All-vanadium redox flow battery electrolyte and application thereof

Abstract

The invention discloses an all-vanadium redox flow battery high-temperature stable electrolyte based on strong inorganic acid and aromatic sulfonic acid and a preparation method thereof. The electrolyte comprises strong inorganic acid, aromatic sulfonic acid and derivatives thereof, and precipitation of the pentavalent vanadium electrolyte at high temperature can be effectively inhibited by adjusting the proportion of the components, so that the battery can stably operate in a high-temperature environment. The electrolyte provided by the invention not only improves the proton concentration, but also inhibits the polymerization of pentavalent vanadium ions at high temperature through coordination, and obviously improves the temperature application range and stability of the all-vanadium redox flow battery. The electrolyte is simple to prepare, raw materials are easy to obtain, the performance of the all-vanadium redox flow battery can be remarkably improved, and the electrolyte has important practical application value.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to vanadium redox flow battery technology, and more particularly to a high-temperature stable electrolyte for vanadium redox flow batteries based on strong inorganic acids and aromatic sulfonic acids. Background Technology

[0002] Vanadium redox batteries are large-scale energy storage devices with advantages such as long lifespan, independently adjustable power and capacity, rapid response, and high safety. They have broad application prospects in renewable energy grid integration, smart grid construction, and distributed generation. Vanadium redox batteries utilize the redox reaction between vanadium ions of different valence states at the positive and negative electrodes to store and release electrical energy. The positive electrode uses a V(IV) / V(V) redox pair, and the negative electrode uses a V(II) / V(III) redox pair.

[0003] However, the practical application of vanadium redox flow batteries still faces some technical challenges, one of the most critical being the stability of pentavalent vanadium ions in the electrolyte at high temperatures. Specifically, when the ambient temperature exceeds 40°C, V(V) ions are prone to hydrolysis, forming insoluble polymeric compounds. These compounds deposit on the electrode surface and in the channels, leading to a series of problems, including reduced battery capacity, increased internal resistance, flow channel blockage, membrane fouling, and shortened cycle life.

[0004] In electrolyte system design, the selection and concentration control of the supporting electrolyte are crucial. Studies have shown that excessively high sulfuric acid concentrations significantly affect the electrochemical performance of the negative electrode, especially accelerating the deposition of divalent vanadium ions at low temperatures (below 5°C), leading to battery capacity decay. Simultaneously, when hydrochloric acid is used as the supporting electrolyte, its concentration also requires strict control. Excessive hydrochloric acid concentration not only generates corrosive acid mist but may also produce chlorine gas during electrolysis, which not only reduces battery life but also poses serious safety hazards.

[0005] Currently, various methods have been proposed in the industry to address the high-temperature stability of V(V) electrolytes. Common methods include adding stabilizers, modifying the supporting electrolyte, reducing vanadium ion concentration, temperature management, and optimizing electrolyte composition. Among these, adding stabilizers and modifying the supporting electrolyte are widely studied methods. For example, CN115863721B discloses the use of polybenzimidazole oligomers as stabilizers for all-vanadium redox flow battery electrolytes; CN114628754A introduces the use of nitroimidazole compounds as stabilizers. Regarding the supporting electrolyte, CN108054413B discloses the use of a mixture of sulfuric acid and hydrochloric acid, while CN117276613A proposes the use of methanesulfonic acid and hydrochloric acid as supporting electrolytes. Although these methods have improved the high-temperature stability of V(V) electrolytes to some extent, many challenges remain. Organic stabilizers may reduce the conductivity of the electrolyte, while inorganic additives may introduce new ionic impurities; modifying the supporting electrolyte may affect the overall performance of the battery; and temperature management systems increase equipment complexity and operating costs. Therefore, developing a novel electrolyte system that can effectively suppress high-temperature precipitation of electrolyte in vanadium redox flow batteries while maintaining excellent electrochemical performance, and which is simple to prepare and inexpensive, remains a key focus and challenge in current research. Summary of the Invention

[0006] The main objective of this invention is to provide a high-temperature stable electrolyte for vanadium redox flow batteries based on strong inorganic acids and aromatic sulfonic acids, aiming to solve the technical problem of poor stability of existing vanadium redox flow battery electrolytes under high-temperature environments. To achieve the above objective, this invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a high-temperature stable electrolyte for a vanadium redox flow battery, wherein the electrolyte contains one or more of inorganic acids, aromatic sulfonic acids and their derivatives, vanadium ions and water.

