JPS6314132A - Electrochromic display element - Google Patents

Abstract

PURPOSE:To permit the formation of a thin film of a tungsten oxide by using the tungsten oxide deposited by electrodeposition to a cathode side from a soln. prepd. by mixing tungsten or the compd. thereof, hydrogen peroxide and water as a color forming material and sandwiching an electrolyte between a counter electrode and a substrate formed with said electrode. CONSTITUTION:An org. soln. of Li-salt such a propylene carbonate soln. of LiCIO4 is used for the electrolyte 5 and a porous alumina substrate, 'Teflon(R)' sheet packed with titanium oxide, etc., are used for a background material 9 to be inserted therein. A solid electrolyte such as Na-beta-Al2O3 is also usable in place of the electrolyte. The counter electrode 6 is formed by using a transparent conductor 6' provide on the glass substrate and a sintered body 6'' which is provided to the transparent conductor and is obtd. by mixing and sintering carbon and transition metal oxide powder such as amorphous iron tungstate Fe2(WO4)3. The sintered body 6'' is provided to the part in contact with the electrolyte 5 and is adhered to a spacer 8 by using an adhesive agent such as epoxy in such a manner that the transparent conductor 6' contacts the spacer 8 directly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrochromic display element, and particularly to an electrochromic display element using a tungsten oxide electrodeposited thin film suitable for reducing manufacturing costs.

[Conventional technology]

Conventionally, amorphous tungsten oxide thin films, which are electrochromic substances used in electrochromic display elements, have been mainly formed by vapor deposition (Japanese Patent Application Laid-open No.
7-8983).

[Problem that the invention seeks to solve]

Since the above-mentioned conventional technology uses vacuum technology, the cost of forming a thin film is high, which is particularly problematic when applied to the large-area electrochromic display element of the present invention. For this reason,
It has been desired to develop a technique for forming tungsten oxide thin films at lower cost.

An object of the present invention is to provide a technique for forming a tungsten oxide thin film using a simple method.

[Means for solving problems]

The above object is achieved by forming a tungsten oxide thin film by a simple electrodeposition method.

[Effect]

In order to form a thin film of tungsten oxide by electrodeposition, the electrodepositing solution must be acidic because tungsten oxide dissolves extremely well in aqueous alkaline solutions.

By the way, when -i such as hydrochloric acid is added to a tungstate aqueous solution to make the solution acidic, an insoluble tungsten oxide hydrate (WO, .nH, o) is produced. Therefore, it cannot be used as an electrolyte as it is.

Additionally, the Journal of the Responsibility reported that when tungstate salts such as sodium tungstate (NalWO) are treated with cation exchange resins, a type of polyacid, estimated to be Hs (HaWaO*t), is produced. -Common Metals 2 (1960) Pages 360 to 371 (Journal of the Less-
Common Metals 2 (1960) pp3
6, page 371). This solution, freshly treated with ion exchange resin, is clear to the naked eye. However, after a while, the solution becomes cloudy and a white paste-like precipitate appears. Therefore, a solution of polytungstic acid treated with an ion exchange resin cannot be used as an electrodeposition solution.

However, when a small amount of hydrogen peroxide is added to a solution treated with an ion exchange resin, no precipitation occurs. This is thought to be due to the presence of tungstic acid peroxide in the solution.
(mentioned above).

Moreover, it has become clear in the course of the present invention that when the amount of hydrogen peroxide added is appropriate, a bluish-colored film is formed on the cathode side when a pair of electrodes is immersed in the solution and electrolyzed.

This coating is considered to be so-called tungsten bronze, and is considered to be a compound represented by the composition formula HxWOs. If the amount of hydrogen peroxide is lower, the resulting coating will be brown, and if the amount of hydrogen peroxide is higher.

A colorless coating is obtained. These films are considered to be films in which the oxidation state of tungsten is tetravalent and hexavalent, respectively.

The above film is formed quickly when the molar ratio of hydrogen peroxide to tungsten is in the range of 1:6 to 1:1, and when the amount of hydrogen peroxide is higher than this, the formation rate becomes slow.

Furthermore, if the current density during electrodeposition is low, it becomes difficult to deposit. It is desirable that the current density be 100 μA//12 or more.

Further, the electrodeposited film develops and discolors by simultaneously injecting and releasing Kt atoms with protons and alkali metal ions at the electrode, and can be applied to electrochromic display elements or variable light transmission elements. These elements are
It can be produced in the same manner as an element using a tungsten oxide vapor deposited film as a coloring film. An example of an electrochromic display element using an electrolyte as an electrolyte is shown in FIG.

In FIG. 1, 1 is a glass substrate on the display electrode side, 2 is a transparent conductor, 3 is a coloring material layer, 4 is a protective film for the transparent conductor 2 formed of, for example, a vapor deposited film of silicon oxide, and 5 is a protective film for the transparent conductor 2. An electrolyte solution, 6 a counter electrode, 7 a glass substrate on the counter electrode side, 8 a spacer, and 9 a background material inserted into the electrolyte solution.

