A high-concentration organic liquid flow battery positive electrolyte and a preparation method thereof

Abstract

The application discloses a high-concentration organic liquid flow battery positive electrolyte and a preparation method thereof. The application first synthesizes methyl tetrathiafulvalene dimethylate by taking carbon disulfide and methyl propiolate as raw materials and under the catalysis of tributyl phosphine, and then synthesizes diethylene glycol monomethyl ether tetrathiafulvalene dimethylate ester by ester exchange reaction of the methyl tetrathiafulvalene dimethylate and diethylene glycol monomethyl ether under the catalysis of sodium hydroxide. The obtained diethylene glycol monomethyl ether tetrathiafulvalene dimethylate ester is a viscous liquid, and can be mixed with ethyl methyl carbonate, ethylene carbonate, propylene carbonate and lithium hexafluorophosphate to obtain the high-concentration organic liquid flow battery positive electrolyte. The obtained electrolyte has the advantages of high volume specific capacity, high redox potential and high cycle stability.

Description

TECHNICAL FIELD

[0001] The application relates to a high-concentration organic liquid flow battery positive electrolyte and a preparation method thereof, and belongs to the field of electrochemical energy storage. BACKGROUND

[0002] A liquid flow battery is a large-scale energy storage device that uses the redox reaction of liquid electrolyte to realize energy storage and release, and is expected to be applied to the new energy storage field represented by wind and solar power generation. In recent years, organic liquid flow batteries based on redox organic compounds have attracted widespread attention. On the one hand, organic active substances have the advantages of molecular structure diversity and structural adjustability, which means that by adjusting the structure of organic molecules, the solubility, redox potential, active site number and the chemical / electrochemical stability can be increased, and the development space is huge. On the other hand, organic active substances are mainly composed of carbon, hydrogen, oxygen, nitrogen, sulfur and other elements, and are rich in sources, and have the potential of low cost. Organic active substances can participate in the cycle of biomass, which is in line with the current theme of sustainable development of society. In 2014, Aziz's research group of Harvard University reported the use of 2,7-anthraquinone disulfonic acid as a liquid flow battery active material. Due to the introduction of sulfonic acid groups, the solubility of 2,7-anthraquinone disulfonic acid in water is greatly improved to more than 1 mol / L, and the battery shows high stability and coulombic efficiency in constant current charge and discharge test (Nature, 2014, 505(7482): 195-198). However, due to the narrow electrochemical window of water, the water-based liquid flow battery cannot provide a high battery voltage to the outside, and many organic active compounds are insoluble or difficult to dissolve in water, so the electrolyte using organic solvents can solve the above problems.

[0003] Tetrathiafulvalene (TTF) is an excellent electron donor, which can undergo a reversible one-electron redox reaction in two steps. It has been applied in the fields of molecular redox switches, redox sensors combined with metal cations, fluorescent probes combined with other luminophores, and molecular devices. TTF has a high redox potential and excellent redox stability. However, most of the reported TTF derivatives have low solubility in organic polar solvents, or have complex preparation processes, low theoretical specific capacity, and uncertain cycle stability, which limit their application and promotion in the positive electrolyte of organic redox flow batteries. TTF has high structural rigidity and is prone to π-π stacking, which makes it difficult to be dissolved in solvents used in conventional organic electrolytes. It is a challenging task to improve the solubility of TTF while retaining its redox stability, which is crucial for the commercial application of TTF-based redox flow batteries. By destroying the structural symmetry of TTF, or introducing large side groups to hinder π-π stacking, or introducing groups with similar polarity and structure to the solvent of the electrolyte to increase the interaction force with the solvent, the solubility of TTF can be improved, but the best modification method still needs to be explored. SUMMARY

[0004] The purpose of the present application is to provide a high-concentration organic redox flow battery positive electrolyte and a preparation method thereof. The obtained electrolyte has high volume specific capacity, high redox potential, and high cycle stability, and has broad commercial prospects in the field of organic redox flow batteries.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] A high-concentration organic redox flow battery positive electrolyte, the formula of which comprises tetrathiafulvalene dimethyl acid diethylene glycol monomethyl ether ester, lithium hexafluorophosphate, and an organic solvent. The organic solvent is a mixed solution of ethyl methyl carbonate, ethylene carbonate, and propylene carbonate. The structural formula of the tetrathiafulvalene dimethyl acid diethylene glycol monomethyl ether ester is as follows:

[0007] .

