A zinc-bromine flow battery electrolyte and battery containing a polyoxyethylene additive

Abstract

This invention discloses a zinc-bromine flow battery electrolyte and battery containing polyoxyethylene additives. The electrolyte includes a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode electrolyte includes a solvent, an electrolyte, a supporting electrolyte, polyoxyethylene additives, and a complexing agent. The negative electrode electrolyte includes a solvent, an electrolyte, a supporting electrolyte, polymeric acid additives, and a complexing agent. In this invention, polyoxyethylene additive molecules can adsorb at the interface between the oil phase and the aqueous phase, reducing interfacial tension, promoting oil-water emulsification, forming uniformly dispersed fine oil droplets, increasing the contact area between the polybrominated complex and the positive electrode, and reducing mass transfer resistance. During discharge, the polyoxyethylene additives on the surface of the oil droplets facilitate the dissociation of the polybrominated complex and the release of bromine, improving the discharge voltage and voltage efficiency. Furthermore, it promotes the renewal of the reaction interface, significantly increasing the dissociation rate of polybrominated compounds and the reduction rate of bromine during discharge, thereby improving voltage efficiency and coulombic efficiency. The zinc-bromine flow battery prepared with the zinc-bromine flow electrolyte of this invention has a coulombic efficiency of 93%-96.7%, a voltage efficiency of 80.8%-85.5%, and an energy efficiency of 76.19%-82.39%.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a zinc-bromine flow battery electrolyte and battery containing polyoxyethylene additives. Background Technology

[0002] With the rapid development of renewable energy, large-scale energy storage technology has become key to solving the intermittency and volatility issues of new energy power generation. Flow batteries, as an important electrochemical energy storage technology, have shown broad application prospects in the field of grid energy storage due to their advantages such as high safety, long lifespan, and independent power and energy design.

[0003] Since its introduction in the 1970s, the zinc-bromine flow battery has become one of the most promising flow battery technologies for industrialization due to its advantages such as high energy density (up to 70 Wh / L or more), low cost (the main active material, zinc bromide, is abundant and inexpensive), and good safety (operating at room temperature and without highly toxic substances).

[0004] However, zinc-bromine flow batteries still face two major technological bottlenecks in their commercial application, which severely restrict the improvement of their energy efficiency and cycle life: (1) Issues related to bromine at the positive electrode Bromine and its polybrominates are highly volatile and corrosive. In aqueous solutions, they readily form volatile Br2, which diffuses through the separator via the concentration gradient to the negative electrode, where it undergoes a self-discharge reaction (Zn + Br2 → ZnBr2), severely reducing the battery's coulombic efficiency. Simultaneously, the toxicity of free bromine poses a threat to the safety of the battery system. To address these issues, current technologies primarily involve adding bromine complexing agents to the electrolyte, such as N-ethyl-N-methylpyrrolidine bromide (MEP), 4-ethyl-4-methylmorpholine bromide (MEM), and 1-ethyl-3-methylimidazolium bromide (EMI). This allows bromine to form oil-phase complexed bromine, thereby reducing its activity and volatility. As the charging process progresses, the oil-phase complexed bromine gradually increases in size and aggregates, eventually adhering to the electrode surface, separator surface, or depositing at the bottom of the storage tank. When complexed bromine covers the electrode surface, it increases the mass transfer resistance of the electrochemical reaction and reduces the effective reaction area of ​​the electrode. When complexed bromine adheres to the membrane surface, it blocks the ion channels and increases the internal resistance. At the same time, because the generated complexed bromine is hydrophobic, polybrominates have difficulty migrating back to the aqueous phase and being reduced to bromide ions during discharge, resulting in a decrease in discharge voltage.

[0005] (2) Issues related to zinc deposition on negative electrodes The negative electrode of a zinc-bromine flow battery involves the electrodeposition / dissolution reaction of zinc. During charging, Zn... 2+The zinc is reduced to metallic zinc and deposited on the negative electrode substrate. However, the zinc deposition process involves two major side reactions: zinc branching growth and hydrogen evolution, which seriously affect the cycle performance and safety of the battery.

