CN119994097A

CN119994097A - Acidic redox flow battery membrane and preparation method thereof

Info

Publication number: CN119994097A
Application number: CN202510165133.2A
Authority: CN
Inventors: 蔡迎军; 李林林; 霍锋; 王钧锐; 闫杰杰; 张海涛; 苑孟辉; 曹浩宁
Original assignee: Longzihu New Energy Laboratory; Zhengzhou Institute of Emerging Industrial Technology
Current assignee: Longzihu New Energy Laboratory; Zhengzhou Institute of Emerging Industrial Technology
Priority date: 2025-02-14
Filing date: 2025-02-14
Publication date: 2025-05-13

Abstract

The invention provides an acidic redox flow battery diaphragm and a preparation method thereof, belongs to the technical field of flow batteries, and aims to solve the technical problems of low energy efficiency and poor cycling stability of the flow battery. The preparation method comprises the steps of preparing sulfonated polyether-ether-ketone solution, coating the sulfonated polyether-ether-ketone solution on one surface of a diaphragm substrate, dispersing and dissolving nano alumina and an adhesive into a solvent to prepare slurry, and coating the slurry on the other surface of the diaphragm substrate. According to the invention, the anode side is coated with a layer of sulfonated polyether-ether-ketone, the hydrophilicity and the ion exchange rate of the modified membrane are improved by regulating and controlling the sulfonation degree and the thickness of the modified layer, the cathode side is coated with Nano-Al ₂O₃, and the aim of improving the mechanical strength of the anode side of the diaphragm and inhibiting zinc dendrite generation is achieved by regulating and controlling the content and the coating thickness of Nano-Al ₂O₃.

Description

Acidic redox flow battery diaphragm and preparation method thereof

Technical Field

The invention belongs to the technical field of flow batteries, and particularly relates to a flow battery diaphragm.

Background

In the aspect of sustainable development of human society, the utilization of renewable energy sources such as wind energy, solar energy and the like is an unavoidable trend. As a bridge technology between supply and consumer, large energy storage systems are receiving increasing attention. Redox flow batteries have the advantages of long cycling, easy operation, flexible battery design, ecological friendliness, easy expansion and the like, and are considered as advanced energy storage technologies. The zinc-bromine flow battery has the advantages of low cost, high safety and theoretical energy density of 430Wh/kg, and is considered as one of the most potential large-scale energy storage technologies due to the fact that the positive and negative electrolytes are consistent, and no cross contamination exists.

The zinc-bromine flow battery is a device for realizing energy storage and release through electrochemical reaction, and the working principle is based on oxidation-reduction reaction between zinc ions and bromine ions. The battery has the advantages of high energy density, long cycle life and high charge and discharge efficiency, and is particularly suitable for large-scale energy storage systems. However, in practical applications, zinc-bromine flow batteries still face challenges, one of which is the choice of separator materials and performance optimization problem.

Currently, zinc bromine flow batteries mainly use perfluorosulfonic acid membranes (e.g., nafion membranes) as the separator material, which, although having good ion selectivity and mechanical strength, also expose some key issues. First, the cost of perfluorosulfonic acid membranes is high, which is a major obstacle for large-scale commercial applications. The high cost not only increases the production cost of the battery, but also limits its popularity in scenes where economic demands are high. Secondly, the perfluorosulfonic acid membrane has poor stability in an acidic environment and is easy to degrade, thereby influencing the long-term stability and the service life of the battery. In addition, this membrane has a problem of bromine permeation, that is, bromine ions may pass through the separator to the negative electrode side during the operation of the battery, resulting in mixing of the positive and negative electrolytes, thereby causing capacity degradation and performance degradation of the battery. In addition to the limitations of the material itself, other properties of perfluorosulfonic acid membranes are not satisfactory. For example, its porosity is low, which is detrimental to the flow of the electrolyte, thereby increasing the resistance inside the battery and reducing the energy conversion efficiency. In addition, due to the limited hydrophilicity of the perfluorinated sulfonic acid membrane, the electrolyte is unevenly distributed in the membrane, and the consistency and reliability of the battery are affected. Therefore, developing a domestic membrane with low price and high performance is one of the important directions in the field of zinc-bromine flow batteries.

