All-vanadium redox flow battery positive electrolyte and application thereof

Abstract

This invention discloses a positive electrode electrolyte for a vanadium redox flow battery and its application. The positive electrode electrolyte contains a composite additive. The composite additive is composed of sodium phosphate and / or hexadecyltrimethylammonium bromide. In the positive electrode electrolyte, the concentration of sodium phosphate is 0-0.05 mol / L and the concentration of hexadecyltrimethylammonium bromide is 0-0.5 mmol / L.

Description

Technical Field

[0001] This invention relates to the field of electrolyte stability technology, specifically to a vanadium redox flow battery positive electrode electrolyte and its application. Background Technology

[0002] With the continuous depletion of fossil fuels and increasingly stringent environmental protection standards, clean energy technologies, represented by wind and solar power, have become a core direction for the global energy structure transformation. Clean energy mainly includes wind, solar, biomass, and ocean energy, all of which can be converted into electricity. However, clean energy power generation is characterized by significant intermittency and instability, making it difficult to directly meet the continuous demand for electricity. Therefore, developing efficient energy storage and conversion devices to achieve peak shaving and valley filling and rational allocation of electricity has become a key technology for the stable connection of clean electricity to the grid. Vanadium redox flow batteries (VFBs) have become one of the most promising technologies for large-scale energy storage in renewable energy power generation, grid peak shaving and valley filling, and emergency and backup power plants due to their outstanding advantages such as independently adjustable system capacity and power, rapid response, safety and reliability, environmental friendliness, long cycle life, and ease of maintenance and regeneration.

[0003] The key materials for vanadium redox flow batteries mainly include electrodes, membranes, and electrolytes. Research on these key materials, particularly in improving their stability, durability, and reducing costs, is therefore crucial. The electrolyte solution is a vital component of the vanadium redox flow battery; its concentration and volume directly determine the battery's energy density. Therefore, the stability of the electrolyte directly affects the overall stability of the vanadium redox flow battery. Currently, electrolyte stability issues include the tendency for solid precipitation and deposition under high-temperature conditions, leading to system instability and capacity loss. Especially during long-term operation, the battery capacity gradually declines, ultimately requiring regular electrolyte maintenance and regeneration to restore performance and capacity, negatively impacting long-term battery operation. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of this invention is to provide a positive electrode electrolyte for vanadium redox flow batteries and its application, so as to solve the problems of poor stability and large capacity loss of the electrolyte in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a positive electrode electrolyte for a vanadium redox flow battery, the positive electrode electrolyte containing a composite additive; the composite additive is composed of sodium phosphate and / or hexadecyltrimethylammonium bromide;

[0007] In the positive electrode electrolyte of the vanadium redox flow battery, the concentration of sodium phosphate is 0–0.05 mol / L and the concentration of hexadecyltrimethylammonium bromide is 0–0.5 mmol / L.

[0008] Preferably, the positive electrode electrolyte further contains VO 2+ VO2 + V2O3 4+ One or more of VO2SO4; and SO4 2- and HSO4 - .

[0009] Preferably, the vanadium ion concentration is 1 mol / L to 2 mol / L, and the sulfate and bisulfate ion concentrations are 3 mol / L to 5.5 mol / L.

[0010] Preferably, the concentration of vanadium oxide in the electrolyte is 1 mol / L to 2 mol / L.

[0011] Preferably, the concentration of sodium phosphate is 0.02 mol / L to 0.03 mol / L, and the concentration of hexadecyltrimethylammonium bromide is 0.15 mmol / L to 0.25 mmol / L.

[0012] Preferably, the concentration of sodium phosphate is 0.025 mol / L and the concentration of hexadecyltrimethylammonium bromide is 0.2 mmol / L.

[0013] Secondly, the present invention provides an application of the positive electrode electrolyte of a vanadium redox flow battery, wherein the above-mentioned positive electrode electrolyte of the vanadium redox flow battery is used in a vanadium redox flow battery.

[0014] Preferably, the vanadium redox flow battery is a battery system composed of one or two of tetravalent and pentavalent vanadium oxide ions, together with sulfuric acid.

[0015] Preferably, the vanadium redox flow battery uses graphite felt electrodes as the positive and negative electrode materials and a perfluorosulfonic acid type proton exchange membrane as the separator.

[0016] Preferably, the negative electrode electrolyte of the all-vanadium redox flow battery contains V 2+ V 3+ It contains one or more of the following: SO42-1, SO2 ... 2- and HSO4 - .