[0006] The reduction deposition of zinc ions on the electrode surface is a non-uniform process. This is due to differences in the electrode surface microstructure, non-uniform current distribution, and the presence of Zn. 2+ Due to concentration polarization, zinc preferentially deposits at certain active sites and gradually forms dendrites. As cycling continues, the dendrites grow and may puncture the diaphragm, causing a short circuit between the positive and negative electrodes; they may also detach from the electrode surface, forming "dead zinc," reducing the utilization rate of the active material; and they may increase the electrode specific surface area, exacerbating side reactions.

[0007] Due to the large kinetic overpotential of zinc deposition, under actual operating conditions, the hydrogen evolution reaction often competes with zinc deposition for electrons, leading to a decrease in coulombic efficiency. Water in the electrolyte is consumed, altering the electrolyte concentration and pH. The accumulation of hydrogen gas generated by hydrogen evolution may pose an explosion risk. Bubbles on the electrode surface hinder uniform zinc deposition and exacerbate dendrite formation. The occurrence of the hydrogen evolution reaction is closely related to the solvation structure of zinc ions. In traditional aqueous electrolytes, Zn... 2+ Mainly composed of [Zn(H2O)6] 2+ In this form, the H2O bonds in the coordinated water molecule are polarized and weakened, making them prone to breaking and releasing protons during electrochemical reactions, thus promoting the hydrogen evolution reaction.

[0008] Currently commonly used techniques include: 1. Adding inorganic inhibitors (such as Sn) to the negative electrode. 2+ Pb 2+ In 3+ 1. Metal ions (such as PEG and amines) can inhibit the hydrogen evolution reaction at the negative electrode, but single-function additives may interact with the complexing agent at the positive electrode, resulting in limited effectiveness; 2. Organic additives (such as PEG and amines) can promote the uniform deposition of zinc, but metal ions may participate in the positive electrode reaction, affecting the electrochemical performance of bromine, and some metal ions are toxic; 3. A high-concentration electrolyte strategy can inhibit the hydrolysis reaction by increasing the electrolyte concentration, but this may increase the viscosity of the electrolyte, reduce the ionic conductivity, and affect mass transfer.

[0009] Therefore, developing a systematic approach that can simultaneously improve the reversibility of the bromine reaction at the positive electrode and the uniformity of zinc deposition at the negative electrode is of great significance for enhancing the overall performance of zinc-bromine flow batteries. Summary of the Invention

[0010] The purpose of this invention is to provide a zinc-bromine flow battery electrolyte and battery containing polyoxyethylene additives, in order to solve the problems of positive electrode bromine management and negative electrode zinc dendrite / hydrogen evolution in the prior art, and to achieve a synergistic improvement in the coulombic efficiency and voltage efficiency of zinc-bromine flow batteries.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: A zinc-bromine flow battery electrolyte containing polyoxyethylene additives includes a positive electrode electrolyte and a negative electrode electrolyte; The positive electrode electrolyte includes a solvent, an electrolyte, a supporting electrolyte, polyoxyethylene additives, and a complexing agent; The negative electrode electrolyte includes a solvent, an electrolyte, a supporting electrolyte, polymeric acid additives, and a complexing agent.

[0012] Furthermore, the electrolyte in both the positive and negative electrode electrolytes is zinc bromide, and the concentration of the electrolyte in both the positive and negative electrode electrolytes is 1.5–2.5 mol / L.

[0013] Furthermore, the solvent for both the positive and negative electrode electrolytes is water; the supporting electrolyte for both the positive and negative electrode electrolytes is one or more of potassium chloride, sodium chloride, methanesulfonic acid, and ammonium chloride, and the concentration of the electrolyte in the positive electrode electrolyte and the concentration of the supporting electrolyte in the negative electrode electrolyte are 1–3 mol / L.

[0014] Furthermore, the complexing agent in the positive and negative electrolytes is one of N-ethyl-N-methylpyrrolidine bromide, 4-ethyl-4-methylmorpholine bromide, and 1-ethyl-3-methylimidazolium bromide, and the concentration of the complexing agent in the positive and negative electrolytes is 0.2–1 mol / L.

