A porous ion-conducting membrane, its preparation method and use in an acidic aqueous-based organic flow battery

Abstract

The application discloses a kind of porous ion conducting membrane and its preparation method and application in acidic aqueous organic liquid flow battery, especially it is related to the application of containing such film in acidic methylene blue-vanadium flow battery.The film is prepared by intermixing flexible hydrophobic polymer, rigid hydrophilic polymer and flexible water-soluble organic matter, using the above resin in the film forming process, relying on the interaction between polymer hydrophobicity and rigidity, making the polymer self-assemble, removing the flexible water-soluble organic matter after film forming to obtain a porous ion conducting membrane with controllable microstructure.The preparation process of this porous ion conducting membrane is simple, environmentally friendly, controllable in microstructure, and easy to realize mass production.The acidic methylene blue-vanadium flow battery assembled by it has good battery performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of porous ion conducting membrane prepared by high molecular self-assembly method and its application in flow battery, in particular to the application of containing such membrane in acidic methylene blue-vanadium flow battery. BACKGROUND

[0002] With the development of economy, the demand for energy is increasing, and the environmental pressure caused by the large consumption of fossil energy is increasing. Renewable energy should be widely used to increase its proportion in energy consumption. Renewable energy generation such as wind energy and solar energy has obvious intermittency, instability and uncontrollability. Large-scale grid connection of renewable energy generation will seriously affect the safe, efficient and reliable operation of power grid. Energy storage technology can balance the contradiction between power generation and user demand, provide peak shaving, frequency modulation, spinning reserve and other services for power system, and improve the grid connection rate of renewable energy and the stability of power grid. Therefore, large-scale energy storage technology is the key core technology for the popularization and application of renewable energy.

[0003] Flow battery is a new electrochemical energy storage technology. Compared with other energy storage technologies, it has the advantages of flexible system design, large storage capacity, free site selection, high energy conversion efficiency, deep discharge, safety and environmental protection, low maintenance cost, etc. It can be widely used in renewable energy generation such as wind energy and solar energy, emergency power supply system, standby power station and power system peak shaving.

[0004] Ion conducting membrane is one of the key materials in flow battery, which plays a role in blocking positive and negative electrolyte and providing ion transport channel. The ion conductivity, chemical stability and ion selectivity of the membrane will directly affect the electrochemical performance and service life of the battery; therefore, ion conducting membrane is required to have low active material permeability (i.e. high selectivity) and low surface resistance (i.e. high ion conductivity), and also good chemical stability and low cost.

[0005] At present, Nafion membrane developed by DuPont Company in the United States is widely used in flow battery, which has excellent performance in electrochemical performance and service life. This kind of membrane is composed of hydrophobic fluorocarbon skeleton and hydrophilic sulfonic acid side chain. Perfluorosulfonic acid membrane has excellent ion conductivity due to the microphase separation structure of hydrophobic skeleton and hydrophilic group in the membrane when applied in battery. However, due to the fixed microphase structure, it has the disadvantages of poor ion selectivity when applied in battery, especially in all-vanadium flow battery. On the other hand, the price of this kind of membrane is high, which limits its large-scale application in flow battery. Therefore, it is very important to develop ion conducting membrane for flow battery with high selectivity, high stability and low cost.

[0006] The porous ion-conducting membrane realizes separation of active substances and separation of charge balance ions through pore size screening, and effectively overcomes the problem of high price of perfluorosulfonic acid ion exchange membrane. The traditional porous ion-conducting membrane is usually prepared by phase inversion method (immersion precipitation phase inversion method, humidity phase inversion method, etc.), and the phase inversion method usually has complex preparation process, and the uniformity of the prepared porous ion-conducting membrane cannot meet the needs of actual application. Therefore, it is urgent to develop a method for preparing porous ion-conducting membrane which is simple and easy to scale up.

