A multifunctional electrolyte for zinc-bromine flow batteries and its preparation method

Abstract

This invention discloses a multifunctional electrolyte for zinc-bromine flow batteries and its preparation method, belonging to the field of electrochemical energy storage technology. The method includes: dissolving an electrolyte in a solvent, and sequentially adding a supporting electrolyte, a positive electrode complexing agent, and a positive electrode additive to obtain a positive electrode electrolyte; the positive electrode additive is zinc iodide; the zinc iodide contains I... ‑ With Br2 / Br ‑ In the reaction system, Br2 forms mixed halide ions, achieving bromine inhibition and improving the overall conductivity and comprehensive electrochemical performance of the electrolyte. The electrolyte is dissolved in a solvent, and a supporting electrolyte and a first negative electrode additive are added sequentially to obtain the negative electrode electrolyte. The first negative electrode additive includes sodium acetate and sodium citrate. The combination of sodium acetate and sodium citrate forms a wide-range buffer system, which can dynamically adjust and stabilize the pH value of the electrolyte, improve the long-term stability of the battery, and extend the cycle life. The positive and negative electrode electrolytes constitute a multifunctional electrolyte for the zinc-bromine flow battery. The zinc deposition behavior is synergistically regulated by sodium salt buffering and ion coordination.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a multifunctional electrolyte for zinc-bromine flow batteries and its preparation method. Background Technology

[0002] With the increasing prominence of clean energy, the demand for energy storage technologies is becoming more diversified. Flow batteries, as a highly efficient and sustainable medium- to long-term energy storage technology, have attracted considerable attention. Zinc-bromine flow batteries, due to their high energy density, low cost, and environmental friendliness, are an important branch of flow batteries. However, existing zinc-bromine flow batteries use bromine / bromine (Br2 / Br4) as the cathode material. - The conversion reaction rate is slow, involves multiple steps, and requires high activation energy. Usually, a complexing agent is added to the positive electrode to complex Br2 to improve solubility, but this makes the Br2 reaction pathway more complicated. The slow Br2 reaction becomes a bottleneck in the overall battery performance, resulting in high polarization voltage, which significantly reduces voltage efficiency and power density, leading to low energy efficiency, limited power density, and low coulombic efficiency.

[0003] A significant challenge in zinc-bromine flow batteries is the formation of zinc dendrites at the negative electrode. During zinc deposition, influenced by the microenvironment at the electrode-electrolyte interface, the reduced zinc tends to preferentially grow along specific crystal orientations, ultimately forming dendritic structures with a tree-like morphology. As charge-discharge cycles continue, these zinc dendrites grow along the kinetically dominant direction, significantly reducing the interfacial stability of the electrochemical system. When the zinc dendrites grow to a critical size, their tips penetrate the separator, causing damage to the internal battery structure and triggering a series of irreversible battery failure mechanisms. On one hand, the bromine at the positive electrode shuttles through the punctured separator, drastically reducing the coulombic efficiency of the zinc-bromine flow battery and severely impacting its performance. On the other hand, contact between zinc dendrites and the positive electrode can cause short circuits, directly leading to battery failure. This severely limits the lifespan and stability of zinc-bromine flow batteries, becoming a key factor hindering their widespread application.

[0004] Therefore, developing a multifunctional additive for zinc-bromine flow batteries and its preparation method is of great significance for improving the performance of zinc-bromine flow batteries and promoting their practical application. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a multifunctional electrolyte for zinc-bromine flow batteries and its preparation method, so as to solve the technical problems of slow positive electrode bromine / bromine conversion reaction rate, high activation energy, and complex reaction path, which lead to low energy efficiency, limited power density, and low coulombic efficiency, as well as the formation of zinc dendrites on the negative electrode affecting battery stability, lifespan and causing failure.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] This invention discloses a method for preparing a multifunctional electrolyte for zinc-bromine flow batteries, comprising:

[0008] The electrolyte is dissolved in a solvent, and a supporting electrolyte, a positive electrode complexing agent, and a positive electrode additive are added sequentially to obtain the positive electrode electrolyte; the positive electrode additive is zinc iodide; the I in zinc iodide... - With Br2 / Br - In the reaction system, Br2 forms mixed halide ions, thus achieving the function of bromine inhibition.

[0009] The electrolyte is dissolved in a solvent, and a supporting electrolyte and a first negative electrode additive are added sequentially to obtain the negative electrode electrolyte; the first negative electrode additive includes sodium acetate and sodium citrate; the combination of sodium acetate and sodium citrate forms a wide-range buffer system.

[0010] The positive and negative electrolytes constitute a multifunctional electrolyte for the zinc-bromine flow battery; zinc deposition behavior is synergistically regulated by sodium salt buffering and ion coordination.

[0011] Preferably, in the positive electrode electrolyte, the molar ratio of electrolyte, supporting electrolyte, positive electrode complexing agent and positive electrode additive is (2.0-2.5):(2.0-3.0):(0.2-0.3):(0.05-0.2).

[0012] Preferably, the electrolyte is a zinc bromide solution and the solvent is deionized water.

[0013] Preferably, the supporting electrolyte is potassium chloride.

[0014] Preferably, the positive electrode complexing agent is 1-methyl-1-ethylpyrrolidine ammonium bromide.

[0015] Preferably, in the negative electrode electrolyte, the molar ratio of electrolyte, supporting electrolyte and first negative electrode additive is (2.0-2.5):(2.0-3.0):(0.2-0.4).

[0016] Preferably, the molar ratio of sodium acetate to sodium citrate is (0.1-0.2):(0.1-0.2).

[0017] Preferably, the negative electrode electrolyte further includes a second negative electrode additive; the second negative electrode additive includes oxalic acid, malonic acid, succinic acid, glutaric acid or adipic acid; the molar ratio of the first negative electrode additive to the second negative electrode additive is (0.2-0.4):(0.05-0.2).

