Complex additive with bis-imidazolium structure as well as preparation method and application of complex additive

Abstract

The invention belongs to the technical field of electrochemical energy storage, and relates to a complex additive with a bis-imidazolium structure as well as a preparation method and application of the complex additive. The method comprises the following steps: dissolving 1-(2-ethoxyl) imidazole and anhydrous potassium carbonate in anhydrous acetonitrile, and stirring to obtain a 1-(2-ethoxyl) imidazole acetonitrile solution; under the protection of nitrogen, dropwise adding 1, 2-dibromoethane into the 1-(2-ethoxyl) imidazole acetonitrile solution, and carrying out heating reflux reaction to obtain a reaction mixture; cooling and filtering the reaction mixture, and collecting filtrate; mixing the filtrate with ethyl acetate, and separating out a solid product A; washing, evaporating and drying the solid product A to obtain the complexing additive with the bis-imidazolium structure. The invention solves the problems of low coulombic efficiency and poor cycle stability of the zinc-bromine flow battery caused by bromine volatilization and shuttle effect in the prior art, and the problems of performance degradation of the traditional complexing agent in high and low temperature environments, easy phase separation of the electrolyte and poor low temperature fluidity.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, and relates to a diimidazole onium structure complex additive, its preparation method and application. Background Technology

[0002] Zinc-bromine flow batteries (ZBFBs), as a high-energy-density, low-cost, and long-life energy storage technology, have shown broad application prospects in large-scale renewable energy storage and grid peak shaving. Their working principle is based on the redox reaction of a zinc / bromine couple, with the positive electrode active material being bromine / polybromine compounds (Br2 / Br3). - The negative electrode active material is zinc / zinc ions (Zn / Zn). 2+ However, the commercial application of zinc-bromine flow batteries still faces several key technological challenges, mainly including: The volatility and shuttle effect of bromine: Elemental bromine (Br2) is highly volatile and corrosive, easily escaping from the electrolyte. This not only causes loss of active materials and reduces battery coulombic efficiency, but also corrodes battery components and shortens battery life. Furthermore, dissolved polybrominated ions (such as Br3)... - Br5 - (e.g.) can migrate through the diaphragm to the negative electrode and undergo an irreversible reaction with the deposited zinc (bromine shuttle), leading to self-discharge and capacity decay.

[0003] Electrolyte phase separation and poor low-temperature performance: Under low-temperature conditions, high-concentration zinc-bromine electrolytes are prone to phase separation, precipitating solid bromides or hydrates. This leads to a sharp increase in electrolyte viscosity, decreased fluidity, and even blockage of flow channels, preventing the battery from operating normally. Traditional complexing agents (such as quaternary ammonium salts) have weakened complexing ability at low temperatures, making it difficult to effectively inhibit bromine precipitation. Furthermore, they may crystallize themselves, further deteriorating low-temperature performance.

[0004] Limitations of complexing agents: While widely used bromine complexing agents (such as N-methyl-N-ethylpyrrolidine onium salt and N-ethyl-N-methylmorpholinonium salt) can complex bromine to some extent, their single-cation structure has limited ability to complex polybrominates, especially at high temperatures or high bromine concentrations, where they are prone to dissociation and cannot completely suppress bromine volatilization. Furthermore, these complexing agent molecules lack flexible side chains, making it difficult to form a stable hydrogen bond network with water molecules in the electrolyte, resulting in limited improvement in low-temperature fluidity. Summary of the Invention

[0005] The purpose of this invention is to provide a bisimidazole-onium complex additive, its preparation method and application, to solve the technical problems of low coulombic efficiency and poor cycle stability in zinc-bromine flow batteries due to bromine volatilization and shuttle effect, as well as the performance degradation of traditional complexing agents under high and low temperature environments, easy phase separation of electrolyte and poor low-temperature fluidity.

