Flashing voltage improver, preparation method and application thereof, and electrolytic capacitor electrolyte

Abstract

This invention discloses a flashover voltage booster, its preparation method, and applications, as well as an electrolyte for electrolytic capacitors. It relates to the technical field of electrolytes for high-voltage electrolytic capacitors. The preparation method includes: heating pure water to 93-97°C, adding boric acid and stirring to dissolve; adding ethyl silicate-40 dropwise at 80-90°C and reacting for 4-5 hours; adding methyltrimethoxysilane and stirring at 80-90°C for 1-1.5 hours; vacuum dehydrating at 78-82°C; adding ethylene glycol when the water content drops to 50%; further dehydrating until the water content is <3%; and cooling to obtain the flashover voltage booster. This invention utilizes the hydrolytic crosslinking of boric acid and ethyl silicate-40, end-capping with methyltrimethoxysilane to inhibit gelation and reduce viscosity, combined with staged dehydration and compatibility with ethylene glycol, to prepare a low-viscosity, highly compatible, and high-temperature stable borosilicate crosslinked booster. This significantly improves the flashover voltage and high-temperature stability of the electrolyte, with minimal impact on conductivity and ESR.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology for high-voltage electrolytic capacitors, specifically to flash voltage boosters and their preparation methods and applications, and electrolytes for electrolytic capacitors. Background Technology

[0002] Electrolytic capacitors are indispensable basic components in electronic circuits, widely used in power supplies, frequency converters, new energy vehicles, industrial control, and other fields. As electronic equipment develops towards miniaturization, high power density, and high reliability, higher requirements are placed on the voltage withstand performance of electrolytic capacitors. With the continuous increase in the operating voltage of high-voltage electrolytic capacitors, the properties of their core material—the electrolyte—directly determine the capacitor's voltage withstand capability and operational stability.

[0003] Flash voltage is one of the key performance indicators of electrolytes, referring to the critical voltage value of the electrolyte before electrical breakdown occurs under applied voltage. Insufficient flash voltage will cause dielectric breakdown of capacitors under high-voltage conditions, leading to equipment failure or even safety accidents. Therefore, improving the flash voltage of electrolytes is an important issue in the development of high-voltage electrolytic capacitor technology.

[0004] Traditional methods for improving flash voltage mainly rely on adding flash voltage boosters to the electrolyte. Commonly used flash voltage boosters include polyvinyl alcohol, polyethylene glycol, boric acid, and borate esters. However, existing flash voltage boosters still have significant shortcomings in practical applications: on the one hand, some boosters are prone to decomposition or volatilization under high-temperature operating conditions, resulting in poor flash voltage stability and making it difficult for capacitors to meet the stringent high-temperature load requirements; on the other hand, while some boosters can improve flash voltage, they significantly increase electrolyte viscosity, drastically reduce conductivity, and affect the capacitor's equivalent series resistance (ESR) and ripple current withstand capability. Furthermore, traditional boosters have limited compatibility with the electrolyte system, and sedimentation or precipitation is likely to occur during long-term use, affecting the consistency and reliability of the capacitor. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art. This invention provides a flash voltage booster, its preparation method and application, and an electrolyte for electrolytic capacitors. By dissolving boric acid in high-temperature pure water, adding ethyl silicate-40 for hydrolysis and crosslinking with boric acid, and using methyltrimethoxysilane for end-capping to inhibit gelation and reduce system viscosity, followed by segmented vacuum dehydration and the addition of ethylene glycol, a low-viscosity, highly compatible, and high-temperature stable borosilicate crosslinked flash voltage booster is obtained. This can significantly improve the flash voltage and high-temperature stability of the electrolyte without significantly reducing conductivity or increasing ESR.

[0006] This invention provides a method for preparing a flashover voltage booster, comprising the following steps: S1. Heat pure water to 93-97°C, then add boric acid and stir until completely dissolved to obtain the first solution; S2. Control the temperature of the first solution at 80-90℃, and add ethyl silicate-40 dropwise. After the addition is complete, continue stirring the reaction for 4-5 hours to obtain the first reaction system. S3. Add methyltrimethoxysilane to the first reaction system and stir the reaction at 80-90°C for 1-1.5 h to obtain the second reaction system; S4. The second reaction system is vacuum dehydrated at 78-82°C. When the water content in the second reaction system drops to 50% of the total mass of the system, ethylene glycol is added, and vacuum dehydration is continued until the water content is <3%. After cooling, the flash voltage booster is obtained.

[0007] Specifically, by weight: In step S1, the amount of pure water is 850-950 parts, and the amount of boric acid is 95-105 parts; in step S2, the amount of ethyl silicate-40 is 110-130 parts; in step S3, the amount of methyltrimethoxysilane is 15-25 parts; and in step S4, the amount of ethylene glycol is 750-850 parts.

[0008] Specifically, the boric acid is electronic grade boric acid, and the purity of the electronic grade boric acid is ≥99.999%.

[0009] Specifically, in step S2, the dropping time of the ethyl silicate-40 is controlled to be 3 to 4 hours.

[0010] Specifically, in step S4, the vacuum degree of the vacuum dehydration is in the range of -0.08 to -0.095 MPa.

[0011] The present invention also provides a flash voltage booster prepared by the preparation method of the flash voltage booster, wherein the flash voltage booster is a borosilicate cross-linked transparent liquid with a moisture content of <3%.

[0012] The present invention also provides an application of the aforementioned flash voltage booster, wherein the flash voltage booster is added to the electrolyte of an electrolytic capacitor to improve the flash voltage and high-temperature stability of the electrolyte.

