Zinc-bromine flow battery electrolyte, negative electrode cosolvent and preparation method of zinc-bromine flow battery electrolyte and negative electrode cosolvent

Abstract

The invention discloses a zinc-bromine flow battery electrolyte, a negative electrode cosolvent and a preparation method thereof, and belongs to the technical field of electrochemical energy storage, the negative electrode cosolvent of the zinc-bromine flow battery electrolyte is a carboxyl-containing butenoic acid substance, the butenoic acid substance is used as the cosolvent, and zinc is induced to preferentially deposit on a (002) plane by modifying a solid-liquid interface, so that the zinc-bromine flow battery electrolyte is obtained. And the deposition process of zinc is converted from an irregular form which tends to form a dendritic crystal shape and a moss shape into a deposition layer which tends to form a flat and compact deposition layer which is parallel to the substrate. The highly uniform zinc deposition fundamentally and effectively inhibits the formation and growth of zinc dendrites, and greatly improves the stability of the negative electrode and the cycle life of the battery. Chlorides improve ionic conductivity to reduce internal resistance, and sodium acetate buffer inhibits hydrogen evolution on stable pH; and synergistic optimization of positive and negative components ensures efficient reaction. And moreover, the raw materials are easy to obtain, the preparation is simple and convenient, the industrialization threshold is reduced, and the large-scale energy storage requirement is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical energy storage, and particularly relates to a zinc-bromine flow battery electrolyte, a negative electrode cosolvent and a preparation method thereof. BACKGROUND

[0002] With the increasing status of clean energy, the demand for energy storage technology has become more diversified. As a high-efficiency and sustainable medium and long-term energy storage technology, liquid flow batteries have attracted much attention. Zinc-bromine flow batteries, due to their high energy density, low cost, and environmental friendliness, are an important branch of liquid flow batteries. However, the existing zinc-bromine flow battery negative electrode zinc dendrite problem has become an important factor limiting the application of zinc-bromine flow batteries. The growth of zinc dendrites not only reduces the performance of the battery, but also can cause short circuits, leading to battery failure.

[0003] In today's energy field, large-scale energy storage technology is crucial for achieving sustainable energy development. Zinc-bromine flow batteries, with many outstanding advantages, have become one of the most promising large-scale energy storage technologies. They mainly rely on the redox reaction of zinc and bromine to realize energy storage and release, with a system voltage of up to 1.82V, a theoretical energy density of up to 430Wh / kg, a relatively low cost, a high safety, and a wide working temperature window. Compared with all-vanadium flow batteries, they also do not require a complex thermal control system, so they have attracted much attention in the field of large-scale energy storage batteries.

[0004] However, zinc-bromine flow batteries face a serious challenge in practical application - the generation of zinc dendrites. In the negative electrode of zinc-bromine flow batteries, zinc deposition and dissolution reactions mainly occur. During zinc deposition, the reduced zinc tends to grow along a specific crystal direction under the influence of the microenvironment at the electrode-electrolyte interface, eventually forming a dendritic structure with a tree-like morphology. With the continuous charging and discharging cycles, these zinc dendrites continue to grow in the direction of kinetic advantage, which significantly reduces the interface stability of the electrochemical system. When the zinc dendrites grow to a critical size, their tips penetrate the separator, causing damage to the internal structure of the battery, which can trigger a series of irreversible battery failure mechanisms. On the one hand, the bromine monomer at the positive electrode can shuttle through the penetrated separator, greatly reducing the coulombic efficiency of the zinc-bromine flow battery, and thus seriously affecting the performance of the battery; on the other hand, the contact between zinc dendrites and the positive electrode can cause short circuits, directly leading to battery failure, which severely limits the service life and stability of zinc-bromine flow batteries, and becomes a key factor hindering their widespread application. SUMMARY

[0005] In order to overcome the above-mentioned defects of the prior art, the present application aims to provide a zinc-bromine flow battery electrolyte, a negative electrode cosolvent and a preparation method thereof, so as to solve the technical problem that the zinc-bromine flow battery is limited in service life and stability due to the formation of zinc dendrites in the zinc deposition process of the negative electrode, which is caused by the influence of the microenvironment, thereby reducing the performance of the battery and causing short circuit or failure.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] The present application discloses a negative electrode cosolvent of a zinc-bromine flow battery electrolyte, which comprises a compound represented by the general formula (I):

[0008]

[0009] In the formula, at least one of R1 and R2 is -COOH.

[0010] Preferably, the negative electrode cosolvent of the zinc-bromine flow battery electrolyte is a butenoic acid substance.

[0011] Further preferably, the butenoic acid substance comprises any one or more of maleic acid, fumaric acid and 2-butenoic acid.