[0015] Furthermore, the concentration of polyoxyethylene additives in the positive electrode electrolyte is 0.1–1 g / L.

[0016] Furthermore, the polyoxyethylene additive is one of Tween-20, Tween-40, lauryl alcohol polyoxyethylene ether-23, and hexaethylene glycol monododecyl ether.

[0017] Furthermore, the polymeric acid additive is polyethylene glycol diacid.

[0018] Furthermore, the molecular weight of polyethylene glycol diacid is 200–2000.

[0019] Furthermore, the concentration of polymeric acid additives in the negative electrode electrolyte is 0.5–5 g / L.

[0020] A zinc-bromine flow battery includes a positive electrode, a negative electrode, an ion exchange membrane, and a zinc-bromine flow battery electrolyte containing polyoxyethylene additives.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The polyoxyethylene additive used in this invention is a nonionic surfactant. Its molecular structure contains a hydrophilic ether group (COC) and a hydrophobic alkyl segment. In the electrolyte of a zinc-bromine flow battery, the polyoxyethylene additive can adsorb onto the interface between the oil phase (polybrominated complex) and the aqueous phase, reducing interfacial tension, promoting oil-water emulsification, forming uniformly dispersed fine oil droplets, increasing the contact area between the polybrominated complex and the positive electrode, and reducing mass transfer resistance. During discharge, the polyoxyethylene layer on the surface of the oil droplets facilitates the dissociation of the polybrominated complex and the release of bromine, improving discharge voltage and voltage efficiency. Simultaneously, it improves electrode surface wettability, promotes reaction interface renewal, and significantly increases the dissociation rate of polybrominated compounds and the reduction rate of bromine during discharge, thereby improving voltage efficiency and coulombic efficiency.

[0022] Furthermore, the polyethylene glycol diacid used as the polymeric acid additive in this invention is a polymeric acid electrolyte with two different types of oxygen atoms: ether oxygen and carboxyl oxygen. The ether oxygen has a strong electron-donating ability and can participate in Zn... 2+ The solvation process of Zn in the electrolyte. 2+ Instead of coordinating solely with water molecules, it forms coordination bonds with the ether oxygen groups of polyethylene glycol diacid, resulting in a mixed solvation structure [Zn(H2O)]. x (eth-O) ] 2+ This change in coordination structure has the following effects: ① It breaks the hydrogen bond network: the ether oxygen group inserts into Zn. 2+ The hydration layer disrupts the original tight hydrogen bond network structure, reducing the water molecule concentration in Zn. 2+ ① The surrounding orientation is ordered; ② The activity of water molecules is reduced: the number of replaced water molecules decreases, and the proportion of free water in the solution is relatively reduced; ③ The HER is inhibited: due to the interaction with Zn 2+ With fewer coordinated water molecules, the probability of water decomposition to produce hydrogen is reduced, the hydrogen evolution reaction is effectively suppressed, the utilization rate of active materials is improved, and the coulombic efficiency of the flow battery is increased. Carboxyl groups (-COOH) have strong adsorption capacity. During electrodeposition, carboxyl oxygen preferentially adsorbs on the zinc electrode surface, especially on the (002) crystal plane of zinc, guiding Zn... 2+ Epitaxial growth along the (002) crystal plane achieves uniform and smooth zinc deposition. At the same time, since zinc grows oriented along the close-packed plane, it is not easy to form sharp dendritic structures, thus preventing diaphragm puncture.

