Polymer dispersion and method for its production, electrolytic capacitor

Abstract

To overcome the problem of insufficient water solubility in existing PBFDO conductive polymers, this invention provides a polymer dispersion comprising a solvent and a conductive polymer dispersed in the solvent. The monomer of the conductive polymer comprises a compound shown in structural formula 1, wherein X is an anion and m is an integer from 1 to 3. This invention also discloses a method for preparing the above polymer dispersion and an electrolytic capacitor. The polymer dispersion provided by this invention introduces -NH3. + The hydrophilic groups make the conductive polymer more soluble in aqueous solvents and improve the uniformity of dispersion of the conductive polymer in aqueous solvents.

Description

Technical Field

[0001] This invention belongs to the field of electrolytic capacitor material technology, specifically relating to a polymer dispersion and its preparation method, and an electrolytic capacitor. Background Technology

[0002] Because PBFDO (polybenzodifuran diketone)-based polymers exhibit higher conductivity and temperature resistance than PEDOT:PSS, their application in the electronics industry will significantly improve device performance, thus attracting the attention of many researchers and application technicians.

[0003] Existing PBFDO solutions have insufficient solubility in aqueous solvents, requiring the use of high-boiling-point solvents such as DMSO, DMF, NMP, and DMAc for dissolution. When the conductive polymer solution is applied to planar substances with relatively small adsorption areas, the solvent removal methods are not too demanding and can be used in industrial production. However, when the applied substance is blocky with a certain thickness and a large adsorption area, solvent removal becomes a challenge. This typically requires prolonged use of high vacuum and high temperature for deep and thorough processing, leading to high energy consumption and significant investment in processing equipment in industrial production. Therefore, using low-boiling-point solvents to dissolve or disperse PBFDO has become the foundation for the further widespread application of PBFDO-based polymers and is a crucial technical problem that urgently needs to be solved. Summary of the Invention

[0004] To address the problem of insufficient water solubility in existing PBFDOs, this invention provides a polymer dispersion, its preparation method, and an electrolytic capacitor.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0006] On one hand, the present invention provides a polymer dispersion comprising a solvent and a conductive polymer dispersed in the solvent, wherein the monomers of the conductive polymer comprise compounds represented by structural formula 1:

[0007]

[0008] Where X is an anion and m is an integer from 1 to 3.

[0009] Optionally, the X m- Selected from SO4 2- I - Cl-, Br - One or more of them.

[0010] Optionally, the monomers of the conductive polymer may further include compounds represented by structural formula 2:

[0011]

[0012] R1 and R2 are each independently selected from O, S, Se, or R5 is selected from H, substituted or unsubstituted straight-chain or branched C1-C18 alkyl, substituted or unsubstituted C5-C12 cycloalkyl, substituted or unsubstituted C1-C4 hydroxyalkyl or hydroxyl, and R3 and R4 are each independently selected from H, substituted or unsubstituted straight-chain or branched C1-C18 alkyl, substituted or unsubstituted C6-C12 aromatic hydrocarbon, amino, C1-C10 carbonyl alkyl, C2-C10 ester, C1-C10 carboxylic acid, C1-C4 hydroxyalkyl or hydroxyl.

[0013] Optionally, the compound shown in structural formula 2 is a benzodifurandione.

[0014] Optionally, the molar ratio of the compound represented by structural formula 1 to the compound represented by structural formula 2 is (0.01-0.05):(0.01-1.0).

[0015] Optionally, the solvent includes one or more of water, alcohols, and dimethyl sulfoxide.

[0016] Optionally, based on the total mass of the polymer dispersion (100%), the mass content of the conductive polymer is 0.05% to 10%, preferably 0.05% to 2%, and more preferably 0.05% to 0.5%.

[0017] In another aspect, the present invention provides an electrolytic capacitor, comprising an anode foil having a dielectric layer on its surface, a cathode foil, an electrolytic paper disposed between the anode foil and the cathode foil, and a conductive polymer layer in contact with the dielectric layer, wherein the conductive polymer layer is obtained by impregnation and curing of a polymer dispersion as described above.

