Electrolyte for all-vanadium redox flow battery containing cyclohexanediamine compound and preparation method thereof

Abstract

The application discloses a kind of cyclohexane diamine compound-containing all-vanadium redox flow battery electrolyte and preparation method thereof, belong to electrochemical energy storage field.The electrolyte includes vanadium ion and 4-methyl-1,2-cyclohexane diamine additive;Wherein, the total concentration of vanadium ion in electrolyte is 2.1-2.5mol / L, and the total concentration of 4-methyl-1,2-cyclohexane diamine in electrolyte is 0.01~0.5 mol / L.The application also discloses the method for preparing cyclohexane diamine compound-containing all-vanadium redox flow battery electrolyte and all-vanadium redox flow battery comprising the electrolyte.The cyclohexane diamine compound-containing all-vanadium redox flow battery electrolyte and preparation method thereof of the application introduce 4-methyl-1,2-cyclohexane diamine as electrolyte additive, break through the stability bottleneck of all-vanadium redox flow battery electrolyte under high concentration, wide temperature range working condition.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage, and in particular to an all-vanadium redox flow battery electrolyte containing cyclohexanediamine compounds and its preparation method. Background Technology

[0002] Vanadium redox flow batteries are a large-scale energy storage technology with great application value. With their core advantages such as high safety, long cycle life (generally exceeding 15,000 cycles) and flexible capacity adjustment, they have been increasingly widely used in fields such as grid peak shaving and renewable energy grid connection.

[0003] The core component of this type of battery is the electrolyte, which is typically composed of vanadium ions in different valence states and a sulfuric acid solution—during charging and discharging, the positive electrode electrolyte contains V... 4+ / V 5+ Vanadium ions in valence state, containing V in the negative electrode solution 2+ / V 3+ Vanadium ions in valence state. However, existing water-based electrolyte systems have several inherent defects, which severely restrict the development of all-vanadium redox flow batteries.

[0004] Currently, the total vanadium concentration in mainstream vanadium redox flow battery electrolytes is typically controlled between 1.6-2.0 M, corresponding to an energy density of approximately 25-35 Wh / L. Once the vanadium concentration exceeds this range, vanadium ions in the electrolyte face a serious risk of precipitation. This is especially true under high-temperature or high-concentration conditions, where the vanadium in the positive electrode electrolyte... 4+ The risk of oxidation and precipitation increases significantly, resulting in a reddish-brown V₂O₅ precipitate. This hydrolysis reaction is significantly accelerated above 45°C, necessitating a sacrifice in energy density to ensure battery safety. Furthermore, the electrolyte stability is extremely sensitive to temperature changes; when the ambient temperature exceeds 40°C, V₂O₅... 5+ The hydrolysis rate increases exponentially. Experimental data shows that after 100 hours of constant temperature storage at 50°C, the vanadium precipitation rate in the electrolyte exceeds 15%. This "heat-sensitive" characteristic makes the battery difficult to adapt to high-temperature environments.

[0005] To overcome the aforementioned technical bottlenecks, existing technologies all have significant limitations: while adding inorganic stabilizers such as phosphoric acid can delay vanadium ion precipitation to some extent, it will severely corrode titanium alloy current collectors; urea-based organic additives are prone to decomposition under high temperature conditions, generating nitrogen oxide gases and causing electrolyte pollution; while compounding organic solvents such as dimethyl sulfoxide can improve the solubility of vanadium ions, it will cause the electrolyte viscosity to exceed 40 cP and increase costs by more than 30%.

[0006] In summary, developing novel all-vanadium redox flow battery electrolytes that combine high concentration tolerance and wide temperature range adaptability remains a technical challenge that still needs to be addressed in current all-vanadium redox flow battery technology. Summary of the Invention

[0007] Based on this, and to address the shortcomings of the existing technology, a vanadium redox flow battery electrolyte containing cyclohexanediamine compounds and its preparation method are provided. This aims to overcome the two core problems of easy vanadium ion precipitation and poor temperature adaptability in the existing technology, and to break through the stability bottleneck of the vanadium redox flow battery electrolyte under high concentration and wide temperature range conditions.

