A low-temperature medium-high voltage aluminum electrolytic capacitor

Abstract

This application relates to the technical field of aluminum electrolytic capacitors, and specifically discloses a low-temperature medium-high voltage aluminum electrolytic capacitor. Among them, the electrolyte of the low-temperature medium-high voltage aluminum electrolytic capacitor includes the following raw materials: main solvent, low-melting-point co-solvent, main solute, auxiliary solute, flashover voltage enhancer, hydrogen scavenger, and waterproofing assistant. Among them, the flashover voltage enhancer is modified nano-silica. In the present invention, vinyl silane coupling agent is used to modify the surface of nano-silica, and then allyl succinic anhydride grafted polyvinyl alcohol is formed by the esterification reaction of polyvinyl alcohol and allyl succinic anhydride, and it is effectively combined with silanized nano-silica, so that the nano-silica particles can be uniformly dispersed in the electrolyte to improve the flashover voltage of the electrolyte. By introducing a low-melting-point co-solvent, the melting point of the electrolyte system can be effectively reduced, so that the capacitor can maintain low viscosity and good electrical performance in a low-temperature environment.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum electrolytic capacitors, and specifically discloses a low-temperature medium-high voltage aluminum electrolytic capacitor. Background Art

[0002] With the rapid development of modern industry, especially the increasing application requirements in extreme environments such as aerospace, military equipment, and polar exploration, the performance requirements for electronic components are getting higher and higher. As an important electronic component, aluminum electrolytic capacitors are widely used in power supply filtering, coupling, bypass and other circuits due to their advantages of large capacitance, small volume, and low cost. However, the performance of traditional aluminum electrolytic capacitors in extreme temperature environments is not satisfactory. Especially in low-temperature environments (below -40°C), their electrical characteristics will significantly decline, making it difficult to meet the actual use requirements.

[0003] In the production of aluminum electrolytic capacitors, the working electrolyte is used to repair the defects that appear on the anodic oxide film at any time, maintaining the performance and life of the capacitor. Traditional aluminum electrolytic capacitors usually use ordinary electrolytes and anode foils, showing good electrical performance at room temperature. However, when the ambient temperature drops below -40°C, the viscosity of the electrolyte will increase significantly, resulting in a sharp decline in its electrical performance, which not only affects the capacitance and equivalent series resistance (ESR) of the capacitor, but may also cause the capacitor to malfunction or even fail in low-temperature environments, thus severely limiting the application of aluminum electrolytic capacitors in extremely low-temperature environments. Summary of the Invention

[0004] In order to improve the electrical performance of aluminum electrolytic capacitors in low-temperature environments and ensure the normal operation of the capacitors, the present application provides a low-temperature medium-high voltage aluminum electrolytic capacitor.

[0005] In a first aspect, a low-temperature medium-high voltage aluminum electrolytic capacitor provided by the present application adopts the following technical solution:

[0006] A low-temperature medium-high voltage aluminum electrolytic capacitor includes an electrolyte, an anode foil, a cathode foil, lead terminals, and a plastic sealing housing;

[0007] Wherein, the electrolyte includes the following raw materials in parts by weight:

[0008] 40 - 50 parts of a main solvent, 20 - 30 parts of a low-melting-point co-solvent, 15 - 25 parts of a main solute, 5 - 15 parts of an auxiliary solute, 5 - 9 parts of a flashover voltage enhancer, 0.7 - 1.3 parts of a hydrogen scavenger, and 1.2 - 1.8 parts of a waterproofing and complexing aid;

[0009] The flashover voltage enhancer is modified nano-silica. The raw materials for preparing the modified nano-silica include polyvinyl alcohol, allyl succinic anhydride, vinyl silane coupling agent and nano-silica. The weight ratio of polyvinyl alcohol, allyl succinic anhydride, vinyl silane coupling agent and nano-silica is (0.6-0.8):(0.3-0.5):(0.13-0.15):1.