[0018] This invention also discloses a multifunctional electrolyte for zinc-bromine flow batteries, which is prepared using the above-described method. The multifunctional electrolyte for zinc-bromine flow batteries includes a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode electrolyte includes an electrolyte, a supporting electrolyte, a positive electrode complexing agent, a positive electrode additive, and a solvent. The negative electrode electrolyte includes an electrolyte, a supporting electrolyte, a first negative electrode additive, and a solvent.

[0019] Preferably, the coulombic efficiency of the zinc-bromine flow battery prepared with the multifunctional electrolyte for zinc-bromine flow batteries is 92.1%-96.2%; the energy efficiency is 77.18%-83.50%; and the voltage efficiency is 83.8%-86.8%.

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

[0021] This invention discloses a method for preparing a multifunctional electrolyte for zinc-bromine flow batteries, by introducing zinc iodide as a positive electrode additive. In Br2 / Br - In the reaction system, I - It can act as a redox mediator, significantly reducing the activation energy of the reaction and improving the battery's charge and discharge efficiency. - It can form mixed halide ions with Br2, competitively reducing the concentration of free Br2, thereby reducing the bromine permeation source from the root, achieving bromine inhibition, reducing side reactions, improving coulombic efficiency, and significantly reducing capacity loss. -Adsorption on the carbon electrode surface alters the double-layer structure, enhancing the charge transfer rate at the electrode / electrolyte interface. This significantly improves the overall conductivity of the electrolyte, thereby reducing the battery's ohmic resistance and increasing voltage efficiency, energy efficiency, and power density. Introducing sodium acetate as a negative electrode additive dynamically adjusts and stabilizes the electrolyte's pH, maintaining it within an optimal range that inhibits hydrogen evolution reaction. pH stability is a key factor in improving the battery's long-term cycle stability. Furthermore, introducing sodium citrate on top of sodium acetate as a negative electrode additive broadens the pH buffer range, further enhancing the battery's long-term stability and extending cycle life. Traditional methods using single bromine complexing agents only delay bromine diffusion but cannot reduce free bromine concentration, while the introduction of zinc iodide achieves source control of bromine permeation through chemical bonding. Existing pH adjusters are mostly single acidic or alkaline substances, unable to cope with dynamic pH changes during charging and discharging, while the combination of sodium acetate and sodium citrate forms a wide-range buffer system. Existing zinc dendrite suppression methods mostly rely on physical barrier layers. This invention, however, synergistically regulates zinc deposition behavior through sodium salt buffering and ion coordination. This effectively reduces the free bromine concentration in the positive electrode electrolyte, minimizing side reactions caused by bromine permeation; maintains stable pH in the negative electrode electrolyte, inhibiting hydrogen evolution reaction corrosion of the electrode; optimizes the zinc ion deposition environment, slowing dendrite growth; and simultaneously enhances the overall conductivity of the electrolyte by supporting the electrolyte, achieving a synergistic improvement in battery efficiency and cycle life.

[0022] Furthermore, excessively high electrolyte concentrations weaken the effect of bromine complexing agents, while excessive addition of complexing agents can lead to the covering of electrode active sites. This invention achieves a complementary concentration gradient between zinc bromide and potassium chloride through a precise quaternary molar ratio, maintaining high conductivity while ensuring the structural stability of the bromine complex. The ratio of zinc iodide to the complexing agent is optimized to both leverage the catalytic effect of iodide ions and prevent excessive occupation of complexing sites.

[0023] Furthermore, in existing technologies using electrolytes such as zinc chloride, chloride ions easily trigger side reactions. However, this invention uses zinc bromide solution to maintain a balanced bromide ion concentration, avoiding excessive consumption of bromide species. This improves the ionic conductivity and chemical stability of the electrolyte system, promotes the kinetic balance of the positive and negative electrode reactions in the zinc-bromine flow battery, and suppresses electrode passivation caused by impurity ions, thereby improving charge transport efficiency and electrochemical performance stability during battery cycling.

[0024] Furthermore, potassium chloride dissociates into potassium ions and chloride ions in the electrolyte. Potassium ions have a high mobility, which can significantly improve the overall conductivity of the electrolyte and reduce ohmic polarization during battery operation. Chloride ions coordinate with zinc ions in the electrolyte to form a stable complex structure, inhibiting the formation of sharp dendrites of zinc metal on the electrode surface. Chloride ions synergistically interact with bromide ions in the zinc bromide electrolyte, optimizing the double-layer structure at the electrode interface and promoting the kinetic efficiency of the charge transfer process. This invention, through the introduction of potassium chloride, constructs a multifunctional ion transport network by utilizing the high mobility of potassium ions and the complexing ability of chloride ions while maintaining chemical stability. This effectively reduces the ohmic internal resistance of the electrolyte system, improves charge transfer efficiency, and results in lower polarization losses during battery charging and discharging. The increased ion migration rate directly enhances the conductivity of the electrolyte, while the regulatory effect of chloride ions on zinc deposition behavior inhibits dendrite formation. The dual effects synergistically improve the energy conversion efficiency and cycle stability of the battery.

[0025] Furthermore, 1-methyl-1-ethylpyrrolidine ammonium bromide, acting as a positive electrode complexing agent, restricts the free movement of bromine molecules through the rigid structure of the pyrrolidine ring, and its steric hindrance effect promotes the formation of stable complexes from elemental bromine. The cation moiety binds to bromide ions through electrostatic interactions to form a complex, inhibiting bromine permeation and migration. The bromide ions released by the ammonium bromide group can compensate for the charge balance in the electrolyte, avoiding ion loss due to complexation. This dual-functionality achieves both efficient bromine fixation and maintenance of the ion balance in the electrolyte system, thereby reducing side reactions. It effectively reduces the concentration of free bromine, inhibits bromine permeation and migration to the negative electrode, reduces side reactions caused by bromine diffusion, and thus improves the coulombic efficiency and cycle stability of the battery. At the same time, the charge balance of the electrolyte system is maintained, avoiding a decrease in conductivity due to ion loss, and ensuring battery operating efficiency.