In order to overcome the above drawbacks and improve the overall performance of zinc bromine flow batteries, researchers have begun to explore methods of modifying existing separator materials. Common modification strategies include the introduction of hydrophilic groups to enhance the water absorption of the membrane, the addition of nanoparticles to improve mechanical properties, the preparation of new membranes using composite materials, and the like. For example, patent publication No. CN 103562268A discloses a method of making a film or membrane comprising (a) dissolving at least one polymer comprising a poly (aryl ketone) into at least one solvent to form a dope, (b) depositing the dope onto a substrate under suitable conditions to form a coated substrate, and (c) drying the coated substrate to form the film or membrane. The dope may also include additional polymers or fillers, such as carbon nanotubes. As another example, patent publication No. CN 118970087A discloses a functionalized membrane modified by titanium oxycarbide applied in a bromine-based flow battery and a preparation method thereof, which is prepared by simple ball milling and calcining of low-cost titanium dioxide (TiO ₂) and titanium carbide (TiC), and then, a low-cost polyethylene-based porous membrane is modified by knife coating through the synergistic effect of TiC _xO_1-x and sulfonated polyether ether ketone (SPEEK) solution. These improvements aim to reduce internal resistance of the battery, reduce occurrence of side reactions, and extend the service life of the battery, thereby paving a road for large-scale commercial application of zinc-bromine flow batteries. Through continuous optimization of the diaphragm material, the energy conversion efficiency and the long-term stability of the zinc-bromine flow battery are expected to be further improved, so that the zinc-bromine flow battery becomes an important component in the future renewable energy source field. At the same time, this will also promote technological advances and sustainable development of the relevant industries.

Disclosure of Invention

Aiming at the technical problems, the invention provides an acid redox flow battery diaphragm and a preparation method thereof, which are used for improving the hydrophilicity, ionic conductivity and mechanical strength of the diaphragm, so as to improve the battery performance, mainly improve the energy efficiency and the cycling stability of the battery.

In order to achieve the above purpose, the technical scheme of the invention is realized as follows:

A preparation method of an acidic redox flow battery diaphragm comprises the steps of preparing a sulfonated polyether-ether-ketone solution, coating the sulfonated polyether-ether-ketone solution on one surface of a diaphragm substrate, dispersing and dissolving nano alumina and an adhesive into a solvent to prepare slurry, and coating the slurry on the other surface of the diaphragm substrate.

The preparation method of the sulfonated polyether-ether-ketone comprises the steps of adding the polyether-ether-ketone into concentrated sulfuric acid for sulfonation reaction, washing and drying after the reaction is finished, and enabling the molecular chain of the sulfonated polyether-ether-ketone to contain sulfonic acid groups (-SO ₃ H) which can attract and bind water molecules to improve the hydrophilicity of the polyether-ether-ketone.

The proportion of the polyether-ether-ketone and the concentrated sulfuric acid is (0.1-1) g (2-20) mL, the temperature of the sulfonation reaction is 50-70 ℃ and the time is 2-10h.

The concentration of the sulfonated polyether-ether-ketone in the sulfonated polyether-ether-ketone solution is 0.05-0.1g/mL, and the solvent is any one or more than two of N-methyl pyrrolidone, dimethylformamide and dimethyl sulfoxide.

The particle size of the nano alumina is 20-50nm, and the concentration in the slurry is 0.001-0.005g/mL.

Preferably, the particle size of the aluminum oxide is 30nm, and the ratio is 170m ²/g.

The adhesive is one or more than two of polyvinylidene fluoride, polyacrylic acid and carboxymethyl cellulose, and the concentration of the adhesive in the slurry is 5-10wt%.

The solvent in the slurry is any one or more than two of N-methyl pyrrolidone, dimethylformamide and dimethyl sulfoxide.

The slurry is also added with a dispersing agent, the concentration of the dispersing agent in the slurry is 0.004-0.012g/mL, and the dispersing agent is any one or more than two of polyethylene glycol, sodium dodecyl sulfate and sodium hexametaphosphate.

The coating thickness of the sulfonated polyether-ether-ketone solution on the diaphragm substrate is 1-5 mu m, and the coating thickness of the slurry on the diaphragm substrate is 1-5 mu m.

The acid redox flow battery diaphragm is of a sandwich structure and comprises a middle diaphragm substrate, a sulfonated polyether-ether-ketone layer and a nano alumina modified layer, wherein the sulfonated polyether-ether-ketone layer and the nano alumina modified layer are respectively arranged on the upper side and the lower side of the middle diaphragm substrate.

