Zinc-bromine flow battery negative electrolyte, preparation method and application thereof

Abstract

The application relates to a zinc-bromine flow battery negative electrolyte as well as a preparation method and application thereof, and belongs to the field of flow batteries. The electrolyte is composed of zinc bromide, ammonium chloride, 1-methyl-1-ethyl-pyrrolidinium bromide, stannous chloride, citric acid, ascorbic acid, polyethylene glycol and deionized water. In the zinc-bromine flow battery negative electrolyte, Sn 2+ under the action of an electric field, is preferentially deposited at protrusions on the surface of a zinc negative electrode, reduces the surface energy and growth rate of zinc at the tip of the zinc negative electrode, and effectively inhibits the generation of zinc dendrites; citric acid is used to inhibit the hydrolysis of stannous chloride, ascorbic acid is used as an antioxidant to prevent Sn 2+ from being oxidized; the additive polyethylene glycol has the effect of a surfactant, can reduce the surface tension of the electrolyte, and enhances the wettability of the electrolyte; and the zinc-bromine flow battery negative electrolyte can significantly improve the cycle stability and cycle life of the zinc-bromine flow battery.

Description

Technical Field

[0001] This invention belongs to the field of flow batteries, specifically relating to a zinc-bromine flow battery negative electrode electrolyte, its preparation method, and its application. Background Technology

[0002] Clean energy sources such as wind and solar power are unevenly distributed in time and space, requiring efficient energy storage devices to store them before integrating them into the grid. Among various energy storage technologies, flow batteries have become a promising large-scale battery energy storage technology due to their advantages such as scalability, long lifespan, high safety, and high energy efficiency. Among the many flow battery systems, zinc-bromine flow batteries have the advantages of high energy density and low cost. The positive and negative electrode electrolytes of zinc-bromine flow batteries are both aqueous solutions of ZnBr2, which are circulated through the surfaces of the positive and negative electrodes by a pump. During charging, zinc is deposited on the negative electrode, and bromine generated at the positive electrode forms an oily substance with the bromine complexing agent in the electrolyte and is deposited at the bottom of the tank; during discharging, the zinc on the surface of the negative electrode dissolves, and the complexed bromine is reduced back to bromide ions, and the electrolyte returns to the zinc bromide state.

[0003] As a deposition-type flow battery, the amount of zinc deposited on the negative electrode side during charging directly affects the battery's capacity. However, at high charging capacities, a large number of deposition sites on the negative electrode are occupied. Due to the growth of zinc dendrites, these deposition sites are not exposed in time during discharge, leading to poor reversibility of the negative electrode and difficulty in maintaining stable coulombic efficiency. This significantly reduces the cycle stability and reliability of the zinc-bromine flow battery, hindering its practical application. Therefore, effectively promoting uniform zinc deposition and suppressing zinc dendrite growth is one of the key strategies for improving the cycle stability of zinc-bromine flow batteries.

