JPH0149924B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a long-life electrochromic display ECD. Conventionally, there has been a device of this type as shown in FIG. In the figure, 1 is a glass plate, 2 is a transparent conductive film, 3 is an electrochromic EC material, 4 is a counter electrode, 5 is a spacer and a seal, 6 is a background plate, and 7
is an electrolyte. Electrolyte 7 is conventionally a propylene carbonate solution with the addition of _LiClO4 , but usually
Since Na and Na ⁺ ions are mixed in from the LiClO ₄ raw material, transparent conductive film, electrochromic material, counter electrode, and background plate, Li ⁺ ions are mixed in as ions in the electrolyte.
In addition, Na ⁺ also coexists. The action of Na ⁺ ions in the electrolyte 7 will be explained. Usually electrochromic substances such as WO ₃
The large amount of Li ⁺ ions in the electrolyte causes the reaction xLi ⁺ +xe ^- +WO ₃ →LixWO ₃ to produce lithium tungsten bronze, which is colored blue. However, the Na ⁺ ions present as impurities also undergo a similar reaction to form xNa ⁺ +xe ^- +WO ₃ →NaxWO ₃ , producing sodium tungsten bronze. However, in NaxWO ₃ , it was found that alkali ions were more difficult to return to the electrolyte through the reverse reaction than in LixWO ₃ , and Na components tended to accumulate more easily in the EC material. The Na component incorporated into the EC material tends to block new ions supplied from the electrolyte during coloring, resulting in a phenomenon in which the EC material becomes difficult to color even when a voltage is applied. For this reason, segments that are driven many times,
Color unevenness begins to occur between segments that are driven less frequently, and the display quality deteriorates, resulting in a shortened lifespan as an ECD. Based on this knowledge, the present invention provides a long-life ECD.
A transparent front substrate with a transparent conductive film and an electrochromic material formed thereon, and a back substrate with a counter electrode are sealed around the periphery and an electrolyte is contained inside. This electrochromic display device is characterized in that a mixture of a lithium salt and an organic solvent is used as the electrolyte, and a sodium component is removed from the electrolyte. In the present invention, sodium components are removed from the electrolyte. For this purpose, it is preferable to remove sodium components not only from the electrolyte itself but also from the materials inside the ECD that elute sodium components into the electrolyte. this
The materials inside the ECD include EC substances, background plates, sealants, injection port sealants, counter electrode materials, transfer materials, background plate fixtures or adhesives, and insulating overcoat materials, but most of them are sodium-based. Items that have no sodium components, items that hardly elute sodium components, or items that are covered with other materials so that sodium components do not elute from that material do not require special treatment to remove sodium components. . Removal of sodium components in the present invention does not mean to completely remove sodium components from each material, but rather to reduce the sodium components that those materials normally have, that is, that are mixed in from raw materials. It means. For this reason, there are two ways to remove sodium: a method that reduces the sodium content by treating commercially available materials to remove sodium, and a method that uses raw materials with almost no sodium content to produce materials with a low sodium content. . The lower the amount of sodium remaining in the electrolyte, the better. It is preferable to keep the number of cations that can be taken in by the EC substance used in ECD to be 100% or less, so that coloring is easy even when running for a long time, and color unevenness between segments is less likely to occur.
The effect is remarkable by keeping it below 20%. In addition, EC substances usually have a small amount of sodium component in their raw materials, which is significantly less than the sodium component present in the electrolyte, but the sodium component already accumulated in the EC material Therefore, the influence is greater than that of the sodium component present in the electrolyte, and it is therefore preferable to carry out a sodium component removal treatment. This amount of sodium is usually a small amount, less than 0.1% compared to the number of cations that can be taken up by the EC substance, but it has been found that even when only sodium component removal treatment is performed, a clear effect of extending the lifespan has been found. Ta. Of course, it is also important to desodium the electrolyte itself and the materials that come into contact with it and cause the elution of sodium components, and it is preferable to keep the amount of residual sodium as described above. Examples of the present invention will be described below. A transparent conductive film of In ₂ O ₃ SnO ₂ was formed on a glass substrate with a 2000 Å thick SiO ₂ overcoat layer, and WO ₃ was evaporated as an EC material on the surface substrate, carbon, and manganese dioxide. A back substrate having a system counter electrode was sealed with a porous alumina background plate via a spacer to form a cell. Lithium perchlorate in this ECD cell
An electrolyte consisting of 1 mol/dissolved propylene carbonate was injected, and the injection port was sealed to prepare a test cell. Table 1 shows the amount of sodium component in each material. This amount is calculated by calculating the amount of sodium that can be eluted from the amount of each material placed in the cell, assuming that the amount of cations that can be taken up is 1 for 8.9 μg of EC substance in the cell. Also, the electrolyte was approximately 0.12cc.

