A working electrolyte for medium and high voltage aluminum electrolytic capacitors and its preparation method

Abstract

The present invention provides a working electrolyte for medium and high voltage aluminum electrolytic capacitors and a preparation method thereof, belonging to the technical field of capacitor preparation. The working electrolyte uses ammonium sebacate as the main solute, alkylammonium sebacate as the secondary solute, polyvinyl alcohol and ethylene glycol as the polymer additives, and at least one of ammonium hydrogen azelate, ammonium dodecanedioate, and ammonium pentaborate as the auxiliary solute. During the preparation process, a polymer is added to control the boiling temperature and heat preservation time of the electrolyte, and the reaction between the polymer additive and the solvent is utilized to enhance the dissolution ability of the polymer; the adsorption of polymers with different molecular chain lengths and polymer molecules containing different types of functional groups on the anode foil is utilized to enhance the ability to repair the defects on the anode surface during the operation of the capacitor. The present invention mainly improves the stability of the working electrolyte for medium and high voltage aluminum electrolytic capacitors and enhances the comprehensive performance of the capacitor by adjusting the electrolyte formula and boiling process.

Description

Technical Field

[0001] The present invention belongs to the technical field of capacitor preparation, and particularly relates to a working electrolyte for medium and high voltage aluminum electrolytic capacitors and a preparation method thereof. Background Art

[0002] Medium and high voltage aluminum electrolytic capacitors are one of the basic components of electronic products and are widely used in the production of automotive electronics, frequency conversion technology, displays, chargers, electronic ballasts, switching power supplies, and energy-saving lamps. In recent years, the rapid development of electronic technology and the further improvement of the integration level have put forward higher requirements for the comprehensive performance of aluminum electrolytic capacitors, driving the development of aluminum electrolytic capacitors towards high voltage, high capacitance, and long life.

[0003] An aluminum electrolytic capacitor mainly consists of a capacitor core and a working electrolyte. The working electrolyte plays a crucial role in the performance of the aluminum electrolytic capacitor, determining the working temperature range, rated voltage, loss factor, impedance, rated ripple current, working life of the capacitor, etc. During the preparation process, the electrolyte formula and cooking process are very critical. During the preparation process, a series of complex chemical reactions such as ammonium acid decomposition, esterification, and transesterification will occur between the components, and a large number of experiments are required to study and determine the preparation process.

[0004] At present, most of the working electrolytes for medium and high voltage aluminum electrolytic capacitors are straight-chain carboxylic acid ammonium salts + boric acid salts + ethylene glycol systems. The higher the number of carbon atoms in the straight-chain carboxylate, the higher the flashover voltage, but its solubility decreases rapidly with the increase of molecular weight. For example, the solubility of ammonium sebacate commonly used in ethylene glycol does not exceed 5%, resulting in an increase in impedance and easy crystallization and precipitation at low temperatures, restricting the working temperature range of the capacitor. Branched polycarboxylates have relatively high solubility in poly-solvents, are not easy to crystallize at low temperatures, have a wide use temperature range, high electrolyte conductivity, and the capacitors prepared have strong withstand voltage ability and high ripple current resistance ability, but branched polycarboxylates have the disadvantage of high cost. In addition, aluminum electrolytic capacitors prepared with common working electrolytes also have disadvantages such as large leakage current and insufficient ripple resistance ability. Moreover, other solutes that can be used as working electrolytes for medium and high voltage aluminum electrolytic capacitors also include straight-chain carboxylate salts such as ammonium azelate, ammonium hydrogen azelate, ammonium sebacate, ammonium dodecanedioate, and ammonium pentaborate, ammonium benzoate, etc., but each has certain disadvantages, such as ammonium dodecanedioate is not easy to obtain, ammonium pentaborate has a high conductivity, and ammonium benzoate is unstable at high temperatures. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a working electrolyte for medium and high voltage aluminum electrolytic capacitors and a preparation method thereof. By adjusting the electrolyte formula and cooking process technology, the stability of the working electrolyte for aluminum electrolytic capacitors is improved, and the comprehensive performance of the capacitor is enhanced.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions:

[0008] A working electrolyte for medium and high voltage aluminum electrolytic capacitors, with ammonium sebacate as the main solute, alkyl ammonium sebacate as the secondary solute, polyvinyl alcohol and ethylene glycol as polymer additives, and at least one of ammonium hydrogen azelate, ammonium dodecanedioate, and ammonium pentaborate as the auxiliary solute. The polyvinyl alcohol is composed of PVA with different molecular weights, and the ethylene glycol is composed of PEG with different molecular weights.

