Aluminum electrolytic capacitor electrolyte and preparation method thereof

Abstract

The invention discloses an aluminum electrolytic capacitor electrolyte and a preparation method thereof, and relates to the technical field of electrolytes. The electrolyte is prepared from the following raw materials in parts by mass: 35 to 45 parts of ethylene glycol, 20 to 30 parts of gamma-butyrolactone, 5 to 10 parts of diethylene glycol monomethyl ether, 3 to 5 parts of ammonium dodecanedioate, 3 to 5 parts of ammonium sebacate, 1 to 2 parts of boric acid, 4 to 6 parts of modified nano silicon dioxide, 1 to 2 parts of sulfonated polyvinyl alcohol, 1 to 2 parts of ammonium dihydrogen phosphate and 0.5 to 1.5 parts of hydrogen elimination agent. The material is suitable for being used at a low temperature of-40 DEG C.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology, and in particular to an aluminum electrolytic capacitor electrolyte and its preparation method. Background Technology

[0002] Aluminum electrolytic capacitors are capacitors that use aluminum foil as the positive electrode and an oxide film formed on its surface as the working medium. They have advantages such as large capacitance per unit volume, high rated voltage, and low cost, playing an important role in daily production and life. With the rapid development of the electronics industry, higher requirements have been placed on the performance of aluminum electrolytic capacitors, such as operating temperature range and safety. The electrolyte of aluminum electrolytic capacitors, as the actual cathode, plays a crucial role in the above-mentioned performance of the capacitor. Currently, electrolytes with ethylene glycol as the main solvent system are commonly used, which can operate normally at low temperatures. However, problems still exist, such as low flashover voltage, insufficient safety, and unsuitability for use at extremely low temperatures of -40℃. Therefore, developing an aluminum electrolytic capacitor electrolyte with excellent low-temperature performance and high safety is of significant practical importance. Summary of the Invention

[0003] Based on the technical problems existing in the background art, the present invention proposes an aluminum electrolytic capacitor electrolyte and its preparation method.

[0004] The present invention provides an electrolyte for aluminum electrolytic capacitors, wherein the electrolyte comprises the following raw materials in parts by weight: 35-45 parts ethylene glycol, 20-30 parts γ-butyrolactone, 5-10 parts diethylene glycol monomethyl ether, 3-5 parts ammonium dodecanoate, 3-5 parts ammonium sebacic acid, 1-2 parts boric acid, 4-6 parts modified nano-silica, 1-2 parts sulfonated polyvinyl alcohol, 1-2 parts ammonium dihydrogen phosphate, and 0.5-1.5 parts hydrogen scavenger;

[0005] The method for preparing the modified nano-silica includes: grafting nano-silica with a silane coupling agent containing double bonds to obtain silane coupling agent-grafted nano-silica; and polymerizing the silane coupling agent-grafted nano-silica with sodium styrene sulfonate and methacrylic acid in the presence of an initiator to obtain the final product.

