CN107546398B - An ion-conducting membrane with microphase separation structure and its preparation and application - Google Patents

Abstract

The invention relates to an ion conducting membrane with a micro-phase separation structure, which is made of one or more than two kinds of hydrophobic polymer resins and one or more than two kinds of hydrophilic polymer resins as raw materials, and is dissolved in an organic solvent. Then, it is prepared by volatilizing the solvent. During the solvent volatilization process, the hydrophilic phase is induced to aggregate, thereby forming an ion-conducting membrane with a microphase separation structure with a hydrophobic region and a hydrophilic region; the concentration of the hydrophobic polymer resin is proportional to the hydrophilic polymer The mass ratio of resin is 0.5‑5. The ion-conducting membrane with the microphase separation structure has a simple process, an environmentally friendly process, a controllable microphase structure, and is easy to achieve mass production. The battery assembled in this way has a good capacity retention rate and excellent battery performance.

Description

An ion-conducting membrane with microphase separation structure and its preparation and application

technical field

The present invention relates to an ion-conducting membrane for a liquid flow battery.

Background technique

Flow battery is a new electrochemical energy storage technology. Compared with other energy storage technologies, flow battery has the advantages of flexible system design, large storage capacity, free site selection, high energy conversion efficiency, deep discharge, safety and environmental protection, and low maintenance costs. It can be widely used in wind energy, solar energy and other renewable energy generation and storage, emergency power system, backup power station and power system peak shaving and valley filling. Vanadium flow battery (VFB) is considered to have good application prospects due to its high safety, good stability, high efficiency, long life (lifetime > 15 years), and low cost.

The battery separator is an important part of the flow battery, which plays the role of blocking the positive and negative electrolytes and providing proton transport channels. The proton conductivity, chemical stability and ion selectivity of the membrane will directly affect the electrochemical performance and service life of the battery; therefore, the membrane is required to have a lower active material permeability (ie, a higher selectivity) and a lower sheet resistance (that is, higher ionic conductivity), and should also have better chemical stability and lower cost. The membrane materials used at home and abroad are mainly Nafion membranes developed by DuPont in the United States. Nafion membranes have excellent electrochemical properties and service life. Such membranes consist of a hydrophobic fluorocarbon backbone and hydrophilic sulfonic acid side chains. Due to its special structure, the perfluorosulfonic acid membrane has a microphase separation structure between the hydrophobic skeleton and the hydrophilic group in the membrane when it is used in the battery, which makes it have excellent proton conductivity. It is precisely because of the microphase structure of this fixed structure that its application in batteries, especially in all-vanadium redox flow batteries, has disadvantages such as poor ion selectivity; on the other hand, this type of membrane is expensive, which limits the membrane industrial application. Therefore, it is crucial to develop battery separators with high selectivity, high stability, and low cost. However, due to the existence of ion exchange groups, the chemical stability of the non-fluorine ion exchange membrane in the all-vanadium redox flow battery is not enough to meet the requirements of long-term use.

Copolymers are often able to form complex structures of different scales and have a wide range of uses in the field of materials technology. Multicomponent polymers such as block or graft are composed of two or more segments with different properties. When the solubility parameters of the monomer segments differ greatly, causing them to be incompatible, there is a tendency for phase separation to occur; however, since the different monomer segments are connected by chemical bonds, macroscopic macroscopic cannot occur in these copolymers. However, only some phase regions in the nanometer or micrometer scale can be formed. This phase separation is called microphase separation, and the structure formed by this microphase separation is called microphase separation structure. Generally, the preparation process of block copolymers that form a microphase-separated structure is complicated and requires a large amount of organic solvents, which is not conducive to the ecological environment, which limits its large-scale application to a certain extent.

SUMMARY OF THE INVENTION

The purpose of the present invention is to prepare an ion conductive membrane with a microphase separation structure, and to prepare ion conductive membranes with different microphase structures by controlling the preparation conditions, so that it has both excellent ion selectivity and ion conductivity, and provides a liquid The application of ion-conducting membrane with microphase separation structure for flow battery in flow battery, especially the application of this kind of membrane in all-vanadium flow battery.

