A method for preparing water-soluble PEDOT-S and its application in solid-state capacitors after conversion to water-insoluble PEDOT.

Abstract

This invention discloses a method for preparing water-soluble PEDOT-S and its conversion into water-insoluble PEDOT for use in solid-state capacitors, belonging to the field of capacitor technology. The method includes: providing water-soluble EDOT monomer; dissolving the water-soluble EDOT monomer in deionized water, adding a catalyst, and stirring until homogeneous to obtain a mixed solution; adding an oxidant solution dropwise to the mixed solution under nitrogen protection to initiate a reaction, obtaining an intermediate product after the reaction is complete; and treating the intermediate product with a dialysis membrane or ion exchange resin to remove low-molecular-weight byproducts, obtaining a water-soluble PEDOT-S solution. The beneficial effects of this invention are: by drying at a certain temperature to convert the water-soluble PEDOT-S cathode into a water-insoluble PEDOT cathode, this temperature-controlled conversion mechanism allows the capacitor to maintain stable capacitance performance during application while avoiding water absorption during long-term storage.

Description

Technical Field

[0001] This invention relates to the field of capacitor technology, specifically to a method for preparing water-soluble PEDOT-S and its application in solid-state capacitors after conversion into water-soluble PEDOT. Background Technology

[0002] Conductive polymers are widely used in electronic components due to their excellent conductivity and electrochemical stability, especially in solid-state capacitors, where they are often used as anode or cathode materials. Traditional poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) dispersions hold an important position in solid-state capacitor cathode materials due to their high conductivity and flexibility. However, PEDOT:PSS has revealed several technical drawbacks in practical applications. Its dispersion particles are relatively large, requiring high-pressure homogenization to achieve uniform dispersion. However, high-pressure homogenization not only places high demands on equipment and increases manufacturing costs but also limits the large-scale industrial application of the material. Furthermore, PEDOT:PSS dispersions are prone to stratification during long-term storage, and their conductivity decreases significantly over time, resulting in poor storage stability and affecting the reliability and lifespan of the final product. Its high viscosity further limits its applicability in fine coating processes, easily leading to uneven coatings and negatively impacting the performance of solid-state capacitors.

[0003] To address the aforementioned issues, the water-soluble self-doped conductive polymer PEDOT-S (sulfonated poly(3,4-ethylenedioxythiophene)) provides a solution. However, capacitors made using water-soluble PEDOT-S as a cathode exhibit unstable performance and absorb water during long-term storage, severely impacting capacitor performance. Therefore, the water absorption problem has become a pressing technical challenge for the application of water-soluble PEDOT-S in capacitors. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing water-soluble PEDOT-S and its conversion into water-insoluble PEDOT for use in solid-state capacitors. By introducing self-doped functional groups (such as sulfonic acid groups) into the molecular structure, PEDOT-S achieves self-dispersion, eliminating the need for additional external dopants. Its optimized aqueous polymerization process can directly prepare conductive polymer solutions with small and uniform particle sizes, without the need for high-pressure homogenization, significantly reducing preparation costs and equipment complexity. Simultaneously, by using a temperature-controlled method to convert water-soluble PEDOT-S into water-insoluble PEDOT, not only can the stability of the capacitor be improved, but the problem of water absorption during long-term storage is also solved. Therefore, at least one of the technical problems mentioned in the background art can be addressed.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0006] This invention provides a method for preparing water-soluble PEDOT-S, comprising the following steps:

[0007] Step S1: Provide water-soluble EDOT monomer;

[0008] Step S2: Dissolve the water-soluble EDOT monomer in deionized water, add the catalyst, and stir until homogeneous to obtain a mixed solution;

[0009] Step S3: Under nitrogen protection, an oxidant solution is added dropwise to the mixed solution to carry out the reaction. After the reaction is completed, an intermediate product is obtained.

[0010] Step S4: The intermediate product is treated with a dialysis membrane or ion exchange resin to remove low molecular weight byproducts, resulting in a water-soluble PEDOT-S solution with high dispersibility and low viscosity.

[0011] Optionally, in step S1, the water-soluble EDOT monomer is prepared as follows:

[0012] Hydroxymethyl EDOT was dissolved in an appropriate amount of deionized water, sodium hydride was added, and the mixture was stirred at room temperature for a certain period of time. Then, sulfonic acid reagent or carboxylation reagent was added dropwise, and the mixture was heated to reflux for a certain period of time. After purification, water-soluble EDOT monomer containing sulfonic acid group or carboxyl group was obtained.

[0013] Optionally, the molar ratio of hydroxymethyl EDOT to sodium hydride is 1:1.0 to 1.5.

[0014] Optionally, the reaction can be stirred at room temperature for 4 hours or refluxed for 15–24 hours.