[0023] Furthermore, in this invention, the complexing agent complexes free bromine into hydrophobic polybrominates, polyoxyethylene additives promote effective contact and reversible reaction between the composite and the electrode, and polyethylene glycol diacid regulates zinc deposition. The three work together to improve the performance of the zinc-bromine flow battery. Detailed Implementation

[0024] To facilitate understanding of the present invention, a more comprehensive description will be provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0025] This invention provides a zinc-bromine flow battery electrolyte containing polyoxyethylene additives, comprising: a positive electrode electrolyte and a negative electrode electrolyte; The positive electrode electrolyte includes: solvent, electrolyte, supporting electrolyte, polyoxyethylene additives, and complexing agent; The negative electrode electrolyte includes: solvent, electrolyte, supporting electrolyte, polymeric acid additives, and complexing agent; This invention also provides a method for preparing a zinc-bromine flow battery electrolyte containing polyoxyethylene additives, comprising the following steps: Positive electrode electrolyte preparation steps: S1: Accurately weigh the required amounts of solvent (deionized water), electrolyte, supporting electrolyte, polyoxyethylene additives and complexing agent; S2: Add the electrolyte to the solvent deionized water and stir until completely dissolved; S3: Add the supporting electrolyte to the solution prepared in step S2 and stir until completely dissolved; S4: Add the polyoxyethylene additive to the solution prepared in step S3 and stir until completely dissolved; S5: Use deionized water to bring the volume to the required level.

[0026] Negative electrode electrolyte preparation steps: S1: Accurately weigh the required amounts of solvent, electrolyte, supporting electrolyte, polymeric acid additives, and complexing agent; S2: Add the electrolyte to the solvent deionized water and stir until completely dissolved; S3: Add the supporting electrolyte to the solution prepared in step S2 and stir until completely dissolved; S4: Add the polymeric acid additive to the solution prepared in step S3 and stir until completely dissolved; S5: Use deionized water to bring the volume to the required level.

[0027] Preferably, the electrolyte used to prepare the positive and negative electrode electrolytes is zinc bromide, and the concentration of the electrolyte in the positive and negative electrode electrolytes is 1.5–2.5 mol / L. The supporting electrolyte for preparing the positive and negative electrode electrolytes is selected from one or more of potassium chloride (KCl), sodium chloride (NaCl), methanesulfonic acid (MSA), and ammonium chloride (NH4Cl), and the concentration of the electrolyte in the positive electrode electrolyte and the concentration of the supporting electrolyte in the negative electrode electrolyte are 1-3 mol / L. The complexing agent used to prepare the positive and negative electrolytes is selected from one of N-ethyl-N-methylpyrrolidine bromide (MEP), 4-ethyl-4-methylmorpholine bromide (MEM), and 1-ethyl-3-methylimidazolium bromide (EMI), and the concentration of the complexing agent in the positive and negative electrolytes is 0.2–1 mol / L.

[0028] Furthermore, the polyoxyethylene additives are selected from one of Tween-20, Tween-40, lauryl polyoxyethylene ether-23, and hexaethylene glycol monododecyl ether; the concentration of the polyoxyethylene additives in the positive electrode electrolyte is 0.1–1 g / L.

[0029] Furthermore, the polymeric acid additive is polyethylene glycol diacid, wherein the molecular weight of the polyethylene glycol diacid is 200-2000, preferably 400-1000; the concentration of the polymeric acid additive in the negative electrode electrolyte is 0.5-5 g / L.

[0030] The present invention also provides a zinc-bromine flow battery, comprising a positive electrode, a negative electrode, an ion exchange membrane, and the zinc-bromine flow battery electrolyte containing polyoxyethylene additives.

