Electrolyte containing composite complexing agent and preparation method thereof

Abstract

The invention discloses an electrolyte containing a composite complexing agent and a preparation method thereof, and the method comprises the following steps: at room temperature, dissolving zinc bromide with a set concentration in a solvent to form a zinc bromide solution, continuously adding choline chloride with a set concentration, and stirring until the choline chloride is completely dissolved in the zinc bromide solution, a zinc bromide solution containing choline chloride is obtained; monitoring the pH value of the zinc bromide solution containing choline chloride, and adding macromolecular acid into the zinc bromide solution containing choline chloride until the pH value of the zinc bromide solution containing choline chloride is stabilized at a preset value; and adding betaine with a set concentration into the zinc bromide solution containing choline chloride with the pH value stabilized at a preset value, and continuously stirring to obtain the electrolyte containing the composite complexing agent. The problem that an existing complexing agent MEP is prone to being attached to the pipe wall and a flow channel, and consequently blockage is caused can be solved.

Description

Technical Field

[0001] The present application belongs to the field of energy storage technology, and specifically relates to an electrolyte containing a composite complexing agent and a preparation method thereof. Background Art

[0002] Zinc-bromine flow battery is an energy storage device. The chemical reaction at the positive electrode is bromide ion (Br - ) is oxidized to bromine (Br2). However, bromine is insoluble in water and is volatile, easily escaping into the air. This not only leads to the loss of reactants, but may also affect the normal operation of the battery due to the lack of sufficient bromine.

[0003] In order to solve the problem of bromine volatilization, a bromine complexing agent is usually added to the battery to ensure that the bromine can stably exist in the reaction system without volatilizing. The commonly used bromine complexing agent is MEP (1-methyl-1-ethylpyrrolidone bromide), which has the characteristics of strong complexing ability and high energy efficiency, but it is expensive and difficult to purchase. In addition, the complex formed by MEP and bromine is oily and easily adheres to the pipe wall and flow channel, causing blockage, so that the pipe wall and flow channel need to be cleaned and maintained frequently. Summary of the invention

[0004] The main purpose of the present application is to provide an electrolyte containing a composite complexing agent and a preparation method thereof. The present application can overcome the problem that the existing complexing agent MEP is easy to adhere to the tube wall and the flow channel, thereby causing blockage.

[0005] A method for preparing an electrolyte containing a composite complexing agent comprises: dissolving zinc bromide of a set concentration in a solvent to form a zinc bromide solution at room temperature, continuously adding choline chloride of a set concentration and stirring until the choline chloride is completely dissolved in the zinc bromide solution to obtain the zinc bromide solution containing choline chloride; monitoring the pH value of the zinc bromide solution containing choline chloride, and adding a macromolecular acid to the zinc bromide solution containing choline chloride until the pH value of the zinc bromide solution containing choline chloride is stabilized at a preset value; adding a quaternary ammonium alkaloid of a set concentration to the zinc bromide solution containing choline chloride whose pH value is stabilized at the preset value, and continuing stirring to obtain the electrolyte containing the composite complexing agent.

[0006] Optionally, the concentrations of zinc bromide, choline chloride and quaternary ammonium alkaloid are set to 2 mol / l, 0.5 mol / l and 0.5 mol / l respectively.

[0007] Optionally, the choline chloride needs to be slowly added to the zinc bromide solution.

[0008] Optionally, the macromolecular acid includes any one of the following: methanesulfonic acid, aminosulfonic acid and citric acid.

[0009] Optionally, the pH value of the zinc bromide solution containing choline chloride is stabilized at 2 to 3.

[0010] Optionally, the quaternary ammonium alkaloid needs to be gradually added to the zinc bromide solution containing choline chloride.

[0011] Optionally, the preparation method further comprises: adding a chloride salt to the composite complexing agent.

[0012] Optionally, the concentration of the chloride salt is greater than or equal to 1.5 mol / l.

[0013] Optionally, the preparation method further comprises: passivating the composite complexing agent.

