Phenyl boron-based compounds as anion receptors for...

Details Phenyl boron-based compounds as anion receptors for... Phenyl boron-based compounds as anion receptors for...

2000-01-27

2002-03-05

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Include electrolyte chemically specified and method

C429S303000, C429S307000, C558S293000, C558S294000

Reexamination Certificate

active

06352798

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to the design, synthesis and application of novel fluorinated boron based compounds which act as anion receptors in non-aqueous battery electrolytes. As a result, the anion receptors of the present invention can be used as additives to enhance the ionic conductivity and cation transference number of non-aqueous electrolytes. More specifically, the family of anion receptors of the present invention includes phenyl boronate, fluorinate phenyl boronate, and fluorinated alkyl substituted phenyl boronate based compounds bearing different fluorinated alkyl and aryl groups.
In the past, research has been conducted on the reduction of ion pairing in non-aqueous electrolytes. The design and synthesis of receptor molecules for the selective complexation of ions has been an active area of research in the last two decades. With respect to lithium batteries, ion pairing accounts for the low lithium transference in non-aqueous electrolytes. To decrease ion pairing, researchers have used either solvents of high dielectric constant or added a neutral ligand to coordinate either the cation or the anion. Coordination with either the cation or anion was expected to increase the cation-anion distance of closest approach and thus decrease ion pair formation. For cation coordination in liquid non-aqueous electrolytes, Salomon [1] has reported the use of crown ether 18-crown-6, Matsuda, et al. [2], the use of 12-crown-4, and Schriever, et al. [3], have used cryptands to decrease ion pair formation in polymer electrolytes.
More recently, research has focused on providing neutral compounds to complex anions. These compounds were summarized in a review article written by F. P. Schmidtchen and M. Berger [4]. However, because anion complexation occurs through hydrogen bonding, these neutral compounds cannot be used in lithium batteries. Lee, et al. have utilized aza-ether based compounds as anion receptor molecules. Electron withdrawing groups were used to substitute amine hydrogen atoms in linear aza-ethers, multi-branched aza-ethers, and cyclic aza-crown ethers [5].
U.S. Pat. No. 5,849,432 to Angell et al. discloses liquid boron-containing electrolyte solvents and liquid boron-containing electrolyte solutions, wherein the backbones of the boron compounds have either an O
3
B or O
2
B-X structure, where X is limited to a halogen atom. However, Angell et al. do not disclose boron compounds wherein the backbone structure is O
2
BR, where R is a phenyl group.
Anion coordination is much more important than cation coordination in lithium battery electrolytes because it offers the ability of increasing both conductivity and lithium transference number. Accordingly, there is still a need in the art of lithium batteries for electrolyte additives which can complex anions, yet are stable in lithium batteries. There is also a need in the art of lithium batteries to enhance the conductivity of inexpensive and environmentally friendly inorganic salts such as LiF, LiCl, LiBr and LiI. In addition, there is a need to increase the transference number of the Li
+
ion. In many non-aqueous electrolytes, in particular polymer electrolytes, the transference number of the Li
+
ion is low. This introduces additional polarization losses in batteries and reduces the utilization of the cathode material.
It is therefore, an object of the present invention to provide a new family of compounds which enhances the conductivity of lithium battery electrolytes by complexing with the anion moiety of the salt, and also increases the transference number of the Li
+
ion in electrolytes.
Another object of the present invention is to increase the conductivity of cost effective electrolyte salts such as LiF, LiCl, LiBr and LiI.