[0031] Example 1 Preparation of positive electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 11.18g potassium chloride (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.05g of Tween-20 and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0032] Preparation of negative electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 11.18g potassium chloride (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.20g of polyethylene glycol diacid and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0033] Example 2 Preparation of positive electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 11.18g potassium chloride (1.5mol / L), and 8.40g 4-ethyl-4-methylmorpholine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add 4-ethyl-4-methylmorpholine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.05g of Tween-20 and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0034] Preparation of negative electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 11.18g potassium chloride (1.5mol / L), and 8.40g 4-ethyl-4-methylmorpholine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add 4-ethyl-4-methylmorpholine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.20g of polyethylene glycol diacid and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0035] Example 3 Preparation of positive electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 11.18g potassium chloride (1.5mol / L), and 7.64g 1-ethyl-3-methylimidazolium bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add 1-ethyl-3-methylimidazolium bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.05g of Tween-20 and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0036] Preparation of negative electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 11.18g potassium chloride (1.5mol / L), and 7.64g 1-ethyl-3-methylimidazolium bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add 1-ethyl-3-methylimidazolium bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.20g of polyethylene glycol diacid and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0037] Example 4 Preparation of positive electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 8.77g sodium chloride (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add sodium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.05g of Tween-20 and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0038] Preparation of negative electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 8.77g sodium chloride (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add sodium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.20g of polyethylene glycol diacid and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0039] Example 5 Preparation of positive electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.26g methanesulfonic acid (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add methanesulfonic acid to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.05g of Tween-20 and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0040] Preparation of negative electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 14.26g methanesulfonic acid (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add methanesulfonic acid to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.20g of polyethylene glycol diacid and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0041] Example 6 Preparation of positive electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 7.46g potassium chloride (1.0mol / L), 4.80g methanesulfonic acid (0.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add methanesulfonic acid to the solution prepared in step S3 and stir until completely dissolved; S5: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S4 and stir until completely dissolved; S6: Weigh 0.05g of Tween-20 and add it to the solution in step S5. Stir until completely dissolved and bring the volume up to 100mL.

[0042] Preparation of negative electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 7.46g potassium chloride (1.0mol / L), 4.80g methanesulfonic acid (0.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add methanesulfonic acid to the solution prepared in step S3 and stir until completely dissolved; S5: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S4 and stir until completely dissolved; S6: Weigh 0.50g of polyethylene glycol diacid and add it to the solution in step S5. Stir until completely dissolved and bring the volume up to 100mL.

[0043] Example 7 Preparation of positive electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 5.35g ammonium chloride (1.0mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add methanesulfonic acid to the solution prepared in step S3 and stir until completely dissolved; S5: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S4 and stir until completely dissolved; S6: Weigh 0.10g of Tween-20 and add it to the solution in step S5. Stir until completely dissolved and bring the volume up to 100mL.

[0044] Preparation of negative electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 5.35g ammonium chloride (1.0mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add methanesulfonic acid to the solution prepared in step S3 and stir until completely dissolved; S5: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S4 and stir until completely dissolved; S6: Weigh 0.20g of polyethylene glycol diacid and add it to the solution in step S5. Stir until completely dissolved and bring the volume up to 100mL.

[0045] Example 8 Preparation of positive electrode electrolyte: S1: Accurately weigh 33.78g zinc bromide (1.5mol / L), 22.37g potassium chloride (3.0mol / L), and 3.88g N-ethyl-N-methylpyrrolidine bromide (0.2mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add methanesulfonic acid to the solution prepared in step S3 and stir until completely dissolved; S5: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S4 and stir until completely dissolved; S6: Weigh 0.05g of Tween-40 and add it to the solution in step S5. Stir until completely dissolved and bring the volume up to 100mL.

[0046] Preparation of negative electrode electrolyte: S1: Accurately weigh 33.78g zinc bromide (1.5mol / L), 22.37g potassium chloride (3.0mol / L), and 3.88g N-ethyl-N-methylpyrrolidine bromide (0.2mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add methanesulfonic acid to the solution prepared in step S3 and stir until completely dissolved; S5: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S4 and stir until completely dissolved; S6: Weigh 0.20g of polyethylene glycol diacid and add it to the solution in step S5. Stir until completely dissolved and bring the volume up to 100mL.

