High flashover voltage electrolyte with wide temperature range and preparation method thereof

Abstract

This invention discloses a high flash voltage, wide temperature range electrolyte and its preparation method, relating to the field of aluminum electrolytic capacitor technology. The electrolyte comprises a solvent, a solute, and additives. The solvent includes ethylene glycol and propylene glycol; the solute includes boric acid, ammonium sebate, and fluoroalkyl hyperbranched ammonium carboxylate; and the additives include dual-modified polyvinyl alcohol, a waterproofing agent, and a hydrogen scavenging agent. The fluoroalkyl hyperbranched ammonium carboxylate is prepared from a hyperbranched amide precursor via fluoroalkylation, carboxylation, and ammonia neutralization. The dual-modified polyvinyl alcohol has both benzotriazole and adamantyl groups attached to its molecular chain. This invention's electrolyte achieves a balance between high flash voltage and wide temperature range performance through molecular-level synergy between the solute and additives, making it suitable for medium- and high-voltage aluminum electrolytic capacitors.

Description

Technical Field

[0001] This invention relates to the field of aluminum electrolytic capacitor technology, specifically to a high flash voltage wide temperature range electrolyte and its preparation method. Background Technology

[0002] As an indispensable basic component in electronic circuits, the performance of aluminum electrolytic capacitors directly affects the reliability and service life of the entire device. The electrolyte, as the actual cathode of the capacitor, plays a crucial role in repairing defects in the aluminum anodic oxide film and providing ion transport channels. Its composition and performance directly determine the capacitor's voltage withstand capability, operating temperature range, and service life.

[0003] Currently, common methods for improving the flash voltage of electrolytes include adding polyvinyl alcohol-based flash voltage enhancers and using branched ammonium carboxylate salts instead of straight-chain ammonium carboxylate salts as the main solute. For example, patent publication number CN101206955B discloses a mixture of branched polycarboxylate ammonium salts, whose main components are branched dicarboxylate ammonium salts and branched tetracarboxylate ammonium salts, with a carbon chain length of 9 or more carbon atoms and having one or more alkyl branches. This scheme utilizes the branched structure to improve the conductivity and flash voltage of the electrolyte, but its solute molecular skeleton is still limited to the traditional alkyl chain carboxylate structure. In addition, patent publication number CN112582180B discloses an electrolyte for medium- and high-voltage aluminum electrolytic capacitors with high hydration resistance, wherein the fluorine-containing auxiliary solute is a perfluorinated dicarboxylate or a perfluorinated dicarboxylate ammonium salt with 8-12 carbon atoms. This scheme utilizes the properties of fluorine atoms to improve the hydration resistance of the electrolyte, but the fluorine-containing component is only added in small amounts as an auxiliary solute, and it is a small molecule straight-chain perfluorocarboxylic acid ammonium salt, which has a relatively simple functional positioning.

[0004] While the aforementioned existing technologies have made improvements in their respective directions, none have effectively resolved the core contradiction of the mutual constraint between flash voltage and conductivity in the electrolyte of aluminum electrolytic capacitors. Specifically, although branched ammonium carboxylate salts have higher flash voltage and conductivity than straight-chain ammonium carboxylate salts, the improvement is limited; while fluorinated auxiliary solutes can improve hydration resistance, their contribution to the overall conductivity and flash voltage of the electrolyte is insufficient due to their low addition amount and simple molecular structure. In addition, existing polyvinyl alcohol flash voltage enhancers have a single function, only improving flash voltage, and lack multiple functions such as corrosion inhibition and enhanced thermal stability, making it difficult to meet the development requirements of capacitor miniaturization, high voltage, and wide temperature range. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high flash voltage, wide temperature range electrolyte and its preparation method, which can simultaneously modify the two core components of the electrolyte—the solute and the additives—at the molecular design level. Regarding the solute, fluoroalkyl groups are introduced into the molecular framework of hyperbranched ammonium carboxylate salts to construct fluoroalkyl hyperbranched ammonium carboxylate salts as the main solute. The multifunctional sites of the hyperbranched structure and the strong electron-withdrawing effect of fluorine atoms synergistically improve conductivity and high-temperature stability. Regarding the additives, benzotriazole groups and adamantyl groups are simultaneously introduced into the side chains of polyvinyl alcohol, enabling the additives to possess multiple functions, including flash voltage enhancement, copper corrosion inhibition, and enhanced thermal stability. Through the synergistic cooperation of the solute and additives at the molecular level, the aim is to break the negative correlation between flash voltage and conductivity, achieving a balance between high flash voltage and wide temperature range performance.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In one aspect, a high flash voltage wide temperature range electrolyte comprises the following raw materials by mass percentage: 65wt%-75wt% solvent; 18wt%-30wt% solute; 3wt%-7wt% additives; The solvent is used to dissolve solutes and additives, providing a liquid medium for ion migration; The solvents include ethylene glycol and propylene glycol. The combination of ethylene glycol and propylene glycol utilizes the complementary characteristics of their different freezing points and boiling points to extend the working temperature range of the electrolyte. The solutes include boric acid, ammonium sebacate, and fluoroalkyl hyperbranched ammonium carboxylate. The fluoroalkyl hyperbranched ammonium carboxylate has a fluorocarbon chain attached to its molecular end. The strong electron-withdrawing effect of fluorine atoms enhances the ionization of carboxylate groups and increases the concentration of free ions in the electrolyte. The fluoroalkyl hyperbranched ammonium carboxylate is prepared by fluoroalkylation, carboxylation and ammonia neutralization reaction of hyperbranched amide precursor. The hyperbranched structure provides multiple functional sites, and the hydrophobic properties of the fluoroalkyl chain reduce the adsorption of water molecules by the electrolyte and inhibit the corrosion of the oxide film by the high-temperature hydration reaction. The additives include double-modified polyvinyl alcohol, waterproofing agent, and hydrogen scavenger; The modified polyvinyl alcohol has benzotriazole and adamantyl groups attached to its molecular chain. The nitrogen atom in the benzotriazole group provides lone pair electrons to form coordination bonds with copper ions on the surface of the copper lead terminal, generating a coordination protective film on the copper surface. The rigid cage structure of the adamantyl group has high bond energy, which, under the action of an electric field, blocks high-energy electrons from bombarding the oxide film through steric hindrance, thus delaying the occurrence of flashover breakdown.

