Electrolyte additive for all-vanadium redox flow battery

Abstract

The invention relates to the technical field of energy storage, and discloses an all-vanadium redox flow battery electrolyte additive which comprises the following components in percentage by mass: 45-55% of modified coumarin, 40-50% of amino acetylacetone and 5-15% of nitrobenzaldehyde, the modified coumarin comprises at least one hydroxyl group; the amino acetylacetone is prepared by reacting acetylacetone with an ammonia source; the nitrobenzaldehyde is prepared by introducing at least one nitro group on an aromatic ring of benzaldehyde through nitration reaction. According to the electrolyte additive disclosed by the invention, the modified coumarin, the amino acetylacetone and the nitrobenzaldehyde are introduced, so that the stability of an electrolyte under a high-temperature condition is remarkably improved, and self-agglutination and precipitation of pentavalent vanadium ions in the electrolyte are reduced, so that possible safety problems such as short circuit or instability of the electrolyte are avoided; and the maintenance and replacement frequency of the electrolyte is also reduced.

Description

Technical Field

[0001] The invention relates to the technical field of energy storage, in particular to an electrolyte additive for an all-vanadium liquid flow battery. Background Art

[0002] Vanadium redox flow battery (VRFB) is a typical rechargeable energy storage system that has attracted widespread attention due to its high energy efficiency, long life and good scalability. This type of battery uses the conversion of vanadium ions between different valence states to store and release energy. Although VRFB has many advantages, its promotion of commercial application still faces some key technical challenges.

[0003] In the prior art, the thermal stability of the electrolyte is one of the main factors limiting the performance of all-vanadium flow batteries. During battery operation, especially in high temperature environments, pentavalent vanadium ions tend to self-aggregate and eventually precipitate, which not only affects the battery's charge and discharge efficiency, but may also lead to a decrease in the chemical stability of the electrolyte and a shortened battery life. In addition, the existing electrolyte is prone to performance degradation during long-term operation or repeated charge and discharge, which greatly limits the battery's availability and economic benefits.

[0004] Traditional solutions often try to solve these problems by adding stabilizers or adjusting the electrolyte formula. However, these methods do not fundamentally solve the problem of pentavalent vanadium ions self-polymerization at high temperatures, and often introduce new chemicals that may have an adverse effect on the electrochemical window of the electrolyte and the overall battery efficiency. For example, although some additives can inhibit the precipitation of vanadium ions to a certain extent, they may increase the viscosity of the electrolyte or cause other unstable chemical reactions. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides an electrolyte additive for an all-vanadium liquid flow battery, which solves the technical problem that under high-temperature operating conditions of the all-vanadium liquid flow battery, pentavalent vanadium ions are prone to self-aggregation and precipitation, resulting in decreased electrolyte stability and battery performance.

[0006] To achieve the above objectives, the present invention is implemented by the following technical scheme: an all-vanadium liquid flow battery electrolyte additive, the additive comprising the following components in mass percentage:

[0007] Modified coumarin 45~55%

[0008] The modified coumarin enhances the complexation with pentavalent vanadium ions by introducing hydroxyl groups into its molecular structure. Due to its multi-point binding characteristics, hydroxyl groups can form stable complexes with vanadium ions, reducing the free state of vanadium ions in the electrolyte, thereby preventing the self-aggregation and precipitation of vanadium ions at high temperatures.

[0009] Compared with traditional coumarin, the introduction of modified coumarin significantly improves the thermal and chemical stability of the complex, allowing the electrolyte to maintain functionality over a wider temperature range.

[0010] Aminoacetylacetone 40~50%

[0011] The amino group of aminoacetylacetone is introduced to increase the electron affinity of the acetylacetone molecule. This modification makes the complex with the pentavalent vanadium ion more solid, and the charge attraction between the positive charge of the amino group and the negative charge of the vanadium ion enhances the overall stability of the complex.

[0012] The introduction of amino groups not only enhances the complexation, but also improves the overall solubility and ionic conductivity of the electrolyte due to their polar properties.

[0013] Nitrobenzaldehyde 5~15%

[0014] The introduction of nitrobenzaldehyde is mainly to enhance the electrochemical stability and reaction efficiency of the electrolyte. As a strong electron-attracting group, the nitro group can improve the electrochemical activity of benzaldehyde and help optimize the redox reaction of the electrolyte.

[0015] While improving the electrochemical properties of the electrolyte, nitrobenzaldehyde also enhances the additive's resistance to high temperatures and chemical reactions, further preventing performance degradation during battery operation.

[0016] These three modified compounds do not act alone, but form a synergistic effect in the electrolyte, cooperating with each other to improve the overall performance of the electrolyte. Through this special ratio, the present invention not only improves the stabilization treatment of pentavalent vanadium ions by the electrolyte, but also optimizes the charge and discharge efficiency and cycle life of the battery under complex working conditions. The efficient complexing ability of the modified coumarin, the stable chelation of aminoacetylacetone, and the electrochemical activity of nitrobenzaldehyde work together to enable the electrolyte to maintain high performance under high temperature conditions, effectively avoiding the self-aggregation and precipitation of pentavalent vanadium ions.

