A composite bipolar molecule for a water-soluble dual-electrode flow battery system and a preparation method and applications thereof

Abstract

The application discloses a water-soluble bipolar molecule for a double-electrode flow battery system and a preparation method and application thereof, wherein the water-soluble bipolar molecule material for the double-electrode flow battery system comprises the following preparation steps: S1, acyl chloride reaction is carried out by taking nitroxide piperidinol and acyl chloride as raw materials and adding a catalyst; and S2, quaternary ammonium reaction is further carried out with 1-propanesulfonic acid-4,4'-dipyridine to synthesize the water-soluble bipolar composite molecule structure. The bipolar composite molecule can be used for positive and negative electrode materials of a water-soluble organic flow battery system, so that the influence caused by cross contamination between electrode materials can be avoided, and the stability of battery circulation is improved. Meanwhile, the organic double-electrode flow battery system is suitable for a battery environment using in-situ generated electrolyte, has the advantages of low cost, stable charging and discharging performance, high safety and high solubility of active materials, and can meet large-scale energy storage requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of liquid flow battery, in particular to a composite bipolar molecule for water-soluble dual electrode liquid flow battery system and a preparation method and application thereof. BACKGROUND

[0002] With the increasing energy demand and environmental problems, the development and utilization of clean energy is of great significance. However, the renewable energy dominated by wind energy and solar energy has the characteristics of volatility and intermittency, which directly connected to the grid brings stability challenges to the power system. Therefore, the application design of large-scale energy storage system technology is the key to balance the peak and valley difference of the power grid and realize stable power supply. As a new type of large-scale and efficient electrochemical energy storage technology, liquid flow battery energy storage realizes the mutual conversion of electrical energy and chemical energy through the redox of active substances, and has the advantages of flexible design, long service life and large storage capacity.

[0003] At present, the commercial liquid flow battery mostly uses inorganic materials as active substances, which has the defects of high cost and strong toxicity, limiting the large-scale development of liquid flow battery. Organic active substances are low in cost, rich in resources and easy to adjust molecular energy level, and have gradually become the focus of electrode material research of liquid flow battery. However, the traditional organic small molecule liquid flow battery system generally has the problem of electrode cross infection, which affects the stability of the battery.

[0004] In summary, there is an urgent need for a water-soluble dual electrode liquid flow battery system composite bipolar molecule. The composite bipolar molecule is a water-soluble bipolar composite molecule material, which can be applied to both positive and negative electrode materials in the cycle of water-soluble dual electrode liquid flow battery by covalently combining Viologen and TEMPO with excellent electrochemical activity, effectively avoiding the irreversible influence of electrode cross, thereby improving the cycle stability of battery capacity. SUMMARY

[0005] The technical problem to be solved by the present application is:

[0006] A water-soluble dual electrode liquid flow battery system composite bipolar molecule and a preparation method and application thereof are provided. The composite bipolar molecule is a water-soluble bipolar composite molecule material, which can be applied to both positive and negative electrode materials in the cycle of water-soluble dual electrode liquid flow battery by covalently combining Viologen and TEMPO with excellent electrochemical activity, effectively avoiding the irreversible influence of electrode cross, thereby improving the cycle stability of battery capacity.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0008] A water-soluble dual electrode liquid flow battery system composite bipolar molecule material, the chemical structure formula of the water-soluble bipolar composite molecule is:

[0009]

[0010] A preparation method of a composite bipolar molecular material for a water-soluble bipolar electrode flow battery system, comprising the following preparation steps:

[0011] S1 acyl chloride reaction is carried out by taking nitroxide piperidinol and acyl chloride as raw materials and adding a catalyst;

[0012] S2 and 1-propanesulfonic acid-4,4'-bipyridine are subjected to quaternary ammonium reaction to synthesize the water-soluble bipolar composite molecular structure.

[0013] As a further improvement of the present solution, the preparation method specifically comprises the following preparation steps:

[0014] S1 acyl chloride reaction is carried out by taking nitroxide piperidinol and acyl chloride as raw materials and adding a catalyst

[0015] Nitroxide piperidinol and an appropriate amount of solvent are added to a container, and stirred thoroughly at room temperature; after the solid is completely dissolved, a catalyst is added, and stirring is carried out in a nitrogen environment to remove oxygen; acyl chloride is dissolved in an appropriate amount of solvent, and added dropwise into the above-mentioned container; after the dropwise addition is completed, the reaction is continued; after the reaction is completed, the precipitate is removed by filtration, and the filtrate is washed with different extraction liquids in sequence; the obtained organic phase solution is dried to remove water, and then further purified by an alkaline aluminum oxide column, and finally the solvent is removed by rotary evaporation to obtain a deep red viscous liquid;

[0016] The reaction formula of S1 is as follows:

[0017]

[0018] S2 and 1-propanesulfonic acid-4,4'-bipyridine are subjected to quaternary ammonium reaction to synthesize the water-soluble bipolar composite molecular structure

[0019] The deep red viscous liquid obtained in S1 is dissolved in a mixed solvent, and an appropriate amount of 1-propanesulfonic acid-4,4'-bipyridine is added, and a heating reflux reaction is carried out;

[0020] After the reaction is completed, a brown-yellow solid sample is obtained by precipitation with a precipitant;

[0021] The reaction formula of S2 is as follows:

[0022]

[0023] As a further improvement of the present solution, in S1,

[0024] The catalyst is at least one of pyridine, triethylamine, and 4-dimethylaminopyridine;

[0025] The acyl chloride structure is at least one of 5-bromo-pentanoyl chloride, 5-chloro-pentanoyl chloride, 4-bromo-butyryl chloride, 4-chloro-butyryl chloride, 3-bromo-propionyl chloride, 3-chloro-propionyl chloride, 2-bromo-acetyl chloride, 2-chloro-acetyl chloride;

[0026] The organic desiccant is at least one of anhydrous sodium sulfate, anhydrous magnesium sulfate;

[0027] The solvent is at least one of dichloromethane, acetonitrile, chloroform, toluene, ethanol, N,N-dimethylformamide;

[0028] The extraction liquid is at least one of deionized water, saturated sodium bicarbonate solution, 2% dilute hydrochloric acid solution, saturated sodium chloride solution;

[0029] The basic alumina in the basic alumina column has a particle size of one of 100-200 mesh and 200-300 mesh.

[0030] As a further improvement of the present solution, in S1,

[0031] The molar ratio of the raw material nitroxide piperidinol to the acyl chloride is 1:1-1:2;

[0032] The molar ratio of the raw material nitroxide piperidinol to the catalyst is 1:1-1:2;

[0033] The mass percentage of the nitroxide piperidinol in the solvent is 7%-13%, and the mass percentage of the acyl chloride is 8%-20%.

[0034] As a further improvement of the present solution, in S1,

[0035] The dropping temperature is 0-5°C, the acyl chloride reaction temperature is 25-30°C, and the reaction time is 20-40h.

[0036] As a further improvement of the present solution, in S2,

[0037] The mass percentage of the raw material 1-propanesulfonic acid-based 4,4'-dipyridine is 10%-15%, the heating reaction temperature is 65-85°C, and the reaction time is 6-10 days;

[0038] The volume ratio of the organic phase to the aqueous phase in the mixed solvent is 1:2-3:1.

[0039] As a further improvement of the present solution, the precipitant is at least one of acetone and cold ethyl acetate;

[0040] The mixed solvent is at least one of N,N-dimethylformamide and water, ethanol and water, acetonitrile and water, and trifluoroethanol and water.

[0041] The application of a composite bipolar molecule material for a water-soluble dual-electrode flow battery system, the composite bipolar molecule material is used in a dual-electrode flow battery system, and the composite bipolar molecule material can be simultaneously applied to positive and negative electrode materials in a water-soluble dual-electrode flow battery cycle.

[0042] As a further improvement of the present solution, the flow battery system comprises two electrolyte storage tanks and a flow battery stack, the two electrolyte storage tanks are arranged at intervals, each electrolyte storage tank is an electrolyte storage tank or a salt cave with a physical solution cavity formed after salt mining, the battery material is directly dissolved or dispersed in a system with water as a solvent in a bulk form, the flow battery stack comprises a battery separator, the battery separator separates the flow battery stack into an anode region and a cathode region distributed at intervals, the anode region is in communication with one electrolyte storage tank, and the cathode region is in communication with another electrolyte storage tank.

[0043] As a further preferred embodiment, the electrolyte concentration of the positive electrode battery material and the negative electrode battery material is 0.1mol·L -1 ~2.5mol·L -1 The inert gas is nitrogen or argon.

[0044] The battery separator is an anion exchange membrane, a cation exchange membrane or a porous membrane.

[0045] The supporting electrolyte is a NaCl salt solution, and the molar concentration of the supporting electrolyte is 0.5mol·L -1 ~2.0mol·L -1 .

