Electrolyte for high-voltage boron-free aluminum electrolytic capacitor and preparation method thereof

Abstract

The application discloses a high-voltage boron-free electrolyte for aluminum electrolytic capacitors, and relates to the technical field of electrolytic capacitors, aiming to solve the problem of poor high-temperature reliability of existing boron-free electrolytes. The electrolyte does not contain boron and is composed of the following components in percentage by weight: 5-20% of pure water as an auxiliary solvent; 5-10% of at least one organic amine salt of carboxylic acid as a solute; and the balance of a main solvent. The application effectively inhibits the increase of the tangent value of loss of the capacitor under high-temperature load by using the organic amine salt of carboxylic acid with excellent thermal stability and the pure water with a specific proportion, avoids abnormal heating and early failure, significantly prolongs the service life of the capacitor and improves the reliability.

Description

Technical Field

[0002] This invention relates to the field of electrolytic capacitor technology, and more particularly to an electrolyte for high-voltage boron-free aluminum electrolytic capacitors. Background Technology

[0003] Aluminum electrolytic capacitors are widely used due to their high capacitance density and low cost. The electrolyte, their core material, plays a decisive role in key performance characteristics such as voltage withstand capability, lifespan, and temperature characteristics. Traditional high-voltage aluminum electrolytic capacitors commonly use boric acid-containing electrolyte systems to improve voltage withstand capability and lifespan. However, due to relevant environmental regulations (such as the EU REACH regulation) listing boric acid and its salts as substances of very high concern, the application and export of boron-containing electrolytes face significant regulatory obstacles.

[0004] To address this challenge, the industry has begun developing boron-free alternatives. A common approach is to use a combination of organic solvents and inorganic ammonium salts. However, this approach has serious drawbacks. Capacitors using this electrolyte experience a rapid increase in loss tangent during high-temperature load testing, leading to accelerated internal losses, abnormal heating, and ultimately failure due to overheating. This approach fails to meet the requirements for long lifespan and high reliability. Therefore, developing a high-voltage boron-free electrolyte with comprehensive performance that complies with environmental regulations while ensuring long lifespan and high reliability is a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to provide an electrolyte for high-voltage boron-free aluminum electrolytic capacitors, its preparation method, and its application, aiming to solve the technical problems in the prior art where the loss tangent of boron-free high-voltage electrolytes increases rapidly during long-term operation at high temperatures, leading to capacitor overheating failure and poor reliability.

[0006] To address the aforementioned technical problems, this invention provides an electrolyte for high-voltage boron-free aluminum electrolytic capacitors. This electrolyte does not contain boron or its compounds and comprises the following components by weight percentage: 5% to 20% pure water as a co-solvent; 5% to 10% an organic amine salt of at least one carboxylic acid as a solute; and the balance being a main solvent. The main solvent is selected from at least one of alcohol solvents, ether solvents, amide solvents, and polyol ester solvents. The organic amine salt of the carboxylic acid is a salt formed by the reaction of a carboxylic acid moiety and an organic amine moiety. The carboxylic acid moiety is selected from at least one of straight-chain carboxylic acids, branched-chain carboxylic acids, and cyclic carboxylic acids, and the organic amine moiety is selected from at least one of methylamine, ethylamine, ethanolamine, isopropanolamine, dimethylamine, diethylamine, diethanolamine, trimethylamine, triethylamine, and triethanolamine.

[0007] Optionally, the electrolyte comprises the following components by weight percentage: 8% to 15% pure water as a co-solvent; 6% to 9% an organic amine salt of at least one carboxylic acid as a solute; and the balance being a main solvent.

[0008] Optionally, the main solvent is ethylene glycol or γ-butyrolactone.

[0009] Optionally, the carboxylic acid moiety is selected from at least one of adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, isoserbacic acid, and 2-methylazelaic acid.

[0010] Optionally, the carboxylic acid portion is azelaic acid or sebacic acid.

[0011] Optionally, the organic amine portion is diethanolamine or triethanolamine.

[0012] Optionally, the solute is triethanolamine azelaic acid or diethanolamine sebacate.

[0013] Optionally, the main solvent is ethylene glycol.

