Electrolyte solution for electric double-layer capacitor, containing additive, and electric double-layer capacitor using same

Abstract

The present invention relates to an electrolyte solution for an electric double-layer capacitor, containing an additive, and an electric double-layer capacitor using same. The technical subject matter of the present invention provides the electrolyte solution for an electric double-layer capacitor, the solution comprising an electrolyte salt, an organic solvent and an additive, wherein the additive is boron trifluoride (BF3), and a reaction thereof with moisture (H2O), which is present in the electric double-layer capacitor, produces hydrogen fluoride (HF) and removes moisture, thereby allowing the electric double-layer capacitor to have high-temperature stability.

Description

Electrolyte for electric double layer capacitors containing additives, electric double layer capacitor using the same

[0001] The present invention relates to an electrolyte for an electric double layer capacitor containing an additive, and an electric double layer capacitor using the same.

[0002] Electric Double Layer Capacitors (EDLCs) consist of electrodes containing activated carbon and an electrolyte, offering the advantages of a simple structure and excellent durability. Due to these characteristics, EDLCs are suitable as energy storage devices that undergo repeated charging and discharging over long periods, and are widely utilized in various fields, including industry and electronic devices. In particular, EDLCs maintain their performance well even with repeated use, making them suitable for applications requiring a long lifespan.

[0003] However, electric double layer capacitors have the disadvantage of low energy density compared to batteries, which store large amounts of energy through high energy density. In other words, while electric double layer capacitors offer high output and long lifespan, their low energy density still limits their use in applications requiring high-density energy.

[0004] To overcome this, increasing the operating voltage of electric double layer capacitors is considered a critical task. Since energy density increases proportionally to the square of the voltage as the operating voltage rises, increasing the voltage can be a key approach to expanding the application range of electric double layer capacitors. The operating voltage of electric double layer capacitors is determined by the stability limits of materials such as activated carbon and electrolyte salts; therefore, technology is required to overcome physical and chemical limitations by withstanding high voltages, either by lowering the impurity content of the materials constituting existing electric double layer capacitors or by fabricating them with new materials.

[0005] Accordingly, the development of additives that suppress degradation of electric double layer capacitors and enable stable operation even at high voltages, while maintaining the existing activated carbon electrode and electrolyte composition, has emerged as an important task. To address these technical requirements, the inventors have developed a technology that significantly improves voltage stability and durability by utilizing a specific additive while maintaining the existing activated carbon electrode and electrolyte composition, thereby completing the present invention.

[0006] The present invention was developed to resolve the aforementioned problems, and its technical objective is to provide an electrolyte for an electric double layer capacitor containing an additive, and an electric double layer capacitor using the same, which possesses long lifespan and high-temperature stability while maintaining the existing activated carbon electrode and electrolyte composition, thereby suppressing degradation and enabling stable operation even at high voltages, as well as overcoming the limitations of low energy density and operating voltage.

[0007] To solve the above technical problem, the present invention provides an electrolyte for an electric double layer capacitor comprising an electrolyte salt, an organic solvent, and an additive, wherein the additive is boron trifluoride (BF3), and the additive is characterized by removing the moisture (H2O) present in the electric double layer capacitor by generating hydrogen fluoride (HF) through a reaction with the moisture, thereby providing high-temperature stability of the electric double layer capacitor.

[0008] In the present invention, the electrolyte is characterized by enabling the electric double layer capacitor to have high temperature stability at least 70°C.

[0009] In the present invention, the concentration of the electrolyte salt is characterized as being 0.5 to 2 M.

[0010] In the present invention, the additive is characterized by being included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0011] In the present invention, the electrolyte salt is characterized by comprising at least one cation among alkylammonium and alkylpyrrolidinium; and a tetrafluoroborate anion.

[0012] Meanwhile, in order to solve the above technical problem, the present invention provides an electric double layer capacitor comprising an anode, a cathode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte.

[0013] According to the present invention, which provides a means for solving the above problem, by using a boron trifluoride (BF3) additive, degradation occurring during the charging and discharging process of an electric double layer capacitor can be suppressed while maintaining the electrode composition of the existing electrolyte. Through this, the stability of capacitance is maintained even under conditions of high current density, and there is an advantage of significantly improving the reliability of the electric double layer capacitor in various application environments.

