and PVC. According to further features in preferred embodiments of the invention

described below, M' is selected from the group consisting of magnesium and

calcium, Z is aluminum, R is at least one type of alkyl radical, and m is 2.

According to further features in preferred embodiments of the invention

described below, the intercalation cathode is a Chevrel-phase intercalation

cathode.

According to further features in preferred embodiments of the invention

described below, the Chevrel-phase intercalation cathode is represented by the

formula

Cu Mg_yMo₆S₈

wherein 1 > x > 0 and 2 > y > 0.

According to further features in preferred embodiments of the invention

described below, the metal anode is magnesium.

According to further features in preferred embodiments of the invention

described below, the polymer compound is selected from the group consisting

ofPVdF, PEO and PVC.

According to further features in preferred embodiments of the invention

described below, the solvent is selected from the group consisting of THF and

tetraglyme.

The present invention successfully addresses the shortcomings of the

presently known solid gel electrolytes and provides the basis for the production of a viable, rechargeable battery based on magnesium, calcium, and aluminum,

and having a nominal voltage exceeding 1.5 volts.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with

reference to the accompanying drawings, wherein:

FIG. 1 is a graph displaying typical cyclic voltammogram of solid gel

electrolyte containing a matrix of Mg(AlCl₂Bυ£t)₂ salt and tetraglyme in

poly(vinylidene fluoride) (PVdF) using a gold electrode, according to the

present invention;

FIG. 2 is a graph of the voltage patterns of an electrochemical cell

consisting of a Chevrel-phase cathode, magnesium metal anode, and a solid gel

electrolyte containing a matrix of Mg(AlCl₂BuEt)₂ salt and tetraglyme in

poly(vinylidene fluoride) (PVdF), according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a new type of solid gel electrolyte for use in

electrochemical cells. The properties of the solid gel electrolyte include high

conductivity and an electrochemical window that can exceed 2.2V vs.

Mg/Mg⁺². The use of the solid gel electrolyte in an appropriate cell promotes the substantially reversible deposition of magnesium metal on the anode current

collector and the reversible intercalation of magnesium in the cathode material.

Although alkali metals are readily ionized, the use of other metal anodes,

such as magnesium or aluminum has decided advantages. Magnesium and

aluminum are very inexpensive relative to alkali metals. Alkali metals are

highly reactive and highly flammable, and alkali fire is extremely difficult to

extinguish. Lithium in particular is poisonous, and lithium compounds are

known for their severe physiological effects, even in minute quantities. As a

result, the use of alkali metals requires specialized facilities, such as dry rooms,

specialized equipment and specialized procedures.

Magnesium and aluminum are reactive, but undergo rapid passivation of

the surface, such that for all practical purposes, the metals are highly stable.

Magnesium and aluminum are available and inexpensive, non-toxic, non-

hazardous, and easy to work with, and as such, are highly desirable raw

materials for electrochemical cells and for electrolytic solutions and solid gel

electrolytes in particular.

Although primary electrochemical cells based on magnesium are known,

such cells are non-rechargeable and are used solely for military applications.

Sustaining a voltage of 1.5 volts is problematic or impossible with the usual

intercalation cathodes and electrolytes according to prior art. Magnesium

batteries operating at 1.5 volts are particularly prone to electrolyte

decomposition and to encrustation/passivation of the electrode surface. We have discovered that despite the known difficulties delineated above,

a polymeric matrix in conjunction with a polar organic solvent, can dissolve the

inventive electrolyte of the form:

M' (ZR_nX_q-n)_m This mixture creates a polymeric gel that exhibits sufficient conductivity at

room temperature and that electrochemically deposits and dissolves the cation

M' with high reversibility, despite all the limitations discussed above. The

cation M' is selected from the group consisting of magnesium, calcium, and

aluminum. More preferably, the cation M' is magnesium.

