Porous ion conduction membrane for alkaline zinc-iron flow battery as well as preparation method and application of porous ion conduction membrane

Abstract

The invention discloses a preparation method of a porous ion conducting membrane for an alkaline zinc-iron flow battery as well as a product and application of the porous ion conducting membrane. The preparation method comprises the following steps: (1) dissolving organic polymer resin in an organic solvent A to obtain a membrane casting solution; (2) uniformly mixing dibenzo 18-crown-6 ether with an organic solvent B to obtain a dispersion liquid, uniformly smearing the dispersion liquid on a substrate, and drying to obtain a substrate smeared with the dibenzo 18-crown-6 ether; and (3) uniformly smearing the membrane casting solution prepared in the step (1) on the substrate smeared with dibenzo 18-crown-6 ether prepared in the step (2), and preparing the porous ion conduction membrane by an immersion precipitation phase inversion method. A dibenzo 18-crown-6 ether functional layer is compounded on one side of the prepared porous ion conduction membrane, and the porous ion conduction membrane has unique pore size distribution, so that the alkaline zinc-iron flow battery assembled by taking the porous ion conduction membrane as a diaphragm has excellent coulombic efficiency, voltage efficiency, energy efficiency and power density.

Description

Technical Field

[0001] The present invention relates to the technical field of aqueous zinc-ion batteries, and particularly to a porous ion-conducting membrane for an alkaline zinc-iron flow battery, a preparation method thereof, and an application thereof. Background Art

[0002] Alkaline zinc-iron flow batteries have the advantages of high safety, low cost, high open-circuit voltage, and high power density, and are one of the electrochemical energy storage technologies expected to achieve long-duration energy storage. The separator is one of the key materials of the flow battery. It plays a role in transporting charge carriers to form an internal circuit of the battery, and at the same time prevents cross-contamination of redox active substances from reducing the capacity. The comprehensive performance of the separator deeply affects the core electrochemical indexes of the flow battery, such as Coulomb efficiency, voltage efficiency, energy efficiency, and power density. At the same time, its cost is also directly related to the economic feasibility of the entire battery system. An ideal separator material should have high ionic conductivity to promote the improvement of voltage efficiency, and at the same time maintain good ionic selectivity to maintain Coulomb efficiency. However, there is often a trade-off between the two: high ionic conductivity may be accompanied by a decrease in ionic selectivity, which in turn affects the overall performance of the battery. In addition, to promote the large-scale commercial application of flow batteries, reducing the cost of the separator has become a key problem to be solved urgently. At present, a membrane material widely used in the field of alkaline zinc-iron flow batteries is the perfluorosulfonic acid ion exchange membrane Nafion developed by Chemours Company (formerly DuPont Company) in the United States. Although this material has certain technical advantages, its high price and performance that do not fully meet the requirements of high-power density operation of alkaline zinc-iron flow batteries have become bottlenecks restricting the wide application of this technology.

[0003] Porous ion-conducting membranes are low-cost and are considered potential substitutes for Nafion membranes. It selectively transports ions through a size sieving mechanism, but it is difficult to precisely control its pore size, and it is often difficult to simultaneously meet the high ionic conductivity and high ionic selectivity of the membrane. By introducing cation exchange groups into the porous ion-conducting membrane, the negatively charged redox active substances in the alkaline zinc-iron flow battery can be hindered from penetrating through the separator by the Donnan effect, thereby improving the Coulomb efficiency of the battery.

[0004] For example, a Chinese patent document with application publication number CN 111261912 A discloses the application of a porous ion conductive membrane in a neutral zinc-iron liquid flow battery. The porous ion conductive membrane is a type of porous ion conductive membrane containing nitrogen functional groups, which is prepared by a phase inversion method using a polymer resin containing at least one nitrogen-containing functional group, or a polymer resin containing at least one nitrogen-containing functional group and a type of polymer resin without nitrogen as raw materials; the polymer resin containing nitrogen functional groups is one or more of polyetherimide, polyimide, chloromethylated polysulfone grafted with nitrogen functional groups, polyoxadiazole, and polynaphthalene polyetheretherketone grafted with nitrogen functional groups. However, according to the best performance described in Example 2, the imidazole-grafted chloromethylated polysulfone porous ion conductive membrane prepared by pore size optimization has a low charge / discharge rate of 40 mA cm in a neutral zinc-iron liquid flow battery assembled therewith. -2 Under the current density conditions, the battery's voltage efficiency is 84% ​​and the coulombic efficiency is 96%.