[0014] Furthermore, the electrolyte of the present invention suppresses electrolyte salt decomposition and electrode degradation under high temperature and high voltage conditions, thereby significantly improving the lifespan compared to conventional electrolytes even under harsh accelerated degradation conditions. This not only enables the long-term use of electric double-layer capacitors in high-temperature environments but also has the effect of simultaneously ensuring long lifespan and high-temperature stability.

[0015] Furthermore, the addition of BF3 allows for the maintenance of high voltage stability and energy density without capacity degradation, thereby enhancing the potential for use in energy storage devices requiring high power and high energy density. This implies that it can contribute to expanding the usability of electric double-layer capacitors in various high-value-added applications, such as electric vehicles, smart grids, and energy storage systems.

[0016] Furthermore, the electrolyte of the present invention provides an economical and efficient technology that improves the performance and durability of electric double-layer capacitors using only a small amount of BF3 additive without the need to change materials or manufacturing processes, and thus has the practical advantage of being easily applicable to existing equipment without increasing the complexity of the production process.

[0017] Figure 1 is a graph comparing the change in capacity with increasing current when using the electrolyte according to Example 1 and Comparative Example 1.

[0018] Figure 2 is a graph showing the change in capacity retention rate due to accelerated degradation to determine the high-temperature stability characteristics when using the electrolyte according to Example 1 and Comparative Example 1.

[0019] Figure 3 is a graph comparing the change in capacity with increasing current when using the electrolyte according to Example 2 and Comparative Example 2.

[0020] Figure 4 is a graph showing the change in capacity retention rate due to accelerated degradation to determine the high-temperature stability characteristics when using the electrolyte according to Example 2 and Comparative Example 2.

[0021] Figure 5 is a graph comparing the change in capacity with increasing current when using the electrolyte according to Example 3 and Comparative Example 3.

[0022] Figure 6 is a graph showing the change in capacity retention rate due to accelerated degradation to determine the high-temperature stability characteristics when using the electrolyte according to Example 3 and Comparative Example 3.

[0023] Figure 7 is a graph showing the change in capacity retention rate due to accelerated degradation to determine the high-temperature stability characteristics when using the electrolyte according to Example 4 and Comparative Example 4.

[0024] Figure 8 is a graph showing the change in capacity retention rate due to accelerated degradation to determine the high-temperature stability characteristics when using the electrolyte according to Example 5 and Comparative Example 5.

[0025] Figure 9 is a graph comparing the change in capacity retention rate due to accelerated degradation to determine the high-temperature stability characteristics when using the electrolyte according to Example 6 and Comparative Example 6.

[0026] The present invention is susceptible to various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the invention to specific embodiments, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention. Similar reference numerals have been used for similar components in the description of each drawing.

[0027] The terms used in this invention are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this invention, terms such as "comprising" or "having" are intended to specify the presence of the features, numbers, steps, reactions, components, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, reactions, components, or combinations thereof.

[0028] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0029] The present invention relates to an electrolyte for an electric double layer capacitor comprising an additive. The present invention is characterized in that the electrolyte for an electric double layer capacitor comprises an electrolyte salt, an organic solvent, and an additive, wherein the additive is boron trifluoride (BF3), and the additive removes moisture by generating hydrogen fluoride (HF) through a reaction with moisture (H2O) present in the electric double layer capacitor, thereby providing high-temperature stability to the electric double layer capacitor.

[0030] Electrolyte salts dissolve in organic solvents and dissociate into cations and anions to transmit electric current, acting as electrolytes in electric double-layer capacitors. When the concentration of the electrolyte salt is in the range of 0.5 to 2 M, optimal ionic conductivity and electrochemical stability can be provided in electric double-layer capacitors. If the electrolyte salt concentration is less than 0.5 M, the ion density in the electrolyte decreases, leading to reduced ionic conductivity and potentially degrading the capacitance and performance of the electric double-layer capacitor; if it exceeds 2 M, ion interactions become stronger, which may restrict ion movement and reduce the efficiency of the electrochemical reaction. Preferably, the electrolyte salt concentration is 1 M.