[0017] Preferably, the modified coumarin includes at least one hydroxyl group, and the hydroxyl group is introduced into the aromatic ring of coumarin through a hydroxylation reaction.

[0018] The introduction of hydroxyl groups into the aromatic ring of coumarins is usually achieved by hydroxylation. This reaction can be carried out by a variety of methods, such as reduction or direct hydroxylation using nitrobenzene. The hydroxylation process usually needs to be carried out under specific conditions, such as in an alkaline or acidic environment, using a catalyst such as sodium borohydride or under the action of an oxidant.

[0019] The introduction of hydroxyl groups significantly changes the chemical properties of coumarin. Due to its polarity and electronegativity, hydroxyl groups can form strong coordination bonds with vanadium ions. The formation of such bonds helps stabilize pentavalent vanadium ions and prevents them from self-aggregation and precipitation in the electrolyte.

[0020] Preferably, the aminoacetylacetone is prepared by reacting acetylacetone with an ammonia source selected from one or more amino chemicals.

[0021] The amino group provides additional coordination sites to form a stable complex with the pentavalent vanadium ion, which helps prevent the vanadium ions from moving freely and aggregating in the electrolyte and reduces precipitation at high temperatures. In addition, the electron-donating properties of the amino group also help stabilize the oxidation state of the vanadium ion and improve the electrochemical stability of the battery.

[0022] The structural characteristics of aminoacetylacetone make it more resistant to decomposition caused by high temperature in the electrolyte. Compared with unmodified acetylacetone, its higher thermal stability helps to maintain the overall stability of the electrolyte.

[0023] Preferably, the nitrobenzaldehyde is prepared by introducing at least one nitro group into the aromatic ring of benzaldehyde through a nitration reaction.

[0024] As a strong electron-attracting group, the nitro group can increase the electrochemical activity of the benzaldehyde molecule. This improves the ability of nitrobenzaldehyde to participate in redox reactions in the electrolyte, thereby enhancing the battery's charge and discharge efficiency. During the battery charge and discharge process, nitrobenzaldehyde can act as an electron transfer medium to increase the reaction rate and efficiency.

[0025] The introduction of nitrobenzaldehyde not only enhances its solubility in the electrolyte, but also improves its stability under high temperature and long-term cycling conditions, which is crucial to improving the overall life and performance of the battery.

[0026] Although the main function of nitrobenzaldehyde is to improve electrochemical activity, it can also form a certain complexation with pentavalent vanadium ions, which helps to stabilize the vanadium ions in the electrolyte and reduce their self-aggregation and precipitation at high temperatures.

[0027] The present invention also provides a method for preparing an all-vanadium liquid flow battery electrolyte additive, comprising the following steps:

[0028] S1. Synthesis of Hydroxycoumarin

[0029] 1. Reaction materials: coumarin and brominating agent (usually bromine or cuprous bromide is used as the brominating agent).

[0030] 2. Reaction medium: The reaction is carried out in anhydrous dimethyl sulfoxide (DMSO), which helps to dissolve the reactants and promote the reaction.

[0031] 3. Catalyst: Add 10-20% volume of triethylamine as a basic catalyst to help the brominating agent react more effectively with the aromatic ring of coumarin.

[0032] 4. Reaction conditions: Stir at room temperature for 24 to 48 hours to ensure that the reaction proceeds fully.

[0033] 5. Post-treatment: Slowly add the reaction mixture into 2 to 5 volumes of water to precipitate the hydroxycoumarin, and then purify it by column chromatography.

[0034] S2. Synthesis of aminoacetylacetone

[0035] 1. Reaction materials: acetylacetone and nitroaniline.

[0036] 2. Molar ratio: Mix at a ratio of 1:1 to 1.5 to ensure that each acetylacetone molecule can react with enough nitroaniline.

[0037] 3. Reaction solvent: It is carried out in anhydrous ethanol, which serves as a good solvent and reaction medium.

[0038] 4. Catalyst: Add 1-5% volume of acetic acid to promote the reaction.

[0039] 5. Reaction conditions: Heat under reflux for 12 to 24 hours, then cool to room temperature.

[0040] 6. Post-treatment: Add 3 to 6 volumes of water to the reaction mixture to precipitate aminoacetylacetone, and purify by recrystallization.

[0041] S3. Synthesis of nitrobenzaldehyde

[0042] 1. Reaction material: benzaldehyde.

[0043] 2. Nitrating agent: a mixture of nitric acid and sulfuric acid (volume ratio is 1:2~3).

[0044] 3. Reaction conditions: Carry out nitration reaction at low temperature of 0-5°C for 1-2 hours.

[0045] 4. Post-treatment: Pour the reaction mixture into 4 to 8 volumes of ice water for neutralization and precipitation, and purify by column chromatography.

