Acid redox flow battery diaphragm and preparation method thereof

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 flow batteries. The preparation method comprises the following steps: preparing a sulfonated polyetheretherketone solution, and coating one surface of a diaphragm substrate with the sulfonated polyetheretherketone solution; and dispersing and dissolving nano aluminum oxide and an adhesive into a solvent to prepare slurry, and coating the slurry on the other surface of the diaphragm substrate. The positive electrode side is coated with a layer of sulfonated polyetheretherketone, the hydrophilicity and ion exchange rate of the modified membrane are improved by regulating and controlling the sulfonation degree and the thickness of a modified layer, the negative electrode side is coated with Nano-Al2O3, and the purposes of improving the mechanical strength of the positive electrode side of the diaphragm and inhibiting zinc dendrite generation are achieved by regulating and controlling the content of Nano-Al2O3 and the coating thickness.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid flow batteries, and in particular relates to a liquid flow battery diaphragm. Background Art

[0002] In terms of sustainable development of human society, the use of renewable energy such as wind power and solar energy is an inevitable trend. As a bridge technology between supply and consumers, large-scale energy storage systems are receiving more and more attention. Redox flow batteries have the advantages of long cycle life, easy operation, flexible battery design, eco-friendliness, and easy expansion, and are considered to be advanced energy storage technologies. Zinc-bromine flow batteries are considered to be one of the most promising large-scale energy storage technologies because of their consistent positive and negative electrolytes, no cross-contamination, low cost, high safety, and theoretical energy density of up to 430Wh / kg.

[0003] Zinc-bromine flow battery is a device that stores and releases energy through electrochemical reactions. Its working principle is based on the redox reaction between zinc ions and bromide ions. This type of 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 some challenges, one of which is the selection of diaphragm materials and performance optimization.

[0004] At present, zinc-bromine flow batteries mainly use perfluorosulfonic acid membranes (such as Nafion membranes) as diaphragm materials. Although this membrane has good ion selectivity and mechanical strength, it also exposes some key problems. 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 scenarios with high economic requirements. Secondly, the stability of perfluorosulfonic acid membranes in acidic environments is poor and they are prone to degradation, which affects the long-term stability and service life of the battery. In addition, this membrane also has the problem of bromine penetration, that is, during the operation of the battery, bromide ions may pass through the diaphragm into the negative electrode side, resulting in the mixing of positive and negative electrolytes, which in turn causes battery capacity decay and performance degradation. In addition to the limitations of the material itself, other properties of the perfluorosulfonic acid membrane are also unsatisfactory. For example, its low porosity is not conducive to the flow of electrolyte, thereby increasing the resistance inside the battery and reducing the energy conversion efficiency. In addition, due to the limited hydrophilicity of the perfluorosulfonic acid membrane, the electrolyte is unevenly distributed in the membrane, affecting the consistency and reliability of the battery. Therefore, developing low-cost and high-performance domestic membranes will be one of the more important directions in the field of zinc-bromine flow batteries.

[0005] In order to overcome the above shortcomings and improve the overall performance of zinc-bromine flow batteries, researchers began to explore methods for modifying existing diaphragm materials. Common modification strategies include introducing hydrophilic groups to enhance the water absorption of the membrane, adding nanoparticles to improve mechanical properties, and using composite materials to prepare new diaphragms. For example, patent publication number CN103562268A discloses a method for manufacturing a membrane or diaphragm, comprising: (a) dissolving at least one polymer including a poly(aryl ketone) in at least one solvent to form a viscous substance: (b) depositing the viscous substance on a substrate under appropriate conditions to form a coated substrate; and (c) drying the coated substrate to form the membrane or diaphragm. The viscous substance may also include additional polymers or fillers, such as carbon nanotubes. For example, patent publication number CN 118970087 A discloses a functionalized diaphragm modified with titanium oxycarbide for use in bromine-based flow batteries and a preparation method thereof, which is prepared by simple ball milling and calcination of low-cost titanium dioxide (TiO2) and titanium carbide (TiC), and then TiC x O 1-x In synergy with sulfonated polyetheretherketone (SPEEK) solution, a low-cost polyethylene-based porous diaphragm is modified by blade coating. These improvements are aimed at reducing the internal resistance of the battery, reducing the occurrence of side reactions, and extending the battery life, thus paving the way for the large-scale commercial application of zinc-bromine flow batteries. Through the continuous optimization of diaphragm materials, it is expected to further improve the energy conversion efficiency and long-term stability of zinc-bromine flow batteries, making them an important part of the future renewable energy field. At the same time, this will also promote technological progress and sustainable development of related industries. Summary of the invention

