Preparation method of nitrogen heterocyclic modified quaternary ammonium salt TEMPO and application thereof in aqueous flow battery

Abstract

The application discloses a preparation method of aza ring modified quaternary ammonium salt TEMPO and application thereof in a water-based liquid flow battery. The specific preparation method is as follows: raw material carbonyl TEMPO is completely dissolved in a corresponding Lewis acid solution, mixed with corresponding aza rings (tetrahydropyrrole, hexahydropyridine and morpholine), then a corresponding reducing agent is added to obtain a cyclic amine substituted TEMPO intermediate, and the aza ring modified quaternary ammonium salt TEMPO generated by reacting with halomethane is further used as an active component of a positive electrolyte of the water-based liquid flow battery. The aza ring modified quaternary ammonium salt TEMPO synthesized has a structure of a compound of formula (I), (II) and (III); and the active substance in the negative electrolyte has a structure of a compound of formula (VIII). The aza ring modified quaternary ammonium salt TEMPO has high solubility in water and good stability, is applied to the water-based liquid flow battery, and is beneficial to improving the volume capacity of the liquid flow battery and finally improving the performance of the liquid flow battery.

Description

Technical Field

[0001] This invention belongs to the field of flow battery energy storage technology, specifically designing a method for preparing nitrogen heterocyclic modified quaternary ammonium salt TEMPO and its application in aqueous flow batteries. Background Technology

[0002] Energy storage technology can effectively regulate the instability of renewable energy power generation. Flow batteries, as a large-capacity electrochemical energy storage device, have the unique advantage of energy and power decoupling, making them one of the preferred technologies for large-scale energy storage.

[0003] Based on the different active species in the electrolyte solutions at the positive and negative electrodes, flow batteries can be classified into inorganic or organic systems. Currently, inorganic flow battery technology is relatively mature, including iron-chromium flow batteries, zinc-bromine flow batteries, all-iron flow batteries, and all-vanadium flow batteries, all with varying degrees of commercial demonstration cases. However, traditional inorganic flow batteries rely on transition metal electroactive materials, and the electrolytes are expensive and highly corrosive, hindering their further large-scale application. Therefore, developing novel electroactive molecules is of practical value. Compared to inorganic metal materials, aqueous organic flow batteries use water-soluble organic electroactive molecules as electrolytes, offering advantages such as abundant raw material sources and easy performance control, thus possessing broader application prospects.

[0004] Organic electroactive molecules are widely available, and their physicochemical properties, including redox potential and solubility, can be tuned through rational molecular engineering modification. TEMPO-type electroactive molecules are widely available and possess advantages such as reversible single-electron storage and rapid electron transfer rates, thus attracting widespread attention in various fields. The active NO single bond in TEMPO molecules is spatially protected by four adjacent methyl groups, exhibiting high stability. However, TEMPO molecules themselves are almost insoluble in water and have a low redox potential, making direct application in aqueous flow batteries difficult. To address these issues, molecular engineering design is typically used to modify TEMPO and its derivatives, such as grafting hydrophilic groups like hydroxyl groups, sulfonic acid groups, or quaternary ammonium salts at position 4 of the TEMPO molecule. Through electron-withdrawing inductive effects, the redox potential of TEMPO molecule derivatives can also be increased, thereby improving energy density in aqueous flow batteries.

[0005] Aqueous flow batteries possess advantages such as high safety, long lifespan, and energy-power decoupling, making them promising candidates for large-scale energy storage. Currently, TEMPO is a common choice for the positive electrode active material in aqueous flow batteries, attracting widespread attention due to its low cost, easy availability, readily modifiable molecular structure, and high redox potential (>0.75V vs. SHE). However, many TEMPO molecular derivatives designed through molecular engineering still have room for improvement in redox potential and water solubility. Summary of the Invention

[0006] The purpose of this invention is to provide a nitrogen-modified TEMPO derivative with high solubility and high potential (>0.90V vs. SHE) and its application in aqueous flow batteries to address the problems of low redox potential and poor water solubility of the TEMPO molecule itself. This invention leverages the strong electron-withdrawing inductive effect of quaternary ammonium salts and their good water solubility to improve the performance of nitrogen-modified TEMPO derivative molecules as the cathode in aqueous flow batteries.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A nitrogen-heterocyclic modified quaternary ammonium salt TEMPO, wherein the positive electrode active material is a nitrogen-heterocyclic modified quaternary ammonium salt TEMPO, comprising the structures described in (I) to (III):

[0009]

[0010] A method for preparing nitrogen-modified quaternary ammonium salt TEMPO, wherein the method for preparing nitrogen-modified quaternary ammonium salt TEMPO(Ⅰ)~(Ⅱ) includes the following steps:

[0011] After 4-carbonyl TEMPO is completely dissolved in 2,2,2-trifluoroethanol, tetrahydropyrrole or hexahydropyridine is added and reacted. Finally, sodium borohydride is added as a reducing agent to obtain the corresponding nitrogen-modified 4-cyclic amine substituted TEMPO intermediates. The reaction is carried out at room temperature, and the reaction formulas are shown in formulas (Ⅳ) to (Ⅴ).

