High-concentration wide-temperature-range composite vanadium electrolyte, preparation method thereof and vanadium flow battery

Abstract

This application relates to the field of vanadium redox flow battery energy storage technology, and discloses a high-concentration, wide-temperature-range composite vanadium electrolyte, its preparation method, and a vanadium redox flow battery. The electrolyte has an average valence state of 3.5 and is composed of a vanadium source, sulfuric acid, methanesulfonic acid, inorganic phosphate stabilizer, organic multidentate phosphonic acid complexing agent, halide conductive antifreeze agent, polyether-based antipermeation ligand, polycarboxylic acid dispersant, and deionized water. The total vanadium concentration is 2.2~2.8 mol / L. It is prepared by mixing acid solution, electrolytic reduction to prepare base solution, adding additives, and dissolving and filtering. It can be used for both positive and negative electrodes of the battery. The operating temperature range is −10℃~60℃, with a coulombic efficiency ≥98.5%, energy efficiency ≥86%, and 200-cycle capacity retention ≥92%. Through the synergistic effect of the mixed acid system and the five-element additives, it has the advantages of high concentration, wide temperature range, low vanadium shuttle, and high interfacial activity. The preparation is simple and versatile, which is conducive to the high performance and large-scale application of vanadium redox flow batteries.

Description

Technical Field

[0001] This invention belongs to the field of vanadium redox flow battery energy storage technology, specifically relating to high-concentration wide-temperature-range composite vanadium electrolyte and its preparation method, and vanadium redox flow battery. Background Technology

[0002] Vanadium redox flow batteries, as a core technology for large-scale electrochemical energy storage, possess advantages such as long cycle life, high safety, environmental friendliness, and independent design of power and capacity. They have broad application prospects in areas such as renewable energy grid integration, grid peak shaving, and microgrids, and are considered one of the most promising energy storage technologies for large-scale energy storage systems. However, despite significant progress in electrochemical performance in recent years, vanadium redox flow batteries still face some key challenges, such as low coulombic efficiency due to vanadium shuttle between the positive and negative electrode electrolytes; low vanadium ion concentration; narrow operating temperature range; slow electrode interface reaction kinetics; and the difficulty in achieving synergistic effects due to the limited functionality of traditional additives.

[0003] Most existing technologies design electrolytes separately for the positive and negative electrodes, resulting in complex systems, high maintenance costs, and a lack of suitable multi-component composite stabilizing systems for vanadium electrolytes. Therefore, developing a general-purpose composite vanadium electrolyte with high concentration, wide temperature range, high stability, and high efficiency is of great significance for promoting the high performance and large-scale application of vanadium redox flow batteries. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a high-concentration, wide-temperature-range composite vanadium electrolyte, its preparation method, and its applications. This invention employs a uniform average vanadium valence state of 3.5 valence electrolyte and achieves high-concentration stability, high-temperature non-precipitation, low-temperature non-crystallization, vanadium permeation inhibition, and improved interfacial kinetics through a synergistic five-element composite of inorganic phosphate, organic multidentate phosphonic acid, halide salt, polyether coordinating agent, and polycarboxylic acid dispersant. Furthermore, the preparation is simple, highly versatile, and suitable for direct use in all-vanadium redox flow batteries.

[0005] In a first aspect, the present invention provides a high-concentration, wide-temperature-range composite vanadium electrolyte, wherein the average valence state of the composite vanadium electrolyte is 3.5, and the composite vanadium electrolyte is composed of a vanadium source, sulfuric acid, methanesulfonic acid, composite additives, and deionized water; the composite additives include inorganic phosphate stabilizers, organic multidentate phosphonic acid complexing agents, halide conductive antifreeze agents, polyether-based antipermeation ligands, and polycarboxylic acid dispersants. The inorganic phosphate stabilizer is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, and sodium pyrophosphate. The organic polydentate phosphonic acid complexing agent is selected from at least one of hydroxyethylidene diphosphonic acid, hexamethylenediaminetetramethylidene phosphonic acid, ethylenediaminetetramethylenephosphonic acid, and diethylenetriaminepentamethylenephosphonic acid; The halide conductive antifreeze agent is selected from at least one of potassium chloride, sodium chloride, and lithium chloride; The polyether-based antipermeation ligand is selected from at least one of tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and diethylene glycol dimethyl ether. The polycarboxylic acid dispersant is selected from at least one of polyacrylic acid, polymethacrylic acid, and polycarboxylic acid ether, and the weight-average molecular weight of the polycarboxylic acid dispersant is 2000 to 5000.

