Electrolyte for electrochemical device

Details Electrolyte for electrochemical device Electrolyte for electrochemical device

2000-07-25

2002-11-26

Weiner, Laura (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Include electrolyte chemically specified and method

C429S322000, C252S062200, C544S054000

Reexamination Certificate

active

06485868

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an electrolyte including an ionic metal complex having a novel chemical structure, an ionic conductor including the electrolyte, and electrochemical devices including the electrolyte, such as lithium cells, lithium ion cells, electrical double-layer capacitors.
Accompanying the evolution of portable equipment in recent years, there has been active development of electrochemical devices utilizing electrochemical phenomena, such as cells for use as their power supplies and capacitors. In addition, electrochromic devices (ECD), in which a color change occurs due to an electrochemical reaction, are examples of electrochemical devices for uses other than power supplies.
These electrochemical devices are typically composed of a pair of electrodes and an ionic conductor filled between them. The ionic conductor contains a salt (AB) as an electrolyte, which is dissolved in a solvent, polymer or mixture thereof such that the salt is dissociated into cations (A
+
) and anions (B
−
), resulting in ionic conduction. In order to obtain the required level of ion conductivity for the device, it is necessary to dissolve a sufficient amount of this electrolyte in solvent or polymer. In actuality, there are many cases in which a solvent other than water is used, such as organic solvents and polymers. Electrolytes having sufficient solubility in such organic solvents and polymers are presently limited to only a few types. For example, electrolytes having sufficient solubility for use in lithium cells are only LiClO
4
, LiPF
6
, LiBF
4
, LiAsF
6
, LiN(CF
3
SO)
2
and LiCF
3
SO
3
. Although the cation type of the electrolyte is frequently limited by the device as is the case with the lithium ion of lithium cells, any anion can be used for the electrolyte provided it satisfies the condition of having high solubility.
Amidst the considerable diversity of the application range of these devices, efforts are made to seek out the optimum electrolyte for each application. Under the present circumstances, however, optimization efforts have reached their limit due to the limited types of available anions. In addition, existing electrolytes have various problems, thereby creating the need for an electrolyte having a novel anion portion. More specifically, since ClO
4
ion of LiClO
4
is explosive and AsF
6
ion of LiAsF
6
is toxic, they cannot be used for reasons of safety. Since LiN(CF
3
SO
2
)
2
and LiCF
3
SO
3
corrode the aluminum collector inside the cell when a potential is applied, their use presents difficulties. Even the only practical electrolyte of LiPF
6
ends up decomposing at temperatures of 70° C. and above, having problems including heat resistance and hydrolysis resistance.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a useful novel electrolyte, a novel ion conductor containing the electrolyte, and a novel electrochemical device containing the ion conductor.
According to the present invention, there is provided an electrolyte for an electrochemical device. This electrolyte comprises an ionic metal complex represented by the general formula (1):
wherein M is a transition metal selected from the group consisting of elements of groups 3-11 of the periodic table, or an element selected from the group consisting of elements of groups 12-15 of the periodic table; A
a+
represents a metal ion, onium ion or proton; a represents a number from 1 to 3; b represents a number from 1 to 3; p is b/a; m represents a number from 1 to 3; n represents a number from 0 to 4; q is 0 or 1; X
1
represents O, S or NR
5
R
6
; each of R
1
and R
2
independently represents H, a halogen, a C
1
-C
10
alkyl group or C
1
-C
10
halogenated alkyl group; R
3
represents a C
1
-C
10
alkylene group, C
1
-C
10
halogenated alkylene group, C
4
-C
20
aryl group or C
4
-C
20
halogenated aryl group; R
4
represents a halogen, C
1
-C
10
alkyl group, C
1
-C
10
halogenated alkyl group, C
4
-C
20
aryl group, C
4
-C
20
halogenated aryl group or X
2
R
7
; X
2
represents O, S or NR
5
R
6
; each of R
5
and R
6
represents H or a C
1
-C
10
alkyl group; and R
7
represents a C
1
-C
10
alkyl group, C
1
-C
10
halogenated alkyl group, C
4
-C
20
aryl group or C
4
-C
20
halogenated aryl group.
According to the present invention, there is provided an ion conductor for an electrochemical device. This ion conductor comprises the electrolyte; and a member selected from the group consisting of a nonaqueous solvent, a polymer and a mixture thereof, said member dissolving therein said electrolyte.
According to the present invention, there is provided an electrochemical device comprising (a) first and second electrodes; and (b) the ion conductor receiving therein said first and second electrodes.
An electrolyte according to the present invention has high heat resistance and hydrolysis resistance as compared with conventional electrolytes. Thus, the electrolyte can advantageously be used for electrochemical devices such as lithium cell, lithium ion cell and electrical double-layer capacitor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the invention, the alkyl groups, halogenated alkyl groups, aryl groups and halogenated aryl groups, which are contained in the ionic metal complex and the raw materials for synthesizing the same, may be branched and/or may have other functional groups such as hydroxyl groups and ether bonds.
The followings are specific nine examples of the ionic metal complex represented by the general formula (1) of the present invention.
Here, although lithium ion is indicated as an example of A
a+
of the general formula (1), examples of other cations that can be used other than lithium ion include sodium ion, potassium ion, magnesium ion, calcium ion, barium ion, cesium ion, silver ion, zinc ion, copper ion, cobalt ion, iron ion, nickel ion, manganese ion, titanium ion, lead ion, chromium ion, vanadium ion, ruthenium ion, yttrium ion, lanthanoid ion, actinoid ion, tetrabutylammonium ion, tetraethylammonium ion, tetramethylammonium ion, triethylmethylammonium ion, triethylammonium ion, pyridinium ion, imidazolium ion, proton, tetraethylphosphonium ion, tetramethylphosphonium ion, tetraphenylphosphonium ion, triphenylsulfonium ion, and triethylsulfonium ion. In the case of considering the application of the ionic metal complex for electrochemical devices and the like, lithium ion, tetraalkylammonium ion and proton are preferable. As shown in the general formula (1), the valency (valence) of the A
a+
cation is preferably from 1 to 3. If the valency is larger than 3, the problem occurs in which it becomes difficult to dissolve the ionic metal complex in solvent due to the increase in crystal lattice energy. Consequently, in the case of requiring solubility of the ionic metal complex, a valency of 1 is preferable. As shown in the general formula (1), the valency (b−) of the anion is similarly preferably from 1 to 3, and a valency of 1 is particularly preferable. The constant p expresses the ratio of the valency of the anion to the valency of the cation, namely b/a.
In the general formula (1), M at the center of the ionic metal complex of the present invention is selected from elements of groups 3-15 of the periodic table. It is preferably Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf or Sb, and more preferably Al, B or P. Although it is possible to use various elements for the M other than these preferable examples, synthesis is relatively easy in the case of using Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf or Sb. In addition to ease of synthesis, the ionic metal complex has excellent properties in terms of low toxicity, stability and production cost in the case of using Al, B or P.
In the general formula (1), the organic or inorganic portion bonded to M is referred to as the ligand. As mentioned above, X
1
in the general formula (1) represents O, S or NR
5
R
6
, and is bonded to M through its hetero atom (O, S or N). Althou

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