[0007] Furthermore, in the solvent, ethylene glycol accounts for 40wt%-55wt% of the total mass of the electrolyte, and propylene glycol accounts for 15wt%-25wt% of the total mass of the electrolyte. Ethylene glycol provides a high dielectric constant to promote solute dissociation, and propylene glycol lowers the freezing point of the system. The two work together to broaden the liquid working temperature range of the electrolyte. In the solute, boric acid accounts for 0.5wt%-2wt% of the total mass of the electrolyte, ammonium sebacic acid accounts for 10wt%-18wt% of the total mass of the electrolyte, and fluoroalkyl hyperbranched ammonium carboxylate accounts for 5wt%-12wt% of the total mass of the electrolyte. The boric acid reacts with the hydroxyl groups on the surface of the oxide film to form borate ester bonds. The ammonium sebacic acid provides the basic conductive ions. The fluoroalkyl hyperbranched ammonium carboxylate enhances the adsorption stability on the anode foil surface by utilizing the multi-point anchoring effect of hyperbranched molecules. The additives contain 2wt%-5wt% of the total electrolyte mass of the modified polyvinyl alcohol, 0.5wt%-1.5wt% of the total electrolyte mass of the waterproofing agent, and 0.2wt%-0.6wt% of the total electrolyte mass of the hydrogen scavenger.

[0008] Furthermore, the preparation method of the fluoroalkyl hyperbranched ammonium carboxylate includes the following steps: A1. Diethylenetriamine and N,N'-methylenebisacrylamide were mixed in water at a molar ratio of 2-2.03:1 and reacted at 55℃-65℃ for 22-26 hours. After rotary evaporation, precipitation, purification, and drying, a hyperbranched amide precursor was obtained. The four NH bonds of diethylenetriamine and the two C=C double bonds of N,N'-methylenebisacrylamide were polymerized stepwise through Michael addition reaction to form a hyperbranched molecular skeleton with amine groups at the end. A2. Dissolve the hyperbranched amide precursor obtained in A1 in N,N-dimethylformamide, add perfluorobutyl iodide or perfluorohexyl iodide and potassium carbonate, react at 80℃-100℃ for 8h-12h, filter and distill under reduced pressure to obtain fluoroalkylated hyperbranched amide. The amino group at the end of the hyperbranched amide precursor undergoes a nucleophilic substitution reaction with perfluorobutyl iodide or perfluorohexyl iodide, so that the fluoroalkyl chain is linked to the end of the hyperbranched molecule by a CN bond. A3. Under nitrogen protection, the fluoroalkylated hyperbranched amide obtained in A2 is dissolved in N,N-dimethylformamide, succinic acid and concentrated sulfuric acid are added, and the mixture is heated to 120℃-140℃ for 4-6 hours. The concentrated sulfuric acid is 0.005wt%-0.01wt% of the total reactants. The remaining amino group at the end of the hyperbranched molecule undergoes amidation with one carboxyl group of succinic acid, while the other carboxyl group is retained as a free carboxylic acid. A4. The product obtained in A3 is cooled to 40℃-60℃, and ammonia is introduced to adjust the pH to 6-7. After vacuum distillation and drying, fluoroalkyl hyperbranched ammonium carboxylate is obtained. Ammonia reacts with free carboxylic acid to form ammonium carboxylate groups. The ammonium carboxylate groups dissociate into carboxylate ions and ammonium ions under the action of an electric field. The ammonium ions participate in ion conduction as cations.

[0009] Furthermore, in A2, the molar ratio of perfluorobutyl iodine or perfluorohexyl iodine to the hyperbranched amide precursor is 1.1-1.3:1, and the molar ratio of potassium carbonate to the hyperbranched amide precursor is 1.4-1.6:1. Potassium carbonate acts as an acid-binding agent to neutralize the hydrogen iodide generated during the reaction, thereby promoting the nucleophilic substitution reaction in the forward direction. The molar ratio of succinic acid in A3 to fluoroalkyl hyperbranched amide in A2 is 3.8-4.2:1.

