JPH05100253A - Electrochromic element - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent the occurrence of color residue and color unevenness of the electrochromic element, and realize an electrochromic element having stable cycle characteristics. [Structure] The counter electrode opposite to the display electrode of the ECD is used as a polarizable electrode, an electric double layer capacitor is formed by the polarizable electrode and an electrolyte, and a large-capacity capacitor is formed in the built-in type to simply convert the ECD into an ECD. By connecting a DC power supply, applying voltage, short-circuiting, and repeating coloring and decoloring, E
It is possible to significantly extend the life of the CD and obtain stable cycle characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochromic device (ECD), and more particularly to an electrochromic device which is free from color unevenness and color residue even after repeated use.

[0002]

2. Description of the Related Art At present, a liquid crystal display element with low power consumption and high response speed is used for display of calculators, watches, etc., but since polarized light is used as a display mechanism, it has viewing angle dependency, Further, since only black and white display is possible, eye fatigue cannot be ignored when used for a long time like a computer or an OA device. Therefore, as a new display element replacing the liquid crystal display element, an ECD in which the color of a substance reversibly changes upon application of a voltage is drawing attention.

Since the ECD uses ordinary light which does not depend on the viewing angle, it causes less eye fatigue, has low power consumption, has a memory property, and is capable of displaying a large area. It is used for stock price displays, large-sized display boards such as message boards and guide boards, and light control elements such as anti-glare mirrors, light control glass, and sunglasses for automatic operators.

Such ECD will be described with reference to FIG. FIG. 5A shows an example of a reflection type ECD, in which a thin film of a current collector (ITO) 32 is formed on a transparent glass 31 by a reactive sputtering method or the like, and tungsten oxide (WO ₃ ) is formed thereon as a display electrode. 33 is formed by vacuum vapor deposition or the like, and a glass plate 37, a counter electrode 36, and a counter electrode 36 are provided on the opposite electrode side with the electrolyte 34 interposed therebetween.
The background plate 35 has a laminated structure. When a DC voltage is applied to such an element between the ITO 32 and the counter electrode 36 so that the ITO 32 side is (−) from the power source (not shown), an ionic current flows through the electrolyte 34, and as a result, a reduction reaction occurs in WO ₃ 33, The light absorption property of WO ₃ changes to develop color. Therefore, the color development of WO ₃ can be observed by observing the reflected light from the glass 31 side. When both electrodes are short-circuited, an electric current flows in the opposite direction, an opposite reaction occurs, and the color disappears.

FIG. 5B shows an example of a transmission type ECD.
The display layer 40 (for example, iridium oxide that develops a color by an oxidation reaction), the ITO 41 without the background plate of FIG.
By observing the transmitted light from the glass 37 side, it is possible to observe the color development in which WO ₃ and the display layer are subtractively mixed.

[0006]

As described above, the ECD is colored by the oxidation and reduction reactions, but the color is thin immediately after the application of the DC voltage because the degree of the reaction is small, and the color becomes dark as the integrated amount of the current increases. Then, the reaction saturates and a constant concentration of color is developed. In this state, the ionic current is almost zero, and a kind of secondary battery is formed between the oxidation electrode and the reduction electrode, in which energy corresponding to the amount of electricity is stored. Therefore, when both electrodes are short-circuited, a discharge occurs and the oxidation and reduction electrodes cause a reaction opposite to that at the time of color development, resulting in decolorization. Therefore, as shown in FIG. 6, when a voltage is applied and a short circuit is performed in a cycle of about 5 seconds, coloring and decoloring are repeated. By the way, if coloring and erasing are repeated a number of times, color unevenness and color residue occur, and it becomes unusable, and conventional ECD has a limit of about 2000 times at most.
There was a problem that the cycle characteristics were not good.

An object of the present invention is to solve the above problems, and an object of the present invention is to provide an electrochromic device capable of preventing the occurrence of color residue and color unevenness and obtaining stable cycle characteristics.

