Non-aqueous electrolyte for rechargeable magnesium ion cell

Abstract

A non-aqueous Magnesium electrolyte comprising: (a) at least one organic solvent; (b) at least one electrolytically active, soluble, inorganic Magnesium (Mg) salt complex represented by the formula: Mg.sub.aZ.sub.bX.sub.c wherein a, b, and c are selected to maintain neutral charge of the molecule, and Z and X are selected such that Z and X form a Lewis Acid, and 1a10, 1b5, and 2c30. Further Z is selected from a group consisting of aluminum, boron, phosphorus, titanium, iron, and antimony; X is selected from the group consisting of I, Br, Cl, F and mixtures thereof. Rechargeable, high energy density Magnesium cells containing an cathode, an Mg metal anode, and an electrolyte of the above-described type are also disclosed.

Claims

1. A non-aqueous electrolyte solution comprising: (a) at least one organic solvent; and (b) at least one electrolytically active, soluble, inorganic magnesium (Mg) salt complex represented by the formula Mg.sub.aZ.sub.bX.sub.c, and Z and X are selected such that Z and X forma Lewis Acid; and 1a10, 1b5, and 2c30, wherein Z is selected from the group consisting of aluminum, boron, phosphorus, titanium, iron, and antimony; and X is selected from the group consisting of I, Br, Cl, F and mixtures thereof, and wherein the Mg:Z ratio is greater than 1:2.

2. The non-aqueous electrolyte solution of claim 1, wherein a, b, and c are selected to maintain neutral charge of the molecule.

3. The non-aqueous electrolyte solution of claim 1, wherein 1a10, 1b2, and 3c30.

4. The non-aqueous electrolyte solution of claim 1, wherein the magnesium (Mg) salt complex is represented by formula Mg.sub.nZX.sub.3+(2*n), wherein n is from 1 to 5.

5. A method of preparing a non-aqueous electrolyte solution of claim 1, comprising: combining a source of magnesium, and a source of Z, in an electrolyte solvent.

6. An electrochemical cell, comprising: a non-aqueous electrolyte solution according to claim 1; a magnesium-containing anode and a cathode capable of reversible electrochemical reaction with magnesium.

7. The electrochemical cell of claim 6, wherein the magnesium anode is selected from the group consisting of Mg, Mg alloys, electrodeposited Mg, anatase TiO.sub.2, rutile TiO.sub.2, Mo.sub.6S.sub.8, FeS.sub.2, TiS.sub.2, and MoS.sub.2.

8. The electrochemical cell of claim 6, wherein the cathode is selected from the group consisting of Chevrel phase Mo.sub.6S.sub.8, MnO.sub.2, CuS, Cu.sub.2S, Ag.sub.2S, CrS.sub.2, VOPO.sub.4, layered TiS.sub.2, V.sub.2O.sub.5, MgVO.sub.3, MoS.sub.2, MgV.sub.2O.sub.5, MoO.sub.3, spinel CuCr.sub.2S.sub.4, MgCr.sub.2S.sub.4, MgMn.sub.2O.sub.4, MgNiMnO.sub.4, Mg.sub.2MnO.sub.4, NASICON MgFe.sub.2(PO.sub.4).sub.3 and MgV.sub.2(PO.sub.4).sub.3, olivine MgMnSiO.sub.4 and MgFe.sub.2(PO.sub.4).sub.2, tavorite Mg.sub.0.5VPO.sub.4F, TiP.sub.2O.sub.7, VP.sub.2O.sub.7, MgMnF.sub.4, and FeF.sub.3.

9. The non-aqueous electrolyte solution of claim 1, wherein the Mg molarity in the electrolyte solution is at least 0.1 M.

10. The non-aqueous electrolyte solution of claim 1, wherein the at least one organic solvent is one or more solvent selected from the group consisting of ethers, organic carbonates, lactones, ketones, nitriles, ionic liquids, aliphatic and aromatic hydrocarbon solvents and organic nitro solvents.

11. The non-aqueous electrolyte solution of claim 1, wherein the at least one organic solvent is one or more solvent selected from the group consisting of THF, 2-methyl THF, dimethoxyethane, diglyme, ethyl diglyme, butyl diglyme, triglyme, tetraglyme, diethoxyethane, diethylether, proglyme, dimethylsulfoxide, dimethyl sulfite, sulfolane, acetonitrile, hexane, toluene, nitromethane, 1-3 dioxalane, 1-4 dioxane, trimethyl phosphate, tri-ethyl phosphate, hexa-methyl-phosphoramide (HMPA), N,N-propyl-methyl-pyrrolidinium-bis(trifluoromethylsulfonyl)imide (P13-TFSI), N,N-propyl-methyl-pyrrolidinium-diacetamide (P13-DCA), propyl-methyl-pyrrolidinium-bis(fluorosulfonyl)imide (P13-FSI), ethyl-dimethyl-propyl-ammonium-bis(trifluoromethylsulfonyl)imide (PDEA-TFSI), 1-(methoxyethyl)-1-methylpiperidinium-bis(trifluoromethylsulfonyl)imide (MOEMPP-TFSI), and ionic liquids.

