All-vanadium redox flow battery electrolyte containing fluorine sulfonic acid stabilizer and application of all-vanadium redox flow battery electrolyte

Abstract

The invention discloses a high-temperature stable electrolyte of an all-vanadium redox flow battery based on a fluorine-containing sulfonic acid compound and a preparation method of the high-temperature stable electrolyte. The fluorine-containing sulfonic acid with C1-C8 carbon chains is selected as the stabilizer, so that the proton concentration is improved, the polymerization of pentavalent vanadium ions at high temperature is inhibited through the coordination effect of fluorine-containing sulfonate ions, and the temperature application range and the stability of the all-vanadium redox flow battery are remarkably improved. The electrolyte can stably exist for more than 30 days at the temperature of 50 DEG C and can stably exist for more than 10 days at the temperature of 60 DEG C. In addition, a battery test result shows that the all-vanadium redox flow battery adopting the electrolyte has excellent electrochemical performance, the coulombic efficiency can reach 99% or above, the energy efficiency can reach 87% or above, and the capacity retention rate after 200 cycles reaches 96% or above. 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 relates to the field of electrochemical energy storage technology, specifically to a high-temperature stable electrolyte for vanadium redox flow batteries, particularly a vanadium redox flow battery electrolyte containing fluorosulfonic acid compounds as stabilizers and its application. Background Technology

[0002] Vanadium redox flow batteries (VFBs), as a large-scale energy storage device, have attracted widespread attention since their invention in the 1980s by Professor Maria Skyllas-Kazacos' team at the University of New South Wales, Australia, due to their unique technological advantages. Compared with traditional batteries, VFBs offer advantages such as independently designable energy capacity and power, fast response speed, long cycle life, no damage to battery life during deep discharge, and recyclable electrolyte. They have significant application value in areas such as renewable energy grid integration, smart grid construction, and distributed generation.

[0003] However, in the practical application of vanadium redox flow batteries, the temperature stability of the electrolyte has always been a key technical bottleneck restricting their development. Vanadium redox flow batteries use vanadium ions of different valence states as redox pairs, with the positive electrode using a V(IV) / V(V) redox pair and the negative electrode using a V(II) / V(III) redox pair. In actual operation, especially at higher temperatures (>40℃), the V(V) ions at the positive electrode are highly susceptible to thermal hydrolysis, generating insoluble V₂O₅ precipitates. These precipitates not only reduce the concentration of active materials in the electrolyte, causing battery capacity loss, but also clog electrode pores, pipes, and pumps, affecting electrolyte flow and potentially damaging the battery assembly.

[0004] To address the thermal stability issue of electrolytes, researchers have conducted extensive research. Currently, sulfuric acid is the commonly used supporting electrolyte, but using sulfuric acid alone fails to achieve ideal stabilization. Studies have shown that adding hydrochloric acid to sulfuric acid can significantly improve electrolyte stability; however, due to its low vapor pressure, hydrochloric acid is prone to generating acid mist, thus its addition is strictly limited, which significantly restricts further improvements in stabilization. Researchers have also tried other organic acid compounds as stabilizers, such as methanesulfonic acid and ethylsulfonic acid. While these compounds exhibit good stabilizing effects, they may be oxidized and decomposed by V(V) during long-term operation. Inorganic additives such as phosphates and fluorides have also been extensively studied, but these anions may affect V(II) and V(III), making it difficult to achieve ideal performance in full-cell systems. Furthermore, the introduction of new ionic impurities may affect the long-term stability of the battery.

[0005] While reducing the vanadium ion concentration can improve solution stability, this directly reduces the battery's energy density, which is detrimental to practical applications. Furthermore, controlling the electrolyte temperature by adding a cooling system significantly increases system complexity and operating costs. Therefore, developing a supporting electrolyte that combines high-temperature stability with strong acidity is of great significance. 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 fluorosulfonic acid compounds. This invention adds fluorosulfonic acid compounds, especially trifluoromethanesulfonic acid, to the electrolyte, which not only has strong acidity and high thermal stability, but also its anions have unique coordination properties, thus solving the technical problem of poor stability of existing vanadium redox flow battery electrolytes under high-temperature conditions.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A high-temperature stable electrolyte for a vanadium redox flow battery, the electrolyte containing a strong inorganic acid, a fluorosulfonic acid compound, vanadium ions and water.