[0006] In response to the above technical problems, the present invention proposes an acidic redox flow battery membrane and a preparation method thereof, which improves the hydrophilicity, ion conductivity and mechanical strength of the membrane, thereby improving battery performance, mainly improving the energy efficiency and cycle stability of the battery.

[0007] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0008] A method for preparing an acidic redox flow battery diaphragm comprises the following steps: preparing a sulfonated polyetheretherketone solution, and applying the sulfonated polyetheretherketone solution to one side of a 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.

[0009] The preparation method of the sulfonated polyetheretherketone is as follows: adding polyetheretherketone to concentrated sulfuric acid for sulfonation reaction, washing and drying after the reaction is completed, and the sulfonation treatment makes the molecular chain contain sulfonic acid groups (-SO3H), which can attract and bind water molecules to improve the hydrophilicity of polyetheretherketone.

[0010] 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 hours.

[0011] 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.

[0012] The particle size of the nano-alumina is 20-50 nm, and the concentration in the slurry is 0.001-0.005 g / mL.

[0013] Preferably, the particle size of the aluminum oxide is 30 nm, which is 170 nm. 2 / g.

[0014] The adhesive is any one or more of polyvinylidene fluoride, polyacrylic acid and carboxymethyl cellulose; the concentration of the adhesive in the slurry is 5-10wt%.

[0015] The solvent in the slurry is any one or more of N-methylpyrrolidone, dimethylformamide and dimethyl sulfoxide.

[0016] 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 lauryl sulfate and sodium hexametaphosphate.

[0017] 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.

[0018] An acidic redox flow battery diaphragm has a sandwich structure, comprising a diaphragm substrate in the middle, and a sulfonated polyetheretherketone layer and a nano-alumina modified layer respectively located on the upper and lower sides.

[0019] The diaphragm is a commonly used porous diaphragm on the market, such as a polyethylene-based porous diaphragm, a polypropylene (PP) porous diaphragm, a polyvinylidene fluoride (PVDF) porous diaphragm, or a cellulose-based diaphragm, an inorganic ceramic diaphragm, and the like.

[0020] When assembling the battery, the sulfonated polyetheretherketone layer is located on the positive electrode side, and the nano-aluminum oxide modified layer (Nano-Al2O3) is located on the negative electrode side.

[0021] Beneficial effects of the present invention:

[0022] (1) After the present invention coats a layer of sulfonated polyetheretherketone on the diaphragm, sulfonated polyetheretherketone is a highly hydrophilic polymer containing sulfonic acid groups (-SO3H) on its molecular chain. These groups can attract and bind water molecules to form more hydrated ion channels. This makes it easier for ions in the electrolyte to pass through the membrane, thereby improving the ion conductivity, reducing the ohmic resistance inside the battery, and improving the energy conversion efficiency. Coating the SPEEK layer can significantly increase the hydrophilicity of the diaphragm, making it better match the electrolyte. Enhanced hydrophilicity helps the electrolyte to be more evenly distributed in the membrane, avoiding uneven performance caused by local concentration differences, thereby improving the stability and consistency of the battery. SPEEK itself has good mechanical strength and chemical stability. After being coated on the surface of the domestic membrane, it can not only enhance the mechanical properties of the original membrane, but also improve its tolerance to corrosive electrolytes. This helps to extend the service life of the membrane and ensure the stability of the battery during long-term operation.

[0023] (2) The Nano-Al2O3 modified layer of the present invention greatly improves the mechanical strength of the diaphragm and can effectively inhibit zinc dendrites. Through the coating process, the pore size and porosity of the membrane can be adjusted to make it more suitable for the working conditions of zinc-bromine flow batteries. The optimized membrane structure can more effectively balance the requirements of ion conduction and electronic isolation, further improving battery performance.

