Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0567—Liquid materials characterised by the additives
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0568—Liquid materials characterised by the solutes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0569—Liquid materials characterised by the solvents
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/058—Construction or manufacture
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M6/00—Primary cells; Manufacture thereof
  • H01M6/14—Cells with non-aqueous electrolyte
  • H01M6/16—Cells with non-aqueous electrolyte with organic electrolyte
  • H01M6/162—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte
  • H01M6/164—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte by the solvent
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M6/00—Primary cells; Manufacture thereof
  • H01M6/14—Cells with non-aqueous electrolyte
  • H01M6/16—Cells with non-aqueous electrolyte with organic electrolyte
  • H01M6/162—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte
  • H01M6/166—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte by the solute
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M6/00—Primary cells; Manufacture thereof
  • H01M6/14—Cells with non-aqueous electrolyte
  • H01M6/16—Cells with non-aqueous electrolyte with organic electrolyte
  • H01M6/162—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte
  • H01M6/168—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte by additives
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0017—Non-aqueous electrolytes
  • H01M2300/0025—Organic electrolyte
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0017—Non-aqueous electrolytes
  • H01M2300/0025—Organic electrolyte
  • H01M2300/0028—Organic electrolyte characterised by the solvent
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49002—Electrical device making
  • Y10T29/49108—Electric battery cell making

Definitions

• the present disclosure relates to primary and secondary electrochemical cells that include magnesium electrode materials and electrolytes for the same.
• Hideyuku et al. have designed a secondary battery that has a sulfur positive electrode and a negative electrode that contains at least one of magnesium metal, magnesium alloy, magnesium oxide, silicon, carbon, and transition metal sulfide as an active material.
• the battery has a non-aqueous electrolyte containing a magnesium salt such as magnesium
• Shimamura et al. Journal of Power Sources, 196, 1586-1588 (201 1) have both reported the deposition and dissolution of magnesium from an ionic liquid.
• NuLi has reported electrochemical magnesium deposition and dissolution on a silver substrate in the ionic liquid N-methyl-N- propylpiperidinium bis(trifluoromethanesulfonylimide) containing 1M Mg[(CF 3 S0 2 ) 2 ] 2 .
• Shimamura has reported electrochemical reduction and oxidation of magnesium cation in ionic liquids containing simple magnesium salts.
• the ionic liquid that they used was N,N-diethyl-N-methyl-(2- methoxyethyl) ammonium bis(trifluoromethanesulfonyl)imide.
• Magnesium analogues of common electrolyte salts e.g.
• Mg(PF 6 ) 2 , Mg(C10 4 )2, Mg(S0 3 CF 3 ) 2 ) generally have low solubility in electrolyte solvents.
• Nonaqueous magnesium electrolytes in which magnesium electrochemistry can be conducted at low overpotentials are typically solutions that contain Grignard reagents.
• Such solutions typically are composed of a solution of magnesium alkyl halide in tetrahydrofuran.
• Such solutions are toxic and react spontaneously with oxygen in the air, making them not compatible with dry room environments. They also are oxidatively unstable, limiting the voltage of magnesium batteries to below about 2.5 V.
• magnesium metal can be stripped at low overpotentials.
• Efficient magnesium intercalation at voltages of 0.5 V or greater can be achieved only when acetonitrile or adiponitrile is used as the solvent. Since acetonitrile and adiponitrile are much more oxidatively stable than THF or the Grignard reagents currently used, electrolytes made from Mg(TFSI)2 and acetonitrile or adiponitrile may be highly useful as electrolytes for high voltage magnesium batteries.
• an electrochemical cell in one aspect, includes at least one electrode comprising a magnesium intercalation compound, and an electrolyte.
• the electrolyte includes a fluorinated imide salt or a fluorinated methide salt substantially dissolved in an oxidatively stable solvent.
• the at least one electrode can include a magnesium intercalation compound selected from transition metal sulfides, transition metal oxides, magnesium transition metal sulfides, magnesium transition metal oxides, and carbon fluorides.
• the provided electrochemical cell can include a negative electrode comprising magnesium.
• the provided electrochemical cell can be a primary (or non-rechargeable) electrochemical cell or a secondary (or rechargeable) electrochemical cell. In some embodiments, the provided electrochemical cell can be operated at temperatures greater than about 40°C and/or at voltages at or above 3.0V vs. Li/Li + .
• a method of making an electrochemical cell includes dissolving a fluorinated imide or fluorinated methide salt in an oxidatively stable solvent to form an electrolyte, immersing at least one electrode that includes a magnesium intercalation compound into the electrolyte, and immersing a second electrode comprising magnesium into the electrolyte.
• the at least one electrode can be selected from transition metal sulfides, transition metal oxides, magnesium transition metal sulfides, magnesium transition metal oxides, and carbon fluorides.