[0004] In zinc-bromine flow batteries, the composition of the electrolyte has a decisive influence on battery performance. Chinese patent document CN120261651A discloses an electrolyte for high areal capacity zinc-bromine flow batteries, its preparation method, and its application. This technology modifies the solvation structure of zinc ions by adding an organic sulfonate complexing agent to the electrolyte, causing them to adsorb onto the surface of deposited zinc atoms, inhibiting zinc diffusion at the two-dimensional interface, and inducing preferential deposition of Zn(002) crystal planes, thereby effectively mitigating zinc dendrite formation. However, due to the limited variety of electrolyte additives, the inhibitory effect on zinc dendrites is limited, and significant energy efficiency decay occurs after 80 stable cycles. Therefore, developing novel zinc-bromine flow battery electrolytes with synergistic effects of multiple additives and long-term stability is of great significance for realizing the large-scale application of zinc-bromine flow batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a negative electrode electrolyte for zinc-bromine flow batteries, its preparation method, and its application. This invention can solve the technical problems of reduced cycle stability and reliability of zinc-bromine flow batteries due to the deterioration of negative electrode reversibility and unstable coulombic efficiency caused by zinc dendrite growth. This invention achieves the technical effect of improving the electrochemical stability and cycle life of zinc-bromine flow batteries.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a zinc-bromine flow battery negative electrode electrolyte, comprising the following components: zinc bromide, ammonium chloride, 1-methyl-1-ethyl-pyrrolidine bromide, stannous chloride, citric acid, ascorbic acid, polyethylene glycol, and deionized water; the concentration of each component in the zinc-bromine flow battery negative electrode electrolyte, based on the total volume of deionized water, is as follows: The concentration of stannous chloride is 1.5-5 mmol / L; The concentration of citric acid is twice that of stannous chloride; The concentration of ascorbic acid is twice that of stannous chloride; The concentration of zinc bromide is 2-4 mol / L; The concentration of polyethylene glycol is 0.2% of the mass of zinc bromide; The concentration of ammonium chloride is 3-5 mol / L; The concentration of 1-methyl-1-ethyl-pyrrolidine bromide is 0.1-2 mol / L; The remainder is deionized water.

[0007] This invention also provides a method for preparing the negative electrode electrolyte of the zinc-bromine flow battery, comprising the following steps: Preparing each component according to its concentration. (1) Zinc bromide, ammonium chloride and 1-methyl-1-ethyl-pyrrolidine bromide were dissolved in deionized water to prepare a basic electrolyte; (2) Add stannous chloride and citric acid to deionized water and stir to dissolve. Then add ascorbic acid and stir thoroughly until completely dissolved to obtain a clear and transparent solution. (3) Add the solution obtained in step (2) to the basic electrolyte obtained in step (1) and stir until completely dissolved. Add polyethylene glycol and stir to dissolve it to obtain the negative electrode electrolyte of zinc-bromine flow battery.

[0008] The present invention also provides a zinc-bromine flow battery comprising the above-mentioned zinc-bromine flow battery negative electrode electrolyte.

[0009] The present invention also provides an application of the zinc-bromine flow battery described above, wherein the zinc-bromine flow battery is suitable for one of the following operating conditions: the operating current density is not less than 60 mA / cm². 2 Charging capacity not less than 20mA·h / cm 2 .

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The zinc-bromine flow battery negative electrode electrolyte provided by the present invention adopts the synergistic effect of multiple additive components, and the multiple effects are superimposed, which can maintain the cycle stability of the zinc-bromine flow battery for a long time. At the same time, the electrolyte preparation method is simple and easy to mass-produce.

[0011] (2) This invention uses stannous chloride as a deposition morphology modifier, utilizing its Sn 2+ Under the influence of an electric field, Sn preferentially deposits on the protrusions of the zinc anode surface, thereby reducing the surface energy and growth rate of zinc at the anode tip and inhibiting zinc dendrite growth. By using citric acid as a hydrolysis inhibitor, Sn is effectively complexed. 2+ This inhibits the hydrolysis reaction of stannous chloride in the electrolyte, maintains the clarity and stability of the electrolyte, and achieves Sn... 2+ Long-term effective preservation of active ingredients. This is achieved by introducing ascorbic acid as an antioxidant stabilizer to prevent Sn... 2+ Oxidized to Sn 4+ This maintains the durability of the deposition regulation function and achieves the chemical stability of key additives in the electrolyte system.

[0012] (3) By adding polyethylene glycol as a surfactant, this invention can reduce the surface tension of the electrolyte, enhance the wettability of the electrolyte on the carbon felt electrode surface, and improve the Zn content. 2+ The diffusion rate on the electrode surface promotes uniform Zn deposition.