[0005] For example, the Chinese patent document with application publication number CN 116154205 A discloses the application of side chain functionalized polybenzimidazole porous membrane in bromine-based liquid flow batteries. This type of membrane is made of polybenzimidazole as raw material, and side chains containing quaternary ammonium bromide groups are grafted onto its main chain through a nucleophilic substitution reaction with a bromoammonium bromide-based compound, and then the polybenzimidazole porous ion conductive membrane is prepared using the side chain functionalized polybenzimidazole as raw material. Among them, the quaternary ammonium bromide group on the side chain can be complexed with bromine to fix the bromine diffused to the negative electrode on the membrane surface or in the membrane pores, thereby preventing the bromine from migrating from the positive electrode side to the negative electrode side through the membrane, and reacting with the active material on the negative electrode side to cause the battery to self-discharge. However, according to the data recorded in Example 3 with the best performance, the zinc-bromine liquid flow battery prepared with the porous membrane prepared therefrom has a low charge / discharge rate at 40 mA cm -2 Under the current density conditions, the battery's voltage efficiency is 88.14% and the coulombic efficiency is 99.32%.

[0006] Nevertheless, as the performance requirements for alkaline zinc-iron flow batteries continue to increase, especially in the pursuit of higher power density operation, the performance of current membranes is still insufficient. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention discloses a method for preparing a porous ion conductive membrane. One side of the prepared porous ion conductive membrane is composited with a dibenzo-18-crown-6 ether functional layer and has a unique pore size distribution. The alkaline zinc-iron liquid flow battery assembled with the porous ion conductive membrane as a diaphragm has excellent coulombic efficiency, voltage efficiency, energy efficiency and power density.

[0008] The specific technical solutions are as follows:

[0009] A preparation method of a porous ion-conducting membrane for an alkaline zinc-iron flow battery, comprising the following steps:

[0010] (1) Dissolve an organic polymer resin in organic solvent A to obtain a casting solution;

[0011] The organic polymer resin includes polyethersulfone and sulfonated polyether ether ketone;

[0012] (2) Mix dibenzo-18-crown-6 ether with organic solvent B evenly to obtain a dispersion liquid, apply the dispersion liquid evenly on a substrate, and obtain a substrate coated with dibenzo-18-crown-6 ether after drying;

[0013] (3) Apply the casting solution prepared in step (1) evenly on the substrate coated with dibenzo-18-crown-6 ether prepared in step (2), and prepare the porous ion-conducting membrane by the immersion precipitation phase inversion method.

[0014] In step (1):

[0015] The organic polymer resin includes polyethersulfone and sulfonated polyether ether ketone;

[0016] It is found through experiments that the selection of the organic polymer resin in the present invention has its particularity, and it is also the key to ensuring that the alkaline zinc-iron flow battery assembled with the prepared porous ion-conducting membrane has excellent coulombic efficiency, voltage efficiency, energy efficiency and power density.

[0017] By comparison, it is found that if a casting solution is prepared by using only polyethersulfone or only polyether ether ketone, or by blending polyethersulfone and unsulfonated polyether ether ketone, the electrochemical performance of the alkaline zinc-iron flow battery assembled with the membranes prepared respectively will deteriorate significantly.

[0018] Preferably:

[0019] The mass ratio of polyethersulfone to sulfonated polyether ether ketone is (70-93):(7-30); specifically, it can be 70:30, 75:25, 80:20, 85:15, 90:10, 93:7 or any ratio within the above range;

[0020] It is further preferably (75-95):(15-25); and even more preferably 80:20.

[0021] With the continuous optimization of the above raw material dosages, the alkaline zinc-iron flow battery assembled with the prepared membranes has more excellent coulombic efficiency, voltage efficiency, energy efficiency and power density.

[0022] Sulfonated polyether ether ketone can be prepared by a method well known in the art. For example, it can be obtained by sulfonating polyether ether ketone in concentrated sulfuric acid;

[0023] Preferably, the sulfonation temperature is 40 to 80 °C, specifically it can be 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C or any value within the above range;

[0024] The sulfonation time is 2 to 10 h, specifically it can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h or any value within the above range.

[0025] In step (1):

[0026] The organic solvent A is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide;

[0027] The concentration of the organic polymer resin in the casting solution is 20 to 50 wt%, specifically it can be 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt% or any value within the above range; preferably it is 30 to 40 wt%.

