Liquid aluminum electrolytic capacitor

Abstract

This invention discloses a liquid aluminum electrolytic capacitor, relating to the field of electrolytic capacitor technology. The liquid aluminum electrolytic capacitor of this invention is manufactured by the following method: an anode foil, a first electrolytic paper, a cathode foil, and a second electrolytic paper are sequentially overlapped and wound into a core package; the core package is impregnated with an electrolyte, then encapsulated to obtain the liquid aluminum electrolytic capacitor; the electrolyte comprises at least the following raw materials in parts by weight: 60-75 parts N,N-dimethylformamide; 15-25 parts ethylene glycol; 3-5 parts boric acid; 1.5-3 parts ammonium formate; 1-3 parts silicon-boron modified polyethylene adipate; 0.5-1.5 parts triethylamine; 0.3-0.7 parts ammonium hypophosphite; and 0.2-0.5 parts p-nitrobenzoic acid. The electrolyte prepared in this application imparts wide temperature range adaptability, high voltage withstand capability, and long-life stability to the liquid aluminum electrolytic capacitor.

Description

Technical Field

[0001] This invention relates to the field of electrolytic capacitor technology, and more specifically to liquid aluminum electrolytic capacitors. Background Technology

[0002] With the rapid development of electronic component research, aluminum electrolytic capacitors are gradually evolving towards miniaturization, wide operating temperature range, long lifespan, and high safety. As one of the most important basic electronic components, aluminum electrolytic capacitors not only play a role in filtering, coupling, and bypassing in electronic circuits, but also exert special influence in correction circuits and power supply circuits. As research into aluminum electrolytic capacitors deepens, the temperature requirements for the devices are gradually increasing, expanding from the initial 0-80℃ to the current −55-105℃; the voltage withstand requirements are also gradually rising. Aluminum electrolytic capacitors mainly consist of a capacitor core and a working electrolyte. The electrolyte plays a crucial role in the capacitor's performance, determining its operating temperature range, rated voltage, losses, impedance, ripple current, and service life.

[0003] The electrolyte is the actual cathode of an aluminum electrolytic capacitor, providing oxygen ions and repairing the anodic oxide film. Therefore, a high-performance electrolyte plays a crucial role in ensuring the quality of aluminum electrolytic capacitors. The electrolyte of an aluminum electrolytic capacitor consists of solute, solvent, and additives. The main solute supports the electrolyte's performance, providing ions to repair the oxide film during operation. Additives can improve and enhance the electrolyte's performance, such as increasing flashover voltage, reducing leakage current, and expanding the operating temperature range. Although additives constitute a small proportion of the working electrolyte, they have a significant effect on improving its performance and are an indispensable component.

[0004] With the rapid development of aluminum electrolytic capacitor technology, in addition to increasingly stringent requirements for raw materials such as aluminum foil, rubber stoppers, and electrolytic paper, stricter requirements are also being placed on the types and performance of electrolyte additives. Different solute-solvent systems and additive combinations play different roles. Appropriate combinations will improve electrolyte performance; otherwise, they will negatively impact electrolyte performance. Currently, traditional electrolytes mostly use straight-chain carboxylates and solvent systems, with additives including phosphates and nitro compounds, but these suffer from problems such as low flash voltage, high vapor pressure, and poor high-temperature stability. In recent years, polyester polyols have been studied as additives, which can improve flash voltage and thermal stability, but their low-temperature performance declines and they lack functional modifications. In existing technologies, most polyester polyols have a straight-chain structure, which cannot be effectively adsorbed onto the oxide film surface, resulting in limited performance improvement. Furthermore, high-end additives rely on imports, leading to high costs. Therefore, there is an urgent need for a new type of electrolyte additive that can achieve a breakthrough in comprehensive performance through material modification. Summary of the Invention

[0005] The purpose of this invention is to provide a liquid aluminum electrolytic capacitor, solving the following technical problems: Existing liquid aluminum electrolytic capacitors suffer from problems such as short lifespan at high temperatures, low flash voltage, and poor performance at low temperatures.