[0006] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a bis(imidazolium) complexing additive, wherein the complexing additive is 1,1'-(ethane-1,2-diyl)bis(3-(2-hydroxyethyl)imidazolium)dibromide; the structural formula of the complexing additive is: .

[0007] Secondly, the present invention provides a method for preparing a diimidazole-onium complex additive, comprising the following steps: Dissolve 1-(2-hydroxyethyl)imidazol and anhydrous potassium carbonate in anhydrous acetonitrile and stir to obtain a 1-(2-hydroxyethyl)imidazol acetonitrile solution. Under nitrogen protection, 1,2-dibromoethane was added dropwise to the 1-(2-hydroxyethyl)imidazolium acetonitrile solution, and the mixture was heated under reflux to obtain the reaction mixture. The reaction mixture was cooled and filtered, and the filtrate was collected; the filtrate was mixed with ethyl acetate to precipitate solid product A; The solid product A was washed, evaporated, and dried to obtain the bisimidazole complex additive.

[0008] Preferably, the molar ratio of 1-(2-hydroxyethyl)imidazole, anhydrous potassium carbonate and 1,2-dibromoethane is 2:2.2:1.

[0009] Preferably, the heating reaction is carried out at 60-70°C for 12-24 hours.

[0010] Preferably, the filtration includes: separating the solid using reduced pressure filtration and washing the solid with acetonitrile.

[0011] Preferably, the washing is performed using ethyl acetate.

[0012] Preferably, the drying conditions are: vacuum drying at 60~70℃ for 18~24h.

[0013] Thirdly, the present invention provides an application of a bisimidazole-onium complex additive in the field of zinc-bromine flow battery technology, wherein the zinc-bromine flow battery electrolyte includes the aforementioned complex additive.

[0014] Preferably, the zinc-bromine flow battery electrolyte further includes zinc bromide, a supporting electrolyte, other additives, and water; wherein the other additives are 1-methyl-1-ethylpyrrolidine bromide, N-ethyl-N-methylmorpholine bromide, choline bromide, choline chloride, ethylene glycol, glycerol, N,N dimethylamide, or dimethyl sulfoxide; and the supporting electrolyte is potassium chloride, sodium chloride, ammonium chloride, zinc chloride, or lithium chloride.

[0015] Preferably, the molar concentration of the complexing additive in the zinc-bromine flow battery electrolyte is 0.1~1.5 mol / L, the molar concentration of zinc bromide is 0.5~3.5 mol / L, the molar concentration of the supporting electrolyte is 1.0~4.5 mol / L, and the molar concentration of other additives is 0~1 mol / L.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The complexing additive of this invention uses a bisimidazole onion cation as its backbone. Through strong electrostatic interactions generated at the centers of two positively charged imidazole rings, it can efficiently complex polybrominated anions (such as Br3) in the electrolyte. - This process forms a stable, spatially confined structure, which significantly suppresses the volatilization and shuttle effect of bromine, thereby improving the coulombic efficiency and cycle stability of the battery. At the same time, the hydroxyethyl side chain introduced into the molecule has strong hydrophilicity and can form a wide range of multiple hydrogen bond networks with water molecules and polybrominated ions. This synergistic effect not only enhances the bromine immobilization ability, but also effectively disrupts the crystallization tendency of the electrolyte at low temperatures, significantly reduces the freezing point of the system, improves low-temperature fluidity, and avoids phase separation, enabling the battery to maintain the homogeneous stability and high performance of the electrolyte over a wide temperature range. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram illustrating the performance of the zinc-bromine flow battery during cycle testing in Example 6. Detailed Implementation

[0019] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0020] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0021] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0022] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0023] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0024] The present invention will now be described in further detail with reference to the accompanying drawings: The first objective of this invention is to provide a bis(imidazolium) complexing additive, wherein the complexing additive is 1,1'-(ethane-1,2-diyl)bis(3-(2-hydroxyethyl)imidazolium)dibromide, with the chemical formula [HOEtImC2ImEtOH]Br2; the structural formula of the complexing additive is: .

