Aluminum electrolytic capacitor electrolyte containing branched dicarboxylic acid or salt thereof and aluminum electrolytic capacitor

Abstract

The invention relates to the technical field of electrolytes of aluminum electrolytic capacitors, in particular to an aluminum electrolytic capacitor electrolyte containing branched-chain dicarboxylic acid or salt thereof and an aluminum electrolytic capacitor. The structural formula of the long-carbon-chain hydroxyl-containing branched-chain dicarboxylic acid is shown in the formula (I), in the formula (1), R1 represents alkyl or benzyl with the hydrogen atom number or the carbon atom number being 1-6, and n is an integer ranging from 2 to 8.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology for aluminum electrolytic capacitors, and more specifically, to an aluminum electrolytic capacitor electrolyte containing a branched dicarboxylic acid or its salt, and an aluminum electrolytic capacitor. Background Technology

[0002] As an electrolyte for energy storage devices, especially for driving electrolytic capacitors in medium and high voltage applications, electrolytes using ethylene glycol as a solvent and boric acid or ammonium borate as the electrolyte are used because they can achieve relatively high voltage withstand. However, such electrolytes have low conductivity, and the esterification reaction between ethylene glycol and boric acid produces a large amount of water. Furthermore, at temperatures above 100°C, the internal pressure increases due to water evaporation, making them unsuitable for use in high-temperature environments.

[0003] Existing electrolytes used in electrolytic capacitor drives, especially medium- and high-voltage electrolytes, typically consist of a solution primarily composed of ethylene glycol with added boric acid or ammonium borate as the electrolyte. In boric acid-containing electrolytes, boric acid reacts with ethylene glycol to generate a large amount of condensed water, leading to an increased water content in the electrolyte system. This water reacts with the aluminum oxide film used as electrodes, causing electrode degradation. Furthermore, when using boric acid-based electrolytes at temperatures exceeding 100°C, the water in the electrolyte evaporates, simultaneously increasing the internal pressure within the capacitor casing and potentially damaging the capacitor. To mitigate these drawbacks, electrolytes containing linear saturated diacids or their salts are used as solutes. However, linear saturated diacids have very low solubility in solvents such as ethylene glycol. Therefore, at low temperatures, linear saturated diacids easily crystallize, inevitably resulting in excessive current and deterioration of the capacitor's low-temperature characteristics.

[0004] Therefore, in recent years, branched saturated or unsaturated dicarboxylic acids, such as 2-butyloctanoic acid (GB1429105, US3946070, JP49-115992), have been prepared by oxidation with cyclohexanone. Generally, the main product is dodecyl dicarboxylic acid, and the yield of branched 2-butyloctanoic acid is very low. 7-ethylenediene-9-hexadecene-1,16-dicarboxylic acid dicarboxylic acid or its salts (Japanese Patent Application Laid-Open No. 4-186713) are unstable in electrolytes at high temperatures due to the presence of olefin bonds, resulting in large variations in electrolyte conductivity. Therefore, compositions suitable for high-voltage electrolytic capacitors, especially those for high-voltage electrolytic capacitors, are desirable, as they should exhibit minimal decrease in electrolyte conductivity (mS / cm) or spark initiation voltage (Vsp) even after prolonged use. Summary of the Invention

[0005] This invention provides an electrolyte for aluminum electrolytic capacitors containing branched dicarboxylic acids or their salts, and an aluminum electrolytic capacitor. It provides an electrolyte for aluminum electrolytic capacitors that has high voltage resistance, excellent solubility, and high safety and reliability.

[0006] In a first aspect, the present invention provides a branched dicarboxylic acid or a salt thereof, wherein the long carbon chain branched dicarboxylic acid has the structural formula shown in formula (I).

[0007] General formula (1)

[0008] In general formula (1), R1 represents an alkyl or benzyl group with 1 to 6 hydrogen atoms or carbon atoms, and n is an integer from 2 to 8.

[0009] Preferably, the branched dicarboxylic acid or its salt is synthesized by hydrolysis of an ester compound.