[0006] In a preferred embodiment, the vanadium electrolyte contains a total vanadium concentration of 2.2–2.8 mol / L, a sulfuric acid concentration of 3.0–4.0 mol / L, a methanesulfonic acid concentration of 1.0–2.0 mol / L, an inorganic phosphate stabilizer of 0.1–0.8 wt%, an organic polydentate phosphonic acid complexing agent of 0.2–1.0 wt%, a halide conductive antifreeze agent of 0.2–0.8 wt%, a polyether-based antipermeation agent of 0.1–0.5 wt%, and a polycarboxylic acid dispersant of 0.05–0.2 wt%.

[0007] In a second aspect, the present invention provides a method for preparing the above-described high-concentration, wide-temperature-range composite vanadium electrolyte, comprising the following steps: 1) Add sulfuric acid and methanesulfonic acid to deionized water, stir well, and prepare a mixed acid solution; 2) Add vanadium source to the mixed acid solution, stir and place it at the negative electrode of the electrolysis device for electrolytic reduction to obtain vanadium 3.5 valence electrolyte base solution; 3) Add the following to the 3.5 vanadium electrolyte base solution in sequence: inorganic phosphate stabilizer, organic multidentate phosphonic acid complexing agent, halide conductive antifreeze agent, polyether-based antipermeation ligand, and polycarboxylic acid dispersant; 4) Stir at room temperature until completely dissolved, filter, and the composite vanadium electrolyte is obtained.

[0008] In a preferred embodiment, the vanadium source is vanadium sulfate hydrate with a purity of 99.9% or vanadium pentoxide with a purity of 99.5%.

[0009] In a preferred embodiment, the stirring speed is 200-300 rpm.

[0010] In a preferred embodiment, the stirring time at room temperature is 2 hours.

[0011] In a third aspect, the present invention provides a vanadium redox flow battery, wherein the vanadium redox flow battery uses the high-concentration wide-temperature-range composite vanadium electrolyte described above or the high-concentration wide-temperature-range composite vanadium electrolyte prepared by the preparation method described above.

[0012] In a preferred embodiment, the high-concentration, wide-temperature-range composite vanadium electrolyte is simultaneously contained in both the positive electrode storage tank and the negative electrode storage tank of the vanadium redox flow battery.

[0013] In a preferred embodiment, the ion exchange membrane of the vanadium redox flow battery is a perfluorosulfonic acid membrane with a thickness of 40–50 μm. The electrodes of the vanadium redox flow battery are graphite felt electrodes with a thickness of 2.5–4.2 mm. The electrode plate of the vanadium redox flow battery is a flexible graphite plate with a thickness of 0.6 to 0.8 mm.

[0014] In a preferred embodiment, the vanadium redox flow battery has an operating temperature range of -10°C to 60°C, a coulombic efficiency of ≥98.5%, an energy efficiency of ≥86%, and a capacity retention rate of ≥92% after 200 cycles.

[0015] The beneficial effects of this application are as follows: 1. This invention employs a sulfuric acid-methanesulfonic acid mixed acid system, wherein the methanesulfonate ion (CH3SO3) - The volume is much larger than that of sulfate (SO4). 2- It can adsorb onto the surface of vanadium ions through weak coordination to form a steric hindrance layer, effectively inhibiting the aggregation, dehydration and condensation of vanadium ions, significantly improving the solubility of vanadium ions, and thus increasing the concentration of vanadium electrolyte.

