JPH0152736B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an electrochromic (hereinafter abbreviated as EC) element, and more specifically, by improving the counter electrode, display quality and contrast are improved, and the driving method thereof is improved. It is simple and concerns EC elements.

As shown in Figure 1, conventional EC elements
EC such as an amorphous WO _{3 film} and a M ₀ O ₃ film is formed on a transparent substrate 1 equipped with a transparent electrode 2 made of SnO 2 , In ₂ O ₃ , etc.
A display electrode substrate on which a substance 3 is formed and a counter electrode plate on which an EC substance 6 similar to that of the display electrode plate is formed are arranged facing each other on an electrode 5 formed on a substrate 4 made of glass or the like, and the periphery is sealed. It is known that an electrolyte 8 containing ions capable of coloring the EC substance is placed in a gap formed by sealing with a member 7, and a porous body 9 that provides a background for display as required.

In addition, as shown in Fig. 2, another type of EC element known in the past includes an EC material or graphite disposed in a binder as a counter electrode, or an EC element disposed in a binder as a counter electrode. Layer 1, which is a mixture of substance and graphite
One using 0 is known.

The type of EC element shown in Figure 1 is often called a symmetrical cell because its structure is symmetrical, but usually some method is used to color the EC material 6 on the counter electrode in advance. It is used in a state. This is because the EC material in its uncolored state is a high resistance material, and the normally used 1.0~
This is because it is difficult to display at a voltage of about 1.5V. In order to facilitate this, the EC on the counter electrode is used before or after device fabrication.
A method such as coloring the substance 6 in an electrolytic solution has been adopted. It is known that the EC element obtained in this way exhibits extremely good EC characteristics even when driven at low voltage. The EC characteristics referred to here refer to the response speed during coloring/decolorization, and by applying a voltage of 1.0 to 1.5V, a well-balanced response speed of about 0.1 to 0.5 seconds can be obtained. The reason why such a relatively fast response speed is obtained is that the EC material that has been colored in advance has a negative electromotive force, and especially when it is colored, the voltage applied from the outside is further affected by the coloring. This is because the electromotive force of the EC substance in the state is superimposed and becomes a larger driving force.

Although they have such excellent properties, this type of EC element has a problem in that the EC material, which has been colored in advance, gradually returns to its original transparent state and no longer exhibits the desired performance. It is known to exhibit deterioration phenomena. This is thought to be caused by oxygen in the electrolyte.
It is thought that the colored, or reduced, EC substance is gradually oxidized by this oxygen and loses its color and electromotive force. Therefore, unless measures are taken to prevent the EC material on the counter electrode from discoloring, it cannot actually be used for a long period of time.

On the other hand, graphite or
In an EC element using an EC material or a mixture of both graphite and EC material and a binder10, these counter electrodes can smoothly function as counter electrodes when voltage is applied without any special treatment in advance. It differs from the EC element shown in FIG. 1 in that it can function and display information. This counter electrode using graphite or the like generally has no electromotive force with respect to the EC substance on the display electrode, or only has a very small electromotive force of about ±0.3V or less, and does not respond well when colored. The speed is slower than the symmetrical EC element.
Although the details of the electrode reaction occurring on the graphite counter electrode during coloring are not clear, the characteristics of the device are similar to those of charging and discharging a capacitor. That is, when coloring, it is necessary to apply a voltage from the outside, but when decoloring, the display coloring is erased by simply shorting the display electrode and the counter electrode.

Generally, when an EC element performs coloring/decoloring as shown in FIG. 3, negative and positive DC voltages are applied to the display electrodes, respectively. Note that the broken line indicates an open state. The display contrast is determined by the surface charge density injected into the display pole at this time. Therefore, in order to maintain a constant contrast between a plurality of display segment electrodes, it is necessary to vary the amount of electricity injected into each segment depending on the segment area. For this reason, it is necessary to take measures such as making the area of each display segment the same and making the electrode resistivity of the lead part the same.

Furthermore, although a constant voltage drive circuit as shown in Figure 3 is the easiest to obtain, the response speed of an EC element is relatively temperature dependent due to its characteristics, and when driven with a constant voltage and pulse width, the temperature The surface charge density of the display electrode varies depending on the display electrode, and the contrast changes. For this purpose, the voltage depends on the temperature,
Alternatively, it is necessary to add a temperature compensation circuit to the drive circuit for changing the pulse width, which inevitably makes the circuit complicated.

A constant current circuit can be considered as a circuit that does not require temperature compensation. In this case, the amount of electricity sent to each display segment can be kept strictly constant by accurately controlling the time, but it is also necessary to take measures such as making the area of each segment constant. There are restrictions on pattern shapes.