[0018] In another aspect, the present invention provides a method for preparing the polymer dispersion as described above, comprising the following steps:

[0019] The compound shown in structural formula 1, the compound shown in structural formula 2, and the oxidant were mixed in a solvent and polymerized at a reaction temperature of 70℃~140℃ to obtain a polymer dispersion.

[0020] Optionally, the oxidant is tetramethylbenzoquinone.

[0021] Optionally, the compound represented by structural formula 1 is prepared by the following method:

[0022] Benzodifurandione and copper nitrate were reacted under acetic anhydride conditions to give the compound shown in structural formula 3;

[0023]

[0024] The compound of structural formula 3 was reacted with hydrogen gas under Pd / C catalysis to obtain the compound shown in structural formula 4.

[0025]

[0026] The compound shown in structural formula 4 was reacted with Me2SO4 to give the compound shown in structural formula 1.

[0027] According to the polymer dispersion provided by the present invention, a compound of structural formula 1 is added to the monomers of a conductive polymer. The compound of structural formula 1 has a main structure similar to benzodifurandione and can undergo polymerization reaction with other monomers to obtain a copolymer with high electrical conductivity. At the same time, the compound of structural formula 1 introduces -NH3 into the main structure. + The hydrophilic groups of the conductive polymer improve its water solubility, resulting in higher solubility in aqueous solvents and improved dispersion uniformity. Consequently, during the impregnation of electrolytic capacitors, the conductive polymer particles can fully penetrate the pores of the dielectric layer, improving capacitance extraction, reducing dielectric loss, decreasing dependence on high-boiling-point organic solvents, and reducing the difficulty of solvent removal during curing. This also avoids the impact of solvent residue on the electrochemical performance of the capacitor. Detailed Implementation

[0028] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] One embodiment of the present invention provides a polymer dispersion comprising a solvent and a conductive polymer dispersed in the solvent, wherein the monomers of the conductive polymer comprise compounds represented by structural formula 1:

[0030]

[0031] Where X is an anion and m is an integer from 1 to 3.

[0032] According to the polymer dispersion provided by the present invention, a compound of structural formula 1 is added to the monomers of a conductive polymer. The compound of structural formula 1 has a main structure similar to benzodifurandione and can undergo polymerization reaction with other monomers to obtain a copolymer with high electrical conductivity. At the same time, the compound of structural formula 1 introduces -NH3 into the main structure. +The hydrophilic groups of the conductive polymer improve its water solubility, resulting in higher solubility in aqueous solvents and improved dispersion uniformity. Consequently, during the impregnation of electrolytic capacitors, the conductive polymer particles can fully penetrate the pores of the dielectric layer, improving capacitance extraction, reducing dielectric loss, decreasing dependence on high-boiling-point organic solvents, and reducing the difficulty of solvent removal during curing. This also avoids the impact of solvent residue on the electrochemical performance of the capacitor.

[0033] In some embodiments, the X m- Selected from SO4 2- I - Cl-, Br - One or more of them.

[0034] In some embodiments, the conductive polymer is a homopolymer of the compound represented by structural formula 1.

[0035] In some embodiments, the monomers of the conductive polymer further include compounds represented by structural formula 2:

[0036]

[0037] R1 and R2 are each independently selected from O, S, Se, or R5 is selected from H, substituted or unsubstituted straight-chain or branched C1-C18 alkyl, substituted or unsubstituted C5-C12 cycloalkyl, substituted or unsubstituted C1-C4 hydroxyalkyl or hydroxyl, and R3 and R4 are each independently selected from H, substituted or unsubstituted straight-chain or branched C1-C18 alkyl, substituted or unsubstituted C6-C12 aromatic hydrocarbon, amino, C1-C10 carbonyl alkyl, C2-C10 ester, C1-C10 carboxylic acid, C1-C4 hydroxyalkyl or hydroxyl.

[0038] In some embodiments, the compound represented by structural formula 2 is a benzodifurandione.