[0016] 2. The inorganic phosphate of this invention provides rapid and strong coordination sites, while the organic multidentate phosphonic acid provides long-lasting multidentate chelating sites. The two form a double-layer stable coordination shell on the surface of vanadium ions, blocking the dehydration condensation path of pentavalent vanadium ions, which can inhibit the nucleation and growth of V2O5, so that the electrolyte does not precipitate at 60°C, and significantly widens the high-temperature operating window of the battery.

[0017] 3. The additive of this invention is a halide anion (Cl... - It can reconstruct the vanadium ion hydration structure, disrupt ice crystal growth, lower the electrolyte freezing point, and inhibit the low-temperature precipitation of vanadium ions through weak coordination, so that the electrolyte does not freeze, crystallize, or precipitate at -10℃, greatly expanding the low-temperature operating window of the battery.

[0018] 4. The polyether-based antipermeation ligand of this invention can significantly increase the effective hydration radius of vanadium ions by polydentate coordination between ether oxygen atoms and vanadium ions, making its size exceed the nanochannel pore size of the proton exchange membrane. By relying on the size sieving effect, it physically blocks the shuttle of vanadium ions across the membrane, greatly reducing self-discharge, thereby improving the coulombic efficiency and long-term cycle capacity retention of the battery.

[0019] 5. The polycarboxylic acid molecular chain of this invention contains a large number of carboxyl groups (-COOH), which dissociate into carboxylate ions (-COO-) in a strong acid system. -Vanadium ions can be firmly adsorbed onto the surface of vanadium ions through oxygen coordination. Like charges repel each other, keeping vanadium ions highly dispersed and reducing the viscosity of the vanadium electrolyte. In addition, polycarboxylic acid can be adsorbed on the graphite felt electrode fibers, increasing the number of active sites on the electrode, thereby improving the diffusion rate of vanadium ions and the mass transfer capacity of the electrode interface, and improving the energy and voltage efficiency of the battery. Attached Figure Description

[0020] Figure 1 The images show scanning electron microscope (SEM) images of the graphite felt electrode and the corresponding O element mapping diagrams after the stack cycling of Embodiment 1 and Comparative Example 6 of the present invention. Detailed Implementation

[0021] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0022] Example 1: The following technical solution is adopted. A high-concentration, wide-temperature-range composite vanadium electrolyte comprises: total vanadium concentration: 2.8 mol / L, sulfuric acid: 4.0 mol / L, methanesulfonic acid: 2.0 mol / L, inorganic phosphate stabilizer ammonium dihydrogen phosphate: 0.8 wt%, organic multidentate phosphonic acid complexing agent hydroxyethylidene diphosphonic acid: 1.0 wt%, halide conductivity antifreeze agent potassium chloride: 0.8 wt%, polyether-based permeation inhibitor and complexing agent tetraethylene glycol dimethyl ether: 0.5 wt%, polycarboxylic acid dispersant polyacrylic acid (Mw≈3000): 0.2 wt%, and deionized water as the balance.

[0023] Preparation steps: 1) Add sulfuric acid and methanesulfonic acid to deionized water according to the ratio, and stir at 250 rpm until homogeneous to obtain a mixed acid solution; 2) Add 99.9% vanadium oxide hydrate sulfuric acid to the mixed acid solution, stir to dissolve, and then place it in an electrolysis device for electrolytic reduction. Adjust the average valence state to 3.5 to obtain the vanadium electrolyte base solution. 3) Add ammonium dihydrogen phosphate, hydroxyethylidene diphosphonic acid, potassium chloride, tetraethylene glycol dimethyl ether, and polyacrylic acid dispersant in sequence; 4) Stir at room temperature for 2 hours until completely dissolved, then filter to obtain a high-concentration, wide-temperature-range composite vanadium electrolyte.