[0028] When preparing the casting solution, it can be heated to 30 to 80 °C for sufficient stirring, specifically it can be carried out for sufficient stirring at 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C or any value within the above range.

[0029] In step (2):

[0030] The organic solvent B is selected from one or more of methanol, ethanol, and isopropanol; preferably it is ethanol.

[0031] The dispersion liquid has a concentration of 0.1 to 100 mg / mL -1 specifically it can be 0.1 mg / mL -1 1 mg / mL -1 5 mg / mL -1 10 mg / mL -1 15 mg / mL -1 20 mg / mL -1 25 mg / mL -1 30 mg / mL -1 35 mg / mL -1 40 mg / mL -1 45 mg / mL -1 50 mg / mL -1 55 mg / mL -1 60 mg / mL -1 65 mg / mL -1 70 mg / mL -1 75 mg / mL-1 、 80 mg / mL -1 、 85 mg / mL -1 、 90 mg / mL -1 、 95 mg / mL -1 、 100 mg / mL -1 or any value within the above range; preferably 10 - 50 mg / mL -1 。

[0032] There are no special requirements for the substrate, and it can be selected from common types in the art, such as glass plates, ceramics, metal plates, plastic plates, etc.

[0033] The drying is carried out by conventional means in the art, preferably drying at 40 - 100 °C for 0.5 - 4 h; specifically, it can be carried out at 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C or any value within the above range.

[0034] In step (3), the immersion precipitation phase inversion method specifically includes immersing the entire substrate in the poor solvent of the organic polymer resin.

[0035] When the organic polymer resin includes polyethersulfone and sulfonated polyether ether ketone, the poor solvent is selected from one or more of water, ethanol, and isopropanol.

[0036] The immersion time is 60 - 3600 s, and specifically can be 60 s, 120 s, 180 s, 240 s, 300 s, 360 s, 720 s, 900 s, 1200 s, 1440 s, 2400 s, 2880 s, 3000 s, 3600 s or any value within the above range.

[0037] Preferably, the operating environment temperature is 10 - 40 °C, and the relative humidity of the operating environment is 1 - 20%.

[0038] The present invention also discloses a porous ion conductive membrane prepared according to the above method, with a membrane thickness of 70 - 130 μm, wherein the thickness of the membrane layer with a pore size of 0.05 - 0.29 μm is 20 - 50 μm, and the thickness of the membrane layer with a pore size of 0.70 - 1.65 μm is 50 - 80 μm.

[0039] It has been found through experiments that this unique pore size distribution is directly related to the modification of dibenzo - 18 - crown - 6 ether in step (2). If only a casting solution prepared by compounding polyethersulfone and sulfonated polyether ether ketone is used without the modification of dibenzo - 18 - crown - 6 ether, the prepared membrane does not have a unique distribution.

[0040] Further preferably, the membrane thickness is 90 - 120 μm, wherein the thickness of the membrane layer with a pore size of 0.05 - 0.29 μm is 30 - 45 μm, and the thickness of the membrane layer with a pore size of 0.70 - 1.65 μm is 60 - 75 μm.

[0041] The present invention also discloses an alkaline zinc - iron flow battery, comprising a positive electrode, a negative electrode and a separator, wherein the separator uses the porous ion - conducting membrane described above.

[0042] Both the positive electrode and the negative electrode are selected from graphite felts.

[0043] The alkaline zinc - iron flow battery further comprises an electrolyte. The positive - electrode electrolyte is an aqueous solution mixture of ferrocyanide and a strong base, and the negative - electrode electrolyte is an aqueous solution mixture of zinc oxide and / or zinc salt and a strong base.

[0044] The active substance in the positive - electrode electrolyte is selected from one or more of sodium ferrocyanide, potassium ferrocyanide, sodium ferricyanide, potassium ferricyanide;

[0045] The active substance in the negative - electrode electrolyte is selected from one or more of zinc oxide, zinc chloride, zinc sulfate;

[0046] The concentration of the active substance in the positive and negative electrode electrolytes is 0.01 - 3 mol / L.

[0047] The strong base in the positive and negative electrolytes is independently selected from one or more of potassium hydroxide, sodium hydroxide, lithium hydroxide, and its concentration in the aqueous solution is 0.01 - 10 mol / L.