[0031] As the electrolyte salt, a compound containing at least one cation selected from alkylammonium and alkylpyrrolidinium and a tetrafluoroborate anion may be used. For example, tetraethylammonium tetrafluoroborate (TEA BF4) and 1,1-dimethylpyrrolidinium tetrafluoroborate (Py 11 It may be composed of at least one of BF4), triethylmethylammonium tetrafluoroborate (1-Methyldiethylammonium tetrafluoroborate, TEMA BF4), and trimethylethylammonium tetrafluoroborate (1-Ethyltrimethylammonium tetrafluoroborate, TMEA BF4).

[0032] Among them, TEA BF4 consists of tetraethylammonium cations and tetrafluoroborate (BF4 - It is a compound composed of anions, represented by the following chemical structure 1.

[0033] [Chemical Structure 1]

[0034]

[0035] Also Py 11 In the case of BF4, 1,1-dimethylpyrrolidinium cation and tetrafluoroborate (BF4 - It is a compound composed of anions, represented by the following chemical structure 2.

[0036] [Chemical Structure 2]

[0037]

[0038] In addition, TMEA BF4 is trimethylethylammonium tetrafluoroborate (1-Ethyltrimethylammonium tetrafluoroborate), represented by the following chemical structure 3.

[0039] [Chemical Structure 3]

[0040]

[0041] Organic solvents dissolve electrolyte salts and dissociate them into cations and anions, and nitrile-based organic solvents can be used, and acetonitrile is an example of a nitrile-based organic solvent.

[0042] The additive added to the electrolyte is preferably boron trifluoride (BF3) represented by the following chemical structure 4. Boron trifluoride of chemical structure 4 is a molecule in which a central atom, boron, and three fluorine atoms are symmetrically arranged and bonded around the boron.

[0043] [Chemical Structure 4]

[0044]

[0045] When BF3 reacts with trace amounts of water present inside the pores of the activated carbon of the electrode or in the electrolyte, the water is consumed to form B2O3 and HF, acting as a water scavenger. In an electric double layer capacitor, water consists of water molecules embedded inside the pores of the activated carbon or impurities present in minute amounts of about a few ppm in the electrolyte. Although activated carbon has high adsorption capacity and retains water well, water molecules located deep within the micropores are difficult to remove even with a vacuum pump.

[0046] For this reason, in order to remove trace amounts of water present in the activated carbon or electrolyte within the electrode, the BF3 additive first generates hydrogen fluoride (HF) through the following reaction scheme 1 by reacting with water molecules.

[0047] [Reaction Equation 1]

[0048] 3H2O + 2BF3 → 6HF + B2O3

[0049] B2O3 generated in reaction equation 1 has low solubility in organic solvents such as acetonitrile in electric double layer capacitors, so it remains in the electric double layer capacitor in a solid state and does not participate in chemical reactions.

[0050] B2O3 can separate the HF generated together from the activated carbon and dilute it in the electrolyte, but since it does not act as an acid in acetonitrile, it does not have a significant effect of corroding the electrode with acid.

[0051] The electrolysis of water produces hydrogen and oxygen gases, while the CO and CO2 gases generated by the decomposition of activated carbon at high temperatures and voltages cause the pressure in the electric double layer capacitor to rise rapidly. To safely protect against an abnormal rise in internal pressure, the use of the electric double layer capacitor is terminated by opening the safety vent, a safety device that releases excessive pressure.

[0052] Various functional groups on the electrode surface undergo secondary and tertiary reactions with gases such as CO and CO2, generating and accumulating various types of organic substances on the electrode. This degrades the original properties of activated carbon and increases the resistance of the electrode. Therefore, even a small amount of water can effectively dissociate acids and promote electrochemical reactions as a highly polar substance; however, when water is removed, the intensity of the reaction affecting the degradation of the electrode becomes very weak.

[0053] Water, present in small amounts as an impurity on the electrodes, gradually leaks out as the electric double layer capacitor operates; at this time, the water [contains] tetrafluoroborate anions (BF4) in the electric double layer capacitor electrolyte. - It causes a reaction such as Equation 2 with ) and results in an additional increase in resistance. The reaction products such as Equation 2 play a role in promoting the activity of the acid by the trace amount of water that remains unreacted.