[0046] Compared with the prior art, the present application has the following advantages:

[0047] 1) The present application takes TEMPO and Viologen as the main body, and connects them through a covalent bond to prepare a composite molecule electrode material with a bifunctional group, and uses ion groups on the structure to increase the solubility of the material;

[0048] 2) A water-soluble dual-electrode organic small molecule with excellent electrochemical activity is introduced as a redox couple to obtain a symmetric flow battery with good stability;

[0049] 3) Attenuated to 11.6 mAh after 500 cycles (theoretical capacity is 40.2 mAh, the first cycle discharge capacity is 22.5 mAh), the capacity retention rate is 51.55%, and the average capacity decay rate per cycle is 0.095%. Using the double-electrode active material as the electrode material can effectively avoid the irreversible influence caused by the cross contamination between the active materials, reduce the capacity decline of the battery, improve the stability of the battery, obtain the flow battery system with the advantages of easy preparation of active material, stable charge-discharge performance and the like, and meet the large-scale energy storage demand. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 is a structural schematic diagram of a double-electrode flow battery system of an embodiment of the present application;

[0051] Figure 2 is a nuclear magnetic hydrogen spectrum diagram of the water-soluble bipolar complex molecule prepared in Example 1 in a D2O solvent;

[0052] Figure 3 is an ESI-MS diagram of the water-soluble bipolar complex molecule prepared in Example 1;

[0053] Figure 4 is a CV diagram of the water-soluble bipolar complex molecule (concentration is 3 mg·mL -1 , in a sodium chloride aqueous solution with pH = 7) of Example 1 of the present application at different scanning rates;

[0054] Figure 5 is a charge-discharge capacity diagram of a flow battery system with the water-soluble bipolar complex molecule of Example 1 of the present application as the positive and negative electrode material at different current densities;

[0055] Figure 6 is a positive and negative charge-discharge voltage-time diagram of a flow battery system with the water-soluble bipolar complex molecule of Example 1 of the present application as the positive and negative electrode material;

[0056] Figure 7 is a cycle stability diagram of a flow battery system with the water-soluble bipolar complex molecule of Example 1 of the present application as the positive and negative electrode material;

[0057] Reference signs:

[0058] A double-electrode flow battery system 100;

[0059] An electrolyte storage tank 20;

[0060] An electrode plate 21; positive and negative electrolyte current collectors 22 and 23; a battery separator 24; a circulating pump 25. DETAILED DESCRIPTION

[0061] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application is further described below in conjunction with embodiments.

[0062] The positive and negative electrode materials of the water-soluble organic flow battery system 100 are the water-soluble bipolar composite molecules described above, that is, simultaneously having the positive active group 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and the negative active group viologen.

[0063] As shown in Figure 1 The all-polymer flow battery system 100 according to the embodiment of the present application includes two electrolyte storage tanks 20 and a flow battery stack (21-24). The two electrolyte storage tanks 20 are arranged at intervals, and each electrolyte storage tank 20 is an electrolyte storage tank or a salt cave with a physical solution cavity formed after salt mining. The battery material is directly dissolved or dispersed in a system with water as a solvent in a bulk form. The flow battery stack includes a battery separator 24, which separates the flow battery stack into an anode region and a cathode region distributed at intervals. The anode region is in communication with one electrolyte storage tank 20, and the cathode region is in communication with the other electrolyte storage tank 20. The design of the bifunctional electrode material can effectively prevent the capacity decay problem caused by cross contamination between ions, thereby improving the cycle stability of the flow battery.

[0064] A water-soluble bipolar electrode flow battery system electrode material and a preparation method thereof according to an embodiment of the present application are described below with reference to the accompanying drawings.

[0065] In the cyclic voltammetry test, the electrochemical performance of the bifunctional small molecule electrode material was tested by using a CH series electrochemical workstation of Shanghai Chenhua Company. The working electrode was a glassy carbon electrode (Shanghai Chenhua Company), the reference electrode was an Ag / AgCl electrode, and the counter electrode was a platinum electrode. The positive scanning range was 0.2V-0.8V, and the negative scanning range was -0.8V- -0.2V.

[0066] Example 1

[0067] In a 500 mL three-necked flask, 4-bromo-butyryl chloride (40.06 g, 216 mmol) was dissolved in 80 mL of dichloromethane. Nitroxide piperidinol (33.76 g, 196 mmol) was dissolved in 120 mL of dichloromethane. Pyridine was used as catalyst (17.06 g, 216 mmol). After 30 min of nitrogen purging, the 4-bromo-butyryl chloride solution was added dropwise through a constant pressure dropping funnel under ice-bath condition. After the addition was completed, the ice-bath was removed and the reaction was continued at room temperature for 24 h. During the reaction, the solution became turbid and solid was precipitated. After the reaction was completed, the precipitate was removed by filtration. The filtrate was washed successively with deionized water, saturated sodium bicarbonate solution, 2% dilute hydrochloric acid solution, and saturated sodium chloride solution. The obtained organic phase solution was dried over anhydrous sodium sulfate and further purified by passing through a basic alumina column with 100-200 mesh. Finally, the solvent was removed by rotary evaporation to obtain 4-(l-oxyl-2,2,6,6-tetramethylpiperidinyl)-4-bromo-4-butyl ester as a dark red viscous liquid with a yield of 90%.