[0014] Optionally, in the electrolyte composition, a portion of the main solvent is replaced by 3% to 15% of additives; the additives are selected from at least one of corrosion inhibitors, hydrogen absorbers, and pressure enhancers and high-temperature stabilizers.

[0015] Optionally, the additive comprises phosphoric acid as a corrosion inhibitor and / or p-nitrophenol as a hydrogen absorber.

[0016] Optionally, the additive comprises 0.1% to 1% phosphoric acid and / or 0.5% to 2% p-nitrophenol by weight.

[0017] The present invention also provides a method for preparing the electrolyte according to any of the preceding claims, comprising the following steps: mixing the main solvent in the components required for preparing the electrolyte with an organic amine salt of a carboxylic acid; if the electrolyte is an electrolyte containing additives, further mixing the additives to obtain a first mixture; adding the pure water to the first mixture and stirring until homogeneous to obtain the electrolyte.

[0018] The present invention also provides the application of the electrolyte described in any of the foregoing claims in the preparation of high-voltage boron-free aluminum electrolytic capacitors.

[0019] The electrolyte provided by this invention, by using an organic amine salt of a carboxylic acid with excellent thermal stability as the solute and introducing a specific proportion of pure water as the co-solvent, produces significant beneficial effects. First, the decomposition temperature of the organic amine salt is much higher than that of the unstable inorganic ammonium salt used in existing boron-free solutions, fundamentally inhibiting the decomposition of the electrolyte at high temperatures. Simultaneously, the addition of pure water synergistically works with the organic amine salt, further suppressing the rapid increase in the loss tangent of the capacitor under high-temperature loads, avoiding abnormal heating and premature failure of the capacitor, thereby significantly extending the capacitor's lifespan and improving reliability. Second, the introduction of pure water effectively improves the conductivity of the electrolyte, reduces the equivalent series resistance of the capacitor, reduces internal losses during operation, and also enhances the solubility of the solute at low temperatures, preventing its precipitation in low-temperature environments and ensuring the capacitor's ability to operate over a wide temperature range. Finally, the electrolyte formulation of this invention is completely free of boron and its compounds, complying with environmental regulations. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. 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 an electrolyte preparation method according to an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram comparing the performance results of embodiments of the present invention and several comparative examples in high-temperature load life tests. The reference numerals are explained as follows: 101: Step of mixing the main solvent, solute, and optional additives; 102: Step of stirring the mixture until completely dissolved; 103: Step of adding pure water; 104: Step of continuing stirring until the system is homogeneous; 200: Schematic diagram of performance comparison; 201: Coordinate system; 202: Abscissa; 203: Y-axis; 204: Curve A, representing the performance curve of the embodiment of the present invention; 205: Curve B, representing the performance curve of Comparative Example 1 (boron-containing scheme); 206: Curve C, representing the performance curve of Comparative Example 2 (inorganic ammonium salt scheme); 207: Curve D, representing the performance curve of Comparative Example 3 (scheme without pure water). Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The described embodiments should not be regarded as limitations on this application. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] Unless otherwise defined, all technical and scientific terms used in the embodiments of this application have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in the embodiments of this application is for the purpose of describing the embodiments of this application only and is not intended to limit this application.

[0025] Before providing a further detailed description of the embodiments of this application, the nouns and terms involved in the embodiments of this application will be explained, and the nouns and terms involved in the embodiments of this application shall be interpreted as follows.

[0026] (1) Main solvent: refers to the component with the highest content in the electrolyte, which serves as the basic solvent medium and plays the role of dissolving other components. In the technical solution of this application, it can be selected from at least one of alcohol solvents, ether solvents, amide solvents and polyol ester solvents to provide the basic physicochemical environment for the electrolyte system.

[0027] (2) Co-solvent: refers to pure water as specifically mentioned in this application. Its function is not simply as a filler or diluent, but rather to work synergistically with the main solvent and be added in a specific ratio to significantly adjust the conductivity of the electrolyte, reduce the equivalent series resistance (ESR) of the capacitor, and improve the solubility of the solute at low temperatures to prevent precipitation, thereby optimizing the overall electrical performance and temperature characteristics of the capacitor.