[0025] The bisimidazole ring structure in the molecular skeleton of this complexing additive can efficiently complex polybrominated ions through strong electrostatic interactions, significantly inhibiting bromine volatilization and shuttle effects, thereby improving the coulombic efficiency and cycle stability of the battery. Simultaneously, the unique hydroxyethyl side chain in the molecule can form a multiple hydrogen bond network with water molecules and polybrominated ions. This unique interaction mechanism not only endows it with excellent bromine complexing ability but also effectively disrupts the crystallization tendency under low-temperature conditions. By regulating the intermolecular hydrogen bond interactions, it significantly lowers the freezing point of the electrolyte system, greatly improves the low-temperature fluidity of the electrolyte, and avoids phase separation. This complexing additive can maintain a homogeneous and stable electrolyte system over a wide temperature range, thereby significantly expanding the operating temperature range of the electrolyte and significantly improving the cycle stability of the battery system, solving the key technical problem of performance degradation of traditional complexing agents under high and low temperature environments.

[0026] A second objective of this invention is to provide a method for preparing a diimidazole-onium complex additive, comprising the following steps: Dissolve 1-(2-hydroxyethyl)imidazol and anhydrous potassium carbonate in anhydrous acetonitrile and stir to obtain a 1-(2-hydroxyethyl)imidazol acetonitrile solution. Under nitrogen protection, 1,2-dibromoethane was added dropwise to the 1-(2-hydroxyethyl)imidazolium acetonitrile solution, and the mixture was heated under reflux at 60-70°C for 12-24 h to obtain the reaction mixture. The reaction mixture was cooled and the solid was separated by vacuum filtration. The solid was washed with acetonitrile and the filtrate was collected. The filtrate was mixed with ethyl acetate to precipitate solid product A. The solid product A was washed with ethyl acetate, evaporated, and vacuum dried at 60-70°C for 18-24 hours to obtain a light yellow to brown bisimidazole complex additive.

[0027] This invention uses 1-(2-hydroxyethyl)imidazolium and 1,2-dibromoethane as raw materials. In an anhydrous acetonitrile environment, anhydrous potassium carbonate is introduced as a highly efficient acid scavenger, ensuring the high efficiency and completeness of the quaternization nucleophilic substitution reaction and effectively suppressing the potential damage of HBr byproducts to the reaction process and the imidazolium ring structure. The entire preparation process is carried out under inert gas protection, significantly avoiding oxidation side reactions of the raw materials and the imidazolium salt product at high temperatures, ensuring the purity and chemical stability of the product. Secondly, acetonitrile washing effectively removes inorganic salt byproducts, and the extremely low solubility of the target product in ethyl acetate enables efficient precipitation and separation of the product. This process effectively removes unreacted raw materials and small molecule byproducts. Finally, a vacuum drying process thoroughly removes residual solvent and moisture, yielding a high-purity bisimidazoleium complex additive. The entire process of this invention is characterized by mild conditions, simple operation, and good reproducibility. The resulting product has a clear chemical structure and high purity, and the functional groups of its bisimidazole ring and hydroxyethyl side chain are perfectly preserved, laying a solid foundation for its excellent bromine complexing ability and the formation of a stable hydrogen bond network in the electrolyte.

[0028] The molar ratio of 1-(2-hydroxyethyl)imidazole, anhydrous potassium carbonate, and 1,2-dibromoethane is 2:2.2:1. This concentration of 1-(2-hydroxyethyl)imidazole is intended to drive the quaternization reaction in the forward direction, ensuring that the 1,2-dibromoethane reactant is fully consumed, thereby improving atom economy. The use of a slight excess of anhydrous potassium carbonate (relative to the theoretical amount) can promptly and thoroughly neutralize the continuously generated hydrogen bromide byproducts during the reaction, effectively suppressing potential protonation degradation and catalytic hydrolysis of the imidazole onium salt product by HBr, maintaining a neutral environment in the reaction system, and ensuring the integrity and stability of the bisimidazole ring molecular structure.