[0054] [Reaction Equation 2]

[0055] H2O + BF4 - → HF + OH - + BF3

[0056] HF acts as a weak acid only in the presence of water, and its role as an acid is extremely limited in organic solvents from which water has been removed. When water inside the pores of activated carbon is electrolyzed, hydrogen and oxygen are generated at both electrodes, respectively, and hydrogen ions and hydroxide ions are also produced, which promotes corrosion and deterioration of the electrode components. By removing water, deterioration caused by such products is also suppressed (see Reaction Equation 3).

[0057] [Reaction Equation 3]

[0058] Cathode: 2H2O + 2e - → H2 + 2OH -

[0059] Anode: H2O → 1 / 2O2 + 2H + + 2e -

[0060] Furthermore, when the temperature rises due to the operation of the electric double layer capacitor, it accelerates reactions that corrode the electrodes and cause degradation, especially OH - It has the effect of weakening organic materials such as binders.

[0061] Ultimately, water infiltrated into the pores of the activated carbon constituting the electrode, which have a diameter of less than a few nanometers, or functional groups on the surface of the activated carbon, degrades the performance of the electric double layer capacitor. Furthermore, increases in voltage and temperature cause rapid degradation of the electrode, preventing it from functioning properly physically and electrochemically. Accordingly, to increase the voltage of the electric double layer capacitor and ensure durability even at high temperatures, it is important to remove the water from within the pores.

[0062] The BF3 additive may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte. If the BF3 additive is added in an amount less than 0.1 wt%, there is insufficient amount to react with water that has penetrated into the pores of the activated carbon of the electrode or with trace amounts of water present in the electrolyte, and if it exceeds 5 wt%, it is undesirable as it may instead cause side reactions. More preferably, it may be included in a range of 0.3 to 3 wt%.

[0063] Therefore, in the present invention, water, which is one of the major impurities that initiate such degradation, is reacted with a BF3 additive, but the reactivity is drastically reduced and the starting point of the continuous degradation reaction is eliminated, thereby allowing the lifespan of the electric double layer capacitor to be extended even when used at high temperatures or when the voltage is increased.

[0064] The embodiments of the present invention will be described in more detail below. However, the following embodiments are provided merely to aid in understanding the present invention and do not limit the scope of the present invention.

[0065] <Example 1>

[0066] A 1 M electrolyte was prepared by dissociating TEA BF4 electrolyte salt in acetonitrile, and a BF3 additive was added at 0.3 wt% relative to the total weight of the electrolyte to complete the electrolyte.

[0067] <Example 2>

[0068] Py in acetonitrile 11 A 1 M electrolyte was prepared by dissociating BF4 electrolyte salt, and a BF3 additive was added at 0.2 wt% relative to the total weight of the electrolyte to complete the electrolyte.

[0069] <Example 3>

[0070] A 1 M electrolyte was prepared by dissociating TMEA BF4 electrolyte salt in acetonitrile, and a BF3 additive was added at 0.3 wt% relative to the total weight of the electrolyte to complete the electrolyte.

[0071] <Example 4>

[0072] 0.5 M TEA BF4 electrolyte salt and 0.5 M Py in acetonitrile 11 An electrolyte solution with a total electrolyte concentration of 1 M was prepared by dissociating BF4 electrolyte salt, and a BF3 additive was added at 3 wt% of the total weight of the electrolyte to complete the electrolyte solution.

[0073] <Example 5>

[0074] An electrolyte solution with a total electrolyte concentration of 1 M was prepared by dissociating 0.5 M TEA BF4 electrolyte salt and 0.5 M TMEA BF4 electrolyte salt in acetonitrile, and an electrolyte solution was completed by adding 0.3 wt% of a BF3 additive to the total weight of the electrolyte solution.

[0075] <Example 6>

[0076] 0.5 M TMEA BF4 electrolyte salt and 0.5 M Py in acetonitrile 11 An electrolyte solution with a total electrolyte concentration of 1 M was prepared by dissociating BF4 electrolyte salt, and an electrolyte solution was completed by adding 0.3 wt% of BF3 additive to the total weight of the electrolyte solution.