[0008] Further, the volume ratio of ethyl methyl carbonate, ethylene carbonate, and propylene carbonate in the organic solvent is 5-10:2-5:1.

[0009] Further, the concentration of tetrathiafulvalene dimethyl acid diethylene glycol monomethyl ether ester in the high-concentration organic redox flow battery positive electrolyte is 1-5 mol / L.

[0010] Further, the use amount ratio of the tetra-thiafulvalene dimethyl acid diethylene glycol monomethyl ether ester, lithium hexafluorophosphate and organic solvent is 0.5 ~ 4.0 g: 1 g: 10 ~ 20 mL.

[0011] The preparation method of the high-concentration organic liquid flow battery positive electrolyte includes the following steps:

[0012] (1) Methyl propiolate and carbon disulfide are added to dry tetrahydrofuran, and tributylphosphine is added as a catalyst, and the reaction is carried out at -70 ℃ for 12 hours under argon protection. The reaction mixture is filtered and dried, and the crude product is purified by column chromatography using a mixed solvent of cyclohexane and ethyl acetate in a volume ratio of 5:1 to obtain solid tetra-thiafulvalene dimethyl acid methyl ester. The reaction formula is as follows:

[0013] .

[0014] (2) The methyl tetra-thiafulvalene dimethyl acid ester obtained in step (1) is added to diethylene glycol monomethyl ether, and sodium hydroxide aqueous solution is added dropwise, and the reaction is carried out at 120 ℃ for 12 hours under argon protection, and then poured into deionized water. Dichloromethane is used for extraction and collection of organic phase, and the collected organic phase is vacuumed to remove dichloromethane, and then purified by column chromatography using a mixed solvent of dichloromethane and cyclohexane in a volume ratio of 2:1 to obtain oil-like tetra-thiafulvalene dimethyl acid diethylene glycol monomethyl ether ester. The reaction formula is as follows:

[0015] .

[0016] (3) Ethyl methyl carbonate, ethylene carbonate, and propylene carbonate are added to the tetra-thiafulvalene dimethyl acid diethylene glycol monomethyl ether ester obtained in step (2), and stirred and mixed uniformly, and then lithium hexafluorophosphate is added and stirred to dissolve, thereby obtaining the high-concentration organic liquid flow battery positive electrolyte.

[0017] Further, the molar ratio of carbon disulfide, methyl propiolate and tributylphosphine in step (1) is 1 ~ 4: 1: 1 ~ 4, and the amount of dry tetrahydrofuran is 12 ~ 36 mL per gram of methyl propiolate.

[0018] Further, the concentration of the sodium hydroxide aqueous solution in step (2) is 0.5 ~ 2 mol / L.

[0019] Further, the amount ratio of the tetra-thiafulvalene dimethyl acid methyl ester, diethylene glycol monomethyl ether and sodium hydroxide aqueous solution in step (2) is 1 g: 100 ~ 200 mL: 2 ~ 5 mL.

[0020] Further, the volume of deionized water in step (2) is 2 ~ 20 times that of diethylene glycol monomethyl ether.

[0021] Further, the volume of dichloromethane used in the extraction in step (2) is 0.5 ~ 2 times that of deionized water.

[0022] Further, the volume ratio of ethyl methyl carbonate, ethylene carbonate and propylene carbonate in the mixed solution in step (3) is 5 ~ 10: 2 ~ 5: 1.

[0023] Organic flow battery uses the redox reaction of active substances dissolved in organic solvents to realize energy storage and release. As a key material, the concentration of active substances determines the volume specific capacity of electrolyte. Although the redox potential of tetrathiafulvalene is high, reaching more than 3V, most of the tetrathiafulvalene derivatives reported at present have low solubility in organic polar solvents, and the preparation process is complex, which seriously limits its commercial application prospect. + The present application has the following beneficial effects compared with the prior art:

[0024] 1. The synthesis process of tetrathiafulvalene diethylene glycol monomethyl ether ester is simple and convenient for large-scale production.