[0026] Furthermore, by synergistically combining two carboxylates, a multiple buffer system is constructed, which can maintain electrolyte stability over a wider pH range. Existing technologies often only consider the dissociation constant of a single substance when selecting buffer concentrations, while this invention optimizes the molar ratio of the two substances to achieve a synergistic effect of dissociation equilibrium, effectively suppressing the hydrogen evolution reaction. This achieves dynamic and stable control of the electrolyte pH, suppresses the continuous occurrence of the hydrogen evolution side reaction at the negative electrode, and reduces the formation rate of zinc dendrites. The stability of the electrolyte interfacial chemical environment is improved, the zinc deposition process becomes more homogenized, and the battery cycle life is extended.

[0027] Furthermore, by controlling the molar ratio of the first and second negative electrode additives, sodium acetate and sodium citrate form a wide-range buffer system. Simultaneously, dicarboxylic acid molecules of different chain lengths exhibit a gradient coordination effect with zinc ions, achieving synergistic optimization of pH stability and dendrite suppression. This enables the electrolyte to maintain a stable pH environment during cycling, effectively suppressing hydrogen evolution side reactions. Through the directional adsorption of zinc ions by carboxylic acid molecules, the zinc deposition crystal orientation is altered, reducing sharp dendrite formation. Simultaneously, the electrolyte ionic conductivity remains unaffected by excessive additives, ultimately improving the cycle stability and lifespan of the zinc-bromine flow battery. It effectively slows down anisotropic growth during zinc deposition, promoting a more dense and uniform deposition of zinc metal on the electrode surface. The selective adsorption of dicarboxylic acid molecules on the zinc crystal face inhibits dendrite tip growth, reducing local current density on the electrode surface and thus extending battery cycle life. Medium-chain-length glutaric acid, by constructing a stable adsorption interface, gives the zinc deposition layer a smoother microstructure, improving electrode structural stability.

[0028] This invention also discloses a multifunctional electrolyte for zinc-bromine flow batteries prepared by the above-mentioned method. The introduction of iodine ions into the positive electrode electrolyte plays a dual role in the bromine reaction system: on the one hand, it acts as a redox mediator to lower the activation energy of the reaction and improve electrochemical kinetics; on the other hand, it competitively binds bromine molecules to reduce the concentration of free bromine, thereby inhibiting capacity decay caused by bromine permeation at its source. In the negative electrode electrolyte, the synergistic effect of sodium acetate and sodium citrate widens the pH buffer range and maintains the acid-base stability of the electrolyte. Meanwhile, carboxylic acid molecules in the second negative electrode additive adsorb onto specific sites on the zinc crystal surface, altering the zinc ion diffusion path and deposition orientation, promoting uniform planar deposition of zinc. The synergistic effect of the positive and negative electrode electrolyte components achieves the triple functions of blocking bromine permeation, stabilizing the pH environment, and inhibiting dendrite growth. This effectively reduces the probability of side reactions caused by bromine molecule permeation, inhibits hydrogen evolution side reactions caused by electrolyte pH fluctuations, and mitigates the damage of zinc dendrites to the battery structure, thereby significantly improving the battery's coulombic efficiency, cycle stability, and energy conversion efficiency.

[0029] Furthermore, the introduction of zinc iodide into the positive electrode electrolyte can form mixed halide ions with bromine, reducing the concentration of free bromine and thus inhibiting bromine permeation and side reactions, while improving the charge transfer rate. In the negative electrode electrolyte, sodium acetate and sodium citrate form a multiple buffer system, dynamically adjusting the electrolyte pH and inhibiting the hydrogen evolution reaction. Simultaneously, carboxylic acid molecules alter the deposition path of zinc ions through complexation, promoting uniform and dense zinc deposition. The positive electrode complexing agent enhances reaction kinetics by lowering the activation energy of the bromine reaction, while the adsorption of carboxylic acid molecules on the electrode surface slows down the normal growth of zinc crystals, inhibiting dendrite formation. Through the combination of positive and negative electrode additives, a synergistic effect is achieved in bromine inhibition, pH stability, and dendrite suppression, resolving the contradiction between efficiency improvement and cycle stability that cannot be simultaneously achieved with single-function additives. This results in a balanced optimization of the battery's overall electrochemical performance. The improvement in coulombic efficiency stems from the effective suppression of bromine permeation and side reactions; the improvement in energy efficiency is attributed to increased conductivity and reduced ohmic resistance; and the optimization of voltage efficiency is directly related to enhanced reaction kinetics and the regulation of the zinc deposition process. Meanwhile, through the synergistic effect of multiple buffer systems and crystallization regulation mechanisms, the cycle life of the battery was significantly extended and the operational stability was improved. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0032] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0033] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0034] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0035] In this invention, unless otherwise specified, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" indicates that all real numbers between "6~22" have been listed in this document, and "6~22" is simply a shortened representation of these numerical combinations.

[0036] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0037] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0038] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0039] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0040] Existing zinc-bromine flow battery electrolytes suffer from several problems: bromine permeation triggering side reactions, pH fluctuations leading to hydrogen evolution reactions, and zinc dendrite growth shortening cycle life. Traditional methods typically employ single-function additives, such as using complexing agents to inhibit bromine diffusion or acid regulators to stabilize pH, but these methods cannot simultaneously address the coupled issues of multiple factors. During electrolyte cycling, the permeation of free bromine can trigger self-discharge reactions, pH fluctuations accelerate electrode corrosion, and zinc dendrites piercing the separator can lead to battery failure. These problems severely restrict the reliability and lifespan of the battery.

