Fluoroalkyl containing salts combined with fluorinated solvents for electrolytes

• US 9,012,094 B2
• Filed: 06/04/2013
• Issued: 04/21/2015
• 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, Erickson, Michael Jason
• Primary Examiner(s): JELSMA, JONATHAN G
• Application Number:
  US13/910,108
• Publication Number:
  US 20130337341A1
• Time in Patent Office: 686 Days
• Field of Search: 429/326
• US Class Current: 429/326
• 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 may include a fluoroalkyl-substituted LiPF₆ salt or a fluoroalkyl-substituted LiBF₄ salt. In some embodiments, at least one fluorinated alkyl of the salt has a chain length of from 1 to 8 or, more specifically, between about 2 and 8. These fluorinated alkyl groups, in particular, relatively large fluorinated alkyl groups improve solubility of these salts in fluorinated solvents that are less flammable than, for example, conventional carbonate solvents. At the same time, the size of fluoroalkyl-substituted salts should be limited to ensure adequate concentration of the salt in an electrolyte and low viscosity of the electrolyte. In some embodiments, the concentration of a fluoroalkyl-substituted salt is at least about 0.5M. Examples of fluorinated solvents include various fluorinated esters, fluorinated ethers, and fluorinated carbonates, such a 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.

Claims

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

an electrolyte salt having a concentration of at least about 0.5M,

the electrolyte salt selected from the group consisting of;

i) a fluoroalkyl-substituted lithium hexafluorophosphate having a general structure LiPF_XR_6-X, where x is from 1 to 5 and at least one R is a fluorinated alkyl of 1 to 8 carbon atoms or a combination of a fluorinated alkyl of 1 to 8 carbon atoms and a sulfonyl group;

ii) a fluoroalkyl-substituted lithium tetrafluoroborate having a general structure LiBF_xR_4-x, where x is from 1 to 3 and at least one R is a fluorinated alkyl of 1 to 8 carbon atoms or a combination of a fluorinated alkyl of 1 to 8 carbon atoms and a sulfonyl group;

iii) a fluoroalkyl-substituted lithium oxalatoborate having a general structure of LiBC₂O₄R₂, where at least one R is a fluorinated alkyl of 1 to 8 carbon atoms or a combination of a fluorinated alkyl of 1 to 8 carbon atoms and a sulfonyl group,

iv) a salt represented by one of general formulas

2. The electrolyte according to claim 1, wherein the fluorinated solvent is 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.

3. The electrolyte according to claim 1, wherein the fluorinated solvent comprises methyl nonafluorobutyl ether.

4. The electrolyte according to claim 1, wherein the fluorinated alkyl of the electrolyte salt has the chain length of at least 2 carbon atoms.

5. The electrolyte according to claim 1, wherein the electrolyte salt comprises one of LiPF₅C₂F₅, LiPF₅C₄F₉, LiPF₅C₃F₇, LiPF₃(C₂F₅)₃, LiPF₃(CF₃)₃, LiPF₃(C₃F₇)₃, LiPF₃(C₄F₉)₃, LiPF₂(C₂F₅)₄, or LiPF(C₂F₅)₅.

6. The electrolyte according to claim 1, wherein the electrolyte salt comprises one of LiBF₃CF₃, LiBF₃C₂F₅, LiBF₃C₃F₇, LiBF₃C₄F₉, LiBF₂(CF₃)₂, LiBF₂(C₂F₅)₂, LiBF₂(C₃F₇)₂, or LiBF₂(C₄F₉)₂.

7. The electrolyte according to claim 1, further comprising a secondary electrolyte salt,

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

the secondary electrolyte salt comprising at least one carbon atom and at least two fluoride atoms and selected from the group consisting of:

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

SO₂—

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

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

SO₂—

R—

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

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

SO₂—

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

8. The electrolyte according to claim 7, wherein the secondary electrolyte salt comprises one of LiN(SO₂CF₂CF₃)₂, LiN(SO₂CF₃)₂, LiN(SO₂F)₂, LiC(SO₂CF₃)₃, or LiC(SO₂CF₂CF₃)₃.