[0010] By adopting the above technical solution, the flashover voltage enhancer uses nano-silica as the matrix. Through the esterification reaction between polyvinyl alcohol and allyl succinic anhydride, a reactive double bond is introduced to provide active sites for subsequent grafting reactions. Moreover, the surface of nano-silica is modified with a vinyl silane coupling agent to introduce double bonds on the surface of nano-silica. The vinyl groups undergo grafting reactions with the double bonds of allyl succinic anhydride. At the same time, its siloxane groups (Si-O) undergo condensation reactions with the hydroxyl groups (-OH) on the surface of nano-silica, effectively binding nano-silica with the polyvinyl alcohol matrix, enabling the nano-silica particles to be evenly dispersed in the electrolyte, forming a "shielding effect" and reducing the local electric field concentration in the electrolyte. And local electric field concentration is one of the main reasons for the breakdown of the electrolyte. The presence of modified nano-silica can evenly distribute the electric field and reduce the formation of local high electric field regions, thereby enhancing the flashover voltage of the electrolyte and reducing the leakage current of the capacitor. In addition, the main solvent provides the basic dissolution ability and conductivity of the electrolyte. By introducing a low melting point co-solvent, the melting point of the electrolyte system can be effectively reduced, enabling the capacitor to maintain low viscosity and good electrical performance in a low temperature environment; the main solute and auxiliary solute provide conductive ions, and the solute system has high solubility in the solvent system, improving the conductivity of the electrolyte in a low temperature environment and ensuring the efficient operation of the capacitor.

[0011] Preferably, the preparation method of the modified nano-silica is as follows:

[0012] (1) Dissolve polyvinyl alcohol in deionized water, add allyl succinic anhydride and benzoyl peroxide at 60-70 °C, stir and react for 2-3 h. After the reaction is completed, add acetone to precipitate, wash and dry to obtain allyl succinic anhydride grafted polyvinyl alcohol;

[0013] (2) Dissolve the vinyl silane coupling agent in 95% ethanol to form a silane hydrolysis solution. Add nano-silica to the silane hydrolysis solution and ultrasonically oscillate for 1-2 h to obtain silanized nano-silica;

[0014] (3) Add the silylated nano-silica into deionized water, ultrasonically disperse for 30 - 40 min, add allyl succinic anhydride grafted polyvinyl alcohol, continue to ultrasonically disperse for 1 - 2 h, add the mixed solution of benzoyl peroxide and sulfuric acid, mix evenly, stir and react for 3 - 4 h, and obtain the modified nano-silica after drying.

[0015] By adopting the above technical solution, the vinyl silane coupling agent undergoes a condensation reaction with the hydroxyl groups on the surface of nano-silica through its siloxy groups to form chemical bonds, thereby forming an organic modification layer on the surface of nano-silica. And allyl succinic anhydride grafted polyvinyl alcohol undergoes a grafting reaction with the vinyl groups on the surface of silylated nano-silica through its double bonds to form stable chemical bonds. The surface modification and grafting reaction of nano-silica improve its compatibility with the electrolyte, reduce the aggregation of nano-silica particles, and thus improve the overall stability of the electrolyte.

[0016] Preferably, the vinyl silane coupling agent is at least one of vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltriisopropoxysilane.

[0017] By adopting the above technical solution, the vinyl silane coupling agent contains vinyl and siloxy groups, can undergo a condensation reaction with the hydroxyl groups on the surface of nano-silica, and at the same time, the vinyl can undergo a grafting reaction with the double bonds on polyvinyl alcohol.

[0018] Preferably, the main solvent is ethylene glycol monomethyl ether.

[0019] Preferably, the low melting point co-solvent is prepared by compounding acetonitrile and dibutyl carbonate, and the weight ratio of acetonitrile to dibutyl carbonate is 1:(0.5 - 0.9).

