Polymer capacitor and preparation method thereof

Abstract

The invention provides a polymer capacitor which is a solid electrolytic capacitor, and polydopamine is arranged between a dielectric layer on a valve metal surface of the capacitor and a polymer conductive polymer layer. Polydopamine is introduced between the dielectric layer and the high-molecular conductive polymer layer, the polydopamine is formed by self-polymerization of dopamine, the surface of the polydopamine contains groups such as phenolic hydroxyl groups and amino groups, the polydopamine and-OH on the surface of the dielectric layer of the metal oxide film can form hydrogen bonds, and meanwhile, the polydopamine and a continuous conjugated pi electron system ring of conductive high-molecular can form pi-pi accumulation; therefore, the bonding capacity between the metal oxide film dielectric layer and the high-molecular conductive polymer in the high-molecular solid electrolytic capacitor is improved, and the problem that the bonding capacity between the metal oxide film dielectric layer and the high-molecular conductive polymer in the high-molecular solid electrolytic capacitor is weak is solved. The invention also provides a preparation method of the polymer capacitor.

Description

Technical Field

[0001] This application relates to the field of capacitor manufacturing technology, and in particular to a polymer capacitor and its manufacturing method. Background Technology

[0002] A polymer solid electrolytic capacitor is an electrolytic capacitor that uses a conductive polymer as the solid electrolyte. The structure of a polymer solid capacitor is similar to that of a traditional electrolytic capacitor. Its anode uses a valve metal (such as aluminum, tantalum, niobium) or its alloy, and a uniform metal oxide dielectric layer is formed on the surface through electrochemical oxidation. The solid electrolyte layer uses a conductive polymer to handle ion transport and charge conduction. The inner layer of the cathode is a conductive adhesive to enhance contact with the electrolyte, and the outer layer is a metal current collector for current dissipation. It is encapsulated in a resin or metal casing.

[0003] While polymer solid electrolytic capacitors offer advantages such as long lifespan and high temperature resistance, they still have some drawbacks due to the limitations of their materials. For example, because polymer solid electrolytes are solid-state structures, they lack the buffering effect of liquid electrolytes. This makes them prone to problems such as electrolyte decomposition, electrode peeling, or oxide film breakdown when subjected to instantaneous overcurrent or overvoltage shocks, ultimately leading to capacitor failure. Summary of the Invention

[0004] The inventors discovered that one of the important reasons for the problems existing in the prior art is the weak bonding ability between the dielectric layer of the metal oxide film and the conductive polymer.

[0005] Therefore, the first technical problem to be solved by this application is: to solve the problem of weak bonding between the metal oxide film dielectric layer and the polymer conductive polymer in polymer solid electrolytic capacitors.

[0006] To address the aforementioned technical problems, this application provides a polymer capacitor, which is a solid electrolytic capacitor, wherein polydopamine is present between the dielectric layer on the valve metal surface of the capacitor and the polymer conductive layer.

[0007] In this application, polydopamine is introduced between the dielectric layer and the conductive polymer layer. Polydopamine is formed by dopamine self-polymerization and has phenolic hydroxyl and amino groups on its surface. It can form hydrogen bonds with the -OH groups on the surface of the metal oxide dielectric layer and simultaneously form π-π stacking with the continuous conjugated π electron system rings of the conductive polymer. This improves the bonding ability between the metal oxide dielectric layer and the conductive polymer in the polymer solid electrolytic capacitor and solves the problem of weak bonding ability between the metal oxide dielectric layer and the conductive polymer in the polymer solid electrolytic capacitor.

[0008] Optionally, polydopamine is coated over the entire area between the dielectric layer and the conductive polymer layer; or, polydopamine is coated over a portion of the area between the dielectric layer and the conductive polymer layer.

[0009] Optionally, the conductive polymer contains at least one effective conductive component selected from polyaniline, polyphenylene ether, polyphenylene sulfide, polythiophene, polyfuran, polypyrrole, polymethylpyrrole and their substituted derivatives and copolymers.

[0010] Optionally, the conductive polymer contains at least one of the following effective conductive components: polyaniline, polypyrrole, and polythiophene.

