Vanadium battery positive electrolyte based on p-cds synergistic stabilization and application thereof

Abstract

The application belongs to the technical field of electrolyte of all-vanadium redox flow battery, and particularly relates to a vanadium battery positive electrolyte based on P-CDs synergistic stabilization and application thereof. The vanadium battery positive electrolyte provided by the application comprises vanadium ions, a supporting electrolyte and an additive, and the additive comprises phosphorus-doped carbon quantum dots. The application takes phosphorus-doped carbon quantum dots (P-CQDs) as an additive of the vanadium battery positive electrolyte, the additive has a synergistic stabilization mechanism, can effectively block the precipitation path of pentavalent vanadium ions, and significantly improves the high-temperature stability of the pentavalent vanadium electrolyte.

Description

Technical Field

[0001] This invention belongs to the field of vanadium redox flow battery electrolyte technology, specifically a vanadium battery cathode electrolyte based on P-CDs synergistic stabilization and its application. Background Technology

[0002] Vanadium redox flow batteries (vanadium batteries) are characterized by high safety and reliability, long lifespan, and environmental friendliness, making them the preferred choice for large-scale, long-term energy storage. They can be applied to renewable energy storage, grid peak shaving, and backup power. The electrolyte is the energy storage carrier in a vanadium redox flow battery system and a crucial component, directly affecting the system's stability and economics. However, due to the tendency of pentavalent vanadium ions to hydrolyze at high temperatures to form vanadium pentoxide precipitate and the tendency of low-valent vanadium to crystallize at low temperatures, the vanadium ion concentration in commercially available electrolytes is generally controlled at 1.6~1.7 mol / L, with an operating temperature range of -5~40℃. This results in low electrolyte energy density, large footprint, and low overall energy efficiency.

[0003] To improve the stability of pentavalent vanadium ions at high temperatures, researchers have attempted to modify the supporting electrolyte system and add additives to improve the stability of the pentavalent electrolyte. Hydrochloric acid and hydrochloric acid-sulfuric acid mixed acid electrolyte systems can raise the upper limit of vanadium battery operating temperature from 40°C to 45°C, but both carry the risk of HCl volatilization and Cl2 generation, and therefore have not been widely adopted. Methylsulfonic acid, aminosulfonic acid, and trifluoromethanesulfonic acid are relatively expensive, and their introduction into the electrolyte would increase costs. Adding additives to the electrolyte is another method that can significantly improve the stability of the positive electrode electrolyte, but existing additives have limited effect on improving the stability of pentavalent vanadium ions at temperatures of 50°C and above. Small molecule additives (such as oxalic acid) are easily oxidized and decomposed, while polymer additives (such as polyacrylic acid and polyphosphates) are prone to chain breakage. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a vanadium battery cathode electrolyte based on P-CDs synergistic stability and its application. This invention adds phosphorus-doped carbon quantum dots (P-CDs) to the vanadium battery cathode electrolyte, which effectively improves the stability of pentavalent vanadium electrolyte at high temperatures and expands the temperature adaptation range of vanadium batteries.

[0005] This invention provides a vanadium battery cathode electrolyte based on P-CDs synergistic stabilization, comprising vanadium ions, supporting electrolyte, and additives, wherein the additives include phosphorus-doped carbon quantum dots.

[0006] Preferably, the phosphorus doping amount of the phosphorus-doped carbon quantum dots is 5~15 at%.

[0007] Preferably, the phosphorus-doped carbon quantum dots have a particle size of 1~10 nm.

[0008] Preferably, the phosphorus-doped carbon quantum dots are prepared according to the following steps:

[0009] A hydrothermal reaction was carried out by mixing a carbon source and a phosphorus source in water to obtain phosphorus-doped carbon quantum dots.

[0010] Preferably, the carbon source is one or more of malic acid, tartaric acid, and fructose; and the phosphorus source is one or more of phosphoric acid, sodium dihydrogen phosphate, and phytic acid.