The membrane is a porous membrane commonly used in the market, such as a polyethylene-based porous membrane, a polypropylene (PP) porous membrane, a polyvinylidene fluoride (PVDF) porous membrane, or a cellulose-based membrane, an inorganic ceramic membrane, etc.

When the battery is assembled, the sulfonated polyether-ether-ketone layer is positioned on the positive electrode side, and the Nano aluminum oxide modified layer (Nano-Al ₂O₃) is positioned on the negative electrode side.

The invention has the beneficial effects that:

(1) After the membrane is coated with a layer of sulfonated polyether-ether-ketone, the sulfonated polyether-ether-ketone is a polymer with high hydrophilicity, and the molecular chain of the sulfonated polyether-ether-ketone contains sulfonic acid groups (-SO ₃ H) which can attract and combine with water molecules to form more hydrated ion channels. This makes the ions in the electrolyte more easily pass through the membrane, thereby improving ion conductivity, reducing ohmic resistance inside the battery, and improving energy conversion efficiency. Coating the SPEEK layer can significantly increase the hydrophilicity of the separator to better match the electrolyte. The enhanced hydrophilicity facilitates more uniform distribution of the electrolyte within the membrane, avoids performance non-uniformity caused by local concentration differences, and thereby improves stability and consistency of the battery. The SPEEK has better mechanical strength and chemical stability, and after being coated on the surface of a domestic membrane, the SPEEK not only can strengthen the mechanical property of the original membrane, but also can improve the tolerance of the SPEEK to corrosive electrolyte. This helps to extend the useful life of the membrane and ensures stability of the battery over long periods of operation.

(2) The Nano-Al ₂O₃ modified layer greatly improves the mechanical strength of the diaphragm, can effectively inhibit zinc dendrites, and can adjust the aperture and the porosity of the diaphragm through a coating process, so that the diaphragm is more suitable for the working conditions of a zinc-bromine flow battery. The optimized membrane structure can more effectively balance the requirements of ion conduction and electronic isolation, and further improve the battery performance.

(3) The preparation modified film of the invention stably runs to 500 circles in the circulating process, and the energy efficiency is improved from 68.4% to 74.2%, so that the energy efficiency and the stability of the battery are greatly improved.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a graph of the cycle life of the modified film prepared in example 1 and the original film of comparative example 1.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without any inventive effort, are intended to be within the scope of the invention.

Example 1

An acidic redox flow battery separator, the preparation method of which comprises the following steps:

Polyether ether ketone (PEEK) is dried for 24 hours at 100 ℃ in a vacuum drying oven, 1g of PEEK is placed in a round bottom flask containing 20mL of 98% concentrated sulfuric acid, the PEEK is reacted for 4 hours at a constant temperature of 70 ℃, the reacted product is placed in an ice-water mixture, distilled water is used for washing to be neutral, the product is dissolved by 100 ℃ hot water, after most of water is removed at room temperature, the PEEK is placed in a 90 ℃ forced air drying oven 12 hours and a 100 ℃ vacuum drying oven for 24 hours, and sulfonated polyether ether ketone (SPEEK) is obtained. The dried 0.1g SPEEK was dissolved in 1 mLN-methylpyrrolidone, and after 4 hours of reaction the solution was coated on a polyethylene-based porous membrane with a coating thickness of 5. Mu.m. PVDF with the mass fraction of 6% is dissolved in 100mLNMP at 70 ℃ for 30 minutes until dissolved, 0.4g nano-Al ₂O₃ (particle size of 30 nm) and 1.2g PEG are added, the mixture is stirred for 4 hours to fully disperse the PEG, and after cooling to room temperature, the mixture is scraped on the negative side of the separator, and the thickness of the scraped coating is 3 mu m. The complete battery is assembled, the charge-discharge current density is 80mA/cm ², the surface capacity is 5mAh/cm ², and the discharge cut-off voltage is 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. After the battery is subjected to multiple normal charge and discharge cycles, the electrolyte can stably run for 500 circles, the average energy efficiency of the battery is 74.2%, and the coulomb efficiency is 98.5%.