Z is selected from the group consisting of aluminum, boron, phosphorus,

antimony and arsenic; R represents at least one type of radical selected from the

following groups: alkyl, alkenyl, aryl, phenyl, benzyl, and amido; X is a

halogen (I, Br, Cl, F); m = 2-3; and n = 0-5 and q = 6 in the case of Z =

phosphorus, antimony and arsenic, and n = 0-3 and q = 4 in the case of Z =

aluminum and boron.

As used herein in the specification and in the claims section that follows,

the radical "R" refers to at least one type of radical selected from the following

groups: alkyl, alkenyl, aryl, phenyl, benzyl, and amido. Examples of

electrolytically active salts having different R groups are Mg[butylethylAlCl₂]_2,

Mg[benzylethylmethylAlCl]₂₎ and Ca[butylphenylAlCl₂]_2.

As used herein in the specification and in the claims section that follows,

"PEO" refers to polyethylene oxide; "PVdF" refers to poly(vinylidene fluoride); "PVC" refers to poly(vinylchloride); "Bu" refers to a butyl group; "Et" refers to

an ethyl group, and "THF" refers to tetrahydrofuran.

As described above, the electrochemical window of a cell with a solid

gel electrolyte according to the present invention and an appropriate anode-

cathode pair is 2.2 volts, such that the cell can be operated in a stable, reversible

fashion at 1.5 volts without decomposition of the solid gel electrolyte and

encrustation of the electrodes.

In a preferred embodiment of the invention, the solid gel electrolyte

according to the invention functions in an electrochemical cell with a metal

anode and an intercalation cathode.

Certain non-aqueous electrolytes are known to perform well λvith a

particular anode-cathode couple and be ineffective or significantly less

effective with other anode-cathode couples, either because the electrolyte is not

inert or because it degrades during cycling. It is relevant, therefore, to treat the

electrolyte, not only as an independent entity, but also as a unit within a system

containing an appropriate anode-cathode pair.

Hence, according to further features in preferred embodiments of the

invention described below, the solid gel electrolyte according to the present

invention is incorporated into specific electrochemical cells containing an

appropriate anode-cathode pair.

While various metals are suitable as anodes for the solid gel electrolytic

system, including magnesium, lithium, aluminum and calcium, a particularly

appropriate battery includes the solid gel electrolyte according to the present invention, a magnesium metal anode and a magnesium insertion compound

cathode.

In yet another preferred embodiment, the magnesium insertion-

compound cathode is a magnesium-Chevrel intercalation cathode of the form

Cu_xMg_vMo₆S₈

wherein x = 0-1 and y = 0-2 .

The principles and operation of an electrolytic cell with an improved

electrolyte according to the present invention may be better understood with the

description provided hereinbelow and with reference to the drawings and the

accompanying description provided in the Examples.

The solid electrolyte composition of the present invention includes a

polymer compound, an organic solvent and electrochemically-active

organometallic salts of the form M'(ZR_nX_q-n)_m, as described above.

Organometallic salts of this form may be combined with compatible non-

organometallic salts or with compatible organometallic salts of other forms.

Many types of polymer compounds can be use as matrix compound to

form the solid gel electrolyte of the present invention, including poly(ethylene

oxide) (PEO), poly(propylene oxide) (PPO), polyfvinylidene fluoride) (PVdF),

poly(hexafluoropropylene) (HFP), poly(vinylchloride) (PVC), poly(methyl

metacrylate) (PMMA), poly(acrylonitrile) (PAN), (PEEK), (MEEP) and

mixtures thereof. Intercalation cathodes used in conjunction with the solid gel electrolyte

according to the present invention include transition metal oxides,

chalcogenides and halogenides and combinations thereof. More specifically,

the transition metal oxides include V₂0₅, TiS₂, MoS₂, ZrS₂, Co₃0₄, Mn0₂,

Mn₂0₄, and the chalcogenides include Chevrel-phase compounds.