• a magnesium electrochemical cell in yet another aspect includes a liquid organic electrolyte, wherein the electrochemical cell is operated at a temperature greater than 40°C.
• active or “electrochemically active” refers to a material that can undergo magnesiation and demagnesiation by reaction with magnesium;
• chevrel refers to chalcogenides that include molybdenum sulfides, selenides and tellurides that have structures that can intercalate magnesium; "inactive” or “electrochemical inactive” refers to a material that does not react with magnesium and does not undergo magnesiation or demagnesiation;
• magnesium or “demagnesiation” refer to the processes of reactively inserting magnesium into an active material such as a magnesium intercalation compound or removing magnesium from an active material such as a magnesium intercalation material respectively;
• intercalation refers to a processes in which magnesium can be reversibly inserted into and removed from a magnesium intercalation compound without substantially changing the crystal structure of the magnesium intercalation host compound;
• negative electrode refers to an electrode (often called an anode) where electrochemical oxidation and demagnesiation occurs during a discharging process
• Positive electrode refers to an electrode (often called a cathode) where electrochemical reduction and magnesiation occurs during a discharging process.
• the provided electrochemical cells and methods of making the same provide an electrolyte salt that has high solubility in nitrile-containing solvents. Furthermore, the provided electrochemical cells and methods resist the formation of a blocking solid electrolyte interphase layer that can impede electrochemical reactions essential to the efficient operation of magnesium electrochemical cells.
• Fig. 1 shows the voltage curve of the MoeSg vs. Mg coin cell of Example 1.
• Fig. 2 shows the x-ray diffraction pattern of the discharged MoeSg electrode of Example 1.
• Fig. 3 shows the voltage curve of the MoeSg vs. Mg coin cell of Example 2.
• Fig. 4 shows the x-ray diffraction pattern of the discharged MoeSg electrode of Example 1.
• Fig. 5 shows the voltage curve of the MoeSg vs. Mg coin cell with Mg wire reference electrode of Example 4.
• Fig. 6 shows the voltage curve of the Mo 6 S 8 vs. discharged Mo 6 S 8 coin cell of Example 5.
• Fig. 7 shows the voltage curve of the Mo 6 S 8 vs. Mg coin cell of Example 6.
• Fig. 8 shows the cyclic voltammagram of the cell described in Example 7.
• Electrochemical cells include at least one electrode that includes a magnesium intercalation compound and an electrolyte that includes a fluorinated imide salt or a fluorinated methide salt that is substantially dissolved in an oxidatively stable solvent.
• exemplary materials include T1S 2 , V 6 O 13 , V 2 O 5 , WO 3 , M0O 3 , Mn0 2 , InSe, and some sulfides of molybdenum. These materials are discussed, for example, in P. G. Bruce et al., "Chemical Intercalation of Magnesium into Solid Hosts", J. Mater. Chem., 1(4), 705-706 (1991) and Z.
• Magnesium chevrel phases can have various stoichiometries such as MgMo 3 S 4 or Mg 2 Mo 6 Sg. Since magnesium intercalates into the chevrel materials, the amount of magnesium can vary depending upon the amount of intercalation. Other intercalation electrode materials that may be useful are described in International PCT Pat. App. Publ. No. WO201 1/150093 (Doe et al.).
• the provided electrochemical cells may include a current collector comprising one or more elements selected from the group consisting of carbon, Al, Cu, Ti, Ni, stainless steel, and alloys thereof, as described in U. S. Pat. App. Publ. No. 201 1/0159381 (Doe et al.).
• the provided electrochemical cells include an electrolyte that includes a fluorinated imide salt or a fluorinated methide salt substantially dissolved in an oxidatively stable solvent.
• the fluorinated imide or fluorinated methide salts include a bis(trifluoromethylsulfonyl)imide anion or a
• each R f group is, independently, F or a fluoroalkyl group having 1 -4 carbon atoms, which may optionally contain catenary oxygen or nitrogen atoms within the carbon chain, and wherein any two adjacent R f groups may optionally be liked to form a 5-7 membered ring.
• the salts can have cations selected from ammonium, imidazolium, pyrazolium, triazolium, thiazolium, oxazolium, pyridinium, pyridazinium, pyrimidonium, and pyrazinium.
• the cations can be metals such as sodium, lithium, potassium, or magnesium.
• at least some of the cations are magnesium cations.
• [bis(trifluoromethanesulfonyl)imide] 2 can be produced by reacting magnesium carbonate or magnesium hydroxide or magnesium metal with bis-(trifluoromethanesulfonyl)imide acid.
• Magnesium [tris(trifluoromethanesulfonyl)methide]2 can be produced in an analogous manner from tris-(trifluoromethanesulfonyl)methide acid.