12. A non-aqueous magnesium electrolyte solution comprising a complex of an inorganic magnesium halide, wherein the inorganic magnesium halide comprises magnesium chloride, and an inorganic compound more Lewis-acidic than the inorganic magnesium halide in at least one organic solvent.

13. The non-aqueous magnesium electrolyte solution of claim 12, wherein the compound is a Lewis acid.

14. The non-aqueous magnesium electrolyte solution of claim 12, wherein the molar ratio of inorganic magnesium halide to the compound is greater than 1.

15. The non-aqueous electrolyte solution of claim 12, wherein the compound is selected from the group consisting of BI.sub.3, BBr.sub.3, BCl.sub.3, BF.sub.3, AlI.sub.3, AlBr.sub.3, AlCl.sub.3, AlF.sub.3, PI.sub.3, PBr.sub.3, PCl.sub.3, PF.sub.3, TiI.sub.4, TiBr.sub.4, TiCl.sub.3, TiCl.sub.4, TiF.sub.3, TiF.sub.4, FeI.sub.2, FeBr.sub.3, FeBr.sub.2, FeCl.sub.3, FeCl.sub.2, FeF.sub.3, FeF.sub.2, SbI.sub.3 SbBr.sub.3, SbCl.sub.3, and SbF.sub.3.

16. The non-aqueous electrolyte solution of claim 12, wherein the complex comprises a reaction product of MgCl.sub.2 and AlCl.sub.3.

17. The non-aqueous electrolyte solution of claim 16, wherein the Mg:Al ratio is in the range of greater than 0.5.

18. The non-aqueous electrolyte solution of claim 12, wherein the Mg molarity in the electrolyte solution is at least 0.1 M.

19. The non-aqueous electrolyte solution of claim 12, wherein the at least one organic solvent is one or more solvent selected from the group consisting of ethers, organic carbonates, lactones, ketones, nitriles, ionic liquids, aliphatic and aromatic hydrocarbon solvents and organic nitro solvents.

20. The non-aqueous electrolyte solution of claim 12, wherein the at least one organic solvent is one or more solvent selected from the group consisting of THF, 2-methyl THF, dimethoxyethane, diglyme, ethyl diglyme, butyl diglyme, triglyme, tetraglyme, diethoxyethane, diethylether, proglyme, dimethylsulfoxide, dimethyl sulfite, sulfolane, acetonitrile, hexane, toluene, nitromethane, 1-3 dioxalane, 1-4 dioxane, trimethyl phosphate, tri-ethyl phosphate, hexa-methyl-phosphoramide (HMPA), N,N-propyl-methyl-pyrrolidinium-bis(trifluoromethylsulfonyl)imide (P13-TFSI), N,N-propyl-methyl-pyrrolidinium-diacetamide (P13-DCA), propyl-methyl-pyrrolidinium-bis(fluorosulfonyl)imide (P13-FSI), ethyl-dimethyl-propyl-ammonium-bis(trifluoromethylsulfonyl)imide (PDEA-TFSI), 1-(methoxyethyl)-1-methylpiperidinium-bis(trifluoromethylsulfonyl)imide (MOEMPP-TFSI), and ionic liquids.

21. The non-aqueous electrolyte solution of claim 12, for use in a magnesium electrochemical cell.

22. The non-aqueous electrolyte solution of claim 12, for use in a magnesium plating bath.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is herein described for purposes of illustration and by way of example only with reference to the accompanying drawings. The principles and operation of an electrolytic cell with an improved electrolyte according to the present invention may be better understood with reference to the drawings and the accompanying description.

(2) FIG. 1 is a graph displaying a typical cyclic voltammogram of the all-inorganic Magnesium Aluminum Chloride complex dissolved in tetrahydrofuran (THF). The experiment utilized 25 mV/s scan rate and a platinum working electrode, and Mg for the counter and reference electrodes.

(3) FIG. 2 depicts the MgAlCl ternary phase diagram derived from the ab initio calculated energies of compounds within that system. Each point represents a thermodynamically stable compound and the space within each triangular plane represents compositional space wherein a mixture of the 3 vertex compounds is thermodynamically stable to the voltage vs. Mg/Mg.sup.2+ indicated within that triangle.

(4) FIG. 3 shows representative cyclic voltammogram of the all-inorganic Magnesium Aluminum Chloride complex dissolved in tetrahydrofuran (THF) using a platinum working electrode, and Mg for the counter and reference electrodes. The voltammogram depicted in black illustrates the significant hysteresis between Mg plating and stripping while the voltammogram depicted in grey depicts the same solution with significantly improved plating ability due to electrochemical conditioning. The experiment utilized 25 mV/s scan rate and a platinum working electrode, and Mg for the counter and reference electrodes.

(5) FIG. 4 displays chronopotentiometry of a symmetric cell wherein all electrodes are Mg metal. The data was taken for 100 hours at an applied current of 0.1 mA/cm.sup.2.

(6) FIG. 5 is a graph of cyclic voltammetry for Mo.sub.6S.sub.8 cathode in Magnesium-Aluminum-Chloride Complex solution. This experiment utilizes Mg counter and reference electrode. The current response obtained corresponds to about 80 mAh/g over multiple charge/discharge cycles.