[0013] The present invention also provides an electrolyte for an electrolytic capacitor, comprising a base electrolyte and the aforementioned flash voltage booster, wherein the mass fraction of the flash voltage booster is 3% to 10% of the base electrolyte.

[0014] Specifically, the basic electrolyte comprises, by mass percentage: 80.0%–88.0% ethylene glycol, 5.0%–9.0% ammonium sebacate, 1.0%–3.0% 1,6-dodecanoic acid, 1.0%–3.0% polyethylene glycol, and 3.0%–7.0% composite additives.

[0015] Specifically, the electrolyte of the electrolytic capacitor has a conductivity of 2.10–2.15 mS / cm, a pH value of 6.5, and a flashover voltage of 460–498 V.

[0016] Compared with the prior art, the beneficial effects of the present invention are: The preparation method of this invention involves the directional cross-linking of silicic acid generated by the hydrolysis of boric acid and ethyl silicate-40 under controlled temperature conditions, and the use of methyltrimethoxysilane to end-cap the residual active hydroxyl groups in the system. This effectively inhibits the self-polymerization and gelation of silicic acid and the excessive thickening of the system, keeping the flashover voltage booster in a stable low-viscosity state. Therefore, when this flashover voltage booster is added to the electrolyte, problems such as increased electrolyte viscosity and increased equivalent series resistance caused by excessively high additive viscosity can be avoided. While improving the flashover voltage, the conductivity and electrical conductivity of the electrolyte are well taken into account.

[0017] Moreover, by adopting a segmented vacuum dehydration process combined with the addition of ethylene glycol, the moisture content of the product can be controlled at a low level (<3%), which significantly improves the compatibility between the flash voltage booster and the ethylene glycol-based high-voltage electrolyte. This makes it less prone to crystallization, precipitation, or stratification during long-term high-temperature use, overcoming the defects of traditional boosters such as limited compatibility and easy sedimentation and precipitation. This helps maintain the working stability of the capacitor and extend its high-temperature load life.

[0018] Furthermore, the borosilicate cross-linked flash voltage booster can form a relatively dense and uniform high-temperature resistant protective layer at the oxide film interface of the electrode foil, which significantly improves the flash voltage of the electrolyte and solves the problem of insufficient flash voltage boosting by traditional boosters. Moreover, the protective layer is structurally stable under high-temperature conditions, avoiding the decrease in flash voltage caused by the decomposition or volatilization of the booster.

[0019] In summary, the flash voltage booster prepared by the method of the present invention can improve the flash voltage while having little impact on the conductivity of the electrolyte. It can effectively balance high voltage withstand performance and conductivity, and significantly improve the overall high temperature stability and long-term reliability. This helps to extend the service life of high-voltage electrolytic capacitors under high temperature and high pressure conditions, and better meet the needs of high-end application scenarios for high-reliability and long-life electrolytic capacitors. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic flowchart of the preparation method of the flash voltage booster in an embodiment of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0023] This invention provides a method for preparing a flashover voltage booster. Figure 1 A schematic flowchart of the preparation method of the flashover voltage booster in an embodiment of the present invention is shown, including the following steps: S1. Heat pure water to 93-97°C, then add boric acid and stir until completely dissolved to obtain the first solution; Heating pure water to 93–97°C significantly increases the solubility of boric acid and promotes its dissociation, forming [B(OH)4] containing tetrahydroxyborate ions. The acidic aqueous solution provides sufficient active sites for subsequent cross-linking reactions. If the pure water temperature is below 93℃, the dissolution rate of boric acid slows down significantly, and undissolved solid particles are easily formed, leading to uneven local reactions and reducing the degree of borosilicate cross-linking and product stability. If the pure water temperature is above 97℃, the system approaches boiling, and a large amount of water evaporates. At the same time, boric acid is easily lost through volatilization with the water vapor, causing the actual reaction ratio to deviate from the design value and affecting the structure and performance of the flashover voltage booster.

[0024] Optionally, the pure water can be heated to 93°C, 94°C, 95°C, 96°C, or 97°C; preferably, heating the pure water to 95°C makes it easy to achieve an excellent balance between the boric acid dissolution rate, system stability, and boric acid retention rate.

[0025] In some specific embodiments, the boric acid is electronic-grade boric acid with a purity ≥99.999%. Using high-purity electronic-grade boric acid minimizes metal ions, anionic / cationic impurities, and particulate contaminants in the system, preventing impurity ions from migrating, accumulating, and breaking down the oxide film under a high-voltage electric field, thereby significantly improving the high-voltage withstand capability and high-temperature stability of the electrolyte. If the boric acid purity is insufficient, impurity ions will significantly reduce the flashover voltage, shorten the capacitor's lifespan, and even lead to increased leakage current and breakdown failure. Therefore, selecting electronic-grade boric acid with a purity ≥99.999% ensures the purity and stability of the flashover voltage booster, making it more suitable for the stringent requirements of high-voltage electrolytic capacitors.

[0026] S2. Control the temperature of the first solution at 80-90℃, and add ethyl silicate-40 dropwise. After the addition is complete, continue stirring the reaction for 4-5 hours to obtain the first reaction system. Maintaining the temperature of the first solution at 80–90°C ensures the stable hydrolysis of ethyl silicate-40 to generate active silicic acid, preventing excessively rapid hydrolysis from causing localized self-aggregation or gelation. Simultaneously, this temperature range promotes the directional borosilicate-oxygen crosslinking reaction between the silanol groups of silicic acid and the boronol groups of boric acid, gradually forming a stable borosilicate crosslinked network structure. This provides the core structural basis for improving the flash voltage of the electrolyte. If the temperature is below 80°C, the hydrolysis of ethyl silicate-40 is insufficient, and the crosslinking reaction rate is slow, easily leading to insufficient crosslinking degree and a weaker flash voltage improvement effect. If the temperature is above 90°C, the hydrolysis and crosslinking reactions are too vigorous, easily producing large molecular aggregates, causing a sharp increase in system viscosity and a decrease in transparency, affecting subsequent compatibility and performance.