[0009] Further, the working electrolyte for medium and high voltage aluminum electrolytic capacitors includes the following components by mass percentage: auxiliary solvent 2-4%, main solute 5%, secondary solute 2%, mannitol 2%, ammonium pentaborate 3%, ammonium hydrogen azelate 0.9%, ammonium dodecanedioate 0.4%, hydrogen scavenger 0.4%, forming agent 0.4%, and polymer additive 1.2-1.4%, with the balance being the main solvent.

[0010] Further, the main solvent is ethylene glycol, the auxiliary solvent is one or more of γ-butyrolactone, glycerol, and diethylene glycol, the hydrogen scavenger is p-nitrobenzoic acid, and the forming agent is ammonium hypophosphite.

[0011] The present invention selects polyvinyl alcohol with different molecular weights and ethylene glycol with different molecular weights, and formulates them in a certain proportion as the polymer additive of the electrolyte. One is to utilize the electrostatic and physical adsorption effects of different functional groups on different polymers on the surface of the anode foil, and the other is to utilize the difference in the molecular weights of the polymers to exert the adsorption effects of different lengths of molecular chains on the surface of the anode foil. Therefore, on the one hand, different types of polymers are selected, and on the other hand, polymers with different molecular chain lengths are selected and formulated in a certain proportion, so as to increase the flashover voltage of the working electrolyte, enhance the repair ability of the electrolyte to the surface defects of the capacitor dielectric film, improve the voltage withstand ability of the aluminum electrolytic capacitor, etc., and reduce the leakage current of the capacitor.

[0012] Further, the mass ratio of polyvinyl alcohol to ethylene glycol in the polymer additive is 1:1.3-2.

[0013] Further, the polyvinyl alcohol is composed of two or more of PVA 105 , PVA 117 , and PVA 124 , and the ethylene glycol is composed of two or more of triethylene glycol, PEG 200 , PEG 400 , and PEG 600 .

[0014] One of the working electrolytes of the present invention is added with ammonium pentaborate, ammonium hydrogen azelate and ammonium dodecanedioate, which can enhance the conductivity of the electrolyte and solve the problems of low solubility of ammonium sebacate and insufficient conductivity of the electrolyte; the other is to add branched-chain ammonium alkyl sebacate as a secondary solute, and utilize the high solubility of branched-chain polycarboxylates in the solvent, not easy to crystallize at low temperature, improve the operating temperature range of the electrolyte, and enhance the capacitor's withstand voltage and high ripple current resistance ability.

[0015] Technical solution two:

[0016] A preparation method of the working electrolyte for the medium and high voltage aluminum electrolytic capacitor described above, comprising the following steps:

[0017] (1) Weigh each component according to the described mass percentage and set aside;

[0018] (2) Mix the auxiliary solvent and the main solvent to obtain a mixed solvent, and add the main solute, mannitol, ammonium hydrogen azelate and ammonium dodecanedioate to the solvent under heating conditions, and obtain mixture A after dissolution;

[0019] (3) Add polyvinyl alcohol to the mixture A, heat and keep warm, and then cool naturally. After that, add ammonium pentaborate and ethylene glycol monomethyl ether, keep warm and cool to obtain mixture B;

[0020] (4) Add the secondary solute, hydrogen scavenger and forming agent to mixture B, keep warm for a period of time, and cool to room temperature to obtain the working electrolyte for the medium and high voltage aluminum electrolytic capacitor described above.

[0021] Further, step (2) is specifically: mix the auxiliary solvent and the main solvent to obtain a mixed solvent, heat the mixed solvent to 60 °C and then add the main solute, heat to 80 °C after complete dissolution, add mannitol, ammonium hydrogen azelate and ammonium dodecanedioate, and continue to heat to 130 °C to obtain mixture A after complete dissolution.

[0022] Further, step (3) is a boiling process. Add the polymer polyvinyl alcohol and heat to a temperature of 145 °C - 160 °C, keep warm for 30 min, cool naturally to 130 °C, add ammonium pentaborate and ethylene glycol monomethyl ether, keep warm at 130 °C for 35 min, and cool to 100 °C.

[0023] Further, in step (4), after adding the secondary solute, hydrogen scavenger and forming agent, keep warm at 100 °C for 35 min and cool to room temperature.

[0024] In the preparation process of the working electrolyte for medium and high voltage aluminum electrolytic capacitors of the present invention, the addition time of the secondary solute alkyl ammonium sebacate and the polymer, and the boiling temperature have a great influence on the performance of the electrolyte. In the present invention, alkyl ammonium sebacate is added in the final heat preservation stage of the boiling process of the electrolyte to maintain the relative stability of its composition and structure, prevent this substance from undergoing complex chemical reactions with solvents, polymer additives, etc. at high temperatures, change its molecular structure, and reduce the performance of the electrolyte.