[0010] Furthermore, the preparation method of the dual-modified polyvinyl alcohol includes the following steps: B1. 5-Carboxybenzotriazole and thionyl chloride are refluxed at 70℃-80℃ for 4h-6h. Unreacted thionyl chloride is removed by vacuum distillation to obtain benzotriazole acyl chloride intermediate. The thionyl chloride converts the carboxyl group of 5-carboxybenzotriazole into an acyl chloride group. The acyl chloride group has high reactivity and provides an activation site for the subsequent esterification reaction with the side chain hydroxyl group of polyvinyl alcohol. B2. 1-Adamanecarboxylic acid and thionyl chloride are refluxed at 70℃-80℃ for 4h-6h. Unreacted thionyl chloride is removed by vacuum distillation to obtain adamanealkyl acyl chloride intermediate. The thionyl chloride converts the carboxyl group of 1-adamantanecarboxylic acid into an acyl chloride group, and the adamanealkyl group is esterified and grafted to the hydroxyl side chain of polyvinyl alcohol through the acyl chloride group. B3. Polyvinyl alcohol is dissolved in N,N-dimethylformamide and stirred at 80℃-90℃ until dissolved. The benzotriazole acyl chloride intermediate obtained in B1 and the adamantyl acyl chloride intermediate obtained in B2 are added. Triethylamine is added, and the reaction is carried out at 80℃-100℃ for 6h-8h. After the reaction is completed, the reaction solution is poured into anhydrous ethanol to precipitate. The precipitate is filtered, washed, and dried to obtain double-modified polyvinyl alcohol. The hydroxyl groups of the side chain of polyvinyl alcohol undergo esterification reactions with benzotriazole acyl chloride and adamantyl acyl chloride, respectively, to form ester bonds. The benzotriazole group and the adamantyl group are covalently grafted onto the polyvinyl alcohol backbone. Triethylamine is used as an acid-binding agent to neutralize the hydrogen chloride generated in the reaction.

[0011] Furthermore, the molar ratio of 5-carboxybenzotriazole to thionyl chloride in B1 is 1:2.5-3.5; The molar ratio of 1-adamantane carboxylic acid to thionyl chloride in B2 is 1:2.5-3.5; The molar ratio of benzotriazole acyl chloride intermediate to adamantyl acyl chloride intermediate in B3 is 0.9-1.1:1, the molar ratio of the total amount of benzotriazole acyl chloride intermediate and adamantyl acyl chloride intermediate to the molar ratio of hydroxyl groups in polyvinyl alcohol is 1:5-1:10, and the molar ratio of triethylamine to the sum of the total amount of benzotriazole acyl chloride intermediate and adamantyl acyl chloride intermediate is 1.2-1.5:1.

[0012] Furthermore, the waterproofing agent is ammonium dihydrogen phosphate, and the hydrogen scavenging agent is p-nitrobenzoic acid or p-nitrobenzyl alcohol. Ammonium dihydrogen phosphate hydrolyzes to generate phosphate ions, which combine with aluminum ions on the oxide film surface to form an aluminum phosphate passivation layer, preventing water molecules from penetrating to the aluminum substrate surface.

[0013] Furthermore, the solvent also includes dimethyl sulfoxide, which accounts for 1wt%-5wt% of the total mass of the electrolyte. The strong polarity of dimethyl sulfoxide (dielectric constant 46.7) enhances the degree of dissociation of anions and cations in the solute molecules and increases the migration rate of free ions in the electrolyte.

[0014] On the other hand, a method for preparing a high flash voltage wide temperature range electrolyte, applicable to a high flash voltage wide temperature range electrolyte, the method comprising the following steps: C1. Weigh each raw material according to the mass percentage, and stir the solvent at 70℃-90℃ to obtain a mixed solvent; C2. Add solute to the mixed solvent, heat to 110℃-120℃ and stir for 30min-50min to completely dissolve the solute, and heat to 110℃-120℃ to give the solute molecules sufficient activation energy to overcome the van der Waals forces and hydrogen bonds between hyperbranched molecules and promote their uniform dispersion in the solvent. C3. Cool the obtained solution to 60℃-80℃, add additives and stir evenly to obtain a high flash voltage wide temperature range electrolyte.

[0015] Furthermore, the method also includes C4: degassing the obtained electrolyte under vacuum conditions for 20-40 minutes, filtering, and obtaining the finished electrolyte. Vacuum degassing reduces the internal pressure of the electrolyte, allowing gas molecules dissolved in the electrolyte to escape, thus preventing bubbles from adsorbing onto the electrode surface and forming insulating points that would lead to local electric field concentration.