[0012] The present application also discloses a zinc-bromine flow battery electrolyte, which comprises: a positive electrode electrolyte and a negative electrode electrolyte; the negative electrode electrolyte comprises the above-mentioned negative electrode cosolvent of the zinc-bromine flow battery electrolyte.

[0013] Preferably, the positive electrode electrolyte comprises: an electrolyte, a supporting electrolyte, a positive electrode additive and a solvent; the molar ratio of the electrolyte, the supporting electrolyte and the positive electrode additive is (2.0-2.5):(2.0-3.0):(0.3-0.4).

[0014] Further preferably, the electrolyte is zinc bromide; the supporting electrolyte is any one of potassium chloride, sodium chloride and ammonium chloride; the positive electrode additive is any one of 1-methyl-1-ethylpyrrolidinium bromide and 4-methyl-4-ethylmorpholinium bromide; and the solvent is deionized water.

[0015] Preferably, the negative electrode electrolyte comprises: an electrolyte, a supporting electrolyte, a negative electrode additive, a negative electrode cosolvent and a solvent; the molar ratio of the electrolyte, the supporting electrolyte and the negative electrode additive is (2.0-2.5):(2.0-3.0):(0.1-0.3); and the volume ratio of the negative electrode cosolvent and the solvent is (2-4):(6-8).

[0016] Further preferably, the electrolyte is a zinc bromide solution; the supporting electrolyte is any one of potassium chloride, sodium chloride and ammonium chloride; the negative electrode additive is sodium acetate; and the solvent is deionized water.

[0017] The application further discloses a preparation method of the zinc-bromine flow battery electrolyte, and a preparation method of the positive electrode electrolyte, which comprises sequentially dissolving electrolyte, supporting electrolyte and positive electrode additive in a solvent.

[0018] The application further discloses a preparation method of the zinc-bromine flow battery electrolyte, and a preparation method of the negative electrode electrolyte, which comprises sequentially dissolving negative electrode cosolvent, electrolyte, supporting electrolyte and negative electrode additive in a solvent.

[0019] The application further discloses a zinc-bromine flow battery, wherein the electrolyte of the zinc-bromine flow battery comprises the negative electrode cosolvent of the zinc-bromine flow battery electrolyte, the coulomb efficiency of the zinc-bromine flow battery is 94.1%-96.5%, the voltage efficiency is 79.2%-83.7%, the energy efficiency is 74.5%-79.5%, and the energy efficiency is 72.5%-78.2% after 50 cycles.

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] The application discloses a negative electrode cosolvent of a zinc-bromine flow battery electrolyte, wherein the negative electrode cosolvent contains a carboxyl group, has high hydrophilicity, and has high compatibility with the electrolyte, so that the carboxyl group can form a strong hydrogen bond network with water molecules, inhibit the decomposition of active water, and reduce the occurrence of side reactions. 2+ Meanwhile, the cosolvent can adjust the solvation structure of zinc ions and induce the preferential deposition of zinc on the (002) crystal surface, thereby inhibiting the growth of high-energy surfaces (101) and preventing the formation of zinc dendrites.

[0022] Further, the butenoic acid substance contains a carboxyl group and a carbon-carbon double bond, the double bond can enhance the adsorption stability of the molecule and the electrode surface, and the carboxyl group is beneficial to the compatibility with the electrolyte and can replace water molecules in the solvation sheath of zinc ions, change the solvation structure, and can specifically induce the growth of Zn (002) plane, thereby improving the reliability and specificity of the inhibition of zinc dendrites.

[0023] Further, the butenoic acid substance is any one of maleic acid, fumaric acid and 2-butenoic acid; the conjugation effect of the carboxyl group position and the double bond can optimize the coordination ability to zinc ions, and the solubility in the electrolyte is moderate, so that the electrolyte stability is not affected by excessive dissolution or precipitation.

[0024] The application discloses a zinc-bromine flow battery electrolyte, a co-solvent is integrated into the electrolyte system, so that the negative electrolyte has the core function of inhibiting zinc dendrites, and through the synergistic design of the positive and negative electrolyte, the overall performance imbalance caused by single optimization of the negative electrode is avoided. The structure ensures that the battery is uniform and dense in the charging and discharging cycle, the positive electrode zinc deposition is dominated by the (002) plane, the oxidation and reduction reaction of the positive electrode bromine is stable, and the cycle life and safety of the battery are improved from the system level. Compared with the traditional zinc-bromine flow battery electrolyte technology, the butenoic acid co-solvent is added to the negative electrode, the solid-liquid interface can be modified, and the effect of inhibiting the generation of zinc dendrites can be achieved. The addition of the butenoic acid co-solvent in the electrolyte induces Zn to grow on the (002) plane during the deposition process, the nucleation and growth speed of the Zn (002) plane is slower than that of the Zn (100) and Zn (101) planes, and generally, the slower the crystal surface growth speed is, the larger the area retained is, so that the butenoic acid additive changes the deposition process of zinc from the irregular morphology (commonly seen in the (101) high-energy plane dominant growth) of dendritic and mossy shape to the (002) deposition layer which is more inclined to form parallel to the substrate, flat and dense. The highly uniform zinc deposition fundamentally effectively inhibits the formation and growth of zinc dendrites, and greatly improves the stability of the negative electrode and the cycle life of the battery.

