All-vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additive and application of all-vanadium redox flow battery electrolyte

Abstract

The invention discloses an all-vanadium redox flow battery electrolyte containing an imidazole phosphate ionic liquid additive and application of the all-vanadium redox flow battery electrolyte, and belongs to the technical field of all-vanadium redox flow battery energy storage. According to the invention, an imidazole phosphate ionic liquid additive is added into the electrolyte of the all-vanadium redox flow battery, and the concentration of the additive in the electrolyte is 0.01 g / L-5 g / L. The cation in the imidazole phosphate ionic liquid additive is imidazole cation, the anion in the imidazole phosphate ionic liquid additive is phosphate anion, the imidazole cation is one or two or more of 1-ethyl-3-methylimidazole, 1-vinyl-3-methylimidazole, 1-butyl-3-methylimidazole and 1-hydroxyethyl-3-methylimidazole, the anion in the imidazole phosphate ionic liquid additive is phosphate anion, and the cation in the imidazole phosphate ionic liquid additive is one or more of 1-ethyl-3-methylimidazole, 1-vinyl-3-methylimidazole, 1-vinyl-3-methylimidazole, 1-butyl-3-methylimidazole and 1-hydroxyethyl-3-methylimidazole. And the phosphate anions are one or two or more of phosphate, hydrophosphate, dihydric phosphate and pyrophosphate. The method is simple in process operation, energy-saving, environment-friendly and low in cost, and meanwhile, stable operation of the electrolyte in the battery can be realized.

Description

Technical Field

[0001] This invention belongs to the field of vanadium redox flow battery energy storage technology, and specifically relates to a vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives and its application. Background Technology

[0002] With the advancement of global modernization, traditional fossil fuels are becoming increasingly scarce, and the environmental problems caused by burning fossil fuels are becoming increasingly serious. Under this dual pressure, people are paying more and more attention to the development of clean and renewable energy. Clean and renewable energy mainly includes wind energy, solar energy, biomass energy, and ocean energy. However, these clean energy sources are geographically limited and have disadvantages such as intermittency and volatility, threatening grid security. Therefore, by implementing secondary battery technology in large-scale energy storage systems, new energy sources can be used efficiently and reliably through energy conversion and storage. In order to smooth and stabilize the power generation output of renewable energy and resolve the time difference between power generation and consumption, and improve power quality and grid reliability, it is necessary to develop efficient energy storage technologies. Vanadium redox flow batteries (VFRBs) have become one of the most promising technologies for large-scale energy storage in renewable energy generation, grid peak shaving and valley filling, emergency and backup power stations 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 performance and reliability of vanadium redox flow batteries are highly dependent on the concentration control and thermodynamic stability of the electrolyte. As the core of the battery system, the concentration and volume of the electrolyte directly determine the battery's energy density and capacity. However, limited by the solubility of vanadium ions in sulfuric acid (typically ≤2M), its energy density is difficult to exceed. When the concentration exceeds 1.8M or the operating temperature is above 50℃, the pentavalent vanadium (VO₂) in the positive electrode electrolyte... + Vanadium ions readily precipitate as vanadium pentoxide (V₂O₅), causing flow channel blockage, capacity decay, and even system failure. Simultaneously, vanadium ion crosstalk during charging and discharging exacerbates local concentration imbalances, further inducing crystallization. These phase transition behaviors not only limit energy density improvements but also significantly increase thermal management costs (requiring an additional 20% energy consumption for temperature control). Therefore, improving energy density necessitates enhancing the stability of high-concentration electrolytes. Furthermore, the stability control of electrolytes (especially high-concentration pentavalent vanadium ions) at high temperatures plays a decisive role in the stable and reliable operation of batteries and has been a key focus for many researchers. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned problems and provide an electrolyte for vanadium redox flow batteries with imidazole phosphate ionic liquid additives, so as to achieve efficient and stable operation of vanadium redox flow batteries.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A vanadium redox flow battery electrolyte containing an imidazole phosphate ionic liquid additive is provided by adding an imidazole phosphate ionic liquid additive to a vanadium redox flow battery electrolyte. The imidazole phosphate ionic liquid additive contains an imidazole cation and a phosphate anion. The imidazole cation is one or more of 1-ethyl-3-methylimidazolium, 1-vinyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, and 1-hydroxyethyl-3-methylimidazolium. The phosphate anion is one or more of phosphate, hydrogen phosphate, dihydrogen phosphate, and pyrophosphate.