[0008] The aromatic sulfonic acids and their derivatives are selected from one or more of the following: benzenesulfonic acid, p-toluenesulfonic acid, m-toluenesulfonic acid, o-toluenesulfonic acid, dimethylbenzenesulfonic acid, trimethylbenzenesulfonic acid, or tert-butylbenzenesulfonic acid.

[0009] Preferably, the aromatic sulfonic acid and its derivatives are one or more of benzenesulfonic acid, p-toluenesulfonic acid or m-toluenesulfonic acid.

[0010] The aromatic sulfonic acids and their derivatives introduced in this invention have a dual mechanism of action: firstly, the sulfonic acid group (-SO3H) in the molecule can donate protons, improving the conductivity of the electrolyte; secondly, the aromatic ring structure can form a stable coordination with vanadium ions, effectively inhibiting the polymerization of V(V) at high temperatures. This synergistic effect makes them ideal electrolyte additives.

[0011] Further, one or more of the aromatic sulfonic acids and their derivatives are added to the electrolyte, and their concentration in the electrolyte is 0.1-1 mol / L. Preferably, the concentration of the aromatic sulfonic acids and their derivatives is 0.2-0.8 mol / L.

[0012] Furthermore, the inorganic acid in the electrolyte includes sulfuric acid, or a mixture of sulfuric acid and hydrochloric acid.

[0013] Furthermore, the concentration of sulfuric acid is 2-4 mol / L, and the concentration of hydrochloric acid is 0-4 mol / L.

[0014] Preferably, the concentration of the hydrochloric acid is 1-2 mol / L.

[0015] Furthermore, the concentration of vanadium ions in the electrolyte is 1-2.5 mol / L.

[0016] Preferably, the concentration of vanadium ions is 1.5-2.2 mol / L.

[0017] Secondly, the present invention provides an application of the above-mentioned electrolyte as a battery electrolyte in a vanadium redox flow battery.

[0018] Furthermore, the operating temperature of the vanadium redox flow battery is 20-60℃.

[0019] Furthermore, the operating pH value of the vanadium redox flow battery is -2.5 to -0.1.

[0020] The beneficial results of this invention are as follows:

[0021] The electrolyte of this invention, by adding specific aromatic sulfonic acids and their derivatives, can effectively inhibit the hydrolysis and precipitation of pentavalent vanadium at high temperatures, thus solving the problem of performance degradation of traditional all-vanadium redox flow batteries under high-temperature environments.

[0022] The electrolyte of this invention maintains high conductivity and good electrochemical activity, ensuring efficient battery operation and improving energy utilization. Simultaneously, by reducing the formation of precipitates under high-temperature conditions, it significantly extends battery life and cycle life, improving battery economics.

[0023] The aromatic sulfonic acids and their derivatives used in this invention are readily available, the preparation process is simple, and no complex equipment is required, resulting in good cost-effectiveness. Furthermore, the selected additives have low toxicity and good biodegradability, reducing potential environmental impact.

[0024] This invention optimizes the electrolyte pH within the range of -2.5 to -0.1, allowing aromatic sulfonic acids and their derivatives to maintain optimal dissociation. The sulfonic acid groups (-SO3H) effectively coordinate, stabilizing pentavalent vanadium ions and inhibiting their polymerization and precipitation at high temperatures. This pH range also ensures a sufficiently high proton concentration, creating a synergistic effect with the aromatic sulfonic acids. This provides adequate proton carriers to maintain the electrolyte's high conductivity and facilitates the formation of a stable coordination structure between the aromatic sulfonic acids and vanadium ions. Compared to the lower pH systems used in traditional vanadium redox flow batteries, the pH range selected in this invention effectively mitigates acidic corrosion of the battery components, extends equipment lifespan, and reduces the potential environmental hazards of the electrolyte. This optimized pH design, combined with the addition of aromatic sulfonic acids, creates a unique synergistic effect, ensuring both high-temperature battery stability and considering equipment lifespan and environmental friendliness, significantly improving the overall performance and practical value of the battery system.