[0008] To achieve the above objectives, the following technical solution is adopted:

[0009] This invention provides an all-vanadium redox flow battery electrolyte containing cyclohexanediamine compounds, comprising vanadium ions and 4-methyl-1,2-cyclohexanediamine additive; wherein the total concentration of vanadium ions in the electrolyte is 2.1-2.5 mol / L, and the total concentration of 4-methyl-1,2-cyclohexanediamine in the electrolyte is 0.01-0.5 mol / L.

[0010] In some embodiments, the purity of 4-methyl-1,2-cyclohexanediamine is ≥99.5%; the vanadium ion is tetravalent vanadium ion.

[0011] According to the present invention, a vanadium redox flow battery is also provided, comprising an electrolyte according to the above description.

[0012] According to the present invention, a method for preparing the all-vanadium redox flow battery electrolyte containing cyclohexanediamine compounds as described above is also provided, comprising the following steps:

[0013] Step S101: Synthesize 4-methyl-1,2-cyclohexanediamine additive;

[0014] Step S102: Convert vanadium ions in the acidic vanadium-containing solution to tetravalent vanadium ions to obtain a tetravalent vanadium-containing solution;

[0015] Step S103: Add 4-methyl-1,2-cyclohexanediamine additive to the tetravalent vanadium-containing solution to obtain a mixed solution;

[0016] Step S104: The mixture is precipitated and then treated with ultrasound to obtain a vanadium redox flow battery electrolyte containing a specific substituted cyclohexanediamine compound.

[0017] In some embodiments, in step S101, the method for synthesizing 4-methyl-1,2-cyclohexanediamine includes: dissolving 1,2-cyclohexanediamine in a mixed solvent of methanol and water under an inert gas protection to obtain a mixed solution; then cooling the mixed solution and slowly adding an aqueous formaldehyde solution to carry out a low-temperature reaction; adding a quantitative reducing agent in batches, gradually increasing the temperature, and controlling the pH value to be alkaline throughout the reaction; and after drying and removing water from the reaction product, purifying it by molecular distillation to obtain 4-methyl-1,2-cyclohexanediamine.

[0018] In some embodiments, under inert gas protection, 1,2-cyclohexanediamine is dissolved in a mixed solvent of methanol and water to obtain a mixed solution, wherein the molar concentration of 1,2-cyclohexanediamine in the mixed solution is 1.0-1.5 mol / L; then the mixed solution is cooled to 0-5°C, and formaldehyde aqueous solution is slowly added at a rate of ≤5 mL / min•kg, wherein the molar ratio of formaldehyde to cyclohexanediamine is 1.05-1.15, to carry out a low-temperature reaction; sodium cyanoborohydride, with a total molar amount of 2.0-2.2 times that of 1,2-cyclohexanediamine, is added in batches, and the temperature is gradually increased to 30±2°C at a gradient of 0.5-1°C / min, and the mixture is continuously stirred for 8-12 hours, with the pH value controlled at 10.0-10.5 throughout the reaction.

[0019] In some embodiments, molecular distillation purification includes: a first stage: removing light components with a boiling point <100°C at 80°C; and a second stage: collecting the main fraction at a temperature of 125±3°C.

[0020] In some embodiments, in step S102, the method for converting vanadium ions in an acidic vanadium-containing solution into tetravalent vanadium ions includes: adding oxalic acid solution to the acidic vanadium-containing solution under a non-oxidizing atmosphere, controlling the temperature within the range of 20~40°C for initial reduction, then raising the temperature to 80±2°C, and continuously stirring the reaction for 5 hours to continue the full reduction, thereby obtaining a solution containing tetravalent vanadium ions; finally, raising the temperature to 80°C and continuing stirring for 4-8 hours to obtain a homogeneous tetravalent vanadium-containing solution.

[0021] In some embodiments, the total concentration of 4-methyl-1,2-cyclohexanediamine in the electrolyte is 0.01~0.5 mol / L; the total concentration of tetravalent vanadium ions in the electrolyte is 2.1-2.5 mol / L.

[0022] In some embodiments, in step S104, the precipitation process includes: transferring the mixture to a sealed container, raising the temperature from 25°C to 45°C at a rate of 1~5°C / h, and then maintaining the temperature for 48~72 hours; the ultrasonic treatment after precipitation includes: ultrasonic treatment for 10~60 minutes using a 40kHz ultrasonic processor.