[0020] By adopting the above technical solution, the mixed solvent system contains ether bonds, has a lower liquid viscosity and melting point. In addition, dibutyl carbonate has a low melting point and a moderate viscosity. By adding the low melting point co-solvent prepared by compounding acetonitrile and dibutyl carbonate into the ethylene glycol monomethyl ether solvent, the melting point of the mixed solvent can be further reduced, the crystallization of the electrolyte at low temperature can be reduced, the electrolyte has a higher conductivity, which is beneficial to improving the low temperature performance of the electrolyte, expanding the reliable working temperature range of the capacitor, and obtaining a capacitor with excellent working performance in an extreme temperature environment.

[0021] Preferably, the main solute is at least one of ammonium hydrogen phosphate, ammonium sebacate, and ammonium azelate; the auxiliary solute is spirobipyrrolidine quaternary ammonium tetrafluoroborate.

[0022] By adopting the above technical solution, the cation of the spirobipyrrolidinium tetrafluoroborate is composed of two spiro rings, presenting a symmetrical "8" shape, having higher solubility in the above mixed solvent system, and having smaller steric hindrance, making it easier to adsorb and desorb ions during the charge and discharge process. Therefore, the ionic mobility is higher, enabling the electrolyte to have higher conductivity and more stable electrochemical performance.

[0023] Preferably, the hydrogen scavenger is at least one of p-nitrophenol, p-nitrobenzyl alcohol, m-nitroacetophenone, and o-nitroanisole.

[0024] Preferably, the water-proofing and hydration assistant is at least one of phosphoric acid, hypophosphorous acid, mannitol, polyvinyl alcohol, adipic diamide, and sorbitol.

[0025] By adopting the above technical solution, the hydrogen scavenger contains strong electron-withdrawing groups such as nitro (-NO 2 ), which can significantly increase the electronegativity of the molecule, thereby inhibiting the evolution of hydrogen, improving the stability of the electrolyte, and ensuring the sealing and use safety of the capacitor. The main function of the water-proofing and hydration assistant is to prevent the water in the electrolyte from reacting with the aluminum electrode by hydration, thereby avoiding the corrosion of aluminum and the decomposition of the electrolyte.

[0026] Preferably, the preparation method of the electrolyte is as follows:

[0027] Heat the main solvent to 70 - 80°C, add the auxiliary solvent thereto, mix and homogenize, then heat to 130 - 140°C, add the main solute and the auxiliary solute, keep warm and stir for 30 - 40 min, then cool down to 110 - 120°C, add the flashover voltage enhancer and the water-proofing and hydration assistant, keep warm and stir for 30 - 40 min, cool down to 100 - 105°C, and finally add the hydrogen scavenger, keep warm and stir for 30 - 40 min, and naturally cool to room temperature to obtain the electrolyte.

[0028] By adopting the above technical solution, the electrolyte prepared by the above method has high conductivity, a wide electrochemical window, a high concentration of conductive ions, and good stability at low temperatures.

[0029] Preferably, the anode foil and the cathode foil are parallel to each other and are inserted into the plastic package body. The anode foil and the cathode foil are led out by lead terminals, and the electrolyte is stored in the plastic package body.

[0030] Preferably, the aluminum purity of the anode foil is above 99.99%; the aluminum purity of the cathode foil is above 99.6%; the plastic package body is made of polytetrafluoroethylene material, and the temperature resistance range of the plastic package body is -60°C to +150°C; the lead terminals are made of silver-plated copper alloy.

[0031] By adopting the above technical solutions, the dense oxide film formed on the surface of the high-purity aluminum anode foil effectively improves the insulation performance and energy storage capacity of the capacitor; the plastic-sealed housing made of polytetrafluoroethylene cold-resistant material ensures the overall tightness of the capacitor, reduces the entry of moisture and other impurities into the interior, and extends the service life of the capacitor; the use of silver-plated copper alloy leads enhances the welding performance, reduces the contact resistance, and further improves the reliability and durability of the capacitor.