[0012]

[0013] In the above method, the molar ratio of 4-carbonyl TEMPO to tetrahydropyrrole or hexahydropyridine and sodium borohydride is 1:(1.1~1.5):(1.2~1.5); the molar ratio of 4-carbonyl TEMPO to 2,2,2-trifluoroethanol is 1:(10.0~15.0).

[0014] In the above method, the preparation method of nitrogen-modified quaternary ammonium salt TEMPO(III) is as follows: after the 4-carbonyl TEMPO is completely dissolved in tetraisopropoxy titanium, morpholine is added, and finally sodium cyanoborohydride and ethanol are added as reducing agents to obtain nitrogen-modified substituted 4-morpholinamine TEMPO intermediate. The reaction is carried out at room temperature, and the reaction formula is as shown in formula (VI):

[0015]

[0016] In the above method, the molar ratio of 4-carbonyl TEMPO to morpholine, tetraisopropoxy titanium, and sodium cyanoborohydride is 1:(1.5-2):(1.2-1.5):(1.-1.5); the molar ratio of 4-carbonyl TEMPO to ethanol is 1:(10.0-15.0).

[0017] In the above method, the preparation of nitrogen-modified quaternary ammonium salts TEMPO(Ⅰ)~(Ⅲ) involves dissolving the 4-amine-substituted TEMPO intermediate in acetone, adding halomethane, reacting at room temperature, and filtering to obtain the precipitate, as shown in reaction formula (Ⅶ):

[0018]

[0019] Nitrogen heterocyclic modified quaternary ammonium salt TEMPO was used as the positive electrode active material, supporting electrolyte, and negative electrode active material to prepare an electrolyte for use in aqueous flow batteries.

[0020] An aqueous flow battery includes a separator, an electrolyte, electrodes, a peristaltic pump, tubing, and a battery testing system; the electrolyte includes a negative electrode active material, a positive electrode active material, a supporting electrolyte, and an aqueous solvent; the negative electrode active material is a quaternary ammonium salt bipyridine, and the positive electrode active material is a nitrogen-modified quaternary ammonium salt TEMPO.

[0021] Preferably, the membrane is an anion exchange membrane (DSVN membrane).

[0022] Preferably, the supporting electrolyte is either potassium chloride or sodium chloride.

[0023] Preferably, the electrolyte solvent is water.

[0024] Preferably, the negative electrode active material of the electrolyte is a quaternary ammonium salt bipyridine, with the following structural formula:

[0025]

[0026] Preferably, the positive electrode active material of the electrolyte is one or more quaternary ammonium salt TEMPO derivatives, with the following structural formula:

[0027]

[0028] Preferably, the aqueous flow battery includes a single cell or a single cell stack, which consists of a separator, positive and negative electrolytes, electrodes, a peristaltic pump and pipes to form a single cell, or a separator, positive and negative electrolytes, a stack device and a pump to form a single cell stack.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] This invention provides a reasonable and simple synthesis method for nitrogen-modified TEMPO derivatives, which exhibit structural stability, better water solubility, and higher redox potential. When matched with a suitable negative electrode, they can form a high-potential, high-performance aqueous current battery. This battery improves the water solubility and redox potential of the TEMPO derivative organic electrolyte, significantly enhancing battery performance. It provides a reference for developing high-performance aqueous all-organic current batteries and can be used in large-scale energy storage technologies. Attached Figure Description

[0031] Figures 1-3 These are cyclic voltammetry test results for compounds (Ⅰ) to (Ⅲ) used in Example 4 of this invention;

[0032] Figure 4 This is a cycle stability diagram of the flow battery of Embodiment 5 of the present invention;

[0033] Figure 5 This is a cycle stability diagram of the flow battery of Embodiment 6 of the present invention;

[0034] Figure 6 This is a cycle stability diagram of the flow battery in Embodiment 7 of the present invention. Detailed Implementation

[0035] The following embodiments are further illustrations of the present invention, but are not intended to limit the scope of the invention.

[0036] In the following examples, the synthesis room temperature was 25°C.