Example 2

Polyether ether ketone (PEEK) is dried for 24 hours at 100 ℃ in a vacuum drying oven, 1g of PEEK is placed in a round bottom flask containing 20mL of 98% concentrated sulfuric acid, the PEEK is reacted for 2 hours at a constant temperature of 70 ℃, the reacted product is placed in an ice-water mixture, distilled water is washed to be neutral, the product is dissolved by 100 ℃ hot water, after most of water is removed at room temperature, the PEEK is placed in a 90 ℃ forced air drying oven 12 hours and a 100 ℃ vacuum drying oven 24 hours, and sulfonated polyether ether ketone (SPEEK) is obtained. The dried 0.1g SPEEK was dissolved in 1 mLN-methylpyrrolidone, and after 4 hours of reaction the solution was coated on a polyethylene-based porous membrane with a coating thickness of 5. Mu.m. PVDF with the mass fraction of 6% is dissolved in 100mLNMP at 70 ℃ for 30 minutes until dissolved, 0.4g nano-Al ₂O₃ (particle size of 30 nm) and 1.2g PEG are added, the mixture is stirred for 4 hours to fully disperse the PEG, and after cooling to room temperature, the mixture is scraped on the negative side of the separator, and the thickness of the scraped coating is 3 mu m. The complete battery is assembled, the charge-discharge current density is 80mA/cm ², the surface capacity is 5mAh/cm ², and the discharge cut-off voltage is 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. After the battery is subjected to multiple normal charge and discharge cycles, the average energy efficiency of the battery is 69.4%, the coulomb efficiency is 96.5%, and the cycle number is less than 200.

Example 3

Polyether ether ketone (PEEK) is dried for 24 hours at 100 ℃ in a vacuum drying oven, 1g of PEEK is placed in a round bottom flask containing 20mL of 98% concentrated sulfuric acid, the PEEK is reacted for 6 hours at a constant temperature of 70 ℃, the reacted product is placed in an ice-water mixture, distilled water is used for washing to be neutral, the product is dissolved by 100 ℃ hot water, after most of water is removed at room temperature, the PEEK is placed in a 90 ℃ forced air drying oven 12 hours and a 100 ℃ vacuum drying oven 24 hours, and sulfonated polyether ether ketone (SPEEK) is obtained. The dried 0.1g SPEEK was dissolved in 1 mLN-methylpyrrolidone, and after 4 hours of reaction the solution was coated on a polyethylene-based porous membrane with a coating thickness of 5. Mu.m. PVDF with the mass fraction of 6% is dissolved in 100mLNMP at 70 ℃ for 30 minutes until dissolved, 0.4g nano-Al ₂O₃ (particle size of 30 nm) and 1.2g PEG are added, the mixture is stirred for 4 hours to fully disperse the PEG, and after cooling to room temperature, the mixture is scraped on the negative side of the separator, and the thickness of the scraped coating is 3 mu m. The complete battery is assembled, the charge-discharge current density is 80mA/cm ², the surface capacity is 5mAh/cm ², and the discharge cut-off voltage is 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. After the battery is subjected to multiple normal charge and discharge cycles, the average energy efficiency of the battery is 71.6%, the coulomb efficiency is 97.8%, and the cycle number is less than 300.

Example 4

Polyether ether ketone (PEEK) is dried for 24 hours at 100 ℃ in a vacuum drying oven, 1g of PEEK is placed in a round bottom flask containing 20mL of 98% concentrated sulfuric acid, the PEEK is reacted for 8 hours at a constant temperature of 70 ℃, the reacted product is placed in an ice-water mixture, distilled water is washed to be neutral, the product is dissolved by 100 ℃ hot water, after most of water is removed at room temperature, the PEEK is placed in a 90 ℃ forced air drying oven 12 hours and a 100 ℃ vacuum drying oven 24 hours, and sulfonated polyether ether ketone (SPEEK) is obtained. The dried 0.1g SPEEK was dissolved in 1 mLN-methylpyrrolidone, and after 4 hours of reaction the solution was coated on a polyethylene-based porous membrane with a coating thickness of 5. Mu.m. PVDF with the mass fraction of 6% is dissolved in 100mLNMP at 70 ℃ for 30 minutes until dissolved, 0.4g nano-Al ₂O₃ (particle size of 30 nm) and 1.2g PEG are added, the mixture is stirred for 4 hours to fully disperse the PEG, and after cooling to room temperature, the mixture is scraped on the negative side of the separator, and the thickness of the scraped coating is 3 mu m. The complete battery is assembled, the charge-discharge current density is 80mA/cm ², the surface capacity is 5mAh/cm ², and the discharge cut-off voltage is 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. After the electrolyte is subjected to multiple normal charge and discharge cycles, the average energy efficiency of the battery is 70.6%, the coulomb efficiency is 97.3%, and the cycle number is less than 200.