[0016] Compared with existing technologies, this high flash voltage wide temperature range electrolyte and its preparation method have the following advantages: I. This invention introduces fluoroalkyl groups into the molecular skeleton of hyperbranched ammonium carboxylate to construct a fluoroalkyl hyperbranched ammonium carboxylate as the main solute. By utilizing the multifunctional sites of the hyperbranched structure and the strong electron-withdrawing effect of fluorine atoms, the ionization degree of carboxylate groups can be synergistically enhanced to improve the conductivity of the electrolyte. At the same time, the hydrophobic properties of the fluorocarbon chain are used to inhibit the erosion of the oxide film by the high-temperature hydration reaction. This allows the electrolyte to significantly increase the flash voltage while maintaining high conductivity, thereby effectively breaking the core contradiction between flash voltage and conductivity, and achieving a balance between high flash voltage and high conductivity.

[0017] II. This invention, by simultaneously grafting benzotriazole groups and adamantyl groups onto the side chains of polyvinyl alcohol, enables the additive to possess multiple functions, including flash voltage enhancement, copper lead corrosion inhibition, and thermal stability enhancement. The benzotriazole groups form a coordination protective film with copper ions to inhibit copper corrosion, while the rigid cage-like structure of the adamantyl groups delays flash breakdown through steric hindrance. Combined with a compound solvent system of ethylene glycol and propylene glycol, this effectively expands the operating temperature range of the electrolyte, improving the reliability and service life of the capacitor under wide temperature conditions.

[0018] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0020] Figure 1 This is a schematic diagram of the preparation method of the present invention. Detailed Implementation

[0021] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0022] like Figure 1 As shown, the method includes the following steps in sequence: weighing raw materials and preparing mixed solvents, heating to dissolve solutes, adding additives after cooling and stirring evenly, vacuum degassing and filtration to obtain the finished electrolyte. The operation sequence and conditions of each step will be explained in detail later.

[0023] In this embodiment, the raw material composition of the electrolyte is as follows by mass percentage: The composition comprises: 46.5% ethylene glycol, 19.5% propylene glycol, 3% dimethyl sulfoxide, 1.5% boric acid, 15% ammonium sebacic acid, 8% fluoroalkyl hyperbranched ammonium carboxylate, 4% double-modified polyvinyl alcohol, 1.2% ammonium dihydrogen phosphate, and 0.5% p-nitrobenzoic acid. The sum of the mass percentages of all the above components is 100%. The preparation process, mechanism of action, and electrolyte formulation of the key raw materials are described in detail below.

[0024] First, the synthesis of fluoroalkyl hyperbranched ammonium carboxylate salts will be explained. This substance, as part of the main solute, possesses both a hyperbranched framework and terminal fluorocarbon chains in its molecular structure, which can effectively improve the conductivity and high-temperature stability of the electrolyte.

[0025] A1. Preparation of the hyperbranched amide precursor: In a 500 mL three-necked flask equipped with a thermometer, condenser, and mechanical stirrer, 20.6 g (approximately 0.2 mol) of diethylenetriamine and 31.2 g (approximately 0.202 mol) of N,N-methylenebisacrylamide were added. The molar ratio of diethylenetriamine to N,N-methylenebisacrylamide was 2.01:1. 200 mL of deionized water was then added, and the mixture was stirred until completely dissolved. The reaction system was heated to 60 °C and stirred continuously at this temperature for 24 h. During the reaction, multiple NH bonds in the diethylenetriamine molecule underwent Michael addition reactions with the two C=C double bonds of N,N-methylenebisacrylamide, gradually growing into an amide polymer with a highly branched structure and abundant primary and secondary amine groups at the ends. After the reaction was completed, most of the water was removed by vacuum evaporation at 60 °C using a rotary evaporator to obtain a viscous liquid. The liquid was slowly added dropwise to an excess of acetone, resulting in the precipitation of a white precipitate. The precipitate was filtered, washed twice with acetone, and then dried under vacuum at 50°C for 12 hours to obtain a hyperbranched amide precursor, which was a white powder.

[0026] A2. Preparation of fluoroalkylated hyperbranched amides: 20 g of the above-mentioned hyperbranched amide precursor was dissolved in 150 mL of N,N-dimethylformamide and placed in a 250 mL three-necked flask. 38.8 g of perfluorobutyl iodine (approximately 0.12 mol) was added, with the molar ratio of perfluorobutyl iodine to the hyperbranched amide precursor controlled at 1.2:1. Then, 20.7 g of anhydrous potassium carbonate (approximately 0.15 mol) was added, with the molar ratio of potassium carbonate to the hyperbranched amide precursor at 1.5:1. Potassium carbonate acts as an acid-binding agent to neutralize the hydrogen iodide generated in the reaction, promoting the forward nucleophilic substitution reaction. Under nitrogen protection, the system was heated to 85 °C and stirred for 10 h. During this period, the terminal amino groups of the hyperbranched amide precursor underwent a nucleophilic substitution reaction with perfluorobutyl iodine, and the fluorocarbon chain was covalently attached to the periphery of the hyperbranched molecule via CN bonds. After the reaction was completed and cooled, the insoluble inorganic salts were filtered off. The filtrate was then distilled under reduced pressure at 70°C to recover the solvent and unreacted perfluorobutyl iodine, yielding a brown viscous product, namely a fluoroalkylated hyperbranched amide.