[0014] The present application also provides an electrolyte containing a composite complexing agent, wherein the electrolyte containing a composite complexing agent comprises a composite complexing agent and a solvent, wherein the composite complexing agent comprises zinc bromide, choline chloride and a quaternary ammonium alkaloid at set concentrations.

[0015] The present application has the following beneficial effects: The present application provides an electrolyte containing a composite chelating agent and a preparation method thereof. The present application can overcome the problems of bromine volatilization, adhesion and low-temperature coagulation existing in traditional single chelating agents by precisely controlling the component ratio and pH value. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic flow chart of a method for preparing an electrolyte containing a composite complexing agent provided in one embodiment of the present application;

[0017] Figure 2 is a schematic diagram of the molecular structure of MEP provided in another embodiment of the present application;

[0018] Figure 3 is a schematic diagram of the molecular structure of a composite complexing agent provided in another embodiment of the present application;

[0019] Figure 4 is a schematic diagram of the MEP provided by another embodiment of the present application after being left to stand in a storage bottle;

[0020] Figure 5 This is a schematic diagram of the composite complexing agent provided by another embodiment of the present application after being left to stand in a storage bottle. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0022] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0023] In this application, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0024] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present application, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in the field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0025] Figure 1 FIG. 1 is a schematic flow diagram of a method for preparing an electrolyte containing a composite complexing agent according to an embodiment of the present application, such as Figure 1 As shown, the preparation method comprises the following steps:

[0026] S1: At room temperature, zinc bromide (2 mol / l) is added to a reaction vessel, and fully dissolved in a solvent (usually water) by stirring to form a uniform zinc bromide solution. Then, choline chloride (0.5 mol / l) is slowly added to the reaction vessel by a dropping device or a peristaltic pump, and stirring is continued until the choline chloride is completely dissolved in the zinc bromide solution to obtain a zinc bromide solution containing choline chloride;

[0027] In this step, the choline chloride is slowly added to the zinc bromide solution at a rate of 10ml / min to 20ml / min (preferably 15ml / min), that is, if 100ml of choline chloride solution is to be added, the entire addition process lasts for about 5 to 10min. It should be noted that if the speed of adding choline chloride is too fast, after inspection, it will cause the local concentration to be too high instantly, thereby causing supersaturation, and then forming precipitation or uneven distribution, which will affect the product quality of the composite complexing agent. And the mode of slow addition is adopted, which helps to ensure that the choline chloride and the zinc bromide solution have enough time to fully mix, avoid forming too high concentration in the local area, and help to obtain a more uniform composite complexing agent. Further, the application sets the addition rate of choline chloride to 10ml / min to 20ml / min, which is a conclusion drawn after a large number of experimental tests. Within this rate range, the amount of choline chloride added each time is relatively small, which can ensure that it is quickly mixed and dissolved with the zinc bromide solution, helps to form a uniform solution, and avoids too high local concentration. In addition, the addition of choline chloride will change the pH value of the zinc bromide solution. Adding at this rate can more accurately monitor and adjust the pH value of the solution to stabilize it within the desired range (between 2 and 3). Too fast an addition rate (e.g., greater than 20 ml / min) will make it difficult to control the pH value and maintain it within the desired range; while too slow an addition rate (e.g., less than 10 ml / min) will make the pH value of the zinc bromide solution too slowly to adjust, delaying the time to reach the target pH value, thereby affecting the operation of subsequent steps.