Example 5

polyether ether ketone (PEEK) is dried for 24 hours at 100 ℃ in a vacuum drying oven, 1g of PEEK is placed in a round bottom flask containing 20mL of 98% concentrated sulfuric acid, the PEEK is reacted for 4 hours at a constant temperature of 70 ℃, the reacted product is placed in an ice-water mixture, distilled water is used for washing to be neutral, the product is dissolved by 100 ℃ hot water, after most of water is removed at room temperature, the PEEK is placed in a 90 ℃ forced air drying oven 12 hours and a 100 ℃ vacuum drying oven for 24 hours, and sulfonated polyether ether ketone (SPEEK) is obtained. The dried 0.1g SPEEK was dissolved in 1 mLN-methylpyrrolidone, and after 4 hours of reaction the solution was coated on a polyethylene-based porous membrane with a thickness of 1. Mu.m. PVDF with the mass fraction of 6% is dissolved in 100mLNMP at 70 ℃ for 30 minutes until dissolved, 0.4g nano-Al ₂O₃ (particle size of 30 nm) and 1.2g PEG are added, the mixture is stirred for 4 hours to fully disperse the PEG, and after cooling to room temperature, the mixture is scraped on the negative side of the separator, and the thickness of the scraped coating is 3 mu m. The complete battery is assembled, the charge-discharge current density is 80mA/cm ², the surface capacity is 5mAh/cm ², and the discharge cut-off voltage is 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. After the electrolyte is subjected to multiple normal charge and discharge cycles, the average energy efficiency of the battery is 69.9%, the coulomb efficiency is 96.8%, and the cycle number is less than 150.

Example 6

Polyether ether ketone (PEEK) is dried for 24 hours at 100 ℃ in a vacuum drying oven, 1g of PEEK is placed in a round bottom flask containing 20mL of 98% concentrated sulfuric acid, the PEEK is reacted for 4 hours at a constant temperature of 70 ℃, the reacted product is placed in an ice-water mixture, distilled water is used for washing to be neutral, the product is dissolved by 100 ℃ hot water, after most of water is removed at room temperature, the PEEK is placed in a 90 ℃ forced air drying oven 12 hours and a 100 ℃ vacuum drying oven for 24 hours, and sulfonated polyether ether ketone (SPEEK) is obtained. The dried 0.1g SPEEK was dissolved in 1 mLN-methylpyrrolidone, and after 4 hours of reaction the solution was coated on a polyethylene-based porous membrane with a coating thickness of 5. Mu.m. PVDF with the mass fraction of 6% is dissolved in 100mLNMP at 70 ℃ for 30 minutes until dissolved, nano-Al ₂O₃ (particle size of 30 nm) with 0.2g of PEG is added, stirring is carried out for 4 hours to fully disperse the PEG, after cooling to room temperature, the PEG is scraped on the negative side of the diaphragm, and the thickness of the scraping is 1 μm. The complete battery is assembled, the charge-discharge current density is 80mA/cm ², the surface capacity is 5mAh/cm ², and the discharge cut-off voltage is 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. After the electrolyte is subjected to multiple normal charge and discharge cycles, the average energy efficiency of the battery is 70.5%, the coulomb efficiency is 98.3%, and the cycle number is less than 250.