[0025] This electrolyte effectively suppresses the precipitation of pentavalent vanadium ions at high temperatures, enabling the battery to operate stably in high-temperature environments. The electrolyte of this invention not only increases the proton concentration but also inhibits the polymerization of pentavalent vanadium ions at high temperatures through coordination, significantly improving the temperature range and stability of the vanadium redox flow battery. This electrolyte is simple to prepare, uses readily available raw materials, and can significantly improve the performance of vanadium redox flow batteries, possessing significant practical application value. Attached Figure Description

[0026] To further illustrate the present invention, the following description is provided in conjunction with the accompanying drawings:

[0027] Figure 1 This is a comparison graph of the discharge capacity of Sample 2 containing 0.5 mol / L benzenesulfonic acid stabilizer in Example 6 and the electrolyte of Comparative Example 14 at 50°C.

[0028] Figure 2 The electrolyte of Comparative Example 14 is used to measure battery performance at 50°C.

[0029] Figure 3 The battery performance of sample 2 containing 0.5 mol / L benzenesulfonic acid stabilizer in Example 6 at 50°C. Detailed Implementation

[0030] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0031] Comparative Example 1

[0032] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis with a sulfuric acid concentration of 2.0 mol / L, without the addition of hydrochloric acid or aromatic sulfonic acid stabilizers. The solution was kept at a constant temperature of 50°C in a water bath, and its state was observed.

[0033] Comparative Example 2

[0034] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with 0.5 mol / L citric acid added as a stabilizer, and the sulfuric acid concentration was 2.0 mol / L. The solution was placed in a 50℃ water bath for constant temperature, and the state of the solution was observed.

[0035] Comparative Example 3

[0036] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with 0.5 mol / L acetic acid added as a stabilizer, and the sulfuric acid concentration was 2.0 mol / L. The solution was placed in a water bath at 50°C and the state of the solution was observed.

[0037] Comparative Example 4

[0038] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with 0.5 mol / L benzoic acid added as a stabilizer, and the sulfuric acid concentration was 2.0 mol / L. The solution was placed in a water bath at 50℃ and the state of the solution was observed.

[0039] Comparative Example 5

[0040] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with sulfuric acid and hydrochloric acid concentrations both at 2.0 mol / L. The solution was kept at a constant temperature of 50°C in a water bath, and its state was observed.

[0041] Comparative Example 6

[0042] A 1.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with sulfuric acid and hydrochloric acid concentrations of 2.0 mol / L. The solution was placed in a water bath at 50°C and the state of the solution was observed.

[0043] Comparative Example 7

[0044] A 2.5 mol / L pentavalent vanadium solution was prepared by electrolysis, with sulfuric acid and hydrochloric acid concentrations of 2.0 mol / L. The solution was placed in a water bath at 50°C and its state was observed.

[0045] Comparative Example 8

[0046] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with a sulfuric acid concentration of 1.5 mol / L and a hydrochloric acid concentration of 2.0 mol / L. The solution was placed in a water bath at 50°C and the state of the solution was observed.

[0047] Comparative Example 9

[0048] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with a sulfuric acid concentration of 3.0 mol / L and a hydrochloric acid concentration of 2.0 mol / L. The solution was placed in a water bath at 50°C and the state of the solution was observed.

[0049] Comparative Example 10

[0050] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with a sulfuric acid concentration of 2.0 mol / L and a hydrochloric acid concentration of 1.0 mol / L. The solution was placed in a water bath at 50°C and the state of the solution was observed.

[0051] Comparative Example 11

[0052] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with a sulfuric acid concentration of 2.0 mol / L and a hydrochloric acid concentration of 3.0 mol / L. The solution was placed in a water bath at 50°C and the state of the solution was observed.

[0053] Comparative Example 12

[0054] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with sulfuric acid and hydrochloric acid concentrations of 2.0 mol / L and 0.05 mol / L benzenesulfonic acid added. The solution was kept at a constant temperature of 50°C in a water bath, and its state was observed.

[0055] Comparative Example 13

[0056] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with sulfuric acid and hydrochloric acid concentrations of 2.0 mol / L and 1.5 mol / L benzenesulfonic acid added. The solution was placed in a 50°C water bath for constant temperature, during which it was observed that some benzenesulfonic acid could not be completely dissolved.

[0057] Note: Stabilization time is defined as the time it takes for a visible precipitate or turbidity to appear in a solution at a specified temperature.