[0009] Furthermore, the fluorosulfonic acid compound is selected from one or more of the following: fluorosulfonic acids with C1-C8 carbon chains, specifically including: trifluoromethanesulfonic acid, pentafluoroethylsulfonic acid, heptafluoropropylsulfonic acid, perfluorobutylsulfonic acid, perfluoropentylsulfonic acid, perfluorohexylsulfonic acid, perfluoroheptylsulfonic acid, and perfluorooctylsulfonic acid.

[0010] Preferably, the fluorosulfonic acid compound is a fluorosulfonic acid with a C1-C4 carbon chain;

[0011] More preferably, the fluorosulfonic acid compound is trifluoromethanesulfonic acid.

[0012] Furthermore, the concentration of the fluorosulfonic acid compound in the electrolyte is 0.1-4.0 mol / L.

[0013] Preferably, the concentration of the fluorosulfonic acid compound is 0.2-2.0 mol / L.

[0014] Furthermore, the strong inorganic acid is sulfuric acid.

[0015] Furthermore, the concentration of sulfuric acid in the electrolyte is 1.5-5.0 mol / L;

[0016] Preferably, the concentration of sulfuric acid in the electrolyte is 1.5-3.0 mol / L.

[0017] Furthermore, the concentration of vanadium ions in the electrolyte is 1.0-2.5 mol / L;

[0018] Preferably, the concentration of vanadium ions in the electrolyte is 1.5-2.2 mol / L.

[0019] Secondly, the present invention provides an application of the above-mentioned electrolyte as a battery electrolyte in a vanadium redox flow battery.

[0020] Furthermore, the operating temperature of the vanadium redox flow battery is 20-60℃.

[0021] Furthermore, the operating pH value of the vanadium redox flow battery is -2.5 to -0.1.

[0022] The beneficial effects of this invention are as follows:

[0023] This invention is the first systematic study of the stabilizing effect of fluorosulfonic acid compounds with different carbon chain lengths on the electrolyte of a vanadium redox flow battery. It was found that fluorosulfonic acids with C1-C8 carbon chains all have a certain stabilizing effect, with those with C1-C4 carbon chains exhibiting the best overall performance. These compounds can effectively inhibit the hydrolysis and precipitation of pentavalent vanadium at high temperatures, solving the problem of performance degradation in traditional vanadium redox flow batteries under high-temperature environments. Experimental results show that the electrolyte can remain stable for more than 30 days at 50℃ and for more than 10 days at 60℃.

[0024] The electrolyte of this invention maintains high conductivity and good electrochemical activity, ensuring efficient battery operation and improving energy utilization. The strong acidity of fluorosulfonic acid compounds provides ample proton conduction channels, while fluorosulfonate ions exhibit good coordination properties with vanadium ions of various valence states. Simultaneously, by reducing the formation of precipitates under high-temperature conditions, the battery's lifespan and cycle life are significantly extended, improving the battery's economic efficiency.

[0025] This invention optimizes and controls the electrolyte pH within the range of -2.5 to -0.1. This pH range allows fluorosulfonic acid compounds to maintain an ideal dissociation state. The strong electron-withdrawing fluorine and sulfonic acid groups (-SO3H) synergistically enhance their coordination ability with vanadium ions, more effectively inhibiting the polymerization and precipitation of pentavalent vanadium ions. This pH range not only ensures sufficient proton concentration to maintain the high conductivity of the electrolyte but also promotes the formation of a more stable coordination structure between fluorosulfonic acid ions and vanadium ions. Compared with traditional electrolytes with lower pH values, the pH range selected in this invention significantly reduces acid corrosion of the battery assembly. Simultaneously, due to the excellent chemical stability of fluorosulfonic acid compounds, they can maintain activity for a long time under this pH condition, providing a lasting stable effect. This precise pH control and the strong coordination effect of fluorosulfonic acid compounds create a unique synergistic effect, not only achieving long-term stable operation of the battery at high temperatures but also extending the service life of the battery assembly, demonstrating the technical advantages of this invention in practical applications.