[0077] <Comparative Example 1>

[0078] 1 M TEA BF4 (tetraethylammonium tetrafluoroborate) in AN (acetonitrile), which is commonly used in electric double layer capacitors, was prepared as the electrolyte.

[0079] <Comparative Example 2>

[0080] 1 M Py, commonly used in electric double layer capacitors 11 BF4 (1,1-Dimethylpyrrolidinium tetrafluoroborate) in AN (acetonitrile) was prepared as the electrolyte. For this purpose, Py 11 A 1 M electrolyte was prepared by dissociating BF4 into AN.

[0081] <Comparative Example 3>

[0082] 1 M TMEA BF4in AN(acetonitrile) was prepared as the electrolyte in acetonitrile.

[0083] <Comparative Example 4>

[0084] 0.5 M TEA BF4 electrolyte salt and 0.5 M Py in acetonitrile 11 An electrolyte solution with a total electrolyte concentration of 1 M was prepared by dissociating BF4 electrolyte salt.

[0085] <Comparative Example 5>

[0086] An electrolyte solution with a total electrolyte concentration of 1 M was prepared by dissociating 0.5 M TEA BF4 electrolyte salt and 0.5 M TMEA BF4 electrolyte salt in acetonitrile.

[0087] <Comparative Example 6>

[0088] 0.5 M TMEA BF4 electrolyte salt and 0.5 M Py in acetonitrile 11 An electrolyte solution with a total electrolyte concentration of 1 M was prepared by dissociating BF4 electrolyte salt.

[0089] <Test Example 1> Analysis of Long Life and High Temperature Stability of Example 1 and Comparative Example 1

[0090] In this test example, 1 M TEA BF4 (Comparative Example 1) and 1 M TEA BF4 + 0.3 wt% BF3 (Example 1) electrolytes were used in electric double layer capacitors to compare the change in capacitance with increasing current (high-power characteristics) and analyze high-temperature stability under accelerated degradation conditions.

[0091] First, high-output characteristics were compared. In this regard, Figure 1 shows the current density (0.1 A g -1 ~ 10 A g -1 This is a graph showing the relationship between specific capacitance (F / g) and the number of cycles according to the change. However, the charging and discharging in Fig. 1 represent the capacitance when charged to 2.7 V and discharged to 0 V at 25°C.

[0092] Referring to FIG. 1, both Comparative Example 1 (1 M TEA BF4) and Example 1 (1 M TEA BF4 + 0.3 wt% BF3) showed a tendency for specific capacitance to gradually decrease as current density increased. Example 1, containing the BF3 additive, at a high current density of 10 A g -1 The specific capacitance was stably maintained even under these conditions. This indicates that the BF3 additive operates without adverse effects that impair capacity during the charging and discharging process, and that the capacity of Example 1 is similar to that of Comparative Example 1 even when the current density is increased, meaning that the capacity is not reduced even when the BF3 additive is added.

[0093] Next, an accelerated degradation test was compared. In this regard, Figure 2 is a graph showing the change in capacity-specific capacitance according to accelerated degradation (h).

[0094] For severe conditions of accelerated degradation, the charge was applied up to 3.0 V, a voltage higher than the upper charge limit in Fig. 1. Both electrolytes were then charged at 0.1 A g in a constant temperature bath at 70°C. -1 After charging to 3.0 V under these conditions, the change in capacitance was observed after charging at a constant voltage of 3.0 V and maintaining the voltage for 50 hours. Capacitance verification was performed at 25°C to compare the changes before and after degradation. The capacitance of the degraded capacitor was 0.1 A g after cooling the capacitor, which had been exposed to high temperature and high voltage, to 25°C for 24 hours. -1 It was obtained by charging to 2.7 V and discharging to 0 V under constant current conditions. After checking the capacity, it was returned to 3.0 V and 70°C to continue accelerated degradation.

[0095] Looking at the graph in Fig. 2, Example 1 (1 M TEA BF4 + 0.3 wt% BF3) showed a decrease in capacitance initially (up to about 100 hours), but the specific capacitance remained stable after 200 hours. On the other hand, Comparative Example 1 (1 M TEA BF4) experienced a rapid decrease in capacitance after 200 hours, causing the capacitor's lifespan to end.