[0025] The molecular weight of the polymer polyvinyl alcohol used in the working electrolyte of the present invention is relatively large, and it is difficult to dissolve in the solvent ethylene glycol at general temperatures. During the boiling process, PVA can only be completely dissolved by means of high temperature, and it will precipitate again due to the decrease in solubility at low temperatures, which will affect the performance of the electrolyte and aluminum electrolytic capacitors. In the boiling process adopted by the present invention, after adding polyvinyl alcohol, the heating temperature of the electrolyte is not lower than 145 °C and not higher than 160 °C, and the heat preservation time is relatively long. By using high temperature and controlling the heat preservation time, the functional groups of this polymer undergo a certain degree of complex chemical reaction with the solvent under suitable boiling conditions, especially at high temperatures, to improve the solubility of this polymer and maintain its stability in the solvent without precipitation at low temperatures.

[0026] Technical solution three:

[0027] The application of the working electrolyte for medium and high voltage aluminum electrolytic capacitors in medium and high voltage aluminum electrolytic capacitors.

[0028] Compared with the prior art, the present invention has the following advantages and technical effects:

[0029] By adjusting the electrolyte formula and boiling process technology, the present invention improves the stability of the working electrolyte for aluminum electrolytic capacitors and the comprehensive performance of the capacitors. The overall performance of the working electrolyte for medium and high voltage aluminum electrolytic capacitors obtained by the present invention is as follows: at 40 °C, the pH is about 5.94, the conductivity exceeds 2200 μS / cm, the flashover voltage reaches 500 V. The aluminum electrolytic capacitors (400V - 6.8uF) prepared with this have good comprehensive electrochemical performance: the capacitance is 6.6 - 6.7 μF, the leakage current ≤ 12 μA, the loss tanδ is about 0.05, and it has good ripple resistance, and the service life at 105 °C exceeds 8kh. Detailed implementation manners

[0030] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be regarded as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0031] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0032] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0033] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention's specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0034] Regarding terms such as "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0035] The present invention provides a working electrolyte for medium and high voltage aluminum electrolytic capacitors, with ammonium sebacate as the main solute, alkyl ammonium sebacate as the secondary solute, polyvinyl alcohol and ethylene glycol as polymer additives, and at least one of ammonium hydrogen azelate, ammonium dodecanedioate, and ammonium pentaborate as auxiliary solutes. The polyvinyl alcohol is composed of PVA with different molecular weights, and the ethylene glycol is composed of PEG with different molecular weights.

[0036] In some embodiments of the present invention, the working electrolyte comprises the following components by mass percentage: auxiliary solvent 2 - 4%, main solute 5%, secondary solute 2%, mannitol 2%, ammonium pentaborate 3%, ammonium hydrogen azelate 0.9%, ammonium dodecanedioate 0.4%, hydrogen scavenger 0.4%, forming agent 0.4%, and polymer additive 1.2 - 1.4%, with the balance being the main solvent.

[0037] In some embodiments of the present invention, the main solvent is ethylene glycol, the auxiliary solvent is one or more of γ - butyrolactone, glycerol, and diethylene glycol, the hydrogen scavenger is p - nitrobenzoic acid, and the forming agent is ammonium hypophosphite.

[0038] Ammonium sebacate has low solubility in solvents, which can lead to insufficient conductivity of the electrolyte. Based on the above considerations, in some preferred embodiments of the present invention, on the one hand, ammonium pentaborate, ammonium hydrogen azelate, and ammonium dodecanedioate are added to the working electrolyte of the present invention as auxiliary solutes, which can enhance the conductivity of the electrolyte and solve the problem of insufficient conductivity of the electrolyte due to the low solubility of ammonium sebacate. On the other hand, ammonium alkyl sebacate with branched chains is added as a secondary solute, and the branched polycarboxylate has high solubility in solvents, is not easy to crystallize at low temperatures, can increase the operating temperature range of the electrolyte, and enhance the voltage resistance and high ripple current resistance of the capacitor.