[0026] The fluorosulfonic acid compounds used in this invention are all commercially available products, with simple preparation processes that require no complex equipment, resulting in good cost-effectiveness. Furthermore, these compounds have low vapor pressures and are not easily volatilized at high temperatures, avoiding the acid mist problem encountered when using hydrochloric acid, thus improving system safety and environmental friendliness. Attached Figure Description

[0027] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the embodiments will be briefly described below:

[0028] Figure 1 This is a comparison chart of the discharge capacity of sample 6b containing 1.0 mol / L trifluoromethanesulfonic acid in Example 6 and blank control example 10 at 50°C.

[0029] Figure 2 This is a battery performance graph of sample 6b containing 1.0 mol / L trifluoromethanesulfonic acid in Example 6 at 50°C, including changes in coulombic efficiency and energy efficiency with the number of cycles. 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 any other stabilizers. The solution was kept at a constant temperature of 50°C in a water bath, and its state was observed. A clear precipitate appeared after approximately 12 hours.

[0033] Comparative Example 2

[0034] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with the sulfuric acid concentration reduced to 1.5 mol / L, without the addition of any other stabilizers. The solution was kept at a constant temperature of 50°C in a water bath, and its state was observed. A noticeable precipitate appeared after approximately 4 hours.

[0035] Comparative Example 3

[0036] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with the sulfuric acid concentration increased to 3.5 mol / L. The solution was placed in a 50°C water bath and the state of the solution was observed. A significant precipitate appeared after approximately 72 hours.

[0037] Comparative Example 4

[0038] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis with 2.0 mol / L sulfuric acid and 3.0 mol / L hydrochloric acid. The solution was kept at a constant temperature of 50°C in a water bath, and its state was observed. Although no precipitation was observed within 120 hours, significant acid fumes were produced, indicating increased corrosiveness.

[0039] Comparative Example 5

[0040] A 2.0 mol / L pentavalent vanadium solution was prepared by electrolysis, with a sulfuric acid concentration of 2.0 mol / L and the addition of 1.0 mol / L methanesulfonic acid. The solution was kept at a constant temperature of 50°C in a water bath, and its state was observed. After 30 days, a color change was observed in the solution, indicating that the stabilizer may have decomposed.

[0041] Comparative Example 6

[0042] To investigate the stabilizing effect of nonpolar fluorinated compounds, 1.0 mol / L of perfluorooctane (C8F18) was added to a 2.0 mol / L pentavalent vanadium solution with a sulfuric acid concentration of 2.0 mol / L. The results showed that the compound was immiscible with the electrolyte and exhibited significant stratification within 4 hours at room temperature.

[0043] Comparative Example 7

[0044] 1.0 mol / L of perfluorooctanol (C8F17CH2OH) was added to a base electrolyte with the same formulation. The solution was kept at a constant temperature of 50°C in a water bath, and precipitation occurred after approximately 16 hours. The viscosity of this electrolyte formulation was measured to be 6.2 mPa·s at 25°C, indicating a high viscosity and significantly reduced fluidity.

[0045] Comparative Example 8

[0046] 1.0 mol / L of perfluoromethyl propyl ether (C4F9OCH3) was added to the basic electrolyte. The solution was kept at a constant temperature of 50°C in a water bath, and precipitation occurred after ~24 hours. The viscosity of the electrolyte with this formulation was measured to be 5.6 mPa·s at 25°C. The electrolyte viscosity was high, and the fluidity was significantly reduced.

[0047] Comparative Example 9

[0048] 1.0 mol / L of CF3SO3Na was added to the basic electrolyte. The solution was kept at a constant temperature of 50°C in a water bath, and precipitation occurred after approximately 24 hours. The viscosity of the electrolyte formulated with this method was measured to be 5.1 mPa·s at 25°C. This comparative example shows that although sodium-containing additives possess similar anionic coordinating groups, they have significant shortcomings in practical applications, failing to maintain a low pH. Furthermore, the addition of sodium salts significantly reduces the conductivity of the electrolyte.

[0049] Example 1

[0050] A 1.6 mol / L pentavalent vanadium solution was prepared by electrolysis, with a sulfuric acid concentration of 2.5 mol / L. Different concentrations of trifluoromethanesulfonic acid were then added.

