JPH07301828A - Electrolyte solution for electrochromic element - Google Patents

Abstract

PURPOSE:To use excellent electrochromic(EC) coloring characteristics of a viologen deriv. and to obtain an electrolyte soln. for an EC element having low voltage driving property and low haze by dissolving a specified viologen deriv. in a solvent containing a specified alcohol. CONSTITUTION:N,N'-substd.4,4'-bipyridyl (viologen deriv.) expressed by formula II is dissolved in a solvent containing at least one kind of alcohol expressed by HO(CH1CH2O)nR<3>, wherein R is a lower alkyl group and n is an integer 1 to 3. In formula, R<5> and R<6> are independently selected from groups containing aliphatic hydrocarbon or aromatic hydrocarbon. As for the EC display element, for example, it has a laminated structure comprising, from the bottom, glass layer 1, counter electrode 2, back plate 3, solid electrolyte film 4, transparent conductive film 5 and glass plate 6. The solid electrolyte film 4 is produced by impregnating pores of a polymer porous film with the electrolyte soln. above described.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electrolyte for an electrochromic device.

[0002]

2. Description of the Related Art There is an increasing interest in devices that apply an electrochromic (EC) phenomenon in which the color of a substance reversibly changes with voltage. Electrochromic device (EC
D) has features such as bright and easy-to-see, large-area display, and memory characteristics (low power consumption),
Applications that take advantage of these features include large-scale display boards such as stock price displays, message boards, and guide boards, as well as light control elements such as automobile antiglare mirrors, light control glass (windows), and sunglasses.

[0003] A typical ECD structure is formed by disposing an electrolyte between an electrochromic electrode (WO ₃ ) and a counter electrode. When a voltage is applied between both electrodes, WO ₃ causes ions from the electrolyte and electrons from a power source. It is cathodically reduced by and colored.

An aqueous solution of viologen has been studied as the liquid electrolyte, and a viologen derivative dissolved in a solid polymer electrolyte of polyethylene oxide and sandwiched between the working electrode and the counter electrode can be used as the ECD. Is disclosed.

[0005]

As described above, when an aqueous solution of viologen is used as the electrolyte, the applied voltage of 2 to 3 V is not appropriate (electrolysis of water occurs) because of the aqueous solution system. The ECD formed by dissolving a viologen derivative in a polyethylene oxide polymer solid electrolyte has low film strength because it uses polymer solid polyethylene oxide, and it is difficult to increase the area, and the operating voltage is 10V.
Since it is manufactured by heat or photopolymerization, there is a problem that after the device is assembled, the reaction is slightly advanced to easily cause deterioration.

[0006]

To achieve the above object, the present invention provides (1) the following general formula (I)

[0007]

[Chemical 2]

(In the formula, R ⁵ and R ⁶ are each independently selected from an aliphatic hydrocarbon-containing group and an aromatic hydrocarbon-containing group.), N, N′-substituted 4,4 ′ -Bipyridyl (viologen derivative) is represented by the general formula HO (CH ₂ C
H ₂ O) _n R ³ [wherein R ³ is a lower alkyl group,
n is an integer of 1 to 3. ] At least 1
An electrolyte solution for an electrochromic device, characterized by being dissolved in a solvent containing one kind of alcohol; and (2) the N, N′-substituted 4,4′-bipyridyl as described in the above item (1). There is provided an electrolyte thin film for an electrochromic device, characterized in that the porous thin film is impregnated and immobilized with the alcohol according to the item 1) and an electrolyte solution dissolved in a solvent having a higher refractive index than the alcohol.

The preferred embodiments of the present invention are listed below. (3) The electrolyte for an electrochromic device according to item (1) or (2), wherein R ^{3 of the} solvent alcohol is hydrogen or a C _{1 to} C ₄ linear alkyl group. (4) Solvent alcohol is 2-methoxyethanol, 2-
The electrolyte for an electrochromic device according to item (1) or (2), which is ethoxyethanol (R ³ is methyl or ethyl, and n = 1).

(5) In the formula (I), R ⁵ and R ⁶ are R ⁵ = R ⁶
The electrolyte for an electrochromic device according to any one of (1) to (4). (6) In the formula (I), R ⁵ and R ⁶ are R ⁵ = R ⁶ , and are linear or branched alkyl groups having 1 to 8 carbon atoms,
An electrolyte for an electrochromic device according to any one of items (1) to (4). (7) In formula (I), R ⁵ and R ⁶ are heptyl groups,
An electrolyte for an electrochromic device according to any one of items (1) to (4).

