TWI602206B - Capacitor structure - Google Patents

Description

Capacitor structure

The present disclosure relates to capacitor structures, and more particularly to the composition of their organic-inorganic composite layers.

For a long time, a major issue in the development of electrolytic capacitors has been to improve the conductivity of the electrolyte to reduce the equivalent series resistance of the capacitor, to achieve high frequency and low impedance and high reliability. Since the conductive polymer is more salty than the liquid electrolyte used in the conventional electrolytic capacitor or the solid organic semiconductor, such as the TCNQ composite salt, has higher conductivity and moderate high-temperature insulating properties, the conductive polymer becomes the present day. The development trend of solid electrolytes used in electrolytic capacitors.

Although the conductive conjugated polymer synthesized by the in-situ polymerization method has the advantages of low impedance and good thermal stability compared with the conventional liquid electrolyte, the withstand voltage characteristic of the conductive conjugated polymer is far less than that of the liquid electrolyte. . Therefore, the low operating voltage becomes the biggest obstacle to the use of the conductive conjugated polymer in electrolytic capacitors.

In summary, there is a need for a new capacitor structure to overcome the above problems.

The capacitor structure provided by an embodiment includes: a positive electrode; a dielectric layer on the positive electrode; and an organic-inorganic composite layer on the dielectric layer And a negative electrode; and a conductive conjugated polymer electrolyte between the organic-inorganic composite layer and the negative electrode.

10‧‧‧Capacitor structure

11A‧‧‧ positive

11B‧‧‧ dielectric layer

11C‧‧‧Organic-inorganic composite layer

13‧‧‧ Electrolytes

15‧‧‧negative

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a capacitor structure in an embodiment.

In the embodiment shown in FIG. 1, the capacitor structure 10 includes a positive electrode 11A, a dielectric layer 11B on the positive electrode 11A, an organic-inorganic composite layer 11C on the dielectric layer 11B, a negative electrode 15, and an organic layer- The electrolyte 13 between the inorganic composite layer 11C and the anode 15. In one embodiment, the valve metal used for the positive electrode 11A includes aluminum, tantalum, niobium, titanium, zirconium, or alloys thereof. The shape of the positive electrode 11A may be a sheet-like foil or sintered into a porous ingot shape. Etching can be performed as needed to obtain a larger specific surface area.

In an embodiment, the dielectric layer 11B may be an oxide of the above positive electrode 11A. For example, the surface of the positive electrode 11A may be chemically treated to form the dielectric layer 11B on the surface of the positive electrode 11A. In other embodiments, the dielectric layer 11B may be formed in other ways, such as by sputtering a metal oxide on the positive electrode 11A.

The above organic-inorganic composite layer 11C may be a composite layer of a single layer or a multilayer structure. In one embodiment, the organic-inorganic composite layer 11C is formed by mixing an insulating polymer and an inorganic material. For example, the monomer or precursor of the insulating polymer may be mixed with the inorganic substance and then polymerized into an insulating polymer. Alternatively, the monomer or precursor of the insulating polymer may be polymerized into an insulating polymer and then mixed with the inorganic material.

In one embodiment, the organic-inorganic composite layer 11C has a high insulation. The molecule may be a nitrogen-containing polymer such as poly(vinyl pyrrolidone, PVP); an oxygen-containing polymer such as poly(ethylene oxide) (PEO); or a blend of the above.

The molecular weight of the insulating polymer of the above organic-inorganic composite layer is not particularly limited, but the number average molecular weight of the linear insulating polymer may be between 1,000 and 2,000,000. When the molecular weight is too low, the linear polymer exhibits a liquid state at room temperature, and it is not easy to form a stable layered structure on the surface of the dielectric layer. If the molecular weight is too high, the organic-inorganic composite layer is affected to form a film on the surface of the dielectric layer.

The inorganic substance may be first mixed with an insulating polymer or an insulating polymer precursor in the form of a precursor, and then reacted to form an inorganic substance. In addition, the inorganic precursor may be first reacted to form an inorganic substance, and then mixed with an insulating polymer or an insulating polymer precursor.