[0048] After testing, the alkaline zinc - iron flow battery assembled with it as the separator has excellent Coulomb efficiency, voltage efficiency, energy efficiency and power density.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The present invention discloses a preparation method of a porous ion - conducting membrane for an alkaline zinc - iron flow battery. A specific raw material including polyethersulfone and sulfonated polyether ether ketone is used as the organic polymer resin to prepare the membrane, and a dibenzo - 18 - crown - 6 ether functional layer is modified and compounded on one side of the membrane. Based on the above combination, a porous ion - conducting membrane with a unique pore size distribution is not only prepared, but also endows it with hydrophilicity and ionic conductivity, and suppresses the shuttle of the active substances in the positive and negative electrode electrolytes of the alkaline zinc - iron flow battery through the Donnan effect, thereby effectively improving the voltage efficiency, Coulomb efficiency and energy efficiency of the alkaline zinc - iron flow battery. Description of the Drawings

[0051] Figure 1 Figure (a) is the cross - sectional morphology of the porous ion - conducting membrane prepared in Example 1, and Figure (b) is an enlarged view of the circular area in Figure (a);

[0052] Figure 2 (a) is the cross-sectional morphology of the porous ion-conducting membrane prepared in Comparative Example 1, and (b) is an enlarged view of the circular area in (a);

[0053] Figure 3 Figure showing the comparison of Coulombic efficiency, voltage efficiency, and energy efficiency of an alkaline zinc-iron flow battery assembled using the porous ion-conducting membrane prepared in Example 1 under different current density conditions;

[0054] Figure 4 Figure showing the comparison of Coulombic efficiency, voltage efficiency, and energy efficiency of an alkaline zinc-iron flow battery assembled using the porous ion-conducting membrane prepared in Example 2 under different current density conditions;

[0055] Figure 5 Figure showing the comparison of Coulombic efficiency, voltage efficiency, and energy efficiency of an alkaline zinc-iron flow battery assembled using the porous ion-conducting membrane prepared in Example 3 under different current density conditions;

[0056] Figure 6 Figure showing the comparison of Coulombic efficiency, voltage efficiency, and energy efficiency of an alkaline zinc-iron flow battery assembled using the porous ion-conducting membrane prepared in Comparative Example 1 under different current density conditions;

[0057] Figure 7 Figure showing the comparison of Coulombic efficiency, voltage efficiency, and energy efficiency of an alkaline zinc-iron flow battery assembled using the ion-conducting membrane in Comparative Example 2 under different current density conditions;

[0058] Figure 8 Polarization curves of alkaline zinc-iron flow batteries assembled using the ion-conducting membranes in Example 1, Comparative Example 1, and Comparative Example 2, respectively. Detailed Description of the Invention

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0060] The features and properties of the present invention will be further described in detail below in conjunction with the embodiments.

[0061] Example 1

[0062] 10 g of polyether ether ketone (Mv ~ 35,000, coarse powder) was placed in 100 mL of concentrated sulfuric acid and stirred thoroughly at 50 °C for 5 h to sulfonate the polyether ether ketone into sulfonated polyether ether ketone.

[0063] Using polyethersulfone (molecular weight 58,000) and sulfonated polyether ether ketone as organic polymer resins, dissolve the two in the organic solvent N,N-dimethylacetamide, and stir well at 40 °C for 6 h to obtain a casting solution with a mass concentration of 35% of the organic polymer resin, where the mass ratio of polyethersulfone to sulfonated polyether ether ketone is 80:20.

[0064] Pour dibenzo-18-crown-6 ether into ethanol and ultrasonically treat it for 3 h to obtain an ethanol dispersion of dibenzo-18-crown-6 ether with a concentration of 20 mg / mL. -1 Coat it evenly on a clean glass plate, and then dry it at 60 °C for 2 h to obtain a glass plate evenly coated with dibenzo-18-crown-6 ether.

[0065] Coat the above-prepared casting solution on the glass plate evenly coated with dibenzo-18-crown-6 ether, and then through the immersion precipitation phase inversion method, immerse the entire glass plate in water for 2400 s at a temperature of 25 °C and a relative humidity of 5% to obtain a porous ion-conducting membrane with a dibenzo-18-crown-6 ether functional layer and a unique pore size distribution, denoted as PM20@18-C-6.