[0047] Example 9 Preparation of positive electrode electrolyte: S1: Accurately weigh 56.30g zinc bromide (2.5mol / L), 11.18g potassium chloride (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.02g of lauryl alcohol polyoxyethylene ether-23 and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0048] Preparation of negative electrode electrolyte: S1: Accurately weigh 56.30g zinc bromide (2.5mol / L), 11.18g potassium chloride (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.05g of polyethylene glycol diacid and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0049] Example 10 Preparation of positive electrode electrolyte: S1: Accurately weigh 45.04 g zinc bromide (2 mol / L), 11.18 g potassium chloride (1.5 mol / L), and 19.41 g N-ethyl-N-methylpyrrolidine bromide (1.0 mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.05g of hexaethylene glycol monododecyl ether and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0050] Preparation of negative electrode electrolyte: S1: Accurately weigh 45.04 g zinc bromide (2 mol / L), 11.18 g potassium chloride (1.5 mol / L), and 19.41 g N-ethyl-N-methylpyrrolidine bromide (1.0 mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.20g of polyethylene glycol diacid and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0051] Example 11 Preparation of positive electrode electrolyte: S1: Accurately weigh 45.04 g zinc bromide (2 mol / L), 11.18 g potassium chloride (1.5 mol / L), and 19.41 g N-ethyl-N-methylpyrrolidine bromide (1.0 mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.01g of Tween-20 and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0052] Preparation of negative electrode electrolyte: S1: Accurately weigh 45.04 g zinc bromide (2 mol / L), 11.18 g potassium chloride (1.5 mol / L), and 19.41 g N-ethyl-N-methylpyrrolidine bromide (1.0 mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.20g of polyethylene glycol diacid and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0053] Comparative Example 1 Preparation of positive electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 11.18g potassium chloride (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Make up to 100 mL.

[0054] Preparation of negative electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 11.18g potassium chloride (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.20g of polyethylene glycol diacid and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0055] Comparative Example 2 Preparation of positive electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 11.18g potassium chloride (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Weigh 0.05g of Tween-20 and add it to the solution prepared in step S4. Stir until completely dissolved and bring the volume up to 100mL.

[0056] Preparation of negative electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 11.18g potassium chloride (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Make up to 100 mL.

[0057] Comparative Example 3 Preparation of positive electrode electrolyte: S1: Accurately weigh 45.04g zinc bromide (2mol / L), 11.18g potassium chloride (1.5mol / L), and 7.76g N-ethyl-N-methylpyrrolidine bromide (0.4mol / L). S2: Add zinc bromide to deionized water and stir until completely dissolved; S3: Add potassium chloride to the solution prepared in step S2 and stir until completely dissolved; S4: Add N-ethyl-N-methylpyrrolidine bromide to the solution prepared in step S3 and stir until completely dissolved; S5: Make up to 100 mL.

[0058] The negative electrode electrolyte is the same as the positive electrode electrolyte.

[0059] Table 1 shows the composition and proportion of each key component in Examples 1-11 and Comparative Examples 1-3; Table 1 clearly shows the selection of preparation conditions for each example and comparative example.

[0060] Table 1 Electrolyte formulations for Examples 1-11 and Comparative Examples 1-3

[0061] The zinc-bromine flow battery electrolytes containing polyoxyethylene additives prepared in Examples 1-11 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 100mL. The battery performance in the examples and comparative examples was tested under the same conditions, and the test results are shown in Table 2.

[0062] Table 2 Comparison of single-flow battery performance test results of zinc-bromine flow battery electrolytes containing polyoxyethylene additives prepared in Examples 1-11 and Comparative Examples 1-3

[0063] Table 2 compares the performance test results of the electrolytes prepared in Examples 1-11 and Comparative Examples 1-3 in zinc-bromine flow batteries. As shown in Table 2, the coulombic efficiency of the zinc-bromine flow batteries prepared with the zinc-bromine flow electrolyte of this invention is 93%-96.7%, the voltage efficiency is 80.8%-85.5%, and the energy efficiency is 76.19%-82.39%. The coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) values ​​in Examples 1-11 are all greater than those in the comparative examples. By adding complexing agents, polyoxyethylene additives, and polymeric acid additives to the positive and negative electrode electrolytes, the complexing agents complex free bromine into hydrophobic polybrominates, the polyoxyethylene substances promote the effective contact and reversible reaction between the complex and the electrode, and the polyethylene glycol diacid regulates zinc deposition. The three substances each play their respective functions at the positive and negative electrodes without interfering with each other, thereby improving the coulombic efficiency, voltage efficiency, energy efficiency, and cycle stability of the zinc-bromine flow battery.

