Gel electrolyte composition for electrochromism and flexible electrochromism device

Abstract

The invention discloses a gel electrolyte composition for electrochromism and a flexible electrochromism device, and belongs to the technical field of electronic devices. The gel electrolyte composition comprises a monofunctional monomer, a polar solvent, a sodium salt and a photoinitiator, in the gel electrolyte composition, the sodium salt is used for replacing the lithium salt, so that the production and use safety is improved, and the ionic conductivity of the gel electrolyte composition is higher than that of an equivalent lithium salt system under the synergy of the polar solvent. The gel electrolyte composition also uses a monofunctional monomer with a glass transition temperature of less than 10 DEG C, and the monofunctional monomer with a low glass transition temperature can form an electrolyte layer with high adhesion with a polar solvent after being subjected to photoinitiator polymerization, so that the interface adhesion between the electrolyte layer and an electrochromic layer and between the electrolyte layer and a transparent conductive film is improved. According to the invention, the sodium salt is applied to the gel electrolyte of the flexible electrochromic device to replace the traditional lithium salt for the first time, so that the prepared flexible electrochromic device has rapid color fading performance and better color fading contrast.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic devices, and particularly relates to a gel electrolyte composition for electrochromism and a flexible electrochromic device. Background Art

[0002] Electrochromism refers to the phenomenon that electrochromic materials of a material undergo oxidation and reduction in a corresponding electrochemical reaction system, resulting in stable and reversible color changes in the optical properties (reflectivity, transmittance, absorbance, etc.) of the material, and appearing as reversible changes in color and transparency in appearance. Electrochromic devices have great potential in decoration, display, smart windows, automotive anti-glare rearview mirrors, automotive sunroof dimming, building dimming, etc.

[0003] Electrochromic devices can be classified into three types from a structural perspective: solution type, hybrid type, and thin film type. The device structure of the solution type is relatively simple, generally consisting of a transparent conductive layer, an electrochromic layer, and a transparent conductive layer. The electrochromic layer is composed of an electrolyte, an electrochromic material, and a solvent, and its form is generally a solution. The electrochromic material is generally an organic small molecule (viologen, dye, etc.). Such devices have been widely used in fields such as automotive anti-glare rearview mirrors. The device structure of the hybrid type generally consists of a transparent conductive layer, an electrochromic layer, an electrolyte layer, and a transparent conductive layer. The electrochromic layer is generally a transition metal oxide or a conjugated polymer. The electrolyte layer uses the electrochromic layer of the solution type device to achieve more color conversions and more stable ion storage. The structure of the thin film type electrochromic device is a transparent conductive layer, an electrochromic layer, an electrolyte layer, an ion storage layer, and a transparent conductive layer. The electrochromic layer and the ion storage layer are generally transition metal oxides or conjugated polymers, and can be selected according to the optical properties of oxidation and reduction. In some structures, the electrolyte layer or the transparent conductive layer can also be used as an ion storage layer.

[0004] Electrochromic devices can be classified according to the selection of the substrate of the transparent conductive layer. Those using glass as the substrate of the transparent conductive layer can be called rigid electrochromic devices, and those using plastic film as the substrate of the transparent conductive layer are called flexible electrochromic devices.

[0005] Since the electrolyte layer or the electrochromic layer using a solution in solution type and hybrid type electrochromic devices is prone to leakage and difficult to encapsulate, and the organic small molecules contained therein have poor weather resistance and short cycle life, it is difficult to use them to manufacture flexible electrochromic devices. Therefore, the structure of thin film type electrochromic devices is the current research focus for the industrialization of flexible electrochromic devices.

[0006] As an optoelectronic component, the electrolyte layer is crucial in flexible electrochromic devices. First of all, the electrolyte layer needs to meet the optical requirements of high light transmittance and low haze. Secondly, the electrolyte layer also seriously affects the coloring / fading response time, coloring / fading contrast, etc. of the device, and its main parameters are ion conductivity and electrochromic layer matching. Finally, in the processes of production, manufacturing, processing and die-cutting, etc., in order to prevent layer peeling of the device during bending or die-cutting, the electrolyte layer also needs to have sufficient adhesion for bonding the electrochromic layer and the transparent conductive layer, but this point has not been mentioned in the currently published literature.