[0066] Assemble the PM20@18-C-6 membrane into an alkaline zinc-iron flow battery for charge-discharge testing. The charge-discharge test conditions are as follows: both the positive and negative electrodes use graphite felt as the electrode (area 4 cm 2 ); the positive electrode electrolyte is 0.6 mol / L -1 Fe(CN) 4 6 - + 3 mol / L -1 OH - solution, and the negative electrode electrolyte is 0.3 mol / L -1 Zn(OH) 2 4 - + 5 mol / L -1 OH - solution; the volume of the positive and negative electrode electrolytes is 30 mL each; the battery adopts a constant current charge-discharge mode, and is charged at current densities of 80 mA / cm -2 , 160 mA / cm -2 and 200 mA / cm -2 for 1 h, 0.5 h and 0.4 h respectively, and then discharged to 0.1 V at current densities of 80 mA / cm -2 , 160 mA / cm -2 and 200 mA / cm -2 respectively.

[0067] The PM20@18-C-6 membrane was assembled into an alkaline zinc-iron flow battery for battery polarization curve testing. The conditions for polarization curve testing were as follows: Graphite felts were used as electrodes for both the positive and negative electrodes (with an area of 4 cm 2 ); The electrolytes for the positive and negative electrodes were the same as those described in the above charge-discharge tests; The battery was first charged to SOC = 80% at a current density of 100 mA cm -2 , and then discharged with a gradually increasing current density, and the battery voltage corresponding to each current density was recorded.

[0068] As Figure 1 shown, from the cross-sectional morphology diagram, the PM20@18-C-6 membrane has a unique pore size distribution. Among them, the membrane layer with a pore size of 0.05 - 0.29 μm has a thickness of approximately 38 μm, and the membrane layer with a pore size of 0.70 - 1.65 μm has a thickness of approximately 74 μm.

[0069] As Figure 3 shown, the alkaline zinc-iron flow battery assembled with the PM20@18-C-6 membrane exhibited excellent constant current charge-discharge performance at current densities of 80 mA cm -2 , 160 mA cm -2 , and 200 mA cm -2 . Especially at a high current density of 200 mA cm -2 , the battery still had a Coulombic efficiency (CE) of 98.7%, a voltage efficiency (VE) of 86.3%, and an energy efficiency (EE) of 85.2%.

[0070] As Figure 8 shown, with the increase in the discharge current density, the battery polarization of the alkaline zinc-iron flow battery assembled with the PM20@18-C-6 membrane increased less. When the discharge current density reached 600 mA cm -2 , the discharge voltage of the battery still remained at a very high 1.42 V. When the discharge current density was 700 mA cm -2 , the peak power density of the battery was as high as 893 mW cm -2 .

[0071] Example 2

[0072] The preparation process was basically the same as that of Example 1, except that when preparing the casting solution, the mass ratio of polyethersulfone to sulfonated polyether ether ketone was changed to 93:7, and a porous ion-conducting membrane was prepared, denoted as PM7@18-C-6.

[0073] The PM7@18-C-6 membrane was assembled into an alkaline zinc-iron flow battery for charge-discharge testing. The conditions for charge-discharge testing were as follows: Graphite felts were used as electrodes for both the positive and negative electrodes (with an area of 4 cm 2 ); The positive electrode electrolyte was 0.6 mol L-1 Fe(CN) 4 6 - + 3 mol / L -1 OH - solution, and the negative electrolyte is 0.3 mol / L -1 Zn(OH) 2 4 - + 5 mol / L -1 OH - solution; the volumes of the positive and negative electrode electrolytes are both 30 mL; the battery adopts a constant current charge-discharge mode, and is charged for 2 h, 1 h, and 0.5 h respectively under the current density conditions of 40 mA / cm -2 , 80 mA / cm -2 , and 160 mA / cm -2 , and then discharged to 0.1 V respectively under the current density conditions of 40 mA / cm -2 , 80 mA / cm -2 , and 160 mA / cm -2 .

[0074] As Figure 4 shown, for the alkaline zinc-iron flow battery assembled with the PM7@18-C-6 membrane, as the current density of the charge-discharge test increases, the voltage efficiency of the battery decreases significantly, which may be due to the relatively small content of sulfonated polyether ether ketone in the PM7@18-C-6 membrane and the low ionic conductivity.

[0075] Example 3

[0076] The preparation process is basically the same as that of Example 1, except that when preparing the casting solution, the mass ratio of polyethersulfone to sulfonated polyether ether ketone is changed to 70:30, and a porous ion-conducting membrane is prepared, denoted as PM30@18-C-6.