[0023] The present invention has the following beneficial technical effects:

[0024] This invention relates to a vanadium redox flow battery electrolyte containing cyclohexanediamine compounds and its preparation method. The introduction of 4-methyl-1,2-cyclohexanediamine as an electrolyte additive overcomes the stability bottleneck of vanadium redox flow battery electrolytes under high concentration and wide temperature range conditions. Through the unique steric hindrance-coordination dual-functional mechanism of 4-methyl-1,2-cyclohexanediamine, dual performance improvements are achieved: the vanadium ion concentration in the electrolyte exceeds 2.5 M; the critical time for precipitation in the high-temperature region (55°C) is extended to 240 hours. This technology simultaneously solves the multi-dimensional failure problems of electrolytes through a single-component additive, providing a material basis for constructing high-energy-density, all-climate-suitable vanadium battery systems. Attached Figure Description

[0025] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart of the method for preparing an all-vanadium redox flow battery electrolyte containing cyclohexanediamine compounds according to the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0028] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0029] Based on the above objectives, a first aspect of the present invention provides an all-vanadium redox flow battery electrolyte containing cyclohexanediamine compounds, comprising vanadium ions and 4-methyl-1,2-cyclohexanediamine additive; wherein the total concentration of vanadium ions in the electrolyte is 2.1-2.5 mol / L, and the total concentration of 4-methyl-1,2-cyclohexanediamine in the electrolyte is 0.01-0.5 mol / L.

[0030] Among them, the purity of 4-methyl-1,2-cyclohexanediamine is ≥99.5%, and 4-methyl-1,2-cyclohexanediamine is a colorless and transparent liquid; the vanadium ion is a tetravalent vanadium ion.

[0031] The structural formula of 4-methyl-1,2-cyclohexanediamine is:

[0032] .

[0033] A second aspect of the present invention provides an all-vanadium redox flow battery comprising an electrolyte as described above.

[0034] A third aspect of the embodiments of the present invention provides a method for preparing an all-vanadium redox flow battery electrolyte containing cyclohexanediamine compounds as described above, such as... Figure 1 As shown, the method includes the following steps:

[0035] Step S101: Synthesize 4-methyl-1,2-cyclohexanediamine additive;

[0036] Step S102: Convert vanadium ions in the acidic vanadium-containing solution to tetravalent vanadium ions to obtain a tetravalent vanadium-containing solution;

[0037] Step S103: Add 4-methyl-1,2-cyclohexanediamine additive to the tetravalent vanadium-containing solution to obtain a mixed solution, and adjust the volume of tetravalent vanadium ions in the mixed solution to 2.1-2.5 mol / L;

[0038] Step S104: The mixture is precipitated and then treated with ultrasound to obtain a vanadium redox flow battery electrolyte containing a specific substituted cyclohexanediamine compound.

[0039] In a preferred embodiment of the present invention, in step S101, the method for synthesizing 4-methyl-1,2-cyclohexanediamine includes: dissolving 1,2-cyclohexanediamine in a mixed solvent of methanol and water under an inert gas protection to obtain a mixed solution; then cooling the mixed solution and slowly adding an aqueous formaldehyde solution to carry out a low-temperature reaction; adding a quantitative reducing agent in batches, gradually increasing the temperature and controlling the pH value to be alkaline throughout the reaction; and purifying the reaction product by molecular distillation after drying to obtain 4-methyl-1,2-cyclohexanediamine.

[0040] Specifically, under inert gas protection, 1,2-cyclohexanediamine is dissolved in a mixed solvent of methanol and water to obtain a mixed solution with a molar concentration of 1.0-1.5 mol / L. The mixed solution is then cooled to 0-5℃, and formaldehyde aqueous solution is slowly added at a rate of ≤5 mL / min•kg, with a formaldehyde:cyclohexanediamine molar ratio of 1.05-1.15, to carry out a low-temperature reaction. Sodium cyanoborohydride, with a total molar amount of 2.0-2.2 times that of 1,2-cyclohexanediamine, is added in batches, and the temperature is gradually increased to 30±2℃ at a gradient of 0.5-1℃ / min, with continuous stirring for 8-12 hours, and the pH is maintained at 10.0-10.5 throughout the reaction.

[0041] The inert gas atmosphere is selected from argon (Ar) or helium (He).

[0042] The volume ratio of the methanol and water mixture is 3:1 ± 0.5.

[0043] The low-temperature reaction is maintained for 0.5-1 hour, which effectively suppresses the condensation side reaction of the imine intermediate and controls the by-product formation rate to ≤0.3%.