[0025] Further, the molar ratio of the electrolyte, the supporting electrolyte and the positive electrode additive is (2.0-2.5):(2.0-3.0):(0.3-0.4); the electrolyte in the positive electrode provides sufficient active ions, the supporting electrolyte provides high ion conductivity, and the positive electrode additive effectively complexes bromine to inhibit the shuttle effect. If the ratio is too high, the viscosity of the electrolyte will increase, and ion migration will be blocked; if the ratio is too low, the active substance will be insufficient, and the capacity will decrease. The range balances ion conduction, reaction activity and additive efficacy, and improves the energy efficiency and stability of the positive electrode.

[0026] Further, the application selects the supporting electrolyte to include any one of potassium chloride, sodium chloride and ammonium chloride. Chloride ions have excellent migration rate, can significantly improve the overall ion conductivity of the electrolyte, effectively reduce the internal resistance of the battery, reduce ohmic polarization loss, and thus improve the energy efficiency and power output capacity of the battery. Zinc bromide provides zinc and bromine active ions for battery reaction, and is a core carrier for energy storage and release; the supporting electrolyte such as potassium chloride can significantly improve the electrolyte conductivity due to the high migration rate of chloride ions, and reduce ohmic polarization; the specific quaternary ammonium salt additive can form a stable complex with bromine, and reduce the shuttle of bromine element to the negative electrode; and the deionized water as the solvent can eliminate the interference of impurity ions on the electrode reaction. The component selection ensures that the positive electrode reaction is efficient and stable, and is synergistic with the dendrite inhibition function of the negative electrode, and improves the overall performance of the battery.

[0027] Further, the application introduces sodium acetate as a negative electrode additive. Sodium acetate / organic acid forms an effective buffer pair, which can dynamically adjust and stabilize the pH value of the electrolyte, maintaining it within the optimal range to inhibit the hydrogen evolution reaction. The pH stability is one of the key factors to improve the long-term cycle stability of the battery.

[0028] Further, the molar ratio of the electrolyte, supporting electrolyte, and negative electrode additive is (2.0-2.5):(2.0-3.0):(0.1-0.3); the volume ratio of the negative electrode co-solvent and the solvent is (2-4):(6-8); this ratio balances the negative electrode zinc ion concentration, ion conductivity, pH buffering capacity, and the interface modification effect of the co-solvent. Too high a proportion of the co-solvent will increase the viscosity of the electrolyte and reduce ion migration, and too low a proportion will not effectively modify the interface; the additive proportion ensures the formation of a stable buffer pair with organic acid to inhibit hydrogen evolution. The overall proportion optimizes the negative electrode to simultaneously inhibit zinc dendrites, have high conductivity, and stable pH, improving cycle stability.

[0029] Further, zinc bromide provides zinc ions for deposition / dissolution; supporting electrolytes such as potassium chloride improve conductivity and reduce internal resistance; sodium acetate and the carboxyl group in the co-solvent in the electrolyte dissociate to form a buffer pair, dynamically stabilizing the pH within the range that inhibits hydrogen evolution, and avoiding zinc electrode corrosion; deionized water ensures the purity of the electrolyte. This combination of components allows the negative electrode to inhibit dendrites while maintaining efficient zinc deposition / dissolution reactions, and cooperates with the positive electrode to improve the cycle life and energy efficiency of the battery.

[0030] The application also discloses a preparation method for the above-mentioned zinc-bromine flow battery electrolyte. The electrolyte components used in the application are simple, and the formula is easy to accurately adjust and optimize according to specific battery design parameters (such as target concentration, etc.). The simplicity of the preparation process, good adjustability, and easy availability of raw materials make the technical solution of the application very suitable for large-scale industrial production and practical application, significantly reducing manufacturing costs and technical barriers. The zinc-bromine flow battery prepared using the zinc-bromine flow battery electrolyte disclosed in the application contains the negative electrode co-solvent of the above-mentioned zinc-bromine flow battery electrolyte. Integrating the optimized electrolyte into the battery system achieves synergistic optimization. The negative electrode suppresses zinc dendrites through the co-solvent, and the positive electrode improves the reaction stability through component optimization. The overall solution to the short circuit and failure problems caused by dendrites in traditional batteries significantly improves the cycle life, energy efficiency, and safety of the battery, making it more suitable for large-scale energy storage applications. Under the combined action of the co-solvent-induced dense deposition of the (002) plane of zinc and the sodium acetate buffer pair stabilizing the pH to inhibit hydrogen evolution, the coulombic efficiency, voltage efficiency, energy efficiency, and cycle stability of the zinc-bromine flow battery are significantly improved. DETAILED DESCRIPTION

[0031] The technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0032] In the present application, all the embodiments and preferred embodiments mentioned in the present application can be combined to form new technical solutions, unless otherwise specified.