DETAILED DESCRIPTION

(7) An electrolyte is described herein for transferring Mg-ions between electrodes. The properties of the electrolyte include high conductivity and an electrochemical window that can exceed 3.0 V vs. Mg/Mg.sup.2+. The use of an inorganic salt complex in an electrolyte promotes the substantially-reversible deposition of magnesium metal on the anode current collector and the reversible intercalation of magnesium in the cathode material.

(8) In some embodiments, the electrolyte is for use in electrochemical cells, e.g., a magnesium electrochemical cell. In other embodiments, the electrolyte can be used in Magnesium plating baths, where electrochemical deposits of high purity Mg, or Mg-containing materials are prepared upon electronically conductive substrates. In such systems the electrolyte enables transfer of Mg ions from an Mg source being oxidized, e.g., low purity Magnesium electrode, to a cathode wherein the Mg ions are reduced onto an electronically conducting substrate, so as to create an Mg containing surface layer, which may be further processed.

(9) In one aspect, a non-aqueous Magnesium electrolyte solution is described, including a mixture of Magnesium halide and a Lewis Acid in at least one organic solvent. The molar ratio of Magnesium halide to Lewis Acid can be 1, greater than 1, or less than 1. In some embodiments, the molar ratio of Magnesium halide to Lewis Acid is greater than 1, and the mixture is referred to as a basic mixture. In other embodiments, the molar ratio of Magnesium halide to Lewis Acid is less than 1, and the mixture is referred to as an acidic mixture.

(10) In some embodiments, the non-aqueous electrolyte solution contains the active cation for the electrochemical cell, e.g., magnesium ion. The non-aqueous electrolyte solution can include a magnesium inorganic salt complex, which may be a reaction product of magnesium halide and a compound more Lewis acidic than the magnesium halide. In some embodiments, the compound is a Lewis acid. The non-aqueous electrolyte solution can include a mixture of a magnesium halide and a Lewis acid. The mixture can be a magnesium halide-Lewis acid complex, so as to form an Mg-halide species, which may can a monovalent charge in solution, or involve multiple Mg and halide species.

(11) The term Lewis Acid, is well-known in the art and may include any compound generally considered as a Lewis acid or a compound which is more Lewis-acidic than the magnesium halide. In certain embodiments, MgCl.sub.2, can be used as Lewis acid due to its stronger Lewis-acidity in comparison with certain magnesium halides.

(12) In one aspect, a non-aqueous electrolyte for use in an electrochemical cell includes (a) at least one organic solvent; and (b) at least one electrolytically active, soluble, inorganic Magnesium (Mg) salt complex represented by the formula: Mg.sub.aZ.sub.bX.sub.c wherein a, b, and c are selected to maintain neutral charge of the molecule, and Z and X are selected such that Z and X form a Lewis Acid; and 1a10, 1b5, and 2c30. In some embodiments, Z is selected from a group consisting of aluminum, boron, phosphorus, titanium, iron, and antimony. In certain embodiments, X is selected from the group consisting of I, Br, Cl, F and mixtures thereof.

(13) In certain embodiments, a can be in the range of: 1a10, 1a5, 1a4, 1a3, 1a2, 1a1.5, 2a10, 2a5, 2a4, 2a3, 2a2.5, 3a10, 3a5, 4a10, 4a5, or 4.5a5. In certain embodiments, b can be in the range of: 1b5, 1b4, 1b3, 1b2, 1b1.5, 2b5, 2b4, 2b3, 2b2.5, 3b5, 4b5, or 4.5b5. In certain embodiments, c can be in the range of: 2c30, 3c30, 4c30, 5c30, 10c30, 15c30, 20c30, 25c30, 2c25, 3c25, 4c25, 5c25, 10c25, 15c25, 20c25, 2c20, 3c20, 4c20, 5c20, 10c20, 15c20, 2c15, 3c15, 4c15, 5c15, 10c15, 2c10, 3c10, 4c10, 5c10, 2c5, 3c5, or 4c5. In these embodiments, any range of a can be used in combination with any range of b and any range of c in the Mg salt complex described herein. Likewise, any range of b can be used in combination with any range of a and any range of c in the Mg salt complex described herein. Furthermore, any range of c can be used in combination with any range of a and any range of b in the Mg salt complex described herein.

(14) In certain embodiments, the Mg salt complex is represented by formula Mg.sub.aZ.sub.bX.sub.c wherein 1a10, 1b2, and 3c30.

(15) In another aspect, a non-aqueous electrolyte for use in an electrochemical cell includes (a) at least one organic solvent; and (b) at least one electrolytically active, soluble, inorganic Magnesium (Mg) salt complex represented by the formula: Mg.sub.nZX.sub.3+(2*n), in which Z is selected from a group consisting of aluminum, boron, phosphorus, titanium, iron, and antimony; X is a halogen (I, Br, Cl, F or mixture thereof) and n=15. The ratio of Mg to Z can vary from 1:2 to 5:1. In certain embodiments, the ratio of Mg to Z is 5:1, 4:1, 3:1, 2:1, 1:1, or 1:2; however, any non-whole number ratio may also be used. In certain embodiments, the ratio of Mg to Z is from 1:2 to 4:1, from 1:2 to 3:1, from 1:2 to 2:1, from 1:2 to 1:1, from 1:1 to 5:1, from 1:1 to 4:1, from 1:1 to 3:1, from 1:1 to 2:1, from 1:1 to 1.5, from 2:1 to 5:1, from 2:1 to 4:1, from 2:1 to 3:1, from 3:1 to 5:1, from 3:1 to 4:1, or from 4:1 to 5:1.