[0013] (4) By optimizing the concentration ratio of each component (e.g., stannous chloride 1.5–5 mmol / L, citric acid and ascorbic acid twice that amount), the side reactions were avoided while ensuring the effectiveness of the function, thus maximizing the performance of the electrolyte and minimizing the side reactions.

[0014] (5) This invention constructs a multi-component synergistic additive system composed of stannous chloride, citric acid, ascorbic acid, and polyethylene glycol. Through synergistic effects, it significantly improves the electrochemical stability of the battery and extends its cycle life. Experimental results show that the battery achieves good performance at a current density of 80 mA / cm². 2 The charging capacity is 20mAh / cm². 2 Under these conditions, it can stably cycle 400-600 times with a coulombic efficiency maintained above 98%; in contrast, when the battery uses a base electrolyte without additives, significant fluctuations appear after 200 cycles. Furthermore, when the charging capacity is increased to 40mA / cm... 2 Even then, the battery can still cycle stably for 300 times. Attached Figure Description

[0015] Figure 1 The graph shows the cycle performance of zinc-bromine flow batteries in Example 1 and Comparative Example 1. Figure 2 The graph shows the cycle performance of the zinc-bromine flow battery in Comparative Example 6. Figure 3 The contact angle diagrams of the electrolytes prepared in Example 1 and Comparative Example 1 on the carbon felt surface are shown. Figure 4 Tafel curves of the three-electrode systems of the zinc-bromine flow battery negative electrode electrolytes prepared in Example 1 and Comparative Example 1 are shown. Figure 5 Chronocurrent CA diagrams of the three-electrode systems of the zinc-bromine flow battery negative electrode electrolytes prepared in Example 1 and Comparative Example 1; Figure 6 The images are scanning electron microscope (SEM) images of the negative electrode of the zinc-bromine flow battery assembled in Example 1 and Comparative Example 1 after 100 cycles; where a and b are SEM images of Comparative Example 1; and c and d are SEM images of Example 1. Detailed Implementation Example 1

[0016] (1) Add 0.5 mol (112.6 g) zinc bromide, 1 mol ammonium chloride, and 0.125 mol 1-methyl-1-ethylpyrrolidine bromide (MEP) to 245 ml of deionized water, stir to dissolve completely, and prepare the basic electrolyte; (2) Weigh 0.875 mmol stannous chloride and 1.75 mmol citric acid and add them to 5 ml of deionized water and stir to dissolve. Then add 1.75 mmol ascorbic acid and stir thoroughly until completely dissolved to obtain a clear and transparent solution. (3) Add the solution obtained in step (2) dropwise to the basic electrolyte obtained in step (1) and stir vigorously until completely dissolved; add 0.225g of polyethylene glycol and stir to dissolve it to obtain the zinc bromine flow battery negative electrode electrolyte; In the prepared zinc-bromine flow battery negative electrode electrolyte, based on the total volume of deionized water, the concentrations of each component are as follows: The concentration of stannous chloride was 3.5 mmol / L; The citric acid concentration was 7 mmol / L; The ascorbic acid concentration was 7 mmol / L; The zinc bromide concentration is 2 mol / L; The concentration of polyethylene glycol is 0.2% of the mass of zinc bromide; The ammonium chloride concentration is 4 mol / L; The concentration of 1-methyl-1-ethyl-pyrrolidine bromide is 0.5 mol / L; The remainder is deionized water. Example 2