[0011] Optionally, the valve metal comprises a metal or a metal oxide, for example, the valve metal includes at least one selected from niobium oxide, tantalum, niobium, aluminum, and titanium. Correspondingly, the dielectric layer comprises Nb₂O. 5、 At least one of Ta2O5, Al2O3, and TiO2.

[0012] On the other hand, the technical problem to be solved by this application is to provide a method for preparing a polymer capacitor according to the first aspect above. The method for preparing this polymer capacitor, which involves depositing polydopamine on the surface of the dielectric layer, includes: The valve metal with the dielectric layer is immersed in dopamine-tris(hydroxymethyl)aminomethane hydrochloride buffer solution, so that the generated polydopamine is spontaneously deposited onto the electrode surface. After polydopamine is formed on the surface of the valve metal with the dielectric layer, it is removed and dried, thus completing the coating of polydopamine on the surface of the dielectric layer.

[0013] The monomer of polydopamine is 3,4-dihydroxyphenylethylamine, i.e., dopamine. The dopamine molecule contains both catechol and amino groups, which are largely retained and derived into various active functional groups after polymerization. Specifically, some catechol structures are not completely oxidized during polymerization; the retained phenolic hydroxyl groups are core sites for forming hydrogen bonds and coordination bonds (e.g., forming hydrogen bonds with hydroxyl groups on the surface of Nb₂O₅, and coordination bonds with metal ions). Some amino groups (-NH₂) participate in cross-linking reactions, generating Schiff bases (-C=N-) structures; unreacted amino groups can provide proton acceptor sites, forming hydrogen bonds with materials containing carboxyl and hydroxyl groups. Under weakly alkaline conditions, catechol is oxidized by oxygen in the air to a benzoquinone structure. The quinone group (-C=O) has strong electrophilicity and can combine with groups containing active hydrogen (such as thiol and amino groups) through Michael addition reactions, serving as important active sites for polydopamine cross-linking and adhesion. This enables enhanced bonding between dielectric layers and conductive polymers.

[0014] Preferably, the tris(hydroxymethyl)aminomethane hydrochloride buffer solution is weakly alkaline, and more preferably, the pH value is between 8 and 8.5. Polydopamine is a cross-linked polymer formed by the self-oxidative polymerization of dopamine under weakly alkaline conditions. Its structure does not have regular repeating units and belongs to an amorphous, low-crystallinity three-dimensional network polymer. Its core structural characteristics revolve around the diversity of functional groups, cross-linking network, and surface properties. Therefore, it can act as an "interfacial bridge" to enhance the bonding ability of conductive polymers on dielectric layers.

[0015] Preferably, the process of setting polydopamine on the surface of the dielectric layer is carried out in a room temperature, light-protected environment.

[0016] Preferably, the surface of the dielectric layer is cleaned before polydopamine is applied to the surface of the dielectric layer.

[0017] The technical advantages of this application are as follows: In this application, polydopamine is introduced between the dielectric layer and the conductive polymer layer. Polydopamine is formed by dopamine self-polymerization and has phenolic hydroxyl and amino groups on its surface. It can form hydrogen bonds with the -OH groups on the surface of the metal oxide dielectric layer and simultaneously form π-π stacking with the continuous conjugated π electron system rings of the conductive polymer. This improves the bonding ability between the metal oxide dielectric layer and the conductive polymer in the polymer solid electrolytic capacitor and solves the problem of weak bonding ability between the metal oxide dielectric layer and the conductive polymer in the polymer solid electrolytic capacitor. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the molded polymer capacitor provided in this application; Figure 2 This is a schematic diagram of the leadless chip polymer capacitor structure provided in this application; Explanation of reference numerals in the attached figures: 11. Valve metal; 12. Dielectric layer; 13. Anode lead; 2. Polydopamine layer; 3. Conductive polymer layer; 4. First conductive layer; 5. Second conductive layer; 6. Encapsulation layer; 7. Anode end; 8. Cathode end. Detailed Implementation

[0019] The embodiments of the technical solution of this application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples and should not be used to limit the scope of protection of this application.

[0020] The inventors discovered that the reason why polymer solid electrolytic capacitors are prone to problems such as electrolyte decomposition, electrode peeling, or oxide film breakdown is that the bonding ability between the dielectric layer of the metal oxide film and the polymer conductive polymer is weak.