(8) In the formula (I), R ⁵ and R ⁶ are R ⁵ = R ⁶
And a phenyl group, a benzyl group, or a group in which any position of these groups is substituted with a halogen atom, a cyano group, or an alkyl group having 1 to 4 carbon atoms,
An electrolyte for an electrochromic device according to any one of items (1) to (4). (9) In the formula (I), R ⁵ and R ⁶ are R ⁵ = R ⁶ , and are a phenyl group, a benzyl group or a 4-cyanophenyl group,
An electrolyte for an electrochromic device according to any one of items (1) to (4).

(10) The electrolyte for an electrochromic device according to any one of items (1) to (9), wherein the amount of the viologen derivative of the formula (I) added is 1 to 35% by weight. (11) The addition amount of the viologen derivative of the formula (I) is 4 to 3
The electrolyte for an electrochromic device according to any one of (1) to (9), which is 0% by weight. (12) The electrolyte for an electrochromic device according to any one of (1) to (11) above, which contains an electrophile. (13) The electrolyte for an electrochromic device according to the item (12), wherein the electrophile is a Lewis acid. (14) The electrolyte for an electrochromic device according to the item (12), wherein the electrophile is a proton-releasing frensed acid. (15) The electrolyte for an electrochromic device according to item (12), wherein the electrophile is selected from nitric acid, hydrochloric acid and sulfuric acid. (16) The electrolyte for an electrochromic device according to the item (12), wherein the electrophile is nitric acid. When an electrochromic device is formed by using such an electrolyte solution, it can be driven at a low voltage of about 2.5 V while retaining the excellent coloring property of the viologen derivative, and has excellent cycle characteristics. In addition, a wide transmittance change (7 to 80%) is possible. Such effects can be exhibited even when the electrolyte solution is used as a solution as it is, but when impregnated and fixed in a stable solid porous thin film, it can be handled as a solid even though it is a solution system, It is easy to handle, and even if it breaks, problems such as splashing of the solution can be suppressed. In addition, a uniform gap can be obtained in a large area, and seal damage due to dripping can be suppressed.

The viologen derivative is a derivative of 4,4'-bipyridine, which is a redox compound which is colorless in the oxidized form and blue to purple in the reduced form and is represented by the following general formula.

[0014]

[Chemical 3]

In the above formula, R ⁵ and R ⁶ are independently selected from a group selected from an aliphatic hydrocarbon-containing group and an aromatic hydrocarbon-containing group, but R ⁵ and R ⁶ are the same. Preferably there is. The aliphatic hydrocarbon-containing group is preferably a linear or branched alkyl group, more preferably a linear or branched alkyl group having 1 to 8 carbon atoms, and particularly an n-heptyl group. Alternatively, as the aromatic hydrocarbon-containing group, a phenyl group, a benzyl group, or a group in which any position of these groups is substituted with a halogen atom, a cyano group or an alkyl group having 1 to 4 carbon atoms, and more preferably Are a phenyl group, a benzyl group and a 4-cyanophenyl group. More specific examples include methylated and benzylated derivatives of 4,4'-bipyridine, and the following compounds. This viologen derivative has an advantage that multicolor can be realized by selecting the kind of the derivative.

[0016]

[Chemical 4]

Such a viologen derivative has the general formula H
It is soluble in a solvent consisting of at least one alcohol represented by O (CH ₂ CH ₂ O) _n R ³ [wherein R ³ is a lower alkyl group and n is an integer of 1 to 3].

Preferred solvents are those in which R ³ is hydrogen or a straight chain lower alcohol (especially 1 to 4 carbon atoms) in the above formula, more preferably R ³ is methyl or ethyl and n = 1. 2-methoxyethanol and 2-ethoxyethanol.

The amount of the viologen derivative added to the solvent is 1 to 35% by weight, more preferably 5 to 30% by weight. If it is less than 1% by weight, there is a drawback that the transmittance on the colored side at the time of performing the coloring and decoloring operation is not sufficiently lowered, and if it is more than 35% by weight, there is a drawback that it is difficult to dissolve in a solvent and color remains easily. . The amount of 5 to 30% by weight is most preferable because the transmittance at the time of performing the coloring and decoloring operation is 10% or less, and the solubility of the viologen derivative is good.