[0037] Example 1

[0038] A solution of 4-carbonyl TEMPO (1.70 g, 10 mmol) and 2,2,2-trifluoroethanol (20 mL) was magnetically stirred at room temperature for 5 minutes. Tetrahydropyrrole (0.77 g, 11 mmol) and sodium borohydride (0.456 g, 12 mmol) were added sequentially. The reaction was analyzed on thin-layer silica gel (hexane-ethyl acetate, 4:1) and the process was recorded. After the reaction was complete, the mixture was filtered, and the residue was washed with 20 mL of 2,2,2-trifluoroethanol. The filtrate was collected. The filtrate was rotary evaporated to give 2.04 g of the intermediate product, as shown in reaction (IV), with a yield of 91%.

[0039] Example 2

[0040] A solution of 4-carbonyl TEMPO (1.70 g, 10 mmol) and 2,2,2-trifluoroethanol (20 mL) was magnetically stirred at room temperature for 5 minutes. Hexahydropyridine (0.94 g, 11 mmol) and sodium borohydride (0.456 g, 12 mmol) were added sequentially. The reaction was analyzed on thin-layer silica gel (hexane-ethyl acetate, 4:1) and the process was recorded. After the reaction was complete, the mixture was filtered, and the residue was washed with 20 mL of 2,2,2-trifluoroethanol. The filtrate was collected. The filtrate was rotary evaporated to give 1.94 g of the intermediate product. The reaction formula is shown in (V), with a yield of 81%.

[0041] Example 3

[0042] A solution of 4-carbonyl TEMPO (1.70 g, 10 mmol) and tetraisopropyl titanate (3.59 mL, 12 mmol) was magnetically stirred at room temperature for 20 minutes. Morpholine (1.74 mL, 20 mmol) was then added, and stirring continued for 2 hours. Subsequently, anhydrous ethanol (8.5 mL) and sodium cyanoborohydride (0.754 g, 12 mmol) were added, and stirring continued for 12 hours. The reaction was quenched by adding 10 mL of water. The aqueous layer was extracted with ethyl acetate and treated with anhydrous sodium sulfate. The organic layer was desolventized under vacuum. 1.37 g of the intermediate was obtained, with the reaction formula shown in (VI), yielding 57%.

[0043] Example 4

[0044] 10 mmol of the intermediate product obtained above was dissolved in 10 mL of acetone. Iodomethane (2.84 g, 20 mmol) was added, and the mixture was magnetically stirred for 24 h. The precipitate was collected and washed three times with 5 mL of acetone. Finally, the resulting powder solid was dissolved in 10 mL of deionized water and... IRA-900 chloride-form anion exchange resin was rinsed through an anion exchange column and then evaporated to dryness. The final product was a red or pink powder with the structural formulas shown in (I) to (III). The yield was over 90%. The standard electrode potentials of the compounds (I) to (III) obtained by cyclic voltammetry were as follows: Figures 1-3 As shown, the potentials are 0.96V vs. standard hydrogen electrode, 0.93V vs. standard hydrogen electrode, and 0.98V vs. standard hydrogen electrode, respectively.

[0045] Example 5

[0046] A redox flow cell was constructed using 1.0 mol / L compound (Ⅳ) and compound (Ⅷ).

[0047] Dissolve 1.3792 g of compound (Ⅳ) and 0.3728 g of potassium chloride in water and bring the volume to 5.0 mL to prepare a 5.0 mL positive electrolyte of 1.0 mol / L compound (Ⅳ); dissolve 5.0 g of compound (Ⅷ) and 0.7455 g of potassium chloride in water and bring the volume to 10.0 mL to prepare a 10.0 mL negative electrolyte of 1.0 mol / L compound (Ⅷ); use a 5 mm thick carbon felt, and separate the positive and negative electrodes with an anion exchange membrane (AMVN); the electrode area is 9 cm². 2 The carbon felt. The electrolyte flow rate is 60 mL / min. -1 At 60mA cm -2 The constant current deep charge-discharge test showed stability with a capacity retention of 99.94%, an average coulombic efficiency of 99.47%, and an average energy efficiency of 81.37%. Figure 4 As shown.

[0048] Example 6

[0049] A redox flow cell was constructed using 1.5 mol / L compound (V) and compound (VIII).