[0046] S4. Final mixing and drying of additives

[0047] 1. Mixing: Mix the purified hydroxycoumarin, aminoacetylacetone and nitrobenzaldehyde in a predetermined ratio.

[0048] 2. Solvent: Dissolve in dichloromethane or ethyl acetate and mix evenly.

[0049] 3. Drying: Remove the solvent under reduced pressure at 30-40°C to obtain a dry additive.

[0050] The preparation method of the present invention synthesizes a new type of electrolyte additive for all-vanadium liquid flow batteries by controlling the chemical reaction and conditions of each step. This additive not only improves the thermal stability and electrochemical performance of the battery, but also helps to improve the cycle life and charge and discharge efficiency of the battery.

[0051] Preferably, the step of purifying hydroxycoumarin by column chromatography in step S1 comprises: using silica gel as the stationary phase and using a mixed solvent system of ethyl acetate and n-hexane for gradient elution, wherein the volume ratio of ethyl acetate to n-hexane is 1:1-3.

[0052] Preferably, the recrystallization step in step S2 comprises: using a mixed solvent of ethanol and water, wherein the volume ratio of ethanol to water is 1:1 to 3.

[0053] Preferably, the step of column chromatography purification to obtain nitrobenzaldehyde in step S3 comprises: using silica gel as the stationary phase and using a mixed solvent system of ethyl acetate and n-hexane for gradient elution, wherein the volume ratio of ethyl acetate to n-hexane is 1:1 to 2.

[0054] The present invention provides an electrolyte additive for an all-vanadium liquid flow battery. It has the following beneficial effects:

[0055] 1. The electrolyte additive of the present invention significantly improves the stability of the electrolyte under high temperature conditions by introducing modified coumarin, aminoacetylacetone and nitrobenzaldehyde. The modified coumarin forms a stable complex with pentavalent vanadium ions through its hydroxyl group, effectively inhibiting the self-aggregation and precipitation of vanadium ions at high temperatures. This characteristic enables the electrolyte to maintain chemical stability in a wider temperature range, thereby improving the reliability and safety of the battery.

[0056] 2. The additive of the present invention significantly improves the electrochemical activity of the electrolyte by introducing aminoacetylacetone and nitrobenzaldehyde. Aminoacetylacetone improves its electrochemical stability and charge-discharge efficiency by increasing the coordination sites with vanadium ions. Nitrobenzaldehyde enhances the redox reaction ability of the electrolyte and improves the current efficiency during the charge-discharge process. These improvements not only improve the performance of the battery, but also extend the service life of the battery.

[0057] 3. The additive of the present invention can provide a more stable electrolyte environment at the chemical level, significantly improving the cycle stability of the battery. The synergistic effect of modified coumarin and aminoacetylacetone enables the electrolyte to maintain good chemical stability during repeated charge and discharge, reducing performance degradation.

[0058] 4. The use of the additive of the present invention reduces the self-aggregation and precipitation of pentavalent vanadium ions in the electrolyte, which not only avoids possible safety problems such as short circuit or electrolyte instability, but also reduces the maintenance and replacement frequency of the electrolyte. From an economic point of view, improving the stability of the electrolyte and the cycle life of the battery can reduce the cost of long-term operation and maintenance, making the all-vanadium liquid flow battery system more cost-effective. DETAILED DESCRIPTION

[0059] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0060] Embodiment 1:

[0061] Step S1: Preparation of hydroxycoumarin

[0062] Reactants: coumarin 10g, brominating agent (bromine water) 20mL

[0063] Reaction conditions: 100 mL of anhydrous dimethyl sulfoxide (DMSO), 15 mL of triethylamine (15% volume)

[0064] Stirring time: 48 hours at room temperature

[0065] Post-treatment: Add the reaction mixture into 400 mL of water to precipitate the product.

[0066] Purification: 8.5 g of hydroxycoumarin was obtained by column chromatography (silica gel, ethyl acetate: n-hexane = 1:1 gradient elution).

[0067] Step S2: Preparation of aminoacetylacetone

[0068] Reactants: 10 g acetylacetone, 11 g nitroaniline (molar ratio 1:1.2)

[0069] Reaction conditions: 100 mL of anhydrous ethanol, 2 mL of acetic acid (2% volume)

[0070] Heating time: 24 hours under reflux conditions

[0071] Post-treatment: After cooling to room temperature, add 500 mL of water to precipitate the product

[0072] Purification: 9.2 g of aminoacetylacetone was obtained by recrystallization (ethanol: water = 1:1).

[0073] Step S3: Preparation of nitrobenzaldehyde

[0074] Reactants: benzaldehyde 10g, nitric acid and sulfuric acid mixture (volume ratio 1:2) 30mL

[0075] Reaction conditions: 0-5℃, nitration reaction for 1.5 hours

[0076] Post-treatment: Pour the reaction mixture into 240 mL of ice water to precipitate the product

[0077] Purification: 8.8 g of nitrobenzaldehyde was obtained by column chromatography (silica gel, ethyl acetate: n-hexane = 1:2 gradient elution).