[0006] This invention uses a mixture of ethylene glycol, γ-butyrolactone, and diethylene glycol monomethyl ether as a solvent, and a mixture of ammonium dodecanoate, ammonium sebacate, and boric acid as a solute. Modified nano-silica, sulfonated polyvinyl alcohol, ammonium dihydrogen phosphate, and a hydrogen scavenger are added as additives to obtain an electrolyte for aluminum electrolytic capacitors. The mixture of ethylene glycol, γ-butyrolactone, and diethylene glycol monomethyl ether lowers the melting point, maintains good stability at low temperatures, and provides a high flash voltage. The mixture of ammonium dodecanoate, ammonium sebacate, and boric acid is well-suited to the above solvent system and can improve the flash voltage of the electrolyte. The modified nano-silica contains carboxyl and sulfonic acid groups on its surface. When combined with sulfonated polyvinyl alcohol, the carboxyl and sulfonic acid groups on the surface of the nano-silica have a synergistic effect, effectively improving the dispersibility of the nano-silica and enabling it to disperse evenly at low temperatures. The components are evenly dispersed in the electrolyte system to avoid aggregation or precipitation. The sulfonic acid groups in sulfonated polyvinyl alcohol also help improve its stability in the electrolyte, thereby enhancing its ability to repair the oxide film and effectively increasing the flash voltage of the electrolyte. On the other hand, the modified nano-silica and sulfonated polyvinyl alcohol contain a large number of sulfonic acid groups, which can improve conductivity and improve the fluidity of the electrolyte system at low temperatures, reducing capacity loss at low temperatures. Ammonium dihydrogen phosphate acts as a waterproofing agent, and the hydrogen scavenger eliminates hydrogen in the system, protecting the oxide film. Through the optimization and synergistic effect of the above components, the electrolyte obtained by this invention has high flash voltage and excellent low-temperature stability, making it suitable for use at temperatures as low as -40°C.

[0007] Preferably, the method for preparing the modified nano-silica includes:

[0008] (1) Add nano-silica to a mixed solvent of glacial acetic acid, anhydrous ethanol and water and disperse it evenly. Then add a silane coupling agent containing double bonds and heat it at 60~75℃ for 2~4h to obtain nano-silica grafted with silane coupling agent. The mass ratio of nano-silica to silane coupling agent containing double bonds is 1:0.3~0.5.

[0009] (2) The nano-silica grafted with the silane coupling agent is added to the solvent along with sodium styrene sulfonate, methacrylic acid and initiator in a mass ratio of 1:0.1~0.3:0.05~0.1:0.01~0.02 and heated at 70~90℃ for 2~5h under a nitrogen atmosphere to obtain the product.

[0010] Preferably, the silane coupling agent containing double bonds is selected from at least one of silane coupling agent KH-570, silane coupling agent A-151, and silane coupling agent A-171.

[0011] Preferably, the initiator is selected from at least one of azobisisobutyronitrile, ammonium persulfate, and sodium persulfate.

[0012] Preferably, in step (1), the mass ratio of glacial acetic acid, anhydrous ethanol and water is 5~8:40~50:5~10.

[0013] Preferably, in step (2), the solvent is at least one of acetonitrile and N,N-dimethylacetamide.

[0014] In step (1), after the reaction is complete, conventional post-processing steps may also be included, which may include: solid-liquid separation (e.g., centrifugation, filtration), washing, and drying.

[0015] In step (2), after the reaction is complete, conventional post-processing steps may also be included, which may include: solid-liquid separation (e.g., centrifugation, filtration), washing, and drying.

[0016] Preferably, the preparation method of the sulfonated polyvinyl alcohol includes: adding polyvinyl alcohol to water, stirring and dissolving it at 90~95℃, then placing it in an ice-water bath, adding concentrated sulfuric acid dropwise while stirring, and stirring and reacting at 40~50℃ for 5~8 hours after the addition is complete. After the reaction is complete, adding anhydrous ethanol until a solid precipitates, and washing the solid with anhydrous ethanol to obtain the product. The mass ratio of polyvinyl alcohol to concentrated sulfuric acid is 1:2~2.5.

[0017] Preferably, in the method for preparing sulfonated polyvinyl alcohol, the mass ratio of polyvinyl alcohol to water is 1:15~25, and the mass concentration of concentrated sulfuric acid is 80%~98%.

[0018] Preferably, the polyvinyl alcohol is selected from at least one of PVA-105, PVA-117, and PVA-124.

[0019] Preferably, the hydrogen scavenger is selected from at least one of p-nitrobenzyl alcohol, p-nitrophenol, and m-nitroacetophenone.