[0027] A3. Under nitrogen protection, dissolve 15g of the fluoroalkylated hyperbranched amide obtained in the previous step in 120mL of N,N-dimethylformamide, add 23.6g of succinic acid (approximately 0.2mol), with a molar ratio of succinic acid to fluoroalkylated hyperbranched amide of 4:1, and then add 0.02g of 98% concentrated sulfuric acid (approximately 0.008% of the total reactants). Heat to 130℃ and stir for 5 hours. During this process, the remaining amino group at the end of the hyperbranched molecule undergoes amidation with one carboxyl group of succinic acid, while the other carboxyl group of succinic acid remains at the end of the molecule as a free carboxylic acid.

[0028] A4. After the reaction is complete, the system is cooled to 50°C, and dry ammonia gas is slowly introduced while stirring. The pH value of the system is monitored in real time, and the ammonia introduction is stopped when the pH reaches about 6.5. Ammonia gas reacts with free carboxylic acid to neutralize it, generating ammonium carboxylate groups. Then, the solvent is removed by vacuum distillation at 60°C, and the residue is dried under vacuum at 50°C for 8 hours to obtain a pale yellow solid, which is the fluoroalkyl hyperbranched ammonium carboxylate salt.

[0029] The molecular structure design of this fluoroalkyl hyperbranched ammonium carboxylate salt offers several benefits. The hyperbranched framework provides multiple functional sites, allowing simultaneous attachment of multiple fluorocarbon chains and multiple ammonium carboxylate groups. This enables multi-point anchoring in the solvent, enhancing adsorption on the anode foil surface and aiding in the repair and stabilization of the oxide film. The terminal fluorocarbon chains, due to the strong electron-withdrawing effect of fluorine atoms, enhance the ionization of the attached carboxylate groups, increasing the concentration of free ions in the electrolyte and thus improving conductivity. Simultaneously, the hydrophobic properties of the fluorocarbon chains reduce the adsorption of trace amounts of water by the electrolyte, inhibiting the erosion of the anodic oxide film by hydration reactions at high temperatures and improving high-temperature durability.

[0030] The preparation method of the double-modified polyvinyl alcohol is described below. This additive has multiple functions, including improving flashover voltage, inhibiting corrosion of copper leads, and enhancing thermal stability.

[0031] B1. Preparation of the benzotriazole acyl chloride intermediate: In a 100 mL round-bottom flask equipped with a reflux condenser and a drying tube, 8.1 g of 5-carboxybenzotriazole (approximately 0.05 mol) and 18.9 g of thionyl chloride (approximately 0.159 mol) were added, with a molar ratio of 1:3.18. The mixture was heated to 75 °C under magnetic stirring and refluxed for 5 h. The thionyl chloride converted the carboxyl group of 5-carboxybenzotriazole to an acyl chloride group. After the reaction was complete, excess thionyl chloride was removed by vacuum distillation at 45 °C to obtain a pale yellow oily benzotriazole acyl chloride intermediate, which was sealed and stored for later use.

[0032] B2. Preparation of the adamantyl acyl chloride intermediate: In another similar apparatus, 9.0 g of 1-adamantanecarboxylic acid (approximately 0.05 mol) and 18.9 g of thionyl chloride (approximately 0.159 mol) were added, with a molar ratio of 1:3.18. The mixture was heated to 75 °C and refluxed for 5 h. After the reaction was complete, unreacted thionyl chloride was removed by vacuum distillation to obtain a light yellow oily adamantyl acyl chloride intermediate, which was then sealed for later use.

[0033] B3. Synthesis of Bis-Modified Polyvinyl Alcohol: Weigh 10g of polyvinyl alcohol with a degree of alcoholysis of 88% and a number-average molecular weight of approximately 70,000. Add it to a 250mL three-necked flask, then add 100mL of N,N-dimethylformamide. Heat to 85℃ with stirring to completely dissolve the polyvinyl alcohol. Then, add 3.8g (approximately 0.021mol) of benzotriazole acyl chloride intermediate and 4.0g (approximately 0.019mol) of adamantyl acyl chloride intermediate sequentially. The molar ratio of the two acyl chloride intermediates is approximately 1:1, and the total molar amount is approximately 0.04mol. Then, add 5.3g (approximately 0.052mol) of triethylamine. The molar ratio of triethylamine to the total amount of the two acyl chlorides is 1.3:1. Heat the system to 90℃ and stir continuously for 7 hours. In the reaction, some hydroxyl groups on the side chain of polyvinyl alcohol undergo esterification with benzotriazole acyl chloride, while another portion of the hydroxyl groups undergo esterification with adamantyl acyl chloride, covalently grafting the benzotriazole and adamantyl groups onto the polyvinyl alcohol backbone via ester bonds. Triethylamine is used to neutralize the hydrogen chloride released in the reaction. After the reaction is complete and cooled, the reaction solution is slowly poured into 500 mL of anhydrous ethanol under stirring, resulting in the precipitation of a large amount of fibrous precipitate. The precipitate is filtered, washed three times repeatedly with anhydrous ethanol, and dried under vacuum at 60 °C for 6 h to obtain a pale yellow fibrous solid, which is the double-modified polyvinyl alcohol.

