Low molecular weight salts combined with fluorinated solvents for electrolytes

• US 9,184,467 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:
  US13/910,098
• Publication Number:
  US 20130337339A1
• 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. An electrolyte includes at least one salt having a molecular weight less than about 250. Such salts allow forming electrolytes with higher salt concentrations and ensure high conductivity and ion transport in these electrolytes. The low molecular weight salt may have a concentration of at least about 0.5M and may be combined with one or more other salts, such as linear and cyclic imide salts and/or methide salts. The concentration of these additional salts may be less than that of the low molecular weight salt, in some embodiments, twice less. The additional salts may have a molecular weight greater than about 250. The electrolyte may also include one or more fluorinated solvents and may be capable of maintaining single phase solutions at between about −30° C. to about 80° C.

Claims

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

a low molecular weight first electrolyte salt having a high salt concentration of at least 0.5 M and a molecular weight less than about 250 grams per mole, wherein the first electrolyte salt comprises one of LiPF₆, LiBF₄, LiClO₄, LiBOB, or LiN(SO₂F)₂;

a non-fluorinated linear carboxylic acid ester; and

one or more fluorinated solvents to include 1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)-pentane, the one or more fluorinated solvents being over 30% by weight of the electrolyte, excluding any electrolyte salt;

wherein the low molecular weight first electrolyte salt at the high salt concentration is soluble in the electrolyte; and

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

30°

C.

2. The electrolyte according to claim 1, wherein the one or more fluorinated solvents further includes 1-methoxyheptafluoropropane, methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-(trifluoromethyl)-pentane, and/or 3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-trifluoromethyl-hexane.

3. The electrolyte according to claim 2, wherein a concentration of the 1-methoxyheptafluoropropane, methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-(trifluoromethyl)-pentane, and/or 3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-trifluoromethyl-hexane is less than a concentration of 1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)-pentane.

4. The electrolyte according to claim 2, wherein the one or more fluorinated solvents are between 30% and 80% by weight of the electrolyte excluding any electrolyte salt.

5. The electrolyte according to claim 1, further comprising a second electrolyte salt,

different from the first electrolyte salt and having a lower concentration than the first electrolyte salt,

the second electrolyte salt comprising at least one carbon atom and at least two fluorine atoms per formula unit and selected from the group consisting of:

i) a fluoroalkyl-substituted LiPF₆ salt 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;

ii) a fluoroalkyl-substituted LiBF₄ salt 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;

iii) a linear imide salt having a general structure LiN(—

SO₂—

R)₂, where at least one R is a fluorinated alkyl group of 1 to 8 carbon atoms;

iv) a cyclic imide salt having a general structure LiN(—

SO₂—

R—

), where R is a fluorinated alkyl group of 1 to 8 carbon atoms; and

v) a methide salt having a general structure LiC(—

SO₂—

R)₃, where at least one R is fluorinated alkyl group of 1 to 8 carbon atoms.

6. The electrolyte according to claim 5, wherein the second electrolyte salt comprises one of LiN(SO₂CF₂CF₃)₂, LiN(SO₂CF₃)₂, LiN(SO₂F)₂, LiC(SO₂CF₃)₃, or LiC(SO₂CF₂CF₃)₃.

7. The electrolyte according to claim 5, wherein the second electrolyte salt comprises LiN(SO₂CF₂CF₃)₂.

8. The electrolyte according to claim 1, wherein the non-fluorinated carboxylic acid ester includes methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and/or ethyl butyrate.

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

10. The electrolyte according to claim 9, wherein the flame-retardant additive comprises a phosphate, phosphite, phosphine, and/or 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 about 1% to about 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 includes methyl butyrate and/or ethyl butyrate.

18. The electrolyte according to claim 1 wherein the electrolyte includes 10% or less non-fluorinated cyclic carbonate ester by weight, excluding any electrolyte salt.

19. The electrolyte according to claim 1 wherein the electrolyte includes about 7% non-fluorinated cyclic carbonate ester by weight, excluding any electrolyte salt.

20. The electrolyte according to claim 1 wherein the electrolyte includes about 5% non-fluorinated cyclic carbonate ester by weight, excluding any electrolyte salt.

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

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

a low molecular weight first electrolyte salt having a high salt concentration of at least 0.5 M and a molecular weight less than about 250 grams per mole, wherein the first electrolyte salt comprises one of LiPF₆, LiBF₄, LiClO₄, LiBOB, or LiN(SO₂F)₂;

one or more fluorinated solvents to include 1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)-pentane, the one or more fluorinated solvents being over 30% by weight of the electrolyte, excluding the electrolyte salt;

one of ethyl butyrate or ethyl propionate at about 10% to 30% by weight of the electrolyte, excluding any electrolyte salt; and

a cyclic phosphazene at between about 5% and 15% by weight of the electrolyte, excluding any electrolyte salt,

wherein the low molecular weight first electrolyte salt at the high salt concentration is soluble in the electrolyte; and

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;

a low molecular weight first electrolyte salt having a high salt concentration of at least 0.5 M and a molecular weight less than about 250 grams per mole, wherein the first electrolyte salt comprises one of LiPF₆, LiBF₄, LiClO₄, LiBOB, or LiN(SO₂F)₂;

a non-fluorinated carboxylic acid ester; and

one or more fluorinated solvents to include 1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)-pentane, the one or more fluorinated solvents being over 30% by weight of the electrolyte, excluding any electrolyte salt;

wherein the low molecular weight first electrolyte salt at the high salt concentration is soluble in the electrolyte; and

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

30°

C.