[0039] In some embodiments of the present invention, polyvinyl alcohol with different molecular weights and ethylene glycol oligomers with different molecular weights are selected and formulated in a ratio of 1:1.3 - 2 as the polymer additives of the electrolyte. Among them, the polyvinyl alcohol is composed of two or more of PVA 105 , PVA 117 and PVA 124 , and the ethylene glycol oligomers are composed of two or more of triethylene glycol diethyl ether, PEG 200 , PEG 400 and PEG 600 . In this way, the electrostatic and physical adsorption effects of different functional groups on different polymers on the surface of the anode foil, as well as the adsorption effects of different lengths of molecular chains on the surface of the anode foil, can be utilized to increase the flashover voltage of the working electrolyte and enhance the ability of the electrolyte to repair surface defects of the capacitor dielectric film, improve the voltage resistance and other capabilities of the aluminum electrolytic capacitor, and reduce the leakage current of the capacitor.

[0040] The present invention also provides a preparation method of the working electrolyte for the medium - high voltage aluminum electrolytic capacitor, specifically as follows:

[0041] (1) Mix the auxiliary solvent and the main solvent to obtain a mixed solvent. Heat the mixed solvent to 60°C, then add the main solute. After complete dissolution, raise the temperature to 80°C, add mannitol, ammonium hydrogen azelate, and ammonium dodecanedioate, and continue heating to 130°C. After complete dissolution, obtain mixture A;

[0042] (2) Boiling process: Add the polymer polyvinyl alcohol to the mixture A, heat to a temperature of 145°C - 160°C, keep warm for 30 min, naturally cool to 130°C, add ammonium pentaborate and ethylene glycol oligomers, keep warm at 130°C for 35 min, and then cool to 100°C to obtain mixture B;

[0043] (3) Add the secondary solute, hydrogen scavenger, and forming agent to mixture B, keep warm at 100°C for 35 min, and then cool to room temperature to obtain the working electrolyte for the medium - high voltage aluminum electrolytic capacitor.

[0044] During the preparation of the working electrolyte for medium and high voltage aluminum electrolytic capacitors of the present invention, the addition sequence of the secondary solute alkyl sebacate ammonium and the boiling temperature have a great influence on the performance of the electrolyte. In the present invention, alkyl sebacate ammonium is added in the final heat preservation stage of the boiling process of the electrolyte to maintain the relative stability of its composition and structure, and prevent this substance from undergoing complex chemical reactions with solvents, polymer additives, etc. at high temperatures, changing its molecular structure and reducing the performance of the electrolyte.

[0045] The molecular weight of the polymer polyvinyl alcohol used in the working electrolyte of the present invention is relatively large, and it is difficult to dissolve in the solvent ethylene glycol at general temperatures. During the boiling process, PVA can only be completely dissolved with the help of high temperature, and it will precipitate again due to the decrease in solubility at low temperatures, which will seriously affect the performance of the electrolyte and aluminum electrolytic capacitors. In the boiling process adopted by the present invention, after adding polyvinyl alcohol, the heating temperature of the electrolyte is not lower than 145 °C and not higher than 160 °C, and the heat preservation time is relatively long. By using the appropriate boiling conditions for this polymer, especially long-term high-temperature heat preservation, the functional groups undergo a certain degree of complex chemical reaction with the solvent to improve the solubility of this polymer and maintain its stability in the solvent without precipitation at low temperatures.

[0046] All components used in the examples of the present invention are obtained by purchasing commercially.

[0047] The technical solutions of the present invention are further described below through examples. The examples and comparative examples are only for helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0048] Example 1

[0049] (1) Weigh the following components by mass percentage: auxiliary solvent 2.5% (mass ratio of γ-butyrolactone to diethylene glycol is 1:1), main solute (ammonium sebacate) 5%, secondary solute (alkyl sebacate ammonium) 2%, mannitol 2%, ammonium pentaborate 3%, ammonium hydrogen azelate 0.9%, ammonium dodecanedioate 0.4%, hydrogen elimination agent (p-nitrobenzoic acid) 0.4%, forming agent (ammonium hypophosphite) 0.4%, polymer additive 1.4% (PVA 105 0.4%, PVA 117 0.2%, PEG 200 and PEG 400 0.4% each), and the balance is the main solvent (ethylene glycol).

[0050] (2) Mix the main solvent and the auxiliary solvent to obtain a mixed solvent, heat the mixed solvent to 60 °C, add the main solute (ammonium sebacate), and after complete dissolution, raise the temperature to 80 °C, add mannitol, ammonium hydrogen azelate and ammonium dodecanedioate, and continue heating to 130 °C to obtain mixture A;

[0051] (3) Polyvinyl alcohol is added to the mixture A, and the temperature is heated to 145 °C. After maintaining the temperature for 30 min and cooling to 130 °C, ammonium pentaborate and ethylene glycol are added, and after maintaining the temperature, it is cooled to 100 °C to obtain mixture B.