[0011] Preferably, the temperature of the hydrothermal reaction is 140~180℃; and the time of the hydrothermal reaction is 10~16h.

[0012] Preferably, the content of the phosphorus-doped carbon quantum dots in the vanadium battery cathode electrolyte is 0.01~0.5wt%.

[0013] Preferably, the vanadium ions include pentavalent vanadium ions; the content of the pentavalent vanadium ions in the positive electrode electrolyte of the vanadium battery is 1.6~3 mol / L.

[0014] Preferably, the supporting electrolyte includes sulfuric acid; the sulfate content in the vanadium battery positive electrode electrolyte is 3~6 mol / L.

[0015] The present invention also provides an application of the vanadium battery positive electrode electrolyte described above in a vanadium redox flow battery.

[0016] Compared with the prior art, the present invention provides a vanadium battery cathode electrolyte based on P-CDs synergistic stabilization and its application. The vanadium battery cathode electrolyte provided by the present invention comprises vanadium ions, supporting electrolyte and additives, wherein the additives include phosphorus-doped carbon quantum dots. The present invention uses phosphorus-doped carbon quantum dots (P-CQDs) as additives for vanadium battery cathode electrolytes, which have a synergistic stabilization mechanism and can effectively block the precipitation path of pentavalent vanadium ions. Specifically, (1) Complexation effect: The phosphorus groups and oxygen-containing functional groups (such as -P=O, -PO3H, -COOH, -OH, etc.) on the surface of P-CQDs can react with pentavalent vanadium ions (VO2+, 2-hydroxyl ions ... (1) Forming a stable five-membered ring chelate, effectively inhibiting its deprotonation process and preventing the formation of VO(OH)3 intermediate; (2) Strong steric hindrance effect: P-CQDs have extremely small nano-size and highly hydrophilic surface, which enables them to be highly dispersed in electrolyte. These uniformly dispersed nanoparticles form a strong steric hindrance barrier around VO(OH)3 intermediate, which significantly hinders its condensation reaction.

[0017] The technical solution provided by this invention has at least the following beneficial effects:

[0018] (1) In this invention, phosphorus-doped carbon quantum dots are added to the positive electrode electrolyte of vanadium batteries. The phosphorus-doped carbon quantum dots have a synergistic stabilization mechanism, which can effectively block the precipitation path of pentavalent vanadium ions and significantly improve the stability of the pentavalent vanadium ion electrolyte.

[0019] (2) Phosphorus-doped carbon quantum dots have good stability and are not easily oxidized;

[0020] (3) The phosphorus-doped carbon quantum dots used in this invention can be produced by hydrothermal reaction. The raw materials are widely available and inexpensive, the preparation process is simple, and it is easy to industrialize. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0022] Figure 1 This is a TEM image of phosphorus-doped carbon quantum dots provided in Embodiment 2 of the present invention. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention provides a vanadium battery cathode electrolyte based on P-CDs synergistic stabilization, the components of which include vanadium ions, supporting electrolyte, additives and water, wherein the additives include phosphorus-doped carbon quantum dots.

[0025] In the vanadium battery cathode electrolyte provided by the present invention, the phosphorus doping amount of the phosphorus-doped carbon quantum dots is preferably 5~15at, specifically 5at%, 5.5at%, 5.8at%, 6at%, 6.5at%, 7at%, 7.5at%, 8at%, 8.5at%, 9at%, 9.3at%, 9.5at%, 10at%, 10.5at%, 11at%, 11.5at%, 12at%, 12.5at%, 12.6at%, 13at%, 13.5at%, 14at%, 14.5at%, or 15at.

[0026] In the vanadium battery cathode electrolyte provided by the present invention, the particle size of the phosphorus-doped carbon quantum dots is preferably 1~10nm, more preferably 2~5nm, and specifically can be 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 5.5nm, 6nm, 6.5nm, 7nm, 7.5nm, 8nm, 8.5nm, 9nm, 9.5nm or 10nm.