Example 7

Polyether ether ketone (PEEK) is dried for 24 hours at 100 ℃ in a vacuum drying oven, 1g of PEEK is placed in a round bottom flask containing 20mL of 98% concentrated sulfuric acid, the PEEK is reacted for 4 hours at a constant temperature of 70 ℃, the reacted product is placed in an ice-water mixture, distilled water is used for washing to be neutral, the product is dissolved by 100 ℃ hot water, after most of water is removed at room temperature, the PEEK is placed in a 90 ℃ forced air drying oven 12 hours and a100 ℃ vacuum drying oven for 24 hours, and sulfonated polyether ether ketone (SPEEK) is obtained. The dried 0.1g SPEEK was dissolved in 1 mLN-methylpyrrolidone, and after 4 hours of reaction the solution was coated on a polyethylene-based porous membrane with a coating thickness of 5. Mu.m. PVDF with the mass fraction of 6% is dissolved in 100mLNMP at 70 ℃ for 30 minutes until dissolved, nano-Al ₂O₃ (particle size of 30 nm) with 0.2g of PEG is added, stirring is carried out for 4 hours to fully disperse the PEG, after cooling to room temperature, the PEG is scraped on the negative side of the diaphragm, and the thickness of the scraping is 5 mu m. The complete battery is assembled, the charge-discharge current density is 80mA/cm ², the surface capacity is 5mAh/cm ², and the discharge cut-off voltage is 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. The average energy efficiency of the battery is 71.5%, the coulomb efficiency is 97.8%, and the cycle number is less than 200.

Example 8

Polyether ether ketone (PEEK) is dried for 24 hours at 100 ℃ in a vacuum drying oven, 1g of PEEK is placed in a round bottom flask containing 20mL of 98% concentrated sulfuric acid, the PEEK is reacted for 4 hours at a constant temperature of 70 ℃, the reacted product is placed in an ice-water mixture, distilled water is used for washing to be neutral, the product is dissolved by 100 ℃ hot water, after most of water is removed at room temperature, the PEEK is placed in a 90 ℃ forced air drying oven 12 hours and a 100 ℃ vacuum drying oven for 24 hours, and sulfonated polyether ether ketone (SPEEK) is obtained. The dried 0.1g SPEEK was dissolved in 1 mLN-methylpyrrolidone, and after 4 hours of reaction the solution was coated on a polyethylene-based porous membrane with a coating thickness of 5. Mu.m. PVDF with the mass fraction of 6% is dissolved in 100mLNMP at 70 ℃ for 30 minutes until dissolved, nano-Al ₂O₃ (particle size of 30 nm) with 0.1g of PEG is added, stirring is carried out for 4 hours to fully disperse the PEG, after cooling to room temperature, the PEG is scraped on the negative side of the diaphragm, and the thickness of the scraping is 3 mu m. The complete battery is assembled, the charge-discharge current density is 80mA/cm ², the surface capacity is 5mAh/cm ², and the discharge cut-off voltage is 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. After the electrolyte is subjected to multiple normal charge and discharge cycles, the average energy efficiency of the battery is 70.6%, the coulomb efficiency is 97.4%, and the cycle number is less than 150.

Example 9

Polyether ether ketone (PEEK) is dried for 24 hours at 100 ℃ in a vacuum drying oven, 1g of PEEK is placed in a round bottom flask containing 20mL of 98% concentrated sulfuric acid, the PEEK is reacted for 4 hours at a constant temperature of 70 ℃, the reacted product is placed in an ice-water mixture, distilled water is used for washing to be neutral, the product is dissolved by 100 ℃ hot water, after most of water is removed at room temperature, the PEEK is placed in a 90 ℃ forced air drying oven 12 hours and a 100 ℃ vacuum drying oven for 24 hours, and sulfonated polyether ether ketone (SPEEK) is obtained. The dried 0.1g SPEEK was dissolved in 1 mLN-methylpyrrolidone, and after 4 hours of reaction the solution was coated on a polyethylene-based porous membrane with a coating thickness of 5. Mu.m. PVDF with the mass fraction of 6% is dissolved in 100mLNMP at 70 ℃ for 30 minutes until dissolved, nano-Al ₂O₃ (particle size of 30 nm) with PEG with the mass fraction of 0.5g and PEG with the mass fraction of 1.0g are added on the negative side, the PEG is fully dispersed by stirring for 4 hours, and after cooling to room temperature, the PEG is scraped on the negative side of a diaphragm, and the thickness of the scraping is 3 mu m. The complete battery is assembled, the charge-discharge current density is 80mA/cm ², the surface capacity is 5mAh/cm ², and the discharge cut-off voltage is 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. After the electrolyte is subjected to multiple normal charge and discharge cycles, the average energy efficiency of the battery is 70.9%, the coulomb efficiency is 96.3%, and the cycle number is less than 170.