[0020] The present invention also proposes a method for preparing the electrolyte of the aluminum electrolytic capacitor, comprising the following steps:

[0021] After mixing ethylene glycol, γ-butyrolactone, and diethylene glycol monomethyl ether evenly, the mixture is heated to 80-90°C. Ammonium dodecanoate and ammonium sebacate are added, and the mixture is then heated to 130-140°C. The mixture is stirred to dissolve and kept at this temperature for 60-90 minutes. The mixture is then cooled to 90-100°C, and boric acid, modified nano-silica, sulfonated polyvinyl alcohol, ammonium dihydrogen phosphate, and a hydrogen scavenger are added. The mixture is stirred to dissolve and then cooled to room temperature to obtain the final product.

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

[0023] This invention uses a mixture of ethylene glycol, γ-butyrolactone, and diethylene glycol monomethyl ether as a solvent, and a mixture of ammonium dodecanoate, ammonium sebacate, and boric acid as a solute. Modified nano-silica, sulfonated polyvinyl alcohol, ammonium dihydrogen phosphate, and a hydrogen scavenger are added as additives to obtain an electrolyte for aluminum electrolytic capacitors. The mixture of ethylene glycol, γ-butyrolactone, and diethylene glycol monomethyl ether lowers the melting point, maintains good stability at low temperatures, and provides a high flash voltage. The mixture of ammonium dodecanoate, ammonium sebacate, and boric acid is well-suited to the above solvent system and can improve the flash voltage of the electrolyte. The modified nano-silica contains carboxyl and sulfonic acid groups on its surface. When combined with sulfonated polyvinyl alcohol, the carboxyl and sulfonic acid groups on the surface of the nano-silica have a synergistic effect, effectively improving the dispersibility of the nano-silica and enabling it to be uniformly dispersed at low temperatures. In the electrolyte system, agglomeration or precipitation is avoided. The sulfonic acid groups in sulfonated polyvinyl alcohol also help improve its stability in the electrolyte, thereby enhancing its ability to repair the oxide film and effectively increasing the flash voltage of the electrolyte. On the other hand, the modified nano-silica and sulfonated polyvinyl alcohol contain a large number of sulfonic acid groups, which can improve conductivity and have a synergistic effect, improving the fluidity of the electrolyte system at low temperatures and reducing capacity loss at low temperatures. Ammonium dihydrogen phosphate acts as a waterproofing agent, and the hydrogen scavenger eliminates hydrogen in the system, protecting the oxide film. Through the optimization of the above components and their synergistic effect, the electrolyte obtained by this invention has high flash voltage and excellent low-temperature stability, making it suitable for use at temperatures as low as -40°C. Detailed Implementation

[0024] The technical solution of the present invention will now be described in detail through specific embodiments.

[0025] Example 1

[0026] An electrolyte for aluminum electrolytic capacitors, the electrolyte being composed of the following raw materials in parts by weight: 40 parts ethylene glycol, 25 parts γ-butyrolactone, 8 parts diethylene glycol monomethyl ether, 4 parts ammonium dodecanoate, 4 parts ammonium sebacate, 1.5 parts boric acid, 5 parts modified nano-silica, 1.5 parts sulfonated polyvinyl alcohol, 1.5 parts ammonium dihydrogen phosphate, and 1 part p-nitrobenzyl alcohol;

[0027] The preparation method of modified nano-silica is as follows:

[0028] (1) Mix glacial acetic acid, anhydrous ethanol and water in a mass ratio of 6:45:8 to obtain a mixed solvent; add nano silica to the above mixed solvent and disperse it evenly, then add silane coupling agent KH-570, heat and react at 70°C for 3 hours, then centrifuge, wash and vacuum dry to obtain silane coupling agent grafted nano silica, wherein the mass ratio of nano silica to silane coupling agent KH-570 is 1:0.4 and the mass ratio of nano silica to mixed solvent is 1:50;

[0029] (2) Add silane coupling agent-grafted nano-silica to sodium styrene sulfonate, methacrylic acid and azobisisobutyronitrile in a mass ratio of 1:0.2:0.08:0.015 to acetonitrile. Heat the mixture at 80°C for 3 hours under a nitrogen atmosphere. Then centrifuge, wash and vacuum dry to obtain the silane coupling agent-grafted nano-silica with a mass ratio of 1:50 to acetonitrile.