[0041] To address the above problems, this invention provides a method for preparing a multifunctional electrolyte for zinc-bromine flow batteries, comprising:

[0042] 1) Positive electrode electrolyte preparation steps:

[0043] S1: Accurately weigh the required amounts of solvent, electrolyte, supporting electrolyte, positive electrode complexing agent, and positive electrode additive;

[0044] S2: Add the electrolyte to the solvent and stir until completely dissolved;

[0045] S3: Add the supporting electrolyte to the solution prepared in step S2 and stir until completely dissolved;

[0046] S4: Add the positive electrode complexing agent to the solution prepared in step S3 and stir until completely dissolved;

[0047] S5: Add the positive electrode additive to the solution prepared in step S4 and stir until completely dissolved;

[0048] S6: Adjust the volume to the required capacity.

[0049] In the preparation of the positive electrode electrolyte, iodide ions from zinc iodide preferentially combine with bromine to form complex ions, reducing the concentration of free bromine and minimizing bromine permeation at its source. Simultaneously, iodide ions adsorb onto the electrode surface, forming charge transport channels and increasing the interfacial reaction rate. In the negative electrode electrolyte, the acetate ions of sodium acetate and the citrate ions of sodium citrate form a multi-level buffer pair, which, through H+... + The release and absorption of these components dynamically regulate pH, inhibiting the hydrogen evolution reaction. The sodium ions from both sodium salts enhance electrolyte conductivity and optimize the zinc ion deposition environment. Stepwise addition ensures complete dissolution of each component, avoiding localized precipitation due to concentration gradients.

[0050] The electrolyte is a 2.0-2.5 mol / L zinc bromide solution. This satisfies the requirements for the electrochemical reaction of zinc ions while avoiding excessive solution viscosity that could hinder ion migration.

[0051] Supporting electrolytes include 2.0-3.0 mol / L potassium chloride. This improves conductivity while preventing excessive chloride ion concentration from destabilizing the bromide complex.

[0052] The positive electrode complexing agent includes 0.2-0.3 mol / L of 1-methyl-1-ethylpyrrolidine ammonium bromide. By forming a stable complex with bromine molecules through the quaternary ammonium cation, the diffusion and permeation of bromine are effectively inhibited.

[0053] The positive electrode additive includes 0.05-0.2 mol / L zinc iodide. Iodide ions, as a redox mediator, can lower the reaction energy barrier, while preventing excessive iodide ions from forming a dense adsorption layer on the electrode surface that hinders charge transfer.

[0054] The solvent is deionized water. Its low impurity characteristics avoid the introduction of interfering ions, ensuring the chemical stability of the electrolyte system. At the same time, its high dielectric constant promotes the complete dissociation of the electrolyte, forming a uniform ion transport network.

[0055] The above technical solution achieves synergistic optimization of electrolyte conductivity and bromine permeation suppression, effectively balancing charge transport efficiency and side reaction suppression requirements. The precise ratio of zinc bromide to potassium chloride ensures zinc ion migration rate and solution conductivity; the accurate addition of 1-methyl-1-ethylpyrrolidine ammonium bromide maintains the stable complexation state of bromine molecules; and the specific concentration range of zinc iodide reduces the activation energy of the reaction while preventing electrode passivation. The components, within their defined proportions, form a mutually restrictive relationship, optimizing the overall electrochemical performance of the electrolyte system.

[0056] 2) Negative electrode electrolyte preparation steps:

[0057] S1: Accurately weigh the required amounts of solvent, electrolyte, supporting electrolyte, first negative electrode additive, and second negative electrode additive;

[0058] S2: Add the electrolyte to the solvent and stir until completely dissolved;

[0059] S3: Add the supporting electrolyte to the solution prepared in step S2 and stir until completely dissolved;

[0060] S4: Add the first negative electrode additive to the solution prepared in step S3 and stir until completely dissolved;

[0061] S5: Add the second negative electrode additive to the solution prepared in step S4 and stir until completely dissolved;

[0062] S6: Adjust the volume to the required capacity.

[0063] The electrolyte is a 2.0-2.5 mol / L zinc bromide solution, which provides zinc ions and bromide ions as active substances.

[0064] The supporting electrolyte includes 2.0-3.0 mol / L potassium chloride, which is used to improve the ionic conductivity of the electrolyte.

[0065] The first negative electrode additive comprises 0.1-0.2 mol / L sodium acetate and 0.1-0.2 mol / L sodium citrate, forming a multi-level anion buffer system. The monocarboxylate ions of sodium acetate and the tricarboxylate ions of sodium citrate form a complementary buffer system, covering a pH adjustment range from weakly acidic to neutral. During charge and discharge, the carboxylate ions of both buffers dynamically capture locally generated hydrogen ions, suppressing drastic fluctuations in hydrogen ion concentration. This range ensures that the concentrations of the two buffers are within the synergistic effect range, avoiding both increased ion migration resistance due to excessively high concentrations in a single buffer system and insufficient buffer capacity due to excessively low concentrations.

[0066] The second negative electrode additive includes 0.05-0.2 mol / L of oxalic acid, malonic acid, succinic acid, glutaric acid, or adipic acid, which coordinate with zinc ions. When dicarboxylic acid compounds are introduced into the electrolyte, their carboxylic acid anions form complexes with zinc ions, altering the solvation structure of zinc ions at the electrode interface. Dicarboxylic acids with different carbon chain lengths exhibit differentiated adsorption on the electrode surface through their carboxyl groups. Glutaric acid, in particular, exhibits a planar adsorption configuration on specific crystal orientations of the zinc crystal face. This adsorption restricts the diffusion rate of zinc ions on the normal crystal face, promoting uniform deposition of zinc ions on parallel crystal faces. The carbon-oxygen double bond structure enhances the binding strength between the molecule and the electrode surface, replacing water molecules in the zinc ion solvation sheath and inhibiting sharp dendrite growth.