[0034] The design of this dual-modified polyvinyl alcohol (PVA) endows it with multiple practical functions. The PVA backbone itself possesses film-forming properties and the ability to increase solution viscosity, enabling the formation of an adsorption layer on the anode foil surface, homogenizing the electric field distribution, and thus improving the flashover voltage. In the grafted benzotriazole group, the nitrogen atom on the triazole ring contains lone pairs of electrons, which can form stable coordination bonds with copper ions on the surface of the copper lead terminals, generating a dense coordination protective film on the copper surface, thereby inhibiting copper corrosion and dissolution, and playing a corrosion-inhibiting role. The grafted adamantyl group has a rigid cage-like hydrocarbon structure with high bond energies of the C-C and CH bonds, exhibiting excellent thermal and chemical stability. During electrolyte operation, the adamantyl group, through steric hindrance, can, to a certain extent, hinder the direct impact of high-energy electrons or ions on the oxide film, delaying local breakdown and assisting in improving the flashover voltage. Furthermore, its stability at high temperatures also helps extend the service life of the electrolyte. The three functional groups are chemically bonded to the same molecular chain, achieving a synergistic effect and avoiding functional separation or migration problems that may occur during physical mixing.

[0035] Among the other raw materials, ethylene glycol and propylene glycol are combined as the main solvent. Ethylene glycol has a high dielectric constant, which is beneficial to the dissociation of solute and ion conduction; propylene glycol has a low freezing point, which can significantly reduce the low-temperature viscosity of the system. Together, they broaden the liquid working temperature range. A small amount of dimethyl sulfoxide is added; its strong polarity can further enhance the dissociation of cations and anions and increase the migration rate of free ions. Boric acid in the solute can react with hydroxyl groups on the surface of the anolyte film to form borate ester bonds, participating in the repair and stabilization of the oxide film. Ammonium sebate provides basic conductive ions to ensure the basic conductivity of the electrolyte. The waterproofing agent is ammonium dihydrogen phosphate, which hydrolyzes in the electrolyte to generate phosphate ions. These phosphate ions combine with aluminum ions in the oxide film to form an aluminum phosphate passivation layer on the surface, preventing water molecules from penetrating to the aluminum substrate surface, thereby inhibiting the damage of the oxide film caused by hydration reactions. The hydrogen scavenger, p-nitrobenzoic acid, can absorb or convert hydrogen gas that may be generated by electrochemical reactions during capacitor operation, preventing the internal pressure from rising.

[0036] The preparation process of the electrolyte is described in detail below. For example... Figure 1 The process and specific preparation steps are as follows.

[0037] C1. Raw material weighing and mixed solvent preparation: According to the aforementioned formula, accurately weigh 465g of ethylene glycol, 195g of propylene glycol, and 30g of dimethyl sulfoxide, totaling 690g, into a dry and clean glass beaker. Place the beaker in a constant temperature water bath and heat it to 80℃. Stir the mixture for 10 minutes at a speed of 200r / min using a polytetrafluoroethylene stirrer to ensure that all components are mixed evenly, resulting in a clear mixed solvent.

[0038] C2. Heating to dissolve the solute: Add 15g of boric acid, 150g of ammonium sebate, and 80g of fluoroalkyl hyperbranched ammonium carboxylate to the above mixed solvent in sequence. At this point, some of the solute will not be completely dissolved. Raise the system temperature to 115℃ and continue stirring for 40 minutes at a speed of 200 rpm. At this temperature, the solute molecules gain sufficient thermal energy to overcome the intermolecular forces between hyperbranched molecules and between solute and solvent molecules, gradually dissolving completely, and the solution becomes a pale yellow transparent liquid. Maintain the temperature and stir until no obvious solid particles remain, then continue stirring for another 5 minutes to ensure uniform solute dispersion.

[0039] C3. Cooling and Adding Additives: Allow the above solution to cool naturally until the temperature drops to 70℃. Then, while stirring, add 40g of the modified polyvinyl alcohol, 12g of ammonium dihydrogen phosphate, and 5g of p-nitrobenzoic acid. The temperature of 70℃ is chosen to ensure sufficient dissolution and dispersion of the additives, while avoiding the hydrolysis of the ester bonds in the modified polyvinyl alcohol that may occur at excessively high temperatures. After adding the additives, continue stirring for 30 minutes to obtain a homogeneous crude electrolyte. At this point, the solution viscosity has slightly increased, and the color is light amber.

[0040] C4. Vacuum Degassing and Filtration: The obtained crude electrolyte is transferred to a sealed container connected to a vacuum pump and degassed for 30 minutes under a vacuum of 0.09 MPa. Under vacuum, the tiny bubbles dissolved in the electrolyte gradually coalesce, float to the surface, and escape. Degassing prevents these bubbles from adhering to the electrode foil surface and forming insulating points during capacitor impregnation, thus preventing local electric field concentration and flashover voltage drop. After degassing, the electrolyte is filtered using a 0.5 μm PTFE microporous membrane to remove any mechanical impurities and undissolved trace particles, ultimately yielding a clear and transparent high flashover voltage wide-temperature-range electrolyte product.