(16) The electrolyte salt complex can be used at any concentration. In certain embodiments, the Mg concentration in molarity ranges up to 1M or 2 M. In one or more embodiments, the electrolyte salt complex has a Mg concentration in molarity of about 0.25 to about 0.5 M. In one or more embodiments, the electrolyte salt complex has a Mg concentration in molarity of at least about 0.1, 0.25, 0.5, 1.0, 1.5, or 2 M.

(17) In some embodiments, n is greater than 0. In some embodiments, n is greater than 0.5. In some embodiments, n is 0.5, 0.6, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, or 6.

(18) Previously, the only electrolyte solutions proven to reversibly electrodeposit Mg metal at or near room temperature required a Grignard reagent, or another organometallic reagent with metal-organic bonds. However, the organometallic compounds, and complexes thereof, do not provide operating stability at voltages greater than 2 V. It has been surprisingly discovered that the non-aqueous electrolyte as disclosed herein provides operating stability at voltages greater than 2 V. According to one or more embodiments, the non-aqueous electrolyte as disclosed herein is capable of higher voltage stability while maintaining the ability to electrochemically deposit and strip Mg-ions in facile, reversible manner with low overpotential.

(19) While not being bound by any particular mode of operation, it is hypothesized that the capability for reversible Mg deposition is accomplished via the formation of Magnesium halide salt cations, e.g., MgCl.sup.+ and/or Mg.sub.2Cl.sub.3.sup.+ species in solution. It is suggested that these species undergo two-electron reduction of Mg.sup.2+ to Mg.sup.0 while avoiding reduction of the anion by reactions similar to the following:
2MgCl.sup.++2e.sup..fwdarw.MgCl.sub.2+Mg.sup.0.
Cationic species using other halides, such as MgF.sup.+ and/or Mg.sub.2F.sub.3.sup.+ species may also be suitable for reversible Mg deposition.

(20) A suitable anion is used to maintain charge balance, enable complex formation, solubility in organic solvents, and ionic dissociation. In one preferred embodiment, this is demonstrated by a strong Lewis Acid such as AlCl.sub.3 reacting with Lewis Basic MgCl.sub.2, which drives the following example reaction:
2MgCl.sub.2+AlCl.sub.3.fwdarw.Mg.sub.2Cl.sub.3.sup.++AlCl.sub.4.sup.
The product can be described as Mg.sub.2AlCl.sub.7 salt or more generally as a Magnesium-Halide Complex or more specifically as a Magnesium-Aluminum Chloride Complex (MACC) solution. The product of this reaction enables reversible, facile electrochemical plating and stripping of Mg-ions onto an electrode without the use of organometallic reagents for the first time.
The non-aqueous electrolyte solution including MACC can employ MgCl.sub.2 and AlCl.sub.3 over a range of proportions to provide a range of Mg:Al ratios. In certain embodiments, the Mg:Al ratio is in the range of 1:1 to 5:1 with preferable being 4:1, 3:1, 2:1 or any ratio between. For example, any non-whole number ratio may also be used.

(21) Although MgCl.sub.2 is generally regarded as insoluble or poorly soluble in many organic solvents, it has been surprisingly demonstrated that non-aqueous electrolyte solutions including magnesium chloride complexes and in particular using MACC are possible, wherein the Mg molarity, e.g., concentration, ranging up to 1 M or 2 M, and for example at about 0.25 to about 0.5 M for Mg.

(22) Other Lewis acids may be used; in preferred embodiments the Lewis acid meets the requirements of electrochemical stability throughout the window of cell operation. Such Lewis acids can be inorganic, that is, they do not contain any metal-organic bonds. Exemplary Lewis acids include AlCl.sub.3, AlBr.sub.3, AlF.sub.3, AlI.sub.3, PCl.sub.3, PF.sub.3, PBr.sub.3, PI.sub.3, BCl.sub.3, BF.sub.3, BBr.sub.3, BI.sub.3, SbCl.sub.3, SbF.sub.3, SbBr.sub.3, SbI.sub.3.

