Phosphonium-based ionic liquids for lithium metal-based batteries
An electrolyte for Li-ion and other secondary electrochemical cells includes an FSI anion and at least one of methyltriethylphosphonium; trimethylisobutylphosphonium; methyltributylphosphonium; and trihexyltetradecylphosphonium. The electrolyte uniquely enables stable cell cycling even when water is present in the electrolyte at levels as high as 5000 ppm. Methyltriethylphosphonium and trimethylisobutylphosphonium-containing electrolytes are particularly effective in this water-stabilizing capacity.
1. A secondary electrochemical cell comprising:
an anode;
a cathode; and
an electrolyte comprising:
a salt comprising an active metal cation, configured to be reduced at the anode during charging, and bis(fluorosulfonyl)imide (FSI);
an ionic liquid comprising FSI and an organic cation selected from the group consisting of:
methyltriethylphosphonium;
trimethylisobutylphosphonium;
methyltributylphosphonium; and
trihexyltetradecylphosphonium; and
water, present at a concentration of at least 50 ppm.
2. The cell as recited in claim 1 , wherein the active metal cation comprises Li+.
3. The cell as recited in claim 2 , wherein the anode comprises lithium metal.
4. The cell as recited in claim 1 , wherein the salt is present, relative to the ionic liquid, at a molar ratio of at least 1:1.
5. The cell as recited in claim 1 , wherein the salt is present at its saturation point in the ionic liquid.
6. The cell as recited in claim 1 , wherein the organic cation comprises trimethylisobutylphosphonium.
7. The cell as recited in claim 1 , wherein the organic cation comprises methyltriethylphosphonium.
8. The cell as recited in claim 1 , wherein water is present at a concentration of at least 100 ppm.
9. The cell as recited in claim 1 , wherein water is present at a concentration of at least 500 ppm.
10. The cell as recited in claim 1 , wherein water is present at a concentration of at least 1000 ppm.
11. The cell as recited in claim 1 , wherein water is present at a concentration of at least 4000 ppm.
12. An electrolyte composition comprising:
a salt comprising an active metal cation and bis(fluorosulfonyl)imide (FSI);
an ionic liquid comprising FSI and an organic cation selected from the group consisting of:
methyltriethylphosphonium;
trimethylisobutylphosphonium;
methyltributylphosphonium; and
trihexyltetradecylphosphonium; and
water, present at a concentration of at least 50 ppm.
13. The electrolyte composition as recited in claim 12 , wherein the active metal cation comprises Li+.
14. The electrolyte composition as recited in claim 12 , wherein the organic cation comprises trimethylisobutylphosphonium.
15. The electrolyte composition as recited in claim 12 , wherein the organic cation comprises methyltriethylphosphonium.
16. The electrolyte composition as recited in claim 12 , wherein water is present at a concentration of at least 100 ppm.
17. The electrolyte composition as recited in claim 12 , wherein water is present at a concentration of at least 500 ppm.
18. The electrolyte composition as recited in claim 12 , wherein water is present at a concentration of at least 1000 ppm.
19. The electrolyte composition as recited in claim 12 , wherein water is present at a concentration of at least 4000 ppm.
20. The electrolyte composition as recited in claim 12 , wherein the salt is present at its saturation point in the ionic liquid.