[0007] In view of the above problems, the application discloses a preparation method of a porous ion-conducting membrane and application of the porous ion-conducting membrane in an acidic organic liquid flow battery system, and particularly relates to application of the porous ion-conducting membrane in an acidic methylene blue-vanadium liquid flow battery. The porous ion-conducting membrane is prepared by mixing a flexible hydrophobic polymer, a rigid hydrophilic polymer and a flexible water-soluble organic substance, and by removing the flexible water-soluble organic substance after film formation, so that the porous ion-conducting membrane with controllable microstructure is prepared. The porous ion-conducting membrane has simple preparation process, environmental protection, controllable microstructure and easy batch production SUMMARY

[0008] The application aims to prepare a porous ion-conducting membrane by using the rigidity, flexibility, hydrophilicity and hydrophobicity of organic polymers, to prepare the porous ion-conducting membrane with controllable microstructure by controlling the preparation conditions, to make the porous ion-conducting membrane have excellent ion selectivity and ion conductivity, and to provide a porous ion-conducting membrane for an acidic organic liquid flow battery, and particularly application of the porous ion-conducting membrane in an acidic methylene blue-vanadium liquid flow battery.

[0009] To achieve the above object, the technical scheme adopted by the application is as follows:

[0010] The preparation method of the porous ion-conducting membrane is that the flexible hydrophobic polymer, the rigid hydrophilic polymer and the flexible water-soluble organic substance are dissolved in an organic solvent, and the solvent is evaporated to form a film after being uniformly mixed.

[0011] During the film formation, the difference in interaction among the organic solvent, the flexible hydrophobic polymer, the rigid hydrophilic polymer and the flexible water-soluble organic substance causes the polymer to self-assemble, and the porous ion-conducting membrane with controllable microstructure is prepared by removing the flexible water-soluble organic substance after film formation.

[0012] The flexible hydrophobic polymer is one or more than two of polytetrafluoroethylene and polyvinylidene fluoride.

[0013] The rigid hydrophilic polymer is one or more of sulfonated or carboxylated polysulfone, sulfonated or carboxylated polyimide, sulfonated or carboxylated polyether ketone, sulfonated or carboxylated polybenzimidazole, quaternized chloromethylated polysulfone, and quaternized phosphonium chloromethylated polysulfone;

[0014] The flexible water-soluble organic matter is one or more of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol.

[0015] The preparation method of the porous ion-conducting membrane, wherein the solid content of the flexible hydrophobic polymer and the rigid hydrophilic polymer is 10wt%-25wt% (mass fraction of the flexible hydrophobic polymer and the rigid hydrophilic polymer in the organic solvent), the mass ratio of the flexible hydrophobic polymer and the rigid hydrophilic polymer is 3:1-6:1, and the flexible water-soluble organic matter accounts for 2wt%-8wt% of the total mass of the flexible hydrophobic polymer and the rigid hydrophilic polymer.

[0016] The porous ion-conducting membrane is prepared by the following steps:

[0017] (1) dissolving the flexible hydrophobic polymer, the rigid hydrophilic polymer, and the flexible water-soluble organic matter in an organic solvent, and fully stirring at a temperature of 10-50℃ for 5-48h to prepare a uniformly blended solution;

[0018] (2) uniformly coating the blended solution prepared in step (1) on a non-woven fabric substrate or a glass plate, then heat treating at a temperature of 40-60℃ for 0.5h-2h, and then placing it in deionized water to remove the flexible water-soluble organic matter in the membrane; during the solvent evaporation and film formation, the differences in the interactions among the organic solvent, the flexible hydrophobic polymer, the rigid hydrophilic polymer, and the flexible water-soluble organic matter cause the self-assembly and rearrangement of the polymers, and after the removal of the flexible water-soluble organic matter in the membrane, a porous ion-conducting membrane with controllable microstructure is obtained; the thickness of the membrane is 30-100μm, preferably 40-60μm.

[0019] The organic solvent is one or more of dimethyl sulfoxide (DMSO), N,N'-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), and N,N'-dimethylformamide (DMF).

[0020] The porous ion-conducting membrane is applied in an acidic organic flow battery.

[0021] The acidic organic flow battery is a methylene blue-vanadium flow battery.

[0022] Advantages of the present application

[0023] 1.The porous ion-conducting membrane prepared by the application is applied to a liquid flow battery, different microstructures of the ion-conducting membrane are prepared by controlling the polymer ratio in the casting solution, the ion-conducting membrane has excellent ion selectivity and ion conductivity, and the application provides a porous ion-conducting membrane for a water-based organic liquid flow battery, in particular, the application of the membrane in an acidic organic liquid flow battery.