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. In its research on the positive electrode electrolyte of vanadium redox flow batteries, this invention unexpectedly discovered that sodium phosphate and hexadecyltrimethylammonium bromide have different effects on the stability of the positive electrode electrolyte: when the concentration of one of the sodium phosphate or hexadecyltrimethylammonium bromide remains constant while the concentration of the other is gradually increased, the precipitation rate of the electrolyte under high-temperature conditions exhibits a fluctuating change of first increasing, then decreasing, and then increasing again. This indicates that with the increase of the concentration of these two additives, the high-temperature stability of the electrolyte exhibits a fluctuating change of first decreasing, then increasing, and then decreasing again. At the same time, under the premise that both additives are present, the adverse effect of increasing the concentration of hexadecyltrimethylammonium bromide is greater than that of sodium phosphate. Moreover, this invention also unexpectedly discovered the synergistic effect between sodium phosphate and hexadecyltrimethylammonium bromide. When their concentrations are within a suitable range, they can effectively suppress precipitation during long-term cycling at high temperatures, thereby suppressing the capacity decay of the electrolyte during high-temperature operation and achieving stable operation of the electrolyte. Especially under high-temperature conditions, this allows the positive electrode electrolyte of the vanadium redox flow battery to adapt to more working environments.

[0019] 2. The electrolyte preparation process described in this invention is simple to operate, energy-saving, environmentally friendly, and low in cost. At the same time, it can achieve stable operation of the electrolyte in the battery, making the positive electrode electrolyte of the all-vanadium redox flow battery described in this invention have good prospects for industrial application. Attached Figure Description

[0020] Figure 1 The graph shows a comparison of the electrolyte stability at 50°C for Examples 6-8 and Example 1.

[0021] Figure 2 The XRD patterns are comparison diagrams of the electrolyte thermal stability of Examples 6-8 and Example 1.

[0022] Figure 3 Raman comparison diagrams of the electrolytes in Examples 6-8 and Example 1.

[0023] Figure 4 A comparison chart of battery performance after the electrolytes of Examples 1 and 6 were used to make batteries.

[0024] Figure 5 A comparison chart showing the capacity decay of batteries made from the electrolytes of Examples 1 and 6. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the present invention are within the scope of protection of the present invention.

[0026] Unless otherwise specified in the specific circumstances, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within that range, but are not limited to the specific values ​​listed when the range is defined.

[0027] I. A positive electrode electrolyte for an all-vanadium redox flow battery

[0028] The positive electrode electrolyte of the vanadium redox flow battery of the present invention contains a composite additive; the composite additive is composed of sodium phosphate and hexadecyltrimethylammonium bromide; wherein, in the positive electrode electrolyte of the vanadium redox flow battery, the concentration of sodium phosphate is 0.01 mol / L to 0.05 mol / L, and the concentration of hexadecyltrimethylammonium bromide is 0.1 mmol / L to 0.5 mmol / L.

[0029] This invention, based on in-depth research into the positive electrode electrolyte of vanadium redox flow batteries, reveals that because the electrolyte solution continuously circulates within the system, phase transitions such as solid precipitation and deposition can cause blockages in the liquid flow channels and internal battery channels, affecting system stability. Therefore, it is essential to ensure the electrolyte maintains high activity and stability during operation. Furthermore, due to the limited solubility of vanadium ions in sulfuric acid, precipitation occurs in the positive electrode electrolyte during charge and discharge when the concentration of pentavalent vanadium ions exceeds 1.8 mol / L or the operating temperature exceeds 50°C, resulting in electrolyte capacity loss and limiting the improvement of system energy density. Moreover, as vanadium ions of various valence states in the electrolytes at both the positive and negative electrodes cross the battery separator, they mix and undergo side reactions with other vanadium ion states. With continued cycling, these cross-contamination-induced side reactions become increasingly severe, gradually leading to an imbalance in the valence states and the amount of vanadium ions in the electrolytes on both sides, ultimately affecting battery efficiency and capacity. Therefore, this invention addresses how to reduce capacity loss while ensuring stable operation of the battery.