[0028] (3) Solute: refers to the organic amine salt of at least one carboxylic acid specifically mentioned in this application. It is the core functional component in the electrolyte that provides conductive ions, and its chemical structural stability directly determines the lifespan and reliability of the capacitor under high temperature and high pressure operating conditions. The solute is a salt formed by one or more carboxylic acid molecules and one or more organic amine molecules through an acid-base neutralization reaction.

[0029] (4) Additives: These are optional functional components in this application, added to further improve a specific property of the electrolyte. For example, corrosion inhibitors and passivators are used to protect the surface of the aluminum electrode, hydrogen absorbers are used to eliminate trace gases that may be generated during the electrochemical reaction, and voltage withstand enhancers and high-temperature stabilizers are used to enhance the stability of the capacitor under extreme operating conditions. When additives are added, they replace an equal amount of the main solvent to maintain the balance of the overall formulation system.

[0030] (5) Loss Tangent (DF value): This is a key electrical performance parameter used to measure the energy loss of a capacitor. An ideal capacitor has zero energy loss, while in actual capacitors, energy loss exists due to factors such as dielectric polarization, leakage current, and resistance. The smaller the DF value, the smaller the energy loss, the higher the efficiency, and the less heat generated during operation. In high-temperature load life tests of capacitors, the rate of change of the DF value is a core indicator for evaluating the chemical stability of the electrolyte and the long-term reliability of the capacitor. A stable and slowly increasing DF value means that the capacitor has a longer service life.

[0031] This application aims to provide a high-performance electrolyte for high-voltage boron-free aluminum electrolytic capacitors, addressing the technical challenges of existing boron-free electrolyte solutions that suffer from a sharp increase in loss tangent (DF value), poor reliability, and short lifespan under high-temperature loads due to the use of unstable inorganic ammonium salts. The core technical concept of this application lies in constructing a novel boron-free electrolyte system that synergistically combines a specific main solvent, an organic amine salt of a carboxylic acid as a solute, and pure water as a co-solvent. This system achieves, and even surpasses, the electrical performance and long-term operational stability of traditional boron-containing solutions while ensuring full compliance with environmental regulations.

[0032] Specifically, this application provides an electrolyte for a high-voltage boron-free aluminum electrolytic capacitor that does not contain any boron or its compounds. The basic composition of this electrolyte consists of 5% to 20% by weight of pure water as a co-solvent, 5% to 10% by weight of an organic amine salt of at least one carboxylic acid as a solute, and the balance being a main solvent. This ternary system design is the fundamental structure of this invention. The main solvent can be selected from a wide range of solvents, including at least one of alcohols, ethers, amides, and polyol esters, providing a basic dissolution environment for the system. Unlike the prior art that directly uses inorganic ammonium salts, this application uses an organic amine salt of a carboxylic acid as the solute. The design aims to utilize the much higher thermal stability of organic amine salts compared to inorganic ammonium salts to fundamentally suppress the decomposition of the electrolyte at high temperatures. This is because organic amine salts have a higher decomposition temperature, and even after long-term operation of the capacitor, when the electrolyte environment may change from weakly acidic to weakly alkaline, they can still maintain structural stability and are less prone to decomposition and gas generation, thereby avoiding an increase in internal pressure and rapid performance degradation of the capacitor. By employing organic amine salts with excellent thermal stability, the core defect of existing boron-free solutions, which suffer from short lifespan due to solute instability, has been solved, thus achieving high reliability for the capacitor.

[0033] Furthermore, a key innovation of this invention lies in the introduction of 5% to 20% pure water as a co-solvent. In existing technologies, the presence of water is typically avoided to achieve high voltage resistance. However, through extensive experimental research, the inventors discovered that in organic amine salt systems, a specific amount of pure water is not only harmless but also brings significant synergistic benefits. The principle is that pure water, as a strongly polar solvent, effectively promotes the dissociation of organic amine salts, thereby significantly improving the ionic conductivity of the electrolyte. High conductivity means lower equivalent series resistance (ESR) for the capacitor, which directly reduces the capacitor's energy loss and heat generation during operation, thus contributing to extended lifespan. Simultaneously, the introduction of pure water improves the solubility of organic amine salts in nonpolar or weakly polar main solvents, especially at low temperatures, effectively preventing solute precipitation and ensuring the capacitor's normal operation over a wide temperature range, such as -40°C. By introducing a specific proportion of pure water as a co-solvent, this invention solves the problems of low conductivity and limited low-temperature performance in traditional anhydrous organic amine salt systems, achieving a comprehensive improvement in electrical performance.