[0078] Step S4: Mixing of composite additives

[0079] Mixture: 4.5g hydroxycoumarin, 4g aminoacetylacetone, 1g nitrobenzaldehyde

[0080] Dissolution conditions: Dissolve in 100 mL of dichloromethane

[0081] Remove the solvent: evaporate dichloromethane at 30°C under reduced pressure to obtain 9g of dry powder of additive

[0082] Example 2

[0083] Step S1: Preparation of hydroxycoumarin

[0084] Reactants: Coumarin 12g, brominating agent (bromine water) 25mL

[0085] Reaction conditions: 120 mL of anhydrous dimethyl sulfoxide (DMSO), 18 mL of triethylamine (15% volume)

[0086] Stirring time: 36 hours at room temperature

[0087] Post-treatment: Add the reaction mixture into 480 mL of water to precipitate the product.

[0088] Purification: 10.2 g of hydroxycoumarin was obtained by column chromatography (silica gel, ethyl acetate: n-hexane = 1:2 gradient elution).

[0089] Step S2: Preparation of aminoacetylacetone

[0090] Reactants: 12 g acetylacetone, 13 g nitroaniline (molar ratio 1:1.3)

[0091] Reaction conditions: 120 mL of anhydrous ethanol, 3 mL of acetic acid (2.5% volume)

[0092] Heating time: 20 hours under reflux conditions

[0093] Post-treatment: After cooling to room temperature, add 600 mL of water to precipitate the product.

[0094] Purification: 11 g of aminoacetylacetone was obtained by recrystallization (ethanol: water = 1:2).

[0095] Step S3: Preparation of nitrobenzaldehyde

[0096] Reactants: 12 g benzaldehyde, 36 mL nitric acid and sulfuric acid mixture (volume ratio 1:3)

[0097] Reaction conditions: 0-5℃, nitration reaction for 1.5 hours

[0098] Post-treatment: Pour the reaction mixture into 300 mL of ice water to precipitate the product.

[0099] Purification: 10.5 g of nitrobenzaldehyde was obtained by column chromatography (silica gel, ethyl acetate: n-hexane = 1:1 gradient elution).

[0100] Step S4: Mixing of composite additives

[0101] Mixture: 5.5g hydroxycoumarin, 5g aminoacetylacetone, 1.5g nitrobenzaldehyde

[0102] Dissolution conditions: Dissolve in 120 mL of dichloromethane

[0103] Removal of solvent: dichloromethane was evaporated at 35°C under reduced pressure to obtain 11.5 g of dry powder of additive Example 3

[0104] Step S1: Preparation of hydroxycoumarin

[0105] Reactants: Coumarin 15g, brominating agent (bromine water) 30mL

[0106] Reaction conditions: 150 mL of anhydrous dimethyl sulfoxide (DMSO), 22.5 mL of triethylamine (15% volume)

[0107] Stirring time: 48 hours at room temperature

[0108] Post-treatment: Add the reaction mixture into 600 mL of water to precipitate the product.

[0109] Purification: 12.7 g of hydroxycoumarin was obtained by column chromatography (silica gel, ethyl acetate: n-hexane = 1:1 gradient elution).

[0110] Step S2: Preparation of aminoacetylacetone

[0111] Reactants: 15 g acetylacetone, 16 g nitroaniline (molar ratio 1:1.4)

[0112] Reaction conditions: 150 mL of anhydrous ethanol, 3.75 mL of acetic acid (2.5% volume)

[0113] Heating time: 24 hours under reflux conditions

[0114] Post-treatment: After cooling to room temperature, add 750 mL of water to precipitate the product

[0115] Purification: 13.5 g of aminoacetylacetone was obtained by recrystallization (ethanol: water = 1:2).

[0116] Step S3: Preparation of nitrobenzaldehyde

[0117] Reactants: 15 g benzaldehyde, 45 mL nitric acid and sulfuric acid mixture (volume ratio 1:2)

[0118] Reaction conditions: 0-5℃, nitration reaction for 1.5 hours

[0119] Post-treatment: Pour the reaction mixture into 375 mL of ice water to precipitate the product

[0120] Purification: 13.3 g of nitrobenzaldehyde was obtained by column chromatography (silica gel, ethyl acetate: n-hexane = 1:2 gradient elution).

[0121] Step S4: Mixing of composite additives

[0122] Mixture: 6g hydroxycoumarin, 5.5g aminoacetylacetone, 1.5g nitrobenzaldehyde

[0123] Dissolution conditions: Dissolve in 150 mL of dichloromethane

[0124] Remove the solvent: evaporate dichloromethane at 35°C under reduced pressure to obtain 13g of dry powder of additive

[0125] Example 4

[0126] Step S1: Preparation of hydroxycoumarin

[0127] Reactants: Coumarin 18g, brominating agent (bromine water) 36mL

[0128] Reaction conditions: 180 mL of anhydrous dimethyl sulfoxide (DMSO), 27 mL of triethylamine (15% volume)

[0129] Stirring time: 36 hours at room temperature

[0130] Post-treatment: Add the reaction mixture into 720 mL of water to precipitate the product.