[0007] Gel electrolytes are mainly composed of polymers, high-boiling solvents and electrolyte salts, and their ion conductivity is much higher than that of solid electrolytes. Due to the characteristics of easy processing, fast reaction gel and high production efficiency of the photocuring reaction, the lithium salt gel electrolyte based on the photocuring reaction has been widely studied in the field of flexible electrochromics. However, traditional lithium salts, etc. have strong corrosiveness and toxicity, and safety accidents often occur in the production process, and the packaging requirements are extremely high. For example, the common lithium salt lithium hexafluorophosphate belongs to Class 6.1 hazardous chemicals in the MSDS. Contact with skin, inhalation or ingestion may all cause poisoning, and long-term exposure can lead to respiratory system damage. In addition, the cost of lithium salts is high and the price fluctuates greatly (70 - 600 yuan / kg). Therefore, it is urgent to find electrolyte salts with low price and higher safety, while taking into account gel electrolytes with high ion conductivity.

[0008] In the Chinese invention patent CN2022105207370, a scheme of using ionic liquids to replace lithium salts as electrolyte compositions for electrochromic devices is disclosed. Although ionic liquids have good safety, the addition amount of ionic liquids > 30%, and the cost is extremely high (> 500 yuan / kg), making it difficult to commercialize. Sodium salts have the advantages of good safety, small addition amount (addition amount < 10%) and low cost (< 50 yuan / kg). However, the existing research on sodium salt-based gel electrolytes mostly focuses on the field of sodium ion batteries. In the battery field, aluminum foil and copper foil are generally used as conductive substrates, hard carbon is used as the negative electrode, and polyanion is used as the positive electrode. While flexible electrochromic devices commonly use ITO-PET as the transparent conductive substrate and conductive polymers as the cathode or anode. Therefore, there are huge differences between the requirements of sodium ion batteries and electrochromic devices (such as optical transparency, interfacial adhesion, electrochemical corrosion, etc.). There is a blank in the field of electrochromics for sodium salt-based gel electrolytes. Therefore, it is also of great significance to apply sodium salts to the field of electrochromic devices. Summary of the Invention

[0009] In view of the deficiencies of the prior art, the first object of the present invention is to provide a gel electrolyte composition for electrochromism. Through the combination of a sodium salt and a monofunctional monomer with a low glass transition temperature, and synergistically with a polar solvent, free radicals are generated by an ultraviolet photoinitiator, and the monofunctional monomer free radicals are rapidly polymerized to form a sodium salt gel electrolyte with good optical properties, which has better safety and ionic conductivity compared with a lithium salt gel electrolyte.

[0010] The second object of the present invention is to provide a flexible electrochromic device comprising the gel electrolyte composition for electrochromism. The electrolyte layer formed by the gel electrolyte composition has better coloration-fading contrast and response time in the flexible electrochromic device, and has good adhesion to the interfaces of the electrochromic layer and the transparent conductive film.

[0011] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0012] A gel electrolyte composition for electrochromism, characterized by comprising the following components in parts by mass:

[0013]

[0014] In the above-mentioned gel electrolyte composition for electrochromism, the monofunctional monomer is selected from monomers with a glass transition temperature < 10 °C, including but not limited to one or more combinations of 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, tetrahydrofurfuryl acrylate, methoxypolyethylene glycol monacrylate, and ethoxyethoxyethyl acrylate;

[0015] Preferably, the monofunctional monomer is selected from one or more combinations of 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxybutyl acrylate.

[0016] In the above-mentioned gel electrolyte composition for electrochromism, the polar solvent is selected from solvents with a boiling point > 150 °C, including but not limited to one or more combinations of ethylene carbonate, propylene carbonate, butylene carbonate, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide;

[0017] Preferably, the polar solvent is selected from one or more combinations of propylene carbonate and N-methylpyrrolidone.

[0018] In the above-mentioned gel electrolyte composition for electrochromism, the sodium salt is selected from one or more combinations of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium bis(oxalato)borate, sodium trifluoromethyltrifluoroborate, sodium pentafluoroethyltrifluoroborate, sodium heptafluoropropyltrifluoroborate, sodium nonafluorobutyltrifluoroborate, and sodium tris(trifluoromethanesulfonyl)methyl;

[0019] Preferably, the sodium salt is selected from one or more combinations of sodium hexafluorophosphate, sodium tetrafluoroborate, and sodium bis(fluorosulfonyl)imide.