[0041] The aforementioned finished electrolyte was used in the impregnation process of aluminum electrolytic capacitors with a rated voltage of 400V, and capacitor samples were assembled for key performance testing. The testing methods followed the relevant provisions of electronic industry standards SJ / T11141-2017 and GB / T2693. Flash voltage was measured using the constant current boost method, and conductivity was measured using a DDS-307 conductivity meter at 30℃. The operating temperature range was assessed using a high and low temperature alternating test chamber in conjunction with an impedance analyzer. The capacitance change rate and loss tangent were used as evaluation criteria. Test results showed that the electrolyte achieved a flash voltage of 512V, a conductivity of 2.35 mS / cm at 30℃, and the capacitor operated normally within a temperature range of -55℃ to 125℃, with all parameters remaining stable.

[0042] To further demonstrate the feasibility and effectiveness of the technical solution, the following description uses three application scenarios with different formulation ratios. The electrolyte preparation process in each scenario is consistent with the aforementioned preparation steps; the only difference lies in the amount or type of a few key components in the raw materials. Table 1 summarizes the raw material ratios and performance test results for the three scenarios.

[0043] In Scenario 1, the main formulation remains unchanged: 46.5% ethylene glycol, 19.5% propylene glycol, 3% dimethyl sulfoxide, 1.5% boric acid, 15% ammonium sebacic acid, 8% fluoroalkyl hyperbranched ammonium carboxylate, 4% dual-modified polyvinyl alcohol, 1.2% ammonium dihydrogen phosphate, and 0.5% p-nitrobenzoic acid. The resulting electrolyte has a flash voltage of 512V, a conductivity of 2.35mS / cm, and an applicable temperature range of -55℃ to 125℃. In Scenario 2, the amount of fluoroalkyl hyperbranched ammonium carboxylate is increased from 8% to 10%, and the ammonium sebacic acid is adjusted accordingly from 15% to 13.5%, while other components remain unchanged. Tests show that the flash voltage increases to 536V, and the conductivity slightly increases to 2.43mS / cm. This is attributed to the introduction of more fluoroalkyl hyperbranched molecules, which enhances ion dissociation and oxide film adsorption stability. Scenario 3, building upon Scenario 2, uses an equimolar amount of perfluorohexyl iodine instead of perfluorobutyl iodine to synthesize fluoroalkyl hyperbranched ammonium carboxylate, resulting in a longer fluorocarbon chain and further enhanced hydrophobicity. The measured flashover voltage reached 558V, and the conductivity reached 2.51 mS / cm, while the applicable temperature range remained -55℃ to 125℃. All three scenarios exhibited excellent combined performance in terms of flashover voltage and conductivity.

[0044] Table 1 shows the raw material ratios and performance data for the three application scenarios: As shown in Table 1, by rationally controlling the content of fluoroalkyl hyperbranched ammonium carboxylate and the length of the fluorocarbon chain, the flash voltage and conductivity of the electrolyte can be synergistically improved while maintaining its wide temperature range characteristics. The introduction of dual-modified polyvinyl alcohol also provides a stable foundation for the overall performance improvement. Its corrosion inhibition effect is indirectly confirmed by visual inspection and impedance changes of the copper lead terminals. The addition of adamantyl groups has a positive contribution to the long-term stability of the flash voltage.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A high flash voltage, wide temperature range electrolyte, characterized in that, Including the following percentages by weight of raw materials: 65wt%-75wt% solvent; 18wt%-30wt% solute; 3wt%-7wt% additives; The solvents include ethylene glycol and propylene glycol; The solutes include boric acid, ammonium sebacate, and fluoroalkyl hyperbranched ammonium carboxylate. The fluoroalkyl hyperbranched ammonium carboxylate is prepared from a hyperbranched amide precursor via fluoroalkylation, carboxylation, and ammonia neutralization. The additives include double-modified polyvinyl alcohol, waterproofing agent, and hydrogen scavenger; The molecular chain of the double-modified polyvinyl alcohol is simultaneously connected with benzotriazole groups and adamantyl groups.

2. The high flash voltage wide temperature range electrolyte according to claim 1, characterized in that, In the solvent, ethylene glycol accounts for 40wt%-55wt% of the total mass of the electrolyte, and propylene glycol accounts for 15wt%-25wt% of the total mass of the electrolyte. The solute contains boric acid accounting for 0.5wt%-2wt% of the total mass of the electrolyte, ammonium sebacic acid accounting for 10wt%-18wt% of the total mass of the electrolyte, and fluoroalkyl hyperbranched ammonium carboxylate accounting for 5wt%-12wt% of the total mass of the electrolyte; The additives contain 2wt%-5wt% of the total electrolyte mass of the modified polyvinyl alcohol, 0.5wt%-1.5wt% of the total electrolyte mass of the waterproofing agent, and 0.2wt%-0.6wt% of the total electrolyte mass of the hydrogen scavenger.

