Preparation method and application of low-temperature-resistant composite ionic liquid-based all-vanadium redox flow battery electrolyte
By preparing a composite ionic liquid-based vanadium redox flow battery electrolyte, the problems of vanadium ion crystallization and decreased conductivity at low temperatures in traditional sulfuric acid-based vanadium redox flow batteries have been solved, thereby improving the stability and conductivity of the electrolyte and making it suitable for vanadium redox flow battery energy storage systems in extremely cold regions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-22
- Publication Date
- 2026-03-20
AI Technical Summary
Traditional sulfuric acid-based vanadium redox flow batteries are prone to problems such as vanadium ion crystallization, decreased ionic conductivity, and reduced electrolyte-electrode interface reactivity in low-temperature environments, resulting in a sharp drop in battery capacity and efficiency. Furthermore, existing single-solvent modified electrolytes cannot simultaneously meet the requirements of complexation capacity and conductivity, limiting their application in extremely cold regions.
A primary and secondary ionic liquid was prepared by quaternization reaction of a strongly polar nitrogen heterocyclic compound with a haloalkanes. A composite ionic liquid was formed through anion exchange and pre-complexation reaction. Combined with a solvent with a high dielectric constant and a composite surfactant, a low-temperature resistant composite ionic liquid-based vanadium redox flow battery electrolyte was prepared.
It significantly suppresses vanadium ion crystallization, maintains electrolyte fluidity and conductivity, enhances the uniformity and stability of the electrolyte system, improves cycle life and low-temperature operation reliability, and is suitable for all-vanadium redox flow battery energy storage systems in extremely cold environments.
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Figure CN121709671A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of vanadium redox flow battery technology, and in particular to a method for preparing a low-temperature resistant composite ionic liquid-based vanadium redox flow battery electrolyte and its application. Background Technology
[0002] In recent years, the proportion of renewable energy power generation (wind power, photovoltaic power, etc.) has risen rapidly. However, due to its inherent intermittency and volatility, large-scale grid connection has had a great impact on the power grid system, requiring the introduction of safe and reliable energy storage technology to mitigate its impact on the power grid. Vanadium redox flow batteries, as a large-scale electrochemical energy storage device, have the advantages of intrinsic safety, long cycle life, no pollution, and flexible installation, making them one of the ideal energy storage forms to meet the needs of large-scale renewable energy power generation and smart grid construction.
[0003] As a core component of vanadium redox batteries, the electrolyte's physicochemical properties directly affect the system's performance and stability. In low-temperature environments, traditional sulfuric acid-based vanadium redox flow battery electrolytes face two major bottlenecks: first, active vanadium ions easily crystallize and precipitate, leading to pipe blockage and system failure; second, decreased ionic conductivity and reduced electrolyte-electrode interface reactivity cause a sharp drop in battery capacity and efficiency. While existing single-solvent modified electrolytes can alleviate the low-temperature problem to some extent, they suffer from insufficient stability in the complexation of ionic liquids with vanadium ions, and a single solvent cannot simultaneously meet the dual requirements of complexation capacity and conductivity. Furthermore, insufficient mixing uniformity and post-processing precision limit their large-scale application in extremely cold regions. Therefore, developing low-temperature electrolytes that combine high complexation activity, excellent conductivity, and strong stability has become a key breakthrough. Summary of the Invention
[0004] To achieve the above objectives, this invention provides a method for preparing a low-temperature resistant composite ionic liquid-based all-vanadium redox flow battery electrolyte and its application.
[0005] A method for preparing a low-temperature resistant composite ionic liquid-based vanadium redox flow battery electrolyte includes the following steps: S1: A highly polar nitrogen heterocyclic compound is quaternized with a haloalkane to obtain a main ionic liquid containing a halo anion; a secondary ionic liquid containing a halo anion is prepared using the same method; the main ionic liquid and the secondary ionic liquid are mixed at a predetermined mass ratio to obtain a composite ionic liquid precursor. S2: The composite ionic liquid precursor obtained in S1 is subjected to an anion exchange reaction with the target anion salt. After the reaction is completed, it is evaporated and dried to obtain a low-temperature resistant composite ionic liquid containing protic acid anions. S3: The low-temperature resistant composite ionic liquid obtained in S2 is mixed with a solvent with a high dielectric constant and stirred to dissolve, thus obtaining a functional precursor liquid; S4: Under an inert atmosphere, the functional precursor liquid obtained in S3 is mixed with the basic vanadium redox flow battery electrolyte, and a pre-complexation reaction is carried out under predetermined temperature and stirring conditions to form a pre-complexed electrolyte. S5: Add a composite surfactant to the pre-complexed electrolyte obtained in S4, stir evenly, and then sequentially filter, vacuum degas, and microfilter to obtain the finished low-temperature resistant composite ionic liquid-based vanadium redox flow battery electrolyte.