[0028] S2: using a pH meter to monitor the pH value of the zinc bromide solution containing choline chloride, and gradually adding methanesulfonic acid to the zinc bromide solution containing choline chloride until the pH value of the solution is stabilized between 2 and 3;

[0029] In this step, the pH value of the solution needs to be stabilized between 2 and 3 because: 1. Betaine and choline chloride, as complexing agents, can more effectively combine with bromine element within this pH range to form a stable complex. When the pH value is between 2 and 3, betaine and choline chloride can maintain the optimal structure and function, ensuring that the bromine element will not easily volatilize or precipitate. According to tests, if the pH value is too high (for example, more than 3), precipitation will occur, and even unnecessary side reactions will be triggered. A too low pH value (lower than 2) will cause the complexing agent to be over-protonated, affecting its complexing ability. 2. The electrode materials in zinc-bromine batteries (such as graphite plates, carbon felt, etc.) are susceptible to corrosion under extremely acidic or alkaline conditions. A weakly acidic environment with a pH value between 2 and 3 can effectively reduce the corrosion risk of electrode materials and extend the service life of the battery.

[0030] In addition, the methane sulfonic acid needs to be added step by step, that is, it can be added at a lower speed (e.g., 0.5 mL / min) at the beginning to ensure that the amount added each time can be quickly and evenly dispersed in the solution. After each addition of methane sulfonic acid, the pH value is measured and recorded immediately, for example, the pH value can be detected every 1 to 2 minutes. During the detection process, if the pH value drops rapidly (e.g., more than 0.2 units / minute), the addition speed is slowed down to 0.25 mL / min or even lower; if the pH value is close to but does not reach the target range (2 to 3), the current addition speed can be maintained unchanged; when the pH value is close to the target lower limit (e.g., about 2.2), the addition speed can be further reduced to 0.1 mL / min or less to finely adjust the pH value. When the pH value is very close to the target interval (e.g., 2.0 to 2.1), switch to the manual drop mode, add only a few drops of methane sulfonic acid each time, then stir well and wait for at least 1 minute before measuring the pH value again. Once the pH value is detected to be stable between 2 and 3, stop adding methane sulfonic acid immediately and continue stirring for at least 5 minutes to ensure that the entire solution is evenly mixed. It should be noted that if a large amount of methane sulfonic acid is added at one time, it will cause excessive local concentration and form an over-acid area, which will not only affect the structure and function of the complexing agent, but may also corrode the electrode material to a certain extent.

[0031] In summary, the gradual addition of methane sulfonic acid can, firstly, more accurately control the change in the pH value of the solution, and secondly, reduce the probability of unnecessary side reactions (such as structural changes or decomposition of the complexing agent) caused by sudden changes in the chemical environment.

[0032] S3: Adding a quaternary ammonium alkaloid (such as betaine) (0.5 mol / l) to a zinc bromide solution containing choline chloride with a stable pH value between 2 and 3, and continuing stirring to obtain an electrolyte containing a composite complexing agent.

[0033] In this step, betaine is a zwitterionic compound with a positively charged quaternary ammonium head and a negatively charged carboxylate tail. This structure gives betaine good water solubility and the ability to interact with polar molecules or ions. Within the above pH range (2 to 3), betaine can more effectively combine with bromine to form a stable complex, which helps to inhibit the volatilization of bromine and ensure its solubility and stability in the electrolyte. In addition, the complex formed by betaine will not become an oily substance like MEP (1-methyl-1-ethylpyrrolidine bromide), but will maintain high water solubility and uniform dispersion, which can reduce the risk of the complexing agent adhering to the tube wall or flow channel of the battery system.

[0034] In addition, when betaine is used together with choline chloride, a synergistic effect can be produced between the two to further enhance the complexation effect. The cations provided by choline chloride help stabilize the charge distribution in the solution, while betaine provides additional complexation sites. The synergistic effect of the two can ensure that bromine does not easily volatilize or precipitate.

[0035] In another exemplary embodiment, the present application also provides a method for preparing an electrolyte containing a composite complexing agent, the preparation method comprising the following steps:

[0036] S10: adding zinc bromide (2 mol / l) to a reaction container at room temperature, and fully dissolving it in a solvent (for example, a green solvent such as a bio-based solvent instead of water) by stirring to form a uniform zinc bromide solution, then slowly adding choline chloride (0.5 mol / l) to the reaction container, and continuing to stir until the choline chloride is completely dissolved in the zinc bromide solution to obtain a zinc bromide solution containing choline chloride;

[0037] In this step, the green solvent has low toxicity and biodegradability. The green solvent is more easily decomposed into harmless products by microorganisms in the natural environment, thereby reducing the risk of environmental pollution. Therefore, by using green solvents instead of water solvents, the impact on the environment can be reduced, thereby improving the environmental friendliness of the electrolyte.