(23) A variety of organic solvents are suitable for use in the electrolyte of the present invention. Suitable solvent(s) provide appreciable solubility to the Mg salt complex. Further, suitable solvent(s) do not electrochemically oxidize prior to the salt complex, or reduce above the Mg plating potential. Exemplary solvents include ethers, organic carbonates, lactones, ketones, nitriles, ionic liquids, aliphatic and aromatic hydrocarbon solvents and organic nitro solvents. More specifically, suitable solvents include THF, 2-methyl THF, dimethoxyethane, diglyme, ethyl diglyme, butyl diglyme triglyme, tetraglyme, diethoxyethane, diethylether, proglyme, dimethylsulfoxide, dimethylsulfite, sulfolane, acetonitrile, hexane, toluene, nitromethane, 1-3 dioxalane, 1-4 dioxane, trimethyl phosphate, tri-ethyl phosphate, hexa-methyl-phosphoramide (HMPA), N,N-propyl-methyl-pyrrolidinium-bis(trifluoromethylsulfonyl)imide (P13-TFSI), N,N-propyl-methyl-pyrrolidinium-diacetamide (P13-DCA), propyl-methyl-pyrrolidinium-bis(fluorosulfonyl)imide (P13-FSI), ethyl-dimethyl-propyl-ammonium-bis(trifluoromethylsulfonyl)imide (PDEA-TFSI), and 1-(methoxyethyl)-1-methylpiperidinium-bis(trifluoromethylsulfonyl)imide (MOEMPP-TFSI), ionic liquids, or combinations of any or all solvents listed with each other or a solvent not listed.

(24) In one or more embodiments, the solvent is THF or dimethoxyethane for a solution containing the reaction product(s) of MgCl.sub.2 and AlCl.sub.3; the electrolyte assists in the reversible, electrochemical deposition and stripping of Mg when used in an electrochemical cell or plating bath.

(25) While the concept of the above reaction results from effort to surpass the high voltage limitations of all previous organometallic-based electrolytic solutions, it is surprising to someone with expertise in the field that the invention described herein works for at least the following reasons: 1) The only electrolyte solutions proven to reversibly electrodeposit Mg metal at or near room temperature required the utilization of Grignard reagent, or another organometallic reagent with metal-organic bonds. Previously, no entirely inorganic salt solutions had ever shown such behavior; 2) The low solubility of MgCl.sub.2 in various solvents steered others to conclude co-dissolution and reaction was not favorable, or even possible; 3) MgCl.sub.2 is a chemically inert inorganic magnesium salt. It does not dissociate in solutions based on aprotic organic solvents to appreciable extent and displays little to no conductivity in solution. Furthermore, MgCl.sub.2 alone is electrochemically inactive in such solutions, enabling no Mg deposition, dissolution or intercalation.

(26) The magnesium electrolyte salt can be prepared by combining a source of magnesium, e.g., a magnesium halide, and a source of Z, e.g., a halide based on the metal Z in the electrolyte solvent with stirring and heating. Exemplary reaction times include 1, 5, 10, 12, 24, and 48 hours; exemplary reaction temperatures include greater than or equal to 20 degrees Celsius. Heating under inert atmosphere is preferred to avoid water contamination and formation of oxide species.

(27) In some embodiments, it is preferable to condition the solution prior to use in an electrochemical cell, by elimination or mitigation of harmful species inevitably found in the raw materials and/or the as-prepared solution. In some embodiments, additives are provided in the electrolyte to mitigate the deleterious species, without the production of side reaction or unwanted, harmful chemicals. Water, oxygen, and peroxide(s) are non-limiting examples of deleterious species.

(28) Conditioning is accomplished by control of variables including, but not limited to, Mg:Al ratio, constituent molarity, solvent choice, precursor and solvent purity, impurity removal, reaction temperature, time, mixing, and electrochemical conditions could yield the first solution containing an all inorganic salt capable of reversible deposition of Mg. The electrolyte can be conditioned using a variety of processes, including physical, chemical and electrochemical process. The process of conditioning includes the following non-limiting examples: 1) Using Al as an example for Z, physical processes that enable a high degree of Mg complex formation and removal of deleterious species/impurities including: heating, freezing, distillation, maintaining an Mg:Al ratio between 1:1 and 5:1, maintaining molarities that saturate the solution, etc. In some embodiments, the electrolyte solution is heated to help the dissolution of the Mg salt and the Lewis acids. In some embodiments, the Mg:Al ratio is adjusted so that a saturated electrolyte solution with high concentration of the electrolytically active Mg salt complex is obtained. In some specific embodiments, the Mg:Al ratio is 1:1, 2:1, 3:1, 4:1, or 5:1. Similarly, in the case where Z is a metal other than Al, the Mg:Z ratio can be adjusted to result in a high concentration of electrolytically active Mg salt complex. Non-limiting examples of the Mg:Z ratios include those between 0.5:1 and 5:1; 2) Chemical processes in order to remove deleterious species such as addition of minute quantities of proton/water scavengers, such as Grignard's, organoaluminum, molecular sieves, gamma-alumina, silica, Magnesium metal, etc.; 3) Electrochemical processes like potentiostatic, potentiodynamic or galvanostatic electrolysis that enable a high degree of Mg complex formation and removal of deleterious species/impurities. This can be accomplished at reducing or oxidizing potentials, which reduce or oxidize deleterious species and/or drive the reaction of reactants to products. It can be exercised with inert electrodes, sacrificial electrodes, like Mg or, within a complete cell, with an auxiliary electrode or with the cathode serving as the working electrode. In some specific embodiments, the electrolyte is subjected to multiple cycles of potentiostatic, potentiodynamic or galvanostatic electrolysis. In some specific embodiments, the electrolyte is potentiostatically polarized for 5 cycles, 10 cycles, 15 cycles, 20 cycles, or 30 cycles.