[0044] The preferred method involves adding sodium cyanoborohydride (2.0-2.2 times the total molar amount of 1,2-cyclohexanediamine) in batches, gradually increasing the temperature to 30±2℃ at a gradient of 0.5-1℃ / min, and continuously stirring for 8-12 hours while maintaining the pH at 10.0-10.5 throughout the reaction.

[0045] "After the reaction product is dried and dehydrated", it is preferable to use an organic layer and dry it with molecular sieves until the moisture content is ≤100ppm.

[0046] Molecular distillation purification is carried out using a molecular distillation apparatus and consists of two steps: the first stage: removal of light components with boiling points <100℃ at 80℃; and the second stage: collection of the main fraction at a temperature of 125±3℃.

[0047] In step S102, the method for converting vanadium ions in an acidic vanadium-containing solution into tetravalent vanadium ions includes: adding oxalic acid solution to the acidic vanadium-containing solution under a non-oxidizing atmosphere, controlling the temperature within the range of 20~40℃ for initial reduction, then raising the temperature to 80±2℃, and continuously stirring the reaction for 5 hours to continue the full reduction, thereby obtaining a solution containing tetravalent vanadium ions; finally, raising the temperature to 80℃ and continuing stirring for 4-8 hours to fully dissolve the vanadium species, thereby obtaining a homogeneous tetravalent vanadium-containing solution.

[0048] The acidic vanadium-containing solution is preferably prepared by mixing high-purity vanadium pentoxide with a pre-cooled sulfuric acid solution (the temperature of the sulfuric acid solution is ≤10℃ and the concentration of the sulfuric acid solution is 4mol / L).

[0049] The oxalic acid solution is added at a rate of 1~50 mL / min, preferably using a 1.5 mol / L oxalic acid solution.

[0050] The initial reduction is considered complete when the solution changes from orange-yellow to a blue suspension; at this point, V... 5+ →V 4+ Intermediate state.

[0051] The criterion for complete reduction is that the solution turns a deep blue color. The reaction equation for the complete reduction of vanadium by oxalic acid is: V₂O₅ + C₂O₄ 2- + 6H + → 2VO 2+ + 2CO2↑ + 3H2O.

[0052] In step S104, the precipitation process includes: transferring the mixture to a sealed container, raising the temperature from 25°C to 45°C at a rate of 1-5°C / h, and then maintaining the temperature at this rate for 48-72 hours. This process eliminates the risk of phase separation caused by sudden temperature changes. The ultrasonic treatment after precipitation includes: ultrasonic treatment with a 40kHz ultrasonic processor for 10-60 minutes to promote the reaction of 4-methyl-1,2-cyclohexanediamine molecules with VO. 2+ A stable coordination structure is formed. The sonicated solution is then filtered under pressure through a 0.45 μm PES filter membrane to obtain a clear all-vanadium redox flow battery electrolyte containing specific substituted cyclohexanediamine compounds.

[0053] Ultrasound can significantly shorten the synthesis time and improve the efficiency of complex synthesis. Ultrasound generates localized high temperatures, high pressures, and microjets through cavitation (the formation, growth, and collapse of tiny bubbles in a liquid). The microjets generated by cavitation accelerate the reaction of ligands with VO2+. 2+ Collisions and mass transfer shorten diffusion distances and increase reaction rates.

[0054] The present invention will be further illustrated by the following examples.

[0055] Example 1

[0056] (1) Synthesis of additive 4-methyl-1,2-cyclohexanediamine

[0057] Under an inert gas atmosphere, 1,2-cyclohexanediamine was dissolved in a methanol-water mixture (3:1 v / v) and stirred to form a solution with a molar concentration of 1.0 mol / L. The system was then cooled to 0°C, and an aqueous formaldehyde solution (formaldehyde:cyclohexanediamine molar ratio 1.05) was added at a rate of 5 mL / min·kg. The reaction was maintained at this low temperature for 0.5 hours. Subsequently, sodium cyanoborohydride (2.0 times the total molar amount of diamine) was added in six portions, and the temperature was gradually increased to 30°C at a gradient of 0.5°C / min with continuous stirring for 8 hours. The pH was maintained at 10.0 (5% NaOH solution) throughout the reaction. After the reaction was complete, the organic layer was dried using a molecular sieve and then transferred to a molecular distillation apparatus. The light components were removed at 80°C, and the main fraction was collected in the second stage at 125°C to obtain a colorless, transparent liquid.

