A composite ion exchange membrane for alkaline system zinc-iron flow battery and preparation and application thereof

Abstract

This invention discloses a cavitation compound composite ion exchange membrane for alkaline zinc-iron flow batteries and its application in such batteries. The membrane uses an ion exchange membrane prepared from one or more organic polymer resins as a matrix, into which a cavitation compound is mixed to form the composite ion exchange membrane. This composite ion exchange membrane features a simple preparation method and environmentally friendly process. Compared with traditional ion exchange membranes, this type of composite ion exchange membrane exhibits higher ion conductivity and ion selectivity, effectively suppressing electrolyte migration, improving battery cycle life and performance, and solving the capacity decay problem.

Description

Technical Field

[0001] This invention relates to a polymer electrolyte membrane material for alkaline zinc-iron flow batteries, and particularly to a composite ion exchange membrane for alkaline zinc-iron flow batteries, its preparation method, and its application in alkaline zinc-iron flow batteries. Background Technology

[0002] Flow batteries are a new electrochemical energy storage technology. Compared with other energy storage technologies, they have advantages such as high energy conversion efficiency, flexible system design, large storage capacity, flexible site selection, deep discharge capability, safety and environmental friendliness, and low maintenance costs. They can be widely used in energy storage for renewable energy generation such as wind and solar power, emergency power systems, backup power stations, and peak shaving and valley filling in power systems. Alkaline zinc-iron flow batteries are considered to have high development potential due to their high safety, good stability, long lifespan (>15 years), and low cost.

[0003] The battery separator is a crucial component of flow batteries, serving to block the electrolytes at the positive and negative electrodes while providing a channel for hydroxide ion transport. The membrane's chemical stability and ionic conductivity directly affect the battery's electrochemical performance and lifespan; therefore, the membrane is required to have high ionic conductivity and low sheet resistivity, while also possessing good chemical stability and low cost. Currently, the most commonly used membrane material both domestically and internationally is the Nafion membrane developed by DuPont. While Nafion membranes exhibit excellent performance in electrochemical properties and lifespan, their high cost, particularly their poor ionic conductivity in alkaline zinc-iron flow batteries, limits their industrial application. Meanwhile, another major category of commonly used membrane materials is the anion exchange membrane. In alkaline systems, anion exchange membranes possess excellent ionic conductivity, but their poor chemical stability limits their application under long-term battery operation conditions.

[0004] Currently developed and used alkaline zinc-iron flow battery membranes are all single-ion exchange membranes. In alkaline systems, a single ion exchange membrane, besides conducting hydroxide ions (OH-) that participate in the battery's electrochemical reactions, only... - In addition to, it also conducts a large amount of potassium (K) + ), sodium (Na + Cations such as α and β can cause cross-contamination and migration in the electrolyte, severely affecting battery performance and lifespan. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of existing single ion exchange membranes used in alkaline zinc-iron flow batteries, and to provide a composite ion exchange membrane for alkaline zinc-iron flow batteries. This composite ion exchange membrane can significantly improve the ion conductivity and ion selectivity of the membrane, effectively suppress electrolyte migration, improve battery cycle life and performance, and solve the problem of capacity decay.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A composite ion exchange membrane, which uses an ion exchange membrane prepared from one or more organic polymer resins as raw materials as a matrix, and a composite cavitation compound is formed in the matrix to form a composite ion exchange membrane.

[0008] The cavitary compound is a macrocyclic complex, generally a bicyclic or polycyclic molecule containing nitrogen or sulfur atoms. The cavitary compound suitable for this invention is bicyclic polyether 2.1.1 or bicyclic polyether 2.2.2 (see...). Figure 3 (It can be used in one or more ways).

[0009] Preferably, the organic polymer resin used to prepare the ion exchange membrane matrix is ​​one or more of polysulfones, polyketides, polyacrylonitrile, polyimide, polytetrafluoroethylene, polyvinylidene fluoride, polybenzimidazole, or polyvinylpyridine.

[0010] Preferably, the composite ion exchange membrane has a thickness of 10–200 μm and the mass fraction of the cavitary compound in the composite ion exchange membrane is 1–40 wt%, preferably 10–20 wt%.