[0058] Example 1

[0059] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis. The sulfuric acid concentration was 2.0 mol / L. Benzenesulfonic acid of the following concentrations was then added:

[0060] Sample 1a: 0.3 mol / L;

[0061] Sample 1b: 0.5 mol / L;

[0062] Sample 1c: 0.8 mol / L.

[0063] After thorough mixing and stirring, the mixture was placed in a water bath at 50°C and kept at a constant temperature. The state of the solution was observed to investigate the effect of the stabilizer on the thermal stability of pentavalent vanadium.

[0064] Example 2

[0065] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis. The sulfuric acid concentration was 2.0 mol / L, and the hydrochloric acid concentration was 2.0 mol / L. Benzenesulfonic acid of the following concentrations was then added:

[0066] Sample 2a: 0.3 mol / L added;

[0067] Sample 2b: Add 0.5 mol / L;

[0068] Sample 2c: Add 0.8 mol / L.

[0069] After thorough mixing and stirring, the mixture was placed in a water bath at 50°C and kept at a constant temperature. The state of the solution was observed to investigate the effect of the stabilizer on the thermal stability of pentavalent vanadium.

[0070] Example 3

[0071] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis. The sulfuric acid concentration was 2.0 mol / L, and the hydrochloric acid concentration was 2.0 mol / L. Different aromatic sulfonic acids were then added at 0.5 mol / L each.

[0072] Sample 3a: Added benzenesulfonic acid;

[0073] Sample 3b: p-Toluenesulfonic acid added;

[0074] Sample 3c: Added m-toluenesulfonic acid;

[0075] Sample 3d: o-Toluenesulfonic acid added;

[0076] Sample 3e: Dimethylbenzenesulfonic acid added;

[0077] Sample 3f: Trimethylbenzenesulfonic acid was added.

[0078] After thorough mixing and stirring, the mixture was placed in a water bath at 50°C and kept at a constant temperature. The state of the solution was observed to investigate the effect of the stabilizer on the thermal stability of pentavalent vanadium.

[0079] Example 4

[0080] Pentavalent vanadium solutions of different concentrations were prepared by electrolysis, with sulfuric acid concentration of 2.0 mol / L, hydrochloric acid concentration of 2.0 mol / L, and benzenesulfonic acid concentration of 0.5 mol / L.

[0081] Sample 4a: 1.5 mol / L pentavalent vanadium

[0082] Sample 4b: 1.8 mol / L pentavalent vanadium

[0083] The above solution was placed in a 50°C water bath for static stability testing.

[0084] Example 5:

[0085] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with a sulfuric acid concentration of 2.0 mol / L and a benzenesulfonic acid concentration of 0.5 mol / L. The hydrochloric acid concentration was adjusted accordingly.

[0086] Sample 5a: 1.0 mol / L hydrochloric acid

[0087] Sample 5b: 3.0 mol / L hydrochloric acid

[0088] The above solution was placed in a 50°C water bath for static stability testing.

[0089] Table 1 shows the static stability test results. In Comparative Example 1, without any stabilizer, the stability time of pentavalent vanadium at 50℃ is approximately 10 hours. Comparative Examples 2-4, with the addition of non-sulfonic acid organic acids (citric acid, acetic acid, and benzoic acid), showed limited stabilizing effects, with stability times of only 12-20 hours. Comparative Examples 5-7 investigated the effect of V ion concentration. The results showed that as the V ion concentration increased from 1.0 mol / L to 2.5 mol / L, the stability time decreased from 96 hours to 24 hours, indicating that a higher V ion concentration is detrimental to the thermal stability of the electrolyte.

[0090] Comparative Examples 8-11 investigated the effect of supporting electrolyte concentration. When the sulfuric acid concentration was below or above 2.0 mol / L (Comparative Examples 8 and 9), the stabilization times were 36 hours and 42 hours, respectively, both lower than the stability at 2.0 mol / L. Similarly, changes in hydrochloric acid concentration (Comparative Examples 10 and 11) showed a similar trend, indicating that there is an optimal value for the supporting electrolyte concentration.

[0091] Comparative Examples 12 and 13 investigated the critical effect of aromatic sulfonic acid concentration. When the benzenesulfonic acid concentration was too low (0.05 mol / L), the stability time was only 52 hours, showing limited improvement compared to no stabilizer; when the concentration was too high (1.5 mol / L), solubility problems occurred.