[0006] The objective of this invention can be achieved through the following technical solutions: A liquid aluminum electrolytic capacitor, said liquid aluminum electrolytic capacitor being manufactured by the following method: The anode foil, the first electrolytic paper, the cathode foil, and the second electrolytic paper are sequentially overlapped and wound into a core package; The core package is impregnated with electrolyte, then encapsulated and packaged to obtain a liquid aluminum electrolytic capacitor. The electrolyte comprises at least the following parts by weight of raw materials: 60-75 parts of N,N-dimethylformamide; 15-25 parts of ethylene glycol; 3-5 parts of boric acid; 1.5-3 parts of ammonium formate; 1-3 parts of silicon-boron modified polyethylene adipate; 0.5-1.5 parts of triethylamine; 0.3-0.7 parts of ammonium hypophosphite; 0.2-0.5 parts of p-nitrobenzoic acid.

[0007] As a further aspect of the present invention, the preparation method of the silicon-boron modified polyethylene adipate includes at least the following preparation steps: Adipic acid, ethylene glycol, and triethyl γ-aminopropyltriethoxysilaneborate were mixed and subjected to a stepwise heating reaction under nitrogen gas. Then, the nitrogen gas was turned off and a polycondensation reaction was carried out under negative pressure. After cooling, silicon-boron modified polyethylene adipate was obtained.

[0008] As a further aspect of the present invention: the molar ratio of the adipic acid, the ethylene glycol, the γ-aminopropyltriethoxysilane and the triethyl borate is 3-5:2-4:0.2-0.5:0.1-0.4.

[0009] As a further aspect of the present invention: the stepped heating reaction is set to react at 150-155℃ for 2-3 hours and at 165-175℃ for 2-3 hours.

[0010] As a further aspect of the present invention: the temperature of the polycondensation reaction is 220-230℃, the time is 3-5h, and the pressure is 20-30kPa.

[0011] As a further aspect of the present invention: the temperature of the impregnation electrolyte is 80-90°C and the time is 30-60 min.

[0012] As a further aspect of the present invention: the method for preparing the electrolyte includes at least: N,N-dimethylformamide, ethylene glycol, boric acid, ammonium formate, and triethylamine are heated to 110-120℃ and stirred at a constant temperature for 60-100 min. The temperature is then lowered to 75-90℃, and silicon-boron modified polyethylene adipate, ammonium hypophosphite, and p-nitrobenzoic acid are added. The mixture is stirred at a constant temperature for 10-30 min and then cooled to room temperature to obtain the electrolyte.

[0013] The beneficial effects of this invention are: The main solvent of the electrolyte in the liquid aluminum electrolytic capacitor provided in this invention is a eutectic mixture of ethylene glycol and N,N-dimethylformamide, which significantly lowers the freezing point of the electrolyte, ensuring that it remains liquid and free of precipitates even at extreme low temperatures of -55°C, thus laying the foundation for the cold start-up and stable operation of electrical equipment. The main solute is a combination of ammonium formate and boric acid. Ammonium formate provides sufficient conductive ions to ensure the ionic conductivity of the electrolyte, while boric acid reacts with ethylene glycol to form borate esters, providing a material basis for the subsequent interface layer construction. In the additive system, ammonium hypophosphite reacts at defects in the anodic oxide film to form a stable aluminum phosphate protective film, achieving initial repair of the oxide film. p-Nitrobenzoic acid can further enhance... The electrolyte's flash voltage enhances stability under high-voltage environments. Triethylamine, acting as a buffer, precisely stabilizes the electrolyte's pH within the optimal range of 5.5-7.5, preventing hydration corrosion of the dielectric oxide film in excessively acidic or alkaline environments. The core functional additive, silicon-boron modified polyethylene adipate, inhibits electrolyte crystallization through flexible silicon segments in its molecular structure, synergistically enhancing low-temperature adaptability with a eutectic solvent. Its excellent tolerance to acid and alkaline environments, combined with the triethylamine buffer system, ensures the capacitor's performance stability throughout its entire lifespan. Furthermore, the silicon and boron elements in its molecules participate in interface layer construction and oxide film repair, forming a dual repair mechanism with ammonium hypophosphite, further reducing leakage current and slowing capacity decay. Through these complementary and synergistic effects, the components ultimately enable the electrolyte to simultaneously possess wide temperature range adaptability, high voltage tolerance, and long-life stability, perfectly solving the technical challenge of mutual constraints among these performance indicators in traditional electrolytes.