[0024] 2.The porous ion-conducting membrane prepared by the application has controllable microstructure and is easy to realize mass production.

[0025] 3.The porous ion-conducting membrane prepared by the blending method of the application only needs to use an aqueous solution of ion exchange resin and a clean solvent, and the preparation process is clean and environmentally friendly.

[0026] 4.The application can realize the controllability of the battery efficiency and capacity of the acidic organic liquid flow battery.

[0027] 5.The porous ion-conducting membrane prepared by the application widens the types of membrane structures for water-based organic liquid flow batteries. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 SEM images of the surfaces of PVDF / SPEEK membranes with different PEG contents;

[0029] Figure 2 SEM images of the cross sections of PVDF / SPEEK membranes with different PEG contents;

[0030] Figure 3 Surface resistance (a) and conductivity (b) tests of PVDF / SPEEK membranes with different PEG contents. DETAILED DESCRIPTION

[0031] The following examples are further illustrations of the application and are not intended to limit the scope of the application.

[0032] Performance test of acidic methylene blue-vanadium liquid flow battery: carbon felt is used as the electrode for both the positive electrode and the negative electrode, the positive electrode electrolyte is 40 mL of 0.01 mol / L MB -1 + 3 mol / L H2SO4 solution; the negative electrode electrolyte is 40 mL of 0.3 mol / L V(II) -1 + 3 mol / L H2SO4 solution; the battery uses a constant current charging and discharging mode, the working current density is 40 mA / cm -1 ; the upper limit of the charging voltage is 1.3 V, and the lower limit of the discharging voltage is 0.3 V. - 1 H2SO4 solution; the battery uses a constant current charging and discharging mode, the working current density is 40 mA / cm -2 ; the upper limit of the charging voltage is 1.3 V, and the lower limit of the discharging voltage is 0.3 V.

[0033] Comparative Example 1

[0034] Accurately take 1 g of sulfonated polyether ether ketone (SPEEK) resin and 4 g of polyvinylidene fluoride (PVDF) resin, put them into a 40x70 weighing bottle, prepare a casting solution with a solid content of 18wt% using N,N'-dimethylacetamide (DMAc) as the solvent, stir for 24 h at room temperature, and then stand for 24 h to degas. Uniformly coat the above-mentioned casting solution on a clean glass plate, heat it at 50°C for 0.5 h to remove the solvent, and then place it in deionized water to prepare a PVDF / SPEEK membrane. The cross-sectional morphology of the prepared PVDF / SPEEK membrane is characterized, and it can be seen that the cross-section of the PVDF / SPEEK membrane has a uniform and dense structure.

[0035] The prepared PVDF / SPEEK membrane is tested for battery performance in an acidic methylene blue-vanadium flow battery. Due to the large membrane resistance, the battery assembled with it cannot be normally charged and discharged at a working current density of 40 mA cm -2 .

[0036] Comparative Example 2

[0037] Accurately take 1 g of sulfonated polyether ether ketone (SPEEK) resin and 4 g of polyvinylidene fluoride (PVDF) resin, put them into a 40x70 weighing bottle, prepare a casting solution with a solid content of 18wt% using N,N'-dimethylacetamide (DMAc) as the solvent, stir for 24 h at room temperature, and then stand for 24 h to degas. Uniformly coat the above-mentioned casting solution on a clean glass plate, and place the above-mentioned glass cup in a sink to prepare a PVDF / SPEEK membrane by immersion precipitation phase inversion. The cross-sectional morphology of the prepared PVDF / SPEEK membrane is characterized, and it can be seen that the cross-section of the PVDF / SPEEK membrane has a porous structure.

[0038] The prepared PVDF / SPEEK porous membrane is tested for battery performance in an acidic methylene blue-vanadium flow battery. The battery assembled with it has a battery coulomb efficiency of 91.33% and a voltage efficiency of 91.52% at a working current density of 40 mA cm -2 .