In one embodiment, the inorganic material may be alumina, zinc oxide, a combination of boric acid and zinc oxide, or a combination of boric acid and aluminum hydroxide. In one embodiment, the inorganic material is in a particulate state, and the average particle diameter may be less than or equal to 1000 μm to be well dispersed in the organic-inorganic composite layer 11C. In one embodiment, the inorganic material has an average particle size of between 10 nm and 100 nm. The weight ratio of the insulating polymer to the inorganic substance of the organic-inorganic composite layer 11C may be between 1:100 and 100:1, such as 100:40. In other words, the above organic-inorganic composite layer 11C may contain 1 part by weight of the insulating polymer and 100 to 0.01 parts by weight of the inorganic substance.

The above negative electrode 15 may be a metal foil, and may be etched on the surface of the metal foil to obtain a larger surface area as needed, or may be attached with other substances such as carbon or titanium to enhance chemical stability or increase electrical capacity. In an embodiment, the anode 15 may also be a conductive silver paste or a carbon paste attached to the electrolyte 13.

The electrolyte 13 may be a conductive conjugated polymer such as a polythiophene, a polypyrrole, or a polyaniline in a doped state, or a derivative thereof. In one embodiment, the conductive conjugated polymer may be poly(3,4-ethylenedioxythiophene) (PEDOT), or a copolymer or blend containing the above structure. .

In order to make the conjugated polymer have excellent conductivity, the conjugated polymer is preferably in a doped state. The dopant may be a sulfonic acid compound such as methanesulfonic acid, benzenesulfonic acid, or p-toluenesulfonic acid; a sulfonic acid polymer such as poly(styrene sulfonic acid, PSS) or a copolymer thereof; An acid compound such as benzoic acid, phthalic acid, or succinic acid; an acid polymer such as polyacrylic acid or a copolymer thereof; an amino acid such as glycine; a phosphate compound such as phosphoric acid or etidron (Etidronic) Acid), or diphenyl phosphate; or a combination of the above.

The conjugated polymer may be doped by first polymerizing into a conjugated polymer, then doping with a dopant, adding a dopant during the polymerization of the conjugated polymer, or initiating a conjugated polymer with an oxidizing agent. The by-products generated during the polymerization are doped as a dopant, for example, p-toluenesulfonic acid generated as a dopant when the conjugated polymer is initiated by iron p-toluenesulfonate.

The above-mentioned conductive conjugated polymer synthesis method may be an in-situ chemical polymerization method in which a conductive conjugated polymer precursor is polymerized on the surface of the organic-inorganic composite layer 11C; and an electrochemical polymerization method is used. The conductive conjugated polymer monomer is electrochemically polymerized on the surface of the organic-inorganic composite layer 11C; and the synthesized water-soluble conductive polymer such as PEDOT:PSS aqueous solution is coated or impregnated on the surface of the organic-inorganic composite layer 11C. Conductive conjugated polymer. Above in situ chemistry The oxidizing agent used in the polymerization method may be a salt containing iron ions or a salt containing copper ions. The above iron ion-containing salts include iron benzenesulfonate, iron p-toluenesulfonate, iron chloride, iron nitrate, iron sulfate, or a combination thereof. The above copper ion-containing salts include copper persulfate.

In one embodiment, the aluminum foil can be electrochemically etched to form a high surface area aluminum foil with a carbon layer attached thereto as the negative electrode 15. Then, a separator paper (not shown) may be interposed between the positive electrode 11 and the negative electrode 15 as needed, and then wound into a solid electrolytic capacitor element. In some embodiments, the solid electrolytic capacitor element described above may be treated with an aqueous solution of an organic acid to repair the damaged dielectric layer 11B. In one embodiment, the organic acid can be oxalic acid or acetic acid.

Next, the solid electrolytic capacitor element is impregnated into the aqueous liquid of the organic-inorganic composite, and then heated to remove water to form the organic-inorganic composite layer 11C on the dielectric layer 11B. In one embodiment, the insulating polymer may be a nitrogen-containing or oxygen-containing polymer such as polyvinylpyrrolidone (PVP) or polyethylene oxide having a number average molecular weight of between 1,000 and 2,000,000. In an embodiment, the inorganic material may be aluminum oxide or zinc oxide. In one embodiment, the inorganic material is alumina. In one embodiment, the inorganic material is zinc oxide. In one embodiment, the inorganic material is a combination of boric acid and zinc oxide. In one embodiment, the inorganic material is a combination of boric acid and aluminum hydroxide.