[0030] The preparation method of sulfonated polyvinyl alcohol is as follows: Polyvinyl alcohol PVA-124 is added to water and stirred to dissolve at 95°C. Then, it is placed in an ice-water bath, and concentrated sulfuric acid with a mass concentration of 98% is added dropwise while stirring. After the addition is complete, the mixture is stirred at 40°C for 6 hours. After the reaction is complete, anhydrous ethanol is added until a solid precipitates. The solid is washed with anhydrous ethanol until pH=6 to obtain the product. The mass ratio of polyvinyl alcohol PVA-124 to concentrated sulfuric acid is 1:2.2, and the mass ratio of polyvinyl alcohol PVA-124 to water is 1:20.

[0031] The preparation method of the electrolyte for the above-mentioned aluminum electrolytic capacitor is as follows:

[0032] After mixing ethylene glycol, γ-butyrolactone, and diethylene glycol monomethyl ether evenly, the mixture is heated to 85°C, and ammonium dodecanoate and ammonium sebacate are added. The mixture is then heated to 130-140°C, stirred to dissolve, and kept at this temperature for 85 minutes. After cooling to 95°C, boric acid, modified nano-silica, sulfonated polyvinyl alcohol, ammonium dihydrogen phosphate, and a hydrogen scavenger are added, stirred to dissolve, and then cooled to room temperature to obtain the final product.

[0033] Example 2

[0034] An electrolyte for an aluminum electrolytic capacitor, the electrolyte being composed of the following raw materials in parts by weight: 35 parts ethylene glycol, 20 parts γ-butyrolactone, 5 parts diethylene glycol monomethyl ether, 5 parts ammonium dodecanoate, 3 parts ammonium sebacic acid, 1 part boric acid, 4 parts modified nano silica, 1 part sulfonated polyvinyl alcohol, 1 part ammonium dihydrogen phosphate, and 0.5 parts p-nitrobenzyl alcohol;

[0035] The preparation method of modified nano-silica is as follows:

[0036] (1) Mix glacial acetic acid, anhydrous ethanol and water in a mass ratio of 5:40:5 to obtain a mixed solvent; add nano silica to the above mixed solvent and disperse it evenly, then add silane coupling agent KH-570, heat and react at 60°C for 2 hours, then centrifuge, wash and vacuum dry to obtain silane coupling agent grafted nano silica, wherein the mass ratio of nano silica to silane coupling agent KH-570 is 1:0.3 and the mass ratio of nano silica to mixed solvent is 1:50;

[0037] (2) Add silane coupling agent-grafted nano-silica to sodium styrene sulfonate, methacrylic acid and azobisisobutyronitrile in a mass ratio of 1:0.1:0.05:0.01 to acetonitrile, heat and react at 70°C for 2 hours under nitrogen atmosphere, then centrifuge, wash and vacuum dry to obtain the silane coupling agent-grafted nano-silica to acetonitrile mass ratio of 1:50.

[0038] The preparation method of sulfonated polyvinyl alcohol is as follows: Polyvinyl alcohol PVA-124 is added to water and stirred to dissolve at 90°C. Then, it is placed in an ice-water bath, and concentrated sulfuric acid with a mass concentration of 98% is added dropwise while stirring. After the addition is complete, the mixture is stirred at 40°C for 5 hours. After the reaction is completed, anhydrous ethanol is added until a solid precipitates. The solid is washed with anhydrous ethanol until pH=6 to obtain the product. The mass ratio of polyvinyl alcohol PVA-124 to concentrated sulfuric acid is 1:2, and the mass ratio of polyvinyl alcohol PVA-124 to water is 1:15.