9. The electrolyte according to claim 1, wherein the electrolyte salt comprises the fluoroalkyl-substituted lithium hexafluorophosphate salt having the general structure LiPF_xR_6-x, wherein x is from 1 to 5 and at least one R comprises the fluorinated alkyl of 1 to 8 carbon atoms or the combination of the fluorinated alkyl of 1 to 8 carbon atoms and the sulfonyl group.

10. The electrolyte according to claim 1, wherein the electrolyte salt comprises the fluoroalkyl-substituted lithium tetrafluoroborate salt having the general structure LiPF_xR_4-x, where x is from 1 to 3 and at least one R comprises the combination of the fluorinated alkyl of 1 to 8 carbon atoms and the sulfonyl group.

11. The electrolyte according to claim 1, wherein the electrolyte salt comprises the fluoroalkyl-substituted lithium oxalatoborate salt having the general structure of LiBC₂O₄R₂, where at least one R is the fluorinated alkyl of 1 to 8 carbon atoms or the combination of the fluorinated alkyl of 1 to 8 carbon atoms and the sulfonyl group.

12. The electrolyte according to claim 1, wherein the electrolyte salt comprises the fluoroalkyl-substituted lithium oxalatoborate salt having the general structure of LiBC₂O₄R₂, where at least one R is the combination of the fluorinated alkyl of 1 to 8 carbon atoms and the sulfonyl group.

13. The electrolyte according to claim 1, wherein the electrolyte salt comprises the salt represented by the general formula

14. The electrolyte according to claim 1, wherein the electrolyte salt comprises the salt represented by the general formula

15. The electrolyte according to claim 1, further comprising a flame-retardant additive, the flame-retardant additive comprising a cyclic phosphazene.

16. The electrolyte according to claim 1, further comprising an ionic liquid, wherein the ionic liquid is present at a concentration ranging from about 1% to about 25% by weight of the electrolyte, excluding the electrolyte salt.

17. The electrolyte according to claim 16, wherein the ionic liquid comprises one or more of pyridinium, piperidinium, imidazolium, and/or phosphonium cations.

18. The electrolyte according to claim 1, wherein the fluorinated solvent has a dynamic viscosity ranging from about 0.3 cP to about 5.0 cP.

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

an electrolyte salt having a concentration of at least about 0.5M,

the electrolyte salt selected from the group consisting of LiPF₅C₂F₅, LiPF₅C₄F₉, LiPF₅C₃F₇, LiPF₃(C₂F₅)₃, LiPF₃(CF₃)₃, LiPF₃(C₃F₇)₃, LiPF₃(C₄F₉)₃, LiPF₂(C₂F₅)₄, LiPF(C₂F₅)₅, LiBF₃CF₃, LiBF₃C₂F₅, LiBF₃C₃F₇, LiBF₃C₄F₉, LiBF₂(CF₃)₂, LiBF₂(C₂F₅)₂, LiBF₂(C₃F₇)₂, and LiBF₂(C₄F₉)₂;

a fluorinated solvent selected from the 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; and

one or more non-fluorinated esters, the electrolyte including a non-fluorinated cyclic carbonate ester, wherein the non-fluorinated cyclic carbonate ester is present at no more than 10% by weight, excluding the electrolyte salt,

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

30°

C.

20. 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 having a concentration of at least about 0.5M,

the electrolyte salt is selected from the group consisting of;

i) a fluoroalkyl-substituted lithium hexafluorophosphate having a general structure LiPF_XR_6-X, where x is from 1 to 5 and at least one R is a fluorinated alkyl of 1 to 8 carbon atoms or a combination of a fluorinated alkyl of 1 to 8 carbon atoms and a sulfonyl group;

ii) a fluoroalkyl-substituted lithium tetrafluoroborate having a general structure LiBF_xR_4-x, where x is from 1 to 3 and at least one R is a fluorinated alkyl of 1 to 8 carbon atoms or a combination of a fluorinated alkyl of 1 to 8 carbon atoms and a sulfonyl group;

iii) a fluoroalkyl-substituted lithium oxalatoborate having a general structure of LiBC₂O₄R₂, where at least one R is a fluorinated alkyl of 1 to 8 carbon atoms or a combination of a fluorinated alkyl of 1 to 8 carbon atoms and a sulfonyl group,

iv) a salt represented by one of general formulas