An acidic redox flow battery membrane and method of making the same

Abstract

The application provides an acid redox flow battery diaphragm and a preparation method thereof, and belongs to the technical field of liquid flow batteries, and aims to solve the technical problems of low energy efficiency and poor cycle stability of the liquid flow battery.The preparation method comprises the following steps: preparing a sulfonated polyether ether ketone solution, and coating the sulfonated polyether ether ketone solution on one side of a diaphragm substrate; dispersing and dissolving nano-aluminum oxide and a glue adhesive into a solvent to prepare slurry, and coating the slurry on the other side of the diaphragm substrate.The application coats a layer of sulfonated polyether ether ketone on the positive electrode side, adjusts the sulfonation degree and the thickness of the modified layer to improve the hydrophilicity and ion exchange rate of the modified film, coats Nano-Al2O3 on the negative electrode side, adjusts the content and coating thickness of the Nano-Al2O3, and achieves the purpose of improving the mechanical strength of the diaphragm positive electrode side and inhibiting the generation of zinc dendrites.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of flow batteries, and particularly relates to a flow battery separator. BACKGROUND

[0002] In terms of sustainable development of human society, the use of renewable energy such as wind 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, ecological friendliness, easy expansion, etc., and are considered as advanced energy storage technology. Zinc-bromine flow battery is considered as one of the most potential large-scale energy storage technologies due to its consistent positive and negative electrolyte, no cross contamination, low cost, high safety, and high theoretical energy density of 430 Wh / kg.

[0003] Zinc-bromine flow battery is a device that realizes energy storage and release through electrochemical reaction, and its working principle is based on the redox reaction between zinc ions and bromine ions. This battery has the advantages of high energy density, long cycle life and high charging and discharging efficiency, and is particularly suitable for large-scale energy storage systems. However, in practical application, zinc-bromine flow battery still faces some challenges, one of which is the selection and performance optimization of separator materials.

[0004] Currently, zinc-bromine flow battery mainly uses perfluorosulfonic acid membrane (such as Nafion membrane) as separator material, although this membrane has good ion selectivity and mechanical strength, but also exposes some key problems. First, the cost of perfluorosulfonic acid membrane is high, which is a big obstacle for large-scale commercial application. The high cost not only increases the production cost of the battery, but also limits its popularity in scenarios with high economic requirements. Second, the stability of perfluorosulfonic acid membrane in acidic environment is poor, which is easy to degrade, thereby affecting the long-term stability and service life of the battery. In addition, this membrane also has the problem of bromine permeation, that is, during the operation of the battery, bromine ions may penetrate through the separator into the negative electrode side, causing the mixing of positive and negative electrolytes, and then causing the capacity decay and performance decline of the battery. In addition to the limitations of the material itself, the performance of perfluorosulfonic acid membrane is also not satisfactory. For example, its porosity is low, which is not conducive to the flow of electrolyte, thereby increasing the internal resistance of the battery and reducing the energy conversion efficiency. In addition, due to the limited hydrophilicity of perfluorosulfonic acid membrane, the distribution of electrolyte in the membrane is uneven, which affects the consistency and reliability of the battery. Therefore, developing low-cost and high-performance domestic membranes will be one of the important directions in the field of zinc-bromine flow battery.

[0005] To overcome the above-mentioned shortcomings and improve the overall performance of zinc-bromine flow batteries, researchers have begun to explore methods to modify existing separator 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 separators. For example, Patent Publication No. CN103562268A discloses a method for manufacturing a membrane or separator, comprising: (a) dissolving at least one polymer comprising a poly(aryl ketone) into at least one solvent to form a viscous substance: (b) depositing the viscous substance onto a substrate under appropriate conditions to form a coated substrate; and (c) drying the coated substrate to form the membrane or separator. The viscous substance can also include additional polymers or fillers, such as carbon nanotubes. For example, Patent Publication No. CN118970087A discloses a class of functionalized separators modified by titanium oxide carbon for application 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). Subsequently, through the synergistic effect of TiC x O 1-x with sulfonated polyether ether ketone (SPEEK) solution, a low-cost polyvinyl porous separator is modified by blade coating. These improvements aim to reduce the internal resistance of the battery, reduce the occurrence of side reactions, and prolong the service life of the battery, thereby paving the way for large-scale commercial application of zinc-bromine flow batteries. Through continuous optimization of the separator material, 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 future renewable energy fields. At the same time, this will also promote the technological progress and sustainable development of related industries. SUMMARY