[0058] (2) Preparation of electrolyte system

[0059] 6.25 mol of high-purity vanadium pentoxide was added to an acid-resistant reactor, followed by 3 L of pre-cooled 4 mol / L sulfuric acid solution (5°C). The stirrer was turned on, and under nitrogen protection, 1.563 L (6.25 mol) of 4 mol / L oxalic acid solution was added dropwise through a constant-pressure funnel at a rate of 5 mL / min. Initial reduction was carried out at 40°C, during which the solution changed from orange-yellow to a blue suspension. The temperature was then raised to 80°C, and the reaction was continuously stirred for 5 hours to obtain a solution containing 12.5 mol of vanadium pentoxide. 4+ The solution was a deep blue color, with a total volume of approximately 4.563 L. The temperature was raised to 80 °C and stirring was continued for 4 hours. Then, 2.5 mol of 4-methyl-1,2-cyclohexanediamine was added, and the mixture was magnetically stirred for 2 hours until completely dissolved. The volume was then adjusted to 5 L.

[0060] (3) Electrolyte stabilization enhancement

[0061] The mixture was transferred to a sealed aging tank and placed in a programmable temperature-controlled oven for gradient heating: from 25°C to 45°C at a rate of 4°C / h, held at this temperature for 60 hours, and then ultrasonically treated for 30 minutes using a 40kHz ultrasonic processor. Finally, it was pressure filtered through a 0.45μm PES filter membrane to obtain a clear vanadium redox flow battery electrolyte (2.5MV) containing specific substituted cyclohexanediamine compounds. 4+ / 0.5M 4-methyl-1,2-cyclohexanediamine).

[0062] Example 2

[0063] (1) Synthesis of additive 4-methyl-1,2-cyclohexanediamine

[0064] Under an inert gas atmosphere, 1,2-cyclohexanediamine was dissolved in a methanol-water mixture with a volume ratio of 3:1.5 and stirred to form a solution with a molar concentration of 1.5 mol / L. The system was then cooled to 5°C, and an aqueous formaldehyde solution (formaldehyde:cyclohexanediamine molar ratio 1.15) was added at a rate of 2 mL / min·kg. The reaction was maintained at this low temperature for 1 hour. Subsequently, sodium cyanoborohydride (a reducing agent, with a total molar amount 2.0 times that of the diamine) was added in four portions, and the temperature was gradually increased to 32°C at a gradient of 1°C / min with continuous stirring for 12 hours. The pH was maintained at 10.5 (5% NaOH solution concentration) throughout the process. After the reaction was complete, the organic layer was dried using a molecular sieve and then transferred to a molecular distillation apparatus. The light components were removed at 80°C, and the main fraction was collected in the second stage at 128°C to obtain a colorless, transparent liquid.

[0065] (2) Preparation of electrolyte system

[0066] 6.25 mol of high-purity vanadium pentoxide was added to an acid-resistant reactor, followed by 3 L of pre-cooled 4 mol / L sulfuric acid solution (10°C). The stirrer was turned on, and under nitrogen protection, 1.563 L (6.25 mol) of 4 mol / L oxalic acid solution was added dropwise through a constant-pressure funnel at a rate of 25 mL / min. Initial reduction was carried out at 30°C, during which the solution changed from orange-yellow to a blue suspension. The temperature was then raised to 82°C, and the reaction was continuously stirred for 5 hours to obtain a solution containing 12.5 mol of vanadium pentoxide. 4+ The solution was a deep blue color, with a total volume of approximately 4.563 L. The temperature was raised to 80 °C and stirring was continued for 8 hours. Then, 0.5 mol of 4-methyl-1,2-cyclohexanediamine was added, and the mixture was magnetically stirred for 2 hours until completely dissolved. The volume was then adjusted to 5 L.

[0067] (3) Electrolyte stabilization enhancement

[0068] The mixture was transferred to a sealed aging tank and placed in a programmable temperature-controlled oven for gradient heating: from 25°C to 45°C at a rate of 1°C / h, held at this temperature for 72 hours, and then ultrasonically treated for 60 minutes using a 40kHz ultrasonic processor. Finally, it was pressure filtered through a 0.45μm PES filter membrane to obtain a clear vanadium redox flow battery electrolyte (2.5MV) containing specific substituted cyclohexanediamine compounds. 4+ / 0.1M 4-methyl-1,2-cyclohexanediamine).