[0010] Secondly, the present invention provides an electrolyte for aluminum electrolytic capacitors, wherein the electrolyte for aluminum electrolytic capacitors contains a branched dicarboxylic acid or its salt.

[0011] Preferably, the branched dicarboxylic acid salt is selected from ammonium salts and / or amine salts.

[0012] Preferably, the ammonium salt is selected from at least one of 2-benzyl adipate diammonium or 2,5-dibenzyl adipate diammonium; the amine salt is selected from at least one of 2-benzyl adipate di(ethylamine) salt or 2,5-dibenzyl adipate di(dimethylamine) salt.

[0013] Preferably, the electrolyte for the aluminum electrolytic capacitor further includes a solvent, additives, and a hydrogen scavenger, wherein the solvent is selected from at least one of alcohols, lactones, carbonates, amides, nitriles, sulfoxides, and sulfones;

[0014] The additive is selected from at least one of the following: phosphoric acid compounds, phosphorous acid compounds, phosphate ester compounds, nitro compounds, nitrile compounds, boric acid compounds, sulfonic acid compounds, phenols, polyols, polyvinyl alcohol, polyvinyl ether, polyethylene glycol, and polypropylene glycol.

[0015] The hydrogen scavenger is selected from at least one of m-nitroacetophenone, p-nitroanisole, and p-nitrobenzoic acid.

[0016] Preferably, the alcohol is selected from at least one of water, ethylene glycol, diethylene glycol, propylene glycol, glycerol, and 1,4-butanediol;

[0017] The lactones are selected from at least one of γ-butyrolactone, β-butyrolactone, γ-valerolactone, and δ-valerolactone;

[0018] The carbonates are selected from at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate.

[0019] The amides are selected from at least one of formamide, methylformamide, dimethylformamide, ethylformamide, diethylformamide, methylacetamide, dimethylacetamide, ethylacetamide, diethylacetamide, and N-methylpyrrolidone;

[0020] The nitrile is selected from at least one of acetonitrile, propionitrile, and adiponitrile; the sulfoxide is selected from dimethyl sulfoxide; and the sulfone is selected from at least one of dimethyl sulfone and sulfolane.

[0021] Preferably, the electrolyte for the aluminum electrolytic capacitor further contains other carboxylic acids or carboxylates, wherein the other carboxylic acids or carboxylates are selected from at least one of the following: iodic acid, pimelic acid, octanoic acid, azelaic acid, 1,7-octanedicarboxylic acid, sebacic acid, 1,10-decanedicarboxylic acid, 2-methylazelaic acid, 1,6-decanedicarboxylic acid, and dodecanoic acid.

[0022] Preferably, the electrolyte for the aluminum electrolytic capacitor contains 50.0% to 90.0% solvent and 0.5% to 20.0% branched dicarboxylic acid or its salt.

[0023] Thirdly, an aluminum electrolytic capacitor is provided, including a positive foil, a negative foil, electrolytic paper, and an electrolyte for the aluminum electrolytic capacitor.

[0024] In summary, the present invention has the following beneficial effects:

[0025] 1. In this invention, the branched dicarboxylic acid or its salt has a steric hindrance in the side groups, resulting in a solubility in polar solvents such as ethylene glycol that is several times higher than that of straight-chain carboxylic acids. This avoids low-temperature crystallization and improves low-temperature performance. While maintaining high conductivity, the branched carboxylic acid, due to its molecular structure, prevents electrolyte decomposition, resulting in a flash voltage significantly higher than that of straight-chain salts of the same concentration. Its unique branched structure significantly improves solubility, thermal stability, and electrical performance, making the capacitor perform better in high-voltage, wide-temperature-range, and long-life applications.

[0026] 2. This invention provides an electrolyte for aluminum electrolytic capacitors that has high voltage resistance, excellent solubility, and high safety and reliability.

[0027] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the scope of protection of the present invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments can be obtained from commercially available sources.