[0027] Optionally, the temperature of the first solution can be controlled at 80°C, 82°C, 85°C, 87°C, or 90°C; preferably, the temperature of the first solution is controlled at 85°C, so that the hydrolysis uniformity, cross-linking sufficiency, and system stability are in excellent balance.

[0028] After the addition is complete, continue stirring for 4-5 hours to allow for complete hydrolysis of ethyl silicate-40 and a complete and uniform borosilicate crosslinking reaction with boric acid. This ensures the formation of a stable borosilicate crosslinked network structure, improving the voltage resistance and high-temperature stability of the flashover voltage booster. If the reaction time is less than 4 hours, insufficient hydrolysis and crosslinking will easily lead to a low degree of crosslinking, a weak flashover voltage boosting effect, and poor system stability. If the reaction time exceeds 5 hours, it will easily result in an excessively long production cycle, increased energy consumption, no significant improvement in the degree of crosslinking, and may even lead to an abnormal increase in the system viscosity.

[0029] Optionally, after the addition is complete, the reaction can be stirred for 4 hours, 4.5 hours, or 5 hours; preferably, the reaction can be stirred for 4.5 hours to make the hydrolysis and cross-linking more complete and the product performance more stable.

[0030] In some specific embodiments, the dropping time of ethyl silicate-40 is controlled to be 3-4 hours. This allows ethyl silicate-40 to be dispersed uniformly and evenly in the reaction system, achieving mild and complete hydrolysis and gradually undergoing a directional borosilicate crosslinking reaction with boric acid. This avoids problems such as excessively high local concentrations, rapid agglomeration and gelation, and system turbidity and thickening caused by excessively rapid dropping. If the dropping time is less than 3 hours, the hydrolysis and crosslinking reactions are prone to runaway and violent, forming agglomerated gels that affect the product structure and performance. If the dropping time exceeds 4 hours, it will lead to excessively long production cycles, reduced efficiency, and no significant improvement in product performance.

[0031] Optionally, the dropping time of ethyl silicate-40 can be 3 hours, 3.5 hours, or 4 hours; preferably, the dropping time is 3.5 hours, so that the dispersion uniformity, hydrolysis stability and crosslinking fullness can achieve an excellent balance.

[0032] S3. Add methyltrimethoxysilane to the first reaction system and stir the reaction at 80-90°C for 1-1.5 h to obtain the second reaction system; Controlling the reaction temperature at 80–90°C allows methyltrimethoxysilane to fully react with the residual active silanol and boronol groups in the system, effectively sealing excess active sites, inhibiting silicic acid self-polymerization and gelation, significantly reducing system viscosity, and ensuring the long-term storage stability and good flowability of the additive. If the temperature is below 80°C, the end-capping reaction is insufficient, and a large number of active hydroxyl groups remain in the system, which is prone to slow gelation and increased viscosity during storage. If the temperature is above 90°C, it can easily lead to localized overreaction or slight hydrolysis of methyltrimethoxysilane, destroying the end-capping effect and causing the system to darken in color.

[0033] Optionally, the temperature can be controlled at 80℃, 82℃, 85℃, 87℃, or 90℃; preferably, the temperature is controlled at 85℃, which achieves an excellent balance between end-capping efficiency, anti-adhesion effect, and system transparency.

[0034] Optionally, the reaction time is 1 hour, 1.2 hours, 1.3 hours, 1.4 hours, or 1.5 hours; preferably, the reaction time is 1.2 hours, which can improve production efficiency while ensuring complete end-capping.

[0035] S4. The second reaction system is vacuum dehydrated at 78-82°C. When the water content in the second reaction system drops to 50% of the total mass of the system, ethylene glycol is added, and vacuum dehydration is continued until the water content is <3%. After cooling, the flash voltage booster is obtained. Controlling the dehydration temperature between 78 and 82°C ensures rapid moisture removal without damaging the existing borosilicate cross-linked structure, while also preventing high-temperature volatilization, decomposition, or discoloration of ethylene glycol. A segmented dehydration process is employed, first dehydrating to a moisture content of 50% before adding ethylene glycol. The high compatibility between ethylene glycol and the borosilicate cross-linked product aids in dehydration, ensuring a final moisture content consistently below 3%. This significantly improves the compatibility of the additive with the high-voltage electrolyte, preventing precipitation, stratification, and sedimentation during long-term high-temperature use. If the temperature is below 78°C, the dehydration rate is too slow, resulting in an excessively long production cycle; if the temperature is above 82°C, ethylene glycol volatilization loss and localized overheating of the system can easily occur, leading to unstable moisture control and fluctuations in product performance.

[0036] Optionally, the dehydration temperature can be controlled at 78℃, 79℃, 80℃, 81℃, or 82℃; preferably, the temperature is controlled at 80℃, which achieves an excellent balance between dehydration efficiency, product stability, and ethylene glycol retention rate.

[0037] Specifically, the vacuum degree range of the vacuum dehydration is -0.08 to -0.095 MPa. In a high vacuum environment, the product can be dehydrated quickly under mild conditions without damaging the borosilicate cross-linked structure, thus ensuring stable product quality.