For achieving the above object, the technical scheme adopted in the present invention is as follows:

An ion-conducting membrane with a micro-phase separation structure is made of one or more of hydrophobic polymer resins and one or more of hydrophilic polymer resins as raw materials, dissolved in an organic solvent, and volatilized. It is prepared from a solvent, and the hydrophilic phase is induced to aggregate during the volatilization process of the solvent, thereby forming an ion-conducting membrane with a microphase separation structure with a hydrophobic region and a hydrophilic region;

The mass ratio of the hydrophobic polymer resin to the hydrophilic polymer resin is 0.5-5.

The hydrophobic polymer resin is polyether sulfone, polysulfone, polyether ketone, polytetrafluoroethylene, polyvinylidene fluoride or polystyrene; the hydrophilic polymer resin is sulfonated polysulfone, sulfonated Polyimides, sulfonated polyetherketones, sulfonated polybenzimidazoles, polyvinylpyrrolidones or polyethylene glycols.

Wherein, the phase separation structure is a layered structure, a co-continuous structure, a spherical structure or a columnar structure.

The ion-conducting membrane with the microphase separation structure is prepared by the following steps:

(1) Dissolve the hydrophobic polymer resin and the hydrophilic polymer resin in an organic solvent, and fully stir at a temperature of 20 to 100 ° C for 20 to 60 hours to make a uniform blended solution; wherein the hydrophobic polymer resin and the hydrophilic polymer resin are mixed. The mass ratio of the water-based polymer resin is between 0.5-5; the mass concentration of the hydrophobic polymer resin and the hydrophilic polymer resin in the organic solvent is 10-50%.

(2) Pour the blended solution prepared in step (1) on a non-woven fabric substrate or directly on a glass plate, volatilize the solvent for 0 to 60 seconds, and then evaporate the solvent to dryness at a temperature of 40 to 200° C. to form a film; the solvent volatilizes Induce the aggregation of the hydrophilic phase to obtain a membrane with a microphase separation structure; the thickness of the membrane is between 20 and 500 μm.

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

The ion-conducting membrane with the micro-phase separation structure is used in a flow battery.

The flow battery includes an all-vanadium flow battery, a zinc/cerium flow battery, a vanadium/bromine flow battery or an iron/chromium flow battery.

Beneficial Results of the Invention

1. The blending method used in the present invention is to obtain a homogeneous film casting liquid by blending the hydrophobic high molecular polymer and the hydrophilic high molecular polymer uniformly and dissolving it in an organic solvent, and the film casting liquid is uniformly coated on the Non-woven fabrics or clean glass plates are then evaporated to form films. During the evaporation of the solvent, the solvent induces the aggregation of the hydrophilic polymer resin so that the mixture undergoes microphase separation. The prepared ion-conducting membrane with microphase separation structure is used in a flow battery, and ion-conducting membranes with different microphase structures are prepared by controlling the preparation conditions, so that it has both excellent ion selectivity and ion conductivity, and provides a The application of ion-conducting membranes with microphase separation structure for flow batteries in flow batteries, especially the application of such membranes in all-vanadium flow batteries.

2. The ion conducting membrane with the microphase separation structure prepared by the present invention has an adjustable microphase structure and is easy to realize mass production.

3. The blending method adopted in the present invention prepares the ion conducting membrane with the microphase separation structure, only needs to use the aqueous solution of the ion exchange resin and the cleaning solvent, and the preparation process is clean and environmentally friendly.

4. The present invention can realize the controllability of the battery efficiency and capacity of the flow battery, especially the all-vanadium flow battery.

Description of drawings

Fig. 1 SEM images of the surface and cross-section of the microphase ion-conducting membrane prepared in Example 1

(a: SEM image of the surface of the film facing the air side; b: enlarged image of the surface at the white dotted line in Figure a; c: SEM image of the surface of the film facing the glass plate side; d: SEM image of the cross section of the as-prepared film).

Fig. 2 The sheet resistance of the ion conducting membrane with microphase separation structure and the Nafion115 membrane prepared under different conditions are obtained by the two-electrode AC impedance test (Solartron Electrochemical System). Fully soaked in L ^-1 sulfuric acid aqueous solution for 24 hours; then put the membrane in a test cell filled with 0.5mol L ^-1 dilute sulfuric acid, use a graphite plate with a fixed electrode spacing as an electrode, and use an AC impedance meter in the range of 1kHZ-1MHZ. Scanning, the measured resistance is r ₁ ; finally, the film is taken out, and the resistance of the blank sample is measured again by AC impedance as r ₂ . The effective area S of the film is 1 cm ² , and the formula for calculating the sheet resistance is: r=(r ₁ -r ₂ )xS.

