Metal-air cell comprising an electrolyte with a room temperature ionic liquid and hygroscopic additive
View Patent ↗An electrochemical cell comprising an electrolyte comprising water and a hydrophobic ionic liquid comprising positive ions and negative ions. The electrochemical cell also includes an air electrode configured to absorb and reduce oxygen. A hydrophilic or hygroscopic additive modulates the hydrophobicity of the ionic liquid to maintain a concentration of the water in the electrolyte is between 0.001 mol % and 25 mol %.
1. An electrochemical cell comprising:
an ionically conductive medium comprising a hydrophobic low temperature ionic liquid comprising positive ions and negative ions and at least one hygroscopic additive selected from the group consisting of ZnCl 2 , Zn(BF 4 ) 2 , Zn(acetate) 2 , and mixtures thereof;
a fuel electrode for oxidizing a fuel; and
an air electrode for absorbing and reducing gaseous oxygen,
wherein the hygroscopic additive modulates the hydrophobicity of the ionically conductive medium to maintain a concentration of water in the ionically conductive medium between 0.001 mol % and 25 mol % when the ionically conductive medium is allowed to equilibrate with an ambient air laboratory environment at 22° C. across a relative humidity of 20% to 40%.
2. The electrochemical cell of claim 1 , wherein the air electrode comprises polytetrafluoroethylene (PTFE).
3. The electrochemical cell of claim 1 , wherein the air electrode is porous.
4. The electrochemical cell according to claim 1 , wherein the fuel electrode comprises a metal fuel.
5. The electrochemical cell of claim 1 , wherein the fuel electrode is porous.
6. The electrochemical cell of claim 1 , wherein the low temperature ionic liquid is aprotic.
7. The electrochemical cell of claim 1 , wherein the hydrophobic ionic liquid is selected from the group consisting of choline bis(trifluoromethylsulfonyl)imide, butylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide (c4 mPyrTFSI), and n-ethyl n-methylmorpholinium bis(trifluoromethylsulfonyl)imide (c2 nmm TFSI).
8. The electrochemical cell of claim 1 , wherein the concentration of the hygroscopic additive is between 10 and 500 mM.
9. The electrochemical cell of claim 8 , wherein the concentration of the hygroscopic additive is between 10 and 100 mM.
10. The electrochemical cell of claim 9 , wherein the hydrophobicity of the ionically conductive medium is such that the water content rises from essentially zero to approximately 13000 ppm (1.3%) in an hour when the ionically conductive medium is initially exposed to the ambient air.
11. The electrochemical cell of claim 10 , wherein the hydrophobicity of the ionically conductive medium is such that the water content reaches a steady state concentration of approximately 15000 ppm (1.5%) in 24 hours when the ionically conductive medium is initially exposed to the ambient air.
12. The electrochemical cell of claim 8 , wherein the hydrophobicity of the ionically conductive medium is such that the water content rises from essentially zero to approximately 15000 ppm (1.5%) in an hour when the ionically conductive medium is initially exposed to the ambient air.
13. The electrochemical cell of claim 12 , wherein the hydrophobicity of the ionically conductive medium is such that the water content reaches a steady state concentration of approximately 17000 ppm (1.7%) in 24 hours when the ionically conductive medium is initially exposed to the ambient air.
14. The electrochemical cell of claim 8 , wherein the hydrophobicity of the ionically conductive medium is such that the water content rises from essentially zero to approximately 41000 ppm (4.1%) in an hour when the ionically conductive medium is initially exposed to the ambient air.
15. The electrochemical cell of claim 14 , wherein the hydrophobicity of the ionically conductive medium is such that the water content reaches a steady state concentration of approximately 52000 ppm (5.2%) in 24 hours when the ionically conductive medium is initially exposed to the ambient air.
16. The electrochemical cell of claim 1 , wherein the low temperature ionic liquid comprises a vapor pressure at or below 1 mm Hg at 20° C. above its melting point.
17. The electrochemical cell of claim 1 , wherein the low temperature ionic liquid comprises an anion comprising bis(trifluoromethylsulfonyl)imide (TFSI).
18. The electrochemical cell of claim 1 , wherein the low temperature ionic liquid comprises cations selected from the group consisting of Choline, butylmethylpyrrolidinium (c4 mPyr), n-ethyl n-methylmorpholinium, butyl pyridinium, and alkyl imidizolium.
19. The electrochemical cell of claim 1 , wherein the air electrode includes a catalyst.
20. The electrochemical cell of claim 19 , wherein, the catalyst is selected from the group consisting of manganese oxide, nickel, pyrolized cobalt, activated carbon, silver, platinum, and mixtures thereof.
21. The electrochemical cell of claim 1 , wherein the ionically conductive medium consists of the hydrophobic low temperature ionic liquid and the at least one hygroscopic additive.
22. The electrochemical cell of claim 1 , wherein the ionically conductive medium consists essentially of the ionic liquid and the at least one hydrophilic additive.
23. An ionically conductive medium for use in an electrochemical cell comprising a fuel electrode and an air electrode for absorbing and reducing gaseous oxygen, comprising:
a hydrophobic low temperature ionic liquid comprising positive ions and negative ions; and
at least one hygroscopic additive selected from the group consisting of ZnCl 2 , Zn(BF 4 ) 2 , Zn(acetate) 2 , and mixtures thereof, wherein the hygroscopic additive modulates the hydrophobicity of the ionic liquid to maintain a concentration of water in the ionically conductive medium between 0.001 mol % and 25 mol % when the ionically conductive medium is allowed to equilibrate with an ambient air laboratory environment at 22° C. across a relative humidity of 20% to 40%.