Combinations of fluorinated solvents with imide salts or methide salts for electrolytes

• US 9,184,468 B2
• Filed: 06/04/2013
• Issued: 11/10/2015
• Est. Priority Date: 06/19/2012
• Status: Expired due to Fees

• Current Assignee: A123 Systems Incorporated
• Original Assignee: A123 Systems Incorporated
• Inventors: Tikhonov, Konstantin, Yip, Ka Ki, Lin, Tzu-Yuan, Lei, Norman, Guerrero-Zavala, Guillermo, Kwong, Kristie W.
• Primary Examiner(s): Ruddock, Ula C
• Assistant Examiner(s): Park, Lisa S
• Application Number:
  US13/910,105
• Publication Number:
  US 20130337340A1
• Time in Patent Office: 889 Days
• US Class Current: 1/1
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: H01M 10/0567 characterised by the additives
• CPC Class Codes: H01M 10/0568 characterised by the solutes
• CPC Class Codes: H01M 10/0569 characterised by the solvents
• CPC Class Codes: H01M 2300/0034 Fluorinated solvents
• CPC Class Codes: H01M 2300/0037 Mixture of solvents
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

Provided are electrochemical cells and electrolytes used to build such cells. The electrolytes include imide salts and/or methide salts as well as fluorinated solvents capable of maintaining single phase solutions at between about −30° C. to about 80° C. The fluorinated solvents, such as fluorinated carbonates, fluorinated esters, and fluorinated esters, are less flammable than their non-fluorinated counterparts and improve safety characteristics of cells containing these solvents. The amount of fluorinated solvents in electrolytes may be between about 30% and 80% by weight not accounting weight of the salts. Linear and cyclic imide salts, such as LiN(SO₂CF₂CF₃)₂, and LiN(SO₂CF₃)₂, as well as methide salts, such as LiC(SO₂CF₃)₃ and LiC(SO₂CF₂CF₃)₃, may be used in these electrolytes. Fluorinated alkyl groups enhance solubility of these salts in the fluorinated solvents. In some embodiments, the electrolyte may also include a flame retardant, such as a phosphazene, and/or one or more ionic liquids.

Claims

1. An electrolyte for use in an electrochemical cell, the electrolyte comprising:

an electrolyte salt including an imide or methide having at least one fluorinated alkyl group of 1 to 8 carbon atoms; and

a non-fluorinated carboxylic acid ester wherein the non-fluorinated carboxylic acid ester is selected from a group consisting of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate, and a fluorinated solvent selected from a group consisting of 1-methoxyheptafluoropropane, methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-(trifluoromethyl)-pentane, 3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-trifluoromethyl-hexane, and 1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)-pentane, the fluorinated solvent being over 30% by weight of the electrolyte excluding the electrolyte salt;

wherein the electrolyte is a one-phase solution at a temperature of about −

30°

C.

2. The electrolyte according to claim 1, wherein the fluorinated solvent comprises 1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)-pentane.

3. The electrolyte according to claim 1, wherein the electrolyte salt comprises one of LiC(SO₂CF₃)₃ or LiC(SO₂CF₂CF₃)₃.

4. The electrolyte according to claim 1, wherein the electrolyte salt comprises LiC(SO₂CF₂CF₃)₃.

5. The electrolyte according to claim 1, wherein the fluorinated solvent is between 50% and 75% by weight of the electrolyte excluding the electrolyte salt.

6. The electrolyte according to claim 1, wherein the electrolyte salt is a first electrolyte salt, wherein the electrolyte further includes a second electrolyte salt different from the first electrolyte salt, and wherein the second electrolyte salt has a lower concentration than the first electrolyte salt.

7. The electrolyte according to claim 6, wherein the second electrolyte salt has a concentration less than 0.5 M.

8. The electrolyte according to claim 6, wherein the second electrolyte salt comprises LiPF₆, LiBF₄, or a fluoroalkyl-substituted LiPF₆ having a general structure LiPF_xR_1-x, where x is from 1 to 5 and at least one R is a fluorinated alkyl group of 1 to 8 carbon atoms, or a fluoroalkyl-substituted LiBF₄ having a general structure LiBF_xR_1-x, where x is from 1 to 4 and at least one R is a fluorinated alkyl group of 1 to 8 carbon atoms.

9. The electrolyte according to claim 1, further comprising a flame-retardant additive at a concentration ranging from about 1% to about 10% by weight of the electrolyte.

10. The electrolyte according to claim 9, wherein the flame-retardant additive comprises one or more of a phosphate, phosphite, phosphine, and phosphazene.

11. The electrolyte according to claim 9, wherein the flame-retardant additive comprises P₃N₃F_x(OR)_6-x such that R is an aryl group or an alkyl group of 1 to 12 carbon atoms, and x is from 1 to 6.

12. The electrolyte according to claim 9, wherein the flame-retardant additive comprises a cyclic phosphazene.

13. The electrolyte according to claim 1, further comprising an ionic liquid at 1 to 25% by weight of the electrolyte.

14. The electrolyte according to claim 13, wherein the ionic liquid comprises one or more of a pyridinium, piperidinium, imidazolium, and phosphonium cations.

17. The electrolyte according to claim 1, wherein the non-fluorinated carboxylic acid ester is selected from a group consisting of methyl butyrate and ethyl butyrate.

18. The electrolyte according to claim 1, wherein the fluorinated solvent mixture further includes one or more non-fluorinated cyclic carbonate esters.

19. The electrolyte according to claim 18 wherein the electrolyte includes 10% or less non-fluorinated cyclic carbonate ester by weight, excluding the electrolyte salt.

20. The electrolyte according to claim 18 wherein the electrolyte includes about 7% non-fluorinated cyclic carbonate ester by weight, excluding the electrolyte salt.

21. The electrolyte according to claim 18 wherein the electrolyte includes about 5% non-fluorinated cyclic carbonate ester by weight, excluding the electrolyte salt.

22. The electrolyte according to claim 1 wherein the electrolyte includes substantially no non-fluorinated cyclic carbonate ester.

23. The electrolyte according to claim 1 wherein the fluorinated solvent is 1,1,1,2,3-hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)pentane.

15. An electrolyte for use in an electrochemical cell, the electrolyte comprising:

an electrolyte salt including an imide or methide having at least one fluorinated alkyl group of 1 to 8 carbon atoms present at a concentration between 0.6 M and about 2 M;

3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-trifluoromethyl-hexane at 60% to 80% by weight of the electrolyte excluding the electrolyte salt;

ethyl butyrate or ethyl propionate at 10% to 30% by weight excluding the electrolyte salt; and

a cyclic phosphazene at a concentration of 5% to 15% by weight excluding the electrolyte salt,

wherein the electrolyte is a one-phase solution at a temperature of about −

30°

C.

16. An electrochemical cell comprising:

a positive electrode;

a negative electrode;

an electrolyte providing ionic exchange between the positive electrode and negative electrode and comprising;

an electrolyte salt including an imide or methide having at least one fluorinated alkyl group of 1 to 8 carbon atoms;

a non-fluorinated carboxylic acid ester wherein the non-fluorinated carboxylic acid ester is selected from a group consisting of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate;

and a fluorinated solvent selected from a group consisting of 1-methoxyheptafluoropropane, methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-(trifluoromethyl)-pentane, 3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-trifluoromethyl-hexane, and 1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)-pentane, the fluorinated solvent being over 30% by weight of the electrolyte excluding the electrolyte salt;

wherein the electrolyte is a one-phase solution at a temperature of about −

30°

C.