[0068] The dark red viscous liquid (51.33 g, 160 mmol) obtained in the previous step was dissolved in 300 mL of a mixed solvent of N,N-dimethylformamide and deionized water (volume ratio of 2: 1). 1-Propanesulfonic acid-4,4'-dipyridine (42.24 g, 160 mmol) was added and heated to 85°C for 7 days. The solution was precipitated with acetone three times to obtain a brownish yellow solid with a yield of 87%.

[0069] Figure 2 is the nuclear magnetic resonance spectrum of the water-soluble bipolar complex molecule prepared in Example 1 in D2O solvent;

[0070] Figure 3 is the ESI-MS spectrum of the water-soluble bipolar complex molecule prepared in Example 1.

[0071] Example 2

[0072] In a 250 mL three-necked flask, add nitroxide piperidinol (20.62 g, 120 mmol) and dissolve in 100 mL dichloromethane with vigorous stirring, then add triethylamine as catalyst (13.64 g, 135 mmol). Dissolve 4-bromo-butyryl chloride (25.04 g, 135 mmol) in 50 mL dichloromethane in advance. After 30 min of nitrogen bubbling, add the 4-bromo-butyryl chloride solution dropwise through a constant pressure dropping funnel under ice bath, after the addition is completed, remove the ice bath, continue to react at room temperature for 24 h, and a light yellow solid is precipitated during the reaction. After the reaction is completed, remove the precipitate by filtration, and wash the filtrate with deionized water and saturated sodium chloride solution in sequence; dry the obtained organic phase solution with anhydrous sodium sulfate, and further purify it by passing through a 100-200 mesh basic alumina column. Finally, remove the solvent by rotary evaporation to obtain a dark red viscous liquid 4-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-4-bromo-4-butyl ester with a yield of 76%.

[0073] Dissolve the dark red viscous liquid (27.28 g, 85 mmol) of the previous step in a mixture of 180 mL N,N-dimethylformamide and deionized water (volume ratio of 2:1). Add 1-propanesulfonic acid-based 4,4'-dipyridine (21.12 g, 80 mmol) and heat to 75°C for 7 days. Precipitate with acetone to obtain a brown solid with a yield of 83%.

[0074] Example 3

[0075] In a 250 mL three-necked flask, add nitroxide piperidinol (3.44 g, 20 mmol) and dissolve in 20 mL dichloromethane with vigorous stirring, then add triethylamine (4.04 g, 40 mmol) and 4-dimethylpyridine (0.035 g, 1 wt%) as catalyst. Dissolve 4-bromo-butyryl chloride (7.42 g, 40 mmol) in 10 mL dichloromethane in advance. After 30 min of nitrogen bubbling, add the 4-bromo-butyryl chloride solution dropwise through a constant pressure dropping funnel under ice bath, after the addition is completed, remove the ice bath, continue to react at room temperature for 24 h, and a light yellow solid is precipitated during the reaction. After the reaction is completed, remove the precipitate by filtration, and wash the filtrate with deionized water, saturated sodium bicarbonate solution, 2% dilute hydrochloric acid solution, and saturated sodium chloride solution in sequence; dry the obtained organic phase solution with anhydrous sodium sulfate, and further purify it by passing through a basic alumina column. Finally, remove the solvent by rotary evaporation to obtain a dark red viscous liquid 4-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-4-bromo-4-butyl ester with a yield of 65%.

[0076] Example 4

[0077] In a 500 mL three-necked flask, add nitroxide piperidinol (25.80 g, 150 mmol) and dissolve in 120 mL dichloromethane with vigorous stirring, then add triethylamine as catalyst (16.89 g, 165 mmol). Dissolve 4-bromo-butyryl chloride (24.98 g, 150 mmol) in 80 mL dichloromethane in advance. After 30 min of nitrogen bubbling, add the 4-bromo-butyryl chloride solution dropwise through a constant pressure dropping funnel under ice bath, after the addition is completed, remove the ice bath and continue to react at room temperature for 40 h, during which light yellow solid precipitates. After the reaction is completed, remove the precipitate by filtration, and then wash the filtrate with deionized water, saturated sodium bicarbonate solution, 2% dilute hydrochloric acid solution, and saturated sodium chloride solution successively; dry the obtained organic phase solution with anhydrous sodium sulfate and further purify it by passing through a 100-200 mesh basic alumina column. Finally, remove the solvent by rotary evaporation to obtain a dark red viscous liquid with a yield of 82%.

[0078] Dissolve the dark red viscous liquid (44.94 g, 140 mmol) obtained in the previous step in a mixture of 200 mL N,N-dimethylformamide and deionized water (volume ratio of 3:1) and heat to 65°C. Add 1-propanesulfonic acid-4,4'-dipyridine (26.41 g, 100 mmol) and react for 10 days. Precipitate with acetone three times to obtain a brown solid with a yield of 78%.