[0034] In a preferred embodiment, the component content of the above-mentioned basic formulation has been further optimized. In this embodiment, the electrolyte consists of 8% to 15% pure water, 6% to 9% organic amine salt of carboxylic acid, and the balance being the main solvent by weight percentage. This narrower content range is a performance-optimized range obtained through extensive experimental screening based on a wide range. Its design aims to achieve a good balance of various performance indicators of the electrolyte. For example, when the pure water content is too low (below 8%), the improvement effect on conductivity is not significant; while when it is too high (above 15%), although the conductivity continues to increase, it may have a potential negative impact on the long-term withstand voltage and high-temperature stability of the capacitor. Similarly, a solute content in the range of 6% to 9% can maintain the fluidity and viscosity of the system at an ideal state while ensuring sufficient conductive ions. By limiting the component content to this preferred range, capacitor products with good performance consistency and superior overall performance can be manufactured with a higher yield.

[0035] In another preferred embodiment, the specific type of the main solvent is specified, preferably ethylene glycol or γ-butyrolactone. This specification is based on a comprehensive consideration of cost, performance, and process applicability. Ethylene glycol, as a common alcohol solvent, is widely available, inexpensive, and possesses good solubility and a wide liquid temperature range, making it a cost-effective and performance-balanced choice for achieving the technical solution of this invention, suitable for large-scale industrial production. γ-Butyrolactone, as an ester solvent, has a high dielectric constant, which imparts higher conductivity to the electrolyte, thereby resulting in a lower ESR value for the capacitor. Therefore, when the application scenario has extremely high requirements for capacitor loss, using γ-butyrolactone as the main solvent can achieve superior electrical performance. This specific selection of the main solvent provides a flexible technical path for different application needs and cost objectives.

[0036] Furthermore, to obtain superior and stable performance, the chemical structure of the organic amine salt of the carboxylic acid, serving as the core solute, was refined. In a preferred embodiment, the carboxylic acid portion of the organic amine salt is selected from at least one of adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, isoserbanoic acid, and 2-methylazelaic acid. These are all medium- to long-chain dicarboxylic acids, designed to form salt molecules with longer chains and greater steric hindrance, which helps to form a more stable and denser protective layer on the electrode surface. Simultaneously, their salts generally exhibit better thermal stability than short-chain carboxylic acid salts. By providing this validated list of preferred carboxylic acids, clear guidance is provided for solute selection, ensuring that the formed organic amine salt possesses excellent fundamental properties.

[0037] Building upon the above, a more preferred embodiment further limits the carboxylic acid portion to azelaic acid or sebacic acid. Azelaic acid and sebacic acid stand out in the above list, and experimental data show that the organic amine salts formed from them exhibit particularly outstanding performance in terms of thermal stability, solubility, and synergistic effects with pure water and the main solvent. Electrolytes prepared using these two carboxylic acids produce capacitors with a relatively gradual increase in DF value during stringent high-temperature load life tests, demonstrating excellent lifespan performance. Therefore, limiting the carboxylic acid portion to azelaic acid or sebacic acid represents a preferred technical practice direction of the present invention.

[0038] Correspondingly, in another preferred embodiment, the organic amine portion of the organic amine salt of the carboxylic acid is limited, preferably to diethanolamine or triethanolamine. Both are alkanolamines, containing both an amino group capable of reacting with the carboxylic acid to form a salt and a hydrophilic hydroxyl group. This structural characteristic results in salts with good thermal stability and better compatibility with pure water in the system, contributing to the formation of a homogeneous and stable solution system. Triethanolamine, in particular, has a more sterically hindered molecular structure, resulting in salts that are more effective in suppressing electrolyte decomposition. By limiting the organic amine portion to these two proven preferred alkanolamines, the overall performance of the solute is further ensured.