(29) In one or more embodiments, the electrolyte salt solution is conditioned to improve the electrochemical properties through electrochemical polarization.

(30) In one or more embodiments, the electrolyte salt solution is conditioned to improve the electrochemical properties by reacting with insoluble active metals Mg, Al, Ca, Li, Na, K., and/or reacting with insoluble acids/bases, adsorbing agents such as molecular sieves, CaH.sub.2, alumina, silica, MgCO.sub.3, etc.

(31) In one or more embodiments, the electrolyte salt solution is conditioned improve the electrochemical properties by providing additives to scavenge contaminants such as organo-Mg, organo-Al, organo-B, organometallics, trace water, oxygen and CO.sub.2, and protic contaminants.

(32) As described above, the electrochemical window of a cell with an electrolyte as described herein and an appropriate anode-cathode pair is 2.9-3.1 volts, such that the cell can be operated in a stable, reversible fashion at 2.0-2.6 volts without decomposition of the electrolyte.

(33) In one or more embodiments, an electrochemical cell is provided including an electrolyte having at least one electrolytically active, soluble, inorganic Magnesium (Mg) salt complex represented by the formula Mg.sub.aZ.sub.bX.sub.c wherein a, b, and c are selected to maintain neutral charge of the molecule, and Z and X are selected such that Z and X form a Lewis Acid; and 1a10, 1b10, and 2c30. The electrochemical cell includes a metal anode and an intercalation cathode.

(34) In one or more embodiments, a battery includes the electrolyte according to the present invention, a magnesium metal anode and a magnesium insertion compound cathode.

(35) In one or more embodiments, the magnesium insertion-compound cathode includes a magnesium-Chevrel intercalation cathode of the formula, Mo.sub.6S.sub.8.

(36) The electrolyte composition of the present invention includes an organic solvent and electrochemically-active, soluble, inorganic salt of the formula Mg.sub.nZX.sub.3+(2*n), in which Z is selected from a group consisting of aluminum, boron, phosphorus, titanium, iron, and antimony; X is a halogen (I, Br, Cl, F or mixture thereof) and n=15. Inorganic salts of this form may, in certain cases, be combined with compatible organometallic salts or with compatible inorganic salts of other forms.

(37) Intercalation cathodes used in conjunction with the electrolyte according to the present invention preferably include transition metal oxides, transition metal oxo-anions, chalcogenides, and halogenides and combinations thereof. Non-limiting examples of positive electrode active material for the Mg battery include Chevrel phase Mo.sub.6S.sub.8, MnO.sub.2, CuS, Cu.sub.2S, Ag.sub.2S, CrS.sub.2, VOPO.sub.4, layered structure compounds such as TiS.sub.2, V.sub.2O.sub.5, MgVO.sub.3, MoS.sub.2, MgV.sub.2O.sub.5, MoO.sub.3, Spinel structured compounds such as CuCr.sub.2S.sub.4, MgCr.sub.2S.sub.4, MgMn.sub.2O.sub.4, MgNiMnO.sub.4, Mg.sub.2MnO.sub.4, NASICON structured compounds such as MgFe.sub.2(PO.sub.4).sub.3 and MgV.sub.2(PO.sub.4).sub.3, Olivine structured compounds such as MgMnSiO.sub.4 and MgFe.sub.2(PO.sub.4).sub.2, Tavorite structured compounds such as Mg.sub.0.5VPO.sub.4F, pyrophosphates such as TiP.sub.2O.sub.7 and VP.sub.2O.sub.7, and fluorides such as MgMnF.sub.4 and FeF.sub.3.

(38) In some embodiments, the positive electrode layer further includes an electronically conductive additive. Non-limiting examples of electronically conductive additives include carbon black, Super P, Super C65, Ensaco black, Ketjen black, acetylene black, synthetic graphite such as Timrex SFG 6, Timrex SFG 15, Timrex SFG 44, Timrex KS 6, Timrex KS 15, Timrex KS 44, natural flake graphite, carbon nanotubes, fullerenes, hard carbon, or mesocarbon microbeads.

(39) In some embodiments, the positive electrode layer further includes a polymer binder. Non-limiting examples of polymer binders include poly-vinylidene fluoride (PVdF), poly(vinylidene fluoride-co-hexafluoropropene) (PVdF-HFP), Polytetrafluoroethylene (PTFE), Kynar Flex 2801, Kynar Powerflex LBG, and Kynar HSV 900, or Teflon.

(40) Negative electrodes used in conjunction with the present invention comprise a negative electrode active material that can accept Mg-ions. Non-limiting examples of negative electrode active material for the Mg battery include Mg, common Mg alloys such as AZ31, AZ61, AZ63, AZ80, AZ81, AZ91, AM50, AM60, Elektron 675, ZK51, ZK60, ZK61, ZC63, M1A, ZC71, Elektron 21, Elektron 675, Elektron, Magnox, or insertion materials such as Anatase TiO.sub.2, rutile TiO.sub.2, Mo.sub.6S.sub.8, FeS.sub.2, TiS.sub.2, MoS.sub.2.