[0032] The present application has the following beneficial effects:

[0033] In the present application, the flashover voltage promoter uses nano-silica as the matrix. Through the esterification reaction of polyvinyl alcohol and allyl succinic anhydride, a reactive double bond is introduced to provide active sites for subsequent grafting reactions. Moreover, the surface of nano-silica is modified with vinyl silane coupling agent to introduce double bonds on the surface of nano-silica. The double bonds of vinyl and allyl succinic anhydride undergo grafting reactions, and at the same time, its siloxane group (Si-O) undergoes a condensation reaction with the hydroxyl group (-OH) on the surface of nano-silica, effectively combining nano-silica with the polyvinyl alcohol matrix, enabling the nano-silica particles to be evenly dispersed in the electrolyte, forming a "shielding effect" and reducing the local electric field concentration in the electrolyte. And the local electric field concentration is one of the main reasons for the breakdown of the electrolyte. The presence of the modified nano-silica can evenly distribute the electric field and reduce the formation of local high-electric-field regions, thereby increasing the flashover voltage of the electrolyte. In addition, the main solvent provides the basic dissolution ability and conductivity of the electrolyte. By introducing a low-melting-point co-solvent, the melting point of the electrolyte system can be effectively reduced, enabling the capacitor to maintain low viscosity and good electrical performance in a low-temperature environment; the main solute and auxiliary solute provide conductive ions, and the solute system has high solubility in the solvent system, improving the conductivity of the electrolyte in a low-temperature environment and ensuring the efficient operation of the capacitor. Specific embodiments

[0034] The following further elaborates on the present application in conjunction with embodiments.

[0035] Preparation Example 1

[0036] Preparation of modified nano-silica:

[0037] (1) Dissolve 30 g of polyvinyl alcohol in 100 mL of deionized water, add 15 g of allyl succinic anhydride and 2 g of benzoyl peroxide at 60 °C, stir and react for 2 h. After the reaction is completed, add acetone to precipitate, wash and dry to obtain allyl succinic anhydride-grafted polyvinyl alcohol;

[0038] (2) Dissolve 6.4 g of vinyltrimethoxysilane in 95% ethanol to form a silane hydrolysis solution. Add 50 g of nano-silica to the silane hydrolysis solution and ultrasonically oscillate for 1 h to obtain silanized nano-silica;

[0039] (3) Add the silanized nano-silica to 100 mL of deionized water, ultrasonically disperse for 30 min, add allyl succinic anhydride grafted polyvinyl alcohol, continue to ultrasonically disperse for 1 h, add a mixed solution of benzoyl peroxide and sulfuric acid and mix evenly, stir and react for 3 h, and obtain modified nano-silica after drying.

[0040] Preparation Example 2

[0041] Preparation of modified nano-silica:

[0042] (1) Dissolve 49 g of polyvinyl alcohol in 100 mL of deionized water. Add 28 g of allyl succinic anhydride and 3 g of benzoyl peroxide at 65 °C, stir and react for 3 h. After the reaction is completed, add acetone to precipitate, wash and dry to obtain allyl succinic anhydride grafted polyvinyl alcohol;

[0043] (2) Dissolve 9.8 g of vinyltriethoxysilane in 95% ethanol to form a silane hydrolysis solution. Add 70 g of nano-silica to the silane hydrolysis solution and ultrasonically oscillate for 2 h to obtain silanized nano-silica;

[0044] (3) Add the silanized nano-silica to 120 mL of deionized water, ultrasonically disperse for 35 min, add allyl succinic anhydride grafted polyvinyl alcohol, continue to ultrasonically disperse for 2 h, add a mixed solution of benzoyl peroxide and sulfuric acid and mix evenly, stir and react for 3.5 h, and obtain modified nano-silica after drying.