[0006] To solve the above technical problems, the present application provides an acidic redox flow battery separator and a preparation method thereof, which improves the hydrophilicity, ion conductivity and mechanical strength of the separator, thereby improving the performance of the battery, mainly improving the energy efficiency and cycle stability of the battery.

[0007] To achieve the above-mentioned purposes, the technical scheme of the present application is as follows:

[0008] A preparation method of an acidic redox flow battery separator, comprising the following steps: preparing a sulfonated polyether ether ketone solution, coating the sulfonated polyether ether ketone solution to one side of the separator substrate; dispersing and dissolving nano-aluminum oxide and adhesive into a solvent to configure a slurry, and coating the slurry to the other side of the separator substrate.

[0009] The preparation method of the sulfonated polyether ether ketone is: polyether ether ketone is added to concentrated sulfuric acid for sulfonation reaction, and after the reaction is completed, it is washed and dried to obtain. Through sulfonation treatment, the molecular chain contains sulfonic acid groups (-SO3H), which can attract and combine water molecules, thereby improving the hydrophilicity of polyether ether ketone.

[0010] The ratio of the polyether ether ketone to 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.

[0011] The concentration of the sulfonated polyether ether ketone in the sulfonated polyether ether ketone solution is 0.05-0.1 g / mL, and the solvent is any one or two or more of N-methylpyrrolidone, dimethylformamide and dimethyl sulfoxide.

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

[0013] Preferably, the particle size of the nano-aluminum oxide is 30 nm, and the specific surface area is 170 m 2 / g.

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

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

[0016] The slurry further comprises a dispersant, and the concentration of the dispersant in the slurry is 0.004-0.012 g / mL; the dispersant is any one or two or more of polyethylene glycol, sodium dodecyl sulfate and sodium hexametaphosphate.

[0017] The coating thickness of the sulfonated polyether ether ketone solution on the diaphragm substrate is 1-5 μm; and the coating thickness of the slurry on the diaphragm substrate is 1-5 μm.

[0018] An acidic redox flow battery diaphragm, which is a sandwich structure comprising a middle diaphragm substrate, and a sulfonated polyether ether ketone layer and a nano-aluminum oxide modified layer located on the upper and lower sides, respectively.

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

[0020] In the assembly of the battery, the sulfonated polyether ether ketone 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] The beneficial effects of the present application are:

[0022] (1) The invention coats a layer of sulfonated polyether ether ketone on the separator. Sulfonated polyether ether ketone is a polymer with high hydrophilicity, containing sulfonic acid groups (-SO3H) in its molecular chain. These groups can attract and bind water molecules, forming more hydrated ion channels. This makes it easier for ions in the electrolyte to pass through the membrane, thereby improving ion conductivity, reducing internal ohmic resistance, and improving energy conversion efficiency. Coating the SPEEK layer can significantly increase the hydrophilicity of the separator, making it better match the electrolyte. Enhanced hydrophilicity helps the electrolyte distribute more evenly within the membrane, avoiding performance inconsistencies caused by local concentration differences, thereby improving battery stability and consistency. SPEEK itself has good mechanical strength and chemical stability, and after being coated on the surface of the domestic membrane, it not only enhances the mechanical properties of the original membrane, but also improves its resistance to corrosive electrolyte. 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 modification layer greatly improves the mechanical strength of the separator, effectively inhibits zinc dendrites, and through the coating process, the pore size and porosity of the membrane can be adjusted to better suit the working conditions of the zinc-bromine flow battery. The optimized membrane structure can more effectively balance the needs of ion conduction and electronic isolation, further improving battery performance.

[0024] (3) The modified membrane prepared in the invention can stably operate for 500 cycles in the cycle process, 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 DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings described below are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of these drawings.