[0039] The preparation method of the electrolyte for the above-mentioned aluminum electrolytic capacitor is as follows:

[0040] After mixing ethylene glycol, γ-butyrolactone, and diethylene glycol monomethyl ether evenly, the mixture is heated to 80°C, and ammonium dodecanoate and ammonium sebacate are added. The mixture is then heated to 130°C, stirred to dissolve, and kept at this temperature for 60 minutes. After cooling to 90°C, boric acid, modified nano-silica, sulfonated polyvinyl alcohol, ammonium dihydrogen phosphate, and a hydrogen scavenger are added, stirred to dissolve, and then cooled to room temperature to obtain the final product.

[0041] Example 3

[0042] An electrolyte for an aluminum electrolytic capacitor, the electrolyte being composed of the following raw materials in parts by weight: 45 parts ethylene glycol, 30 parts γ-butyrolactone, 10 parts diethylene glycol monomethyl ether, 3 parts ammonium dodecanoate, 5 parts ammonium sebacate, 2 parts boric acid, 6 parts modified nano silica, 2 parts sulfonated polyvinyl alcohol, 2 parts ammonium dihydrogen phosphate, and 1.5 parts p-nitrobenzyl alcohol;

[0043] The preparation method of modified nano-silica is as follows:

[0044] (1) Mix glacial acetic acid, anhydrous ethanol and water in a mass ratio of 8:50:10 to obtain a mixed solvent; add nano silica to the above mixed solvent and disperse it evenly, then add silane coupling agent KH-570, heat and react at 75°C for 4 hours, then centrifuge, wash and vacuum dry to obtain silane coupling agent grafted nano silica, wherein the mass ratio of nano silica to silane coupling agent KH-570 is 1:0.5 and the mass ratio of nano silica to mixed solvent is 1:50;

[0045] (2) Add silane coupling agent-grafted nano-silica to sodium styrene sulfonate, methacrylic acid and azobisisobutyronitrile in a mass ratio of 1:0.3:0.1:0.02 to acetonitrile. Heat the mixture at 90°C for 5 hours under a nitrogen atmosphere. Then centrifuge, wash and vacuum dry to obtain the silane coupling agent-grafted nano-silica with a mass ratio of 1:50 to acetonitrile.

[0046] The preparation method of sulfonated polyvinyl alcohol is as follows: Polyvinyl alcohol PVA-124 is added to water and stirred to dissolve at 95°C. Then, it is placed in an ice-water bath, and concentrated sulfuric acid with a mass concentration of 98% is added dropwise while stirring. After the addition is complete, the mixture is stirred at 50°C for 8 hours. After the reaction is complete, anhydrous ethanol is added until a solid precipitates. The solid is washed with anhydrous ethanol until pH=6 to obtain the product. The mass ratio of polyvinyl alcohol PVA-124 to concentrated sulfuric acid is 1:2.5, and the mass ratio of polyvinyl alcohol PVA-124 to water is 1:25.

[0047] The preparation method of the electrolyte for the above-mentioned aluminum electrolytic capacitor is as follows:

[0048] After mixing ethylene glycol, γ-butyrolactone, and diethylene glycol monomethyl ether evenly, the mixture is heated to 90°C, and ammonium dodecanoate and ammonium sebacate are added. The mixture is then heated to 140°C, stirred to dissolve, and kept at this temperature for 90 minutes. After cooling to 100°C, boric acid, modified nano-silica, sulfonated polyvinyl alcohol, ammonium dihydrogen phosphate, and a hydrogen scavenger are added, stirred to dissolve, and then cooled to room temperature to obtain the final product.