[0038] It should be noted that ethylene glycol is added when the moisture content in the second reaction system drops to 50% of the total mass. The main considerations are as follows: Firstly, removing moisture to 50% allows for the rapid removal of most of the volatile free water in the system, preventing excessive entrainment and loss of ethylene glycol due to prolonged vacuum dehydration under high water content, thus ensuring the complete retention of ethylene glycol in the product. If ethylene glycol is added at a high moisture level, the system's high water content and large polarity differences can easily lead to localized agglomeration, turbidity, or slow gelation of the borosilicate crosslinking product. When the moisture content drops to 50%, the system viscosity is moderate. Adding ethylene glycol at this point allows the borosilicate crosslinking product to dissolve uniformly and disperse stably, maintaining the product's transparent and low-viscosity state. Ethylene glycol has excellent compatibility with the borosilicate crosslinking product; its addition improves mass transfer, making it easier to remove the remaining small amount of bound water under gentle vacuum, stably controlling the moisture content to <3%, meeting the stringent low-moisture requirements of high-voltage electrolytes. The addition of this node enables the flash voltage booster to form a uniform and stable ethylene glycol solution, which is highly compatible with ethylene glycol-based high-voltage electrolytes. It is miscible, does not separate into layers, does not precipitate at high temperatures, and does not settle, significantly improving the long-term reliability of the electrolyte.

[0039] The moisture content of the obtained flash voltage booster is controlled at <3%. After being added to the base electrolyte at 3% to 10%, the moisture content of the final electrolyte can still meet the process requirements of high voltage electrolytic capacitors for low moisture content (usually <1%), thus avoiding the flash voltage drop or high temperature stability deterioration caused by the introduction of moisture.

[0040] In some specific embodiments, by weight: the pure water in step S1 is 850-950 parts, the boric acid is 95-105 parts; the ethyl silicate-40 in step S2 is 110-130 parts; the methyltrimethoxysilane in step S3 is 15-25 parts; and the ethylene glycol in step S4 is 750-850 parts.

[0041] By strictly limiting the weight ratio of each raw material, the borosilicate crosslinking, end-capping inhibition, and solvent compatibility among boric acid, ethyl silicate-40, and methyltrimethoxysilane are achieved in an excellent proportion, ensuring the formation of a borosilicate crosslinked flashover voltage booster with stable structure, moderate viscosity, and excellent compatibility.

[0042] 850-950 parts of pure water: This provides an appropriate reaction medium for the dissolution of boric acid and the hydrolysis of ethyl silicate-40, ensuring the system's fluidity and reaction uniformity. Too little pure water results in an overly viscous system and localized gelation; too much pure water leads to a high load on subsequent dehydration, high energy consumption, and a prolonged production cycle. Optionally, the pure water content can be 850, 900, or 950 parts; 900 parts is preferred to balance the dissolution and hydrolysis effects as well as the subsequent dehydration effect.

[0043] Boric acid (95-105 parts): Provides boron-oxygen crosslinking centers, determining the density and voltage resistance of the borosilicate network. Insufficient boric acid results in insufficient crosslinking sites and a weak flash voltage increase; excessive boric acid easily leaves unreacted boron sources, leading to electrolyte pH shift and decreased stability. Optionally, the amount of boric acid is 95 parts, 100 parts, or 105 parts; preferably 100 parts, which provides excellent crosslinking strength and system stability.

[0044] Ethyl silicate-40, 110-130 parts: As a silicon source, it forms a borosilicate-oxygen backbone structure with boric acid. Too little ethyl silicate-40 results in an incomplete borosilicate network and poor enhancement effect; too much leads to self-polymerization, a sharp increase in system viscosity, and easy gelation. Optionally, ethyl silicate-40 is 110 parts, 120 parts, or 130 parts; preferably 120 parts, as it ensures sufficient cross-linking and is less prone to gelation.

[0045] 15-25 parts of methyltrimethoxysilane: used for end-capping of active hydroxyl groups, inhibiting gelation and reducing viscosity. Insufficient dosage results in inadequate end-capping and thickening over time; excessive dosage leads to raw material waste and may weaken the borosilicate network strength. Optionally, the amount of methyltrimethoxysilane is 15 parts, 20 parts, or 25 parts; preferably 20 parts, which provides excellent gelation inhibition and flowability control.

[0046] Ethylene glycol 750-850 parts: As a compatibility solvent, it improves compatibility with the electrolyte and assists in dehydration. Too little ethylene glycol results in poor product compatibility and easy stratification; too much dilutes the active ingredient and leads to insufficient flash voltage increase. Optionally, the amount of ethylene glycol is 750 parts, 800 parts, or 850 parts; preferably 800 parts, balancing compatibility and effective concentration.

[0047] The preparation method of the flashover voltage booster of the present invention involves the directional cross-linking of silicic acid generated by the hydrolysis of boric acid and ethyl silicate-40 under controlled temperature conditions, and the use of methyltrimethoxysilane to end-cap the residual active hydroxyl groups in the system, effectively inhibiting the self-polymerization and gelation of silicic acid and the excessive thickening of the system, so that the flashover voltage booster maintains a stable low viscosity state. Therefore, when the flashover voltage booster is added to the electrolyte, problems such as increased electrolyte viscosity and increased equivalent series resistance caused by excessively high additive viscosity can be avoided. While improving the flashover voltage, the conductivity and electrical conductivity of the electrolyte are well taken into account.

[0048] Moreover, by adopting a segmented vacuum dehydration process combined with the addition of ethylene glycol, the moisture content of the product can be controlled at a low level (<3%), which significantly improves the compatibility between the flash voltage booster and the ethylene glycol-based high-voltage electrolyte. This makes it less prone to crystallization, precipitation, or stratification during long-term high-temperature use, overcoming the defects of traditional boosters such as limited compatibility and easy sedimentation and precipitation. This helps maintain the working stability of the capacitor and extend its high-temperature load life.