[0024] (3) The modified membrane prepared according to the present invention can stably operate up to 500 cycles during the cycle, and the energy efficiency is increased from 68.4% to 74.2%, which greatly improves the energy efficiency and stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 Cycle life diagram of the modified membrane prepared in Example 1 and the original membrane in Comparative Example 1. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Example 1

[0029] An acidic redox flow battery membrane, the preparation method of which comprises the following steps:

[0030] Polyetheretherketone (PEEK) was dried in a vacuum oven at 100°C for 24h, 1g of PEEK was placed in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, and reacted in a constant temperature oil bath at 70°C for 4h. The product after the reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved in 100°C hot water, and after most of the water was removed at room temperature, placed in a 90°C forced air drying oven for 12h, and in a 100°C vacuum drying oven for 24h to obtain sulfonated polyetheretherketone (SPEEK). 0.1g of SPEEK after drying was dissolved in 1mL of N-methylpyrrolidone, reacted for 4h, and then the solution was coated on a polyethylene porous diaphragm with a coating thickness of 5μm. On the negative electrode side, 6% PVDF was dissolved in 100 mL NMP and stirred at 70 ° C for 30 minutes until dissolved. 0.4 g of nano-Al2O3 (particle size 30 nm) and 1.2 g of PEG were added and stirred for 4 hours to fully disperse the PEG. After cooling to room temperature, it was scraped on the negative electrode side of the separator with a scraping thickness of 3 μm. The complete battery was assembled with a charge and discharge current density of 80 mA / cm 2 , surface capacity 5mAh / cm 2 , the discharge cut-off voltage is 0.8V. The battery stack is a single cell, which is assembled in sequence by the positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. After the battery has undergone multiple normal charge and discharge cycles, the electrolyte can run stably for 500 cycles, and the average energy efficiency of the battery is 74.2%, and the coulomb efficiency is 98.5%.

[0031] Example 2

[0032] An acidic redox flow battery membrane, the preparation method of which comprises the following steps:

[0033] Polyetheretherketone (PEEK) was dried in a vacuum oven at 100°C for 24h, 1g of PEEK was placed in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, and reacted in a constant temperature oil bath at 70°C for 2h. The product after the reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved in 100°C hot water, and after most of the water was removed at room temperature, placed in a 90°C forced air drying oven for 12h, and a 100°C vacuum drying oven for 24h to obtain sulfonated polyetheretherketone (SPEEK). 0.1g of SPEEK after drying was dissolved in 1mL of N-methylpyrrolidone, and after reacting for 4h, the solution was coated on a polyethylene porous diaphragm with a coating thickness of 5μm. On the negative electrode side, 6% PVDF was dissolved in 100 mL NMP and stirred at 70 ° C for 30 minutes until dissolved. 0.4 g of nano-Al2O3 (particle size 30 nm) and 1.2 g of PEG were added and stirred for 4 hours to fully disperse the PEG. After cooling to room temperature, it was scraped on the negative electrode side of the separator with a scraping thickness of 3 μm. The complete battery was assembled with a charge and discharge current density of 80 mA / cm 2 , surface capacity 5mAh / cm 2 , the discharge cut-off voltage is 0.8V. The battery stack is a single cell, which is assembled in sequence by the positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. After the battery has undergone multiple normal charge and discharge cycles, the average energy efficiency of the battery is 69.4%, the coulomb efficiency is 96.5%, and the number of cycles is less than 200.

[0034] Example 3

[0035] An acidic redox flow battery membrane, the preparation method of which comprises the following steps:

[0036] Polyetheretherketone (PEEK) was dried in a vacuum oven at 100°C for 24h, 1g of PEEK was placed in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, and reacted in a constant temperature oil bath at 70°C for 6h. The product after the reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved in 100°C hot water, and after most of the water was removed at room temperature, placed in a 90°C forced air drying oven for 12h, and in a 100°C vacuum drying oven for 24h to obtain sulfonated polyetheretherketone (SPEEK). 0.1g of SPEEK after drying was dissolved in 1mL of N-methylpyrrolidone, reacted for 4h, and then the solution was coated on a polyethylene porous diaphragm with a coating thickness of 5μm. On the negative electrode side, 6% PVDF was dissolved in 100 mL NMP and stirred at 70 ° C for 30 minutes until dissolved. 0.4 g of nano-Al2O3 (particle size 30 nm) and 1.2 g of PEG were added and stirred for 4 hours to fully disperse the PEG. After cooling to room temperature, it was scraped on the negative electrode side of the separator with a scraping thickness of 3 μm. The complete battery was assembled with a charge and discharge current density of 80 mA / cm 2, surface capacity 5mAh / cm 2 , the discharge cut-off voltage is 0.8V. The battery stack is a single cell, which is assembled in sequence by the positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. After the battery has undergone multiple normal charge and discharge cycles, the average energy efficiency of the battery is 71.6%, the coulomb efficiency is 97.8%, and the number of cycles is less than 300.

[0037] Example 4

[0038] An acidic redox flow battery membrane, the preparation method of which comprises the following steps:

[0039] Polyetheretherketone (PEEK) was dried in a vacuum oven at 100°C for 24h, 1g of PEEK was placed in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, and reacted in a constant temperature oil bath at 70°C for 8h. The product after the reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved in 100°C hot water, and after most of the water was removed at room temperature, placed in a 90°C forced air drying oven for 12h, and in a 100°C vacuum drying oven for 24h to obtain sulfonated polyetheretherketone (SPEEK). 0.1g of SPEEK after drying was dissolved in 1mL of N-methylpyrrolidone, reacted for 4h, and then the solution was coated on a polyethylene porous diaphragm with a coating thickness of 5μm. On the negative electrode side, 6% PVDF was dissolved in 100 mL NMP and stirred at 70 ° C for 30 minutes until dissolved. 0.4 g of nano-Al2O3 (particle size 30 nm) and 1.2 g of PEG were added and stirred for 4 hours to fully disperse the PEG. After cooling to room temperature, it was scraped on the negative electrode side of the separator with a scraping thickness of 3 μm. The complete battery was assembled with a charge and discharge current density of 80 mA / cm 2 , surface capacity 5mAh / cm 2 , the discharge cut-off voltage is 0.8V. The battery stack is a single cell, which is assembled in sequence by the positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. After the battery has undergone multiple normal charge and discharge cycles, the average energy efficiency of the battery is 70.6%, the coulomb efficiency is 97.3%, and the number of cycles is less than 200.

[0040] Example 5

[0041] An acidic redox flow battery membrane, the preparation method of which comprises the following steps:

[0042] Polyetheretherketone (PEEK) was dried in a vacuum oven at 100°C for 24h, 1g of PEEK was placed in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, and reacted in a constant temperature oil bath at 70°C for 4h. The product after the reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved in 100°C hot water, and after most of the water was removed at room temperature, placed in a 90°C forced air drying oven for 12h, and in a 100°C vacuum drying oven for 24h to obtain sulfonated polyetheretherketone (SPEEK). 0.1g of SPEEK after drying was dissolved in 1mL of N-methylpyrrolidone, reacted for 4h, and then the solution was coated on a polyethylene porous diaphragm with a coating thickness of 1μm. On the negative electrode side, 6% PVDF was dissolved in 100 mL NMP and stirred at 70 ° C for 30 minutes until dissolved. 0.4 g of nano-Al2O3 (particle size 30 nm) and 1.2 g of PEG were added and stirred for 4 hours to fully disperse the PEG. After cooling to room temperature, it was scraped on the negative electrode side of the separator with a scraping thickness of 3 μm. The complete battery was assembled with a charge and discharge current density of 80 mA / cm 2 , surface capacity 5mAh / cm 2 , the discharge cut-off voltage is 0.8V. The battery stack is a single cell, which is assembled in sequence by the positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. After the battery has undergone multiple normal charge and discharge cycles, the average energy efficiency of the battery is 69.9%, the coulomb efficiency is 96.8%, and the number of cycles is less than 150.