[0007] Furthermore, in the above-mentioned vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives, the concentration of the imidazole phosphate ionic liquid additives in the vanadium redox flow battery electrolyte is 0.01 g / L to 5 g / L.

[0008] Preferably, the concentration of the imidazole phosphate ionic liquid additive in the vanadium redox flow battery electrolyte is 0.1 g / L to 2 g / L.

[0009] Furthermore, the above-mentioned vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives, wherein the vanadium redox flow battery electrolyte contains V 2+ V 3+ VO 2+ VO2 + and V 5+ An aqueous solution of one or more of the following: sulfate ions.

[0010] Furthermore, in the aforementioned vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives, the sulfate ion is SO4. 2- or HSO4 - .

[0011] Furthermore, in the above-mentioned vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives, the concentration of vanadium in the vanadium redox flow battery electrolyte is 0.5 mol / L to 5 mol / L, and the concentration of sulfate is 1 mol / L to 6 mol / L.

[0012] Preferably, the concentration of vanadium in the electrolyte of the all-vanadium redox flow battery is 1 mol / L to 4 mol / L, and the concentration of sulfate is 2 mol / L to 4 mol / L.

[0013] The application of the vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives as described above in vanadium redox flow batteries.

[0014] Furthermore, the above-described application refers to the use of a vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives as both the positive and negative electrode electrolytes in vanadium redox flow batteries.

[0015] The beneficial results of this invention are as follows: By introducing an imidazole-phosphate composite additive, this invention significantly improves the high-temperature stability and energy density of vanadium redox flow batteries. The nitrogen atom in the imidazole ring binds to vanadium oxide ions through dynamic coordination, forming a stable coordination structure that effectively inhibits the hydrolysis and precipitation of vanadium ions at high temperatures. Simultaneously, the phosphate ion regulates the acidic environment of the electrolyte through a pH buffering effect, reducing corrosive side reactions and thus significantly improving the cycle stability of the battery. Furthermore, the π-π conjugated system of imidazole forms a solvation layer with vanadium ions, weakening interionic association, while the electrostatic shielding effect of the phosphate ion further releases the concentration of active vanadium ions, synergistically improving the solubility of vanadium ions in the electrolyte and optimizing energy density. This additive can be directly incorporated into conventional vanadium-sulfuric acid electrolyte systems, with a simple preparation process that does not require high temperature, high pressure, or complex purification steps. Its high thermal stability and low volatility ensure the reliability of long-term electrolyte operation, while also being low-cost and environmentally friendly, providing an efficient and sustainable solution for large-scale energy storage. Attached Figure Description

[0016] Figure 1 This is a comparison of the cyclic voltammetry curves of the electrolyte with added 1-hydroxyethyl-3-methylimidazolium dihydrogen phosphate in Example 9 and the blank electrolyte.

[0017] Figure 2 This is a comparison chart of coulombic efficiency and energy efficiency between the electrolyte with added 1-hydroxyethyl-3-methylimidazolium phosphate and the blank electrolyte in Example 10.

[0018] Figure 3 This is a comparison chart of capacity decay when assembling batteries with the electrolyte containing 1-hydroxyethyl-3-methylimidazolium dihydrogen phosphate added in Example 10 and with the blank electrolyte. Detailed Implementation

[0019] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0020] Comparative Example 1

[0021] A vanadium redox flow battery electrolyte was prepared for single-cell experiments. The vanadium concentration in the electrolyte was 1.6 M. 3+ With VO 2+ The ratio is 1:1, the H2SO4 concentration is 3M, the diaphragm is Nafion 212, the electrode is carbon felt, and the electrode area is 9 cm². 2The volume of electrolyte at both the positive and negative electrodes is 20 mL, and the current density is 200 mA / cm². 2 The charging and discharging voltage range is 1-1.6V.

[0022] Tested at room temperature, the average performance after 100 cycles was 94% coulombic efficiency, 77% voltage efficiency, and 73% energy efficiency. After 100 cycles, the electrolyte capacity decreased by 45%.