[0017] (1) Add 0.5 mol (112.6 g) zinc bromide, 1 mol ammonium chloride, and 0.125 mol 1-methyl-1-ethylpyrrolidine bromide (MEP) to 245 ml of deionized water, stir to dissolve completely, and prepare the basic electrolyte; (2) Weigh 0.375 mmol stannous chloride and 0.75 mmol citric acid and add them to 5 ml of deionized water and stir to dissolve. Then add 0.75 mmol ascorbic acid and stir thoroughly until completely dissolved to obtain a clear and transparent solution. (3) Add the solution obtained in step (2) dropwise to the basic electrolyte obtained in step (1) and stir vigorously until completely dissolved; add 0.225g of polyethylene glycol and stir to dissolve it to obtain the zinc bromine flow battery negative electrode electrolyte; In the prepared zinc-bromine flow battery negative electrode electrolyte, based on the total volume of deionized water, the concentrations of each component are as follows: The concentration of stannous chloride was 1.5 mmol / L; The citric acid concentration is 3 mmol / L; The ascorbic acid concentration was 3 mmol / L; The zinc bromide concentration is 2 mol / L; The concentration of polyethylene glycol is 0.2% of the mass of zinc bromide; The ammonium chloride concentration is 4 mol / L; The concentration of 1-methyl-1-ethyl-pyrrolidine bromide is 0.5 mol / L; The remainder is deionized water. Example 3

[0018] (1) Add 1 mol (225.2 g) zinc bromide, 1 mol ammonium chloride, and 0.125 mol 1-methyl-1-ethylpyrrolidine bromide (MEP) to 245 ml of deionized water, stir to dissolve completely, and prepare the basic electrolyte; (2) Weigh 1.25 mmol stannous chloride and 2.50 mmol citric acid and add them to 5 ml of deionized water and stir to dissolve. Then add 2.50 mmol ascorbic acid and stir thoroughly until completely dissolved to obtain a clear and transparent solution. (3) Add the solution obtained in step (2) dropwise to the basic electrolyte obtained in step (1) and stir vigorously until completely dissolved; add 0.45g of polyethylene glycol and stir to dissolve it to obtain the negative electrode electrolyte of zinc bromine flow battery; In the prepared zinc-bromine flow battery negative electrode electrolyte, based on the total volume of deionized water, the concentrations of each component are as follows: The concentration of stannous chloride is 5 mmol / L; The citric acid concentration is 10 mmol / L; The ascorbic acid concentration was 10 mmol / L; The zinc bromide concentration is 4 mol / L; The concentration of polyethylene glycol is 0.2% of the mass of zinc bromide; The ammonium chloride concentration is 4 mol / L; The concentration of 1-methyl-1-ethyl-pyrrolidine bromide is 0.5 mol / L; The remainder is deionized water. Comparative Example 1

[0019] The difference from Example 1 is that no additives were added to the negative electrode electrolyte. The specific preparation steps are as follows: Add 0.5 mol (112.6 g) zinc bromide, 1 mol ammonium chloride, and 0.125 mol 1-methyl-1-ethylpyrrolidine bromide (MEP) to 250 ml of deionized water and stir until fully dissolved to obtain the negative electrode electrolyte for the zinc-bromine flow battery. In the prepared zinc-bromine flow battery negative electrode electrolyte, based on the total volume of deionized water, the concentrations of each component are as follows: The zinc bromide concentration is 2 mol / L; The ammonium chloride concentration is 4 mol / L; The concentration of 1-methyl-1-ethyl-pyrrolidine bromide is 0.5 mol / L; The remainder is deionized water. Comparative Example 2

[0020] The difference from Example 1 is that stannous chloride, citric acid, and ascorbic acid were not added to the negative electrode electrolyte. The specific preparation steps are as follows: (1) Add 0.5 mol (112.6 g) zinc bromide, 1 mol ammonium chloride, and 0.125 mol 1-methyl-1-ethylpyrrolidine bromide (MEP) to 250 ml of deionized water, stir to dissolve completely, and prepare the basic electrolyte; (2) Add 0.225g of polyethylene glycol to the basic electrolyte prepared in step (1) and stir to dissolve it to obtain the negative electrode electrolyte of zinc-bromine flow battery; In the prepared zinc-bromine flow battery negative electrode electrolyte, based on the total volume of deionized water, the concentrations of each component are as follows: The zinc bromide concentration is 2 mol / L; The concentration of polyethylene glycol is 0.2% of the mass of zinc bromide; The ammonium chloride concentration is 4 mol / L; The concentration of 1-methyl-1-ethyl-pyrrolidine bromide is 0.5 mol / L; The remainder is deionized water. Comparative Example 3