As shown in Figure 4, one way to eliminate these circuit difficulties is to use a driving method in which no voltage is applied during coloring, the counter electrode is short-circuited with a predetermined electromotive force, and voltage is applied only when decoloring. has been proposed by the applicant. This driving method colors the display using the electromotive force of the counter electrode, and each segment electrode is short-circuited with the counter electrode for a predetermined period of time when displaying. According to this method, a current flows until the potential of the display electrode becomes constant with that of the opposing electrode without being affected by the area of each segment electrode or the ambient temperature, and the display contrast is kept constant.

In order to perform such driving, it is necessary that the counter electrode or the EC layer 6 (FIG. 1) in contact with the counter electrode has a negative electromotive force. It is of course possible to perform display using this driving method using the symmetrical element shown in Figure 1, but for the reasons mentioned above, this element cannot withstand long-term use unless some kind of auxiliary means is used. do not have. Furthermore, in this driving method, the potential of the counter electrode directly corresponds to the contrast of the display electrode, so an extremely stable counter electrode potential is required, and conventional thin film
In the case of the EC layer, this requirement could not always be fully met. In addition, in the element using a counter electrode such as graphite shown in Fig. 2, as mentioned above, these materials have almost no electromotive force, so the fourth
It is clear that the drive method shown in the figure cannot be used.

The present invention was discovered against this background, and has a counter electrode having a stable potential for carrying out the driving method shown in FIG. 4, and is a transparent electrode formed on a transparent substrate. , an electrolytic solution containing an ion capable of coloring the electrochromic material is provided between the display electrode substrate comprising the electrochromic material layer formed on the transparent electrode and the counter substrate. The electrochromic device is characterized in that the opposing electrode has a stable negative potential capable of coloring the electrochromic substance.

The present invention makes it possible to obtain a counter electrode that always has a constant negative electromotive force for long-term use, exhibits smooth coloring and discoloration when energized, and eliminates ions that cause side reactions. It is possible to obtain a counter electrode, and thereby a practical EC element can be obtained with a simple drive circuit.

As the counter electrode of the present invention, one having a stable negative potential capable of coloring the electrochromic substance disposed on the display electrode side is used.

When using _WO3 , which is commonly used as an electrochromic material on the display electrode side,
A counter electrode is provided that has a stable potential of -0.4 to -1.0 V over a wide range at a charge injection amount of 0.1 to 0.5 C/cm ² . This is because a charge of about several to ^several + mC/cm2 is normally injected into the electrochromic material on the display electrode side during coloring, and about 10 times that amount of charge is stored in the counter electrode, according to WO ₃ . The voltage is set at -0.4 to -1.0V because the coloring/discoloration becomes insufficient rapidly below -0.4V and it is preferable to lower the voltage supplied to the drive circuit.

This includes a mixture of graphite containing W ₁₈ O ₄₉ and W ₂₀ O ₅₈ that can form intercalation compounds with metal ions such as Li and exhibits a potential of −0.4 to −1.0 V upon reduction.
This is preferable because a stable potential of -0.6 V or more can be obtained with a charge injection amount of 0.1 C/cm ² over a wide range of charge injection amount.

The counter electrode must have a certain stable negative potential, and when it is short-circuited with the display electrode, it can quickly release electrons and ions and turn the display electrode into a colored state. In order to achieve this, it is necessary that the counter electrode material has electronic conductivity and high ionic conductivity. In particular, ionic conductivity is considered to be a property inherent to the material such as the oxide in the counter electrode. Both W ₁₈ O ₄₇ and W ₂₀ O ₅₈ have similar crystal structures to WO ₃ , but have better ion mobility than WO ₃ .

By using graphite in combination with this, electronic conductivity can be supplemented.

In an electrochromic device, it is desirable to mold the device without using a binder, and it is preferable to use expanded graphite as the graphite suitable for this purpose. In this case, a plate-shaped molded body can be obtained together with the various oxides without using a binder, and is suitable for placement inside an element. The higher the amount of graphite, the better the moldability, but in order to store charge at a higher density, the higher the proportion of the oxide, etc., the better.
Preferably it is 80%.

A detailed explanation will be given below based on examples and comparative examples of the present invention.

Figure 5 shows an amorphous WO ₃ film (film thickness approximately 3000 Å).
This figure shows the relationship between the amount of electricity injected into a WO ₃ film and the change in potential when colored in a Li-based electrolyte. From this figure, it can be seen that 8 mC/cm ² using a WO ₃ film with a thickness of about 3000 Å, which is used in ordinary EC devices.
The potential of the display electrode is approximately - for an amount of injected electricity of approximately
It will be about 0.6V. This is WO ₃ when the amount of electricity is 0
This is the difference between the potential of approximately +0.2 V and -0.4 V for platinum at 8 mC/cm ² . Therefore, in this case, in order to drive by the method shown in FIG. 4 and obtain a predetermined contrast, that is, the amount of injected charge, the potential of the opposing electrode needs to be -0.6 V or more.