[0033] In the present application, all the technical features and preferred features mentioned in the present application can be combined to form new technical solutions, unless otherwise specified.

[0034] In the present application, unless otherwise specified, the percentage (%) or part refers to the percentage by weight or weight part of the composition.

[0035] In the present application, unless otherwise specified, each component or its preferred component involved can be combined to form a new technical solution.

[0036] In the present application, unless otherwise specified, the numerical range "a~b" represents a shorthand notation for any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "6~22" represents that all the real numbers between "6~22" have been listed in the present application, and "6~22" is only a shorthand notation for these numerical combinations

[0037] The lower limit and upper limit of the range disclosed in the present application can be one or more lower limits and one or more upper limits, respectively.

[0038] In the present application, the term "and / or" used in the present application means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0039] In the present application, unless otherwise specified, each reaction or operation step can be carried out sequentially or according to the sequence. Preferably, the reaction method in the present application is carried out sequentially.

[0040] Unless otherwise specified, the professional and scientific terms used in the present application have the same meaning as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content can also be applied in the present application.

[0041] The present application provides a negative electrode cosolvent of a zinc-bromine flow battery electrolyte, and the structure of the negative electrode cosolvent is as follows:

[0042]

[0043] In the formula, at least one of R1 and R2 is a carboxyl group, i.e., -COOH.

[0044] The negative electrode co-solvent is a butenoic acid substance, including any one of maleic acid, fumaric acid and 2-butenoic acid.

[0045] The application provides a zinc-bromine flow battery electrolyte, comprising: a positive electrolyte and a negative electrolyte.

[0046] The positive electrolyte comprises: an electrolyte, a supporting electrolyte, a positive electrode additive and a solvent.

[0047] The negative electrolyte comprises: an electrolyte, a supporting electrolyte, a negative electrode additive, a negative electrode co-solvent and a solvent.

[0048] The application further provides a preparation method of the zinc-bromine flow battery electrolyte, comprising the following steps:

[0049] The preparation step of the positive electrolyte comprises the following steps:

[0050] S1: accurately weighing the required amount of solvent, electrolyte, supporting electrolyte and positive electrode additive;

[0051] S2: adding the electrolyte into the solvent deionized water and stirring until completely dissolved;

[0052] S3: adding the supporting electrolyte into the solution prepared in the step S2 and stirring until completely dissolved;

[0053] S4: adding the positive electrode additive into the solution prepared in the step S3 and stirring until completely dissolved;

[0054] S5: constant volume to the required capacity.

[0055] The preparation step of the negative electrolyte comprises the following steps:

[0056] S1: accurately weighing the required amount of solvent, co-solvent, electrolyte, supporting electrolyte and negative electrode additive;

[0057] S2: stirring and uniformly mixing the solvent deionized water and the co-solvent according to the proportion;

[0058] S3: adding the electrolyte into the solution prepared in the step S2 and stirring until completely dissolved;

[0059] S4: adding the supporting electrolyte and the negative electrode additive into the solution prepared in the step S3 and stirring until completely dissolved;

[0060] S5: constant volume to the required capacity by using the mixed solution of deionized water and the co-solvent.

[0061] Preferably, the electrolyte is a 2.0-2.5 mol / L zinc bromide solution.

[0062] Preferably, the supporting electrolyte comprises 2.0-3.0 mol / L of any one of potassium chloride, sodium chloride and ammonium chloride.

[0063] Preferably, the positive electrode additive comprises 0.3-0.4 mol / L of any one of 1-methyl-1-ethylpyrrolidinium bromide and 4-methyl-4-ethylmorpholinium bromide.

[0064] Preferably, the solvent is deionized water.

[0065] Preferably, the negative electrode additive comprises 0.1-0.3 mol / L of sodium acetate.

[0066] Preferably, the ratio of the negative electrode co-solvent to the deionized water is 2:8-4:6.

[0067] The application also provides a zinc-bromine flow battery, wherein the electrolyte of the zinc-bromine flow battery comprises the negative electrode co-solvent of the electrolyte of the zinc-bromine flow battery.