[0021] The difference from Example 1 is that the concentrations of stannous chloride, citric acid, and ascorbic acid change in step (2). The specific preparation steps are as follows: Add 0.5 mol (112.6 g) zinc bromide, 1 mol ammonium chloride, and 0.125 mol 1-methyl-1-ethylpyrrolidine bromide (MEP) to 245 ml of deionized water and stir until fully dissolved to prepare the basic electrolyte. Weigh 0.25 mmol stannous chloride and 0.50 mmol citric acid, add them to 5 ml of deionized water and stir to dissolve. Then add 0.50 mmol ascorbic acid and stir thoroughly until completely dissolved to obtain a clear and transparent solution. The solution obtained in step (2) is added dropwise to the basic electrolyte obtained in step (1) and stirred vigorously until completely dissolved; 0.225g of polyethylene glycol is added to it and stirred to dissolve it, thus obtaining the negative electrode electrolyte of zinc-bromine flow battery; In the prepared zinc-bromine flow battery negative electrode electrolyte, based on the total volume of deionized water, the concentrations of each component are as follows: The concentration of stannous chloride is 1 mmol / L; The concentration of citric acid is 2 mmol / L; The ascorbic acid concentration was 2 mmol / L; The zinc bromide concentration is 2 mol / L; The concentration of polyethylene glycol is 0.2% of the mass of zinc bromide; The ammonium chloride concentration is 4 mol / L; The concentration of 1-methyl-1-ethyl-pyrrolidine bromide is 0.5 mol / L; The remainder is deionized water. Comparative Example 4

[0022] The difference from Example 1 is that the concentrations of stannous chloride, citric acid, and ascorbic acid change in step (2). The specific preparation steps are as follows: (1) Add 0.5 mol (112.6 g) zinc bromide, 1 mol ammonium chloride, and 0.125 mol 1-methyl-1-ethylpyrrolidine bromide (MEP) to 245 ml of deionized water, stir to dissolve completely, and prepare the basic electrolyte; (2) Weigh 1.75 mmol stannous chloride and 3.50 mmol citric acid and add them to 5 ml of deionized water and stir to dissolve. Then add 3.50 mmol ascorbic acid and stir thoroughly until completely dissolved to obtain a clear and transparent solution. (3) Add the solution obtained in step (2) dropwise to the basic electrolyte obtained in step (1) and stir vigorously until completely dissolved; add 0.225g of polyethylene glycol and stir to dissolve it to obtain the zinc bromine flow battery negative electrode electrolyte; In the prepared zinc-bromine flow battery negative electrode electrolyte, based on the total volume of deionized water, the concentrations of each component are as follows: The concentration of stannous chloride was 7 mmol / L; The citric acid concentration was 14 mmol / L; The ascorbic acid concentration was 14 mmol / L; The zinc bromide concentration is 2 mol / L; The concentration of polyethylene glycol is 0.2% of the mass of zinc bromide; The ammonium chloride concentration is 4 mol / L; The concentration of 1-methyl-1-ethyl-pyrrolidine bromide is 0.5 mol / L; The remainder is deionized water. Comparative Example 5