In the present invention, N, N′-substituted 4,4′-bipyridyl is represented by the general formula HO (CH ₂ CH ₂ O) _n R ³ [wherein R ³ is a lower alkyl group and n is 1 to 1]. It is an integer of 3. ] By dissolving in at least one alcohol represented by and a solvent having a higher refractive index than the alcohol, the pores of the solid polymer porous thin film are filled in the same manner as in JP-A-3-67227. Can form an electrolyte thin film. This mixed solvent has a refractive index of 1.45 to 1.53, which is close to the general refractive index of polymer porous thin films of 1.49 to 1.53. Has the effect of reducing the haze ratio. General formula HO
_{(CH 2 CH 2 O) n} R 3 [wherein R ³ is a lower alkyl radical, n is an integer of 1-3. The solvent to be mixed with the alcohol represented by the above formula is not particularly limited as long as it has a higher refractive index than the alcohol, and examples thereof include aromatic nitriles such as diphenylpropionitrile. This electrolyte thin film retains the strength of a solid polymer porous thin film and can be made thin and have a large area. The solid polymer porous thin film of the present invention has a thickness of 0.1 μm to
50 μm, porosity 40% to 90%, breaking strength 200
kg / cm ² or more, average through-hole diameter 0.01 μm to 0.7 μ
Those of m are preferably used.

The thickness of the thin film is generally 0.1 μm to 50 μm.
And preferably 1.0 μm to 25 μm. If the thickness is less than 0.1 μm, it is difficult to put it into practical use in terms of reduction in mechanical strength as a support film and handling.
On the other hand, when it exceeds 50 μm, it is not preferable from the viewpoint of suppressing the effective resistance to be low. The porosity of the porous thin film is 4
It is good to set it to 0% to 90%, preferably 60% to 90%.
% Range. When the porosity is less than 40%, the ionic conductivity as an electrolyte becomes insufficient, while when it exceeds 90%, the mechanical strength as a supporting film becomes small and it is difficult to put it into practical use.

The average diameter of the through holes is not limited as long as the ionic conductor can be fixed in the pores, but generally 0.01 μm to 0.7 μm.
m. The preferable average through-hole diameter depends on the material of the polymer film and the shape of the holes. The breaking strength of polymer membranes is generally 200 kg
/ Cm ² or more, more preferably 500 kg / cm ² or more, it is suitable for practical use as a supporting film. The porous thin film used in the present invention functions as a support for the above-mentioned ionic conductor and is made of a polymer material having excellent mechanical strength.

From the viewpoint of chemical stability, for example, polyolefin, polytetrafluoroethylene, or polyvinylidene fluoride can be used, but from the viewpoint of designing the porous structure of the present invention and facilitating compatibility between thinning and mechanical strength. An example of a suitable polymer material is a polymer having a weight average molecular weight of 5 × 10 5.
It is a polyolefin of ⁵ or more. That is, it is a crystalline linear polyolefin of an olefin homopolymer or a copolymer having a weight average molecular weight of 5 × 10 ⁵ or more, preferably 1 × 10 ⁶ to 1 × 10 ⁷ . For example,
Polyethylene, polypropylene, ethylene-propylene copolymer, polybutene-1, poly-4-methylpentene-
1 and so on. Of these, polyethylene or polypropylene having a weight average molecular weight of 5 × 10 ⁵ or more is preferable. The weight average molecular weight of polyolefin affects the mechanical strength of the obtained permeable membrane. Ultra-high molecular weight polyolefin enables ultra-thin and high-strength film formation by ultra-stretching, and is used as a support for high-ion conductive thin film with low effective resistance. A polyolefin having a weight average molecular weight of less than 5 × 10 ⁵ can be used at the same time, but a weight average molecular weight of 5 ×
In a system containing no 10 ⁵ or more polyolefin, an ultrathin and high-strength film cannot be obtained by super stretching.