[0092] The thermal stability of the electrolyte was significantly improved upon the introduction of an appropriate amount of aromatic sulfonic acid. In Example 1, the stability time increased from 72 hours to 120 hours as the concentration of benzenesulfonic acid increased from 0.3 mol / L to 0.8 mol / L. In Example 2, the sulfuric acid-hydrochloric acid-aromatic sulfonic acid ternary system exhibited even better stabilization, with the formulation of 2.0 mol / L sulfuric acid + 2.0 mol / L hydrochloric acid + 0.8 mol / L benzenesulfonic acid achieving a stability time of 168 hours.

[0093] Example 3 investigated the stabilizing effects of different aromatic sulfonic acids. The results showed that benzenesulfonic acid performed best, achieving a stability time of 144 hours at a concentration of 0.5 mol / L. p-Toluenesulfonic acid and m-Toluenesulfonic acid were next, with stability times of approximately 120 hours. o-Toluenesulfonic acid had a stability time of 96 hours, while the stability times of dimethylbenzenesulfonic acid and trimethylbenzenesulfonic acid decreased to 72 hours. This difference indicates that the position and number of substituents on the aromatic ring significantly affect its stabilizing effect; simpler aromatic sulfonic acid structures exhibit better stability.

[0094] Examples 4 and 5 investigated the effects of other component concentrations under conditions containing a 0.5 mol / L benzenesulfonic acid stabilizer. Example 4 studied the effect of V ion concentration, showing that when the V ion concentration decreased from 2.0 mol / L to 1.5 mol / L, the stabilization time increased from approximately 96 hours to approximately 168 hours. This indicates that even in the presence of a stabilizer, reducing the V ion concentration still improves the thermal stability of the electrolyte, and the presence of aromatic sulfonic acid can further extend the stabilization time. Example 5 studied the effect of hydrochloric acid concentration, showing that optimal stability (approximately 144 hours) was obtained at 2.0 mol / L, while when the hydrochloric acid concentration decreased to 1.0 mol / L, the stabilization time decreased to approximately 96 hours, possibly due to insufficient chloride ion coordination effect. When the hydrochloric acid concentration increased to 3.0 mol / L, significant acid mist was observed, which is detrimental to the long-term stable operation of the battery. This indicates that even with the addition of aromatic sulfonic acid stabilizers, optimizing the hydrochloric acid concentration remains crucial, requiring a balance between stability and practical application requirements.

[0095] Table 1. Stability test results of electrolytes with different formulations at 50℃

[0096]

[0097]

[0098] Note: "~" indicates that the corresponding phenomenon was observed within ±5% of that time point.

[0099] Example 6

[0100] Based on the results of static stability tests, benzenesulfonic acid formulations with concentrations of 0.3 mol / L, 0.5 mol / L, and 0.8 mol / L were selected for battery performance testing. The battery test conditions are as follows:

[0101] Electrolyte: Vanadium ion concentration 2.0 mol / L, sulfuric acid concentration 2.0 mol / L, hydrochloric acid concentration 2.0 mol / L, with benzenesulfonic acid added at concentrations of 0.3 mol / L, 0.5 mol / L, and 0.8 mol / L respectively (samples 1, 2, and 3);

[0102] Diaphragm: Nafion115

[0103] Electrode: carbon felt;

[0104] Electrode area: 48cm² 2 ;

[0105] The volume of the positive and negative electrode electrolytes is 60 mL each. The positive and negative electrode electrolytes are the same. The positive electrode is tetravalent and pentavalent vanadium, and the negative electrode is divalent and trivalent vanadium.

[0106] Current density: 80 mA / cm 2 ;

[0107] Charging cut-off voltage: 1.6V;

[0108] Discharge cutoff voltage: 0.8V;

[0109] Experimental temperature: 50℃.

[0110] The battery performance of the above flow batteries was tested, as shown in Table 2.

[0111] Example 7

[0112] Based on the optimal stabilizer formulation (0.5 mol / L benzenesulfonic acid), the effects of different V-ion concentrations on battery performance were investigated.

[0113] Electrolyte: sulfuric acid concentration 2.0 mol / L, hydrochloric acid concentration 2.0 mol / L, benzenesulfonic acid concentration 0.5 mol / L, vanadium ion concentrations were set at 1.5 mol / L and 1.8 mol / L respectively (samples 4 and 5).