(41) In some embodiments, the negative electrode layer further comprises an electronically conductive additive. Non-limiting examples of electronically conductive additives include carbon black, Super P, Super C65, Ensaco black, Ketjen black, acetylene black, synthetic graphite such as Timrex SFG 6, Timrex SFG 15, Timrex SFG 44, Timrex KS 6, Timrex KS 15, Timrex KS 44, natural flake graphite, carbon nanotubes, fullerenes, hard carbon, or mesocarbon microbeads.

(42) In some embodiments, the negative electrode layer further comprises a polymer binder. Non-limiting examples of polymer binders include poly-vinylidene fluoride (PVdF), poly(vinylidene fluoride-co-hexafluoropropene) (PVdF-HFP), Polytetrafluoroethylene (PTFE), Kynar Flex 2801, Kynar Powerflex LBG, and Kynar HSV 900, or Teflon.

(43) In some embodiments, the Mg battery used in conjunction with the electrolyte described herein comprises a positive electrode current collector comprising carbonaceous material. In some embodiments, the Mg battery described herein comprises a negative electrode current collector comprising carbonaceous material. In other embodiments, the Mg battery described herein comprises positive and negative electrode current collectors comprising carbonaceous material.

(44) In some embodiments, the Mg battery disclosed herein is a button or coin cell battery consisting of a stack of negative electrode, porous polypropylene or glass fiber separator, and positive electrode disks sit in a can base onto which the can lid is crimped. In other embodiments, the Mg battery used in conjunction with the electrolyte disclosed herein is a stacked cell battery. In other embodiments, the Mg battery disclosed herein is a prismatic, or pouch, cell consisting of one or more stacks of negative electrode, porous polypropylene or glass fiber separator, and positive electrode sandwiched between current collectors wherein one or both current collectors comprise carbonaceous materials. The stack(s) are folded within a polymer coated aluminum foil pouch, vacuum and heat dried, filled with electrolyte, and vacuum and heat sealed. In other embodiments, the Mg battery disclosed herein is a prismatic, or pouch, bi-cell consisting of one or more stacks of a positive electrode which is coated with active material on both sides and wrapped in porous polypropylene or glass fiber separator, and a negative electrode folded around the positive electrode wherein one or both current collectors comprise carbonaceous materials. The stack(s) are folded within a polymer coated aluminum foil pouch, dried under heat and/or vacuum, filled with electrolyte, and vacuum and heat sealed. In some embodiments of the prismatic or pouch cells used in conjunction with the electrolyte described herein, an additional tab composed of a metal foil or carbonaceous material of the same kind as current collectors described herein, is affixed to the current collector by laser or ultrasonic welding, adhesive, or mechanical contact, in order to connect the electrodes to the device outside the packaging.

(45) In other embodiments, the Mg battery used in conjunction with the electrolyte disclosed herein is a wound or cylindrical cell consisting of wound layers of one or more stacks of a positive electrode which is coated with active material on one or both sides, sandwiched between layers of porous polypropylene or glass fiber separator, and a negative electrode wherein one or both current collectors comprise carbonaceous materials. The stack(s) are wound into cylindrical roll, inserted into the can, dried under heat and/or vacuum, filled with electrolyte, and vacuum and welded shut. In some embodiments of the cylindrical cells described herein, an additional tab composed of a metal foil or carbonaceous material of the same kind as current collectors described herein, is affixed to the current collector by laser or ultrasonic welding, adhesive, or mechanical contact, in order to connect the electrodes to the device outside the packaging.

(46) The invention is illustrated by way of the following examples, which are presented by way of illustration only and are not intended to be limiting of the invention.

EXAMPLE 1

(47) FIG. 1 is a graph displaying a typical cyclic voltammogram of the all-inorganic salt Magnesium Aluminum Chloride complex. Solutions utilize tetrahydrofuran (THF) as the solvent and Platinum as the working electrode while Magnesium serves as both the auxiliary and reference electrodes.

(48) The data depicted in FIG. 1 shows the potentiodynamic behavior of Mg.sub.2AlCl.sub.7 complex inorganic salt obtained with THF solution from the reaction of 2MgCl.sub.2+1AlCl.sub.3. The peak displaying maximum current density at 1 V is due to the deposition of magnesium metal while the peak with maximum current density at about 0.3 V is attributed to the subsequent electrochemical dissolution of the magnesium metal. The electrochemical window obtained with this system exceeds 3.1 V vs Mg/Mg.sup.2+. It is clearly evident from the cyclic voltammogram that the process of magnesium deposition and dissolution is fully reversible.