[0008]

In the electrochromic device of the present invention, a display electrode and a polarizable electrode formed on a current collector are arranged to face each other with an electrolyte in between, and the polarizable electrode and the electrolyte are electrically connected to each other. It is characterized in that a multilayer capacitor is formed. Further, it is characterized in that two electrochromic elements incorporating an electric double layer capacitor are integrated with each other by using a common collector on the polarizable electrode side.

[0009]

According to the present invention, the counter electrode, which is arranged opposite to the display electrode of the ECD with the electrolyte in between, is used as a polarizable electrode, and the polarizable electrode and the electrolyte form an electric double layer capacitor, and a voltage is applied between the display electrode and the polarizable electrode. By applying and short-circuiting and repeating coloring and decoloring, it is possible to realize an ECD in which the occurrence of residual color and uneven color is prevented.

[0010]

EXAMPLES The electrochromic device of the present invention is notable for color unevenness and color residue when driven by a high voltage or when a voltage of the same voltage is applied for a long time.
When a capacitor is connected in series to the ECD, a capacitor is incorporated in the ECD, and current is supplied / discharged through this capacitor.

FIG. 1 is a diagram showing an electrochromic device of the present invention, FIG. 2 is a diagram for explaining a driving system in which a capacitor is connected in series to an ECD, FIG. 3 is a voltage waveform diagram, and FIG. 4 is an electric double layer capacitor. It is a figure for explaining. In the figure, 1, 5 and 9 are collectors, 2 and 8 are display electrodes, 3 and 7 are electrolytes, 4 and 6 are polarizable electrodes, 11 is ECD, C is a capacitor, E is a DC power supply, and S1 is ON. / Off switch, 12
Is an on / off device, 21 is a current collector, 22 is a polarizable electrode,
Reference numeral 23 is a separator, and 24 is a sealing material.

First, the operating principle of the present invention will be described with reference to FIG. In FIG. 2, the ECD 11 has the same structure as described with reference to FIG. 5, and the capacitor C is connected in series to this. Then, the switch S1 is turned on / off at an interval of, for example, 5 seconds by the on / off device 12 including a timer, and the ECD1 is repeatedly energized / discharged through the capacitor C by application of a DC voltage or short circuit. The voltage applied to ECD1 at this time is as shown in FIG. That is, immediately after the switch S1 is turned off, the power source E is supplied to the ECD.
Voltage is applied as it is, but since the capacitor C is charged, the voltage applied to the ECD by the charging voltage increase CV decreases exponentially, and an exponentially decreasing current flows between the electrodes to cause oxidation / reduction reaction. Causes color development. When switch S1 is turned on after 5 seconds, charging voltage CV of capacitor C
Is added in the opposite direction, the energy stored in the ECD and the capacitor is discharged at the same time and a decoloring reaction occurs, and eventually the ECD
The applied voltage to is 0 and the color is completely erased.

By such driving, it was possible to prevent the occurrence of color unevenness and color residue even after repeating the coloring / decoloring cycle at least 10 times or more as compared with the conventional one. This is because the voltage applied to the ECD is reduced by the charging voltage of the capacitor and the capacitance of the capacitor is E.
It is considered that one of the causes is that the total capacitance is reduced and the time constant is shortened because the capacitors are connected in series to the capacitance of the CD, and the time during which the current is flowing is shortened.

As described above, the cycle characteristics can be improved by connecting the capacitor to the ECD in series. However, in the present invention, instead of connecting the capacitor to the ECD in series, the ECD is connected to the ECD as shown in FIG. The feature is that it is formed by incorporating a capacitor.