Next, the solid electrolytic capacitor element is impregnated into the precursor of the conductive conjugated polymer, and the precursor is polymerized to form a conductive conjugated polymer as the electrolyte 13 between the positive electrode 11 and the negative electrode 15. In one embodiment, the conductive conjugated polymer may be doped polythiophene, polypyrrole, polyaniline, or poly(3,4-ethylenedioxythiophene).

For solid capacitor structures, due to defects or thickness of the dielectric layer The unevenness of the local dielectric layer is poor. Ideally, the withstand voltage characteristics of the local dielectric layer can be improved by a partial insulation reaction of the conductive conjugated polymer electrolyte. However, when the voltage is too high or the dielectric layer is seriously defective, the conductive conjugated polymer electrolyte may be largely insulated, causing the capacitance of the capacitor to be greatly degraded, the impedance to rise, and the leakage current to be excessively large. A short circuit occurs because it cannot withstand the operating voltage. The above organic-inorganic composite layer can fill a local dielectric layer (thinner portion) and structural defects to increase the withstand voltage of the capacitor and reduce the chance of insulation of the conductive conjugated polymer electrolyte. As a result, the impedance and capacitance of the capacitor will remain stable for a long time.

The above and other objects, features, and advantages of the present invention will become more apparent and understood.

Example

Comparative example 1

The positive electrode aluminum foil was treated by 21 V electrochemical electrolysis to form an alumina dielectric layer on the positive electrode aluminum foil. The negative electrode carbon foil is electrochemically etched to form a high surface area negative carbon foil. A separator paper is interposed between the positive electrode and the negative electrode, and then wound into a solid electrolytic capacitor element. The solid electrolytic capacitor element is treated with an aqueous solution of an organic acid to repair the damaged alumina dielectric layer.

Next, the above solid electrolytic capacitor element was impregnated with a mixture of 3,4-ethylenedioxythiophene (EDOT) monomer and a 50 wt% toluenesulfonic acid iron ethanol solution, and the mixture was heated to accelerate the polymerization. At the time of polymerization, the highest temperature can reach 170 ° C to ensure the reaction is complete. After the above polymerization reaction, a conductive conjugated polymer such as doped PEDOT is formed between the positive electrode and the negative electrode. Then, the solid electrolytic capacitor element is placed in an aluminum shell, and the rubber cap is sealed to complete the solid. State electrolytic capacitors are fabricated and tested for characteristics of solid electrolytic capacitors. Finally, the capacitor was subjected to an overvoltage load test by applying a current of 16 V for 12 hours at 125 ° C, and its electrical properties are listed in Table 2.

Comparative example 2

Similar to Comparative Example 1, the difference is that the solid electrolytic capacitor element is impregnated with a mixture of 3,4-ethylenedioxythiophene (EDOT) monomer and a concentration of 50% by weight of an iron toluenesulfonic acid solution. The capacitor element is impregnated with an aqueous solution of PVP (number average molecular weight of about 1,300,000) (see Table 1). After heating to 60 ° C, it was maintained for one hour, and then heated to 125 ° C for one hour to remove water, that is, a PVP layer was formed on the alumina dielectric layer. Then, steps such as doping PEDOT, sealing, characteristic test, and overvoltage load test were formed, which were similar to Comparative Example 1. The electrical properties of the capacitor of this embodiment are listed in Table 2.

Example 1

Similar to Comparative Example 1, the difference is that the solid electrolytic capacitor element is impregnated with a mixture of 3,4-ethylenedioxythiophene (EDOT) monomer and a concentration of 50% by weight of an iron toluenesulfonic acid solution. The capacitor element is impregnated with an aqueous solution of PVP (number average molecular weight of about 1,300,000) and γ-Al ₂ O ₃ (particle size of between 40 nm and 80 nm) (see Table 1). After heating to 60 ° C, it was maintained for one hour, and then heated to 125 ° C for one hour to remove water, that is, an organic-inorganic composite layer of PVP-γ-Al ₂ O ₃ was formed on the alumina dielectric layer. Then, steps such as doping PEDOT, sealing, characteristic test, and overvoltage load test were formed, which were similar to Comparative Example 1. The electrical properties of the capacitor of this embodiment are listed in Table 2.