[0114] Other test conditions are the same as in Example 6.

[0115] Example 8

[0116] Based on the optimal stabilizer formulation, the effect of hydrochloric acid concentration on battery performance was studied.

[0117] Electrolyte: Vanadium ion concentration 2.0 mol / L, sulfuric acid concentration 2.0 mol / L, benzenesulfonic acid concentration 0.5 mol / L, and hydrochloric acid concentrations of 1.0 mol / L and 3.0 mol / L (samples 6 and 7), respectively.

[0118] Other test conditions are the same as in Example 6.

[0119] Example 9

[0120] The effects of different types of aromatic sulfonic acids on battery performance were studied based on the optimal concentration of benzenesulfonic acid (0.5 mol / L).

[0121] Electrolyte: Vanadium ion concentration 2.0 mol / L, sulfuric acid concentration 2.0 mol / L, hydrochloric acid concentration 2.0 mol / L, with 0.5 mol / L of p-toluenesulfonic acid, m-toluenesulfonic acid, o-toluenesulfonic acid, dimethylbenzenesulfonic acid, and trimethylbenzenesulfonic acid (samples 8, 9, 10, 11, and 12) added respectively.

[0122] Comparative Example 14

[0123] A single-cell experiment was conducted using an electrolyte with a vanadium ion concentration of 2.0 mol / L and a sulfuric acid concentration of 2.0 mol / L. The battery testing conditions were the same as in Example 4 above.

[0124] Comparative Example 15

[0125] Based on Comparative Example 14, hydrochloric acid with a final concentration of 2.0 mol / L was added, while other conditions remained the same as in Comparative Example 14.

[0126] Table 2 Battery performance parameters for different electrolyte formulations (50℃)

[0127]

[0128]

[0129] Table 2 shows that the type and position of substituents in different aromatic sulfonic acids significantly affect battery performance. Under the same concentration (0.5 mol / L), p-toluenesulfonic acid exhibits the best performance, with a coulombic efficiency (CE) of 96.8%, a voltage efficiency (VE) of 87.2%, and an energy efficiency (EE) of 84.4%. Battery performance decreases with increasing methyl substituent numbers, with trimethylbenzenesulfonic acid showing the lowest performance across all indicators, at CE 95.5% and EE only 82.1%. Among the positional isomers, the para-substituent performs best, while the ortho-substituent performs relatively poorly (CE 96.0%, EE 83.0%), possibly due to steric hindrance affecting the coordination of the sulfonic acid group with vanadium ions. Overall, benzenesulfonic acid and p-toluenesulfonic acid, with their simple structures, exhibit optimal performance, providing an important basis for the selection of electrolyte additives.

[0130] The battery performance test results in Table 2 also show that the addition of benzenesulfonic acid significantly improved battery performance. With increasing benzenesulfonic acid concentration, battery performance first increased and then decreased, reaching its optimal level at 0.5 mol / L. At this concentration, the coulombic efficiency (CE) reached 97.2%, the voltage efficiency (VE) was 87.5%, and the energy efficiency (EE) reached 85.1%, significantly higher than Comparative Example 14 (2.0 M H₂SO₄) and Comparative Example 15 (2.0 M H₂SO₄ + 2.0 M HCl). When the benzenesulfonic acid concentration was further increased to 0.8 mol / L, the performance indicators decreased slightly, with CE dropping to 96.5% and EE to 83.7%. This may be because excessively high concentrations of benzenesulfonic acid affect the conductivity of the electrolyte.

[0131] The effect of V ion concentration on battery performance was investigated at the same stabilizer concentration (0.5 mol / L). The results showed that battery performance gradually improved as the V ion concentration increased from 1.5 mol / L to 2.0 mol / L, with CE increasing from 95.6% to 97.2% and EE from 82.0% to 85.1%. This indicates that increasing the V ion concentration is beneficial for improving battery performance, but a trade-off must be made regarding thermal stability requirements.

[0132] Regarding the effect of hydrochloric acid concentration, experimental results show that 2.0 mol / L is the optimal concentration, at which the highest performance indicators are obtained. When the hydrochloric acid concentration is reduced to 1.0 mol / L, all indicators decrease significantly, with CE dropping to 95.2% and EE only 81.3%. When the hydrochloric acid concentration is increased to 3.0 mol / L, although the performance decrease is smaller, obvious acid mist will appear, which is not conducive to the long-term operation of the battery.