[0039] In the description of this invention, the term "substituted straight-chain or branched C1-C18 alkyl" refers to a straight-chain or branched C1-C18 alkyl group in which some or all of the hydrogen atoms are substituted by other functional groups, wherein the other functional groups may be halogens, haloalkyl groups, carboxyl groups, ester groups, nitrogen-containing groups, or silicon-containing groups, etc. "Substituted or unsubstituted C5-C12 cycloalkyl" and "substituted or unsubstituted C1-C4 hydroxyalkyl" can be understood in this definition.

[0040] In some embodiments, the molar ratio of the compound represented by structural formula 1 to the compound represented by structural formula 2 is (0.01–0.05):(0.01–1.0).

[0041] Specifically, the molar ratio of the compound represented by structural formula 1 to the compound represented by structural formula 2 can be 0.05:0.01, 0.05:0.05, 0.05:0.08, 0.05:0.1, 0.05:0.2, 0.05:0.2, 0.05:0.3, 0.05:0.4, 0.05:0.5, 0.05:0.6, 0.05:0.7, 0.05:0.8, 0.05:0.9, 0.05:1.0, 0.03:0.01, 0.03:0.05, 0.03:0.08, 0.03:0.1, or 0.03:0. 2, 0.03:0.2, 0.03:0.3, 0.03:0.4, 0.03:0.5, 0.03:0.6, 0.03:0.7, 0.03:0.8, 0.03:0.9, 0.03:1.0, 0.01:0.01, 0.01:0.05, 0.01:0.08, 0.01:0.1, 0.01:0.2, 0.01:0.2, 0.01:0.3, 0.01:0.4, 0.01:0.5, 0.01:0.6, 0.01:0.7, 0.01:0.8, 0.01:0.9 or 0.01:1.0.

[0042] The water solubility of the conductive polymer increases with the increase of the content of the compound shown in structural formula 1. In different embodiments, the water solubility of the conductive polymer can be adjusted by adjusting the relative molar ratio of the compound shown in structural formula 1 and the compound shown in structural formula 2 to adapt to different application scenarios.

[0043] In some embodiments, the solvent includes one or more of water, alcohols, and dimethyl sulfoxide.

[0044] In a preferred embodiment, the solvent comprises water and dimethyl sulfoxide, wherein the mass ratio of dimethyl sulfoxide to water is (0.1–5):(5–15).

[0045] In some embodiments, the mass content of the conductive polymer is 0.05% to 10% based on the total mass of the polymer dispersion as 100%.

[0046] In a preferred embodiment, the mass content of the conductive polymer is 0.05%-2% based on the total mass of the polymer dispersion being 100%.

[0047] In a preferred embodiment, the mass content of the conductive polymer is 0.05%-0.5% based on the total mass of the polymer dispersion being 100%.

[0048] If the content of conductive polymer in the polymer dispersion is too low, the amount of conductive polymer that penetrates to the surface of the dielectric layer during the impregnation process of the electrolytic capacitor will also be small, making it difficult to form a complete electrolyte layer. This requires multiple impregnation operations, which affects the processing efficiency. If the content of conductive polymer in the polymer dispersion is too high, it will result in excessively high viscosity of the polymer dispersion, affecting the filling of the pores of the capacitor anode foil by the polymer dispersion.

[0049] Another embodiment of the present invention provides an electrolytic capacitor, comprising an anode foil having a dielectric layer on its surface, a cathode foil, electrolytic paper disposed between the anode foil and the cathode foil, and a conductive polymer layer in contact with the dielectric layer, wherein the conductive polymer layer is obtained by impregnation and curing of a polymer dispersion as described above.

[0050] Due to the hydrophilicity of the conductive polymer in the polymer dispersion as described above, the conductive polymer in the polymer dispersion can be fully dispersed and has a high degree of uniformity. During the impregnation operation, the conductive polymer can enter the pores of the capacitor anode foil more fully, forming a conductive polymer layer of sufficient thickness and uniformity, which is beneficial to improving the capacitance extraction rate of the electrolytic capacitor. Furthermore, the sufficiently thick and uniform conductive polymer layer makes the equivalent series resistance (ESR) of the capacitor lower.