EXAMPLE 1

A magnesium-Chevrel intercalation cathode for use in conjunction with

the solid gel electrolyte according to the present invention was synthesized

according to the procedure developed by Goecke and Schδlhorn, (E. Goecke,

R. Schόlhorn, G. Aselmann and W. Muller-Warmuth) published in Inorg.

Chem. 26, 1805 (1987). Elemental sulfur, molybdenum and copper of high

purity were added in a stoichiometric ratio of 4:3:1. After intimate mixing and

pressing into pellets, the mixture was sealed in a quartz ampoule under a

vacuum of 10^"5 Torr. The ampoule was placed in a furnace, and the

temperature was raised at a rate of 400°C/h to 450°C. The temperature was

maintained at 450°C for 24 hours. Again, the temperature was raised at a rate

of 400°C h to 700°C and was maintained at 700°C for 24 hours. The

temperature was then raised at a rate of 120°C/h to 1050°C and was maintained

at 1050°C for 48 hours. After cooling to room temperature at a rate of 120°C/h, the ampoule was broken open. The copper molybdenum sυlfide (Cu₂Mo₆S₈)

obtained was milled into fine powder using mortar and pestle.

The copper molybdenum sυlfide powder was mixed with Teflon-loaded

carbon black (CB). The resulting paste was spread on stainless steel mesh and

pressed. The composite electrode formed was dried under vacuum af room

temperature for 24 hours.

The electrode was subsequently subjected to either chemical or

electrochemical pretreatment in which some of the copper ions in the host

matrix (Cu₂Mo₆S₈) were deinserted. The electrochemical deintercalation of

copper was performed in a non-aqueous medium, a IM solution of Mg(C10 )₂

in acetonitrile. The deinsertion was performed by a galvanostatic charging

process in which the upper limit of the potential was controlled. A chemical

deintercalation of the copper was carried out by a direct reaction of Cu₂Mo₆Sg

with aqueous acidic solution containing FeCl₃ as an oxidizer.

After thorough washing in acetonitrile and subsequent drying of the

electrode, charging-discharging cycles were conducted in a IM solution of

Mg(C10₄)₂ in acetonitrile at various scan rates between -1.6V and 0.01 V,

relative to the Ag/Ag⁺¹ reference electrode. A pronounced electrochemical

redox activity was observed, with a main oxidation peak at -1.219 V vs.

Ag/Ag⁺ and a corresponding main reduction peak at -1.41 V vs. Ag/Ag⁺. The

charge associated with the intercalation-deintercalation process was 71mAh/g

and 72mAh/g, respectively, which correspond to y = 1.09-1.12 in the formula

Cu_0.ι₃Mg_vMo₆S₈ The chemical and electrochemical reversibility of the intercalation

process was demonstrated over multiple cycles.

EXAMPLE 2

Referring now to the drawings, FIG. 1 is a graph displaying typical

cyclic voltammogram of an electrochemical cell including using a gold

electrode, a solid gel electrolyte containing a PVdF matrix with an ether-

magnesium organo-halo-aluminates salt and tetraglyme solvent.

FIG. 1 shows the potentiodynamic behavior of Mg(AlCl₂BuEt)₂

obtained with tetraglyme in a PVdF matrix using a gold working electrode. The

peak at -0.8V is due to the deposition of magnesium metal, and the peak at

around 0.7V is attributed to the subsequent electrochemical dissolution of the

magnesium metal. The electrochemical window obtained with this system

exceeds 2.2V. It is clearly evident from the cyclic voltammogram that the

process of magnesium deposition and dissolution is fully reversible.

EXAMPLE 3

An electrochemical cell was prepared consisting of a Chevrel-phase

cathode, a magnesium metal anode, and a solid gel electrolyte containing PVdF,

Mg(AlCl₂BuEt)₂ salt and tetraglyme. The cathode, weighing 74.3 mg, was

made from a mixture of copper-leached Chevrel-phase material containing 10 weight-% carbon black and 10 weight-% PVdF as a binder, spread on stainless

steel mesh. The solid gel electrolyte was prepared from 0.25 Molar

Mg(AlCl₂BuEt)₂ salt and tetraglyme in a PVdF matrix. The anode was a disc

of pure magnesium metal, with a diameter of 16 mm and a thickness of 0.2 mm.