[0096] It can be confirmed that the chemical stability and electrochemical performance of the electrolyte are maintained as the electric double layer capacitor operates stably for a long time in a high-temperature environment of at least 70°C or higher. Through this, the electrolyte containing the BF3 additive possesses strong durability against electrochemical degradation even under high temperature and high voltage conditions, thereby extending the lifespan of the electric double layer capacitor. Therefore, since it has been proven that the electrolyte containing the BF3 additive has superior charge-discharge stability and lifespan performance under accelerated degradation conditions compared to conventional electrolytes, this demonstrates that it is an effective electrolyte with high-temperature stability and long-life characteristics for electric double layer capacitors.

[0097] <Test Example 2> Analysis of Long Life and High Temperature Stability of Example 2 and Comparative Example 2

[0098] In this test example, 1 M Py in an electric double layer capacitor 11 BF4 (Comparative Example 2) and 1 M Py 11 Capacity and accelerated degradation were compared using an electrolyte of BF4 + 0.2 wt% BF3 (Example 2). In addition, the electrolyte performance was comprehensively analyzed by including the results of 1 M TEA BF4 (Comparative Example 1).

[0099] First, FIG. 3 shows the current density (0.1 A g) when using the electrolyte according to Example 2 and Comparative Example 2. -1 ~ 10 A g -1This is a graph showing the relationship between specific capacitance (F / g) and cycle number according to change. However, the charging and discharging in Fig. 3 represent the capacitance when charged to 2.7 V and discharged to 0 V at 25℃.

[0100] Comparative Example 2 (1 M Py 11 BF4) and Example 2 (1 M Py 11 BF4 + 0.2 wt% BF3) showed a tendency for the specific capacitance to gradually decrease as the current density increased. However, Example 2 showed a high current density (10 A g -1 The specific capacitance was maintained stably even in ), and no reduction in capacity due to the BF3 additive was observed. This demonstrates that the BF3 additive operates without adverse effects that impair the electric double layer capacitor capacitance during the charge-discharge process, and that the capacity of Example 2 is similar to that of Comparative Example 2 even when the current density is increased. Through this, it was confirmed that Example 2, containing the BF3 additive, provides stable charge-discharge performance without capacity degradation, and that its electrochemical performance at room temperature and under normal operation is equivalent to that of the conventional electrolyte.

[0101] Meanwhile, FIG. 4 is a graph showing the change in specific capacitance under accelerated degradation (h) conditions. Referring to FIG. 4, electric double layer capacitors using three types of electrolytes (Comparative Example 1, Comparative Example 2, Example 2) were all subjected to 0.1 A g in a constant temperature bath at 70°C. -1 Under these conditions, the capacitance was checked after charging to 3.0 V, followed by 3.0 V constant voltage charging and maintaining the voltage for 50 hours. Capacitance verification was performed at 25°C to compare the changes before and after degradation. The capacitance of the degraded electric double layer capacitor was 0.1 A g after cooling the electric double layer capacitor, which had been exposed to high temperature and high voltage, to 25°C for 24 hours. -1It was obtained by charging to 2.7 V and discharging to 0 V under constant current conditions. After checking the capacity, it was returned to 3.0 V and 70°C to continue accelerated degradation.

[0102] Comparative Example 1 (1 M TEA BF4) showed a rapid decrease in specific capacitance after approximately 200 hours, and the electric double layer capacitor lifespan ended. Comparative Example 2 (1 M Py 11 BF4) maintained specific capacitance for up to approximately 300 hours, which is longer than Comparative Example 1, but subsequently decreased rapidly and reached the end of its lifespan. On the other hand, Example 2 (1 M Py 11 BF4 (0.2 wt% BF3) showed a decrease in capacity for approximately 100 hours initially, but after 300 hours, the life-maintaining effect of the BF3 additive became clearly apparent, and the specific capacitance was maintained stably.

[0103] Through this test example, it was confirmed that the electrolyte containing the BF3 additive (Example 2) showed superior results compared to the conventional electrolyte (Comparative Example 1, Comparative Example 2) in charge / discharge performance and accelerated degradation life tests.