[0023] Tested at 50°C, the average performance after 100 cycles was 90% coulombic efficiency, 76% voltage efficiency, and 68% energy efficiency. After 100 cycles, the electrolyte capacity decreased by 70%.

[0024] Examples 1-7

[0025] A single-cell experiment was conducted using an all-vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives. The vanadium concentration in the electrolyte was 1.6 M. 3+ With VO 2+ The ratio was 1:1, the H2SO4 concentration was 3M, the types and concentrations of imidazole phosphate ionic liquid additives are shown in Table 1, the diaphragm was Nafion 212, the electrode was carbon felt, and the electrode area was 9 cm². 2 The volume of electrolyte at both the positive and negative electrodes is 20 mL, and the current density is 200 mA / cm². 2 The charging and discharging voltage range is 1-1.6V. Normal temperature and high temperature tests were conducted, and the test results are shown in Table 1.

[0026] Table 1. Detailed experimental parameters and battery performance of Comparative Example 1 and Examples 1-7.

[0027]

[0028]

[0029] As shown in Table 1, the battery performance was significantly improved compared to the blank experiment (Comparative Example 1) after adding imidazole phosphate ionic liquid additives, indicating that this type of additive can improve battery performance. Meanwhile, the high-temperature capacity decay at 50℃ was also significantly reduced compared to the blank experiment, indicating that this type of additive can also improve the stability of the electrolyte.

[0030] Example 8

[0031] A 1.6 mol / L pentavalent vanadium solution was prepared by electrolysis. 1-hydroxyethyl-3-methylimidazolium dihydrogen phosphate was added to 10 mL of the pentavalent vanadium solution to achieve concentrations of 0.05 g / L, 0.5 g / L, and 2 g / L in the positive electrode electrolyte of a vanadium redox flow battery, respectively. After thorough mixing and stirring, the solution was placed together with a blank pentavalent vanadium sample in a 50°C water bath and heated. The state of the solution was observed to investigate the effect of different dosages on the thermal stability of pentavalent vanadium.

[0032] Table 2. Effects of different additive contents on electrolyte stability.

[0033] Additive dosage (g / L) Settling time / h 0 20 0.05 37 0.5 48 2 40

[0034] Note: Stabilization time refers to the time from when the electrolyte is placed in a high-temperature environment until solid precipitation is observed.

[0035] When pentavalent vanadium is placed in a high-temperature water bath, a blank pentavalent vanadium solution quickly produces a red V₂O₅ precipitate. However, under the same conditions, with increasing addition of 1-hydroxyethyl-3-methylimidazolium dihydrogen phosphate, the stabilization time of pentavalent vanadium initially increases, but after reaching a peak, further increases in addition shorten the stabilization time. This indicates that the addition of 1-hydroxyethyl-3-methylimidazolium dihydrogen phosphate significantly inhibits the precipitation of the electrolyte. This is because the addition of a small amount of additive, after complexing with pentavalent vanadium ions in the electrolyte to form a new state, significantly reduces the precipitation reaction of V₂O₅, thus achieving long-term stability of the electrolyte at high temperatures. This result has a positive effect on the operation of electrolytes at high temperatures and is beneficial for ensuring the long-term stable operation of vanadium redox flow batteries in high-temperature environments.

[0036] Example 9

[0037] A 1.6 mol / L pentavalent vanadium solution was prepared by electrolysis. The solution was added to 50 mL of 1.6 mol / L vanadium solution. 5+ The CV test electrolyte was prepared by adding 0.5 g / L 1-hydroxyethyl-3-methylimidazolium dihydrogen phosphate to a positive electrode electrolyte of +3 mol / L H2SO4 and stirring thoroughly to dissolve it. The solution was then compared with a pentavalent vanadium electrolyte (1.6 mol / L V) without any additives. 5+ +3 mol / L H₂SO₄ was used as a blank electrolyte for comparison. Cyclic voltammetry was performed using a three-electrode system (working electrode: graphite felt; counter electrode: platinum sheet electrode; reference electrode: saturated calomel electrode). The scan range was 0.2–1.4 V, and the scan rate was 5 mV / s. Figure 1 The comparison shows that the addition of 1-hydroxyethyl-3-methylimidazolium dihydrogen phosphate significantly improves the reactivity and reversibility of the electrolyte.