[0069] Example 3

[0070] (1) Synthesis of additive 4-methyl-1,2-cyclohexanediamine

[0071] Under an inert gas atmosphere, 1,2-cyclohexanediamine was dissolved in a methanol-water mixture with a volume ratio of 3:1.25 and stirred to form a solution with a molar concentration of 1.25 mol / L. The system was then cooled to 3°C, and an aqueous formaldehyde solution (formaldehyde:cyclohexanediamine molar ratio 1.1) was added at a rate of 3 mL / min·kg. The reaction was maintained at this low temperature for 1 hour. Subsequently, sodium cyanoborohydride (a reducing agent with a total molar amount 2.1 times that of the diamine) was added in five portions, and the temperature was gradually increased to 31°C at a gradient of 0.8°C / min with continuous stirring for 10 hours. The pH was maintained at 10.2 (NaOH solution concentration 8%) throughout the process. After the reaction was complete, the organic layer was dried using a molecular sieve and then transferred to a molecular distillation apparatus. The lighter components were removed at 80°C, and the main fraction was collected in the second stage at 125°C to obtain a colorless, transparent liquid.

[0072] (2) Preparation of electrolyte system

[0073] 6.25 mol of high-purity vanadium pentoxide was added to an acid-resistant reactor, followed by 3 L of pre-cooled 4 mol / L sulfuric acid solution (3°C). The stirrer was turned on, and under nitrogen protection, 1.563 L (6.25 mol) of 4 mol / L oxalic acid solution was added dropwise through a constant-pressure funnel at a rate of 50 mL / min. Initial reduction was carried out at 20°C, during which the solution changed from orange-yellow to a blue suspension. The temperature was then raised to 82°C, and the reaction was continuously stirred for 5 hours to obtain a solution containing 12.5 mol of vanadium pentoxide. 4+ The solution was a deep blue color, with a total volume of approximately 4.563 L. The temperature was raised to 80 °C and stirring was continued for 8 hours. Then, 0.5 mol of 4-methyl-1,2-cyclohexanediamine was added, and the mixture was magnetically stirred for 2 hours until completely dissolved. The volume was then adjusted to 5 L.

[0074] (3) Electrolyte stabilization enhancement

[0075] The mixture was transferred to a sealed aging tank and placed in a programmable temperature-controlled oven for gradient heating: from 25°C to 45°C at a rate of 1°C / h, held at this temperature for 72 hours, and then ultrasonically treated for 60 minutes using a 40kHz ultrasonic processor. Finally, it was pressure filtered through a 0.45μm PES filter membrane to obtain a clear vanadium redox flow battery electrolyte (2.5MV) containing specific substituted cyclohexanediamine compounds. 4+ / 0.1M 4-methyl-1,2-cyclohexanediamine).

[0076] Comparative Example

[0077] (1) Preparation of electrolyte system

[0078] 6.25 mol of high-purity vanadium pentoxide was added to an acid-resistant reactor, followed by 3 L of pre-cooled 4 mol / L sulfuric acid solution (10°C). The stirrer was turned on, and under nitrogen protection, 1.563 L (6.25 mol) of 4 mol / L oxalic acid solution was added dropwise through a constant-pressure funnel at a rate of 25 mL / min. Initial reduction was carried out at 30°C, during which the solution changed from orange-yellow to a blue suspension. The temperature was then raised to 82°C, and the reaction was continuously stirred for 5 hours to obtain a solution containing 12.5 mol of vanadium pentoxide. 4+ The solution was a deep blue color, with a total volume of approximately 4.563 L. The temperature was raised to 80°C and stirring continued for 8 hours.

[0079] (2) Electrolyte stabilization enhancement

[0080] The mixture was transferred to a sealed aging tank and placed in a programmable temperature-controlled oven for gradient heating: from 25°C to 45°C at a rate of 1°C / h, and held at a constant temperature for 72 hours. Finally, it was filtered under pressure through a 0.45μm PES filter membrane to obtain the vanadium redox flow battery electrolyte.