[0051] In some embodiments, the impregnation operation of the electrolytic capacitor includes the following operations:

[0052] Under negative pressure, the polymer dispersion is used to impregnate capacitor elements, which are then baked and cured. This process is repeated 1 to 9 times. After assembly, sealing, cleaning, and aging, an electrolytic capacitor is prepared.

[0053] In some embodiments, the capacitor elements are treated with a silane coupling agent before impregnation.

[0054] In some embodiments, the electrolytic capacitor is an aluminum electrolytic capacitor or a tantalum capacitor.

[0055] Another embodiment of the present invention provides a method for preparing the polymer dispersion as described above, comprising the following steps:

[0056] The compound shown in structural formula 1, the compound shown in structural formula 2, and the oxidant were mixed in a solvent and polymerized at a reaction temperature of 70℃~140℃ to obtain a polymer dispersion.

[0057] In some embodiments, the reaction of the compound represented by structural formula 1, the compound represented by structural formula 2, and the oxidant is carried out in an ultrasonic water bath for 2-3 hours. During the reaction, ultrasonic treatment is performed at a frequency of 1-2 minutes every 10-30 minutes.

[0058] In some embodiments, the oxidant is tetramethylbenzoquinone.

[0059] In some embodiments, the compound represented by structural formula 1 is prepared by the following method:

[0060] Benzodifurandione and copper nitrate were reacted under acetic anhydride conditions to give the compound shown in structural formula 3;

[0061]

[0062] The compound of structural formula 3 was reacted with hydrogen gas under Pd / C catalysis to obtain the compound shown in structural formula 4.

[0063]

[0064] The compound shown in structural formula 4 was reacted with Me2SO4 to give the compound shown in structural formula 1.

[0065] For details of the reaction process, please refer to the following synthetic route:

[0066]

[0067] In some embodiments, the molar ratio of the benzodifurandione to the copper nitrate is (0.5-2):(5-20).

[0068] In some embodiments, the reaction of the benzodifuran dione and the copper nitrate is carried out under a protective gas atmosphere at a temperature of 40°C to 80°C for 5 to 20 hours. After the reaction is completed, the filtrate is filtered, and the filter cake is washed three times with 100 eq chloroform. All filtrates are collected, and 200 eq water is added to the filtrate in an ice-water bath and stirred for 10 minutes. The organic phase is then separated and the reaction is repeated three times. The organic phase is then rotary evaporated to obtain the solid product of the compound shown in structural formula 3.

[0069] In some embodiments, the molar ratio of the compound of structural formula 3 to the Pd / C is 1:(0.001 to 0.05).

[0070] In some embodiments, the compound of formula 3 and the Pd / C catalyst were added to a high-pressure reactor, followed by the addition of DCM (dichloromethane). The reactor was purged with nitrogen three times, then purged with hydrogen three times. The reactor was then shut off, and the reaction was carried out at 50°C for 6 hours. After the reaction, the filtrate was filtered, and the filter cake was washed three times with DCM. All filtrates were collected, and water was added to the filtrate in an ice-water bath. Then, 10% hydrochloric acid was slowly added dropwise until the pH reached 2. The mixture was stirred for 10 minutes, and the aqueous phase was separated and retained. The aqueous phase was then washed three times with DCM. All aqueous phases were combined, and 10% sodium hydroxide solution was slowly added dropwise to the solution in an ice-water bath until the pH was greater than 8. The solid was filtered, and the filter cake was washed three times with cold water. The filter cake was then dried at room temperature under vacuum for 24 hours to obtain the compound shown in formula 4.

[0071] In some embodiments, the molar ratio of the compound represented by structural formula 4 to the Me2SO4 is 1:(5-15).