[0052] (4) Sub-solute, hydrogen scavenger and forming agent are added to mixture B, and it is maintained at 100 °C for 35 min and then cooled to room temperature to obtain the working electrolyte for medium and high voltage aluminum electrolytic capacitors.

[0053] Example 2

[0054] (1) Weigh the following components by mass percentage: auxiliary solvent 2.5% (the mass ratio of γ-butyrolactone to diethylene glycol is 1:1), main solute (ammonium sebacate) 5%, sub-solute (alkyl ammonium sebacate) 2%, mannitol 2%, ammonium pentaborate 3%, ammonium hydrogen azelate 0.9%, ammonium dodecanedioate 0.4%, hydrogen scavenger (p-nitrobenzoic acid), forming agent (ammonium hypophosphite) 0.4% each, polymer additive 1.2% (PVA 105 0.2%, PVA 124 0.2%, PEG 200 and PEG 600 0.4% each), and the balance is the main solvent (ethylene glycol).

[0055] (2) The main solvent and the auxiliary solvent are mixed to obtain a mixed solvent, and the mixed solvent is heated to 60 °C, then the main solute (ammonium sebacate) is added. After complete dissolution, the temperature is raised to 80 °C, and mannitol, ammonium hydrogen azelate and ammonium dodecanedioate are added, and it is continuously heated to 130 °C to obtain mixture A;

[0056] (3) Polyvinyl alcohol is added to the mixture A, and the temperature is heated to 160 °C. After maintaining the temperature for 30 min and cooling to 130 °C, ammonium pentaborate and ethylene glycol are added, and after maintaining the temperature, it is cooled to 100 °C to obtain mixture B.

[0057] (4) Sub-solute, hydrogen scavenger and forming agent are added to mixture B, and it is maintained for 35 min and then cooled to room temperature to obtain the working electrolyte for medium and high voltage aluminum electrolytic capacitors.

[0058] Comparative Example 1 (omitting the addition of the sub-solute alkyl ammonium sebacate):

[0059] Same as Example 1, the difference is only that the addition of the sub-solute (alkyl ammonium sebacate) is omitted, specifically:

[0060] (1) Auxiliary solvent 2.5% (mass ratio of γ-butyrolactone to diethylene glycol is 1:1), main solute (ammonium sebacate) 5%, secondary solute (alkylammonium sebacate) 2%, mannitol 2%, ammonium pentaborate 3%, ammonium hydrogen azelate 0.9%, ammonium dodecanedioate 0.4%, hydrogen scavenger (p-nitrobenzoic acid) 0.4%, forming agent (ammonium hypophosphite) 0.4%, polymer additive 1.4% (PVA 105 0.4%, PVA 117 0.2%, PEG 200 and PEG 400 each 0.4%), and the rest is the main solvent (ethylene glycol).

[0061] Weigh the following components by mass percentage: auxiliary solvent 2.5% (γ-butyrolactone and diethylene glycol each account for 50%), main solute (ammonium sebacate) 5%, mannitol 2%, ammonium pentaborate 3%, ammonium hydrogen azelate 0.9%, ammonium dodecanedioate 0.4%, hydrogen scavenger (p-nitrobenzoic acid), forming agent (ammonium hypophosphite) each 0.4% and polymer additive 1.4% (PVA 105 0.4%, PVA 117 0.2%, PEG 200 and PEG 400 each 0.4%), and the balance is the main solvent (ethylene glycol).

[0062] (2) Mix the main solvent and the auxiliary solvent to obtain a mixed solvent, heat the mixed solvent to 60 °C, add the main solute (ammonium sebacate), after complete dissolution, raise the temperature to 80 °C, add mannitol, ammonium hydrogen azelate and ammonium dodecanedioate, and continue heating to 130 °C to obtain mixture A;

[0063] (3) Add polyvinyl alcohol to the mixture A, heat to a temperature of 145 °C, keep warm for 30 min, cool to 130 °C, add ammonium pentaborate and ethylene glycol, keep warm, and then cool to 100 °C to obtain mixture B.

[0064] (4) Add the hydrogen scavenger and the forming agent to mixture B, keep warm for 35 min, and cool to room temperature to obtain the working electrolyte for medium and high voltage aluminum electrolytic capacitors.

[0065] Comparative Example 2 (the type of polymer is a single polyvinyl alcohol)

[0066] Same as Example 2, the difference is only that the polymer is a single polyvinyl alcohol PVA 105 . Specifically:

[0067] 1) Weigh the following components by mass percentage: auxiliary solvent 2.5% (the mass ratio of γ-butyrolactone to diethylene glycol is 1:1), main solute (ammonium sebacate) 5%, secondary solute (alkylammonium sebacate) 2%, mannitol 2%, ammonium pentaborate 3%, ammonium hydrogen azelate 0.9%, ammonium dodecanedioate 0.4%, hydrogen scavenger (p-nitrobenzoic acid), forming agent (ammonium hypophosphite) 0.4% each, and the polymer additive is PVA 105 1.2%, and the balance is the main solvent (ethylene glycol).