[0011] The above-mentioned composite ion exchange membrane is prepared by the following steps:

[0012] (1) Dissolve the organic polymer resin in an organic solvent and stir thoroughly to prepare a blend solution;

[0013] (2) Add the cavitation compound to the blend solution prepared in step (1), and stir thoroughly to prepare a homogeneous mixed casting solution;

[0014] (3) The mixed casting solution prepared in step (1) is coated onto a PET substrate or glass plate to form a casting solution coating of a certain thickness. Then it is dried until the organic solvent in the casting solution coating evaporates completely to obtain a dry composite ion exchange membrane.

[0015] Preferably, the concentration of organic polymer resin in the blend solution is between 5 and 50 wt.%.

[0016] Preferably, the organic solvent is one or more of DMSO, DMAC, NMP, and DMF; the coating method of the mixed casting solution is one or more of the following methods: casting, blade coating, spraying, spin coating, etc.

[0017] Preferably, in step (1), the stirring temperature is 20-100℃ and the stirring time is 0.5-10h; in step (2), the stirring temperature is 20-100℃ and the stirring time is 0.5-6h; in step (3), the drying temperature is 20-80℃ and the drying time is 0.5-48h.

[0018] The composite ion exchange membrane can be used in alkaline zinc-iron flow batteries.

[0019] Preferably, the alkaline zinc-iron flow battery is a flow battery in which Fe(II) / Fe(III) is used as the active material for the positive electrode electrolyte and Zn(II) / Zn is used as the active material for the negative electrode electrolyte, and the positive and negative electrode electrolytes circulate between the positive electrode and the separator, and between the negative electrode and the separator, respectively; wherein the pH of the positive and negative electrode electrolytes is >7, preferably >10.

[0020] This composite ion exchange membrane features a simple preparation method and environmentally friendly process. Compared with the original ion exchange membrane, this type of composite ion exchange membrane has higher ion conductivity and ion selectivity, which can effectively suppress electrolyte migration, improve battery cycle life and performance, and solve the problem of capacity decay.

[0021] Beneficial results of the present invention:

[0022] (1) The present invention prepares a composite ion exchange membrane by blending a cavitary compound with an organic polymer resin in a certain appropriate ratio. This not only ensures the membrane material's ability to exchange hydroxide ions (OH-) - The conductivity of the membrane material is reduced due to the complexation effect of the cavitation compound on alkali metal ions, and the conductivity of the membrane material to potassium (K) is also significantly reduced. + ), sodium (Na + The conductivity of cations such as ions improves the ion selectivity of the membrane material, inhibits the migration of electrolyte solution, improves the cycle life and performance of the battery, and solves the problem of capacity decay.

[0023] (2) The composite ion exchange membrane prepared by this invention has an adjustable proportion of cavitary compounds and a controllable thickness. By adjusting the above parameters, the battery performance can be controlled and adjusted.

[0024] (3) This invention expands the types and application scope of membrane materials for alkaline zinc-iron flow batteries.

[0025] The preparation method of this type of composite ion exchange membrane is simple, the process is environmentally friendly, and the ion selectivity is adjustable. Compared with the original ion exchange membrane, the composite ion exchange membrane has better ion conductivity and ion selectivity, and the alkaline zinc-iron flow battery assembled with it has higher overall performance. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the application principle of the composite ion exchange membrane of the present invention in an alkaline zinc-iron flow battery.

[0027] Figure 2 The composite ion exchange membrane prepared in Example 1 and Comparative Example 1 were tested in an alkaline zinc-iron flow battery at 80 mA / cm². -2 A comparison of charge and discharge performance at different current densities.

[0028] Figure 3 The structures of the cavitation compounds of the present invention are bicyclic polyether 2.1.1 and bicyclic polyether 2.2.2. Detailed Implementation

[0029] The following embodiments are further illustrations of the present invention, but are not intended to limit the scope of the invention.

[0030] Example 1

[0031] 7.5 g of sulfonated polyether ether ketone organic resin was dissolved in 30 ml of organic solvent DMSO and stirred for 5 hours to form a blend solution. Then, 1.5 g of bicyclic polyether 2.1.1 was added to bring the mass fraction to 16.7 wt%, and the mixture was stirred for 2 hours to prepare a mixed casting solution. The prepared mixed casting solution was coated onto a glass plate using a blade coating method and placed on a heating platform at 50°C for 24 hours to form a uniform and dense composite ion exchange membrane with a thickness of 50 μm.