[0020] For the above-mentioned gel electrolyte composition for electrochromism, the photoinitiator is selected from one or more combinations of 2,4,6-trimethylbenzoyldiphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoyl phenylphosphinate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one, 2-(4-methylbenzyl)-2-(dimethylamino)-1-(4-morpholinophenyl)butan-1-one, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, and 2-isopropylthioxanthone;

[0021] Preferably, the photoinitiator is selected from ethyl 2,4,6-trimethylbenzoyl phenylphosphinate.

[0022] A flexible electrochromic device, characterized in that it includes an electrolyte layer, and the electrolyte layer is prepared by photocuring the above-mentioned gel electrolyte composition for electrochromism.

[0023] For the above-mentioned electrolyte layer, it is characterized in that: the thickness of the electrolyte layer is 5-100 μm, the photocuring uses ultraviolet light with a wavelength of 200-450 nm, and the light intensity ≥ 500 mW / cm 2 , and the curing time ≤ 10 seconds.

[0024] A flexible electrochromic device, characterized in that the flexible electrochromic device sequentially includes: a transparent conductive film, an electrochromic layer, an electrolyte layer, and a transparent conductive film.

[0025] The aforementioned transparent conductive film refers to a glass with a transparent conductive layer formed by coating or plating a transparent conductive material on a plastic substrate. The thickness of the transparent conductive layer is 50-500 nm, and the sheet resistance is 1-500 ohms. The type, thickness, and sheet resistance of the transparent conductive material are not limited and can be appropriately selected according to the purpose.

[0026] The aforementioned transparent conductive materials include but are not limited to inorganic materials such as indium tin oxide (ITO) doped with tin, gallium zinc oxide doped with titanium (GZO), antimony-doped tin oxide (ATO), fluorine-doped tin oxide (FTO), transparent carbon nanotubes, silver nanowires, gold nanowires, platinum nanowires, and copper nanowires, or one or more combinations thereof.

[0027] The aforementioned electrochromic layer can be one or more combinations of polyaniline, polypyrrole, polythiophene and its derivatives, transition metal oxides, and hexacyano metal salts.

[0028] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0029] 1. The lithium salts used in traditional gel electrolytes are highly corrosive and toxic, while the gel electrolyte composition for electrochromic use in the present invention uses sodium salts (such as NaPF 6 , NaFSI, etc.), which have more stable chemical properties and high safety in production and use;

[0030] 2. After the gel electrolyte composition for electrochromic use in the present invention undergoes photoinitiator polymerization to form a gel electrolyte layer, with the synergistic effect of polar solvents, its ionic conductivity is higher than that of the equivalent lithium salt system;

[0031] 3. The monofunctional monomer with a low glass transition temperature used in the present invention has the advantages of low viscosity and high double bond conversion rate. After photoinitiator polymerization, it can form an electrolyte layer with high adhesion force with polar solvents, improving the interfacial adhesion force between the electrolyte layer and the electrochromic layer and the transparent conductive film;

[0032] 4. The present invention first applies sodium salts to the gel electrolyte composition of flexible electrochromic devices to replace traditional lithium salts. The flexible electrochromic devices prepared thereby have fast coloring and fading performance and better coloring and fading contrast. Description of the Drawings

[0033] Figure 1 Photograph of the gel electrolyte composition for electrochromic use after photocuring in Example 1

[0034] Figure 2 Photograph comparison of the colored states of the flexible electrochromic devices prepared in Example 1 (left) and Comparative Example 1 (right)

[0035] Figure 3 Photograph comparison of the faded states of the flexible electrochromic devices prepared in Example 1 (left) and Comparative Example 1 (right)

[0036] Figure 4 Adhesion force test comparison diagram between Example 1 and Comparative Example 4

[0037] Figure 5 Coloring and fading spectral curve of the flexible electrochromic device prepared in Example 1 Detailed Description of the Invention

[0038] The gel electrolyte composition for electrochromism and the flexible electrochromic device provided by the present invention. The gel electrolyte composition is made of the following components by weight: 50 - 90 parts of monofunctional monomer; 9 - 40 parts of polar solvent; 0.5 - 5 parts of sodium salt; 0.3 - 5 parts of photoinitiator. In the gel electrolyte composition, sodium salt is used to replace lithium salt, which improves the safety of production and use. And with the coordination of the polar solvent, its ionic conductivity is higher than that of the equivalent lithium salt system. In the gel electrolyte composition, a monofunctional monomer with a glass transition temperature < 10 °C is also used. After the photoinitiator polymerization, the monofunctional monomer with a low glass transition temperature can form an electrolyte layer with high adhesion force with the polar solvent, enhancing the interfacial adhesion force between the electrolyte layer and the electrochromic layer and the transparent conductive film. The flexible electrochromic device prepared with this gel electrolyte composition has fast coloring and fading performance and better coloring and fading contrast.