[0029] A third objective of this invention is to provide an application of a diimidazole-onium complex additive in the field of zinc-bromine flow battery technology, wherein the zinc-bromine flow battery electrolyte includes the aforementioned complex additive. The zinc-bromine flow battery electrolyte further includes zinc bromide, a supporting electrolyte, other additives, and water; wherein the other additives are 1-methyl-1-ethylpyrrolidine bromide, N-ethyl-N-methylmorpholine bromide, choline bromide, choline chloride, ethylene glycol, glycerol, N,N dimethylamide, or dimethyl sulfoxide; and the supporting electrolyte is potassium chloride, sodium chloride, ammonium chloride, zinc chloride, or lithium chloride.

[0030] This complexing additive, with its unique bisimidazole ring and hydroxyethyl side chain structure, can not only efficiently complex elemental bromine and polybrominated ions, significantly suppressing the volatilization and shuttle effect of bromine, and improving the coulombic efficiency and cycle stability of the battery; the hydrogen bond network it introduces also has a strong synergistic effect with water, supporting electrolyte and other additives (such as choline salt or organic solvent) in the electrolyte, together maintaining the homogeneous stability of the electrolyte, effectively widening the operating temperature range and improving low-temperature fluidity.

[0031] The zinc-bromine flow battery electrolyte contains a complexing additive with a molar concentration of 0.1–1.5 mol / L, which fully utilizes its strong bromine complexing ability to effectively suppress bromine shuttle and volatilization, while avoiding excessive viscosity due to high concentration. The zinc bromide has a molar concentration of 0.5–3.5 mol / L, which balances energy density and solubility stability, ensuring sufficient active material loading. The supporting electrolyte has a molar concentration of 1.0–4.5 mol / L, effectively maintaining ionic strength and conductivity, ensuring efficient charge transfer and uniform zinc deposition. Other additives have a molar concentration of 0–1 mol / L, providing flexible adjustment space for regulating electrolyte viscosity, freezing point, and auxiliary complexation.

[0032] This invention also provides a zinc-bromine flow battery, comprising positive and negative electrolyte storage tanks, a circulation pump, and a battery stack. The battery stack includes end plates, current collectors, electrodes, electrode frames, and a separator. The positive and negative electrolyte storage tanks are respectively connected to the positive and negative electrode chambers of the battery stack via the circulation pump, forming a closed electrolyte circulation loop. The battery stack adopts a stacked structure, with the current collector, electrodes (carbon-plastic bipolar plates or carbon felt), electrode frames, and separator sequentially pressed together from the metal end plates (positive and negative end plates) at both ends. The current collector (such as a gold-plated copper plate) is in close contact with the electrodes to ensure current collection. The separator (such as a porous ion-conducting membrane) separates the positive and negative electrode chambers, and the zinc-bromine flow battery electrolyte is located in the positive and negative electrode chambers on both sides of the separator, allowing selective ion migration. The electrode frames form electrolyte flow channels, allowing the zinc-bromine flow battery electrolyte of this invention to flow uniformly across the electrode surface under the drive of the pump.

[0033] For example, the metal endplate is made of aluminum alloy or stainless steel, and the porous ion-conducting membrane has a precise pore size control of 0.01–0.1 μm and a porosity of 20%–60%. It can be made of perfluorosulfonic acid membranes, polyolefin membranes (such as Daramic 900 μm polyethylene membranes), sulfonated polyether ether ketone membranes, or polybenzimidazole membranes, etc., to achieve efficient ion-selective transport. Through material selection and structural parameter optimization, this zinc-bromine flow battery can adapt to a wide temperature range of -20–40°C, improving the stability and energy density of the zinc-bromine flow battery at low temperatures, maintaining a viscosity of <80 mPa·s at -20°C, and a capacity retention of >90% at -20°C.