[0027] In the vanadium battery cathode electrolyte provided by the present invention, the phosphorus-doped carbon quantum dots are preferably prepared according to the following steps:

[0028] A hydrothermal reaction was carried out by mixing a carbon source and a phosphorus source in water to obtain phosphorus-doped carbon quanta.

[0029] In the above-mentioned phosphorus-doped carbon quantum preparation steps provided by the present invention, the carbon source is preferably one or more of malic acid, tartaric acid and fructose; the phosphorus source is preferably one or more of phosphoric acid, sodium dihydrogen phosphate and phytic acid.

[0030] In the phosphorus-doped carbon quantum preparation steps provided by the present invention, the molar ratio of the carbon source to the phosphorus source is preferably 15:(5~15), specifically 15:5, 15:5.5, 15:6, 15:6.5, 15:7, 15:7.5, 15:8, 15:8.5, 15:9, 15:9.5, 15:10, 15:10.5, 15:11, 15:11.5, 15:12, 15:12.5, 15:13, 15:13.5, 15:14, 15:14.5 or 15:15.

[0031] In the above-mentioned phosphorus-doped carbon quantum preparation steps provided by the present invention, the temperature of the hydrothermal reaction is preferably 140~180℃, specifically 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃ or 180℃; the time of the hydrothermal reaction is preferably 10~16h, specifically 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13h, 13.5h, 14h, 14.5h, 15h, 15.5h or 16h.

[0032] In the above-mentioned phosphorus-doped carbon quantum preparation steps provided by the present invention, after the hydrothermal reaction is completed, it is preferable to perform post-processing on the reaction product. The post-processing process preferably includes: sequentially dialysis purification and freeze-drying the reaction product.

[0033] In the vanadium battery cathode electrolyte provided by the present invention, the content of the phosphorus-doped carbon quantum dots in the vanadium battery cathode electrolyte is preferably 0.01~0.5wt%, specifically 0.01wt%, 0.03wt%, 0.05wt%, 0.07wt%, 0.1wt%, 0.12wt%, 0.15wt%, 0.17wt%, 0.2wt%, 0.23wt%, 0.25wt%, 0.27wt%, 0.3wt%, 0.32wt%, 0.35wt%, 0.37wt%, 0.4wt%, 0.43wt%, 0.45wt%, 0.47wt%, or 0.5wt%.

[0034] In the vanadium battery positive electrode electrolyte provided by the present invention, the vanadium ions preferably include pentavalent vanadium ions; the content of pentavalent vanadium ions in the vanadium battery positive electrode electrolyte is preferably 1.6~3 mol / L, specifically 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, 2.9 mol / L or 3 mol / L.

[0035] In the vanadium battery positive electrode electrolyte provided by the present invention, the supporting electrolyte preferably includes sulfuric acid; the sulfate content in the vanadium battery positive electrode electrolyte is preferably 3~6 mol / L, specifically 3 mol / L, 3.2 mol / L, 3.5 mol / L, 3.7 mol / L, 4 mol / L, 4.2 mol / L, 4.5 mol / L, 4.7 mol / L, 5 mol / L, 5.2 mol / L, 5.5 mol / L, 5.7 mol / L or 6 mol / L.

[0036] The present invention also provides an application of the vanadium battery positive electrode electrolyte described above in a vanadium redox flow battery.

[0037] The technical solution provided by this invention uses phosphorus-doped carbon quantum dots (P-CQDs) as an additive for the positive electrode electrolyte of vanadium batteries. It has a synergistic stabilization mechanism, which can effectively block the precipitation path of pentavalent vanadium ions and significantly improve the stability of pentavalent vanadium ion electrolyte.

[0038] For clarity, the following examples will be used to provide a detailed description.