The battery was encased in a stainless steel "coin type" cell configuration

without a separator. The cell was cycled on a standard charger-discharger with

a current density of 23.3 milliamperes/gram. The potential limits for the

cycling λvere between 0.5V at the fully discharged state and 1.8V for the fully

charged state.

The battery was subjected to continuous cycling over 3 months. The

good cyclability of the battery is clearly evident from FIG. 2, in which several

cycles are represented. The battery performance remains strong over the entire

length of the experiment. The measured charge density obtained in each

discharge is 61 mAh per gram of the cathode material.

EXAMPLE 4

A solid gel electrolyte according to the present invention was prepared

as follows: commercial, reagent-grade MgBu₂, was dissolved in heptane.

Commercial, reagent-grade AlEtCl₂ was added drop wise to the MgBu₂ solution

according to the molar ratio. The mixture was stirred for 48 hours under an

inert gas, and Mg(BuEtAlCl₂)₂ was crystallized out of solution. The solvent

was removed by evacuation. Ether solvents were added very slowly to the organomagnesiυm salt to produce a saturated solution (around 0.5M). A

commercially available PVdF powder for gel polymer application was added to

the above solution and the mixture was stirred and heated until a one phase

polymeric gel was formed.

It Λvill be appreciated that the above descriptions are intended only to

serve as examples, and that many other embodiments are possible within the

spirit and the scope of the present invention.

Claims (27)

WHAT IS CLAIMED IS:

1. A solid, gel type non-aqueous electrolyte for use in an

electrochemical cell, the electrolyte comprising:

(a) at least one polymer compound

(b) at least one organic solvent and

(c) at least one electrolytically active salt represented by the formula:

M'(ZR_nX_q-n)_m in which:

M' is selected from the group consisting of magnesium, calcium, and aluminum;

Z is selected from the group consisting of aluminum, boron, phosphorus, antimony and arsenic;

R represents radicals selected from the following groups: alkyl, alkenyl, aryl, phenyl, benzyl, and amido;

X is a halogen (I, Br, Cl, F); m = 2-3; n = 0-5 and q = 6 for Z = phosphorus, antimony, and arsenic, and n = 0-3 and q = 4 for Z = aluminum and boron.

wherein said polymer compound, said organic solvent, and said electrolytically

active salt interact to form a non-aqueous electrolyte having a solid, gel type

structure.

2. The non-aqueous electrolyte of claim 1, wherein Z is aluminum.

3. The non-aqueous electrolyte of claim 2, wherein M' is

magnesium.

4. The non-aqueous electrolyte of claim 2, wherein M' is calcium.

5. The non-aqueous electrolyte of claim 1, wherein said

electrolytically active salt is Mg[butylAlCl₃]₂.

6. The non-aqueous electrolyte of claim 1 , wherein said

electrolytically active salt is Mg[butylethylAlCl₂]₂

7. The solid gel non-aqueous electrolyte of claim 1, wherein M' is

selected from the group consisting of magnesium and calcium, Z is aluminum,

R represents at least one type of alkyl radical, and m is 2.

8. The solid gel non-aqueous electrolyte of claim 6, wherein said

organic solvent contains tetraglyme.

9. The solid gel non-aqueous electrolyte of claim 6, wherein said

organic solvent contains tetrahydrofuran.

10. The solid gel non-aqueous electrolyte of claim 1, wherein said

polymer compound serves as a matrix.

11. The solid gel non-aqueous electrolyte of claim 1, wherein said

polymer compound is selected from the group consisting of PVdF, PEO and

PVC.