[0038] S20: using a pH meter to monitor the pH value of the zinc bromide solution containing choline chloride, and gradually adding aminosulfonic acid to the zinc bromide solution containing choline chloride until the pH value of the solution is stabilized between 2 and 3;

[0039] S30: First add 1-ethyl-3-methylimidazolium bromide (0.05 mol / l) to a zinc bromide solution containing choline chloride with a stable pH value between 2 and 3, continue stirring to fully dissolve it and evenly distribute it, and then continue to add betaine (0.45 mol / l), keep stirring until all ingredients are completely dissolved and mixed evenly, so as to obtain an electrolyte containing a composite complexing agent.

[0040] In this step, the present application adds 1-ethyl-3-methylimidazolium bromide on the basis of the previous embodiment, and the 1-ethyl-3-methylimidazolium bromide is an ionic liquid with stronger complexing ability and higher stability, which can form a more stable complex with bromine, thereby further improving the solubility of bromine in the electrolyte and reducing the risk of volatilization and precipitation. In addition, due to its ionic properties, 1-ethyl-3-methylimidazolium bromide can increase the ion concentration in the electrolyte, which helps to improve the conductivity of the electrolyte, and high conductivity means that the ion migration speed is faster, which is conducive to improving the charge and discharge efficiency of the battery. Further, compared with 1-methyl-1-ethyl pyrrolidine bromide, the complex formed by the composite complexing agent composed of betaine and 1-ethyl-3-methylimidazolium bromide will not become an oily substance, but maintains a high degree of water solubility and uniform dispersion, which can reduce the risk of complexing agent adhering to the battery system wall or flow channel, thereby reducing the maintenance frequency.

[0041] In another exemplary embodiment, the present application also provides a method for preparing an electrolyte containing a composite complexing agent, the preparation method comprising the following steps:

[0042] Different from the previous embodiment, this embodiment uses citric acid instead of aminosulfonic acid. In addition, this embodiment uses a microreactor instead of a reaction vessel. For example, at room temperature, zinc bromide (2 mol / l) is injected into the microreactor (a microreactor is a device that uses microchannels to perform chemical reactions, and its characteristic size is usually between micrometers and millimeters. These tiny sizes give the microreactor some unique advantages, such as efficient mass transfer and heat transfer performance, rapid mixing ability, and a high degree of control over reaction conditions) by a micropump. The efficient mass transfer and heat transfer performance in the microreactor is utilized to ensure that zinc bromide is quickly and evenly dissolved in the solvent in a short time to form a uniform zinc bromide solution.

[0043] This embodiment adopts microreactor technology, which can not only achieve more precise control and higher reaction efficiency in each step, but also effectively improve the uniformity of the product and reduce the phenomenon of excessively high or low local concentrations.

[0044] In another exemplary embodiment, the present application also provides a method for preparing an electrolyte containing a composite complexing agent. Different from the aforementioned embodiments, after ensuring that the other components have been fully mixed and reached the desired pH value, the present application further adds a chloride salt (such as potassium chloride or sodium chloride) with a concentration of 1.5 mol / l or more to the electrolyte containing the composite complexing agent as a supporting electrolyte to prevent the electrolyte containing the composite complexing agent from solidifying at minus 20°C, and the battery can operate normally (the chloride salt will dissociate into ions after dissolving in water, and the presence of these ions will significantly reduce the electrolyte Freezing point. According to Raoult's law, the addition of solutes will cause the vapor pressure of the electrolyte to decrease, which in turn requires a lower temperature for the electrolyte to solidify. Therefore, adding an appropriate amount of chloride salt can effectively reduce the freezing point of the electrolyte to well below 0°C, and can even remain liquid at minus 20°C or lower; in addition, the large number of ions produced by the dissociation of chloride salts can increase the carrier concentration in the electrolyte, thereby increasing the conductivity of the electrolyte, which helps to maintain the current transmission efficiency inside the battery, and even under low temperature conditions, it can ensure sufficient ion migration speed and reaction rate, thereby ensuring the normal operation of the battery).