[0045] Preparation Example 3

[0046] Preparation of modified nano-silica:

[0047] (1) Dissolve 72 g of polyvinyl alcohol in 100 mL of deionized water. Add 45 g of allyl succinic anhydride and 4 g of benzoyl peroxide at 70 °C, stir and react for 3 h. After the reaction is completed, add acetone to precipitate, wash and dry to obtain allyl succinic anhydride grafted polyvinyl alcohol;

[0048] (2) Dissolve 13.5 g of vinyltriisopropoxysilane in 95% ethanol to form a silane hydrolysis solution. Add 90 g of nano-silica to the silane hydrolysis solution and ultrasonically oscillate for 2 h to obtain silanized nano-silica;

[0049] (3) Add the silylated nano-silica into 150 mL of deionized water, ultrasonically disperse for 40 min, add allyl succinic anhydride grafted polyvinyl alcohol, continue to ultrasonically disperse for 2 h, add the mixed solution of benzoyl peroxide and sulfuric acid, mix evenly, stir and react for 4 h, and obtain the modified nano-silica after drying.

[0050] Example 1

[0051] A low-temperature medium-high voltage aluminum electrolytic capacitor includes an electrolyte, an anode foil, a cathode foil, lead terminals, and a plastic-sealed housing.

[0052] Among them, the raw materials of the electrolyte include:

[0053] 400 g of ethylene glycol monomethyl ether, 130 g of acetonitrile, 70 g of dibutyl carbonate, 150 g of ammonium sebacate, 50 g of spirobipyrrolidinium tetrafluoroborate quaternary ammonium salt, 50 g of flashover voltage booster (modified nano-silica prepared in Preparation Example 1), 7 g of p-nitrophenol, 6 g of hypophosphorous acid, and 6 g of phosphoric acid.

[0054] Among them, the preparation method of the electrolyte includes the following steps:

[0055] Heat the ethylene glycol monomethyl ether to 70 °C, add acetonitrile and dibutyl carbonate to it, mix and heat to 130 °C after mixing evenly, add ammonium sebacate and spirobipyrrolidinium tetrafluoroborate quaternary ammonium salt, keep warm and stir for 30 min, then cool down to 110 °C, add the modified nano-silica, hypophosphorous acid, and phosphoric acid, keep warm and stir for 30 min, cool down to 100 °C, finally add p-nitrophenol, keep warm and stir for 30 min, and naturally cool to room temperature to obtain the electrolyte.

[0056] Example 2

[0057] A low-temperature medium-high voltage aluminum electrolytic capacitor includes an electrolyte, an anode foil, a cathode foil, lead terminals, and a plastic-sealed housing.

[0058] Among them, the raw materials of the electrolyte include:

[0059] 450 g of ethylene glycol monomethyl ether, 150 g of acetonitrile, 100 g of dibutyl carbonate, 200 g of ammonium hydrogen phosphate, 100 g of spirobipyrrolidinium tetrafluoroborate quaternary ammonium salt, 70 g of flashover voltage booster (modified nano-silica prepared in Preparation Example 2), 10 g of p-nitrobenzyl alcohol, 7 g of mannitol, and 8 g of polyvinyl alcohol.

[0060] Among them, the preparation method of the electrolyte includes the following steps:

[0061] Heat ethylene glycol monomethyl ether to 75 °C, add acetonitrile and dibutyl carbonate to it. After mixing evenly, heat to 135 °C, add ammonium hydrogen phosphate and spirobipyrrolidinium tetrafluoroborate quaternary ammonium salt, keep warm and stir for 35 min. Then cool down to 115 °C, add modified nano-silica, mannitol and polyvinyl alcohol, keep warm and stir for 35 min. Cool down to 103 °C, and finally add p-nitrobenzyl alcohol, keep warm and stir for 35 min. Naturally cool to room temperature to obtain the electrolyte solution.