[0049] Furthermore, the borosilicate cross-linked flash voltage booster can form a relatively dense and uniform high-temperature resistant protective layer at the oxide film interface of the electrode foil, which significantly improves the flash voltage of the electrolyte and solves the problem of insufficient flash voltage boosting by traditional boosters. Moreover, the protective layer is structurally stable under high-temperature conditions, avoiding the decrease in flash voltage caused by the decomposition or volatilization of the booster.

[0050] In summary, the flash voltage booster prepared by the method of the present invention can improve the flash voltage while having little impact on the conductivity of the electrolyte. It can effectively balance high voltage withstand performance and conductivity, and significantly improve the overall high temperature stability and long-term reliability. This helps to extend the service life of high-voltage electrolytic capacitors under high temperature and high pressure conditions, and better meet the needs of high-end application scenarios for high-reliability and long-life electrolytic capacitors.

[0051] This invention also provides a flash voltage booster prepared by the aforementioned method, wherein the flash voltage booster is a borosilicate cross-linked transparent liquid with a moisture content of <3%. It appears as a borosilicate cross-linked transparent liquid, free from turbidity, precipitation, and gel particles. It is rapidly miscible with ethylene glycol-based high-voltage electrolytes and does not separate over a long period. The moisture content is strictly controlled to <3%. Even after being added to the base electrolyte at 3%–10%, the final electrolyte still meets the low moisture requirements (typically <1%) for high-voltage electrolytic capacitors, preventing a decrease in flash voltage or degradation of high-temperature stability due to moisture introduction. It also prevents moisture from causing hydrolysis, gelation, and precipitation of additives, ensuring high-temperature and storage stability. The <3% moisture content is achieved through staged vacuum dehydration combined with ethylene glycol formulation: first, dehydration is carried out to 50% moisture content, then ethylene glycol is added. The high compatibility between ethylene glycol and the borosilicate cross-linked product assists in dehydration, ultimately achieving a stable low moisture content, ensuring product purity and improving compatibility with the electrolyte.

[0052] This invention also provides an application of the aforementioned flashover voltage booster, which is added to the electrolyte of an electrolytic capacitor to improve the flashover voltage and high-temperature stability of the electrolyte. This flashover voltage booster is particularly suitable for high-voltage electrolytic capacitor electrolytes operating at 450V and above and 125℃, significantly improving the flashover voltage and widening the safe operating voltage range of the electrolyte; it also greatly enhances high-temperature stability, inhibiting decomposition, volatilization, and precipitation at high temperatures, thus extending the high-temperature load life of the capacitor; moreover, it has minimal impact on conductivity and ESR, balancing voltage withstand and conductivity.

[0053] The core mechanism of this flashover voltage booster is that the borosilicate cross-linked structure forms a dense, uniform, high-temperature resistant protective layer at the interface of the electrode foil oxide film, which enhances the oxide film's voltage resistance, seals defect sites, reduces leakage current and breakdown risk, and ensures structural stability and no failure at high temperatures.

[0054] The present invention also provides an electrolyte for an electrolytic capacitor, comprising a base electrolyte and the aforementioned flash voltage booster, wherein the mass fraction of the flash voltage booster is 3% to 10% of the base electrolyte.

[0055] The binary compound system of basic electrolyte and flash voltage booster is easy to prepare and has excellent compatibility. Simply add the flash voltage booster to the basic electrolyte in proportion and stir until homogeneous. No special equipment is required, making it suitable for industrial production.

[0056] Adding 3% to 10% of flash voltage booster can significantly increase the flash voltage of the electrolyte in electrolytic capacitors, significantly extend their high-temperature life, maintain the conductivity essentially unchanged, and prevent a significant increase in ESR. If the mass fraction of flash voltage booster added is less than 3%, the flash voltage increase will be insufficient, and the improvement in high-temperature stability will be limited. If the mass fraction of flash voltage booster added is greater than 10%, the viscosity of the system will increase slightly, which may affect wettability and production processes, resulting in a decrease in cost-effectiveness.

[0057] Optionally, the mass fraction of the flashover voltage booster can be 3%, 5%, 7%, 9%, or 10%; preferably, the mass fraction of the flashover voltage booster is 5%, which results in excellent flashover voltage boosting effect.

[0058] Specifically, the basic electrolyte comprises, by mass percentage: 80.0%–88.0% ethylene glycol, 5.0%–9.0% ammonium sebacate, 1.0%–3.0% 1,6-dodecanoic acid, 1.0%–3.0% polyethylene glycol, and 3.0%–7.0% composite additives.

[0059] Ethylene glycol 80.0%–88.0%: As the main solvent, it has a high boiling point and low volatility, exhibits excellent compatibility with flash voltage boosters, and provides a stable dissolution and conductivity environment for the electrolyte. Too little ethylene glycol results in insufficient solute dissolution, high system viscosity, and decreased wettability; too much dilutes the solute concentration, leading to insufficient conductivity and poor high-temperature stability. Optionally, the ethylene glycol content can be 80.0%, 84.5%, or 88.0%; preferably 84.5%, balancing dissolution capacity, conductivity, and high-temperature stability.

[0060] Ammonium sebacate (5.0%–9.0%): As the main solute, it provides the core ion-carrying capacity of the electrolyte, ensuring its conductivity and performance. Too little ammonium sebacate results in low conductivity and increased capacitor impedance; too much limits solubility and leads to crystallization at high temperatures. Optionally, the ammonium sebacate content can be 5.0%, 7.0%, or 9.0%; preferably 7.0%, balancing conductivity, solubility, and high-temperature stability.