[0045] In this embodiment, the chloride salt will dissociate into ions after being dissolved in water, and the presence of these ions significantly reduces the freezing point of the electrolyte. According to Raoult's law, if the concentration of the chloride salt is lower than 1.5 mol / l, the electrolyte may solidify or become too viscous in a low temperature environment (such as minus 20°C), thereby affecting the normal operation of the battery. Once the electrolyte solidifies, the ion migration is blocked, and the battery will not be able to effectively perform charge and discharge cycles. In addition, the ions generated by the dissociation of the chloride salt are carriers in the electrolyte. When the concentration is lower than 1.5 mol / l, the number of carriers is not enough to significantly increase the conductivity of the electrolyte. This may lead to low current transmission efficiency, especially under low temperature conditions, the ion migration speed and reaction rate may not be sufficient to maintain the normal operation of the battery, thereby affecting energy efficiency and power output.

[0046] In summary, the present application has found through a series of experimental tests that the chloride salt concentration below 1.5 mol / l cannot achieve the expected performance improvement. Only when the chloride salt concentration is greater than or equal to 1.5 mol / l can the electrolyte be ensured to remain liquid at low temperatures, provide sufficient conductivity and stability, and avoid unnecessary side reactions or adverse phenomena.

[0047] In another exemplary embodiment, as an improvement on the above-mentioned embodiment, the present application also provides a method for preparing an electrolyte containing a composite complexing agent, that is, after preparing the composite complexing agent or the composite complexing agent containing chloride, it is passivated by a filtration device or a centrifuge (including preliminary filtration, centrifugal separation and other steps) to remove insoluble impurities that may exist therein, thereby ensuring the high uniformity and purity of the electrolyte to prevent impurities from contaminating the electrodes and affecting the operating stability of the battery.

[0048] In the above embodiments, the molar amounts of zinc bromide, choline chloride and betaine are set to 2mol / l, 0.5mol / l, 0.5mol / l, respectively, and this specific value is the optimal value determined after multiple experiments. Zinc bromide, choline chloride and betaine with this specific molar concentration can provide the best complexing effect. Choline chloride and betaine, as complexing agents, can more effectively combine with bromine element at this concentration to form a stable complex, ensuring that bromine element will not easily volatilize or precipitate. In addition, through experiments, if the concentration is too high, it will cause the complexing agent to be over-protonated and affect its complexing ability, while if the concentration is too low, it is not enough to form enough complexes to suppress the volatilization of bromine.

[0049] In the above embodiments, methanesulfonic acid, aminosulfonic acid, and citric acid are all macromolecular acids. In the preparation process described in the present application, the reason why macromolecular acids are needed is that: first, the chemical properties of macromolecular acids in zinc-bromine battery electrolytes are relatively stable, and they will not have unnecessary side reactions with other components in the system (such as zinc bromide, complexing agents, etc.). Macromolecular acids can effectively adjust the pH value without affecting the performance of complexing agents or causing undesirable chemical changes; second, macromolecular acids are partially dissociated and show relatively weak acidity in water, which is suitable for precise control of pH value. This property helps to maintain the stability of the solution and the effectiveness of the complexing agent, and can ensure that the battery maintains the best working state during operation; third, macromolecular acids have good compatibility with most experimental equipment and container materials, and are not easy to cause corrosion or other damage. On the contrary, small molecule acids (such as hydrochloric acid and hydrobromic acid) and strong oxidizing acids are not suitable for this preparation process because: First, strong oxidizing acids have strong oxidizing properties, which will directly cause bromide ions to be oxidized to elemental bromine, change the performance of the composite complexing agent, and thus cause battery efficiency to decrease or malfunction; Second, small molecule acids (such as hydrochloric acid and hydrobromic acid), due to their small size and high activity, are prone to unnecessary side reactions with other components in the system. These side reactions may generate unwanted products, thereby affecting the purity of the electrolyte and possibly reducing the performance of the battery.