[0034] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0035] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0036] Example 1 Dissolve 1-(2-hydroxyethyl)imidazol and anhydrous potassium carbonate in anhydrous acetonitrile and stir to obtain a 1-(2-hydroxyethyl)imidazol acetonitrile solution. Under nitrogen protection, 1,2-dibromoethane was added dropwise to the 1-(2-hydroxyethyl)imidazolium acetonitrile solution, and the mixture was heated under reflux at 60°C for 24 h to obtain the reaction mixture. The reaction mixture was cooled and the solid was separated by vacuum filtration. The solid was washed with acetonitrile and the filtrate was collected. The filtrate was mixed with ethyl acetate to precipitate solid product A. The solid product A was washed three times with ethyl acetate, subjected to rotary evaporation, and then vacuum dried at 60°C for 24 hours to obtain a diimidazole-onium complex additive.

[0037] The molar ratio of 1-(2-hydroxyethyl)imidazole, anhydrous potassium carbonate and 1,2-dibromoethane is 2:2.2:1.

[0038] Example 2 Dissolve 1-(2-hydroxyethyl)imidazol and anhydrous potassium carbonate in anhydrous acetonitrile and stir to obtain a 1-(2-hydroxyethyl)imidazol acetonitrile solution. Under nitrogen protection, 1,2-dibromoethane was added dropwise to the 1-(2-hydroxyethyl)imidazolium acetonitrile solution, and the mixture was heated under reflux at 60°C for 24 h to obtain the reaction mixture. The reaction mixture was cooled and the solid was separated by vacuum filtration. The solid was washed with acetonitrile and the filtrate was collected. The filtrate was mixed with ethyl acetate to precipitate solid product A. The solid product A was washed three times with ethyl acetate, subjected to rotary evaporation, and then vacuum dried at 60°C for 24 hours to obtain a diimidazole-onium complex additive.

[0039] The molar ratio of 1-(2-hydroxyethyl)imidazole, anhydrous potassium carbonate and 1,2-dibromoethane is 2:2.2:1.

[0040] Example 3 Dissolve 1-(2-hydroxyethyl)imidazol and anhydrous potassium carbonate in anhydrous acetonitrile and stir to obtain a 1-(2-hydroxyethyl)imidazol acetonitrile solution. Under nitrogen protection, 1,2-dibromoethane was added dropwise to the 1-(2-hydroxyethyl)imidazolium acetonitrile solution, and the mixture was heated under reflux at 65°C for 18 h to obtain the reaction mixture. The reaction mixture was cooled and the solid was separated by vacuum filtration. The solid was washed with acetonitrile and the filtrate was collected. The filtrate was mixed with ethyl acetate to precipitate solid product A. The solid product A was washed twice with ethyl acetate, subjected to rotary evaporation, and vacuum dried at 65°C for 20 h to obtain a diimidazole-onium complex additive.

[0041] The molar ratio of 1-(2-hydroxyethyl)imidazole, anhydrous potassium carbonate and 1,2-dibromoethane is 2:2.2:1.

[0042] Example 4 Dissolve 1-(2-hydroxyethyl)imidazol and anhydrous potassium carbonate in anhydrous acetonitrile and stir to obtain a 1-(2-hydroxyethyl)imidazol acetonitrile solution. Under nitrogen protection, 1,2-dibromoethane was added dropwise to the 1-(2-hydroxyethyl)imidazolium acetonitrile solution, and the mixture was heated under reflux at 70°C for 12 h to obtain the reaction mixture. The reaction mixture was cooled and the solid was separated by vacuum filtration. The solid was washed with acetonitrile and the filtrate was collected. The filtrate was mixed with ethyl acetate to precipitate solid product A. The solid product A was washed twice with ethyl acetate, subjected to rotary evaporation, and vacuum dried at 70°C for 18 hours to obtain a diimidazole-onium complex additive.