[0030] Based on this, the present invention considers adding additives to improve the stability of the electrolyte. Therefore, sodium phosphate and hexadecyltrimethylammonium bromide are selected as additives because vanadium ions, the active material in the electrolyte, can generate specific interactions with sodium phosphate, which helps to promote the stability of the pentavalent vanadium structure and results in a relatively high capacity retention rate during battery cycling. However, sodium phosphate, as an active material in a sulfuric acid-supported electrolyte, will generate self-precipitated hydrated vanadium oxyphosphate, which will cause a loss of battery capacity and reduce the efficiency of the flow battery. On the other hand, hexadecyltrimethylammonium bromide (CTAB) forms micelles in the electrolyte, and its quaternary ammonium head groups interact with pentavalent vanadium (V... 5+The CTAB (Carbon Cockatoyl Alcohol) acts as a micelle to prevent further polymerization of vanadium, thus inhibiting the crystallization of pentavalent vanadium. Simultaneously, CTAB forms stable hemispherical particles at the electrode and electrolyte interface, acting as a micelle catalyzer for the V(IV) / V(V) redox couple, thereby improving the electrochemical reactivity of the electrolyte. Therefore, after in-depth research, this invention unexpectedly discovered that sodium phosphate and hexadecyltrimethylammonium bromide have different effects on the stability of the positive electrode electrolyte in vanadium redox flow batteries: when the concentration of one of the sodium phosphate or hexadecyltrimethylammonium bromide remains constant while the concentration of the other gradually increases, the precipitation rate of the electrolyte under high-temperature conditions exhibits a fluctuating change of first increasing, then decreasing, and then increasing again. This indicates that with the increase of the concentration of these two additives, the high-temperature stability of the electrolyte exhibits a fluctuating change of first decreasing, then increasing, and then decreasing again. Furthermore, under the premise that both additives are present, the adverse effect of increasing the concentration of hexadecyltrimethylammonium bromide is greater than that of sodium phosphate. Therefore, this invention further uses hexadecyltrimethylammonium bromide and sodium phosphate as composite additives in the electrolyte of vanadium redox flow batteries. CTAB, through micelle encapsulation of phosphate ions, regulates their reaction with V(IV) / V(V) redox couple. 5+ The coordination rate of sodium phosphate is reduced, thus decreasing heterogeneous nucleation caused by local supersaturation and inhibiting precipitation formation; simultaneously, the PO4 of sodium phosphate... 3- A dynamic equilibrium is formed with the quaternary ammonium cation of CTAB to optimize V. 5+ The solvation structure of the electrolyte delays the stratification of the electrolyte and keeps the electrolyte structure stable. CTAB forms an adsorption layer on the electrode surface to suppress side reactions (such as oxygen evolution reaction). At the same time, the buffering effect of sodium phosphate maintains the pH stability of the electrolyte. It can not only maintain the original redox reaction of vanadium, but also adjust the interaction between the additive and vanadium, ultimately changing the stability and electrochemical performance of the electrolyte.

[0031] In some embodiments of the present invention, the positive electrode electrolyte further comprises VO 2+ VO2 + V2O3 4+ One or more of VO2SO4; and SO4 2- and HSO4 - .

[0032] In some embodiments of the present invention, the vanadium ion concentration is 1 mol / L to 2 mol / L, and the sulfate and bisulfate ion concentrations are 3 mol / L to 5.5 mol / L.

[0033] In some embodiments of the present invention, the concentration of vanadium oxide in the electrolyte is 1 mol / L to 2 mol / L.

[0034] In some embodiments of the present invention, the composite additive in the electrolyte is composed of sodium phosphate and hexadecyltrimethylammonium bromide. The concentration of sodium phosphate is 0.02 mol / L to 0.03 mol / L, and the concentration of hexadecyltrimethylammonium bromide is 0.15 mmol / L to 0.25 mmol / L. When the concentration of hexadecyltrimethylammonium bromide remains constant, the precipitation rate of the electrolyte decreases significantly when the concentration of sodium phosphate increases from 0.01 mol / L to 0.025 mol / L. Conversely, the precipitation rate increases significantly when the concentration of sodium phosphate increases from 0.025 mol / L to 0.05 mol / L, but the increase is more gradual. Therefore, the concentration of sodium phosphate can be 0.02 mol / L, 0.025 mol / L, or 0.03 mol / L. The values ​​fall within the range defined by any two of the aforementioned specific values ​​as endpoints. When the sodium phosphate concentration remains constant, the stability of the electrolyte changes with increasing hexadecyltrimethylammonium bromide concentration, following the aforementioned trend. Therefore, the concentration of hexadecyltrimethylammonium bromide can be 0.15 mmol / L, 0.20 mmol / L, or 0.25 mmol / L, or fall within the range defined by any two of the aforementioned specific values ​​as endpoints. It should be understood that, in the implementation scheme, any of the aforementioned ranges can be combined with any other range.