[0006] Optionally, the strongly polar nitrogen heterocyclic compound in S1 is an imidazole, pyridine, piperidine, pyrrolidine, quaternary ammonium salt, or quaternary phosphine salt; the haloalkane is a chlorinated hydrocarbon or a bromine hydrocarbon.
[0007] Optionally, the molar ratio of cation and anion groups in the quaternization reaction in S1 is 1:1-1.05, the reaction temperature is 60-120℃, and the reaction time is 2-36 hours; the mixing mass ratio of the main ionic liquid to the auxiliary ionic liquid is 2-4:1.
[0008] Optionally, the anion provided by the target anionic salt in S2 is sulfate, acetate, methanesulfonate, tetrafluoroborate, trifluoroacetate, molybdate, tungstate, or phosphotungstate.
[0009] Optionally, the molar ratio of the composite ionic liquid precursor to the target anionic salt in S2 is 1:1-1.2; the temperature of the anion exchange reaction is 25-100℃, and the reaction time is 2-48 hours.
[0010] Optionally, the high dielectric constant solvent in S3 has a dielectric constant ≥70, and is methanol, acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide, or ethyl acetate.
[0011] Optionally, the amount of functional precursor liquid added in S4 is 0.001wt%-5wt% of the mass of the basic vanadium redox flow battery electrolyte; the temperature of the pre-complexation reaction is 25-45℃, the stirring speed is 300-500rpm, and the reaction time is 2-12 hours.
[0012] Optionally, the composite surfactant in S5 is ethylene glycol, hexadecyltrimethylammonium bromide, or OP-10; the concentration of the composite surfactant in the pre-complexed electrolyte is 0.001-0.005 wt%.
[0013] Optionally, the microfiltration pore size in S5 is 0.22-0.45 μm, the vacuum degree is preferably less than 10 Pa, and the processing time is 1-2 hours.
[0014] The aforementioned battery electrolyte is used in the field of vanadium redox flow battery energy storage, and is especially suitable for energy storage systems in extremely cold environments of -30℃.
[0015] The beneficial effects of this invention are: This invention, by constructing a master-auxiliary composite ionic liquid system, simultaneously enhances the complexation stability and low-temperature conductivity of vanadium ions, effectively suppressing vanadium ion crystallization at -30℃ while maintaining the fluidity and conductivity of the electrolyte, thus solving the problems of crystallization blockage and electrochemical performance degradation of traditional sulfuric acid systems at low temperatures.
[0016] This invention removes localized concentration inhomogeneities, microbubbles, and impurities through a pre-complexing process and deep post-treatment, making the electrolyte system uniform and stable, thereby significantly enhancing cycle life and low-temperature operation reliability, and making it suitable for vanadium redox flow battery energy storage systems in extremely cold regions. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in this 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 for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 This is a schematic diagram of the battery electrolyte preparation method according to an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the working principle of the all-vanadium redox flow battery according to an embodiment of the present invention. Detailed Implementation
[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.
[0020] It should be noted that the use of terms such as "an embodiment," "an embodiment," "an exemplary embodiment," and "some embodiments" in the specification indicates that the described embodiment may include a specific feature, structure, or characteristic, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments (whether explicitly described or not) should be within the knowledge of those skilled in the art.
[0021] Generally, terms can be understood at least partly from their use in context. For example, depending at least partly on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in a singular sense, or a combination of features, structures, or characteristics in a plural sense. Additionally, the term "based on" can be understood not necessarily to convey an exclusive set of factors, but rather, alternatively, depending at least partly on the context, to allow for the presence of other factors that are not necessarily explicitly described.