[0072] In some embodiments, the compound shown in structural formula 4 and a magnetic particle were added to a three-necked flask. A vacuum pump, a constant-pressure dropping funnel with a flip-top stopper, and a flip-top rubber stopper were then inserted. After purging with nitrogen three times, anhydrous THF (tetrahydrofuran) was added through the flip-top rubber stopper under nitrogen protection. Me₂SO₄ was then added to the dropping funnel, and the addition was performed slowly dropwise in an ice-water bath. After the addition was complete, the temperature was raised to room temperature and the reaction was allowed to proceed for 4 hours. The reaction was monitored by TLC (Thin Layer Chromatography). After the reaction was complete, the mixture was rapidly filtered, and the filter cake was washed three times with THF. The filter cake was then recrystallized from the filter cake with anhydrous methanol. The filtered solid was dried at room temperature under vacuum for 24 hours to obtain the compound shown in structural formula 1.

[0073] The present invention will be further illustrated by the following examples.

[0074] Table 1

[0075]

[0076]

[0077] Example 1

[0078] This embodiment illustrates the polymer dispersion and its preparation method disclosed in this invention, including the following steps:

[0079] Referring to the molar ratios shown in Table 1, the compounds shown in structural formula 1, structural formula 2, tetramethylbenzoquinone, and a magnetic spool were added to a three-necked flask. A glass stopper with a thermometer, a serpentine condenser with a three-way evacuation nozzle, and a rubber stopper with a flip-top were inserted into the three necks, respectively. After purging with nitrogen three times, water and DMSO (dimethyl sulfoxide) in the corresponding molar ratio were added through the rubber stopper under nitrogen protection. The mixture was then reacted in an ultrasonic water bath at 100°C for 2.5 h, with ultrasonic treatment performed during the process. The ultrasonic program was 1 min of ultrasonic treatment every 20 min of reaction.

[0080] After the reaction was completed, the mixture was cooled to room temperature to obtain a polymer dispersion.

[0081] Examples 2-5

[0082] Examples 2-5 illustrate the polymer dispersion and its preparation method disclosed in this invention, and include most of the operations in Example 1, except that:

[0083] In Examples 2-5, the molar amounts of the compound represented by structural formula 1, the compound represented by structural formula 2, tetramethylbenzoquinone, water, and DMSO are shown in Table 1.

[0084] Comparative Example 1

[0085] This comparative example is used to illustrate the polymer dispersion and its preparation method disclosed in this invention, including most of the operations in Example 1, with the following differences:

[0086] In Comparative Example 1, the molar amounts of the compound represented by structural formula 1, the compound represented by structural formula 2, tetramethylbenzoquinone, water, and DMSO added are shown in Table 1.

[0087] Preparation results:

[0088] Polymer dispersions without significant sedimentation were prepared in Examples 1-5 and Comparative Example 1.

[0089] The preparation results show that increasing the proportion of the compound shown in structural formula 1 improves the water solubility of the conductive polymer. Therefore, the required proportion of the cosolvent DMSO is gradually reduced without affecting the dispersion effect of the conductive polymer in the solution.

[0090] Examples 6-10

[0091] Examples 6-10 illustrate the aluminum electrolytic capacitor and its preparation method disclosed in this invention, and include the following operations:

[0092] 1) Immerse the core of a 16V 470 solid electrolytic capacitor in an ethanol solution of 0.5% silane coupling agent under negative voltage and then dry it;

[0093] 2) The pretreated solid electrolytic capacitor core is immersed in the polymer dispersion for 30 minutes under negative pressure and then dried. The above steps are repeated 3 times, and then the core is sealed and assembled into an aluminum electrolytic capacitor.

[0094] In this example, Example 6 uses the polymer dispersion of Example 1, Example 7 uses the polymer dispersion of Example 2, Example 8 uses the polymer dispersion of Example 3, Example 9 uses the polymer dispersion of Example 4, and Example 10 uses the polymer dispersion of Example 5.