[0035] II. Application of a vanadium redox flow battery positive electrode electrolyte

[0036] This invention relates to the application of the positive electrode electrolyte of a vanadium redox flow battery in a vanadium redox flow battery. Specifically, the vanadium redox flow battery is a battery system composed of one or two of tetravalent and pentavalent vanadium oxide ions, along with sulfuric acid. The vanadium redox flow battery uses graphite felt electrodes as both the positive and negative electrode materials, and a perfluorosulfonic acid type proton exchange membrane as the separator. The negative electrode electrolyte of the vanadium redox flow battery contains V... 2+ V 3+ It contains one or more of the following: SO42-1, SO2 ... 2- and HSO4 - .

[0037] III. Examples and Comparative Examples

[0038] Example 1

[0039] Sodium phosphate and hexadecyltrimethylammonium bromide were added to the electrolyte (with a V(V) ion concentration of 2.0 mol / L, a sulfate concentration of 5.5 mol / L, and a SOC of 90%), and the mixture was stirred thoroughly before being placed into a sealed glass bottle. The concentration of sodium phosphate in the electrolyte was 0.025 mol / L, and the concentration of hexadecyltrimethylammonium bromide was 0.2 mmol / L.

[0040] Example 2

[0041] This example is an adjustment to Example 1, except that the concentration of sodium phosphate in the electrolyte is 0.01 mol / L. All other steps are exactly the same as in Example 1.

[0042] Example 3

[0043] This example is an adjustment to Example 1, except that the concentration of sodium phosphate in the electrolyte is 0.05 mol / L. All other steps are exactly the same as in Example 1.

[0044] Example 4

[0045] The experiment was modified from Example 1, except that the concentration of hexadecyltrimethylammonium bromide in the electrolyte was 0.1 mmol / L. All other steps were exactly the same as in Example 1.

[0046] Example 5

[0047] This example is an adjustment to Example 1, except that the concentration of hexadecyltrimethylammonium bromide in the electrolyte is 0.5 mmol / L. All other steps are identical to those in Example 1.

[0048] Example 6

[0049] This example is an adjustment based on Example 1, except that sodium phosphate and hexadecyltrimethylammonium bromide are not added. All other steps are exactly the same as in Example 1.

[0050] Example 7

[0051] This example is an adjustment to Example 1, except that only sodium phosphate is added. All other steps are exactly the same as in Example 1.

[0052] Example 8

[0053] This example is an adjustment to Example 1, except that only hexadecyltrimethylammonium bromide is added. All other steps are exactly the same as in Example 1.

[0054] IV. Performance Comparison

[0055] 1. Changes in V(V) concentration in electrolyte under high temperature conditions

[0056] The electrolytes prepared in the examples and comparative examples were placed in a constant temperature water bath at 50°C, and the changes in V(V) concentration in the electrolyte were observed and recorded regularly over 7 days, as shown in Table 1.

[0057] Table 1

[0058]

[0059]

[0060] As shown in Table 1, high temperatures generally increase the reaction rate constant, promote electrochemical reaction kinetics, and simultaneously reduce electrolyte viscosity, thereby improving ion transport efficiency. However, when the temperature exceeds a certain range (e.g., above 40°C), the stability of vanadium ions decreases, making them prone to precipitation. In vanadium redox flow batteries, V(V) ions easily form V₂O₅ precipitates at high temperatures, leading to the precipitation of active materials in the electrolyte, clogging the flow channels, and affecting battery performance. Changes in the concentrations of sodium phosphate and hexadecyltrimethylammonium bromide significantly affect the high-temperature stability of the electrolyte.

[0061] (1) For sodium phosphate, when the concentration of hexadecyltrimethylammonium bromide remained constant, the precipitation rate increased significantly (from 12.78% to 14.31%) when the sodium phosphate concentration increased from 0 (Example 8) to 0.01 mol / L (Example 2), indicating that the stability of the electrolyte decreased. When the sodium phosphate concentration was further increased to 0.025 mol / L, the precipitation rate decreased significantly (to 8.33%). However, when the sodium phosphate concentration increased to 0.05 mol / L, the stability of the electrolyte decreased again, but it was still better than the stability without the addition of sodium phosphate (Example 8). When the sodium phosphate concentration remained constant, the effect of the change in the concentration of hexadecyltrimethylammonium bromide on the stability of the electrolyte was similar to that of sodium phosphate, but the effect of hexadecyltrimethylammonium bromide on the precipitation rate was greater.

