JPS63104030A - Electrochromic display device - Google Patents

Abstract

PURPOSE:To obtain a low-cost counter electrode for an electrochromic display device having superior flexibility by using fine carbon powder and fine polytetrafluoroethylene powder. CONSTITUTION:When an electrochromic display device having a display electrode 1, a counter electrode 2 and an electrolyte 5 is produced, the counter electrode 2 is formed with fine carbon powder and fine polytetrafluoroethylene powder 12. Since the electrochemically active fin carbon powder 11 having a large specific surface area is bonded by the fine polytetrafluoroethylene powder 12, a low-cost counter electrode 2 having superior flexibility and satisfactory electrochemical characteristics can be formed. The counter electrode enables the production of a low-cost electrochromic display device having high reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an electrochromic display element in which the light absorption characteristics of a display electrode are changed by electrochemical oxidation or reduction.

[Prior art and its problems]

With the development of electronics, display elements have become indispensable. Display elements can be roughly divided into self-luminous types such as electroluminescence, and non-luminous types such as liquid crystal.

Electrochromic display elements belong to the latter non-emissive type, and perform reversible coloring/decoloring reactions by electrochemically controlling light absorption characteristics.

As shown in FIG. 3, the electrochromic display element is
The background plate 4 is composed of a display electrode 1 prepared by depositing iron phthalocyanine as an electrochromic substance on a transparent electrode such as TO, an electrolyte 5 such as a saturated potassium chloride aqueous solution, a counter electrode 2, etc. Highlighting the coloring of the electrode 1, the Luggin tubule 3 precisely controls the potential of the display electrode 1 via the reference electrode.

When the potential of the iron phthalocyanine (F, PC) H surface water electrode on the display electrode is changed, its absorption property changes and the color changes. For example, when the potential of the display electrode is Ov with respect to the reference electrode of the saturated Amagi electrode, the color is blue.

When cathodically reduced at -1.3V, it becomes red. On the contrary, +1
．． When anodic oxidation is performed at 3VK, the color becomes yellow. Since the coloring of iron-7 thalocyanine changes reversibly depending on the potential of the display electrode, it is considered to be promising as a color display element.

Conventionally, the counter electrode of such an electrochromic display element is a noble metal electrode such as a platinum electrode, or a noble metal electrode such as a platinum electrode, or
As disclosed in No. 4533, an electrode is known in which a counter electrode material such as iron nitungstate or manganese dioxide is bonded and molded with carbon paste (contains a small amount of epoxy resin, and this epoxy resin has a binding effect). There is.

However, the disadvantage of using platinum electrodes is that they are expensive, and the counter electrodes molded from the counter electrode material and carbon paste are not flexible and cannot be self-supported by themselves, so they always require a substrate and are not uniform. There were problems such as difficulty in forming a film due to its thickness.

[Purpose of the invention]

The present invention has been made in view of the above points, and its object is to provide a counter electrode for an electrochromic display element that is inexpensive and has excellent flexibility.

[Key points of the invention]

The present invention achieves its purpose in an electrochromic display element having a display electrode, a counter electrode, and an electrolyte, since the counter electrode is formed using fine carbon powder and fine powder of polytetrafluoroethylene.

In other words, the carbon fine powder is facing 1! It is intended to be used as an electrode material and a conductive material, and to bond fine carbon powder with polytetrafluoroethylene fine powder.

[Embodiments of the invention]

Next, embodiments of the present invention will be described based on the drawings. Carbon black with a specific surface area of 10 Onl//l 10.
9 was well dispersed in 400 tnl of water using ultrasonic waves, 800 ml of isopropyl alcohol was added thereto, and the materials were thoroughly mixed. This plus 0.1 to 03
Polytetrafluoroethylene (PT) with a particle size of μm
(abbreviated as FE) 10. V was added, and the resulting mixture was formed into a sheet with a thickness of 0.2 m using a calender roll. After drying this, fire it at 350 tl and face it! It was cold (
(See Figure 1) 0 For comparison, the comparative area is 10tr? /g and 30d/g of graphite and 60m2/g, 200trl/&
Similar counter electrodes were prepared using carbon black of , 500 m2/9 and 800 m2/p.

The electrode after firing was cut into a size of 10α×10cts, and the film thickness was measured at nine points in total, including a point 1ctR inside each side and a point in the center, and the average value and deviation were determined.

Table 1 summarizes the difficulty of molding during the production of the sheet, the average value and deviation of the film thickness after firing, and the appearance after firing.

