Electrolyte for a magnesium sulfur battery

1. An electrochemical device, comprising:

an anode comprising magnesium;

a cathode stable to a voltage of at least 3.2 V relative to a magnesium reference; and

a non-nucleophilic electrolyte;

wherein

the electrolyte comprises an electrochemically active salt of a solvated cation species, prepared in a medium, the salt comprising a magnesium ion dimer of formula (III):

[Mg 7 Cl 3 ] +   (III)

and

an anion of formula (IV):

[AlCl 3 (B)] −   (IV)

the electrochemically active salt having been crystallized and removed from the medium of preparation and redissolved in an ether solvent to obtain the electrolyte,

wherein

B is a non-nucleophilic base comprising nitrogen.

2. The electrochemical device according to claim 1 , wherein the non-nucleophilic base comprising nitrogen is a sterically hindered secondary amine or an aromatic heterocyclic nitrogen system.

3. The electrochemical device according to claim 2 , wherein the non-nucleophilic base comprising nitrogen is at least one sterically hindered secondary amine selected from the group consisting of diisopropylamine, tetramethylpiperidine and hexamethyldisilylamine.

4. The electrochemical device according to claim 1 , wherein the ether solvent is selected from the group consisting of tetrahydrofuran, ethylene glycol dimethyl ether and bis 2-methoxy ethyl ether.

5. The electrochemical device according to claim 4 , wherein the ether is tetrahydrofuran.

6. The electrochemical device according to claim 1 , wherein

the ether solvent is tetrahydrofuran, and

the electrolyte comprises an active salt of formula (I)

[Mg 2 Cl 3 -6(C 4 H 8 O)] + [AlCl 3 ((CH 3 ) 3 Si) 2 N)] −   (I).

7. The electrochemical device according to claim 1 , wherein

the electrochemically active salt is obtained by a method comprising admixture of a magnesium salt of a non-nucleophlic base comprising nitrogen and aluminum trichloride in an ether solvent in a molar ratio of the magnesium salt of a non-nucleophilic base comprising nitrogen to the aluminum trichloride of from 3/2 to 5/1.

8. The electrochemical device according to claim 1 , wherein the cathode stable to a voltage of at least 3.2 V relative to a magnesium reference comprises sulfur.

9. The electrochemical device according to claim 8 , wherein the cathode comprising sulfur comprises elemental sulfur.

10. The electrochemical device according to claim 9 , wherein the cathode comprising elemental sulfur further comprises a divided carbon.

11. A method for preparing an electrochemical device, comprising:

connecting an anode comprising magnesium and a cathode stable to a voltage of at least 3.2 V relative to a magnesium reference via an external electrically conductive structure; and

contacting the anode and cathode with a non-nucleophilic electrolyte

wherein

the electrolyte comprises an electrochemically active salt of a solvated cation specie, prepared in a medium, the salt comprising a magnesium ion dimer of formula (III):

[Mg 9 Cl 3 ] +   (III)

and

an anion of formula (IV):

[AlCl 3 (B)] −   (IV)

the electrochemically active salt having been crystallized and removed from the medium of preparation and redissolved in an ether solvent to obtain the electrolyte,

wherein

B is a non-nucleophilic base comprising nitrogen.

12. The method according to claim 11 , wherein the the non-nucleophilic base comprising nitrogen is hexamethyldisilylamine and

the ether solvent is tetrahydrofuran.

13. The method according to claim 11 , wherein the electrolyte is obtained by combining a magnesium salt of a non-nucleophilic base comprising nitrogen with aluminum trichloride in a molar ratio of the magnesium salt of a non-nucleophilic base comprising nitrogen to the aluminum trichloride of from 3/2 to 5/1.

14. The method according to claim 11 , wherein the cathode stable to a voltage of at least 3.2 V relative to a magnesium reference comprises elemental sulfur.