[0068] The application aims at the problem of zinc dendrite of the zinc-bromine flow battery, and provides a zinc-bromine flow battery, an electrolyte, a negative electrode co-solvent and a preparation method. By adding butenoic acid co-solvent to the negative electrode electrolyte, the main effects include: the addition of butenoic acid co-solvent in the electrolyte induces Zn to preferentially grow on the (002) plane during the deposition process, and more tends to form a parallel, flat and dense (002) deposition layer. This highly uniform zinc deposition fundamentally effectively suppresses the formation and growth of zinc dendrites, and greatly improves the stability of the negative electrode and the cycle life of the battery. The supporting electrolyte selected by the application comprises chlorides (such as sodium chloride, potassium chloride, etc.) and sodium acetate. Chloride ions have excellent mobility, can significantly improve the overall ionic conductivity of the electrolyte, effectively reduce the internal resistance of the battery, reduce the ohmic polarization loss, and thus improve the energy efficiency and power output capacity of the battery; the application introduces sodium acetate as a component of the electrolyte, and sodium acetate / organic acid forms an effective buffer pair, which can dynamically adjust and stabilize the pH value of the electrolyte, and maintain it in a relatively optimal range to inhibit the occurrence of hydrogen evolution reaction. This pH stability is one of the key factors to improve the long-term cycle stability of the battery.

[0069] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. The components in the embodiments of the present application can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0070] Embodiment 1

[0071] A preparation method of a zinc-bromine flow battery electrolyte, comprising:

[0072] Preparation of positive electrolyte:

[0073] S1: accurately weigh 45.04 g of zinc bromide (2 mol / L), 14.9 g of potassium chloride (2 mol / L), and 5.82 g of 1-methyl-1-ethylpyrrolidinium bromide (0.3 mol / L);

[0074] S2: add zinc bromide to deionized water and stir until completely dissolved;

[0075] S3: add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0076] S4: add 1-methyl-1-ethylpyrrolidinium bromide to the solution in S3 and stir until completely dissolved;

[0077] S5: dilute to 100 ml.

[0078] Preparation of negative electrolyte:

[0079] S1: accurately weigh 45.04 g of zinc bromide (2 mol / L), 14.9 g of potassium chloride (2 mol / L), and 1.83 g of sodium acetate (0.1 mol / L);

[0080] S2: mix maleic acid and deionized water in a volume ratio of 2:8 and stir until uniform;

[0081] S3: add zinc bromide to the solution prepared in S2 and stir until completely dissolved;

[0082] S4: add potassium chloride and sodium acetate to the solution prepared in S3 and stir until completely dissolved;

[0083] S5: dilute with the mixed solution of maleic acid and deionized water to 100 ml.

[0084] Example 2

[0085] A preparation method of a zinc-bromine flow battery electrolyte, comprising:

[0086] Preparation of positive electrolyte:

[0087] S1: accurately weigh 56.30 g of zinc bromide (2.5 mol / L), 14.6 g of sodium chloride (2.5 mol / L), and 7.76 g of 1-methyl-1-ethylpyrrolidinium bromide (0.4 mol / L);

[0088] S2: add zinc bromide to deionized water and stir until completely dissolved;

[0089] S3: add sodium chloride to the solution prepared in S2 and stir until completely dissolved;

[0090] S4: add 1-methyl-1-ethylpyrrolidinium bromide to the solution prepared in S3 and stir until completely dissolved;

[0091] S5: dilute to 100 ml with deionized water.

[0092] Preparation of negative electrolyte:

[0093] S1: accurately weigh 46.30 g of zinc bromide (2.5 mol / L), 14.6 g of sodium chloride (2.5 mol / L), and 1.83 g of sodium acetate (0.1 mol / L);

[0094] S2: mix fumaric acid and deionized water in a volume ratio of 3:7 and stir until uniform;

[0095] S3: add zinc bromide to the solution prepared in S2 and stir until completely dissolved;

[0096] S4: add sodium chloride and sodium acetate to the solution prepared in S3 and stir until completely dissolved;

[0097] S5: dilute to 100 ml with the mixed solution of fumaric acid and deionized water.

[0098] Example 3

[0099] A preparation method of a zinc-bromine flow battery electrolyte, comprising:

[0100] Preparation of positive electrolyte:

[0101] S1: accurately weigh 45.04 g of zinc bromide (2 mol / L), 16.0 g of ammonium chloride (3 mol / L), and 6.30 g of 4-methyl-4-ethyl morpholinium bromide (MEM) (0.3 mol / L);

[0102] S2: add zinc bromide to deionized water and stir until completely dissolved;

[0103] S3: ammonium chloride is added to the solution prepared in S2, and stirred until completely dissolved;

[0104] S4: 4-methyl-4-ethyl morpholinium bromide is added to the solution prepared in S3, and stirred until completely dissolved;

[0105] S5: constant volume to 100 ml with deionized water.