[0050] In addition, it should be noted that in the above embodiments, after testing, methanesulfonic acid can be used as the best choice for preparing zinc-bromine battery composite complexing agent. Among them, methanesulfonic acid exhibits extremely high chemical stability in aqueous solution and will not easily decompose or react with other components. In contrast, although aminosulfonic acid is also a stable acid, it may undergo pyrolysis or react with specific substances under certain conditions; while citric acid is prone to redox reactions, especially at high temperatures or in an aerobic environment. In addition, as a macromolecular acid, methanesulfonic acid partially dissociates, which can provide gentle and precise pH adjustment, help maintain the stability of the electrolyte and the effectiveness of the complexing agent, and its pH adjustment range is moderate, which can avoid problems caused by extreme pH values. In contrast, citric acid, as a tricarboxylic acid, has a more complex pH adjustment effect and may be difficult to control; while aminosulfonic acid can also effectively adjust the pH, but its behavior may change at different temperatures. Further, methanesulfonic acid can optimize the complexing efficiency of the complexing agent, improve the solubility of bromine in the electrolyte, and reduce the volatilization loss of bromine. In comparison, although citric acid and aminosulfonic acid can also play a certain role, they are not as significant as methanesulfonic acid in improving the complexing effect.

[0051] In the above embodiment, betaine and choline chloride are used as complexing agents, which can more effectively combine with bromine element in a specific pH range (between 2 and 3) to form a stable water-soluble complex, that is, the complex can be completely dissolved in water and can be evenly dispersed in the electrolyte, rather than forming an oily substance and precipitating, so it is not easy to adhere to the tube wall or flow channel of the battery system (betaine is a zwitterionic compound with a positively charged quaternary ammonium head and a negatively charged carboxylate tail. This unique structure enables it to maintain good solubility in water and can serve as an effective hydrogen bond donor and acceptor to promote interaction with other polar molecules or ions. Choline chloride Chloride) is also a quaternary ammonium salt with positively charged nitrogen atoms. It also has good water solubility and can provide additional cations to stabilize the charge distribution in the solution. In addition, under pH conditions of 2 to 3, bromine (Br) exists in molecular form, but when it comes into contact with water, it partially dissociates into bromide ions (Br-). The positively charged groups in betaine and choline chloride can combine with these bromide ions through electrostatic attraction to form complexes. Although bromine itself is hydrophobic, under appropriate pH conditions, through the polar environment provided by the complexing agent, bromine can be encapsulated in a "cage" composed of complexing agent molecules, thereby enhancing its solubility in water. Due to the above mechanism, the resulting complex is not only different from the oily substance formed by MEP and bromine in physical form, but also more stable in chemical properties. The components in the complex are tightly bound together by a variety of non-covalent interactions, including but not limited to hydrogen bonds, van der Waals forces and π-π stacking, ensuring that the complex is not easy to decompose or precipitate, and therefore not easy to adhere to the tube wall or flow channel of the battery system).