[0104] <Test Example 3> Analysis of Long Life and High Temperature Stability of Example 3 and Comparative Example 3

[0105] In this test example, the capacitance and accelerated degradation were compared using an electrolyte of 1 M TMEA BF4 + 0.3 wt% BF3 (Example 3) in an electric double layer capacitor. In addition, the performance of the electrolyte was comprehensively analyzed by including the results of 1 M TMEA BF4 (Comparative Example 3).

[0106] FIG. 5 shows the current density (0.1 A g) when using the electrolyte according to Example 3 and Comparative Example 3. -1 ~ 10 A g -1This is a graph showing the relationship between specific capacitance (F / g) and cycle number according to change. However, the charging and discharging in Fig. 5 represent the capacitance when charged to 2.7 V and discharged to 0 V at 25℃.

[0107] Referring to FIG. 5, Example 3 (1 M TMEA BF4 + 0.3 wt% BF3) and Comparative Example 3 (1 M TMEA BF4) showed a tendency for the specific capacitance to gradually decrease as the current density increased. In the case of Example 3, similar to Example 1, at a high current density (10 A g -1 Specific capacitance was stably maintained even in ), and no reduction in volume due to the BF3 additive was observed.

[0108] This demonstrates that the BF3 additive operates without adverse effects that impair the capacitance of the electric double layer capacitor during the charging and discharging process, and that the capacitance of Example 3 is similar to that of Comparative Example 3 even when the current density is increased. Through this, it was confirmed that Example 3, containing the BF3 additive, provides stable charging and discharging performance without a decrease in capacity, and that its electrochemical performance at room temperature and under normal operation is equivalent to that of the conventional electrolyte. In other words, in Example 3 and Comparative Example 3, no adverse effects, such as a decrease in capacitance (capacitance) depending on the use of the BF3 additive, were observed.

[0109] Figure 6 is a graph comparing the change in capacitance retention rate due to accelerated degradation to investigate the high-temperature stability characteristics when using the electrolytes according to Example 3 and Comparative Example 3. Figure 6 shows the change in specific capacitance under the Accelerated degradation (h) condition, wherein electric double layer capacitors using Example 3 and Comparative Example 3 are subjected to 0.1 A g in a constant temperature bath at 70°C. -1Under these conditions, the capacitance was checked after charging to 3.0 V, followed by 3.0 V constant voltage charging and maintaining the voltage for 50 hours. Capacitance verification was performed at 25°C to compare the changes before and after degradation. The capacitance of the degraded electric double layer capacitor was 0.1 A g after cooling the electric double layer capacitor, which had been exposed to high temperature and high voltage, to 25°C for 24 hours. -1 It was obtained by charging to 2.7 V and discharging to 0 V under constant current conditions. After checking the capacity, it was returned to 3.0 V and 70°C to continue accelerated degradation.

[0110] In particular, as shown in Fig. 6, Comparative Example 3 (1 M TMEA BF4) and Example 3 (1 M TMEA BF4 + 0.3 wt% BF3) showed similar levels of lifespan performance up to 300 hours, but from 350 hours, the superiority of Example 3 compared to Comparative Example 3 can be confirmed.

[0111] <Test Example 4> Analysis of Long Life and High Temperature Stability of Examples 4, 5, and 6 and Comparative Examples 4, 5, and 6

[0112] In this test example, high-temperature stability characteristics were analyzed by comparing the change in capacity retention rate due to accelerated degradation of the electrolytes prepared in Examples 4, 5, and 6 and Comparative Examples 4, 5, and 6. However, since no decrease in capacity due to the addition of BF3 additive was confirmed in any of the electrolytes of Examples 4, 5, and 6 and Comparative Examples 4, 5, and 6, the comparison of capacity at room temperature was omitted, and high-temperature stability characteristics were determined by comparing the change in capacity retention rate due to accelerated degradation.

[0113] In this regard, FIG. 7 is a graph comparing the change in capacity-specific capacitance according to accelerated degradation (h) to investigate the high-temperature stability characteristics when using the electrolytes according to Example 4 and Comparative Example 4, where both electrolytes 0.1 A g in a constant temperature bath at 70°C -1Under these conditions, the change in capacitance was observed after charging to 3.0 V, followed by 3.0 V constant voltage charging and maintaining the voltage for 50 hours. Capacitance verification was performed at 25°C to compare changes before and after degradation. The capacitance of the degraded capacitor was 0.1 A g after cooling the capacitor, which had been exposed to high temperature and high voltage, to 25°C for 24 hours. -1 It was obtained by charging to 2.7 V and discharging to 0 V under constant current conditions. After checking the capacity, it was returned to 3.0 V and 70°C to continue accelerated degradation.