[Table] In Table 1, lithium perchloride is shown by the amount actually dissolved, and other materials are shown by the amount of sodium eluted. As a result, those in which almost no sodium component was detected, such as transparent conductive films and propylene carbonate, were marked with a △ mark. In addition,
Since the EC material contained a sodium component of approximately 0.03% of the number of cations that the EC material could incorporate, a sodium component removal process was further performed before vapor deposition. Since lithium perchlorate contains a large amount of sodium as an electrolyte, after mixing it with propylene carbonate, the sodium component was selectively separated using an ultra-high purity ion exchanger, zirconium phosphate. During the operation process, no glass or metal jigs were used, but fluorine resin or quartz jigs that had been thoroughly cleaned with high-purity hydrochloric acid were used. Further, the counter electrode material, spacer, and background plate were washed with heated high-purity perchloric acid, and then dehydrated by heating under reduced pressure. For the EC substance material, the raw material powder before vapor deposition was washed with heated high-purity perchloric acid, and then the EC substance film was formed by vapor deposition using the same raw material that was dried by vacuum heating and dehydration. In this way, sodium components were removed.
We formed an ECD cell and conducted a drive test to compare it with an ECD cell with a conventional configuration. The results are shown in FIG. Figure 2A shows the ECD cell of the present invention, and when the sodium component in the electrolyte was measured by atomic absorption spectrometry before operation, it was found that 20% of the amount of cations that can be adsorbed by WO ₃
%, there was almost no change in contrast until about 10 ⁶ times, and the contrast decreased slightly after about 5 x 10 ⁶ times. On the other hand, the conventional configuration shown in B
A clear decrease in contrast occurred after approximately 10 ⁶ times of driving. In the present invention, by reducing the sodium components eluted and remaining in the electrolyte in this manner, it is possible to obtain an ECD that is less likely to cause a decrease in contrast. In addition, although the method for removing Na from the electrolytic solution 7 was explained in the above example, the same effect can be obtained even if high-purity Li is prepared and dissolved in an organic solvent to prepare the electrolytic solution 7. can get. As a method for synthesizing high-purity Li salt, ultra-high purity Li metal may be used as the starting material. Note that the structure of the ECD is not limited to the above embodiments, and may include a third electrode, an EC material for the counter electrode, a concave substrate as the back substrate, a liquid crystal element using a ceramic substrate, a metal substrate, Various applications such as laminating color filters, ultraviolet cut filters, and masks, and providing transfers are also possible. As described above, according to the present invention, since Na is removed from the element components, an electrochromic display device with a long life can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an electrochromic display device. 1 glass plate, 2 transparent conductive film, 3 electrochromic material, 4 counter electrode, 5 spacer and seal, 6 background plate, 7 electrolyte. FIG. 2 is a graph showing the relationship between the number of color development/decolorization drives and contrast. (a) An electrochromic display device of the present invention; (b) A conventional electrochromic display device.

Claims (1)

[Claims] 1. A transparent front substrate having a transparent conductive film and an electrochromic substance formed thereon, and a back substrate having a counter electrode, sealed around the periphery and filled with an electrolyte. An electrochromic display device characterized in that a mixture of a lithium salt and an organic solvent is used as an electrolyte, and a sodium component is removed from the electrolyte. 2. The electrochromic display device according to claim 1, wherein the remaining amount of sodium component in the electrolyte is 20% or less of the number of cations that can be taken up by the electrochromic substance.