(49) FIG. 2 depicts the MgAlCl ternary phase diagram derived from the ab initio calculated energies of compounds within that system. Each point in the diagram represents a thermodynamically stable compound (e.g., Mg, MgCl.sub.2, MgAl.sub.2Cl.sub.8 etc.) and the space within each triangular plane represents compositional space wherein a mixture of the three vertex compounds is thermodynamically favored over a single ternary compound within that region up until the voltage vs. Mg/Mg.sup.2+ indicated within that triangle. The phase diagram indicates that compounds existing along the tie line between MgCl.sub.2 and AlCl.sub.3, such as MgAl.sub.2Cl.sub.8, will oxidize when the voltage is >3.1-3.3 V vs. Mg/Mg.sup.2+. This result corroborates the cyclic voltammogram depicted in FIG. 1, which suggests 3.1 V vs. Mg/Mg.sup.2+ is the limit of oxidative stability for Magnesium Aluminum Chloride Complexes resulting from the reaction of 2MgCl.sub.2+1AlCl.sub.3. Furthermore it is important to note MgCl.sub.2 is in direct equilibrium with Mg metal because it can be a soluble species and will not disproportionate into undesirable products in the presence of Mg metal. Similar observations can be made for reaction of MgCl.sub.2 with any of the following: BCl.sub.3, PCl.sub.3, SbCl.sub.3, PCl.sub.3.

EXAMPLE 2

(50) In a typical preparation of an electrochemically active MACC solution such as 0.267 M Mg.sub.2AlCl.sub.7, one may undertake the following reaction:
2MgCl.sub.2+1AlCl.sub.3.fwdarw.Mg.sub.2AlCl.sub.7,
by placing both 0.508 g MgCl.sub.2 powder (99.99%) and 0.356 AlCl.sub.3 (99.999%) into a single glass container with a stir bar under inert atmosphere. Thereafter add 20.0 ml of tetrahydrofuran (THF, anhydrous <20 ppm H.sub.2O) and stir vigorously because the initial dissolution is exothermic in nature. Subsequently stir and heat to 30.0 degrees Celsius for minimum of one hour after which solution may be returned to room temperature. The resulting solution is clear to light yellow or brown color with no precipitation. In some embodiments it is preferable to let the final solution sit over Mg metal powder in order to condition the solution for improved electrochemical response by reducing residual water and other impurities.

(51) In a typical preparation of an electrochemically active MACC solution such as 0.4 M MgAlCl.sub.5, one may undertake the following reaction:
1MgCl.sub.2+1AlCl.sub.3.fwdarw.MgAlCl.sub.5,
by placing both 1.1424 g MgCl.sub.2 powder (99.99%) and 1.6002 AlCl.sub.3 (99.999%) into a single glass container with a stir bar under inert atmosphere. Thereafter add 30.0 ml of 1,2-dimethoxymethane (DME, anhydrous <20 ppm H.sub.2O) and stir vigorously because the initial dissolution is exothermic in nature. Subsequently stir and heat to 70.0 degrees Celsius for minimum of several hours after which solution may be returned to room temperature. The resulting solution is clear with no precipitation. In some embodiments it is preferable to let the final solution sit over Mg metal powder in order to condition the solution for improved electrochemical response by reducing residual water and other impurities.

(52) FIG. 3 depicts representative cyclic voltammogram of the all-inorganic Magnesium Aluminum Chloride complex dissolved in tetrahydrofuran (THF) using a platinum working electrode, and Mg for the counter and reference electrodes. The voltammogram depicted in black illustrates the significant hysteresis between Mg plating and stripping of the as produced solution while the voltammogram depicted in grey depicts the same solution with significantly improved plating ability due to electrochemical conditioning by galvanostatic and/or potentiostatic polarization. The electrolyte solution was potentiostatically polarized within the same voltage window for 15 cycles. The cyclic voltammetry utilized 25 mV/s scan rate and a platinum working electrode, and Mg for the counter and reference electrodes.

EXAMPLE 3

(53) Referring now to FIG. 4, which displays a graph of the potential response of resulting during chronopotentiometry experiments carried out with Mg.sub.2AlCl.sub.2 complex inorganic salt obtained with THF solution from the reaction of 2MgCl.sub.2+1AlCl.sub.3. This test utilizes Magnesium electrodes in a symmetric cell fashion and an applied current of 0.1 mA/cm2, which switches polarity every one hour. The overpotential for dissolution is quite small (0.05 V vs. Mg) throughout the test while the overpotential for deposition varies between 0.1 and 0.5 V vs. Mg metal. The results suggest the overpotential for Mg deposition is at most 0.5 V vs. Mg/Mg.sup.2+, but that the mean within the 100 hour period is about 0.25 V vs. Mg/Mg.sup.2+.

EXAMPLE 4

(54) An electrochemical cell was prepared consisting of a Chevrel-phase cathode, a magnesium metal anode, and an electrolyte containing Magnesium Aluminum Chloride complex salt. The cathode 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 Pt mesh current collector. The electrolyte solution containing Mg.sub.3AlCl.sub.9, was prepared from the reaction of 3MgCl.sub.2+1AlCl.sub.3 in THF solution. The anode and reference electrode was composed of pure magnesium metal. The glass cell was filled under inert atmosphere. FIG. 4 depicts a graph of the results from cyclic voltammetry carried out on this cell. A scan rate of 0.1 mV/s was applied, so as not to limit the current response by the rate of Mg solid-state diffusion into Chevrel. The current response of the voltammogram corresponds with 80 mAh/g over eight charge/discharge cycles at voltages comparable to those observed in prior art with organo-Mg complex salt solutions.

(55) 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.