[0131] Purification: 15.3 g of hydroxycoumarin was obtained by column chromatography (silica gel, ethyl acetate: n-hexane = 1:1 gradient elution).

[0132] Step S2: Preparation of aminoacetylacetone

[0133] Reactants: 18 g acetylacetone, 19 g nitroaniline (molar ratio 1:1.3)

[0134] Reaction conditions: 180 mL of anhydrous ethanol, 4.5 mL of acetic acid (2.5% volume)

[0135] Heating time: 24 hours under reflux conditions

[0136] Post-treatment: After cooling to room temperature, add 900 mL of water to precipitate the product.

[0137] Purification: 16.2 g of aminoacetylacetone was obtained by recrystallization (ethanol: water = 1:2).

[0138] Step S3: Preparation of nitrobenzaldehyde

[0139] Reactants: 18 g benzaldehyde, 54 mL nitric acid and sulfuric acid mixture (volume ratio 1:3)

[0140] Reaction conditions: 0-5℃, nitration reaction for 1.5 hours

[0141] Post-treatment: Pour the reaction mixture into 450 mL of ice water to precipitate the product

[0142] Purification: 16 g of nitrobenzaldehyde was obtained by column chromatography (silica gel, ethyl acetate: n-hexane = 1:1 gradient elution).

[0143] Step S4: Mixing of composite additives

[0144] Mixture: 7.5g hydroxycoumarin, 6g aminoacetylacetone, 2g nitrobenzaldehyde

[0145] Dissolution conditions: Dissolve in 180 mL of dichloromethane

[0146] Removal of solvent: dichloromethane was evaporated at 35°C under reduced pressure to obtain 15.5 g of dry powder of additive Example 5

[0147] Step S1: Preparation of hydroxycoumarin

[0148] Reactants: Coumarin 20g, brominating agent (bromine water) 40mL

[0149] Reaction conditions: 200 mL of anhydrous dimethyl sulfoxide (DMSO), 30 mL of triethylamine (15% volume)

[0150] Stirring time: 48 hours at room temperature

[0151] Post-treatment: Add the reaction mixture into 800 mL of water to precipitate the product.

[0152] Purification: 17 g of hydroxycoumarin was obtained by column chromatography (silica gel, ethyl acetate: n-hexane = 1:1 gradient elution).

[0153] Step S2: Preparation of aminoacetylacetone

[0154] Reactants: 20 g acetylacetone, 22 g nitroaniline (molar ratio 1:1.4)

[0155] Reaction conditions: 200 mL of anhydrous ethanol, 5 mL of acetic acid (2.5% volume)

[0156] Heating time: 24 hours under reflux conditions

[0157] Post-treatment: After cooling to room temperature, add 1000 mL of water to precipitate the product.

[0158] Purification: 18 g of aminoacetylacetone was obtained by recrystallization (ethanol: water = 1:2).

[0159] Step S3: Preparation of nitrobenzaldehyde

[0160] Reactants: 20 g benzaldehyde, 60 mL nitric acid and sulfuric acid mixture (volume ratio 1:3)

[0161] Reaction conditions: 0-5℃, nitration reaction for 1.5 hours

[0162] Post-treatment: Pour the reaction mixture into 500 mL of ice water to precipitate the product.

[0163] Purification: 18 g of nitrobenzaldehyde was obtained by column chromatography (silica gel, ethyl acetate: n-hexane = 1:1 gradient elution).

[0164] Step S4: Mixing of composite additives

[0165] Mixture: 9g hydroxycoumarin, 8g aminoacetylacetone, 3g nitrobenzaldehyde

[0166] Dissolution conditions: Dissolve in 200 mL of dichloromethane

[0167] Remove the solvent: evaporate dichloromethane at 35°C under reduced pressure to obtain 20g of dry powder of additive

[0168] Comparative Examples 1-5:

[0169] Comparative Example 1: The difference from the example is that unmodified coumarin, acetylacetone and benzaldehyde are used, and the remaining steps are the same. Formula: 50% coumarin, 45% acetylacetone, 5% benzaldehyde.

[0170] Comparative Example 2: The difference from the example is that the modified coumarin is 100% (only hydroxycoumarin, without other ingredients), and the other steps are the same. Formula: modified coumarin 100%.

[0171] Comparative Example 3: The difference from the example is that aminoacetylacetone is 100% (without other ingredients), and the remaining steps are the same. Formula: aminoacetylacetone 100%.

[0172] Comparative Example 4: The difference from the example is that nitrobenzaldehyde is 100% (without other ingredients), and the remaining steps are the same. 100% nitrobenzaldehyde.

[0173] Comparative Example 5: EDTA commonly used in the market is used as a metal complexing agent to replace the additives in the present invention. Formula: EDTA 100%.

[0174] Comparative experiment 1:

[0175] Purpose: To test the stability of different additives in electrolyte at high temperature (60°C).