Example 10

Polyether ether ketone (PEEK) is dried for 24 hours at 100 ℃ in a vacuum drying oven, 1g of PEEK is placed in a round bottom flask containing 10mL of 98% concentrated sulfuric acid, the PEEK is reacted for 10 hours at a constant temperature of 50 ℃, the reacted product is placed in an ice-water mixture, distilled water is washed to be neutral, the product is dissolved by 100 ℃ hot water, after most of water is removed at room temperature, the PEEK is placed in a 90 ℃ forced air drying oven 12 hours and a 100 ℃ vacuum drying oven 24 hours, and sulfonated polyether ether ketone (SPEEK) is obtained. The dried 0.05g SPEEK was dissolved in 1mL dimethylformamide and after 4h of reaction the solution was coated on a polyethylene based porous membrane to a thickness of 5. Mu.m. PVDF with the mass fraction of 10% is dissolved in 100mLNMP at 70 ℃ for 30 minutes until the PVDF is dissolved, 0.1g nano-Al ₂O₃ and 1.2g sodium dodecyl sulfate are added, the stirring is carried out for 4 hours to fully disperse the sodium dodecyl sulfate, the PVDF is cooled to room temperature, and then the PVDF is scraped on the negative side of a diaphragm, and the scraping thickness is 3 mu m. The complete battery is assembled, the charge-discharge current density is 80mA/cm ², the surface capacity is 5mAh/cm ², and the discharge cut-off voltage is 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. After the battery is subjected to multiple normal charge and discharge cycles, the electrolyte can stably run for 200 circles, the average energy efficiency of the battery is 71.2%, and the coulomb efficiency is 97.5%.

Comparative example 1 (separator unmodified)

The polyethylene-based porous separator used in examples 1 to 9 was assembled into a complete battery, and the charge-discharge current density was 80mA/cm ², the surface capacity was 5mAh/cm ², and the discharge cut-off voltage was 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. After the electrolyte is subjected to multiple normal charge and discharge cycles, the average energy efficiency of the battery is 70.9%, the coulomb efficiency is 96.3%, and the cycle number is less than 170. It can be seen from fig. 1 that the unmodified separator makes up a cell that runs less than two hundred turns with reduced energy efficiency and coulombic efficiency.

Comparative example 2 (coating only the positive electrode)

A battery separator, the method of making comprising the steps of:

Polyether ether ketone (PEEK) is dried for 24 hours at 100 ℃ in a vacuum drying oven, 1g of PEEK is placed in a round bottom flask containing 20mL of 98% concentrated sulfuric acid, the PEEK is reacted for 4 hours at a constant temperature of 70 ℃, the reacted product is placed in an ice-water mixture, distilled water is used for washing to be neutral, the product is dissolved by 100 ℃ hot water, after most of water is removed at room temperature, the PEEK is placed in a 90 ℃ forced air drying oven 12 hours and a 100 ℃ vacuum drying oven for 24 hours, and sulfonated polyether ether ketone (SPEEK) is obtained. The dried 0.1g SPEEK was dissolved in 1 mLN-methylpyrrolidone, and after 4 hours of reaction the solution was coated on a polyethylene-based porous membrane with a coating thickness of 5. Mu.m. The complete battery is assembled, the charge-discharge current density is 80mA/cm ², the surface capacity is 5mAh/cm ², and the discharge cut-off voltage is 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. After the electrolyte is subjected to multiple normal charge and discharge cycles, the average energy efficiency of the battery is 70.4%, the coulomb efficiency is 96.5%, and the cycle number is less than 200.

Comparative example 3 (coating only negative electrode)

A battery separator, the method of making comprising the steps of:

PVDF with the mass fraction of 6% is dissolved in 100mLNMP at 70 ℃ for 30 minutes until dissolved, 0.4g nano-Al ₂O₃ and 1.2g PEG are added, stirring is carried out for 4 hours to fully disperse the PEG, and after cooling to room temperature, the PEG is scraped on the negative side of the diaphragm, and the scraping thickness is 3 mu m. The complete battery is assembled, the charge-discharge current density is 80mA/cm ², the surface capacity is 5mAh/cm ², and the discharge cut-off voltage is 0.8V. The galvanic pile is a single cell, and is formed by sequentially arranging and assembling a positive electrode end plate, a current collector, a graphite plate, a carbon felt, a diaphragm, a carbon felt, a graphite plate, a current collector and a negative electrode end plate. After the electrolyte is subjected to multiple normal charge and discharge cycles, the average coulomb efficiency of the battery is 96.7%, the energy efficiency is 70.6%, and the cycle number is less than 100.