[0021] Therefore, this application proposes a polymer capacitor, which is a solid electrolytic capacitor, wherein polydopamine is present between the dielectric layer on the valve metal surface and the conductive polymer layer. In some embodiments, the polydopamine is coated over the entire region between the dielectric layer and the conductive polymer layer; or, the polydopamine is coated over a portion of the region between the dielectric layer and the conductive polymer layer. In some embodiments, the conductive polymer comprises at least one effective conductive component selected from polyaniline, polyphenylene ether, polyphenylene sulfide, polythiophene, polyfuran, polypyrrole, polymethylpyrrole, and their substituted derivatives and copolymers. In some embodiments, the conductive polymer comprises at least one effective conductive component selected from polyaniline, polypyrrole, and polythiophene. In some embodiments, the valve metal comprises a metal or metal oxide, for example, the valve metal comprises at least one of niobium oxide, tantalum, niobium, aluminum, and titanium. Correspondingly, the dielectric layer comprises Nb₂O. 5、 At least one of Ta2O5, Al2O3, and TiO2. Although only an example of a niobium oxide polymer capacitor is given in the specific embodiments below, those skilled in the art can undoubtedly determine through these embodiments that the technical problems proposed in this application can also be solved by using other valve metals or conductive polymers.

[0022] In some embodiments, the polymer capacitor provided by the present invention can be used to prepare any type of solid electrolytic capacitor, such as leadless chip polymer capacitor, molded chip polymer capacitor, etc., and further, such as chip niobium oxide polythiophene polymer capacitor, chip tantalum polythiophene polymer capacitor, etc.

[0023] like Figure 1 and Figure 2 The diagrams illustrate a chip-type niobium oxide polythiophene polymer capacitor provided in the application. The capacitor includes: a niobium oxide valve metal 11, a niobium pentoxide dielectric layer 12 on the surface of the niobium oxide valve metal 11, an anode lead 13 extending from the niobium oxide valve metal 11, the anode lead 13 being made of niobium wire and connected to the anode terminal 7, a polydopamine layer 2 coated on the niobium pentoxide dielectric layer 12, a polythiophene polymer conductive layer 3 disposed outside the polydopamine layer 2, a first conductive layer 4 disposed outside the polythiophene polymer conductive layer 3, and a second conductive layer 5 disposed outside the first conductive layer 4, the second conductive layer 5 being connected to the cathode terminal 8. The entire capacitor is encapsulated by a resin encapsulation layer 6.

[0024] This invention also provides a method for preparing a niobium oxide polymer capacitor, wherein the method for preparing a polydopamine on the surface of the dielectric layer includes: The valve metal with the dielectric layer is immersed in dopamine-tris(hydroxymethyl)aminomethane hydrochloride buffer solution, so that the generated polydopamine is spontaneously deposited onto the electrode surface. After polydopamine is formed on the surface of the valve metal with the dielectric layer, it is removed and dried, thus completing the coating of polydopamine on the surface of the dielectric layer.

[0025] In some embodiments, the tris(hydroxymethyl)aminomethane hydrochloride buffer solution used in the capacitor fabrication method is weakly alkaline; in preferred embodiments, the pH value is between 8 and 8.5. Polydopamine is a cross-linked polymer formed by the self-oxidative polymerization of dopamine under weakly alkaline conditions. Its structure lacks regular repeating units and is an amorphous, low-crystallinity three-dimensional network polymer. Its core structural characteristics revolve around functional group diversity, cross-linking network, and surface properties, thus acting as an "interfacial bridge" to enhance the bonding ability of the conductive polymer on the dielectric layer. In some embodiments, the process of applying polydopamine to the dielectric layer surface is carried out at room temperature in a light-protected environment. In some embodiments, the dielectric layer surface is cleaned before applying polydopamine.

[0026] The following example of preparing niobium oxide polythiophene capacitors illustrates the preparation method of polymer capacitors provided in this application. It should be emphasized that many process conditions affect the performance of capacitors. However, under the same conditions, the problems raised in this application can be solved by using the control conditions of similar embodiments and comparative examples.