[0043] Example 6

[0044] An acidic redox flow battery membrane, the preparation method of which comprises the following steps:

[0045] Polyetheretherketone (PEEK) was dried in a vacuum oven at 100°C for 24h, 1g of PEEK was placed in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, and reacted in a constant temperature oil bath at 70°C for 4h. The product after the reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved in 100°C hot water, and after most of the water was removed at room temperature, placed in a 90°C forced air drying oven for 12h, and in a 100°C vacuum drying oven for 24h to obtain sulfonated polyetheretherketone (SPEEK). 0.1g of SPEEK after drying was dissolved in 1mL of N-methylpyrrolidone, reacted for 4h, and then the solution was coated on a polyethylene porous diaphragm with a coating thickness of 5μm. On the negative electrode side, 6% PVDF was dissolved in 100 mL NMP and stirred at 70 ° C for 30 minutes until dissolved. 0.2 g of nano-Al2O3 (particle size 30 nm) and 0.8 g of PEG were added and stirred for 4 hours to fully disperse the PEG. After cooling to room temperature, it was scraped on the negative electrode side of the separator with a scraping thickness of 1 μm. The complete battery was assembled with a charge and discharge current density of 80 mA / cm 2, surface capacity 5mAh / cm 2 , the discharge cut-off voltage is 0.8V. The battery stack is a single cell, which is assembled in sequence by the positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. After the battery has undergone multiple normal charge and discharge cycles, the average energy efficiency of the battery is 70.5%, the coulomb efficiency is 98.3%, and the number of cycles is less than 250.

[0046] Example 7

[0047] An acidic redox flow battery membrane, the preparation method of which comprises the following steps:

[0048] Polyetheretherketone (PEEK) was dried in a vacuum oven at 100°C for 24h, 1g of PEEK was placed in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, and reacted in a constant temperature oil bath at 70°C for 4h. The product after the reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved in 100°C hot water, and after most of the water was removed at room temperature, placed in a 90°C forced air drying oven for 12h, and in a 100°C vacuum drying oven for 24h to obtain sulfonated polyetheretherketone (SPEEK). 0.1g of SPEEK after drying was dissolved in 1mL of N-methylpyrrolidone, reacted for 4h, and then the solution was coated on a polyethylene porous diaphragm with a coating thickness of 5μm. On the negative electrode side, 6% PVDF was dissolved in 100 mL NMP and stirred at 70 ° C for 30 minutes until dissolved. 0.2 g of nano-Al2O3 (particle size 30 nm) and 0.8 g of PEG were added and stirred for 4 hours to fully disperse the PEG. After cooling to room temperature, it was scraped on the negative electrode side of the separator with a scraping thickness of 5 μm. The complete battery was assembled with a charge and discharge current density of 80 mA / cm 2 , surface capacity 5mAh / cm 2 , discharge cut-off voltage 0.8V. The battery stack is a single cell, which is assembled in sequence by positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. The average energy efficiency of the battery is 71.5%, the coulomb efficiency is 97.8%, and the number of cycles is less than 200.

[0049] Example 8

[0050] An acidic redox flow battery membrane, the preparation method of which comprises the following steps:

[0051] Polyetheretherketone (PEEK) was dried in a vacuum oven at 100°C for 24h, 1g of PEEK was placed in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, and reacted in a constant temperature oil bath at 70°C for 4h. The product after the reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved in 100°C hot water, and after most of the water was removed at room temperature, placed in a 90°C forced air drying oven for 12h, and in a 100°C vacuum drying oven for 24h to obtain sulfonated polyetheretherketone (SPEEK). 0.1g of SPEEK after drying was dissolved in 1mL of N-methylpyrrolidone, reacted for 4h, and then the solution was coated on a polyethylene porous diaphragm with a coating thickness of 5μm. On the negative electrode side, 6% PVDF was dissolved in 100 mL NMP and stirred at 70 ° C for 30 minutes until dissolved. 0.1 g of nano-Al2O3 (particle size 30 nm) and 0.4 g of PEG were added and stirred for 4 hours to fully disperse the PEG. After cooling to room temperature, it was scraped on the negative electrode side of the separator with a scraping thickness of 3 μm. The complete battery was assembled with a charge and discharge current density of 80 mA / cm 2 , surface capacity 5mAh / cm 2 , the discharge cut-off voltage is 0.8V. The battery stack is a single cell, which is assembled in sequence by the positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. After the battery has undergone multiple normal charge and discharge cycles, the average energy efficiency of the battery is 70.6%, the coulomb efficiency is 97.4%, and the number of cycles is less than 150.