[0015] Optionally, in step S2, the molar ratio of catalyst to EDOT monomer is 0.2 to 1:1.

[0016] Optionally, in step S2, the catalyst is ferrous sulfate or ferric sulfate.

[0017] Optionally, in step S3, the molar ratio of the oxidant to the water-soluble EDOT monomer is 1 to 2:1.

[0018] Optionally, in step S3, the oxidant is sodium persulfate or ammonium persulfate.

[0019] Optionally, in step S3, the dropping time shall not exceed 30 minutes and the reaction temperature shall be 25°C.

[0020] The application of the water-soluble PEDOT-S prepared by the method described above in the preparation of water-insoluble PEDOT solid capacitors includes:

[0021] A capacitor is immersed in a water-soluble PEDOT-S solution and fully wetted to obtain a capacitor with a water-soluble PEDOT-S cathode. The capacitor is then dried at a temperature of 150–180°C to convert the water-soluble PEDOT-S cathode into a water-insoluble PEDOT cathode, thus obtaining a water-insoluble PEDOT solid capacitor.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. This invention eliminates the need for high-voltage homogenization in capacitor applications, significantly simplifying the production process. By optimizing the molecular design of the conductive polymer and utilizing self-doped functional groups to enhance the material's dispersibility, the water-soluble conductive polymer can directly form a homogeneous solution in an aqueous system. Experimental results show that the prepared conductive polymer solution has a uniform particle size distribution (D50≤80nm) and low viscosity (≤8mPa·s), making it suitable for impregnation processes and avoiding the high-voltage homogenization required in the preparation of traditional PEDOT:PSS dispersions. This simplified process effectively reduces equipment costs and energy consumption while improving the efficiency of industrial-scale material preparation.

[0024] 2. The conductive polymer solution exhibits excellent stability during storage, completely solving the problem of easy stratification in PEDOT:PSS dispersions during storage. This invention introduces self-doped groups into the molecular structure, ensuring that the conductive polymer dispersion remains uniform and stratified throughout long-term storage, without precipitation. Experimental results show that after 30 days of storage at 60℃ and 90% humidity, the conductive polymer dispersion retains over 95% of its conductivity, significantly outperforming the rapid performance degradation caused by stratification in traditional PEDOT:PSS dispersions under the same conditions.

[0025] 3. In capacitor applications, the performance can achieve functional expansion and diversified application scenarios. The conductive polymer prepared in this invention exhibits excellent electrochemical performance and outperforms traditional materials in high temperature and high humidity environments. This makes its application in solid-state capacitors more extensive, and also provides potential applications for other electronic components such as sensors, electrolytic capacitors, and flexible electronic devices, demonstrating great potential for functional expansion and multi-scenario adaptation.

[0026] 4. This invention converts the water-soluble conductive polymer (PEDOT-S) cathode into a non-water-soluble PEDOT cathode, thereby maintaining stable capacitor performance while avoiding the problem of water absorption during long-term storage of the capacitor. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0028] Figure 1 This is the XPS sulfur spectrum of the dried film at 120°C provided by the present invention;

[0029] Figure 2 This is the XPS sulfur spectrum of the dried film at 180°C provided by the present invention;

[0030] Figure 3 This is a diagram illustrating the side chain fracture mechanism provided by the present invention. Detailed Implementation

[0031] The technical solutions of this invention will now be clearly and completely described in conjunction with the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0032] Example 1

[0033] Example 1 provides a method for preparing water-soluble PEDOT-S, comprising the following steps:

[0034] Step S1: Provide a water-soluble EDOT monomer. The preparation method of the water-soluble EDOT monomer is as follows:

[0035] Hydroxymethyl EDOT (3,4-ethylenedioxythiophene-2-methanol) was dissolved in an appropriate amount of deionized water, and sodium hydride was added. The molar ratio of hydroxymethyl EDOT to sodium hydride was 1:1. After stirring at room temperature for 4 hours, sulfonic acid reagent or carboxylation reagent was added dropwise. Then the temperature was raised to reflux for 15 hours. After purification, water-soluble EDOT monomer containing sulfonic acid group or carboxyl group was obtained.

[0036] Step S2: Dissolve the water-soluble EDOT monomer in deionized water, add ferrous sulfate, the molar ratio of ferrous sulfate to water-soluble EDOT monomer is 0.2:1, stir evenly to obtain a mixed solution;

[0037] Step S3: Under nitrogen protection, sodium persulfate solution is added dropwise to the mixed solution to carry out the reaction. The molar ratio of water-soluble EDOT monomer to sodium persulfate is 1:1. The addition time is 25 minutes and the reaction temperature is 25°C. After the reaction is completed, an intermediate product is obtained.

[0038] Step S4: The intermediate product is treated with a dialysis membrane or ion exchange resin to remove low molecular weight byproducts, resulting in a water-soluble PEDOT-S solution with high dispersibility and low viscosity.