[0026] Figure 1 Cycle life chart of modified membrane for Example 1 and original membrane for Comparative Example 1. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0028] Example 1

[0029] An acidic redox flow battery separator, the preparation method comprising the following steps:

[0030] Polyether ether ketone (PEEK) was dried in a vacuum drying 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 reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved in hot water at 100°C, and then placed in a 90°C air-drying oven for 12h and a 100°C vacuum drying oven for 24h to obtain sulfonated polyether ether ketone (SPEEK). 0.1g of dried SPEEK was dissolved in 1mL of N-methylpyrrolidone, and after 4h of reaction, the solution was coated on a polyethylene porous separator with a coating thickness of 5μm. A mass fraction of 6% PVDF was dissolved in 100mL of NMP, stirred at 70°C for 30 minutes until dissolved, 0.4g of nano-Al2O3 (particle size 30nm) and 1.2g of PEG were added, and the PEG was fully dispersed by stirring for 4h. After cooling to room temperature, it was blade-coated on the negative electrode side of the separator with a blade-coating thickness of 3μm. A complete battery was assembled, and the charge and discharge current density was 80mA / cm 2 , the face capacity was 5mAh / cm 2 , and the discharge cut-off voltage was 0.8V. The stack was a single cell, which was assembled in order of positive end plate, current collector, graphite plate, carbon felt, separator, carbon felt, graphite plate, current collector, and negative end plate. After the battery underwent multiple normal charge and discharge cycles, the electrolyte could be stably operated for 500 cycles, the average energy efficiency of the battery was 74.2%, and the coulombic efficiency was 98.5%.

[0031] Example 2

[0032] An acidic redox flow battery separator, the preparation method comprising the following steps:

[0033] The polyether ether ketone (PEEK) was dried in a vacuum drying 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 reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved with hot water at 100°C, and after most of the water was removed at room temperature, placed in a 90°C air-drying oven for 12h and a 100°C vacuum drying oven for 24h to obtain sulfonated polyether ether ketone (SPEEK). 0.1g of dried SPEEK was dissolved in 1mL of N-methylpyrrolidone, and after 4h of reaction, the solution was coated on a polyethylene porous separator with a coating thickness of 5μm. On the negative side, 6% PVDF by mass was dissolved in 100mL of NMP, stirred at 70°C for 30 minutes until dissolved, 0.4g of nano-Al203 (particle size 30nm) and 1.2g of PEG were added, and the PEG was fully dispersed by stirring for 4h. After cooling to room temperature, it was blade-coated on the negative side of the separator with a blade-coating thickness of 3μm. A complete battery was assembled with a charge-discharge current density of 80mA / cm 2 , a surface capacity of 5mAh / cm 2 , and a discharge cut-off voltage of 0.8V. The stack was a single cell, which was assembled in order of positive end plate, current collector, graphite plate, carbon felt, separator, carbon felt, graphite plate, current collector, negative end plate. After the battery was subjected to multiple normal charge-discharge cycles, the average energy efficiency of the battery was 69.4%, the coulombic efficiency was 96.5%, and the cycle number was <200 cycles.

[0034] Example 3

[0035] An acidic redox flow battery separator, the preparation method comprising the following steps:

[0036] The polyether ether ketone (PEEK) was dried in a vacuum drying 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 reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved with hot water at 100°C, and after most of the water was removed at room temperature, placed in a 90°C air-drying oven for 12h and a 100°C vacuum drying oven for 24h to obtain sulfonated polyether ether ketone (SPEEK). 0.1g of dried SPEEK was dissolved in 1mL of N-methylpyrrolidone, and after 4h of reaction, the solution was coated on a polyethylene porous separator with a coating thickness of 5μm. On the negative side, 6% PVDF by mass was dissolved in 100mL of NMP, stirred at 70°C for 30 minutes until dissolved, 0.4g of nano-Al203 (particle size 30nm) and 1.2g of PEG were added, and the PEG was fully dispersed by stirring for 4h. After cooling to room temperature, it was blade-coated on the negative side of the separator with a blade-coating thickness of 3μm. A complete battery was assembled with a charge-discharge current density of 80mA / cm 2, face capacity 5 mAh / cm 2 , discharge cut-off voltage 0.8 V. The stack is a single cell, which is assembled by positive end plate, current collector, graphite plate, carbon felt, separator, carbon felt, graphite plate, current collector, negative end plate in turn. After the electrolyte in the battery after a number of normal charge and discharge cycle, the average energy efficiency of the battery is 71.6%, the coulomb efficiency is 97.8%, and the cycle number is <300 cycles.