[0106] Preparation of negative electrolyte:

[0107] S1: accurately weigh 45.04 g of zinc bromide (2 mol / L), 16.0 g of ammonium chloride (3 mol / L), and 1.83 g of sodium acetate (0.1 mol / L);

[0108] S2: 2-butenoic acid is mixed with deionized water in a volume ratio of 4:6 and stirred until uniform;

[0109] S3: zinc bromide is added to the solution prepared in S2, and stirred until completely dissolved;

[0110] S4: ammonium chloride and sodium acetate are added to the solution prepared in S3, and stirred until completely dissolved;

[0111] S4: constant volume to 100 ml with the mixed solution of 2-butenoic acid and deionized water.

[0112] Example 4

[0113] A method for preparing an electrolyte of a zinc-bromine flow battery, comprising:

[0114] S1: accurately weigh 45.04 g of zinc bromide (2 mol / L), 13.4 g of ammonium chloride (2.5 mol / L), and 8.40 g of 4-methyl-4-ethyl morpholinium bromide (MEM) (0.4 mol / L);

[0115] S2: zinc bromide is added to deionized water, and stirred until completely dissolved;

[0116] S3: ammonium chloride is added to the solution prepared in S2, and stirred until completely dissolved;

[0117] S4: 4-methyl-4-ethyl morpholinium bromide is added to the solution prepared in S3, and stirred until completely dissolved;

[0118] S5: constant volume to 100 ml with deionized water.

[0119] Preparation steps of negative electrolyte:

[0120] S1: accurately take 45.04 g of zinc bromide (2 mol / L), 13.4 g of ammonium chloride (2.5 mol / L), 1.83 g of sodium acetate (0.1 mol / L);

[0121] S2: mix maleic acid and deionized water in a volume ratio of 3:7 and stir until uniform;

[0122] S3: add zinc bromide to the solution prepared in S2 and stir until completely dissolved;

[0123] S4: add ammonium chloride and sodium acetate to the solution prepared in S3 and stir until completely dissolved;

[0124] S5: dilute the mixed solution of maleic acid and deionized water to 100 ml.

[0125] Example 5

[0126] A method for preparing a zinc-bromine flow battery electrolyte, comprising:

[0127] Preparation of positive electrolyte:

[0128] S1: accurately take 49.54 g of zinc bromide (2.2 mol / L), 14.9 g of potassium chloride (2 mol / L), and 6.79 g of 1-methyl-1-ethylpyrrolidinium bromide (0.3 mol / L);

[0129] S2: add zinc bromide to deionized water and stir until completely dissolved;

[0130] S3: add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0131] S4: add 1-methyl-1-ethylpyrrolidinium bromide to the solution prepared in S3 and stir until completely dissolved;

[0132] S5: dilute to 100 ml.

[0133] Preparation of negative electrolyte:

[0134] S1: accurately take 45.04 g of zinc bromide (2.2 mol / L), 14.9 g of potassium chloride (2 mol / L), and 3.66 g of sodium acetate (0.2 mol / L);

[0135] S2: mix maleic acid and deionized water in a volume ratio of 2:8 and stir until uniform;

[0136] S3: add zinc bromide to the solution prepared in S2 and stir until completely dissolved;

[0137] S4: add potassium chloride and sodium acetate to the solution prepared in S3 and stir until completely dissolved;

[0138] S5: constant volume to 100ml with the mixed solution of maleic acid and deionized water.

[0139] Example 6

[0140] A preparation method of a zinc-bromine flow battery electrolyte, comprising:

[0141] Preparation of positive electrolyte:

[0142] S1: accurately weigh 56.30g of zinc bromide (2.5mol / L), 14.6g of sodium chloride (2.5mol / L), and 7.76g of 1-methyl-1-ethylpyrrolidinium bromide (0.3mol / L);

[0143] S2: add zinc bromide to deionized water and stir until completely dissolved;

[0144] S3: add sodium chloride to the solution prepared in S2 and stir until completely dissolved;

[0145] S4: add 1-methyl-1-ethylpyrrolidinium bromide to the solution prepared in S3 and stir until completely dissolved;

[0146] S5: constant volume to 100ml with deionized water.

[0147] Preparation of negative electrolyte:

[0148] S1: accurately weigh 46.30g of zinc bromide (2.5mol / L), 14.6g of sodium chloride (2.5mol / L), and 5.49g of sodium acetate (0.3mol / L);

[0149] S2: mix maleic acid and fumaric acid in a mass ratio of 1:1, then mix with deionized water in a volume ratio of 3:7;

[0150] S3: add zinc bromide to the solution prepared in S2 and stir until completely dissolved;

[0151] S4: add sodium chloride and sodium acetate to the solution prepared in S3 and stir until completely dissolved;

[0152] S5: constant volume to 100ml with the mixed solution of fumaric acid and deionized water.