[0025] 2. Tetrathiafulvalene dimethyl acid diethylene glycol monomethyl ether ester is a viscous liquid, which is easy to configure high-concentration electrolyte.

[0026] 3. The concentration of tetrathiafulvalene dimethyl acid diethylene glycol monomethyl ether ester in the conventional organic polar solvent used in the battery can be as high as 5 mol / L, so the prepared electrolyte has the advantages of high volume specific capacity, high redox potential and high cycle stability.

[0027] 4. The prepared high-concentration organic flow battery positive electrolyte has the advantages of simple process, excellent battery performance, and broad commercialization prospect. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 NMR spectrum of tetrathiafulvalene dimethyl acid diethylene glycol monomethyl ether ester prepared in Example 2;

[0029] Figure 2The infrared spectrum of the tetra-thiafulvalene di-methylate diethylene glycol mono- methyl ether ester prepared in Example 2;

[0030] Figure 3 The infrared spectrum of the tetra-thiafulvalene di-methylate diethylene glycol mono- methyl ether ester prepared in Example 2;

[0031] Figure 4 The charge-discharge curve of the organic flow battery prepared in Application Example 1;

[0032] Figure 5 The discharge volume specific capacity change curve of the organic flow battery prepared in Application Example 1;

[0033] Figure 6 The coulombic efficiency of the organic flow battery prepared in Application Example 1. DETAILED DESCRIPTION

[0034] In order to further disclose but not limit the present application, the present application is further described in detail below in combination with examples.

[0035] Example 1 Synthesis of tetra-thiafulvalene di-methylate

[0036] Under the protection of nitrogen, 8.4 g (0.1 mol) of methyl propiolate, 12.56 g (0.16 mol) of carbon disulfide, 20.2 g (0.1 mol) of tributyl phosphine and 100 ml of tetrahydrofuran were added into a 200 ml three-necked flask, and the reaction was stirred magnetically at -70 ℃ for 12 hours, and then naturally restored to room temperature. Then 150 ml of dichloromethane was added to dilute the three-necked flask, and the solid was collected by suction filtration and placed in a ventilated drying box at 80 ℃ for drying for 10 hours. Purification was performed by silica gel column separation with a mixed solution of cyclohexane and ethyl acetate (volume ratio 5:1) as the mobile phase to obtain 2.1 g of tetra-thiafulvalene di-methylate.

[0037] Example 2 Synthesis of tetra-thiafulvalene di-methylate diethylene glycol mono-methyl ether ester

[0038] Under the protection of nitrogen, 2.1 g of tetra-thiafulvalene di-methylate, 250 mL of diethylene glycol mono-methyl ether were added into a 500 ml three-necked flask, 5 ml of 1 mol / L sodium hydroxide aqueous solution was added dropwise, and the reaction was stirred magnetically at 120 ℃ for 12 hours, and then the heating was stopped and the temperature was naturally cooled to room temperature. Then the mixture in the three-necked flask was poured into 1000 ml of deionized water, and then 1000 ml of dichloromethane was added. The dichloromethane phase was collected by extraction, concentrated and purified by silica gel column separation with a mixed solution of dichloromethane and cyclohexane (volume ratio 2:1) as the mobile phase to obtain 2.6 g of tetra-thiafulvalene di-methylate diethylene glycol mono-methyl ether ester.

[0039] Preparation of high-concentration organic redox flow battery positive electrolyte

[0040] According to the formula shown in Table 1, ethyl methyl carbonate, ethylene carbonate and propylene carbonate were added to the tetra-thiafulvalene di-carboxylic acid diethylene glycol monomethyl ether ester in turn, stirred and mixed, and then lithium hexafluorophosphate was added and stirred to dissolve, thereby obtaining the corresponding high-concentration organic redox flow battery positive electrolyte.

[0041]

[0042] Formulation of redox flow battery positive electrolyte based on ethyl tetra-thiafulvalene di-carboxylate in Comparative Example 1-2

[0043] Ethyl tetra-thiafulvalene di-carboxylate was prepared according to the literature (CN 112271314 B), and its solubility in a mixed solution of ethyl methyl carbonate, ethylene carbonate and propylene carbonate (volume ratio of 5:4:1) was measured to be 0.032 mol / L. Ethyl tetra-thiafulvalene di-carboxylate was dissolved in a mixed solution of ethyl methyl carbonate, ethylene carbonate and propylene carbonate (volume ratio of 5:4:1), and then lithium hexafluorophosphate was added to obtain the corresponding redox flow battery positive electrolyte based on ethyl tetra-thiafulvalene di-carboxylate. The composition formula of the material is shown in Table 2.