[0037] Example 4

[0038] An acidic redox flow battery separator, the preparation method comprising the following steps:

[0039] Polyether ether ketone (PEEK) is dried in a vacuum drying box at 100°C for 24h, 1g of PEEK is placed in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, and reacted in a 70°C constant temperature oil bath for 8h. The product after reaction is placed in an ice-water mixture, washed with distilled water until neutral, dissolved in hot water at 100°C, and then placed in a 90°C air-drying oven for 12h and a 100°C vacuum drying box for 24h to obtain sulfonated polyether ether ketone (SPEEK). 0.1g of dried SPEEK is dissolved in 1mL of N-methylpyrrolidone, and the solution is coated on a polyvinyl porous separator after reacting for 4h, with a coating thickness of 5μm. A mass fraction of 6% PVDF is dissolved in 100mL of NMP, stirred at 70°C for 30 minutes until dissolved, 0.4g of nano-Al2O3 (particle size 30nm) and 1.2g of PEG are added, and the PEG is fully dispersed by stirring for 4h. After cooling to room temperature, it is scraped and coated on the negative side of the separator, with a scraping thickness of 3μm. A complete battery is assembled, and the charge and discharge current density is 80mA / cm 2 , face capacity 5 mAh / cm 2 , discharge cut-off voltage 0.8 V. The stack is a single cell, which is assembled by positive end plate, current collector, graphite plate, carbon felt, separator, carbon felt, graphite plate, current collector, negative end plate in turn. After the electrolyte in the battery after a number of normal charge and discharge cycle, the average energy efficiency of the battery is 71.6%, the coulomb efficiency is 97.8%, and the cycle number is <300 cycles.

[0040] Example 5

[0041] An acidic redox flow battery separator, the preparation method comprising the following steps:

[0042] The polyether ether ketone (PEEK) was dried in a vacuum drying 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 reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved with hot water at 100°C, and after most of the water was removed at room temperature, placed in a 90°C air-drying oven for 12h and a 100°C vacuum drying oven for 24h to obtain sulfonated polyether ether ketone (SPEEK). 0.1g of dried SPEEK was dissolved in 1mL of N-methylpyrrolidone, and after 4h of reaction, the solution was coated on a polyethylene porous separator with a coating thickness of 1μm. On the negative side, 6% PVDF by mass was dissolved in 100mL of NMP, stirred at 70°C for 30 minutes until dissolved, 0.4g of nano-Al2O3 (particle size 30nm) and 1.2g of PEG were added, and the PEG was fully dispersed by stirring for 4h. After cooling to room temperature, it was blade-coated on the negative side of the separator with a blade-coating thickness of 3μm. A complete battery was assembled with a charge-discharge current density of 80mA / cm 2 , a surface capacity of 5mAh / cm 2 , and a discharge cut-off voltage of 0.8V. The stack was a single cell, which was assembled in order of positive end plate, current collector, graphite plate, carbon felt, separator, carbon felt, graphite plate, current collector, negative end plate. After the battery was subjected to multiple normal charge-discharge cycles, the average energy efficiency of the battery was 69.9%, the coulombic efficiency was 96.8%, and the cycle number was <150 cycles.