Example 2

Similar to Example 1, the difference is that the aqueous solution of PVP and γ-Al ₂ O ₃ is replaced by an aqueous solution of PVP and ZnO (particle size of about 20 nm) (see Table 1) to form an organic PVP-ZnO. The inorganic composite layer is on the alumina dielectric layer. The electrical properties of the capacitor of this embodiment are listed in Table 2.

Comparative example 3

Similar to Example 1, the difference is that the aqueous solution of PVP and γ-Al ₂ O ₃ is replaced with an aqueous solution of PVP and TiO ₂ (particle size less than 25 nm) (see Table 1) to form PVP-TiO ₂ . The organic-inorganic composite layer is on the alumina dielectric layer. The electrical properties of the capacitor of this comparative example are listed in Table 2.

As shown in Table 2, after the capacitor was sealed, the capacitances of the other comparative examples and the examples were similar to those of the 100 kHz ESR except that the 100 kHz ESR of Comparative Example 1 was relatively high.

The alumina dielectric layers formed by the 21 V electrochemical electrolysis reactions of Examples 1 and 2 and Comparative Examples 1 to 3 were suitable for a maximum operating voltage of 10 V before being treated with the organic inorganic protective layer. After 12 hours of 16V overvoltage load test at 125°C, the characteristics of the different capacitors showed great differences. The capacitance of the capacitor of Comparative Example 1 (the dielectric layer directly contacts the conductive conjugated polymer electrolyte) was 17.51%, and the ESR of 100 kHz was also greatly increased. The average leakage current of 16 V was also as high as 1743 μA, and the short-circuit rate of the capacitor was as high as 60%. The capacitor of Comparative Example 2 (with the PVP layer on the dielectric layer) had a capacitance degradation of 8.69% after the overvoltage load test, and the 100 kHz ESR increased from 14.43 mΩ after sealing to 18.18 mΩ, an increase of about 26%. As for the solid capacitor having the organic-inorganic composite layer on the dielectric layer, the capacitors of Example 1 (PVP-alumina) and Example 2 (PVP-Zinc Oxide) have a capacitance of about 2.7%, 100 kHz ESR. Slightly increased by 15%, and there is no short circuit or excessive leakage current. While the solid capacitor of Comparative Example 3 (PVP-titanium oxide) has an organic-inorganic composite layer on the dielectric layer, the capacitance of the capacitor is reduced by 13.76%, and the leakage current is as high as 4080 μA, which is more in the overvoltage load test. A 20% capacitor has a short circuit.

In summary, only a specific composition of the organic-inorganic composite layer such as PVP-alumina, and PVP-zinc oxide on the dielectric layer can effectively improve the withstand voltage characteristics of the capacitor. The above organic-inorganic composite layer allows the capacitor to maintain better capacitance, impedance and leakage current characteristics under overvoltage conditions and to prevent short circuiting of the capacitor.

Comparative Examples 4 to 8 and Examples 3 to 4

The positive electrode aluminum foil was treated by electrochemical electrolysis at 67 V to form an aluminum oxide dielectric layer on the positive electrode aluminum foil. The negative electrode carbon foil is electrochemically etched to form a high surface area negative carbon foil. A separator paper is interposed between the positive electrode and the negative electrode, and then wound into a solid electrolytic capacitor element. The solid electrolytic capacitor element is treated with an aqueous solution of an organic acid to repair the damaged alumina dielectric layer.

The solid electrolytic capacitor elements are impregnated with a different composition of aqueous liquid (see Table 3), wherein the number average molecular weight of PVP is about 1,300,000. After heating to 60 ° C, it was maintained for one hour, and then heated to 125 ° C for one hour to remove water, that is, an organic-inorganic composite layer was formed on the alumina dielectric layer.

Next, the above solid electrolytic capacitor element was impregnated with a mixture of ethylene dioxythiophene (EDOT) monomer and a 50 wt% aqueous solution of iron toluenesulfonic acid, and the mixture was heated to accelerate the polymerization. At the time of polymerization, the highest temperature can reach 170 ° C to ensure the reaction is complete. After the above polymerization reaction, a conductive conjugated polymer such as doped PEDOT is formed between the positive electrode and the negative electrode. Then, the solid electrolytic capacitor element is placed in an aluminum shell, sealed with a rubber cap, and the solid electrolytic capacitor is fabricated and tested for the characteristics of the solid electrolytic capacitor. Finally, the capacitor was subjected to an overvoltage load test at a current of 40.5 V for 6 hours at 125 ° C, and its electrical properties are listed in Tables 4 and 5.