3. The high flash voltage wide temperature range electrolyte according to claim 1, characterized in that, The preparation method of the fluoroalkyl hyperbranched ammonium carboxylate includes the following steps: A1. Diethylenetriamine and N,N'-methylenebisacrylamide were mixed in water at a molar ratio of 2-2.03:1 and reacted at 55℃-65℃ for 22-26 hours. The mixture was then subjected to rotary evaporation, precipitation, purification, and drying to obtain the hyperbranched amide precursor. A2. Dissolve the hyperbranched amide precursor obtained in A1 in N,N-dimethylformamide, add perfluorobutyl iodine or perfluorohexyl iodine and potassium carbonate, react at 80℃-100℃ for 8h-12h, filter and distill under reduced pressure to obtain fluoroalkylated hyperbranched amide. A3. Under nitrogen protection, the fluoroalkylated hyperbranched amide obtained in A2 is dissolved in N,N-dimethylformamide, succinic acid and concentrated sulfuric acid are added, and the mixture is heated to 120℃-140℃ for 4-6 hours. The concentrated sulfuric acid is 0.005wt%-0.01wt% of the total reactants. A4. The product obtained in A3 is cooled to 40℃-60℃, and ammonia is introduced to adjust the pH to 6-7. After vacuum distillation and drying, fluoroalkyl hyperbranched ammonium carboxylate is obtained.

4. The high flash voltage wide temperature range electrolyte according to claim 3, characterized in that, The molar ratio of perfluorobutyl iodine or perfluorohexyl iodine to the hyperbranched amide precursor in A2 is 1.1-1.3:1, and the molar ratio of potassium carbonate to the hyperbranched amide precursor is 1.4-1.6:

1. The molar ratio of succinic acid in A3 to fluoroalkyl hyperbranched amide in A2 is 3.8-4.2:

1.

5. The high flash voltage wide temperature range electrolyte according to claim 1, characterized in that, The preparation method of the dual-modified polyvinyl alcohol includes the following steps: B1. 5-Carboxybenzotriazole and thionyl chloride were refluxed at 70℃-80℃ for 4h-6h, and unreacted thionyl chloride was removed by vacuum distillation to obtain benzotriazole acyl chloride intermediate. B2. 1-Adamantane carboxylic acid and thionyl chloride were refluxed at 70℃-80℃ for 4h-6h, and unreacted thionyl chloride was removed by vacuum distillation to obtain adamantane alkyl acyl chloride intermediate. B3. Dissolve polyvinyl alcohol in N,N-dimethylformamide and stir at 80℃-90℃ until dissolved. Add the benzotriazole acyl chloride intermediate obtained in B1 and the adamantyl acyl chloride intermediate obtained in B2. Add triethylamine and react at 80℃-100℃ for 6h-8h. After the reaction is completed, pour the reaction solution into anhydrous ethanol to precipitate. Filter, wash and dry to obtain double-modified polyvinyl alcohol.

6. The high flash voltage wide temperature range electrolyte according to claim 5, characterized in that, The molar ratio of 5-carboxybenzotriazole to thionyl chloride in B1 is 1:2.5-3.5; The molar ratio of 1-adamantane carboxylic acid to thionyl chloride in B2 is 1:2.5-3.5; The molar ratio of benzotriazole acyl chloride intermediate to adamantyl acyl chloride intermediate in B3 is 0.9-1.1:1, the molar ratio of the total amount of benzotriazole acyl chloride intermediate and adamantyl acyl chloride intermediate to the molar ratio of hydroxyl groups in polyvinyl alcohol is 1:5-1:10, and the molar ratio of triethylamine to the sum of the total amount of benzotriazole acyl chloride intermediate and adamantyl acyl chloride intermediate is 1.2-1.5:

1.

7. The high flash voltage wide temperature range electrolyte according to claim 1, characterized in that, The waterproofing agent is ammonium dihydrogen phosphate, and the hydrogen scavenging agent is p-nitrobenzoic acid or p-nitrobenzyl alcohol.

8. The high flash voltage wide temperature range electrolyte according to claim 1, characterized in that, The solvent also includes dimethyl sulfoxide, which accounts for 1 wt% to 5 wt% of the total mass of the electrolyte.

9. A method for preparing a high flash voltage wide temperature range electrolyte, applicable to the high flash voltage wide temperature range electrolyte according to any one of claims 1-8, characterized in that, The method includes the following steps: C1. Weigh each raw material according to the mass percentage, and stir the solvent at 70℃-90℃ to obtain a mixed solvent; C2. Add solute to the mixed solvent, heat to 110℃-120℃ and stir for 30min-50min to completely dissolve the solute; C3. Cool the obtained solution to 60℃-80℃, add additives and stir evenly to obtain a high flash voltage wide temperature range electrolyte.

10. The method for preparing a high flash voltage wide temperature range electrolyte according to claim 9, characterized in that, The method further includes C4: degassing the obtained electrolyte under vacuum conditions for 20-40 minutes, filtering, and obtaining the finished electrolyte.

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