[0039] To further specify the above preferred embodiments, in a particularly preferred embodiment, the solute is directly limited to triethanolamine azelaic acid salt or diethanolamine sebacate salt. This combines the aforementioned preferred carboxylic acid moiety and preferred organic amine moiety, directly focusing on two specific compounds with excellent performance verified through extensive experimentation. This limitation directly corresponds to the preferred embodiments of the present invention, with clear and significant technical effects, providing performance assurance for the most demanding high-reliability applications. By directly limiting the solute to these two specific salts, a very stable and highly protective technical point is constructed.

[0040] In a more specific preferred embodiment, the above-mentioned technical solutions are combined in a powerful way. This embodiment specifies that when the solute is triethanolamine azelate or diethanolamine sebacate, the main solvent is specifically ethylene glycol. The principle of this combination is to combine a high-performance solute with a cost-effective and performance-balanced main solvent, forming a formulation that combines good technical performance and commercial viability. Ethylene glycol can effectively dissolve these two preferred organic amine salts and forms a stable and homogeneous liquid phase with pure water in the system, working together synergistically. This specific combination directly corresponds to the embodiment of the present invention with excellent results and has extremely high practical value.

[0041] To further expand the functionality of the electrolyte and adapt to more diverse application needs, in one optional embodiment, additives are introduced based on any of the aforementioned electrolyte components. Specifically, a portion of the main solvent is replaced by 3% to 15% of the additive. This "replacement" approach is designed to introduce new functional components by sacrificing a portion of the main solvent's volume, without altering the ratio of the auxiliary solvent (pure water) to the core solute or disrupting the synergistic effect of the basic ternary system. The additives can be selected from at least one of corrosion inhibitors, hydrogen absorbers, and voltage enhancers and high-temperature stabilizers. By introducing these functional additives, while maintaining the excellent performance of the basic system, secondary problems such as electrode corrosion and trace gas generation that may occur during long-term capacitor operation can be specifically addressed, thereby further improving the overall reliability and durability of the capacitor.

[0042] In a further embodiment, the specific types of the above-mentioned additives are defined, preferably including phosphoric acid as a corrosion inhibitor and / or p-nitrophenol as a hydrogen absorber. Phosphoric acid is a very effective corrosion inhibitor and passivator for aluminum anode foil, forming a dense aluminum phosphate protective film on the aluminum foil surface, effectively preventing the electrolyte from corroding the electrodes, especially under high-temperature environments. p-Nitrophenol is a highly efficient hydrogen absorber (or depolarizer), capable of reacting with and consuming trace amounts of hydrogen that may be generated during the electrochemical process, thereby preventing gas from accumulating inside the capacitor and generating pressure, avoiding the risk of capacitor bulging or even bursting. By introducing these two specific and proven effective additives, the long-term operational reliability of the capacitor can be significantly improved.

[0043] In a more refined embodiment, the dosage of the two preferred additives is limited. Specifically, the additives comprise 0.1% to 1% phosphoric acid and / or 0.5% to 2% p-nitrophenol by weight. This content range is an optimal dosage range determined based on extensive experimental data. Too low a dosage will result in ineffective corrosion inhibition or hydrogen absorption; too high a dosage may introduce other side reactions or adversely affect the basic electrical properties of the electrolyte. For example, excessive phosphoric acid may affect the acid-base balance of the electrolyte. Therefore, precisely controlling the additive dosage within this range aims to achieve maximum functional gain with minimal addition while avoiding any potential negative effects, thus enabling fine-tuning of performance.

[0044] This application also provides a method for preparing any of the above-described electrolytes. Please refer to... Figure 1This figure is a schematic flowchart of an electrolyte preparation method provided in an embodiment of this application. The method includes the following steps: First, a mixing step 101 is performed, in which the main solvent of the components required for preparing the electrolyte and the organic amine salt of the carboxylic acid as a solute are mixed in a clean container equipped with a stirring device at room temperature (e.g., 25°C). If the formulation contains additives, the additives are added in this step. Subsequently, a dissolution step 102 is performed, in which the mixture in the container is continuously stirred until all solid components (such as the organic amine salt and some solid additives) are completely dissolved in the main solvent, forming a clear first mixture. The purpose of this step is to ensure that the functional solid components are sufficiently dispersed and dissolved before the subsequent addition of water, avoiding solid precipitation or dissolution difficulties caused by local concentration changes due to the addition of pure water. After the first mixture is formed, a water addition step 103 is performed, in which a predetermined amount of pure water as an auxiliary solvent is slowly added to the first mixture. Finally, homogenization step 104 is performed, in which pure water is added and stirring is continued for a period of time, for example, 15 minutes, to ensure that the pure water and the first mixture of organic phases are fully miscible, ultimately yielding a clear, homogeneous, and stable target electrolyte. This specific order of addition—that is, dissolving the solids in the main organic solvent first, and then adding pure water last—is a key process step to ensure the uniformity and stability of the final electrolyte quality.