[0067] The solvent is deionized water.

[0068] The present invention also discloses a multifunctional electrolyte for zinc-bromine flow batteries prepared by the above preparation method, comprising: a positive electrode electrolyte and a negative electrode electrolyte; the positive electrode electrolyte comprises: an electrolyte, a supporting electrolyte, a positive electrode complexing agent, a positive electrode additive, and a solvent; the negative electrode electrolyte comprises: an electrolyte, a supporting electrolyte, a first negative electrode additive, a second negative electrode additive, and a solvent.

[0069] This invention adds zinc iodide as a positive electrode additive to the positive electrode electrolyte, which can reduce the bromine permeation source and bromine reaction activation energy, improve the overall conductivity and comprehensive electrochemical performance of the electrolyte, including coulombic efficiency, voltage efficiency, and energy efficiency, and further reduce the ohmic internal resistance of the battery. Sodium acetate and sodium citrate are added as the first negative electrode additives to the negative electrode electrolyte, forming multiple acid anion buffer pairs, which can dynamically adjust and stabilize the pH value of the electrolyte, further improving the long-term stability of the battery and extending its cycle life. In the second negative electrode additive, glutaric acid exhibits a planar adsorption configuration on the Zn(002) crystal surface, restricting Zn... 2+ Diffusion towards this crystal plane slows down the normal growth rate of the Zn crystal plane, reduces the formation of sharp dendrites, and significantly improves the stability and cycle life of the zinc-bromine flow battery.

[0070] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0071] Example 1

[0072] A method for preparing a multifunctional electrolyte for zinc-bromine flow batteries, comprising:

[0073] Preparation of positive electrode electrolyte:

[0074] S1: Accurately weigh 45.04g zinc bromide (2.0mol / L), 22.37g potassium chloride (3.0mol / L), 5.82g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.3mol / L) and 3.19g zinc iodide (0.1mol / L).

[0075] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0076] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0077] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0078] S5: Add zinc iodide to the solution prepared in S4 and stir until completely dissolved;

[0079] S6: Adjust the volume to 100ml.

[0080] Preparation of negative electrode electrolyte:

[0081] S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.9g potassium chloride (3mol / L), 1.64g sodium acetate (0.2mol / L) and 2.58g sodium citrate (0.1mol / L).

[0082] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0083] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0084] S4: Add sodium acetate and sodium citrate to the solution prepared in step S3 and stir until completely dissolved;

[0085] S5: Adjust the volume to 100ml.

[0086] Example 2

[0087] A method for preparing a multifunctional electrolyte for zinc-bromine flow batteries, comprising:

[0088] Preparation of positive electrode electrolyte:

[0089] S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L), 5.82g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.3mol / L) and 3.19g zinc iodide (0.1mol / L).

[0090] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0091] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0092] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0093] S5: Add zinc iodide to the solution prepared in S4 and stir until completely dissolved;

[0094] S6: Adjust the volume to 100ml.

[0095] Preparation of negative electrode electrolyte:

[0096] S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.9g potassium chloride (3mol / L), 0.82g sodium acetate (0.1mol / L) and 5.16g sodium citrate (0.2mol / L).

[0097] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0098] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0099] S4: Add sodium acetate and sodium citrate to the solution prepared in step S3 and stir until completely dissolved;

[0100] S5: Adjust the volume to 100ml.

[0101] Example 3

[0102] A method for preparing a multifunctional electrolyte for zinc-bromine flow batteries, comprising:

[0103] Preparation of positive electrode electrolyte:

[0104] S1: Accurately weigh 56.30g zinc bromide (2.5mol / L), 22.37g potassium chloride (3.0mol / L), 5.82g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.3mol / L) and 3.19g zinc iodide (0.1mol / L).

[0105] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0106] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0107] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0108] S5: Add zinc iodide to the solution prepared in S4 and stir until completely dissolved;

[0109] S6: Adjust the volume to 100ml.

[0110] Preparation of negative electrode electrolyte:

[0111] S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.9g potassium chloride (3mol / L), 1.64g sodium acetate (0.2mol / L), 2.58g sodium citrate (0.1mol / L) and 0.90g oxalic acid (0.1mol / L).

[0112] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0113] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0114] S4: Add sodium acetate and sodium citrate to the solution prepared in S3 and stir until completely dissolved;

[0115] S5: Add oxalic acid to the solution prepared in S4 and stir until completely dissolved;

[0116] S6: Adjust the volume to 100ml.

[0117] Example 4

[0118] A method for preparing a multifunctional electrolyte for zinc-bromine flow batteries, comprising:

[0119] Preparation of positive electrode electrolyte:

[0120] S1: Accurately weigh 45.04g zinc bromide (2.0mol / L), 7.46g potassium chloride (1.0mol / L), 5.82g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.3mol / L) and 3.19g zinc iodide (0.1mol / L).

[0121] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0122] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0123] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0124] S5: Add zinc iodide to the solution prepared in S4 and stir until completely dissolved;

[0125] S6: Adjust the volume to 100ml.

[0126] Preparation of negative electrode electrolyte:

[0127] S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.9g potassium chloride (3mol / L), 1.64g sodium acetate (0.2mol / L), 2.58g sodium citrate (0.1mol / L) and 1.04g malonic acid (0.1mol / L).

[0128] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0129] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0130] S4: Add sodium acetate and sodium citrate to the solution prepared in step S3 and stir until completely dissolved;

[0131] S5: Add malonic acid to the solution prepared in S4 and stir until completely dissolved;

[0132] S6: Adjust the volume to 100ml.

[0133] Example 5

[0134] A method for preparing a zinc-bromine flow battery electrolyte, comprising:

[0135] Preparation of positive electrode electrolyte:

[0136] S1: Accurately weigh 45.04g zinc bromide (2.0mol / L), 14.91g potassium chloride (2.0mol / L), 5.82g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.3mol / L) and 3.19g zinc iodide (0.1mol / L).