[0052] Example 9

[0053] An acidic redox flow battery membrane, the preparation method of which comprises the following steps:

[0054] Polyetheretherketone (PEEK) was dried in a vacuum oven at 100°C for 24h, 1g of PEEK was placed in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, and reacted in a constant temperature oil bath at 70°C for 4h. The product after the reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved in 100°C hot water, and after most of the water was removed at room temperature, placed in a 90°C forced air drying oven for 12h, and in a 100°C vacuum drying oven for 24h to obtain sulfonated polyetheretherketone (SPEEK). 0.1g of SPEEK after drying was dissolved in 1mL of N-methylpyrrolidone, reacted for 4h, and then the solution was coated on a polyethylene porous diaphragm with a coating thickness of 5μm. On the negative electrode side, 6% PVDF was dissolved in 100 mL NMP and stirred at 70 ° C for 30 minutes until dissolved. 0.5 g of nano-Al2O3 (particle size 30 nm) and 1.0 g of PEG were added and stirred for 4 hours to fully disperse the PEG. After cooling to room temperature, it was scraped on the negative electrode side of the separator with a scraping thickness of 3 μm. The complete battery was assembled with a charge and discharge current density of 80 mA / cm 2, surface capacity 5mAh / cm 2 , the discharge cut-off voltage is 0.8V. The battery stack is a single cell, which is assembled in sequence by the positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. After the battery has undergone multiple normal charge and discharge cycles, the average energy efficiency of the battery is 70.9%, the coulomb efficiency is 96.3%, and the number of cycles is less than 170.

[0055] Example 10

[0056] An acidic redox flow battery membrane, the preparation method of which comprises the following steps:

[0057] Polyetheretherketone (PEEK) was dried in a vacuum oven at 100°C for 24h, 1g of PEEK was placed in a round-bottom flask containing 10mL of 98% concentrated sulfuric acid, and reacted in a constant temperature oil bath at 50°C for 10h, the product after the reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved in 100°C hot water, and after most of the water was removed at room temperature, placed in a 90°C forced air drying oven for 12h, and a 100°C vacuum drying oven for 24h to obtain sulfonated polyetheretherketone (SPEEK). 0.05g of SPEEK after drying was dissolved in 1mL of dimethylformamide, reacted for 4h, and the solution was coated on a polyethylene porous diaphragm with a coating thickness of 5μm. On the negative electrode side, 10% PVDF was dissolved in 100 mL NMP and stirred at 70 °C for 30 minutes until dissolved. 0.1 g of nano-Al2O3 and 1.2 g of sodium dodecyl sulfate were added and stirred for 4 h to fully disperse the sodium dodecyl sulfate. After cooling to room temperature, it was scraped on the negative electrode side of the separator with a scraping thickness of 3 μm. The complete battery was assembled with a charge and discharge current density of 80 mA / cm 2 , surface capacity 5mAh / cm 2 , the discharge cut-off voltage is 0.8V. The battery stack is a single cell, which is assembled in sequence by the positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. After the battery has undergone multiple normal charge and discharge cycles, the electrolyte can stably operate for 200 cycles, and the average energy efficiency of the battery is 71.2%, and the coulomb efficiency is 97.5%.

[0058] Comparative Example 1 (unmodified diaphragm)

[0059] The polyethylene-based porous separator used in Examples 1-9 was assembled into a complete battery with a charge and discharge current density of 80 mA / cm 2 , surface capacity 5mAh / cm 2, discharge cut-off voltage 0.8V. The battery stack is a single cell, which is assembled in sequence by positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. After the battery has undergone multiple normal charge and discharge cycles, the average energy efficiency of the battery is 70.9%, the coulomb efficiency is 96.3%, and the number of cycles is less than 170. Figure 1 It can be seen that the energy efficiency and coulombic efficiency of the battery composed of unmodified diaphragms decrease after running for less than two hundred cycles.