[0062] (2) As can be seen from the changes in the examples, when the concentration of sodium phosphate is 0.025 mol / L and the concentration of hexadecyltrimethylammonium bromide is 0.2 mmol / L, sodium phosphate and hexadecyltrimethylammonium bromide begin to play a synergistic role. The phosphate ions provided by sodium phosphate can form a stable complex with V(V) ions, reducing the activity of free vanadium ions and thus inhibiting precipitation. CTAB is a cationic surfactant that reduces surface tension or forms a protective layer by adsorbing on vanadium ions or potential nucleation sites, preventing particle aggregation and precipitation. When the concentrations of the two reach an appropriate range, they play a stabilizing role through a dual pathway. Sodium phosphate coordinates with V(V) in the bulk phase, and CTAB forms a protective layer at the interface, jointly blocking the precipitation chain reaction. At the same time, CTAB reduces interfacial impedance, and sodium phosphate maintains ion mobility, thereby improving the overall reversibility of the reaction through electrochemical synergy. High-temperature adaptability is formed. At 50°C, the composite additive offsets the thermal effect. Evidence suggests that the mixed additive can extend the stable temperature window of the electrolyte to above 50°C.

[0063] (3) In the composite additive, the concentrations of sodium phosphate and hexadecyltrimethylammonium bromide have an optimal range. When the concentration of one of them deviates from the optimal value, it will lead to an increase in V(V) precipitation rate by disrupting the bulk phase-interface balance (such as excessive sodium phosphate causing secondary precipitation, or excessive CTAB increasing viscosity) or weakening the protection mechanism (such as insufficient concentration). Therefore, the composite additive can achieve the best stability through synergistic effect.

[0064] 2. XRD test

[0065] Following Example 1, the solid precipitate after the thermal stability test was collected, filtered, and dried in a 100°C oven for 24 hours. It was then ground for approximately 30 minutes, passed through a 200-mesh sieve, and the powder was collected for later use. XRD tests were performed on both the blank sample and the pentavalent vanadium sample with additives. Figure 2 As shown.

[0066] XRD analysis showed that the peak of hydrated vanadium pentoxide decreased continuously with the addition of additives, which also indicates the effect of additives on pentavalent vanadium ions.

[0067] The precipitate formed in the electrolyte of Example 6 was mainly identified as V₂O₅·1.6H₂O, with a small amount of V₂O₅·H₂O. The precipitate in the electrolyte with Na₃PO₄ additive was also mainly V₂O₅·1.6H₂O, but with a small amount of VOPO₄·2H₂O, indicating that the introduction of Na₃PO₄ altered the V₂O content in the solution. 5+ The ions formed VOP bonds. The electrolyte precipitate with added CTAB showed the same characteristic peaks as the blank group and no impurity diffraction peaks were produced. This may be because CTAB is mainly present in the electrolyte, acting as a dispersant to prevent vanadium pentoxide particles from agglomerating and inhibiting precipitation, or it may be that the amount of CTAB added was too small, limiting the detection accuracy of XRD.

[0068] 3. Electrolyte stability

[0069] Take 10 mL of the electrolyte from Example 1 and Example 6 respectively, and dilute it to 1 mol / L VO2. + .

[0070] The electrolytes from Examples 6 and 1 were subjected to Raman spectroscopy. The Raman spectra revealed five peaks with wavenumbers of 416, 590, 931, 979, and 1051 cm⁻¹. -1 HSO4 - and VOS, HSO4 - VO2 + SO4 2- HSO4 - HSO4- and VO2 + The plasma exhibits stretching and contraction mechanisms such as VOS and V=O. No significant effect of additives on the ionic structure of vanadium (V) electrolytes was observed in Raman experiments. Although free VO2... + The peak intensities did not change significantly, but the decrease in the intensity of these peaks may be due to the addition of Na3PO4 and CTAB, which complex or encapsulate high-valence vanadium ions, reducing free vanadium ions, thereby reducing vanadium ion polymerization and dehydration precipitation, and promoting the stability of the electrolyte.

[0071] 4. Performance comparison of electrolytes after application in batteries

[0072] Take 30 mL of the electrolyte from Example 1 and Example 6 respectively as the positive electrode electrolyte, 2 mol / L V 3+ A vanadium redox flow single cell was assembled using 5.5 mol / L H₂SO₄ as the negative electrode electrolyte. The battery separator was Nafion 117 (DuPont), with an effective membrane area of ​​25 cm⁻². 2 The electrodes are made of activated graphite felt, the bipolar plates are graphite plates, and the current density is 80 mA / cm². 2 .