For the electrolytic solution 5, an organic solution of Li-salt such as LiCIO4 or pyrene carbonate solution is used, and the background material 9 inserted therein includes a porous alumina substrate, titanium oxide, etc. A Teflon sheet etc. filled with is used. Na-β-A/,,0. It is also possible to use solid electrolytes such as The counter electrode 6 is
A transparent conductor 6' provided on a glass substrate and carbon and amorphous iron tungstate Few provided on the transparent conductor.
It is formed using a sintered body 6 which is mixed and sintered with a transition metal oxide powder such as CWO4)s. In this case, the sintered body 6
" is provided at a portion in contact with the electrolytic solution 5, and the transparent conductor 6' is bonded to the spacer 8 using an adhesive such as epoxy so that it is in direct contact with the spacer 8.

〔Example〕

Hereinafter, the content of the present invention will be explained in more detail with reference to specific examples.

Example 1 0.015 mol of sodium tungstate in 100 ml
The solution, which was poured into a strong acid type ion exchange resin column in which K was dissolved and made into an H type in advance, was dripped from the 0 column and was yellowish and transparent.

Then, pure water was poured into the column to flush out the tungstic acid generated in the column. The total amount of solution poured out is 4
00mt. A commercially available dihydrogen peroxide solution and water were added to this solution to make a total amount of 500 mt, and a dipping was prepared in which the molar ratio of hydrogen peroxide to tungsten was 2:3. The concentration of tungsten in this solution is 0.03 mot/l. After the prepared solution was left at room temperature for one day, it was used as an electrolyte and analyzed for 30 minutes at a flow density of 300 pA/cm" C1t. Here, the cathode electrode was
A transparent conductive film mainly composed of indium oxide and having a sheet resistance of 10 Ω/stripe 2 was formed on a glass substrate, and a gold plate was used as the anode electrode. As a result of electrodeposition, the thickness was 0.6
A blue colored coating of .mu.m was obtained.

Example 2 A blue colored film prepared by a method similar to that shown in Example 1 was heat-treated, and the heat treatment affected the reversibility of the color development/decolorization reaction in a 1 mot/4 lithium perchlorate propylene carbonate solution. Temperature shadow 4'y! This is an example investigated by t-cyclic voltammetry. The Boldamogram was measured using a gold plate as the counter electrode and a silver-silver chloride electric standard as the reference electrode. The blue colored film becomes a colorless and transparent film by heat treatment at 100C for 1 hour or more. In addition, the electrochromic reaction is caused by Loo as shown in Figure 2.
Excellent reversibility is shown when heat treatment is performed for C, 1 hour or more and 220C, 11 hours or less. Note that the portamogram has a sweep speed of 0. It was determined as IV/S.

Example 3 In the same manner as in Example 1, indium oxide (Inxoa) with the wiring portion covered with a vapor-deposited film of silicon monoxide was placed on a glass substrate.
) is the main component, and the sheet resistance is 10Ω/cIn! A 0.6 μm thick color-forming film was formed on the exposed transparent conductive film portion. This was heat treated at 18 CI' for 1 hour in the air. The thickness of the electrodeposited film after the heat treatment was 0.4 μm. The device shown in FIG. 1 was fabricated using the thus fabricated polarizer.

A 1 moA/l LiC20+ propylene carbonate solution was used as the electrolytic solution 5 in Fig. 1, and a porous Teflon sheet filled with titanium oxide powder, which is a white pigment, was used as the background material 9 inserted therein. . As the counter electrode 6, an electrode was used in which a mixed sintered body 6'' of amorphous iron tungstate as an active material and carbon in a weight ratio of 2:1 was formed on a transparent conductor 4 6'.

Applying a 1.2V, IHz square wave to the created element,
The cycle of developing and decoloring was repeated. The charge injected and released during color development and decolorization was approximately 5 mC/CIr1''.
The contrast ratio during color development with charge of "C7 cm" injected to that during erasing was about 3.0.

Even after repeating 107 cycles of one shot and decoloring, almost no deterioration was observed.

〔Effect of the invention〕

As described above, according to the present invention, a coloring material can be formed by a simple and inexpensive method, and the cost of an electrochromic display element can be reduced, and its industrial value is high.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an electrochromic display device of the present invention, and FIG. 2 is a diagram for explaining the present invention in detail. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Transparent conductor, 3... Coloring material layer, 4... Protective film, 5... Electrolyte, 6... Opposing'
B pole, 7... board. 8... Spacer, 9... Background material.

Claims (1)

[Claims] 1. Tungsten oxide is deposited on the cathode side by electrodeposition from a solution obtained by mixing tungsten or its compound, hydrogen peroxide, and water as a coloring material, and the counter electrode is An electrochromic display element characterized in that an electrolyte is sandwiched between a formed substrate and an electrolyte. 2. The tungsten oxide obtained by depositing on the cathode side by the above electrodeposition is heat-treated at 100°C for 1 hour or more and 220°C for 1 hour or less, and used as a coloring film. The electrochromic display element according to scope 1.