• Fluorinated imide or methide salts such as, for example, magnesium
• [tris(trifluoromethylsulfonyl)methide]2 (Mg(TFSM) 2 )
• Mg(TFSM) 2 can be dissolved in oxidatively stable solvents such as organic carbonates, nitriles, and pyridine solvent systems.
• oxidatively stable solvents such as organic carbonates, nitriles, and pyridine solvent systems.
• the disclosed Mg(TFSI)2 or Mg(TFSM) 2 electrolyte salts can provide a number of surprising benefits when used in primary or secondary Mg cells. These salts can be both highly soluble and highly dissociated in oxidatively and reductively stable, nonaqueous organic solvents, including but not limited to, organic carbonates, nitriles, and pyridines.
• the oxidatively stable organic solvents can include aliphatic nitriles such as acetonitrile, propionitrile, valeronitrile, isobutylnitrile, isopentylnitrile, t- butylnitrile, and dinitriles such as succinonitrile, malononitrile, or adiponitrile.
• aliphatic nitriles such as acetonitrile, propionitrile, valeronitrile, isobutylnitrile, isopentylnitrile, t- butylnitrile, and dinitriles such as succinonitrile, malononitrile, or adiponitrile.
• Mg(TFSI)2 electrolyte salt, concentrations up to 1.0 M (molar) or higher are possible, depending on the choice of solvents.
• Mg(TFSI) 2 can be dissolved in acetonitrile to form solutions having a concentration of at least 0.1M, at least 0.5M, or even at least 1.0 M at room temperature.
• the solubility of Mg(TFSI) 2 can be even greater at elevated temperatures such as at temperatures greater than about 40°C.
• Solvents such as organic carbonates, nitriles, and pyridines provide a wide electrochemical stability window and thus enable production of high voltage Mg batteries.
• Acetonitrile has been found to be a particularly useful solvent because it is capable of supporting reversible Mg electrochemistry at relatively low overpotentials.
• Mg(TFSI)2 Another advantage of Mg(TFSI)2 is that it is chemically stable to air and moisture, unlike certain background art electrolytes, like Grignard reagents, which are extremely difficult to handle due to their air and moisture sensitivity and their pyrophoric nature.
• Grignard reagents are oxidatively unstable and therefore limit overall cell potentials for Mg batteries
• Mg(TFSI)2 is much more stable to oxidation and thereby enables production of high voltage Mg batteries.
• the thermally stable nature of electrolytes that include Mg(TFSI)2 or Mg(TFSM) 2 and solvents such as organic carbonates, nitriles, and pyridine enables batteries comprising these electrolytes to be operated a elevated temperature.
• batteries comprising these electrolytes can be operated at temperatures above 30°C, or above 40°C, or above 50°C or above 60°C, or even higher.
• the limiting temperature factor can be the boiling point of the most volatile solvent in the electrolyte solution.
• High purity Mg chips 99.98% from Aesar, 9.350g
• 150 g of deionized water (18 MOhm) were charged to a 1.0 L flask equipped with a condenser, nitrogen line, Claisen adapter and an addition funnel.
• a 55.5 weight percent (wt%) solution of H-N(S0 2 CF 3 ) 2 in water (360.36 g, prepared according to PCT Pat. Appl. Publ. No. WO 97/23448, Example #12) was added dropwise with magnetic stirring at room temperature causing a mild exotherm and moderate gas evolution.
• the recovered filtrate was concentrated by short path distillation at atmospheric pressure to a final weight of 321.57 g and the concentrate was filtered again by suction through a 0.2 micron filter membrane to remove a small amount of insoluble solids.
• the filtered concentrate was transferred to a Pyrex crystallizing dish and evaporated to near dryness at 145°C in a convection oven and then dried more completely in a vacuum oven at the same temperature. Once dry, the fused white solid was chipped out of the crystallizing dish and transferred to a mortar and pestle where it was ground to a fine powder and immediately transferred to a glass canning jar for further vacuum drying overnight at 145°C to a final pressure of 45 mTorr.
• Chevrel phase Mo 6 S 8 was prepared by chemical extraction of Cu from Cu 2 Mo 6 S8. 5.0839 g of Cu powder (Alfa Aesar, -325 mesh, 10% max +325 mesh, 99% metals basis), 7.7136 g Mo powder (Sigma Aldrich, 1-2 ⁇ , >99.9%, trace metals basis) and 25.6209 g of MoS 2 powder (Alfa Aesar, -325 mesh, 99% metals basis) were blended together by hand and placed in an alumina boat. The powder mixture was then heated under vacuum at 150°C for 12 hours, ramped to 985°C at a rate of 500°C/hr and held at 985°C for 150 hours. The sample was then cooled to room temperature over 12 hours under vacuum. X-ray diffraction measurement showed that the product was Cu 2 Mo 6 Sg.
• coin cells were constructed from 2325 coin cell hardware.