[0073] A single cell was subjected to constant current charge and discharge at a high temperature of 55°C, with a cutoff voltage of 0.8-1.65V, from which the following results were obtained: Figure 4 The graph shows a comparison of the performance of batteries with the composite additive electrolyte and those with the blank electrolyte. Figure 4 It can be seen that, compared with the battery corresponding to the blank electrolyte, the efficiency of the battery with composite additive (Na3PO4+CTAB) is more stable due to the interaction between the composite additive and vanadium ions. The CV, VE, and EE are all greater than the efficiency of the blank group, indicating that at high temperatures, the battery with composite additive performs better than the battery with blank.

[0074] Table 2

[0075] category Coulomb efficiency Voltage efficiency Energy efficiency Example 6 95.79％ 86.49％ 82.85％ Example 1 95.81％ 89.47％ 85.72％

[0076] 5. Battery capacity

[0077] Take 30 mL each of the electrolyte from Example 1 and the comparative example as the positive electrode electrolyte, 2 mol / L V. 3+ A vanadium redox flow single cell was assembled using 5.5 mol / L H₂SO₄ as the negative electrode electrolyte. The battery separator was Nafion 117 (DuPont), with an effective membrane area of ​​25 cm⁻². 2 The electrodes are made of activated graphite felt, the bipolar plates are graphite plates, and the current density is 80 mA / cm². 2 A single cell was subjected to constant current charge and discharge at a high temperature of 55°C, with a cutoff voltage of 0.8-1.65V, from which the following results were obtained: Figure 5 The battery capacity decay curve is shown within 60 cycles.

[0078] Depend on Figure 5 As can be seen, compared with batteries without additives, the addition of appropriate amounts of composite additives can slow down the capacity decay of the battery during cycling due to the interaction between the composite additives and vanadium ions. Therefore, the addition of composite additives can significantly improve the stability of the electrolyte during long-term operation, increase the battery's capacity retention rate, and achieve long-term stable operation of vanadium redox flow batteries.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A positive electrode electrolyte for an all-vanadium redox flow battery, characterized in that, The positive electrode electrolyte of the vanadium redox battery contains a composite additive; the composite additive is composed of sodium phosphate and hexadecyltrimethylammonium bromide. In the positive electrode electrolyte of the vanadium redox flow battery, the concentration of sodium phosphate is 0.01 mol / L to 0.05 mol / L, and the concentration of hexadecyltrimethylammonium bromide is 0.1 mmol / L to 0.5 mmol / L.

2. The vanadium redox flow battery positive electrode electrolyte according to claim 1, characterized in that, The positive electrode electrolyte also contains VO 2+ VO2 + V2O3 4+ One or more of VO2SO4; and SO4 2- and HSO4 - .

3. The vanadium redox flow battery positive electrode electrolyte according to claim 2, characterized in that, The vanadium ion concentration is 1 mol / L to 2 mol / L, and the sulfate and bisulfate ion concentrations are 3 mol / L to 5.5 mol / L.

4. The vanadium redox flow battery positive electrode electrolyte according to claim 3, characterized in that, In the electrolyte, the concentration of vanadium oxide is 1 mol / L to 2 mol / L.

5. The vanadium redox flow battery positive electrode electrolyte according to claim 1, characterized in that, The concentration of sodium phosphate was 0.02 mol / L to 0.03 mol / L, and the concentration of hexadecyltrimethylammonium bromide was 0.15 mmol / L to 0.25 mmol / L.

6. The vanadium redox flow battery positive electrode electrolyte according to claim 5, characterized in that, The concentration of sodium phosphate was 0.025 mol / L, and the concentration of hexadecyltrimethylammonium bromide was 0.2 mmol / L.

7. An application of a positive electrode electrolyte in a vanadium redox flow battery, characterized in that, The application of the positive electrode electrolyte of the vanadium redox flow battery according to any one of claims 1 to 6 in the vanadium redox flow battery.

8. The application according to claim 7, characterized in that, The vanadium redox flow battery is a battery system composed of one or two of the tetravalent and pentavalent vanadium oxide ions, and sulfuric acid.

9. The application according to claim 8, characterized in that, The vanadium redox flow battery uses graphite felt electrodes as the positive and negative electrode materials and a perfluorosulfonic acid type proton exchange membrane as the separator.

10. The application according to claim 7, characterized in that, The negative electrode electrolyte of the all-vanadium redox flow battery contains V 2+ V 3+ One or more of the following; also contains SO4 2- and HSO4 - .

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