[0068] (2) Mix the main solvent and the auxiliary solvent to obtain a mixed solvent. After heating the mixed solvent to 60 °C, add the main solute (ammonium sebacate). After complete dissolution, raise the temperature to 80 °C, add mannitol, ammonium hydrogen azelate and ammonium dodecanedioate, and continue heating to 130 °C to obtain mixture A;

[0069] (3) Add the polymer additive PVA to the mixture A 105 , heat to 160 °C, keep warm for 30 min, cool to 130 °C, then add ammonium pentaborate, keep warm, and then cool to 100 °C to obtain mixture B.

[0070] (4) Add the secondary solute, hydrogen scavenger and forming agent to mixture B, keep warm for 35 min, and cool to room temperature to obtain the working electrolyte for medium and high voltage aluminum electrolytic capacitors.

[0071] Comparative Example 3 (changing the type of polymer to single ethylene glycol)

[0072] Same as Example 2, the difference is only that the polymer is single PEG 200 . Specifically:

[0073] (1) Weigh the following components by mass percentage: auxiliary solvent 2.5% (the mass ratio of γ-butyrolactone to diethylene glycol is 1:1), main solute (ammonium sebacate) 5%, secondary solute (alkylammonium sebacate) 2%, mannitol 2%, ammonium pentaborate 3%, ammonium hydrogen azelate 0.9%, ammonium dodecanedioate 0.4%, hydrogen scavenger (p-nitrobenzoic acid), forming agent (ammonium hypophosphite) 0.4% each, and the polymer additive is PEG 200 1.2%, and the balance is the main solvent (ethylene glycol).

[0074] (2) Mix the main solvent and the auxiliary solvent to obtain a mixed solvent. After heating the mixed solvent to 60 °C, add the main solute (ammonium sebacate). After complete dissolution, raise the temperature to 80 °C, add mannitol, ammonium hydrogen azelate and ammonium dodecanedioate, and continue heating to 130 °C to obtain mixture A;

[0075] (3) Add PEG to the mixture A 200 , ammonium pentaborate, keep warm for 30 min, and then cool to 100 °C to obtain mixture B.

[0076] (4) Add secondary solute, hydrogen scavenger and forming agent to mixture B, keep warm for 35 min, and cool to room temperature to obtain the working electrolyte for medium and high voltage aluminum electrolytic capacitors.

[0077] Comparative Example 4 (changing the addition time of secondary solute alkylammonium sebacate)

[0078] Same as Example 1, the only difference is that the secondary solute and the primary solute are added simultaneously. Specifically:

[0079] (1) Weigh the following components by mass percentage: auxiliary solvent 2.5% (γ-butyrolactone and diethylene glycol each account for 50%), primary solute (ammonium sebacate) 5%, secondary solute (alkylammonium sebacate) 2%, mannitol 2%, ammonium pentaborate 3%, ammonium hydrogen azelate 0.9%, ammonium dodecanedioate 0.4%, hydrogen scavenger (p-nitrobenzoic acid), forming agent (ammonium hypophosphite) each 0.4%, polymer additive 1.4% (PVA 105 0.4%, PVA 117 0.2%, PEG 200 and PEG 400 each 0.4%), and the rest is the main solvent (ethylene glycol);

[0080] (2) Mix the main solvent and the auxiliary solvent to obtain a mixed solvent, heat the mixed solvent to 60 °C, add the primary solute and the secondary solute, after complete dissolution, raise the temperature to 80 °C, add mannitol, ammonium hydrogen azelate and ammonium dodecanedioate, and continue heating to 130 °C to obtain mixture A;

[0081] (3) Add polyvinyl alcohol to the mixture A, heat to a temperature of 150 °C, keep warm for 30 min, cool to 130 °C, add ammonium pentaborate and diglycol, keep warm, and then cool to 100 °C to obtain mixture B.

[0082] (4) Add hydrogen scavenger and forming agent to mixture B, keep warm for 35 min, and cool to room temperature to obtain the working electrolyte for medium and high voltage aluminum electrolytic capacitors.