[0029] Preparation Example

[0030] Preparation Example 1

[0031] Synthesis of 2-benzyl adipic acid:

[0032] A mixture of 264 g of dimethyl 2-benzyl adipate and 580 g of 15% sodium hydroxide was heated and stirred at 110 °C for 3 h. After the reaction was completed, methanol was distilled off under reduced pressure, the solution was adjusted to acidity with dilute sulfuric acid, washed repeatedly with water, and dissolved by heating with deionized water. The solution was then cooled and crystallized to obtain 230 g of white crystalline 2-benzyl adipate.

[0033] Preparation Example 2

[0034] Synthesis of 2,5-dibenzyl adipic acid:

[0035] A mixture of 380 g of dimethyl 2,5-dibenzyl adipate and 580 g of 15% sodium hydroxide was heated and stirred at 110 °C for 6 h. After the reaction was completed, methanol was distilled off under reduced pressure, the solution was adjusted to acidity with dilute sulfuric acid, washed repeatedly with water, and dissolved by heating with deionized water. The solution was then cooled and crystallized to obtain 320 g of white crystalline 2,5-dibenzyl adipate.

[0036] Example

[0037] Example 1

[0038] The dicarboxylic acid obtained in Preparation Example 1 was dissolved in ethylene glycol, and neutralized by blowing in ammonia gas to obtain ethylene glycol solutions (electrolyte compositions) of the corresponding ammonium salts (10% and 5%). The pH of the resulting solutions was 6.5–7.0. 1.5% pure water was added to these solutions, and the conductivity and spark voltage were measured. As Comparative Example 1, 2-butyloctanoic acid was purchased commercially and an electrolyte was prepared according to the above procedure. The conductivity and spark voltage of this electrolyte were tested. These results are shown in Table 1.

[0039] Example 2

[0040] The dicarboxylic acid obtained in Preparation Example 2 was dissolved in ethylene glycol, and neutralized by blowing in ammonia gas, yielding ethylene glycol solutions (electrolyte compositions) of the corresponding ammonium salts (10% and 5%). The resulting solutions had a pH of 6.5–7.0. 1.5% pure water was added to these solutions, and the conductivity and spark voltage were measured. Additionally, as Comparative Example 1, 2-butyloctanoic acid was purchased commercially and an electrolyte was prepared according to the above procedure. The conductivity and spark voltage of this electrolyte were tested. These results are shown in Table 1.

[0041] Comparative Example 1

[0042] The same preparation method as in Example 1 was used, except that 2-butyloctanoic acid was used instead of the dicarboxylic acid in Example 1.

[0043] The spark voltage test method involves immersing a 10cm² piece of etched aluminum foil in an electrolyte solution, applying a constant current of 2mA at 85°C, and continuously increasing the voltage until breakdown discharge occurs. The voltage value measured at this point is the spark voltage. The higher the voltage value, the stronger the insulation strength and self-healing capability of the electrolyte-oxide film combination.

[0044] Appearance, electrolyte preparation, placed in a -25℃ refrigerator for 5 hours, and the clarity of the solution was visually inspected;

[0045] Electrical conductivity is measured at a constant temperature (e.g., 25°C) using a conductivity meter to measure its initial conductivity, and then measured again after high-temperature aging. The rate of change in conductivity is calculated to assess its stability and lifespan.

[0046] Table 1. Test results of conductivity and spark voltage.

[0047]

[0048] Using the ammonium salt prepared from 2-butyloctanoic acid used in Preparation Example 1, Preparation Example 2, and Comparative Example 1, a 5% ethylene glycol solution was prepared. 0.1% ammonium hypophosphite and 0.5% m-nitroacetophenone were added to prepare the electrolyte, which was then placed in a stainless steel bottle and sealed. The stability data were tested at 125°C and are shown in Table 2.

[0049] Table 2 Stability Test Results

[0050]

[0051] As can be clearly seen from Tables 1 and 2 above, the 2-benzyl adipic acid and 2,5-dibenzyl adipic acid containing the present invention exhibit excellent performance in terms of voltage resistance, conductivity, solubility, and thermal stability in the electrolyte for aluminum electrolytic capacitors.