[0039] Example 1

[0040] 2 g of malic acid (0.015 mol) and 4.95 g of phytic acid (0.0075 mol) were added to 100 mL of deionized water and dissolved with stirring. The mixture was reacted at 180 °C for 12 h, purified by dialyzing, and freeze-dried to obtain carbon quantum dots with a phosphorus doping content of 5.8 at% and a particle size of 2-5 nm.

[0041] Example 2

[0042] 2 g of malic acid (0.015 mol) and 6.6 g of phytic acid (0.01 mol) were added to 100 mL of deionized water and dissolved with stirring. The mixture was reacted at 180 °C for 12 h, purified by dialyzing, and freeze-dried to obtain carbon quantum dots with a phosphorus doping content of 9.3 at% and a particle size of 2-5 nm.

[0043] The phosphorus-doped carbon quantum dots prepared in this embodiment were observed by transmission electron microscopy (TEM), and the results are as follows: Figure 1 As shown, Figure 1 This is a TEM image of phosphorus-doped carbon quantum dots provided in Embodiment 2 of the present invention. Figure 1 It can be seen that the prepared phosphorus-doped carbon quantum dots have a uniform particle size distribution, with a particle size of 2~5nm, and good dispersibility.

[0044] Example 3

[0045] 2 g of malic acid (0.015 mol) and 8.25 g of phytic acid (0.0125 mol) were added to 100 mL of deionized water and dissolved with stirring. The mixture was reacted at 180 °C for 12 h, purified by dialyzing, and freeze-dried to obtain carbon quantum dots with a phosphorus doping content of 12.6 at% and a particle size of 2-5 nm.

[0046] Example 4

[0047] (1) Effect of different phosphorus doping concentrations of carbon quantum dots on the stability of pentavalent vanadium ion electrolyte

[0048] Experimental group: Using deionized water as solvent, an electrolyte with a pentavalent vanadium ion concentration of 1.7 mol / L and an H2SO4 concentration of 3 mol / L (1.7 MV(V) + 3 M H2SO4 electrolyte) was prepared. Phosphorus-doped carbon quantum dots prepared in Examples 1-3 were added as additives at a total electrolyte concentration of 0.2 wt%. The electrolytes were then sonicated at 30 °C for 30 min to obtain experimental groups 1-3.

[0049] Control group 1: Similar to the experimental group, the only difference is that no additives were added, i.e., blank electrolyte;

[0050] Control group 2: Similar to the experimental group, the only difference is that the additive is ammonium dihydrogen phosphate, and the amount added is 1.5 wt% of the total electrolyte.

[0051] Control group 3: Similar to the experimental group, the only difference is that the additive is polyacrylic acid (number average molecular weight 10000), and the amount added is 2wt% of the total electrolyte.

[0052] Control group 4: Similar to the experimental group, the only difference is that the additive is carbon quantum dots, and the amount added is 0.2wt% of the total electrolyte. The preparation process of the carbon quantum dots is as follows: 1g of glucose is dissolved in 60mL of water, poured into 100mL of hydrothermal reactor, and reacted at 200℃ for 6h to obtain carbon quantum dots.

[0053] Control group 5: The same as the experimental group, except that the additive is B-doped carbon quantum dots, and the amount added is 0.2wt% of the total electrolyte. The preparation process of the B-doped carbon quantum dots is as follows: 1g of glucose and 0.5g of boric acid are dissolved in 60mL of water, poured into 100mL of hydrothermal reactor, and reacted at 200℃ for 6h to obtain B-doped carbon quantum dots.

[0054] Control group 6: Similar to the experimental group, the only difference is that the additive is N-doped carbon quantum dots, and the amount added is 0.2wt% of the total electrolyte. The preparation process of the N-doped carbon quantum dots is as follows: 1g of glucose and 0.5g of urea are dissolved in 60mL of water, poured into a 100mL hydrothermal reactor, and reacted at 200℃ for 6h to obtain N-doped carbon quantum dots.