[0049] Comparative Example 1

[0050] The only difference between Comparative Example 1 and Example 1 is the preparation method of the modified nano-silica, as detailed below:

[0051] An electrolyte for aluminum electrolytic capacitors, the electrolyte being composed of the following raw materials in parts by weight: 40 parts ethylene glycol, 25 parts γ-butyrolactone, 8 parts diethylene glycol monomethyl ether, 8 parts ammonium dodecanoate, 4 parts ammonium sebacate, 1.5 parts boric acid, 5 parts modified nano-silica, 1.5 parts sulfonated polyvinyl alcohol, 1.5 parts ammonium dihydrogen phosphate, and 1 part p-nitrobenzyl alcohol;

[0052] The preparation method of modified nano-silica is as follows:

[0053] (1) Mix glacial acetic acid, anhydrous ethanol and water in a mass ratio of 6:45:8 to obtain a mixed solvent; add nano silica to the above mixed solvent and disperse it evenly, then add silane coupling agent KH-570, heat and react at 70°C for 3 hours, then centrifuge, wash and vacuum dry to obtain silane coupling agent grafted nano silica, wherein the mass ratio of nano silica to silane coupling agent KH-570 is 1:0.4 and the mass ratio of nano silica to mixed solvent is 1:50;

[0054] (2) Add silane coupling agent-grafted nano-silica, sodium styrene sulfonate, and azobisisobutyronitrile to acetonitrile in a mass ratio of 1:0.2:0.015. Heat the mixture at 80°C for 3 hours under a nitrogen atmosphere. Then centrifuge, wash, and vacuum dry to obtain the silane coupling agent-grafted nano-silica with a mass ratio of 1:50 to acetonitrile.

[0055] The preparation method of sulfonated polyvinyl alcohol is the same as in Example 1.

[0056] Comparative Example 2

[0057] The only difference between Comparative Example 2 and Example 1 is the preparation method of the modified nano-silica, as detailed below:

[0058] An electrolyte for aluminum electrolytic capacitors, the electrolyte being composed of the following raw materials in parts by weight: 40 parts ethylene glycol, 25 parts γ-butyrolactone, 8 parts diethylene glycol monomethyl ether, 8 parts ammonium dodecanoate, 4 parts ammonium sebacate, 1.5 parts boric acid, 5 parts modified nano-silica, 1.5 parts sulfonated polyvinyl alcohol, 1.5 parts ammonium dihydrogen phosphate, and 1 part p-nitrobenzyl alcohol;

[0059] The preparation method of modified nano-silica is as follows:

[0060] (1) Mix glacial acetic acid, anhydrous ethanol and water in a mass ratio of 6:45:8 to obtain a mixed solvent; add nano silica to the above mixed solvent and disperse it evenly, then add silane coupling agent KH-570, heat and react at 70°C for 3 hours, then centrifuge, wash and vacuum dry to obtain silane coupling agent grafted nano silica, wherein the mass ratio of nano silica to silane coupling agent KH-570 is 1:0.4 and the mass ratio of nano silica to mixed solvent is 1:50;

[0061] (2) Add silane coupling agent-grafted nano-silica to acetonitrile with methacrylic acid and azobisisobutyronitrile in a mass ratio of 1:0.08:0.015, heat and react at 80°C for 3 hours under nitrogen atmosphere, then centrifuge, wash and vacuum dry to obtain the silane coupling agent-grafted nano-silica to acetonitrile mass ratio of 1:50.

[0062] The preparation method of sulfonated polyvinyl alcohol is the same as in Example 1.

[0063] Comparative Example 3

[0064] The only difference between Comparative Example 3 and Example 1 is that sulfonated polyvinyl alcohol is replaced with polyvinyl alcohol, as detailed below:

[0065] An electrolyte for aluminum electrolytic capacitors, the electrolyte being composed of the following raw materials in parts by weight: 40 parts ethylene glycol, 25 parts γ-butyrolactone, 8 parts diethylene glycol monomethyl ether, 8 parts ammonium dodecanoate, 4 parts ammonium sebacate, 1.5 parts boric acid, 5 parts modified nano silica, 1.5 parts polyvinyl alcohol PVA-124, 1.5 parts ammonium dihydrogen phosphate, and 1 part p-nitrobenzyl alcohol;

[0066] The preparation method of modified nano-silica is the same as in Example 1.