[0032] Performance Testing: An alkaline zinc-iron flow battery was assembled using the prepared composite ion exchange membrane. The electrodes were carbon felt (positive and negative electrodes), the bipolar plates were graphite plates, and the effective area of ​​the membrane was 48 cm². 2 The current density is 80 mA / cm⁻¹ 2 The hydroxide ion concentration in the electrolyte (positive and negative electrode electrolytes) is 3 mol / L. -1 The zincate ion concentration is 0.5 mol / L. -1 The concentration of ferrocyanide ions is 1 mol L. -1 The assembled alkaline zinc-iron flow battery exhibited a coulombic efficiency (CE) of 98.8%, a voltage efficiency (VE) of 89.1%, and an energy efficiency (EE) of 88.0%. The battery life exceeded 2000 cycles. After 2000 cycles, the measured volume change rate of the electrolyte at both the positive and negative electrodes was 1.3%.

[0033] Comparative Example 1

[0034] The performance testing process was the same as in Example 1, except that the membrane was replaced with a Nafion 115 ion exchange membrane manufactured by DuPont, while other conditions remained unchanged. The battery coulombic efficiency was 88.6%, voltage efficiency was 83.3%, and energy efficiency was 73.8%. The battery life was <150 cycles. After 150 cycles, the volume change rate of the electrolyte at both the positive and negative electrodes was 54.2%.

[0035] Compared to Nafion 115 ion exchange membranes, the composite ion exchange membranes show significant improvements in coulombic efficiency, energy efficiency, and cycle life. This indicates that the composite ion exchange membrane, prepared by blending cavitary compounds with organic polymer resins, effectively improves the membrane's ion conductivity and ion selectivity, and blocks cross-contamination of alkali metal ions in the electrolyte at both the positive and negative electrodes, thus enhancing the battery's coulombic efficiency and stability. Simultaneously, because the cross-contamination of alkali metal ions in the electrolyte is reduced, the electrolyte water migration caused by this cross-contamination is also reduced. Therefore, the electrolyte migration rate of a single cell assembled with the composite ion exchange membrane is much lower than that of a single cell assembled with Nafion membranes.

[0036] Comparative Example 2

[0037] The process and conditions were the same as in Example 1, except that the membrane was replaced with a simple sulfonated polyether ether ketone resin ion exchange membrane (without adding bicyclic polyether 2.1.1), while other conditions remained unchanged. The battery's coulombic efficiency was tested to be 90.2%, voltage efficiency to be 87.3%, and energy efficiency to be 78.7%. The battery life was <1000 cycles. After 1000 cycles, the volume change rate of the positive and negative electrolytes was 12.4%.

[0038] Compared to a simple sulfonated polyether ether ketone (PEEK) ion exchange membrane, the composite ion exchange membrane exhibits slightly improved coulombic efficiency and energy efficiency, while significantly enhancing the battery's cycle life. This indicates that the composite ion exchange membrane, prepared by blending the cavitation compound with an organic polymer resin, effectively improves the membrane's ion selectivity and blocks cross-contamination of alkali metal ions in the electrolyte at both the positive and negative electrodes, thereby improving the battery's coulombic efficiency and stability. Simultaneously, because the cross-contamination of alkali metal ions in the electrolyte is reduced, the electrolyte water migration caused by this cross-contamination is also reduced. Therefore, the electrolyte migration rate of a single cell assembled with the composite ion exchange membrane is significantly lower than that of a single cell assembled with a simple sulfonated PEEK ion exchange membrane.

[0039] Comparative Example 3

[0040] The process and conditions were the same as in Example 1, except that bicyclic polyether 2.1.1 was added to the positive electrode electrolyte at a final concentration of 20 wt%, while other conditions remained unchanged. The battery was tested and found to have a coulombic efficiency of 96.8%, a voltage efficiency of 87.5%, and an energy efficiency of 84.9%. After 2000 cycles, the volume change rate of the positive and negative electrode electrolytes was 5.8%.