The porous thin film as described above can be manufactured by the following method. Ultrahigh molecular weight polyolefin is heated and dissolved in a solvent such as liquid paraffin in an amount of 1 to 15% by weight to form a uniform solution. Form a sheet from this solution,
Quench to give a gel sheet. The amount of solvent contained in this gel-like sheet is extracted by a volatile solvent such as methylene chloride to 10 wt% to 90 wt%. This gel-like sheet is heated at a temperature equal to or lower than the melting point of polyolefin and stretched to have a surface magnification of 10 times or more. The solvent contained in this stretched film is extracted and removed with a volatile solvent such as methylene chloride, and then dried.

Another example of a suitable polymeric material is polycarbonate, in which case the solid polymeric porous thin film is a polycarbonate thin film which is irradiated with charged particles in a nuclear reactor to carry out alkali etching on the tracks that the charged particles have passed through. It can also be manufactured by a method of forming a hole. Polycarbonate and polyester products such as Nuclepore membranes are commercially available as such thin films.

In addition, polyester, polymethacrylate, polyacetal, polyvinylidene chloride, tetrafluoropolyethylene and the like can be used. As a method for filling an ionic conductor in a polymer thin film, a solid polymer porous thin film is impregnated with a viologen derivative dissolved in a solvent or a viologen derivative finely dispersed in a solvent in a sol or gel form. , The solvent is removed after coating or spraying, the solution of the viologen derivative in the manufacturing process of the porous thin film, or its sol or gel dispersion solution is mixed to form a film, a monomer of the viologen derivative or a soluble precursor. A method of impregnating the solid polymer porous thin film, coating or spraying, and then reacting in the pores can be used.

To construct an ECD using the above-mentioned electrolyte thin film, the electrolyte thin film is sandwiched between the transparent conductive electrode and the counter electrode.
The transparent conductive electrode may be SnO ₂ , ITO or the like, and the counter electrode may be an electrode such as NiO, IrO _x or Prussian blue which exhibits an oxidative color, or a substance which is colorless in both oxidation and reduction reactions. When the viologen derivative receives electrons from the ITO electrode, it is reduced and color is developed. At this time, if a too high voltage is applied, the ITO is reduced, so 3 V or less is desirable.

An example of manufacturing an electrochromic device will be described with reference to the drawings. FIG. 1 shows an example of an EC display element. In this laminated structure, a glass plate 1, a counter electrode 2, a background plate 3, a solid electrolyte membrane 4, a transparent conductive film 5 and a glass plate 6 are arranged from the bottom. Since this display element is in the reflection mode, the glass plate 1 does not necessarily have to be a transparent plate, and may be a resin plate or the like. The counter electrode 2 is made of an electronically conductive material that generates little hydrogen and oxygen, has good reversibility with respect to an electrochemical redox reaction, and has a large electric capacity. Specifically, there are carbon and a composite material of a transition metal and carbon. Counter electrode 2
Has a thickness of about 0.1 to 10 μm.

The background plate 3 is generally a white background plate, and for example, a sheet formed by kneading alumina powder with a binder and molding it can be used. The counter plate 2 can also serve as the background plate 3. The solid electrolyte membrane 4 is obtained, for example, by impregnating the pores of a polymer porous membrane with an electrolyte solution in which the specific solvent and the viologen compound are dissolved, and has a thickness of 4 to 2
It is a solid electrolyte membrane having an ionic conductivity of 0 μm and 1.5 to 2.5 × 10 ⁻⁴ S / cm.

The transparent conductive film 5 is a collecting electrode, and is made of indium tin oxide (ITO) tin oxide or the like and has a thickness of 0.1 to 0.1.
It is 0.2 μm and is formed on the glass plate 6. The voltage applied between the transparent conductive film 5 and the counter electrode 2 may be about 2.5V.
At this time, if a too high voltage is applied, the ITO is reduced, which is not preferable. The EC element thus prepared has an electrolyte fixed in a polymer membrane and can be handled as a substantially solid membrane, and therefore has a simple structure and is easy to assemble and easy to assemble. There is no risk of liquid leakage even if it breaks, so special care is not required as in the case of liquid electrolyte.

The structure of FIG. 2 differs from that of FIG. 1 in that the counter electrode 13 is made of IrO _x, etc.
It is formed in a thickness of 2 μm and is light transmissive.

In the structure shown in FIG. 1, the background plate 3 is opaque to light, and the counter electrode 2 may be opaque or opaque.
In the structure of FIG. 2, by applying a voltage between the conductive films 12 and 15 with the conductive film 15 being a negative voltage, the light control glass (EC
Acts as a window). In this structure, the counter electrode 1
If 3 is patterned, it can be used as a transmissive display element.