[0095] Comparative Example 2

[0096] Comparative Example 2 is used to illustrate the aluminum electrolytic capacitor and its preparation method disclosed in this invention, and includes the following operations:

[0097] 1) Immerse the core of a 16V 470 solid electrolytic capacitor in an ethanol solution of 0.5% silane coupling agent under negative voltage and then dry it;

[0098] 2) Immerse the pretreated solid electrolytic capacitor core in the polymer dispersion under negative pressure for 30 minutes and dry it. Repeat the above steps 3 times, and then seal and assemble it into an aluminum electrolytic capacitor.

[0099] Comparative Example 2 uses the polymer dispersion of Comparative Example 1.

[0100] Performance testing

[0101] 1. The aluminum electrolytic capacitors prepared in Examples 6-10 and Comparative Example 2 were subjected to 1000 charge-discharge cycles. The capacitance Cap, loss tangent DF, equivalent series resistance ESR, and capacitance decay rate ΔC (%) were measured. The test results are shown in Table 2.

[0102] Table 2

[0103]

[0104]

[0105] 2. The aluminum electrolytic capacitors prepared in Examples 6-10 and Comparative Example 2, after undergoing charge-discharge tests, were then subjected to high-temperature load life tests. The test results are shown in Table 3.

[0106] Table 3

[0107]

[0108] As shown in Tables 2 and 3, for wound aluminum electrolytic capacitors, the increasing water solubility of the polymer enhances its wetting effect on the aluminum foil, allowing the conductive polymer to fully penetrate the pores of the aluminum foil, thus significantly improving the capacitance extraction rate. Examples 6-9 also show that the ESR of the polymer increases with the increase in the proportion of the monomer of the compound shown in Structural Formula 1. This is because, compared to BFDO, the quaternary ammonium groups of the compound shown in Structural Formula 1 affect the planar structure of the polymer to some extent, leading to a decrease in the polymer's conductivity. Comparative Example 2 shows the highest ESR, possibly due to the poor water solubility of the PBFDO conductive polymer resulting in a poor impregnation effect, thus failing to form a sufficiently thick and uniform conductive polymer layer. Furthermore, the test results in Tables 2 and 3 indicate that the copolymer of the compound shown in Structural Formula 1 and BFDO, when applied to aluminum electrolytic capacitors, can effectively balance the performance requirements of both ESR and capacitance extraction rate.

[0109] Examples 11-15

[0110] Examples 11-15 illustrate the tantalum capacitor and its preparation method disclosed in this invention, and include the following operations:

[0111] A 2.5V22 tantalum core was immersed in a polymer dispersion under negative pressure and dried. This process was repeated six times. A carbon paste and silver paste cathode lead-out layer were then sequentially coated according to the standard tantalum capacitor process.

[0112] In this example, Example 11 uses the polymer dispersion of Example 1, Example 12 uses the polymer dispersion of Example 2, Example 13 uses the polymer dispersion of Example 3, Example 14 uses the polymer dispersion of Example 4, and Example 15 uses the polymer dispersion of Example 5.

[0113] Comparative Example 3

[0114] Comparative Example 3, used to illustrate the tantalum capacitor and its preparation method disclosed in this invention, includes the following operations:

[0115] The 2.5V22 tantalum core was immersed in a polymer dispersion under negative pressure and dried, and the above steps were repeated 6 times. A carbon paste and a silver paste cathode lead-out layer were then sequentially coated according to the general process for tantalum capacitors.

[0116] Comparative Example 3 uses the polymer dispersion of Comparative Example 1.

[0117] Performance testing

[0118] The tantalum electrolytic capacitors prepared in Examples 11-15 and Comparative Example 3 were charged and discharged to measure the capacitance (CAP), loss tangent (DF), and equivalent series resistance (ESR). The tantalum electrolytic capacitors were then placed in a 270°C oven for 3 minutes, and after removal, the capacitance (CAP), loss tangent (DF), and equivalent series resistance (ESR) were measured. The test results are shown in Table 4.