[0022] Example 1 S1: 20 mmol N-methylimidazole and 20.4 mmol 1-bromobutane (molar ratio 1:1.02) were added to 100 mL dichloromethane and stirred under reflux at 80 °C for 12 h. After the reaction was completed, the solvent was removed by rotary evaporation and the mixture was dried under vacuum at 60 °C and 10 Pa for 24 h to obtain the main ionic liquid. The auxiliary ionic liquid was prepared by the same method and mixed with the main ionic liquid at a mass ratio of 3:1 to obtain the composite ionic liquid precursor. S2: The precursor obtained in S1 was mixed with sodium methanesulfonate solution at a molar ratio of 1:1.1 and stirred at 60°C for 24 h to complete the anion exchange. Then, the water was evaporated at 65°C and further dried under vacuum at 60°C for 12 h to obtain a low-temperature resistant composite ionic liquid containing protic acid anions. S3: Add 10g of the obtained composite ionic liquid to a mixed solvent consisting of 45g DMSO and 45g acetonitrile (dielectric constant approximately 78, total solvent mass 90g), and stir at 25℃ for 12h to obtain a uniform and transparent functional precursor liquid. S4: The precursor liquid obtained in S3 was added to the basic vanadium redox flow battery electrolyte at 0.5 wt%, and pre-complexed at 400 rpm for 10 h at 30 °C to allow the ionic liquid to fully contact the vanadium ions and form a stable complex structure. S5: Add 0.003wt% ethylene glycol as a composite surfactant to the S4 system and stir evenly. Then, pass it through a 0.45μm filter, vacuum degassing at a vacuum degree of <10Pa for 1.5h, and 0.22μm microfiltration in sequence to finally obtain the finished low-temperature resistant composite ionic liquid-based vanadium electrolyte.
[0023] Example 2 S1: Take 25 mmol of N-ethylpyridine and 25.75 mmol of 1-chlorobutane (molar ratio 1:1.03) and add them to 100 mL of dichloromethane. Reflux at 75 °C for 18 h to obtain the main ionic liquid. After removing the residual solvent by vacuum drying at 60 °C and 10 Pa for 24 h, mix it with a pyrrolidine-based auxiliary ionic liquid at a mass ratio of 4:1 to obtain the composite ionic liquid precursor. S2: The precursor and sodium sulfate were mixed at a molar ratio of 1:1.2 and anion exchange reaction was carried out at 70℃ for 36 h. After the reaction was completed, the mixture was evaporated at 65℃ for 12 h and then vacuum dried at 60℃ for 12 h to obtain a low-temperature resistant composite ionic liquid containing sulfate. S3: Add 10g of the obtained ionic liquid to a high dielectric constant mixed solvent (total mass 100g) consisting of 50g acetonitrile and 50g DMF, and stir at 25℃ for 12h to form a homogeneous functional precursor solution; S4: Add the functional precursor liquid to the basic vanadium electrolyte at a ratio of 1wt%, and stir at 500rpm for 12h at 35℃ for pre-complexation to allow the system to fully form a stable ionic liquid-vanadium complex structure. S5: Add 0.001wt% cetyltrimethylammonium bromide as a composite surfactant to the pre-complexed electrolyte, stir evenly, and then perform 0.45μm filtration, degassing under vacuum <10Pa for 2h, and 0.22μm microfiltration in sequence to finally obtain an electrolyte with excellent low-temperature stability.
[0024] Example 3 S1: 30 mmol N-ethylpiperidine and 31.5 mmol bromoethane (molar ratio 1:1.05) were added to 100 mL dichloromethane, refluxed at 70 °C for 20 h and dried under vacuum at 60 °C and 10 Pa for 24 h to obtain the main ionic liquid. Then, it was mixed with the auxiliary ionic liquid prepared by the same method at a mass ratio of 2:1 to obtain the composite ionic liquid precursor. S2: The precursor and sodium tetrafluoroborate were mixed in a 1:1 molar ratio and stirred at 50°C for 18 h to complete the anion exchange. Then, the mixture was evaporated at 65°C for 12 h and vacuum dried at 60°C for 12 h to obtain a composite ionic liquid containing tetrafluoroborate. S3: Add 10g of the obtained ionic liquid to 90g of ethyl acetate (dielectric constant about 74), stir at 25℃ for 10h to dissolve, and obtain a transparent and uniform functional precursor liquid; S4: Add the precursor liquid to the basic vanadium redox flow battery electrolyte at a ratio of 2wt%, and stir at 30℃ and 400rpm for 8h to achieve pre-complexation and form a stable complex structure. S5: Add 0.002wt% OP-10 as a surfactant to the system and stir evenly. Then filter through 0.22μm, degas under vacuum <10Pa for 1h, and then filter through 0.22μm again to finally obtain the electrolyte product.