[0024] Battery assembly and testing: A uniform 3.5-valent electrolyte is simultaneously injected into the positive and negative electrode tanks; the separator is a 42 μm perfluorosulfonic acid membrane; the electrode is a 4.2 mm graphite felt; the plate is a 0.8 mm flexible graphite plate; the battery operating temperature range is -10℃ to 60℃; the coulombic efficiency is ≥98.5%; the energy efficiency is ≥86%; and the capacity retention rate after 200 cycles is ≥92%.

[0025] Example 2: The following technical solution is adopted. A high-concentration, wide-temperature-range composite vanadium electrolyte comprises: total vanadium concentration: 2.5 mol / L, sulfuric acid: 3.8 mol / L, methanesulfonic acid: 1.7 mol / L, inorganic phosphate stabilizer diammonium hydrogen phosphate: 0.6 wt%, organic multidentate phosphonic acid complexing agent hexamethylenediaminetetramethylenephosphonic acid: 0.7 wt%, halide conductive antifreeze agent sodium chloride: 0.6 wt%, polyether-based antipermeation inhibitor triethylene glycol dimethyl ether: 0.3 wt%, polycarboxylic acid dispersant polymethacrylic acid (Mw≈2000): 0.15 wt%, and deionized water as the balance.

[0026] Preparation steps: 1) Add sulfuric acid and methanesulfonic acid to deionized water according to the ratio, and stir at 300 rpm until homogeneous to obtain a mixed acid solution; 2) Add vanadium pentoxide with a purity of 99.5% to the mixed acid solution, stir to dissolve, and then place it in an electrolysis device for electrolytic reduction. Adjust the average valence state to 3.5 to obtain the vanadium electrolyte base solution. 3) Add diammonium hydrogen phosphate, hexamethylenediaminetetramethylenephosphonic acid, sodium chloride, triethylene glycol dimethyl ether, and polymethacrylic acid dispersant in sequence; 4) Stir at room temperature for 2 hours until completely dissolved, then filter to obtain a high-concentration, wide-temperature-range composite vanadium electrolyte.

[0027] Battery assembly and testing: A uniform 3.5-valent electrolyte is simultaneously injected into the positive and negative electrode tanks; the separator is a 40 μm perfluorosulfonic acid membrane; the electrode is a 2.5 mm graphite felt; the plate is a 0.6 mm flexible graphite plate; the battery operating temperature range is -10℃ to 60℃; the coulombic efficiency is ≥98.5%; the energy efficiency is ≥86%; and the capacity retention rate after 200 cycles is ≥92%.

[0028] Example 3: The following technical solution is adopted. A high-concentration, wide-temperature-range composite vanadium electrolyte comprises: total vanadium concentration: 2.2 mol / L, sulfuric acid: 3.0 mol / L, methanesulfonic acid: 1.0 mol / L, inorganic phosphate stabilizer sodium phosphate: 0.1 wt%, organic multidentate phosphonic acid complexing agent hexamethylenediamine tetramethylenephosphonic acid: 0.2 wt%, halide conductive antifreeze agent lithium chloride: 0.2 wt%, polyether-based permeation inhibitor and complexing agent tetraethylene glycol dimethyl ether: 0.1 wt%, polycarboxylic acid dispersant polycarboxylic acid ether (Mw≈5000): 0.05 wt%, and deionized water as the balance.

[0029] Preparation steps: 1) Add sulfuric acid and methanesulfonic acid to deionized water according to the ratio, and stir at 200 rpm until homogeneous to obtain a mixed acid solution; 2) Add 99.9% vanadium oxide hydrate sulfuric acid to the mixed acid solution, stir to dissolve, and then place it in an electrolysis device for electrolytic reduction. Adjust the average valence state to 3.5 to obtain the vanadium electrolyte base solution. 3) Add sodium phosphate, hexamethylenediaminetetramethylenephosphonic acid, lithium chloride, tetraethylene glycol dimethyl ether, and polycarboxylic acid ether dispersant in sequence; 4) Stir at room temperature for 2 hours until completely dissolved, then filter to obtain a high-concentration, wide-temperature-range composite vanadium electrolyte.