[0176] Experimental conditions:

[0177] Temperature: 60℃

[0178] Electrolyte formula: vanadium sulfate (15%), sulfuric acid (25%), deionized water (60%), additives (5%) Number of charge and discharge cycles: 100 times

[0179] Experimental steps:

[0180] 1. Preparation of electrolyte:

[0181] According to the experimental objects, electrolytes containing the additives of the present invention and those of Comparative Examples 1-5 were prepared respectively.

[0182] The additive formula of each group of electrolyte is as follows:

[0183] The present invention: modified coumarin 50%, aminoacetylacetone 45%, nitrobenzaldehyde 5%

[0184] Comparative Example 1: Coumarin 50%, Acetylacetone 45%, Benzaldehyde 5%

[0185] Comparative Example 2: Modified Coumarin 100%

[0186] Comparative Example 3: Aminoacetylacetone 100%

[0187] Comparative Example 4: Nitrobenzaldehyde 100%

[0188] Comparative Example 5: EDTA 100%

[0189] 2. Prepare experimental equipment:

[0190] Each group of electrolyte is injected into the all-vanadium liquid flow battery system separately.

[0191] The test temperature was set to 60 °C to ensure that the temperature remained constant throughout the experiment.

[0192] 3. Carry out charge and discharge cycle test:

[0193] Each group of electrolytes was subjected to 100 charge and discharge cycles.

[0194] The capacity retention and coulombic efficiency were recorded after each cycle.

[0195] The experimental data are shown in Table 1 and Table 2:

[0196] Table 1 Comparison of capacity retention of all-vanadium liquid flow batteries under high temperature cycle conditions

[0197]

[0198]

[0199] Table 2 Performance of the Coulombic efficiency of all-vanadium liquid flow batteries in high temperature tests

[0200]

[0201]

[0202] From the experimental data in Table 1 and Table 2, we can get:

[0203] 1. Thermal stability analysis:

[0204] The special structural adjustment of the modified coumarin, aminoacetylacetone and nitrobenzaldehyde in the additive of the present invention enhances the complexation with pentavalent vanadium ions, thereby effectively preventing the precipitation and self-aggregation of vanadium ions at high temperatures. In particular, the introduction of hydroxyl groups in coumarin increases its affinity with vanadium ions, while aminoacetylacetone provides additional electron density to stabilize pentavalent vanadium ions. Nitrobenzaldehyde improves the overall solubility and electrochemical activity of the electrolyte through its strong electron attraction properties.

[0205] In contrast, the unmodified formula or the single modified component did not show such synergistic effect, resulting in insufficient thermal stability. Although EDTA, as a traditional metal complexing agent, works well at room temperature, its stabilizing effect on pentavalent vanadium at high temperature is not as good as the additive of the present invention.

[0206] 2. Electrochemical performance analysis

[0207] In the electrochemical performance test, the composite additive of the present invention exhibits lower internal resistance and wider electrochemical stability window. This is because the modified additive not only improves the conductivity of the electrolyte, but also reduces the interface resistance, promoting the effective charge transfer between the electrolyte and the electrode.

[0208] Due to the lack of effective structural optimization and synergistic effect, the comparative examples failed to match the additives of the present invention in terms of electrochemical window and charge-discharge efficiency. In particular, the electrochemical window of EDTA and unmodified mixed components is relatively narrow, which limits its application in battery systems with higher performance requirements.

[0209] 3. Cycle stability and efficiency:

[0210] The results of the cycle stability test show that the additive of the present invention can maintain a high capacity retention rate and coulombic efficiency during long-term cyclic use, which indicates that the additive can effectively inhibit the degradation of the electrolyte and the performance degradation of the battery.

[0211] Compared with the additives of the present invention, the capacity of all comparative examples decays rapidly during the cycle, especially when nitrobenzaldehyde is used alone, the capacity retention rate is low, indicating that a single component cannot provide sufficient electrolyte stability.

[0212] Through detailed analysis of the above experimental data, it can be seen that the innovative part of the additive of the present invention - namely, the thermal stability, electrochemical performance and cycle stability of the all-vanadium liquid flow battery electrolyte are enhanced through chemical modification and synergistic enhancement of components, which significantly improves the overall performance of the battery.

[0213] Comparative experiment 2: Electrochemical performance test

[0214] Objective: To evaluate the effects of additives on the electrochemical window and charge-discharge efficiency of electrolytes.

[0215] Test method:

[0216] Electrochemical Impedance Spectroscopy (EIS): Measures the internal resistance of an electrolyte.

[0217] Cyclic Voltammetry (CV): Measurement of the electrochemical stability window.

[0218] Testing equipment: electrochemical workstation.

[0219] Experimental steps:

[0220] 1. Preparation of test samples:

[0221] According to the experimental objects, electrolytes containing the additive of the present invention (same as comparative experiment 1) and comparative examples 1-5 were prepared respectively.

[0222] Each electrolyte formula contains vanadium sulfate (15%), sulfuric acid (25%), deionized water (59%), and additives (1%).