[0041] Compared to using cavitation compounds as additives in the electrolyte, incorporating cavitation compounds into the ion exchange membrane further improves the coulombic efficiency and energy efficiency of the battery. The reason for this is that the cavitation compounds in the membrane, being encapsulated by polymer chains, do not migrate under the influence of the electric field during the electrochemical reaction, thus preventing concentration changes. This enhances their ability to effectively attract alkali metal ions (K+) participating in the electrochemical reaction. + Na + The complexing ability of cavitary compounds is stronger, resulting in higher selectivity and a lower cross-linking rate of alkali metal ions. Therefore, blending cavitary compounds into ion exchange membranes exhibits higher battery performance and lower electrolyte migration rates compared to adding them directly to the electrolyte.

[0042] Comparative Example 4

[0043] The process and conditions were the same as in Example 1, except that bicyclic polyether 2.1.1 was replaced with bicyclic polyether 2.2.1, while other conditions remained unchanged. The battery's coulombic efficiency was tested to be 90.1%, voltage efficiency to be 85.2%, and energy efficiency to be 76.8%. After 1000 cycles, the volume change rate of the positive and negative electrolytes was measured to be 8.4%.

[0044] Since the complexing ability of cavitary ligands with alkali metal ions is highly correlated with their structure, the complexing ability of bicyclic polyether 2.1.1 with alkali metal ions is much higher than that of bicyclic polyether 2.2.1. Therefore, the composite membrane prepared from bicyclic polyether 2.1.1 exhibits stronger selectivity for ions in the electrolyte, resulting in higher coulombic efficiency and lower electrolyte migration rate. This indicates that the composite ion exchange membrane prepared by blending appropriately structured cavitary compounds with organic polymer resins effectively improves the ion selectivity of the membrane, blocks the cross-contamination of alkali metal ions in the electrolyte at both ends, and improves the overall performance of the battery.

[0045] Example 2

[0046] The process and conditions were the same as in Example 1, except that the amount of bicyclic polyether 2.1.1 added was increased from 1.5g to 3.2g, resulting in a mass fraction of 30wt%, while other conditions remained unchanged. The battery's coulombic efficiency was tested to be 98.4%, voltage efficiency to be 80.2%, and energy efficiency to be 78.9%. After 1000 cycles, the volume change rate of the positive and negative electrolytes was 1.1%.

[0047] Compared to Example 1, increasing the mass fraction of bicyclic polyether 2.1.1 from 16.7 wt% to 30 wt% did not significantly change the coulombic efficiency and electrolyte migration rate of the battery, but the voltage efficiency decreased significantly. This indicates that when the amount of cavitation compound added is too high, it cannot conduct charged ions, thus reducing the conductivity of the membrane material, which in turn affects the battery's internal resistance and causes a decrease in battery efficiency. Therefore, selecting an appropriate amount of cavitation compound can help improve the battery's conductivity, thereby improving the overall battery performance.

[0048] Example 3

[0049] The process and conditions were the same as in Example 1, except that the organic polymer resin was replaced with polyimide, while other conditions remained unchanged. The battery's coulombic efficiency (CE) was 99.2%, voltage efficiency (VE) was 89.0%, and energy efficiency (EE) was 88.3%. After 2000 cycles, the volume change rate of the electrolyte at both the positive and negative electrodes was 1.3%.

[0050] Example 4

[0051] The process and conditions were the same as in Example 1, except that the organic polymer resin was replaced with a 1:1 mixture of perfluorosulfonic acid resin and polybenzimidazole, while other conditions remained unchanged. The battery's coulombic efficiency (CE) was 98.6%, voltage efficiency (VE) was 89.7%, and energy efficiency (EE) was 88.4%. After 2000 cycles, the volume change rate of the electrolyte at both the positive and negative electrodes was 1.3%.

[0052] Example 5

[0053] The process and conditions were the same as in Example 1, except that bicyclic polyether 2.1.1 was replaced with bicyclic polyether 2.2.2, while other conditions remained unchanged. The battery's coulombic efficiency (CE) was 99.6%, voltage efficiency (VE) was 89.2%, and energy efficiency (EE) was 88.8%. After 2000 cycles, the volume change rate of the positive and negative electrolytes was 1.1%.