[0043] The molar ratio of 1-(2-hydroxyethyl)imidazole, anhydrous potassium carbonate and 1,2-dibromoethane is 2:2.2:1.

[0044] Example 5 Dissolve 1-(2-hydroxyethyl)imidazol and anhydrous potassium carbonate in anhydrous acetonitrile and stir to obtain a 1-(2-hydroxyethyl)imidazol acetonitrile solution. Under nitrogen protection, 1,2-dibromoethane was added dropwise to the 1-(2-hydroxyethyl)imidazolium acetonitrile solution, and the mixture was heated under reflux at 70°C for 12 h to obtain the reaction mixture. The reaction mixture was cooled and the solid was separated by vacuum filtration. The solid was washed with acetonitrile and the filtrate was collected. The filtrate was mixed with ethyl acetate to precipitate solid product A. The solid product A was washed four times with ethyl acetate, subjected to rotary evaporation, and then vacuum dried at 70°C for 18 hours to obtain a diimidazole-onium complex additive.

[0045] The molar ratio of 1-(2-hydroxyethyl)imidazole, anhydrous potassium carbonate and 1,2-dibromoethane is 2:2.2:1.

[0046] Performance testing: The bisimidazole-onium complex additive prepared in Example 1 was used to prepare a zinc-bromine flow battery.

[0047] Example 6 An electrolyte for a zinc-bromine flow battery comprises ZnBr2, KCl, [HOEtImC2ImEtOH]Br2, and water. The molar concentrations of ZnBr2, KCl, and [HOEtImC2ImEtOH]Br2 are 0.5 mol / L, 1.0 mol / L, and 0.1 mol / L, respectively. The battery sequentially comprises a positive electrode plate, a current collector, a carbon-plastic bipolar plate, a Daramic 900 μm polyethylene porous membrane, another carbon-plastic bipolar plate, a current collector, and a negative electrode plate. The electrolyte volume on both sides of the Daramic 900 μm polyethylene porous membrane is 50 mL. The peristaltic pump operates at 120 r / min, and the charge / discharge current density is 20 mA / cm². 2 Charging time: 4 hours; Discharge cut-off voltage: 0.5V; Battery operating temperature: -20℃; Cycle duration: 20 cycles; Results are as follows: Figure 1 As shown.

[0048] Example 7 An electrolyte for a zinc-bromine flow battery comprises ZnBr2, NH4Cl, [HOEtImC2ImEtOH]Br2, 1-methyl-1-ethylpyrrolidine bromide, and water. In this electrolyte, the molar concentrations of ZnBr2, NH4Cl, [HOEtImC2ImEtOH]Br2, and 1-methyl-1-ethylpyrrolidine bromide are 1.0 mol / L, 2.0 mol / L, 0.3 mol / L, and 0.5 mol / L, respectively. The battery sequentially comprises a positive electrode plate, a current collector, a carbon-plastic bipolar plate, a Daramic 900 μm polyethylene porous membrane, another carbon-plastic bipolar plate, a current collector, and a negative electrode plate. The electrolyte volume on both sides of the Daramic 900 μm polyethylene porous membrane is 50 mL. The peristaltic pump speed is 120 r / min, and the charge / discharge current density is 20 mA / cm². 2 Charging time: 4 hours; discharge cut-off voltage: 0.5V; battery operating temperature: -10℃; cycle life: 20 times.

[0049] Example 8 An electrolyte for a zinc-bromine flow battery comprises ZnBr2, NaCl, [HOEtImC2ImEtOH]Br2, N-ethyl-N-methylmorpholine bromide, and water. The molar concentrations of ZnBr2, NaCl, [HOEtImC2ImEtOH]Br2, and N-ethyl-N-methylmorpholine bromide in this electrolyte are 1.5 mol / L, 3.0 mol / L, 0.5 mol / L, and 1.0 mol / L, respectively. The battery sequentially comprises a positive electrode plate, a current collector, a carbon-plastic bipolar plate, a Daramic 900 μm polyethylene porous membrane, another carbon-plastic bipolar plate, a current collector, and a negative electrode plate. The electrolyte volume on both sides of the Daramic 900 μm polyethylene porous membrane is 50 mL. The peristaltic pump speed is 120 r / min, and the charge / discharge current density is 20 mA / cm². 2 Charging time: 4 hours; discharge cut-off voltage: 0.5V; battery operating temperature: 10℃; cycle time: 20 times.