[0061] 1,6-Dodecanoic acid 1.0%–3.0%: As an auxiliary solute, it adjusts the electrolyte pH, improves the oxide film repair performance, and inhibits high-temperature corrosion. Too little 1,6-dodecanoic acid results in weak repair ability and insufficient corrosion resistance; too much results in a low pH, affecting system stability and flashover voltage. Optionally, the 1,6-dodecanoic acid content can be 1.0%, 1.5%, or 3.0%; preferably 1.5%, balancing pH adjustment, repair ability, and system stability.

[0062] Polyethylene glycol (PEG) 1.0%–3.0%: As an auxiliary additive, it reduces the surface tension of the electrolyte, improves the wettability of the electrode foil and electrolytic paper, and enhances high-temperature stability. Too little PEG results in insufficient wettability and poor capacitor performance consistency; too much leads to increased viscosity and a slight decrease in conductivity. Optionally, PEG can be 1.0%, 2.0%, or 3.0%; preferably 2.0%, balancing wettability, viscosity, and conductivity.

[0063] Composite additives, ranging from 3.0% to 7.0%, include corrosion inhibitors, stabilizers, and pH buffers to further improve the electrolyte's high-temperature resistance, high-pressure resistance, and long service life. Too little composite additive results in limited improvement in high-temperature service life and pressure resistance; too much increases the risk of impurity introduction and costs. Optionally, the composite additive content can be 3.0%, 5.0%, or 7.0%; preferably 5.0%, balancing overall performance improvement, purity, and cost.

[0064] Furthermore, the electrolyte of the electrolytic capacitor has a conductivity of 2.10–2.15 mS / cm, a pH value of 6.5, and a flashover voltage of 460–498 V. The conductivity of 2.10–2.15 mS / cm is essentially the same as the base solution (2.15 mS / cm), meaning the flashover voltage enhancer hardly reduces conductivity. The pH value of 6.5 is neutral to slightly acidic, ensuring stability and preventing drift, thus protecting the oxide film and inhibiting corrosion. The flashover voltage of 460–498 V represents a significant increase of 30–68 V compared to the base solution (430 V), meeting the requirements of high-voltage capacitors. This demonstrates that under the premise of high flashover voltage, maintaining high conductivity and stable pH solves the problem of traditional enhancers that "increasing voltage inevitably leads to decreased conductivity and increased viscosity," achieving a balance between high voltage, high conductivity, and high-temperature stability.

[0065] Example 1: Preparation of flashover voltage booster (1) Heat 900g of pure water to 95℃, then add 100g of electronic grade boric acid (purity ≥99.999%), stir until completely dissolved, and obtain the first solution; (2) Cool the first solution to 85°C and add 120g of ethyl silicate-40 dropwise at a uniform rate over 3.5h. After the addition is complete, keep the solution warm and stir for 4.5h to obtain the first reaction system. (3) Add 20g of methyltrimethoxysilane to the first reaction system, and stir at 85℃ for 1.2h to obtain the second reaction system; (4) The second reaction system was placed at 80°C and vacuum degree -0.085MPa for vacuum dehydration. When the water content in the system dropped to 50% of the total mass of the system, 800g of ethylene glycol was added and vacuum dehydration was continued until the water content of the system was <3%. The system was cooled to room temperature to obtain a borosilicate cross-linked transparent liquid flash voltage booster.

[0066] Example 2: Electrolyte preparation and performance testing for electrolytic capacitors (1) Preparation of basic electrolyte Weigh out the following by mass percentage: 84.5% ethylene glycol, 7.0% ammonium sebacate, 1.5% 1,6-dodecanoic acid, 2.0% polyethylene glycol, and 5.0% composite additives. Mix them thoroughly and keep them at 125℃ for 2 hours. After cooling, the basic electrolyte is obtained.

[0067] (2) Preparation of electrolyte containing booster Add 1 wt%, 3 wt%, 5 wt%, and 10 wt% of the flash voltage booster prepared in Example 1 to the base electrolyte, respectively, and stir until homogeneous to obtain the corresponding numbered electrolytes.

[0068] (3) Performance test results

[0069] (4) 125℃ high temperature life test Electrolytic capacitors with specifications of 4.7μF / 450V (positive foil LY560VF 0.65~0.67uF, negative foil GYF-T310 3.0VF / 100uF, electrolytic paper TDS20 / 30-W190, and high-voltage forming of guide pin GSH12085) were used. A 2000-hour high-temperature load life test was conducted at 125℃ and 450V rated voltage. The judgment criteria were: capacitance change rate |△C / C|≤20%, leakage current LC≤67.3μA, loss tangent Tanδ≤1.5 times the initial value, and no bulging, leakage, or breakdown. Specific test results are as follows: The capacitor exploded at 110 h during the test of the basic electrolyte group, and the test was terminated due to poor high-temperature stability; the capacitor exploded at 200 h during the test of the group with 1 wt% flashover voltage booster added, and the test was terminated, failing to meet the long-life requirement; the capacitor with 3 wt% flashover voltage booster added passed 2000 h of test, with intact appearance, no bulging or leakage, a capacitance change rate of -18.16%, meeting |△C / C| ≤ 20%, a leakage current of 2.30 μA, far lower than the upper limit of 67.3 μA, and the loss tangent meeting Tanδ ≤ 1.5 times the initial value, being judged qualified; the capacitor with 5 wt% flashover voltage booster added passed 2000 h of test, with intact appearance, no bulging or leakage, a capacitance change rate of -15.20%, meeting |△C / C| ≤ 20%, a leakage current of 2.60 μA, far lower than the upper limit of 67.3 μA, and the loss tangent meeting Tanδ ≤ 1.5 times the initial value, being judged qualified; the capacitor with 10 wt% flashover voltage booster added passed 2000 h of test, with intact appearance, no bulging or leakage, a capacitance change rate of -16.27%, meeting |△C / C| ≤ 20%, a leakage current of 2.59 μA, far lower than the upper limit of 67.3 μA, and the loss tangent meeting Tanδ ≤ 1.5 times the initial value, being judged qualified.