[0079] Example 5

[0080] In a 500 mL three-necked flask, add nitroxide piperidinol (18.95 g, 100 mmol) and dissolve in 100 mL dichloromethane with vigorous stirring, then add pyridine as catalyst (9.48 g, 110 mmol). Dissolve 4-bromo-butyryl chloride (22.20 g, 120 mmol) in 80 mL dichloromethane in advance. After 30 min of nitrogen bubbling, add the 4-bromo-butyryl chloride solution dropwise through a constant pressure dropping funnel under ice bath, after the addition is completed, remove the ice bath and continue to react at room temperature for 40 h, during which light yellow solid precipitates. After the reaction is completed, remove the precipitate by filtration, and then wash the filtrate with deionized water, saturated sodium bicarbonate solution, 2% dilute hydrochloric acid solution, and saturated sodium chloride solution successively; dry the obtained organic phase solution with anhydrous sodium sulfate and further purify it by passing through a 100-200 mesh basic alumina column. Finally, remove the solvent by rotary evaporation to obtain a dark red viscous liquid with a yield of 86%.

[0081] Dissolve the dark red viscous liquid (25.68 g, 80 mmol) from the previous step in 200 mL of a 1:1 volume ratio of N,N-dimethylformamide and deionized water. Add 1-propanesulfonic acid-4,4'-bipyridine (26.41 g, 100 mmol) and heat to 65°C for 10 days. Precipitate with acetone to obtain a brown solid in a 79% yield.

[0082] Example 6

[0083] In a 250mL three-necked flask, nitroxyl piperidinol (5.16g, 30mmol) was added and thoroughly stirred and dissolved in 50ml of dichloromethane. Pyridine was then added as a catalyst (2.37g, 30mmol). Bromoacetyl chloride (5.51g, 35mmol) was dissolved in 20ml of dichloromethane in advance. After nitrogen was passed through for 30min, the bromoacetyl chloride solution was slowly added dropwise through a constant pressure dropping funnel under an ice bath. After the addition was complete, the ice bath was removed and the reaction was continued at room temperature for 24h. During the reaction, a light red solid precipitated. After the reaction was completed, the precipitate was filtered to remove the precipitate, and the filtrate was washed with deionized water, saturated sodium bicarbonate solution, and saturated sodium chloride solution in sequence; the resulting organic phase solution was dried over anhydrous sodium sulfate, and the yield was 51%.

[0084] Dissolve the dark red viscous liquid (5.38 g, 15 mmol) from the previous step in 60 mL of a 1:2 volume ratio of anhydrous ethanol and deionized water. Add 1-propanesulfonic acid-4,4'-bipyridine (6.60 g, 25 mmol) and heat to 70°C for 6 days. Precipitate with acetone to obtain a brownish-red solid in a 60% yield.

[0085] Example 7

[0086] In a 100 mL three-necked flask, piperidinol (3.44 g, 20 mmol) was added and thoroughly stirred to dissolve in 30 mL of dichloromethane. Pyridine (3.16 g, 40 mmol) was then added as a catalyst. 5-Bromo-valeryl chloride (7.96 g, 40 mmol) was previously dissolved in 20 mL of dichloromethane. After nitrogen flow for 30 minutes, the 5-Bromo-valeryl chloride solution was added dropwise through a constant pressure dropping funnel under an ice bath. After the addition was complete, the ice bath was removed and the reaction was continued at room temperature for 40 hours. During the reaction, a light yellow solid precipitated. After the reaction was completed, the precipitate was removed by filtration, and the filtrate was washed sequentially with deionized water, saturated sodium bicarbonate solution, 2% dilute hydrochloric acid solution, and saturated sodium chloride solution. The resulting organic phase solution was dried over anhydrous sodium sulfate and further purified by passing through a 100-200 mesh alkaline alumina column. The solvent was finally removed by rotary evaporation to obtain a dark red viscous liquid with a yield of 82%.

[0087] The deep red viscous liquid (5.91 g, 15 mmol) from the previous step was dissolved in 60 mL of a mixture of N,N-dimethylformamide and deionized water (1:1 by volume). 1-Propanesulfonic acid-4,4'-bipyridine (5.28 g, 20 mmol) was added and heated to 80 °C for 6 days. Precipitation with acetone gave a brownish red solid in 75% yield.

[0088] Results analysis

[0089] Pyridine and triethylamine are weakly basic organic compounds and are also commonly used catalysts for acyl chloride reactions. In the reaction system, they can be used to adsorb the HCl generated by the acyl chloride reaction and accelerate the reaction. Compared with triethylamine, pyridine can better improve the reaction efficiency and product purity. The result may be that when the reaction is carried out with nitrogen-oxygen free radical piperidinol as the reactant, pyridine can better stabilize the intermediate product and achieve higher yield. 4-Dimethylpyridine has a similar structure and cooperates with triethylamine as a catalyst for acyl chloride reactions, but the yield of the product is not high. The result may be that the dimethyl-containing pyridine structure has no significant effect on the stability of small molecules. The results of acyl chloride reactions under different conditions are shown in Table 1.