[0153] Comparative Example 1

[0154] A preparation method of a zinc-bromine flow battery electrolyte, comprising:

[0155] Preparation of positive electrolyte:

[0156] S1: accurately take 45.04 g of zinc bromide (2 mol / L), 14.9 g of potassium chloride (2 mol / L), 5.82 g of 1-methyl-1-ethylpyrrolidine bromide (0.3 mol / L);

[0157] S2: add zinc bromide to deionized water and stir until completely dissolved;

[0158] S3: add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0159] S4: add 1-methyl-1-ethylpyrrolidine bromide to the solution prepared in S3 and stir until completely dissolved;

[0160] S5: dilute to 100 ml.

[0161] Preparation of negative electrolyte:

[0162] S1: accurately take 45.04 g of zinc bromide (2 mol / L), 14.9 g of potassium chloride (2 mol / L);

[0163] S2: add zinc bromide to deionized water and stir until completely dissolved;

[0164] S3: add potassium chloride to the solution prepared in S2 and stir until completely dissolved

[0165] S3: dilute to 100 ml with deionized water.

[0166] Comparative Example 2

[0167] A method for preparing a zinc-bromine flow battery electrolyte, comprising:

[0168] Preparation of positive electrolyte:

[0169] S1: accurately take 56.30 g of zinc bromide (2.5 mol / L), 14.6 g of sodium chloride (2.5 mol / L), 7.76 g of 1-methyl-1-ethylpyrrolidine bromide (0.4 mol / L);

[0170] S2: add zinc bromide to deionized water and stir until completely dissolved;

[0171] S3: add sodium chloride to the solution prepared in S2 and stir until completely dissolved;

[0172] S4: add 1-methyl-1-ethylpyrrolidine bromide to the solution prepared in S3 and stir until completely dissolved;

[0173] S5: dilute to 100 ml.

[0174] Preparation of negative electrolyte:

[0175] S1 : accurately weigh 56.30 g of zinc bromide (2.5 mol / L), 14.6 g of sodium chloride (2.5 mol / L)

[0176] S2: add zinc bromide into deionized water, stir until completely dissolved;

[0177] S3: add sodium chloride into the solution prepared in S2, stir until completely dissolved

[0178] S4: dilute to 100 ml with deionized water.

[0179] Comparative Example 3

[0180] A method for preparing an electrolyte of a zinc-bromine flow battery, comprising:

[0181] Preparation of positive electrolyte:

[0182] S1 : accurately weigh 45.04 g of zinc bromide (2 mol / L), 16.0 g of ammonium chloride (3 mol / L), 6.30 g of 4-methyl-4-ethyl morpholinium bromide (MEM) (0.3 mol / L);

[0183] S2: add zinc bromide into deionized water, stir until completely dissolved;

[0184] S3: add ammonium chloride into the solution prepared in S2, stir until completely dissolved;

[0185] S4: add 1 -methyl- 1 -ethyl pyrrolidinium bromide into the solution prepared in S3, stir until completely dissolved;

[0186] S5: dilute to 100 ml.

[0187] Preparation of negative electrolyte:

[0188] S1 : accurately weigh 45.04 g of zinc bromide (2 mol / L), 16.0 g of ammonium chloride (3 mol / L);

[0189] S2: add zinc bromide into deionized water, stir until completely dissolved;

[0190] S3: add ammonium chloride into the solution prepared in S2, stir until completely dissolved;

[0191] S4: dilute to 100 ml with deionized water.

[0192] Table 1 Comparison of the composition and ratio of each key component in Examples 1-6 and Comparative Examples 1-3

[0193]

[0194] Table 2 is a comparison of the performance test results of the zinc-bromine flow battery electrolyte prepared in Examples 1-6 and Comparative Examples 1-3 in a single flow battery

[0195]

[0196] Table 1 is a comparison of the composition and ratio of each key component in Examples 1-6 and Comparative Examples 1-3; from the table, the preparation conditions of each example and comparative example can be clearly seen. The zinc-bromine flow battery electrolyte prepared in Examples 1-6 and Comparative Examples 1-3 was tested for performance in a single battery, and the experimental conditions were as follows: the electrode was a commercial carbon plastic bipolar plate, the electrode area was 9 cm 2 , the separator was a microporous polyolefin separator, the charge and discharge current density was 20 mA / cm 2 , the charging time was 1 h, the discharge cutoff voltage was 0.5 V, and the positive and negative electrolyte was 50 mL. The test performance of the battery in the examples and comparative examples was tested under the same conditions. Table 2 is a comparison of the performance test results of the electrolyte prepared in Examples 1-6 and Comparative Examples 1-3 in a zinc-bromine flow single battery. As shown in the table, the coulombic efficiency of the zinc-bromine flow battery prepared from the zinc-bromine flow electrolyte prepared by the present application was 94.1%-96.5%; the energy efficiency was 74.5%-79.5%; the voltage efficiency was 79.2%-83.7%; and the energy efficiency after 50 cycles was 72.5%-78.2%. The coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) values of the first cycle and after 50 cycles in Examples 1-6 were all greater than those in the comparative examples. By adding the positive and negative additives and the negative co-solvent, the growth of zinc dendrites can be significantly inhibited, the pH of the electrolyte can be adjusted, the hydrogen evolution reaction can be inhibited, and the coulombic efficiency, voltage efficiency, and energy efficiency of the zinc-bromine flow battery can be improved.