[0043] Example 6

[0044] An acidic redox flow battery separator, the preparation method comprising the following steps:

[0045] The polyether ether ketone (PEEK) was dried in a vacuum drying 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 reaction was placed in an ice-water mixture, washed with distilled water until neutral, dissolved with hot water at 100°C, and after most of the water was removed at room temperature, placed in a 90°C air-drying oven for 12h and a 100°C vacuum drying oven for 24h to obtain sulfonated polyether ether ketone (SPEEK). 0.1g of dried SPEEK was dissolved in 1mL of N-methylpyrrolidone, and after 4h of reaction, the solution was coated on a polyethylene porous separator with a coating thickness of 1μm. On the negative side, 6% PVDF by mass was dissolved in 100mL of NMP, stirred at 70°C for 30 minutes until dissolved, 0.4g of nano-Al2O3 (particle size 30nm) and 1.2g of PEG were added, and the PEG was fully dispersed by stirring for 4h. After cooling to room temperature, it was blade-coated on the negative side of the separator with a blade-coating thickness of 3μm. A complete battery was assembled with a charge-discharge current density of 80mA / cm 2, face capacity 5 mAh / cm 2 , discharge cut-off voltage 0.8 V. The stack is a single cell, which is assembled by positive end plate, current collector, graphite plate, carbon felt, separator, carbon felt, graphite plate, current collector, negative end plate in turn. After the battery 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 <250 cycles.

[0046] Example 7

[0047] An acidic redox flow battery separator, the preparation method thereof comprises the following steps:

[0048] Polyether ether ketone (PEEK) is dried in a vacuum drying box at 100°C for 24h, 1g of PEEK is placed in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, and reacted in a 70°C constant temperature oil bath for 4h. The product after reaction is placed in an ice-water mixture, washed with distilled water until neutral, dissolved in hot water at 100°C, and after most of the water is removed at room temperature, placed in a 90°C air-drying oven for 12h and a 100°C vacuum drying box for 24h to obtain sulfonated polyether ether ketone (SPEEK). 0.1g of dried SPEEK is dissolved in 1mL of N-methylpyrrolidone, and after 4h of reaction, the solution is coated on a polyvinyl porous separator with a coating thickness of 5μm. A mass fraction of 6% PVDF is dissolved in 100mL of NMP, stirred at 70°C for 30 minutes until dissolved, 0.2g of nano-Al2O3 (particle size 30nm) and 0.8g of PEG are added, and the PEG is fully dispersed by stirring for 4h. After cooling to room temperature, it is scraped onto the negative side of the separator with a scraping thickness of 5μm. A complete battery is assembled, and the charge and discharge current density is 80mA / cm 2 , face capacity 5 mAh / cm 2 , discharge cut-off voltage 0.8 V. The stack is a single cell, which is assembled by positive end plate, current collector, graphite plate, carbon felt, separator, carbon felt, graphite plate, current collector, negative end plate in turn. After the battery 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 <250 cycles.

[0049] Example 8

[0050] An acidic redox flow battery separator, the preparation method thereof comprises the following steps:

[0051] The polyether ether ketone (PEEK) was dried in a vacuum drying 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 reaction was placed in an ice water mixture, washed with distilled water until neutral, dissolved with hot water at 100°C, and after most of the water was removed at room temperature, placed in a 90°C air drying oven for 12h, and in a 100°C vacuum drying oven for 24h to obtain sulfonated polyether ether ketone (SPEEK). 0.1g of dried SPEEK was dissolved in 1mL of N-methylpyrrolidone, and after 4h of reaction, the solution was coated on a polyethylene porous separator with a coating thickness of 5μm. On the negative side, 6% PVDF by mass was dissolved in 100mL of NMP, stirred at 70°C for 30 minutes until dissolved, 0.1g of nano-Al2O3 (particle size 30nm) and 0.4g of PEG were added, and stirred for 4h to fully disperse the PEG. After cooling to room temperature, it was blade coated on the negative side of the separator with a blade coating thickness of 3μm. A complete battery was assembled with a charge and discharge current density of 80mA / cm 2 , a face capacity of 5mAh / cm 2 , and a discharge cut-off voltage of 0.8V. The stack was a single cell, which was assembled in order of positive end plate, current collector, graphite plate, carbon felt, separator, carbon felt, graphite plate, current collector, negative end plate. After the battery was subjected to multiple normal charge and discharge cycles, the average energy efficiency of the battery was 70.6%, the coulombic efficiency was 97.4%, and the cycle number was <150 cycles.