[0090] Table 1: Effect of different reaction conditions on the results of acyl chloride reactions

[0091]

[0092] Electrochemical performance detection

[0093] The electrochemical performance of the water-soluble bipolar complex molecule (3 mg·mL -1 -1 , in a sodium chloride aqueous solution with pH = 7) in Example 1 of the present application was studied by cyclic voltammetry (CV), wherein the scan rates were 20 mV·s -1 -1 , 50 mV·s -1 -1 , 100 mV·s -1 -1 , 300 mV·s -1 -1 , and 500 mV·s -1 -1 , respectively.

[0094] Figure 4 The CV curve of the water-soluble bipolar complex molecule in Example 1 of the present application is shown in the figure.

[0095] The curve shows two sets of redox peaks of the bipolar complex molecule. For the positive active material, it shows a reduction peak around 0.635 V (vs. Ag / AgCl) and an oxidation peak around 0.712 V (vs. Ag / AgCl); for the negative active material, it shows a reduction peak around -0.547 V (vs. Ag / AgCl) and an oxidation peak around -0.494 V (vs. Ag / AgCl). The redox couple thus formed can obtain a theoretical output voltage of about 1.2 V.

[0096] Examples of dual electrode material flow battery system applications

[0097] As shown in Figure 1 , the flow battery as an electrochemical energy storage system, its structural design mainly includes two independent liquid storage tanks, electrolyte and electrochemical device connected by pump, through the electrochemical reaction between the two redox electrode materials reversible coordination between electrical energy and chemical energy. Inside the battery chamber is separated into anode and cathode chamber by ion exchange membrane, ion exchange membrane allows specific ion flow, so as to balance the battery charge, and prevent active material cross infection.

[0098] The left negative electrolyte 22 tank is added with 15 mL of 0.1M water-soluble bipolar complex molecule in the application example 1 and 1.5M NaCl mixed solution, and the right positive electrolyte 23 tank is added with 10 mL of 0.1M water-soluble bipolar complex molecule in the application example 1 and 1.5M NaCl mixed solution, the separation membrane uses anion exchange membrane AMVN (3.5cm*3cm*0.45cm), to form a bipolar complex molecule flow battery system.

[0099] When testing, first set 10s of static, constant current charging (set current in turn 40mA, 80mA, 100mA, 150mA, 200mA, cutoff voltage≤1.75V) and constant current discharge (set current in turn 40mA, 80mA, 100mA, 150mA, 200mA, cutoff voltage≥0.3V), each current density cycle test 5 times, finally end test.

[0100] Figure 5 The battery cycle stability diagram under different current densities.

[0101] As Figure 5 can be seen, the composite bipolar molecule electrode material has good electrochemical stability, when the current is gradually increased from 40mA to 150mA, the discharge capacity of the battery is maintained at more than 50% of the theoretical value.

[0102] Under the above concentration conditions, the forward and reverse charge-discharge cycle performance test is carried out. In the positive cycle process, set 60s of static, constant current charging (set current 60mA, cutoff voltage≤1.75V) and constant current discharge (set current 60mA, cutoff voltage≥0.3V), cycle test 5 times; After the end of the test, set the reverse cycle process, first set 60s of static, constant current discharge (set current 60mA, cutoff voltage≥-1.75V) and constant current charging (set current 60mA, cutoff voltage≤-0.3V), cycle test 5 times. Such cycle four times, finally end test. Figure 6The figure is the voltage-time graph of the battery in the forward and reverse charge-discharge process. Stable charge-discharge platforms can be seen in the forward and reverse charge-discharge process, indicating that the electrode cross-infection problem of the bipolar flow battery system has no irreversible effect.

[0103] The stability test of the double-electrode flow battery cycle system. 15 mL of a mixed solution of 0.15 M water-soluble bipolar composite molecules in Example 1 of the application and 1.5 M NaCl is added to the left negative electrolyte 22 tank, and 10 mL of a mixed solution of 0.15 M water-soluble bipolar composite molecules in Example 1 of the application and 1.5 M NaCl is added to the right positive electrolyte 23 tank, and an anion exchange membrane AMVN (3.5 cm*3 cm*0.45 cm) is used as the separator membrane to form a bipolar composite molecule flow battery system. When performing the test, first set the standing time to 10 s, then constant current charging (set the current to 40 mA, and the cutoff voltage is ≤1.75 V) and constant current discharging (set the current to 40 mA, and the cutoff voltage is ≥0.3 V), and cycle test for 500 times, and finally end the test. Figure 7 The figure is the cycle stability graph of the battery. The system has good cycle stability, and the capacity is attenuated to 11.6 mAh after 500 cycles (the theoretical capacity is 40.2 mAh, and the first cycle discharge capacity is 22.5 mAh), the capacity retention rate is 51.55%, and the average capacity attenuation rate per cycle is 0.095%.