[0081] The following methods were used to perform performance tests on the embodiments and comparative examples of this invention:

[0082] 1) Appearance changes: The electrolytes of the examples and comparative examples were placed in sealed glass containers and kept at a constant temperature of 55°C. The appearance characteristics of the electrolytes were observed and recorded at 24h, 72h, and 240h, including: color changes (such as whether it changes from blue to reddish-brown, green, etc.); transparency changes (such as whether turbidity or layering occurs); precipitation formation (such as whether solid particles are precipitated, the color of the precipitate, and its distribution).

[0083] 2) Sedimentation rate

[0084] ① Take 100 mL of electrolyte that has been kept at a constant temperature of 55℃ and filter it under vacuum using a pre-weighed 0.45 μm filter membrane;

[0085] ② Place the filtered membrane in a 105℃ oven to dry to constant weight, and weigh the total mass of the filter membrane and precipitate after cooling;

[0086] ③ Formula for calculating sedimentation rate:

[0087] Sedimentation rate (%) = ×100%

[0088] Where: m0 is the mass of the blank filter membrane (g), m1 is the total mass of the filter membrane + precipitate (g), m 总 The theoretical total mass (g) of vanadium in 100 mL of electrolyte;

[0089] ④ Each group of samples was tested in parallel 3 times, and the average value was taken as the final result.

[0090] 3) Conductivity retention rate

[0091] The electrical conductivity was obtained by testing with a conductivity meter at 55℃ for 0h, 72h, and 240h.

[0092] The conductivity measured at 0h is used as a baseline, and the conductivity retention rate at 0h is 100%.

[0093] The conductivity retention rate after 72 hours or 240 hours is obtained by dividing the difference between the conductivity measured at 72 hours or 240 hours and the conductivity measured at 0 hours by the conductivity measured at 0 hours.

[0094] Table 1. Changes in key performance indicators of vanadium redox flow battery electrolytes prepared in the 55°C high-temperature region for the examples and comparative examples.

[0095]

[0096] As can be seen from the changes in key performance indicators at a high temperature of 55℃ in Table 1, the embodiments of the present invention achieve significant improvements in electrolyte stability and electrochemical performance compared to the comparative examples:

[0097] Examples 1-3: The electrolyte maintained a stable appearance of "clear deep blue → light blue transparent" for 0h, 72h, and 240h, with no turbidity or precipitation. This indicates that the 4-methyl-1,2-cyclohexanediamine additive effectively inhibited the hydrolysis and aggregation of vanadium ions, ensuring the homogeneity of the electrolyte. The precipitation rate at 240h was only 0.16%-0.35%, demonstrating superior high-temperature resistance to precipitation and confirming the effectiveness of the "steric hindrance-coordination" mechanism of 4-methyl-1,2-cyclohexanediamine. The conductivity retention rate at 240h remained at 96.2%-97.1%, with only a slight decrease (≤3.8%), indicating that 4-methyl-1,2-cyclohexanediamine did not interfere with ion transport, and the electrochemical activity of the electrolyte remained basically stable.

[0098] Comparative example: A reddish-brown precipitate appeared after 72 hours, and the precipitate increased further after 240 hours, reflecting the effect of vanadium ions (especially V) in the electrolyte at high temperatures. 5+It is prone to hydrolysis, forming V₂O₅ precipitate, resulting in extremely poor appearance stability. Under certain conditions (such as slightly higher pH, longer operating time, and instability), some tetravalent vanadium ions in the vanadium oxysulfate electrolyte will still be oxidized to pentavalent vanadium ions and remain in the solution. In the comparative example without the addition of 4-methyl-1,2-cyclohexanediamine, some pentavalent vanadium hydrolyzes and precipitates as a reddish-brown precipitate over time. The precipitation rate reached 4.3% after 72 hours and soared to 14.8% after 240 hours, far exceeding practical standards, directly leading to a significant loss of active materials in the electrolyte and failing to meet the long-term operating requirements of the battery. Due to the large amount of precipitation, the ion concentration and uniformity of the electrolyte system are destroyed, the conductivity retention rate decreases significantly, and it loses its core function as a battery electrolyte.

[0099] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. Although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0100] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A vanadium redox flow battery electrolyte comprising a cyclohexanediamine compound, characterized in that, The electrolyte comprises vanadium ions and 4-methyl-1,2-cyclohexanediamine additives; wherein the total concentration of vanadium ions in the electrolyte is 2.1-2.5 mol / L, and the total concentration of 4-methyl-1,2-cyclohexanediamine in the electrolyte is 0.01-0.5 mol / L.