[0014] This invention utilizes the esterification reaction of adipic acid with the carboxyl and hydroxyl groups of ethylene glycol under heating conditions, removing one molecule of water and forming an ester bond, ultimately forming a linear polyethylene adipate prepolymer. Subsequently, γ-aminopropyltriethoxysilane and triethyl borate are introduced for modification. The terminal primary amino group of γ-aminopropyltriethoxysilane exhibits high reactivity, undergoing a nucleophilic substitution reaction with the carboxyl group on the polyester chain, grafting it onto the polyester backbone. The ethoxy group in the triethyl borate molecule undergoes an exchange reaction with the hydroxyl group of ethylene glycol or the terminal hydroxyl group of the polyester chain, introducing boron groups into the polyester chain. No catalyst is required during the preparation process, thus avoiding the impact of impurity ions on the purity of the electrolyte from the source. Furthermore, all raw materials are domestically produced, significantly reducing production costs and dependence on imported high-end additives. In terms of performance, the silicon and boron elements in the silicon-boron modified polyethylene adipate ester molecule can interact with the surface of the anodic oxide film, forming a dense Si-O-Al and BO-Al composite interface layer in conjunction with the borate ester generated from boric acid and ethylene glycol. This effectively shields the electric field, reduces the concentration of negative ions at the interface, increases the flash voltage of the electrolyte, and significantly enhances the capacitor's ability to withstand voltage fluctuations and instantaneous overvoltages. The thermal decomposition temperature of the silicon-boron modified polyethylene adipate ester is low, and the siloxane network structure in the molecule can effectively inhibit the volatilization of solvent molecules such as ethylene glycol at high temperatures, reducing the electrolyte vapor pressure and improving the high-temperature durability of the capacitor. Furthermore, the boron element in the silicon-boron modified polyethylene adipate ester molecule can promote oxygen ion transfer, accelerate the repair process of the anodic oxide film, and form a dual repair mechanism with the aluminum phosphate protective film of ammonium hypophosphite, enabling the capacitor to maintain extremely low leakage current and minimal capacity decay during long-term operation, significantly extending its service life. Meanwhile, the flexible silicon segments introduced into silicon-boron modified polyethylene adipate can effectively suppress the crystallization of the electrolyte at low temperatures, and work synergistically with the eutectic solvent to ensure liquid stability at extreme low temperatures. Detailed Implementation

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1: The preparation method of silicon-boron modified polyethylene adipate includes the following steps: 438.4 g adipic acid, 260.4 g ethylene glycol, 74.7 g γ-aminopropyltriethoxysilane and 23.2 g triethyl borate were mixed and nitrogen gas was introduced at a rate of 50 mL / min for protection. The temperature was increased to 152 °C at 2 °C / min and held for 2.5 hours until the adipic acid was completely melted. Then the temperature was increased to 170 °C at 1.5 °C / min and held for 2.5 hours. Then the temperature was increased to 225 °C at 2 °C / min. The nitrogen gas was turned off and a vacuum was started. The pressure was reduced to a negative pressure of 25 kPa within 30 minutes. The reaction was carried out for 4 hours. The heating was turned off and the mixture was cooled to room temperature to obtain silicon-boron modified polyethylene adipate.

[0017] Example 2: The preparation method of silicon-boron modified polyethylene adipate includes the following steps: 438.4 g adipic acid, 260.4 g ethylene glycol, 49.8 g γ-aminopropyltriethoxysilane, and 46.4 g triethyl borate were mixed and purged with nitrogen at a rate of 50 mL / min. The mixture was heated to 152 °C at a rate of 2 °C / min and held for 2.5 hours until the adipic acid was completely melted. The mixture was then heated to 170 °C at a rate of 1.5 °C / min and held for 2.5 hours. The mixture was then heated to 225 °C at a rate of 2 °C / min. The nitrogen was turned off and a vacuum was started. The pressure was reduced to a negative pressure of 25 kPa within 30 minutes. The reaction was carried out for 4 hours. The heating was then turned off and the mixture was cooled to room temperature to obtain silicon-boron modified polyethylene adipate.