Fig. 3 Vanadium permeability of ion-conducting membrane with microphase separation structure and Nafion115 membrane prepared under different conditions;

The solution composition of the left permeation cell of the vanadium permeation test device is 80mL 3mol L ^-1 VOSO ₄ +3mol L ^-1 H ₂ SO ₄ solution, and the solution composition of the right permeation cell is 80mL 3mol L ^-1 MgSO ₄ +3mol L ^{- 1} H ₂ SO ₄ , in which MgSO ₄ was used to balance the ionic strength of the solutions on both sides to reduce osmotic pressure-induced water migration, and the effective area of the membrane was 9 cm ² . To avoid concentration polarization at the liquid/membrane interface, the solutions on both sides were continuously stirred during the test. Every 24h, 3 mL of sample solution was taken out from the right permeation cell, and the same volume of vanadium solution was supplemented at the same time. The concentration of VO ²⁺ in the sample solution was determined by UV-Vis spectrophotometer.

Figure 4. Single-cell performance of ion-conducting membranes with microphase-separated structures and Nafion115 membranes prepared under different conditions at 80 mAcm ^-2 .

Fig. 5 Cycling stability of polyethersulfone ion-conducting membrane with microphase separation structure under the conditions of 80 mA cm ^-2 and 120 mA cm ^-2 .

Fig. 6 Capacity stability of polyethersulfone ion-conducting membrane with microphase separation structure and Nafion 115 membrane under the condition of 80 mA cm ^-2 .

Detailed ways

The following examples are intended to further illustrate the present invention, but not to limit the scope of the present invention.

Comparative ratio

14.9184g of polyethersulfone (PES) was dissolved in 45.0593g of DMAC, stirred for 48 hours, the resulting polymer solution was spread on a glass plate, and then the glass plate was transferred to a 50°C hot stage and heated for 48 hours. The glass plate was placed in a water bath to obtain a homogeneous polyethersulfone membrane.

An all-vanadium redox flow battery was assembled using the prepared polyethersulfone membrane and commercial Nafion 115 membrane, wherein the catalytic layer was activated carbon felt, the bipolar plate was a graphite plate, the effective area of the membrane was 48cm ² , and the current density was 80mA.cm ^-2 , the vanadium ion concentration in the electrolyte is 1.50 mol L ^-1 , and the H ₂ SO ₄ concentration is 3 mol L ^-1 . Because there is no phase separation structure in the polyethersulfone membrane, the ion transport resistance is relatively large, and the assembled flow battery cannot be charged and discharged normally. 88.30%, and the energy efficiency is 82.45%.

Example 1

1.6087g of polyethersulfone, 0.4028g of sulfonated polyetheretherketone and 1.0029g of polyethylene glycol were dissolved in 8.0655g of DMAC, stirred for 24 hours, and the resulting polymer solution was spread on a glass plate, and then the glass plate was transferred to Heating on a hot stage at 50 °C for 48 hours, the hydrophilic phase sulfonated polyetheretherketone, polyethylene glycol and hydrophobic phase polyethersulfone were induced to separate during the solvent volatilization process to obtain a polyethersulfone membrane with a microphase separation structure (Figure 1). , the glass plate was placed in a water tank after cooling at room temperature, and the film thickness was 22 μm. An all-vanadium redox flow battery was assembled by using the prepared ion-conducting membrane with microphase separation structure, wherein the catalytic layer was activated carbon felt, the bipolar plate was a graphite plate, the effective area of the membrane was 48cm ² , the current density was 80mA.cm ^-2 , and the electrolysis The vanadium ion concentration in the liquid is 1.50mol L ^-1 , and the H ₂ SO ₄ concentration is 3mol L ^-1 . The assembled flow battery had a coulombic efficiency of 91.09%, a voltage efficiency of 90.08%, and an energy efficiency of 82.05% (Figure 3).