Taking this into consideration, the counter electrode was made of graphite alone.
mixture of _TiO2 and graphite, mixture of _Nb2O5 and _graphite ,
Electrolytic reduction was performed in a Li-based electrolyte using a mixture of W ₁₈ O ₄₉ and graphite, a mixture of W ₂₀ O ₅₈ and graphite, and a mixture of MnO ₂ and graphite, and the amount of electricity and potential injected at this time were We investigated the relationship between In addition
W ₁₈ O ₄₉ and W ₂₀ O ₅₈ are prepared by mixing WO ₃ powder and W powder to a predetermined composition ratio, then vacuum-sealing the mixture in a quartz tube,
They were manufactured by heat treatment at 800°C for about 6 hours, and the graphite content was 50% in both cases.

FIG. 6 shows this result.

As is clear from this figure, the potential of graphite _alone changes _{significantly} when it is reduced, that is, when _electricity is injected. There was no significant difference from the example of the mixture, and it was not possible to store the specified amount of electricity at a specified low voltage.

In addition, in the case of mixing MnO ₂ and graphite, the potential change is extremely small, which is −0.4 to −, which is the objective of the present invention.
It was not enough to show a negative potential of 1.0V.

In contrast, the example of W ₁₈ O ₄₉ and graphite and W ₂₀ O ₅₈
The examples of graphite and graphite both have -0.7 to - by applying a current of about 100 mC/cm ² (the thickness of the test piece is 0.3 mm in both cases).
It reached 0.8 V (-0.4 to -0.6 V as a potential with respect to platinum), and the potential change was extremely small with respect to the change in the amount of injected electricity when the amount of injected electricity was around 100 mC/cm ² .

Therefore, the electrode containing W ₁₈ O ₄₉ and W ₂₀ O ₅₈ , which had been subjected to reduction treatment by injecting a predetermined amount of electricity in advance, exhibited a potential that satisfied the predetermined purpose.

Using these two types of opposing electrodes, an element having the structure shown in Fig. 7 is fabricated, and when coloring and decoloring are performed using the driving method shown in Fig. 4, good results can be obtained even when a voltage of 1 Hz and 1.5 V is applied. The characteristics were shown. In addition, in FIG. 7, 11 is a counter electrode of the present invention, which is provided on the electrode 5. This is because when the substrate 4 is an insulating substrate such as a glass substrate, it is difficult to take out the lead wire using only the counter electrode material of the present invention.
In the case where the material is a conductive material, the counter electrode may be formed by directly providing the counter electrode material of the present invention on the substrate as shown in FIG.

By using this driving method, no difference in contrast between segments was observed, and even when the number of segments used for display changed, good display quality was exhibited with no change in contrast observed.

Furthermore, even when this device is energized by a normally used drive circuit that generates a drive wave type with bipolar pulses as shown in Fig. 3, conventional graphite or graphite with WO ₃ , TiO ₂ , Nb Compared to the counter electrode obtained by simply adding ₂ O ₅ and MnO ₂ , the coloring response was extremely fast and exhibited good characteristics.

In this way, a counter electrode that can color the EC material on the display electrode side, especially a transition metal oxide that has been appropriately treated to give a negative potential of about -0.4 to -1.0V, is used as the counter electrode. The EC element used has good response characteristics, and can be combined not only with the driving method shown in FIG. 4 but also with conventionally known driving methods, allowing various applications.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional side views showing a conventional EC element. FIG. 3 is a diagram showing voltage pulses in a conventionally known constant voltage driving method and changes in contrast ratio caused by the voltage pulses. FIG. 4 is a diagram showing a voltage application method that can obtain good results in combination with the EC element according to the present invention. Figure 5 is seen when an amorphous WO ₃ film is colored in a Li-based non-aqueous electrolyte. FIG. 3 is a diagram showing the relationship between the amount of injected electricity and the change in potential. Figure 6 shows the amount of electricity injected and the change in potential when an electrode obtained by mixing various oxides and graphite at a weight ratio of 7:1 and forming it into a plate shape is reduced in a Li-based non-aqueous electrolyte. Diagram showing. FIG. 7 is a cross-sectional side view showing an improved EC element according to the present invention. 1...Transparent substrate, 2...Transparent electrode, 3...EC
Substance, 4... Substrate, 5... Electrode, 6... EC material,
7... Sealing material, 8... Electrolyte, 9... Porous body,
10... Electrode prepared by mixing graphite or a mixture of graphite and EC substance with a binder, 11... Graphite and W ₂₀ O ₅₈ ,
or an electrode consisting of a mixture with W ₁₈ O ₄₉ .

Claims (1)

[Claims] 1. Between a display electrode substrate consisting of a transparent electrode formed on a transparent substrate and an electrochromic material layer formed on the transparent electrode, and a counter substrate, a counter electrode and the electrochromic material are provided. An electrochromic device comprising at least an electrolytic solution containing ions that can be colored, wherein the counter electrode has at least one of W ₁₈ O ₄₉ and W ₂₀ O ₅₈ . element.