[0044]

[0045] Preparation of redox flow battery using high-concentration organic redox flow battery positive electrolyte in Application Examples 1-3.

[0046] A lithium metal sheet was used as the negative electrode, Celgard 2325 was used as the separator, and the effective area of the separator was 3 cm x 3 cm (9 cm 2 ). The lithium sheet negative electrode was wetted with an electrolyte composed of 1.0 mol / L lithium hexafluorophosphate + a mixed solution of ethyl methyl carbonate, ethylene carbonate and propylene carbonate in a volume ratio of 5:4:1 to ensure full contact between the lithium sheet and the separator. The positive electrode used graphite felt as the current collector, and 10 mL of the organic redox flow battery positive electrolyte prepared in Examples 3-5 and Comparative Examples 1-2 was placed in a liquid storage tank, and the positive electrolyte was circulated through the positive electrode side by a peristaltic pump. The current density was 5 mA / cm 2 Constant current charging / discharging was performed, and the voltage interval was set to 3.0-4.0 V, and the cycle number was 100 cycles. The discharge volume specific capacity, discharge volume specific capacity retention rate and coulombic efficiency were used to evaluate the performance of the battery, where the discharge volume specific capacity retention rate = discharge volume specific capacity of the 100th cycle / discharge volume specific capacity of the first cycle x 100%, and the coulombic efficiency of the battery = discharge charge amount / charge charge amount x 100%. The battery performance of the organic redox flow battery prepared in each application example is shown in Table 3.

[0047]

[0048] As can be seen from Table 3, the diethylene glycol monomethyl ether tetra-thiafulvalene di-carboxylate can be used to prepare a positive electrolyte with high volume specific capacity due to its high solubility, while the ethyl tetra-thiafulvalene di-carboxylate can only be used to prepare a positive electrolyte with low volume specific capacity due to its low solubility.

[0049] Figure 1 is the nuclear magnetic resonance hydrogen spectrum of the diethylene glycol monomethyl ether tetra-thiafulvalene di-carboxylate prepared in Example 2, wherein the peak with a chemical shift of 3.40 ppm is attributed to H on the methoxy group at the end of the side chain; the peaks with chemical shifts of 3.56, 3.65, 3.75 and 4.38 ppm are attributed to the methylene H on the ethylene glycol in the side chain; the peak with a chemical shift of 7.28 ppm is attributed to the dichloromethane solvent peak; and the peak with a chemical shift of 7.38 ppm is attributed to the H of the tetra-thiafulvalene unit. The above results prove the chemical structure of the diethylene glycol monomethyl ether tetra-thiafulvalene di-carboxylate. Figure 2 and Figure 3 are the nuclear magnetic resonance carbon spectrum and infrared spectrum of the diethylene glycol monomethyl ether tetra-thiafulvalene di-carboxylate prepared in Example 2, respectively, which can further verify the chemical structure thereof.

[0050] Figure 4 is the charge-discharge curve of the organic flow battery prepared in Application Example 1 at a current of 5 mA / cm 2 As can be seen from the figure, two stable voltage platforms of 3.52 and 3.85 V appear in the charging process, which correspond to the two single-electron oxidation reactions of the diethylene glycol monomethyl ether tetra-thiafulvalene di-carboxylate, respectively; and two stable voltage platforms of 3.35 and 3.67 V appear in the discharging process, which correspond to the two single-electron reduction reactions of the diethylene glycol monomethyl ether tetra-thiafulvalene di-carboxylate, respectively. In summary, the organic flow battery electrolyte based on the diethylene glycol monomethyl ether tetra-thiafulvalene di-carboxylate has a high battery voltage, and the charge-discharge platforms of the battery are stable, which is conducive to maintaining the stability of the battery during operation.

[0051] Figure 5 is the discharge volume specific capacity curve of the organic flow battery prepared in Application Example 1 at a current of 5 mA / cm 2 After 100 cycles, the discharge capacity retention rate is as high as 89.6%, which indicates that the battery has high charge-discharge stability.