[0070] The test results show that when the addition amount of the flashover voltage booster is less than 3%, the continuity and density of the protective layer formed on the surface of the electrode foil oxide film are insufficient, and it cannot effectively inhibit local breakdown and leakage current growth under high temperature and high pressure; when the addition amount reaches 3% or more, the protective layer is completely covered, and there is a significant jump in the flashover voltage boost and high-temperature stability; moreover, when the addition amount is within 10%, the influence on conductivity is small, and the conductivity decrease does not exceed 0.02 mS / cm and can still remain above 2.10 mS / cm, meeting the design requirements of high-voltage electrolytic capacitors for conductivity; when the addition amount is 3 wt% - 10 wt%, the capacitor can pass the 2000 h high-temperature life test, and when the addition amount is 5 wt%, the cost performance is the highest and the comprehensive performance is the best.

[0071] Comparative Example 1 (without methyltrimethoxysilane capping) Compared with Example 1, in this comparative example, methyltrimethoxysilane is not added during the preparation of the flashover voltage booster, and the other raw material ratios, feeding sequences, reaction temperatures, heat preservation times, vacuum degrees and other process parameters are exactly the same as those in Example 1.

[0072] During the reaction process, due to the lack of an active hydroxyl capping agent in the system, the self-polymerization tendency of silicic acid is significantly enhanced, and phenomena such as a rapid increase in viscosity and local microgel occur during the heat preservation reaction stage. The final product is a milky white opaque liquid, and the viscosity of the system is increased by more than 70% compared with Example 1, and obvious white flocculent gel appears after standing at room temperature for 7 d.

[0073] The additive obtained from the comparative example was added to the base electrolyte at a dosage of 5 wt%. Slight turbidity occurred during stirring and mixing, and trace amounts of suspended matter were observed after standing for 24 hours, indicating poor compatibility. Testing revealed that the electrolyte conductivity was only 2.05 mS / cm, a significant decrease compared to Example 2 with the same additive dosage; the flashover voltage only increased to 440V, far lower than the 488V of Example 2.

[0074] Under the same conditions, a 125℃ high-temperature life test was conducted. The capacitors exhibited failure phenomena such as leakage, bulging, and internal breakdown after only 500 hours of continuous load. Test data showed that the capacitance change rate was -26.3%, exceeding the acceptable range of |△C / C|≤20%. The leakage current increased to 82.6μA, exceeding the upper limit of 67.3μA. The loss tangent could not meet the requirement of ≤1.5 times the initial value.

[0075] The experimental results fully demonstrate that methyltrimethoxysilane end-capping is a key step in inhibiting gelation, reducing viscosity, and ensuring compatibility and storage stability. The absence of this step will directly lead to the failure of the booster, making it impossible to achieve the high pressure and long life performance goals.

[0076] Comparative Example 2 (Commercially available traditional borate ester boosters) This comparative example uses commercially available borate ester flash voltage booster commonly used in the electrolyte industry. It is added to the basic electrolyte described in Example 2 at a dosage of 5 wt%. The electrolyte preparation process, stirring conditions, aging process, and testing standards are completely consistent with those of Example 2.

[0077] Tests showed that the conductivity of the comparative electrolyte was only 1.98 mS / cm, which was significantly lower than the 2.15 mS / cm of the base electrolyte, resulting in a significant negative impact on the electrolyte's conductivity. The flashover voltage was 445V, which was far lower than the 488V of Example 1 of this invention, indicating a limited improvement in withstand voltage.

[0078] During the 125℃, 450V high-temperature load test, after the capacitor operated continuously for 800 hours, the electrolyte showed obvious stratification, white crystals precipitated at the bottom, and the upper liquid became turbid. The capacitor bulged and leaked, resulting in failure.

[0079] Test data shows that the capacity change rate is -23.7%, exceeding the acceptable range of |△C / C|≤20%; the leakage current rises to 76.1μA, exceeding the upper limit of 67.3μA; and the loss tangent cannot meet the requirement of ≤1.5 times the initial value.

[0080] The experimental results show that traditional borosilicate ester boosters have inherent defects such as easy decomposition at high temperatures, easy precipitation, reduced conductivity, insufficient flashover voltage boost, and short lifespan. Their overall performance is far inferior to the borosilicate crosslinked flashover voltage booster prepared in this invention, and they cannot meet the requirements for high voltage, long lifespan, and high temperature stability.

[0081] Comparative Example 3 (one-time vacuum dehydration, ethylene glycol added without segmentation) Compared with Example 1, this comparative example does not use a segmented vacuum dehydration process, but performs vacuum dehydration in one go throughout the entire process. Furthermore, ethylene glycol is not added when the moisture content drops to 50%. Instead, ethylene glycol is added all at once after the entire vacuum dehydration process is completed (i.e., when the moisture content of the system is reduced to near the target range). All other raw materials, proportions, temperatures, times, and vacuum levels are consistent with those in Example 1.

[0082] During the dehydration process, the system experienced slow water removal, which could easily lead to problems such as localized overheating and component volatilization. The final additive had a water content of 4.9%, far exceeding the <3% level in Example 1, and exhibited a slightly turbid appearance, unlike the clear and transparent state of Example 1. When added at 5 wt% to the base electrolyte, the system's compatibility deteriorated, and trace amounts of precipitation were prone to occur at high temperatures.