[0137] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0138] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0139] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0140] S5: Add zinc iodide to the solution prepared in S4 and stir until completely dissolved;

[0141] S6: Adjust the volume to 100ml.

[0142] Preparation of negative electrode electrolyte:

[0143] S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.9g potassium chloride (3mol / L), 1.64g sodium acetate (0.2mol / L), 2.58g sodium citrate (0.1mol / L) and 1.18g succinic acid (0.1mol / L).

[0144] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0145] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0146] S4: Add sodium acetate and sodium citrate to the solution prepared in step S3 and stir until completely dissolved;

[0147] S5: Add succinic acid to the solution prepared in S4 and stir until completely dissolved;

[0148] S6: Adjust the volume to 100ml.

[0149] Example 6

[0150] A method for preparing a multifunctional electrolyte for zinc-bromine flow batteries, comprising:

[0151] Preparation of positive electrode electrolyte:

[0152] S1: Accurately weigh 45.04g zinc bromide (2.0mol / L), 22.37g potassium chloride (3.0mol / L), 3.88g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.2mol / L) and 3.19g zinc iodide (0.1mol / L).

[0153] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0154] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0155] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0156] S5: Add zinc iodide to the solution prepared in S4 and stir until completely dissolved;

[0157] S6: Adjust the volume to 100ml.

[0158] Preparation of negative electrode electrolyte:

[0159] S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.9g potassium chloride (3mol / L), 1.64g sodium acetate (0.2mol / L), 2.58g sodium citrate (0.1mol / L) and 1.32g glutaric acid (0.1mol / L).

[0160] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0161] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0162] S4: Add sodium acetate and sodium citrate to the solution prepared in step S3 and stir until completely dissolved;

[0163] S5: Add glutaric acid to the solution prepared in S4 and stir until completely dissolved;

[0164] S6: Adjust the volume to 100ml.

[0165] Example 7

[0166] A method for preparing a multifunctional electrolyte for zinc-bromine flow batteries, comprising:

[0167] Preparation of positive electrode electrolyte:

[0168] S1: Accurately weigh 45.04g zinc bromide (2.0mol / L), 22.37g potassium chloride (3.0mol / L), 5.82g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.3mol / L) and 1.60g zinc iodide (0.05mol / L).

[0169] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0170] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0171] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0172] S5: Add zinc iodide to the solution prepared in S4 and stir until completely dissolved;

[0173] S6: Adjust the volume to 100ml.

[0174] Preparation of negative electrode electrolyte:

[0175] S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.9g potassium chloride (3mol / L), 1.64g sodium acetate (0.2mol / L), 2.58g sodium citrate (0.1mol / L) and 1.46g adipic acid (0.1mol / L).

[0176] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0177] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0178] S4: Add sodium acetate and sodium citrate to the solution prepared in step S3 and stir until completely dissolved;

[0179] S5: Add adipic acid to the solution prepared in S4 and stir until completely dissolved;

[0180] S6: Adjust the volume to 100ml.

[0181] Example 8

[0182] A method for preparing a multifunctional electrolyte for zinc-bromine flow batteries, comprising:

[0183] Preparation of positive electrode electrolyte:

[0184] S1: Accurately weigh 45.04g zinc bromide (2.0mol / L), 22.37g potassium chloride (3.0mol / L), 5.82g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.3mol / L) and 4.79g zinc iodide (0.15mol / L).

[0185] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0186] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0187] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0188] S5: Add zinc iodide to the solution prepared in S4 and stir until completely dissolved;

[0189] S6: Adjust the volume to 100ml.

[0190] Preparation of negative electrode electrolyte:

[0191] S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.9g potassium chloride (3mol / L), 1.64g sodium acetate (0.2mol / L), 2.58g sodium citrate (0.1mol / L) and 0.66g glutaric acid (0.05mol / L).

[0192] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0193] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0194] S4: Add sodium acetate and sodium citrate to the solution prepared in step S3 and stir until completely dissolved;

[0195] S5: Add glutaric acid to the solution prepared in S4 and stir until completely dissolved;

[0196] S6: Adjust the volume to 100ml.

[0197] Example 9

[0198] A method for preparing a multifunctional electrolyte for zinc-bromine flow batteries, comprising:

[0199] Preparation of positive electrode electrolyte:

[0200] S1: Accurately weigh 45.04g zinc bromide (2.0mol / L), 22.37g potassium chloride (3.0mol / L), 5.82g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.3mol / L) and 6.38g zinc iodide (0.20mol / L).

[0201] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0202] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0203] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0204] S5: Add zinc iodide to the solution prepared in S4 and stir until completely dissolved;

[0205] S6: Adjust the volume to 100ml.

[0206] Preparation of negative electrode electrolyte:

[0207] S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.9g potassium chloride (3mol / L), 1.64g sodium acetate (0.2mol / L), 2.58g sodium citrate (0.1mol / L) and 1.98g glutaric acid (0.15mol / L).

[0208] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0209] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0210] S4: Add sodium acetate and sodium citrate to the solution prepared in step S3 and stir until completely dissolved;

[0211] S5: Add glutaric acid to the solution prepared in S4 and stir until completely dissolved;

[0212] S6: Adjust the volume to 100ml.

[0213] Example 10

[0214] A method for preparing a multifunctional electrolyte for zinc-bromine flow batteries, comprising:

[0215] Preparation of positive electrode electrolyte:

[0216] S1: Accurately weigh 45.04g zinc bromide (2.0mol / L), 22.37g potassium chloride (3.0mol / L), 5.82g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.3mol / L) and 7.98g zinc iodide (0.25mol / L);

[0217] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0218] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0219] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0220] S5: Add zinc iodide to the solution prepared in S4 and stir until completely dissolved;

[0221] S6: Adjust the volume to 100ml.