[0033]

Examples (1) Preparation of Solution 10 g of 2-methoxyethanol was taken, and 10 wt% of heptyl viologen and 0.1 wt% of special grade nitric acid were added. Using a stirrer, the mixture was well mixed with stirring in a beaker.

(2) Device Fabrication (Anti-glare Mirror) A spacer was interposed (space 20 μm) between two 40 mm square glass substrates (A, B), and a peripheral seal was sealed with an ultraviolet adhesive. At this time, the injection port for the solution was opened at one place. However, the glass substrate A was an ITO / glass substrate, and the glass substrate B was an ITO / glass substrate with a silver mirror attached to the back surface. The electrolyte solution was injected. The whole is evacuated to about 500 Pa or less in a vacuum chamber, and the solution is immersed in it at room temperature (2
2 ° C). After the injection, the injection port was sealed again with an ultraviolet curing adhesive.

(3) Element Drive Evaluation Initial current-voltage characteristic evaluation was performed. (2-pole type) The driving voltage was 2.5 V, and the residual color was visually confirmed. The results are shown in the table (Example: Table 1, Comparative Example: Table 2). In this embodiment, nitric acid is added to improve cycle characteristics. From this table, it can be seen that the device using the solution containing heptyl viologen and 2-methoxyethanol or 2-ethoxyethanol exhibits good electrochromic properties.

Table 1. Cycle characteristics of EC element (Example) ─────────────────────────────────── Example Solvent Color without leaving Operation Nitric acid concentration Possible number of cycles (times) (wt%) ─────────────────────────── ───── 1 2-Methoxyethanol 2000 ~ 3000 0.12 2-Ethoxyethanol 700 ~ 800 1.0 ───────────────────────────────────

Table 2. Cycle characteristics of EC element (comparative example) ────────────────────────────────── Comparative example Solvent Color without leaving Operation Nitric acid concentration Number of cycles (times) (wt%) ──────────────────────────────── 1 Propylene glycol 0 1. 0 2 1,3-butanediol 0 1.0 3 ethylphenylhydrite 0 1.04 benzyl alcohol 0 1.0 5 2-phenylethanol 200 to 300 1.0 ──────────── ───────────────────────

(4) Reflectance of electrochromic device
Measurement heptyl viologen 10 wt%, nitric acid 0.1 wt% and 2-
EC element (glass / ITO / electrolyte solution layer / ITO / glass / Ag)
Then, the reflectance of this device was measured. The relationship between the driving voltage and the reflectance is shown in the table.

[0039]

[0040]

EFFECTS OF THE INVENTION According to the present invention, there is provided an electrolyte solution for EC devices, which utilizes the excellent electrochromic coloring properties of viologen derivatives and which is driven at low voltage and has a low haze ratio. Further, by impregnating and fixing this electrolytic solution in a solid porous thin film, it can be handled as a solid without losing the ionic conductivity as a liquid electrolyte.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an EC display device of an example.

FIG. 2 is a cross-sectional view showing a transmissive light control element of an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Glass plate 2 ... Counter electrode 3 ... Background plate 4 ... Solid electrolyte membrane 5 ... Transparent conductive film 6 ... Glass plate 11 ... Glass plate 12 ... Transparent conductive film 13 ... Counter electrode 14 ... Solid electrolyte film 15 ... Transparent conductive film 16 ... Glass Board

Claims (2)

[Claims] 1. The following general formula: (In the formula, R ⁵ and R ⁶ are each independently selected from an aliphatic hydrocarbon-containing group and an aromatic hydrocarbon-containing group.), N, N′-substituted 4,4′-bipyridyl ( Viologen derivative) is represented by the general formula HO (CH ₂ CH ₂ O) _n R ³
[In the formula, R ³ is a lower alkyl group, and n is an integer of 1 to 3] An electrolyte solution for an electrochromic device, which is dissolved in a solvent containing at least one alcohol. 2. The N, N′-substituted 4,4 ′ according to claim 1.
An electrolysis solution in which bipyridyl is dissolved in a mixed solvent of at least one alcohol according to claim 1 and a solvent having a refractive index higher than that of the alcohol, and the solution is impregnated and immobilized in a porous thin film. Electrolyte thin film for chromic devices.