[0055] Control group 7: Similar to the experimental group, the only difference is that the additive is S-doped carbon quantum dots, and the amount added is 0.2wt% of the total electrolyte. The preparation process of the S-doped carbon quantum dots is as follows: 1g of glucose and 0.2g of sodium sulfite are dissolved in 60mL of water, and then poured into a 100mL hydrothermal reactor. The mixture is reacted at 200℃ for 6h to obtain S-doped carbon quantum dots.

[0056] The experimental group and the control group were left to stand at 50℃, 55℃ and 60℃ respectively, and the time of precipitation was recorded. The results are shown in Table 1.

[0057] Table 1. Effect of different phosphorus doping concentrations of carbon quantum dots on the stability of pentavalent vanadium ion electrolyte.

[0058]

[0059] As shown in Table 1, the additives prepared in Examples 1-3 of this invention significantly improve the stability of pentavalent vanadium ions in the electrolyte system under high-temperature conditions of 50-60℃, fully demonstrating that the additives prepared in this invention can effectively improve the stability of pentavalent vanadium ion electrolytes. Under similar preparation conditions and at the same temperature and dosage, the stability of the pentavalent vanadium ion electrolyte shows a trend of first increasing and then decreasing with increasing phosphorus doping. The additives have the best stabilizing effect on the pentavalent vanadium ion electrolyte when the phosphorus doping content is around 9wt%. Compared with phosphates (such as ammonium dihydrogen phosphate), the additives prepared in this invention have a stronger stabilizing effect on vanadium ions. Comparing carbon quantum dots with different heteroatom doping, undoped carbon quantum dots, boron-doped carbon quantum dots, n-doped carbon quantum dots, and s-doped carbon quantum dots all have limited effects on improving the stability of pentavalent electrolytes.

[0060] (2) Effect of different amounts of phosphorus-doped carbon quantum dots on the stability of pentavalent vanadium ion electrolyte

[0061] An electrolyte with a pentavalent vanadium ion concentration of 1.7 mol / L and an H2SO4 concentration of 3 mol / L was prepared. Different amounts of phosphorus-doped carbon quantum dots prepared in Example 2 were added, with the addition amounts accounting for 0 wt%, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.4 wt%, and 0.5 wt% of the total electrolyte, respectively. The electrolyte was ultrasonicated at 30 °C for 30 min. The electrolyte was then allowed to stand at 50 °C, 55 °C, and 60 °C, and the time for precipitation was recorded. The results are shown in Table 2.

[0062] Table 2. Effect of different phosphorus-doped carbon quantum dot addition amounts on the stability of pentavalent vanadium ion electrolyte.

[0063]

[0064] As shown in Table 2, the stability of the pentavalent vanadium ion electrolyte first increases and then decreases with the increase of the amount of additive. The additive has the best stabilizing effect on the pentavalent vanadium ion electrolyte when the amount of additive is 0.1~0.4wt%.

[0065] (3) Effect of phosphorus-doped carbon quantum dots on the stability of electrolytes with different concentrations of pentavalent vanadium ions

[0066] Experimental group: Electrolytes with H2SO4 concentration of 3 mol / L and pentavalent vanadium ion concentrations of 1.7 mol / L, 2.0 mol / L, 2.3 mol / L, 2.6 mol / L, and 2.9 mol / L were prepared; phosphorus-doped carbon quantum dots prepared in Example 2 were added as additives at a concentration of 0.2 wt% of the total electrolyte, and the solutions were sonicated at 30 °C for 30 min.

[0067] Control group: Electrolytes were prepared with H2SO4 concentration of 3 mol / L and pentavalent vanadium ion concentrations of 1.7 mol / L, 2.0 mol / L, 2.3 mol / L, 2.6 mol / L, and 2.9 mol / L, respectively.