[0030] Battery assembly and testing: A uniform 3.5-valent electrolyte is simultaneously injected into the positive and negative electrode tanks; the separator is a 50 μm perfluorosulfonic acid membrane; the electrode is a 3.0 mm graphite felt; the plate is a 0.7 mm flexible graphite plate; the battery operating temperature range is -10℃ to 60℃; the coulombic efficiency is ≥98.5%; the energy efficiency is ≥86%; and the capacity retention rate after 200 cycles is ≥92%.

[0031] Example 4: The following technical solution is adopted. A high-concentration, wide-temperature-range composite vanadium electrolyte comprises: total vanadium concentration: 2.6 mol / L, sulfuric acid: 3.5 mol / L, methanesulfonic acid: 1.5 mol / L, inorganic phosphate stabilizer sodium pyrophosphate: 0.5 wt%, organic multidentate phosphonic acid complexing agent ethylenediaminetetramethylenephosphonic acid: 0.6 wt%, halide conductive antifreeze agent potassium chloride: 0.5 wt%, polyether-based antipermeation inhibitor diethylene glycol dimethyl ether: 0.4 wt%, polycarboxylic acid dispersant polyacrylic acid (Mw≈5000): 0.1 wt%, and deionized water as the balance.

[0032] Preparation steps: 1) Add sulfuric acid and methanesulfonic acid to deionized water according to the ratio, and stir at 280 rpm until homogeneous to obtain a mixed acid solution; 2) Add 99.9% vanadium oxide hydrate sulfuric acid to the mixed acid solution, stir to dissolve, and then place it in an electrolysis device for electrolytic reduction. Adjust the average valence state to 3.5 to obtain the vanadium electrolyte base solution. 3) Add sodium pyrophosphate, ethylenediaminetetramethylenephosphonic acid, potassium chloride, diethylene glycol dimethyl ether, and polyacrylic acid dispersant in sequence; 4) Stir at room temperature for 2 hours until completely dissolved, then filter to obtain a high-concentration, wide-temperature-range composite vanadium electrolyte.

[0033] Battery assembly and testing: A uniform 3.5-valent electrolyte is simultaneously injected into the positive and negative electrode tanks; the separator is a 45 μm perfluorosulfonic acid membrane; the electrode is a 2.5 mm graphite felt; the plate is a 0.8 mm flexible graphite plate; the battery operating temperature range is -10℃ to 60℃; the coulombic efficiency is ≥98.5%; the energy efficiency is ≥86%; and the capacity retention rate after 200 cycles is ≥92%.

[0034] Example 5: The following technical solution is adopted. A high-concentration, wide-temperature-range composite vanadium electrolyte comprises: total vanadium concentration: 2.5 mol / L, sulfuric acid: 3.6 mol / L, methanesulfonic acid: 1.6 mol / L, inorganic phosphate stabilizer ammonium dihydrogen phosphate: 0.7 wt%, organic multidentate phosphonic acid complexing agent diethylenetriaminepentamethylenephosphonic acid: 0.8 wt%, halide conductive antifreeze agent sodium chloride: 0.4 wt%, polyether-based permeation inhibitor and complexing agent tetraethylene glycol dimethyl ether: 0.3 wt%, polycarboxylic acid dispersant polyacrylic acid (Mw≈2000): 0.1 wt%, and deionized water as the balance.

[0035] Preparation steps: 1) Add sulfuric acid and methanesulfonic acid to deionized water according to the ratio, and stir at 250 rpm until homogeneous to obtain a mixed acid solution; 2) Add 99.9% vanadium oxide hydrate sulfuric acid to the mixed acid solution, stir to dissolve, and then place it in an electrolysis device for electrolytic reduction. Adjust the average valence state to 3.5 to obtain the vanadium electrolyte base solution. 3) Add ammonium dihydrogen phosphate, diethylenetriaminepentamethylenephosphonic acid, sodium chloride, tetraethylene glycol dimethyl ether, and polyacrylic acid dispersant in sequence; 4) Stir at room temperature for 2 hours until completely dissolved, then filter to obtain a high-concentration, wide-temperature-range composite vanadium electrolyte.