[0045] Furthermore, this application also provides an application of the electrolyte described in any one of claims 1 to 11, which is used in the preparation of high-voltage boron-free aluminum electrolytic capacitors. The specific application process includes: using anode and cathode foils prepared from high-purity aluminum foil through etching and forming processes, with electrolytic paper as an insulating layer, the anode foil, insulating paper, cathode foil, and another layer of insulating paper are sequentially stacked and wound into a capacitor core package. Then, the core package is placed in a vacuum drying oven for drying to remove moisture and volatile impurities. After drying, any of the electrolytes prepared above is injected into the core package under vacuum, ensuring it fully wets the electrode foils and insulating paper. After impregnation, the core package is assembled into an aluminum shell and sealed with a sealing plug. Finally, the packaged capacitor undergoes an aging treatment, i.e., voltage is applied at a certain temperature to repair any minor damage that may have occurred to the electrode foils during processing and to form a stable interface between the electrolyte and the electrode surface. By using the electrolyte of the embodiments of this application, high-voltage aluminum electrolytic capacitors that are boron-free and possess excellent high-temperature life and reliable electrical performance can be successfully manufactured, meeting the dual requirements of modern electronics industry for high performance, long life and environmental protection.

[0046] To illustrate the technical solution of this application more specifically, specific formulations and performance test data will be used for explanation below. It should be noted that the following embodiments and comparative examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0047] First, various electrolytes were prepared according to the following formulation and a standardized preparation method. The general preparation method is as follows: At room temperature (25°C), a predetermined amount of organic main solvent was added to a clean beaker equipped with a magnetic stirrer, and stirring was started. A predetermined amount of an organic amine salt of a carboxylic acid as a solute, along with optional additives, was added slowly and sequentially, stirring continuously until the solid components were completely dissolved. Finally, a predetermined amount of pure water was added as a co-solvent while stirring, and stirring was continued until the system was clear and homogeneous, yielding the target electrolyte.

[0048] Electrolyte A was prepared, comprising, by weight: 700g ethylene glycol as the main solvent, 80g triethanolamine azelaic acid salt as the solute, 150g purified water as the auxiliary solvent, and 10g phosphoric acid and 10g p-nitrophenol as additives. In this formulation, the purified water content is 15%, the solute content is 8%, the additive content is 2%, and the balance is ethylene glycol.

[0049] Electrolyte B was prepared, the only difference between it and electrolyte A being that the solute was replaced with 80g of sebacate diethanolamine salt; all other components and amounts were identical. This example was used to verify the performance of different preferred solutes.

[0050] Electrolyte C was prepared, and its formulation differed from that of electrolyte A only in that the main solvent was replaced with 700g of γ-butyrolactone; all other components and amounts were the same. This example was used to verify the applicability of different main solvents.

[0051] Electrolyte D was prepared, comprising, by weight: 600 g ethylene glycol (60%), 100 g triethanolamine azelaic acid salt (10%), 200 g purified water (20%), and 100 g composite additive (10%, comprising 50 g mannitol and 50 g phosphoric acid). This example is used to verify the effectiveness of the invention at the boundary of the claimed component content range.

[0052] For comparison, three comparative electrolytes were prepared. Comparative electrolyte E (Prior Art - Boron-containing scheme): composed of 850g ethylene glycol, 50g boric acid, and 100g ammonium adipate. Comparative electrolyte F (Prior Art - Boron-free scheme): composed of 900g ethylene glycol and 100g ammonium adipate (inorganic ammonium salt). Comparative electrolyte G (Invention System - Defective Pure Water): composed of 920g ethylene glycol and 80g triethanolamine azelaic acid.