[0064] This invention provides a zinc-bromine flow battery electrolyte containing polyoxyethylene additives and its preparation method. By adding polymeric acid additives and polyoxyethylene additives, the coulombic efficiency, voltage efficiency, and energy efficiency of the zinc-bromine flow battery were tested in a single-flow battery compared to the electrolyte without additives. By comparing the test data of zinc-bromine flow batteries with and without the additive-added electrolyte, the zinc-bromine flow battery electrolyte of this invention can significantly improve the coulombic efficiency, voltage efficiency, and energy efficiency of zinc-bromine flow batteries.

[0065] The polyethylene glycol diacid in this invention is a polymer containing a carboxyl group (-COOH), which is the key end group that distinguishes it from ordinary PEG used in existing technologies, endowing the molecule with bifunctional reactivity. Under different pH conditions, it can exhibit -COOH or -COO. - In this form, it can undergo coupling reactions with amino compounds to form amide bonds, or with alcohols to form ester bonds. The ether bond (-O-) is the backbone of the PEG chain, providing hydrophilicity, a flexible chain conformation, and steric isolation, but it cannot achieve the function of polyethylene glycol diacid in this invention.

[0066] The above description is only of the preferred embodiment of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0067] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A zinc-bromine flow battery electrolyte containing polyoxyethylene additives, characterized in that, Including positive electrode electrolyte and negative electrode electrolyte; The positive electrode electrolyte includes a solvent, an electrolyte, a supporting electrolyte, polyoxyethylene additives, and a complexing agent; The negative electrode electrolyte includes a solvent, an electrolyte, a supporting electrolyte, polymeric acid additives, and a complexing agent.

2. The zinc-bromine flow battery electrolyte containing polyoxyethylene additives according to claim 1, characterized in that, The electrolyte in both the positive and negative electrode electrolytes is zinc bromide, and the concentration of the electrolyte in both the positive and negative electrode electrolytes is 1.5–2.5 mol / L.

3. The zinc-bromine flow battery electrolyte containing polyoxyethylene additives according to claim 1, characterized in that, The solvent for both the positive and negative electrode electrolytes is water; the supporting electrolyte for both the positive and negative electrode electrolytes is one or more of potassium chloride, sodium chloride, methanesulfonic acid, and ammonium chloride, and the concentration of the electrolyte in the positive electrode electrolyte and the concentration of the supporting electrolyte in the negative electrode electrolyte are 1–3 mol / L.

4. The zinc-bromine flow battery electrolyte containing polyoxyethylene additives according to claim 1, characterized in that, The complexing agent for the positive and negative electrolytes is one of N-ethyl-N-methylpyrrolidine bromide, 4-ethyl-4-methylmorpholine bromide, and 1-ethyl-3-methylimidazolium bromide, and the concentration of the complexing agent in the positive and negative electrolytes is 0.2–1 mol / L.

5. The zinc-bromine flow battery electrolyte containing polyoxyethylene additives according to claim 1, characterized in that, The concentration of polyoxyethylene additives in the positive electrode electrolyte is 0.1–1 g / L.

6. The zinc-bromine flow battery electrolyte containing polyoxyethylene additives according to claim 1, characterized in that, The polyoxyethylene additives are one of Tween-20, Tween-40, lauryl alcohol polyoxyethylene ether-23, and hexaethylene glycol monododecyl ether.

7. The zinc-bromine flow battery electrolyte containing polyoxyethylene additives according to claim 1, characterized in that, The polymeric acid additive is polyethylene glycol diacid.

8. The zinc-bromine flow battery electrolyte containing polyoxyethylene additives according to claim 7, characterized in that, The molecular weight of polyethylene glycol diacid is 200-2000.

9. The zinc-bromine flow battery electrolyte containing polyoxyethylene additives according to claim 1, characterized in that, The concentration of polymeric acid additives in the negative electrode electrolyte is 0.5–5 g / L.

10. A zinc-bromine flow battery, characterized in that, Includes a positive electrode, a negative electrode, an ion exchange membrane, and as claimed in claim 1. The zinc-bromine flow battery electrolyte containing polyoxyethylene additives as described in any one of the nine.

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