[0036] Battery assembly and testing: A uniform 3.5-valent electrolyte is simultaneously injected into the positive and negative electrode tanks; the separator is a 42μm perfluorosulfonic acid membrane; the electrode is a 2.5mm graphite felt; the plate is a 0.8mm flexible graphite plate; the battery operating temperature range is -10℃~60℃; the coulombic efficiency is ≥98.5%; the energy efficiency is ≥86%; and the capacity retention rate after 200 cycles is ≥92%.

[0037] Comparative Example 1: The following technical solution is adopted. Same as Example 1, except that no methanesulfonic acid is added, and vanadium electrolyte precipitates at room temperature, which cannot be completely dissolved.

[0038] Comparative Example 2: The following technical solution is adopted. Same as Example 1, except that no inorganic phosphate stabilizer is added.

[0039] Comparative Example 3: The following technical solution is adopted. Same as Example 1, except that no organic multidentate phosphonic acid complexing agent is added.

[0040] Comparative Example 4: The following technical solution is adopted. Same as Example 1, except that no halide conductive antifreeze agent is added.

[0041] Comparative Example 5: The following technical solution is adopted. Same as Example 1, except that no polyether-based antipermeation complexing agent is added.

[0042] Comparative Example 6: The following technical solution was adopted. Same as Example 1, except that no polycarboxylic acid dispersant is added.

[0043] Comparative Example 7: The following technical solution was adopted. A traditional vanadium electrolyte (total vanadium ion concentration 1.7 mol / L, sulfuric acid concentration 4.3 mol / L) was used as the blank electrolyte. The electrolyte was applied to the positive and negative electrode chambers of the vanadium redox flow battery. The ion exchange membrane of the vanadium redox flow battery was a 42 μm perfluorosulfonic acid ion membrane, the electrode material was a 4.2 mm thick graphite felt electrode, and the electrode plate was a 0.8 mm thick flexible graphite plate. The vanadium redox flow battery could operate in the temperature range of 10℃ to 40℃.

[0044] High and low temperature performance testing: The electrolyte was placed in a dual-chamber electrolytic cell and charged (cutoff potential 1.55 V, step current density 200~10 mA / cm²) until the positive electrode electrolyte was completely converted to V(II) and the negative electrode electrolyte was completely converted to V(II). The positive and negative electrode electrolyte samples of the examples and comparative examples were sealed and placed in a 60℃ oven and a -10℃ low temperature chamber, respectively, and allowed to stand for 72 hours. After removal, the presence of crystals at the bottom of the electrolyte was observed.

[0045] Viscosity test: At 25°C, the dynamic viscosity of the electrolytes in the examples and comparative examples was tested using an Ubbelohde viscometer. The kinematic viscosity of the vanadium electrolyte = viscometer constant × total time, and the dynamic viscosity of the vanadium electrolyte = kinematic viscosity × fluid density.

[0046] The vanadium electrolytes prepared in the examples and comparative examples were applied to the positive and negative electrode chambers of vanadium redox flow batteries. The assembled vanadium redox flow batteries were operated for a long period under the same test conditions, and the coulombic efficiency, energy efficiency, voltage efficiency, and capacity retention were recorded. The test results of the examples and comparative examples are shown in Table 1. Table 1 Summary of Test Results

[0047] As shown in Table 1, Comparative Example 1, which did not contain methanesulfonic acid, could not be dissolved in the vanadium electrolyte because it did not contain methanesulfonic acid. This is because the present invention uses a sulfuric acid-methanesulfonic acid mixed acid system, in which methanesulfonate (CH3SO3) is present. - The volume is much larger than that of sulfate (SO4). 2- It can adsorb onto the surface of vanadium ions through weak coordination to form a steric hindrance layer, effectively inhibiting the aggregation, dehydration and condensation of vanadium ions, significantly improving the solubility of vanadium ions, and thus increasing the concentration of vanadium electrolyte.