[0223] 2. Device settings:

[0224] Prepare the electrochemical test cell and fill it with the appropriate electrolyte.

[0225] Platinum electrodes were used as working and counter electrodes, and saturated calomel electrode was used as reference electrode.

[0226] 3. Electrochemical impedance spectroscopy (EIS) test:

[0227] Setting frequency range: 100kHz to 0.01Hz.

[0228] The applied AC voltage amplitude was 10 mV.

[0229] The measurement was performed at room temperature (25°C).

[0230] 4. Cyclic voltammetry (CV) test:

[0231] Scan rate: 10mV / s.

[0232] Potential range: 0V to 1.5V.

[0233] Perform at least three complete cycles at room temperature and record data from the third cycle to ensure stability.

[0234] The experimental data are shown in Table 3:

[0235] Table 3 Comparison of electrochemical performance evaluation of all-vanadium liquid flow battery electrolyte additives

[0236]

[0237] From the experimental data in Table 3, we can get:

[0238] 1. Electrochemical impedance spectroscopy (EIS) analysis

[0239] It can be seen from the experimental data that the internal resistance of the additive of the present invention is the lowest (15.2Ω), which is significantly lower than that of the comparative example. This result reflects the important contribution of the synergistic effect of modified coumarin, aminoacetylacetone and nitrobenzaldehyde in the additive to improving the conductivity of the electrolyte. In particular:

[0240] Modified coumarin: The introduction of hydroxyl groups increases the affinity with vanadium ions, promotes more efficient charge transfer, and reduces the resistance of the electrolyte.

[0241] Aminoacetylacetone: provides additional electron density to stabilize the pentavalent vanadium ion while improving the overall conductive path of the electrolyte through its polarity.

[0242] Nitrobenzaldehyde: Enhances the solubility of the electrolyte, reduces local charge accumulation, and thus reduces overall resistance.

[0243] The conventional complexing agents (such as EDTA) and the unmodified components in the comparative examples significantly increased the internal resistance due to their inability to form such a stable and conductive complex with the vanadium ions. The single-component modified additives, while outperforming the conventional complexing agents, failed to achieve the same effect as the additives of the present invention, confirming the importance of synergistic effects in improving resistance and conductivity.

[0244] 2. Cyclic voltammetry (CV) test analysis

[0245] The additive of the present invention exhibits the widest electrochemical window (1.48V), which not only shows its excellent electrochemical stability, but also indicates that it can operate safely and effectively in a wider range of operating voltages. In addition, the slight change in current from the first cycle to the third cycle shows its good electrochemical reversibility and stability. This is achieved by:

[0246] Modified coumarin: enhances the stability of the complex and reduces decomposition in electrochemical reactions.

[0247] Aminoacetylacetone and nitrobenzaldehyde: The combination of the two provides a more stable chemical environment in the electrolyte, reducing decomposition reactions under high voltage.

[0248] In contrast, the electrochemical windows of the comparative examples are narrower, especially EDTA and unmodified components show higher current decay, which indicates that they have poor stability in the electrochemical reaction and are easily deactivated during cycling.

[0249] Through in-depth analysis of comparative experimental data, it can be seen that the additive of the present invention has significant advantages in improving the electrochemical performance of the electrolyte of the all-vanadium liquid flow battery. These advantages are derived from the unique chemical modification of the components in the additive and the effective synergy between them, which not only improves the conductivity and electrochemical stability of the electrolyte, but also optimizes the performance of the battery under high temperature and high voltage operating conditions. In addition, the additive of the present invention provides a technical basis for achieving a more efficient and stable all-vanadium liquid flow battery by reducing the resistance of the electrolyte and widening the electrochemical window.

[0250] Comparative experiment 3: Cycle stability and efficiency test

[0251] Objective: To evaluate the effect of additives on battery performance after long-term cycling, especially capacity retention and coulombic efficiency.

[0252] Test conditions:

[0253] Temperature: 25℃

[0254] Charge and discharge rate: 0.5C

[0255] Experimental steps:

[0256] 1. Prepare the test electrolyte:

[0257] According to the experimental objects, electrolytes containing the additive of the present invention (same as comparative experiment 1) and comparative examples 1-5 were prepared respectively.

[0258] Basic electrolyte formula: vanadium sulfate (15%), sulfuric acid (25%), deionized water (59%), additives (1%).

[0259] 2. Prepare the battery and test equipment:

[0260] The tests were carried out using a standard all-vanadium flow battery cell.

[0261] Configure a battery test system to control and record charge and discharge parameters.

[0262] 3. Conduct long-term charge and discharge cycle test:

[0263] Each set of electrolytes was subjected to 200 charge and discharge cycles.

[0264] Set the battery to charge to 1.8V and discharge to 0.8V.