[0018] Example 3: The preparation method of an aluminum electrolytic capacitor includes the following steps: 70 parts by weight of N,N-dimethylformamide, 20 parts by weight of ethylene glycol, 2 parts by weight of ammonium formate, 4 parts by weight of boric acid and 1 part by weight of triethylamine were heated to 115°C in a heat-collecting constant-temperature magnetic stirrer and stirred at a constant temperature for 80 min. After cooling to 85°C, 0.4 parts by weight of p-nitrobenzoic acid, 0.6 parts by weight of ammonium hypophosphite and 2 parts by weight of silicon-boron modified polyethylene adipate ester prepared in Example 1 were added and stirred at a constant temperature for 20 min to obtain the electrolyte. High-purity aluminum foil with a thickness of 12 μm was subjected to a 15 wt% sulfuric acid solution at a current density of 25 A / dm. 2 Electrochemical etching at 50℃ for 15 minutes, followed by formation in 5wt% boric acid solution at 25V and 60℃ for 30 minutes, and then cutting to obtain the anode foil; A 10μm thick ordinary aluminum foil is dried at 100℃ for 20 minutes to remove surface oil and then cut to obtain a cathode foil. High-purity cellulose paper with a thickness of 25μm was vacuum dried at 120℃ for 3 hours, and then cut to obtain the first electrolytic paper and the second electrolytic paper. The anode foil, first electrolytic paper, cathode foil, and second electrolytic paper are stacked sequentially and wound into a core package using a core package winding machine. After winding, both ends are fixed with high-temperature tape. Tinned copper wire guide pins are then welded to the anode foil and cathode foil at both ends of the core package using an ultrasonic welding machine. The core package was placed in a vacuum impregnation tank and evacuated to -0.095 MPa for 20 minutes. The prepared electrolyte was then injected into the tank until the liquid level was 5 mm above the core package. The vacuum was maintained for another 30 minutes, and the pressure was slowly restored to normal. The core package was then removed, excess electrolyte was wiped off the surface, and the core package was placed in an aluminum shell. The guide pin was inserted through the sealing plug, and the top of the aluminum shell was mechanically pressed and sealed using a packaging machine. The core package was then charged and aged at the rated voltage for 125°C for 120 minutes to obtain an aluminum electrolytic capacitor.

[0019] Example 4: The preparation method of an aluminum electrolytic capacitor includes the following steps: 70 parts by weight of N,N-dimethylformamide, 20 parts by weight of ethylene glycol, 2 parts by weight of ammonium formate, 4 parts by weight of boric acid and 1 part by weight of triethylamine were heated to 115°C in a heat-collecting constant-temperature magnetic stirrer and stirred at a constant temperature for 80 min. After cooling to 85°C, 0.4 parts by weight of p-nitrobenzoic acid, 0.6 parts by weight of ammonium hypophosphite and 2 parts by weight of silicon-boron modified polyethylene adipate ester prepared in Example 2 were added and stirred at a constant temperature for 20 min to obtain the electrolyte. High-purity aluminum foil with a thickness of 12 μm was subjected to a 15 wt% sulfuric acid solution at a current density of 25 A / dm. 2 Electrochemical etching at 50℃ for 15 minutes, followed by formation in 5wt% boric acid solution at 25V and 60℃ for 30 minutes, and then cutting to obtain the anode foil; A 10μm thick ordinary aluminum foil is dried at 100℃ for 20 minutes to remove surface oil and then cut to obtain a cathode foil. High-purity cellulose paper with a thickness of 25μm was vacuum dried at 120℃ for 3 hours, and then cut to obtain the first electrolytic paper and the second electrolytic paper. The anode foil, first electrolytic paper, cathode foil, and second electrolytic paper are stacked sequentially and wound into a core package using a core package winding machine. After winding, both ends are fixed with high-temperature tape. Tinned copper wire guide pins are then welded to the anode foil and cathode foil at both ends of the core package using an ultrasonic welding machine. The core package was placed in a vacuum impregnation tank and evacuated to -0.095 MPa for 20 minutes. The prepared electrolyte was then injected into the tank until the liquid level was 5 mm above the core package. The vacuum was maintained for another 30 minutes, and the pressure was slowly restored to normal. The core package was then removed, excess electrolyte was wiped off the surface, and the core package was placed in an aluminum shell. The guide pin was inserted through the sealing plug, and the top of the aluminum shell was mechanically pressed and sealed using a packaging machine. The core package was then charged and aged at the rated voltage for 125°C for 120 minutes to obtain an aluminum electrolytic capacitor.