[0067] Comparative Example 4

[0068] The only difference between Comparative Example 4 and Example 1 is that the preparation method of the modified nano-silica is different, and sulfonated polyvinyl alcohol is replaced with polyvinyl alcohol, as detailed below:

[0069] An electrolyte for aluminum electrolytic capacitors, the electrolyte being composed of the following raw materials in parts by weight: 40 parts ethylene glycol, 25 parts γ-butyrolactone, 8 parts diethylene glycol monomethyl ether, 8 parts ammonium dodecanoate, 4 parts ammonium sebacate, 1.5 parts boric acid, 5 parts modified nano silica, 1.5 parts polyvinyl alcohol PVA-124, 1.5 parts ammonium dihydrogen phosphate, and 1 part p-nitrobenzyl alcohol;

[0070] The preparation method of modified nano-silica is as follows:

[0071] Glacial acetic acid, anhydrous ethanol, and water were mixed in a mass ratio of 6:45:8 to obtain a mixed solvent. Nano-silica was added to the mixed solvent and dispersed evenly. Then, silane coupling agent KH-570 was added, and the mixture was heated at 70°C for 3 hours. After centrifugation, washing, and vacuum drying, modified nano-silica was obtained. The mass ratio of nano-silica to silane coupling agent KH-570 was 1:0.4, and the mass ratio of nano-silica to mixed solvent was 1:50.

[0072] Test case

[0073] The conductivity and flashover voltage of the electrolytes in Example 1 and Comparative Examples 1-4 were tested at 30°C. The test parameters were: current 5mA / cm. 2 Aluminum foil area 2cm 2Capacitors were assembled using the electrolytes from Examples 1 and 1-4, respectively. The capacitors were 400V, 15μF, and had an aluminum shell size of Φ12.5mm × 25mm. The capacitance loss rate of the capacitors was tested at 20℃ and -40℃. The capacitance loss rate was calculated using the following formula: Capacitance Loss Rate = (Capacitance 1 - Capacitance 2) / Capacitance 1 × 100%, where Capacitance 1 refers to the capacitance at 20℃ and Capacitance 2 refers to the capacitance at -40℃. The test results are shown in Table 1.

[0074] Table 1

[0075]

[0076] As shown in Table 1, the present invention can significantly improve the flash voltage of the electrolyte by adding specific modified nano-silica and sulfonated polyvinyl alcohol to the electrolyte of aluminum electrolytic capacitors, and can ensure the excellent stability of the electrolyte system at low temperatures, making it suitable for use at -40℃. Comparing Example 1 with Comparative Examples 1 and 2, the modified nano-silica in Comparative Example 1 did not have methacrylic acid added during the polymerization step, resulting in modified nano-silica without carboxyl groups on its surface. In contrast, the modified nano-silica in Comparative Example 2 lacked sulfonic acid groups, leading to a significantly lower flash voltage and greater capacity loss compared to Example 1. This is because the modified nano-silica added in Comparative Examples 1 and 2 exhibited poor dispersibility in the electrolyte system, and the absence of sulfonic acid groups on the surface of the modified nano-silica in Comparative Example 2 resulted in poor low-temperature fluidity of the electrolyte, a significant decrease in ionic conductivity at low temperatures, and increased capacity loss at low temperatures. Comparative Example 3 did not undergo sulfonation modification of polyvinyl alcohol, resulting in poor low-temperature fluidity of the electrolyte and increased capacity loss at low temperatures. Comparative Example 4 only used conventional silane coupling agents to modify nano-silica without sulfonation modification of polyvinyl alcohol, resulting in a significantly lower flash voltage and greater capacity loss at low temperatures in the obtained electrolyte.