The optimum operating voltage of the alumina dielectric layer formed by electrochemical electrochemical reaction of Examples 3 to 4 and Comparative Examples 4 to 8 at 67 V was not 30 V before the treatment with the organic inorganic protective layer. The characteristics of each group of capacitors after sealing are similar. However, after the 40.5V overvoltage load test, the capacitors of Comparative Examples 4 to 6 were short-circuited to different degrees. In Comparative Example 5, the combination of aluminum hydroxide and PVP was used as the capacitance protective layer, and the combination of boric acid and PVP in Comparative Example 6 was used as the capacitance protective layer, and the short-circuit rate was higher than that of the pure PVP as the capacitance protective layer in Comparative Example 4. . On the contrary, when the combination of aluminum hydroxide, boric acid and PVP is used as the capacitor protection layer in Embodiment 3, it can be changed. Good capacitor short circuit condition in overvoltage load test. On the other hand, in Example 4, the combination of zinc oxide, boric acid, and PVP as a capacitive protective layer can also improve the short circuit condition of the capacitor under the overvoltage load test.

As shown in Table 5, when the combination of imidazole and PVP in Comparative Example 7 was used as the capacitance protective layer, the characteristics of the capacitor and the short circuit after the overvoltage load were similar to those of the capacitor of Comparative Example 4 in which the pure PVP was used as the capacitance protective layer. However, when the combination of imidazole, boric acid, and PVP was used as the capacitor protective layer in Comparative Example 8, the capacitor was completely short-circuited after the voltage load test. In summary, when boric acid is combined with a specific inorganic base such as zinc oxide and aluminum hydroxide for the capacitor protection layer, the withstand voltage characteristics of the capacitor can be improved. However, if boric acid is used alone or with an organic base (such as imidazole) as a capacitor protection layer, the voltage withstand characteristics of the capacitor are reduced.

The present disclosure has been disclosed in the above several embodiments, but it is not intended to limit the disclosure, and any one skilled in the art can make any changes and refinements without departing from the spirit and scope of the disclosure. Therefore, the scope of protection of this disclosure is subject to the definition of the scope of the patent application.

10‧‧‧Capacitor structure

11A‧‧‧ positive

11B‧‧‧ dielectric layer

11C‧‧‧Organic-inorganic composite layer

13‧‧‧ Electrolytes

15‧‧‧negative

Claims (10)

A capacitor structure comprising: a positive electrode; a dielectric layer on the positive electrode; an organic-inorganic composite layer on the dielectric layer, wherein the organic-inorganic composite layer is mixed with an insulating polymer and an inorganic substance And a negative electrode; and a conductive conjugated polymer electrolyte between the organic-inorganic composite layer and the negative electrode. The capacitor structure of claim 1, wherein the positive electrode comprises aluminum, tantalum, niobium, titanium, zirconium, or an alloy thereof. The capacitor structure of claim 1, wherein the dielectric layer comprises an oxide of the positive electrode. The capacitor structure according to claim 1, wherein the organic-inorganic composite layer comprises 1 part by weight of an insulating polymer and 100 to 0.01 parts by weight of an inorganic substance. The capacitor structure according to claim 4, wherein the insulating polymer comprises a nitrogen-containing polymer, an oxygen-containing polymer, or a blend of the above. The capacitor structure of claim 5, wherein the nitrogen-containing polymer comprises polyvinylpyrrolidone. The capacitor structure of claim 5, wherein the oxygen-containing polymer comprises polyethylene oxide. The capacitor structure of claim 4, wherein the inorganic substance comprises alumina, zinc oxide, a combination of boric acid and zinc oxide, or boric acid and hydroxide A combination of aluminum. The capacitor structure of claim 1, wherein the negative electrode comprises a metal foil. The capacitor structure according to claim 1, wherein the conductive conjugated polymer electrolyte comprises doped polythiophene, polypyrrole, polyaniline, or poly(3,4-ethylenedioxythiophene).