[0039] Examples 1-3

[0040] Accurately weigh 1 g of sulfonated poly (ether ether ketone) (SPEEK) resin, 4 g of poly (vinylidene fluoride) (PVDF) resin, and 0.15 g, 0.20 g, and 0.25 g of polyethylene glycol (PEG-400), respectively, into a 40x70 weighing bottle. Prepare a casting solution with a solid content of 18 wt% using N,N'-dimethylacetamide (DMAc) as the solvent. Stir at room temperature for 24 h and then let stand for 24 h to degas. Uniformly coat the above casting solution on a clean glass plate, heat at 50°C for 0.5 h to remove the solvent, and then place in deionized water to prepare PVDF / SPEEK / PEG membranes (denoted as P-3, P-4, and P-5, respectively). Characterize the surface and cross-sectional morphology of the prepared P-3, P-4, and P-5 membranes. It can be seen that as the PEG content in the casting solution increases, the membrane surface pores gradually increase and become continuous Figure 1 ), and the cross-section also gradually shows a pore structure Figure 2 ). The main reason for the formation of this pore structure is that the addition of flexible water-soluble PEG can induce phase separation between the rigid hydrophilic SPEEK and the flexible hydrophobic PVDF in the membrane, causing the rigid hydrophilic SPEEK and the flexible water-soluble PEG to self-assemble and aggregate into clusters. After the solvent is volatilized, the aggregated PEG in the membrane dissolves in water, forming a pore structure. As the PEG content in the casting solution increases, the pores formed in the membrane become larger and more continuous, and the surface resistance of the prepared porous ionic conduction membrane also becomes smaller Figure 3 a), and the ionic conductivity increases with increasing PEG content Figure 3 b).

[0041] Test the battery performance of the prepared P-3, P-4, and P-5 porous membranes in an acidic methylene blue-vanadium flow battery. The battery assembled with the membranes has a coulombic efficiency of 97.89%, 96.63%, and 94.24%, respectively, and a voltage efficiency of 82.16%, 88.91%, and 89.41%, respectively, at a working current density of 40 mA cm -2 . These results are consistent with the test results of the surface resistance and conductivity of the membrane materials.

Claims

1. The application of a porous ion-conducting membrane in an acidic organic flow battery, characterized in that: The acidic organic flow battery is a methylene blue-vanadium flow battery; The method for preparing the porous ion-conducting membrane is as follows: a flexible hydrophobic polymer, a rigid hydrophilic polymer, and a flexible water-soluble organic compound are dissolved in an organic solvent, mixed evenly, and then the solvent is evaporated to form a membrane. During the film formation process, the differences in the interaction between organic solvents and flexible hydrophobic polymers, rigid hydrophilic polymers, and flexible water-soluble organic matter enable polymer self-assembly. After film formation, the flexible water-soluble organic matter is removed to prepare a porous ion-conducting membrane with controllable microstructure. The solid content of the flexible hydrophobic polymer and the rigid hydrophilic polymer is 10wt% to 25wt%; the solid content is the mass fraction of the flexible hydrophobic polymer and the rigid hydrophilic polymer in the organic solvent, and the mass ratio between the flexible hydrophobic polymer and the rigid hydrophilic polymer is 3:1 to 6:1; the flexible water-soluble organic matter accounts for 2wt% to 8wt% of the total mass of the flexible hydrophobic polymer and the rigid hydrophilic polymer. The flexible hydrophobic polymer is polyvinylidene fluoride; The rigid hydrophilic polymer is sulfonated polyether ether ketone; The flexible water-soluble organic compound is PEG400.

2. An application according to claim 1, characterized in that: The porous ion-conducting membrane is prepared using the following steps: (1) Dissolve the flexible hydrophobic polymer, the rigid hydrophilic polymer, and the flexible water-soluble organic compound in an organic solvent, and stir thoroughly at a temperature of 10-50℃ for 5-48 hours to prepare a homogeneous blend solution. (2) The blended solution prepared in step (1) is uniformly coated onto a nonwoven fabric substrate or glass plate, and then heat-treated at 40-60℃ for 0.5-2 hours. After that, it is placed in deionized water to remove flexible water-soluble organic matter in the membrane. The thickness of the membrane is between 30 and 100 μm.

3. The application according to claim 2, characterized in that: The organic solvent is one or more of dimethyl sulfoxide (DMSO), N,N'-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), and N,N'-dimethylformamide (DMF).

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