In FIG. 1A, WO ₃ is formed as a display electrode on the current collector 1, and the polarizable electrode 4 is formed on the current collector 5 with the electrolyte 3 sandwiched therebetween. The electrolyte is not particularly limited, but it is desirable to make the electrolyte layer into a solid or thin film in order to solve the problems of liquid leakage and evaporation of the ECD electrolyte, and to increase the area, stacking and handling. Specifically, such a thin film can be obtained by filling and fixing an electrolyte dissolved in an organic solvent in the pores of a polymer porous film. The polymer film is made of polyolefin, polyester, polycarbonate, polytetrafluoroethylene, polyvinylidene fluoride, etc., having a thickness of 0.1 to 50 μm, porosity of 40 to 90%, average pore diameter of 0.001 to 0.1 μm, and fracture. Strength 200kg / cm
² or more. Alkali metal salt as electrolyte,
Especially halogenated Li, LiClO ₄ , LiCF ₃ SO ₄
Li salts are suitable. Examples of the organic solvent include propylene carbonate (PC), low molecular weight polyalkylene oxide or ether compounds thereof, benzaldehyde, benzonitrile, benzyl alcohol, dibenzyl ketone, diphenylpropionitrile and the like.

The polarizable electrode 4 is for forming an electric double layer with the electrolyte 3 to form a large capacity capacitor. The electric double layer is a current collector 2 as shown in FIG.
A polarizable electrode 22 made of activated carbon powder or activated carbon fibers is arranged via an ion-permeable and electrically insulating porous separator 23 between 1 and 21, and is sealed with a sealing material 24. The polar electrode 22 and the separator are impregnated with an electrolyte. At the interface where the polarizable electrode 22 and the impregnated electrolyte come into contact, positive and negative charges are arranged facing each other with an extremely short distance, and an electric double layer is formed, and the activated carbon powder or activated carbon fiber electrode has a large surface area. Therefore, a large capacity capacitor can be obtained.

The polarizable electrode 4 in FIG. 1A forms such an electric double layer capacitor together with the electrolytic solution 3 and also forms a counter electrode for the display electrode of the ECD. Capacitance formed at this time, 0 for ECD1cm ^2.
It may be about 001 to 0.02F. When an ECD having such a structure is repeatedly applied with a voltage and short-circuited between the current collectors 1 and 5, electricity / discharge is performed through the electric double layer capacitor, and as shown in FIG. Due to the presence of, the occurrence of color unevenness and residual color is prevented. Moreover, in the case of FIG. 1, it is not necessary to connect a capacitor to the ECD as compared with the case of FIG. 2, and it is only necessary to connect a DC power source to the ECD, so that the usability is significantly improved. it can.

FIG. 1 (b) is a view in which two electrochromic elements identical to those in FIG. 1 (a) are integrated by commonizing a collector 5 on the polarizable electrode side. In the case of this element, a display electrode is used. Since color development occurs at 2 and 8, it can be used as an element for observing color development from both sides.

[0019]

As described above, according to the present invention, the electric double layer capacitor is formed by one electrode of the ECD and the electrolyte. Therefore, a DC power source is simply connected to the ECD to prevent voltage application and short circuit. By going and repeating coloring and erasing,
It is possible to prevent the occurrence of color unevenness and color residue, to significantly extend the life of the ECD, and to obtain stable cycle characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing an electrochromic device of the present invention.

FIG. 2 is a diagram showing a drive circuit in which a capacitor is connected to an ECD.

FIG. 3 is a voltage waveform diagram.

FIG. 4 is a diagram illustrating an electric double layer.

FIG. 5 is a diagram illustrating a structure of an ECD.

FIG. 6 is a voltage waveform diagram of a conventional driving method.

[Explanation of symbols]

1, 5, 9 ... Current collector, 2, 8 ... Display electrode, 3, 7 ... Electrolyte, 4, 6 ... Polarizable electrode, 21 Current collector, 22 is polarizable electrode, 23 is separator, 24 is sealing material ..

Claims (2)

[Claims] 1. An electrochromic device characterized in that a display electrode and a polarizable electrode formed respectively on a current collector are arranged to face each other with an electrolyte in between, and an electric double layer capacitor is formed by the polarizable electrode and the electrolyte. element. 2. An electrochromic device comprising two electrochromic devices according to claim 1 integrated with a current collector on the polarizable electrode side in common.