[0050] Example 9 An electrolyte for a zinc-bromine flow battery comprises ZnBr2, ZnCl2, [HOEtImC2ImEtOH]Br2, choline chloride, and water. The molar concentrations of ZnBr2, ZnCl2, [HOEtImC2ImEtOH]Br2, and choline chloride are 2.5 mol / L, 4.0 mol / L, 1.0 mol / L, and 0.5 mol / L, respectively. The battery sequentially comprises a positive electrode plate, a current collector, a carbon-plastic bipolar plate, a Daramic 900 μm polyethylene porous membrane, another carbon-plastic bipolar plate, a current collector, and a negative electrode plate. The electrolyte volume on both sides of the Daramic 900 μm polyethylene porous membrane is 50 mL. The peristaltic pump speed is 120 r / min, and the charge / discharge current density is 20 mA / cm². 2 Charging time: 4 hours; discharge cut-off voltage: 0.5V; battery operating temperature: 25℃; cycle time: 20 times.

[0051] Example 10 An electrolyte for a zinc-bromine flow battery comprises ZnBr2, LiCl, [HOEtImC2ImEtOH]Br2, and water. The molar concentrations of ZnBr2, LiCl, and [HOEtImC2ImEtOH]Br2 are 3.5 mol / L, 4.5 mol / L, and 1.5 mol / L, respectively. The battery sequentially comprises a positive electrode plate, a current collector, a carbon-plastic bipolar plate, a Daramic 900 μm polyethylene porous membrane, another carbon-plastic bipolar plate, a current collector, and a negative electrode plate. The electrolyte volume on both sides of the Daramic 900 μm polyethylene porous membrane is 50 mL. The peristaltic pump speed is 120 r / min, and the charge / discharge current density is 20 mA / cm². 2 Charging time: 4 hours; discharge cut-off voltage: 0.5V; battery operating temperature: 40℃; cycle time: 20 times.

[0052] Comparative Example 1 An electrolyte for a zinc-bromine flow battery comprises ZnBr2, KCl, 1-methyl-1-ethylpyrrolidine bromide, and water. The molar concentrations of ZnBr2, KCl, and MEP in this electrolyte are 0.5 mol / L, 1.0 mol / L, and 0.1 mol / L, respectively. The battery sequentially comprises a positive electrode plate, a current collector, a carbon-plastic bipolar plate, a Daramic 900 μm polyethylene porous membrane, another carbon-plastic bipolar plate, a current collector, and a negative electrode plate. The electrolyte volume on both sides of the Daramic 900 μm polyethylene porous membrane is 50 mL. The peristaltic pump operates at a speed of 120 r / min, and the charge / discharge current density is 20 mA / cm². 2 Charging time is 4 hours, discharge cut-off voltage is 0.5V, and battery operating temperature is -20℃.

[0053] Comparative Example 2 An electrolyte for a zinc-bromine flow battery comprises ZnBr2, LiCl, and 1-methyl-1-ethylpyrrolidine bromide aqueous solution. The molar concentrations of ZnBr2, LiCl, and MEP in this electrolyte are 3.5 mol / L, 4.5 mol / L, and 1.5 mol / L, respectively. The battery sequentially comprises a positive electrode plate, a current collector, a carbon-plastic bipolar plate, a Daramic 900 μm polyethylene porous membrane, another carbon-plastic bipolar plate, a current collector, and a negative electrode plate. The electrolyte volume on both sides of the Daramic 900 μm polyethylene porous membrane is 50 mL. The peristaltic pump operates at 120 r / min, and the charge / discharge current density is 20 mA / cm². 2 Charging time: 4 hours; discharge cut-off voltage: 0.5V; battery operating temperature: 40℃; cycle time: 20 times.