[0051] Sample 1a: 0.1 mol / L

[0052] Sample 1b: 0.5 mol / L

[0053] Sample 1c: 1.0 mol / L

[0054] Sample 1 day: 1.5 mol / L

[0055] Sample 1e: 2.0 mol / L

[0056] Sample 1f: 3.0 mol / L

[0057] 1g of sample: 4.0mol / L

[0058] The solutions were placed in a 50°C water bath for static stability testing. The results showed that sample 1a exhibited slight precipitation after 120 h, with a solution viscosity of 4.9 mPa·s (25°C); sample 1b exhibited slight precipitation after 240 h, with a solution viscosity of 5.2 mPa·s (25°C); sample 1c remained stable until approximately 720 h, with a solution viscosity of 5.5 mPa·s (25°C); sample 1d remained stable until approximately 750 h, with a solution viscosity of 5.8 mPa·s (25°C); sample 1e remained stable until approximately 780 h, with a solution viscosity of 6.3 mPa·s (25°C); sample 1f remained stable until approximately 800 h, but the electrolyte viscosity increased to 7.2 mPa·s (25°C); and sample 1g remained stable until approximately 820 h, but the electrolyte viscosity increased to 8.5 mPa·s (25°C). The results showed that the stability of the electrolyte gradually improved with increasing trifluoromethanesulfonic acid concentration, but when the concentration exceeded 1.0 mol / L, the viscosity of the electrolyte increased significantly and the fluidity gradually decreased. Considering both stability and fluidity, 1.0 mol / L was the optimal concentration.

[0059] Example 2

[0060] Pentavalent vanadium solutions of different concentrations were prepared by electrolysis, with sulfuric acid concentration at 2.5 mol / L and trifluoromethanesulfonic acid concentration fixed at 1.0 mol / L.

[0061] Sample 2a: 1.0 mol / L

[0062] Sample 2b: 1.4 mol / L

[0063] Sample 2c: 1.6 mol / L

[0064] Sample 2d: 1.8 mol / L

[0065] Sample 2e: 2.0 mol / L

[0066] Sample 2f: 2.2 mol / L

[0067] Sample 2g: 2.5mol / L

[0068] The above solutions were placed in a 50℃ water bath for static stability testing. The results showed that: no precipitation was observed in sample 2a during the test, with a solution viscosity of 4.8 mPa·s (25℃); no precipitation was also observed in sample 2b during the test, with a solution viscosity of 5.2 mPa·s (25℃); sample 2c remained stable for 720 h, with a solution viscosity of 5.5 mPa·s (25℃); sample 2d showed slight precipitation after approximately 600 h, with a solution viscosity of 5.8 mPa·s (25℃); sample 2e showed slight precipitation after approximately 480 h, with a solution viscosity of 6.2 mPa·s (25℃); sample 2f showed precipitation after approximately 360 h, with a solution viscosity of 6.5 mPa·s (25℃); and sample 2g showed significant precipitation after approximately 240 h, with a solution viscosity of 7.0 mPa·s (25℃). This indicates that the thermal stability of the electrolyte gradually decreases with increasing vanadium ion concentration.

[0069] Example 3

[0070] A 1.6 mol / L pentavalent vanadium solution was prepared by electrolysis, with a trifluoromethanesulfonic acid concentration of 1.0 mol / L. The effect of different sulfuric acid concentrations was investigated.