Table 1 As shown in Table 1, the specific surface area of carbon fine powder is 60
Or 20 On? It can be seen that when carbon black of /fl is used, moldability, reproducibility of film thickness, and appearance are good.

Next, corrosion of the opposing electrode 1a after firing was investigated.

Since the carbon electrode is corroded by anodic oxidation, the amount of corrosion is determined in relation to the specific surface area of the carbon fine powder. For this purpose, the electrode after firing was immersed in a saturated potassium chloride aqueous solution at a temperature of 20°C, and the temperature was +1. O.V.
A potential of was applied. Constant potential anodic oxidation was performed by holding this potential for 10 hours, and the amount of corrosion of the counter electrode after firing was determined from the anode current at that time. Carbon transferred into the solution due to corrosion has an adverse effect on the reversible coloring and decoloring of the display electrode.

Table 2 Table 2 shows the results. It can be seen that the amount of corrosion of carbon is smaller as the specific surface area is smaller.

Next, using carbon black with a specific surface area of 100 m2/I, PTFE was added as a binder during sheet molding.
We considered the quantity. The results are shown in Table 3.

Table 3 Table 3 shows carbon black 10 as the amount of PTFE added.
It is shown that when 20 to 200 parts by weight of PTFE is added to 0 parts by weight, moldability is good and the obtained film has excellent flexibility. However, since 20 parts by weight of PTFE causes a large amount of electrode corrosion, the appropriate amount of PTFE is in the range of 50 to 200 parts by weight.

Within this range, the film thickness reproducibility is good and the appearance is also good.

Based on the above basic studies, we prepared counter electrodes with various combinations of the specific surface area of carbon fine powder and the added amount (parts by weight) of PTFE, and deposited iron phthalocyanine on these and ITO transparent electrodes. An electrochromic display element as shown in Fig. 3 is constructed by combining the display electrodes, and a repetitive rectangular wave voltage of OV, -1, and 3V for 2 seconds each is applied to the display electrodes with the saturated Amagi reference electrode as a reference. (See Figure 2) We observed the reversible red and blue color change of iron phthalocyanine on the display electrode.For comparison, we used a platinum electrode as a counter electrode and a specific surface area of 100 tr? /g carbon black 10g, PTFE 10.9 and iron tungstate 10
A case in which a counter electrode formed by the above method was also used was also investigated. The results are shown in Table 4.

Table 4 Here, "defective" means deterioration of coloring. Specific surface area is 60
When the counter electrode is prepared using 50 to 200 parts by weight of carbon black and 50 to 200 parts by weight of PTFE, the resulting film has excellent flexibility, good reproducibility of film thickness, and good appearance. Also, the amount of electrode corrosion is small.0 When this film is used as a counter electrode to construct an electrochromic display element, as shown in Table 4, even after 50,000 repeated operations, the resistance is lower than when a platinum electrode is used as a counter electrode. Equivalent color change and no color regression.

〔Effect of the invention〕

According to this invention, in an electrochromic display element having a display electrode, a counter electrode, and an electrolyte, the counter electrode is formed using fine carbon powder and fine powder of polytetrafluoroethylene, so that electricity can be generated with a high specific surface area. Chemically active carbon fine powder is bound with polytetrafluoroethylene fine powder, and as a result, it is possible to prepare a counter electrode that is inexpensive, has excellent flexibility, and has good electrochemical properties.
Using this, it becomes possible to construct an inexpensive and highly reliable electrochromic display element.

[Brief Description of the Drawings] Fig. 1 is a schematic cross-sectional view showing a counter electrode according to an embodiment of the present invention, and Fig. 2 is a voltage applied to the display electrode of an electrochromic display element using the counter electrode according to an embodiment of the present invention. FIG. 3 is a side view showing the structure of the electrochromic display element. 2...Counter electrode, 11...Carbon fine powder, 12...PTFE fine powder. Figure 1

Claims (1)

[Claims] 1) An electrochromic display element comprising a display electrode, a counter electrode, and an electrolyte, characterized in that the counter electrode is formed using fine carbon powder and fine powder of polytetrafluoroethylene. Electrochromic display element. 2) In the display element according to claim 1, the carbon fine powder has a specific surface area of 60 m^2/g to 200 m^2/g.
An electrochromic display element characterized by using carbon black of m^2/g. 3) An electrochromic display element according to claim 1 or 2, characterized in that 50 to 200 parts by weight of polytetrafluoroethylene is added to 100 parts by weight of carbon black.