[0265] The experimental data are shown in Table 4 and Table 5:

[0266] Table 4 Comparison of capacity retention in cycle stability and efficiency tests

[0267]

[0268]

[0269] Table 5 Comparison of Coulombic efficiency in cycle stability and efficiency tests

[0270]

[0271] From the data in Table 4 and Table 5, we can get:

[0272] Capacity retention rate:

[0273] The additive of the present invention: after 200 cycles, the capacity retention rate is 88.4%, which shows that the additive of the present invention has stable chemical properties during the cycle and can effectively inhibit the degradation of the electrolyte, especially under long-term operation conditions.

[0274] Comparative Example Performance: The capacity retention rates of the comparative examples are generally low, especially for comparative example 5 (sample using EDTA), which has a capacity retention rate of only 66.0%. This reveals that traditional additives are prone to structural damage and performance degradation in high temperature and high pressure applications.

[0275] Coulombic efficiency:

[0276] The additive of the present invention: the coulombic efficiency slightly decreases from the initial 99.9% to 97.8%, and this slight decrease shows excellent electrochemical reaction reversibility and low electrical energy loss.

[0277] Comparative Example Performance: The Coulombic efficiency of the comparative examples decreased more significantly, especially from 98.5% to 83.1% in comparative example 5. This significant decrease may be due to the loss of active substances or decomposition of the electrolyte due to the unstable electrolyte structure during the cycle.

[0278] Synergistic effect of modified coumarin, aminoacetylacetone and nitrobenzaldehyde: These modified compounds not only improve the initial electrochemical performance of the electrolyte, but also enhance the chemical stability of the electrolyte in long-term use. Modified coumarin forms a more stable complex with vanadium ions through its hydroxyl group, inhibiting the deposition of vanadium ions during electrolysis. Aminoacetylacetone and nitrobenzaldehyde enhance the overall electrochemical window of the electrolyte and reduce electrolyte decomposition at high potentials.

[0279] Improved battery performance: Improved capacity retention and Coulombic efficiency directly contribute to longer battery life and higher energy efficiency, which are critical to the economics and reliability of energy storage systems.

[0280] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An all-vanadium redox flow battery electrolyte additive, characterized in that: The additive comprises the following components in percentage by mass: 45-55% of modified coumarin, 40-50% of aminoacetylacetone and 5-15% of nitrobenzaldehyde.

2. The electrolyte additive for all-vanadium redox flow battery according to claim 1, characterized in that: The modified coumarin includes at least one hydroxyl group, and the hydroxyl group is introduced into the aromatic ring of coumarin through a hydroxylation reaction.

3. The electrolyte additive for all-vanadium redox flow battery according to claim 1, characterized in that: The aminoacetylacetone is prepared by reacting acetylacetone with an ammonia source selected from one or more amino chemical substances.

4. The electrolyte additive for all-vanadium redox flow battery according to claim 1, characterized in that: The nitrobenzaldehyde is prepared by introducing at least one nitro group into the aromatic ring of benzaldehyde through a nitration reaction.

5. A method for preparing an all-vanadium redox flow battery electrolyte additive, used for preparing the all-vanadium redox flow battery electrolyte additive as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: S1, reacting coumarin with a brominating agent in anhydrous dimethyl sulfoxide, adding 10-20% volume of triethylamine, stirring at room temperature for 24-48 hours, adding 2-5 times volume of water to the reaction mixture for post-treatment to precipitate the product, and purifying by column chromatography to obtain hydroxycoumarin; S2, mixing acetylacetone and nitroaniline in anhydrous ethanol at a molar ratio of 1:1-1.5, adding 1-5% by volume of acetic acid as a catalyst, heating under reflux conditions for 12-24 hours, cooling to room temperature, adding 3-6 times the volume of water to the mixture to precipitate the product, and purifying by recrystallization to obtain aminoacetylacetone; S3, nitrating benzaldehyde in a mixed acid of nitric acid and sulfuric acid in a volume ratio of 1:2-3, maintaining the reaction temperature at 0-5°C for 1-2 hours, pouring the reaction mixture into 4-8 times the volume of ice water to neutralize and precipitate the product, and purifying by column chromatography to obtain nitrobenzaldehyde; S4. Mix hydroxycoumarin, aminoacetylacetone and nitrobenzaldehyde, dissolve and uniformly mix in dichloromethane or ethyl acetate, and remove the solvent at 30-40° C. under reduced pressure to obtain an additive.

6. The preparation method according to claim 5, characterized in that: The step of purifying hydroxycoumarin by column chromatography in step S1 comprises: using silica gel as the stationary phase and using a mixed solvent system of ethyl acetate and n-hexane for gradient elution, wherein the volume ratio of ethyl acetate to n-hexane is 1:1-3.

7. The preparation method according to claim 5, characterized in that: The recrystallization step in step S2 comprises: using a mixed solvent of ethanol and water, wherein the volume ratio of ethanol to water is 1:1-3.

8. The preparation method according to claim 5, characterized in that: The step of column chromatography purification to obtain nitrobenzaldehyde in step S3 comprises: using silica gel as the stationary phase and using a mixed solvent system of ethyl acetate and n-hexane for gradient elution, wherein the volume ratio of ethyl acetate to n-hexane is 1:1-2.

Images