• Mg electrodes were prepared by punching 15.60 mm disks from 250 ⁇ Mg foil (99.95%, GalliumSource LLC). Each cell contained a Mg foil electrode, CELGARD 2320 separator, electrolyte, a Mo 6 S 8 disk electrode and a stainless steel spacer.
• Electrolytes were prepared by dissolving Mg(TFSI) 2 salt in either acetonitrile (Sigma Aldrich, >99.9%, for HPLC), pyridine (Sigma Aldrich, 99.8% anhydrous) and a 1 :2 w/w solution of ethylene carbonate (EC) / diethyl carbonate (DEC) (EC/DEC solvent mixture used as received from Novolyte).
• acetonitrile Sigma Aldrich, >99.9%, for HPLC
• pyridine Sigma Aldrich, 99.8% anhydrous
• EC ethylene carbonate
• DEC diethyl carbonate
• a MoeSg vs. Mg coin cell was constructed using an electrolyte consisting of a 0.5 M solution of Mg(TFSI)2 in acetonitrile. The cell was discharged at a rate of C/100 for 100 hours at 60°C. The voltage curve of the cell is shown in Fig. 1. The cell was then disassembled in an argon filled glovebox and the discharged Mo 6 S 8 electrode powder was scraped off the current collector, rinsed with DMC, dried under vacuum and placed in a gas-tight x-ray sample holder with an aluminized MYLAR window. The x-ray diffraction pattern of this sample was measured while helium gas was flowed through the sample holder. The diffraction pattern (Fig. 2) shows that the discharged MoeSg electrode was primarily composed of Mg 2 MoeSg with some MgMoeSg present as a minority phase.
• a Mo 6 S 8 vs Mg coin cell was constructed using an electrolyte consisting of a 0.5 M solution of Mg(TFSI) 2 in pyridine. The cell was discharged and charged at a C/50 rate at 60°C between -0.6 V and 1.2 V and the voltage curve is shown in Figure 3. The negative voltage is likely due to polarization at the Mg metal electrode.
• a separate cell was fully discharged to -0.6 V, disassembled in an argon filled glovebox and the discharged M06S8 electrode powder was scraped off the current collector, rinsed with DMC, dried under vacuum and placed in a gas-tight x-ray sample holder with an aluminized mylar window.
• the x-ray diffraction pattern of this sample was measured while helium gas was flowed through the sample holder.
• the diffraction pattern ( Figure 4) shows that the MoeSg electrode intercalated magnesium during the discharge to form Mg 2 MoeSg and MgMoeSg.
• a MoeSg vs Mg coin cell was constructed as described in Example 1, except that a Mg wire reference electrode was placed between the MoeSg and Mg electrodes. The cell was cycled such that the voltage of the MoeSg vs Mg wire reference electrode was between 0.5 V and 1.5 V at 60°C and a C/50 rate. The voltage curve of this cell is shown in Figure 5, showing reversible cycling of the MoeSg electrode.
• a symmetric MoeSg coin cell was constructed as follows. First a MoeSg vs Mg coin cell was constructed and discharged as described in Example 1. The cell was then disassembled in an argon- filled glovebox and the discharged MoeSg electrode was removed. A new coin cell was then prepared with an electrolyte consisting of a 0.5 M solution of Mg(TFSI) 2 in acetonitrile and one electrode being the discharged MoeSg electrode and the other electrode being a newly prepared MoeSg electrode. The cell was then cycled at a C/40 rate between +/- 0.7 V. The voltage curve of this cell is shown in Figure 6.
• a MoeSg vs Mg coin cell was constructed as described in Example 1, except a solution of 0.5 M Mg(TFSI)2 in adiponitrile was used as the electrolyte. The cell was discharged to -0.8 volts, after which the Mo 6 S 8 electrode reached its full theoretical capacity. The voltage curve of this cell is shown in Figure 7. The negative voltage is likely due to polarization at the Mg metal electrode.
• a three electrode cell with Mg foil reference and counter electrodes and a 4 mm diameter glassy carbon rod working electrode was constructed in a 20 ml glass vial and covered with a rubber stopper with holes for electrical feedthroughs.
• Enough electrolyte comprising a 0.5 M solution of Mg(TFSI) 2 in acetonitrile was added to the vial to cover the electrode surfaces.
• Cyclic voltammetry was conducted with this cell at a scan rate of 20 mV/s between 0.5 V and 4 V vs Mg at 25°C.
• the cyclic voltammagrams obtained are shown in Figure 8.
• the electrolyte showed stability towards oxidative decomposition at voltages up to about 3.2 V vs Mg.
• a Mo 6 S 8 vs. Mg coin cell was constructed using an electrolyte consisting of a 0.5 M solution of Mg(TFSI) 2 in 1 :2 w/w EC:DEC. The cell was discharged at a C/100 rate at 60°C to zero volts and showed almost no capacity.

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