[0025] Example 4: S1: 30 mmol N-ethylpyridine and 30.9 mmol 1-chlorobutane (molar ratio 1:1.03) were added to 150 mL dichloromethane and refluxed at 75 °C for 18 h. Then, the mixture was dried under vacuum at 60 °C and 10 Pa for 24 h to obtain the main ionic liquid. The main ionic liquid was then mixed with an imidazole-based auxiliary ionic liquid at a mass ratio of 3:1 to obtain a composite ionic liquid precursor. S2: The precursor was exchanged with sodium phosphotungsten at a molar ratio of 1:1.1, stirred at 60°C for 24 h, then evaporated at 65°C for 12 h and vacuum dried at 60°C for 12 h to obtain a low-temperature resistant composite ionic liquid containing phosphotungsten ions. S3: Add 10g of the obtained liquid to a mixed solvent consisting of 45g DMF and 45g ethyl acetate, with a total mass of 90g, and stir at 25℃ for 12h to dissolve, thus obtaining a functional precursor solution; S4: Add precursor solution to the basic vanadium electrolyte at a ratio of 3wt%, and stir at 40℃ and 350rpm for 6h for pre-complexation to fully form the vanadium-ion liquid structure. S5: Add 0.005wt% ethylene glycol as a composite surfactant to the pre-complexed electrolyte, stir evenly, and then sequentially complete 0.45μm filtration, degassing at a vacuum degree <10Pa for 1.5h, and 0.22μm microfiltration to finally obtain a finished electrolyte with excellent low-temperature resistance.
[0026] Comparative Example 1 A basic vanadium redox flow battery electrolyte without the addition of any ionic liquid was used as a control system. The total vanadium ion concentration in the electrolyte was set at 1.7 mol / L, and nitrogen protection was maintained throughout the experiment to avoid V². + Oxidation; at 25℃, the electrolyte is homogeneous and transparent with no visible precipitate; after standing for 24 hours in an environment of -30℃, the system undergoes obvious crystallization and precipitation, with a large number of solid particles appearing, and the fluidity of the electrolyte decreases significantly, exhibiting typical low-temperature instability characteristics.
[0027] Comparative Example 2 Comparative Example 2 used the same basic vanadium redox flow battery electrolyte as Comparative Example 1, with a total vanadium ion concentration of 1.7 mol / L, and was operated under a nitrogen atmosphere to avoid oxidation. The difference was that 0.003 wt% ethylene glycol was added to the electrolyte system as a single surfactant. The resulting electrolyte was transparent and precipitate-free at 25°C. However, after standing at -30°C for 24 hours, a large amount of crystals still appeared in the system, with the amount of crystals being comparable to that in Comparative Example 1. This shows that the single ethylene glycol surfactant cannot significantly improve the low-temperature stability of the basic electrolyte, nor can it inhibit the crystallization behavior of vanadium ions in extremely cold environments.
[0028] Table 1. Experimental data of static low-temperature test of electrolyte under different conditions. As shown in Table 1, Examples 1, 2, and 4 remained completely free of precipitation under extremely cold conditions of -30°C, Example 3 showed only a small amount of precipitation, while Comparative Examples 1 and 2 both showed significant crystallization. These results indicate that the composite ionic liquid modification system of the present invention significantly enhances the low-temperature anti-crystallization ability of the electrolyte, exhibiting superior low-temperature stability compared to the unmodified base electrolyte, and can support reliable operation of vanadium redox flow batteries at -30°C.
[0029] Table 2 Comparison of Performance Data of Finished Electrolytes As shown in Table 2, Example 1 exhibits the best performance across all key performance indicators, particularly in terms of no precipitation at -30°C, high conductivity retention of 87%, and viscosity of only 13 mm. 2 The system exhibits significant advantages in terms of performance and electrochemical efficiency reaching 97.60%, fully demonstrating that the synergistic effect of the composite ionic liquid system and the pre-complexation process can effectively enhance the structural stability and electrochemical response performance of the electrolyte in extremely cold environments. The performance of Examples 2 and 4 is similar, both significantly better than the basic electrolyte system. Example 3 showed a small amount of precipitation at low temperatures due to the slightly weaker anion exchange system used, but overall it still maintained high performance. Comparative Examples 1 and 2 both produced a large amount of crystallization at -30℃, with a significant decrease in conductivity, a significant increase in viscosity, and a significant decrease in electrochemical efficiency, indicating that the system without composite ionic liquid regulation cannot adapt to extremely cold environments.