[0133] The optimal formulation sample 2 (2.0M H2SO4 + 2.0M HCl + 0.5M benzenesulfonic acid) was selected for detailed cyclic performance testing, and the results are as follows: Figure 1-3 As shown. From Figure 1 The comparison of discharge capacity shows that sample 2 ( Figure 1 The curve (with stabilizer) maintained a stable capacity of approximately 1.5 amp-hours after 200 cycles, while Comparative Example 14 (2.0 M H2SO4) showed a similar capacity. Figure 1 The blank curve (marked in the middle) shows a sharp drop in capacity to 0 after 80 cycles. Figure 2 The coulombic efficiency and energy efficiency of Comparative Example 14 during the cycling process are shown. Performance gradually decreases with increasing cycle number, and efficiency drops significantly after 80 cycles. In contrast, Figure 3 The cycling performance of Sample 2 was demonstrated, with the coulombic efficiency remaining stable above 95% and the energy efficiency around 85%. The performance showed almost no degradation during 200 cycles, which fully confirms that benzenesulfonic acid can significantly improve the cycle stability and long-term performance of the battery.

[0134] In summary, this invention relates to a high-temperature stable electrolyte for vanadium redox flow batteries based on a strong inorganic acid and an aromatic sulfonic acid. The aromatic sulfonic acid is a chain-like or cyclic organic acid compound; the content of the aromatic sulfonic acid in the electrolyte is 0.1-1 mol / L. The aromatic sulfonic acid used in this invention as a stabilizer for the electrolyte effectively improves the stability of the electrolyte under high-temperature conditions, achieving stable battery operation, while also increasing the battery's energy density. The preparation process of this invention is simple, energy-saving, environmentally friendly, and low-cost, while simultaneously enabling stable operation of the electrolyte in the battery.

[0135] It should be noted that the multiple solutions provided in this patent include their own basic solutions, which are independent of each other and do not restrict each other. However, they can also be combined with each other without conflict to achieve multiple effects.

[0136] The foregoing demonstration and description illustrate the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention; various changes and modifications can be made without departing from the spirit and scope of the invention, and all such changes and modifications fall within the scope of the claims.

Claims

1. A vanadium redox flow battery electrolyte, characterized in that: The electrolyte contains one or more of the following: inorganic acids, aromatic sulfonic acids and their derivatives, vanadium ions, and water.

2. The electrolyte according to claim 1, characterized in that: The aromatic sulfonic acid and its derivatives are selected from one or more of the following: benzenesulfonic acid, p-toluenesulfonic acid, m-toluenesulfonic acid, o-toluenesulfonic acid, dimethylbenzenesulfonic acid, trimethylbenzenesulfonic acid or tert-butylbenzenesulfonic acid; Preferably, the aromatic sulfonic acid and its derivatives are one or more of benzenesulfonic acid, p-toluenesulfonic acid or m-toluenesulfonic acid.

3. The electrolyte according to claim 1 or 2, characterized in that: One or more of the aromatic sulfonic acids and their derivatives are added to the electrolyte, and their concentration in the electrolyte is 0.1-1 mol / L; Preferably, the concentration of the aromatic sulfonic acid and its derivatives is 0.2-0.8 mol / L.

4. The electrolyte according to claim 1 or 2, characterized in that: The inorganic acid in the electrolyte includes sulfuric acid, or a mixture of sulfuric acid and hydrochloric acid; The concentration of the sulfuric acid is 2-4 mol / L; The concentration of the hydrochloric acid is 0-4 mol / L; preferably, the concentration of the hydrochloric acid is 2-4 mol / L.

5. The electrolyte according to claim 1 or 2, characterized in that: The concentration of vanadium ions in the electrolyte is 1-2.5 mol / L; Preferably, the concentration of vanadium ions is 1.5-2.2 mol / L.

6. The application of the electrolyte according to any one of claims 1-5 as a battery electrolyte in a vanadium redox flow battery.

7. The application according to claim 6, characterized in that: The operating temperature of the vanadium redox flow battery is 20-60℃.

8. The application according to claim 6, characterized in that: The operating pH value of the vanadium redox flow battery is -2.5 to -0.1.

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