[0114] Looking at the graph in Fig. 7, Example 4 (0.5 M TEA BF4 + 0.5 M Py 11 It can be confirmed that the addition of BF3 additive in BF4+ 3 wt% BF3 helped improve lifespan.

[0115] Figure 8 is a graph comparing the change in capacity retention rate due to accelerated degradation to investigate the high-temperature stability characteristics when using the electrolytes according to Example 5 and Comparative Example 5. Referring to Figure 8, in the accelerated degradation test of Example 5 (0.5 M TEA BF4 + 0.5 M TMEA BF4 + 0.3 wt% BF3) and Comparative Example 5 (0.5 M TEA BF4 + 0.5 M TMEA BF4), it was confirmed that after 100 hours, the life retention effect was superior in Example 5, which has the BF3 additive added, compared to Comparative Example 5.

[0116] Figure 9 is a graph comparing the change in capacity retention rate due to accelerated degradation to investigate the high-temperature stability characteristics when using the electrolytes according to Example 6 and Comparative Example 6. Referring to Figure 9, Example 6 (0.5 M TMEA BF4 + 0.5 M Py 11 BF4+ 0.3 wt% BF3) and Comparative Example 6 (0.5 M TMEA BF4+ 0.5 M Py 11As a result of the accelerated degradation test of BF4), it can be confirmed that the lifespan maintenance by the BF3 additive in Example 6 is superior from 100 hours onwards compared to Comparative Example 6.

[0117] From the results of Test Example 4, it was found that the BF3 additive improved the lifespan of the electric double layer capacitor not only in a single electrolyte salt but also in a complex electrolyte salt containing at least two types. In particular, since the use of the BF3 additive did not show the disadvantage of reducing capacitance, the lifespan improvement effect can be supported by the use of the BF3 additive.

[0118] In summary, the present invention is characterized by improving the long lifespan and high-temperature stability of an electric double layer capacitor through an electrolyte containing a BF3 additive. According to these characteristics, it is possible to realize an electric double layer capacitor capable of suppressing degradation under high temperature and high voltage conditions and maintaining the stability of specific capacitance while maintaining the existing activated carbon electrode and electrolyte composition, which is of significant importance for the development of high-performance energy storage devices. In particular, since it can exhibit excellent lifespan characteristics even under high current density and accelerated degradation conditions without capacitance reduction caused by the BF3 additive, it is expected that an electric double layer capacitor capable of stable energy storage for a long time and providing reliable performance even in high-temperature environments can be secured.

[0119] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not to limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such embodiments. The scope of protection of the present invention shall be interpreted by the claims, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

Claims

1. An electrolyte for an electric double layer capacitor comprising an electrolyte salt, an organic solvent, and an additive, wherein The above additive is boron trifluoride (BF3), and Hydrogen fluoride (HF) is generated by a reaction with moisture (H2O) present in the electric double layer capacitor, thereby removing the moisture, Electrolyte for an electric double layer capacitor containing an additive, characterized by providing high-temperature stability of the electric double layer capacitor.

2. In Paragraph 1, The above electrolyte is, Electrolyte for an electric double layer capacitor containing an additive, characterized in that the electric double layer capacitor has high temperature stability at least 70°C.

3. In Paragraph 1, The concentration of the above electrolyte salt is, Electrolyte for an electric double layer capacitor containing an additive, characterized by being 0.5 to 2 M.

4. In Paragraph 1, The above additive is, Electrolyte for an electric double layer capacitor containing an additive, characterized by being included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

5. In Paragraph 1, The above electrolyte is, At least one cation among alkylammonium and alkylpyrrolidinium; and Electrolyte for an electric double layer capacitor containing an additive, characterized by including a tetrafluoroborate anion.

6. An electric double layer capacitor comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein An electric double layer capacitor characterized in that the above electrolyte is an electrolyte according to any one of claims 1 to 5.

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