[0030] Overall, the data fully validates the significant advantages of the low-temperature resistant composite ionic liquid-based electrolyte prepared in this invention in operation in extremely cold regions, providing reliable support for the stable application of vanadium redox flow batteries at -30°C or even lower temperatures.
[0031] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.
[0032] 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 method for preparing a low-temperature resistant composite ionic liquid-based all-vanadium redox flow battery electrolyte, characterized in that, Includes the following steps: S1: A highly polar nitrogen heterocyclic compound is quaternized with a haloalkane to obtain a main ionic liquid containing a halo anion; a secondary ionic liquid containing a halo anion is prepared using the same method; the main ionic liquid and the secondary ionic liquid are mixed at a predetermined mass ratio to obtain a composite ionic liquid precursor. S2: The composite ionic liquid precursor obtained in S1 is subjected to an anion exchange reaction with the target anion salt. After the reaction is completed, it is evaporated and dried to obtain a low-temperature resistant composite ionic liquid containing protic acid anions. S3: The low-temperature resistant composite ionic liquid obtained in S2 is mixed with a solvent with a high dielectric constant and stirred to dissolve, thus obtaining a functional precursor liquid; S4: Under an inert atmosphere, the functional precursor liquid obtained in S3 is mixed with the basic vanadium redox flow battery electrolyte, and a pre-complexation reaction is carried out under predetermined temperature and stirring conditions to form a pre-complexed electrolyte. S5: Add a composite surfactant to the pre-complexed electrolyte obtained in S4, stir evenly, and then sequentially filter, vacuum degas, and microfilter to obtain the finished low-temperature resistant composite ionic liquid-based vanadium redox flow battery electrolyte.
2. The method for preparing a low-temperature resistant composite ionic liquid-based all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The strongly polar nitrogen heterocyclic compound in S1 is an imidazole, pyridine, piperidine, pyrrolidine, quaternary ammonium salt, or quaternary phosphine salt; the haloalkane is a chlorinated hydrocarbon or a bromine hydrocarbon.
3. The method for preparing a low-temperature resistant composite ionic liquid-based all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The molar ratio of cation and anion groups in the quaternization reaction in S1 is 1:1-1.05, the reaction temperature is 60-120℃, and the reaction time is 2-36 hours; the mass ratio of the main ionic liquid to the auxiliary ionic liquid is 2-4:
1.
4. The method for preparing a low-temperature resistant composite ionic liquid-based all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The target anion salt in S2 provides anion such as sulfate, acetate, methanesulfonate, tetrafluoroborate, trifluoroacetate, molybdate, tungstate, or phosphotungstate.
5. The method for preparing a low-temperature resistant composite ionic liquid-based all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The molar ratio of the composite ionic liquid precursor to the target anionic salt in S2 is 1:1-1.2; the temperature of the anion exchange reaction is 25-100℃, and the reaction time is 2-48 hours.
6. The method for preparing a low-temperature resistant composite ionic liquid-based all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The high dielectric constant solvent in S3 has a dielectric constant ≥70, and is methanol, acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide, or ethyl acetate.
7. The method for preparing a low-temperature resistant composite ionic liquid-based all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The amount of functional precursor liquid added in S4 is 0.001wt%-5wt% of the mass of the basic vanadium redox flow battery electrolyte; the temperature of the pre-complexation reaction is 25-45℃, the stirring speed is 300-500rpm, and the reaction time is 2-12 hours.
8. The method for preparing a low-temperature resistant composite ionic liquid-based all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The composite surfactant in S5 is ethylene glycol, hexadecyltrimethylammonium bromide, or OP-10; the concentration of the composite surfactant in the pre-complexed electrolyte is 0.001-0.005 wt%.
9. The method for preparing a low-temperature resistant composite ionic liquid-based all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The microfiltration pore size in S5 is 0.22-0.45μm, the vacuum degree is preferably less than 10Pa, and the processing time is 1-2 hours.
10. The battery electrolyte according to any one of claims 1-9 is applied to the field of vanadium redox flow battery energy storage, and is particularly suitable for energy storage systems in extremely cold environments of -30℃.