[0039] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only demonstrations or examples of applying the principles of the present invention. Those skilled in the art can design many variations and alternative compositions, methods, and systems without departing from the spirit and scope of the present invention, and all fall within the protection scope of the present invention.

[0040] The raw materials used in the embodiments of the present invention are shown in Table 1 below

[0041] Table 1 Raw Materials for Embodiments

[0042]

[0043]

[0044] Example 1

[0045] Preparation of Gel Electrolyte Composition for Electrochromism

[0046] Mix 2.5 g of NaPF 6 , 70 g of HEA, and 26.5 g of PC together in a beaker, heat to 60 °C and stir to dissolve for 120 min. Then add 1 g of TPO-L and stir for another 30 min to obtain the gel electrolyte composition for electrochromism.

[0047] Preparation of Flexible Electrochromic Device

[0048] A PEDOT:PSS coating was applied as an electrochromic layer on an ITO-PET film (sheet resistance 20 Ω / sq, light transmittance 85%) using a 50-μm wire bar and dried at 100 °C for 3 min. Then, the prepared gel electrolyte composition for electrochromics was directly coated on the electrochromic layer using a 50-μm doctor blade, and then laminated with an ITO-PET (sheet resistance 20 Ω / sq, light transmittance 85%) film; thereafter, a LED curing light source with a light intensity of 1000 mW / cm2 and an emission wavelength of 395 nm was used to initiate the curing of the gel into an electrolyte layer, and finally a flexible electrochromic device was obtained; the flexible electrochromic device was cut into a size of 5 cm × 5 cm, and various performance indexes of the flexible electrochromic device were tested.

[0049] The specific component ratios of Examples 2 to 14 and Comparative Examples 1 to 5 are shown in Table 2. The preparation methods of Examples 2 to 14 and Comparative Examples 1 to 5 are similar to that of Example 1 and will not be elaborated herein.

[0050] Performance test and evaluation of the gel electrolyte composition for electrochromics and the flexible electrochromic device:

[0051] 1. Leakage

[0052] One layer of the ITO-PET film of the flexible electrochromic device was torn off, and while wearing gloves, the electrolyte layer was pressed firmly with fingers for observation and evaluation.

[0053] ◎: Solid film-like, no liquid transferred to the gloves;

[0054] ○: Viscoelastic, liquid transferred to the gloves;

[0055] ×: Liquid-like, liquid transferred to the gloves.

[0056] 2. Curing time

[0057] A stopwatch was used to record the time when the gel electrolyte composition for electrochromics was completely gelled.

[0058] 3. Adhesion

[0059] A universal tensile testing machine was used to test the adhesion between the electrolyte layer and the transparent conductive layer and the electrochromic layer in the flexible electrochromic device.

[0060] 4. Coloration and fading performance

[0061] The flexible electrochromic device was subjected to 10 coloration and fading performance tests at a driving voltage of 3 V using a DC power supply. A stopwatch was used to record the coloration and fading times respectively. Finally, a haze meter was used to test the colored light transmittance and faded light transmittance of the flexible electrochromic device, and the difference in light transmittance △T between the colored state and the faded state was calculated;

[0062] 5. Light transmittance and haze

[0063] Use two glass slides, control the gap at 200 μm, inject the gel electrolyte composition, and then perform photocuring to obtain the electrolyte film. Take out the electrolyte film and test the transmittance and haze.

[0064] 6. Test the bleaching spectral curve

[0065] Use a UV-visible spectrophotometer to test the spectral curve in the bleaching state.

[0066] 7. Ionic conductivity

[0067] Use an electrochemical workstation to measure the AC impedance of the electrolyte film at 30 °C, and calculate the conductivity of the electrolyte film through the formula σ = 1 / (R·S).