[0083] Testing revealed that the electrolyte conductivity was 2.08 mS / cm and the flashover voltage was only 452 V, both inferior to the performance indicators of Example 2 with the same dosage. In a 125°C high-temperature life test, the capacitor exhibited problems such as a sharp increase in leakage current and rapid capacity decay after only 1200 hours of operation, ultimately leading to premature failure.

[0084] Experimental results prove that segmented vacuum dehydration combined with the addition of ethylene glycol midway is the core process for achieving low moisture content, high transparency, and high compatibility. This process ensures that the booster and the high-voltage electrolyte are highly compatible, and that the product does not separate or precipitate during long-term high-temperature use, maintaining stable performance.

[0085] Comparative Example 4 (without boric acid, no borosilicate cross-linking structure) Compared with Example 1, this comparative example does not add boric acid components, but retains only pure water, ethyl silicate-40, methyltrimethoxysilane, and ethylene glycol. The raw material ratio and other parameters of the preparation process are the same as those in Example 1.

[0086] During the reaction, ethyl silicate-40 hydrolyzes under hydrothermal conditions to generate a large amount of silica monomers. Because boric acid is absent from the system for coordination and cross-linking, the silica monomers readily undergo self-condensation polymerization, forming linear and branched polysilicic acid particles, leading to a rapid increase in the system viscosity. The final product is a slightly opalescent, translucent, viscous liquid. Although it is end-capped with methyltrimethoxysilane, it is still dominated by highly polymerized polysiloxane, failing to form a borosilicate hybrid cross-linked network, resulting in significantly insufficient structural density and high-temperature resistance.

[0087] When the product was added to the base electrolyte at a dosage of 5 wt%, tests showed that the electrolyte conductivity was 2.10 mS / cm, and the flashover voltage only increased to 442 V, with a negligible improvement in withstand voltage, far lower than the 488 V in Example 2. In the 125℃ high-temperature life test, due to the easy rearrangement and insufficient density of the polysilicic acid structure under high-temperature electric fields, a stable and dense protective layer could not be formed on the anodic oxide film surface. The capacitor exhibited failure phenomena such as dielectric film breakdown, internal short circuit, and a surge in leakage current after only 700 hours of continuous load, with significant capacity decay, failing to meet the requirements of high-voltage, long-life operation.

[0088] Experimental results show that boric acid not only provides the system with boron-containing high-voltage components, but also forms a boron-silicon crosslinked hybrid structure with the hydrolysis products of silica, effectively inhibiting excessive self-polymerization of silica, and constructing a three-dimensional network that is resistant to high temperature and breakdown. The lack of boric acid will lead to the system being dominated by polysilicic acid self-polymers, resulting in poor structural stability and a significant loss of the flashover voltage improvement and high-temperature life improvement effects.

[0089] The flash voltage booster, its preparation method and application, and the electrolyte for electrolytic capacitors provided in the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing a flashover voltage booster, characterized in that, Includes the following steps: S1. Heat pure water to 93-97°C, then add boric acid and stir until completely dissolved to obtain the first solution; S2. Control the temperature of the first solution at 80-90℃, and add ethyl silicate-40 dropwise. After the addition is complete, continue stirring the reaction for 4-5 hours to obtain the first reaction system. S3. Add methyltrimethoxysilane to the first reaction system and stir the reaction at 80-90°C for 1-1.5 h to obtain the second reaction system; S4. The second reaction system is vacuum dehydrated at 78-82°C. When the water content in the second reaction system drops to 50% of the total mass of the system, ethylene glycol is added, and vacuum dehydration is continued until the water content is <3%. After cooling, the flash voltage booster is obtained.

2. The preparation method of the flashover voltage booster as described in claim 1, characterized in that, By weight: In step S1, the amount of pure water is 850-950 parts, and the amount of boric acid is 95-105 parts; in step S2, the amount of ethyl silicate-40 is 110-130 parts; in step S3, the amount of methyltrimethoxysilane is 15-25 parts; and in step S4, the amount of ethylene glycol is 750-850 parts.

3. The preparation method of the flashover voltage booster as described in claim 1, characterized in that, The boric acid is electronic grade boric acid, and the purity of the electronic grade boric acid is ≥99.999%.

4. The preparation method of the flashover voltage booster as described in claim 1, characterized in that, In step S2, the dropping time of the ethyl silicate-40 is controlled to be 3 to 4 hours.

5. The preparation method of the flashover voltage booster as described in claim 1, characterized in that, In step S4, the vacuum degree of the vacuum dehydration is in the range of -0.08 to -0.095 MPa.

6. A flash voltage booster prepared by the method for preparing the flash voltage booster according to any one of claims 1 to 5, characterized in that, The flashover voltage booster is a borosilicate cross-linked transparent liquid with a moisture content of <3%.

7. The application of the flashover voltage booster as described in claim 6, characterized in that, The flash voltage booster is added to the electrolyte of the electrolytic capacitor to improve the flash voltage and high-temperature stability of the electrolyte.

8. An electrolyte for an electrolytic capacitor, characterized in that, It comprises a base electrolyte and a flash voltage booster as described in claim 6, wherein the mass fraction of the flash voltage booster is 3% to 10% of the base electrolyte.

9. The electrolyte for an electrolytic capacitor as described in claim 8, characterized in that, The basic electrolyte comprises, by mass percentage: 80.0%–88.0% ethylene glycol, 5.0%–9.0% ammonium sebacate, 1.0%–3.0% 1,6-dodecanoic acid, 1.0%–3.0% polyethylene glycol, and 3.0%–7.0% composite additives.

10. The electrolyte for an electrolytic capacitor as described in claim 8, characterized in that, The electrolyte of the electrolytic capacitor has a conductivity of 2.10–2.15 mS / cm, a pH value of 6.5, and a flashover voltage of 460–498 V.

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