[0053] Basic physicochemical properties of the prepared electrolytes A to G were tested. The conductivity of each electrolyte was measured at 25°C, and their state was observed at -40°C. The test results showed that the conductivity of electrolytes A, B, C, and D (containing pure water) was significantly higher than that of the comparative electrolyte G (not containing pure water) (e.g., electrolyte A was 4.5 mS / cm, while electrolyte G was only 2.5 mS / cm). This strongly demonstrates that pure water, as a co-solvent, can effectively improve the conductivity of the electrolyte, thereby reducing the ESR of the capacitor. Furthermore, at -40°C, all electrolytes of the present invention remained clear liquids, without solute precipitation or solidification, exhibiting excellent low-temperature performance.

[0054] Most importantly, using the aforementioned seven electrolytes and employing the same electrode foil, insulating paper, and other materials, aluminum electrolytic capacitors with specifications of 450V / 100μF were assembled. All capacitors were placed in a 105℃ constant temperature chamber and subjected to a rated DC voltage of 450V for a high-temperature load life test lasting up to 2000 hours. At specific time points during the test (0h, 500h, 1000h, 2000h), the capacitors were removed and allowed to return to room temperature before their key performance indicator—loss tangent (DF)—was tested.

[0055] Please see Figure 2 Figure 200 is a schematic diagram comparing the performance of embodiments of this application with several comparative examples in high-temperature load life tests. In the coordinate system 201 of this figure, the horizontal axis 202 represents the test time (unit: hours), and the vertical axis 203 represents the measured loss tangent (DF). Four performance comparison curves are plotted in the figure. Curve A 204 represents the performance of the capacitor using electrolyte A of the basic embodiment of this invention. As can be seen from the figure, its DF value increases very slowly and linearly throughout the 2000-hour test, steadily increasing from an initial 0.12 to 0.18 after 2000 hours, showing excellent stability. Curve B 205 represents the capacitor using the comparative example electrolyte E of the conventional boron-containing scheme. Its DF value change trend is very close to that of curve A 204, reaching 0.20 after 2000 hours. This indicates that the boron-free scheme of this invention is completely comparable to or even superior to mature boron-containing technology in terms of life stability.

[0056] In stark contrast, curve C 206 represents a capacitor using a comparative electrolyte F with an existing boron-free defect-free solution (inorganic ammonium salt). Its DF value rises sharply shortly after the start of the test, reaching 0.45 after approximately 1000 hours, at which point the capacitor fails due to excessive internal losses and severe overheating. This vividly illustrates the technical defects described in the background section. Finally, curve D 207 represents a capacitor using a comparative electrolyte G lacking the core component, pure water. Although it also uses a stable organic amine salt, the lack of synergistic effect from pure water results in a significantly steeper DF value increase than curve A 204, reaching 0.40 after 2000 hours, a performance far inferior to the complete solution of this invention. Figure 2 The comparative test results demonstrate the correctness and advancement of the core technology concept of "organic amine salt + pure water" in this invention. Through this synergistic system, the technical problems of short lifespan and poor reliability of existing boron-free electrolytes have been successfully solved.

[0057] In a preferred embodiment of this application, an electrolyte for high-voltage boron-free aluminum electrolytic capacitors with excellent overall performance is provided. The electrolyte is prepared strictly according to the following proportions: the main solvent is ethylene glycol, the solute is triethanolamine azelaic acid, the co-solvent is pure water, and phosphoric acid and p-nitrophenol are added as functional additives. Specifically, the weight percentages are: approximately 70% ethylene glycol, 8% triethanolamine azelaic acid, 15% pure water, 1% phosphoric acid, and 1% p-nitrophenol.

[0058] In this preferred embodiment, each component plays a precise and synergistic role. Ethylene glycol, as a well-balanced and inexpensive main solvent, forms the basic framework of the electrolyte. Azelaic acid triethanolamine salt, as a solute formed from a preferred C9 diacid and a preferred triethanolamine, possesses a long-chain and steric hindrance structure that endows the system with high thermal stability, providing technical assurance for the capacitor to withstand high temperatures and pressures over extended periods. 15% pure water, as a key auxiliary solvent, not only improves the system's conductivity to an ideal level, reducing the capacitor's internal resistance and power consumption, but also ensures complete dissolution of the solute throughout the entire operating temperature range (especially in the low-temperature region), preventing performance drift. Furthermore, 1% phosphoric acid forms a robust passivation film on the anode aluminum foil surface, effectively resisting electrochemical corrosion, while 1% p-nitrophenol serves to absorb and eliminate any trace amounts of hydrogen gas that may be generated, helping to eliminate the safety hazard of pressure buildup inside the capacitor.