[0052] On the basis of the above-mentioned embodiments, the present application adds nanomaterials (such as nano silicon dioxide or nano carbon tubes) and ionic liquids (such as 1-ethyl-3-methylimidazolium tetrafluoroborate) to the prepared electrolyte containing a composite complexing agent, wherein the nanomaterials can increase the specific surface area of ​​the electrolyte, enhance the dispersibility of the complexing agent, and reduce the adhesion of the complexing agent in the tube wall and the flow channel, thereby improving the stability and conductivity of the electrolyte. The ionic liquid, due to its extremely low freezing point and good electrochemical stability, can further improve the conductivity of the electrolyte while improving the low-temperature performance of the electrolyte. Below, the present application compares the composite complexing agent prepared by the present method with a single complexing agent (i.e., one of MEP, betaine, and choline chloride) through various performance tests (specifically including short-term energy efficiency test, long-term cycle stability test, and low-temperature performance test). The standard single cell configuration used in the test is: positive terminal plate, 9×9 cm graphite plate as positive electrode, positive electrode frame, carbon felt, Daramic membrane as diaphragm, carbon felt, negative electrode frame, 9×9 cm graphite plate as negative electrode, and negative terminal plate. All tests were performed at 25°C.

[0053] Comparative Example 1:

[0054] Zinc bromide (ZnBr) concentration: 2 mol / l

[0055] Potassium chloride (KCl) concentration: 1.5 mol / l

[0056] MEP (methyl ethyl pyrrolidone) concentration: 1 mol / l

[0057] Comparative Example 2:

[0058] Zinc bromide (ZnBr) concentration: 2 mol / l

[0059] Potassium chloride (KCl) concentration: 1.5 mol / l

[0060] Betaine concentration: 1 mol / l

[0061] Comparative Example 3:

[0062] Zinc bromide (ZnBr) concentration: 2 mol / l

[0063] Potassium chloride (KCl) concentration: 1.5 mol / l

[0064] Choline chloride concentration: 1 mol / l

[0065] After the above tests are completed, the following test results can be obtained:

[0066] 1. Short-term energy efficiency test:

[0067] After battery performance testing, it was found that the energy efficiency of the composite complexing agent prepared by the present application can reach or even exceed the comparative example of using a single complexing agent. In particular, in long-term cycle tests, the composite complexing agent exhibited excellent stability:

[0068] At a current density of 40 mA, the composite complexing agent can stably operate for more than 150 cycles; MEP (4-methoxyphenol) can stably operate for 70 to 100 cycles; betaine can stably operate for 80 to 120 cycles; and choline chloride can stably operate for 60 to 90 cycles.

[0069] At a current density of 20 mA, the composite complexing agent can stably operate for more than 250 cycles without significant energy attenuation; MEP (4-methoxyphenol) can stably operate for 120 to 180 cycles; betaine can stably operate for 150 to 200 cycles; and choline chloride can stably operate for 100 to 150 cycles.

[0070] In contrast, a single complexing agent cannot maintain the same performance level under the same conditions.

[0071] 2. Long-term cycle stability test:

[0072] When using a single complexing agent, at 40mA / cm 2 At a current density of 2.5 ...

[0073] 3. Low temperature performance test:

[0074] In a low temperature environment of -20°C and a current density of 20 mA, all comparative samples solidified, while the composite complexing agent prepared by the present application can still maintain good performance even under low temperature conditions. The performance test can be shown in Table 1, as follows:

[0075] Table 1

[0076]

[0077] As can be seen from Table 1, at a temperature of -20°C and a current density of 20 mA, the composite complexing agent can still operate stably for more than 50 cycles, and its energy efficiency can reach 69%, showing its excellent low-temperature adaptability and performance stability.

[0078] Figure 2 It is a schematic diagram of the molecular structure of MEP; Figure 3 It is a schematic diagram of the molecular structure of the composite complexing agent; by comparison, it can be found that Figure 2 Among them, the molecular weight of MEP is relatively small, which means that it has fewer functional groups and lower polarity, making it easier to form hydrophobic substances. In addition, due to the lack of a complex hydrogen bond network or other strong interactions, the binding force between MEP molecules is weak, making its complex easier to flow and more difficult to remove, and it is easy to remain on the contact surface. Figure 3 In the composite complexing agent, multiple components are connected by hydrogen bonds, forming a large and complex molecular structure. This macromolecule is not easy to form a tight adsorption layer on the surface, thereby reducing the possibility of adhesion. In addition, the hydrogen bond network not only enhances the internal stability of the composite complexing agent, but also may give its surface a certain lubrication effect, thereby reducing the friction and adhesion between it and the solid surface. In addition, hydrogen bonds can also make the composite complexing agent more soluble in water, thereby further reducing the adhesion phenomenon.