[0023] The difference from Example 1 is that ascorbic acid was not added in step (2). The specific preparation steps are as follows: (1) Add 0.5 mol (112.6 g) zinc bromide, 1 mol ammonium chloride, and 0.125 mol 1-methyl-1-ethylpyrrolidine bromide (MEP) to 245 ml of deionized water, stir to dissolve completely, and prepare the basic electrolyte; (2) Weigh 0.875 mmol stannous chloride and 1.75 mmol citric acid and add them to 5 ml of deionized water. Stir to dissolve and obtain a clear and transparent solution. (3) Add the solution obtained in step (2) dropwise to the basic electrolyte obtained in step (1) and stir vigorously until completely dissolved; add 0.225g of polyethylene glycol and stir to dissolve it to obtain the zinc bromine flow battery negative electrode electrolyte; In the prepared zinc-bromine flow battery negative electrode electrolyte, based on the total volume of deionized water, the concentrations of each component are as follows: The concentration of stannous chloride was 3.5 mmol / L; The citric acid concentration was 7 mmol / L; The zinc bromide concentration is 2 mol / L; The concentration of polyethylene glycol is 0.2% of the mass of zinc bromide; The ammonium chloride concentration is 4 mol / L; The concentration of 1-methyl-1-ethyl-pyrrolidine bromide is 0.5 mol / L; The remainder is deionized water. Comparative Example 6

[0024] The difference from Example 1 lies in the current density and charging capacity during the charge / discharge test. Specifically, the test current density in Example 1 was 80 mA / cm². 2 The charging capacity is 20mA·h / cm2 The test current density for Comparative Example 6 was 60 mA / cm². 2 The charging capacity is 40mA·h / cm 2 .

[0025] In the prepared zinc-bromine flow battery negative electrode electrolyte, based on the total volume of deionized water, the concentrations of each component are as follows: The concentration of stannous chloride was 3.5 mmol / L; The citric acid concentration was 7 mmol / L; The ascorbic acid concentration was 7 mmol / L; The zinc bromide concentration is 2 mol / L; The concentration of polyethylene glycol is 0.2% of the mass of zinc bromide; The ammonium chloride concentration is 4 mol / L; The concentration of 1-methyl-1-ethyl-pyrrolidine bromide is 0.5 mol / L; The remainder is deionized water. Comparative Example 7

[0026] The differences from Example 1 are: (1) no additives were added to the negative electrode electrolyte; and (2) the current density during the charge-discharge test was 60 mA / cm². 2 The charging capacity is 40mA·h / cm 2 .

[0027] The specific preparation steps for the negative electrode electrolyte are as follows: Add 0.5 mol (112.6 g) zinc bromide, 1 mol ammonium chloride, and 0.125 mol 1-methyl-1-ethylpyrrolidine bromide (MEP) to 250 ml of deionized water and stir until fully dissolved to obtain the negative electrode electrolyte for the zinc-bromine flow battery. In the prepared zinc-bromine flow battery negative electrode electrolyte, based on the total volume of deionized water, the concentrations of each component are as follows: The zinc bromide concentration is 2 mol / L; The ammonium chloride concentration is 4 mol / L; The concentration of 1-methyl-1-ethyl-pyrrolidine bromide is 0.5 mol / L; The remainder is deionized water.

[0028] Zinc-bromine flow battery assembly: The carbon felt was cut to a size of 3×3×0.4cm and assembled with the separator, current collector, and end plate into a zinc-bromine flow battery device. 50mL of negative electrode electrolyte and 50mL of positive electrode electrolyte (2MZnBr2+4MNH4Cl+1M 1-methyl-1-ethyl-bromopyrrolidine) prepared in Examples 1-3 and Comparative Examples 1-7 were injected into the electrolyte tank, and a peristaltic pump was installed to assemble the zinc-bromine flow battery.

[0029] Battery performance test: The zinc-bromine flow batteries assembled using the negative electrode electrolytes prepared in Examples 1-3 and Comparative Examples 1-7 were subjected to charge-discharge tests, respectively. The test current density for Examples 1-3 and Comparative Examples 1-5 was 80 mA / cm². 2 The charging capacity is 20mA·h / cm 2 The test current density for Comparative Examples 6-7 was 60 mA / cm². 2 The charging capacity is 40mA·h / cm 2 The discharge cutoff voltage is 0.6V. Coulombic efficiency (CE), energy efficiency (EE), and cycle life data are shown in Table 1; the cycle performance graphs of the zinc-bromine flow batteries of Example 1 and Comparative Example 1 are shown below. Figure 1 As shown; the cycle performance diagram of Comparative Example 6 is as follows. Figure 2 As shown.