[0062] Example 3

[0063] A low-temperature medium-high voltage aluminum electrolytic capacitor includes an electrolyte solution, an anode foil, a cathode foil, lead terminals and a plastic-sealed housing;

[0064] Among them, the raw materials of the electrolyte solution include:

[0065] 500 g of ethylene glycol monomethyl ether, 160 g of acetonitrile, 140 g of dibutyl carbonate, 250 g of ammonium azelate, 150 g of spirobipyrrolidinium tetrafluoroborate quaternary ammonium salt, 90 g of a flashover voltage booster (modified nano-silica prepared in Preparation Example 3), 13 g of m-nitroacetophenone, 9 g of adipic diamide and 9 g of sorbitol.

[0066] Among them, the preparation method of the electrolyte solution includes the following steps:

[0067] Heat ethylene glycol monomethyl ether to 80 °C, add acetonitrile and dibutyl carbonate to it. After mixing evenly, heat to 140 °C, add ammonium azelate and spirobipyrrolidinium tetrafluoroborate quaternary ammonium salt, keep warm and stir for 40 min. Then cool down to 120 °C, add modified nano-silica, adipic diamide and sorbitol, keep warm and stir for 40 min. Cool down to 105 °C, and finally add m-nitroacetophenone, keep warm and stir for 40 min. Naturally cool to room temperature to obtain the electrolyte solution.

[0068] Comparative Example 1

[0069] A low-temperature medium-high voltage aluminum electrolytic capacitor, different from Example 2, in the raw materials of the electrolyte solution, an equal amount of manganese dioxide is used to replace the modified nano-silica in the flashover voltage booster.

[0070] Comparative Example 2

[0071] A low-temperature medium-high voltage aluminum electrolytic capacitor, different from Example 2, in the raw materials of the electrolyte solution, an equal amount of polyvinyl alcohol is used to replace the modified nano-silica in the flashover voltage booster.

[0072] Comparative Example 3

[0073] A low-temperature medium-high voltage aluminum electrolytic capacitor, different from Example 2, in the raw materials of the electrolyte solution, nano-silica is directly added as the flashover voltage booster.

[0074] Comparative Example 4

[0075] A low-temperature medium-high voltage aluminum electrolytic capacitor, which is different from Example 2 in that in the electrolyte raw materials, a flashover voltage enhancer is not added, that is, modified nano-silica is not added.

[0076] Comparative Example 5

[0077] A low-temperature medium-high voltage aluminum electrolytic capacitor, which is different from Example 2 in that in the electrolyte raw materials, spirobipyrrolidinium tetrafluoroborate is not added.

[0078] Comparative Example 6

[0079] A low-temperature medium-high voltage aluminum electrolytic capacitor, which is different from Example 2 in that in the electrolyte raw materials, acetonitrile is separately added as a low-melting-point co-solvent, that is, the electrolyte raw materials in this comparative example include:

[0080] 450 g of ethylene glycol monomethyl ether, 250 g of acetonitrile, 200 g of ammonium hydrogen phosphate, 100 g of spirobipyrrolidinium tetrafluoroborate, 70 g of a flashover voltage enhancer (modified nano-silica prepared in Preparation Example 2), 10 g of p-nitrobenzyl alcohol, 7 g of mannitol, and 8 g of polyvinyl alcohol.

[0081] Among them, the preparation method of the electrolyte includes the following steps:

[0082] Heat ethylene glycol monomethyl ether to 75 °C, add acetonitrile thereto, mix and heat to 135 °C, add ammonium hydrogen phosphate and spirobipyrrolidinium tetrafluoroborate, keep warm and stir for 35 min, then cool to 115 °C, add modified nano-silica, mannitol and polyvinyl alcohol, keep warm and stir for 35 min, cool to 103 °C, and finally add p-nitrobenzyl alcohol, keep warm and stir for 35 min, and naturally cool to room temperature to obtain the electrolyte.