[0048] Compared to Example 1, Comparative Example 2 did not contain an inorganic phosphate stabilizer, and Comparative Example 3 did not contain an organic polydentate phosphonic acid complexing agent. Both vanadium electrolytes showed precipitation at a high temperature of 60°C. This is because the inorganic phosphate of the present invention provides rapid and strong coordination sites, and the organic polydentate phosphonic acid provides long-lasting polydentate chelating sites. The two form a double-layer stable coordination shell on the surface of vanadium ions, blocking the V (V) dehydration condensation pathway, which can inhibit V2O5 nucleation and growth, so that the electrolyte does not precipitate at 60°C, and significantly widens the high-temperature operating window of the battery.

[0049] Compared to Example 1, Comparative Example 4 did not contain a halide-based conductive antifreeze agent, yet the vanadium electrolyte crystallized at -10°C. This is because the halide anion (Cl) added in this invention... - It can reconstruct the vanadium ion hydration structure, disrupt ice crystal growth, lower the electrolyte freezing point, and inhibit the low-temperature precipitation of vanadium ions through weak coordination, so that the electrolyte does not freeze, crystallize, or precipitate at -10℃, greatly expanding the low-temperature operating window of the battery.

[0050] Compared to Example 1, which did not contain a polyether-based anti-permeation ligand, Comparative Example 5 exhibits lower coulombic efficiency and capacity retention. This is because the polyether-based anti-permeation ligand of the present invention can significantly increase the effective hydration radius of vanadium ions by undergoing polydentate coordination with vanadium ions through ether oxygen atoms, making its size exceed the nanochannel pore size of the proton exchange membrane. By relying on the size sieving effect, it physically blocks the vanadium ion shuttle across the membrane, greatly reducing self-discharge, thereby improving the coulombic efficiency and long-term cycle capacity retention of the battery.

[0051] Comparative Example 6, compared to Example 1 which did not contain a polycarboxylic acid dispersant, exhibits lower energy efficiency and voltage efficiency. This is because the polycarboxylic acid molecular chain of the present invention contains a large number of carboxyl groups (-COOH), which dissociate into carboxylate ions (-COO) in a strong acid system. - Vanadium ions can be firmly adsorbed onto the surface of vanadium ions through oxygen coordination. Like charges repel each other, maintaining a high degree of dispersion of vanadium ions and reducing the viscosity of the vanadium electrolyte. As shown in Table 1, the dynamic viscosity of Example 1 is lower than that of Comparative Example 1. Furthermore, as... Figure 1 As shown, Figure 1 Image (a1) is a scanning electron microscope image of the graphite felt electrode from Example 1. Figure 1 (a2) in the diagram is the O-element mapping diagram corresponding to Example 1. Figure 1 Image (b1) in the image is a scanning electron microscope image of the graphite felt electrode in Comparative Example 6. Figure 1 (b2) is the O element mapping diagram corresponding to Comparative Example 6. The O element content of Comparative Example 6 is significantly increased compared to Example 1. This is because polycarboxylic acid can be adsorbed on the graphite felt electrode fibers, increasing the active sites of the electrode, thereby improving the vanadium ion diffusion rate and the mass transfer capacity of the electrode interface, and improving the energy and voltage efficiency of the battery.

[0052] In summary, as shown in Table 1, the vanadium electrolyte prepared in the examples has advantages over the traditional vanadium electrolyte in Comparative Example 7, such as higher concentration, wider temperature range, higher battery efficiency, and higher capacity retention.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-concentration, wide-temperature-range composite vanadium electrolyte, characterized in that, The average valence state of the composite vanadium electrolyte is 3.