[0052] Example 9

[0053] An acidic redox flow battery separator, the preparation method comprising the following steps:

[0054] The polyether ether ketone (PEEK) was dried in a vacuum drying 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 reaction was placed in an ice water mixture, washed with distilled water until neutral, dissolved with hot water at 100°C, and after most of the water was removed at room temperature, placed in a 90°C air drying oven for 12h, and in a 100°C vacuum drying oven for 24h to obtain sulfonated polyether ether ketone (SPEEK). 0.1g of dried SPEEK was dissolved in 1mL of N-methylpyrrolidone, and after 4h of reaction, the solution was coated on a polyethylene porous separator with a coating thickness of 5μm. On the negative side, 6% PVDF by mass was dissolved in 100mL of NMP, stirred at 70°C for 30 minutes until dissolved, 0.1g of nano-Al2O3 (particle size 30nm) and 0.4g of PEG were added, and stirred for 4h to fully disperse the PEG. After cooling to room temperature, it was blade coated on the negative side of the separator with a blade coating thickness of 3μm. A complete battery was assembled with a charge and discharge current density of 80mA / cm 2Surface capacity 5mAh / cm 2 The discharge cutoff voltage is 0.8V. The battery stack is a single cell, which is assembled from a positive terminal plate, current collector, graphite plate, carbon felt, separator, carbon felt, graphite plate, current collector, and negative terminal plate arranged in sequence. After the battery has undergone multiple normal charge-discharge cycles, the average energy efficiency is 70.9%, the coulombic efficiency is 96.3%, and the number of cycles is <170.

[0055] Example 10

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

[0057] Polyether ether ketone (PEEK) was dried in a vacuum drying oven at 100℃ for 24 h. 1 g of PEEK was placed in a round-bottom flask containing 10 mL of 98% concentrated sulfuric acid and reacted in a constant-temperature oil bath at 50℃ for 10 h. The product was then placed in an ice-water mixture and washed with distilled water until neutral. The product was dissolved in 100℃ hot water, and after most of the water was removed at room temperature, it was placed in a 90℃ forced-air drying oven for 12 h, followed by a 100℃ vacuum drying oven for 24 h to obtain sulfonated polyether ether ketone (SPEEK). 0.05 g of the dried SPEEK was dissolved in 1 mL of dimethylformamide, and after reacting for 4 h, the solution was coated onto a polyethylene porous membrane with a coating thickness of 5 μm. On the negative electrode side, 10% PVDF was dissolved in 100 mL of NMP and stirred at 70 °C for 30 minutes until dissolved. Then, 0.1 g of nano-Al₂O₃ and 1.2 g of sodium dodecyl sulfate were added, and the mixture was stirred for 4 hours to fully disperse the sodium dodecyl sulfate. After cooling to room temperature, the mixture was coated onto the negative electrode side of the separator to a thickness of 3 μm. The complete battery was assembled, and the charge / discharge current density was 80 mA / cm². 2 Surface capacity 5mAh / cm 2 The discharge cutoff voltage is 0.8V. The stack is a single cell, assembled sequentially from a positive terminal plate, current collector, graphite plate, carbon felt, separator, carbon felt, graphite plate, current collector, and negative terminal plate. After multiple normal charge-discharge cycles, the electrolyte can operate stably for 200 cycles, with an average energy efficiency of 71.2% and a coulombic efficiency of 97.5%.

[0058] Comparative Example 1 (Unmodified diaphragm)

[0059] The polyethylene-based porous separators used in Examples 1-9 were used to assemble complete batteries, with a charge / discharge current density of 80 mA / cm². 2 Surface capacity 5mAh / cm 2, discharge cut-off voltage 0.8V. The stack is a single cell, which is assembled by positive end plate, current collector, graphite plate, carbon felt, separator, carbon felt, graphite plate, current collector, negative end plate in turn. After the electrolyte in the battery undergoes 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 <170 cycles. By Figure 1 It can be seen that the energy efficiency and coulomb efficiency of the battery composed of the unmodified separator decrease after less than 200 cycles.