Mechanical property test the diaphragms prepared in example 1 and comparative examples 1-3 were cut and then subjected to a tensile test, and the results are shown in table 1. As shown in comparative examples 2 and 3 and comparative example 1, the mechanical properties of the diaphragms can be improved by coating modification, and the tensile strength of the diaphragms prepared in comparative example 3 is higher than that of comparative example 2, so that the Nano-Al ₂O₃ modified layer is proved to greatly improve the mechanical strength of the diaphragms. In addition, the tensile strength of the sandwich structure separator prepared in the embodiment 1 reaches 13.2Mpa, which is far higher than that of a battery separator which is not coated with the modified and single-side coated separator, and the improvement of mechanical properties by double-layer coating in the embodiment 1 is not a simple superposition of the tensile strength of a coated cathode and a coated anode, and the improvement of mechanical properties before the two layers has a synergistic effect.

Table 1 mechanical tensile strength comparison of the respective separators

Type(s)	Film size (cm ²)	Maximum force (N)	Tensile Strength (Mpa)
				Comparative example 1	4	18	6.1
Comparative example 2	4	24	7.5
				Comparative example 3	4	28	9.5
Example 1	4	35	13.2

The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.

Claims

1. A method for preparing an acidic redox flow battery diaphragm, characterized in that it includes the following steps: preparing a sulfonated polyetheretherketone solution, and applying the sulfonated polyetheretherketone solution to one side of the diaphragm substrate; dispersing and dissolving nano-alumina and an adhesive in a solvent to form a slurry, and applying the slurry to the other side of the diaphragm substrate.

2. The method for preparing an acidic redox flow battery membrane according to claim 1, characterized in that the sulfonated polyetheretherketone is prepared by adding polyetheretherketone to concentrated sulfuric acid for sulfonation reaction, and washing and drying after the reaction is completed.

3. The method for preparing an acidic redox flow battery membrane according to claim 2 is characterized in that the ratio of polyetheretherketone to concentrated sulfuric acid is (0.1-1) g: (2-20) mL; the temperature of the sulfonation reaction is 50-70°C and the time is 2-10 h.

4. The method for preparing an acidic redox flow battery membrane according to claim 3, characterized in that the concentration of sulfonated polyetheretherketone in the sulfonated polyetheretherketone solution is 0.05-0.1 g/mL, and the solvent is any one or more of N-methylpyrrolidone, dimethylformamide and dimethyl sulfoxide.

5. The method for preparing an acidic redox flow battery membrane according to claim 4, characterized in that the particle size of the nano-alumina is 20-50 nm, and the concentration in the slurry is 0.001-0.005 g/mL.

6. The method for preparing an acidic redox flow battery membrane according to claim 5, characterized in that the adhesive is any one or more of polyvinylidene fluoride, polyacrylic acid and carboxymethyl cellulose; and the concentration of the adhesive in the slurry is 5-10wt%.

7 . The method for preparing an acidic redox flow battery membrane according to claim 6 , wherein the solvent in the slurry is any one or more of N-methylpyrrolidone, dimethylformamide and dimethyl sulfoxide.

8. The method for preparing an acidic redox flow battery membrane according to claim 1 is characterized in that a dispersant is also added to the slurry, and the concentration of the dispersant in the slurry is 0.004-0.012 g/mL; the dispersant is any one or more of polyethylene glycol, sodium dodecyl sulfate and sodium hexametaphosphate.

9. The method for preparing an acidic redox flow battery diaphragm according to claim 1, characterized in that the coating thickness of the sulfonated polyetheretherketone solution on the diaphragm substrate is 1-5 μm; the coating thickness of the slurry on the diaphragm substrate is 1-5 μm.

10. An acidic redox flow battery membrane prepared by the method according to any one of claims 1 to 9, characterized in that the acidic redox flow battery membrane is a sandwich structure, including a membrane substrate located in the middle, and a sulfonated polyetheretherketone layer and a nano-alumina modified layer located on the upper and lower sides respectively.