5. The composite vanadium electrolyte is composed of vanadium source, sulfuric acid, methanesulfonic acid, composite additives and deionized water. The composite additives include inorganic phosphate stabilizers, organic multidentate phosphonic acid complexing agents, halide conductive antifreeze agents, polyether-based antipermeation agents and polycarboxylic acid dispersants. The inorganic phosphate stabilizer is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, and sodium pyrophosphate. The organic polydentate phosphonic acid complexing agent is selected from at least one of hydroxyethylidene diphosphonic acid, hexamethylenediaminetetramethylidene phosphonic acid, ethylenediaminetetramethylenephosphonic acid, and diethylenetriaminepentamethylenephosphonic acid; The halide conductive antifreeze agent is selected from at least one of potassium chloride, sodium chloride, and lithium chloride; The polyether-based antipermeation ligand is selected from at least one of tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and diethylene glycol dimethyl ether. The polycarboxylic acid dispersant is selected from at least one of polyacrylic acid, polymethacrylic acid, and polycarboxylic acid ether, and the weight-average molecular weight of the polycarboxylic acid dispersant is 2000 to 5000.

2. The high-concentration, wide-temperature-range composite vanadium electrolyte according to claim 1, characterized in that, The vanadium electrolyte contains a total vanadium concentration of 2.2–2.8 mol / L, a sulfuric acid concentration of 3.0–4.0 mol / L, a methanesulfonic acid concentration of 1.0–2.0 mol / L, an inorganic phosphate stabilizer of 0.1–0.8 wt%, an organic multidentate phosphonic acid complexing agent of 0.2–1.0 wt%, a halide conductive antifreeze agent of 0.2–0.8 wt%, a polyether-based antipermeation agent of 0.1–0.5 wt%, and a polycarboxylic acid dispersant of 0.05–0.2 wt%.

3. A method for preparing the high-concentration, wide-temperature-range composite vanadium electrolyte as described in claim 1 or 2, characterized in that, Including the following steps: 1) Add sulfuric acid and methanesulfonic acid to deionized water, stir well, and prepare a mixed acid solution; 2) Add vanadium source to the mixed acid solution, stir and place it at the negative electrode of the electrolysis device for electrolytic reduction to obtain vanadium 3.5 valence electrolyte base solution; 3) Add the following to the 3.5 vanadium electrolyte base solution in sequence: inorganic phosphate stabilizer, organic multidentate phosphonic acid complexing agent, halide conductive antifreeze agent, polyether-based antipermeation ligand, and polycarboxylic acid dispersant; 4) Stir at room temperature until completely dissolved, filter, and the composite vanadium electrolyte is obtained.

4. The preparation method according to claim 3, characterized in that, The vanadium source is vanadium sulfate hydrate with a purity of 99.9% or vanadium pentoxide with a purity of 99.5%.

5. The preparation method according to claim 3, characterized in that, The stirring speed is 200-300 rpm.

6. The preparation method according to claim 3, characterized in that, The stirring time at room temperature is 2 hours.

7. A vanadium redox flow battery, characterized in that, The vanadium redox flow battery uses the high-concentration wide-temperature-range composite vanadium electrolyte as described in any one of claims 1-2 or the high-concentration wide-temperature-range composite vanadium electrolyte prepared by the preparation method described in any one of claims 3-6.

8. The vanadium redox flow battery according to claim 7, characterized in that, The high-concentration, wide-temperature-range composite vanadium electrolyte is simultaneously contained in both the positive and negative electrode storage tanks of the vanadium redox flow battery.

9. The vanadium redox flow battery according to claim 7, characterized in that, The ion exchange membrane of the vanadium redox flow battery is a perfluorosulfonic acid membrane with a thickness of 40-50 μm. The electrodes of the vanadium redox flow battery are graphite felt electrodes with a thickness of 2.5–4.2 mm. The electrode plate of the vanadium redox flow battery is a flexible graphite plate with a thickness of 0.6 to 0.8 mm.

10. The vanadium redox flow battery according to claim 7, characterized in that, The vanadium redox flow battery has an operating temperature range of -10℃ to 60℃, a coulombic efficiency of ≥98.5%, an energy efficiency of ≥86%, and a capacity retention rate of ≥92% after 200 cycles.

Images