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

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

[0062] Polyether ether ketone (PEEK) is dried in a vacuum drying box at 100°C for 24h, 1g of PEEK is placed in a round-bottom flask containing 20mL of 98% concentrated sulfuric acid, and reacted in a 70°C constant-temperature oil bath for 4h. The product after reaction is placed in an ice-water mixture, washed with distilled water until neutral, dissolved in hot water at 100°C, and then placed in a 90°C air-drying oven for 12h and a 100°C vacuum drying box for 24h to obtain sulfonated polyether ether ketone (SPEEK). 0.1g of dried SPEEK is dissolved in 1mL of N-methylpyrrolidone, and the solution is coated on a polyethylene porous separator after reacting for 4h. The coating thickness is 5μm. A complete battery is assembled, and the charge and discharge current density is 80mA / cm 2 , the surface capacity is 5mAh / cm 2 , and the discharge cut-off voltage is 0.8V. The stack is a single cell, which is assembled by positive end plate, current collector, graphite plate, carbon felt, separator, carbon felt, graphite plate, current collector, negative end plate in turn. After the electrolyte in the battery undergoes 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 <200 cycles.

[0063] Comparative example 3 (only coating the negative electrode)

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

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

[0066] Mechanical property test: the prepared separators in Example 1 and Comparative Examples 1-3 were cut and subjected to tensile test, and the results are shown in Table 1. By comparing Comparative Examples 2 and 3 with Comparative Example 1, it can be seen that the modification coating can improve the mechanical properties of the separator, and the tensile strength of the prepared separator in Comparative Example 3 is higher than that in Comparative Example 2, which proves that the Nano-Al2O3 modification layer greatly improves the mechanical strength of the separator. In addition, the tensile strength of the prepared sandwich structure separator in Example 1 is 13.2 Mpa, which is much higher than that of the battery separator without modification coating and the battery separator coated on one side. The improvement of the mechanical properties in Example 1 is not a simple superposition of the tensile strength of the battery separator coated on the negative electrode and the battery separator coated on the positive electrode, and there is a synergistic effect between the two on the improvement of the mechanical properties.

[0067] Table 1: Comparison of mechanical tensile strength of each separator

[0068] Type 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

[0069] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing an acidic redox flow battery separator, characterized in that, Includes the following steps: Prepare a sulfonated polyether ether ketone solution and coat the sulfonated polyether ether ketone solution onto one side of the separator substrate; Nano-alumina and adhesive are dispersed and dissolved in a solvent to prepare a slurry, which is then coated onto the other side of the membrane substrate. The sulfonated polyether ether ketone is prepared by adding polyether ether ketone to concentrated sulfuric acid for sulfonation reaction, and washing and drying after the reaction is completed. The ratio of polyetheretherketone to concentrated sulfuric acid is (0.1-1) g: (2-20) mL; the sulfonation reaction temperature is 50-70℃ and the time is 2-10 h; The coating thickness of the sulfonated polyether ether ketone solution on the separator substrate is 1-5 μm; the coating thickness of the slurry on the separator substrate is 1-5 μm. The concentration of the nano-alumina in the slurry is 0.001-0.005 g / mL.

2. The method for preparing the acidic redox flow battery separator according to claim 1, characterized in that, The concentration of sulfonated polyether ether ketone in the sulfonated polyether ether ketone solution is 0.05-0.1 g / mL, and the solvent is any one or more of N-methylpyrrolidone, dimethylformamide, and dimethyl sulfoxide.

3. The method for preparing the acidic redox flow battery separator according to claim 2, characterized in that, The particle size of the nano-alumina is 20-50 nm.

4. The method for preparing the acidic redox flow battery separator according to claim 3, 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 5-10 wt%.

5. The method for preparing the acidic redox flow battery separator according to claim 4, characterized in that, The solvent in the slurry is any one or more of N-methylpyrrolidone, dimethylformamide, and dimethyl sulfoxide.

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

7. The acidic redox flow battery separator prepared by the method according to any one of claims 1-6, characterized in that, The acidic redox flow battery separator has a sandwich structure, including a separator substrate in the middle, and a sulfonated polyether ether ketone layer and a nano-alumina modified layer on the upper and lower sides, respectively.

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