[0038] Example 10

[0039] Add 0.5 g / L 1-hydroxyethyl-3-methylimidazolium phosphate solution to 50 mL of positive electrode electrolyte (1.6 mol / L VOSO4 + 3 mol / L H2SO4), stir thoroughly until completely dissolved, to prepare the electrolyte to be tested. Use the electrolyte containing 1-hydroxyethyl-3-methylimidazolium phosphate and the blank electrolyte (1.6 mol / L VOSO4 + 3 mol / L H2SO4) as the positive electrode electrolyte, respectively. 3+ Two vanadium redox flow single cells were assembled using 3 mol / L H₂SO₄ as the negative electrode electrolyte. The battery separator was Nafion 212 (DuPont), with an effective membrane area of ​​9 cm⁻². 2 The electrodes are made of activated carbon felt, the bipolar plates are graphite plates, and the current density is 200 mA cm⁻¹. 2 A single cell was subjected to constant current charge and discharge at 45°C, with a cutoff voltage of 1.0-1.55V, from which the following results were obtained: Figure 2 The battery coulombic efficiency and energy efficiency curves over 50 cycles are shown below. Figure 3 The figure shows the battery capacity decay curves over 50 cycles. When the battery reaches the end of the charging period, V₂O₅ precipitates due to the instability of pentavalent vanadium in the electrolyte, causing loss of active material and blockage of the pores on the carbon felt surface, leading to capacity decay and a decrease in coulombic efficiency and energy efficiency. As can be seen from the figure, compared to the battery without additives, the interaction between 1-hydroxyethyl-3-methylimidazolium phosphate and vanadium ions not only significantly improves the thermal stability of pentavalent vanadium but also effectively suppresses the capacity decay caused by the precipitation of pentavalent vanadium at the cathode during the end of the charging period. Therefore, 1-hydroxyethyl-3-methylimidazolium phosphate can significantly improve the stability of the electrolyte during long-term operation, increase the battery capacity retention rate, and achieve more stable operation of the all-vanadium redox flow battery.

Claims

1. A vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives, characterized in that, An imidazole phosphate ionic liquid additive is added to the electrolyte of a vanadium redox flow battery; the imidazole phosphate ionic liquid additive contains an imidazole cation and a phosphate anion; the imidazole cation is one or more of 1-ethyl-3-methylimidazolium, 1-vinyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, and 1-hydroxyethyl-3-methylimidazolium; the phosphate anion is one or more of phosphate, hydrogen phosphate, dihydrogen phosphate, and pyrophosphate.

2. The all-vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives according to claim 1, characterized in that, The concentration of the imidazole phosphate ionic liquid additive in the vanadium redox flow battery electrolyte is 0.01 g / L to 5 g / L.

3. The all-vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives according to claim 2, characterized in that, The concentration of the imidazole phosphate ionic liquid additive in the vanadium redox flow battery electrolyte is 0.1 g / L to 2 g / L.

4. The all-vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives according to claim 1, characterized in that, The electrolyte of the all-vanadium redox flow battery contains V 2+ V 3+ VO 2+ VO2 + and V 5+ An aqueous solution of one or more of the following: sulfate ions.

5. The all-vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives according to claim 4, characterized in that, The sulfate ion is SO4. 2- or HSO4 - .

6. The all-vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives according to claim 4, characterized in that, The vanadium concentration in the electrolyte of the vanadium redox flow battery is 0.5 mol / L to 5 mol / L, and the sulfate concentration is 1 mol / L to 6 mol / L.

7. The all-vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additives according to claim 6, characterized in that, The vanadium redox flow battery electrolyte has a vanadium concentration of 1 mol / L to 4 mol / L and a sulfate concentration of 2 mol / L to 4 mol / L.

8. The application of the vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additive as described in any one of claims 1-7 as a battery electrolyte in a vanadium redox flow battery.

9. The application according to claim 8, characterized in that, The application of the vanadium redox flow battery electrolyte containing imidazole phosphate ionic liquid additive as both positive and negative electrode electrolyte in vanadium redox flow batteries.

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