[0068] Table 2: Formulations and performance test results of examples and comparative examples

[0069]

[0070] In Comparative Example 1 and Comparative Example 2, LiPF 6 and KPF 6 are used respectively, and the ionic conductivity is still much lower than that of Example 1, indicating that the monofunctional monomer with a low glass transition temperature in the present invention has obvious selectivity for sodium salts under the synergistic effect of polar solvents. It can be seen more clearly from the appendix Figure 2 that under the same voltage drive, the electrochromic effect of Example 1 is significantly better than that of Comparative Example 1.

[0071] HEA (glass transition temperature -15 °C) is used in Example 1 and CTFA (glass transition temperature 10 °C) is used in Comparative Example 3 for comparison. The result is that the ionic conductivity of using CTFA has a large decrease, and the adhesion and △T of the prepared flexible electrochromic device are both poor, indicating that the glass transition temperature has a great influence on the migration of sodium ions.

[0072] In Example 1, the monofunctional monomer HEA (glass transition temperature -15 °C) and the bifunctional monomer PEG(600)DA (glass transition temperature -42 °C) are used in Comparative Example 4. Although the ionic conductivity reaches 2.59 S / cm, it can be seen from Figure 4 that the adhesion of Comparative Example 4 is low, and the △T of the prepared flexible electrochromic device is poor. It shows that the adhesion has an obvious influence on the attenuation of the flexible electrochromic device. The inventor of the present invention speculates that because the bifunctional monomer does not contain hydroxyl groups and has poor cohesive force, which affects the adhesion, resulting in interface debonding and serious device attenuation due to the repeated migration of sodium ions after the bleaching and coloring performance tests.

[0073] In Comparative Example 5, the ionic conductivity of the monofunctional oligomer 65352 (glass transition temperature -42 °C) used was still low, and the adhesion, △T, and cycle life of the prepared flexible electrochromic device were all poor. The inventor speculated that it was due to the relatively high molecular weight of the oligomer, the restricted movement of molecular segments, and the few ionic channels formed in the electrolyte layer during the photocuring process, resulting in difficult sodium ion migration.

[0074] Finally, it should be emphasized that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A gel electrolyte composition for electrochromic application, characterized in that The composition comprises the following components in parts by weight: 50-90 parts of monofunctional monomer; 9 to 40 parts of polar solvent; 0.5-5 parts of sodium salt; 0.5 to 5 parts of photoinitiator.

2. The electrochromic gel electrolyte composition according to claim 1, characterized in that: The monofunctional monomer is selected from monomers with a glass transition temperature of less than 10°C, including but not limited to a combination of one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, tetrahydrofuran acrylate, methoxy polyethylene glycol monoacrylate, and ethoxyethoxyethyl acrylate.

3. The electrochromic gel electrolyte composition according to claim 1, characterized in that: The polar solvent is selected from solvents with a boiling point greater than 150° C., including but not limited to one or more combinations of ethylene carbonate, propylene carbonate, butylene carbonate, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

4. The electrochromic gel electrolyte composition according to claim 1, characterized in that: The sodium salt is selected from the group consisting of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium bis(oxalatoborate), sodium trifluoromethyl trifluoroborate, sodium pentafluoroethyl trifluoroborate, sodium heptafluoropropyl trifluoroborate, sodium nonafluorobutyl trifluoroborate, and sodium tris(trifluoromethanesulfonyl)methyl.

5. The electrochromic gel electrolyte composition according to claim 1, characterized in that: The photoinitiator is selected from 2,4,6-trimethylbenzoyldiphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 1-hydroxycyclohexyl benzophenone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, 2-(4-methylbenzyl)-2-(dimethylamino)-1-(4-morpholinophenyl)-1-butanone, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone, and a combination of one or more thereof.

6. A flexible electrochromic device, characterized in that The invention comprises an electrolyte layer, wherein the electrolyte layer is prepared by photocuring the electrochromic gel electrolyte composition according to any one of claims 1 to 5.

7. The electrolyte layer of a flexible electrochromic device according to claim 6, characterized in that: The thickness of the electrolyte layer is 5-100 μm, and the light curing uses ultraviolet light with a wavelength of 200-450 nm and a light intensity of ≥500 mW / cm 2 , curing time ≤10s.

8. A flexible electrochromic device according to claim 6 or 7, characterized in that: The flexible electrochromic device comprises in sequence: a transparent conductive film, an electrochromic layer, an electrolyte layer, and a transparent conductive film.

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