[0020] Example 5: The preparation method of an aluminum electrolytic capacitor includes the following steps: 65 parts by weight of N,N-dimethylformamide, 25 parts by weight of ethylene glycol, 3 parts by weight of ammonium formate, 4 parts by weight of boric acid and 1 part by weight of triethylamine were heated to 115°C in a heat-collecting constant-temperature magnetic stirrer and stirred at a constant temperature for 80 min. After cooling to 85°C, 0.4 parts by weight of p-nitrobenzoic acid, 0.6 parts by weight of ammonium hypophosphite and 1 part by weight of silicon-boron modified polyethylene adipate ester prepared in Example 1 were added and stirred at a constant temperature for 20 min to obtain the electrolyte. High-purity aluminum foil with a thickness of 12 μm was subjected to a 15 wt% sulfuric acid solution at a current density of 25 A / dm. 2 Electrochemical etching at 50℃ for 15 minutes, followed by formation in 5wt% boric acid solution at 25V and 60℃ for 30 minutes, and then cutting to obtain the anode foil; A 10μm thick ordinary aluminum foil is dried at 100℃ for 20 minutes to remove surface oil and then cut to obtain a cathode foil. High-purity cellulose paper with a thickness of 25μm was vacuum dried at 120℃ for 3 hours, and then cut to obtain the first electrolytic paper and the second electrolytic paper. The anode foil, first electrolytic paper, cathode foil, and second electrolytic paper are stacked sequentially and wound into a core package using a core package winding machine. After winding, both ends are fixed with high-temperature tape. Tinned copper wire guide pins are then welded to the anode foil and cathode foil at both ends of the core package using an ultrasonic welding machine. The core package was placed in a vacuum impregnation tank and evacuated to -0.095 MPa for 20 minutes. The prepared electrolyte was then injected into the tank until the liquid level was 5 mm above the core package. The vacuum was maintained for another 30 minutes, and the pressure was slowly restored to normal. The core package was then removed, excess electrolyte was wiped off the surface, and the core package was placed in an aluminum shell. The guide pin was inserted through the sealing plug, and the top of the aluminum shell was mechanically pressed and sealed using a packaging machine. The core package was then charged and aged at the rated voltage for 125°C for 120 minutes to obtain an aluminum electrolytic capacitor.

[0021] Example 6: The method for preparing an electrolytic capacitor includes the following steps: 65 parts by weight of N,N-dimethylformamide, 25 parts by weight of ethylene glycol, 3 parts by weight of ammonium formate, 4 parts by weight of boric acid and 1 part by weight of triethylamine were heated to 115°C in a heat-collecting constant-temperature magnetic stirrer and stirred at a constant temperature for 80 min. After cooling to 85°C, 0.4 parts by weight of p-nitrobenzoic acid, 0.6 parts by weight of ammonium hypophosphite and 1 part by weight of silicon-boron modified polyethylene adipate ester prepared in Example 1 were added and stirred at a constant temperature for 20 min to obtain the electrolyte. High-purity aluminum foil with a thickness of 12 μm was subjected to a 15 wt% sulfuric acid solution at a current density of 25 A / dm. 2 Electrochemical etching at 50℃ for 15 minutes, followed by formation in 5wt% boric acid solution at 25V and 60℃ for 30 minutes, and then cutting to obtain the anode foil; A 10μm thick ordinary aluminum foil is dried at 100℃ for 20 minutes to remove surface oil and then cut to obtain a cathode foil. High-purity cellulose paper with a thickness of 25μm was vacuum dried at 120℃ for 3 hours, and then cut to obtain the first electrolytic paper and the second electrolytic paper. The anode foil, first electrolytic paper, cathode foil, and second electrolytic paper are stacked sequentially and wound into a core package using a core package winding machine. After winding, both ends are fixed with high-temperature tape. Tinned copper wire guide pins are then welded to the anode foil and cathode foil at both ends of the core package using an ultrasonic welding machine. The core package was placed in a vacuum impregnation tank and evacuated to -0.095 MPa for 20 minutes. The prepared electrolyte was then injected into the tank until the liquid level was 5 mm above the core package. The vacuum was maintained for another 30 minutes, and the pressure was slowly restored to normal. The core package was then removed, excess electrolyte was wiped off the surface, and the core package was placed in an aluminum shell. The guide pin was inserted through the sealing plug, and the top of the aluminum shell was mechanically pressed and sealed using a packaging machine. The core package was then charged and aged at the rated voltage for 125°C for 120 minutes to obtain an aluminum electrolytic capacitor.