Another object of the present invention is to provide improved electrochemical cells by use of electrolyte additives.
SUMMARY OF THE INVENTION
The present invention, which addresses the needs of the prior art, provides novel fluorinated boron-based compounds which act as anion receptors in non-aqueous battery electrolytes. When added to non-aqueous electrolytes, the receptors of the present invention complex the anion moiety of the electrolyte salt, thereby increasing the conductivity of the electrolytes and the transference number of Li
+
ion in electrolytes. The present invention also relates to the use of fluorinated boron-based anion receptors as electrolyte additives for both primary and secondary lithium batteries. Electrolytes used for the electrochemical cells of the present invention include liquid electrolytes using organic solvents, polymer electrolytes, and gel electrolytes.
As a result of the present invention, stable anion receptor compounds are provided which increase dramatically the conductivity of electrolytes for lithium batteries. The electrolyte conductivity is increased because the fluorinated boron-based compounds of the present invention complex anion moieties in non-aqueous electrolytes thereby increasing the concentration of lithium cations available for transport. As a result of using the anion receptors of the present invention, lithium batteries are provided which have significantly increased rate capability or discharge current density. The enhanced batteries of the present invention also have increased cathode utilization because of the increased Li
+
ion transference number.
The anion receptors of the present invention include a boron-based compound of the formula QO
2
BR or (QO)
2
BR, wherein R is a phenyl, a fluorinated phenyl, or a fluorinated alkyl substituted phenyl and Q is a fluorine bearing moiety. R is selected from the group consisting of C
6
H
5
, C
6
H
4
F, C
6
H
3
F
2
, C
6
H
2
F
3
, C
6
HF
4
, C
6
F
5
, C
6
H
4
CF
3
, and C
6
H
3
(CF
3
)
2
and Q is selected from the group consisting of —C
6
H
3
F—, —C
6
H
2
F
2
—, —C
6
HF
3
—, —C
6
F
4
—, —((CF
3
)
2
C)
2
—, —C
6
F
5
, and —(CF
3
)
2
CH.
A preferred embodiment of the present invention is an electrochemical cell which includes a non-aqueous electrolyte solvent and an electrolyte additive that includes a boron-based anion receptor, wherein said boron-based anion receptor is a compound having the formula QO
2
BR or (QO)
2
BR, wherein R is a phenyl, a fluorinated phenyl, or a fluorinated alkyl substituted phenyl and Q is a fluorine bearing moiety. R is selected from the group consisting of C
6
H
5
, C
6
H
4
F, C
6
H
3
F
2
, C
6
H
2
F
3
, C
6
HF
4
, C
6
F
5
, C
6
H
4
CF
3
, and C
6
H
3
(CF
3
)
2
and Q is selected from the group consisting of —C
6
H
3
F—, —C
6
H
2
F
2
—, —C
6
HF
3
—, —C
6
F
4
—, —((CF
3
)
2
C)
2
—, —C
6
F
5
, and —(CF
3
)
2
CH. The non-aqueous electrolyte solvent for the electrochemical cell is selected from the group consisting of tetrahydrofuran, 2-methyl furan, 4-methyldioxolane, 1,3-dioxolane, 1,2-dimethoxyethane, dimethoxymethane, ethylene carbonate, propylene carbonate, &ggr;-butyrolactone, methyl formate, sulfolane, acetonitrile and 3-methyl-2-oxazolidinone, dimethyl carbonate, dimethyl ether, 1-methyl-2-pyrrolidinone and poly(ethylene oxide). In one embodiment, the non-aqueous electrolyte solvent is a gel electrolyte selected from the group consisting of poly(acrylo nitrile) and poly(vinylidene flouride-hexafluoro propylene).
The electrochemical cell can include a lithium salt in a liquid organic solvent wherein the lithium salt is selected from the group consisting of LiF, LiCl, LiBr, LiI, CF
3
COOLi, C
2
F
5
COOLi, C
6
F
5
COOLi and mixtures thereof. In a preferred embodiment, the liquid organic solvent is a compound selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, dimethyl ether, &ggr;-butyrolactone, 3-methyl-2-oxazolidinone, 1-methyl-2-pyrrolidinone and mixtures thereof.
In another embodiment, the electrochemical cell includes an electrolyte solute selected from the group consisting of LiF, LiCl, LiBr, LiI, CF
3
COOLi, C
2
F
5
COOLi, and mixtures thereof.
A preferred embodiment of the electrochemical cell includes an anod

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