[0071] Sample 3a: 1.5 mol / L H2SO4

[0072] Sample 3b: 2.0 mol / L H2SO4

[0073] Sample 3c: 2.5 mol / L H2SO4

[0074] Sample 3d: 3.0 mol / L H2SO4

[0075] Sample 3e: 4.0 mol / L H2SO4

[0076] Sample 3f: 5.0 mol / L H2SO4

[0077] The above solutions were subjected to static stability testing in a 50℃ water bath. The results showed that: sample 3a showed precipitation after approximately 240 hours, with a solution viscosity of 4.6 mPa·s (25℃); sample 3b showed slight precipitation after approximately 360 hours, with a solution viscosity of 5.0 mPa·s (25℃); sample 3c remained stable until 720 hours, with a solution viscosity of 5.5 mPa·s (25℃); sample 3d remained stable until 750 hours, with a solution viscosity of 5.8 mPa·s (25℃); sample 3e remained stable until 780 hours, with a solution viscosity of 6.2 mPa·s (25℃); and sample 3f remained stable until 820 hours, with a solution viscosity of 6.8 mPa·s (25℃). The results indicate that the stability of the electrolyte gradually improves with increasing sulfuric acid concentration; however, when the sulfuric acid concentration exceeds 4.0 mol / L, although the stability continues to improve, the corrosiveness of the electrolyte significantly increases, and the viscosity also rises markedly. Taking into account stability, corrosiveness, and fluidity, a sulfuric acid concentration of 2.5 mol / L is the optimal choice.

[0078] Example 4

[0079] The optimal formulation (1.6 mol / L V, 2.5 mol / L sulfuric acid, 1.0 mol / L trifluoromethanesulfonic acid) was selected for stability testing under different temperature conditions:

[0080] Sample 4a: 40℃

[0081] Sample 4b: 50℃

[0082] Sample 4c: 60℃

[0083] Sample 4d: 70℃

[0084] The results showed that the electrolyte remained stable during the test period (720h) at 40℃ and 50℃; at 60℃, the electrolyte could remain stable for ~240h; and at 70℃, precipitation began to appear in the electrolyte after ~60h.

[0085] Example 5

[0086] A 1.6 mol / L pentavalent vanadium solution was prepared by electrolysis, with a sulfuric acid concentration of 2.5 mol / L. Fluorosulfonic acids with different carbon chain lengths were then added.

[0087] Sample 5a: 1.0 mol / L trifluoromethanesulfonic acid (CF3SO3H)

[0088] Sample 5b: 1.0 mol / L pentafluoroethylsulfonic acid (C2F5SO3H)

[0089] Sample 5c: 1.0 mol / L heptafluoropropylsulfonic acid (C3F7SO3H)

[0090] Sample 5d: 1.0 mol / L perfluorobutylsulfonic acid (C4F9SO3H)

[0091] The above solutions were subjected to static stability testing in a 50℃ water bath. The results showed that sample 5a remained stable for 720 h with a solution viscosity of 5.5 mPa·s (25℃); sample 5b showed slight precipitation after approximately 600 h with a solution viscosity of 5.8 mPa·s (25℃); sample 5c showed slight precipitation after approximately 480 h with a solution viscosity of 6.2 mPa·s (25℃); and sample 5d showed precipitation after approximately 360 h with a solution viscosity of 6.5 mPa·s (25℃). With increasing carbon chain length, the viscosity of the electrolyte gradually increased, and the stability gradually decreased.

[0092] Note: All time data marked with "~" indicate that the corresponding phenomenon was observed within ±5% of that time point.

[0093] This invention, through systematic research, discovered that using trifluoromethanesulfonic acid as a stabilizer can significantly improve the thermal stability of pentavalent vanadium electrolyte. After optimization, the optimal formulation is a combination of 1.6 mol / L pentavalent vanadium, 2.5 mol / L sulfuric acid, and 1.0 mol / L trifluoromethanesulfonic acid. This formulation exhibits excellent stability at 50°C and also possesses suitable viscosity and good flowability.

[0094] Studies have shown that the concentration of trifluoromethanesulfonic acid has a significant impact on electrolyte performance: at low concentrations, the stabilizing effect is insufficient; as the concentration increases, the stability of the electrolyte gradually improves; however, when the concentration exceeds a certain value, although the stability continues to improve, the solution viscosity increases significantly, and the fluidity deteriorates, which is not conducive to practical applications. Therefore, considering both stability and fluidity, 1.0 mol / L is the optimal concentration.

[0095] Furthermore, the study found that the carbon chain length of fluorosulfonic acid compounds has a significant impact on the stabilization effect. With increasing carbon chain length, the electrolyte stability gradually decreases, while the viscosity shows an upward trend. This may be due to the enhanced steric hindrance effect of long-chain fluorosulfonic acids, affecting their coordination with vanadium ions. Regarding temperature, this preferred formulation exhibits excellent stability in the 40-50℃ range, but the stabilization time significantly shortens with further increases in temperature.