[0022] Comparative Example 1: The preparation method of silicon-modified polyethylene adipate includes the following steps: 438.4 g adipic acid, 260.4 g ethylene glycol, and 74.7 g γ-aminopropyltriethoxysilane were mixed and purged with nitrogen at a rate of 50 mL / min. The mixture was heated to 152 °C at a rate of 2 °C / min and held for 2.5 hours until the adipic acid was completely melted. The mixture was then heated to 170 °C at a rate of 1.5 °C / min and held for 2.5 hours. The mixture was then heated to 225 °C at a rate of 2 °C / min. The nitrogen was turned off and a vacuum was started. The pressure was reduced to a negative pressure of 25 kPa within 30 minutes. The reaction was carried out for 4 hours. The heating was then turned off and the mixture was cooled to room temperature to obtain silicon-modified polyethylene adipate.

[0023] Comparative Example 2: The preparation method of boron-modified polyethylene adipate includes the following steps: 438.4 g adipic acid, 260.4 g ethylene glycol, and 23.2 g triethyl borate were mixed and purged with nitrogen at a rate of 50 mL / min. The mixture was heated to 152 °C at a rate of 2 °C / min and held for 2.5 hours until the adipic acid was completely melted. The mixture was then heated to 170 °C at a rate of 1.5 °C / min and held for 2.5 hours. The mixture was then heated to 225 °C at a rate of 2 °C / min. The nitrogen was turned off and a vacuum was started. The pressure was reduced to a negative pressure of 25 kPa within 30 minutes. The reaction was carried out for 4 hours. The heating was then turned off and the mixture was cooled to room temperature to obtain boron-modified polyethylene adipate.

[0024] Comparative Example 3: The preparation method of polyethylene adipate includes the following steps: 438.4 g of adipic acid and 260.4 g of ethylene glycol were mixed, and nitrogen gas was introduced at a rate of 50 mL / min for protection. The temperature was increased to 152 °C at 2 °C / min and held for 2.5 hours until the adipic acid was completely melted. Then, the temperature was increased to 170 °C at 1.5 °C / min and held for 2.5 hours. Finally, the temperature was increased to 225 °C at 2 °C / min. The nitrogen gas was turned off, and a vacuum was started. The pressure was reduced to a negative pressure of 25 kPa within 30 minutes, and the reaction was carried out for 4 hours. The heating was then turned off and the mixture was cooled to room temperature to obtain polyethylene adipate. Compared with Example 3, Comparative Example 4 only replaced the silicon-boron modified polyethylene adipate prepared in Example 1 with the silicon-modified polyethylene adipate prepared in Comparative Example 1 by the same mass. The remaining components and preparation methods were completely the same as those in Example 3.

[0025] Compared with Example 3, Comparative Example 4 only replaced the silicon-boron modified polyethylene adipate prepared in Example 1 with the boron modified polyethylene adipate prepared in Comparative Example 2. The remaining components and preparation methods were completely the same as those in Example 3.

[0026] Compared with Example 3, Comparative Example 5 only replaced the silicon-boron modified polyethylene adipate prepared in Example 1 with polyethylene adipate prepared in Comparative Example 3 by the same mass. The remaining components and preparation methods were completely the same as those in Example 3.

[0027] Performance testing Conductivity testing: The conductivity of the electrolyte was tested using a DDS-307A conductivity meter. The electrolyte temperature must be kept constant at 30℃ before testing. The test results are shown in Table 1. pH value determination: The pH value of the electrolyte was tested using a PHS-3E pH meter. The electrolyte temperature must be kept constant at 30℃ before the test. The test results are shown in Table 1. Flash voltage determination: The flash voltage of the electrolyte was tested using a TV-1CH intelligent testing system. The test current was 4mA and the delay time was 60s. The flash voltage was taken as the voltage of the first flash point on the positive electrode foil. The test results are shown in Table 1. Vapor pressure determination: Vapor pressure was determined according to Standard Method A in GB / T 8017-2012. The liquid chamber of the vapor pressure tester was filled with the cooled sample and connected to the gas chamber, which had been heated to 37.8℃ in a water bath. The tester was then immersed in the 37.8℃ water bath until a constant pressure value was observed. This value is the vapor pressure of the sample at 37.8℃; the test results are shown in Table 1. Determination of precipitation temperature: The precipitation temperature was determined according to the method in SH / T 0090-91. Take 100 mL of the sample and pour it into a test tube. Turn on the freezing point tester and stir the sample in the test tube at a uniform speed. Simultaneously, start the cooling process and use ethanol (the heat transfer medium) to cool the sample. Record the temperature every minute. The temperature at which the electrolyte begins to show precipitation and turbidity is the precipitation temperature of the sample. The test results are shown in Table 1. Table 1: Statistical table of electrolyte performance test data in Examples 3-6 and Comparative Examples 4-6