[0060] Comparative Example 2 (coating only the positive electrode)

[0061] A battery separator, the preparation method of which comprises the following steps:

[0062] Dry polyetheretherketone (PEEK) in a vacuum drying oven at 100°C for 24 hours, take 1g of PEEK and put it in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, react in a constant temperature oil bath at 70°C for 4 hours, place the product after the reaction in an ice-water mixture, wash with distilled water until neutral, dissolve the product with 100°C hot water, and after most of the water is removed at room temperature, place it in a 90°C forced air drying oven for 12 hours and a 100°C vacuum drying oven for 24 hours to obtain sulfonated polyetheretherketone (SPEEK). Dissolve 0.1g of dried SPEEK in 1mL of N-methylpyrrolidone, react for 4 hours, and then coat the solution on a polyethylene porous diaphragm with a coating thickness of 5μm. Assemble a complete battery with a charge and discharge current density of 80mA / cm 2 , surface capacity 5mAh / cm 2 , the discharge cut-off voltage is 0.8V. The battery stack is a single cell, which is assembled in sequence by the positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. After the battery has undergone multiple normal charge and discharge cycles, the average energy efficiency of the battery is 70.4%, the coulomb efficiency is 96.5%, and the number of cycles is less than 200.

[0063] Comparative Example 3 (only negative electrode coating)

[0064] A battery separator, the preparation method of which comprises the following steps:

[0065] On the negative electrode side, 6% PVDF was dissolved in 100 mL NMP and stirred at 70 °C for 30 minutes until dissolved. 0.4 g of nano-Al2O3 and 1.2 g of PEG were added and stirred for 4 hours to fully disperse the PEG. After cooling to room temperature, it was scraped on the negative electrode side of the separator with a scraping thickness of 3 μm. The complete battery was assembled with a charge and discharge current density of 80 mA / cm 2 , surface capacity 5mAh / cm 2, the discharge cut-off voltage is 0.8V. The battery stack is a single cell, which is assembled in sequence by the positive terminal plate, current collector, graphite plate, carbon felt, diaphragm, carbon felt, graphite plate, current collector, and negative terminal plate. After the battery has undergone multiple normal charge and discharge cycles, the average coulomb efficiency of the battery is 96.7%, the energy efficiency is 70.6%, and the number of cycles is less than 100.

[0066] Mechanical properties test: The prepared diaphragms in Example 1 and Comparative Examples 1-3 were cut and subjected to tensile tests. The results are shown in Table 1. By comparing Comparative Examples 2 and 3 with Comparative Example 1, it can be seen that coating modification can improve the mechanical properties of the diaphragm. The tensile strength of the diaphragm prepared in Comparative Example 3 is higher than that in Comparative Example 2, proving that the Nano-Al2O3 modified layer greatly improves the mechanical strength of the diaphragm. In addition, the tensile strength of the sandwich structure diaphragm prepared in Example 1 reached 13.2Mpa, which is much higher than that of the battery diaphragm without coating modification and single-side coating. The improvement of mechanical properties by double-layer coating in Example 1 is not a simple superposition of tensile strength by coating the negative electrode and coating the positive electrode. There is a synergistic effect between the two in improving mechanical properties.

[0067] Table 1 Comparison of mechanical tensile strength of various diaphragms

[0068] type <![CDATA[Membrane 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

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing an acidic redox flow battery membrane, characterized in that: The following steps are involved: preparing a sulfonated polyetheretherketone solution, and coating the sulfonated polyetheretherketone solution on one side of the diaphragm substrate; The nano-alumina and adhesive are dispersed and dissolved in a solvent to form a slurry, and the slurry is coated on 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 preparation method of the sulfonated polyetheretherketone is as follows: adding polyetheretherketone into 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, 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 hours.

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; 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, characterized in that: 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, 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 lauryl sulfate and sodium hexametaphosphate.

9. The method for preparing an acidic redox flow battery membrane 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 diaphragm is a sandwich structure, comprising a diaphragm substrate in the middle, and a sulfonated polyetheretherketone layer and a nano-alumina modified layer respectively located on the upper and lower sides.

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