[0096] This invention not only solves the technical problem of poor thermal stability of pentavalent vanadium electrolyte, but also uses trifluoromethanesulfonic acid which has good chemical stability, avoiding the defects of easy decomposition of traditional organic stabilizers, and providing reliable technical support for the practical application of all-vanadium redox flow batteries.

[0097] Table 1. Stability test results of electrolytes with different formulations at 50℃

[0098]

[0099]

[0100] Note:

[0101] 1) "-" indicates that no precipitation was observed.

[0102] 2) "~" indicates that the corresponding phenomenon was observed within ±5% of that time point.

[0103] Example 6

[0104] A 1.6 mol / L pentavalent vanadium solution was prepared by electrolysis, with a sulfuric acid concentration of 2.5 mol / L. Different concentrations of trifluoromethanesulfonic acid were then added.

[0105] Sample 6a: 1.6M V + 2.5M H2SO4 + 0.5M CF3SO3H

[0106] Sample 6b: 1.6M V + 2.5M H₂SO₄ + 1.0M CF₃SO₃H

[0107] Sample 6c: 1.6M V + 2.5M H2SO4 + 1.5M CF3SO3H

[0108] Sample 6d: 1.6M V + 2.5M H2SO4 + 2.0M CF3SO3H

[0109] Sample 6e: 1.6M V + 2.5M H₂SO₄ + 3.0M CF₃SO₃H

[0110] Sample 6f: 1.6M V + 2.5M H₂SO₄ + 4.0M CF₃SO₃H

[0111] Diaphragm: Nafion 115

[0112] Electrode: carbon felt

[0113] Electrode area: 48cm² 2

[0114] Current density: 80 mA / cm 2

[0115] Charging cut-off voltage: 1.65V

[0116] Discharge cutoff voltage: 0.8V

[0117] Experimental temperature: 50℃

[0118] After assembling the battery, performance testing is conducted.

[0119] Example 7

[0120] A 1.6 mol / L pentavalent vanadium solution was prepared by electrolysis, and the trifluoromethanesulfonic acid concentration was 1.0 mol / L. The effect of different sulfuric acid concentrations on battery performance was investigated.

[0121] Sample 7a: 1.6M V + 3.0M H2SO4 + 1.0M CF3SO3H

[0122] Sample 7b: 1.6M V + 4.0M H2SO4 + 1.0M CF3SO3H

[0123] Sample 7c: 1.6M V + 5.0M H2SO4 + 1.0M CF3SO3 H

[0124] Other test conditions are the same as in Example 6.

[0125] Example 8

[0126] The optimal formulation from Example 6 (1.6M V + 2.5M H2SO4 + 1.0M CF3SO3H) was used to test battery performance at different temperatures.

[0127] Sample 8a: 25℃

[0128] Sample 8b: 40℃

[0129] Sample 8c: 50℃

[0130] Sample 8 days: 60℃

[0131] Other test conditions are the same as in Example 6.

[0132] Comparative Example 10

[0133] Single-cell tests were conducted under the basic electrolyte formulation (1.6 M V + 2.5 M H2SO4), and the battery test conditions were the same as in Example 6.

[0134] Comparative Example 11

[0135] Single-cell tests were conducted using methanesulfonic acid as a stabilizer (1.6M V + 2.5M H2SO4 + 1.0M CH3SO3H), and the battery test conditions were the same as in Example 6.

[0136] Comparative Example 12

[0137] Single-cell tests were conducted using perfluoromethyl propyl ether as a stabilizer (1.6 M V + 2.5 M H2SO4 + 1.0 M C4F9OCH3), and the battery test conditions were the same as in Example 6.

[0138] Comparative Example 13

[0139] Sodium trifluoromethanesulfonate was used as a stabilizer (1.6M V + 2.5M H2SO4 + 1.0M CF3SO3Na) for single-cell testing, and the battery testing conditions were the same as in Example 6.