[0028] Performance testing of liquid aluminum electrolytic capacitors: The capacitance C, loss factor DF, impedance Z (test frequency 120Hz), and leakage current Lc of aluminum electrolytic capacitors were measured using a VICTOR4090A benchtop digital bridge and a TH2686N electrolytic capacitor leakage current tester for low-temperature characteristics (-55℃) and high-temperature DC durability test (125℃, 2000h). The test results are shown in Table 2. Table 2: Statistical table of capacitor performance test data in Examples 3-6 and Comparative Examples 4-6

[0029] As shown in Tables 1 and 2, the electrolyte prepared by this invention has excellent wide temperature adaptability, strong high voltage tolerance, good thermal stability, and stable physicochemical properties. Furthermore, the liquid aluminum electrolytic capacitor containing the electrolyte of this invention has excellent and outstanding high-temperature long-life characteristics. In Comparative Example 4, the polyester additive was only modified with silicon, and the obtained capacitor had certain thermal stability, but the flash voltage improvement was limited, and the low-temperature performance deteriorated severely. In Comparative Example 5, the polyester additive was only modified with boron, and the obtained capacitor maintained good low-temperature performance, but its flash voltage was the lowest, and its long-term stability at high temperatures was poor. In Comparative Example 6, the polyester additive was not modified, and the obtained capacitor completely failed in the high-temperature durability test.

[0030] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0031] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A liquid aluminum electrolytic capacitor, characterized in that, The liquid aluminum electrolytic capacitor is manufactured by the following method: The anode foil, the first electrolytic paper, the cathode foil, and the second electrolytic paper are sequentially overlapped and wound into a core package; The core package is impregnated with electrolyte, then encapsulated and packaged to obtain a liquid aluminum electrolytic capacitor. The electrolyte comprises at least the following parts by weight of raw materials: 60-75 parts N,N-dimethylformamide; 15-25 parts ethylene glycol; 3-5 parts boric acid; 1.5-3 parts ammonium formate; 1-3 parts silicon-boron modified polyethylene adipate; 0.5-1.5 parts triethylamine; 0.3-0.7 parts ammonium hypophosphite; 0.2-0.5 parts p-nitrobenzoic acid; The preparation method of the silicon-boron modified polyethylene adipate includes at least the following preparation steps: Adipic acid, ethylene glycol, γ-aminopropyltriethoxysilane, and triethyl borate were mixed and subjected to a stepwise heating reaction by purging with nitrogen gas. Then, the nitrogen gas was turned off and a polycondensation reaction was carried out under negative pressure. After cooling, silicon-boron modified polyethylene adipate was obtained.

2. The liquid aluminum electrolytic capacitor according to claim 1, characterized in that, The molar ratio of the adipic acid, the ethylene glycol, the γ-aminopropyltriethoxysilane, and the triethyl borate is 3-5:2-4:0.2-0.5:0.1-0.

4.

3. The liquid aluminum electrolytic capacitor according to claim 1, characterized in that, The stepped heating reaction was set to react at 150-155℃ for 2-3 hours and at 165-175℃ for 2-3 hours.

4. The liquid aluminum electrolytic capacitor according to claim 1, characterized in that, The polycondensation reaction is carried out at a temperature of 220-230℃, a time of 3-5 hours, and a pressure of 20-30 kPa.

5. The liquid aluminum electrolytic capacitor according to claim 1, characterized in that, The temperature of the impregnation electrolyte is 80-90℃ and the time is 30-60 minutes.

6. The liquid aluminum electrolytic capacitor according to claim 1, characterized in that, The method for preparing the electrolyte includes at least the following: N,N-dimethylformamide, ethylene glycol, boric acid, ammonium formate, and triethylamine are heated to 110-120℃ and stirred at a constant temperature for 60-100 min. The temperature is then lowered to 75-90℃, and silicon-boron modified polyethylene adipate, ammonium hypophosphite, and p-nitrobenzoic acid are added. The mixture is stirred at a constant temperature for 10-30 min and then cooled to room temperature to obtain the electrolyte.

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