[0027] Example 1: Fabrication of anode elements: The anode element comprises a sintered niobium oxide body, niobium wire, and a dielectric layer of niobium pentoxide, specifically: Niobium monoxide powder with a CV value of 80000 μF·V / g was selected. Niobium wire with a diameter of 0.29 mm was used as the anode lead. Niobium oxide capacitor anode core with a specification of 10V 220μF was pressed and sintered in a vacuum sintering furnace at 1500℃ for 20 min to obtain a porous anode body. The sintered anode body was then subjected to formation in a 0.1% phosphoric acid aqueous solution at 40V for 7 hours to form a dielectric layer containing niobium pentoxide on the surface of the sintered body and some leads. After drying, the anode element was obtained.

[0028] Preparation of dopamine tris(hydroxymethyl)aminomethane hydrochloride solution: Dopamine hydrochloride powder and Tris-HCl buffer were mixed to obtain a dopamine solution with a mass concentration of 2 mg / mL, and the pH was adjusted to 8.5 using a pH buffer to obtain a dopamine tris(hydroxymethyl)aminomethane hydrochloride solution.

[0029] Coating the surface of the anode element with polydopamine:Under normal temperature and light-protected conditions, the surface-cleaned anode element is immersed in a dopamine tris(hydroxymethyl)aminomethane hydrochloride solution, allowing the generated polydopamine to spontaneously deposit onto the electrode surface for 24 hours. After drying, an anode element with polydopamine coating is obtained.

[0030] A conductive polymer, polythiophene, is coated onto the surface of an anode element that is coated with polydopamine. An anode element coated with polydopamine was immersed in an isopropanol solution of 18% 3,4-ethylidene dioxythiophene with a mass concentration of 18% and left to stand for 5 minutes. Then it was taken out and dried at 25℃~30℃ for 30 minutes to carry out oxidative polymerization. After drying, polythiophene was formed on the surface of the anode element. This process was repeated 5 times. After washing and drying, a polythiophene conductive polymer was coated on the surface of the anode element coated with polydopamine, thus obtaining a capacitor element.

[0031] The capacitor element was immersed in a colloidal graphite emulsion solution with a pH of 10 and a mass concentration of 4% for 2 minutes, then dried. After drying, it was immersed in silver paste with a concentration of 46% to a thickness of 60% of the product. After being left in the air for 30 minutes, it was dried again. Then it was connected to the cathode lead as the cathode lead-out. Finally, it was encapsulated with epoxy resin material to form a niobium oxide polymer capacitor.

[0032] Example 2 The only difference between Example 2 and Example 1 is that in the step of "coating polydopamine on the surface of the anode element", the deposition time is 12 hours. The other steps are the same as in Example 1.

[0033] Example 3 The only difference between Example 3 and Example 1 is that in the step of "coating polydopamine on the surface of the anode element", the deposition time is 5 hours, and the other steps are the same as in Example 1.

[0034] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the step of "coating the anode element surface with polydopamine" is omitted; the other steps are the same as in Example 1. The structure of the prepared capacitor includes: a niobium oxide valve metal, a niobium pentoxide dielectric layer on the surface of the niobium oxide valve metal, and a niobium wire anode lead drawn from the niobium oxide valve metal. A polythiophene polymer conductive layer is disposed on the niobium pentoxide dielectric layer, a first conductive layer is disposed outside the polythiophene polymer conductive layer, and a second conductive layer is disposed outside the first conductive layer, with the second conductive layer connected to the cathode terminal. The entire capacitor is encapsulated in resin.

[0035] The capacitors obtained in the above embodiments and comparative examples were subjected to equivalent series resistance (ESR), breakdown voltage, and leakage current tests at 100 kHz. Table 1 shows the test results of the obtained solid electrolytic capacitors.

[0036] Table 1. Capacitor test results obtained from the examples and comparative examples. As can be seen from Examples 1 to 3, the performance of the capacitors varies due to different deposition times of polydopamine. It is speculated that this is because the deposition time is related to the deposition amount. A longer deposition time increases the breakdown voltage and decreases the leakage current, but also increases the ESR. Conversely, a shorter deposition time results in a lower breakdown voltage, increased leakage current, and a higher ESR.

[0037] As can be seen from the examples and Comparative Example 1, the addition of polydopamine can significantly reduce leakage current and ESR, while improving breakdown voltage.