Example 2

7.4592g of polyethersulfone, 7.5062g of polyvinylpyrrolidone (PVP) were dissolved in 45.1121g of DMAC, stirred for 48 hours, the resulting polymer solution was spread on a glass plate, and then the glass plate was transferred to a 50°C hot stage and heated for 48 After 1 hour, the PVP phase separation was induced during the solvent evaporation process, and a polyethersulfone membrane (PES) with a microphase separation structure was obtained. After cooling at room temperature, the glass plate was placed in a water tank, and the membrane thickness was 55 μm. An all-vanadium redox flow battery was assembled by using the prepared ion-conducting membrane with microphase separation structure, wherein the catalytic layer was activated carbon felt, the bipolar plate was a graphite plate, the effective area of the membrane was 48cm ² , the current density was 80mA.cm ^-2 , and the electrolysis The vanadium ion concentration in the liquid is 1.50mol L ^-1 , and the H ₂ SO ₄ concentration is 3mol L ^-1 . The coulombic efficiency of the assembled flow battery is 99.09%, the voltage efficiency is 89.55%, and the energy efficiency is 88.74% (Fig. 4), and the battery has no obvious performance degradation after more than 8,000 cycles, showing excellent stability (Fig. 5). ). Compared with the Nafion 115 membrane, the single cells assembled with the polyethersulfone ion-conducting membrane with the microphase-separated structure exhibited excellent capacity retention (Fig. 6).

Example 3

3.0396g polysulfone (PSF), 3.1204g polyethersulfone (PES) and 6.003g polyvinyl alcohol 6000 (PEG-6000) were dissolved in 42.6982g DMAC, stirred for 48 hours, the resulting polymer solution was spread on a glass plate , and then transfer the glass plate to a 50°C hot stage for 48 hours, induce PEG-6000 phase separation during the solvent volatilization process, and obtain a polysulfone/polyethersulfone membrane (PSF) with a microphase separation structure. After cooling at room temperature, the The glass plate was placed in a water bath with a film thickness of 52 μm. An all-vanadium redox flow battery was assembled by using the prepared ion-conducting membrane with microphase separation structure, wherein the catalytic layer was activated carbon felt, the bipolar plate was a graphite plate, the effective area of the membrane was 48cm ² , the current density was 80mA.cm ^-2 , and the electrolysis The vanadium ion concentration in the liquid is 1.50mol L ^-1 , and the H ₂ SO ₄ concentration is 3mol L ^-1 . The assembled flow battery had a coulombic efficiency of 98.87%, a voltage efficiency of 91.14%, and an energy efficiency of 90.11% (Fig. 4).

Example 4

6.3019g polysulfone (PSF), 4.8015g polyvinylpyrrolidone (PVP) were dissolved in 48.0144g DMAC, stirred for 48 hours, the resulting polymer solution was spread on a glass plate, and then the glass plate was transferred to a 50°C hot stage After heating for 48 hours, the PVP phase separation was induced during the solvent evaporation process, and a polysulfone membrane with a microphase separation structure was obtained. After cooling at room temperature, the glass plate was placed in a water tank, and the membrane thickness was 42 μm. An all-vanadium redox flow battery was assembled by using the prepared ion-conducting membrane with microphase separation structure, wherein the catalytic layer was activated carbon felt, the bipolar plate was a graphite plate, the effective area of the membrane was 48cm ² , the current density was 80mA.cm ^-2 , and the electrolysis The vanadium ion concentration in the liquid is 1.50mol L ^-1 , and the H ₂ SO ₄ concentration is 3mol L ^-1 . The assembled flow battery had a coulombic efficiency of 99.36%, a voltage efficiency of 88.66%, and an energy efficiency of 88.10% (Fig. 4).

Example 5

7. 2048g polyvinylidene fluoride (PVDF), 4.8015g polyvinylpyrrolidone (PVP) were dissolved in 45.3598g DMAC, stirred for 48 hours, the resulting polymer solution was spread on a glass plate, and then the glass plate was transferred to 50 ℃ heat Heating on the stage for 48 hours, the PVP phase separation was induced during the solvent volatilization process to obtain a polyvinylidene fluoride film (PVDF) with a microphase separation structure. After cooling at room temperature, the glass plate was placed in a water tank with a film thickness of 45 μm. An all-vanadium redox flow battery was assembled by using the prepared ion-conducting membrane with microphase separation structure, wherein the catalytic layer was activated carbon felt, the bipolar plate was a graphite plate, the effective area of the membrane was 48cm ² , the current density was 80mA.cm ^-2 , and the electrolysis The vanadium ion concentration in the liquid is 1.50mol L ^-1 , and the H ₂ SO ₄ concentration is 3mol L ^-1 . The coulombic efficiency of the assembled flow battery was 97.62%, the voltage efficiency was 89.39%, and the energy efficiency was 87.26%.