[0104] The all-polymer flow battery system 100 according to the embodiment of the application has the advantages of easy preparation of active materials, stable charge-discharge performance, etc., and meets the large-scale energy storage demand.

[0105] The performance of the double-electrode flow battery system in the prior art and the application is compared in detail in Table 2.

[0106] Table 2: Comparison of the performance of the reported double-electrode flow battery system

[0107]

[0108] The reference file [1] in the prior art is:

[0109] Liu, T., et al., A Total Organic Aqueous Redox Flow Battery Employing a Low Cost and Sustainable Methyl Viologen Anolyte and 4-HO-TEMPO Catholyte. Advanced Energy Materials, 2015. 6(3).

[0110] Prior art reference [2] is:

[0111] Winsberg, J., et al., TEMPO / Phenazine Combi-Molecule: A Redox-Active Material for Symmetric Aqueous Redox-Flow Batteries. ACS Energy Letters, 2016. 1(5): p. 976-980.

[0112] Prior art reference [3] is:

[0113] Janoschka, T., et al., An Approach Toward Replacing Vanadium: A Single Organic Molecule for the Anode and Cathode of an Aqueous Redox-Flow Battery. Chemistry Open, 2017. 6(2): p. 216-220.

[0114] Prior art reference [4] is: Gabriel Sikukuu, N., et al., An organic bifunctional redox active material for symmetric aqueous redox flow battery. Nano Energy, 2021. 89: p. 106422.

[0115] Prior art reference file [5] is: Yingzhong, Z., et al., Enhanced cyclability of organic redox flow batteries enabled by an artificial bipolar molecule in neutral aqueous electrolyte. Journal of Power Sources, 2019. 417: p. 83-89.

[0116] In summary, the water-soluble bipolar complex molecule of the present application takes TEMPO as the positive active material and Viologen as the negative active material, and is prepared into a bifunctional complex small molecule through acyl chloride and quaternary ammonium. The water-soluble bipolar complex molecule has the following advantages: 1. The solubility of the bipolar complex molecule is increased by the quaternary ammonium salt and ionic groups on the bipolar complex molecule, thereby further improving the energy density of the battery; 2. The water-soluble bipolar complex molecule is used as the electrode material, and the same active material is used for the positive and negative electrodes, which can effectively avoid the adverse effects caused by cross contamination between active materials, thereby maintaining the stability of the battery capacity. The water-soluble bipolar complex molecule flow battery system 100 of the present application introduces a complex molecule with excellent positive and negative electrode electrochemical activity as a redox couple, and obtains a full-organic bipolar complex molecule flow battery with good stability, which meets the demand of large-scale energy storage.

[0117] The dual-electrode flow battery can avoid the influence caused by electrode cross infection, and can be stably cycled in air.

[0118] The performance of the dual-electrode aqueous flow battery system reported so far is shown in Table 2. Compared with the prior art, the bipolar small molecule structure of the present application not only has the best water solubility, but also has excellent system cycle stability, and can be expected to be applied in large-scale flow battery energy storage.

[0119] The above description is only a preferred embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent transformation made by using the present application is within the patent protection scope of the present application.

Claims

1. A composite bipolar molecular material for a water-soluble two-electrode liquid flow battery system, characterized in that: The chemical structural formula of the water-soluble bipolar composite molecule is: 。 2. A method for preparing a composite bipolar molecular material for a water-soluble two-electrode liquid flow battery system according to claim 1, characterized in that: The method comprises the following preparation steps: S1 uses the nitroxide free radical piperidinol and acyl chloride as raw materials and adds a catalyst to carry out acyl chlorination reaction; S2 is further reacted with 1-propanesulfonic acid-4,4'-bipyridine to undergo quaternization reaction to synthesize the water-soluble bipolar composite molecular structure.