[0222] Preparation of negative electrode electrolyte:

[0223] S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.9g potassium chloride (3mol / L), 1.64g sodium acetate (0.2mol / L), 2.58g sodium citrate (0.1mol / L) and 2.64g glutaric acid (0.20mol / L).

[0224] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0225] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0226] S4: Add sodium acetate and sodium citrate to the solution prepared in step S3 and stir until completely dissolved;

[0227] S5: Add glutaric acid to the solution prepared in S4 and stir until completely dissolved;

[0228] S6: Adjust the volume to 100ml.

[0229] Comparative Example 1

[0230] A method for preparing a zinc-bromine flow battery electrolyte, comprising:

[0231] Preparation of positive electrode electrolyte:

[0232] S1: Accurately weigh 45.04g zinc bromide (2.0mol / L), 22.37g potassium chloride (3.0mol / L) and 5.82g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.3mol / L).

[0233] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0234] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0235] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0236] S5: Adjust the volume to 100ml.

[0237] Preparation of negative electrode electrolyte:

[0238] S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.9g potassium chloride (3mol / L) and 2.46g sodium acetate (0.3mol / L).

[0239] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0240] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0241] S4: Add sodium acetate to the solution prepared in step S3 and stir until completely dissolved;

[0242] S5: Adjust the volume to 100ml.

[0243] Comparative Example 2

[0244] A method for preparing a zinc-bromine flow battery electrolyte, comprising:

[0245] Preparation of positive electrode electrolyte:

[0246] S1: Accurately weigh 49.54g zinc bromide (2.2mol / L), 22.37g potassium chloride (3.0mol / L) and 5.82g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.3mol / L).

[0247] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0248] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0249] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0250] S5: Adjust the volume to 100ml.

[0251] Preparation of negative electrode electrolyte:

[0252] S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.9g potassium chloride (3mol / L) and 7.74g sodium citrate (0.3mol / L).

[0253] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0254] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0255] S4: Add sodium citrate to the solution prepared in step S3 and stir until completely dissolved;

[0256] S5: Adjust the volume to 100ml.

[0257] Comparative Example 3

[0258] A method for preparing a zinc-bromine flow battery electrolyte, comprising:

[0259] Preparation of positive electrode electrolyte:

[0260] S1: Accurately weigh 56.30g zinc bromide (2.5mol / L), 22.37g potassium chloride (3.0mol / L) and 5.82g 1-methyl-1-ethylpyrrolidine ammonium bromide (0.3mol / L).

[0261] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0262] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0263] S4: Add 1-methyl-1-ethylpyrrolidine ammonium bromide to the solution prepared in S3 and stir until completely dissolved;

[0264] S5: Adjust the volume to 100ml.

[0265] Preparation of negative electrode electrolyte:

[0266] S1: Accurately weigh 56.30g zinc bromide (2.2mol / L), 14.9g potassium chloride (3mol / L), 1.64g sodium acetate (0.2mol / L) and 2.58g sodium citrate (0.1mol / L).

[0267] S2: Add zinc bromide to deionized water and stir until completely dissolved;

[0268] S3: Add potassium chloride to the solution prepared in S2 and stir until completely dissolved;

[0269] S4: Add sodium acetate and sodium citrate to the solution prepared in step S3 and stir until completely dissolved;

[0270] S5: Adjust the volume to 100ml.

[0271] The zinc-bromine flow battery electrolytes prepared in Examples 1-10 and Comparative Examples 1-3 were used to test the performance of zinc-bromine flow batteries using single cells. The experimental conditions were as follows: the electrode was a commercial carbon-plastic bipolar plate with an electrode area of ​​9 cm². 2 The diaphragm is a microporous polyolefin diaphragm with a charge / discharge current density of 20 mA / cm². 2 The charging time was 1 hour, the discharge cutoff voltage was 0.5V, and the positive and negative electrolytes were 50mL. The test performance of each group of batteries in the examples and comparative examples was tested under the same conditions. The test results are shown in Table 2.

[0272] Table 1 Comparison of key components and dosages in Examples 1-10 and Comparative Examples 1-3

[0273]

[0274] Table 2. Comparison of performance test results of zinc-bromine flow batteries prepared with the multifunctional electrolytes for zinc-bromine flow batteries disclosed in Examples 1-10 and the electrolytes for zinc-bromine flow batteries disclosed in Comparative Examples 1-3.

[0275]

[0276] Table 1 compares the key components and dosages in Examples 1-10 and Comparative Examples 1-3; Table 2 compares the test results of zinc-bromine flow batteries prepared with the multifunctional electrolyte for zinc-bromine flow batteries disclosed in Examples 1-10 and the electrolyte for zinc-bromine flow batteries disclosed in Comparative Examples 1-3. As shown in the tables, the coulombic efficiency of the zinc-bromine flow battery prepared with the multifunctional electrolyte for zinc-bromine flow batteries disclosed in this invention is 92.1%-96.2%; the energy efficiency is 77.18%-83.50%; and the voltage efficiency is 83.8%-86.8%. By adding zinc iodide as a positive electrode additive, the permeation source of bromine is reduced at its source, thereby achieving bromine inhibition, reducing side reactions, accelerating bromine reaction kinetics, and improving coulombic efficiency. The addition of sodium acetate, sodium citrate, and dicarboxylic acid molecules with different alkyl chain lengths as negative electrode additives can significantly inhibit the growth of zinc dendrites, adjust the electrolyte pH, inhibit hydrogen evolution reaction, and improve the coulombic efficiency, voltage efficiency, energy efficiency, and cycle stability of the zinc-bromine flow battery.