[0083] Take the aluminum electrolytic capacitors prepared in Examples 1-3 and Comparative Examples 1-6 as samples for low-temperature performance tests, and test the capacitance, equivalent series resistance (ESR) value, leakage current performance, and impedance of the capacitors at room temperature of 25 °C or low temperature of -45 °C. The test results are shown in Table 1 below.

[0084] Table 1

[0085]

[0086] According to the data in Example 2, Comparative Example 1, and Table 1: In the invention of the present application, the modified silica is used as the flashover voltage enhancer, which can not only enhance the dielectric strength of the electrolyte, effectively increase the flashover voltage threshold, and reduce the breakdown risk in the electrochemical system, but also play a role in reducing viscosity and increasing the fluidity of the electrolyte in a low-temperature environment. Although manganese dioxide has a high dielectric constant, it can effectively increase the flashover voltage threshold and reduce the breakdown risk in the electrochemical system, but it may increase the viscosity of the electrolyte in a low-temperature environment, hinder ion migration, and reduce the overall conductivity.

[0087] According to the data in Example 2, Comparative Examples 2-3, and Table 1: Using polyvinyl alcohol alone as the flashover voltage enhancer in the electrolyte may increase the viscosity of the electrolyte and lead to a decrease in conductivity. In addition, directly using nano-silica as the flashover voltage enhancer, due to the easy precipitation or aggregation of nano-silica in the electrolyte, the performance of the electrolyte is unstable, which severely limits its application in harsh environments. In the present application, however, using modified nano-silica as the flashover voltage enhancer in the electrolyte can increase the fluidity of the electrolyte. Moreover, the nano-silica modified by polyvinyl alcohol, allyl succinic anhydride, and vinyl silane coupling agent can be evenly dispersed in the electrolyte, significantly improving the precipitation or aggregation phenomenon to maintain the stability of the electrolyte, keeping the viscosity of the electrolyte at a low level, and making ion conduction smoother.

[0088] According to the data in Example 2, Comparative Example 4, and Table 1: Without adding a flashover voltage enhancer, all performances are relatively poor. When working at low temperatures, the viscosity of the electrolyte increases, resulting in a decrease in conductivity and a significant decline in electrical characteristics, making it difficult to meet the actual use requirements. In the present invention, however, using modified silica as the flashover voltage enhancer significantly reduces the viscosity of the electrolyte and improves the ion conduction efficiency. Even in a low-temperature environment, the electrolyte can maintain good fluidity.

[0089] According to the data in Example 2, Comparative Example 5, and Table 1: Without adding spirobipyrrolidinium tetrafluoroborate, the conductivity of the electrolyte at low temperatures is relatively poor. By adding spirobipyrrolidinium tetrafluoroborate, spirobipyrrolidinium tetrafluoroborate has a high solubility in the solvent, which is beneficial to increasing the ion concentration in the electrolyte. At a low temperature of -45°C, the electrolyte can still maintain a high conductivity, enabling the capacitor to still work normally at ultra-low temperatures.

[0090] According to the data in Example 2, Comparative Example 6 and Table 1: Using acetonitrile alone as the low melting point co-solvent has limited improvement effect on the low temperature resistance of the solvent system. By introducing butylene carbonate and acetonitrile for compounding, the melting point of the mixed solvent system is effectively reduced, thereby inhibiting the crystallization of the solvent at low temperature, further reducing the precipitation of electrolyte salts, enabling the electrolyte to have a high conductivity, and improving the stability of the electrolyte solution at low temperature.