[0039] Example 2

[0040] Example 2 provides a method for preparing water-soluble PEDOT-S, comprising the following steps:

[0041] Step S1: Provide a water-soluble EDOT monomer. The preparation method of the water-soluble EDOT monomer is as follows:

[0042] Hydroxymethyl EDOT (3,4-ethylenedioxythiophene-2-methanol) was dissolved in an appropriate amount of deionized water, and sodium hydride was added. The molar ratio of hydroxymethyl EDOT to sodium hydride was 1:1.3. After stirring at room temperature for 4 hours, sulfonic acid reagent or carboxylating reagent was added dropwise. Then the temperature was raised to reflux for 20 hours. After purification, water-soluble EDOT monomer containing sulfonic acid group or carboxyl group was obtained.

[0043] Step S2: Dissolve the water-soluble EDOT monomer in deionized water, add ferrous sulfate, and homogenize the solution by mixing ferrous sulfate and water-soluble EDOT monomer at a molar ratio of 0.7:1.

[0044] Step S3: Under nitrogen protection, sodium persulfate solution is added dropwise to the mixed solution to carry out the reaction. The molar ratio of sodium persulfate to water-soluble EDOT monomer is 1.5:1, the reaction temperature is 25℃, and the intermediate product is obtained after the reaction is completed.

[0045] Step S4: The intermediate product is treated with a dialysis membrane or ion exchange resin to remove low molecular weight byproducts, resulting in a water-soluble PEDOT-S solution with high dispersibility and low viscosity.

[0046] Example 3

[0047] Example 3 provides a method for preparing water-soluble PEDOT-S, comprising the following steps:

[0048] Step S1: Provide a water-soluble EDOT monomer. The preparation method of the water-soluble EDOT monomer is as follows:

[0049] Hydroxymethyl EDOT (3,4-ethylenedioxythiophene-2-methanol) was dissolved in an appropriate amount of deionized water, and sodium hydride was added. The molar ratio of hydroxymethyl EDOT to sodium hydride was 1:1.5. After stirring at room temperature for 4 hours, sulfonic acid reagent or carboxylating reagent was added dropwise. Then the temperature was raised to reflux for 24 hours. After purification, water-soluble EDOT monomer containing sulfonic acid group or carboxyl group was obtained.

[0050] Step S2: Dissolve the water-soluble EDOT monomer in deionized water, add ferrous sulfate, the molar ratio of water-soluble EDOT monomer to ferrous sulfate is 1:1, stir evenly to obtain a mixed solution;

[0051] Step S3: Under nitrogen protection, ammonium persulfate solution is added dropwise to the mixed solution to carry out the reaction. The molar ratio of sodium persulfate to water-soluble EDOT monomer is 2:1, the dropwise addition time is 29 minutes, the reaction temperature is 25°C, and the intermediate product is obtained after the reaction is completed.

[0052] Step S4: The intermediate product is treated with a dialysis membrane or ion exchange resin to remove low molecular weight byproducts, resulting in a water-soluble PEDOT-S solution with high dispersibility and low viscosity.

[0053] It should be noted that by modifying the molecular structure, various hydrophilic functional groups (such as sulfonic acid groups, carboxyl groups, amino groups or polyether chains) are introduced. These functional groups enhance the water solubility and dispersibility of the monomer through intramolecular self-doping effect, and achieve a balance between electrical conductivity and chemical stability.

[0054] In the synthesis of water-soluble PEDOT-S, sodium persulfate (Na2S2O8) was selected as the oxidant and iron salts (such as FeSO4) as the catalyst. Precise control of the polymerization rate and product structure was achieved by adjusting the molar ratio of the oxidant to the water-soluble EDOT monomer (1:1 to 2:1) and the molar ratio of the catalyst to the water-soluble EDOT monomer (0.2:1 to 0.6:1). Furthermore, changes in the reaction medium environment (such as vacuum, air, or nitrogen) further optimized the polymerization efficiency and final conductivity. After polymer preparation, byproducts were removed using ion exchange membranes or ion exchange resins, ultimately yielding a uniformly dispersed, small-particle-size, and highly stable water-soluble PEDOT-S solution.

[0055] The water-soluble PEDOT-S solution prepared using the method provided in this invention exhibits superior physical and chemical properties. It has a uniform particle size distribution (D50 ≤ 80 nm), low solution viscosity (≤ 8 mPa·s), high electrical conductivity (≥ 100 S / cm), and shows no stratification or precipitation during long-term storage, retaining over 95% of its electrical conductivity. This water-soluble conductive polymer material significantly outperforms traditional PEDOT:PSS in terms of conductivity, uniformity, and storage stability.