[0077] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An electrolyte for aluminum electrolytic capacitors, characterized in that, The electrolyte comprises the following raw materials in parts by weight: 35-45 parts ethylene glycol, 20-30 parts γ-butyrolactone, 5-10 parts diethylene glycol monomethyl ether, 3-5 parts ammonium dodecanoate, 3-5 parts ammonium sebacic acid, 1-2 parts boric acid, 4-6 parts modified nano silica, 1-2 parts sulfonated polyvinyl alcohol, 1-2 parts ammonium dihydrogen phosphate, and 0.5-1.5 parts hydrogen scavenger; The method for preparing the modified nano-silica includes: grafting nano-silica with a silane coupling agent containing double bonds to obtain silane coupling agent-grafted nano-silica; and polymerizing the silane coupling agent-grafted nano-silica with sodium styrene sulfonate and methacrylic acid in the presence of an initiator to obtain the final product.

2. The electrolyte for aluminum electrolytic capacitors according to claim 1, characterized in that, The method for preparing the modified nano-silica includes: (1) Add nano-silica to a mixed solvent of glacial acetic acid, anhydrous ethanol and water and disperse it evenly. Then add a silane coupling agent containing double bonds and heat it at 60~75℃ for 2~4h to obtain nano-silica grafted with silane coupling agent. The mass ratio of nano-silica to silane coupling agent containing double bonds is 1:0.3~0.

5. (2) The nano-silica grafted with the silane coupling agent is added to the solvent along with sodium styrene sulfonate, methacrylic acid and initiator in a mass ratio of 1:0.1~0.3:0.05~0.1:0.01~0.02 and heated at 70~90℃ for 2~5h under a nitrogen atmosphere to obtain the product.

3. The aluminum electrolytic capacitor electrolyte according to claim 2, characterized in that, The silane coupling agent containing double bonds is selected from at least one of silane coupling agent KH-570, silane coupling agent A-151, and silane coupling agent A-171.

4. The electrolyte for aluminum electrolytic capacitors according to claim 2, characterized in that, The initiator is selected from at least one of azobisisobutyronitrile, ammonium persulfate, and sodium persulfate.

5. The electrolyte for aluminum electrolytic capacitors according to claim 1, characterized in that, The method for preparing the sulfonated polyvinyl alcohol includes: adding polyvinyl alcohol to water, stirring and dissolving it at 90-95°C, then placing it in an ice-water bath, adding concentrated sulfuric acid dropwise while stirring, and stirring and reacting at 40-50°C for 5-8 hours after the addition is complete. After the reaction is complete, adding anhydrous ethanol until a solid precipitates, and washing the solid with anhydrous ethanol to obtain the product. The mass ratio of polyvinyl alcohol to concentrated sulfuric acid is 1:2-2.

5.

6. The electrolyte for aluminum electrolytic capacitors according to claim 5, characterized in that, The polyvinyl alcohol is selected from at least one of PVA-105, PVA-117, and PVA-124.

7. The electrolyte for aluminum electrolytic capacitors according to claim 1, characterized in that, The hydrogen scavenger is selected from at least one of p-nitrobenzyl alcohol, p-nitrophenol, and m-nitroacetophenone.

8. A method for preparing the electrolyte for an aluminum electrolytic capacitor as described in any one of claims 1 to 7, characterized in that, The process includes the following steps: ethylene glycol, γ-butyrolactone, and diethylene glycol monomethyl ether are mixed evenly, heated to 80-90°C, ammonium dodecanoate and ammonium sebacate are added, then the temperature is raised to 130-140°C, stirred to dissolve, kept at this temperature for 60-90 minutes, cooled to 90-100°C, boric acid, modified nano-silica, sulfonated polyvinyl alcohol, ammonium dihydrogen phosphate, and hydrogen scavenging agent are added, stirred to dissolve, and then cooled to room temperature to obtain the final product.

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