JPS6332368B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a display device that utilizes an electrochemical redox reaction, and particularly to a binder for a counter electrode formed by pressure molding powder.

Display devices that utilize electrochemical redox reactions (electrochromic display devices, hereinafter abbreviated as ECD) are known to be of liquid type and solid type. For liquid type, water or
An EC material (for example, heptyl viologen bromide) melted in an electrolytic solution is held between two substrates with opposing electrodes, and when it is reduced at the display electrode, it is colored and displayed; conversely, when it is oxidized, It returns to its original state and is erased. Also, solid type
ECD is a cell in which a thin film of EC material (for example, tungsten trioxide) is attached to the display electrode side, and an electrolytic solution is held between the electrodes.As before, coloring and decoloring are performed based on redox reactions. This is what we do.

The present invention is applied to the second solid-state ECD.

FIG. 1 is a schematic diagram showing an example of a cell structure of a solid-state ECD. 1 is a substrate on the display electrode side;
Usually it is transparent glass with transparent electrodes 2.
Further, the transparent electrode is patterned according to the content of the display. Furthermore, within this transparent electrode pattern,
The EC material is made into a thin film and attached as the display electrode 3. 4 is a protective layer for the transparent electrode formed as necessary. Further, 5 is a white porous plate for providing contrast in display. Reference numeral 6 denotes a counter electrode, which is energized by a lead wire 7. 8 is a rear container for holding electrolyte solution 9.

Conventionally, an aqueous sulfuric acid solution has been used as an electrolyte for ECD. However, although this liquid has a fast response speed for writing and erasing, it is a strong acid solution and the transparent electrode film is soaked in it, shortening the lifespan of the ECD. Electrolyte systems with long-term stability, in which a Lewis salt-type supporting electrolyte is added, have become mainstream. In addition, the counter electrode is made of the same EC material as the display electrode.
Various materials have been proposed, including platinum, graphite, and gold.
These can be easily made into thin films and are effective in making ECD cells thinner, but when using EC substances, the equilibrium potential and reaction overvoltage of the EC substance change depending on the coloring concentration of the EC substance, so the coloration remains constant. Concentration cannot be obtained. When using platinum or graphite, the applied voltage is unstable.
The use of gold has various problems, such as electrochemical dissolution at the counter electrode and the dissolution depositing on the display electrode.

The present invention is a counter electrode made by pressure-molding activated carbon or carbon black powder, which has been improved to overcome the drawbacks of conventional counter electrode materials.

That is, a more reliable electrochromic display device was created by using water-soluble polymeric cellulose as a binder for the powder-formed counter electrode.

The effect of activated carbon and carbon black compacted powder counter electrodes is the ultrafine structure and three-dimensional chain structure of activated carbon and carbon black, as well as their large surface area.
Utilizing the effect of absorbing and retaining a large amount of electrolyte, it is expected to effectively equalize the depolarization effect of the counter electrode, and at the same time have an ion adsorption effect, stabilizing the counter electrode potential, resulting in high electrochemical stability. The opposite of ECD is obtained.

Furthermore, numerous subsequent experiments have shown that it is important to improve the binder in order to make the effect of this counter electrode even more reliable over the long term. That is, in the case of the conventional binder counter electrode, the response time slows down little by little in repeated writing and erasing tests. The cause of this is not that the counter electrode material itself is unstable, but that the strength of the counter electrode gradually decreases.
In other words, it is presumed that this is due to the fact that the counter electrode gradually swells and the contact resistance between the particles of the counter electrode increases, which slows down the response speed. Under these circumstances, we have conducted experiments on various binding materials and found that the use of water-soluble polymer celluloses is extremely effective. The water-soluble polymeric cellulose in the present invention belongs to the group selected from viscose, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, and alkali metal salts thereof.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 First, a method for making an ECD cell will be described with reference to FIG.
A transparent glass substrate 1 was washed with alkali, water, and dried, and In ₂ O ₃ was deposited to a thickness of about 3000 Å by electron beam vacuum evaporation using a metal mask to form a transparent electrode 2.
form. Next, WO ₃ was formed as an EC material to a thickness of approximately 3000 Å by electron beam vacuum evaporation.
shall be. The substrate temperature at this time was approximately 100°C, and a metal mask was used to create a pattern that could be used to display time. Next, the counter electrode 6 is made by adding carboxymethylcellulose sodium powder to the activated carbon powder at a weight ratio of approximately 4:1, and further adding pure water at a weight ratio of 2.5 to 3.5 to the powder to provide an adhesive effect. death,
Mix well in the milk drum. This was pressure-formed using a hydraulic press using an expanded metal (wire mesh) made of titanium with a cut of about 2 mm as a core.
The press pressure at this time is approximately 1 to 7 ton/cm ² . It was cured by evaporating moisture in a constant temperature bath at about 100 to 150°C. Next, a part of this molded body is broken to expose the core titanium current collector, a titanium lead wire 7 is spot-welded to this, and a bag made of non-woven polypropylene is covered to prevent the powder from coming out into the liquid. , was used as a counter electrode.