[0083] Comparative Example 5 (changing the addition time and temperature of the polymer)

[0084] Same as Example 1, the only difference is that two types of polymer additives are added simultaneously and the electrolyte boiling temperature is different. Specifically:

[0085] (1) Weigh the following components by mass percentage: auxiliary solvent 2.5% (γ-butyrolactone and diethylene glycol each account for 50%), main solute (ammonium sebacate) 5%, secondary solute (alkylammonium sebacate) 2%, mannitol 2%, ammonium pentaborate 3%, ammonium hydrogen azelate 0.9%, ammonium dodecanedioate 0.4%, hydrogen scavenger (p-nitrobenzoic acid), forming agent (ammonium hypophosphite) each 0.4%, polymer additive 1.4% (PVA 105 0.4%, PVA 117 0.2%, PEG 200 and PEG 400 each 0.4%), and the balance is the main solvent (ethylene glycol);

[0086] (2) Mix the main solvent and the auxiliary solvent to obtain a mixed solvent, heat the mixed solvent to 60 °C, add the main solute (ammonium sebacate), after complete dissolution, raise the temperature to 80 °C, add mannitol, ammonium hydrogen azelate and ammonium dodecanedioate, and continue to heat to 130 °C to obtain mixture A;

[0087] (3) Add PVA 105 , PVA 117 , PEG 200 and PEG 400 , and ammonium pentaborate to the mixture A, keep it warm at 130 °C, and then cool it to 100 °C to obtain mixture B.

[0088] (4) Add the secondary solute, hydrogen scavenger and forming agent to mixture B, keep it warm for 35 min, and cool it to room temperature to obtain the working electrolyte for medium and high voltage aluminum electrolytic capacitors.

[0089] Comparative Example 6

[0090] Same as Example 1, the difference is only that no polymer is added. Specifically:

[0091] (1) Weigh the following components by mass percentage: auxiliary solvent 2.5% (the mass ratio of γ-butyrolactone to diethylene glycol is 1:1), main solute (ammonium sebacate) 5%, secondary solute (alkylammonium sebacate) 2%, mannitol 2%, ammonium pentaborate 3%, ammonium hydrogen azelate 0.9%, ammonium dodecanedioate 0.4%, hydrogen scavenger (p-nitrobenzoic acid) 0.4%, forming agent (ammonium hypophosphite) 0.4%, and the balance is the main solvent (ethylene glycol).

[0092] (2) Mix the main solvent and the auxiliary solvent to obtain a mixed solvent, heat the mixed solvent to 60 °C, add the main solute (ammonium sebacate), after complete dissolution, raise the temperature to 80 °C, add mannitol, ammonium hydrogen azelate and ammonium dodecanedioate, and continue to heat to 130 °C to obtain mixture A;

[0093] (3) Ammonium pentaborate is added to the mixture A and kept warm, and then cooled to 100 °C to obtain mixture B.

[0094] (4) A secondary solute, a hydrogen scavenger, and a forming agent are added to mixture B, kept warm for 35 min, and cooled to room temperature to obtain the working electrolyte for medium and high voltage aluminum electrolytic capacitors.

[0095] Performance test: The pH and conductivity σ of the prepared capacitor working electrolyte are measured at a constant temperature of 40 °C in a sealed state, and the flashover voltage of the anode foil is measured by applying a constant current (3 mA) to increase the voltage. As a medium and high voltage aluminum electrolytic capacitor, it is required that the initial flashover voltage Us of the working electrolyte ≥ 400 V, and the flashover time is less than 130 s when it reaches 500 V, which meets the oxidation efficiency requirements.

[0096] Capacitors with a specification of 400 v - 6.8 μF are prepared using the said electrolyte. After aging, a durability test is carried out. The test adopts a high temperature (105 °C) accelerated life test to measure the performance of the capacitors.

[0097] Table 1 shows the performance test results of the working electrolytes obtained from Examples 1 - 2 and Comparative Examples 1 - 6, and Table 2 shows the electrochemical performance of each capacitor prepared with this electrolyte.

[0098] Table 1 Performance test results of the working electrolytes of Examples and Comparative Examples

[0099]

[0100]

[0101] Table 2 Electrochemical performance of aluminum electrolytic capacitors prepared with the working electrolytes of Examples and Comparative Examples

[0102] Capacitance / μF Leakage current / μA Loss tangent δ Example 1 6.73 11.6 0.047 Example 2 6.69 12.0 0.049 Comparative Example 1 6.25 14.9 0.058 Comparative Example 2 6.19 15.4 0.061 Comparative Example 3 6.22 16.1 0.063 Comparative Example 4 6.65 13.3 0.056 Comparative Example 5 6.18 16.2 0.064 Comparative Example 6 6.15 16.7 0.067