[0056] Example 4

[0057] The present invention describes the application of water-soluble PEDOT-S prepared by the aforementioned method in the conversion of water-soluble PEDOT into non-water-soluble PEDOT in solid-state capacitors, including:

[0058] A capacitor is immersed in a water-soluble PEDOT-S solution and fully wetted to obtain a capacitor with a water-soluble PEDOT-S cathode. The capacitor is then dried at a temperature of 150–180°C to convert the water-soluble PEDOT-S cathode into a water-insoluble PEDOT cathode, thus producing a water-insoluble PEDOT solid capacitor.

[0059] Combination Figure 1 and Figure 2 As shown, X-ray photoelectron spectroscopy (XPS) analysis of cathode films dried at 120℃ and 180℃ revealed that at 120℃, the ratio of sulfur (S) in sulfonate to S in thiophene was 1:1, indicating that the side chains were not broken and the material still existed in the form of water-soluble PEDOT-S. However, when the temperature was increased to 180℃, the ratio of S in sulfonate to S in thiophene decreased to 0.62:1, indicating that some side chains were broken (mechanism diagram shown). Figure 3 As shown in Table 1, this leads to a decrease in the ratio and a change in water solubility, i.e., from water-soluble to non-water-soluble. The change in performance can be seen in Table 1. In other words, by controlling the temperature, water-soluble PEDOT-S is converted into non-water-soluble PEDOT, thereby maintaining the stability of capacitor performance while avoiding the problem of water absorption during long-term storage of the capacitor.

[0060] Table 1 Comparison of material properties under different drying temperatures

[0061]

[0062] It should be noted that a water-soluble PEDOT-S cathode is formed in the capacitor through an impregnation process, followed by drying at 150–180°C to form a non-water-soluble PEDOT cathode, thus producing a non-water-soluble PEDOT solid-state capacitor. Testing shows that the non-water-soluble PEDOT solid-state capacitor exhibits high capacitance per unit area (CAP), low leakage current (Lc), and low ESR. Its overall performance is superior to capacitors using traditional PEDOT:PSS, solving problems associated with traditional PEDOT:PSS such as large particle size, delamination, and the need to add dopants to improve conductivity. Because the water-soluble PEDOT-S is converted into non-water-soluble PEDOT, not only is the capacitor performance more stable, but the problem of water absorption during long-term storage is also avoided.

[0063] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0064] Furthermore, it should be noted that the scope of the methods in the embodiments of the present invention and their application in capacitors is not limited to performing functions in the order shown or discussed. It may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0065] The embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

Claims

1. An application of water-soluble PEDOT-S in the preparation of solid-state capacitors, characterized in that, Including cathodes prepared by the following methods: The steps for preparing a water-soluble PEDOT-S solution include: Step S1: Provide water-soluble EDOT monomer; Step S2: Dissolve the water-soluble EDOT monomer in deionized water, add the catalyst, stir until homogeneous, and obtain a mixed solution. The catalyst is ferrous sulfate or ferric sulfate, and the molar ratio of the catalyst to the water-soluble EDOT monomer is 0.2~1:

1. Step S3: Under nitrogen protection, an oxidant solution is added dropwise to the mixed solution to carry out the reaction. The oxidant is sodium persulfate or ammonium persulfate. The molar ratio of the oxidant to the water-soluble EDOT monomer is 1~2:

1. The dropwise addition time does not exceed 30 minutes. The reaction temperature is 25°C. After the reaction is completed, an intermediate product is obtained. Step S4: The intermediate product is treated with a dialysis membrane or ion exchange resin to remove low molecular weight byproducts, resulting in a water-soluble PEDOT-S solution with high dispersibility and low viscosity. The water-soluble PEDOT-S solution has a particle size D50 ≤ 80 nm and a viscosity ≤ 8 mPa·s. And the steps for preparing the capacitor cathode: The capacitor anode carrier is immersed in the water-soluble PEDOT-S solution, fully wetted, and then dried at 150~180℃ to convert the water-soluble PEDOT-S cathode into a non-water-soluble PEDOT cathode. In the XPS sulfur spectrum of the non-water-soluble PEDOT cathode, the ratio of the number of S atoms in the sulfonate group to the number of S atoms in the thiophene ring is less than 0.62:

1.

2. The application of water-soluble PEDOT-S according to claim 1 in the preparation of solid-state capacitors, characterized in that, In step S1, the preparation method of the water-soluble EDOT monomer is as follows: Hydroxymethyl EDOT was dissolved in an appropriate amount of deionized water, sodium hydride was added, and the mixture was stirred at room temperature for 4 hours. Then, sulfonic acid reagent or carboxylation reagent was added dropwise, and the mixture was heated to reflux for 15-24 hours. After purification, water-soluble EDOT monomer containing sulfonic acid group or carboxyl group was obtained.

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