[0054] The performance of the batteries assembled in Examples 6-10 was tested using a Blue Electric testing instrument. The results after 20 cycles are shown in Table 1. Table 1 Battery Performance Comparison

[0055] As shown in Table 1, at low temperatures, [HOEtImC2ImEtOH]Br2 can enhance the fluidity and stability of the electrolyte, inhibit the damage of zinc dendrites to the electrode structure, and slow down capacity decay. At higher temperatures, the electrode reaction kinetics are further optimized, the loss of active material is reduced, and the capacity retention rate under high temperature conditions is better, reflecting that the electrolyte has good cycling stability at different temperatures.

[0056] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A diimidazole-onium complex additive, characterized in that, The complexing additive is 1,1'-(ethane-1,2-diyl)bis(3-(2-hydroxyethyl)imidazolium)dibromide; the structural formula of the complexing additive is: 。 2. A method for preparing a diimidazole-onium complex additive, characterized in that, Includes the following steps: Dissolve 1-(2-hydroxyethyl)imidazol and anhydrous potassium carbonate in anhydrous acetonitrile and stir to obtain a 1-(2-hydroxyethyl)imidazol acetonitrile solution. Under nitrogen protection, 1,2-dibromoethane was added dropwise to the 1-(2-hydroxyethyl)imidazolium acetonitrile solution, and the mixture was heated under reflux to obtain the reaction mixture. The reaction mixture was cooled and filtered, and the filtrate was collected; the filtrate was mixed with ethyl acetate to precipitate solid product A; The solid product A was washed, evaporated, and dried to obtain the bisimidazole complex additive.

3. The method for preparing a diimidazole-onium complex additive according to claim 2, characterized in that, The molar ratio of 1-(2-hydroxyethyl)imidazolium, anhydrous potassium carbonate, and 1,2-dibromoethane is 2:2.2:

1.

4. The method for preparing a diimidazole-onium complex additive according to claim 2, characterized in that, The heating reaction conditions are: reacting at 60~70℃ for 12~24h.

5. The method for preparing a diimidazole-onium complex additive according to claim 2, characterized in that, The filtration process includes: separating the solids using reduced pressure filtration and washing the solids with acetonitrile.

6. The method for preparing a diimidazole-onium complex additive according to claim 2, characterized in that, The washing process was performed using ethyl acetate.

7. The method for preparing a diimidazole-onium complex additive according to claim 2, characterized in that, The drying conditions are: vacuum drying at 60~70℃ for 18~24h.

8. The application of a bisimidazole-onium complex additive in the field of zinc-bromine flow battery technology, characterized in that, The zinc-bromine flow battery electrolyte includes the complexing additive as described in claim 1.

9. The application according to claim 8, characterized in that, The zinc-bromine flow battery electrolyte further includes zinc bromide, a supporting electrolyte, other additives, and water; wherein the other additives are 1-methyl-1-ethylpyrrolidine bromide, N-ethyl-N-methylmorpholine bromide, choline bromide, choline chloride, ethylene glycol, glycerol, N,N dimethylamide, or dimethyl sulfoxide; and the supporting electrolyte is potassium chloride, sodium chloride, ammonium chloride, zinc chloride, or lithium chloride.

10. The application according to claim 8, characterized in that, The zinc-bromine flow battery electrolyte contains a complexing additive with a molar concentration of 0.1–1.5 mol / L, a zinc bromide molar concentration of 0.5–3.5 mol / L, a supporting electrolyte molar concentration of 1.0–4.5 mol / L, and other additives molar concentrations of 0–1 mol / L.

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