[0030] Table 1. Battery performance comparison table for Examples 1-3 and Comparative Examples 1-7 Analyze Example 1 and Comparative Example 1, and combine the data in Table 1 and Figure 1 The results show that the zinc-bromine flow battery negative electrode electrolyte provided by this invention contains a variety of additive components, which synergistically combine the zinc affinity of metallic Sn and the surfactant effect of polyethylene glycol, significantly reducing the nucleation energy barrier of Zn and enhancing the Zn nucleation efficiency. 2+ The diffusion rate on the electrode surface is reduced, and uniform deposition is induced, thereby effectively suppressing the growth of zinc dendrites on the electrode surface. Specifically, the zinc-bromine flow battery of Comparative Example 1, without any additives, showed significant fluctuations after 200 cycles; in contrast, the zinc-bromine flow battery of Example 1 exhibited excellent electrochemical stability, capable of stable cycling for 600 cycles.

[0031] Analyzing Example 1 and Comparative Examples 1-4, and combining the data results in Table 1, when the concentration of stannous chloride in Comparative Examples 2-3 is below 1.5 mmol / L, the cycle life of the zinc-bromine flow battery is slightly improved due to the surface wetting effect of polyethylene glycol, and the battery can stably cycle for 300 cycles. When the concentration of stannous chloride in Comparative Example 4 is above 5 mmol / L, the battery can stably cycle for 260 cycles, but the electrolyte becomes turbid due to the hydrolysis of stannous chloride to produce Sn(OH)2, which reduces the stability of the battery.

[0032] Analysis of Example 1 and Comparative Example 5 shows that the main function of ascorbic acid is to prevent Sn. 2+ Further oxidized to Sn 4+ This leads to Sn in the electrolyte 2+The concentration of Sn decreased. Combined with the data in Table 1, it can be seen that, compared to Example 1, Comparative Example 5, which did not add ascorbic acid, showed a decrease in Sn concentration in the electrolyte during charge and discharge. 2+ As the concentration of [agent] gradually decreases, its stabilizing effect on the battery gradually weakens, and the battery's cycle life is 300 cycles.

[0033] Analyze Example 1 and Comparative Examples 6-7, and combine the data in Table 1 and Figure 2 The results show that, compared with Example 1, the charging capacity of Comparative Example 6 is increased to 40mAh / cm³. 2 At that time, the coulombic efficiency of the zinc-bromine flow battery still exceeded 98%, indicating that the negative electrode has excellent reversibility; compared with Comparative Example 7, Comparative Example 6 showed better electrochemical stability and was able to cycle stably for 300 cycles.

[0034] Electrochemical performance testing: 1. Contact angle tests were performed on the electrolytes of Example 1 and Comparative Example 1. Test method: Add electrolyte to the surface of carbon felt and test the change in the contact angle of electrolyte on the carbon felt surface; Test results: such as Figure 3 As shown, compared to Comparative Example 1, the contact angle of the electrolyte in Example 1 on the carbon felt surface is significantly reduced, indicating that the polyethylene glycol additive can significantly enhance the wettability of the electrolyte to the electrode material, which is beneficial for Zn. 2+ Diffusion and uniform deposition on the electrode surface.

[0035] 2. Tafel curve tests were performed on Example 1 and Comparative Example 1. Electrode system: carbon felt working electrode, platinum sheet counter electrode, zinc sheet reference electrode; Test conditions: Voltage range -0.3-0.3V, scan rate 1mV / s; Test results: such as Figure 4 As shown, compared to Comparative Example 1, the corrosion current in the Tafel curve of Example 1 containing additives decreased from 19.20 mA to 18.57 mA, and the corrosion voltage shifted positively from -20 mV to -10 mV, indicating that the electrolyte containing additives can inhibit the growth of zinc anode dendrites and reduce the corrosion rate of zinc anode.