12. An electrochemical cell comprising:

(a) a metal anode;

(b) an intercalation cathode; and

(c) a solid gel non-aqueous electrolyte including:

i) at least one polymer compound

ii) at least one organic solvent and

iii) at least one electrolytically active salt represented by the

formula:

M'(ZR_nX_q-n)_m in which:

M' is selected from the group consisting of magnesium, calcium, and aluminum;

Z is selected from the group consisting of aluminum, boron, phosphorus, antimony and arsenic;

R represents radicals selected from the following groups: alkyl, alkenyl, aryl, phenyl, benzyl, and amido;

X is a halogen (I, Br, Cl, F); m = 2-3; n = 0-5 and q = 6 for Z = phosphorus, antimony, and arsenic, and n = 0-3 and q = 4 for Z = aluminum and boron.

13. The electrochemical cell of claim 12, wherein M' in said solid

gel electrolyte is selected from the group consisting of magnesium and calcium,

Z is aluminum, R is at least one type of alkyl radical, and m is 2.

14. The electrochemical cell of claim 12, wherein said intercalation

cathode is a Chevrel-phase intercalation cathode.

15. The electrochemical cell of claim 14, wherein said Chevrel-phase

intercalation cathode is represented by the formula

Cu_xMg_yMo₆S₈

wherein 1 > x > 0 and 2 > y > 0.

16. The electrochemical cell of claim 12, wherein said metal anode is

magnesium.

17. The electrochemical cell of claim 12, wherein said polymer

compound is selected from the group consisting of PVdF, PEO and PVC.

18. The electrochemical cell of claim 12, wherein said solvent is

selected from the group consisting of THF and tetraglyme.

19. A non-aqueous electrolyte for use in an electrochemical cell, the

electrolyte comprising:

(a) at least one organic solvent, and

(b) at least one electrolytically active salt represented by the formula:

^■ M'(ZR_nX_q-n)_m in which:

M' is selected from the group consisting of magnesium, calcium, and aluminum;

Z is selected from the group consisting of aluminum, boron, phosphorus, antimony and arsenic;

R represents radicals selected from the following groups: alkyl, alkenyl, aryl, phenyl, benzyl, and amido;

X is a halogen (I, Br, Cl, F); m = 2-3; n = 0-5 and q = 6 for Z = phosphorus, antimony, and arsenic, and n = 0-3 and q = 4 for Z = aluminum and boron.

20. The non-aqueous electrolyte of claim 19, wherein Z is aluminum.

21. The non-aqueous electrolyte of claim 19, wherein M' is

magnesium.

22. The non-aqueous electrolyte of claim 19, wherein M' is calcium.

23. The non-aqueous electrolyte of claim 19, wherein said

electrolytically active salt is Mg[butylAlCl₃]_2.

24. The non-aqueous electrolyte of claim 19, wherein said

electrolytically active salt is Mg[butylethylAlCl₂]₂.

25. The non-aqueous electrolyte of claim 19, wherein M' is selected

from the group consisting of magnesium and calcium, Z is aluminum, R

represents at least one type of alkyl radical, and m is 2.

26. The non-aqueous electrolyte of claim 25, wherein said organic

solvent contains tetraglyme.

27. An electrochemical cell comprising:

(a) a metal anode;

(b) an intercalation cathode; and

(c) a non-aqueous electrolyte including:

(i) at least one organic solvent and

(ii) at least one electrolytically active salt represented by the formula:

M'(ZR_nX_q-n)_m in which:

M' is selected from the group consisting of magnesium, calcium, and aluminum;

Z is selected from the group consisting of aluminum, boron, phosphorus, antimony and arsenic;

R represents radicals selected from the following groups: alkyl, alkenyl, aryl, phenyl, benzyl, and amido;

X is a halogen (I, Br, Cl, F); m = 2-3; n = 0-5 and q = 6 for Z = phosphorus, antimony, and arsenic, and n = 0-3 and q = 4 for Z = aluminum and boron.