[0197] In summary, the present application provides a zinc-bromine flow battery electrolyte, a negative electrode co-solvent, and a preparation method thereof. By adding the negative electrode additive and the co-solvent, the coulombic efficiency, voltage efficiency, and energy efficiency of the zinc-bromine flow battery electrolyte prepared by the present application can be significantly improved compared to the zinc-bromine flow battery electrolyte without the additive and co-solvent. The test data of the zinc-bromine flow battery with the additive and co-solvent added and the zinc-bromine flow battery without the additive and co-solvent added show that the coulombic efficiency, voltage efficiency, and energy efficiency of the zinc-bromine flow battery electrolyte prepared by the present application can be significantly improved, and the coulombic efficiency, voltage efficiency, and energy efficiency of the single flow battery after 50 cycles in the single battery are significantly improved. Therefore, the electrolyte prepared in the present application has good cyclic use effect and can improve the cycle life of the zinc-bromine flow battery.

[0198] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A negative electrode co-solvent for a zinc-bromine flow battery electrolyte, characterized in that: The negative electrode co-solvent of the zinc-bromine flow battery electrolyte comprises a compound represented by general formula (I): In the formula, at least one of R1 and R2 is -COOH.

2. The negative electrode co-solvent of the zinc-bromine flow battery electrolyte according to claim 1, characterized in that The negative electrode co-solvent of the zinc-bromine flow battery electrolyte is a butenoic acid substance.

3. The negative electrode co-solvent of the zinc-bromine flow battery electrolyte according to claim 2, characterized in that The butenoic acid substances include any one or more of maleic acid, fumaric acid and 2-butenoic acid.

4. A zinc-bromine flow battery electrolyte, characterized in that include: A positive electrode electrolyte and a negative electrode electrolyte; the negative electrode electrolyte contains the negative electrode co-solvent of the zinc-bromine flow battery electrolyte according to any one of claims 1 to 3.

5. The zinc-bromine flow battery electrolyte according to claim 4, characterized in that The positive electrode electrolyte comprises: an electrolyte, a supporting electrolyte, a positive electrode additive and a solvent; the molar ratio of the electrolyte, the supporting electrolyte and the positive electrode additive is (2.0-2.5): (2.0-3.0): (0.3-0.4).

6. The zinc-bromine flow battery electrolyte according to any one of claim 5, characterized in that The electrolyte is zinc bromide; the supporting electrolyte is any one of potassium chloride, sodium chloride and ammonium chloride; the positive electrode additive is any one of 1-methyl-1-ethylpyrrolidinoammonium bromide and 4-methyl-4-ethylmorpholinium bromide; and the solvent is deionized water.

7. The zinc-bromine flow battery electrolyte according to claim 4, characterized in that The negative electrode electrolyte comprises: an electrolyte, a supporting electrolyte, a negative electrode additive, a negative electrode co-solvent and a solvent; the molar ratio of the electrolyte, the supporting electrolyte and the negative electrode additive is (2.0-2.5): (2.0-3.0): (0.1-0.3); the volume ratio of the negative electrode co-solvent and the solvent is (2-4): (6-8).

8. The zinc-bromine flow battery electrolyte according to claim 7, characterized in that The electrolyte is zinc bromide; the supporting electrolyte is any one of potassium chloride, sodium chloride and ammonium chloride; the negative electrode additive is sodium acetate; and the solvent is deionized water.

9. The method for preparing a zinc-bromine flow battery electrolyte according to any one of claims 4 to 8, characterized in that: The method for preparing the positive electrode electrolyte comprises: dissolving an electrolyte, a supporting electrolyte and a positive electrode additive in a solvent in sequence.

10. The method for preparing a zinc-bromine flow battery electrolyte according to any one of claims 4 to 8, characterized in that: The method for preparing the negative electrode electrolyte comprises: dissolving a negative electrode co-solvent, an electrolyte, a supporting electrolyte and a negative electrode additive in a solvent in sequence.

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