[0038] The speculated reason is that polydopamine forms a tight bond with the dielectric layer through hydrogen bonds (e.g., hydrogen bonds with hydroxyl groups on the Nb₂O₅ surface, and coordination bonds with metal ions) via phenolic hydroxyl groups. The benzene rings in polydopamine bind to the conjugated benzene rings in the conductive polymer through π-π stacking interactions, thus enhancing the bonding ability between the polydopamine-formed dielectric layer and the conductive polymer. This results in a lower interfacial impedance, increased transmission efficiency between the dielectric layer and the conductive polymer, reduced leakage current, and improved stability.

[0039] A uniform and dense polydopamine nanoscale barrier can be formed on the surface of the dielectric layer by deposition, which effectively fills the micropores and defects of the metal anodic oxide film, inhibits the formation of electrical breakdown channels, and polydopamine has excellent mechanical toughness, which can effectively disperse the stress generated by instantaneous overcurrent / overvoltage, protect the electrode interface, significantly improve the resistance to mechanical and electrical shocks, prevent electrolyte decomposition and electrode stripping, and make up for the lack of liquid buffer in solid polymer electrolytic capacitors.

[0040] Therefore, it can be explained that the polydopamine surface containing phenolic hydroxyl and amino groups introduced between the dielectric layer and the conductive polymer layer can form hydrogen bonds with the -OH on the surface of the metal oxide film dielectric layer, and at the same time can form π-π stacking with the continuous conjugated π electron system ring of the conductive polymer. This improves the bonding ability between the metal oxide film dielectric layer and the conductive polymer in the polymer solid electrolytic capacitor, solves the problem of weak bonding ability between the metal oxide film dielectric layer and the conductive polymer in the polymer solid electrolytic capacitor, and further solves the problem of the lack of buffering effect of liquid electrolyte in polymer solid electrolytic capacitor, which leads to problems such as electrolyte decomposition, electrode peeling or oxide film breakdown when subjected to instantaneous overcurrent or overvoltage impact.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A polymer capacitor, which is a solid electrolytic capacitor, characterized by comprising: The dielectric layer between the valve metal surface of the capacitor and the polymer conductive polymer layer has polydopamine.

2. The polymer capacitor according to claim 1, wherein The polydopamine covers all areas between the dielectric layer and the polymer conductive polymer layer; or, the polydopamine covers part of the areas between the dielectric layer and the polymer conductive polymer layer.

3. The polymer capacitor according to claim 1, wherein The polymer conductive polymer at least contains any one of effective conductive components in polyaniline, polyphenyl ether, polyphenyl sulfide, polythiophene, polyfuran, polypyrrole, polymethylpyrrole, and substituted derivatives and copolymers thereof.

4. The polymer capacitor according to claim 1, wherein The valve metal includes metal or metal oxide.

5. The polymer capacitor according to claim 1 or 4, wherein The valve metal includes at least one of niobium oxide, tantalum, niobium, aluminum, titanium.

6. The polymer capacitor according to claim 1, wherein The dielectric layer includes Nb2O 5、 at least one of Ta2O5, Al2O3, TiO2.

7. A method for producing a polymer capacitor, for producing the polymer capacitor according to any one of claims 1 to 6, characterized by The method for setting polydopamine on the surface of the dielectric layer includes: The valve metal with the dielectric layer is soaked in a dopamine-trihydroxymethyl aminomethane hydrochloride buffer solution, and the generated polydopamine is spontaneously deposited to the electrode surface, after the polydopamine is formed on the surface of the valve metal with the dielectric layer, the valve metal is taken out and dried, and the setting of the polydopamine on the surface of the dielectric layer is completed.

8. The preparation method according to claim 5, characterized in that, The trihydroxymethyl aminomethane hydrochloride buffer solution is weakly alkaline, and preferably, the pH value is between 8 and 8.

5.

9. The preparation method according to claim 5, characterized in that, The process of setting polydopamine on the surface of the dielectric layer is carried out in a normal temperature light-proof environment.

10. The method of claim 5, wherein, The surface of the dielectric layer is cleaned before the polydopamine is set on the surface of the dielectric layer.

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