[0077] The PM30@18-C-6 membrane is assembled into an alkaline zinc-iron flow battery for charge-discharge testing, and the testing conditions are the same as those in Example 2.

[0078] As Figure 5 shown, the alkaline zinc-iron flow battery assembled with the PM30@18-C-6 membrane has a relatively high voltage efficiency. However, at this time, the mechanical strength of the membrane is relatively low, and the cross-over of the redox active substances at the positive and negative electrodes of the battery is serious. Therefore, the Coulomb efficiency and energy efficiency of the battery are relatively low; this may be due to the relatively large content of sulfonated polyether ether ketone in the PM30@18-C-6 membrane and the too high ionic conductivity.

[0079] Comparative Example 1

[0080] 10 g of polyether ether ketone was placed in 100 mL of concentrated sulfuric acid and stirred thoroughly at 50 °C for 5 h to sulfonate the polyether ether ketone into sulfonated polyether ether ketone.

[0081] Using polyethersulfone and sulfonated polyether ether ketone as organic polymer resins, the two were dissolved in the organic solvent N,N-dimethylacetamide and stirred thoroughly at 40 °C for 6 h to obtain a casting solution with an organic polymer resin mass concentration of 35%, where the mass ratio of polyethersulfone to sulfonated polyether ether ketone was 80:20.

[0082] The casting solution was coated on a glass plate, and then through the immersion precipitation phase inversion method, at a temperature of 25 °C and a relative humidity of 5%, the entire glass plate was immersed in water for 2400 s to obtain a porous ion-conducting membrane, denoted as PM20.

[0083] The PM20 membrane was used to assemble an alkaline zinc-iron flow battery, and charge-discharge tests and battery polarization curve tests were carried out. The test method was the same as in Example 1.

[0084] As Figure 2 shown, from the cross-sectional morphology diagram, the pore size of the PM20 membrane was 0.40 - 1.73 μm, and there was no unique pore size distribution similar to that of the PM20@18-C-6 membrane.

[0085] As Figure 6 shown, the alkaline zinc-iron flow battery assembled using the PM20 membrane had inferior charge-discharge performance compared to the PM20@18-C-6 membrane under current density conditions of 80 mA cm -2 、160 mA cm -2 and 200 mA cm -2 . Especially under the current density condition of 200 mA cm -2 , due to the too high current density, the voltage efficiency and energy efficiency of the flow battery decreased significantly, being 77.2% and 74.5% respectively.

[0086] As Figure 8 shown, when the discharge current density reached 600 mA cm -2 , the discharge voltage of the battery was 1.21 V. When the discharge current density was 700 mA cm -2 , the peak power density of the battery was 766 mW cm -2 .

[0087] Comparative Example 2

[0088] The Nafion 212 membrane was used to assemble an alkaline zinc-iron flow battery, and charge-discharge tests and battery polarization curve tests were carried out. The test method was the same as in Example 1.

[0089] As Figure 7As shown, the alkaline zinc-iron flow battery assembled with Nafion 212 membrane has far lower charge-discharge performance than PM20@18-C-6 membrane and PM 20 membrane under the current density conditions of 80 mA cm -2 , 160 mA cm -2 and 200 mA cm -2 . Under the high current density condition of 200 mA cm -2 , due to the too high current density, the voltage efficiency and energy efficiency of the flow battery are only 65.6% and 64.5% respectively.

[0090] As Figure 8 shown, when the discharge current density reaches 600 mA cm -2 , the discharge voltage of the battery is only 0.95 V, and the peak power density is only 571 mW cm -2 .

[0091] Comparative Example 3

[0092] The preparation process is basically the same as that of Example 1, except that when preparing the casting solution, only polyethersulfone is used as the organic polymer resin alone, and the obtained membrane is denoted as PES@18-C-6.

[0093] The PES@18-C-6 membrane is assembled into an alkaline zinc-iron flow battery for charge-discharge testing. The charge-discharge test conditions are as follows: Graphite felts are used as electrodes for both the positive and negative electrodes (area 4 cm 2 ); The positive electrode electrolyte is 0.6 mol L -1 Fe(CN) 4 6 - + 3 mol L -1 OH - solution, and the negative electrode electrolyte is 0.3 mol L -1 Zn(OH) 2 4 - + 5 mol L -1 OH - solution; The volumes of the positive and negative electrode electrolytes are both 30 mL. The battery adopts a constant current charge-discharge mode. After testing, the ionic conductivity is extremely low, and the battery cannot even operate normally under the low current density of 40 mA cm -2 .