[0052] This provides possibilities for the industry. The 2-benzyl adipic acid and 2,5-dibenzyl adipic acid contained in this invention are used as electrolytes for aluminum electrolytic capacitors. They exhibit excellent performance in terms of voltage resistance, conductivity, solubility, and thermal stability, and are particularly suitable for medium and high voltage aluminum electrolytic capacitors.

[0053] The above description is merely an exemplary embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A branched dicarboxylic acid or its salt, characterized in that, The structural formula of this long carbon chain hydroxyl-branched dicarboxylic acid is shown in formula (I). General formula (1) In general formula (1), R1 represents an alkyl or benzyl group with 1 to 6 hydrogen atoms or carbon atoms, and n is an integer from 2 to 8.

2. An electrolyte for aluminum electrolytic capacitors, characterized in that, The electrolyte for the aluminum electrolytic capacitor contains the branched dicarboxylic acid or its salt as described in claim 1.

3. The electrolyte for aluminum electrolytic capacitors according to claim 2, characterized in that, The branched dicarboxylic acid salt is selected from ammonium salts and / or amine salts.

4. The electrolyte for aluminum electrolytic capacitors according to claim 3, characterized in that, The ammonium salt is selected from at least one of 2-benzyl adipate diammonium or 2,5-dibenzyl adipate diammonium; the amine salt is selected from at least one of 2-benzyl adipate di(ethylamine) salt or 2,5-dibenzyl adipate di(dimethylamine) salt.

5. The electrolyte for aluminum electrolytic capacitors according to claim 2, characterized in that, The electrolyte for the aluminum electrolytic capacitor further includes a solvent, additives, and a hydrogen scavenger, wherein the solvent is selected from at least one of alcohols, lactones, carbonates, amides, nitriles, sulfoxides, and sulfones; The additive is selected from at least one of the following: phosphoric acid compounds, phosphorous acid compounds, phosphate ester compounds, nitro compounds, nitrile compounds, boric acid compounds, sulfonic acid compounds, phenols, polyols, polyvinyl alcohol, polyvinyl ether, polyethylene glycol, and polypropylene glycol. The hydrogen scavenger is selected from at least one of m-nitroacetophenone, p-nitroanisole, and p-nitrobenzoic acid.

6. The electrolyte for aluminum electrolytic capacitors according to claim 5, characterized in that, The alcohol is selected from at least one of water, ethylene glycol, diethylene glycol, propylene glycol, glycerol, and 1,4-butanediol; The lactones are selected from at least one of γ-butyrolactone, β-butyrolactone, γ-valerolactone, and δ-valerolactone; The carbonates are selected from at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate.

7. The electrolyte for aluminum electrolytic capacitors according to claim 5, characterized in that, The amides are selected from at least one of formamide, methylformamide, dimethylformamide, ethylformamide, diethylformamide, methylacetamide, dimethylacetamide, ethylacetamide, diethylacetamide, and N-methylpyrrolidone; The nitrile is selected from at least one of acetonitrile, propionitrile, and adiponitrile; the sulfoxide is selected from dimethyl sulfoxide; and the sulfone is selected from at least one of dimethyl sulfone and sulfolane.

8. The electrolyte for aluminum electrolytic capacitors according to claim 2, characterized in that, The electrolyte for the aluminum electrolytic capacitor also contains other carboxylic acids or carboxylates, wherein the other carboxylic acids or carboxylates are selected from at least one of the following: iodic acid, pimelic acid, octanoic acid, azelaic acid, 1,7-octanedicarboxylic acid, sebacic acid, 1,10-decanedicarboxylic acid, 2-methylazelaic acid, 1,6-decanedicarboxylic acid, and dodecanoic acid.

9. The electrolyte for aluminum electrolytic capacitors according to claim 3, characterized in that, The electrolyte for the aluminum electrolytic capacitor contains 50.0% to 90.0% solvent and 0.5% to 20.0% branched dicarboxylic acid or its salt.

10. An aluminum electrolytic capacitor, characterized in that, It includes positive foil, negative foil, electrolytic paper, and electrolyte for aluminum electrolytic capacitors as described in any one of claims 1 to 9.

Images