3. The method for preparing a composite bipolar molecular material for a water-soluble two-electrode liquid flow battery system according to claim 2, characterized in that: Specifically comprising the following preparation steps: S1: Using the nitrogen oxide free radical piperidinol and acyl chloride as raw materials, adding a catalyst to carry out acyl chlorination reaction The method comprises the following steps: adding a nitroxyl piperidinol radical and an appropriate amount of solvent into a container and stirring the mixture at room temperature; adding a catalyst after the solid is completely dissolved, stirring and deoxygenating the mixture in a nitrogen environment; dissolving an acyl chloride in an appropriate amount of solvent and adding the solution dropwise into the container; continuing to stir the solution for reaction after the addition is complete; filtering to remove the precipitate, and washing the filtrate with different extracts in sequence; drying the obtained organic phase solution with an organic phase desiccant to remove water, and then further purifying the solution with an alkaline alumina column; and finally removing the solvent by rotary evaporation to obtain a dark red viscous liquid; Among them, the reaction formula of S1 is as follows: ； S2 is further quaternized with 1-propanesulfonic acid-4,4'-bipyridine to synthesize the water-soluble bipolar composite molecular structure The dark red viscous liquid obtained in S1 was dissolved in a mixed solvent, and an appropriate amount of 1-propanesulfonic acid-4,4'-bipyridine was added, and the mixture was heated under reflux for reaction; After the reaction is completed, a brown solid sample is obtained by precipitation with a precipitant; Among them, the reaction formula of S2 is as follows: 。 4. The method for preparing a composite bipolar molecular material for a water-soluble two-electrode liquid flow battery system according to claim 3, characterized in that: In S1, The catalyst is at least one of pyridine, triethylamine, and 4-dimethylaminopyridine; The acyl chloride structure is at least one of 5-bromo-valeryl chloride, 5-chloro-valeryl chloride, 4-bromo-butyryl chloride, 4-chloro-butyryl chloride, 3-bromo-propionyl chloride, 3-chloro-propionyl chloride, 2-bromo-acetyl chloride, and 2-chloro-acetyl chloride; The organic phase desiccant is at least one of anhydrous sodium sulfate and anhydrous magnesium sulfate; The solvent is at least one of dichloromethane, acetonitrile, chloroform, toluene, ethanol, and N,N-dimethylformamide; The extract is at least one of deionized water, saturated sodium bicarbonate solution, 2% dilute hydrochloric acid solution, and saturated sodium chloride solution; The particle size of the basic alumina in the basic alumina column is one of 100-200 mesh and 200-300 mesh.

5. The method for preparing a composite bipolar molecular material for a water-soluble two-electrode liquid flow battery system according to claim 3, characterized in that: In S1, The molar ratio of the raw material nitroxyl piperidinol to the acyl chloride is 1:1 to 1:2; The molar ratio of the raw material nitroxyl piperidinol to the catalyst is 1:1 to 1:2; The mass percentage of the nitroxide free radical piperidinol in the solvent is 7% to 13%, and the mass percentage of the acyl chloride is 8% to 20%.

6. The method for preparing a composite bipolar molecular material for a water-soluble two-electrode liquid flow battery system according to claim 3, characterized in that: In S1, The dropwise addition temperature is 0°C to 5°C, the acyl chlorination reaction temperature is 25°C to 30°C, and the reaction time is 20 to 40 h.

7. The method for preparing a composite bipolar molecular material for a water-soluble two-electrode liquid flow battery system according to claim 3, characterized in that: In S2, The mass percentage of the raw material 1-propanesulfonic acid-4,4'-bipyridine is 10% to 15%, the heating reaction temperature is 65 to 85°C, and the reaction time is 6 to 10 days; The volume ratio of the organic phase to the aqueous phase in the mixed solvent is 1:2~3:

1.

8. The method for preparing a composite bipolar molecular material for a water-soluble two-electrode liquid flow battery system according to claim 3, characterized in that: The precipitant is at least one of acetone and cold ethyl acetate; The mixed solvent is at least one of N,N-dimethylformamide and water, ethanol and water, acetonitrile and water, and trifluoroethanol and water.

9. An application of a composite bipolar molecular material for a water-soluble two-electrode liquid flow battery system, characterized in that: The composite bipolar molecule for the water-soluble two-electrode liquid flow battery system in claim 1 is used in the two-electrode liquid flow battery system, and the composite bipolar molecule material can be simultaneously used as the positive and negative electrode materials in the water-soluble two-electrode liquid flow battery cycle.

10. The use of the composite bipolar molecular material for a water-soluble two-electrode liquid flow battery system according to claim 9, characterized in that: The liquid flow battery system (100) includes: two electrolyte reservoirs (20) and a liquid flow battery stack (21-24), the two electrolyte reservoirs (20) are spaced apart, each electrolyte reservoir (20) is a storage tank for storing electrolyte or a salt cave with a physical dissolution cavity formed after salt mining, the battery material is directly dissolved or dispersed in a system with water as a solvent in the form of a bulk, and the liquid flow battery stack includes a battery separator (24), and the battery separator (24) separates the liquid flow battery stack into an anode area and a cathode area that are spaced apart and distributed, the anode area is connected to one electrolyte reservoir (20), and the cathode area is connected to the other electrolyte reservoir (20).

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