[0059] When preparing the electrolyte of this preferred embodiment, strict adherence to... Figure 1The process is as follows: First, 80g of triethanolamine azelaic acid, 10g of phosphoric acid, and 10g of p-nitrophenol are dissolved in 700g of ethylene glycol and stirred until completely dissolved, yielding a clear first mixture. Then, 150g of pure water is slowly added while continuously stirring, and stirring continues until the entire system is homogeneous and transparent. The capacitor prepared using this electrolyte exhibits the following performance in high-temperature load life testing: Figure 2 As shown by curve A 204, this embodiment exhibits a long and stable lifespan comparable to traditional boron-containing solutions, while also helping to mitigate the environmental regulatory risks associated with boron. This embodiment integrates all the preferred features of the present invention, achieving a comprehensive technical effect of environmental protection, high efficiency, long lifespan, and high reliability through precise synergy among the components. It is a specific technical solution of the present invention.

Claims

1. An electrolyte for high-voltage boron-free aluminum electrolytic capacitors, characterized in that, The electrolyte does not contain boron or its compounds. It consists of the following components by weight percentage: 5% to 20% pure water as a co-solvent; 5% to 10% of an organic amine salt of at least one carboxylic acid as a solute; and the balance being the main solvent; The main solvent is selected from at least one of alcohol solvents, ether solvents, amide solvents, and polyol ester solvents; The organic amine salt of the carboxylic acid is a salt formed by the reaction of the carboxylic acid moiety and the organic amine moiety. The carboxylic acid moiety is selected from at least one of straight-chain carboxylic acids, branched-chain carboxylic acids, and cyclic carboxylic acids, and the organic amine moiety is selected from at least one of methylamine, ethylamine, ethanolamine, isopropanolamine, dimethylamine, diethylamine, diethanolamine, trimethylamine, triethylamine, and triethanolamine.

2. The electrolyte according to claim 1, characterized in that, The electrolyte consists of the following components by weight percentage: 8% to 15% pure water as a co-solvent; 6% to 9% an organic amine salt of at least one carboxylic acid as a solute; and the balance being the main solvent.

3. The electrolyte according to claim 1 or 2, characterized in that, The main solvent is ethylene glycol or γ-butyrolactone.

4. The electrolyte according to any one of claims 1 to 3, characterized in that, The carboxylic acid moiety is selected from at least one of the following: iodic acid, pimelic acid, octanoic acid, azelaic acid, sebacate, undecanoic acid, isoserbanoic acid, and 2-methylazelaic acid.

5. The electrolyte according to claim 4, characterized in that, The carboxylic acid portion is azelaic acid or sebacic acid.

6. The electrolyte according to any one of claims 1 to 5, characterized in that, The organic amine portion is diethanolamine or triethanolamine.

7. The electrolyte according to claim 1, characterized in that, The solute is triethanolamine azelaic acid or diethanolamine sebacate.

8. The electrolyte according to claim 7, characterized in that, The main solvent is ethylene glycol.

9. The electrolyte according to any one of claims 1 to 8, characterized in that, In the electrolyte composition, a portion of the main solvent is replaced by 3% to 15% additives; the additives are selected from at least one of corrosion inhibitors, hydrogen absorbers, and pressure enhancers and high-temperature stabilizers, and the additives contain phosphoric acid as a corrosion inhibitor and / or p-nitrophenol as a hydrogen absorber. The additive contains 0.1% to 1% phosphoric acid and / or 0.5% to 2% p-nitrophenol by weight.

10. A method for preparing the electrolyte according to any one of claims 1 to 9, characterized in that, Includes the following steps: The main solvent in the components required for preparing the electrolyte is mixed with an organic amine salt of carboxylic acid. If the electrolyte is an electrolyte containing additives as defined in claim 9, the additives are further mixed to obtain a first mixture. The pure water is added to the first mixture and stirred until homogeneous to obtain the electrolyte.

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