[0091] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-temperature medium- and high-voltage aluminum electrolytic capacitor, characterized in that: It includes electrolyte, anode foil, cathode foil, lead terminal and plastic package shell; Wherein, the electrolyte comprises the following raw materials in parts by weight: 40-50 parts of main solvent, 20-30 parts of low melting point co-solvent, 15-25 parts of main solute, 5-15 parts of auxiliary solute, 5-9 parts of flash voltage enhancer, 0.7-1.3 parts of hydrogen remover, 1.2-1.8 parts of waterproofing auxiliary agent; The flash voltage enhancer is modified nano-silicon dioxide, and the raw materials for preparing the modified nano-silicon dioxide include polyvinyl alcohol, allyl succinic anhydride, vinyl silane coupling agent and nano-silicon dioxide, and the weight ratio of the polyvinyl alcohol, allyl succinic anhydride, vinyl silane coupling agent and nano-silicon dioxide is (0.6-0.8): (0.3-0.5): (0.13-0.15): 1; The vinyl silane coupling agent is at least one of vinyl trimethoxy silane, vinyl triethoxy silane and vinyl triisopropoxy silane; The preparation method of the modified nano silicon dioxide is: (1) Dissolve polyvinyl alcohol in deionized water, add allyl succinic anhydride and benzoyl peroxide at 60-70°C, stir and react for 2-3 hours, add acetone after the reaction is completed to precipitate, wash and dry to obtain allyl succinic anhydride grafted polyvinyl alcohol; (2) dissolving the vinyl silane coupling agent in 95% ethanol to form a silane hydrolyzate, adding nano-silica to the silane hydrolyzate, and ultrasonically oscillating for 1-2 hours to obtain silanized nano-silica; (3) Add silanized nano-silica to deionized water, ultrasonically disperse for 30-40 minutes, add allyl succinic anhydride grafted polyvinyl alcohol, continue ultrasonically dispersing for 1-2 hours, add a mixture of benzoyl peroxide and sulfuric acid, mix evenly, stir to react for 3-4 hours, and dry to obtain modified nano-silica.

2. A low-temperature medium- and high-voltage aluminum electrolytic capacitor according to claim 1, characterized in that: The main solvent is ethylene glycol monomethyl ether.

3. The low-temperature medium- and high-voltage aluminum electrolytic capacitor according to claim 1, characterized in that: The low melting point co-solvent is prepared by compounding acetonitrile and dibutyl carbonate, and the weight ratio of the acetonitrile to dibutyl carbonate is 1:(0.5-0.9).

4. The low-temperature medium- and high-voltage aluminum electrolytic capacitor according to claim 1, characterized in that: The main solute is at least one of ammonium hydrogen phosphate, ammonium sebacate and ammonium azelate; the auxiliary solute is tetrafluoroborate spirocyclic bipyrrolidine quaternary ammonium salt.

5. The low-temperature medium- and high-voltage aluminum electrolytic capacitor according to claim 1, characterized in that: The hydrogen remover is at least one of p-nitrophenol, p-nitrobenzyl alcohol, m-nitroacetophenone and o-nitroanisole.

6. The low-temperature medium- and high-voltage aluminum electrolytic capacitor according to claim 1, characterized in that: The waterproofing auxiliary agent is at least one of phosphoric acid, hypophosphorous acid, mannitol, polypropylene alcohol, adipic acid diamide, and sorbitol.

7. The low-temperature medium- and high-voltage aluminum electrolytic capacitor according to claim 1, characterized in that: The preparation method of the electrolyte is: Heat the main solvent to 70-80°C, add the auxiliary solvent thereto, mix well and heat to 130-140°C, add the main solute and the auxiliary solute, keep warm and stir for 30-40 minutes, then cool to 110-120°C, add the flash voltage enhancer and the waterproofing auxiliary agent, keep warm and stir for 30-40 minutes, cool to 100-105°C, finally add the dehydrogenating agent, keep warm and stir for 30-40 minutes, and naturally cool to room temperature to obtain the electrolyte.

8. The low-temperature medium- and high-voltage aluminum electrolytic capacitor according to claim 1, characterized in that: The anode foil and the cathode foil are parallel to each other and are inserted into the plastic-sealed shell. The anode foil and the cathode foil are led out through lead terminals. The electrolyte is stored in the plastic-sealed shell.

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