[0050] Dissolve 2.1888g of compound (V) and 0.3728g of potassium chloride in water and bring the volume to 5.0mL to prepare a 5.0mL positive electrolyte of 1.5mol / L compound (V); dissolve 5.0g of compound (VIII) and 0.7455g of potassium chloride in water and bring the volume to 10.0mL to prepare a 10.0mL negative electrolyte of 1.0mol / L compound (VIII); use a 5mm thick carbon felt, and separate the positive and negative electrodes with an anion exchange membrane (AMVN); the electrode area is 9cm². 2 The carbon felt. The electrolyte flow rate is 60 mL / min. -1 At 60mA cm -2 Stability was demonstrated during constant current deep charge-discharge testing, with a capacity retention of 99.98%, an average coulombic efficiency of 99.75%, and an average energy efficiency of 71.36%. Figure 5 As shown.

[0051] Example 7

[0052] A redox flow cell was constructed using 2.0 mol / L compound (VI) and compound (VIII).

[0053] Dissolve 2.9184 g of compound (VI) and 0.3728 g of potassium chloride in water and bring the volume to 5.0 mL to prepare a 5.0 mL positive electrolyte solution of 2.0 mol / L compound (VI). Dissolve 5.0 g of compound (VIII) and 1.1183 g of potassium chloride in water and bring the volume to 15.0 mL to prepare a 15.0 mL negative electrolyte solution of 1.0 mol / L compound (VIII). Use a 5 mm thick carbon felt, and separate the positive and negative electrodes with an anion exchange membrane (AMVN). The electrode area is 9 cm². 2 The carbon felt. The electrolyte flow rate is 60 mL / min. -1 At 60mA cm -2 The constant current deep charge-discharge test showed stability with a capacity retention of 99.88%, an average coulombic efficiency of 99.19%, and an average energy efficiency of 77.22%. Figure 6 As shown.

[0054] It should be understood that the above detailed description of the technical solutions of the present invention with reference to optimized embodiments is illustrative and not restrictive. It should not be considered that the specific implementation of the present invention is limited to this. For those skilled in the art, any modifications to the technical solutions described in the embodiments or equivalent substitutions of some technical features without departing from the concept of the present invention should be considered as falling within the scope of patent protection defined by the claims submitted by the present invention.

[0055] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. The application of a nitrogen-modified quaternary ammonium salt TEMPO as a positive electrode active material in an aqueous flow battery, characterized in that, The nitrogen-modified quaternary ammonium salt TEMPO is a compound represented by formula (I), (II), or (III) below: （Ⅰ）； （Ⅱ）； （Ⅲ）； The nitrogen-modified quaternary ammonium salt TEMPO, as shown in formula (I), (II), or (III), is used as the positive electrode active material, and the quaternary ammonium salt bipyridine (VIII) is used as the negative electrode active material. The supporting electrolyte is composed of potassium chloride or sodium chloride and an aqueous solvent. The concentration of the positive electrode active material is 0.1 ~ 2.0 mol / L, the concentration of the negative electrode active material quaternary ammonium salt bipyridine is 0.1 ~ 1.5 mol / L, and the concentration of the supporting electrolyte is 0.5 ~ 2.0 mol / L. The structure of the quaternary ammonium salt bipyridine is formula (VIII): .

2. The application according to claim 1, characterized in that... The nitrogen-modified quaternary ammonium salt TEMPO was prepared by a method comprising the following steps: (a) For the preparation of nitrogen-modified quaternary ammonium salt TEMPO with structure (I) or (II): 4-carbonyl TEMPO is dissolved in 2,2,2-trifluoroethanol, then tetrahydropyrrole or hexahydropyridine is added for reaction, followed by the addition of sodium borohydride as a reducing agent to obtain the corresponding 4-cyclic amine substituted TEMPO intermediate; wherein the molar ratio of 4-carbonyl TEMPO to tetrahydropyrrole or hexahydropyridine and sodium borohydride is 1:(1.1~1.5):(1.2~1.5); the molar ratio of 4-carbonyl TEMPO to 2,2,2-trifluoroethanol is 1:(10.0~15.0); or, (b) For the preparation of nitrogen-modified quaternary ammonium salt TEMPO with structure (Ⅲ): 4-carbonyl TEMPO is dissolved in tetraisopropoxy titanium, then morpholine is added, followed by the reducing agent sodium cyanoborohydride and ethanol to obtain 4-morpholinamine-substituted TEMPO intermediate; wherein the molar ratio of 4-carbonyl TEMPO to morpholine, tetraisopropoxy titanium, and sodium cyanoborohydride is 1:(1.5~2):(1.2~1.5):(1~1.5); the molar ratio of 4-carbonyl TEMPO to ethanol is 1:(10.0~15.0); (c) Dissolve the 4-amine-substituted TEMPO intermediate obtained in step (a) or (b) in acetone, add halomethane to carry out quaternization reaction, and obtain the nitrogen-modified quaternary ammonium salt TEMPO.

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