[0079] Figure 4 This is a schematic diagram of the MEP after it has been left to rest in the storage bottle; Figure 5 It is a schematic diagram of the composite complexing agent after being left to stand in the storage bottle. Figure 4 In the process, after standing, the complex formed by MEP and bromine will precipitate at the bottom of the solution and form an oil layer. This is because the complex has low polarity and high hydrophobicity, which makes it insoluble in the aqueous phase, but aggregates together to form an independent oily layer. Among them, the oil layer easily adheres to the pipe wall and other flow channel surfaces, which not only reduces the amount of effective reactants, but also may cause pipeline blockage or increase the workload of cleaning and maintenance. In addition, due to the presence of the oil layer, the transmission of reactants will be hindered, which will affect the concentration of reactants near the electrode, and then affect the performance and efficiency of the battery. Figure 5 In the experiment, after standing, the complex formed by choline chloride and bromine can be evenly distributed in the solution. This even distribution is due to the high polarity and good water solubility of the complex, which keeps it in a stable dispersed state throughout the solution. Since the complex is evenly distributed in the solution, it is not easy to adhere to the pipe wall or other contact surfaces, which helps to keep the pipeline unobstructed, reduce maintenance requirements, and ensure that the reactants can reach the designated location efficiently. In addition, the evenly distributed complex can ensure that the reactants have a constant concentration around the electrode, thereby optimizing the chemical environment inside the battery and improving reaction efficiency and battery performance.

[0080] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing an electrolyte containing a composite complexing agent, characterized in that: The preparation method comprises: At room temperature, dissolving zinc bromide of a set concentration in a solvent to form a zinc bromide solution, and continuously adding choline chloride of a set concentration and stirring until the choline chloride is completely dissolved in the zinc bromide solution to obtain a zinc bromide solution containing choline chloride; Monitoring the pH value of the zinc bromide solution containing choline chloride, and adding a macromolecular acid to the zinc bromide solution containing choline chloride until the pH value of the zinc bromide solution containing choline chloride is stabilized at a preset value; A quaternary ammonium alkaloid of a set concentration is added to the zinc bromide solution containing choline chloride with a pH value stabilized at a preset value, and the solution is stirred continuously to obtain an electrolyte containing a composite complexing agent.

2. The preparation method according to claim 1, characterized in that: The concentrations of zinc bromide, choline chloride and quaternary ammonium alkaloid are set to 2 mol / l, 0.5 mol / l and 0.5 mol / l respectively.

3. The preparation method according to claim 1, characterized in that: The choline chloride needs to be slowly added into the zinc bromide solution.

4. The preparation method according to claim 1, characterized in that: The macromolecular acid includes any one of the following: methanesulfonic acid, aminosulfonic acid and citric acid.

5. The preparation method according to claim 1, characterized in that: The pH value of the zinc bromide solution containing choline chloride is stabilized at 2 to 3.

6. The preparation method according to claim 1, characterized in that: The quaternary ammonium alkaloid needs to be gradually added into the zinc bromide solution containing choline chloride.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The preparation method further comprises: A chloride salt is added to the electrolyte containing the composite complexing agent.

8. The preparation method according to claim 7, characterized in that: The concentration of the chloride salt is greater than or equal to 1.5 mol / l.

9. The preparation method according to claim 7, characterized in that: The preparation method further comprises: The electrolyte containing the composite complexing agent is passivated.

10. An electrolyte containing a composite complexing agent, characterized in that: The electrolyte containing the composite complexing agent comprises a composite complexing agent and a solvent, wherein the composite complexing agent comprises zinc bromide, choline chloride and quaternary ammonium alkaloids at set concentrations.

Images