[0054] Example 6

[0055] The process and conditions were the same as in Example 1, except that bicyclic polyether 2.1.1 was replaced with a 1:1 mixture of bicyclic polyether 2.1.1 and bicyclic polyether 2.2.2, while other conditions remained unchanged. The battery's coulombic efficiency (CE) was 98.9%, voltage efficiency (VE) was 89.4%, and energy efficiency (EE) was 88.4%. After 2000 cycles, the volume change rate of the positive and negative electrolytes was 1.2%.

[0056] Example 7

[0057] The process and conditions were the same as in Example 1, except that the organic solvent was replaced with NMP, while other conditions remained unchanged. The battery's coulombic efficiency (CE) was 98.7%, voltage efficiency (VE) was 89.2%, and energy efficiency (EE) was 88.0%. After 2000 cycles, the volume change rate of the electrolyte at both the positive and negative electrodes was 1.4%.

[0058] Example 8

[0059] The process and conditions were the same as in Example 1, except that the amount of bicyclic polyether 2.1.1 added was reduced from 1.5g to 0.5g, resulting in a mass fraction of 6.25wt%, while other conditions remained unchanged. The battery's coulombic efficiency was tested to be 95.4%, voltage efficiency to be 88.7%, and energy efficiency to be 84.6%. After 1000 cycles, the volume change rate of the positive and negative electrolytes was measured to be 5%.

[0060] Compared to Example 1, reducing the mass fraction of bicyclic polyether 2.1.1 resulted in a decrease in coulombic efficiency, voltage efficiency, and electrolyte migration rate after 1000 battery cycles, although these were still improved compared to the pure membrane material in Comparative Example 2. This demonstrates that selecting an appropriate amount of the added cavitary compound can help improve the battery's conductivity and ion selectivity, thereby enhancing overall battery performance.

Claims

1. A composite ion exchange membrane, characterized in that: The composite ion exchange membrane comprises an organic polymer resin and a cavitation compound; the cavitation compound comprises one or two of bicyclic polyether 2.1.1 and bicyclic polyether 2.2.2; the mass fraction of the cavitation compound in the composite ion exchange membrane is 1-40 wt%; the composite ion exchange membrane is used in an alkaline zinc-iron flow battery. The method for preparing the composite ion exchange membrane includes the following steps: (1) Dissolve the organic polymer resin in an organic solvent and stir to prepare a blend solution; (2) Add a cavity compound to the blend solution and stir to prepare a homogeneous mixed casting solution; (3) The mixed casting solution is coated on a substrate or plate to form a casting solution coating, and the composite ion exchange membrane is obtained after drying.

2. The composite ion exchange membrane according to claim 1, characterized in that: The organic polymer resin is one or more of the following: polysulfone, polyketone, polyacrylonitrile, polyimide, polytetrafluoroethylene, polyvinylidene fluoride, polybenzimidazole, or polyvinylpyridine.

3. The composite ion exchange membrane according to claim 1, characterized in that: The thickness of the composite ion exchange membrane is 10–200 μm.

4. The composite ion exchange membrane according to claim 1, characterized in that: The mass fraction of the cavitary compound in the composite ion exchange membrane is 10–20 wt%.

5. The composite ion exchange membrane according to claim 1, characterized in that: The concentration of organic polymer resin in the blend solution is between 5 and 50 wt.%.

6. The composite ion exchange membrane according to claim 1, characterized in that: The organic solvent is one or more of DMSO, DMAC, NMP, and DMF; The coating method of the mixed casting liquid is one or more of the following: casting method, blade coating method, spraying method, spin coating method.

7. The composite ion exchange membrane according to claim 1, characterized in that: In step (1), the stirring temperature is 20-100℃ and the stirring time is 0.5-10h; in step (2), the stirring temperature is 20-100℃ and the stirring time is 0.5-6h; in step (3), the drying temperature is 20-80℃ and the drying time is 0.5-48h.

8. A claim 1 7. Application of any of the composite ion exchange membranes described above in alkaline zinc-iron flow batteries.

9. The application according to claim 8, characterized in that: The alkaline zinc-iron flow battery is a flow battery that uses Fe(II) / Fe(III) as the active material for the positive electrode electrolyte and Zn(II) / Zn as the active material for the negative electrode electrolyte. The positive and negative electrolytes circulate between the positive electrode and the separator, and between the negative electrode and the separator, respectively. The pH of the positive and negative electrolytes is greater than 7.

Images