Then, the glass substrate 1 created earlier, with holes for the liquid injection port 10 and the lead wire outlet 11, was bonded to the washed and dried rear container substrate 8. On this occasion,
A white porous plate 5 made of Al ₂ O ₃ and a counter electrode 6 were sealed inside to provide contrast in display. The electrolytic solution 9 was injected into the ECD cell thus prepared through the injection port 10, and after completely permeating the counter electrode and the white porous plate, the injection port 10 was sealed.
A 1 mol-LiBF ₄ propylene carbonate solution was used as the electrolyte.

The ECD configured in this way has a response speed of approximately 350 m at -1 V with respect to the opposite electrode at a reflectance of 40%.
sec, and quickly disappeared under reverse voltage. Further, using this cell, the change in response time was investigated by square wave driving with a display/erase time of 500 msec, and the change rate was 20 to 30% after about 1×10 ⁶ times, which was extremely good. For comparison, the rate of change in response speed for the activated carbon counter electrode using an epoxy binder at the same number of times is 80~
It was 90%.

Example 2 Instead of the binder for the counter electrode used in Example 1, hydroxyethyl cellulose was mixed with activated carbon powder and about 8
An ECD having the same structure as in Example 1 was prepared by adding the mixed powder in a ratio of 1:1, further mixing with pure water at a ratio of about half of the mixed powder, press-molding to evaporate water, and using it as a counter electrode. As a result of investigating its characteristics,
They showed almost the same performance.

Example 3 Instead of the electrolyte used in Example 1, 1 mol-
ECD using _LiClO4 /propylene carbonate
After investigating the manufacturing characteristics, the initial writing speed was
Even in repeated tests of 1×10 ⁶ times at 410 m·sec, the rate of change was approximately 15%, which was extremely good.

Example 4 Instead of the activated carbon used in Example 1, a counter electrode was created using acetylene black powder, an ECD similar to that in Example 1 was created, and the characteristics were investigated, and almost the same characteristics were obtained. .

Example 5 Instead of the electrolyte used in Example 1, 1 mol-
A counter electrode prepared by mixing _LiBF4・γ-butyllactone solution and methyl cellulose as a binder in the same ratio as in Example 1 and press-molding was prepared using the same ECD as in Example 1.
When we created and investigated the characteristics, similar characteristics were obtained.

Further, the present invention can also be applied to a counter electrode formed by powder molding using other counter electrode materials, such as a cyano complex of monoiron graphite.

As described above, according to the present invention, since water-soluble polymer cellulose is used as a binder for the counter electrode made of a compacted powder, stable display characteristics over a long period of time, i.e., writing/erasing response time An electrochromic display device with very little change in temperature and high long-term reliability can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a cell structure of a solid-state ECD. 1...Display electrode substrate, 2...Transparent electrode, 3...
Display electrode, 4...protective film, 5...white porous plate,
6... Counter electrode, 7... Lead wire, 8... Rear container substrate, 9... Electrolyte, 10... Inlet, 11...
...Lead wire outlet.

Claims (1)

[Scope of Claims] 1. In an electrochromic display device having a display electrode made of an electrochromic material, an electrolytic solution in which a supporting electrolyte is dissolved in an inert solvent, and a counter electrode made of a compacted powder, the counter electrode An electrochromic display device characterized in that the binding material is water-soluble polymer cellulose. 2. The electrochromic display device according to claim 1, wherein the counter electrode powder is activated carbon, carbon black, or a mixture thereof.