2. The cyclohexanediamine-containing electrolyte for a vanadium redox flow battery according to claim 1, characterized in that, The purity of 4-methyl-1,2-cyclohexanediamine is ≥99.5%, and the vanadium ions are tetravalent vanadium ions.

3. An all-vanadium redox flow battery characterized by, The electrolyte comprises vanadium ions and 4-methyl-1,2-cyclohexanediamine additives; wherein the total concentration of vanadium ions in the electrolyte is 2.1-2.5 mol / L, and the total concentration of 4-methyl-1,2-cyclohexanediamine in the electrolyte is 0.01-0.5 mol / L.

4. A method of preparing an electrolyte for a vanadium redox flow battery containing a cyclohexanediamine compound according to any one of claims 1 to 2, characterised in that, The method comprises the following steps: Step S101, synthesizing 4-methyl-1,2-cyclohexanediamine additives; Step S102, converting vanadium ions in an acidic vanadium-containing solution into tetravalent vanadium ions to obtain a tetravalent vanadium-containing solution; Step S103, adding 4-methyl-1,2-cyclohexanediamine additives to the tetravalent vanadium-containing solution to obtain a mixed solution; Step S104, performing sedimentation on the mixed solution, and then performing ultrasonic treatment on the sedimented solution to obtain a full-vanadium liquid flow battery electrolyte containing a specific substituted cyclohexanediamine compound.

5. The method of claim 4, wherein, In step S101, the synthesis method of 4-methyl-1,2-cyclohexanediamine comprises the following steps: under inert gas protection, dissolving 1,2-cyclohexanediamine in a mixed solvent of methanol and water to obtain a mixed solution, then performing cooling on the mixed solution, slowly adding an aqueous formaldehyde solution, and performing low-temperature reaction; adding a quantitative reducing agent in batches, gradient heating, and controlling the pH value to be alkaline during the whole reaction process; after drying the reaction product to remove water, purifying it by molecular distillation to obtain 4-methyl-1,2-cyclohexanediamine.

6. The method of claim 5, wherein, Under inert gas protection, 1,2-cyclohexanediamine is dissolved in a mixed solvent of methanol and water to obtain a mixed solution, the molar concentration of 1,2-cyclohexanediamine in the mixed solution is 1.0-1.5 mol / L; then the mixed solution is cooled to 0-5℃, an aqueous formaldehyde solution is slowly added at a rate of ≤5 mL / min·kg, the molar ratio of formaldehyde to cyclohexanediamine is 1.05-1.15, and low-temperature reaction is performed; the total molar amount of sodium cyanoborohydride is 2.0-2.2 times that of 1,2-cyclohexanediamine, the temperature is increased at a gradient of 0.5-1℃ / min to 30±2℃, and the pH value is controlled to be 10.0-10.5 during the whole reaction process.

7. The method of claim 5, wherein, The molecular distillation purification comprises the following steps: in the first stage, removing light components with a boiling point <100℃ at 80℃; and in the second stage, collecting the main fraction at a temperature of 125±3℃.

8. The method of claim 4, wherein, In step S102, the method for converting vanadium ions in an acidic vanadium-containing solution into tetravalent vanadium ions comprises the following steps: under a non-oxidizing atmosphere, adding an oxalic acid solution to the acidic vanadium-containing solution, controlling the temperature in the range of 20-40℃ to perform preliminary reduction, then increasing the temperature to 80±2℃, continuously stirring for 5 hours to continue sufficient reduction, and obtaining a solution containing tetravalent vanadium ions; finally, increasing the temperature to 80℃ and continuously stirring for 4-8 hours to obtain a homogeneous tetravalent vanadium-containing solution.

9. The method of claim 4, wherein, The total concentration of 4-methyl-1,2-cyclohexanediamine in the electrolyte is 0.01-0.5 mol / L, and the total concentration of tetravalent vanadium ions in the electrolyte is 2.1-2.5 mol / L.

10. The method of claim 4, wherein, In step S104, the precipitation process includes: transferring the mixed solution into a sealed container, increasing the temperature from 25℃ to 45℃ at a rate of 1~5℃ / h, and then keeping the temperature constant for 48~72 hours; the ultrasonic treatment after precipitation includes: using a 40kHz ultrasonic processor for ultrasonic treatment for 10~60 minutes.

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