[0036] 3. Perform timing current (CA) tests on Example 1 and Comparative Example 1. Electrode system: carbon felt working electrode, platinum sheet counter electrode, zinc sheet reference electrode; Test conditions: Constant voltage discharge for 1000s at -150mV; Test results: such as Figure 5As shown, the current in Comparative Example 1 increases with time, indicating unrestricted two-dimensional diffusion, leading to zinc cluster formation and dendrite growth; in contrast, the current in Example 1 is smaller and does not change with time, indicating that in the electrolyte containing additives, Zn 2+ The deposition process is dominated by three-dimensional diffusion, thus realizing Zn 2+ Uniform deposition.

[0037] 4. Characterization of zinc deposition morphology (SEM) After 100 charge-discharge cycles in Example 1 and Comparative Example 1, the carbon felt negative electrode was removed for scanning electron microscopy (SEM) characterization.

[0038] Test results: such as Figure 6 As shown in a and 6b, the surface of the carbon felt negative electrode in Comparative Example 1 is covered with a large number of zinc dendrites, which exhibit a distinct hexagonal lamellar structure; in contrast, as Figure 6 As shown in c and 6d, the zinc deposited on the carbon felt negative electrode surface of Example 1 is uniformly distributed, indicating that the zinc-bromine flow battery negative electrode electrolyte effectively inhibits the growth of zinc dendrites and promotes uniform zinc deposition.

[0039] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Those skilled in the art, without departing from the scope of the technical solutions of this application, may make some changes or modifications to the above-disclosed technical content, which are equivalent to equivalent implementations and all fall within the scope of the technical solutions.

Claims

1. A negative electrode electrolyte for a zinc-bromine flow battery, characterized in that, The electrolyte comprises the following components: zinc bromide, ammonium chloride, 1-methyl-1-ethyl-pyrrolidine bromide, stannous chloride, citric acid, ascorbic acid, polyethylene glycol, and deionized water; In the zinc-bromine flow battery negative electrode electrolyte, based on the total volume of deionized water, the concentrations of each component are as follows: The concentration of stannous chloride is 1.5-5 mmol / L; The concentration of citric acid is twice that of stannous chloride; The concentration of ascorbic acid is twice that of stannous chloride; The concentration of zinc bromide is 2-4 mol / L; The concentration of polyethylene glycol is 0.2% of the mass of zinc bromide; The concentration of ammonium chloride is 3-5 mol / L; The concentration of 1-methyl-1-ethyl-bromopyrrolidine is 0.1-2 mol / L; The remainder is deionized water.

2. A method for preparing the negative electrode electrolyte of a zinc-bromine flow battery as described in claim 1, characterized in that, Prepare each component according to its concentration, including the following steps: (1) Zinc bromide, ammonium chloride and 1-methyl-1-ethyl-pyrrolidine bromide were dissolved in deionized water to prepare a basic electrolyte; (2) Add stannous chloride and citric acid to deionized water and stir to dissolve. Then add ascorbic acid and stir thoroughly until completely dissolved to obtain a clear and transparent solution. (3) Add the solution obtained in step (2) to the basic electrolyte obtained in step (1) and stir until completely dissolved. Add polyethylene glycol and stir to dissolve it to obtain the negative electrode electrolyte of zinc-bromine flow battery.

3. A zinc-bromine flow battery, characterized in that, It contains the zinc-bromine flow battery negative electrode electrolyte as described in claim 1.

4. An application of the zinc-bromine flow battery as described in claim 3, characterized in that, The zinc-bromine flow battery is suitable for one of the following operating conditions: operating current density not less than 60 mA / cm². 2 Charging capacity not less than 20mA·h / cm 2 .

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