[0068] The experimental group and the control group were left to stand at 50℃, 55℃ and 60℃ respectively, and the time of precipitation was recorded. The results are shown in Table 3.

[0069] Table 3. Effect of phosphorus-doped carbon quantum dots on the stability of electrolytes with different concentrations of pentavalent vanadium ions.

[0070]

[0071] As can be seen from Table 3, at an addition amount of 0.2 wt%, the phosphorus-doped carbon quantum dots prepared in Example 2 significantly improve the stability of high-concentration pentavalent vanadium ion electrolyte at high temperatures.

[0072] (4) Antioxidant test

[0073] An electrolyte with a pentavalent vanadium ion concentration of 1.7 mol / L and an H2SO4 concentration of 3 mol / L was prepared. Phosphorus-doped carbon quantum dots prepared in Example 2, polyacrylic acid (number average molecular weight 10000), oxalic acid, and citric acid were added as additives, accounting for 0.4 wt% of the total electrolyte. The electrolyte was kept at 50 °C for 24 h. The percentage of tetravalent vanadium ions in the total vanadium ions in the electrolyte was measured and calculated by potentiometric titration. The results are shown in Table 4.

[0074] Table 4. Results of antioxidant experiments on additives

[0075]

[0076] As shown in Table 4, after the pentavalent vanadium ion electrolyte prepared by adding 0.4 wt% of P-CDs in Example 2 was left to stand at 50°C for 24 h, no low-valence vanadium ions were detected in the solution. However, when using the same amount of organic additives such as polyacrylic acid, oxalic acid, and citric acid under the same experimental conditions, a large number of low-valence vanadium ions appeared in the reaction system. This indicates that although organic additives have a certain stabilizing effect on vanadium ions, their antioxidant properties are weak.

[0077] In summary, the results fully demonstrate that the vanadium battery cathode electrolyte additive prepared by this invention has excellent antioxidant properties and stability.

[0078] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A vanadium battery cathode electrolyte based on P-CDs synergistic stabilization, characterized in that, It includes vanadium ions, a supporting electrolyte, and additives, wherein the additives include phosphorus-doped carbon quantum dots; the phosphorus doping amount of the phosphorus-doped carbon quantum dots is 8~10 at.

2. The vanadium battery positive electrode electrolyte according to claim 1, characterized in that, The phosphorus-doped carbon quantum dots have a particle size of 1~10 nm.

3. The vanadium battery positive electrode electrolyte according to claim 1, characterized in that, The phosphorus-doped carbon quantum dots were prepared according to the following steps: A hydrothermal reaction was carried out by mixing a carbon source and a phosphorus source in water to obtain phosphorus-doped carbon quantum dots.

4. The vanadium battery positive electrode electrolyte according to claim 3, characterized in that, The carbon source is one or more of malic acid, tartaric acid, and fructose; the phosphorus source is one or more of phosphoric acid, sodium dihydrogen phosphate, and phytic acid.

5. The vanadium battery positive electrode electrolyte according to claim 3, characterized in that, The hydrothermal reaction temperature is 140~180℃; the hydrothermal reaction time is 10~16h.

6. The vanadium battery positive electrode electrolyte according to claim 1, characterized in that, The content of the phosphorus-doped carbon quantum dots in the vanadium battery cathode electrolyte is 0.01~0.5wt%.

7. The vanadium battery positive electrode electrolyte according to claim 1, characterized in that, The vanadium ions include pentavalent vanadium ions; the content of the pentavalent vanadium ions in the positive electrode electrolyte of the vanadium battery is 1.6~3 mol / L.

8. The vanadium battery positive electrode electrolyte according to claim 1, characterized in that, The supporting electrolyte includes sulfuric acid; the sulfate content in the vanadium battery positive electrode electrolyte is 3~6 mol / L.

9. The application of the vanadium battery positive electrode electrolyte according to any one of claims 1 to 8 in a vanadium redox flow battery.

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