[0119] Table 4

[0120]

[0121] As shown in Table 4, for tantalum capacitors, due to their relatively large pores and the absence of tightly overlapping positive and negative electrode foils, the polymer dispersion is more easily wetted. Therefore, the requirement for the solubility of the conductive polymer is not as high as that for wound aluminum electrolytic capacitors. The results indicate that when the ratio of compound to BFDO shown in Formula 1 exceeds 1:15, the increased water solubility of the conductive polymer does not further affect the capacitance extraction rate. This means that there is no need to further improve water solubility. Based on the capacitor's requirements for other performance characteristics, a conductive polymer with a higher BFDO ratio can be selected to obtain a tantalum capacitor with a lower ESR.

[0122] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polymer dispersion, characterized in that, Includes a solvent and a conductive polymer dispersed in the solvent, wherein the monomers of the conductive polymer include compounds represented by structural formula 1: Structural Formula 1 Wherein, X m- Selected from SO4 2- I - Cl - ,Br - One or more of the following, where m is an integer from 1 to 3; The solvent includes one or more of water, alcohols, and dimethyl sulfoxide.

2. The polymer dispersion according to claim 1, characterized in that, The monomers of the conductive polymer also include compounds shown in structural formula 2: Structural Formula 2 R1 and R2 are each independently selected from O, S, Se, or R5 is selected from H, substituted or unsubstituted straight-chain or branched C1-C18 alkyl, substituted or unsubstituted C5-C12 cycloalkyl, substituted or unsubstituted C1-C4 hydroxyalkyl or hydroxyl, and R3 and R4 are each independently selected from H, substituted or unsubstituted straight-chain or branched C1-C18 alkyl, substituted or unsubstituted C6-C12 aromatic hydrocarbon, amino, C1-C10 carbonyl alkyl, C2-C10 ester, C1-C10 carboxylic acid, C1-C4 hydroxyalkyl or hydroxyl.

3. The polymer dispersion according to claim 2, characterized in that, The molar ratio of the compound shown in structural formula 1 to the compound shown in structural formula 2 is (0.01~0.05):(0.01~1.0).

4. The polymer dispersion according to claim 1, characterized in that, Based on the total mass of the polymer dispersion as 100%, the mass content of the conductive polymer is 0.05% to 10%.

5. An electrolytic capacitor, characterized in that, It includes an anode foil having a dielectric layer on its surface, a cathode foil, an electrolytic paper disposed between the anode foil and the cathode foil, and a conductive polymer layer in contact with the dielectric layer, wherein the conductive polymer layer is obtained by impregnation and curing of a polymer dispersion as described in any one of claims 1 to 4.

6. The method for preparing the polymer dispersion according to any one of claims 1 to 4, characterized in that, The following steps are included: The compounds shown in structural formula 1 and structural formula 2, along with an oxidant, are mixed in a solvent and polymerized. The oxidant is tetramethylbenzoquinone. The reaction temperature is 70℃~140℃ to obtain a polymer dispersion. Structural Formula 2 R1 and R2 are each independently selected from O, S, Se, or R5 is selected from H, substituted or unsubstituted straight-chain or branched C1-C18 alkyl, substituted or unsubstituted C5-C12 cycloalkyl, substituted or unsubstituted C1-C4 hydroxyalkyl or hydroxyl, and R3 and R4 are each independently selected from H, substituted or unsubstituted straight-chain or branched C1-C18 alkyl, substituted or unsubstituted C6-C12 aromatic hydrocarbon, amino, C1-C10 carbonyl alkyl, C2-C10 ester, C1-C10 carboxylic acid, C1-C4 hydroxyalkyl or hydroxyl.

7. The method for preparing the polymer dispersion according to claim 6, characterized in that, The compound represented by structural formula 1 was prepared by the following method: Benzodifurandione and copper nitrate were reacted under acetic anhydride conditions to give the compound shown in structural formula 3; Structural Formula 3 The compound of structural formula 3 was reacted with hydrogen gas under Pd / C catalysis to obtain the compound shown in structural formula 4. Structural Formula 4 The compound shown in structural formula 4 was reacted with Me2SO4 to give the compound shown in structural formula 1.

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