[0103] It can be seen from Table 1 and Table 2 that the working electrolyte prepared in the examples of the present invention has good conductivity, can meet the use requirements of aluminum electrolytic capacitors, and the performance of the prepared capacitors is within the qualified range. Compared with the results of the comparative examples, the overvoltage tolerance of the aluminum electrolytic capacitors is improved, and the leakage current of the capacitors is significantly reduced. When the performance of the working electrolyte for medium and high voltage aluminum electrolytic capacitors obtained in the present invention is at 40 °C, the pH is about 5.94, the conductivity exceeds 2200 μS / cm, and the flashover voltage reaches 500 V. The aluminum electrolytic capacitors (400 V - 6.8 uF) prepared with this have good comprehensive electrochemical performance: the capacitance is 6.6 - 6.7 μF, the leakage current is about 12 μA, and the loss tanδ ≤ 0.05, having good comprehensive performance. The service life of this capacitor exceeds 8 kh at 105 °C.

[0104] The above are only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A working electrolyte for medium and high voltage aluminum electrolytic capacitors, characterized in that, Using ammonium sebacate as the main solute, alkylammonium sebacate as the secondary solute, polyvinyl alcohol and ethylene glycol as the polymer additives, and at least one of ammonium hydrogen azelate, ammonium dodecanedioate, and ammonium pentaborate as the auxiliary solute, wherein the polyvinyl alcohol is composed of PVA with different molecular weights, and the ethylene glycol is composed of PEG with different molecular weights; The working electrolyte for medium and high voltage aluminum electrolytic capacitors comprises the following components by mass percentage: auxiliary solvent 2-4%, main solute 5%, secondary solute 2%, mannitol 2%, ammonium pentaborate 3%, ammonium hydrogen azelate 0.9%, ammonium dodecanedioate 0.4%, hydrogen scavenger 0.4%, forming agent 0.4%, and polymer additive 1.2-1.4%, with the balance being the main solvent.

2. The working electrolyte for medium and high voltage aluminum electrolytic capacitors according to claim 1, characterized in that, The main solvent is ethylene glycol, the auxiliary solvent is one or more of γ-butyrolactone, glycerol, and diethylene glycol, the hydrogen scavenger is p-nitrobenzoic acid, and the forming agent is ammonium hypophosphite.

3. The working electrolyte for medium-high voltage aluminum electrolytic capacitors according to claim 1, characterized in that, In the polymer additive, the mass ratio of polyvinyl alcohol to ethylene glycol is 1:1.3-2.

4. The working electrolyte for medium and high voltage aluminum electrolytic capacitors according to claim 1, characterized in that, The polyvinyl alcohol is composed of two or more of PVA 105 , PVA 117 and PVA 124 . The diglycol is composed of two or more of triethylene glycol, PEG 200 , PEG 400 and PEG 600 .

5. A method for preparing the working electrolyte for medium and high voltage aluminum electrolytic capacitors according to any one of claims 1-4, characterized in that, It includes the following steps: (1) Weigh each component according to the above mass percentage and set aside. (2) Mix the auxiliary solvent and the main solvent to obtain a mixed solvent, and add the main solute, mannitol, ammonium hydrogen azelate, and ammonium dodecanedioate under heating conditions. After heating and dissolving, obtain mixture A. (3) Add polyvinyl alcohol to the mixture A, heat and keep warm, then cool naturally. After that, add ammonium pentaborate and ethylene glycol, keep warm and cool to obtain mixture B. (4) Add the secondary solute, hydrogen scavenger, and forming agent to mixture B, keep warm, and cool to room temperature to obtain the working electrolyte for medium and high voltage aluminum electrolytic capacitors.

6. The preparation method according to claim 5, characterized in that, Step (2) is specifically: Mix the auxiliary solvent and the main solvent to obtain a mixed solvent. Heat the mixed solvent to 60°C and then add the main solute. After complete dissolution, raise the temperature to 80°C, add mannitol, ammonium hydrogen azelate, and ammonium dodecanedioate, and continue heating to 130°C. After complete dissolution, obtain mixture A.

7. The preparation method according to claim 5, characterized in that, In step (3), add polyvinyl alcohol and heat to a temperature of 145°C - 160°C, keep warm for 30 minutes and then cool to 130°C. Add ammonium pentaborate and ethylene glycol and keep warm.

8. The preparation method according to claim 5, characterized in that, In step (4), after adding the secondary solute, hydrogen scavenger, and forming agent, keep warm at 100°C for 35 minutes.

9. Application of the working electrolyte for medium and high voltage aluminum electrolytic capacitors according to any one of claims 1-4 in medium and high voltage aluminum electrolytic capacitors.

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