Figure 1 shows the prepared topography with microphase separation structure. It can be seen that the surface facing the air-side membrane (Figure 1a and b) has a more obvious microphase separation structure, which is mainly because the water vapor in the air can further induce the inner membrane of the membrane. Separation of hydrophilic and hydrophobic phases, resulting in the formation of structured membranes with different degrees of microphase separation.

It can be seen from the surface resistance test in Figure 2 that the surface resistance of the ion-conducting membrane with microphase separation structure is lower than that of the Nafion 115 membrane, so this type of membrane should be used in flow batteries, especially in all-vanadium flow batteries. With high ionic conductivity, single cells assembled with this type are expected to achieve high voltage efficiency.

Figure 3. The vanadium permeation test shows that the vanadium ion permeation rate of the ion-conducting membrane with microphase separation structure is much lower than that of the Nafion 115 membrane. Therefore, this type of membrane is used in flow batteries, especially all-vanadium The flow battery should have high ion selectivity, and the single cell assembled with this type is expected to obtain high coulombic efficiency.

It can be seen from Fig. 4 that due to the special microphase separation structure in the membrane, compared with Nafion115 membrane, the single cell assembled with the ion conducting membrane with the microphase separation structure has excellent performance under the condition of 80mA cm ^-2 battery performance.

It can be seen from the battery cycle stability test in Figure 5 that the polyethersulfone ion-conducting membrane with microphase separation structure has excellent stability in the all-vanadium redox flow battery.

It can be seen from Figure 6 that the single cell assembled with the polyethersulfone ion-conducting membrane with a microphase-separated structure has an excellent capacity retention rate compared with the Nafion 115 membrane under the condition of 80 mA cm ^-2 .

Claims (5)

1. An application of an ion-conducting membrane with a microphase separation structure, characterized in that: one or more of the hydrophobic polymer resin and one or more of the hydrophilic polymer resin are used as raw materials , after being dissolved in an organic solvent, it is prepared by volatilizing the solvent, and the hydrophilic phase is induced to aggregate during the solvent volatilization process, thereby forming an ion-conducting membrane with a micro-phase separation structure with a hydrophobic region and a hydrophilic region; The mass ratio of the hydrophobic polymer resin to the hydrophilic polymer resin is 0.5-5; the ion-conducting membrane with the microphase separation structure is used in a flow battery; The ion-conducting membrane with the microphase separation structure is prepared by the following steps: (1) Dissolve the hydrophobic polymer resin and the hydrophilic polymer resin in an organic solvent, and fully stir at a temperature of 20 to 100 ° C for 20 to 60 h to make a uniform blended solution; wherein the hydrophobic polymer resin and The mass ratio of hydrophilic polymer resin is between 0.5-5; (2) Pour the blended solution prepared in step (1) onto a non-woven fabric substrate or directly onto a glass plate, volatilize the solvent for 0 to 60 seconds, and then evaporate the solvent to form a film at a temperature of 40 to 200°C; the solvent evaporates Induce the aggregation of the hydrophilic phase to obtain a membrane with a micro-phase separation structure; the thickness of the membrane is between 20 and 500 μm. 2. The application according to claim 1, wherein the hydrophobic polymer resin is polyethersulfone, polysulfone, polyetherketone, polytetrafluoroethylene, polyvinylidene fluoride or polystyrene One or more of the two; the hydrophilic polymer resin is among sulfonated polysulfone, sulfonated polyimide, sulfonated polyether ketone, sulfonated polybenzimidazole, polyvinylpyrrolidone or polyethylene glycol. one or two or more. 3 . The application according to claim 1 , wherein, the microphase separation structure is one or more of a layered structure, a co-continuous structure, a spherical structure or a columnar structure. 4 . 4. The application according to claim 1, wherein the organic solvent is dimethyl sulfoxide (DMSO), N,N'-dimethylacetamide (DMAC), N-methylpyrrolidone ( One or more of NMP), N,N'-dimethylformamide (DMF) and tetrahydrofuran (THF); the mass concentration of hydrophobic polymer resin in organic solvent is 10-50%, hydrophilic The mass concentration of the polymer resin in the organic solvent is 10-50%. 5. The application according to claim 1, wherein the flow battery is an all-vanadium flow battery, a zinc/cerium flow battery, a vanadium/bromine flow battery or an iron/chromium flow battery.

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