[0094] Comparative Example 4

[0095] The preparation process is basically the same as that of Example 1, except that when preparing the casting solution, only un-sulfonated polyether ether ketone is used as the organic polymer resin alone, and the obtained membrane is denoted as PEEK@18-C-6.

[0096] The PEEK@18-C-6 membrane was assembled into an alkaline zinc-iron flow battery for charge-discharge tests under the same test conditions as in Comparative Example 3. Similarly, the ionic conductivity was extremely low, and the battery could not even operate normally at a low current density of 40 mA / cm -2 .

[0097] Comparative Example 5

[0098] The preparation process was basically the same as that of Example 1, except that polyethersulfone and unsulfonated polyetheretherketone were used as organic polymer resins when preparing the casting solution, and the obtained membrane was denoted as PES-PEEK@18-C-6.

[0099] The PES-PEEK@18-C-6 membrane was assembled into an alkaline zinc-iron flow battery for charge-discharge tests under the same test conditions as in Comparative Example 3. Similarly, the ionic conductivity was extremely low, and the battery could not even operate normally at a low current density of 40 mA / cm -2 .

[0100] The above-disclosed are preferred embodiments, but the protection scope of the present invention is not limited thereto. Those of ordinary skill in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and changes, but as long as they do not depart from the spirit of the present invention, they are within the protection scope of the present invention.

Claims

1. A method for preparing a porous ion-conducting membrane for an alkaline zinc-iron flow battery, characterized in that: The steps include: (1) dissolving an organic polymer resin in an organic solvent A to obtain a casting solution; The organic polymer resin includes polyethersulfone and sulfonated polyetheretherketone; (2) mixing dibenzo-18-crown-6 ether and organic solvent B to obtain a dispersion, applying the dispersion to a substrate, and drying to obtain a substrate coated with dibenzo-18-crown-6 ether; (3) The casting solution prepared in step (1) is evenly applied on the substrate coated with dibenzo-18-crown-6 ether prepared in step (2), and the porous ion conductive membrane is prepared by an immersion precipitation phase conversion method.

2. The method for preparing a porous ion conductive membrane for an alkaline zinc-iron flow battery according to claim 1, characterized in that: In step (1): The mass ratio of polyethersulfone to sulfonated polyetheretherketone is (70-93):(7-30).

3. The method for preparing a porous ion conductive membrane for an alkaline zinc-iron flow battery according to claim 2, characterized in that: The sulfonated polyetheretherketone is obtained by sulfonating polyetheretherketone in concentrated sulfuric acid; The sulfonation temperature is 40-80°C, and the sulfonation time is 2-10 hours.

4. The method for preparing a porous ion conductive membrane for an alkaline zinc-iron flow battery according to claim 1, characterized in that: In step (1): The organic solvent A is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; The concentration of the organic polymer resin in the casting solution is 20-50 wt %.

5. The method for preparing a porous ion conductive membrane for an alkaline zinc-iron flow battery according to claim 1, characterized in that: In step (2): The organic solvent B is selected from one or more of methanol, ethanol and isopropanol; The dispersion has a concentration of 0.1 to 100 mg mL -1 ; The substrate is selected from one or more of a glass plate, a ceramic plate, a metal plate, and a plastic plate.

6. The method for preparing a porous ion conductive membrane for an alkaline zinc-iron flow battery according to claim 1, characterized in that: In step (3), the immersion precipitation phase conversion method specifically includes immersing the entire substrate in a poor solvent for the organic polymer resin.

7. The method for preparing a porous ion-conducting membrane for an alkaline zinc-iron flow battery according to claim 6, characterized in that: The poor solvent is selected from one or more of water, ethanol and isopropanol; The immersion time is 60 to 3600 seconds.

8. The method for preparing a porous ion-conducting membrane for an alkaline zinc-iron flow battery according to any one of claims 1 to 7, characterized in that: The mass ratio of polyethersulfone to sulfonated polyetheretherketone is (75-95):(15-25).

9. A porous ion conducting membrane prepared by the method according to any one of claims 1 to 8.

10. An alkaline zinc-iron flow battery, comprising a positive electrode, a negative electrode and a separator, characterized in that: The separator is the porous ion-conducting membrane according to claim 9.

Images