[0140] Table 2 Battery performance parameters with different electrolyte formulations

[0141]

[0142] This invention systematically evaluates the battery performance of electrolytes with different formulations. Experimental results show that the basic formulation (1.6 M V + 2.5 M H₂SO₄) exhibits poor battery performance, with a coulombic efficiency of only 92.5% and an energy efficiency of only 78.5%. While adding organic stabilizers (methanesulfonic acid) or fluorinated ethers can improve performance, the improvement is limited. In contrast, the electrolyte system with added trifluoromethanesulfonic acid demonstrates excellent electrochemical performance, especially under the optimal formulation (1.6 M V + 2.5 M H₂SO₄ + 1.0 MCF₃SO₃H), achieving a coulombic efficiency of 98.2%, a voltage efficiency of 87.5%, and an energy efficiency of 85.9% at 50°C. The study found that the concentration of trifluoromethanesulfonic acid significantly affects battery performance, with 1.0 M being the optimal concentration; excessively high or low concentrations lead to performance degradation. A sulfuric acid concentration of 2.5-3.0 M is most suitable. Within the temperature range of 25-60°C, 50°C is the optimal operating temperature.

[0143] Example 9

[0144] The formulation sample 6b (1.6M V + 2.5M H2SO4 + 1.0M CF3SO3H) with the best performance in Table 2 was selected and compared with Comparative Example 6 (1.6M V + 2.5M H2SO4) for long-cycle performance testing. The test conditions are as follows:

[0145] Diaphragm: Nafion 115

[0146] Electrode: carbon felt

[0147] Electrode area: 48cm² 2

[0148] Current density: 80 mA / cm 2

[0149] Charging cut-off voltage: 1.65V

[0150] Discharge cutoff voltage: 0.8V

[0151] Experimental temperature: 50℃

[0152] Number of loops: 200

[0153] Test results are as follows Figure 1-2 As shown. From Figure 1 It can be seen that sample 6b with added 1.0M trifluoromethanesulfonic acid exhibits excellent cycle stability, with its discharge capacity slowly decreasing from an initial 1.35 Ah to 1.02 Ah after 200 cycles, showing a high capacity retention rate. In contrast, comparative sample 10 (blank sample) showed significant capacity decay, with a sharp decrease in capacity after 100 cycles, and only about 0.1 Ah remaining after 200 cycles.

[0154] Figure 2 The coulombic efficiency and energy efficiency of sample 6b during cycling are shown. The results indicate that after the addition of trifluoromethanesulfonic acid, the coulombic efficiency of the battery remained stable above 98%, and the energy efficiency remained above 85%, with almost no degradation in any performance indicator during 200 cycles. This result fully confirms that trifluoromethanesulfonic acid can not only significantly improve the cycle stability of the battery but also ensure that the battery maintains excellent electrochemical performance during long-term cycling.

Claims

1. A vanadium redox flow battery electrolyte containing a fluorosulfonic acid stabilizer, characterized in that: The electrolyte contains a strong inorganic acid, a fluorosulfonic acid compound, vanadium ions, and water.

2. The electrolyte according to claim 1, characterized in that: The fluorosulfonic acid compounds are selected from one or more of the following: fluorosulfonic acids with C1-C8 carbon chains, specifically including: trifluoromethanesulfonic acid, pentafluoroethylsulfonic acid, heptafluoropropylsulfonic acid, perfluorobutylsulfonic acid, perfluoropentylsulfonic acid, perfluorohexylsulfonic acid, perfluoroheptylsulfonic acid, and perfluorooctylsulfonic acid. Preferably, the fluorosulfonic acid compound is a fluorosulfonic acid with a C1-C4 carbon chain; More preferably, the fluorosulfonic acid compound is trifluoromethanesulfonic acid.

3. The electrolyte according to claim 1 or 2, characterized in that: The concentration of the fluorosulfonic acid compound in the electrolyte is 0.1-4.0 mol / L; Preferably, the concentration of the fluorosulfonic acid compound is 0.2-2.0 mol / L.

4. The electrolyte according to claim 1 or 2, characterized in that: The concentration of vanadium ions in the electrolyte is 1.0-2.5 mol / L; Preferably, the concentration of vanadium ions in the electrolyte is 1.5-2.2 mol / L.

5. The electrolyte according to claim 1 or 2, characterized in that: The strong inorganic acid is sulfuric acid; The concentration of sulfuric acid in the electrolyte is 1.5-5.0 mol / L; Preferably, the concentration of sulfuric acid in the electrolyte is 1.5-3.0 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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