[0277] In summary, this invention provides a multifunctional electrolyte for zinc-bromine flow batteries and its preparation method, by introducing zinc iodide as a positive electrode additive. In Br2 / Br - In the reaction system, I - It can act as a redox mediator, significantly reducing the activation energy of the reaction and improving the battery's charge and discharge efficiency. -It can form mixed halide ions with Br2, competitively reducing the concentration of free Br2, thereby reducing the bromine permeation source from the root, achieving bromine inhibition, reducing side reactions, improving coulombic efficiency, and significantly reducing capacity loss. - Adsorption on the carbon electrode surface alters the double-layer structure and enhances the charge transfer rate at the electrode / electrolyte interface, significantly improving the overall conductivity of the electrolyte. This reduces the battery's ohmic internal resistance and increases voltage efficiency, energy efficiency, and power density. Introducing sodium acetate as a negative electrode additive dynamically adjusts and stabilizes the electrolyte's pH, maintaining it within an optimal range that inhibits hydrogen evolution reaction. pH stability is a key factor in improving the battery's long-term cycle stability. Furthermore, introducing sodium citrate on top of sodium acetate as a negative electrode additive expands the pH buffer range, further enhancing the battery's long-term stability and extending cycle life. The carboxylic acid anions in dicarboxylic acid molecules with different alkyl chain lengths can react with Zn... 2+ The Zn atoms coordinate with each other, forming complexes or more complex forms. This complexation alters the Zn atoms' composition. 2+ The reduction potential and charge transfer rate of ions at the electrode / solution interface affect the diffusion and deposition process of zinc ions. The formed complexes preferentially adsorb onto specific active sites on the electrode surface, altering the crystallization habit of zinc, promoting more uniform and dense zinc deposition, reducing the formation of sharp dendrites, and improving the stability and cycle life of the electrode. Dicarboxylic acid molecules with different alkyl chain lengths contain both carboxyl groups and carbon-oxygen double bonds. The double bonds can enhance the adsorption stability of the molecule on the electrode surface. The carboxyl group is conducive to compatibility with the electrolyte, replacing water molecules in the zinc ion solvation sheath, changing the solvation structure, and can specifically induce Zn planar growth, improving the reliability and specificity of inhibiting zinc dendrites. Glutaric acid molecules with medium alkyl chain lengths have the lowest adsorption energy on the Zn crystal surface. Therefore, glutaric acid exhibits a planar adsorption configuration on the Zn(002) crystal surface, resulting in strong adsorption and a Zn-GA metal-molecular bridging interface, thus limiting Zn adsorption. 2+ Diffusion towards this crystal plane slows down the normal growth rate of the Zn crystal plane, reduces the formation of sharp dendrites, and improves the stability and cycle life of the battery.

[0278] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of preparing a multifunctional electrolyte for a zinc-bromine flow battery, characterized in that, The application relates to a zinc-bromine flow battery multifunctional electrolyte, which comprises a positive electrolyte and a negative electrolyte. The electrolyte is dissolved in a solvent, and a supporting electrolyte, a positive electrode complexing agent and a positive electrode additive are sequentially added to obtain a positive electrode electrolyte; the positive electrode additive is zinc iodide; the electrolyte is a zinc bromide solution; the supporting electrolyte is potassium chloride; I - and Br2 / Br - The Br2 in the reaction system forms mixed halogen ions to achieve the function of blocking bromine; in the positive electrode electrolyte, the molar ratio of the electrolyte, the supporting electrolyte, the positive electrode complexing agent and the positive electrode additive is (2.0-2.5):(2.0-3.0):(0.2-0.3):(0.05-0.2); The electrolyte is dissolved in a solvent, a supporting electrolyte and a first negative electrode additive are sequentially added to obtain a negative electrode electrolyte; the first negative electrode additive comprises sodium acetate and sodium citrate; the sodium acetate and the sodium citrate form a wide-range buffer system in combination; in the negative electrode electrolyte, the molar ratio of the electrolyte, the supporting electrolyte and the first negative electrode additive is (2.0-2.5):(2.0-3.0):(0.2-0.4); the molar ratio of the sodium acetate to the sodium citrate is (0.1-0.2):(0.1-0.2); the negative electrode electrolyte further comprises a second negative electrode additive; the second negative electrode additive comprises oxalic acid, malonic acid, succinic acid, glutaric acid or adipic acid. The positive electrolyte and the negative electrolyte constitute the zinc-bromine flow battery multifunctional electrolyte; the zinc deposition behavior is synergistically controlled through sodium salt buffering and ion coordination.

2. The method of claim 1, wherein the zinc-bromine flow battery multi-functional electrolyte is prepared by the steps of: The solvent is deionized water.

3. The method of claim 1, wherein the zinc-bromine flow battery multi-functional electrolyte is prepared by the steps of: The positive complexing agent is 1-methyl-1-ethylpyrrolidinium bromide.

4. The method of claim 1, wherein the zinc-bromine flow battery multi-functional electrolyte is prepared by the steps of: The molar ratio of the first negative electrode additive to the second negative electrode additive is (0.2-0.4):(0.05-0.2).

5. A zinc-bromine flow battery multi-functional electrolyte, characterized in that, The zinc-bromine flow battery multifunctional electrolyte is prepared by the preparation method of the zinc-bromine flow battery multifunctional electrolyte in any one of claims 1-4, and the zinc-bromine flow battery multifunctional electrolyte comprises a positive electrolyte and a negative electrolyte; the positive electrolyte comprises an electrolyte, a supporting electrolyte, a positive complexing agent, a positive electrode additive and a solvent; and the negative electrolyte comprises an electrolyte, a supporting electrolyte, a first negative electrode additive and a solvent.

6. The zinc-bromine flow battery multi-functional electrolyte of claim 5, wherein, The zinc-bromine flow battery prepared from the zinc-bromine flow battery multifunctional electrolyte has a coulombic efficiency of 92.1%-96.2%, an energy efficiency of 77.18%-83.50% and a voltage efficiency of 83.8%-86.8%.

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