[0052] Figure 6 is the discharge volume specific capacity curve of the organic flow battery prepared in Application Example 1 at a current of 5 mA / cm 2The coulomb efficiency curve of the battery under continuous charge and discharge for 100 times at the current of 0.5C is shown in FIG. 6. The coulomb efficiency of the battery after stabilization reached 90.4% or above.

[0053] The above description is merely that of the preferred embodiments of the application, and any changes and modifications that come within the scope of the claims of the application are to be embraced by the application.

Claims

1. A method of making a high-concentration organic flow battery positive electrolyte, the method comprising: The organic liquid flow battery positive electrolyte is composed of tetra-thiafulvalene dimethyl acid diethylene glycol monomethyl ether ester, lithium hexafluorophosphate and an organic solvent; the organic solvent is a mixed solution of ethyl methyl carbonate, ethylene carbonate and propylene carbonate; the chemical structure of the tetra-thiafulvalene dimethyl acid diethylene glycol monomethyl ether ester is as follows: ​ ； The preparation method of the high-concentration organic liquid flow battery positive electrolyte comprises the following steps: (1) methyl propiolate and carbon disulfide are added to dry tetrahydrofuran, and tributyl phosphine is added as a catalyst, and the reaction is carried out at-70 ℃ for 12 h under argon protection, the reaction mixture is filtered and dried, and the crude product is purified by column chromatography using a mixed solvent of cyclohexane and ethyl acetate with a volume ratio of 5:1 as a mobile phase to obtain solid tetra-thiafulvalene dimethyl acid methyl ester; (2) the tetra-thiafulvalene dimethyl acid methyl ester obtained in step (1) is added to diethylene glycol monomethyl ether, and sodium hydroxide aqueous solution is added dropwise, and the reaction is carried out at 120 ℃ for 12 h under argon protection, then it is poured into deionized water, dichloromethane is used for extraction and the organic phase is collected, the dichloromethane in the collected organic phase is removed under vacuum, and column chromatography is carried out using a mixed solvent of dichloromethane and cyclohexane with a volume ratio of 2:1 as a mobile phase to obtain oil-like tetra-thiafulvalene dimethyl acid diethylene glycol monomethyl ether ester; (3) ethyl methyl carbonate, ethylene carbonate and propylene carbonate are added to the tetra-thiafulvalene dimethyl acid diethylene glycol monomethyl ether ester obtained in step (2), and stirred and mixed uniformly, then lithium hexafluorophosphate is added, and stirred and dissolved to obtain the high-concentration organic liquid flow battery positive electrolyte.

2. The production method according to claim 1, characterized by, The volume ratio of ethyl methyl carbonate, ethylene carbonate and propylene carbonate in the organic solvent is 5-10:2-5:

1.

3. The preparation method according to claim 1, characterized in that, The concentration of tetra-thiafulvalene dimethyl acid diethylene glycol monomethyl ether ester in the organic liquid flow battery positive electrolyte is 1-5 mol / L.

4. The method of claim 1, wherein, The amount ratio of tetra-thiafulvalene dimethyl acid diethylene glycol monomethyl ether ester, lithium hexafluorophosphate and the organic solvent is 0.5-4.0 g:1 g:10-20 mL.

5. The preparation method according to claim 1, characterized in that, The molar ratio of carbon disulfide, methyl propiolate and tributyl phosphine in step (1) is 1-4:1:1-4, and the amount of dry tetrahydrofuran is 12-36 mL per gram of methyl propiolate.

6. The method of claim 1, wherein, The concentration of the sodium hydroxide aqueous solution in step (2) is 0.5-2 mol / L.

7. The preparation method according to claim 5, characterized in that, The amount ratio of tetra-thiafulvalene dimethyl acid methyl ester, diethylene glycol monomethyl ether and the sodium hydroxide aqueous solution in step (2) is 1 g:100-200 mL:2-5 mL.

8. The method of claim 1, wherein, The volume of deionized water in step (2) is 5-20 times that of diethylene glycol monomethyl ether.

9. The method of claim 1, wherein, The volume of dichloromethane used for extraction in step (2) is 1-2 times that of deionized water.

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